Hormonal Regulation of Surfactant Protein mRNA Stability

表面活性蛋白是肺表面活性物质的重要功能成分，肺表面活性物质是一种复杂的脂蛋白，可降低肺泡表面张力。SP-A、SP-B、SP-C和SP-D等表面活性蛋白编码基因在胎肺组织中的表达受发育调控。由于缺乏足够的表面活性物质合成，早产儿可能会发展为呼吸窘迫综合征(RDS)。在发达国家，RDS是新生儿发病率和死亡率的主要原因。用糖皮质激素治疗婴儿和孕妇可加速肺成熟，降低RDS的风险。表面活性蛋白B(SP-B)是表面活性物质发挥作用的关键成分。SP-B蛋白缺乏的表面活性物质会导致足月儿呼吸衰竭，而SP-B蛋白水平降低的表面活性物质在降低肺泡表面张力方面并不有效。糖皮质激素通过转录激活和改变表面活性蛋白mRNA的稳定性来改变人胎肺表面活性蛋白的表达。尤其是糖皮质激素可增加SP-bmRNA的转录表达和稳定性。由于糖皮质激素在临床上用于治疗早产儿，了解糖皮质激素调节胎肺II型上皮细胞表面活性蛋白基因表达的分子机制(S)是很重要的。本研究的目的是明确糖皮质激素稳定人SP-bmRNA而破坏SP-amRNA稳定的分子机制(S)。我们提出了以下具体目标：(1)对介导糖皮质激素在体内调节人SP-BmRNA稳定性的SP-BmRNA区域(S)进行功能定位；(2)鉴定体外信使核糖核酸：介导糖皮质激素调节人SP-BmRNA稳定性的顺式作用元件(S)上的蛋白质相互作用；以及(3)鉴定介导调节人SP-BmRNA稳定性的蛋白(S)并研究其调控。本研究的目的是明确糖皮质激素在胎肺发育过程中通过转录后机制促进SP-B基因表达和降低SP-A基因表达的分子机制，从而为提高产前糖皮质激素促进胎肺表面活性物质合成和预防RDS的治疗方案的设计提供依据。

Surfactant proteins are important functional components of pulmonary surfactant, a complex lipoprotein that acts to reduce lung alveolar surface tension. Expression of the genes encoding surfactant proteins, SP-A, SP-B, SP-C, and SP-D is developmentally regulated in fetal lung tissue. Prematurely born infants can develop Respiratory Distress Syndrome (RDS), due to a lack of adequate surfactant synthesis. RDS is the leading cause of neonatal morbidity and mortality in developed countries. Treatment of infants and pregnant mothers with glucocorticoids accelerates lung maturity, decreasing the risk of RDS. Surfactant protein B (SP-B) is a critical component in the function of surfactant. Surfactant that is deficient in SP-B protein results respiratory failure in full term infants, and surfactant that contains reduced levels of SP-B protein is not effective in the ability to reduce lung alveolar surface tension. Glucocorticoids alter surfactant protein expression in fetal human lung via both transcriptional activation and by altering the stability of surfactant protein mRNA. In particular, glucocorticoids increase both the transcriptional expression and the stability of SP-B mRNA. Since glucocorticoids are used clinically in treatment of premature infants, it is important to understand the molecular mechanism(s) by which glucocorticoids act to regulate surfactant protein gene expression in type II epithelial cells in fetal lung. The objective of the proposed research is to define the molecular mechanism(s) by which glucocorticoids stabilize human SP-B mRNA while destabilizing SP- A mRNA. The following specific aims are proposed: (1) functionally localize the region(s) in the SP-B mRNA that mediates regulation of human SP-B mRNA stability by glucocorticoids in vivo; (2) characterize the in vitro mRNA:protein interactions at the cis-acting element(s) that mediate regulation of human SP-B mRNA stability by glucocorticoids; and (3) identify the protein(s) that mediates regulation of human SP-B mRNA stability and study its regulation. The goal of this research is to define the molecular mechanisms whereby glucocorticoids enhance SP-B gene expression and reduce SP-A gene expression by post-transcriptional mechanisms during fetal lung development and, therefore provide insight into the design of treatment regimens that increase the effectiveness of antenatal glucocorticoids in the enhancement of surfactant synthesis by the fetal lung and prevent RDS.