Determining the impact of mitochondrial dysfunction on stem cell dynamics and proliferation within the colon

PhD ThesisClonally expanded mitochondrial DNA (mtDNA) point mutations have been shown to cause mitochondrial dysfunction in the form of cytochrome c oxidase deficiency (COX deficiency) within ageing human colonic epithelium. Currently, there are a lack of robust stem cell markers within human colonic epithelium, however the detection of mitochondrial dysfunction has been shown to be a useful stem cell lineage marker, enabling the investigation of stem cell dynamics within colonic crypts. Using the most robust data set of COX deficiency frequency and mtDNA mutation number, a computational model that simulates stem cell dynamics within human colonic crypts was constructed. In silico stem cell modelling suggests: there are approximately 5 stem cells within human colonic crypts, stem cell divisions occur asymmetrically the majority of the time, and that infrequent symmetric stem cell division permits niche succession of individual stem cell clones. However, the in silico data was unable to match the biological data when a model simulating neutral drift stem cell dynamics was used, suggesting a change in stem cell biology when mitochondrial dysfunction was present. In order to assess the impact of mitochondrial dysfunction within colonic stem cells in vivo, a mouse model of mitochondrial dysfunction was crossed with a mouse model enabling the visualisation of cells expressing Lgr5 (a well-accepted stem cell marker). Double thymidine analogue labelling was used to identify cells traversing through the cell cycle, together with a marker of proliferation. This data suggests that stem cells with mitochondrial dysfunction have a small but significant increase in cell cycle progression rate compared to normal stem cells. When these data were included in the model, a better fit to the biological data was achieved. These findings suggest that mitochondrial dysfunction does significantly impact on stem cell homeostasis. As stem cells with mitochondrial dysfunction are more likely to out-compete normal stem cells over time, this may have potential implications for an increased risk of cancer propagation within the colon

Predominant Asymmetrical Stem Cell Fate Outcome Limits the Rate of Niche Succession in Human Colonic Crypts.

Stem cell (SC) dynamics within the human colorectal crypt SC niche remain poorly understood, with previous studies proposing divergent hypotheses on the predominant mode of SC self-renewal and the rate of SC replacement. Here we use age-related mitochondrial oxidative phosphorylation (OXPHOS) defects to trace clonal lineages within human colorectal crypts across the adult life-course. By resolving the frequency and size distribution of OXPHOS-deficient clones, quantitative analysis shows that, in common with mouse, long-term maintenance of the colonic epithelial crypt relies on stochastic SC loss and replacement mediated by competition for limited niche access. We find that the colonic crypt is maintained by ~5 effective SCs. However, with a SC loss/replacement rate estimated to be slower than once per year, our results indicate that the vast majority of individual SC divisions result in asymmetric fate outcome. These findings provide a quantitative platform to detect and study deviations from human colorectal crypt SC niche homeostasis during the process of colorectal carcinogenesis.Wellcome Trus

Theory and Research From the Communication Field: Discourses That Constitute and Reflect Families

From the disciplinary perspective of communication studies, we review theory and research in family communication, including a brief history of the family communication field; the contributions of a family communication perspective; and 5 theories of family communication: communication accommodation theory, communication privacy management theory, family communication patterns theory, narrative theor(ies), and relational dialectics theory. We then illustrate the concept of discourse dependence in family communication processes and discuss current trends in family communication research. We also suggest emerging directions for family communication scholarship

A review of the phytochemical support for the shifting defence hypothesis

Several theories have been developed to explain why invasive species are very successful and develop into pest species in their new area. The shifting defence hypothesis (SDH) argues that invasive plant species quickly evolve towards new defence levels in the invaded area because they lack their specialist herbivores but are still under attack by local (new) generalist herbivores. The SDH predicts that plants should increase their cheap, toxic defence compounds and lower their expensive digestibility reducing compounds. As a net result resources are saved that can be allocated to growth and reproduction giving these plants a competitive edge over the local plant species. We conducted a literature study to test whether toxic defence compounds in general are increased in the invaded area and if digestibility reducing compounds are lowered. We specifically studied the levels of pyrrolizidine alkaloids, a toxin which is known for its beneficial and detrimental impact against specialists and generalists, respectively. Digestibility reducers did not show a clear trend which might be due to the small number of studies and traits measured. The meta analysis showed that toxic compounds in general and pyrrolizidine alkaloid levels specifically, increased significantly in the invaded area, supporting the predictions of the SDH that a fast evolution takes place in the allocation towards defence

Traditions of research into interruptions in healthcare: A conceptual review

Background Researchers from diverse theoretical backgrounds have studied workplace interruptions in healthcare, leading to a complex and conflicting body of literature. Understanding pre-existing viewpoints may advance the field more effectively than attempts to remove bias from investigations. Objective To identify research traditions that have motivated and guided interruptions research, and to note research questions posed, gaps in approach, and possible avenues for future research. Methods A critical review was conducted of research on interruptions in healthcare. Two researchers identified core research communities based on the community’s motivations, philosophical outlook, and methods. Among the characteristics used to categorise papers into research communities were the predominant motivation for studying interruptions, the research questions posed, and key contributions to the body of knowledge on interruptions in healthcare. In cases where a paper approached an equal number of characteristics from two traditions, it was placed in a blended research community. Results A total of 141 papers were identified and categorised; all papers identified were published from 1994 onwards. Four principal research communities emerged: epidemiology, quality improvement, cognitive systems engineering (CSE), and applied cognitive psychology. Blends and areas of mutual influence between the research communities were identified that combine the benefits of individual traditions, but there was a notable lack of blends incorporating quality improvement initiatives. The question most commonly posed by researchers across multiple communities was: what is the impact of interruptions? Impact was measured as a function of task time or risk in the epidemiology tradition, situation awareness in the CSE tradition, or resumption lag (time to resume an interrupted task) in the applied cognitive psychology tradition. No single question about interruptions in healthcare was shared by all four of the core communities. Conclusions Much research on workplace interruptions in healthcare can be described in terms of fundamental values of four distinct research traditions and the communities that bring the values and methods: of those research traditions to their investigations. Blends between communities indicate that mutual influence has occurred as interruptions research has progressed. It is clear from this review that there is no single or privileged perspective to study interruptions. Instead, these findings suggest that researchers investigating interruptions in healthcare would benefit from being more aware of different perspectives from their own, especially when they consider workplace interventions to reduce interruptions

Fc Effector Function Contributes to the Activity of Human Anti-CTLA-4 Antibodies.

With the use of a mouse model expressing human Fc-gamma receptors (FcγRs), we demonstrated that antibodies with isotypes equivalent to ipilimumab and tremelimumab mediate intra-tumoral regulatory T (Treg) cell depletion in vivo, increasing the CD8+ to Treg cell ratio and promoting tumor rejection. Antibodies with improved FcγR binding profiles drove superior anti-tumor responses and survival. In patients with advanced melanoma, response to ipilimumab was associated with the CD16a-V158F high affinity polymorphism. Such activity only appeared relevant in the context of inflamed tumors, explaining the modest response rates observed in the clinical setting. Our data suggest that the activity of anti-CTLA-4 in inflamed tumors may be improved through enhancement of FcγR binding, whereas poorly infiltrated tumors will likely require combination approaches