Targeted silencing of miRNA-132-3p expression rescues disuse osteopenia by promoting mesenchymal stem cell osteogenic differentiation and osteogenesis in mice

Background: Skeletal unloading can induce severe disuse osteopenia that often occurs in spaceflight astronauts or in patients subjected to prolonged bed-rest or immobility. Previously, we revealed a mechano-sensitive factor, miRNA-132-3p, that is closely related to the osteoblast function. The aim of this study was to investigate whether miRNA-132-3p could be an effective target for treating disuse osteopenia. Methods: The 2D-clinostat device and the hindlimb-unloaded (HU) model were used to copy the mechanical unloading condition at the cellular and animal levels, respectively. Mimics or inhibitors of miRNA-132-3p were used to interfere with the expression of miRNA-132-3p in bone marrow-derived mesenchymal stem cells (BMSCs) in vitro for analyzing the effects on osteogenic differentiation. The special in vivo antagonists of miRNA-132-3p was delivered to the bone formation regions of HU mice for treating disuse osteopenia by a bone-targeted (AspSerSer)₆-cationic liposome system. The bone mass, microstructure, and strength of the hindlimb bone tissue were analyzed for evaluating the therapeutic effect in vivo. Results: miRNA-132-3p expression was declined under normal conditions and increased under gravitational mechanical unloading conditions during osteogenic differentiation of BMSCs in vitro. The upregulation of miRNA-132-3p expression resulted in the inhibition of osteogenic differentiation, whereas the downregulation of miRNA-132-3p expression enhanced osteogenic differentiation. The inhibition of miRNA-132-3p expression was able to attenuate the negative effects of mechanical unloading on BMSC osteogenic differentiation. Most importantly, the targeted silencing of miRNA-132-3p expression in the bone tissues could effectively preserve bone mass, microstructure, and strength by promoting osteogenic differentiation and osteogenesis in HU mice. Conclusion: The overexpression of miRNA-132-3p induced by mechanical unloading is disadvantageous for BMSC osteogenic differentiation and osteogenesis. Targeted silencing of miRNA-132-3p expression presents a potential therapeutic target for the prevention and treatment of disuse osteoporosis.