Pathophysiological roles of endogenous calcitonin gene-related peptide in mouse model of laser induced choroidal neovascularization.

Abstract

Purpose: Calcitonin gene-related peptide (CGRP) is a neuropeptide that has a variety of physiological functions. Recently, angiogenic potency of CGRP is reported in tumor angiogenesis model. We also reported the angiogenic potency of endogenous CGRP in eye using oxygen-induced retinopathy model in CGRP knockout mice (ARVO 2013). On the other hand, CGRP is also involved in the regulation of inflammation; CGRP directly acts on macrophages and regulate their production of cytokines. Choroidal neovascularization (CNV) is a common symptom of age-related macular degeneration (AMD). In the pathophysiology of CNV, both angiogenic and inflammatory molecules play important roles. In the current study, we analyzed the pathophysiological roles of endogenous CGRP in CNV by introducing laser-induced CNV in CGRP knockout mice.

Methods: CNV was induced by laser photocoagulation (200mW, 50μm, 50msec). Four laser burns were placed in eyes of wild-type C57BL/6 mice (WT) and homozygous knockout mice of CGRP (KO). Fourteen days after laser injury, fluorescein angiography (FA) was performed. Areas of CNV were determined in retinal pigment epithelium-choroid-sclera (choroidal) flat mounts using perfused fluorescein-labeled dextran. Macrophage infiltration was evaluated by immunostaining of choroidal flat mounts on Day 7. F4/80 positive cells around CNV were counted.

Results: Significantly larger CNV lesions with greater leakage on FA developed in KO(23458±1679µm2) compared to WT(17232±1122µm2) on day14. Laser photocoagulation scar area was not different between KO and WT. KO mice showed increased infiltration with F4/80-positive cells around the laser irradiated area in comparison with WT.

Conclusions: Endogenous CGRP suppresses the development of CNV thorough regulation of macrophage infiltration and inflammation. CGRP could be a promising therapeutic target of AMD.

Keywords: 412 age-related macular degeneration • 453 choroid: neovascularization