Regulation of Cellular Phenotype Change in Thoracic Aortic Aneurysms

描述（由申请人提供）： 胸主动脉瘤（TAA）的发展是由于主动脉细胞外基质（ECM）的异常重塑。TAA的发展受到一系列相互关联的机制的影响，这些机制通过刺激蛋白水解途径（如基质金属蛋白酶（MMP））和ECM蛋白的产生和沉积的失调来破坏ECM稳态。重要的是，这些机制部分通过主动脉壁内常驻细胞成分的变化介导。大量研究表明，主动脉扩张伴随着平滑肌细胞的凋亡损失，这表明主动脉成纤维细胞可能是动脉瘤形成过程中ECM重塑的关键细胞介质。此外，该实验室的最新证据表明，主动脉成纤维细胞经历稳定的转化为肌成纤维细胞表型，其特征在于肌球蛋白染色增加（DDR2/Myh 11）和MMP和ECM蛋白的产生增加。假设成纤维细胞的转分化对于TAA进展是必不可少的。然而，在TAA发育过程中调节成纤维细胞向肌成纤维细胞转变的介质仍不确定。一种能够调节主动脉ECM结构和组成的上游信号蛋白，已知在介导成纤维细胞向肌成纤维细胞转化中发挥重要作用，是转化生长因子β（TGF-β）。TGF-？是一种可溶性肽生长因子，由主动脉壁内的多种细胞类型产生，已知在继发于马凡氏综合征的主动脉根部扩张中起重要作用，但其参与TAA的非MFS病因学仍不明确。TGF-？被隔离在细胞外基质中，被潜在的TGF-β结合？结合蛋白这些潜在的复合物是在TAA发展过程中诱导的关键MMP（MT 1-MMP）的蛋白水解靶标。因此，使用一个建立的小鼠模型的TAA，和分离的主动脉成纤维细胞培养物（正常和TAA），成纤维细胞转分化的作用，在TAA的发展将审查与中央的假设，MT 1-MMP依赖性TGF-？通过调节主动脉成纤维细胞表型变化，信号传导对于TAA的发展是必不可少的。这一假设将通过证明成纤维细胞转分化的选择性靶向可以调节TAA的形成和进展，增加TGF-？信号在TAA的发展是一个直接的结果改变MT 1-MMP依赖释放TGF-？从潜在的ECM结合商店，和间接药理学抑制TGF-？信号传导导致TAA发育的减弱。从这个统一的目标集的结果将建立一个因果关系MT 1-MMP激活，TGF-？依赖性肌成纤维细胞分化和TAA发育。

DESCRIPTION (provided by applicant): Thoracic aortic aneurysms (TAAs) develop as a consequence to abnormal remodeling of the aortic extracellular matrix (ECM). TAA development is influenced by a series of interrelated mechanisms that disrupt ECM homeostasis through the stimulation of proteolytic pathways, such as the matrix metalloproteinases (MMPs) and dysregulation of the production and deposition of ECM proteins. Importantly, these mechanisms are mediated in part through changes in the resident cellular constituents within the aortic wall. Numerous studies have demonstrated that aortic dilatation is accompanied by the apoptotic loss of smooth muscle cells, suggesting that the aortic fibroblast may be the key cellular mediator of ECM remodeling during aneurysm formation. Moreover, recent evidence from this laboratory suggests that aortic fibroblasts undergo a stable transformation to a myofibroblast phenotype, that is characterized by increased myosin staining (DDR2/Myh11) and enhanced production of both MMPs and ECM proteins. It is hypothesized that the transdifferentiation of fibroblasts is essential for TAA progression. However, the mediator(s) regulating this fibroblast-to-myofibroblast transition during TAA development remain undefined. One upstream signaling protein capable of regulating the structure and composition of the aortic ECM, and known to play an important role in mediating the fibroblast-to- myofibroblast transformation, is transforming growth factor-beta (TGF-?). TGF-? is a soluble peptide growth factor, produced by multiple cell types within the aortic wall, and is known to play a significant role in aortic root dilatation secondary to Marfan syndrome, but its involvement remains undefined in non-MFS etiologies of TAA. TGF-? is sequestered within the ECM, bound by latent TGF-? binding proteins. These latent complexes are proteolytic targets for key MMPs (MT1-MMP) that are induced during TAA development. Accordingly, using an established mouse model of TAA, and isolated primary aortic fibroblast cultures (normal and TAA), the role of fibroblast transdifferentiation in TAA development will be examined with the central hypothesis that MT1-MMP- dependent TGF-? signaling is essential for TAA development through the modulation of aortic fibroblast phenotype change. This hypothesis will be tested by demonstrating that selective targeting of fibroblast transdifferentiation can modulate TAA formation and progression, that increased TGF-? signaling during TAA development is a direct result of altered MT1-MMP-dependent release of TGF-? from latent ECM bound stores, and that indirect pharmacological inhibition of TGF-? signaling results in the attenuation of TAA development. The outcomes from this unified set of aims will establish a cause-effect relationship between MT1-MMP activation, TGF-? dependent myofibroblast differentiation, and TAA development.