Induction of the manganese superoxide dismutase gene by sphingomyelinase and ceramide

The present study reports the effect of ceramide generated by hydrolysis of membrane sphingomyelin with bacterial sphingomyelinase (SMase) and of cell -permeable ceramide analogues on the expression of manganese superoxide dis mutase (MnSOD), Incubation of the rat primary astrocytes with SMase led to a time- and dose-dependent increase in MnSOD activity. The increase in MnSO D activity was accompanied by an increase in MnSOD protein and mRNA. A simi lar effect on the expression of MnSOD was observed with the addition of cel l-permeable ceramide analogues (C-2 and C-6). On the other hand, C-2-dihydr oceramide (N-acetylsphinganine), which lacks the functional critical double bond, was ineffective in inducing the expression of MnSOD. Nuclear run-on analysis showed that SMase and ceramide increased the rate of transcription of the MnSOD gene. Besides astrocytes, SMase was also found to induce the expression of MnSOD in rat mesangial cells, C-6 glial cells, PC12 cells, an d human skin fibroblasts. Markedly higher expression of mRNA, protein, and activity of MnSOD in skin fibroblasts from patients with Farber disease, a human disorder with pathognomonic accumulation of ceramide due to a deficie ncy of ceramidase, than in normal skin fibroblasts indicate that ceramide m ay act as a physiological inducer of MnSOD gene expression. However, stimul ation of ceramide-mediated DNA fragmentation by antisense knockdown of MnSO D suggests that induction of MnSOD by ceramide is a protective response of the cell.