Understanding the mechanism of host deacetylase SIRT1 and SIRT3 in the modulation of Salmonella pathogenesis

Abstract

Host sirtuins are one of the important modulators of host immuno-metabolic regulation. However, the role of sirtuins in the modulation of the immune metabolism pertaining to Salmonellosis is largely unknown. Here, we investigated the role of two important sirtuins, SIRT1 and SIRT3 in the modulation of Salmonella pathogenesis. Our study indicated the ability of the live Salmonella Typhimurium to differentially regulate the levels of SIRT1 and SIRT3 within infected macrophages. Upon SIRT1 or SIRT3 knockdown or inhibition, the metabolism in intracellular Salmonella switched to high fatty acid oxidation and low glycolysis. This switch led to decreased proliferation of Salmonella in the macrophages. Further, Salmonella-induced higher levels of SIRT1 and SIRT3 led to a skewed polarization state of the macrophages from a pro-inflammatory M1 state toward an immunosuppressive M2 state by modulating p65 NF-κB acetylation. SIRT1 and SIRT3 also skew Salmonella-induced host metabolic switch by regulating the acetylation status of HIF-1α and PDHA1. Interestingly, in in vivo mice-model of infection, inhibition of SIRT1 and SIRT3 led to more dissemination and higher organ burden owing to enhanced ROS and IL-6 production. Hence our report suggests that Salmonella modulates SIRT1 and SIRT3 levels to maintain its own metabolism for successful pathogenesis. Mitochondrial health is another crucial determinant of the outcome of several bacterial infections. Therefore, we have explored the role of SIRT1 and SIRT3 in the modulation of mitochondrial bioenergetics and dynamics pertaining to Salmonella infection. Here, we show that inhibition of SIRT1 or SIRT3 function either by shRNA-mediated knockdown or by the application of specific catalytic inhibitors leads to increased mitochondrial dysfunction in the Salmonella-infected macrophages. The increased mitochondrial ROS generation in the infected macrophages coincides with mitochondrial membrane hyperpolarization, increased proton leakage and respiration rate, and a decline in ATP production and ETC function upon knockdown or inhibitor treatment of SIRT1 and SIRT3. The mitochondrial bioenergetic alteration triggers increased acidification of the cytosolic pH which in turn skewed the intra-bacterial pH of the intracellular bacteria within the SIRT1 and SIRT3 knockdown and inhibitor-treated macrophages leading to decreased SPI-2 gene expression. Alongside the decline in mitochondrial bioenergetics, the S. Typhimurium infected macrophages depict alteration in mitochondrial dynamics with increased mitochondrial fission and mitophagy alongside decreased mitochondrial fusion dynamics. Together, our results suggest the role of SIRT1 and SIRT3 in preserving the mitochondrial bioenergetics and dynamics in S. Typhimurium infection scenario and thereby influencing the bacterial intracellular niche. Enteric pathogens such as Salmonella enterica can cross the mucus and intestinal epithelial barrier, ultimately leading to Gut Vascular Barrier (GVB) damage and systemic dissemination. The gut microbiota plays another major role in the maintenance of the intestinal epithelial barrier. Our previous study highlighted the role of SIRT1 and SIRT3 in regulating Salmonella dissemination in blood, liver, and spleen by skewing inflammatory response. Here, we aimed to understand this exact mechanism of Salmonella dissemination and whether colonization with a gut commensal like Odoribacter splanchnicus could ameliorate the increased Salmonella-induced inflammation and in turn its pathogenic dissemination. Our study depicts the capability of O. splanchnicus in reversing the Salmonella- associated pathogenesis in mice. O.splanchnicus gut colonization mitigates the Salmonella-associated epithelial tight junction disruption by restoring epithelial tight junction function and by preventing gut vascular barrier disruption, angiogenesis, and inflammatory response.

Salmonella-induced SIRT1 and SIRT3 together play a pivotal role in the maintenance of the intracellular replication niche of Salmonella Typhimurium by regulating both host and bacterial metabolism and via the modulation of mitochondrial bioenergetics and dynamics within the infected macrophages. SIRT1 and SIRT3 regulate Salmonella dissemination by suppressing host inflammatory responses in in vivo mice model of infection. O.splanchnicus, a gut commensal, gut colonization reverses the Salmonella-associated pathogenesis in mice by restoring epithelial tight junction function, inhibiting the inflammatory response, and preventing gut vascular barrier disruption.