Apelin Is Required For Non-sprouting Vascular Remodelling In The Developing And Pathogenic Retina

Abstract

Purpose: : Sprouting angiogenesis and non-sprouting vascular remodelling occur during retinal vascular development and frequently accompany retinal degeneration. The molecular mechanisms that distinguish the latter, however, are poorly understood. The objective of this study was to identify novel regulators of non-sprouting vascular remodelling.

Methods: : Gene expression profiling of control vessels and remodelled vessels derived from the retinas of the dystrophic Royal College of Surgeons (RCS) rat and Retinal Dystrophy (RD)1 mouse was carried out using Affymetrix microarray analysis. Differentially expressed genes were validated by quantitative PCR, western blot analysis and immunohistochemistry. Vascular structure was determined using retinal whole mounts stained for vascular markers and imaged by epifluorescence and confocal microscopy. Choroidal neovascularisation was induced by laser burns to the retina and neovascularisation evaluated by fluorescein angiography.

Results: : Gene profiling revealed significant changes in 60 genes in remodelled vessels derived from both the RCS rat and RD1 mouse. Of these apelin (APLN), and its receptor (APLNR), were significantly upregulated. In Apln-null mutant mice developmental retinal angiogenesis was largely normal. Similarly, deletion of APLN had no effect on laser-induced choroidal neovascularisation or intraretinal neoangiogenesis, as observed in the very low density lipoprotein receptor (Vldlr)-null mutant mouse. In contrast, the absence of APLN severely attenuated developmental remodelling of retinal radial veins, and in RD1 mice substantially reduced retinal vascular telangiectasia.

Conclusions: : APLN impacts minimally on sprouting retinal angiogenesis but contributes significantly to developmental and pathogenic non-sprouting vascular remodelling.

Keywords: neovascularization • retina • retinal neovascularization