Miakotina O L, Dekowski S A, Snyder J M
Department of Pediatrics, University of Iowa College of Medicine, Iowa City, IA 52242, USA.
Biochim Biophys Acta. 1998 Oct 23;1442(1):60-70. doi: 10.1016/s0167-4781(98)00121-3.
Fetuses of mothers with uncontrolled gestational diabetes have an increased risk of developing neonatal respiratory distress syndrome and are frequently hyperinsulinemic, thus it has been proposed that high levels of insulin delay fetal lung maturation. We have shown previously that insulin inhibits the accumulation of mRNA for the surfactant-associated proteins A and B (SP-A and SP-B) in human fetal lung explants maintained in vitro. To test the hypothesis that the inhibitory effects of insulin on the surfactant proteins are the result of a direct action of insulin on the lung epithelial cell, we evaluated the effects of insulin in the H441 cell line, a human pulmonary adenocarcinoma cell line that expresses SP-A and SP-B mRNA. We observed that insulin treatment for 48 h decreased SP-A mRNA and protein levels in a concentration-dependent manner when compared to controls. The inhibitory effect of insulin on SP-A mRNA levels was apparent as early as after 4 h of exposure. SP-B mRNA levels were also significantly decreased by insulin in a concentration-dependent manner. Insulin, at 2.5 microg/ml, inhibited SP-A gene transcription by approx. 67%, and inhibited SP-B gene transcription by about 32%. There was no significant effect of insulin on SP-A or SP-B mRNA stability. Thus, we have observed a pattern of insulin inhibition of SP-A and SP-B gene expression in the H441 lung epithelial cell line similar to that previously observed in human fetal lung explants, which are comprised of both epithelial and mesenchymal cells. Our findings provide further evidence that insulin may delay fetal lung maturation by inhibiting SP-A and SP-B gene expression. Furthermore, our findings suggest that the inhibitory effects of insulin are, at least partially, the result of a direct action on the lung epithelial cell.
患有未得到控制的妊娠期糖尿病的母亲所怀胎儿发生新生儿呼吸窘迫综合征的风险增加，且常常出现高胰岛素血症，因此有人提出高水平胰岛素会延迟胎儿肺成熟。我们之前已经表明，胰岛素会抑制体外培养的人胎儿肺组织中表面活性物质相关蛋白A和B（SP-A和SP-B）的mRNA积累。为了检验胰岛素对表面活性物质蛋白的抑制作用是胰岛素直接作用于肺上皮细胞的结果这一假说，我们评估了胰岛素对H441细胞系的影响，H441是一种表达SP-A和SP-B mRNA的人肺腺癌细胞系。我们观察到，与对照组相比，胰岛素处理48小时会以浓度依赖的方式降低SP-A mRNA和蛋白水平。胰岛素对SP-A mRNA水平的抑制作用在暴露4小时后就很明显。胰岛素也会以浓度依赖的方式显著降低SP-B mRNA水平。2.5微克/毫升的胰岛素可使SP-A基因转录受到约67%的抑制，并使SP-B基因转录受到约32%的抑制。胰岛素对SP-A或SP-B mRNA稳定性没有显著影响。因此，我们在H441肺上皮细胞系中观察到胰岛素抑制SP-A和SP-B基因表达的模式，类似于之前在由上皮细胞和间充质细胞组成的人胎儿肺组织中观察到的模式。我们的研究结果进一步证明，胰岛素可能通过抑制SP-A和SP-B基因表达来延迟胎儿肺成熟。此外，我们的研究结果表明，胰岛素的抑制作用至少部分是对肺上皮细胞直接作用的结果。
