Retinal Ischemia Reperfusion: Role of Arginase 2

Abstract

Purpose : We have previously shown the involvement of the mitochondrial enzyme arginase 2 (A2) in inducing neurovascular degeneration in retinal ischemia reperfusion (I/R) injury (Shosha et al, 2016). A2 deletion significantly protected against neurovascular degeneration, retinal thinning and cell death. The present study was undertaken to determine the role of A2 in I/R induced retinal detachment, hyperpermeability and mitochondrial dynamics and to model the I/R injury in vitro.

Methods : We used mice lacking both copies of arginase 2 (A2-/-) and wild type (WT) controls. I/R insult was conducted on the right eye and the left eye was used as control. Optical coherence tomography (OCT) imaging was used to evaluate retinal detachment. Western blot was used to assess vascular permeability by measuring albumin extravasation and to evaluate mitochondrial injury by measuring the mitochondrial fission marker dynamin related protein 1 (Drp1). Oxygen glucose deprivation/reperfusion (OGD/R) was used to simulate I/R injury in bovine retinal endothelial (BRE) cells in vitro. A2 expression in relation to cell death and survival pathways were evaluated by western blot.

Results :
OCT showed a marked distortion of retinal layers, retinal detachment and edema in WT retinas at 1 week after I/R injury (n=5). A2-/- I/R retinas (n=4) showed more preserved retinal structure, less retinal detachment and edema, and more normal fundus compared to WT I/R. At 5 weeks post injury, the retinal detachment and edema were resolved in all mice. I/R injury caused a prominent extravasation of mouse albumin at 2 days post injury (P<0.001, n=4). This was significantly reduced in the A2-/- I/R retinas (P<0.05, n=4). Levels of Drp1 were significantly increased at 3h after I/R in WT retinas (P<0.05, n=3). This I/R-induced increase in Drp1 was prevented by A2 deletion (n=3). For OGD/R studies, we found an increase in A2 expression after 6h OGD followed by 6h reperfusion (n=3). The A2 increase was associated with increases in phosphorylation of the stress marker P38 (P<0.01, n=3) and reduced phosphorylation of the survival marker AKT (n=2) along with increases in the cell death marker cleaved poly ADP-ribose polymerase (PARP) (P<0.01, n=3).

Conclusions :
This study shows for the first time A2 deletion protects against retinal detachment and vascular permeability increase after I/R injury through a mechanism associated with mitochondrial fission.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.