Proximal Tubule Angiotensin AT 2 Receptors Mediate an Anti-Inflammatory Response via Interleukin-10

Abstract

The angiotensin type 2 receptor (AT 2 R) has been shown to lower inflammation in the kidney. However, the role of the anti-inflammatory cytokine interleukin (IL)-10 in AT 2 R-mediated attenuation of inflammation has not been elucidated. We hypothesized that AT 2 R 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 (human kidney-2 [HK-2]) was activated with lipopolysaccharide (10 μg/mL) and AT 2 R agonist C21 (1 μmol/L) for 24 hours, and media cytokine levels were assessed. Lipopolysaccharide modestly downregulated AT 2 R expression. Treatment with C21 lowered lipopolysaccharide-induced levels of both tumor necrosis factor-α and IL-6, but increased IL-10 levels. Treatment with neutralizing IL-10 antibody (1 μg/mL) or NO synthase inhibitor L-NAME (1 mmol/L) abolished this effect. For in vivo studies, prehypertensive obese Zucker rats and age-matched lean Zucker rats were treated for 2 weeks with C21 (300 μg/kg per day, IP) and AT 2 R antagonist (PD123319; 50 μg/kg per minute, SC infusion). Compared with lean Zucker rats, obese Zucker rats had higher levels of renal AT 2 R expression, tumor necrosis factor-α, and IL-6. C21 treatment decreased levels of tumor necrosis factor-α by 75% and IL-6 by 60%. Conversely, PD treatment lowered the renal IL-10 levels in obese Zucker rats by ≈60%. Renal morphometry revealed increased mesangial matrix expansion and glomerular macrophage infiltration, which was improved by C21 treatment in obese Zucker rats. Our findings suggest that proximal tubule AT 2 R 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.