Dysfunction of bone marrow mesenchymal stem cells (BMSCs) is recognized critical in bone deteriorations of osteoporosis. However, the specific mechanisms that determine the fate of BMSCs remain elusive. MicroRNA-133a (miR-133a), a highly conserved microRNA, was investigated under both in vitro and in vivo conditions. In the in vitro study, cell proliferation, cell apoptosis, and osteoblast/adipocyte differentiation of BMSCs as a result of overexpression or knockdown of miR-133a was investigated. In the in vivo study, the ovariectomy (OVX) model was applied on mice, with further treatment of the models with BMSC-specific miR-133a antagomir through femur intramedullary injection. Microcomputed tomography scanning and histological analysis of the proximal and middle femur were performed to evaluate the morphological changes. The results revealed that overexpression of miR-133a suppressed cell proliferation, cell viability, and osteoblast differentiation of BMSCs, but increased adipocyte differentiation. We also found that FGFR1, an important upstream regulator of mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) signal pathway, was a major target of miR-133a. We also recorded that BMSC-specific knockdown of miR-133a attenuates bone loss in OVX mice. Our study suggested that miR-133a played an important role in maintaining the viability and balance between osteoblast and adipocyte differentiation of BMSCs through the MAPK/ERK signaling pathway by targeting FGFR1.
Keywords: adipocyte differentiation; bone marrow mesenchymal stem cells; microRNA-133a; osteoblast differentiation; osteoporosis.