VITAMIN A EFFECTS ON ALVEOLAR FORMATION

肺泡形成受损与早产儿（支气管肺发育不良或BPD）或羊水排出时间延长（羊水过少）的慢性肺病（CLD）有关。 这两种疾病抑制肺泡形成的机制仍不清楚，降低其发生率或严重程度的治疗策略充其量也取得了一定的成功。 我们已经开发了一个模型的BPD在羔羊再现的病理生理学和病理这种疾病，包括损害肺泡形成。 羔羊早产，机械通气3-4周。它们的肺有受损的肺泡次级嵴（隔膜）的生长，导致肺泡数量减少。 肺泡毛细血管不长入异常的次级嵴。 这些病理变化与呼吸功能不全有关。 我们的免疫组化，生物化学和分子分析表明，细胞外基质成分和生长因子的表达受到不利影响（弹性蛋白基因表达上调;弹性纤维和蛋白多糖积累过多;血管内皮生长因子蛋白表达减少）。 初步研究表明，这些变化可以通过每天胃肠外给予维生素A（视黄醇）来逆转。 这些变化是如何发生的尚不清楚，这是我们申请资助的基础。 我们建议研究肺泡形成的调节，包括维甲酸的作用，在我们的羔羊模型的BPD，并在胎儿羊水过少的羔羊模型，这将使我们能够调查子宫内肺泡形成的调节。 每天分别用或不用类维生素A处理成对的早产和胎羊，以检验3个假设：（1）类维生素A将通过调节促进间充质、内皮和上皮发育的生长因子的表达来逆转受损的肺泡形成，从而发生更正常的肺泡分隔;（2）维甲酸类药物会有早期效果（出生后第3-4天）对细胞外基质成分和生长因子的影响，所述细胞外基质成分和生长因子可能涉及远端空气间充质、内皮和上皮的发育;和（3）类维生素A将通过增加促进间充质、内皮和上皮发育的生长因子的表达来逆转子宫内胎儿发育期间肺泡形成和肺发育不全的停滞。 这项工作应该提供重要的见解的分子机制，有助于损害肺泡形成的2个大动物，慢性模型的2个重要的儿科疾病。这些实验也有助于建立维甲酸潜在治疗益处的分子基础。

Impaired alveolar formation is associated with chronic lung disease (CLD) of prematurity (bronchopulmonary dysplasia or BPD) or prolonged drainage of amniotic liquid (oligohydramnios). The mechanisms by which alveolar formation is inhibited with both diseases remain unclear, and treatment strategies to reduce their incidence or severity have achieved modest success at best. We have developed a model of BPD in lambs that reproduces the pathophysiology and pathology of this disease, including impairment of alveolar formation. The lambs are delivered prematurely and mechanically ventilated for 3-4 wks. Their lungs have impaired growth of alveolar secondary crests (septa), resulting in reduced numbers of alveoli. Alveolar capillaries do not grow into the abnormal secondary crests. These pathological changes are associated with respiratory insufficiency. Our immunohistochemical, biochemical, and molecular analysis suggest that extracellular matrix components and growth factor expression are adversely affected (elastin gene expression is upregulated; elastic fiber and proteoglycan accumulation are excessive; vascular endothelial growth factor protein expression is reduced). Preliminary studies suggest that these changes can be reversed by daily parenteral administration of vitamin A (retinol). How these changes occur is not known and is the basis of our grant application. We propose to study the regulation of alveolar formation, including the role of retinoids, in our lamb model of BPD, and in a fetal lamb model of oligohydramnios that will allow us to investigate the regulation of alveolar formation in utero. Paired preterm and fetal lambs, respectively, will be treated with or without retinoids daily to test 3 hypotheses: (1) retinoids will reverse the impaired alveolar formation by regulating the expression of growth factors that promote mesenchymal, endothelial, and epithelial development such that more normal alveolar septation occurs; (2) retinoids will have an early effect (postnatal days 3-4) on extracellular matrix components and growth factors that are likely to be involved with development of distal airspace mesenchyme, endothelium, and epithelium; and (3) retinoids will reverse arrest of alveolar formation and lung hypoplasia during fetal development in utero by augmenting the expression of growth factors that promote mesenchymal, endothelial, and epithelial development. This work should provide important insights into the molecular mechanisms that contribute to impairment of alveolar formation in 2 large-animal, chronic models of 2 important pediatric diseases. The experiments also should help establish the molecular basis for the potentially therapeutic benefit of retinoids.