Administration of the protein synthesis inhibitor, anisomycin, has distinct sleep-promoting effects in lateral preoptic and perifornical hypothalamic sites in rats

Evolutionarily Conserved Regulation of Sleep by the Protein Translational Regulator PERK

Sleep is a cross-species phenomenon whose evolutionary and biological function remain poorly understood. Clinical and animal studies suggest that sleep disturbance is significantly associated with disruptions in protein homeostasis-or proteostasis-in the brain, but the mechanism of this link has not been explored. In the cell, the protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK) pathway modulates proteostasis by transiently inhibiting protein synthesis in response to proteostatic stress. In this study, we examined the role of the PERK pathway in sleep regulation and provide the first evidence that PERK signaling is required to regulate normal sleep in both vertebrates and invertebrates. We show that pharmacological inhibition of PERK reduces sleep in both Drosophila and zebrafish, indicating an evolutionarily conserved requirement for PERK in sleep. Genetic knockdown of PERK activity also reduces sleep in Drosophila, whereas PERK overexpression induces sleep. Finally, we demonstrate that changes in PERK signaling directly impact wake-promoting neuropeptide expression, revealing a mechanism through which proteostatic pathways can affect sleep and wake behavior. Taken together, these results demonstrate that protein synthesis pathways like PERK could represent a general mechanism of sleep and wake regulation and provide greater insight into the relationship between sleep and proteostasis.

Transcriptional Profiling of Cholinergic Neurons From Basal Forebrain Identifies Changes in Expression of Genes Between Sleep and Wake

Study objective

To assess differences in gene expression in cholinergic basal forebrain cells between sleeping and sleep-deprived mice sacrificed at the same time of day.

Methods

Tg(ChAT-eGFP)86Gsat mice expressing enhanced green fluorescent protein (eGFP) under control of the choline acetyltransferase (Chat) promoter were utilized to guide laser capture of cholinergic cells in basal forebrain. Messenger RNA expression levels in these cells were profiled using microarrays. Gene expression in eGFP(+) neurons was compared (1) to that in eGFP(-) neurons and to adjacent white matter, (2) between 7:00 am (lights on) and 7:00 pm (lights off), (3) between sleep-deprived and sleeping animals at 0, 3, 6, and 9 hours from lights on.

Results

There was a marked enrichment of ChAT and other markers of cholinergic neurons in eGFP(+) cells. Comparison of gene expression in these eGFP(+) neurons between 7:00 am and 7:00 pm revealed expected differences in the expression of clock genes (Arntl2, Per1, Per2, Dbp, Nr1d1) as well as mGluR3. Comparison of expression between spontaneous sleep and sleep-deprived groups sacrificed at the same time of day revealed a number of transcripts (n = 55) that had higher expression in sleep deprivation compared to sleep. Genes upregulated in sleep deprivation predominantly were from the protein folding pathway (25 transcripts, including chaperones). Among 42 transcripts upregulated in sleep was the cold-inducible RNA-binding protein.

Conclusions

Cholinergic cell signatures were characterized. Whether the identified genes are changing as a consequence of differences in behavioral state or as part of the molecular regulatory mechanism remains to be determined.

LBP-4a improves insulin resistance via translocation and activation of GLUT4 in OLETF rats

Lycium barbarum polysaccharide (LBP) has been shown to ameliorate insulin resistance, but the identification of compounds from LBP and the mechanisms have not been clarified. In this study, LBP-4a was purified from Lycium barbarum by DEAE cellulose and Sephadex G-100 column chromatography, and the effects of LBP-4a on insulin resistance were investigated. The results indicated that LBP-4a caused translocation of the glucose transporter isoform 4 (GLUT4) to the cell surface, which in turn stimulated glucose uptake, and the effect was sensitive to wortmannin, an inhibitor of phosphoinositol 3-kinase (PI3-K), and SB203580, an inhibitor of p38 mitogen activated protein kinase (p38 MAPK (α, β)). Furthermore, the effects of LBP-4a on p38 MAPK activities were abrogated by pretreatment of rat adipocytes using SB203580. In summary, LBP-4a improved insulin resistance via translocation and activation of GLUT4 in OLETF rats, and the activation of PI3-K and p38 MAPK contributed to these effects.

Lowered insulin signalling ameliorates age-related sleep fragmentation in Drosophila

Reduced insulin signaling improves sleep quality in flies and is protective against age-related sleep deterioration.

Sleep fragmentation, particularly reduced and interrupted night sleep, impairs the quality of life of older people. Strikingly similar declines in sleep quality are seen during ageing in laboratory animals, including the fruit fly Drosophila. We investigated whether reduced activity of the nutrient- and stress-sensing insulin/insulin-like growth factor (IIS)/TOR signalling network, which ameliorates ageing in diverse organisms, could rescue the sleep fragmentation of ageing Drosophila. Lowered IIS/TOR network activity improved sleep quality, with increased night sleep and day activity and reduced sleep fragmentation. Reduced TOR activity, even when started for the first time late in life, improved sleep quality. The effects of reduced IIS/TOR network activity on day and night phenotypes were mediated through distinct mechanisms: Day activity was induced by adipokinetic hormone, dFOXO, and enhanced octopaminergic signalling. In contrast, night sleep duration and consolidation were dependent on reduced S6K and dopaminergic signalling. Our findings highlight the importance of different IIS/TOR components as potential therapeutic targets for pharmacological treatment of age-related sleep fragmentation in humans.

Sleep is essential for human health, but the quality of this fundamental physiological process declines with age and reduces quality of life. We therefore investigated the mechanisms by which ageing impairs sleep. We used the fruit fly Drosophila, whose sleep has many features in common with that of humans, including the age-related decline in quality. We examined the role of the insulin/IGF (IIS) and TOR signaling network, which has an evolutionarily conserved role in ageing. We found that flies with reduced IIS activity had improved sleep quality at night and higher activity levels by day. Importantly, day activity and night sleep were regulated through distinct mechanisms—day activity by the key IIS transcription factor dFOXO, adipokinetic hormone, and octopaminergic signalling—whereas night sleep was mediated through TOR and dopaminergic signalling. Surprisingly, acute inhibition of TOR, by rapamycin, even in old flies, improved sleep quality, suggesting that age-related sleep decline is reversible even after it has commenced. Given the high evolutionarily conservation of IIS and TOR function, our results implicate potential therapeutic targets to improve sleep quality in humans.

Contribution of transcriptional and translational mechanisms to the recovery aspect of sleep regulation

Sleep parallels brain functioning and mental health. Neuronal activity during wakefulness leads to a subsequent increase in sleep intensity as measured using electroencephalographic slow-wave activity (SWA; index of neuronal synchrony in the low-frequency range). Wakefulness, and particularly prolonged wakefulness, also drives important changes in brain gene expression and changes in protein regulation. The role of these two cellular mechanisms in sleep-wake regulation has typically been studied independently, and their exact contribution to SWA remains poorly defined. In this review, we highlight that many transcriptional pathways driven by sleep deprivation are associated to protein regulation. We first describe the relationship between cytokines, clock genes, and markers of sleep need with an emphasis on transcriptional processes. Observations regarding the role of protein metabolism in sleep-wake regulation are then depicted while presenting interconnections between transcriptional and translational responses driven by sleep loss. Lastly, a manner by which this integrated response can feed back on neuronal network activity to determine sleep intensity is proposed. Overall, the literature supports that a complex cross-talk between transcriptional and translational regulation during prolonged wakefulness drives the changes in sleep intensity as a function of the sleep/wake history.

Sleep, plasticity and the pathophysiology of neurodevelopmental disorders: the potential roles of protein synthesis and other cellular processes

Sleep is important for neural plasticity, and plasticity underlies sleep-dependent memory consolidation. It is widely appreciated that protein synthesis plays an essential role in neural plasticity. Studies of sleep-dependent memory and sleep-dependent plasticity have begun to examine alterations in these functions in populations with neurological and psychiatric disorders. Such an approach acknowledges that disordered sleep may have functional consequences during wakefulness. Although neurodevelopmental disorders are not considered to be sleep disorders per se, recent data has revealed that sleep abnormalities are among the most prevalent and common symptoms and may contribute to the progression of these disorders. The main goal of this review is to highlight the role of disordered sleep in the pathology of neurodevelopmental disorders and to examine some potential mechanisms by which sleep-dependent plasticity may be altered. We will also briefly attempt to extend the same logic to the other end of the developmental spectrum and describe a potential role of disordered sleep in the pathology of neurodegenerative diseases. We conclude by discussing ongoing studies that might provide a more integrative approach to the study of sleep, plasticity, and neurodevelopmental disorders.

Salubrinal, an endoplasmic reticulum stress blocker, modulates sleep homeostasis and activation of sleep- and wake-regulatory neurons

Endoplasmic reticulum (ER) stress has been associated with the regulation of sleep and wake. We have previously shown that i.c.v. administration of a specific ER stress modulator, Salubrinal (SALUB), which inhibits global protein translation by blocking the dephosphorylation of eukaryotic initiation factor 2α (p-eIF2α), increased non-rapid eye movement (NREM) sleep. Here we report on the relationship between ER stress response and sleep homeostasis by measuring the amount and intensity of homeostatic recovery sleep in response to the i.c.v. administration of SALUB in adult freely behaving rats. We have also tested the hypothesis that SALUB induces sleep by activating sleep-promoting neurons and inhibiting wake-promoting neurons in the basal forebrain (BF) and hypothalamus by quantifying the effects of SALUB treatment on c-Fos expression in those neuronal groups. The present study found that i.c.v. administration of SALUB significantly modified the homeostatic sleep response. SALUB administered during sleep deprivation increased sleep intensity, indicated by slow-wave activity (SWA), during recovery sleep, whereas its administration during recovery sleep increased the amount of recovery sleep. We also found that SALUB induced c-Fos activation of GABAergic neurons in the sleep-promoting rostral median preoptic nucleus while simultaneously reducing c-Fos activation of wake-promoting lateral hypothalamic orexin-expressing neurons and magnocellular BF cholinergic neurons. The current findings suggest that ER stress pathway plays a role in the homeostatic control of NREM sleep in response to sleep deprivation and provides a mechanistic explanation for the sleep modulation by molecules signaling the need for brain protein synthesis.

Salubrinal, an inhibitor of protein synthesis, promotes deep slow wave sleep

Previous work showed that sleep is associated with increased brain protein synthesis and that arrest of protein synthesis facilitates sleep. Arrest of protein synthesis is induced during the endoplasmic reticulum (ER) stress response, through phosphorylation of eukaryotic initiation factor 2alpha (p-eIF2alpha). We tested a hypothesis that elevation of p-eIF2alpha would facilitate sleep. We studied the effects of intracerebroventricular infusion of salubrinal (Salub), which increases p-eIF2alpha by inhibiting its dephosphorylation. Salub increased deep slow wave sleep by 255%, while reducing active waking by 49%. Delta power within non-rapid eye movement (NREM) sleep was increased, while power in the sigma, beta, and gamma bands during NREM was reduced. We found that Salub increased expression of p-eIF2alpha in the basal forebrain (BF) area, a sleep-wake regulatory brain region. Therefore, we quantified the p-eIF2alpha-immunolabeled neurons in the BF area; Salub administration increased the number of p-eIF2alpha-expressing noncholinergic neurons in the caudal BF. In addition, Salub also increased the intensity of p-eIF2alpha expression in both cholinergic and noncholinergic neurons, but this was more widespread among the noncholinergic neurons. Our findings support a hypothesis that sleep is facilitated by signals associated with the ER stress response.