The Sirt1/FOXO signal pathway involves in regulating osteomyelitis progression via modulating mitochondrial dysfunctions and osteogenic differentiation

The Sirtuin-1 (Sirt1) gene has been reported to be closely associated with the progression of multiple diseases, but its role in regulating osteomyelitis (OM) pathogenesis has not been explored. The murine long bone-derived osteocyte-like MLO-Y4 cells and osteoblast-like MC3T3-E1 cells were exposed to Staphylococcal protein A (SpA) treatment to establish the in vitro OM models. The expression levels of Osteoblast-specific genes (OCN, OPN and RUNX2), osteoclastic genes (CTSK, MMP9 and ACP5) and the FOXO pathway-related proteins (FOXO1, p-FOXO1, FOXO3 and p-FOXO3) were detected by performing Real-Time qPCR and Western Blot analysis. Osteoblastic differentiation of the cells were evaluated by using the alizarin red S staining assay and TRAP staining assay, and membrane potential and superoxide production were measured to evaluate the mitochondrial functions of the cells. SpA treatment significantly suppressed osteogenic differentiation and induced mitochondrial dysfunction in MLO-Y4 and MC3T3-E1 cells, and promoting osteoclastogenesis in RAW264.7 cells, suggesting that the in vitro OM models were successfully established. Of note, SpA decreased the expression levels of Sirt1 in the OM cells, and SpA-induced detrimental effects on the OM cells were all reversed by overexpressing Sirt1. Mechanistically, Sirt1-overexpression increased the levels of phosphorylated FOXO-related proteins (p-FOXO1 and p-FOXO3) to activate the FOXO signal pathway and ameliorated OM progression in SpA-treated cells. Collectively, it was revealed in the present study that overexpression of Sirt1 activated the FOXO signal pathway to ameliorate SpA-induced detrimental effects in the OM cells, and Sirt1 could be potentially used as therapeutic agent for OM in clinic.