Mitochondrial DNA methylation ; cardiovascular diseases risk and response to diet

Abstract

Background: Cardiovascular diseases (CVD) are the leading cause of death worldwide. CVD are complex, multifactorial disorders caused by both genetic and environmental factors. Approximately 80% of CVD burden is attributable to modifiable risk factors, including poor diet, smoking, lack of physical activity, and air pollution. Higher body mass index (BMI) is considered an intermediate risk factor for the development of CVD. Currently, 66% of men and 58% of women in the UK have overweight or obesity. Although excessive adiposity is a risk factor for CVD, not everyone with overweight or obesity will develop CVD. As yet, there is no established biomarker that distinguishes those adults with overweight and obesity who will develop CVD from those adults who will remain CVD-free. This project was designed to test the hypothesis that participants with overweight/obesity who will develop CVDs show different mitochondrial DNA methylation pattern compared to those who remain CVD-free. Mitochondria have a central role in ageing and in the development of age-related diseases, including CVD, which is linked with dysregulated reactive oxygen species (ROS) production, and mitochondrial DNA (mtDNA) instability. Platelets, anucleated cells that contain only mtDNA, have a greater reactivity in adults with overweight and obesity, and are an indicator of CVD risk. Additionally, platelet number and reactivity have been shown to be ameliorated by the Mediterranean diet and by plant extracts. Furthermore, platelets derive from megakaryocytes, which are affected negatively by inflammation, dysregulated adipocytes, and obesity. Experimental studies: First, I investigated the effects of selected polyphenolic compounds on mtDNA methylation in megakaryocytes in vitro. This experiment was devised to test the effects of treatment with specific polyphenols on patterns of mtDNA methylation in the megakaryocyte, MEG-01 cell. Secondly, I conducted a nested case-control study within the SPHERE cohort of Italian adults with overweight and obesity who were otherwise healthy at Baseline. In a prospective study design, I used a targeted approach to investigate mtDNA methylation at Baseline in those who developed CVD over the following 5 years compared with those who remained diseasefree. I identified three specific genomic loci within mtDNA i.e. MT-CO1 nt6807, MT-CO3 nt9444, and MT-TL1 nt3254, that predicted future CVD risk. MtDNA methylation level at ii these loci was independent of conventional adiposity-related CVD risk factors and so may represent an environment-related predictor of future CVD in adults with overweight/obesity. In addition, I investigated the associations between mtDNA methylation in platelets and adherence to the Mediterranean diet. Higher adherence to the Mediterranean diet, as evaluated with the MeDiet Score, was associated with lower methylation at the D-loop nt16383 and higher methylation at MT-CO2 nt8113.However, the MeDiet Score and the methylation level at these two genes are not associated with future CVD outcome. In summary, this is the first study investigating patterns of platelet mtDNA methylation in relation to future risk of CVD. I observed that higher mtDNA methylation of MT-CO1 nt6807, MT-CO3 nt9444, and MT-TL1 nt3254 in platelets was associated with a higher risk of developing CVD within five years. In addition, this appeared to be a dose-dependent relationship so that participants with Score 2 (high methylation at two or three loci) were more likely to develop CVD than the participants with Score 1 (higher methylation at one locus) and Score 0 (no loci with high methylation).