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

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 activated with lipopolysaccharide (LPS, 10 μg/ml) and/or AT2R agonist C21 (1μmol/L) for 24 hours and media cytokine levels were assessed. LPS modestly downregulated AT2R expression. Treatment with C21 lowered LPS-induced levels of both, TNF-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, pre-hypertensive obese Zucker rats (OZR) and age-matched lean Zucker rats were treated for 2 weeks 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 of renal AT2R expression, TNF-α and IL-6. C21 treatment decreased levels of TNF-α by 75% and IL-6 by 60%. Conversely, PD treatment lowered the renal IL-10 levels in OZR by ~60%. Renal morphometry revealed increased mesangial matrix expansion and glomerular macrophage infiltration which was improved by C21 treatment in OZR. 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.

Prevention of diabetic nephropathy by compound 21, selective agonist of angiotensin type 2 receptors, in Zucker diabetic fatty rats

“…Since tubulointerstitial fibrosis shows the best correlation with the progression of renal disease (4), these evidences strongly suggest that direct stimulation of the AT 2 receptor could counteract an important hallmark of progression of nephropathy. In this regard, we can speculate that the beneficial effects of C21 on the kidney tissue of ZDF rats might depend on the renal upregulation of AT 2 receptor expression, as previously described for obese Zucker rats (1,8,28).…”

“…In renovascular hypertensive rats, C21 administration reduced inflammatory cell infiltration and transforming growth factor-␤1 expression in the clipped kidney (17). In obese rats, C21 treatment reduced renal inflammation, not only decreasing the expression of TNF-␣ and IL-6 and monocyte/macrophage infiltration, but also inducing the expression of IL-10, a potent anti-inflammatory cytokine (8).…”

“…In obese Zucker rats, the C21 anti-inflammatory effect in the kidney is mediated by an increase in IL-10 production by proximal tubule epithelial cells (8).…”

AT2R Agonist, Compound 21, Is Reno-Protective Against Type 1 Diabetic Nephropathy

“…Given that the affinity of C21 for the AT 2 R is 25 000-fold higher than for the AT 1 R 37 and its ability to inhibit inflammatory markers was markedly abolished by the AT 2 R antagonist, PD123319 38 consistently demonstrates that the effects of C21 are specifically mediated through the AT 2 R. Future studies are warranted to further elucidate the signaling transduction pathway of the AT 2 R, in particular its involvement with the nitric oxide pathway 32,39 and its interaction with the AT 1 R because these receptors have been previously reported to act as heterodimers. 17,40 Potential interaction between the 2 Ang II receptor subtypes may involve the ability of either receptor to alter the expression of the other receptor.…”

The angiotensin II type 2 receptor agonist Compound 21 is protective in experimental diabetes-associated atherosclerosis

“…Strikingly, Ang II negatively regulates its classical actions through the angiotensin II type 2 receptors (AT 2 Rs) [5], with this receptor subtype being markedly upregulated in numerous diseased states, including atherosclerosis [6,7], possibly to counterbalance the adverse effects mediated by the AT 1 R. Taken together, these actions highlight the potential of the AT 2 R as a key therapeutic target. With numerous studies focusing on the role of the AT 2 R in the non-diabetes setting [8][9][10], the vascular actions of this receptor in the context of diabetes still remains unclear. Given our previous findings that selective activation of the AT 2 R by a novel non-peptide agonist, Compound 21 (C21), significantly ameliorated the progression of nephropathy in an insulin-deficient model [11], we aimed to further investigate the protective role of C21 on macrovascular disease in this diabetes model.…”