The Mechanism Of MiR-146a Mediate Modulation Of Postmenopausal Osteoporosis

【Background and Objective】Osteoporosis is usually happened on old population and postmenopausal women.It can be classified as age-related osteoporosis and postmenopausal osteoporosis.This disease leads to low bone mineral density(BMD),less trabecular bone and high risk of skeleton fractures.In addition,osteoporosis induces a series of complication,which seriously affects quality of life and brings socioeconomic problems.Osteoporosis is a metabolic degenerative disease.Bone homeostasis is controlled by bone formatting osteoblasts and bone resorbing osteoclasts.Osteoporosis is caused by excessive osteoclast activities.Clinical therapeutic drugs have been aimed at regulating osteoblasts and osteoclasts function.MicroRNA is a class of noncoding RNAs,18-25 nucleotides in length,controlling gene expression at the post-transcriptional level by degrading 3’-UTR on post-transcript and translation level.Previous studies reported that miRNAs regulate proliferation,differentiation and apoptosis of osteoblasts and osteoclasts.Meanwhile,some research demonstrated miRNAs play important role on genesis,developments and diagnose of osteoporosis.in this study,we found dysregulated miRNA in postmenopausal osteoporosis by miRNA microarray,and investigate the impact on osteoblasts and osteoclasts differentiation.We attempt to find a new therapeutic target and mechanism of postmenopausal osteoporosis.【Methods】In this study,the effects of estrogen on the proliferation,apoptosis,and osteoclast differentiation of bone marrow mononuclear macrophages(BMM)were examined using estrogen stimulation and OVX-induced estrogen depletion models.Estrogen receptors were blocked by estrogen receptor inhibitors to verify whether the effect of estrogen on BMM proliferation,apoptosis,and osteoclast differentiation was mediated through estrogen receptor(ER).Meanwhile,we established ovariectomy(OVX)induced osteoporosis mice model.We found significantly dysregulated miR-146 a between sham and OVX mice.Then,we used miR-146 a knock out(miR-146a-/-)mice and performed OVX surgery on WT and miR-146a-/-mice.Related osteoblasts and osteoclasts markers were detected in bone tissue,serum and cells.Subsequently,miR-146 a was up and down regulated by mimic and inhibitor in vitro to examine osteoblasts and osteoclasts differentiation.We also performed co-culture of osteoblasts from WT-sham,WT-OVX,miR-146a-/--sham and miR-146a-/--OVX and osteoclasts to assess the cytokines in supernatant.【Results】Estrogen inhibited BMM proliferation and osteoclast differentiation,as well as promoted BMM apoptosis,and this effect is mediated through ER.miR-146 a was upregulated on OVX-induced osteoporosis.miR-146 a miR-146a-/-mice displayed same bone mass but high bone turnover compared with WT mice.miR-146 a inhibited osteoblasts and osteoclasts differentiation.WT-OVX mice presented bone loss and excessive bone resorption but miR-146a-/--OVX mice are protected from osteoporosis and displayed low osteoclasts activities.M-CSF,RANKL/OPG were downregulated in bone microenvironment.【Conclusion】miR-146 a is a negatively regulator of both osteoblasts and osteoclasts differentiation.Inhibition of miR-146 a prevents estrogen deficiency-induced osteoporosis by less M-CSF and RANKL/OPG from bone microenvironment and impaired osteoclasts activities.