Abnormal Sleep Behaviours Across the Spectrum of Alzheimer's Disease Severity: Influence of APOE Genotypes and Lewy Bodies

Sleep-wake modulation and pathogenesis of Alzheimer disease: Suggestions for postponement and treatment

Sleep-wake disorders are recognized as one of the earliest symptoms of Alzheimer disease (AD). Accumulating evidence has highlighted a significant association between sleep-wake disorders and AD pathogenesis, suggesting that sleep-wake modulation could be a promising approach for postponing AD onset. The suprachiasmatic nucleus (SCN) and the pineal hormone melatonin are major central modulating components of the circadian rhythm system. Cerebrospinal fluid (CSF) melatonin levels are dramatically decreased in AD. Interestingly, the number of neurofibrillary tangles in the hippocampus, which is one of the two major neuropathologic AD biomarkers, increases in parallel with the decrease in CSF melatonin levels. Furthermore, a decrease in salivary melatonin levels in middle-aged persons is a significant risk factor for the onset of the early stages of AD. Moreover, the disappearance of rhythmic fluctuations in melatonin may be one of the best biomarkers for AD diagnosis. Light therapy combined with melatonin supplementation is the recommended first-line treatment for sleep-wake disorders in AD patients and may be beneficial for ameliorating cognitive impairment. Sleep-wake cycle modulation based on AD risk gene presence is a promising early intervention for AD onset postponement.

Roles of ApoE4 on the Pathogenesis in Alzheimer's Disease and the Potential Therapeutic Approaches

The Apolipoprotein E ε4 (ApoE ε4) allele, encoding ApoE4, is the strongest genetic risk factor for late-onset Alzheimer's disease (LOAD). Emerging epidemiological evidence indicated that ApoE4 contributes to AD through influencing β-amyloid (Aβ) deposition and clearance. However, the molecular mechanisms of ApoE4 involved in AD pathogenesis remains unclear. Here, we introduced the structure and functions of ApoE isoforms, and then we reviewed the potential mechanisms of ApoE4 in the AD pathogenesis, including the effect of ApoE4 on Aβ pathology, and tau phosphorylation, oxidative stress; synaptic function, cholesterol transport, and mitochondrial dysfunction; sleep disturbances and cerebrovascular integrity in the AD brains. Furthermore, we discussed the available strategies for AD treatments that target to ApoE4. In general, this review overviews the potential roles of ApoE4 in the AD development and suggests some therapeutic approaches for AD. ApoE4 is genetic risk of AD. ApoE4 is involved in the AD pathogenesis. Aβ deposition, NFT, oxidative stress, abnormal cholesterol, mitochondrial dysfunction and neuroinflammation could be observed in the brains with ApoE4. Targeting the interaction of ApoE4 with the AD pathology is available strategy for AD treatments.

Connections between ApoE, sleep, and Aβ and tau pathologies in Alzheimer's disease

In this issue of the JCI, Wang and colleagues investigate the relationship between sleep disturbances, an environmental risk factor for Alzheimer's disease (AD), and the apolipoprotein 4 (APOEε4) allele, a strong genetic risk factor for AD. The authors subjected an amyloid mouse model expressing human APOE3 or APOE4, with and without human AD-tau injection, to sleep deprivation and observed that amyloid and tau pathologies were worsened in the presence of APOE4. Moreover, decreased microglial clustering and increased dystrophic neurites around plaques were observed in sleep-deprived APOE4 mice. In addition, aquaporin 4, important for clearing amyloid-β through the glymphatic system, was reduced and less polarized to astrocytic endfeet. These APOE4-induced changes caused alterations in sleep behavior during recovery from sleep deprivation, suggesting a feed-forward cycle of sleep disturbance and increased AD pathology that can further disrupt sleep in the presence of APOE4.

APOE-ε4 synergizes with sleep disruption to accelerate Aβ deposition and Aβ-associated tau seeding and spreading

Alzheimer's disease (AD) is the most common cause of dementia. The APOE-ε4 allele of the apolipoprotein E (APOE) gene is the strongest genetic risk factor for late-onset AD. The APOE genotype modulates the effect of sleep disruption on AD risk, suggesting a possible link between apoE and sleep in AD pathogenesis, which is relatively unexplored. We hypothesized that apoE modifies Aβ deposition and Aβ plaque-associated tau seeding and spreading in the form of neuritic plaque-tau (NP-tau) pathology in response to chronic sleep deprivation (SD) in an apoE isoform-dependent fashion. To test this hypothesis, we used APPPS1 mice expressing human APOE-ε3 or -ε4 with or without AD-tau injection. We found that SD in APPPS1 mice significantly increased Aβ deposition and peri-plaque NP-tau pathology in the presence of APOE4 but not APOE3. SD in APPPS1 mice significantly decreased microglial clustering around plaques and aquaporin-4 (AQP4) polarization around blood vessels in the presence of APOE4 but not APOE3. We also found that sleep-deprived APPPS1:E4 mice injected with AD-tau had significantly altered sleep behaviors compared with APPPS1:E3 mice. These findings suggest that the APOE-ε4 genotype is a critical modifier in the development of AD pathology in response to SD.

ApoE in Alzheimer’s disease: pathophysiology and therapeutic strategies

Alzheimer’s disease (AD) is the most common cause of dementia worldwide, and its prevalence is rapidly increasing due to extended lifespans. Among the increasing number of genetic risk factors identified, the apolipoprotein E (APOE) gene remains the strongest and most prevalent, impacting more than half of all AD cases. While the ε4 allele of the APOE gene significantly increases AD risk, the ε2 allele is protective relative to the common ε3 allele. These gene alleles encode three apoE protein isoforms that differ at two amino acid positions. The primary physiological function of apoE is to mediate lipid transport in the brain and periphery; however, additional functions of apoE in diverse biological functions have been recognized. Pathogenically, apoE seeds amyloid-β (Aβ) plaques in the brain with apoE4 driving earlier and more abundant amyloids. ApoE isoforms also have differential effects on multiple Aβ-related or Aβ-independent pathways. The complexity of apoE biology and pathobiology presents challenges to designing effective apoE-targeted therapeutic strategies. This review examines the key pathobiological pathways of apoE and related targeting strategies with a specific focus on the latest technological advances and tools.

Possible Neuropathology of Sleep Disturbance Linking to Alzheimer's Disease: Astrocytic and Microglial Roles

Sleep disturbances not only deteriorate Alzheimer’s disease (AD) progress by affecting cognitive states but also accelerate the neuropathological changes of AD. Astrocytes and microglia are the principal players in the regulation of both sleep and AD. We proposed that possible astrocyte-mediated and microglia-mediated neuropathological changes of sleep disturbances linked to AD, such as astrocytic adenosinergic A1, A2, and A3 regulation; astrocytic dopamine and serotonin; astrocyte-mediated proinflammatory status (TNFα); sleep disturbance-attenuated microglial CX3CR1 and P2Y12; microglial Iba-1 and astrocytic glial fibrillary acidic protein (GFAP); and microglia-mediated proinflammatory status (IL-1b, IL-6, IL-10, and TNFα). Furthermore, astrocytic and microglial amyloid beta (Aβ) and tau in AD were reviewed, such as astrocytic Aβ interaction in AD; astrocyte-mediated proinflammation in AD; astrocytic interaction with Aβ in the central nervous system (CNS); astrocytic apolipoprotein E (ApoE)-induced Aβ clearance in AD, as well as microglial Aβ clearance and aggregation in AD; proinflammation-induced microglial Aβ aggregation in AD; microglial-accumulated tau in AD; and microglial ApoE and TREM2 in AD. We reviewed astrocytic and microglial roles in AD and sleep, such as astrocyte/microglial-mediated proinflammation in AD and sleep; astrocytic ApoE in sleep and AD; and accumulated Aβ-triggered synaptic abnormalities in sleep disturbance. This review will provide a possible astrocytic and microglial mechanism of sleep disturbance linked to AD.

Sleep-Wake Disorders in Alzheimer's Disease: A Review

Alzheimer's disease (AD) is a multifactorial disease, and it has become a serious health problem in the world. Senile plaques (SPs) and neurofibrillary tangles (NFTs) are two main pathological characters of AD. SP mainly consists of aggregated β-amyloid (Aβ), and NFT is formed by hyperphosphorylated tau protein. Sleep-wake disorders are prevalent in AD patients; however, the links and mechanisms of sleep-wake disorders on the AD pathogenesis remain to be investigated. Here, we referred to the sleep-wake disorders and reviewed some evidence to demonstrate the relationship between sleep-wake disorders and the pathogenesis of AD. On one hand, the sleep-wake disorders may lead to the increase of Aβ production and the decrease of Aβ clearance, the spreading of tau pathology, as well as oxidative stress and inflammation. On the other hand, the ApoE4 allele, a risk gene for AD, was reported to participate in sleep-wake disorders. Furthermore, some neurotransmitters, such as acetylcholine, glutamate, serotonin, melatonin, and orexins, and their receptors were suggested to be involved in AD development and sleep-wake disorders. We discussed and suggested some possible therapeutic strategies for AD treatment based on the view of sleep regulation. In general, this review explored different views to find novel targets of diagnosis and therapy for AD.

The Role of Amyloid, Tau, and APOE Genotype on the Relationship Between Informant-Reported Sleep Disturbance and Alzheimer's Disease Risks

BACKGROUND

The association between sleep and Alzheimer's disease (AD) biomarkers are well-established, but little is known about how they interact to change the course of AD.

OBJECTIVE

To determine the potential interaction between sleep disturbance and Aβ, tau, and APOE4 on brain atrophy and cognitive decline.

METHODS

Sample included 351 participants (mean age 72.01 ± 6.67, 50.4%female) who were followed for approximately 5 years as part of the Alzheimer's Disease Neuroimaging Initiative. Informant-reported sleep disturbance (IRSD) was measured using the Neuropsychiatric Inventory (NPI). Changes in magnetic resonance imaging (MRI)-measured AD signature brain regions and cognitive performance and IRSD's interaction with cerebrospinal fluid amyloid-β (Aβ42) and p-Tau depositions and APOE4 status were examined using the linear mixed models.

RESULTS

Baseline IRSD was not significantly associated with the rate of atrophy after adjusting for covariates (age, sex, education, total NPI severity score, and sleep medications). However, there was a significant interaction between IRSD and AD biomarkers on faster atrophy rates in multiple brain regions, including the cortical and middle temporal volumes. Post-hoc analyses indicated that Aβ and p-Tau/Aβ predicted a faster decline in these regions/domains in IRSD, compared with biomarker-negative individuals with IRSD (ps≤0.001). There was a significant IRSD*APOE4 interaction for brain atrophy rate (ps≤0.02) but not for cognition.

CONCLUSION

IRSD may increase the future risk of AD by contributing to faster brain atrophy and cognitive decline when combined with the presence of AD biomarkers and APOE4. Early intervention for sleep disturbance could help reduce the risk of developing AD.

Sleep duration, Health Promotion Index (HPI), sRAGE and ApoE-ε4 genotype are associated with telomere length (TL) in healthy elderly Australians

Significant alterations in sleep duration and/or quality of sleep become more pronounced as people get older. Poor sleep in elderly people is associated with adverse health outcomes and cellular ageing. We examined the relationship between TL and sleep duration, Health Promotion Index (HPI), and tested whether the presence of ApoE-ε4 allele impacts both sleep and TL. The present study was carried out in 174 healthy elderly subjects (21% male; mean age 53.79 years) from South Australia. Lymphocyte telomere length (TL) was measured by real-time qPCR and ApoE genotype was determined by TaqMan assay. HPI was calculated from a questionnaire regarding 8 lifestyle habits, including sleeping hours. Multivariate regression analysis was used to establish these associations adjusted for specified confounders. TL was found to be inversely associated with age (r = - 0.199; p = 0.008) and BMI (r = - 0.121; p = 0.11), and was significantly shorter in participants who slept for <7 hours (p = 0.001) relative to those sleeping ≥7 hours. TL was positively correlated with HPI (r = 0.195; p = 0.009). ApoE-ε4 allele carriers who slept for less than 7 hours had shortest TL (p = 0.01) compared to non-carriers. Plasma sRAGE level was significantly (p = 0.001) lower in individuals who sleep <7 hours and ApoE-ϵ4 carriers. Our results suggest that inadequate sleep duration or poor HPI is associated with shorter TL in cognitively normal elderly people and that carriage of APOE-ε4 genotype may influence the extent of these effects.

APOE Genotype and Alzheimer's Disease: The Influence of Lifestyle and Environmental Factors

Alzheimer's disease (AD) is the most common neurodegenerative disorder with obscure pathogenesis and no disease-modifying therapy to date. AD is multifactorial disease that develops from the complex interplay of genetic factors and environmental exposures. The E4 allele of the gene encoding apolipoprotein E (APOE) is the most common genetic risk factor for AD, whereas the E2 allele acts in a protective manner. A growing amount of epidemiological evidence suggests that several lifestyle habits and environmental factors may interact with APOE alleles to synergistically affect the risk of AD development. Among them, physical exercise, dietary habits including fat intake and ketogenic diet, higher education, traumatic brain injury, cigarette smoking, coffee consumption, alcohol intake, and exposure to pesticides and sunlight have gained increasing attention. Although the current evidence is inconsistent, it seems that younger APOE4 carriers in preclinical stages may benefit mostly from preventive lifestyle interventions, whereas older APOE4 noncarriers with dementia may show the most pronounced effects. The large discrepancies between the epidemiological studies may be attributed to differences in the sample sizes, the demographic characteristics of the participants, including age and sex, the methodological design, and potential related exposures and comorbidities as possible cofounding factors. In this Review, we aim to discuss available evidence of the prominent APOE genotype-environment interactions in regard to cognitive decline with a focus on AD, providing an overview of the current landscape in this field and suggesting future directions.

Sleep Disturbances in MCI and AD: Neuroinflammation as a Possible Mediating Pathway

Mild cognitive impairment (MCI) and Alzheimer's disease (AD) affect a high proportion of the elderly population with an increasing prevalence. Sleep disturbances are frequent in those with MCI and AD. This review summarizes existing research on sleep disturbances and neuroinflammation in MCI and AD. Although strong evidence supports various pathways linking sleep and AD pathology, the temporal direction of this central relationship is not yet known. Improved understanding of sleep disturbance and neuroinflammation in MCI and AD may aid in the identification of targets for their prevention.

Actigraphy for Assessing Light Effects on Sleep and Circadian Activity Rhythm in Alzheimer's Dementia: A Narrative Review

Background:

Alzheimer's Disease (AD) is often accompanied by severe sleep problems and circadian rhythm disturbances which may to some extent be attributed to a dysfunction in the biological clock. The 24-h light/dark cycle is the strongest Zeitgeber for the biological clock. People with AD, however, often live in environments with inappropriate photic Zeitgebers. Timed bright light exposure may help to consolidate sleep- and circadian rest/activity rhythm problems in AD, and may be a low-risk alternative to pharmacological treatment.

Objective & Method:

In the present review, experts from several research disciplines summarized the results of twenty-seven light intervention studies which used wrist actigraphy to measure sleep and circadian activity in AD patients.

Results:

Taken together, the findings remain inconclusive with regard to beneficial light effects. However, the considered studies varied substantially with respect to the utilized light intervention, study design, and usage of actigraphy. The paper provides a comprehensive critical discussion of these issues.

Conclusion:

Fusing knowledge across complementary research disciplines has the potential to critically advance our understanding of the biological input of light on health and may contribute to architectural lighting designs in hospitals, as well as our homes and work environments.

Bidirectional relationship between sleep and Alzheimer's disease: role of amyloid, tau, and other factors

As we age, we experience changes in our nighttime sleep and daytime wakefulness. Individuals afflicted with Alzheimer's disease (AD) can develop sleep problems even before memory and other cognitive deficits are reported. As the disease progresses and cognitive changes ensue, sleep disturbances become even more debilitating. Thus, it is imperative to gain a better understanding of the relationship between sleep and AD pathogenesis. We postulate a bidirectional relationship between sleep and the neuropathological hallmarks of AD; in particular, the accumulation of amyloid-β (Aβ) and tau. Our research group has shown that extracellular levels of both Aβ and tau fluctuate during the normal sleep-wake cycle. Disturbed sleep and increased wakefulness acutely lead to increased Aβ production and decreased Aβ clearance, whereas Aβ aggregation and deposition is enhanced by chronic increased wakefulness in animal models. Once Aβ accumulates, there is evidence in both mice and humans that this results in disturbed sleep. New findings from our group reveal that acute sleep deprivation increases levels of tau in mouse brain interstitial fluid (ISF) and human cerebrospinal fluid (CSF) and chronic sleep deprivation accelerates the spread of tau protein aggregates in neural networks. Finally, recent evidence also suggests that accumulation of tau aggregates in the brain correlates with decreased nonrapid eye movement (NREM) sleep slow wave activity. In this review, we first provide a brief overview of the AD and sleep literature and then highlight recent advances in the understanding of the relationship between sleep and AD pathogenesis. Importantly, the effects of the bidirectional relationship between the sleep-wake cycle and tau have not been previously discussed in other reviews on this topic. Lastly, we provide possible directions for future studies on the role of sleep in AD.