Abstract
Purpose: :
In ocular development, retinal physiological hypoxia in response to the retinal metabolic activity controls retinal vascular development, which is regulated by variable angiogenic factors. Herein, we demonstrated that hypoxia-induced IGF-II could contribute to retinal vascularization in ocular development.
Methods: :
In developing mouse, immunohistochemistry for IGF-II as well as immunofluorescence staining of IGF-II with vWF were performed. In human retinal microvascular endothelial cells (HRMEC), IGF-2 and VEGF expression were measured by RT-PCR and Western blot analysis under hypoxic condition (1%). To investigate IGF-2 induced regulation of VEGF expression in HRMEC, western blot analysis for VEGF, ERK-1/2, p-ERK-1/2, Akt, and p-Akt was performed with treatment of IGF-II. In addition, VEGF expression in HRMEC was evaluated under hypoxia with treatment of a blocking antibody to IGF-2 by RT-PCR and Western blot analysis. To confirm the direct angiogenic activity of IGF-II, angiogenesis assays of migration & tube formation was performed as well.
Results: :
In the developing retina, IGF-II expression appears to be predominant on retinal vessels, which was chronologically increased and peaked during active retinal angiogenesis similar to VEGF expression. Under hypoxic condition, IGF-II as well as VEGF was significantly up-regulated in HRMEC. In addition, IGF-II treatment could also increase VEGF expression in HRMEC. The VEGF expression induced by IGF-II was mediated by ERK-1/2 activation. Moreover, IGF-II strongly promoted angiogenic processes of migration and tube formation of HRMEC.
Conclusions: :
Our results provided that hypoxia-induced IGF-II may regulate retinal vascular development not only directly by IGF-II-mediated angiogenic activity, but also indirectly by IGF-II-induced VEGF expression. Therefore, the potential contribution of IGF-II to pathological retinal angiogenesis should be furthermore explored for the development of novel treatments to vaso-proliferative retinopathies.
Keywords: development • retinal neovascularization • growth factors/growth factor receptors