Increased Nox2 expression and activity in ageing-related loss of locomotor function and neuronal damage

L Geng, S Cahill-Smith, JM Li. University of Surrey, Guildford, UK

Excessive reactive oxygen species (ROS) production in the central nervous system including microvasculature has been recognised as an important mechanism underlying the development of neurodegenerative diseases in ageing. Although several enzymatic sources can be involved in brain ROS generation, recently a Nox2-containing NADPH oxidase has been suggested as a major source of superoxide production in both microglial cells and brain vascular endothelial cells which contributes to neuron oxidative damage and neuronal death in ageing. In this study, we used age-matched C57BL/6 wild-type (WT) and Nox2 knockout (Nox2-/-) mice at young (3-4 month old) and old age (18-21 month old) to investigate the role of Nox2-derived ROS in ageing-related loss of locomotor activity in vivo and the damage of cerebral microvasculature and neurons ex vivo. Compared to young mice, WT (but not Nox2-/-) ageing mice had a significant decrease in overall free-running activity (p<0.05) during the 12:12h light-dark period. The loss of locomotor activity in WT ageing mice was accompanied by significant increases (2.7±0.7 fold, p<0.05) in the brain ROS production as detected by lucigenin-chemiluminescence and dihydroethidium (DHE) fluorescence and increases in the levels of expression of Nox2 and p47phox (the main regulatory subunit of Nox2) as detected by Western blots. The oxidative stress in the WT ageing brain is associated with an increase in microglial cell population (1.8±0.3 fold, p<0.05) and decreases in both neuronal cells (2.9±0.5 fold, p<0.05) and capillary numbers (2.4±0.8 fold, p<0.05) as detected by immunofluorescence. However, all these ageing-related brain oxidative stress and pathophysiological changes found in WT ageing brain were significantly reduced in Nox2-/- mice and locomotor activity was effectively prevented in Nox2-/- ageing mice. In conclusion, Nox2-derived ROS plays an important role in the pathogenesis of neurodegeneration and the loss of locomotor function in old age. Targeting Nox2 may present a novel therapeutic strategy to treat oxidative stress-related neurodegenerative diseases and to prevent dementia in ageing.