Inhibitor of Differentiation Gene: Expression, Localization and Role in Human Cornea

Abstract

Purpose : Inhibitor of differentiation (Id) genes are DNA-binding transcription factors and shown to regulate cell proliferation, migration, angiogenesis and fibrosis. The expression and role Id genes in the cornea are still unknown. We sought to characterize the expression of Id proteins and their interactions with the profibrotic cytokine transforming growth factor β1 (TGFβ1) and anti-fibrotic cytokine bone morphogenic protein 7 (BMP7) in human cornea.

Methods : Human donor corneas procured from Eye Bank were used. Id proteins were localized in human corneal sections using immunofluorescence. Primary cultures of human corneal fibroblasts (HCF) were established and treated with either TGFβ1 (5ng/ml) or BMP7 (10ng/ml) for 24 hrs in serum free medium. Expression of Id’s in response to TGFβ1, BMP7 and TGFβ1+BMP7 was measured with qPCR and immunoblotting.

Results : All three major cell types of human cornea expressed Id1-4 genes. Id1 and Id2 proteins were ubiquitously expressed in epithelial cells and stromal keratocytes in the human cornea with Id1 predominantly in basal epithelial cells. The Ids were differentially regulated with TGFβ1 and BMP7 in a time dependent manner. Id proteins are exclusively expressed in human corneal fibroblasts but not in human corneal myofibroblasts. TGFβ1 and BMP7 regulated Id gene expression at different time points. Treatment of TGFβ1 to HCF showed a significant increase in Id1, Id2 and Id4 at earlier time point (2h; Id1, p<0.001; Id2, p<0.01 and Id4, p<0.001) followed by a decrease in mRNA expression at late time points (12h, 24h, and 48h). Contrary to this, BMP7 treatment showed a gradual increase in the expression of Id1 (24h p<0.005; 48h p<0.001), Id2 (24h p<0.01) and Id3 (48h p<0.001) in a time-dependent manner. Combined treatment of TGFβ1+BMP7 to HCFs showed a significant increase in Id1, Id3 and Id4 expression.

Conclusions : Id genes are expressed in human cornea and play vital role in corneal wound healing and fibrosis development by regulating TGFβ1 and BMP7 activities. Id genes can be a target for restoring and maintaining corneal transparency.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.