Changes in the activities and mRNA expression levels of lipoprotein lipase (LPL), hormone-sensitive lipase (HSL) and fatty acid synthetase (FAS) of Nile tilapia (Oreochromis niloticus) during fasting and re-feeding

Abstract

This study aimed to characterize the dynamic changes in the growth and proximate composition of liver and muscle tissue in the Nile tilapia (Oreochromis niloticus) during feed restriction followed by re-feeding. In addition, we measured triacylglycerol (TAG), high density lipoprotein-cholesterol (HDL-C) and glucose (GLU) levels in serum and the mRNA levels and the activity levels of lipoprotein lipase (LPL), hormone-sensitive lipase (HSL) and fatty acid synthetase (FAS) in liver. Nile tilapia with an initial body weight of 62.50±3.44g were starved for 28days and then fed for 21days under a controlled indoor environment. Fish were sampled at days 0, 7, 14, 21 and 28 of fasting (F0, F7, F14, F21 and F28, respectively) and days 14 and 21 of re-feeding (RF14 and RF21, respectively). The results indicate that body weight decreased significantly by F14, and significantly increased at RF21 (P<0.05). The hepatosomatic index was significantly decreased throughout the experiment (P<0.05). The fat content in liver and muscle decreased significantly by F7 and F14 (P<0.05), and the protein content decreased significantly by F7 and F28 (P<0.05), respectively. Significant reductions were observed in the serum content of TAG and GLU during fasting. Following re-feeding, values for these indices recovered to varying degrees. There was no change in serum HDL-C levels during the experiment (P>0.05). The activity and relative mRNA expression of FAS in the liver both significantly decreased under fasting conditions, but were significantly increased at RF21 (P<0.05). LPL and HSL mRNA hepatic levels were significantly upregulated during fasting, and LPL activity increased in response to fasting, whereas HSL activity increased by F14, and decreased to basal levels at F28. Following re-feeding, the activity and mRNA expression of LPL decreased. The hepatic expression of HSL mRNA decreased, but hepatic HSL activity increased (P<0.05).