Striatal amyloid plaque density predicts Braak neurofibrillary stage and clinicopathological Alzheimer's disease: implications for amyloid imaging

Molecular neuroimaging in dominantly inherited versus sporadic early-onset Alzheimer's disease

Approximately 5% of Alzheimer's disease patients develop symptoms before age 65 (early-onset Alzheimer's disease), with either sporadic (sporadic early-onset Alzheimer's disease) or dominantly inherited (dominantly inherited Alzheimer's disease) presentations. Both sporadic early-onset Alzheimer's disease and dominantly inherited Alzheimer's disease are characterized by brain amyloid-β accumulation, tau tangles, hypometabolism and neurodegeneration, but differences in topography and magnitude of these pathological changes are not fully elucidated. In this study, we directly compared patterns of amyloid-β plaque deposition and glucose hypometabolism in sporadic early-onset Alzheimer's disease and dominantly inherited Alzheimer's disease individuals. Our analysis included 134 symptomatic sporadic early-onset Alzheimer's disease amyloid-Positron Emission Tomography (PET)-positive cases from the University of California, San Francisco, Alzheimer's Disease Research Center (mean ± SD age 59.7 ± 5.6 years), 89 symptomatic dominantly inherited Alzheimer's disease cases (age 45.8 ± 9.3 years) and 102 cognitively unimpaired non-mutation carriers from the Dominantly Inherited Alzheimer Network study (age 44.9 ± 9.2). Each group underwent clinical and cognitive examinations, 11C-labelled Pittsburgh Compound B-PET and structural MRI. 18F-Fluorodeoxyglucose-PET was also available for most participants. Positron Emission Tomography scans from both studies were uniformly processed to obtain a standardized uptake value ratio (PIB50-70 cerebellar grey reference and FDG30-60 pons reference) images. Statistical analyses included pairwise global and voxelwise group comparisons and group-independent component analyses. Analyses were performed also adjusting for covariates including age, sex, Mini-Mental State Examination, apolipoprotein ε4 status and average composite cortical of standardized uptake value ratio. Compared with dominantly inherited Alzheimer's disease, sporadic early-onset Alzheimer's disease participants were older at age of onset (mean ± SD, 54.8 ± 8.2 versus 41.9 ± 8.2, Cohen's d = 1.91), with more years of education (16.4 ± 2.8 versus 13.5 ± 3.2, d = 1) and more likely to be apolipoprotein ε4 carriers (54.6% ε4 versus 28.1%, Cramer's V = 0.26), but similar Mini-Mental State Examination (20.6 ± 6.1 versus 21.2 ± 7.4, d = 0.08). Sporadic early-onset Alzheimer's disease had higher global cortical Pittsburgh Compound B-PET binding (mean ± SD standardized uptake value ratio, 1.92 ± 0.29 versus 1.58 ± 0.44, d = 0.96) and greater global cortical 18F-fluorodeoxyglucose-PET hypometabolism (mean ± SD standardized uptake value ratio, 1.32 ± 0.1 versus 1.39 ± 0.19, d = 0.48) compared with dominantly inherited Alzheimer's disease. Fully adjusted comparisons demonstrated relatively higher Pittsburgh Compound B-PET standardized uptake value ratio in the medial occipital, thalami, basal ganglia and medial/dorsal frontal regions in dominantly inherited Alzheimer's disease versus sporadic early-onset Alzheimer's disease. Sporadic early-onset Alzheimer's disease showed relatively greater 18F-fluorodeoxyglucose-PET hypometabolism in Alzheimer's disease signature temporoparietal regions and caudate nuclei, whereas dominantly inherited Alzheimer's disease showed relatively greater hypometabolism in frontal white matter and pericentral regions. Independent component analyses largely replicated these findings by highlighting common and unique Pittsburgh Compound B-PET and 18F-fluorodeoxyglucose-PET binding patterns. In summary, our findings suggest both common and distinct patterns of amyloid and glucose hypometabolism in sporadic and dominantly inherited early-onset Alzheimer's disease.

Parkinson's Disease Dementia Patients: Expression of Glia Maturation Factor in the Brain

Parkinson's disease (PD) is the second most common progressive neurodegenerative disease characterized by the presence of dopaminergic neuronal loss and motor disorders. PD dementia (PDD) is a cognitive disorder that affects many PD patients. We have previously demonstrated the proinflammatory role of the glia maturation factor (GMF) in neuroinflammation and neurodegeneration in AD, PD, traumatic brain injury (TBI), and experimental autoimmune encephalomyelitis (EAE) in human brains and animal models. The purpose of this study was to investigate the expression of the GMF in the human PDD brain. We analyzed the expression pattern of the GMF protein in conjunction with amyloid plaques (APs) and neurofibrillary tangles (NFTs) in the substantia nigra (SN) and striatum of PDD brains using immunostaining. We detected a large number of GMF-positive glial fibrillary acidic protein (GFAP) reactive astrocytes, especially abundant in areas with degenerating dopaminergic neurons within the SN and striatum in PDD. Additionally, we observed excess levels of GMF in glial cells in the vicinity of APs, and NFTs in the SN and striatum of PDD and non-PDD patients. We found that the majority of GMF-positive immunoreactive glial cells were co-localized with GFAP-reactive astrocytes. Our findings suggest that the GMF may be involved in the pathogenesis of PDD.

Longitudinal clinical, cognitive and biomarker profiles in dominantly inherited versus sporadic early-onset Alzheimer's disease

Approximately 5% of Alzheimer's disease cases have an early age at onset (<65 years), with 5-10% of these cases attributed to dominantly inherited mutations and the remainder considered as sporadic. The extent to which dominantly inherited and sporadic early-onset Alzheimer's disease overlap is unknown. In this study, we explored the clinical, cognitive and biomarker profiles of early-onset Alzheimer's disease, focusing on commonalities and distinctions between dominantly inherited and sporadic cases. Our analysis included 117 participants with dominantly inherited Alzheimer's disease enrolled in the Dominantly Inherited Alzheimer Network and 118 individuals with sporadic early-onset Alzheimer's disease enrolled at the University of California San Francisco Alzheimer's Disease Research Center. Baseline differences in clinical and biomarker profiles between both groups were compared using t-tests. Differences in the rates of decline were compared using linear mixed-effects models. Individuals with dominantly inherited Alzheimer's disease exhibited an earlier age-at-symptom onset compared with the sporadic group [43.4 (SD ± 8.5) years versus 54.8 (SD ± 5.0) years, respectively, P < 0.001]. Sporadic cases showed a higher frequency of atypical clinical presentations relative to dominantly inherited (56.8% versus 8.5%, respectively) and a higher frequency of APOE-ε4 (50.0% versus 28.2%, P = 0.001). Compared with sporadic early onset, motor manifestations were higher in the dominantly inherited cohort [32.5% versus 16.9% at baseline (P = 0.006) and 46.1% versus 25.4% at last visit (P = 0.001)]. At baseline, the sporadic early-onset group performed worse on category fluency (P < 0.001), Trail Making Test Part B (P < 0.001) and digit span (P < 0.001). Longitudinally, both groups demonstrated similar rates of cognitive and functional decline in the early stages. After 10 years from symptom onset, dominantly inherited participants experienced a greater decline as measured by Clinical Dementia Rating Sum of Boxes [3.63 versus 1.82 points (P = 0.035)]. CSF amyloid beta-42 levels were comparable [244 (SD ± 39.3) pg/ml dominantly inherited versus 296 (SD ± 24.8) pg/ml sporadic early onset, P = 0.06]. CSF phosphorylated tau at threonine 181 levels were higher in the dominantly inherited Alzheimer's disease cohort (87.3 versus 59.7 pg/ml, P = 0.005), but no significant differences were found for t-tau levels (P = 0.35). In summary, sporadic and inherited Alzheimer's disease differed in baseline profiles; sporadic early onset is best distinguished from dominantly inherited by later age at onset, high frequency of atypical clinical presentations and worse executive performance at baseline. Despite these differences, shared pathways in longitudinal clinical decline and CSF biomarkers suggest potential common therapeutic targets for both populations, offering valuable insights for future research and clinical trial design.

TREM2 gene expression associations with Alzheimer's disease neuropathology are region-specific: implications for cortical versus subcortical microglia

Previous post-mortem assessments of TREM2 expression and its association with brain pathologies have been limited by sample size. This study sought to correlate region-specific TREM2 mRNA expression with diverse neuropathological measures at autopsy using a large sample size (N = 945) of bulk RNA sequencing data from the Religious Orders Study and Rush Memory and Aging Project (ROS/MAP). TREM2 gene expression of the dorsolateral prefrontal cortex, posterior cingulate cortex, and caudate nucleus was assessed with respect to core pathology of Alzheimer's disease (amyloid-β, and tau), cerebrovascular pathology (cerebral infarcts, arteriolosclerosis, atherosclerosis, and cerebral amyloid angiopathy), microglial activation (proportion of activated microglia), and cognitive performance. We found that cortical TREM2 levels were positively related to AD diagnosis, cognitive decline, and amyloid-β neuropathology but were not related to the proportion of activated microglia. In contrast, caudate TREM2 levels were not related to AD pathology, cognition, or diagnosis, but were positively related to the proportion of activated microglia in the same region. Diagnosis-stratified results revealed caudate TREM2 levels were inversely related to AD neuropathology and positively related to microglial activation and longitudinal cognitive performance in AD cases. These results highlight the notable changes in TREM2 transcript abundance in AD and suggest that its pathological associations are brain-region-dependent.

Human striatal glia differentially contribute to AD- and PD-specific neurodegeneration

The commonalities and differences in cell-type-specific pathways that lead to Alzheimer disease (AD) and Parkinson disease (PD) remain unknown. Here, we performed a single-nucleus transcriptome comparison of control, AD and PD striata. We describe three astrocyte subpopulations shared across different brain regions and evolutionarily conserved between humans and mice. We reveal common features between AD and PD astrocytes and regional differences that contribute toward amyloid pathology and neurodegeneration. In contrast, we found that transcriptomic changes in microglia are largely unique to each disorder. Our analysis identified a population of activated microglia that shared molecular signatures with murine disease-associated microglia (DAM) as well as disease-associated and regional differences in microglia transcriptomic changes linking microglia to disease-specific amyloid pathology, tauopathy and neuronal death. Finally, we delineate undescribed subpopulations of medium spiny neurons (MSNs) in the striatum and provide neuronal transcriptomic profiles suggesting disease-specific changes and selective neuronal vulnerability.

Cognitive Trajectories and Associated Biomarkers in Patients with Mild Cognitive Impairment

BACKGROUND

To diagnose mild cognitive impairment (MCI) patients at risk of progression to dementia is clinically important but challenging.

OBJECTIVE

We classified MCI patients based on cognitive trajectories and compared biomarkers among groups.

METHODS

This study analyzed amnestic MCI patients with at least three Clinical Dementia Rating (CDR) scores available over a minimum of 36 months from the Alzheimer's Disease Neuroimaging Initiative database. Patients were classified based on their progression using trajectory modeling with the CDR-sum of box scores. We compared clinical and neuroimaging biomarkers across groups.

RESULTS

Of 569 eligible MCI patients (age 72.7±7.4 years, women n = 223), three trajectory groups were identified: stable (58.2%), slow decliners (24.6%), and fast decliners (17.2%). In the fifth year after diagnosis, the CDR-sum of box scores increased by 1.2, 5.4, and 11.8 points for the stable, slow, and fast decliners, respectively. Biomarkers associated with cognitive decline were amyloid-β 42, total tau, and phosphorylated tau protein in cerebrospinal fluid, hippocampal volume, cortical metabolism, and amount of cortical and subcortical amyloid deposits. Cortical metabolism and the amount of amyloid deposits were associated with the rate of cognitive decline.

CONCLUSION

Data-driven trajectory analysis provides new insights into the various cognitive trajectories of MCI. Baseline brain metabolism, and the amount of cortical and subcortical amyloid burden can provide additional information on the rate of cognitive decline.

Effects of Striatal Amyloidosis on the Dopaminergic System and Behavior: A Comparative Study in Male and Female 5XFAD Mice

BACKGROUND

Nearly two-thirds of patients diagnosed with Alzheimer's disease (AD) are female. In addition, female patients with AD have more significant cognitive impairment than males at the same disease stage. This disparity suggests there are sex differences in AD progression. While females appear to be more affected by AD, most published behavioral studies utilize male mice. In humans, there is an association between antecedent attention-deficit/hyperactivity disorder and increased risk of dementia. Functional connectivity studies indicate that dysfunctional cortico-striatal networks contribute to hyperactivity in attention deficit hyperactivity disorder. Higher plaque density in the striatum accurately predicts the presence of clinical AD pathology. In addition, there is a link between AD-related memory dysfunction and dysfunctional dopamine signaling.

OBJECTIVE

With the need to consider sex as a biological variable, we investigated the influence of sex on striatal plaque burden, dopaminergic signaling, and behavior in prodromal 5XFAD mice.

METHODS

Six-month-old male and female 5XFAD and C57BL/6J mice were evaluated for striatal amyloid plaque burden, locomotive behavior, and changes in dopaminergic machinery in the striatum.

RESULTS

5XFAD female mice had a higher striatal amyloid plaque burden than male 5XFAD mice. 5XFAD females, but not males, were hyperactive. Hyperactivity in female 5XFAD mice was associated with increased striatal plaque burden and changes in dopamine signaling in the dorsal striatum.

CONCLUSION

Our results indicate that the progression of amyloidosis involves the striatum in females to a greater extent than in males. These studies have significant implications for using male-only cohorts in the study of AD progression.

The significance of glycolysis index and its correlations with immune infiltrates in Alzheimer’s disease

Alzheimer’s disease (AD) is a common neurodegenerative disorder without an effective treatment, and results in an increasingly serious health problem. However, its pathogenesis is complex and poorly understood. Nonetheless, the exact role of dysfunctional glucose metabolism in AD pathogenesis remains unclear. We screened 28 core glycolysis-related genes and introduced a novel metric, the glycolysis index, to estimate the activation of glycolysis. The glycolysis index was significantly lower in the AD group in four different brain regions (frontal cortex, FC; temporal cortex, TC; hippocampus, HP; and entorhinal cortex, EC) than that in the control group. Combined with differential expression and over-representation analyses, we determined the clinical and pathological relevance of glycolysis in AD. Subsequently, we investigated the role of glycolysis in the AD brain microenvironment. We developed a glycolysis-brain cell marker connection network, which revealed a close relationship between glycolysis and seven brain cell types, most of which presented abundant variants in AD. Using immunohistochemistry, we detected greater infiltrated microglia and higher expression of glycolysis-related microglia markers in the APP/PS1 AD model than that in the control group, consistent with our bioinformatic analysis results. Furthermore, the excellent predictive value of the glycolysis index has been verified in different populations. Overall, our present findings revealed the clinical and biological significance of glycolysis and the brain microenvironment in AD.

Brain 18 F-Florbetapir PET/CT Findings in an Early-onset Alzheimer Disease Patient Carrying Presenilin-1 G378E Mutation

Positron emission tomography (PET) with 18 F-Fluorodeoxyglucose ( 18 F-FDG) plays an outstanding role in the diagnostic work-up of dementia. Amyloid PET imaging is a complementary imaging technique for the early detection of Alzheimer disease (AD). β-amyloid precursor protein ( APP ), Presenilin-1 ( PSEN1 ) and Presenilin-2 ( PSEN2 ) are the 3 main causative genes responsible for autosomal dominant early-onset Alzheimer disease (EOAD). This is the first report of 18 F-Florbetapir amyloid imaging findings in a 35-year-old male patient with EOAD carrying the G378E mutation in PSEN1 gene. Brain computed tomography (CT) and magnetic resonance imaging scans showed remarkable cerebral atrophy with dilatation of the cerebrospinal fluid spaces; furthermore, a 18 F-Florbetapir PET/CT scan demonstrated also widespread remarkable accumulation of the amyloid tracer in the cerebral cortex, with reduction of the normal contrast between white and gray matter and flattening of the external cortical margins. Furthermore, PET/CT showed intense 18 F-florbetapir uptake in the striatum and in the thalamus bilaterally. Our case supports the usefulness of amyloid PET imaging in the diagnostic work-up of EOAD.

Localization of Thioredoxin-Interacting Protein in Aging and Alzheimer's Disease Brains

Thioredoxin-Interacting Protein (TXNIP) has been shown to have significant pathogenic roles in many human diseases, particularly those associated with diabetes and hyperglycemia. Its main mode of action is to sequester thioredoxins, resulting in enhanced oxidative stress. The aim of this study was to identify if cellular expression of TXNIP in human aged and Alzheimer's disease (AD) brains correlated with pathological structures. This study employed fixed tissue sections and protein extracts of temporal cortex from AD and aged control brains. Studies employed light and fluorescent immunohistochemical techniques using the monoclonal antibody JY2 to TXNIP to identify cellular structures. Immunoblots were used to quantify relative amounts of TXNIP in brain protein extracts. The major finding was the identification of TXNIP immunoreactivity in selective neuronal populations and structures, particularly in non-AD brains. In AD brains, less neuronal TXNIP but increased numbers of TXNIP-positive plaque-associated microglia were observed. Immunoblot analyses showed no significant increase in levels of TXNIP protein in the AD samples tested. In conclusion, this study identified altered patterns of expression of TXNIP in human brains with progression of AD pathology.

A History of Senile Plaques: From Alzheimer to Amyloid Imaging

Senile plaques have been studied in postmortem brains for more than 120 years and the resultant knowledge has not only helped us understand the etiology and pathogenesis of Alzheimer disease (AD), but has also pointed to possible modes of prevention and treatment. Within the last 15 years, it has become possible to image plaques in living subjects. This is arguably the single greatest advance in AD research since the identification of the Aβ peptide as the major plaque constituent. The limitations and potentialities of amyloid imaging are still not completely clear but are perhaps best glimpsed through the perspective gained from the accumulated postmortem histological studies. The basic morphological classification of plaques into neuritic, cored and diffuse has been supplemented by sophisticated immunohistochemical and biochemical analyses and increasingly detailed mapping of plaque brain distribution. Changes in plaque classification and staging have in turn contributed to changes in the definition and diagnostic criteria for AD. All of this information continues to be tested by clinicopathological correlations and it is through the insights thereby gained that we will best be able to employ the powerful tool of amyloid imaging.

Distinctive Temporal Trajectories of Alzheimer’s Disease Biomarkers According to Sex and APOE Genotype: Importance of Striatal Amyloid

Purpose

Previously, sex and apolipoprotein E (APOE) genotype had distinct effects on the cognitive trajectory across the Alzheimer’s disease (AD) continuum. We therefore aimed to investigate whether these trajectory curves including β-amyloid (Aβ) accumulation in the cortex and striatum, and tau accumulation would differ according to sex and APOE genotype.

Methods

We obtained 534 subjects for 18F-florbetapir (AV45) PET analysis and 163 subjects for 18F-flortaucipir (AV1451) PET analysis from the Alzheimer’s Disease Neuroimaging Initiative database. For cortical Aβ, striatal Aβ, and tau SUVR, we fitted penalized splines to model the slopes of SUVR value as a non-linear function of baseline SUVR value. By integrating the fitted splines, we obtained the predicted SUVR curves as a function of time.

Results

The time from initial SUVR to the cutoff values were 14.9 years for cortical Aβ, 18.2 years for striatal Aβ, and 22.7 years for tau. Although there was no difference in cortical Aβ accumulation rate between women and men, striatal Aβ accumulation was found to be faster in women than in men, and this temporal difference according to sex was more pronounced in tau accumulation. However, APOE ε4 carriers showed faster progression than non-carriers regardless of kinds of AD biomarkers’ trajectories.

Conclusion

Our temporal trajectory models illustrate that there is a distinct progression pattern of AD biomarkers depending on sex and APOE genotype. In this regard, our models will be able to contribute to designing personalized treatment and prevention strategies for AD in clinical practice.

Recent Updates on PET Imaging in Neurodegenerative Diseases

양전자방출단층촬영(PET)을 이용한 단백질병리의 생체영상기술은 퇴행성 치매의 질병 기전을 이해하는데 필요한 정보를 제공할 뿐 아니라, 질병의 조기 발견과 치료법 개발에서 중요한 역할을 수행하고 있다. 베타아밀로이드와 타우 PET 영상은 인체 뇌병리에 기반한 알츠하이머병 연속체에 대한 진단 바이오마커로 확립되어 조기진단과 감별진단을 용이하게 하고, 질병 예후를 예측하고 있다. 또한, 치매치료제 개발에서 예후 및 대리 바이오마커로의 역할이 커지고 있다. 이 종설에서는 치매를 유발하는 알츠하이머병 및 기타 퇴행성 뇌질환에서 베타아밀로이드와 타우 단백질의 뇌축적을 영상화하는 PET의 최근 임상적 적용과 최근 동향을 살펴보고, 잠재적 유용성을 소개하고자 한다.

Loss of Lysosomal Proteins Progranulin and Prosaposin Associated with Increased Neurofibrillary Tangle Development in Alzheimer Disease

Alzheimer disease (AD) is a progressive neurodegenerative disease causing cognitive decline in the aging population. To develop disease-modifying treatments, understanding the mechanisms behind the pathology is important, which should include observations using human brain samples. We reported previously on the association of lysosomal proteins progranulin (PGRN) and prosaposin (PSAP) with amyloid plaques in non-demented aged control and AD brains. In this study, we investigated the possible involvement of PGRN and PSAP in tangle formation using human brain tissue sections of non-demented aged control subjects and AD cases and compared with cases of frontotemporal dementia with granulin (GRN) mutations. The study revealed that decreased amounts of PGRN and PSAP proteins were detected even in immature neurofibrillary tangles, while colocalization was still evident in adjacent neurons in all cases. Results suggest that neuronal loss of PGRN preceded loss of PSAP as tangles developed and matured. The GRN mutation cases exhibited almost complete absence of PGRN in most neurons, while PSAP signal was preserved. Although based on correlative data, we suggest that reduced levels of PGRN and PSAP and their interaction in neurons might predispose to accumulation of p-Tau protein.

Amyloid Deposition Is Greater in Cerebral Gyri than in Cerebral Sulci with Worsening Clinical Diagnosis Across the Alzheimer's Disease Spectrum

BACKGROUND

Histopathologic studies have demonstrated differential amyloid-β (Aβ) burden between cortical sulci and gyri in Alzheimer's disease (AD), with sulci having a greater Aβ burden.

OBJECTIVE

To characterize Aβ deposition in the sulci and gyri of the cerebral cortex in vivo among subjects with normal cognition (NC), mild cognitive impairment (MCI), and AD, and to evaluate if these differences could improve discrimination between diagnostic groups.

METHODS

T1-weighted 3T MR and florbetapir (amyloid) positron emission tomography (PET) data were obtained from the Alzheimer's Disease Neuroimaging Initiative (ADNI). T1 images were segmented and the cortex was separated into sulci/gyri based on pial surface curvature measurements. T1 images were registered to PET images and regional standardized uptake value ratios (SUVr) were calculated. A linear mixed effects model was used to analyze the relationship between clinical variables and amyloid PET SUVr measurements in the sulci/gyri. Receiver operating characteristic (ROC) analysis was performed to define amyloid positivity. Logistic models were used to evaluate predictive performance of clinical diagnosis using amyloid PET SUVr measurements in sulci/gyri.

RESULTS

719 subjects were included: 272 NC, 315 MCI, and 132 AD. Gyral and sulcal Aβ increased with worsening cognition, however there was a greater increase in gyral Aβ. Females had a greater gyral and sulcal Aβ burden. Focusing on sulcal and gyral Aβ did not improve predictive power for diagnostic groups.

CONCLUSION

While there were significant differences in Aβ deposition in cerebral sulci and gyri across the AD spectrum, these differences did not translate into improved prediction of diagnosis. Females were found to have greater gyral and sulcal Aβ burden.

Head-to-Head Comparison of 18F-Florbetaben and 18F-Flutemetamol in the Cortical and Striatal Regions

BACKGROUND

18F-florbetaben (FBB) and 18F-flutemetamol (FMM) amyloid PET have been developed and approved for clinical use. It is important to understand the distinct features of these ligands to compare and correctly interpret the results of different amyloid PET studies.

OBJECTIVE

We performed a head-to-head comparison of FBB and FMM to compare with regard to imaging characteristics, including dynamic range of retention, and differences in quantitative measurements between the two ligands in cortical, striatal, and white matter (WM) regions.

METHODS

Paired FBB and FMM PET images were acquired in 107 participants. Correlations of FBB and FMM amyloid deposition in the cortex, striatum, and WM were investigated and compared in different reference regions (cerebellar gray matter (CG), whole cerebellum (WC), WC with brainstem (WC + B), and pons).

RESULTS

The cortical SUVR (R2 = 0.97) and striatal SUVR (R2 = 0.95) demonstrated an excellent linear correlation between FBB and FMM using a WC as reference region. There was no difference in the cortical SUVR ratio between the two ligands (p = 0.90), but the striatal SUVR ratio was higher in FMM than in FBB (p < 0.001). Also, the effect size of differences in striatal SUVR seemed to be higher with FMM (2.61) than with FBB (2.34). These trends were similarly observed according to four different reference regions (CG, WC, WC + B, and pons).

CONCLUSION

Our findings suggest that FMM might be better than FBB to detect amyloid burden in the striatum, although both ligands are comparable for imaging AD pathology in vivo.

Cognitive trajectories of patients with focal ß-amyloid deposition

Background

The presence of ß-amyloid (Aß) in the brain can be identified using amyloid PET. In clinical practice, the amyloid PET is interpreted based on dichotomous visual rating, which renders focal Aß accumulation be read as positive for Aß. However, the prognosis of patients with focal Aß deposition is not well established. Thus, we investigated cognitive trajectories of patients with focal Aß deposition.

Methods

We followed up 240 participants (112 cognitively unimpaired [CU], 78 amnestic mild cognitive impairment [aMCI], and 50 Alzheimer’s disease (AD) dementia [ADD]) for 2 years from 9 referral centers in South Korea. Participants were assessed with neuropsychological tests and ¹⁸F-flutemetamol (FMM) positron emission tomography (PET). Ten regions (frontal, precuneus/posterior cingulate (PPC), lateral temporal, parietal, and striatum of each hemisphere) were visually examined in the FMM scan, and participants were divided into three groups: No-FMM, Focal-FMM (FMM uptake in 1–9 regions), and Diffuse-FMM. We used mixed-effects model to investigate the speed of cognitive decline in the Focal-FMM group according to the cognitive level, extent, and location of Aß involvement, in comparison with the No- or Diffuse-FMM group.

Results

Forty-five of 240 (18.8%) individuals were categorized as Focal-FMM. The rate of cognitive decline in the Focal-FMM group was faster than the No-FMM group (especially in the CU and aMCI stage) and slower than the Diffuse-FMM group (in particular in the CU stage). Within the Focal-FMM group, participants with FMM uptake to a larger extent (7–9 regions) showed faster cognitive decline compared to those with uptake to a smaller extent (1–3 or 4–6 regions). The Focal-FMM group was found to have faster cognitive decline in comparison with the No-FMM when there was uptake in the PPC, striatum, and frontal cortex.

Conclusions

When predicting cognitive decline of patients with focal Aß deposition, the patients’ cognitive level, extent, and location of the focal involvement are important.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-021-00787-7.

Association of PET-based stages of amyloid deposition with neuropathological markers of Aβ pathology

OBJECTIVE

To determine if PET-based stages of regional amyloid deposition are associated with neuropathological phases of Aβ pathology.

METHODS

We applied data-driven regional frequency-based and a-priori striatum-based PET staging approaches to ante-mortem 18F-Florbetapir-PET scans of 30 cases from the Alzheimer's Disease Neuroimaging Initiative autopsy cohort, and used Bayesian regression analysis to study the associations of these in vivo amyloid stages with neuropathological Thal phases of regional Aβ plaque distribution and with semi-quantitative ratings of neocortical and striatal plaque densities.

RESULTS

Bayesian regression revealed extreme evidence for an association of both PET-based staging approaches with Thal phases, and these associations were about 44 times more likely for frequency-based stages and 89 times more likely for striatum-based stages than for global cortical 18F-Florbetapir-PET signal. Early (i.e., neocortical-only) PET-based amyloid stages also predicted the absence of striatal/diencephalic cored plaques. Receiver operating characteristics curves revealed highly accurate discrimination between low/high Thal phases and the presence/absence of regional plaques. The median areas under the curve were 0.99 for frequency-based staging (95% credibility interval 0.97-1.00), 0.93 for striatum-based staging (0.83-1.00), and 0.87 for global 18F-Florbetapir-PET signal (0.72-0.98).

INTERPRETATION

Our data indicate that both regional frequency- and striatum-based amyloid-PET staging approaches were superior to standard global amyloid-PET signal for differentiating between low and high degrees of regional amyloid pathology spread. Despite this, we found no evidence for the ability of either staging scheme to differentiate between low and moderate degrees of amyloid pathology which may be particularly relevant for early, preclinical stages of Alzheimer's disease.

Association of Cortical and Subcortical β-Amyloid With Standardized Measures of Depressive and Anxiety Symptoms in Adults Without Dementia

OBJECTIVE

The purpose of this study was to test the hypothesis that subcortical β-amyloid (Aβ) deposition was associated with elevated scores on standardized measures of depressive and anxiety symptoms when compared with cortical (Aβ) deposition in persons without dementia.

METHODS

The authors performed a cross-sectional study, derived from the population-based Mayo Clinic Study of Aging, comprising participants aged ≥70 years (N=1,022; 55% males; 28% apolipoprotein E [APOE] ε4 carriers; without cognitive impairment, N=842; mild cognitive impairment; N=180). To assess Aβ deposition in cortical and subcortical (the amygdala, striatum, and thalamus) regions, participants underwent Pittsburgh Compound B positron emission tomography (PiB-PET) and completed the Beck Depression Inventory-II (BDI-II) and the Beck Anxiety Inventory (BAI). The investigators ran linear regression models to examine the association between PiB-PET standardized uptake value ratios (SUVRs) in the neocortex and subcortical regions and depressive and anxiety symptoms (BDI-II and BAI total scores). Models were adjusted for age, sex, education level, and APOE ε4 carrier status and stratified by cognitive status (without cognitive impairment, mild cognitive impairment).

RESULTS

Cortical PiB-PET SUVRs were associated with depressive symptoms (β=0.57 [SE=0.13], p<0.001) and anxiety symptoms (β=0.34 [SE=0.13], p=0.011). PiB-PET SUVRs in the amygdala were associated only with depressive symptoms (β=0.80 [SE=0.26], p=0.002). PiB-PET SUVRs in the striatum and thalamus were associated with depressive symptoms (striatum: β=0.69 [SE=0.18], p<0.001; thalamus: β=0.61 [SE=0.24], p=0.011) and anxiety symptoms (striatum: β=0.56 [SE=0.18], p=0.002; thalamus: β=0.65 [SE=0.24], p=0.008). In the mild cognitive impairment subsample, Aβ deposition, regardless of neuroanatomic location, was associated with depressive symptoms but not anxiety symptoms.

CONCLUSIONS

Elevated amyloid deposition in cortical and subcortical brain regions was associated with higher depressive and anxiety symptoms, although these findings did not significantly differ by cortical versus subcortical Aβ deposition. This cross-sectional observation needs to be confirmed by a longitudinal study.

Older, non-demented apolipoprotein ε4 carrier males show hyperactivation and structural differences in odor memory regions: a blood-oxygen-level-dependent and structural magnetic resonance imaging study

The current study sought to examine the interaction of sex and Apolipoprotein ε₄ status on olfactory recognition memory within non-demented, older individuals. We separated 39 participants into groups based on ε₄ status and sex. Each participant completed an olfactory memory recognition task during 2 functional magnetic resonance imaging scans and 1 structural scan. The ε₄ carriers had greater functional recruitment of memory regions during false positives relative to ε₄ non-carriers. During hits, the male ε₄ carriers showed greater functional recruitment compared to female ε₄ carriers. The ε₄ carriers had larger bilateral putamen volumes relative to ε₄ non-carriers. Neuroimaging data were significantly associated with Dementia Rating Scale scores solely in males. Results suggest differential olfactory memory processing in relation to sex and ε₄ status. Male ε₄ carriers in particular, demonstrated hyperactivation during recognition memory, which we suspect reflects neuronal compensation to maintain functional performance. Future studies should consider examining underlying mechanisms that contribute to these sex differences within ε₄ carriers.

Patterns of Expression of Purinergic Receptor P2RY12, a Putative Marker for Non-Activated Microglia, in Aged and Alzheimer's Disease Brains

Neuroinflammation is considered a key pathological process in neurodegenerative diseases of aging, including Alzheimer's disease (AD). Many studies have defined phenotypes of reactive microglia, the brain-resident macrophages, with different antigenic markers to identify those potentially causing inflammatory damage. We took an alternative approach with the goal of characterizing the distribution of purinergic receptor P2RY12-positive microglia, a marker previously defined as identifying homeostatic or non-activated microglia. We examined the expression of P2RY12 by dual-color light and fluorescence immunohistochemistry using sections of middle temporal gyrus from AD, high plaque and low plaque non-demented cases in relation to amyloid beta (Aβ) plaques and phosphorylated tau, markers of pathology, and HLA-DR, IBA-1, CD68, and progranulin, microglial phenotype markers. In low plaque cases, P2RY12-positive microglia mostly had non-activated morphologies, while the morphologies of P2RY12-positive microglia in AD brains were highly variable, suggesting its expression could encompass a wider range of phenotypes than originally hypothesized. P2RY12 expression by microglia differed depending on the types of plaques or tangles they were associated with. Areas of inflammation characterized by lack of P2RY12-positive microglia around mature plaques could be observed, but many diffuse plaques showed colocalization with P2RY12-positive microglia. Based on these results, P2RY12 expression by microglia should not be considered solely a marker of resting microglia as P2RY12 immunoreactivity was identifying microglia positive for CD68, progranulin and to a limited extent HLA-DR, markers of activation.

Association of anxiety with subcortical amyloidosis in cognitively normal older adults

Late-life anxiety has been associated with increased progression from normal cognition to amnestic MCI, suggesting that anxiety may be a neuropsychiatric symptom of Alzheimer's disease (AD) pathological changes and a possible marker of anatomical progression in preclinical AD. This study examined whether cortical or subcortical amyloidosis, indicating earlier or later stages of preclinical AD, was associated with greater self-reported anxiety among 118 cognitively normal volunteers, aged 65-90 years, and whether this association was stronger in APOEε4 carriers. Participants underwent Pittsburgh Compound B Positron Emission Tomography (PiB-PET) to assess fibrillar amyloid-β burden in cortical and subcortical regions, and measurement of anxiety using the Hospital Anxiety and Depression Scale-anxiety subscale. Higher PiB-PET measures in the subcortex (striatum, amygdala, and thalamus), but not in the cortex, were associated with greater anxiety, adjusting for demographics, cognition, and depression. Findings were similar using a cortico-striatal staging system and continuous PET measurements. Anxiety was highest in APOEε4 carriers with subcortical amyloidosis. This work supports in vivo staging of amyloid-β deposition in both cortical and subcortical regions as a promising approach to the study of neuropsychiatric symptoms such as anxiety in cognitively normal older individuals. Elevated anxiety symptoms in combination with high-risk biological factors such as APOEε4 and subcortical amyloid-β may identify participants closest to MCI for secondary prevention trials.

Staging and quantification of florbetaben PET images using machine learning: impact of predicted regional cortical tracer uptake and amyloid stage on clinical outcomes

Purpose

We developed a machine learning–based classifier for in vivo amyloid positron emission tomography (PET) staging, quantified cortical uptake of the PET tracer by using a machine learning method, and investigated the impact of these amyloid PET parameters on clinical and structural outcomes.

Methods

A total of 337 ¹⁸F-florbetaben PET scans obtained at Samsung Medical Center were assessed. We defined a feature vector representing the change in PET tracer uptake from grey to white matter. Using support vector machine (SVM) regression and SVM classification, we quantified the cortical uptake as predicted regional cortical tracer uptake (pRCTU) and categorised the scans as positive and negative. Positive scans were further classified into two stages according to the striatal uptake. We compared outcome parameters among stages and further assessed the association between the pRCTU and outcome variables. Finally, we performed path analysis to determine mediation effects between PET variables.

Results

The classification accuracy was 97.3% for cortical amyloid positivity and 91.1% for striatal positivity. The left frontal and precuneus/posterior cingulate regions, as well as the anterior portion of the striatum, were important in determination of stages. The clinical scores and magnetic resonance imaging parameters showed negative associations with PET stage. However, except for the hippocampal volume, most outcomes were associated with the stage through the complete mediation effect of pRCTU.

Conclusion

Using a machine learning algorithm, we achieved high accuracy for in vivo amyloid PET staging. The in vivo amyloid stage was associated with cognitive function and cerebral atrophy mostly through the mediation effect of cortical amyloid.

Electronic supplementary material

The online version of this article (10.1007/s00259-019-04663-3) contains supplementary material, which is available to authorized users.

Characterization of lysosomal proteins Progranulin and Prosaposin and their interactions in Alzheimer's disease and aged brains: increased levels correlate with neuropathology

Progranulin (PGRN) is a protein encoded by the GRN gene with multiple identified functions including as a neurotrophic factor, tumorigenic growth factor, anti-inflammatory cytokine and regulator of lysosomal function. A single mutation in the human GRN gene resulting in reduced PGRN expression causes types of frontotemporal lobar degeneration resulting in frontotemporal dementia. Prosaposin (PSAP) is also a multifunctional neuroprotective secreted protein and regulator of lysosomal function. Interactions of PGRN and PSAP affect their functional properties. Their roles in Alzheimer's disease (AD), the leading cause of dementia, have not been defined. In this report, we examined in detail the cellular expression of PGRN in middle temporal gyrus samples of a series of human brain cases (n = 45) staged for increasing plaque pathology. Immunohistochemistry showed PGRN expression in cortical neurons, microglia, cerebral vessels and amyloid beta (Aβ) plaques, while PSAP expression was mainly detected in neurons and Aβ plaques, and to a limited extent in astrocytes. We showed that there were increased levels of PGRN protein in AD cases and corresponding increased levels of PSAP. Levels of PGRN and PSAP protein positively correlated with amyloid beta (Aβ), with PGRN levels correlating with phosphorylated tau (serine 205) levels in these samples. Although PGRN colocalized with lysosomal-associated membrane protein-1 in neurons, most PGRN associated with Aβ plaques did not. Aβ plaques with PGRN and PSAP deposits were identified in the low plaque non-demented cases suggesting this was an early event in plaque formation. We did not observe PGRN-positive neurofibrillary tangles. Co-immunoprecipitation studies of PGRN from brain samples identified only PSAP associated with PGRN, not sortilin or other known PGRN-binding proteins, under conditions used. Most PGRN associated with Aβ plaques were immunoreactive for PSAP showing a high degree of colocalization of these proteins that did not change between disease groups. As PGRN supplementation has been considered as a therapeutic approach for AD, the possible involvement of PGRN and PSAP interactions in AD pathology needs to be further considered.

Microglial Phenotyping in Neurodegenerative Disease Brains: Identification of Reactive Microglia with an Antibody to Variant of CD105/Endoglin

Inflammation is considered a key pathological process in neurodegenerative diseases, including Alzheimer’s disease (AD) and Parkinson’s disease (PD), but there are still mechanisms not understood. In the brain, most microglia are performing essential homeostatic functions, but can also respond to pathogenic stimuli by producing harmful pro-inflammatory cytokines or free radicals. Distinguishing between damaging and homeostatic microglia in human diseased brain tissues is a challenge. This report describes findings using a monoclonal antibody to CD105/Endoglin (R&D Systems MAB1097) that identifies subtypes of activated microglia. CD105/Endoglin is a co-receptor for transforming growth factor beta (TGFβ) receptor that antagonizes TGFβ signaling. CD105/Endoglin is a marker for vascular endothelial cells, but was originally identified as a marker for activated macrophages. This antibody did not identify endothelial cells in brain sections, only microglia-like cells. In this study, we examined with this antibody tissue section from middle temporal gyrus derived from human brains from normal control subjects with low-plaque pathology, high-plaque pathology, and AD cases, and also substantia nigra samples from control and PD cases, in conjunction with antibodies to markers of pathology and microglia. In low-plaque pathology cases, CD105-positive microglia were mostly absent, but noticeably increased with increasing pathology. CD105-positive cells strongly colocalized with amyloid-beta plaques, but not phosphorylated tau positive tangles. In substantia nigra, strong microglial CD105 staining was observed in microglia associated with degenerating dopaminergic neurons and neuromelanin. In PD cases with few surviving dopaminergic neurons, this staining had decreased. By Western blot, this antibody identified polypeptide bands of 70 kDa in brain samples, and samples from microglia, macrophages, and brain endothelial cells. In comparison with other tested CD105 antibodies, this antibody did not recognize the glycosylated forms of CD105 on Western blots. Overall, the data indicate that this antibody and this marker could have utility for subtyping of microglia in pathologically-involved tissue.

Subcortical amyloid load is associated with shape and volume in cognitively normal individuals

Amyloid-beta (Aβ) deposition is one of the main hallmarks of Alzheimer's disease. The study assessed the associations between cortical and subcortical ¹¹ C-Pittsburgh Compound B (PiB) retention, namely, in the hippocampus, amygdala, putamen, caudate, pallidum, and thalamus, and subcortical morphology in cognitively normal individuals. We recruited 104 cognitive normal individuals who underwent extensive neuropsychological assessment, PiB-positron emission tomography (PET) scan, and 3-T magnetic resonance imaging (MRI) acquisition of T1-weighted images. Global, cortical, and subcortical regional PiB retention values were derived from each scan and subcortical morphology analyses were performed to investigate vertex-wise local surface and global volumes, including the hippocampal subfields volumes. We found that subcortical regional Aβ was associated with the surface of the hippocampus, thalamus, and pallidum, with changes being due to volume and shape. Hippocampal Aβ was marginally associated with volume of the whole hippocampus as well as with the CA1 subfield, subiculum, and molecular layer. Participants showing higher subcortical Aβ also showed worse cognitive performance and smaller hippocampal volumes. In contrast, global and cortical PiB uptake did not associate with any subcortical metrics. This study shows that subcortical Aβ is associated with subcortical surface morphology in cognitively normal individuals. This study highlights the importance of quantifying subcortical regional PiB retention values in these individuals.

The de-Alzheimerization of age-related dementias: implications for drug targets and approaches to effective therapeutics

Alzheimer's disease (AD) was differentiated from senile dementia (SD) in 1910 due to its early onset and pathological severity. In 1976, this distinction was upended when SD was redesignated as AD to focus efforts and funding in dementia-related research. AD then became conflated with amyloid plaques and, to a lesser degree, neurofibrillary tangles complicating efforts in understanding dementia causality and its treatment. The resultant four-decade search for therapies-based almost exclusively on amyloid was an exercise in futility. While dementia is a complex, multifactorial syndrome, AD is viewed as a homogeneous, linear disease. An amyloid-agnostic approach is necessary to discover therapeutics for age-related dementias.

PET staging of amyloidosis using striatum

INTRODUCTION

Amyloid positron emission tomography (PET) data are commonly expressed as binary measures of cortical deposition. However, not all individuals with high cortical amyloid will experience rapid cognitive decline. Motivated by postmortem data, we evaluated a three-stage PET classification: low cortical; high cortical, low striatal; and high cortical, high striatal amyloid; hypothesizing this model could better reflect Alzheimer's dementia progression than a model based only on cortical measures.

METHODS

We classified PET data from 1433 participants (646 normal, 574 mild cognitive impairment, and 213 AD), explored the successive involvement of cortex and striatum using 3-year follow-up PET data, and evaluated the associations between PET stages, hippocampal volumes, and cognition.

RESULTS

Follow-up data indicated that PET detects amyloid first in cortex and then in striatum. Our three-category staging including striatum better predicted hippocampal volumes and subsequent cognition than a three-category staging including only cortical amyloid.

DISCUSSION

PET can evaluate amyloid expansion from cortex to subcortex. Using striatal signal as a marker of advanced amyloidosis may increase predictive power in Alzheimer's dementia research.

Amyloid involvement in subcortical regions predicts cognitive decline

PURPOSE

We estimated whether amyloid involvement in subcortical regions may predict cognitive impairment, and established an amyloid staging scheme based on degree of subcortical amyloid involvement.

METHODS

Data from 240 cognitively normal older individuals, 393 participants with mild cognitive impairment, and 126 participants with Alzheimer disease were acquired at Alzheimer's Disease Neuroimaging Initiative sites. To assess subcortical involvement, we analyzed amyloid deposition in amygdala, putamen, and caudate nucleus. We staged participants into a 3-stage model based on cortical and subcortical amyloid involvement: 382 with no cortical or subcortical involvement as stage 0, 165 with cortical but no subcortical involvement as stage 1, and 203 with both cortical and subcortical involvement as stage 2.

RESULTS

Amyloid accumulation was first observed in cortical regions and spread down to the putamen, caudate nucleus, and amygdala. In longitudinal analysis, changes in MMSE, ADAS-cog 13, FDG PET SUVR, and hippocampal volumes were steepest in stage 2 followed by stage 1 then stage 0 (p value <0.001). Stage 2 showed steeper changes in MMSE score (β [SE] = -0.02 [0.004], p < 0.001), ADAS-cog 13 (0.05 [0.01], p < 0.001), FDG PET SUVR (-0.0008 [0.0003], p = 0.004), and hippocampal volumes (-4.46 [0.65], p < 0.001) compared to stage 1.

CONCLUSIONS

We demonstrated a downward spreading pattern of amyloid, suggesting that amyloid accumulates first in neocortex followed by subcortical structures. Furthermore, our new finding suggested that an amyloid staging scheme based on subcortical involvement might reveal how differential regional accumulation of amyloid affects cognitive decline through functional and structural changes of the brain.

Region-Specific Association of Subjective Cognitive Decline With Tauopathy Independent of Global β-Amyloid Burden

Importance

The ability to explore associations between reports of subjective cognitive decline (SCD) and biomarkers of early Alzheimer disease (AD) pathophysiologic processes (accumulation of neocortical β-amyloid [Aβ] and tau) provides an important opportunity to understand the basis of SCD and AD risk.

Objective

To examine associations between SCD and global Aβ and tau burdens in regions of interest in clinically healthy older adults.

Design, Setting, and Participants

This imaging substudy of the Harvard Aging Brain Study included 133 clinically healthy older participants (Clinical Dementia Rating Scale global scores of 0) participating in the Harvard Aging Brain Study who underwent cross-sectional flortaucipir F 18 (previously known as AV 1451, T807) positron emission tomography (FTP-PET) imaging for tau and Pittsburgh compound B carbon 11-labeled PET (PiB-PET) imaging for Aβ. The following 2 regions for tau burden were identified: the entorhinal cortex, which exhibits early signs of tauopathy, and the inferior temporal region, which is more closely associated with AD-related pathologic mechanisms. Data were collected from June 11, 2012, through April 7, 2016.

Main Outcomes and Measures

Subjective cognitive decline was measured using a previously published method of z-transforming subscales from the Memory Functioning Questionnaire, the Everyday Cognition battery, and a 7-item questionnaire. The Aβ level was measured according to a summary distribution volume ratio of frontal, lateral temporal and parietal, and retrosplenial PiB-PET tracer uptake. The FTP-PET measures were computed as standardized uptake value ratios. Linear regression models focused on main and interactive effects of Aβ, entorhinal cortical, and inferior temporal tau on SCD, controlling for age, sex, educational attainment, and Geriatric Depression Scale score.

Results

Of the 133 participants, 75 (56.3%) were women and 58 (43.6%) were men; mean (SD) age was 76 (6.9) years (range, 55-90 years). Thirty-nine participants (29.3%) exhibited a high Aβ burden. Greater SCD was associated with increasing entorhinal cortical tau burden (β = 0.35; 95% CI, 0.19-.52; P < .001) and Aβ burden (β = 0.24; 95% CI, 0.08-.40; P = .005), but not inferior temporal tau burden (β = 0.10; 95% CI, -0.08 to 0.28; P = .27). This association between entorhinal cortical tau burden and SCD was largely unchanged after accounting for Aβ burden (β = 0.36; 95% CI, 0.15-.58; P = .001), and no interaction influenced SCD (β = -0.36; 95% CI, -0.34 to 0.09; P = .25). An exploratory post hoc whole-brain analysis also indicated that SCD was predominantly associated with greater tau burden in the entorhinal cortex.

Conclusions and Relevance

Subjective cognitive decline is indicative of accumulation of early tauopathy in the medial temporal lobe, specifically in the entorhinal cortex, and to a lesser extent, elevated global levels of Aβ. Our findings suggest multiple underlying pathways that motivate SCD that do not necessarily interact to influence SCD endorsement. As such, multiple biological factors must be considered when assessing SCD in clinically healthy older adults.

In vivo staging of regional amyloid deposition

OBJECTIVES

To estimate a regional progression pattern of amyloid deposition from cross-sectional amyloid-sensitive PET data and evaluate its potential for in vivo staging of an individual's amyloid pathology.

METHODS

Multiregional analysis of florbetapir (18F-AV45)-PET data was used to determine individual amyloid distribution profiles in a sample of 667 participants from the Alzheimer's Disease Neuroimaging Initiative cohort, including cognitively normal older individuals (CN) as well as patients with mild cognitive impairment and Alzheimer disease (AD) dementia. The frequency of regional amyloid positivity across CN individuals was used to construct a 4-stage model of progressing amyloid pathology, and individual distribution profiles were used to evaluate the consistency of this hierarchical stage model across the full cohort.

RESULTS

According to a 4-stage model, amyloid deposition begins in temporobasal and frontomedial areas, and successively affects the remaining associative neocortex, primary sensory-motor areas and the medial temporal lobe, and finally the striatum. Amyloid deposition in these brain regions showed a highly consistent hierarchical nesting across participants, where only 2% exhibited distribution profiles that deviated from the staging scheme. The earliest in vivo amyloid stages were mostly missed by conventional dichotomous classification approaches based on global florbetapir-PET signal, but were associated with significantly reduced CSF Aβ42 levels. Advanced in vivo amyloid stages were most frequent in patients with AD and correlated with cognitive impairment in individuals without dementia.

CONCLUSIONS

The highly consistent regional hierarchy of PET-evidenced amyloid deposition across participants resembles neuropathologic observations and suggests a predictable regional sequence that may be used to stage an individual's progress of amyloid pathology in vivo.

Studies on Colony Stimulating Factor Receptor-1 and Ligands Colony Stimulating Factor-1 and Interleukin-34 in Alzheimer's Disease Brains and Human Microglia

Microglia are dependent on signaling through the colony stimulating factor-1 receptor (CSF-1R/CD115) for growth and survival. Activation of CSF-1R can lead to cell division, while blocking CSF-1R can lead to rapid microglia cell death. CSF-1R has two ligands, the growth factors colony stimulating factor-1 (CSF-1) and the more recently identified interleukin-34 (IL-34). Studies of IL-34 activation of rodent microglia and human macrophages have suggested it has different properties to CSF-1, resulting in an anti-inflammatory reparative phenotype. The goal of this study was to identify if the responses of human postmortem brain microglia to IL-34 differed from their responses to CSF-1 with the aim of identifying different phenotypes of microglia as a result of their responses. To approach this question, we also sought to identify differences between IL-34, CSF-1, and CSF-1R expression in human brain samples to establish whether there was an imbalance in Alzheimer's disease (AD). Using human brain samples [inferior temporal gyrus (ITG) and middle temporal gyrus (MTG)] from distinct cohorts of AD, control and high pathology, or mild cognitive impairment cases, we showed that there was increased expression of CSF-1R and CSF-1 mRNAs in both series of AD cases, and reduced expression of IL-34 mRNA in AD ITG samples. There was no change in expression of these genes in RNA from cerebellum of AD, Parkinson's disease (PD), or control cases. The results suggested an imbalance in CSF-1R signaling in AD. Using RNA sequencing to compare gene expression responses of CSF-1 and IL-34 stimulated human microglia, a profile of responses to CSF-1 and IL-34 was identified. Contrary to earlier work with rodent microglia, IL-34 induced primarily a classical activation response similar to that of CSF-1. It was not possible to identify any genes expressed significantly different by IL-34-stimulated microglia compared to CSF-1-stimulated microglia, but both cytokines did induce certain alternative activation-associated genes. These profiles also showed that a number of genes associated with lysosomal function and Aβ removal were downregulated by IL-34 and CSF-1 stimulation. Compared to earlier results our data indicate that CSF-1R stimulation by IL-34 or CSF-1 produced similar types of responses by elderly postmortem brain-derived microglia.

Cognitive decline and brain amyloid-β accumulation across 3 years in adults with Down syndrome

Adults with Down syndrome (DS) have a high incidence of Alzheimer's disease (AD), providing a unique opportunity to explore the early, preclinical stages of AD neuropathology. We examined change in brain amyloid-β accumulation via the positron emission tomography tracer [11C] Pittsburgh compound B (PiB) across 2 data collection cycles, spaced 3 years apart, and decline in cognitive functioning in 58 adults with DS without clinical AD. PiB retention increased in the anterior cingulate gyrus, precuneus cortex, parietal cortex, and anterior ventral striatum. Across the 2 cycles, 14 (27.5%) participants were consistently PiB+, 31 (60.8%) were consistently PiB-, and 6 (11.7%) converted from PiB- at cycle 1 to PiB+ at cycle 2. Increased global amyloid-β was related to decline in verbal episodic memory, visual episodic memory, executive functioning, and fine motor processing speed. Participants who were consistently PiB+ demonstrated worsening of episodic memory, whereas participants who were consistently PiB- evidenced stable or improved performance. Amyloid-β accumulation may be a contributor to or biomarker of declining cognitive functioning in preclinical AD in DS.

Subcortical Shape Changes, Hippocampal Atrophy and Cortical Thinning in Future Alzheimer's Disease Patients

Efficacy of future treatments depends on biomarkers identifying patients with mild cognitive impairment at highest risk for transitioning to Alzheimer's disease. Here, we applied recently developed analysis techniques to investigate cross-sectional differences in subcortical shape and volume alterations in patients with stable mild cognitive impairment (MCI) (n = 23, age range 59–82, 47.8% female), future converters at baseline (n = 10, age range 66–84, 90% female) and at time of conversion (age range 68–87) compared to group-wise age and gender matched healthy control subjects (n = 23, age range 61–81, 47.8% female; n = 10, age range 66–82, 80% female; n = 10, age range 68–82, 70% female). Additionally, we studied cortical thinning and global and local measures of hippocampal atrophy as known key imaging markers for Alzheimer's disease. Apart from bilateral striatal volume reductions, no morphometric alterations were found in cognitively stable patients. In contrast, we identified shape alterations in striatal and thalamic regions in future converters at baseline and at time of conversion. These shape alterations were paralleled by Alzheimer's disease like patterns of left hemispheric morphometric changes (cortical thinning in medial temporal regions, hippocampal total and subfield atrophy) in future converters at baseline with progression to similar right hemispheric alterations at time of conversion. Additionally, receiver operating characteristic curve analysis indicated that subcortical shape alterations may outperform hippocampal volume in identifying future converters at baseline. These results further confirm the key role of early cortical thinning and hippocampal atrophy in the early detection of Alzheimer's disease. But first and foremost, and by distinguishing future converters but not patients with stable cognitive abilities from cognitively normal subjects, our results support the value of early subcortical shape alterations and reduced hippocampal subfield volumes as potential markers for the early detection of Alzheimer's disease.

Detection of Striatal Amyloid Plaques with [18F]flutemetamol: Validation with Postmortem Histopathology

Amyloid imaging is limited by an inconsistent relationship between cerebral cortex amyloid- β (Aβ) plaques and dementia. Autopsy studies suggest that Aβ plaques first appear in the cerebral cortex while subcortical plaques are present only later in the disease course. The presence of abundant plaques in both cortex and striatum is more strongly correlated with the presence of dementia than cortical Aβ plaques alone. Additionally, detection of striatal plaques may allow, for the first time, pathology-based clinical staging of AD. Striatal plaques are reportedly identifiable by amyloid imaging but the accuracy and reliability of striatal amyloid imaging has never been tested against postmortem histopathology. To determine this, we correlated the presence of histopathologically-demonstrated striatal Aβ deposits with a visually positive panel consensus decision of a positive [18F]flutemetamol striatal PET signal in 68 subjects that later came to autopsy. The sensitivity of [18F]flutemetamol PET striatal amyloid imaging, for several defined density levels of histological striatal Aβ deposits, ranged between 69% and 87% while the specificity ranged between 96% and 100%. Sensitivity increased with higher histological density thresholds while the reverse was found for specificity. In general, as compared with PET alone, PET with CT had slightly higher sensitivities but slightly lower specificities. In conclusion, amyloid imaging of the striatum with [18F]flutemetamol PET has reasonable accuracy for the detection of histologically-demonstrated striatal Aβ plaques when present at moderate or frequent densities. Amyloid imaging of the cerebral cortex and striatum together may allow for a more accurate clinicopathological diagnosis of AD and enable pathology-based clinical staging of AD.

Altered Expression Patterns of Inflammation-Associated and Trophic Molecules in Substantia Nigra and Striatum Brain Samples from Parkinson's Disease, Incidental Lewy Body Disease and Normal Control Cases

Evidence of inflammation has been consistently associated with pathology in Parkinson's disease (PD)-affected brains, and has been suggested as a causative factor. Dopaminergic neurons in the substantia nigra (SN) pars compacta, whose loss results in the clinical symptoms associated with PD, are particularly susceptible to inflammatory damage and oxidative stress. Inflammation in the striatum, where SN dopaminergic neurons project, is also a feature of PD brains. It is not known whether inflammatory changes occur first in striatum or SN. Many animal models of PD have implicated certain inflammatory molecules with dopaminergic cell neuronal loss; however, there have been few studies to validate these findings by measuring the levels of these and other inflammatory factors in human PD brain samples. This study also included samples from incidental Lewy body disease (ILBD) cases, since ILBD is considered a non-symptomatic precursor to PD, with subjects having significant loss of tyrosine hydroxylase-producing neurons. We hypothesized that there may be a progressive change in key inflammatory factors in ILBD samples intermediate between neurologically normal and PD. To address this, we used a quantitative antibody-array platform (Raybiotech-Quantibody arrays) to measure the levels of 160 different inflammation-associated cytokines, chemokines, growth factors, and related molecules in extracts of SN and striatum from clinically and neuropathologically characterized PD, ILBD, and normal control cases. Patterns of changes in inflammation and related molecules were distinctly different between SN and striatum. Our results showed significantly different levels of interleukin (IL)-5, IL-15, monokine induced by gamma interferon, and IL-6 soluble receptor in SN between disease groups. A different panel of 13 proteins with significant changes in striatum, with IL-15 as the common feature, was identified. Although the ability to detect some proteins was limited by sensitivity, patterns of expression indicated involvement of certain T-cell cytokines, vascular changes, and loss of certain growth factors, with disease progression. The results demonstrate the feasibility of profiling inflammatory molecules using diseased human brain samples, and have provided additional targets to validate in relation to PD pathology.

Propagation of Aß pathology: hypotheses, discoveries, and yet unresolved questions from experimental and human brain studies

In brains of patients with Alzheimer's disease (AD), Aβ peptides accumulate in parenchyma and, almost invariably, also in the vascular walls. Although Aβ aggregation is, by definition, present in AD, its impact is only incompletely understood. It occurs in a stereotypical spatiotemporal distribution within neuronal networks in the course of the disease. This suggests a role for synaptic connections in propagating Aβ pathology, and possibly of axonal transport in an antero- or retrograde way-although, there is also evidence for passive, extracellular diffusion. Striking, in AD, is the conjunction of tau and Aβ pathology. Tau pathology in the cell body of neurons precedes Aβ deposition in their synaptic endings in several circuits such as the entorhino-dentate, cortico-striatal or subiculo-mammillary connections. However, genetic evidence suggests that Aβ accumulation is the first step in AD pathogenesis. To model the complexity and consequences of Aβ aggregation in vivo, various transgenic (tg) rodents have been generated. In rodents tg for the human Aβ precursor protein, focal injections of preformed Aβ aggregates can induce Aβ deposits in the vicinity of the injection site, and over time in more distant regions of the brain. This suggests that Aβ shares with α-synuclein, tau and other proteins the property to misfold and aggregate homotypic molecules. We propose to group those proteins under the term "propagons". Propagons may lack the infectivity of prions. We review findings from neuropathological examinations of human brains in different stages of AD and from studies in rodent models of Aβ aggregation and discuss putative mechanisms underlying the initiation and spread of Aβ pathology.

Relationship of regional brain β-amyloid to gait speed

OBJECTIVE

To investigate in vivo the relationship of regional brain β-amyloid (Aβ) to gait speed in a group of elderly individuals at high risk for dementia.

METHODS

Cross-sectional associations between brain Aβ as measured with [18F]florbetapir PET and gait speed were examined in 128 elderly participants. Subjects ranged from healthy to mildly cognitively impaired enrolled in the control arm of the multidomain intervention in the Multidomain Alzheimer Preventive Trial (MAPT). Nearly all participants presented spontaneous memory complaints. Regional [18F]florbetapir (AV45) standardized uptake volume ratios were obtained via semiautomated quantitative analysis using the cerebellum as reference region. Gait speed was measured by timing participants while they walked 4 meters. Associations were explored with linear regression, correcting for age, sex, education, body mass index (BMI), and APOE genotype.

RESULTS

We found a significant association between Aβ in the posterior and anterior putamen, occipital cortex, precuneus, and anterior cingulate and slow gait speed (all corrected p < 0.05). A multivariate model emphasized the locations of the posterior putamen and the precuneus. Aβ burden explained up to 9% of the variance in gait speed, and significantly improved regression models already containing demographic variables, BMI, and APOE status.

CONCLUSIONS

The present PET study confirms, in vivo, previous postmortem evidence showing an association between Alzheimer disease (AD) pathology and gait speed, and provides additional evidence on potential regional effects of brain Aβ on motor function. More research is needed to elucidate the neural mechanisms underlying these regional associations, which may involve motor and sensorimotor circuits hitherto largely neglected in the pathophysiology of AD.

Striatal and Cortical β-Amyloidopathy and Cognition in Parkinson's Disease

INTRODUCTION

Although most previous cognitive studies of β-amyloidopathy in PD focused on cortical plaque deposition, recent postmortem studies point to an important role of striatal β-amyloid plaque deposition. The aim of this study was to investigate the relative contributions of striatal and cortical β-amyloidopathy to cognitive impairment in PD.

METHODS

Patients with PD (n = 62; age, 68.9 ± 6.4 years; H & Y stage: 2.7 ± 0.5; MoCA score: 25.2 ± 3.0) underwent [(11) C]Pittsburgh compound B β-amyloid, [(11) C]dihydrotetrabenazine monoaminergic, and [(11) C]methyl-4-piperidinyl propionate acetylcholinesterase brain PET imaging and neuropsychological assessment. [(11) C]Pittsburgh compound B β-amyloid data from young to middle-aged healthy subjects were used to define elevated [(11) C]Pittsburgh compound B binding in patients.

RESULTS

Elevated cortical and striatal β-amyloid deposition were present in 37% and 16%, respectively, of this predominantly nondemented cohort of patients with PD. Increased striatal β-amyloid deposition occurred in half of all subjects with increased cortical β-amyloid deposition. In contrast, increased striatal β-amyloid deposition did not occur in the absence of increased cortical β-amyloid deposition. Analysis of covariance using global composite cognitive z scores as the outcome parameter showed significant regressor effects for combined striatal and cortical β-amyloidopathy (F = 4.18; P = 0.02) after adjusting for covariate effects of cortical cholinergic activity (F = 5.67; P = 0.02), caudate nucleus monoaminergic binding, duration of disease, and age (total model: F = 3.55; P = 0.0048). Post-hoc analysis showed significantly lower cognitive z score for combined striatal and cortical β-amyloidopathy, compared to cortical-only β-amyloidopathy and non-β-amyloidopathy subgroups.

CONCLUSIONS

The combined presence of striatal and cortical β-amyloidopathy is associated with greater cognitive impairment than cortical β-amyloidopathy alone in PD.

The pattern of amyloid accumulation in the brains of adults with Down syndrome

INTRODUCTION

Adults with Down syndrome (DS) invariably develop Alzheimer's disease (AD) neuropathology. Understanding amyloid deposition in DS can yield crucial information about disease pathogenesis.

METHODS

Forty-nine adults with DS aged 25-65 underwent positron emission tomography with Pittsburgh compound-B (PIB). Regional PIB binding was assessed with respect to age, clinical, and cognitive status.

RESULTS

Abnormal PIB binding became evident from 39 years, first in striatum followed by rostral prefrontal-cingulo-parietal regions, then caudal frontal, rostral temporal, primary sensorimotor and occipital, and finally parahippocampal cortex, thalamus, and amygdala. PIB binding was related to age, diagnostic status, and cognitive function.

DISCUSSION

PIB binding in DS, first appearing in striatum, began around age 40 and was strongly associated with dementia and cognitive decline. The absence of a substantial time lag between amyloid accumulation and cognitive decline contrasts to sporadic/familial AD and suggests this population's suitability for an amyloid primary prevention trial.

Clinical use of amyloid-positron emission tomography neuroimaging: Practical and bioethical considerations

Until recently, estimation of β-amyloid plaque density as a key element for identifying Alzheimer's disease (AD) pathology as the cause of cognitive impairment was only possible at autopsy. Now with amyloid-positron emission tomography (amyloid-PET) neuroimaging, this AD hallmark can be detected antemortem. Practitioners and patients need to better understand potential diagnostic benefits and limitations of amyloid-PET and the complex practical, ethical, and social implications surrounding this new technology. To complement the practical considerations, Eli Lilly and Company sponsored a Bioethics Advisory Board to discuss ethical issues that might arise from clinical use of amyloid-PET neuroimaging with patients being evaluated for causes of cognitive decline. To best address the multifaceted issues associated with amyloid-PET neuroimaging, we recommend this technology be used only by experienced imaging and treating physicians in appropriately selected patients and only in the context of a comprehensive clinical evaluation with adequate explanations before and after the scan.

Neuropathological comparisons of amnestic and nonamnestic mild cognitive impairment

BACKGROUND

Although there are studies investigating the pathologic origins of mild cognitive impairment (MCI), they have revolved around comparisons to normal elderly individuals or those with Alzheimer's disease (AD) or other dementias. There are few studies directly comparing the comprehensive neuropathology of amnestic (aMCI) and nonamnestic (naMCI) MCI.

METHODS

The database of the Brain and Body Donation Program ( www.brainandbodydonationprogram.org ), a longitudinal clinicopathological study of normal aging and neurodegenerative disorders, was queried for subjects who were carrying a diagnosis of aMCI or naMCI at the time of autopsy. Neuropathological lesions, including neuritic plaques, neurofibrillary tangles (NFTs), Lewy bodies (LBs), infarcts, cerebral white matter rarefaction (CWMR), cerebral amyloid angiopathy (CAA), and concurrent major clinicopathological diagnoses, including Parkinson's disease (PD) were analyzed.

RESULTS

Thirty four subjects with aMCI and 15 naMCI met study criteria. Subjects with aMCI were older at death (88 vs. 83 years of age, p = 0.03). Individuals with naMCI had higher densities of LBs within the temporal lobe (p = 0.04) while subjects with aMCI had a propensity for increased NFTs in parietal and temporal lobes (p values = 0.07). After adjusting for age at death, the only significant difference was greater densities of temporal lobe NFTs within the aMCI group. Other regional pathology scores for plaques, NFTs, and LBs were similar between groups. Subjects met clinico-pathological criteria for co-existent PD in 24 % aMCI and 47 % naMCI while neuropathological criteria for AD were met in equal percentages of aMCI and of naMCI cases (53 %); these proportional differences were not significant (p values > 0.35). Furthermore, regardless of amnestic status, there was a greater presence of CAA (71 % of MCI with executive dysfunction vs. 39 % without p = 0.03) and a greater presence of CWMR (81 % of MCI with executive dysfunction and 54 % without p = 0.046) in MCI cases with executive dysfunction.

CONCLUSIONS

No single pathologic entity strongly dichotomized MCI groups, perhaps due to the pathologic heterogeneity found within both entities. However, these data suggest the possibility for naMCI to have a propensity for increased LBs and aMCI for increased NFTs in select anatomic regions.

Amyloid PET in European and North American cohorts; and exploring age as a limit to clinical use of amyloid imaging

Purpose

Several radiotracers that bind to fibrillar amyloid-beta in the brain have been developed and used in various patient cohorts. This study aimed to investigate the comparability of two amyloid positron emission tomography (PET) tracers as well as examine how age affects the discriminative properties of amyloid PET imaging.

Methods

Fifty-one healthy controls (HCs), 72 patients with mild cognitive impairment (MCI) and 90 patients with Alzheimer’s disease (AD) from a European cohort were scanned with [11C]Pittsburgh compound-B (PIB) and compared with an age-, sex- and disease severity-matched population of 51 HC, 72 MCI and 84 AD patients from a North American cohort who were scanned with [18F]Florbetapir. An additional North American population of 246 HC, 342 MCI and 138 AD patients with a Florbetapir scan was split by age (55–75 vs 76–93 y) into groups matched for gender and disease severity. PET template-based analyses were used to quantify regional tracer uptake.

Results

The mean regional uptake patterns were similar and strong correlations were found between the two tracers across the regions of interest in HC (ρ = 0.671, p = 0.02), amyloid-positive MCI (ρ = 0.902, p < 0.001) and AD patients (ρ = 0.853, p < 0.001). The application of the Florbetapir cut-off point resulted in a higher proportion of amyloid-positive HC and a lower proportion of amyloid-positive AD patients in the older group (28 and 30 %, respectively) than in the younger group (19 and 20 %, respectively).

Conclusions

These results illustrate the comparability of Florbetapir and PIB in unrelated but matched patient populations. The role of amyloid PET imaging becomes increasingly important with increasing age in the diagnostic assessment of clinically impaired patients.

Electronic supplementary material

The online version of this article (doi:10.1007/s00259-015-3115-5) contains supplementary material, which is available to authorized users.

Arizona Study of Aging and Neurodegenerative Disorders and Brain and Body Donation Program

The Brain and Body Donation Program (BBDP) at Banner Sun Health Research Institute (http://www.brainandbodydonationprogram.org) started in 1987 with brain-only donations and currently has banked more than 1600 brains. More than 430 whole-body donations have been received since this service was commenced in 2005. The collective academic output of the BBDP is now described as the Arizona Study of Aging and Neurodegenerative Disorders (AZSAND). Most BBDP subjects are enrolled as cognitively normal volunteers residing in the retirement communities of metropolitan Phoenix, Arizona. Specific recruitment efforts are also directed at subjects with Alzheimer's disease, Parkinson's disease and cancer. The median age at death is 82. Subjects receive standardized general medical, neurological, neuropsychological and movement disorders assessments during life and more than 90% receive full pathological examinations by medically licensed pathologists after death. The Program has been funded through a combination of internal, federal and state of Arizona grants as well as user fees and pharmaceutical industry collaborations. Subsets of the Program are utilized by the US National Institute on Aging Arizona Alzheimer's Disease Core Center and the US National Institute of Neurological Disorders and Stroke National Brain and Tissue Resource for Parkinson's Disease and Related Disorders. Substantial funding has also been received from the Michael J. Fox Foundation for Parkinson's Research. The Program has made rapid autopsy a priority, with a 3.0-hour median post-mortem interval for the entire collection. The median RNA Integrity Number (RIN) for frozen brain and body tissue is 8.9 and 7.4, respectively. More than 2500 tissue requests have been served and currently about 200 are served annually. These requests have been made by more than 400 investigators located in 32 US states and 15 countries. Tissue from the BBDP has contributed to more than 350 publications and more than 200 grant-funded projects.

Expression of suppressor of cytokine signaling genes in human elderly and Alzheimer's disease brains and human microglia

Multiple cellular systems exist to prevent uncontrolled inflammation in brain tissues; the suppressor of cytokine signaling (SOCS) proteins have key roles in these processes. SOCS proteins are involved in restricting cellular signaling pathways by enhancing the degradation of activated receptors and removing the stimuli for continued activation. There are eight separate SOCS genes that code for proteins with similar structures and properties. All SOCS proteins can reduce signaling of activated transcription factors Janus kinase (JAK) and signal transducer and activator of transcription (STAT), but they also regulate many other signaling pathways. SOCS-1 and SOCS-3 have particular roles in regulating inflammatory processes. Chronic inflammation is a key feature of the pathology present in Alzheimer's disease (AD)-affected brains resulting from responses to amyloid plaques or neurofibrillary tangles, the pathological hallmarks of AD. The goal of this study was to examine SOCS gene expression in human non-demented (ND) and AD brains and in human brain-derived microglia to determine if AD-related pathology resulted in a deficit of these critical molecules. We demonstrated that SOCS-1, SOCS-2, SOCS-3 and cytokine-inducible SH2 containing protein (CIS) mRNA expression was increased in amyloid beta peptide (Aβ)- and inflammatory-stimulated microglia, while SOCS-6 mRNA expression was decreased by both types of treatments. Using human brain samples from the temporal cortex from ND and AD cases, SOCS-1 through SOCS-7 and CIS mRNA and SOCS-1 through SOCS-7 protein could be detected constitutively in ND and AD human brain samples. Although, the expression of key SOCS genes did not change to a large extent as a result of AD pathology, there were significantly increased levels of SOCS-2, SOCS-3 and CIS mRNA and increased protein levels of SOCS-4 and SOCS-7 in AD brains. In summary, there was no evidence of a deficit of these key inflammatory regulating proteins in aged or AD brains.