Regulation of Cellular Phenotype Change in Thoracic Aortic Aneurysms

描述(由申请人提供)： 胸主动脉瘤(TAA)的发生是由于主动脉细胞外基质(ECM)异常重构的结果。TAA的发生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分解途径，如基质金属蛋白酶(MMPs)和ECM蛋白的产生和沉积的失调来破坏ECM的动态平衡。重要的是，这些机制在一定程度上是通过主动脉壁内驻留细胞成分的变化来调节的。大量研究表明，主动脉扩张伴随着平滑肌细胞的凋亡丢失，提示主动脉成纤维细胞可能是动脉瘤形成过程中细胞外基质重塑的关键细胞介质。此外，本实验室的最新证据表明，主动脉成纤维细胞经历了稳定的向肌成纤维细胞表型的转化，其特征是肌球蛋白染色(DDR2/MYH11)增加，MMPs和ECM蛋白的产生增加。假设成纤维细胞的转分化对TAA的进展是必不可少的。然而，调控成纤维细胞向肌成纤维细胞转变的介体(S)在三叉神经性关节炎的发生过程中仍未明确。转化生长因子-β是一种上游信号蛋白，能够调节主动脉ECM的结构和组成，并在介导成纤维细胞向肌成纤维细胞的转化过程中发挥重要作用。转化生长因子-？是一种可溶性的多肽生长因子，由主动脉壁内多种类型的细胞产生，已知在继发于马凡综合征的主动脉根部扩张中发挥重要作用，但其参与TAA的非MFS病因尚不明确。转化生长因子-？是否隔离在ECM内，与潜在的转化生长因子结合？结合蛋白。这些潜在的复合体是TAA发育过程中诱导的关键MMPs(MT1-MMPs)的蛋白水解靶。因此，利用已建立的TAA小鼠模型和分离的原代主动脉成纤维细胞培养物(正常和TAA)，将根据以下中心假设来检验成纤维细胞转分化在TAA发育中的作用：MT1-基质金属蛋白酶依赖的转化生长因子？通过调节主动脉成纤维细胞的表型变化，信号转导对TAA的发生发展起着至关重要的作用。这一假说将通过证明成纤维细胞转分化的选择性靶向可以调节TAA的形成和进展来检验，即增加TGF-？TAA发育过程中的信号转导是MT1-基质金属蛋白酶依赖的转化生长因子？释放改变的直接结果。从潜在的ECM结合库，以及间接药理抑制的转化生长因子？信号转导导致TAA发育的减弱。这套统一目标的结果将在MT1-基质金属蛋白酶激活、转化生长因子？依赖肌成纤维细胞分化和TAA的发生。

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.