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Review

MicroRNA-150 (miR-150) and Diabetic Retinopathy: Is miR-150 Only a Biomarker or Does It Contribute to Disease Progression?

by
Gladys Y.-P. Ko
1,2,*,
Fei Yu
1,
Kayla J. Bayless
3 and
Michael L. Ko
1,4
1
Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX 77843, USA
2
Texas A&M Institute for Neuroscience, Texas A&M University, College Station, TX 77843, USA
3
Department of Molecular & Cellular Medicine, College of Medicine, Texas A&M University, College Station, TX 77843, USA
4
Department of Biology, Division of Natural and Physical Sciences, Blinn College, Bryan, TX 77802, USA
*
Author to whom correspondence should be addressed.
Int. J. Mol. Sci. 2022, 23(20), 12099; https://doi.org/10.3390/ijms232012099
Submission received: 26 July 2022 / Revised: 5 October 2022 / Accepted: 6 October 2022 / Published: 11 October 2022
(This article belongs to the Special Issue Molecular Mechanisms and Pathophysiology of Cardiovascular and Cerebrovascular Diseases)
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Abstract

:
Diabetic retinopathy (DR) is a chronic disease associated with diabetes mellitus and is a leading cause of visual impairment among the working population in the US. Clinically, DR has been diagnosed and treated as a vascular complication, but it adversely impacts both neural retina and retinal vasculature. Degeneration of retinal neurons and microvasculature manifests in the diabetic retina and early stages of DR. Retinal photoreceptors undergo apoptosis shortly after the onset of diabetes, which contributes to the retinal dysfunction and microvascular complications leading to vision impairment. Chronic inflammation is a hallmark of diabetes and a contributor to cell apoptosis, and retinal photoreceptors are a major source of intraocular inflammation that contributes to vascular abnormalities in diabetes. As the levels of microRNAs (miRs) are changed in the plasma and vitreous of diabetic patients, miRs have been suggested as biomarkers to determine the progression of diabetic ocular diseases, including DR. However, few miRs have been thoroughly investigated as contributors to the pathogenesis of DR. Among these miRs, miR-150 is downregulated in diabetic patients and is an endogenous suppressor of inflammation, apoptosis, and pathological angiogenesis. In this review, how miR-150 and its downstream targets contribute to diabetes-associated retinal degeneration and pathological angiogenesis in DR are discussed. Currently, there is no effective treatment to stop or reverse diabetes-caused neural and vascular degeneration in the retina. Understanding the molecular mechanism of the pathogenesis of DR may shed light for the future development of more effective treatments for DR and other diabetes-associated ocular diseases.

1. Overview of Diabetic Retinopathy

Diabetes is a disease characterized by hyperglycemia associated with either insulin deficiency or resistance, and the incidence of diabetes is projected to increase to 33% of the US population by 2050 owing to the obesity epidemic [1], of which 90–95% of diabetic patients will have type 2 diabetes (T2D) [2]. Diabetic retinopathy (DR) is a chronic complication associated with both T1D and T2D. It impacts 4.2 million people in the US and 93 million worldwide [3] and is a leading cause of blindness among the working population in the US [4]. Overall, DR is diagnosed in 30% of diabetic patients: approximately 90% of T1D and 60% of T2D patients develop DR [5]. The risk factors for developing DR include the duration of diabetes (≥20 years), poor control over blood glucose levels, hypertension, and obesity [6].
Clinically, DR has been diagnosed and treated as a vascular disease, but it also affects the neural retina [7]. Diabetic insults impair the integrity of retinal microvasculature and induces pathological angiogenesis [8]. Depending on the severity of the vascular pathologies, DR is divided into non-proliferative and proliferative phases clinically. Non-proliferative DR (NPDR) manifests mild-to-moderate vascular abnormalities including microaneurysms, intraretinal hemorrhages, and venous beading, while proliferative DR (PDR) displays neovascularization and pre-retinal hemorrhages [5]. In addition, the decreased retinal light responses recorded by electroretinogram (ERG) correlate with more severe vascular pathologies in NPDR patients [9]. As chronic diabetic conditions adversely impact the neural retina and retinal vasculature, the interaction between retinal neurons and vascular cells could further contribute to the pathogenesis of DR.
Laser photocoagulation is a commonly used therapy for PDR but is invasive and often induces blind spots in the retina [5]. The most used therapy for DR is the intraocular injections of anti-vascular endothelial growth factor (VEGF) agents [10]. However, nearly 30% of patients do not respond well to anti-VEGFs [11,12], and less than 50% of patients have improved vision after 1–2 years of anti-VEGF therapies [13]. As repeated anti-VEGF treatments are needed to conquer the recurrent neovascularization, they often cause unwanted side effects, including retinal detachment [13]. In addition, current therapies for DR mainly target neovascularization at the later stages of DR and rarely restore normal visual function [5]. Therefore, it is critical to understand the mechanisms underlying the pathogenesis of DR and develop therapeutic strategies to either target the early stage of DR or to prevent its development.

1.1. Retinal Neural Dysfunction and Degeneration in DR

Neural dysfunction and degeneration occur early in the diabetic retina. Distorted color vision in patients with early diabetes was previously reported [14,15,16], and dysfunction of the neural retina can be detected in diabetic patients by ERG before any vascular pathologies are detected [17,18,19]. Diabetic patients without DR vascular complications usually have lower ERG amplitudes and longer implicit times than healthy subjects [20]. Apoptotic non-vascular cells can be found in the retina of diabetic patients before the onset of DR [21]. In T1D patients without retinopathy, the thickness of the retinal nerve fiber layer (NFL) decreases compared with healthy subjects, suggesting the loss of axons from retinal ganglion cells (RGCs) [22], and the dampened vision correlates with thinner neural layers [23]. While most apoptotic neurons are found in the retinal ganglion cell layer (GCL), the outer nuclear layer (ONL; photoreceptors) also displays apoptosis [24]. In patients with six years of diabetes duration, the apoptotic cells increase in the retina from the ONL to GCL [25]. The apoptotic markers are detected in the retina of diabetic patients, including caspase-3, a protease for apoptosis, in the GCL and Fas ligand (FasL) in major retinal layers (from NFL to ONL) [26]. Adolescents with T2D for an average of two years have reduced retinal thickness measured by optical coherence tomography (OCT) and dampened light responses measured by ERG [27]. In T2D patients without retinopathy, the thickness of retinal layers from GCL to the outer plexiform layer (OPL) decrease after one year of follow-up [28]. In T2D patients with mild NPDR (microaneurysms), the thicknesses of retinal NFL, GCL, and inner plexiform layer (IPL) decrease, indicating neurodegeneration in the initial stage of DR [29,30]. The decreased thickness of NFL correlates with the severity of DR in T2D patients, suggesting that neurodegeneration in the diabetic retina might exacerbate the development of DR [31].
In diabetic animal models, decreased thickness of the retinal inner nuclear layer (INL) and IPL occur in the retina of T1D mice (Ins2Atita) with increased expression of caspase-3 [32]. The number of cells decreases while the expression of caspase-3 increases in the GCL after ten weeks of diabetes in streptozotocin (STZ)-induced T1D mice [33]. In a mouse model of T2D (KKAY), the terminal UTP nick-end label (TUNEL) staining shows an increased number of apoptotic neurons in the GCL [34], and neuronal apoptosis in the retina occurs in T2D (db/db) mice starting from twenty weeks old [35]. These findings reveal the degeneration of the inner retina in diabetes, which may explain the dampened light response reflected by the decreased amplitude and increased implicit time of ERG b-waves [36,37].
Among retinal neurons, photoreceptors undergo apoptosis shortly after the onset of diabetes [38,39]. The ERG a-waves from diabetic patients [40] and animals [41] display decreased amplitudes and increased implicit times compared with healthy counterparts, which indicate a diabetes-induced impairment to the photoreceptors. In T2D patients, decreased thicknesses of the ONL and the inner and outer segments of photoreceptors are associated with the development of retinopathy [28]. In patients with metabolic syndromes, the thickness of the photoreceptor layer decreases compared with healthy subjects [42]. Apoptotic photoreceptors can be detected in STZ rats 4 weeks after the onset of diabetes [38], while the thickness of the ONL decreases in STZ mice after 10 weeks of diabetes [33]. Electron microscopy shows disorganization and degeneration of the outer segments of photoreceptors in STZ rats [43]. In addition, 28-week-old T2D mice (db/db) have decreased thickness of the ONL accompanied by dampened light responses on ERG [35]. Interestingly, long-term diabetic patients with retinitis pigmentosa (RP), a genetic disease with loss of photoreceptors, rarely develop DR even though these patients develop other diabetes-related vascular diseases [44,45]. In a mouse model of RP, during the period when photoreceptors are undergoing apoptosis, the retinal vasculature is also degenerating. Once the photoreceptors are completely lost, the vascular degeneration stops [46]. Hence, photoreceptor apoptosis not only contributes to the neural dysfunction under diabetes but may also adversely impact diabetic microvascular complications [46]. However, how diabetic insults cause photoreceptor apoptosis remains unclear.

1.2. Retinal Vascular Degeneration and Complications in DR

The TUNEL labelling of microvascular networks in trypsin-digested retinas from diabetic patients shows significantly increased apoptotic endothelial cells and pericytes compared with healthy subjects [47,48]. The loss of pericytes and the formation of acellular capillaries are the major signs of microvascular degeneration that occurs at an earlier stage of DR [7]. Acellular capillaries contain only the basement membrane and remnants of endothelial cells without nuclei, which are typical pathological changes found in trypsin-digested diabetic retinas [49]. Another sign of microvascular degeneration is the loss of pericytes or the existence of “ghost” pericytes that appear as light-stained pockets around the basement membrane [50]. Degenerated vessels are detected in the eyes of patients with mild NPDR and may contribute to the formation of microaneurysms [51].
In alloxan-induced T1D rats, the number of apoptotic vascular cells and acellular capillaries are increased in trypsin-digested retinas [52]. Apoptotic endothelial cells are also increased in the retina of STZ-T1D rats, but inhibition of FasL dampens apoptosis [53]. Apoptotic pericytes expressing the pro-apoptotic BCL2 associated X (BAX) protein, an apoptosis regulator, can be detected in the retina of diabetic patients [54]. The TUNEL-positive pericytes are detected in the retina of STZ-T1D rats [55], while a loss of pericytes is found in db/db-T2D mice [56]. The number of acellular capillaries and ghost pericytes are increased in the retina of STZ-T1D and Zucker-T2D rats along with elevated activities of caspase-3, and inhibition of tumor necrosis factor (TNF-α), a pro-inflammatory cytokine that can trigger necrosis or apoptosis, alleviates those pathological changes [57].
Microvascular degeneration may contribute to the breakdown of the blood–retina barrier (BRB) [58] and exacerbate the decrease of blood flow and local hypoxia in the diabetic retina [59]. Retinal hypoxia stimulates the secretion of angiogenic factors such as VEGF from various cell types in the retina, including astrocytes and Müller glia [60]. The upregulated VEGF eventually leads to pathological angiogenesis and neovascularization in DR.

2. Pathogenesis of Diabetes-Induced Degeneration in Retinal Neurons and Microvasculature: Oxidative Stress, Inflammation, and Glutamate Excitotoxicity

2.1. Oxidative Stress in the Diabetic Retina

Oxidative stress is due to overproduction or decreased removal of reactive oxygen species (ROS) in cells. Mitochondria are the major organelle that produce OS during oxidative phosphorylation [61]. Normally, the electrons donated by reduced nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FADH2) are transferred from complex I to complex IV in the inner mitochondrial membrane by coenzyme Q and cytochrome C. Meanwhile, protons are transferred to the intermembrane space to generate a gradient of protons between the mitochondrial matrix and the intermembrane space. The influx of protons drives the synthesis of ATP while the electrons are consumed to produce H2O [62]. Diabetes-associated hyperglycemic conditions promote the generation of electron donors NADH and FADH2, which pushes the proton gradient to the threshold and ultimately hinders the transfer of electrons. Alternatively, electrons are provided to O2 by coenzyme Q to generate superoxide and ROS [63]. Nicotinamide adenine dinucleotide phosphate (NADPH) also donates electrons to O2 through the membrane proteins NADPH oxidases (Nox) [64]. Under diabetic conditions, protein kinase C (PKC) is activated that further increases the activity of Nox [65]. The Nox proteins are highly expressed in the vasculature, so ROS generated from Nox contributes to impaired vascular function [66]. The increased ROS in mitochondria promotes the opening of mitochondrial permeability transition pores (mPTP) and increases the release of cytochrome C [67], which eventually induces apoptosis.
Eight-hydroxydeoxyguanosine (8-OHdG) is a biomarker for oxidative stress-induced DNA damage which is increased in the vitreous of T2D patients indicating upregulated oxidative stress in the retina [68]. Antioxidant reagents have been used to alleviate the diabetes-caused apoptosis of retinal neurons and endothelial cells [61]. Glutathione (GSH) is a major endogenous antioxidant that removes ROS and suppresses oxidative stress. In STZ-induced diabetic mice, GSH is decreased in the mitochondria of the retina, which correlates to the increase of degenerated (acellular) retinal capillaries [69]. Antioxidant α-lipoic acid treatment decreases the apoptotic microvascular cells after 11 months of STZ-induced diabetes, and it decreases 8-OHdG and increases GSH in the retina [70]. Treatment with the antioxidant lutein reduces the activity of caspase-3, an enzyme leading to apoptosis, and alleviates STZ-induced neural dysfunction [71].

2.2. Inflammation in the Diabetic Retina

Inflammation is a hallmark of diabetes that manifests in the diabetic retina [72]. A functional blood–retina barrier (BRB) in the diabetic retina protects the neural retina from the invasion of immune cells in the circulation [73]. Before the breakdown of the BRB in the advanced stages of DR, the retinal glial cells, neurons, and endothelial cells are the major sources of diabetes-induced inflammation [74,75,76]. The innate immune system in the retina responds to diabetic insults by activating microglia and secreting pro-inflammatory molecules. Retinal microglia are the resident immune cells derived from monocytes. In addition, the circulating macrophages can differentiate into microglia upon stimulation by low expression of CD45. Resting retinal microglia reside in the inner and outer plexiform layers with ramified shapes, while the activated microglia change to an amoeboid shape and migrate to various retinal layers [73].
In mouse retinas under oxidative stress, the apoptosis of photoreceptors increases concurrently with the activation of microglia in the photoreceptor layers.
Activated microglia secrete pro-inflammatory factors, including TNF-α and interleukins (ILs), which exacerbate inflammatory reactions and promote apoptosis in vascular cells and neurons [77]. In cultured human retinal endothelial cells (HRECs), treatments of IL-1β and TNF-α increase the activities of caspase-3 and caspase-8 [78], activate the pro-inflammatory nuclear factor kappa B (NFĸB), and upregulate the expressions of intracellular adhesion molecule (ICAM)-1 and vascular cell adhesion molecule (VCAM)-1 [79]. Increased activities of caspase-3 and -8 indicate an increase of cell apoptosis, and upregulations of ICAM-1 and VCAM-1 induce leukostasis (adherence of leukocytes) in the retinal vessels and promote further inflammatory reactions by mediating the migration of leukocytes [80]. Knocking out the type 1 interleukin-1 receptor (IL1R1) in STZ-diabetic mice largely decreases the activities of the caspases and the number of acellular capillaries [81], and inhibition of TNF-α decreases the activities of caspase-3 and -8 and the apoptosis of RECs in STZ-induced diabetic rats. Furthermore, diabetic mice with deficient TNF-α receptors (TNFR1 and TNFR2) have decreased acellular capillaries and increased pericytes compared with wild-type diabetic mice [82]. These data clearly demonstrate that inhibition of pro-inflammatory factors or their receptors will decrease apoptosis of endothelial cells and preserve the retinal microvasculature.
Increased IL-1β and TNF-α also induce apoptosis in retinal neurons. Under hypoxia, the expressions of IL-1β and TNF-α in retinal microglia and the corresponding receptors IL-1R1 and TNFR1 in retinal ganglion cells (RGCs) are increased, which leads to apoptosis of RGCs. Neutralizing IL-1β and TNF-α with antibodies suppresses the apoptosis of RGCs [83]. In the retinal degeneration 1 (rd1) mouse model, blocking the downstream signaling of interleukin-1 receptors (IL-1R) alleviates the degeneration of photoreceptors and improves the light responses of the retina [84]. Thus, diabetes-elicited secretion of pro-inflammatory molecules from microglia triggers apoptosis in the neural retina.
The astrocytes and Müller glia cells also contribute to the inflammation in the diabetic retina. Under hyperglycemia, astrocytes have increased activation of NFĸB and production of ROS as well as elevated levels of pro-inflammatory factors including IL-1β, TNF-α, and monocyte chemoattractant protein-1 (MCP-1) [85]. The MCP-1 may further recruit and activate microglia, which accelerate the local inflammatory response [86]. The Müller glial cells in the retina of STZ-induced diabetic rats have increased expression of pro-inflammatory factors, such as ICAM-1 [87]. Increased IL-1β in the diabetic retina can stimulate the expression of IL-6 and activate NFĸB in Müller cells, suggesting that the Müller cells mediate the exacerbation of inflammation in the diabetic retina [88]. In addition, the production and secretion of anti-inflammatory pigment epithelium-derived factor (PEDF) [89] are decreased in Müller cells under hyperglycemic [90] or hypoxic [91] conditions, but the expression of pro-inflammatory VEGF in Müller cells is increased under these conditions [92,93]. Taken together, microglia, astrocytes, and Müller cells are all involved in diabetes-elicited inflammation and contribute to apoptosis in the neural retina.

2.3. Glutamate Toxicity in the Diabetic Retina

One mechanism of neuronal apoptosis in the diabetic retina is glutamate excitotoxicity. Glutamate, an excitatory neurotransmitter, mediates the synaptic transmission in the retina [94]. Uptake of glutamate in the synaptic cleft by neurons and glial cells is necessary to maintain the concentration of extracellular glutamate and cease the activation of the postsynaptic receptors [95]. In the diabetic retina, glutamate [96] and its receptors are upregulated [97]. In addition, the activity of glutamate transporters is reduced in Müller glia cells under diabetes [98,99]. Increased glutamate release and reduced glutamate transporters induce extended activation of the glutamate receptors allowing excessive influx of calcium into neurons [100]. The elevated intracellular calcium is transported into the mitochondrial matrix and activates the PTP, which facilitates the release of cytochrome C and production of ROS and leads to the apoptosis of neurons [101]. Hence, diabetes-elicited changes in glutamate, its receptors, and glutamate transporters in the retina cause glutamate toxicity that also contributes to neuronal apoptosis.

3. MicroRNAs and DR

3.1. Overview of microRNAs and DR

MicroRNAs (miRs) are short, non-coding, single-stranded RNAs approximately 23 nucleotides in size, and they target one or more downstream messenger RNAs (mRNAs) causing post-transcriptional degradation or translational repression [102,103,104]. The mature miR is derived from a precursor sequence transcribed from the genome by either RNA polymerase II or III, and miR expression shows tissue- and developmental-stage-specific patterns [102,103]. MicroRNAs inhibit the translation of target mRNAs by preventing the initiation of translation [105,106,107,108], inhibiting the elongation of translation [109,110,111], and inducing the degradation of target mRNAs [102,103,112].
MicroRNAs represent a set of modulators that regulate metabolism, inflammation, and angiogenesis [113], and they have also been linked to DR [114,115]. Changes of miR levels in various organs or blood have been reported in diabetic patients and animals, and in particular, changes in circulating or retinal miRs correlate to some disease progressions and have been suggested as biomarkers for chronic diseases associated with diabetes including DR [114,116]. In STZ-induced diabetic rats, at least 86 miRs are altered in the retina [115,117,118]. Patients with T1D have circulating miR-29a, miR-148a, miR-181a, and miR-200a upregulated, while miR-21a, miR-93, miR-126, and miR-146a are downregulated [119]. The level of miR-126 negatively correlates with the risk of developing PDR [120]. The decreased miR-150 and increased miR-30b detected from the plasma of T1D patients are associated with the development of DR [121]. In the plasma of T2D patients and obese-hyperglycemic mice (ob/ob), the levels of miR-15a, miR-20b, miR-21, miR-24, miR-126, miR-191, miR-197, miR-320, miR-486, and miR-150 are decreased [122]. The downregulation of miR-20b in the serum of T2D patients correlates with the development of DR and may be used to predict the severity of DR [123]. While diabetes-associated changes of miRs clearly demonstrate a correlation between miRs and DR progression, few miRs have been shown to directly contribute to the pathogenesis of DR.

3.2. Evidence of miRs Involved in Inflammation, Oxidative Stress, and Apoptosis in DR

As described in previous sections, inflammation, oxidative stress, and cell apoptosis are part of the pathogenesis of DR, and changed miRs in the blood or retina could be involved in these processes [124]. In cultured retinal ganglion cells (RGCs) treated with a high concentration of glucose (HG), the expression of miR-495 is increased. Overexpression of miR-495 further exacerbates the HG-induced RGC apoptosis, while its inhibition protects RGCs against cell death [125]. In the retina of high-fat-diet-induced T2D rats, retinal miR-93-5p is decreased. Overexpression of miR-93-5p in the diabetic retina alleviates the microvascular degeneration, downregulates pro-inflammatory factors (IL-1β, IL-6, and TNF-α), and elevates antioxidant levels, including GSH and superoxide dismutase (SOD) [126]. MiR-21 is decreased in the retina of T2D mice (db/db) and in RECs treated with palmitic acid, a condition mimicking an extracellular high-fat environment. Knocking out miR-21 in T2D mice alleviates the degeneration and leukostasis of the retinal microvasculature, decreases the levels of pro-inflammatory factors (TNF-α and VCAM-1), and upregulates the antioxidant PPARα in the retina [127]. Overexpression of miR-145 in cultured RECs alleviates the HG-induced apoptosis in part because the activation of toll-like receptor 4 (TLR4) mediates inflammatory responses and promotes the activation of NFĸB [128], and TLR4 is a downstream target of miR-145. In HG-treated RECs, overexpression of miR-145 suppresses the expression of TLR4 and inhibits the activation of NFĸB and production of other pro-inflammatory factors (IL-1β and TNF-α) [129].
In STZ-diabetic rats, miR-195 is increased in the retinal GCL, INL, ONL, and RECs compared with non-diabetic rats. The upregulation of miR-195 also occurs in cultured RECs treated with HG. The expression of manganese superoxide dismutase (MnSOD), an endogenous antioxidant, is decreased in the STZ-diabetic retina and cultured RECs treated with HG, which correlates with increased oxidative stress and apoptosis [130,131]. Inhibition of miR-195 mitigates the STZ-diabetes- and HG-induced suppression of MnSOD, thus alleviates diabetes and HG-elicited apoptosis [132]. MiR-146a is downregulated in the circulation of T2D patients [133] and also decreased in cultured RECs treated with HG [134]. Decreased miR-146a correlates with escalated inflammation [135]. In STZ-diabetic rats, intraocular injection of miR-146a suppresses the diabetes-induced increase of the pro-inflammatory intercellular adhesion molecule 1 (ICAM1) and mitigates the damage to retinal light response and microvascular integrity [118]. Overexpression of miR-146a inhibits the inflammatory response in HG-treated RECs by suppressing the expressions of TLR4, phosphorylated NFĸB, and TNF-α and blocking the downstream signaling of TLR4 [134]. MiR-15a is decreased in the RECs of diabetic patients compared with non-diabetic subjects. Overexpression of miR-15a in the mouse retina inhibits the expression of pro-inflammatory factors, including IL-1β, IL-6, and TNF-α [136]. MiR-20b is decreased in the serum of T2D patients compared with healthy subjects, and T2DR patients have further decreases of miR-20b compared with T2D patients without retinopathy [123]. Overexpression of miR-20b-3p in the eyes of STZ-diabetic rats alleviates the visual dysfunction as well as neural and vascular degeneration in the retina by reducing BAX but increasing BCL-2, thus reducing apoptosis in the retina of STZ-diabetic rats. In addition, the expressions of pro-inflammatory factors (IL-1β and TNF-α) are downregulated by overexpressing miR-20b-3p in the diabetic retina [137]. These examples further demonstrate the crucial roles of miRs in the development of DR. (Table 1).

4. MicroRNA-150 and DR

4.1. Decreased microRNA-150 (miR-150) Is Correlated with the Development of DR

MicroRNA-150 is downregulated in patients with obesity [138], T1D [139,140], and T2D [121]. In high-fat-diet (HFD)-induced T2D mice, miR-150 is decreased in the plasma and retina [141,142]. Downregulation of miR-150 is also observed in the heart of STZ-diabetic rats [143] and in the ischemic retina of mice [144]. Inhibition of miR-150 promotes apoptosis [145], while its overexpression alleviates the apoptosis of cells under hypoxia [146], in which local hypoxia occurs in the diabetic retina [147,148]. Overexpression of miR-150 also protects the retinal vasculature from degeneration induced by oxygen-induced retinopathy, a model for hypoxia-induced angiogenesis [149]. Moreover, miR-150 is an intrinsic suppressor of inflammation [113]. Overexpression of miR-150 downregulates TNF-α and NFĸB induced by lipopolysaccharide (LPS) in endothelial cells [150]. Deletion of miR-150 (miR-150−/−) exacerbates the increase of IL-1β, IL-6, and TNF-α in mice with HFD-induced T2D [113]. We observed that plasma and retinal miR-150 is decreased in mice fed with an HFD even before diabetes develops [142]. The miR-150 knockout (miR-150−/−) mice with HFD-induced T2D display more severe retinal neural dysfunction and vascular pathologies compared with wild-type (WT) mice with HFD-T2D (Figure 1A) [141,142]. Therefore, decreased miR-150 correlates with the development of diabetes and may facilitate the development of DR by promoting apoptosis and inflammation in the neural and vascular retina.

4.2. The Targets of miR-150 in Diabetes

MicroRNAs often have many targets, and a single mRNA can also be targeted by multiple miRs [102,103,151], and the biological processes mediated by miRs and their targets are often tissue- and cell-type-specific [103,152]. Decreased miR-150 may promote apoptosis and inflammation in the diabetic retina through upregulating its downstream target genes. There are confirmed target genes of miR-150 that can regulate inflammation. In HFD-induced T2D mice, decreased miR-150 upregulates its target genes MYB proto-oncogene (Myb), ETS-domain transcription factor 1 (Elk1), and eukaryotic translation termination factor 1 (Etf1). Knocking down Myb, Elk1, or Etf1 suppresses the inflammatory response by inhibiting the activation of B cells [113]. Early growth response 1 (Egr1) is another target gene of miR-150 [153], and knockdown of this target alleviates the diabetes-induced inflammation in mouse mesangial cells by downregulating pro-inflammatory factors (IL-1β, IL-6, and TNF-α) [154,155]. Moreover, these target genes of miR-150 (Myb, Elk1, Etf1, and Egr1) are also involved in the regulation of apoptosis. Knocking out Myb upregulates the apoptosis of mouse colorectal carcinoma cells [156], and overexpressing Myb decreases the production of ROS and alleviates the apoptosis in cardiomyocytes after hypoxia/reoxygenation injury [157]. Overexpression of ELK1 protein has been found to induce apoptosis in neurons by interacting with the mitochondrial permeability transition pore complex (PTP) [158]. Transfection of Elk1 in the dendrites of primary neurons induces apoptosis [159], while inhibition of Elk1 alleviates the apoptosis of neurons under oxygen–glucose deprivation [160]. Upregulated Etf1 is associated with decreased apoptosis in mouse pre-osteoblast cells [161]. Increased expression of Egr1 is associated with the apoptosis of squamous cell carcinoma cells and breast cancer cells, while knocking down Egr1 mitigates apoptosis [162,163]. In addition to Myb and Egr2 (direct targets of miR-150) that are known to promote angiogenesis by increasing the population of hemogenic endothelial cells [164] or upregulating vascular endothelial growth factor (VEGF) and its receptor 2 (VEGFR2) expressions [165,166], respectively, both VEGF and VEGFR2 are downstream of miR-150 [141,149]. VEGF and its principal receptor for angiogenesis VEGFR2 are both upregulated in diabetic eyes [167,168,169], and anti-VEGF therapies have been used to treat neovascularization in DR [169,170,171]. As miR-150 is downregulated in diabetes and DR, its downstream targets are upregulated and correlate with diabetes-associated inflammation, oxidative stress, apoptosis, and pathological angiogenesis. Thus, miR-150 is not only a biomarker for diabetes and DR, but it could also be a potential therapeutic target for treating diabetes-associated chronic diseases and DR.

4.3. miR-150 and Inflammation in the Diabetic Retina

As mentioned previously, inflammation is a major contributor to DR [72,172]. Chronic meta-inflammation is a hallmark of obesity and obesity-associated type 2 diabetes (T2D) [173,174], but numerous studies have indicated that intraocular rather than systemic inflammation is more closely associated with the vascular complications in DR [46,74,175,176,177,178,179,180,181,182,183,184]. Interestingly, diabetic patients who also have retinitis pigmentosa (RP), a congenital blindness with initial degeneration of rod photoreceptors, rarely develop DR [185,186,187], and there is a clear inverse correlation between RP and DR [185,186]. The RP patients who had been diabetic for nearly 40 years developed other non-retinal vascular complications, but none had retinal microaneurysms, exudates, or any clinical DR [185,186,187]. In mice, genetic deletion of rod photoreceptors or pharmacological inhibition of photoreceptors reduces retinal inflammation and alleviates progression of DR [188,189]. Therefore, retinal photoreceptors are a major source of intraocular inflammation and directly contribute to vascular abnormalities in diabetes [6,22,23,24,33,34,36].
MiR-150 is an intrinsic suppressor of inflammation [114] since it suppresses the expression of pro-inflammatory molecules and cytokines, including nuclear factor kappa B (NF-ĸB), TNFα, IL1β, and IL6 [113,190,191,192,193,194]. Overexpression of miR-150 downregulates lipopolysaccharide (LPS)-induced expression of TNF-α and NF-ĸB in endothelial cells [150], while deletion of miR-150 in mice (miR-150−/−) augments LPS-stimulated inflammatory responses [113]. MiR-150−/− mice with HFD-induced T2D have further elevated serum pro-inflammatory cytokines (TNFα, IL1β, IL6, CCL2) and lower anti-inflammatory cytokine (IL10) [113]. Compared with wild-type (WT) mice with HFD-induced T2D, these miR-150−/−-T2D mice display more severe T2D with increased glucose intolerance and insulin resistance [113] and significantly reduced retinal light responses [141,142]. Thus, miR-150 exhibits anti-inflammatory [113] properties, and diabetes-associated decrease of miR-150 may contribute to ocular inflammation and further exacerbate the development of DR.
We previously showed that miR-150−/−-T2D mice have more severe inflammation in photoreceptors and exacerbated vascular degeneration compared with the WT-HFD mice [142]. Since the biological processes mediated by microRNAs and their targets are often tissue- and cell-type-dependent as stated earlier [152,195], after screening the top 30 predicted target genes of miR-150 [113,193] and identifying new bona fide targets that are pro-inflammatory [113], multiple transcription factors including the eukaryotic translation termination factor 1 (Etf1), early growth response 1 (Egr1), MYB proto-oncogene (Myb), and ETS-domain transcription factor 1 (Elk1) were found to be expressed in retinal photoreceptors and endothelial cells [196]. Downregulation of miR-150 correlates with an upregulation of Etf1, Egr1, Myb, and Elk1 and pro-inflammatory cytokines, while overexpression of miR-150 or knocking down any of these transfection factors decrease the expression of pro-inflammatory cytokines in cultured adipose B lymphocytes [113].
In the diabetic retina, photoreceptors are one of the major sources of retinal inflammation [175,189]. Using cultured murine photoreceptors treated with palmitic acid (PA) to mimic obesity-associated T2D, we found that PA elicited an increase of phosphorylated NF-ĸB (pP65), an inflammation marker, which persisted for 24 h and correlated with a persisting decrease of miR-150 and increase of Elk1. However, PA elicited only temporary increases of Etf1, Egr1, or Myb, although these three transcription factors are direct downstream targets of miR-150 and expressed in the neural retina [196]. Overexpression of miR-150 or knocking down Elk1 not only decreased the expression of ELK1 (protein) but also relieved PA-induced increase of inflammation.
Phosphorylated ELK1 at S383 (pELK1S383) translocates from the cytoplasm to the nucleus at which time it then activates its downstream genes to promote inflammation [197,198]. The level of pELK1S383 was increased in the retinal outer nuclear layer of obesity-associated T2D mice and the nuclei of palmitic acid-treated murine photoreceptors in cultures, and the increased nuclear pELK1S383 correlated with the upregulated pP65. Deletion of miR-150 not only upregulated ELK1 but also cytoplasmic pELK1S383 in photoreceptors. The miR-150−/− mice with obesity-associated T2DR had further exacerbated retinal photoreceptor inflammation compared with the WT-T2DR mice, and the photoreceptor inflammation correlated with an increase of pELK1S383 in the retinal outer nuclear layer [196]. The nuclear/cytoplasmic (N/C) ratio represents the cytoplasm-to-nucleus translocation of pELK1S383, and PA treatments increased the N/C ratio of pELK1S383 in cultured photoreceptors, and knocking down Elk1 decreased nuclear pELK1S383 and the N/C ratio of pELK1S383 in PA-treated photoreceptors, which also correlated with the downregulation of pP65. Hence, T2D-associated inflammation in photoreceptors was in part mediated by a decrease of miR-150 that caused an increase of nuclear pELK1S383 and led to photoreceptor inflammation. Therefore, overexpression of miR-150 or knocking down of Elk1 may restrain the development of DR by mitigating the inflammation in the neural retina, especially in photoreceptors [196].

4.4. miR-150 and Neural Apoptosis in the Diabetic Retina

The neural retina has the highest oxygen consumption rate among all tissues, including the brain [199], thus making it (especially the photoreceptors) prone to hypoxia-induced apoptosis. There is local hypoxia in the diabetic retina, and among retinal neurons, photoreceptors undergo apoptosis shortly after the onset of diabetes [38,39]. Patients with T1D have thinner neural layers in the retina and visual dysfunction before the diagnostics of DR [23]. Adolescents with T2D for an average of two years have reduced retinal thickness and dampened light responses [27]. The loss of retinal neurons starts 10 weeks after STZ-induced T1D in mice [33], and neuronal apoptosis in the retina occurs in T2D (db/db) mice from 20 weeks of age [35]. Apoptotic photoreceptors can be detected in STZ-diabetic rats 4 weeks after the onset of diabetes [38]. In addition, the dysfunction of photoreceptors in STZ-diabetic mice is associated with the reduced thickness of the outer nuclear layer [200]. Furthermore, diabetic patients with retinitis pigmentosa (RP), a genetic disease with loss of photoreceptors, rarely develop DR, even though these patients develop other diabetes-related vascular diseases [44,45]. In a mouse model of RP, during the period when photoreceptors are undergoing apoptosis, the retinal vasculature is also degenerating. Once all photoreceptors have died, the vascular degeneration stops [46]. Hence, photoreceptor apoptosis in diabetes not only contributes to the neural dysfunction but may also adversely impact diabetic microvascular complications [46,200] and lead to DR.
Subsets of miRs are known to regulate cell proliferation and apoptosis [139]. Among them, inhibition of miR-150 promotes apoptosis of cells under hypoxia [145], and local hypoxia occurs in the early diabetic retina [147,148]. Overexpression of miR-150 alleviates the apoptosis of hypoxic cells [146]. In our HFD/obesity-associated T2D mouse model, not only did HFD-T2D mice have more severe retinal neural dysfunction and apoptotic photoreceptors versus mice fed with a normal diet [141,142], the miR-150−/− mice with HFD-T2D had even more neural dysfunction and the highest numbers of apoptotic photoreceptors compared with the WT mice with HFD-T2D [196]. To further verify the relationship between miR-150 and photoreceptor apoptosis, we treated cultured photoreceptors with PA to elicit cell apoptosis. Interestingly, knocking down miR-150 in photoreceptors caused a significant increase in apoptosis regardless of PA treatments. However, transfections with miR-150 mimics did attenuate the PA-induced apoptosis. Thus, overexpression of miR-150 only in photoreceptors alone might not be enough to overturn PA-induced apoptosis, but an adequate level of miR-150 is necessary for the survival of photoreceptors [196].
Among the major targets of miR-150 expressed in photoreceptors, Elk1 is known to promote apoptosis in neurons [159,201], as overexpression of ELK1 protein has been found to promote apoptosis in neurons. Transfection of Elk1 in the dendrites of primary neurons induces apoptosis [159], while inhibition of Elk1 alleviates the apoptosis of neurons under oxygen–glucose deprivation [160]. As mentioned previously, the activation of ELK1 requires its phosphorylation, and phosphorylation of ELK1 at threonine 417 (pELK1T417) specifically is essential for ELK1-mediated neuronal apoptosis [158]. Thus, we analyzed the levels of ELK1 and pELK1T417 in the inner and outer segments of photoreceptors (IS + OS) as well as in the outer nuclear layer (ONL) from the retinas of HFD-T2D mice [196]. We found that the levels of ELK1 in the cytoplasm (IS + OS) and nuclei (ONL) of photoreceptors were significantly increased in both WT and miR-150−/− mice with HFD-T2D. Knockout of miR-150 (miR-150−/−) upregulated pELK1T417 in the IS + OS of photoreceptors, while increased pELK1T417 was observed in the ONL of all HFD-T2D retinas. It is possible that HFD-induced apoptosis in photoreceptors was mediated by an increase in nuclear pELK1T417, and the upregulation of cytoplasmic pELK1T417 caused by miR-150 knockout exacerbated the HFD-induced apoptosis.
To further determine the relationship of miR-150, ELK1/pELK1T417 and photoreceptor apoptosis, we employed PA-induced apoptosis in cultured photoreceptors [196]. After photoreceptors were treated with PA, the levels of ELK1 significantly increased in a time-dependent manner, which correlated with increased apoptosis. As treatments with PA (24 h) significantly increased ELK1 in all cells, knocking down miR-150 further elevated the PA-elicited increase in ELK1. However, overexpression of miR-150 did not attenuate the PA-induced increase of ELK1 suggesting that overexpression of miR-150 is not sufficient to downregulate PA-stimulated ELK1, which echoes that overexpression of miR-150 in photoreceptors alone might not be enough to overturn PA-induced apoptosis.
In order to verify the functions of ELK1 and pELK1T417 in regulating apoptosis in photoreceptors, we knocked down Elk1 with siRNA (siElk1) in cultured photoreceptors and found that PA-elicited increase of ELK1 was blocked by siElk1, and knocking down Elk1 decreased cytoplasmic pELK1T417 and also arrested the PA-induced increase in nuclear pELK1T417. Thus, knocking down Elk1 effectively inhibited the PA-elicited increase in ELK1 and pELK1T417. Unfortunately, PA-induced apoptosis was not dampened by siElk1, so knockdown of Elk1 alone cannot attenuate PA-induced apoptosis, which is consistent with our data where upregulation of miR-150 in photoreceptors alone was not enough to conquer PA-induced apoptosis [196].
Cell apoptosis can be mediated by the mitochondrial permeability transition pore complex (PTP) that initiates mitochondrial swelling and membrane potential depolarization that leads to cell death [202]. There is a protein–protein interaction between ELK1 and PTP in the brain, and cytoplasmic ELK1 can be isolated from purified mitochondrial fractions. Furthermore, cell apoptosis induced by Elk1 overexpression can be blocked by a PTP inhibitor in cultured primary neurons [201]. Thus, under T2D conditions, upregulated cytoplasmic pELK1T417 would have increased interactions with mitochondrial PTP, which might further accelerate photoreceptor apoptosis. However, while overexpression of miR-150 or downregulation of Elk1 decreases cytoplasmic pELK1T417, it does not reduce nuclear pELK1T417 or overcome PA-elicited apoptosis. In PA-treated photoreceptors, the nuclear/cytoplasmic (N/C) ratio of pELK1T417 remains comparable with cells with/without overexpression of miR-150 and cells with/without knockdown of Elk1. The N/C ratio represents the cytoplasm-to-nucleus translocation of pELK1T417, which is important for trans-activating the downstream targets of Elk1 and regulating apoptosis [203,204]. The translocation of pELK1T417 to the cell nucleus correlates with increased apoptosis in neurons [205]. Therefore, in addition to dampening the expression of ELK1, blocking the translocation of pELK1T417 to the nucleus may be more critical to mitigate diabetes-associated apoptosis in photoreceptors [196].

4.5. miR-150 and Angiogenesis

As neural miR-150 is important for protecting the retina under diabetic insults (described above), decreased miR-150 in vascular endothelial cells may also contribute to ocular angiogenesis. Overexpression of miR-150 in mouse eyes protects the retinal microvasculature from degeneration induced by oxygen-induced retinopathy, a model for pathological angiogenesis in retinopathy of prematurity [205,206], and deletion of miR-150 exacerbates T2D-associated microvascular leakage and degeneration [141,142]. Since well-known diabetic mouse models do not have pathological neovascularization like in PDR patients, we used a three-dimensional collagen matrix culture system of endothelial cells to evaluate the effect of endothelial miR-150 in vascular sprouting, an indicator of neovascularization (Figure 1). We found that overexpression of miR-150 dampened endothelial sprouting and invasion, but inhibition of miR-150 did not affect normal endothelial sprouting (Figure 1B). Furthermore, overexpression of miR-150 decreased the expression of VEGFR2 in cultured endothelial cells [141]. Interestingly, VEGFR2 is not a direct downstream target of miR-150, since the VEGFR2 gene lacks compatible paired sequences. Conversely, the miRNAs predicted to target the 3′-UTR (1479 bp) of the mouse VEGFR2 gene do not include miR-150 [141]. One direct target of miR-150 that may regulate the expression of VEGFR2 is the transcription factor Myb, which binds to a 5′-YAACKG-3′ sequence in the promoter region and regulates the expression of a group of genes involved in cell lineage- and fate-determination in the immune system. The gene encoding VEGFR2 (Vegfr2) has four Myb binding sites in its promoter region, so Vegfr2 can be turned on by Myb [67]. Overexpression of Myb increases the population of hemogenic endothelial cells during embryonic development [68]. We found that overexpression of miR-150 also decreased the expression of MYB in cultured endothelial cells [141], making Myb the most likely downstream target of miR-150 that regulates VEGFR2 expression in vascular endothelial cells. Table 2 is a list of the direct targets of miR-150 discussed above.

5. Conclusions

As decreased miR-150 in the diabetic retina correlates with the development of DR, the action and downstream targets of miR-150 in neural versus vascular retina are different, but all contribute to the pathogenesis of DR (Figure 2). In the neural retina, diabetes-associated decrease of miR-150 promotes inflammation and apoptosis of photoreceptors via Elk1, which contribute to the microvascular degeneration in DR. In the retina vasculature, diabetes-associated decrease of miR-150 promotes endothelial cell sprouting via Myb, which contributes to neovascularization in DR (Figure 2). MiR-150 is expressed in the neural and vascular retina and is also abundant in the circulation, so diabetes-elicited changes in circulating miR-150 are reported in both T1D and T2D patients. Hence, miR-150 is not only a biomarker for DR, it is indeed involved in the pathogenesis and the disease progression of DR. With extensive investigation of miR-150 as an example, diabetes-associated changes in other miRs not only serve as biomarkers to indicate the pathological progression of DR, but they might also actively contribute to the pathogenesis of DR.

Author Contributions

Conceptualization: G.Y.-P.K. and F.Y.; Methodology: F.Y. and K.J.B.; Validation: F.Y., K.J.B. and G.Y.-P.K.; Formal analysis: F.Y., K.J.B. and G.Y.-P.K.; Resources: G.Y.-P.K.; Data Curation: F.Y. and K.J.B.; Writing, Original draft: G.Y.-P.K. and F.Y.; Writing, Review and Editing: G.Y.-P.K. and M.L.K.; Supervision: G.Y.-P.K.; Project Administration: G.Y.-P.K. and M.L.K.; Funding Acquisition: G.Y.-P.K.; All authors have read and agreed to the published version of the manuscript.

Funding

This work is in part supported by a grant from the National Eye Institute, National Institutes of Health, USA (NIHR21EY031813-01A1), a philanthropic gift fund to G.Y.-P.K., and CVMBS graduate student research fellowships (2018 and 2020) to F.Y.

Institutional Review Board Statement

The animal protocol (AUP# 2019-0424) used for this research was approved by the Institutional Animal Care and Use Committee of Texas A&M University.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

We thank Colette Abbey for technical support.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Boyle, J.P.; Thompson, T.J.; Gregg, E.W.; Barker, L.E.; Williamson, D.F. Projection of the year 2050 burden of diabetes in the US adult population: Dynamic modeling of incidence, mortality, and prediabetes prevalence. Popul. Health Metr. 2010, 8, 29. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  2. Engelgau, M.M.; Geiss, L.S.; Saaddine, J.B.; Boyle, J.P.; Benjamin, S.M.; Gregg, E.W.; Tierney, E.F.; Rios-Burrows, N.; Mokdad, A.H.; Ford, E.S.; et al. The evolving diabetes burden in the United States. Ann. Intern. Med. 2004, 140, 945–950. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  3. Barsegian, A.; Kotlyar, B.; Lee, J.; Salifu, M.O.; McFarlane, S.I. Diabetic Retinopathy: Focus on Minority Populations. Int. J. Clin. Endocrinol. Metab. 2017, 3, 034–045. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  4. Barber, A.J. A new view of diabetic retinopathy: A neurodegenerative disease of the eye. Prog. Neuro-Psychopharmacol. Biol. Psychiatry 2003, 27, 283–290. [Google Scholar] [CrossRef]
  5. Wong, T.Y.; Cheung, C.M.; Larsen, M.; Sharma, S.; Simo, R. Diabetic retinopathy. Nat. Rev. Dis. Primers 2016, 2, 16012. [Google Scholar] [CrossRef]
  6. Simó-Servat, O.; Hernández, C.; Simó, R. Diabetic Retinopathy in the Context of Patients with Diabetes. Ophthalmic Res. 2019, 62, 211–217. [Google Scholar] [CrossRef]
  7. Moran, E.P.; Wang, Z.; Chen, J.; Sapieha, P.; Smith, L.E.; Ma, J.X. Neurovascular cross talk in diabetic retinopathy: Pathophysiological roles and therapeutic implications. Am. J. Physiol. Heart Circ. Physiol. 2016, 311, H738–H749. [Google Scholar] [CrossRef] [Green Version]
  8. Cheng, R.; Ma, J.-X. Angiogenesis in diabetes and obesity. Rev. Endocr. Metab. Disord. 2015, 16, 67–75. [Google Scholar] [CrossRef] [Green Version]
  9. Zeng, Y.; Cao, D.; Yang, D.; Zhuang, X.; Hu, Y.; He, M.; Yu, H.; Wang, J.; Yang, C.; Zhang, L. Retinal vasculature–function correlation in non-proliferative diabetic retinopathy. Doc. Ophthalmol. 2020, 140, 129–138. [Google Scholar] [CrossRef]
  10. Simo, R.; Sundstrom, J.M.; Antonetti, D.A. Ocular Anti-VEGF therapy for diabetic retinopathy: The role of VEGF in the pathogenesis of diabetic retinopathy. Diabetes Care 2014, 37, 893–899. [Google Scholar] [CrossRef]
  11. Gallemore, R.P.; Nguyen, D. When Anti-VEGF Treatment Fails. Review of Ophthalmology 2008, March. Available online: http://www.reviewofophthalmology.com/content/d/retinal_insider/i/1230/c/23141/ (accessed on 19 May 2019).
  12. Lux, A.; Llacer, H.; Heussen, F.M.; Joussen, A.M. Non-responders to bevacizumab (Avastin) therapy of choroidal neovascular lesions. Br. J. Ophthalmol. 2007, 91, 1318–1322. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  13. Cheung, N.; Wong, I.Y.; Wong, T.Y. Ocular anti-VEGF therapy for diabetic retinopathy: Overview of clinical efficacy and evolving applications. Diabetes Care 2014, 37, 900–905. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  14. North, R.V.; Farrell, U.; Banford, D.; Jones, C.; Gregory, J.W.; Butler, G.; Owens, D.R. Visual function in young IDDM patients over 8 years of age. A 4-year longitudinal study. Diabetes Care 1997, 20, 1724–1730. [Google Scholar] [CrossRef] [PubMed]
  15. Sawicki, P.T.; Karschny, L.; Stolpe, V.; Wolf, E.; Berger, M. Color discrimination and accuracy of blood glucose self-monitoring in type I diabetic patients. Diabetes Care 1991, 14, 135–137. [Google Scholar] [CrossRef] [PubMed]
  16. Shoji, T.; Sakurai, Y.; Sato, H.; Chihara, E.; Takeuchi, M. Do type 2 diabetes patients without diabetic retinopathy or subjects with impaired fasting glucose have impaired colour vision? The Okubo Color Study Report. Diabet. Med. 2011, 28, 865–871. [Google Scholar] [CrossRef] [PubMed]
  17. Harrison, W.W.; Bearse, M.A., Jr.; Ng, J.S.; Jewell, N.P.; Barez, S.; Burger, D.; Schneck, M.E.; Adams, A.J. Multifocal electroretinograms predict onset of diabetic retinopathy in adult patients with diabetes. Investig. Ophthalmol. Vis. Sci. 2011, 52, 772–777. [Google Scholar] [CrossRef] [Green Version]
  18. Lecleire-Collet, A.; Audo, I.; Aout, M.; Girmens, J.F.; Sofroni, R.; Erginay, A.; Le Gargasson, J.F.; Mohand-Said, S.; Meas, T.; Guillausseau, P.J.; et al. Evaluation of retinal function and flicker light-induced retinal vascular response in normotensive patients with diabetes without retinopathy. Investig. Ophthalmol. Vis. Sci. 2011, 52, 2861–2867. [Google Scholar] [CrossRef]
  19. Yamamoto, S.; Kamiyama, M.; Nitta, K.; Yamada, T.; Hayasaka, S. Selective reduction of the S cone electroretinogram in diabetes. Br. J. Ophthalmol. 1996, 80, 973–975. [Google Scholar] [CrossRef] [Green Version]
  20. Tzekov, R.; Arden, G.B. The Electroretinogram in Diabetic Retinopathy. Surv. Ophthalmol. 1999, 44, 53–60. [Google Scholar] [CrossRef]
  21. Barber, A.J.; Lieth, E.; Khin, S.A.; Antonetti, D.A.; Buchanan, A.G.; Gardner, T.W. Neural apoptosis in the retina during experimental and human diabetes. Early onset and effect of insulin. J. Clin. Investig. 1998, 102, 783–791. [Google Scholar] [CrossRef] [PubMed]
  22. Lopes De Faria, J.M.; Russ, H.; Costa, V.P. Retinal nerve fibre layer loss in patients with type 1 diabetes mellitus without retinopathy. Br. J. Ophthalmol. 2002, 86, 725–728. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  23. van Dijk, H.W.; Verbraak, F.D.; Stehouwer, M.; Kok, P.H.; Garvin, M.K.; Sonka, M.; DeVries, J.H.; Schlingemann, R.O.; Abramoff, M.D. Association of visual function and ganglion cell layer thickness in patients with diabetes mellitus type 1 and no or minimal diabetic retinopathy. Vis. Res 2011, 51, 224–228. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  24. Carrasco, E.; Hernandez, C.; Miralles, A.; Huguet, P.; Farres, J.; Simo, R. Lower Somatostatin Expression Is an Early Event in Diabetic Retinopathy and Is Associated with Retinal Neurodegeneration. Diabetes Care 2007, 30, 2902–2908. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  25. Garcia-Ramírez, M.; Hernández, C.; Villarroel, M.; Canals, F.; Alonso, M.A.; Fortuny, R.; Masmiquel, L.; Navarro, A.; García-Arumí, J.; Simo, R. Interphotoreceptor retinoid-binding protein (IRBP) is downregulated at early stages of diabetic retinopathy. Diabetologia 2009, 52, 2633–2641. [Google Scholar] [CrossRef] [Green Version]
  26. El-Asrar, A.M.A.; Dralands, L.; Missotten, L.; Al-Jadaan, I.A.; Geboes, K. Expression of Apoptosis Markers in the Retinas of Human Subjects with Diabetes. Investig. Ophthalmol. Vis. Sci. 2004, 45, 2760. [Google Scholar] [CrossRef]
  27. Bronson-Castain, K.W.; Bearse, M.A., Jr.; Neuville, J.; Jonasdottir, S.; King-Hooper, B.; Barez, S.; Schneck, M.E.; Adams, A.J. Adolescents with Type 2 diabetes: Early indications of focal retinal neuropathy, retinal thinning, and venular dilation. Retina 2009, 29, 618–626. [Google Scholar] [CrossRef] [Green Version]
  28. Tavares Ferreira, J.; Proença, R.; Alves, M.; Dias-Santos, A.; Santos, B.O.; Cunha, J.P.; Papoila, A.L.; Abegão Pinto, L. Retina and Choroid of Diabetic Patients Without Observed Retinal Vascular Changes: A Longitudinal Study. Am. J. Ophthalmol. 2017, 176, 15–25. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  29. Van Dijk, H.W.; Verbraak, F.D.; Kok, P.H.B.; Stehouwer, M.; Garvin, M.K.; Sonka, M.; Devries, J.H.; Schlingemann, R.O.; Abràmoff, M.D. Early Neurodegeneration in the Retina of Type 2 Diabetic Patients. Investig. Ophthalmol. Vis. Sci. 2012, 53, 2715. [Google Scholar] [CrossRef] [Green Version]
  30. Chhablani, J.; Sharma, A.; Goud, A.; Peguda, H.K.; Rao, H.L.; Begum, V.U.; Barteselli, G. Neurodegeneration in Type 2 Diabetes: Evidence from Spectral-Domain Optical Coherence Tomography. Investig. Ophthalmol. Vis. Sci. 2015, 56, 6333. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  31. Frydkjaer-Olsen, U.; Hansen, R.S.; Peto, T.; Grauslund, J. Structural neurodegeneration correlates with early diabetic retinopathy. Int. Ophthalmol. 2018, 38, 1621–1626. [Google Scholar] [CrossRef]
  32. Barber, A.J.; Antonetti, D.A.; Kern, T.S.; Reiter, C.E.; Soans, R.S.; Krady, J.K.; Levison, S.W.; Gardner, T.W.; Bronson, S.K. The Ins2Akita mouse as a model of early retinal complications in diabetes. Investig. Ophthalmol. Vis. Sci. 2005, 46, 2210–2218. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  33. Martin, P.M.; Roon, P.; Van Ells, T.K.; Ganapathy, V.; Smith, S.B. Death of retinal neurons in streptozotocin-induced diabetic mice. Investig. Ophthalmol. Vis. Sci. 2004, 45, 3330–3336. [Google Scholar] [CrossRef] [Green Version]
  34. Ning, X.; Baoyu, Q.; Yuzhen, L.; Shuli, S.; Reed, E.; Li, Q. Neuro-optic cell apoptosis and microangiopathy in KKAY mouse retina. Int. J. Mol. Med. 2004, 13, 87–92. [Google Scholar] [CrossRef] [PubMed]
  35. Yang, Q.; Xu, Y.; Xie, P.; Cheng, H.; Song, Q.; Su, T.; Yuan, S.; Liu, Q. Retinal Neurodegeneration in db/db Mice at the Early Period of Diabetes. J. Ophthalmol. 2015, 2015, 757412. [Google Scholar] [CrossRef] [Green Version]
  36. Ahmadieh, H.; Behbahani, S.; Safi, S. Continuous wavelet transform analysis of ERG in patients with diabetic retinopathy. Doc. Ophthalmol. 2021, 142, 305–314. [Google Scholar] [CrossRef] [PubMed]
  37. Kim, M.; Kim, R.Y.; Park, W.; Park, Y.G.; Kim, I.B.; Park, Y.H. Electroretinography and retinal microvascular changes in type 2 diabetes. Acta Ophthalmol. 2020, 98, e807–e813. [Google Scholar] [CrossRef] [PubMed]
  38. Park, S.H.; Park, J.W.; Park, S.J.; Kim, K.Y.; Chung, J.W.; Chun, M.H.; Oh, S.J. Apoptotic death of photoreceptors in the streptozotocin-induced diabetic rat retina. Diabetologia 2003, 46, 1260–1268. [Google Scholar] [CrossRef]
  39. Zhang, J.; Wu, Y.; Jin, Y.; Ji, F.; Sinclair, S.H.; Luo, Y.; Xu, G.; Lu, L.; Dai, W.; Yanoff, M.; et al. Intravitreal injection of erythropoietin protects both retinal vascular and neuronal cells in early diabetes. Investig. Ophthalmol. Vis. Sci. 2008, 49, 732–742. [Google Scholar] [CrossRef] [PubMed]
  40. McAnany, J.J.; Park, J.C. Cone Photoreceptor Dysfunction in Early-Stage Diabetic Retinopathy: Association Between the Activation Phase of Cone Phototransduction and the Flicker Electroretinogram. Investig. Ophthalmol. Vis. Sci. 2019, 60, 64. [Google Scholar] [CrossRef] [Green Version]
  41. Kim, A.J.; Chang, J.Y.; Shi, L.; Chang, R.C.; Ko, M.L.; Ko, G.Y. The Effects of Metformin on Obesity-Induced Dysfunctional Retinas. Investig. Ophthalmol. Vis. Sci. 2017, 58, 106–118. [Google Scholar] [CrossRef]
  42. Karaca, C.; Karaca, Z. Beyond Hyperglycemia, Evidence for Retinal Neurodegeneration in Metabolic Syndrome. Investig. Ophthalmol. Vis. Sci. 2018, 59, 1360–1367. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  43. Énzsöly, A.; Szabó, A.; Kántor, O.; Dávid, C.; Szalay, P.; Szabó, K.; Szél, Á.; Németh, J.; Lukáts, Á. Pathologic Alterations of the Outer Retina in Streptozotocin-Induced Diabetes. Investig. Ophthalmol. Vis. Sci. 2014, 55, 3686. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  44. Arden, G.B. The absence of diabetic retinopathy in patients with retinitis pigmentosa: Implications for pathophysiology and possible treatment. Br. J. Ophthalmol. 2001, 85, 366–370. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  45. Lahdenranta, J.P.R.; Schlingemann, R.O.; Hagedorn, M.; Stallcup, W.B.; Bucana, C.D.; Sidman, R.L.; Arap, W. An anti-angiogenic state in mice and humans with retinal photoreceptor cell degeneration. Proc. Natl. Acad. Sci. USA 2001, 98, 6. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  46. Liu, H.; Tang, J.; Du, Y.; Saadane, A.; Tonade, D.; Samuels, I.; Veenstra, A.; Palczewski, K.; Kern, T.S. Photoreceptor Cells Influence Retinal Vascular Degeneration in Mouse Models of Retinal Degeneration and Diabetes. Investig. Ophthalmol. Vis. Sci. 2016, 57, 4272–4281. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  47. Mizutani, M.; Kern, T.S.; Lorenzi, M. Accelerated death of retinal microvascular cells in human and experimental diabetic retinopathy. J. Clin. Investig. 1996, 97, 2883–2890. [Google Scholar] [CrossRef]
  48. Li, W.; Myron, Y.; Liu, X.; Ye, X. Retinal capillary pericyte apoptosis in early human diabetic retinopathy. Chin. Med. J. 1997, 110, 659–663. [Google Scholar] [PubMed]
  49. Barber, A.J.; Gardner, T.W.; Abcouwer, S.F. The Significance of Vascular and Neural Apoptosis to the Pathology of Diabetic Retinopathy. Investig. Ophthalmol. Vis. Sci. 2011, 52, 1156. [Google Scholar] [CrossRef]
  50. Beltramo, E.; Porta, M. Pericyte Loss in Diabetic Retinopathy: Mechanisms and Consequences. Curr. Med. Chem. 2013, 20, 3218–3225. [Google Scholar] [CrossRef] [Green Version]
  51. Curtis, T.M.; Gardiner, T.A.; Stitt, A.W. Microvascular lesions of diabetic retinopathy: Clues towards understanding pathogenesis? Eye 2009, 23, 1496–1508. [Google Scholar] [CrossRef] [PubMed]
  52. Kern, T.S.; Tang, J.; Mizutani, M.; Kowluru, R.A.; Nagaraj, R.H.; Romeo, G.; Podesta, F.; Lorenzi, M. Response of Capillary Cell Death to Aminoguanidine Predicts the Development of Retinopathy: Comparison of Diabetes and Galactosemia. Investig. Ophthalmol. Vis. Sci. 2000, 41, 3972–3978. [Google Scholar]
  53. Joussen, A.M.; Poulaki, V.; Mitsiades, N.; Cai, W.Y.; Suzuma, I.; Pak, J.; Ju, S.T.; Rook, S.L.; Esser, P.; Mitsiades, C.; et al. Suppression of Fas-FasL-induced endothelial cell apoptosis prevents diabetic blood-retinal barrier breakdown in a model of streptozotocin-induced diabetes. FASEB J. 2003, 17, 76–78. [Google Scholar] [CrossRef] [PubMed]
  54. Podestà, F.; Romeo, G.; Liu, W.-H.; Krajewski, S.; Reed, J.C.; Gerhardinger, C.; Lorenzi, M. Bax Is Increased in the Retina of Diabetic Subjects and Is Associated with Pericyte Apoptosis in Vivo and in Vitro. Am. J. Pathol. 2000, 156, 1025–1032. [Google Scholar] [CrossRef] [Green Version]
  55. Sugiyama, T.; Kobayashi, M.; Kawamura, H.; Li, Q.; Puro, D.G. Enhancement of P2 × 7-Induced Pore Formation and Apoptosis: An Early Effect of Diabetes on the Retinal Microvasculature. Investig. Ophthalmol. Vis. Sci. 2004, 45, 1026. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  56. Cheung, A.K.H.; Fung, M.K.L.; Lo, A.C.Y.; Lam, T.T.L.; So, K.F.; Chung, S.S.M.; Chung, S.K. Aldose Reductase Deficiency Prevents Diabetes-Induced Blood-Retinal Barrier Breakdown, Apoptosis, and Glial Reactivation in the Retina of db/db Mice. Diabetes 2005, 54, 3119–3125. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  57. Behl, Y.; Krothapalli, P.; Desta, T.; Dipiazza, A.; Roy, S.; Graves, D.T. Diabetes-Enhanced Tumor Necrosis Factor-α Production Promotes Apoptosis and the Loss of Retinal Microvascular Cells in Type 1 and Type 2 Models of Diabetic Retinopathy. Am. J. Pathol. 2008, 172, 1411–1418. [Google Scholar] [CrossRef] [Green Version]
  58. Huang, H.; Gandhi, J.K.; Zhong, X.; Wei, Y.; Gong, J.; Duh, E.J.; Vinores, S.A. TNFα Is Required for Late BRB Breakdown in Diabetic Retinopathy, and Its Inhibition Prevents Leukostasis and Protects Vessels and Neurons from Apoptosis. Investig. Ophthalmol. Vis. Sci. 2011, 52, 1336. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  59. Durham, J.T.; Herman, I.M. Microvascular Modifications in Diabetic Retinopathy. Curr. Diabetes Rep. 2011, 11, 253–264. [Google Scholar] [CrossRef]
  60. Penn, J.S.; Madan, A.; Caldwell, R.B.; Bartoli, M.; Caldwell, R.W.; Hartnett, M.E. Vascular endothelial growth factor in eye disease. Prog. Retin. Eye Res. 2008, 27, 331–371. [Google Scholar] [CrossRef] [Green Version]
  61. Kang, Q.; Yang, C. Oxidative stress and diabetic retinopathy: Molecular mechanisms, pathogenetic role and therapeutic implications. Redox. Biol. 2020, 37, 101799. [Google Scholar] [CrossRef]
  62. Letts, J.A.; Sazanov, L.A. Clarifying the supercomplex: The higher-order organization of the mitochondrial electron transport chain. Nat. Struct. Mol. Biol. 2017, 24, 800–808. [Google Scholar] [CrossRef] [PubMed]
  63. Brownlee, M. The Pathobiology of Diabetic Complications: A Unifying Mechanism. Diabetes 2005, 54, 1615–1625. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  64. Panday, A.; Sahoo, M.K.; Osorio, D.; Batra, S. NADPH oxidases: An overview from structure to innate immunity-associated pathologies. Cell. Mol. Immunol. 2015, 12, 5–23. [Google Scholar] [CrossRef] [Green Version]
  65. Kizub, I.V.; Klymenko, K.I.; Soloviev, A.I. Protein kinase C in enhanced vascular tone in diabetes mellitus. Int. J. Cardiol. 2014, 174, 230–242. [Google Scholar] [CrossRef] [PubMed]
  66. Zhang, Y.; Murugesan, P.; Huang, K.; Cai, H. NADPH oxidases and oxidase crosstalk in cardiovascular diseases: Novel therapeutic targets. Nat. Rev. Cardiol. 2020, 17, 170–194. [Google Scholar] [CrossRef]
  67. Neginskaya, M.A.; Pavlov, E.V.; Sheu, S.S. Electrophysiological properties of the mitochondrial permeability transition pores: Channel diversity and disease implication. Biochim. Biophys. Acta (BBA)-Bioenerg. 2021, 1862, 148357. [Google Scholar] [CrossRef]
  68. Wakabayashi, Y.; Usui, Y.; Shibauchi, Y.; Uchino, H.; Goto, H. Increased levels of 8-hydroxydeoxyguanosine in the vitreous of patients with diabetic retinopathy. Diabetes Res. Clin. Pract. 2010, 89, e59–e61. [Google Scholar] [CrossRef]
  69. Kanwar, M.; Chan, P.-S.; Kern, T.S.; Kowluru, R.A. Oxidative Damage in the Retinal Mitochondria of Diabetic Mice: Possible Protection by Superoxide Dismutase. Investig. Ophthalmol. Vis. Sci. 2007, 48, 3805. [Google Scholar] [CrossRef] [Green Version]
  70. Kowluru, R.A.; Odenbach, S. Effect of Long-Term Administration of-Lipoic Acid on Retinal Capillary Cell Death and the Development of Retinopathy in Diabetic Rats. Diabetes 2004, 53, 3233–3238. [Google Scholar] [CrossRef] [Green Version]
  71. Sasaki, M.; Ozawa, Y.; Kurihara, T.; Kubota, S.; Yuki, K.; Noda, K.; Kobayashi, S.; Ishida, S.; Tsubota, K. Neurodegenerative influence of oxidative stress in the retina of a murine model of diabetes. Diabetologia 2010, 53, 971–979. [Google Scholar] [CrossRef] [Green Version]
  72. Tang, J.; Kern, T.S. Inflammation in diabetic retinopathy. Prog. Retin. Eye Res. 2011, 30, 343–358. [Google Scholar] [CrossRef] [PubMed]
  73. Xu, H.; Chen, M. Diabetic retinopathy and dysregulated innate immunity. Vis. Res. 2017, 139, 39–46. [Google Scholar] [CrossRef] [PubMed]
  74. Yu, Y.; Chen, H.; Su, S.B. Neuroinflammatory responses in diabetic retinopathy. J. NeuroInflamm. 2015, 12, 141. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  75. Mulfaul, K.; Ozaki, E.; Fernando, N.; Brennan, K.; Chirco, K.R.; Connolly, E.; Greene, C.; Maminishkis, A.; Salomon, R.G.; Linetsky, M.; et al. Toll-like Receptor 2 Facilitates Oxidative Damage-Induced Retinal Degeneration. Cell Rep. 2020, 30, 2209–2224.e2205. [Google Scholar] [CrossRef] [Green Version]
  76. Lee, J.-J.; Wang, P.-W.; Yang, I.H.; Huang, H.-M.; Chang, C.-S.; Wu, C.-L.; Chuang, J.-H. High-Fat Diet Induces Toll-Like Receptor 4-Dependent Macrophage/Microglial Cell Activation and Retinal Impairment. Investig. Ophthalmol. Vis. Sci. 2015, 56, 3041. [Google Scholar] [CrossRef] [Green Version]
  77. Grigsby, J.G.; Cardona, S.M.; Pouw, C.E.; Muniz, A.; Mendiola, A.S.; Tsin, A.T.C.; Allen, D.M.; Cardona, A.E. The Role of Microglia in Diabetic Retinopathy. J. Ophthalmol. 2014, 2014, 705783. [Google Scholar] [CrossRef] [Green Version]
  78. Busik, J.V.; Mohr, S.; Grant, M.B. Hyperglycemia-Induced Reactive Oxygen Species Toxicity to Endothelial Cells Is Dependent on Paracrine Mediators. Diabetes 2008, 57, 1952–1965. [Google Scholar] [CrossRef] [Green Version]
  79. Chen, W.; Esselman, W.J.; Jump, D.B.; Busik, J.V. Anti-inflammatory Effect of Docosahexaenoic Acid on Cytokine-Induced Adhesion Molecule Expression in Human Retinal Vascular Endothelial Cells. Investig. Ophthalmol. Vis. Sci. 2005, 46, 4342. [Google Scholar] [CrossRef]
  80. Rübsam, A.; Parikh, S.; Fort, P. Role of Inflammation in Diabetic Retinopathy. Int. J. Mol. Sci. 2018, 19, 942. [Google Scholar] [CrossRef] [Green Version]
  81. Vincent, J.A.; Mohr, S. Inhibition of Caspase-1/Interleukin-1 Signaling Prevents Degeneration of Retinal Capillaries in Diabetes and Galactosemia. Diabetes 2007, 56, 224–230. [Google Scholar] [CrossRef] [Green Version]
  82. Joussen, A.M.; Doehmen, S.; Le, M.L.; Koizumi, K.; Radetzky, S.; Krohne, T.U.; Poulaki, V.; Semkova, I.; Kociok, N. TNF-alpha mediated apoptosis plays an important role in the development of early diabetic retinopathy and long-term histopathological alterations. Mol. Vis. 2009, 15, 1418–1428. [Google Scholar] [PubMed]
  83. Sivakumar, V.; Foulds, W.S.; Luu, C.D.; Ling, E.-A.; Kaur, C. Retinal ganglion cell death is induced by microglia derived pro-inflammatory cytokines in the hypoxic neonatal retina. J. Pathol. 2011, 224, 245–260. [Google Scholar] [CrossRef] [PubMed]
  84. Syeda, S.; Patel, A.K.; Lee, T.; Hackam, A.S. Reduced photoreceptor death and improved retinal function during retinal degeneration in mice lacking innate immunity adaptor protein MyD88. Exp. Neurol. 2015, 267, 1–12. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  85. Shin, E.S.; Huang, Q.; Gurel, Z.; Sorenson, C.M.; Sheibani, N. High Glucose Alters Retinal Astrocytes Phenotype through Increased Production of Inflammatory Cytokines and Oxidative Stress. PLoS ONE 2014, 9, e103148. [Google Scholar] [CrossRef] [Green Version]
  86. Zhang, K.; Luo, J. Role of MCP-1 and CCR2 in alcohol neurotoxicity. Pharmacol. Res. 2019, 139, 360–366. [Google Scholar] [CrossRef]
  87. Gerhardinger, C.; Costa, M.B.S.; Coulombe, M.C.; Toth, I.; Hoehn, T.; Grosu, P. Expression of Acute-Phase Response Proteins in Retinal Muüller Cells in Diabetes. Investig. Ophthalmol. Vis. Sci. 2005, 46, 349. [Google Scholar] [CrossRef] [PubMed]
  88. Liu, X.; Ye, F.; Xiong, H.; Hu, D.N.; Limb, G.A.; Xie, T.; Peng, L.; Zhang, P.; Wei, Y.; Zhang, W.; et al. IL-1beta induces IL-6 production in retinal Muller cells predominantly through the activation of p38 MAPK/NF-kappaB signaling pathway. Exp. Cell Res. 2015, 331, 223–231. [Google Scholar] [CrossRef]
  89. Zhang, S.X.; Wang, J.J.; Gao, G.; Shao, C.; Mott, R.; Ma, J.X. Pigment epithelium-derived factor (PEDF) is an endogenous antiinflammatory factor. FASEB J. 2006, 20, 323–325. [Google Scholar] [CrossRef] [PubMed]
  90. Mu, H.; Zhang, X.-M.; Liu, J.-J.; Dong, L.; Feng, Z.-L. Effect of high glucose concentration on VEGF and PEDF expression in cultured retinal Müller cells. Mol. Biol. Rep. 2009, 36, 2147–2151. [Google Scholar] [CrossRef]
  91. Lange, J.; Yafai, Y.; Reichenbach, A.; Wiedemann, P.; Eichler, W. Regulation of Pigment Epithelium–Derived Factor Production and Release by Retinal Glial (Muüller) Cells under Hypoxia. Investig. Ophthalmol. Vis. Sci. 2008, 49, 5161. [Google Scholar] [CrossRef] [Green Version]
  92. Le, Y.Z. VEGF production and signaling in Muller glia are critical to modulating vascular function and neuronal integrity in diabetic retinopathy and hypoxic retinal vascular diseases. Vis. Res. 2017, 139, 108–114. [Google Scholar] [CrossRef]
  93. Wang, J.J.; Zhu, M.; Le, Y.Z. Functions of Muller cell-derived vascular endothelial growth factor in diabetic retinopathy. World J. Diabetes 2015, 6, 726–733. [Google Scholar] [CrossRef] [PubMed]
  94. Thoreson, W. Glutamate receptors and circuits in the vertebrate retina. Prog. Retin. Eye Res. 1999, 18, 765–810. [Google Scholar] [CrossRef]
  95. Iovino, L.; Tremblay, M.E.; Civiero, L. Glutamate-induced excitotoxicity in Parkinson’s disease: The role of glial cells. J. Pharmacol. Sci. 2020, 144, 151–164. [Google Scholar] [CrossRef]
  96. Ambati, J. Elevated γ-Aminobutyric Acid, Glutamate, and Vascular Endothelial Growth Factor Levels in the Vitreous of Patients with Proliferative Diabetic Retinopathy. Arch. Ophthalmol. 1997, 115, 1161. [Google Scholar] [CrossRef]
  97. Santiago, A.R.; Hughes, J.M.; Kamphuis, W.; Schlingemann, R.O.; Ambrósio, A.F. Diabetes changes ionotropic glutamate receptor subunit expression level in the human retina. Brain Res. 2008, 1198, 153–159. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  98. Ma, M.; Zhao, S.; Zhang, J.; Sun, T.; Fan, Y.; Zheng, Z. High Glucose-Induced TRPC6 Channel Activation Decreases Glutamate Uptake in Rat Retinal Muller Cells. Front. Pharm. 2019, 10, 1668. [Google Scholar] [CrossRef]
  99. Li, Q.; Puro, D.G. Diabetes-Induced Dysfunction of the Glutamate Transporter in Retinal Muüller Cells. Investig. Ophthalmol. Vis. Sci. 2002, 43, 3109–3116. [Google Scholar]
  100. Rao, V.R.; Finkbeiner, S. NMDA and AMPA receptors: Old channels, new tricks. Trends Neurosci. 2007, 30, 284–291. [Google Scholar] [CrossRef]
  101. Ureshino, R.P.; Erustes, A.G.; Bassani, T.B.; Wachilewski, P.; Guarache, G.C.; Nascimento, A.C.; Costa, A.J.; Smaili, S.S.; da Silva Pereira, G.J. The Interplay between Ca2+ Signaling Pathways and Neurodegeneration. Int. J. Mol. Sci. 2019, 20, 6004. [Google Scholar]
  102. Bartel, D.P. MicroRNAs: Genomics, biogenesis, mechanism, and function. Cell 2004, 116, 281–297. [Google Scholar] [CrossRef] [Green Version]
  103. Bartel, D.P. MicroRNAs: Target recognition and regulatory functions. Cell 2009, 136, 215–233. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  104. Xu, S. microRNA expression in the eyes and their significance in relation to functions. Prog. Retin. Eye Res. 2009, 28, 87–116. [Google Scholar] [CrossRef]
  105. Humphreys, D.T.; Westman, B.J.; Martin, D.I.; Preiss, T. MicroRNAs control translation initiation by inhibiting eukaryotic initiation factor 4E/cap and poly(A) tail function. Proc. Natl. Acad. Sci. USA 2005, 102, 16961–16966. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  106. Mathonnet, G.; Fabian, M.R.; Svitkin, Y.V.; Parsyan, A.; Huck, L.; Murata, T.; Biffo, S.; Merrick, W.C.; Darzynkiewicz, E.; Pillai, R.S.; et al. MicroRNA inhibition of translation initiation in vitro by targeting the cap-binding complex eIF4F. Science 2007, 317, 1764–1767. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  107. Semler, B.L.; Waterman, M.L. IRES-mediated pathways to polysomes: Nuclear versus cytoplasmic routes. Trends Microbiol. 2008, 16, 1–5. [Google Scholar] [CrossRef]
  108. Aitken, C.E.; Lorsch, J.R. A mechanistic overview of translation initiation in eukaryotes. Nat. Struct. Mol. Biol. 2012, 19, 568–576. [Google Scholar] [CrossRef]
  109. Nottrott, S.; Simard, M.J.; Richter, J.D. Human let-7a miRNA blocks protein production on actively translating polyribosomes. Nat. Struct. Mol. Biol. 2006, 13, 1108–1114. [Google Scholar] [CrossRef]
  110. Vislovukh, A.; Kratassiouk, G.; Porto, E.; Gralievska, N.; Beldiman, C.; Pinna, G.; El’skaya, A.; Harel-Bellan, A.; Negrutskii, B.; Groisman, I. Proto-oncogenic isoform A2 of eukaryotic translation elongation factor eEF1 is a target of miR-663 and miR-744. Br. J. Cancer. 2013, 108, 2304–2311. [Google Scholar] [CrossRef] [Green Version]
  111. Richter, J.D.; Coller, J. Pausing on Polyribosomes: Make Way for Elongation in Translational Control. Cell 2015, 163, 292–300. [Google Scholar] [CrossRef] [Green Version]
  112. Friedman, R.C.; Farh, K.K.; Burge, C.B.; Bartel, D.P. Most mammalian mRNAs are conserved targets of microRNAs. Genome Res. 2009, 19, 92–105. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  113. Ying, W.; Tseng, A.; Chang, R.C.; Wang, H.; Lin, Y.L.; Kanameni, S.; Brehm, T.; Morin, A.; Jones, B.; Splawn, T.; et al. miR-150 regulates obesity-associated insulin resistance by controlling B cell functions. Sci. Rep. 2016, 6, 20176. [Google Scholar]
  114. Joglekar, M.V.; Januszewski, A.S.; Jenkins, A.J.; Hardikar, A.A. Circulating microRNA Biomarkers of Diabetic Retinopathy. Diabetes 2016, 65, 22–24. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  115. Kovacs, B.; Lumayag, S.; Cowan, C.; Xu, S. MicroRNAs in early diabetic retinopathy in streptozotocin-induced diabetic rats. Investig. Ophthalmol. Vis. Sci. 2011, 52, 4402–4409. [Google Scholar] [CrossRef] [PubMed]
  116. Gong, Q.; Su, G. Roles of miRNAs and long noncoding RNAs in the progression of diabetic retinopathy. Biosci. Rep. 2017, 37, BSR20171157. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  117. Cowan, C.; Muraleedharan, C.K.; O’Donnell, J.J., 3rd; Singh, P.K.; Lum, H.; Kumar, A.; Xu, S. MicroRNA-146 inhibits thrombin-induced NF-kappaB activation and subsequent inflammatory responses in human retinal endothelial cells. Investig. Ophthalmol. Vis. Sci. 2014, 55, 4944–4951. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  118. Zhuang, P.; Muraleedharan, C.K.; Xu, S. Intraocular Delivery of miR-146 Inhibits Diabetes-Induced Retinal Functional Defects in Diabetic Rat Model. Investig. Ophthalmol. Vis. Sci. 2017, 58, 1646–1655. [Google Scholar] [CrossRef] [Green Version]
  119. Miao, C.; Chang, J.; Zhang, G.; Fang, Y. MicroRNAs in type 1 diabetes: New research progress and potential directions. Biochem. Cell Biol. 2018, 96, 498–506. [Google Scholar] [CrossRef]
  120. Barutta, F.; Bruno, G.; Matullo, G.; Chaturvedi, N.; Grimaldi, S.; Schalkwijk, C.; Stehouwer, C.D.; Fuller, J.H.; Gruden, G. MicroRNA-126 and micro-/macrovascular complications of type 1 diabetes in the EURODIAB Prospective Complications Study. Acta. Diabetol. 2017, 54, 133–139. [Google Scholar] [CrossRef]
  121. Mazzeo, A.; Beltramo, E.; Lopatina, T.; Gai, C.; Trento, M.; Porta, M. Molecular and functional characterization of circulating extracellular vesicles from diabetic patients with and without retinopathy and healthy subjects. Exp. Eye Res. 2018, 176, 69–77. [Google Scholar] [CrossRef]
  122. Zampetaki, A.; Kiechl, S.; Drozdov, I.; Willeit, P.; Mayr, U.; Prokopi, M.; Mayr, A.; Weger, S.; Oberhollenzer, F.; Bonora, E.; et al. Plasma microRNA profiling reveals loss of endothelial miR-126 and other microRNAs in type 2 diabetes. Circ. Res. 2010, 107, 810–817. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  123. Shaker, O.G.; Abdelaleem, O.O.; Mahmoud, R.H.; Abdelghaffar, N.K.; Ahmed, T.I.; Said, O.M.; Zaki, O.M. Diagnostic and prognostic role of serum miR-20b, miR-17–3p, HOTAIR, and MALAT1 in diabetic retinopathy. IUBMB Life 2019, 71, 310–320. [Google Scholar] [CrossRef] [PubMed]
  124. Barutta, F.; Bellini, S.; Mastrocola, R.; Bruno, G.; Gruden, G. MicroRNA and Microvascular Complications of Diabetes. Int. J. Endocrinol. 2018, 2018, 6890501. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  125. Zhang, X.; Yang, Y.; Feng, Z. Suppression of microRNA-495 alleviates high-glucose-induced retinal ganglion cell apoptosis by regulating Notch/PTEN/Akt signaling. Biomed. Pharm. 2018, 106, 923–929. [Google Scholar] [CrossRef] [PubMed]
  126. Wang, H.; Su, X.; Zhang, Q.Q.; Zhang, Y.Y.; Chu, Z.Y.; Zhang, J.L.; Ren, Q. MicroRNA-93–5p participates in type 2 diabetic retinopathy through targeting Sirt1. Int. Ophthalmol. 2021, 41, 3837–3848. [Google Scholar] [CrossRef]
  127. Chen, Q.; Qiu, F.; Zhou, K.; Matlock, H.G.; Takahashi, Y.; Rajala, R.V.S.; Yang, Y.; Moran, E.; Ma, J.X. Pathogenic Role of microRNA-21 in Diabetic Retinopathy Through Downregulation of PPARalpha. Diabetes 2017, 66, 1671–1682. [Google Scholar] [CrossRef] [Green Version]
  128. Rocha, D.M.; Caldas, A.P.; Oliveira, L.L.; Bressan, J.; Hermsdorff, H.H. Saturated fatty acids trigger TLR4-mediated inflammatory response. Atherosclerosis 2016, 244, 211–215. [Google Scholar] [CrossRef]
  129. Hui, Y.; Yin, Y. MicroRNA-145 attenuates high glucose-induced oxidative stress and inflammation in retinal endothelial cells through regulating TLR4/NF-kappaB signaling. Life Sci. 2018, 207, 212–218. [Google Scholar] [CrossRef]
  130. Kanwar, M.; Kowluru, R.A. Role of glyceraldehyde 3-phosphate dehydrogenase in the development and progression of diabetic retinopathy. Diabetes 2009, 58, 227–234. [Google Scholar] [CrossRef] [Green Version]
  131. Zhong, Q.; Kowluru, R.A. Epigenetic changes in mitochondrial superoxide dismutase in the retina and the development of diabetic retinopathy. Diabetes 2011, 60, 1304–1313. [Google Scholar] [CrossRef] [Green Version]
  132. Mortuza, R.; Feng, B.; Chakrabarti, S. miR-195 regulates SIRT1-mediated changes in diabetic retinopathy. Diabetologia 2014, 57, 1037–1046. [Google Scholar] [CrossRef] [PubMed]
  133. Mensa, E.; Giuliani, A.; Matacchione, G.; Gurau, F.; Bonfigli, A.R.; Romagnoli, F.; De Luca, M.; Sabbatinelli, J.; Olivieri, F. Circulating miR-146a in healthy aging and type 2 diabetes: Age- and gender-specific trajectories. Mech. Ageing Dev. 2019, 180, 1–10. [Google Scholar] [CrossRef] [PubMed]
  134. Ye, E.A.; Steinle, J.J. miR-146a Attenuates Inflammatory Pathways Mediated by TLR4/NF-kappaB and TNFalpha to Protect Primary Human Retinal Microvascular Endothelial Cells Grown in High Glucose. Mediat. Inflamm. 2016, 2016, 3958453. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  135. Roganovic, J. Downregulation of microRNA-146a in diabetes, obesity and hypertension may contribute to severe COVID-19. Med. Hypotheses 2021, 146, 110448. [Google Scholar] [CrossRef] [PubMed]
  136. Wang, Q.; Navitskaya, S.; Chakravarthy, H.; Huang, C.; Kady, N.; Lydic, T.A.; Chen, Y.E.; Yin, K.J.; Powell, F.L.; Martin, P.M.; et al. Dual Anti-Inflammatory and Anti-Angiogenic Action of miR-15a in Diabetic Retinopathy. EBioMedicine 2016, 11, 138–150. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  137. Wang, S.; Du, S.; Lv, Y.; Wang, W.; Zhang, F. Elevated microRNA-20b-3p and reduced thioredoxin-interacting protein ameliorate diabetic retinopathy progression by suppressing the NLRP3 inflammasomes. IUBMB Life 2020, 72, 1433–1448. [Google Scholar] [CrossRef]
  138. Yury, O.; Lopez, N.; Garufi, G.; Seyhan, A. Altered levels of circulating cytokines and microRNAs in lean and obese individuals with prediabetes and type 2 diabetes. Mol. BioSyst. 2017, 13, 106–121. [Google Scholar]
  139. Assmann, T.S.; Recamonde-Mendoza, M.; De Souza, B.M.; Crispim, D. MicroRNA expression profiles and type 1 diabetes mellitus: Systematic review and bioinformatic analysis. Endocr. Connect. 2017, 6, 773–790. [Google Scholar] [CrossRef] [Green Version]
  140. Wang, G.; Gu, Y.; Xu, N.; Zhang, M.; Yang, T. Decreased expression of miR-150, miR146a and miR424 in type 1 diabetic patients: Association with ongoing islet autoimmunity. Biochem. Biophys. Res. Commun. 2018, 498, 382–387. [Google Scholar] [CrossRef]
  141. Shi, L.; Kim, A.J.; Chang, R.C.; Chang, J.Y.; Ying, W.; Ko, M.L.; Zhou, B.; Ko, G.Y. Deletion of miR-150 Exacerbates Retinal Vascular Overgrowth in High-Fat-Diet Induced Diabetic Mice. PLoS ONE 2016, 11, e0157543. [Google Scholar] [CrossRef] [Green Version]
  142. Yu, F.; Chapman, S.; Pham, D.L.; Ko, M.L.; Zhou, B.; Ko, G.Y. Decreased miR-150 in obesity-associated type 2 diabetic mice increases intraocular inflammation and exacerbates retinal dysfunction. BMJ Open Diabetes Res. Care 2020, 8, e001446. [Google Scholar] [CrossRef] [PubMed]
  143. Duan, Y.; Zhou, B.; Su, H.; Liu, Y.; Du, C. miR-150 regulates high glucose-induced cardiomyocyte hypertrophy by targeting the transcriptional co-activator p300. Exp. Cell Res. 2013, 319, 173–184. [Google Scholar] [CrossRef] [PubMed]
  144. Shen, J.; Yang, X.; Xie, B.; Chen, Y.; Swaim, M.; Hackett, S.F.; Campochiaro, P.A. MicroRNAs regulate ocular neovascularization. Mol. Ther. 2008, 16, 1208–1216. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  145. Zhu, J.; Yao, K.; Guo, J.; Shi, H.; Ma, L.; Wang, Q.; Liu, H.; Gao, W.; Sun, A.; Zou, Y.; et al. miR-181a and miR-150 regulate dendritic cell immune inflammatory responses and cardiomyocyte apoptosis via targeting JAK1-STAT1/c-Fos pathway. J. Cell Mol. Med. 2017, 21, 2884–2895. [Google Scholar] [CrossRef] [PubMed]
  146. Ma, J.L.; Guo, W.L.; Chen, X.M. Overexpressing microRNA-150 attenuates hypoxia-induced human cardiomyocyte cell apoptosis by targeting glucose-regulated protein-94. Mol. Med. Rep. 2018, 17, 4181–4186. [Google Scholar] [CrossRef] [PubMed]
  147. Linsenmeier, R.A.; Zhang, H.F. Retinal oxygen: From animals to humans. Prog. Retin. Eye Res. 2017, 58, 115–151. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  148. Wright, W.S.; McElhatten, R.M.; Messina, J.E.; Harris, N.R. Hypoxia and the expression of HIF-1alpha and HIF-2alpha in the retina of streptozotocin-injected mice and rats. Exp. Eye Res. 2010, 90, 405–412. [Google Scholar] [CrossRef] [Green Version]
  149. Liu, C.H.; Sun, Y.; Li, J.; Gong, Y.; Tian, K.T.; Evans, L.P.; Morss, P.C.; Fredrick, T.W.; Saba, N.J.; Chen, J. Endothelial microRNA-150 is an intrinsic suppressor of pathologic ocular neovascularization. Proc. Natl. Acad. Sci. USA 2015, 112, 12163–12168. [Google Scholar] [CrossRef] [Green Version]
  150. Liu, L.; Yan, L.N.; Sui, Z. MicroRNA-150 affects endoplasmic reticulum stress via MALAT1-miR-150 axis-mediated NF-kappaB pathway in LPS-challenged HUVECs and septic mice. Life Sci. 2021, 265, 118744. [Google Scholar] [CrossRef]
  151. Ruvkun, G. The perfect storm of tiny RNAs. Nat. Med. 2008, 14, 1041–1045. [Google Scholar] [CrossRef]
  152. Agrawal, S.; Chaqour, B. MicroRNA signature and function in retinal neovascularization. World J. Biol. Chem. 2014, 5, 1–11. [Google Scholar] [CrossRef] [PubMed]
  153. Shen, J.; Xing, W.; Gong, F.; Wang, W.; Yan, Y.; Zhang, Y.; Xie, C.; Fu, S. MiR-150–5p retards the progression of myocardial fibrosis by targeting EGR1. Cell Cycle 2019, 18, 1335–1348. [Google Scholar] [CrossRef] [PubMed]
  154. Peng, W.; Huang, S.; Shen, L.; Tang, Y.; Li, H.; Shi, Y. Long noncoding RNA NONHSAG053901 promotes diabetic nephropathy via stimulating Egr-1/TGF-beta-mediated renal inflammation. J. Cell Physiol. 2019, 234, 18492–18503. [Google Scholar] [CrossRef]
  155. Zha, F.; Qu, X.; Tang, B.; Li, J.; Wang, Y.; Zheng, P.; Ji, T.; Zhu, C.; Bai, S. Long non-coding RNA MEG3 promotes fibrosis and inflammatory response in diabetic nephropathy via miR-181a/Egr-1/TLR4 axis. Aging 2019, 11, 3716–3730. [Google Scholar] [CrossRef] [PubMed]
  156. Qu, X.; Yan, X.; Kong, C.; Zhu, Y.; Li, H.; Pan, D.; Zhang, X.; Liu, Y.; Yin, F.; Qin, H. c-Myb promotes growth and metastasis of colorectal cancer through c-fos-induced epithelial-mesenchymal transition. Cancer Sci. 2019, 110, 3183–3196. [Google Scholar] [CrossRef] [PubMed]
  157. Chen, C.; Jia, K.Y.; Zhang, H.L.; Fu, J. MiR-195 enhances cardiomyocyte apoptosis induced by hypoxia/reoxygenation injury via downregulating c-myb. Eur. Rev. Med. Pharm. Sci. 2016, 20, 3410–3416. [Google Scholar]
  158. Barrett, L.E.; Van Bockstaele, E.J.; Sul, J.Y.; Takano, H.; Haydon, P.G.; Eberwine, J.H. Elk-1 associates with the mitochondrial permeability transition pore complex in neurons. Proc. Natl. Acad. Sci. USA 2006, 103, 5155–5160. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  159. Barrett, L.E.; Sul, J.Y.; Takano, H.; Van Bockstaele, E.J.; Haydon, P.G.; Eberwine, J.H. Region-directed phototransfection reveals the functional significance of a dendritically synthesized transcription factor. Nat. Methods 2006, 3, 455–460. [Google Scholar] [CrossRef]
  160. Lu, Z.; Miao, Z.; Zhu, J.; Zhu, G. ETS-domain containing protein (Elk1) suppression protects cortical neurons against oxygen-glucose deprivation injury. Exp. Cell Res. 2018, 371, 42–49. [Google Scholar] [CrossRef] [PubMed]
  161. Park, S.J.; Kim, S.H.; Choi, H.S.; Rhee, Y.; Lim, S.K. Fibroblast growth factor 2-induced cytoplasmic asparaginyl-tRNA synthetase promotes survival of osteoblasts by regulating anti-apoptotic PI3K/Akt signaling. Bone 2009, 45, 994–1003. [Google Scholar] [CrossRef] [PubMed]
  162. Ding, Y.; Chen, X.; Liu, C.; Ge, W.; Wang, Q.; Hao, X.; Wang, M.; Chen, Y.; Zhang, Q. Identification of a small molecule as inducer of ferroptosis and apoptosis through ubiquitination of GPX4 in triple negative breast cancer cells. J. Hematol. Oncol. 2021, 14, 19. [Google Scholar] [CrossRef]
  163. Yoon, T.M.; Kim, S.A.; Lee, D.H.; Lee, J.K.; Park, Y.L.; Lee, K.H.; Chung, I.J.; Joo, Y.E.; Lim, S.C. EGR1 regulates radiation-induced apoptosis in head and neck squamous cell carcinoma. Oncol. Rep. 2015, 33, 1717–1722. [Google Scholar] [CrossRef] [Green Version]
  164. Dai, G.; Sakamoto, H.; Shimoda, Y.; Fujimoto, T.; Nishikawa, S.; Ogawa, M. Over-expression of c-Myb increases the frequency of hemogenic precursors in the endothelial cell population. Genes Cells 2006, 11, 859–870. [Google Scholar] [CrossRef]
  165. Nagarajan, R.; Svaren, J.; Le, N.; Araki, T.; Watson, M.; Milbrandt, J. EGR2 mutations in inherited neuropathies dominant-negatively inhibit myelin gene expression. Neuron 2001, 30, 355–368. [Google Scholar] [CrossRef] [Green Version]
  166. Joseph, L.J.; Le Beau, M.M.; Jamieson, G.A., Jr.; Acharya, S.; Shows, T.B.; Rowley, J.D.; Sukhatme, V.P. Molecular cloning, sequencing, and mapping of EGR2, a human early growth response gene encoding a protein with “zinc-binding finger” structure. Proc. Natl. Acad. Sci. USA 1988, 85, 7164–7168. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  167. Abcouwer, S.F. Angiogenic Factors and Cytokines in Diabetic Retinopathy. J. Clin. Cell Immunol. 2013, 11 (Suppl. 1), 1–12. [Google Scholar] [CrossRef]
  168. Aiello, L.P.; Avery, R.L.; Arrigg, P.G.; Keyt, B.A.; Jampel, H.D.; Shah, S.T.; Pasquale, L.R.; Thieme, H.; Iwamoto, M.A.; Park, J.E.; et al. Vascular endothelial growth factor in ocular fluid of patients with diabetic retinopathy and other retinal disorders. N. Engl. J. Med. 1994, 331, 1480–1487. [Google Scholar] [CrossRef] [PubMed]
  169. Wirostko, B.; Wong, T.Y.; Simo, R. Vascular endothelial growth factor and diabetic complications. Prog. Retin Eye Res. 2008, 27, 608–621. [Google Scholar] [CrossRef] [PubMed]
  170. Crawford, T.N.; Alfaro, D.V., 3rd; Kerrison, J.B.; Jablon, E.P. Diabetic retinopathy and angiogenesis. Curr. Diabetes Rev. 2009, 5, 8–13. [Google Scholar] [CrossRef]
  171. Diabetic Retinopathy Clinical Research, N. Randomized clinical trial evaluating intravitreal ranibizumab or saline for vitreous hemorrhage from proliferative diabetic retinopathy. JAMA. Ophthalmol. 2013, 131, 283–293. [Google Scholar]
  172. Patel, N. Targeting leukostasis for the treatment of early diabetic retinopathy. Cardiovasc. Hematol. Disord. Drug Targets 2009, 9, 222–229. [Google Scholar] [CrossRef]
  173. Agrawal, N.K.; Kant, S. Targeting inflammation in diabetes: Newer therapeutic options. World J. Diabetes 2014, 5, 697–710. [Google Scholar] [CrossRef]
  174. Sell, H.; Habich, C.; Eckel, J. Adaptive immunity in obesity and insulin resistance. Nat. Rev. Endocrinol. 2012, 8, 709–716. [Google Scholar] [CrossRef] [PubMed]
  175. Tonade, D.; Liu, H.; Kern, T.S. Photoreceptor Cells Produce Inflammatory Mediators That Contribute to Endothelial Cell Death in Diabetes. Investig. Ophthalmol. Vis. Sci. 2016, 57, 4264–4271. [Google Scholar] [CrossRef] [PubMed]
  176. Tonade, D.; Liu, H.; Palczewski, K.; Kern, T.S. Photoreceptor cells produce inflammatory products that contribute to retinal vascular permeability in a mouse model of diabetes. Diabetologia 2017, 60, 2111–2120. [Google Scholar] [CrossRef] [Green Version]
  177. Mima, A.; Qi, W.; Hiraoka-Yamomoto, J.; Park, K.; Matsumoto, M.; Kitada, M.; Li, Q.; Mizutani, K.; Yu, E.; Shimada, T.; et al. Retinal not systemic oxidative and inflammatory stress correlated with VEGF expression in rodent models of insulin resistance and diabetes. Investig. Ophthalmol. Vis. Sci. 2012, 53, 8424–8432. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  178. Ola, M.S.; Nawaz, M.I.; Siddiquei, M.M.; Al-Amro, S.; Abu El-Asrar, A.M. Recent advances in understanding the biochemical and molecular mechanism of diabetic retinopathy. J. Diabetes Complicat. 2012, 26, 56–64. [Google Scholar] [CrossRef]
  179. Zheng, L.; Howell, S.J.; Hatala, D.A.; Huang, K.; Kern, T.S. Salicylate-based anti-inflammatory drugs inhibit the early lesion of diabetic retinopathy. Diabetes 2007, 56, 337–345. [Google Scholar] [CrossRef] [Green Version]
  180. Robinson, R.; Barathi, V.A.; Chaurasia, S.S.; Wong, T.Y.; Kern, T.S. Update on animal models of diabetic retinopathy: From molecular approaches to mice and higher mammals. Dis. Model Mech. 2012, 5, 444–456. [Google Scholar] [CrossRef] [Green Version]
  181. Nguyen, T.T.; Alibrahim, E.; Islam, F.M.; Klein, R.; Klein, B.E.; Cotch, M.F.; Shea, S.; Wong, T.Y. Inflammatory, hemostatic, and other novel biomarkers for diabetic retinopathy: The multi-ethnic study of atherosclerosis. Diabetes Care 2009, 32, 1704–1709. [Google Scholar] [CrossRef] [Green Version]
  182. Lim, L.S.; Tai, E.S.; Mitchell, P.; Wang, J.J.; Tay, W.T.; Lamoureux, E.; Wong, T.Y. C-reactive protein, body mass index, and diabetic retinopathy. Investig. Ophthalmol. Vis. Sci. 2010, 51, 4458–4463. [Google Scholar] [CrossRef] [PubMed]
  183. Figueras-Roca, M.; Molins, B.; Sala-Puigdollers, A.; Matas, J.; Vinagre, I.; Rios, J.; Adan, A. Peripheral blood metabolic and inflammatory factors as biomarkers to ocular findings in diabetic macular edema. PLoS ONE 2017, 12, e0173865. [Google Scholar] [CrossRef] [PubMed]
  184. Vujosevic, S.; Simo, R. Local and Systemic Inflammatory Biomarkers of Diabetic Retinopathy: An Integrative Approach. Investig. Ophthalmol. Vis. Sci. 2017, 58, BIO68–BIO75. [Google Scholar] [CrossRef]
  185. Arden, G.B.; Wolf, J.E.; Tsang, Y. Does dark adaptation exacerbate diabetic retinopathy? Evidence and a linking hypothesis. Vis. Res. 1998, 38, 1723–1729. [Google Scholar] [CrossRef] [Green Version]
  186. Sternberg, P., Jr.; Landers, M.B., 3rd; Wolbarsht, M. The negative coincidence of retinitis pigmentosa and proliferative diabetic retinopathy. Am. J. Ophthalmol. 1984, 97, 788–789. [Google Scholar] [CrossRef]
  187. Landers, M.B., 3rd; Stefansson, E.; Wolbarsht, M. Panretinal photocoagulation and retinal oxygenation. Retina 1982, 2, 167–175. [Google Scholar] [CrossRef] [PubMed]
  188. de Gooyer, T.E.; Stevenson, K.A.; Humphries, P.; Simpson, D.A.; Gardiner, T.A.; Stitt, A.W. Retinopathy is reduced during experimental diabetes in a mouse model of outer retinal degeneration. Investig. Ophthalmol. Vis. Sci. 2006, 47, 5561–5568. [Google Scholar] [CrossRef]
  189. Du, Y.; Veenstra, A.; Palczewski, K.; Kern, T.S. Photoreceptor cells are major contributors to diabetes-induced oxidative stress and local inflammation in the retina. Proc. Natl. Acad. Sci. USA 2013, 110, 16586–16591. [Google Scholar] [CrossRef] [Green Version]
  190. Karkeni, E.; Bonnet, L.; Marcotorchino, J.; Tourniaire, F.; Astier, J.; Ye, J.; Landrier, J.F. Vitamin D limits inflammation-linked microRNA expression in adipocytes in vitro and in vivo: A new mechanism for the regulation of inflammation by vitamin D. Epigenetics 2017, 13, 156–162. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  191. Slattery, M.L.; Mullany, L.E.; Sakoda, L.; Samowitz, W.S.; Wolff, R.K.; Stevens, J.R.; Herrick, J.S. The NF-kappaB signalling pathway in colorectal cancer: Associations between dysregulated gene and miRNA expression. J. Cancer Res. Clin. Oncol. 2018, 144, 269–283. [Google Scholar] [CrossRef] [Green Version]
  192. Xue, H.; Li, M.X. MicroRNA-150 protects against cigarette smoke-induced lung inflammation and airway epithelial cell apoptosis through repressing p53: MicroRNA-150 in CS-induced lung inflammation. Hum. Exp. Toxicol. 2018, 37, 920–928. [Google Scholar] [CrossRef]
  193. Bousquet, M.; Zhuang, G.; Meng, C.; Ying, W.; Cheruku, P.S.; Shie, A.T.; Wang, S.; Ge, G.; Wong, P.; Wang, G.; et al. miR-150 blocks MLL-AF9-associated leukemia through oncogene repression. Mol. Cancer Res. 2013, 11, 912–922. [Google Scholar] [CrossRef] [Green Version]
  194. Zhou, B.; Wang, S.; Mayr, C.; Bartel, D.P.; Lodish, H.F. miR-150, a microRNA expressed in mature B and T cells, blocks early B cell development when expressed prematurely. Proc. Natl. Acad. Sci. USA 2007, 104, 7080–7085. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  195. Bartel, D.P. Metazoan MiroRNAs. Cell 2018, 173, 20–51. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  196. Yu, F.; Ko, M.L.; Ko, G.Y. Decreased MicroRNA-150 Exacerbates Neuronal Apoptosis in the Diabetic Retina. Biomedicines 2021, 9, 1135. [Google Scholar] [CrossRef] [PubMed]
  197. Kasza, A.W.P.; Horwacik, I.; Tymoszuk, P.; Mizgalska, D.; Palmer, K.; Rokita, H.; Sharrocks, A.D.; Jura, J. Transcription factors Elk-1 and SRF are engaged in IL1-dependent regulation of ZC3H12A expression. BMC Mol. Biol. 2010, 11, 14. [Google Scholar] [CrossRef]
  198. Lin, C.C.; Lin, W.N.; Hou, W.C.; Hsiao, L.D.; Yang, C.M. Endothelin-1 induces VCAM-1 expression-mediated inflammation via receptor tyrosine kinases and Elk/p300 in human tracheal smooth muscle cells. Am. J. Physiol. Lung Cell Mol. Physiol. 2015, 309, L211–L225. [Google Scholar] [CrossRef]
  199. Wong-Riley, M.T. Energy metabolism of the visual system. Eye Brain 2010, 2, 99–116. [Google Scholar] [CrossRef] [Green Version]
  200. Lv, J.; Bao, S.; Liu, T.; Wei, L.; Wang, D.; Ye, W.; Wang, N.; Song, S.; Li, J.; Chudhary, M.; et al. Sulforaphane delays diabetes-induced retinal photoreceptor cell degeneration. Cell Tissue Res. 2020, 382, 477–486. [Google Scholar] [CrossRef]
  201. Sharma, A.; Callahan, L.M.; Sul, J.Y.; Kim, T.K.; Barrett, L.; Kim, M.; Powers, J.M.; Federoff, H.; Eberwine, J. A neurotoxic phosphoform of Elk-1 associates with inclusions from multiple neurodegenerative diseases. PLoS ONE 2010, 5, e9002. [Google Scholar] [CrossRef]
  202. Halestrap, A.P.M.G.; Clarke, S.J. The permeability transition pore complex: Another view. Biochimie 2002, 84, 14. [Google Scholar] [CrossRef]
  203. Lavaur, J.; Bernard, F.; Trifilieff, P.; Pascoli, V.; Kappes, V.; Pages, C.; Vanhoutte, P.; Caboche, J. A TAT-DEF-Elk-1 peptide regulates the cytonuclear trafficking of Elk-1 and controls cytoskeleton dynamics. J. Neurosci. 2007, 27, 14448–14458. [Google Scholar] [CrossRef] [Green Version]
  204. Wu, W.; Mosteller, R.D.; Broek, D. Sphingosine kinase protects lipopolysaccharide-activated macrophages from apoptosis. Mol. Cell. Biol. 2004, 24, 7359–7369. [Google Scholar] [CrossRef] [Green Version]
  205. Smith, L.E.; Wesolowski, E.; McLellan, A.; Kostyk, S.K.; D’Amato, R.; Sullivan, R.; D’Amore, P.A. Oxygen-induced retinopathy in the mouse. Investig. Ophthalmol. Vis. Sci. 1994, 35, 101–111. [Google Scholar]
  206. Wesolowski, E.; Smith, L.E. Effect of light on oxygen-induced retinopathy in the mouse. Invest Ophthalmol Vis Sci 1994, 35, 112–119. [Google Scholar]
  207. Yu, F.; Ko, M.L.; Ko, G.Y. MicroRNA-150 and its target ETS-domain transcription factor 1 contribute to inflammation in diabetic photoreceptors. J. Cell Mol. Med. 2021, 25, 10724–10735. [Google Scholar] [CrossRef] [PubMed]
  208. Maric, G.; Rose, A.A.; Annis, M.G.; Siegel, P.M. Glycoprotein non-metastatic b (GPNMB): A metastatic mediator and emerging therapeutic target in cancer. Onco. Targets 2013, 6, 839–852. [Google Scholar]
  209. Becker, P.M.; Waltenberger, J.; Yachechko, R.; Mirzapoiazova, T.; Sham, J.S.; Lee, C.G.; Elias, J.A.; Verin, A.D. Neuropilin-1 regulates vascular endothelial growth factor-mediated endothelial permeability. Circ. Res. 2005, 96, 1257–1265. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  210. Narasaraju, T.; Shukla, D.; More, S.; Huang, C.; Zhang, L.; Xiao, X.; Liu, L. Role of microRNA-150 and glycoprotein nonmetastatic melanoma protein B in angiogenesis during hyperoxia-induced neonatal lung injury. Am. J. Respir. Cell Mol. Biol. 2015, 52, 253–261. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  211. Ishida, M.; El-Mounayri, O.; Kattman, S.; Zandstra, P.; Sakamoto, H.; Ogawa, M.; Keller, G.; Husain, M. Regulated expression and role of c-Myb in the cardiovascular-directed differentiation of mouse embryonic stem cells. Circ. Res. 2012, 110, 253–264. [Google Scholar] [CrossRef]
Ijms 23 12099 g001 550
Figure 1. MiR-150 is anti-angiogenic. (A) Deletion of miR-150 exacerbates high-fat-diet (HFD)/obesity-associated DR microvascular complication. The retinas were taken from wild-type (WT) and miR-150−/− that were fed with a normal (control) or an HFD (60% fat calories) for six months. The whole mount retinas were trypsin-digested and stained with H&E stain. Global knockout of miR-150 further promotes microvascular complications (such as capillary degeneration) in the vascular retina. * indicates the statistical differences from the WT control. Data taken from Yu et al., 2020 [142]. (B) Overexpression of miR-150 dampens endothelial sprouting, a foundation step of angiogenesis. Three-dimensional (3D) endothelial cell sprouting/invasion assays were used in this study. Primary human umbilical vein endothelial cells (HUVECs) were first transfected with 50 nM miR 150-5p mimics (miR-150 mimics), 30 nM miR 150-5p antagomir (miR-150 inhibitor), or vehicle (control) using a transfection kit. Forty-eight hours after transfections, cells were seeded onto collagen matrices containing sphingosine 1-phosphate, type I collagen isolated from rat tails, and basal fibroblast growth factor (bFGF) and VEGF. Cells were allowed to invade overnight at 37 °C with 5% CO2 before fixation with 3% glutaraldehyde. After 24 h of invasion, overexpression of miR-150 (miR-150 mimics) dampens the EC sprouting/invasion. * indicates the statistical significance from the control. One-way ANOVA with Tukey post hoc tests was used for statistical analysis for both (A,B).
Figure 1. MiR-150 is anti-angiogenic. (A) Deletion of miR-150 exacerbates high-fat-diet (HFD)/obesity-associated DR microvascular complication. The retinas were taken from wild-type (WT) and miR-150−/− that were fed with a normal (control) or an HFD (60% fat calories) for six months. The whole mount retinas were trypsin-digested and stained with H&E stain. Global knockout of miR-150 further promotes microvascular complications (such as capillary degeneration) in the vascular retina. * indicates the statistical differences from the WT control. Data taken from Yu et al., 2020 [142]. (B) Overexpression of miR-150 dampens endothelial sprouting, a foundation step of angiogenesis. Three-dimensional (3D) endothelial cell sprouting/invasion assays were used in this study. Primary human umbilical vein endothelial cells (HUVECs) were first transfected with 50 nM miR 150-5p mimics (miR-150 mimics), 30 nM miR 150-5p antagomir (miR-150 inhibitor), or vehicle (control) using a transfection kit. Forty-eight hours after transfections, cells were seeded onto collagen matrices containing sphingosine 1-phosphate, type I collagen isolated from rat tails, and basal fibroblast growth factor (bFGF) and VEGF. Cells were allowed to invade overnight at 37 °C with 5% CO2 before fixation with 3% glutaraldehyde. After 24 h of invasion, overexpression of miR-150 (miR-150 mimics) dampens the EC sprouting/invasion. * indicates the statistical significance from the control. One-way ANOVA with Tukey post hoc tests was used for statistical analysis for both (A,B).
Ijms 23 12099 g001
Ijms 23 12099 g002 550
Figure 2. An illustration of how miR-150 contributes to microvascular complications and neovascularization in diabetic retinopathy (DR) as summarized in the conclusion.
Figure 2. An illustration of how miR-150 contributes to microvascular complications and neovascularization in diabetic retinopathy (DR) as summarized in the conclusion.
Ijms 23 12099 g002
Table
Table 1. A list of microRNAs changed in diabetes reviewed in Section C.
Table 1. A list of microRNAs changed in diabetes reviewed in Section C.
Upregulated miRDownregulated miR
In T1D patientsmiR-29a, miR-30b, miR-148a, miR-181a, and miR-200a [119,121]miR-21a, miR-93, miR-126, miR-146a, and miR-150 [119,120,121]
In STZ-induced T1D rodentsmiR-195 [130,131], miR-495 [125].
In STZ-induced diabetic rats, at least 86 miRs are significantly altered in the retina [115,117,118]
In T2D patients and T2D mice miR-15a, miR-20b [137], miR-21 [127], miR-24, miR-93, miR-126, miR-146a, miR-150, miR-191, miR-197, miR-320, and miR-486 [122,123]
Table
Table 2. A list of the direct targets of miR-150 discussed in Section D.
Table 2. A list of the direct targets of miR-150 discussed in Section D.
Direct Target of miR-150Reference
Cxcr4 (C-X-C chemokine receptor type 4)Liu (2015) [149]
Dll4 (Delta like ligand 4)Liu (2015) [149]
Egr1 (Early growth response 1)Ying (2016) [113]
Shen (2019) [153]
Egr2 (Early growth response 2): verified downstream angiogenic targets are VEGF and VEGFR2Nagarajan (2001) [165]
Joseph (1988) [166]
Elk1 (ETS-domain transcription factor)Shi (2016) [141]
Zhu (2017) [145]
Ying (2016) [113]
Yu (2020, 2021) [196,207]
Etf1 (Eukaryotic translation termination factor 1)Ying (2016) [113]
Fzd4 (Frizzled-4)Liu 2015 [149]
GPNMB (Glycoprotein nonmetastatic melanoma protein B): verified downstream angiogenic target is Neuropilin-1 (NRP-1)Maric (2013) [208]
Becker (2005) [209]
Narasaraju (2015) [210]
Myb (MYB proto-oncogene): verified downstream angiogenic target is VEGFR2Ishida (2012) [211]
Dai (2006) [164]
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Ko, G.Y.-P.; Yu, F.; Bayless, K.J.; Ko, M.L. MicroRNA-150 (miR-150) and Diabetic Retinopathy: Is miR-150 Only a Biomarker or Does It Contribute to Disease Progression? Int. J. Mol. Sci. 2022, 23, 12099. https://doi.org/10.3390/ijms232012099

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Ko GY-P, Yu F, Bayless KJ, Ko ML. MicroRNA-150 (miR-150) and Diabetic Retinopathy: Is miR-150 Only a Biomarker or Does It Contribute to Disease Progression? International Journal of Molecular Sciences. 2022; 23(20):12099. https://doi.org/10.3390/ijms232012099

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Ko, Gladys Y.-P., Fei Yu, Kayla J. Bayless, and Michael L. Ko. 2022. "MicroRNA-150 (miR-150) and Diabetic Retinopathy: Is miR-150 Only a Biomarker or Does It Contribute to Disease Progression?" International Journal of Molecular Sciences 23, no. 20: 12099. https://doi.org/10.3390/ijms232012099

APA Style

Ko, G. Y.-P., Yu, F., Bayless, K. J., & Ko, M. L. (2022). MicroRNA-150 (miR-150) and Diabetic Retinopathy: Is miR-150 Only a Biomarker or Does It Contribute to Disease Progression? International Journal of Molecular Sciences, 23(20), 12099. https://doi.org/10.3390/ijms232012099

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