Sleep: A Novel Mechanistic Pathway, Biomarker, and Treatment Target in the Pathology of Alzheimer's Disease?

Profound degeneration of wake-promoting neurons in Alzheimer's disease

INTRODUCTION

Sleep-wake disturbances are a common and early feature in Alzheimer's disease (AD). The impact of early tau pathology in wake-promoting neurons (WPNs) remains unclear.

METHODS

We performed stereology in postmortem brains from AD individuals and healthy controls to identify quantitative differences in morphological metrics in WPNs. Progressive supranuclear palsy (PSP) and corticobasal degeneration were included as disease-specific controls.

RESULTS

The three nuclei studied accumulate considerable amounts of tau inclusions and showed a decrease in neurotransmitter-synthetizing neurons in AD, PSP, and corticobasal degeneration. However, substantial neuronal loss was exclusively found in AD.

DISCUSSION

WPNs are extremely vulnerable to AD but not to 4 repeat tauopathies. Considering that WPNs are involved early in AD, such degeneration should be included in the models explaining sleep-wake disturbances in AD and considered when designing a clinical intervention. Sparing of WPNs in PSP, a condition featuring hyperinsomnia, suggest that interventions to suppress the arousal system may benefit patients with PSP.

Sleep as a Potential Biomarker of Tau and β-Amyloid Burden in the Human Brain

Recent proposals suggest that sleep may be a factor associated with accumulation of two core pathological features of Alzheimer's disease (AD): tau and β-amyloid (Aβ). Here we combined PET measures of Aβ and tau, electroencephalogram sleep recordings, and retrospective sleep evaluations to investigate the potential utility of sleep measures in predicting in vivo AD pathology in male and female older adults. Regression analyses revealed that the severity of impaired slow oscillation-sleep spindle coupling predicted greater medial temporal lobe tau burden. Aβ burden was not associated with coupling impairment but instead predicted the diminished amplitude of <1 Hz slow-wave-activity, results that were statistically dissociable from each other. Additionally, comparisons of AD pathology and retrospective, self-reported changes in sleep duration demonstrated that changes in sleep across the lifespan can predict late-life Aβ and tau burden. Thus, quantitative and qualitative features of human sleep represent potential noninvasive, cost-effective, and scalable biomarkers (current and future forecasting) of AD pathology, and carry both therapeutic and public health implications.SIGNIFICANCE STATEMENT Several studies have linked sleep disruption to the progression of Alzheimer's disease (AD). Tau and β-amyloid (Aβ), the primary pathological features of AD, are associated with both objective and subjective changes in sleep. However, it remains unknown whether late life tau and Aβ burden are associated with distinct impairments in sleep physiology or changes in sleep across the lifespan. Using polysomnography, retrospective questionnaires, and tau- and Aβ-specific PET, the present study reveals human sleep signatures that dissociably predict levels of brain tau and Aβ in older adults. These results suggest that a night of polysomnography may aid in evaluating tau and Aβ burden, and that treating sleep deficiencies within decade-specific time windows may serve in delaying AD progression.

Sleep and EEG Power Spectral Analysis in Three Transgenic Mouse Models of Alzheimer's Disease: APP/PS1, 3xTgAD, and Tg2576

BACKGROUND

Sleep disturbances have long been associated with Alzheimer's disease (AD), and there is a growing interest in how these disturbances might impact AD pathophysiology. Despite this growing interest, surprisingly little is known about how sleep architecture and the broader neuronal network are affected in widely used transgenic mouse models of AD.

OBJECTIVE

We analyzed sleep and electroencephalography (EEG) power in three transgenic mouse models of AD, using identical and commercially available hardware and analytical software. The goal was to assess the suitability of these mouse lines to model sleep and the broader neuronal network dysfunction measured by EEG in AD.

METHODS

Tg2576, APP/PS1, and 3xTgAD transgenic AD mice were studied using in vivo EEG recordings for sleep/wake time and power spectral analysis.

RESULTS

Both the APP/PS1 model at 8- 10 months and the Tg2576 model at 12 months of age exhibited stage-dependent decreases in theta and delta power, and shifts in the power spectra toward higher frequencies. Stage-dependent power spectral analyses showed no changes in the 3xTgAD model at 18 months of age. The percentage of time spent awake, in non-rapid eye movement sleep (NREM), or in rapid-eye-movement sleep (REM) was not different between genotypes in any of the transgenic lines.

CONCLUSION

Our findings are consistent with data from several other transgenic AD models as well as certain studies in patients with mild cognitive impairment. Further studies will be needed to better understand the correlation between EEG spectra and AD pathophysiology, both in AD models and the human condition.

Neuropsychiatric Symptoms as Predictors of Clinical Course in Neurodegeneration. A Longitudinal Study

Background: To study the extent to which neuropsychiatric symptoms (NPS) influence the cognitive and functional decline in frontotemporal degeneration (FTD) and Alzheimer’s disease (AD).

Methods: We assessed the progression of NPS and their influence on cognitive and functional progression in a group of FTD (n = 36) and AD patients (n = 47) at two different stages of the disease (2.5 years). A standardized scale was used to assess NPS—the Columbia University Scale for Psychopathology in Alzheimer’s Disease (CUSPAD)—which tracks different symptoms including depression, psychotic symptoms, as well as sleep and conduct problems. In addition, in a subsample of patients (AD n = 14 and FTD n = 14), we analyzed another group of NPS by using the Neuropsychiatric Inventory (NPI). Cognitive declines were tracked by using the Montreal Cognitive Assessment (MoCA) and the Mini-Mental State Examination (MMSE), while functionality was tracked by using the Lawton scale and the Barthel Index.

Results: The presence of NPS impacts cognitive and functional decline in both groups of patients 2.5 years after disease onset. However, we observed a dissociable profile of the affectation of NPS in each group. In the AD group, results indicate that the progression of depressive symptoms and sleep problems predict cognitive and functional decline. In contrast, the progression of a mixed group of NPS, including conduct problems and delusions, predicts cognitive and functional decline in FTD.

Conclusion: The presence of NPS has a critical impact on the prediction of cognitive decline in FTD and AD patients after 2.5 years of disease progression. Our results demonstrate the importance of assessing different types of NPS in neurodegenerative disorders which, in turn, predict disease progression. Future studies should assess the role of NPS in predicting different neurocognitive pathways and in neurodegeneration.

Pineal gland dysfunction in Alzheimer's disease: relationship with the immune-pineal axis, sleep disturbance, and neurogenesis

Alzheimer’s disease (AD) is a globally common neurodegenerative disease, which is accompanied by alterations to various lifestyle patterns, such as sleep disturbance. The pineal gland is the primary endocrine organ that secretes hormones, such as melatonin, and controls the circadian rhythms. The decrease in pineal gland volume and pineal calcification leads to the reduction of melatonin production. Melatonin has been reported to have multiple roles in the central nervous system (CNS), including improving neurogenesis and synaptic plasticity, suppressing neuroinflammation, enhancing memory function, and protecting against oxidative stress. Recently, reduced pineal gland volume and pineal calcification, accompanied by cognitive decline and sleep disturbances have been observed in AD patients. Here, I review current significant evidence of the contribution of pineal dysfunction in AD to the progress of AD neuropathology. I suggest new insights to understanding the relationship between AD pathogenesis and pineal gland function.

Alzheimer's Disease and Sleep-Wake Disturbances: Amyloid, Astrocytes, and Animal Models

Sleep-wake abnormalities are common in patients with Alzheimer's disease, and can be a major reason for institutionalization. However, an emerging concept is that these sleep-wake disturbances are part of the causal pathway accelerating the neurodegenerative process. Recently, new findings have provided intriguing evidence for a positive feedback loop between sleep-wake dysfunction and β-amyloid (Aβ) aggregation. Studies in both humans and animal models have shown that extended periods of wakefulness increase Aβ levels and aggregation, and accumulation of Aβ causes fragmentation of sleep. This perspective is aimed at presenting evidence supporting causal links between sleep-wake dysfunction and aggregation of Aβ peptide in Alzheimer's disease, and explores the role of astrocytes, a specialized type of glial cell, in this context underlying Alzheimer's disease pathology. The utility of current animal models and the unexplored potential of alternative animal models for testing mechanisms involved in the reciprocal relationship between sleep disruption and Aβ are also discussed.Dual Perspectives Companion Paper: Microglia-Mediated Synapse Loss in Alzheimer's Disease by Lawrence Rajendran and Rosa Paolicelli.

Acoustic enhancement of sleep slow oscillations in mild cognitive impairment

OBJECTIVE

Slow-wave activity (SWA) during sleep is reduced in people with amnestic mild cognitive impairment (aMCI) and is related to sleep-dependent memory consolidation. Acoustic stimulation of slow oscillations has proven effective in enhancing SWA and memory in younger and older adults. In this study we aimed to determine whether acoustic stimulation during sleep boosts SWA and improves memory performance in people with aMCI.

METHODS

Nine adults with aMCI (72 ± 8.7 years) completed one night of acoustic stimulation (stim) and one night of sham stimulation (sham) in a blinded, randomized crossover study. Acoustic stimuli were delivered phase-locked to the upstate of the endogenous sleep slow-waves. Participants completed a declarative recall task with 44 word-pairs before and after sleep.

RESULTS

During intervals of acoustic stimulation, SWA increased by >10% over sham intervals (P < 0.01), but memory recall increased in only five of the nine patients. The increase in SWA with stimulation was associated with improved morning word recall (r = 0.78, P = 0.012).

INTERPRETATION

Acoustic stimulation delivered during slow-wave sleep over one night was effective for enhancing SWA in individuals with aMCI. Given established relationships between SWA and memory, a larger or more prolonged enhancement may be needed to consistently improve memory in aMCI.

Sleep and β-Amyloid Deposition in Alzheimer Disease: Insights on Mechanisms and Possible Innovative Treatments

The growing interest in the preclinical stage of Alzheimer's disease (AD) led investigators to identify modifiable risk and predictive factors useful to design early intervention strategies. The preclinical stage of AD is characterized by β-amyloid (Aβ) aggregation into amyloid plaques and tau phosphorylation and aggregation into neurofibrillary tangles. There is a consensus on the importance of sleep within this context: the bidirectional relationship between sleep and AD pathology is supported by growing evidence that proved that the occurrence of sleep changes starting from the preclinical stage of AD, many years before the onset of cognitive decline. Hence, we review the most recent studies on sleep disturbances related to Aβ and the effects of sleep deprivation on Aβ accumulation in animal and human models. We also discuss evidence on the role of sleep in clearing the brain of toxic metabolic by-products, with original findings of the clearance activity of the glymphatic system stimulated by sleep. Furthermore, starting from new recent advances about the relationship between slow-wave sleep (SWS) and Aβ burden, we review the results of recent electroencephalographic (EEG) studies in order to clarify the possible role of SWS component disruption as a novel mechanistic pathway through which Aβ pathology may contribute to cognitive decline and, conversely, the eventual useful role of SWS in facilitating Aβ clearance. Finally, we discuss some promising innovative, effective, low-risk, non-invasive interventions, although empirical evidence on the efficacy of sleep interventions in improving the course of AD is at the very beginning.

The Independent Associations of Physical Activity and Sleep with Cognitive Function in Older Adults

BACKGROUND

Current evidence suggests physical activity (PA) and sleep are important for cognitive health; however, few studies examining the role of PA and sleep for cognitive health have measured these behaviors objectively.

OBJECTIVE

We cross-sectionally examined whether 1) higher PA is associated with better cognitive performance independently of sleep quality; 2) higher sleep quality is associated with better cognitive performance independently of PA; and 3) whether higher PA is associated with better sleep quality.

METHODS

We measured PA, subjective sleep quality using the Pittsburgh Sleep Quality Index (PSQI), and objective sleep quality (i.e., fragmentation, efficiency, duration, and latency) using the MotionWatch8© in community-dwelling adults (N = 137; aged 55+). Cognitive function was indexed using the Alzheimer's Disease Assessment Scale-Plus. Correlation analyses were performed to determine relationships between PA, sleep quality, and cognitive function. We then used latent variable modelling to examine the relationships of PA with cognitive function independently of sleep quality, sleep quality with cognitive function independently of PA, and PA with sleep quality.

RESULTS

We found greater PA was associated with better cognitive performance independently of 1) PSQI (β= -0.03; p < 0.01); 2) sleep fragmentation (β= -0.02; p < 0.01); 3) sleep duration (β= -0.02; p < 0.01); and 4) sleep latency (β= -0.02; p < 0.01). In addition, better sleep efficiency was associated with better cognitive performance independently of PA (β= -0.01; p = 0.04). We did not find any associations between PA and sleep quality.

CONCLUSIONS

PA is associated with better cognitive performance independently of sleep quality, and sleep efficiency is associated with better cognitive performance independently of PA. However, PA is not associated with sleep quality and thus PA and sleep quality may be related to cognitive performance through independent mechanisms.

Sleep and Memory: The Promise of Precision Medicine

Given the complex and bidirectional nature of sleep and mild cognitive impairment/Alzheimer's disease and related dementias, a precision medicine approach to education, lifestyle changes, and early assessment in patients with a family history of snoring, sleep apnea, diabetes, and heart disease is warranted. Furthermore, a team-based approach allows for a coordinated precision diagnosis and management of common comorbid chronic illnesses. The significance of sleep disturbances in this population, contributing factors, assessment and diagnostic challenges, common sleep disorders and mechanisms, tailored behavioral and pharmacologic interventions, knowledge gaps, and future research ideas are discussed.

Enhancing face validity of mouse models of Alzheimer's disease with natural genetic variation

Classical laboratory strains show limited genetic diversity and do not harness natural genetic variation. Mouse models relevant to Alzheimer's disease (AD) have largely been developed using these classical laboratory strains, such as C57BL/6J (B6), and this has likely contributed to the failure of translation of findings from mice to the clinic. Therefore, here we test the potential for natural genetic variation to enhance the translatability of AD mouse models. Two widely used AD-relevant transgenes, APPswe and PS1de9 (APP/PS1), were backcrossed from B6 to three wild-derived strains CAST/EiJ, WSB/EiJ, PWK/PhJ, representative of three Mus musculus subspecies. These new AD strains were characterized using metabolic, functional, neuropathological and transcriptional assays. Strain-, sex- and genotype-specific differences were observed in cognitive ability, neurodegeneration, plaque load, cerebrovascular health and cerebral amyloid angiopathy. Analyses of brain transcriptional data showed strain was the greatest driver of variation. We identified significant variation in myeloid cell numbers in wild type mice of different strains as well as significant differences in plaque-associated myeloid responses in APP/PS1 mice between the strains. Collectively, these data support the use of wild-derived strains to better model the complexity of human AD.

Quantitative electroencephalography measures in rapid eye movement and nonrapid eye movement sleep are associated with apnea–hypopnea index and nocturnal hypoxemia in men

Study Objectives

Quantitative electroencephalography (EEG) measures of sleep may identify vulnerability to obstructive sleep apnea (OSA) sequelae, however, small clinical studies of sleep microarchitecture in OSA show inconsistent alterations. We examined relationships between quantitative EEG measures during rapid eye movement (REM) and non-REM (NREM) sleep and OSA severity among a large population-based sample of men while accounting for insomnia.

Methods

All-night EEG (F4-M1) recordings from full in-home polysomnography (Embletta X100) in 664 men with no prior OSA diagnosis (age ≥ 40) were processed following exclusion of artifacts. Power spectral analysis included non-REM and REM sleep computed absolute EEG power for delta, theta, alpha, sigma, and beta frequency ranges, total power (0.5–32 Hz) and EEG slowing ratio.

Results

Apnea–hypopnea index (AHI) ≥10/h was present in 51.2% (severe OSA [AHI ≥ 30/h] 11.6%). In mixed effects regressions, AHI was positively associated with EEG slowing ratio and EEG power across all frequency bands in REM sleep (all p < 0.05); and with beta power during NREM sleep (p = 0.06). Similar associations were observed with oxygen desaturation index (3%). Percentage total sleep time with oxygen saturation <90% was only significantly associated with increased delta, theta, and alpha EEG power in REM sleep. No associations with subjective sleepiness were observed.

Conclusions

In a large sample of community-dwelling men, OSA was significantly associated with increased EEG power and EEG slowing predominantly in REM sleep, independent of insomnia. Further study is required to assess if REM EEG slowing related to nocturnal hypoxemia is more sensitive than standard PSG indices or sleepiness in predicting cognitive decline.

Building your best day for healthy brain aging-The neuroprotective effects of optimal time use

As the number of older people increases, so too does the prevalence of neurodegenerative disease. Worldwide, health organisations have identified the need for practical, affordable interventions to slow or delay the onset of neurodegenerative diseases such as dementia, for which there are multiple modifiable risk factors. The effects of various interventions on brain health has been investigated, including achieving sufficient physical activity, getting appropriate amounts and quality of sleep, and limiting sedentary behaviours. Few of these studies, though, have taken into account more than one lifestyle behaviour within a single study. Epidemiologists have recently initiated a paradigm shift to move away from studying the independent effects of each physical activity, sleep and sedentary behaviour, and towards an integrated 24-h time-use paradigm. Time is finite, and thus to increase time in one activity (for example physical activity), equal time must be taken away from other activities (sleep and sedentary behaviour). This 24-h time-use paradigm has begun to be used when studying obesity, adiposity and quality of life; however, to the authors' knowledge, it has not yet been adopted by cognitive neuroscientists for the study of cognition or brain function. This narrative review synthesises the evidence for the neurophysiological effects of physical activity, sleep and sedentary behaviour independently, with a particular focus on brain structure, function and neurodegenerative disease risk. Then, we conclude with a call to action, addressing the need for studies to move towards an integrated 24-h time-use paradigm.

Non-REM Sleep Characteristics Predict Early Cognitive Impairment in an Aging Population

Objective: Recent research suggests that sleep disorders or changes in sleep stages or EEG waveform precede over time the onset of the clinical signs of pathological cognitive impairment (e.g., Alzheimer's disease). The aim of this study was to identify biomarkers based on EEG power values and spindle characteristics during sleep that occur in the early stages of mild cognitive impairment (MCI) in older adults. Methods: This study was a case-control cross-sectional study with 1-year follow-up of cases. Patients with isolated subjective cognitive complaints (SCC) or MCI were recruited in the Bordeaux Memory Clinic (MEMENTO cohort). Cognitively normal controls were recruited. All participants were recorded with two successive polysomnography 1 year apart. Delta, theta, and sigma absolute spectral power and spindle characteristics (frequency, density, and amplitude) were analyzed from purified EEG during NREM and REM sleep periods during the entire second night. Results: Twenty-nine patients (8 males, age = 71 ± 7 years) and 29 controls were recruited at T0. Logistic regression analyses demonstrated that age-related cognitive impairment were associated with a reduced delta power (odds ratio (OR) 0.072, P < 0.05), theta power (OR 0.018, P < 0.01), sigma power (OR 0.033, P < 0.05), and spindle maximal amplitude (OR 0.002, P < 0.05) during NREM sleep. Variables were adjusted on age, gender, body mass index, educational level, and medication use. Seventeen patients were evaluated at 1-year follow-up. Correlations showed that changes in self-reported sleep complaints, sleep consolidation, and spindle characteristics (spectral power, maximal amplitude, duration, and frequency) were associated with cognitive impairment (P < 0.05). Conclusion: A reduction in slow-wave, theta and sigma activities, and a modification in spindle characteristics during NREM sleep are associated very early with a greater risk of the occurrence of cognitive impairment. Poor sleep consolidation, lower amplitude, and faster frequency of spindles may be early sleep biomarkers of worsening cognitive decline in older adults.

Effect of sleep quality on amnestic mild cognitive impairment vulnerable brain regions in cognitively normal elderly individuals

STUDY OBJECTIVES

This study aims to evaluate the extent to which sleep quality impacts amnestic mild cognitive impairment (aMCI)-related brain regions in a cognitively normal cohort of individuals.

METHODS

Seventy-four participants were rigorously evaluated using a battery of cognitive tests and a detailed clinical assessment to verify normal cognitive status. We then screened for sleep quality using the Pittsburgh Sleep Quality Index (PSQI) and depressive symptoms using the Geriatric Depression Scale (GDS). Five subjects were excluded due to mild depression. Overall 38 individuals with mean age 70.7 ± 7 were classified as poor sleepers and 31 with mean age of 69.6 ± 6 years as normal sleepers. Structural MRI and Freesurfer brain parcellation were used to measure aMCI-related brain regions.

RESULTS

Relative to normal sleepers, poor sleepers exhibited significant reductions in cortical and subcortical volumes bilaterally in the hippocampi, as well as in the superior parietal lobules and left amygdala. The effects were strongest in the left superior parietal lobule (p < .015), followed by the hippocampi. Diffuse patterns of cortical thinning were observed in the frontal lobes, but significant effects were concentrated in the right mesial frontal cortex. Lower sleep duration was most correlated with cortical volume and thickness reductions among all subjects.

CONCLUSIONS

Atrophy related to poor sleep quality impacted a number of regions implicated in aMCI and Alzheimer's disease (AD). As such, interventions targeted towards improving sleep quality amongst the elderly may prove an effective tool for modulating the course of aMCI and AD.

Dementia in Down syndrome: unique insights for Alzheimer disease research

Virtually all adults with Down syndrome (DS) show the neuropathological changes of Alzheimer disease (AD) by the age of 40 years. This association is partially due to overexpression of amyloid precursor protein, encoded by APP, as a result of the location of this gene on chromosome 21. Amyloid-β accumulates in the brain across the lifespan of people with DS, which provides a unique opportunity to understand the temporal progression of AD and the epigenetic factors that contribute to the age of dementia onset. This age dependency in the development of AD in DS can inform research into the presentation of AD in the general population, in whom a longitudinal perspective of the disease is not often available. Comparison of the risk profiles, biomarker profiles and genetic profiles of adults with DS with those of individuals with AD in the general population can help to determine common and distinct pathways as well as mechanisms underlying increased risk of dementia. This Review evaluates the similarities and differences between the pathological cascades and genetics underpinning DS and AD with the aim of providing a platform for common exploration of these disorders.

Sleep oscillation-specific associations with Alzheimer's disease CSF biomarkers: novel roles for sleep spindles and tau

BACKGROUND

Based on associations between sleep spindles, cognition, and sleep-dependent memory processing, here we evaluated potential relationships between levels of CSF Aβ42, P-tau, and T-tau with sleep spindle density and other biophysical properties of sleep spindles in a sample of cognitively normal elderly individuals.

METHODS

One-night in-lab nocturnal polysomnography (NPSG) and morning to early afternoon CSF collection were performed to measure CSF Aβ42, P-tau and T-tau. Seven days of actigraphy were collected to assess habitual total sleep time.

RESULTS

Spindle density during NREM stage 2 (N2) sleep was negatively correlated with CSF Aβ42, P-tau and T-tau. From the three, CSF T-tau was the most significantly associated with spindle density, after adjusting for age, sex and ApoE4. Spindle duration, count and fast spindle density were also negatively correlated with T-tau levels. Sleep duration and other measures of sleep quality were not correlated with spindle characteristics and did not modify the associations between sleep spindle characteristics and the CSF biomarkers of AD.

CONCLUSIONS

Reduced spindles during N2 sleep may represent an early dysfunction related to tau, possibly reflecting axonal damage or altered neuronal tau secretion, rendering it a potentially novel biomarker for early neuronal dysfunction. Given their putative role in memory consolidation and neuroplasticity, sleep spindles may represent a mechanism by which tau impairs memory consolidation, as well as a possible target for therapeutic interventions in cognitive decline.

The Neurobiological Basis of Sleep and Sleep Disorders

The functions of sleep remain a mystery. Yet they must be important since sleep is highly conserved, and its chronic disruption is associated with various metabolic, psychiatric, and neurodegenerative disorders. This review will cover our evolving understanding of the mechanisms by which sleep is controlled and the complex relationship between sleep and disease states.

Delayed daily activity and reduced NREM slow-wave power in the APPswe/PS1dE9 mouse model of Alzheimer's disease

Alzheimer's disease (AD) is associated with disrupted circadian rhythms and sleep, which are thought to reflect an impairment of internal circadian timekeeping that contribute to clinical symptoms and disease progression. To evaluate these hypotheses, a suitable preclinical model of AD is needed. We performed a comprehensive assessment of circadian rhythms and sleep in the APP_swe/PS1_dE9 (APP/PS1) mouse model using long-term in vivo electroencephalogram (EEG) monitoring and behavioral assays from 5 to 22 months of age. APP/PS1 mice were crossed with a PERIOD2::LUCIFERASE (PER2::LUC) mouse model to evaluate synchrony among peripheral circadian oscillators. The APP/PS1 mice exhibited a mild but persistent phase delay of nocturnal activity onset in 12:12h light:dark conditions, as well as a shift toward higher frequencies in the EEG power spectra compared to littermate controls. Our results suggest that APP/PS1 mice may not be the optimal preclinical model for studying the specific circadian changes associated with AD but that quantitative EEG may offer a sensitive measure of AD-associated changes in sleep quality that can be modeled in APP/PS1 mice.

Sex differences in sleep and sleep loss-induced cognitive deficits: The influence of gonadal hormones

Males and females can respond differentially to the same environmental stimuli and experimental conditions. Chronic sleep loss is a frequent and growing problem in many modern societies and has a broad variety of negative outcomes for health and well-being. While much has been done to explore the deleterious effects of sleep deprivation (SD) on cognition in both human and animal studies over the last few decades, very little attention has been paid to the part played by sex differences and gonadal steroids in respect of changes in cognitive functions caused by sleep loss. The effects of gonadal hormones on sleep regulation and cognitive performances are well established. Reduced gonadal function in menopausal women and elderly men is associated with sleep disturbances and cognitive decline as well as dementia, which suggests that sex steroids play a key role in modulating these conditions. Finding out whether there are sex differences in respect of the effect of insufficient sleep on cognition, and how neuroendocrine mediators influence cognitive impairment induced by SD could provide valuable insights into the best therapies for each sex. In this review, we aim to highlight the involvement of sex differences and gonadal hormone status on the severity of cognitive deficits induced by sleep deficiency in both human and animal studies.

Implications of sleep disturbance and inflammation for Alzheimer's disease dementia

Nearly half of all adults older than 60 years of age report sleep disturbance, as characterised either by reports of insomnia complaints with daytime consequences, dissatisfaction with sleep quality or quantity, or the diagnosis of insomnia disorder. Accumulating evidence shows that sleep disturbance contributes to cognitive decline and might also increase the risk of Alzheimer's disease dementia by increasing β-amyloid burden. That sleep disturbance would be a candidate risk factor for Alzheimer's disease might seem surprising, given that disturbed sleep is usually considered a consequence of Alzheimer's disease. However, a bidirectional relationship between sleep and Alzheimer's disease is supported by advances in our understanding of sleep disturbance-induced increases in systemic inflammation, which can be viewed as an early event in the course of Alzheimer's disease. Inflammation increases β-amyloid burden and is thought to drive Alzheimer's disease pathogenesis. Improved understanding of the mechanisms linking sleep disturbance and Alzheimer's disease risk could facilitate the identification of targets for prevention, given that both sleep disturbance and inflammatory activation might be modifiable risk factors for Alzheimer's disease.

Effects of Six-Month Aerobic Exercise Intervention on Sleep in Healthy Older Adults in the Brain in Motion Study: A Pilot Study

Background

Sleep disturbances have been shown to be associated with the presence of the apolipoprotein (APOE) ɛ4 allele, the well-known genetic risk factor for late-onset sporadic Alzheimer's disease (AD).

Objective

This study quantifies the effects of a six-month aerobic exercise intervention on objective and subjective sleep quality in middle-aged to older individuals including those at increased genetic risk for late-onset sporadic Alzheimer's disease (AD), who carry the apolipoprotein (APOE) ɛ4 risk allele.

Methods

199 sedentary men and women without significant cognitive impairments were enrolled in the Brain in Motion study, a quasi-experimental single group pre-test/post-test study with no control group. Participants completed a six-month aerobic exercise intervention and consented to genetic testing. Genotyping of APOE confirmed that 54 individuals were carriers of the ɛ4 allele. Participants' subjective quality of sleep was assessed with the Pittsburgh Sleep Quality Index (PSQI) pre- and post-intervention. A convenience sample of participants (n = 29, APOE ɛ4+ = 7) consented to undergo two nights of in-home polysomnography (PSG) pre- and post intervention. Sleep architecture and respiratory variables were assessed.

Results

The six-month aerobic exercise intervention significantly improved participants' total PSQI score, sleep efficiency, and sleep latency in the full sample (n = 199). PSG results showed that total sleep time and sleep onset latency significantly improved over the course of the exercise intervention only in individuals who carried the APOE ɛ4 allele. These results are, however, exploratory and need to be carefully interpreted due to the rather small number of APOE ɛ4+ in the PSG subgroup.

Conclusions

The six-month aerobic exercise intervention significantly improved participants' sleep quality with beneficial effects on PSG shown in individuals at increased genetic risk for late-onset sporadic AD.

Insulin Peptides as Mediators of the Impact of Life Style in Alzheimer's disease

The search for the cause of Alzheimer's disease (AD), that affects millions of people worldwide, is currently one of the most important scientific endeavors from a clinical perspective. There are so many mechanisms proposed, and so disparate changes observed, that it is becoming a challenging task to provide a comprehensive view of possible pathogenic processes in AD. Tauopathy (intracellular neurofibrillary tangles) and amyloidosis (extracellular amyloid plaques) are the anatomical hallmarks of the disease, and the formation of these proteinaceous aggregates in specific brain areas is widely held as the ultimate pathogenic mechanism. However, the triggers of this dysproteostasis process remain unknown. Further, neurofibrillary tangles and plaques may only constitute the last stages of a process of still uncertain origin. Thus, without an established knowledge of its etiology, and no cure in the horizon, prevention - or merely delaying its development, has become a last-resort goal in AD research. As with other success stories in preventive medicine, epidemiological studies have provided basic knowledge of risk factors in AD that may contribute to understand its etiology. Disregarding old age, gender, and ApoE4 genotype as non preventable risk factors, there are diverse life-style traits - many of them closely related to cardiovascular health, that have been associated to AD risk. Most prominent among them are diet, physical and mental activity, exposure to stress, and sleep/wake patterns. We argue that all these life-style factors engage insulinergic pathways that affect brain function, providing a potentially unifying thread for life-style and AD risk. Although further studies are needed to firmly establish a link between faulty insulinergic function and AD, we herein summarize the evidence that this link should be thoroughly considered.

Disorders of Body Weight, Sleep and Circadian Rhythm as Manifestations of Hypothalamic Dysfunction in Alzheimer's Disease

While cognitive decline and memory loss are the major clinical manifestations of Alzheimer’s disease (AD), they are now recognized as late features of the disease. Recent failures in clinical drug trials highlight the importance of evaluating and treating patients with AD as early as possible and the difficulties in developing effective therapies once the disease progresses. Since the pathological hallmarks of AD including the abnormal aggregation of amyloid-beta (Aβ) and tau can occur decades before any significant cognitive decline in the preclinical stage of AD, it is important to identify the earliest clinical manifestations of AD and elucidate their underlying cellular and molecular mechanisms. Importantly, metabolic and non-cognitive manifestations of AD such as weight loss and alterations of peripheral metabolic signals can occur before the onset of cognitive symptoms and worsen with disease progression. Accumulating evidence suggests that the major culprit behind these early metabolic and non-cognitive manifestations of AD is AD pathology causing dysfunction of the hypothalamus, a brain region critical for integrating peripheral signals with essential homeostatic physiological functions. Here, we aim to highlight recent developments that address the role of AD pathology in the development of hypothalamic dysfunction associated with metabolic and non-cognitive manifestations seen in AD. Understanding the mechanisms underlying hypothalamic dysfunction in AD could give key new insights into the development of novel biomarkers and therapeutic targets.

The hidden variables problem in Alzheimer's disease clinical trial design

As the leading cause of dementia worldwide, Alzheimer's disease has garnered intense academic and clinical interest. Yet, trials in search of a disease-modifying therapy have failed overwhelmingly. We suggest that, in part, this may be attributable to the influence of disruptive variables inherent to the framework of a clinical trial. Specifically, we observe that everyday factors such as diet, education, mental exertion, leisure participation, multilingualism, sleep, trauma, and physical activity, as well as clinical/study parameters including environment, family coaching, concurrent medications, and illnesses may serve as potent confounders, disruptors, or sources of bias to an otherwise significant drug-disease interaction. This perspective briefly summarizes the potential influence of these hidden variables on the outcomes of clinical trials and suggests strategies to abate their impact.

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Clinical trials in Alzheimer's disease have failed overwhelmingly.

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In part, this may be due to interference by clinical and daily variables.

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The role of these variables in Alzheimer's disease risk and progression is reviewed.

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Strategies to abate a disruptive influence in Alzheimer's disease clinical trials are suggested.

Dynamic Contributions of Slow Wave Sleep and REM Sleep to Cognitive Longevity

Purpose of review

The purpose of this paper was to address how sleep changes with aging, with the broader goal of informing how REM sleep and slow wave activity mechanisms interact to promote cognitive longevity.

Recent findings

We conducted novel analyses based on the National Sleep Research Resource database. Over approximately five years, middle-to-older aged adults, on average, showed dramatically worse sleep fragmentation, a steady decrease in slow wave sleep, and yet a small increase in REM sleep. Averaging across participants, however, masked a major theme: Individuals differ substantially in their longitudinal trajectories for specific components of sleep. We considered this individual variability in light of recent theoretical and empirical work that has shown disrupted sleep and decreased slow wave activity to impair frontal lobe restoration, glymphatic system functioning, and memory consolidation. Based on multiple recent longitudinal studies, we contend that preserved or enhanced REM sleep may compensate for otherwise disrupted sleep in advancing age.

Summary

The scientific community has often debated whether slow wave activity or REM sleep mechanisms are more important to cognitive aging. We propose that a more fruitful approach for future work will be to investigate how REM and slow wave processes dynamically interact to affect cognitive longevity.

Amyloid β and tau are involved in sleep disorder in Alzheimer's disease by orexin A and adenosine A(1) receptor

Sleep disorder is confirmed as a core component of Alzheimer's disease (AD), while the accumulation of amyloid β (Aβ) in brain tissue is an important pathological feature of AD. However, how Aβ affects AD‑associated sleep disorder is not yet well understood. In the present study, experiments on animal and cell models were performed to detect the association between sleep disorder and Aβ. It was observed that Aβ25‑35 administration significantly decreased non‑rapid eye movement sleep, while it increased wakefulness in mice. In addition, reverse transcription‑quantitative polymerase chain reaction and western blot analysis revealed that the expression levels of tau, p‑tau, orexin A and orexin neurons express adenosine A1 receptor (A1R) were markedly upregulated in the brain tissue of AD mice compared with that in samples obtained from control mice. Furthermore, the in vitro study revealed that the expression levels of tau, p‑tau, orexin A and adenosine A1R were also significantly increased in human neuroblastoma SH‑SY5Y cells treated with Aβ25‑35 as compared with the control cells. In addition, the tau inhibitor TRx 0237 significantly reversed the promoting effects of Aβ25‑35 on tau, p‑tau, orexin A and adenosine A1R expression levels, and adenosine A1R or orexin A knockdown also inhibited tau and p‑tau expression levels mediated by Aβ25‑35 in AD. These results indicate that Aβ and tau may be considered as novel biomarkers of sleep disorder in AD pathology, and that they function by regulating the expression levels of orexin A and adenosine A1R.

Circadian monitoring as an aging predictor

The ageing process is associated with sleep and circadian rhythm (SCR) frailty, as well as greater sensitivity to chronodisruption. This is essentially due to reduced day/night contrast, decreased sensitivity to light, napping and a more sedentary lifestyle. Thus, the aim of this study is to develop an algorithm to identify a SCR phenotype as belonging to young or aged subjects. To do this, 44 young and 44 aged subjects were recruited, and their distal skin temperature (DST), activity, body position, light, environmental temperature and the integrated variable TAP rhythms were recorded under free-living conditions for five consecutive workdays. Each variable yielded an individual decision tree to differentiate between young and elderly subjects (DST, activity, position, light, environmental temperature and TAP), with agreement rates of between 76.1% (light) and 92% (TAP). These decision trees were combined into a unique decision tree that reached an agreement rate of 95.3% (4 errors out of 88, all of them around the cut-off point). Age-related SCR changes were very significant, thus allowing to discriminate accurately between young and aged people when implemented in decision trees. This is useful to identify chronodisrupted populations that could benefit from chronoenhancement strategies.

An Update on Dual Orexin Receptor Antagonists and Their Potential Role in Insomnia Therapeutics

STUDY OBJECTIVES

Current pharmacological options for the treatment of insomnia insufficiently meet the needs of all insomnia patients. Approved treatments are not consistently effective in improving sleep onset and sleep maintenance, while also having complicated safety profiles. These limitations highlight the unmet need for additional medications and treatment strategies. Initial research suggests that the dual orexin receptor antagonists (DORAs) may offer an additional pharmaceutical option to treat insomnia in some patients.

METHODS

We reviewed the existing literature on dual orexin receptor antagonists in PubMed databases using the search terms "orexin receptor antagonist," "almorexant" "filorexant," "lembroexant" and "suvorexant"; searches were limited to English language primary research articles, clinical trials, and reviews.

RESULTS

Targeting the orexin receptor system for treatment of insomnia offers an additional and alternative pharmacological approach to more common gamma aminobutyric acid agonist sedative hypnotic treatment. Effectiveness is not well established in the current literature; however, the literature does suggest efficacy. Preclinical reports also suggest the potential for treatment in individuals with comorbid Alzheimer disease and insomnia.

CONCLUSIONS

DORAs offer an additional treatment option for insomnia. More clinical trials are needed to robustly evaluate their safety and effectiveness in several subclasses of individuals with insomnia. Given the published literature, head-to-head comparisons to existing treatment for insomnia are warranted.

Intracerebroventricular streptozotocin-induced Alzheimer's disease-like sleep disorders in rats: Role of the GABAergic system in the parabrachial complex

AIM

Sleep disorders are common in Alzheimer's disease (AD) and assumed to directly influence cognitive function and disease progression. This study evaluated sleep characteristics in a rat model of AD that was induced by intracerebroventricular streptozotocin (STZ) administration and assessed the possible underlying mechanisms.

METHODS

Cognition ability was assessed in the Morris water maze in rats. Sleep parameters were analyzed by electroencephalographic and electromyographic recordings. Neuronal activity in brain areas that regulate sleep-wake states was evaluated by double-staining immunohistochemistry. High-performance liquid chromatography with electrochemical detection was used to detect neurotransmitter levels.

RESULTS

Fourteen days after the STZ injection, the rats exhibited sleep disorders that were similar to those in AD patients, reflected by a significant increase in wakefulness and decreases in nonrapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. The c-Fos expression analysis indicated that neuronal activity and the number of neurons in the dorsal raphe nucleus and locus coeruleus decreased in STZ-injected rats. In the ventrolateral preoptic nucleus (VLPO), the activity of γ-aminobutyric acid (GABA) neurons was suppressed. In the arousal-driving parabrachial nucleus (PBN), GABAergic activity was suppressed, whereas glutamatergic activity was promoted. The neurotransmitter analysis revealed a reduction in GABA in the VLPO and PBN and elevation of glutamate in the PBN. A direct injection of the GABA_A receptor antagonist bicuculline in the PBN in normal rats induced a similar pattern of sleep disorder as in STZ-injected rats. A microinjection of GABA in the PBN improved sleep disorders that were induced by STZ.

CONCLUSION

These results suggest that the reduction in GABAergic inhibition in the PBN and VLPO may be involved in sleep disorders that are induced by STZ. Our novel findings encourage further studies that investigate mechanisms of sleep regulation in sporadic AD.

Structural brain correlates of obstructive sleep apnoea in older adults at risk for dementia

This study aimed to investigate associations between obstructive sleep apnoea (OSA) and cortical thickness in older adults with subjective and objective cognitive difficulties, who are considered "at-risk" for dementia.83 middle-aged to older adults (51-88 years) underwent neuropsychological testing, polysomnography assessment of OSA and a structural magnetic resonance imaging brain scan. A principal components analysis was performed on OSA measures. Cortical thickness and subcortical volumes were compared to extracted components of "oxygen desaturation" and "sleep disturbance".Oxygen desaturation was significantly related to reduced cortical thickness in the bilateral temporal lobes (left: r=-0.44, p<0.001; right: r=-0.39, p=0.003). Conversely, sleep disturbance was associated with increased thickness in the right postcentral gyrus (r=0.48, p<0.001), pericalcarine (r=0.50, p=0.005) and pars opercularis (r=0.46, p=0.009) and increased volume of the hippocampus and amygdala. Decreased thickness in the bilateral temporal regions was associated with reduced verbal encoding (r=0.28, p=0.010).Given the clinical significance of this sample in terms of dementia prevention, these changes in grey matter reveal how OSA might contribute to neurodegenerative processes in older adults.

Why could meditation practice help promote mental health and well-being in aging?

Psycho-affective states or traits such as stress, depression, anxiety and neuroticism are known to affect sleep, cognition and mental health and well-being in aging populations and to be associated with increased risk for Alzheimer's disease (AD). Mental training for stress reduction and emotional and attentional regulation through meditation practice might help reduce these adverse factors. So far, studies on the impact of meditation practice on brain and cognition in aging are scarce and have limitations but the findings are encouraging, showing a positive effect of meditation training on cognition, especially on attention and memory, and on brain structure and function especially in frontal and limbic structures and insula. In line with this, we showed in a pilot study that gray matter volume and/or glucose metabolism was higher in six older adult expert meditators compared to 67 age-matched controls in the prefrontal, anterior and posterior cingulate cortex, insula and temporo-parietal junction. These preliminary findings are important in the context of reserve and brain maintenance as they suggest that long-term meditation practice might help preserve brain structure and function from progressive age-related decline. Further studies are needed to confirm these results with larger samples and in randomized controlled trials and to investigate the mechanisms underlying these meditation-related effects. The European Commission-funded project Silver Santé Study will address these challenges by studying 316 older adults including 30 expert meditators and 286 meditation-naïve participants (either cognitively normal or with subjective cognitive decline). Two randomized controlled trials will be conducted to assess the effects of 2-month and 18-month meditation, English learning or health education training programs (versus a passive control) on behavioral, sleep, blood sampling and neuroimaging measures. This European research initiative illustrates the progressive awareness of the benefit of such non-pharmacological approaches in the prevention of dementia and the relevance of taking into account the psycho-affective dimension in endeavoring to improve mental health and well-being of older adults.

Circadian and Brain State Modulation of Network Hyperexcitability in Alzheimer's Disease

Network hyperexcitability is a feature of Alzheimer' disease (AD) as well as numerous transgenic mouse models of AD. While hyperexcitability in AD patients and AD animal models share certain features, the mechanistic overlap remains to be established. We aimed to identify features of network hyperexcitability in AD models that can be related to epileptiform activity signatures in AD patients. We studied network hyperexcitability in mice expressing amyloid precursor protein (APP) with mutations that cause familial AD, and compared a transgenic model that overexpresses human APP (hAPP) (J20), to a knock-in model expressing APP at physiological levels (APP^NL/F). We recorded continuous long-term electrocorticogram (ECoG) activity from mice, and studied modulation by circadian cycle, behavioral, and brain state. We report that while J20s exhibit frequent interictal spikes (IISs), APP^NL/F mice do not. In J20 mice, IISs were most prevalent during daylight hours and the circadian modulation was associated with sleep. Further analysis of brain state revealed that IIS in J20s are associated with features of rapid eye movement (REM) sleep. We found no evidence of cholinergic changes that may contribute to IIS-circadian coupling in J20s. In contrast to J20s, intracranial recordings capturing IIS in AD patients demonstrated frequent IIS in non-REM (NREM) sleep. The salient differences in sleep-stage coupling of IIS in APP overexpressing mice and AD patients suggests that different mechanisms may underlie network hyperexcitability in mice and humans. We posit that sleep-stage coupling of IIS should be an important consideration in identifying mouse AD models that most closely recapitulate network hyperexcitability in human AD.

β-Amyloid accumulation in the human brain after one night of sleep deprivation

The effects of acute sleep deprivation on β-amyloid (Aβ) clearance in the human brain have not been documented. Here we used PET and 18F-florbetaben to measure brain Aβ burden (ABB) in 20 healthy controls tested after a night of rested sleep (baseline) and after a night of sleep deprivation. We show that one night of sleep deprivation, relative to baseline, resulted in a significant increase in Aβ burden in the right hippocampus and thalamus. These increases were associated with mood worsening following sleep deprivation, but were not related to the genetic risk (APOE genotype) for Alzheimer's disease. Additionally, baseline ABB in a range of subcortical regions and the precuneus was inversely associated with reported night sleep hours. APOE genotyping was also linked to subcortical ABB, suggesting that different Alzheimer's disease risk factors might independently affect ABB in nearby brain regions. In summary, our findings show adverse effects of one-night sleep deprivation on brain ABB and expand on prior findings of higher Aβ accumulation with chronic less sleep.

Quantifying sleep architecture dynamics and individual differences using big data and Bayesian networks

The pattern of sleep stages across a night (sleep architecture) is influenced by biological, behavioral, and clinical variables. However, traditional measures of sleep architecture such as stage proportions, fail to capture sleep dynamics. Here we quantify the impact of individual differences on the dynamics of sleep architecture and determine which factors or set of factors best predict the next sleep stage from current stage information. We investigated the influence of age, sex, body mass index, time of day, and sleep time on static (e.g. minutes in stage, sleep efficiency) and dynamic measures of sleep architecture (e.g. transition probabilities and stage duration distributions) using a large dataset of 3202 nights from a non-clinical population. Multi-level regressions show that sex effects duration of all Non-Rapid Eye Movement (NREM) stages, and age has a curvilinear relationship for Wake After Sleep Onset (WASO) and slow wave sleep (SWS) minutes. Bayesian network modeling reveals sleep architecture depends on time of day, total sleep time, age and sex, but not BMI. Older adults, and particularly males, have shorter bouts (more fragmentation) of Stage 2, SWS, and they transition less frequently to these stages. Additionally, we showed that the next sleep stage and its duration can be optimally predicted by the prior 2 stages and age. Our results demonstrate the potential benefit of big data and Bayesian network approaches in quantifying static and dynamic architecture of normal sleep.

Resistance vs resilience to Alzheimer disease: Clarifying terminology for preclinical studies

Preventing or delaying Alzheimer disease (AD) through lifestyle interventions will come from a better understanding of the mechanistic underpinnings of (1) why a significant proportion of elderly remain cognitively normal with AD pathologies (ADP), i.e., amyloid or tau; and (2) why some elderly individuals do not have significant ADP. In the last decades, concepts such as brain reserve, cognitive reserve, and more recently brain maintenance have been proposed along with more general notions such as (neuro)protection and compensation. It is currently unclear how to effectively apply these concepts in the new field of preclinical AD specifically separating the 2 distinct mechanisms of coping with pathology vs avoiding pathology. We propose a simplistic conceptual framework that builds on existing concepts using the nomenclature of resistance in the context of avoiding pathology, i.e., remaining cognitively normal without significant ADP, and resilience in the context of coping with pathology, i.e., remaining cognitively normal despite significant ADP. In the context of preclinical AD studies, we (1) define these concepts and provide recommendations (and common scenarios) for their use; (2) discuss how to employ this terminology in the context of investigating mechanisms and factors; (3) highlight the complementarity and clarity they provide to existing concepts; and (4) discuss different study designs and methodologies. The application of the proposed framework for framing hypotheses, study design, and interpretation of results and mechanisms can provide a consistent framework and nomenclature for researchers to reach consensus on identifying factors that may prevent ADP or delay the onset of cognitive impairment.