SP-C AND SURFACTANT HOMEOSTASIS

虽然SP-C是肺发育过程中最早出现的表面活性剂成分，但SP-C的功能是表面活性剂蛋白中最不为人所知的。有几条证据有力地支持了SP-C对表面活性剂功能和周转很重要的假设：以重组SP-C作为唯一蛋白质成分的替代表面活性剂在体外和体内都具有天然表面活性剂的功能特性；最重要的是，一些SP-A和SP-B水平正常但SP-C蛋白检测不到的足月人类婴儿迅速发展为严重的RDS，并最终死于该疾病。该项目的总体目标是评估SP-C在表面活性剂稳态中的作用。SP-C的细胞内运输（特异性目的1）和分泌（特异性目的2）将在分离的II型上皮细胞中表现出来。SP-C在表面活性剂稳态中的作用将通过描述与体内突变或缺失SP-C构建体表达相关的病理生理学来评估（具体目的3和4）。SP-C构建体将在SP-C敲除小鼠的II型细胞中表达，以便在零背景下实现人转基因的表达。人类转基因基因在零背景下的转基因表达效果。转基因表达对肺结构和功能的影响将通过对胎儿和出生后后代表面活性剂系统的生化、形态学和生理学分析来评估。将建立转基因小鼠模型，研究酰基化对成熟SP-C功能的重要性（特异性目标3）和成熟肽最佳生物活性的结构基础（特异性目标4）。实验方法将允许在整个动物以及分离的II型细胞的背景下表征SP-C的功能，并有助于鉴定其在表面活性剂稳态中的作用。

Although SP-C is the first surfactant component to appear during lung development, the function of SP-C is the least understood of the surfactant proteins. Several lines of evidence strongly support the hypothesis that SP-C is important for surfactant function and turnover: Replacement surfactants with recombinant SP-C as the sole protein component have the functional properties of natural surfactant in vitro and in vivo: and, most importantly, several term human infants with normal levels of SP-A and SP-B but undetectable SP-C protein rapidly developed severe RDS and ultimately succumbed to the disease. The overall goal of this project is to assess the role of SP-C in surfactant homeostasis. Intracellular trafficking, (specific aim 1) and secretion (specific aim 2) of SP-C will be characterized in isolated Type II epithelial cells. The role of SP-C in surfactant homeostasis will be assessed by characterizing the pathophysiology associated with expression of mutated or deleted SP-C constructs in vivo (specific aims 3 and 4). SP-C constructs will be expressed in Type II cells of SP-C knockout mice in order to achieve expression of the human transgene in a null background. The effect of transgene expression of the human transgene in a null background. The effect of transgene expression on lung structure and function will be assessed by biochemical, morphological and physiological analyses of the surfactant system in fetal and postnatal offspring. Transgenic mouse models will be generated to study the importance of acylation for mature SP-C function (specific aim 3) and the structural basis for optimal biologic activity of the mature peptide (specific aim 4). The experimental approach will permit characterization of the function of SP-C in the context of the whole animal as well as the isolated Type II cell and facilitate identification of its role in surfactant homeostasis.