Inhibition of neuronal apoptosis by docosahexaenoic acid (22 : 6n-3) - Role of phosphatidylserine in antiapoptotic effect

Enrichment of Neuro 2A cells with docosahexaenoic acid (22:6n-3) decreased apoptotic cell death induced by serum starvation as evidenced by the reduce d DNA fragmentation and caspase-3 activity. The protective effect of 22:6n- 3 became evident only after at least 24 h of enrichment before serum starva tion and was potentiated as a function of the enrichment period, During enr ichment 22:6n-3 incorporated into phosphatidylserine (PS) steadily, resulti ng in a significant increase in the total PS content. Similar treatment wit h oleic acid (18:1n-9) neither altered PS content nor resulted in protectiv e effect. Hindering PS accumulation by enriching cells in a serine-free med ium diminished the protective effect of 22:6n-3. Membrane translocation of Raf-l was significantly enhanced by 22:6n-3 enrichment in Neuro 2A cells. C onsistently, in vitro biomolecular interaction between PS/phosphatidylethan olamine /phosphatidylcholine liposomes, and Raf-l increased in a PS concent ration-dependent manner. Collectively, enrichment of neuronal cells with 22 :6n-3 increases the PS content and Raf-l translocation, down-regulates casp ase-3 activity, and prevents apoptotic cell death. Both the antiapoptotic e ffect of 22:6n-3 and Raf-l translocation are sensitive to 22:6n-3 enrichmen t-induced PS accumulation, strongly suggesting that the protective effect o f 22:6n-3 may be mediated at least in part through the promoted accumulatio n of PS in neuronal membranes.