Andrographolide (Andro), a component from Chinese medicinal herb Andrographis paniculata, could alleviate pulmonary fibrosis in rodents. Yet, whether and how Andro mitigates epithelial‐mesenchymal transition (EMT) induced by TGF‐β1 remain unknown. This study aimed to explore the effect of Andro on TGF‐β1‐induced EMT in human alveolar epithelial cells (AECs) and the mechanisms involved. We illustrated that Andro inhibited TGF‐β1‐induced EMT and EMT‐related transcription factors in alveolar epithelial A549 cells. Andro also reduced TGF‐β1‐induced cell migration and synthesis of pro‐fibrotic factors (ie CCN‐2, TGF‐β1), matrix metalloproteinases (ie MMP‐2, MMP‐9) and extracellular matrix (ECM) components (ie collagen 1), implying the inhibiting effect of Andro on TGF‐β1‐induced EMT‐like cell behaviours. Mechanistically, Andro treatment not only repressed TGF‐β1‐induced Smad2/3 phosphorylation and Smad4 nuclear translocation, but also suppressed TGF‐β1‐induced Erk1/2 phosphorylation and nuclear translocation in A549 cells. And treatment with ALK5 inhibitor (SB431542) or Erk1/2 inhibitors (SCH772984 and PD98059) remarkably reduced EMT evoked by TGF‐β1. In addition, Andro also reduced TGF‐β1‐induced intracellular ROS generation and NOX4 expression, and elevated antioxidant superoxide dismutase 2 (SOD2) expression, demonstrating the inhibiting effect of Andro on TGF‐β1‐induced oxidative stress, which is closely linked to EMT. Furthermore, Andro remarkably attenuated TGF‐β1‐induced down‐regulation of sirtuin1 (Sirt1) and forkhead box O3 (FOXO3), implying that Andro protects AECs from EMT partially by activating Sirt1/FOXO3‐mediated anti‐oxidative stress pathway. In conclusion, Andro represses TGF‐β1‐induced EMT in AECs by suppressing Smad2/3 and Erk1/2 signalling pathways and is also closely linked to the activation of sirt1/FOXO3‐mediated anti‐oxidative stress pathway.

中文翻译：

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穿心莲内酯可减轻肺泡上皮细胞中TGF-β1诱导的上皮间质转化。

穿心莲内酯（Andro），是中药穿心莲中的一种成分，可以减轻啮齿动物的肺纤维化。然而，Andro是否以及如何减轻TGF-β1诱导的上皮-间质转化（EMT）仍然未知。这项研究旨在探讨Andro对TGF-β1诱导的人肺泡上皮细胞（AEC）中EMT的作用及其机制。我们证明了Andro抑制了肺泡上皮A549细胞中TGF-β1诱导的EMT和EMT相关转录因子。Andro还减少了TGF-β1诱导的细胞迁移以及促纤维化因子（即CCN-2，TGF-β1），基质金属蛋白酶（即MMP-2，MMP-9）和细胞外基质（ECM）成分（即胶原蛋白）的合成1），暗示Andro对TGF-β1诱导的EMT样细胞行为具有抑制作用。从机制上讲，Andro治疗不仅抑制了TGF-β1诱导的Smad2 / 3磷酸化和Smad4核易位，而且还抑制了TGF-β1诱导的A549细胞Erk1 / 2磷酸化和核易位。用ALK5抑制剂（SB431542）或Erk1 / 2抑制剂（SCH772984和PD98059）处理可显着降低TGF-β1引起的EMT。此外，Andro还减少了TGF-β1诱导的细胞内ROS生成和NOX4表达，并提高了抗氧化超氧化物歧化酶2（SOD2）的表达，证明了Andro对TGF-β1诱导的氧化应激的抑制作用，这与EMT密切相关。此外，Andro显着减弱了TGF-β1诱导的sirtuin1（Sirt1）和叉头盒O3（FOXO3）的下调，这意味着Andro通过激活Sirt1 / FOXO3介导的抗氧化应激途径来部分保护AEC免受EMT侵害。结论，