Choline deficiency-induced apoptosis in PC12 cells is associated with diminished membrane phosphatidylcholine and sphingomyelin, accumulation of ceramide and diacylglycerol, and activation of a caspase

It is not well appreciated that nutritional status can modulate apoptosis, a process that eliminates unwanted or damaged cells. Choline is an essentia l nutrient, and its absence induces apoptosis. When PC12 cells were cultiva ted in a choline-free medium, apoptosis was induced (27.4% of cells apoptot ic at 72 h as compared to 4.4% in control medium). In choline-free medium a t 72 h, there was a 49% decrease in phosphatidylcholine concentration (P<0. 01) and a 34% decrease in sphingomyelin concentration (P<0.01); however, th ere was no change in phosphatidylethanolamine concentration. Before detecti ng increased apoptosis in choline-deficient cells, we measured a significan t increase in ceramide (218% control) and diacyglycerol (155% control) conc entrations. The addition of a cell-permeable ceramide to cells in control m edium induced apoptosis; however, adding a cell-permeable diacyglycerol did not induce apoptosis. Caspase is a common mediator of apoptosis, and choli ne deficiency-induced apoptosis was prevented completely by replacing choli ne or adding a caspase inhibitor into the medium within 48 h of initial cho line deprivation. In those cells rescued by replacing choline at 36 h, the concentrations of phosphatidylcholine, sphingomyelin, ceramide, and diacygl ycerol returned to levels of control cells. In those cells rescued by addin g a caspase inhibitor at 36 h, the concentrations of sphingomyelin and cera mide returned to control levels, but the concentrations of phosphatidylchol ine and diacyglycerol did not return to normal. We propose that availabilit y of dietary factors (choline in this model) can modulate apoptosis. Mechan isms that we identify using this model may help us to explain why dietary c holine influences brain development.