S1P/SREBP2介导自噬调控破骨细胞分化的机制研究

Dysfunction of osteoclast differentiation is an important cause of bone metabolic diseases including osteoporosis. In-depth study of the differentiation regulating mechanism has important implications for the discovery of novel therapeutic targets. Studies showed that S1P (Membrane-bound transcription factor site-1 protease) was an important gene for bone development, while its role in osteoclast remains unclear. Our results indicated S1P may be a potential regulator of osteoclastogenesis: the expression of S1P was significantly upregulated during osteoclastogenesis, while S1P knockout inhibited osteoclast formation; in addition, bone mass was increased in S1P conditional knockout mice. Based on bioinformatics analysis and literature researches, we hypothesized that S1P/SREBP2 signaling regulates osteoclast formation and resorption function through mediating autophagy. In the present study, we will use conditional knockout mice model and clinical samples to explore the function and mechanism of S1P on molecular, cellular and animal levels. Our study will provide new theoretical basis for further understanding the mechanism of osteoclastogenesis and bone metabolic diseases.

破骨细胞分化及功能的异常是导致骨质疏松等骨代谢疾病发生的重要原因，深入研究其分化调控机制对于发现新的治疗靶点具有重要意义。研究发现，S1P（Membrane-bound transcription factor site-1 protease）是调控骨骼发育的重要基因，但它在破骨细胞中的作用尚不清楚。申请人前期实验表明，S1P是破骨细胞分化的潜在调控因子：S1P在破骨细胞分化中表达显著升高，敲除S1P显著抑制破骨细胞分化；构建S1P条件敲除小鼠，发现其骨量明显增加。进一步结合生物信息学分析和文献调研，我们推测S1P/SREBP2信号轴通过调节自噬，影响破骨细胞分化及骨吸收功能。在本课题的研究中，申请人将利用S1P条件性敲除小鼠，结合临床样本，从分子、细胞和动物整体水平探索S1P的功能和自噬调控机制。从而为深入理解破骨细胞分化及相关骨代谢疾病的致病机理提供新的理论依据。

S1P (site-1 protease)是一种高尔基定位蛋白，通过激活特异的转录因子，从而在内质网应激、脂质代谢、炎症反应和溶酶体功能中起关键作用。S1P突变患者表现为严重的骨骼发育不良，伴有脊柱后凸、面部畸形和鸡胸。然而，S1P是否通过影响破骨细胞的形成来调节骨重塑尚不清楚。我们研究发现S1P是破骨细胞形成的正向调节因子。与野生型同窝仔相比，小鼠S1P敲除导致明显的骨硬化。机制研究发现，S1P在破骨细胞形成过程中表达上调，并受miR-9-5p的直接调控。骨髓单核细胞（BMM）中S1P缺失抑制ATF6和SREBP2成熟，随后抑制CHOP/SREBP2复合物诱导的LC3表达和自噬通量。转染LC3腺病毒明显挽救了S1P缺乏的BMM的破骨细胞生成。同时，我们还通过免疫共沉淀(Co-IP)和分子对接鉴定了CHOP与SREBP2的相互作用区域。此外，S1P缺失或抑制剂在体内有效地挽救了卵巢切除（OVX）和LPS诱导的骨丢失。总之，我们发现S1P以LC3依赖的方式调节破骨细胞分化，是骨质疏松症的潜在治疗靶点。