A fibroblast-dependent TGF-β1/sFRP2 noncanonical Wnt signaling axis promotes epithelial metaplasia in idiopathic pulmonary fibrosis

Abstract

Reciprocal interactions between alveolar fibroblasts and epithelial cells are crucial for lung homeostasis, injury repair, and fibrogenesis, but underlying mechanisms remain unclear. To investigate, we administered the fibroblast-selective TGFb1 signaling inhibitor, epigallocatechin gallate (EGCG), to Interstitial Lung Disease (ILD) patients undergoing diagnostic lung biopsy and conducted single-cell RNA sequencing on spare tissue. Biopsies from untreated patients showed higher fibroblast TGFb1 signaling compared to non-disease donor or end-stage ILD tissues. In vivo, EGCG downregulated TGFb1 signaling and several pro-inflammatory and stress pathways in biopsy samples. Notably, EGCG reduced fibroblast secreted frizzle-like receptor protein 2 (sFRP2), an unrecognized TGFb1 fibroblast target gene induced near type II alveolar epithelial cells (AEC2s) in situ. Using AEC2-fibroblast coculture organoids and precision cut lung slices (PCLS) from non-diseased donors, we found TGFb1 signaling promotes a spread AEC2 KRT17+ basaloid state, whereupon sFRP2 then activates a mature Krt5+ basal cell program. Wnt-receptor Frizzled 5 (Fzd5) expression and downstream calcineurin signaling were required for sFRP2-induced nuclear NFATc3 accumulation and KRT5 expression. These findings highlight stage-specific TGFb1 signaling in ILD, the therapeutic potential of EGCG in reducing IPF-related transcriptional changes, and identify TGFb1-noncanonical Wnt pathway crosstalk via sFRP2 as a mechanism for dysfunctional epithelial signaling in Idiopathic Pulmonary Fibrosis/ILD.