Insights into the potential role of BMSCs-exo delivered USP14 on SIRT1 deubiquitination in Staphylococcus aureus-induced model of osteomyelitis

Osteomyelitis resulting from a traumatic fracture is a recurrent and difficult-to-treat bone infection. Ubiquitin-specific protease 14 (USP14), a deubiquitinating enzyme, and Sirtuin-1 (SIRT1), an NAD+-dependent deacetylase, both play critical roles in regulating cellular processes, including inflammation. It has been discovered that exosomes originated from bone marrow mesenchymal stem cells (BMSCs-exo) can promote the repair and regeneration of bone fractures. In this study, we aimed to investigate the role of BMSCs-exo in osteoblast differentiation in osteomyelitis and the related molecular mechanisms. MC3T3-E1 cells induced with S. aureus were used as an in vitro model of osteomyelitis. BMSCs-exo were isolated and characterized using ultracentrifugation, transmission electron microscopy (TEM), and Western blot. RT-qPCR, Western blot, CCK-8, ALP staining, ELISA, and CO-IP were utilized to evaluate USP14 and SIRT1 levels, the osteogenic differentiation ability of MC3T3-E1 cells, and the deubiquitination level of SIRT1. Low expression of USP14 and SIRT1 was observed in the bone tissue of osteomyelitis patients. BMSCs-exo could upregulate the expression of USP14 and promote the expression of SIRT1 protein in the cell model of osteomyelitis. In addition, BMSCs-exo reduced the levels of inflammatory factors TNFα and IL-6, enhanced cell viability, promoted the expression of osteogenic differentiation markers RUNX2 and OCN in MC3T3-E1 cells, and improved cell osteogenic capacity. However, these trends were significantly reversed in MC3T3-E1 cells following treatment with BMSCs-exo transfected with si-USP14. Furthermore, knockdown of USP14 promoted SIRT1 ubiquitination and degradation, the process that was reversed by the proteasome inhibitor MG132, whereas USP14 overexpression inhibited SIRT1 ubiquitination. In MC3T3-E1 cells infected with S. aureus, BMSCs-exo delivers USP14, which may enhance SIRT1 deubiquitination and increase SIRT1 protein activity. This process inhibits inflammation and promotes osteogenesis, warranting further investigation into its mechanisms and in vivo efficacy.