VITAMIN A EFFECTS ON ALVEOLAR FORMATION

肺泡形成受损与早产儿慢性肺病（CLD）（支气管肺发育不良或BPD）或羊水引流时间过长（羊水过少）有关。这两种疾病抑制肺泡形成的机制尚不清楚，减少其发病率或严重程度的治疗策略充其量只取得了适度的成功。我们已经开发了羔羊BPD模型，该模型再现了这种疾病的病理生理和病理，包括肺泡形成的损害。羔羊早产，机械通气3-4周。肺泡继发性嵴（间隔）生长受损，导致肺泡数量减少。肺泡毛细血管不长成异常的次级嵴。这些病理改变与呼吸功能不全有关。我们的免疫组织化学、生化和分子分析表明，细胞外基质成分和生长因子表达受到不利影响（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静脉注射维生素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。我们建议在我们的BPD羔羊模型和羊水过少的胎儿羔羊模型中研究肺泡形成的调节，包括类维生素a的作用，这将使我们能够研究子宫内肺泡形成的调节。配对的早产儿和胎羊将分别接受每日含或不含维甲酸治疗，以检验3个假设：(1)维甲酸将通过调节促进间充质、内皮和上皮细胞发育的生长因子的表达来逆转受损的肺泡形成，从而使肺泡分隔发生更正常；(2)类维生素a会对细胞外基质成分和生长因子产生早期影响（出生后3-4天），这些成分和生长因子可能参与远端空域间充质、内皮和上皮的发育；(3)类维生素a可以通过增加促进间质、内皮细胞和上皮细胞发育的生长因子的表达，逆转胎儿在子宫内发育过程中肺泡形成和肺发育不全的停滞。这项工作将为两种重要儿科疾病的两种大型动物慢性模型中肺泡形成损伤的分子机制提供重要见解。这些实验也应该有助于为类维生素a的潜在治疗益处建立分子基础。

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.