Arginase 2 deletion limits neuroglial injury following optic nerve trauma

Abstract

Purpose : Traumatic ocular injury is frequently associated with degeneration of retinal ganglion cells (RGCs) due to primary trauma to their axons in the optic nerve and may also involve degeneration of other retinal neurons secondary to oxidative stress, vascular dysfunction, ischemia and edema. Our previous studies have shown that deletion of the arginase 2 (A2) gene significantly reduces neuronal injury in models of retinopathy of prematurity and ischemia/reperfusion injury. To evaluate whether A2 could be a therapeutic target for limiting traumatic retinal injury, we determined the effect of A2 deletion on neuronal cell loss and gliosis in a mouse model of optic nerve crush (ONC).

Methods : ONC surgery was performed on the left eye of wild type (WT, C57Bl6J) and A2-/- mice. After incision of the limbal conjunctiva and deflection of the intraocular muscles, self-closing N7 forceps were used to clamp the optic nerve at 2 mm from the eyeball for 3 seconds. Sham control surgery was performed on the right eye. At 7 days after the surgeries retinas and optic nerves were prepared for analysis. Confocal immunofluorescence imaging of NeuN-positive cells in the ganglion cell layer (GCL) was used to determine the effects of ONC and A2 deletion on neuronal survival. Immunofluorescence imaging of retinal or optic nerve sections was used to examine expression of glial fibrillary acidic protein (GFAP) and microglia/microphage markers Iba1 and CD68.

Results : ONC injury caused a 60% reduction in numbers of NeuN positive GCL neurons in the WT retinas as compared to the controls (p<0.01). This neuronal cell loss was blunted to 40% in the A2-/- mice (p<0.01). GFAP expression was increased in WT ONC retinas and this was attenuated in the A2-/- animals. Following ONC the microglial/macrophage population (Iba1 and CD68 positive) was increased in the optic nerve of WT but not in the A2-/- mice.

Conclusions : A2 deficiency reduces the loss of GCL neurons and limits the activation of retinal glial cells following ONC injury. Deletion of A2 also blocks the increases in numbers of microglia/macrophage cells in the injured optic nerves. These data demonstrate that A2 plays an important role in neuronal degeneration and gliosis after ONC. Inactivation of A2 may offer a therapeutic strategy for preventing neuronal cell death in traumatic retinal injury.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.