Proceedings of The Physiological Society

University of Oxford (2011) Proc Physiol Soc 23, C12

Oral Communications

Adrenomedullin 2 enhances macrovascular endothelial barrier function while it disrupts coronary microvascular barrier via differential regulation of Rac1

M. Aslam1,2, S. Rohrbach1, R. Schulz1, H. Piper1, T. Noll1, D. Guenduez2

1. Institute of Physiology, Justus Liebig University, Giessen, Germany. 2. Medical Clinic I, Cardiology and Angiology, University Hospital Giessen and Marburg, Giessen, Germany.

Aims: Adrenomedullin 2 (ADM2) is a novel member of calcitonin-gene-related-peptide (CGRP) family which acts via increased production of cAMP via calcitonin-receptor-like-receptors (CRLR). Recently, it has been shown that ADM2 expression is enhanced in failing myocardium. The main objective of the present study was to analyse the effects and molecular mechanisms of ADM2 on macromolecule permeability of coronary microvascular and venular macrovascular endothelium. Methods: In cultured rat coronary microvascular endothelial cells (RCEC) and human umbilical vein endothelial cells (HUVEC), the effects of ADM2 (10 nM) on monolayer permeability (albumin flux), RhoA, Rac1 and cdc42 activation (pulldown assay), actin cytoskeleton and VE-cadherin (confocal microscopy) translocation and contractile activation (myosin light chain phosphorylation; Western blotting) were analysed. Results: ADM2 increased permeability of RCEC and reduced permeability of HUVEC monolayers and increased intracellular cAMP concentrations in both cell types in a concentration dependent manner. These IMD effects could be blocked by CGRP receptor inhibitor in RCEC while by adrenomedullin receptor 1 (AM1) in HUVEC monolayers. ADM2 caused a derangement of actin cytoskeleton accompanied by loss of VE-cadherin in RCEC, while it causes a rearrangement of actin cytoskeleton and VE-cadherin at cell-cell junctions in HUVEC monolayers. ADM2 inactivated RhoA/Rock pathway in both cell types; however, it inactivated Rac1 in RCEC, while activating Rac1 in HUVEC. Inhibition of RhoA/Rock pathway in RCEC but not in HUVEC resulted in inactivation of Rac1, derangement of actin cytoskeleton, and loss of barrier function. On the other hand activation of either RhoA or Rac1 in RCEC with specific activators rescued the ADM2-induced increased permeability of RCEC but not HUVEC monolayers. Conclusion: The data of present study demonstrate that ADM2 has differential effect on permeability of RCEC and HUVEC. This differential effect of ADM2 is due to differential regulation of actin cytoskeleton dynamics and Rac1 activity. Moreover, Rac1 activity is regulated by RhoA/Rock pathway in RCEC but not in HUVEC. Furthermore, the study suggests that enhanced expression of ADM2 in failing myocardium could be deleterious factor leading to myocardial oedema.

Where applicable, experiments conform with Society ethical requirements