Inflammatory cytokines combined with hyperglycemia induces retinopathy phenotypes in Ins2^Akita mice

Abstract

Purpose : Diabetic retinopathy (DR) is the leading cause of blindness in working-age adults. The Ins2^Akita mouse is a spontaneous Type I diabetic mouse model, and based on previous work with this model, hyperglycemia alone does not induce pathological changes relevant to late stage DR phenotypes. TNFα and IL-6 have been shown to be increased in the vitreous of DR patients. Therefore, we sought to discover if hyperglycemia in addition to constant ocular expression of pro-inflammatory cytokines would induce advanced DR phenotypes, and give us a better understanding of the role of these cytokines in diabetic retinopathy.

Methods : Heterozygous male diabetic Ins2^Akita and wild-type, age-matched littermate wildtype (WT) mice (n= 15 WT, 21 Ins2^Akita diabetic mice; 6-8 weeks age) on a C57BL/6J background were injected with adenovirus expressing AAV2-Null, AAV2-sCMV-TNFα or AAV-sCMV-IL6 intravitreally (IVT). The dose of adenovirus for AAV2-Null and AAV2-IL6 was 5x10⁸ vector genomes (vg) per eye, and the dose for AAV2-TNFα was 1x10⁸ vg per eye. Vascular leakage was quantified at 4, 8, and 12 weeks post-IVT using scanning laser ophthalmoscopy (SLO) and MatLab software. Morphologic changes were observed via histopathology, and cytokine and chemokine levels in whole eyes were measured at 6 weeks post-IVT.

Results : AAV2-TNFα induced significant vascular leakage in WT mice compared to AAV2-Null at 8 and 12 weeks post-IVT (p = 0.004 and p < 0.0001), with a trend of increased leakage in diabetic mice at these time points. AAV2-IL6 did not induce vascular leakage at any time points measured in WT mice, but showed a trend of increased leakage in diabetic mice at 12 weeks post-IVT. Histopathology showed retinal edema, retinal folding and significant cellular infiltrates in only diabetic mice treated with AAV2-TNFα compared to WT mice. Diabetic mice treated with AAV2-IL6 showed an increase in cellular infiltrates compared to WT. Increased expression of various cytokines and chemokines was observed in AAV2-TNFα treated mice compared to AAV2-Null 6 weeks post-IVT, specifically TNFα, GRO/KC, MCP-1, VCAM and VEGF. Eyes from diabetic mice compared to WT mice treated with AAV2-IL6 showed significant increases in both IL-1β and IFNγ.

Conclusions : Chronic exposure of both pro-inflammatory cytokines TNFα and IL6 in combination with hyperglycemia induced late-stage diabetic retinopathy phenotypes in mice.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.