Claudin extracellular domains determine paracellular charge selectivity and resistance but not tight junction fibril architecture

TLDR

Tight junctions regulate paracellular permeability, and claudin proteins modulate transepithelial electrical resistance and charge selectivity. The study aims to determine whether the extracellular domains of claudin‑4 and claudin‑2 dictate their distinct paracellular properties. The authors interchanged the extracellular domains between claudin‑4 and claudin‑2 and evaluated the resulting effects on resistance and ion selectivity. Swapping the first extracellular domain of claudin‑4 onto claudin‑2 increased TER severalfold and markedly reduced Na⁺ permeability, whereas placing claudin‑2 domains onto claudin‑4 raised TER only modestly and altered charge selectivity slightly, supporting a model that the first extracellular domain alone determines paracellular charge selectivity and resistance. Reference: J Clin Invest 107: 1319–1327, 2001.

Abstract

Tight junctions (TJs) regulate paracellular permeability across epithelia and vary widely in their transepithelial electrical resistance (TER) and charge selectivity. The claudin family of transmembrane proteins influences these properties. We previously reported that claudin-4 increased TER ∼300% when expressed in low-resistance Madin-Darby canine kidney (MDCK) II cells and decreased the paracellular permeability for Na + more than Cl − (Van Itallie C, Rahner C, and Anderson JM. J Clin Invest 107: 1319–1327, 2001). In comparison, we report here that expression of claudin-2 increases TER by only ∼20% and does not change the ionic selectivity of MDCK II cells from their cation-selective background. To test whether the extracellular domains of claudins-4 and -2 determine their unique paracellular properties, we determined the effects of interchanging these domains between claudins-4 and -2. Inducible expression of wild-type claudins and extracellular domain chimeras increased both the number and depth of fibrils, but the characteristic fibril morphologies of claudin-4 or -2 were not altered by switching extracellular domains. Like claudin-4, chimeras expressing the first or both extracellular domains of claudin-4 on claudin-2 increased TER severalfold and profoundly decreased the permeability of Na + relative to Cl − . In contrast, chimeras expressing the first or both extracellular domains of claudin-2 on claudin-4 increased the TER by only ∼60 and ∼40%, respectively, and only modestly altered charge selectivity. These results support a model in which the claudins create paracellular channels and the first extracellular domain is sufficient to determine both paracellular charge selectivity and TER.