Abstract
Purpose: :
Fetal bovine serum (FBS) is a potent stimulator of cell proliferation in human retinal pigment epithelial cells (hRPE). Connective tissue growth factor (CTGF) is known to play a role in pathologic fibrosis. Studies have shown increased expression of CTGF in the retinas of patients with proliferative diabetic retinopathy (PDR), as well as in proliferative vitreoretinopathy (PVR). Since simvastatin, an antilipidemic agent, is shown to inhibit cell growth and profibrogenic marker expression, we studied the effect of simvastatin on FBS–stimulated hRPE growth and on CTGF expression in hRPE cells.
Methods: :
Primary hRPE cell cultures were established from human eyes obtained from the Michigan Eye Bank. Cells were allowed to grow to confluence and then incubated in media containing Ham’s F12 medium alone (control), and Ham’s F12 + FBS with or without simvastatin. Cell proliferation was measured by 3H–thymidine incorporation as well as the trypan blue exclusion method. Expression of CTGF was measured using 14C–methionine incorporation and immunoprecipitation with COOH terminal specific anti–CTGF. All values represent the mean ± SEM and differences between two groups of data were tested by Student’s t–test. A p<0.05 was used to assess significant differences between two groups.
Results: :
Fetal bovine serum stimulated 3H–thymidine incorporation in hRPE cells and increased cell number in a dose dependent manner. Simvastatin significantly inhibited 10% FBS–stimulated 3H–thymidine incorporation when compared with control (5714.96 ± 977.67 CPM ± SEM vs. 759.99 ± 88.39 CPM ± SEM, p<0.05, n=12). Fetal bovine serum also stimulated synthesis of immunoprecipitated 14C–methionine–CTGF in a dose dependent manner. Simvastatin significantly inhibited 10% FBS–stimulated 14C–methionine–CTGF synthesis when compared with control (6809.61 ± 1392.59 CPM ± SEM vs. 3797.60 ± 467.71 CPM ± SEM, p<0.05, n=12). Immunohistochemical studies confirm increased immunoreactivity of CTGF in hRPE cells exposed to FBS, and this increase was blocked by exposure to simvastatin.
Conclusions: :
FBS increases hRPE cell proliferation, as well as CTGF production. Simvastatin inhibits FBS–stimulated hRPE growth, and CTGF expression in FBS–stimulated hRPE cells. There are several compounds under investigation to prevent neovascularization in diabetic retinopathy but few have been studied for anti–fibrotic effects. Simvastatin may be a novel therapeutic agent in the prevention of fibrotic membrane formation in PDR.
Keywords: retinal pigment epithelium • diabetic retinopathy • signal transduction: pharmacology/physiology