The protected survivor model: Using resistant successful cognitive aging to identify protection in the very old

Cognitive synaptopathy: synaptic and dendritic spine dysfunction in age-related cognitive disorders

Cognitive impairment is a leading component of several neurodegenerative and neurodevelopmental diseases, profoundly impacting on the individual, the family, and society at large. Cognitive pathologies are driven by a multiplicity of factors, from genetic mutations and genetic risk factors, neurotransmitter-associated dysfunction, abnormal connectomics at the level of local neuronal circuits and broader brain networks, to environmental influences able to modulate some of the endogenous factors. Otherwise healthy older adults can be expected to experience some degree of mild cognitive impairment, some of which fall into the category of subjective cognitive deficits in clinical practice, while many neurodevelopmental and neurodegenerative diseases course with more profound alterations of cognition, particularly within the spectrum of the dementias. Our knowledge of the underlying neuropathological mechanisms at the root of this ample palette of clinical entities is far from complete. This review looks at current knowledge on synaptic modifications in the context of cognitive function along healthy ageing and cognitive dysfunction in disease, providing insight into differential diagnostic elements in the wide range of synapse alterations, from those associated with the mild cognitive changes of physiological senescence to the more profound abnormalities occurring at advanced clinical stages of dementia. I propose the term "cognitive synaptopathy" to encompass the wide spectrum of synaptic pathologies associated with higher brain function disorders.

Neuropathologic Burden and Dementia in Nonagenarians and Centenarians: Comparison of 2 Community-Based Cohorts

BACKGROUND AND OBJECTIVES

The aim of this study was to compare 2 large clinicopathologic cohorts of participants aged 90+ and to determine whether the association between neuropathologic burden and dementia in these older groups differs substantially from those seen in younger-old adults.

METHODS

Autopsied participants from The 90+ Study and Adult Changes in Thought (ACT) Study community-based cohort studies were evaluated for dementia-associated neuropathologic changes. Associations between neuropathologic variables and dementia were assessed using logistic or linear regression, and the weighted population attributable fraction (PAF) per type of neuropathologic change was estimated.

RESULTS

The 90+ Study participants (n = 414) were older (mean age at death = 97.7 years) and had higher amyloid/tau burden than ACT <90 (n = 418) (mean age at death = 83.5 years) and ACT 90+ (n = 401) (mean age at death = 94.2 years) participants. The ACT 90+ cohort had significantly higher rates of limbic-predominant age-related TDP-43 encephalopathy (LATE-NC), microvascular brain injury (μVBI), and total neuropathologic burden. Independent associations between individual neuropathologic lesions and odds of dementia were similar between all 3 groups, with the exception of μVBI, which was associated with increased dementia risk in the ACT <90 group only (odds ratio 1.5, 95% CI 1.2-1.8, p < 0.001). Weighted PAF scores indicated that eliminating μVBI, although more prevalent in ACT 90+ participants, would have little effect on dementia. Conversely, eliminating μVBI in ACT <90 could theoretically reduce dementia at a similar rate to that of AD neuropathologic change (weighted PAF = 6.1%, 95% CI 3.8-8.4, p = 0.001). Furthermore, reducing LATE-NC in The 90+ Study could potentially reduce dementia to a greater degree (weighted PAF = 5.1%, 95% CI 3.0-7.3, p = 0.001) than either ACT cohort (weighted PAFs = 1.69, 95% CI 0.4-2.7).

DISCUSSION

Our results suggest that specific neuropathologic features may differ in their effect on dementia among nonagenarians and centenarians from cohorts with different selection criteria and study design. Furthermore, microvascular lesions seem to have a more significant effect on dementia in younger compared with older participants. The results from this study demonstrate that different populations may require distinct dementia interventions, underscoring the need for disease-specific biomarkers.

Conceptualizing healthy cognitive aging: the role of time and variability

The interest in healthy cognitive aging (HCA) has increased substantially over the past decade. Researchers are interested in exploring how health can be promoted and cognitive decline mitigated when pathology is not present. Identifying the necessary strategies is crucial as the gradual accumulation of small declines can lead to negative effects on quality of life over time. However, the conceptualization of HCA is not agreed upon. In fact, authors often turn to the use of traditional pathology screeners in the context of HCA because of their clear threshold results and their wide use in the different fields. This leads to the assumption that individuals are either cognitively unhealthy and therefore may have some form of dementia or are dementia-free and cognitively healthy. We believe that this view is an overly simplistic approach to the understanding of the aging process. In this work, we explore how HCA has been defined and conceptualized within the different fields. We further discuss how time and variability are key concepts that are often missing when studying HCA and propose a definition that aims to unify the findings from the multidisciplinary research that studies HCA and simplify the translation of knowledge. Incorporating these two novel dimensions to the study of HCA has already been proposed methodologically but has yet been discussed at the conceptual level. We believe that the proposed new approach will allow the identification of individual factors that cause changes in cognitive health and will help build new cognitive health strategies and mitigate further declines.

Limited evidence of a shared genetic relationship between C-reactive protein levels and cognitive function in older UK adults of European ancestry

Introduction

Previous studies have shown associations between cognitive function and C-reactive protein (CRP) levels in older adults. Few studies have considered the extent to which a genetic predisposition for higher CRP levels contributes to this association.

Methods

Data was analyzed from 7,817 UK participants aged >50 years as part of the PROTECT study, within which adults without dementia completed a comprehensive neuropsychological battery. We constructed a polygenic risk score (PRS-CRP) that explained 9.61% of the variance in serum CRP levels (p = 2.362 × 10-7) in an independent cohort. Regressions were used to explore the relationship between PRS-CRP and cognitive outcomes.

Results

We found no significant associations between PRS-CRP and any cognitive measures in the sample overall. In older participants (>62 years), we observed a significant positive association between PRS-CRP and self-ordered search score (i.e., spatial working memory).

Conclusion

Whilst our results indicate a weak positive relationship between PRS-CRP and spatial working memory that is specific to older adults, overall, there appears to be no strong effects of PRS-CRP on cognitive function.

Cancer and Vascular Comorbidity Effects on Dementia Risk and Neuropathology in the Oldest-Old

BACKGROUND

Dementia, vascular disease, and cancer increase with age, enabling complex comorbid interactions. Understanding vascular and cancer contributions to dementia risk and neuropathology in oldest-old may improve risk modification and outcomes.

OBJECTIVE

Investigate the contributions of vascular factors and cancer to dementia and neuropathology.

METHODS

Longitudinal clinicopathologic study of prospectively followed Mayo Clinic participants dying≥95 years-old who underwent autopsy. Participants were stratified by dementia status and compared according to demographics, vascular risk factors, cancer, and neuropathology.

RESULTS

Participants (n = 161; 83% female; 99% non-Hispanic whites)≥95 years (95-106 years-old) with/without dementia did not differ based on demographics. APOE ɛ2 frequency was higher in no dementia (20/72 [28%]) versus dementia (11/88 [12%]; p = 0.03), but APOE ɛ4 frequency did not differ. Coronary artery disease was more frequent in no dementia (31/72 [43%]) versus dementia (23/89 [26%]; p = 0.03) associated with 56% lower dementia odds (odds ratio [OR] = 0.44 [confidence interval (CI) = 0.19-0.98]; p = 0.04) and fewer neuritic/diffuse plaques. Diabetes had an 8-fold increase in dementia odds (OR = 8.42 [CI = 1.39-163]; p = 0.02). Diabetes associated with higher cerebrovascular disease (Dickson score; p = 0.05). Cancer associated with 63% lower dementia odds (OR = 0.37 [CI = 0.17-0.78]; p < 0.01) and lower Braak stage (p = 0.01).

CONCLUSION

Cancer exposure in the oldest-old was associated with lower odds of dementia and tangle pathology, whereas history of coronary artery disease was associated with lower odds of dementia and amyloid-β plaque pathology. History of diabetes mellitus was associated with increased odds of dementia and cerebrovascular disease pathology. Cancer-related mechanisms and vascular risk factor reduction strategies may alter dementia risk and neuropathology in oldest-old.

An accelerated degeneration of white matter microstructure and networks in the nondemented old-old

The nondemented old-old over the age of 80 comprise a rapidly increasing population group; they can be regarded as exemplars of successful aging. However, our current understanding of successful aging in advanced age and its neural underpinnings is limited. In this study, we measured the microstructural and network-based topological properties of brain white matter using diffusion-weighted imaging scans of 419 community-dwelling nondemented older participants. The participants were further divided into 230 young-old (between 72 and 79, mean = 76.25 ± 2.00) and 219 old-old (between 80 and 92, mean = 83.98 ± 2.97). Results showed that white matter connectivity in microstructure and brain networks significantly declined with increased age and that the declined rates were faster in the old-old compared with young-old. Mediation models indicated that cognitive decline was in part through the age effect on the white matter connectivity in the old-old but not in the young-old. Machine learning predictive models further supported the crucial role of declines in white matter connectivity as a neural substrate of cognitive aging in the nondemented older population. Our findings shed new light on white matter connectivity in the nondemented aging brains and may contribute to uncovering the neural substrates of successful brain aging.

Subjective views of aging in very old age: Predictors of 2-year change in gains and losses

This study examined trajectories of awareness of age-related change (AARC; Diehl & Wahl, 2010) across 2 years in a large representative sample of very old adults. We also examined the predictive role of health, functional status, cognitive functioning, and engagement with life for AARC change. The initial sample comprised 1,863 individuals aged 80 years or older. Of the 1,612 individuals recontacted 2 years later, 912 took part in the follow-up. Measures included the AARC-Short Form, assessing perceived AARC Gains and AARC Losses. Measures of multimorbidity and functional health, a cognitive screening test, and indicators of engagement with life (e.g., leisure activity) were examined as predictors of AARC change, using semi-cross-lagged fixed effects modeling. Higher overall levels of AARC Gains were observed compared to AARC Losses for all but respondents aged 90 years or older. Intra-individual levels of AARC Gains decreased significantly over the 2-year period, whereas a significant increase was found for AARC Losses. AARC Losses across time were predicted by loss of instrumental activities of daily living (IADL) independence, but not by change in multimorbidity, cognitive performance, or engagement with life. One indicator of engagement with life, reduced leisure activity, predicted smaller AARC Gains at wave 2. These results were robust in models controlling for potential reverse causation. These findings suggest that a significant increase in perceived AARC Losses appears to be an inherent characteristic of very old age. Very old age may be a stage in life in which changes in multimorbidity and cognitive performance no longer impact individuals' views on aging. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Genome-wide DNA methylation profiling in nonagenarians suggests an effect of PM20D1 in late onset Alzheimer's disease

Background

The aim of this study is to identify differentially methylated regions (DMRs) in the genomes of a sample of cognitively healthy individuals and a sample of individuals with LOAD, all of them nonagenarians from Costa Rica.

Methods

In this study, we compared whole blood DNA methylation profiles of 32 individuals: 21 cognitively healthy and 11 with LOAD, using the Infinium MethylationEPIC BeadChip. First, we calculated the epigenetic age of the participants based on Horvath’s epigenetic clock. DMRcate and Bumphunter were used to identify DMRs. After in silico and knowledge-based filtering of the DMRs, we performed a methylation quantitative loci (mQTL) analysis (rs708727 and rs960603).

Results

On average, the epigenetic age was 73 years in both groups, which represents a difference of over 20 years between epigenetic and chronological age in both affected and unaffected individuals. Methylation analysis revealed 11 DMRs between groups, which contain six genes and two pseudogenes. These genes are involved in cell cycle regulation, embryogenesis, synthesis of ceramides, and migration of interneurons to the cerebral cortex. One of the six genes is PM20D1, for which altered expression has been reported in LOAD. After genotyping previously reported mQTL SNPs for the gene, we found that average methylation in the PM20D1 DMR differs between genotypes for rs708727, but not for rs960603.

Conclusions

This work supports the possible role of PM20D1 in protection against AD, by showing differential methylation in blood of affected and unaffected nonagenarians. Our results also support the influence of genetic factors on PM20D1 methylation levels.

A slower rate of sulcal widening in the brains of the nondemented oldest old

The relationships between aging and brain morphology have been reported in many previous structural brain studies. However, the trajectories of successful brain aging in the extremely old remain underexplored. In the limited research on the oldest old, covering individuals aged 85 years and older, there are very few studies that have focused on the cortical morphology, especially cortical sulcal features. In this paper, we measured sulcal width and depth as well as cortical thickness from T1-weighted scans of 290 nondemented community-dwelling participants aged between 76 and 103 years. We divided the participants into young old (between 76 and 84; mean = 80.35±2.44; male/female = 76/88) and oldest old (between 85 and 103; mean = 91.74±5.11; male/female = 60/66) groups. The results showed that most of the examined sulci significantly widened with increased age and that the rates of sulcal widening were lower in the oldest old. The spatial pattern of the cortical thinning partly corresponded with that of sulcal widening. Compared to females, males had significantly wider sulci, especially in the oldest old. This study builds a foundation for future investigations of neurocognitive disorders and neurodegenerative diseases in the oldest old, including centenarians.

Associations of hemoglobin A1c with cognition reduced for long diabetes duration

Introduction

Associations of some risk factors with poor cognition, identified prior to age 75, are reduced or reversed in very old age. The Protected Survivor Model predicts this interaction due to enhanced survival of those with extended risk factor duration. In a younger sample, this study examines the association of cognition with the mean hemoglobin A1c risk factor over the time at risk, according to its duration.

Methods

The interaction of mean hemoglobin A1c (average = 9.8%), evaluated over duration (average = 116.8 months), was examined for overall cognition and three cognitive domains in a sample of 150 “young-old” veterans (mean age = 70) with type 2 diabetes.

Results

The predicted interactions were significant for overall cognition and attention, but not executive functions/language and memory.

Discussion

Findings extend the Protected Survivor Model to a “young-old” sample, from the very old. This model suggests focusing on individuals with good cognition despite prolonged high risk when seeking protective factors.

Distinct age-related associations for body mass index and cognition in cognitively healthy very old veterans

ABSTRACTAssociations between high body mass index (BMI) and subsequent cognitive decline, reported in elderly averaging below age 75, become less consistent at older ages. We compared the associations of BMI with cognition in moderately old (ages 75-84, N = 154) and oldest-old (85+, N = 93) samples. BMI and cognition were assessed cross-sectionally in cognitively intact elderly (mean age = 84.5, SD = 4.4) male veterans. Regression analyses of three cognitive domains - executive functions/language, attention, and memory-compared relationship with BMI between the moderately old and oldest-old. Higher BMI was associated with relatively poorer executive functions/language performance in the moderately old, while the opposite relationship, higher BMI associated with relatively better performance, was found in the oldest-old. Associations for the other two cognitive domains did not differ significantly between age groups. The reversal of association direction for executive functions/language performance with higher BMI is consistent with the protected survivor model. This model posits a minority subpopulation with a protective factor-genetic or otherwise-against both mortality and cognitive decline associated with risk factor status. The very old who remain cognitively intact despite the presence of risk factors are more likely to possess protection.

Outcome age-based prediction of successful cognitive aging by total cholesterol

INTRODUCTION

Some associations of high total cholesterol with dementia risk diminish as the outcome age-age at cognitive assessment-increases.

METHODS

The Framingham Heart Study provided 1897 participants with intact cognition at entry. Cox regression analysis for incident marked cognitive decline included "time-dependent" coefficients, with associations between total cholesterol and covariates changing by outcome age. Decline within age categories of 75-84 and 85-94 years was also examined.

RESULTS

Significant associations of rising total cholesterol linear slope, low entry age, low education, and statin nonuse with risk diminished significantly by outcome age. At 85-94 years, falling linear slope was significant.

DISCUSSION

The protected survival model posits a minority subpopulation with protection against mortality and cognitive decline associated with total cholesterol risk factors. It predicts the observed diminished or reversed cholesterol associations with increasing age. Protection is particularly likely for successful cognitive aging-intact cognition at very old age-despite increased risk from cholesterol.