Exercise Engagement as a Moderator of the Effects of APOE Genotype on Amyloid Deposition

Memorcise and Alzheimer's disease

Alzheimer's disease (AD) is a debilitating disease influencing a multitude of outcomes, including memory function. Recent work suggests that memory may be influenced by exercise ('memorcise'), even among those with AD. The present narrative review details (1) the underlying mechanisms of AD; (2) whether exercise has a protective effect in preventing AD; (3) the mechanisms through which exercise may help to prevent AD; (4) the mechanisms through which exercise may help attenuate the progression of AD severity among those with existing AD; (5) the effects and mechanisms through which exercise is associated with memory among those with existing AD; and (6) exercise recommendations for those with existing AD. Such an understanding will aid clinicians in their ability to use exercise as a potential behavioral strategy to help prevent and treat AD.

Effects of aquatic and land-based exercises on amyloid beta, heat shock protein 27, and pulse wave velocity in elderly women

BACKGROUND

Alzheimer's disease is a neurodegenerative brain disease resulting from the deterioration of neuronal cells and vascular dementia, the latter of which results from cerebrovascular disorders. Exercise is effective in preventing and treating degenerative brain diseases as it activates blood flow to the brain, increases nerve production in the hippocampus, and promotes the expression of synaptic plasticity-related proteins. Therefore, this study investigated the effects of 16-week aquatic and land-based exercise programs on amyloid beta (Aβ), heat shock protein (HSP) 27 levels, and pulse wave velocity (PWV).

MATERIALS AND METHODS

Forty elderly women, aged 60-70 years, voluntarily participated in the study. They were divided into control (n = 12), aquatic exercise (n = 14), and land-based exercise groups (n = 14). The variables of amyloid beta, heat shock protein 27, and pulse wave velocity were measured in all the participants before and after the 16-week study.

RESULTS

Significantly higher levels of serum HSP27 (p < 0.05) and significantly lower levels of vascular elasticity (p < 0.05) were found in the aquatic exercise group after 16 weeks of exercise compared with the control group. Aβ did not significantly differ between groups. Thirty minutes after the first exercise, Aβ in the aquatic exercise group (p < 0.01) and HSP27 in the land-based exercise group (p < 0.05) were significantly higher than the corresponding levels in the resting condition before exercise. 30 min after the last exercise, Aβ (p < 0.01) and HSP27 (p < 0.05) were significantly higher.

CONCLUSIONS

Aquatic and land-based exercises increased serum Aβ and HSP27 and decreased pulse wave velocity. Thus, they may play a positive role in the prevention of degenerative brain diseases and improvement of brain function in elderly people.

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

Preventing or delaying Alzheimer disease (AD) through lifestyle interventions will come from a better understanding of the mechanistic underpinnings of (1) why a significant proportion of elderly remain cognitively normal with AD pathologies (ADP), i.e., amyloid or tau; and (2) why some elderly individuals do not have significant ADP. In the last decades, concepts such as brain reserve, cognitive reserve, and more recently brain maintenance have been proposed along with more general notions such as (neuro)protection and compensation. It is currently unclear how to effectively apply these concepts in the new field of preclinical AD specifically separating the 2 distinct mechanisms of coping with pathology vs avoiding pathology. We propose a simplistic conceptual framework that builds on existing concepts using the nomenclature of resistance in the context of avoiding pathology, i.e., remaining cognitively normal without significant ADP, and resilience in the context of coping with pathology, i.e., remaining cognitively normal despite significant ADP. In the context of preclinical AD studies, we (1) define these concepts and provide recommendations (and common scenarios) for their use; (2) discuss how to employ this terminology in the context of investigating mechanisms and factors; (3) highlight the complementarity and clarity they provide to existing concepts; and (4) discuss different study designs and methodologies. The application of the proposed framework for framing hypotheses, study design, and interpretation of results and mechanisms can provide a consistent framework and nomenclature for researchers to reach consensus on identifying factors that may prevent ADP or delay the onset of cognitive impairment.

Lifestyle and vascular risk effects on MRI-based biomarkers of Alzheimer's disease: a cross-sectional study of middle-aged adults from the broader New York City area

OBJECTIVE

To investigate the effects of lifestyle and vascular-related risk factors for Alzheimer's disease (AD) on in vivo MRI-based brain atrophy in asymptomatic young to middle-aged adults.

DESIGN

Cross-sectional, observational.

SETTING

Broader New York City area. Two research centres affiliated with the Alzheimer's disease Core Center at New York University School of Medicine.

PARTICIPANTS

We studied 116 cognitively normal healthy research participants aged 30-60 years, who completed a three-dimensional T1-weighted volumetric MRI and had lifestyle (diet, physical activity and intellectual enrichment), vascular risk (overweight, hypertension, insulin resistance, elevated cholesterol and homocysteine) and cognition (memory, executive function, language) data. Estimates of cortical thickness for entorhinal (EC), posterior cingulate, orbitofrontal, inferior and middle temporal cortex were obtained by use of automated segmentation tools. We applied confirmatory factor analysis and structural equation modelling to evaluate the associations between lifestyle, vascular risk, brain and cognition.

RESULTS

Adherence to a Mediterranean-style diet (MeDi) and insulin sensitivity were both positively associated with MRI-based cortical thickness (diet: β_s≥0.26, insulin sensitivity β_s≥0.58, P≤0.008). After accounting for vascular risk, EC in turn explained variance in memory (P≤0.001). None of the other lifestyle and vascular risk variables were associated with brain thickness. In addition, the path associations between intellectual enrichment and better cognition were significant (β_s≥0.25 P≤0.001), as were those between overweight and lower cognition (β_s≥-0.22, P≤0.01).

CONCLUSIONS

In cognitively normal middle-aged adults, MeDi and insulin sensitivity explained cortical thickness in key brain regions for AD, and EC thickness predicted memory performance in turn. Intellectual activity and overweight were associated with cognitive performance through different pathways. Our findings support further investigation of lifestyle and vascular risk factor modification against brain ageing and AD. More studies with larger samples are needed to replicate these research findings in more diverse, community-based settings.

Recent Progress in Alzheimer's Disease Research, Part 2: Genetics and Epidemiology

This is the second part of a three-part review series reviewing the most important advances in Alzheimer's disease (AD) research since 2010. This review covers the latest research on genetics and epidemiology. Epidemiological and genetic studies are revealing important insights into the etiology of, and factors that contribute to AD, as well as areas of priority for research into mechanisms and interventions. The widespread adoption of genome wide association studies has provided compelling evidence of the genetic complexity of AD with genes associated with such diverse physiological function as immunity and lipid metabolism being implicated in AD pathogenesis.

Moderate intensity physical activity associates with CSF biomarkers in a cohort at risk for Alzheimer's disease

INTRODUCTION

Alzheimer's disease (AD) is characterized by the presence of amyloid β (Aβ) plaques, neurofibrillary tangles, and neurodegeneration, evidence of which may be detected in vivo via cerebrospinal fluid (CSF) sampling. Physical activity (PA) has emerged as a possible modifier of these AD-related pathological changes. Consequently, the aim of this study was to cross-sectionally examine the relationship between objectively measured PA and CSF levels of Aβ42 and tau in asymptomatic late-middle-aged adults at risk for AD.

METHODS

Eighty-five cognitively healthy late-middle-aged adults (age = 64.31 years, 61.2% female) from the Wisconsin Registry for Alzheimer's Prevention participated in this study. They wore an accelerometer (ActiGraph GT3X+) for one week to record free-living PA, yielding measures of sedentariness and various intensities of PA (i.e., light, moderate, and vigorous). They also underwent lumbar puncture to collect CSF, from which Aβ42, total tau, and phosphorylated tau were immunoassayed. Regression analyses were used to examine the association between accelerometer measures and CSF biomarkers, adjusting for age, sex, and other relevant covariates.

RESULTS

Engagement in moderate PA was associated with higher Aβ42 (P = .008), lower total tau/Aβ42 (P = .006), and lower phosphorylated tau/Aβ42 (P = .030). In contrast, neither light nor vigorous PA was associated with any of the biomarkers. Increased sedentariness was associated with reduced Aβ42 (P = .014).

DISCUSSIONS

In this cohort, moderate PA, but not light or vigorous, was associated with a favorable AD biomarker profile, while sedentariness was associated with greater Aβ burden. These findings suggest that a physically active lifestyle may play a protective role against the development of AD.

Cerebrospinal Fluid Amyloid Beta and Tau Concentrations Are Not Modulated by 16 Weeks of Moderate- to High-Intensity Physical Exercise in Patients with Alzheimer Disease

BACKGROUND

Physical exercise may have some effect on cognition in patients with Alzheimer disease (AD). However, the underlying biochemical effects are unclear. Animal studies have shown that amyloid beta (Aβ), one of the pathological hallmarks of AD, can be altered with high levels of physical activity.

AIM

The objective of this study was to elucidate the effect of 16 weeks of moderate- to high-intensity physical exercise on the biomarkers of AD, with special emphasis on the amyloidogenic pathway.

METHODS

From a total of 53 patients with AD participating in the Preserving Cognition, Quality of Life, Physical Health and Functional Ability in Alzheimer's Disease: The Effect of Physical Exercise (ADEX) study we analyzed cerebrospinal fluid samples for Aβ species, total tau (t-tau), phosphorylated tau (p-tau) and soluble amyloid precursor protein (sAPP) species. We also assessed the patients for apolipoprotein E ε4 (ApoE ε4) genotype.

RESULTS

We found no effect of 16 weeks of physical exercise on the selected biomarkers, and no effect of ApoE ε4 genotype.

CONCLUSION

Our findings suggest that the possible effect of physical exercise on cognition in patients with AD is not due to modulation of Aβ, t-tau, p-tau and sAPP species.

Habitual exercise levels are associated with cerebral amyloid load in presymptomatic autosomal dominant Alzheimer's disease

INTRODUCTION

The objective of this study was to evaluate the relationship between self-reported exercise levels and Alzheimer's disease (AD) biomarkers, in a cohort of autosomal dominant AD mutation carriers.

METHODS

In 139 presymptomatic mutation carriers from the Dominantly Inherited Alzheimer Network, the relationship between self-reported exercise levels and brain amyloid load, cerebrospinal fluid (CSF) Aβ42, and CSF tau levels was evaluated using linear regression.

RESULTS

No differences in brain amyloid load, CSF Aβ42, or CSF tau were observed between low and high exercise groups. Nevertheless, when examining only those already accumulating AD pathology (i.e., amyloid positive), low exercisers had higher mean levels of brain amyloid than high exercisers. Furthermore, the interaction between exercise and estimated years from expected symptom onset was a significant predictor of brain amyloid levels.

DISCUSSION

Our findings indicate a relationship exists between self-reported exercise levels and brain amyloid in autosomal dominant AD mutation carriers.

Sushi repeat-containing protein 1: a novel disease-associated molecule in cerebral amyloid angiopathy

Sporadic cerebral amyloid angiopathy (CAA) is characterized by cerebrovascular amyloid beta (Aβ) deposits and causes cerebral hemorrhage and dementia. The exact molecules that co-accumulate with cerebrovascular Aβ deposits are still not fully known. In our study here, we performed proteomic analyses with microdissected leptomeningeal arteries and cerebral neocortical arterioles from 8 cases with severe CAA, 12 cases with mild CAA, and 10 control cases without CAA, and we determined the levels of highly expressed proteins in cerebral blood vessels in CAA. We focused on sushi repeat-containing protein 1 (SRPX1), which is specifically expressed in CAA-affected cerebral blood vessels. Because SRPX1, which is known as a tumor suppressor gene, reportedly induced apoptosis in tumor cells, we hypothesized that SRPX1 may play an important role in Aβ-induced apoptosis in CAA. Immunohistochemical studies revealed that SRPX1 co-accumulated with Aβ deposits in cerebral blood vessels of all autopsied cases with severe CAA. In contrast, no SRPX1 co-accumulated with Aβ deposits in senile plaques. Furthermore, we demonstrated that both Aβ40 and Aβ42 bound to SRPX1 in vitro and enhanced SRPX1 expression in primary cultures of cerebrovascular smooth muscle cells. SRPX1 enhanced caspase activity induced by Aβ40. Knockdown of SRPX1, in contrast, reduced the formation of Aβ40 accumulations and the activity of caspase in cultured cerebrovascular smooth muscle cells. SRPX1 may thus be a novel molecule that is up-regulated in cerebrovascular Aβ deposits and that may increase Aβ-induced cerebrovascular degeneration in CAA.

Role of Inactivity in Chronic Diseases: Evolutionary Insight and Pathophysiological Mechanisms

This review proposes that physical inactivity could be considered a behavior selected by evolution for resting, and also selected to be reinforcing in life-threatening situations in which exercise would be dangerous. Underlying the notion are human twin studies and animal selective breeding studies, both of which provide indirect evidence for the existence of genes for physical inactivity. Approximately 86% of the 325 million in the United States (U.S.) population achieve less than the U.S. Government and World Health Organization guidelines for daily physical activity for health. Although underappreciated, physical inactivity is an actual contributing cause to at least 35 unhealthy conditions, including the majority of the 10 leading causes of death in the U.S. First, we introduce nine physical inactivity-related themes. Next, characteristics and models of physical inactivity are presented. Following next are individual examples of phenotypes, organ systems, and diseases that are impacted by physical inactivity, including behavior, central nervous system, cardiorespiratory fitness, metabolism, adipose tissue, skeletal muscle, bone, immunity, digestion, and cancer. Importantly, physical inactivity, itself, often plays an independent role as a direct cause of speeding the losses of cardiovascular and strength fitness, shortening of healthspan, and lowering of the age for the onset of the first chronic disease, which in turn decreases quality of life, increases health care costs, and accelerates mortality risk.

Exercise Training and Functional Connectivity Changes in Mild Cognitive Impairment and Healthy Elders

BACKGROUND

Effective interventions are needed to improve brain function in mild cognitive impairment (MCI), an early stage of Alzheimer's disease (AD). The posterior cingulate cortex (PCC)/precuneus is a hub of the default mode network (DMN) and is preferentially vulnerable to disruption of functional connectivity in MCI and AD.

OBJECTIVE

We investigated whether 12 weeks of aerobic exercise could enhance functional connectivity of the PCC/precuneus in MCI and healthy elders.

METHODS

Sixteen MCI and 16 healthy elders (age range = 60-88) engaged in a supervised 12-week walking exercise intervention. Functional MRI was acquired at rest; the PCC/precuneus was used as a seed for correlated brain activity maps.

RESULTS

A linear mixed effects model revealed a significant interaction in the right parietal lobe: the MCI group showed increased connectivity while the healthy elders showed decreased connectivity. In addition, both groups showed increased connectivity with the left postcentral gyrus. Comparing pre to post intervention changes within each group, the MCI group showed increased connectivity in 10 regions spanning frontal, parietal, temporal and insular lobes, and the cerebellum. Healthy elders did not demonstrate any significant connectivity changes.

CONCLUSION

The observed results show increased functional connectivity of the PCC/precuneus in individuals with MCI after 12 weeks of moderate intensity walking exercise training. The protective effects of exercise training on cognition may be realized through the enhancement of neural recruitment mechanisms, which may possibly increase cognitive reserve. Whether these effects of exercise training may delay further cognitive decline in patients diagnosed with MCI remains to be demonstrated.

Physical activity and beta-amyloid pathology in Alzheimer's disease: A sound mind in a sound body

Alzheimer's disease (AD) is the most common type of dementia worldwide. Since curative treatment has not been established for AD yet and due to heavy financial and psychological costs of patients' care, special attention has been paid to preventive interventions such as physical activity. Evidence shows that physical activity has protective effects on cognitive function and memory in AD patients. Several pathologic factors are involved in AD-associated cognitive impairment some of which are preventable by physical activity. Also, various experimental and clinical studies are in progress to prove exercise role in the beta-amyloid (Aβ) pathology as a most prevailing hypothesis explaining AD pathogenesis. This study aims to review the role of physical activity in Aβ-related pathophysiology in AD.

Association between educational attainment and amyloid deposition across the spectrum from normal cognition to dementia: neuroimaging evidence for protection and compensation

The brain mechanisms underlying the effect of intellectual enrichment may evolve along the normal aging Alzheimer's disease (AD) cognitive spectrum and may include both protective and compensatory mechanisms. We assessed the association between early intellectual enrichment (education, years) and average cortical florbetapir standardized uptake value ratio as well as performed voxel-wise analyses in a total of 140 participants, including cognitively normal older adults, mild cognitive impairment (MCI), and AD patients. Higher education was associated with lower cortical florbetapir positron emission tomography (florbetapir-PET) uptake, notably in the frontal lobe in normal older adults, but with higher uptake in frontal, temporal, and parietal regions in MCI after controlling for global cognitive status. No association was found in AD. In MCI, we observed an increased fluorodeoxyglucose positron emission tomography (FDG-PET) uptake with education within the regions of higher florbetapir-PET uptake, suggesting a compensatory increase. Early intellectual enrichment may be associated with protection and compensation for amyloid beta (Aβ) deposition later in life, before the onset of dementia. Previous investigations have been controversial as regard to the effects of intellectual enrichment variables on Aβ deposition; the present findings call for approaches aiming to evaluate mechanisms of resilience across disease stages.

α-Synuclein Aggregates with β-Amyloid or Tau in Human Red Blood Cells: Correlation with Antioxidant Capability and Physical Exercise in Human Healthy Subjects

Neurodegenerative disorders (NDs) are characterized by abnormal accumulation/misfolding of specific proteins, primarily α-synuclein (α-syn), β-amyloid_1-42 (Aβ), and tau, in both brain and peripheral tissue. In addition to homo-oligomers, the role of α-syn interactions with Aβ or tau has gradually emerged. The altered protein accumulation has been related to both oxidative stress and physical activity; nevertheless, no correlation among the presence of peripheral α-syn hetero-aggregates, antioxidant capacity, and physical exercise has been discovered as of yet. Herein, the content of α-syn, Aβ, tau, and of their heterocomplexes was determined in red blood cells (RBCs) of healthy subjects (sedentary and athletes). Such parameters were related to the extent of the antioxidant capability (AOC), a key marker of oxidative stress in aging-related pathologies, and to physical exercise, which is known to play an important preventive role in NDs and to modulate oxidative stress. Tau content and plasma AOC toward hydroxyl radicals were both reduced in older or sedentary subjects; in contrast, α-syn and Aβ accumulated in elderly subjects and showed an inverse correlation with both hydroxyl AOC and the level of physical activity. For the first time, α-syn heterocomplexes with Aβ or tau were quantified and demonstrated to be inversely related to hydroxyl AOC. Furthermore, α-syn/Aβ aggregates were significantly reduced in athletes and inversely correlated with physical activity level, independent of age. The positive correlation between antioxidant capability/physical activity and reduced protein accumulation was confirmed by these data and suggested that peripheral α-syn heterocomplexes may represent new indicators of ND-related protein misfolding.

Physical activity predicts reduced plasma β amyloid in the Cardiovascular Health Study

Objective

Higher levels of physical activity (PA) reduce the risk of cognitive impairment, but the underlying mechanisms are unclear. Using longitudinal data from the Cardiovascular Health Study, we examined whether PA predicted plasma Aβ levels and risk for cognitive decline 9–13 years later.

Methods

Linear and logistic regressions (controlling for APOE status, age, gender, body mass index, cardiovascular disease, brain white matter lesions, and cystatin C levels) tested associations between PA, Aβ, and cognitive impairment in a sample of 149 cognitively normal older adults (mean age 83 years).

Results

More PA at baseline predicted lower levels of Aβ 9–13 years later. Higher Aβ levels at year 9 predicted greater risk for cognitive impairment at year 13. Levels of Aβ at year 9 mediated the relationship between PA and cognitive impairment.

Interpretation

Greater PA may reduce plasma levels of a neurotoxic peptide at an age when the risk for cognitive impairment is especially high.

Cardiorespiratory fitness alters the influence of a polygenic risk score on biomarkers of AD

OBJECTIVE

To examine whether a polygenic risk score (PRS) derived from APOE4, CLU, and ABCA7 is associated with CSF biomarkers of Alzheimer disease (AD) pathology and whether higher cardiorespiratory fitness (CRF) modifies the association between the PRS and CSF biomarkers.

METHODS

Ninety-five individuals from the Wisconsin Registry for Alzheimer's Prevention were included in these cross-sectional analyses. They were genotyped for APOE4, CLU, and ABCA7, from which a PRS was calculated for each participant. The participants underwent lumbar puncture for CSF collection. β-Amyloid 42 (Aβ₄₂), Aβ₄₀, total tau (t-tau), and phosphorylated tau (p-tau) were quantified by immunoassays, and Aβ₄₂/Aβ₄₀ and tau/Aβ₄₂ ratios were computed. CRF was estimated from a validated equation incorporating sex, age, body mass index, resting heart rate, and self-reported physical activity. Covariate-adjusted regression analyses were used to test for associations between the PRS and CSF biomarkers. In addition, by including a PRS×CRF term in the models, we examined whether these associations were modified by CRF.

RESULTS

A higher PRS was associated with lower Aβ₄₂/Aβ₄₀ (p < 0.001), higher t-tau/Aβ₄₂ (p = 0.012), and higher p-tau/Aβ₄₂ (p = 0.040). Furthermore, we observed PRS × CRF interactions for Aβ₄₂/Aβ₄₀ (p = 0.003), t-tau/Aβ₄₂ (p = 0.003), and p-tau/Aβ₄₂ (p = 0.001). Specifically, the association between the PRS and these CSF biomarkers was diminished in those with higher CRF.

CONCLUSIONS

In a late-middle-aged cohort, CRF attenuates the adverse influence of genetic vulnerability on CSF biomarkers. These findings support the notion that increased cardiorespiratory fitness may be beneficial to those at increased genetic risk for AD.

The effect of an interactive cycling training on cognitive functioning in older adults with mild dementia: study protocol for a randomized controlled trial

BACKGROUND

To date there is no cure or an effective disease-modifying drug to treat dementia. Available acetylcholine-esterase inhibiting drugs or memantine only produce small benefits on cognitive and behavioural functioning and their clinical relevance remains controversial. Combined cognitive-aerobic interventions are an appealing alternative or add-on to current pharmacological treatments. The primary aim of this study is to investigate the efficacy of a combined cognitive-aerobic training and a single aerobic training compared to an active control group in older adults with mild dementia. We expect to find a beneficial effect on executive functioning in both training regimes, compared to the control intervention, with the largest effect in the combined cognitive-aerobic group. Secondary, intervention effects on cognitive functioning in other domains, physical functioning, physical activity levels, activities of daily living, frailty and quality of life are studied.

METHODS

The design is a single-blind, randomized controlled trial (RCT) with three groups: a combined cognitive-aerobic bicycle training (interactive cycling), a single aerobic bicycle training and a control intervention, which consists of stretching and toning exercises. Older adults with mild dementia follow a 12-week training program consisting of three training sessions of 30-40 min per week. The primary study outcome is objective executive functioning measured with a neuropsychological assessment. Secondary measures are objective cognitive functioning in other domains, physical functioning, physical activity levels, activities of daily living, frailty, mood and quality of life. The three groups are compared at baseline, after 6 and 12 weeks of training, and at 24-week follow-up.

DISCUSSION

This study will provide novel information on the effects of an interactive cycling training on executive function in older adults with mild dementia. Furthermore, since this study has both a combined cognitive-aerobic training and a single aerobic training group the effectiveness of the different components of the intervention can be identified. The results of this study may be used for physical and mental activity recommendations in older adults with dementia.

TRIAL REGISTRATION

The Netherlands National Trial Register NTR5581 . Registered 14 February 2016.

Timing of Physical Activity, Apolipoprotein E ε4 Genotype, and Risk of Incident Mild Cognitive Impairment

OBJECTIVES

To investigate the timing (mid- vs late life) of physical activity, apolipoprotein (APO)E ε4, and risk of incident mild cognitive impairment (MCI).

DESIGN

Prospective cohort study.

SETTING

Mayo Clinic Study of Aging (Olmsted County, MN).

PARTICIPANTS

Cognitively normal elderly adults (N = 1,830, median age 78, 50.2% female).

MEASUREMENTS

Light, moderate, and vigorous physical activities in mid- and late life were assessed using a validated questionnaire. An expert consensus panel measured MCI based on published criteria. Cox proportional hazards models were used to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) with age as a time scale after adjusting for sex, education, medical comorbidity, and depression.

RESULTS

Light (HR = 0.58, 95% CI = 0.43-0.79) and vigorous (HR = 0.78, 95% CI = 0.63-0.97) physical activity in midlife were associated with lower risk of incident MCI. The association between moderate activity and incident MCI was not significant (HR = 0.85, 95% CI = 0.67-1.09). In late life, light (HR = 0.75, 95% CI = 0.58-0.97) and moderate (HR = 0.81, 95% CI = 0.66-0.99) but not vigorous physical activity were associated with lower risk of incident MCI. A synergistic interaction was also observed between mid- and late-life activity in reducing risk of incident MCI. Furthermore, APOE ε4 carriers who did not exercise had a higher risk of incident MCI than noncarriers who reported physical activity.

CONCLUSION

Physical activity reduced the risk of incident MCI. Exercising in mid- and late life had an additive synergistic interaction in reducing the risk of MCI.

Association between APOE Genotype and Change in Physical Function in a Population-Based Swedish Cohort of Older Individuals Followed Over Four Years

The association between decline in physical function and age-related conditions, such as reduced cognitive performance and vascular disease, may be explained by genetic influence on shared biological pathways of importance for aging. The apolipoprotein E (APOE) gene is well-known for its association with Alzheimer’s disease, but has also been related to other disorders of importance for aging. The aim of this study was to investigate possible associations between APOE allele status and physical function in a population-based longitudinal study of older individuals. In 2005, at the age of 75, 622 individuals underwent neuropsychiatric and physical examinations, including tests of physical function, and APOE-genotyping. Follow-up examinations were performed at age 79. A significantly larger decline in grip strength (p = 0.015) between age 75 and 79 was found when comparing APOE 𝜀4 allele carriers with non-carriers [10.3 (±10.8) kg versus 7.8 (±10.1) kg]. No association was seen with decline in gait speed, chair-stand, or balance. The association with grip strength remained after correction for cognitive and educational level, depression, cardiovascular disease, stroke, and BMI.

Physical activity and inflammation: effects on gray-matter volume and cognitive decline in aging

Physical activity has been positively associated with gray-matter integrity. In contrast, pro-inflammatory cytokines seem to have negative effects on the aging brain and have been related to dementia. It was investigated whether an inactive lifestyle and high levels of inflammation resulted in smaller gray-matter volumes and predicted cognitive decline across 6 years in a population-based study of older adults (n = 414). Self-reported physical activity (fitness-enhancing, health-enhancing, inadequate) was linked to gray-matter volume, such that individuals with inadequate physical activity had the least gray matter. There were no overall associations between different pro-and anti-inflammatory markers (IL-1β, IL-6, IL-10, IL-12p40, IL-12p70, G-CSF, and TNF-α) and gray-matter integrity. However, persons with inadequate activity and high levels of the pro-inflammatory marker IL-12p40 had smaller volumes of lateral prefrontal cortex and hippocampus and declined more on the Mini-Mental State Examination test over 6 years compared with physically inactive individuals with low levels of IL-12p40 and to more physically active persons, irrespective of their levels of IL-12p40. These patterns of data suggested that inflammation was particularly detrimental in inactive older adults and may exacerbate the negative effects of physical inactivity on brain and cognition in old age. Hum Brain Mapp 37:3462-3473, 2016. © 2016 Wiley Periodicals, Inc.

The Relationship between Sleep Quality and Brain Amyloid Burden

STUDY OBJECTIVES

To evaluate the association between self-reported sleep quality and levels of brain β-amyloid (Aβ) burden, and to determine the effect of the apolipoprotein E (APOE) ε4 allele on any associations found.

METHODS

This study is a cross-sectional analysis of 184 cognitively healthy men and women aged over 60 y. We measured sleep quality factors: specifically, sleep duration, latency (time taken to fall asleep), disturbances, efficiency, daytime dysfunction, and overall sleep quality, using the Pittsburgh Sleep Quality Index. All participants underwent Aβ positron emission tomography imaging for the quantification of brain Aβ burden and were APOE genotyped. Linear regression analyses were used to evaluate the relationship between sleep quality factors and brain Aβ burden, adjusting for age, body mass index, cardiovascular disease, and symptoms of depression, with APOE ε4 carriage entered as a moderator.

RESULTS

Of the sleep factors, longer sleep latency was associated with higher levels of brain Aβ (B = 0.003 [standard error = 0.001], P = 0.02). APOE ε4 allele (carrier/noncarrier) did not moderate the relationship between sleep latency and brain Aβ burden.

CONCLUSIONS

Our findings suggest a relationship between brain Aβ burden and sleep latency, independent of APOE ε4 genotype.

Genetic risk factor APOEε4 associates with plasma amyloid beta in amnestic mild cognitive impairment and alzheimer’s disease

Background: APOEε4 is a strong genetic risk factor for Alzheimer’s disease (AD). AD itself has been associated with reduced Aβ clearance from the brain and plasma. Understanding the potential pathogenic link between APOEε4 and plasma Aβ might allow for earlier identification of people at risk of developing AD. The aim of this study is to find out the correlation between APOEε4 and plasma Aβ in amnestic mild cognitive impairment (aMCI) and AD patients.Methods: This is a comparative cross-sectional study of patients attending a memory clinic in Siloam Hospital Lippo Karawaci, Tangerang, during the period of 2013-2014. Subjects were categorized into three categories: normal aging, aMCI, and AD. We performed blood test to examine APOEε4, plasma Aβ4o level, and plasma Aβ42 level. All data analyses were performed using correlation test and logistic regression.Results: Sixty subjects (normal aging = 23, aMCI = 17, AD = 20) were included. There were 19 (31.7%) subjects with APOEε4 positive. Subjects carrying ε4 allele were more likely to have AD by 3.9-fold than subjects with APOE ε4 allele negative. There is a significant difference between the mean of plasma Aβ40 in aMCI group and AD group. We also found correlation between APOEε4 (+) and higher plasma Aβ42 (p<0.05).Conclusion: There is a correlation between APOEε4 and plasma Aβ42 level, which supports the hypothesis that this genetic isoform accelerates the rate and progression of AD through Aβ-dependent pathways.

Preclinical Alzheimer's disease: Definition, natural history, and diagnostic criteria

During the past decade, a conceptual shift occurred in the field of Alzheimer's disease (AD) considering the disease as a continuum. Thanks to evolving biomarker research and substantial discoveries, it is now possible to identify the disease even at the preclinical stage before the occurrence of the first clinical symptoms. This preclinical stage of AD has become a major research focus as the field postulates that early intervention may offer the best chance of therapeutic success. To date, very little evidence is established on this "silent" stage of the disease. A clarification is needed about the definitions and lexicon, the limits, the natural history, the markers of progression, and the ethical consequence of detecting the disease at this asymptomatic stage. This article is aimed at addressing all the different issues by providing for each of them an updated review of the literature and evidence, with practical recommendations.

Effect of intellectual enrichment on AD biomarker trajectories: Longitudinal imaging study

Objective:

To investigate the effect of age, sex, APOE4 genotype, and lifestyle enrichment (education/occupation, midlife cognitive activity, and midlife physical activity) on Alzheimer disease (AD) biomarker trajectories using longitudinal imaging data (brain β-amyloid load via Pittsburgh compound B PET and neurodegeneration via ¹⁸fluorodeoxyglucose (FDG) PET and structural MRI) in an elderly population without dementia.

Methods:

In the population-based longitudinal Mayo Clinic Study of Aging, we studied 393 participants without dementia (340 clinically normal, 53 mild cognitive impairment; 70 years and older) who had cognitive and physical activity measures and at least 2 visits with imaging biomarkers. We dichotomized participants into high (≥14 years) and low (<14 years) education levels using the median. For the entire cohort and the 2 education strata, we built linear mixed models to investigate the effect of the predictors on each of the biomarker outcomes.

Results:

Age was associated with amyloid and neurodegeneration trajectories; APOE4 status appears to influence only the amyloid and FDG trajectories but not hippocampal volume trajectory. In the high-education stratum, high midlife cognitive activity was associated with lower amyloid deposition in APOE4 carriers. APOE4 status was associated with lower FDG uptake in the entire cohort and in participants with lower education but not the high-education cohort.

Conclusions:

There were minimal effects of lifestyle enrichment on AD biomarker trajectories (specifically rates). Lifetime intellectual enrichment (high education, high midlife cognitive activity) is associated with lower amyloid in APOE4 carriers. High education is protective from the APOE4 effect on FDG metabolism. Differing education levels may explain the conflicting results seen in the literature.

The Utility of Cerebral Blood Flow as a Biomarker of Preclinical Alzheimer's Disease

There is accumulating evidence suggesting that changes in brain perfusion are present long before the clinical symptoms of Alzheimer's disease (AD), perhaps even before amyloid-β accumulation or brain atrophy. This evidence, consistent with the vascular hypothesis of AD, implicates cerebral blood flow (CBF) in the pathogenesis of AD and suggests its utility as a biomarker of preclinical AD. The extended preclinical phase of AD holds particular significance for disease modification, as treatment would likely be most effective in this early asymptomatic stage of disease. This highlights the importance of identifying reliable and accurate biomarkers of AD that can differentiate normal aging from preclinical AD prior to clinical symptom manifestation. Cerebral perfusion, as measured by arterial spin labeling magnetic resonance imaging (ASL-MRI), has been shown to distinguish between normal controls and adults with AD. In addition to demonstrating diagnostic utility, CBF has shown usefulness as a tool for identifying those who are at risk for AD and for predicting subtle cognitive decline and conversion to mild cognitive impairment and AD. Taken together, this evidence not only implicates CBF as a useful biomarker for tracking disease severity and progression, but also suggests that ASL-measured CBF may be useful for identifying candidates for future AD treatment trials, especially in the preclinical, asymptomatic phases of the disease.

High-Fat Diet Changes Hippocampal Apolipoprotein E (ApoE) in a Genotype- and Carbohydrate-Dependent Manner in Mice

Alzheimer’s disease is a currently incurable neurodegenerative disease affecting millions of individuals worldwide. Risk factors for Alzheimer’s disease include genetic risk factors, such as possession of ε4 allele of apolipoprotein E (ApoE4) over the risk-neutral ApoE3 allele, and lifestyle risk factors, such as diet and exercise. The intersection of these two sources of disease risk is not well understood. We investigated the impact of diet on ApoE levels by feeding wildtype, ApoE3, and ApoE4 targeted replacement (TR) mice with chow, high-fat, or ketogenic (high-fat, very-low-carbohydrate) diets. We found that high-fat diet affected both plasma and hippocampal levels of ApoE in an isoform-dependent manner, with high-fat diet causing a surprising reduction of hippocampal ApoE levels in ApoE3 TR mice. Conversely, the ketogenic diet had no effect on hippocampal ApoE. Our findings suggest that the use of dietary interventions to slow the progression AD should take ApoE genotype into consideration.

Genetic and degenerative disorders primarily causing dementia

Neuroimaging comprises a powerful set of instruments to diagnose the different causes of dementia, clarify their neurobiology, and monitor their treatment. Magnetic resonance imaging (MRI) depicts volume changes with neurodegeneration and inflammation, as well as abnormalities in functional and structural connectivity. MRI arterial spin labeling allows for the quantification of regional cerebral blood flow, characteristically altered in Alzheimer's disease, diffuse Lewy-body disease, and the frontotemporal dementias. Positron emission tomography allows for the determination of regional metabolism, with similar abnormalities as flow, and for the measurement of β-amyloid and abnormal tau deposition in the brain, as well as regional inflammation. These instruments allow for the quantification in vivo of most of the pathologic features observed in disorders causing dementia. Importantly, they allow for the longitudinal study of these abnormalities, having revealed, for instance, that the deposition of β-amyloid in the brain can antecede by decades the onset of dementia. Thus, a therapeutic window has been opened and the efficacy of immunotherapies directed at removing β-amyloid from the brain of asymptomatic individuals is currently being tested. Tau and inflammation imaging, still in their infancy, combined with genomics, should provide powerful insights into these disorders and facilitate their treatment.

Gene-Environment Interplay in Physical, Psychological, and Cognitive Domains in Mid to Late Adulthood: Is APOE a Variability Gene?

Despite emerging interest in gene-environment interaction (GxE) effects, there is a dearth of studies evaluating its potential relevance apart from specific hypothesized environments and biometrical variance trends. Using a monozygotic within-pair approach, we evaluated evidence of G×E for body mass index (BMI), depressive symptoms, and cognition (verbal, spatial, attention, working memory, perceptual speed) in twin studies from four countries. We also evaluated whether APOE is a 'variability gene' across these measures and whether it partly represents the 'G' in G×E effects. In all three domains, G×E effects were pervasive across country and gender, with small-to-moderate effects. Age-cohort trends were generally stable for BMI and depressive symptoms; however, they were variable-with both increasing and decreasing age-cohort trends-for different cognitive measures. Results also suggested that APOE may represent a 'variability gene' for depressive symptoms and spatial reasoning, but not for BMI or other cognitive measures. Hence, additional genes are salient beyond APOE.

Cardiorespiratory Fitness Attenuates the Influence of Amyloid on Cognition

The aim of this study was to examine cross-sectionally whether higher cardiorespiratory fitness (CRF) might favorably modify amyloid-β (Aβ)-related decrements in cognition in a cohort of late-middle-aged adults at risk for Alzheimer's disease (AD). Sixty-nine enrollees in the Wisconsin Registry for Alzheimer's Prevention participated in this study. They completed a comprehensive neuropsychological exam, underwent 11C Pittsburgh Compound B (PiB)-PET imaging, and performed a graded treadmill exercise test to volitional exhaustion. Peak oxygen consumption (VO2peak) during the exercise test was used as the index of CRF. Forty-five participants also underwent lumbar puncture for collection of cerebrospinal fluid (CSF) samples, from which Aβ42 was immunoassayed. Covariate-adjusted regression analyses were used to test whether the association between Aβ and cognition was modified by CRF. There were significant VO2peak*PiB-PET interactions for Immediate Memory (p=.041) and Verbal Learning & Memory (p=.025). There were also significant VO2peak*CSF Aβ42 interactions for Immediate Memory (p<.001) and Verbal Learning & Memory (p<.001). Specifically, in the context of high Aβ burden, that is, increased PiB-PET binding or reduced CSF Aβ42, individuals with higher CRF exhibited significantly better cognition compared with individuals with lower CRF. In a late-middle-aged, at-risk cohort, higher CRF is associated with a diminution of Aβ-related effects on cognition. These findings suggest that exercise might play an important role in the prevention of AD.

A perspective on the future role of brain pet imaging in exercise science

Positron Emission Tomography (PET) bears a unique potential for examining the effects of physical exercise (acute or chronic) within the central nervous system in vivo, including cerebral metabolism, neuroreceptor occupancy, and neurotransmission. However, application of Neuro-PET in human exercise science is as yet surprisingly sparse. To date the field has been dominated by non-invasive neuroelectrical techniques (EEG, MEG) and structural/functional magnetic resonance imaging (sMRI/fMRI). Despite PET having certain inherent disadvantages, in particular radiation exposure and high costs limiting applicability at large scale, certain research questions in human exercise science can exclusively be addressed with PET: The "metabolic trapping" properties of (18)F-FDG PET as the most commonly used PET-tracer allow examining the neuronal mechanisms underlying various forms of acute exercise in a rather unconstrained manner, i.e. under realistic training scenarios outside the scanner environment. Beyond acute effects, (18)F-FDG PET measurements under resting conditions have a strong prospective for unraveling the influence of regular physical activity on neuronal integrity and potentially neuroprotective mechanisms in vivo, which is of special interest for aging and dementia research. Quantification of cerebral glucose metabolism may allow determining the metabolic effects of exercise interventions in the entire human brain and relating the regional cerebral rate of glucose metabolism (rCMRglc) with behavioral, neuropsychological, and physiological measures. Apart from FDG-PET, particularly interesting applications comprise PET ligand studies that focus on dopaminergic and opioidergic neurotransmission, both key transmitter systems for exercise-related psychophysiological effects, including mood changes, reward processing, antinociception, and in its most extreme form 'exercise dependence'. PET ligand displacement approaches even allow quantifying specific endogenous neurotransmitter release under acute exercise interventions, to which modern PET/MR hybrid technology will be additionally fruitful. Experimental studies exploiting the unprecedented multimodal imaging capacities of PET/MR in human exercise sciences are as yet pending.

Hot Topics in Research: Preventive Neuroradiology in Brain Aging and Cognitive Decline

Preventive neuroradiology is a new concept supported by growing literature. The main rationale of preventive neuroradiology is the application of multimodal brain imaging toward early and subclinical detection of brain disease and subsequent preventive actions through identification of modifiable risk factors. An insightful example of this is in the area of age-related cognitive decline, mild cognitive impairment, and dementia with potentially modifiable risk factors such as obesity, diet, sleep, hypertension, diabetes, depression, supplementation, smoking, and physical activity. In studying this link between lifestyle and cognitive decline, brain imaging markers may be instrumental as quantitative measures or even indicators of early disease. The purpose of this article is to provide an overview of the major studies reflecting how lifestyle factors affect the brain and cognition aging. In this hot topics review, we will specifically focus on obesity and physical activity.

Interaction between years of education and APOE ε4 status on frontal and temporal metabolism

Objective:

To examine interactions between years of education and APOE ε4 status on gray matter volume and metabolism in cognitively healthy participants.

Methods:

Seventy-two healthy participants (28 APOE ε4 carriers and 44 noncarriers; from 23 to 84 years of age) with FDG-PET and structural MRI were included. A subgroup also underwent florbetapir-PET. We tested the interaction effect between years of education and APOE ε4 status (carrier vs noncarrier) on FDG-PET and structural MRI within the whole brain (voxel-wise) adjusting for age and sex. Computed florbetapir standardized uptake value ratios were used for complementary analyses.

Results:

We found an interaction between years of education and APOE ε4 status on frontotemporal FDG-PET metabolism, such that higher education was positively related to frontotemporal metabolism only in APOE ε4 carriers. Complementary analyses revealed that (1) this interaction was independent from amyloid load; (2) increased metabolism in APOE ε4 carriers in this region correlated with episodic memory performances; (3) lower educated APOE ε4 carriers showed decreased metabolism relative to noncarriers in medial temporal and prefrontal areas, while higher educated carriers were comparable to noncarriers in these areas and showed increased metabolism in the middle temporal lobe.

Conclusions:

Our results showed that education may counteract the effects of APOE ε4 on metabolism independently of amyloid deposition. Higher metabolism in higher (compared to lower) educated APOE ε4 carriers was found in regions that sustain episodic memory. Overall, our results point to education as a protective factor that may help to postpone cognitive changes in APOE ε4 carriers.

Age and amyloid effects on human central nervous system amyloid-beta kinetics

OBJECTIVE

Age is the single greatest risk factor for Alzheimer's disease (AD), with the incidence doubling every 5 years after age 65. However, our understanding of the mechanistic relationship between increasing age and the risk for AD is currently limited. We therefore sought to determine the relationship between age, amyloidosis, and amyloid-beta (Aβ) kinetics in the central nervous system (CNS) of humans.

METHODS

Aβ kinetics were analyzed in 112 participants and compared to the ages of participants and the amount of amyloid deposition.

RESULTS

We found a highly significant correlation between increasing age and slowed Aβ turnover rates (2.5-fold longer half-life over five decades of age). In addition, we found independent effects on Aβ42 kinetics specifically in participants with amyloid deposition. Amyloidosis was associated with a higher (>50%) irreversible loss of soluble Aβ42 and a 10-fold higher Aβ42 reversible exchange rate.

INTERPRETATION

These findings reveal a mechanistic link between human aging and the risk of amyloidosis, which may be owing to a dramatic slowing of Aβ turnover, increasing the likelihood of protein misfolding that leads to deposition. Alterations in Aβ kinetics associated with aging and amyloidosis suggest opportunities for diagnostic and therapeutic strategies. More generally, this study provides an example of how changes in protein turnover kinetics can be used to detect physiological and pathophysiological changes and may be applicable to other proteinopathies.

Cognitive reserve and lifestyle: moving towards preclinical Alzheimer's disease

The large majority of neuroimaging studies in Alzheimer’s disease (AD) patients have supported the idea that lifestyle factors may protect against the clinical manifestations of AD rather than influence AD neuropathological processes (the cognitive reserve hypothesis). This evidence argues in favor of the hypothesis that lifestyle factors act as moderators between AD pathology and cognition, i.e., through indirect compensatory mechanisms. In this review, we identify emerging evidence in cognitively normal older adults that relate lifestyle factors to established AD neuroimaging biomarkers. While some of these investigations are in agreement with the compensatory view of cognitive reserve, other studies have revealed new clues on the neural mechanisms underlying beneficial effects of lifestyle factors on the brain. Specifically, they provide novel evidence suggesting direct effects of lifestyle factors on AD neuropathological processes. We propose a tentative theoretical model where lifestyle factors may act via direct neuroprotective and/or indirect compensatory mechanisms. Importantly, we suggest that neuroprotective mechanisms may have a major role during early stages and compensatory mechanisms in later stages of the disease. In the absence of an effective treatment for AD and considering the potential of lifestyle factors in AD prevention, understanding the neural mechanisms underlying lifestyle effects on the brain seems crucial. We hope to provide an integrative view that may help to better understand the complex effects of lifestyle factors on AD neuropathological processes, starting from the preclinical stage.

Interactive effects of physical activity and APOE-ε4 on white matter tract diffusivity in healthy elders

Older adult apolipoprotein-E epsilon 4 (APOE-ε4) allele carriers vary considerably in the expression of clinical symptoms of Alzheimer's disease (AD), suggesting that lifestyle or other factors may offer protection from AD-related neurodegeneration. We recently reported that physically active APOE-ε4 allele carriers exhibit a stable cognitive trajectory and protection from hippocampal atrophy over 18months compared to sedentary ε4 allele carriers. The aim of this study was to examine the interactions between genetic risk for AD and physical activity (PA) on white matter (WM) tract integrity, using diffusion tensor imaging (DTI) MRI, in this cohort of healthy older adults (ages of 65 to 89). Four groups were compared based on the presence or absence of an APOE-ε4 allele (High Risk; Low Risk) and self-reported frequency and intensity of leisure time physical activity (PA) (High PA; Low PA). As predicted, greater levels of PA were associated with greater fractional anisotropy (FA) and lower radial diffusivity in healthy older adults who did not possess the APOE-ε4 allele. However, the effects of PA were reversed in older adults who were at increased genetic risk for AD, resulting in significant interactions between PA and genetic risk in several WM tracts. In the High Risk-Low PA participants, who had exhibited episodic memory decline over the previous 18-months, radial diffusivity was lower and fractional anisotropy was higher, compared to the High Risk-High PA participants. In WM tracts that subserve learning and memory processes, radial diffusivity (DR) was negatively correlated with episodic memory performance in physically inactive APOE-ε4 carriers, whereas DR was positively correlated with episodic memory performance in physically active APOE-ε4 carriers and the two Low Risk groups. The common model of demyelination-induced increase in radial diffusivity cannot directly explain these results. Rather, we hypothesize that PA may protect APOE-ε4 allele carriers from selective neurodegeneration of individual fiber populations at locations of crossing fibers within projection and association WM fiber tracts.

Physical Activity and Amyloid-β Brain Levels in Elderly Adults with Intact Cognition and Mild Cognitive Impairment

OBJECTIVES

To examine the associations between amyloid-β brain deposition and physical activity (PA) in elderly adults without dementia and to investigate whether the association has a dose-response relationship.

DESIGN

Cross-sectional study.

SETTING

French community-dwelling people.

PARTICIPANTS

Elderly adults with normal or mildly impaired cognition (mean age 74.7 ± 4.2; 60.4% female) with available information on current self-reported PA and amyloid-β brain deposition measured using positron emission tomography (PET) using the PET-ligand florbetapir F 18 (n = 268).

MEASUREMENTS

A standardized uptake value ratio (SUVR) was obtained for each subject. Participants were divided according to amyloid plaque cortical retention defined according to a SUVR cutoff of 1.10 (SUVR+ vs SUVR-).

RESULTS

Bivariate and multivariate analyses showed that PA was not significantly associated with SUVR. SUVR+ and SUVR- participants did not differ in terms of volume (continuous PA variables) and levels (categorical PA variables) of PA. PA was not correlated with SUVR in apolipoprotein E ε4 carriers or noncarriers. PA was not associated with cognitive function.

CONCLUSION

Although PA protects against dementia, there is no solid evidence that this protection involves a reduction in amyloid-β brain deposition. Further studies are needed to determine whether PA (ideally measured at several time-points using objective measures) is involved in the pathophysiology of Alzheimer's disease.

Cognitive activity relates to cognitive performance but not to Alzheimer disease biomarkers

OBJECTIVE

We aimed to determine whether there was a relationship between lifestyle factors and Alzheimer disease biomarkers.

METHODS

In a cross-sectional study, we evaluated self-reported histories of recent and past cognitive activity, self-reported history of recent physical activity, and objective recent walking activity in 186 clinically normal individuals with mean age of 74 ± 6 years. Using backward elimination general linear models, we tested the hypotheses that greater cognitive or physical activity would be associated with lower Pittsburgh compound B-PET retention, greater (18)F-fluorodeoxyglucose-PET metabolism, and larger hippocampal volume, as well as better cognitive performance on neuropsychological testing.

RESULTS

Linear regression demonstrated that history of greater cognitive activity was correlated with greater estimated IQ and education, as well as better neuropsychological testing performance. Self-reported recent physical activity was related to objective exercise monitoring. However, contrary to hypotheses, we did not find evidence of an association of Pittsburgh compound B retention, (18)F-fluorodeoxyglucose uptake, or hippocampal volume with past or current levels of cognitive activity, or with current physical activity.

CONCLUSIONS

We conclude that a history of lifelong cognitive activity may support better cognitive performance by a mechanism that is independent of brain β-amyloid burden, brain glucose metabolism, or hippocampal volume.

Genetic risk for Alzheimer's disease alters the five-year trajectory of semantic memory activation in cognitively intact elders

Healthy aging is associated with cognitive declines typically accompanied by increased task-related brain activity in comparison to younger counterparts. The Scaffolding Theory of Aging and Cognition (STAC) (Park and Reuter-Lorenz, 2009; Reuter-Lorenz and Park, 2014) posits that compensatory brain processes are responsible for maintaining normal cognitive performance in older adults, despite accumulation of aging-related neural damage. Cross-sectional studies indicate that cognitively intact elders at genetic risk for Alzheimer's disease (AD) demonstrate patterns of increased brain activity compared to low risk elders, suggesting that compensation represents an early response to AD-associated pathology. Whether this compensatory response persists or declines with the onset of cognitive impairment can only be addressed using a longitudinal design. The current prospective, 5-year longitudinal study examined brain activation in APOE ε4 carriers (N=24) and non-carriers (N=21). All participants, ages 65-85 and cognitively intact at study entry, underwent task-activated fMRI, structural MRI, and neuropsychological assessments at baseline, 18, and 57 months. fMRI activation was measured in response to a semantic memory task requiring participants to discriminate famous from non-famous names. Results indicated that the trajectory of change in brain activation while performing this semantic memory task differed between APOE ε4 carriers and non-carriers. The APOE ε4 group exhibited greater activation than the Low Risk group at baseline, but they subsequently showed a progressive decline in activation during the follow-up periods with corresponding emergence of episodic memory loss and hippocampal atrophy. In contrast, the non-carriers demonstrated a gradual increase in activation over the 5-year period. Our results are consistent with the STAC model by demonstrating that compensation varies with the severity of underlying neural damage and can be exhausted with the onset of cognitive symptoms and increased structural brain pathology. Our fMRI results could not be attributed to changes in task performance, group differences in cerebral perfusion, or regional cortical atrophy.

Self-reported physical activity and objective aerobic fitness: differential associations with gray matter density in healthy aging

Aerobic fitness (AF) and self-reported physical activity (srPA) do not represent the same construct. However, many exercise and brain aging studies interchangeably use AF and srPA measures, which may be problematic with regards to how these metrics are associated with brain outcomes, such as morphology. If AF and PA measures captured the same phenomena, regional brain volumes associated with these measures should directly overlap. This study employed the general linear model to examine the differential association between objectively-measured AF (treadmill assessment) and srPA (questionnaire) with gray matter density (GMd) in 29 cognitively unimpaired community-dwelling older adults using voxel based morphometry. The results show significant regional variance in terms of GMd when comparing AF and srPA as predictors. Higher AF was associated with greater GMd in the cerebellum only, while srPA displayed positive associations with GMd in occipito-temporal, left perisylvian, and frontal regions after correcting for age. Importantly, only AF level, and not srPA, modified the relationship between age and GMd, such that higher levels of AF were associated with increased GMd in older age, while decreased GMd was seen in those with lower AF as a function of age. These results support existing literature suggesting that both AF and PA exert beneficial effects on GMd, but only AF served as a buffer against age-related GMd loss. Furthermore, these results highlight the need for use of objective PA measurement and comparability of tools across studies, since results vary dependent upon the measures used and whether these are objective or subjective in nature.

Correlation between decreased CSF α-synuclein and Aβ₁₋₄₂ in Parkinson disease

Accumulation of misfolded α-synuclein (α-syn) protein in Lewy bodies and neurites is the cardinal pathologic feature of Parkinson disease (PD), but abnormal deposition of other proteins may also play a role. Cerebrospinal fluid (CSF) levels of proteins known to accumulate in PD may provide insight into disease-associated changes in protein metabolism and their relationship to disease progression. We measured CSF α-syn, amyloid β₁₋₄₂ (Aβ₁₋₄₂), and tau from 77 nondemented PD and 30 control participants. CSF α-syn and Aβ₁₋₄₂ were significantly lower in PD compared with controls. In contrast with increased CSF tau in Alzheimer disease, CSF tau did not significantly differ between PD and controls. CSF protein levels did not significantly correlate with ratings of motor function or performance on neuropsychological testing. As expected, CSF Aβ₁₋₄₂ inversely correlated with [(11)C]-Pittsburgh compound B (PiB) mean cortical binding potential, with PiB(+) PD participants having lower CSF Aβ₁₋₄₂ compared with PiB(-) PD participants. Furthermore, CSF α-syn positively correlated with Aβ₁₋₄₂ in PD participants but not in controls, suggesting a pathophysiologic connection between the metabolisms of these proteins in PD.