Neuroprotection from optic nerve trauma by deletion of arginase 2

Abstract

ObjectiveThe ureohydrolase enzyme arginase has been implicated in several retinal diseases. We have previously shown that deletion of the arginase 2 (A2) gene reduces neurovascular injury in mouse models of ischemic retinopathy. The aim of this study was to characterize the specific involvement of A2 expression in traumatic optic neuropathy (TON).MethodsTo accomplish this, wild‐type (WT) or A2 knockout (A2−/−) mice were subjected to optic nerve crush (ONC) on the left eye. The right eye served as sham control. Loss of retinal ganglion cells (RGC) was assessed in retinal whole mounts. RGC axon loss was evaluated by imaging TUJ1. Axonal regeneration was evaluated by morphometric analysis of Cholera Toxin B transport and western blot analysis of GAP43. Glial and microglial activation was determined by morphometric analysis of GFAP and Iba1, respectively. Inflammation was evaluated by western blot and quantitative PCR of inflammatory mediators.ResultsNumbers of NeuN‐positive neurons as well as Brn3a‐ and RBPMS‐positive RGC were decreased in the WT retinas at 14 days after ONC as compared to the sham controls. This ONC‐induced neuronal loss was diminished in the A2−/− retinas. Similarly, axonal degeneration was reduced by A2 deletion whereas axon regeneration was enhanced. Significant retinal thinning was seen in WT retinas at 21 days after ONC, and this was abrogated in A2−/− mice. Cell death studies showed an increase in TUNEL positive cells in the RGC layer at 5 days after ONC in the WT retinas, and this was attenuated by A2 deletion. Activation of glial and microglial cells was increased in WT retinas after ONC and this was significantly reduced by A2 deletion. Western blotting showed a marked increase in the neurotrophin, brain derived neurotrophic factor (BDNF) and its downstream signaling in A2−/− retinas after ONC as compared with the WT controls. This was associated with increases in the axonal regeneration marker GAP‐43 in A2−/− retinas versus WT at 5 and 7 days after ONC. Furthermore, A2−/− retinas showed decreased NLRP3 inflammasome activation and lower IL‐1β/IL‐18 levels as compared to WT retinas subjected to ONC. The intracellular adhesion molecule (ICAM) showed significant increases in WT retinas and this was attenuated in A2−/− mice.ConclusionsCollectively, our results show that deletion of A2 limits ONC‐induced neurodegeneration and glial activation, and promotes axon regeneration by a mechanism involving increases in BDNF and decreases in inflammation. These data demonstrate that A2 plays an important role in ONC‐induced retinal damage. Blockade of A2 activity may offer a therapeutic strategy for preventing vision loss induced by TON.Support or Funding InformationThis work was supported by: NIH grant R01‐EY11766 to R.B.C., VA grant BX001233 to R.B.C., the Culver Vision Discovery Institute at Augusta University, and AHA postdoctoral fellowship 18POST34060036 to A.Y.F.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.