Surfactant protein C (SP-C) is a 35 amino acid lung-specific hydrophobic peptide that enhances the biophysical activity of surfactant phospholipid. Recently, the importance of SP-C to lung health and disease has been underscored by the observations that heterozygous expression of over 14 different mutations in the SP-C gene in humans is associated with chronic interstitial lung disease (ILD), accumulation of unprocessed SP-C precursors, and selective absence of alveolar SP-C. The overall goal of this project is to further understand the molecular mechanisms underlying the consequences of mutant SP-C expression in the pathophysiology of interstitial lung disease. We hypothesize that mutations in the SP-C gene induce the development of interstitial lung disease by a pathway in which the aberrant protein products adopt nonnative conformations that lead to aggregation, mis-targeting, generation of dominant negative effects and production of a toxic gain of function. The experimental approach involves both reductionist and integrative approaches to dissect out the consequences of key mutations in the SP-C sequence for the targeting and post-translational processing of proSP-C in the secretory pathway and to relate this back to the pathogenesis of ILD. The phenotype of mutant forms of SP-C described to date will first be functionally assessed in vitro with studies characterizing intracellular trafficking and processing using well characterized transfected cell line models (Aim 1). These results will then be extended to in vivo mouse models using transgenic expression of selected SP-C constructs to assess long-term effects of mutant proSP-C expression (Aim 2). In concert with Aims 1 and 2, the prevalence and functional significance of SP-C mutants in adult interstitial lung disease will then be assessed in a well-defined population of patients with interstitial lung disease using sequence based screening of genomic DNA (Aim 3). Abnormal SP-C sequences identified by this screening process will then be expressed in both the in vitro (cell-line) as well as the in vivo (transgenic mouse) model systems to develop a complete pathophysiological profile. This will permit a full functional assessment of a genetic etiology for ILD in humans through population-based screening coordinated with operational characterization of identified SP-C mutants expressed in the presence and absence of endogenous SP-C and in the context of both single cells and the whole animal. ? ?
