Sustained sleep fragmentation affects brain temperature, food intake and glucose tolerance in mice

Independent relationship between sleep apnea-specific hypoxic burden and glucolipid metabolism disorder: a cross-sectional study

OBJECTIVES

Obstructive sleep apnea (OSA) is associated with abnormal glucose and lipid metabolism. However, whether there is an independent association between Sleep Apnea-Specific Hypoxic Burden (SASHB) and glycolipid metabolism disorders in patients with OSA is unknown.

METHODS

We enrolled 2,173 participants with suspected OSA from January 2019 to July 2023 in this study. Polysomnographic variables, biochemical indicators, and physical measurements were collected from each participant. Multiple linear regression analyses were used to evaluate independent associations between SASHB, AHI, CT90 and glucose as well as lipid profile. Furthermore, logistic regressions were used to determine the odds ratios (ORs) for abnormal glucose and lipid metabolism across various SASHB, AHI, CT90 quartiles.

RESULTS

The SASHB was independently associated with fasting blood glucose (FBG) (β = 0.058, P = 0.016), fasting insulin (FIN) (β = 0.073, P < 0.001), homeostasis model assessment of insulin resistance (HOMA-IR) (β = 0.058, P = 0.011), total cholesterol (TC) (β = 0.100, P < 0.001), total triglycerides (TG) (β = 0.063, P = 0.011), low-density lipoprotein cholesterol (LDL-C) (β = 0.075, P = 0.003), apolipoprotein A-I (apoA-I) (β = 0.051, P = 0.049), apolipoprotein B (apoB) (β = 0.136, P < 0.001), apolipoprotein E (apoE) (β = 0.088, P < 0.001) after adjustments for confounding factors. Furthermore, the ORs for hyperinsulinemia across the higher SASHB quartiles were 1.527, 1.545, and 2.024 respectively, compared with the lowest quartile (P < 0.001 for a linear trend); the ORs for hyper-total cholesterolemia across the higher SASHB quartiles were 1.762, 1.998, and 2.708, compared with the lowest quartile (P < 0.001 for a linear trend) and the ORs for hyper-LDL cholesterolemia across the higher SASHB quartiles were 1.663, 1.695, and 2.316, compared with the lowest quartile (P < 0.001 for a linear trend). Notably, the ORs for hyper-triglyceridemia{1.471, 1.773, 2.099} and abnormal HOMA-IR{1.510, 1.492, 1.937} maintained a consistent trend across the SASHB quartiles.

CONCLUSIONS

We found SASHB was independently associated with hyperinsulinemia, abnormal HOMA-IR, hyper-total cholesterolemia, hyper-triglyceridemia and hyper-LDL cholesterolemia in Chinese Han population. Further prospective studies are needed to confirm that SASHB can be used as a predictor of abnormal glycolipid metabolism disorders in patients with OSA.

TRIAL REGISTRATION

ChiCTR1900025714 { http://www.chictr.org.cn/ }; Prospectively registered on 6 September 2019; China.

Effects of Chronic Sleep Restriction on Transcriptional Sirtuin 1 Signaling Regulation in Male Mice White Adipose Tissue

Chronic sleep restriction (CSR) is a prevalent issue in modern society that is associated with several pathological states, ranging from neuropsychiatric to metabolic diseases. Despite its known impact on metabolism, the specific effects of CSR on the molecular mechanisms involved in maintaining metabolic homeostasis at the level of white adipose tissue (WAT) remain poorly understood. Therefore, this study aimed to investigate the influence of CSR on sirtuin 1 (SIRT1) and the peroxisome proliferator-activated receptor γ (PPARγ) signaling pathway in the WAT of young male mice. Both genes interact with specific targets involved in multiple metabolic processes, including adipocyte differentiation, browning, and lipid metabolism. The quantitative PCR (qPCR) results demonstrated a significant upregulation of SIRT-1 and some of its target genes associated with the transcriptional regulation of lipid homeostasis (i.e., PPARα, PPARγ, PGC-1α, and SREBF) and adipose tissue development (i.e., leptin, adiponectin) in CSR mice. On the contrary, DNA-binding transcription factors (i.e., CEBP-β and C-myc), which play a pivotal function during the adipogenesis process, were found to be down-regulated. Our results also suggest that the induction of SIRT1-dependent molecular pathways prevents weight gain. Overall, these findings offer new, valuable insights into the molecular adaptations of WAT to CSR, in order to support increased energy demand due to sleep loss.

Sleep fragmentation reduces explorative behaviors and impairs motor coordination in male mice

Sleep fragmentation (SF), which refers to discontinuous and fragmented sleep, induces cognitive impairment and anxiety-like behavior in mice. However, whether SF can affect motor capability in healthy young wild-type mice and the underlying mechanisms remain unknown. We performed seven days of sleep fragmentation (SF 7d) interventions in young wild-type male mice. While SF mice experienced regular sleep disruption between Zeitgeber time (ZT) 0-12, control mice were allowed to have natural sleep (NS) cycles. Homecage analysis and conventional behavioral tests were conducted to assess the behavioral alterations in behavioral patterns in general and motor-related behaviors. Sleep structures and the power spectrum of electroencephalograms (EEGs) were compared between SF 7d and NS groups. Neuronal activation was measured using c-Fos immunostaining and quantified in multiple brain regions. SF of 7 days significantly decreased bouts of rearing and sniffing and the duration of rearing and impaired motor coordination. An increase in the total sleep time and a decrease in wakefulness between ZT12-24 was found in SF 7d mice. In SF 7d mice, EEG beta1 power was increased in rapid eye movement (REM) sleep while theta power was decreased during wakefulness. SF 7d resulted in significant suppression in c-Fos (+) cell counts in the motor cortex and hippocampus but an increase in c-Fos (+) cell counts in the substantia nigra pars compacta (SNc). In summary, SF 7d suppressed explorative behaviors and impaired motor coordination as compared to NS. EEG power and altered neuronal activity detected by c-Fos staining might contribute to the behavioral changes.

Obstructive sleep apnoea heterogeneity and cardiovascular disease

Obstructive sleep apnoea (OSA), characterized by recurrent periods of upper airway obstruction and intermittent hypoxaemia, is prevalent in patients with cardiovascular disease (CVD), and is therefore important to consider in the prevention and management of CVD. Observational studies indicate that OSA is a risk factor for incident hypertension, poorly controlled blood pressure, stroke, myocardial infarction, heart failure, cardiac arrhythmias, sudden cardiac death and all-cause death. However, clinical trials have not provided consistent evidence that treatment with continuous positive airway pressure (CPAP) improves cardiovascular outcomes. These overall null findings might be explained by limitations in trial design and low levels of adherence to CPAP. Studies have also been limited by the failure to consider OSA as a heterogeneous disorder that consists of multiple subtypes resulting from variable contributions from anatomical, physiological, inflammatory and obesity-related risk factors, and resulting in different physiological disturbances. Novel markers of sleep apnoea-associated hypoxic burden and cardiac autonomic response have emerged as predictors of OSA-related susceptibility to adverse health outcomes and treatment response. In this Review, we summarize our understanding of the shared risk factors and causal links between OSA and CVD and emerging knowledge on the heterogeneity of OSA. We discuss the varied mechanistic pathways that result in CVD that also vary across subgroups of OSA, as well as the potential role of new biomarkers for CVD risk stratification.

Worse sleep and increased energy expenditure yet no movement changes in sub-urban wild boar experiencing an influx of human visitors (anthropulse) during the COVID-19 pandemic

Expansion of urban areas, landscape transformation and increasing human outdoor activities strongly affect wildlife behaviour. The outbreak of the COVID-19 pandemic in particular led to drastic changes in human behaviour, exposing wildlife around the world to either reduced or increased human presence, potentially altering animal behaviour. Here, we investigate behavioural responses of wild boar (Sus scrofa) to changing numbers of human visitors to a suburban forest near Prague, Czech Republic, during the first 2.5 years of the COVID-19 epidemic (April 2019-November 2021). We used bio-logging and movement data of 63 GPS-collared wild boar and human visitation data based on an automatic counter installed in the field. We hypothesised that higher levels of human leisure activity will have a disturbing effect on wild boar behaviour manifested in increased movements and ranging, energy spent, and disrupted sleep patterns. Interestingly, whilst the number of people visiting the forest varied by two orders of magnitude (from 36 to 3431 people weekly), even high levels of human presence (>2000 visitors per week) did not affect weekly distance travelled, home range size, and maximum displacement of wild boar. Instead, individuals spent 41 % more energy at high levels of human presence (>2000 visitors per week), with more erratic sleep patterns, characterised by shorter and more frequent sleeping bouts. Our results highlight multifaceted effects of increased human activities ('anthropulses'), such as those related to COVID-19 countermeasures, on animal behaviour. High human pressure may not affect animal movements or habitat use, especially in highly adaptable species such as wild boar, but may disrupt animal activity rhythms, with potentially detrimental fitness consequences. Such subtle behavioural responses can be overlooked if using only standard tracking technology.

A single night of moderate at-home sleep restriction increases hunger and food intake in overweight young adults

OBJECTIVES

Experimental studies under laboratory conditions have shown a close link between acute sleep restriction and metabolic disorders. The aim of this study was to assess the effect of a single night of moderate sleep restriction implemented under ambulatory settings on sleep organization, food intake, blood pressure, and heart rate in overweight young adults.

METHODS

In a non-randomized experimental study, we evaluated 15 young, overweight adults (mean age [± SEM] 20.8 ± 0.6 y) with a mean body mass index (BMI) 27.5 ± 6.2 kg/m2 (BMI range 18.9-36.6 kg/m2). Each participant was recorded at home during two successive nights under: 1) Regular sleep routine (from 2330 to 0730 h, 'night1') and 2) Restricted sleep (6 h in bed, from 0300 to 0900 h, "night2"). Sleep was assessed by a non-invasive mobile system (Watch-PAT200) placed on the non-dominant wrist, measuring peripheral arterial tonometry. We measured sleep duration, rapid eye movement sleep (REM), light sleep (LS), deep sleep (DS), and waking. Starting 2 d before night1, four consecutive food records assessed daily food intake. Preceding and succeeding each night, hunger/satiety feelings (measured by self-reported visual analog scales), blood pressure, and heart rate were also evaluated.

RESULTS

Total sleep time was reduced in night2 (P = 0.007), with higher DS percentage (P = 0.03). Sleep onset and REM sleep latencies, LS time, and the number of wake episodes did not differ between nights. Energy intake was increased the day after night2 (P = 0.007), with increased fat and protein intakes (both P < 0.01) and feelings of hunger (P = 0.002). Systolic blood pressure was higher and heart rate faster in the morning after night2 (both P < 0.05).

CONCLUSIONS

An acute moderate at-home sleep restriction exacerbated food intake and feelings of hunger, and impaired blood pressure and heart rate regulation in young, overweight adults.

Association between Wakeup Frequency at Night and Atherogenic Dyslipidemia: Evidence for Sex Differences

AIM

This study aimed to determine whether sleep disturbance, defined as the wakeup frequency at night, is associated with atherogenic dyslipidemia and to explore possible sex differences.

METHODS

A total of 1,368 adults aged 19-70 years were included in the study of lifestyles and atherogenic dyslipidemia at the National Taiwan University Hospital in the period of 2008-2012. They completed a questionnaire regarding lifestyle information and sleep quality, including sleep hour duration, use of sleeping pills, and wakeup frequency during nighttime sleep. The measured lipid profiles included total cholesterol, triglycerides, low- and high-density lipoprotein cholesterol (LDL-C and HDL-C, respectively), non-HDL-C, and small dense LDL-C (sdLDL-C). Multivariate logistic regression was performed to determine habitual interrupted sleep and the odds ratio of atherogenic dyslipidemia following adjustment for conventional risk factors and for sex-based subgroup analysis.

RESULTS

A wakeup frequency ≥ 3 times per night was independently associated with an increased risk [odds ratio (95% confidence interval)] of dyslipidemia was 1.96 (1.17-3.28), and non-HDL-C ≥ 160 mg/dL was 1.78 (1.09-2.89). A higher wakeup frequency was associated with increased atherogenic dyslipidemia in women than in men. The multivariate adjusted relative risks for non-HDL ≥ 160 mg/dL and cholesterol ≥ 200 mg/dL were 3.05 (1.27-7.34) and 4.01(1.29-12.45) for female individuals with insomnia and those with a wakeup frequency ≥ 2 times per night, respectively.

CONCLUSION

A higher wakeup frequency was associated with atherogenic dyslipidemia in Taiwanese adults, particularly in women. This study also provided another evidence of increasing cardiovascular diseases in subjects with habitual interrupted sleep.

Relationship between Obstructive Sleep Apnea and Liver Abnormalities in Older Patients: A Cross-Sectional Study

BACKGROUND

Older age is a risk factor for obstructive sleep apnea (OSA), which is associated with the development of nonalcoholic fatty liver disease (NAFLD). We aimed to investigate the correlation between OSA and liver injury among older patients. Study Design. This is a cross-sectional study.

METHODS

Consecutive older (≥60 years) snoring patients were included. Subjects were divided into no OSA, mild OSA, moderate OSA, and severe OSA groups according to the apnea-hypopnea index (AHI) and were also separated into liver injury and nonliver injury groups based on liver function. Logistic regression analysis was applied to analyze the independent risk factors for liver injury.

RESULTS

We studied 227 patients (155 male, 72 female). The prevalence of liver injury exhibited an increasing trend among groups with mild-to-severe OSA. In addition, body mass index, AHI, and TG showed significant differences between the liver injury and nonliver injury groups. Logistic regression analysis revealed that AHI and TG were the major contributing factors for liver injury in older patients (adjusted odds ratio [OR] = 1.055, p=0.013, and OR = 1.485, p=0.039, respectively).

CONCLUSIONS

Older patients with OSA have an increased risk of liver injury and NAFLD, and sleep apnea and high TG are important factors in contributing to the development of liver injury.

A daily temperature rhythm in the human brain predicts survival after brain injury

Patients undergo interventions to achieve a 'normal' brain temperature; a parameter that remains undefined for humans. The profound sensitivity of neuronal function to temperature implies the brain should be isothermal, but observations from patients and non-human primates suggest significant spatiotemporal variation. We aimed to determine the clinical relevance of brain temperature in patients by establishing how much it varies in healthy adults. We retrospectively screened data for all patients recruited to the Collaborative European NeuroTrauma Effectiveness Research in Traumatic Brain Injury (CENTER-TBI) High Resolution Intensive Care Unit Sub-Study. Only patients with direct brain temperature measurements and without targeted temperature management were included. To interpret patient analyses, we prospectively recruited 40 healthy adults (20 males, 20 females, 20-40 years) for brain thermometry using magnetic resonance spectroscopy. Participants were scanned in the morning, afternoon, and late evening of a single day. In patients (n = 114), brain temperature ranged from 32.6 to 42.3°C and mean brain temperature (38.5 ± 0.8°C) exceeded body temperature (37.5 ± 0.5°C, P < 0.0001). Of 100 patients eligible for brain temperature rhythm analysis, 25 displayed a daily rhythm, and the brain temperature range decreased in older patients (P = 0.018). In healthy participants, brain temperature ranged from 36.1 to 40.9°C; mean brain temperature (38.5 ± 0.4°C) exceeded oral temperature (36.0 ± 0.5°C) and was 0.36°C higher in luteal females relative to follicular females and males (P = 0.0006 and P < 0.0001, respectively). Temperature increased with age, most notably in deep brain regions (0.6°C over 20 years, P = 0.0002), and varied spatially by 2.41 ± 0.46°C with highest temperatures in the thalamus. Brain temperature varied by time of day, especially in deep regions (0.86°C, P = 0.0001), and was lowest at night. From the healthy data we built HEATWAVE-a 4D map of human brain temperature. Testing the clinical relevance of HEATWAVE in patients, we found that lack of a daily brain temperature rhythm increased the odds of death in intensive care 21-fold (P = 0.016), whilst absolute temperature maxima or minima did not predict outcome. A warmer mean brain temperature was associated with survival (P = 0.035), however, and ageing by 10 years increased the odds of death 11-fold (P = 0.0002). Human brain temperature is higher and varies more than previously assumed-by age, sex, menstrual cycle, brain region, and time of day. This has major implications for temperature monitoring and management, with daily brain temperature rhythmicity emerging as one of the strongest single predictors of survival after brain injury. We conclude that daily rhythmic brain temperature variation-not absolute brain temperature-is one way in which human brain physiology may be distinguished from pathophysiology.

The relationship between fasting-induced torpor, sleep, and wakefulness in laboratory mice

STUDY OBJECTIVES

Torpor is a regulated and reversible state of metabolic suppression used by many mammalian species to conserve energy. Whereas the relationship between torpor and sleep has been well-studied in seasonal hibernators, less is known about the effects of fasting-induced torpor on states of vigilance and brain activity in laboratory mice.

METHODS

Continuous monitoring of electroencephalogram (EEG), electromyogram (EMG), and surface body temperature was undertaken in adult, male C57BL/6 mice over consecutive days of scheduled restricted feeding.

RESULTS

All animals showed bouts of hypothermia that became progressively deeper and longer as fasting progressed. EEG and EMG were markedly affected by hypothermia, although the typical electrophysiological signatures of non-rapid eye movement (NREM) sleep, rapid eye movement (REM) sleep, and wakefulness enabled us to perform vigilance-state classification in all cases. Consistent with previous studies, hypothermic bouts were initiated from a state indistinguishable from NREM sleep, with EEG power decreasing gradually in parallel with decreasing surface body temperature. During deep hypothermia, REM sleep was largely abolished, and we observed shivering-associated intense bursts of muscle activity.

CONCLUSIONS

Our study highlights important similarities between EEG signatures of fasting-induced torpor in mice, daily torpor in Djungarian hamsters and hibernation in seasonally hibernating species. Future studies are necessary to clarify the effects on fasting-induced torpor on subsequent sleep.

Anxiogenic Potential of Experimental Sleep Fragmentation Is Duration-Dependent and Mediated via Oxidative Stress State

Sleep architecture alterations, among which sleep fragmentation is highly prevalent, represent risk factors for a variety of diseases, ranging from cardiovascular to brain disorders, including anxiety. What mediates anxiety occurrence upon sleep fragmentation is still a matter of debate. We hypothesized that the sleep fragmentation effects on anxiety are dependent on its duration and mediated by increased oxidative stress and alterations in the number of parvalbumin (PV+) interneurons in the hippocampus. Sleep was fragmented in rats by the treadmill method during a period of 14 days (SF group). Rats with undisturbed sleep in the treadmill (TC group) and those receiving equal amounts of treadmill belt motion (EC group) served as controls. To assess anxiety, we subjected rats to the open field, elevated plus maze, and light-dark tests on the 0, 7^th, and 14^th day. Upon the last test, brain structures were sampled for oxidative stress assessment and PV+ interneuron immunohistochemistry. The results of ethological tests of anxiety-linked behavior suggested duration-dependent anxiogenic potential of sleep fragmentation. Rats' anxiety-linked behavior upon sleep fragmentation significantly correlated with oxidative stress. The rats with fragmented sleep (SF) showed significantly higher oxidative stress in the hippocampus, thalamus, and cortex, compared to controls (TC and EC), while the antioxidant enzymes' activity was significantly decreased. No significant differences were observed in hippocampal PV+ interneurons among these groups. Our results showed that duration of sleep fragmentation is a significant determinant of anxiety-linked behavior, and these effects are mediated through oxidative distress in the brain. Herein, it is revealed that the sleep fragmentation-oxidative stress-anxiety axis contributes to our better understanding of pathophysiological processes, occurring due to disrupted sleep patterns.

Role of the Preoptic Area in Sleep and Thermoregulation

Sleep and body temperature are tightly interconnected in mammals: warming up our body helps to fall asleep and the body temperature in turn drops while falling asleep. The preoptic area of the hypothalamus (POA) serves as an essential brain region to coordinate sleep and body temperature. Understanding how these two behaviors are controlled within the POA requires the molecular identification of the involved circuits and mapping their local and brain-wide connectivity. Here, we review our current understanding of how sleep and body temperature are regulated with a focus on recently discovered sleep- and thermo-regulatory POA neurons. We further discuss unresolved key questions including the anatomical and functional overlap of sleep- and thermo-regulatory neurons, their pathways and the role of various signaling molecules. We suggest that analysis of genetically defined circuits will provide novel insights into the mechanisms underlying the coordinated regulation of sleep and body temperature in health and disease.

The Effect of Obstructive Sleep Apnea and Continuous Positive Airway Pressure Therapy on Skeletal Muscle Lipid Content in Obese and Nonobese Men

Obstructive sleep apnea (OSA), independently of obesity (OBS), predisposes to insulin resistance (IR) for largely unknown reasons. Because OSA-related intermittent hypoxia triggers lipolysis, overnight increases in circulating free fatty acids (FFAs) including palmitic acid (PA) may lead to ectopic intramuscular lipid accumulation potentially contributing to IR. Using 3-T-¹H-magnetic resonance spectroscopy, we therefore compared intramyocellular and extramyocellular lipid (IMCL and EMCL) in the vastus lateralis muscle at approximately 7 am between 26 male patients with moderate-to-severe OSA (17 obese, 9 nonobese) and 23 healthy male controls (12 obese, 11 nonobese). Fiber type composition was evaluated by muscle biopsies. Moreover, we measured fasted FFAs including PA, glycated hemoglobin A_1c, thigh subcutaneous fat volume (ScFAT, 1.5-T magnetic resonance tomography), and maximal oxygen uptake (VO₂max). Fourteen patients were reassessed after continuous positive airway pressure (CPAP) therapy. Total FFAs and PA were significantly (by 178% and 166%) higher in OSA patients vs controls and correlated with the apnea-hypopnea index (AHI) (r ≥ 0.45, P < .01). Moreover, IMCL and EMCL were 55% (P < .05) and 40% (P < .05) higher in OSA patients, that is, 114% and 103% in nonobese, 24.4% and 8.4% in obese participants (with higher control levels). Overall, PA, FFAs (minus PA), and ScFAT significantly contributed to IMCL (multiple r = 0.568, P = .002). CPAP significantly decreased EMCL (–26%) and, by trend only, IMCL, total FFAs, and PA. Muscle fiber composition was unaffected by OSA or CPAP. Increases in IMCL and EMCL are detectable at approximately 7 am in OSA patients and are partly attributable to overnight FFA excesses and high ScFAT or body mass index. CPAP decreases FFAs and IMCL by trend but significantly reduces EMCL.

Sleep fragmentation and working memory in healthy adults

Introduction

Sleep is essential for performing cognitive function in humans. We have hypothesized that sleep fragmentation compared to sleep efficiency may have a negative impact on the working memory.

Material and Methods

Twenty-eight healthy adults (18 males and 10 females; mean age 27.8±15.5 years) were enrolled in this study. We measured the total sleep time (TST), sleep efficiency, %stage wakefulness (W), %stage rapid eye movement (REM), %stage N1, %stage N2, %stage N3, wake after sleep onset (WASO), and arousal index using polysomnography. Working memory, executive function, and sustained attention of three domains of cognitive function were evaluated with the number of back task (N-back task), Wisconsin card sorting test (WCST), and continuous performance test-identical pairs (CPT-IP), respectively.

Results

The percentage of correct answers on the 2-back task was significantly correlated with %stage REM, %stage N1, and %stage N2 (%stage REM: r=0.505, p=0.006; %stage N1: r=-0.637, p<0.001; %stage N2: r=0.670, p<0.001), and multiple regression analysis including the stepwise forward selection method revealed that %stage N2 was the most significant factor (%stage N2: β=0.670, p<0.001). The percentage of correct answers on the 2-back task was also significantly correlated with TST, sleep efficiency, WASO, and arousal index (TST: r=0.492, p=0.008; sleep efficiency: r=0.622, p<0.001; WASO: r=-0.721, p<0.001; arousal index: r=-0.656, p<0.001), and WASO was the significant factor (β=-2.086, p=0.007). The WCST category achievement and CPT-IP d-prime score were correlated with none of the sleep variables.

Conclusion

Increased WASO and a decrease in %stage N2 were associated with worse working memory.

Sub-minute prediction of brain temperature based on sleep-wake state in the mouse

Although brain temperature has neurobiological and clinical importance, it remains unclear which factors contribute to its daily dynamics and to what extent. Using a statistical approach, we previously demonstrated that hourly brain temperature values co-varied strongly with time spent awake (Hoekstra et al., 2019). Here we develop and make available a mathematical tool to simulate and predict cortical temperature in mice based on a 4-s sleep-wake sequence. Our model estimated cortical temperature with remarkable precision and accounted for 91% of the variance based on three factors: sleep-wake sequence, time-of-day ('circadian'), and a novel 'prior wake prevalence' factor, contributing with 74%, 9%, and 43%, respectively (including shared variance). We applied these optimized parameters to an independent cohort of mice and predicted cortical temperature with similar accuracy. This model confirms the profound influence of sleep-wake state on brain temperature, and can be harnessed to differentiate between thermoregulatory and sleep-wake-driven effects in experiments affecting both.

Addiction-like response in brain and behavior in a rat experimental model of night-eating syndrome

STUDY OBJECTIVES

Individuals ailing from night eating syndrome (NES) consume more than 25% of their daily food intake during the normal sleep time, delaying their sleep or waking up in the middle of the night to eat. This study explored two experimental conditions resembling NES in Wistar rats by offering palatable food during the sleep phase, alone or combined with sleep delay. Also we explored their impact on addiction-like changes in the brain and behavior.

METHODS

Experiment 1 explored the brain response after a first NES-like event; experiment 2 and 3 explored addiction-like behaviors c-Fos and FosB/ΔFosB in corticolimbic regions after 4 weeks exposition to NES-like conditions and after one week of withdrawal, respectively. For all 3 experiments 6 experimental groups were used: 1. Control; 2. Restricted access (1 h) to high-sugar diet (HSD) or to 3. high-fat diet (HFD); 4., Sleep delay for 4 h (SD) (from ZT0-ZT4, rats using slow rotating wheels); 5. SD + HSD; 6. SD + HFD.

RESULTS

A first event of eating a palatable diet with or without SD was sufficient to stimulate c-Fos and ΔFosB. Along 4 weeks of exposure to the palatable diets rats exhibited escalation and binge eating, which was highest for the HFD. At this stage, SD did not influence behavioral changes nor the neuronal response. After one-week in withdrawal, rats exhibited craving and effort to obtain their palatable diet. The brains of rats previously exposed to sleep delay maintained high levels of FosB/ΔFosB in the accumbens shell and high c-Fos activation in the insular cortex.

CONCLUSIONS

In our experimental models of NES-like a HFD in the sleep phase and SD are risk factors to develop binge eating and addiction-like behaviors.

Sleep Loss Can Cause Death through Accumulation of Reactive Oxygen Species in the Gut

The view that sleep is essential for survival is supported by the ubiquity of this behavior, the apparent existence of sleep-like states in the earliest animals, and the fact that severe sleep loss can be lethal. The cause of this lethality is unknown. Here we show, using flies and mice, that sleep deprivation leads to accumulation of reactive oxygen species (ROS) and consequent oxidative stress, specifically in the gut. ROS are not just correlates of sleep deprivation but drivers of death: their neutralization prevents oxidative stress and allows flies to have a normal lifespan with little to no sleep. The rescue can be achieved with oral antioxidant compounds or with gut-targeted transgenic expression of antioxidant enzymes. We conclude that death upon severe sleep restriction can be caused by oxidative stress, that the gut is central in this process, and that survival without sleep is possible when ROS accumulation is prevented. VIDEO ABSTRACT.

Sleep and immune function among people living with human immunodeficiency virus (HIV)

People living with HIV are at increased risk for sleep disturbances. Up to 75% of the HIV-infected individuals in the United States experience sleep disturbances of some kind. Previous studies have suggested an association between patient-reported sleep disturbances and impaired immune function. This study evaluates data obtained via sleep actigraphy to evaluate the relationship between objectively measured sleep, HIV viral load, and immune function. While this study found no relationship between objective sleep and CD4+ T- lymphocyte count, higher sleep efficiency was weakly correlated with lower HIV viral loads, τ_b(93)= -.165, p = .043. More research is warranted to clarify the nature of these relationships.

Obstructive Sleep Apnea, Hypoxia, and Nonalcoholic Fatty Liver Disease

Recent studies have demonstrated that obstructive sleep apnea (OSA) is associated with the development and evolution of nonalcoholic fatty liver disease (NAFLD), independent of obesity or other shared risk factors. Like OSA, NAFLD is a prevalent disorder associated with major adverse health outcomes: Patients with NAFLD may develop cirrhosis, liver failure, and hepatocellular carcinoma. One major finding that has emerged from these studies is that the OSA-NAFLD association is related to the degree of nocturnal hypoxemia in OSA. Animal models have therefore largely focused on intermittent hypoxia, a key manifestation of OSA, to shed light on the mechanisms by which OSA may give rise to the complex metabolic disturbances that are seen in NAFLD. Intermittent hypoxia leads to tissue hypoxia and can result in oxidative stress, mitochondrial dysfunction, inflammation, and overactivation of the sympathetic nervous system, among many other maladaptive effects. In such models, intermittent hypoxia has been shown to cause insulin resistance, dysfunction of key steps in hepatic lipid metabolism, atherosclerosis, and hepatic steatosis and fibrosis, each of which is pertinent to the development and/or progression of NAFLD. However, many intriguing questions remain unanswered: Principally, how aggressively should the clinician screen for NAFLD in patients with OSA, and vice versa? In this review, we attempt to apply the best evidence from animal and human studies to highlight the relationship between these two disorders and to advocate for further trials aimed at defining these relationships more precisely.

Epidemiological and pathophysiological evidence supporting links between obstructive sleep apnoea and Type 2 diabetes mellitus

Obstructive sleep apnoea (OSA) and Type 2 diabetes mellitus (T2DM) are common diseases. The global prevalence of OSA is between 2% and 7% in general population cohorts. The worldwide prevalence of T2DM among adults (aged 20-79 years) was estimated to be 6.4%. The concurrent presence of OSA and T2DM can be expected in the same patient, given their high prevalence and similar predisposition. We reviewed the overlapping pathophysiology of OSA and T2DM in this article.

Effect of cyclical intermittent hypoxia on Ad5CMVCre induced solitary lung cancer progression and spontaneous metastases in the KrasG12D+; p53fl/fl; myristolated p110fl/fl ROSA-gfp mouse

BACKGROUND

Epidemiological data suggests that obstructive sleep apnea (OSA) is associated with increased cancer incidence and mortality. We investigate the effects of cyclical intermittent hypoxia (CIH), akin to the underlying pathophysiology of OSA, on lung cancer progression and metastatic profile in a mouse model.

METHODS

Intrathoracic injection of Ad5CMVCre virus into a genetically engineered mouse (GEM) KrasG12D+/-; p53fl/fl; myristolated-p110αfl/fl-ROSA-gfp was utilized to induce a solitary lung cancer. Male mice were then exposed to either CIH or Sham for 40-41 days until harvest. To monitor malignant progression, serial micro CT scans with respiratory gating (no contrast) was performed. To detect spontaneous metastases in distant organs, H&E and immunohistochemistry were performed.

RESULTS

Eighty-eight percent of injected Ad5CMVCre virus was recovered from left lung tissue, indicating reliable and accurate injections. Serial micro CT demonstrated that CIH increases primary lung tumor volume progression compared to Sham on days 33 (p = 0.004) and 40 (p<0.001) post-injection. In addition, CIH increases variability in tumor volume on day 19 (p<0.0001), day 26 (p<0.0001), day 33 (p = 0.025) and day 40 (p = 0.004). Finally, metastases are frequently detected in heart, mediastinal lymph nodes, and right lung using H&E and immunohistochemistry.

CONCLUSIONS

Using a GEM mouse model of metastatic lung cancer, we report that male mice with solitary lung cancer have accelerated malignant progression and increased variability in tumor growth when exposed to cyclical intermittent hypoxia. Our results indicate that cyclical intermittent hypoxia is a pathogenic factor in non-small cell lung cancer that promotes the more rapid growth of developing tumors.

Obstructive sleep apnea and comorbidities: a dangerous liaison

Obstructive sleep apnea (OSA) is a highly prevalent disease, and is traditionally associated with increased cardiovascular risk. The role of comorbidities in OSA patients has emerged recently, and new conditions significantly associated with OSA are increasingly reported. A high comorbidity burden worsens prognosis, but some data suggest that CPAP might be protective especially in patients with comorbidities. Aim of this narrative review is to provide an update on recent studies, with special attention to cardiovascular and cerebrovascular comorbidities, the metabolic syndrome and type 2 diabetes, asthma, COPD and cancer. Better phenotypic characterization of OSA patients, including comorbidities, will help to provide better individualized care. The unsatisfactory adherence to CPAP in patients without daytime sleepiness should prompt clinicians to examine the overall risk profile of each patient in order to identify subjects at high risk for worse prognosis and provide the optimal treatment not only for OSA, but also for comorbidities.

Mechanisms of sleep deprivation-induced hepatic steatosis and insulin resistance in mice

Sleep deprivation is associated with increased risk for type 2 diabetes mellitus. However, the underlying mechanisms of sleep deprivation-induced glucose intolerance remain elusive. The aim of this study was to investigate the mechanisms of sleep deprivation-induced glucose intolerance in mice with a special focus on the liver. We established a mouse model of sleep deprivation-induced glucose intolerance using C57BL/6J male mice. A single 6-h sleep deprivation by the gentle handling method under fasting condition induced glucose intolerance. Hepatic glucose production assessed by a pyruvate challenge test was significantly increased, as was hepatic triglyceride content (by 67.9%) in the sleep deprivation group, compared with freely sleeping control mice. Metabolome and microarray analyses were used to evaluate hepatic metabolites and gene expression levels and to determine the molecular mechanisms of sleep deprivation-induced hepatic steatosis. Hepatic metabolites, such as acetyl coenzyme A, 3β-hydroxybutyric acid, and certain acylcarnitines, were significantly increased in the sleep deprivation group, suggesting increased lipid oxidation in the liver. In contrast, fasted sleep-deprived mice showed that hepatic gene expression levels of elongation of very long chain fatty acids-like 3, lipin 1, perilipin 4, perilipin 5, and acyl-CoA thioesterase 1, which are known to play lipogenic roles, were 2.7, 4.5, 3.7, 2.9, and 2.8 times, respectively, those of the fasted sleeping control group, as assessed by quantitative RT-PCR. Sleep deprivation-induced hepatic steatosis and hepatic insulin resistance seem to be mediated through upregulation of hepatic lipogenic enzymes.

Independent relationships between cardinal features of obstructive sleep apnea and glycometabolism: a cross-sectional study

BACKGROUND

Obstructive sleep apnea (OSA) is associated with abnormal glycometabolism; however, the cardinal features of OSA, such as sleep fragmentation (SF) and intermittent hypoxia (IH), have yet to show clear, independent associations with glycometabolism.

METHODS

We enrolled 1834 participants with suspected OSA from July 2008 to July 2013 to participate in this study. Polysomnographic variables, biochemical indicators, and physical measurements were collected for each participant. Multiple linear regression analyses were used to evaluate independent associations between cardinal features of OSA and glycometabolism. Logistic regressions were used to determine the odds ratios (ORs) for abnormal glucose metabolism across microarousal index (MAI) and oxygen desaturation index (ODI) quartiles. The effect of the interaction between MAI and ODI on glycometabolism was also evaluated.

RESULTS

The MAI was independently associated with fasting insulin levels (β = 0.024, p = 0.001) and the homeostasis model assessment of insulin resistance (HOMA-IR; β = 0.006, p = 0.002) after multiple adjustments of confounding factors. In addition, the ORs for hyperinsulinemia across higher MAI quartiles were 1.081, 1.349, and 1.656, compared with the lowest quartile (p = 0.015 for a linear trend). Similarly, the ODI was independently associated with fasting glucose levels (β = 0.003, p < 0.001), fasting insulin levels (β = 0.037, p < 0.001), and the HOMA-IR (β = 0.010, p < 0.001) after adjusting for multiple factors. The ORs for hyperglycemia across higher ODI quartiles were 1.362, 1.231, and 2.184, compared with the lowest quartile (p < 0.05 for a linear trend). In addition, the ORs for hyperinsulinemia and abnormal HOMA-IR across ODI quartiles had the same trends. There was no interaction between MAI and ODI with respect to glycometabolism.

CONCLUSION

SF was independently associated with hyperinsulinemia, and IH was independently associated with hyperglycemia, hyperinsulinemia, and an abnormal HOMA-IR. We found no interaction between SF and IH with respect to OSA-related abnormal glycometabolism.

Disturbed sleep and diabetes: A potential nexus of dementia risk

Type 2 diabetes (T2D) and sleep disturbance (e.g., insomnia, sleep-disordered breathing) are prevalent conditions among older adults that are associated with cognitive decline and dementia, including Alzheimer's disease (AD). Importantly, disturbed sleep is associated with alterations in insulin sensitivity and glucose metabolism, and may increase the risk of T2D, and T2D-related complications (e.g., pain, nocturia) can negatively affect sleep. Despite these associations, little is known about how interactions between T2D and sleep disturbance might alter cognitive trajectories or the pathological changes that underlie dementia. Here, we review links among T2D, sleep disturbance, cognitive decline and dementia-including preclinical and clinical AD-and identify gaps in the literature, that if addressed, could have significant implications for the prevention of poor cognitive outcomes.

Protein-Tyrosine Phosphatase-1B Mediates Sleep Fragmentation-Induced Insulin Resistance and Visceral Adipose Tissue Inflammation in Mice

Study Objectives

Sleep fragmentation (SF) is highly prevalent and has emerged as an important contributing factor to obesity and metabolic syndrome. We hypothesized that SF-induced increases in protein tyrosine phosphatase-1B (PTP-1B) expression and activity underlie increased food intake, inflammation, and leptin and insulin resistance.

Methods

Wild-type (WT) and ObR-PTP-1b-/- mice (Tg) were exposed to SF and control sleep (SC), and food intake was monitored. WT mice received a PTP-1B inhibitor (RO-7d; Tx) or vehicle (Veh). Upon completion of exposures, systemic insulin and leptin sensitivity tests were performed as well as assessment of visceral white adipose tissue (vWAT) insulin receptor sensitivity and macrophages (ATM) polarity.

Results

SF increased food intake in either untreated or Veh-treated WT mice. Leptin-induced hypothalamic STAT3 phosphorylation was decreased, PTP-1B activity was increased, and reduced insulin sensitivity emerged both systemic and in vWAT, with the latter displaying proinflammatory ATM polarity changes. All of the SF-induced effects were abrogated following PTP-1B inhibitor treatment and in Tg mice.

Conclusions

SF induces increased food intake, reduced leptin signaling in hypothalamus, systemic insulin resistance, and reduced vWAT insulin sensitivity and inflammation that are mediated by increased PTP-1B activity. Thus, PTP-1B may represent a viable therapeutic target in the context of SF-induced weight gain and metabolic dysfunction.

Shift-work: is time of eating determining metabolic health? Evidence from animal models

The circadian disruption in shift-workers is suggested to be a risk factor to develop overweight and metabolic dysfunction. The conflicting time signals given by shifted activity, shifted food intake and exposure to light at night occurring in the shift-worker are proposed to be the cause for the loss of internal synchrony and the consequent adverse effects on body weight and metabolism. Because food elicited signals have proven to be potent entraining signals for peripheral oscillations, here we review the findings from experimental models of shift-work and verify whether they provide evidence about the causal association between shifted feeding schedules, circadian disruption and altered metabolism. We found mainly four experimental models that mimic the conditions of shift-work: protocols of forced sleep deprivation, of forced activity during the normal rest phase, exposure to light at night and shifted food timing. A big variability in the intensity and duration of the protocols was observed, which led to a diversity of effects. A common result was the disruption of temporal patterns of activity; however, not all studies explored the temporal patterns of food intake. According to studies that evaluate time of food intake as an experimental model of shift-work and studies that evaluate shifted food consumption, time of food intake may be a determining factor for the loss of balance at the circadian and metabolic level.

Acute sleep disruption- and high-fat diet-induced hypothalamic inflammation are not related to glucose tolerance in mice

Chronic insufficient sleep is a major societal problem and is associated with increased risk of metabolic disease. Hypothalamic inflammation contributes to hyperphagia and weight gain in diet-induced obesity, but insufficient sleep-induced neuroinflammation has yet to be examined in relation to metabolic function. We therefore fragmented sleep of adult male C57BL/6J mice for 18 h daily for 9 days to determine whether sleep disruption elicits inflammatory responses in brain regions that regulate energy balance and whether this relates to glycemic control. To additionally test the hypothesis that exposure to multiple inflammatory factors exacerbates metabolic outcomes, responses were compared in mice exposed to sleep fragmentation (SF), high-fat diet (HFD), both SF and HFD, or control conditions. Three or 9 days of high-fat feeding reduced glucose tolerance but SF alone did not. Transient loss of body mass in SF mice may have affected outcomes. Comparisons of pro-inflammatory cytokine concentrations among central and peripheral metabolic tissues indicate that patterns of liver interleukin-1β concentrations best reflects observed changes in glucose tolerance. However, we demonstrate that SF rapidly and potently increases Iba1 immunoreactivity (-ir), a marker of microglia. After 9 days of manipulations, Iba1-ir remains elevated only in mice exposed to both SF and HFD, indicating a novel interaction between sleep and diet on microglial activation that warrants further investigation.

Body Temperature Measurements for Metabolic Phenotyping in Mice

Key Points Rectal probing is subject to procedural bias. This method is suitable for first-line phenotyping, provided probe depth and measurement duration are standardized. It is also useful for detecting individuals with out-of-range body temperatures (during hypothermia, torpor).The colonic temperature attained by inserting the probe >2 cm deep is a measure of deep (core) body temperature.IR imaging of the skin is useful for detecting heat leaks and autonomous thermoregulatory alterations, but it does not measure body temperature.Temperature of the hairy or shaved skin covering the inter-scapular brown adipose tissue can be used as a measure of BAT thermogenesis. However, obtaining such measurements of sufficient quality is very difficult, and interpreting them can be tricky. Temperature differences between the inter-scapular and lumbar areas can be a better measure of the thermogenic activity of inter-scapular brown adipose tissue.Implanted probes for precise determination of BAT temperature (changes) should be fixed close to the Sulzer's vein. For measurement of BAT thermogenesis, core body temperature and BAT temperature should be recorded simultaneously.Tail temperature is suitable to compare the presence or absence of vasoconstriction or vasodilation.Continuous, longitudinal monitoring of core body temperature is preferred over single probing, as the readings are taken in a non-invasive, physiological context.Combining core body temperature measurements with metabolic rate measurements yields insights into the interplay between heat production and heat loss (thermal conductance), potentially revealing novel thermoregulatory phenotypes. Endothermic organisms rely on tightly balanced energy budgets to maintain a regulated body temperature and body mass. Metabolic phenotyping of mice, therefore, often includes the recording of body temperature. Thermometry in mice is conducted at various sites, using various devices and measurement practices, ranging from single-time probing to continuous temperature imaging. Whilst there is broad agreement that body temperature data is of value, procedural considerations of body temperature measurements in the context of metabolic phenotyping are missing. Here, we provide an overview of the various methods currently available for gathering body temperature data from mice. We explore the scope and limitations of thermometry in mice, with the hope of assisting researchers in the selection of appropriate approaches, and conditions, for comprehensive mouse phenotypic analyses.

Acute partial sleep deprivation due to environmental noise increases weight gain by reducing energy expenditure in rodents

OBJECTIVE

Chronic partial sleep deprivation (SD) by environmental noise exposure increases weight gain and feeding in rodents, which contrasts weight loss after acute SD by physical methods. This study tested whether acute environmental noise exposure reduced sleep and its effect on weight gain, food intake, physical activity, and energy expenditure (EE). It was hypothesized that acute exposure would (1) increase weight gain and feeding and (2) reduce sleep, physical activity, and EE (total and individual components); and (3) behavioral changes would persist throughout recovery from SD.

METHODS

Three-month old male Sprague-Dawley rats slept ad libitum, were noise exposed (12-h light cycle), and allowed to recover (36 h). Weight gain, food intake, sleep/wake, physical activity, and EE were measured.

RESULTS

Acute environmental noise exposure had no effect on feeding, increased weight gain (P < 0.01), and reduced sleep (P < 0.02), physical activity (P < 0.03), total EE (P < 0.05), and several components (P < 0.05). Reductions in EE and physical activity persisted during recovery.

CONCLUSIONS

Reductions in EE during sleep, rest, and physical activity reduce total EE and contribute to weight gain during acute SD and recovery from SD. These data emphasize the importance of increasing physical activity after SD to prevent obesity.

Sleep restriction acutely impairs glucose tolerance in rats

Chronic sleep curtailment in humans has been related to impairment of glucose metabolism. To better understand the underlying mechanisms, the purpose of the present study was to investigate the effect of acute sleep deprivation on glucose tolerance in rats. A group of rats was challenged by 4-h sleep deprivation in the early rest period, leading to prolonged (16 h) wakefulness. Another group of rats was allowed to sleep during the first 4 h of the light period and sleep deprived in the next 4 h. During treatment, food was withdrawn to avoid a postmeal rise in plasma glucose. An intravenous glucose tolerance test (IVGTT) was performed immediately after the sleep deprivation period. Sleep deprivation at both times of the day similarly impaired glucose tolerance and reduced the early-phase insulin responses to a glucose challenge. Basal concentrations of plasma glucose, insulin, and corticosterone remained unchanged after sleep deprivation. Throughout IVGTTs, plasma corticosterone concentrations were not different between the control and sleep-deprived group. Together, these results demonstrate that independent of time of day and sleep pressure, short sleep deprivation during the resting phase favors glucose intolerance in rats by attenuating the first-phase insulin response to a glucose load. In conclusion, this study highlights the acute adverse effects of only a short sleep restriction on glucose homeostasis.

Effects of chronic sleep deprivation on glucose homeostasis in rats

Epidemiological studies have shown that chronic sleep disturbances resulted in metabolic disorders. The purpose of this study was to assess the relationship between chronic sleep deprivation (CSD) and the glucose homeostasis in rats. Twenty-four rats were randomly divided into CSD group and control (CON) group. The CSD rats were intervened by a modified multiple platform method (MMPM) to establish an animal model of chronic sleep disturbances. After 3-month intervention, all rats were subjected to an intraperitoneal glucose tolerance test (IPGTT) and an insulin tolerance test (ITT), and the body weight, aspartate aminotransferase (AST), alanine aminotransferase (ALT), creatinine, lipid profile group, and homeostasis model assessment-IR (HOMA-IR) were measured. Both the CSD and CON groups had an attenuation of weight gain after 3-month intervention. The plasma glucose level of CSD group was higher than that of the CON group during the IPGTT (P < 0.01). The CSD rats showed a marked increase in HOMA-IR and ITT compared with the CON group (P < 0.01). There were no significant differences of AST, ALT, creatinine, and most lipid parameters between the CSD and CON groups (P > 0.05). The CSD has a marked effect on glucose homeostasis, comprising glucose intolerance and insulin resistance.

Sleep fragmentation alters brain energy metabolism without modifying hippocampal electrophysiological response to novelty exposure

Sleep is viewed as a fundamental restorative function of the brain, but its specific role in neural energy budget remains poorly understood. Sleep deprivation dampens brain energy metabolism and impairs cognitive functions. Intriguingly, sleep fragmentation, despite normal total sleep duration, has a similar cognitive impact, and in this paper we ask the question of whether it may also impair brain energy metabolism. To this end, we used a recently developed mouse model of 2 weeks of sleep fragmentation and measured 2-deoxy-glucose uptake and glycogen, glucose and lactate concentration in different brain regions. In order to homogenize mice behaviour during metabolic measurements, we exposed them to a novel environment for 1 h. Using an intra-hippocampal electrode, we first showed that hippocampal electroencephalograph (EEG) response to exploration was unaltered by 1 or 14 days of sleep fragmentation. However, after 14 days, sleep fragmented mice exhibited a lower uptake of 2-deoxy-glucose in cortex and hippocampus and lower cortical lactate levels than control mice. Our results suggest that long-term sleep fragmentation impaired brain metabolism to a similar extent as total sleep deprivation without affecting the neuronal responsiveness of hippocampus to a novel environment.

Restriction of rapid eye movement sleep during adolescence increases energy gain and metabolic efficiency in young adult rats

NEW FINDINGS

What is the central question of this study? Sleep curtailment in infancy and adolescence may lead to long-term risk for obesity, but the mechanisms involved have not yet been determined. This study examined the immediate and long-term metabolic effects produced by sleep restriction in young rats. What is the main finding and its importance? Prolonged sleep restriction reduced weight gain (body fat stores) in young animals. After prolonged recovery, sleep-restricted rats tended to save more energy and to store more fat, possibly owing to increased gross food efficiency. This could be the first step to understand this association. Sleep curtailment is associated with obesity and metabolic changes in adults and children. The aim of the present study was to evaluate the immediate and long-term metabolic alterations produced by sleep restriction in pubertal male rats. Male Wistar rats (28 days old) were allocated to a control (CTL) group or a sleep-restricted (SR) group. This was accomplished by the single platform technique for 18 h per day for 21 days. These groups were subdivided into the following four time points for assessment: sleep restriction and 1, 2 and 4 months of recovery. Body weight and food intake were monitored throughout the experiment. At the end of each time period, blood was collected for metabolic profiling, and the carcasses were processed for measurement of body composition and energy balance. During the period of sleep restriction, SR animals consumed less food in the home cages. This group also displayed lower body weight, body fat, triglycerides and glucose levels than CTL rats. At the end of the first month of recovery, despite eating as much as CTL rats, SR animals showed greater energy and body weight gain, increased gross food efficiency and decreased energy expenditure. At the end of the second and fourth months of recovery, the groups were no longer different, except for energy gain and gross food efficiency, which remained higher in SR animals. In conclusion, sleep restriction affected weight gain of young animals, owing to reduction of fat stores. Two months were sufficient to recover this deficit and to reveal that SR rats tended to save more energy and to store more fat.

Eight Hours of Nightly Continuous Positive Airway Pressure Treatment of Obstructive Sleep Apnea Improves Glucose Metabolism in Patients with Prediabetes. A Randomized Controlled Trial

RATIONALE

Although obstructive sleep apnea (OSA) is associated with impaired glucose tolerance and diabetes, it remains unclear whether OSA treatment with continuous positive airway pressure (CPAP) has metabolic benefits.

OBJECTIVES

To determine the effect of 8-hour nightly CPAP treatment on glucose metabolism in individuals with prediabetes and OSA.

METHODS

In a randomized controlled parallel group study, 39 participants were randomly assigned to receive either 8-hour nightly CPAP (n = 26) or oral placebo (n = 13). Sleep was polysomnographically recorded in the laboratory on each night. CPAP adherence was ensured by continuous supervision. Participants continued their daily routine activities outside the laboratory. Glucose metabolism was assessed at baseline and after 2 weeks of assigned treatment using both the oral and intravenous glucose tolerance tests. The primary outcome was the overall glucose response as quantified by the area under the curve for glucose during 2-hour oral glucose tolerance testing. Secondary outcomes included fasting and 2-hour glucose and insulin, the area under the curves for insulin and insulin secretion, norepinephrine, insulin sensitivity, acute insulin response to glucose, and 24-hour blood pressure.

MEASUREMENTS AND MAIN RESULTS

The overall glucose response was reduced (treatment difference: -1,276.9 [mg/dl] · min [95% confidence interval, -2,392.4 to -161.5]; P = 0.03) and insulin sensitivity was improved (treatment difference: 0.77 [mU/L](-1) · min(-1) [95% confidence interval, 0.03-1.52]; P = 0.04) with CPAP as compared with placebo. Additionally, norepinephrine levels and 24-hour blood pressure were reduced with CPAP as compared with placebo.

CONCLUSIONS

In patients with prediabetes, 8-hour nightly CPAP treatment for 2 weeks improves glucose metabolism compared with placebo. Thus, CPAP treatment may be beneficial for metabolic risk reduction. Clinical trial registered with www.clinicaltrials.gov (NCT 01156116).

Degeneration in Arousal Neurons in Chronic Sleep Disruption Modeling Sleep Apnea

Chronic sleep disruption (CSD) is a cardinal feature of sleep apnea that predicts impaired wakefulness. Despite effective treatment of apneas and sleep disruption, patients with sleep apnea may have persistent somnolence. Lasting wake disturbances in treated sleep apnea raise the possibility that CSD may induce sufficient degeneration in wake-activated neurons (WAN) to cause irreversible wake impairments. Implementing a stereological approach in a murine model of CSD, we found reduced neuronal counts in representative WAN groups, locus coeruleus (LC) and orexinergic neurons, reduced by 50 and 25%, respectively. Mice exposed to CSD showed shortened sleep latencies lasting at least 4 weeks into recovery from CSD. As CSD results in frequent activation of WAN, we hypothesized that CSD promotes mitochondrial metabolic stress in WAN. In support, CSD increased lipofuscin within select WAN. Further, examining the LC as a representative WAN nucleus, we observed increased mitochondrial protein acetylation and down-regulation of anti-oxidant enzyme and brain-derived neurotrophic factor mRNA. Remarkably, CSD markedly increased tumor necrosis factor-alpha within WAN, and not in adjacent neurons or glia. Thus, CSD, as observed in sleep apnea, results in a composite of lasting wake impairments, loss of select neurons, a pro-inflammatory, pro-oxidative mitochondrial stress response in WAN, consistent with a degenerative process with behavioral consequences.

Degeneration in Arousal Neurons in Chronic Sleep Disruption Modeling Sleep Apnea

Chronic sleep disruption (CSD) is a cardinal feature of sleep apnea that predicts impaired wakefulness. Despite effective treatment of apneas and sleep disruption, patients with sleep apnea may have persistent somnolence. Lasting wake disturbances in treated sleep apnea raise the possibility that CSD may induce sufficient degeneration in wake-activated neurons (WAN) to cause irreversible wake impairments. Implementing a stereological approach in a murine model of CSD, we found reduced neuronal counts in representative WAN groups, locus coeruleus (LC) and orexinergic neurons, reduced by 50 and 25%, respectively. Mice exposed to CSD showed shortened sleep latencies lasting at least 4 weeks into recovery from CSD. As CSD results in frequent activation of WAN, we hypothesized that CSD promotes mitochondrial metabolic stress in WAN. In support, CSD increased lipofuscin within select WAN. Further, examining the LC as a representative WAN nucleus, we observed increased mitochondrial protein acetylation and down-regulation of anti-oxidant enzyme and brain-derived neurotrophic factor mRNA. Remarkably, CSD markedly increased tumor necrosis factor-alpha within WAN, and not in adjacent neurons or glia. Thus, CSD, as observed in sleep apnea, results in a composite of lasting wake impairments, loss of select neurons, a pro-inflammatory, pro-oxidative mitochondrial stress response in WAN, consistent with a degenerative process with behavioral consequences.

The impact of sleep disorders on glucose metabolism: endocrine and molecular mechanisms

Modern lifestyle has profoundly modified human sleep habits. Sleep duration has shortened over recent decades from 8 to 6.5 hours resulting in chronic sleep deprivation. Additionally, irregular sleep, shift work and travelling across time zones lead to disruption of circadian rhythms and asynchrony between the master hypothalamic clock and pacemakers in peripheral tissues. Furthermore, obstructive sleep apnea syndrome (OSA), which affects 4 - 15% of the population, is not only characterized by impaired sleep architecture but also by repetitive hemoglobin desaturations during sleep. Epidemiological studies have identified impaired sleep as an independent risk factor for all cause of-, as well as for cardiovascular, mortality/morbidity. More recently, sleep abnormalities were causally linked to impairments in glucose homeostasis, metabolic syndrome and Type 2 Diabetes Mellitus (T2DM). This review summarized current knowledge on the metabolic alterations associated with the most prevalent sleep disturbances, i.e. short sleep duration, shift work and OSA. We have focused on various endocrine and molecular mechanisms underlying the associations between inadequate sleep quality, quantity and timing with impaired glucose tolerance, insulin resistance and pancreatic β-cell dysfunction. Of these mechanisms, the role of the hypothalamic-pituitary-adrenal axis, circadian pacemakers in peripheral tissues, adipose tissue metabolism, sympathetic nervous system activation, oxidative stress and whole-body inflammation are discussed. Additionally, the impact of intermittent hypoxia and sleep fragmentation (key components of OSA) on intracellular signaling and metabolism in muscle, liver, fat and pancreas are also examined. In summary, this review provides endocrine and molecular explanations for the associations between common sleep disturbances and the pathogenesis of T2DM.

Sustained sleep fragmentation induces sleep homeostasis in mice

STUDY OBJECTIVES

Sleep fragmentation (SF) is an integral feature of sleep apnea and other prevalent sleep disorders. Although the effect of repetitive arousals on cognitive performance is well documented, the effects of long-term SF on electroencephalography (EEG) and molecular markers of sleep homeostasis remain poorly investigated. To address this question, we developed a mouse model of chronic SF and characterized its effect on EEG spectral frequencies and the expression of genes previously linked to sleep homeostasis including clock genes, heat shock proteins, and plasticity-related genes.

DESIGN

N/A.

SETTING

Animal sleep research laboratory.

PARTICIPANTS

Sixty-six C57BL6/J adult mice.

INTERVENTIONS

Instrumental sleep disruption at a rate of 60/h during 14 days.

MEASUREMENTS AND RESULTS

Locomotor activity and EEG were recorded during 14 days of SF followed by recovery for 2 days. Despite a dramatic number of arousals and decreased sleep bout duration, SF minimally reduced total quantity of sleep and did not significantly alter its circadian distribution. Spectral analysis during SF revealed a homeostatic drive for slow wave activity (SWA; 1-4 Hz) and other frequencies as well (4-40 Hz). Recordings during recovery revealed slow wave sleep consolidation and a transient rebound in SWA, and paradoxical sleep duration. The expression of selected genes was not induced following chronic SF.

CONCLUSIONS

Chronic SF increased sleep pressure confirming that altered quality with preserved quantity triggers core sleep homeostasis mechanisms. However, it did not induce the expression of genes induced by sleep loss, suggesting that these molecular pathways are not sustainably activated in chronic diseases involving SF.

The impact of sleep disorders on glucose metabolism: endocrine and molecular mechanisms

Modern lifestyle has profoundly modified human sleep habits. Sleep duration has shortened over recent decades from 8 to 6.5 hours resulting in chronic sleep deprivation. Additionally, irregular sleep, shift work and travelling across time zones lead to disruption of circadian rhythms and asynchrony between the master hypothalamic clock and pacemakers in peripheral tissues. Furthermore, obstructive sleep apnea syndrome (OSA), which affects 4 - 15% of the population, is not only characterized by impaired sleep architecture but also by repetitive hemoglobin desaturations during sleep. Epidemiological studies have identified impaired sleep as an independent risk factor for all cause of-, as well as for cardiovascular, mortality/morbidity. More recently, sleep abnormalities were causally linked to impairments in glucose homeostasis, metabolic syndrome and Type 2 Diabetes Mellitus (T2DM). This review summarized current knowledge on the metabolic alterations associated with the most prevalent sleep disturbances, i.e. short sleep duration, shift work and OSA. We have focused on various endocrine and molecular mechanisms underlying the associations between inadequate sleep quality, quantity and timing with impaired glucose tolerance, insulin resistance and pancreatic β-cell dysfunction. Of these mechanisms, the role of the hypothalamic-pituitary-adrenal axis, circadian pacemakers in peripheral tissues, adipose tissue metabolism, sympathetic nervous system activation, oxidative stress and whole-body inflammation are discussed. Additionally, the impact of intermittent hypoxia and sleep fragmentation (key components of OSA) on intracellular signaling and metabolism in muscle, liver, fat and pancreas are also examined. In summary, this review provides endocrine and molecular explanations for the associations between common sleep disturbances and the pathogenesis of T2DM.

Chronic sleep fragmentation induces endothelial dysfunction and structural vascular changes in mice

STUDY OBJECTIVES

Sleep fragmentation (SF) is a common occurrence and constitutes a major characteristic of obstructive sleep apnea (OSA). SF has been implicated in multiple OSA-related morbidities, but it is unclear whether SF underlies any of the cardiovascular morbidities of OSA. We hypothesized that long-term SF exposures may lead to endothelial dysfunction and altered vessel wall structure.

METHODS AND RESULTS

Adult male C57BL/6J mice were fed normal chow and exposed to daylight SF or control sleep (CTL) for 20 weeks. Telemetric blood pressure and endothelial function were assessed weekly using a modified laser-Doppler hyperemic test. Atherosclerotic plaques, elastic fiber disruption, lumen area, wall thickness, foam cells, and macrophage recruitment, as well as expression of senescence-associated markers were examined in excised aortas. Increased latencies to reach baseline perfusion levels during the post-occlusive period emerged in SF mice with increased systemic BP values starting at 8 weeks of SF and persisting thereafter. No obvious atherosclerotic plaques emerged, but marked elastic fiber disruption and fiber disorganization were apparent in SF-exposed mice, along with increases in the number of foam cells and macrophages in the aorta wall. Senescence markers showed reduced TERT and cyclin A and increased p16INK4a expression, with higher IL-6 plasma levels in SF-exposed mice.

CONCLUSIONS

Long-term sleep fragmentation induces vascular endothelial dysfunction and mild blood pressure increases. Sleep fragmentation also leads to morphologic vessel changes characterized by elastic fiber disruption and disorganization, increased recruitment of inflammatory cells, and altered expression of senescence markers, thereby supporting a role for sleep fragmentation in the cardiovascular morbidity of OSA.

Metabolic dysfunction in obstructive sleep apnea: A critical examination of underlying mechanisms

It has recently become clear that obstructive sleep apnea (OSA) is an independent risk factor for the development of metabolic syndrome, a disorder of defective energy storage and use. Several mechanisms have been proposed to explain this finding, drawing upon the characteristics that define OSA. In particular, intermittent hypoxia, sleep fragmentation, elevated sympathetic tone, and oxidative stress - all consequences of OSA - have been implicated in the progression of poor metabolic outcomes in OSA. In this review we examine the evidence to support each of these disease manifestations of OSA as a unique risk for metabolic dysfunction. Tissue hypoxia and sleep fragmentation are each directly connected to insulin resistance and hypertension, and each of these also may increase sympathetic tone, resulting in defective glucose homeostasis, excessive lipolysis, and elevated blood pressure. Oxidative stress further worsens insulin resistance and in turn, metabolic dysfunction also increases oxidative stress. However, despite many studies linking each of these individual components of OSA to the development of metabolic syndrome, there are very few reports that actually provide a coherent narrative about the mechanism underlying metabolic dysfunction in OSA.

Sleep fragmentation has differential effects on obese and lean mice

Chronic sleep fragmentation (SF), common in patients with sleep apnea, correlates with the development of obesity. We hypothesized that SF differentially affects neurobehavior in lean wild-type (WT) and obese pan-leptin receptor knockout (POKO) mice fed the same normal diet. First, we established an SF paradigm by interrupting sleep every 2 min during the inactive light span. The maneuver was effective in decreasing sleep duration and bout length, and in increasing sleep state transition and waking, without significant rebound sleep in the dark span. Changes of sleep architecture were evident in the light span and consistent across days 1-10 of SF. There was reduced NREM, shortened sleep latency, and increased state transitions. During the light span of the first day of SF, there also was reduction of REM and increased delta power of slow-wave sleep. Potential effects of SF on thermal pain threshold, locomotor activity, and anxiety were then tested. POKO mice had a lower circadian amplitude of pain latency than WT mice in the hot plate test, and both groups had lowest tolerance at 4 pm (zeitgeber time (ZT) 10) and longest latency at 4 am (ZT 22). SF increased the pain threshold in WT but not in POKO mice when tested at 8 a.m. (ZT 2). Both the POKO mutation and SF resulted in reduced physical activity and increased anxiety, but there was no additive effect of these two factors. Overall, SF and the POKO mutation differentially regulate mouse behavior. The results suggest that obesity can blunt neurobehavioral responses to SF.

Sleep fragmentation in mice induces nicotinamide adenine dinucleotide phosphate oxidase 2-dependent mobilization, proliferation, and differentiation of adipocyte progenitors in visceral white adipose tissue

BACKGROUND

Chronic sleep fragmentation (SF) without sleep curtailment induces increased adiposity. However, it remains unclear whether mobilization, proliferation, and differentiation of adipocyte progenitors (APs) occurs in visceral white adipose tissue (VWAT), and whether nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 2 (Nox2) activity plays a role.

METHODS

Changes in VWAT depot cell size and AP proliferation were assessed in wild-type and Nox2 null male mice exposed to SF and control sleep (SC). To assess mobilization, proliferation, and differentiation of bone marrow mesenchymal stem cells (BM-MSC), Sca-1+ bone marrow progenitors were isolated from GFP+ or RFP+ mice, and injected intravenously to adult male mice (C57BL/6) previously exposed to SF or SC.

RESULTS

In comparison with SC, SF was associated with increased weight accrual at 3 w and thereafter, larger subcutaneous and visceral fat depots, and overall adipocyte size at 8 w. Increased global AP numbers in VWAT along with enhanced AP BrDU labeling in vitro and in vivo emerged in SF. Systemic injections of GFP+ BM-MSC resulted in increased AP in VWAT, as well as in enhanced differentiation into adipocytes in SF-exposed mice. No differences occurred between SF and SC in Nox2 null mice for any of these measurements.

CONCLUSIONS

Chronic sleep fragmentation (SF) induces obesity in mice and increased proliferation and differentiation of adipocyte progenitors (AP) in visceral white adipose tissue (VWAT) that are mediated by increased Nox2 activity. In addition, enhanced migration of bone marrow mesenchymal stem cells from the systemic circulation into VWAT, along with AP differentiation, proliferation, and adipocyte formation occur in SF-exposed wild-type but not in oxidase 2 (Nox2) null mice. Thus, Nox2 may provide a therapeutic target to prevent obesity in the context of sleep disorders.

Sleep duration predicts cardiometabolic risk in obese adolescents

OBJECTIVE

To examine the independent contributions of objectively measured sleep duration and fragmentation on cardiometabolic risk accumulation in free-living obese adolescents.

STUDY DESIGN

Characteristics of metabolic syndrome (waist circumference, mean arterial pressure, fasting high-density lipoprotein cholesterol, triglycerides, glucose) were measured in obese adolescents and standardized residuals (z-scores) were summed (inverse high-density lipoprotein cholesterol) to create a continuous cardiometabolic risk score (cMetScore), adjusted for age, sex, and race. Sleep and physical activity were objectively measured in habitual, free-living conditions for 7 days (SenseWear Pro3, BodyMedia, Pittsburgh, Pennsylvania; n = 37; 54% female, ages 11-17 years). Associations between sleep duration and cMetScore were assessed via multiple linear regression.

RESULTS

Body mass index, total sleep time, and sleep session length were each correlated with cMetScore (P < .05 all). Total sleep time was inversely and independently associated with cMetScore (r = -0.535, P = .001) and was the best independent predictor of metabolic risk.

CONCLUSIONS

Sleep duration inversely predicts cardiometabolic risk in obese adolescents, even when we controlled for various measures of physical activity, anthropometry, and adiposity. Further research should investigate the biological mechanism of this relationship and the potential treatment effect of sleep intervention in decreasing cardiometabolic risk in this population.

Mice with altered brain lipoprotein metabolism display maladaptive responses to environmental challenges that may predispose to weight gain

BACKGROUND

Three-month-old neuron-specific lipoprotein lipase (LPL)-depleted mice (NEXLP(-/-)) mice are preobese and have normal body weight before developing obesity by 4.5 months. This series of experiments investigated responses to novel environment stimuli and acute sleep deprivation in preobese NEXLPL(-/-)) mice to test the hypothesis that neuron-specific LPL deletion alters normal adaptive metabolic responses to environmental challenges.

METHODS

Three-month-old, age- and weight-matched, male NEXLPL(-/-)) (n=10) and wild-type (WT) (n=10) mice were housed in individual metabolic chambers with a 12-hr dark cycle. Food and water intake, locomotor activity, and calorimetry data were recorded in 12-min intervals. Novel environmental responses were elicited by first-time introduction to chambers at dark onset, followed by acclimation, baseline recording, and 6-hr of sleep deprivation on subsequent experimental days.

RESULTS

NEXLPL(-/-)) mice displayed a 1.5-fold greater increase in activity in response to a novel environment than seen in WT controls (P=0.0308), and a two-fold greater increase in food intake following acute sleep deprivation (P=0.0117). NEXLPL(-/-)) mice averaged a 27% higher metabolic rate than WT mice throughout the experiments (P<0.0001). Body weight, composition, and temperature did not differ between murine groups throughout the experiments. Levels of free fatty acid, insulin, glucose, and triglycerides were similar between groups at the terminus.

CONCLUSIONS

A deficiency in neuronal LPL signaling disrupts normal responses to novel environmental exposure and acute sleep deprivation, a maladaptive response that may contribute to weight gain in genetically predisposed mice, and perhaps humans.

Chronic sleep fragmentation promotes obesity in young adult mice

OBJECTIVES

Short sleep confers a higher risk of obesity in humans. Restricted sleep increases appetite, promotes higher calorie intake from fat and carbohydrate sources, and induces insulin resistance. However, the effects of fragmented sleep (SF), such as occurs in sleep apnea, on body weight, metabolic rates, and adipose tissue distribution are unknown.

METHODS

C57BL/6 mice were exposed to SF for 8 weeks. Their body weight, food consumption, and metabolic expenditure were monitored over time, and their plasma leptin levels measured after exposure to SF for 1 day as well as for 2 weeks. In addition, adipose tissue distribution was assessed at the end of the SF exposure using MRI techniques.

RESULTS

Chronic SF-induced obesogenic behaviors and increased weight gain in mice by promoting increased caloric intake without changing caloric expenditure. Plasma leptin levels initially decreased and subsequently increased. Furthermore, increases in both visceral and subcutaneous adipose tissue volumes occurred.

CONCLUSIONS

These results suggest that SF, a frequent occurrence in many disorders and more specifically in sleep apnea, is a potent inducer of obesity via activation of obesogenic behaviors and possibly leptin resistance, in the absence of global changes in energy expenditure.