title: Quercetin enhances intestinal barrier function through the assembly of zonula [corrected] occludens-2, occludin, and claudin-1 and the expression of claudin-4 in Caco-2 cells.
abstract: Dietary flavonoids provide various beneficial effects for our health. We investigated the promotive effects of quercetin and myricetin on the intestinal barrier function in human intestinal Caco-2 cell monolayers. Transepithelial electrical resistance (TER) across the monolayers increased rapidly during incubation with quercetin, peaking at 6 h. Lucifer yellow flux, a paracellular marker, was dose-dependently lower after quercetin and myricetin treatments, although quercetin exhibited a more potent effect. Immunoblot analysis of tight junction (TJ) proteins revealed that zonula occludens (ZO)-2, occludin, and claudin-1 were distributed to the actin cytoskeleton fraction by quercetin without increasing their respective whole-cell levels and this distribution was correlated with the increases in TER. The claudin-4 level was elevated by quercetin in both the cytoskeleton fraction and whole cells after 12 h. Confocal microscopy showed the assembly of claudin-1 and -4 at the TJ by quercetin. An inhibitor of protein kinase Cdelta (PKCdelta), rottlerin, enhanced the barrier function with changes in the distribution and expression of TJ proteins in a manner very similar to that of quercetin. Phosphorylation of PKCdelta indicating the enzymatic activity in the cells was decreased by quercetin after 1 h. In the kinase assay, quercetin exhibits direct inhibition of the PKCdelta isoform. This study demonstrates that quercetin enhances the intestinal barrier function through the assembly of ZO-2, occludin, and claudin-1 by inhibiting PKCdelta and the increase in claudin-4 expression has an additional role after 12 h.
authors.affiliation: Division of Applied Bioscience, Research Faculty of Agriculture, Hokkaido University Kita-9, Nishi-9, Kita-ku, Sapporo 060-8589, Japan.
authors.forename: Takuya
authors.initials: T
authors.lastname: Suzuki
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Hara
mesh_terms: D000098:Acetophenones / Q000494:pharmacology; D001578:Benzopyrans / Q000494:pharmacology; D018938:Caco-2 Cells; D002463:Cell Membrane Permeability / Q000187:drug effects; D062445:Claudin-1; D062506:Claudin-4; D017097:Electric Impedance; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D015151:Immunoblotting; D007422:Intestines / Q000737:chemistry / Q000187:drug effects* / Q000502:physiology; D007700:Kinetics; D008565:Membrane Proteins / Q000032:analysis*; D018613:Microscopy, Confocal; D062793:Occludin; D051745:Protein Kinase C-delta / Q000037:antagonists & inhibitors / Q000378:metabolism; D011794:Quercetin / Q000494:pharmacology*; D011994:Recombinant Proteins / Q000378:metabolism; D062827:Zonula Occludens-2 Protein
chemical_list: D000098:Acetophenones; D001578:Benzopyrans; C568108:CLDN1 protein, human; C568157:CLDN4 protein, human; D062445:Claudin-1; D062506:Claudin-4; D004791:Enzyme Inhibitors; D005419:Flavonoids; D008565:Membrane Proteins; C568985:OCLN protein, human; D062793:Occludin; D011994:Recombinant Proteins; C569046:TJP2 protein, human; D062827:Zonula Occludens-2 Protein; C040015:myricetin; D011794:Quercetin; C085746:rottlerin; D051745:Protein Kinase C-delta