Angiogenic potency of endogenous calcitonin gene-related peptide (CGRP) in mouse model of oxygen-induced retinopathy

Abstract

Purpose: Calcitonin gene-related peptide (CGRP) is a neuropeptide that has a variety of physiological functions. Because of its similar structure, CGRP has been identified as a family peptide of Adrenomedullin (AM), which is a well-known angiogenic factor. CGRP and AM share the same receptor, calcitonin-receptor-like receptor (CLR), which associates with one of the accessory proteins, called receptor activity-modifying proteins (RAMPs). By interacting with RAMP1, CLR exhibits a high affinity for CGRP, whereas by interacting with either RAMP2 or -3, CLR exhibits a high affinity for AM. We have been reported that AM-RAMP2 system plays a critical role in retinal angiogenesis (ARVO 2011, 2012). Recently, as well as AM, angiogenic potency of CGRP is reported in tumor angiogenesis model. However, angiogenic potency of CGRP in retina remains to be elucidated. In the current study, we analyzed the role of endogenous CGRP in retina by oxygen-induced retinopathy (OIR) model using CGRP knockout mice.

Methods: Homozygous knockout mice of CGRP (KO) and wild-type C57BL/6 mice (WT) at postnatal day 7 (P7) were exposed to 75% oxygen for 5 days (P12) and allowed to recover in room air to induce retinal neovascularization. In flat-mount specimens of retina stained with isolectin B4, avascular area and preretinal neovascularization were quantified.

Results: In physiological angiogenesis, the number of branches and vascular density were not different between KO and WT neonates. In OIR model, retinal avascular area was not different between KO and WT. Preretinal neovascularization in KO was slightly decreased compared with WT. In both avascular area and neovascularization, variation among individuals was notably observed in KO.

Conclusions: The study of knockout mice first clarified the difference in retinal angiogenesis between endogenous AM and CGRP. Compared with AM-RAMP2 system, involvement of CGRP in retinal neovascularization appears to be low.

Keywords: 700 retinal neovascularization