Abstract 200: Inhibition of TNFa-Induced ICAM-1 Expression by AT2 Activation Involves ACE2

Abstract

The renin-angiotensin system (RAS) is a coordinated hormonal cascade involved in cardiovascular control, with angiotensin II (Ang II) as the main effector peptide. Both Ang II type 2 receptor (AT2) and angiotensin I-converting enzyme 2 (ACE2) are important in RAS system, and counteract the vasoconstrictor and pro-inflammatory effects of Ang II. Recent studies have suggested a link between AT2 and ACE2. However, the role of ACE2 in mediating the anti-inflammatory effects of AT2 has not been established. Tumor necrosis factor (TNFα) is a cytokine involved in Ang II signaling and promotes the inflammatory response via NF-kB. We hypothesized that activation of AT2 prevents TNFα stimulation of intercellular adhesion molecule-1 (ICAM-1) expression in human coronary artery endothelial cells (HCREC) through ACE2. Cultured HCREC were pretreated with AT2 antagonists PD123319 (10 μM) or ACE2 antagonist DX 600 (1 μM) for 30 min, then AT2 agonist CGP42112A (0.1 μM) for 30 min and then stimulated with TNFα (0.5 ng/ml). ICAM-1 and p -IkB expression were measured by Western Blot. ACE2 mRNA was measured by real-time RT-PCR. ICAM-1 expression was very low in untreated cells and greatly increased by TNFα treatment. Pretreatment with AT2 agonist CGP42112A inhibited TNFα-induced ICAM-1 expression by 47% ± 5% ( p <0.01). This effect was diminished by AT2 antagonist PD123319. Interestingly, activation of AT2 with agonist CGP42112A increased ACE2 mRNA expression by 1.82 ± 0.09 fold (p<0.01). This increase was further enhanced by overexpression of AT2 in the presence of CGP42112A. Pretreatment with ACE2 antagonist DX 600 prevented the inhibitory effects of AT2 stimulation on TNFα-induced ICAM-1 expression ( p <0.01), whereas DX 600 itself had no effect. Furthermore, we found that TNFα increased p -IKB expression by 7.46 ± 0.51 fold ( p <0.01) compared to untreated cells and this effect was diminished by activation of AT2 with CGP42112A. Our findings suggest that stimulation of AT2 reduces TNFα-induced ICAM-1 expression, which is partly through ACE2. NF-kB may be involved in this signaling cascade.