Epithelial barrier dysfunction in lymphocytic colitis through cytokine-dependent internalization of claudin-5 and -8
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Watery diarrhea is the cardinal symptom of lymphocytic colitis (LC). We have previously shown that colonic Na malabsorption is one of the major pathologic alterations of LC and found evidence for an epithelial barrier defect. On these grounds, this study aimed to identify the inherent mechanisms of this epithelial barrier dysfunction and its regulatory features.
Epithelial resistance (R epi) was determined by one-path impedance spectroscopy and 3H-mannitol fluxes were performed on biopsies from sigmoid colon in miniaturized Ussing chambers. Tight junction proteins were analyzed by Western blot and confocal microscopy. Inflammatory signaling was characterized in HT-29/B6 cells. Apoptosis and mucosal surface parameters were quantified morphologically.
R epi was reduced to 53% and 3H-mannitol fluxes increased 1.7-fold in LC due to lower expression of claudin-4, -5, and -8 and altered subcellular claudin-5 and -8 distributions off the tight junction. TNFα and IFNγ could mimic subcellular redistribution in HT-29/B6 cells, a process which was independent on MLCK activation. Epithelial apoptosis did not contribute to barrier dysfunction in LC and mucosal surface area was unchanged.
Epithelial barrier dysfunction in LC occurs through downregulation of claudin-4, -5, and -8, and redistribution of claudin-5 and -8 off the tight junction, which contributes to diarrhea by a leak-flux mechanism. The key effector cytokines TNFα and IFNγ turned out to be the trigger for redistribution of claudin-5 and -8. Thus, alongside sodium malabsorption, leak-flux is yet another important diarrheal mechanism in LC.
KeywordsLymphocytic colitis Tight junction Claudin Cytokines
We thank Detlef Sorgenfrei († January 2015) for excellent technical support.
Compliance with ethical standards
This work was supported by the Deutsche Forschungsgemeinschaft (DFG) Grants Schu 559/10-2, FOR 721/2 and the Volkswagenstiftung (Lichtenberg Program to MRS).
Conflict of interest
Britta Siegmund has served as consultant for Abbvie, Janssen, Hospira, MSD, Mundipharma, Takeda, received speaker fees from Abbvie, Falk, Ferring, Hospira, MSD, Takeda and received a research grant from Hospira. All other authors declare that they have no conflicts of interest.
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