Neophobia, NQO1 and SIRT1 as premorbid and prodromal indicators of AD in 3xTg-AD mice

Increased oxidative stress seems to be a key factor underlying natural processes of aging, but also to occur prior to neuropathological hallmarks of neurodegenerative diseases. The present work studied the temporal variation of three key antioxidant enzymes in cortex and hippocampus during the development of behavioral and cognitive symptoms in 3xTg-AD mice, and as compared to age-matched controls. At 2 months of age, when no intraneuronal Aβ immunoreactivity has been reported, increased neophobia shown as a delayed and reduced rearing, evidenced the onset of BPSD-like symptoms at premorbid stages of disease. In these animals, NQO1 was found increased in both the hippocampus (800%) and cortex (400%) and progressively diminished at older ages. SOD1 was increased in the hippocampus at 4 months of age, when neuronal Aβ accumulation has been established. These hippocampal increases of antioxidants before the prodromal emergence of cognitive symptoms support their role as defense mechanisms. SIRT1 levels showed opposite age-dependent changes in cortex (increase) and hippocampus (decrease) relative to controls. Prodromal cognitive deficits emerged at 6 months of age, concomitantly to cortical overexpression of SIRT1 but down-regulation of NQO1 and SIRT1 in the hippocampus, suggesting inadequate antioxidative protection to prevent or delay the subjacent neuronal damage. The present data further support the link between oxidative status and the anxious profile. Their crosstalk may underline AD-pathological mechanisms that may lead to deranged physiology and selective neuronal degeneration. It also points out increased neophobia and high expression of NQO1 among the first indicators of disease in the 3xTg-AD mice. © 2014.