Mechanisms of Pulmonary Fibrosis in Hermansky-Pudlak Syndrome

描述（由申请人提供）：肺纤维化是多种间质性肺疾病（ILD）的最终共同途径。目前，大多数肺纤维化疾病没有有效的治疗方法，对肺泡纤维化的细胞和分子机制的不完全了解仍然限制了预防和治疗策略的发展。单基因疾病提供了一个独特的机会，从一个主要的分子缺陷的有利位置研究肺纤维化。Hermansky-Pudlak综合征（HPS）是一个常染色体隐性遗传病家族，涉及细胞内运输功能障碍和溶酶体相关细胞器生物发生异常。肺纤维化在HPS 1型、2型和4型中具有高渗透性，但在其他HPS亚型中不发生。在有纤维化倾向的HPS患者中，肺泡上皮II型细胞增生，有不规则的板层体和脂质堆积。此外，巨噬细胞介导的炎症先于HPS患者的肺纤维化。我们已经证明，自然产生的HPS小鼠可靠地模拟了人类疾病的重要特征，包括HPS基因型特异性肺泡巨噬细胞（AM）激活和对促纤维化刺激的易感性。此外，我们最近证明肺泡上皮是纤维化易感性的主要驱动因素，因为转基因上皮特异性纠正HPS2缺陷可显著减轻II型细胞凋亡，过量的单核细胞趋化蛋白-1 （MCP-1）分泌，AM激活和对博莱霉素诱导的纤维化的易感性。尽管HPS转运缺陷调节II型细胞表型的机制尚不清楚，但我们的初步数据表明，HPS2突变小鼠的II型细胞中存在过量的氧化应激，并且Nox4的表达显著增加。基于这些数据，我们提出了HPS运输缺陷导致Nox4依赖性活性氧（ROS）产生增加和包括MCP-1在内的介质分泌增加的假设，这些介质在局部微环境中招募和激活AMs。暴露于有害刺激后，轻度代偿的II型细胞凋亡的风险增加，这与活化的am一起加速了纤维化反应。为了验证这一假设，我们提出了以下具体目标，利用实验模拟人类疾病的HPS模型：1)确定氧化应激在HPS II型细胞功能障碍中的作用；2)研究HPS小鼠对博莱霉素诱导的II型细胞凋亡和加速纤维化的易感性机制；3)确定HPS中调节AM活化的上皮源性因子以及活化的AMs在HPS相关肺纤维化中的作用。总的来说，我们的研究将有助于提高对HPS中II型细胞功能障碍机制的理解，并可能促进这种致命疾病的治疗策略。由于II型细胞功能障碍是许多纤维化肺部疾病的一个统一特征，因此进一步研究HPS转运缺陷将有可能阐明具有广泛相关性的肺纤维化机制。

DESCRIPTION (provided by applicant): Pulmonary fibrosis is a final common pathway in many forms of interstitial lung diseases (ILD). Currently there are no effective treatments for most fibrotic lung diseases, and the development of preventative and therapeutic strategies remains limited by incomplete understanding of the cellular and molecular mechanisms underlying alveolar fibrosis. Monogenic disorders provide a unique opportunity to study lung fibrogenesis from the vantage point of a primary molecular defect. Hermansky-Pudlak Syndrome (HPS) is a family of autosomal recessive disorders involving dysfunction of intracellular trafficking and abnormal lysosome-related organelle biogenesis. Pulmonary fibrosis is highly penetrant in HPS types 1, 2, and 4, but does not occur in other HPS subtypes. In HPS patients with fibrotic predisposition, alveolar epithelial type II cells are hyperplastic with irreular lamellar bodies and lipid accumulation. In addition, macrophage-mediated inflammation precedes pulmonary fibrosis in HPS patients. We have shown that naturally-occurring HPS mice reliably model important features of the human disease, including HPS genotype-specific alveolar macrophage (AM) activation and susceptibility to pro-fibrotic stimuli. In addition, we have recently demonstrated that the alveolar epithelium is the primary driver of fibrotic susceptibility, as transgenic epithelial-specific correction of the HPS2 defect significantly attenuated type II cell apoptosis, excess monocyte-chemotactic protein-1 (MCP-1) secretion, AM activation, and susceptibility to bleomycin-induced fibrosis. Although the mechanisms by which HPS trafficking defects regulate type II cell phenotype remain poorly defined, our preliminary data demonstrate excess oxidative stress in type II cells of HPS2 mutant mice, as well as markedly increased expression of Nox4. Based on these data, we propose the hypothesis that HPS trafficking defects result in increased Nox4- dependent reactive oxygen species (ROS) production and enhanced secretion of mediators, including MCP-1, that recruit and activate AMs in the local microenvironment. After exposure to injurious stimuli, marginally compensated type II cells are at increased risk for apoptosis, which accelerates the fibrotic response in conjunction with activated AMs. To test this hypothesis, we propose the following specific aims using HPS models which experimentally mimic human disease: 1) to define the role of oxidative stress in HPS type II cell dysfunction, 2) to investigate the mechanisms underlying susceptibility to bleomycin-induced type II cell apoptosis and accelerated fibrosis in HPS mice, and 3) to determine the epithelial-derived factors regulating AM activation in HPS and the role of activated AMs in HPS-related pulmonary fibrosis. Overall, our studies will lead to improved understanding of the mechanisms of type II cell dysfunction in HPS and could facilitate therapeutic strategies for this fatal disorder. Because type II cell dysfunction is a unifying feature of many fibrotic lung diseases, further study of HPS trafficking defects will likey elucidate mechanisms of pulmonary fibrosis with broad relevance.