Endothelial arginase 2 mediates retinal ischemia/reperfusion injury by inducing mitochondrial dysfunction

Abstract

Objective Retinal ischemic disease is a major cause of vision loss. Current treatment options are limited to late-stage diseases, and the molecular mechanisms of the initial insult are not fully understood. We have previously shown that the deletion of the mitochondrial arginase isoform, arginase 2 (A2), limits neurovascular injury in models of ischemic retinopathy. Here, we investigated the involvement of A2-mediated alterations in mitochondrial dynamics and function in the pathology. Methods We used wild-type (WT), global A2 knockout (A2KO-) mice, cell-specific A2 knockout mice subjected to retinal ischemia/reperfusion (I/R), and bovine retinal endothelial cells (BRECs) subjected to an oxygen-glucose deprivation/reperfusion (OGD/R) insult. We used western blotting to measure levels of cell stress and death markers and the mitochondrial fragmentation protein, dynamin related protein 1 (Drp1). We also used live cell mitochondrial labeling and Seahorse XF analysis to evaluate mitochondrial fragmentation and function, respectively. Results We found that the global deletion of A2 limited the I/R-induced disruption of retinal layers, fundus abnormalities, and albumin extravasation. The specific deletion of A2 in endothelial cells was protective against I/R-induced neurodegeneration. The OGD/R insult in BRECs increased A2 expression and induced cell stress and cell death, along with decreased mitochondrial respiration, increased Drp1 expression, and mitochondrial fragmentation. The overexpression of A2 in BREC also decreased mitochondrial respiration, promoted increases in the expression of Drp1, mitochondrial fragmentation, and cell stress and resulted in decreased cell survival. In contrast, the overexpression of the cytosolic isoform, arginase 1 (A1), did not affect these parameters. Conclusions This study is the first to show that A2 in endothelial cells mediates retinal ischemic injury through a mechanism involving alterations in mitochondrial dynamics and function.

Novel Therapeutics for Diabetic Retinopathy and Diabetic Macular Edema: A Pathophysiologic Perspective

“…Nuclear factor erythroid 2-related factor 2 (Nrf2) is a novel potential target that upregulates transcription of antioxidant proteins and has shown great promise in the treatment of retinal diseases (Nakagami, 2016). Finally, our group has demonstrated the complex roles of the arginase isoforms in the development and progression of DR, illustrating the potential therapeutic benefit of targeting these enzymes in diseases that impact the neurovasculature (Patel et al, 2013;Caldwell et al, 2015;Shosha et al, 2016Shosha et al, , 2021Atawia et al, 2020).…”

“…In contrast to Arg1, global or EC-specific deletion of Arg2 in mice results in reduced oxidative and nitrative stress, decreased neurovascular damage, and absence of glial activation in the retina after I/R injury (Shosha et al, 2016(Shosha et al, , 2021. In both the I/R in vivo model and in EC exposed to oxygen and glucose deprivation/reperfusion (OGD/R), Arg2 mRNA and protein expression were markedly increased (Shosha et al, 2016(Shosha et al, , 2021. Furthermore, overexpression of Arg2 in EC subjected to OGD/R resulted in increased mitochondrial dysfunction and fragmentation, and amplified cell stress and apoptosis (Shosha et al, 2021).…”

“…In both the I/R in vivo model and in EC exposed to oxygen and glucose deprivation/reperfusion (OGD/R), Arg2 mRNA and protein expression were markedly increased (Shosha et al, 2016(Shosha et al, , 2021. Furthermore, overexpression of Arg2 in EC subjected to OGD/R resulted in increased mitochondrial dysfunction and fragmentation, and amplified cell stress and apoptosis (Shosha et al, 2021). Interestingly, pan-arginase inhibition in EC with ABH resulted in inhibition of OGD/R-induced cell stress but did not promote cell survival.…”

Current and Novel Therapeutic Approaches for Treatment of Diabetic Macular Edema

“…The increased shunting of glucose through the hexosamine pathway has been shown to promote insulin resistance as well as injury and inflammation by inducing the expression of nuclear factor κB (NF-κB)-dependent genes [ 23 ]. More recently, the upregulation of arginase, an enzyme that catalyzes L-ornithine and urea from L-arginine, has been linked to oxidative stress and peripheral vascular dysfunction in diabetes [ 24 , 25 , 26 ]. Another recent work utilizing a quadra-omics approach (proteomics, lipidomics, metabolomics, and transcriptomics) examined blood samples from patients with Type 1 DM and discovered the activation of TGF-β, VEGF, NF-κB, and arginase with the inhibition of miRNA Let-7a-5p [ 27 ].…”

Arginase: shedding light on the mechanisms and opportunities in cardiovascular diseases

“…In ECs, expression of ARG1 can be stimulated by thrombin [ 47 ], oxidative species, NADPH oxidase 2 [ 49 ], and tumor necrosis factor-alpha (TNF-α) [ 48 ], while ARG2 can be regulated by hypoxia [ 50 ], ET-1 [ 51 ], oxidized low-density lipoprotein [ 52 ], oscillatory shear stress [ 53 ], and aging [ 54 ]. Both ARG1 and ARG2 in ECs have been demonstrated to be involved in the regulation of NO production and vasodilation [ 55 , 56 ]. Arginase was also found to be present in VSMCs [ 57 ].…”