Senior R M, Griffin G L, Mudd M S, Moxley M A, Longmore W J, Pierce R A
Division of Respiratory/Critical Care, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri, USA.
Am J Respir Cell Mol Biol. 1996 Mar;14(3):239-47. doi: 10.1165/ajrcmb.14.3.8845174.
Although the composition of the subepithelial basement membrane of the alveolar septum has been studied in detail, there is relatively little information about which cells produce it. We examined intact rat lung and isolated rat alveolar type II cells for the expression of entactin, an integral basement membrane component that binds laminin and type IV collagen. By Northern analysis, late gestation and early neonatal rat lungs expressed high levels of entactin mRNA whereas lungs from adult animals had only minimal levels of entactin mRNA. These latter findings were confirmed by in situ hybridization, which showed prominent signal for entactin mRNA in cells in the alveolar walls of neonatal animals and no signal for entactin mRNA in the alveolar walls of lungs from adult animals. The entactin mRNA throughout the alveolar walls of neonatal animals was not limited to cells that expressed surfactant-associated protein C mRNA, a marker of alveolar type II cells. Freshly harvested adult alveolar type II cells and alveolar type II cells in culture for < 6 days expressed none to minimal entactin mRNA or protein. However, with longer periods in culture, both entactin mRNA and entactin protein synthesis were evident and progressively increased. In situ hybridization indicated that >60% of the alveolar epithelial cells expressed entactin mRNA with increasing time in culture. When cultured on Engelbreth-Holm-Swarm matrix, alveolar type II cells showed the same time course of entactin mRNA expression as cells cultured on plastic. Neonatal lung mesenchymal cells produced abundant entactin in culture, consistent with the likelihood that these cells are the principal source of entactin in alveolar walls in the developing lung. These results indicate that entactin production in the normal alveolar wall occurs primarily during lung development and that mesenchymal cells are probably the principal source of production. However, because adult alveolar epithelial cells synthesize entactin in culture, it is possible that alveolar epithelium contributes to the entactin in the alveolar subepithelial basement membrane.
尽管对肺泡隔上皮下基底膜的组成已进行了详细研究，但关于哪些细胞产生该基底膜的信息相对较少。我们检测了完整的大鼠肺和分离出的大鼠肺泡Ⅱ型细胞中巢蛋白（一种与层粘连蛋白和Ⅳ型胶原结合的基底膜整合成分）的表达情况。通过Northern分析，妊娠晚期和新生早期大鼠肺表达高水平的巢蛋白mRNA，而成年动物的肺中巢蛋白mRNA水平极低。原位杂交证实了后一结果，其显示新生动物肺泡壁细胞中有明显的巢蛋白mRNA信号，而成年动物肺的肺泡壁中无巢蛋白mRNA信号。新生动物整个肺泡壁中的巢蛋白mRNA并不局限于表达表面活性物质相关蛋白C mRNA（肺泡Ⅱ型细胞的标志物）的细胞。新鲜收获的成年肺泡Ⅱ型细胞及培养时间小于6天的培养肺泡Ⅱ型细胞表达的巢蛋白mRNA或蛋白极少甚至无表达。然而，随着培养时间延长，巢蛋白mRNA和巢蛋白蛋白合成均明显且逐渐增加。原位杂交表明，随着培养时间增加，超过60%的肺泡上皮细胞表达巢蛋白mRNA。当在Engelbreth-Holm-Swarm基质上培养时，肺泡Ⅱ型细胞巢蛋白mRNA表达的时间进程与在塑料上培养的细胞相同。新生大鼠肺间充质细胞在培养中产生大量巢蛋白，这与这些细胞可能是发育中肺肺泡壁巢蛋白的主要来源这一可能性相符。这些结果表明，正常肺泡壁中的巢蛋白产生主要发生在肺发育过程中，间充质细胞可能是主要的产生来源。然而，由于成年肺泡上皮细胞在培养中能合成巢蛋白，肺泡上皮有可能对肺泡上皮下基底膜中的巢蛋白有贡献。
