Oxidized LDL induces apoptosis of human retinal pigment epithelium through activation of ERK-Bax/Bcl-2 signaling pathways.

PURPOSE: Retinal pigment epithelium (RPE) cell dysfunction and death play a vital role in the pathogenesis of age-related macular degeneration (AMD). We previously reported that oxidized low-density lipoprotein (OX-LDL) induces retinal degeneration in vivo. In this study, we investigated the role of the ERK-Bax/Bcl-2 signaling pathways in OX-LDL-induced apoptosis in human RPE.

METHODS: ARPE-19 cells were incubated with 10-100 mg/mL n-LDL or OX-LDL for 24 h. Cell viability was assessed using the Cell Titer 96 Aqueous One Solution cell proliferation assay. RPE apoptosis was measured with a flow cytometer. Reverse transcription polymerase chain reaction was used to detect Bcl-2 and Bax mRNA levels in RPE cells. Bcl-2 and Bax protein expression was measured by western blotting. Activation of extracellular signal-regulated kinase (ERK) protein was evaluated by western blot analysis. One-way analysis of variance was used to compare differences.

RESULTS: OX-LDL treatment decreased ARPE-19 cell viability in a dose-dependent manner, whereas n-LDL had no effect. Compared with the control group, OX-LDL significantly increased the apoptosis of RPE, 10 mg/mL, 50 mg/mL, 100 mg/mL apoptosis rate was 6.43 ± 0.19%, 5.12 ± 0.27%, 5.53 ± 0.35%, respectively. OX-LDL also increased Bcl-2 expression and decreased Bax expression significantly. The Bcl-2 to Bax ratio was elevated after OX-LDL treatment. Inhibition of ERK downregulated Bax and was associated with RPE apoptosis.

CONCLUSIONS: Our data suggest that apoptosis induced by OX-LDL in RPE partly depends on Erk-Bax/Bcl-2 signaling pathway activation. These results may provide further information regarding the effects of OX-LDL in human RPE and their potential role in AMD pathogenesis.