Ceramide Synthase 6 Knockout Reprograms Energy Metabolism in Mice

Objectives Ceramides, a group of bioactive lipids and important signaling molecules, have been implicated in the development of cardiometabolic disease, diabetes, and cancer. Recent studies have shown that targeting Ceramide Synthases (CerS), the enzymes producing ceramides, protected from glucose intolerance and diet induced obesity. We investigated metabolomic responses to high fat diet consumption in livers and plasma of wild type (WT) and CerS6 knockout (KO) mice to obtain mechanistic understanding of the protection provided by the enzyme knockout. Methods Upon weaning, male WT and CerS6 KO mice were placed on a high fat (HFD) or control (Ctrl) diet for 16 weeks. After 14 weeks on diet, mice were placed in calorimetry cages for 48 hours. Body composition was assessed before dietary intervention and before necropsy. Plasma and snap-frozen liver samples were subjected to untargeted metabolomic analysis at Metabolon®. Results CerS6 KO mice gained significantly less weight on HFD than WT mice. Calorimetry measurements revealed that over 24 hours CerS6 KO mice did not move more than WT in either x-, y- or z-planes. Interestingly, CerS6 KO mice on a HFD consumed significantly less food, and despite the higher caloric content of the diet, they also consumed fewer calories over the 24 hour period. No differences in fat excretion between WT and CerS6 KO mice were found, measured by fecal lipid content. Calorimetry data demonstrated that on HFD, regardless of genotype, animals oxidized fat for energy. On the Ctrl diet WT mice burned a mix of substrates while CerS6 KO mice preferentially oxidized glucose for energy during the light cycle. This indicates that during the active phase of the light cycle a switch in energy source occurred in KO but not WT mice. Untargeted metabolomics revealed significant differences in intermediates of glycolysis both in liver and plasma of the KO vs WT animals. Moreover, significant increases in multiple TCA cycle metabolites in KO vs WT plasma were seen in HFD fed mice. Conclusions We found a significant shift in tissue-level and whole-body energetics in CerS6 KO mice. This shift could be responsible for the beneficial metabolic effects of targeting CerS6 when HFD is consumed. Further studies will help determine how CerS6 and ceramides influence tissue and whole body metabolism. Funding Sources This work was funded by R01 CA193782 grant to NK.