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Title: Studies of molecular responses in models of successful ageing
Author: Calvert, Shaun
ISNI:       0000 0004 7428 5977
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2018
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Ageing is a major socioeconomic concern and a risk factor in most diseases. As such, a better understanding of the ageing process could provide major insights into many disease treatments and prognoses. It is still not completely clear why organisms age, though multitudes of theories exist. There is large variation within and between species in lifespan and ageing progression. Superior maintenance of cognitive and physical function with age and avoidance of age-related morbidities is known as successful ageing. Understanding how this successful ageing occurs could be key to manipulating the ageing phenotype and mitigating age-related morbidity. Caloric restriction has been shown to increase lifespan in a number of organisms and delay the ageing phenotype. This is regarded as the most robust intervention for the extension of lifespan to date. Caloric restriction is difficult to implement in humans, so the use of drugs that mimic the effects of caloric restriction are needed to take advantage of this intervention. We performed a microarray analysis of nematode worms (Caenorhabditis elegans) undergoing caloric restriction or being treated with predicted caloric restriction mimetics. These compounds act similarly to caloric restriction, but a large number of differentially expressed genes were observed between treatments and calorically restricted worms. This suggests that these compounds act through distinct mechanisms to caloric restriction. This was principally due to variations in worm development likely caused by varying levels of developmental delay. In addition to this developmental caveat, cell cycle and cell surface genes were found to be differentially expressed in a number of comparisons particularly with worms treated with the caloric restriction mimetic rapamycin. The naked mole rat (Heterocephalus glaber, NMR) is the longest-lived rodent, living over 30 years. It is also cancer resistant. This lifespan is considerably longer than similarly sized mice (Mus musculus) at up to 4 years and comes with a delayed ageing phenotype. NMR cells have been reported to be more resistant to DNA damage, which is thought to be a major contributor to ageing and cancer. We hypothesise that this DNA damage resistance is responsible for the NMR's long-lived and cancer-resistant phenotype. By studying cells derived from these animals, comparative studies can be performed to identify potential causes for the observed differences in lifespan. As DNA damage is thought to be a causative factor in ageing we performed survival assays and calculated LD50 (the dose at which 50% of the cells die, known as the 'lethal dose 50') values for two DNA damaging compounds, camptothecin and chromium (vi) oxide in mouse and NMR cells. NMR cells appear to have higher LD50 values for both compounds and hence are more resistant as has been previously shown. NMR cells surviving treatment were also less prone to become irreversibly senescent. RNAseq was performed on the mouse and NMR primary fibroblast treated with camptothecin or chromium (vi) oxide. NMR skin fibroblasts appear to show reduced expression of DNA damage repair genes, in contrast to what has been reported previously in NMR liver cells. Functional enrichment revealed significant differences at the cell surface between the two species. Cell adhesion genes were found to be expressed significantly greater in the NMR. NMR cells were shown to adhere to a culture plate more slowly than mouse cells after genotoxic treatment, confirming differences in cellular adhesion dynamics. We conclude that differences in mouse and NMR phenotype are not down to differences in DNA damage repair gene expression. Instead, we propose the hypothesis that the observed differences in cell surface chemistry contribute to the NMR's cancer-resistant phenotype.
Supervisor: De Magalhães, João Pedro Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral