Vangl2在老年骨质疏松中的作用和机制研究

Senile osteoporosis (SOP) is primarily caused by age-related bone loss. However, the regulatory mechanism of age-related bone loss has not been fully elucidated. In our preliminary study, the expression of Vangl2 has been revealed to be markedly enhanced in bone marrow mesenchymal stem cells (BMMSC) of SAMP6 mice, the widely-accepted SOP mice model. In addition, when compared to young mice (3M), significant enhancement of Vangl2 expression in femoral MSC has been confirmed in aging mice (13M), as manifested by immunofluorescence staining. Furthermore, Vangl2 promotes adipogenesis and suppresses osteogenesis of both human and mice MSC. Moreover, Vangl2 suppresses the transcriptional activity of TCF4, one of the most important osteogenic transcriptional factors activated by Wnt signals, in a β-Catenin independent manner. In our current project, both conditional and inducible MSC-specific Vangl2 knockout mice will be constructed to study whether higher peak mass can be achieved and whether SOP can be prevented by MSC-specific Vangl2 ablation. Additionally, the mechanism by which Vangl2 modulates MSC osteogenic/adipogenic differentiation, as well as its functional role in age-related bone loss will be further studied at molecular, cellular, and whole-body level. Collectively, our study will provide novel insights into the regulatory mechanism of bone metabolism and a novel rationale for targeting Vangl2 to prevent and treat SOP.

增龄性骨丢失是老年骨质疏松发生的主要原因，但机制尚未阐明。课题组在前期研究中筛选出早衰型SAMP6小鼠的骨髓间充质干细胞（BMMSC）中Vangl2 表达相对于SAMR1对照小鼠显著增强，免疫荧光结果证实13月龄C57/B6小鼠股骨MSC中Vangl2表达水平较3月龄小鼠表达也显著升高。进一步研究发现，Vangl2可抑制人和小鼠间充质干细胞（MSC）的成骨分化并促进其成脂分化， Vangl2通过不依赖β-Catenin的途径抑制Wnt通路关键成骨分化转录因子TCF4的活性。本项目拟构建MSC中特异敲除Vangl2的小鼠模型（条件性敲除和可诱导敲除），研究MSC中 Vangl2缺失是否可增加小鼠峰值骨量并预防老年骨质疏松，并在分子、细胞和整体水平进一步阐明Vangl2通过调控MSC成骨/成脂定向分化导致增龄性骨丢失的作用和机制，为骨代谢的调节机制提供新观点，为老年骨质疏松的防治提供新靶点。

溶酶体是细胞循环中心和营养信号中枢，我们单组学结果表明溶酶体也调控间充质干细胞的分化。分子伴侣介导的自噬（Chaperone-mediated Autophagy,CMA）溶酶体通过选择性的抑制成骨的抑制因子(成脂分化TLE3,ZNF423,和软骨的SOX-9)促进成骨分化。CMA溶酶体是由Van-Gogh-Like 2(Vangl2)调控的。Vangl2 通过直接与Lysosome-associated membrane protein 2A (LAMP-2A) 结合并降解，特异性的敲除间充质干细胞的Vangl2可以提高LAMP-2A表达，从而提高CMA溶酶体的数量，抑制骨髓的脂肪形成，促进成骨。在人和小鼠的间充质干细胞中的Vangl2与LAMP-2A的比例可以促进成骨分化，我们的研究阐明了Vangl2-LAMP-2A信号通路在MSC细胞系溶酶体中的重要作用和调控机制。