Cellular and Biochemical Features of Skeletal Muscle in Obese Yucatan Minipigs*

Abstract

To examine cellular and biochemical features of skeletal muscle in response to dietary-induced obesity in a novel Yucatan minipig model of childhood obesity. From 4 to 16 months of age, minipigs were fed either a recommended human-type diet (NF; n = 4) or were overfed a western-type diet with saturated fat and high-glycemic index carbohydrates (OF, n = 4). Muscle samples (biceps femoris) were histochemically stained for the identification of intramuscular adipocytes, intramyocellular lipid aggregates (oil red O), and myofiber types (myosin ATPase, succinate dehydrogenase). Gene expressions and/or activities of factors involved in lipogenesis, lipolysis, or energetic metabolism were quantified in muscle. Cross-sectional areas of myofibers paralleled pig body weight (r = 0.86, p < 0.01). The size of intramuscular adipocytes, the relative proportion of oil red O-stained fibers, and total muscle lipid content tended (p < or = 0.10) to increase in response to OF diet. Hormone-sensitive lipase, carnitine palmityl transferase-I, and uncoupling protein 2 mRNA levels were lower (p < 0.05) in OF pigs than in NF pigs. Activities of beta-hydroxyacyl-coenzyme A dehydrogenase and citrate synthase assessing post-carnitine palmityl transferase I events and the proportion of oxidative myofibers were not altered by OF diet. Activity and gene expression of fatty acid synthase were lower (p < 0.02) in OF pigs than in NF pigs. Overfeeding in Yucatan minipigs reduced the expression levels of three catabolic steps in skeletal muscle that are involved also in the etiology of human obesity.