Osteoimmune reaction caused by a novel silicocarnotite bioceramic promoting osteogenesis through the MAPK pathway

The host immune response to an implant is a key factor in determining the fate of bone grafts, which is thought to be a regulator of tissue regeneration. Figuring out the effects of the osteoimmune microenvironment on the osteogenesis of bone grafts can be a valuable strategy for their design and can further enhance the healing of bone defects. Our previous study demonstrated that the silicocarnotite (Ca₅(PO₄)₂SiO₄, CPS) bioceramic can significantly promote osteogenesis. The aim of this study is to investigate the immune reaction of CPS, the effects of the immune microenvironment on osteogenesis, and the related molecular mechanisms. Compared to hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HA), the results showed that CPS could downregulate the pro-inflammatory phenotype and upregulate the anti-inflammatory phenotype, showing the lower levels of TNF-α and increased expression of IL-10. We further found that CPS could regulate the expression of NPPA, EDN1, and MMP9 in RAW 264.7 by RNA sequencing, which may be related to its superiority in osteogenesis. The osteogenic differentiation of rat bone marrow mesenchymal stem cells (rBMSCs) was subsequently studied in a macrophage-conditioned medium pretreated with CPS, and the medium caused a significant promotion of the osteogenic differentiation of rBMSCs, demonstrating that CPS can generate a favorable immune microenvironment to promote rBMSCs differentiation. In terms of mechanism, CPS in the macrophage-conditioned medium promoted osteogenic differentiation through the MAPK pathway, including ERK1/2, JNK and P38. Our study demonstrated that osteogenic differentiation was influenced by the immune microenvironment generated via the implant, and also presented an effective tool for studying the mechanisms of macrophage polarization as well as functions.