Hastings Center for Pulmonary Research and Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California.
Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania.
Am J Physiol Lung Cell Mol Physiol. 2020 Jul 1;319(1):L173-L184. doi: 10.1152/ajplung.00519.2019. Epub 2020 May 20.
The alveolar epithelium is comprised of two cell types, alveolar epithelial type 1 (AT1) and type 2 (AT2) cells, the latter being capable of self-renewal and transdifferentiation into AT1 cells for normal maintenance and restoration of epithelial integrity following injury. MicroRNAs (miRNAs) are critical regulators of several biological processes, including cell differentiation; however, their role in establishment/maintenance of cellular identity in adult alveolar epithelium is not well understood. To investigate this question, we performed genome-wide analysis of sequential changes in miRNA and gene expression profiles using a well-established model in which human AT2 (hAT2) cells transdifferentiate into AT1-like cells over time in culture that recapitulates many aspects of transdifferentiation in vivo. We defined three phases of miRNA expression during the transdifferentiation process as "early," "late," and "consistently" changed, which were further subclassified as up- or downregulated. miRNAs with altered expression at all time points during transdifferentiation were the largest subgroup, suggesting the need for consistent regulation of signaling pathways to mediate this process. Target prediction analysis and integration with previously published gene expression data identified glucocorticoid signaling as the top pathway regulated by miRNAs. Serum/glucocorticoid-regulated kinase 1 (SGK1) emerged as a central regulatory factor, whose downregulation correlated temporally with gain of hsa-miR-424 and hsa-miR-503 expression. Functional validation demonstrated specific targeting of these miRNAs to the 3'-untranslated region of SGK1. These data demonstrate the time-related contribution of miRNAs to the alveolar transdifferentiation process and suggest that inhibition of glucocorticoid signaling is necessary to achieve the AT1-like cell phenotype.
肺泡上皮由两种细胞类型组成，即肺泡上皮细胞 1 型（AT1）和 2 型（AT2），后者具有自我更新和转分化为 AT1 细胞的能力，以维持正常上皮完整性并在损伤后进行修复。微小 RNA（miRNA）是多个生物学过程的关键调节因子，包括细胞分化；然而，它们在成年肺泡上皮细胞中建立/维持细胞身份的作用尚未得到很好的理解。为了研究这个问题，我们使用一种已建立的模型，对 miRNA 和基因表达谱的顺序变化进行了全基因组分析，该模型中，人 AT2（hAT2）细胞在培养中随着时间的推移转分化为 AT1 样细胞，这在很大程度上模拟了体内转分化的许多方面。我们将 miRNA 表达在转分化过程中的三个阶段定义为“早期”、“晚期”和“持续”变化，进一步细分为上调或下调。在转分化过程中的所有时间点表达改变的 miRNA 是最大的亚组，这表明需要一致调节信号通路来介导这个过程。靶基因预测分析和与先前发表的基因表达数据的整合表明，糖皮质激素信号是受 miRNA 调节的最重要途径。血清/糖皮质激素调节激酶 1（SGK1）作为一个核心调节因子出现，其表达的下调与 hsa-miR-424 和 hsa-miR-503 表达的获得在时间上相关。功能验证表明，这些 miRNA 特异性靶向 SGK1 的 3'-非翻译区。这些数据表明，miRNA 对肺泡转分化过程的时间相关贡献，并表明抑制糖皮质激素信号是实现 AT1 样细胞表型所必需的。
