Effects of concentration of amyloid ß (Aß) on viability of cultured retinal pigment epithelial cells.

ABSTRACT

BACKGROUND: Amyloid beta (Aß) is a constituent of drusen that is a common sign of age-related macular degeneration (AMD). The purpose of this study was to investigate the effect of Aß on human retinal pigment epithelial (RPE) cells in culture. METHODS: Cells from a human RPE cell line (ARPE-19) were exposed to 0 to 25 µM of Aß 1-40 for 48 h, and the number of living cells was determined by WST-8 cleavage. Replicative DNA synthesis was measured by the incorporation of 5'-bromo-2'-deoxyuridine. The cell death pathway was investigated by the WST-8 cleavage assay after the addition of caspase-9 inhibitor, an anti-apoptotic factor. Real-time qRT-PCR was performed using Aß-exposed cellular RNA to determine the level of vascular endothelial growth factor (VEGF)-A and pigment epithelium derived factor (PEDF). To determine the effect of receptor-for-advanced glycation end products (RAGE), the siRNA for RAGE was inserted into ARPE-19 treated with Aß, and the levels of expression of VEGF-A and PEDF were determined. RESULTS: The number of living ARPE-19 cells was increased by exposure to 5 µM Aß but was decreased by exposure to 25 µM of Aß. Replicative DNA synthesis by ARPE-19 cells exposed to 25 µM of Aß was significantly decreased indicating that 25 µM of Aß inhibited cell proliferation. Real-time RT-PCR showed that the level of the mRNA of PEDF was increased by exposure to 5 µM Aß, and the levels of the mRNAs of PEDF and VEGF-A were also increased by exposure to 25 µM Aß. The addition of an inhibitor of caspase-9 blocked the decrease the number of ARPE-19 cells exposed to 25 µM Aß. Exposure to si-RAGE attenuated the increase of VEGF-A and PEDF mRNA expression in ARPE-19 exposed to Aß. CONCLUSIONS: Exposure of ARPE-19 cells to low concentrations of Aß increases the level of PEDF which then inhibits the apoptosis of ARPE-19 cells leading to RPE cell proliferation. Exposure to high concentrations of Aß induces RPE cell death and enhances the expression of the mRNA of VEGF-A in RPE cells. The Aß-RAGE pathway may lead to the expression VEGF-A and PEDF in RPE cells. These results suggest that Aß is strongly related to the pathogenesis of choroidal neovascularization.