Chronic Sleep Disturbances Alters Sleep Structure and Tau Phosphorylation in AβPP/PS1 AD Mice and Their Wild-Type Littermates

Melatonin Mitigates Sleep Restriction-Induced Cognitive and Glymphatic Dysfunction Via Aquaporin-4 Polarization

Chronic sleep restriction (SR) impairs the glymphatic clearance of macromolecular toxic metabolites, which is associated with the loss of perivascular polarization of aquaporin-4 (AQP4). Melatonin (Mel) has been shown to maintain the circadian rhythm of AQP4 polarization. However, the role of AQP4 polarization in Mel's protective effects against SR-induced brain dysfunction remains unclear. In the present study, using a modified rotating rod SR mouse model, we demonstrated the time-dependent effect of SR on short-term memory deficits and AQP4 mislocalization in the hippocampus. Subsequent experiments characterized the dose-dependent pattern of Mel ameliorating SR-induced impairments of cognitive function and AQP4 polarity. Mel's treatment enhanced glymphatic transport in SR mice, as revealed by cerebrospinal tracer experiments, and reduced hippocampal amyloid-beta and phosphorylated tau levels. Additionally, Mel significantly decreased glial cell activation, pro-inflammatory cytokine production, and synaptic protein loss in the hippocampus of SR mice. However, in AQP4 knockout mice, Mel's protective effects against SR-induced pathophysiological alterations described above were largely abolished. Mechanistically, Mel activated the vitamin D receptor and then upregulated expression of DTNA (Dystrobrevin Alpha), a key component of the dystrophin-associated complex, which in turn restored AQP4 polarization during chronic SR conditions. This finding indicates that AQP4-mediated lymphatic clearance is necessary for Mel to combat chronic SR-induced brain impairment.

Disruption of sleep macro- and microstructure in Alzheimer's disease: overlaps between neuropsychology, neurophysiology, and neuroimaging

Alzheimer's disease (AD) is the leading cause of dementia, often associated with impaired sleep quality and disorganized sleep structure. This study aimed to characterize changes in sleep macrostructure and K-complex density in AD, in relation to neuropsychological performance and brain structural changes. We enrolled 30 AD and 30 healthy control participants, conducting neuropsychological exams, brain MRI, and one-night polysomnography. AD patients had significantly reduced total sleep time (TST), sleep efficiency, and relative durations of non-rapid eye movement (NREM) stages 2 (S2), 3 (S3), and rapid eye movement (REM) sleep (p < 0.01). K-complex (KC) density during the entire sleep period and S2 (p < 0.001) was significantly decreased in AD. We found strong correlations between global cognitive performance and relative S3 (p < 0.001; r = 0.86) and REM durations (p < 0.001; r = 0.87). TST and NREM stage 1 (S1) durations showed a moderate negative correlation with amygdaloid and hippocampal volumes (p < 0.02; r = 0.51-0.55), while S3 and REM sleep had a moderate positive correlation with cingulate cortex volume (p < 0.02; r = 0.45-0.61). KC density strongly correlated with global cognitive function (p < 0.001; r = 0.66) and the thickness of the anterior cingulate cortex (p < 0.05; r = 0.45-0.47). Our results indicate significant sleep organization changes in AD, paralleling cognitive decline. Decreased slow wave sleep and KCs are strongly associated with cingulate cortex atrophy. Since sleep changes are prominent in early AD, they may serve as prognostic markers or therapeutic targets.

Transient sleep apnea results in long-lasting increase in β-amyloid generation and tau hyperphosphorylation

Sleep apnea is regarded as an important risk factor in the pathogenesis of Alzheimer disease (AD). Chronic intermittent hypoxia treatment (IHT) given during the sleep period of the circadian cycle in experimental animals is a well-established sleep apnea model. Here we report that transient IHT for 4 days on AD model mice causes Aβ overproduction 2 months after IHT presumably via upregulation of synaptic BACE1, side-by-side with tau hyperphosphorylation. These results suggest that even transient IHT may be sufficient to cause long-lasting changes in the molecules measured as AD biomarkers in the brain.

Impaired sleep is associated with tau deposition on 18F-flortaucipir PET and accelerated cognitive decline, accounting for medications that affect sleep

BACKGROUND

Impaired sleep is commonly associated with Alzheimer's disease (AD), although the underlying mechanisms remain unclear. Furthermore, the moderating effects of sleep-affecting medications, which have been linked to AD pathology, are incompletely characterized. Using data from the Alzheimer's Disease Neuroimaging Initiative, we investigated whether a medical history of impaired sleep, informant-reported nighttime behaviors, and sleep-affecting medications are associated with beta-amyloid and tau deposition on PET and cognitive change, cross-sectionally and longitudinally.

METHODS

We included 964 subjects with 18F-florbetapir PET scans. Measures of sleep impairment and medication use were obtained from medical histories and the Neuropsychiatric Inventory Questionnaire. Multivariate models, adjusted for covariates, were used to assess associations among sleep-related features, beta-amyloid and tau, and cognition. Cortical tau deposition, categorized by Braak stage, was assessed using the standardized uptake value peak alignment (SUVP) method on 18F-flortaucipir PET.

RESULTS

Medical history of sleep impairment was associated with greater baseline tau in the meta-temporal, Braak 1, and Braak 4 regions (p = 0.04, p < 0.001, p = 0.025, respectively). Abnormal nighttime behaviors were also associated with greater baseline tau in the meta-temporal region (p = 0.024), and greater cognitive impairment, cross-sectionally (p = 0.007) and longitudinally (p < 0.001). Impaired sleep was not associated with baseline beta-amyloid (p > 0.05). Short-term use of selective serotonin reuptake inhibitors and benzodiazepines slightly weakened the sleep-tau relationship.

CONCLUSIONS

Sleep impairment was associated with tauopathy and cognitive decline, which could be linked to increased tau secretion from neuronal hyperactivity. Clinically, our results help identify high-risk individuals who could benefit from sleep-related interventions aimed to delay cognitive decline and AD.

Relationship of Sleep Disorder with Neurodegenerative and Psychiatric Diseases: An Updated Review

Sleep disorders affect many people worldwide and can accompany neurodegenerative and psychiatric diseases. Sleep may be altered before the clinical manifestations of some of these diseases appear. Moreover, some sleep disorders affect the physiological organization and function of the brain by influencing gene expression, accelerating the accumulation of abnormal proteins, interfering with the clearance of abnormal proteins, or altering the levels of related hormones and neurotransmitters, which can cause or may be associated with the development of neurodegenerative and psychiatric diseases. However, the detailed mechanisms of these effects are unclear. This review mainly focuses on the relationship between and mechanisms of action of sleep in Alzheimer's disease, depression, and anxiety, as well as the relationships between sleep and Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. This summary of current research hotspots may provide researchers with better clues and ideas to develop treatment solutions for neurodegenerative and psychiatric diseases associated with sleep disorders.