Hormonal Regulation of Surfactant Protein mRNA Stability

表面活性剂蛋白是肺表面活性剂的重要功能成分，是一种降低肺泡表面张力的复合脂蛋白。表面活性剂蛋白、SP-A、SP-B、SP-C和SP-D编码基因的表达在胎儿肺组织中受发育调控。早产婴儿可发展呼吸窘迫综合征（RDS），由于缺乏足够的表面活性剂合成。在发达国家，RDS是新生儿发病和死亡的主要原因。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。表面活性剂蛋白B （SP-B）是表面活性剂功能的重要组成部分。缺乏SP-B蛋白的表面活性剂会导致足月婴儿呼吸衰竭，而含有SP-B蛋白水平降低的表面活性剂在降低肺泡表面张力方面不起作用。糖皮质激素通过转录激活和改变表面活性剂蛋白mRNA的稳定性来改变胎儿人肺中表面活性剂蛋白的表达。特别是，糖皮质激素增加了SP-B mRNA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，因此了解糖皮质激素调节胎儿肺II型上皮细胞中表面活性剂蛋白基因表达的分子机制非常重要。本研究的目的是确定糖皮质激素稳定人SP- b mRNA而破坏SP- A mRNA的分子机制。提出了以下具体目标：(1)在体内通过糖皮质激素调节人SP-B mRNA稳定性的SP-B mRNA中功能定位区域；(2)表征体外mRNA：糖皮质激素介导人SP-B mRNA稳定性的顺式作用元件的蛋白质相互作用；(3)鉴定介导人SP-B mRNA稳定性调控的蛋白并研究其调控作用。本研究的目的是明确糖皮质激素在胎儿肺发育过程中通过转录后机制增强SP-B基因表达和降低SP-A基因表达的分子机制，从而为设计治疗方案提供见解，从而提高产前糖皮质激素在增强胎儿肺表面活性剂合成和预防RDS方面的有效性。

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.