Crosstalk of HDAC4, PP1, and GSDMD in controlling pyroptosis.

Gasdermin D (GSDMD) functions as a pivotal executor of pyroptosis, eliciting cytokine secretion following cleavage by inflammatory caspases. However, the role of posttranslational modifications (PTMs) in GSDMD-mediated pyroptosis remains largely unexplored. In this study, we demonstrate that GSDMD can undergo acetylation at the Lysine 248 residue, and this acetylation enhances pyroptosis. We identify histone deacetylase 4 (HDAC4) as the specific deacetylase responsible for mediating GSDMD deacetylation, leading to the inhibition of pyroptosis both in vitro and in vivo. Deacetylation of GSDMD impairs its ubiquitination, resulting in the inhibition of pyroptosis. Intriguingly, phosphorylation of HDAC4 emerges as a critical regulatory mechanism promoting its ability to deacetylate GSDMD and suppress GSDMD-mediated pyroptosis. Additionally, we implicate Protein phosphatase 1 (PP1) catalytic subunits (PP1α and PP1γ) in the dephosphorylation of HDAC4, thereby nullifying its deacetylase activity on GSDMD. This study reveals a complex regulatory network involving HDAC4, PP1, and GSDMD. These findings provide valuable insights into the interplay among acetylation, ubiquitination, and phosphorylation in the regulation of pyroptosis, offering potential targets for further investigation in the field of inflammatory cell death.

Sanguinarine ameliorates DSS induced ulcerative colitis by inhibiting NLRP3 inflammasome activation and modulating intestinal microbiota in C57BL/6 mice.

BACKGROUND: Sanguinarine (SAN) is an important natural anti-inflammatory constitutes and dietary supplementation with SAN could improve the relative length of the intestine, alter gut microbiota, and enhance growth performance of pigs, broiler chickens, and cattle. However, it is unclear whether it has the therapeutic effect on ulcerative colitis (UC). PURPOSE: This study aimed to investigate the therapeutic effect of SAN on UC and explore its mechanisms of action. STUDY DESIGN AND METHODS: Several efficacy indexes of SAN on dextran sulfate sodium (DSS)-induced C57BL/6 mice were evaluated. ELISA kit and western blot analysis were used to evaluate it's anti-inflammatory effect and the mechanism of action. 16S rDNA sequencing detection was used to determine the impact of SAN on gut microbiota. RESULTS: SAN and Sulfasalazine could significantly improve the colon length, the weight loss, the symptoms and the pathological injury of colon in DSS-induced mice. Meanwhile, SAN could decrease the levels of pro-inflammatory cytokines (TNF-α, IFN-γ, IL-1ß, IL-6, IL-13 and IL-18) and increase the levels of anti-inflammatory cytokines (IL-4 and IL-10) in colon, and suppress DSS-induced high expressions of NLRP3, caspase-1 and IL-1ß. In addition, SAN (0.5, 1 µM) could inhibit the expression level of NLRP3 and the activation of caspase-1 and IL-1ß in lipopolysaccharide-stimulated THP-1 cells in non-cytotoxic doses, which was similar to that of MCC950, a specific inhibitor of NLRP3 inflammasome activation. The abundance changes of many genera such as Muribaculaceae_unclassified, Escherichia-Shigella, Lachnospiraceae_NK4A136_group and Helicobacter were also closely related to the improvement of SAN on intestinal inflammatory response. CONCLUSION: SAN exhibited therapeutic effect on DSS-induced colitis by blocking NLRP3-(Caspase-1)/IL-1ß pathway and improving intestinal microbial dysbiosis. SAN might be developed to treat UC and other disorders associated with microbial dysbiosis.

E3 ubiquitin ligase SYVN1 is a key positive regulator for GSDMD-mediated pyroptosis.

Gasdermin D (GSDMD) participates in the activation of inflammasomes and pyroptosis. Meanwhile, ubiquitination strictly regulates inflammatory responses. However, how ubiquitination regulates Gasdermin D activity is not well understood. In this study, we show that pyroptosis triggered by Gasdermin D is regulated through ubiquitination. Specifically, SYVN1, an E3 ubiquitin ligase of gasdermin D, promotes GSDMD-mediated pyroptosis. SYVN1 deficiency inhibits pyroptosis and subsequent LDH release and PI uptake. SYVN1 directly interacts with GSDMD, and mediates K27-linked polyubiquitination of GSDMD on K203 and K204 residues, promoting GSDMD-induced pyroptotic cell death. Thus, our findings revealed the essential role of SYVN1 in GSDMD-mediated pyroptosis. Overall, GSDMD ubiquitination is a potential therapeutic module for inflammatory diseases.