Inhibition of mitochondrial ROS turns LC3-associated phagocytosis to autophagy upon resveratrol treatment for group A Streptococcus clearance in endothelial cells

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Group A Streptococcus (GAS; Streptococcus pyogenes ), which causes a broad spectrum of diseases, has been found to invade cells to avoid host immune clearance and antibiotic killing. Our previous findings have shown that the virulence factors of GAS—NAD-glycohydrolase depletes intracellular NAD + to inhibit xenophagy, and streptolysin O increases the production of intracellular reactive oxygen species (ROS) to promote ineffective LC3-associated phagocytosis (LAP), thereby impairing GAS clearance in endothelial cells. However, how endothelial cells counteract these strategies for GAS clearance has yet to be comprehensively investigated. We therefore speculated that resveratrol (RSV), a potent antioxidant and NAD + -dependent deacetylase—sirtuin activator, could be a potential antibacterial drug upon GAS infection in endothelial cells. To investigate the effect and the underlying mechanism of RSV on GAS infection, RSV was supplemented to human microvascular endothelial cell line-1 (HMEC-1) upon GAS infection, followed by detection of bacterial growth and examination the cellular regulation to LAP and xenophagy pathway. RSV significantly inhibited intracellular GAS multiplication in endothelial cells through increasing acidification and double-membrane formation of LC3-positive GAS-containing vacuoles. RSV upregulated the expression of autophagy-related proteins but downregulated the LAP-related proteins in GAS-infected endothelial cells. Knockdown of sirtuin 3 (SIRT3) dismissed the effect of RSV on enhancement of autophagic clearance of GAS and suppression of mtROS, which may participate in regulation of acidification of LC3-positive GAS-containing vacuoles and LAP-related proteins expression. RSV promotes intracellular GAS clearance in endothelial cells by shifting the ineffective LAP pathway to functional xenophagy through SIRT3-mediated inhibition of mtROS.

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