The impact of exercise interventions and omega-3 polyunsaturated fatty acid supplementation on DNA methylation and gene expression

Abstract

Epigenetics is a rapidly developing field of study which investigates chemical modifications to the genome, independent of the DNA sequence, which regulate gene expression profiles. The most commonly studied epigenetic modification, DNA methylation, has been demonstrated to be influenced by lifestyle factors including diet and exercise. The modulation of DNA methylation by lifestyle factors is one potential mechanism for the reduction in disease risk induced by a healthy lifestyle. This thesis aimed to identify the impact of exercise on DNA methylation and mRNA expression and determine whether fatty acid supplementation may modulate this response.Custom assays were developed and validated (Chapter 4) to assess the DNA methylation of peroxisome proliferative activated receptor gamma coactivator 1 alpha (PPARGC1A), interleukin 6 (IL6) and tumor necrosis factor alpha (TNF) at specific cytosine bases in genomic locations previously identified to be biologically relevant. Assays to investigate the mRNA expression of PPARGC1A, IL6, TNF and the DNA methyltransferases (DNMT) were validated to ensure accurate results. In Chapter 5, DNMT mRNA expression decreased following an acute bout of exercise to volitional fatigue; whereas, no changes in DNA methylation were identified as a result of exercise or supplementation of omega-3 polyunsaturated fatty acids (n-3 PUFAs). However, an interaction was determined between exercise and n-3 PUFA supplementation for the DNA methylation of a single IL6 CpG site. Following exercise, decreased DNA methylation and increased mRNA expression of IL6 was detected after n-3 PUFA supplementation compared to the trial before supplementation. IL6 methylation was correlated to the n-3 PUFA content in whole blood following supplementation suggesting increased n-3 PUFA content following supplementation may prime the cells for future exercise stimuli.Chapter 6 sought to investigate whether acute exercise of an increased duration would modulate DNA methylation profiles and adopted a double-blind randomised repeated measures design to try and confirm the interaction between exercise and n-3 PUFA supplementation. Following a one-hour cycling bout, consisting of 45 mins cycling at 70% of VO2 followed by a 15 min time trial, we determined global hypomethylation, a reduction in PPARGC1A DNA methylation and increased mRNA expression of PPARGC1A. These methylation changes were associated with a similar reduction in DNMT expression as reported in Chapter 5. In line with the positive correlations between whole blood n-3 PUFA content in the previous chapter, an increase in IL6 methylation was determined following n-3 PUFA supplementation compared to the impact of supplementation with extra virgin olive oil; however, this relationship was not further modulated by exercise. The focus of Chapter 7 was the impact of acute resistance exercise on DNA methylation profiles and whether resistance training and fatty acid supplementation could modulate the epigenetic response. Acute resistance exercise was sufficient to increase DNA methylation of PPARGC1A and IL6, and decrease TNF DNA methylation in both leukocytes and skeletal muscle. However, neither resistance training nor fatty acid supplementation modulated this response. The magnitude of modulated DNA methylation of the cytokines IL6 and TNF was greater in skeletal muscle than it was in leukocytes and the mRNA expression of these cytokines increased as a result of acute resistance exercise in skeletal muscle but not leukocytes suggesting tissue-specificity in the inflammatory response to exercise. The resistance exercise-induced methylation of an alternative promoter of the PPARGC1A, shown for the first time, suggests changes in DNA methylation may be critical for exercise-induced expression of transcript variants. In accordance with the impact of aerobic exercise (Chapters 5 and 6), resistance exercise was sufficient to reduce the mRNA expression of DNMT3a and DNMT3b.The data in this thesis indicates acute exercise can alter DNA methylation profiles; whereas, fatty acid supplementation has a limited impact on DNA methylation. Aerobic and resistance exercise was sufficient to alter DNA methylation in leukocytes; however, a more extensive response was determined in skeletal muscle following resistance exercise. Acute exercise, independent of mode, was sufficient to reduce the mRNA expression of DNMTs; whereas, resistance exercise training did not alter DNA methylation or mRNA expression of candidate genes. Despite the novel findings presented in this thesis, a number of fundamental questions remain to fully understand the epigenetic response to exercise and nutritional interventions before they can be used to target the aberrant methylation profiles