Pathophysiological Role Of Adrenomedullin-ramp2 System In Retinal Neovascularization

Abstract

Purpose: : Ischemic proliferative retinopathy, characterized by pathological retinal neovascularization, is a major cause of blindness. Adrenomedullin (AM) is an endogenous peptide first identified as a strong vasodilating molecule. We showed AM knockout mice (AM-/-) are embryonic lethal with abnormal vascular development and first proved AM also possesses angiogenic function. AM-receptor, CLR associates with one of the subtype of accessory proteins, RAMPs. We also showed among knockout mice of RAMPs, only RAMP2-/- are lethal with the similar phenotypes of AM-/-, suggesting AM-RAMP2 system is specifically important for angiogenesis. AM is also expressed in retina and strongly induced under ischemia. In this study, to clarify the pathophysiological roles of AM-RAMP2 system in retina, we analyzed oxygen-induced retinopathy (OIR) model using RAMP2 knockout mice.

Methods: : Wild-type C57BL/6 mice (WT) and heterozygotic RAMP2 knockout mice (RAMP2+/-) were exposed to 75% oxygen from postnatal day (P)7 to P12 and returned to room air. Both genotypes of mice, which were kept in room air, were used for control. Eyes were collected at P17 and mRNA was extracted from retinas to analyze the gene expression by quantitative real-time PCR. Retinal neovascularization, avascular area, and hypoxic area were analyzed using flat-mount specimens of retina stained with isolectin B4 and hypoxyprobe-1. Neovascularization was also assessed in retinal sections by HE staining.

Results: : Both in WT and RAMP2+/- retinas with OIR, AM expression was upregulated than those in room air. In the OIR, neovascularization in RAMP2+/- was significantly reduced than that in WT. On the other hand, there was no significant difference in avascular area and hypoxic area between WT and RAMP2+/-.

Conclusions: : We first found that AM-RAMP2 system is crucially involved in retinal pathological angiogenesis. Modulation of AM-RAMP2 signaling could be applied for the management of retinal neovascularization in future.

Keywords: retinal neovascularization • hypoxia