Background: The renin–angiotensin (Ang) system controls blood pressure, in part, by regulating renal tubular sodium transport. In the kidney, activation of the angiotensin II type 1 (AT1) receptor increases renal sodium reabsorption, whereas the angiotensin II type 2 (AT2) receptor produces the opposite effect. We hypothesized that the AT2 receptor regulates AT1 receptor expression and function in the kidney.
Methods and results: In immortalized renal proximal tubule (RPT) cells from Wistar–Kyoto rats, CGP42112, an AT2 receptor agonist, decreased AT1 receptor mRNA and protein expression (P < 0.05), as assessed by reverse transcriptase-polymerase chain reaction and immunoblotting. The inhibitory effect of the AT2 receptor on AT1 receptor expression was blocked by the AT2 receptor antagonist, PD123319 (10−6 mol/l), the nitric oxide synthase inhibitor Nw-nitro-L-arginine methyl ester (10−4 mol/l), or the nitric oxide-dependent soluble guanylate cyclase inhibitor 1H-[1,2,4] oxadiazolo-[4,3-a] quinoxalin-1-one (10−5 mol/l), indicating that both nitric oxide and cyclic guanosine monophosphate (cGMP) were involved in the signaling pathway. Furthermore, CGP42112 decreased Sp1 serine phosphorylation and reduced the binding of Sp1 to AT1 receptor DNA. Stimulation with Ang II (10−11 mol/l per 30 min) enhanced Na+-K+-ATPase activity in RPT cells, which was prevented by pretreatment with CGP42112 (10−7 mol/l per 24 h) (P < 0.05). The above-mentioned results were confirmed in RPT cells from AT2 receptor knockout mice; AT1 receptor expression and Ang II-stimulated Na+-K+-ATPase activity were greater in these cells than in RPT cells from wild-type mice (P < 0.05). AT1/AT2 receptors co-localized and co-immunoprecipitated in RPT cells; short-term CGP42112 (10−7 mol/l per 30 min) treatment increased AT1/AT2 receptor co-immunoprecipitation (P < 0.05).
Conclusions: These results indicate that the renal AT2 receptor, via nitric oxide/cGMP/Sp1 pathway, regulates AT1 receptor expression and function, which may be important in the regulation of sodium excretion and blood pressure.