Role of extracellular HSP27 in idiopathic pulmonary fibrosis (IPF)

Introduction: Idiopathic pulmonary fibrosis (IPF) is a chronic and diffuse form of interstitial lung disease, of unknown etiology and with fatal outcome. We have shown that the small intracellular heat shock protein 27 (HSP27) 1) is overexpressed in IPF patient lungs, 2) promotes fibrogenesis and 3) that its inhibition protects against mice-induced lung fibrosis (FASEB 2013 (4) 1549-60). Preliminary data suggest the involvement of extracellular HSP27 (exHSP27) in the development of fibrosis. Our aim is to characterize secretion pathways and ex HSP27 functions. Methods: Primary mice lung fibroblast, lung epithelial cells (A549) or pleural cells (MET5A) have been cultivated with recombinant rhTGF-s1. HSP27 has been quantified in supernatant and extracellular vesicles (EVs). These cells have been stimulated by recombinant humain (rh)TGF-s1 and/or rhHSP27 and myofibroblast differenciation have been assessed. The effect of rhHSP27 on cellular migration has been tested by transwell assay. Results: ExHSP27 was over-expressed in broncho-alveolar fluids from rodent fibrosis models. In vitro TGF-s1 treatment induced an increase of HSP27 level in supernatant and in EVs. HSP27 is able to potentiate TGF-s1 effects on several of its downstream genes (e-Cadherin, vimentin, a-SMA) as well as its pro-migration effects. Indeed, transfer of TGF-s1-treated cell supernatant into a second cell culture induced in that culture myofibroblast differenciation and these effects are strongly decreased by HSP27 immunodepletion. Conclusion: Pro-fibrotic conditions increased HSP27 secretion in pulmonary cells EVs. ExHSP27 is able to potentiate TGF-s1 effects. Targeting exHSP27 may be of interest to treat IPF.