TGF-beta receptor signaling in scleroderma

描述(申请人提供)：我们研究的总体目标是了解硬皮病病理性纤维化(SSC)的机制，重点是识别和表征参与疾病过程的关键信号通路。目前还没有治疗SSc的方法，这些知识是开发新的有效的抗纤维化疗法的先决条件。众所周知，转化生长因子-2信号通路的激活在SSC和其他纤维化疾病的纤维化过程中处于中心地位，但转化生长因子-2信号通路在纤维化中的慢性性质的基础仍不清楚。可能的机制包括改变转化生长因子-2信号通路的组成成分，导致结构性通路激活或其他关键信号分子的改变，从而增强和/或延长转化生长因子-2信号通路的持续时间。在过去的资助期间，我们的研究揭示了这两种机制在SSC纤维化中的具体作用。具体地说，我们已经阐明了一条新的促纤维化信号通路，它位于转化生长因子-2受体I型下游(转化生长因子-2RI或ALK-5)下游，由转化生长因子-2受体的比例改变而触发，导致Smad1和ERK1/2通路的激活，而不激活典型的Smad3通路。这种信号级联反应的激活导致结缔组织生长因子(CCN2)的产生增加，CCN2是促纤维化反应的关键介质。我们的研究还表明，CCN2的相对丰度在其作为促纤维化介质的功能中起着关键作用。中等水平的CCN2诱导胶原蛋白，而高水平的CCN2蛋白表达抑制胶原蛋白的产生并刺激MMP1。到目前为止，我们已经证实Smad1-ERK1/2通路是CCN2基因表达的正向调节因子，而Akt的激活则抑制CCN2的产生，从而防止其过度积累。在SSC成纤维细胞中，Smad1和Akt均呈结构性升高，这两条信号通路之间的平衡最终决定了CCN2的表达水平。更多的初步数据显示，在SSC成纤维细胞和SSC皮肤中，mTOR/Akt通路的组成成分发生了相当大的变化，这与SSC中该通路的激活是一致的。这些研究将验证一种假说，即依赖于Smad1/ERK1/2和Akt/mTOR通路的持续激活的转化生长因子-2RI决定了CCN2基因激活的幅度，并最终导致SSC的慢性纤维化。为了验证这一假说，并进一步了解这些信号通路在纤维化中的作用，我们提出了以下具体目标：在目标1中，我们将确定Smad1-ERK1/2-CCN2轴在SSC纤维化中的作用。在目标2中，我们将确定Akt/mTOR通路在SSC纤维化中的作用。在目标3中，我们将建立一种基于成纤维细胞特异性过度表达转化生长因子-2RI的SSC的体内模型。 公共卫生相关性：SSc的发病机制仍然知之甚少，目前还没有有效的抗纤维化治疗方法来治疗SSc或其他纤维化疾病。对SSC中转化生长因子-2和Akt/mTOR信号的特异性异常的分析将有助于更好地了解这些通路在纤维化中慢性激活的机制，并可能导致开发有效的治疗策略。

DESCRIPTION (provided by applicant): The overall goal of our research is to understand the mechanism of pathologic fibrosis in scleroderma (SSc) focusing on identification and characterization of the key signaling pathways involved in the disease process. There is currently no treatment for SSc and such knowledge is prerequisite for the development of new and effective antifibrotic therapies. While it is well established that activation of the TGF-2 signaling pathway is central to the process of fibrosis in SSc and other fibrotic disorders, the basis for the chronic nature of TGF-2 signaling in fibrosis remains unknown. The possible mechanisms may involve alterations of the components of the TGF-2 signaling pathway resulting in the constitutive pathway activation or alterations of other key signaling molecules that enhance and/or extend the duration of TGF-2 signaling. Our studies during the past funding period uncovered the specific roles for both of these mechanisms in SSc fibrosis. Specifically, we have elucidated a novel profibrotic signaling pathway downstream from the TGF-2 receptor type I (TGF-2RI or ALK 5) that is triggered by an altered ratio of the TGF-2 receptors and leads to activation of Smad1 and ERK1/2 pathways in the absence of activation of the canonical Smad3 pathway. Activation of this signaling cascade results in increased production of connective tissue growth factor (CCN2), a key mediator of the profibrotic response. Our studies have also revealed that the relative abundance of CCN2 plays a critical role in its function as a profibrotic mediator. Whereas moderately elevated levels of CCN2 induce collagen, high expression levels of CCN2 inhibit collagen production and stimulate MMP1. Hitherto, we have established that the Smad1-ERK1/2 pathway is a positive regulator of CCN2 gene expression whereas, activation of Akt inhibits CCN2 production, thus preventing its excessive accumulation. Both, Smad1 and Akt are constitutively elevated in SSc fibroblasts and the balance between these two signaling pathways ultimately determines the expression levels of CCN2. Additional preliminary data have revealed considerable alterations in the components of the mTOR/Akt pathway in SSc fibroblasts and in SSc skin in vivo, consistent with the activation of this pathway in SSc. The proposed studies will test the hypothesis that the TGF-2RI dependent persistent activation of Smad1/ERK1/2 and Akt/mTOR pathways determines the magnitude of CCN2 gene activation and ultimately leads to chronic fibrosis in SSc. To test this hypothesis and to gain additional insights into the fibrogenic role of these signaling pathways we propose the following specific aims: In Aim 1we will determine the role of Smad1-Erk1/2-CCN2 axis in SSc fibrosis. In Aim 2 we will determine the role of the Akt/mTOR pathway in SSc fibrosis. In Aim 3 we will establish and characterize an in vivo model of SSc based on fibroblast-specific overexpression of TGF-2RI. PUBLIC HEALTH RELEVANCE: The pathogenesis of SSc is still poorly understood and there are no effective anti-fibrotic treatments for SSc or other fibrotic diseases. Proposed analyses of the specific aberrations of the TGF-2 and Akt/mTOR signaling in SSc will provide a better understanding of the mechanisms responsible for chronic activation of these pathways in fibrosis and may lead to development of effective therapeutic strategies.