Role of PI3K/Akt and MEK/ERK in Mediating Hypoxia-Induced Expression of Hypoxia-Inducible Factor 1alpha and Vascular Endothelial Growth Factor in Laser-Induced Rat Choroidal Neovascularization
Xiu Mei Yang 1,
Yu-sheng Wang 2,
Jian Zhang 3,
Yan Li 4,
Jian Feng Xu 1,
Jie Zhu 1,
Wei Zhao 1,
Da Ke Chu 5,
and
Peter Wiedemann 6
1 Department of Ophthalmology, Fourth Military Medical University, Xi'an, China
2 Department of Ophthalmology, Fourth Military Medical University, Xi'an, Shaanxi Province, China
3 Department of Biochemistry and Molecular Biology, Fourth Military Medical University, Xi'an, China
4 Department of Biochemistry and Molecular Biology, Fourth Military Medical University, Xi'an, Shaan Xi, China
5 Department of Gastrointestinal Surgery, Fourth Military Medical University, Xi'an, China
6 Eye Hospital, University of Leipzig, leipzig, Germany
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Abstract |
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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-1alpha. Hypoxia plays an important role in the development of choroidal neovascularization (CNV). Expression of HIF-1alpha has been demonstrated in CNV. Vascular endothelial growth factor (VEGF) is one of the most well characterized angiogenic factors in CNV, which is under the regulation of HIF-1. The aim of the current study was to explore the upstream signaling pathways involved in regulating hypoxia-induced expression of both HIF-1alpha and VEGF in laser-induced rat CNV.
METHODS. A well-established rat model of CNV and cultured human retinal pigment epithelium (hRPE) were used to investigate the role of PI3K/Akt and MEK/ERK pathways in regulating HIF-1alpha and VEGF expression in both CNV in rat and hRPE under hypoxia by immunohistochemistry, western blot, Real-Time PCR and ELISA.
RESULTS. pAkt, pERK, HIF-1alpha and VEGF were up-regulated both in vivo and in vitro. PI3K inhibitor (Ly294002) significantly decreased pAkt activity and HIF-1alpha and VEGF expression both in vivo and in vitro; While MEK inhibitor (PD98059) reduced ERK phosphorylation and the expression of VEGF, but had no effect on HIF-1alpha. Both LY294002 and PD98059 severely inhibited the formation of CNV.
CONCLUSIONS. PI3K/Akt pathway was required for hypoxia-induced expression of both HIF-1alpha and VEGF, whereas MEK/ERK pathway is only required for VEGF in laser-induced rat CNV.
Key Words:
phosphoinositide 3-kinase, retinal pigment epithelium, extracellular signal-responsive kinse, hypoxia-inducible factor 1 alpha, vascular endothelial growth factor, choroidal neovascularization
