Role of PI3K/Akt and MEK/ERK in mediating hypoxia-induced expression of HIF-1α and VEGF in laser-induced rat choroidal neovascularization

Purpose: The transcription factor hypoxia-inducible factor (HIF)-1 plays a central physiological role in oxygen and energy homeostasis and is activated during hypoxia by stabilization of the subunit HIF-1α. Hypoxia plays an important role in the development of choroidal neovascularization (CNV). Expression of HIF-1α has been demonstrated in CNV. Vascular endothelial growth factor (VEGF) is one of the most well-character-ized angiogenic factors in CNV, which is under the regulation of HIF-1. The aim of the present study was to explore the upstream signaling pathways involved in regulating hypoxia-induced expression of HIF-1α and VEGF in laser-induced rat CNV. Methods: A well-established rat model of CNV and cultured human retinal pigment epithelium (hRPE) was used to investigate the role of PI3K/Akt and MEK/ERK pathways in regulating HIF-1α and VEGF expression in CNV in rat and hRPE under hypoxia by immunohistochemistry, Western blot analysis, real-time PCR, and ELISA. Results: pAkt, pERK, HIF-1α, and VEGF were upregulated in vivo and in vitro. PI3K inhibitor (Ly294002) significantly de-creased pAkt activity and HIF-1α and VEGF expression in vivo and in vitro, whereas MEK inhibitor (PD98059) reduced ERK phosphorylation and the expression of VEGF but had no effect on HIF-1α. LY294002 and PD98059 severely inhibited the for-mation of CNV. Conclusions: The PI3K/Akt pathway was required for hypoxia-induced expression of HIF-1α and VEGF, whereas the MEK/ERK pathway was required only for VEGF in laser-induced rat CNV.