Resistance vs resilience to Alzheimer disease: Clarifying terminology for preclinical studies

Multilingualism and Dementia Risk: Longitudinal Analysis of the Nun Study

BACKGROUND

Multilingualism is associated with enhanced executive function and may thus prevent cognitive decline and reduce the risk of dementia.

OBJECTIVE

To determine whether multilingualism is associated with delayed onset or reduced risk of dementia.

METHODS

Dementia was diagnosed in the Nun Study, a longitudinal study of religious sisters aged 75+ years. Multilingualism was self-reported. Dementia likelihood was determined in 325 participants using discrete-time survival analysis; sensitivity analyses (n = 106) incorporated additional linguistic measures (idea density and grammatical complexity).

RESULTS

Multilingualism did not delay the onset of dementia. However, participants speaking four or more languages (but not two or three) were significantly less likely to develop dementia than monolinguals (OR = 0.13; 95% CI = 0.01, 0.65, adjusted for age, apolipoprotein E, and transition period). This significant protective effect of speaking four or more languages weakened (OR = 0.53; 95% CI = 0.06, 4.91) in the presence of idea density in models adjusted for education and apolipoprotein E.

CONCLUSION

Linguistic ability broadly was a significant predictor of dementia, although it was written linguistic ability (specifically idea density) rather than multilingualism that was the strongest predictor. The impact of language on dementia may extend beyond number of languages spoken to encompass other indicators of linguistic ability. Further research to identify the characteristics of multilingualism most salient for risk of dementia could clarify the value, target audience, and design of interventions to promote multilingualism and other linguistic training as a strategy to reduce the risk of dementia and its individual and societal impacts.

Variants in PPP2R2B and IGF2BP3 are associated with higher tau deposition

Tau deposition is a key biological feature of Alzheimer's disease that is closely related to cognitive impairment. However, it remains poorly understood why certain individuals may be more susceptible to tau deposition while others are more resistant. The recent availability of in vivo assessment of tau burden through positron emission tomography provides an opportunity to test the hypothesis that common genetic variants may influence tau deposition. We performed a genome-wide association study of tau-positron emission tomography on a sample of 754 individuals over age 50 (mean age 72.4 years, 54.6% men, 87.6% cognitively unimpaired) from the population-based Mayo Clinic Study of Aging. Linear regression was performed to test nucleotide polymorphism associations with AV-1451 (18F-flortaucipir) tau-positron emission tomography burden in an Alzheimer's-signature composite region of interest, using an additive genetic model and covarying for age, sex and genetic principal components. Genome-wide significant associations with higher tau were identified for rs76752255 (P = 9.91 × 10-9, β = 0.20) in the tau phosphorylation regulatory gene PPP2R2B (protein phosphatase 2 regulatory subunit B) and for rs117402302 (P  = 4.00 × 10-8, β = 0.19) near IGF2BP3 (insulin-like growth factor 2 mRNA-binding protein 3). The PPP2R2B association remained genome-wide significant after additionally covarying for global amyloid burden and cerebrovascular disease risk, while the IGF2BP3 association was partially attenuated after accounting for amyloid load. In addition to these discoveries, three single nucleotide polymorphisms within MAPT (microtubule-associated protein tau) displayed nominal associations with tau-positron emission tomography burden, and the association of the APOE (apolipoprotein E) ɛ4 allele with tau-positron emission tomography was marginally nonsignificant (P  = 0.06, β = 0.07). No associations with tau-positron emission tomography burden were identified for other single nucleotide polymorphisms associated with Alzheimer's disease clinical diagnosis in prior large case-control studies. Our findings nominate PPP2R2B and IGF2BP3 as novel potential influences on tau pathology which warrant further functional characterization. Our data are also supportive of previous literature on the associations of MAPT genetic variation with tau, and more broadly supports the inference that tau accumulation may have a genetic architecture distinct from known Alzheimer's susceptibility genes, which may have implications for improved risk stratification and therapeutic targeting.

Education as a Moderator of the Relationship Between Episodic Memory and Amyloid Load in Normal Aging

The current study explored whether education, a proxy of cognitive reserve, modifies the association between episodic memory (EM) performance and βeta-amyloid load (Aβ), a biomarker of Alzheimer's disease, in a cohort of cognitively normal older adults. One hundred and four participants (mean age 73.3 years) evenly spread out in three bands of education were recruited. Participants underwent neuropsychological assessment, structural MRI as well as PET imaging to quantify Aβ load. Moderation analyses and the Johnson-Neyman technique were carried out to examine the interaction of education with Aβ load to predict EM performance. Linear regressions were then performed within each group of education to better illustrate the interaction effect (all analyses were controlled for age and sex). The interaction between education and Aβ load was significant (p < .05) for years of education, reaching a cutoff point of 13.5 years, above which the relationship between Aβ load and EM was no longer significant. Similarly, significant associations were found between Aβ and EM among participants with secondary (p < .01) and pre-university education (p < .01), but not with a university degree (p = .253). EM performance is associated with Aβ load in cognitively normal older individuals, and this relationship is moderated by educational attainment.

Association of education with Aβ burden in preclinical familial and sporadic Alzheimer disease

OBJECTIVE

To determine whether years of education and the ε4 risk allele at APOE influence β-amyloid (Aβ) pathology similarly in asymptomatic individuals with a family history of sporadic Alzheimer disease (AD) and presymptomatic autosomal dominant AD mutation carriers.

METHODS

We analyzed cross-sectional data from 106 asymptomatic individuals with a parental history of sporadic AD (PREVENT-AD cohort; age 67.28 ± 4.72 years) and 117 presymptomatic autosomal dominant AD mutation carriers (DIAN cohort; age 35.04 ± 9.43 years). All participants underwent structural MRI and Aβ-PET imaging. In each cohort we investigated the influence of years of education, APOE ε4 status, and their interaction on Aβ-PET.

RESULTS

Asymptomatic individuals with a parental history of sporadic AD showed increased Aβ burden associated with APOE ε4 carriage and lower level of education, but no interaction between these. Presymptomatic mutation carriers of autosomal dominant AD showed no relation between APOE ε4 and Aβ burden, but increasing level of education was associated with reduced Aβ burden. The association between educational attainment and Aβ burden was similar in the 2 cohorts.

CONCLUSIONS

While the APOE ε4 allele confers increased tendency toward Aβ accumulation in sporadic AD only, protective environmental factors, like increased education, may promote brain resistance against Aβ pathology in both sporadic and autosomal dominant AD.

Resting-state functional connectivity and amyloid burden influence longitudinal cortical thinning in the default mode network in preclinical Alzheimer's disease

Proteinopathies are key elements in the pathogenesis of age-related neurodegenerative diseases, particularly Alzheimer's disease (AD), with the nature and location of the proteinopathy characterizing much of the disease phenotype. Susceptibility of brain regions to pathology may partly be determined by intrinsic network structure and connectivity. It remains unknown, however, how these networks inform the disease cascade in the context of AD biomarkers, such as beta-amyloid (Aβ), in clinically-normal older adults.The default-mode network (DMN), a prominent intrinsic network, is heavily implicated in AD due to its spatial overlap with AD atrophy patterns and tau deposition. We investigated the influence of baseline Aβ positron emission tomography (PET) signal and intrinsic DMN connectivity on DMN-specific cortical thinning in 120 clinically-normal older adults from the Harvard Aging Brain Study (73 ± 6 years, 58% Female, CDR = 0). Participants underwent11C Pittsburgh Compound-B (PiB) PET, 18F flortaucipir (FTP) PET, and resting-state MRI scans at baselineand longitudinal MRI (3.6 ± 0.96 scans; 5.04 ± 0.8 years). Linear mixed models tested relationships between baseline PiB and DMN connectivity on cortical thinning in a composite of DMN regions. Lower DMN connectivity was associated with faster cortical thinning, but only in those with elevated baseline PiB-PET signal. This relationship was network specific, in that the frontoparietal control network did not account for the observed association. Additionally, the relationship was independent of inferior temporal lobe FTP-PET signal. Our findings provide evidence that compromised DMN connectivity, in the context of preclinical AD, foreshadows neurodegeneration in DMN regions.

Beyond Alzheimer's disease: Can bilingualism be a more generalized protective factor in neurodegeneration?

Bilingualism has been argued to have an impact on cognition and brain structure. Effects have been reported across the lifespan: from healthy children to ageing adults, including clinical (ageing) populations. It has been argued that active bilingualism may significantly contribute to the delaying of the expression of Alzheimer's disease symptoms. If bilingualism plays an ameliorative role against the expression of neurodegeneration in dementia, it is possible that it could have similar effects for other neurodegenerative disorders, including Multiple Sclerosis, Parkinson's and Huntington's Diseases. To date, however, direct relevant evidence remains limited, not least because the necessary scientific motivations for investigating this with greater depth have not yet been fully articulated. Herein, we provide a roadmap that reviews the relevant literatures, highlighting potential links across neurodegenerative disorders and bilingualism more generally.

Interaction between Cognitive Reserve and Biomarkers in Alzheimer Disease

Patients with comparable degree of neuropathology could show different cognitive impairments. This could be explained with the concept of cognitive reserve (CR), which includes a passive and an active component. In particular, CR is used to explain the gap between tissue damage and clinical symptoms that has been observed in dementia and, in particular, in patients affected by Alzheimer disease (AD). Different studies confirm brain neuroplasticity. Our preliminary study demonstrated that AD patients with high education showed a CR inversely associated with glucose uptake measured in fluorodeoxyglucose positron emission tomography (FDG-PET), whereas the inverse correlation was observed in AD patients with low education. In other words, our findings suggest that CR compensates the neurodegeneration and allows the maintenance of patients’ cognitive performance. Best understanding of the concept of CR could lead to interventions to slow cognitive aging or reduce the risk of dementia.

Cognitive Resilience to Alzheimer's Disease Pathology in the Human Brain

BACKGROUND

Past research has focused on risk factors for developing dementia, with increasing recognition of "resilient" people who live to old age with intact cognitive function despite pathological features of Alzheimer's disease (AD).

OBJECTIVE

To evaluate demographic factors, mid-life characteristics, and non-AD neuropathology findings that may be associated with cognitive resilience to AD pathology.

METHODS

We analyzed data from 276 autopsy cases with intermediate or high levels of AD pathology from the Adult Changes in Thought study. We defined cognitive resilience as having Cognitive Abilities Screening Instrument scores ≥86 within two years of death and no clinical dementia diagnosis; non-resilient people had dementia diagnoses from AD or other causes before death. We compared mid-life characteristics, demographics, and additional neuropathology findings between resilient and non-resilient people. We used multivariable logistic regression to estimate odds ratios (ORs) with 95% confidence intervals (CIs) for being resilient compared to not being resilient adjusting for demographic and neuropathology factors.

RESULTS

We classified 68 (25%) people as resilient and 208 (75%) as not resilient. A greater proportion of resilient people had a college degree (50%) compared with non-resilient (32%, p = 0.01). The odds of being resilient were significantly increased among people with a college education (OR = 2.01, 95% CI = 1.01-3.99) and significantly reduced among people with additional non-AD neuropathology findings such as hippocampal sclerosis (OR = 0.28, 95% CI = 0.09-0.89) and microinfarcts (OR = 0.34, 95% CI = 0.15-0.78).

CONCLUSION

Increased education and absence of non-AD pathology may be independently associated with cognitive resilience, highlighting the importance of evaluating co-morbid factors in future research on mechanisms of cognitive resilience.

Predicting resistance to amyloid-beta deposition and cognitive resilience in the oldest-old

OBJECTIVE

To explore long-term predictors of avoiding β-amyloid (Aβ) deposition and maintaining unimpaired cognition as outcomes in the oldest old.

METHODS

In a longitudinal observational cohort study, 100 former participants of the Ginkgo Evaluation of Memory Study (GEMS; 2000-2008) completed biannual Pittsburgh compound B-PET imaging and annual clinical-cognitive evaluations beginning in 2010. Most recent Aβ status and cognitive status were selected for each participant. Longitudinal outcomes included change in serial Aβ and cognitive tests. Baseline predictors from GEMS included neuropsychological tests, daily functioning, APOE genotype, lifestyle variables, occupational measures, health history, sleep, subjective memory, physical and cognitive activities, depressive symptoms, and physical performance and health indices, among others.

RESULTS

Mean age at the last cognitive evaluation was 92.0 (range 86-100) years. Mean follow-up time from baseline to last measured Aβ status was 12.3 (SD 1.9) years and to last cognitive evaluation was 14.1 (SD 1.9) years. The APOE*2 allele predicted last Aβ status (n = 34 Aβ negative vs n = 66 Aβ positive). Baseline cognition predicted cognitive status (n = 30 unimpaired vs n = 70 impaired). Predictors of cognitive status among Aβ-positive participants only (n = 14 normal cognition vs n = 52 impaired) were baseline cognitive test scores and smoking history. Baseline pulse pressure predicted longitudinal Aβ increase; paid work engagement and life satisfaction predicted less cognitive decline.

CONCLUSIONS

The APOE*2 allele and lower pulse pressure predict resistance to Aβ deposition in advanced aging. Cognitive test scores 14 years prior, likely reflecting premorbid abilities, predict cognitive status and maintenance of unimpaired cognition in the presence of Aβ. Several lifestyle factors appear protective.

Identifying the molecular systems that influence cognitive resilience to Alzheimer's disease in genetically diverse mice

Individual differences in cognitive decline during normal aging and Alzheimer's disease (AD) are common, but the molecular mechanisms underlying these distinct outcomes are not fully understood. We utilized a combination of genetic, molecular, and behavioral data from a mouse population designed to model human variation in cognitive outcomes to search for the molecular mechanisms behind this population-wide variation. Specifically, we used a systems genetics approach to relate gene expression to cognitive outcomes during AD and normal aging. Statistical causal-inference Bayesian modeling was used to model systematic genetic perturbations matched with cognitive data that identified astrocyte and microglia molecular networks as drivers of cognitive resilience to AD. Using genetic mapping, we identified Fgf2 as a potential regulator of the astrocyte network associated with individual differences in short-term memory. We also identified several immune genes as regulators of a microglia network associated with individual differences in long-term memory, which was partly mediated by amyloid burden. Finally, significant overlap between mouse and two different human coexpression networks provided strong evidence of translational relevance for the genetically diverse AD-BXD panel as a model of late-onset AD. Together, this work identified two candidate molecular pathways enriched for microglia and astrocyte genes that serve as causal AD cognitive biomarkers, and provided a greater understanding of processes that modulate individual and population-wide differences in cognitive outcomes during AD.

Cerebrolysin in the therapy of mild cognitive impairment and dementia due to Alzheimer's disease: 30 years of clinical use

Alzheimer's disease (AD) is the most common neurocognitive disorder and a global health problem. The prevalence of AD is growing dramatically, especially in low- and middle-income countries, and will reach 131.5 million cases worldwide by 2050. Therefore, developing a disease-modifying therapy capable of delaying or even preventing the onset and progression of AD has become a world priority, and is an unmet need. The pathogenesis of AD, considered as the result of an imbalance between resilience and risk factors, begins many years before the typical clinical picture develops and involves multiple pathophysiological mechanisms. Since the pathophysiology of AD is multifactorial, it is not surprising that all attempts done to modify the disease course with drugs directed towards a single therapeutic target have been unsuccessful. Thus, combined modality therapy, using multiple drugs with a single mechanism of action or multi-target drugs, appears as the most promising strategy for both effective AD therapy and prevention. Cerebrolysin, acting as a multitarget peptidergic drug with a neurotrophic mode of action, exerts long-lasting therapeutic effects on AD that could reflect its potential utility for disease modification. Clinical trials demonstrated that Cerebrolysin is safe and efficacious in the treatment of AD, and may enhance and prolong the efficacy of cholinergic drugs, particularly in moderate to advanced AD patients. In this review, we summarize advances of therapeutic relevance in the pathogenesis and the biomarkers of AD, paying special attention to neurotrophic factors, and present results of preclinical and clinical investigations with Cerebrolysin in AD.

Association between transactive response DNA-binding protein of 43 kDa type and cognitive resilience to Alzheimer's disease: a case-control study

Association between the transactive response DNA-binding protein of 43 kDa (TDP-43), its newly described types (type α/type β), and resilience to Alzheimer's disease neuropathological change (ADNC) defined as preservation of normal cognitive functioning despite advanced ADNC has been evaluated in this case-control study of 63 older adults. Twenty-one resilient to ADNC individuals were matched 1:2 to nonresilient (Alzheimer's dementia) using propensity scores, accounting for age at death, neuritic plaque density, and neurofibrillary tangle stage. Resilient and matched nonresilient participants were similar in terms of gender, apolipoprotein E ε4 carriership, education, occupation, AD, and other pathologies. Resilient participants had lower frequency of TDP-43 co-pathology compared to nonresilient (19% vs. 62%, p = 0.002). Among TDP-43-positive cases, TDP-43 type α inclusions were absent in resilient to ADNC participants and were dominant in matched nonresilient cases (65%, p = 0.03). TDP-43 and TDP-43 types appear to be one of the key pathological determinants of loss of cognitive resilience to ADNC and hence are important in the understanding of the clinical expression of ADNC.

Association of years to parent's sporadic onset and risk factors with neural integrity and Alzheimer biomarkers

OBJECTIVE

To evaluate the hypothesis that proximity to parental age at onset (AAO) in sporadic Alzheimer disease (AD) is associated with greater AD and neural injury biomarker alterations during midlife and to assess the role of nonmodifiable and modifiable factors.

METHODS

This observational study included 290 cognitively unimpaired (CU) participants with a family history (FH) of clinically diagnosed sporadic AD (age 49-73 years) from the Alzheimer's and Families (ALFA) study. [¹⁸F]flutemetamol-PET standardized uptake value ratios, CSF β-amyloid_42/40 ratio, and phosphorylated tau were used as AD biomarkers. Hippocampal volumes and CSF total tau were used as neural injury biomarkers. Mental and vascular health proxies were calculated. In multiple regression models, we assessed the effect of proximity to parental AAO and its interaction with age on AD and neural injury biomarkers. Then, we evaluated the effects of FH load (number of parents affected), sex, APOE ε4, education, and vascular and mental health.

RESULTS

Proximity to parental AAO was associated with β-amyloid, but not with neural injury biomarkers, and interacted with sex and age, showing that women and older participants had increased β-amyloid. FH load and APOE ε4 showed independent contributions to β-amyloid load. Education and vascular and mental health proxies were not associated with AD biomarkers. However, lower mental health proxies were associated with decreased hippocampal volumes with age.

CONCLUSION

The identification of the earliest biomarker changes and modifiable factors to be targeted in early interventions is crucial for AD prevention. Proximity to parental AAO may offer a timeline for detection of incipient β-amyloid changes in women. In risk-enriched middle-aged cohorts, mental health may be a target for early interventions.

CLINICALTRIALSGOV IDENTIFIER

NCT02485730.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that in CU adults with FH of sporadic AD, proximity to parental AAO was associated with β-amyloid but not with neural injury biomarkers.

Centenarians as Models of Resistance and Resilience to Alzheimer's Disease and Related Dementias

The majority of research to understand the pathogenesis of and contributors to Alzheimer’s disease (AD) pathology, dementia, and disease progression has focused on studying individuals who have the disease or are at increased risk of having the disease. Yet there may be much to learn from individuals who have a paradoxical decreased risk of AD suggesting underlying protective factors. Centenarians demonstrate exceptional longevity that for a subset of the cohort is associated with an increased health span characterized by the delay or escape of age-related diseases including dementia. Here, I give evidence of the association of exceptional longevity with resistance and resilience to AD and describe how cohorts of centenarians and their offspring may serve as models of neuroprotection from AD. Discoveries of novel genetic, environmental, and behavioral factors that are associated with a decreased risk of AD may inform the development of interventions to slow or prevent AD in the general population. Centenarian cohorts may also be instrumental in serving as controls to individuals with AD to identify additional risk factors.

Better stress coping associated with lower tau in amyloid-positive cognitively unimpaired older adults

OBJECTIVE

Research in animals has shown that chronic stress exacerbates tau pathology. In humans, psychological stress has been associated with higher risk of Alzheimer disease clinical syndrome. The objective of this cross-sectional study was to assess the hypothesis that stress coping ability (assessed via the Brief Resilience Scale [BRS]) is associated with tau burden and to evaluate whether these associations differed by sex and amyloid status (A+/A-) in cognitively unimpaired (CU) older adults.

METHODS

We included 225 CU participants (mean age 70.4 ± 10.2 years, 48% female) enrolled in the population-based Mayo Clinic Study of Aging who completed the BRS and underwent amyloid-PET (Pittsburgh compound B-PET) and tau-PET (AV1451-PET). We fitted multiple regression and analysis of covariance models to assess the associations between BRS and tau-PET and the interaction with amyloid status and sex. We focused on entorhinal cortex (ERC) tau burden and also performed voxel-wise analyses. Age, sex, education, depression, and anxiety were considered as covariates.

RESULTS

Higher stress coping ability was associated with lower tau burden in the medial temporal lobe (including ERC) and occipito-temporal and cuneal/precuneal cortices. The association was present in both A+ and A- but weaker in A- CU older adults. There was an interaction between amyloid status and stress coping ability that was restricted to the medial temporal lobe tau such that A+ CU older adults with lower stress coping abilities showed higher tau. There were no significant interactions between stress coping and sex.

CONCLUSIONS

A faster termination of the stress response (higher coping ability) may limit the negative effects of stress on tau deposition. Conversely, lower stress coping ability may be an early sign of accumulating tau pathology. Longitudinal studies are warranted to clarify whether stress mechanisms act to exacerbate tau pathology or tau influences stress-related brain mechanisms and lowers the ability to cope with stress.

Improving the resistance and resilience framework for aging and dementia studies

Background

The "resistance vs resilience" to Alzheimer’s disease (AD) framework (coping vs avoiding) has gained interest in the field in the last year. In this viewpoint, our effort is (i) to provide clarity to the usage of the framework in the context of the ATN (amyloid/tau/neurodegeneration) system as well as in lifespan and cognitive aging studies and (ii) to discuss the challenges of matching these concepts to specific biological mechanisms.

Main body

In the context of the ATN system, the main goal of the resistance vs resilience framework is to make a fundamental distinction between risk factors that may help halt the development of AD pathologies (AT) (“resistance”) vs delay processes downstream to AT, i.e., neurodegeneration (N) and the clinical expression of the disease (“resilience”). The process of resilience in dementia and aging research should be envisioned as a process that is developed over the lifespan. Greater neurobiological capital to start with (initial brain reserve), maintaining brain structure and function (brain maintenance), or greater adaptability of cognitive strategies to perform a task (cognitive reserve) could all contribute to higher resilience to pathologies later in life. Simply put, resilience is not only a response to pathological processes (i.e. increased brain function to compensate for increasing AD pathology) but also reflects individual differences in brain structure and function that can be built over the lifespan (e.g., through education, lifetime cognitive, and physical activities). Further, the resistance vs resilience terminology can be extended to study other pathological processes such as cerebrovascular lesions, Lewy body disease, or TDP-43. However, some challenges do exist: (i) when studying multiple neuropathologies, the study design and framework will drive the usage of terminology; (ii) it is unavoidable that the measurements of resilience (brain structure and function) will reflect both the effect of pathologies and the impact of several risk and protective factors throughout the lifespan. Therefore, identifying resilience brain markers across lifespan, aging, and dementia studies, notably with longitudinal study designs, will be an important step towards understanding mechanisms of action.

Conclusions

While the field advances towards consensus definitions of existing concepts, the resistance vs resilience terminology may provide clarity in the communication of results in aging and dementia studies as well as provide a framework for the development of both hypotheses and study designs.

Biological subtypes of Alzheimer disease: A systematic review and meta-analysis

OBJECTIVE

To test the hypothesis that distinct subtypes of Alzheimer disease (AD) exist and underlie the heterogeneity within AD, we conducted a systematic review and meta-analysis on AD subtype studies based on postmortem and neuroimaging data.

METHODS

EMBASE, PubMed, and Web of Science databases were consulted until July 2019.

RESULTS

Neuropathology and neuroimaging studies have consistently identified 3 subtypes of AD based on the distribution of tau-related pathology and regional brain atrophy: typical, limbic-predominant, and hippocampal-sparing AD. A fourth subtype, minimal atrophy AD, has been identified in several neuroimaging studies. Typical AD displays tau-related pathology and atrophy both in hippocampus and association cortex and has a pooled frequency of 55%. Limbic-predominant, hippocampal-sparing, and minimal atrophy AD had a pooled frequency of 21%, 17%, and 15%, respectively. Between-subtype differences were found in age at onset, age at assessment, sex distribution, years of education, global cognitive status, disease duration, APOE ε4 genotype, and CSF biomarker levels.

CONCLUSION

We identified 2 core dimensions of heterogeneity: typicality and severity. We propose that these 2 dimensions determine individuals' belonging to one of the AD subtypes based on the combination of protective factors, risk factors, and concomitant non-AD brain pathologies. This model is envisioned to aid with framing hypotheses, study design, interpretation of results, and understanding mechanisms in future subtype studies. Our model can be used along the A/T/N classification scheme for AD biomarkers. Unraveling the heterogeneity within AD is critical for implementing precision medicine approaches and for ultimately developing successful disease-modifying drugs for AD.

Reserve in Alzheimer's disease: update on the concept, functional mechanisms and sex differences

PURPOSE OF REVIEW

Epidemiological evidence suggests that higher reserve significantly delays the dementia onset in Alzheimer's disease. Yet, confusion in terminology of reserve and related concepts exists and the lack of quantitative measures and unclear neural substrates of reserve have hampered progress. We review here the latest advances in the concept, measures and functional brain mechanisms of reserve, as well as their moderating factors including sex and gender.

RECENT FINDINGS

The definition of reserve has been revised towards a more simplified concept, and the development of quantitative measurements of a cognitive advantage in disease has been advanced. Functional MRI and FDG-PET studies have provided for the first time converging evidence for the involvement of the cognitive control and salience network and temporal pole in reserve. Women tend to show lower resilience than men at advanced stages of AD.

SUMMARY

Neuroimaging studies have provided substantial evidence for putative brain mechanisms supporting reserve in Alzheimer's disease. However, the findings are still somewhat disparate and call for the development of unifying and testable theory of functional and structural brain properties that subserve reserve. Sex differences emerged as a moderating factor of reserve in Alzheimer's disease and need to be made a major research focus in Alzheimer's disease.

Longitudinal Maintenance of Cognitive Health in Centenarians in the 100-plus Study

IMPORTANCE

Some individuals who reach ages beyond 100 years in good cognitive health may be resilient against risk factors associated with cognitive decline. Exploring the processes underlying resilience may contribute to the development of therapeutic strategies that help to maintain cognitive health while aging.

OBJECTIVE

To identify individuals who escape cognitive decline until extreme ages and to investigate the prevalence of associated risk factors.

DESIGN, SETTING, AND PARTICIPANTS

The 100-plus Study is a prospective observational cohort study of community-based Dutch centenarians enrolled between 2013 and 2019 who were visited annually until death or until participation was no longer possible. The centenarians self-reported their cognitive health, as confirmed by a proxy. Of the 1023 centenarians approached for study inclusion, 340 fulfilled the study criteria and were included in analyses. Data analysis was performed from April 2019 to December 2019.

MAIN OUTCOMES AND MEASURES

Cognition was assessed using the Mini-Mental State Examination (MMSE). To identify centenarians who escape cognitive decline, this study investigated the association of baseline cognition with survivorship and cognitive trajectories for at least 2 years of follow-up using linear mixed models, adjusted for sex, age, and education. This study investigated the prevalence of apolipoprotein E (APOE) genotypes and cardiovascular disease as risk factors associated with cognitive decline.

RESULTS

At baseline, the median age of 340 centenarians was 100.5 years (range, 100.0-108.2 years); 245 participants (72.1%) were female. The maximum survival estimate plateaued at 82% per year (95% CI, 77% to 87%) across centenarians who scored 26 to 30 points on the baseline MMSE (hazard ratio, 0.56; 95% CI, 0.42 to 0.75; P < .001), suggesting that an MMSE score of 26 or higher is representative of both cognitive and physical health. Among the 79 centenarians who were followed up for 2 years or longer, those with baseline MMSE score less than 26 experienced a decline in MMSE score of 1.68 points per year (95% CI, -2.45 to -0.92 points per year; P = .02), whereas centenarians with MMSE scores of 26 or higher at baseline experienced a decline of 0.71 point per year (95% CI, -1.08 to -0.35 points per year). For 73% of the centenarians with baseline MMSE scores of 26 or higher, no cognitive changes were observed, which often extended to ensuing years or until death. It is estimated that this group is representative of less than 10% of Dutch centenarians. In this group, 18.6% carried at least 1 APOE-ε4 allele, compared with 5.6% of the centenarians with lower and/or declining cognitive performance.

CONCLUSIONS AND RELEVANCE

Most centenarians who scored 26 or higher on the MMSE at baseline maintained high levels of cognitive performance for at least 2 years, in some cases despite the presence of risk factors associated with cognitive decline. Investigation of this group might reveal the processes underlying resilience against risk factors associated with cognitive decline.

Brain imaging measurements of fibrillar amyloid-β burden, paired helical filament tau burden, and atrophy in cognitively unimpaired persons with two, one, and no copies of the APOE ε4 allele

INTRODUCTION

We previously characterized associations between brain imaging measurements of amyloid-β (Aβ) plaque burden and apolipoprotein E (APOE) ε4 gene dose in a small number of cognitively unimpaired late-middle-aged APOE ε4 homozygotes (HMs), heterozygotes (HTs), and noncarriers (NCs). We now characterize cross-sectional Aβ plaque, tau tangle, and cortical atrophy (neurodegeneration) measurements, classifications, and associations with age in a larger number of unimpaired HMs, HTs, and NCs over a wider age range.

METHODS

We analyzed ¹¹ C Pittsburgh compound B (Aβ) positron emission tomography (PET), flortaucipir (tau) PET, and volumetric magnetic resonance imaging data from 164 study participants of age 47-86 years, including 26 APOE ε4 HMs, 48 HTs, and 90 NCs matched for age and sex.

RESULTS

Aβ PET measurements rose, plateaued at the respective ages of 68 and 76, and then declined with age in unimpaired HM and HT groups. Compared with NCs, these two groups began to have significantly higher Aβ PET measurements at ages 62 and 70, respectively, and no longer had significantly higher measurements by ages 71 and 78, respectively. They began to have significantly higher entorhinal cortex tau PET measurements at ages 66 and 70, respectively, and no longer had significantly higher measurements by ages 74 and 78, respectively. Brain atrophy measurements tended to decline slowly with age in all three genetic groups. Their elevated tau PET measurements were attributable to those with positive Aβ PET scans. 41.0%, 18.0%, and 5.0% of the 47- to 70-year-old HMs, HTs, and NCs and 25.0%, 79.0%, and 38.0% of the 71- to 86-year-old HMs, HTs, and NCs had positive Aβ PET scans, and the long-term recall memory scores are significantly higher in the older HMs than in HT and NC groups, suggesting resistance to Aβ deposition in those HMs who remained unimpaired at older ages.

CONCLUSIONS

This study provides information about Aβ plaque burden, tau tangle burden, and neurodegeneration in cognitively unimpaired persons at three levels of genetic risk for AD. Unimpaired APOE ε4 HMs can be studied before their 70s to evaluate the understanding of factors, processes, and interventions involved in the predisposition to and prevention of AD, and after their 70s, to discover factors, processes, and interventions involved in the resilience or resistance to and prevention of AD.

CRJ, Knopman DS, Vemuri P. Relationship Between Risk Factors and Brain Reserve in Late Middle Age: Implications for Cognitive Aging

Background

Brain reserve can be defined as the individual variation in the brain structural characteristics that later in life are likely to modulate cognitive performance. Late midlife represents a point in aging where some structural brain imaging changes have become manifest but the effects of cognitive aging are minimal, and thus may represent an ideal opportunity to determine the relationship between risk factors and brain imaging biomarkers of reserve.

Objective

We aimed to assess neuroimaging measures from multiple modalities to broaden our understanding of brain reserve, and the late midlife risk factors that may make the brain vulnerable to age related cognitive disorders.

Methods

We examined multimodal [structural and diffusion Magnetic Resonance Imaging (MRI), FDG PET] neuroimaging measures in 50-65 year olds to examine the associations between risk factors (Intellectual/Physical Activity: education-occupation composite, physical, and cognitive-based activity engagement; General Health Factors: presence of cardiovascular and metabolic conditions (CMC), body mass index, hemoglobin A1c, smoking status (ever/never), CAGE Alcohol Questionnaire (>2, yes/no), Beck Depression Inventory score), brain reserve measures [Dynamic: genu corpus callosum fractional anisotropy (FA), posterior cingulate cortex FDG uptake, superior parietal cortex thickness, AD signature cortical thickness; Static: intracranial volume], and cognition (global, memory, attention, language, visuospatial) from a population-based sample. We quantified dynamic proxies of brain reserve (cortical thickness, glucose metabolism, microstructural integrity) and investigated various protective/risk factors.

Results

Education-occupation was associated with cognition and total intracranial volume (static measure of brain reserve), but was not associated with any of the dynamic neuroimaging biomarkers. In contrast, many general health factors were associated with the dynamic neuroimaging proxies of brain reserve, while most were not associated with cognition in this late middle aged group.

Conclusion

Brain reserve, as exemplified by the four dynamic neuroimaging features studied here, is itself at least partly influenced by general health status in midlife, but may be largely independent of education and occupation.

Cognitive reserve and rate of change in Alzheimer's and cerebrovascular disease biomarkers among cognitively normal individuals

We examined whether cognitive reserve (CR) impacts level of, or rate of change in, biomarkers of Alzheimer's disease (AD) and small-vessel cerebrovascular disease in >250 individuals who were cognitively normal and middle-aged and older at the baseline. The four primary biomarker categories commonly examined in studies of AD were measured longitudinally: cerebrospinal fluid measures of amyloid (A) and tau (T); cerebrospinal fluid and neuroimaging measures of neuronal injury (N); and neuroimaging measures of white matter hyperintensities (WMHs) to assess cerebrovascular pathology (V). CR was indexed by a composite score including years of education, reading, and vocabulary test performance. Higher CR was associated with lower levels of WMHs, particularly among those who subsequently progressed from normal cognition to MCI. CR was not associated with WMH trajectories. In addition, CR was not associated with either levels of, or rate of change in, A/T/N biomarkers. This may suggest that higher CR is associated with lifestyle factors that reduce levels of cerebrovascular disease, allowing individuals with higher CR to better tolerate other types of pathology.

Peripheral Maintenance of the Axis SIRT1-SIRT3 at Youth Level May Contribute to Brain Resilience in Middle-Aged Amateur Rugby Players

Physical exercise performed regularly is known to improve health and to reduce the risk of age-related diseases. Furthermore, there is some evidence of cognitive improvement in physically active middle-aged and older adults. We hypothesized that long-term physically active middle-aged men may have developed brain resilience that can be detected with the analysis of peripheral blood markers. We aimed to analyze the activation of pathways potentially modulated by physical activity in a cohort of healthy amateur rugby players (n = 24) and control subjects with low physical activity (n = 25) aged 45–65 years. We had previously reported neuropsychological improvement in immediate memory responses in the player group compared to the controls. Here, we tested the expression of selected genes of longevity, inflammation, redox homeostasis, and trophic signaling in whole blood mRNA. Analyses were also performed on blood samples of young (aged 15–25 years) control subjects with low physical activity (n = 21). Physical activity and other lifestyle factors were thoroughly recorded with standardized questionnaires. Interestingly, middle-aged control subjects showed lower levels of expression of SIRT1, SIRT3, CAT, and SOD1 than the young controls, although rugby players maintained the expression levels of these genes at a young-like level. Middle-aged players showed lower levels of IL1B than the non-physically active groups. However, there was a tendency towards a decrease in trophic and transduction factors in middle-aged groups as compared to the young controls. A statistical study of Spearman’s correlations supported a positive effect of sporting activity on memory and executive functions, and on peripheral gene expression of SIRT1, SIRT3 and downstream genes, in the middle-aged rugby players. Our results indicate that the SIRT1-SIRT3 axis, and associated neuroprotective signaling, may contribute to the anti-aging resilience of the brain mediated by physical exercise.

Amyloid, Vascular, and Resilience Pathways Associated with Cognitive Aging

OBJECTIVE

To investigate the multifactorial processes underlying cognitive aging based on the hypothesis that multiple causal pathways and mechanisms (amyloid, vascular, and resilience) influence longitudinal cognitive decline in each individual through worsening brain health.

METHODS

We identified 1,230 elderly subjects (aged ≥50 years) with an average of 4.9 years of clinical follow-up and with amyloid positron emission tomography, diffusion tensor imaging, and structural magnetic resonance imaging scans from the population-based Mayo Clinic Study of Aging. We examined imaging markers of amyloid and brain health (white matter microstructural integrity and cortical thinning), systemic vascular health preceding the imaging markers, and early to midlife intellectual enrichment to predict longitudinal cognitive trajectories. We used latent growth curve models for modeling longitudinal cognitive decline.

RESULTS

All the pathways (amyloid, vascular, resilience) converged through their effects on cortical thinning and worsening cognition and together explained patterns in cognitive decline. Resilience and vascular pathways (aging process, sex differences, education/occupation, and systemic vascular health) had significant impact on white matter microstructural integrity. Education/occupation levels contributed to white matter integrity through systemic vascular health. Worsening white matter integrity contributed to significant cortical thinning and subsequently longitudinal cognitive decline. Baseline amyloidosis contributed to a significant proportion of cognitive decline that accelerated with longer follow-up times, and its primary impact was through cortical thinning.

INTERPRETATION

We developed an integrated framework to help explain the dynamic and complex process of cognitive aging by considering key causal pathways. Such an approach is important for both better comprehension of cognitive aging processes and will aid in the development of successful intervention strategies. ANN NEUROL 2019;86:866-877.

Basal forebrain metabolism in Alzheimer's disease continuum: relationship with education

We analyzed education, as a proxy of cognitive reserve, and the cholinergic pathway in Alzheimer's disease (AD), to test the hypothesis that education might modulate the relationship between clinical symptoms and metabolic and structural changes in AD. We included 84 subjects and compared between diagnostic groups and different educational levels the glucose metabolism of basal forebrain (BFM) and volume of the basal forebrain, the major cholinergic structure, and hippocampus (HM) (and hippocampal volume), a relevant projection site for the basal forebrain. Correlations with the global cognitive status and education in the whole sample were also performed. Patients with AD dementia showed reduced basal forebrain volume, hippocampal volume, and HM compared with controls. In the whole group, the global cognitive status was positively correlated with BFM and HM. Among high-educated subjects, mild cognitive impairment showed higher BFM and HM in comparison to other diagnostic groups. Our results suggest that in mild cognitive impairment subjects with a higher educational level, cholinergic activity is upregulated and this appears to have a compensatory effect, which may be lost in later symptomatic stages.

Cognitive Reserve from the Perspective of Preclinical Alzheimer Disease: 2020 Update

The concept of cognitive reserve (CR) was proposed to account for the discrepancy between levels of brain pathologic process or damage and clinical and cognitive function. We provide a detailed review of prospective longitudinal studies that have investigated the interaction between CR and Alzheimer disease (AD) biomarkers on clinical and cognitive outcomes among individuals with normal cognition at baseline. Current evidence is consistent with the view that higher levels of CR are associated with a delay in the onset of symptoms of mild cognitive impairment and that there may be multiple pathways by which CR exerts its protective effects.

Hospitalization, Alzheimer's Disease and Related Neuropathologies, and Cognitive Decline

Objective

To test the hypothesis that Alzheimer's disease and related neuropathologies contribute to the association between hospitalization and cognitive decline in old age.

Methods

As part of a longitudinal clinical–pathologic cohort study, 526 older persons (mean age at death = 90.9 years, 71% female) without dementia at baseline completed annual cognitive testing and were autopsied at death. Hospitalization information was obtained from linked Medicare claims records. Neuropathologic examination assessed β‐amyloid burden, tau tangle density, neocortical Lewy bodies, hippocampal sclerosis, chronic gross and microscopic cerebral infarcts, and transactive response DNA binding protein 43 kDa.

Results

Over a mean of 5.1 years, a total of 1,383 hospitalizations occurred, and the mean annual rate of hospitalization was 0.5 (standard deviation = 0.6, median = 0.4). Higher rate of hospitalization was not directly related to higher burden for any of the neuropathologic markers. Higher rate of hospitalization was associated with more rapid cognitive decline (estimate = −0.042, standard error [SE] = 0.012, p < 0.001), and after controlling for all 7 neuropathologic markers, the association was essentially the same (estimate = −0.040, SE = 0.013, p = 0.002). In a multivariable model with 3‐way interactions of neuropathologic markers with hospitalization rate and time, the association between hospitalization rate and faster cognitive decline was greater in persons with more tangle pathology (estimate for interaction = −0.007, SE = 0.002, p = 0.002) and in persons with neocortical Lewy bodies (estimate for interaction = −0.117, SE = 0.042, p = 0.005).

Interpretation

Older persons with more hospitalizations experienced faster rates of cognitive decline, and this association was more pronounced in persons with more tau tangle density and with neocortical Lewy body pathologies. ANN NEUROL 2019;86:844–852

Latent class analysis identifies functional decline with Amsterdam IADL in preclinical Alzheimer's disease

Introduction

Trials in Alzheimer's disease (AD) now include participants at the earliest stages to prevent further decline. However, the lack of tools sensitive to subtle functional changes in early-stage AD hinders the development of new therapies as it is difficult to prove their clinical relevance.

Methods

We assessed functional changes over three years in 289 elderly memory complainers from the Investigation of Alzheimer's Predictors in subjective memory complainers cohort using the Amsterdam Instrumental-Activities-of-Daily-Living questionnaire (A-IADL-Q).

Results

No overall functional decline related to AD imaging markers was evidenced. However, five distinct classes of A-IADL-Q trajectories were identified. The largest class (212 [73.4%]) had stable A-IADL-Q scores over 3 years. A second group (23 [8.0%]) showed a persistent functional decline, higher amyloid load (P = .0005), and lower education (P = .0392).

Discussion

The A-IADL-Q identified a subtle functional decline in asymptomatic at-risk AD individuals. This could have important implications in the field of early intervention in AD.

Association of Apolipoprotein E ɛ4, Educational Level, and Sex With Tau Deposition and Tau-Mediated Metabolic Dysfunction in Older Adults

Importance

While amyloidosis is an early event in the Alzheimer disease (AD) biomarker cascade, a complex interplay among the apolipoprotein E (APOE) ɛ4 allele, educational levels, and sex may be associated with an individual's resilience to dementia.

Objective

To assess whether APOE ɛ4, educational levels, and sex are associated with regional tau deposition and tau-mediated metabolic dysfunction in older adults.

Design, Setting, and Participants

Population-based cohort study of individuals aged 65 years and older enrolled between January 1, 2004, and May 1, 2018, in the Mayo Clinic Study of Aging, a prospective longitudinal study of cognitive aging in Olmsted County, Minnesota.

Main Outcomes and Measures

The primary outcomes were cross-sectional tau burden and the fluorodeoxyglucose (FDG) to tau ratio (as a measure of tau-mediated metabolic dysfunction) assessed by positron emission tomography for 43 atlas-defined regions, with specific focus on the entorhinal, inferior temporal, and posterior cingulate cortices.

Exposures

Using linear regression, APOE ɛ4 status and years of education were the primary exposure variables, with sex additionally investigated through interaction models.

Results

The sample included 325 individuals (173 [53%] male; mean [SD] age, 76.1 [7.2] years; 291 [90%] cognitively unimpaired). Although APOE ɛ4 was nominally associated with higher tau deposition (β = 0.05 [95% CI, 0.02-0.09]; P = .001; Cohen d = 0.40) and lower FDG to tau ratio (β = -0.05 [95% CI, -0.08 to -0.01]; P = .008; Cohen d = 0.33) in the entorhinal cortex, these associations were completely attenuated after controlling for global amyloid burden. Education was not associated with regional tau burden or FDG to tau ratio. In the 3 regions of interest, global amyloid burden accounted for the largest proportion of variance in tau deposition among the candidate variables assessed. In the entorhinal cortex, significant interactions were identified between APOE ɛ4 and global amyloid burden on tau (β = 0.25; SE = 0.06; P < .001) and between sex and tau burden on FDG metabolism (β = 0.10; SE = 0.05; P = .049).

Conclusions and Relevance

These results suggest that (1) tau deposition is most significantly associated with amyloidosis; (2) in the presence of abundant amyloidosis, APOE ɛ4 may be associated with accelerated entorhinal cortex tau deposition; and (3) women may have lower resilience to tau, manifested by a higher degree of metabolic dysfunction in the entorhinal cortex in response to tau pathology.

Association of Lifespan Cognitive Reserve Indicator With Dementia Risk in the Presence of Brain Pathologies

IMPORTANCE

Evidence on the association of lifespan cognitive reserve (CR) with dementia is limited, and the strength of this association in the presence of brain pathologies is unknown.

OBJECTIVE

To examine the association of lifespan CR with dementia risk, taking brain pathologies into account.

DESIGN, SETTING, AND PARTICIPANTS

This study used data from 2022 participants in the Rush Memory and Aging Project, an ongoing community-based cohort study with annual follow-up from 1997 to 2018 (mean follow-up, 6 years; maximum follow-up, 20 years). After excluding 420 individuals who had prevalent dementia, missing data on CR, or dropped out, 1602 dementia-free adults were identified at baseline and evaluated to detect incident dementia. During follow-up, 611 died and underwent autopsies. Data were analyzed from May to September 2018.

EXPOSURES

Information on CR factors (education; early-life, midlife, and late-life cognitive activities; and social activities in late life) was obtained at baseline. Based on these factors, lifespan CR scores were captured using a latent variable from a structural equation model and was divided into tertiles (lowest, middle, and highest).

MAIN OUTCOMES AND MEASURES

Dementia was diagnosed following international criteria. Neuropathologic evaluations for Alzheimer disease and other brain pathologies were performed in autopsied participants. The association of lifespan CR with dementia or brain pathologies was estimated using Cox regression models or logistic regression.

RESULTS

Of the 1602 included participants, 1216 (75.9%) were women, and the mean (SD) age was 79.6 (7.5) years. During follow-up, 386 participants developed dementia (24.1%), including 357 participants with Alzheimer disease-related dementia (22.3%). The multiadjusted hazards ratios (HRs) of dementia were 0.77 (95% CI, 0.59-0.99) for participants in the middle CR score tertile and 0.61 (95% CI, 0.47-0.81) for those in the highest CR score tertile compared with those in the lowest CR score tertile. In autopsied participants, CR was not associated with most brain pathologies, and the association of CR with dementia remained significant after additional adjustment for brain pathologies (HR, 0.60; 95% CI, 0.42-0.86). The highest CR score tertile was associated with a reduction in dementia risk, even among participants with high Alzheimer disease pathology (HR, 0.57; 95% CI, 0.37-0.87) and any gross infarcts (HR, 0.34; 95% CI, 0.18-0.62).

CONCLUSIONS AND RELEVANCE

High lifespan CR is associated with a reduction in dementia risk, even in the presence of high brain pathologies. Our findings highlight the importance of lifespan CR accumulation in dementia prevention.

Combining non-invasive brain stimulation with functional magnetic resonance imaging to investigate the neural substrates of cognitive aging

As aging population is increasing, new methodologies to apprehend and enhance the mechanisms related to optimal brain function in advancing age become urgent. This review describes how the combined use of non-invasive brain stimulation (NIBS) with functional magnetic resonance imaging (fMRI) provides novel experimental data on the putative neurophysiological mechanisms underlying inter-individual differences in cognitive status among older adults, also further illuminating our understanding of theoretical models proposed within the cognitive neuroscience of aging literature. In addition, it explores published evidence of how this combined procedure entails the capacity to modify the activity and connectivity of specific brain networks in older adults, potentially leading to improvements in cognitive function and other measures reflecting mental health status. Although additional research is needed, combining NIBS with fMRI might provide innovative understanding of how fundamental brain plasticity mechanisms operate in advancing age, a knowledge that may be eventually used to refine more individually tailored approaches to promote brain health in aged populations.

Hypothesis: cerebrospinal fluid protein markers suggest a pathway toward symptomatic resilience to AD pathology

INTRODUCTION

We sought biological pathways that explained discordance between Alzheimer's disease (AD) pathology and symptoms.

METHODS

In 306 Alzheimer's Disease Neuroimaging Initiative (ADNI)-1 participants across the AD clinical spectrum, we investigated association between cognitive outcomes and 23 cerebrospinal fluid (CSF) analytes associated with abnormalities in the AD biomarkers amyloid β_1-42 and total-tau. In a 200-person "training" set, Least Absolute Shrinkage and Selection Operator regression estimated model weights for the 23 proteins, and for the AD biomarkers themselves, as predictors of ADAS-Cog₁₁ scores. In the remaining 106 participants ("validation" set), fully adjusted regression models then tested the Least Absolute Shrinkage and Selection Operator-derived models and a related protein marker summary score as predictors of ADAS-Cog₁₁, ADNI diagnostic category, and longitudinal cognitive trajectory.

RESULTS

AD biomarkers alone explained 26% of the variance in validation set cognitive scores. Surprisingly, the 23 AD-related proteins explained 31% of this variance. The biomarkers and protein markers appeared independent in this respect, jointly explaining 42% of test score variance. The composite protein marker score also predicted ADNI diagnosis and subsequent cognitive trajectory. Cognitive outcome prediction redounded principally to ten markers related to lipid or vascular functions or to microglial activation or chemotaxis. In each analysis, apoE protein and four markers in the latter immune-activation group portended better outcomes.

DISCUSSION

CSF markers of vascular, lipid-metabolic and immune-related functions may explain much of the disjunction between AD biomarker abnormality and symptom severity. In particular, our results suggest the hypothesis that innate immune activation improves cognitive outcomes in persons with AD pathology. This hypothesis should be tested by further study of cognitive outcomes related to CSF markers of innate immune activation.

Early Secure Attachment as a Protective Factor Against Later Cognitive Decline and Dementia

The etiology of neurodegenerative disorders such as dementia is complex and incompletely understood. Interest in a developmental perspective to these pathologies is gaining momentum. An early supportive social environment seems to have important implications for social, affective and cognitive abilities across the lifespan. Attachment theory may help to explain the link between these early experiences and later outcomes. This theory considers early interactions between an infant and its caregiver to be crucial to shaping social behavior and emotion regulation strategies throughout adult life. Furthermore, research has demonstrated that such early attachment experiences can, potentially through epigenetic mechanisms, have profound neurobiological and cognitive consequences. Here we discuss how early attachment might influence the development of affective, cognitive, and neurobiological resources that could protect against cognitive decline and dementia. We argue that social relations, both early and late in life, are vital to ensuring cognitive and neurobiological health. The concepts of brain and cognitive reserve are crucial to understanding how environmental factors may impact cognitive decline. We examine the role that attachment might play in fostering brain and cognitive reserve in old age. Finally, we put forward the concept of affective reserve, to more directly frame the socio-affective consequences of early attachment as protectors against cognitive decline. We thereby aim to highlight that, in the study of aging, cognitive decline and dementia, it is crucial to consider the role of affective and social factors such as attachment.

Left frontal connectivity attenuates the adverse effect of entorhinal tau pathology on memory

OBJECTIVE

To investigate whether higher global left frontal cortex (gLFC) connectivity, a putative neural substrate of cognitive reserve, attenuates the effect of entorhinal tau PET levels on episodic memory in older adults.

METHODS

Cross-sectional ¹⁸F-AV-1451 PET (to assess tau pathology), ¹⁸F-AV-45 or ¹⁸F-BAY94-9172 PET (to assess β-amyloid [Aβ]), and resting-state fMRI were obtained in 125 elderly participants from the Alzheimer's Neuroimaging Initiative, including 82 cognitively normal participants (amyloid PET-positive [Aβ+], n = 27) and 43 patients with amnestic mild cognitive impairment (Aβ+ = 15). Resting-state fMRI gLFC connectivity was computed for each participant as the average functional connectivity between the left frontal cortex (LFC) (seed) and each remaining voxel in the gray matter. As a measure of tau pathology, we assessed the mean tau PET uptake in the entorhinal cortex. In linear mixed-effects regression analysis, we tested the interaction term gLFC connectivity × entorhinal tau PET on delayed free recall performance. In addition, we assessed whether higher connectivity of the whole frontoparietal control network (FPCN), of which the LFC is a major hub, is associated with reserve.

RESULTS

Higher entorhinal tau PET was strongly associated with poorer delayed free recall performance (β/SE = -0.49/0.07, p < 0.001). A significant gLFC connectivity × entorhinal tau PET interaction was found (β/SE = 0.19/0.06, p = 0.003), such that at higher levels of gLFC connectivity, the decrease in memory score per unit of entorhinal tau PET was attenuated. The FPCN connectivity × tau interaction was also significant (β/SE = 0.10/0.04, p = 0.012).

CONCLUSION

Both gLFC and FPCN connectivity are associated with higher resilience against the adverse effect of early-stage entorhinal tau pathology on memory performance.

Refining the PoinTER “human firewall” pentesting framework

Purpose

Penetration tests have become a valuable tool in the cyber security defence strategy in terms of detecting vulnerabilities. Although penetration testing has traditionally focussed on technical aspects, the field has started to realise the importance of the human in the organisation, and the need to ensure that humans are resistant to cyberattacks. To achieve this, some organisations “pentest” their employees, testing their resilience and ability to detect and repel human-targeted attacks. In a previous paper, the authors reported on PoinTER (Prepare TEst Remediate), a human pentesting framework, tailored to the needs of SMEs. This paper aims to propose improvements to refine the framework. The improvements are based on a derived set of ethical principles that have been subjected to ethical scrutiny

Design/methodology/approach

The authors conducted a systematic literature review of academic research, a review of actual hacker techniques, industry recommendations and official body advice related to social engineering techniques. To meet the requirements to have an ethical human pentesting framework, the authors compiled a list of ethical principles from the research literature which they used to filter out techniques deemed unethical.

Findings

Drawing on social engineering techniques from academic research, reported by the hacker community, industry recommendations and official body advice and subjecting each technique to ethical inspection, using a comprehensive list of ethical principles, the authors propose the refined GDPR-compliant and privacy respecting PoinTER framework. The list of ethical principles, as suggested, could also inform ethical technical pentests.

Originality/value

Previous work has considered penetration testing humans, but few have produced a comprehensive framework such as PoinTER. PoinTER has been rigorously derived from multiple sources and ethically scrutinised through inspection, using a comprehensive list of ethical principles derived from the research literature.

Level of education mitigates the impact of tau pathology on neuronal function

PURPOSE

Using PET imaging in a group of patients with Alzheimer's disease (AD), we investigated whether level of education, a proxy for resilience, mitigates the harmful impact of tau pathology on neuronal function.

METHODS

We included 38 patients with mild-to-moderate AD (mean age 67 ± 7 years, mean MMSE score 24 ± 4, mean years of education 14 ± 4; 20 men, 18 women) in whom a [¹⁸F]AV-1451 scan (a measure of tau pathology) and an [¹⁸F]FDG scan (a measure of neuronal function) were available. The preprocessed PET scans were z-transformed using templates for [¹⁸F]AV-1451 and [¹⁸F]FDG from healthy controls, and subsequently thresholded at a z-score of ≥3.0, representing an one-tailed p value of 0.001. Next, three volumes were computed in each patient: the tau-specific volume (tau pathology without neuronal dysfunction), the FDG-specific volume (neuronal dysfunction without tau pathology), and the overlap volume (tau pathology and neuronal dysfunction). Mean z-scores and volumes were extracted and used as dependent variables in regression analysis with years of education as predictor, and age and MMSE score as covariates.

RESULTS

Years of education were positively associated with tau-specific volume (β = 0.362, p = 0.022), suggesting a lower impact of tau pathology on neuronal function in patients with higher levels of education. Concomitantly, level of education was positively related to tau burden in the overlap volume (β = 0.303, p = 0.036) implying that with higher levels of education more tau pathology is necessary to induce neuronal dysfunction.

CONCLUSION

In patients with higher levels of education, tau pathology is less paralleled by regional and remote neuronal dysfunction. The data suggest that early life-time factors such as level of education support resilience mechanisms, which ameliorate AD-related effects later in life.

Resistance and resilience to Alzheimer's disease pathology are associated with reduced cortical pTau and absence of limbic-predominant age-related TDP-43 encephalopathy in a community-based cohort

Alzheimer's disease neuropathologic change (ADNC) is defined by progressive accumulation of β-amyloid plaques and hyperphosphorylated tau (pTau) neurofibrillary tangles across diverse regions of brain. Non-demented individuals who reach advanced age without significant ADNC are considered to be resistant to AD, while those burdened with ADNC are considered to be resilient. Understanding mechanisms underlying ADNC resistance and resilience may provide important clues to treating and/or preventing AD associated dementia. ADNC criteria for resistance and resilience are not well-defined, so we developed stringent pathologic cutoffs for non-demented subjects to eliminate cases of borderline pathology. We identified 14 resistant (85+ years old, non-demented, Braak stage ≤ III, CERAD absent) and 7 resilient (non-demented, Braak stage VI, CERAD frequent) individuals out of 684 autopsies from the Adult Changes in Thought study, a long-standing community-based cohort. We matched each resistant or resilient subject to a subject with dementia and severe ADNC (Braak stage VI, CERAD frequent) by age, sex, year of death, and post-mortem interval. We expanded the neuropathologic evaluation to include quantitative approaches to assess neuropathology and found that resilient participants had lower neocortical pTau burden despite fulfilling criteria for Braak stage VI. Moreover, limbic-predominant age-related TDP-43 encephalopathy neuropathologic change (LATE-NC) was robustly associated with clinical dementia and was more prevalent in cases with high pTau burden, supporting the notion that resilience to ADNC may depend, in part, on resistance to pTDP-43 pathology. To probe for interactions between tau and TDP-43, we developed a C. elegans model of combined human (h) Tau and TDP-43 proteotoxicity, which exhibited a severe degenerative phenotype most compatible with a synergistic, rather than simply additive, interaction between hTau and hTDP-43 neurodegeneration. Pathways that underlie this synergy may present novel therapeutic targets for the prevention and treatment of AD.

Subthreshold amyloid and its biological and clinical meaning: Long way ahead

The development of in vivo imaging of the pathologic hallmark of Alzheimer disease (AD), β-amyloid (Aβ), altered the framing of its pathophysiology and formulation of inclusion criteria for clinical trials. Recent evidence suggests that in vivo measures of Aβ deposition below a threshold indicative of Aβ positivity carry critical information on future cognitive decline and accumulation of AD pathology, potentially already at a younger age. Here, we integrate the existing literature on histopathology of Aβ and its convergence and divergence with in vivo Aβ imaging. The evidence presented amounts to a reconceptualization, in which we advocate for a closer look into Aβ accumulation rates in earlier life, the factors that promote accumulation, comparative studies with different markers of Aβ, and longitudinal designs to elucidate when AD pathology rises and how it shifts from benign to malignant stages that ultimately define AD. These efforts open a new window of opportunity for disease-modifying interventions.

Reframing Alzheimer's Disease: Guided by a New Research Framework, the Field is Poised For Greater Precision and Promising Horizons

This in-depth article on the sixth leading cause of death in the U.S. reports on the optimism of cutting-edge leaders in Alzheimer's disease research. The author examines key considerations such as the status of biomarker tests, and the search for new biomarkers; securing an accurate definition of the disease; risk factors; clinical trials and non-pharmacological studies.

The metabolic brain signature of cognitive resilience in the 80+: beyond Alzheimer pathologies

Research into cognitive resilience imaging markers may help determine the clinical significance of Alzheimer's disease pathology among older adults over 80 years (80+). In this study, we aimed to identify a fluorodeoxyglucose (FDG)-PET based imaging marker of cognitive resilience. We identified 457 participants ≥ 80 years old (357 cognitively unimpaired, 118 cognitively impaired at baseline, mean age of 83.5 ± 3.2 years) from the population-based Mayo Clinic Study of Aging (MCSA) with baseline MRI, Pittsburgh compound B-PET and FDG-PET scans and neuropsychological evaluation. We identified a subset of 'resilient' participants (cognitively stable 80+, n = 192) who maintained normal cognition for an average of 5 years (2-10 years). Global PIB ratio, FDG-PET ratio and cortical thickness from Alzheimer's disease signature regions were used as Alzheimer's disease imaging biomarker outcomes and global cognitive z-score was used as a cognitive outcome. First, using voxel-wise multiple regression analysis, we identified the metabolic areas underlying cognitive resilience in cognitively stable 80+ participants, which we call the 'resilience signature'. Second, using multivariate linear regression models, we evaluated the association of risk and protective factors with the resilience signature and its added value for predicting global cognition beyond established Alzheimer's disease imaging biomarkers in the full 80+ sample. Third, we evaluated the utility of the resilience signature in conjunction with amyloidosis in predicting longitudinal cognition using linear mixed effect models. Lastly, we assessed the utility of the resilience signature in an independent cohort using ADNI (n = 358, baseline mean age of 80 ± 3.8). Our main findings were: (i) FDG-PET uptake in the bilateral anterior cingulate cortex and anterior temporal pole was associated with baseline global cognition in cognitively stable 80+ (the resilience signature); (ii) established Alzheimer's disease imaging biomarkers did not predict baseline global cognition in this subset of participants; (iii) in the full MCSA 80+ and ADNI cohorts, amyloid burden and FDG-PET in the resilience signature were the stronger predictors of baseline global cognition; (iv) sex and systemic vascular health predicted FDG-PET in the resilience signature, suggesting vascular health maintenance as a potential pathway to preserve the metabolism of these areas; and (v) the resilience signature provided significant information about global longitudinal cognitive change even when considering amyloid status in both the MCSA and ADNI cohorts. The FDG-PET resilience signature may be able to provide important information in conjunction with other Alzheimer's disease biomarkers for the determination of clinical prognosis. It may also facilitate identification of disease targeting modifiable risk factors such as vascular health maintenance.