Investigation of the mechanisms underlying the effect of oleic acid and docosahexaenoic acid on DNA methylation in Jurkat cells

There is evidence that olive oil, rich in oleic acid (OA), and fish oil, rich in docosa-hexaenoic acid (DHA), can modify the DNA methylation in human blood cells in vivo. However, the mechanisms underlying such effect are not well understood. To address this, a model to study DNA methylation changes was developed using the in vitro treatment of Jurkat cells with OA or DHA. Analysis showed that 15μM OA or DHA treatment for eight days altered the DNA methylation of 563 or 1596 CpG sites (294 or 508 increased), respectively, using the Infinium Methylation EPIC BeadChip. Only 78 CpG sites were altered in common by both treatments. Further characterisation of 5 candidate CpG sites showed that DNA methylation changes were just significant after the 3rd day of DHA treatment which suggested and indirect mechanism. Pathway analysis of genes with at least one CpG site with altered DNA methylation by OA or DHA treatment (348 or 935, respectively) showed an enrichment of genes under the control of peroxisome proliferator-activated receptor alpha (PPARα) in DHA-treated cells only. PPARα has been reported to participate in the global hypermethylation of THP1 monocytes induced by arachidonic acid treatment. How-ever, treatment of Jurkat cells with PPARα agonist GW7647 or PPARα antagonist GW6471 showed no difference in the DNA methylation of 5 candidate CpG sites analysed here by pyrosequencing. Therefore, other factors related to DNA methylation such as chromatin modification of histones and DNA motifs were investigated. Results showed that H3K4me3 was decreased in 5 candidate regions that changed DNA methylation status. Motif analysis indicated that sequences in the proximity of CpG sites that changed methylation were enriched in response elements including those for transcription factor SP1 and SP3. To further characterise the participation of transcription factors, transcriptome changes by OA or DHA were assessed using the Human HT-12 v4 Expression BeadChip. Analysis showed that DHA, but not OA treatment, downregulated SP3mRNA and altered the activity of different transcription factors and enzymes. Together, results showed in this thesis suggest that DNA methylation changes by OA or DHA showed specificity, took more than three days to be established and may be associated with decrease H3K4me3 and the activity of different transcription factors and enzymes