Increased hippocampal activation in mild cognitive impairment compared to normal aging and AD

Synaptic and synchronic impairments in subcortical brain regions associated with early non-cognitive dysfunction in Alzheimer's disease

For many decades, Alzheimer's disease research has primarily focused on impairments within cortical and hippocampal regions, which are thought to be related to cognitive dysfunctions such as memory and language deficits. The exact cause of Alzheimer's disease is still under debate, making it challenging to establish an effective therapy or early diagnosis. It is widely accepted that the accumulation of amyloid-beta peptide in the brain parenchyma leads to synaptic dysfunction, a critical step in Alzheimer's disease development. The traditional amyloid cascade model is initiated by accumulating extracellular amyloid-beta in brain areas essential for memory and language. However, while it is possible to reduce the presence of amyloid-beta plaques in the brain with newer immunotherapies, cognitive symptoms do not necessarily improve. Interestingly, recent studies support the notion that early alterations in subcortical brain regions also contribute to brain damage and precognitive decline in Alzheimer's disease. A body of recent evidence suggests that early Alzheimer's disease is associated with alterations (e.g., motivation, anxiety, and motor impairment) in subcortical areas, such as the striatum and amygdala, in both human and animal models. Also, recent data indicate that intracellular amyloid-beta appears early in subcortical regions such as the nucleus accumbens, locus coeruleus, and raphe nucleus, even without extracellular amyloid plaques. The reported effects are mainly excitatory, increasing glutamatergic transmission and neuronal excitability. In agreement, data in Alzheimer's disease patients and animal models show an increase in neuronal synchronization that leads to electroencephalogram disturbances and epilepsy. The data indicate that early subcortical brain dysfunctions might be associated with non-cognitive symptoms such as anxiety, irritability, and motivation deficits, which precede memory loss and language alterations. Overall, the evidence reviewed suggests that subcortical brain regions could explain early dysfunctions and perhaps be targets for therapies to slow disease progression. Future research should focus on these non-traditional brain regions to reveal early pathological alterations and underlying mechanisms to advance our understanding of Alzheimer's disease beyond the traditionally studied hippocampal and cortical circuits.

Dynamic modeling of astrocyte-neuron interactions under the influence of Aβ deposition

β-amyloid (Aβ) protein accumulation is recognized as a key factor in Alzheimer's disease (AD) pathogenesis. Its effects on astrocyte function appear primarily as disturbances to intracellular calcium signaling, which, in turn, affects neuronal excitability. We propose an innovative neuron-astrocyte interaction model to examine how Aβ accumulation influences astrocyte calcium oscillation and neuronal excitability, emphasizing its significance in AD pathogenesis. This comprehensive model describes not only the response of the astrocyte to presynaptic neuron stimulation but also the release of the downstream signaling glutamate and its consequential feedback on neurons. Our research concentrates on changes within two prominent pathways affected by Aβ: the creation of Aβ astrocyte membrane pores and the enhanced sensitivity of ryanodine receptors. By incorporating these adjustments into our astrocyte model, we can reproduce previous experimental findings regarding aberrant astrocyte calcium activity and neural behavior associated with Aβ from a neural computational viewpoint. Within a specified range of Aβ influence, our numerical analysis reveals that astrocyte cytoplasmic calcium rises, calcium oscillation frequency increases, and the time to the first calcium peak shortens, indicating the disrupted astrocyte calcium signaling. Simultaneously, the neuronal firing rate and cytosolic calcium concentration increase while the threshold current for initiating repetitive firing diminishes, implying heightened neuronal excitability. Given that increased neuronal excitability commonly occurs in early AD patients and correlates with cognitive decline, our findings may highlight the importance of Aβ accumulation in AD pathogenesis and provide a theoretical basis for identifying neuronal markers in the early stages of the disease.

Pharmacological reduction of reverse-translated hippocampal hyperactivity in mouse: relevance for psychosis

Hippocampal hyperactivity (HH) is a potential biomarker in schizophrenia psychosis, which also appears in several other brain disorders, compromising specificity. We hypothesized that the reversal of HH in an established, reverse-translational animal preparation, coupled with a behavioral marker of psychosis may be a predictor of antipsychotic efficacy of a medication. We used a chemogenetic reverse-translational mouse preparation relevant to schizophrenia psychosis which shows HH and aberrant psychosis-relevant behaviors, specifically disrupted social recognition memory (SRM). Mice with and without HH were treated with three drugs; two known antipsychotics and one HH-reducing anticonvulsant, to assess their effects on both HH and SRM performance. All animals received one of the four treatments: vehicle (N = 15-24), haloperidol (N = 8-15), xanomeline (N = 8-13) or levetiracetam (N = 6-15) and were subsequently tested for baseline c-Fos protein expression within the hippocampal subfields (CA3 and CA1) as a measure of neuronal activity, or tested with the SRM task as a measure of social memory. All three drugs acutely reduced baseline HH compared to vehicle treatment. Subacute administration of haloperidol or xanomeline, the two drugs known to have antipsychotic activity, but not levetiracetam, normalized the SRM behavior to control levels. These results suggest that the reversal of HH alone cannot be a predictor of antipsychotic efficacy of an experimental drug and HH as a biomarker could benefit from a more sensitive readout approach.

Increased excitability of dentate gyrus mossy cells occurs early in life in the Tg2576 model of Alzheimer's disease

BACKGROUND

Hyperexcitability in Alzheimer's disease (AD) is proposed to emerge early and contribute to disease progression. The dentate gyrus (DG) and its primary cell type, granule cells (GCs) are implicated in hyperexcitability in AD. Hence, we hypothesized that mossy cells (MCs), important regulators of GC excitability, contribute to early hyperexcitability in AD. Indeed, MCs and GCs are linked to hyperexcitability in epilepsy.

METHODS

Using the Tg2576 model of AD and WT mice (~ 1 month-old), we compared MCs and GCs electrophysiologically and morphologically, assessed the activity marker c-Fos, Aβ expression and a hippocampal- and MC-dependent memory task that is impaired at 3-4 months of age in Tg2576 mice.

RESULTS

Tg2576 MCs had increased spontaneous excitatory events (sEPSP/Cs) and decreased spontaneous inhibitory currents (sIPSCs), increasing the excitation/inhibition ratio. Additionally, Tg2576 MC intrinsic excitability was enhanced. Consistent with in vitro results, Tg2576 MCs showed enhanced c-Fos protein expression. Tg2576 MCs had increased intracellular Aβ expression, suggesting a reason for increased excitability. GCs showed increased excitatory and inhibitory input without changes in intrinsic properties, consistent with effects of increased MC activity. In support, increased GC activity was normalized by an antagonist of MC input to GCs. Also in support, Tg2576 MC axons showed sprouting to the area of GC dendrites. These effects occurred before an impairment in the memory task, suggesting they are extremely early alterations.

CONCLUSIONS

Alterations in Tg2576 MCs and GCs early in life suggest an early role for MCs in increased GC excitability. MCs may be a novel target to intervene in AD pathophysiology at early stages.

G protein-gated inwardly rectifying K+ (GIRK/Kir3) channels: Molecular, cellular, and subcellular diversity

G protein-gated inwardly rectifying K+ (GIRK/Kir3) channels are mainly expressed in excitable cells such as neurons and atrial myocytes, where they can respond to a wide variety of neurotransmitters. Four GIRK subunits have been found in mammals (GIRK1-4) and act as downstream targets for various Gαi/o-linked G protein-coupled receptors (GPCRs). Activation of GIRK channels produces a postsynaptic efflux of potassium from the cell, responsible for hyperpolarization/inhibition of the neuron. A growing body of evidence suggests that dysregulation of GIRK signalling can lead to excessive or deficient neuronal excitability, which contributes to neurological diseases and disorders. Therefore, GIRK channels are proposed as new pharmacological targets. The function of GIRK channels in neurons is not only determined by their biophysical properties but also by their cellular and subcellular localization patterns and densities on the neuronal surface. GIRK channels can be located within several subcellular compartments, where they have many different functional implications. This subcellular localization changes dynamically along the neuronal surface in response to drug intake. Ongoing research is focusing on determining the proteins that form macromolecular complexes with GIRK channels and are responsible for fast and precise signalling under physiological conditions, and how their alteration is implicated in pathological conditions. In this review, the distinct regional, cellular, and subcellular distribution of GIRK channel subunits in the brain will be discussed in view of their possible functional and pathological implications.

Cannabidiol ameliorates cognitive decline in 5×FAD mouse model of Alzheimer's disease through potentiating the function of extrasynaptic glycine receptors

Emerging evidence supports the therapeutic potential of cannabinoids in Alzheimer's disease (AD), but the underlying mechanism upon how cannabinoids impact brain cognition and AD pathology remains unclear. Here we show that chronic cannabidiol (CBD) administration significantly mitigates cognitive deficiency and hippocampal β-amyloid (Aβ) pathology in 5×FAD mouse model of AD. CBD achieves its curative effect mainly through potentiating the function of inhibitory extrasynaptic glycine receptor (GlyR) in hippocampal dentate gyrus (DG). Based on the in vitro and in vivo electrophysiological recording and calcium imaging, CBD mediated anti-AD effects via GlyR are mainly accomplished by decreasing neuronal hyperactivity of granule cells in the DG of AD mice. Furthermore, the AAV-mediated ablation of DG GlyRα1, or the GlyRα1S296A mutation that exclusively disrupts CBD binding, significantly intercepts the anti-AD effect of CBD. These findings suggest a GlyR dependent mechanism underlying the therapeutic potential of CBD in the treatment of AD.

Predicting cognitive change using functional, structural, and neuropsychological predictors

To effectively address Alzheimer's disease, it is crucial to understand its earliest manifestations, underlying mechanisms and early markers of progression. Recent findings of very early brain activation anomalies highlight their potential for early disease characterization and predicting future cognitive decline. Our objective was to evaluate the value of brain activation-both individually and in combination with structural and neuropsychological measures-for predicting cognitive change. The study included 105 individuals from the Consortium for the Early Identification of Alzheimer's Disease-Quebec cohort who exhibited subjective cognitive decline or mild cognitive impairment. Cognitive decline was assessed by calculating the slope of Montreal Cognitive Assessment scores using regression models across successive assessments, and individuals were characterized as either decliners or stable based on clinically reliable change. We evaluated cognitive decline predictions using unimodal models for each class of predictors and multimodal models that combined these predictors. Functional activation emerged as a strong predictor of cognitive change (R²=52.5%), with 87.6% accuracy and 98.7% specificity, performing comparably to structural and neuropsychological measures. Although the unimodal functional model exhibited high specificity, indicating that functional abnormalities frequently predict future decline, it had low sensitivity (60%), meaning that the absence of abnormalities does not rule out future decline. Multimodal models provided greater explanatory power than unimodal models and greater sensitivity than the functional model. These findings highlight the potential role of early brain activation anomalies in the early detection of future cognitive changes, offering valuable insights for clinicians and researchers in assessing cognitive decline risk and refining clinical trial criteria.

Organelle perturbation in Alzheimer's disease: do intracellular amyloid-ß and the fragmented Golgi mediate early intracellular neurotoxicity?

Alzheimer's disease is a devastating and incurable neurological disease. Most of the current research has focused on developing drugs to clear the extracellular amyloid plaques in the brain of Alzheimer's disease patients. However, this approach is limited as it does not treat the underlying cause of the disease. In this review, we highlight the evidence in the field showing that the accumulation of intracellular toxic amyloid-ß could underpin very early events in neuronal death in both familial early-onset and sporadic late-onset alzheimer's disease. Indeed, intracellular amyloid-ß, which is produced within intracellular compartments, has been shown to perturb endosomal and secretory organelles, in different neuronal models, and the brain of Alzheimer's patients, leading to membrane trafficking defects and perturbation of neuronal function associated with cognition defects. The Golgi apparatus is a central transport and signaling hub at the crossroads of the secretory and endocytic pathways and perturbation of the Golgi ribbon structure is a hallmark of Alzheimer's disease. Here, we discuss the role of the Golgi as a major player in the regulation of amyloid-β production and propose that the Golgi apparatus plays a key role in a cellular network which can seed the onset of Alzheimer's disease. Moreover, we propose that the Golgi is central in an intracellular feedback loop leading to an enhanced level of amyloid-β production resulting in early neuronal defects before the appearance of clinical symptoms. Further advances in defining the molecular pathways of this intracellular feedback loop could support the design of new therapeutic strategies to target a primary source of neuronal toxicity in this disease.

Reactive EEG Biomarkers for Diagnosis and Prognosis of Alzheimer's Disease and Mild Cognitive Impairment

Alzheimer's disease (AD) is a devastating neurodegenerative condition characterized by progressive cognitive decline with currently no effective treatment available. One of the most critical areas in AD research is the identification of reliable biomarkers, which are essential for accurate diagnosis, prognostic assessment, and the development of targeted therapies. In this study, we introduce two novel reactive EEG (rEEG) biomarkers aimed at enhancing the diagnosis of AD and mild cognitive impairment (MCI). These biomarkers, previously unexplored in the literature, offer new insights into differentiating between various cognitive states. The first biomarker demonstrates a significant ability to distinguish between AD patients and normal controls (NC), while also effectively distinguishing MCI patients from NC. The second biomarker is designed to identify a subset of AD patients exhibiting hyperconductivity or hyperactivity, characterized by distinctive neural electrical patterns. A cohort of 90 elderly participants (mean age 76.63 ± 6.08 years) was recruited, including 30 AD patients, 30 individuals with MCI, and 30 NC subjects. Psychiatric diagnoses of participants were made by qualified professionals at Daejeon St. Mary's Hospital, The Catholic University of Korea, utilizing comprehensive neuropsychological assessments. Notably, the rEEG biomarkers achieved accuracies of 95%, 95%, and 98% in distinguishing between AD and NC, AD and MCI, and MCI and NC groups, respectively. These results underscore the potential of rEEG as a highly accurate and reliable diagnostic tool for cognitive impairments, including AD and MCI.

Longitudinal excitation-inhibition balance altered by sex and APOE-ε4

Neuronal hyperexcitation affects memory and neural processing across the Alzheimer's disease (AD) cognitive continuum. Levetiracetam, an antiepileptic, shows promise in improving cognitive impairment by restoring the neural excitation/inhibition balance in AD patients. We previously identified a hyper-excitable phenotype in cognitively unimpaired female APOE-ε4 carriers relative to male counterparts cross-sectionally. This sex difference lacks longitudinal validation; however, clarifying the vulnerability of female ε4-carriers could better inform antiepileptic treatment efficacy. Here, we investigated this sex-by-ε4 interaction using a longitudinal design. We used resting-state fMRI and diffusion tensor imaging collected longitudinally from 106 participants who were cognitively unimpaired for at least one scan event but may have been assessed to have clinical dementia ratings corresponding to early mild cognitive impairment over time. By including scan events where participants transitioned to mild cognitive impairment, we modeled the trajectory of the whole-brain excitation-inhibition ratio throughout the preclinical cognitively healthy continuum and extended to early impairment. A linear mixed model revealed a significant three-way interaction among sex, ε4-status, and time, with female ε4-carriers showing a significant hyper-excitable trajectory. These findings suggest a possible pathway for preventative therapy targeting preclinical hyperexcitation in female ε4-carriers.

Targeting Neural Oscillations for Cognitive Enhancement in Alzheimer's Disease

Alzheimer's disease (AD), the most prevalent form of dementia, is marked by progressive cognitive decline, affecting memory, language, orientation, and behavior. Pathological hallmarks include extracellular amyloid plaques and intracellular tau tangles, which disrupt synaptic function and connectivity. Neural oscillations, the rhythmic synchronization of neuronal activity across frequency bands, are integral to cognitive processes but become dysregulated in AD, contributing to network dysfunction and memory impairments. Targeting these oscillations has emerged as a promising therapeutic strategy. Preclinical studies have demonstrated that specific frequency modulations can restore oscillatory balance, improve synaptic plasticity, and reduce amyloid and tau pathology. In animal models, interventions, such as gamma entrainment using sensory stimulation and transcranial alternating current stimulation (tACS), have shown efficacy in enhancing memory function and modulating neuroinflammatory responses. Clinical trials have reported promising cognitive improvements with repetitive transcranial magnetic stimulation (rTMS) and deep brain stimulation (DBS), particularly when targeting key hubs in memory-related networks, such as the default mode network (DMN) and frontal-parietal network. Moreover, gamma-tACS has been linked to increased cholinergic activity and enhanced network connectivity, which are correlated with improved cognitive outcomes in AD patients. Despite these advancements, challenges remain in optimizing stimulation parameters, individualizing treatment protocols, and understanding long-term effects. Emerging approaches, including transcranial pulse stimulation (TPS) and closed-loop adaptive neuromodulation, hold promise for refining therapeutic strategies. Integrating neuromodulation with pharmacological and lifestyle interventions may maximize cognitive benefits. Continued interdisciplinary efforts are essential to refine these approaches and translate them into clinical practice, advancing the potential for neural oscillation-based therapies in AD.

Spatiotemporal analysis of gene expression in the human dentate gyrus reveals age-associated changes in cellular maturation and neuroinflammation

The dentate gyrus of the hippocampus is important for many cognitive functions, including learning, memory, and mood. Here, we present transcriptome-wide spatial gene expression maps of the human dentate gyrus and investigate age-associated changes across the lifespan. Genes associated with neurogenesis and the extracellular matrix are enriched in infants and decline throughout development and maturation. Following infancy, inhibitory neuron markers increase, and cellular proliferation markers decrease. We also identify spatio-molecular signatures that support existing evidence for protracted maturation of granule cells during adulthood and age-associated increases in neuroinflammation-related gene expression. Our findings support the notion that the hippocampal neurogenic niche undergoes major changes following infancy and identify molecular regulators of brain aging in glial- and neuropil-enriched tissue.

Structure-function relationships in the human aging brain: An account of cross-sectional and longitudinal multimodal neuroimaging studies

The patterns of brain activation and functional connectivity, task-related and task-free, as a function of age have been well documented over the past 30 years. However, the aging brain undergoes structural changes that are likely to affect the functional properties of the brain. The relationship between brain structure and function started to be investigated more recently. Brain structure and brain function can influence behavioral outcomes independently, and several studies highlight independent contribution of structure and function on cognition. Here, a central assumption is that brain structure also affects behavior indirectly through its influence on brain function. In such a model, structure supports function. Although findings generally suggest that structure may indeed influence function, the direction of the associations, the variability in terms of regional effects and age windows when associations are observed vary greatly. Also, a certain number of studies highlight the independent contribution of structure and function on cognition. A critical aspect of studying aging is the necessity of longitudinal designs, allowing to observe true aging effects - as compared with age differences in cross-sectional designs. This review aims to give an updated account on research dealing with multimodal neuroimaging in aging, and more specifically on the links between structure and function and associated cognitive outcomes, putting in parallel findings from cross-sectional and longitudinal studies. Additionally, we discuss potential mechanisms by which age-related changes in structure may affect function, but also factors (sample characteristics, methodology) that may contribute to the heterogeneity of the findings and the lack of consensus on the associations between structure, function, cognition and aging.

Neural circuit mechanisms underlying aberrantly prolonged functional hyperemia in young Alzheimer's disease mice

Neurovascular defects are one of the most common alterations in Alzheimer's disease (AD) pathogenesis, but whether these deficits develop before the onset of amyloid beta (Aβ) accumulation remains to be determined. Using in vivo optical imaging in freely moving mice, we explored activity-induced hippocampal microvascular blood flow dynamics in AppSAA knock-in and J20 mouse models of AD at early stages of disease progression. We found that prior to the onset of Aβ accumulation, there was a pathologically elevated blood flow response to context exploration, termed functional hyperemia. After the onset of Aβ accumulation, this context exploration-induced hyperemia declined rapidly relative to that in control mice. Using in vivo electrophysiology recordings to explore the neural circuit mechanism underlying this blood flow alteration, we found that hippocampal interneurons before the onset of Aβ accumulation were hyperactive during context exploration. Chemogenetic tests suggest that hyperactive activation of inhibitory neurons accounted for the elevated functional hyperemia. The suppression of nitric oxide (NO) produced from hippocampal interneurons in young AD mice decreased the accumulation of Aβ. Together, these findings reveal that neurovascular coupling is aberrantly elevated before Aβ deposition, and this hyperactive functional hyperemia declines rapidly upon Aβ accumulation.

Amyloid-associated hyperconnectivity drives tau spread across connected brain regions in Alzheimer's disease

In Alzheimer's disease (AD), amyloid-β (Aβ) triggers the aggregation and spreading of tau pathology, which drives neurodegeneration and cognitive decline. However, the pathophysiological link between Aβ and tau remains unclear, which hinders therapeutic efforts to attenuate Aβ-related tau accumulation. Aβ has been found to trigger neuronal hyperactivity and hyperconnectivity, and preclinical research has shown that tau spreads across connected neurons in an activity-dependent manner. Here, we hypothesized that neuronal hyperactivity and hypersynchronicity, resulting in functional connectivity increases, constitute a crucial mechanism by which Aβ facilitates the spreading of tau pathology. By combining Aβ positron emission tomography (PET), resting-state functional magnetic resonance imaging, and longitudinal tau-PET in 69 cognitively normal amyloid-negative controls and 140 amyloid-positive patients covering the AD spectrum, we confirmed that Aβ induces hyperconnectivity of temporal lobe tau epicenters to posterior brain regions that are vulnerable to tau accumulation in AD. This was replicated in an independent sample of 55 controls and 345 individuals with preclinical AD and low cortical tau-PET uptake, suggesting that the emergence of Aβ-related hyperconnectivity precedes neocortical tau spreading . Last, using longitudinal tau-PET and mediation analysis, we confirmed that these Aβ-related connectivity increases in tau epicenters to typical tau-vulnerable brain regions in AD mediated the effect of Aβ on faster tau accumulation, unveiling increased connectivity as a potential causal link between the two AD hallmark pathologies. Together, these findings suggest that Aβ promotes tau spreading by eliciting neuronal hyperconnectivity and that targeting Aβ-related neuronal hyperconnectivity may attenuate tau spreading in AD.

Adenosine deficiency facilitates CA1 synaptic hyperexcitability in the presymptomatic phase of a knockin mouse model of Alzheimer disease

The disease's trajectory of Alzheimer disease (AD) is associated with and negatively correlated to hippocampal hyperexcitability. Here, we show that during the asymptomatic stage in a knockin (KI) mouse model of Alzheimer disease (APPNL-G-F/NL-G-F; APPKI), hippocampal hyperactivity occurs at the synaptic compartment, propagates to the soma, and is manifesting at low frequencies of stimulation. We show that this aberrant excitability is associated with a deficient adenosine tone, an inhibitory neuromodulator, driven by reduced levels of CD39/73 enzymes, responsible for the extracellular ATP-to-adenosine conversion. Both pharmacologic (adenosine kinase inhibitor) and non-pharmacologic (ketogenic diet) restorations of the adenosine tone successfully normalize hippocampal neuronal activity. Our results demonstrated that neuronal hyperexcitability during the asymptomatic stage of a KI model of Alzheimer disease originated at the synaptic compartment and is associated with adenosine deficient tone. These results extend our comprehension of the hippocampal vulnerability associated with the asymptomatic stage of Alzheimer disease.

Revealing excitation-inhibition imbalance in Alzheimer's disease using multiscale neural model inversion of resting-state functional MRI

BACKGROUND

Alzheimer's disease (AD) is a serious neurodegenerative disorder without a clear understanding of pathophysiology. Recent experimental data have suggested neuronal excitation-inhibition (E-I) imbalance as an essential element of AD pathology, but E-I imbalance has not been systematically mapped out for either local or large-scale neuronal circuits in AD, precluding precise targeting of E-I imbalance in AD treatment.

METHOD

In this work, we apply a Multiscale Neural Model Inversion (MNMI) framework to the resting-state functional MRI data from the Alzheimer's Disease Neuroimaging Initiative (ADNI) to identify brain regions with disrupted E-I balance in a large network during AD progression.

RESULTS

We observe that both intra-regional and inter-regional E-I balance is progressively disrupted from cognitively normal individuals, to mild cognitive impairment (MCI) and to AD. Also, we find that local inhibitory connections are more significantly impaired than excitatory ones and the strengths of most connections are reduced in MCI and AD, leading to gradual decoupling of neural populations. Moreover, we reveal a core AD network comprised mainly of limbic and cingulate regions. These brain regions exhibit consistent E-I alterations across MCI and AD, and thus may represent important AD biomarkers and therapeutic targets. Lastly, the E-I balance of multiple brain regions in the core AD network is found to be significantly correlated with the cognitive test score.

CONCLUSIONS

Our study constitutes an important attempt to delineate E-I imbalance in large-scale neuronal circuits during AD progression, which may facilitate the development of new treatment paradigms to restore physiological E-I balance in AD.

Excessive Alcohol Use as a Risk Factor for Alzheimer's Disease: Epidemiological and Preclinical Evidence

Alcohol use has recently emerged as a modifiable risk factor for Alzheimer's disease (AD). However, the neurobiological mechanisms by which alcohol interacts with AD pathogenesis remain poorly understood. In this chapter, we review the epidemiological and preclinical support for the interaction between alcohol use and AD. We hypothesize that alcohol use increases the rate of accumulation of specific AD-relevant pathologies during the prodromal phase and exacerbates dementia onset and progression. We find that alcohol consumption rates are increasing in adolescence, middle age, and aging populations. In tandem, rates of AD are also on the rise, potentially as a result of this increased alcohol use throughout the lifespan. We then review the biological processes in common between alcohol use disorder and AD as a means to uncover potential mechanisms by which they interact; these include oxidative stress, neuroimmune function, metabolism, pathogenic tauopathy development and spread, and neuronal excitatory/inhibitory balance (EIB). Finally, we provide some forward-thinking suggestions we believe this field should consider. In particular, the inclusion of alcohol use assessments in longitudinal studies of AD and more preclinical studies on alcohol's impacts using better animal models of late-onset Alzheimer's disease (LOAD).

APOE ε4-associated heterogeneity of neuroimaging biomarkers across the Alzheimer's disease continuum

INTRODUCTION

While the role of apolipoprotein E (APOE) ε4 in Alzheimer's disease (AD) susceptibility has been studied extensively, much less is known about the differences in disease presentation in APOE ε4 carriers versus non-carriers.

METHODS

To help elucidate these differences, we performed a broad analysis comparing the regional levels of six different neuroimaging biomarkers in the brains of APOE ε4 carriers versus non-carriers who participated in the Alzheimer's Disease Neuroimaging Initiative (ADNI).

RESULTS

We observed significant APOE ε4-associated heterogeneity in regional amyloid beta deposition, tau accumulation, glucose uptake, brain volume, cerebral blood flow, and white matter hyperintensities within each AD diagnostic group. We also observed important APOE ε4-associated differences in cognitively unimpaired individuals who converted to mild cognitive impairment/AD versus those who did not convert.

DISCUSSION

This observed heterogeneity in neuroimaging biomarkers between APOE ε4 carriers versus non-carriers may have important implications regarding the prevention, diagnosis, and treatment of AD in different subpopulations.

HIGHLIGHTS

An extensive study was performed on the apolipoprotein E (APOE) ε4-associated heterogeneity in neuroimaging biomarkers from the Alzheimer's Disease Neuroimaging Initiative. Robust APOE ε4-associated increases in amyloid beta (Aβ) deposition throughout the brain, in every diagnostic group, were observed. APOE ε4-associated increases in tau pathology, decreases in glucose uptake, and increases in brain atrophy, which expand in regional scope and magnitude with disease progression, were observed. Significant sex- and age-related differences in APOE ε4-associated neuroimaging biomarker heterogeneity, with overall increases in pathological presentation in female APOE ε4 carriers, were observed. Regional differences in Aβ deposition, tau accumulation, glucose uptake, ventricle size, and white matter hyperintensities were observed in cognitively normal participants who converted to mild cognitive impairment/Alzheimer's disease, which may hold potential predictive value.

Recent developments in translational imaging of in vivo gene therapy outcomes

Gene therapy achieves therapeutic benefits by delivering genetic materials, packaged within a delivery vehicle, to target cells with defective genes. This approach has shown promise in treating various conditions, including cancer, metabolic disorders, and tissue-degenerative diseases. Over the past 5 years, molecular imaging has increasingly supported gene therapy development in both preclinical and clinical studies. High-quality images from positron emission tomography (PET), single-photon emission computed tomography (SPECT), magnetic resonance imaging (MRI), and computed tomography (CT) enable quantitative and reliable monitoring of gene therapy. Most reported studies have applied imaging biomarkers to non-invasively evaluate the outcomes of gene therapy. This review aims to inform researchers in molecular imaging and gene therapy about the integration of these two disciplines. We highlight recent developments in using imaging biomarkers to monitor the outcome of in vivo gene therapy, where the therapeutic delivery vehicle is administered systemically. In addition, we discuss prospects for further incorporating imaging biomarkers to support the development and application of gene therapy.

Rewiring of the glymphatic landscape in metabolic disorders

The incorporation of the glymphatic clearance system in the study of brain physiology aids in the advancement of innovative diagnostic and treatment strategies for neurological disorders. Exploring the glymphatic system across (from) neurological and (to) metabolic diseases may provide a better link between obesity and neurological disorders. Recent studies indicate the role of metabolic dysfunction as a risk factor for cognitive decline and neurological disorders through the disruption of the glymphatic system. Further investigation into how metabolic dysfunction disrupts glymphatic homeostasis and the domino effects on the neurovascular landscape, including neurovascular uncoupling, cerebral blood flow disruptions, blood-brain barrier leakage, and demyelination, can provide mechanistic insights into the link between obesity and neurological disorders.

Correlation Between Swallowing and Cognitive Brain Networks in Older Adults via Functional MRI

BACKGROUND

Clinical evidence supports that swallowing function is correlated with cognition, but the neurobiological mechanism associated with cognitive impairment and dysphagia remains unclear.

OBJECTIVES

To compare the brain activation patterns of the swallowing and the cognitive tasks and explore neural associations between swallowing and cognitive function via task-related functional magnetic resonance imaging (fMRI).

METHODS

A total of 13 healthy older adults (aged > 60 years) were recruited. Participants underwent the clinical dementia rating (CDR) test and the Montreal Cognitive Assessment (MoCA). A block-designed task-related fMRI study was conducted where each participant completed both swallowing and cognitive tasks within a single session. During the swallowing task, participants swallowed 2 mL of thickened water, while the Stroop Colour Word Test (SCWT) served as the cognitive task. First-level analysis of swallowing time-series images utilised the general linear model (GLM) with Statistical Parametric Mapping (SPM), applying a voxel threshold of p < 0.001 for significance. Common activations in brain regions during swallowing and cognitive tasks were extracted at the group level, with significance set at p < 0.05, corrected for multiple comparisons using the false discovery rate (FDR), with a minimum cluster size of 20 voxels. Correlation analysis between behavioural measurements and imaging signals was also conducted.

RESULTS

Some regions were commonly activated in both task networks; these regions were the bilateral occipital lobe, cerebellum, lingual gyrus, fusiform, middle frontal gyrus, precentral and postcentral gyrus, right supramarginal and inferior parietal lobe. Most importantly, the average beta value of cognitive and swallowing tasks in these areas are both significantly negative related to the MoCA score. Furthermore, opposite signal changes were seen in the bilateral prefrontal lobes during the swallowing task, while positive activation in the bilateral prefrontal lobes was observed during the SCWT. Postcentral gyrus activation was more extensive than precentral gyrus activation in the swallowing task.

CONCLUSION

The common activation of swallowing and cognitive tasks had multiple foci. The activity of cognitive and swallowing task in these areas is significantly negative correlated with the MoCA score. These findings may help to illustrate the association between dysphagia and cognitive impairment due to the common brain regions involved in cognition and swallowing and may provide a reference for further rehabilitation of dysphagia.

TRIAL REGISTRATION

Clinical Trial: (Chinese Clinical Trial Registry): ChiCTR1900021795.

Impaired spatial coding and neuronal hyperactivity in the medial entorhinal cortex of aged App NL-G-F mice

The progressive accumulation of amyloid beta (Aβ) pathology in the brain has been associated with aberrant neuronal network activity and poor cognitive performance in preclinical mouse models of Alzheimer's disease (AD). Presently, our understanding of the mechanisms driving pathology-associated neuronal dysfunction and impaired information processing in the brain remains incomplete. Here, we assessed the impact of advanced Aβ pathology on spatial information processing in the medial entorhinal cortex (MEC) of 18-month App NL-G-F/NL- G-F knock-in (APP KI) mice as they explored contextually novel and familiar open field arenas in a two-day, four-session recording paradigm. We tracked single unit firing activity across all sessions and found that spatial information scores were decreased in MEC neurons from APP KI mice versus those in age-matched C57BL/6J controls. MEC single unit spatial representations were also impacted in APP KI mice. Border cell firing preferences were unstable across sessions and spatial periodicity in putative grid cells was disrupted. In contrast, MEC border cells and grid cells in Control mice were intact and stable across sessions. We then quantified the stability of MEC spatial maps across sessions by utilizing a metric based on the Earth Mover's Distance (EMD). We found evidence for increased instability in spatially-tuned APP KI MEC neurons versus Controls when mice were re-exposed to familiar environments and exposed to a novel environment. Additionally, spatial decoding analysis of MEC single units revealed deficits in position and speed coding in APP KI mice in all session comparisons. Finally, MEC single unit analysis revealed a mild hyperactive phenotype in APP KI mice that appeared to be driven by narrow-spiking units (putative interneurons). These findings tie Aβ-associated dysregulation in neuronal firing to disruptions in spatial information processing that may underlie certain cognitive deficits associated with AD.

β-amyloid's neurotoxic mechanisms as defined by in vitro microelectrode arrays: a review

Alzheimer's disease is characterized by the aggregation of β-amyloid, a pathological feature believed to drive the neuronal loss and cognitive decline commonly seen in the disease. Given the growing prevalence of this progressive neurodegenerative disease, understanding the exact mechanisms underlying this process has become a top priority. Microelectrode arrays are commonly used for chronic, non-invasive recording of both spontaneous and evoked neuronal activity from diverse in vitro disease models and to evaluate therapeutic or toxic compounds. To date, microelectrode arrays have been used to investigate β-amyloids' toxic effects, β-amyloids role in specific pathological features and to assess pharmacological approaches to treat Alzheimer's disease. The versatility of microelectrode arrays means these studies use a variety of methods and investigate different disease models and brain regions. This review provides an overview of these studies, highlighting their disparities and presenting the status of the current literature. Despite methodological differences, the current literature indicates that β-amyloid has an inhibitory effect on synaptic plasticity and induces network connectivity disruptions. β-amyloid's effect on spontaneous neuronal activity appears more complex. Overall, the literature corroborates the theory that β-amyloid induces neurotoxicity, having a progressive deleterious effect on neuronal signaling and plasticity. These studies also confirm that microelectrode arrays are valuable tools for investigating β-amyloid pathology from a functional perspective, helping to bridge the gap between cellular and network pathology and disease symptoms. The use of microelectrode arrays provides a functional insight into Alzheimer's disease pathology which will aid in the development of novel therapeutic interventions.

Structural and functional remodeling of neural networks in β-amyloid driven hippocampal hyperactivity

Early detection of Alzheimer's disease (AD) is essential for improving the patients outcomes and advancing our understanding of disease, allowing for timely intervention and treatment. However, accurate biomarkers are still lacking. Recent evidence indicates that hippocampal hyperexcitability precedes the diagnosis of AD decades ago, can predict cognitive decline. Thus, could hippocampal hyperactivity be a robust biomarker for early-AD, and what drives hippocampal hyperactivity in early-AD? these critical questions remain to be answered. Increasing clinical and experimental studies suggest that early hippocampal activation is closely associated with longitudinal β-amyloid (Aβ) accumulation, Aβ aggregates, in turn, enhances hippocampal activity. Therefore, in this narrative review, we discuss the role of Aβ-induced altered intrinsic neuronal properties as well as structural and functional remodeling of glutamatergic, GABAergic, cholinergic, noradrenergic, serotonergic circuits in hippocampal hyperactivity. In addition, we analyze the available therapies and trials that can potentially be used clinically to attenuate hippocampal hyperexcitability in AD. Overall, the present review sheds lights on the mechanism behind Aβ-induced hippocampal hyperactivity, and highlights that hippocampal hyperactivity could be a robust biomarker and therapeutic target in prodromal AD.

Astrocyte transcriptomic analysis identifies glypican 5 downregulation as a contributor to synaptic dysfunction in Alzheimer's disease models

Synaptic dysfunction is an early feature in Alzheimer's disease (AD) and correlates with cognitive decline. Astrocytes are essential regulators of synapses, impacting synapse formation, maturation, elimination and function. To understand if synapse-supportive functions of astrocytes are altered in AD, we used astrocyte BacTRAP mice to generate a comprehensive dataset of hippocampal astrocyte transcriptional alterations in two mouse models of Alzheimer's pathology (APPswe/PS1dE9 and Tau P301S), characterizing sex and age-dependent changes. We found that astrocytes from both models downregulate genes important for synapse regulation and function such as the synapse-maturation factor Glypican 5. This transcriptional signature is shared with human post-mortem AD patients. Manipulating a key component of this signature by in vivo overexpression of Glypican 5 in astrocytes is sufficient to prevent early synaptic dysfunction and improve spatial learning in APPswe/PS1dE9 mice. These findings open new avenues to target astrocytic factors to mitigate AD synaptic dysfunction.

Cerebral hyperactivation across the Alzheimer's disease pathological cascade

Neuronal dysfunction in specific brain regions or across distributed brain networks is a known feature of Alzheimer's disease. An often reported finding in the early stage of the disease is the presence of increased functional MRI (fMRI) blood oxygenation level-dependent signal under task conditions relative to cognitively normal controls, a phenomenon known as 'hyperactivation'. However, research in the past decades yielded complex, sometimes conflicting results. The magnitude and topology of fMRI hyperactivation patterns have been found to vary across the preclinical and clinical spectrum of Alzheimer's disease, including concomitant 'hypoactivation' in some cases. These incongruences are likely due to a range of factors, including the disease stage at which the cohort is examined, the brain areas or networks studied and the fMRI paradigm utilized to evoke these functional abnormalities. Additionally, a perennial question pertains to the nature of hyperactivation in the context of Alzheimer's disease. Some propose it reflects compensatory mechanisms to sustain cognitive performance, while others suggest it is linked to the pathological disruption of a highly regulated homeostatic cycle that contributes to, or even drives, disease progression. Providing a coherent narrative for these empirical and conceptual discrepancies is paramount to develop disease models, understand the synergy between hyperactivation and the Alzheimer's disease pathological cascade and tailor effective interventions. We first provide a comprehensive overview of functional brain changes spanning the course from normal ageing to the clinical spectrum of Alzheimer's disease. We then highlight evidence supporting a close relationship between fMRI hyperactivation and in vivo markers of Alzheimer's pathology. We primarily focus on task-based fMRI studies in humans, but also consider studies using different functional imaging techniques and animal models. We then discuss the potential mechanisms underlying hyperactivation in the context of Alzheimer's disease and provide a testable framework bridging hyperactivation, ageing, cognition and the Alzheimer's disease pathological cascade. We conclude with a discussion of future challenges and opportunities to advance our understanding of the fundamental disease mechanisms of Alzheimer's disease, and the promising development of therapeutic interventions incorporating or aimed at hyperactivation and large-scale functional systems.

PS1/gamma-secretase acts as rogue chaperone of glutamate transporter EAAT2/GLT-1 in Alzheimer's disease

The recently discovered interaction between presenilin 1 (PS1), a subunit of γ-secretase involved in amyloid-β (Aβ) peptide production, and GLT-1, the major brain glutamate transporter (EAAT2 in the human), may link two pathological aspects of Alzheimer's disease: abnormal Aβ occurrence and neuronal network hyperactivity. In the current study, we employed a FRET-based fluorescence lifetime imaging microscopy (FLIM) to characterize the PS1/GLT-1 interaction in brain tissue from sporadic AD (sAD) patients. sAD brains showed significantly less PS1/GLT-1 interaction than those with frontotemporal lobar degeneration or non-demented controls. Familial AD (fAD) PS1 mutations, inducing a "closed" PS1 conformation similar to that in sAD brain, and gamma-secretase modulators (GSMs), inducing a "relaxed" conformation, respectively reduced and increased the interaction. Furthermore, PS1 influences GLT-1 cell surface expression and homomultimer formation, acting as a chaperone but not affecting GLT-1 stability. The diminished PS1/GLT-1 interaction suggests that these functions may not work properly in AD.

The HOPE4MCI study: AGB101 treatment slows progression of entorhinal cortex atrophy in APOE ε4 non-carriers with mild cognitive impairment due to Alzheimer's disease

Introduction

Hippocampal hyperactivity is a hallmark of prodromal Alzheimer's disease (AD) that predicts progression in patients with amnestic mild cognitive impairment (aMCI). AGB101 is an extended-release formulation of levetiracetam in the dose range previously demonstrated to normalize hippocampal activity and improve cognitive performance in aMCI. The HOPE4MCI study was a 78-week trial to assess the progression of MCI due to AD. As reported in Mohs et al., the decline in the Clinical Dementia Rating Sum of Boxes score (CDR-SB) was reduced by 40% in apolipoprotein E (APOE) ε4 non-carriers over the 78-week duration of the study with a negligible effect in carriers. Here we report an exploratory analysis of the effects of AGB101 on neuroimaging and biomarker measures in the 44 APOE ε4 non-carriers who completed the 78-week protocol.

Methods

Structural magnetic resonance imaging scans obtained at baseline and after 78 weeks were analyzed using the Automated Segmentation of Hippocampal Subfields software providing volume measures of key structures of the medial temporal lobe relevant to AD progression. Blood samples collected at 78 weeks in the study were analyzed for plasma biomarkers.

Results

Treatment with AGB101 significantly reduced atrophy of the left entorhinal cortex (ERC) compared to placebo. This reduction in atrophy was correlated with less decline in the CDR-SB score over 78 weeks and with lower neurofilament light chain (NfL), a marker of neurodegeneration.

Discussion

The HOPE4MCI study showed that APOE ε4 non-carriers treated with AGB101 demonstrated a substantially more favorable treatment effect compared to carriers. Here we report that treatment with AGB101 in non-carriers of APOE ε4 significantly reduced atrophy of the left ERC over 78 weeks. That reduction in atrophy was closely coupled with the change in CDR-SB and with plasma NfL indicative of neurodegeneration in the brain. These exploratory analyses are consistent with a reduction in neurodegeneration in APOE ε4 non-carriers treated with AGB101 before a clinical diagnosis of dementia.

Highlights

AGB101 slows entorhinal cortex (ERC) atrophy in apolipoprotein E (APOE) ε4 non-carriers with mild cognitive impairment (MCI) due to Alzheimer's disease (AD).Slowing ERC atrophy by AGB101 is associated with less Clinical Dementia Rating Sum of Boxes decline.Slowing ERC atrophy by AGB101 is associated with lower neurofilament light chain.AGB101 treatment reduces neurodegeneration in APOE ε4 non-carriers with MCI due to AD.

Age differences in BOLD modulation to task difficulty as a function of amyloid burden

Effective cognitive performance often requires the allocation of additional neural resources (i.e. blood-oxygen-level-dependent [BOLD] activation) as task demands increase, and this demand-related modulation is affected by amyloid-beta deposition and normal aging. The present study investigated these complex relationships between amyloid, modulation, and cognitive function (i.e. fluid ability). Participants from the Dallas Lifespan Brain Study (DLBS, n = 252, ages 50-89) completed a semantic judgment task during functional magnetic resonance imaging (fMRI) where the judgments differed in classification difficulty. Amyloid burden was assessed via positron emission tomography (PET) using 18F-florbetapir. A quadratic relationship between amyloid standardized value uptake ratios (SUVRs) and BOLD modulation was observed such that modulation was weaker in those with moderately elevated SUVRs (e.g. just reaching amyloid-positivity), whereas those with very high SUVRs (e.g. SUVR > 1.5) showed strong modulation. Greater modulation was related to better fluid ability, and this relationship was strongest in younger participants and those with lower amyloid burden. These results support the theory that effective demand-related modulation contributes to healthy cognitive aging, especially in the transition from middle age to older adulthood, whereas high modulation may be dysfunctional in those with substantial amyloid deposition.

Chronic Neuronal Hyperexcitation Exacerbates Tau Propagation in a Mouse Model of Tauopathy

The intracerebral spread of tau is a critical mechanism associated with functional decline in Alzheimer's disease (AD) and other tauopathies. Recently, a hypothesis has emerged suggesting that tau propagation is linked to functional neuronal connections, specifically driven by neuronal hyperactivity. However, experimental validation of this hypothesis remains limited. In this study, we investigated how tau propagation from the entorhinal cortex to the hippocampus, the neuronal circuit most susceptible to tau pathology in AD, is affected by the selective stimulation of neuronal activity along this circuit. Using a mouse model of seed-induced propagation combined with optogenetics, we found that the chronic stimulation of this neuronal connection over a 4-week period resulted in a significant increase in insoluble tau accumulation in both the entorhinal cortex and hippocampus. Importantly, the ratio of tau accumulation in the hippocampus relative to that in the entorhinal cortex, serving as an indicator of transcellular spreading, was significantly higher in mice subjected to chronic stimulation. These results support the notion that abnormal neuronal activity promotes tau propagation, thereby implicating it in the progression of tauopathy.

β-amyloid monomer scavenging by an anticalin protein prevents neuronal hyperactivity in mouse models of Alzheimer's Disease

Hyperactivity mediated by synaptotoxic β-amyloid (Aβ) oligomers is one of the earliest forms of neuronal dysfunction in Alzheimer's disease. In the search for a preventive treatment strategy, we tested the effect of scavenging Aβ peptides before Aβ plaque formation. Using in vivo two-photon calcium imaging and SF-iGluSnFR-based glutamate imaging in hippocampal slices, we demonstrate that an Aβ binding anticalin protein (Aβ-anticalin) can suppress early neuronal hyperactivity and synaptic glutamate accumulation in the APP23xPS45 mouse model of β-amyloidosis. Our results suggest that the sole targeting of Aβ monomers is sufficient for the hyperactivity-suppressing effect of the Aβ-anticalin at early disease stages. Biochemical and neurophysiological analyses indicate that the Aβ-anticalin-dependent depletion of naturally secreted Aβ monomers interrupts their aggregation to neurotoxic oligomers and, thereby, reverses early neuronal and synaptic dysfunctions. Thus, our results suggest that Aβ monomer scavenging plays a key role in the repair of neuronal function at early stages of AD.

Abnormal cerebral blood flow and brain function in type 2 diabetes mellitus

PURPOSE

Type 2 diabetes mellitus (T2DM) lead to impaired cerebral blood perfusion, which leads to changes in brain function and affects the cognitive function of patients. In this study, cerebral blood flow (CBF) was used to evaluate the effect of T2DM on cerebral perfusion, and functional connectivity (FC) analysis was further used to explore whether the FC between the abnormal CBF region and the whole brain was changed. In addition, amplitude of low-frequency fluctuation (ALFF) and degree centrality (DC) were used to investigate the changes in spontaneous activity and connectivity strength of the brain network.

METHODS

We recruited 40 T2DM patients and 55 healthy controls (HCs). They underwent 3D-T1WI, rs-fMRI, arterial spin labeling (ASL) sequence scans and a series of cognitive tests. Cognitive test scores and brain imaging indicators were compared between the two groups, and the relationships among laboratory indicators, cognitive test scores, and brain imaging indicators were explored in the T2DM group.

RESULTS

Compared to HCs, The CBF values of Calcarine_L and Precuneus_R in the T2DM group were lower. The DC value of Paracentral_Lobule_L and Precuneus_L, and the ALFF value of Hippocampus_L in the T2DM group were higher. In addition, the CBF values of Calcarine_L was negatively correlated with fasting insulin and HOMA_IR.

CONCLUSION

This study found that there were regions of cerebral hypoperfusion in T2DM patients, which are associated with insulin resistance. In addition, we found abnormally elevated brain activity and enhanced functional connectivity in T2DM patients, which we speculated was the compensatory mechanism of brain neural activity.

Three dimensional and four dimensional live imaging to study mechanisms of progressive neurodegeneration

Neurodegenerative diseases are complex and progressive, posing challenges to their study and understanding. Recent advances in microscopy imaging technologies have enabled the exploration of neurons in three spatial dimensions (3D) over time (4D). When applied to 3D cultures, tissues, or animals, these technologies can provide valuable insights into the dynamic and spatial nature of neurodegenerative diseases. This review focuses on the use of imaging techniques and neurodegenerative disease models to study neurodegeneration in 4D. Imaging techniques such as confocal microscopy, two-photon microscopy, miniscope imaging, light sheet microscopy, and robotic microscopy offer powerful tools to visualize and analyze neuronal changes over time in 3D tissue. Application of these technologies to in vitro models of neurodegeneration such as mouse organotypic culture systems and human organoid models provide versatile platforms to study neurodegeneration in a physiologically relevant context. Additionally, use of 4D imaging in vivo, including in mouse and zebrafish models of neurodegenerative diseases, allows for the investigation of early dysfunction and behavioral changes associated with neurodegeneration. We propose that these studies have the power to overcome the limitations of two-dimensional monolayer neuronal cultures and pave the way for improved understanding of the dynamics of neurodegenerative diseases and the development of effective therapeutic strategies.

Endogenous tau released from human ReNCell VM cultures by neuronal activity is phosphorylated at multiple sites

Tau is an intracellular protein but also known to be released into the extracellular fluid. Tau release mechanisms have drawn intense attention as these are known to play a key role in Alzheimer's disease (AD) pathology. However, tau can also be released under physiological conditions although its physiological function and release mechanisms have been poorly characterized, especially in human neuronal cells. We investigated endogenous tau release in ReNCell VM, a human neuroprogenitor cell line, under physiological conditions and found that tau is spontaneously released from cells. To study activity-dependent release of endogenous tau, human ReNCell VM culture was stimulated by 100μM AMPA or 50mM KCl for one-hour, tau was actively released to the culture medium. The released tau was highly phosphorylated at nine phosphorylation sites (pSites) detected by phospho-specific tau antibodies including AT270 (T175/T181), AT8 (S202/T205), AT100 (T212/S214), AT180 (T231), and PHF-1 (S396/S404), showing that these pSites are important for activity-dependent tau release from human ReNCell VM. Intracellular tau showed various phosphorylation status across these sites, with AT270 and PHF-1 highly phosphorylated while AT8 and AT180 were minimally phosphorylated, suggesting that AT8 and AT180 pSites exhibit a propensity for secretion rather than being retained intracellularly. This activity-dependent tau release was significantly decreased by inhibition of GSK-3β, demonstrating that GSK3β-dependent phosphorylation of tau plays an important role in its release by neuronal activity. In this study, we showed that ReNCell VM serves as a valuable model for studying endogenous physiological tau release. Further, ReNCell model can be also used to study pathological release of human tau that will contribute to our understanding of the progression of AD and related dementias.

Synaptic adhesion molecule protocadherin-γC5 mediates β-amyloid-induced neuronal hyperactivity and cognitive deficits in Alzheimer's disease

Neuronal hyperactivity induced by β-amyloid (Aβ) is an early pathological feature in Alzheimer's disease (AD) and contributes to cognitive decline in AD progression. However, the underlying mechanisms are still unclear. Here, we revealed that Aβ increased the expression level of synaptic adhesion molecule protocadherin-γC5 (Pcdh-γC5) in a Ca2+-dependent manner, associated with aberrant elevation of synapses in both Aβ-treated neurons in vitro and the cortex of APP/PS1 mice in vivo. By using Pcdhgc5 gene knockout mice, we demonstrated the critical function of Pcdh-γC5 in regulating neuronal synapse formation, synaptic transmission, and cognition. To further investigate the role of Pcdh-γC5 in AD pathogenesis, the aberrantly enhanced expression of Pcdh-γC5 in the brain of APP/PS1 mice was knocked down by shRNA. Downregulation of Pcdh-γC5 efficiently rescued neuronal hyperactivity and impaired cognition in APP/PS1 mice. Our findings revealed the pathophysiological role of Pcdh-γC5 in mediating Aβ-induced neuronal hyperactivity and cognitive deficits in AD and identified a novel mechanism underlying AD pathogenesis.

Biomarker evidence of early vision and rod energy-linked pathophysiology benefits from very low dose DMSO in 5xFAD mice

Here, we test whether early visual and OCT rod energy-linked biomarkers indicating pathophysiology in nicotinamide nucleotide transhydrogenase (Nnt)-null 5xFAD mice also occur in Nnt-intact 5xFAD mice and whether these biomarkers can be pharmacologically treated. Four-month-old wild-type or 5xFAD C57BL/6 substrains with either a null (B6J) Nnt or intact Nnt gene (B6NTac) and 5xFAD B6J mice treated for one month with either R-carvedilol + vehicle or only vehicle (0.01% DMSO) were studied. The contrast sensitivity (CS), external limiting membrane-retinal pigment epithelium (ELM-RPE) thickness (a proxy for low pH-triggered water removal), profile shape of the hyperreflective band just posterior to the ELM (i.e., the mitochondrial configuration within photoreceptors per aspect ratio [MCP/AR]), and retinal laminar thickness were measured. Both wild-type substrains showed similar visual performance indices and dark-evoked ELM-RPE contraction. The lack of a light-dark change in B6NTac MCP/AR, unlike in B6J mice, is consistent with relatively greater mitochondrial efficiency. 5xFAD B6J mice, but not 5xFAD B6NTac mice, showed lower-than-WT CS. Light-adapted 5xFAD substrains both showed abnormal ELM-RPE contraction and greater-than-WT MCP/AR contraction. The inner retina and superior outer retina were thinner. Treating 5xFAD B6J mice with R-carvedilol + DMSO or DMSO alone corrected CS and ELM-RPE contraction but not supernormal MCP/AR contraction or laminar thinning. These results provide biomarker evidence for prodromal photoreceptor mitochondrial dysfunction/oxidative stress/oxidative damage, which is unrelated to visual performance, as well as the presence of the Nnt gene. This pathophysiology is druggable in 5xFAD mice.

Perturbation-based dual task assessment in older adults with mild cognitive impairment

Background

Dual tasking (i.e., concurrent performance of motor and cognitive task) is significantly impaired in older adults with mild cognitive impairment (OAwMCI) compared to cognitively intact older adults (CIOA) and has been associated with increased fall risk. Dual task studies have primarily examined volitionally driven events, and the effects of mild cognitive impairment on reactive balance control (i.e., the ability to recover from unexpected balance threats) are unexplored. We examined the effect of cognitive tasks on reactive balance control in OAwMCI compared to CIOA.

Methods

Adults >55 years were included and completed the Montreal Cognitive Assessment (MoCA) to categorize them as OAwMCI (MoCA: 18-24, n = 15) or CIOA (MoCA: ≥25, n = 15). Both OAwMCI [MoCA: 22.4 (2.2), 65.4 (6.1) years, 3 females] and CIOA [MoCA: 28.4 (1.3), 68.2 (5.5) years, 10 females] responded to large magnitude stance slip-like perturbations alone (single task) and while performing perceptual cognitive tasks targeting the visuomotor domain (target and tracking game). In these tasks, participants rotated their head horizontally to control a motion mouse and catch a falling target (target game) or track a moving object (track). Margin of stability (MOS) and fall outcome (harness load cell >30% body weight) were used to quantify reactive balance control. Cognitive performance was determined using performance error (target) and sum of errors (tracking). A 3 × 2 repeated measures ANOVA examined the effect of group and task on MOS, and generalized estimating equations (GEE) model was used to determine changes in fall outcome between groups and tasks. 2 × 2 repeated measures ANOVAs examined the effect of group and task on cognitive performance.

Results

Compared to CIOA, OAwMCI exhibited significantly deteriorated MOS and greater number of falls during both single task and dual task (p < 0.05), and lower dual task tracking performance (p < 0.01). Compared to single task, both OAwMCI and CIOA exhibited significantly deteriorated perceptual cognitive performance during dual task (p < 0.05); however, no change in MOS or fall outcome between single task and dual task was observed.

Conclusion

Cognitive impairment may diminish the ability to compensate and provide attentional resources demanded by sensory systems to integrate perturbation specific information, resulting in deteriorated ability to recover balance control among OAwMCI.

Familial Alzheimer's Disease Neurons Bearing Mutations in PSEN1 Display Increased Calcium Responses to AMPA as an Early Calcium Dysregulation Phenotype

Familial Alzheimer's disease (FAD) can be caused by mutations in PSEN1 that encode presenilin-1, a component of the gamma-secretase complex that cleaves amyloid precursor protein. Alterations in calcium (Ca2+) homeostasis and glutamate signaling are implicated in the pathogenesis of FAD; however, it has been difficult to assess in humans whether or not these phenotypes are the result of amyloid or tau pathology. This study aimed to assess the early calcium and glutamate phenotypes of FAD by measuring the Ca2+ response of induced pluripotent stem cell (iPSC)-derived neurons bearing PSEN1 mutations to glutamate and the ionotropic glutamate receptor agonists NMDA, AMPA, and kainate compared to isogenic control and healthy lines. The data show that in early neurons, even in the absence of amyloid and tau phenotypes, FAD neurons exhibit increased Ca2+ responses to glutamate and AMPA, but not NMDA or kainate. Together, this suggests that PSEN1 mutations alter Ca2+ and glutamate signaling as an early phenotype of FAD.

Functional connectivity favors aberrant visual network c-Fos expression accompanied by cortical synapse loss in a mouse model of Alzheimer's disease

While Alzheimer's disease (AD) has been extensively studied with a focus on cognitive networks, sensory network dysfunction has received comparatively less attention despite compelling evidence of its significance in both Alzheimer's disease patients and mouse models. We recently found that neurons in the primary visual cortex of an AD mouse model expressing human amyloid protein precursor with the Swedish and Indiana mutations (hAPP mutations) exhibit aberrant c-Fos expression and altered synaptic structures at a pre-amyloid plaque stage. However, it is unclear whether aberrant c-Fos expression and synaptic pathology vary across the broader visual network and to what extent c-Fos abnormality in the cortex is inherited through functional connectivity. Using both sexes of 4-6-month AD model mice with hAPP mutations (J20[PDGF-APPSw, Ind]), we found that cortical regions of the visual network show aberrant c-Fos expression and impaired experience-dependent modulation while subcortical regions do not. Interestingly, the average network-wide functional connectivity strength of a brain region in wild type (WT) mice significantly predicts its aberrant c-Fos expression, which in turn correlates with impaired experience-dependent modulation in the AD model. Using in vivo two-photon and ex vivo imaging of presynaptic termini, we observed a subtle yet selective weakening of excitatory cortical synapses in the visual cortex. Intriguingly, the change in the size distribution of cortical boutons in the AD model is downscaled relative to those in WT mice, suggesting that synaptic weakening may reflect an adaptation to aberrant activity. Our observations suggest that cellular and synaptic abnormalities in the AD model represent a maladaptive transformation of the baseline physiological state seen in WT conditions rather than entirely novel and unrelated manifestations.

Spatiotemporal analysis of gene expression in the human dentate gyrus reveals age-associated changes in cellular maturation and neuroinflammation

The dentate gyrus of the hippocampus is important for many cognitive functions, including learning, memory, and mood. Here, we investigated age-associated changes in transcriptome-wide spatial gene expression in the human dentate gyrus across the lifespan. Genes associated with neurogenesis and the extracellular matrix were enriched in infants, while gene markers of inhibitory neurons and cell proliferation showed increases and decreases in post-infancy, respectively. While we did not find evidence for neural proliferation post-infancy, we did identify molecular signatures supporting protracted maturation of granule cells. We also identified a wide-spread hippocampal aging signature and an age-associated increase in genes related to neuroinflammation. Our findings suggest major changes to the putative neurogenic niche after infancy and identify molecular foci of brain aging in glial and neuropil enriched tissue.

A nonlinear meccano for Alzheimer's emergence by amyloid β-mediated glutamatergic hyperactivity

The pathophysiological process of Alzheimer's disease (AD) is believed to begin many years before the formal diagnosis of AD dementia. This protracted preclinical phase offers a crucial window for potential therapeutic interventions, yet its comprehensive characterization remains elusive. Accumulating evidence suggests that amyloid-β (Aβ) may mediate neuronal hyperactivity in circuit dysfunction in the early stages of AD. At the same time, neural activity can also facilitate Aβ accumulation through intricate feed-forward interactions, complicating elucidating the conditions governing Aβ-dependent hyperactivity and its diagnostic utility. In this study, we use biophysical modeling to shed light on such conditions. Our analysis reveals that the inherently nonlinear nature of the underlying molecular interactions can give rise to the emergence of various modes of hyperactivity. This diversity in the mechanisms of hyperactivity may ultimately account for a spectrum of AD manifestations.

Adenosine deficiency facilitates CA1 synaptic hyperexcitability in the presymptomatic phase of a knock in mouse model of Alzheimer's disease

The disease's trajectory of Alzheimer's disease (AD) is associated with and worsened by hippocampal hyperexcitability. Here we show that during the asymptomatic stage in a knock in mouse model of Alzheimer's disease (APPNL-G-F/NL-G-F; APPKI), hippocampal hyperactivity occurs at the synaptic compartment, propagates to the soma and is manifesting at low frequencies of stimulation. We show that this aberrant excitability is associated with a deficient adenosine tone, an inhibitory neuromodulator, driven by reduced levels of CD39/73 enzymes, responsible for the extracellular ATP-to-adenosine conversion. Both pharmacologic (adenosine kinase inhibitor) and non-pharmacologic (ketogenic diet) restorations of the adenosine tone successfully normalize hippocampal neuronal activity. Our results demonstrated that neuronal hyperexcitability during the asymptomatic stage of a KI model of Alzheimer's disease originated at the synaptic compartment and is associated with adenosine deficient tone. These results extend our comprehension of the hippocampal vulnerability associated with the asymptomatic stage of Alzheimer's disease.

Baseline functional connectivity predicts who will benefit from neuromodulation: evidence from primary progressive aphasia

Background

Identifying the characteristics of individuals who demonstrate response to an intervention allows us to predict who is most likely to benefit from certain interventions. Prediction is challenging in rare and heterogeneous diseases, such as primary progressive aphasia (PPA), that have varying clinical manifestations. We aimed to determine the characteristics of those who will benefit most from transcranial direct current stimulation (tDCS) of the left inferior frontal gyrus (IFG) using a novel heterogeneity and group identification analysis.

Methods

We compared the predictive ability of demographic and clinical patient characteristics (e.g., PPA variant and disease progression, baseline language performance) vs. functional connectivity alone (from resting-state fMRI) in the same cohort.

Results

Functional connectivity alone had the highest predictive value for outcomes, explaining 62% and 75% of tDCS effect of variance in generalization (semantic fluency) and in the trained outcome of the clinical trial (written naming), contrasted with <15% predicted by clinical characteristics, including baseline language performance. Patients with higher baseline functional connectivity between the left IFG (opercularis and triangularis), and between the middle temporal pole and posterior superior temporal gyrus, were most likely to benefit from tDCS.

Conclusions

We show the importance of a baseline 7-minute functional connectivity scan in predicting tDCS outcomes, and point towards a precision medicine approach in neuromodulation studies. The study has important implications for clinical trials and practice, providing a statistical method that addresses heterogeneity in patient populations and allowing accurate prediction and enrollment of those who will most likely benefit from specific interventions.

Identification of PS1/gamma-secretase and glutamate transporter GLT-1 interaction sites

The recently discovered interaction between Presenilin 1 (PS1), a catalytic subunit of γ-secretase responsible for generating amyloid-β peptides, and GLT-1, a major glutamate transporter in the brain (EAAT2), provides a mechanistic link between these two key factors involved in Alzheimer's disease (AD) pathology. Modulating this interaction can be crucial to understand the consequence of such crosstalk in AD context and beyond. However, the interaction sites between these two proteins are unknown. Herein, we utilized an alanine scanning approach coupled with FRET-based fluorescence lifetime imaging microscopy to identify the interaction sites between PS1 and GLT-1 in their native environment within intact cells. We found that GLT-1 residues at position 276 to 279 (TM5) and PS1 residues at position 249 to 252 (TM6) are crucial for GLT-1-PS1 interaction. These results have been cross validated using AlphaFold Multimer prediction. To further investigate whether this interaction of endogenously expressed GLT-1 and PS1 can be prevented in primary neurons, we designed PS1/GLT-1 cell-permeable peptides (CPPs) targeting the PS1 or GLT-1 binding site. We used HIV TAT domain to allow for cell penetration which was assayed in neurons. First, we assessed the toxicity and penetration of CPPs by confocal microscopy. Next, to ensure the efficiency of CPPs, we monitored the modulation of GLT-1-PS1 interaction in intact neurons by fluorescence lifetime imaging microscopy. We saw significantly less interaction between PS1 and GLT-1 with both CPPs. Our study establishes a new tool to study the functional aspect of GLT-1-PS1 interaction and its relevance in normal physiology and AD models.

Intrinsic Plasticity Mechanisms of Repetitive Transcranial Magnetic Stimulation

Repetitive transcranial magnetic stimulation (rTMS) has become an increasingly popular tool to modulate neural excitability and induce neural plasticity in clinical and preclinical models; however, the physiological mechanisms in which it exerts these effects remain largely unknown. To date, studies have primarily focused on characterizing rTMS-induced changes occurring at the synapse, with little attention given to changes in intrinsic membrane properties. However, accumulating evidence suggests that rTMS may induce its effects, in part, via intrinsic plasticity mechanisms, suggesting a new and potentially complementary understanding of how rTMS alters neural excitability and neural plasticity. In this review, we provide an overview of several intrinsic plasticity mechanisms before reviewing the evidence for rTMS-induced intrinsic plasticity. In addition, we discuss a select number of neurological conditions where rTMS-induced intrinsic plasticity has therapeutic potential before speculating on the temporal relationship between rTMS-induced intrinsic and synaptic plasticity.

Native-state proteomics of Parvalbumin interneurons identifies unique molecular signatures and vulnerabilities to early Alzheimer's pathology

Dysfunction in fast-spiking parvalbumin interneurons (PV-INs) may represent an early pathophysiological perturbation in Alzheimer's Disease (AD). Defining early proteomic alterations in PV-INs can provide key biological and translationally-relevant insights. We used cell-type-specific in-vivo biotinylation of proteins (CIBOP) coupled with mass spectrometry to obtain native-state PV-IN proteomes. PV-IN proteomic signatures include high metabolic and translational activity, with over-representation of AD-risk and cognitive resilience-related proteins. In bulk proteomes, PV-IN proteins were associated with cognitive decline in humans, and with progressive neuropathology in humans and the 5xFAD mouse model of Aβ pathology. PV-IN CIBOP in early stages of Aβ pathology revealed signatures of increased mitochondria and metabolism, synaptic and cytoskeletal disruption and decreased mTOR signaling, not apparent in whole-brain proteomes. Furthermore, we demonstrated pre-synaptic defects in PV-to-excitatory neurotransmission, validating our proteomic findings. Overall, in this study we present native-state proteomes of PV-INs, revealing molecular insights into their unique roles in cognitive resiliency and AD pathogenesis.

RyR2-dependent modulation of neuronal hyperactivity: A potential therapeutic target for treating Alzheimer's disease

Increasing evidence suggests that simply reducing β-amyloid (Aβ) plaques may not significantly affect the progression of Alzheimer's disease (AD). There is also increasing evidence indicating that AD progression is driven by a vicious cycle of soluble Aβ-induced neuronal hyperactivity. In support of this, it has recently been shown that genetically and pharmacologically limiting ryanodine receptor 2 (RyR2) open time prevents neuronal hyperactivity, memory impairment, dendritic spine loss and neuronal cell death in AD mouse models. By contrast, increased RyR2 open probability (Po) exacerbates the onset of familial AD-associated neuronal dysfunction and induces AD-like defects in the absence of AD-causing gene mutations. Thus, RyR2-dependent modulation of neuronal hyperactivity represents a promising new target for combating AD.

Hyperfunction of post-synaptic density protein 95 promotes seizure response in early-stage aβ pathology

Accumulation of amyloid-beta (Aβ) can lead to the formation of aggregates that contribute to neurodegeneration in Alzheimer's disease (AD). Despite globally reduced neural activity during AD onset, recent studies have suggested that Aβ induces hyperexcitability and seizure-like activity during the early stages of the disease that ultimately exacerbate cognitive decline. However, the underlying mechanism is unknown. Here, we reveal an Aβ-induced elevation of postsynaptic density protein 95 (PSD-95) in cultured neurons in vitro and in an in vivo AD model using APP/PS1 mice at 8 weeks of age. Elevation of PSD-95 occurs as a result of reduced ubiquitination caused by Akt-dependent phosphorylation of E3 ubiquitin ligase murine-double-minute 2 (Mdm2). The elevation of PSD-95 is consistent with the facilitation of excitatory synapses and the surface expression of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors induced by Aβ. Inhibition of PSD-95 corrects these Aβ-induced synaptic defects and reduces seizure activity in APP/PS1 mice. Our results demonstrate a mechanism underlying elevated seizure activity during early-stage Aβ pathology and suggest that PSD-95 could be an early biomarker and novel therapeutic target for AD.

Abnormal brain activities of cognitive processes in cerebral small vessel disease: A systematic review of task fMRI studies

Cerebral small vessel disease (CSVD) is characterized by widespread functional changes in the brain, as evident from abnormal brain activations during cognitive tasks. However, the existing findings in this area are not yet conclusive. We systematically reviewed 25 studies reporting task-related fMRI in five cognitive domains in CSVD, namely executive function, working memory, processing speed, motor, and affective processing. The findings highlighted: (1) CSVD affects cognitive processes in a domain-specific manner; (2) Compensatory and regulatory effects were observed simultaneously in CSVD, which may reflect the interplay between the negative impact of brain lesion and the positive impact of cognitive reserve. Combined with behavioral and functional findings in CSVD, we proposed an integrated model to illustrate the relationship between altered activations and behavioral performance in different stages of CSVD: functional brain changes may precede and be more sensitive than behavioral impairments in the early pre-symptomatic stage; Meanwhile, compensatory and regulatory mechanisms often occur in the early stages of the disease, while dysfunction/decompensation and dysregulation often occur in the late stages. Overall, abnormal hyper-/hypo-activations are crucial for understanding the mechanisms of small vessel lesion-induced behavioral dysfunction, identifying potential neuromarker and developing interventions to mitigate the impact of CSVD on cognitive function.