Regulation of cell-mediated collagen gel contraction in human retinal pigment epithelium cells by vascular endothelial growth factor compared with transforming growth factor-β2.

Background: To explore the potential role of vascular endothelial growth factor compared with transforming growth factor-beta 2 in the regulation of human retinal pigment epithelium cell-mediated collagen gel contraction. Methods: The retinal pigment epithelium cell mediated type I collagen gel contraction assay was performed to evaluate and compare the effect of vascular endothelial growth factor and transforming growth factor-beta 2. The number of viable retinal pigment epithelium cells in the gel and the expression of a-smooth muscle actin were analysed. Results: Both vascular endothelial growth factor and transforming growth factor-beta 2 caused a time dependent gel contraction, associated with over expression of alpha-smooth muscle actin in retinal pigment epithelium cells undergoing a fibroblast like transformation. The decrease in volume of the collagen gel and increase in alpha-smooth muscle actin expression were more significant in the transforming growth factor-beta 2-treated group than in vascular endothelial growth factor-treated group beginning at day 2, and the growth of retinal pigment epithelium cells was significantly more inhibited in the transforming growth factor-beta 2-treated group compared with the vascular endothelial growth factor-treated group after day 1 (P < 0.05). Transforming growth factor-beta 2 stimulation increased both vascular endothelial growth factor mRNA expression and secretion. The alpha-smooth muscle actin expression and the change in volume of collagen gel were significantly positively correlated in both experimental groups. Conclusions: Both vascular endothelial growth factor and transforming growth factor-beta 2 can cause induction of retinal pigment epithelium cell-mediated collagen gel contraction in vitro via partial upregulation of alpha-smooth muscle actin expression.