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，重点是识别和表征疾病过程中涉及的关键信号通路。目前没有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。虽然已充分确定TGF-2信号传导途径的活化是SSc和其他纤维化病症中纤维化过程的中心，但纤维化中TGF-2信号传导的慢性性质的基础仍然未知。可能的机制可能涉及TGF-2信号传导途径的组分的改变，导致组成性途径活化或增强和/或延长TGF-2信号传导的持续时间的其他关键信号传导分子的改变。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。具体来说，我们已经阐明了一种新的促纤维化信号通路下游的TGF-2受体I型（TGF-2 RI或ALK 5），这是由改变比例的TGF-2受体，并导致激活的Smad 1和ERK 1/2途径的经典Smad 3途径的激活的情况下激活。这种信号级联的激活导致结缔组织生长因子（CCN 2）的产生增加，CCN 2是促纤维化反应的关键介质。我们的研究还表明，CCN 2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。CCN 2的适度升高水平诱导胶原蛋白，而CCN 2的高表达水平抑制胶原蛋白的产生并刺激MMP 1。目前，我们已经确定Smad 1-ERK 1/2通路是CCN 2基因表达的正调节因子，而Akt的激活抑制CCN 2的产生，从而防止其过度积累。Smad 1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CCN 2的表达水平。额外的初步数据已经揭示了SSc成纤维细胞和体内SSc皮肤中mTOR/Akt通路的组分的相当大的改变，与SSc中该通路的激活一致。本研究将验证以下假设：TGF-2 RI依赖性Smad 1/ERK 1/2和Akt/mTOR通路的持续激活决定了CCN 2基因激活的程度，并最终导致SSc的慢性纤维化。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，我们提出了以下具体目标：在目标1中，我们将确定Smad 1-Erk 1/2-CCN 2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，我们将建立并表征一个基于成纤维细胞特异性过度表达TGF-2 RI的SSc体内模型。 公共卫生相关性：SSc的发病机制仍然知之甚少，并且对于SSc或其他纤维化疾病没有有效的抗纤维化治疗。对SSc中TGF-2和Akt/mTOR信号传导的特异性畸变的拟议分析将提供对纤维化中这些通路慢性激活的机制的更好理解，并可能导致有效治疗策略的开发。

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.