Molecular cloning, expression profiling of adipose triglyceride lipase (ATGL) and forkhead box O1 (FoxO1), and effects of dietary carbohydrate level on their expression in hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂)

Adipose triglyceride lipase (ATGL) has been considered as the rate-limiting enzyme involved in lipolysis. In the present study, the ATGL gene and forkhead box O1 (FoxO1), a transcription factor involved in regulation of lipid metabolism, in hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂) were isolated and characterized, and their gene expression in response to dietary carbohydrate was investigated. Additionally, cell transfection and luciferase assays were used to explore the potential regulation of FoxO1 on the expression of ATGL. The full-length cDNA sequence of ATGL and FoxO1 was 2922 bp and 5471 bp, respectively, encoding 515 amino acid (AA) and 677 AA, respectively. ATGL mRNA was highly expressed in liver, and the expression of FoxO1 was mainly detected in heart and liver. The expression of ATGL decreased significantly in response to high dietary carbohydrate, and the expression of FoxO1 followed the similar pattern with ATGL. The results of dual-luciferase reporter assays showed that grouper ATGL reporter activity was significantly elevated by over-expression of FoxO1, indicating the positive regulation of FoxO1 on ATGL. Meanwhile, insulin significantly repressed the expression of ATGL and FoxO1 in the intraperitoneal injection study. Therefore, the increase of plasma insulin content in the present study may contribute to the accumulation of hepatic triglyceride through down-regulation of FoxO1 and ATGL in transcriptional level. These findings may contribute to further understanding the effects of dietary carbohydrate on lipid metabolism in fish species.