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

Targeting Sleep Physiology to Modulate Glymphatic Brain Clearance

Sleep has been postulated to play an important role in the removal of potentially neurotoxic molecules, such as amyloid-β, from the brain via the glymphatic system. Disturbed sleep, on the other hand, may contribute to the accumulation of neurotoxins in brain tissue, eventually leading to neuronal death. A bidirectional relationship has been proposed between impaired sleep and neurodegenerative processes, which start years before the onset of clinical symptoms associated with conditions like Alzheimer's and Parkinson's diseases. Given the heavy burden these conditions place on society, it is imperative to develop interventions that promote efficient brain clearance, thereby potentially aiding in the prevention or slowing of neurodegeneration. In this review, we explore whether the metabolic clearance function of sleep can be enhanced through sensory (e.g., auditory, vestibular) or transcranial (e.g., magnetic, ultrasound, infrared light) stimulation, as well as pharmacological (e.g., antiepileptics) and behavioral (e.g., sleeping position, physical exercise, cognitive intervention) modulation of sleep physiology. A particular focus is placed on strategies to enhance slow-wave activity during nonrapid eye movement sleep as a driver of glymphatic brain clearance. Overall, this review provides a comprehensive overview on the potential preventative and therapeutic applications of sleep interventions in combating neurodegeneration, cognitive decline, and dementia.

The Role of the Urea Cycle in the Alzheimer's Disease Brain

Alzheimer's Disease (AD) is a neurodegenerative disorder classified as the leading form of dementia in the elderly. Classical hallmarks of AD pathology believed to cause AD include Amyloid-beta (Aβ) plaques as well as neurofibrillary tau tangles (NTT). However, research into these classical hallmarks has failed to account for a causative link or therapeutic success. More recently, metabolic hallmarks of AD pathology have become a popular avenue of research. Elevated urea and ammonia detected in cases of AD point towards a dysfunctional urea cycle involved in AD. This review covers the expansive body of literature surrounding the work of researchers deciphering the role of the urea cycle in AD pathology through the study of urea cycle enzymes, metabolites, and transporters in the AD brain. Urea cycle enzymes of interest in AD pathology include OTC, NOS isoforms, ARG1, ARG2, MAOB, and ODC, which all present as promising therapeutic targets. Urea metabolites indicated in AD pathology have varying concentrations across the regions of the brain and the different cell types (neurons, microglia, astrocytes). Finally, the role of UT-B as a clearance modulator presents this protein as a key target for research in the role of the urea cycle in the AD brain. In the future, these key enzymes, pathways, and proteins relating to the urea cycle in AD should be further investigated to better understand the cell-specific urea cycle profiles in the AD brain and uncover their therapeutic potential.

Beyond plaques and tangles: The role of immune cell dysfunction in Alzheimer's disease

The interplay between immune cell dysfunction and associated neuroinflammation plays a critical role in the pathogenesis of Alzheimer's disease. Neuroinflammation, orchestrated by microglia and peripheral immune cells, exacerbates synaptic dysfunction and neurodegeneration in AD. Emerging evidence suggests a systemic immune response in AD, challenging traditional views of neurocentric pathology. Therapeutic strategies targeting neuroinflammation hold promise, yet translating preclinical findings into clinical success remains elusive. This article presents recent advances in AD scientific studies, highlighting the pivotal role of immune cell dysfunction and signaling pathways in disease progression. We also discussed therapeutic studies targeting immune cell dysregulation, as treatment methods. This advocates for a paradigm shift towards holistic approaches that integrate peripheral and central immune responses, fostering a comprehensive understanding of AD pathophysiology and paving the way for transformative interventions.

Glymphatic system impairment in normal tension glaucoma evaluated by diffusion tensor image analysis along the perivascular space

Disruption of the glymphatic system plays a vital role in pathogenesis of neurodegeneration in normal tension glaucoma (NTG). We evaluated the impairment of glymphatic system of NTG patients by diffusion tensor image analysis along the perivascular space (DTI-ALPS), and explored the correlation between the ALPS index and dysfunction of visual cortices in resting state. DTI-ALPS was applied to 37 normal controls (NCs) and 37 NTG patients. Multidirectional diffusivity maps and fractional anisotropy (FA) maps were reconstructed to calculate ALPS index. The Amplitude of low-frequency fluctuation (ALFF) in visual cortices (V1-V5) were calculated using resting-state fMRI. Clinical data and ALPS indexes were compared between the groups. Lateralization of ALPS indexes and differences in visual field of two eyes were analyzed. Subsequently, regression analyses between ALPS indexes and mean deviation (MD) values of bilateral eyes and ALFF of visual cortices were performed. The bilateral ALPS indexes of NTG patients decreased significantly. In NCs and NTG patients, ALPS indexes in right hemisphere were lower than that in left hemisphere. The right ALPS indexes of NTG patients were positively correlated with the MD values of the left eyes. In NTG patients, decreased ALFF was detected in right V1 and bilateral V2-5, and the left ALPS indexes were positively correlated with ALFF in bilateral V1, V2, V5, and right V3V area. The ALPS index decreased in NTG patients, correlated with visual defects and ALFF, indicating impairment of the glymphatic system and the potential to be a biomarker in the future.

Emerging Technologies to Track and Improve Sleep Health

This review explores cutting-edge advancements, including wearable sleep trackers, brain age assessments, transcranial electrical stimulation (TES), acoustic stimulation, and glymphatic system modulation. Sleep trackers provide continuous monitoring of sleep patterns, while brain age estimation offers insights into brain health and early detection of accelerated aging. TES shows promise in improving mood, memory, and sleep. Acoustic stimulation during slow-wave sleep has been demonstrated to enhance memory consolidation. Additionally, optimizing the glymphatic system may facilitate brain waste clearance, crucial in preventing neurodegenerative diseases like Alzheimer's. However, significant challenges remain, including the need for rigorous longitudinal studies to validate these technologies' efficacy and safety.

Brain Health in Sleep Disorders

Sleep is a critical determinant of brain health, influencing cognitive, emotional, and physiologic functions. The complex bidirectional relationship between sleep and brain health underscores the importance of sleep in maintaining cognitive function, regulating brain homeostasis, and facilitating the clearance of metabolic waste through the glymphatic system. Chronic sleep deprivation and sleep disorders such as insomnia and obstructive sleep apnea have been shown to negatively impact brain structures and functions. This review discusses the impact of sleep disorders on brain health. It also explores the implications of impaired sleep on cardiovascular health, immune function, and neuroplasticity.

Test-retest reliability of coupling between cerebrospinal fluid flow and global brain activity after normal sleep and sleep deprivation

The glymphatic system (GS) plays a key role in maintaining brain homeostasis by clearing metabolic waste during sleep, with the coupling between global blood-oxygen-level-dependent (gBOLD) and cerebrospinal fluid (CSF) signals serving as a potential marker for glymphatic clearance function. However, the test-retest reliability and spatial heterogeneity of gBOLD-CSF coupling after different sleep conditions remain unclear. In this study, we assessed the test-retest reliability of gBOLD-CSF coupling following either normal sleep or total sleep deprivation (TSD) in 64 healthy adults under controlled laboratory conditions. The reliability was high after normal sleep (ICC = 0.763) but decreased following TSD (ICC = 0.581). Moreover, spatial heterogeneity was evident in participants with normal sleep, with lower-order networks (visual, somatomotor, and attention) showing higher ICC values compared to higher-order networks (default-mode, limbic, and frontoparietal). This spatial variation was less distinct in the TSD group. These results demonstrate the robustness of the gBOLD-CSF coupling method and emphasize the significance of considering sleep history in glymphatic function research.

Behavioural pharmacology predicts disrupted signalling pathways and candidate therapeutics from zebrafish mutants of Alzheimer's disease risk genes

By exposing genes associated with disease, genomic studies provide hundreds of starting points that should lead to druggable processes. However, our ability to systematically translate these genomic findings into biological pathways remains limited. Here, we combine rapid loss-of-function mutagenesis of Alzheimer's risk genes and behavioural pharmacology in zebrafish to predict disrupted processes and candidate therapeutics. FramebyFrame, our expanded package for the analysis of larval behaviours, revealed that decreased night-time sleep was common to F0 knockouts of all four late-onset Alzheimer's risk genes tested. We developed an online tool, ZOLTAR, which compares any behavioural fingerprint to a library of fingerprints from larvae treated with 3677 compounds. ZOLTAR successfully predicted that sorl1 mutants have disrupted serotonin signalling and identified betamethasone as a drug which normalises the excessive day-time sleep of presenilin-2 knockout larvae with minimal side effects. Predictive behavioural pharmacology offers a general framework to rapidly link disease-associated genes to druggable pathways.

Glymphatic system: a self-purification circulation in brain

The glymphatic system theory introduces a new perspective on fluid flow and homeostasis in the brain. Here, cerebrospinal fluid and interstitial fluid (CSF-ISF) moves from the perivascular spaces (PVS) of arteries to those of veins for drainage. Aquaporin-4 (AQP4) plays a crucial role in driving fluid within the PVS. The impairment to AQP4 is closely linked to the dysfunction of the glymphatic system. The function of the glymphatic system is less active during waking but enhanced during sleep. The efficiency of the glymphatic system decreases with aging. Damage to the glymphatic system will give rise to the development and progression of many brain diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), chronic traumatic encephalopathy (CTE), and vascular dementia (VaD). Here, we reviewed previous research associated with the glymphatic system, including its concepts, principles, and influencing factors. We hypothesize that AQP4 could be a target for the prevention and treatment of certain brain diseases through the regulation on the glymphatic system.

Norepinephrine-mediated slow vasomotion drives glymphatic clearance during sleep

As the brain transitions from wakefulness to sleep, processing of external information diminishes while restorative processes, such as glymphatic removal of waste products, are activated. Yet, it is not known what drives brain clearance during sleep. We here employed an array of technologies and identified tightly synchronized oscillations in norepinephrine, cerebral blood volume, and cerebrospinal fluid (CSF) as the strongest predictors of glymphatic clearance during NREM sleep. Optogenetic stimulation of the locus coeruleus induced anti-correlated changes in vasomotion and CSF signal. Furthermore, stimulation of arterial oscillations enhanced CSF inflow, demonstrating that vasomotion acts as a pump driving CSF into the brain. On the contrary, the sleep aid zolpidem suppressed norepinephrine oscillations and glymphatic flow, highlighting the critical role of norepinephrine-driven vascular dynamics in brain clearance. Thus, the micro-architectural organization of NREM sleep, driven by norepinephrine fluctuations and vascular dynamics, is a key determinant for glymphatic clearance.

Reduction of orexin-expressing neurons and a unique sleep phenotype in the Tg-SwDI mouse model of Alzheimer's disease

Sleep disturbances are common in Alzheimer's disease (AD) and AD-related dementia (ADRD). We performed a sleep study on Tg-SwDI mice, a cerebral amyloid angiopathy (CAA) model, and age-matched wild-type (WT) control mice. The results showed that at 12 months of age, the hemizygous Tg-SwDI mice spent significantly more time in non-rapid eye movement (NREM) sleep (44.6 ± 2.4% in Tg-SwDI versus 35.9 ± 2.5% in WT) and had a much shorter average length of wake bout during the dark (active) phase (148.5 ± 8.7 s in the Tg-SwDI versus 203.6 ± 13.0 s in WT). Histological analysis revealed stark decreases of orexin immunoreactive (orexin-IR) neuron number and soma size in these Tg-SwDI mice (cell number: 2187 ± 97.1 in Tg-SwDI versus 3318 ± 137.9 in WT. soma size: 109.1 ± 8.1 μm2 in Tg-SwDI versus 160.4 ± 6.6 μm2 in WT), while the number and size of melanin-concentrating hormone (MCH) immunoreactive (MCH-IR) neurons remained unchanged (cell number: 4256 ± 273.3 in Tg-SwDI versus 4494 ± 326.8 in WT. soma size: 220.1 ± 13.6 μm2 in Tg-SwDI versus 202.0 ± 7.8 μm2 in WT). The apoptotic cell death marker cleaved caspase-3 immunoreactive (Caspase-3-IR) percentage in orexin-IR neurons was significantly higher in Tg-SwDI mice than in WT controls. This selective loss of orexin-IR neurons could be associated with the abnormal sleep phenotype in these Tg-SwDI mice. Further studies are needed to determine the cause of the selective death of orexin-IR cells and relevant effects on cognition impairments in this mouse model of microvascular amyloidosis.

Epileptic activity on foramen ovale electrodes is associated with sleep and tau pathology in Alzheimer's disease

Both sleep alterations and epileptiform activity are associated with the accumulation of amyloid-β and tau pathology and are currently investigated for potential therapeutic interventions in Alzheimer's disease. However, a bidirectional intertwining relationship between sleep and neuronal hyperexcitability might modulate the effects of Alzheimer's disease pathology on the corresponding associations. To investigate this, we performed multiple day simultaneous foramen ovale (FO) plus scalp EEG and polysomnography recordings and acquired 18F-MK6240 tau PET-MR in three patients in the prodromal stage of Alzheimer's disease and in two patients with mild and moderate dementia due to Alzheimer's disease, respectively. As an eligibility criterion for the present study, subjects either had a history of a recent seizure (n = 2) or subclinical epileptiform activity (SEA) on a previous scalp EEG taken in a research context (n = 3). The 18F-MK6240 standard uptake value ratio (SUVR) and asymmetry index (AI) were calculated in a priori-defined volumes of interest. Linear mixed-effects models were used to study associations between interictal epileptiform discharges (IEDs), polysomnography parameters and 18F-MK6240 SUVR. Epileptiform activity was bilateral but asymmetrically present on FO electrodes in all patients and ≥95% of IEDs were not visible on scalp EEG. In one patient, two focal seizures were detected on FO electrodes, both without visual scalp EEG correlate. We observed lateralized periodic discharges, brief potentially ictal rhythmic discharges and lateralized rhythmic delta activity on FO electrodes in four patients. Unlike scalp EEG, intracranial electrodes showed a lateralization of epileptiform activity. Although the amount of IEDs on intracranial electrodes was not associated to the 18F-MK6240 SUVR binding in different volumes of interest, there was a congruent asymmetry of the 18F-MK6240 binding towards the most epileptic hemisphere for the mesial (P = 0.007) and lateral temporal cortex (P = 0.006). IEDs on intracranial electrodes were most abundant during slow wave sleep (SWS) (92/h) and non-REM sleep 2 (N2, 81/h), followed by non-REM sleep 1 (N1, 33/h) and least frequent during wakefulness (17/h) and REM sleep (9/h). The extent of IEDs during sleep was not reflected in the relative time in each sleep stage spent [REM% (P = 0.415), N1% (P = 0.668), N2% (P = 0.442), SWS% (P = 0.988)], and not associated with the arousal index (P = 0.317), apnoea-hypopnoea index (P = 0.846) or oxygen desaturation index (P = 0.746). Together, our observations suggest a multi-directional interaction between sleep, epileptiform activity and tau pathology in Alzheimer's disease.

New perspectives on the glymphatic system and the relationship between glymphatic system and neurodegenerative diseases

Neurodegenerative diseases (ND) are characterized by the accumulation of aggregated proteins. The glymphatic system, through its rapid exchange mechanisms between cerebrospinal fluid (CSF) and interstitial fluid (ISF), facilitates the movement of metabolic substances within the brain, serving functions akin to those of the peripheral lymphatic system. This emerging waste clearance mechanism offers a novel perspective on the removal of pathological substances in ND. This article elucidates recent discoveries regarding the glymphatic system and updates relevant concepts within its model. It discusses the potential roles of the glymphatic system in ND, including Alzheimer's disease (AD), Parkinson's disease (PD), and multiple system atrophy (MSA), and proposes the glymphatic system as a novel therapeutic target for these conditions.

Association of rapid eye movement sleep latency with multimodal biomarkers of Alzheimer's disease

INTRODUCTION

Sleep disturbances are associated with Alzheimer's disease (AD) and Alzheimer's disease and related dementias (ADRD), but the relationship between sleep architecture, particularly rapid eye movement (REM) sleep, and AD/ADRD biomarkers remains unclear.

METHODS

We enrolled 128 adults (64 with Alzheimer's disease, 41 with mild cognitive impairment [MCI], and 23 with normal cognition [NC]), mean age 70.8 ± 9.6 years, 56.9% female, from a tertiary hospital in China. Participants underwent overnight polysomnography (PSG), amyloid β (Aβ) positron emission tomography (PET), and plasma biomarker analysis: phosphorylated tau at threonine 181 (p-tau181), neurofilament light (NfL), and brain-derived neurotrophic factor (BDNF).

RESULTS

After adjusting for demographics, apolipoprotein E (APOE) ε4 status, cognition, and comorbidities, the highest tertile of REM latency was associated with higher Aβ burden (β = 0.08, 95% confidence interval [CI]: 0.03 to 0.13, p = 0.002), elevated p-tau181 (β = 0.19, 95% CI: 0.02 to 0.13, p = 0.002), and reduced BDNF levels (β = -0.47, 95% CI: -0.68 to -0.13, p = 0.013), compared to the lowest tertile.

DISCUSSION

Prolonged REM latency may serve as a novel marker or risk factor for AD/ADRD pathogenesis.

HIGHLIGHTS

Rapid eye movement latency (REML) may be a potential marker for Alzheimer's disease and Alzheimer's disease and related dementias (AD/ADRD) pathogenesis. Prolonged REML was associated with higher amyloid beta (Aβ) burden, phosphorylated tau-181 (p-tau181), and lower brain-derived neurotrophic factor (BDNF) levels. Intervention trial is needed to determine if targeting REML can modify AD/ADRD risk. Slow-wave sleep was not associated with AD/ADRD biomarkers.

The impact of sleep and exercise on brain atrophy in mild cognitive impairment

Chronic sleep deprivation and lack of physical exercise may have detrimental effects on overall health, particularly in terms of brain health, with significant implications for cognitive function and well-being. This review explores the impact of chronic sleep deprivation and physical exercise on brain atrophy in mild cognitive impairment (MCI) and Alzheimer's disease (AD). Drawing insights from 40 selected studies, the review synthesizes evidence on these lifestyle factors' correlations with neurodegenerative changes. Chronic sleep deprivation disrupts circadian rhythms and neurochemical pathways, potentially accelerating brain atrophy, while physical exercise preserves brain structure by enhancing vascular health, reducing inflammation, and supporting synaptic plasticity, particularly in regions like the hippocampus. Results highlight distinct patterns of brain atrophy in AD and MCI, underscoring the potential for targeted interventions to mitigate cognitive decline. Understanding the relationship between sleep disruption and brain health provides insights into strategies for possibly delaying neurodegenerative diseases like MCI, which represents a milder form of Alzheimer's, and AD. The findings underscore the potential utility of integrating sleep therapy and physical exercise interventions in clinical practice for early detection of mild cognitive impairment and potentially delaying disease progression. This integrated approach has been found to promote healthy aging, reduce atrophy rates, and enhance cognitive resilience across aging populations.

Emerging non-invasive MRI techniques for glymphatic system assessment in neurodegenerative disease

The discovery of the glymphatic system has revolutionized our understanding of brain physiology, particularly in waste clearance and fluid dynamics within the central nervous system. This pathway, essential for nutrient distribution and waste removal, operates predominantly during sleep and has been implicated in neurodegenerative diseases like Alzheimer's and Parkinson's. Recent advances in non-invasive MRI techniques, including diffusion tensor imaging along the perivascular space (DTI-ALPS), perivascular space (PVS) analysis, and free water (FW) indices, have improved our ability to study glymphatic function and its alterations in disease states. This review discusses the glymphatic system's ultrastructure, physiology, and the latest imaging methods to assess this critical pathway. We highlight how these non-invasive MRI techniques can enhance the understanding of glymphatic function in health and disease, with a focus on neurodegenerative conditions. By integrating insights from current research, this review underscores the diagnostic and therapeutic implications of glymphatic dysfunction. Understanding these mechanisms can pave the way for novel strategies to enhance waste clearance and improve neurological health, offering potential benefits for early diagnosis and intervention in neurodegenerative diseases.

The Brain Toxin Cleansing of Sleep Achieved During Wakefulness

A primary purpose of sleep for humans is to remove toxins and metabolic wastes from the brain (e.g., Aβ, tau, lactate) that would otherwise build up and compromise brain functionality. There are currently no drugs or devices that have been clinically shown in humans to enhance brain toxin removal, either during sleep or wakefulness. This perspective article focuses on a recently (re)discovered major route of toxin drainage from the human brain through meningeal lymphatic vessels (mLVs) and the primary enhancer of their flow-the cytokine Vascular Endothelial Growth Factor (VEGF). The purpose of this perspective article is to present pre-clinical and clinical evidence relevant to a new bioengineered technology (Transcranial Radiofrequency Treatment; TRFT) that appears to enhance mLV flow to increase brain toxin cleansing in humans during wakefulness. In being both safe and non-invasive, TRFT is administered in-home, presently through a device called "MemorEM". Two months of daily TRFT during wakefulness increased the typically low plasma/brain levels of VEGF in Alzheimer's Disease (AD) subjects, which was associated with increased Aβ and tau toxin removal from their brains during wakefulness-ostensibly through VEGF-increased mLV flow. Even irrespective of baseline VEGF levels, brain toxin cleansing was increased by TRFT in AD subjects, who also experienced a notable reversal of their cognitive impairment after TRFT. Additional clinical studies are nonetheless required to firmly establish TRFT's brain cleansing abilities during wakefulness. In performing a major duty of sleep, TRFT during wakefulness is proposed as a viable intervention to counter the decline in nighttime brain toxin cleansing that occurs with aging and in multiple brain diseases, most notably Alzheimer's Disease. The implications of TRFT for insomnia and for sleep deprivation are also discussed, as is the potential for TRFT to extend healthy human longevity.

WuYou decoction effectively reduces neuronal damage, synaptic dysfunction, and Aβ production in rats exposed to chronic sleep deprivation by modulating the Aβ-related enzymes and SIRT1/Nrf2/NF-κB pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Chronic sleep deprivation (CSD) can result in neuronal damage, synaptic dysfunction, Aβ production, neuroinflammation, and ultimately cognitive deterioration. WuYou Decoction (WYD), a contemporary prescription, has shown promise in enhancing sleep quality and cognitive performance in individuals with insomnia. However, the specific molecular mechanisms responsible for the neuroprotective effects of WYD on CSD remain incompletely understood.

AIM OF THE STUDY

This study aimed to investigate the neuroprotective effects of WYD on the CSD model and its molecular mechanism.

MATERIALS AND METHODS

UHPLC-MS/MS analysis was utilized to analyze the active ingredients of WYD extract. The study employed the multi-platform water environment method to establish the CSD model in rats. Subsequent to treatment with varying doses of WYD in CSD rats, cognitive function and pathological alterations in hippocampus and cortex, including neuronal damage, synaptic dysfunction, Aβ production, and neuroinflammation, were evaluated through a combination of Morris Water Maze test, HE staining, Nissl staining, Golgi-Cox staining, Transmission electron microscope, ELISA, Immunohistochemistry staining, Immunofluorescence staining and Western blot.

RESULTS

UHPLC-MS/MS analysis revealed a total of 99 active ingredients were identified from the WYD extract. The administration of WYD exhibited a mitigation of cognitive decline in the model of CSD, as evidenced by increased neuron count in the hippocampus and cortex, and improved density and length of dendritic spines in these brain regions. Furthermore, WYD was found to suppress the Aβ production, and inhibit the expression of BACE1, PS1, GFAP, IBA1, IL-1β, IL-6, TNF-α, phosphorylated IκBα (Ser32) and phosphorylated NF-κB p65 (Ser536) in the hippocampus and cortex, while also increasing the levels of PSD95, SYN1, ADAM10, IDE, SIRT1 and Nrf2.

CONCLUSIONS

WYD exhibits neuroprotective properties in CSD, potentially through modulation of the Aβ-related enzymes and SIRT1/Nrf2/NF-κB pathway.

Sleep Patterns and Human Brain Health

It is a widely held opinion that sleep is important for human brain health. Here we examine the evidence for this view, focusing on normal variations in sleep patterns. We discuss the functions of sleep and highlight the paradoxical implications of theories seeing sleep as an adaptive capacity versus the theory that sleep benefits clearance of metabolic waste from the brain. We also evaluate the proposition that sleep plays an active role in consolidation of memories. Finally, we review research on possible effects of chronic sleep deprivation on brain health. We find that the evidence for a causal role of sleep in human brain health is surprisingly weak relative to the amount of attention to sleep in science and society. While there are well-established associations between sleep parameters and aspects of brain health, results are generally not consistent across studies and measures, and it is not clear to what extent alterations in sleep patterns represent symptoms or causes. Especially, the proposition that long sleep (>8 hours) in general is beneficial for long-term brain health in humans seems to lack empirical support. We suggest directions for future research to establish a solid foundation of knowledge about a role of sleep in brain health based on longitudinal studies with frequent sampling, attention to individual differences, and more ecologically valid intervention studies.

Perivascular brain clearance as a therapeutic target in cerebral amyloid angiopathy and Alzheimer's disease

Although distinct diseases, both cerebral amyloid angiopathy (CAA) and Alzheimer's disease (AD) are characterized by the aggregation and accumulation of amyloid-β (Aβ). This is thought to be due, in part, to impaired perivascular Aβ clearance from the brain. This shared failure in both diseases presents a common opportunity for therapeutic intervention. In this review we discuss the idea that promoting perivascular brain clearance could be an effective strategy for safely reducing Aβ levels in CAA and AD thereby improving clinical outcomes, most notably hemorrhagic stroke and cognitive decline. We will explore the evidence for the different forces that are thought to drive perivascular brain clearance, review the literature on potential strategies for potentiating these driving forces, and finally we will discuss the substantial translational challenges and considerations that would accompany such an intervention.

Stimulus-driven cerebrospinal fluid dynamics is impaired in glaucoma patients

Cerebrospinal fluid (CSF) dynamics, driven by sensory stimulation-induced neuronal activity, is crucial for maintaining homeostasis and clearing metabolic waste. However, it remains unclear whether such CSF flow is impaired in age-related neurodegenerative diseases of the visual system. This study addresses this gap by examining CSF flow during visual stimulation in glaucoma patients and healthy older adults using functional magnetic resonance imaging. The findings reveal that in glaucoma, CSF inflow becomes decoupled from visually evoked blood-oxygenation-level-dependent (BOLD) response. Furthermore, stimulus-locked CSF patterns, characterized by decreases following stimulus onset and increases after offset, diminish as glaucoma severity worsens. Mediation analysis suggests that this flattened CSF pattern is driven by a flatter BOLD slope, resulting in a shallower CSF trough and a reduced rebound. These findings unveil a novel pathophysiological mechanism underlying disrupted stimulation-driven CSF dynamics in glaucoma and highlight potential in vivo biomarkers for monitoring CSF in the glaucomatous brain.

From single nucleotide variations to genes: identifying the genetic links between sleep and psychiatric disorders

STUDY OBJECTIVES

Sleep disorders and psychiatric disorders frequently coexist and interact, yet the shared genetic basis linking these two domains remains poorly understood.

METHODS

We investigated the genetic correlation and overlap between seven sleep/circadian traits and three psychiatric disorders at the level of genome-wide association studies (GWAS), utilizing LDSC, HDL, and GPA. To identify potential polygenic single nucleotide variations (SNVs) within each trait pair, we used PLACO, while gene-level analyses were performed using MAGMA and POPS. Furthermore, the functions and biological mechanisms, enriched phenotypes, tissues, cellular features, and pathways were thoroughly investigated using FUMA, deTS, and enrichment analyses at the biological pathway level.

RESULTS

Our study revealed extensive genetic associations and overlaps in all 21 trait pairs. We identified 18 494 SNVs and 543 independent genomic risk loci, with 113 confirmed as causative through colocalization analysis. These loci collectively spanned 196 unique chromosomal regions. We pinpointed 43 distinct pleiotropic genes exhibiting significant enrichment in behavioral/physiological phenotypes, nervous system phenotypes, and brain tissue. Aberrations in synaptic structure and function, neurogenesis and development, as well as immune responses, particularly involving the MAPK pathway, emerged as potential underpinnings of the biology of sleep/circadian traits and psychiatric disorders.

CONCLUSIONS

We identified shared loci and specific sets of genes between sleep/circadian traits and psychiatric disorders, shedding light on the genetic etiology. These discoveries hold promise as potential targets for novel drug interventions, providing valuable insights for the development of therapeutic strategies for these disorders.

Impact of sleep deprivation on dynamic functional connectivity states

Sleep deprivation (SD) is an experimental procedure to study the effects of sleep loss on the human brain. Neuroimaging techniques, such as functional magnetic resonance imaging (fMRI) and electroencephalography (EEG), have been pivotal in studying these effects. The present chapter aims to retrace the state of the art regarding the literature that examines the SD effects on the brain through functional connectivity (FC) evaluated in fMRI and EEG settings, separately. Specifically, we focused on the cognitive domains mainly affected by sleep loss and the underlying brain connectivity alterations. SD disrupts homeostatic and circadian processes, negatively affecting cognitive and cerebral functionality explored through FC. All evidence confirms the detrimental role of SD on brain connectivity impacting several resting-state networks and resulting in cognitive impairments. To conclude, SD may offer useful insights into pathogenic mechanisms likely resembling those induced by chronic sleep loss that might find their application in the clinical context.

The Common Alzheimer's Disease Research Ontology (CADRO) for biomarker categorization

Biomarkers are vital to Alzheimer's disease (AD) drug development and clinical trials, and will have an increasing role in clinical care. In this narrative review, we demonstrate the use of the National Institutes on Aging/Alzheimer's Association (NIA/AA) Common Alzheimer's Disease Research Ontology (CADRO) system for the categorization of biomarkers based on the primary mechanism on which they report. We show that biomarkers are available (in various levels of validation) for all CADRO processes. Application of the CADRO system demonstrates gaps in the field where novel biomarkers are needed for specific aspects of the disease, and assays to detect and measure biological changes, in individuals with symptomatic or preclinical AD. We demonstrate the CADRO system as a means of categorizing established and candidate AD biomarkers, showing the feasibility and practicality of the system. CADRO can assist with biomarker selection for AD clinical trials and drug development, and may eventually be applied to implementing biomarkers in patient care.

Highlights

The Common Alzheimer's Disease Research Ontology (CADRO) system can be used to categorize biomarkers for drug development.We demonstrate the use of CADRO with Alzheimer's disease (AD) biomarkers.We identified AD biomarkers in each of the CADRO categories.CADRO can be incorporated into current AD drug development and clinical trial systems.

Bilingualism, sleep, and cognition: An integrative view and open research questions

Sleep and language are fundamental to human existence and have both been shown to substantially affect cognitive functioning including memory, attentional performance, and cognitive control. Surprisingly, there is little-to-no research that examines the shared impact of bilingualism and sleep on cognitive functions. In this paper, we provide a general overview of existing research on the interplay between bilingualism and sleep with a specific focus on executive functioning. First, we highlight their interconnections and the resulting implications for cognitive performance. Second, we emphasize the need to explore how bilingualism and sleep intersect at cognitive and neural levels, offering insights into potential ways of studying the interplay between sleep, language learning, and bilingual language use. Finally, we suggest that understanding these relationships could enhance our knowledge of reserve and its role in mitigating age-related cognitive decline.

The Associations Between Sleep Duration and Various Metabolic Health Indices Among Adults in the United States: A Multivariate Analysis of Variance (MANOVA) Using National Health and Nutrition Examination Survey (NHANES) 2021 to 2023 Dataset

OBJECTIVE

This study explores the associations between various sleep durations and metabolic health indices, including systolic blood pressure (SBP), diastolic blood pressure (DBP), total cholesterol levels, high-density lipoprotein (HDL) cholesterol, and waist circumference.

METHODS

Data from the National Health and Nutrition Examination Survey (NHANES) 2021 to 2023, were analyzed. MANOVA and Bonferroni-adjusted ANOVAs were conducted to examine the relationships between sleep duration (sleep deprivation (≤5 h), short sleep (5-7 h), recommended sleep (7-9 h), and long sleep (>9 h)) and metabolic health indices.

RESULTS

MANOVA revealed significant group differences between sleep duration and metabolic health indices, with Wilks' Lambda (Λ) = .98, F (3, 5095) = 4.26, P < .001. Compared to recommended sleep duration, both sleep deprivation and short sleep were associated with higher DBP (Ps < .01) and waist circumference (Ps < .001), and lower HDL levels (Ps < .05) Long sleep was associated with lower HDL levels (P < .01) and lower total cholesterol (P < .01).

CONCLUSION

The study highlights the detrimental associations of both sleep deprivation and short sleep with metabolic health, such as elevated blood pressure and waist circumference, and lowered HDL cholesterol. Long sleep may also negatively impact metabolic health by reducing HDL.

The Microbiota-Gut-Brain Axis: Key Mechanisms Driving Glymphopathy and Cerebral Small Vessel Disease

The human microbiota constitute a very complex ecosystem of microorganisms inhabiting both the inside and outside of our bodies, in which health maintenance and disease modification are the main regulatory features. The recent explosion of microbiome research has begun to detail its important role in neurological health, particularly concerning cerebral small vessel disease (CSVD), a disorder associated with cognitive decline and vascular dementia. This narrative review represents state-of-the-art knowledge of the intimate, complex interplay between microbiota and brain health through the gut-brain axis (GBA) and the emerging role of glymphatic system dysfunction (glymphopathy) and circulating cell-derived microparticles (MPs) as mediators of these interactions. We discuss how microbial dysbiosis promotes neuroinflammation, vascular dysfunction, and impaired waste clearance in the brain, which are critical factors in the pathogenesis of CSVD. Further, we discuss lifestyle factors that shape the composition and functionality of the microbiota, focusing on sleep as a modifiable risk factor in neurological disorders. This narrative review presents recent microbiome research from a neuroscientific and vascular perspective to establish future therapeutic avenues in targeting the microbiota to improve brain health and reduce the burden of CSVD.

Diffusion Tensor Imaging Analysis Along the Perivascular Space (DTI-ALPS) Demonstrates That Sleep Disorders Exacerbate Glymphatic Circulatory Impairment and Cognitive Impairment in Patients with Alzheimer's Disease

Objective

Sleep disorders are common in Alzheimer's disease (AD) patients and can impair the glymphatic system, leading to cognitive decline. This study aimed to investigate whether AD patients with sleep disorders exhibit worse glymphatic function and more severe cognitive impairment compared to those without sleep disorders and to explore the underlying molecular imaging mechanisms.

Methods

This study included 40 AD patients with sleep disorders (ADSD), 39 cognitively matched AD patients without sleep disorders (ADNSD), and 25 healthy middle-aged and elderly controls (NC). Participants underwent functional magnetic resonance imaging (fMRI), and cognitive and sleep assessments. The ALPS (Along the Perivascular Space) index was calculated, followed by intergroup comparisons, correlation analyses, and mediation analyses. The diagnostic utility of the ALPS index was assessed using a receiver operating characteristic (ROC) curve.

Results

The ALPS index was lower in the ADNSD and ADSD groups compared to the NC group. In the ADSD group, PSQI scores were negatively correlated with MMSE scores. The ALPS index was positively correlated with MMSE scores and negatively with PSQI scores. Mediation analyses indicated that the ALPS index partially mediated the effect of sleep disturbances on cognitive impairment (indirect effect = -0.134; mediation effect = 30.505%). The area under the ROC curve (AUROC) for distinguishing ADSD from ADNSD was 0.86, with a cutoff ALPS index value 1.309.

Conclusion

Sleep disorders worsen glymphatic function and cognitive impairment in AD patients. The ALPS index partially mediates the impact of sleep disorders on cognitive function and shows moderate accuracy in distinguishing between patients with ADSD and ADNSD.

BMAL1 upregulates STX17 levels to promote autophagosome-lysosome fusion in hippocampal neurons to ameliorate Alzheimer's disease

We aim to investigate muscle ARNT-like protein 1 (BMAL1) regulation of syntaxin17 (STX17) in mouse hippocampal neurons, focusing on autophagy and amyloid-β (Aβ) deposition. Autophagosome-lysosome fusion in APP/PS1 hippocampal tissues was observed using transmission electron microscopy, while mRNA levels of LC3II and P62 were measured via reverse-transcription PCR (RT-PCR) after Amyloid precursor protein (APP) overexpression. STX17, linked to autophagy and differentially expressed in Alzheimer's disease (AD) brains, was knocked down or overexpressed to assess its effects. The results showed that reduced STX17 impairs autophagosome-lysosome fusion, leading to abnormal Aβ deposition. Coimmunoprecipitation (Co-IP) and immunofluorescence confirmed STX17 interaction with SNAP29 and VAMP8 to form SNARE complexes. Furthermore, BMAL1 binding to STX17 was examined using luciferase assays. Circadian rhythm disturbances and decreased BMAL1 expression in APP/PS1 mice were noted, while BMAL1 overexpression upregulated STX17 expression and promoted autophagy to reduce Aβ deposition. Thus, the BMAL1 protein can promote STX17 transcription to induce STX17-SNAP29-VAMP8 complex formation to clear intracellular Aβ through autophagy.

Loss of glymphatic homeostasis in heart failure

Heart failure (HF) is associated with progressive reduction in cerebral blood flow (CBF) and neurodegenerative changes leading to cognitive decline. The glymphatic system is crucial for the brain's waste removal, and its dysfunction is linked to neurodegeneration. In this study, we used a mouse model of HF, induced by myocardial infarction (MI), to investigate the effects of HF with reduced ejection fraction on the brain's glymphatic function. Using dynamic contrast-enhanced MRI and high-resolution fluorescence microscopy, we found increased solute influx from the CSF spaces to the brain, i.e. glymphatic influx, at 12 weeks post MI. Two-photon microscopy revealed that cerebral arterial pulsatility, a major driver of the glymphatic system, was potentiated at this timepoint, and could explain this increase in glymphatic influx. However, clearance of proteins from the brain parenchyma did not increase proportionately with influx, while a relative increase in brain parenchyma volume was found at 12 weeks post MI, suggesting dysregulation of brain fluid dynamics. Additionally, our results showed a correlation between brain clearance and CBF. These findings highlight the role of CBF as a key regulator of the glymphatic system, suggesting its involvement in the development of brain disorders associated with reduced CBF. This study paves the way for future investigations into the effects of cardiovascular diseases on the brain's clearance mechanisms, which may provide novel insights into the prevention and treatment of cognitive decline.

Sleep induced by mechanosensory stimulation provides cognitive and health benefits in Drosophila

STUDY OBJECTIVES

Sleep is a complex phenomenon regulated by various factors, including sensory input. Anecdotal observations have suggested that gentle rocking helps babies fall asleep, and experimental studies have verified that rocking promotes sleep in both humans and mice. Recent studies have expanded this understanding, demonstrating that gentle vibration also induces sleep in Drosophila. Natural sleep serves multiple functions, including learning and memory, synaptic downscaling, and reduction of harmful substances associated with neurodegenerative diseases. Here, we investigated whether vibration-induced sleep (VIS) provides similar cognitive and health benefits in Drosophila.

METHODS

We administered gentle vibration to flies that slept very little due to a forced activation of wake-promoting neurons and investigated how the vibration influenced learning and memory in the courtship conditioning paradigm. Additionally, we examined the effects of VIS on synaptic downscaling by counting synaptic varicosities of select neurons. Finally, we determined whether vibration could induce sleep in Drosophila models of Alzheimer's disease (AD) and suppress the accumulation of Amyloid β (Aβ) and Tubulin Associated Unit (TAU).

RESULTS

VIS enhanced performance in a courtship conditioning paradigm and reduced the number of synaptic varicosities in select neurons. Moreover, vibration improved sleep in Drosophila models of AD, reducing Aβ and TAU levels.

CONCLUSIONS

Mechanosensory stimulation offers a promising noninvasive avenue for enhancing sleep, potentially providing associated cognitive and health benefits.

Ameliorating Effect of Fermented Perilla frutescens on Sleep Deprivation-Induced Cognitive Impairment Through Antioxidant and BDNF Signaling in Mice

Background: Adequate sleep is essential for maintaining cognitive function, as evidenced by literature. Perilla frutescens var. acuta Kudo (PF) is a traditional medicinal herb reported to improve vascular cognitive impairment and induce sedation. However, the effects of PF on cognitive impairment caused by sleep deprivation (SD) have not yet been evaluated. This study aims to evaluate the effects of fermented PF (FPF) and its underlying mechanisms in a model of SD-induced cognitive impairment. Methods: Mice were subjected to SD to establish cognitive impairment, and FPF was administered once daily for 3 days. Cognitive performance was assessed using Y-maze and passive avoidance tests, followed by molecular mechanisms analyses. Results: FPF treatment improved SD-induced cognitive impairment, as evidenced by increased spontaneous alternation and extended latency time. Histological analysis revealed that SD impaired the hippocampus, and this impairment was alleviated by FPF treatment. FPF demonstrated antioxidant activity by increasing glutathione levels and decreasing malondialdehyde levels. Furthermore, the decreased levels of brain-derived neurotrophic factor (BDNF) observed in sleep-deprived mice were restored with FPF treatment. FPF also enhanced the phosphorylation of tropomyosin receptor kinase B, extracellular signal-regulated kinase, and cAMP response element-binding protein. Conclusions: These results indicate that FPF may have beneficial effects on SD-induced cognitive impairment by protecting against oxidative stress and increasing BDNF expression.

Sleep disturbances and racial-ethnic disparities in 10-year dementia risk among a national sample of older adults in the USA

BACKGROUND

Race/ethnicity and sleep disturbances are associated with dementia risk.

AIMS

To explore racial-ethnic disparities in sleep disturbances, and whether race/ethnicity moderates the relationship between sleep disturbances and dementia risk among older adults.

METHOD

We analysed ten annual waves (2011-2020) of prospective cohort data from the National Health and Aging Trends Study, a nationally representative USA sample of 6284 non-Hispanic White (n = 4394), non-Hispanic Black (n = 1311), Hispanic (n = 342) and non-Hispanic Asian (n = 108) community-dwelling older adults. Sleep disturbances were converted into three longitudinal measures: (a) sleep-initiation difficulty (trouble falling asleep within 30 min), (b) sleep-maintenance difficulty (trouble falling asleep after waking up early) and (c) sleep medication usage (taking medication to sleep). Cox proportional hazards models analysed time to dementia, after applying sampling weights and adjusting for sociodemographic characteristics and health.

RESULTS

Black, Hispanic and Asian respondents exhibited higher frequencies of sleep-initiation and sleep-maintenance difficulties, but had less sleep medication usage, compared with White older adults. Among Hispanic respondents, sleep-initiation difficulty was associated with significantly decreased dementia risk (adjusted hazard ratio (aHR) = 0.34, 95% CI 0.15-0.76), but sleep-maintenance difficulty was associated with increased dementia risk (aHR = 2.68, 95% CI 1.17-6.13), compared with White respondents. Asian respondents using sleep medications had a significantly higher dementia risk (aHR = 3.85, 95% CI 1.64-9.04). There were no significant interactions for Black respondents.

CONCLUSIONS

Sleep disturbances are more frequent among older Black, Hispanic and Asian adults, and should be considered when addressing dementia disparities. Research is needed to explore how certain sleep disturbances may elevate dementia risk across different racial and ethnic subgroups.

Multi-night acoustic stimulation is associated with better sleep, amyloid dynamics, and memory in older adults with cognitive impairment

Sleep is a potential early, modifiable risk factor for cognitive decline and dementia. Impaired slow wave sleep (SWS) is pronounced in individuals with cognitive impairment (CI). Cognitive decline and impairments of SWS are bi-directionally linked in a vicious cycle. SWS can be enhanced non-invasively using phase-locked acoustic stimulation (PLAS), potentially breaking this vicious cycle. Eighteen healthy older adults (HC, agemean±sd, 68.3 ± 5.1) and 16 older adults (agemean±sd, 71.9 ± 3.9) with CI (Montreal Cognitive Assessment ≤ 25) underwent one baseline (sham-PLAS) night and three consecutive stimulation nights (real-PLAS). EEG responses and blood-plasma amyloid beta Aβ42/Aβ40 ratio were measured pre- and post-intervention, as was episodic memory. The latter was again evaluated 1 week and 3 months after the intervention. In both groups, PLAS induced a significant electrophysiological response in both voltage- and time-frequency analyses, and memory performance improved in association with the magnitude of this response. In the CI group, both electrophysiological and associated memory effects were delayed compared to the healthy group. After 3 intervention nights, electrophysiological response to PLAS was no longer different between CI and HC groups. Only in the CI sample, stronger electrophysiological responses were significantly associated with improving post-intervention Aβ42/Aβ40 ratios. PLAS seems to improve SWS electrophysiology, memory, and amyloid dynamics in older adults with CI. However, effects on memory require more time to unfold compared to healthy older adults. This indicates that PLAS may become a potential tool to ameliorate cognitive decline, but longer interventions are necessary to compensate for declining brain integrity. This study was pre-registered (clinicaltrials.gov: NCT04277104).

Sleep Deficiency in the Elderly

With aging, there are normative changes to sleep physiology and circadian rhythmicity that may predispose older adults to sleep deficiency, whereas many health-related and psychosocial/behavioral factors may precipitate sleep deficiency. In this article, we describe age-related changes to sleep and describe how the health-related and psychosocial/behavioral factors typical of aging may converge in older adults to increase the risk for sleep deficiency. Next, we review the consequences of sleep deficiency in older adults, focusing specifically on important age-related outcomes, including mortality, cognition, depression, and physical function. Finally, we review treatments for sleep deficiency, highlighting safe and effective nonpharmacologic interventions.

Perivascular space diffusivity and brain microstructural measures are associated with circadian time and sleep quality

The glymphatic system is centred around brain cerebrospinal fluid flow and is enhanced during sleep, and the synaptic homeostasis hypothesis proposes that sleep acts on brain microstructure by selective synaptic downscaling. While so far primarily studied in animals, we here examine in humans if brain diffusivity and microstructure is related to time of day, sleep quality and cognitive performance. We use diffusion weighted images from 916 young healthy individuals, aged between 22 and 37 years, collected as part of the Human Connectome Project to assess diffusion tensor image analysis along the perivascular space index, white matter fractional anisotropy, intra-neurite volume fraction and extra-neurite mean diffusivity. Next, we examine if these measures are associated with circadian time of acquisition, the Pittsburgh Sleep Quality Index (high scores correspond to low sleep quality) and age-adjusted cognitive function total composite score. Consistent with expectations, we find that diffusion tensor image analysis along the perivascular space index and orbitofrontal grey matter extra-neurite mean diffusivity are negatively and white matter fractional anisotropy positively correlated with circadian time. Further, we find that grey matter intra-neurite volume fraction correlates positively with Pittsburgh Sleep Quality Index, and that this correlation is driven by sleep duration. Finally, we find positive correlations between grey matter intra-neurite volume fraction and cognitive function total composite score, as well as negative interaction effects between cognitive function total composite score and Pittsburgh Sleep Quality Index on grey matter intra-neurite volume fraction. Our findings propose that perivascular flow is under circadian control and that sleep downregulates the intra-neurite volume in healthy adults with positive impact on cognitive function.

Sleep deprivation leads to non-adaptive alterations in sleep microarchitecture and amyloid-β accumulation in a murine Alzheimer model

Impaired sleep is a common aspect of aging and often precedes the onset of Alzheimer's disease. Here, we compare the effects of sleep deprivation in young wild-type mice and their APP/PS1 littermates, a murine model of Alzheimer's disease. After 7 h of sleep deprivation, both genotypes exhibit an increase in EEG slow-wave activity. However, only the wild-type mice demonstrate an increase in the power of infraslow norepinephrine oscillations, which are characteristic of healthy non-rapid eye movement sleep. Notably, the APP/PS1 mice fail to enhance norepinephrine oscillations 24 h after sleep deprivation, coinciding with an accumulation of cerebral amyloid-β protein. Proteome analysis of cerebrospinal fluid and extracellular fluid further supports these findings by showing altered protein clearance in APP/PS1 mice. We propose that the suppression of infraslow norepinephrine oscillations following sleep deprivation contributes to increased vulnerability to sleep loss and heightens the risk of developing amyloid pathology in early stages of Alzheimer's disease.

From Fundamentals to Innovation in Alzheimer's Disease: Molecular Findings and Revolutionary Therapies

Alzheimer's disease (AD) is a global health concern and the leading cause of dementia in the elderly. The prevalence of this neurodegenerative condition is projected to increase concomitantly with increased life expectancy, resulting in a significant economic burden. With very few FDA-approved disease-modifying drugs available for AD, there is an urgent need to develop new compounds capable of impeding the progression of the disease. Given the unclear etiopathogenesis of AD, this review emphasizes the underlying mechanisms of this condition. It explores not only well-studied aspects, such as the accumulation of Aβ plaques and neurofibrillary tangles, but also novel areas, including glymphatic and lymphatic pathways, microbiota and the gut-brain axis, serotoninergic and autophagy alterations, vascular dysfunction, the metal hypothesis, the olfactory pathway, and oral health. Furthermore, the potential molecular targets arising from all these mechanisms have been reviewed, along with novel promising approaches such as nanoparticle-based therapy, neural stem cell transplantation, vaccines, and CRISPR-Cas9-mediated genome editing techniques. Taking into account the overlap of these various mechanisms, individual and combination therapies emerge as the future direction in the AD strategy.

Attentional failures after sleep deprivation represent moments of cerebrospinal fluid flow

Sleep deprivation rapidly disrupts cognitive function, and in the long term contributes to neurological disease. Why sleep deprivation has such profound effects on cognition is not well understood. Here, we use simultaneous fast fMRI-EEG to test how sleep deprivation modulates cognitive, neural, and fluid dynamics in the human brain. We demonstrate that after sleep deprivation, sleep-like pulsatile cerebrospinal fluid (CSF) flow events intrude into the awake state. CSF flow is coupled to attentional function, with high flow during attentional impairment. Furthermore, CSF flow is tightly orchestrated in a series of brain-body changes including broadband neuronal shifts, pupil constriction, and altered systemic physiology, pointing to a coupled system of fluid dynamics and neuromodulatory state. The timing of these dynamics is consistent with a vascular mechanism regulated by neuromodulatory state, in which CSF begins to flow outward when attention fails, and flow reverses when attention recovers. The attentional costs of sleep deprivation may thus reflect an irrepressible need for neuronal rest periods and widespread pulsatile fluid flow.

Oxidative Stress-mediated Loss of Hippocampal Parvalbumin Interneurons Contributes to Memory Precision Decline After Acute Sleep Deprivation

Sleep is pivotal to memory consolidation, and sleep deprivation (SD) after learning can impede this process, leading to memory disorders. In the present study, we aimed to explore the effects of acute sleep deprivation (ASD) on memory disorders and the underlying mechanisms. ASD model was induced by subjecting the mice to 6 h of SD following fear conditioning training. Different cohorts were used for behavioral, biochemical, and electrophysiological tests. Here, we showed that memory precision decline was induced by ASD, concomitant with a notable elevation in oxidative stress within PV interneurons, loss of PV, and disturbed neuronal oscillation in the CA1 region. Notably, chemogenetic activation of PV interneurons effectively ameliorated abnormal gamma oscillation and memory precision decline observed in ASD mice. Meanwhile, chemogenetic inhibition of PV interneurons successfully mimicked the abnormal brain oscillations and memory precision decline observed in ASD mice. Additionally, prior administration of the antioxidant medication N-acetylcysteine effectively reversed memory precision decline and mitigated PV loss and abnormal oscillation triggered by ASD. Collectively, our findings indicated that ASD increased oxidative stress in PV interneurons, thereby disrupting neural oscillation in the CA1 and ultimately leading to memory precision decline.

The impact of body position on neurofluid dynamics: present insights and advancements in imaging

The intricate neurofluid dynamics and balance is essential in preserving the structural and functional integrity of the brain. Key among these forces are: hemodynamics, such as heartbeat-driven arterial and venous blood flow, and hydrodynamics, such as cerebrospinal fluid (CSF) circulation. The delicate interplay between these dynamics is crucial for maintaining optimal homeostasis within the brain. Currently, the widely accepted framework for understanding brain functions is the Monro-Kellie's doctrine, which posits a constant sum of intracranial CSF, blood flow and brain tissue volumes. However, in recent decades, there has been a growing interest in exploring the dynamic interplay between these elements and the impact of external factors, such as daily changes in body position. CSF circulation in particular plays a crucial role in the context of neurodegeneration and dementia, since its dysfunction has been associated with impaired clearance mechanisms and accumulation of toxic substances. Despite the implementation of various invasive and non-invasive imaging techniques to investigate the intracranial hemodynamic or hydrodynamic properties, a comprehensive understanding of how all these elements interact and are influenced by body position remains wanted. Establishing a comprehensive overview of this topic is therefore crucial and could pave the way for alternative care approaches. In this review, we aim to summarize the existing understanding of intracranial hemodynamic and hydrodynamic properties, fundamental for brain homeostasis, along with factors known to influence their equilibrium. Special attention will be devoted to elucidating the effects of body position shifts, given their significance and remaining ambiguities. Furthermore, we will explore recent advancements in imaging techniques utilized for real time and non-invasive measurements of dynamic body fluid properties in-vivo.

Regulation of proteostasis by sleep through autophagy in Drosophila models of Alzheimer's disease

Sleep and circadian rhythm dysfunctions are common clinical features of Alzheimer's disease (AD). Increasing evidence suggests that in addition to being a symptom, sleep disturbances can also drive the progression of neurodegeneration. Protein aggregation is a pathological hallmark of AD; however, the molecular pathways behind how sleep affects protein homeostasis remain elusive. Here we demonstrate that sleep modulation influences proteostasis and the progression of neurodegeneration in Drosophila models of tauopathy. We show that sleep deprivation enhanced Tau aggregational toxicity resulting in exacerbated synaptic degeneration. In contrast, sleep induction using gaboxadol led to reduced toxic Tau accumulation in neurons as a result of modulated autophagic flux and enhanced clearance of ubiquitinated Tau, suggesting altered protein processing and clearance that resulted in improved synaptic integrity and function. These findings highlight the complex relationship between sleep and regulation of protein homeostasis and the neuroprotective potential of sleep-enhancing therapeutics to slow the progression or delay the onset of neurodegeneration.

Sleep disorders and risk of alzheimer's disease: A two-way road

Substantial sleep impairment in patients with Alzheimer's disease (AD) is one of the emerging points for continued efforts to better understand the disease. Individuals without cognitive decline, an important marker of the clinical phase of AD, may show early alterations in the sleep-wake cycle. The objective of this critical narrative review is to explore the bidirectional pathophysiological correlation between sleep disturbances and Alzheimer's Disease. Specifically, it examines how the disruption of sleep homeostasis in individuals without dementia could contribute to the pathogenesis of AD, and conversely, how neurodegeneration in individuals with Alzheimer's Disease might lead to dysregulation of the sleep-wake cycle. Recent scientific results indicate that sleep disturbances, particularly those related to impaired glymphatic clearance, may act as an important mechanism associated with the genesis of Alzheimer's Disease. Additionally, amyloid deposition and tau protein hyperphosphorylation, along with astrocytic hyperactivation, appear to trigger changes in neurotransmission dynamics in areas related to sleep, which may explain the onset of sleep disturbances in individuals with AD. Disruption of sleep homeostasis appears to be a modifiable risk factor in Alzheimer's disease. Whenever possible, the use of non-pharmacological strategies becomes important in this context. From a different perspective, additional research is needed to understand and treat the dysfunction of the sleep-wake cycle in individuals already affected by AD. Early recognition and correction of sleep disturbances in this population could potentially mitigate the progression of dementia and improve the quality of life for those with AD.

Cerebral small vessel disease and glymphatic system dysfunction in multiple sclerosis: A narrative review

As the multiple sclerosis (MS) population ages, the prevalence of vascular comorbidities increases, potentially accelerating disease progression and brain atrophy. Recent studies highlight the prevalence of cerebral small vessel disease (CSVD) in MS, suggesting a potential link between vascular comorbidities and accelerated disability. CSVD affects the brain's small vessels, often leading to identifiable markers on MRI such as enlarged perivascular spaces (EPVS). EPVS are increasingly recognized also in MS and have been associated with vascular comorbidities, lower percentage of MS-specific perivenular lesions, brain atrophy and aging. The exact sequence of event leading to MRI visible EPVS is yet to be determined, but an impaired perivascular brain fluid drainage appears a possible physiopathological explanation for EPVS in both CSVD and MS. In this context, a dysfunction of the brain fluid clearance system - also known as "glymphatic system" - appears associated in MS to aging, neuroinflammation, and vascular dysfunction. Advanced imaging techniques show an impaired glymphatic function in both MS and CSVD. Additionally, lifestyle factors such as physical exercise, diet, and sleep quality appear to influence glymphatic function, potentially revealing novel therapeutic strategies to mitigate microangiopathy and neuroinflammation in MS. This review underscores the potential role of glymphatic dysfunction in the complex and not-yet elucidated interplay between neuroinflammation and CSVD in MS.

Chronic Sleep Deprivation Altered the Expression of Memory-Related Genes and Caused Cognitive Memory Dysfunction in Mice

Lack of sleep, whether acute or chronic, is quite common and negatively affects an individual's memory and cognitive function. The question of whether chronic sleep deprivation (CSD) causes cognitive impairment to arise and progress is not well studied. To investigate the effects of CSD on memory and cognition, this study began by establishing a CSD mouse model. Behavioral experiments on animals revealed that CSD induced cognitive behavioral abnormalities reminiscent of Alzheimer's disease. Western blot experiments further demonstrated a considerable increase in amyloid-β (Aβ) expression in the mouse brain following CSD. Meanwhile, the hub gene Prkcg was searched for in the cerebellum using RNA-seq and bioinformatics analysis. PKCγ (Prkcg) expression was significantly reduced, as demonstrated by RT-qPCR and Western blot validations. Additionally, CSD was associated with downregulated CREB expression, decreased expression of the endothelin-converting enzyme (ECE1), and increased phosphorylation of ERK1/2 downstream of PKCγ. These findings suggested that CSD down-regulated PKCγ expression, decreased ECE1 expression, impaired Aβ degradation, and affected the PKCγ/ERK/CREB pathway and the synthesis of memory-related proteins. Overall, this study highlighted how CSD modulated PKCγ-related metabolism, impacting Aβ clearance and the production of memory-related proteins. Such insights are crucial for understanding and preventing sporadic Alzheimer's disease (sAD) associated with CSD.

Effects of sleep on the glymphatic functioning and multimodal human brain network affecting memory in older adults

Understanding how sleep affects the glymphatic system and human brain networks is crucial for elucidating the neurophysiological mechanism underpinning aging-related memory declines. We analyzed a multimodal dataset collected through magnetic resonance imaging (MRI) and polysomnographic recording from 72 older adults. A proxy of the glymphatic functioning was obtained from the Diffusion Tensor Image Analysis along the Perivascular Space (DTI-ALPS) index. Structural and functional brain networks were constructed based on MRI data, and coupling between the two networks (SC-FC coupling) was also calculated. Correlation analyses revealed that DTI-ALPS was negatively correlated with sleep quality measures [e.g., Pittsburgh Sleep Quality Index (PSQI) and apnea-hypopnea index]. Regarding human brain networks, DTI-ALPS was associated with the strength of both functional connectivity (FC) and structural connectivity (SC) involving regions such as the middle temporal gyrus and parahippocampal gyrus, as well as with the SC-FC coupling of rich-club connections. Furthermore, we found that DTI-ALPS positively mediated the association between sleep quality and rich-club SC-FC coupling. The rich-club SC-FC coupling further mediated the association between DTI-ALPS and memory function in good sleepers but not in poor sleepers. The results suggest a disrupted glymphatic-brain relationship in poor sleepers, which underlies memory decline. Our findings add important evidence that sleep quality affects cognitive health through the underlying neural relationships and the interplay between the glymphatic system and multimodal brain networks.

Optogenetic targeting of cortical astrocytes selectively improves NREM sleep in an Alzheimer's disease mouse model

Alzheimer's disease (AD) is a progressive neurodegenerative condition marked by memory impairments and distinct histopathological features such as amyloid-beta (Aβ) accumulations. Alzheimer's patients experience sleep disturbances at early stages of the disease. APPswe/PS1dE9 (APP) mice exhibit sleep disruptions, including reductions in non-rapid eye movement (NREM) sleep, that contribute to their disease progression. In addition, astrocytic calcium transients associated with a sleep-dependent brain rhythm, slow oscillations prevalent during NREM sleep, are disrupted in APP mice. However, at present it is unclear whether restoration of circuit function by targeting astrocytic activity could improve sleep in APP mice. To that end, APP mice expressing channelrhodopsin-2 (ChR2) targeted to astrocytes underwent optogenetic stimulation at the slow oscillation frequency. Optogenetic stimulation of astrocytes significantly increased NREM sleep duration but not duration of rapid eye movement (REM) sleep. Optogenetic treatment increased delta power and reduced sleep fragmentation in APP mice. Thus, optogenetic activation of astrocytes increased sleep quantity and improved sleep quality in an AD mouse model. Astrocytic activity provides a novel therapeutic avenue to pursue for enhancing sleep and slowing AD progression.

Neuronal subtype-specific transcriptomic changes in the cerebral neocortex associated with sleep pressure

Sleep is homeostatically regulated by sleep pressure, which increases during wakefulness and dissipates during sleep. Recent studies have suggested that the cerebral neocortex, a six-layered structure composed of various layer- and projection-specific neuronal subtypes, is involved in the representation of sleep pressure governed by transcriptional regulation. Here, we examined the transcriptomic changes in neuronal subtypes in the neocortex upon increased sleep pressure using single-nucleus RNA sequencing datasets and predicted the putative intracellular and intercellular molecules involved in transcriptome alterations. We revealed that sleep deprivation (SD) had the greatest effect on the transcriptome of layer 2 and 3 intratelencephalic (L2/3 IT) neurons among the neocortical glutamatergic neuronal subtypes. The expression of mutant SIK3 (SLP), which is known to increase sleep pressure, also induced profound changes in the transcriptome of L2/3 IT neurons. We identified Junb as a candidate transcription factor involved in the alteration of the L2/3 IT neuronal transcriptome by SD and SIK3 (SLP) expression. Finally, we inferred putative intercellular ligands, including BDNF, LSAMP, and PRNP, which may be involved in SD-induced alteration of the transcriptome of L2/3 IT neurons. We suggest that the transcriptome of L2/3 IT neurons is most impacted by increased sleep pressure among neocortical glutamatergic neuronal subtypes and identify putative molecules involved in such transcriptional alterations.