Intermedin (adrenomedullin-2): a potential protective role in human aortic endothelial cells

Intermedin (IMD) is a novel peptide with significant vasodilator and cardiac protective actions similar to the related peptide adrenomedullin (ADM). Unlike those of ADM the actions and expression of IMD in endothelial cells are poorly characterised. ADM expression can be increased during cardiovascular disease/stress in vitro and in vivo where it may have a role in several cardiovascular protective actions. To characterise IMD mRNA expression cultured human aortic endothelial cells (HAEC) were stressed by removing serum and bicarbonate, and the addition of hydrogen peroxide. The responses were compared to those of ADM mRNA. We also compared the effects of ADM and IMD on caspase activity and cell viability, and investigated if IMD actions could be altered by a CGRP receptor antagonist.

Using the cell immunoblot assay, immunoreactive IMD was shown to be secreted by HAEC. IMD mRNA expression was also detected in HAEC grown in endothelial growth media (but at markedly lower levels than that of ADM). Absence of bicarbonate, a redox-mediated regulator of endothelial response to various stresses, increased IMD mRNA and ADM mRNA expression. However IMD mRNA, but not ADM mRNA, was markedly increased over time in HAEC in conditions of cell stress including incubation with serum-free Dulbecco's modified Eagle's medium (DMEM) and in response to hydrogen peroxide (H2O2). These vigorous responses in IMD mRNA expression were further enhanced by incubation in 5% serum in DMEM without bicarbonate, but in a selective manner since ADM expression was suppressed by serum. We also observed that IMD mRNA was markedly increased and ADM mRNA suppressed in HAEC following a period of suspension and replating. Finally, we observed that IMD, like ADM, increased cell viability in HAEC in DMEM without serum but only IMD reduced caspase activity, perhaps via and a yet to be defined receptor system.

HAECs express IMD mRNA and secrete IMD peptide. IMD mRNA expression is markedly dependent on metabolic conditions and is selectively regulated in a contrary fashion to ADM mRNA. IMD mRNA expression in endothelial cells is markedly sensitive to oxidative stress, and IMD peptide itself has antiapoptotic activity in human endothelial cells. Our data suggest that IMD has a different role to ADM and may perform a protective function in humans.