The role of type II alveolar epithelial stem cells (AEC II) for alveolar repair in radiation‐induced lung fibrosis (RILF) remains largely unknown, mainly because of AEC II phenotype's spontaneous change in vitro. Cell differentiation status is determined by Lin28 and let‐7 miRNAs in see‐saw‐pattern. Lin28, a repressor of let‐7 and a stem cell marker, is activated by β‐catenin. The expression of β‐catenin is regulated by GSK‐3β/TGF‐β1 signaling. To understand the true role of AEC II in RILF, we freshly isolated primary AEC II directly from thoracically irradiated lungs. We then explored the expressions of cell phenotype markers and differentiation regulators in these isolated AEC II to analyze the correlation between GSK‐3β/TGF‐β1/β‐catenin signaling pathway, lin28/let‐7 balance, and AEC II phenotypes at different injury phases following irradiation. Results showed that isolated single primary cells displayed AEC II ultrastructural features and proSP‐C positive. The gene expressions of prosp‐c (an AEC II biomarker) and hopx (an AEC I marker) significantly increased in isolated AEC II during injury repair phase (P < .001 and P < .05) but decreased at end‐stage of injury, while mesenchymal markers increased in both isolated AEC II and irradiated lungs. mRNA levels of gsk‐3β, tgf‐β1, and β‐catenin increased in all irradiated AEC II, but more pronounced in the second half of injury phase (P < .05‐P < .001). Similarly, the expression of lin28 was also significantly elevated in isolated AEC II at the late phase (P < .05‐P < .001). Four let‐7 miRNAs were significantly upregulated in all irradiated AEC II groups (P < .05‐P < .001). The time‐dependent and highly consistent uptrends for four lin28/let‐7 ratios in sorted AEC II contrasted to downtrends in irradiated lungs. In conclusion, RILF occurred when GSK‐3β/TGF‐β1 signaling increased β‐catenin levels, which led to the augmentation of AEC II population by elevated lin28/let‐7 ratio and the transcription of profibrotic cytokines and factors, thereby inducing AEC II to undergo transdifferentiation into mesenchymal cells.

中文翻译：

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糖原合酶激酶-3β 通过调节 β-catenin/lin28 信号网络来确定 II 型肺泡干细胞转分化状态促进辐射诱导的肺纤维化

II型肺泡上皮干细胞（AEC II）在辐射诱导的肺纤维化（RILF）中用于肺泡修复的作用仍然未知，主要是因为体外AEC II表型的自发变化。细胞分化状态由 Lin28 和 let-7 miRNA 以跷跷板模式决定。Lin28 是 let-7 的阻遏物和干细胞标记物，被 β-catenin 激活。β-catenin 的表达受 GSK-3β/TGF-β1 信号的调控。为了了解 AEC II 在 RILF 中的真正作用，我们直接从胸部照射的肺中新鲜分离出原代 AEC II。然后我们探索了这些分离的 AEC II 中细胞表型标志物和分化调节因子的表达，以分析 GSK-3β/TGF-β1/β-catenin 信号通路、lin28/let-7 平衡、照射后不同损伤阶段的 AEC II 表型。结果表明，分离的单个原代细胞显示出 AEC II 超微结构特征和 proSP-C 阳性。prosp-c（AEC II 生物标志物）和 hopx（AEC I 标志物）的基因表达在损伤修复阶段分离的 AEC II 中显着增加（P < .001 和 P < .05），但在损伤末期降低，而间充质标志物在孤立的 AEC II 和辐射肺中均增加。gsk-3β、tgf-β1 和 β-catenin 的 mRNA 水平在所有受照射的 AEC II 中均增加，但在损伤阶段的后半段更为明显（P < .05-P < .001）。同样，lin28 的表达在晚期孤立的 AEC II 中也显着升高（P < .05-P < .001）。在所有照射的 AEC II 组中，4 个 let-7 miRNA 显着上调（P < .05-P < .001）。排序的 AEC II 中四个 lin28/let-7 比率的时间依赖性和高度一致的上升趋势与辐射肺中的下降趋势形成对比。总之，当 GSK-3β/TGF-β1 信号增加 β-catenin 水平时发生 RILF，这导致 AEC II 群体通过升高的 lin28/let-7 比率和促纤维化细胞因子和因子的转录增加，从而诱导 AEC II转分化为间充质细胞。