Abstract
Sterol regulatory-element binding proteins (SREBPs), sirtuin (SIRT1), and liver X receptor α (LXRα) play important roles in regulating cholesterol metabolism in mammals. However, little is known about the relationship between cholesterol metabolism and SIRT1, LXRα, and SREBP-1 in fish. In addition, knowledge of the effects of salinity on hepatic cholesterol metabolism in euryhaline teleosts is fragmented. This study revealed that hepatic cholesterol content was significantly different between fresh water (FW)- and seawater (SW)-acclimated Indian medaka. Gene expression analysis indicated srebp-1 , lxrα , and sirt1 transcripts were not affected by changes in ambient salinity. However, SREBP-1, but not LXRα and SIRT1 protein expression, was significantly induced in the liver of FW-acclimated medaka. When SREBP-1 Vivo-MO inhibited SREBP-1 translation, hepatic cholesterol content was predominantly downregulated in FW- and SW-acclimated medaka. This is the first study to show that SREBP-1 is involved in cholesterol biosynthesis in fish. Furthermore, SREBP-1 knockdown had different effects on the expression of hmgcr and fdps , which encode the key enzymes involved in cholesterol biosynthesis. This study further enhances our knowledge of cholesterol metabolism in the livers of euryhaline teleosts during salinity acclimation.