The role of circadian rhythm genes in the regulation of energy balance and substrate metabolism in muscle and liver

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Obesity is increasing at an alarming rate worldwide and as the standard of living increases in developing countries such as India and China, the incidence of obesity and its related diseases of diabetes, cardiovascular disease and cancer will become the major health problem of the 21st century. The epidemic of obesity appears to be due to a complex interaction between genetic background and changes in the environment such as reduced physical activity and increased availability and consumption of high energy food. The accumulation of excess body fat in most individuals is not a precipitous event that occurs over a few days or weeks. Obesity actually occurs insidiously over a period years and is essentially the cumulative result of small differences in daily energy balance. In humans and animals energy balance is subject to diurnal or day-night variations in body temperature, feeding behaviour and physical activity (sleep-wake cycles). Recent research has determined that all tissues in the body have the same genes that regulate circadian (daily) rhythms in the brain. It has also become clear that the expression of these gene cycles over 24 hours in muscle liver and fat tissue the same way that they do in the brain. What is not understood is the extent to which these circadian genes control energy metabolism pathways such as glucose and fat utilisation and storage in liver and muscle. The aim of this grant is to test the effects of changing diet, feeding times and circulating hormones on metabolism and gene expression in muscle and liver to determine the extent to which circadian rhythm genes regulate the normal diurnal metabolism of glucose and fat and whether dysregulation of these systems contributes to metabolic disease.