Daily rhythms of lipid metabolic gene expression in zebra fish liver: Response to light/dark and feeding cycles

Despite numerous studies about fish nutrition and lipid metabolism, very little is known about the daily rhythm expression of lipogenesis and lipolysis genes. This research aimed to investigate the existence of daily rhythm expressions of the genes involved in lipid metabolism and their synchronization to different light/dark (LD) and feeding cycles in zebra fish liver. For this purpose, three groups of zebra fish were submitted to a 12: 12 h LD cycle. A single daily meal was provided to each group at various times: in the middle of the light phase (ML); in the middle of the dark phase (MD); at random times. After 20 days of acclimation to these experimental conditions, liver samples were collected every 4 h in one 24-h cycle. The results revealed that most genes displayed a significant daily rhythm with an acrophase of expression in the dark phase. The acrophase of lipolytic genes (lipoprotein lipase - lpl, peroxisome proliferator-activated receptor - ppar alpha and hydroxyacil CoA dehydrogenase - hadh) was displayed between ZT 02: 17 h and ZT 18: 31 h. That of lipogenic genes (leptin-a -lepa, peroxisome proliferator-activated receptor - ppar alpha, liver X receptor - lxr, insulin-like growth factor - igf1, sterol regulatory element-binding protein - srebp and fatty acid synthase - fas) was displayed between ZT 15: 25 h and 20: 06 h (dark phase). Feeding time barely influenced daily expression rhythms, except for lxr in the MD group, whose acrophase shifted by about 14 h compared with the ML group (ZT 04: 31 h versus ZT 18: 29 h, respectively). These results evidence a strong synchronization to the LD cycle, but not to feeding time, and most genes showed a nocturnal acrophase. These findings highlight the importance of considering light and feeding time to optimize lipid metabolism and feeding protocols in fish farming.