Abstract 620: Angiotensin AT2 Receptor Exerts an Anti-inflammatory Response in Lipopolysaccharide-activated THP-1 Macrophages

Abstract

Macrophages have been shown to be an important contributor to the pathogenesis of hypertension and stroke. The angiotensin AT2 receptor (AT2R), which is expressed in macrophages, is known to promote vasodialation, natriuresis and lower inflammation. The goal of the present study was to explore the anti-inflammatory role of AT2R stimulation in human macrophage-like THP-1 cells activated by lipopolysaccharide (LPS). Phorbol 12-myristate 13-acetate (PMA) differentiated macrophage-like THP-1 cells were treated with AT2R agonist C21 (1 μmol/L) for 30 minutes prior to activation with LPS (1 μg/ml). Media and cells were collected after 24 hours and were analyzed for levels of pro- and anti-inflammatory cytokines and proteins. Pre-treatment with C21 resulted in a 4-fold increase (104.8±6.1 vs 406.7±52.3) in anti-inflammatory interleukin-10 (IL-10) production and a 5-fold decrease (3560±237 vs 588.8±15.94) in pro-inflammatory tumor necrosis factor-α (TNF-α) levels in the media in response to LPS. Predictably, LPS resulted in a 6-fold up-regulation of iNOS expression which was prevented with C21 pre-treatment. A modest decrease in the anti-inflammatory macrophage mannose receptor C type 2 (MRC2) expression was detected with LPS treatment. AT2R agonist pre-treatment, however, increased this receptor expression by ~70% after LPS activation. C21 alone also resulted in a 20% increase in MRC2 expression compared to untreated controls. The anti-inflammatory effect of AT2R activation was abolished in the presence of neutralizing IL-10 antibody (1 μg/ml), indicating a central role for IL-10 in mediating the beneficial response to C21 in LPS activated macrophages. Further, inhibition of nitric oxide (NO) by L-NAME prior to C21 pre-treatment also prevented the decrease in TNF-α and increase in IL-10 in response to AT2R agonist, which suggests that the anti-inflammatory response to C21 may be mediated via increase in NO production prior to LPS activation of macrophages. In conclusion, AT2R stimulation may potentially suppress the inflammatory response of macrophages to LPS by shifting the balance from pro- to anti-inflammatory cytokine production and may prove to be beneficial in the control of the inflammatory component of stroke and hypertension.