The effect of a ceramide analog, N-acetylsphingosine on the induction of proliferation and IL-2 synthesis in T cells from young and old F344 rats

Ceramide is a physiological mediator of extracellular signals that control various cellular functions, including proliferation and apoptosis. In the present study, we examined the effects of cell-permeable ceramide analog, N-acetyl-sphingosine (C₂-ceramide) on the induction of proliferation and interleukin-2 (IL-2) synthesis in T cells from young and old rats. Splenic T cells from 6- and 24-month-old Fischer 344 rats were treated with C₂-ceramide and then incubated with anti-CD3 antibody for 24 or 48 h. The induction of proliferation and IL-2 production by anti-CD3 was significantly (P<0.001) lower in T cells from old rats compared to T cells from young rats. C₂-ceramide treatment resulted in suppression of proliferation and IL-2 production in a concentration-dependent manner. The suppressive effect of C₂-ceramide on proliferation and IL-2 production was greater in T cells from old rats than T cells from young rats. We investigated whether this decreased responsiveness was due to induction of program cell death (apoptosis) and found that there was a significant increase in DNA fragmentation in C₂-ceramide treated and anti-CD3 stimulated T cells from both young and old rats. The increase in DNA fragmentation was paralleled with an increase in caspase-3 activation. C₂-ceramide-induced caspase-3 activation and DNA fragmentation was significantly (P<0.5) higher in stimulated T cells from old rats compared to stimulated T cells from young rats. These results suggest that the sphingomyelin-ceramide signaling pathway may play an important regulatory role in the well-documented age-related decline in immune function.