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 essential nutrient, and its absence induces apoptosis. When PC12 cells were cultivated in a choline-free medium, apoptosis was induced (27.4% of cells apoptotic at 72 h as compared to 4.4% in control medium). In choline-free medium at 72 h, there was a 49% decrease in phosphatidylcholine concentration (P<0.01) and a 34% decrease in sphingomyelin concentration (P<0.01); however, there was no change in phosphatidylethanolamine concentration. Before detecting increased apoptosis in choline-deficient cells, we measured a significant increase in ceramide (218% control) and diacyglycerol (155% control) concentrations. The addition of a cell-permeable ceramide to cells in control medium induced apoptosis; however, adding a cell-permeable diacyglycerol did not induce apoptosis. Caspase is a common mediator of apoptosis, and choline deficiency-induced apoptosis was prevented completely by replacing choline or adding a caspase inhibitor into the medium within 48 h of initial choline deprivation. In those cells rescued by replacing choline at 36 h, the concentrations of phosphatidylcholine, sphingomyelin, ceramide, and diacyglycerol returned to levels of control cells. In those cells rescued by adding a caspase inhibitor at 36 h, the concentrations of sphingomyelin and ceramide returned to control levels, but the concentrations of phosphatidylcholine and diacyglycerol did not return to normal. We propose that availability of dietary factors (choline in this model) can modulate apoptosis. Mechanisms that we identify using this model may help us to explain why dietary choline influences brain development.