近年研究提示自噬对成骨细胞发育和骨稳态维持有重要作用。申请人前期体内外研究发现SPRY4抑制骨髓间充质干细胞成骨分化而促进其成脂分化。机制研究证实SPRY4除通过拮抗ERK1/2而抑制经典Wnt通路外，也可激活PI3K/AKT/mTOR通路，引起骨髓间充质干细胞自噬水平降低。因此提出假说：SPRY4通过PI3K/AKT/mTOR通路抑制自噬而调节成骨细胞分化，进而影响机体骨形成。为验证此假说，本研究将完善SPRY4通过 PI3K/AKT/mTOR通路调节自噬，进而决定骨髓间充质干细胞分化命运的机制；在此基础上，采用OVX小鼠模型，观察Spry4 siRNA对骨髓间充质干细胞自噬和成骨分化及骨形成的影响；进一步构建成骨前体细胞Atg7敲除小鼠，观察该小鼠自噬的降低是否阻断Spry4 siRNA调节的小鼠成骨细胞分化和骨形成。本研究将深化对骨稳态规律的认识，为防治骨质疏松等疾病提供新的靶点。

Recent emerging studies have suggested that autophagy plays an important role in the development of osteoblasts and the maintenance of bone homeostasis. Our previous in vitro and in vivo data have demonstrated that Sprouty4 (SPRY4) inhibits osteogenic differentiation of bone mesenchymal stem cells and promotes adipogenic differentiation. Mechanistic investigations have demonstrated that SPRY4 not only inhibits canonical Wnt pathway by antagonizing ERK1/2, but also activates PI3K/AKT/mTOR signaling pathway, which leads to the inhibition of autophagy in bone mesenchymal stem cells. Therefore, we hypothesize that SPRY4 regulates osteoblast differentiation by inhibiting autophagy through PI3K/AKT/mTOR signaling pathway, thereby affecting body bone formation and bone mass. To verify this hypothesis, this study will further elucidate the mechanism by which SPRY4 regulates autophagy, and then determine the differentiation fate of bone mesenchymal stem cells. Then, OVX mice model will be used to observe the effects of Spry4 siRNA on the autophagy of bone mesenchymal stem cells, osteoblast differentiation and bone formation in mice; Furthermore, we will make osteoblast progenitor-specific Atg7 knockout mice and test whether the decrease of autophagy blocks the differentiation of osteoblasts and bone formation in mice following in vivo transfection of Spry4 siRNA. This study will enrich our understanding of bone homeostasis and provide a new target for the prevention and treatment of metabolic bone disorders such as osteoporosis.