Mg2+ in β-TCP/Mg-Zn composite enhances the differentiation of human bone marrow stromal cells into osteoblasts through MAPK-regulated Runx2/Osx

Inducing the osteogenic differentiation from bone marrow stromal cells (BMSCs) might be a potent strategy for treating bone loss and nonunion during fracture and improving fracture healing. Among several signaling pathways involved, mitogen-activated protein kinases (MAPKs) have been reported to play a critical role. Magnesium (Mg)-based alloys, including Mg-Zn alloy, have been used clinically as implants in the musculoskeletal field and could promote BMSC osteogenic differentiation. However, the underlying mechanisms remain unclear. In this study, we produced Mg-Zn alloy consists of Mg and low concentrations of Zn, calcium carbonate, and beta-tricalcium phosphate (beta-TCP; manifesting process not shown), prepared Mg, Zn, and Mg-Zn extracts, and investigated the specific effects of these extracts on human BMSC (hBMSC) osteogenic differentiation and MAPK signaling. Mg extracts and Mg-Zn extracts could significantly promote the osteogenic differentiation of hBMSCs as manifested as increased alkaline phosphatase levels, enhanced calcium nodules formation, and increased messenger RNA expression and protein levels of osteogenesis markers, including BMPs, Col-I, Runx2, and Osx; in the meantime, Mg culture medium (CM) and Mg-Zn CM both significantly enhanced the activation of MAPK signaling in hBMSCs. By adding ERK1/2 signaling, p38 signaling, or JNK signaling inhibitor to Mg-Zn CM, or conducting p38 MAPK silence in hBMSCs, we revealed that these extracts might promote hBMSC osteogenic differentiation via p38 MAPK signaling and MAPK-regulated Runx2/Osx. In conclusion, Mg2+ in beta-TCP/Mg-Zn extract promotes the osteogenic differentiation of hBMSCs via MAPK-regulated Runx2/Osx interaction.