Activation of WNT co-receptor LRP5 is required for WNT and TGF-ß1 induced fibroblast activation

Abstract

Rationale: Idiopathic Pulmonary Fibrosis (IPF) is a progressive pulmonary disorder usually associated with epithelial damage and fibroblast activation and involves numerous molecular signalling cascades governing activation, differentiation, proliferation and matrix remodelling. Canonical Wingless/integrase-1 (WNT) / s-catenin signalling pathway operates via phosphorylation of its co-receptor LRP5 upon Wnt ligand binding and positively regulates proliferation and cell survival in many types of cells. Moreover, WNT signalling is dysregulated in IPF and has been linked to pulmonary disease pathogenesis and progression. However, the direct role of LRP5 is not fully understood. Hypothesis: Decrease in Wnt/s-catenin pathway activity and stabilization of LRP5 plays a role in fibroblast activation and differentiation in pulmonary fibrosis. Methods and Results: Our study focused mainly on the contribution of Wnt ligand stimulation (Wnt1, 3A and 7A) on normal human lung fibroblast (NHLF) activity. Stimulation of NHLF (2 donors) with Wnt ligands for 24h induced fibroblast to myofibroblast transition as assessed by phase-contrast microscopy and by proliferation. We found a dramatic increase in aSMA expression and cell proliferation, with Wnt7A showing the most prominent effect. LRP5 knockdown followed by treatment with WNT ligands and/or TGF- s1 stimulation for 24h partially abrogated the WNT and TGF-s1 induced changes. Conclusions: Our findings suggest that elevation of aSMA expression and cell proliferation are modulated by LRP5 with a key role in fibroblast activation, differentiation and proliferation.