The Impact of Ageing, Replication and Stress on Genome Stability in Hematopoietic Stem Cells

The acquisition of mutations within the genome of hematopoietic stem cells (HSCs) is of particular importance as this is a likely driver of malignant transformation for many leukemias, as well as a hallmark of ageing. Importantly, the study of normal physiologic mediators of HSC mutation acquisition is a largely underdeveloped area. The advent of next generation sequencing (NGS) technologies provides a route to interrogate this phenomenon but is complicated by the fact that a genome-wide analysis at the clonal level is necessary to determine the mutational signature of individual HSCs. We have developed an in vitro model that allows for the sensitive assessment of clonal mutations occurring within single HSCs using whole genome sequencing. In order to optimize our clonal mutation analysis, we performed a benchmarking exercise where we deeply sequenced an individual HSC colony to ~90X coverage and performed somatic nucleotide variant (SNV) analysis at various down-sampled coverages. Importantly, we established that the number of mutations called increases in an almost linear fashion with increasing coverage, until a plateau is reached at around 30X coverage. We additionally developed optimal filtering parameters, which demonstrated a much-improved capacity for discerning true positive and false positive mutations at low coverage, compared to previously published methodologies. Using this optimized sequencing pipeline, we collected and sequenced HSC clones from young and old mice, as well as those exposed to stress agonists known to induce HSC cycling. We additionally employed a genetic label-retention system to segregate dormant and actively cycling HSCs in order to assess whether mutations are predominantly acquired during replication. Genomic coverage of the majority of these HSC colonies ranged from 30-40X. As seen in humans, we found a progressive increase in mutation burden with age within the murine HSC compartment, corresponding to a rate of ~40 SNVs per year. Furthermore, these HSCs had mutational signatures corresponding to that observed in aged human tissues. In contrast to previous reports, data from the label-retention model demonstrated that this age-associated increase in mutation burden correlated with HSC replication, as dormant aged HSCs had similar mutation burdens to young HSCs. Seemingly contradictory to this finding, we observed no difference in mutation burden upon stress-induced cycling of HSCs. However, it appears we have unintentionally introduced a large selection bias with regards to the agonist-treated clones and future work will focus on rectifying this caveat. In summary, we have developed a sensitive and specific analysis to accurately detect mutations within individual HSCs. From our results we have clearly demonstrated that mutation acquisition within HSCs accumulates with age and that this increase correlates with an increase in replication history. We envisage that these findings will be an important step towards interrogating whether replication stress is a biologically relevant driver of genome instability in HSCs

A Study Into the Effects of Inhibition and Emotion on Perspective-Taking in Younger and Older Adults

A decline in Theory of Mind (ToM) perspective-taking abilities in old age is thought to result from an inability to inhibit the self-perspective. Such reduced inhibitory capacities in old age could also impact upon an attentional reorienting and selection processes thought to be required to successfully move from the self to the other perspective in a ToM task. We sought to investigate both of these hypotheses by administering modified versions of Samson et al.’s (2005) high and low inhibition condition false-belief tasks to young and old participants (N=59), introducing affective conditions through use of positive, negative, and neutrally affective stimuli. Results indicated a general age effect on performance across all conditions in the false-belief tasks, with no further interactions or between-subject effects to report. However, each inhibition task-type was failed for different reasons in older participants. High-inhibition tasks were failed due to apparent inability to inhibit the self-perspective whilst low inhibition tasks were failed due to an inability to utilise the information that the woman had being deceived when making a judgement on one’s own perspective. These results provide further support for the importance of inhibitory control when selecting the appropriate perspective in ToM abilities

Effectiveness and implementation of models of cancer survivorship care: An overview of systematic reviews

Purpose: To critically assess the effectiveness and implementation of different models of post-treatment cancer survivorship care compared to specialist-led models of survivorship care assessed in published systematic reviews. Methods: MEDLINE, CINAHL, Embase, and Cochrane CENTRAL databases were searched from January 2005 to May 2021. Systematic reviews that compared at least two models of cancer survivorship care were included. Article selection, data extraction, and critical appraisal were conducted independently by two authors. The models were evaluated according to cancer survivorship care domains, patient and caregiver experience, communication and decision-making, care coordination, quality of life, healthcare utilization, costs, and mortality. Barriers and facilitators to implementation were also synthesized. Results: Twelve systematic reviews were included, capturing 53 primary studies. Effectiveness for managing survivors’ physical and psychosocial outcomes was found to be no different across models. Nurse-led and primary care provider-led models may produce cost savings to cancer survivors and healthcare systems. Barriers to the implementation of different models of care included limited resources, communication, and care coordination, while facilitators included survivor engagement, planning, and flexible services. Conclusions: Despite evidence regarding the equivalent effectiveness of nurse-led, primary care-led, or shared care models, these models are not widely adopted, and evidence-based recommendations to guide implementation are required. Further research is needed to address effectiveness in understudied domains of care and outcomes and across different population groups. Implications for Cancer Survivors: Rather than aiming for an optimal “one-size fits all” model of survivorship care, applying the most appropriate model in distinct contexts can improve outcomes and healthcare efficiency

Somatic mutation rates scale with lifespan across mammals.

The rates and patterns of somatic mutation in normal tissues are largely unknown outside of humans1-7. Comparative analyses can shed light on the diversity of mutagenesis across species, and on long-standing hypotheses about the evolution of somatic mutation rates and their role in cancer and ageing. Here we performed whole-genome sequencing of 208 intestinal crypts from 56 individuals to study the landscape of somatic mutation across 16 mammalian species. We found that somatic mutagenesis was dominated by seemingly endogenous mutational processes in all species, including 5-methylcytosine deamination and oxidative damage. With some differences, mutational signatures in other species resembled those described in humans8, although the relative contribution of each signature varied across species. Notably, the somatic mutation rate per year varied greatly across species and exhibited a strong inverse relationship with species lifespan, with no other life-history trait studied showing a comparable association. Despite widely different life histories among the species we examined-including variation of around 30-fold in lifespan and around 40,000-fold in body mass-the somatic mutation burden at the end of lifespan varied only by a factor of around 3. These data unveil common mutational processes across mammals, and suggest that somatic mutation rates are evolutionarily constrained and may be a contributing factor in ageing