Disrupted prefrontal neuronal oscillations and morphology induced by sleep deprivation in young APP/PS1 transgenic AD mice

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

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

Urolithin A Prevents Sleep-deprivation-induced Neuroinflammation and Mitochondrial Dysfunction in Young and Aged Mice

Sleep deprivation (SD) has reached epidemic proportions worldwide and negatively affects people of all ages. Cognitive impairment induced by SD involves neuroinflammation and mitochondrial dysfunction, but the underlying mechanisms are largely unknown. Urolithin A (UA) is a natural compound that can reduce neuroinflammation and improve mitochondrial health, but its therapeutic effects in a SD model have not yet been studied. Young (3-months old) and aged (12-months old) mice were sleep deprived for 24 h, and UA (2.5 mg/kg or 10 mg/kg) was injected intraperitoneally for 7 consecutive days before the SD period. Immunofluorescent staining, western blotting, and RT-PCR were employed to evaluate levels of proteins involved in neuroinflammation and mitochondrial function. Transmission electron microscope and Golgi-Cox staining were used to evaluate mitochondrial and neuronal morphology, respectively. Finally, contextual fear conditioning and the Morris water maze test were conducted to assess hippocampal learning and memory. In the hippocampus of young (3 months-old) and aged (12 months-old) mice subjected to 24 h SD, pretreatment with UA prevented the activation of microglia and astrocytes, NF-κB-NLRP3 signaling and IL-1β, IL6, TNF-α cytokine production, thus ameliorating neuroinflammation. Furthermore, UA also attenuated SD-induced mitochondrial dysfunction, normalized autophagy and mitophagy and protected hippocampal neuronal morphology. Finally, UA prevented SD-induced hippocampal memory impairment. Cumulatively, the results show that UA imparts cognitive protection by reducing neuroinflammation and enhancing mitochondrial function in SD mice. This suggests that UA shows promise as a therapeutic for the treatment of SD-induced neurological disorders.

Longitudinal characterization of behavioral, morphological and transcriptomic changes in a tauopathy mouse model

Neurodegenerative disorders, such as Alzheimer's disease (AD), have the gradual onset of neurobiological changes preceding clinical diagnosis by decades. To elucidate how brain dysfunction proceeds in neurodegenerative disorders, we performed longitudinal characterization of behavioral, morphological, and transcriptomic changes in a tauopathy mouse model, P301S transgenic mice. P301S mice exhibited cognitive deficits as early as 3 months old, and deficits in social preference and social cognition at 5-6 months. They had a significant decrease of arborization in basal dendrites of hippocampal pyramidal neurons from 3 months and apical dendrites of PFC pyramidal neurons at 9 months. Transcriptomic analysis of genome-wide changes revealed the enrichment of synaptic gene upregulation at 3 months of age, while most of these synaptic genes were downregulated in PFC and hippocampus of P301S mice at 9 months. These time-dependent changes in gene expression may lead to progressive alterations of neuronal structure and function, resulting in the manifestation of behavioral symptoms in tauopathies.

Gallic Acid Ameliorates Cognitive Impairment Caused by Sleep Deprivation through Antioxidant Effect

Sleep deprivation (SD) has a profound impact on the central nervous system, resulting in an array of mood disorders, including depression and anxiety. Despite this, the dynamic alterations in neuronal activity during sleep deprivation have not been extensively investigated. While some researchers propose that sleep deprivation diminishes neuronal activity, thereby leading to depression. Others argue that short-term sleep deprivation enhances neuronal activity and dendritic spine density, potentially yielding antidepressant effects. In this study, a two-photon microscope was utilized to examine the calcium transients of anterior cingulate cortex (ACC) neurons in awake SD mice in vivo at 24-hour intervals. It was observed that SD reduced the frequency and amplitude of Ca2+ transients while increasing the proportions of inactive neurons. Following the cessation of sleep deprivation, neuronal calcium transients demonstrated a gradual recovery. Moreover, whole-cell patch-clamp recordings revealed a significant decrease in the frequency of spontaneous excitatory post-synaptic current (sEPSC) after SD. The investigation also assessed several oxidative stress parameters, finding that sleep deprivation substantially elevated the level of malondialdehyde (MDA), while simultaneously decreasing the expression of Nuclear Factor erythroid 2-Related Factor 2 (Nrf2) and activities of Superoxide dismutase (SOD) in the ACC. Importantly, the administration of gallic acid (GA) notably mitigated the decline of calcium transients in ACC neurons. GA was also shown to alleviate oxidative stress in the brain and improve cognitive impairment caused by sleep deprivation. These findings indicate that the calcium transients of ACC neurons experience a continuous decline during sleep deprivation, a process that is reversible. GA may serve as a potential candidate agent for the prevention and treatment of cognitive impairment induced by sleep deprivation.

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

Background: Emerging evidence indicates that sleep disorders are the common non-cognitive symptoms of Alzheimer’s disease (AD), and they may contribute to the pathogenesis of this disease. Objective: In this study, we aim to investigate the effect of chronic sleep deprivation (CSD) on AD-related pathologies with a focus on tau phosphorylation and the underlying DNA methylation regulation. Methods: AβPPswe/PS1ΔE9 AD mice and their wild-type (WT) littermates were subjected to a two-month CSD followed by electroencephalography and electromyography recording. The mice were examined for learning and memory evaluation, then pathological, biochemical, and epigenetic assessments including western blotting, immunofluorescence, dot blotting, and bisulfite sequencing. Results: The results show that CSD caused sleep disorders shown as sleep pattern change, poor sleep maintenance, and increased sleep fragmentation. CSD increased tau phosphorylation at different sites and increased the level of tau kinases in AD and WT mice. The increased expression of cyclin-dependent kinase 5 (CDK5) may result from decreased DNA methylation of CpG sites in the promoter region of CDK5 gene, which might be associated with the downregulation of DNA methyltransferase 3A and 3B. Conclusion: CSD altered AD-related tau phosphorylation through epigenetic modification of tau kinase gene. The findings in this study may give insights into the mechanisms underlying the effects of sleep disorders on AD pathology and provide new therapeutic targets for the treatment of this disease.

Long-term gamma transcranial alternating current stimulation improves the memory function of mice with Alzheimer’s disease

Background

The main manifestation of Alzheimer’s disease (AD) in patients and animal models is impaired memory function, characterized by amyloid-beta (Aβ) deposition and impairment of gamma oscillations that play an important role in perception and cognitive function. The therapeutic effect of gamma band stimulation in AD mouse models has been reported recently. Transcranial alternating current stimulation (tACS) is an emerging non-invasive intervention method, but at present, researchers have not completely understood the intervention effect of tACS. Thus, the intervention mechanism of tACS has not been fully elucidated, and the course of treatment in clinical selection also lacks theoretical support. Based on this issue, we investigated the effect of gamma frequency (40 Hz) tACS at different durations in a mouse model of AD.

Materials and methods

We placed stimulating electrodes on the skull surface of APP/PS1 and wild-type control mice (n = 30 and n = 5, respectively). Among them, 20 APP/PS1 mice were divided into 4 groups to receive 20 min 40 Hz tACS every day for 1–4 weeks. The other 10 APP/PS1 mice were equally divided into two groups to receive sham treatment and no treatment. No intervention was performed in the wild-type control mice. The short-term memory function of the mice was examined by the Y maze. Aβ levels and microglia in the hippocampus were measured by immunofluorescence. Spontaneous electroencephalogram gamma power was calculated by the average period method, and brain connectivity was examined by cross-frequency coupling.

Results

We found that the long-term treatment groups (21 and 28 days) had decreased hippocampal Aβ levels, increased electroencephalogram spontaneous gamma power, and ultimately improved short-term memory function. The treatment effect of the short-term treatment group (7 days) was not significant. Moreover, the treatment effect of the 14-day treatment group was weaker than that of the 21-day treatment group.

Conclusion

These results suggest that long-term gamma-frequency tACS is more effective in treating AD by reducing Aβ load and improving gamma oscillation than short-term gamma-frequency tACS.

Minocycline inhibits sleep deprivation-induced aberrant microglial activation and Keap1-Nrf2 expression in mouse hippocampus

Sleep deprivation (SD) is a hallmark of modern society and associated with many neuropsychiatric disorders, including depression and anxiety. However, the cellular and molecular mechanisms underlying SD-associated depression and anxiety remain elusive. Does the neuroinflammation play a role in mediating the effects of SD? In this study, we investigated SD-induced cellular and molecular alterations in the hippocampus and asked whether treatment with an anti-inflammatory drug, minocycline, could attenuate these alterations. We found that SD animals exhibit activated microglia and decreased levels of Keap1 and Nrf2 (antioxidant and anti-inflammatory factors) in the hippocampus. In vivo local field potential recordings show decreased theta and beta oscillations, but increased high gamma oscillations, as a result of SD. Behavioral analysis revealed increased immobility time in the forced swim and tail suspension tests, and decreased sucrose intake in SD mice, all indicative of depressive-like behavior. Moreover, open field test and elevated plus maze test results indicated that SD increases anxiety-like behavior. Interestingly, treatment with the microglial modulator minocycline prevented SD-induced microglial activation, restored Keap1 and Nrf2 levels, normalized neuronal oscillations, and alleviated depressive-like and anxiety-like behavior. The present study reveals that microglial activation and Keap1-Nrf2 signaling play a crucial role in SD-induced behavioral alteration, and that minocycline treatment has a protective effect on these alterations.