The Effects Of MiR-146a On Osteoclast Differentiation And Its Mechanism In Regulating Senile Osteoporosis

Osteoporosis is a systemic disease characterized by reduced bone mass and degradation of bone tissue microstructure, which can lead to increased bone fragility. The main harm of osteoporosis is the fracture, which causes the disease and the physical and mental trauma, reduces the quality of life, and increases the social cost. Recent decades, with the acceleration of the aging society, the average age of the population increases, senile osteoporosis increased significantly. At the same time, fracture incidence raised drasticly, which seriously affected the health and safety of the elders. The pathogenesis for the formation of osteoporosis is the increase of bone resorption and the negative balance of bone metabolism caused by the decrease of bone formation. The bone resorption caused by osteoclasts play a vital part in senile osteoporosis. At present, the regulation mechanism of the differentiation and maturation of osteoclast under physiological and pathophysiological conditions is still not very clear.MiR-146a is closely related with immune and inflammatory reaction, the target protein TNF receptor associated factor 6 (TRAF6) plays an important role in the process of osteoclastogenesis. At the same time as the miR-146a regulation of inflammatory reaction, it indirectly participates in the differentiation of osteoclasts.In this experiment, we used the 12 month old miR-146a gene knockout mice to simulate senile osteoporosis process. Using micro-CT technology to detect bone related parameters, the results indicated that knockout mice had low trabecular bone volume; using tartrate resistant acid phosphatase (TRAP) staining to identify the osteoclast activity in lumbar vertebral bodies, the result showed that knockout mice had more osteoclast numbers wild-type mice, which indicated that miR-146a knockdown can increase the osteoclastogenesis; immunohistochemistry of inflammation related proteins (TRAF6, IL-6, TLR4) and osteoclast differentiation protein (Nfatcl), produced by osteoblasts Protein (OPG, osteocalcin) were detected, TRAF6, IL-6 and TLR4 expression in miR-146a gene knockout mice increased, Nfatcl expression also increased, and into bone indices decreased; finally, in vitro experiment was used to study the mechanism of regulation of miR-146a on osteoclast formation. Bone marrow-derived mononuclear cells from both WT and knowout mice were induced to osteoclast. Osteoclastgenesis related genes and proteins were detected, which ultimately showed that miR-146a can regulate osteoclast formation through RANKL/Nfatcl signaling pathway.In summary, miR-146a can regulate osteoclast formation pathway-RANKL/Nfatcl-through the inflammation pathway, also it can influence the OPG protein signaling pathway, which contribute to the osteoclast differentiation.