Deletion of serine palmitoyl transferase 2 in hepatocytes impairs ceramide/sphingomyelin balance, prevents obesity and leads to liver damage in mice

AbstractCeramides (Cer) have been shown as lipotoxic inducers, which disturb numerous cell signalling pathways especially insulin signalling pathway leading to metabolic disorders such as type 2 diabetes. In this study, we aimed to determine the role of de novo hepatic Cer synthesis on energy and liver homeostasis in mice. We generated mice lacking serine palmitoyltransferase 2 (Sptlc2), the rate limiting enzyme of Cer de novo synthesis, in hepatocytes.Despite lower expression of hepatic Sptlc2, we observed an increased concentration of hepatic Cer, especially C16:0-Cer and C18:0-Cer associated with an increased neutral sphingomyelinase 2 expression, and a decreased sphingomyelin content in the liver. Sptlc2ΔHep mice were protected against obesity induced by high fat diet. Bile acid (BA) hydrophobicity was drastically decreased in KO mice, and was associated with a defect in lipid absorption. In addition, an important increase of tauro-muricholic acid in BA pool composition was associated with a downregulation of the nuclear BA receptor FXR target genes. Sptlc2 deficiency also enhanced glucose tolerance and attenuated hepatic glucose production. Finally, Sptlc2 disruption promoted apoptosis, inflammation and progressive development of hepatic fibrosis worsening with age.Our data suggest a compensatory mechanism to regulate hepatic Cer content from sphingomyelin hydrolysis, with deleterious impact on liver homeostasis. In addition, our results show the implication of hepatic sphingolipid modulation on BA metabolism and hepatic glucose production in an insulinin-dependent manner, which demonstrates the role of Cer in many metabolic functions still under-researched.