High resolution microscopy reveals claudin‐18 as a basolateral and not a tight junction‐associated protein in stomach (1111.6)

Abstract

Background: Claudin‐18 (Cldn18) is the most highly expressed tight junction protein in the stomach. Cldn18, however, also localizes to the basolateral membrane of gastric epithelial cells. We aimed to determine whether cldn18 is actually a tight junction protein using high resolution microscopy techniques. Methods: Immunostaining for cldn18 and for ZO‐1, a well‐established protein that is limited to tight junctions, was done on sections from mouse stomach. Structured illumination microscopy (SIM) was used to examine the high resolution 3‐D pattern of cldn18 and ZO‐1 localization in parietal and chief cells. Results: 3‐D SIM data revealed that cldn18 is solely a basolateral membrane‐associated cldn that runs in discontinuous anastomosing bundles along the basolateral membrane (in a basket‐like configuration) to completely enclose parietal cells. Although still present, the discontinuous bundles of cldn18 are spaced further apart in chief cells. ZO‐1 in parietal cells localizes to a shallow cleft bounded by cldn18 while in chief cells, cldn18 spirals around ZO‐1 with wide spaces between each spiral. Conclusions: Despite current thinking, cldn18 is spatially distinct from the tight junction. Our data suggests that the regulation of cation permeation by cldn18 is due to specific structural constraints on ion movement through the paracellular pathway rather than by distinct properties of the tight junction.