Cerebral endothelium and astrocytes cooperate in supplying docosahexaenoic acid to neurons.

These findings confirm that astrocytes and cerebral endothelium, not neurons, are the cells primarily responsible for the desaturation of essential fatty acids in the brain. They suggest that cerebral endothelial cells can target omega-3 fatty acids for release from their basolateral surface and thus aid in the enrichment of omega-3 fatty acids observed in the brain. The studies further suggest that endothelium and astrocytes play an important supportive role in the brain by cooperating in the elongation and desaturation of omega-3 essential fatty acid precursors in the brain and in the transfer of DHA to neurons. In doing so, endothelium and astrocytes may contribute positively to the high level of fatty acid desaturation necessary for normal neuronal function. In composite, the present studies and previously published work support a model for supplying DHA to central nervous system neurons that could utilize either DHA or its omega-3 fatty acid precursors circulating in the blood (Figure 4). If preformed DHA were available, the cerebral endothelium would take it up and transfer it into the brain. An additional sequential pathway would utilize circulating linolenic acid or EPA. In this pathway cerebral endothelium would take up omega-3 fatty acid precursors and target them preferentially into the brain, performing some elongation and desaturation in the process. Astrocytes would subsequently complete the conversion of precursors to DHA, releasing it for uptake by neurons.