SIRT1 regulation of wakefulness and senescence-like phenotype in wake neurons.

Wake neurons in the basal forebrain and brainstem provide critical inputs to optimize alertness and attention. These neurons, however, evidence heightened vulnerability to a diverse array of metabolic challenges, including aging. SIRT1 is an nicotinamide adenine dinucleotide responsive deacetylase serving diverse adaptive responses to metabolic challenges, yet this metabolic rheostat may be downregulated under conditions of significant oxidative stress. We hypothesized that SIRT1 might serve as a critical neuroprotectant for wake neurons in young animals but that this protectant would be lost upon aging, rendering the neurons more vulnerable to metabolic insults. In this collection of studies, we first established the presence of nuclear SIRT1 in wake neurons throughout the forebrain and brainstem. Supporting functional and behavioral roles for SIRT1 in wake-active neurons, transgenic whole animal, and conditional loss of brain SIRT1 in the adult mouse impart selective impairments in wakefulness, without disrupting non-rapid eye movement or rapid eye movement sleep. Populations of wake neurons, including the orexinergic, locus ceruleus, mesopontine cholinergic, and dopaminergic wake neurons, evidence loss of dendrites and neurotransmitter synthesis enzymes and develop accelerated accumulation of lipofuscin, consistent with a senescence-like phenotype in wake neurons. Normal aging results in a progressive loss of SIRT1 in wake-active neurons, temporally coinciding with lipofuscin accumulation. SIRT1 is a critical age-sensitive neuroprotectant for wake neurons, and its deficiency results in impaired wakefulness.