Abstract 444: Proximal Tubule Angiotensin AT2 Receptors Mediate Anti-inflammatory Response via Interleukin-10: Role in Renoprotection in Obese Rats.

Abstract

The angiotensin AT2 receptor (AT2R) has been shown to lower inflammation in the kidney. However the role of the anti-inflammatory cytokine IL-10 in AT2R mediated attenuation of inflammation has not been elucidated. We hypothesized that AT2R activation is renoprotective by directly increasing the levels of anti-inflammatory cytokine IL-10 in the kidney via nitric oxide (NO) signaling. For in vitro studies, the human proximal tubule epithelial cell-line (HK-2) was treated with lipopolysaccharide (LPS, 1 μg/ml) and/or AT2R agonist C21 (1μM) for 24 hrs and media cytokine levels were assessed. Compared to control, LPS treatment significantly increased TNF-α (1.25 ± 0.22 vs 46.27 ± 3.22 pg/ml), IL-6 (1.43 ± 0.06 vs 5.204 ± 0.41 ng/ml) and IL-10 (5.11 ± 0.46 vs 13.35 ± 0.74 pg/ml) levels. C21 treatment with LPS lowered the levels of both, TNF-α and IL-6 by 65% but caused 55% increase in IL-10 levels. C21 treatment alone significantly increased IL-10 levels (5.11 ± 0.46 vs 18.37 ± 0.87 pg/ml) while there was no effect on TNF-α or IL-6 levels. The anti-inflammatory effect of C21 was abolished in the presence of neutralizing IL-10 antibody (1 μg/ml). Also, pre-incubation with NO synthase inhibitor L-NAME (1 mM) prevented the C21-mediated decrease in IL-6 levels and increase in IL-10 levels in activated cells. For in vivo studies, 5 wk old lean and obese Zucker rats (OZR) were treated for 2 wks with C21 (300 μg/kg/day, i.p) and/or AT2R antagonist (PD123319, 50 μg/kg/min, s.c. infusion). Compared to LZR, OZR had higher levels (pg/mg protein) of renal TNF-α (1.42 ± 0.14 vs 2.78 ± 0.42) and IL-6 (6.59 ± 0.77 vs 11.71 ± 0.42). C21 treatment decreased levels of TNF-α by 75% and IL-6 by 60% while PD had no effect. Conversely, PD treatment lowered the renal IL-10 levels in OZR (8.5 ± 0.49 vs 3.69 ± 0.65 pg/mg protein) while C21 had no effect. Renal morphometry revealed increased mesangial matrix expansion score in OZR (0.27 ± 0.08 vs 1.3 ± 0.12) which was worsened by PD (1.97 ± 0.16) and improved by C21 treatment (0.8 ± 0.13). Our findings suggest that proximal tubule AT2R activation is anti-inflammatory by increasing IL-10 production which is largely NO-dependent and thus offers renoprotection by preventing early inflammation-induced renal injury in obesity.