Correlation of Alzheimer disease neuropathologic changes with cognitive status: a review of the literature

Advances and applications of fluids biomarkers in diagnosis and therapeutic targets of Alzheimer's disease

AIMS

Alzheimer's disease (AD) is a neurodegenerative disease with challenging early diagnosis and effective treatments due to its complex pathogenesis. AD patients are often diagnosed after the appearance of the typical symptoms, thereby delaying the best opportunity for effective measures. Biomarkers could be the key to resolving the challenge. This review aims to provide an overview of application and potential value of AD biomarkers in fluids, including cerebrospinal fluid, blood, and saliva, in diagnosis and treatment.

METHODS

A comprehensive search of the relevant literature was conducted to summarize potential biomarkers for AD in fluids. The paper further explored the biomarkers' utility in disease diagnosis and drug target development.

RESULTS

Research on biomarkers mainly focused on amyloid-β (Aβ) plaques, Tau protein abnormal phosphorylation, axon damage, synaptic dysfunction, inflammation, and related hypotheses associated with AD mechanisms. Aβ₄₂ , total Tau (t-Tau), and phosphorylated Tau (p-Tau), have been endorsed for their diagnostic and predictive capability. However, other biomarkers remain controversial. Drugs targeting Aβ have shown some efficacy and those that target BACE1 and Tau are still undergoing development.

CONCLUSION

Fluid biomarkers hold considerable potential in the diagnosis and drug development of AD. However, improvements in sensitivity and specificity, and approaches for managing sample impurities, need to be addressed for better diagnosis.

Dimensional clinical phenotyping using post-mortem brain donor medical records: Association with neuropathology

INTRODUCTION

Transdiagnostic dimensional phenotypes are essential to investigate the relationship between continuous symptom dimensions and pathological changes. This is a fundamental challenge to postmortem work, as assessment of newly developed phenotypic concepts needs to rely on existing records.

METHODS

We adapted well-validated methodologies to compute NIMH research domain criteria (RDoC) scores using natural language processing (NLP) from electronic health records (EHRs) obtained from post-mortem brain donors and tested whether RDoC cognitive domain scores were associated with hallmark Alzheimer's disease (AD) neuropathological measures.

RESULTS

Our results confirm an association of EHR-derived cognitive scores with hallmark neuropathological findings. Notably, higher neuropathological load, particularly neuritic plaques, was associated with higher cognitive burden scores in the frontal (ß=0.38, p=0.0004), parietal (ß=0.35, p=0.0008), temporal (ß=0.37, p=0. 0004) and occipital (ß=0.37, p=0.0003) lobes.

DISCUSSION

This proof of concept study supports the validity of NLP-based methodologies to obtain quantitative measures of RDoC clinical domains from postmortem EHR.

Hippocampal GFAP-positive astrocyte responses to amyloid and tau pathologies

INTRODUCTION

In Alzheimer's disease clinical research, glial fibrillary acidic protein (GFAP) released/leaked into the cerebrospinal fluid and blood is widely measured and perceived as a biomarker of reactive astrogliosis. However, it was demonstrated that GFAP levels differ in individuals presenting with amyloid-β (Aβ) or tau pathologies. The molecular underpinnings behind this specificity are little explored. Here we investigated biomarker and transcriptomic associations of hippocampal GFAP-positive astrocytes with Aβ and tau pathologies in humans and mouse models.

METHODS

We studied 90 individuals with plasma GFAP, Aβ- and Tau-PET to investigate the association between biomarkers. Then, transcriptomic analysis in hippocampal GFAP-positive astrocytes isolated from mouse models presenting Aβ (PS2APP) or tau (P301S) pathologies was conducted to explore differentially expressed genes (DEGs), Gene Ontology terms, and protein-protein interaction networks associated with each phenotype.

RESULTS

In humans, we found that plasma GFAP associates with Aβ but not tau pathology. Unveiling the unique nature of hippocampal GFAP-positive astrocytic responses to Aβ or tau pathologies, mouse transcriptomics showed scarce overlap of DEGs between the Aβ. and tau mouse models. While Aβ GFAP-positive astrocytes were overrepresented with DEGs associated with proteostasis and exocytosis-related processes, tau hippocampal GFAP-positive astrocytes presented greater abnormalities in functions related to DNA/RNA processing and cytoskeleton dynamics.

CONCLUSION

Our results offer insights into Aβ- and tau-driven specific signatures in hippocampal GFAP-positive astrocytes. Characterizing how different underlying pathologies distinctly influence astrocyte responses is critical for the biological interpretation of astrocyte biomarkers and suggests the need to develop context-specific astrocyte targets to study AD.

FUNDING

This study was supported by Instituto Serrapilheira, Alzheimer's Association, CAPES, CNPq and FAPERGS.

Tau filaments are tethered within brain extracellular vesicles in Alzheimer's disease

The abnormal assembly of tau protein in neurons is the pathological hallmark of multiple neurodegenerative diseases, including Alzheimer's disease (AD). In addition, assembled tau associates with extracellular vesicles (EVs) in the central nervous system of patients with AD, which is linked to its clearance and prion-like propagation between neurons. However, the identities of the assembled tau species and the EVs, as well as how they associate, are not known. Here, we combined quantitative mass spectrometry, cryo-electron tomography and single-particle cryo-electron microscopy to study brain EVs from AD patients. We found filaments of truncated tau enclosed within EVs enriched in endo-lysosomal proteins. We observed multiple filament interactions, including with molecules that tethered filaments to the EV limiting membrane, suggesting selective packaging. Our findings will guide studies into the molecular mechanisms of EV-mediated secretion of assembled tau and inform the targeting of EV-associated tau as potential therapeutic and biomarker strategies for AD.

Tau in cerebrospinal fluid induces neuronal hyperexcitability and alters hippocampal theta oscillations

Alzheimer's disease (AD) and other tauopathies are characterized by the aggregation of tau into soluble and insoluble forms (including tangles and neuropil threads). In humans, a fraction of both phosphorylated and non-phosphorylated N-terminal to mid-domain tau species, are secreted into cerebrospinal fluid (CSF). Some of these CSF tau species can be measured as diagnostic and prognostic biomarkers, starting from early stages of disease. While in animal models of AD pathology, soluble tau aggregates have been shown to disrupt neuronal function, it is unclear whether the tau species present in CSF will modulate neural activity. Here, we have developed and applied a novel approach to examine the electrophysiological effects of CSF from patients with a tau-positive biomarker profile. The method involves incubation of acutely-isolated wild-type mouse hippocampal brain slices with small volumes of diluted human CSF, followed by a suite of electrophysiological recording methods to evaluate their effects on neuronal function, from single cells through to the network level. Comparison of the toxicity profiles of the same CSF samples, with and without immuno-depletion for tau, has enabled a pioneering demonstration that CSF-tau potently modulates neuronal function. We demonstrate that CSF-tau mediates an increase in neuronal excitability in single cells. We then observed, at the network level, increased input-output responses and enhanced paired-pulse facilitation as well as an increase in long-term potentiation. Finally, we show that CSF-tau modifies the generation and maintenance of hippocampal theta oscillations, which have important roles in learning and memory and are known to be altered in AD patients. Together, we describe a novel method for screening human CSF-tau to understand functional effects on neuron and network activity, which could have far-reaching benefits in understanding tau pathology, thus allowing for the development of better targeted treatments for tauopathies in the future.

RGS6 mediates exercise-induced recovery of hippocampal neurogenesis, learning, and memory in an Alzheimer's mouse model

Hippocampal neuronal loss causes cognitive dysfunction in Alzheimer's disease (AD). Adult hippocampal neurogenesis (AHN) is reduced in AD patients. Exercise stimulates AHN in rodents and improves memory and slows cognitive decline in AD patients. However, the molecular pathways for exercise-induced AHN and improved cognition in AD are poorly understood. Here, we show that voluntary running in APP SWE mice restores their hippocampal cognitive impairments to that of control mice. This cognitive rescue was abolished by RGS6 deletion in dentate gyrus (DG) neuronal progenitors (NPs), which also abolished running-mediated increases in AHN. AHN was reduced in sedentary APP SWE mice versus control mice, with basal AHN reduced by RGS6 deletion in DG NPs. RGS6 expression is significantly lower in the DG of AD patients. Thus, RGS6 mediates exercise-induced rescue of impaired cognition and AHN in AD mice, identifying RGS6 in DG NPs as a potential target to combat hippocampal neuron loss in AD.

Teaser

RGS6 expression in hippocampal NPCs promotes voluntary running-induced neurogenesis and restored cognition in APP SWE mice.

Field Codes

RGS6, Alzheimer's disease, adult hippocampal neurogenesis, neural precursor cells, dentate gyrus, exercise, learning/memory.

Fine particulate air pollution and neuropathology markers of Alzheimer's disease in donors with and without APOE ε4 alleles - results from an autopsy cohort

Introduction

Higher fine particulate matter (PM2.5) exposure has been found to be associated with Alzheimer's disease (AD). PM2.5 has been hypothesized to cause inflammation and oxidative stress in the brain, contributing to neuropathology. A major genetic risk factor of AD, the apolipoprotein E (APOE) gene, has also been hypothesized to modify the association between PM2.5 and AD. However, little prior research exisits to support these hypotheses. Therefore, this paper aims to investigate the association between traffic-related PM2.5 and AD hallmark pathology, including effect modification by APOE genotype, in an autopsy cohort.

Methods

Brain tissue donors enrolled in the Emory Goizueta Alzheimer's Disease Research Center (ADRC) who died before 2020 (n=224) were assessed for AD pathology including Braak Stage, Consortium to Establish a Registry for AD (CERAD) score, and the combined AD neuropathologic change (ABC score). Traffic-related PM2.5 concentrations were modeled for the metro-Atlanta area during 2002-2019 with a spatial resolution of 200-250m. One-, 3-, and 5-year average PM2.5 concentrations prior to death were matched to participants home address. We assessed the association between traffic-related PM2.5 and AD hallmark pathology, as well as effect modification by APOE genotype, using adjusted ordinal logistic regression models.

Results

Traffic-related PM2.5 was significantly associated with CERAD score for the 1-year exposure window (OR: 1.92; 95% CI: 1.12, 3.30), and the 3-year exposure window (OR: 1.87; 95%-CI: 1.01, 3.17). PM2.5 had harmful, but non-significant associations on Braak Stage and ABC score. The strongest associations between PM2.5 and neuropathology markers were among those without APOE ε4 alleles (e.g., for CERAD and 1-year exposure window, OR: 2.31; 95% CI: 1.36, 3.94), though interaction between PM2.5 and APOE genotype was not statistically significant.

Conclusions

Our study found traffic-related PM2.5 exposure was associated with CERAD score in an autopsy cohort, contributing to epidemiologic evidence that PM2.5 affects Aβ deposition in the brain. This association was particularly strong among donors without APOE ε4 alleles. Future studies should further investigate the biological mechanisms behind this assocation.

The Effects of a Blood-Brain Barrier Penetrating Erythropoietin in a Mouse Model of Tauopathy

Erythropoietin (EPO), a hematopoietic neurotrophin, is a potential therapeutic for Alzheimer's disease (AD) but has limited blood-brain barrier (BBB) permeability. EPO fused to a chimeric transferrin receptor monoclonal antibody (cTfRMAb) enters the brain via TfR-mediated transcytosis across the BBB. We previously showed that cTfRMAb-EPO is protective in a mouse model of amyloidosis, but its effects on tauopathy are not known. Given that amyloid and tau pathology are characteristics of AD, the effects of cTfRMAb-EPO were studied in a tauopathy mouse model (PS19). Six-month-old PS19 mice were injected intraperitoneally with either saline (PS19-Saline; n = 9) or cTfRMAb-EPO (PS19-cTfRMAb-EPO, 10 mg/kg; n = 10); every two or three days on alternate weeks for 8 weeks. Age-matched, saline-treated, wildtype littermates (WT-Saline; n = 12) were injected using the same protocol. After 8 weeks, locomotion, hyperactivity, and anxiety were assessed via the open-field test, and brains were harvested and sectioned. Cerebral cortex, hippocampus, amygdala, and entorhinal cortex sections were analyzed for phospho-tau (AT8) and microgliosis (Iba1). Hippocampal cellular density (H&E) was also assessed. PS19-Saline mice were hyperactive and less anxious compared to WT-Saline mice, and these behavioral phenotypes were significantly reduced in the PS19-cTfRMAb-EPO mice compared to the PS19-Saline mice. cTfRMAb-EPO significantly reduced AT8 load by ≥50% in all of the brain regions analyzed and microgliosis in the entorhinal cortex and amygdala compared to the PS19-Saline mice. Hippocampal pyramidal and granule cell layer density did not differ significantly between the PS19-cTfRMAb-EPO and PS19-Saline mice. This proof-of-concept study demonstrates the therapeutic effects of the BBB-penetrating cTfRMAb-EPO in PS19 mice.

Neural atrophy produced by AAV tau injections into hippocampus and anterior cortex of middle-aged mice

Animal models of tauopathy help in understanding the role of mutations in tau pathobiology. Here, we used adeno-associated viral (AAV) vectors to administer three tau genetic variants (tauwild-type, tauP301L, and tauR406W) intracranially into 12-month-old C57BL/6Nia mice and collected tissue at 16 months. Vectors designed to express green fluorescent protein controlled for surgical procedures and exogenous protein expression by AAV. The tau genetic variants produced considerably different phenotypes. Tauwild-type and tauP301L caused memory impairments. The tauP301L caused increased amounts of aggregated tau, measured both neurochemically and histologically. Tauwild-type produced elevated levels of soluble tau and phosphorylated tau by ELISA and increased staining for phosphorylated forms of tau histologically. However, only the tauwild-type caused localized atrophy of brain tissue at the sites near the injection. The tauR406W had low protein expression and produced no atrophy or memory impairments. This supports the potential use of AAV expressing tauwild-type in aged mice to examine events leading to neurodegeneration in Alzheimer's disease pathology.

Assessment of complementary white matter microstructural changes and grey matter atrophy in a preclinical model of Alzheimer's disease

Alzheimer's disease (AD) has been associated with amyloid and tau pathology, as well as neurodegeneration. Beyond these hallmark features, white matter microstructural abnormalities have been observed using MRI. The objective of this study was to assess grey matter atrophy and white matter microstructural changes in a preclinical mouse model of AD (3xTg-AD) using voxel-based morphometry (VBM) and free-water (FW) diffusion tensor imaging (FW-DTI). Compared to controls, lower grey matter density was observed in the 3xTg-AD model, corresponding to the small clusters in the caudate-putamen, hypothalamus, and cortex. DTI-based fractional anisotropy (FA) was decreased in the 3xTg model, while the FW index was increased. Notably, the largest clusters for both FW-FA and FW index were in the fimbria, with other regions including the anterior commissure, corpus callosum, forebrain septum, and internal capsule. Additionally, the presence of amyloid and tau in the 3xTg model was confirmed with histopathology, with significantly higher levels observed across many regions of the brain. Taken together, these results are consistent with subtle neurodegenerative and white matter microstructural changes in the 3xTg-AD model that manifest as increased FW, decreased FW-FA, and decreased grey matter density.

Uncovering tau in wasteosomes (corpora amylacea) of Alzheimer’s disease patients

Brain corpora amylacea, recently renamed as wasteosomes, are polyglucosan bodies that appear during aging and some neurodegenerative conditions. They collect waste substances and are part of a brain cleaning mechanism. For decades, studies on their composition have produced inconsistent results and the presence of tau protein in them has been controversial. In this work, we reanalyzed the presence of this protein in wasteosomes and we pointed out a methodological problem when immunolabeling. It is well known that to detect tau it is necessary to perform an antigen retrieval. However, in the case of wasteosomes, an excessive antigen retrieval with boiling dissolves their polyglucosan structure, releases the entrapped proteins and, thus, prevents their detection. After performing an adequate pre-treatment, with an intermediate time of boiling, we observed that some brain wasteosomes from patients with Alzheimer’s disease (AD) contained tau, while we did not detect tau protein in those from non-AD patients. These observations pointed the different composition of wasteosomes depending on the neuropathological condition and reinforce the role of wasteosomes as waste containers.

Anterograde and Retrograde Propagation of Inoculated Human Tau Fibrils and Tau Oligomers in a Non-Transgenic Rat Tauopathy Model

The tauopathy of Alzheimer's disease (AD) is first observed in the brainstem and entorhinal cortex, spreading trans-synaptically along specific pathways to other brain regions with recognizable patterns. Tau propagation occurs retrogradely and anterogradely (trans-synaptically) along a given pathway and through exosomes and microglial cells. Some aspects of in vivo tau spreading have been replicated in transgenic mice models expressing a mutated human MAPT (tau) gene and in wild-type mice. In this study, we aimed to characterize the propagation of different forms of tau species in non-transgenic 3-4 months old wild-type rats after a single unilateral injection of human tau oligomers and tau fibrils into the medial entorhinal cortex (mEC). We determined whether different variants of the inoculated human tau protein, tau fibrils, and tau oligomers, would induce similar neurofibrillary changes and propagate in an AD-related pattern, and how tau-related pathological changes would correlate with presumed cognitive impairment. We injected human tau fibrils and tau oligomers stereotaxically into the mEC and examined the distribution of tau-related changes at 3 days and 4, 8, and 11 months post-injection using antibodies AT8 and MC1, which reveal early phosphorylation and aberrant conformation of tau, respectively, HT7, anti-synaptophysin, and the Gallyas silver staining method. Human tau oligomers and tau fibrils exhibited some similarities and some differences in their ability to seed and propagate tau-related changes. Both human tau fibrils and tau oligomers rapidly propagated from the mEC anterogradely into the hippocampus and various parts of the neocortex. However, using a human tau-specific HT7 antibody, 3 days post-injection we found inoculated human tau oligomers in the red nucleus, primary motor, and primary somatosensory cortex, a finding not seen in animals inoculated with human tau fibrils. In animals inoculated with human tau fibrils, 3 days post-injection the HT7 antibody showed fibrils in the pontine reticular nucleus, a finding explained only by uptake of human tau fibrils by incoming presynaptic fibers to the mEC and retrograde transport of inoculated human tau fibrils to the brainstem. Rats inoculated with human tau fibrils showed as early as 4 months after inoculation a spread of phosphorylated tau protein at the AT8 epitopes throughout the brain, dramatically faster propagation of neurofibrillary changes than with human tau oligomers. The overall severity of tau protein changes 4, 8, and 11 months after inoculation of human tau oligomers and tau fibrils correlated well with spatial working memory and cognition impairments, as measured by the T-maze spontaneous alternation, novel object recognition, and object location tests. We concluded that this non-trangenic rat model of tauopathy, especially when using human tau fibrils, demonstrates rapidly developing pathologic alterations in neurons, synapses, and identifiable pathways together with cognitive and behavioral changes, through the anterograde and retrograde spreading of neurofibrillary degeneration. Therefore, it represents a promising model for future experimental studies of primary and secondary tauopathies, especially AD.

Effectiveness of dexmedetomidine on postoperative cognitive dysfunction in elderly patients with fracture: A systematic review

BACKGROUND

Previous studies have explored the effectiveness of dexmedetomidine on postoperative cognitive dysfunction (POCD) in elderly patients with fracture. However, no systematic review has addressed this issue. Thus, this systematic review investigated the effectiveness of dexmedetomidine on POCD in elderly patients with fracture.

METHODS

In this study, we searched electronic databases of PubMed, EMBASE, Cochrane Library, China National Knowledge Infrastructure, Wang Fang and China Science and Technology Journal Database from their initiation to July 1, 2022. We considered randomized controlled trials of dexmedetomidine on POCD in elderly patients with fracture in this study. Primary outcome was measured by mini-mental state examination. Secondary outcomes were measured by total occurrence rate of postoperative cognitive dysfunction, occurrence rate of delirium, visual analogue scale and occurrence rate of adverse events.

RESULTS

A total of 10 studies involving 969 elderly patients with fracture are included in this study. Meta-analysis results showed that there were significant differences on mini-mental state examination at 1-day post-surgery [mean difference (MD) = 2.17; random 95% confidence interval (CI), 1.06, 3.28; P < .001; I²=98%], 3-day post-surgery (MD = 2.70; random 95% CI, 1.51, 3.89; P < .001; I²=98%), and 7-day post-surgery (MD = 1.21; random 95% CI, 0.50, 1.93; P < .001; I²=86%), total occurrence rate of postoperative cognitive dysfunction (odds ratio [OR] = 0.26; fixed 95% CI, 0.11, 0.60; P = .002; I²= 0%), occurrence rate of delirium (OR = 0.29; fixed 95% CI, 0.11, 0.78; P = .01; I²= 0%), visual analogue scale (MD = -1.23; random 95% CI, -1.74, -0.72; P < .001; I²=95%), and occurrence rate of adverse events (OR = 0.32; fixed 95% CI, 0.20, 0.50; P < .001; I²= 0%) between the 2 groups.

CONCLUSION

The results of this study showed that dexmedetomidine could effectively manage POCD in elderly patients with fracture. However, the overall quality of included trials is not too high. Thus, the present findings should be cautiously referred.

Plasma phospho-tau in Alzheimer's disease: towards diagnostic and therapeutic trial applications

As the leading cause of dementia, Alzheimer's disease (AD) is a major burden on affected individuals, their families and caregivers, and healthcare systems. Although AD can be identified and diagnosed by cerebrospinal fluid or neuroimaging biomarkers that concord with neuropathological evidence and clinical symptoms, challenges regarding practicality and accessibility hinder their widespread availability and implementation. Consequently, many people with suspected cognitive impairment due to AD do not receive a biomarker-supported diagnosis. Blood biomarkers have the capacity to help expand access to AD diagnostics worldwide. One such promising biomarker is plasma phosphorylated tau (p-tau), which has demonstrated specificity to AD versus non-AD neurodegenerative diseases, and will be extremely important to inform on clinical diagnosis and eligibility for therapies that have recently been approved. This review provides an update on the diagnostic and prognostic performances of plasma p-tau181, p-tau217 and p-tau231, and their associations with in vivo and autopsy-verified diagnosis and pathological hallmarks. Additionally, we discuss potential applications and unanswered questions of plasma p-tau for therapeutic trials, given their recent addition to the biomarker toolbox for participant screening, recruitment and during-trial monitoring. Outstanding questions include assay standardization, threshold generation and biomarker verification in diverse cohorts reflective of the wider community attending memory clinics and included in clinical trials.

New Pathways Identify Novel Drug Targets for the Prevention and Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is an incurable, progressive neurodegenerative disorder. AD is a complex and multifactorial disease that is responsible for 60-80% of dementia cases. Aging, genetic factors, and epigenetic changes are the main risk factors for AD. Two aggregation-prone proteins play a decisive role in AD pathogenesis: β-amyloid (Aβ) and hyperphosphorylated tau (pTau). Both of them form deposits and diffusible toxic aggregates in the brain. These proteins are the biomarkers of AD. Different hypotheses have tried to explain AD pathogenesis and served as platforms for AD drug research. Experiments demonstrated that both Aβ and pTau might start neurodegenerative processes and are necessary for cognitive decline. The two pathologies act in synergy. Inhibition of the formation of toxic Aβ and pTau aggregates has been an old drug target. Recently, successful Aβ clearance by monoclonal antibodies has raised new hopes for AD treatments if the disease is detected at early stages. More recently, novel targets, e.g., improvements in amyloid clearance from the brain, application of small heat shock proteins (Hsps), modulation of chronic neuroinflammation by different receptor ligands, modulation of microglial phagocytosis, and increase in myelination have been revealed in AD research.

Ketogenic Diet as a Promising Non-Drug Intervention for Alzheimer’s Disease: Mechanisms and Clinical Implications

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder that is mainly characterized by cognitive deficits. Although many studies have been devoted to developing disease-modifying therapies, there has been no effective therapy until now. However, dietary interventions may be a potential strategy to treat AD. The ketogenic diet (KD) is a high-fat and low-carbohydrate diet with adequate protein. KD increases the levels of ketone bodies, providing an alternative energy source when there is not sufficient energy supply because of impaired glucose metabolism. Accumulating preclinical and clinical studies have shown that a KD is beneficial to AD. The potential underlying mechanisms include improved mitochondrial function, optimization of gut microbiota composition, and reduced neuroinflammation and oxidative stress. The review provides an update on clinical and preclinical research on the effects of KD or medium-chain triglyceride supplementation on symptoms and pathophysiology in AD. We also detail the potential mechanisms of KD, involving amyloid and tau proteins, neuroinflammation, gut microbiota, oxidative stress, and brain metabolism. We aimed to determine the function of the KD in AD and outline important aspects of the mechanism, providing a reference for the implementation of the KD as a potential therapeutic strategy for AD.

Effects of Sideritis scardica Extract on Scopolamine-Induced Learning and Memory Impairment in Mice

BACKGROUND

The neurodegenerative process in Alzheimer's disease, one of the most common types of dementia worldwide, mostly affects the cholinergic neurotransmitter system and, to a lesser extent, the monoaminergic one. The antioxidant acetylcholinesterase (AChE) and triple monoamine reuptake inhibitory activity of Sideritis scardica (S. scardica) and other Sideritis species has already been reported.

OBJECTIVE

To investigate the effects of S. scardica water extracts on the learning and memory processes, anxiety-like behavior, and locomotor activities in scopolamine (Sco)-induced dementia in mice.

METHODS

Male Albino IRC mice were used. The plant extract was administered for 11 consecutive days in the presence or absence of Sco (1 mg/kg, i.p). The behavioural performance of the animals was evaluated by passive avoidance, T-maze, and hole-board tests. The effects of extract on AChE activity, brain noradrenalin (NA), and serotonin (Sero) content, and antioxidant status were also monitored.

RESULTS

Our experimental data revealed that the S. scardica water extract caused a reduction in degree of memory impairment and anxiety-like behaviour in mice with scopolamine-induced dementia. The extract did not affect changed by the Sco AChE activity but impact reduced brain NA and Sero levels and demonstrated moderate antioxidant activity. In healthy mice we did not confirm the presence of anxiolytic-like and AChE inhibitory effects of the S. scardica water extract. The extract did not change the control Sero brain levels and reduce those of NA.

CONCLUSION

S. scardica water extract demonstrated memory preserving effect in mice with scopolamine-induced dementia and deserve further attention.

Blood-brain barrier opening of the default mode network in Alzheimer's disease with magnetic resonance-guided focused ultrasound

The blood-brain barrier (BBB) protects the brain but is also an important obstacle for the effective delivery of therapeutics in Alzheimer's disease and other neurodegenerative disorders. Transcranial magnetic resonance-guided focused ultrasound (MRgFUS) has been shown to reversibly disrupt the BBB. However, treatment of diffuse regions across the brain along with the effect on Alzheimer's disease relevant pathology need to be better characterized. This study is an open-labelled single-arm trial (NCT04118764) to investigate the feasibility of modulating BBB permeability in the default mode network and the impact on cognition, amyloid and tau pathology as well as BBB integrity. Nine participants [mean age 70.2 ± 7.2 years, mean Mini-Mental State Examination (MMSE) 21.9] underwent three biweekly procedures with follow-up visits up to 6 months. The BBB permeability of the bilateral hippocampi, anterior cingulate cortex and precuneus was transiently increased without grade 3 or higher adverse events. Participants did not experience worsening trajectory of cognitive decline (ADAS-cog11, MMSE). Whole brain vertex-based analysis of the 18F-florbetaben PET imaging demonstrated clusters of modest SUVR reduction in the right parahippocampal and inferior temporal lobe. However, CSF and blood biomarkers did not demonstrate any amelioration of Alzheimer's disease pathology (P-tau181, amyloid-β42/40 ratio), nor did it show persistent BBB dysfunction (plasma PDGFRbeta and CSF-to-plasma albumin ratio). This study provides neuroimaging and fluid biomarker data to characterize the safety profile of MRgFUS BBB modulation in neurodegeneration as a potential strategy for enhanced therapeutic delivery.

Hypoperfusion Precedes Tau Deposition in the Entorhinal Cortex: A Retrospective Evaluation of ADNI-2 Data

BACKGROUND AND PURPOSE

Tau deposition in the entorhinal cortex is the earliest pathological feature of Alzheimer's disease (AD). However, this feature has also been observed in cognitively normal (CN) individuals and those with mild cognitive impairment (MCI). The precise pathophysiology for the development of tau deposition remains unclear. We hypothesized that reduced cerebral perfusion is associated with the development of tau deposition.

METHODS

A subset of the Alzheimer's Disease Neuroimaging Initiative data set was utilized. Included patients had undergone arterial spin labeling perfusion MRI along with [¹⁸F]flortaucipir tau PET at baseline, within 1 year of the MRI, and a follow-up at 6 years. The association between baseline cerebral blood flow (CBF) and the baseline and 6-year tau PET was assessed. Univariate and multivariate linear modeling was performed, with p<0.05 indicating significance.

RESULTS

Significant differences were found in the CBF between patients with AD and MCI, and CN individuals in the left entorhinal cortex (p=0.013), but not in the right entorhinal cortex (p=0.076). The difference in maximum standardized uptake value ratio between 6 years and baseline was significantly and inversely associated with the baseline mean CBF (p=0.042, R²=0.54) in the left entorhinal cortex but not the right entorhinal cortex. Linear modeling demonstrated that CBF predicted 6-year tau deposition (p=0.015, R²=0.11).

CONCLUSIONS

The results of this study suggest that a reduction in CBF at the entorhinal cortex precedes tau deposition. Further work is needed to understand the mechanism underlying tau deposition in aging and disease.

Amyloid-β targeting immunisation in aged non-human primate (Microcebus murinus)

Non-human primates have an important translational value given their close phylogenetic relationship to humans. Studies in these animals remain essential for evaluating efficacy and safety of new therapeutic approaches, particularly in aging primates that display Alzheimer's disease (AD) -like pathology. With the objective to improve amyloid-β (Aβ) targeting immunotherapy, we investigated the safety and efficacy of an active immunisation with an Aβ derivative, K6Aβ1-30-NH2, in old non-human primates. Thirty-two aged (4-10 year-old) mouse lemurs were enrolled in the study, and received up to four subcutaneous injections of the vaccine in alum adjuvant or adjuvant alone. Even though antibody titres to Aβ were not high, pathological examination of the mouse lemur brains showed a significant reduction in intraneuronal Aβ that was associated with reduced microgliosis, and the vaccination did not lead to microhemorrhages. Moreover, a subtle cognitive improvement was observed in the vaccinated primates, which was probably linked to Aβ clearance. This Aβ derivative vaccine appeared to be safe as a prophylactic measure based on the brain analyses and because it did not appear to have detrimental effects on the general health of these old animals.

Early tau detection in flortaucipir images: validation in autopsy-confirmed data and implications for disease progression

BACKGROUND

There is an increasing interest in utilizing tau PET to identify patients early in Alzheimer's disease (AD). In this work, a temporal lobe composite (Eτ) volume of interest (VOI) was evaluated in a longitudinal flortaucipir cohort and compared to a previously described global neocortical VOI. In a separate autopsy-confirmed study, the sensitivity of the Eτ VOI for identifying intermediate (B2) neurofibrillary tangle (NFT) pathology was evaluated.

METHODS

A total of 427 subjects received flortaucipir, florbetapir, MRI, and cognitive evaluation at baseline and 18 months. In a separate autopsy study, 67 subjects received ante-mortem flortaucipir scans, and neuropathological findings were recorded according to NIA-AA recommendations by two experts. Two VOIs: Eτ comprising FreeSurfer volumes (bilateral entorhinal cortex, fusiform, parahippocampal, and inferior temporal gyri) transformed to MNI space and a previously published global AD signature-weighted neocortical VOI (AD_signature) (Devous et al., J Nucl Med 59:937-43, 2018), were used to calculate SUVr relative to a white matter reference region (PERSI) (Southekal et al., J Nucl Med Off Publ Soc Nucl Med 59:944-51, 2018). SUVr cutoffs for positivity were determined based on a cohort of young, cognitively normal subjects. Subjects were grouped based on positivity on both VOIs (Eτ+/AD_signature+; Eτ+/AD_signature-; Eτ-/AD_signature-). Groupwise comparisons were performed for baseline SUVr, 18-month changes in SUVr, neurodegeneration, and cognition. For the autopsy study, the sensitivity of Eτ in identifying intermediate Braak pathology (B2) subjects was compared to that of AD signature-weighted neocortical VOI. The average surface maps of subjects in the Eτ+/AD_signature- group and B2 NFT scores were created for visual evaluation of uptake.

RESULTS

Sixty-four out of 390 analyzable subjects were identified as Eτ+/AD_signature-: 84% were Aβ+, 100% were diagnosed as MCI or AD, and 59% were APOE ε4 carriers. Consistent with the hypothesis that Eτ+/AD_signature- status reflects an early stage of AD, Eτ+/AD_signature- subjects deteriorated significantly faster than Eτ-/AD_signature- subjects, but significantly slower than Eτ+/AD_signature+ subjects, on most measures (i.e., change in AD_signature SUVr, Eτ ROI cortical thickness, and MMSE). The AD_signature VOI was selective for subjects who came to autopsy with a B3 NFT score. In the autopsy study, 12/15 B2 subjects (including 10/11 Braak IV) were Eτ+/AD_signature-. Surface maps showed that flortaucipir uptake was largely captured by the Eτ VOI regions in B2 subjects.

CONCLUSION

The Eτ VOI identified subjects with elevated temporal but not global tau (Eτ+/AD_signature-) that were primarily Aβ+, APOE ε4 carriers, and diagnosed as MCI or AD. Eτ+/AD_signature- subjects had greater accumulation of tau, greater atrophy, and higher decline on MMSE in 18 months compared to Eτ-/AD_signature- subjects. Finally, the Eτ VOI identified the majority of the intermediate NFT score subjects in an autopsy-confirmed study. As far as we know, this is the first study that presents a visualization of ante-mortem FTP retention patterns that at a group level agree with the neurofibrillary tangle staging scheme proposed by Braak. These findings suggest that the Eτ VOI may be sensitive for detecting impaired subjects early in the course of Alzheimer's disease.

Associations between different tau-PET patterns and longitudinal atrophy in the Alzheimer's disease continuum: biological and methodological perspectives from disease heterogeneity

BACKGROUND

Subtypes and patterns are defined using tau-PET (tau pathology) and structural MRI (atrophy) in Alzheimer's disease (AD). However, the relationship between tau pathology and atrophy across these subtypes/patterns remains unclear. Therefore, we investigated the biological association between baseline tau-PET patterns and longitudinal atrophy in the AD continuum; and the methodological characterization of heterogeneity as a continuous phenomenon over the conventional discrete subgrouping.

METHODS

In 366 individuals (amyloid-beta-positive cognitively normal, prodromal AD, AD dementia; amyloid-beta-negative cognitively normal), we examined the association between tau-PET patterns and longitudinal MRI. We modeled tau-PET patterns as a (a) continuous phenomenon with key dimensions: typicality and severity; and (b) discrete phenomenon by categorization into patterns: typical, limbic predominant, cortical predominant and minimal tau. Tau-PET patterns and associated longitudinal atrophy were contextualized within the Amyloid/Tau/Neurodegeneration (A/T/N) biomarker scheme.

RESULTS

Localization and longitudinal atrophy change vary differentially across different tau-PET patterns in the AD continuum. Atrophy, a downstream event, did not always follow a topography akin to the corresponding tau-PET pattern. Further, heterogeneity as a continuous phenomenon offered an alternative and useful characterization, sharing correspondence with the conventional subgrouping. Tau-PET patterns also show differential A/T/N profiles.

CONCLUSIONS

The site and rate of atrophy are different across the tau-PET patterns. Heterogeneity should be treated as a continuous, not discrete, phenomenon for greater sensitivity. Pattern-specific A/T/N profiles highlight differential multimodal interactions underlying heterogeneity. Therefore, tracking multimodal interactions among biomarkers longitudinally, modeling disease heterogeneity as a continuous phenomenon, and examining heterogeneity across the AD continuum could offer avenues for precision medicine.

Aducanumab-Hope or Disappointment for Alzheimer's Disease

In June 2021, the world was informed about a new drug for Alzheimer's disease approved by the FDA. Aducanumab (BIIB037, ADU), being a monoclonal antibody IgG1, is the newest AD treatment. The activity of the drug is targeted towards amyloid β, which is considered one of the main causes of Alzheimer's disease. Clinical trials have revealed time- and dose-dependent activity towards Aβ reduction, as well as cognition improvement. Biogen, the company responsible for conducting research and introducing the drug to the market, presents the drug as a solution to cognitive impairment, but its limitations, costs, and side effects are controversial. The framework of the paper focuses on the mechanism of aducanumab's action along with the positive and negative sides of the therapy. The review presents the basis of the amyloid hypothesis that is the cornerstone of therapy, as well as the latest information about aducanumab, its mechanism of action, and the possibility of the use of the drug.

A Mitochondrial Perspective on Noncommunicable Diseases

Mitochondria are the center of energy metabolism in eukaryotic cells and play a central role in the metabolism of living organisms. Mitochondrial diseases characterized by defects in oxidative phosphorylation are the most common congenital diseases. Meanwhile, mitochondrial dysfunction caused by secondary factors such as non-inherited genetic mutations can affect normal physiological functions of human cells, induce apoptosis, and lead to the development of various diseases. This paper reviewed several major factors and mechanisms that contribute to mitochondrial dysfunction and discussed the development of diseases closely related to mitochondrial dysfunction and drug treatment strategies discovered in recent years.

Ingestion of Soybean Sprouts Containing a HASPIN Inhibitor Improves Condition in a Mouse Model of Alzheimer's Disease

The MATP/tau protein is hyperphosphorylated in Alzheimer's patients. Therefore, research into the regulation of tau protein phosphorylation is important for understanding Alzheimer's disease. HASPIN is a serine/threonine kinase that is expressed in various cells. To examine whether HASPIN is involved in the onset of Alzheimer's disease through tau protein phosphorylation, we investigated the effects of a diet including soybean sprouts rich in the HASPIN inhibitor coumestrol in a mouse model of Alzheimer's disease (5xFAD). The results showed that HASPIN was expressed in the hippocampus and phosphorylated tau protein, while the ingestion of soybean sprouts containing coumestrol suppressed the development of spatial cognitive dysfunction in 5xFAD. These results indicate that HASPIN may be one of the target molecules for the repression of tau phosphorylation in the treatment of Alzheimer's disease.

Detection, Visualization and Quantification of Protein Complexes in Human Alzheimer's Disease Brains using Proximity Ligation Assay

Examination of healthy and diseased human brain is essential to translational neuroscience. Protein-protein interactions play a pivotal role in physiological and pathological processes, but their detection is difficult, especially in aged and fixed human brain tissue. We used the proximity ligation assay (PLA) to broaden the range of molecular interactions assessable in-situ in human neuropathology. We adapted fluorescent in-situ PLA to detect ubiquitin-modified proteins in human brains with Alzheimer's disease (AD), including approaches for the management of autofluorescence and quantification using a high-content image analysis system. We confirmed that hyperphosphorylated microtubule-associated protein tau (Serine202, Threonine205) aggregates were modified by ubiquitin and that phospho-tau-ubiquitin complexes were increased in hippocampal and frontal cortex regions in AD compared to non-AD brains. Overall, we refined PLA for use in human neuropathology, which has revealed a profound change in the distribution of ubiquitin in AD brain and its association with characteristic tau pathologies.

Alzheimer's Disease: A Brief History of Immunotherapies Targeting Amyloid β

Alzheimer's disease (AD) is the most common form of dementia and may contribute to 60-70% of cases. Worldwide, around 50 million people suffer from dementia and the prediction is that the number will more than triple by 2050, as the population ages. Extracellular protein aggregation and plaque deposition as well as accumulation of intracellular neurofibrillary tangles, all leading to neurodegeneration, are the hallmarks of brains with Alzheimer's disease. Therapeutic strategies including active and passive immunizations have been widely explored in the last two decades. Several compounds have shown promising results in many AD animal models. To date, only symptomatic treatments are available and because of the alarming epidemiological data, novel therapeutic strategies to prevent, mitigate, or delay the onset of AD are required. In this mini-review, we focus on our understanding of AD pathobiology and discuss current active and passive immunomodulating therapies targeting amyloid-β protein.

Depression-related phenotypes at early stages of Aβ and tau accumulation in inducible Alzheimer's disease mouse model: Task-oriented and concept-driven interpretations

Depression is highly prevalent in Alzheimer Disease (AD); however, there is paucity of studies that focus specifically on the assessment of depression-relevant phenotypes in AD mouse models. Conditional doxycycline-dependent transgenic mouse models reproducing amyloidosis (TetOffAPPsi) and/or tau (TetOffTauP301L) pathology starting at middle age (6 months) were used in this study. As AD patients can experience depressive symptoms relatively early in disease, testing was conducted at early, pre-pathology stages of Aβ and/or tau accumulation (starting from 45 days of transgenes expression). Tau-related differences were detected in the Novelty Suppressed Feeding task (NSF), whereas APP-related differences were observed predominantly in measures of the Open Field (OF) and Forced Swim tasks (FST). Effects of combined production of Aβ and tau were detected in immobility during the 1st half of the Tail Suspension task (TST). These data demonstrate that results from different tasks are difficult to reconcile using task/variable-centered interpretations in which a single task/variable is assigned an ad-hoc meaning relevant to depression. An alternative, concept-oriented, approach is based on multiple variables/tests, with an understanding of their possible inter-dependence and utilization of statistical approaches that handle correlated data sets. The existence of strong correlations within and between some of the tasks supported utilization of factor analyses (FA). FA explained a similar amount of variability across the genotypes (∼80%) and identified two factors stable across genotypes and representing motor activity and anxiety measures in OF. In contrast, variables related to FST, TST, and NSFT did not demonstrate a structure of factor loadings that would support the existence of a single integral factor of "depressive state" measured by these tasks. In addition, factor loadings varied between genotypes, indicating that genotype-specific between-task correlations need to be considered for interpretations of findings in any single task. In general, this study demonstrates that utilization of multiple tasks to characterize behavioral phenotypes, an approach that is finally gaining more widespread adoption, requires a step of data integration across different behavioral tests for appropriate interpretations.

Untangling the Role of Tau in Huntington's Disease Pathology

There is increasing evidence for the presence of pathological forms of tau in tissues of both Huntington's disease (HD) patients and animal models of this condition. While cumulative studies of the past decade have led to the proposition that this disorder could also be considered a tauopathy, the implications of tau in cellular toxicity and consequent behavioral impairments are largely unknown. In fact, recent animal work has challenged the contributory role of tau in HD pathogenesis/pathophysiology. This review presents the supporting and opposing arguments for the involvement of tau in HD, highlighting the discrepancies that have emerged. Reflecting on what is known in other tauopathies, the putative mechanisms through which tau could initiate and/or contribute to pathology are discussed, shedding light on the future research directions that could be considered to confirm, or rule out, the clinical relevance of tau in HD.

Distinguishing Curable from Progressive Dementias for Defining Cancer Care Options

The likelihood of a diagnosis of dementia increases with a person's age, as is also the case for many cancers, including melanoma and multiple myeloma, where the median age of diagnosis is above 60 years. However, patients diagnosed with dementia are less likely to be offered invasive curative therapies for cancer. Together with analysis of diet and medication history, advanced imaging methods and genetic profiling can now indicate more about syndromes causing the neurological symptoms. Cachexia, malnutrition, dehydration, alcohol consumption, and even loneliness can all accentuate or cause the "3Ds" of dementia, delirium and depression. Many common drugs, especially in the context of polypharmacy, can cause cognitive difficulties resembling neurodegenerative disease. These syndromes may be reversed by diet, social and caregiver changes, and stopping potentially inappropriate medications (PIMs). More insidious are immune reactions to many different autoantigens, some of which are related to cancers and tumors. These can induce movement and cognitive difficulties that mimic Alzheimer's and Parkinson's diseases and other ataxias associated with aging. Paraneoplastic neurological syndromes may be reversed by directed immunotherapies if detected in their early stages but are best treated by removal of the causative tumor. A full genetic workup should be done for all individuals as soon as possible after diagnosis, to guide less invasive treatments suitable for frail individuals. While surgical interventions may be contraindicated, genetic profile guided immunotherapies, oral treatments, and radiation may be equally curative in a significant number of cancers.

Definition of the contribution of an Osteopontin-producing CD11c+ microglial subset to Alzheimer's disease

Alzheimer's disease (AD) is the most common form of incurable dementia and represents a critical public health issue as the world's population ages. Although microglial dysregulation is a cardinal feature of AD, the extensive heterogeneity of these immunological cells in the brain has impeded our understanding of their contribution to this disease. Here, we identify a pathogenic microglial subset which expresses the CD11c surface marker as the sole producer of Osteopontin (OPN) in the 5XFAD mouse model of AD. OPN production divides Disease-Associated Microglia (DAM) into two functionally distinct subsets, i.e., a protective CD11c+OPN- subset that robustly ingests amyloid β (Aβ) in a noninflammatory fashion and a pathogenic CD11c+OPN+ subset that produces proinflammatory cytokines and fails to ingest significant amounts of Aβ. Genetic ablation of OPN or administration of monoclonal anti-OPN antibody to 5XFAD mice reduces proinflammatory microglia, plaque formation, and numbers of dystrophic neurites and results in improved cognitive function. Analysis of brain tissue from AD patients indicates that levels of OPN-producing CD11c+ microglia correlate strongly with the degree of cognitive deficit and AD neuropathology. These findings define an OPN-dependent pathway to disease driven by a distinct microglial subset, and identify OPN as a novel therapeutic target for potentially effective immunotherapy to treat AD.

An empirical measure of resilience explains individual differences in the effect of tau pathology on memory change in aging

Accurately measuring resilience to preclinical Alzheimer's disease (AD) pathology is essential to understanding an important source of variability in cognitive aging. In a cohort of cognitively normal older adults (n = 123, age 76.75 ± 6.15 yr), we built a multifactorial measure of resilience which moderated the effect of AD pathology on longitudinal cognitive change. Linear residuals-based measures of resilience, along with other proxy measures (education and vocabulary), were entered into a hierarchical partial least-squares path model defining a putative consolidated resilience latent factor (model goodness of fit = 0.77). In a set of validation analyses using linear mixed models predicting longitudinal cognitive change, there was a significant three-way interaction among consolidated resilience, tau and time on episodic memory change (P = 0.001) such that higher resilience blunted the effect of tau pathology on episodic memory decline. Interactions between consolidated resilience and amyloid pathology on non-memory cognition decline suggested that resilience moderates pathology-specific effects on different cognitive domains.

LATE-NC staging in routine neuropathologic diagnosis: an update

An international consensus report in 2019 recommended a classification system for limbic-predominant age-related TDP-43 encephalopathy neuropathologic changes (LATE-NC). The suggested neuropathologic staging system and nomenclature have proven useful for autopsy practice and dementia research. However, some issues remain unresolved, such as cases with unusual features that do not fit with current diagnostic categories. The goal of this report is to update the neuropathologic criteria for the diagnosis and staging of LATE-NC, based primarily on published data. We provide practical suggestions about how to integrate available genetic information and comorbid pathologies [e.g., Alzheimer's disease neuropathologic changes (ADNC) and Lewy body disease]. We also describe recent research findings that have enabled more precise guidance on how to differentiate LATE-NC from other subtypes of TDP-43 pathology [e.g., frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS)], and how to render diagnoses in unusual situations in which TDP-43 pathology does not follow the staging scheme proposed in 2019. Specific recommendations are also made on when not to apply this diagnostic term based on current knowledge. Neuroanatomical regions of interest in LATE-NC are described in detail and the implications for TDP-43 immunohistochemical results are specified more precisely. We also highlight questions that remain unresolved and areas needing additional study. In summary, the current work lays out a number of recommendations to improve the precision of LATE-NC staging based on published reports and diagnostic experience.

Tau as a biomarker of cognitive impairment and neuropsychiatric symptom in Alzheimer's disease

The A/T/N research framework has been proposed for the diagnosis and prognosis of Alzheimer's disease (AD). However, the spatial distribution of ATN biomarkers and their relationship with cognitive impairment and neuropsychiatric symptoms (NPS) need further clarification in patients with AD. We scanned 83 AD patients and 38 cognitively normal controls who independently completed the mini-mental state examination and Neuropsychiatric Inventory scales. Tau, Aβ, and hypometabolism spatial patterns were characterized using Statistical Parametric Mapping together with [18F]flortaucipir, [18F]florbetapir, and [18F]FDG positron emission tomography. Piecewise linear regression, two-sample t-tests, and support vector machine algorithms were used to explore the relationship between tau, Aβ, and hypometabolism and cognition, NPS, and AD diagnosis. The results showed that regions with tau deposition are region-specific and mainly occurred in inferior temporal lobes in AD, which extensively overlaps with the hypometabolic regions. While the deposition regions of Aβ were unique and the regions affected by hypometabolism were widely distributed. Unlike Aβ, tau and hypometabolism build up monotonically with increasing cognitive impairment in the late stages of AD. In addition, NPS in AD were associated with tau deposition closely, followed by hypometabolism, but not with Aβ. Finally, hypometabolism and tau had higher accuracy in differentiating the AD patients from controls (accuracy = 0.88, accuracy = 0.85) than Aβ (accuracy = 0.81), and the combined three were the highest (accuracy = 0.95). These findings suggest tau pathology is superior over Aβ and glucose metabolism to identify cognitive impairment and NPS. Its results support tau accumulation can be used as a biomarker of clinical impairment in AD.

Amyloid precursor protein 𝛽CTF accumulates in synapses in sporadic and genetic forms of Alzheimer's disease

AIMS

Amyloid precursor protein (APP) 𝛽-C-terminal fragment (𝛽CTF) may have a neurotoxic role in Alzheimer's disease (AD). 𝛽CTF accumulates in the brains of patients with sporadic (SAD) and genetic forms of AD. Synapses degenerate early during the pathogenesis of AD. We studied whether the 𝛽CTF accumulates in synapses in SAD, autosomal dominant AD (ADAD) and Down syndrome (DS).

METHODS

We used array tomography to determine APP at synapses in human AD tissue. We measured 𝛽CTF, A𝛽40, A𝛽42 and phosphorylated tau181 (p-tau181) concentrations in brain homogenates and synaptosomes of frontal and temporal cortex of SAD, ADAD, DS and controls.

RESULTS

APP colocalised with pre- and post-synaptic markers in human AD brains. APP 𝛽CTF was enriched in AD synaptosomes.

CONCLUSIONS

We demonstrate that 𝛽CTF accumulates in synapses in SAD, ADAD and DS. This finding might suggest a role for 𝛽CTF in synapse degeneration. Therapies aimed at mitigating 𝛽CTF accumulation could be potentially beneficial in AD.

Features of Cerebral Small Vessel Disease Contributes to the Differential Diagnosis of Alzheimer's Disease

BACKGROUND

Cerebral small vessel disease (CSVD), which comprises the typical features of white matter hyperintensity (WMH) and Vichor-Robin spaces (VRSs) in the brain, is one of the leading causes of aging-related cognitive decline and, ultimately, contributes to the occurrence of dementia, including Alzheimer's disease (AD).

OBJECTIVE

To investigate whether CSVD imaging markers modify the pathological processes of AD and whether these markers improve AD diagnosis.

METHODS

208 participants were enrolled in the China Aging and Neurodegenerative Initiative (CANDI). Fluid AD biomarkers were detected using a single-molecule array, and cerebral small vessel dysfunction was determined using magnetic resonance imaging.

RESULTS

WMH contributed to AD pathology only within the NC and MCI groups (CDR ≤0.5), whereas VRSs had no effect on AD pathology. The associations between AD biomarkers and cognitive mental status were consistent with the presence of CSVD pathology. That is, within individuals without CSVD pathology, the MMSE scores were correlated with AD fluid biomarkers, except for plasma Aβ42 and Aβ40. Increased plasma p-Tau levels were associated with worse cognitive performance in individuals with WMH (β= -0.465, p = 0.0016) or VRSs (β= -0.352, p = 0.0257) pathology. Plasma AD biomarkers combined with CSVD markers showed high accuracy in diagnosing dementia.

CONCLUSION

Findings from this cross-sectional cohort study support the notion that CSVD is a risk factor for dementia and highlights that vascular pathology can promote AD biomarker levels, especially in the early course of the disease. Moreover, our results suggest that adding a vascular category to the ATN framework improves the diagnostic accuracy of AD.

Clinical and Economic Assessment in Early-Stage Dementia by Severity and Amyloid-β Status: A 5-Year Retrospective Claims Study of GERAS-US Patients

BACKGROUND

The high burden of dementia and Alzheimer's disease (AD) increases substantially as disease progresses. Characterizing early patterns of health care utilization among patients who develop cognitive impairment may deepen our understanding of early disease trajectory and potentially facilitate timely diagnosis and management.

OBJECTIVE

Describe clinical characteristics, healthcare utilization, and costs in early-stage dementia by disease severity and amyloid-β status before enrollment in an observational study (GERAS-US).

METHODS

Consented patients' GERAS-US data were linked to available five-years of Medicare claims history before GERAS-US enrollment. Clinical characteristics, comorbidity, and pre-/post-diagnosis healthcare use and costs were assessed. Continuous and categorical variables were compared between severity and amyloid-status cohorts using t-test and Chi-square statistics; linear regression models were used to compare cost and utilization measures after adjusting for differences in patients' observation time. Relative likelihood of observed diagnoses, comorbidity, and prescription drug use among cohorts were presented as OR and 90% confidence interval (CI).

RESULTS

Of 174 patients clinically diagnosed with early dementia (mild cognitive impairment (MCI): 101; mild dementia (MILD): 73), 55% were amyloid-positive. Memory loss was more likely in MILD versus MCI (OR:1.85, 90% CI 1.10-3.09) and in amyloid-positive versus amyloid-negative cohorts (OR:1.98, 90% CI 1.19-3.29). Mean annual healthcare costs after cognitive impairment/dementia diagnosis were significantly higher for MILD versus MCI ($1191 versus $712, p = 0.067) and amyloid-negative versus amyloid-positive ($1281 versus $701, p = 0.034). Diabetes was more prevalent in MILD and amyloid-negative cohorts.

CONCLUSION

Comorbidity and economic burden increased in earliest stages of MCI and MILD and were higher in patients who were amyloid-negative.

Cognitive resistance to and resilience against multiple comorbid neurodegenerative pathologies and the impact of APOE status

Alzheimer disease (AD) is currently the leading cause of cognitive decline and dementia worldwide. Recently, studies have suggested that other neurodegenerative comorbidities such as limbic-predominant age-related TDP-43 encephalopathy neuropathologic change (LATE-NC), Lewy body disease (LBD), and cerebrovascular disease frequently co-occur with Alzheimer disease neuropathologic change (ADNC) and may have significant cognitive effects both in isolation and synergistically with ADNC. Herein, we study the relative clinical impact of these multiple neurodegenerative pathologies in 704 subjects. Each of these pathologies is relatively common in the cognitively impaired population, while cerebrovascular pathology and ADNC are the most common in cognitively normal individuals. Moreover, while the number of concurrent neuropathologic entities rises with age and has a progressively deleterious effect on cognition, 44.3% of cognitively intact individuals are resistant to having any neurodegenerative proteinopathy (compared to 15.2% of cognitively impaired individuals) and 83.5% are resistant to having multiple concurrent proteinopathies (compared to 64.6% of cognitively impaired individuals). The presence of at least 1 APOE ε4 allele was associated with impaired cognition and the presence of multiple proteinopathies, while APOE ε2 was protective against cumulative proteinopathies. These results indicate that maintenance of normal cognition may depend on resistance to the development of multiple concurrent proteinopathies.

The Dual Role of Astrocyte-Derived Exosomes and Their Contents in the Process of Alzheimer's Disease

Millions of patients worldwide are affected by Alzheimer's disease (AD), and the number of patients with AD is increasing. However, current treatment can only improve symptoms but cannot cure the disease. Astrocytes, glial cells in the central nervous system, play important roles in support, nutrition, protection, and information transmission in the nervous system. Pathological changes in astrocytes are closely associated with the development and progression of AD. As carriers for material and information exchange between astrocytes and other neural cells, astrocyte-derived exosomes (ADEs) have been widely studied in recent years, and ADE secretion has been shown to be increased in patients with AD and animal models of AD. ADEs contain a variety of substances, including nucleic acids, proteins, and lipids. The contents of ADEs can effectively control oxidative stress and detoxification during the early development of AD, thereby playing positive and negative roles in the occurrence and development of AD. In this review, we elaborate on the functions of ADEs and their components in AD and discuss their applications in AD research and clinical practice.

Microglial autophagy in Alzheimer's disease and Parkinson's disease

Alzheimer's disease (AD) and Parkinson's disease (PD) are the most common neurodegenerative diseases, characterized by gradual and selective loss of neurons in the central nervous system. They affect more than 50 million people worldwide, and their incidence increases with age. Although most cases of AD and PD are sporadic, some are caused by genetic mutations that are inherited. Both sporadic and familial cases display complex neuropathology and represent the most perplexing neurological disorders. Because of the undefined pathogenesis and complex clinical manifestations, there is still no effective treatment for both AD and PD. Understanding the pathogenesis of these important neurodegenerative diseases is important for developing successful therapies. Increasing evidence suggests that microglial autophagy is associated with the pathogenesis of AD and PD, and its dysfunction has been implicated in disease progression. In this review, we focus on the autophagy function in microglia and its dysfunction in AD and PD disease models in an attempt to help our understanding of the pathogenesis and identifying new therapeutic targets of AD and PD.

Melanocortin receptor agonist NDP-α-MSH improves cognitive deficits and microgliosis but not amyloidosis in advanced stages of AD progression in 5XFAD and 3xTg mice

Introduction

Alzheimer's disease (AD) is the most frequent cause of dementia and still lacks effective therapy. Clinical signs of AD include low levels of endogenous melanocortins (MCs) and previous studies have shown that treatment with MC analogs induces neuroprotection in the early stages of AD.

Methods

We investigated the neuroprotective role of MCs in two transgenic mouse models of severe AD using 5 and 7 month-old (mo) 5XFAD mice and 9 and 12 mo 3xTg mice. These mice were subjected to a chronic stimulation of MC receptors (MCRs) with MC analogue Nle4-D-Phe7-α-melanocyte stimulating hormone (NDP-α-MSH, 340 μg/kg, i.p.). Mouse behavior and ex-vivo histological and biochemical analyses were performed after 50 days of treatment.

Results

Our analysis demonstrated an improvement in cognitive abilities of AD mice at late stage of AD progression. We also showed that these protective effects are associated with decreased levels of hyperphosphorylated Tau but not with Aβ burden, that was unaffected in the hippocampus and in the cortex of AD mice. In addition, an age-dependent NDP effect on glial reactivity was observed only in 3xTg mice whereas a global downregulation of p38 mitogen-activated protein kinase was selectively observed in 7 mo 5XFAD and 14 mo 3xTg mice.

Conclusion

Our results suggest that MCR stimulation by NDP-α-MSH could represent a promising therapeutic strategy in managing cognitive decline also at late stage of AD, whereas the effects on neuroinflammation may be restricted to specific stages of AD progression.

Genome-wide association study of brain biochemical phenotypes reveals distinct genetic architecture of Alzheimer's disease related proteins

BACKGROUND

Alzheimer's disease (AD) is neuropathologically characterized by amyloid-beta (Aβ) plaques and neurofibrillary tangles. The main protein components of these hallmarks include Aβ40, Aβ42, tau, phosphor-tau, and APOE. We hypothesize that genetic variants influence the levels and solubility of these AD-related proteins in the brain; identifying these may provide key insights into disease pathogenesis.

METHODS

Genome-wide genotypes were collected from 441 AD cases, imputed to the haplotype reference consortium (HRC) panel, and filtered for quality and frequency. Temporal cortex levels of five AD-related proteins from three fractions, buffer-soluble (TBS), detergent-soluble (Triton-X = TX), and insoluble (Formic acid = FA), were available for these same individuals. Variants were tested for association with each quantitative biochemical measure using linear regression, and GSA-SNP2 was used to identify enriched Gene Ontology (GO) terms. Implicated variants and genes were further assessed for association with other relevant variables.

RESULTS

We identified genome-wide significant associations at seven novel loci and the APOE locus. Genes and variants at these loci also associate with multiple AD-related measures, regulate gene expression, have cell-type specific enrichment, and roles in brain health and other neuropsychiatric diseases. Pathway analysis identified significant enrichment of shared and distinct biological pathways.

CONCLUSIONS

Although all biochemical measures tested reflect proteins core to AD pathology, our results strongly suggest that each have unique genetic architecture and biological pathways that influence their specific biochemical states in the brain. Our novel approach of deep brain biochemical endophenotype GWAS has implications for pathophysiology of proteostasis in AD that can guide therapeutic discovery efforts focused on these proteins.

SPOP loss of function protects against tauopathy

The pathological accumulation of the microtubule binding protein tau drives age-related neurodegeneration in a variety of disorders, collectively called tauopathies. In the most common tauopathy, Alzheimer's disease (AD), the accumulation of pathological tau strongly correlates with cognitive decline. The underlying molecular mechanisms that drive neurodegeneration in tauopathies remain incompletely understood and no effective disease modifying pharmacological interventions currently exist. Here, we show that tau toxicity depends on the highly conserved nuclear E3 ubiquitin ligase adaptor protein SPOP in a Caenorhabditis elegans model of tauopathy. Loss of function mutations in the C. elegans spop-1 gene significantly improves behavioral deficits in tau transgenic animals, while neuronal overexpression of SPOP-1 protein significantly worsens behavioral deficits. In addition, loss of spop-1 rescues a variety of tau-related phenotypes including the accumulation of total and phosphorylated tau protein, neurodegeneration, and shortened lifespan. Knockdown of SPOP-1's E3 ubiquitin ligase cul-3/Cullin3 does not improve tauopathy suggesting a non-degradative mechanism of action for SPOP-1. Suppression of disease-related phenotypes occurs independently of the nuclear speckle resident poly(A)-binding protein SUT-2/MSUT2. MSUT2 modifies tauopathy in mammalian neurons and in AD. Our work identifies SPOP as a novel modifier of tauopathy and a conceptual pathway for therapeutic intervention.

Chronic TREM2 activation exacerbates Aβ-associated tau seeding and spreading

Variants in the triggering receptor expressed on myeloid cells 2 (TREM2) gene are associated with increased risk for late-onset AD. Genetic loss of or decreased TREM2 function impairs the microglial response to amyloid-β (Aβ) plaques, resulting in more diffuse Aβ plaques and increased peri-plaque neuritic dystrophy and AD-tau seeding. Thus, microglia and TREM2 are at a critical intersection of Aβ and tau pathologies in AD. Since genetically decreasing TREM2 function increases Aβ-induced tau seeding, we hypothesized that chronically increasing TREM2 signaling would decrease amyloid-induced tau-seeding and spreading. Using a mouse model of amyloidosis in which AD-tau is injected into the brain to induce Aβ-dependent tau seeding/spreading, we found that chronic administration of an activating TREM2 antibody increases peri-plaque microglial activation but surprisingly increases peri-plaque NP-tau pathology and neuritic dystrophy, without altering Aβ plaque burden. Our data suggest that sustained microglial activation through TREM2 that does not result in strong amyloid removal may exacerbate Aβ-induced tau pathology, which may have important clinical implications.

White Matter Hyperintensity Volume and Amyloid-PET Synergistically Impact Memory Independent of Tau-PET in Older Adults Without Dementia

BACKGROUND

Alzheimer's disease (AD) and cerebrovascular disease are common, co-existing pathologies in older adults. Whether the effects of cerebrovascular disease and AD biomarkers on cognition are additive or synergistic remains unclear.

OBJECTIVE

To examine whether white matter hyperintensity (WMH) volume moderates the independent association between each AD biomarker and cognition.

METHODS

In 586 older adults without dementia, linear regressions tested the interaction between amyloid-β (Aβ) positron emission tomography (PET) and WMH volume on cognition, independent of tau-PET. We also tested the interaction between tau-PET and WMH volume on cognition, independent of Aβ-PET.

RESULTS

Adjusting for tau-PET, the quadratic effect of WMH interacted with Aβ-PET to impact memory. There was no interaction between either the linear or quadratic effect of WMH and Aβ-PET on executive function. There was no interaction between WMH volume and tau-PET on either cognitive measure.

CONCLUSION

Results suggest that cerebrovascular lesions act synergistically with Aβ to affect memory, independent of tau, highlighting the importance of incorporating vascular pathology into biomarker assessment of AD.

A Function of Amyloid-β in Mediating Activity-Dependent Axon/Synapse Competition May Unify Its Roles in Brain Physiology and Pathology

Amyloid-β protein precursor (AβPP) gives rise to amyloid-β (Aβ), a peptide at the center of Alzheimer's disease (AD). AβPP, however, is also an ancient molecule dating back in evolution to some of the earliest forms of metazoans. This suggests a possible ancestral function that may have been obscured by those that evolve later. Based on literature from the functions of Aβ/AβPP in nervous system development, plasticity, and disease, to those of anti-microbial peptides (AMPs) in bacterial competition as well as mechanisms of cell competition uncovered first by Drosophila genetics, I propose that Aβ/AβPP may be part of an ancient mechanism employed in cell competition, which is subsequently co-opted during evolution for the regulation of activity-dependent neural circuit development and plasticity. This hypothesis is supported by foremost the high similarities of Aβ to AMPs, both of which possess unique, opposite (i.e., trophic versus toxic) activities as monomers and oligomers. A large body of data further suggests that the different Aβ oligomeric isoforms may serve as the protective and punishment signals long predicted to mediate activity-dependent axonal/synaptic competition in the developing nervous system and that the imbalance in their opposite regulation of innate immune and glial cells in the brain may ultimately underpin AD pathogenesis. This hypothesis can not only explain the diverse roles observed of Aβ and AβPP family molecules, but also provide a conceptual framework that can unify current hypotheses on AD. Furthermore, it may explain major clinical observations not accounted for and identify approaches for overcoming shortfalls in AD animal modeling.

Cognitive and Neuropsychological Profiles in Alzheimer's Disease and Primary Age-Related Tauopathy and the Influence of Comorbid Neuropathologies

BACKGROUND

Alzheimer's disease neuropathologic change (ADNC) is defined by the progression of both hyperphosphorylated-tau (p-tau) and amyloid-β (Aβ) and is the most common underlying cause of dementia worldwide. Primary age-related tauopathy (PART), an Aβ-negative tauopathy largely confined to the medial temporal lobe, is increasingly being recognized as an entity separate from ADNC with diverging clinical, genetic, neuroanatomic, and radiologic profiles.

OBJECTIVE

The specific clinical correlates of PART are largely unknown; we aimed to identify cognitive and neuropsychological differences between PART, ADNC, and subjects with no tauopathy (NT).

METHODS

We compared 2,884 subjects with autopsy-confirmed intermediate-high stage ADNC to 208 subjects with definite PART (Braak stage I-IV, Thal phase 0, CERAD NP score "absent") and 178 NT subjects from the National Alzheimer's Coordinating Center dataset.

RESULTS

PART subjects were older than either ADNC or NT patients. The ADNC cohort had more frequent neuropathological comorbidities as well as APOE ɛ4 alleles than the PART or NT cohort, and less frequent APOE ɛ2 alleles than either group. Clinically, ADNC patients performed significantly worse than NT or PART subjects across cognitive measures, but PART subjects had selective deficits in measures of processing speed, executive function, and visuospatial function, although additional cognitive measures were further impaired in the presence of neuropathologic comorbidities. In isolated cases of PART with Braak stage III-IV, there are additional deficits in measures of language.

CONCLUSION

Overall, these findings demonstrate underlying cognitive features specifically associated with PART, and reinforce the concept that PART is a distinct entity from ADNC.

Hypothesis review: Alzheimer's overture guidelines

National Institute on Aging-Alzheimer's Association definition and classification of sporadic Alzheimer's disease (sAD) is based on the assumption that β-amyloid drives the pathogenesis of sAD, and therefore, β-amyloid pathology is the sine-qua-non condition for the diagnosis of sAD. The neuropathological diagnosis is based on the concurrence of senile plaques (SPs) and neurofibrillary tangles (NFTs) designated as Alzheimer's disease neuropathological changes. However, NFTs develop in the brain decades before the appearance of SPs, and their distribution does not parallel the distribution of SPs. Moreover, NFTs are found in about 85% of individuals at age 65 and around 97% at age 80. SPs occur in 30% at age 65 and 50%-60% at age 80. More than 70 genetic risk factors have been identified in sAD; the encoded proteins modulate cell membranes, synapses, lipid metabolism, and neuroinflammation. Alzheimer's disease (AD) overture provides a new concept and definition of brain aging and sAD for further discussion. AD overture proposes that sAD is: (i) a multifactorial and progressive neurodegenerative biological process, (ii) characterized by the early appearance of 3R + 4Rtau NFTs, (iii) later deposition of β-amyloid and SPs, (iv) with particular non-overlapped regional distribution of NFTs and SPs, (v) preceded by or occurring in parallel with molecular changes affecting cell membranes, cytoskeleton, synapses, lipid and protein metabolism, energy metabolism, neuroinflammation, cell cycle, astrocytes, microglia, and blood vessels; (vi) accompanied by progressive neuron loss and brain atrophy, (vii) prevalent in human brain aging, and (viii) manifested as pre-clinical AD, and progressing not universally to mild cognitive impairment due to AD, and mild, moderate, and severe AD dementia.

Development, initial validation, and application of a visual read method for [18F]MK-6240 tau PET

Background

The positron emission tomography (PET) radiotracer [18F]MK-6240 exhibits high specificity for neurofibrillary tangles (NFTs) of tau protein in Alzheimer's disease (AD), high sensitivity to medial temporal and neocortical NFTs, and low within-brain background. Objectives were to develop and validate a reproducible, clinically relevant visual read method supporting [18F]MK-6240 use to identify and stage AD subjects versus non-AD and controls.

Methods

Five expert readers used their own methods to assess 30 scans of mixed diagnosis (47% cognitively normal, 23% mild cognitive impairment, 20% AD, 10% traumatic brain injury) and provided input regarding regional and global positivity, features influencing assessment, confidence, practicality, and clinical relevance. Inter-reader agreement and concordance with quantitative values were evaluated to confirm that regions could be read reliably. Guided by input regarding clinical applicability and practicality, read classifications were defined. The readers read the scans using the new classifications, establishing by majority agreement a gold standard read for those scans. Two naïve readers were trained and read the 30-scan set, providing initial validation. Inter-rater agreement was further tested by two trained independent readers in 131 scans. One of these readers used the same method to read a full, diverse database of 1842 scans; relationships between read classification, clinical diagnosis, and amyloid status as available were assessed.

Results

Four visual read classifications were determined: no uptake, medial temporal lobe (MTL) only, MTL and neocortical uptake, and uptake outside MTL. Inter-rater kappas were 1.0 for the naïve readers gold standard scans read and 0.98 for the independent readers 131-scan read. All scans in the full database could be classified; classification frequencies were concordant with NFT histopathology literature.

Discussion

This four-class [18F]MK-6240 visual read method captures the presence of medial temporal signal, neocortical expansion associated with disease progression, and atypical distributions that may reflect different phenotypes. The method demonstrates excellent trainability, reproducibility, and clinical relevance supporting clinical use.

Highlights

A visual read method has been developed for [18F]MK-6240 tau positron emission tomography.The method is readily trainable and reproducible, with inter-rater kappas of 0.98.The read method has been applied to a diverse set of 1842 [18F]MK-6240 scans.All scans from a spectrum of disease states and acquisitions could be classified.Read classifications are consistent with histopathological neurofibrillary tangle staging literature.