High calorie diet augments age-associats sleep impairment in Drosophila

Preference of position in the proximity of various sugars revealed by location analysis of Drosophila melanogaster

Feeding behaviors are determined by two main factors. One is the internal state, such as hunger or previous experiences; the other is external factors, such as sensory stimulation. During starvation, animals must balance food-seeking behavior with energy conservation. The fruit fly, Drosophila melanogaster, serves as a useful model for studying food selectivity and various behaviors related to food intake. However, few studies have directly connected food selectivity with other behaviors, such as locomotor activity and sleep. In this study, we report that flies exhibited a preference for specific positions and spent more time in the proximity of sweet sugars, such as sucrose and sucralose, but not non-sweet and nutritious sugars like xylitol and sorbitol. On the other hand, prolonged exposure to sorbitol increased the staying time of flies in the proximity of sorbitol. Additionally, after starvation, flies immediately exhibited a position preference in the proximity of sorbitol. These findings suggest that flies prefer the proximity of sweet food, and starvation alters their preference for nutritious food, which may be beneficial for their survival.

Chronic sleep loss sensitizes Drosophila melanogaster to nitrogen stress

Chronic sleep loss profoundly impacts metabolic health and shortens lifespan, but studies of the mechanisms involved have focused largely on acute sleep deprivation.1,2 To identify metabolic consequences of chronically reduced sleep, we conducted unbiased metabolomics on heads of three adult Drosophila short-sleeping mutants with very different mechanisms of sleep loss: fumin (fmn), redeye (rye), and sleepless (sss).3,4,5,6,7 Common features included elevated ornithine and polyamines, with lipid, acyl-carnitine, and TCA cycle changes suggesting mitochondrial dysfunction. Studies of excretion demonstrate inefficient nitrogen elimination in adult sleep mutants, likely contributing to their polyamine accumulation. Increasing levels of polyamines, particularly putrescine, promote sleep in control flies but poison sleep mutants. This parallels the broadly enhanced toxicity of high dietary nitrogen load from protein in chronically sleep-restricted Drosophila, including both sleep mutants and flies with hyper-activated wake-promoting neurons. Together, our results implicate nitrogen stress as a novel mechanism linking chronic sleep loss to adverse health outcomes-and perhaps for linking food and sleep homeostasis at the cellular level in healthy organisms.

The regulation of circadian rhythm by insulin signaling in Drosophila

Circadian rhythm is well conserved across species and relates to numerous biological functions. Circadian misalignment impairs metabolic function. Insulin signaling is a key modulator of metabolism in the fruit fly as well as mammals and its defects cause metabolic disease. Daily diet timing affects both circadian rhythmicities of behavior and metabolism. However, the relationship between the circadian clock and insulin signaling is still elusive. Here, we report that insulin signaling regulates circadian rhythm in Drosophila melanogaster. We found the insulin receptor substrate mutant, chico¹, showed a shorter free-running circadian period. The knockdown of insulin receptor (InR), or another signaling molecule downstream of InR, dp110, or the expression of a dominant-negative form of InR resulted in the shortening of the circadian period and diminished its amplitude. The impairment of insulin signaling both in all neurons and restricted circadian clock neurons altered circadian period length, indicating that the insulin signaling plays a role in the regulation of circadian rhythm in clock cells. Among 3 insulin-like ligands expressed in the brain, dilp5 showed the largest effect on circadian phenotype when deleted. These results suggested that insulin signaling contributes to the robustness of the circadian oscillation and coordinates metabolism and behavior.

Insulin signaling in clock neurons regulates sleep in Drosophila

Sleep relates to numerous biological functions, including metabolism. Both dietary conditions and genes related to metabolism are known to affect sleep behavior. Insulin signaling is well conserved across species including the fruit fly and relates to both metabolism and sleep. However, the neural mechanism of sleep regulation by insulin signaling is poorly understood. Here, we report that insulin signaling in specific neurons regulates sleep in Drosophila melanogaster. We analyzed the sleep behavior of flies with the mutation in insulin-like ligands expressed in the brain and found that three insulin-like ligands participate in sleep regulation with some redundancy. We next used 21 Gal4 drivers to express a dominant-negative form of the insulin receptor (InR DN) in various neurons including circadian clock neurons, which express the clock gene, and the pars intercerebralis (PI). Inhibition of insulin signaling in the anterior dorsal neuron group 1 (DN1a) decreased sleep. Additionally, the same manipulation in PI also decreased sleep. Pan-neuronal induced expression of InR DN also decreased sleep. These results suggested that insulin signaling in DN1a and PI regulates sleep.

Effects of D-amino acids on sleep in Drosophila

Sleep and metabolism are closely related and nutritional elements such as sugars and amino acids are known to regulate sleep differently. Here we comprehensively investigated the effects of D-amino acids fed in the diet on the sleep of Drosophila melanogaster. Among 19 amino acids examined, both D-serine (Ser) and D-glutamine (Gln) induced a significant increase in sleep amount and the effect of D-Ser was the largest at the same concentration of 1% of the food. The effects were proportional to its concentration and significant above 0.5% (about 50 mM). D-Ser is known to bind NR1 subunit of NMDA type glutamate receptor (NMDAR) and activate it. D-Ser did not increase the sleep of the NR1 hypomorphic mutant flies indicating its effects on sleep is mediated by NMDAR. In addition, hypomorphic mutants of D-amino acid oxidase (Daao1), which catabolizes D-amino acids and its disruption is known to increase D-Ser in the brain, showed increase in sleep. These results altogether suggested that D-Ser activated NMDAR in the brain thus increase sleep, and that D-Ser work physiologically to regulate sleep.

Short-term maintenance on a high-sucrose diet alleviates aging-induced sleep fragmentation in drosophila

Sleep is a fundamental behavior in an animal’s life influenced by many internal and external factors, such as aging and diet. Critically, poor sleep quality places people at risk of serious medical conditions. Because aging impairs quality of sleep, measures to improve sleep quality for elderly people are needed. Given that diet can influence many aspects of sleep, we investigated whether a high-sucrose diet (HSD) affected aging-induced sleep fragmentation using the fruit fly, Drosophila melanogaster. Drosophila is a valuable model for studying sleep due to its genetic tractability and many similarities with mammalian sleep. Total sleep duration, sleep bout numbers (SBN), and average sleep bout length (ABL) were compared between young and old flies on a normal sucrose diet (NSD) or HSD. On the NSD, old flies slept slightly more and showed increased SBN and reduced ABL, indicating increased sleep fragmentation. Short-term maintenance of flies in HSD (up to 8 days), but not long-term maintenance (up to 35 days), suppressed aging-induced sleep fragmentation. Our study provides meaningful strategies for preventing the deterioration of sleep quality in the elderly.

Dietary fatty acids promote sleep through a taste-independent mechanism

Consumption of foods that are high in fat contribute to obesity and metabolism-related disorders. Dietary lipids are comprised of triglycerides and fatty acids, and the highly palatable taste of dietary fatty acids promotes food consumption, activates reward centers in mammals and underlies hedonic feeding. Despite the central role of dietary fats in the regulation of food intake and the etiology of metabolic diseases, little is known about how fat consumption regulates sleep. The fruit fly, Drosophila melanogaster, provides a powerful model system for the study of sleep and metabolic traits, and flies potently regulate sleep in accordance with food availability. To investigate the effects of dietary fats on sleep regulation, we have supplemented fatty acids into the diet of Drosophila and measured their effects on sleep and activity. We found that flies fed a diet of hexanoic acid, a medium-chain fatty acid that is a by-product of yeast fermentation, slept more than flies starved on an agar diet. To assess whether dietary fatty acids regulate sleep through the taste system, we assessed sleep in flies with a mutation in the hexanoic acid receptor Ionotropic receptor 56D, which is required for fatty acid taste perception. We found that these flies also sleep more than agar-fed flies when fed a hexanoic acid diet, suggesting the sleep promoting effect of hexanoic acid is not dependent on sensory perception. Taken together, these findings provide a platform to investigate the molecular and neural basis for fatty acid-dependent modulation of sleep.

Loss of angiotensin-converting enzyme-related (ACER) peptidase disrupts behavioural and metabolic responses to diet in Drosophila melanogaster

Drosophila Acer (Angiotensin-converting enzyme-related) encodes a member of the angiotensin-converting enzyme (ACE) family of metallopeptidases that in mammals play roles in the endocrine regulation of blood homeostasis. ACE is also expressed in adipose tissue, where it is thought to play a role in metabolic regulation. Drosophila ACER is expressed in the adult fat body of the head and abdomen and is secreted into the haemolymph. Acer null mutants have previously been found to have reduced night-time sleep and greater sleep fragmentation. ACER may thus be part of a signalling system linking metabolism with sleep. To further understand the role of ACER in response to diet, we measured sleep and other nutrient-responsive phenotypes in Acer null flies under different dietary conditions. We show that loss of Acer disrupts the normal response of sleep to changes in nutrition. Other nutrient-sensitive phenotypes, including survival and glycogen storage, were also altered in the Acer mutant but lipid storage was not. Although the physiological substrate of the ACER peptidase has not been identified, an alteration of the normal nutrient-dependent control of Drosophila insulin-like peptide 5 protein in the Acer mutant suggests insulin/IGF-like signalling as a candidate pathway modulated by ACER in the nutrient-dependent control of sleep, survival and metabolism.

RNA-Sequencing of Drosophila melanogaster Head Tissue on High-Sugar and High-Fat Diets

Obesity has been shown to increase risk for cardiovascular disease and type-2 diabetes. In addition, it has been implicated in aggravation of neurological conditions such as Alzheimer’s. In the model organism Drosophila melanogaster, a physiological state mimicking diet-induced obesity can be induced by subjecting fruit flies to a solid medium disproportionately higher in sugar than protein, or that has been supplemented with a rich source of saturated fat. These flies can exhibit increased circulating glucose levels, increased triglyceride content, insulin-like peptide resistance, and behavior indicative of neurological decline. We subjected flies to variants of the high-sugar diet, high-fat diet, or normal (control) diet, followed by a total RNA extraction from fly heads of each diet group for the purpose of Poly-A selected RNA-Sequencing. Our objective was to identify the effects of obesogenic diets on transcriptome patterns, how they differed between obesogenic diets, and identify genes that may relate to pathogenesis accompanying an obesity-like state. Gene ontology analysis indicated an overrepresentation of affected genes associated with immunity, metabolism, and hemocyanin in the high-fat diet group, and CHK, cell cycle activity, and DNA binding and transcription in the high-sugar diet group. Our results also indicate differences in the effects of the high-fat diet and high-sugar diet on expression profiles in head tissue of flies, despite the reportedly similar phenotypic impacts of the diets. The impacted genes, and how they may relate to pathogenesis in the Drosophila obesity-like state, warrant further experimental investigation.

Sweetness induces sleep through gustatory signalling independent of nutritional value in a starved fruit fly

Starvation reduces sleep in various animal species including humans and fruit flies. Immediate hunger and the following insufficient nutritional status resulting from starvation may affect sleep and arousal differently. In order to clarify the mechanism underlying the relationship between diet and sleep, we analysed the sleep behaviour of Drosophila melanogaster that were either starved or fed with different types of sugars. Starved flies showed longer activity bouts, short sleep bouts and a decreased arousal threshold. Non-nutritive sweeteners such as sucralose and arabinose, which are sweet but not nutritive, induced sleep in starved flies, but sleep bout length and the arousal threshold was short and decreased, respectively. On the other hand, sorbitol, which is not sweet but nutritive, did not induce sleep, but slightly increased the lowered arousal threshold. Activation of sweetness receptor expressing neurons induced sleep in starved flies. These results suggest that sweetness alone is sufficient to induce sleep in starved flies and that the nutritional status affects sleep homeostasis by decreasing the arousal threshold, which resulted in short sleep bouts in Drosophila.

An Ecological Perspective on Sleep Disruption

Despite its evolutionary importance and apparent ubiquity among animals, the ecological significance of sleep is largely unresolved. The ecology of sleep has been particularly neglected in invertebrates. In insects, recent neurobehavioral research convincingly demonstrates that resting behavior shares several common characteristics with sleep in vertebrates. Laboratory studies have produced compelling evidence that sleep disruption can cause changes in insect daily activity patterns (via "sleep rebound") and have consequences for behavioral performance during active periods. However, factors that could cause insect sleep disruption in nature have not been considered nor have the ecological consequences. Drawing on evidence from laboratory studies, we argue that sleep disruption may be an overlooked component of insect ecology and could be caused by a variety of anthropogenic and nonanthropogenic factors in nature. We identify several candidate sleep-disrupting factors and provide new insights on the potential consequences of sleep disruption on individual fitness, species interactions, and ecosystem services. We propose an experimental framework to bridge the current gap in knowledge between laboratory and field studies. We conclude that sleep disruption is a potential mechanism underpinning variation in behavioral, population, and community-level processes associated with several aspects of global change.

AxGxE: Using Flies to Interrogate the Complex Etiology of Neurodegenerative Disease

Progressive and late-onset neurological disorders such as Parkinson's disease and Alzheimer's disease affect up to 50 million people globally-a number postulated to double every 20 years in a continually aging population. While predisposing allelic variants in several genes clearly confer risk, individual age and specific environmental influences are equally important discriminators of disease onset age and progression. However, none of these factors can independently predict disease with significant precision. Therefore, we must actively develop models that accommodate contributions from all factors, potentially resulting in an A × G × E (age-gene-environment) metric that reflects individual cumulative risk and reliably forecasts disease outcomes. This effort can only be enabled by a deep quantitative understanding of the contribution of these factors to neurodegenerative disease, both individually and in combination. This is also an important consideration because neuronal loss typically precedes clinical presentation and disease-modifying therapies are contingent on early diagnosis that is likely to be informed by an accurate estimation of individual risk. Although epidemiological studies continue to make strong advances in these areas with the advent of powerful "omics"-based approaches, systematic phenotypic modeling of AxGxE interactions is currently more feasible in model organisms such as Drosophila melanogaster where all three parameters can be manipulated with manageable experimental burden. Here, we outline the advantages of using fruit flies for investigating these complex interactions and highlight potential approaches that might help synthesize existing information from diverse fields into a cogent description of age-dependent, environmental, and genetic risk factors in the pathophysiology of neurological disorders.

FMRFamide signaling promotes stress-induced sleep in Drosophila

Enhanced sleep in response to cellular stress is a conserved adaptive behavior across multiple species, but the mechanism of this process is poorly understood. Drosophila melanogaster increases sleep following exposure to septic or aseptic injury, and Caenorhabditis elegans displays sleep-like quiescence following exposure to high temperatures that stress cells. We show here that, similar to C. elegans, Drosophila responds to heat stress with an increase in sleep. In contrast to Drosophila infection-induced sleep, heat-induced sleep is not sensitive to the time-of-day of the heat pulse. Moreover, the sleep response to heat stress does not require Relish, the NFκB transcription factor that is necessary for infection-induced sleep, indicating that sleep is induced by multiple mechanisms from different stress modalities. We identify a sleep-regulating role for a signaling pathway involving FMRFamide neuropeptides and their receptor FR. Animals mutant for either FMRFamide or for the FMRFamide receptor (FR) have a reduced recovery sleep in response to heat stress. FR mutants, in addition, show reduced sleep responses following infection with Serratia marcescens, and succumb to infection at a faster rate than wild-type controls. Together, these findings support the hypothesis that FMRFamide and its receptor promote an adaptive increase in sleep following stress. Because an FMRFamide-like neuropeptide plays a similar role in C. elegans, we propose that FRMFamide neuropeptide signaling is an ancient regulator of recovery sleep which occurs in response to cellular stress.

Sleep, Performance, and Memory in Flies

Drosophila has proven to be a powerful model to identify genes and circuits that impact sleep. While the majority of studies have primarily been interested in identifying manipulations that alter sleep time, a growing body of work has begun to focus on how changing sleep influences functional outcomes such as cognitive performance, structural plasticity, and metabolism to name a few. Evaluating sleep time provides an appropriate entry point into elucidating sleep function. However, it is not possible to fully understand how a manipulation has impacted sleep regulation without first establishing how it has affected the animals’ well-being. Synaptic plasticity and memory are important functional outcomes that can be used to asses an animal’s status. In this manuscript, we review recent advances in studies examining sleep, memory, and performance. We conclude that as Drosophila sleep researchers expand their analysis beyond sleep time, the opportunities to discover the function of sleep will be enhanced.

Functional characterization of dopamine transporter in vivo using Drosophila melanogaster behavioral assays

Dopamine mediates diverse functions such as motivation, reward, attention, learning/memory and sleep/arousal. Recent studies using model organisms including the fruit fly, have elucidated various physiological functions of dopamine, and identified specific neural circuits for these functions. Flies with mutations in the Drosophila dopamine transporter (dDAT) gene show enhanced dopamine signaling, and short sleep and memory impairment phenotypes. However, understanding the mechanism by which dopamine signaling causes these phenotypes requires an understanding of the dynamics of dopamine release. Here we report the effects of dDAT expression on behavioral traits. We show that dDAT expression in a subset of dopaminergic neurons is sufficient for normal sleep. dDAT expression in other cell types such as Kenyon cells and glial cells can also rescue the short sleep phenotype of dDAT mutants. dDAT mutants also show a down-regulation of the D1-like dopamine receptor dDA1, and this phenotype is rescued when dDAT is expressed in the same cell types in which it rescues sleep. On the other hand, dDAT overexpression in mushroom bodies, which are the target of memory forming dopamine neurons, abolishes olfactory aversive memory. Our data demonstrate that expression of extrasynaptic dopamine transporters can rescue some aspects of dopamine signaling in dopamine transporter mutants. These results provide novel insights into regulatory systems that modulate dopamine signaling.

Human longevity is associated with regular sleep patterns, maintenance of slow wave sleep, and favorable lipid profile

Some individuals are able to successfully reach very old ages, reflecting higher adaptation against age-associated effects. Sleep is one of the processes deeply affected by aging; however few studies evaluating sleep in long-lived individuals (aged over 85) have been reported to date. The aim of this study was to characterize the sleep patterns and biochemical profile of oldest old individuals (N = 10, age 85–105 years old) and compare them to young adults (N = 15, age 20–30 years old) and older adults (N = 13, age 60–70 years old). All subjects underwent full-night polysomnography, 1-week of actigraphic recording and peripheral blood collection. Sleep electroencephalogram spectral analysis was also performed. The oldest old individuals showed lower sleep efficiency and REM sleep when compared to the older adults, while stage N3 percentage and delta power were similar across the groups. Oldest old individuals maintained strictly regular sleep-wake schedules and also presented higher HDL-cholesterol and lower triglyceride levels than older adults. The present study revealed novel data regarding specific sleep patterns and maintenance of slow wave sleep in the oldest old group. Taken together with the favorable lipid profile, these results contribute with evidence to the importance of sleep and lipid metabolism regulation in the maintenance of longevity in humans.

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.

Deleterious effect of suboptimal diet on rest-activity cycle in Anastrepha ludens manifests itself with age

Activity patterns and sleep-wake cycles are among the physiological processes that change most prominently as animals age, and are often good indicators of healthspan. In this study, we used the video-based high-resolution Behavioral Monitoring System (BMS) to monitor the daily activity cycle of tephritid fruit flies Anastrepha ludens over their lifetime. Surprisingly, there was no dramatic change in activity profile with respect to age if flies were consistently fed with a nutritionally balanced diet. However, if flies were fed with sugar-only diet, their activity profile decreased in amplitude at old age, suggesting that suboptimal diet affected activity patterns, and its detrimental effect may not manifest itself until the animal ages. Moreover, by simulating different modes of behavior monitoring with a range of resolution and comparing the resulting conclusions, we confirmed the superior performance of video-based monitoring using high-resolution BMS in accurately representing activity patterns in an insect model.

Diet quality mediates activity patterns in adult Queensland fruit fly (Bactrocera tryoni)

Studies linking resource acquisition and trait expression have traditionally treated nutritional resources as a single currency, but recent research has shown that trait expression can depend as much on diet quality (nutrient composition) as on diet quantity (calories). Here, we investigate the role of nutrient composition and diet concentration on activity levels of adult Queensland fruit flies (Bactrocera tryoni Froggatt: Tephritidae). Male and female flies were fed diets that varied in the proportion of protein and carbohydrate as well as total amounts of protein and carbohydrate. Daily activity levels were then quantified using locomotor activity monitors during both light and dark phases. During the light phase, both sexes increased the proportion of time spent active and their rate of activity as diets became more carbohydrate-rich and concentrated. In contrast, during the dark phase, nutrient composition and concentration had no effect on the proportion of time spent active for either sex, although when active during the dark phase, activity rates were higher for flies fed more carbohydrate-rich and concentrated diets. Overall, nutritional composition of the diet affected activity levels to a greater extent than the total energetic content of the diet.

Molecular mechanisms of age-related sleep loss in the fruit fly - a mini-review

Across phyla, aging is associated with reduced sleep duration and efficiency. Both aging and sleep involve complex genetic architecture and diverse cell types and are heavily influenced by diet and environment. Therefore, understanding the molecular mechanisms of age-dependent changes in sleep will require integrative approaches that go beyond examining these two processes independently. The fruit fly, Drosophila melanogaster, provides a genetically amenable system for dissecting the molecular basis of these processes. In this review, we examine the role of metabolism and circadian rhythms in age-dependent sleep loss.

Pan-neuronal knockdown of the c-Jun N-terminal Kinase (JNK) results in a reduction in sleep and longevity in Drosophila

Sleep is a unique behavioral state that is conserved between species, and sleep regulation is closely associated to metabolism and aging. The fruit fly, Drosophila melanogaster has been used to study the molecular mechanism underlying these physiological processes. Here we show that the c-Jun N-terminal Kinase (JNK) gene, known as basket (bsk) in Drosophila, functions in neurons to regulate both sleep and longevity in Drosophila. Pan-neuronal knockdown of JNK mRNA expression by RNA interference resulted in a decrease in both sleep and longevity. A heterozygous knockout of JNK showed similar effects, indicating the molecular specificity. The JNK knockdown showed a normal arousal threshold and sleep rebound, suggesting that the basic sleep mechanism was not affected. JNK is known to be involved in the insulin pathway, which regulates metabolism and longevity. A JNK knockdown in insulin-producing neurons in the pars intercerebralis had slight effects on sleep. However, knocking down JNK in the mushroom body had a significant effect on sleep. These data suggest a unique sleep regulating pathway for JNK.