Molecular mechanisms of lung branching morphogenesis

描述(由申请人提供)：新生儿呼吸窘迫仍然是新生儿死亡和发病的重要原因。大多数病例是由表面活性物质缺乏和随后的新生儿呼吸适应异常引起的。然而，导致围产期肺成熟受损和肺表面活性物质缺乏的致病机制尚不完全清楚。我们的初步研究表明，BMP信号对新生儿呼吸至关重要，也可能有助于糖皮质激素增强的表面活性物质蛋白的表达。明确BMP信号促进围产期肺成熟和适应的相关机制，以及介导糖皮质激素对肺生长的刺激作用，将有助于突破新生儿呼吸窘迫防治的关键障碍。因此，我们提出了三个特定的目标来验证这一假说：外周肺上皮细胞中的BMP信号是围产期肺成熟和新生儿呼吸适应所必需的，它通过上调NFATc3和Lpcat1的表达来促进内源性表面活性物质的产生，进而促进糖皮质激素促进的肺成熟。因此，BMP信号的缺陷可能导致新生儿呼吸衰竭。目的1.探讨外周肺上皮细胞BMP信号在围产期肺成熟和新生儿呼吸适应中的作用。在围产期小鼠肺的生长和适应过程中，BMP信号活性的动态变化将与表面活性物质的产生和功能相关。BMP信号在新生儿呼吸中的作用将在体内通过基因缺失BMP受体(Alk3)或下游Smad1，或通过在小鼠体内应用针对BMP受体Alk3的小分子抑制剂来确定。此外，BMP信号激活治疗应用于增加围产期小鼠肺组织表面活性物质产生的有效性也将通过外源性BMP4注射或通过诱导结构性活性的Alk3转基因过表达来确定。目的2.探讨BMP信号正向调节NFATc3和Lpcat1表达的转录调控机制。我们的初步数据表明，BMP-Smad1可能直接调节NFATc3和Lpcat1的基因表达，这两个基因在促进表面活性物质蛋白表达和磷脂酰胆碱合成中起重要作用。因此，Smad1对这些基因的转录调控机制，包括Smad1与启动子DNA的相互作用，将在围产期肺上皮细胞中得到确定。目的3.探讨骨形态发生蛋白(BMP)信号在糖皮质激素促进围产期肺成熟中的作用。糖皮质激素治疗是否增强肺BMP信号通路将在体内确定。在Alk3或Smad1基因敲除的围产期小鼠中，BMP途径激活在介导糖皮质激素对表面活性物质产生的刺激作用中的作用将被确定。相关的分子机制将在肺泡上皮细胞中被剖析。 公共卫生相关性：这项拟议的项目将揭示一种新的分子机制，BMP信号通过该机制促进围产期肺成熟和新生儿呼吸适应。此外，BMP信号在产前糖皮质激素治疗促进早产肺成熟中的新作用将被确定。获得的新知识将有助于突破关键障碍，开发新的治疗策略来预防和治疗新生儿呼吸窘迫。

DESCRIPTION (provided by applicant): Neonatal respiratory distress remains an important cause of neonatal mortality and morbidity. The majority of cases are caused by surfactant deficiency and subsequent abnormality in neonatal respiratory adaptation. However, the causative mechanisms leading to impaired perinatal lung maturation and surfactant deficiency are not fully understood. Our preliminary studies suggest that BMP signaling is critical to neonatal respiration, and may also contribute to glucocorticoid-augmented surfactant protein expression. Determination of the related mechanisms of BMP signaling in enhancing perinatal lung maturation and adaptation, as well as in mediating antenatal glucocorticoid's stimulatory effects on lung growth will help to break through the critical barrier for prevention and treatment of neonatal respiratory distress. Thus, we propose three specific aims to test the Hypothesis: BMP signaling in peripheral lung epithelial cells is essential for perinatal lung maturation and neonatal respiratory adaptation by promoting endogenous surfactant production through upregulating Nfatc3 and Lpcat1 expression, which in turn contributes to glucocorticoid-enhanced lung maturation. Thus, deficient BMP signaling may result in neonatal respiratory failure. Aim 1. To determine whether BMP signaling in peripheral lung epithelial cells is essential for perinatal lung maturation and neonatal respiratory adaptation. Dynamic changes in BMP signaling activity will be determined in association with surfactant production and function during perinatal mouse lung growth and adaptation. The role of BMP signaling in neonatal respiration will be defined in vivo by genetically deleting BMP receptor (Alk3) or downstream Smad1, or by administering a small molecule inhibitor specifically against BMP receptor Alk3 in mice. In addition, the efficacy of therapeutic application of BMP signal activation to increase surfactant production in perinatal mouse lung tissue will also be determined by exogenous BMP4 administration or by induction of constitutively active Alk3 transgenic overexpression. Aim 2. To determine the transcriptional regulatory mechanisms by which BMP signaling positively regulates Nfatc3 and Lpcat1 expression. Our preliminary data suggest that BMP-Smad1 may directly regulate gene expression of Nfatc3 and Lpcat1, which are important in promoting surfactant protein expression and phosphatidylcholine synthesis. Therefore, the transcriptional regulatory mechanisms of these genes by Smad1, including Smad1-promoter DNA interaction, will be determined in perinatal lung epithelial cells. Aim 3. To determine the role of BMP signaling in mediating glucocorticoid effects on promoting perinatal lung maturation. Whether glucocorticoid treatment enhances the pulmonary BMP signaling pathway will be determined in vivo. The role of BMP pathway activation in mediating glucocorticoid stimulatory effects on surfactant production will then be determined in perinatal mice with Alk3 or Smad1 gene knockout. Related molecular mechanisms will be dissected in alveolar epithelial cells. PUBLIC HEALTH RELEVANCE: This proposed project will unveil a novel molecular mechanism by which BMP signaling enhances perinatal lung maturation and neonatal respiratory adaptation. Moreover, a new role of BMP signaling in mediating antenatal glucocorticoid treatment to promote preterm lung maturation will be determined. The obtained new knowledge will help to break through the critical barrier for developing novel therapeutic strategies to prevent and treat neonatal respiratory distress.