Renal cortical cyclooxygenase 2 expression is differentially regulated by angiotensin II AT(1) and AT(2) receptors

Abstract

Macula densa cyclooxygenase 2 (COX-2)-derived prostaglandins serve as important modulators of the renin-angiotensin system, and cross-talk exists between these two systems. Cortical COX-2 induction by angiotensin-converting enzyme (ACE) inhibitors or AT(1) receptor blockers (ARBs) suggests that angiotensin II may inhibit cortical COX-2 by stimulating the AT(1) receptor pathway. In the present studies we determined that chronic infusion of either hypertensive or nonhypertensive concentrations of angiotensin II attenuated cortical COX-2. Angiotensin II infusion reversed cortical COX-2 elevation induced by ACE inhibitors. However, we found that angiotensin II infusion further stimulated cortical COX-2 elevation induced by ARBs, suggesting a potential role for an AT(2) receptor-mediated pathway when the AT(1) receptor was inhibited. Both WT and AT(2) receptor knockout mice were treated for 7 days with either ACE inhibitors or ARBs. Cortical COX-2 increased to similar levels in response to ACE inhibition in both knockout and WT mice. In WT mice ARBs increased cortical COX-2 more than ACE inhibitors, and this stimulation was attenuated by the AT(2) receptor antagonist PD123319. In the knockout mice ARBs led to significantly less cortical COX-2 elevation, which was not attenuated by PD123319. PCR confirmed AT(1a) and AT(2) receptor expression in the cultured macula densa cell line MMDD1. Angiotensin II inhibited MMDD1 COX-2, and CGP42112A, an AT(2) receptor agonist, stimulated MMDD1 COX-2. In summary, these results demonstrate that macula densa COX-2 expression is oppositely regulated by AT(1) and AT(2) receptors and suggest that AT(2) receptor-mediated cortical COX-2 elevation may mediate physiologic effects that modulate AT(1)-mediated responses.

Fig. 1.

Effects of angiotensin II (AII) infusion on blood pressure and COX-2 expression in rat kidney cortex. (A) Blood pressure increased in rats treated with a high dose (300 μg/day) but not a low dose (100 μg/day) of AII. ∗, P < 0.001 vs. control and low-dose groups. (B) Both low and high doses of AII inhibited cortical COX-2 expression. ∗, P < 0.001 vs. control group. (C) Captopril (Cap)-mediated COX-2 elevation was completely reversed by angiotensin II infusion (100 μg/day) but not by the bradykinin B2 receptor antagonist HOE-140. ∗, P < 0.001 vs. control group; †, P < 0.001 vs. captopril group.

Fig. 2.

COX-2 expression in kidney cortex. (A–D) Compared with control rats (A), reduced COX-2-ir in macula densa/cTAL was observed in rats with angiotensin II infusion (B), and increased COX-2-ir was observed in rats with candesartan treatment (C), with a further increase in COX-2-ir in rats treated with candesartan plus angiotensin II (D). (E and F) Moderate to intense macula densa COX-2-ir was observed in WT mice at 21 days of age (E), but only weak macula densa COX-2-ir was observed in the age-matched AT₂ receptor KO mice (F). (G–I) Compared with undetectable macula densa COX-2-ir in adult WT or AT₂ receptor KO mice (G), more macula densa COX-2-ir was observed in adult WT mice after candesartan treatment (H) compared with AT₂ receptor KO mice (I). Arrows, macula densa; arrowheads, cTAL. (Image widths: A–D, 160 μm; E and F, 360 μm; G–I, 450 μm.)

Fig. 3.

Angiotensin II (AII) and macula densa/cTAL COX-2 expression in vivo. (A) Candesartan (CN)-mediated renal cortical COX-2 elevation was augmented by angiotensin II infusion (100 μg/day). ∗, P < 0.001 vs. control; †, P < 0.001 vs. candesartan. (B and C) In rats given either tap water (B) or 0.5% NaCl in the drinking water (C), bumetanide (Bumet)-mediated renal cortical COX-2 elevation was augmented by angiotensin II infusion (100 μg/day), although angiotensin II inhibited renal cortical COX-2 expression when given as a single agent. ∗, P < 0.001 vs. control; †, P < 0.001 vs. angiotensin II; ‡, P < 0.001 vs. bumetanide. (D) In rat kidney cortex the elevated COX-2 expression induced by candesartan and angiotensin II was attenuated by the AT₂ receptor selective antagonist PD123319.

Fig. 4.

COX-2 expression in kidney cortex of AT₂ receptor KO mice and cultured macula densa cells. (A) Renal cortical COX-2 expression was higher in WT mice than AT₂ receptor KO mice at 21 days of age. (B) Renal cortical COX-2-ir was undetectable in both normal adult WT and AT₂ receptor KO mice but increased to similar levels after captopril (Cap) treatment. ∗, P < 0.001 vs. control. (C) In WT mice candesartan (CN) led to significant increases in cortical COX-2 expression, which was attenuated by PD123319, whereas candesartan led to less significant increases in cortical COX-2 expression in AT₂ receptor KO mice, which was not attenuated by PD123319. ∗, P < 0.001 vs. control; †, P < 0.001 vs. candesartan. (D) RT-PCR showed that both AT_1a and AT₂ receptor mRNA was expressed in MMDD1 cells. (E) In cultured MMDD1 cells angiotensin II (AII) alone inhibited COX-2 expression but had no effect on COX-2 expression in the presence of the NKCC2 inhibitor bumetanide (Bumet). ∗, P < 0.001 vs. control; †, P < 0.001 vs. angiotensin II. (F) COX-2 expression in MMDD1 cells was stimulated by CGP-42112A dose-dependently.

Fig. 5.

Neither nNOS inhibitor 7-NI nor bradykinin B2 receptor antagonist HOE-140 affected renal cortical COX-2 expression in rats treated with candesartan (CN) and angiotensin II (AII).