Amandine Valomon

Regulation of alternative splicing by the circadian clock and food related cues

BackgroundThe circadian clock orchestrates daily rhythms in metabolism, physiology and behaviour that allow organisms to anticipate regular changes in their environment, increasing their adaptation. Such circadian phenotypes are underpinned by daily rhythms in gene expression. Little is known, however, about the contribution of post-transcriptional processes, particularly alternative splicing.ResultsUsing Affymetrix mouse exon-arrays, we identified exons with circadian alternative splicing in the liver. Validated circadian exons were regulated in a tissue-dependent manner and were present in genes with circadian transcript abundance. Furthermore, an analysis of circadian mutant Vipr2-/- mice revealed the existence of distinct physiological pathways controlling circadian alternative splicing and RNA binding protein expression, with contrasting dependence on Vipr2-mediated physiological signals. This view was corroborated by the analysis of the effect of fasting on circadian alternative splicing. Feeding is an important circadian stimulus, and we found that fasting both modulates hepatic circadian alternative splicing in an exon-dependent manner and changes the temporal relationship with transcript-level expression.ConclusionsThe circadian clock regulates alternative splicing in a manner that is both tissue-dependent and concurrent with circadian transcript abundance. This adds a novel temporal dimension to the regulation of mammalian alternative splicing. Moreover, our results demonstrate that circadian alternative splicing is regulated by the interaction between distinct physiological cues, and illustrates the capability of single genes to integrate circadian signals at different levels of regulation.

Human Melatonin and Alerting Response to Blue-Enriched Light Depend on a Polymorphism in the Clock Gene PER3

CONTEXT Light exposure, particularly at the short-wavelength range, triggers several nonvisual responses in humans. However, the extent to which the melatonin-suppressing and alerting effect of light differs among individuals remains unknown. OBJECTIVE Here we investigated whether blue-enriched polychromatic light impacts differentially on melatonin and subjective and objective alertness in healthy participants genotyped for the PERIOD3 (PER3) variable-number, tandem-repeat polymorphism. DESIGN, SETTING, AND PARTICIPANTS Eighteen healthy young men homozygous for the PER3 polymorphism (PER3(5/5)and PER3(4/4)) underwent a balanced crossover design during the winter season, with light exposure to compact fluorescent lamps of 40 lux at 6500 K and at 2500 K during 2 h in the evening. RESULTS In comparison to light at 2500 K, blue-enriched light at 6500 K induced a significant suppression of the evening rise in endogenous melatonin levels in PER3(5/5) individuals but not in PER3(4/4). Likewise, PER3(5/5) individuals exhibited a more pronounced alerting response to light at 6500 K than PER3(4/4) volunteers. Waking electroencephalographic activity in the theta range (5-7 Hz), a putative correlate of sleepiness, was drastically attenuated during light exposure at 6500 K in PER3(5/5) individuals as compared with PER3(4/4). CONCLUSIONS We provide first evidence that humans homozygous for the PER3 5/5 allele are particularly sensitive to blue-enriched light, as indexed by the suppression of endogenous melatonin and waking theta activity. Light sensitivity in humans may be modulated by a clock gene polymorphism implicated in the sleep-wake regulation.

Genetic polymorphisms of DAT1 and COMT differentially associate with actigraphy-derived sleep–wake cycles in young adults

Accumulating evidence suggests that dopamine plays a key role in sleep–wake regulation. Cerebral dopamine levels are regulated primarily by the dopamine transporter (DAT) in the striatum and by catechol-O-methyl-transferase (COMT) in the prefrontal cortex. We hypothesized that the variable-number-tandem-repeat (VNTR) polymorphism in the 3′-untranslated region of the gene encoding DAT (DAT1, SLC6A3; rs28363170) and the Val158Met polymorphism of COMT (rs4680) differently affect actigraphy-derived rest-activity cycles and sleep estimates in healthy adults (65 men; 45 women; age range: 19–35 years). Daytime sleepiness, continuous rest-actigraphy and sleep diary data during roughly 4-weeks were analyzed. Nine-repeat (9R) allele carriers of DAT1 (n = 48) more often reported elevated sleepiness (Epworth sleepiness score ≥10) than 10-repeat (10R) allele homozygotes (n = 62, p < 0.02). Moreover, male 9R allele carriers showed higher wrist activity, whereas this difference was not present in women (“DAT1 genotype” × “gender” interaction: p < 0.005). Rest-activity patterns did not differ among COMT genotypes. Nevertheless, a significant “COMT genotype” × “type of day” (workdays vs. rest days) interaction for sleep duration was observed (p = 0.04). The Val/Val (n = 36) and Met/Met (n = 24) homozygotes habitually prolonged sleep on rest days compared to workdays by more than 30 min, while Val/Met heterozygotes (n = 50) did not significantly extend their sleep (mean difference: 7 min). Moreover, whereas the proportion of women among the genotype groups did not differ, COMT genotype affected body-mass-index (BMI), such that Val/Met individuals had lower BMI than the homozygous genotypes (p < 0.04). While awaiting independent replication and confirmation, our data support an association of genetically-determined differences in cerebral dopaminergic neurotransmission with daytime sleepiness and individual rest-activity profiles, as well as other sleep-associated health characteristics such as the regulation of BMI. The differential associations of DAT1 and COMT polymorphisms may reflect the distinct local expression of the encoded proteins in the brain.

Light modulation of human sleep depends on a polymorphism in the clock gene Period3

Non-image-forming (NIF) responses to light powerfully modulate human physiology. However, it remains scarcely understood how NIF responses to light modulate human sleep and its EEG hallmarks, and if there are differences across individuals. Here we investigated NIF responses to light on sleep in individuals genotyped for the PERIOD3 (PER3) variable-number tandem-repeat (VNTR) polymorphism. Eighteen healthy young men (20-28 years; mean ± SEM: 25.9 ± 1.2) homozygous for the PER3 polymorphism were matched by age, body-mass index, and ethnicity. The study protocol comprised a balanced cross-over design during the winter, during which participants were exposed to either light of 40 lx at 6,500 K (blue-enriched) or light at 2,500 K (non-blue enriched), during 2h in the evening. Compared to light at 2,500 K, light at 6,500 K induced a significant increase in all-night NREM sleep slow-wave activity (SWA: 1.0-4.5 Hz) in the occipital cortex for PER3(5/5) individuals, but not for PER3(4/4) volunteers. Dynamics of SWA across sleep cycles revealed increased occipital NREM sleep SWA for virtually all sleep episode only for PER3(5/5) individuals. Furthermore, they experienced light at 6,500 K as significantly brighter. Intriguingly, this subjective perception of brightness significantly predicted their increased occipital SWA throughout the sleep episode. Our data indicate that humans homozygous for the PER3(5/5) allele are more sensitive to NIF light effects, as indexed by specific changes in sleep EEG activity. Ultimately, individual differences in NIF light responses on sleep may depend on a clock gene polymorphism involved in sleep-wake regulation.

Sleep Pharmacogenetics: Personalized Sleep-Wake Therapy

Research spanning (genetically engineered) animal models, healthy volunteers, and sleep-disordered patients has identified the neurotransmitters and neuromodulators dopamine, serotonin, norepinephrine, histamine, hypocretin, melatonin, glutamate, acetylcholine, γ-amino-butyric acid, and adenosine as important players in the regulation and maintenance of sleep-wake-dependent changes in neuronal activity and the sleep-wake continuum. Dysregulation of these neurochemical systems leads to sleep-wake disorders. Most currently available pharmacological treatments are symptomatic rather than causal, and their beneficial and adverse effects are often variable and in part genetically determined. To evaluate opportunities for evidence-based personalized medicine with present and future sleep-wake therapeutics, we review here the impact of known genetic variants affecting exposure of and sensitivity to drugs targeting the neurochemistry of sleep-wake regulation and the pathophysiology of sleep-wake disturbances. Many functional polymorphisms modify drug response phenotypes relevant for sleep. To corroborate the importance of these and newly identified variants for personalized sleep-wake therapy, human sleep pharmacogenetics should be complemented with pharmacogenomic investigations, research about sleep-wake-dependent pharmacological actions, and studies in mice lacking specific genes. These strategies, together with future knowledge about epigenetic mechanisms affecting sleep-wake physiology and treatment outcomes, may lead to potent and safe novel therapies for the increasing number of sleep-disordered patients (e.g., in aged populations).

Functional Polymorphisms in Dopaminergic Genes Modulate Neurobehavioral and Neurophysiological Consequences of Sleep Deprivation

Sleep deprivation impairs cognitive performance and reliably alters brain activation in wakefulness and sleep. Nevertheless, the molecular regulators of prolonged wakefulness remain poorly understood. Evidence from genetic, behavioral, pharmacologic and imaging studies suggest that dopaminergic signaling contributes to the behavioral and electroencephalographic (EEG) consequences of sleep loss, although direct human evidence thereof is missing. We tested whether dopamine neurotransmission regulate sustained attention and evolution of EEG power during prolonged wakefulness. Here, we studied the effects of functional genetic variation in the dopamine transporter (DAT1) and the dopamine D2 receptor (DRD2) genes, on psychomotor performance and standardized waking EEG oscillations during 40 hours of wakefulness in 64 to 82 healthy volunteers. Sleep deprivation consistently enhanced sleepiness, lapses of attention and the theta-to-alpha power ratio (TAR) in the waking EEG. Importantly, DAT1 and DRD2 genotypes distinctly modulated sleep loss-induced changes in subjective sleepiness, PVT lapses and TAR, according to inverted U-shaped relationships. Together, the data suggest that genetically determined differences in DAT1 and DRD2 expression modulate functional consequences of sleep deprivation, supporting the hypothesis that striato-thalamo-cortical dopaminergic pathways modulate the neurobehavioral and neurophysiological consequences of sleep loss in humans.

Integrative Transcriptome Profiling of Cognitive Aging and Its Preservation through Ser/Thr Protein Phosphatase Regulation.

Environmental enrichment has been reported to delay or restore age-related cognitive deficits, however, a mechanism to account for the cause and progression of normal cognitive decline and its preservation by environmental enrichment is lacking. Using genome-wide SAGE-Seq, we provide a global assessment of differentially expressed genes altered with age and environmental enrichment in the hippocampus. Qualitative and quantitative proteomics in naïve young and aged mice was used to further identify phosphorylated proteins differentially expressed with age. We found that increased expression of endogenous protein phosphatase-1 inhibitors in aged mice may be characteristic of long-term environmental enrichment and improved cognitive status. As such, hippocampus-dependent performances in spatial, recognition, and associative memories, which are sensitive to aging, were preserved by environmental enrichment and accompanied by decreased protein phosphatase activity. Age-associated phosphorylated proteins were also found to correspond to the functional categories of age-associated genes identified through transcriptome analysis. Together, this study provides a comprehensive map of the transcriptome and proteome in the aging brain, and elucidates endogenous protein phosphatase-1 inhibition as a potential means through which environmental enrichment may ameliorate age-related cognitive deficits.

Effects of COMT genotype and tolcapone on lapses of sustained attention after sleep deprivation in healthy young men

Tolcapone, a brain penetrant selective inhibitor of catechol-O-methyltransferase (COMT) devoid of psychostimulant properties, improves cognition and cortical information processing in rested volunteers, depending on the genotype of the functional Val158Met polymorphism of COMT. The impact of this common genetic variant on behavioral and neurophysiological markers of increased sleep need after sleep loss is controversial. Here we investigated the potential usefulness of tolcapone to mitigate consequences of sleep deprivation on lapses of sustained attention, and tested the hypothesis that dopamine signaling in the prefrontal cortex (PFC) causally contributes to neurobehavioral and neurophysiological markers of sleep homeostasis in humans. We first quantified in 73 young male volunteers the impact of COMT genotype on the evolution of attentional lapses during 40 h of extended wakefulness. Subsequently, we tested in an independent group of 30 young men whether selective inhibition of COMT activity with tolcapone counteracts attentional and neurophysiological markers of elevated sleep need in a genotype-dependent manner. Neither COMT genotype nor tolcapone affected brain electrical activity in wakefulness and sleep. By contrast, COMT genotype and tolcapone modulated the sleep loss-induced impairment of vigilant attention. More specifically, Val/Met heterozygotes produced twice as many lapses after a night without sleep than Met/Met homozygotes. Unexpectedly, tolcapone further deteriorated the sleep loss-induced performance deficits when compared to placebo, particularly in Val/Met and Met/Met genotypes. The findings suggest that PFC dopaminergic tone regulates sustained attention after sleep loss according to an inverse U-shape relationship, independently of neurophysiological markers of elevated sleep need.

Genotype-dependent deterioration of sustained attention by the COMT inhibitor tolcapone after sleep deprivation

Introduction Elevated sleepiness and impaired vigilance due to medical disorders, is often treated by drugs that enhance dopaminergic neurotransmission, including modafinil, caffeine or cocaine [1]. Tolcapone is a brain penetrant selective inhibitor of catechol-O-methyltransferase (COMT) devoid of psychostimulant properties that leads to relatively specific increases in prefrontal cortex (PFC) dopamine signaling [2,3]. Because it hardly affects striatal domapinergic transmission, tolcapone may mitigate subjective and behavioral consequences of sleep deprivation without unwanted psychostimulant adverse effects [2]. Tolcapone also improves cognition and cortical information processing in rested volunteers, depending on the genotype of the functional Val158Met polymorphism of COMT [3]. The impact of this common genetic variant for efficient treatment of hypersomnolence and behavioral markers of increased sleep need after sleep loss is controversial. Here we investigated the potential usefulness of tolcapone to mitigate consequences of sleep deprivation on lapses of sustained attention, and tested the hypothesis that dopamine signaling in the prefrontal cortex (PFC) causally contributes to neurobehavioral and neurophysiological markers of human sleep homeostasis. Methods We first quantified the impact of COMT genotype (SNP-Id: rs4680) on the evolution of attentional lapses during two days of extended wakefulness in a non-tolcapone treated group of 73 volunteers. Subsequently, in an independent group of 30 healthy male study participants, we tested whether selective inhibition of COMT activity by tolcapone counteracts attentional and neurophysiological markers of elevated sleep need in a COMT genotype-dependent manner. 2 x 100 mg tolcapone were administered after 11 and 23 hours, in a randomized, double-blind, placebo-controlled, cross-over design. The psychomotor Vigilance Test (PVT) and objective electroencephalogram (EEG) recordings were carried out in three-hour intervals among all 103 volunteers across the 40 hours of prolonged wakefulness. Repeated measure linear mixed-models were applied, followed by multiple comparison corrected post-hoc testing when appropriate. Results Both COMT genotype and tolcapone modulated the sleep-loss induced impairment of vigilant attention. More specifically, data from the non-tolcapone treated group revealed that Val/Met heterozygotes produced twice as many lapses after a night without sleep compared to Met/Met homozygotes (p Conclusions The current results demonstrate that PFC dopaminergic neurotransmission regulates attentional lapses during sleep deprivation without changing neurophysiological markers of sleep homeostasis. Intriguingly, selective inhibition of COMT can even reverse the expected beneficial effects of pharmacologically enhanced dopaminergic tone after prolonged wakefulness. These findings may have important implications, given the increased use of stimulants in healthy people aimed at improving vigilance and cognitive functions [1,4].