ASTROCYTES ARE MAINLY RESPONSIBLE FOR THE POLYUNSATURATED FATTY-ACID ENRICHMENT IN BLOOD-BRAIN-BARRIER ENDOTHELIAL-CELLS IN-VITRO

To determine the respective roles of endothelial cells from brain capi llaries and astrocytes in the conversion of circulating 18:2n-6 and 18 :3n-3 into 20:4n-6 and 22:6n-3, respectively, a coculture of the two c ell types mimicking the in vivo blood-brain barrier was used. During t he culture period, endothelial cells cultured on an insert were set ab ove the medium of a Petri dish containing or not a stabilized culture of astrocytes. Five days after confluence, labeled 18:2n-6 and 18:3n-3 (10 mu M each) were added to the endothelial cells and incubated for 48 h, Analogous experiments were also performed by using each cell typ e cultured alone in the culture device. The distribution of radioactiv ity in lipids and fatty acids was studied in all the compartments of t he culture device. Endothelial cells cultured alone weakly converted t he precursor fatty acids into 20:4n-6 and 22:6n-3, When endothelial ce lls were cocultured with astrocytes, their content of polyunsaturated fatty acids increased dramatically, This effect was associated with th e uptake of polyunsaturated fatty acids from the lower medium (astrocy te medium). These fatty acids were released by astrocytes after they w ere synthesized from the precursor fatty acids that passed through the endothelial cell monolayer into the lower medium. Polyunsaturated fat ty acids were released by astrocytes as unesterified fatty acids and a s phospholipids (mainly phosphatidylcholine and lysophosphatidylcholin e) even when the medium was devoid of serum. These results suggest tha t astrocytes could play a major role in the delivery of essential poly unsaturated fatty acids to the barrier itself and to the brain.