NEUROVASCULAR DEGENERATION FOLLOWING RETINAL ISCHEMIA REPERFUSION INJURY: ROLE OF ARGINASE 2

Abstract

Ischemic retinopathies such as retinopathy of prematurity, central retinal artery occlusion and diabetic retinopathy are leading causes of visual impairment and blindness. These pathologies share common features of oxidative stress, activation of inflammatory pathways and neurovascular damage. There is no clinically effective treatment for these conditions because the underlying mechanisms are still not fully understood. In the current study, we used a mouse model of retinal ischemia reperfusion (I/R) insult to explore the underlying mechanisms of neurovascular degeneration in ischemic retinopathies. The arginase enzyme utilizes the L-arginine amino acid for the production of L-ornithine and urea. Here, we investigated the role of the mitochondrial arginase isoform, arginase 2 (A2) in retinal I/R induced neurovascular injury. We found that retinal I/R induced neurovascular degeneration, superoxide and nitrotyrosine formation, glial activation, cell death by necroptosis and impairment of inner retinal function in wild type (WT) mice. A2 homozygous deletion (A2-/-) significantly protected against the neurovascular degeneration after retinal I/R. That was attributed to decreased oxidative stress and glial activation. A2 deletion protected against I/R induced retinal function impairment. Using Optical coherence tomography (OCT), we evaluated the retinal structure in live animals and found that A2-/- retinas showed a more preserved structure and less retinal detachment. To investigate the underlying mechanisms of A2 induced vascular damage after I/R, we used an in vitro model of oxygen glucose deprivation/ reperfusion (OGD/R) in bovine retinal endothelial cells (BRECs). Analysis of oxidative metabolism showed impaired mitochondrial function. We also found an increase in dynamin elated protein 1 (Drp1), a mitochondrial fission marker. Mitochondria labeling studies showed fragmented mitochondria after OGD/R. Arginase inhibition reduced mitochondrial fragmentation in OGD/R insult. This dissertation presents A2 as a new therapeutic target in reducing neurovascular damage in ischemic retinopathies.