TGF-beta receptor signaling in scleroderma

描述（由申请人提供）：我们研究的总体目标是了解硬皮病（SSc）病理性纤维化的机制，重点是识别和表征参与疾病过程的关键信号通路。目前尚无针对SSc的治疗方法，这些知识是开发新的有效抗纤维化疗法的先决条件。虽然已经确定TGF-2信号通路的激活是SSc和其他纤维化疾病纤维化过程的核心，但TGF-2信号通路在纤维化中的慢性性质的基础仍不清楚。可能的机制可能涉及TGF-2信号通路组分的改变，导致构成通路激活或其他关键信号分子的改变，从而增强和/或延长TGF-2信号传导的持续时间。我们在过去资助期内的研究揭示了这两种机制在SSc纤维化中的具体作用。具体来说，我们已经阐明了TGF-2受体I型（TGF-2RI或alk5）下游的一种新的纤维化信号通路，该通路由TGF-2受体比例改变触发，并导致Smad1和ERK1/2通路在没有标准Smad3通路激活的情况下被激活。这一信号级联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。适度升高的CCN2水平可诱导胶原生成，而高水平的CCN2表达可抑制胶原生成并刺激MMP1。到目前为止，我们已经确定Smad1-ERK1/2通路是CCN2基因表达的正调节因子，而Akt的激活抑制CCN2的产生，从而防止其过度积累。Smad1和Akt在SSc成纤维细胞中组成性升高，这两种信号通路之间的平衡最终决定了CCN2的表达水平。其他初步数据显示，体内SSc成纤维细胞和SSc皮肤中mTOR/Akt通路的成分发生了相当大的变化，这与该通路在SSc中的激活一致。拟议的研究将验证TGF-2RI依赖性Smad1/ERK1/2和Akt/mTOR途径的持续激活决定CCN2基因激活的大小并最终导致SSc慢性纤维化的假设。为了验证这一假设并进一步了解这些信号通路的纤维化作用，我们提出以下具体目标：在Aim 1中，我们将确定Smad1-Erk1/2-CCN2轴在SSc纤维化中的作用。在Aim 2中，我们将确定Akt/mTOR通路在SSc纤维化中的作用。在Aim 3中，我们将建立并表征基于成纤维细胞特异性TGF-2RI过表达的SSc体内模型。

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.