Molecular and cellular pathways contributing to brain aging

Aging is the leading risk factor for several age-associated diseases such as neurodegenerative diseases. Understanding the biology of aging mechanisms is essential to the pursuit of brain health. In this regard, brain aging is defined by a gradual decrease in neurophysiological functions, impaired adaptive neuroplasticity, dysregulation of neuronal Ca2+ homeostasis, neuroinflammation, and oxidatively modified molecules and organelles. Numerous pathways lead to brain aging, including increased oxidative stress, inflammation, disturbances in energy metabolism such as deregulated autophagy, mitochondrial dysfunction, and IGF-1, mTOR, ROS, AMPK, SIRTs, and p53 as central modulators of the metabolic control, connecting aging to the pathways, which lead to neurodegenerative disorders. Also, calorie restriction (CR), physical exercise, and mental activities can extend lifespan and increase nervous system resistance to age-associated neurodegenerative diseases. The neuroprotective effect of CR involves increased protection against ROS generation, maintenance of cellular Ca2+ homeostasis, and inhibition of apoptosis. The recent evidence about the modem molecular and cellular methods in neurobiology to brain aging is exhibiting a significant potential in brain cells for adaptation to aging and resistance to neurodegenerative disorders.

Emerging risk of environmental factors: insight mechanisms of Alzheimer's diseases

Neurodegenerative disorders are typically sporadic in nature in addition to usually influenced through an extensive range of environmental factors, lifestyle, and genetic elements. Latest observations have hypothesized that exposure of environmental factors may increase the prospective risk of Alzheimer's diseases (AD). However, the role of environmental factors as a possible dangerous issue has extended importance concerned in AD pathology, although actual etiology of the disorder is still not yet clear. Thus, the aim of this review is to highlight the possible correlation between environmental factors and AD, based on the present literature view. Environmental risk factors might play an important role in decelerating or accelerating AD progression. Among well-known environmental risk factors, prolonged exposure to several heavy metals, for example, aluminum, arsenic, cadmium, lead, and mercury; particulate air, and some pesticides as well as metal-containing nanoparticles have been participated to cause AD. These heavy metals have the capacity to enhance amyloid β (Aβ) peptide along with tau phosphorylation, initiating amyloid/senile plaques, as well as neurofibrillary tangle formation; therefore, neuronal cell death has been observed. Furthermore, particulate air, pesticides, and heavy metal exposure have been recommended to lead AD susceptibility and phenotypic diversity though epigenetic mechanisms. Therefore, this review deliberates recent findings detailing the mechanisms for a better understanding the relationship between AD and environmental risk factors along with their mechanisms of action on the brain functions.

Psychometric Characteristics of Cognitive Reserve: How High Education Might Improve Certain Cognitive Abilities in Aging

BACKGROUND

The capacity to mitigate dementia symptomology despite the prevailing brain pathology has been attributed to cognitive reserve.

OBJECTIVES

This study aimed to investigate how psychometric performance differs between individuals with a high school versus college education (surrogate measures for medium and high cognitive reserves) given the same level of brain pathology assessed using quantitative structural MRI.

METHODS

We used data from the Aging Brain: Vasculature, Ischemia, and Behavior Study (ABVIB). Cognition was assessed using a neuropsychological battery that included those contained in the National Alzheimer's Coordinating Center (NACC) uniform data set. Participants with a medium and high cognitive reserve were matched by level of structural MRI changes, gender, and age.

RESULTS

Matched-pair regression analyses indicated that individuals with a higher education had a significantly better performance in recognition and verbal fluency animals, working memory, and processing speed in complex tasks. Moreover, they had a better performance in interference trails compared to individuals with a high school education (medium cognitive reserve).

CONCLUSIONS

Our findings suggest that, given the same level of brain pathology, individuals with a higher education (cognitive reserve) benefit from a superior performance in semantic memory and executive functioning. Differences in these cognitive domains may be key pathways explaining how individuals with a high cognitive reserve are able to diminish dementia symptomatology despite physical changes in the brain.

Alzheimer's Disease Progression: Factors Influencing Cognitive Decline

BACKGROUND

Alzheimer's disease (AD) patients present high variability in the rate of cognitive decline. Despite the wide knowledge on factors influencing dementia risk, little is known on what accounts for AD progression. Previous studies on this topic have mainly analyzed each factor separately without taking into account the interaction between genetic and non-genetic factors.

OBJECTIVE

The aim of the present study is to evaluate the role of demographic, clinical, therapeutic, and genetic factors and their interaction on cognitive decline among newly diagnosed AD patients.

METHODS

We retrospectively selected 160 AD patients diagnosed at the Neurology Unit of Careggi University Hospital of Florence. We evaluated the occurrence of rapid cognitive changes defined as the worsening of more than four points at the Mini-Mental State Examination after 2-year follow up period.

RESULTS

Among the 160 AD patients, 50% presented rapid disease progression. Extrapyramidal signs at disease onset were predictors of worse outcome (OR 2.2), especially among Apolipoprotein E (APOE) ɛ4 allele carriers, while the presence of family history for dementia decreased the risk of rapid progression by about 50%. Higher educated ɛ4-carriers showed a slower AD progression. We identified the chronic use of aspirin as potential secondary preventative strategy for the non ɛ4-carriers.

CONCLUSION

At dementia onset, some clinical and demographic data can be predictors of future progression. The outcomes of the present study support the already hypothesized interaction between genetic and non-genetic factors during disease course and suggest genetic-based approaches.

Cognitive reserve maps the core loci of neurodegeneration in corticobasal degeneration

BACKGROUND AND PURPOSE

Cognitively stimulating life experiences and activities are deemed to moderate the clinical impact of brain damage progressively building a neural and cognitive reserve (CR). CR has been studied extensively in various neurodegenerative disorders, but not in corticobasal degeneration (CBD).

METHODS

Using Statistical Parametric Mapping 8, years of education, as a determinant of CR, was correlated with tracer uptake on positron emission tomography with ¹⁸ F-fluorodeoxyglucose, as a marker of neurodegeneration, in 35 patients with various phenotypes of CBD, including a cognitive-motor composite score or symptoms duration as covariates for controlling disease stage.

RESULTS

A cluster of relative hypometabolism was found associated with higher education in the left inferior regions of pre- and post-rolandic gyri and insula, which represent typical loci of neurodegeneration in CBD regardless of clinical presentation.

CONCLUSIONS

The present findings extend to CBD the evidence gathered in other neurodegenerative disorders that a higher CR has a protective effect against the clinical manifestations of brain degeneration.

EFAD transgenic mice as a human APOE relevant preclinical model of Alzheimer's disease

Identified in 1993, APOE4 is the greatest genetic risk factor for sporadic Alzheimer's disease (AD), increasing risk up to 15-fold compared with APOE3, with APOE2 decreasing AD risk. However, the functional effects of APOE4 on AD pathology remain unclear and, in some cases, controversial. In vivo progress to understand how the human (h)-APOE genotypes affect AD pathology has been limited by the lack of a tractable familial AD-transgenic (FAD-Tg) mouse model expressing h-APOE rather than mouse (m)-APOE. The disparity between m- and h-apoE is relevant for virtually every AD-relevant pathway, including amyloid-β (Aβ) deposition and clearance, neuroinflammation, tau pathology, neural plasticity and cerebrovascular deficits. EFAD mice were designed as a temporally useful preclinical FAD-Tg-mouse model expressing the h-APOE genotypes for identifying mechanisms underlying APOE-modulated symptoms of AD pathology. From their first description in 2012, EFAD mice have enabled critical basic and therapeutic research. Here we review insights gleaned from the EFAD mice and summarize future directions.

Lifestyle Modulators of Neuroplasticity: How Physical Activity, Mental Engagement, and Diet Promote Cognitive Health during Aging

The number of the elderly across the globe will approximate 2.1 billion by 2050. Juxtaposed against this burgeoning segment of the population is evidence that nonpathological aging is associated with an increased risk for cognitive decline in a variety of domains, changes that can cause mild disability even before the onset of dementia. Given that pharmacological treatments that mitigate dementia are still outstanding, alternative therapeutic options are being investigated increasingly. The results from translational studies have shown that modifiable lifestyle factors-including physical activity, cognitive engagement, and diet-are a key strategy for maintaining brain health during aging. Indeed, a multiplicity of studies has demonstrated relationships between lifestyle factors, brain structure and function, and cognitive function in aging adults. For example, physical activity and diet modulate common neuroplasticity substrates (neurotrophic signaling, neurogenesis, inflammation, stress response, and antioxidant defense) in the brain whereas cognitive engagement enhances brain and cognitive reserve. The aims of this review are to evaluate the relationship between modifiable lifestyle factors, neuroplasticity, and optimal brain health during aging; to identify putative mechanisms that contribute positive brain aging; and to highlight future directions for scientists and clinicians. Undoubtedly, the translation of cutting-edge knowledge derived from the field of cognitive neuroscience will advance our understanding and enhance clinical treatment interventions as we endeavor to promote brain health during aging.

Interactions between inflammation, sex steroids, and Alzheimer's disease risk factors

Alzheimer's disease (AD) is an age-related neurodegenerative disorder for which there are no effective strategies to prevent or slow its progression. Because AD is multifactorial, recent research has focused on understanding interactions among the numerous risk factors and mechanisms underlying the disease. One mechanism through which several risk factors may be acting is inflammation. AD is characterized by chronic inflammation that is observed before clinical onset of dementia. Several genetic and environmental risk factors for AD increase inflammation, including apolipoprotein E4, obesity, and air pollution. Additionally, sex steroid hormones appear to contribute to AD risk, with age-related losses of estrogens in women and androgens in men associated with increased risk. Importantly, sex steroid hormones have anti-inflammatory actions and can interact with several other AD risk factors. This review examines the individual and interactive roles of inflammation and sex steroid hormones in AD, as well as their relationships with the AD risk factors apolipoprotein E4, obesity, and air pollution.

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.

Obesity and sex interact in the regulation of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder, for which a number of genetic, environmental, and lifestyle risk factors have been identified. A significant modifiable risk factor is obesity in mid-life. Interestingly, both obesity and AD exhibit sex differences and are regulated by sex steroid hormones. Accumulating evidence suggests interactions between obesity and sex in regulation of AD risk, although the pathways underlying this relationship are unclear. Inflammation and the E4 allele of apolipoprotein E have been identified as independent risk factors for AD and both interact with obesity and sex steroid hormones. We review the individual and cooperative effects of obesity and sex on development of AD and examine the potential contributions of apolipoprotein E, inflammation, and their interactions to this relationship.

Relationship between Brain Age-Related Reduction in Gray Matter and Educational Attainment

Inter-subject variability in age-related brain changes may relate to educational attainment, as suggested by cognitive reserve theories. This voxel-based morphometry study investigated the impact of very low educational level on the relationship between regional gray matter (rGM) volumes and age in healthy elders. Magnetic resonance imaging data were acquired in elders with low educational attainment (less than 4 years) (n = 122) and high educational level (n = 66), pulling together individuals examined using either of three MRI scanners/acquisition protocols. Voxelwise group comparisons showed no rGM differences (p<0.05, family-wise error corrected for multiple comparisons). When within-group voxelwise patterns of linear correlation were compared between high and low education groups, there was one cluster of greater rGM loss with aging in low versus high education elders in the left anterior cingulate cortex (p<0.05, FWE-corrected), as well as a trend in the left dorsomedial prefrontal cortex (p<0.10). These results provide preliminary indication that education might exert subtle protective effects against age-related brain changes in healthy subjects. The anterior cingulate cortex, critical to inhibitory control processes, may be particularly sensitive to such effects, possibly given its involvement in cognitive stimulating activities at school or later throughout life.

Exploring strategies to operationalize cognitive reserve: A systematic review of reviews

INTRODUCTION

The cognitive reserve hypothesis suggests that across the lifespan, higher education, regular participation in social or mentally stimulating activities, and complexity of occupation increase an individual's resistance to dementia. However, there is currently no consensus regarding how to assess or measure cognitive reserve.

METHOD

We performed a systematic review of reviews focused on the concept of cognitive reserve to examine key elements of the definition and highlight limitations. We searched Embase.com, MEDLINE (OvidSP), the Cochrane Library, Web of Science, Scopus, Google Scholar, and PubMed.

RESULTS

Five systematic reviews were identified. These incorporated findings from cohort, cross-sectional, and case-control studies, and the outcomes examined included Alzheimer's disease, vascular dementia, nonspecified dementia, all dementias, and cognitive decline or cognitive impairment. Education, occupation, and leisure or mentally stimulating activities were suggested to supply cognitive reserve and offer a protective effect against the risk of dementia. Premorbid IQ and socioeconomic status have not been investigated as thoroughly and showed inconsistent results. Two of the reviews showed that when combining different indicators in the analyses/definition, including education, occupation, mentally stimulating activities, and premorbid IQ, cognitive reserve had a protective effect against cognitive decline. However, other indicators may also supply the reserve, including dietary habits and genetic indicators, but research is lacking with regard to creating a full cognitive reserve model.

CONCLUSIONS

This review highlights the lack of consensus regarding a definition of cognitive reserve. Further research is required to clarify how the indicators already identified may provide cognitive reserve and offer a protective effect against dementia. Agreement on the indicators that constitute the cognitive reserve model is needed before testing possible interventions that may increase the reserve supply and improve cognition.

Paths to Alzheimer's disease prevention: from modifiable risk factors to biomarker enrichment strategies

Alzheimer's disease (AD) represents an increasing worldwide healthcare epidemic. Secondary preventive disease-modifying treatments under clinical development are considered most effective when initiated as early as possible in the pathophysiological course and progression of the disease. Major targets are to enhance clearance and to reduce cerebral accumulation of amyloid, decrease hyperphosphorylation of tau and the generation of neurofibrillary tangles, reduce inflammation, and finally progressive neurodegeneration. Comprehensive sets of biological markers are needed to characterize the pathophysiological mechanisms, indicate effects of treatment and to facilitate early characterisation and detection of AD during the prodromal or even at asymptomatic stages. No primary or secondary preventive treatments for AD have been approved. Epidemiological research, however, has provided evidence of specifically modifiable risk and protective factors. Among them are vascular, lifestyle and psychological risk factors that may act both independently and by potentiating each other. These factors may be substantially impacted by single or multi-domain strategies to prevent or postpone the onset of AD-related pathophysiology. Researchers have recently started the European Dementia Prevention Initiative (EDPI), an international consortium to improve strategies for preventing dementia. EDPI, in particular, includes the Finnish Geriatric Intervention Study to Prevent Cognitive Impairment and Disability (FINGER) which aims at optimizing the early identification of subjects at increased risk of late-life cognitive deterioration, and at the evaluation of multi-domain intervention strategies. The ongoing discussion on new diagnostic criteria provided by the International Working Group (IWG), as well as by the recommendations summoned by the National Institute on Aging and Alzheimer's Association (NIA-AA) initiative, has inspired the creation of novel study designs and the definition of earlier target populations for trials in pre- and asymptomatic at-risk and prodromal stages of AD. As a result, a number of promising international prevention trials are currently ongoing. In this review, we critically discuss the main paths to AD prevention through control of modifiable risk factors and lifestyle changes. We will also review the role of biomarkers to identify subgroups of patients who would most likely benefit from secondary prevention strategies, and to evaluate the benefit of treatment in such patients.

Future directions in Alzheimer's disease from risk factors to prevention

The increase in life expectancy has resulted in a high occurrence of dementia and Alzheimer's disease (AD). Research on AD has undergone a paradigm shift from viewing it as a disease of old age to taking a life course perspective. Several vascular, lifestyle, psychological and genetic risk factors influencing this latent period have been recognized and they may act both independently and by potentiating each other. These risk factors have consequently been used to derive risk scores for predicting the likelihood of dementia. Despite population differences, age, low education and vascular risk factors were identified as key factors in all scoring systems. Risk scores can help to identify high-risk individuals who might benefit from different interventions. The European Dementia Prevention Initiative (EDPI), an international collaboration, encourages data sharing between different randomized controlled trials. At the moment, it includes three large ongoing European trials: Finnish Geriatric Intervention Study to Prevent Cognitive Impairment and Disability (FINGER), Prevention of Dementia by Intensive Vascular Care (preDIVA), and Multidomain Alzheimer Prevention study (MAPT). Recently EDPI has developed a "Healthy Aging through Internet Counseling in Elderly" (HATICE) program, which intends to manage modifiable risk factors in an aged population through an easily accessible Internet platform. Thus, the focus of dementia research has shifted from identification of potential risk factors to using this information for developing interventions to prevent or delay the onset of dementia as well as identifying special high-risk populations who could be targeted in intervention trials.