Clinicopathologic correlations in a large Alzheimer disease center autopsy cohort: neuritic plaques and neurofibrillary tangles "do count" when staging disease severity

Intraneuronal tau aggregation precedes diffuse plaque deposition, but amyloid-β changes occur before increases of tau in cerebrospinal fluid

In comparison to the levels in age and gender-matched controls, reduced levels of pathological amyloid-β protein in cerebrospinal fluid routinely precede the onset of Alzheimer's disease-related symptoms by several years, whereas elevated soluble abnormal tau fractions (phosphorylated tau, total tau protein) in cerebrospinal fluid are detectable only with the onset and progression of clinical symptoms. This sequence of events in cerebrospinal fluid (amyloid-β changes detectable prior to abnormal tau changes) contrasts with that in which both proteins develop in the brain, where intraneuronal tau inclusions (pretangles, neurofibrillary tangles, neuropil threads) appear decades before the deposition of amyloid-β plaques (diffuse plaques, neuritic plaques). This viewpoint attempts to address questions arising in connection with this apparent sequential discrepancy-questions and issues for which there are currently no clear-cut answers.

A study of small RNAs from cerebral neocortex of pathology-verified Alzheimer's disease, dementia with lewy bodies, hippocampal sclerosis, frontotemporal lobar dementia, and non-demented human controls

MicroRNAs (miRNAs) are small (20-22 nucleotides) regulatory non-coding RNAs that strongly influence gene expression. Most prior studies addressing the role of miRNAs in neurodegenerative diseases (NDs) have focused on individual diseases such as Alzheimer's disease (AD), making disease-to-disease comparisons impossible. Using RNA deep sequencing, we sought to analyze in detail the small RNAs (including miRNAs) in the temporal neocortex gray matter from non-demented controls (n = 2), AD (n = 5), dementia with Lewy bodies (n = 4), hippocampal sclerosis of aging (n = 4), and frontotemporal lobar dementia (FTLD) (n = 5) cases, together accounting for the most prevalent ND subtypes. All cases had short postmortem intervals, relatively high-quality RNA, and state-of-the-art neuropathological diagnoses. The resulting data (over 113 million reads in total, averaging 5.6 million reads per sample) and secondary expression analyses constitute an unprecedented look into the human cerebral cortical miRNome at a nucleotide resolution. While we find no apparent changes in isomiR or miRNA editing patterns in correlation with ND pathology, our results validate and extend previous miRNA profiling studies with regard to quantitative changes in NDs. In agreement with this idea, we provide independent cohort validation for changes in miR-132 expression levels in AD (n = 8) and FTLD (n = 14) cases when compared to controls (n = 8). The identification of common and ND-specific putative novel brain miRNAs and/or short-hairpin molecules is also presented. The challenge now is to better understand the impact of these and other alterations on neuronal gene expression networks and neuropathologies.

Synthesis and preliminary evaluation of 2-arylhydroxyquinoline derivatives for tau imaging

Alzheimer's disease (AD) is the most common cause of dementia. Senile plaques, consisting of β-amyloid, and neurofibrillary tangles (NFTs), composed of tau protein, are representative pathological hallmarks of AD. It is believed that the accumulation of NFTs precedes the onset of clinical symptoms of AD and correlates with the progression of memory dysfunction. Thus, the use of noninvasive detection techniques including radiolabeled probes and positron emission tomography (PET) will facilitate early diagnosis or staging of AD. In this study, we synthesized and evaluated novel hydroxylated 2-arylquinoline derivatives as tau imaging PET probes. The binding affinities of compounds for tau were evaluated by fluorescent staining of the AD hippocampal section and a competitive binding assay using [(18) F]THK-523. THK-951 showed high binding affinity for tau pathology in an AD brain section and K18Δ280K fibrils (Ki  = 20.7 nM); thus, we radiosynthesized a (11) C-labeled THK-951 and further studied its potential as a tau PET probe. The [(11) C]THK-951 demonstrated excellent kinetics in a normal mouse brain (3.23% ID/g at 2 min postinjection and 0.15% ID/g at 30 min postinjection) and showed the labeling of NFTs in an AD brain section by autoradiography assay. These findings indicate the availability of [(11) C]THK-951 for in vivo PET imaging of tau pathology in AD.

Neuropathological approaches to cerebral aging and neuroplasticity

Cerebral aging is a complex and heterogenous process related to a large variety of molecular changes involving multiple neuronal networks, due to alterations of neurons (synapses, axons, dendrites, etc), particularly affecting strategically important regions, such as hippocampus and prefrontal areas. A substantial proportion of nondemented, cognitively unimpaired elderly subjects show at least mild to moderate, and rarely even severe, Alzheimer-related lesions, probably representing asymptomatic preclinical Alzheimer's disease, and/or mixed pathologies. While the substrate of resilience to cognitive decline in the presence of abundant pathologies has been unclear, recent research has strengthened the concept of cognitive or brain reserve, based on neuroplasticity or the ability of the brain to manage or counteract age-related changes or pathologies by reorganizing its structure, connections, and functions via complex molecular pathways and mechanisms that are becoming increasingly better understood. Part of neuroplasticity is adult neurogenesis in specific areas of the brain, in particular the hippocampal formation important for memory function, the decline of which is common even in “healthy” aging. To obtain further insights into the mechanisms of brain plasticity and adult neurogenesis, as the basis for prevention and potential therapeutic options, is a major challenge of modern neurosciences.

Neuroinflammatory phenotypes and their roles in Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is characterized pathologically by the presence of amyloid plaques and neurofibrillary tangles in the brain. While once considered immunologically privileged due to the blood-brain barrier, it is now understood that the glial cells of the brain are capable of complex inflammatory responses.

OBJECTIVE

The goal of the study is to assess the neuroinflammatory state of the early and late AD brain using the macrophage categorizations of M1, M2a, M2b and M2c.

METHODS

We used quantitative real-time RT-PCR to assess a number of inflammatory markers in the frontal cortex and cerebellar tissue from early and late AD patients. We then used neuropathological and clinical outcomes to determine whether there were any correlations.

RESULTS

We found that the AD brain is capable of generating all macrophage-like responses. In addition, we found that early AD is distinct from late AD with respect to the inflammatory profiles expressed in the brain. Most interestingly, however, we found that the early AD samples were biased to one of two phenotypes, M1 or M2a.

CONCLUSION

Heterogeneity in the neuroinflammatory state of the early AD brain.

APOE-ε2 and APOE-ε4 correlate with increased amyloid accumulation in cerebral vasculature

The APOE-ε4 allele correlates with increased risk of Alzheimer disease (AD) and increased parenchymal amyloid plaques. We tested how the APOE genotype correlated with cerebral amyloid angiopathy (CAA) by analyzing 371 brains for parenchymal and meningeal CAA in 4 brain regions (frontal, parietal, temporal, and occipital neocortex). The overall severity of CAA was highest in the occipital lobe. APOE-ε4/4 brains (n = 22) had the highest levels of CAA across regions. In the occipital lobe, nearly all APOE-ε4/4 cases were scored with the highest level of CAA (meninges, 95% of cases; parenchyma, 81%). In this brain region as in others, APOE-ε3/4 brains (n = 115) showed consistently less CAA than APOE-ε4/4 brains (meninges, 43%; parenchyma, 43%). APOE-ε3/3 brains (n = 182) showed even less CAA (meninges, 19%; parenchyma, 19%). Interestingly, APOE-ε2/3 cases (n = 42) had more CAA than APOE-ε3/3 (meninges, 44%; parenchyma, 32%), despite a reduced risk for AD in the APOE-ε2/3 individuals. APOE-ε4/4 brains also had the fewest regions without CAA, whereas APOE-ε3/3 brains had the most. Ordinal regression analyses demonstrated significant impacts of APOE-ε2 and APOE-ε4 on CAA at least in some brain regions. These data demonstrate that APOE genotype correlations with Aβ deposition in CAA only incompletely correspond to other AD-linked brain pathologies.

Non-Alzheimer neurodegenerative pathologies and their combinations are more frequent than commonly believed in the elderly brain: a community-based autopsy series

Neurodegenerative diseases are characterised by neuronal loss and cerebral deposition of proteins with altered physicochemical properties. The major proteins are amyloid-β (Aβ), tau, α-synuclein, and TDP-43. Although neuropathological studies on elderly individuals have emphasised the importance of mixed pathologies, there have been few observations on the full spectrum of proteinopathies in the ageing brain. During a community-based study we performed comprehensive mapping of neurodegeneration-related proteins and vascular pathology in the brains of 233 individuals (age at death 77-87; 73 examined clinically in detail). While all brains (from individuals with and without dementia) showed some degree of neurofibrillary degeneration, Aβ deposits were observed only in 160 (68.7 %). Further pathologies included α-synucleinopathies (24.9 %), non-Alzheimer tauopathies (23.2 %; including novel forms), TDP-43 proteinopathy (13.3 %), vascular lesions (48.9 %), and others (15.1 %; inflammation, metabolic encephalopathy, and tumours). TDP-43 proteinopathy correlated with hippocampal sclerosis (p < 0.001) and Alzheimer-related pathology (CERAD score and Braak and Braak stages, p = 0.001). The presence of one specific variable (cerebral amyloid angiopathy, Aβ parenchymal deposits, TDP-43 proteinopathy, α-synucleinopathy, vascular lesions, non-Alzheimer type tauopathy) did not increase the probability of the co-occurrence of others (p = 0.24). The number of observed pathologies correlated with AD-neuropathologic change (p < 0.0001). In addition to AD-neuropathologic change, tauopathies associated well with dementia, while TDP-43 pathology and α-synucleinopathy showed strong effects but lost significance when evaluated together with AD-neuropathologic change. Non-AD neurodegenerative pathologies and their combinations have been underestimated, but are frequent in reality as demonstrated here. This should be considered in diagnostic evaluation of biomarkers, and for better clinical stratification of patients.

Hippocampal sclerosis of aging, a prevalent and high-morbidity brain disease

Hippocampal sclerosis of aging (HS-Aging) is a causative factor in a large proportion of elderly dementia cases. The current definition of HS-Aging rests on pathologic criteria: neuronal loss and gliosis in the hippocampal formation that is out of proportion to AD-type pathology. HS-Aging is also strongly associated with TDP-43 pathology. HS-Aging pathology appears to be most prevalent in the oldest-old: autopsy series indicate that 5-30 % of nonagenarians have HS-Aging pathology. Among prior studies, differences in study design have contributed to the study-to-study variability in reported disease prevalence. The presence of HS-Aging pathology correlates with significant cognitive impairment which is often misdiagnosed as AD clinically. The antemortem diagnosis is further confounded by other diseases linked to hippocampal atrophy including frontotemporal lobar degeneration and cerebrovascular pathologies. Recent advances characterizing the neurocognitive profile of HS-Aging patients have begun to provide clues that may help identify living individuals with HS-Aging pathology. Structural brain imaging studies of research subjects followed to autopsy reveal hippocampal atrophy that is substantially greater in people with eventual HS-Aging pathology, compared to those with AD pathology alone. Data are presented from individuals who were followed with neurocognitive and neuroradiologic measurements, followed by neuropathologic evaluation at the University of Kentucky. Finally, we discuss factors that are hypothesized to cause or modify the disease. We conclude that the published literature on HS-Aging provides strong evidence of an important and under-appreciated brain disease of aging. Unfortunately, there is no therapy or preventive strategy currently available.

Contribution of cerebrovascular disease in autopsy confirmed neurodegenerative disease cases in the National Alzheimer's Coordinating Centre

Cerebrovascular disease and vascular risk factors are associated with Alzheimer's disease, but the evidence for their association with other neurodegenerative disorders is limited. Therefore, we compared the prevalence of cerebrovascular disease, vascular pathology and vascular risk factors in a wide range of neurodegenerative diseases and correlate them with dementia severity. Presence of cerebrovascular disease, vascular pathology and vascular risk factors was studied in 5715 cases of the National Alzheimer's Coordinating Centre database with a single neurodegenerative disease diagnosis (Alzheimer's disease, frontotemporal lobar degeneration due to tau, and TAR DNA-binding protein 43 immunoreactive deposits, α-synucleinopathies, hippocampal sclerosis and prion disease) based on a neuropathological examination with or without cerebrovascular disease, defined neuropathologically. In addition, 210 'unremarkable brain' cases without cognitive impairment, and 280 cases with pure cerebrovascular disease were included for comparison. Cases with cerebrovascular disease were older than those without cerebrovascular disease in all the groups except for those with hippocampal sclerosis. After controlling for age and gender as fixed effects and centre as a random effect, we observed that α-synucleinopathies, frontotemporal lobar degeneration due to tau and TAR DNA-binding protein 43, and prion disease showed a lower prevalence of coincident cerebrovascular disease than patients with Alzheimer's disease, and this was more significant in younger subjects. When cerebrovascular disease was also present, patients with Alzheimer's disease and patients with α-synucleinopathy showed relatively lower burdens of their respective lesions than those without cerebrovascular disease in the context of comparable severity of dementia at time of death. Concurrent cerebrovascular disease is a common neuropathological finding in aged subjects with dementia, is more common in Alzheimer's disease than in other neurodegenerative disorders, especially in younger subjects, and lowers the threshold for dementia due to Alzheimer's disease and α-synucleinopathies, which suggests that these disorders should be targeted by treatments for cerebrovascular disease.

Comparison of symptomatic and asymptomatic persons with Alzheimer disease neuropathology

OBJECTIVES

We sought to identify demographic and clinical features that were associated with expression of symptoms in the presence of Alzheimer disease (AD) neuropathologic changes.

METHODS

We studied 82 asymptomatic (Clinical Dementia Rating global score = 0) and 824 symptomatic subjects (Clinical Dementia Rating score >0) with low to high AD neuropathologic changes at autopsy who were assessed at 1 of 34 National Institute on Aging-funded Alzheimer's Disease Centers. All subjects underwent a clinical examination within 1 year of death. Logistic regression was used to evaluate factors associated with the odds of being asymptomatic vs symptomatic.

RESULTS

Asymptomatic subjects tended to have low neurofibrillary tangle scores but a wide range of neuritic plaque frequencies. There were, however, a few asymptomatic subjects with very high tangle and neuritic plaque burden, as well as symptomatic subjects with few changes. In the multivariable model, asymptomatic subjects were older (odds ratio [OR] = 1.04; 95% confidence interval [CI] = 1.01-1.07), had lower clinical Hachinski Ischemic Score (OR = 0.82; 95% CI = 0.69-0.97), were less likely to have an APOE ε4 allele (OR = 0.36; 95% CI = 0.16-0.83), and had lower neurofibrillary tangle score (OR = 0.28; 95% CI = 0.17-0.45) compared with symptomatic subjects.

CONCLUSIONS

Dissociating clinical symptoms from pathologic findings better allows for investigation of preclinical AD. Our results suggest that although the severity of the pathology, particularly neurofibrillary tangles, has a large role in determining the extent of symptoms, other factors, including age, APOE status, and comorbidities such as cerebrovascular disease also explain differences in clinical presentation.

Neuropathological approaches to cerebral aging and neuroplasticity

Cerebral aging is a complex and heterogenous process related to a large variety of molecular changes involving multiple neuronal networks, due to alterations of neurons (synapses, axons, dendrites, etc), particularly affecting strategically important regions, such as hippocampus and prefrontal areas. A substantial proportion of nondemented, cognitively unimpaired elderly subjects show at least mild to moderate, and rarely even severe, Alzheimer-related lesions, probably representing asymptomatic preclinical Alzheimer's disease, and/or mixed pathologies. While the substrate of resilience to cognitive decline in the presence of abundant pathologies has been unclear, recent research has strengthened the concept of cognitive or brain reserve, based on neuroplasticity or the ability of the brain to manage or counteract age-related changes or pathologies by reorganizing its structure, connections, and functions via complex molecular pathways and mechanisms that are becoming increasingly better understood. Part of neuroplasticity is adult neurogenesis in specific areas of the brain, in particular the hippocampal formation important for memory function, the decline of which is common even in "healthy" aging. To obtain further insights into the mechanisms of brain plasticity and adult neurogenesis, as the basis for prevention and potential therapeutic options, is a major challenge of modern neurosciences.

Postmortem Pittsburgh Compound B (PiB) binding increases with Alzheimer's disease progression

The development of imaging reagents is of considerable interest in the Alzheimer's disease (AD) field. Some of these, such as Pittsburgh Compound B (PiB), were designed to bind to the amyloid-β peptide (Aβ), the major component of amyloid deposits in the AD brain. Although these agents were designed for imaging amyloid deposits in vivo, a major avenue of evaluation relies on postmortem cross validation with established indices of AD pathology. In this study, we evaluated changes in the postmortem binding of PiB and its relationship to other aspects of Aβ-related pathology in a series of AD cases and age-matched controls. We also examined cases of preclinical AD (PCAD) and amnestic mild cognitive impairment (MCI), both considered early points in the AD continuum. PiB binding was found to increase with the progression of the disease and paralleled increases in the less soluble forms of Aβ, including SDS-stable Aβ oligomers. Increased PiB binding and its relationship to Aβ was only significant in a brain region vulnerable to the development of AD pathology (the superior and middle temporal gyri) but not in an unaffected region (cerebellum). This implies that the amyloid deposited in disease-affected regions may possess fundamental, brain region specific characteristics that may not as yet be fully appreciated. These data support the idea that PiB is a useful diagnostic tool for AD, particularly in the early stage of the disease, and also show that PiB could be a useful agent for the discovery of novel disease-related properties of amyloid.

Neuropathological profile of mild cognitive impairment from a population perspective

Whether the neuropathological profile of mild cognitive impairment (MCI) reflects an intermediate state between normal aging and dementia is not clear. Identifying which phenomena initiate disease and which occur secondary to the neuropathological process is important for targeted disease prevention. Current definitions of MCI include amnestic (aMCI), nonamnestic (nMCI), and multidomain (mMCI) subtypes. In an unbiased population-based cohort of brain donors, we have determined how many individuals fulfill these criteria in the period leading up to death [n=10 (5 multidomain MCI, 4 amnestic MCI, 1 nonamnestic MCI)]. All MCI cases were collapsed into 1 group and we tested whether their pathologic profile, including markers of Alzheimer disease (AD) and vascular disease (VD), is intermediate to individuals (matched for age, sex, and education) without cognitive impairment (n=20) or dementia (n=20). The main findings are of a significant linear trend in the odds of neuritic plaques (entorhinal/hippocampus), atrophy (hippocampal and cortical), infarcts, and small vessel disease (SVD) with increased cognitive impairment. Neuropathologically, MCI is complex, with 10% of MCI brains classified as normal, 10% as VD, 10% as AD, and 40% as mixed AD/VD, with the remaining showing other pathologies. Rather than pure pathologic changes, several different factors seem to contribute to the impairment of MCI. In MCI, both AD and non-AD pathology should be considered as possible intervention targets.

Pittsburgh compound B and the postmortem diagnosis of Alzheimer disease

OBJECTIVE

Deposition of the amyloid-β (Aβ) peptide in neuritic plaques is a requirement for the diagnosis of Alzheimer disease (AD). Although the continued development of in vivo imaging agents such as Pittsburgh compound B (PiB) is promising, the diagnosis of AD is still challenging. This can be partially attributed to our lack of a detailed understanding of the interrelationship between the various pools and species of Aβ and other common indices of AD pathology. We hypothesized that recent advances in our ability to accurately measure Aβ postmortem (for example, using PiB), could form the basis of a simple means to deliver an accurate AD diagnosis.

METHODS

We conducted a comprehensive analysis of the amount of Aβ40 and Aβ42 in increasingly insoluble fractions, oligomeric Aβ, and fibrillar Aβ (as defined by PiB binding), as well as plaques (diffuse and neuritic), and neurofibrillary tangles in autopsy specimens from age-matched, cognitively normal controls (n = 23) and AD (n = 22) cases, across multiple brain regions.

RESULTS

Both PiB binding and the amount of sodium dodecyl sulfate (SDS)-soluble Aβ were able to predict disease status; however, SDS-soluble Aβ was a better measure. Oligomeric Aβ was not a predictor of disease status. PiB binding was strongly related to plaque count, although diffuse plaques were a stronger correlate than neuritic plaques.

INTERPRETATION

Although postmortem PiB binding was somewhat useful in distinguishing AD from control cases, SDS-soluble Aβ measured by standard immunoassay was substantially better. These findings have important implications for the development of imaging-based biomarkers of AD.

Overview and findings from the rush Memory and Aging Project

The Memory and Aging Project is a longitudinal, epidemiologic clinical-pathologic cohort study of common chronic conditions of aging with an emphasis on decline in cognitive and motor function and risk of Alzheimer's disease (AD). In this manuscript, we first summarize the study design and methods. Then, we present data on: (1) the relation of motor function to cognition, disability, and death; (2) the relation of risk factors to cognitive and motor outcomes, disability and death; (3) the relation of neuropathologic indices to cognitive outcomes; (4) the relation of risk factors to neuropathologic indices; and (5) additional study findings. The findings are discussed and contextualized.

University of Kentucky Sanders-Brown healthy brain aging volunteers: donor characteristics, procedures and neuropathology

Cognitively intact elderly research volunteers at the University of Kentucky have been recruited, followed longitudinally, and autopsied with extensive neuropathological evaluations since 1989. To date, the cohort has recruited 1,030 individuals with 552 participants being actively followed, 363 deceased, and 273 autopsied. An extensive database has been constructed with continuous updates that include textured clinical, neuropsychological, neuroimaging, and pathological information. The history, demographics, clinical observations, and pathological features of this research cohort are described. We also explain some of the evolving methodologies and the academic contributions that have been made due to this motivated group of older Kentuckians.

Digital pathology and image analysis for robust high-throughput quantitative assessment of Alzheimer disease neuropathologic changes

Quantitative neuropathologic methods provide information that is important for both research and clinical applications. The technologic advancement of digital pathology and image analysis offers new solutions to enable valid quantification of pathologic severity that is reproducible between raters regardless of experience. Using an Aperio ScanScope XT and its accompanying image analysis software, we designed algorithms for quantitation of amyloid and tau pathologies on 65 β-amyloid (6F/3D antibody) and 48 phospho-tau (PHF-1)-immunostained sections of human temporal neocortex. Quantitative digital pathologic data were compared with manual pathology counts. There were excellent correlations between manually counted and digitally analyzed neuropathologic parameters (R² = 0.56-0.72). Data were highly reproducible among 3 participants with varying degrees of expertise in neuropathology (intraclass correlation coefficient values, >0.910). Digital quantification also provided additional parameters, including average plaque area, which shows statistically significant differences when samples are stratified according to apolipoprotein E allele status (average plaque area, 380.9 μm² in apolipoprotein E [Latin Small Letter Open E]4 carriers vs 274.4 μm² for noncarriers; p < 0.001). Thus, digital pathology offers a rigorous and reproducible method for quantifying Alzheimer disease neuropathologic changes and may provide additional insights into morphologic characteristics that were previously more challenging to assess because of technical limitations.

Neuroinflammatory phenotype in early Alzheimer's disease

Alzheimer's disease (AD) involves progressive neurodegeneration in the presence of misfolded proteins and poorly-understood inflammatory changes. However, research has shown that AD is genetically, clinically, and pathologically heterogeneous. In frozen brain samples of frontal cortex (diseased) and cerebellum (nondiseased) from the University of Kentucky Alzheimer's Disease Center autopsy cohort, we performed gene expression analysis for genes categorizing inflammatory states (termed M1 and M2) from early and late stage AD, and age-matched nondemented controls. We performed analysis of the serum samples for a profile of inflammatory proteins and examined the neuropathologic data on these samples. Striking heterogeneity was found in early AD. Specifically, early-stage AD brain samples indicated apparent polarization toward either the M1 or M2 brain inflammatory states when compared with age-matched nondisease control tissue. This polarization was observed in the frontal cortex and not in cerebellar tissue. We were able to detect differences in AD neuropathology, and changes in serum proteins that distinguished the individuals with apparent M1 versus M2 brain inflammatory polarization.

Alzheimer's disease: pathological mechanisms and recent insights

Amyloidopathies cause neurodegeneration in a substantial portion of the elderly population. Improvements in long term health care have made elderly individuals a large and growing demographic group, marking these diseases as a major public health concern. Alzheimer's Disease (AD) is the most studied form of neurodegenerative amyloidopathy. Although our understanding of AD is far from complete, several decades of research have advanced our knowledge to the point where it is conceivable that some form of disease modifying therapy may be available in the near future. These advances have been built on a strong mechanistic understanding of the disease from its underlying genetics, molecular biology and clinical pathology. Insights derived from the study of other neurodegenerative diseases, such as some forms of frontotemporal dementia, have been critical to this process. This knowledge has allowed researchers to construct animal models of the disease process that have paved the way towards the development of therapeutics. However, what was once thought to be a straightforward problem has evolved into a series of disappointing outcomes. Examination of pathways common to all neurodegenerative diseases, including the cellular mechanisms that clear misfolded proteins and their regulation, may be the best way to move forward.

Overview and findings from the religious orders study

The Religious Orders Study is a longitudinal clinical-pathologic cohort study of aging and Alzheimer's disease (AD). In this manuscript, we summarize the study methods including the study design and describe the clinical evaluation, assessment of risk factors, collection of ante-mortem biological specimens, brain autopsy and collection of selected postmortem data.

THE RESULTS

(1) review the relation of neuropathologic indices to clinical diagnoses and cognition proximate to death; (2) examine the relation of risk factors to clinical outcomes; (3) examine the relation of risk factors to measures of neuropathology; and (4) summarize additional study findings. We then discuss and contextualize the study findings.

MicroRNA-153 physiologically inhibits expression of amyloid-β precursor protein in cultured human fetal brain cells and is dysregulated in a subset of Alzheimer disease patients

Regulation of amyloid-β (Aβ) precursor protein (APP) expression is complex. MicroRNAs (miRNAs) are expected to participate in the molecular network that controls this process. The composition of this network is, however, still undefined. Elucidating the complement of miRNAs that regulate APP expression should reveal novel drug targets capable of modulating Aβ production in AD. Here, we investigated the contribution of miR-153 to this regulatory network. A miR-153 target site within the APP 3'-untranslated region (3'-UTR) was predicted by several bioinformatic algorithms. We found that miR-153 significantly reduced reporter expression when co-transfected with an APP 3'-UTR reporter construct. Mutation of the predicted miR-153 target site eliminated this reporter response. miR-153 delivery in both HeLa cells and primary human fetal brain cultures significantly reduced APP expression. Delivery of a miR-153 antisense inhibitor to human fetal brain cultures significantly elevated APP expression. miR-153 delivery also reduced expression of the APP paralog APLP2. High functional redundancy between APP and APLP2 suggests that miR-153 may target biological pathways in which they both function. Interestingly, in a subset of human AD brain specimens with moderate AD pathology, miR-153 levels were reduced. This same subset also exhibited elevated APP levels relative to control specimens. Therefore, endogenous miR-153 inhibits expression of APP in human neurons by specifically interacting with the APP 3'-UTR. This regulatory interaction may have relevance to AD etiology, where low miR-153 levels may drive increased APP expression in a subset of AD patients.

National Institute on Aging-Alzheimer's Association guidelines for the neuropathologic assessment of Alzheimer's disease

A consensus panel from the United States and Europe was convened recently to update and revise the 1997 consensus guidelines for the neuropathologic evaluation of Alzheimer's disease (AD) and other diseases of brain that are common in the elderly. The new guidelines recognize the pre-clinical stage of AD, enhance the assessment of AD to include amyloid accumulation as well as neurofibrillary change and neuritic plaques, establish protocols for the neuropathologic assessment of Lewy body disease, vascular brain injury, hippocampal sclerosis, and TDP-43 inclusions, and recommend standard approaches for the workup of cases and their clinico-pathologic correlation.

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

Clinicopathologic correlation studies are critically important for the field of Alzheimer disease (AD) research. Studies on human subjects with autopsy confirmation entail numerous potential biases that affect both their general applicability and the validity of the correlations. Many sources of data variability can weaken the apparent correlation between cognitive status and AD neuropathologic changes. Indeed, most persons in advanced old age have significant non-AD brain lesions that may alter cognition independently of AD. Worldwide research efforts have evaluated thousands of human subjects to assess the causes of cognitive impairment in the elderly, and these studies have been interpreted in different ways. We review the literature focusing on the correlation of AD neuropathologic changes (i.e. β-amyloid plaques and neurofibrillary tangles) with cognitive impairment. We discuss the various patterns of brain changes that have been observed in elderly individuals to provide a perspective for understanding AD clinicopathologic correlation and conclude that evidence from many independent research centers strongly supports the existence of a specific disease, as defined by the presence of Aβ plaques and neurofibrillary tangles. Although Aβ plaques may play a key role in AD pathogenesis, the severity of cognitive impairment correlates best with the burden of neocortical neurofibrillary tangles.

Mild cognitive impairment: statistical models of transition using longitudinal clinical data

Mild cognitive impairment (MCI) refers to the clinical state between normal cognition and probable Alzheimer's disease (AD), but persons diagnosed with MCI may progress to non-AD forms of dementia, remain MCI until death, or recover to normal cognition. Risk factors for these various clinical changes, which we term "transitions," may provide targets for therapeutic interventions. Therefore, it is useful to develop new approaches to assess risk factors for these transitions. Markov models have been used to investigate the transient nature of MCI represented by amnestic single-domain and mixed MCI states, where mixed MCI comprised all other MCI subtypes based on cognitive assessments. The purpose of this study is to expand this risk model by including a clinically determined MCI state as an outcome. Analyses show that several common risk factors play different roles in affecting transitions to MCI and dementia. Notably, APOE-4 increases the risk of transition to clinical MCI but does not affect the risk for a final transition to dementia, and baseline hypertension decreases the risk of transition to dementia from clinical MCI.

Experimental inhibition of fibrillogenesis and neurotoxicity by amyloid-beta (Aβ) and other disease-related peptides/proteins by plant extracts and herbal compounds

Amyloid-β (Aβ) fibrillogenesis and associated cyto/neurotoxicity are major pathological events and hallmarks in diseases such as Alzheimer's disease (AD). The understanding of Aβ molecular pathogenesis is currently a pharmacological target for rational drug design and discovery based on reduction of Aβ generation, inhibition of Aβ fibrillogenesis and aggregation, enhancement of Aβ clearance and amelioration of associated cytotoxicity. Molecular mechanisms for other amyloidoses, such as transthyretin amyloidosis, AL-amyloidosis, as well as α-synuclein and prion protein are also pharmacological targets for current drug therapy, design and discovery. We report on natural herbal compounds and extracts that are capable binding to and inhibiting different targets associated with AD and other amyloid-associated diseases, providing a basis for future therapeutic strategies. Many herbal compounds, including curcumin, galantamine, quercetin and other polyphenols, are under active investigation and hold considerable potential for future prophylactic and therapeutic treatment against AD and other neurodegenerative diseases, as well as systemic amyloid diseases. A common emerging theme throughout many studies is the anti-oxidant and anti-inflammatory properties of the compounds or herbal extracts under investigation, within the context of the inhibition of cyto/neurotoxicity and anti-amyloid activity.

White Matter Changes in Bipolar Disorder, Alzheimer Disease, and Mild Cognitive Impairment: New Insights from DTI

Neuropathological and neuroimaging studies have reported significant changes in white matter in psychiatric and neurodegenerative diseases. Diffusion tensor imaging (DTI), a recently developed technique, enables the detection of microstructural changes in white matter. It is a noninvasive in vivo technique that assesses water molecules' diffusion in brain tissues. The most commonly used parameters are axial and radial diffusivity reflecting diffusion along and perpendicular to the axons, as well as mean diffusivity and fractional anisotropy representing global diffusion. Although the combination of these parameters provides valuable information about the integrity of brain circuits, their physiological meaning still remains controversial. After reviewing the basic principles of DTI, we report on recent contributions that used this technique to explore subtle structural changes in white matter occurring in elderly patients with bipolar disorder and Alzheimer disease.

Prediction of preclinical Alzheimer's disease: longitudinal rates of change in cognition

Preclinical Alzheimer's disease (pAD) reflects neuropathological findings of AD in cognitively normal subjects. The present study represents an effort to determine if differences could be identified in the longitudinal patterns of cognitive performance in persons classified as pAD compared to those who did not meet criteria for AD at autopsy. We included 121 subjects who were cognitively normal from baseline through their last assessment before death and who underwent autopsy. Participants were classified into two groups: pathologically normal (PN; NIA-Reagan low or no-likelihood of AD, n = 89) and preclinical AD (pAD; NIA-Reagan criteria of intermediate or high-likelihood of AD in the absence of clinical dementia symptoms, n = 32) followed for a mean 7.5 years prior to death. Longitudinal rates and patterns of change in scores on a standard cognitive battery were compared between these two groups. While cognitive results at baseline and last evaluations revealed no clear cross sectional group differences after adjustment for age, ApoE status, education, and gender, statistically significant differences between the pAD and PN groups in slope of decline were seen on a composite score of cognitive function. Further analyses showed three components of this score reached significance: constructional praxis, delayed recall of a word list, and category verbal fluency. Despite being clinically viewed as normal at enrollment and at the final exam, there are significant differences in rates of cognitive decline in participants classified as pAD compared to those without this pathology. Longitudinal changes in slope of decline in specific cognitive test measures can serve as non-invasive methods for the detection of pAD.

"End-stage" neurofibrillary tangle pathology in preclinical Alzheimer's disease: fact or fiction?

Among individuals who were cognitively intact before death, autopsies may reveal some Alzheimer's disease-type pathology. The presence of end-stage pathology in cognitively intact persons would support the hypothesis that pathological markers are epiphenomena. We assessed advanced neurofibrillary (Braak stages V and VI) pathology focusing on nondemented individuals. Data from the National Alzheimer's Coordinating Center database (n = 4,690 included initially) and from the Nun Study (n = 526 included initially) were analyzed, with antemortem information about global cognition and careful postmortem studies available from each case. Global cognition (final Mini-Mental State Examination scores (MMSE) and clinical 'dementia' status) was correlated with neuropathology, including the severity of neurofibrillary pathology (Braak stages and neurofibrillary tangle counts in cerebral neocortex). Analyses support three major findings: 1. Braak stage V cases and Braak VI cases are significantly different from each other in terms of associated antemortem cognition; 2. There is an appreciable range of pathology within the category of Braak stage VI based on tangle counts such that brains with the most neurofibrillary tangles in neocortex always had profound antemortem cognitive impairment; and 3. There was no nondemented case with final MMSE score of 30 within a year of life and Braak stage VI pathology. It may be inappropriate to combine Braak stages V and VI cases, particularly in patients with early cognitive dysfunction, since the two pathological stages appear to differ dramatically in terms of both pathological severity and antemortem cognitive status. There is no documented example of truly end-stage neurofibrillary pathology coexisting with intact cognition.

Staging neurodegenerative disorders: structural, regional, biomarker, and functional progressions

The notion of staging in the neurodegenerative disorders is modulated by the constant and progressive loss of several aspects of brain structural integrity, circuitry, and neuronal processes. These destructive processes eventually remove individuals' abilities to perform at sufficient and necessary functional capacity at several levels of disease severity. The classification of (a) patients on the basis of diagnosis, risk prognosis, and intervention outcome, forms the basis of clinical staging, and (b) laboratory animals on the basis of animal model of brain disorder, extent of insult, and dysfunctional expression, provides the components for the clinical staging and preclinical staging, respectively, expressing associated epidemiological, biological, and genetic characteristics. The major focus of clinical staging in the present account stems from the fundamental notions of Braak staging as they describe the course and eventual prognosis for Alzheimer's disease, Lewy Body dementia, and Parkinson's disease. Mild cognitive impairment, which expresses the decline in episodic and semantic memory performance below the age-adjusted normal range without marked loss of global cognition or activities of daily living, and the applications of longitudinal magnetic resonance imaging, major instruments for the monitoring of either disease progression in dementia, present important challenges for staging concepts. Although Braak notions present the essential basis for further developments, current staging conceptualizations seem inadequate to comply with the massive influx of information dealing with neurodegenerative processes in brain, advanced both under clinical realities, and discoveries in the laboratory setting. The contributions of various biomarkers of disease progression, e.g., amyloid precursor protein, and neurotransmitter system imbalances, e.g., dopamine receptor supersensitivity and interactive propensities, await their incorporation into the existing staging models thereby underlining the ongoing, dynamic feature of the staging of brain disorders.

Neuropathologic features associated with Alzheimer disease diagnosis: age matters

OBJECTIVE

To examine whether the association between clinical Alzheimer disease (AD) diagnosis and neuropathology and the precision by which neuropathology differentiates people with clinical AD from those with normal cognition varies by age.

METHODS

We conducted a cross-sectional analysis of 2,014 older adults (≥70 years at death) from the National Alzheimer's Coordinating Center database with clinical diagnosis of normal cognition (made ≤1 year before death, n = 419) or AD (at ≥65 years, n = 1,595) and a postmortem neuropathologic examination evaluating AD pathology (neurofibrillary tangles, neuritic plaques) and non-AD pathology (diffuse plaques, amyloid angiopathy, Lewy bodies, macrovascular disease, microvascular disease). We used adjusted logistic regression to analyze the relationship between clinical AD diagnosis and neuropathologic features, area under the receiver operating characteristic curve (c statistic) to evaluate how precisely neuropathology differentiates between cognitive diagnoses, and an interaction to identify effect modification by age group.

RESULTS

In a model controlling for coexisting neuropathologic features, the relationship between clinical AD diagnosis and neurofibrillary tangles was significantly weaker with increasing age (p < 0.001 for interaction). The aggregate of all neuropathologic features more strongly differentiated people with clinical AD from those without in younger age groups (70-74 years: c statistic, 95% confidence interval: 0.93, 0.89-0.96; 75-84 years: 0.95, 0.87-0.95; ≥85 years: 0.83, 0.80-0.87). Non-AD pathology significantly improved precision of differentiation across all age groups (p < 0.004).

CONCLUSION

Clinical AD diagnosis was more weakly associated with neurofibrillary tangles among the oldest old compared to younger age groups, possibly due to less accurate clinical diagnosis, better neurocompensation, or unaccounted pathology among the oldest old.

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.

Synaptic loss in the inferior temporal gyrus in mild cognitive impairment and Alzheimer's disease

Alzheimer's disease (AD) is a slowly progressing form of dementia characterized in its earliest stages as a loss of memory. Individuals with amnestic mild cognitive impairment (aMCI) may be in the earliest stages of the disease and represent an opportunity to identify pathological changes related to the progression of AD. Synaptic loss is one of the hallmarks of AD and associated with cognitive impairment. The inferior temporal gyrus plays an important role in verbal fluency, a cognitive function affected early in the onset of AD. Unbiased stereology coupled with electron microscopy was used to quantify total synaptic numbers in lamina 3 of the inferior temporal gyrus from short postmortem autopsy tissue harvested from subjects who died at different cognitive stages during the progression of AD. Individuals with aMCI had significantly fewer synapses (36%) compared to individuals with no cognitive impairment. Individuals with AD showed a loss of synapses very similar to the aMCI cohort. Synaptic numbers correlated highly with Mini Mental State Examination scores and a test of category verbal fluency. These results demonstrate that the inferior temporal gyrus is affected during the prodromal stage of the disease and may underlie some of the early AD-related clinical dysfunctions.

Epigenetic silencing of nucleolar rRNA genes in Alzheimer's disease

Background

Ribosomal deficits are documented in mild cognitive impairment (MCI), which often represents an early stage Alzheimer's disease (AD), as well as in advanced AD. The nucleolar rRNA genes (rDNA), transcription of which is critical for ribosomal biogenesis, are regulated by epigenetic silencing including promoter CpG methylation.

Methodology/Principal Findings

To assess whether CpG methylation of the rDNA promoter was dysregulated across the AD spectrum, we analyzed brain samples from 10 MCI-, 23 AD-, and, 24 age-matched control individuals using bisulfite mapping. The rDNA promoter became hypermethylated in cerebro-cortical samples from MCI and AD groups. In parietal cortex, the rDNA promoter was hypermethylated more in MCI than in advanced AD. The cytosine methylation of total genomic DNA was similar in AD, MCI, and control samples. Consistent with a notion that hypermethylation-mediated silencing of the nucleolar chromatin stabilizes rDNA loci, preventing their senescence-associated loss, genomic rDNA content was elevated in cerebrocortical samples from MCI and AD groups.

Conclusions/Significance

In conclusion, rDNA hypermethylation could be a new epigenetic marker of AD. Moreover, silencing of nucleolar chromatin may occur during early stages of AD pathology and play a role in AD-related ribosomal deficits and, ultimately, dementia.

Hippocampal sclerosis in advanced age: clinical and pathological features

Hippocampal sclerosis is a relatively common neuropathological finding (∼10% of individuals over the age of 85 years) characterized by cell loss and gliosis in the hippocampus that is not explained by Alzheimer's disease. Hippocampal sclerosis pathology can be associated with different underlying causes, and we refer to hippocampal sclerosis in the aged brain as hippocampal sclerosis associated with ageing. Much remains unknown about hippocampal sclerosis associated with ageing. We combined three different large autopsy cohorts: University of Kentucky Alzheimer's Disease Centre, the Nun Study and the Georgia Centenarian Study to obtain a pool of 1110 patients, all of whom were evaluated neuropathologically at the University of Kentucky. We focused on the subset of cases with neuropathology-confirmed hippocampal sclerosis (n=106). For individuals aged≥95 years at death (n=179 in our sample), each year of life beyond the age of 95 years correlated with increased prevalence of hippocampal sclerosis pathology and decreased prevalence of 'definite' Alzheimer's disease pathology. Aberrant TAR DNA protein 43 immunohistochemistry was seen in 89.9% of hippocampal sclerosis positive patients compared with 9.7% of hippocampal sclerosis negative patients. TAR DNA protein 43 immunohistochemistry can be used to demonstrate that the disease is usually bilateral even when hippocampal sclerosis pathology is not obvious by haematoxylin and eosin stains. TAR DNA protein 43 immunohistochemistry was negative on brain sections from younger individuals (n=10) after hippocampectomy due to seizures, who had pathologically confirmed hippocampal sclerosis. There was no association between cases with hippocampal sclerosis associated with ageing and apolipoprotein E genotype. Age of death and clinical features of hippocampal sclerosis associated with ageing (with or without aberrant TAR DNA protein 43) were distinct from previously published cases of frontotemporal lobar degeneration TAR DNA protein 43. To help sharpen our ability to discriminate patients with hippocampal sclerosis associated with ageing clinically, the longitudinal cognitive profile of 43 patients with hippocampal sclerosis associated with ageing was compared with the profiles of 75 controls matched for age, gender, education level and apolipoprotein E genotype. These individuals were followed from intake assessment, with 8.2 (average) longitudinal cognitive assessments. A neuropsychological profile with relatively high-verbal fluency but low word list recall distinguished the hippocampal sclerosis associated with ageing group at intake (P<0.015) and also 5.5-6.5 years before death (P<0.005). This may provide a first step in clinical differentiation of hippocampal sclerosis associated with ageing versus pure Alzheimer's disease in their earliest stages. In summary, in the largest series of autopsy-verified patients with hippocampal sclerosis to date, we characterized the clinical and pathological features associated with hippocampal sclerosis associated with ageing.

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.

Preclinical AD Workgroup staging: pathological correlates and potential challenges

The National Institute on Aging Preclinical Alzheimer's disease Workgroup (PADW) has issued a preliminary report with recommendations for classifying preclinical Alzheimer's disease (pAD) according to 3 early disease stages. Here we examine the PADW recommendations in relation to neuropathological features in a large, consecutive series of cognitively intact elderly persons, autopsied within a year after cognitive testing (n = 126 cognitively intact patients with mean age 83.7 years at death). Subjects were grouped based on a hypothetical construct correlating pathological features with PADW stages. Many cognitively intact individuals were classifiable as pAD (53/126 or 43%), as expected based on epidemiological and biomarker studies. Of these, most (48%) were in "stage 3", which corresponds to amyloid pathology with early neurodegeneration. As with prior studies, our data indicate that the development of neocortical neurofibrillary tangles is the key pathological event that is not observed in pAD cases: Braak stages III or IV pathology are hence not truly a substrate for "intermediate likelihood" that cognitive impairment is due to Alzheimer's disease (AD). We also stress the importance of comorbid non-Alzheimer's disease brain pathologies (hippocampal sclerosis, neocortical alpha-synucleinopathy, cerebrovascular disease, and brains with hippocampal neurofibrillary tangles but no cortical amyloid plaques) that can contribute to the development of cognitive impairment, or which may serve as confounds in the application of the PADW recommendations. While the final recommendations from the PADW working group have not yet been released, this preliminary analysis provides a perspective on those recommendations from a neuropathological point of view.

Modeling the dementia epidemic

The incidence of dementia increases steeply with age in older people, although from the tenth decade the slope may be smoother, perhaps reflecting different pathological processes in the oldest old. The prevalence depends upon interaction of age with other factors (e.g., comorbidities, genetic or environmental factors) that in turn are subject to change. If onset of dementia could be postponed by modulating its risk factors, this could significantly affect its incidence. Analysis of risk and protection factors should take into account the critical period during which these factors play a role. For example, the impact of education and diabetes mellitus occurs in early- and midlife, respectively, while maintaining optimal physical and mental activity and controlling vascular factors later in life may slow the rate of cognitive decline. Modifying factors need to be evaluated for different clinical groups, taking into account genetic background, age, and duration at exposure. The aim of the present article is to try to take stock of epidemiological data concerning factors affecting the prevalence of dementia and predict future developments, as well as to look for possible interventions that could affect outcome.

Patterns of microRNA expression in normal and early Alzheimer's disease human temporal cortex: white matter versus gray matter

MicroRNA (miRNA) expression was assessed in human cerebral cortical gray matter (GM) and white matter (WM) in order to provide the first insights into the difference between GM and WM miRNA repertoires across a range of Alzheimer's disease (AD) pathology. RNA was isolated separately from GM and WM portions of superior and middle temporal cerebral cortex (N = 10 elderly females, postmortem interval < 4 h). miRNA profiling experiments were performed using state-of-the-art Exiqon(©) LNA-microarrays. A subset of miRNAs that appeared to be strongly expressed according to the microarrays did not appear to be conventional miRNAs according to Northern blot analyses. Some well-characterized miRNAs were substantially enriched in WM as expected. However, most of the miRNA expression variability that correlated with the presence of early AD-related pathology was seen in GM. We confirm that downregulation of a set of miRNAs in GM (including several miR-15/107 genes and miR-29 paralogs) correlated strongly with the density of diffuse amyloid plaques detected in adjacent tissue. A few miRNAs were differentially expressed in WM, including miR-212 that is downregulated in AD and miR-424 which is upregulated in AD. The expression of certain miRNAs correlates with other miRNAs across different cases, and particular subsets of miRNAs are coordinately expressed in relation to AD-related pathology. These data support the hypothesis that patterns of miRNA expression in cortical GM may contribute to AD pathogenetically, because the aggregate change in miRNA expression observed early in the disease would be predicted to cause profound changes in gene expression.

Proteolysis of calcineurin is increased in human hippocampus during mild cognitive impairment and is stimulated by oligomeric Abeta in primary cell culture

Recent reports demonstrate that the activation and interaction of the protease calpain (CP) and the protein phosphatase calcineurin (CN) are elevated in the late stages of Alzheimer's disease (AD). However, the extent to which CPs and CN interact during earlier stages of disease progression remains unknown. Here, we investigated CP and CN protein levels in cytosolic, nuclear, and membrane fractions prepared from human postmortem hippocampal tissue from aged non-demented subjects, and subjects diagnosed with mild cognitive impairment (MCI). The results revealed a parallel increase in CP I and the 48 kDa CN-Aα (ΔCN-Aα48) proteolytic fragment in cytosolic fractions during MCI. In primary rat hippocampal cultures, CP-dependent proteolysis and activation of CN was stimulated by application of oligomeric Aβ((1-42)) peptides. Deleterious effects of Aβ on neuronal morphology were reduced by blockade of either CP or CN. NMDA-type glutamate receptors, which help regulate cognition and neuronal viability, and are modulated by CPs and CN, were also investigated in human hippocampus. Relative to controls, MCI subjects showed significantly greater proteolytic levels of the NR2B subunit. Within subjects, the extent of NR2B proteolysis was strongly correlated with the generation of ΔCN-Aα48 in the cytosol. A similar proteolytic pattern for NR2B was also observed in primary rat hippocampal cultures treated with oligomeric Aβ and prevented by inhibition of CP or CN. Together, the results demonstrate that the activation and interaction of CPs and CN are increased early in cognitive decline associated with AD and may help drive other pathologic processes during disease progression.

Immunotherapy for Alzheimer's disease

In the year 1999, a vaccine approach was found to reduce amyloid deposits in transgenic mice overproducing the amyloid precursor protein. This was followed closely by demonstrations that vaccines or passive immunotherapy could rescue memory deficits in these mice. Initial human clinical trials revealed apparent autoimmune reactions in a subset of patients, but also some cases of cognitive benefit and amyloid clearance. Further work with passive immunotherapy in mouse models confirmed exceptional clearing abilities of anti-amyloid antibodies even in older mice. However, in parallel with parenchymal amyloid clearance was the appearance of microhaemorrhages and increased vascular amyloid deposition. Additional clinical trials with passive immunotherapy confirmed occasional appearance of microhaemorrhage and occurrence of vasogenic oedema in some patients, particularly those with the apolipoprotein E4 genotype. Recent data with positron emission tomography demonstrates trial participants passively immunized with anti-Aß antibodies have reduced signals with amyloid binding ligands after 18 months of therapy. Several anti-Aß immunotherapies have reached phase 3 testing, and immunotherapy is likely to be the first test of the amyloid hypothesis of Alzheimer's disease. Identifying antibody variants that retain amyloid clearance with fewer adverse reactions remains a major focus of translational research in this area.

Oxidative modification to LDL receptor-related protein 1 in hippocampus from subjects with Alzheimer disease: implications for Aβ accumulation in AD brain

Alzheimer disease (AD) is a neurodegenerative disorder characterized histopathologically by the presence of senile plaques (SPs), neurofibrillary tangles, and synapse loss. The main component of SPs is amyloid-β peptide (Aβ), which has been associated with increased oxidative stress, leading to oxidative modification of proteins and consequently to neurotoxicity and neurodegeneration. Low-density lipoprotein receptor-related protein 1 (LRP1) is the primary moiety responsible for the efflux of Aβ from the brain to the blood across the blood-brain barrier. Impaired brain-to-blood transport of Aβ by LRP1 has been hypothesized to contribute to increased levels of Aβ in AD brain. The cause of LRP1 dysfunction is unknown, but we have hypothesized that Aβ oxidizes LRP1, thus damaging its own transporter. Consistent with this notion, we report in this study a significant increase in the levels of the lipid peroxidation product 4-hydroxy-2-nonenal bound to transmembrane LRP1 in AD hippocampus. In contrast, the levels of LRP1-resident 3-nitrotyrosine did not show a significant increase in AD hippocampus compared to age-matched controls. Based on this study, we propose that Aβ impairs its own efflux from the brain by oxidation of its transporter LRP1, leading to increased Aβ deposition in brain, thereby contributing to subsequent cognitive impairment in AD.

MiR-107 is reduced in Alzheimer's disease brain neocortex: validation study

MiR-107 is a microRNA (miRNA) that we reported previously to have decreased expression in the temporal cortical gray matter early in the progression of Alzheimer's disease (AD). Here we study a new group of well-characterized human temporal cortex samples (N=19). MiR-107 expression was assessed, normalized to miR-124 and let-7a. Correlation was observed between decreased miR-107 expression and increased neuritic plaque counts (P< 0.05) and neurofibrillary tangle counts (P< 0.02) in adjacent brain tissue. Adjusted miR-107 and BACE1 mRNA levels tended to correlate negatively (trend with regression P< 0.07). In sum, miR-107 expression tends to be lower relative to other miRNAs as AD progresses.

Conceptual evolution in Alzheimer's disease: implications for understanding the clinical phenotype of progressive neurodegenerative disease

Over the past several decades, our understanding of Alzheimer's disease (AD) has seen an evolution from the dichotomous concept of normal versus AD in the dementia state to a more accurate and complete appreciation of AD as a progressive disorder with clinical, biological, and pathological features occurring along a continuum from normal to end-stage disease. Integrating our understanding of the relationships and interplay between the clinical, biological, and pathological features of AD may allow the identification of AD at even preclinical, completely asymptomatic stages of the disease. This review attempts to summarize the clinical stages of AD in terms of epidemiology, historical evolution of disease stage diagnoses, cognitive/neuropsychologic features, psychiatric/behavioral manifestations, and functional decline in the context of our developing understanding of the biological processes responsible for the pathogenesis of AD described in detail in the accompanying articles.

The neuropathology of older persons with and without dementia from community versus clinic cohorts

Community-based cohorts of older persons may differ neuropathologically from clinic-based cohorts. This study investigated age-related pathologies in persons with and without dementia and included autopsied participants from two community-based cohorts, the Rush Religious Orders Study (n=386) and the Memory and Aging Project (n=195), and one clinic-based cohort, the Clinical Core of the Rush Alzheimer's Disease Center (n=392). Final clinical diagnoses included no cognitive impairment (n=202), mild cognitive impairment (MCI) (n=150), probable Alzheimer's disease (AD) (n=474), possible AD (n=88), and other dementias (n=59). Postmortem diagnoses included pathologic AD, cerebral infarcts, and Lewy body disease. Community-based persons with clinical AD had less severe AD pathology (p<0.001) and had more cerebral infarcts (p<0.001) compared to clinic-based persons. Additionally, community-based persons with MCI had more infarcts compared to clinic-based persons. Overall, there was a higher proportion of Lewy bodies and atypical pathologies in the clinic-based compared to the community-based cohorts (p<0.001). Community-based persons with probable AD show less severe AD pathology and more often have infarcts and mixed pathologies; those with MCI more often have infarcts and mixed pathologies. Overall, clinic-based persons have more Lewy bodies and atypical pathologies. The spectrum of pathologies underlying cognitive impairment in clinic-based cohorts differs from community-based cohorts.

Association between male gender and cortical Lewy body pathology in large autopsy series

Sex-linked factors may alter risk for neurodegenerative diseases. Definitive diagnoses are not established until autopsy, so neuropathological studies are critical. There have not been reported gender-related differences in neocortical Lewy bodies (LBs) using large multi-center autopsy series. We evaluated the associations between gender and pathologically characterized neurodegenerative diseases. Cases with Alzheimer's disease (AD), neocortical LBs, AD + neocortical LBs, or neither pathology were evaluated as separate groups. Results were corrected for possible confounders including age at death, smoking history, and education. The settings were the University of Kentucky Alzheimer's Disease Center and the National Alzheimer's Coordinating Center (NACC) Registry autopsy series; 3,830 subjects met inclusion criteria. Patients with neocortical ("diffuse") or intermediate ("limbic") LB pathologies tended to be male (male:female odds ratios ~2.9 with 95% CI 2.02-4.18). The preponderance of males dying with neocortical LB pathology was seen consistently across age groups and was not due to the potential confounders evaluated. By contrast, individuals dying with AD pathology were more likely to be female if dying over 80 (male:female odds ratio 0.66, 95% CI 0.50-0.88), but that tendency was not seen in individuals dying with AD pathology prior to age 80. Increased understanding of the male predominance in neocortical LB pathology may help guide clinicians, because males are more likely to be "undercalled" for neocortical LBs clinically, and females are more likely to be "overcalled" (P < 0.05 for both). Males are far more likely than females to die with neocortical LB pathology. This phenomenon may help guide medical practice including clinical trial study design.