Role of SFTPC in Pathogenesis of Interstitial Lung Disease

描述(申请人提供)：特发性肺纤维化(IPF)是一种慢性进行性间质性肺疾病(ILD)，没有有效的治疗选择，确诊后平均存活3年。由于缺乏合适的动物模型，人们对该病的自然病史知之甚少。该病的家族性形式占IPF病例总数的不到5%，其特点是常染色体显性遗传，与遗传修饰因素和环境因素的影响有关，具有可变的外显性。表面活性蛋白C编码基因(SFTPC)(SP-C、外显子4和SP-CL188Q)的突变为确定家族性ILD的分子机制提供了独特的机会。我们在细胞培养中的初步研究发现，与突变SP-C的检测和快速降解有关的独特分子复合体；此外，我们还表明，表达突变SP-C的细胞和感染呼吸道合胞病毒的细胞积累错误折叠的SP-C，并且比表达野生型蛋白的细胞更容易受到病毒诱导的细胞死亡。这些关键的体外发现导致了一个中心假设，即环境应激叠加在SFTPC突变上会导致错误折叠的细胞毒性SP-C的积累，进而导致2型上皮细胞损伤/死亡，这是SFTPC相关家族性ILD的激发事件。提出了三个特定的目标来检验这一假说：特定的目标1将检验ERAD(一种细胞保护途径)快速识别和降解突变的SP-C以防止细胞内积聚、2型上皮细胞凋亡和进展为ILD的假设。Sftpc突变叠加病毒感染导致细胞毒性SP-C积聚和2型上皮细胞凋亡，进而触发ILD的发生或加速发病。特定目标3将检验这样一种假设，即抑制突变的SP-C在体内的积累将防止进展为ILD。在这项申请中提出的研究将产生第一个家族性IPF的小鼠模型，并确定环境侮辱是否绝对是疾病发生所必需的；此外，该模型将允许测试体外研究结果的生物学相关性，特别是细胞毒性SP-C的积累推动进展为ILD的假设。该小鼠模型还将促进转译研究，其长期目标是：(1)测试通过移植成体祖细胞逆转纤维化过程的可行性，(2)确定能够增强突变SP-C(以及潜在的其他致病突变蛋白)在受影响小鼠中的清除并预防ILD的新药，以及(3)确定用于无症状患者早期发现疾病的候选基因。因此，这项建议的总体长期目标是确定一种疾病的新诊断和治疗策略，在这种疾病中，目前的治疗标准是姑息治疗。公共卫生相关性：SFTPC基因突变和家族性IPF之间的关联代表着一个真正独特的机会，可以为一种具有未知自然病史的致命性疾病建立动物模型。尽管SFTPC相关的IPF是一种非常罕见的疾病亚型，但导致上皮细胞凋亡的分子途径可能与其他家族性疾病形式相同(例如，TERT或TR的突变)，而凋亡下游的途径可能对非家族性、特发性IPF很有信息。为此，我们提出了围绕Sftpc突变小鼠模型的广泛研究，该模型将有助于开发/识别新的疾病生物标记物、药物/药物靶点和治疗方法。

DESCRIPTION (provided by applicant): Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive interstitial lung disease (ILD) with no effective treatment options and a mean survival of 3 years after diagnosis. The natural history of the disease is poorly understood because of the lack of an appropriate animal model. Familial forms of the disease account for less than 5% of total IPF cases and are characterized by autosomal dominant inheritance with variable penetrance related to the influence of both genetic modifiers and environmental factors. Mutations in the gene (SFTPC) encoding surfactant protein C (SP-C?exon4 and SP-CL188Q) provide a unique opportunity to identify molecular pathways underlying familial ILD. Our preliminary studies in cell culture have identified unique molecular complexes involved in the detection and rapid degradation of mutant SP-C; further, we have shown that cells expressing mutant SP-C and infected with respiratory syncticial virus accumulate misfolded SP-C and are much more susceptible to viral-induced cell death than cells expressing the wild type protein. These key in vitro findings lead to the central hypothesis that environmental stress superimposed on a SFTPC mutation leads to accumulation of misfolded, cytotoxic SP-C that, in turn, results in type 2 epithelial cell injury/death, which is the inciting event in SFTPC-associated familial ILD. Three specific aims are proposed to test this hypothesis: Specific Aim 1 will test the hypothesis that ERAD (a cytoprotective pathway) rapidly identifies and degrades mutant SP-C preventing intracellular accumulation, type 2 epithelial cell apoptosis, and progression to ILD. Specific Aim 2 will test the hypothesis that viral infection superimposed on an Sftpc mutation leads to accumulation of cytotoxic SP-C and type 2 epithelial cell apoptosis that, in turn, triggers the onset of ILD or accelerates pathogenesis. Specific Aim 3 will test the hypothesis that inhibiting accumulation of mutant SP-C in vivo will prevent progression to ILD. Studies proposed in this application will generate the first mouse model of familial IPF and determine if an environmental insult is absolutely required for onset of the disease; further, this model will permit testing of the biologic relevance of findings from in vitro studies, in particular the hypothesis that accumulation of cytotoxic SP-C drives progression to ILD. The mouse model will also facilitate translational studies with the long-term goals of (1) testing the feasibility of reversing the fibrogenic process by transplantation of adult progenitor cells, (2) identifying new drugs that enhance clearance of mutant SP-C (and, potentially, other disease-causing mutant proteins) and prevent ILD in affected mice, and (3) identifying candidate genes for early detection of disease in asymptomatic patients. Thus, the overall, long term-goal of this proposal is to identify novel diagnostic and treatment strategies for a disease in which the current standard of care is palliative. PUBLIC HEALTH RELEVANCE: The association between mutations in the SFTPC locus and familial IPF represents a truly unique opportunity to generate an animal model for a lethal disease with an uncharacterized natural history. Although SFTPC-associated IPF is a very rare disease subset, it is likely that the molecular pathways leading to epithelial cell apoptosis may be shared with other familial forms of the disease (e.g. mutations in TERT or TR) and pathways downstream of apoptosis may well be informative for non-familial, idiopathic IPF. For this reason, we have proposed a broad range of studies centered around an Sftpc mutant mouse model that will facilitate development/identification of novel disease biomarkers, drugs/drug targets, and therapies.