Mechanisms of Pulmonary Fibrosis in Hermansky-Pudlak Syndrome

描述(申请人提供)：肺纤维化是许多形式的间质性肺疾病(ILD)的最终共同途径。目前，大多数纤维化肺疾病尚无有效的治疗方法，而且由于对肺泡纤维化的细胞和分子机制的不完全了解，预防和治疗策略的发展仍然受到限制。单基因疾病为从原发分子缺陷的角度研究肺纤维化提供了独特的机会。Hermansky-Pudlak综合征(HPS)是一类常染色体隐性遗传病，涉及细胞内转运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、2和4型中高度渗透，但在其他HPS亚型中不发生。在HPS伴纤维化倾向的患者中，肺泡II型上皮细胞增生，板层小体不规则，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，自然发生的HPS小鼠可以可靠地模拟人类疾病的重要特征，包括HPS基因型特异性的肺泡巨噬细胞(AM)激活和对促纤维化刺激的敏感性。此外，我们最近已经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缺陷显著减少了II型细胞的凋亡、过度的单核细胞趋化蛋白-1(MCP-1)的分泌、AM的激活以及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型细胞中存在过度的氧化应激，以及NOX4的表达显著增加。基于这些数据，我们提出假设，HPS转运缺陷导致NOX4依赖的活性氧(ROS)产生增加，并增加包括MCP-1在内的介质的分泌，这些介质在局部微环境中招募和激活AM。在暴露于损伤性刺激后，边缘代偿的II型细胞面临更高的凋亡风险，这与激活的AM一起加速了纤维化反应。为了验证这一假说，我们利用实验模拟人类疾病的HPS模型提出了以下具体目标：1)确定氧化应激在HPS II型细胞功能障碍中的作用；2)研究博莱霉素诱导的HPS小鼠II型细胞凋亡和加速纤维化的易感性机制；3)确定调节HPS中AM激活的上皮衍生因子以及激活的AM在HPS相关肺纤维化中的作用。总体而言，我们的研究将有助于更好地理解HPS中II型细胞功能障碍的机制，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疾病的共同特征，进一步研究HPS转运缺陷将有助于阐明肺纤维化的机制，具有广泛的现实意义。

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.