Polyunsaturated fatty acids induce tight junctions to form in brain capillary endothelial cells

Tight junctions create a rate-limiting barrier to the diffusion of solutes between vertebrate epithelial cells and endothelial cells. They are also controlled within individual cells by a variety of physiologically relevant signals. We investigated the effects of polyunsaturated fatty acids on the formation of tight junctions in brain capillary endothelial cells, monitoring the transepithelial electrical resistance, and analyzed the expression of occludin messenger RNA. Brain-capillary endothelial cells were grown to confluence on filters and exposed to eicosapentaenoic acids, gamma linolenic acid and linoleic acid. Transepithelial electrical resistance was determined with voltage-measuring electrodes. The messenger RNA expression of occludin was quantitated by real-time quantitative reverse transcriptase-polymerase chain reaction. The basal resistance across monolayers of porcine brain capillary endothelial cells was 83+/-8.1 Omega cm(2). Cells cultured in eicosapentaenoic acids and gamma linolenic acid, but not linolenic acid, displayed a 2.7-fold increase in transepithelial electrical resistance at 10 microM in brain capillary endothelial cells. The expression level of occludin messenger RNA increased markedly immediately after the exposure to eicosapentaenoic acids or gamma linolenic acid. Following an 8 h exposure to exogenous eicosapentaenoic acids or gamma linolenic acid, occludin messenger RNA levels were significantly increased. In addition, the rise in transepithelial electrical resistance induced by eicosapentaenoic acids and gamma linolenic acid was markedly inhibited by the tyrosine kinase inhibitors genistein and PP2 and protein kinase C inhibitor, calphostin C. In contrast, the rise in transepithelial electrical resistance induced by eicosapentaenoic acids and gamma linolenic acid was not inhibited by the PI 3-kinase inhibitor, LY294002. We conclude that eicosapentaenoic acids and gamma linolenic acid increased the transepithelial electrical resistance and the expression of occludin messenger RNA in brain capillary endothelial cells. This gamma linolenic acid and eicosapentaenoic acid induced assembly of tight junction is likely to be regulated by protein kinase C and tyrosine kinase activity.