Ceramide Synthase 6 Plays a Critical Role in the Development of Experimental Autoimmune Encephalomyelitis

Ceramides are mediators of apoptosis and inflammatory processes. In an animal model of multiple sclerosis (MS), the experimental autoimmune encephalomyelitis (EAE) model, we observed a significant elevation of C-16:0-Cer in the lumbar spinal cord of EAE mice. This was caused by a transiently increased expression of ceramide synthase (CerS) 6 in monocytes/macrophages and astroglia. Notably, this corresponds to the clinical finding that C-16:0-Cer levels were increased 1.9-fold in cerebrospinal fluid of MS patients. NO and TNF-alpha secreted by 1FN-gamma-activated macrophages play an essential role in the development of MS. In murine peritoneal and mouse-derived RAW 264.7 macrophages, IFN-gamma-mediated expression of inducible NO synthase (iNOS)/TNF-alpha and NO/TNF-alpha release depends on upregulation of CerS6/C-16:0-Cer. Downregulation of CerS6 by RNA interference or endogenous upregulation of C-16:0-Cer mediated by palmitic acid in RAW 264.7 macrophages led to a significant reduction or increase in NO/TNF-alpha release, respectively. EAE/IFN-gamma knockout mice showed a significant delay in disease onset accompanied by a significantly less pronounced increase in CerS6/C-16:0-Cer, iNOS, and TNF-alpha compared with EAE/wild-type mice. Treatment of EAE mice with L-cycloserine prevented the increase in C-16:0-Cer and iNOS/TNF-alpha expression and caused a remission of the disease. In conclusion, CerS6 plays a critical role in the onset of MS, most likely by regulating NO and TNF-alpha synthesis. CerS6 may represent a new target for the inhibition of inflammatory processes promoting MS development. The Journal of Immunology, 2012, 188: 5723-5733.