LUNG ELASTIN IN BRONCHOPULMONARY DYSPLASIA

这项建议的重点是描述在早产儿肺通气导致的支气管肺发育不良(BPD)发展过程中控制弹性蛋白合成和周转的机制。弹性蛋白赋予肺泡和肺泡管、细支气管和血管等肺结构必要的弹性回缩特性，因此对肺功能至关重要。我们之前已经在BPD的一个实验模型中显示了异常的弹性纤维沉积，其他的也显示了BPD肺中弹性溶解活性的增加。尽管如此，BPD弹性纤维异常的根本原因尚不清楚。我们假设早产儿肺间充质细胞通过增加弹性细胞外基质成分的表达和沉积而对机械通气的应变做出反应，这与肺泡化所需的弹性细胞外基质成分的比例不成比例。暴露在高氧环境下，可能会产生和释放破坏弹性纤维的弹性酶，如中性粒细胞弹性蛋白酶或基质金属蛋白酶，以及改变肺成纤维细胞外基质基因表达的细胞因子或生长因子。这些事件导致在新的肺泡壁发育失败的部位过度沉积无序的弹性纤维。这些部位杂乱无章的弹力纤维的堆积可能会限制伤情恢复的能力。为了确定BPD发展过程中弹性纤维异常沉积的原因，我们建议研究弹性蛋白、纤维蛋白1和2以及赖氨酰氧化酶的表达，这些都是正常弹性纤维合成所必需的，并对损伤肺中存在的弹性酶进行表征。我们的实验方法将包括通过核糖核酸酶保护试验定量分析弹性纤维相关和弹性蛋白酶mRNA的表达，以及通过原位杂交和免疫组织化学分析来定位表达。调节原弹性蛋白表达的分子机制将通过评估原弹性蛋白基因转录的变化来确定，通过结合底物酶谱、免疫组织化学和原位杂交来评估原弹性蛋白在BPD肺中的蛋白质合成、表达和活性。确定干预性治疗对弹性纤维相关基因表达和弹性纤维酶表达的影响将检验这样一种假设，即预防BPD的治疗也将恢复弹性纤维相关基因表达和弹性纤维沉积的正常模式。

The focus of this proposal is to characterize mechanisms controlling elastin synthesis and turnover during the development of bronchopulmonary dysplasia (BPD) resulting from ventilation of the premature lung. Elastin confers the requisite property of elastic recoil to such lung structures as alveoli and alveolar ducts, bronchioles, and blood vessels, and thus is essential for lung function. We have previously demonstrated abnormal elastic fiber deposition in an experimental model of BPD, and others have demonstrated increased elastolytic activity in the BPD lung. Still, the root causes of elastic fiber abnormalities in BPD are not known. We hypothesize that mesenchymal cells of the premature lung respond to the strain of mechanical ventilation by increasing the expression and deposition of elastic extracellular matrix components out of proportion to what is required for alveolarization. Exposure to hyperoxia may result in the production and release of elastases such as neutrophil elastase or matrix metalloproteinases that damage elastic fibers, as well as cytokines or growth factors that alter extracellular matrix gene expression by lung fibroblasts. These events result in the excess deposition of disordered elastic fibers at sites of failed development of new alveolar walls. The accumulation of disorganized elastic fibers at these sites may limit the ability to recover from injury. To determine the causes of abnormal elastic fiber deposition during the development of BPD, we propose to study the expression of elastin, fibrillins 1 and 2, and lysyl oxidase, all required for normal elastic fiber synthesis, and to characterize the elastases present in the injured lung. Our experimental approaches will include quantitative analysis of elastic fiber-related and elastase mRNA expression by RNAse protection assays, as well as localization of expression by in situ hybridization and immunohistochemical analyses. The molecular mechanisms regulating tropoelastin expression during normal baboon lung development and the development of BPD will be determined by assessing changes in tropoelastin gene transcription, steady-state mRNA levels, and protein synthesis, expression and activity of elastases in the BPD lung will be assessed by a combination of substrate zymography, immunohistochemistry, and in situ hybridization. Determining the effects of interventive treatments on the expression of elastic fiber-related genes and the elaboration of elastases will test the hypothesis that treatments which prevent BPD will also restore normal patterns of elastic fiber-related gene expression and elastic fiber deposition.