Sleep restoration by optogenetic targeting of GABAergic neurons reprograms microglia and ameliorates pathological phenotypes in an Alzheimer's disease model

Beyond surgery: Repurposing anesthetics for treatment of central nervous system disorders

The development of new drugs is a complex, expensive, and time-consuming process, often fraught with a high likelihood of failure. Amid these obstacles, drug repurposing, which identifies new therapeutic applications for already existing medications, offers a more economical and time-saving approach, particularly in the challenging field of neurological and psychiatric disorders. This narrative review explores both preclinical and clinical studies to examine the potential of anesthetics such as ketamine, nitrous oxide, isoflurane, sevoflurane, propofol, dexmedetomidine, and sodium oxybate in treating central nervous system disorders. Various research highlights the potential of anesthetics to provide rapid antidepressant effects, enhance learning and memory, improve synaptic plasticity, and offer neuroprotective benefits, demonstrating promise for treating depression, post-traumatic stress disorder, cognitive decline, traumatic brain injury, and neurodegenerative disorders. Anesthetics appear to alleviate symptoms in neurological conditions, likely by modulating GABAergic and glutamatergic pathways. However, challenges such as dose-dependent neurotoxicity, variability in preclinical and clinical outcomes, as well as environmental concerns remain significant issues. Future research is essential to optimize dosing strategies, ensure long-term safety, and gain a deeper understanding of the precise mechanisms of action. The concept of anesthetics' repurposing presents a unique solution to tackle the challenges in neurological and psychiatric therapy by providing a platform for the development of new and improved therapies.

Latent mechanisms of plasticity are upregulated during sleep

Sleep is thought to serve an important role in learning and memory, but the mechanisms by which sleep promotes plasticity remain unclear. Even in the absence of plastic changes in neuronal function, many molecular, cellular, and physiological processes linked to plasticity are upregulated during sleep. Therefore, sleep may be a state in which latent plasticity mechanisms are poised to respond following novel experiences during prior wake. Many of these plasticity-related processes can promote both synaptic strengthening and weakening. Signaling pathways activated during sleep may interact with complements of proteins, determined by the content of prior waking experience, to establish the polarity of plasticity. Furthermore, precise reactivation of neuronal spiking patterns during sleep may interact with ongoing neuromodulatory, dendritic, and network activity to strengthen and weaken synapses. In this review, we will discuss the idea that sleep elevates latent plasticity mechanisms, which drive bidirectional plasticity depending on prior waking experience.

Application of Optogenetic Neuromodulation in Regulating Depression

Depression is a multifaceted disorder with a largely unresolved etiology influenced by a complex interplay of pathogenic factors. Despite decades of research, it remains a major condition that significantly diminishes patients' quality of life. Advances in optogenetics have introduced a powerful tool for exploring the neural mechanisms underlying depression. By selectively expressing optogenes in specific cell types in mice, researchers can study the roles of these cells through targeted light stimulation, offering new insights into central nervous system disorders. The use of viral vectors to express opsins in distinct neuronal subtypes enables precise activation or inhibition of these neurons via light. When combined with behavioral, morphological, and electrophysiological analyses, optogenetics provides an invaluable approach to investigating the neural mechanisms of psychiatric conditions. This review synthesizes current research on the application of optogenetics to understand the mechanisms of depression. This study aims to enhance our knowledge of optogenetic strategies for regulating depression and advancing antidepressant research.

Preoperative Sleep Deprivation Exacerbates Anesthesia/Surgery-induced Abnormal GABAergic Neurotransmission and Neuronal Damage in the Hippocampus in Aged Mice

Older adults with anesthesia and surgery often suffer from postoperative cognitive dysfunction (POCD), which puts a heavy burden on rehabilitation. Preoperative sleep disorder, a common phenomenon in elderly anesthesia patients, is closely associated with POCD, but the underlying mechanism is still not fully understood. Hippocampal gamma-aminobutyric acid (GABA)ergic neurotransmission has been reported to play an important role in sleep disorder and cognitive impairment. The aim of this study was to elucidate the effect of preoperative acute sleep deprivation (SD) on anesthesia/surgery-induced POCD and the potential mechanism of hippocampal GABAergic neurotransmission. In the aged (18-20-month-old) male mice, we used a rotating rod to deprive sleep for 24 h and induced a POCD model using sevoflurane exposure combined with laparotomy exploration. A sequential set of behavioral tests, including open field test (OFT), Y-maze, and novel object recognition (NOR), was conducted to assess cognitive performances. In vivo magnetic resonance imaging (MRI) technique was used to observe hippocampal axonal microstructural changes. The levels of GABAergic neurotransmitter markers glutamic acid decarboxylase (GAD) 67, vesicular GABA transporter (VGAT), GABA transporter (GAT)-1, and GABA in the hippocampus were detected with enzyme-linked immunosorbent assay (ELISA). The reactivity of GABAergic neurons and neuronal damage in different subregions of the hippocampus were observed by immunofluorescence and Nissl staining, respectively. Compared the anesthesia/surgery (A/S) mice, 24-h SD combined with A/S induced shorter stay time in the central area of the open field, less the percent of novel arm preference in the Y maze, and lower recognition index in the NOR, as well as significantly enhanced hippocampal GABAergic neurotransmission, decreased hippocampal axonal integrity and density, and increased GAD67 reactivity and reduced the number of neurons in hippocampal CA1. Preoperative 24-h SD exacerbated anesthesia/surgery-induced POCD in aged mice, with the cumulative effect of abnormal GABAergic neurotransmission and neuronal damage in the hippocampus.

The night's watch: Exploring how sleep protects against neurodegeneration

Sleep loss is often regarded as an early manifestation of neurodegenerative diseases given its common occurrence and link to cognitive dysfunction. However, the precise mechanisms by which sleep disturbances contribute to neurodegeneration are not fully understood, nor is it clear why some individuals are more susceptible to these effects than others. This review addresses critical unanswered questions in the field, including whether sleep disturbances precede or result from neurodegenerative diseases, the functional significance of sleep changes during the preclinical disease phase, and the potential role of sleep homeostasis as an adaptive mechanism enhancing resilience against cognitive decline and neurodegeneration.

Could sleep be a brain/cognitive/neural reserve-builder factor? A systematic review on the cognitive effects of sleep modulation in animal models

The brain/cognitive/neural reserve concept suggests that lifelong experiences, from early life through adulthood, make the brain more resilient to neuronal damage. Modifiable lifestyle factors, such as sleep, can support the development and enhance such a reserve, helping to counteract age- or disease-related brain changes and their impact on cognition. Sleep plays a crucial role in cognitive functioning, and disruptions or disorders may increase neurodegenerative risks. This systematic review aims to explore how functional and disturbed sleep impacts cognitive functions and neuromorphological mechanisms in rodents, aiming to better understand its role in brain/cognitive/neural reserve development. This systematic review, registered on PROSPERO (ID: CRD42023423901) and conducted according to PRISMA-P guidelines, searched PubMed, Scopus, Web of Science, and Embase databases for studies up to June 2022, with terms related to sleep, rodents, and cognitive functions. Of the 28,666 articles identified, 142 met the inclusion criteria. Main results showed significant cognitive decline after sleep deprivation, especially in memory performance. These findings supports the importance of sleep as a critical factor in modulating brain/cognitive/neural reserve.

Pharmacological enhancement of slow-wave activity at an early disease stage improves cognition and reduces amyloid pathology in a mouse model of Alzheimer's disease

Introduction

Improving sleep in murine Alzheimer's disease (AD) is associated with reduced brain amyloidosis. However, the window of opportunity for successful sleep-targeted interventions, regarding the reduction in pathological hallmarks and related cognitive performance, remains poorly characterized.

Methods

Here, we enhanced slow-wave activity (SWA) during sleep via sodium oxybate (SO) oral administration for 2 weeks at early (6 months old) or moderately late (11 months old) disease stages in Tg2576 mice and evaluated resulting neuropathology and behavioral performance.

Results

We observed that the cognitive performance of 6-month-old Tg2576 mice significantly improved upon SO treatment, whereas no change was observed in 11-month-old mice. Histochemical assessment of amyloid plaques demonstrated that SO-treated 11-month-old Tg2576 mice had significantly less plaque burden than placebo-treated ones, whereas ELISA of insoluble protein fractions from brains of 6-month-old Tg2576 mice indicated lower Aβ-42/Aβ-40 ratio in SO-treated group vs. placebo-treated controls.

Discussion

Altogether, our results suggest that SWA-dependent reduction in brain amyloidosis leads to alleviated behavioral impairment in Tg2576 mice only if administered early in the disease course, potentially highlighting the key importance of early sleep-based interventions in clinical cohorts.

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.

S100A8 knockdown activates the PI3K/AKT signaling pathway to inhibit microglial autophagy and improve cognitive impairment mediated by chronic sleep deprivation

OBJECTIVE

Cognitive dysfunction is one of the major symptoms of chronic sleep deprivation (CSD). Abnormal autophagy and apoptosis are thought to be important mechanisms. S100 Calcium Binding Protein A8 (S100A8) plays a key role in autophagy and apoptosis of microglia. This study investigated whether S100A8 knockdown can effectively inhibit aberrant autophagy in microglia and improve cognitive function by activating the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) signaling pathway under CSD conditions.

METHODS

CSD mouse models and BV2 cell autophagy models were established in vivo and in vitro. Transcriptome sequencing was used to determine the key regulator related to autophagy. The Morris water maze test was used to evaluate the cognitive behavior of the mice. RT-qPCR and western blot were conducted to examine S100A8 expression and autophagy signalling. HE, TUNEL, transmission electron microscopy, immunofluorescence, and histochemistry were performed to detect pathological changes, neuronal autophagy, apoptosis, or positive cells in hippocampal tissues, respectively.

RESULTS

Transcriptome sequencing showed that S100A8 was significantly elevated in CSD mice, and fluorescence colocalization results further suggested that S100A8 mainly colocalizes with microglia. In vivo studies revealed that knockdown of S100A8 alleviated CSD-induced cognitive impairment in mice. Through further mechanistic investigations employing both in vivo and in vitro models, we demonstrated that silencing S100A8 can activate the PI3K/AKT pathway, thereby reducing CSD-induced abnormal autophagy and apoptosis in microglia. Aberrant autophagy and apoptosis in microglia were reversed with the PI3K/AKT pathway inhibitor LY294002.

CONCLUSION

The S100A8/PI3K/AKT axis plays a crucial role in chronic sleep deprivation-mediated autophagy and apoptosis in microglia.

Alzheimer's disease and sleep disorders: A bidirectional relationship

Alzheimer's disease (AD) is the most prevalent dementia, pathologically featuring abnormal accumulation of amyloid-β (Aβ) and hyperphosphorylated tau, while sleep, divided into rapid eye movement sleep (REM) and nonrapid eye movement sleep (NREM), plays a key role in consolidating social and spatial memory. Emerging evidence has revealed that sleep disorders such as circadian disturbances and disruption of neuronal rhythm activity are considered as both candidate risks and consequence of AD, suggesting a bidirectional relationship between sleep and AD. This review will firstly grasp basic knowledge of AD pathogenesis, then highlight macrostructural and microstructural alteration of sleep along with AD progression, explain the interaction between accumulation of Aβ and hyperphosphorylated tau, which are two critical neuropathological processes of AD, as well as neuroinflammation and sleep, and finally introduce several methods of sleep enhancement as strategies to reduce AD-associated neuropathology. Although theories about the bidirectional relationship and relevant therapeutic methods in mice have been well developed in recent years, the knowledge in human is still limited. More studies on how to effectively ameliorate AD pathology in patients by sleep enhancement and what specific roles of sleep play in AD are needed.

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.

Frontiers and hotspots evolution in anti-inflammatory studies for Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative disorder that seriously affects the quality of the elderly's lives worldwide. The main pathological features of AD are amyloid plaques formed by β-amyloid (Aβ) and neuronal fibrillary tangls (NFTs) formed by hyperphosphorylated Tau protein. The formation process of these pathological features is closely related to inflammatory response, so anti-inflammatory treatment has become a potential treatment for AD. In recent years, more and more research has shown that the anti-inflammatory therapy can relieve the symptoms of AD and improve cognitive function, which provides a valuable research direction for the treatment of AD strategy. Therefore, a comprehensive understanding of the hotspots and development trends of AD anti-inflammatory research is important for promoting the further development of this field and improving the quality of life of patients.

METHODS

This study used bibliometric methods, with AD and anti-inflammatory as key words, collected 7638 AD anti-inflammatory studies collected in Web of Science Core Collection (WoSCC) literature database since 2000, and conducted an in-depth analysis of the research hotspots and potential trends in this field.

RESULTS

The depth and breadth of AD anti-inflammatory research are in the stage of rapid development, and the hot focus is on exploring the role of inflammation in the pathogenesis of AD, especially the interaction of microglia in the neuroinflammatory mechanism. Secondly, the treatment effect and potential risks of anti-inflammatory drugs such as non-steroidal anti-inflammatory drugs (NSAIDs) on AD are also the focus of research. Therefore, researchers have carried out a series of animal experiments and prospective clinical studies on anti-inflammatory drugs for the treatment of AD, forming a comprehensive research system from basic research to clinical research. As for the future development trend, we believe that the further exploration of inflammation in the pathogenesis of AD will still be one of the key directions, and the application of big data and artificial intelligence technology is expected to provide strong support for the association between inflammation and AD progression. Moreover, the development of novel anti-inflammatory drugs for the inflammatory mechanism of AD will be another major trend for future research. At the same time, personalized treatment strategies and alternative supplements of medicine will also become one of the hotspots of future research. Through the comprehensive use of anti-inflammatory drugs, nutritional supplements, lifestyle intervention and other means, more comprehensive and effective treatment plans for AD patients are expected.

CONCLUSION

This research analyzes the overall development trend of AD anti-inflammatory research field since 2000, and provides a comprehensive perspective for the progress of AD anti-inflammatory research. Overall, the field of AD anti-inflammatory research is facing a broad development prospect. In the future, with further research and technological advances, we have resason to expect more effective and safer treatment options for AD patients to help them improve their quality of life and delay disease progression.

Exploring the Significance of Microglial Phenotypes and Morphological Diversity in Neuroinflammation and Neurodegenerative Diseases: From Mechanisms to Potential Therapeutic Targets

Studying various microglial phenotypes and their functions in neurodegenerative diseases is crucial due to the intricate nature of their phenomics and their vital immunological role. Microglia undergo substantial phenomic changes, encompassing morphological, transcriptional, and functional aspects, resulting in distinct cell types with diverse structures, functions, properties, and implications. The traditional classification of microglia as ramified, M1 (proinflammatory), or M2 (anti-inflammatory) phenotypes is overly simplistic, failing to capture the wide range of recently identified microglial phenotypes in various brain regions affected by neurodegenerative diseases. Altered and activated microglial phenotypes deviating from the typical ramified structure are significant features of many neurodegenerative conditions. Understanding the precise role of each microglial phenotype is intricate and sometimes contradictory. This review specifically focuses on elucidating recent modifications in microglial phenotypes within neurodegenerative diseases. Recognizing the heterogeneity of microglial phenotypes in diseased states can unveil novel therapeutic strategies for targeting microglia in neurodegenerative diseases. Moreover, the exploration of the use of healthy isolated microglia to mitigate disease progression has provided an innovative perspective. In conclusion, this review discusses the dynamic landscape of mysterious microglial phenotypes, emphasizing the need for a nuanced understanding to pave the way for innovative therapeutic strategies for neurodegenerative diseases.

The role of AMPKα subunit in Alzheimer's disease: In-depth analysis and future prospects

The AMP-activated protein kinase α (AMPKα) subunit is the catalytic subunit in the AMPK complex, playing a crucial role in AMPK activation. It has two isoforms: AMPKα1 and AMPKα2. Emerging evidence suggests that the AMPKα subunit exhibits subtype-specific effects in Alzheimer's disease (AD). This review discusses the role of the AMPKα subunit in the pathogenesis of AD, including its impact on β-amyloid (Aβ) pathology, Tau pathology, metabolic disorders, inflammation, mitochondrial dysfunction, inflammasome and pyroptosis. Additionally, it reviews the distinct roles of its isoforms, AMPKα1 and AMPKα2, in AD, which may provide more precise targets for future drug development in AD.

Propofol improves sleep deprivation-induced sleep structural and cognitive deficits via upregulating the BMAL1 expression and suppressing microglial M1 polarization

BACKGROUND

Sleep deprivation (SD) is a growing global health problem with many deleterious effects, such as cognitive impairment. Microglia activation-induced neuroinflammation may be an essential factor in this. Propofol has been shown to clear sleep debt after SD in rats. This study aims to evaluate the effects of propofol-induced sleep on ameliorating sleep quality impairment and cognitive decline after 48 h SD.

METHODS

Almost 8-12-week-old rats were placed in the SD system for 48 h of natural sleep or continuous SD. Afterwards, rats received propofol (20 mg·kg-1·h-1, 6 h) via the tail or slept naturally. The Morris water maze (MWM) and Y-maze test assessed spatial learning and memory abilities. Rat EEG/EMG monitored sleep. The expression of brain and muscle Arnt-like protein 1 (BMAL1), brain-derived neurotrophic factor (BDNF) in the hippocampus and BMAL1 in the hypothalamus were assessed by western blot. Enzyme-linked immunosorbent assay detected IL-6, IL-1β, arginase 1 (Arg1), and IL-10 levels in the hippocampus. Immunofluorescence was used to determine microglia expression as well as morphological changes.

RESULTS

Compared to the control group, the sleep-deprived rats showed poor cognitive performance on both the MWM test and the Y-maze test, accompanied by disturbances in sleep structure, including increased total sleep time, and increased time spent and delta power in non-rapid eye movement sleep. In addition, SD induces abnormal expression of the circadian rhythm protein BMAL1, activates microglia, and causes neuroinflammation and nerve damage. Propofol reversed these changes and saved sleep and cognitive impairment. Furthermore, propofol treatment significantly reduced hippocampal IL-1β and IL-6 levels, increased BDNF, Arg1, and IL-10 levels, and switched microglia surface markers from the inflammatory M1 type to the anti-inflammatory M2 type.

CONCLUSION

Propofol reduces SD-induced cognitive impairment and circadian rhythm disruption, possibly by lowering neuronal inflammation and switching the microglia phenotype from an M1 to an M2 activated state, thus exerting neuroprotective effects.

Sleep-Deep-Learner is taught sleep-wake scoring by the end-user to complete each record in their style

Sleep-wake scoring is a time-consuming, tedious but essential component of clinical and preclinical sleep research. Sleep scoring is even more laborious and challenging in rodents due to the smaller EEG amplitude differences between states and the rapid state transitions which necessitate scoring in shorter epochs. Although many automated rodent sleep scoring methods exist, they do not perform as well when scoring new datasets, especially those which involve changes in the EEG/EMG profile. Thus, manual scoring by expert scorers remains the gold standard. Here we take a different approach to this problem by using a neural network to accelerate the scoring of expert scorers. Sleep-Deep-Learner creates a bespoke deep convolution neural network model for individual electroencephalographic or local-field-potential (LFP) records via transfer learning of GoogLeNet, by learning from a small subset of manual scores of each EEG/LFP record as provided by the end-user. Sleep-Deep-Learner then automates scoring of the remainder of the EEG/LFP record. A novel REM sleep scoring correction procedure further enhanced accuracy. Sleep-Deep-Learner reliably scores EEG and LFP data and retains sleep-wake architecture in wild-type mice, in sleep induced by the hypnotic zolpidem, in a mouse model of Alzheimer's disease and in a genetic knock-down study, when compared to manual scoring. Sleep-Deep-Learner reduced manual scoring time to 1/12. Since Sleep-Deep-Learner uses transfer learning on each independent recording, it is not biased by previously scored existing datasets. Thus, we find Sleep-Deep-Learner performs well when used on signals altered by a drug, disease model, or genetic modification.

Sleep-Deep-Net learns sleep wake scoring from the end-user and completes each record in their style

Sleep-wake scoring is a time-consuming, tedious but essential component of clinical and pre-clinical sleep research. Sleep scoring is even more laborious and challenging in rodents due to the smaller EEG amplitude differences between states and the rapid state transitions which necessitate scoring in shorter epochs. Although many automated rodent sleep scoring methods exist, they do not perform as well when scoring new data sets, especially those which involve changes in the EEG/EMG profile. Thus, manual scoring by expert scorers remains the gold-standard. Here we take a different approach to this problem by using a neural network to accelerate the scoring of expert scorers. Sleep-Deep-Net (SDN) creates a bespoke deep convolution neural network model for individual electroencephalographic or local-field-potential records via transfer learning of GoogleNet, by learning from a small subset of manual scores of each EEG/LFP record as provided by the end-user. SDN then automates scoring of the remainder of the EEG/LFP record. A novel REM scoring correction procedure further enhanced accuracy. SDN reliably scores EEG and LFP data and retains sleep-wake architecture in wild-type mice, in sleep induced by the hypnotic zolpidem, in a mouse model of Alzheimer's disease and in a genetic knock-down study, when compared to manual scoring. SDN reduced manual scoring time to 1/12. Since SDN uses transfer learning on each independent recording, it is not biased by previously scored existing data sets. Thus, we find SDN performs well when used on signals altered by a drug, disease model or genetic modification.