Inhibition of NLRP3 inflammasome activation by A20 through modulation of NEK7

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.

A20 attenuates oxidized self-DNA-mediated inflammation in acute kidney injury

The ubiquitin-editing enzyme A20 is known to regulate inflammation and maintain homeostasis, but its role in self-DNA-mediated inflammation in acute kidney injury (AKI) is not well understood. Here, our study demonstrated that oxidized self-DNA accumulates in the serum of AKI mice and patients. This oxidized self-DNA exacerbates the progression of AKI by activating the cGAS-STING pathway and NLRP3 inflammasome. While inhibition of the STING pathway only slightly attenuates AKI progression, suppression of NLRP3 inflammasome-mediated pyroptosis significantly alleviates AKI progression and improves the survival of AKI mice. Subsequently, we found that Tnfaip3 (encoding A20) is significantly upregulated following oxidized self-DNA treatment. A20 significantly alleviates AKI development by dampening STING signaling pathway and NLRP3-mediated pyroptosis. Moreover, A20-derived peptide (P-II) also significantly alleviates ox-dsDNA-induced pyroptosis and improves the survival and renal injury of AKI mice. Mechanistically, A20 competitively binds with NEK7 and thus inhibiting NLRP3 inflammasome. A20 and P-II interfere with the interaction between NEK7 and NLRP3 through Lys140 of NEK7. Mutation of Lys140 effects on the interaction of NEK7 with A20 and/or NLRP3 complex. Conditional knockout of NEK7 in macrophages or pharmacological inhibition of NEK7 both significantly rescue AKI mouse models. This study reveals a new mechanism by which A20 attenuates oxidized self-DNA-mediated inflammation and provides a new therapeutic strategy for AKI.

The entrenchment of NLRP3 inflammasomes in autoimmune disease-related inflammation

Autoinflammation and autoimmunity are almost "opposite" phenomena characterized by chronic activation of the immune system, 'innate' in the first and 'adaptive' in the second, leading to inflammation of several tissues with specific protean effectors of tissue damage. The mechanism of involvement of multiprotein complexes called 'inflammasomes' within autoimmune pictures, differently from autoinflammatory conditions, is yet undeciphered. In this review we provide a comprehensive overview on NLRP3 inflammasome contribution into the pathogenesis of some autoimmune diseases. In response to autoantibodies against nucleic acids or tissue-specific antigens the NLRP3 inflammasome is activated within dendritic cells and macrophages of patients with systemic lupus erythematosus. Crucial is NLRP3 inflammasome to amplify tissue inflammation with interleukin-1 overexpression and matrix metalloproteinase production at the joint level in rheumatoid arthritis. A deregulated NLRP3 inflammasome activation occurs in the serous acini of salivary and lacrimal glands prone to Sjogren's syndrome, but also in the inflammatory process involving endothelial cells, leucocyte recruitment, and platelet plugging of vasculitides. Furthermore, organ-specific autoimmune diseases such as thyroiditis and hepatitis may display hyperactive NLRP3 inflammasomes at the level of resident immune cells within thyroid or liver, respectively. Therefore, it is not unexpected that preclinical studies have shown how specific inflammasome inhibitors may significantly overthrow the severity of different autoimmune diseases and slow down their trend towards an ominous progression. Specific markers of inflammasome activation could also reveal subclinical inflammatory components escaping conventional diagnostic approaches or improve monitoring of autoimmune diseases and personalizing their treatment.

Genetic Regulation of Cell Death: Insights from Autoinflammatory Diseases

Metazoans have evolved innate antimicrobial defenses that promote cellular survival and proliferation. Countering the inevitable molecular mechanisms by which microbes sabotage these pathways, multicellular organisms rely on an alternative, perhaps more ancient, strategy that is the immune equivalent of suicide bombing: Infection triggers cell death programs that summon localized or even systemic inflammation. The study of human genetics has now unveiled a level of complexity that refutes the naive view that cell death is merely a blunt instrument or an evolutionary afterthought. To the contrary, findings from patients with rare diseases teach us that cell death-induced inflammation is a sophisticated, tightly choreographed process. We herein review the emerging body of evidence describing a group of illnesses-inborn errors of cell death, which define many of the molecular building blocks and regulatory elements controlling cell death-induced inflammation in humans-and provide a possible road map to countering this process across the spectrum of rare and common illnesses.

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.

Anemoside B4 targets NEK7 to inhibit NLRP3 inflammasome activation and alleviate MSU-induced acute gouty arthritis by modulating the NF-κB signaling pathway

BACKGROUND

Acute gouty arthritis is a metabolic disorder caused by monosodium urate (MSU) accumulation, leading to NLRP3 inflammasome activation and joint inflammation. Anemoside B4 (B4), a pentacyclic triterpenoid saponin, exerts significant anti-inflammatory effects. However, the precise molecular mechanisms underlying its therapeutic action, particularly its targeting of key components in NLRP3 inflammasome activation, remain unclear.

PURPOSE

The aim of this study was to elucidate the therapeutic mechanisms and target of B4 in treating MSU-induced macrophage pyroptosis and acute gouty arthritis, focusing specifically, on its interaction with NEK7, a critical regulator of NLRP3 inflammasome activation.

METHODS

Comprehensive in vitro and in vivo methods were employed to examine the effects and mechanisms of B4. In vitro analyses included Western blot, co-immunoprecipitation (Co-IP), and immunofluorescence assays to assess NLRP3 inflammasome components and NEK7-NLRP3 interactions. The binding of B4 to NEK7 was evaluated using molecular docking, surface plasmon resonance (SPR), cellular thermal shift assay (CETSA), drug affinity responsive target stability (DARTS), NEK7 gene silencing, and site-specific amino acid mutation experiments. In vivo, MSU-induced acute gouty arthritis mouse models and NEK7 knockdown mouse models were used to demonstrate the therapeutic effects and specificity of B4.

RESULTS

This study provides the first evidence that B4 significantly inhibits MSU-induced inflammation and pyroptosis in macrophages by directly targeting NEK7 and disrupting the NEK7-NLRP3 complex, thereby reducing NLRP3 inflammasome activation. Additionally, B4 effectively suppressed MSU-induced ROS production, mitochondrial damage, and NF-κB activation. In vivo, B4 alleviated symptoms of acute gouty arthritis, reduced NLRP3 expression, and demonstrated specificity for NEK7 in NEK7 knockdown mouse models.

CONCLUSION

This study highlights B4 as an effective inhibitor of NLRP3 inflammasome activation by directly targeting NEK7, thereby mitigating inflammation and pyroptosis in acute gouty arthritis. These findings position B4 as a prospective therapeutic candidate for the management of acute gouty arthritis, providing insights into its molecular targets and mechanisms.

Scaffold hopping-driven optimization for the identification of NLRP3 inhibitors as potential gout therapeutics

Gout as a common inflammatory arthritis seriously affects the quality of life of a large number of people. Targeting NLRP3 inflammasome has been certified as a promising therapeutic strategy for gout. This study, a series of new imidazolidinone derivatives were validated as NLRP3 inhibitors by scaffold hopping from the reported NLRP3 inhibitor CSC-6. In contrast to the poor physicochemical properties of the template molecule, the representative compound 23 showed good plasma stability, water solubility, and no significant inhibitory toxicity to CYP450 enzymes. Surface plasmon resonance and immunoblotting experiments showed that compound 23 binds NLRP3 and inhibits NLRP3 activation. Finally, compound 23 showed good anti-inflammatory and analgesic effects in acute peritonitis and arthritis. Overall, the present study provides NLRP3 inhibitors with favorable pharmacological properties, which may not only serve as a tool molecule for studying NLRP3-related functions, but also may further facilitate the gout treatment.