Mesenchymal Cell Fate Determination by Extracellular Matrix Stiffness

描述（由申请人提供）：特发性肺纤维化（IPF）是一种纤维化肺部疾病，其特征是活化的间充质细胞（肌成纤维细胞）在称为纤维母细胞灶的上皮下聚集。这些纤维母细胞灶的丰富程度与这种疾病的惨淡预后相关，其中位生存期仅为2-3年。没有药物干预能改善IPF患者的生存，迫切需要新的有效的治疗方法来治疗这种疾病。IPF的发病机制涉及对慢性/复发性肺泡上皮损伤的功能失调反应。肺僵硬增加是肺纤维化的生理相关，被认为是由肌成纤维细胞积累和细胞外基质（ECM）过度沉积引起的。最近的研究表明，在肝纤维化中，组织硬度的增加先于肌成纤维细胞的积累和基质的产生。这些发现表明，组织硬度增加可能不是纤维化的简单后果；它可能直接促进纤维的形成。然而，先前关于肌成纤维细胞命运调节的研究主要集中在可溶性介质（转化生长因子β -1和内皮素-1）的作用上，使用具有超生理硬度的刚性塑料基质。机械转导在调节肌成纤维细胞命运中的作用尚不清楚，而来自ECM的生物力学信号如何调节来自可溶性因子的生化信号以调节成纤维细胞存活/凋亡的机制也知之甚少。局灶黏附激酶（FAK）是机械转导信号的一个组成部分，对维持肌成纤维细胞的存活至关重要。FAK在纤维化肺中增加，抑制FAK可减轻博莱霉素诱导的小鼠纤维化。此外，诱发肌成纤维细胞凋亡的纤溶蛋白介导的ECM蛋白水解与FAK活性的丧失有关。FAK在肺纤维化和肌成纤维细胞存活调节中的核心作用激发了我们的中心假设，即与肺实质硬度增加相关的机械信号对间充质细胞抵抗凋亡至关重要，因此，肺纤维化的发病机制。该提案的具体目的是：(1)确定具有生理和病理硬度的底物差异调节间充质细胞凋亡的机制；(2)明确机械刺激如何调节可溶性介质对间充质细胞凋亡的影响；(3)确定肺顺应性、纤维生成和间充质细胞积累之间的关系。这些研究将增强我们对肌成纤维细胞命运在生理和病理性伤口愈合中的调节的基本理解，并有助于确定新的抗纤维化靶点来干预肺纤维化。

DESCRIPTION (provided by applicant): Idiopathic Pulmonary Fibrosis (IPF) is a fibrotic lung disease characterized by the accumulation of activated mesenchymal cells (myofibroblasts) within subepithelial clusters called fibroblastic foci. The abundance of these fibroblastic foci correlates with the dismal prognosis of this disease, which has a median survival of only 2-3 years. No pharmacologic intervention has improved survival for patients with IPF, and there is an urgent need for novel and efficacious therapies to treat this disease. IPF pathogenesis involves a dysfunctional response to chronic/recurrent alveolar epithelial injury. Increased lung stiffness is a physiologic correlate of pulmonary fibrosis that has been thought to result from myofibroblast accumulation and excessive deposition of extracellular matrix (ECM). Calling this paradigm of fibrogenesis into question, recent studies show that increased tissue stiffness precedes myofibroblast accumulation and matrix production in liver fibrosis. These findings suggest that increased tissue stiffness may not be a simple consequence of fibrosis; it may directly contribute to fibrogenesis. Prior studies of the myofibroblast fate regulation, however, have focused on the effects of soluble mediators (transforming growth factor beta-1 and endothelin-1), using rigid plastic substrates with supra-physiologic stiffness. The role of mechanotransduction in the regulation of myofibroblast fate is not known, and the mechanisms by which biomechanical signals from the ECM modulate biochemical signals from soluble factors to regulate fibroblast survival/apoptosis are poorly understood. Focal adhesion kinase (FAK) is an integral component of mechanotransduction signaling that is critical for the maintenance of myofibroblast survival. FAK is increased in fibrotic lungs, and inhibition of FAK attenuates bleomycin-induced fibrosis in mice. Moreover, plasmin-mediated ECM proteolysis, which induces myofibroblast apoptosis, is associated with the loss of FAK activity. The central role of FAK in pulmonary fibrosis and in the regulation of myofibroblast survival motivates our central hypothesis that mechanical signals associated with increased lung parenchymal stiffness are critical for mesenchymal cell resistance to apoptosis and, therefore, the pathogenesis of pulmonary fibrosis. The specific aims of this proposal are to (1) determine the mechanisms by which substrates with physiologic and pathologic stiffness differentially regulate mesenchymal cell apoptosis; (2) define how mechanical stimuli modulate the effects of soluble mediators on mesenchymal cell apoptosis; and (3) determine the relationship between lung compliance, fibrogenesis, and mesenchymal cell accumulation. The proposed studies will enhance our fundamental understanding of myofibroblast fate regulation in physiologic and pathologic wound healing and facilitate identification of novel anti-fibrotic targets for intervention in pulmonary fibrosis.