SPA inhibits hBMSC osteogenic differentiation and M1 macrophage polarization by suppressing SETD2 in acute suppurative osteomyelitis.

To clarify the impact of SETD2 on macrophage function in pediatric patients with acute suppurative osteomyelitis and to elucidate the precise underlying mechanism. To gain insights into the potential functions of SETD2, a comprehensive study was conducted utilizing a co-culture model of human bone mesenchymal stem cells (hBMSCs) and bone marrow-derived macrophages (THP-1). A range of techniques were employed, including quantitative polymerase chain reaction, western blotting, ELISA, alkaline phosphatase activity assays, alizarin red S staining, luciferase reporter gene assays, and chromatin immunoprecipitation, to unravel the intricate interactions and molecular mechanisms involving SETD2 in this system. It was observed that SETD2 expression was reduced in THP-1 cells stimulated by staphylococcal protein A (SPA). Furthermore, the downregulation of SETD2 resulted in elevated M1 macrophage polarization and glycolysis, effects that were mitigated by SPA stimulation. Notably, SPA-stimulated THP-1 cells exhibited an increase in HIF-1α expression, which exhibited an inverse correlation with SETD2 levels. Moreover, it was discovered that SETD2 functioned as a catalyst for H3K36me3 and bound to the HIF-1α gene, which, in turn, regulated HIF-1α expression. Furthermore, the suppression of HIF-1α abrogated the consequences of SETD2 downregulation on glycolysis and M1 macrophage polarization. Lastly, the study demonstrated that M1 macrophage polarization serves as a mediator for BMP4's inhibitory effect on osteogenic differentiation of hBMSCs. This research has uncovered a previously unknown role of SETD2 in macrophages during osteomyelitis, revealing its significance in the pathogenesis of this condition. These findings suggest SETD2 as a novel target for the treatment of osteomyelitis.