C/EBPγ interacts with C/EBPα and activates the β-catenin pathway in idiopathic pulmonary fibrosis.

Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal interstitial lung disease characterized by an abnormal epithelial‒mesenchymal transition (EMT) and fibroblast activation, although the molecular mechanisms driving these processes remain unclear. Here, we report that the expression of CCAAT enhancer binding protein γ (C/EBPγ), a transcription factor, is significantly upregulated in lung tissues from patients with IPF and the lungs of mice with bleomycin-induced fibrosis. In A549 epithelial cells, C/EBPγ overexpression promoted the EMT, as indicated by decreased E-cadherin expression and increased N-cadherin and vimentin expression. In MRC-5 fibroblasts, C/EBPγ overexpression increased cell migration and upregulated the expression of fibrotic markers, including collagen I, fibronectin, and α-SMA. Mechanistically, C/EBPγ activated the β-catenin pathway by stabilizing β-catenin through the transcriptional repression of AXIN1, a key component of the degradation complex. This repression occurred via an interaction with C/EBPα, antagonizing its promotion of AXIN1 expression, as confirmed by ChIP‒qPCR, luciferase assays, coimmunoprecipitation, immunofluorescence staining, and rescue experiments. In vivo, adeno-associated virus-mediated C/EBPγ overexpression aggravated bleomycin-induced pulmonary fibrosis in mice, increasing collagen deposition, inflammation, and β-catenin expression, whereas C/EBPγ knockdown alleviated these changes. Collectively, these findings suggest that the downregulation of C/EBPγ expression attenuates fibrosis progression through the C/EBPα-AXIN1-β-catenin axis, underscoring its involvement in β-catenin pathway regulation and advancing the understanding of IPF pathogenesis.