Targeting eIF2α in TBI-induced traumatic optic neuropathy: Effects of Salubrinal and the Integrated Stress Response Inhibitor.

Traumatic brain injury (TBI) can induce traumatic axonal injury in the optic nerve, which is referred to as traumatic optic neuropathy (TON). TON occurs in up to 5% of TBI cases and leads to irreversible visual deficits. TON-induced phosphorylation of eIF2, a downstream ER stress activator in the PERK pathway presents a potential point for therapeutic intervention. For eIF2 phosphorylation can lead to apoptosis or adaptation to stress. We hypothesized that dephosphorylation, rather than phosphorylation, of eIF2 would lead to reduced apoptosis and improved visual performance and retinal cell survival. Adult male mice were injected with Salubrinal (increases p-eIF2) or ISRIB (decreases p-eIF2) 60 minutes post-injury. Contrary to literature, both drugs hindered control animal visual function with minimal improvements in injured mice. Additionally, differences in eIF2 phosphorylation, antioxidant responses, and protein folding chaperones were different when examining protein expression between the retina and its axons in the optic nerve. These results reveal important compartmentalized ER stress responses to axon injury and suggest that interventions in the PERK pathway may alter necessary homeostatic regulation of the UPR in the retina.