Quantitative phosphoproteomic analysis of the molecular substrates of sleep need

Abstract

Sleep and wake have global effects on brain physiology, from molecular changes and neuronal activities to synaptic plasticity. Sleep-wake homeostasis is maintained by the generation of a sleep need that accumulates during waking and dissipates during sleep. Here we investigate the molecular basis of sleep need using quantitative phosphoproteomic analysis of the sleep-deprived and Sleepy mouse models of increased sleep need. Sleep deprivation induces cumulative phosphorylation of the brain proteome, which dissipates during sleep. Sleepy mice, owing to a gain-of-function mutation in the Sik3 gene , have a constitutively high sleep need despite increased sleep amount. The brain proteome of these mice exhibits hyperphosphorylation, similar to that seen in the brain of sleep-deprived mice. Comparison of the two models identifies 80 mostly synaptic sleep-need-index phosphoproteins (SNIPPs), in which phosphorylation states closely parallel changes of sleep need. SLEEPY, the mutant SIK3 protein, preferentially associates with and phosphorylates SNIPPs. Inhibition of SIK3 activity reduces phosphorylation of SNIPPs and slow wave activity during non-rapid-eye-movement sleep, the best known measurable index of sleep need, in both Sleepy mice and sleep-deprived wild-type mice. Our results suggest that phosphorylation of SNIPPs accumulates and dissipates in relation to sleep need, and therefore SNIPP phosphorylation is a molecular signature of sleep need. Whereas waking encodes memories by potentiating synapses, sleep consolidates memories and restores synaptic homeostasis by globally downscaling excitatory synapses. Thus, the phosphorylation-dephosphorylation cycle of SNIPPs may represent a major regulatory mechanism that underlies both synaptic homeostasis and sleep-wake homeostasis.

A salt-induced kinase (SIK) is required for the metabolic regulation of sleep

“…It regulates gene transcription via interaction with the nuclear factors MEF-2 and HDA-4 [77]. In contrast, the mammalian KIN-29 homolog SIK3 protein has been proposed to act in the cytosol to phosphorylate synaptic proteins [30]. To determine where KIN-29 acts to regulate sleep, we began by assessing its subcellular localization during sleep.…”

“…There are three SIKs in mammals, two in Drosophila and one in C. elegans called KIN-29 [29]. Gain-of-function mouse mutants of SIK3 are sleepy [27] with a phosphoprotein profile that mimics that of sleep-deprived mice [30], indicating that SIK3 signaling promotes sleep need. The Drosophila SIK3 and C. elegans KIN-29 loss-of-function mutants have reduced sleep [27].…”

“…Experimental mobilization of triglycerides in these fat stores restores sleep. While mouse SIK3 acts in the cytoplasm to phosphorylate multiple brain targets [30], we find that C. elegans kin-29 acts in the nucleus to regulate sleep and energy homeostasis via just a single gene called hda-4 , which encodes a class IIa histone-deacytelase. KIN-29 and HDA-4 act in the same metabolically-responsive sensory neurons upstream of fat homeostasis and of the activation of the sleep-promoting neurons ALA and RIS.…”

An essential role for MEF2C in the cortical response to loss of sleep

“…About two thirds of the significant changes in gene expression observed in response to sleep deprivation were maintained when two hours of recovery sleep followed four hours of sleep loss indicating that direct recovery of sleep deprivation-induced transcriptional changes is delayed. This result suggests 5 additional post-transcriptional mechanisms are also key to sleep-loss molecular mechanisms as for example, in synaptosomes, the translation of DEGs to proteins is at least, in part, dependent on sleep (Noya et al, 2019) or, more generally, the sleep loss associated increase in phosphorylation of the proteome (Wang et al, 2018).…”

Visual imagery and visual perception induce similar changes in occipital slow waves of sleep

“…However, changes in SWA may also reflect changes in on the neuromodulatory tone and the balance between excitation and inhibition, independent of changes in synaptic strength (Cirelli, 2017;Frank & Cantera, 2014). Moreover, the wake-dependent accumulation of metabolites and of molecular factors reflecting an increased cellular stress have been also suggested to potentially affect SWA at both global and local level (Krueger et al, 2008;Qi et al, 2016;Vyazovskiy & Harris, 2013;Wang et al, 2018).…”