Cigarette Smoke Targets Glutaredoxin 1, Increasing S-glutathionylation and Epithelial Cell Death

It is established that cigarette smoke causes irreversible oxidations in lung epithelial cells and can lead to their death. However, its impact on reversible and physiologically relevant redox-dependent protein modifications remains to be investigated. Glutathione is an important anti-oxidant against inhaled reactive oxygen species as a direct scavenger, but it can also covalently bind protein thiols upon mild oxidative stress to protect them against irreversible oxidation. This posttranslational modification, known as S-glutathionylation, can be reversed under physiological conditions by the enzyme glutaredoxin 1 (Grx1). The aim of this study was to investigate if cigarette smoke modifies Grx1 and if this impacts on protein S-glutathionylation and epithelial cell death. Upon exposure of alveolar epithelial cells to cigarette smoke extract (CSE) a decrease in Grx1 mRNA and protein expression was observed, in conjunction with decreased activity and increased protein S-glutathionylation. Using mass spectrometry, irreversible oxidation of recombinant Grx1 by CSE and acrolein was demonstrated, which was associated with attenuated enzyme activity. Furthermore, carbonylation of Grx1 in epithelial cells after exposure to CSE was shown. Overexpression of Grx1 attenuated CSE-induced increases in protein S-glutathionylation and increased survival. Conversely, primary tracheal epithelial cells of mice lacking Grx1 were more sensitive to cigarette smoke-induce cell death with corresponding increases in protein S-glutathionylation. These results show that cigarette smoke can modulate Grx1 not only at the expression level, but can also directly modify Grx1 itself, decreasing its activity. These findings demonstrate a role for the Grx1/S-glutathionylation redox system in cigarette smoke induced lung epithelial cell death.