Bone marrow mesenchymal stem cell-derived exosomal METTL14 promotes the osteogenic differentiation of MC3T3-E1 cells by regulating BMP2 in bone fracture recovery.

Bone fracture healing is a complex physiologic process that aims at restoring the damaged bone to its pre-injury state and cellular composition. Exosomes secreted by bone marrow mesenchymal stem cells (BMSCs) are emerging as a promising strategy to promote bone regeneration due to exosomal bioactive cargos. Furthermore, N6-Methyladenosine (m6A) methylation affects osteoblastic differentiation and bone remodeling. This study is designed to clarify the role and mechanism of BMSC-derived exosomal Methyltransferase-like 14 (METTL14) in osteogenesis. METTL14 and bone morphogenetic protein 2 (BMP2) levels were detected by RT-qPCR. METTL14, exosome-specific markers, BMP2, and IGF2BP1 protein levels were determined using Western blot. Cell viability, proliferation, and apoptosis were examined using MTT, EdU, and flow cytometry. The degree of osteogenic differentiation was verified by the Alizarin Red S staining assay and ALP activity assay. The interaction between METTL14 and BMP2 was analyzed using methylated RNA immunoprecipitation (MeRIP)-qPCR and RIP assays. METTL14 and BMP2 levels were decreased in delayed fracture healing (DFH), a common complication after fracture surgery. METTL14 upregulation expedited MC3T3-E1 cell viability, proliferation, and repressed apoptosis. METTL14 promotes osteogenic differentiation of MC3T3-E1 cells by enhancing ALP activity and mineralized formation. After co-culturing BMSC-derived exosomes and MC3T3-E1 cells, BMSC-derived exosomal METTL14 expedited the osteoblast activity. Mechanistically, METTL14 stabilized BMP2 mRNA through the m6A-IGF2BP1-dependent mechanism. These findings indicated that BMSC-derived exosomes encapsulate METTL14 and transport it into MC3T3-E1 cells, and the transported METTL14 could accelerate the osteogenesis by regulating the stability of BMP2 mRNA, which provided a potentially effective therapeutic strategy for bone regeneration.