Claudin-16 and claudin-19 interact and form a cation-selective tight junction complex

TLDR

Tight junctions mediate paracellular ion reabsorption in the kidney, and mutations in the TJ proteins claudin‑16 and claudin‑19 cause familial hypomagnesemia with hypercalciuria and nephrocalcinosis, but the mechanisms of their roles remain unclear. In pig kidney epithelial cells, claudin‑19 acts as a chloride blocker while claudin‑16 functions as a sodium channel, and their co‑expression creates a cation‑selective tight junction through a synergistic interaction that is disrupted by FHHNC‑associated mutants, indicating that the CLDN16–CLDN19 complex confers cation selectivity and explaining the disease mechanism.

Abstract

Tight junctions (TJs) play a key role in mediating paracellular ion reabsorption in the kidney. Familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC) is an inherited disorder caused by mutations in the genes encoding the TJ proteins claudin-16 (CLDN16) and CLDN19; however, the mechanisms underlying the roles of these claudins in mediating paracellular ion reabsorption in the kidney are not understood. Here we showed that in pig kidney epithelial cells, CLDN19 functioned as a Cl– blocker, whereas CLDN16 functioned as a Na+ channel. Mutant forms of CLDN19 that are associated with FHHNC were unable to block Cl– permeation. Coexpression of CLDN16 and CLDN19 generated cation selectivity of the TJ in a synergistic manner, and CLDN16 and CLDN19 were observed to interact using several criteria. In addition, disruption of this interaction by introduction of FHHNC-causing mutant forms of either CLDN16 or CLDN19 abolished their synergistic effect. Our data show that CLDN16 interacts with CLDN19 and that their association confers a TJ with cation selectivity, suggesting a mechanism for the role of mutant forms of CLDN16 and CLDN19 in the development of FHHNC.