(6) The Impact of Anemia on the Ang-Tie System of Vascular Remodeling in a Rat Model of Oxygen-induced Retinopathy

Husaam Qureishy, University of Minnesota Medical School, Eagan, MN, United States; Mandkhai Molomjamts, University of Minnesota, United States; Ellen Ingolfsland, University of Minnesota Medical School, United States

Background: Retinopathy of Prematurity (ROP) is a disease that affects about 14,000 preterm infants per year in the United States, occurring in 66% of infants that weigh 1,250 g or less and 82% infants that weigh 1,000 g or less at birth. ROP is known to cause abnormal neovascular growth within the retina, which can eventually lead to blindness if not treated. While preterm infants are under intensive care, they experience several comorbidities and therapies. One such comorbidity is anemia, which, according to retrospective epidemiological studies, have been found to have both a positive and negative relationship between its presence and the risk of ROP.

The angiopoietin/Tie receptor tyrosine kinase pathway is involved in neonatal vascular development primarily through its role in angiogenesis. Angiopoietin-1 (Ang-1) and Angiopoietin-2 (Ang-2) are ligands that competitively bind to the Tie-2 receptor. Ang-1 induces vessel maturation and normal vessel development whereas Ang-2, in conjunction with VEGF, promotes increased vascular permeability and neovascularization. Due to their large role in retinal vascular development, Ang-1 and Ang-2 have been implicated in the development of ROP.

Objectives: To determine the effect of anemia in an oxygen induced retinopathy (OIR) model on the change of mRNA expression of Tie-1, Tie-2, Ang-1, and Ang-2.

Design/Methods: Retinopathy was induced with the 50/10 OIR model in Sprague Dawley rat pups. Anemia was induced by phlebotomy to a hematocrit of 18-20%, a 50% reduction from baseline hematocrit. Rats were euthanized at P20 and retinas from 5-6 pups/group underwent RNA extraction, cDNA synthesis, and quantitative polymerase chain reaction (qPCR) with Ang-1, Ang-2, Tie-1, and Tie-2.

Results: Anemic rats treated with the 50/10 OIR model were found to have statistically significant differences in the expression of Ang-2, Tie-1, and Tie-2 showing increases of 2-fold (p=0.000297), 1.5-fold (p=0.0199), and 1.5-fold (p=0.0123) respectively, compared to non-anemic OIR control pups. Anemic rats reared in room air showed no significant change in the same proteins. Protein confirmation by western blot is pending as are retinal flatmounts to measure change in neovascular and avascular area.

Conclusion: Increased expression of Ang-2 and Tie2 in the presence of unchanged Ang1 in 50/10 OIR treated anemic rats suggests that anemia may promote retinal neovascularization. Protein and anatomical outcomes will provide additional clarity.