Purpose: Native and oxidized (OX) low-density lipoprotein (LDL) may contribute to the pathogenesis of age related macular degeneration (AMD). In this study, we investigated the effects of lipoproteins, including LDL and ox-LDL, on cell viability, apoptosis, and vascular endothelial growth factor (VEGF) and pigment epithelium-derived factor (PEDF) expression in cultured human retinal pigment epithelial (RPE) cells.
Method: ARPE-19 cells were incubated with 10-100 mg/ml n-LDL, ox-LDL for 24 hr. Cell viability was assessed using the Cell Titer 96 Aqueous One Solution cell proliferation assay. The apoptosis of RPE was measured with TUNEL. Reverse transcription polymerase chain reaction (RT-PCR) was used to detect the levels of VEGF and PEDF mRNA in RPE cells. The expression of VEGF and PEDF protein was measured by western blotting. To examine the role of MAPK signal transduction in LDL- and OX-LDL-induced VEGF and PEDF protein expression, ARPE-19 cells were pretreated with one of several MAPK inhibitors for 2 hr and then incubated with native LDL or OX-LDL for 24 hr. One-way analysis of variance was used to compare the differences.
Results: OX-LDL treatment decreased ARPE-19 cell viability in a dose-dependent manner, whereas native LDL had no effect. Incubation of ARPE-19 cells with 10 mg/mL OX-LDL induced marked apoptosis, compared with untreated control cells. OX-LDL also increased VEGF expression and decreased PEDF expression, whereas native LDL had no significant effect. The VEGF-to-PEDF ratio was elevated after OX-LDL treatment. OX-LDL-induced VEGF protein synthesis was partly abolished by inhibiting p38 and JNK, while inhibiting ERK did not show a significant effect.
Conclusions: OX-LDL treatment induced cellular changes in ARPE-19 cells that appeared to reflect pathogenic events in neovascular AMD, providing potential insight into the roles of OX-LDL in human RPE cells and its potential role in the pathogenesis of AMD.