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Abdelrahman Fouda, Zhimin Xu, Esraa Shosha, William Caldwell, S. Priya Narayanan, Ruth B Caldwell; Protective Role of Arginase 1 in Retinal Ischemia Reperfusion Injury. Invest. Ophthalmol. Vis. Sci. 2017;58(8):5895.
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© ARVO (1962-2015); The Authors (2016-present)
Studies from our lab and others have demonstrated the involvement of the arginase enzyme in different neurovascular diseases. Arginase competes with nitric oxide synthase (NOS) enzymes in endothelial cells (eNOS) leading to endothelial dysfunction and in myeloid cells (iNOS) thus promoting a reparative phenotype. We have recently shown that the mitochondrial isoform, arginase 2 (A2), has a key role in retinal ischemia/reperfusion (IR) injury. Here we aimed to examine the role of the cytosolic isoform A1 in retinal IR injury.
Wild type (WT), A1+/- knock out (KO), endothelial (Cdh5-cre;A1f/f) KO, and myeloid specific (LysM-cre;A1f/f) KO mice were subjected to retinal IR (40 min, right eye - left eye served as sham control). A cohort of WT mice were treated with intravitreal injection of pegylated A1 or PBS 3h before IR. Another cohort of WT mice received clodronate or control liposomes (200 uL, i.p., 1 d before and 3 d after IR) to deplete systemic monocytes/macrophages. Retinas were collected at different time points for analysis. Neurodegeneration and microglia/macrophage activation were analyzed at 7 d using NeuN and Iba-1 flat-mount staining followed by confocal microscopy. Vascular injury was assessed by acellular capillary formation. Necrotic cell death was studied by propidium iodide (PI) labelling and western blot for RIP3.
A1 deletion exacerbated IR-induced neuronal and vascular injury as measured by reduced NeuN positive cells and increased acellular capillaries by 50 % (p<0.05, n=4-6). Furthermore, A1+/- mice showed reduced retinal thickness (H&E stain) by 5% (p<0.05, n=4-5) and increased necroptosis demonstrated by a 70% increase in the number of PI+ cells (p<0.05, n=5) as well as increased RIP3 expression at 6 h after IR. Western blotting showed increased levels of the mitochondrial fission protein, Drp-1, and the stress marker p-p38 in A1+/- mice compared to WT 3 h after IR (figure). Treatment with peg A1 restored neuron survival in WT mice, whereas macrophage depletion with clodronate liposomes increased neuron loss. Cell specific deletion of A1 in myeloid cells showed exacerbated neuron loss but deletion of A1 in endothelial cell had no effect (table).
In contrast to A2, A1 is neurovascular protective in retinal IR via decreasing necroptosis and mitochondrial dysfunction. Myeloid derived A1 could play a role in mediating a protective effect of macrophages after retinal IR.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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