The Cx43 Carboxyl-Terminal Mimetic Peptide alphaCT1 Protects Endothelial Barrier Function in a ZO1 Binding-Competent Manner
The Cx43 CT mimetic peptide, CT1, originally designed to bind to ZO1 and thereby inhibit Cx43/ZO1 interaction, was used as a tool to probe the role of Cx43/ZO1 association in regulation of epithelial/endothelial barrier function. Using both in vitro and ex vivo methods of barrier function measurement, including Electric Cell-Substrate Impedance Sensing(ECIS), a FITC-dextran transwell permeability assay, and a FITC-dextran cardiovascular leakage protocol involving Langendorff-perfused mouse hearts, CT1 was found to protect the endothelium from thrombin-induced breakdown in cell-cell contacts. Barrier protection was accompanied by significant remodeling of the F-actin cytoskeleton, characterized by a redistribution of F-actin away from the cytoplasmic and nuclear regions of the cell, towards the endothelial cell periphery, in association with alterations in cellular orientation distribution. In line with observations of increased cortical F-actin, CT1 upregulated cell-cell border localization of endothelial VE-cadherin, the Tight Junction protein Zonula Occludens 1 (ZO1), and the Gap Junction Protein (GJ) Connexin43 (Cx43). A ZO1-binding-incompetent variant of CT1, CT1-I, indicated that these effects on barrier function and barrier-associated proteins, were likely associated with Cx43 CT sequences retaining ability to interact with ZO1. These results implicate the Cx43 CT and its interaction with ZO1, in the regulation of endothelial barrier function, while revealing the therapeutic potential of CT1 in the treatment of vascular edema.