Insulin-like growth factor binding protein-4 exerts antifibrotic activity by reducing levels of connective tissue growth factor and the C-X-C chemokine receptor 4.

Yunyun Su,Joseph M Pilewski,Carol Feghali-Bostwick,Stanley Hoffman,Xinh-Xinh Nguyen,Tetsuya Nishimoto

doi:10.1096/fba.2018-00015

Abstract

The insulin‐like growth factor (IGF) system plays an important role in variety cellular biological functions; we previously reported levels of IGF binding proteins (IGFBP)‐3 and ‐5 are increased in dermal and pulmonary fibrosis associated with the prototypic fibrosing disease systemic sclerosis (SSc), induce extracellular matrix (ECM) production, and promote fibrosis. We sought to examine the effects of another member of the family, IGFBP‐4, on ECM production and fibrosis using cell‐based, ex vivo organ culture and in vivo mouse lung fibrosis models. IGFBP‐4 mRNA levels were significantly decreased in pulmonary fibroblasts of patients with SSc. ECM components were significantly reduced by endogenous and exogenous IGFBP‐4. IGFBP‐4 also blocked TGF‐β–induced ECM production, and inhibited ECM production ex vivo in human lung and skin in organ culture. In vivo, IGFBP‐4 reduced bleomycin‐induced collagen production and histologic evidence of fibrosis. Silencing IGFBP‐4 expression to mimic levels observed in SSc lung fibroblasts resulted in increased ECM production. IGFBP‐4 reduced mRNA and protein levels of the chemokine receptor CXCR4 and the profibrotic factor CTGF. Furthermore, CTGF silencing potentiated the antifibrotic effects of IGFBP‐4. Reduced IGFBP‐4 levels in SSc lung fibroblasts may contribute to the fibrotic phenotype via loss of IGFBP‐4 antifibrotic activity.

Highlights

Systemic sclerosis (SSc) is a connective tissue disease characterized by vascular injury, immune system abnormalities, and organ fibrosis
We further reported that IGF binding proteins (IGFBP)‐5 induced pulmonary and dermal fibrosis in vivo and both proteins induced dermal fibrosis ex vivo in human skin maintained in organ culture[7,8]
Since IGFBP‐4 reduces baseline and transforming growth factor‐beta (TGF‐ß)– induced extracellular matrix (ECM) production and connective tissue growth factor (CTGF) is a mediator of the profibrotic effects of TGF‐ß,23,24 we examined the effect of IGFBP‐4 on CTGF

Summary

| INTRODUCTION

Systemic sclerosis (SSc) is a connective tissue disease characterized by vascular injury, immune system abnormalities, and organ fibrosis. We previously reported that two members of the IGFBP family of proteins, IGFBP‐3 and IGFBP‐5, induce ECM production and deposition and promote fibrosis in an IGF‐independent manner.[4,5,6] We further reported that IGFBP‐5 induced pulmonary and dermal fibrosis in vivo and both proteins induced dermal fibrosis ex vivo in human skin maintained in organ culture[7,8]. IGFBP‐5 exerted chemotactic activity and triggered epithelial to mesenchymal transition.[7,9] In contrast to IGFBP‐3 and IGFBP‐5, IGFBP‐4 did not promote fibrosis in our ex vivo skin model.[10] The reported activities of IGFBP‐4 have included its antiangiogenic and antitumorigenic activity in endothelial cells and glioblastoma cells,[11] respectively, which have been shown to be IGF independent.[12] In addition, Gimbel et al reported that intraperitoneal treatment of rats with IGFBP‐4 reduced tissue adhesions after abdominal surgery.[13] We sought to examine the effects of IGFBP‐4 on ECM production and fibrosis in our in vitro, in vivo, and ex vivo models of pulmonary fibrosis. The antifibrotic effects of IGFBP‐4 are mediated via downregulation of the chemokine stromal cell‐derived factor (SDF‐1) receptor C‐X‐C chemokine receptor 4 (CXCR4) and inhibition of connective tissue growth factor (CTGF)

| MATERIALS AND METHODS

| RESULTS

| DISCUSSION

Findings

CONFLICT OF INTEREST