GLUT4 gene expression and GLUT4 protein levels in muscle of high sucrose-fed rats: effect of dietary fish oil

Abstract

High sucrose feeding is known to induce the symptoms of so-called metabolic X syndrome (e.g., hypertriglyceridemia, hyperinsulinemia, insulin resistance, and hypertension) in rats. To elucidate whether the latter may also involve an alteration of the glucose transport in skeletal muscle, we determined GLUT4 gene expression and GLUT4 protein levels in muscle quadriceps femoris of Wistar rats fed ad libitum a basal or high (63 cal%) sucrose diet for 21 days. To test a possible beneficial effect of dietary omega-3 polyunsaturated fatty acids on the above parameters, additional groups of rats were fed the diets supplemented with marine fish oil (30 wt% omega-3 polyunsaturated fatty acids). A twofold increase in GLUT4 gene expression (dot blot analysis) was observed in the muscle of rats fed the high sucrose diet. Dietary fish oil reduced the GLUT4 gene expression in high sucrose-fed animals by about 50% of the values obtained in rats fed the basal diet plus fish oil. Western blot analysis of total muscle membrane fractions using specific antibodies against GLUT4 revealed no changes in the transporter levels in high sucrose-fed rats, and even a decrease in both, with fish oil-supplemented groups of animals. These data suggest that feeding high sucrose diet to rats is associated with an uncoupling between muscle GLUT4 mRNA and protein levels. On the other hand, it is notable that the decrease of GLUT4 protein found in rats fed the fish oil-supplemented diets was more pronounced in the group of animals fed the high sucrose diet.