Mechanisms of altered redox regulation in neurodegenerative diseases--focus on S--glutathionylation.

Significance: Neurodegenerative diseases are characterized by progressive loss of neurons. A common feature is oxidative stress, which arises when reactive oxygen species (ROS) and/or reactive nitrogen species (RNS) exceed amounts required for normal redox signaling. An imbalance in ROS/RNS alters functionality of cysteines and perturbs thiol-disulfide homeostasis. Many cysteine modifications may occur, but reversible protein mixed disulfides with glutathione (GSH) likely represents the common steady-state derivative due to cellular abundance of GSH and ready conversion of cysteine-sulfenic acid and S-nitrosocysteine precursors to S-glutathionylcysteine disulfides. Thus, S-glutathionylation acts in redox signal transduction and serves as a protective mechanism against irreversible cysteine oxidation. Reversal of protein-S-glutathionylation is catalyzed specifically by glutaredoxin which thereby plays a critical role in cellular regulation. This review highlights the role of oxidative modification of proteins, notably S-glutathionylation, and alterations in thiol homeostatic enzyme activities in neurodegenerative diseases, providing insights for therapeutic intervention.

Recent Advances: Recent studies show that dysregulation of redox signaling and sulfhydryl homeostasis likely contributes to onset/progression of neurodegeneration. Oxidative stress alters the thiol-disulfide status of key proteins that regulate the balance between cell survival and cell death.

Critical Issues: Much of the current information about redox modification of key enzymes and signaling intermediates has been gleaned from studies focused on oxidative stress situations other than the neurodegenerative diseases.

Future Directions: The findings in other contexts are expected to apply to understanding neurodegenerative mechanisms. Identification of selectively glutathionylated proteins in a quantitative fashion will provide new insights about neuropathological consequences of this oxidative protein modification.