Transcriptome analysis of liver lipid metabolism disorders of the turbot Scophthalmus maximus in response to low salinity stress

Abstract The turbot Scophthalmus maximus is one of the most economically important fish harvested from the coastal areas of northern China. Low salinity stress is an important obstacle to the development of the turbot industry. However, the underlying molecular mechanisms response to low salinity stress in turbot have not been fully investigated, especially in metabolism. In the present study, liver transcriptome analysis was performed to identify genes and pathways involved in the responses of turbot to different salinity conditions (0 psu fresh water [FW] and 30 psu sea water [SW]). Related changes in blood biochemical parameters were also assessed. A total of 826 differentially expressed genes (DEGs) were identified, of which 245 were down-regulated while 581 were up-regulated. KEGG pathway analysis indicated that 11 pathways were enriched, involving lipid metabolism, the endocrine system, endocrine and metabolic diseases, signaling molecules and interactions, the digestive system, and signal transduction. Further analysis showed that a significant portion of the pathways were related to energy metabolism, especially lipid metabolism. The verified DEGs involved in lipid metabolism basically showed a significant downward trend under low salinity stress, including acetyl-CoA carboxylase alpha (ACC), carnitine O-palmitoyltransferase 1 (CPT-1), cholesterol 7-alpha-monooxygenase (CYP7A1), liver X receptor alpha (LXRα), apolipoprotein A-IV (ApoAIV), fatty acid binding protein (FABP), and sterol regulatory element-binding protein 1 (SREBP-1). Almost all of these genes were related to LXRα. Moreover, the physiological results showed that serum cholesterol content remained stable in both the SW and FW groups, while the serum triglyceride content significantly decreased with time in the FW group. These results show that low salinity stress inhibits lipid absorption and synthesis via the LXRα signaling pathway and can result in liver lipid metabolism disorders in turbot. These findings provide new insights into the molecular mechanism of turbot in response to low salinity stress and turbot culture under low salinity. It is possible that lipid metabolites in blood can be selected as phenotype traits for breeding under low- salinity conditions, although further verification is needed.