Canonical and non-canonical functions of NLRP3

Downregulation of the HCN1 Channel Alleviates Anxiety- and Depression-Like Behaviors in Mice With Cerebral Ischemia-Reperfusion Injury by Suppressing the NLRP3 Inflammasome

BACKGROUND

Post-stroke depression (PSD) is a prevalent neuropsychiatric complication of stroke. However, the mechanisms underlying PSD are still unclear. Here, we aimed to investigate the role of HCN1 (hyperpolarization-activated cyclic nucleotide-gated cation channel 1) in the pathogenesis of PSD and its underlying mechanisms.

METHODS

The PSD mice model was established by middle cerebral artery occlusion in vivo. Four weeks after middle cerebral artery occlusion, anxiety- and depression-like behaviors of mice were evaluated by various behavioral tests. HCN channels were downregulated by pharmacological inhibitor or neuron-specific adeno-associated virus. The oxygen-glucose deprivation/reoxygenation model in SY5Y cells was used to study the pathogenesis of PSD in vitro.

RESULTS

Mice exhibited anxiety- and depression-like behavior 4 weeks after middle cerebral artery occlusion, along with a significant increase in HCN1 protein expression in the ischemic hippocampus. Furthermore, the Ih current on neurons in the hippocampus was notably enhanced, whereas neuronal excitability was decreased in PSD mice. Treatment with HCN channel selective inhibitor ZD7288 protected SY5Y cells against oxygen-glucose deprivation/reoxygenation injury by suppressing K+ efflux. Additionally, we observed a significant increase in protein expressions of NLRP3 (nucleotide-binding domain-like receptor protein 3) inflammasome pathway-related molecules in the ischemic hippocampus of PSD mice. Knockdown of HCN1 channels via virus injection into the hippocampus resulted in decreased protein expressions of NLRP3 inflammasome-related molecules and improvement in anxiety- and depression-like behaviors in PSD mice.

CONCLUSIONS

Downregulation of HCN1 channels has a beneficial effect on PSD by suppressing the NLRP3 inflammasome pathway, thus offering promise as a strategy for preventing and treating PSD.

Inactivated SARS-CoV-2 induces acute skeletal muscle damage in human K18-hACE2 transgenic mice

The pandemic due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) resulted in over 7 million global fatalities and billions of individuals diagnosed with COVID-19. Acute and chronic muscle impairment associated with SARS-CoV-2 infection affected a substantial number of patients, leading to the development of symptoms such as fatigue, muscle pain, and exercise intolerance. Our study introduces an animal model to improve understanding of the pathogenicity caused by SARS-CoV-2 in human skeletal muscle. In this investigation, human angiotensin-converting enzyme 2 under a cytokeratin 18 promoter transgenic mice were subjected to intratracheal instillation with either inactivated SARS-CoV-2 or the virus-free culture medium, with or without pre-treatment with the P2X receptor inhibitor Brilliant Blue G (BBG). Muscle strength, morphology, and inflammatory mediators were measured. Inactivated SARS-CoV-2 induced a significant decrease in mice muscle strength, accompanied by histopathological changes in gastrocnemius and diaphragm muscles, including leukocytic infiltrates, cytoplasmic vacuoles, and centralized nuclei. Also, a notable increase in caspase 3 amount was observed, suggesting muscle apoptosis. Significant elevations were noted in inflammatory mediators in the muscle of inactivated SARS-CoV-2 mice, including high mobility group box-1, tumor necrosis factor-alpha, phospho-nuclear factor kappa B, caspase 11, and pannexin-1. On the other hand, pyroptosis markers such as caspase 1, interleukin-1β, and gasdermin D remained unaltered in all experimental groups. Treatment with BBG mitigated the observed effects, indicating that inhibition of purinergic signaling pathways protects muscles from the inflammatory impact induced by inactivated SARS-CoV-2. This study emphasizes the potential efficacy of purinergic inhibition in ameliorating SARS-CoV-2-induced muscular impairments.

Targeting the NLRP3 in macrophages contributes to senescence cell clearance in radiation-induced skin injury

BACKGROUND

The persistent accumulation of senescence cells is one of the characteristics of radiation-induced skin injury (RISI), leading to fibrosis and impaired healing. However, the reasons why these senescence cells are resistant to clearance remain unclear.

METHODS

The mouse RISI model was established using an X-ray generator, and a shield was used to cover all areas except the skin of the right leg or back for protecting surrounding tissue. ScRNA sequencing, immunohistochemistry, immunofluorescence, qPCR, western blot, primary cell co-culture system and fluorescence microsphere phagocytosis assay were performed for the functional and mechanistic investigations.

RESULTS

The dynamic changes of senescence cell levels and multiple immune cell levels during RISI were evaluated, we found that macrophages could remove senescence cells from the dermis, and the clearance ability gradually strengthens over time. ScRNA sequencing revealed that macrophages with high senescence clearance capacity exhibited increased NOD-like receptor family pyrin domain-containing 3 (NLRP3) expression compared to those with low senescence clearance capacity. Inhibition or conditional knockout of Nlrp3 in macrophages led to senescence cell clearance dysfunction and impaired healing. Further studies found that interleukin-33 secreted by senescence cells inhibited the expression of NLRP3 in macrophages and their ability to phagocytize senescence cells, especially in the early stages after radiation. In addition, Nocardia rubra cell wall skeleton (Nr-CWS), an approved immunomodulator, was found to activate macrophage NLRP3 expression, reduce senescence cell burden, and accelerate the healing of RISI.

CONCLUSION

This study underscored NLRP3 in macrophages as a critical intervention target for senescence cell immunosurveillance and emphasized Nr-CWS as a potential therapeutic agent for accelerating senescence cell clearance in RISI.

3-Acetyldeoxynivalenol induces pyroptosis in leydig cells via METTL3-mediated N6-methyladenosine modification of NLRP3

3-acetyldeoxynivalenol (3-ADON), an acetylated derivative of deoxynivalenol, is a prevalent contaminant found in food products contaminated with mycotoxins. While the toxicological effects of 3-ADON on human and animal health are well-documented, its specific impact on the reproductive system remains underexplored. In this study, we comprehensively examined the toxicological effects of 3-ADON on TM3 Leydig cells through both in vivo and in vitro experimental models. Our results demonstrate that 3-ADON exposure leads to substantial testicular damage in vivo and significantly reduces cell viability while increasing mortality in TM3 cells in vitro (P = 0.012). Mechanistic investigations further revealed that 3-ADON exposure triggers pyroptosis in TM3 cells, as evidenced by upregulation of NLRP3, activation of caspase-1, ASC, and GSDMD. Moreover, 3-ADON treatment resulted in a significant upregulation of METTL3 expression and increased global mRNA m6A modification levels. m6A sequencing and functional assays established that METTL3-mediated m6A modification of NLRP3 mRNA enhances its stability and expression. RNA immunoprecipitation (RIP) assays further demonstrated that IGF2BP1 selectively recognizes m6A-modified NLRP3 mRNA, contributing to its stabilization. Notably, IGF2BP1 was found to inhibit the recruitment of the BTG2/CCR4-NOT complex by competitively binding to PABPC1, thereby preventing the deadenylation of NLRP3 mRNA and maintaining its expression. Additionally, we identified that METTL3 also methylates and stabilizes c-MyB mRNA, which subsequently binds to the promoter region of NLRP3, thereby enhancing its transcription. Collectively, our findings reveal a novel mechanism by which 3-ADON exerts its reproductive toxicity, underscoring the pivotal role of METTL3-mediated m6A modifications in regulating Leydig cell dysfunction.

P2X7 receptors from the perspective of NLRP3 inflammasome pathway in depression: Potential role of cannabidiol

Many patients with depressive disorder do not respond to conventional antidepressant treatment. There is an ongoing interest in investigating potential mechanisms of treatment resistance in depression to provide alternative treatment options involving inflammatory mechanisms. Increasing evidence implicates the NOD-like receptor pyrin domain containing 3 (NLRP3) inflammasome as a critical factor in neuroinflammation. ATP-induced P2X7 receptor (P2X7R) activation is a major trigger for inflammation, activating the canonical NLRP3 inflammatory cascade. Psychosocial stress, the primary environmental risk factor for depression, is associated with changes in ATP-mediated P2X7R signaling. Depression and stress response can be alleviated by Cannabidiol (CBD). CBD has an anti-inflammatory activity related to the regulation of NLRP3 inflammasome activation. However, CBD's effects on the inflammasome pathway are poorly understood in central nervous system (CNS) cells, including microglia, astrocytes, and neurons. This review will emphasize some findings for neuroinflammation and NLRP3 inflammasome pathway involvement in depression, particularly addressing the ATP-induced P2X7R activation. Moreover, we will underline evidence for the effect of CBD on depression and address its potential impacts on neuroinflammation through the NLRP3 inflammasome cascade.

Pathophysiological role and potential drug target of NLRP3 inflammasome in the metabolic disorders

NLRP3 plays a role in the development of autoinflammatory diseases. NLRP3, ASC, and Caspases 1 or 8 make up the NLRP3 inflammasome, which is an important part of innate immune system. The NLRP3 inflammasome-mediated inflammatory cytokines may also participate in metabolic disorders, such as diabetes, hyperlipidemia, atherosclerosis, non-alcoholic fatty liver disease, and gout. Hence, an overview of the NLRP3 regulation in these metabolic diseases and the potential drugs targeting NLRP3 is the focus of this review.

Inflammasome activity regulation by PUFA metabolites

Oxidative stress and the accompanying chronic inflammation constitute an important metabolic problem that may lead to pathology, especially when the body is exposed to physicochemical and biological factors, including UV radiation, pathogens, drugs, as well as endogenous metabolic disorders. The cellular response is associated, among others, with changes in lipid metabolism, mainly due to the oxidation and the action of lipolytic enzymes. Products of oxidative fragmentation/cyclization of polyunsaturated fatty acids (PUFAs) [4-HNE, MDA, 8-isoprostanes, neuroprostanes] and eicosanoids generated as a result of the enzymatic metabolism of PUFAs significantly modify cellular metabolism, including inflammation and the functioning of the immune system by interfering with intracellular molecular signaling. The key regulators of inflammation, the effectiveness of which can be regulated by interacting with the products of lipid metabolism under oxidative stress, are inflammasome complexes. An example is both negative or positive regulation of NLRP3 inflammasome activity by 4-HNE depending on the severity of oxidative stress. 4-HNE modifies NLRP3 activity by both direct interaction with NLRP3 and alteration of NF-κB signaling. Furthermore, prostaglandin E2 is known to be positively correlated with both NLRP3 and NLRC4 activity, while its potential interference with AIM2 or NLRP1 activity is unproven. Therefore, the influence of PUFA metabolites on the activity of well-characterized inflammasome complexes is reviewed.

Anti-Inflammatory Role of the Klotho Protein and Relevance to Aging

The α-Klotho protein (hereafter Klotho) is an obligate coreceptor for fibroblast growth factor 23 (FGF23). It is produced in the kidneys, brain and other sites. Klotho insufficiency causes hyperphosphatemia and other anomalies. Importantly, it is associated with chronic pathologies (often age-related) that have an inflammatory component. This includes atherosclerosis, diabetes and Alzheimer's disease. Its mode of action in these diseases is not well understood, but it inhibits or regulates multiple major pathways. Klotho has a membrane form and a soluble form (s-Klotho). Cytosolic Klotho is postulated but not well characterized. s-Klotho has endocrine properties that are incompletely elucidated. It binds to the FGF receptor 1c (FGFR1c) that is widely expressed (including endothelial cells). It also attaches to soluble FGF23, and FGF23/Klotho binds to FGFRs. Thus, s-Klotho might be a roaming FGF23 coreceptor, but it has other functions. Notably, Klotho (cell-bound or soluble) counteracts inflammation and appears to mitigate related aging (inflammaging). It inhibits NF-κB and the NLRP3 inflammasome. This inflammasome requires priming by NF-κB and produces active IL-1β, membrane pores and cell death (pyroptosis). In accord, Klotho countered inflammation and cell injury induced by toxins, damage-associated molecular patterns (DAMPs), cytokines, and reactive oxygen species (ROS). s-Klotho also blocks the TGF-β receptor and Wnt ligands, which lessens fibrotic disease. Low Klotho is associated with loss of muscle mass (sarcopenia), as occurs in aging and chronic diseases. s-Klotho counters the inhibitory effects of myostatin and TGF-β on muscle, reduces inflammation, and improves muscle repair following injury. The inhibition of TGF-β and other factors may also be protective in diabetic retinopathy and age-related macular degeneration (AMD). This review examines Klotho functions especially as related to inflammation and potential applications.

The role of the NLRP3 inflammasome in atherosclerotic disease: Systematic review and meta-analysis

Atherosclerosis is a chronic, progressive cardiovascular disease characterized by cholesterol deposition within blood vessel walls. Recent literature has suggested that the NLRP3 [NOD (nucleotide oligomerization domain)-, LRR (leucine-rich repeat)-, and PYD (pyrin domain)-containing protein 3] inflammasome is a key mediator in the development, progression, and destabilization of atherosclerotic plaques. This review aims to evaluate the current literature on the role of NLRP3 in human atherosclerosis. This systematic review was registered on the PROSPERO database (ID = CRD42022340039) and involved the search of a total of 8 databases. Records were screened in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. A total of 20 studies were included and quality assessed using the NIH: NHLBI tool. Six were eligible for meta-analysis using RevMan 5.4.1. We identified 20 relevant articles representing 3388 participants. NLRP3 mRNA levels and downstream cytokines, interleukin (IL)-1β and IL-18 were found to be associated with atherosclerotic disease. Fold changes in NLRP3 mRNA levels were most strongly associated with high risk atherosclerotic disease, compared to controls [0.84 (95 % CI: 0.41-1.28)]. IL-1β mRNA fold change was more robustly associated with high-risk atherosclerotic disease [0.61 (95 % CI: 0.10-1.13)] than IL-18 [0.47 (95 % CI: 0.02-0.91)]. NLRP3, IL-1β, and IL-18 are associated with high-risk atherosclerotic disease. However, given the scope of this review, the role of this inflammasome and its cytokine counterparts in acting as prognosticators of coronary artery disease severity is unclear. Several upstream activators such as cholesterol crystals are involved in the canonical or non-canonical activation of the NLRP3 inflammasome and its downstream cytokines. These findings highlight the necessity for further research to delineate the exact mechanisms of NLRP3 inflammasome activation and potential drug targets.

Comparison of the Antioxidant and Cytoprotective Properties of Extracts from Different Cultivars of Cornus mas L

Cornus mas L. is a rich source of vitamin C and polyphenols. Due to their health-benefit properties, C. mas L. extracts have been used in, e.g., dermatology and cosmetology, and as a food supplement. Peroxisome proliferator-activated receptor gamma (PPARγ) and its co-activator (PGC-1α) are now suspected to be the main target of active substances from C. mass extracts, especially polyphenols. Moreover, the PPARγ pathway is involved in the development of different diseases, such as type 2 diabetes mellitus (DM2), cancers, skin irritation, and inflammation. Therefore, the aim of the present study was to evaluate the PPARγ pathway activation by the most popular water and ethanol extracts from specific C. mas L. cultivars in an in vitro model of the human normal fibroblast (BJ) cell line. We analyzed the content of biologically active compounds in the extracts using the UPLC-DAD-MS technique and revealed the presence of many polyphenols, including gallic, quinic, protocatechuic, chlorogenic, and ellagic acids as well as iridoids, with loganic acid being the predominant component. In addition, the extracts contained cyanidin 3-O-galactoside, pelargonidin 3-O-glucoside, and quercetin 3-glucuronide. The water-ethanol dark red extract (DRE) showed the strongest antioxidant activity. Cytotoxicity was assessed in a normal skin cell line, and positive effects of all the extracts with concentrations ranging from 10 to 1000 µg/mL on the cells were shown. Our data show that the studied extracts activate the PPARγ/PGC-1α molecular pathway in BJ cells and, through this mechanism, initiate antioxidant response. Moreover, the activation of this molecular pathway may increase insulin sensitivity in DM2 and reduce skin irritation.

New Insights on NLRP3 Inflammasome: Mechanisms of Activation, Inhibition, and Epigenetic Regulation

Inflammasomes are important modulators of inflammation. Dysregulation of inflammasomes can enhance vulnerability to conditions such as neurodegenerative diseases, autoinflammatory diseases, and metabolic disorders. Among various inflammasomes, Nucleotide-binding oligomerization domain leucine-rich repeat and pyrin domain-containing protein 3 (NLRP3) is the best-characterized inflammasome related to inflammatory and neurodegenerative diseases. NLRP3 is an intracellular sensor that recognizes pathogen-associated molecular patterns and damage-associated patterns resulting in the assembly and activation of NLRP3 inflammasome. The NLRP3 inflammasome includes sensor NLRP3, adaptor apoptosis-associated speck-like protein (ASC), and effector cysteine protease procaspase-1 that plays an imperative role in caspase-1 stimulation which further initiates a secondary inflammatory response. Regulation of NLRP3 inflammasome ameliorates NLRP3-mediated diseases. Much effort has been invested in studying the activation, and exploration of specific inhibitors and epigenetic mechanisms controlling NLRP3 inflammasome. This review gives an overview of the established NLRP3 inflammasome assembly, its brief molecular mechanistic activations as well as a current update on specific and non-specific NLRP3 inhibitors that could be used in NLRP3-mediated diseases. We also focused on the recently discovered epigenetic mechanisms mediated by DNA methylation, histone alterations, and microRNAs in regulating the activation and expression of NLRP3 inflammasome, which has resulted in a novel method of gaining insight into the mechanisms that modulate NLRP3 inflammasome activity and introducing potential therapeutic strategies for CNS disorders.

Targeting NLRP3 Inflammasome: Structure, Function, and Inhibitors

Inflammasomes are multimeric protein complexes that can detect various physiological stimuli and danger signals. As a result, they perform a crucial function in the innate immune response. The NLRP3 inflammasome, as a vital constituent of the inflammasome family, is significant in defending against pathogen invasion and preserving cellhomeostasis. NLRP3 inflammasome dysregulation is connected to various pathological conditions, including inflammatory diseases, cancer, and cardiovascular and neurodegenerative diseases. This profile makes NLRP3 an applicable target for treating related diseases, and therefore, there are rising NLRP3 inhibitors disclosed for therapy. Herein, we summarized the updated advances in the structure, function, and inhibitors of NLRP3 inflammasome. Moreover, we aimed to provide an overview of the existing products and future directions for drug research and development.

Redox regulation of the NLRP3-mediated inflammation and pyroptosis

The review considers modern data on the mechanisms of activation and redox regulation of the NLRP3 inflammasome and gasdermins, as well as the role of selenium in these processes. Activation of the inflammasome and pyroptosis represent an evolutionarily conserved mechanism of the defense against pathogens, described for various types of cells and tissues (macrophages and monocytes, microglial cells and astrocytes, podocytes and parenchymal cells of the kidneys, periodontal tissues, osteoclasts and osteoblasts, as well as cells of the digestive and urogenital systems, etc.). Depending on the characteristics of redox regulation, the participants of NLRP3 inflammation and pyroptosis can be subdivided into 2 groups. Members of the first group block the mitochondrial electron transport chain, promote the formation of reactive oxygen species and the development of oxidative stress. This group includes granzymes, the mitochondrial antiviral signaling protein MAVS, and others. The second group includes thioredoxin interacting protein (TXNIP), erythroid-derived nuclear factor-2 (NRF2), Kelch-like ECH-associated protein 1 (Keap1), ninjurin (Ninj1), scramblase (TMEM16), inflammasome regulatory protein kinase NLRP3 (NEK7), caspase-1, gasdermins GSDM B, D and others. They have redox-sensitive domains and/or cysteine residues subjected to redox regulation, glutathionylation/deglutathionylation or other types of regulation. Suppression of oxidative stress and redox regulation of participants in NLRP3 inflammation and pyroptosis depends on the activity of the antioxidant enzymes glutathione peroxidase (GPX) and thioredoxin reductase (TRXR), containing a selenocysteine residue Sec in the active site. The expression of GPX and TRXR is regulated by NRF2 and depends on the concentration of selenium in the blood. Selenium deficiency causes ineffective translation of the Sec UGA codon, translation termination, and, consequently, synthesis of inactive selenoproteins, which can cause various types of programmed cell death: apoptosis of nerve cells and sperm, necroptosis of erythrocyte precursors, pyroptosis of infected myeloid cells, ferroptosis of T- and B-lymphocytes, kidney and pancreatic cells. In addition, suboptimal selenium concentrations in the blood (0.86 μM or 68 μg/l or less) have a significant impact on expression of more than two hundred and fifty genes as compared to the optimal selenium concentration (1.43 μM or 113 μg/l). Based on the above, we propose to consider blood selenium concentrations as an important parameter of redox homeostasis in the cell. Suboptimal blood selenium concentrations (or selenium deficiency states) should be used for assessment of the risk of developing inflammatory processes.

The Role of P2X7 Purinoceptors in the Pathogenesis and Treatment of Muscular Dystrophies

Muscular dystrophies are inherited neuromuscular diseases, resulting in progressive disability and often affecting life expectancy. The most severe, common types are Duchenne muscular dystrophy (DMD) and Limb-girdle sarcoglycanopathy, which cause advancing muscle weakness and wasting. These diseases share a common pathomechanism where, due to the loss of the anchoring dystrophin (DMD, dystrophinopathy) or due to mutations in sarcoglycan-encoding genes (LGMDR3 to LGMDR6), the α-sarcoglycan ecto-ATPase activity is lost. This disturbs important purinergic signaling: An acute muscle injury causes the release of large quantities of ATP, which acts as a damage-associated molecular pattern (DAMP). DAMPs trigger inflammation that clears dead tissues and initiates regeneration that eventually restores normal muscle function. However, in DMD and LGMD, the loss of ecto-ATPase activity, that normally curtails this extracellular ATP (eATP)-evoked stimulation, causes exceedingly high eATP levels. Thus, in dystrophic muscles, the acute inflammation becomes chronic and damaging. The very high eATP over-activates P2X7 purinoceptors, not only maintaining the inflammation but also tuning the potentially compensatory P2X7 up-regulation in dystrophic muscle cells into a cell-damaging mechanism exacerbating the pathology. Thus, the P2X7 receptor in dystrophic muscles is a specific therapeutic target. Accordingly, the P2X7 blockade alleviated dystrophic damage in mouse models of dystrophinopathy and sarcoglycanopathy. Therefore, the existing P2X7 blockers should be considered for the treatment of these highly debilitating diseases. This review aims to present the current understanding of the eATP-P2X7 purinoceptor axis in the pathogenesis and treatment of muscular dystrophies.