Parkin coregulates glutathione metabolism in adult mammalian brain
Daniel N. El-Kodsi, Jacqueline M. Tokarew, Rajib Sengupta, Nathalie A. Lengacher, Ajanta Chatterji, Angela Nguyen, Heather Boston, Qiubo Jiang, Carina Palmberg, Chantal A. Pileggi, Chet E. Holterman, Bojan Shutinoski, Juan Li, Travis K. Fehr, Matthew J. LaVoie, Rajiv R. Ratan, Gary S. Shaw, Masashi Takanashi, Nobutaka Hattori, C. Kennedy, Mary‐Ellen Harper, Arne Holmgren, Julianna J. Tomlinson, Michael G. Schlossmacher
Abstract
animals did not develop dopamine cell loss in the S. nigra, they had more reactive oxidative species and a higher concentration of carbonylated proteins in the brain; bi-genic mice also showed a trend for more nitrotyrosinated proteins. Because these redox changes were seen in the cytosol rather than mitochondria, we next explored the thiol network in the context of PRKN expression. We detected a parkin deficiency-associated increase in the ratio of reduced glutathione (GSH) to oxidized glutathione (GSSG) in murine brain, PRKN-linked human cortex and several cell models. This shift resulted from enhanced recycling of GSSG back to GSH via upregulated glutathione reductase activity; it also correlated with altered activities of redox-sensitive enzymes in mitochondria isolated from mouse brain (e.g., aconitase-2; creatine kinase). Intriguingly, human parkin itself showed glutathione-recycling activity in vitro and in cells: For each GSSG dipeptide encountered, parkin regenerated one GSH molecule and was S-glutathionylated by the other (GSSG + P-SH [Formula: see text] GSH + P-S-SG), including at cysteines 59, 95 and 377. Moreover, parkin's S-glutathionylation was reversible by glutaredoxin activity. In summary, we found that PRKN gene expression contributes to the network of available thiols in the cell, including by parkin's participation in glutathione recycling, which involves a reversible, posttranslational modification at select cysteines. Further, parkin's impact on redox homeostasis in the cytosol can affect enzyme activities elsewhere, such as in mitochondria. We posit that antioxidant functions of parkin may explain many of its previously described, protective effects in vertebrates and invertebrates that are unrelated to E3 ligase activity.