骨质疏松目前在我国乃至全球都是一个值得关注的严重的健康问题。miR-664-3p是本课题组筛选出的成骨细胞分化过程中下调倍数最大的miRNA。我们已经证明BMP信号通路的信号转导分子Smad4和成骨细胞分化关键调节因子Osterix是miR-664-3p的靶基因。我们还发现：成骨细胞分化过程中miR-664-3p的表达持续下调；骨质疏松小鼠骨组织以及骨质疏松病人血清中的miR-664-3p的水平显著高于对照组。由此我们推测：miR-664-3p具有抑制成骨细胞分化的功能，其表达上调促进骨质疏松的发生。本项目拟通过细胞实验、成骨细胞特异性转基因小鼠构建和临床标本检测对此假说进行验证；并对miR-664-3p作用的分子机制进行深入探讨。本项目的研究结果不仅可以有助于成骨细胞分化和骨质疏松发病的分子机制的阐明；而且可以为骨质疏松的预防和治疗提供新的靶点，为其诊断/辅助诊断提供新的生物标志物。

Osteoporosis (OP) is becoming a serious health care issue in the countries worldwide including China now. MiR-664-3p is one of the differentially expressed miRNAs during the osteoblast differentiation screened by our group using high-throughput sequencing, whose expression was down-regulated with the maximal fold. We have demonstrated that both Smad4 and Osterix were target genes of miR-664-3p. Smad4 is a common Smad of BMP2 signal pathway. Osterix is a key regulator of osteoblast differentiation. Moreover, we found that miR-664-3p was down-regulated continuously in the process of osteoblast differentiation. However, the levels of miR-664-3p were markedly increased in the bone tissues of ovariectomy-induced osteoporotic mice. Furthermore, we found that the levels of miR-664-3p in the serum of osteoporotic patients were much higher than that of the matched control (13 patient vs 10 control). Based on our findings and information from the literatures, we postulate that miR-664-3p plays an inhibitory role in osteoblast differentiation and its overexpression promotes the occurrence of OP. We will test this hypothesis using osteoblast differentiation model, osteoblast-specific transgenic mice construction as well as clinical investigations. In addition, the underlying mechanisms by which miR-664-3p inhibits osteoblast differentiation and promotes OP genesis will be explored by gene overexpression and knockdown assays. Results of this project will not only shed new light on the molecular mechanisms underlying osteoblast differentiation and OP occurrence, but also provide a novel target for the prevention and treatment of OP. At the same time, results of this project may provide a novel biomarker for the diagnosis/auxiliary diagnosis of OP.