Hyperglycemia-induced aggravation of neovascularization is induced by upregulation of the mTOR pathway

Abstract

Purpose : Neovascular retinopathies such as diabetic retinopathy (DR) and retinopathy of prematurity (ROP) are among the major causes of blindness in their respective age group. Despite the large number of affected patients, there is surprisingly a paucity of treatment options. For both DR and ROP, ablative procedures, particularly with laser coagulation, are a mainstay, despite the fact that significant areas of potentially functional retina are sacrificed for the sake of less neovascularization. Intravitreal anti-VEGF injections have revolutionized treatment; however, a significant number of patients do not benefit from this intervention and it does not address the root cause of neovascularization. Hyperglycemia changes metabolism and molecular signaling, yet no therapeutic intervention addresses this issue. We strived to elucidate how hyperglycemia may affect neovascularization in oxygen induced retinopathy (OIR).

Methods : Wild Type (WT) mice were injected with streptozotocin (STZ) (or PBS control) to induce hyperglycemia and both groups were subjected to oxygen-induced retinopathy (OIR) or room air control. At P12 and P17 mice were sacrificed and glucose and insulin levels recorded. Vaso-obliteration (VO) as well as neovascularization (NV) was quantified. Retinal changes without the influence of oxygen were examined at P10. mTOR and components of this pathway were measured using quantitative PCR and western blotting. Functional outcome was measured using ERG.

Results : At P12 the amount of VO was comparable between hyperglycemic and normoglycemic mice. This changed however at P17, when VO and NV were significantly increased in the hyperglycemic group. (STZ – WT VO: 2.0; NV: 1.5) Insulin levels were lower in the STZ group while glucose was upregulated. mTOR, S6K1 and 4E-BP1 were upregulated in STZ treated mice while IRS-1 was downregulated compared to the PBS injected control group. In vitro results confirmed this trend. The sensitivity of both a- and b-wave was attenuated in the hyperglycemic group.

Conclusions : MTOR is a crucial pathway in proliferation and growth of retinopathy. Hyperglycemic mice show more NV and worse functional outcome compared to controls. Our data suggest an important role for mTOR in hyperglycemic-exacerbated retinopathy making it a possible target for future therapies.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.