Apolipoproteins and aging: emerging mechanisms

The Impact of Apolipoprotein E (APOE) Epigenetics on Aging and Sporadic Alzheimer's Disease

Sporadic Alzheimer's disease (AD) derives from an interplay among environmental factors and genetic variants, while epigenetic modifications have been expected to affect the onset and progression of its complex etiopathology. Carriers of one copy of the apolipoprotein E gene (APOE) ε4 allele have a 4-fold increased AD risk, while APOE ε4/ε4-carriers have a 12-fold increased risk of developing AD in comparison with the APOE ε3-carriers. The main longevity factor is the homozygous APOE ε3/ε3 genotype. In the present narrative review article, we summarized and described the role of APOE epigenetics in aging and AD pathophysiology. It is not fully understood how APOE variants may increase or decrease AD risk, but this gene may affect tau- and amyloid-mediated neurodegeneration directly or indirectly, also by affecting lipid metabolism and inflammation. For sporadic AD, epigenetic regulatory mechanisms may control and influence APOE expression in response to external insults. Diet, a major environmental factor, has been significantly associated with physical exercise, cognitive function, and the methylation level of several cytosine-phosphate-guanine (CpG) dinucleotide sites of APOE.

Are apolipoprotein E fragments a promising new therapeutic target for Alzheimer’s disease?

Human apolipoprotein E (ApoE) is a 299-amino acid secreted glycoprotein that binds cholesterol and phospholipids. ApoE exists as three common isoforms (ApoE2, ApoE3, and ApoE4) and heterozygous carriers of the ε4 allele of the gene encoding ApoE (APOE) have a fourfold greater risk of developing Alzheimer’s disease (AD). The enzymes thrombin, cathepsin D, α-chymotrypsin-like serine protease, and high-temperature requirement serine protease A1 are responsible for ApoE proteolytic processing resulting in bioactive C-terminal-truncated fragments that vary depending on ApoE isoforms, brain region, aging, and neural injury. The objectives of the present narrative review were to describe ApoE processing, discussing current hypotheses about the potential role of various ApoE fragments in AD pathophysiology, and reviewing the current development status of different anti-ApoE drugs. The exact mechanism by which APOE gene variants increase/decrease AD risk and the role of ApoE fragments in the deposition are not fully understood, but APOE is known to directly affect tau-mediated neurodegeneration. ApoE fragments co-localize with neurofibrillary tangles and amyloid β (Aβ) plaques, and may cause neurodegeneration. Among anti-ApoE approaches, a fascinating strategy may be to therapeutically overexpress ApoE2 in APOE ε4/ε4 carriers through vector administration or liposomal delivery systems. Another approach involves reducing ApoE4 expression by intracerebroventricular antisense oligonucleotides that significantly decreased Aβ pathology in transgenic mice. Differences in the proteolytic processing of distinct ApoE isoforms and the use of ApoE fragments as mimetic peptides in AD treatment are also under investigation. Treatment with peptides that mimic the structural and biological properties of native ApoE may reduce Aβ deposition, tau hyperphosphorylation, and glial activation in mouse models of Aβ pathology. Alternative strategies involve the use of ApoE4 structure correctors, passive immunization to target a certain form of ApoE, conversion of the ApoE4 aminoacid sequence into that of ApoE3 or ApoE2, and inhibition of the ApoE-Aβ interaction.

Apolipoprotein E Polymorphism and Frailty: Apolipoprotein ε4 Allele Is Associated with Fatigue but Not Frailty Syndrome in a Community-Dwelling Older Population Cohort

OBJECTIVE

Frailty is known to be influenced by genetics, however, little evidence on the association of Apolipoprotein E (ApoE) genotype and frailty exists which we aim to investigate.

DESIGN

This study is a cross-sectional analysis from a prospective longitudinal study cohort.

SETTING AND PARTICIPANTS

Community-dwelling individuals aged 55 years and older from Beijing region in China.

MEASUREMENTS

A total of 3,569 older adults with a mean age of 75.06(±6.79) years were included. We investigated the association between ApoE polymorphism and frailty syndrome using the frailty index (FI) and frailty phenotype (including association with individual components of the frailty phenotype). Logistic regressions were performed to investigate the relation between ApoE variants and frailty.

RESULTS

There was no significant association between ApoE variants and frailty as assessed by the FI. In the age and sex-adjusted model, compared to the ApoE e3/e3 carriers ApoE e4 carriers had almost 1.5 times higher odds of being frail as assessed by the frailty phenotype. However, the significance was lost on the model with adjustment for cognitive impairment. Compared to the ApoE e3/e3 carriers ApoE e4 carriers had almost two times higher odds of fatigue. ApoE e4 heterozygotes had higher odds of fatigue compared to ApoE e4 non-carriers. No significant association was found between ApoE variants and other components of frailty phenotype.

CONCLUSIONS

Our findings do not support an association between ApoE genotype and frailty irrespective of the frailty assessment tools. Fatigue in older adults is the only component of frailty phenotype influenced by ApoE genotype.

Cohort profile: the Diet and Healthy Aging (DaHA) study in Singapore

How diet is related with cognition and health has not been systematically examined in Asians whose eating habits are very different from their counterparts in the West and the biological mechanisms underlying such links are not well known yet. The diet and healthy aging (DaHA) study is a community-based longitudinal study conducted to examine the role of diet and nutrition in promoting cognitive, emotional, and physical health among community-living elderly Singaporeans. The first wave of DaHA, conducted from 2011 to 2017, provided detailed information on diet and baseline cognitive function and health from 1010 community-living elderly in Singapore. Biomarkers of oxidative stress, systemic inflammation, and genetic information were collected. The ongoing second wave of DaHA is conducted from 2017 to 2020, which provides follow- up assessments using established cognitive tests and clinical tools. This well-characterized cohort, with its archived biological samples and high-quality data on diet and lifestyle factors will allow researchers to explore the relationships among diet, nutrition, genes, cognition, mental and physical health in an extremely cost-effective manner. Translations of the research findings into clinical and public health practices will potentially help to promote cognitive health at the population level and reduce healthcare costs related to cognitive impairment.

Nuances in Alzheimer's Genetic Risk Reveal Differential Predictions of Non-demented Memory Aging Trajectories: Selective Patterns by APOE Genotype and Sex

BACKGROUND

Apolipoprotein E (APOE) is a prominent genetic risk factor for Alzheimer's disease (AD) and a frequent target for associations with non-demented and cognitively impaired aging. APOE offers a unique opportunity to evaluate two dichotomous comparisons and selected gradations of APOE risk. Some evidence suggests that APOE effects may differ by sex and emerge especially in interaction with other AD-related biomarkers (e.g., vascular health).

METHODS

Longitudinal trajectories of non-demented adults (n = 632, 67% female, Mage = 68.9) populated a 40-year band of aging. Focusing on memory performance and individualized memory trajectories, a sequence of latent growth models was tested for predictions of (moderation between) APOE and pulse pressure (PP) as stratified by sex. The analyses (1) established robust benchmark PP effects on memory trajectories, (2) compared predictions of alternative dichotomous groupings (ε4- vs ε4+, ε2- vs ε2+), and (3) examined precision-based predictions by disaggregated APOE genotypes.

RESULTS

Healthier (lower) PP was associated with better memory performance and less decline. Therefore, all subsequent analyses were conducted in the interactive context of PP effects and sex stratification. The ε4-based dichotomization produced no differential genetic predictions. The ε2-based analyses showed sex differences, including selective protection for ε2-positive females. Exploratory follow-up disaggregated APOE genotype analyses suggested selective ε2 protection effects for both homozygotic and heterozygotic females.

CONCLUSION

Precision analyses of AD genetic risk will advance the understanding of underlying mechanisms and improve personalized implementation of interventions.

Genetic Associations with Aging Muscle: A Systematic Review

The age-related decline in skeletal muscle mass, strength and function known as 'sarcopenia' is associated with multiple adverse health outcomes, including cardiovascular disease, stroke, functional disability and mortality. While skeletal muscle properties are known to be highly heritable, evidence regarding the specific genes underpinning this heritability is currently inconclusive. This review aimed to identify genetic variants known to be associated with muscle phenotypes relevant to sarcopenia. PubMed, Embase and Web of Science were systematically searched (from January 2004 to March 2019) using pre-defined search terms such as "aging", "sarcopenia", "skeletal muscle", "muscle strength" and "genetic association". Candidate gene association studies and genome wide association studies that examined the genetic association with muscle phenotypes in non-institutionalised adults aged ≥50 years were included. Fifty-four studies were included in the final analysis. Twenty-six genes and 88 DNA polymorphisms were analysed across the 54 studies. The ACTN3, ACE and VDR genes were the most frequently studied, although the IGF1/IGFBP3, TNFα, APOE, CNTF/R and UCP2/3 genes were also shown to be significantly associated with muscle phenotypes in two or more studies. Ten DNA polymorphisms (rs154410, rs2228570, rs1800169, rs3093059, rs1800629, rs1815739, rs1799752, rs7412, rs429358 and 192 bp allele) were significantly associated with muscle phenotypes in two or more studies. Through the identification of key gene variants, this review furthers the elucidation of genetic associations with muscle phenotypes associated with sarcopenia.

A Quarter Century of APOE and Alzheimer's Disease: Progress to Date and the Path Forward

Alzheimer's disease (AD) is considered a polygenic disorder. This view is clouded, however, by lingering uncertainty over how to treat the quasi "monogenic" role of apolipoprotein E (APOE). The APOE4 allele is not only the strongest genetic risk factor for AD, it also affects risk for cardiovascular disease, stroke, and other neurodegenerative disorders. This review, based mostly on data from human studies, ranges across a variety of APOE-related pathologies, touching on evolutionary genetics and risk mitigation by ethnicity and sex. The authors also address one of the most fundamental question pertaining to APOE4 and AD: does APOE4 increase AD risk via a loss or gain of function? The answer will be of the utmost importance in guiding future research in AD.

Multifaceted intervention to enhance cognition in older people at risk of cognitive decline: study protocol for the Protein Omega-3 and Vitamin D Exercise Research (PONDER) study

INTRODUCTION

An increasing number of people are living with cognitive impairment and dementia. Current pharmacological therapies at best reduce Alzheimer's disease symptomatology but do not delay dementia onset in those at high risk. Structured exercise interventions can enhance cognition in older people; however, to produce long lasting, clinically relevant cognitive benefits, it is proposed that a multifaceted approach incorporating exercise with dietary supplements will address a wider range of mechanisms involved in cognitive decline. The Protein Omega-3 aNd vitamin D Exercise Research (PONDER) study aims to investigate the cognitive effects of a multimodal exercise programme combined with nutritional supplementation in older adults with subjective memory impairment (SMI).

METHODS AND ANALYSIS

The PONDER study is a single-centre, 12-month, community-based, parallel group, randomised, double-blind, placebo controlled trial involving a 6-month multifaceted intervention with a further 6-month follow-up. Participants will be 148 people from Melbourne, Australia, aged 60-85 years with SMI who will be randomised (1:1 ratio) to either a 6-month supervised multimodal exercise programme combined with omega-3 fatty acid, vitamin D and protein supplementation or a stretching/flexibility exercise programme combined with placebo supplements. The primary outcome is the change in cognition after 6 months as assessed by the Trail Making Test and global cognitive function assessed from the Cogstate Computerised battery. Secondary outcomes will include memory, working memory/learning and attention/psychomotor function, the Montreal Cognitive Assessment, mood, quality of life, muscle strength, physical function, body composition, cardiovascular health and sleep quality. Cognition at 12 months will represent a secondary outcome.

ETHICS AND DISSEMINATION

This study has been approved by the Deakin University Human Research Ethics Committee (project 2016-260). Informed consent will be obtained from all participants. The authors intend to submit the findings of the study to peer-reviewed journals or academic conferences to be published.

TRIAL REGISTRATION NUMBER

ACTRN12616001549415; Pre-results.

Effects of exercise training on stroke risk factors, homocysteine concentration, and cognitive function according the APOE genotype in stroke patients

The apolipoprotein E (APOE) gene has been suggested to be associated with stroke and dementia. However, the effects of exercise training on dementia according to the APOE genotype are not consistent to those reported by previous studies. Therefore, we examined the effects of exercise training on stroke risk factors including blood pressure, lipid profiles, homocysteine (Hcy) concentrations, and cognitive function according to the APOE genotype in stroke patients. We examined the stroke risk factors, Hcy, and cognitive function in 28 ischemic stroke patients before and after 6 months of exercise training. After exercise training, body weight, body mass index (BMI), and percent body fat decreased significantly in both APOE groups. According to the APOE genotype, the changes in BMI in the APOE ɛ4 group higher than those in APOE ɛ3 group significantly. Total cholesterol (TC), low-density lipoprotein (LDL)-C, triglyceride (TG), and Hcy decreased and high-density lipoprotein (HDL)-C increased significantly in the both groups. According to the APOE genotype, systolic blood pressure in the APOE ɛ4 group decreased, but in the APOE ɛ3 group increased after exercise training. TC, LDL-C, and TG in the APOE ɛ4 group decreased more extensively than those in the APOE ɛ3 group after exercise training. VO_2max (maximal oxygen consumption) and cognition increased significantly in both groups. Folate acid intake also increased significantly in both groups. The APOE genotype affects variations in the risk factors of stroke after exercise training. However, the Hcy and cognitive function did not differ based on the APOE genotype.

Alzheimer disease genetic risk factor APOE e4 and cognitive abilities in 111,739 UK Biobank participants

BACKGROUND

the apolipoprotein (APOE) e4 locus is a genetic risk factor for dementia. Carriers of the e4 allele may be more vulnerable to conditions that are independent risk factors for cognitive decline, such as cardiometabolic diseases.

OBJECTIVE

we tested whether any association with APOE e4 status on cognitive ability was larger in older ages or in those with cardiometabolic diseases.

SUBJECTS

UK Biobank includes over 500,000 middle- and older aged adults who have undergone detailed medical and cognitive phenotypic assessment. Around 150,000 currently have genetic data. We examined 111,739 participants with complete genetic and cognitive data.

METHODS

baseline cognitive data relating to information processing speed, memory and reasoning were used. We tested for interactions with age and with the presence versus absence of type 2 diabetes (T2D), coronary artery disease (CAD) and hypertension.

RESULTS

in several instances, APOE e4 dosage interacted with older age and disease presence to affect cognitive scores. When adjusted for potentially confounding variables, there was no APOE e4 effect on the outcome variables.

CONCLUSIONS

future research in large independent cohorts should continue to investigate this important question, which has potential implications for aetiology related to dementia and cognitive impairment.

Apolipoprotein E ɛ4, Cognitive Function, and Pain Experience in Down Syndrome: A Pilot Study

OBJECTIVE

The presence of apolipoprotein E (ApoE) ɛ4 allele might be related to higher pain experience due to increased risk for potentially painful physical conditions and cognitive impairment (less efficient coping with pain). This hypothesis is clinically relevant to examine in adults with Down syndrome (DS) because they are at risk for painful physical conditions, their presence of ApoE ε4 is related to cognitive impairment, and their pain experience is unclear. The present pilot study addressed the associations between ApoE genotype, cognition, and pain in DS.

METHOD

DNA analysis of saliva, neuropsychological tests (assessing memory and executive functioning), and self-reporting pain scales (in rest and after movement) were used with a cross-sectional design in 146 adults with DS (mean age 39.1 years, mild to moderate intellectual disabilities, 46% men, 30% ApoE ɛ4 carrier).

RESULTS

The difference between ApoE ɛ4 carriers and noncarriers was not statistically significant for cognitive function, pain experience, and prevalence of potentially painful conditions. Among ɛ4 carriers, the presence of potentially painful conditions was associated with worse executive functioning (p = .022, r = .39).

CONCLUSIONS

The clinical implication of the results is that ApoE ɛ4 in DS may play a role in pain, although the theoretical explanation via associations with pain experience and cognition remains unclear. Further research should include a large sample of adults with DS selected on diagnosed painful conditions to obtain more insight into the possible role of ApoE genotype (and its association with cognition) in the pain experience of this target group.

The ApoE gene is related with exceptional longevity: a systematic review and meta-analysis

The objective of this meta-analysis was to determine the association of the apolipoprotein E (ApoE) gene with exceptional longevity (EL) (i.e., reaching 100+ years) by identifying possible unequal distribution of alleles/genotypes in the common variants ε2, ε3, and ε4 among centenarians and younger population. The association of ApoE with EL was analyzed in a total of 2776 centenarians (cases) and 11,941 younger controls (from 13 case-control studies) using the chi-squared test with the Yates correction. We conducted combined and separate analyses for all ethnic groups studied in the literature (Caucasian and Asian). The main result for all ethnic groups combined was that the likelihood of reaching EL was negatively associated with ε4 allele carriage [pooled odds ratio (OR)=0.43; 95% confidence interval (CI) 0.36, 0.50; p<0.001] and with ε4/ε4 (OR=0.18; 95% CI 0.08, 0.39; p<0.001), ε3/ε4 (OR=0.44; 95% CI 0.37, 0.53; p<0.001) and ε2/ε4 genotypes (OR=0.48; 95% CI 0.31, 0.74; p<0.001). In contrast, the ε2/ε3 genotype was positively associated with EL (OR=1.35; 95% CI 1.06, 1.72; p=0.017). When compared with the ε3 allele, the ε2 allele was not associated with increased odds of EL (OR=1.08; 95% CI 0.77, 1.50, p=0.660). The present meta-analysis confirms that, besides its previously documented influence on Alzheimer's and cardiovascular disease risk, the ApoE gene is associated with the likelihood of reaching EL.

Association of common variants in TOMM40/APOE/APOC1 region with human longevity in a Chinese population

Apolipoprotein E (APOE), translocase of outer mitochondrial membrane 40 homolog (TOMM40) and apolipoprotein C-I (APOC1) may extend lifespan by marked delay or escape from age-related diseases. This study aimed to elucidate the association of human longevity with genetic variations in TOMM40/APOE/APOC1 region in a Chinese population. Ten tag single-nucleotide polymorphisms (SNPs) in the TOMM40/APOE/APOC1 region were successfully genotyped in 616 unrelated long-lived individuals and 846 younger controls. Of the 10 SNPs, rs7254892 in 5' upstream of TOMM40 showed significant association with human longevity (G/A-A/A vs G/G: odds ratio (OR)=1.59, 95% confidence interval (CI)=1.20-2.09, P=0.0011, Bonferroni corrected P (Pc)=0.033). The haplotype analysis suggested that individuals carrying the haplotype A-A-A-A-T-A-T-G-C-A (rs7254892-rs157580-rs2075649-rs2075650-rs157582-rs8106922-rs1160985-rs405697-rs439401-rs445925) tended to have longer lifespan than those carrying the most common haplotype G-G-A-A-C-A-C-A-T-G (OR=1.59, 95% CI=1.19-2.12, P=0.0018, Pc=0.0216). These findings indicated that variants in TOMM40/APOE/APOC1 region might be associated with human longevity. Further studies are needed to identify the causal genetic variants influencing human longevity.

Integration of 'omics' data in aging research: from biomarkers to systems biology

Age is the strongest risk factor for many diseases including neurodegenerative disorders, coronary heart disease, type 2 diabetes and cancer. Due to increasing life expectancy and low birth rates, the incidence of age-related diseases is increasing in industrialized countries. Therefore, understanding the relationship between diseases and aging and facilitating healthy aging are major goals in medical research. In the last decades, the dimension of biological data has drastically increased with high-throughput technologies now measuring thousands of (epi) genetic, expression and metabolic variables. The most common and so far successful approach to the analysis of these data is the so-called reductionist approach. It consists of separately testing each variable for association with the phenotype of interest such as age or age-related disease. However, a large portion of the observed phenotypic variance remains unexplained and a comprehensive understanding of most complex phenotypes is lacking. Systems biology aims to integrate data from different experiments to gain an understanding of the system as a whole rather than focusing on individual factors. It thus allows deeper insights into the mechanisms of complex traits, which are caused by the joint influence of several, interacting changes in the biological system. In this review, we look at the current progress of applying omics technologies to identify biomarkers of aging. We then survey existing systems biology approaches that allow for an integration of different types of data and highlight the need for further developments in this area to improve epidemiologic investigations.

APOE Genotype Affects Cognitive Training Response in Healthy Shanghai Community-Dwelling Elderly Individuals

BACKGROUND

Cognitive training may contribute to the ability to maintain cognitive function in healthy elderly adults. Whether genotype modifies training effects remains unknown.

OBJECTIVE

Assess influence of APOE on cognitive function over time in community-dwelling elderly adults participating in multi-domain cognitive training.

METHODS

Healthy individuals ≥70 years of age were screened from one urban community in Shanghai. 145 healthy Chinese older adults met inclusion criteria and were assigned to intervention (n = 88) or control (n = 57) groups. Multi-domain cognitive training involved 24 sessions of different content taking place over 12 weeks. Neuropsychological testing was administered at baseline, immediately after training, six months and twelve months post-intervention; composite measures of cognitive function were identified via factor analysis.

RESULTS

Three factors explained the majority of variance in function (verbal memory, processing speed, executive function). The intervention attenuated 12-month declines in processing speed, regardless of APOE genotype (p = 0.047). Executive function declined in APOEɛ4 carriers over 12 months, regardless of intervention (p = 0.056). There was a significant interaction after 12 months where intervention ɛ4 carriers had better processing speed than ɛ4 controls (p = 0.003). Intervention ɛ2 carriers had better executive function immediately after training (p = 0.02) and had better verbal memory 6-months post-intervention (p = 0.04). These effects remained significant after false-discovery rate correction.

CONCLUSION

Multi-domain cognitive training reduces declines in processing speed over time. APOEɛ4 is associated with reductions in executive function over time, and training may attenuate ɛ4-associated declines in processing speed. APOEɛ2 carriers may also benefit from training, particularly on measures of executive function and verbal memory.

Whole genome sequences of 2 octogenarians with sustained cognitive abilities

Although numerous genetic variants affecting aging and mortality have been identified, for example, apolipoprotein E ε4, the genetic component influencing cognitive aging has not been fully defined yet. A better knowledge of the genetics of aging will prove helpful in understanding the underlying biological processes. Here, we describe the whole genome sequences of 2 female octogenarians. We provide the repertoire of genomic variants that the 2 octogenarians have in common. We also describe the overlap with the previously reported genomes of 2 supercentenarians—individuals aged ≥110 years. We assessed the genetic disease propensities of the octogenarians and non-aged control genomes and could not find support for the hypothesis that long-lived healthy individuals might exhibit greater genetic fitness than the general population. Furthermore, there is no evidence for an accumulation of previously described variants promoting longevity in the 2 octogenarians. These findings suggest that genetic fitness, as currently defined, is not the sole factor enabling an increased life span. We identified a number of healthy-cognitive-aging candidate genetic loci awaiting confirmation in larger studies.

ApoE and pulse pressure interactively influence level and change in the aging of episodic memory: Protective effects among ε2 carriers

OBJECTIVE

We tested independent and interactive effects of Apolipoprotein E (ApoE) and pulse pressure (PP) concurrently and longitudinally across 9 years (3 waves) of episodic (EM) and semantic memory (SM) data from the Victoria Longitudinal Study.

METHOD

We assembled a sample of older adults (n = 570, baseline M age = 71, age range = 53-95) and used latent growth modeling to test 4 research goals.

RESULTS

First, the best fitting memory model was 2 single latent variables for EM and SM, each exhibiting configural, metric, and partial scalar invariance. This model was analyzed as a parallel process model. Second, baseline level of PP predicted EM performance at centering age (75) and rate of 9-year EM change. Third, we observed no main effects of ApoE on EM or SM. Fourth, EM was affected by higher PP but differentially less so for carriers of the ApoE ε2 allele than the ε3 or ε4 alleles.

CONCLUSIONS

PP is confirmed as a risk factor for concurrent and changing cognitive health in aging, but the effects operate differently across risk and protective allelic distribution of the ApoE gene.

IDE (rs6583817) polymorphism and pulse pressure are independently and interactively associated with level and change in executive function in older adults

OBJECTIVE

We report a gene × environment (health) study focusing on concurrent performance and longitudinal change in a latent-variable executive function (EF) phenotype. Specifically, we tested the independent and interactive effects of a recently identified insulin degrading enzyme genetic polymorphism (IDE rs6583817) and pulse pressure (PP; one prominent aging-related vascular health indicator) across up to 9 years of EF data in a sample of older adults from the Victoria Longitudinal Study. Both factors vary across a continuum of risk-elevating to risk-reducing and have been recently linked to normal and impaired cognitive aging.

METHOD

We assembled a genotyped and typically aging group of older adults (n = 599, M age = 66 years at baseline), following them for up to 3 longitudinal waves (M interval = 4.4 years). We used confirmatory factor analyses, latent growth modeling, and path analyses to pursue 3 main research goals.

RESULTS

First, the EF single factor model was confirmed comprising 4 executive function tasks and it demonstrated measurement invariance across the waves. Second, older adults with the major IDE G allele exhibited better EF outcomes than homozygotes for the minor A allele at the centering age of 75 years. Adults with higher PP performed more poorly on EF tasks at age 75 years and exhibited greater EF longitudinal decline. Third, gene × health interaction analyses showed that worsening vascular health (higher PP) differentially affected EF performance in older adults with the IDE G allele.

CONCLUSION

Genetic interaction analyses can reveal differential and magnifying effects on cognitive phenotypes in aging. In the present case, pulse pressure is confirmed as a risk factor for concurrent and changing cognitive health in aging, but the effects operate differently across the risk and protective allelic distribution of this IDE gene.

Exercise, APOE genotype, and the evolution of the human lifespan

Humans have exceptionally long lifespans compared with other mammals. However, our longevity evolved when our ancestors had two copies of the apolipoprotein E (APOE) ɛ4 allele, a genotype that leads to a high risk of Alzheimer's disease (AD), cardiovascular disease, and increased mortality. How did human aging evolve within this genetic constraint? Drawing from neuroscience, anthropology, and brain-imaging research, we propose the hypothesis that the evolution of increased physical activity approximately 2 million years ago served to reduce the amyloid plaque and vascular burden of APOE ɛ4, relaxing genetic constraints on aging. This multidisciplinary approach links human evolution with health and provides a complementary perspective on aging and neurodegenerative disease that may help identify key mechanisms and targets for intervention.

Apolipoprotein E gene polymorphism and Alzheimer's disease in Chinese population: a meta-analysis

The relationship between Apolipoprotein E (ApoE) genotype and the risk of Alzheimer's disease (AD) is relatively well established in Caucasians, but less established in other ethnicities. To examine the association between ApoE polymorphism and the onset of AD in Chinese population, we searched the commonly used electronic databases between January 2000 and November 2013 for relevant studies. Total 20 studies, including 1576 cases and 1741 controls, were retrieved. The results showed statistically significant positive association between risk factor ε4 allele carriers and AD in Chinese population (OR = 3.93, 95% CI = 3.37-4.58, P < 0.00001). Genotype ApoE ε4/ε4 and ε4/ε3 have statistically significant association with AD as well (ε4/ε4: OR = 11.76, 95% CI = 6.38-21.47, P < 0.00001; ε4/ε3: OR = 3.08, 95% CI = 2.57-3.69, P < 0.00001). Furthermore, the frequency of the ApoE ε3 is lower in AD than that in the health controls, and the difference of ε3 allele is also statistically significant (OR = 0.42, 95% CI = 0.37-0.47, P < 0.00001). No significant heterogeneity was observed among all studies. This meta-analysis suggests that the subject with at least one ApoE ε4 allele has higher risk suffering from AD than controls in Chinese population. The results also provide a support for the protection effect of ApoE ε3 allele in developing AD.

ApoE gene and exceptional longevity: Insights from three independent cohorts

The ApoE gene is associated with the risk of Alzheimer or cardiovascular disease but its influence on exceptional longevity (EL) is uncertain. Our primary purpose was to determine, using a case-control design, if the ApoE gene is associated with EL. We compared ApoE allele/genotype frequencies among the following cohorts: cases (centenarians, most with 1+ major disease condition; n=163, 100-111years) and healthy controls (n=1039, 20-85years) from Spain; disease-free cases (centenarians; n=79, 100-104years) and healthy controls (n=597, age 27-81years) from Italy; and cases (centenarians and semi-supercentenarians, most with 1+ major disease condition; n=729, 100-116years) and healthy controls (n=498, 23-59years) from Japan. Our main findings were twofold. First, the ε4-allele was negatively associated with EL in the three cohorts, with the following odds ratio (OR) values (adjusted by sex) having been found: 0.55 (95% confidence interval (CI): 0.33, 0.94), P=0.030 (Spain); 0.41 (95%CI: 0.18, 0.99), P=0.05 (Italy); and 0.35 (95%CI: 0.26, 0.57), P<0.001 (Japan). Second, although no association was found in the Spanish cohort (OR=1.42 (95%CI: 0.89, 2.26), P=0.145), the ε2-allele was positively associated with EL in the Italian (OR=2.14 (95%CI: 1.18, 3.45), P=0.01) and Japanese subjects (OR=1.81 (95%CI: 1.25, 2.63), P=0.002). Notwithstanding the limitations of case-control designs, our data suggest that the ApoE might be a candidate to influence EL. The ε4-allele appears to decrease the likelihood of reaching EL among individuals of different ethnic/geographic origins. An additional, novel finding of our study was that the ε2-allele might favor EL, at least in the Italian and Japanese cohorts.

Molecular cloning and characterization of the promoter region of the porcine apolipoprotein E gene

Apolipoprotein E (APOE), a component of lipoproteins plays an important role in the transport and metabolism of cholesterol, and is associated with hyperlipoproteinemia and Alzheimer's disease. In order to further understand the characterization of APOE gene, the promoter of APOE gene of Landrace pigs was analyzed in the present study. The genomic structure and amino acid sequence in pigs were analyzed and found to share high similarity in those of human but low similarity in promoter region. Real-time PCR revealed the APOE gene expression pattern of pigs in diverse tissues. The highest expression level was observed in liver, relatively low expression in other tissues, especially in stomach and muscle. Furthermore, the promoter expressing in Hepa 1-6 was significantly better at driving luciferase expression compared with C2C12 cell. After analysis of porcine APOE gene promoter regions, potential transcription factor binding sites were predicted and two GC signals, a TATA box were indicated. Results of promoter activity analysis indicated that one of potential regulatory elements was located in the region -669 to -259, which was essential for a high expression of the APOE gene. Promoter mutation and deletion analysis further suggested that the C/EBPA binding site within the APOE promoter was responsible for the regulation of APOE transcription. Electrophoretic mobility shift assays also showed the binding site of the transcription factor C/EBPA. This study advances our knowledge of the promoter of the porcine APOE gene.

Additive genetic effect of APOE and BDNF on hippocampus activity

Human memory is a highly heritable polygenic trait with complex inheritance patterns. To study the genetics of memory and memory-related diseases, hippocampal functioning has served as an intermediate phenotype. The importance of investigating gene-gene effects on complex phenotypes has been emphasized, but most imaging studies still focus on single polymorphisms. APOE ε4 and BDNF Met, two of the most studied gene variants for variability in memory performance and neuropsychiatric disorders, have both separately been related to poorer episodic memory and altered hippocampal functioning. Here, we investigated the combined effect of APOE and BDNF on hippocampal activation (N=151). No non-additive interaction effects were seen. Instead, the results revealed decreased activation in bilateral hippocampus and parahippocampus as a function of the number of APOE ε4 and BDNF Met alleles present (neither, one, or both). The combined effect was stronger than either of the individual effects, and both gene variables explained significant proportions of variance in BOLD signal change. Thus, there was an additive gene-gene effect of APOE and BDNF on medial temporal lobe (MTL) activation, showing that a larger proportion of variance in brain activation attributed to genetics can be explained by considering more than one gene variant. This effect might be relevant for the understanding of normal variability in memory function as well as memory-related disorders associated with APOE and BDNF.

Variability in APOE genotype status in human-derived cell lines: a cause for concern in cell culture studies?

Although cell culture studies have provided landmark discoveries in the basic and applied life sciences, it is often under-appreciated that cells grown in culture are prone to generating artifacts. Here, we introduce the genotype status (exemplified by apolipoprotein E) of human-derived cells as a further important parameter that requires attention in cell culture experiments. Epidemiological and clinical studies indicate that variations from the main apolipoprotein E3/E3 genotype might alter the risk of developing chronic diseases, especially neurodegeneration, cardiovascular disease, and cancer. Whereas the apolipoprotein E allele distribution in human populations is well characterized, the apolipoprotein E genotype of human-derived cell lines is only rarely considered in interpreting cell culture data. However, we find that primary and immortalized human cell lines show substantial variation in their apolipoprotein E genotype status. We argue that the apolipoprotein E genotype status and corresponding gene expression level of human-derived cell lines should be considered to better avoid (or at least account for) inconsistencies in cell culture studies when different cell lines of the same tissue or organ are used and before extrapolating cell culture data to human physiology in health and disease.

Apolipoprotein-E genotype and human immunodeficiency virus-associated neurocognitive disorder: the modulating effects of older age and disease severity

BACKGROUND

The apolipoprotein-E (APOE) ε4 allele is a risk factor for vascular dementia and Alzheimer's disease. Recent studies are equivocal with regards to whether or not the ε4 allele confers increased risk for the development of human immunodeficiency virus (HIV)-associated neurocognitive disorder (HAND), but suggest that age and/or disease severity may be modulating factors. The aim of this study was to assess the interactions and contributions of APOE genotype, age, and HIV disease severity as risk factors for HAND in HIV-infected adults.

METHODS

Participants were 259 HIV-positive individuals who underwent APOE genotyping, a standardized neurological evaluation, a comprehensive neuropsychological evaluation, and laboratory testing.

RESULTS

Older ε4 carriers showed a higher frequency of HAND compared with age-matched non-ε4 carriers. Analysis by discrete neurocognitive domain revealed that advanced age modulated the effect of the ε4 allele, such that older ε4 allele carriers showed reduced executive functioning and information processing speed. Exploratory analyses assessing the relationship between ε4 and disease severity in the overall sample revealed that disease severity modulated the effect of the ε4 allele on cognition. Lower absolute CD4+ cell count among ε4 allele carriers was associated with poorer working memory ability.

CONCLUSION

Advancing age and degree of immunosuppression may influence the association between APOE ε4 allele status and HAND. These two factors need to be taken into account in future research.

Social disorder, APOE-E4 genotype, and change in cognitive function among older adults living in Chicago

The goal of this paper is to describe the simultaneous influence of social and genetic risk factors on declines in cognitive functioning among older American adults. We use detailed information about the social characteristics of older adults' neighborhoods from the Chicago Health and Aging Project (n = 1655; ages 65+) in conjunction with information about respondent's APOE genotype to predict changes in cognitive function over time. Results indicate that the presence of the ε4 allele is associated with a significantly lower cognitive function score at baseline and greater declines in cognitive function compared to those without this risk allele. Importantly, we also show significant variation in the effect of the ε4 allele across neighborhoods and our results indicate that this genotype is more strongly associated with cognitive function for residents of neighborhoods with the lowest levels of social disorder. Our findings support the non-causal social push gene-environment interaction model.

APOE E4 status predicts age-related cognitive decline in the ninth decade: longitudinal follow-up of the Lothian Birth Cohort 1921

Carriers of the APOE E4 allele have an increased risk of developing Alzheimer's disease. However, it is less clear whether APOE E4 status may also be involved in non-pathological cognitive ageing. The present study investigated the associations between APOE genotypes and cognitive change over 8 years in older community-dwelling individuals. APOE genotype was determined in 501 participants of the Lothian Birth Cohort 1921, whose intelligence had been measured in childhood in the Scottish Mental Survey 1932. A polymorphic variant of TOMM40 (rs10524523) was included to differentiate between the effects of the APOE E3 and E4 allelic variants. Cognitive performance on the domains of verbal memory, abstract reasoning and verbal fluency was assessed at mean age 79 years (n=501), and again at mean ages of 83 (n=284) and 87 (n=187). Using linear mixed models adjusted for demographic variables, vascular risk factors and IQ at age 11 years, possession of the APOE E4 allele was associated with a higher relative rate of cognitive decline over the subsequent 8 years for verbal memory and abstract reasoning. Individuals with the long allelic variant of TOMM40, which is linked to APOE E4, showed similar results. Verbal fluency was not affected by APOE E4 status. APOE E2 status was not associated with change in cognitive performance over 8 years. In non-demented older individuals, possession of the APOE E4 allele predicted a higher rate of cognitive decline on tests of verbal memory and abstract reasoning between 79 and 87 years. Thus, possession of the APOE E4 allele may not only predispose to Alzheimer's disease, but also appears to be a risk factor for non-pathological decline in verbal memory and abstract reasoning in the ninth decade of life.

Effect of the APOE Polymorphism and Age Trajectories of Physiological Variables on Mortality: Application of Genetic Stochastic Process Model of Aging

We evaluated effects of the APOE polymorphism (carriers versus noncarriers of the e4 allele) and age trajectories of total cholesterol (CH) and diastolic blood pressure (DBP) on mortality risk in the Framingham Heart Study (original cohort). We found that long-lived carriers and noncarriers have different average age trajectories and long-lived individuals have consistently higher levels and less steep declines at old ages compared to short-lived individuals. We applied the stochastic process model of aging aimed at joint analyses of genetic and nongenetic subsamples of longitudinal data and estimated different aging-related characteristics for carriers and noncarriers which otherwise cannot be evaluated from data. We found that such characteristics differ in carriers and noncarriers: (1) carriers have better adaptive capacity than noncarriers in case of CH, whereas for DBP the opposite situation is observed; (2) mean allostatic trajectories are higher in carriers and they differ from “optimal” trajectories minimizing mortality risk; (3) noncarriers have lower baseline mortality rates at younger ages but they increase faster than those for carriers resulting in intersection at the oldest ages. Such observations strongly indicate the presence of a genetic component in respective aging-related mechanisms. Such differences may contribute to patterns of allele- and sex-specific mortality rates.

Apolipoprotein E-e4, processing speed, and white matter volume in a genetically enriched sample of midlife adults

Healthy midlife children of a parent with Alzheimer's disease ([AD] N = 23; 9 male) participated in neuropsychological testing, and magnetic resonance imaging (MRI) of brain volumetrics were obtained. In all, 35% of the sample were apolipoprotein E (ApoE)-e4 positive (n = 8; 5 male). The ApoE-e4 group exhibited significantly slower performances on an executive function and processing speed measure and had less white matter volume than the non-ApoE-e4 group. Lesser white matter volume was significantly correlated with slower processing speed. Processing speed and changes in white matter volume might be indicators of preclinical decline in AD.

Variations in apolipoprotein E frequency with age in a pooled analysis of a large group of older people

Variation in the apolipoprotein E gene (APOE) has been reported to be associated with longevity in humans. The authors assessed the allelic distribution of APOE isoforms ε2, ε3, and ε4 among 10,623 participants from 15 case-control and cohort studies of age-related macular degeneration (AMD) in populations of European ancestry (study dates ranged from 1990 to 2009). The authors included only the 10,623 control subjects from these studies who were classified as having no evidence of AMD, since variation within the APOE gene has previously been associated with AMD. In an analysis stratified by study center, gender, and smoking status, there was a decreasing frequency of the APOE ε4 isoform with increasing age (χ(2) for trend = 14.9 (1 df); P = 0.0001), with a concomitant increase in the ε3 isoform (χ(2) for trend = 11.3 (1 df); P = 0.001). The association with age was strongest in ε4 homozygotes; the frequency of ε4 homozygosity decreased from 2.7% for participants aged 60 years or less to 0.8% for those over age 85 years, while the proportion of participants with the ε3/ε4 genotype decreased from 26.8% to 17.5% across the same age range. Gender had no significant effect on the isoform frequencies. This study provides strong support for an association of the APOE gene with human longevity.

Trade-off in the effects of the apolipoprotein E polymorphism on the ages at onset of CVD and cancer influences human lifespan

Progress in unraveling the genetic origins of healthy aging is tempered, in part, by a lack of replication of effects, which is often considered a signature of false-positive findings. We convincingly demonstrate that the lack of genetic effects on an aging-related trait can be because of trade-offs in the gene action. We focus on the well-studied apolipoprotein E (APOE) e2/3/4 polymorphism and on lifespan and ages at onset of cardiovascular diseases (CVD) and cancer, using data on 3924 participants of the Framingham Heart Study Offspring cohort. Kaplan-Meier estimates show that the e4 allele carriers live shorter lives than the non-e4 allele carriers (log rank = 0.016). The adverse effect was attributed to the poor survival of the e4 homozygotes, whereas the effect of the common e3/4 genotype was insignificant. The e3/4 genotype, however, was antagonistically associated with onsets of those diseases predisposing to an earlier onset of CVD and a later onset of cancer compared to the non-e4 allele genotypes. This trade-off explains the lack of a significant effect of the e3/4 genotype on survival; adjustment for it in the Cox regression model makes the detrimental effect of the e4 allele highly significant (P = 0.002). This trade-off is likely caused by the lipid-metabolism-related (for CVD) and nonrelated (for cancer) mechanisms. An evolutionary rationale suggests that genetic trade-offs should not be an exception in studies of aging-related traits. Deeper insights into biological mechanisms mediating gene action are critical for understanding the genetic regulation of a healthy lifespan and for personalizing medical care.

The effects of APOE on brain activity do not simply reflect the risk of Alzheimer's disease

Possession of the APOE-ε4 allele is the best established genetic risk factor for sporadic Alzheimer's disease (AD), while the ε2 allele may confer protection against the disease. Previous functional magnetic resonance imaging (fMRI) studies have shown an effect of APOE genotype on brain function, typically by comparing only ε4 carriers with noncarriers. Here we included a wide range of genotype groups to determine how closely the effects of APOE on brain function are related to differences in relative risk for AD. We used functional magnetic resonance imaging (fMRI) to compare the pattern of activation during an episodic encoding task and during a counting Stroop task in 76 adults, aged 32 to 55, with different APOE genotypes (23 ε2/ε3, 20 ε3/ε3, 26 ε3/ε4, and 7 ε4/ε4). Strikingly, participants with an increased risk (ε4 carriers) and with a decreased risk (ε2 carriers) for AD both showed increased activation, relative to ε3 homozygotes, during both tasks. The increased activation was due to decreased deactivation or paradoxical activation of nontask-related regions of the brain, which suggests an intrinsic effect of APOE on the differentiation of functional cortical networks. These results question the often assumed link between APOE, the blood oxygenation level dependent (BOLD) response, and AD risk.

Inflammatory gene variants in the Tsimane, an indigenous Bolivian population with a high infectious load

The Tsimane of lowland Bolivia are an indigenous forager-farmer population living under conditions resembling pre-industrial European populations, with high infectious morbidity, high infection and inflammation, and shortened life expectancy. Analysis of 917 persons ages 5 to 60+ showed that allele frequencies of 9 SNPs examined in the apolipoprotein E (apoE), C-reactive protein (CRP), and interleukin-6 (IL-6) genes differed from some European, African, and north Asian-derived populations. The apoE2 allele was absent, whereas four SNPs related to CRP and IL-6 were monomorphic: CRP (rs1800947, rs3093061, and rs3093062) and IL-6 (rs1800795). No significant differences in apoE, CRP, and IL-6 variants across age were found CRP levels were higher in carriers of two CRP proinflammatory SNPs, whereas they were lower in carriers of apoE4. Taken together the evidence for (1) different allele frequencies between the Tsimane and other populations and (2) the correlations of CRP and apoE alleles with blood CRP may suggest that these variants are under selection in response to a high infection environment.

Influence of apolipoprotein E varepsilon4 on rates of cognitive and functional decline in mild cognitive impairment

BACKGROUND

Apolipoprotein E varepsilon4 (APOE varepsilon4) allele carrier status has been well established as a risk factor for developing Alzheimer's disease. However, the specific influence of APOE varepsilon4 allele status on cognitive and functional rates of decline in mild cognitive impairment (MCI) is poorly understood. We examine the prospective association of APOE varepsilon4 allele status on measures of cognitive and functional decline in subjects with amnestic MCI (aMCI).

METHODS

A total of 516 aMCI participants aged 55-90 years who received placebo or vitamin E from the Alzheimer's Disease Cooperative Study's MCI treatment trial were evaluated. During the 36-month study period, neurocognitive and functional measures were collected. These measures were assessed over time for change and association with APOE varepsilon4 status. Generalized Estimating Equations were performed to model each outcome measure over the study period.

RESULTS

APOE varepsilon4 status had a significant impact on cognitive and functional decline on multiple measures; those who were APOE varepsilon4 positive had significantly more rapid decline in performance on all cognitive and functional measures except Number Cancellation and Maze tracing (P < .05). The greatest decline was seen in global measures of cognition and function including the Clinical Diagnostic Rating scale, followed by the Mini-Mental State Examination, Global Deterioration scale, and the Alzheimer's Disease Assessment Scale-Cognitive Subscale.

CONCLUSIONS

These findings demonstrate that APOE varepsilon4 genotype is predictive of increased general rates of decline with global measures of cognition and function most affected. With accelerated declines in common clinical trial primary efficacy measures, APOE varepsilon4 status needs to be accounted for in treatment trials of MCI.

Worldwide allele frequencies of the human apolipoprotein E gene: climate, local adaptations, and evolutionary history

The epsilon4 allele of the apolipoprotein E (APOE) gene is associated with increased cholesterol levels and heart disease. Population allele frequencies of APOE have previously been shown to vary, with epsilon4 frequencies generally increasing with latitude. We hypothesize that this trend resulted from natural selection protecting against low-cholesterol levels. In high-latitude cold environments and low-latitude hot environments, metabolic rate is elevated, which could require higher cholesterol levels. To explore this hypothesis, we compiled APOE allele frequencies, latitude, temperature, and elevation from populations around the world. epsilon4 allele frequencies show a curvilinear relationship with absolute latitude, with lowest frequencies found in the mid-latitudes where temperatures generally require less expenditure on cooling/thermogenesis. Controlling for population structure in a subset of populations did not appreciably change this pattern of association, consistent with selection pressures that vary by latitude shaping epsilon4 allele frequencies. Temperature records also predict APOE frequency in a curvilinear fashion, with lowest epsilon4 frequencies at moderate temperatures. The model fit between historical temperatures and epsilon4 is less than between latitude and epsilon4, but strengthened after correcting for estimated temperature differences during the Paleolithic. Contrary to our hypothesis, we find that elevation did not improve predictive power, and an integrated measure of the cholesterol effect of multiple APOE alleles was less related to latitude than was epsilon4 alone. Our results lend mixed support for a link between past temperature and human APOE allele distribution and point to the need to develop better models of past climate in future analyses.

Between destiny and disease: genetics and molecular pathways of human central nervous system aging

Aging of the human brain is associated with "normal" functional, structural, and molecular changes that underlie alterations in cognition, memory, mood and motor function, amongst other processes. Normal aging also imposes a robust constraint on the onset of many neurological diseases, ranging from late onset neurodegenerative diseases, such as Alzheimer's (AD) and Parkinson's diseases (PD), to early onset psychiatric disorders, such as bipolar disorder (BPD) and schizophrenia (SCZ). The molecular mechanisms and genetic underpinnings of age-related changes in the brain are understudied, and, while they share some overlap with peripheral mechanisms of aging, many are unique to the largely non-mitotic brain. Hence, understanding mechanisms of brain aging and identifying associated modulators may have profound consequences for the prevention and treatment of age-related impairments and diseases. Here we review current knowledge on age-related functional and structural changes, their molecular and genetic underpinnings, and discuss how these pathways may contribute to the vulnerability to develop age-related neurological diseases. We highlight recent findings from human post-mortem brain microarray studies, which we hypothesize, point to a potential genetically controlled transcriptional program underlying molecular changes and age-gating of neurological diseases. Finally, we discuss the implications of this model for understanding basic mechanisms of brain aging and for the future investigation of therapeutic approaches.

The role of genetic variants in human longevity

Human longevity is a complex phenotype with a strong genetic predisposition. Increasing evidence has revealed the genetic antecedents of human longevity. This article aims to review the data of various case/control association studies that examine the difference in genetic polymorphisms between long-lived people and younger subjects across different human populations. There are more than 100 candidate genes potentially involved in human longevity; this article particularly focuses on genes of the insulin/IGF-1 pathway, FOXO3A, FOXO1A, lipoprotein metabolism (e.g., APOE and PON1), and cell-cycle regulators (e.g., TP53 and P21). Since the confirmed genetic components for human longevity are few to date, further precise assessment of the genetic contributions is required. Gaining a better understanding of the contribution of genetics to human longevity may assist in the design of improved treatment methods for age-related diseases, delay the aging process, and, ultimately, prolong the human lifespan.

Serum iron parameters, HFE C282Y genotype, and cognitive performance in older adults: results from the FACIT study

Although iron homeostasis is essential for brain functioning, the effects of iron levels on cognitive performance in older individuals have scarcely been investigated. In the present study, serum iron parameters and hemochromatosis (HFE) C282Y genotype were determined in 818 older individuals who participated in a 3-year randomized, placebo-controlled double-blind trial examining the effects of folic acid on carotid intima-media thickness. All participants had slightly elevated homocysteine levels and were vitamin B12 replete. Cognitive functioning was assessed at baseline and after 3 years by means of a neuropsychological test battery. At baseline, increased serum ferritin was associated with decreased sensorimotor speed, complex speed, and information-processing speed and increased serum iron was associated with decreased sensorimotor speed. Cognitive performance over 3 years was not associated with HFE C282Y genotype or iron parameters. In conclusion, serum iron parameters do not show a straightforward relationship with cognitive functioning, although elevated iron levels may decrease cognitive speed in older individuals susceptible to cognitive impairment.

Selection on alleles affecting human longevity and late-life disease: the example of apolipoprotein E

It is often claimed that genes affecting health in old age, such as cardiovascular and Alzheimer diseases, are beyond the reach of natural selection. We show in a simulation study based on known genetic (apolipoprotein E) and non-genetic risk factors (gender, diet, smoking, alcohol, exercise) that, because there is a statistical distribution of ages at which these genes exert their influence on morbidity and mortality, the effects of selection are in fact non-negligible. A gradual increase with each generation of the ε2 and ε3 alleles of the gene at the expense of the ε4 allele was predicted from the model. The ε2 allele frequency was found to increase slightly more rapidly than that for ε3, although there was no statistically significant difference between the two. Our result may explain the recent evolutionary history of the epsilon 2, 3 and 4 alleles of the apolipoprotein E gene and has wider relevance for genes affecting human longevity.

The effect of old age on apolipoprotein E and its receptors in rat liver

Apolipoprotein E (apoE) is associated with aging and some age-related diseases. The majority of apoE is produced by hepatocytes for the receptor-mediated uptake of lipoproteins. Here, the effects of age on the hepatic expression and distribution of apoE and its receptors were determined using immunofluorescence, Western blots, and quantitative PCR in rat liver tissue and isolated hepatocytes. The expression of apoE mRNA and protein was not influenced significantly by aging. Immunofluorescence studies in isolated hepatocytes showed that apoE was more likely to be co-localized with early endosomes, golgi, and microtubules in isolated old hepatocytes. The mRNA expression of the receptor involved in sequestration of apoE, heparan sulfate proteoglycan was reduced in old age, without any significant effect on the expression of either the low-density lipoprotein receptor or low density-lipoprotein receptor-related protein. Old age is associated with changes in hepatic apoE intracellular trafficking and heparan sulfate proteoglycan expression that might contribute to age-related disease.

Apolipoprotein E and its role in aging and survival

The study of biological aging has seen spectacular progress in the last decade and markers are increasingly employed for understanding physiological processes that change with age. Recently, it has been demonstrated that apolipoprotein E (apoE) has a major impact on longevity, but its mechanisms are still not fully understood. ApoE-deficient (E(o)) mice have proved to be a very popular model for studying spontaneous hypercholesterolemia and the subsequent development of atherosclerotic lesions, but only limited data are available with regard to aging and aging changes. We used this murine model to better characterize the involvement of apoE in aging and to evaluate its role in the maintenance of normal organ morphology. Our results show that E(0) mice at different ages (6, 12, 20 weeks old) developed age-dependent morphological and biochemical alterations, including fibrosis (newly formed collagen), pro-inflammatory cytokine (IL-6 and iNOS), lipofuscin accumulation, and decrease of antioxidant enzymes (superoxide dismutase and catalase) in several organs (kidney, liver and heart). It is significant that the observed degenerative findings in E(0) mice at different ages (6, 12, 20 weeks old) were not identified in control mice (C57BL), at 6, 12 and 20 weeks of age. Consequently, since these mice showed enzymatic and structural alterations, normally linked to the age, such as increase of lipofuscin, pro-inflammatory cytokines and decrease of antioxidant enzymes, we can conclude that apoE is a useful player in studies of longevity and age-related diseases, such as inflammatory status and atherosclerosis that are known risk factors for functional decline and early mortality. Moreover, it is possible that apoE may also play a role in other pathological conditions including, for example, cancer, rheumatoid arthritis and macular degeneration.