Abstract
Purpose :
Despite decades of research showing the involvement of oxidative and endoplasmic reticulum (ER) stress after traumatic brain injury (TBI), antioxidant and ER interventions generally fail upon reaching the clinical level. Using a mouse model of TBI-induced traumatic optic neuropathy (TON), which damages the optic nerve just ahead of the chiasm, we found that the ER stress response varied based on the cellular compartment (I.e., cell body versus axon) and distance from the injury site. Because ER and oxidative stress overlap considerably, we hypothesize that the failure of antioxidants may be due to conflicting interactions with ER stress responses within distinct cellular compartments.
Methods :
To prevent acute oxidative stress, six-week-old male and female mice were given 3mg/kg Edaravone (an antioxidant) or saline six hours before closed-head weight-drop TBI. Seven- and thirty-days post injury retinas and optic nerve sections both proximal (i.e., toward the cell body) and distal (chiasm and tract) to the site of injury were isolated for mass spectrometry (n=3), western blot (WB; n=9), immunofluorescence (IF; n=5), or glutathione (n=6) assays to assess global changes in protein expression and the effects of Edaravone/cellular compartment on ER and oxidative stress responses and retinal cell survival.
Results :
The antioxidant Nrf2 was significantly increased in the nerve (predicted; p=0.008) and decreased in the retina (not predicted, p=0.04) in uninjured mice (WB). In injured mice, preliminary results suggest a similar pattern of expression. Unexpectedly, it may also now be important to consider the role of glia in the ER-oxidative stress response as a shared transcription factor of these two mechanisms, Activating Transcription Factor 4 (ATF4), was upregulated in the retina and nerve after injury (WB) but was not localized in the axons of the optic nerve (IF). Instead, ATF4 only appears in the nuclei of other, unidentified cells.
Conclusions :
Although assays are ongoing, preliminary results support our hypothesis that the axon responds differently from the soma, even in uninjured cells. Intriguingly, despite having shown ER stress in retinal samples, we have not yet confirmed this increase in optic nerve axons. Instead, we might need to consider glial cells in the web of stress responses that occur after axon injury.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.