Knockout of Ceramide Kinase Aggravates Pathological and Lethal Responses in Mice with Experimental Colitis

Sphingolipids and their metabolic enzymes are implicated in ulcerative colitis. Ceramide kinase (CerK) catalyzes the phosphorylation of ceramide to ceramide-1-phosphate (C1P). Previous studies showed the activation of CerK by the pro-inflammatory cytokine interleukin-1β, the C1P-induced up-regulation of prostanoids exerting protective effects against colitis, and the C1P-induced down-regulation of the pro-inflammatory cytokine tumor necrosis factor-α. In order to elucidate CerK/C1P functions in colitis, we examined the severity of dextran sodium sulfate (DSS)-induced colitis in wild-type (WT) and CerK deletion (CerK^(-/-)) mice. Lethal responses were observed in C57BL/6 mice treated with DSS in dose- and time-dependent manners. The depletion of CerK enhanced DSS-induced lethal responses without affecting the onset of these responses. In colons from mice treated with 2.5% DSS for 10 d, epithelial damage was significantly enhanced by the depletion of CerK by day 5, whereas decreases in occluding and E-cadherin levels were similar in both mice. On day 5, the DSS treatment increased spleen weights and colonic levels of cyclooxygenase-2, but not cytosolic phospholipase A₂α, and induced a contractile dysfunction in the colons of both mice. The DSS-induced increase in the damage activity index score between days 5 and 10 was slightly enhanced and the decrease in this score from day 10 was slower in CerK^(-/-) mice than in WT mice. On day 7 after the DSS treatment, spleen weights slightly decreased and increased in WT and CerK^(-/-) mice, respectively. These results indicate that the depletion of CerK enhances the pathology of colitis and lethal responses in DSS-treated mice.