TGF-beta, matrix, and myofibroblasts in hepatic fibrosis

描述(申请人提供)：肝纤维化和肝硬变是由多种原因引起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。当多种类型的细胞激活成纤维形成的、表达α-SMA的肌成纤维细胞时，就会在细胞水平上发生纤维化。在肝脏中，肝星状细胞(HSC)和门脉成纤维细胞(PF)被认为是经历激活的两种最重要的细胞类型。尽管经过十年的深入研究，但对调节HSC和PF激活的因素知之甚少。我们研究了HSC的体外激活过程，并提出了一个初步的两步模型，在该模型中，肌成纤维细胞的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在细胞外基质(ECM)的机械张力下表达α-SMA，然后在胞浆信号中间体Smads的转化生长因子-β信号的影响下，将α-SMA组织成应力纤维，成为完全激活的肌成纤维细胞。这项建议的目的是在体外和体内详细了解机械因素(粘附性机械张力)在肝肌成纤维细胞激活中的作用。我们的假设是，在转化生长因子-β信号背景下，ECM的机械特性对于HSC和PF在纤维化过程中激活成肌成纤维细胞至关重要。我们建议通过三个具体的目标来解决这一目标和假说：1)确定整合素及其下游信号转导通路在体外HSC激活中的作用；2)确定基质刚性在PF激活中的作用，并建立包含HSC和PF激活的肝脏力学模型；3)确定体内基质刚性的中介因素，并确定它们在纤维化中的作用。建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，特别是在识别调控早期纤维化的新因素方面提供显著进展的潜力。

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.