Selective decrease in paracellular conductance of tight junctions: role of the first extracellular domain of claudin-5.
Claudin-5 is a protein component of many endothelial tight junctions, including those at the blood-brain barrier, a barrier that limits molecular exchanges between the central nervous system and the circulatory system. To test the contribution of claudin-5 to this barrier function of tight junctions, we expressed murine claudin-5 in Madin-Darby canine kidney II cells. The result was a fivefold increase in transepithelial resistance in claudin-5 transductants and a reduction in conductance of monovalent cations. However, the paracellular flux of neither neutral nor charged monosaccharides was significantly changed in claudin-5 transductants compared to controls. Therefore, expression of claudin-5 selectively decreased the permeability to ions. Additionally, site-directed mutations of particular amino acid residues in the first extracellular domain of claudin-5 altered the properties of the tight junctions formed in response to claudin-5 expression. In particular, the conserved cysteines were crucial: mutation of either cysteine abolishted the ability of claudin-5 to increase transepithelial resistance, and mutation of Cys(64) strikingly increased the paracellular flux of monosaccharides. These new insights into the functions of claudin-5 at the molecular level in tight junctions may account for some aspects of the blood-brain barrier's selective permeability.
Wen
Huajie
H
Department of Neuropharmacology, The Scripps Research Institute, La Jolla, CA 92037, USA.
Watry
Debbie D
DD
Marcondes
M Cecilia G
MC
Fox
Howard S
HS
D000595:Amino Acid Sequence; D000818:Animals; D003545:Cysteine / Q000235:genetics / Q000378:metabolism; D008353:Mannitol / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D009154:Mutation; D019108:Tight Junctions / Q000378:metabolism*
D008565:Membrane Proteins; D008353:Mannitol; D003545:Cysteine