TGF-beta, matrix, and myofibroblasts in hepatic fibrosis

描述（由申请人提供）：肝纤维化和肝硬化是多种原因导致的慢性肝病的最终结果，在美国每年影响40万人，导致2万多人死亡。当多种细胞类型激活成纤维性、表达α -平滑肌肌动蛋白（α - sma）的肌成纤维细胞时，纤维化发生在细胞水平。在肝脏中，肝星状细胞（HSC）和门静脉成纤维细胞（PF）被认为是两种最重要的细胞类型。尽管经过十年的深入研究，介导HSC和PF活化的因素仍知之甚少。我们在体外研究了HSC的激活过程，并提出了一个初步的两步模型，其中肌成纤维细胞表型是机械因素和可溶性因素相互作用的结果。在这个模型中，HSC在受到来自细胞外基质（ECM）的机械张力时表达α - sma，然后在tgf - β信号的影响下，通过细胞质信号传导中间体SmadS，将α - sma组织成应激纤维，成为完全活化的肌成纤维细胞。本提案的目标是详细了解机械因素（粘连依赖性机械张力）在体外和体内肝肌成纤维细胞活化中的作用。我们的假设是，在tgf - β信号的背景下，ECM的机械特性对于纤维化中HSC和PF对肌成纤维细胞的激活至关重要。我们提出通过三个具体目标来解决这一目标和假设：1)确定整合素和下游信号转导途径在体外HSC激活的机械传感中的作用；2)确定基质刚度在PF激活中的作用，并建立结合HSC和PF激活的肝脏力学模型；3)在体内鉴定基质硬度的介质，确定其在纤维化中的作用。拟议的研究将提供有关肝纤维化中肌成纤维细胞转分化相关因素的重要新信息，为理解和治疗纤维化，特别是识别调节早期纤维化的新因素提供重大进展的潜力。

DESCRIPTION (provided by applicant): Liver fibrosis and cirrhosis are the end result of chronic liver disease from multiple causes, affecting 400,000 people and resulting in more than 20,000 deaths in the United States annually. Fibrosis occurs at the cellular level when a variety of cell types activate to fibrogenic, alpha-smooth muscle actin (alpha-SMA)- expressing myofibroblasts. In the liver, hepatic stellate cells (HSC) and portal fibroblasts (PF) are considered the two most important cell types to undergo activation. Factors mediating the activation of HSC and PF are poorly understood in spite of a decade of intensive study. We have studied the process of HSC activation in vitro, and have proposed a preliminary two-step model in which the myofibroblast phenotype results from an interplay between mechanical and soluble factors. In this model, HSC express alpha-SMA when subjected to mechanical tension from the extracellular matrix (ECM) and then, under the influence of TGF-beta signaling via the cytoplasmic signaling intermediate SmadS, organize the alpha-SMA into stress fibers, becoming fully activated myofibroblasts. The goal of this proposal is to develop a detailed understanding of the role of mechanical factors (adhesion-dependent mechanical tension) in hepatic myofibroblast activation in vitro and in vivo. Our hypothesis is that the mechanical properties of the ECM in the context of TGF-beta signaling are critical for the activation of HSC and PF to myofibroblasts in fibrosis. We propose to address this goal and hypothesis through three specific aims: 1) To determine the role of integrins and downstream signal transduction pathways in mechanosensing in HSC activation in vitro; 2) To determine the role of matrix stiffness in PF activation and to develop a mechanical model of the liver that incorporates HSC and PF activation; 3) To identify the mediators of matrix stiffness in vivo and to determine their role in fibrosis. The proposed studies will provide important new information about the factors involved in myofibroblast transdifferentiation in liver fibrosis, offering the potential for significant advancement in understanding and treating fibrosis, particularly in the identification of new factors regulating early fibrosis.