Degradation of membrane phospholipids in the cultured human astroglial cell line UC-11MG during ATP depletion.
The exposure of brain cells to adverse conditions, such as ATP depletion, induces the degradation of membrane phospholipids and the accumulation of free fatty acids. We have investigated the mechanism of membrane breakdown in an in vitro cell injury model. Confluent cells from the human astroglial cell line UC-11MG were treated with sodium iodoacetate to deplete their intracellular ATP. Large amounts of saturated (palmitic acid) and unsaturated (oleic, linoleic and arachidonic acid) free fatty acids as well as diacylglycerols containing prelabeled fatty acids were released from the cells prior to the loss of plasma membrane integrity. The capacity of the cells to reincorporate free fatty acid into membrane phospholipids decreased in parallel with the loss of intracellular ATP, indicating the failure of the acyltransferase pathway. The addition of the phospholipase A2 inhibitors manoalide, mepacrine, or U-26384, or the phospholipase C inhibitor U-73122, reduced the severity of cell injury, but did not maintain cell viability. The addition of a battery of protease inhibitors with or without the phospholipase inhibitors had no protective effect. These results suggest that the activation of phospholipases A2 and C coupled with the loss of the reacylation process lead to the breakdown of membrane components during lethal cell injury.