The sleep-wake cycle and Alzheimer's disease: what do we know?

Causal relationship between sleep disorders and the risk of Alzheimer's disease: A Mendelian randomization study

BACKGROUND AND OBJECTIVE

Epidemiological studies have shown that sleep disorders are risk factors for Alzheimer's disease (AD), but the causal relationship between sleep disorders and AD risk is unknown. We aim to assess the potential genetic causal association between sleep characteristics and AD, which may contribute to early identification and prediction of risk factors for AD.

METHODS

Seven sleep-related traits and the outcome phenotype AD were selected from published genome-wide association studies (GWASs). These sleep-related characteristics and instrumental variables (IVs) for AD were extracted. Two-sample and multivariate Mendelian randomization (MR) analyses were performed to assess the causal relationships between sleep characteristics and AD. The inverse variance weighted (IVW), weighted median (WME), weighted mode (WM), MR-Egger regression (MR-Egger) and simple mode (SM) models were used to evaluate causality. The existence of pleiotropy was detected and corrected by MR-Egger regression, MR pleiotropy residuals and outliers.

RESULTS

A two-sample MR study revealed a positive causal association between sleep duration and the onset of AD (OR = 1.002, 95 % CI: 1.000-1.004), and the risk of AD increased with increasing sleep duration. The MR-Egger regression method and MR-PRESSO were used to identify and correct pleiotropy, indicating that there was no horizontal pleiotropy. Heterogeneity was evaluated by Cochran's Q, which indicated no heterogeneity. In a multivariate MR study with seven sleep characteristics corrected for each other, we found that sleep duration remained causally associated with AD (OR = 1.004, 95 % CI: 1.000-1.007). Moreover, we found that after mutual correction, daytime napping had a causal relationship with the onset of AD, and daytime napping may reduce the risk of AD (OR = 0.995, 95 % CI: 0.991-1.000).

CONCLUSION

This study is helpful for the early identification and prediction of risk factors for AD, long sleep durations are a risk factor for AD, and daytime napping can reduce the risk of AD.

Sleep-wake behavior and responses to sleep deprivation and immune challenge of protein kinase RNA-activated knockout mice

Protein Kinase RNA-activated (PKR) is an enzyme that plays a role in many systemic processes, including modulation of inflammation, and is implicated in neurodegenerative diseases, such as Alzheimer's disease (AD). PKR phosphorylation results in the production of several cytokines involved in the regulation / modulation of sleep, including interleukin-1β, tumor necrosis factor-α and interferon-γ. We hypothesized targeting PKR would alter spontaneous sleep of mice, attenuate responses to sleep deprivation, and inhibit responses to immune challenge. To test these hypotheses, we determined the sleep-wake phenotype of mice lacking PKR (knockout; PKR-/-) during undisturbed baseline conditions; in responses to six hours of sleep deprivation; and after immune challenge with lipopolysaccharide (LPS). Adult male mice (C57BL/6J, n = 7; PKR-/-, n = 7) were surgically instrumented with EEG recording electrodes and an intraperitoneal microchip to record core body temperature. During undisturbed baseline conditions, PKR -/- mice spent more time in non-rapid eye movement sleep (NREMS) and rapid-eye movement sleep (REMS), and less time awake at the beginning of the dark period of the light:dark cycle. Delta power during NREMS, a measure of sleep depth, was less in PKR-/- mice during the dark period, and core body temperatures were lower during the light period. Both mouse strains responded to sleep deprivation with increased NREMS and REMS, although these changes did not differ substantively between strains. The initial increase in delta power during NREMS after sleep deprivation was greater in PKR-/- mice, suggesting a faster buildup of sleep pressure with prolonged waking. Immune challenge with LPS increased NREMS and inhibited REMS to the same extent in both mouse strains, whereas the initial LPS-induced suppression of delta power during NREMS was greater in PKR-/- mice. Because sleep regulatory and immune responsive systems in brain are redundant and overlapping, other mediators and signaling pathways in addition to PKR are involved in the responses to acute sleep deprivation and LPS immune challenge.

Mid-life sleep is associated with cognitive performance later in life in aging American Indians: data from the Strong Heart Study

Background

Sleep-related disorders have been associated with cognitive decline and neurodegeneration. American Indians are at increased risk for dementia. Here, we aim to characterize, for the first time, the associations between sleep characteristics and subsequent cognitive performance in a sample of aging American Indians.

Methods

We performed analyses on data collected in two ancillary studies from the Strong Heart Study, which occurred approximately 10 years apart with an overlapping sample of 160 American Indians (mean age at follow-up 73.1, standard deviation 5.6; 69.3% female and 80% with high school completion). Sleep measures were derived by polysomnography and self-reported questionnaires, including sleep timing and duration, sleep latency, sleep stages, indices of sleep-disordered breathing, and self-report assessments of poor sleep and daytime sleepiness. Cognitive assessment included measures of general cognition, processing speed, episodic verbal learning, short and long-delay recall, recognition, and phonemic fluency. We performed correlation analyses between sleep and cognitive measures. For correlated variables, we conducted separate linear regressions. We analyzed the degree to which cognitive impairment, defined as more than 1.5 standard deviations below the average Modified Mini Mental State Test score, is predicted by sleep characteristics. All regression analyses were adjusted for age, sex, years of education, body mass index, study site, depressive symptoms score, difference in age from baseline to follow-up, alcohol use, and presence of APOE e4 allele.

Results

We found that objective sleep characteristics measured by polysomnography, but not subjective sleep characteristics, were associated with cognitive performance approximately 10 years later. Longer sleep latency was associated with worse phonemic fluency (β = -0.069, p = 0.019) and increased likelihood of being classified in the cognitive impairment group later in life (odds ratio 1.037, p = 0.004). Longer duration with oxygen saturation < 90% was associated with better immediate verbal memory, and higher oxygen saturation with worse total learning, short and long-delay recall, and processing speed.

Conclusion

In a sample of American Indians, sleep characteristics in midlife were correlated with cognitive performance a decade later. Sleep disorders may be modifiable risk factors for cognitive impairment and dementia later in life, and suitable candidates for interventions aimed at preventing neurodegenerative disease development and progression.

Nature's Toolbox for Alzheimer's Disease: A Review on the Potential of Natural Products as Alzheimer's Disease Drugs

Numerous clinical trials involving natural products have been conducted to observe cognitive performances and biomarkers in Alzheimer's Disease (AD) patients. However, to date, no natural-based drugs have been approved by the FDA as treatments for AD. In this review, natural product-based compounds that were tested in clinical trials from 2011 to 2023, registered at www.clinicaltrials.gov were reviewed. Thirteen compounds, encompassing 7 different mechanisms of action were covered. Several observations were deduced, which are: i) several compounds showed cognitive improvement, but these improvements may not extend to AD, ii) compounds that are endogenous to the human body showed better outcomes, and iii) Docosahexaenoic acid (DHA) and cerebrolysin had the most potential as AD drugs among the 13 compounds. Based on the current findings, natural products may be more suitable as a supplement than AD drugs in most cases. However, the studies covered here were conducted in a relatively short amount of time, where compounds acting on AD pathways may take time to show any effect. Given the diverse pathways that these natural products are involved in, they may potentially produce synergistic effects that would be beneficial in treating AD. Additionally, natural products benefit from both physicochemical properties being in more favorable ranges and active transport playing a more significant role than it does for synthetic compounds.

2024 Alzheimer's disease facts and figures

This article describes the public health impact of Alzheimer's disease (AD), including prevalence and incidence, mortality and morbidity, use and costs of care and the ramifications of AD for family caregivers, the dementia workforce and society. The Special Report discusses the larger health care system for older adults with cognitive issues, focusing on the role of caregivers and non-physician health care professionals. An estimated 6.9 million Americans age 65 and older are living with Alzheimer's dementia today. This number could grow to 13.8 million by 2060, barring the development of medical breakthroughs to prevent or cure AD. Official AD death certificates recorded 119,399 deaths from AD in 2021. In 2020 and 2021, when COVID-19 entered the ranks of the top ten causes of death, Alzheimer's was the seventh-leading cause of death in the United States. Official counts for more recent years are still being compiled. Alzheimer's remains the fifth-leading cause of death among Americans age 65 and older. Between 2000 and 2021, deaths from stroke, heart disease and HIV decreased, whereas reported deaths from AD increased more than 140%. More than 11 million family members and other unpaid caregivers provided an estimated 18.4 billion hours of care to people with Alzheimer's or other dementias in 2023. These figures reflect a decline in the number of caregivers compared with a decade earlier, as well as an increase in the amount of care provided by each remaining caregiver. Unpaid dementia caregiving was valued at $346.6 billion in 2023. Its costs, however, extend to unpaid caregivers' increased risk for emotional distress and negative mental and physical health outcomes. Members of the paid health care and broader community-based workforce are involved in diagnosing, treating and caring for people with dementia. However, the United States faces growing shortages across different segments of the dementia care workforce due to a combination of factors, including the absolute increase in the number of people living with dementia. Therefore, targeted programs and care delivery models will be needed to attract, better train and effectively deploy health care and community-based workers to provide dementia care. Average per-person Medicare payments for services to beneficiaries age 65 and older with AD or other dementias are almost three times as great as payments for beneficiaries without these conditions, and Medicaid payments are more than 22 times as great. Total payments in 2024 for health care, long-term care and hospice services for people age 65 and older with dementia are estimated to be $360 billion. The Special Report investigates how caregivers of older adults with cognitive issues interact with the health care system and examines the role non-physician health care professionals play in facilitating clinical care and access to community-based services and supports. It includes surveys of caregivers and health care workers, focusing on their experiences, challenges, awareness and perceptions of dementia care navigation.

Pharmacological interventions to improve sleep in people with Alzheimer's disease: a meta-analysis of randomized controlled trials

INTRODUCTION

This systematic review and meta-analysis evaluates the evidence from randomized controlled trials (RCTs) involving pharmacological interventions for improving sleep in people with Alzheimer's disease (AD).

METHODS

A systematic literature search in eight databases from January 2000 to July 2023 focusing on RCTs that compared a pharmacological intervention with a placebo for enhancing sleep in people with AD. The authors registered the study protocol at Prospero, followed the PRISMA guidelines, and produced the pooled estimates using random-effect or IVhet models.

RESULTS

Eight different interventions and 29 different sleep outcomes were examined in 14 RCTs included in this review. Eszopiclone positively affected sleep efficiency, as did orexin antagonists. However, there was no difference when melatonin was used. The interventions demonstrated low discontinuation rates and a few adverse drug reactions.

CONCLUSION

Although melatonin was the most investigated intervention, the evidence for its efficacy is inconclusive. On the other hand, trazodone and orexin receptor antagonists showed promising results; however, more RCTs are needed for definite answers.

Sleep deprivation: A risk factor for the pathogenesis and progression of Alzheimer's disease

Sleep deprivation refers to an intentional or unintentional reduction in sleep time, resulting in insufficient sleep. It is often caused by sleep disorders, work demands (e.g., night shifts), and study pressure. Sleep deprivation promotes Aβ deposition and tau hyperphosphorylation, which is a risk factor for the pathogenesis and progression of Alzheimer's disease (AD). Recent research has demonstrated the potential involvement of sleep deprivation in both the pathogenesis and progression of AD through glial cell activation, the glial lymphatic system, orexin system, circadian rhythm system, inflammation, and the gut microbiota. Thus, investigating the molecular mechanisms underlying the association between sleep deprivation and AD is crucial, which may contribute to the development of preventive and therapeutic strategies for AD. This review aims to analyze the impact of sleep deprivation on AD, exploring the underlying pathological mechanisms that link sleep deprivation to the initiation and progression of AD, which offers a theoretical foundation for the development of drugs aimed at preventing and treating AD.

The amyloid precursor protein intracellular domain induces sleep disruptions and its nuclear localization fluctuates in circadian pacemaker neurons in Drosophila and mice

The most prominent symptom of Alzheimer's disease (AD) is cognitive decline; however, sleep and other circadian disruptions are also common in AD patients. Sleep disruptions have been connected with memory problems and therefore the changes in sleep patterns observed in AD patients may also actively contribute to cognitive decline. However, the underlying molecular mechanisms that connect sleep disruptions and AD are unclear. A characteristic feature of AD is the formation of plaques consisting of Amyloid-β (Aβ) peptides generated by cleavage of the Amyloid Precursor Protein (APP). Besides Aβ, APP cleavage generates several other fragments, including the APP intracellular domain (AICD) that has been linked to transcriptional regulation and neuronal homeostasis. Here we show that overexpression of the AICD reduces the early evening expression of two core clock genes and disrupts the sleep pattern in flies. Analyzing the subcellular localization of the AICD in pacemaker neurons, we found that the AICD levels in the nucleus are low during daytime but increase at night. While this pattern of nuclear AICD persisted with age, the nighttime levels were higher in aged flies. Increasing the cleavage of the fly APP protein also disrupted AICD nuclear localization. Lastly, we show that the day/nighttime nuclear pattern of the AICD is also detectable in neurons in the suprachiasmatic nucleus of mice and that it also changes with age. Together, these data suggest that AD-associated changes in APP processing and the subsequent changes in AICD levels may cause sleep disruptions in AD.

Impact of sleep duration and sleep disturbances on the incidence of dementia and Alzheimer's disease: A 10-year follow-up study

The nature of the relationship between sleep problems and dementia remains unclear. This study investigated the relationship between sleep measures and dementia in older adults (≥ 65) using data from the English Longitudinal Study of Ageing (ELSA) and further investigated the causal association in Mendelian randomization (MR) analysis. In total of 7,223 individuals, 5.7 % developed dementia (1.7 % Alzheimer's disease (AD)) within an average of 8 (± 2.9) years. Cox regression models and MR were employed. Long sleep duration (>8 h) was associated with 64 % increased risk of incident dementia and 2-fold high risk of AD compared to ideal sleep duration (7-8 h). This association was particularly evident in older-older adults (≥70 years) and those who consumed alcohol. Short sleep duration (<7 h) was associated with lower risk of incident dementia among older-older but higher risk among younger-older adults. Sleep disturbances and perceived sleep quality were not associated with dementia or AD. The MR study did not reveal causal associations between sleep duration and dementia. These findings suggest that self-reported short sleep in younger-older and long sleep in older-older adults and those with frequent alcohol consumption are associated with dementia. Early detection of these sleep patterns may help identify individuals at higher dementia risk.

Evaluating Fatty Acid Amide Hydrolase as a Suitable Target for Sleep Promotion in a Transgenic TauP301S Mouse Model of Neurodegeneration

Sleep disruption is an expected component of aging and neurodegenerative conditions, including Alzheimer's disease (AD). Sleep disruption has been demonstrated as a driver of AD pathology and cognitive decline. Therefore, treatments designed to maintain sleep may be effective in slowing or halting AD progression. However, commonly used sleep aid medications are associated with an increased risk of AD, highlighting the need for sleep aids with novel mechanisms of action. The endocannabinoid system holds promise as a potentially effective and novel sleep-enhancing target. By using pharmacology and genetic knockout strategies, we evaluated fatty acid amide hydrolase (FAAH) as a therapeutic target to improve sleep and halt disease progression in a transgenic Tau P301S (PS19) model of Tauopathy and AD. We have recently shown that PS19 mice exhibit sleep disruption in the form of dark phase hyperarousal as an early symptom that precedes robust Tau pathology and cognitive decline. Acute FAAH inhibition with PF3845 resulted in immediate improvements in sleep behaviors in male and female PS19 mice, supporting FAAH as a potentially suitable sleep-promoting target. Moreover, sustained drug dosing for 5-10 days resulted in maintained improvements in sleep. To evaluate the effect of chronic FAAH inhibition as a possible therapeutic strategy, we generated FAAH-/- PS19 mice models. Counter to our expectations, FAAH knockout did not protect PS19 mice from progressive sleep loss, neuroinflammation, or cognitive decline. Our results provide support for FAAH as a novel target for sleep-promoting therapies but further indicate that the complete loss of FAAH activity may be detrimental.

Orexin Receptor Antagonism: Normalizing Sleep Architecture in Old Age and Disease

Sleep is essential for human well-being, yet the quality and quantity of sleep reduce as age advances. Older persons (>65 years old) are more at risk of disorders accompanied and/or exacerbated by poor sleep. Furthermore, evidence supports a bidirectional relationship between disrupted sleep and Alzheimer's disease (AD) or related dementias. Orexin/hypocretin neuropeptides stabilize wakefulness, and several orexin receptor antagonists (ORAs) are approved for the treatment of insomnia in adults. Dysregulation of the orexin system occurs in aging and AD, positioning ORAs as advantageous for these populations. Indeed, several clinical studies indicate that ORAs are efficacious hypnotics in older persons and dementia patients and, as in adults, are generally well tolerated. ORAs are likely to be more effective when administered early in sleep/wake dysregulation to reestablish good sleep/wake-related behaviors and reduce the accumulation of dementia-associated proteinopathic substrates. Improving sleep in aging and dementia represents a tremendous opportunity to benefit patients, caregivers, and health systems.

Orexin 2 receptor antagonism sex-dependently improves sleep/wakefulness and cognitive performance in tau transgenic mice

BACKGROUND AND PURPOSE

Tau pathology contributes to a bidirectional relationship between sleep disruption and neurodegenerative disease. Tau transgenic rTg4510 mice model tauopathy symptoms, including sleep/wake disturbances, which manifest as marked hyperarousal. This phenotype can be prevented by early transgene suppression; however, whether hyperarousal can be rescued after onset is unknown.

EXPERIMENTAL APPROACH

Three 8-week experiments were conducted with wild-type and rTg4510 mice after age of onset of hyperarousal (4.5 months): (1) Tau transgene suppression with doxycycline (200 ppm); (2) inactive phase rapid eye movement (REM) sleep enhancement with the dual orexin receptor antagonist suvorexant (50 mg·kg-1 ·day-1 ); or (3) Active phase non-NREM (NREM) and REM sleep enhancement using the selective orexin 2 (OX2 ) receptor antagonist MK-1064 (40 mg·kg-1 ·day-1 ). Sleep was assessed using polysomnography, cognition using the Barnes maze, and tau pathology using immunoblotting and/or immunohistochemistry.

KEY RESULTS

Tau transgene suppression improved tauopathy and hippocampal-dependent spatial memory, but did not modify hyperarousal. Pharmacological rescue of REM sleep deficits did not improve spatial memory or tau pathology. In contrast, normalising hyperarousal by increasing both NREM and REM sleep via OX2 receptor antagonism restored spatial memory, independently of tauopathy, but only in male rTg4510 mice. OX2 receptor antagonism induced only short-lived hypnotic responses in female rTg4510 mice and did not improve spatial memory, indicating a tau- and sex-dependent disruption of OX2 receptor signalling.

CONCLUSIONS AND IMPLICATIONS

Pharmacologically reducing hyperarousal corrects tau-induced sleep/wake and cognitive deficits. Tauopathy causes sex-dependent disruptions of OX2 receptor signalling/function, which may have implications for choice of hypnotic therapeutics in tauopathies.

Air pollution, glymphatic impairment, and Alzheimer's disease

Epidemiological evidence demonstrates a link between air pollution exposure and the onset and progression of cognitive impairment and Alzheimer's disease (AD). However, current understanding of the underlying pathophysiological mechanisms is limited. This opinion article examines the hypothesis that air pollution-induced impairment of glymphatic clearance represents a crucial etiological event in the development of AD. Exposure to airborne particulate matter (PM) leads to systemic inflammation and neuroinflammation, increased metal load, respiratory and cardiovascular dysfunction, and sleep abnormalities. All these factors are known to reduce the efficiency of glymphatic clearance. Rescuing glymphatic function by restricting the impact of causative agents, and improving sleep and cardiovascular system health, may increase the efficiency of waste metabolite clearance and subsequently slow the progression of AD. In sum, we introduce air pollution-mediated glymphatic impairment as an important mechanistic factor to be considered when interpreting the etiology and progression of AD as well as its responsiveness to therapeutic interventions.

In vivo synaptic potency, short-term and long-term plasticity at the hippocampal Schaffer collateral-CA1 synapses: Role of different light-dark cycles in male rats

The changes in the light-dark(L/D) cycle could modify cellular mechanisms in some brain regions. The present study compared the effects of various L/D cycles on invivo synaptic potency, short-term and long-term plasticity in the hippocampal CA1 area, adrenal glands weight(AGWs), corticosterone (CORT) levels, and body weight differences(BWD) in male rats. Male rats were assigned into different L/D cycle groups: L4/D20, L8/D16, L12/D12(control), L16/D8, and L20/D4. The slope, amplitude, and the area under curve(AUC) related to the field excitatory postsynaptic potentials(fEPSPs) were assessed, using the input-output(I/O) functions, paired-pulse(PP) responses at different interpulse intervals, and after the induction of long-term potentiation(LTP) in the hippocampal CA1 area. Also, the CORT levels, AGWs, and BWDs were measured in all groups. The slope, amplitude, and AUC of fEPSP in the I/O functions, all three phases of PP, before and after the LTP induction, were significantly decreased in all experimental groups, especially in the L20/D4 and L4/D20 groups. As such, the CORT levels and AGWs were significantly increased in all experimental groups, especially in the L20/D4 group. Overall, the uncommon L/D cycles (minimum and particularly maximum durations of light) significantly reduced the cellular mechanism of learning and memory. Also, downtrends were observed in synaptic potency, as well as short-term and long-term plasticity. The changes in PP with high interpulse intervals, or activity of GABAB receptors, were more significant than the changes in other PP phases with different L/D durations. Additionally, the CORT levels, adrenal glands, and body weight gain occurred time-independently concerning different L/D lengths.

Closed-loop auditory stimulation of sleep slow oscillations: Basic principles and best practices

Sleep is essential for our physical and mental well-being. During sleep, despite the paucity of overt behavior, our brain remains active and exhibits a wide range of coupled brain oscillations. In particular slow oscillations are characteristic for sleep, however whether they are directly involved in the functions of sleep, or are mere epiphenomena, is not yet fully understood. To disentangle the causality of these relationships, experiments utilizing techniques to detect and manipulate sleep oscillations in real-time are essential. In this review, we first overview the theoretical principles of closed-loop auditory stimulation (CLAS) as a method to study the role of slow oscillations in the functions of sleep. We then describe technical guidelines and best practices to perform CLAS and analyze results from such experiments. We further provide an overview of how CLAS has been used to investigate the causal role of slow oscillations in various sleep functions. We close by discussing important caveats, open questions, and potential topics for future research.

The Relationships Among Metal Homeostasis, Mitochondria, and Locus Coeruleus in Psychiatric and Neurodegenerative Disorders: Potential Pathogenetic Mechanism and Therapeutic Implications

While alterations in the locus coeruleus-noradrenergic system are present during early stages of neuropsychiatric disorders, it is unclear what causes these changes and how they contribute to other pathologies in these conditions. Data suggest that the onset of major depressive disorder and schizophrenia is associated with metal dyshomeostasis that causes glial cell mitochondrial dysfunction and hyperactivation in the locus coeruleus. The effect of the overactive locus coeruleus on the hippocampus, amygdala, thalamus, and prefrontal cortex can be responsible for some of the psychiatric symptoms. Although locus coeruleus overactivation may diminish over time, neuroinflammation-induced alterations are presumably ongoing due to continued metal dyshomeostasis and mitochondrial dysfunction. In early Alzheimer's and Parkinson's diseases, metal dyshomeostasis and mitochondrial dysfunction likely induce locus coeruleus hyperactivation, pathological tau or α-synuclein formation, and neurodegeneration, while reduction of glymphatic and cerebrospinal fluid flow might be responsible for β-amyloid aggregation in the olfactory regions before the onset of dementia. It is possible that the overactive noradrenergic system stimulates the apoptosis signaling pathway and pathogenic protein formation, leading to further pathological changes which can occur in the presence or absence of locus coeruleus hypoactivation. Data are presented in this review indicating that although locus coeruleus hyperactivation is involved in pathological changes at prodromal and early stages of these neuropsychiatric disorders, metal dyshomeostasis and mitochondrial dysfunction are critical factors in maintaining ongoing neuropathology throughout the course of these conditions. The proposed mechanistic model includes multiple pharmacological sites that may be targeted for the treatment of neuropsychiatric disorders commonly.

Phytotherapeutic alternatives for neurodegenerative dementias: Scientific review, discussion and therapeutic proposal

The incidence and prevalence of age-related neurodegenerative dementias have been increasing. There is no curative therapy and conventional drug treatment can cause problems for patients. Medicinal plants traditionally used for problems associated with ageing are emerging as a therapeutic resource. The main aim is to give a proposal for use and future research based on scientific knowledge and tradition. A literature search was conducted in several searchable databases. The keywords used were related to neurodegenerative dementias, ageing and medicinal plants. Boolean operators and filters were used to focus the search. As a result, there is current clinical and preclinical scientific information on 49 species used in traditional medicine for ageing-related problems, including neurodegenerative dementias. There are preclinical and clinical scientific evidences on their properties against protein aggregates in the central nervous system and their effects on neuroinflammation, apoptosis dysregulation, mitochondrial dysfunction, gabaergic, glutamatergic and dopaminergic systems alterations, monoamine oxidase alterations, serotonin depletion and oestrogenic protection. In conclusion, the potential therapeutic effect of the different medicinal plants depends on the type of neurodegenerative dementia and its stage of development, but more clinical and preclinical research is needed to find better, safer and more effective treatments.

Sex, Age, and Regional Differences in CHRM1 and CHRM3 Genes Expression Levels in the Human Brain Biopsies: Potential Targets for Alzheimer's Disease-related Sleep Disturbances

BACKGROUND

Cholinergic hypofunction and sleep disturbance are hallmarks of Alzheimer's disease (AD), a progressive disorder leading to neuronal deterioration. Muscarinic acetylcholine receptors (M1-5 or mAChRs), expressed in hippocampus and cerebral cortex, play a pivotal role in the aberrant alterations of cognitive processing, memory, and learning, observed in AD. Recent evidence shows that two mAChRs, M1 and M3, encoded by CHRM1 and CHRM3 genes, respectively, are involved in sleep functions and, peculiarly, in rapid eye movement (REM) sleep.

METHODS

We used twenty microarray datasets extrapolated from post-mortem brain tissue of nondemented healthy controls (NDHC) and AD patients to examine the expression profile of CHRM1 and CHRM3 genes. Samples were from eight brain regions and stratified according to age and sex.

RESULTS

CHRM1 and CHRM3 expression levels were significantly reduced in AD compared with ageand sex-matched NDHC brains. A negative correlation with age emerged for both CHRM1 and CHRM3 in NDHC but not in AD brains. Notably, a marked positive correlation was also revealed between the neurogranin (NRGN) and both CHRM1 and CHRM3 genes. These associations were modulated by sex. Accordingly, in the temporal and occipital regions of NDHC subjects, males expressed higher levels of CHRM1 and CHRM3, respectively, than females. In AD patients, males expressed higher levels of CHRM1 and CHRM3 in the temporal and frontal regions, respectively, than females.

CONCLUSION

Thus, substantial differences, all strictly linked to the brain region analyzed, age, and sex, exist in CHRM1 and CHRM3 brain levels both in NDHC subjects and in AD patients.

The Role of Sleep in Cognitive Function: The Value of a Good Night's Rest

As a universal, evolutionarily conserved phenomenon, sleep serves many roles, with an integral role in memory. This interplay has been examined in a variety of research. The purpose of this article will be to review the literature of sleep, aging, cognition, and the impact of two common clinical conditions (obstructive sleep apnea and insomnia) on cognitive impairment. This article will review data from meta-analyses, population studies, smaller cohort studies, neuropsychological studies, imaging, and bench data. Considerations are given to the current data trends and their limitations. This paper will explore the impact of sleep on cognitive impairment. Finally, we will conclude with integrating the separate mechanisms towards more generalized common pathways: disruption of sleep quality and reduction in sleep quantity lead to excessive neuronal activity without sufficient time for homeostasis. Sleep apnea and chronic insomnia can lead to oxidative stress and neuronal damage. These changes predispose and culminate in the development of cognitive impairment.

Sleep deficiency promotes Alzheimer's disease development and progression

Sleep disorders are a common health problem in modern society. Long-term sleep deficiency increases the risk for Alzheimer's disease. However, the exact mechanisms by which sleep deficiency affects Alzheimer's disease remain unclear. Therefore, we reviewed the relevant studies and investigated the role of sleep deprivation in Alzheimer's disease pathogenesis. Sleep deficiency was found to be associated with oxidative stress, β-amyloid protein deposition, tau hyperphosphorylation, and neuroinflammation, which are known to increase the risk for Alzheimer's disease. In addition, insufficient sleep also increases glucocorticoid levels, decreases brain-derived neurotrophic factor levels, and reduces the number of synapses in the central nervous system. These factors also promote Alzheimer's disease development and progression. The present study showed that a growing body of evidence supports an association between sleep disturbances and Alzheimer's disease. It discusses the role of sleep insufficiency in Alzheimer's disease pathogenesis, which may provide a theoretical basis for effective treatment and prevention strategies.

Clinical Spectrum and Trajectory of Innovative Therapeutic Interventions for Insomnia: A Perspective

Increasing incidences of insomnia in adults, as well as the aging population, have been reported for their negative impact on the quality of life. Insomnia episodes may be associated with neurocognitive, musculoskeletal, cardiovascular, gastrointestinal, renal, hepatic, and metabolic disorders. Epidemiological evidence also revealed the association of insomnia with oncologic and asthmatic complications, which has been indicated as bidirectional. Two therapeutic approaches including cognitive behavioral therapy (CBT) and drugs-based therapies are being practiced for a long time. However, the adverse events associated with drugs limit their wide and long-term application. Further, Traditional Chinese medicine, acupressure, and pulsed magnetic field therapy may also provide therapeutic relief. Notably, the recently introduced cryotherapy has been demonstrated as a potential candidate for insomnia which could reduce pain, by suppressing oxidative stress and inflammation. It seems that the synergistic therapeutic approach of cryotherapy and the above-mentioned approaches might offer promising prospects to further improve efficacy and safety. Considering these facts, this perspective presents a comprehensive summary of recent advances in pathological aetiologies of insomnia including COVID-19, and its therapeutic management with a greater emphasis on cryotherapy.

Effect and Mechanism of Exogenous Melatonin on Cognitive Deficits in Animal Models of Alzheimer's Disease: A Systematic review and Meta-analysis

Melatonin (MT) has been reported to control and prevent Alzheimer's disease (AD) in the clinic; however, the effect and mechanism of MT on AD have not been specifically described. Therefore, the main purpose of this meta-analysis was to explore the effect and mechanism of MT on AD models by studying behavioural indicators and pathological features. Seven databases were searched and 583 articles were retrieved. Finally, nine studies (13 analyses, 294 animals) were included according to pre-set criteria. Three authors independently judged the selected literature and the methodological quality. Meta-analysis showed that MT markedly ameliorated the learning ability by reducing the escape latency (EL), and the memory deficit was significantly corrected by increasing the dwell time in the target quadrant and crossings over the platform location in the Morris Water Maze (MWM). Among the pathological features, subgroup analysis found that MT may ease the symptoms of AD mainly by reducing the deposition of Aβ40 and Aβ42 in the cortex. In addition, MT exerted a superior effect on ameliorating the learning ability of senescence-related and metabolic AD models, and corrected the memory deficit of the toxin-induced AD model. The study was registered at PROSPERO (CRD42021226594).

A Dichotomous Role for FABP7 in Sleep and Alzheimer's Disease Pathogenesis: A Hypothesis

Fatty acid binding proteins (FABPs) are a family of intracellular lipid chaperone proteins known to play critical roles in the regulation of fatty acid uptake and transport as well as gene expression. Brain-type fatty acid binding protein (FABP7) is enriched in astrocytes and has been implicated in sleep/wake regulation and neurodegenerative diseases; however, the precise mechanisms underlying the role of FABP7 in these biological processes remain unclear. FABP7 binds to both arachidonic acid (AA) and docosahexaenoic acid (DHA), resulting in discrete physiological responses. Here, we propose a dichotomous role for FABP7 in which ligand type determines the subcellular translocation of fatty acids, either promoting wakefulness aligned with Alzheimer's pathogenesis or promoting sleep with concomitant activation of anti-inflammatory pathways and neuroprotection. We hypothesize that FABP7-mediated translocation of AA to the endoplasmic reticulum of astrocytes increases astrogliosis, impedes glutamatergic uptake, and enhances wakefulness and inflammatory pathways via COX-2 dependent generation of pro-inflammatory prostaglandins. Conversely, we propose that FABP7-mediated translocation of DHA to the nucleus stabilizes astrocyte-neuron lactate shuttle dynamics, preserves glutamatergic uptake, and promotes sleep by activating anti-inflammatory pathways through the peroxisome proliferator-activated receptor-γ transcriptional cascade. Importantly, this model generates several testable hypotheses applicable to other neurodegenerative diseases, including amyotrophic lateral sclerosis and Parkinson's disease.

Sleep in Alzheimer's disease: a systematic review and meta-analysis of polysomnographic findings

Polysomnography (PSG) studies of sleep changes in Alzheimer's disease (AD) have reported but not fully established the relationship between sleep disturbances and AD. To better detail this relationship, we conducted a systematic review and meta-analysis of reported PSG differences between AD patients and healthy controls. An electronic literature search was conducted in EMBASE, MEDLINE, All EBM databases, CINAHL, and PsycINFO inception to Mar 2021. Twenty-eight studies were identified for systematic review, 24 of which were used for meta-analysis. Meta-analyses revealed significant reductions in total sleep time, sleep efficiency, and percentage of slow-wave sleep (SWS) and rapid eye movement (REM) sleep, and increases in sleep latency, wake time after sleep onset, number of awakenings, and REM latency in AD compared to controls. Importantly, both decreased SWS and REM were significantly associated with the severity of cognitive impairment in AD patients. Alterations in electroencephalogram (EEG) frequency components and sleep spindles were also observed in AD, although the supporting evidence for these changes was limited. Sleep in AD is compromised with increased measures of wake and decreased TST, SWS, and REM sleep relative to controls. AD-related reductions in SWS and REM sleep correlate with the degree of cognitive impairment. Alterations in sleep EEG frequency components such as sleep spindles may be possible biomarkers with relevance for diagnosing AD although their sensitivity and specificity remain to be clearly delineated. AD-related sleep changes are potential targets for early therapeutic intervention aimed at improving sleep and slowing cognitive decline.

Grounding the Body Improves Sleep Quality in Patients with Mild Alzheimer’s Disease: A Pilot Study

Background: Grounding refers to having direct contact with the Earth, such as by walking barefoot or lying on the ground. Research has found that grounding can improve inflammation, free radical damage, blood pressure, sleep quality, pain, stress, mood, and wound healing. However, there has been no research on the effect of utilizing grounding for patients with Alzheimer’s disease (AD). Thus, in this study, we investigated the effectiveness of grounding as a non-pharmacological therapy for treating sleep disturbances, anxiety, and depression in patients with mild AD. Methods: Patients with mild AD were enrolled in the study. The electrochemical analyzer CHI 1205b was employed to check the electrochemical signals at acupoints KI1 and GV16. We used the Pittsburgh Sleep Quality Index (PSQI), Beck Anxiety Inventory (BAI), and Beck Depression Inventory-II (BDI-II) to evaluate sleep quality, anxiety, and depression, respectively, at weeks 0 and 12. Results: This 12-week placebo-controlled study enrolled 22 patients, but only 15 patients completed the 12-week intervention and survey. Grounding significantly improved PSQI scores compared to the sham-grounding group (mean ± SD: 0.3 ± 0.7 vs. 3.0 ± 1.9, p = 0.006). The scores on the BAI and BDI-II did not change significantly after grounding in comparison to the sham-grounding group. Conclusions: Grounding can improve sleep quality, but it does not significantly improve anxiety and depression among patients with mild AD.

The Bidirectional Link Between Sleep Disturbances and Traumatic Brain Injury Symptoms: A Role for Glymphatic Dysfunction?

Mild traumatic brain injury (mTBI), often referred to as concussion, is a major cause of morbidity and mortality worldwide. Sleep disturbances are common after mTBI. Moreover, subjects who develop subjective sleep complaints after mTBI also report more severe somatic, mental health, and cognitive impairment and take longer to recover from mTBI sequelae. Despite many previous studies addressing the role of sleep in post-mTBI morbidity, the mechanisms linking sleep to recovery after mTBI remain poorly understood. The glymphatic system is a brainwide network that supports fluid movement through the cerebral parenchyma and the clearance of interstitial solutes and wastes from the brain. Notably, the glymphatic system is active primarily during sleep. Clearance of cellular byproducts related to somatic, mental health, and neurodegenerative processes (e.g., amyloid-β and tau, among others) depends in part on intact glymphatic function, which becomes impaired after mTBI. In this viewpoint, we review the current knowledge regarding the association between sleep disturbances and post-mTBI symptoms. We also discuss the role of glymphatic dysfunction as a potential link between mTBI, sleep disruption, and posttraumatic morbidity. We outline a model where glymphatic dysfunction and sleep disruption caused by mTBI may have an additive effect on waste clearance, leading to cerebral dysfunction and impaired recovery. Finally, we review the novel techniques being developed to examine glymphatic function in humans and explore potential interventions to alter glymphatic exchange that may offer a novel therapeutic approach to those experiencing poor sleep and prolonged symptoms after mTBI.

Differential sleep/wake response and sex effects following acute suvorexant, MK-1064 and zolpidem administration in the rTg4510 mouse model of tauopathy

Background and Purpose

Transgenic mouse models of tauopathy display prominent sleep/wake disturbances which manifest primarily as a hyperarousal phenotype during the active phase, suggesting that tau pathology contributes to sleep/wake changes. However, no study has yet investigated the effect of sleep‐promoting compounds in these models. Such information has implications for the use of hypnotics as potential therapeutic tools in tauopathy‐related disorders.

Experimental Approach

This study examined polysomnographic recordings in 6‐6.5‐month‐old male and female rTg4510 mice following acute administration of suvorexant (50 mg·kg⁻¹), MK‐1064 (30 mg·kg⁻¹) or zolpidem (10 mg·kg⁻¹), administered at the commencement of the active phase.

Key Results

Suvorexant, a dual OX receptor antagonist, promoted REM sleep in rTg4510 mice, without affecting wake or NREM sleep. MK‐1064, a selective OX₂ receptor antagonist, reduced wake and increased NREM and total sleep time. MK‐1064 normalised the hyperarousal phenotype of male rTg4510 mice, whereas female rTg4510 mice exhibited a more transient response. Zolpidem, a GABA_A receptor positive allosteric modulator, decreased wake and increased NREM sleep in both male and female rTg4510 mice. Of the three compounds, the OX₂ receptor antagonist MK‐1064 promoted and normalised physiologically normal sleep, especially in male rTg4510 mice.

Conclusions and Implications

Our findings indicate that hyperphosphorylated tau accumulation and associated hyperarousal does not significantly alter the responses of tauopathy mouse models to hypnotics. However, the sex differences observed in the sleep/wake response of rTg4510 mice to MK‐1064, but not suvorexant or zolpidem, raise questions about therapeutic implications for the use of OX₂ receptor antagonists in human neurodegenerative disorders.

Orexin A peptidergic system: comparative sleep behavior, morphology and population in brains between wild type and Alzheimer’s disease mice

Sleep disturbance is common in patients with Alzheimer’s disease (AD), and orexin A is a pivotal neurotransmitter for bidirectionally regulating the amyloid-β (Aβ) deposition of AD brain and poor sleep. In the present study, we examined the characteristic of sleep–wake architecture in APPswe/PSldE9 (APP/PS1) and Aβ-treated mice using electroencephalogram (EEG) and electromyographic (EMG) analysis. We compared the expression of orexin A, distribution, and morphology of the corresponding orexin A-positive neurons using innovative methods including three-dimensional reconstruction and brain tissue clearing between wild type (WT) and APP/PS1 mice. Results from our study demonstrated that increased wakefulness and reduced NREM sleep were seen in APP/PS1 and Aβ treated mice, while the expression of orexin A was significantly upregulated. Higher density and distribution of orexin A-positive neurons were seen in APP/PS1 mice, with a location of 1.06 mm–2.30 mm away from the anterior fontanelle compared to 1.34 mm–2.18 mm away from the anterior fontanelle in WT mice. These results suggested that the population and distribution of orexin A may play an important role in the progression of AD.

A Growing Link between Circadian Rhythms, Type 2 Diabetes Mellitus and Alzheimer's Disease

Type 2 diabetes mellitus (T2DM) patients are at a higher risk of developing Alzheimer’s disease (AD). Mounting evidence suggests the emerging important role of circadian rhythms in many diseases. Circadian rhythm disruption is considered to contribute to both T2DM and AD. Here, we review the relationship among circadian rhythm disruption, T2DM and AD, and suggest that the occurrence and progression of T2DM and AD may in part be associated with circadian disruption. Then, we summarize the promising therapeutic strategies targeting circadian dysfunction for T2DM and AD, including pharmacological treatment such as melatonin, orexin, and circadian molecules, as well as non-pharmacological treatments like light therapy, feeding behavior, and exercise.

Neuropsychiatric Inventory-Questionnaire Assessed Nighttime Behaviors in Cognitively Asymptomatic Patients with Pathologically Confirmed Alzheimer's Disease Predict More Rapid Cognitive Deterioration

BACKGROUND

The temporal relationship between sleep, Alzheimer's disease (AD), and cognitive impairment remains to be further elucidated.

OBJECTIVE

First, we aim to determine whether the Neuropsychiatric Inventory-Questionnaire (NPI-Q) assessed nighttime behaviors prior to cognitive decline influence the rate of cognitive deterioration in pathologically confirmed AD, and second, to assess the possible interactions with APOE allele and cerebral amyloid angiopathy (CAA).

METHODS

The rate of cognitive decline between cognitively asymptomatic participants from the National Alzheimer Coordinating Center who eventually received a neuropathologic diagnosis of AD with (+NTB) or without (-NTB) nighttime behaviors were compared using independent samples t-test. Participants were stratified by APOE carrier and CAA status. Demographic and patient characteristics were assessed using descriptive statistics, and the independent samples t-test was used for continuous variables and chi-square test for categorical variables. The significance level was set at p≤0.05.

RESULTS

The rate of cognitive decline was greater in +NTB (n = 74; 3.30 points/year) than -NTB (n = 330; 2.45 points/year) (p = 0.016), even if there was no difference in cognitive status at onset. This difference was restricted to APOE ɛ4 carriers (p = 0.049) and positive CAA participants (p = 0.020). Significance was not reached in non-carriers (p = 0.186) and negative CAA (p = 0.364). APOE and CAA were not differentially distributed between the NTB groups.

CONCLUSION

NPI-Q assessed nighttime behaviors, a surrogate for sleep disturbances, are associated with more rapidly deteriorating cognition in patients with AD neuropathology who are also carriers of APOE ɛ4 or show CAA.

Relationship between Cortical Thickness and EEG Alterations during Sleep in the Alzheimer's Disease

Recent evidence showed that EEG activity alterations that occur during sleep are associated with structural, age-related, changes in healthy aging brains, and predict age-related decline in memory performance. Alzheimer's disease (AD) patients show specific EEG alterations during sleep associated with cognitive decline, including reduced sleep spindles during NREM sleep and EEG slowing during REM sleep. We investigated the relationship between these EEG sleep alterations and brain structure changes in a study of 23 AD patients who underwent polysomnographic recording of their undisturbed sleep and 1.5T MRI scans. Cortical thickness measures were correlated with EEG power in the sigma band during NREM sleep and with delta- and beta-power during REM sleep. Thinning in the right precuneus correlated with all the EEG indexes considered in this study. Frontal-central NREM sigma power showed an inverse correlation with thinning of the left entorhinal cortex. Increased delta activity at the frontopolar and temporal regions was significantly associated with atrophy in some temporal, parietal, and frontal cortices, and with mean thickness of the right hemisphere. Our findings revealed an association between sleep EEG alterations and the changes to AD patients' brain structures. Findings also highlight possible compensatory processes involving the sources of frontal-central sleep spindles.

Chronic stress induces NPD-like behavior in APPPS1 and WT mice with subtle differences in gene expression

Neuropsychiatric disturbances (NPDs) are considered hallmarks of Alzheimer's disease (AD). Nevertheless, treatment of these symptoms has proven difficult and development of safe and effective treatment options is hampered by the limited understanding of the underlying pathophysiology. Thus, robust preclinical models are needed to increase knowledge of NPDs in AD and develop testable hypotheses and novel treatment options. Abnormal activity of the hypothalamic-pituitary-adrenal (HPA) axis is implicated in many psychiatric symptoms and might contribute to both AD and NPDs development and progression. We aimed to establish a mechanistic preclinical model of NPD-like behavior in the APPPS1 mouse model of AD and wildtype (WT) littermates. In APPPS1 and WT mice, we found that chronic stress increased anxiety-like behavior and altered diurnal locomotor activity suggestive of sleep disturbances. Also, chronic stress activated the HPA axis, which, in WT mice, remained heightened for additional 3 weeks. Chronic stress caused irregular expression of circadian regulatory clock genes (BMAL1, PER2, CRY1 and CRY2) in both APPPS1 and WT mice. Interestingly, APPPS1 and WT mice responded differently to chronic stress in terms of expression of serotonergic markers (5-HT_1A receptor and MAOA) and inflammatory genes (IL-6, STAT3 and ADMA17). These findings indicate that, although the behavioral response to chronic stress might be similar, the neurobiochemical response was different in APPPS1 mice, which is an important insight in the efforts to develop safe and effective treatments options for NPDs in AD patients. Further work is needed to substantiate these findings.

Sleep, neuronal hyperexcitability, inflammation and neurodegeneration: Does early chronic short sleep trigger and is it the key to overcoming Alzheimer's disease?

Evidence links neuroinflammation to Alzheimer's disease (AD); however, its exact contribution to the onset and progression of the disease is poorly understood. Symptoms of AD can be seen as the tip of an iceberg, consisting of a neuropathological build-up in the brain of extracellular amyloid-β (Aβ) plaques and intraneuronal hyperphosphorylated aggregates of Tau (pTau), which are thought to stem from an imbalance between its production and clearance resulting in loss of synaptic health and dysfunctional cortical connectivity. The glymphatic drainage system, which is particularly active during sleep, plays a key role in the clearance of proteinopathies. Poor sleep can cause hyperexcitability and promote Aβ and tau pathology leading to systemic inflammation. The early neuronal hyperexcitability of γ-aminobutyric acid (GABA)-ergic inhibitory interneurons and impaired inhibitory control of cortical pyramidal neurons lie at the crossroads of excitatory/inhibitory imbalance and inflammation. We outline, with a prospective framework, a possible vicious spiral linking early chronic short sleep, neuronal hyperexcitability, inflammation and neurodegeneration. Understanding the early predictors of AD, through an integrative approach, may hold promise for reducing attrition in the late stages of neuroprotective drug development.

Metabolism-Based Gene Differences in Neurons Expressing Hyperphosphorylated AT8- Positive (AT8+) Tau in Alzheimer's Disease

Metabolic adaptations in the brain are critical to the establishment and maintenance of normal cellular functions and to the pathological responses to disease processes. Here, we have focused on specific metabolic pathways that are involved in immune-mediated neuronal processes in brain using isolated neurons derived from human autopsy brain sections of normal individuals and individuals diagnosed as Alzheimer's disease (AD). Laser capture microscopy was used to select specific cell types in immune-stained thin brain sections followed by NanoString technology to identify and quantify differences in mRNA levels between age-matched control and AD neuronal samples. Comparisons were also made between neurons isolated from AD brain sections expressing pathogenic hyperphosphorylated AT8- positive (AT8+) tau and non-AT8+ AD neurons using double labeling techniques. The mRNA expression data showed unique patterns of metabolic pathway expression between the subtypes of captured neurons that involved membrane based solute transporters, redox factors, and arginine and methionine metabolic pathways. We also identified the expression levels of a novel metabolic gene, Radical-S-Adenosyl Domain1 (RSAD1) and its corresponding protein, Rsad1, that impact methionine usage and radical based reactions. Immunohistochemistry was used to identify specific protein expression levels and their cellular location in NeuN+ and AT8+ neurons. APOE4 vs APOE3 genotype-specific and sex-specific gene expression differences in these metabolic pathways were also observed when comparing neurons from individuals with AD to age-matched individuals.

EEG alterations during wake and sleep in mild cognitive impairment and Alzheimer's disease

Patients with Alzheimer's disease (AD) undergo a slowing of waking electroencephalographic (EEG) rhythms since prodromal stages, which could be ascribed to poor sleep quality. We examined the relationship between wake and sleep alterations by assessing EEG activity during sleep and (pre-sleep/post-sleep) wakefulness in AD, mild cognitive impairment (MCI) and healthy controls. AD and MCI show high sleep latency and less slow-wave sleep. Reduced sigma activity characterizes non-rapid eye movement (NREM) sleep, reflecting sleep spindles loss. The EEG slowing characterizes REM sleep and wakefulness of AD and MCI, with strong correlations among the two phenomena suggesting common neuropathological mechanisms. Evening-to-morning variations in waking EEG revealed the gradual disappearance in MCI and AD of overnight changes in delta activity, indicating a progressive decay of sleep restorative functions on diurnal activity that correlates with the impairment of sleep high-frequency activity in AD. Our findings support a linkage between wake and sleep alterations, and the importance of sleep-related processes in Alzheimer's disease progression.

Neuropathology of the Brainstem to Mechanistically Understand and to Treat Alzheimer's Disease

Alzheimer’s disease (AD) is a devastating neurodegenerative disorder as yet without effective therapy. Symptoms of this disorder typically reflect cortical malfunction with local neurohistopathology, which biased investigators to search for focal triggers and molecular mechanisms. Cortex, however, receives massive afferents from caudal brain structures, which do not only convey specific information but powerfully tune ensemble activity. Moreover, there is evidence that the start of AD is subcortical. The brainstem harbors monoamine systems, which establish a dense innervation in both allo- and neocortex. Monoaminergic synapses can co-release neuropeptides either by precisely terminating on cortical neurons or, when being “en passant”, can instigate local volume transmission. Especially due to its early damage, malfunction of the ascending monoaminergic system emerges as an early sign and possible trigger of AD. This review summarizes the involvement and cascaded impairment of brainstem monoaminergic neurons in AD and discusses cellular mechanisms that lead to their dysfunction. We highlight the significance and therapeutic challenges of transmitter co-release in ascending activating system, describe the role and changes of local connections and distant afferents of brainstem nuclei in AD, and summon the rapidly increasing diagnostic window during the last few years.

Genesis of the Master Circadian Pacemaker in Mice

The suprachiasmatic nucleus (SCN) of the hypothalamus is the central circadian clock of mammals. It is responsible for communicating temporal information to peripheral oscillators via humoral and endocrine signaling, ultimately controlling overt rhythms such as sleep-wake cycles, body temperature, and locomotor activity. Given the heterogeneity and complexity of the SCN, its genesis is tightly regulated by countless intrinsic and extrinsic factors. Here, we provide a brief overview of the development of the SCN, with special emphasis on the murine system.

Decreased Orexin Receptor 1 mRNA Expression in the Locus Coeruleus in Both Tau Transgenic rTg4510 and Tau Knockout Mice and Accompanying Ascending Arousal System Tau Invasion in rTg4510

BACKGROUND

Sleep/wake disturbances (e.g., insomnia and sleep fragmentation) are common in neurodegenerative disorders, especially Alzheimer's disease (AD) and frontotemporal dementia (FTD). These symptoms are somewhat reminiscent of narcolepsy with cataplexy, caused by the loss of orexin-producing neurons. A bidirectional relationship between sleep disturbance and disease pathology suggests a detrimental cycle that accelerates disease progression and cognitive decline. The accumulation of brain tau fibrils is a core pathology of AD and FTD-tau and clinical evidence supports that tau may impair the orexin system in AD/FTD. This hypothesis was investigated using tau mutant mice.

OBJECTIVE

To characterize orexin receptor mRNA expression in sleep/wake regulatory brain centers and quantify noradrenergic locus coeruleus (LC) and orexinergic lateral hypothalamus (LH) neurons, in tau transgenic rTg4510 and tau-/- mice.

METHODS

We used i n situ hybridization and immunohistochemistry (IHC) in rTg4510 and tau-/- mice.

RESULTS

rTg4510 and tau-/- mice exhibited a similar decrease in orexin receptor 1 (OX1R) mRNA expression in the LC compared with wildtype controls. IHC data indicated this was not due to decreased numbers of LC tyrosine hydroxylase-positive (TH) or orexin neurons and demonstrated that tau invades TH LC and orexinergic LH neurons in rTg4510 mice. In contrast, orexin receptor 2 (OX2R) mRNA levels were unaffected in either model.

CONCLUSION

The LC is strongly implicated in the regulation of sleep/wakefulness and expresses high levels of OX1R. These findings raise interesting questions regarding the effects of altered tau on the orexin system, specifically LC OX1Rs, and emphasize a potential mechanism which may help explain sleep/wake disturbances in AD and FTD.

Multicenter Study on Sleep and Circadian Alterations as Objective Markers of Mild Cognitive Impairment and Alzheimer’s Disease Reveals Sex Differences

Background: Circadian and sleep disturbances are associated with increased risk of mild cognitive impairment (MCI) and Alzheimer’s disease (AD). Wearable activity trackers could provide a new approach in diagnosis and prevention. Objective: To evaluate sleep and circadian rhythm parameters, through wearable activity trackers, in MCI and AD patients as compared to controls, focusing on sex dissimilarities. Methods: Based on minute level data from consumer wearable devices, we analyzed actigraphic sleep parameters by applying an electromedical type I registered algorithm, and the corresponding circadian variables in 158 subjects: 86 females and 72 males (42 AD, 28 MCI, and 88 controls). Moreover, we used a confusion-matrix chart method to assess accuracy, precision, sensitivity, and specificity of two decision-tree models based on actigraphic data in predicting disease or health status. Results: Wake after sleep onset (WASO) was higher (p < 0.001) and sleep efficiency (SE) lower (p = 0.003) in MCI, and Sleep Regularity Index (SRI) was lower in AD patients compared to controls (p = 0.004). SE was lower in male AD compared to female AD (p = 0.038) and SRI lower in male AD compared to male controls (p = 0.008), male MCI (p = 0.047), but also female AD subjects (p = 0.046). Mesor was significantly lower in males in the overall population. Age reduced the dissimilarities for WASO and SE but demonstrated sex differences for amplitude (p = 0.009) in the overall population, controls (p = 0.005), and AD subjects (p = 0.034). The confusion-matrices showed good predictive power of actigraphic data. Conclusion: Actigraphic data could help identify disease or health status. Sex (possibly gender) differences could impact on neurodegeneration and disease trajectory with potential clinical applications.

Sleep, major depressive disorder, and Alzheimer disease: A Mendelian randomization study

OBJECTIVE

To explore the causal relationships between sleep, major depressive disorder (MDD), and Alzheimer disease (AD).

METHODS

We conducted bidirectional 2-sample Mendelian randomization analyses. Genetic associations were obtained from the largest genome-wide association studies currently available in UK Biobank (n = 446,118), Psychiatric Genomics Consortium (n = 18,759), and International Genomics of Alzheimer's Project (n = 63,926). We used the inverse variance-weighted Mendelian randomization method to estimate causal effects and weighted median and Mendelian randomization-Egger for sensitivity analyses to test for pleiotropic effects.

RESULTS

We found that higher risk of AD was significantly associated with being a "morning person" (odds ratio [OR] 1.01, p = 0.001), shorter sleep duration (self-reported: β = -0.006, p = 1.9 × 10^-4; accelerometer based: β = -0.015, p = 6.9 × 10^-5), less likely to report long sleep (β = -0.003, p = 7.3 × 10^-7), earlier timing of the least active 5 hours (β = -0.024, p = 1.7 × 10^-13), and a smaller number of sleep episodes (β = -0.025, p = 5.7 × 10^-14) after adjustment for multiple comparisons. We also found that higher risk of AD was associated with lower risk of insomnia (OR 0.99, p = 7 × 10^-13). However, we did not find evidence that these abnormal sleep patterns were causally related to AD or for a significant causal relationship between MDD and risk of AD.

CONCLUSION

We found that AD may causally influence sleep patterns. However, we did not find evidence supporting a causal role of disturbed sleep patterns for AD or evidence for a causal relationship between MDD and AD.

Genetic Risk of Alzheimer's Disease and Sleep Duration in Non-Demented Elders

Growing evidence has suggested an association between sleep duration and Alzheimer's disease (AD), but it is unclear if sleep duration is a manifestation of the AD disease process. We studied whether genetic liability for AD predicts sleep duration using a genetic risk score (GRS) for AD (AD-GRS), in 406,536 UK Biobank participants with European ancestry and without dementia at enrollment. Higher AD-GRS score was associated with shorter sleep (b = -0.014, 95% confidence interval [CI] = -0.022 to -0.006), especially in those aged 55+. Using AD-GRS as an instrumental variable for AD diagnosis, incipient AD reduced sleep duration by 1.87 hours (95% CI = 0.96, 2.78). Short sleep duration might be an early marker of AD. ANN NEUROL 2021;89:177-181.

The Bidirectional Relationship Between Sleep and Inflammation Links Traumatic Brain Injury and Alzheimer's Disease

Traumatic brain injury (TBI) and Alzheimer's disease (AD) are diseases during which the fine-tuned autoregulation of the brain is lost. Despite the stark contrast in their causal mechanisms, both TBI and AD are conditions which elicit a neuroinflammatory response that is coupled with physical, cognitive, and affective symptoms. One commonly reported symptom in both TBI and AD patients is disturbed sleep. Sleep is regulated by circadian and homeostatic processes such that pathological inflammation may disrupt the chemical signaling required to maintain a healthy sleep profile. In this way, immune system activation can influence sleep physiology. Conversely, sleep disturbances can exacerbate symptoms or increase the risk of inflammatory/neurodegenerative diseases. Both TBI and AD are worsened by a chronic pro-inflammatory microenvironment which exacerbates symptoms and worsens clinical outcome. Herein, a positive feedback loop of chronic inflammation and sleep disturbances is initiated. In this review, the bidirectional relationship between sleep disturbances and inflammation is discussed, where chronic inflammation associated with TBI and AD can lead to sleep disturbances and exacerbated neuropathology. The role of microglia and cytokines in sleep disturbances associated with these diseases is highlighted. The proposed sleep and inflammation-mediated link between TBI and AD presents an opportunity for a multifaceted approach to clinical intervention.

Molecular and cellular mechanisms underlying the pathogenesis of Alzheimer's disease

Alzheimer’s disease (AD) is the most common neurodegenerative disorder seen in age-dependent dementia. There is currently no effective treatment for AD, which may be attributed in part to lack of a clear underlying mechanism. Studies within the last few decades provide growing evidence for a central role of amyloid β (Aβ) and tau, as well as glial contributions to various molecular and cellular pathways in AD pathogenesis. Herein, we review recent progress with respect to Aβ- and tau-associated mechanisms, and discuss glial dysfunction in AD with emphasis on neuronal and glial receptors that mediate Aβ-induced toxicity. We also discuss other critical factors that may affect AD pathogenesis, including genetics, aging, variables related to environment, lifestyle habits, and describe the potential role of apolipoprotein E (APOE), viral and bacterial infection, sleep, and microbiota. Although we have gained much towards understanding various aspects underlying this devastating neurodegenerative disorder, greater commitment towards research in molecular mechanism, diagnostics and treatment will be needed in future AD research.

The impact of neurovascular, blood-brain barrier, and glymphatic dysfunction in neurodegenerative and metabolic diseases

The cerebral vasculature serves as the crossroads of the CNS, supporting exchange of nutrients, metabolic wastes, solutes and cells between the compartments of the brain, including the blood, brain interstitium, and cerebrospinal fluid (CSF). The blood-brain barrier (BBB) regulates the entry and efflux of molecules into brain tissue. The cells of the neurovascular unit regulate cerebral blood flow, matching local metabolic demand to blood supply. The blood-CSF barrier at the choroid plexus secretes CSF, which supports the brain and provides a sink for interstitial solutes not cleared across the BBB. Recent studies have characterized the glymphatic system, a brain-wide network of perivascular spaces that supports CSF and interstitial fluid exchange and the clearance of interstitial solutes to the CSF. The critical role that these structures play in maintaining brain homeostasis is illustrated by the established and emerging roles that their dysfunctions play in the development of neurodegenerative diseases, such as Alzheimer's disease (AD). Loss of BBB and blood-CSF barrier function is reported both in rodent models of AD, and in human AD subjects. Cerebrovascular dysfunction and ischemic injury are well established contributors to both vascular dementia and to a large proportion of cases of sporadic AD. In animal models, the slowed glymphatic clearance of interstitial proteins, such as amyloid β or tau, are proposed to contribute to the development of neurodegenerative diseases, including AD. In total, these findings suggest that cellular and molecular changes occurring within and around the cerebral vasculature are among the key drivers of neurodegenerative disease pathogenesis.

Disease-Associated Mutant Tau Prevents Circadian Changes in the Cytoskeleton of Central Pacemaker Neurons

A hallmark feature of Alzheimer's disease (AD) and other Tauopathies, like Frontotemporal Dementia with Parkinsonism linked to chromosome 17 (FTDP-17), is the accumulation of neurofibrillary tangles composed of the microtubule-associated protein Tau. As in AD, symptoms of FTDP-17 include cognitive decline, neuronal degeneration, and disruptions of sleep patterns. However, mechanisms by which Tau may lead to these disturbances in sleep and activity patterns are unknown. To identify such mechanisms, we have generated novel Drosophila Tauopathy models by replacing endogenous fly dTau with normal human Tau (hTau) or the FTDP-17 causing hTau^V337M mutation. This mutation is localized in one of the microtubule-binding domains of hTau and has a dominant effect. Analyzing heterozygous flies, we found that aged hTau^V337M flies show neuronal degeneration and locomotion deficits when compared to wild type or hTau^WT flies. Furthermore, hTau^V337M flies are hyperactive and they show a fragmented sleep pattern. These changes in the sleep/activity pattern are accompanied by morphological changes in the projection pattern of the central pacemaker neurons. These neurons show daily fluctuations in their connectivity, whereby synapses are increased during the day and reduced during sleep. Synapse formation requires cytoskeletal changes that can be detected by the accumulation of the end-binding protein 1 (EB1) at the site of synapse formation. Whereas, hTau^WT flies show the normal day/night changes in EB1 accumulation, hTau^V337M flies do not show this fluctuation. This suggests that hTau^V337M disrupts sleep patterns by interfering with the cytoskeletal changes that are required for the synaptic homeostasis of central pacemaker neurons.

Free Radical Oxidation and Sleep Disorders in Andro- and Menopause (Literature Review)

This review presents data on changes in the physiology of sleep during reproductive aging. It is noted that insomnia and obstructive sleep apnea syndrome (OSAS) are the main sleep disorders. The results of foreign and domestic studies in the field of free radical oxidation during sleep deprivation in animal models are presented, indicating the dependence of processes on the duration of sleep deprivation. The largest number of studies of free radical processes in a person with somnological pathology was carried out in the study of OSAS. Blood, urine, saliva, condensate of exhaled air can be biomaterial for determining the parameters of free radical oxidation. It was shown that the intensity of oxidative stress depends on the severity of OSAS, as evidenced by the positive correlation of the level of active products of thiobarbituric acid, the products of oxidation of proteins and carbonyl groups with the apnea/hypopnea index, determining the development of not only oxidative, but also carbonyl stress in patients with a severe degree OSAS. Biomarkers such as thioredoxin, malondialdehyde, superoxide dismutase, and reduced iron have shown a more stable relationship between increased oxidative stress and OSA. Despite the results obtained, the question of the association of oxidative stress and hypoxia in OSA remains debatable, which is associated with the opposite results of some studies. Insomnia, which occurs mainly in females, is accompanied by a high level of end products of lipid peroxidation with a decrease in the activity of antioxidants such as paraoxonase, an enzymatic component of the glutathione system. Along with this, menopausal women present low levels of uric acid, which correlates with high scores of the Pittsburgh sleep quality index questionnaire. Recent studies have identified an association between the activity of the «lipoperoxidation – antioxidants» system and the Clock 3111T/C gene polymorphism in menopausal Caucasian women, indicating the protective role of the minor allele.

Sleep Regulates Glial Plasticity and Expression of the Engulfment Receptor Draper Following Neural Injury

Chronic sleep disturbance is associated with numerous health consequences, including neurodegenerative disease and cognitive decline [1]. Neurite damage due to apoptosis, trauma, or genetic factors is a common feature of aging, and clearance of damaged neurons is essential for maintenance of brain function. In the central nervous system, damaged neurites are cleared by Wallerian degeneration, in which activated microglia and macrophages engulf damaged neurons [2]. The fruit fly Drosophila melanogaster provides a powerful model for investigating the relationship between sleep and Wallerian degeneration [3]. Several lines of evidence suggest that glia influence sleep duration, sleep-mediated neuronal homeostasis, and clearance of toxic substances during sleep, raising the possibility that glial engulfment of damaged axons is regulated by sleep [4]. To explore this possibility, we axotomized olfactory receptor neurons and measured the effects of sleep loss or gain on the clearance of damaged neurites. Mechanical and genetic sleep deprivation impaired the clearance of damaged neurites. Conversely, treatment with the sleep-promoting drug gaboxadol accelerated clearance, while genetic induction of sleep promotes Draper expression. In sleep-deprived animals, multiple markers of glial activation were delayed, including activation of the JAK-STAT pathway, upregulation of the cell corpse engulfment receptor Draper, and innervation of the antennal lobe by glial membranes. These markers were all enhanced following genetic and pharmacological sleep induction. Taken together, these findings reveal a critical association between sleep and glial activation following neural injury, providing a platform for further investigations of the molecular mechanisms underlying sleep-dependent modulation of glial function and neurite clearance.

Circadian learning and memory changes in Aβ1-42 induced Alzheimer's mice

Alzheimer disease (AD) is a growing health problem globally, which causes a progressive decline in learning and memory and multiple disturbances of circadian rhythms. Six Alzheimer's mice and six wild type (WT) mice were involved in this study. Morris Water Maze (MWM) tasks were conducted hourly to evaluate their circadian learning and memory performance. We used a single cosinor-based method to evaluate the circadian learning and memory of Alzheimer's mice and WT mice, respectively. An area sensor was used to record locomotor activity for 2 weeks continuously, including 7 days of 12 h light/12 h dark (LD) conditions and 7 days of 12 h dark/12 h dark (DD) conditions. All WT mice showed circadian rhythm presence in learning and memory, and the peak of escape latency appeared at circadian time (CT) 12. Only one in six Alzheimer's mice showed a circadian rhythm, but the peak of escape latency was postponed to CT20. Alzheimer's mice showed rhythm absence under LD or DD conditions. Under LD conditions, the WT mice activity was higher than that in the Alzheimer's mice during ZT0-5 (p = 0.007) and ZT18-23 (p = 0.353) but lower during ZT6-11 (p < 0.001) and ZT12-17 (p < 0.001). Learning and memory of wild type mice is proved to have a circadian variation throughout a day. In Alzheimer's mice, rhythmic locomotor activity and circadian learning and memory performance were disrupted. Understanding the role of rhythmic disturbances in the process of AD may assist to identify therapeutic targets.