The Endoplasmic Reticulum Stress and Unfolded Protein Responses in Sulfur Mustard induced Mouse Skin Wound Repair

Abstract

The endoplasmic reticulum stress (ERS) pathways activate the unfolded protein response (UPR) to mediate cell survival against severe stress in an attempt to prevent ERS mediated apoptosis. Sulfur mustard (SM), a chemical warfare vesicating agent, causes significant delayed wound repair in skin. This study explored the contribution of UPR and ERS to SM cutaneous injury in mice. We performed time course studies using the mouse ear vesicant model and showed histopathology changes over time. RT‐PCR demonstrated at least a 2‐fold increased of the ER stress survival gene, GRP78; UPR gene, ATF6; and proapoptotic gene, CHOP as time progressed from 24h to 168h post‐SM exposure. Western blot analysis demonstrated increased GRP78, CHOP, and full length and cleaved (activated) forms of ATF6 as time progressed. This was confirmed by immunofluorescence which showed significant nuclear staining of cleaved ATF6 in the hyperplastic epidermis at 168h post exposure. Double immunofluorescent labeling for GRP78 and CHOP at 72h post exposure showed abundant cytoplasmic staining of GRP78 in the basal, proliferating epidermis. In contrast, the expression of CHOP was more numerous in the migrating keratinocytes. This suggests that the migrating cells are targeted for apoptosis while the basal, proliferating cells are targeted for survival. The continued proliferation of the basal cells and their subsequent conversion to migrating cells may in part explain the delayed wound repair frequently observed in SM skin injury.Grant Funding Source: NIH grants AR055073, EY09056, and ES005022.