ClC-2 is required for rapid restoration of epithelial tight junctions in ischemic-injured murine jejunum

Background and aims: Involvement of the epithelial chloride channel ClC-2 has been implicated in barrier recovery following ischemic injury, possibly via a mechanism involving ClC-2 localization to the tight junction. The present study investigated mechanisms of intestinal barrier repair following ischemic injury in ClC-2^-/- mice. Methods: Wild type, ClC-2 heterozygous and ClC-2^-/- murine jejunal mucosa was subjected to complete ischemia, after which recovery of barrier function was monitored by measuring in vivo blood-to-lumen clearance of ³H-mannitol. Tissues were examined by light and electron microscopy. The role of ClC-2 in re-assembly of the tight junction during barrier recovery was studied by immunoblotting, immunolocalization and immunoprecipitation. Results: Following ischemic injury, ClC-2^-/- mice had impaired barrier recovery compared to wild type mice, defined by increases in epithelial paracellular permeability independent of epithelial restitution. The recovering ClC-2^-/- mucosa also had evidence of ultrastructural paracellular defects. The tight junction proteins occludin and claudin-1 shifted significantly to the detergent soluble membrane fraction during post-ischemic recovery in ClC-2^-/- mice whereas wild type mice had a greater proportion of junctional proteins in the detergent insoluble fraction. Occludin was co-immunoprecipitated with ClC-2 in uninjured wild type mucosa, and the association between occludin and ClC-2 was re-established during ischemic recovery. Based on immunofluorescence studies, re-localization of occludin from diffuse sub-apical areas to apical tight junctions was impaired in ClC-2^-/- mice. Conclusions: These data demonstrate a pivotal role of ClC-2 in recovery of the intestinal epithelium barrier by anchoring assembly of tight junctions following ischemic injury.