BACKGROUND AND PURPOSE
Intermedin is a member of the calcitonin gene-related-peptide (CGRP) family expressed in endothelial cells and acts via
calcitonin receptor-like receptors (CLRs). Here we have analysed the receptors for intermedin and its effect on the endothelial
barrier in monolayers of human umbilical vein endothelial cells (HUVECs).
EXPERIMENTAL APPROACH
We analysed the effect of intermedin on albumin permeability, contractile machinery, actin cytoskeleton and VE-cadherin in
cultured HUVECs.
KEY RESULTS
Intermedin concentration-dependently reduced basal endothelial permeability to albumin and antagonized thrombin-induced
hyperpermeability. Intermedin was less potent (EC 50 1.29 ? 0.12 nM) than adrenomedullin (EC 50 0.24 ? 0.07 nM) in
reducing endothelial permeability. These intermedin effects were inhibited by AM 22–52 and higher concentrations of aCGRP 8–37 ,
with pA 2 values of aCGRP 8–37 of 6.4 for both intermedin and adrenomedullin. PCR data showed that HUVEC expressed only
the CLR/RAMP2 receptor complex. Intermedin activated cAMP/PKA and cAMP/Epac signalling pathways. Intermedin’s effect
on permeability was blocked by inhibition of PKA but not of eNOS. Intermedin antagonized thrombin-induced contractile
activation, RhoA activation and stress fibre formation. It also induced Rac1 activation, enhanced cell–cell adhesion and
antagonized thrombin-induced loss of cell–cell adhesion. Treatment with a specific inhibitor of Rac1 prevented
intermedin-mediated barrier stabilization.
CONCLUSION AND IMPLICATIONS
Intermedin stabilized endothelial barriers in HUVEC monolayers via CLR/RAMP2 receptors. These effects were mediated via
cAMP-mediated inactivation of contractility and strengthening of cell–cell adhesion. These findings identify intermedin as a
barrier stabilizing agent and suggest intermedin as a potential treatment for vascular leakage in inflammatory conditions.
Abbreviations
AJ , adherens junctions ; CGRP , calcitonin gene related peptide ; CLR , calcitonin receptor-like receptor ; Epac , exchange
protein directly activated by cAMP ; HUVEC , human umbilical vein endothelial cells ; L-NAME , N G -nitro-L-Arginine
methyl ester ; L-NNA , N G -nitro-L-Arginine ; MLCs , myosin light chain ; MLCK , myosin light chain kinase ; MLCP myosin
light chain phosphatase ; RAMP , receptor activity modifying protein ; Rock , Rho kinase