CKAP4促进TGF-beta1蛋白合成并抑制腹主动脉瘤形成的作用及机制研究

转化生长因子（TGF-beta1）水平下调导致的血管平滑肌细胞（VSMC）去分化和细胞骨架蛋白功能异常是导致主动脉瘤（AAA）的重要原因，但机理尚不清楚。预实验发现细胞骨架关联蛋白4（CKAP4）在AAA组织及去分化的VSMC中表达降低。通过构建Ckap4基因敲除小鼠和动物模型，我们发现Ckap4敲除促进AAA形成及VSMC去分化。进一步研究揭示Ckap4敲除小鼠AAA组织TGF-beta1蛋白水平降低，而RNA水平不变。前期实验结果还发现CKAP4不但与Tgfb1 mRNA结合，还与eIF4A1结合。因此我们提出假说：CKAP4是抑制AAA形成的重要因子，其通过与eIF4A1及Tgfb1 mRNA结合招募形成翻译预起始复合物并促进TGF-beta1蛋白合成，维持VSMC的收缩表型从而抑制AAA形成。本研究首次从细胞骨架调控蛋白合成的角度解释AAA的形成机制，有望为AAA的防治提供新靶点。

The vascular smooth muscle cell (VSMC) dedifferentiation and cytoskeleton malfunction caused by transforming growth factor-beta 1 (TGF-beta1) downregulation are the important factors for abdominal aortic aneurysm (AAA) formation, whereas the underlying mechanism is unclear. Our preliminary data discovered the downregulation of CKAP4 (cytoskeletal associated protein 4) in human AAA tissue and dedifferentiated mouse VSMC. By establishing Ckap4 gene knockout (Ckap4-/-) mouse, we found Ckap4 depletion results in more severe AAA formation and VSMC dedifferentiation. Further study revealed TGF-beta1 protein level, but not RNA level, is significantly downregulated in mouse AAA tissue. Moreover, overexpression of TGF-beta1 could rescue the dedifferentiation phenotype caused by Ckap4 deletion. Using RIP-seq and mass spectrometry, we discovered that CKAP4 can bind with Tgfb1 mRNA and eIF4A1. Together, we hypothesize: CKAP4 is an important repressive protein in AAA formation. On one hand, CKAP4 associates with eIF4A1 and assists translation preinitiation complex recruitment; on the other hand, CKAP4 binds with Tgfb1 mRNA as a noncanonical RNA binding protein. Together, CKAP4 promotes TGF-beta1 protein synthesis, maintains VSMC contractile phenotype, and suppresses AAA formation. In this proposal, we aim to clarify the molecular mechanism of AAA formation via investigating the protein synthesis regulatory function of the cytoskeletal protein, and hopefully provide a new therapeutic target for AAA treatment in the future.