Alzheimer's disease phenotypes show different sleep architecture

Chinese formula Guben-Jiannao Ye alleviates the dysfunction of circadian and sleep rhythms in APP/PS1 mice implicated in activation of the PI3K/AKT/mTOR signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

The Chinese formula Guben-Jiannao Ye (GBJNY) formula has a long history of usage in traditional Chinese medicine (TCM) for the treatment of learning and memory disorders as well as senile insomnia. This formulation is derived from Sun Simiao's five tonic pills. Furthermore, modern pharmacological investigations have revealed its ability to improve cognitive impairment and ameliorate sleep-wake circadian rhythm disorders. However, the precise mechanism underlying its efficacy remains elusive.

AIM OF THE STUDY

The current research explored the modulatory effects and possible mechanisms of GBJNY in circadian rhythm sleep-wake disorders and cognitive dysfunction in Alzheimer's disease using transcriptome sequencing and experimental validation.

MATERIALS AND METHODS

The LC-MS/MS tandem technology was utilized to qualitatively discern the active components present in GBJNY. The APP/PS1 mice received continuous treatment with GBJNY or Melatonin for 3 months. The learning and memory abilities of mice were assessed utilizing the Morris water maze (MWM) test, while sleep changes were studied utilizing the electroencephalogram (EEG) and electromyogram (EMG). Concurrently, mice's hippocampus clock gene rhythmicity was investigated. Subsequently, we employed HE staining, Golgi staining, and immunofluorescence to observe GBJNY's impact on synaptic damage and neuronal loss. We performed high-throughput sequencing to analyze the mRNA expression profiles of mice, aiming to identify differentially expressed genes (DEGs). Subsequently, we conducted GO and KEGG enrichment analyses to explore associated signaling pathways. Furthermore, we evaluated the expression levels of proteins involved in the PI3K/AKT/mTOR pathway and Aβ deposition in the hippocampus of mice. Through this comprehensive approach, we sought to elucidate and validate the potential mechanisms of action of GBJNY in APP/PS1 mice.

RESULTS

Results showed 216 DEGs. Following this, we conducted GO enrichment and KEGG pathway analyses to delve deeper into the distinctions and fundamental functions of the mRNA target genes. The enrichment analysis underscored the prominence of the PI3K/Akt/mTOR signaling pathway as the most pivotal among them. Through in vivo experiments, it was further demonstrated that the administration of GBJNY enhanced memory and learning capacities in APP/PS1 mice. Additionally, GBJNY treatment resulted in alterations in the sleep-wake circadian rhythm, characterized by reduced wakefulness and an increase in non-rapid eye movement (NREM) sleep. Moreover, alterations in the peak expression of Per1, Per2, Clock, Cry1, Cry2, and Bmal1 mRNA were noted in the hippocampus of treated mice. Particularly noteworthy were the observed reductions in amyloid-beta (Aβ) deposition within the hippocampus, improvements in neuronal synaptic integrity, and upregulation of mTOR, Akt, and PI3K protein expression in the hippocampal region. These findings underscore the critical involvement of the PI3K/Akt/mTOR signaling pathway in mitigating disturbances in sleep-wake circadian rhythms.

CONCLUSIONS

GBJNY enhanced the cognitive performance of APP/PS1 mice and altered clock gene expression patterns, alleviating sleep-wake circadian rhythm disruptions. The fundamental mechanism appears to be linked to the PI3K/Akt/mTOR pathway regulation, offering a foundation for potential clinical applications.

Ascorbate insufficiency disrupts glutamatergic signaling and alters electroencephalogram phenotypes in a mouse model of Alzheimer's disease

Clinical studies have reported that increased epileptiform and subclinical epileptiform activity can be detected in many patients with an Alzheimer's disease (AD) diagnosis using electroencephalogram (EEG) and this may correlate with poorer cognition. Ascorbate may have a specific role as a neuromodulator in AD as it is released concomitantly with glutamate reuptake following excitatory neurotransmission. Insufficiency may therefore result in an exacerbated excitatory/inhibitory imbalance in neuronal signaling. Using a mouse model of AD that requires dietary ascorbate (Gulo-/-APPswe/PSEN1dE9), EEG was recorded at baseline and during 4 weeks of ascorbate depletion in young (5-month-old) and aged (20-month-old) animals. Data were scored for changes in quantity of spike trains, individual spikes, sleep-wake rhythms, sleep fragmentation, and brainwave power bands during light periods each week. We found an early increase in neuronal spike discharges with age and following ascorbate depletion in AD model mice and not controls, which did not correlate with brain amyloid load. Our data also show more sleep fragmentation with age and with ascorbate depletion. Additionally, changes in brain wave activity were observed within different vigilance states in both young and aged mice, where Gulo-/-APPswe/PSEN1dE9 mice had shifts towards higher frequency bands (alpha, beta, and gamma) and ascorbate depletion resulted in shifts towards lower frequency bands (delta and theta). Microarray data supported ascorbate insufficiency altering glutamatergic transmission through the decreased expression of glutamate related genes, however no changes in protein expression of glutamate reuptake transporters were observed. These data suggest that maintaining optimal brain ascorbate levels may support normal brain electrical activity and sleep patterns, particularly in AD patient populations where disruptions are observed.

The Role of Circadian Rhythm in Neurological Diseases: A Translational Perspective

Intrinsic biological clocks drive the circadian rhythm, which coordinates the physiological and pathophysiological processes in the body. Recently, a bidirectional relationship between circadian rhythms and several neurological diseases has been reported. Neurological diseases can lead to the disruption of circadian homeostasis, thereby increasing disease severity. Therefore, optimizing the current treatments through circadian-based approaches, including adjusted dosing, changing lifestyle, and targeted interventions, offer a promising opportunity for better clinical outcomes and precision medicine. In this review, we provide detailed implications of the circadian rhythm in neurological diseases through bench-to-bedside approaches. Furthermore, based on the unsatisfactory clinical outcomes, we critically discuss the potential of circadian-based interventions, which may encourage more studies in this discipline, with the hope of improving treatment efficacy in neurological diseases.

REM sleep and neurodegeneration

Several brainstem, subcortical and cortical areas are involved in the generation of rapid eye movement (REM) sleep. The alteration of these structures as a result of a neurodegenerative process may therefore lead to REM sleep anomalies. REM sleep behaviour disorder is associated with nightmares, dream-enacting behaviours and increased electromyographic activity in REM sleep. Its isolated form is a harbinger of synucleinopathies such as Parkinson's disease or dementia with Lewy bodies, and neuroprotective interventions are advocated. This link might also be present in patients taking antidepressants, with post-traumatic stress disorder, or with a history of repeated traumatic head injury. REM sleep likely contributes to normal memory processes. Its alteration has also been proposed to be part of the neuropathological changes occurring in Alzheimer's disease.

The wake- and sleep-modulating neurons of the lateral hypothalamic area demonstrate a differential pattern of degeneration in Alzheimers disease

BACKGROUND

Sleep-wake dysfunction is an early and common event in Alzheimer's disease (AD). The lateral hypothalamic area (LHA) regulates the sleep and wake cycle through wake-promoting orexinergic neurons (OrxN) and sleep-promoting melanin-concentrating hormone or MCHergic neurons (MCHN). These neurons share close anatomical proximity with functional reciprocity. This study investigated LHA OrxN and MCHN loss patterns in AD individuals. Understanding the degeneration pattern of these neurons will be instrumental in designing potential therapeutics to slow down the disease progression and remediate the sleep-wake dysfunction in AD.

METHODS

Postmortem human brain tissue from donors with AD (across progressive stages) and controls were examined using unbiased stereology. Formalin-fixed, celloidin-embedded hypothalamic sections were stained with Orx-A/MCH, p-tau (CP13), and counterstained with gallocyanin. Orx or MCH-positive neurons with or without CP13 inclusions and gallocyanin-stained neurons were considered for stereology counting. Additionally, we extracted RNA from the LHA using conventional techniques. We used customized Neuropathology and Glia nCounter (Nanostring) panels to study gene expression. Wald statistical test was used to compare the groups, and the genes were considered differentially expressed when the p-value was <.05.

RESULTS

We observed a progressive decline in OrxN alongside a relative preservation of MCHN. OrxN decreased by 58% (p=0.03) by Braak stages (BB) 1-2 and further declined to 81% (p=0.03) by BB 5-6. Conversely, MCHN demonstrated a non-statistical significant decline (27%, p=0.1088) by BB 6. We observed a progressive increase in differentially expressed genes (DEGs), starting with glial profile changes in BB2. While OrxN loss was observed, Orx-related genes showed upregulation in BB 3-4 compared to BB 0-1. GO and KEGG terms related to neuroinflammatory pathways were mainly enriched.

CONCLUSIONS

To date, OrxN loss in the LHA represents the first neuronal population to die preceding the loss of LC neurons. Conversely, MCHN shows resilience to AD p-tau accumulation across Braak stages. The initial loss of OrxN correlates with specific neuroinflammation, glial profile changes, and an overexpression of HCRT, possibly due to hyperexcitation following compensation mechanisms. Interventions preventing OrxN loss and inhibiting p-tau accumulation in the LHA could prevent neuronal loss in AD and, perhaps, the progression of the disease.

Neuronal and glial vulnerability of the suprachiasmatic nucleus in tauopathies: evidence from human studies and animal models

Tauopathies, a group of neurodegenerative diseases that includes Alzheimer's disease, commonly lead to disturbances in sleep-wake patterns and circadian rhythm disorders. The circadian rhythm, a recurring 24-hour cycle governing human biological activity, is regulated by the hypothalamic suprachiasmatic nucleus (SCN) and endogenous transcriptional-translational feedback loops. Surprisingly, little attention has been given to investigating tauopathy-driven neuropathology in the SCN and the repercussions of SCN and circadian gene dysfunction in the human brain affected by tauopathies. This review aims to provide an overview of the current literature on the vulnerability of the SCN in tauopathies in humans. Emphasis is placed on elucidating the neuronal and glial changes contributing to the widespread disruption of the molecular circadian clock. Furthermore, this review identifies areas of knowledge requiring further investigation.

Predicting neurodegeneration from sleep related biofluid changes

Sleep-wake disturbances are common in neurodegenerative diseases and may occur years before the clinical diagnosis, potentially either representing an early stage of the disease itself or acting as a pathophysiological driver. Therefore, discovering biomarkers that identify individuals with sleep-wake disturbances who are at risk of developing neurodegenerative diseases will allow early diagnosis and intervention. Given the association between sleep and neurodegeneration, the most frequently analyzed fluid biomarkers in people with sleep-wake disturbances to date include those directly associated with neurodegeneration itself, such as neurofilament light chain, phosphorylated tau, amyloid-beta and alpha-synuclein. Abnormalities in these biomarkers in patients with sleep-wake disturbances are considered as evidence of an underlying neurodegenerative process. Levels of hormonal sleep-related biomarkers such as melatonin, cortisol and orexin are often abnormal in patients with clinical neurodegenerative diseases, but their relationships with the more standard neurodegenerative biomarkers remain unclear. Similarly, it is unclear whether other chronobiological/circadian biomarkers, such as disrupted clock gene expression, are causal factors or a consequence of neurodegeneration. Current data would suggest that a combination of fluid biomarkers may identify sleep-wake disturbances that are most predictive for the risk of developing neurodegenerative disease with more optimal sensitivity and specificity.

Proteostasis failure exacerbates neuronal circuit dysfunction and sleep impairments in Alzheimer's disease

Failed proteostasis is a well-documented feature of Alzheimer's disease, particularly, reduced protein degradation and clearance. However, the contribution of failed proteostasis to neuronal circuit dysfunction is an emerging concept in neurodegenerative research and will prove critical in understanding cognitive decline. Our objective is to convey Alzheimer's disease progression with the growing evidence for a bidirectional relationship of sleep disruption and proteostasis failure. Proteostasis dysfunction and tauopathy in Alzheimer's disease disrupts neurons that regulate the sleep-wake cycle, which presents behavior as impaired slow wave and rapid eye movement sleep patterns. Subsequent sleep loss further impairs protein clearance. Sleep loss is a defined feature seen early in many neurodegenerative disorders and contributes to memory impairments in Alzheimer's disease. Canonical pathological hallmarks, β-amyloid, and tau, directly disrupt sleep, and neurodegeneration of locus coeruleus, hippocampal and hypothalamic neurons from tau proteinopathy causes disruption of the neuronal circuitry of sleep. Acting in a positive-feedback-loop, sleep loss and circadian rhythm disruption then increase spread of β-amyloid and tau, through impairments of proteasome, autophagy, unfolded protein response and glymphatic clearance. This phenomenon extends beyond β-amyloid and tau, with interactions of sleep impairment with the homeostasis of TDP-43, α-synuclein, FUS, and huntingtin proteins, implicating sleep loss as an important consideration in an array of neurodegenerative diseases and in cases of mixed neuropathology. Critically, the dynamics of this interaction in the neurodegenerative environment are not fully elucidated and are deserving of further discussion and research. Finally, we propose sleep-enhancing therapeutics as potential interventions for promoting healthy proteostasis, including β-amyloid and tau clearance, mechanistically linking these processes. With further clinical and preclinical research, we propose this dynamic interaction as a diagnostic and therapeutic framework, informing precise single- and combinatorial-treatments for Alzheimer's disease and other brain disorders.

Understanding Sleep Regulation in Normal and Pathological Conditions, and Why It Matters

Sleep occupies a peculiar place in our lives and in science, being both eminently familiar and profoundly enigmatic. Historically, philosophers, scientists and artists questioned the meaning and purpose of sleep. If Shakespeare's verses from MacBeth depicting "Sleep that soothes away all our worries" and "relieves the weary laborer and heals hurt minds" perfectly epitomize the alleviating benefits of sleep, it is only during the last two decades that the growing understanding of the sophisticated sleep regulatory mechanisms allows us to glimpse putative biological functions of sleep. Sleep control brings into play various brain-wide processes occurring at the molecular, cellular, circuit, and system levels, some of them overlapping with a number of disease-signaling pathways. Pathogenic processes, including mood disorders (e.g., major depression) and neurodegenerative illnesses such Huntington's or Alzheimer's diseases, can therefore affect sleep-modulating networks which disrupt the sleep-wake architecture, whereas sleep disturbances may also trigger various brain disorders. In this review, we describe the mechanisms underlying sleep regulation and the main hypotheses drawn about its functions. Comprehending sleep physiological orchestration and functions could ultimately help deliver better treatments for people living with neurodegenerative diseases.