Postprandial change in glucose metabolism at the molecular level in the adipose tissue of omnivorous GIFT Oreochromis niloticus

Abstract

The study reported here is the first to systematically investigate the postprandial change in glucose metabolism in the adipose tissue (AT) of an omnivorous fish. Sub-adult Genetically Improved Farmed Tilapia (GIFT) Oreochromis niloticus were sampled at 0, 1, 3, 8 and 24 h after feeding (HAF), and the time course of changes in glucose transport and glycolipid metabolism at the transcript level were analyzed in the AT. The plasma glucose level increased between 1 and 8 HAF, and the expression of glucose transporter 1a (glut1a) and glut4 in the AT were stimulated at the same time. Concomitantly, the mRNA levels of glycolytic genes, such as hexokinase 1a (hk1a), hk1b, glucokinase and liver type of phosphofructokinase, were upregulated. The expression of glycogen synthase 1 and glycogen level in the AT increased between 3 and 8 HAF, suggesting that AT has the capacity to store excess glucose in tilapia. The decreased glycogen level together with upregulated transcription of glucose-6-phosphatase catalytic subunit a2 (g6pca2) at 24 HAF suggests that glycogen breakdown and glucose release from AT might contribute to circular glucose in tilapia. The opposite expression patterns between g6pca2 and phosphoenolpyruvate carboxykinase (pck) paralogs suggest that pck might participate in glyceroneogenesis rather than gluconeogenesis in the AT of tilapia. The mRNA levels of both cytosolic pck1 and mitochondrial pck2 increased during the period 1–8 HAF, and the expressions of lipogenic genes, such as acetyl-CoA carboxylase α and fatty acid synthase, were upregulated between 3 and 8 HAF, suggesting that glyceroneogenesis was probably stimulated as a source of glyceride–glycerol for triglyceride synthesis in the AT of tilapia. Taken together, our preliminary data suggest that AT plays an important role in the regulation of postprandial glucose homeostasis in the omnivorous tilapia, at least at the molecular level.