AANAT1 functions in astrocytes to regulate sleep homeostasis

Summary Characteristic features of sleep are conserved among species [1], and from humans to insects sleep is influenced by neural circuits involving monoamines such as serotonin and dopamine [2]. Glial cells have been increasingly implicated in mechanisms of baseline and homeostatic sleep regulation in mammals and flies [3–11], but it remains unknown whether and how glia might influence monoaminergic control of sleep. Sleep is regulated by circadian rhythms and a homeostatic drive to compensate for prolonged wakefulness, and growing evidence suggests that neural mechanisms controlling homeostatic sleep can be discriminated from those controlling baseline sleep [12–15]. In Drosophila , mutants of arylalkylamine N-acetyltransferase 1 ( AANAT1 lo ) have normal baseline amounts of sleep and motor activity, but increased rebound sleep following deprivation [16]. AANAT1 can acetylate and inactivate monoamines in vitro [17], but the role of AANAT1 in vivo remains poorly understood. We find AANAT1 to be expressed in astrocytes and subsets of neurons in the adult Drosophila brain, with levels in astrocytes declining markedly overnight. In sleep-deprived AANAT1 mutant flies, heightened rebound sleep is accompanied by increased serotonin and dopamine levels in the brain. In neurons, AANAT1 functions to limit the quantity and consolidation of nighttime sleep, but in astrocytes AANAT1 constrains the amount of rebound sleep that flies take in response to sleep deprivation. These findings distinguish sleep-control functions of AANAT1 in neurons and astrocytes, and identify a critical role for astrocytes in the regulation of monoamine bioavailability and calibration of the response to sleep need. Highlights The monoamine catabolic enzyme arylalkylamine N-acetyltransferase 1 (AANAT1) is expressed by astrocytes and subsets of serotonergic, glutamatergic, GABAergic and cholinergic neurons in the adult brain of Drosophila . AANAT1 limits accumulation of serotonin and dopamine in the brain upon sleep deprivation. Loss of AANAT1 from astrocytes, but not from neurons, causes flies to increase their daytime rebound sleep in response to overnight sleep deprivation.