Quantitative Localization of IGF/Insulin System mRNA in Retinal Blood Vessels and Neurons during Oxygen-Induced Retinopathy in Mice

Abstract

Purpose: : The insulin/insulin-like growth factor system and associated binding proteins are implicated in the pathological angiogenesis of retinopathy of prematurity and diabetic retinopathy. Understanding the expression and localization of these molecules within the retina and under disease conditions is relevant to potential therapeutic manipulation.

Methods: : Retinopathy was induced in C57/Bl6 mouse pups (Taconic) by exposure to 75 % oxygen from postnatal day 7 to 12 followed by exposure to room air until sacrifice. RNA was isolated from samples enriched in the outer nuclear layer, inner nuclear layer, ganglion cell layer and endothelium by laser capture microdissection. cDNA was then created and assayed by quantitative real-time PCR for expression of target genes in the IGF/insulin system.

Results: : The prominent retinal receptor in the IGF-1/insulin family is Igf-1r (Igf-1r expression > 100 fold Ir) and is expressed primarily in photoreceptors and blood vessels. Igf-2 is the major retinal IGF-related growth factor (100-1000 fold > Igf-1) and is expressed in photoreceptors and vessels. Igfbp-3 mRNA expression increases > 5 fold with the induction of retinopathy, particularly in neovascular tufts. Igfbp-2,4,5 expression does not vary with retinal development or induction of retinopathy. Igfbp-1 and Igfbp-6 mRNA is upregulated in retinopathy but at low expression levels.

Conclusions: : This study of quantitative localization of IGF-family growth factors, receptors and binding proteins elucidates the local contribution of these molecules in the retina throughout development and in oxygen-induced retinopathy.

Keywords: retinal neovascularization • growth factors/growth factor receptors • ischemia