Modifier Genes of SP-C Induced ILD

间质性肺病（ILD）是一种慢性、进行性肺部疾病，有许多潜在的病因;然而，大多数病因尚不清楚。患有这些疾病的患者通常在临床上难以区分，表现为与运动受限、呼吸急促和呼吸短促相关的进展性ILD。病理学上，各种形式的ILD都与肺泡炎症、结缔组织基质和白细胞的肺间质浸润、肺泡结构的进行性丧失和肺纤维化有关。尽管有公认的组织学和临床表现，但ILD发病机制的分子机制仍难以阐明。许多已知的家族性遗传性疾病具有ILD组分，包括肺泡蛋白沉积症、戈谢病、赫-普综合征、内-皮克病、神经纤维瘤病和结节性硬化症。然而，除了已知的疾病外，对ILD的易感性被认为只有很小的家族成分。最近，人类ILD与一种常染色体显性突变相关， 表面活性蛋白C（SP-C）基因。这导致上皮中II型细胞特异性SP-C蛋白的功能丧失，导致肺泡细胞损伤并诱发各种形式的ILD。这些发现扩展了早期的研究，即诊断为家族性ILD的家族成员中SP-C基因突变和蛋白质缺乏相关。家族性ILD的一个有趣但麻烦的属性是在受累个体中观察到的组织病理学模式的高度变异性，强烈暗示ILD严重程度中的修饰基因。ILD修饰基因的其他证据来自敲除小鼠。当SP-C在FVB/N小鼠中被基因靶向时， 记录肺力学和组织学。相反，129 S6/SvEvTac（129/Sv）SP-C敲除小鼠发生了重度和进行性肺部疾病，具有许多与ILD一致的组织学特征;因此，129/Sv品系中的SP-C缺陷代表ILD的小鼠模型。拟议研究的中心假设是，SP-C无效状态下的ILD严重程度由一个或多个基因修饰，这可以使用FVB/N-129/Sv小鼠模型的遗传和分子分析来描述。影响ILD严重程度的修饰基因的鉴定将使用4个特定目的完成：1）确定每个中间ILD表型的可能遗传模式，并估计影响不同ILD表型的基因座的最小数量。 SP-C敲除小鼠模型中的肺反应（分离分析）; 2）在由两个SP-C无效菌株产生的大型回交组群中鉴定与表型差异相关的染色体区域（QTL分析）; 3）鉴定与SP-C敲除小鼠中的品系差异相关的候选和位置候选修饰基因（微阵列分析）;和4）评估SP-C无效小鼠模型中的位置候选ILD修饰基因（功能分析）。基因鉴定应产生有价值的信息，需要进一步评估治疗策略和遗传变异影响易感性和结果的表面活性剂相关的肺部疾病。

Interstitial lung diseases (ILDs) are chronic, progressive lung diseases with many potential causes; however, most etiologies are unknown. Patients with these disorders are often clinically indistinguishable, presenting with advancing ILD that is associated with exercise limitation, tachypnea, and shortness of breath. Pathologically, the various forms of ILD are all associated with alveolar inflammation, pulmonary interstitial infiltration with connective tissue matrix and leukocytes, progressive loss of alveolar structure, and pulmonary fibrosis. Despite well-recognized histological and clinical manifestations, the molecular mechanisms involved in ILD pathogenesis have been elusive. Many known familial genetic disorders have an ILD component, including pulmonary alveolar proteinosis, Gaucher disease, Hermansky-Pudlak syndrome, Neimann-Pick disease, neurofibromatosis, and tuberous sclerosis. Susceptibility to ILDs beyond those for known disorders, however, is believed to have only a minor familial component. Recently, human ILD was associated with an autosomal dominant mutation in the surfactant protein-C (SP-C) gene. This resulted in a functional loss of Type II cell specific SP-C protein in the epithelium, causing alveolar cell injury and predisposing to various forms of ILD. These findings extended earlier studies that associated SP-C gene mutations and protein deficiency in family members diagnosed with familial ILD. An intriguing, but troublesome attribute of familial ILD is the high variability in histopathologic patterns seen among affected individuals, strongly implicating modifier genes in ILD severity. Additional evidence for modifier genes of ILD stems from knockout mice. When SP-C was gene-targeted in FVB/N mice, only subtle changes in lung mechanics and histology were noted. To the contrary, 129S6/SvEvTac (129/Sv) SP-C null mice developed severe and progressive pulmonary disease with many histological features consistent with ILD; thus, SP-C deficiency in the 129/Sv strain represents a mouse model of ILD. The central hypothesis of the proposed research is that ILD severity in a SP-C null state is modified by one or more genes, which can be delineated using genetic and molecular analyses of the FVB/N-129/Sv mouse model. Identification of modifier genes affecting ILD severity will be accomplished using 4 Specific Aims: 1) determine the likely mode of inheritance for each intermediate ILD phenotype and estimate the minimum number of loci affecting the disparate lung responses in the SP-C null mouse model (segregation analysis); 2) identify chromosomal regions linked to phenotype differences in a large backcross cohort generated from the two SP-C null strains (QTL analysis); 3) identify candidate and positional candidate modifier genes associated with strain differences in SP-C null mice (microarray analysis); and 4) assess positional candidate ILD modifier genes in the SP-C null mouse model (functional analysis). Gene identification should yield valuable information needed to further assess therapeutic strategies and genetic variations affecting susceptibility and outcome of surfactant-associated lung diseases.