Widespread tissue distribution and synthetic pathway of polyunsaturated C24:2 sphingolipids in mammals

Sphingolipids are multifunctional lipids and a major constituent of the cell membranes of eukaryotes. Although the fatty acid (FA) moiety of sphingolipids is usually a saturated or monounsaturated FA, polyunsaturated FA (PUFA)-containing species also exist in mammalian tissues. In the present study, we showed that C24:2 PUFA-containing ceramide is one of the seven major ceramide species in a wide range of tissues. C24:2 ceramide levels were especially high in spleen and small intestine; in the former, it was the fourth most abundant ceramide species. However, both the synthetic pathway and the physiological function of C24:2 ceramide had yet to be identified. Tracer analysis using deuterium-labeled linoleic acid (C18:2) revealed that C24:2 ceramide is produced via elongation of linoleic acid. We also found that the FA elongase ELOVL1 and the ceramide synthase CERS2 were involved in C24:2 ceramide production. Sphingolipids are known to form lipid microdomains in membranes; however, in a detergent-resistant membrane (DRM) assay, we observed a lower proportion of C24:2 sphingomyelin in the DRM fraction than of saturated sphingomyelins, suggesting that C24:2 sphingolipids may act to negatively regulate lipid microdomain formation. Our findings expand our knowledge of sphingolipid diversity, and provide insight into how different sphingolipid molecular species play different functions in biological membranes.