Developing strategies to cope with increase in the ageing population and age-related chronic diseases is one of the societies biggest challenges. The characteristics of the ageing process shows significant inter-individual variation. Building genomic signatures that could account for variation in health outcomes with age may facilitate early prognosis of individual age-correlated diseases (e.g. cancer, coronary artery diseases and dementia) and help in developing better targeted treatments provided years in advance of acquiring disabling symptoms for these diseases. The aim of this thesis was to explore methods for diagnosing molecular features of human ageing. In particular, we utilise multi-platform transcriptomics, independent clinical data and classification methods to evaluate which human tissues demonstrate a reproducible molecular signature for age and which clinical phenotypes correlated with these new RNA biomarkers.

Objectives: Extending working lives is a major strategy in policy responses to ageing populations. This is currently being implemented by means of the increasing UK state pension age. However, the health effects of such changes are highly debatable. A systematic review conducted by this thesis revealed that previous research on the topic has provided a diverse set of findings. One of the reasons for the lack of agreement between previous studies is the high degree of heterogeneity in the study samples of older adults. This is statistically revealed by a meta-analysis conducted in this study. The research presented within this thesis examines whether extending working lives is beneficial for health, and focuses on the importance of accounting for quality of work when considering these effects. Methods: The study used respondents from waves 1 to 5 of the English Longitudinal Study of Ageing who worked until state pension age and then entered either later-life employment or retirement. Linear spline regressions examined trajectories of depression, self-rated health and cognitive function across the retirement age period, stratified by work quality and retirement. Propensity score matching was subsequently used to estimate unbiased treatment effects of extended working as opposed to retirement, and then of poor and good quality work individually in relation to retirement. Results: The spline models indicated entering retirement from work was associated with a significant change in patterns of depression and self-rated health, but continuation of work was not. Retiree trajectories consistently showed poorer outcomes than those of respondents who were working. The results of the propensity score matching found no significant differences in health on the basis of belonging to the group of overall workers compared to retirees. However when work was stratified on the basis of its quality, significant differences became apparent. Belonging to the group of poor quality workers was associated with significantly worse depression than belonging to both the good quality workers and retirees, and belonging to the group of good quality worker was associated with significantly better self-rated health than belonging to the group of retirees. Discussion: The heterogeneous socio-demographic and health characteristics of the older working population should be taken into account when examining impacts of employment on health. Failure to account for differences in quality of work may lead to the incorrect assumption that extended employment is beneficial to the health of all workers. If older people are going to be encouraged to work for longer periods of time, beneficial effects need to apply to all working groups. Employers need to ensure adjustments to individual working patterns and environments are made in order to suit the needs of an ageing workforce.

Background: Healthy cognitive ageing entails a number of neurobiological processes which may contribute to optimal functioning and quality of life in ageing. While the full extent of the underlying mechanisms of healthy ageing are yet to be described, there is an important interplay between brain structure, function, and genetic makeup that determines ageing trajectories. Notably, the Apolipoprotein E (APOE) gene has been established in the Alzheimer’s disease (AD) literature to impact brain structure and function, and may also show congruent effects in healthy older adults, although findings in this population are much less consistent. Structural Magnetic Resonance Imaging (MRI), Diffusion Tensor Imaging (DTI), and neuropsychological measures present as useful, non-invasive tools to investigate the impact of APOE allele status on grey matter structure, white matter integrity, and cognitive functioning, respectively. Few studies have used these measures together to describe healthy ageing, and findings are mixed (e.g., no differences seen, different suggested regions of difference, etc.). The current study aims to describe the impact of APOE genotype on brain structure and function in healthy older adults using multimodal methods. Method: Data were obtained from the Alzheimer’s Disease Initiative phase 3 (ADNI3) database. Baseline MRI, DTI and cognitive composite scores for memory (ADNI-Mem) and EF (ADNI-EF) were acquired from 116 healthy controls. Participants were grouped according to APOE allele presence (APOE-ε2+ N= 17, APOE-ε3ε3 N= 64, APOE-ε4+ N=35). Voxel-based morphometry (VBM) and tract based spatial statistics (TBSS) were used to compare grey matter volume (GMV) and white matter integrity respectively between APOE-ε2+ and APOE-ε3ε3 controls, and again between APOE-ε4+ and APOE-ε3ε3 controls. Multivariate analysis of covariance (MANCOVA) was used to examine the effects of APOE polymorphism on memory and EF across all APOE groups with covariates of age, sex, and education, and cognitive scores were correlated (Pearson r) with imaging metrics within groups. Results: No significant differences were seen across groups or within-groups in MRI metrics or cognitive performance (p>0.05, corrected for multiple comparisons). Non-significant trend-level results suggested 1) Increased fractional anisotropy (FA) and GMV was present in APOE-ε2+ compared to APOE-ε3ε3. 2) Increased mean diffusivity (MD) and decreased GMV was present in APOE-ε4+ compared to APOE-ε3ε3 (p<0.2, corrected for multiple comparisons). Non-significant moderate effect sizes were seen for a positive trend between GMV and EF (r= 0.36, p= 0.18) in APOE-ε2+ and a negative trend between MD and EF in APOE-ε4+ (r= -0.33, p= 0.05). Conclusions: APOE polymorphisms do not appear to impact brain structure and function differently in healthy ageing. Trend-level findings align with reports from previous research, although results remain mixed. Overall, this study suggests neurostructural and functional differences across APOE genotype are not present in cognitively healthy older adults, and future studies should aim to clarify APOE mechanisms in healthy ageing with the addition of other variables (e.g., imaging, cognitive, & lifestyle factors), longitudinal design, and in a larger sample. / Graduate / 2022-08-17

Natural ageing is known to have a negative effect on the formability and bake-hardening response of Al-Mg-Si alloys. This is attributed to the formation of Mg and Si clusters during natural ageing. The clustering process was the subject of many studies in the literature, however, the formation mechanism and kinetics of it, continues to be poorly understood. The aim of this project is to shed some light on the cluster formation mechanism and measure clustering kinetics at low temperatures. A series of electrical resistivity measurements, positron annihilation lifetime spectroscopy and hardness tests were performed on samples aged over the temperature range of -20 to 50°C following solution treatment at temperatures of 525 and 560°C. A very good correlation between the results of various techniques was observed. In addition, three different stages in the clustering process were detected. Not surprisingly it was found that the excess quenched-in vacancies are the key players in the cluster formation process. In the first stage, annihilation of near-sink vacancies occurs while other vacancies start to bind with solute atoms and form clusters. In the second stage, clustering continues to take place but its rate slows down since the effective diffusion coefficient of vacancies decreases as they bind with more solute. Finally, the clustering process enters the third stage with much slower kinetics. Interestingly, positron annihilation lifetime also reaches a constant value at the beginning of stage III which suggests the stabilization of vacancies. Two hypothesis were then developed to explain the existence of stage III: one based on the immobilization of vacancies due to the increased binding with solute atoms and another one which considers the overlapping of solute diffusion profiles around the clusters. Finally it was shown that the resistivity change in stage II can be used to find the activation energy of clustering which is calculated to be approximately 46 kJ/mol. This is very close to the migration energy of vacancies and Mg atoms. Thus it was concluded that migration of these species is the major rate controlling parameter for the clustering process. / Thesis / Master of Applied Science (MASc)

No / While most positional acuity tasks exhibit an age-related decline in performance, the effect of ageing upon vernier acuity continues to be the subject of some debate. In the present study we employed a stimulus design that enabled the simultaneous determination of bisection and vernier acuities in 36 subjects, aged between 22 and 84 years. This approach provided a means for directly testing the hypothesis that ageing affects bisection acuity but not vernier acuity by ensuring that differences in stimulus configuration and in the subject¿s task were kept to an absolute minimum. Optimum thresholds increased as a function of age for both bisection and vernier tasks. Inter-subject threshold variability also increased with age. Issues surrounding the comparison of absolute vernier thresholds across different studies are discussed and two important methodological factors are identified: the precise statistical method used to estimate thresholds, and the magnitude, in angular terms, of the smallest spatial offset of the elements of the vernier stimulus which can be displayed. Comparison with previously published data indicates that the discrepancy between this study and most previous investigations with respect to the effect of age upon vernier performance can be at least partly accounted for by differences in the minimum displayable vernier offset. Vernier thresholds do increase with age. The increased variability of vernier thresholds in older subjects would appear to limit the diagnostic value of the test as a means of enabling normal ageing to be distinguished from visual loss due to pathology of the eye or visual system.

In this thesis, I investigated effects of conflict strength and ageing on cognitive control. Conflict strength was manipulated in the Eriksen flanker task using two different approaches: 1. independent variation of flanker and target contrast; 2. manipulation of stimulus onset asynchrony (SOA). Reducing flanker contrast relative to target contrast decreased conflict strength, as shown by a reduction in compatibility effects, when contrast conditions were presented in a randomized fashion but not when they were presented block-wise. An SOA of 100 ms did lead to increased compatibility effects compared to SOAs of 0 ms and 200 ms. Effects of conflict appear to be reflected in the N2 component of the ERP. Although priming played a crucial role in the emergence of the sequential adjustment effect, conflict strength also influenced this effect to a certain degree, supporting the claim that sequential adjustments represent an adaptation of cognitive control. Post-error slowing and error-related ERP components, on the other hand, were not affected by the conflict manipulations, suggesting that errors cannot be explained in terms of conflict processing. Effects of ageing on cognitive control were investigated in a group of middle-aged participants. Although physiological indicators of conflict and error processing were compromised in this age group and overall response times were increased, compatibility, sequential adjustment, and post-error slowing effects were of comparable size as in young adults. These findings suggest that participants could successfully compensate for age-related physiological changes at this early stage of ageing. In conclusion, the research presented in this thesis provided important information to extend our knowledge of factors influencing cognitive control processes.

While the need for web accessibility for people with disabilities is widely accepted, the same visibility does not apply to the accessibility needs of older adults. This research initially explored developer behaviour in terms of how they presented accessibility on their websites as well as their own accessibility practices in terms of presentation of accessibility statements, the mention of accessibility as a selling point to potential clients and homepage accessibility of company websites. Following from this starting point the research focused in on web accessibility for ageing in particular. A questionnaire was developed to explore the differences between developer views of general accessibility and accessibility for older people. The questionnaire findings indicated that ageing is not seen as an accessibility issue by a majority of developers. Awareness of ageing accessibility documentation was also very low, highlighting the need for raising awareness of accessibility practices for ageing. Current age-related documentation developed by the Web Accessibility Initiative was then examined and critiqued. The findings show a tension between the machine-centric Web Content Accessibility Guidelines 2.0 (WCAG 2.0) and the needs of older people. Examination of guidelines when compared to research-derived findings reveal that the Assistive Technology (AT) centric structure of the documentation does not appropriately highlight accessibility practices in a context that matches the observed behaviour of older people. The documentation also fails to appropriately address the psycho-social ramifications of how older people choose to interact with technology as well as how they identify themselves in relation to any conditions they have which may be considered disabling. The need for a novel, engaging and awareness-raising tool resulted in the development of what is essentially a "Virtual third-age simulator". This ageing simulator is the first to combine multiple impairments in an active simulation and uses eye-tracking technology to increase the fidelity of conditions resulting in partial sightedness. It also allows for developers to view their own web content in addition to the lessons provided using the simulations presented in the software. The simulator was then validated in terms of its ability to raise awareness as well as its ability to affect web industry professionals' intentions towards accessible practices that benefit older people.

As humans age, specific mental faculties deteriorate even in the absence of dementia. Age related cognitive decline affects quality of life, and has significant implications from a socio-economic perspective; however not everyone declines to equal degrees, at equal rates, or from the same baseline. This PhD examined a large sample of community-dwelling older adults called the Lothian Birth Cohort 1936, most of whom completed an intelligence test at age 11 years, and again around age 73 as part of a detailed assessment that also included detailed brain magnetic resonance imaging (N range = 700-866). I investigated the independent effects of two linked genetic loci which have been associated with greater risk of Alzheimer’s disease – the APOE ε haplotype (commonly ‘genotype’) and a poly-T repeat in the TOMM40 gene. Are 'risk' variants in these loci associated with specific measures of cognitive ageing and brain structure - specifically white matter microstructural integrity, hippocampal volumes, white matter lesions or cerebral microbleeds – in this sample? Firstly, a pilot study aimed to replicate significant associations between the ADRB2 gene and brain imaging/cognitive phenotypes, that had previously been reported in a smaller subsample of the cohort that had by that time undergone MRI (n = 132). Previously reported significant associations were not significant in the larger, full LBC1936 sample (n = 700-866), but novel significant associations were found (P < 0.05). Specifically, integrity of the left arcuate fasciculus white matter tract significantly mediated part of the association between specific genetic variations at ADRB2, and the Digit Symbol Coding task of information processing speed. These findings indicated that this approach – testing three-way genetic/brain imaging/cognitive associations for mediation - was viable for the main APOE/TOMM40 analyses. Results in the main APOE/TOMM40 analyses showed that specific variants in the APOE and TOMM40 gene loci were statistically significantly associated (at raw P value <0.05) with white matter tract microstructural integrity, but not white matter lesions, hippocampal volume or cerebral microbleeds. Inconsistencies with previous, positive reports showing significant associations between APOE ε and these latter phenotypes may reflect a degree of type 1 error or more study-specific discrepancies (which are detailed throughout). APOE ε was significantly associated with average scores on a large proportion of cognitive tests, independent of age 11 intelligence (i.e. ‘cognitive ageing’; Deary et al., 2004). These associations were partly – but not completely – mediated by white matter tract microstructural integrity. TOMM40 poly-T repeat genotype was associated with cognitive ageing to a much lesser extent. A range of brain phenotypes may form the anatomical basis for significant associations between APOE genotype and cognitive ageing, among which includes white matter tract microstructural integrity.

Blood pressure has previously been associated with decline in memory over time, though the exact mechanism behind this effect is uncertain. Infections, which can lead to systemic inflammation have also been linked to some cardiovascular damage to the brain, known as microbleeds, which have themselves been linked to greater declines in cognition in old age. The present study investigates whether blood pressure, a self-reported history of infection, and an indirect measure of inflammation known as the erythrocyte sedimentation rate have any association with on episodic and semantic memory and visuospatial skills in the Betula study, a Swedish longitudinal population study. The effect of elevated blood pressure (over 140 mm Hg systolic and/or 90 mm Hg diastolic), high blood sedimentation (top 33% against bottom 33% of participants), and self-reported infection were all found to not have any significant effect on episodic memory, semantic memory or visuospatial skills. Some of the possible explanations are elaborated in the discussion. / Högt blodtryck har associerats med minnesnedsättning men den exakta mekanismen hur ett samband kan förstås är dock oklar. Infektioner har visat sig ge systematiska inflammationer och har också satts i samband med vissa kardiovaskulära förändringar i hjärnan, så kallade mikroblödningar, vilka i sig har associerats med ökad risk för kognitive nedsättning i hög ålder. Denna uppsats syftar till att undersöka om blodtryck och infektion (självrapporterad infektion samt infektion indirekt mätt genom sänkereaktion) kan relateras till episodiskt och semantisk minne samt visuospatial förmåga i Betula studien, som är en svensk longitudinell populationsbaserad studie. Resultatet visade att varken högt blodtryck (över 140 mm Hg systoliskt eller 90 mm Hg diastoliskt), hög sänkereaktion (de 33 % med högst värde jämfört med de 33 % med lägst värde) eller självrapporterad infektion hade någon signifikant effekt för episodiskt minne, semantiskt minne eller visuospatial förmåga. Några möjliga förklaringar till detta resultat utvecklas i diskussionen. / The Betula Study

The structural and functional decline of the ageing human brain varies by brain region, cognitive function and individual. The underlying biological mechanisms are poorly understood. One potentially important mechanism is exposure to glucocorticoids (GCs; cortisol in humans); GC production is increasingly varied with age in humans, and chronic exposure to high levels is hypothesised to result in cognitive decline via cerebral remodelling. However, studies of GC exposure in humans are scarce and methodological differences confound cross-study comparison. Furthermore, there has been little focus on the effects of GCs on the frontal lobes and key white matter tracts in the ageing brain. This thesis therefore examines relationships among cortisol levels, structural brain measures and cognitive performance in 90 healthy, elderly community-dwelling males from the Lothian Birth Cohort 1936. Salivary cortisol samples characterised diurnal (morning and evening) and reactive profiles (before and after a cognitive test battery). Structural variables comprised Diffusion Tensor Imaging measures of major brain tracts and a novel manual parcellation method for the frontal lobes. The latter was based on a systematic review of current manual methods in the context of putative function and cytoarchitecture. Manual frontal lobe brain parcellation conferred greater spatial and volumetric accuracy when compared to both single- and multi-atlas parcellation at the lobar level. Cognitive ability was assessed via tests of general cognitive ability, and neuropsychological tests thought to show differential sensitivity to the integrity of frontal lobe sub-regions. The majority of, but not all frontal lobe test scores shared considerable overlap with general cognitive ability, and cognitive scores correlated most consistently with the volumes of the anterior cingulate. This is discussed in light of the diverse connective profile of the cingulate and a need to integrate information over more diffuse cognitive networks according to proposed de-differentiation or compensation in ageing. Individuals with higher morning, evening or pre-test cortisol levels showed consistently negative relationships with specific regional volumes and tract integrity. Participants whose cortisol levels increased between the start and end of cognitive testing showed selectively larger regional volumes and lower tract diffusivity (correlation magnitudes <.44). The significant relationships between cortisol levels and cognition indicated that flatter diurnal slopes or higher pre-test levels related to poorer test performance. In contrast, higher levels in the morning generally correlated with better scores (correlation magnitudes <.25). Interpretation of all findings was moderated by sensitivity to type I error, given the large number of comparisons conducted. Though there were limited candidates for mediation analysis, cortisol-function relationships were partially mediated by tract integrity (but not sub-regional frontal volumes) for memory and post-error slowing. This thesis offers a novel perspective on the complex interplay among glucocorticoids, cognition and the structure of the ageing brain. The findings suggest some role for cortisol exposure in determining age-related decline in complex cognition, mediated via brain structure.