Gene-environment Interactions in Late Life: Linking Psychosocial Stress with Brain Aging

Dyadic contagion in cognitive function: A nationally-representative longitudinal study of older U.S. couples

Later-life cognitive function is strongly influenced by one's environment. At this life stage, a partner's behaviors and attributes-including their own cognitive status-are a key environmental determinant. A recent "social allostasis" theory also yields specific predictions on patterns of mutual influence-or "contagion"-in cognitive function. Yet, no population representative studies have examined these coupled dynamics. Using recently developed fixed-effects cross-lagged panel modeling (FE-CLPM) methods and ten-year data from the Health and Retirement Study-nationally-representative of U.S. adults over 50-the current study filled this gap. Results supported dyadic cognitive contagion over the long- but not short-run. Short-term associations suggested intriguing "cognitive cycling" possibilities among both men and women that need further investigation. Overall, results supported a theoretical model of coupled "cognitive careers," and relational inducement of allostatic load. Especially among men, recurrent impulses also cumulatively induced substantial path-dependent cognitive improvements, supporting the added value of repeated over one-time interventions. Theoretical and substantive implications are discussed.

Age-related impact of social isolation in mice: Young vs middle-aged

Social isolation is a chronic mild stressor and a significant risk factor for mental health disorders. Herein we explored the impact of social isolation on depression- and anxiety-like behaviours, as well as spatial memory impairments, in middle-aged male mice compared to post-weaning mice. We aimed to quantify and correlate social isolation-induced behaviour discrepancies with changes in hippocampal glial cell reactivity and pro-inflammatory cytokine levels. Post-weaning and middle-aged C57BL7/J6 male mice were socially isolated for a 3-week period and behavioural tests were performed on the last five days of isolation. We found that 3 weeks of social isolation led to depressive-like behaviour in the forced swim test, anxiety-like behaviour in the open field test, and spatial memory impairment in the Morris water maze paradigm in middle-aged male mice. These behavioural alterations were not observed in male mice after post-weaning social isolation, indicating resilience to isolation-mediated stress. Increased Iba-1 expression and NLRP3 priming were both observed in the hippocampus of socially isolated middle-aged mice, suggesting a role for microglia and NLRP3 pathway in the detrimental effects of social isolation on cognition and behaviour. Young socially isolated mice also demonstrated elevated NLRP3 priming compared to controls, but no differences in Iba-1 levels and no significant changes in behaviour. Ageing-induced microglia activation and enhancement of IL-1β, TNF-α and IL-6 proinflammatory cytokines, known signs of a chronic low-grade inflammatory state, were also detected. Altogether, data suggest that social isolation, in addition to inflammaging, contributes to stress-related cognitive impairment in middle-aged mice.

Early Adversity and Accelerated Brain Aging: A Mini-Review

Early adversity is an important risk factor that influences brain aging. Diverse animal models of early adversity, including gestational stress and postnatal paradigms disrupting dam-pup interactions evoke not only persistent neuroendocrine dysfunction and anxio-depressive behaviors, but also perturb the trajectory of healthy brain aging. The process of brain aging is thought to involve hallmark features such as mitochondrial dysfunction and oxidative stress, evoking impairments in neuronal bioenergetics. Furthermore, brain aging is associated with disrupted proteostasis, progressively defective epigenetic and DNA repair mechanisms, the build-up of neuroinflammatory states, thus cumulatively driving cellular senescence, neuronal and cognitive decline. Early adversity is hypothesized to evoke an “allostatic load” via an influence on several of the key physiological processes that define the trajectory of healthy brain aging. In this review we discuss the evidence that animal models of early adversity impinge on fundamental mechanisms of brain aging, setting up a substratum that can accelerate and compromise the time-line and nature of brain aging, and increase risk for aging-associated neuropathologies.

Longitudinal association between perceived stress and depression among community-dwelling older adults: Findings from the Irish Longitudinal Study on Ageing

BACKGROUND

Older adults may be particularly vulnerable to the negative effects of stress on depression. However, the impact of perceived stress on late-life depression is understudied in large community samples. Thus, the present study used data from a population-based sample of Irish older adults to examine the longitudinal association between perceived stress and late-life depression.

METHODS

Data from Wave 1 (2009-2011) and Wave 2 (2012-2013) of the Irish Longitudinal Study on Ageing (TILDA) were analyzed. Depression was assessed with the Center for Epidemiologic Studies Depression (CES-D), while the 4-item version of the Perceived Stress Scale was used for perceived stress. Multivariable logistic regression was used to assess the association between perceived stress (exposure) and depression (outcome).

RESULTS

The analytical sample consisted of 5238 individuals aged ≥50 years [mean (SD) age 63.2 (9.1) years; 49.4% females] who did not have depression at Wave 1. The mean perceived stress score at baseline was much lower among those who did not develop depression at Wave 2 compared to those who did (3.85 vs. 6.33). Compared to those in the lowest quartile of levels of perceived stress at baseline, those in the highest quartile had 2.65 (95%CI=1.56-4.49) times higher risk for depression onset.

LIMITATIONS

Some baseline information including that of perceived stress could have changed within the two-year follow-up period.

CONCLUSIONS

Greater levels of perceived stress at baseline was associated with higher risk for depression onset at two-year follow-up among older adults in Ireland. Individualized interventions addressing stress may be beneficial in the prevention of depression among older adults.

Religious attendance and global cognitive function: A fixed-effects cross-lagged panel modeling study of older U.S. adults

OBJECTIVES

Evidence linking religious attendance to better cognitive function is based on flawed study designs. No population representative longitudinal studies on the topic have taken both unobserved confounding and reverse causation into account. Recently developed fixed-effects cross-lagged panel modeling (FE-CLPM) offers simultaneous traction on these issues. It also allows parsing of long-from short-run effects. Using FE-CLPM and ten-year data from the Health and Retirement Study-a national probability sample of U.S. adults over age 50-this study began to fill the gaps above.

METHODS

Gender-specific FE-CLPM models were used to examine bidirectional and within-person linkages of religious attendance with global cognitive function. Granger-Sims "causality" tests further examined short-run effects in both directions. Impulse response analysis was used to explore time patterns in these linkages.

RESULTS

At least among women, religious attendance had negative short-term prospective linkages with global cognitive function. Over successive time points, these associations increased in strength among both genders. Feedback effects-of cognitive status on religious attendance-were found in both women's and men's models, but had a gender-specific pattern.

DISCUSSION

Results contradict a large literature positing cognitive benefits of religiosity. Instead, they lend support to a recent "neural resource depletion" model-especially among women. Overall, findings illustrate the "dark side" of religious engagement, which studies increasingly present as a social determinant with "outcome wide" positive effects on multiple health dimensions.

A Discovery that Reframes the Whole of Global Healthcare in the 21st Century: The Importance of the Imprintome

Within the genome exists a specific subset of genes whose expression is controlled by epigenetic marks. These tags can be modified by lifestyle factors including diet, behavior, environment and social interactions. Differences in genetic expression, despite identical genes, is explained in part through metastable epialleles-alleles that, while genetically indistinguishable, are variably expressed as a function of epigenetic modification. As a group, these metastable epialleles have been given a unique descriptive name: the imprintome. This breakthrough in understanding genetic expression has led to a wider recognition that our genes are fundamentally controlled at two levels. One is the hardware of the genetic code, which is modified slowly by natural selection through mutational changes in the genome over centuries of time. The other is the software that controls the expression of our genetic code, converting nucleotide sequences into phenotype in response to the imprinting of our epigenome. Acting as a rapid translator for real time changes, the imprintome responds to environmental and lifestyle inputs by genomic methylation and histone modifications that affect promoter accessibility and transcription factor activity. In application, this understanding of the plasticity of the imprintome necessitates a rethinking of both health and disease states. It's a concept that cuts across all forms of healthcare: physical, metabolic, and cognitive-behavioral interventions. But at the same time, it is an aggregating concept-one that brings disciplines together to collaborate on the personalization of health and the delivery of truly individualized care. This article reviews the development of the concept of the imprintome, as well as clinical studies supporting its importance as a potential driver of change in global health care.

The relational genomics of cognitive function: A longitudinal study

OBJECTIVES

Research in social genetics indicates a person's genome may influence outcomes of those in close relationships. Implications for cognitive function remain unexplored. The current study examined such "metagenomic" patterns among older U.S. couples.

METHODS

Data were from married or cohabiting couples in the 2006-2016 waves of the Health and Retirement Study, nationally representative of U.S. adults over 50. Measures included cognitive function as well as separate polygenic scores for cognition and for educational attainment. Analysis was through parallel process latent growth models.

RESULTS

Consistent with a recent "genetic externalities" conception, one partner's polygenic score for educational attainment was linked to the other's baseline levels of cognitive function. Contrary to relational moderation speculations, neither a partner's genetic scores nor educational attainment altered individual-level genetic influences.

DISCUSSION

Findings add to the growing evidence that transpersonal genetic influences in one's proximal context have substantively important implications. Research is needed on the role of non-partnership ties in channeling such effects. Implications for life course theory are discussed.

Experience of Elderly People Regarding the Effect of Yoga/Light Exercise on Sedentary Behavior: A Longitudinal Qualitative Study in Madhya Pradesh, India

This study is set on the background of a randomized control trial (RCT) in which intervention was carried to observe the effects of yoga/light exercise on the improvement in health and well-being among the elderly population. A longitudinal qualitative study was conducted as part of RCT interventions to explore the experience of the elderly practicing yoga/light exercise in relation to sedentary behavior in the Ujjain district of Madhya Pradesh, India. Participants of the RCT were selected for this study. Eighteen focus group discussions were conducted—six during each phase of RCT interventions (before, during, and after). The findings regarding motivating and demotivating factors in various phases of intervention were presented in three categories: experience and perception of the effects of yoga/light exercise on sedentary behavior (1) before, (2) during, and (3) after intervention. This study explores the positive effect of yoga/light exercise on sedentary behavior and subjective well-being on the elderly population. They were recognized to have undergone changes in their physical and emotional well-being by consistently practicing yoga/light exercise. The main driving factors were periodic health check-ups and the encouragement of qualified trainers without any cost. This study concludes with the notion that these interventions should be encouraged in the community to use physical exercise as a method to better control the physical and social effects of aging.

Subjective mental health, incidence of depressive symptoms in later life, and the role of epigenetics: results from two longitudinal cohort studies

The role of self-perceived general health in predicting morbidity and mortality among older people is established. The predictive value of self-perceived mental health and of its possible biological underpinnings for future depressive symptoms is unexplored. This study aimed to assess the role of mental health-related quality of life (HRQOL) and of its epigenetic markers in predicting depressive symptoms among older people without lifetime history of depression. Data were based on a subgroup (n = 1 492) of participants of the longitudinal ESTHER study. An epigenome-wide association study (EWAS) of mental HRQOL was conducted using DNA from baseline whole blood samples and logistic regression analyses were performed to assess the predictive value of methylation beta values of EWAS identified CpGs for incidence of depressive symptoms in later life. The methylation analyses were replicated in the independent KORA cohort (n = 890) and a meta-analysis of the two studies was conducted. Results of the meta-analysis showed that participants with beta values of cg27115863 within quartile 1 (Q₁) had nearly a two-fold increased risk of developing depressive symptoms compared to participants with beta values within Q₄ (OR_Q1vsQ4= 1.80; CI 1.25-2.61). In the ESTHER study the predictive value of subjective mental health for future depressive symptoms was also assessed and for 10-unit increase in mental HRQOL scores the odds for incident depressive symptoms were reduced by 54% (OR 0.46; CI 0.40-0.54). These findings suggest that subjective mental health and hypomethylation at cg27115863 are predictive of depressive symptoms, possibly through the activation of inflammatory signaling pathway.

Epigenetic mechanisms activated by childhood adversity

Adverse childhood experiences (ACE) impair health and life expectancy and may result in an epigenetic signature that drives increased morbidity primed during early stages of life. This literature review focuses on the current evidence for epigenetic-mediated programming of brain and immune function resulting from ACE. To address this aim, a total of 88 articles indexed in PubMed before August 2019 concerning ACE and epigenetics were surveyed. Current evidence partially supports epigenetic programming of the hypothalamic-pituitary-adrenal axis, but convincingly shows that ACE impairs immune function. Additionally, the needs and challenges that face this area are discussed in order to provide a framework that may help to clarify the role of epigenetics in the long-lasting effects of ACE.