| Summary: | The superficial digital flexor tendon (SDFT) is one of the most frequently injured tendons in Thoroughbred racehorses. Exercise associated factors including hyperthermia are thought to lead to cellular dysfunction and cell death of the resident tendon fibroblasts, the cells responsible for the repair of the tendon lesions. The main aim of this thesis was to investigate the sensitivity of SDFT fibroblasts to hyperthermia and to compare this with the deep digital flexor tendon (DDFT), a non-injury prone tendon. Understanding the physiological mechanisms of the heat shock response in these cells e.g. the use of protein markers will allow preventative strategies to be devised to protect these cells from damage. I determined whether thermotolerance associated with the induction of heat shock proteins (a survival mechanism that allows cells to withstand a subsequent lethal shock) could be induced with both heat and cold shock in these cells. Firstly, the basal DNA damage levels were quantified in both SDFT and DDFT fibroblasts as the cell culture environment is known to damage cells. My research showed both SDFT and DDFT fibroblasts were susceptible to replication induced DNA damage in vitro. The SDFT in particular had high levels of DNA damage when cultured on a fibronectin matrix in ambient oxygen. SDFT and DDFT fibroblasts were shown to be susceptible to a lethal heat shock (52oC). When a preconditioned sub-lethal heat shock was given to both tendons, induction of thermotolerance occurred and these cells survived a lethal heat shock. Thermotolerance was induced in preconditioned cold shocked SDFT fibroblasts but not in DDFT fibroblasts. Finally, a useful protein marker, DAXX (that is involved in cellular stress pathways as a transcriptional repressor and in apoptosis) was shown to disperse into the nucleoplasm during a mild heat shock in SDFT fibroblasts. One of the limitations of this thesis is that sample size was small and as a result, larger numbers of animals will be required for future experiments to determine whether my results are of biological significance.
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