Calcineurin is a central regulator of process S and governs sleep homeostasis in locus coeruleus
Sleep need accumulates during waking and dissipates during sleep to maintain sleep homeostasis (process S). Besides regulation of daily sleep amount, a hallmark of process S is the homeostatic sleep regulation: sleep loss causes increased amount and intensity of subsequent recovery sleep. The central regulators of process S and specific brain regions that govern sleep homeostasis in mammals remain unclear. Here, we report that enhanced calcineurin activity in the mouse brain neurons sharply increases non-rapid eye movement sleep (NREMS) to average ~17-h/day. Knockout of calcineurin in adult mouse brain diminishes baseline NREMS to average ~4-h/day, but also abolishes recovery NREMS owing to inability to accumulate sleep need during wakefulness. Calcineurin promotes baseline NREMS in both excitatory and inhibitory neurons and by antagonizing PKA and activating SIK3 via S551 dephosphorylation. Moreover, calcineurin is specifically required in the locus coeruleus-noradrenergic (LCNA) neurons for the transcriptomic and homeostatic responses to sleep loss. While chemo-/optogenetic activation of LCNA neurons increases the amount and intensity of NREMS, ablation and inhibition of LCNA neurons diminish recovery NREMS following sleep deprivation. These results establish calcineurin as a central regulator of process S and identify LC as a potential sleep need center that governs NREMS homeostasis in mice. Overall design: Differential expression analysis of locus coeruleus (LC) from normal slept (S6) or 6-h sleep-deprived (SD6) ABC-Ctrl (WT) and ABC-CnB1KO (KO) mice