Gastrin-releasing peptide induces fibrotic response in MRC5s and proliferation in A549s

Abstract

Idiopathic pulmonary fibrosis (IPF) is a complex lung disease, whose build-up scar tissue is induced by severalmolecules. Gastrin-releasing peptide (GRP) is released from pulmonary neuroendocrine cells, alveolar macrophages,and some nerve endings in the lung. A possible role of GRP in IPF is unclear. We aimed to investigate the fibroticresponse to GRP, at the cellular level in MRC5 and A549 cell lines. The proliferative and fibrotic effects of GRP onthese cells were evaluated by using BrdU, immunoblotting, immunofluorescence and qRT-PCR for moleculesassociated with myofibroblast differentiation, TGF-β and Wnt signalling. All doses of GRP increased the amount ofBrdU incorporation in A549 cells. In contrast, the amount of BrdU increased in MRC5 cells in the first 24 h, thoughprogressively decreased by 72 h. GRP did not stimulate epithelial-mesenchymal transition in A549 cells, rather, itstimulated the differentiation of MRC5 cells into myofibroblasts. Furthermore, GRP induced gene and proteinexpressions of p-Smad2/3 and Smad4, and reduced the levels of Smad7 in MRC5 cells. In addition, GRP decreasedWnt5a protein levels and stimulated β-catenin activation by increasing Wnt4, Wnt7a and β-catenin protein levels.GRP caused myofibroblast differentiation by inducing TGF-βand Wnt pathways via paracrine and autocrinesignalling in MRC5 cells. In conclusion, GRP may lead to pulmonary fibrosis due to its proliferative and fibroticeffects on lung fibroblasts. The abrogation of GRP-mediated signal activation might be considered as a treatmentmodality for fibrotic lung diseases.