衰老骨基质外泌体导致骨与血管钙化悖论

Osteoporosis (OP) is frequently accompanied with vascular calcification (VC) in elder people. The simultaneous occurrence of decreased bone density with vascular wall calcification is so-called “calcification paradox”, but the mechanism is still unclear. The osteogenic differentiation decreasing of bone marrow mesenchymal stem cells (BMSCs) and the osteoblast-like phenotype transdifferentiation of vascular smooth muscle cells (VSMCs) are the cellular basis of elder OP and VC, respectively. Our previous study found the young bone matrix exosomes (YB-Exo) increased the osteogenic differentiation of BMSCs, however, the aged bone matrix exosomes (AB-Exo) promoted the adipogenic differentiation of BMSCs and osteoblast-like phenotype transdifferentiation of VSMCs. These results suggest bone matrix exosomes (B-Exo) induces to.“calcification paradox” in elder people. The exosomes tracer model (CD63-GFP transgenic mice) will be constructed to realize the sources and in vivo delivery of B-Exo. The difference enrichment of osteogenic and adipogenic related miRNAs in YB-Exo and AB-Exo will be analyzed to reveal the fates regulation of VSMCs and BMSCs. Finally the relevance between the serum level of AB-Exo and the severity of OP and VC will also be verified. This project aims to explore the molecular mechanism of AB-Exo and “calcification paradox” during aging, which will further provide the new ideas for the clinical purpose of OP and VC.

骨质疏松症（OP）和血管钙化（VC）常在老年人中伴随发生，但“钙化悖论”（OP骨流失与VC异位骨化同时发生）的机制不明。骨髓间充质干细胞（BMSCs）成骨减少成脂增多与血管平滑肌细胞（VSMCs）成骨分别是老年OP与VC的细胞学基础。我们前期发现，年轻骨基质外泌体（YB-Exo）促进BMSCs成骨，而衰老骨基质外泌体（AB-Exo）促进BMSCs成脂并促进VSMCs成骨，提示骨基质外泌体（B-Exo）导致衰老机体“钙化悖论”。我们拟：采用外泌体示踪模型（CD63-GFP转基因小鼠）探明B-Exo的来源细胞与体内转运；揭示YB-Exo与AB-Exo中差异富集的成骨成脂相关miRNAs对BMSCs和VSMCs命运的调控机制；验证人群血液中AB-Exo水平与OP、VC程度的相关性。该项目旨在探索AB-Exo导致衰老机体“钙化悖论”的作用模式与分子机制，为临床OP和VC防治研究提供新思路。

骨髓间充质干/基质细胞（BMSCs）的成脂分化增多、成骨分化减少，导致了与年龄和更年期有关的骨髓脂肪堆积和骨质疏松症的发生。血管钙化常常与骨质疏松症同时发生，这种矛盾的关联被称为 "钙化悖论"。该项目研究发现，在骨吸收过程中来自衰老骨基质的细胞外囊泡（Aged bone matrix derived extracellular vesicles, AB-EVs）有利于BMSC成脂分化，并增强了血管平滑肌细胞的钙化。静脉注射或骨髓内注射AB-EVs可促进成骨-成脂的失衡，加剧维生素D3（VD3）诱导的年轻或老年小鼠的血管钙化。阿仑膦酸钠（ALE）是一种骨吸收抑制剂，可下调AB-EVs的释放，并减轻衰老和卵巢切除术引起的成骨-成脂失衡。在VD3处理的老年小鼠中，ALE抑制了卵巢切除术引起的血管钙化的加重。MiR-483-5p和miR-2861在AB-EVs中富集，对AB-EVs诱导的成骨-成脂失衡和血管钙化的加剧至关重要。我们的研究揭示了AB-EVs通过转移miR-483-5p和miR-2861作为钙化悖论的信使的作用。