Ceramides play a significant role in the pathogenesis of several diseases, including diabetes and heart disease. We have used ceramide synthase 6 (CerS6) knockout mice to evaluate the relationship between dietary fat and sphingolipid metabolism with a focus on liver, plasma, and whole-body metabolism.
CerS6 KO and wild type littermates were maintained on a standard or on high fat diet (HFD) for 16 weeks. Body mass and body composition were assessed before dietary intervention and at treatment end. Energy expenditure, activity, and food intake were assessed in male mice after 14 weeks on diet. Fasting plasma ceramides were measured by the MUSC Lipidomics Analytic Core and expression of sphingolipid genes in liver tissue was evaluated by qPCR. Untargeted metabolomics characterization of both liver and plasma samples was performed by Metabolon ®. We hypothesized that CerS6 KO mice would demonstrate significant differences in sphingolipid species compared to WT mice on both the standard and HFD. Furthermore, we expected the plasma lipid pool to reflect hepatic lipid concentrations.
CerS6 KO mice were protected from diet-induced weight gain and hepatic lipid droplet accumulation on HFD. CerS6 KO mice also displayed differences in respiratory exchange rate (RER) that indicated utilization of different substrates for energy production. With regard to sphingolipids, multiple ceramide and hexosyl-ceramide species differed depending on diet and genotype whereas sphingomyelins were largely affected by HFD feeding only. Importantly, sphingolipid levels were significantly different in male and female mice and also responded differently to dietary fat. Importantly, knockout of CerS6 resulted in significant elevation of mRNA expression of multiple sphingolipid biosynthesis genes. Of note, metabolomics analysis revealed that on both diets absence of CerS6 resulted in a different response of N-palmitoyl-sphingosine (C16:0-ceramide) in the liver compared to plasma.Our data implicate CerS6 in the control of fat accumulation and storage in mice with significant changes in plasma sphingolipids induced by dietary alterations. Profound differences in hepatic and plasma concentrations of ceramide species underscore the need to better understand tissue contribution to sphingolipid pools since plasma ceramides are being increasingly used as biomarkers for diseases.