SIRT1 and SIRT3 impact host mitochondrial function and host-SalmonellapH balance during infection

Abstract

ABSTRACTMitochondria are an important organelle regulating energy homeostasis. Mitochondrial health and dynamics are crucial determinants of the outcome of several bacterial infections. SIRT3, a major mitochondrial sirtuin, along with SIRT1 regulates key mitochondrial functions. This led to considerable interest in understanding the role of SIRT1 and SIRT3 in governing mitochondrial functions during an intravacuolar pathogen,Salmonellainfection. Here, we show that loss of SIRT1 and SIRT3 function either by shRNA-mediated knockdown or inhibitor treatment led to increased mitochondrial dysfunction with alteration in mitochondrial bioenergetics alongside increased mitochondrial superoxide generation in theSalmonella-infected macrophages. Consistent with dysfunctional mitochondria, mitophagy was induced along with altered mitochondrial fusion-fission dynamics inS.Typhimurium-infected macrophages. Additionally, the mitochondrial bioenergetic alteration promotes acidification of the infected macrophage cytosolic pH. This host cytosolic pH imbalance skewed the intra-phagosomal and intra-bacterial pH in the absence of SIRT1 and SIRT3, resulting in decreased SPI-2 gene expression. Our results suggest a novel role of SIRT1 and SIRT3 in maintaining the intracellularSalmonellaniche by modulating the mitochondrial bioenergetics and dynamics in the infected macrophages.SYNOPSISThe loss of SIRT1 and SIRT3 function, achieved through shRNA-mediated knockdown or inhibitor treatment, leads to increased mitochondrial dysfunction in Salmonella-infected macrophages. This dysfunction manifests as alterations in mitochondrial bioenergetics and an upsurge in mitochondrial superoxide generation.The presence of dysfunctional mitochondria triggers mitophagy and affects the balance of mitochondrial fusion-fission dynamics in the infected macrophages.The perturbation in mitochondrial bioenergetics contributes to an acidification of the cytosolic pH in infected macrophages, which, in turn, skews the intravacuolar pH and the pH within the intracellular Salmonella. This altered pH environment ultimately results in decreased expression of the Salmonella Pathogenicity Island-2 (SPI-2) effector genes.Abstract Figure