Mesenchyme associated transcription factor PRRX1: A key regulator of IPF fibroblast

Abstract

Introduction Fibroblast differentiation in myofibroblasts is a key feature of idiopathic pulmonary fibrosis (IPF). Paired-related homeobox (PRRX) transcription factors (TF) regulate mesenchymal cells during development and are key TF at the center of a network coordinating fibroblast differentiation. We hypothesized that PRRX1 modulates fibroblast phenotype in IPF. Material and methods Immunohistochemistry (IHC) and real-time quantitative PCR for PRRX were performed on human lung samples and primary human lung fibroblasts (HLF) cultured from IPF and controls. PRRX1 overexpression was obtained in HLF with plasmid transfection. Functional experiments were performed by seeding HLF on dishes with an elastic modulus (EM) of 1.5 or 28 kPa or on a rigid dish. The effects of the ROCK and PTGS2 inhibitors Fasudil and NS398 on PRRX1 expression were evaluated. Results PRRX1 was upregulated in IPF lung and HLF as compared to controls and was mostly detected in fibroblast foci. PRRX1 expression was controlled by soluble factors and by the extracellular matrix stiffness: Profibrotic factors TGF-β and ET-1 downregulated PRRX1 expression in HLF, while PDGF-AA and PGE2 increased PRRX1 expression only in HLF from IPF patients. Soft matrix (EM 1.5 kPa) enhanced PRRX1 expression in HLF through the activation of PTGS2, while a rigid matrix inhibited PRRX1 expression through ROCK activation. PRRX1 overexpression inhibited PDGF-dependent migration, increased the expression of phosphorylated ERK and promoted control and IPF HLF survival after serum deprivation or FAS-L activation. Conclusion These results indicate that PRRX1 is regulated by the fibrotic environment in the lung and controls lung fibroblast migration and survival.