Occludin and tricellulin facilitate formation of anastomosing tight-junction strand network to improve barrier function.

Affiliation

Saito AC(1), Higashi T(1), Fukazawa Y(2), Otani T(3)(4), Tauchi M(1), Higashi AY(1), Furuse M(3)(4), Chiba H(1).
Author information:
(1)Department of Basic Pathology, Fukushima Medical University, Fukushima 960-1295, Japan.
(2)Division of Brain Structure and Function, Research Center for Child Mental Development, School of Medical Science, University of Fukui, Fukui 910-1193, Japan.
(3)Division of Cell Structure, National Institute for Physiological Sciences, Okazaki, Aichi 444-8787, Japan.
(4)Department of Physiological Sciences, School of Life Science, SOKENDAI
(Graduate University for Advanced Studies), Okazaki, Aichi 444-8585, Japan.

Abstract

Tight junctions (TJs) are composed of a claudin-based anastomosing network of TJ strands at which plasma membranes of adjacent epithelial cells are closely attached to regulate the paracellular permeability. Although the TJ proteins occludin and tricellulin have been known to be incorporated in the TJ strand network, their molecular functions remain unknown. Here, we established tricellulin/occludin-double knockout (dKO) MDCK II cells using a genome editing technique and evaluated the structure and barrier function of these cells. In freeze-fracture replica electron microscopy, the TJ strands of tricellulin/occludin-dKO cells had fewer branches and were less anastomosed compared with the controls. The paracellular permeability of ions and small tracers was increased in the dKO cells. A single KO of tricellulin or occludin had limited effects on the morphology and permeability of TJs. Mathematical simulation using a simplified TJ strand network model predicted that reduced cross-links in TJ strands lead to increased permeability of ions and small macromolecules. Furthermore, overexpression of occludin increased the complexity of TJ strand network and strengthened barrier function. Taken together, our data suggest that tricellulin and occludin mediate the formation and/or stabilization of TJ-strand branching points and contribute to the maintenance of epithelial barrier integrity.