Cerebral cortex pathology in aging and Alzheimer's disease: a quantitative survey of large hospital-based geriatric and psychiatric cohorts

Neurometabolic topography and associations with cognition in Alzheimer's disease: A whole-brain high-resolution 3D MRSI study

INTRODUCTION

Altered neurometabolism, detectable via proton magnetic resonance spectroscopic imaging (1H-MRSI), is spatially heterogeneous and underpins cognitive impairments in Alzheimer's disease (AD). However, the spatial relationships between neurometabolic topography and cognitive impairment in AD remain unexplored due to technical limitations.

METHODS

We used a novel whole-brain high-resolution 1H-MRSI technique, with simultaneously acquired 18F-florbetapir positron emission tomography (PET) imaging, to investigate the relationship between neurometabolic topography and cognitive functions in 117 participants, including 22 prodromal AD, 51 AD dementia, and 44 controls.

RESULTS

Prodromal AD and AD dementia patients exhibited spatially distinct reductions in N-acetylaspartate, and increases in myo-inositol. Reduced N-acetylaspartate and increased myo-inositol were associated with worse global cognitive performance, and N-acetylaspartate correlated with five specific cognitive scores. Neurometabolic topography provides biological insights into diverse cognitive dysfunctions.

DISCUSSION

Whole-brain high-resolution 1H-MRSI revealed spatially distinct neurometabolic topographies associated with cognitive decline in AD, suggesting potential for noninvasive brain metabolic imaging to track AD progression.

HIGHLIGHTS

Whole-brain high-resolution 1H-MRSI unveils neurometabolic topography in AD. Spatially distinct reductions in NAA, and increases in mI, are demonstrated. NAA and mI topography correlates with global cognitive performance. NAA topography correlates with specific cognitive performance.

Aging decreases the precision of visual working memory

OBJECTIVES

As individuals age, cognitive abilities such as working memory (WM), decline. In the current study, we investigated the effect of age on WM, and elucidated sources of errors.

METHOD

A total of 102 healthy individuals, aged 18 to 71, participated in this research. We designed and administered a face-based visual WM task, collecting responses via a graded scale in a delayed match-to-sample reproduction task.

RESULTS

The error of participants increased significantly as they aged. Our analysis revealed a significant age-related rise in the standard deviation of error distribution. However, there was no significant change in uniform probability with age.

CONCLUSION

We found that WM performance declines through the lifespan. Investigating the sources of error, we found that the precision of WM decreased monotonously with age. The results also indicated that the probability of guessing the response as a measure of random response is not affected by age.

Investigating a Novel Neurodegenerative Disease Toxic Mechanism Involving Lipid Binding Specificity of Amyloid Oligomers

Exploring the mechanisms underlying the toxicity of amyloid oligomers (AOs) presents a significant opportunity for discovering cures and developing treatments for neurodegenerative diseases. Recently, using a combination of ion mobility spectrometry-mass spectrometry (IMS-MS) and X-ray crystallography (XRC), we showed that the peptide KVKVLWDVIEV, which is the G95W mutant of αB-Crystallin (90-100) and abbreviated as G6W, self-assembles up to a dodecamer that structurally resembles lipid transport proteins. The glycine to tryptophan mutation promotes not only larger oligomers and enhanced cytotoxicity in brain slices than the wild type but also a narrow hydrophobic cavity suitable for fatty acid or phospholipid binding. Here, we determine the plausibility of a novel cytotoxic mechanism where the G6W's structural motif could perturb lipid homeostasis by determining its lipid binding selectivity and specificity. We show that the G6W oligomers have a strong affinity toward unsaturated phospholipids with a preference toward phospholipids containing 16-C alkyl chains. Molecular dynamics simulations demonstrate how an unsaturated, 16-C phospholipid fits tightly inside and outside G6W's hydrophobic cavity. This binding is exclusive to the G6W peptide, as other amyloid oligomers with different atomic structures, including its wildtype αB-Crystallin (90-100) and several superoxide dismutase 1 (SOD1) peptides that are known to self-assemble into amyloid oligomers (SOD1P28K and SOD1WG-GW), do not experience the same strong binding affinity. While the existing chaperone-lipid hypothesis on amyloid toxicity suggests amyloid-lipid complexes perforate cell membranes, our work provides a new outlook, indicating that soluble amyloid oligomers disrupt lipid homeostasis via selective protein-ligand interactions. The toxic mechanisms may arise from the formation of unique amyloid oligomer structures assisted by lipid ligands or impaired lipid transports.

ScISOr-ATAC reveals convergent and divergent splicing and chromatin specificities between matched cell types across cortical regions, evolution, and in Alzheimer's Disease

Multimodal measurements have become widespread in genomics, however measuring open chromatin accessibility and splicing simultaneously in frozen brain tissues remains unconquered. Hence, we devised Single-Cell-ISOform-RNA sequencing coupled with the Assay-for-Transposase-Accessible-Chromatin (ScISOr-ATAC). We utilized ScISOr-ATAC to assess whether chromatin and splicing alterations in the brain convergently affect the same cell types or divergently different ones. We applied ScISOr-ATAC to three major conditions: comparing (i) the Rhesus macaque (Macaca mulatta) prefrontal cortex (PFC) and visual cortex (VIS), (ii) cross species divergence of Rhesus macaque versus human PFC, as well as (iii) dysregulation in Alzheimer's disease in human PFC. We found that among cortical-layer biased excitatory neuron subtypes, splicing is highly brain-region specific for L3-5/L6 IT_RORB neurons, moderately specific in L2-3 IT_CUX2.RORB neurons and unspecific in L2-3 IT_CUX2 neurons. In contrast, at the chromatin level, L2-3 IT_CUX2.RORB neurons show the highest brain-region specificity compared to other subtypes. Likewise, when comparing human and macaque PFC, strong evolutionary divergence on one molecular modality does not necessarily imply strong such divergence on another molecular level in the same cell type. Finally, in Alzheimer's disease, oligodendrocytes show convergently high dysregulation in both chromatin and splicing. However, chromatin and splicing dysregulation most strongly affect distinct oligodendrocyte subtypes. Overall, these results indicate that chromatin and splicing can show convergent or divergent results depending on the performed comparison, justifying the need for their concurrent measurement to investigate complex systems. Taken together, ScISOr-ATAC allows for the characterization of single-cell splicing and chromatin patterns and the comparison of sample groups in frozen brain samples.

Role of multi-targeted bioactive natural molecules and their derivatives in the treatment of Alzheimer's disease: an insight into structure-activity relationship

Alzheimer's disease (AD) is a complex neurodegenerative disorder involving cognitive dysfunction like short-term memory and behavioral changes as the disease progresses due to other unaltered physiological factors. The solution for this problem is Multi-targeted Drugs (MTDs), which can affect multiple determinants to realize the multifunctional effects. Acetylcholinesterase (AChE) inhibitors donepezil, rivastigmine, galantamine, and N-methyl-D-aspartate (NMDA) receptor antagonist memantine are FDA-approved drugs used to treat AD symptomatically. The key objective of this review is to understand multitargeted bioactive natural molecules that could be considered as leads for further development as effective drugs for treating AD, along with understanding its pharmacology and structure-activity relationship (SAR). Understanding the molecular mechanism of the AD pathophysiology, the role of existing drugs, treatment of AD via amyloid beta (Aβ) plaque, and neurofibrillary tangle (NFT) inhibition by natural bioactive molecules were also discussed in the review. The current quest and recent advancements with natural bioactive compounds like physostigmine, resveratrol, curcumin, and catechins, along with the study of in silico SAR, were reported in the present study. This review summarises the structural properties required for bioactive natural molecules to show anti-Alzheimer's activity by emphasizing on SAR of several bioactive natural molecules targeting various AD pathologies, their key molecular interactions that are critical for target specificity, their role as multitargeted ligands, used with adjunctive therapy for AD followed by related US patents granted recently. This article highlights the significance of the structural features of natural bioactive molecules in the treatment of AD and establishes a connection between them.Communicated by Ramaswamy H. Sarma.

A Method for Bridging Population-Specific Genotypes to Detect Gene Modules Associated with Alzheimer's Disease

BACKGROUND

Genome-wide association studies have successfully identified variants associated with multiple conditions. However, generalizing discoveries across diverse populations remains challenging due to large variations in genetic composition. Methods that perform gene expression imputation have attempted to address the transferability of gene discoveries across populations, but with limited success.

METHODS

Here, we introduce a pipeline that combines gene expression imputation with gene module discovery, including a dense gene module search and a gene set variation analysis, to address the transferability issue. Our method feeds association probabilities of imputed gene expression with a selected phenotype into tissue-specific gene-module discovery over protein interaction networks to create higher-level gene modules.

RESULTS

We demonstrate our method's utility in three case-control studies of Alzheimer's disease (AD) for three different race/ethnic populations (Whites, African descent and Hispanics). We discovered 182 AD-associated genes from gene modules shared between these populations, highlighting new gene modules associated with AD.

CONCLUSIONS

Our innovative framework has the potential to identify robust discoveries across populations based on gene modules, as demonstrated in AD.

Atomic view of an amyloid dodecamer exhibiting selective cellular toxic vulnerability in acute brain slices

Atomic structures of amyloid oligomers that capture the neurodegenerative disease pathology are essential to understand disease-state causes and finding cures. Here we investigate the G6W mutation of the cytotoxic, hexameric amyloid model KV11. The mutation results into an asymmetric dodecamer composed of a pair of 30° twisted antiparallel β-sheets. The complete break between adjacent β-strands is unprecedented among amyloid fibril crystal structures and supports that our structure is an oligomer. The poor shape complementarity between mated sheets reveals an interior channel for binding lipids, suggesting that the toxicity may be due to a perturbation of lipid transport rather than a direct disruption of membrane integrity. Viability assays on mouse suprachiasmatic nucleus, anterior hypothalamus, and cerebral cortex demonstrated selective regional vulnerability consistent with Alzheimer's disease. Neuropeptides released from the brain slices may provide clues to how G6W initiates cellular injury.

Structural differences in amyloid-β fibrils from brains of nondemented elderly individuals and Alzheimer's disease patients

Although amyloid plaques composed of fibrillar amyloid-β (Aβ) assemblies are a diagnostic hallmark of Alzheimer's disease (AD), quantities of amyloid similar to those in AD patients are observed in brain tissue of some nondemented elderly individuals. The relationship between amyloid deposition and neurodegeneration in AD has, therefore, been unclear. Here, we use solid-state NMR to investigate whether molecular structures of Aβ fibrils from brain tissue of nondemented elderly individuals with high amyloid loads differ from structures of Aβ fibrils from AD tissue. Two-dimensional solid-state NMR spectra of isotopically labeled Aβ fibrils, prepared by seeded growth from frontal lobe tissue extracts, are similar in the two cases but with statistically significant differences in intensity distributions of cross-peak signals. Differences in solid-state NMR data are greater for 42-residue amyloid-β (Aβ42) fibrils than for 40-residue amyloid-β (Aβ40) fibrils. These data suggest that similar sets of fibril polymorphs develop in nondemented elderly individuals and AD patients but with different relative populations on average.

Comparative neuropathology in aging primates: A perspective

While humans exhibit a significant degree of neuropathological changes associated with deficits in cognitive and memory functions during aging, non-human primates (NHP) present with more variable expressions of pathological alterations among individuals and species. As such, NHP with long life expectancy in captivity offer an opportunity to study brain senescence in the absence of the typical cellular pathology caused by age-related neurodegenerative illnesses commonly seen in humans. Age-related changes at neuronal population, single cell, and synaptic levels have been well documented in macaques and marmosets, while age-related and Alzheimer's disease-like neuropathology has been characterized in additional species including lemurs as well as great apes. We present a comparative overview of existing neuropathologic observations across the primate order, including classic age-related changes such as cell loss, amyloid deposition, amyloid angiopathy, and tau accumulation. We also review existing cellular and ultrastructural data on neuronal changes, such as dendritic attrition and spine alterations, synaptic loss and pathology, and axonal and myelin pathology, and discuss their repercussions on cellular and systems function and cognition.

Artificial intelligence and leukocyte epigenomics: Evaluation and prediction of late-onset Alzheimer's disease

We evaluated the utility of leucocyte epigenomic-biomarkers for Alzheimer’s Disease (AD) detection and elucidates its molecular pathogeneses. Genome-wide DNA methylation analysis was performed using the Infinium MethylationEPIC BeadChip array in 24 late-onset AD (LOAD) and 24 cognitively healthy subjects. Data were analyzed using six Artificial Intelligence (AI) methodologies including Deep Learning (DL) followed by Ingenuity Pathway Analysis (IPA) was used for AD prediction. We identified 152 significantly (FDR p<0.05) differentially methylated intragenic CpGs in 171 distinct genes in AD patients compared to controls. All AI platforms accurately predicted AD with AUCs ≥0.93 using 283,143 intragenic and 244,246 intergenic/extragenic CpGs. DL had an AUC = 0.99 using intragenic CpGs, with both sensitivity and specificity being 97%. High AD prediction was also achieved using intergenic/extragenic CpG sites (DL significance value being AUC = 0.99 with 97% sensitivity and specificity). Epigenetically altered genes included CR1L & CTSV (abnormal morphology of cerebral cortex), S1PR1 (CNS inflammation), and LTB4R (inflammatory response). These genes have been previously linked with AD and dementia. The differentially methylated genes CTSV & PRMT5 (ventricular hypertrophy and dilation) are linked to cardiovascular disease and of interest given the known association between impaired cerebral blood flow, cardiovascular disease, and AD. We report a novel, minimally invasive approach using peripheral blood leucocyte epigenomics, and AI analysis to detect AD and elucidate its pathogenesis.

Temporal Quantitative Profiling of Newly Synthesized Proteins during Aβ Accumulation

Accumulation of aggregated amyloid beta (Aβ) in the brain is believed to impair multiple cellular pathways and play a central role in Alzheimer's disease pathology. However, how this process is regulated remains unclear. In theory, measuring protein synthesis is the most direct way to evaluate a cell's response to stimuli, but to date, there have been few reliable methods to do this. To identify the protein regulatory network during the development of Aβ deposition in AD, we applied a new proteomic technique to quantitate newly synthesized protein (NSP) changes in the cerebral cortex and hippocampus of 2-, 5-, and 9-month-old APP/PS1 AD transgenic mice. This bio-orthogonal noncanonical amino acid tagging analysis combined PALM (pulse azidohomoalanine labeling in mammals) and HILAQ (heavy isotope labeled AHA quantitation) to reveal a comprehensive dataset of NSPs prior to and post Aβ deposition, including the identification of proteins not previously associated with AD, and demonstrated that the pattern of differentially expressed NSPs is age-dependent. We also found dysregulated vesicle transportation networks including endosomal subunits, coat protein complex I (COPI), and mitochondrial respiratory chain throughout all time points and two brain regions. These results point to a pathological dysregulation of vesicle transportation which occurs prior to Aβ accumulation and the onset of AD symptoms, which may progressively impact the entire protein network and thereby drive neurodegeneration. This study illustrates key pathway regulation responses to the development of AD pathogenesis by directly measuring the changes in protein synthesis and provides unique insights into the mechanisms that underlie AD.

Adenosine Metabolism in the Cerebral Cortex from Several Mice Models during Aging

Adenosine is a neuromodulator that has been involved in aging and neurodegenerative diseases as Alzheimer’s disease (AD). In the present work, we analyzed the possible modulation of purine metabolites, 5’nucleotidase (5′NT) and adenosine deaminase (ADA) activities, and adenosine monophosphate (AMP)-activated protein kinase (AMPK) and its phosphorylated form during aging in the cerebral cortex. Three murine models were used: senescence-accelerated mouse-resistant 1 (SAMR1, normal senescence), senescence-accelerated mouse-prone 8 (SAMP8, a model of AD), and the wild-type C57BL/6J (model of aging) mice strains. Glutamate and excitatory amino acid transporter 2 (EAAT2) levels were also measured in these animals. HPLC, Western blotting, and enzymatic activity evaluation were performed to this aim. 5′-Nucleotidase (5′NT) activity was decreased at six months and recovered at 12 months in SAMP8 while opposite effects were observed in SAMR1 at the same age, and no changes in C57BL/6J mice. ADA activity significantly decreased from 3 to 12 months in the SAMR1 mice strain, while a significant decrease from 6 to 12 months was observed in the SAMP8 mice strain. Regarding purine metabolites, xanthine and guanosine levels were increased at six months in SAMR1 without significant differences in SAMP8 mice. In C57BL/6J mice, inosine and xanthine were increased, while adenosine decreased, from 4 to 24 months. The AMPK level was decreased at six months in SAMP8 without significant changes nor in SAMR1 or C57BL/6J strains. Glutamate and EAAT2 levels were also modulated during aging. Our data show a different modulation of adenosine metabolism participants in the cerebral cortex of these animal models. Interestingly, the main differences between SAMR1 and SAMP8 mice were found at six months of age, SAMP8 being the most affected strain. As SAMP8 is an AD model, results suggest that adenosinergic metabolism is involved in the neurodegeneration of AD.

Mixed dementia: Neglected clinical entity or nosographic artifice?

Clinical and pathological data show that Alzheimer's disease (AD) and vascular dementia (VaD) are the most prevalent types of dementia in the elderly. Medically speaking, mixed dementia (MxD) is a heterogenous disorder mostly referred to the coexistence of AD and VaD. The weight of vascular contribution to AD phenotype is nowadays matter of debate. Despite great efforts in the field of neurodegeneration and cerebrovascular disease, controversy over the exact nature of their relation still remains, hampering progress in the specialty and raising doubts about the MxD concept validity. Is MxD a neglected clinical entity or a nosographic artifice? Starting from the assumption that recent advances in dementia classification and diagnostic criteria make this a propitious time to set up preventive and therapeutic strategies, this narrative review and opinion paper summarizes the literature concerning the questioned etiopathogenic overlap between AD and VaD and challenges the traditional view of MxD as the mere co-occurrence of different pure forms of dementia.

Neural stem cell therapy for neurovascular injury in Alzheimer's disease

Alzheimer's disease (AD), the most common form of dementia, is characterized by progressive neurodegeneration leading to severe cognitive decline and eventual death. AD pathophysiology is complex, but neurotoxic accumulation of amyloid-β (Aβ) and hyperphosphorylation of Tau are believed to be main drivers of neurodegeneration in AD. The formation and deposition of Aβ plaques occurs in the brain parenchyma as well as in the cerebral vasculature. Thus, proper blood-brain barrier (BBB) and cerebrovascular functioning are crucial for clearance of Aβ from the brain, and neurovascular dysfunction may be a critical component of AD development. Further, neuroinflammation and dysfunction of angiogenesis, neurogenesis, and neurorestorative capabilities play a role in AD pathophysiology. Currently, there is no effective treatment to prevent or restore loss of brain tissue and cognitive decline in patients with AD. Based on multifactorial and complex pathophysiological cascades in multiple Alzheimer's disease stages, effective AD therapies need to focus on targeting early AD pathology and preserving cerebrovascular function. Neural stem cells (NSCs) participate extensively in mammalian brain homeostasis and repair and exhibit pleiotropic intrinsic properties that likely make them attractive candidates for the treatment of AD. In the review, we summarize the current advances in knowledge regarding neurovascular aspects of AD-related neurodegeneration and discuss multiple actions of NSCs from preclinical studies of AD to evaluate their potential for future clinical treatment of AD.

Early detection of subtle motor dysfunction in cognitively normal subjects with amyloid-β positivity

Since the current neuropsychological assessments are not sensitive to subtle deficits that may be present in cognitively normal subjects with amyloid-β positivity, more accurate and efficient measures are needed. Our aim was to investigate the presence of subtle motor deficits in this population and its relationship with cerebrospinal fluid (CSF) amyloid-β levels. We adapted the Finger Tapping Task to measure tapping speed and intrasubject variability. Seventy-two right-handed participants completed the study. Subjects were divided into three groups according to their CSF biomarker profile: 37 control participants (negative CSF AD biomarkers, CTR), 20 cognitively normal subjects with amyloid-β positivity (abnormal levels of CSF Aβ₄₂, Aβ+) and 15 AD patients. All subjects underwent lumbar puncture for the CSF analysis, apolipoprotein E genotyping and completed the Finger Tapping Task, a neuropsychological battery and cardiovascular risk factor and physical activity assessments. An overall difference between groups was found both in tapping speed [F(2,66) = 19.37, p < .01] and in intrasubject variability [F(2,66) = 11.40, p < .01]. More specifically, the Aβ+ group showed lower speed [F(1,52) = 5.33, p < .05] and greater intrasubject variability [F(1,52) = 8.48, p < .01] than the CTR group, and higher speed than the AD group [F(1,30) = 13.61, p < .01]. Speed (β = .263, p < .05) and intrasubject variability (β = -.558, p < .01) were significantly associated with CSF amyloid-β levels. The present findings suggest that subtle motor difficulties can be detected in cognitively healthy subjects with amyloid-β positivity and be related to CSF Aβ₄₂ levels. An accurate assessment of motor functions could help on identifying individuals at the earliest stage of the Alzheimer's continuum.

The relationship between the morphological subtypes of microglia and Alzheimer's disease neuropathology

Microglial associations with both the major Alzheimer's disease (AD) pathognomonic entities, β-amyloid-positive plaques and tau-positive neurofibrillary tangles, have been noted in previous investigations of both human tissue and mouse models. However, the precise nature of their role in the pathogenesis of AD is debated; the major working hypothesis is that pro-inflammatory activities of activated microglia contribute to disease progression. In contrast, others have proposed that microglial dystrophy with a loss of physiological and neuroprotective activities promotes neurodegeneration. This immunohistochemical study sought to gain clarity in this area by quantifying the morphological subtypes of microglia in the mildly-affected primary visual cortex (PVC), the moderately affected superior frontal cortex (SFC) and the severely affected inferior temporal cortex (ITC) of 8 AD cases and 15 age and gender-matched, non-demented controls with ranging AD-type pathology. AD cases had increased β-amyloid and tau levels compared to controls in all regions. Neuronal loss was observed in the SFC and ITC, and was associated with atrophy in the latter. A major feature of the ITC in AD was a decrease in ramified (healthy) microglia with image analysis confirming reductions in arborized area and skeletal complexity. Activated microglia were not associated with AD but were increased in non-demented controls with greater AD-type pathology. Microglial clusters were occasionally associated with β-amyloid- and tau-positive plaques but represented less than 2% of the total microglial population. Dystrophic microglia were not associated with AD, but were inversely correlated with brain pH suggesting that agonal events were responsible for this morphological subtype. Overall these novel findings suggest that there is an early microglial reaction to AD-type pathology but a loss of healthy microglia is the prominent feature in severely affected regions of the AD brain.

Exploring the relationship between physical activity, beta-amyloid and tau: A narrative review

Several prospective cohort studies have reported an association between higher levels of physical activity and decreased risk of cognitive decline and dementia, years later. To support physical activity as a preventative measure against dementia, including Alzheimer's disease (AD; the most common form of dementia), evidence regarding the underlying mechanisms is vital. Here, we review previous work examining the role of physical activity in modulating levels of AD pathological hallmarks, beta-amyloid (Aβ) and tau (in the brain, cerebrospinal fluid and blood). Robust evidence from transgenic animal studies suggests that physical activity (voluntary wheel running) and exercise (forced wheel running) are implicated in lowering levels of brain Aβ and tau. Nevertheless, evidence from human studies, utilising measurements from positron emission tomography and cerebrospinal fluid biomarkers, is less consistent. Rigorous randomised controlled trials utilising long exercise interventions are vital to further understand the relationship between physical activity and Alzheimer's disease.

Spinal motor neurons and motor function in older adults

This study examined the relation between lumbar spinal motor neuron (SMN) indices and motor function proximate to death in community-dwelling older adults. Older adults (N = 145) participating in the Rush Memory and Aging Project underwent structured clinical testing proximate to death and brain and spinal cord autopsy at time of death. Ten motor performances were summarized by a composite global motor score. Choline acetyltransferase immunostaining was used to identify spinal motor neurons of the L4/5 segment. SMN counts and area and ventral horn area were collected. Linear regression modeling showed that the association of SMN counts and density with global motor scores proximate to death varied with sex. Separate models in men and women showed that this significant interaction was due to the association of higher SMN counts and density with higher global motor scores proximate to death in men but not women. These associations were unchanged when we controlled for indices of brain pathologies or chronic health conditions. In 38 cases with counts of activated microglia available, higher counts of activated microglia were associated with lower SMN counts. Activated spinal microglia and loss of spinal motor neurons may contribute to motor impairments in older men.

Recent Progress in Alzheimer's Disease Research, Part 1: Pathology

The field of Alzheimer's disease (AD) research has grown exponentially over the past few decades, especially since the isolation and identification of amyloid-β from postmortem examination of the brains of AD patients. Recently, the Journal of Alzheimer's Disease (JAD) put forth approximately 300 research reports which were deemed to be the most influential research reports in the field of AD since 2010. JAD readers were asked to vote on these most influential reports. In this 3-part review, we review the results of the 300 most influential AD research reports to provide JAD readers with a readily accessible, yet comprehensive review of the state of contemporary research. Notably, this multi-part review identifies the "hottest" fields of AD research providing guidance for both senior investigators as well as investigators new to the field on what is the most pressing fields within AD research. Part 1 of this review covers pathogenesis, both on a molecular and macro scale. Part 2 review genetics and epidemiology, and part 3 covers diagnosis and treatment. This part of the review, pathology, reviews amyloid-β, tau, prions, brain structure, and functional changes with AD and the neuroimmune response of AD.

Age-associated memory impairment and related disorders

Complaints of poor memory are common in the healthy elderly and to many it may seem unsurprising that cognitive function declines with ‘normal’ ageing. Virtually every biological system alters with age and, just as a 70-year-old cannot run as fast or hear as well as when he or she was 20, it is perhaps inevitable that cognitive function also becomes impaired. However, far from being straightforward, the nature, classification and clinical significance of age-related cognitive changes that fall short of dementia remain a most controversial and difficult area (see O'Brien & Beats, 1994; Dal Forno & Kawas, 1995). The recent emergence of new drugs for the treatment of Alzheimer's disease (donepezil and rivastigmine) and related disorders has emphasised the need to study groups with milder degrees of cognitive impairment. It is necessary to determine whether such conditions are benign and non-progressive, or harbingers of progressive dementia and so appropriate conditions to target for early therapeutic intervention. The presence of age-related cognitive changes raises other important issues including why such changes occur, how they should be classified and whether, even if ‘benign’, they can and should be treated.

Evidence of Tau Hyperphosphorylation and Dystrophic Microglia in the Common Marmoset

Common marmosets (Callithrix jacchus) have recently gained popularity in biomedical research as models of aging research. Basically, they confer advantages from other non-human primates due to their shorter lifespan with onset of appearance of aging at 8 years. Old marmosets present some markers linked to neurodegeneration in the brain such as amyloid beta (Aβ)_1-42 and Aβ_1-40. However, there are no studies exploring other cellular markers associated with neurodegenerative diseases in this non-human primate. Using immunohistochemistry, we analyzed brains of male adolescent, adult, old, and aged marmosets. We observed accumulation of Aβ_1-40 and Aβ_1-42 in the cortex of aged subjects. Tau hyperphosphorylation was already detected in the brain of adolescent animals and increased with aging in a more fibrillary form. Microglia activation was also observed in the aging process, while a dystrophic phenotype accumulates in aged subjects. Interestingly, dystrophic microglia contained hyperphosphorylated tau, but active microglia did not. These results support previous findings regarding microglia dysfunctionality in aging and neurodegenerative diseases as Alzheimer's disease. Further studies should explore the functional consequences of these findings to position this non-human primate as animal model of aging and neurodegeneration.

Patterns of Cortical and Subcortical Amyloid Burden across Stages of Preclinical Alzheimer's Disease

OBJECTIVES

We examined florbetapir positron emission tomography (PET) amyloid scans across stages of preclinical Alzheimer's disease (AD) in cortical, allocortical, and subcortical regions. Stages were characterized using empirically defined methods.

METHODS

A total of 312 cognitively normal Alzheimer's Disease Neuroimaging Initiative participants completed a neuropsychological assessment and florbetapir PET scan. Participants were classified into stages of preclinical AD using (1) a novel approach based on the number of abnormal biomarkers/cognitive markers each individual possessed, and (2) National Institute on Aging and the Alzheimer's Association (NIA-AA) criteria. Preclinical AD groups were compared to one another and to a mild cognitive impairment (MCI) sample on florbetapir standardized uptake value ratios (SUVRs) in cortical and allocortical/subcortical regions of interest (ROIs).

RESULTS

Amyloid deposition increased across stages of preclinical AD in all cortical ROIs, with SUVRs in the later stages reaching levels seen in MCI. Several subcortical areas showed a pattern of results similar to the cortical regions; however, SUVRs in the hippocampus, pallidum, and thalamus largely did not differ across stages of preclinical AD.

CONCLUSIONS

Substantial amyloid accumulation in cortical areas has already occurred before one meets criteria for a clinical diagnosis. Potential explanations for the unexpected pattern of results in some allocortical/subcortical ROIs include lack of correspondence between (1) cerebrospinal fluid and florbetapir PET measures of amyloid, or between (2) subcortical florbetapir PET SUVRs and underlying neuropathology. Findings support the utility of our novel method for staging preclinical AD. By combining imaging biomarkers with detailed cognitive assessment to better characterize preclinical AD, we can advance our understanding of who is at risk for future progression. (JINS, 2016, 22, 978-990).

(1)H-MRS asymmetry changes in the anterior and posterior cingulate gyrus in patients with mild cognitive impairment and mild Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia worldwide. Amnestic mild cognitive impairment (aMCI) is often the prodromal stage to AD. Most patients with aMCI harbor the pathologic changes of AD and demonstrate transition to AD at a rate of 10%-15% per year. Patients with AD and aMCI experience progressive brain metabolite changes. Accumulating evidence indicates that the asymmetry changes of left and right brain happen in the early stage of AD. However, the features of asymmetry changes in both anterior cingulate gyrus (ACG) and posterior cingulate gyrus (PCG) are still unclear. Here, we examine the left-right asymmetry changes of metabolites in ACG and PCG. Fifteen cases of mild AD patients meeting criteria for probable AD of NINDS-ADRDA, thirteen cases of aMCI according to the Mayo Clinic Alzheimer's Disease Research Center criteria, and sixteen cases of age-matched normal controls (NC) received Proton magnetic resonance spectroscopy ((1)H-MRS) for measurement of NAA/mI, NAA/Cr, Cho/Cr, and mI/Cr ratios in the PCG and ACG bilaterally. We analyzed (1)H-MRS data by paired t-test to validate the left-right asymmetry of (1)H-MRS data in the PCG and ACG. In AD, there was a significant difference in mI/Cr between the left and right ACG (P<0.001) and the left and right PCG (P=0.007). In aMCI, there was a significant difference in mI/Cr between the left and right ACG (P<0.001). In NC, there were no differences in the ratio value of metabolites NAA/mI, NAA/Cr, Cho/Cr, and mI/Cr between the left and right ACG and PCG. Thus, the left-right asymmetry of mI/Cr in the ACG and PCG may be an important biological indicator of mild AD.

Association of White Matter Integrity and Cognitive Functions in Chinese Non-Demented Elderly with the APOE ɛ4 Allele

The apolipoprotein E (APOE) ɛ4 allele is the strongest genetic risk factor for Alzheimer's disease (AD). This study aimed to investigate abnormality of white matter integrity and its relationship to cognitive impairments in Chinese non-demented elderly with and without the ɛ4 allele. We assessed cognitive differences using a series of neuropsychological tests and assessed white matter integrity using tract-based spatial statistics to measure mean diffusivity and fractional anisotropy. We determined that there were no statistically significant group differences in any neuropsychological measures. However, APOEɛ4 carriers without cognitive decline exhibited widespread disruption of the white matter tracts in several areas, including the cingulum, fornix, corpus callosum, and corona radiate. Furthermore, a correlation analysis in ɛ4 carriers indicated that disruption of the right fornix stria terminalis and the genu of the corpus callosum were positively associated with cognitive impairment, including memory, executive function, spatial processing, attention, and language. The present study reveals the deleterious effects of the ɛ4 allele on white matter, and this damage may potentially serve as a biomarker in preclinical investigations. Our promising results encourage further investigation using a multidimensional longitudinal approach with larger samples.

High-speed atomic force microscopy reveals structural dynamics of amyloid β1-42 aggregates

Aggregation of amyloidogenic proteins into insoluble amyloid fibrils is implicated in various neurodegenerative diseases. This process involves protein assembly into oligomeric intermediates and fibrils with highly polymorphic molecular structures. These structural differences may be responsible for different disease presentations. For this reason, elucidation of the structural features and assembly kinetics of amyloidogenic proteins has been an area of intense study. We report here the results of high-speed atomic force microscopy (HS-AFM) studies of fibril formation and elongation by the 42-residue form of the amyloid β-protein (Aβ1-42), a key pathogenetic agent of Alzheimer's disease. Our data demonstrate two different growth modes of Aβ1-42, one producing straight fibrils and the other producing spiral fibrils. Each mode depends on initial fibril nucleus structure, but switching from one growth mode to another was occasionally observed, suggesting that fibril end structure fluctuated between the two growth modes. This switching phenomenon was affected by buffer salt composition. Our findings indicate that polymorphism in fibril structure can occur after fibril nucleation and is affected by relatively modest changes in environmental conditions.

Long-term exposure to ELF-MF ameliorates cognitive deficits and attenuates tau hyperphosphorylation in 3xTg AD mice

Although numerous studies have reported the influence of extremely low frequency magnetic field (ELF-MF) exposure on human health, its effects on cognitive deficits in Alzheimer's disease (AD) have remained under debate. Moreover, the influence of ELF-MF on hyperphosphorylated tau, which is one of the most common pathological hallmarks of AD, has not been reported to date. Therefore, transgenic mice (3xTg) were used in the present study. 3xTg mice, which express an APP/PS1 mutation combined with a tau (P301L) mutation and that develop cognitive deficits at 6 months of age, were subjected to ELF-MF (50Hz, 500μT) exposure or sham exposure daily for 3 months. We discovered that ELF-MF exposure ameliorated cognitive deficits and increased synaptic proteins in 3xTg mice. The protective effects of ELF-MF exposure may have also been caused by the inhibition of apoptosis and/or decreased oxidative stress levels that were observed in the hippocampus tissues of treated mice. Furthermore, tau hyperphosphorylation was decreased in vivo because of ELF-MF exposure, and this decrease was induced by the inhibition of GSK3β and CDK5 activities and activation of PP2Ac. We are the first to report that exposure to ELF-MF can attenuate tau phosphorylation. These findings suggest that ELF-MF exposure could act as a valid therapeutic strategy for ameliorating cognitive deficits and attenuating tau hyperphosphorylation in AD.

Different Scales of Cortical Organization are Selectively Targeted in the Progression to Alzheimer's Disease

Previous studies have shown that the topological organization of the cerebral cortex is altered in Alzheimer's disease (AD). However, it remains unknown whether different levels of the cortical hierarchy are homogeneously affected during disease progression, and which of these levels are mostly involved in the breakdown of metabolic (functional) connectivity. To fulfill these goals, we acquired structural magnetic resonance images (MRI) and positron emission tomography (PET) with the radiotracer 18F-fludeoxyglucose (FDG) in 29 healthy old (HO) adults, 29 amnestic mild cognitive impairment (aMCI) and 29 mild AD patients. Structural and metabolic connections were obtained from inter-regional correlations of cortical thickness and glucose consumption, respectively. Results showed that AD and HO groups differed at all levels of cortical organization (i.e. whole cortex, hemisphere, lobe and node), whereas differences among the three groups were only evident at the lobe and node levels. The correlation between structural and metabolic connectivity (F-S coupling) was also disturbed during AD progression, affecting to different connectivity scales: it decreased at the local level, revealing a progressive increase of metabolic connections in those local communities with fewer structural connections; whereas it increased at the global level, likely due to a parallel reduction of cortical thickness and glucose consumption between long-distance cortical regions. Collectively, these results reveal that different levels of cortical organization are selectively affected during the transition from normal aging to dementia, which could be helpful to track cortical dysfunctions in the progression to AD.

Regional brain hypometabolism is unrelated to regional amyloid plaque burden

In its original form, the amyloid cascade hypothesis of Alzheimer's disease holds that fibrillar deposits of amyloid are an early, driving force in pathological events leading ultimately to neuronal death. Early clinicopathological investigations highlighted a number of inconsistencies leading to an updated hypothesis in which amyloid plaques give way to amyloid oligomers as the driving force in pathogenesis. Rather than focusing on the inconsistencies, amyloid imaging studies have tended to highlight the overlap between regions that show early amyloid plaque signal on positron emission tomography and that also happen to be affected early in Alzheimer's disease. Recent imaging studies investigating the regional dependency between metabolism and amyloid plaque deposition have arrived at conflicting results, with some showing regional associations and other not. We extracted multimodal neuroimaging data from the Alzheimer's disease neuroimaging database for 227 healthy controls and 434 subjects with mild cognitive impairment. We analysed regional patterns of amyloid deposition, regional glucose metabolism and regional atrophy using florbetapir ((18)F) positron emission tomography, (18)F-fluordeoxyglucose positron emission tomography and T1-weighted magnetic resonance imaging, respectively. Specifically, we derived grey matter density and standardized uptake value ratios for both positron emission tomography tracers in 404 functionally defined regions of interest. We examined the relation between regional glucose metabolism and amyloid plaques using linear models. For each region of interest, correcting for regional grey matter density, age, education and disease status, we tested the association of regional glucose metabolism with (i) cortex-wide florbetapir uptake; (ii) regional (i.e. in the same region of interest) florbetapir uptake; and (iii) regional florbetapir uptake while correcting in addition for cortex-wide florbetapir uptake. P-values for each setting were Bonferroni corrected for 404 tests. Regions showing significant hypometabolism with increasing cortex-wide amyloid burden were classic Alzheimer's disease-related regions: the medial and lateral parietal cortices. The associations between regional amyloid burden and regional metabolism were more heterogeneous: there were significant hypometabolic effects in posterior cingulate, precuneus, and parietal regions but also significant positive associations in bilateral hippocampus and entorhinal cortex. However, after correcting for global amyloid burden, few of the negative associations remained and the number of positive associations increased. Given the wide-spread distribution of amyloid plaques, if the canonical cascade hypothesis were true, we would expect wide-spread, cortical hypometabolism. Instead, cortical hypometabolism appears to be linked to global amyloid burden. Thus we conclude that regional fibrillar amyloid deposition has little to no association with regional hypometabolism.

Central Adiposity and Cortical Thickness in Midlife

OBJECTIVES

Excessive visceral fat is associated with greater metabolic fluctuation and increased risk for dementia in older adults. The aim of the current study is to directly determine the impact of central adiposity on brain structure at midlife by examining the thickness of the cerebral cortex.

METHODS

High-resolution magnetization-prepared rapid acquisition gradient-echo images were obtained from 103 participants aged 40 to 60 years (mean [standard deviation] = 49.63 [6.47] years) on a 3-T Siemens Skyra scanner. Visceral fat was measured using dual-energy x-ray absorptiometry.

RESULTS

Individuals with higher visceral fat mass and volume had significantly thicker cortex in the right posterior cingulate gyrus (β = 0.29 [p = .019] and β = 0.31 [p = .011], respectively), controlling for age, systolic blood pressure, total cholesterol level, and blood glucose level.

CONCLUSIONS

Visceral fat was significantly associated with thicker cortex in the posterior cingulate gyrus. Although future studies are necessary, these results indicate that central adiposity is associated with significant metabolic changes that impinge upon the central nervous system in middle age.

Cellular Models of Aggregation-dependent Template-directed Proteolysis to Characterize Tau Aggregation Inhibitors for Treatment of Alzheimer Disease

Alzheimer disease (AD) is a degenerative tauopathy characterized by aggregation of Tau protein through the repeat domain to form intraneuronal paired helical filaments (PHFs). We report two cell models in which we control the inherent toxicity of the core Tau fragment. These models demonstrate the properties of prion-like recruitment of full-length Tau into an aggregation pathway in which template-directed, endogenous truncation propagates aggregation through the core Tau binding domain. We use these in combination with dissolution of native PHFs to quantify the activity of Tau aggregation inhibitors (TAIs). We report the synthesis of novel stable crystalline leucomethylthioninium salts (LMTX®), which overcome the pharmacokinetic limitations of methylthioninium chloride. LMTX®, as either a dihydromesylate or a dihydrobromide salt, retains TAI activity in vitro and disrupts PHFs isolated from AD brain tissues at 0.16 μM. The Ki value for intracellular TAI activity, which we have been able to determine for the first time, is 0.12 μM. These values are close to the steady state trough brain concentration of methylthioninium ion (0.18 μM) that is required to arrest progression of AD on clinical and imaging end points and the minimum brain concentration (0.13 μM) required to reverse behavioral deficits and pathology in Tau transgenic mice.

At the interface of sensory and motor dysfunctions and Alzheimer's disease

Recent evidence indicates that sensory and motor changes may precede the cognitive symptoms of Alzheimer's disease (AD) by several years and may signify increased risk of developing AD. Traditionally, sensory and motor dysfunctions in aging and AD have been studied separately. To ascertain the evidence supporting the relationship between age-related changes in sensory and motor systems and the development of AD and to facilitate communication between several disciplines, the National Institute on Aging held an exploratory workshop titled "Sensory and Motor Dysfunctions in Aging and AD." The scientific sessions of the workshop focused on age-related and neuropathologic changes in the olfactory, visual, auditory, and motor systems, followed by extensive discussion and hypothesis generation related to the possible links among sensory, cognitive, and motor domains in aging and AD. Based on the data presented and discussed at this workshop, it is clear that sensory and motor regions of the central nervous system are affected by AD pathology and that interventions targeting amelioration of sensory-motor deficits in AD may enhance patient function as AD progresses.

The Cerebrovascular Basement Membrane: Role in the Clearance of β-amyloid and Cerebral Amyloid Angiopathy

Cerebral amyloid angiopathy (CAA), the accumulation of β-amyloid (Aβ) peptides in the walls of cerebral blood vessels, is observed in the majority of Alzheimer’s disease (AD) brains and is thought to be due to a failure of the aging brain to clear Aβ. Perivascular drainage of Aβ along cerebrovascular basement membranes (CVBMs) is one of the mechanisms by which Aβ is removed from the brain. CVBMs are specialized sheets of extracellular matrix that provide structural and functional support for cerebral blood vessels. Changes in CVBM composition and structure are observed in the aged and AD brain and may contribute to the development and progression of CAA. This review summarizes the properties of the CVBM, its role in mediating clearance of interstitial fluids and solutes from the brain, and evidence supporting a role for CVBM in the etiology of CAA.

Perforant path synaptic loss correlates with cognitive impairment and Alzheimer's disease in the oldest-old

Alzheimer's disease, which is defined pathologically by abundant amyloid plaques and neurofibrillary tangles concurrent with synaptic and neuronal loss, is the most common underlying cause of dementia in the elderly. Among the oldest-old, those aged 90 and older, other ageing-related brain pathologies are prevalent in addition to Alzheimer's disease, including cerebrovascular disease and hippocampal sclerosis. Although definite Alzheimer's disease pathology can distinguish dementia from normal individuals, the pathologies underlying cognitive impairment, especially in the oldest-old, remain poorly understood. We therefore conducted studies to determine the relative contributions of Alzheimer's disease pathology, cerebrovascular disease, hippocampal sclerosis and the altered expression of three synaptic proteins to cognitive status and global cognitive function. Relative immunohistochemistry intensity measures were obtained for synaptophysin, Synaptic vesicle transporter Sv2 (now known as SV2A) and Vesicular glutamate transporter 1 in the outer molecular layer of the hippocampal dentate gyrus on the first 157 participants of 'The 90+ Study' who came to autopsy, including participants with dementia (n = 84), those with cognitive impairment but no dementia (n = 37) and those with normal cognition (n = 36). Thal phase, Braak stage, cerebrovascular disease, hippocampal sclerosis and Pathological 43-kDa transactive response sequence DNA-binding protein (TDP-43) were also analysed. All measures were obtained blind to cognitive diagnosis. Global cognition was tested by the Mini-Mental State Examinaton. Logistic regression analysis explored the association between the pathological measures and the odds of being in the different cognitive groups whereas multiple regression analyses explored the association between pathological measures and global cognition scores. No measure clearly distinguished the control and cognitive impairment groups. Comparing the cognitive impairment and dementia groups, synaptophysin and SV2 were reduced, whereas Braak stage, TDP-43 and hippocampal sclerosis frequency increased. Thal phase and VGLUT1 did not distinguish the cognitive impairment and dementia groups. All measures distinguished the dementia and control groups and all markers associated with the cognitive test scores. When all markers were analysed simultaneously, a reduction in synaptophysin, a high Braak stage and the presence of TDP-43 and hippocampal sclerosis associated with global cognitive function. These findings suggest that tangle pathology, hippocampal sclerosis, TDP-43 and perforant pathway synaptic loss are the major contributors to dementia in the oldest-old. Although an increase in plaque pathology and glutamatergic synaptic loss may be early events associated with cognitive impairment, we conclude that those with cognitive impairment, but no dementia, are indistinguishable from cognitively normal subjects based on the measures reported here.

Pyramidal neurons of the prefrontal cortex in post-stroke, vascular and other ageing-related dementias

Dementia associated with cerebrovascular disease is common. It has been reported that ∼30% of elderly patients who survive stroke develop delayed dementia (post-stroke dementia), with most cases being diagnosed as vascular dementia. The pathological substrates associated with post-stroke or vascular dementia are poorly understood, particularly those associated with executive dysfunction. Three separate yet interconnecting circuits control executive function within the frontal lobe involving the dorsolateral prefrontal cortex, anterior cingulate cortex and the orbitofrontal cortex. We used stereological methods, along with immunohistological and related cell morphometric analysis, to examine densities and volumes of pyramidal neurons of the dorsolateral prefrontal cortex, anterior cingulate cortex and orbitofrontal cortex in the frontal lobe from a total of 90 elderly subjects (age range 71-98 years). Post-mortem brain tissues from post-stroke dementia and post-stroke patients with no dementia were derived from our prospective Cognitive Function After Stroke study. We also examined, in parallel, samples from ageing controls and similar age subjects pathologically diagnosed with Alzheimer's disease, mixed Alzheimer's disease and vascular dementia, and vascular dementia. We found pyramidal cell volumes in layers III and V in the dorsolateral prefrontal cortex of post-stroke and vascular dementia and, of mixed and Alzheimer's disease subjects to be reduced by 30-40% compared to post-stroke patients with no dementia and controls. There were no significant changes in neuronal volumes in either the anterior cingulate or orbitofrontal cortices. Remarkably, pyramidal neurons within the orbitofrontal cortex were also found to be smaller in size when compared to those in the other two neocortical regions. To relate the cell changes to cognitive function, we noted significant correlations between neuronal volumes and total CAMCOG, orientation and memory scores and clinical dementia ratings. Total estimated neuronal densities were not significantly changed between patients with post-stroke dementia and post-stroke patients with no dementia groups or ageing controls in any of the three frontal regions. In further morphometric analysis of the dorsolateral prefrontal cortex, we showed that neither diffuse cerebral atrophy nor neocortical thickness explained the selective neuronal volume effects. We also noted that neurofilament protein SMI31 immunoreactivity was increased in post-stroke and vascular dementia compared with post-stroke patients with no dementia and correlated with decreased neuronal volumes in subjects with post-stroke dementia and vascular dementia. Our findings suggest selective regional pyramidal cell atrophy in the dorsolateral prefrontal cortex-rather than neuronal density changes per se-are associated with dementia and executive dysfunction in post-stroke dementia and vascular dementia. The changes in dorsolateral prefrontal cortex pyramidal cells were not associated with neurofibrillary pathology suggesting there is a vascular basis for the observed highly selective neuronal atrophy.

Molecular structure of β-amyloid fibrils in Alzheimer's disease brain tissue

In vitro, β-amyloid (Aβ) peptides form polymorphic fibrils, with molecular structures that depend on growth conditions, plus various oligomeric and protofibrillar aggregates. Here, we investigate structures of human brain-derived Aβ fibrils, using seeded fibril growth from brain extract and data from solid-state nuclear magnetic resonance and electron microscopy. Experiments on tissue from two Alzheimer's disease (AD) patients with distinct clinical histories showed a single predominant 40 residue Aβ (Aβ40) fibril structure in each patient; however, the structures were different from one another. A molecular structural model developed for Aβ40 fibrils from one patient reveals features that distinguish in-vivo- from in-vitro-produced fibrils. The data suggest that fibrils in the brain may spread from a single nucleation site, that structural variations may correlate with variations in AD, and that structure-specific amyloid imaging agents may be an important future goal.

Synapse stability in the precuneus early in the progression of Alzheimer's disease

Amnestic mild cognitive impairment (aMCI) is considered to be one of the early stages in the progression from no cognitive impairment (NCI) to Alzheimer's disease (AD). Individuals with aMCI have increased levels of AD-type neuropathology in multiple regions of the neocortex and hippocampus and demonstrate a loss of synaptic connectivity. Recent neuroimaging studies have reported increased levels of 11C-PiB (Pittsburgh, compound B) in regions of the neocortex including the precuneus region of the medial parietal lobe. This cortical region has been implicated in episodic memory, which is disrupted early in the progression of AD. In this study, unbiased stereology coupled with electron microscopy was used to quantify total synaptic numbers in lamina 3 of the precuneus from short postmortem autopsy tissue harvested from subjects who died at different cognitive stages during the progression of AD. Individuals with aMCI did not reveal a statistically significant decline in total synapses compared to the NCI cohort while the AD group did show a modest but significant decline. Synaptic numbers failed to correlate with several different cognitive tasks including the Mini-Mental State Examination scores and episodic memory scores. Although levels of [3H]PiB binding were elevated in both the aMCI and AD groups, it did not strongly correlate with synaptic counts. These results support the idea that despite increased amyloid load, the precuneus region does not show early changes in synaptic decline during the progression of AD.

Foreign language training as cognitive therapy for age-related cognitive decline: a hypothesis for future research

Over the next fifty years, the number of older adults is set to reach record levels. Protecting older adults from the age-related effects of cognitive decline is one of the greatest challenges of the next few decades as it places increasing pressure on families, health systems, and economies on a global scale. The disease-state of age-related cognitive decline-Alzheimer's disease and other dementias-hijacks our consciousness and intellectual autonomy. However, there is evidence that cognitively stimulating activities protect against the adverse effects of cognitive decline. Similarly, bilingualism is also considered to be a safeguard. We propose that foreign language learning programs aimed at older populations are an optimal solution for building cognitive reserve because language learning engages an extensive brain network that is known to overlap with the regions negatively affected by the aging process. It is recommended that future research should test this potentially fruitful hypothesis.

Patterns of striatal degeneration in frontotemporal dementia

Behavioral variant frontotemporal dementia and semantic dementia have been associated with striatal degeneration, but few studies have delineated striatal subregion volumes in vivo or related them to the clinical phenotype. We traced caudate, putamen, and nucleus accumbens on magnetic resonance images to quantify volumes of these structures in behavioral variant frontotemporal dementia, semantic dementia, Alzheimer disease, and healthy controls (n=12 per group). We further related these striatal volumes to clinical deficits and neuropathologic findings in a subset of patients. Behavioral variant frontotemporal dementia and semantic dementia showed significant overall striatal atrophy compared with controls. Moreover, behavioral variant frontotemporal dementia showed panstriatal degeneration, whereas semantic dementia featured a more focal pattern involving putamen and accumbens. Right-sided striatal atrophy, especially in the putamen, correlated with the overall behavioral symptom severity and with specific behavioral domains. At autopsy, patients with behavioral variant frontotemporal dementia and semantic dementia showed striking and severe tau or TAR DNA-binding protein of 43 kDa pathology, especially in ventral parts of the striatum. These results demonstrate that ventral striatum degeneration is a prominent shared feature in behavioral variant frontotemporal dementia and semantic dementia and may contribute to the social-emotional deficits common to both disorders.

Dual immunofluorescence study of citrullinated proteins in Alzheimer diseased frontal cortex

Deimination is a post-translational modification of proteins in which selected arginine amino acids are enzymatically converted to citrullines. Using dual-color immunofluorescence, the present study is the first to examine the frontal cortex of patients with Alzheimer's disease (AD) versus age-matched controls with an established monoclonal antibody (F95) against peptidyl-citrulline moieties. In AD specimens, a number of new findings were discovered, including evidence for deiminated proteins in extracellular plaques, the walls of large blood vessels, the nuclei of selective neurons immunoreactive for phosphorylated tau and numerous reactive astrocytes concentrated around extracellular plaques, ventricular surfaces and at the interface between the gray and white matter of the cortex. Although the identities of these citrullinated proteins remain largely unknown, the present study adds to the growing number of locations in which deiminated proteins may be found in the brains of patients with AD.

Expression of δNp73 in hippocampus of APP/PS1 transgenic mice following GFP-BMSCs transplantation

OBJECTIVE

To study the effect of hippocampal bone marrow stromal cells (GFP-BMSCs) transplantation on spatial memory and DeltaNp73 expression in APP/PS1 transgenic mice.

METHODS

Twelve APP/PS1 transgenic mice randomly received either 10 μl GFP-BMSCs suspension in medium (GFP-BMSCs transplantation group) or 10 μl complete medium (sham-operated group). Learning and memory function of mice in both groups were observed and tested in Morris water maze experiment at 2 weeks after surgery. Senile plaques and DeltaNp73 protein in hippocampuses were determined by immunohistochemistry and western blot at 3 weeks after surgery, respectively.

RESULTS

APP/PS1 mice treated with BMSCs performed significantly better on the water maze test than those in sham-operated group (P<0·05). Immunohistochemistry showed that GFP-BMSCs distributed uniformly and the number of Alzheimer's senile plaques reduced after transplantation. Western blot showed that quantified DeltaNp73 protein expression was significantly higher in BMSCs transplantation group when compared with sham-operated group (P<0·01).

CONCLUSIONS

Our results suggest that BMSCs transplatation could retard Alzheimer's disease (AD) like pathology and upregulate DeltaNp73 expression in hippocampuses of APP/PS1 transgenic mice. GFP-BMSCs transplantation will be a potential treatment for AD.

Aging, synaptic dysfunction, and insulin-like growth factor (IGF)-1

Insulin-like growth factor (IGF)-1 is an important neurotrophic hormone. Deficiency of this hormone has been reported to influence the genesis of cognitive impairment and dementia in the elderly patients. Nevertheless, there are studies indicating that cognitive function can be maintained into old age even in the absence of circulating IGF-1 and studies that link IGF-1 to an acceleration of neurological diseases. Although IGF-1 has a complex role in brain function, synaptic effects appear to be central to the IGF-1-induced improvement in learning and memory. In this review, synaptic mechanisms of learning and memory and the effects of IGF-1 on synaptic communication are discussed. The emerging data indicate that synaptic function decreases with age and that IGF-1 contributes to information processing in the brain. Further studies that detail the specific actions of this important neurotrophic hormone will likely lead to therapies that result in improved cognitive function for the elderly patients.

The molecular pathology of Alzheimer's disease

Neurofibrillary pathology in Alzheimer's disease consists of paired helical filaments comprising tau protein. This pathology is correlated with dementia, but can appear in the first two decades of life. Extracellular amyloid β-protein arises through proteolytic processing of a transmembrane precursor, which involves the action of several enzymes. Mutations in the genes for the precursor and presenilin proteins accelerate the deposition of Aβ. Tau mutations cause other tauopathies in the absence of amyloid deposition, indicating that amyloid deposition is not a prerequisite for dementia. An improved understanding of Alzheimer's disease awaits to be obtained by molecular imaging of these pathologies.

Dysfunctional nucleus tractus solitarius: its crucial role in promoting neuropathogenetic cascade of Alzheimer's dementia--a novel hypothesis

The pathophysiological mechanism(s) underlying Alzheimer's disease (AD) still remain unclear, and no disease-modifying or prophylactic therapies are currently available. Unraveling the fundamental neuropathogenesis of AD is an important challenge. Several studies on AD have suggested lesions in a number of CNS areas including the basal forebrain, hippocampus, entorhinal cortex, amygdale/insula, and the locus coeruleus. However, plausible unifying studies on the upstream factors that involve these heterogeneous regions and herald the onset of AD pathogenesis are not available. The current article presents a novel nucleus tractus solitarius (NTS) vector hypothesis that underpins several disparate biological mechanisms and neural circuits, and identifies relevant hallmarks of major presumptive causative factor(s) linked to the NTS, in older/aging individuals. Aging, obesity, infection, sleep apnea, smoking, neuropsychological states, and hypothermia-all activate inflammatory cytokines and oxidative stress. The synergistic impact of systemic proinflammatory mediators activates microglia and promotes neuroinflammation. Acutely, the innate immune response is protective defending against pathogens/toxins; however, when chronic, it causes neuroinflammation and neuronal dysfunction, particularly in brainstem and neocortex. The NTS in the brainstem is an essential multiple signaling hub, and an extremely important central integration site of baroreceptor, chemoreceptor, and a multitude of sensory afferents from gustatory, gastrointestinal, cardiac, pulmonary, and upper airway systems. Owing to persistent neuroinflammation, the dysfunctional NTS exerts deleterious impact on nucleus ambiguus, dorsal motor nucleus of vagus, hypoglossal, parabrachial, locus coeruleus and many key nuclei in the brainstem, and the hippocampus, entorhinal cortex, prefrontal cortex, amygdala, insula, and basal forebrain in the neocortex. The neuronal and synaptic dysfunction emanating from the inflamed NTS may affect its interconnected pathways impacting almost the entire CNS--which is already primed by neuroinflammation, thus promoting cognitive and neuropsychiatric symptoms. The upstream factors discussed here may underpin the neuropathopgenesis of AD. AD pathology is multifactorial; the current perspective underscores the value of attenuating disparate upstream factors--in conjunction with anticholinesterase, anti-inflammatory, immunosuppressive, and anti-oxidant pharmacotherapy. Amelioration of the NTS pathology may be of central importance in countering the neuropathological cascade of AD. The NTS, therefore, may be a potential target of novel therapeutic strategies.

The case for blood-brain barrier dysfunction in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease that leads to a progressive loss of integrative and memory capacities of the brain. This is the predominant form of neurodegenerative dementia, with a growing prevalence of between 1 in 50 and 1 in 100 in North America. Numerous hypotheses related to the etiology of AD have developed over the years. However, among the various published hypotheses, the predominant one is related to the progressive and prominent accumulation of central nervous system β-amyloid peptide and the ensuing brain burden created. It is, therefore, important to consider the homeostatic mechanisms underlying β-amyloid transport dynamics between the brain and blood vascular compartments. As well, there is a dynamic interrelationship between soluble and insoluble forms of the peptide. Factors that underlie and regulate these dynamic processes are likely relevant to the end accumulation of β-amyloid peptide in the brain compartment and ultimately in insoluble forms, which is characteristic of, and significant for, the pathophysiology of the Alzheimer's brain. Significantly, and in particular relation to the amyloid burden theory mentioned above, it has been postulated that a dysfunctioning blood-brain barrier (BBB) may play a significant, if not critical, role in the pathogenesis of AD. By allowing the influx of injurious materials or agents into the brain or by impeding or blocking the efflux of those materials and/or agents, BBB-related neuronopathies and their associated sequelae could, and do, ensue.

Submicromolar Aβ42 reduces hippocampal glutamate receptors and presynaptic markers in an aggregation-dependent manner

Synaptic pathology in Alzheimer's disease brains is thought to involve soluble Aβ42 peptide. Here, sterile incubation in PBS caused small Aβ42 oligomer formation as well as heterogeneous, 6E10-immunopositive aggregates of 80-100kDa. The high molecular weight aggregates (H-agg) formed in a time-dependent manner over an extended 30-day period. Interestingly, an inverse relationship between dimeric and H-agg formation was more evident when incubations were performed at 37°C as compared to 23°C, thus providing an experimental strategy with which to address synaptic compromise produced by the different Aβ aggregates. H-agg species formed faster and to higher levels at 37°C compared to 23°C, and the two aggregate preparations were evaluated in hippocampal slice cultures, a sensitive system for monitoring synaptic integrity. Applied daily at 80-600nM for 7days, the Aβ42 preparations caused dose-dependent and aggregation-dependent declines in α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) and N-methyl-d-aspartate (NMDA) receptor subunits as well as in presynaptic components. Unlike the synaptic effects, Aβ42 induced only trace cellular degeneration that was CA1 specific. The 37°C preparation was less effective at decreasing synaptic markers, corresponding with its reduced levels of Aβ42 monomers and dimers. Aβ42 dimers decayed significantly faster at 37°C than 23°C, and more rapidly than monomers at either temperature. These findings indicate that Aβ42 can self-aggregate into potent synaptotoxic oligomers as well as into larger aggregates that may serve to neutralize the toxic formations. These results will add to the growing debate concerning whether high molecular weight Aβ complexes that form amyloid plaques are protective through the sequestration of oligomeric species.

Aggregation of amyloids in a cellular context: modelling and experiment

Amyloid-related diseases are a group of illnesses in which an abnormal accumulation of proteins into fibrillar structures is evident. Results from a wide range of studies, ranging from identification of amyloid-β dimers in the brain to biophysical characterization of the interactions between amyloidogenic peptides and lipid membranes during fibril growth shed light on the initial events which take place during amyloid aggregation. Accounts of fibril disaggregation and formation of globular aggregates due to interactions with lipids or fatty acids further demonstrate the complexity of the aggregation process and the difficulty to treat amyloid-related diseases. There is an inherent difficulty in generalizing from studies of aggregation in vitro, but the involvement of too many cellular components limits the ability to follow amyloid aggregation in a cellular (or extracellular) context. Fortunately, the development of experimental methods to generate stable globular aggregates suggests new means of studying the molecular events associated with amyloid aggregation. Furthermore, simulation studies enable deeper understanding of the experimental results and provide useful predictions that can be tested in the laboratory. Computer simulations can nowadays provide molecular or even atomistic details that are experimentally not available or very difficult to obtain. In the present review, recent developments on modelling and experiments of amyloid aggregation are reviewed, and an integrative account on how isolated interactions (as observed in vitro and in silico) combine during the course of amyloid-related diseases is presented. Finally, it is argued that an integrative approach is necessary to get a better understanding of the protein aggregation process.

Alzheimer's disease is not "brain aging": neuropathological, genetic, and epidemiological human studies

Human studies are reviewed concerning whether "aging"-related mechanisms contribute to Alzheimer's disease (AD) pathogenesis. AD is defined by specific neuropathology: neuritic amyloid plaques and neocortical neurofibrillary tangles. AD pathology is driven by genetic factors related not to aging per se, but instead to the amyloid precursor protein (APP). In contrast to genes involved in APP-related mechanisms, there is no firm connection between genes implicated in human "accelerated aging" diseases (progerias) and AD. The epidemiology of AD in advanced age is highly relevant but deceptively challenging to address given the low autopsy rates in most countries. In extreme old age, brain diseases other than AD approximate AD prevalence while the impact of AD pathology appears to peak by age 95 and decline thereafter. Many distinct brain diseases other than AD afflict older human brains and contribute to cognitive impairment. Additional prevalent pathologies include cerebrovascular disease and hippocampal sclerosis, both high-morbidity brain diseases that appear to peak in incidence later than AD chronologically. Because of these common brain diseases of extreme old age, the epidemiology differs between clinical "dementia" and the subset of dementia cases with AD pathology. Additional aging-associated mechanisms for cognitive decline such as diabetes and synapse loss have been linked to AD and these hypotheses are discussed. Criteria are proposed to define an "aging-linked" disease, and AD fails all of these criteria. In conclusion, it may be most fruitful to focus attention on specific pathways involved in AD rather than attributing it to an inevitable consequence of aging.