Sirtuin 5 alleviates excessive mitochondrial fission via desuccinylation of ATPase inhibitory factor 1 in sepsis-induced acute kidney injury.

ABSTRACT: Sepsis-induced acute kidney injury (SAKI) poses a significant clinical challenge with high morbidity and mortality. Excessive mitochondrial fission has been identified as the central pathogenesis of sepsis-associated organ damage, which is also implicated in the early stages of SAKI. Sirtuin 5 (SIRT5) has emerged as a central regulator of cellular mitochondrial function; however, its role in the regulation of sepsis-induced excessive mitochondrial fission in kidney and the underlying mechanism remains unclear.In this study, SAKI was modeled in mice through cecal ligation and puncture (CLP), and in human renal tubular epithelial (HK-2) cells stimulated with lipopolysaccharide (LPS), to mimic the cell SAKI model. Our findings revealed that septic mice with a SIRT5 knockout (SIRT5 KO) exhibited shortened survival times and elevated levels of renal injury compared to wild-type (WT) mice, suggesting the significant involvement of SIRT5 in SAKI pathophysiology. Additionally, we observed that SIRT5 depletion led to increased renal mitochondrial fission, while the use of a mitochondrial fission inhibitor (Mdivi-1) reversed the detrimental effects caused by SIRT5 depletion, emphasizing the pivotal role of SIRT5 in preventing excessive mitochondrial fission. In vitro experiments demonstrated that the overexpression of SIRT5 effectively mitigated the adverse effects of LPS on HK-2 cells viability and mitochondrial fission. Conversely, downregulation of SIRT5 decreased HK-2 cells viability and exacerbated LPS-induced mitochondrial fission. Mechanistically, the protective function of SIRT5 may be in part, ascribed to its desuccinylating action on ATPase inhibitory factor 1 (ATPIF1).In conclusion, this study provides novel insights into the underlying mechanisms of SAKI, suggesting the possibility of identifying future drug targets in terms of improved mitochondrial dynamics by SIRT5.

Novel tripeptide RKH derived from Akkermansia muciniphila protects against lethal sepsis.

OBJECTIVE: The pathogenesis of sepsis is complex, and the sepsis-induced systemic proinflammatory phase is one of the key drivers of organ failure and consequent mortality. Akkermansia muciniphila (AKK) is recognised as a functional probiotic strain that exerts beneficial effects on the progression of many diseases; however, whether AKK participates in sepsis pathogenesis is still unclear. Here, we evaluated the potential contribution of AKK to lethal sepsis development. DESIGN: Relative abundance of gut microbial AKK in septic patients was evaluated. Cecal ligation and puncture (CLP) surgery and lipopolysaccharide (LPS) injection were employed to establish sepsis in mice. Non-targeted and targeted metabolomics analysis were used for metabolites analysis. RESULTS: We first found that the relative abundance of gut microbial AKK in septic patients was significantly reduced compared with that in non-septic controls. Live AKK supplementation, as well as supplementation with its culture supernatant, remarkably reduced sepsis-induced mortality in sepsis models. Metabolomics analysis and germ-free mouse validation experiments revealed that live AKK was able to generate a novel tripeptide Arg-Lys-His (RKH). RKH exerted protective effects against sepsis-induced death and organ damage. Furthermore, RKH markedly reduced sepsis-induced inflammatory cell activation and proinflammatory factor overproduction. A mechanistic study revealed that RKH could directly bind to Toll-like receptor 4 (TLR4) and block TLR4 signal transduction in immune cells. Finally, we validated the preventive effects of RKH against sepsis-induced systemic inflammation and organ damage in a piglet model. CONCLUSION: We revealed that a novel tripeptide, RKH, derived from live AKK, may act as a novel endogenous antagonist for TLR4. RKH may serve as a novel potential therapeutic approach to combat lethal sepsis after successfully translating its efficacy into clinical practice.

Discovery of Ibrutinib-based BTK PROTACs with in vivo anti-inflammatory efficacy by inhibiting NF-κB activation.

As a critical upstream regulator of nuclear factor-κB (NF-κB) activation, Bruton's tyrosine kinase (BTK) has been identified to be an effective therapeutic target for the treatment of acute or chronic inflammatory diseases. Herein, we describe the design, synthesis and structure-activity-relationship analysis of a novel series of Ibrutinib-based BTK PROTACs by recruiting Cereblon (CRBN) ligase. Among them, compound 15 was identified as the most potent degrader with a DC50 of 3.18 nM, significantly better than the positive control MT802 (DC50 of 63.31 nM). Compound 15 could also degrade BTK protein in Lipopolysaccharide (LPS)-stimulated RAW264.7 cells, and suppress the mRNA expression and secretion of proinflammatory cytokines such as IL-1ß and IL-6 by inhibiting NF-κB activation. Furthermore, compound 15 reduced inflammatory responses in a mouse zymosan-induced peritonitis (ZIP) model. Our findings demonstrated for the first time that targeting BTK degradation by PROTACs might be an alternative option for the treatment of inflammatory disorders, and compound 15 represents one of the most efficient BTK PROTACs (DC50 = 3.18 nM; Dmax = 99.90%; near 100% degradation at 8 h) reported so far and could serve as a lead compound for further investigation as an anti-inflammatory agent.