USP22 suppresses the NLRP3 inflammasome by degrading NLRP3 via ATG5-dependent autophagy

Research progress on sepsis-associated encephalopathy by inhibiting pyroptosis

Sepsis is a life-threatening condition characterized by multiple organ dysfunction syndrome resulted from dysregulated host responses to infection. Sepsis-associated encephalopathy (SAE) is one of the most common symptoms of acute-phase sepsis, with nearly 70 % of patients with sepsis ultimately developing SAE. Pyroptosis represents a type of cell death that is initiated by inflammation. This cell death type is associated with various infectious and noninfectious diseases. The gasdermin family proteins are crucial cell death executors and critical components in regulating the canonical pyroptosis pathway in microglia. In this review, we summarize the inhibitory effects of several drugs and genes on the pyroptosis pathway. Our findings suggest that several drugs (puerarin, VX765, HC067047, dexpramipexole, and Danhong injection), erbin gene, and TRIM45 knockdown improve SAE by suppressing the canonical pathway of NLRP3/caspase-1/gasdermin D-mediated pyroptosis. Therefore, they have significant importance in terms of brain protection. Moreover, we review the relevant literature published in recent years and summarize the research status and development prospects in this field to provide a basis for subsequent related research.

USP22 promotes angiotensin II-induced podocyte injury by deubiquitinating and stabilizing HMGB1

BACKGROUND

Chronic kidney disease (CKD) remains a significant global health burden, with hypertensive nephropathy (HN) as one of its primary causes. Podocyte injury is a key factor in the progression of CKD. However, the molecular mechanisms underlying angiotensin II-induced podocyte injury remain incompletely understood. Ubiquitin-specific protease 22 (USP22) has been reported to facilitate a range of cellular processes, including cell proliferation and apoptosis. However, the role of USP22 in HN pathogenesis is unclear.

METHODS

The expression of USP22 was assessed in kidney samples from hypertensive nephropathy patients, angiotensin II-induced hypertensive nephropathy mouse models, and cultured podocytes treated with angiotensin II. Podocyte-specific USP22 knockout mice were used to investigate the effects of USP22 deletion on podocyte injury and inflammation.

RESULTS

USP22 expression was significantly upregulated in kidneys of HN patients, angiotensin II-induced mouse models, and cultured podocytes. Podocyte-specific deletion of USP22 markedly reduced angiotensin II-induced podocyte injury and inflammatory responses. Furthermore, we identified high-mobility group box protein 1 (HMGB1) as a protein that interacts with USP22. USP22 deubiquitinated and stabilized HMGB1 through K48-linked ubiquitination. Downregulation of USP22 expression improved kidney function and pathological changes in HN by promoting HMGB1 degradation.

CONCLUSION

This study identifies USP22 as a key regulator of angiotensin II-induced podocyte injury and inflammation through its interaction with HMGB1. Our findings revealed that following glomerular injury, damage and shedding of tubular cells also occurred. Targeting the USP22-HMGB1 axis offers a promising therapeutic strategy for treating hypertensive nephropathy and other types of CKD.

Updated insights into the molecular networks for NLRP3 inflammasome activation

Over the past decade, significant advances have been made in our understanding of how NACHT-, leucine-rich-repeat-, and pyrin domain-containing protein 3 (NLRP3) inflammasomes are activated. These findings provide detailed insights into the transcriptional and posttranslational regulatory processes, the structural-functional relationship of the activation processes, and the spatiotemporal dynamics of NLRP3 activation. Notably, the multifaceted mechanisms underlying the licensing of NLRP3 inflammasome activation constitute a focal point of intense research. Extensive research has revealed the interactions of NLRP3 and its inflammasome components with partner molecules in terms of positive and negative regulation. In this Review, we provide the current understanding of the complex molecular networks that play pivotal roles in regulating NLRP3 inflammasome priming, licensing and assembly. In addition, we highlight the intricate and interconnected mechanisms involved in the activation of the NLRP3 inflammasome and the associated regulatory pathways. Furthermore, we discuss recent advances in the development of therapeutic strategies targeting the NLRP3 inflammasome to identify potential therapeutics for NLRP3-associated inflammatory diseases. As research continues to uncover the intricacies of the molecular networks governing NLRP3 activation, novel approaches for therapeutic interventions against NLRP3-related pathologies are emerging.

Alpha-Synuclein drives NURR1 and NLRP3 Inflammasome dysregulation in Parkinson's disease: From pathogenesis to potential therapeutic strategies

Parkinson's disease (PD), a progressive neurodegenerative disorder, is characterized by the loss of dopaminergic neurons and pathological aggregation of α-synuclein (α-Syn). Emerging evidence highlights the interplay between genetic susceptibility, neuroinflammation, and transcriptional dysregulation in driving PD pathogenesis. This review brings together the latest information on three important players: α-Syn, the transcription factor Orphan nuclear receptor (NURR1), and the NOD-like receptor 3 (NLRP3) inflammasome. Pathogenic α-syn aggregates cause damage to neurons by disrupting mitochondria and lysosomes and spreading in a way similar to prion proteins. They also turn on the NLRP3 inflammasome, which is a key player in neuroinflammation. NLRP3-driven release of pro-inflammatory cytokines exacerbates neurodegeneration and creates a self-sustaining inflammatory milieu. Meanwhile, reduced NURR1 activity, a pivotal modulator of dopaminergic neuron survival and development, exposes neurons to oxidative stress, neuroinflammation, and α-Syn toxicity, hence exacerbating disease progression. So, targeting this trio exhibits transformative potential against PD pathogenesis.

Mechanisms and therapeutic strategies for NLRP3 degradation via post-translational modifications in ubiquitin-proteasome and autophagy lysosomal pathway

The NLRP3 inflammasome is crucial for immune responses. However, its overactivation can lead to severe inflammatory diseases, underscoring its importance as a target for therapeutic intervention. Although numerous inhibitors targeting NLRP3 exist, regulating its degradation offers an alternative and promising strategy to suppress its activation. The degradation of NLRP3 is primarily mediated by the proteasomal and autophagic pathways. The review not only elaborates on the traditional concepts of ubiquitination and NLRP3 degradation but also investigates the important roles of indirect regulatory modifications, such as phosphorylation, acetylation, ubiquitin-like modifications, and palmitoylation-key post-translational modifications (PTMs) that influence NLRP3 degradation. Additionally, we also discuss the potential targets that may affect NLRP3 degradation during the proteasomal and autophagic pathways. By unraveling these complex regulatory mechanisms, the review aims to enhance the understanding of NLRP3 regulation and its implications for developing therapeutic strategies to combat inflammatory diseases.

Paeoniflorin modulates AGEs/RAGE/P38MAPK/ERK/mTOR autophagy pathway to improve cognitive dysfunction in MRL/lpr mice

OBJECTIVE

The objective of this study was to investigate the therapeutic effects of paeoniflorin (PA) on cognitive impairment and to elucidate its potential mechanisms in MRL/lpr mice, a model of systemic lupus erythematosus-associated cognitive dysfunction.

METHOD

Cognitive performance and behavioral responses were assessed using a comprehensive battery of tests, including the Morris water maze, the Novel object recognition test, and the Y maze. Neuropathological changes in the hippocampal regions were visualized through Nissl, HE and Immunohistochemistry staining. Protein expression levels of receptor for advanced glycation end-products (RAGE) and LC3B were quantified by immunofluorescence, while the ultrastructure of autophagic organelles was examined using transmission electron microscopy (TEM). Inflammatory cytokines, namely tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), and interleukin-6 (IL-6) were quantified in both serum and hippocampal homogenates by enzyme-linked immunosorbent assay (ELISA). The hippocampal expression of advanced glycation end-products (AGEs), RAGE, p62, Beclin-1, and key proteins involved in the mitogen-activated protein kinase (MAPK) pathways, including p38MAPK, ERK, and mTOR were analyzed by Western blotting.

RESULT

Paeoniflorin ameliorates cognitive dysfunction, neuronal damage, pro-inflammatory cytokine production in MRL/lpr mice. Paeoniflorin suppresses RAGE and autophagy levels and P38 MAPK/ERK/mTOR signaling pathway activation in the hippocampus of MRL/lpr mice.

CONCLUSION

Paeoniflorin may exert its neuroprotective effects by modulating the AGEs/RAGE/P38MAPK/ERK/mTOR autophagy signaling pathway.

Role of ubiquitin-specific proteases in programmed cell death of breast cancer cells

Breast cancer (BC) is the most common malignant tumor and the leading cause of cancer-related deaths among women worldwide. Great progress has been recently achieved in controlling breast cancer; however, mortality from breast cancer remains a substantial challenge, and new treatment mechanisms are being actively sought. Programmed cell death (PCD) is associated with the progression and treatment of many types of human cancers. PCD can be divided into multiple pathways including autophagy, apoptosis, mitotic catastrophe, necroptosis, ferroptosis, pyroptosis, and anoikis. Ubiquitination is a post-translational modification process in which ubiquitin, a 76-amino acid protein, is coupled to the lysine residues of other proteins. Ubiquitination is involved in many physiological events and promotes cancer development and progression. This review elaborates the role of ubiquitin-specific protease (USP) in programmed cell death, which is common in breast cancer cells, and lays the foundation for tumor diagnosis and targeted therapy.

USP22 enhances atherosclerotic plaque stability and macrophage efferocytosis by stabilizing PPARγ

Atherosclerosis is a chronic inflammatory disease that strongly threatens human health, and macrophages play a pivotal role in its pathogenesis. Ubiquitin-specific peptidase 22 (USP22) is involved in the regulation of macrophage inflammation. However, its role in the atherosclerotic microenvironment remains unclear. In this study, we found that USP22 overexpression in macrophages alleviated atherosclerosis progression in ApoE-/- mice. In vitro, USP22 silencing enhanced macrophage inflammation and foam cell formation, and macrophage efferocytosis was significantly impaired. Mechanistically, USP22 bound to peroxisome proliferator-activated receptor γ (PPARγ) and inhibited its ubiquitination, thereby stabilizing PPARγ and promoting efferocytosis. In addition, intraperitoneal injection of the USP22 inhibitor USP22i-S02 exacerbated atherosclerosis in ApoE-/- mice. In summary, these findings indicate that USP22 may be a potential therapeutic target for the treatment of atherosclerosis.

OTUB1 enhances fatty acid oxidation in APAP-induced liver injury by mediating ACSL5 deubiquitination

Overdosing on acetaminophen (APAP) is the primary cause of drug-induced liver injury. Recent studies have demonstrated that dysregulated lipid metabolism, particularly decreased fatty acid oxidation (FAO), is a key contributor to APAP-induced acute liver injury (AILI). OTU domain-containing ubiquitin aldehyde-binding protein 1 (OTUB1), a crucial member of the OTU deubiquitinase family, has been involved in the metabolic progression of multiple diseases. Nevertheless, its involvement in AILI as well as FAO remains unclear. Here, we aimed to elucidate the effects of OTUB1 on the regulation of FAO in AILI. Our investigation revealed decreased OTUB1 expression in AILI. OTUB1 overexpression not only alleviated liver injury but also improved FAO in vivo and in vitro. Conversely, opposite biochemical changes were observed in hepatocytes with OTUB1 knockdown. Mechanistically, long-chain acyl-CoA synthase 5 (ACSL5), which plays a crucial role in regulating FAO, was identified as a novel substrate of OTUB1 in AILI via mass spectrometry analysis. OTUB1 interacts with ACSL5 and promotes its deubiquitination and stability. Moreover, the protective effect of OTUB1 on FAO in AILI occurred via the deubiquitination of ACSL5. Overall, the present study revealed that the OTUB1-ACSL5 axis plays an essential role in regulating FAO during AILI progression and might be a novel target for therapeutic intervention.

The role of NLRP3 inflammasome in multiple sclerosis: pathogenesis and pharmacological application

Multiple sclerosis (MS) is widely acknowledged as a chronic inflammatory autoimmune disorder characterized by central nervous system (CNS) demyelination and neurodegeneration. The hyperactivation of immune and inflammatory responses is recognized as a pivotal factor contributing to the pathogenesis and progression of MS. Among various immune and inflammatory reactions, researchers have increasingly focused on the inflammasome, a complex of proteins. The initiation and activation of the inflammasome are intricately involved in the onset of MS. Notably, the NLRP3 inflammasome, the most extensively studied member of the inflammasome complex, is closely linked with MS. This review will delve into the roles of the NLRP3 inflammasome in the pathogenesis and progression of MS. Additionally, therapeutic strategies targeting the NLRP3 inflammasome for the treatment of MS, including natural compounds, autophagy regulators, and other small molecular compounds, will be detailed in this review.

HMBOX1 reverses autophagy mediated 5-fluorouracil resistance through promoting HACE1-induced ubiquitination and degradation of ATG5 in colorectal cancer

Chemotherapy remains the primary treatment for unresectable or advanced postoperative colorectal cancers. However, its effectiveness is compromised by chemoresistance, which adversely affects patient outcomes. Dysregulated macroautophagy/autophagy is a proposed mechanism behind this resistance, with ubiquitination playing a key regulatory role. In this study, we identify the transcription factor HMBOX1 (homeobox containing 1) as a critical regulator of chemoresistance in colorectal cancer. RNA sequencing revealed that HMBOX1 is downregulated in drug-resistant colorectal cancer cells and tissues, with its low expression linked to poor prognosis. An integrated analysis of genes associated with autophagy and 5-fluorouracil (5-FU) resistance was conducted, verified in the colorectal cancer tissues of patients by single-cell RNA sequencing and immunostaining. Mass-spectrometry-based proteomics and RNA sequencing were used to elucidate the underlying molecular mechanisms. Functionally, upregulation of HMBOX1 enhances the sensitivity of colorectal cancer cells to the first-line treatment with 5-FU by inhibiting autophagy. Mechanistically, HMBOX1 promotes the transcription of the E3 ubiquitin ligase HACE1, which in turn enhances ATG5 K63-ubiquitination and subsequent proteasome-mediated degradation. This results in decreased ATG5 levels, inhibiting autophagy and thus reducing 5-FU resistance in colorectal cancer cells both in vitro and in vivo. Furthermore, we confirm that HMBOX1 expression positively correlates with HACE1 expression and inversely correlates with autophagy levels in clinical colorectal cancer tissues. Our findings suggest that HMBOX1 downregulation drives 5-FU resistance through autophagy enhancement in colorectal cancer, highlighting HMBOX1 as a potential target for improving chemosensitivity and patient prognosis.Abbreviation: 3-MA: 3-methyladenine; 5-FU: 5-fluorouracil; ATG: autophagy related; CASP3: caspase 3; C-CASP3: cleaved caspase 3; C-PARP: cleaved PARP; CCK8: cell counting kit-8; ChIP: chromatin immunoprecipitation; CHX: cycloheximide; CNV: copy number variation; co-IP: co-immunoprecipitation; COAD: colorectal adenocarcinoma; CQ: chloroquine; CRC: colorectal cancer; CR: complete response; FHC: fetal human colon; GEO: Gene Expression Omnibus; HACE1: HECT domain and ankyrin repeat containing E3 ubiquitin protein ligase 1; HMBOX1: homeobox containing 1; IHC: immunohistochemistry; LC-MS/MS: liquid chromatography-tandem mass spectrometry; mIHC: multiplexed immunohistochemistry; MUT: mutant; NC: negative control; OS: overall survival; PBS: phosphate-buffered saline; PD: progressive disease; PFA: paraformaldehyde; PFS: progression-free survival; PR: partial response; qPCR: quantitative polymerase chain reaction; RAPA: rapamycin; SD: stable disease; TCGA: The Cancer Genome Atlas; TEM: transmission electron microscopy; TF: translation factor; USP22: ubiquitin specific peptidase 22; WT: wild type.

Ubiquitin Ligases in Control: Regulating NLRP3 Inflammasome Activation

Ubiquitin ligases play pivotal roles in the regulation of NLR family pyrin domain containing 3 (NLRP3) inflammasome activation, a critical process in innate immunity and inflammatory responses. This review explores the intricate mechanisms by which various E3 ubiquitin ligases exert both positive and negative influences on NLRP3 inflammasome activity through diverse post-translational modifications. Negative regulation of NLRP3 inflammasome assembly is mediated by several E3 ligases, including F-box and leucine-rich repeat protein 2 (FBXL2), tripartite motif-containing protein 31 (TRIM31), and Casitas B-lineage lymphoma b (Cbl-b), which induce K48-linked ubiquitination of NLRP3, targeting it for proteasomal degradation. Membrane-associated RING-CH 7 (MARCH7) similarly promotes K48-linked ubiquitination leading to autophagic degradation, while RING finger protein (RNF125) induces K63-linked ubiquitination to modulate NLRP3 function. Ariadne homolog 2 (ARIH2) targets the nucleotide-binding domain (NBD) domain of NLRP3, inhibiting its activation, and tripartite motif-containing protein (TRIM65) employs dual K48 and K63-linked ubiquitination to suppress inflammasome assembly. Conversely, Pellino2 exemplifies a positive regulator, promoting NLRP3 inflammasome activation through K63-linked ubiquitination. Additionally, ubiquitin ligases influence other components critical for inflammasome function. TNF receptor-associated factor 3 (TRAF3) mediates K63 polyubiquitination of apoptosis-associated speck-like protein containing a CARD (ASC), facilitating its degradation, while E3 ligases regulate caspase-1 activation and DEAH-box helicase 33 (DHX33)-NLRP3 complex formation through specific ubiquitination events. Beyond direct inflammasome regulation, ubiquitin ligases impact broader innate immune signaling pathways, modulating pattern-recognition receptor responses and dendritic cell maturation. Furthermore, they intricately control NOD1/NOD2 signaling through K63-linked polyubiquitination of receptor-interacting protein 2 (RIP2), crucial for nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and mitogen-activated protein kinase (MAPK) activation. Furthermore, we explore how various pathogens, including bacteria, viruses, and parasites, have evolved sophisticated strategies to hijack the host ubiquitination machinery, manipulating NLRP3 inflammasome activation to evade immune responses. This comprehensive analysis provides insights into the molecular mechanisms underlying inflammasome regulation and their implications for inflammatory diseases, offering potential avenues for therapeutic interventions targeting the NLRP3 inflammasome. In conclusion, ubiquitin ligases emerge as key regulators of NLRP3 inflammasome activation, exhibiting a complex array of functions that finely tune immune responses. Understanding these regulatory mechanisms not only sheds light on fundamental aspects of inflammation but also offers potential therapeutic avenues for inflammatory disorders and infectious diseases.

Morroniside Ameliorates High-Fat and High-Fructose-Driven Chronic Kidney Disease by Motivating AMPK-TFEB Signal Activation to Accelerate Lipophagy and Inhibiting Inflammatory Response

Studies have substantiated that dietary-fat- and fructose-overconsumption-caused lipid metabolism disorders can trigger renal lipotoxicity to drive the progression of chronic kidney disease (CKD). This study was conducted to evaluate the efficacy of morroniside, a natural active substance extracted from the fruit of Cornus officinalis, in inhibiting the progression of CKD in high-fat and high-fructose-fed mice. Our results showed histological changes such as fatty degeneration of renal tubular cells, tubular dilatation, glomerular fibrosis, and abnormal renal function in the kidneys of high-fat- and high-fructose-fed mice, which was significantly improved after morroniside treatment. Mechanistically, morroniside maintained renal lipid metabolism homeostasis and inhibited NLRP3 inflammatory vesicle activation by activating AMPKα to promote TFEB nuclear translocation-mediated lipophagy. Consistent results were observed in palmitic acid-induced HK-2 cells. Notably, silencing AMPKα or TFEB both reversed the effects of morroniside in promoting lipophagy and inhibiting the activation of inflammatory responses in vivo and in vitro. Therefore, our study provides compelling evidence that morroniside delays CKD progression by promoting AMPK/TFEB-mediated lipophagy and inhibiting NLRP3 inflammasome activation, suggesting that dietary supplementation with morroniside and morroniside-rich foods (such as Cornus officinalis) might be an effective strategy for the prevention of CKD.

FlaA N/C attenuates radiation-induced lung injury by promoting NAIP/NLRC4/ASC inflammasome autophagy and inhibiting pyroptosis

BACKGROUND

Radiation-induced lung injury (RILI) is the most common complication experienced by patients with thoracic tumors after radiotherapy. Among patients receiving thoracic tumor radiotherapy, 14.6-37.2% develop RILI. RILI is characterized by an acute inflammatory response; however, the exact mechanism remains unclear and an ideal drug is still lacking. In this study, we investigated the protective effects of flagellin A with linked C- and N-terminal ends (FlaA N/C) against the development of RILI.

METHODS

Mice and bronchial epithelial cells were exposed to radiation (15 Gy) after FlaA N/C treatment. Lung injury, bronchial epithelial cell injury, and RILI were assessed by histological evaluation in vivo and cell viability and cell death detection in vitro. Pyroptosis was assessed by western blotting (WB), immunofluorescence (IF), and immunohistochemistry (IHC). To explore the molecular mechanisms by which FlaA N/C inhibits RILI, conditional Beclin 1 (Beclin1+/-) and NLR family CARD domain-containing protein 4 (Nlrc4)-knockout (Nlrc4-/-) mice were generated. An autophagy inhibitor was used for in vitro cell assays, and pyroptosis indicators were detected. Data were analyzed using one-way analysis of variance.

RESULTS

FlaA N/C attenuated radiation-induced lung tissue damage, pro-inflammatory cytokine release, and pyroptosis in vivo and cell viability, cell death, and pyroptosis in vitro. Mechanistically, FlaA N/C activated the neuronal apoptosis inhibitory protein (NAIP)/NLRC4/apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) inflammasome, which was then degraded during Beclin 1-mediated autophagy. Deletion of the FlaA N/C D0 domain reversed the inhibitory effect of FlaA N/C on radiation-induced pyroptosis in vivo and in vitro. Similarly, Nlrc4-knockout in vivo or inhibition of autophagy in vitro eliminated the protective effects of FlaA N/C against radiation-induced pyroptosis.

CONCLUSIONS

These results indicate that FlaA N/C attenuates RILI by promoting NAIP/NLRC4/ASC inflammasome autophagy and inhibiting pyroptosis. This study provides a potential approach for RILI intervention.

NOD-like receptor X1 promotes autophagy and inactivates NLR family pyrin domain containing 3 inflammasome signaling by binding autophagy-related gene 5 to alleviate cerebral ischemia/reperfusion-induced neuronal injury

Ischemic strokes pose serious risks to human health. We aimed to elucidate the function of NOD-like receptor X1 (NLRX1) in a rat middle cerebral artery occlusion (MCAO)-induced cerebral ischemia/reperfusion injury (CIRI) model and in an oxygen-glucose deprivation/reperfusion (OGD/R)-treated human microglial cell line (HMC3) model. Following NLRX1 upregulation, infarct volumes were measured with 2,3,5-triphenyltetrazolium chloride staining and pathological examination was conducted with hematoxylin-eosin staining. Results suggested that levels of NLRX1 were decreased in brain tissue of MCAO rats and in OGD/R-stimulated HMC3 cells. NOD-like receptor X1 overexpression mitigated the neuronal damage, reduced tumor necrosis factor-α and interleukin-6 expression, alleviated microglial activation, and induced autophagy in vivo and in vitro. Additionally, a coimmunoprecipitation assay indicated that NLRX1 bound to autophagy-related gene 5 (ATG5) to elevate ATG5 expression in HMC3 cells. Further, the elevated NLR family pyrin domain containing 3 (NLRP3), apoptosis-associated speck-like protein containing a CARD, and cleaved caspase 1 expression in MCAO rats and HMC3 cells with OGD/R induction was reduced after NLRX1 upregulation. Importantly, ATG5 depletion abrogated the effects of NLRX1 elevation on NLRP3 inflammasome signaling. These results indicate that NLRX1 promotes autophagy and inactivates NLRP3 inflammasome signaling by binding ATG5 in experimental cerebral ischemia. These data may help the development of novel therapeutic strategies for ischemic stroke.

Inhibition of SCFKDM2A/USP22-dependent nuclear β-catenin ubiquitylation mediates cerebral ischemic tolerance

Hypoxic postconditioning (HPC) was reported to stabilize nuclear β-catenin by inhibiting lysine (K)-specific demethylase 2 A (KDM2A) in hippocampal CA1 against transient global cerebral ischemia (tGCI). Herein we investigate how HPC inhibits the K48-linked poly-ubiquitination (K48-Ub)-related degradation of nuclear β-catenin in CA1 after tGCI. We confirmed that SCFKDM2A complex targets nuclear β-catenin for degradation via ubiquitin proteasome pathway in vitro. HPC reduced SCFKDM2A complex and the K48-Ub of β-catenin, and increased ubiquitin-specific peptidase 22 (USP22) in nucleus after tGCI. Furthermore, KDM2A knockdown decreased the K48-Ub of nuclear β-catenin and nuclear β-catenin-SCFKDM2A complex interaction after tGCI. Moreover, β-catenin knockdown suppressed nuclear survivin expression and attenuated neuroprotection induced by HPC. In contrast, the overexpression of USP22 promoted nuclear β-catenin deubiquitination and enhanced the neuroprotective effects offered by HPC. Taken together, this study supports that HPC downregulated the K48-Ub of nuclear β-catenin through suppressing SCFKDM2A and increasing USP22, thereby inducing cerebral ischemic tolerance.

Ubiquitin-specific protease 25 improves myocardial ischemia-reperfusion injury by deubiquitinating NLRP3 and negatively regulating NLRP3 inflammasome activity in cardiomyocytes

BACKGROUND

Myocardial ischemia/reperfusion injury (MI/RI) restricts the effect of myocardial reperfusion therapy and lacks effective prevention and treatment methods. Deubiquitinating enzymes (DUBs), especially members of the ubiquitin-specific protease (USP) family of DUBs, are key proteins in the ubiquitination modification process and play a vital role in MI/RI. Therefore, we aimed to investigate the role of USP25, as a member of the USP family, in MI/RI and its molecular mechanism.

METHODS

Transcriptome sequencing was applied to evaluate the differential expression of USP families during hypoxia/reoxygenation (H/R) and validated in human and mouse heart samples and cardiomyocytes by performing quantitative polymerase chain reaction. Wild-type or USP25-/- mice were used to develop the MI/RI model. Co-immunoprecipitation (Co-IP) combined with liquid chromatography-tandem mass spectrometry analysis was used to screen the potential substrate protein of USP25 in H/R-induced cardiomyocyte injury. TUNEL and Hoechst/propidium iodide staining and western blot were used to detect the level of pyroptosis. In addition, cardiomyocyte-specific USP25 overexpression in NLRP3-/- mice with AAV9 vectors was used to validate the biological function of USP25 and NLRP3 interaction.

RESULTS

We found that the expression level of USP25 was significantly decreased in I/R-induced mouse heart tissues and primary cardiomyocytes in a time-dependent manner. USP25 deficiency exacerbated MI/RI and aggravated I/R-induced cardiac remodelling in mice. Mechanistically, USP25 directly binds to NLRP3 protein and K63-linkedly deubiquitinates NLRP3 at residue K243 via its active site C178, thus hindering NLRP3-ASC interaction and ASC oligomerization to inhibit NLRP3 activation and pyroptosis in cardiomyocytes. We further showed that the overexpression of USP25 in cardiomyocytes ameliorated MI/RI in mice, whereas this protective effect disappeared when NLRP3 is knocked out.

CONCLUSIONS

Our study demonstrated that USP25 ameliorates MI/RI by regulating NLRP3 activation and its mediated pyroptosis. This finding extends the protective role of USP25 in cardiovascular disease and provides an experimental basis for future USP25-based drug development for the treatment of MI/RI.

KEY POINTS

The deubiquitinating enzyme USP25 was down-regulated both in myocardial ischemia/reperfusion injury (MI/RI) myocardium tissues. The deficiency of USP25 worsened exacerbated MI/RI in mice, whereas the overexpression of USP25 in cardiomyocytes mitigated this pathological phenotype. USP25 directly interacts with the NLRP3 protein and deubiquitinates it via K63 linkage at residue K243 through its active site C178, thus affecting NLRP3-ASC interaction and ASC oligomerization to inhibit NLRP3 activation and pyroptosis in cardiomyocytes.

Targeting secretory autophagy in solid cancers: mechanisms, immune regulation and clinical insights

Secretory autophagy is a classical form of unconventional secretion that integrates autophagy with the secretory process, relying on highly conserved autophagy-related molecules and playing a critical role in tumor progression and treatment resistance. Traditional autophagy is responsible for degrading intracellular substances by fusing autophagosomes with lysosomes. However, secretory autophagy uses autophagy signaling to mediate the secretion of specific substances and regulate the tumor microenvironment (TME). Cytoplasmic substances are preferentially secreted rather than directed toward lysosomal degradation, involving various selective mechanisms. Moreover, substances released by secretory autophagy convey biological signals to the TME, inducing immune dysregulation and contributing to drug resistance. Therefore, elucidating the mechanisms underlying secretory autophagy is essential for improving clinical treatments. This review systematically summarizes current knowledge of secretory autophagy, from initiation to secretion, considering inter-tumor heterogeneity, explores its role across different tumor types. Furthermore, it proposes future research directions and highlights unresolved clinical challenges.

VANGL2 alleviates inflammatory bowel disease by recruiting the ubiquitin ligase MARCH8 to limit NLRP3 inflammasome activation through OPTN-mediated selective autophagy

Inflammatory bowel disease (IBD) is a chronic and potentially life-threatening inflammatory disease of gastroenteric tissue characterized by episodes of intestinal inflammation, but the underlying mechanisms remain elusive. Here, we explore the role and precise mechanism of Van-Gogh-like 2 (VANGL2) during the pathogenesis of IBD. VANGL2 decreases in IBD patients and dextran sulfate sodium (DSS)-induced colitis in mice. Myeloid VANGL2 deficiency exacerbates the progression of DSS-induced colitis in mice and specifically enhances the activation of NLRP3 inflammasome in macrophages. NLRP3-specific inhibitor MCC950 effectively alleviates DSS-induced colitis in VANGL2 deficient mice. Mechanistically, VANGL2 interacts with NLRP3 and promotes the autophagic degradation of NLRP3 through enhancing the K27-linked polyubiquitination at lysine 823 of NLRP3 by recruiting E3 ligase MARCH8, leading to optineurin (OPTN)-mediated selective autophagy. Notably, decreased VANGL2 in the peripheral blood mononuclear cells from IBD patients results in overt NLRP3 inflammasome activation and sustained inflammation. Taken together, this study demonstrates that VANGL2 acts as a repressor of IBD progression by inhibiting NLRP3 inflammasome activation and provides insights into the crosstalk between inflammation and autophagy in preventing IBD.

Relationship between autophagy and NLRP3 inflammasome during articular cartilage degradation in oestrogen-deficient rats with streptozotocin-induced diabetes

BACKGROUND

Estrogen deficiency and Diabetes mellitus (DM) cause joint tissue deterioration, although the mechanisms are uncertain. This study evaluated the immunoexpression of autophagy and NLRP3-inflammasome markers, in rat articular cartilage with estrogen deficiency and DM.

METHODS

Twenty rats were sham-operated (SHAM) or ovariectomized (OVX) and equally allocated into four groups: SHAM and OVX groups administered with vehicle solution; SHAM and OVX groups treated with 60 mg/kg/body weight of streptozotocin, intraperitoneally, to induce DM (SHAM-DM and OVX-DM groups). After seven weeks, the rats were euthanized, and their joint knees were processed for paraffin embedding. Sections were stained with haematoxylin-eosin, toluidine blue, safranin-O/fast-green or subjected to picrosirius-red-polarisation method; immunohistochemistry to detect beclin-1 and microtubule-associated protein 1B-light chain 3 (autophagy markers), NLRP3 and interleukin-1β (IL-1β) (inflammasome activation markers), along with matrix metalloproteinase-9 (MMP-9), Nuclear factor-kappa B (NFκB), and Vascular endothelial growth factor A (VEGF-A) were performed.

RESULTS

Deterioration of articular cartilage and subchondral bone were greater in SHAM-DM and OVX-DM groups. Higher percentages of immunolabeled chondrocytes to NLRP3, IL-1β, MMP-9, NFκB, and VEGF-A, as well as lower percentages of chondrocytes immunolabeled to autophagy markers, were noticed in estrogen-deficient and diabetic groups. These differences were greater in the OVX-DM group. Percentages of immunolabeled chondrocytes showed negative correlation between autophagy markers v.s IL-1β, NLRP-3, MMP-9, NFκB, and VEGF-A, along with positive correlation between VEGF-A vs. MMP-9, NFκB, IL-1β, and NLRP3, and MMP-9 vs. NFκB.

CONCLUSIONS

In conclusion, autophagy reduction and NLRP3 inflammasome activation in chondrocytes may be implicated in articular cartilage degradation, under estrogen-deficient and DM conditions. Moreover, the combination of estrogen deficiency and DM may potentiate those effects.

Interaction Between Autophagy and the Inflammasome in Human Tumors: Implications for the Treatment of Human Cancers

Autophagy is a physiologically regulated cellular process orchestrated by autophagy-related genes (ATGs) that, depending on the tumor type and stage, can either promote or suppress tumor growth and progression. It can also modulate cancer stem cell maintenance and immune responses. Therefore, targeted manipulation of autophagy may inhibit tumor development by overcoming tumor-promoting mechanisms. The inflammasome is another multifunctional bioprocess that induces a form of pro-inflammatory programmed cell death, called pyroptosis. Dysregulation or overactivation of the inflammasome has been implicated in tumor pathogenesis and development. Additionally, autophagy can inhibit the NLRP3 inflammasome by removing inflammatory drivers. Recent research suggests that the NLRP3 inflammasome, in turn, affects autophagy. Understanding the complex interplay between autophagy and inflammasomes could lead to more precise and effective strategies for cancer treatments. In this review, we summarize the impact of autophagy and inflammasome dysregulation on tumor progression or suppression. We then highlight their targeting for cancer treatment as monotherapy or in combination with other therapies. Furthermore, we discuss the interaction between autophagy and tumor-promoting inflammation or the NLRP3 inflammasome. Finally, based on recent findings, we review the potential of this interaction for cancer treatment.

USP22 inhibits microglial M1 polarization by regulating the PU.1/NLRP3 inflammasome pathway

OBJECTIVE

This study aimed to investigate the effect of Ubiquitin-Specific Peptidase 22 (USP22) on the inflammatory response mediated by BV-2 mouse microglia and explore the role of the PU box binding protein 1 (PU.1)/NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasome in the USP22-induced polarization of BV-2 cells.

METHODS

The BV-2 mouse microglia line was cultured in vitro, and plasmid and siRNA transfection was performed to overexpress or knockdown USP22. Subsequently, BV-2 cells were treated with lipopolysaccharide (LPS) and interferon-gamma (IFN-γ) and interleukin (IL)-4 to induce M1 and M2 polarization, respectively. Western blot was used to detect the expression levels of USP22, PU.1, M1 polarization markers [inducible nitric oxide synthase (iNOS), and cluster of differentiation (CD) 86], M2 polarization markers [arginase 1 (Arg1), and CD206], in BV-2 cells from different treatment groups. Additionally, measurement was performed on the inflammasome NLRP3, and its activation-related proteins [NIMA-related kinase7 (NEK7), cleaved-caspase 1, apoptosis-associated speck-like protein containing a CARD (ASC)]. Enzyme-linked immunosorbent (ELISA) assay was employed to determine the levels of inflammatory cytokines tumor necrosis factor-alpha (TNF-α), IL-1 β, and IL-10 in the cells. Furthermore, immunofluorescence was utilized to analyze the levels of iNOS and Arg1-positive BV-2 cells in different treatment groups. Moreover, the ubiquitination level of PU.1 was detected using immunoprecipitation.

RESULTS

The protein expression level of USP22 was significantly down-regulated in BV-2 cells treated with M1 polarization. Overexpression of USP22 remarkably reduced the protein levels of iNOS and CD86, but markedly increased the protein levels of Arg1 and CD206 in cells. Besides, there was a notable reduction in the levels of TNF-α and IL-1 β in the cell culture medium, while a remarkable increase was observed in the level of IL-10. Additionally, the level of iNOS-positive cells was significantly decreased, while the level of Arg1-positive cells was considerably increased. However, up-regulation of PU.1 expression could reverse the above results and promoted the expression of NLRP3 and its activation-related proteins. Notably, overexpression of USP22 significantly down-regulated the protein expression and ubiquitination level of PU.1.

CONCLUSION

USP22 inhibits the M1 polarization of BV-2 mouse microglia. The PU.1/NLRP3 inflammasome pathway may be a critical regulatory pathway of USP22 in BV-2 cell polarization.

The antiarthritic effect of CBR-470-1 in hypoxic environment is to increase the level of NOD-like receptor family pyrin domain containing 3 ubiquitination by decreasing phosphoglycerate kinase 1 activity

BACKGROUND

Hypoxia can affect the occurrence and development of inflammation in humans, but its effects on the disease progression of osteoarthritis (OA) remain unclear. Synovial macrophages play an essential role in the progression of arthritis. Specifically, the activation of the NOD-like receptor family pyrin domain containing 3 (NLRP3) in macrophages induces the secretion of a series of inflammatory factors, accelerating the progression of OA.

METHODS

The effects of CBR-470-1 were assessed in a mouse model of OA induced by destabilization of the medial meniscus (DMM) by micro-computed tomography imaging, Safranin-O and Fast Green staining, immunofluorescence staining and enzyme-linked immunosorbent assay. Western Blot analysis was used to explore the underlying mechanism of these experimental results. Additionally, a co-culture system of THP-1 and chondrocytes was established to investigate the impact of CBR-470-1 on chondrocyte proliferation, apoptosis, migration and the regulation of chondrocyte-related proteins within the system.

RESULTS

In hypoxic conditions, CBR-470-1 significantly inhibited the progression of OA in the DMM-induced OA mouse model, but that effect disappeared in the DMM-induced OA phosphoglycerate kinase 1 (PGK1)fl/flLyz2-Cre mouse model. Not only that, CBR-470-1 can also improve the proliferation and migration of chondrocytes, reduce the apoptosis rate of chondrocytes, and regulate the expression of chondrocyte-related proteins in the co-culture system of THP-1 and chondrocytes.

CONCLUSIONS

This study conducted a series of in vitro and in vivo experiments, revealing that hypoxia plays a pro-inflammatory role by increasing PGK1 activity and reducing the binding of the deubiquitinating enzyme ubiquitin-specific peptidase 14 to NLRP3, thereby reducing the ubiquitination level of NLRP3. CBR-470-1, a specific inhibitor of PGK1, can reduce PGK1 activity to reverse the role of hypoxia in the progression of OA. These findings lay a foundation for the development of OA treatment in a hypoxic environment.

KEY POINTS

Hypoxia plays a pro-inflammatory role by increasing PGK1 activity and thereby decreasing the ubiquitination level of NLRP3. Hypoxia plays a pro-inflammatory role by increasing PGK1 activity, reducing the binding of the deubiquitinating enzyme USP14 to NLRP3, and reducing the ubiquitination level of NLRP3. CBR-470-1 reverses the role of hypoxia in the progression of osteoarthritis.

Deciphering the mechanisms of the IL-6/CXCL1 and NOD-like receptor signaling pathways in otitis media with effusion in rodents

BACKGROUND

Otitis media with effusion (OME) often leads to pediatric hearing loss and is influenced by innate and adaptive immune responses. Innate immunity serves as the non-specific first line of defense against OME.

METHODS

We induced OME in rats using ovalbumin. We administered IL-6 monoclonal antibodies intranasally to inhibit IL-6, and we injected an NF-κB inhibitor intraperitoneally to explore the role of IL-6 in innate immunity and its interaction with the NOD-like receptor signaling pathway. We analyzed RNA-sequencing data with Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathways to assess signaling pathways involved in OME. We also utilized Western blot, quantitative real-time PCR, and immunohistochemistry on middle ear samples and used microscopy to identify immune cells in ear wash fluids.

RESULTS

Our study suggests a pivotal role for IL-6 in the immune pathways of rats with OME via the regulation of CXCL1-mediated pathways. Increased levels of IL-6 and CXCL1 were observed in the middle ear tissues, and activation of the NLRP3 inflammasome in OME rats led to an immune response via NF-κB, thus promoting IL-6 and CXCL1 production, which was reduced by IL-6 antibody treatment.

CONCLUSIONS

Our findings confirm that IL-6 and CXCL1 play significant roles in the innate immune response in OME in rodents, predominantly via the NOD-like receptor signaling pathway and NLRP3 inflammasome activation. This research sheds light on OME pathogenesis and its immune-related mechanisms.

CircHipk3 serves a dual role in macrophage pyroptosis by promoting NLRP3 transcription and inhibition of autophagy to induce abdominal aortic aneurysm formation

AIMS

CircRNAs could regulate macrophage pyroptosis, which has the potential in promoting the synergistic effect of inflammation and matrix metalloproteinase (MMP) activity in abdominal aortic aneurysm (AAA). But the roles of circRNAs in modulating macrophage pyroptosis in the AAA remain unknown. This study explored the contribution to AAA of circHipk3, which was macrophage pyroptosis promoter, and the underlying mechanism.

METHODS AND RESULTS

CircHipk3 was markedly upregulated in aortic aneurysms compared with that in normal arteries. In mice treated with circHipk3 contributed to macrophage pyroptosis, subsequently promoting the synergistic effect of inflammation and MMP synthesis, and significantly accelerated angiotensin (Ang) II- and porcine pancreatic elastase (PPE)-induced AAA formation. Mechanically, chromatin isolation by RNA purification (ChIRP) indicated that circHipk3 facilitated macrophage pyroptosis by interaction with Stat3, increase the NLRP3 level in the aorta, and by binding Snd1 to promote Ptbp1 mRNA degradation to inhibit autophagy. Therefore, our study revealed the important role of circHipk3 in macrophage pyroptosis and thus significantly improved the outcome of AAA.

CONCLUSIONS

CircHipk3 serves a dual role in augmenting macrophage pyroptosis by interaction with Stat3, increase the NLRP3 level, and by binding Snd1 to promote Ptbp1 mRNA degradation to inhibit autophagy, thereby inducing aneurysm formation and progression.

KEY POINTS

CircHipk3 is significantly upregulated in abdominal aortic aneurysms (AAA) compared to normal arteries, contributing to macrophage pyroptosis. CircHipk3 promotes the synergistic effect of inflammation and matrix metalloproteinase (MMP) activity, accelerating Angiotensin II- and porcine pancreatic elastase-induced AAA formation in mice. Mechanistically, CircHipk3 interacts with Stat3 to elevate NLRP3 levels and binds Snd1 to promote Ptbp1 mRNA degradation, inhibiting autophagy. CircHipk3's dual role in enhancing NLRP3 inflammasome activation and inhibiting autophagy makes it a critical regulator in AAA development and rupture. Targeting CircHipk3 may offer a novel therapeutic strategy to prevent pyroptosis and AAA development, positioning it as a potential treatment target.

Ginsenoside Rg1 reduces cardiac inflammation against myocardial ischemia/reperfusion injury by inhibiting macrophage polarization

Background

Myocardial ischemia/reperfusion (MI/R) injury is the main cause of death worldwide and poses a significant threat to cardiac health. Ginsenoside Rg1 has been shown to have inhibitory effects on inflammatory activation, oxidative stress, and cardiac injury, suggesting that Rg1 may have therapeutic effects on MI/R injury. However, the mechanism remains to be further studied.

Materials and methods

Left anterior descending coronary artery ligation was performed in Sprague-Dawley rats to construct an MI/R model in vivo. Organ index, electrocardiogram, infarct size, histopathological changes, and detection of cardiac injury and inflammatory factors in the rats were used to evaluate myocarditis, macrophage polarization, and fibrosis. We also used rat bone marrow-derived macrophages (BMDMs) to further investigate the effects of Rg1 on absent in melanoma 2 (AIM2) activation and macrophage polarization in vitro.

Results

Administration of Rg1 exhibited dose-dependent cardioprotective effects and effectively reduced MI/R injury. Rg1 significantly attenuated myocardial inflammation and inhibited M1 macrophage polarization during MI/R injury. Furthermore, Rg1 significantly reduced cardiac fibrosis in response to MI/R injury. This anti-fibrotic effect may contribute to the preservation of cardiac structure and function following an ischemic insult. Meanwhile, Rg1 effectively inhibited the activation of the AIM2 inflammasome in vitro, highlighting its potential as a key regulator of inflammatory pathways.

Conclusion

Our findings elucidate the multifaceted mechanisms underlying Rg1's cardioprotective effects, including its ability to mitigate inflammation, modulate macrophage polarization, and inhibit fibrosis.

NLRC4, inflammation and colorectal cancer (Review)

Chronic inflammation is recognized as a major risk factor for cancer and is involved in every phase of the disease. Inflammasomes are central to the inflammatory response and play a crucial role in cancer development. The present review summarizes the role of Nod‑like receptor C4 (NLRC4) in inflammation and colorectal cancer (CRC). Reviews of the literature were conducted using Web of Science, PubMed and CNKI, with search terms including 'NLRC4', 'colorectal cancer', 'auto‑inflammatory diseases' and 'prognosis'. Variants of NLRC4 can cause recessive immune dysregulation and autoinflammation or lead to ulcerative colitis as a heterozygous risk factor. Additionally, genetic mutations in inflammasome components may increase susceptibility to cancer. NLRC4 is considered a tumor suppressor in CRC. The role of NLRC4 in CRC signaling pathways is currently understood to involve five key aspects (caspase 1, NLRP3/IL‑8, IL‑1β/IL‑1, NAIP and p53). The mechanisms by which NLRC4 is involved in CRC are considered to be threefold (through pyroptosis, apoptosis, necroptosis and PANoptosis; regulating the immune response; and protecting intestinal epithelial cells to prevent CRC). However, the impact of NLRC4 mutations on CRC remains unclear. In conclusion, NLRC4 is a significant inflammasome that protects against CRC through various signaling pathways and mechanisms. The association between NLRC4 mutations and CRC warrants further investigation.

Overexpression of USP22 ameliorates LPS-induced endometrial stromal cells inflammation and modulates cells decidualization by inhibiting ferroptosis

Endometritis and the failure of decidualization of the endometrium are important factors contributing to the increased incidence of abortion. USP22 is associated with various inflammatory diseases and has been shown to be involved in endometrial decidualization in mice. This study aims to investigate whether USP22 is involved in the regulation of inflammatory response and decidualization in human endometrial stromal cells (hESCs). In this study, lipopolysaccharide (LPS) was used to induce inflammation in hESCs, and MPA combined with cAMP was used to induce decidualization of hESCs. USP22 overexpression vector was constructed to study the role of USP22 in endometritis. The results showed that the USP22 protein and mRNA levels were decreased in LPS-induced hESCs. LPS induction increased the levels of TNF-α, IL-1β, and IL-6, as well as the expression of iNOS and COX2 proteins in hESCs. In the LPS group, the levels of F-actin, PRL, IGFBP1, SLC7A11, and GPX4 proteins decreased, while the levels of lipid peroxidation and total iron content increased. Additionally, the levels of ACSL4 and TFR1 proteins were up-regulated. Overexpression of USP22 reversed LPS-induced cellular inflammation, attenuated decidualization, and inhibited ferroptosis. However, the use of ferroptosis inducers diminished the regulatory effects of USP22 on inflammatory responses and decidualization. In summary, these suggested that USP22 reduces the LPS-induced inflammatory response and regulates the decidualization of hESCs, and possibly involving ferroptosis.

The role of perirenal adipose tissue deposition in chronic kidney disease progression: Mechanisms and therapeutic implications

Chronic kidney disease (CKD) represents a significant and escalating global health challenge, with morbidity and mortality rates rising steadily. Evidence increasingly implicates perirenal adipose tissue (PRAT) deposition as a contributing factor in the pathogenesis of CKD. This review explores how PRAT deposition may exert deleterious effects on renal structure and function. The anatomical proximity of PRAT to the kidneys not only potentially causes mechanical compression but also leads to the dysregulated secretion of adipokines and inflammatory mediators, such as adiponectin, leptin, visfatin, tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and exosomes. Additionally, PRAT deposition may contribute to renal lipotoxicity through elevated levels of free fatty acids (FFA), triglycerides (TAG), diacylglycerol (DAG), and ceramides (Cer). PRAT deposition is also linked to the hyperactivation of the renin-angiotensin-aldosterone system (RAAS), which further exacerbates CKD progression. Recognizing PRAT deposition as an independent risk factor for CKD underscores the potential of targeting PRAT as a novel strategy for the prevention and management of CKD. This review further discusses interventions that could include measuring PRAT thickness to establish a baseline, managing metabolic risk factors that promote its deposition, and inhibiting key PRAT-induced signaling pathways.

Discovery of natural product derivative triptolidiol as a direct NLRP3 inhibitor by reducing K63-specific ubiquitination

BACKGROUND AND PURPOSE

NLRP3 is up-regulated in inflammatory and autoimmune diseases. The development of NLRP3 inhibitors is challenged by the identification of compounds with distinct mechanisms of action avoiding side effects and toxicity. Triptolide is a natural product with multiple anti-inflammatory activities, but a narrow therapeutic window.

EXPERIMENTAL APPROACH

Natural product triptolide derivatives were screened for NLRP3 inhibitors in human THP-1 and mouse bone marrow-derived macrophages. The efficacy of potent NLRP3 inhibitors was evaluated in LPS-induced acute lung injury and septic shock models.

KEY RESULTS

Triptolidiol was identified as a selective inhibitor of NLRP3 with high potency. Triptolidiol inactivated the NLRP3 inflammasome in human THP-1 and mouse primary macrophages primed with LPS. Triptolidiol specifically inhibited pro-caspase 1 cleavage downstream of NLRP3, but not AIM2 or NLRC4 inflammasomes. Based on the structure-activity relationship study, the C8-β-OH group was critical for its binding to NLRP3. Triptolidiol exhibited a submicromolar KD for NLRP3, binding to residue C280. This binding prevented the interaction of NLRP3 with NEK7, the key regulator of NLRP3 inflammasome oligomerization and assembly, but not with the inflammasome adaptor protein ASC. Triptolidiol decreased the K63-specific ubiquitination of NLRP3, leading NLRP3 to a "closed" inactive conformation. Intraperitoneal administration of triptolidiol significantly attenuated LPS-induced acute lung injury and lethal septic shock.

CONCLUSION AND IMPLICATIONS

Triptolidiol is a novel NLRP3 inhibitor that regulates inflammasome assembly and activation by decreasing K63-linked ubiquitination. Triptolidiol has novel structural features that make it distinct from reported NLRP3 inhibitors and represents a viable therapeutic lead for inflammatory diseases.

Macrophage WDFY3, a protector against autoimmunity

Efficient efferocytosis is essential for maintaining homeostasis. Excessive apoptotic cell (AC) death and impaired macrophage efferocytosis lead to autoantigen release and autoantibody production, immune activation, and organ damage. It remains unclear whether these immunogenic autoantigens are the sole cause of increased autoimmunity or if efferocytosis of ACs directly influences macrophage function, impacting their ability to activate T cells and potentially amplifying autoimmune responses. Additionally, it has not been established if enhancing macrophage efferocytosis or modulating macrophage responses to AC engulfment can be protective in autoimmune-like disorders. Our previous work showed WDFY3 is crucial for efficient macrophage efferocytosis. This study reveals that myeloid knockout of Wdfy3 exacerbates autoimmunity in young mice with increased AC burden by systemic injections of ACs and in middle-aged mice developing spontaneous autoimmunity, whereas ectopic overexpression of WDFY3 suppresses autoimmunity in these models. Macrophages, as efferocytes, can activate T cells and the inflammasome upon engulfing ACs, which are suppressed by overexpressing WDFY3. This work uncovered the role of WDFY3 as a protector against autoimmunity by promoting macrophage efferocytosis thus limiting autoantigen production, as well as mitigating T cell activation and inflammasome activation.

GSNOR negatively regulates the NLRP3 inflammasome via S-nitrosation of MAPK14

Hyperactivation of the NLRP3 inflammasome has been implicated in the pathogenesis of numerous diseases. However, the precise molecular mechanisms that modulate the transcriptional regulation of NLRP3 remain largely unknown. In this study, we demonstrated that S-nitrosoglutathione reductase (GSNOR) deficiency in macrophages leads to significant increases in the Nlrp3 and Il-1β expression levels and interleukin-1β (IL-1β) secretion in response to NLRP3 inflammasome stimulation. Furthermore, in vivo experiments utilizing Gsnor-/- mice revealed increased disease severity in both lipopolysaccharide (LPS)-induced septic shock and dextran sodium sulfate (DSS)-induced colitis models. Additionally, we showed that both LPS-induced septic shock and DSS-induced colitis were ameliorated in Gsnor-/- Nlrp3-/- double-knockout (DKO) mice. Mechanistically, GSNOR deficiency increases the S-nitrosation of mitogen-activated protein kinase 14 (MAPK14) at the Cys211 residue and augments MAPK14 kinase activity, thereby promoting Nlrp3 and Il-1β transcription and stimulating NLRP3 inflammasome activity. Our findings suggested that GSNOR is a regulator of the NLRP3 inflammasome and that reducing the level of S-nitrosylated MAPK14 may constitute an effective strategy for alleviating diseases associated with NLRP3-mediated inflammation.

TRPM2-dependent autophagy inhibition exacerbates oxidative stress-induced CXCL16 secretion by keratinocytes in vitiligo

Vitiligo is a depigmented skin disease due to the destruction of melanocytes. Under oxidative stress, keratinocyte-derived chemokine C-X-C motif ligand 16 (CXCL16) plays a critical role in recruiting CD8+ T cells, which kill melanocytes. Autophagy serves as a protective cell survival mechanism and impairment of autophagy has been linked to increased secretion of the proinflammatory cytokines. However, the role of autophagy in the secretion of CXCL16 under oxidative stress has not been investigated. Herein, we initially found that autophagy was suppressed in both keratinocytes of vitiligo lesions and keratinocytes exposed to oxidative stress in vitro. Autophagy inhibition also promoted CXCL16 secretion. Furthermore, upregulated transient receptor potential cation channel subfamily M member 2 (TRPM2) functioned as an upstream oxidative stress sensor to inhibit autophagy. Moreover, TRPM2-mediated Ca2+ influx activated calpain to shear autophagy related 5 (Atg5) and Atg12-Atg5 conjugate formation was blocked to inhibit autophagy under oxidative stress. More importantly, Atg5 downregulation enhanced the binding of interferon regulatory factor 3 (IRF3) to the CXCL16 promoter region by activating Tank-binding kinase 1 (TBK1), thus promoting CXCL16 secretion. These findings suggested that TRPM2-restrained autophagy promotes CXCL16 secretion via the Atg5-TBK1-IRF3 signaling pathway under oxidative stress. Inhibition of TRPM2 may serve as a potential target for the treatment of vitiligo. © 2024 The Pathological Society of Great Britain and Ireland.

The role of ncRNAs-mediated pyroptosis in diabetes and its vascular complications

Over the past decade, the prevalence of diabetes has increased significantly worldwide, leading to an increase in vascular complications of diabetes (VCD), such as diabetic cardiomyopathy (DCM), diabetic nephropathy (DN), and diabetic retinopathy (DR). Noncoding RNAs (ncRNAs), such as microRNAs (miRNAs), long Noncoding RNAs (lncRNAs), and circular RNAs (circRNAs), play a key role in cellular processes, including the pathophysiology of diabetes and VCD via pyroptosis. ncRNAs (e.g., miR-17, lnc-MEG3, and lnc-KCNQ1OT1) can regulate pyroptosis in pancreatic β cells. Some ncRNAs are involved in VCD progression. For example, miR-21, lnc-KCNQ1OT1, lnc-GAS5, and lnc-MALAT1 were reported in DN and DCM, and lnc-MIAT was identified in DCM and DR. Herein, this review aimed to summarize recent research findings related to ncRNAs-mediated pyroptosis at the onset and progression of diabetes and VCD.

The interplay between α-Synuclein and NLRP3 inflammasome in Parkinson's disease

α-Synuclein is a member of a protein of synucleins, which is a presynaptic neuron protein. It is usually highly expressed in the brain and participates in the formation and transmission of nerve synapses. It has been reported that abnormal aggregation of α-Syn can induce the activation of NLRP3 inflammasome in microglia, increase the production of IL-1β, and aggravate neuroinflammation. Therefore, it is recognized as one of the important factors leading to neuroinflammation in Parkinson's disease. In this paper, we aimed to explore the influence of post-translational modification of α-Syn on its pathological aggregation and summarize various pathways that activate NLRP3 triggered by α-Syn and targeted therapeutic strategies, which provided new insights for further exploring the origin and targeted therapy of Parkinson's disease.

TRIM45 aggravates microglia pyroptosis via Atg5/NLRP3 axis in septic encephalopathy

BACKGROUND

Neuroinflammation mediated by microglial pyroptosis is an important pathogenic mechanism of septic encephalopathy (SAE). It has been reported that TRIM45 is associated with tumours and inflammatory diseases. However, the role of TRIM45 in SAE and the relationship between TRIM45 and microglial pyroptosis are unknown. In this study, we found that TRIM45 played an important role in regulating microglial pyroptosis and the molecular mechanism.

METHODS

SAE was induced by intraperitoneal injection of LPS in WT and AAV-shTRIM45 mice. BV2 cells were treated with LPS/ATP in vitro. Cognitive function was assessed by the Morris water maze. Nissl staining was used to evaluate histological and structural lesions. ELISA was used to dectect neuroinflammation. qPCR was used to detect the mRNA levels of inflammatory cytokines, NLRP3, and autophagy genes. Western blotting and immunofluorescence analysis were used to analyse the expression of the proteins. Changes in reactive oxygen species (ROS) in cells were observed by flow cytometry. Changes in mitochondrial membrane potential in BV2 cells were detected by JC-1 staining. Peripheral blood mononuclear cells were extracted from blood by density gradient centrifugation and then used for qPCR, western blotting and flow detection. To further explore the mechanism, we used the overexpression plasmids TRIM45 and Atg5 as well as siRNA-TRIM45 and siRNA-Atg5 to analyse the downstream pathway of NLRP3. The protein and mRNA levels of TRIM45 in peripheral blood mononuclear cells from sepsis patients were examined.

RESULTS

Knocking down TRIM45 protected against neuronal damage and cognitive impairment in septic mice. TRIM45 knockdown inhibited microglial pyroptosis and the secretion of inflammatory cytokines in vivo and in vitro, which was mediated by NLRP3/Gsdmd-N activation. Overexpression of TRIM45 could activate NLRP3 and downstream proteins. Further examination showed that TRIM45 regulated the activation of NLRP3 by altering Atg5 and regulating autophagic flux. It was also found that overexpression and knockdown of TRIM45 affected the changes in ROS and mitochondrial membrane potential. Thus, knocking down TRIM45 could reduce microglial pyroptosis, the secretion of proinflammatory cytokines, and neuronal damage and improve cognitive function. In addition, the level of TRIM45 protein in septic patients was increased. There was a positive linear correlation between APACHE II score and TRIM45, between SOFA score and TRIM45. Compared to group GCS > 9, level of TRIM45 were increased in group GCS ≤ 8.

CONCLUSION

TRIM45 plays a key role in neuroinflammation caused by LPS, and the mechanism may involve TRIM45-mediated exacerbation of microglial pyroptosis via the Atg5/NLRP3 axis.

Lipopolysaccharide promotes NLRP3 inflammasome activation by inhibiting TFEB-mediated autophagy in NRK-52E cells

The NLRP3 inflammasome is involved in many inflammatory diseases. Its activity must be strictly controlled to alleviate the inflammatory process. Autophagy plays a protective role in the negative regulation of NLRP3 inflammasome activation. However, the regulatory mechanism of autophagy controlling NLRP3 inflammasome activation remains to be further investigated. Here, we showed that in NRK-52E cells, lipopolysaccharide (LPS) and ATP stimulation significantly decreased mitochondrial membrane potential, increased ROS production and mtDNA copy number in cytosol. Moreover, autophagic flux was blocked when challenged with LPS and ATP as evidenced by increased LC3 II and p62 expression, reduced TFEB and CTSD expression, and impaired lysosomal acid environment. Furthermore, TFEB deficiency increased cytosolic mtDNA and enhanced LPS and ATP induced NLRP3 inflammasome activation and proinflammatory cytokine expression. Taken together, these findings reveal that LPS and ATP stimulation promoted NLRP3 inflammasome activation through inhibiting TFEB-mediated autophagy in NRK-52E cells, and TFEB could be a potential therapeutic target for the treatment of NLRP3 inflammasome-related kidney diseases.

Role of the NLRP3 inflammasome in gynecological disease

The NLR family pyrin domain containing 3 (NLRP3) inflammasome is involved in the innate immune system and is a three-part macromolecular complex comprising the NLRP3 protein, apoptosis-associated speck-like protein containing a CARD (ASC) and the cysteine protease pro-caspase-1. When the NLRP3 inflammasome is activated, it can produce interleukin (IL)- 1β and IL-18 and eventually lead to inflammatory cell pyroptosis. Related studies have demonstrated that the NLRP3 inflammasome can induce an immune response and is related to the occurrence and development of gynecological diseases, such as endometriosis, polycystic ovary syndrome and breast cancer. NLRP3 inflammasome inhibitors are beneficial for maintaining cellular homeostasis and tissue health and have been found effective in targeting some gynecological diseases. However, excessive inhibitor concentrations have been found to cause adverse effects. Therefore, proper control of NLRP3 inflammasome activity is critical. This paper summarizes the structure and function of the NLRP3 inflammasome and highlights the therapeutic potential of targeting it in gynecological diseases, such as endometriosis, polycystic ovary syndrome and breast cancer The application of NLRP3 inflammasome inhibitors is also discussed.

Autophagy and Inflammation: Regulatory Roles in Viral Infections

Autophagy is a highly conserved intracellular degradation pathway in eukaryotic organisms, playing an adaptive role in various pathophysiological processes throughout evolution. Inflammation is the immune system's response to external stimuli and tissue damage. However, persistent inflammatory reactions can lead to a range of inflammatory diseases and cancers. The interaction between autophagy and inflammation is particularly evident during viral infections. As a crucial regulator of inflammation, autophagy can either promote or inhibit the occurrence of inflammatory responses. In turn, inflammation can establish negative feedback loops by modulating autophagy to suppress excessive inflammatory reactions. This interaction is pivotal in the pathogenesis of viral diseases. Therefore, elucidating the regulatory roles of autophagy and inflammation in viral infections will significantly enhance our understanding of the mechanisms underlying related diseases. Furthermore, it will provide new insights and theoretical foundations for disease prevention, treatment, and drug development.