GAPDH inhibition mediated by thiol oxidation in human airway epithelial cells exposed to an environmental peroxide
Intracellular redox homeostasis is closely regulated through adaptive signaling and metabolic pathways. However, environmental exposure to xenobiotic stressors such as secondary organic aerosols (SOA) can alter intracellular redox homeostasis that lead to adverse outcomes. Isoprene hydroxy hydroperoxide (ISOPOOH), a ubiquitous volatile organic compound derived from the atmospheric photooxidation of isoprene, is a major contributor of SOA. We have previously demonstrated that exposure of human airway epithelial cells (HAEC) to ISOPOOH induces oxidative stress through multiple mechanisms including lipid peroxidation, glutathione oxidation, and alterations of glycolytic metabolism. By using an experimental approach that primarily relies on using dimedone-based reagents and copper catalyzed azo-alkynyl cycloaddition reactions to tag intracellular protein sulfenic acids, we demonstrate that exposure of HAEC to ISOPOOH induces sulfenylation of cysteinyl thiols in intracellular proteins. Exposure of HAEC to low micromolar concentrations of ISOPOOH induced reversible sulfenylation of cysteinyl thiols in GAPDH that was accompanied by a dose-dependent loss of GAPDH enzymatic activity. These results demonstrate that ISOPOOH induces an oxidative modification of intracellular proteins that results in loss GAPDH activity, which ultimately impacts the dynamic regulation of the intracellular redox homeostasic landscape in HAEC.