Search Results (96)

Despite the critical role of lipid-mediated signaling in regulating host immunity, endorsed by growing evidence, the interaction between lipid metabolism and immune response remains largely unknown. This review aims to elucidate the immunomodulatory role of a lung-enriched lipid metabolic pathway mediated by the phospholipase A2 (PLA₂) family, which comprises a diverse range of lipid-hydrolyzing enzymes. Based on their location, structure, substrate specificity and physiological roles, PLA₂s can be classified into secreted PLA₂s (sPLA₂s), cytosolic PLA₂s (cPLA₂s), calcium-independent PLA₂s (iPLA₂s), and lysosomal-associated PLA₂s (lPLA₂s). These PLA₂ isoforms are similar in that they can all cleave cellular membrane-associated phospholipids, releasing free lysophospholipids and fatty acids such as arachidonic acid, which subsequently serve as precursors for a wide range of bioactive mediators responsible for physiological functions and pathological changes. Respiratory infections, especially those caused by bacteria and viruses, represent a substantial threat to the health of the population worldwide and cause billions of disease cases and millions of deaths annually. Respiratory infections provoke airway inflammation, characterized by increased vascular permeability and the influx of immune cells, resulting in tissue damage, impaired gas exchange, acute respiratory distress syndrome (ARDS) and even death. During infections and inflammatory milieu, airway-expressed PLA₂ can further increase and exhibit protection by restricting pathogens and inflammation or, in contrast, exacerbate the pathogenesis. In this manuscript, we will provide an overview of the current knowledge on the biological functions of PLA₂ isoforms, especially concerning membrane-associated isoforms in respiratory infections, and offer insight into the spatial and temporal regulation of immune responses mediated by PLA₂ and the subsequent modulation of host–pathogen interactions and the balance between protective effects and pathological outcomes. Full article

Schizophrenia, depression, and bipolar disorder may represent neurodegenerative conditions involving both degeneration and aberrant regeneration of monoaminergic axons. Negative and cognitive symptoms could arise from monoaminergic axon degeneration, whereas positive symptoms and manic states might result from excessive axonal regeneration and sprouting. The molecular mechanisms driving these opposing processes remain largely unclear. This review considers the possible role of calcium-independent phospholipase A₂ (iPLA2) in regulating monoamine axon degeneration and hyper-regeneration in schizophrenia. Emerging evidence suggests that pro-inflammatory signaling mediated by cytosolic PLA₂ (cPLA2) may promote monoamine axon degeneration, while anti-inflammatory iPLA2 activity could facilitate regeneration and sprouting. Overactivation of iPLA2 might lead to aberrant axonal sprouting, potentially contributing to positive symptoms through hyperdopaminergic states in the medial prefrontal cortex (mPFC). Conversely, axon degeneration in the same region may underlie negative and cognitive symptoms. The review also discusses a potential interplay between dopamine and N-methyl-D-aspartate (NMDA) receptor signaling in distinct neuronal populations of the mPFC and suggests that targeting iPLA2 and its pathways could represent a promising therapeutic strategy. Viewing schizophrenia and related disorders through the lens of monoamine axon pathology may eventually improve diagnostic precision and inform the development of treatments aimed at restoring the balance between degeneration and regeneration. Full article

We recently reported that phospholipase A2 (PLA2)-mediated production of prostaglandins within the ventromedial hypothalamus (VMH) plays a critical role in systemic glucose homeostasis. However, the role of PLA2 in the VMH in regulating food intake is still unclear. Here, we attempted to investigate the role of PLA2 in regulating food intake and body weight in male mice. We injected an adeno-associated virus encoding short hairpin RNA (AAV-shRNA) targeting cytosolic phospholipase A2 (shPla2g4a) into the VMH. We assessed food intake, body weight, oxygen consumption, glucose tolerance, and insulin sensitivity. Three weeks after the AAV injection, the shPla2g4a group exhibited increased food intake and body weight gain compared to controls (shSCRM). Energy expenditure, oxygen consumption, and respiratory quotient (RQ) were comparable between groups. Our findings suggest that the cPLA2-mediated pathway in the VMH is critical for feeding behavior and maintaining energy homeostasis. Further investigation is needed to elucidate the underlying mechanisms. Full article

Inhibitors of cytosolic phospholipase A₂ (GIVA cPLA₂) have received great attention, since this enzyme is involved in a number of inflammatory diseases, including cancer and auto-immune and neurodegenerative diseases. Traditionally, the effects of GIVA cPLA₂ inhibitors in cells have been studied by determining the inhibition of arachidonic acid release. However, although to a lesser extent, GIVA cPLA₂ may also hydrolyze glycerophospholipids, releasing other free fatty acids (FFAs), such as linoleic acid or oleic acid. In the present work, we applied a liquid chromatography–high-resolution mass spectrometry method to study the levels of intracellular FFAs, after treating cells with selected GIVA cPLA₂ inhibitors. Six inhibitors belonging to different chemical classes were studied, using SH-SY5Y neuroblastoma cells as a model. This lipidomic approach revealed that treatment with each inhibitor created a distinct intracellular FFA profile, suggesting not only inhibitory potency against GIVA cPLA₂, but also other parameters affecting the outcome. Potent inhibitors were found to reduce not only arachidonic acid, but also other long-chain FAs, such as adrenic or linoleic acid, even medium-chain FAs, such as caproic or caprylic acid, suggesting that GIVA cPLA₂ inhibitors may affect FA metabolic pathways in general. The downregulation of intracellular FFAs may have implications in reprogramming FA metabolism in neurodegenerative diseases and cancer. Full article

N-Acylethanolamines (NAEs) are a class of lipid mediators that consist of long-chain fatty acids condensed with ethanolamine and exert various biological activities depending on their fatty acyl groups. NAEs are biosynthesized from membrane phospholipids by two-step reactions or alternative multi-step reactions. In the first reaction, N-acyltransferases transfer an acyl chain from the sn-1 position of phospholipids to the amino group (N position) of phosphatidylethanolamine (PE), generating N-acyl-PE (NAPE), a precursor of NAE. So far, two types of N-acyltransferases have been identified with different levels of Ca²⁺-dependency: cytosolic phospholipase A₂ ε (cPLA₂ε) as a Ca²⁺-dependent N-acyltransferase and phospholipase A and acyltransferase (PLAAT) enzymes as Ca²⁺-independent N-acyltransferases. Recent in vivo studies using knockout mice with cPLA₂ε and PLAAT enzymes, combined with lipidomic approaches, have clarified their roles in the skin and brain and in other physiological events. In this review, we summarize the current understanding of the functions and properties of these enzymes. Full article

Cognitive impairment is a core feature of neurodevelopmental (schizophrenia) and aging-associated (mild cognitive impairment and Alzheimer’s dementia) neurodegenerative diseases. Limited efficacy of current pharmacological treatments warrants further search for new targets for nootropic interventions. The breakdown of myelin, a phospholipids axonal sheath that protects the conduction of nerve impulse between neurons, was proposed as a neuropathological abnormality that precedes and promotes the deposition of amyloid-β in neuritic plaques. The present review of the recent literature and our own pre- and clinical data suggest (for the first time) that the anthranilic acid (AA)-induced activation of microglial-expressed G-protein coupled receptor (GPR109A) inhibits cytosolic phospholipase A2 (cPLA2), an enzyme that triggers the degradation of myelin and consequently attenuates cognitive impairment. The present review suggests that the up-regulation of AA formation is a sex-specific compensatory (adaptive) reaction aimed to prevent/treat cognitive impairment. The AA–GPR109A–cPLA2–myelin–cognition cascade suggests new nootropic interventions, e.g., the administration of pegylated kynureninase, an enzyme that catalyzes AA formation from Kynurenine (Kyn), a tryptophane catabolite; pegylated interferon-alpha; central and peripheral Kyn aminotransferase inhibitors that increase availability of Kyn as a substrate for AA formation; and vagus nerve stimulation. The cascade predicts nootropic activity of exogenous GPR109A agonists that were designed and underwent clinical trials (unsuccessful) as anti-dyslipidemia agents. The proposed cascade might contribute to the pathogenesis of cognitive impairment. Data on AA in neurodegenerative disorders are scarce, and the proposed cascade needs further exploration in pre- and clinical studies Full article

Ampakines—positive allosteric modulators of AMPA-type glutamate receptors (AMPARs)—are drug candidates that have shown substantial promise in pre-clinical models of various neurodegenerative and neuropsychiatric diseases. Much of the study of ampakines has focused on how these drugs modulate neuronal AMPARs to achieve certain therapeutic effects. However, astrocytes also express functional AMPARs and their physiology may be sensitive to modulation by ampakines. Herein, we investigate the effects of multiple ampakines on calcium levels in cortical astrocytes. We find that ampakines augment cytosolic calcium elevations in astrocytes to an extent far greater than that achieved by AMPA alone. This effect is amenable to competitive AMPAR blockade. Furthermore, calcium induction is sensitive to phospholipase C_β antagonism and blockade of inositol triphosphate receptors located on the endoplasmic reticulum. Low-impact ampakines exerted weaker effects on cytosolic calcium levels in astrocytes and higher concentrations were required to observe an effect. Furthermore, high doses of the low-impact ampakine, CX717, were not toxic to cortical astrocytes at high concentrations, which may serve to differentiate low-impact ampakines from classical AMPAR positive modulators like cyclothiazide. As ampakines are further developed for clinical use, it would be prudent to determine the extent to and manner by which they affect astrocytes, as these effects may also underpin their therapeutic utility in CNS pathologies. Full article

Upon degranulation, basophils and mast cells secrete an array of inflammatory mediators, including histamine, which leads to not only allergic inflammation but also other inflammatory diseases. We previously reported that an aqueous extract from enzyme-treated, dried sardine inhibits the degranulation of RBL-2H3 cells and attenuates the symptoms of Japanese cedar pollinosis in mice. This study evaluated an antiallergic effect of dipeptides containing acidic amino acid residue in an antigen-induced degranulation assay using RBL-2H3 cells. The result showed that acidic amino acid residue-containing dipeptides inhibit the degranulation of RBL-2H3 cells without cytotoxicity. Additionally, L-histidyl-L-glutamic acid (His-Glu), one of the acidic amino acid residue-containing dipeptides tested in this study, inhibited calcium ionophore-induced degranulation. We also found that His-Glu suppressed microtubule reorganization in RBL-2H3 cells after antigen stimulation. His-Glu slightly, but not significantly, suppressed the elevation of cytosolic calcium ion concentration leading to degranulation. Immunoblot analysis revealed that His-Glu significantly suppressed the phosphorylation of phosphoinositide 3-kinase and Akt, but not that of Syk or phospholipase Cγ. Overall results suggest that acidic amino acid residue-containing dipeptides can be used as food ingredients with an antiallergic effect. Full article

Platelets assume a pivotal role in the pathogenesis of cardiovascular diseases (CVDs), emphasizing their significance in disease progression. Consequently, addressing CVDs necessitates a targeted approach focused on mitigating platelet activation. Eugenol, predominantly derived from clove oil, is recognized for its antibacterial, anticancer, and anti-inflammatory properties, rendering it a valuable medicinal agent. This investigation delves into the intricate mechanisms through which eugenol influences human platelets. At a low concentration of 2 μM, eugenol demonstrates inhibition of collagen and arachidonic acid (AA)-induced platelet aggregation. Notably, thrombin and U46619 remain unaffected by eugenol. Its modulatory effects extend to ATP release, P-selectin expression, and intracellular calcium levels ([Ca²⁺]i). Eugenol significantly inhibits various signaling cascades, including phospholipase Cγ2 (PLCγ2)/protein kinase C (PKC), phosphoinositide 3-kinase/Akt/glycogen synthase kinase-3β, mitogen-activated protein kinases, and cytosolic phospholipase A2 (cPLA2)/thromboxane A2 (TxA₂) formation induced by collagen. Eugenol selectively inhibited cPLA2/TxA₂ phosphorylation induced by AA, not affecting p38 MAPK. In ADP-treated mice, eugenol reduced occluded lung vessels by platelet thrombi without extending bleeding time. In conclusion, eugenol exerts a potent inhibitory effect on platelet activation, achieved through the inhibition of the PLCγ2–PKC and cPLA2-TxA₂ cascade, consequently suppressing platelet aggregation. These findings underscore the potential therapeutic applications of eugenol in CVDs. Full article

The blood–retinal barrier (BRB) is strongly compromised in diabetic retinopathy (DR) due to the detachment of pericytes (PCs) from retinal microvessels, resulting in increased permeability and impairment of the BRB. Western blots, immunofluorescence and ELISA were performed on adipose mesenchymal stem cells (ASCs) and pericyte-like (P)-ASCs by co-cultured human retinal endothelial cells (HRECs) under hyperglycemic conditions (HG), as a model of DR. Our results demonstrated that: (a) platelet-derived growth factor receptor (PDGFR) and its activated form were more highly expressed in monocultured P-ASCs than in ASCs, and this expression increased when co-cultured with HRECs under high glucose conditions (HG); (b) the transcription factor Nrf2 was more expressed in the cytoplasmic fraction of ASCs and in the P-ASC nuclear fraction, under normal glucose and, even more, under HG conditions; (c) cytosolic phospholipase A₂ activity and prostaglandin E2 release, stimulated by HG, were significantly reduced in P-ASCs co-cultured with HRECs; (d) HO-1 protein content was significantly higher in HG-P-ASCs/HRECs than P-ASCs/HRECs; and (e) VEGF-A levels in media from HG-co-cultures were reduced in P-ASCs/HRECs with respect to ASCs/HRECs. The data obtained highlighted the potential of autologous differentiated ASCs in future clinical applications based on cell therapy to counteract the damage induced by DR. Full article

UDP-Galactose: Glucosylceramide, β-1,4-Galactose transferase-V (β-1,4-GalT-V), is a member of a large glycosyltransferase family, primarily involved in the transfer of sugar residues from nucleotide sugars, such as galactose, glucose mannose, etc., to sugar constituents of glycosphingolipids and glycoproteins. For example, UDP-Galactose: Glucosylceramide, β-1,4-galactosyltransferase (β-1,4-GalT-V), transfers galactose to glucosylceramide to generate Lactosylceramide (LacCer), a bioactive “lipid second messenger” that can activate nicotinamide adenine dinucleotide phosphate(NADPH) oxidase (NOX-1) to produce superoxide’s (O₂⁻) to activate several signaling pathways critical in regulating multiple phenotypes implicated in health and diseases. LacCer can also activate cytosolic phospholipase A-2 to produce eicosanoids and prostaglandins to induce inflammatory pathways. However, the lack of regulation of β-1,4-GalT-V contributes to critical phenotypes central to cancer and cardiovascular diseases, e.g., cell proliferation, migration, angiogenesis, phagocytosis, and apoptosis. Additionally, inflammation that accompanies β-1,4-GalT-V dysregulation accelerates the initiation and progression of cancer, cardiovascular diseases, as well as inflammation-centric diseases, like lupus erythematosus, chronic obstructive pulmonary disease (COPD), and inflammatory bowel diseases. An exciting development in this field of research arrived due to the recognition that the activation of β-1,4-GalT-V is a “pivotal” point of convergence for multiple signaling pathways initiated by physiologically relevant molecules, e.g., growth factors, oxidized-low density lipoprotein(ox- LDL), pro-inflammatory molecules, oxidative and sheer stress, diet, and cigarette smoking. Thus, dysregulation of these pathways may well contribute to cancer, heart disease, skin diseases, and several inflammation-centric diseases in experimental animal models of human diseases and in humans. These observations have been described under post-transcriptional modifications of β-1,4- GalT-V. On the other hand, we also point to the important role of β-1-4 GalT-V-mediated glycosylation in altering the formation of glycosylated precursor forms of proteins and their activation, e.g., β-1 integrin, wingless-related integration site (Wnt)/–β catenin, Frizzled-1, and Notch1. Such alterations in glycosylation may influence cell differentiation, angiogenesis, diminished basement membrane architecture, tissue remodeling, infiltrative growth, and metastasis in human colorectal cancers and breast cancer stem cells. We also discuss Online Mendelian Inheritance in Man (OMIM), which is a comprehensive database of human genes and genetic disorders used to provide information on the genetic basis of inherited diseases and traits and information about the molecular pathways and biological processes that underlie human physiology. We describe cancer genes interacting with the β-1,4-GalT-V gene and homologs generated by OMIM. In sum, we propose that β-1,4-GalT-V gene/protein serves as a “gateway” regulating several signal transduction pathways in oxidative stress and inflammation leading to cancer and other diseases, thus rationalizing further studies to better understand the genetic regulation and interaction of β-1,4-GalT-V with other genes. Novel therapies will hinge on biochemical analysis and characterization of β-1,4-GalT-V in patient-derived materials and animal models. And using β-1,4-GalT-V as a “bonafide drug target” to mitigate these diseases. Full article

Type 2 diabetes mellitus (T2DM) has become a worldwide public health problem. Epimedin C is considered one of the most important flavonoids in Epimedium, a famous edible herb in China and Southeast Asia that is traditionally used in herbal medicine to treat diabetes. In the present study, the therapeutic potential of epimedin C against T2DM was ascertained using a mouse model, and the mechanism underlying the hypoglycemic activity of epimedin C was explored using a label-free proteomic technique for the first time. Levels of fasting blood glucose (FBG), homeostasis model assessment of insulin resistance (HOMA-IR), and oral glucose tolerance, as well as contents of malondialdehyde (MDA) and low-density lipoprotein cholesterol (LDL-C) in the 30 mg·kg⁻¹ epimedin C group (EC30 group), were significantly lower than those in the model control group (MC group) (p < 0.05), while the contents of hepatic glycogen, insulin, and high-density lipoprotein cholesterol (HDL-C), as well as activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) in the EC30 group were notably higher than those in the MC group (p < 0.05). The structures of liver cells and tissues were greatly destroyed in the MC group, whereas the structures of cells and tissues were basically complete in the EC30 group, which were similar to those in the normal control group (NC group). A total of 92 differentially expressed proteins (DEPs) were enriched in the gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. In the EC30 vs. MC groups, the expression level of cytosolic phosphoenolpyruvate carboxykinase (Pck1) was down-regulated, while the expression levels of group XIIB secretory phospholipase A2-like protein (Pla2g12b), apolipoprotein B-100 (Apob), and cytochrome P450 4A14 (Cyp4a14) were up-regulated. According to the KEGG pathway assay, Pck1 participated in the gluconeogenesis and insulin signaling pathways, and Pla2g12b, Apob, and Cyp4a14 were the key proteins in the fat digestion and fatty acid degradation pathways. Pck1, Pla2g12b, Apob, and Cyp4a14 seemed to play important roles in the prevention and treatment of T2DM. In summary, epimedin C inhibited Pck1 expression to maintain FBG at a relatively stable level, promoted Pla2g12b, Apob, and Cyp4a14 expressions to alleviate liver lipotoxicity, and protected liver tissues and cells from oxidant stress possibly by its phenolic hydroxyl groups. Full article

Cell migration is a crucial contributor to metastasis, a critical process associated with the mortality of cancer patients. The initiation of metastasis is triggered by epithelial–mesenchymal transition (EMT), along with the changes in the expression of EMT marker proteins. Inflammation plays a significant role in carcinogenesis and metastasis. Lipopolysaccharide (LPS), a typical inflammatory agent, promoted the generation of superoxide through the activation of p-Tyr42 RhoA, Rho-dependent kinase 2 (ROCK2), and the phosphorylation of p47phox. In addition, p-Tyr42 RhoA activated phospholipase D1 (PLD1), with PLD1 and phosphatidic acid (PA) being involved in superoxide production. PA also regulated the expression of EMT proteins. Consequently, we have identified MHY9 (Myosin IIA, NMIIA) as a PA-binding protein in response to LPS. MYH9 also contributed to cell migration and the alteration in the expression of EMT marker proteins. Co-immunoprecipitation revealed the formation of a complex involving p-Tyr42 RhoA, PLD1, and MYH9. These proteins were found to be distributed in both the cytosol and nucleus. In addition, we have found that p-Tyr42 RhoA PLD1 and MYH9 associate with the ZEB1 promoter. The suppression of ZEB1 mRNA levels was achieved through the knockdown of RhoA, PLD1, and MYH9 using si-RNAs. Taken together, we propose that p-Tyr42 RhoA and PLD1, responsible for producing PA, and PA-bound MYH9 are involved in the regulation of ZEB1 expression, thereby promoting cell migration. Full article

Mammalian egg activation at fertilization is triggered by a long-lasting series of increases in cytosolic Ca²⁺ concentration. These Ca²⁺ oscillations are due to the production of InsP₃ within the egg and the subsequent release of Ca²⁺ from the endoplasmic reticulum into the cytosol. The generation of InsP₃ is initiated by the diffusion of sperm-specific phospholipase Czeta1 (PLCζ) into the egg after gamete fusion. PLCζ enables a positive feedback loop of InsP₃ production and Ca²⁺ release which then stimulates further InsP₃ production. Most cytosolic Ca²⁺ increases in eggs at fertilization involve a fast Ca²⁺ wave; however, due to the limited diffusion of InsP₃, this means that InsP₃ must be generated from an intracellular source rather than at the plasma membrane. All mammalian eggs studied generated Ca²⁺ oscillations in response to PLCζ, but the sensitivity of eggs to PLCζ and to some other stimuli varies between species. This is illustrated by the finding that incubation in Sr²⁺ medium stimulates Ca²⁺ oscillations in mouse and rat eggs but not eggs from other mammalian species. This difference appears to be due to the sensitivity of the type 1 InsP₃ receptor (IP3R1). I suggest that ATP production from mitochondria modulates the sensitivity of the IP3R1 in a manner that could account for the differential sensitivity of eggs to stimuli that generate Ca²⁺ oscillations. Full article

The putative phospholipase Atg15 is required for the intravacuolar lysis of autophagic bodies and MVB vesicles. Intracellular membrane lysis is a highly sophisticated mechanism that is not fully understood. The amino-terminal transmembrane domain of Atg15 contains the sorting signal for entry into the MVB pathway. By replacing this domain, we generated chimeras located in the cytosol, the vacuole membrane, and the lumen. The variants at the vacuole membrane and in the lumen were highly active. Together with the absence of Atg15 from the phagophore and autophagic bodies, this suggests that, within the vacuole, Atg15 can lyse vesicles where it is not embedded. In-depth topological analyses showed that Atg15 is a single membrane-spanning protein with the amino-terminus in the cytosol and the rest, including the active site motif, in the ER lumen. Remarkably, only membrane-embedded Atg15 variants affected growth when overexpressed. The growth defects depended on its active site serine 332, showing that it was linked to the enzymatic activity of Atg15. Interestingly, the growth defects were independent of vacuolar proteinase A and vacuolar acidification. Full article