Selective localization of phosphatidylcholine-derived signaling in detergent-resistant membranes from synaptic endings

Detergent-resistant membranes (DRMs) are a class of specialized microdomains that compartmentalize several signal transduction processes. In this work, DRMs were isolated from cerebral cortex synaptic endings (Syn) on the basis of their relative insolubility in cold Triton X-100 (1%). The lipid composition and marker protein content were analyzed in DRMs obtained from adult and aged animals. Both DRM preparations were enriched in Caveolin, Flotillin-1 and c-Src and also presented significantly higher sphingomyelin (SM) and cholesterol content than purified Syn. Total phospholipid-fatty acid composition presented an increase in 16:0 (35%), and a decrease in 20:4n-6 (67%) and 22:6n-3 (68%) content in DRM from adults when compared to entire synaptic endings. A more dramatic decrease was observed in the 20:4n-6 and 22:6n-3 content in DRMs from aged animals (80%) with respect to the results found in adults. The coexistence of phosphatidylcholine-specific-phospholipase C (PC-PLC) and phospholipase D (PLD) in Syn was previously reported. The presence of these signaling pathways was also investigated in DRMs isolated from adult and aged rats. Both PC-PLC and PLD pathways generate the lipid messenger diacylglycerol (DAG) by catalyzing PC hydrolysis. PC-PLC and PLD1 localization were increased in the DRM fraction. The increase in DAG generation (60%) in the presence of ethanol, confirmed that PC-PLC was also activated when compartmentalized in DRMs. Conversely, PLD2 was excluded from the DRM fraction. Our results show an age-related differential fatty acid composition and a selective localization of PC-derived signaling in synaptic DRMs obtained from adult and aged rats.