The Role of Insulin-Like Growth Factor Binding Protein 2 (IGFBP2) in the Regulation of Corneal Fibroblast Differentiation

PURPOSE. Previously, we reported that keratocyte-conditioned medium (KCM) facilitates the differentiation of human mesenchymal stem cells (hMSCs) into corneal keratocyte-like cells. This study is designed to investigate the roles of insulin-like growth factor binding protein 2 (IGFBP2) for the regulation of corneal fibroblast differentiation as a newly unveiled component of KCM. METHODS. Immunodot blot analysis was performed to identify the factors that are highly secreted, especially in KCM. Then, we investigated whether IGFBP2 differentiates hMSCs into keratocyte-like cells and whether maintains the phenotypes of keratocyte in human corneal fibroblasts (HCFs) by analyzing expression patterns of alpha-smooth muscle actin (alpha-SMA) and keratocyte markers including keratocan, lumican and aldehyde dehydrogenase 1 family member A1 (ALDH1A1). Furthermore, to specify the role of IGFBP2, the expression of a-SMA and keratocyte markers was determined in transforming growth factor beta 1 (TGF beta 1)-induced corneal myofibroblast and in HCFs after knockdown of IGFBP2. RESULTS. The most prominent factor in both KCM and amniotic membrane extract was IGFBP2. Insulin-like growth factor binding protein 2 increased the expression of IGFBP2, keratocan, and ALDH1A1, and decreased alpha-SMA expression in hMSCs and HCFs. Insulin-like growth factor binding protein 2 inhibited TGF beta 1-induced upregulation of alpha-SMA and increased expressions of keratocan and ALDH1A1 in HCFs. Furthermore, the knockdown of IGFBP2 increased alpha-SMA expression and decreased ALDH1A1 level in HCFs. CONCLUSIONS. Insulin-like growth factor binding protein 2 is strongly associated with restoration of keratocyte phenotype in HCFs. Our results show an important novel role of IGFBP2 in regulation of corneal fibroblast differentiation and suggest that IGFBP2 can be a therapeutic candidate for corneal antifibrotic strategy.