Chronic Intermittent Hypoxia Enhances Pathological Tau Seeding, Propagation, and Accumulation and Exacerbates Alzheimer-like Memory and Synaptic Plasticity Deficits and Molecular Signatures

Obstructive sleep apnea and memory impairments: Clinical characterization, treatment strategies, and mechanisms

Obstructive sleep apnea (OSA), is associated with dysfunction in the cardiovascular, metabolic and neurological systems. However, the relationship between OSA and memory impairment, intervention effects, and underlying pathways are not well understood. This review summarizes recent advances in the clinical characterization, treatment strategies, and mechanisms of OSA-induced memory impairments. OSA patients may exhibit significant memory declines, including impairments in working memory from visual and verbal sources. The underlying mechanisms behind OSA-related memory impairment are complex and multifactorial with poorly understood aspects that require further investigation. Neuroinflammation, oxidative stress, neuronal damage, synaptic plasticity, and blood-brain barrier dysfunction, as observed under exposures to intermittent hypoxia and sleep fragmentation are likely contributors to learning and memory dysfunction. Continuous positive airway pressure treatment can provide remarkable relief from memory impairment in OSA patients. Other treatments are emerging but need to be rigorously evaluated for cognitive improvement. Clinically, reliable and objective diagnostic tools are necessary for accurate diagnosis and clinical characterization of cognitive impairments in OSA patients. The complex links between gut-brain axis, epigenetic landscape, genetic susceptibility, and OSA-induced memory impairments suggest new directions for research. Characterization of clinical phenotypic clusters can facilitate advances in precision medicine to predict and treat OSA-related memory deficits.

Chronic intermittent hypoxia-mediated cognitive dysfunction in ovariectomized rats

Obstructive sleep apnoea (OSA) is a prevalent cardiorespiratory disorder associated with significant neurocognitive consequences. Despite the higher prevalence of OSA in men, there is a strong association between OSA and Alzheimer's disease (AD), which disproportionately affects women. This study aimed to investigate the impact of chronic intermittent hypoxia (CIH), a hallmark of OSA, on cognitive function and AD markers in ovariectomized, female rats. At 8 weeks of age, 16 Sprague-Dawley rats underwent ovariectomy and were exposed to CIH for 26 weeks. Cognitive function was assessed using the Morris water maze, revealing significant deficits in spatial learning (P < 0.0001) and memory (P = 0.008) in CIH-exposed rats, compared to controls. Analysis of hippocampal tissue showed increased total tau protein (P = 0.0078), indicative of AD pathology. Additionally, CIH-exposed rats exhibited respiratory dysfunction characterized by increased frequency of apnoeas (P = 0.0328). These findings provide preclinical evidence of the association between OSA, cognitive decline and AD pathology in females, emphasizing the importance of sex-specific research in understanding and addressing these pathophysiological interconnections.

P3a, P3b Characteristics of OSA Patients in the Acute Stroke Population

Objective: To investigate the neurophysiological and cognitive impairments in patients with obstructive sleep apnea (OSA) among the acute stroke population. Methods: A total of 268 acute ischemic stroke patients with OSA underwent sleep monitoring within 24 h of admission and event-related potential tests within three days. They were categorized into groups based on their AHI: stroke only, and stroke with mild, moderate, or severe OSA. This classification served to analyze the electrophysiological profiles associated with stroke and OSA severity. Results: Compared with the control group, in the P3b series, the P3b-FZ amplitude was significantly reduced in the stroke with mild, moderate, and severe OSA group; the N2-PZ latency was significantly prolonged in the stroke with severe OSA group; and the P3b-FZ, P3b-CZ, and P3b-FZ latencies were significantly prolonged in the stroke with mild, moderate, and severe OSA group; in the P3a series, the N2-CZ amplitude was decreased in the stroke with severe OSA group, P2-FZ latency was significantly prolonged in the stroke with mild and moderate OSA group, P3a-FZ latency was significantly prolonged in the stroke with mild OSA group, P3a-CZ latency was significantly prolonged in the stroke with severe OSA group, and P3a-PZ latency was significantly prolonged in the stroke with mild and severe OSA group. Conclusions: The electrophysiologic changes compared with the stroke-only group were mainly characterized by prolonged latencies of the endogenous components P3a and P3b, suggesting that they are related to attention allocation and cognitive control.

Targeting hypoxia-related pathobiology in Alzheimer's disease: strategies for prevention and treatment

INTRODUCTION

Alzheimer's Disease (AD) is a neurodegenerative condition characterised by cognitive decline and memory impairment. Recent research highlights the important role of hypoxia, a state of insufficient oxygen availability, in exacerbating AD pathogenesis.

MATERIALS AND METHODS

Through the use of a number of different search engines like Scopus, PubMed, Bentham, and Elsevier databases, a literature review was carried out for investigating the role of hypoxia mediated pathobiology in AD. Only peerreviewed articles published in reputable journals in English language were included. Conversely, non-peer-reviewed articles, conference abstracts, and editorials were excluded, along with studies lacking experimental or clinical relevance or those unavailable in full text.

CONCLUSION

Hypoxia exacerbates core pathological features such as oxidative stress, neuroinflammation, mitochondrial dysfunction, amyloid-beta (Aβ) dysregulation, and hyperphosphorylation of tau protein. These interlinked mechanisms establish a self-perpetuating cycle of neuronal damage, accelerating disease progression. Addressing hypoxia as a modifiable risk factor offers potential for both prevention and treatment of AD. Exploring hypoxia and the HIF signalling pathway may help counteract the neuropathological and symptomatic effects of neurodegeneration.

Chronic intermittent hypoxia exposure induces a unique microglial transcriptome in 5XFAD mice

Clinical observations suggest that obstructive sleep apnea (OSA) and Alzheimer's disease (AD) pathology may be linked; however, causal mechanisms and relationships are unclear. To investigate the potential interaction between amyloidosis and intermittent hypoxia (IH), a hallmark of OSA, starting at 4-months of age 5XFAD mice were exposed to chronic IH (CIH) consisting of 20 episodes per hour of hypoxia for 12 hours/day, daily for 4- (males) or 6-months (females). CIH did not induce significant changes in amyloid burden or the number of astrocytes in males or females, but there was a slight decrease in the number of microglia observed in the cortex of 5XFAD mice of both sexes. To further explore this effect, we performed bulk RNA sequencing on isolated microglia. In WT mice, the most robust gene changes induced by CIH were identified in male microglia, many of which were pro-inflammatory. In microglia from 5XFAD mice, compared to NX, CIH exposure induced comparatively more DEGs in males. Further, in genes that were upregulated by CIH in WT vs 5XFAD mice of both sexes, there was an enrichment of pathways associated with oxidative phosphorylation, aerobic and cellular respiration, and ATP synthesis. These changes indicate that CIH has a more robust effect on the microglial transcriptome in 5XFAD mice than in WT mice, suggesting that the synergy between AD and OSA pathologies may be driven by metabolic changes in the microglial transcriptome. These observations are particularly interesting given the known sex differences in OSA and AD pathology in human disease.

Prevalence and Misperception: Exploring the Gap Between Objective and Subjective Assessment of Sleep Apnea in a Population at Increased Risk for Dementia

Background: Aging is a well-established independent risk factor for both cognitive impairment and sleep disorders, including obstructive sleep apnea (OSA), a modifiable yet underrecognized condition. OSA has been implicated in biological mechanisms contributing to Alzheimer's disease, including amyloid-β accumulation, tau phosphorylation, and neuroinflammation. This underscores the need to optimize OSA diagnosis in individuals with an increased risk of dementia. Methods: This cross-sectional observational study enrolled adults aged 60-85 years with a CAIDE dementia risk score ≥6. Subjective sleep was evaluated using validated questionnaires (Pittsburgh Sleep Quality Index, Epworth Sleepiness Scale, and the Oviedo Sleep Questionnaire), while objective sleep data were obtained through a single-night peripheral arterial tonometry (PAT)-based wearable device, complemented by a 7-day sleep diary. Participants also completed the STOP-BANG and Berlin questionnaires, with clinically relevant findings communicated to participants. Results: Among 322 participants (48.8% women; mean age 71.4 ± 6.4 years), moderate-to-severe OSA (apnea-hypopnea index [AHI] ≥ 15) was identified in 48.49%, despite the absence of prior diagnoses. Subjective screening tools frequently underestimated OSA severity compared to objective assessments. While no significant sex-based differences were noted, higher AHI values correlated strongly with increased body mass index and elevated dementia risk scores. Conclusions: A marked discrepancy between subjective and objective sleep measurements complicates the accurate diagnosis and management of most sleep disorders, including OSA. Sleep disorders remain significantly underdiagnosed in individuals at increased risk for dementia. Integrating wearable technologies and structured tools such as sleep diaries into routine assessments can enhance diagnostic precision, enabling timely interventions for these modifiable risk factors of dementia.

Chronic Intermittent Hypoxia-Induced Neural Injury: Pathophysiology, Neurodegenerative Implications, and Therapeutic Insights

Obstructive sleep apnea-hypopnea syndrome (OSAHS) is a sleep-related respiratory disorder that poses a global threat to human health. Chronic intermittent hypoxia (CIH) is its main pathological feature. With the advancements in medical research, the study of CIH-induced neural injury has gained increasing attention. Studies have shown that CIH can lead to or aggravate neuroinflammation and apoptosis by increasing blood-brain barrier (BBB) permeability, promoting oxidative stress, activating glial cells, and triggering multiple signaling pathways, ultimately resulting in neural injury. These processes contribute to the development of Alzheimer's disease, Parkinson's disease, and stroke. This review aims to summarize the progress in CIH-induced neural injury and explore various underlying mechanisms, with the goal of providing new insights for the development of therapeutic interventions targeting CIH-related neural damage.

Impact of sleep apnea on alzheimer's disease in relation to sex: an 8-year longitudinal follow-up study of a nationwide cohort

BACKGROUND

We aimed to investigate the association between sleep apnea and incident dementia (dementia of the Alzheimer type [DAT] and vascular dementia) and whether differences in the effects of sleep apnea on dementia depend on sex. Furthermore, we sought to determine whether obesity affects the sex-specific relationship between sleep apnea and dementia.

METHODS

We used de-identified data on patients with sleep apnea and a control group aged ≥ 50 years from the Korean National Health Insurance Service. After propensity score matching to balance age and sex between the patient and control groups, 30,111 individuals with sleep apnea (patient group) and 121,528 individuals without sleep apnea (control group) were included. To investigate the impact of sleep apnea on the development of dementia, we used Cox proportional hazards regression after controlling for potential confounders.

RESULTS

Sleep apnea was predictive of developing DAT in both women (hazard ratio [HR] = 1.30, 95% confidence interval [CI] 1.16-1.44, p < 0.001) and men (HR = 1.13, 95% CI 1.03-1.24, p = 0.012). The adverse effects of sleep apnea on DAT were more prominent in women than in men (p = 0.015 for sleep apnea×sex). Furthermore, obesity affected the sex-specific relationship between sleep apnea and DAT. Specifically, the adverse effects of obese sleep apnea on the DAT were more pronounced in women than in men (p = 0.002 for obese sleep apnea×sex). In contrast, there were no differences in the effects of non-obese sleep apnea on DAT between women and men (p = 0.667 for non-obese sleep apnea×sex).

CONCLUSIONS

Our results highlight sex differences in the adverse effects of sleep apnea on DAT. Furthermore, these results suggest that sex-specific strategies for controlling sleep apnea are necessary to prevent DAT.

Association of Polygenic Risk Score for 5 Diseases With Alzheimer Disease Progression, Biomarkers, and Amyloid Deposition

BACKGROUND AND OBJECTIVES

Alzheimer disease (AD) is a heterogeneous neurodegenerative disorder influenced by genetic and environmental factors. Conditions such as type 2 diabetes (T2D), cardiovascular disease, obesity, depression, and obstructive sleep apnea (OSA) increase AD risk and progression. This study aimed to examine the genetic predisposition to these conditions and their effect on AD pathophysiology, risk, and progression.

METHODS

A retrospective analysis was conducted using data from the Alzheimer's Disease Neuroimaging Initiative (ADNI), a North American prospective cohort. Polygenic risk scores (PRSs) for OSA, T2D, coronary artery disease (CAD), major depression, and body mass index (BMI) were generated for 752 non-Hispanic White participants with whole-genome sequencing data. Logistic regression was used to evaluate associations between PRSs and progression from mild cognitive impairment (MCI) to AD. Time to progression across PRS quartiles was analyzed using Cox proportional hazards models. PET amyloid and tau deposition rates, regional neocortical atrophy, and cognitive composite score declines were compared across OSA PRS quartiles using analysis of variance (ANOVA).

RESULTS

Among 463 ADNI participants with baseline MCI (mean age 72.6 ± 7.3 years, 43.4% female), the OSA PRS, adjusted for BMI, was significantly associated with MCI-to-AD progression. The highest OSA PRS quartile had an odds ratio of 1.86 (95% CI 1.03-3.37) at 3 years and 2.02 (95% CI 1.16-3.51) at 5 years, compared with the lowest quartile. PRSs for T2D, CAD, major depression, and BMI were not associated with MCI-to-AD progression. Participants in the highest OSA PRS quartile had higher PET amyloid deposition and greater cognitive decline. In 752 participants (mean age 74.1 ± 7.3 years, 43.6% female), OSA PRS was significantly associated with baseline levels of PET amyloid, CSF amyloid-β 42, phosphorylated tau (p-tau), visinin-like protein 1, tumor necrosis factor receptor 1, and plasma neurofilament light after multiple testing adjustments.

DISCUSSION

Individuals with high polygenic susceptibility to OSA exhibited an increased risk of MCI-to-AD progression and a higher amyloid deposition rate, suggesting potential modifier effects of OSA or OSA-associated genes on AD progression and pathophysiology. However, the small sample size and lack of objective OSA diagnosis limit interpretation of these genetic effects.

miR-448-3p/miR-1264-3p Participates in Intermittent Hypoxic Response in Hippocampus by Regulating Fam76b/hnRNPA2B1

BACKGROUND

Intermittent hypoxia (IH), as a key pathogenic factor of obstructive sleep apnea syndrome (OSAS), can cause many diseases, such as increased inflammation and oxidative stress, diabetes, cardiovascular disease, and Alzheimer's disease (AD). The response of cells to hypoxia involves multiple levels of regulatory mechanisms, including transcriptional regulation of gene expression, regulation of mRNA stability, post-transcriptional regulation, and post-translational modification regulation.

AIMS

The regulation of miRNA and alternative splicing (AS) in neuronal response to intermittent hypoxia deserve further study.

MATERIALS & METHODS

By establishing a mouse model of intermittent hypoxia, we conducted functional studies on key miRNAs and splicing factor using methods such as miRNA sequencing, bioinformatics, and molecular biology.

RESULTS

In the mouse hippocampus, intermittent hypoxia altered the expression of many miRNAs, with miR-448-3p and miR-1264-3p changing over the course of more than three time periods. Interestingly, the expression of Fam76b, the common target gene of these two miRNAs, also changed under intermittent hypoxia. Further studies showed that Fam76b may regulate the ratio of Nbr1 and Dph3 transcripts in response to hypoxia by affecting the localization of hnRNPA2B1 protein within cells.

DISCUSSION

Research into intermittent hypoxia-induced disorders, including Alzheimer's disease and other neurodegenerative diseases, might benefit from a better understanding of the regulatory mechanisms of miRNA and alternative splicing in hypoxic response at the animal and cell levels.

CONCLUSION

This study demonstrates that intermittent hypoxia alters the expression of miR-448-3p and miR-1264-3p, as well as the localization of the splicing factor hnRNPA2B1 in the cell nucleus. These findings enhance our understanding of the molecular mechanisms of neuronal responses to hypoxia and hold potential implications for treating hypoxia-related diseases like Alzheimer's disease.

Curcumin reverses cognitive deficits through promoting neurogenesis and synapse plasticity via the upregulation of PSD95 and BDNF in mice

Following prolonged exposure to hypoxic conditions, for example, due to ascent to high altitude, aging or stroke, cognitive deficits can develop. The exact nature and genesis of hypoxia-induced cognitive deficits remain unresolved. Curcumin has been reported to stimulate neurogenesis and reduce neuronal degeneration. This study aimed to investigate the effect of curcumin on cognitive deficits in hypoxic-brain injury mice and its potential mechanism. Eight-week-old male C57BL/6J mice were exposure to normobaric-hypoxia (13%O2) 14 days to establish hypoxic-brain injury models. Morris water maze and novel object recognition were used to detect the cognitive function of each mouse. Immunofluorescence assays, including Fluoro-Jade C (FJC) and bromodeoxyuridine (BrdU), were used to detect neuronal degeneration and neurogenesis. Thy1-YFP transgenic mice were used to detect synapse plasticity. Our results showed that curcumin administration rescued the impaired cognition of mice, shown as enhanced BrdU+ and dendritic spine in hippocampus. At the molecular level, curcumin was found to promote the expression of brain-derived neurotrophic factor (BDNF) and postsynaptic density protein 95 (PSD95). The results of primary hippocampal neuron detection showed that curcumin could promote dendritic growth. In conclusion, our study indicates that curcumin, increased BDNF and PSD95 expression and contacted with interneurons, salvaged of interneurons may normalize ambient neuroplasticity, resulting in the preservation of neurogenesis processes as well as contributing to improve cognitive performance.

Melatonin attenuates intermittent hypoxia-induced cognitive impairment in aged mice: The role of inflammation and synaptic plasticity

Intermittent hypoxia (IH), a major pathophysiologic alteration in obstructive sleep apnea syndrome (OSAS), is an important contributor to cognitive impairment. Increasing research suggests that melatonin has anti-inflammatory properties and improves functions related to synaptic plasticity. However, it is unclear whether melatonin has a protective effect against OSAS-induced cognitive dysfunction in aged individuals and the involved mechanisms are also unclear. Therefore, in the study, the effects of exposure to IH alone and IH in combination with daily melatonin treatment were investigated in C57BL/6 J mice aged 18 months. Assessment of the cognitive ability of mice in a Morris water maze showed that melatonin attenuated IH-induced impairment of learning and memory in aged mice. Enzyme-linked immunosorbent assay, polymerase chain reaction, and western blotting molecular techniques showed that melatonin treatment reduced the levels of the proinflammatory cytokines, interleukin-1β, interleukin-6, and tumor necrosis factor-α, decreased the levels of NOD-like receptor thermal protein domain associated protein 3 and nuclear factor kappa-B, lowered the levels of ionized calcium-binding adapter molecule 1 and glial fibrillary acidic protein, and increased the levels of the synaptic proteins, activity-regulated cytoskeleton-associated protein, growth-associated protein-43, postsynaptic density protein 95, and synaptophysin in IH-exposed mice. Moreover, electrophysiological results showed that melatonin ameliorated the decline in long-term potentiation induced by IH. The results suggest that melatonin can ameliorate IH-induced cognitive deficits by inhibiting neuroinflammation and improving synaptic plasticity in aged mice.

MCC950 as a promising candidate for blocking NLRP3 inflammasome activation: A review of preclinical research and future directions

The NOD-like receptor thermal protein domain associated protein 3 (NLRP3) inflammasome is a key component of the innate immune system that triggers inflammation and pyroptosis and contributes to the development of several diseases. Therefore, blocking the activation of the NLRP3 inflammasome has therapeutic potential for the treatment of these diseases. MCC950, a selective small molecule inhibitor, has emerged as a promising candidate for blocking NLRP3 inflammasome activation. Ongoing research is focused on elucidating the specific targets of MCC950 as well as assessfing its metabolism and safety profile. This review discusses the diseases that have been studied in relation to MCC950, with a focus on stroke, Alzheimer's disease, liver injury, atherosclerosis, diabetes mellitus, and sepsis, using bibliometric analysis. It then summarizes the potential pharmacological targets of MCC950 and discusses its toxicity. Furthermore, it traces the progression from preclinical to clinical research for the treatment of these diseases. Overall, this review provides a solid foundation for the clinical therapeutic potential of MCC950 and offers insights for future research and therapeutic approaches.

Hypoxia Pathways in Parkinson's Disease: From Pathogenesis to Therapeutic Targets

The human brain is highly dependent on oxygen, utilizing approximately 20% of the body's oxygen at rest. Oxygen deprivation to the brain can lead to loss of consciousness within seconds and death within minutes. Recent studies have identified regions of the brain with spontaneous episodic hypoxia, referred to as "hypoxic pockets". Hypoxia can also result from impaired blood flow due to conditions such as heart disease, blood clots, stroke, or hemorrhage, as well as from reduced oxygen intake or excessive oxygen consumption caused by factors like low ambient oxygen, pulmonary diseases, infections, inflammation, and cancer. Severe hypoxia in the brain can manifest symptoms similar to Parkinson's disease (PD), including cerebral edema, mood disturbances, and cognitive impairments. Additionally, the development of PD appears to be closely associated with hypoxia and hypoxic pathways. This review seeks to investigate the molecular interactions between hypoxia and PD, emphasizing the pathological role of hypoxic pathways in PD and exploring their potential as therapeutic targets.

Neuronal ferroptosis and ferroptosis-mediated endoplasmic reticulum stress: Implications in cognitive dysfunction induced by chronic intermittent hypoxia in mice

Obstructive sleep apnea, typically characterized by chronic intermittent hypoxia (CIH), is linked to cognitive dysfunction in children. Ferroptosis, a novel form of cell death characterized by lethal iron accumulation and lipid peroxidation, is implicated in neurodegenerative diseases and ischemia-reperfusion injuries. Nevertheless, its contribution to CIH-induced cognitive dysfunction and its interaction with endoplasmic reticulum stress (ERS) remain uncertain. In this study, utilizing a CIH model in 4-week-old male mice, we investigated ferroptosis and its potential involvement in ERS regulation during cognitive dysfunction. Our findings indicate ferroptosis activation in prefrontal cortex neurons, leading to neuron loss, mitochondrial damage, decreased levels of GPX4, SLC7A11, FTL, and FTH, increased levels of reactive oxygen species (ROS), malondialdehyde (MDA), Fe2+, ACSL4, TFRC, along with the activation of ERS-related PERK-ATF4-CHOP pathway. Treatment with the ferroptosis inhibitor liproxstatin-1 (Lip-1) and the iron chelator deferoxamine (DFO) effectively mitigated the neuron injury and cognitive dysfunction induced by CIH, significantly reducing Fe2+ and partly restoring expression levels of ferroptosis-related proteins. Furhermore, the use of Lip-1 and DFO downregulated p-PERK, ATF4 and CHOP, and upregulated Nrf2 expression, suggesting that inhibiting ferroptosis reduce ERS and that the transcription factor Nrf2 is involved in the process. In summary, our findings indicate that cognitive impairment in CIH mice correlates with the induction of neuronal ferroptosis, facilitated by the System xc - GPX4 functional axis, lipid peroxidation, and the iron metabolism pathway, along with ferroptosis-mediated ERS in the prefrontal cortex. Nrf2 has been identified as a potential regulator of ferroptosis and ERS involved in the context of CIH.

Differential expression of genes in the RhoA/ROCK pathway in the hippocampus and cortex following intermittent hypoxia and high-intensity interval training

Structural neuroplasticity such as neurite extension and dendritic spine dynamics is enhanced by brain-derived neurotrophic factor (BDNF) and impaired by types of inhibitory molecules that induce growth cone collapse and actin depolymerization, for example, myelin-associated inhibitors, chondroitin sulfate proteoglycans, and negative guidance molecules. These inhibitory molecules can activate RhoA/rho-associated coiled-coil containing protein kinase (ROCK) signaling (known to restrict structural plasticity). Intermittent hypoxia (IH) and high-intensity interval training (HIIT) are known to upregulate BDNF that is associated with improvements in learning and memory and greater functional recovery following neural insults. We investigated whether the RhoA/ROCK signaling pathway is also modulated by IH and HIIT in the hippocampus, cortex, and lumbar spinal cord of male Wistar rats. The gene expression of 25 RhoA/ROCK signaling pathway components was determined following IH, HIIT, or IH combined with HIIT (30 min/day, 5 days/wk, 6 wk). IH included 10 3-min bouts that alternated between hypoxia (15% O2) and normoxia. HIIT included 10 3-min bouts alternating between treadmill speeds of 50 cm·s-1 and 15 cm·s-1. In the hippocampus, IH and HIIT significantly downregulated Acan and NgR2 mRNA that are involved in the inhibition of neuroplasticity. However, IH and IH + HIIT significantly upregulated Lingo-1 and NgR3 in the cortex. This is the first time IH and HIIT have been linked to the modulation of plasticity-inhibiting pathways. These results provide a fundamental step toward elucidating the interplay between the neurotrophic and inhibitory mechanisms involved in experience-driven neural plasticity that will aid in optimizing physiological interventions for the treatment of cognitive decline or neurorehabilitation.NEW & NOTEWORTHY Intermittent hypoxia (IH) and high-intensity interval training (HIIT) enhance neuroplasticity and upregulate neurotrophic factors in the central nervous system (CNS). We provide evidence that IH and IH + HIIT also have the capacity to regulate genes involved in the RhoA/ROCK signaling pathway that is known to restrict structural plasticity in the CNS. This provides a new mechanistic insight into how these interventions may enhance hippocampal-related plasticity and facilitate learning, memory, and neuroregeneration.

Sleep apnoea, gut dysbiosis and cognitive dysfunction

Sleep disorders are becoming increasingly common, and their distinct effects on physical and mental health require elaborate investigation. Gut dysbiosis (GD) has been reported in sleep-related disorders, but sleep apnoea is of particular significance because of its higher prevalence and chronicity. Cumulative evidence has suggested a link between sleep apnoea and GD. This review highlights the gut-brain communication axis that is mediated via commensal microbes and various microbiota-derived metabolites (e.g. short-chain fatty acids, lipopolysaccharide and trimethyl amine N-oxide), neurotransmitters (e.g. γ-aminobutyric acid, serotonin, glutamate and dopamine), immune cells and inflammatory mediators, as well as the vagus nerve and hypothalamic-pituitary-adrenal axis. This review also discusses the pathological role underpinning GD and altered gut bacterial populations in sleep apnoea and its related comorbid conditions, particularly cognitive dysfunction. In addition, the review examines the preclinical and clinical evidence, which suggests that prebiotics and probiotics may potentially be beneficial in sleep apnoea and its comorbidities through restoration of eubiosis or gut microbial homeostasis that regulates neural, metabolic and immune responses, as well as physiological barrier integrity via the gut-brain axis.

Chronic intermittent hypoxia induces cognitive impairment in Alzheimer's disease mouse model via postsynaptic mechanisms

PURPOSE

Obstructive sleep apnea (OSA) is highly comorbid with Alzheimer's disease (AD) and may represent a risk factor for inducing or accelerating cognitive impairment in AD. Chronic intermittent hypoxia (CIH) has been considered to be a predictor of developing cognitive decline and AD. However, the precise underlying mechanisms by which CIH contributes to cognitive impairment remain unknown. In the present study, we examined the effects of CIH on cognition and hippocampal function in APP/PS1 mice, an animal model of AD.

METHODS

Wild-type (WT) and APP/PS1 mice were subjected to one of the following conditions for 2 weeks: (1) sham condition (continuous room air) or (2) CIH condition. The oxygen concentration of the CIH condition transitioned from 5 to 21%. Behavioral tests, electrophysiological recording, real-time polymerase chain reaction, and Western blot were used to assess the effect of CIH on cognitive performance and synaptic plasticity.

RESULTS

CIH exposure did not affect motor coordination, general locomotor activity, anxiety, or willingness to explore. However, behavioral test results indicated that APP/PS1-CIH mice showed more spatial learning and memory deficits. CIH induced long-term potentiation (LTP) dysfunction of the hippocampus in WT mice. These effects were aggravated in APP/PS1 mice. The N-methyl-D-aspartic acid receptor (NMDAR) NR1 subunit and postsynaptic density 95 (PSD95) in the hippocampus of WT and APP/PS1 mice were downregulated.

CONCLUSIONS

These findings showed that a postsynaptic mechanism was involved in the effect of CIH on cognitive impairment.

Chronic Sustained Hypoxia Leads to Brainstem Tauopathy and Declines the Power of Rhythms in the Ventrolateral Medulla: Shedding Light on a Possible Mechanism

Hypoxia, especially the chronic type, leads to disruptive results in the brain that may contribute to the pathogenesis of some neurodegenerative diseases such as Alzheimer's disease (AD). The ventrolateral medulla (VLM) contains clusters of interneurons, such as the pre-Bötzinger complex (preBötC), that generate the main respiratory rhythm drive. We hypothesized that exposing animals to chronic sustained hypoxia (CSH) might develop tauopathy in the brainstem, consequently changing the rhythmic manifestations of respiratory neurons. In this study, old (20-22 months) and young (2-3 months) male rats were subjected to CSH (10 ± 0.5% O2) for ten consecutive days. Western blotting and immunofluorescence (IF) staining were used to evaluate phosphorylated tau. Mitochondrial membrane potential (MMP or ∆ψm) and reactive oxygen species (ROS) production were measured to assess mitochondrial function. In vivo diaphragm's electromyography (dEMG) and local field potential (LFP) recordings from preBötC were employed to assess the respiratory factors and rhythmic representation of preBötC, respectively. Findings showed that ROS production increased significantly in hypoxic groups, associated with a significant decline in ∆ψm. In addition, tau phosphorylation elevated in the brainstem of hypoxic groups. On the other hand, the power of rhythms declined significantly in the preBötC of hypoxic rats, parallel with changes in the respiratory rate, total respiration time, and expiration time. Moreover, there was a positive and statistically significant correlation between LFP rhythm's power and inspiration time. Our data showed that besides CSH, aging also contributed to mitochondrial dysfunction, tau hyperphosphorylation, LFP rhythms' power decline, and changes in respiratory factors.

Cognitive impairment and hippocampal neuronal damage in β-thalassaemia mice

β-Thalassaemia is one of the most common genetic diseases worldwide. During the past few decades, life expectancy of patients has increased significantly owing to advance in medical treatments. Cognitive impairment, once has been neglected, has gradually become more documented. Cognitive impairment in β-thalassaemia patients is associated with natural history of the disease and socioeconomic factors. Herein, to determined effect of β-thalassaemia intrinsic factors, 22-month-old β-thalassaemia mouse was used as a model to assess cognitive impairment and to investigate any aberrant brain pathology in β-thalassaemia. Open field test showed that β-thalassaemia mice had decreased motor function. However, no difference of neuronal degeneration in primary motor cortex, layer 2/3 area was found. Interestingly, impaired learning and memory function accessed by a Morris water maze test was observed and correlated with a reduced number of living pyramidal neurons in hippocampus at the CA3 region in β-thalassaemia mice. Cognitive impairment in β-thalassaemia mice was significantly correlated with several intrinsic β-thalassaemic factors including iron overload, anaemia, damaged red blood cells (RBCs), phosphatidylserine (PS)-exposed RBC large extracellular vesicles (EVs) and PS-exposed medium EVs. This highlights the importance of blood transfusion and iron chelation in β-thalassaemia patients. In addition, to improve patients' quality of life, assessment of cognitive functions should become part of routine follow-up.

Shaping the future of preclinical development of successful disease-modifying drugs against Alzheimer's disease: a systematic review of tau propagation models

The transcellular propagation of the aberrantly modified protein tau along the functional brain network is a key hallmark of Alzheimer's disease and related tauopathies. Inoculation-based tau propagation models can recapitulate the stereotypical spread of tau and reproduce various types of tau inclusions linked to specific tauopathy, albeit with varying degrees of fidelity. With this systematic review, we underscore the significance of judicious selection and meticulous functional, biochemical, and biophysical characterization of various tau inocula. Furthermore, we highlight the necessity of choosing suitable animal models and inoculation sites, along with the critical need for validation of fibrillary pathology using confirmatory staining, to accurately recapitulate disease-specific inclusions. As a practical guide, we put forth a framework for establishing a benchmark of inoculation-based tau propagation models that holds promise for use in preclinical testing of disease-modifying drugs.

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.

Respiratory Dysfunction in Alzheimer's Disease-Consequence or Underlying Cause? Applying Animal Models to the Study of Respiratory Malfunctions

Alzheimer's disease (AD) is a neurodegenerative brain disease that is the most common cause of dementia among the elderly. In addition to dementia, which is the loss of cognitive function, including thinking, remembering, and reasoning, and behavioral abilities, AD patients also experience respiratory disturbances. The most common respiratory problems observed in AD patients are pneumonia, shortness of breath, respiratory muscle weakness, and obstructive sleep apnea (OSA). The latter is considered an outcome of Alzheimer's disease and is suggested to be a causative factor. While this narrative review addresses the bidirectional relationship between obstructive sleep apnea and Alzheimer's disease and reports on existing studies describing the most common respiratory disorders found in patients with Alzheimer's disease, its main purpose is to review all currently available studies using animal models of Alzheimer's disease to study respiratory impairments. These studies on animal models of AD are few in number but are crucial for establishing mechanisms, causation, implementing potential therapies for respiratory disorders, and ultimately applying these findings to clinical practice. This review summarizes what is already known in the context of research on respiratory disorders in animal models, while pointing out directions for future research.

NLRP3-GSDMD-dependent IL-1β Secretion from Microglia Mediates Learning and Memory Impairment in a Chronic Intermittent Hypoxia-induced Mouse Model

Hypoxia/reoxygenation caused by chronic intermittent hypoxia (CIH) plays an important role in cognitive deficits in patients with obstructive sleep apnea. However, the precise underlying mechanism remains unclear. This study investigated whether the NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome is involved in CIH-induced spatial learning and memory impairment in mice, and the possible underlying upstream and downstream mechanisms. The C57BL/6 male mice were exposed to CIH (21% O2-6% O2, 4 min/cycle, 8 h/day) for 9 weeks to investigate the role of NLRP3 in CIH-induced spatial learning and memory impairment in mice. BV2 cells were exposed to intermittent hypoxia (21% O2-1% O2, 90 min/cycle) for 48 h to investigate the possible mechanisms in vitro. We found that: 1) inhibition of NLRP3 inflammasome activation improved CIH-induced spatial learning and memory impairment in mice. 2) CIH damaged hippocampal neurons but increased the number of microglia in mice hippocampi; CIH activated microglia-specific NLRP3 inflammasome, leading to upregulation of matured IL-1β and N-GSDMD. 3) intermittent hypoxia activated NLRP3 inflammasome via the ROS-NF-κB signaling pathway to promote the release of matured IL-1β from microglia in a GSDMD-dependent manner without pyroptosis. 4) The IL-1β released from microglia might impair the synaptic plasticity of hippocampal CA3-CA1 synapses by acting on IL-1 receptors in hippocampal neurons. Our findings reveal that ROS-NF-κB-NLRP3 inflammasome-GSDMD dependent IL-1β release from microglia may participate in CIH-induced spatial learning and memory impairment by acting on hippocampal neuronal IL-1 receptor, leading to synaptic plasticity impairment.

Tau Protein Alterations Induced by Hypobaric Hypoxia Exposure

Tauopathies are a group of neurodegenerative diseases whose central feature is dysfunction of the microtubule-associated protein tau (MAPT). Although the exact etiology of tauopathies is still unknown, it has been hypothesized that their onset may occur up to twenty years before the clear emergence of symptoms, which has led to questions about whether the prognosis of these diseases can be improved by, for instance, targeting the factors that influence tauopathy development. One such factor is hypoxia, which is strongly linked to Alzheimer's disease because of its association with obstructive sleep apnea and has been reported to affect molecular pathways related to the dysfunction and aggregation of tau proteins and other biomarkers of neurological damage. In particular, hypobaric hypoxia exposure increases the activation of several kinases related to the hyperphosphorylation of tau in neuronal cells, such as ERK, GSK3β, and CDK5. In addition, hypoxia also increases the levels of inflammatory molecules (IL-β1, IL-6, and TNF-α), which are also associated with neurodegeneration. This review discusses the many remaining questions regarding the influence of hypoxia on tauopathies and the contribution of high-altitude exposure to the development of these diseases.

Oxygen metabolism abnormality and Alzheimer's disease: An update

Oxygen metabolism abnormality plays a crucial role in the pathogenesis of Alzheimer's disease (AD) via several mechanisms, including hypoxia, oxidative stress, and mitochondrial dysfunction. Hypoxia condition usually results from living in a high-altitude habitat, cardiovascular and cerebrovascular diseases, and chronic obstructive sleep apnea. Chronic hypoxia has been identified as a significant risk factor for AD, showing an aggravation of various pathological components of AD, such as amyloid β-protein (Aβ) metabolism, tau phosphorylation, mitochondrial dysfunction, and neuroinflammation. It is known that hypoxia and excessive hyperoxia can both result in oxidative stress and mitochondrial dysfunction. Oxidative stress and mitochondrial dysfunction can increase Aβ and tau phosphorylation, and Aβ and tau proteins can lead to redox imbalance, thus forming a vicious cycle and exacerbating AD pathology. Hyperbaric oxygen therapy (HBOT) is a non-invasive intervention known for its capacity to significantly enhance cerebral oxygenation levels, which can significantly attenuate Aβ aggregation, tau phosphorylation, and neuroinflammation. However, further investigation is imperative to determine the optimal oxygen pressure, duration of exposure, and frequency of HBOT sessions. In this review, we explore the prospects of oxygen metabolism in AD, with the aim of enhancing our understanding of the underlying molecular mechanisms in AD. Current research aimed at attenuating abnormalities in oxygen metabolism holds promise for providing novel therapeutic approaches for AD.

Polyherbal and Multimodal Treatments: Kaempferol- and Quercetin-Rich Herbs Alleviate Symptoms of Alzheimer's Disease

Alzheimer's Disease (AD) is a progressive neurodegenerative disorder impairing cognition and memory in the elderly. This disorder has a complex etiology, including senile plaque and neurofibrillary tangle formation, neuroinflammation, oxidative stress, and damaged neuroplasticity. Current treatment options are limited, so alternative treatments such as herbal medicine could suppress symptoms while slowing cognitive decline. We followed PRISMA guidelines to identify potential herbal treatments, their associated medicinal phytochemicals, and the potential mechanisms of these treatments. Common herbs, including Ginkgo biloba, Camellia sinensis, Glycyrrhiza uralensis, Cyperus rotundus, and Buplerum falcatum, produced promising pre-clinical results. These herbs are rich in kaempferol and quercetin, flavonoids with a polyphenolic structure that facilitate multiple mechanisms of action. These mechanisms include the inhibition of Aβ plaque formation, a reduction in tau hyperphosphorylation, the suppression of oxidative stress, and the modulation of BDNF and PI3K/AKT pathways. Using pre-clinical findings from quercetin research and the comparatively limited data on kaempferol, we proposed that kaempferol ameliorates the neuroinflammatory state, maintains proper cellular function, and restores pro-neuroplastic signaling. In this review, we discuss the anti-AD mechanisms of quercetin and kaempferol and their limitations, and we suggest a potential alternative treatment for AD. Our findings lead us to conclude that a polyherbal kaempferol- and quercetin-rich cocktail could treat AD-related brain damage.

Local and Systemic Hypoxia as Inductors of Increased Aluminum and Iron Brain Accumulation Promoting the Onset of Alzheimer's Disease

Human environment is highly contaminated with aluminum, and aluminum is toxic to majority of tissues, particularly to neurons. In previous decades, aluminum exposure was frequently linked with the onset of Alzheimer's disease (AD), and increased levels of Al were detected in the brains of individuals with AD. People who live in a certain area are exposed to aluminum in a similar way (they eat the same vegetable and other foodstuffs, use similar cosmetics, and buy medications from the same manufacturer), nevertheless not all of them develop Alzheimer's disease. Majority of known risk factors for AD promote atherosclerosis and consequently reduce brain blood supply. In this review, we highlighted the significance of local (carotid disease and atherosclerosis of intracranial blood vessels) and systemic hypoxia (chronic obstructive pulmonary disease and anemia) in the development of AD. Nerve tissue is very sophisticated and sensitive to hypoxia and aluminum toxicity. As a side effect of compensatory mechanisms in case of hypoxia, neurons start to uptake aluminum and iron to a greater extent. This makes perfect a background for the gradual onset and development of AD.

Progressive tauopathy disrupts breathing stability and chemoreflexes during presumptive sleep in mice

Rationale: Although sleep apnea occurs in over 50% of individuals with Alzheimer's Disease (AD) or related tauopathies, little is known concerning the potential role of tauopathy in the pathogenesis of sleep apnea. Here, we tested the hypotheses that, during presumptive sleep, a murine model of tauopathy (rTg4510) exhibits: 1) increased breathing instability; 2) impaired chemoreflex function; and 3) exacerbation of these effects with tauopathy progression. Methods: rTg4510 mice initially develop robust tauopathy in the hippocampus and cortex, and eventually progresses to the brainstem. Type I and II post-sigh apnea, Type III (spontaneous) apnea, sigh, and hypopnea incidence were measured in young adult (5-6 months; n = 10-14/group) and aged (13-15 months; n = 22-24/group) non-transgenic (nTg), monogenic control tetracycline transactivator, and bigenic rTg4510 mice using whole-body plethysmography during presumptive sleep (i.e., eyes closed, curled/laying posture, stable breathing for >200 breaths) while breathing room air (21% O2). Peripheral and central chemoreceptor sensitivity were assessed with transient exposures (5 min) to hyperoxia (100% O2) or hypercapnia (3% and 5% CO2 in 21% O2), respectively. Results: We report significant increases in Type I, II, and III apneas (all p < 0.001), sighs (p = 0.002) and hypopneas (p < 0.001) in aged rTg4510 mice, but only Type III apneas in young adult rTg4510 mice (p < 0.001) versus age-matched nTg controls. Aged rTg4510 mice exhibited profound chemoreflex impairment versus age matched nTg and tTA mice. In rTg4510 mice, breathing frequency, tidal volume and minute ventilation were not affected by hyperoxic or hypercapnic challenges, in striking contrast to controls. Histological examination revealed hyperphosphorylated tau in brainstem regions involved in the control of breathing (e.g., pons, medullary respiratory column, retrotrapezoid nucleus) in aged rTg4510 mice. Neither breathing instability nor hyperphosphorylated tau in brainstem tissues were observed in young adult rTg4510 mice. Conclusion: Older rTg4510 mice exhibit profound impairment in the neural control of breathing, with greater breathing instability and near absence of oxygen and carbon-dioxide chemoreflexes. Breathing impairments paralleled tauopathy progression into brainstem regions that control breathing. These findings are consistent with the idea that tauopathy per se undermines chemoreflexes and promotes breathing instability during sleep.

Microglial exosomes alleviate intermittent hypoxia-induced cognitive deficits by suppressing NLRP3 inflammasome

Intermittent hypoxia is the best predictor of developing cognitive decline and Alzheimer's disease progression in patients with obstructive sleep apnea. The nucleotide-binding oligomerization domain-like receptor 3 (NLRP3) inflammasome has been poorly studied as a regulator of neuroinflammation in cognitive impairment caused by intermittent hypoxia. As critical inflammatory cells, exosomes secreted by microglia have been found to affect the spread of pathologic proteins and neuropathology in neurodegenerative diseases. However, the effects of microglial exosomes on neuroinflammation and cognitive outcomes after intermittent hypoxia remain unclear. In this study, the role of miRNAs in microglial exosomes in improving cognitive deficits in mice exposed to intermittent hypoxia was investigated. We demonstrated that miR-146a-5p fluctuated over time in microglial exosomes of mice exposed to intermittent hypoxia for different periods of time, which could regulate neuronal NLRP3 inflammasome and neuroinflammation. In primary neurons, we found that miR-146a-5p regulated mitochondrial reactive oxygen species by targeting HIF1α, thus affecting the NLRP3 inflammasome and secretion of inflammatory factors. Similarly, further studies showed that inhibition of NLRP3 by administering overexpressed miR-146a-5p in microglial exosomes and MCC950 has improved neuroinflammation and cognitive dysfunction in mice after intermittent hypoxia. In conclusion, NLRP3 inflammasome may be a regulatory target for ameliorating cognitive impairment caused by intermittent hypoxia, and microglial exosomal miR-146a-5p may be a promising therapeutic strategy.

CORP: Sources and degrees of variability in whole animal intermittent hypoxia experiments

Chamber exposures are commonly used to evaluate the physiological and pathophysiological consequences of intermittent hypoxia in animal models. Researchers in this field use both commercial and custom-built chambers in their experiments. The purpose of this Cores of Reproducibility in Physiology paper is to demonstrate potential sources of variability in these systems that researchers should consider. Evaluating the relationship between arterial oxygen saturation and inspired oxygen concentration, we found that there are important sex-dependent differences in the commonly used C57BL6/J mouse model. The time delay of the oxygen sensor that provides feedback to the system during the ramp-down and ramp-up phases was different, limiting the number of cycles per hour that can be conducted and the overall stability of the oxygen concentration. The time to reach the hypoxic and normoxic hold stages, and the overall oxygen concentration, were impacted by the cycle number. These variables were further impacted by whether there are animals present in the chamber, highlighting the importance of verifying the cycling frequency with animals in the chamber. At ≤14 cycles/h, instability in the chamber oxygen concentration did not impact arterial oxygen saturation but may be important at higher cycle numbers. Taken together, these data demonstrate the important sources of variability that justify reporting and verifying the target oxygen concentration, cycling frequency, and arterial oxygen concentration, particularly when comparing different animal models and chamber configurations.NEW & NOTEWORTHY Intermittent hypoxia exposures are commonly used in physiology and many investigators use chamber systems to perform these studies. Because of the variety of chamber systems and protocols used, it is important to understand the sources of variability in intermittent hypoxia experiments that can impact reproducibility. We demonstrate sources of variability that come from the animal model, the intermittent hypoxia protocol, and the chamber system that can impact reproducibility.

Intermittent hypoxia-induced enhancement of sociability and working memory associates with CNTNAP2 upregulation

Introduction

Hypoxia is an environmental risk factor for many disorders throughout life. Perinatal hypoxia contributes to autism spectrum disorder (ASD), while hypoxic conditions in the elderly facilitate memory deficits. However, the effects of hypoxia on adolescence remains elusive. CNTNAP2 is a critical molecule in ASD pathogenesis with undefined mechanisms. We investigate hypoxia’s impact on adolescence and the underlying mechanism related to CNTNAP2.

Methods

Three-chamber social approach test, Y maze, Morris Water Maze and Open Field Test were applied to evaluate behavioral alterations. Immunoblotting, 5′- RACE and dual-luciferase reporter assay were performed to examine CNTNAP2 protein expression, transcription start site (TSS) of human CNTNAP2 gene and CNTNAP2 promoter activity, respectively.

Results

Intermittent hypoxia treatment improved social behaviors and working memory in adolescent mice. CNTNAP2 was increased in the brains of hypoxia-treated mice. The sequencing results identified the TSS at 518 bp upstream of the translation start site ATG. Hypoxia upregulated CNTNAP2 by interacting with functional hypoxia response elements in CNTNAP2 promoter.

Conclusion

Intermittent hypoxia enhanced sociability and working memory associated with CNTNAP2 upregulation. Our study provides novel insights into intermittent hypoxia’s impact on development and the interaction between genetic and environmental risk factors in ASD pathogenesis.

Huperzine A-Liposomes Efficiently Improve Neural Injury in the Hippocampus of Mice with Chronic Intermittent Hypoxia

Background

Chronic intermittent hypoxia (CIH) could cause neuronal damage, accelerating the progression of dementia. However, safe and effective therapeutic drugs and delivery are needed for successful CIH therapy.

Purpose

To investigate the neuroprotective effect of Huperzine A (HuA) packaged with nanoliposomes (HuA-LIP) on neuronal damage induced by CIH.

Methods

The stability and release of HuA-LIP in vitro were identified. Mice were randomly divided into the Control, CIH, HuA-LIP, and HuA groups. The mice in the HuA and HuA-LIP groups received HuA (0.1 mg/kg, i.p.), and HuA-LIP was administered during CIH exposure for 21 days. HuA-LIP contains the equivalent content of HuA.

Results

We prepared a novel formulation of HuA-LIP that had good stability and controlled release. First, HuA-LIP significantly ameliorated cognitive dysfunction and neuronal damage in CIH mice. Second, HuA-LIP elevated T-SOD and GSH-Px abilities and decreased MDA content to resist oxidative stress damage induced by CIH. Furthermore, HuA-LIP reduced brain iron levels by downregulating TfR1, hepcidin, and FTL expression. In addition, HuA-LIP activated the PKAα/Erk/CREB/BDNF signaling pathway and elevated MAP2, PSD95, and synaptophysin to improve synaptic plasticity. Most importantly, compared with HuA, HuA-LIP showed a superior performance against neuronal damage induced by CIH.

Conclusion

HuA-LIP has a good sustained-release effect and targeting ability and efficiently protects against neural injury caused by CIH.

Physical Performance and Amyloid-β in Humans: A Systematic Review and Meta-Analysis of Observational Studies

BACKGROUND

Accumulation of amyloid-β (Aβ) plaques is one of the main features of Alzheimer's disease (AD). Physical performance has been related to dementia risk and Aβ, and it has been hypothesized as one of the mechanisms leading to greater accumulation of Aβ. Yet, no evidence synthesis has been performed in humans.

OBJECTIVE

To investigate the association of physical performance with Aβ in humans, including Aβ accumulation on brain, and Aβ abnormalities measured in cerebrospinal fluid (CSF) and blood.

METHODS

A systematic review with multilevel meta-analysis was performed from inception to June 16th, 2022. Studies were eligible if they examined the association of physical performance with Aβ levels, including the measure of physical performance as a predictor and the measure of Aβ as an outcome in humans.

RESULTS

7 articles including 2,619 participants were included in the meta-analysis. The results showed that physical performance was not associated with accumulation of Aβ in the brain (ES = 0.01; 95% CI -0.21 to 0.24; I2 = 69.9%), in the CSF (ES = -0.28; 95% CI -0.98 to 0.41; I2 = 91.0%) or in the blood (ES = -0.19; 95% CI -0.61 to 0.24; I2 = 99.75%). Significant heterogeneity was found across the results , which posed challenges in arriving at consistent conclusions; and the limited number of studies hindered the opportunity to conduct a moderation analysis.

CONCLUSIONS

The association between physical performance and Aβ is inconclusive. This uncertainly arises from the limited number of studies, study design limitations, and heterogeneity of measurement approaches. More studies are needed to determine whether physical performance is related to Aβ levels in humans.

HIF-1α Causes LCMT1/PP2A Deficiency and Mediates Tau Hyperphosphorylation and Cognitive Dysfunction during Chronic Hypoxia

Chronic hypoxia is a risk factor for Alzheimer's disease (AD), and the neurofibrillary tangle (NFT) formed by hyperphosphorylated tau is one of the two major pathological changes in AD. However, the effect of chronic hypoxia on tau phosphorylation and its mechanism remains unclear. In this study, we investigated the role of HIF-1α (the functional subunit of hypoxia-inducible factor 1) in tau pathology. It was found that in Sprague-Dawley (SD) rats, global hypoxia (10% O₂, 6 h per day) for one month induced cognitive impairments. Meanwhile it induced HIF-1α increase, tau hyperphosphorylation, and protein phosphatase 2A (PP2A) deficiency with leucine carboxyl methyltransferase 1(LCMT1, increasing PP2A activity) decrease in the rats' hippocampus. The results were replicated by hypoxic treatment in primary hippocampal neurons and C6/tau cells (rat C6 glioma cells stably expressing human full-length tau441). Conversely, HIF-1α silencing impeded the changes induced by hypoxia, both in primary neurons and SD rats. The result of dual luciferase assay proved that HIF-1α acted as a transcription factor of LCMT1. Unexpectedly, HIF-1α decreased the protein level of LCMT1. Further study uncovered that both overexpression of HIF-1α and hypoxia treatment resulted in a sizable degradation of LCMT1 via the autophagy--lysosomal pathway. Together, our data strongly indicated that chronic hypoxia upregulates HIF-1α, which obviously accelerated LCMT1 degradation, thus counteracting its transcriptional expression. The increase in HIF-1α decreases PP2A activity, finally resulting in tau hyperphosphorylation and cognitive dysfunction. Lowering HIF-1α in chronic hypoxia conditions may be useful in AD prevention.

Proteomic Analysis Reveals That Mitochondria Dominate the Hippocampal Hypoxic Response in Mice

Hypoxic stress occurs in various physiological and pathological states, such as aging, disease, or high-altitude exposure, all of which pose a challenge to many organs in the body, necessitating adaptation. However, the exact mechanisms by which hypoxia affects advanced brain function (learning and memory skills in particular) remain unclear. In this study, we investigated the effects of hypoxic stress on hippocampal function. Specifically, we studied the effects of the dysfunction of mitochondrial oxidative phosphorylation using global proteomics. First, we found that hypoxic stress impaired cognitive and motor abilities, whereas it caused no substantial changes in the brain morphology or structure of mice. Second, bioinformatics analysis indicated that hypoxia affected the expression of 516 proteins, of which 71.1% were upregulated and 28.5% were downregulated. We demonstrated that mitochondrial function was altered and manifested as a decrease in NADH dehydrogenase (ubiquinone) 1 alpha subcomplex 4 expression, accompanied by increased reactive oxygen species generation, resulting in further neuronal injury. These results may provide some new insights into how hypoxic stress alters hippocampal function via the dysfunction of mitochondrial oxidative phosphorylation.

Assessment of Alzheimer’s disease-related biomarkers in patients with obstructive sleep apnea: A systematic review and meta-analysis

Increasing evidence links Alzheimer’s disease (AD) to various sleep disorders, including obstructive sleep apnea (OSA). The core AD cerebrospinal fluid (CSF) biomarkers, including amyloid-β 42 (Aβ42), total tau (t-tau), and phosphorylated tau (p-tau), can reflect key elements of AD pathophysiology before the emergence of symptoms. Besides, the amyloid-β (Aβ) and tau burden can also be tested by positron emission tomography (PET) scans. Electronic databases (PubMed, Embase, Web of Science, and The Cochrane Library) were searched until August 2022 to assess the AD-related biomarkers measured by PET scans and CSF in OSA patients. The overall analysis showed significant differences in Aβ42 levels (SMD = −0.93, 95% CI:−1.57 to −0.29, P < 0.001) and total tau (t-tau) levels (SMD = 0.24, 95% CI: 0.01–0.48, P = 0.308) of CSF, and Aβ burden (SMD = 0.37, 95% CI = 0.13–0.61, P = 0.69) tested by PET scans between the OSA and controls. Furthermore, CSF Aβ42 levels showed significant differences in patients with moderate/severe OSA compared with healthy control, and levels of CSF Aβ42 showed differences in OSA patients with normal cognition as well. Besides, age and BMI have influences on heterogeneity. Our meta-analysis indicated abnormal AD-related biomarkers (CSF and PET scans) in patients with OSA, supporting the current hypothesis that OSA, especially moderate/severe OSA, may start the AD neuropathological process.

Dose-dependent phosphorylation of endogenous Tau by intermittent hypoxia in rat brain

Intermittent hypoxia, or intermittent low oxygen interspersed with normal oxygen levels, has differential effects that depend on the "dose" of hypoxic episodes (duration, severity, number per day, and number of days). Whereas "low dose" daily acute intermittent hypoxia (dAIH) elicits neuroprotection and neuroplasticity, "high dose" chronic intermittent hypoxia (CIH) similar to that experienced during sleep apnea elicits neuropathology. Sleep apnea is comorbid in >50% of patients with Alzheimer's disease-a progressive, neurodegenerative disease associated with brain amyloid and chronic Tau dysregulation (pathology). Although patients with sleep apnea present with higher Tau levels, it is unknown if sleep apnea through attendant CIH contributes to onset of Tau pathology. We hypothesized CIH characteristic of moderate sleep apnea would increase dysregulation of phosphorylated Tau (phospho-Tau) species in Sprague-Dawley rat hippocampus and prefrontal cortex. Conversely, we hypothesized that dAIH, a promising neurotherapeutic, has minimal impact on Tau phosphorylation. We report a dose-dependent intermittent hypoxia effect, with region-specific increases in 1) phospho-Tau species associated with human Tauopathies in the soluble form and 2) accumulated phospho-Tau in the insoluble fraction. The latter observation was particularly evident with higher CIH intensities. This important and novel finding is consistent with the idea that sleep apnea and attendant CIH have the potential to accelerate the progression of Alzheimer's disease and/or other Tauopathies.NEW & NOTEWORTHY Sleep apnea is highly prevalent in people with Alzheimer's disease, suggesting the potential to accelerate disease onset and/or progression. These studies demonstrate that intermittent hypoxia (IH) induces dose-dependent, region-specific Tau phosphorylation, and are the first to indicate that higher IH "doses" elicit both endogenous, (rat) Tau hyperphosphorylation and accumulation in the hippocampus. These findings are essential for development and implementation of new treatment strategies that minimize sleep apnea and its adverse impact on neurodegenerative diseases.

Association between obstructive sleep apnea and Alzheimer's disease-related blood and cerebrospinal fluid biomarkers: A meta-analysis

INTRODUCTION

Recent studies indicate that Alzheimer's disease- (AD) related biomarkers, including amyloid β (Aβ40 and Aβ42) and tau proteins (P-tau and T-tau), in blood and cerebrospinal fluid (CSF) are associated with obstructive sleep apnea (OSA). However, the results have been inconsistent. Therefore, the primary purpose of this meta-analysis was to determine the relationship between blood and CSF AD-related biomarkers and OSA.

METHODS

We searched the Embase, PubMed, Scopus, and Cochrane Library databases for relevant articles till February 2022.

RESULTS

Eight articles were finally included after the literature screening, including 446 patients with OSA and 286 controls. Pooled analysis showed that CSF Aβ42 (SMD = -0.220, P = 0.136), T-tau (SMD = 0.012, P = 0.89), and P-tau (SMD = 0.099, P = 0.274) levels were not different between patients with OSA and controls. In patients with moderate to severe OSA, CSF Aβ42 (SMD = -0.482, P = 0.031) were significantly lower than in controls. Blood T-tau (SMD = 0.560, P = 0.026), P-tau (SMD = 0.621, P < 0.001), and Aβ40 (SMD = 0.656, P < 0.001) levels were significantly higher in patients with OSA than in controls. Blood Aβ42 (SMD = 0.241, P = 0.232) were not different between patients with OSA and controls.

CONCLUSION

OSA is associated with changes in AD-related markers. Higher OSA severity may be associated with the development of AD. AD-related biomarkers, especially in the blood, are clinically efficient, less invasively assessed and monitored, and may be useful for detecting OSA and related cognitive impairments. Further studies are needed to confirm these results.

The Effects of CPAP Treatment on Resting-State Network Centrality in Obstructive Sleep Apnea Patients

Background and Objectives

Obstructive sleep apnea (OSA) is the most common sleep disorder and previous studies have shown that OSA patients suffer from brain network impairments associated with cognitive deficits, and continuous positive airway pressure (CPAP) treatment can improve clinical symptoms. However, the relationship between CPAP treatment and brain network changes remains unclear. This study explored the characteristics of brain network changes in OSA patients before (pre-CPAP) and after one month of CPAP treatment (post-CPAP).

Methods

We collected data, including sleep monitoring, clinical assessment, and magnetic resonance imaging scans, from 21 OSA patients and 21 age-matched healthy controls (HCs). Voxel-level degree centrality (DC) was used to assess whole-brain network connectivity characteristics, a two-sample t-test was used to compare network differences between pre-CPAP OSA patients and HCs, and a paired sample t-test was used to compare the characteristics of brain network changes in OSA patients before and after treatment. The correlations between the DC value and each of the clinical variables were analyzed in the OSA patients.

Results

Compared with HCs, pre-CPAP OSA patients showed increased DC values in the bilateral cerebellar posterior lobes (CPLs) and decreased DC values in the right superior temporal gyrus, left superior frontal gyrus and right middle frontal gyrus. Compared with pre-CPAP OSA patients, post-CPAP OSA patients showed reduced DC values in the bilateral CPL and increased DC values in several brain regions in the frontal, temporal, and insular lobes after CPAP treatment. The Montreal Cognitive Assessment MoCA (MoCA) scores were positively correlated with the DC value of the bilateral cerebellum posterior lobe, right middle temporal gyrus, left superior temporal gyrus, left paracentral lobule and left paracentral lobule. Also, Pittsburgh Sleep Quality Index (PSQI) scores were negatively correlated with the DC value of the right middle temporal gyrus in post-CPAP OSA patients.

Conclusion

CPAP treatment can effectively reverse the compensatory response of the bilateral CPL and functional network damage brought about by OSA, which may provide potential neuroimaging biomarkers for CPAP treatment evaluation.

Oxygen Sensing and Signaling in Alzheimer's Disease: A Breathtaking Story!

Oxygen sensing and homeostasis is indispensable for the maintenance of brain structural and functional integrity. Under low-oxygen tension, the non-diseased brain has the ability to cope with hypoxia by triggering a homeostatic response governed by the highly conserved hypoxia-inducible family (HIF) of transcription factors. With the advent of advanced neuroimaging tools, it is now recognized that cerebral hypoperfusion, and consequently hypoxia, is a consistent feature along the Alzheimer's disease (AD) continuum. Of note, the reduction in cerebral blood flow and tissue oxygenation detected during the prodromal phases of AD, drastically aggravates as disease progresses. Within this scenario a fundamental question arises: How HIF-driven homeostatic brain response to hypoxia "behaves" during the AD continuum? In this sense, the present review is aimed to critically discuss and summarize the current knowledge regarding the involvement of hypoxia and HIF signaling in the onset and progression of AD pathology. Importantly, the promises and challenges of non-pharmacological and pharmacological strategies aimed to target hypoxia will be discussed as a new "hope" to prevent and/or postpone the neurodegenerative events that occur in the AD brain.

Intermittent Hypoxia causes targeted disruption to NMDA receptor dependent synaptic plasticity in area CA1 of the hippocampus

Changed NMDA receptor (NMDAr) physiology is implicated with cognitive deficit resulting from conditions ranging from normal aging to neurological disease. Using intermittent hypoxia (IH) to experimentally model untreated sleep apnea, a clinical condition whose comorbidities include neurocognitive impairment, we recently demonstrated that IH causes a pro-oxidant condition that contributes to deficits in spatial memory and in NMDAr-dependent long-term potentiation (LTP). However, the impact of IH on additional forms of synaptic plasticity remains ill-defined. Here we show that IH prevents the induction of NMDAr-dependent LTP and long-term depression (LTD) in hippocampal brain slices from mice exposed to ten days of IH (IH₁₀) yet spares NMDAr-independent forms of synaptic plasticity. Deficits in synaptic plasticity were accompanied by a reduction in hippocampal GluN1 expression. Acute manipulation of redox state using the reducing agent, Dithiothreitol (DTT) stimulated the NMDAr-dependent fEPSP following IH₁₀. However, acute use of either DTT or MnTMPyP did not restore NMDAr-dependent synaptic plasticity after IH₁₀ or prevent the IH-dependent reduction in GluN1, the obligatory subunit of the NMDAr. In contrast, MnTMPyP during IH₁₀ (10-MnTMPyP), prevented the suppressive effects of IH on both NMDAr-dependent synaptic plasticity and GluN1 expression. These findings indicate that while the IH-dependent pro-oxidant state causes reversible oxidative neuromodulation of NMDAr activity, acute manipulation of redox state is ineffective in rescuing two key effects of IH related to the NMDAr within the hippocampus. These IH-dependent changes associated with the NMDAr may be a primary avenue by which IH enhances the vulnerability to impaired learning and memory when sleep apnea is left untreated in normal aging and in disease.