Mechanisms by which LRP1 Protects the Vasculature

描述(申请人提供)：主动脉瘤和主动脉夹层占西方国家所有死亡人数的1%到2%，通常在破裂之前没有症状，这是最常导致死亡的原因。不幸的是，我们目前对导致动脉瘤形成的分子机制的了解是有限的。全基因组关联研究表明，LRP1基因是腹主动脉瘤的易感基因。LRP1编码低密度脂蛋白受体相关蛋白1(LRP1)，它是一种大的内吞和信号受体，调节重要的生理过程。我们最近的研究表明，在平滑肌细胞中选择性缺失LRP1基因的小鼠(smLRP1-/-鼠)会发生胸主动脉瘤。这些小鼠表现出人类疾病中检测到的所有症状，包括体内广泛的主动脉根部和胸主动脉扩张，弹性板层解体，炎症细胞重新聚集到管壁和过量的胶原沉积。蛋白质组学研究表明，管壁中积累了许多蛋白酶，包括HtrA1(高温需求因子A1)和肥大细胞蛋白酶4(mMCP-4)，这是人类糜酶的小鼠同源基因。这两种蛋白水解酶都参与基质和弹性膜的降解。目标1中的研究将检验SMC LRP1通过调节蛋白酶活性保护血管系统的假设，特别是HtrA1和mMCP-4，这反过来又调节弹性膜的完整性。对smLRP1-/-小鼠主动脉壁的超微结构研究显示SMC异常。转化生长因子信号通路是维持SMC收缩表型的主要途径，我们的初步数据显示，LRP1与多个转化生长因子家族成员结合，是转化生长因子介导的非规范信号转导所必需的。Aim 2的实验将验证LRP1通过调节转化生长因子信号通路来调节SMC表型转变的假说。最后，我们与Dianna Milewicz(德克萨斯大学休斯顿分校)合作启动了研究，她对胸主动脉瘤和急性主动脉夹层患者家族的DNA进行了Exome和Sanger测序。这些研究发现了几个极其罕见的LRP1变异，在这些家庭中与主动脉疾病分离，提供了强有力的证据表明它们与疾病有关。对其中几个变异体的氨基酸替换的分析表明，改变配体结合和 LRP1中的功能改变。Aim 3的研究将检验这样一种假设，即这些罕见的变异会导致 LRP1功能缺陷，进而导致本病的发生。

DESCRIPTION (provided by applicant): Aortic aneurysms and aortic dissections account for 1% to 2% of all deaths in Western countries, and are usually asymptomatic until they rupture which most often results in death. Unfortunately, our current understanding of the molecular mechanisms leading to aneurysm formation is limited. Genome wide association studies reveal that the Lrp1 gene represents a susceptibility locus for abdominal aortic aneurysms. LRP1 encodes the LDL receptor related protein 1 (LRP1), a large endocytic and signaling receptor that regulates important physiological processes. Our recent studies reveal that mice in which the Lrp1 gene is selectively deleted in smooth muscle cells (smLRP1-/- mice) develop thoracic aneurysms. These mice display all of the symptoms detected in the human disease, including extensive in vivo aortic root and thoracic aortic dilatation, elastic lamina disorganization, recruitment of inflammatory cells into the vessel wall and excess collagen deposition. Proteomic studies revealed accumulation of proteases in the vessel wall, including HtrA1 (high-temperature requirement factor A1) and mast cell protease 4 (mMCP-4), the murine ortholog of human chymase. Both of these proteases are involved in matrix and elastic lamina degradation. Studies in Aim 1 will test the hypothesis that SMC LRP1 protects the vasculature by modulating protease activity, especially HtrA1 and mMCP-4, which in turn regulates the integrity of the elastic laminae. Ultrastructure studies of the aortic wall in smLRP1-/- mice reveal abnormal SMC. The TGF signaling pathway is a major pathway that is responsible for maintaining SMC in a contractile phenotype, and our preliminary data reveal that LRP1 binds several TGF family members and is required for the non-canonical signaling mediated by TGF Experiments in Aim 2 will test the hypothesis that LRP1 modulates SMC phenotypic transitions by regulating the TGF signaling pathway. Finally, we have initiated studies in collaboration with Dianna Milewicz (UT Houston) who has performed exome and Sanger sequencing of DNA from families with thoracic aortic aneurysms and acute aortic dissections. These studies identified several extremely rare LRP1 variants that segregate with aortic disease in these families, providing strong evidence that they are associated with the disease. Analysis of the amino acid substitutions in several of these variants suggest a strong rational for altered ligand binding and altered function in LRP1. Studies in Aim 3 will test the hypothesis that these rare variants result in defective LRP1 function, which in turn contributes to the development of this disease.