ABSTRACT
Objective To elucidate the mechanism of angiotensin (Ang) Ⅱ in regulation of renin synthesis and secretion in primary cultured juxtaglomerular granular cells (JGCs). Methods Mice JGCs were isolated and cultured as described before. Real-time PCR was used to demonstrate the expression of angiotensin converting enzyme (CE) and angiotencin receptor (AT1, AT2) in JGCs. Ang Ⅱ was co-cultured with JGCs stimulated by PGE2 and isoproternol or not. Renin activity in supernatant was detected by radioimmunoassay and renin mRNA expression was examined by real-time PCR. Different concentrations of Ang Ⅱ were co-cultured with JGCs with different time (1 h, 4 h and 24 h), cAMP in cell lysate and supernatant was measured by Cayman Cyclic AMP EIA Kit. The cytoplasmic calcium was decreased by BAPTA-AM, and increased by thapsigargin and cyclopiazonic acid, which could be used to observe the cAMP concentration affected by calcium. Adenylyl cyclase type 5, 6 (AC5, AC6) mRNA expression of JGCs co-cultured with Ang Ⅱ was measured by real-time PCR. Results Real-time PCR confirmed the expression of ACE and AT mRNA in JGCs of WT mice. Angiotensin Ⅱ reduced renin secretion in primary cultures of JGCs [(370.6±36.9) vs (299.6±25.7) ng AngI'ml~(-1)·h~(-1), P=0.014]. Angiotensin Ⅱ dose-dependently down-regulated forskolin-stimulated cAMP production in JGCs. Thapsigargin and cyclopiazonic acid decreased cAMP level. BAPTA-AM increased cAMP production obviously [(11.09±0.48) vs (3.55±0.47) nmol/L, P<0.01]. Ang Ⅱ inhibited AC5 mRNA expression by 42.12%, but did not inhibit AC6 mRNA expression. Conclusions Angiotensin Ⅱ can directly inhibit renin synthesis and secrestion maybe through reducing AC-stimulated cAMP levels. Crosstalk between calcium and cAMP system may exist in precise regulation of renin in JGCs.
ABSTRACT
ObjectiveTo investigate the effect and mechanism of prostaglandin E2 (PGE2) in renin regulation at the juxtaglomerular apparatus (JGA). MethodsMacula densa cell line (MMDD1) was cultured on the special filter. In the medium on the apical lateral of the cells, low concentration of sodium chloride, chloride and different doses of angiotensin Ⅱ (Ang Ⅱ) were used to stimulate the PGE2 secretion. The PGE2 concentration was tested by ELISA. In the animal experiment, the response of plasma renin activity (PRA) to acute intraperitoneal administration of captopril (30 mg/kg) was determined, in conscious wild-type (WT) and cyclooxygenase COX-2-/- mice on C57BL/6 genetic backgrounds. PRA was measured in plasma obtained by tail vein puncture. Different concentrations of PGE2 were used to stimulate the renin secretion of primary cultured JGA cells from COX-2-/- mice and wild type mice. In specific Gsα gene delete mice (low renin producing mice), 24 h urine was collected to test the concentration of PGE2. The COX-2 mRNA and protein of the kidney cortex were observed by real-time PCR and immunohistochemicul staining. ResultsLow chloride could stimulate the PGE2 secretion both at the apical and basement of the macula densa cells. In COX-2-/- mice, the base PRA and were obviously lower than wild type mice. Captopril could stimulate the PRA of (COX)-2-/- mice increasing 32.8 times. But Ang Ⅱ had no effect on PGE2 secretion in macula densa cells. In primary cultured JGA cells, the decreasing renin seretion was partly recovered by PGE2 in cells from COX-2-/- mice. In low renin producing mice, the expression of COX-2 mRNA in the kidney cortex increased by (8.07±1.08) times (n=6, P=0.0022). The COX-2 protein of the kidney cortex and the urine PGE2 increased by several times. ConclusionsLow chloride is the primary stimulation messenger of PGE2 secretion in macula densa cells. The PRA in COX-2-/- mice can be stimulated by angiotensin converting enzyme inhibitor, but the Ang Ⅱ has no direct effect on macula densa cells. When renin production is abolished in JGA cells (Gsα delete mice), COX-2 mRNA and protein up-regulation is observed in kidney cortex and macula densa. PGE2 plays an important role in regulation of renin secretion and renin release in JGA by precise feedback mechanism.