park+/+ and park-/- Drosophila have sexually dimorphic brain redox chemistry

Sexual dimorphism in Parkinson's disease (PD) pathophysiology is poorly understood. Elucidating consequences of disease-causing mutations on brain redox chemistry may reveal therapeutic targets for all people with PD. We report that male Drosophila had increased hydrogen peroxide and glutathione (G-SH) redox disequilibrium in vulnerable dopaminergic neuron mitochondria. Levels of cysteine and oxidized cystine were decreased, with cysteine/cystine ratios (indicating less oxidative stress) and G-SH levels being elevated in parkin-null (park-/-) Drosophila brains, and more so in males. We report effects of parkin loss and sex on the levels of low-molecular-weight thiols involved in G-SH synthesis, providing clues as to mechanisms implicated in altered levels of brain G-SH, cysteine and cystine. Protein nitration was decreased in the brain of park-/- flies, especially in females, suggesting that decreased nitric oxide levels compensate for loss of parkin or lack of protective nitric oxide synthase activity. Our results imply that park-/- flies have elevated levels of G-SH that meet antioxidant demand in the absence of parkin in the whole brain, but not in vulnerable neurons. Identification of sexually dimorphic PD risk factors could inform symptom management and highlight sex-specific therapeutic strategies.