Blocking VEGF signaling augments interleukin-8 secretion via MEK/ERK/1/2 axis in human retinal pigment epithelial cells

Aim: To identify proangiogenic factors engaged in neovascular age-related macular degeneration (AMD) except vascular endothelial growth factor (VEGF) from human retinal pigment epithelial (hRPE) cells and investigate the underlying mechanisms.

Methods: VEGF receptor 2 (VEGFR2/KDR/Flk-1) in ARPE-19 cells was depleted by siRNA transfection or overexpressed through adenovirus Infection. The mRNA and the protein levels of interleukin-8 (IL-8) in ARPE-19 cells were measured by quantitative real-time polymerase chain reaction and enzyme-linked immunosorbent assay respectively. The protein levels of Akt, p-AKT, MEK, p-MEK, ERK1/2, p-ERK1/2, JNK, p-JNK, p38 and p-p38 were detected by Western blotting. A selective chemical inhibitor, LY3214996, was employed to inhibit phosphorylation of ERK1/2. Cell viability was determined by MTT assay.

Results: Knockdown of VEGFR2/KDR/Flk-1 in ARPE-19 cells robustly augmented IL-8 production at both the mRNA and the protein levels. Silencing VEGFR2/KDR/Flk-1 substantially enhanced phosphorylation of MEK and ERK1/2 while exerted no effects on phosphorylation of Akt, JNK and p38. Inhibiting ERK1/2 phosphorylation by LY3214996 reversed changes in VEGFR2/KDR/Flk-1 knockdown-induced IL-8 upregulation at the mRNA and the protein levels with no effects on cell viability. VEGFR2/KDR/Flk-1 overexpression significantly reduced IL-8 generation at the mRNA and the protein levels.

Conclusion: Blockade of VEGF signaling augments IL-8 secretion via MEK/ERK1/2 axis and overactivation of VEGF pathway decreases IL-8 production in hRPE cells. Upregulated IL-8 expression after VEGF signaling inhibition in hRPE cells may be responsible for being incompletely responsive to anti-VEGF remedy in neovascular AMD, and IL-8 may serve as an alternative therapeutic target for neovascular AMD.