Insulin–Like Growth Factor Binding Protein–3 Promotes Vessel Survival and Re–Growth of Mouse Retinal Vessels After Hyperoxia–Induced Loss

Abstract

Purpose: : The insulin–like growth factor (IGF) family mediate signaling that is key to regulation of cell survival, differentiation and apoptosis. IGF–1 binding protein–3 (IGFBP–3) has IGF–1 dependent and independent functions. IGFBP–3 has been minimally studied in vivo and may have a regulatory role in angiogenesis in diabetes, ROP and cancer. We examined the role of IGFBP–3 on vascular survival and regrowth in the retina in the mouse model of oxygen–induced retinopathy.

Methods: : To evaluate the effect of high IGFBP–3 on vessel re–growth C57 Bl/6 mice were exposed to 75% oxygen (P7– P12), then given 60µg /d IGFBP–3 or vehicle (P12–P14). Retinas were isolated at P15 for total RNA or area of revascularization. To evaluate the effect of low IGFBP–3 on vessel re–growth IGFBP–3 transgenic and wt sibling mice were exposed to oxygen P7–P12 and area of vessel regrowth evaluated at P17. Serum IGF–I was measured in IGFBP–3 transgenic sibling mice. To evaluate the effect of IGFBP–3 on vessel loss with oxygen exposure transgenic and wt sibling mice were exposed to oxygen from P7–P8 for 18 hours and retinas evaluated for vessel loss.

Results: : There was no difference in serum IGF–1 levels between IGFBP–3^+/+, IGFBP–3^–/–, and IGFBP–3^+/– mice. At P15 there was a 40% increase in vessel regrowth in C57Bl/6 mice treated with IGFBP–3 compared to vehicle control treated mice indicating that IGFBP–3 promotes vessel regrowth. At P17 there was a 31% decrease in retinal vessel regrowth (P<0.005) in the IGFBP–3^–/– compared to IGFBP–3^+/+ mice indicating decreased vessel re–growth with decreased IGFBP–3 confirming the result with high IGFBP–3. IGFBP–3 treatment was associated with a 20% suppression of eNOS mRNA and nNOS mRNA in retina. At P 8 after oxygen exposure there was a IGFBP–3 dose dependent increase in survival with increasing IGFBP–3 in transgenic mice.

Conclusions: : IGFBP–3 appears to help prevent oxygen–induced vessel loss and to promote vascular re–growth after vascular destruction. This effect appears to be independent of IGFBP–3 binding to IGF–1. The effect on vessel survival and regrowth is consistent with eNOS mRNA suppression. Treatment with IGFBP–3 in ROP or diabetes is consistent with promotion of retinal vessel survival and prevention of proliferative retinopathy

Keywords: diabetic retinopathy • growth factors/growth factor receptors • neovascularization