糖胺聚糖修饰的osteoglycin调控慢性肾功能不全并发主动脉瓣钙化的机制研究

Aortic valve calcification is one of the major cardiovascular complications of chronic renal dysfunction. However, the mechanism remains unknown. In previous study, we found the elevation of osteoglycin (OGN) RNA level in early phase of valve calcification. The increase of OGN was validated in the serum of patients with renal dysfunction and valve calcification, and in the tissue of calcified aortic valves. Moreover, not only the elevation of OGN protein level, but also a change of OGN molecular weight was observed in the process of calcification, indicating a modification of glycosaminoglycan. Functional study revealed that glycosaminoglycan modified OGN promoted valve calcification and could interact with Toll like receptor 4(TLR4). Thus, we aim to explore 3 issues in the present study: 1) The model of glycosaminoglycan modification of OGN; 2）The mechanism OGN interact with TLR4 and regulate downstream signaling pathways. 3）Effects of OGN in valve calcification in vivo. This study will demonstrate the exact roles of OGN in the pathogenesis of aortic valve calcification induced by chronic renal dysfunction, and provide information for better understanding of the mechanism of valve calcification.

主动脉瓣钙化是慢性肾功能不全重要的心血管并发症，其发病机理尚不明确。本研究前期发现osteoglycin (OGN)的RNA水平在瓣膜间质细胞钙化的早期即升高，并在肾功能不全合并瓣膜钙化患者血清和组织中验证了OGN的升高。并且，我们发现钙化中升高的OGN蛋白分子量发生变化，提示其经过糖胺聚糖（GAG）修饰。经GAG修饰的OGN可与Toll样受体4(TLR4)结合，并可促进瓣膜间质细胞发生钙化。因此，本课题将研究：1、OGN被GAG修饰的具体模式；2、GAG-OGN作用于TLR4并影响细胞功能、激活下游通路的具体机制；3、在体干预GAG-OGN对肾功能不全并发瓣膜钙化的影响。以期勾画出OGN在经过GAG修饰后，通过与TLR4相互作用，引起钙化相关信号通路激活，从而促进主动脉瓣钙化的病理过程。为阐明慢性肾功能不全并发主动脉瓣钙化的分子机制提供科学依据。

主动脉瓣钙化是慢性肾功能不全重要的心血管并发症，瓣膜间质细胞（ VICs）发生成骨分化是主动脉瓣发生钙化的重要病理基础，而炎症细胞浸润也是主动脉瓣发生钙化的病理改变之一。本研究发现，不管在VICs还是外周血单个核细胞，骨生成诱导因子（OGN）都在钙化的过程中升高。OGN的升高同时也伴随着Toll样受体4（TLR4）的表达升高和激活。升高的OGN具有促进瓣膜钙化的作用，抑制OGN的表达可改善瓣膜钙化。OGN促进瓣膜钙化主要通过TLR4-NF-Κb通路实现。在钙化过程中，OGN存在未经修饰和糖基化修饰两种形式，炎症细胞中主要为未经修饰形式，而VICs中两者兼有。不管是否经过糖基化修饰，OGN都具有促进VICs发生钙化的功能。将OGN糖基化位点突变后，并不能完全阻止VICs发生钙化，仅能起到减轻作用。本研究首次发OGN参与瓣膜钙化的发病过程，并揭示其作为核心因子，连接和促进了模式识别受体 TLR4 信号通路的交互通话，为多重层面抑制主动脉瓣钙化提供治疗新思路。