Tracing the endocytosis of claudin-5 in brain endothelial cells.

Claudin-5 is a transmembrane tight junction protein highly expressed in brain endothelial cells, the site of the blood-brain barrier. The properties of the brain endothelial tight junction complex are considered to be dependent on claudin-5 cell-cell interaction, putting this protein in a position to play a major role in the maintenance of brain endothelial barrier integrity. Thus, alterations in claudin-5 function can lead to "opening" of the paracellular route and increased brain endothelial barrier permeability. Recent work from the authors's laboratory has established that caveolae-dependent internalization/recycling of claudin-5 is a mechanism underlying transient increases in brain endothelial paracellular permeability in the presence of pro-inflammatory mediators. The biochemical and microscopic techniques presented here were used to investigate trafficking of claudin-5 during those changes in paracellular permeability.