A Model Construction of Starvation Induces Hepatic Steatosis and Transcriptome Analysis in Zebrafish Larvae

SIMPLE SUMMARY: Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disorder. Previous studies have focused on NAFLD caused by factors such as obesity or high-fat diets, but in recent years, more and more studies have proved that starvation is also an important cause of NAFLD. It has shown great harm in human health (e.g., dieting and anorexia nervosa) and farming economic benefits (e.g., laying hens and mink). However, the molecular mechanism underlying of starvation-induced NAFLD remain unclear. Regarding the study of NAFLD, zebrafish is currently widely used model organism. Thus, in this study, we used zebrafish to establish a starvation-induced hepatic steatosis model. As we all know, hepatic steatosis is usually a prerequisite for NAFLD. Subsequently, we performed a comparative transcriptome analysis of starvation-induced hepatic steatosis by RNA-Seq. We demonstrated that starvation triggers hepatic steatosis by promoting extrahepatic fatty acid uptake and lipogenesis, and inhibits hepatic fatty acid metabolism and lipid transport. Based on the indications provided by these data, we further revealed that cd36 plays a crucial role in regulating extrahepatic fatty acid uptake and inducing hepatic steatosis during starvation conditions. Altogether, these findings will help us understand the pathogenesis of starvation-induced NAFLD. ABSTRACT: Hepatic steatosis caused by starvation, resulting in non-alcoholic fatty liver disease (NAFLD), has been a research topic of human clinical and animal experiments. To understand the molecular mechanisms underlying the triggering of abnormal liver metabolism by starvation, thus inducing hepatic lipid accumulation, we used zebrafish larvae to establish a starvation-induced hepatic steatosis model and conducted comparative transcriptome analysis by RNA-seq. We demonstrated that the incidence of larvae steatosis is positively correlated with starvation time. Under starvation conditions, the fatty acid transporter (slc27a2a and slc27a6-like) and fatty acid translocase (cd36) were up-regulated significantly to promote extrahepatic fatty acid uptake. Meanwhile, starvation inhibits the hepatic fatty acid metabolism pathway but activates the de novo lipogenesis pathway to a certain extent. More importantly, we detected that the expression of numerous apolipoprotein genes was downregulated and the secretion of very low density lipoprotein (VLDL) was inhibited significantly. These data suggest that starvation induces hepatic steatosis by promoting extrahepatic fatty acid uptake and lipogenesis, and inhibits hepatic fatty acid metabolism and lipid transport. Furthermore, we found that starvation-induced hepatic steatosis in zebrafish larvae can be rescued by targeting the knockout cd36 gene. In summary, these findings will help us understand the pathogenesis of starvation-induced NAFLD and provide important theoretical evidence that cd36 could serve as a potential target for the treatment of NAFLD.