An Angiogenic Role Of Adrenomedullin In Choroidal Neovascularization

Abstract

Purpose: : Adrenomedullin (ADM) takes part in physiologic and pathologic angiogenesis. This study investigated if ADM signaling is involved in choroidal neovascularization (CNV) in a mouse model.

Methods: : CNV was induced by laser photocoagulation in 8-week-old C57BL/6 mice. ADM mRNA expression in the choroid-RPE complex was evaluated by quantitative RT-PCR (qPCR) on days 0, 2, 4, 7 after laser treatment (n=3, respectively). To confirm the expression of ADM receptor (ADM-R) component (CRLR, RAMP2 and RAMP3) in vascular endothelial cells (ECs), we performed qPCR on CD31⁺ CD45^- cells that were sorted from laser treated or non-treated eye (n=8). We also evaluated the effect of ADM antagonist, ADM (22-52) in laser-induced CNV. We intravitreously injected 0.1 or 1mM ADM (22-52) or vehicle on days 0 and 3 after laser treatment and assessed the CNV size with choroidal flat-mount immunochemical staining for CD31 on day 7 (n=16).

Results: : The amount of CRLR, RAMP2 and RAMP3 mRNA were more than three times higher in CD31⁺ CD45^- ECs than CD31^- CD45^- non-ECs, while no significant difference was detected between the laser treated and non-treated group. In contrast, ADM mRNA expression significantly increased after laser treatment, peaking at 4 days after treatment. The mean CNV sizes in 0.1mM ADM (22-52), 1mM ADM (22-52) and vehicle-treated eyes were 22040, 35953, and 42314 μm², respectively. Intravitreal injection of 1mM ADM (22-52) significantly reduced the CNV size compared with vehicle-treated control eyes (p<0.001).

Conclusions: : ADM signaling was involved in CNV formation, i.e., ADM-R expression was higher in ECs compared with non-ECs and ADM expression increased during CNV formation. Moreover, the ADM antagonist significantly inhibited CNV formation. Suppression of ADM signaling might be a valuable alternative treatment for CNV associated with age-related macular degeneration.

Keywords: choroid: neovascularization • retina • age-related macular degeneration