Glyoxalase-1 Over-expression in Retina Attenuates AGE Formation and Protects Against Diabetes-linked Pathology

Abstract

Purpose: : During diabetes many retinal cells show enhanced glycolytic metabolism which leads to high intracellular levels of the dicarbonyl methylglyoxal (MG) which is an important precursor for rapid formation of advanced glycation endproducts (AGEs). The glyoxalase (GLO) enzyme system (including enzymes GLO-1 and GLO-2) can detoxify MG to D-lacate and thus attenuate AGE formation. Using diabetes-induction in a transgenic rat model that over-expresses GLO-1 we have investigated if this enzyme can inhibit retinal AGE formation and prevent key components of diabetic retinopathy.

Methods: : Heterozygous transgenic animals were developed by over-expression of full length GLO-1 cDNA under control of the CMV enhancer/chicken β-actin promoter system. Diabetes was induced in wild-type (WT) and GLO-1 rats using Streptozotocin and the animals were sacrificed after 12 weeks of consistant hyperglycaemia. MG-derived AGEs were analysed (including Nε-(carboxyethyl)-lysine (CEL) and hydroimidazolone (MG-H1) in the retina of diabetic WT and GLO-1 rats with non-diabetic controls.

Results: : Ocular GLO-1 activity was ~25fold increased in the GLO-1 rats compared with WT littermates. GLO-1 over-expression prevented CEL and MG-H1 accumulation in the diabetic retina when compared to WT diabetic counterparts (p<0.01) while diabetes-mediated increases in GFAP activation in the Muller glia was significantly prevented by GLO-1 over-expression (p<0.05). GLO-1 diabetic animals showed less microglial infiltration and activation when compared to WT counterparts.

Conclusions: : This study has shown that MG accumulation in the diabetic retina is a significant source of AGEs. These adducts are linked to pathogenic pathways that may contribute to diabetic retinopathy.

Keywords: diabetic retinopathy • retinal degenerations: cell biology • retinal glia