Mechanisms of Pulmonary Fibrosis in Hermansky-Pudlak Syndrome

Hermansky-Pudlak综合征（HPS）是一个常染色体隐性遗传疾病家族，其特征在于： 眼皮肤白化病和高度渗透性肺纤维化。尽管我们知道潜在的基因 尽管存在这些缺陷，但目前还没有针对HPS肺纤维化的治疗或预防方法。我们 已发表的数据表明，肺泡上皮细胞（AEC）是纤维化易感性的主要驱动因素 然而，AECs功能障碍导致纤维化的潜在机制尚不清楚， 并且代表了纤维化研究领域中的重要知识缺口。目前供资期间的研究 一段时间的研究使我们能够确定HPS AEC的关键表型与纤维化易感性的关系， HPS小鼠。具体地说，我们发现MCP-1的过量产生和Nox4介导的ROS增加， AEC的产生有助于纤维化。该提案的主要目标是定义这些促纤维化蛋白是如何被激活的。 AEC表型与HPS中潜在的分子缺陷有关。为了寻找一种机制， 在HPS中观察到AEC的促纤维化表型，我们最近发现TGF β途径活化增加 在未受刺激的HPS AEC中。活化的I型和II型TGF β受体组成性地再循环到 内体和早期内体已被认为是TGF β信号传导的重要信号细胞器。 基于我们的初步数据，我们建议调查如何损害内体运输导致 来自HPS2的遗传缺陷（AP-3的缺失）改变了蛋白质稳态并失调了TGF β信号传导和AEC 功能我们的假设是HPS内体运输缺陷改变了TGF β受体信号传导， 导致Smad和Erk 1/2信号持续且增加。这些改变的信号通路导致 增加MCP-1、Nox 4和其他介导物的表达， 肺远端的微环境。为了验证这一假设，我们提出了以下具体目标，使用细胞 培养模型和发展自发性和进行性纤维化的疾病相关HPS小鼠模型 1）确定AP-3的缺失如何导致TGF β信号传导和促纤维化蛋白表达增加， 介导的AEC，2）以确定如何AEC促进成纤维细胞活化HPS，和3）调查 HPS肺纤维化的机制，随着年龄的增长。定义AEC机制 HPS功能障碍可以为HPS和其他形式的肺纤维化的发病机制提供新的见解， 从而促进对这种致命疾病的新的治疗和预防策略的开发。

Hermansky-Pudlak Syndrome (HPS) is a family of autosomal recessive disorders characterized by oculocutaneous albinism and highly penetrant pulmonary fibrosis. Despite knowledge of the underlying genetic defects, there are currently no therapeutic or preventative approaches for HPS pulmonary fibrosis. Our published data demonstrate that alveolar epithelial cells (AECs) are the primary drivers of fibrotic susceptibility in HPS; however, the underlying mechanisms by which AECs dysfunction results in fibrosis remain undefined and represent an important knowledge gap in the field of fibrosis research. Studies during the current funding period have enabled us to define key phenotypes of HPS AECs with connections to fibrotic susceptibility in HPS mice. Specifically, we showed excess production of MCP-1 and increased Nox4-mediated ROS production by AECs contributes to fibrosis. A major goal of this proposal is to define how these pro-fibrotic AEC phenotypes relate to the underlying molecular defect in HPS. In search of a mechanism that underlies the observed pro-fibrotic phenotype of AECs in HPS, we recently identified increased TGFβ pathway activation in unstimulated HPS AECs. Activated type I and type II TGFβ receptors are constitutively recycled into endosomes, and early endosomes have been recognized as a vital signaling organelle for TGFβ signaling. Based on our preliminary data, we propose to investigate how compromised endosomal trafficking resulting from the genetic defect in HPS2 (loss of AP-3) alters proteostasis and dysregulates TGFβ signaling and AEC function. Our hypothesis is that defective endosomal trafficking in HPS alters TGFβ receptor signaling, thereby resulting in persistent and increased Smad and Erk1/2 signaling. These altered signaling pathways result in increased expression of MCP-1, Nox4, and other mediators by AECs that create a pro-fibrotic microenvironment in the distal lung. To test this hypothesis, we propose the following specific aims using cell culture models and a disease relevant HPS mouse model that develops spontaneous and progressive fibrosis with aging: 1) to determine how loss of AP-3 results in increased TGFβ signaling and expression of pro-fibrotic mediators by AECs, 2) to determine how AECs promote fibroblast activation in HPS, and 3) to investigate mechanisms of pulmonary fibrosis in HPS that develops with aging. Defining the mechanisms of AEC dysfunction in HPS could provide new insights into pathogenesis of HPS and other forms of pulmonary fibrosis, thus facilitating development of new therapeutic and preventative strategies for this fatal disorder.