Grant: Master's Award: Canada Graduate Scholarships

Anormal body fat content is known to be a risk factor for heart disease. Apolipoprotein E (ApoE) is necessary for normal fat metabolism, a way in which energy is made in the cells of the body allowing them to grow and heal using food such as fats and water. A lack of ApoE hinders clearance of cholesterol, triglycerides and other fats from the blood. Fats will accumulate at a greater rate but will still need to be broken down by the body. Consequently, fats will be metabolized through pathways that do not require oxygen resulting in altered cellular function. Mitochondria, a vital component of any living cell, play a significant role in cellular respiration and in creating cellular energy. Mitochondria in the heart specifically, are important considering the heart muscle consumes the greatest amount of oxygen. The heart muscle's mitochondrial capacity to use oxygen, its oxidative capacity, and to produce energy may be affected by the buildup of cholesterol and fats, due to ApoE deficiency. Mitochondrial oxidative capacity has been studied in mice lacking the ApoE gene and in other deficient models, using the liver, smooth and skeletal muscle tissue, yet remains to be examined in cardiomyocytes; the muscle cells that make up the heart muscle. We will investigate the effects of an altered fat profile, one that is favorable for the development of atherosclerosis, a condition that is characterized by plaque buildup on the walls of blood vessels. This profile will be maintained in a mouse model genetically modified to lack the ApoE gene, to examine how it modifies energy metabolism in cardiomyocytes. We aim to determine the influence of ApoE’s disrupted role in fat metabolism on the heart's mitochondrial oxidative capacity. We hypothesize that the heart's muscle cells will be implicated by a lack of ApoE affecting the nutrient and energy metabolism, as well as the oxygen consumption within these cells. High resolution respirometry (HRR) will be used to quantify mitochondrial oxidative phosphorylation (OXPHOS) capacity in cardiomyocytes. In other words, this will permit a magnified and more efficient analysis of cellular energy production and utilization at the level of the heart's mitochondria. In brief, we will measure the oxygen consumption within the mitochondria of these cells. The implication of the mitochondrial respiratory complexes, cellular units within the mitochondria promoting the final steps of the respiratory and energy production process, will be investigated using a protocol that permits the analysis of disturbed energy metabolism as well as its oxidative capacity. This study will use fresh tissue surgically removed from the left ventricles of female age-matched control and ApoE-deficient experimental mice. There will be a total of 4 groups with 8 animals used in each group; 2-month-old control and experimental groups as well as 8-month-old control and experimental groups. Our findings have the potential to provide important information regarding fats being forced into non oxygen requiring pathways in order to be metabolized. This will ultimately disrupt normal cellular function leading to damaging effects. Results from this study could indicate a shift in the heart's use of its two main nutrients: fats and carbohydrates. Investigating the influence and mechanism of altered mitochondrial oxidative capacity within the heart could expand our understanding of physiological processes in the heart and how they may become susceptible to disease inducing pathways. Knowledge to be gained regarding modified bioenergetics of the heart holds immense promise when considering future clinical applications and research targets, that may potentially benefit the growing number of people afflicted with cardiovascular disease.