Stretch and Vitamin A Effects on Alveolar Formation

描述（由申请人提供）：人体研究表明，早产儿的视黄醇治疗可改善早产和常规通气的病态后果，包括肺泡简化和随后的慢性肺病（CLD）。动物研究进一步揭示了视黄醇信号调节决定肺泡形成的过程，但人类和动物研究都没有解决CLD中视黄醇改善或调节的分子机制。使用早产、常规通气和随后的肺泡简化的羔羊模型，我们确定了常规通气的早产羔羊（vitA+CV）的视黄醇治疗允许肺泡形成，其类似于用持续气道正压通气（CPAP;早产对照）治疗的早产羔羊和足月新生羔羊（妊娠对照）的肺。此外，vitA+CV或CPAP治疗允许表面活性蛋白B（SP-B）、血管内皮生长因子（VEGF）和p53（细胞凋亡的标志物）表达，而CV治疗则相反。我们小组的一个主要的新进展是，在我们的CLD模型中，一种特异性RAR α激动剂在常规通气的情况下刺激正常肺泡形成。我们对分子机制的关注将集中在维生素A对SP-B（直接调控）、VEGF（间接调控）和p53（间接调控）基因的调控上。SP-B和VEGF由肺中的肺泡II型细胞共表达; p53由间充质表达。通过以下3个特定目的检验的总体假设是，维生素A治疗通过经典的类维生素A信号传导途径允许适当的肺泡形成，并导致下游基因产物的直接和间接调节。具体目标1将确定维生素A对长期通气早产羔羊肺泡形成的拯救作用。具体目标2将比较有或无RAR/RXR激动剂的CV与有或无RAR/RXR拮抗剂的CPAP，以确定维生素A的作用机制。该目的将检验我们的模型中维生素A信号传导通过RAR（/RXR）发生的假设。具体目标3将确定维生素A影响SP-B，VEGF和p53启动子功能的分子机制。我们将使用从羔羊分离的肺细胞来概括体内的发现，并瞬时转染稳定的细胞系来分离特定的机制。我们将测试我们的3个靶基因的启动子区域是类维生素A应答的假设。因此，该项目将提供关于CLD中肺泡形成及其失调的新机制见解。

DESCRIPTION (provided by applicant): Human studies suggest that retinol therapy in preterm infants ameliorates the morbid consequences of prematurity and conventional ventilation, which include alveolar simplification and subsequent chronic lung disease (CLD). Animal studies further reveal that retinol signaling regulates the processes that determine alveolar formation, but neither human nor animal studies have addressed the molecular mechanism by which either retinol amelioration or regulation occurs in CLD. Using a lamb model of prematurity, conventional ventilation, and subsequent alveolar simplification, we established that retinol therapy of conventionally ventilated preterm lambs (vitA+CV) permits alveolar formation that resembles the lungs of preterm lambs treated with continuous positive airway pressure (CPAP; preterm control), and term newborn lambs (gestation control). Furthermore, vitA+CV or CPAP treatment permits expression of surfactant protein B (SP-B), vascular endothelial growth factor (VEGF), and p53 (a marker of apoptosis) versus CV treatment. A major novel advancement by our group is that a specific RARa agonist stimulates normal alveolar formation in the face of conventional ventilation in our CLD model. Our focus on molecular mechanisms will be on vitamin A regulation of genes for SP-B (direct regulation), VEGF (indirect regulation), and p53 (indirect regulation). SP-B and VEGF are co-expressed by alveolar type II cells in the lung; p53 is expressed by mesenchyme. The overall hypothesis, tested by the following 3 specific aims, is that vitamin A therapy permits appropriate alveolar formation through the classical retinoid signaling pathway and results in both direct and indirect regulation of downstream gene products. Specific Aim 1 will determine the rescue of alveolar formation by vitamin A in chronically ventilated preterm lambs. Specific Aim 2 will compare CV with or without RAR/RXR agonists versus CPAP with or without RAR/RXR antagonists to identify mechanisms of action of vitamin A. This aim will test the hypothesis that vitamin A signaling in our model occurs through RAR(/RXR. Specific Aim 3 will identify the molecular mechanisms by which vitamin A impacts SP-B, VEGF, and p53 promoter function. We will use lung cells isolated from lambs to recapitulate the in vivo findings, and transient transfection of stable cell lines to isolate specific mechanisms. We will test the hypothesis that the promoter regions of our 3 target genes are retinoid responsive. Thus, this project will provide novel mechanistic insights about alveolar formation and its dysregulation in CLD.