Effect of Connective Tissue Growth Factor (CTGF) on TGF–ß–induced Expression of Fibronectin EDA in RPE Cells

Abstract

Abstract: : Purpose: The alternatively spliced embryonic isoform of fibronectin (FN EDA) is one of the earliest extracellular matrix components expressed by RPE cells in response to injury. Previously, we demonstrated that TGF–ß2 induces the expression of FN EDA in a time– and dose–dependent manner. CTGF has been implicated in tissue fibrosis and is thought to mediate TGFß responses. Here we determine the effect of CTGF on TGF–ß2–induced FN EDA expression. Methods: Human fetal RPE cell cultures (passages 2–4) were treated with increasing concentrations of either TGF–ß2 alone or both TGF–ß2 and increasing concentrations of human recombinant CTGF (rhCTGF). FN EDA mRNA and protein expressions were analyzed at different time points by real–time PCR and Western blot, respectively. Results: rhCTGF synergistically enhanced TGF–ß2–induced FN EDA expression at both mRNA and protein levels. This effect was concentration–dependent and more evident at higher growth factor concentrations. rhCTGF alone had no significant effect on FN EDA expression. Conclusions: The concentration–dependent synergistic effect on FN EDA expression in rhCTGF and TGF–ß2 co–stimulated RPE cells suggests a critical role for CTGF in modulating TGF–ß responses.

Keywords: retinal pigment epithelium • extracellular matrix • growth factors/growth factor receptors