The Involvement of Unfolded Protein Response in the Mechanism of Nitrogen Mustard-Induced Ocular Toxicity

Abstract

Nitrogen mustard (NM) is a known surrogate of sulfur mustard, a chemical-warfare agent that causes a wide range of ocular symptoms, from a permanent reduction in visual acuity to blindness upon exposure. Although it has been proposed that the two blistering agents have a similar mechanism of toxicity, the mode of NM-induced cell death in ocular tissue has not been fully explored. Therefore, we hypothesized that direct ocular exposure to NM in mice leads to retinal tissue injury through chronic activation of the unfolded protein response (UPR) PERK arm in corneal cells and VEGF secretion, eventually causing cell death. We topically applied NM directly to mice to analyze ocular and retinal tissues at 2 weeks postexposure. A dramatic decline in retinal function, measured by scotopic and photopic electroretinogram responses, was detected in the mice. This decline was associated with enhanced TUNEL staining in both corneal and retinal tissues. In addition, exposure of corneal cells to NM revealed 228 differentially and exclusively expressed proteins primarily associated with the UPR, ferroptosis, and necroptosis. Moreover, these cells exhibited activation of the UPR PERK arm and an increase in VEGF secretion. Enhancement of VEGF staining was later observed in the corneas of the exposed mice. Therefore, our data indicated that the mechanism of NM-induced ocular toxicity should be carefully examined and that future research should identify a signaling molecule transmitted via a prodeath pathway from the cornea to the retina. SIGNIFICANCE STATEMENT: This study demonstrated that NM topical exposure in mice results in dramatic decline in retinal function associated with enhanced TUNEL staining in both corneal and retinal tissues. We also found that the NM treatment of corneal cells resulted in 228 differentially and exclusively expressed proteins primarily associated with ferroptosis. Moreover, these cells manifest the UPR PERK activation and an increase in VEGF secretion. The latter was also found in the corneas of the cexposed mice.