Search Results (75)

In contrast to foreign nucleic acids, some of our own endogenously synthesized nucleic acids may become immunologically active without being considered “foreign”. For example, abnormalities in chromatin organization, transcription termination, ribonucleic acid (RNA) splicing, and RNA editing, together with damage to mitochondrial integrity, may render normally functional deoxyribonucleic acid (DNA) and RNA persistently available and aberrantly structured ligands for innate immunity. Z-DNA-binding protein 1 (ZBP1), recently identified as an important component of this innate immune system, recognizes both left-handed DNA (Z-DNA) and left-handed RNA (Z-RNA) using its tandem Z-alpha (Zα) domains and couples recognition of these conformational states to receptor-interacting serine/threonine-protein kinase 1 (RIPK1)-, receptor-interacting serine/threonine-protein kinase 3 (RIPK3)-, and mixed-lineage kinase domain-like pseudokinase (MLKL)-dependent inflammatory and cell-death pathways. More recent studies have also shown that ZBP1 plays a role in recognizing damaged self-nucleic acids associated with tauopathies, Alzheimer’s disease (AD), traumatic brain injury (TBI), and amyloid-associated neuroinflammation. The nucleic-acid forms associated with these conditions include transposable-element activation, extended repeat-containing transcripts, RNA–RNA duplexes or RNA:DNA hybrids, oxidized mitochondrial DNA (mtDNA), and intercellularly transferred nucleic acids, all of which may exhibit substrate structures compatible with Z-form formation. Signaling by ZBP1 does not occur simply based upon nucleic-acid abundance; rather, signaling occurs after prolonged exposure to a nucleic acid when it persists in a structurally competent state, sufficient receptors are present to bind its exposed regions, the receptor proteoforms are competent to participate in signaling, receptor-interacting protein homotypic interaction motif (RHIM)-dependent assembly occurs, and the appropriate adaptor molecules are present. Furthermore, the identity of the cell type expressing ZBP1 determines whether the response produces RIPK3–MLKL-dependent neuronal injury, microglia-mediated inflammation, apoptosis, or mixed cell death. Finally, competition with adenosine deaminase acting on RNA 1 (ADAR1), melanoma differentiation-associated protein 5 (MDA5), double-stranded RNA-dependent protein kinase (PKR), the cyclic guanosine monophosphate–adenosine monophosphate synthase–stimulator of interferon genes (cGAS–STING) pathway, and other nucleic-acid-sensing proteins divides the available pool of endogenous nucleic acids among the outcomes of immune tolerance, type I interferon (IFN-I) signaling, translational inhibition, neuroinflammation, and necroptosis. Full article

Ulcerative colitis (UC) is a type of inflammatory bowel disease without curative therapeutics. Recent studies demonstrate that Akkermansia muciniphila exerts mitigating effects on UC, but the underlying mechanisms remain unclear. In this study, we isolated a strain of A. muciniphila, designated NND9, from the feces of DSS-induced ulcerative colitis model mice and investigated its effects on UC of the mouse model. NND9 significantly alleviated UC severity in the mice by restoring gut barrier integrity through improving colonic mucus layer thickness, mitigating goblet cell depletion, and halting epithelial cell death. Mechanistically, NND9 suppressed the expression of the Tnfrsf10b gene encoding death receptor 5 (DR5) on the surface of colonic epithelial cells. Additionally, NND9 inhibited the phosphorylation of kinase 3 (RIPK3) and the pseudokinase mixed-lineage kinase domain-like protein (MLKL) associated with the necrotic apoptosis pathway, thereby reducing gut epithelial cell death. NND9 also markedly ameliorated the gut microbiome of the colitis mice. Untargeted metabolomics analysis demonstrated that NND9 modulated both tryptophan and bile acid metabolism. In conclusion, NND9 exhibits curative effects on UC by resolving inflammatory reactions of the gut mucosa through the DR5-RIPK3/p-RIPK3-MLKL/p-MLKL pathway and redressing gut dysbiosis. This study provides valuable information for the development of innovative therapeutic strategies for the treatment of UC. Full article

Arsenic exposure increases lung cancer risk, yet its molecular mechanisms remain unclear but are linked to peroxisome proliferator-activated receptor gamma (PPARγ). We investigated PPARγ-related molecules affected by sodium arsenite (NaAR) in non-small cell lung cancer (NSCLC) cells using immunochemical, gene knockdown, and immunoprecipitation approaches. PPARγ was critical for NSCLC growth, as high PPARγ-expressing A549 cells proliferated more than low-expressing H1299 cells after NaAR treatment. In A549 cells, NaAR upregulated polyubiquitinated PPARγ, activating cell cycle arrest and DNA damage response pathways. Rather than inducing significant caspase-dependent apoptosis, NaAR activated nuclear factor-kappa B and downregulated mixed lineage kinase domain-like (MLKL) via K63-linked polyubiquitinated receptor-interacting protein kinase 1, thereby inhibiting apoptosis and necroptosis. PPARγ knockdown or NAD⁺ supplementation induced PARP-1 hyperactivation and MLKL upregulation, leading to DNA damage and necroptosis. PARP-1 inhibition by 3-aminobenzamide induced apoptosis, indicating that PPARγ regulates apoptosis and necroptosis through PARP-1 activation. Proteasome inhibition increased polyubiquitinated PPARγ but not p53. Leptomycin B induced PPARγ degradation and p53 accumulation, promoting necroptosis and apoptosis, suggesting cytoplasmic p53 contributes to cell death. p62 interacted with PPARγ and p53, and its knockdown suppressed their NaAR-induced upregulation. In conclusion, NaAR-induced PPARγ promotes A549 cell survival by enhancing DNA repair and inhibiting apoptosis and necroptosis via cooperation with p53 and p62, highlighting PPARγ as a potential therapeutic target. Full article

Regulated cardiomyocyte death is a central contributor to myocardial infarction (MI)-associated injury. Mixed lineage kinase domain-like protein (MLKL), a key effector of necroptosis, has been implicated in cardiovascular disease; however, its role in MI remains incompletely defined. MLKL expression was evaluated in hypoxia-treated cardiomyocytes, infarcted murine hearts, and human cardiac tissue. MLKL function was investigated using siRNA-mediated knockdown in neonatal mouse cardiomyocytes and genetic deletion in mice subjected to left anterior descending (LAD) coronary artery ligation. Apoptosis- and pyroptosis-related signaling were assessed by immunoblotting and immunostaining. RIP3 expression and regulation were examined at both protein and mRNA levels, and the RIP3 inhibitor GSK’872 was used to assess pathway dependence. MLKL expression was increased in hypoxic cardiomyocytes, infarcted mouse hearts, and human failing cardiac tissue. Unexpectedly, MLKL deficiency was associated with aggravated myocardial injury, impaired cardiac function, and increased fibrosis following MI. Mechanistically, MLKL deficiency was associated with increased RIP3 protein abundance without a corresponding increase in RIP3 mRNA, consistent with post-transcriptional regulation. Further analyses indicated that MLKL deficiency reduced RIP3 ubiquitination and impaired proteasome-mediated degradation, resulting in RIP3 stabilization. Elevated RIP3 levels were accompanied by increased expression of apoptosis- and pyroptosis-related proteins, particularly at early time points after MI. Pharmacological inhibition of RIP3 with GSK’872 was associated with reduced apoptosis- and pyroptosis-related signaling and improved cardiac function. MLKL deficiency is associated with stabilization of RIP3 and enhanced activation of apoptosis- and pyroptosis-related signaling following MI, contributing to aggravated myocardial injury. These findings support a regulatory role for the MLKL–RIP3 axis in cardiomyocyte death and suggest that targeting RIP3 may represent a potential therapeutic strategy in myocardial infarction. Full article

Necroptosis is a regulated form of programmed cell death that helps the body defend itself against infections and cellular stress, especially when apoptosis is blocked. At the center of this process is mixed lineage kinase domain-like (MLKL) protein, the final effector of necroptosis, which is activated downstream of receptor-interacting protein kinase 3 (RIPK3). Once phosphorylated, MLKL changes shape, assembles into oligomers, moves to cellular membranes, and disrupts membrane integrity, ultimately causing cell death. While this RIPK3-MLKL pathway has been well described, it is becoming increasingly clear that MLKL regulation is more complex than originally thought. Recent findings show that MLKL can be modified and activated through alternative mechanisms, even in the absence of RIPK3, and that post-translational modifications such as ubiquitination further fine-tune its activity. Notably, deleting RIPK3 or MLKL does not consistently resolve inflammatory phenotypes in experimental models, suggesting that MLKL has context-dependent functions that extend beyond its role in necroptosis. In line with this idea, MLKL has been implicated in inflammatory signaling, interferon responses, and innate immunity, and is frequently targeted by viruses seeking to evade host defenses. Beyond infections, aberrant MLKL activation contributes to a wide range of chronic diseases, including atherosclerosis, cardiometabolic disorders, liver disease, neurodegeneration, and cancer. In these settings, sustained MLKL-mediated membrane damage and release of danger signals drive ongoing inflammation and tissue injury rather than protective cell elimination. In this review, we provide an overview of MLKL structure, activation, and regulation in both necroptotic and non-necroptotic contexts. We also discuss emerging therapeutic strategies aimed at targeting MLKL activation, membrane engagement, and stability, and highlight key unanswered questions that must be addressed to translate MLKL biology into effective clinical interventions. Full article

As a typical halogenated hydrocarbon environmental pollutant, 1,2-dichloroethane (1,2-DCE) exhibits clinically confirmed hepatotoxicity with incompletely understood mechanisms. This study integrated network toxicology, molecular docking, and in vitro experiments to investigate necroptosis in 1,2-DCE-induced liver injury. Computational analysis predicted involvement of the aryl hydrocarbon receptor (AHR)/cytochrome P450 1A1 (CYP1A1) pathway, and molecular docking suggested potential binding between 1,2-DCE and AHR (−6.5 kcal/mol). CCK-8 assays showed that 1,2-DCE reduced THLE-2 hepatocyte viability in a concentration-dependent manner. Notably, 1,2-DCE triggered rapid AHR nuclear translocation within 1 h and transiently upregulated CYP1A1 at both the transcriptional and protein levels (3–6 h). Further studies revealed elevated intracellular reactive oxygen species (ROS) at 24 h. After 48 h exposure, CYP1A1 expression was significantly suppressed, accompanied by activation of necroptosis markers, including increased lactate dehydrogenase (LDH) release, enhanced propidium iodide (PI) staining, and elevated phosphorylation of receptor-interacting protein kinase 3 (RIPK3) and mixed lineage kinase domain-like protein (MLKL). These findings reveal a dual-phase mechanism: an early adaptive stress response via the AHR-CYP1A1 axis, followed by pathway dysfunction and transition to necroptosis, suggesting AHR as a potential target for intervening in 1,2-DCE-induced hepatotoxicity. Full article

Thyroid hormone (TH) regulates cell proliferation, differentiation, and metabolism. Increased TH levels in circulation are associated with a higher incidence of age-related macular degeneration. In mice, TH treatment causes photoreceptor degeneration, which is accompanied by an increase in receptor-interacting serine/threonine-protein kinase 3 (RIPK3) in the retina. Here, we investigated the contribution of RIPK3/necroptosis to TH-induced photoreceptor degeneration using mice deficient in RIPK3 and the necroptotic mixed lineage kinase domain-like protein (MLKL). Wild-type (C57BL/6) and mutant mice at postnatal day 30 received triiodothyronine (T3, 20 µg/mL in drinking water) for four weeks, followed by the evaluation of photoreceptor survival/death and retinal function. Deletion of Ripk3 preserved photoreceptor integrity against T3-induced degeneration, evidenced by improved retinal morphology, increased cone density, improved retinal light responses, and reduced cell death. This protection was observed in both global and photoreceptor-specific Ripk3 knockout mice. In contrast, the deletion of Mlkl did not protect photoreceptors. This work supports the view that RIPK3, but not MLKL, contributes to TH-induced photoreceptor degeneration. The lack of protection from Mlkl deletion suggests that RIPK3’s action is likely mediated via a necrosome-independent mechanism. These findings provide significant insight into how TH signaling induces photoreceptor degeneration and implicate RIPK3 as a potential therapeutic target. Full article

Polygoni Multiflori Radix Praeparata (PMRP), a processed root of Polygonum multiflorum Thunb. (known as Zhiheshouwu in Chinese medicine), exhibits anti-aging properties and is used to improve ovarian aging. However, its therapeutic mechanism against premature ovarian insufficiency (POI) remains unclear. This study investigates whether PMRP alleviates POI by inhibiting PANoptosis—a cell death pathway characterized by the concurrent occurrence and interplay of pyroptosis, apoptosis, and necroptosis. POI was induced in rats using tripterygium glycosides. We evaluated the estrous cycle, serum hormone levels (follicle-stimulating hormone [FSH], estrogen [E₂], anti-Müllerian hormone [AMH]), follicular development, and the ultrastructure of granulosa cells. PANoptosome assembly (apoptosis-associated speck-like protein containing a CARD [ASC]/caspase-8/receptor-interacting protein kinase 3 [RIPK3] co-localization) and key effectors of PANoptosis (caspase 3, cleaved caspase 3, gasdermin D [GSDMD], cleaved GSDMD, GSDME, RIPK1, mixed-lineage kinase domain-like protein [MLKL], and p-MLKL) were analyzed. PMRP restored the estrous cycle, lowered FSH levels, and increased E₂ and AMH levels in POI rats. It reduced follicular atresia, preserved primordial follicles, and suppressed PANoptosis-like death in granulosa cells. Mechanistically, PMRP disrupted PANoptosome assembly and downregulated key effectors of PANoptosis. PMRP alleviates POI by inhibiting PANoptosis in granulosa cells, overcoming the previous limitations of targeting single death pathways and providing novel insights into the pathogenesis and treatment strategies for POI. Full article

Resistance to cell death is one of the core hallmarks of cancer, with regulatory abnormalities particularly pronounced in the malignant progression and therapeutic resistance of melanoma. This review aims to systematically summarize the roles and mechanisms of regulated cell death (RCD) in melanoma. Currently, distinct types of RCD, including apoptosis, autophagy, pyroptosis, immunogenic cell death, necroptosis, and ferroptosis, have all been found to be involved in melanoma. Autophagy promotes the survival of melanoma cells under stress conditions through metabolic adaptation, yet its excessive activation can trigger cell death. Immunogenic cell death has the capacity to elicit adaptive immune responses in immunocompetent syngeneic hosts. Necroptosis, governed by the receptor-interacting protein kinase 1 (RIPK1)/RIPK3 mixed lineage kinase domain-like protein (MLKL) signaling axis, can synergize with immunotherapy to enhance anti-melanoma immune responses when activated. Pyroptosis, mediated by Gasdermin proteins, induces the release of inflammatory factors that reshape the tumor microenvironment and enhance the efficacy of immune checkpoint inhibitors. Ferroptosis, characterized by lipid peroxidation, can overcome melanoma resistance by targeting the solute carrier family 7 member 11 (SLC7A11)/glutathione peroxidase 4 (GPX4) axis. Therapeutic strategies targeting RCD pathways have demonstrated breakthrough potential. Several agents have been developed to target RCD in order to suppress melanoma. Full article

Butein (3,4,2′,4′-tetrahydroxycalone) is a chalcone derivative and plant polyphenol extracted from Rhus verniciflua Stokes. Butein has an open C-ring structure and a variety of biological activities. Molecular mechanisms by which butein could affect cell viability, ROS levels, mitochondrial function, apoptosis, and necrosis in prostate cancer cells were investigated using 2D monolayer and 3D sphere culture systems. Cytotoxicity and cell cycle monitoring showed that butein treatment decreased cell viability and increased peaks of sub-G₀/G₁ and G₂/M phases analyzed by flow cytometry. These changes were observed with a concurrent induction of DNA damage, apoptosis, and necrosis. Although 3D spheres treated with butein showed decreased cell viability, they were slightly more resistant than cells in 2D cultures. This phenomenon was accompanied by an increase in mediators of apoptosis and necrosis. Monitoring changes of apoptosis-related proteins via Western blot showed that butein decreased caspase-3, PARP, and Bcl-2, but increased Bax. Meanwhile, butein increased levels of p-receptor interacting serine/threonine–protein kinase 3 (p-RIP3) and p-mixed lineage kinase domain-like kinase (p-MLKL) known to be mediators of necrosis. Overall, our data suggest that butein can induce apoptosis and necrosis of prostate cancer cells by regulating pro- and anti-apoptotic proteins via ROS. Thus, butein might be a potential agent for treating prostate cancer. Full article

Scrub typhus is an emerging chigger-borne disease caused by the obligate intracellular bacterium Orientia tsutsugamushi. Necroptosis is a form of programmed cell death (PCD) mediated by RIPK3 (serine/threonine kinase receptor interacting protein 3) and its downstream effector MLKL (mixed-lineage kinase domain-like). While O. tsutsugamushi modulates apoptosis, another form of PCD, its interplay with necroptosis is unknown. Much of Orientia pathobiology is linked to its ankyrin repeat (AR)-containing effectors (Anks). Two of these, Ank1 and Ank6, share similarities with the cowpox AR protein, vIRD (viral inducer of RIPK3 degradation) that prevents necroptosis. Here, we show that Ank1 and Ank6 reduce RIPK3 cellular levels although not as robustly as and mechanistically distinct from vIRD. Orientia infection lowers RIPK3 amounts and does not elicit necroptosis in endothelial cells. In HeLa cells ectopically expressing RIPK3, Orientia fails to inhibit RIPK3 and MLKL phosphorylation as well as cell death. MLKL colocalization with Orientia or Listeria monocytogenes, another intracytoplasmic pathogen, was not observed. Thus, O. tsutsugamushi reduces cellular levels of RIPK3 and does not elicit necroptosis but cannot inhibit this PCD pathway once it is induced. This study is a first step toward understanding how the relationship between Orientia and necroptosis contributes to scrub typhus pathogenesis. Full article

Background: Sepsis is a life-threatening condition that is characterized by systemic inflammation and organ dysfunction, with adrenal dysfunction being a significant complication. This study aimed to investigate the role of necroptosis and hydrogen sulfide (H₂S) in sepsis-induced adrenal dysfunction. Methods: A cecal ligation and puncture (CLP)-induced sepsis mouse model was employed. Adrenocortical-specific mixed lineage kinase domain-like pseudokinase (MLKL) knockout (MLKL-KO) and cystathioneine β-synthase (CBS) knockout (CBS-KO) mice were generated using Cre-loxP technology and adrenocortical-specific Cre tool mice. In vitro experiments utilized TNFα-stimulated Y1 adrenocortical cells. The treatments included the H₂S donor NaHS, TNFα inhibitor R-7050, necroptosis inhibitor NSA and CBS inhibitor AOAA. Pathological assessment involved hematoxylin–eosin (H&E) staining and a Western blot analysis of necroptosis markers (the phosphorylation of MLKL (p-MLKL) and phosphorylation of receptor-interacting protein kinases 1 (p-RIPK1)). Results: Sepsis induced adrenal congestion, elevated TNFα levels, and activated necroptosis (increased p-MLKL/p-RIPK1) in wild-type mice. H₂S treatment attenuated adrenal damage, reduced TNFα, and suppressed necroptosis. MLKL knockout reduced septic adrenal dysfunction, whereas CBS knockout exacerbated septic adrenal dysfunction. In vitro, TNFα induced Y1 cell necroptosis, which was reversed by H₂S or NSA. AOAA exacerbated TNFα-induced necroptosis in Y1 cells. Conclusions: H₂S inhibits TNFα-mediated necroptosis, thereby preserving adrenal integrity in sepsis. Targeting the TNFα–necroptosis axis and enhancing endogenous H₂S production may represent novel therapeutic strategies for sepsis-associated adrenal dysfunction. Full article

Sensory disturbances and central nervous system symptoms are important in patients with Minamata disease. In the peripheral nervous system of these patients, motor nerves are not strongly injured, whereas sensory nerves are predominantly affected. In this study, we investigated the mechanisms underlying the sensory-predominant impairment of the peripheral nervous system caused by methylmercury. We found that the types of cell death in rat dorsal root ganglion (DRG) neurons caused by methylmercury included apoptosis, necrosis, and necroptosis. Methylmercury induced apoptosis in cultured rat DRG neurons but not in anterior horn neurons or Schwann cells. Additionally, methylmercury activated both caspase 8 and caspase 3 in DRG neurons. It increased the expression of tumor necrosis factor (TNF) receptor-1 and the phosphorylation of receptor-interacting protein kinase 3 (RIP3) and mixed-lineage kinase domain-like pseudokinase (MLKL). The expression of TNF-α was increased in macrophage-like RAW264.7 cells by methylmercury. The increase was suggested to be mediated by the NF-κB pathway. Moreover, methylmercury induced neurological symptoms, evaluated by a hindlimb extension response, were significantly less severe in TNF-α knockout mice. Based on these results and our previous studies, we propose the following hypothesis regarding the pathogenesis of sensory nerve-predominant damage by methylmercury: First, methylmercury accumulates within sensory nerve neurons and initiates cell death mechanisms, such as apoptosis, on a small scale. Second, cell death triggers the infiltration of macrophages into the sensory fibers. Third, the macrophages are stimulated by methylmercury and secrete TNF-α through the NF-κB pathway. Fourth, TNF-α induces cell death mechanisms, including necrosis, apoptosis through the caspase 8/3 pathway, and necroptosis through the TNFR1-RIP1-RIP3-MLKL pathway, activated by methylmercury in sensory neurons. Consequently, methylmercury exhibits potent cytotoxicity specific to the DRG/sensory nerve cells in the peripheral nervous system. This chain of events caused by methylmercury may contribute to sensory disturbances in patients with Minamata disease. Full article

Background: Receptor-interacting protein kinases (RIPKs) and mixed-lineage kinase domain-like protein (MLKL) are crucial in regulating innate immune responses and cell death signaling (necroptosis and apoptosis), and are potential candidates for genetic improvement in breeding programs. Knowledge about the RIPK family and MLKL in sea cucumber remains limited. Methods: We searched the genomes of sea cucumber Holothuria leucospilota for genes encoding RIPKs and MLKL, performed phylogenetic tree, motif and functional domain analyses, and examined tissue distribution and embryonic development patterns using qPCR. Results: RIPK5 (Hl-RIPK5), RIPK7 (Hl-RIPK7) and MLKL (Hl-MLKL) were identified in sea cucumber H. leucospilota. Hl-RIPK5 and Hl-RIPK7 were mainly expressed in coelomocytes, suggesting that they play a role in innate immunity, whereas Hl-MLKL exhibited relatively low expression across tissues. During embryonic development, Hl-MLKL was highly expressed from the 2-cell stage to the morula stage, while Hl-RIPK5 and Hl-RIPK7 were primarily expressed after the morula stage, indicating different roles in embryonic development. In primary coelomocytes, Hl-RIPK5 transcriptional activity was significantly depressed by LPS, poly(I:C), or pathogen Vibrio harveyi. Hl-RIPK7 expression levels were unchanged following the same challenges. Hl-MLKL mRNA levels were significantly decreased with poly(I:C) or V. harveyi, but did not change with LPS. Conclusions: These findings provide valuable insights into the evolutionary tree and characterization of RIPK and MLKL genes in sea cucumber, contributing to the broader understanding of the RIPK gene family and MLKL in ancient echinoderms. Full article

In mammals, mixed lineage kinase domain-like protein (MLKL) is the executor of necroptosis. MLKL comprises an N-terminal domain (NTD), which alone suffices to trigger necroptosis by forming pores in the plasma membrane, and a C-terminal domain that inhibits the NTD activity. Evolutionarily, MLKL is poorly conserved in animals and not found in Protostomia. Although MLKL orthologs exist in invertebrate Deuterostomia, the biological activity of invertebrate MLKL is unknown. Herein, we examined 34 metazoan phyla and detected MLKL not only in Deuterostomia but also in Protostomia (Rotifera). The Rotifera MLKL exhibited low identities with non-Rotifera MLKL but shared relatively high identities with non-metazoan MLKL. In invertebrates, MLKL formed two phylogenetic clades, one of which was represented by Rotifera. In vertebrates, MLKL expression was tissue-specific and generally rich in immune organs. When expressed in human cells, the MLKL-NTD of Rotifera, Echinodermata, Urochordata, and Cephalochordata induced strong necroptosis. The necroptotic activity of Rotifera MLKL depended on a number of conserved residues. Together these findings provided new insights into the evolution of MLKL in Metazoa and revealed the biological activity of invertebrate MLKL. Full article