Echinacoside ameliorates bleomycin-induced idiopathic pulmonary fibrosis by regulating macrophage polarization

Idiopathic pulmonary fibrosis (IPF) is identified as a chronic, progressive fibrotic interstitial pneumonia of unknown cause. Echinacoside (ECH) is a phenylethanoid glycoside extracted from Cistanche deserticola, which exhibits noteworthy anti-oxidant and anti-inflammatory activities and can protect against renal, myocardial, and kidney fibrosis. This study aimed to assess the therapeutic effect of ECH on IPF by using cellular and animal experiments. Bleomycin (BLM)-induced IPF mice and transforming growth factor (TGF)-β1-treated human embryonic lung fibroblasts (MRC-5) were respectively used as animal and cellular models of IPF, which were then subjected to ECH treatment. Mouse pulmonary tissues were harvested for hematoxylin and eosin (H&E), Masson's trichrome, immunohistochemical, and immunofluorescence staining, RT-qPCR, and western blotting to determine pulmonary histological changes and the expression of fibrosis-related genes (α-SMA, fibronectin, and COL1A1), M2 macrophage markers (CD206, CD163, Arg-1, and YM-1), and phosphorylated JAK2 and STAT3. Bronchoalveolar lavage fluid (BALF) was collected to detect total protein contents, total inflammatory cell counts, pro-inflammatory cytokine (TNF-α and IL-1β) levels, and pro-fibrosis factor TGF-β content. Cell viability and migration and ⍺-SMA, fibronectin, COL1A1, and phosphorylated JAK2 and STAT3 levels in MRC-5 cells were assessed through CCK-8 assay, wound healing assay, RT-qPCR, and western blotting. ECH administration significantly mitigated BLM-induced pulmonary inflammation and fibrosis in mice. ECH decreased total protein contents, total leukocyte counts, TNF-α and IL-1β levels, and TGF-β contents in BALF as well as hydroxyproline contents and α-SMA, fibronectin, COL1A1, CD206, CD163, Arg-1, and YM-1 levels in pulmonary tissues of BLM-induced IPF mice. In vitro data revealed that ECH markedly inhibited the upregulation of ⍺-SMA, fibronectin, and COL1A1 expression and cell migration induced by TGF-β1 in MRC-5 cells. From a mechanistic standpoint, ECH treatment inhibited phosphorylated JAK2 and STAT3 levels both in vivo and in vitro. ECH exhibits an anti-fibrotic effect in IPF by inhibiting pro-fibrotic M2 macrophage polarization, which might be attributed to its downregulation of the JAK2/STAT3 pathway. This discovery emphasizes the potential of ECH as a promising therapeutic agent for IPF treatment.