Hyperglycemia prolongs severe retinopathy in the OIR mouse model

Abstract

Purpose: Among the most common causes of blindness are Retinopathy of Prematurity (ROP) and Diabetic Retinopathy (DR). Although ROP and proliferative DR manifest at different ages, it is known that insulin plays a role in both diseases, with recent studies suggesting an inverse association of insulin levels and gestational age in preterm infants. In addition, higher glucose levels were observed in preterm infants when compared to term infants, implying a form of insulin resistance, which may be similar to that found in Type 2 diabetics. We therefore studied the effects of insulin and glucose homeostasis in a well-established mouse model of ROP, the oxygen-induced retinopathy model (OIR).

Methods: Wild-type mice (S129) were injected with either streptozotocin (STZ) or PBS for several days after birth and exposed to OIR. Another group was sent through oxygen (OIR) and given insulin at multiple time-points after post-natal day (P)12. We recorded glucose levels and bodyweight and analyzed the extent of retinal vessel obliteration (VO) and neovascularization (NV) from P17-P25. We also measured serum IGF-1, liver FGF-21, and retinal VEGF, PlGF, TNFa and IL-6 levels. Claudin-5 and Occludin were measured as they are important factors in the integrity of the blood retina barrier and their reduction is associated with the development of macular edema in diabetic retinopathy.

Results: Higher glucose levels in mice given STZ resulted in lower levels of FGF-21 (1:2) and IGF-1 (1:4), with increased VO (STZ 15.51% vs. Ctrl 13.75%) and NV (STZ 8.4% vs. Ctrl. 6.79%) at P17 when compared to controls. NV was still detectable at P25 in mice given STZ but not in PBS controls (STZ 5.54% vs. Ctrl 0.25%). Retinal levels of VEGF, PlGF, TNFa and IL-6 had a trent to be higher expressed at P25 but were not significantly different in STZ treated mice compared to PBS injected controls. Mice treated with insulin after OIR also displayed significantly less severe NV at P17 compared to untreated controls. Claudin-5 and Occludin were lower expressed in STZ injected mice. (Occludin: STZ 2x higher; Claudin-5: STZ 1.2x higher)

Conclusions: Our data confirm the clinical association of higher glucose levels at birth in preterm infants with a higher risk of ROP development and a more severe course of retinopathy. Our suggested model of OIR and STZ will allow us to study the mechanisms that are associated with prolonged and pronounced retinopathy in preterm births.