The Effect of Pharmacological and Dietary Modulators of Lipid Metabolism on Gene Expresion in a Porcine Model

Abstract

Modifying the size and/or carcass distribution of adipose tissue in meat producing animals by nutritional and pharmacological means has long been of interest to animal scientists. In pigs, as in other meat animals, a more complete understanding of lipid metabolism and its regulation at the molecular level will be necessary to develop more effective strategies to modify fat deposition in different tissues of animals to improve muscle food quality and production efficiency. Studies in this dissertation describe an experimental model system to determine gene expression responses to dietary catecholamine analog in porcine adipose tissue and to a sudden change of dietary fat content in adipose, skeletal muscle, liver and intestinal epithelium in finishing pigs. Studies described herein were designed to test the hypothesis that: 1) Ractopamine (a catecholamine) modulates lipid metabolism in adipose tissue of pigs in vivo through transcriptional control of genes involved in fatty acid synthesis, fatty acid oxidation transcription factors, and regulatory pathways. 2) Feeding a high fat diet modulates transcription of genes involved in nutrient metabolism pathways, especially those involved in lipid and carbohydrate metabolism in the liver, adipose and muscle tissues of the pig. 3) A sudden shift from a typical high carbohydrate, low fat diet to a fat-supplemented diet in finishing pigs results in metabolic adaptations and changes in transcription of genes associated with triacylglycerol and cholesterol trafficking in the pig. Collectively, results of the first two studies established that microarray can be used as a tool with which to detect transcription changes in the porcine tissues. The first study clearly indicated that long-term (28 days) exposure to the cAMP-elevating agent ractopamine was negative for the expression of genes in fatty acid synthesis in porcine adipose tissue. The second study showed that the short-term (14 days) of a fat enriched diet affected the transcription of lipid metabolism genes in different tissues of the pig. The third study determined the distribution pattern of genes ACAT, LCAT, apoB and HL in the porcine liver, subcutaneous adipose, gut and skeletal muscle tissues, and found that high fat diet depressed the transcription of ACAT in porcine liver.