Nitric oxide inhibits the expression of AT₁ receptors in neurons

Abstract

We have previously observed an increased of angiotensin II (ANG II) type 1 receptor (AT 1R) with enhanced AT 1R-mediated sympathetic outflow and concomitant downregulation of neuronal nitric oxide (NO) synthase (nNOS) with reduced NO-mediated inhibition from the paraventricular nucleus (PVN) in rats with heart failure. To test the hypothesis that NO exerts an inhibitory effect on AT 1R expression in the PVN, we used primary cultured hypothalamic cells of neonatal rats and neuronal cell line NG108-15 as in vitro models. In hypothalamic primary culture, NO donor sodium nitroprusside (SNP) induced dose-dependent decreases in mRNA and protein of AT 1R (10 Ϫ5 M SNP, AT1R protein was 10 Ϯ 2% of control level) while NOS inhibitor N G -monomethyl-L-arginine (L-NMMA) induced dose-dependent increases in mRNA and protein levels of AT 1R (10 Ϫ5 M L-NMMA, AT1R protein was 148 Ϯ 8% of control level). Similar effects of SNP and L-NMMA on AT1R expression were also observed in NG108-15 cell line (10 Ϫ6 M SNP, AT1R protein was 30 Ϯ 4% of control level while at the dose of 10 Ϫ6 M L-NMMA, AT1R protein was 171 Ϯ 15% of the control level). Specific inhibition of nNOS, using antisense, caused an increase in AT 1R expression while overexpression of nNOS, using adenoviral gene transfer (Ad.nNOS), caused an inhibition of AT 1R expression in NG108 cells. Antisense nNOS transfection augmented the increase while Ad.nNOS infection blunted the increase in intracellular calcium concentration in response to ANG II treatment in NG108 cells. In addition, downregulation of AT 1R mRNA as well as protein level in neuronal cell line in response to S-nitroso-Nacetyl pencillamine (SNAP) treatment was blocked by protein kinase G (PKG) inhibitor, while the peroxynitrite scavenger deforxamine had no effect. These results suggest that NO acts as an inhibitory regulator of AT 1R expression and the activation of PKG is the required step in the regulation of AT 1R gene expression via cGMP-dependent signaling pathway. sympathetic nerve activity; angiotensin II; cGMP; protein kinase G ALTERED EXPRESSION OF NEUROTRANSMITTERS plays an important role in the regulation of sympathetic activity in central nervous system (CNS). Among these modulators of neuronal activity within the CNS are nitric oxide (NO) and angiotensin II (ANG II). The interactions between NO and ANG II have been observed in peripheral circulation (3,31,36,37) as well as in the CNS (2,22,27). ANG II exerts its biological activity by binding to G proteincoupled receptor, ANG II type 1 (AT 1 R), which is expressed on CNS neurons, astrocytes, and microglia (5) and is known to play an important role in cardiovascular diseases like heart failure, hypertension, and diabetes (15, 23). Multiple intracellular signaling molecules, including the variety of kinases involved in phosphorylation cascades, phospholipases A 2 , C, and D, adenylate cyclase, and voltage-dependent Ca 2ϩ channels are linked to AT 1 R activation (12). AT 1 R overexpression and activation are related to the risk factors such as hyperte...

Angiotensin II-mediated posttranslational modification of nNOS in the PVN of rats with CHF: role for PIN

“…NG108 cells have neuronal properties, are immunoreactive to renin, and have angiotensin, angiotensinogen, angiotensin-converting enzyme as well as AT 1 and AT 2 receptor subtypes (8,20,39). These cells also have endogenous expression of nNOS (23,37,38) and NMDAR (3,18,25) and therefore serve as a suitable model for studying the interplay between receptors and gene expression at the cellular level in neurons (33,36).…”

Neural Control of Blood Pressure in Chronic Intermittent Hypoxia

“…Neuronal nitric oxide synthase (nNOS), which synthesizes the gaseous neurotransmitter nitric oxide, represses AT1 receptor expression in hypothalamic cell culture via a PKG-mediated mechanism [60]. A significant decrease in neurons expressing nNOS RNA and histological staining for nNOS was observed in the ventral parvocellular PVN of rats after 35 days CIH [61].…”

Nitric oxide synthase, ADMA, SDMA, and nitric oxide activity in the paraventricular nucleus throughout the etiology of renal wrap hypertension

“…Within the PVN, the inhibitory neurotransmitter NO can act as part of negative feedback system for the excitatory glutamatergic system (24). Regarding the downstream influence alterations in NO may have, a recent study (36) has found that within neuronal cell lines, NO serves as a negative regulator of angiotensin type 1 receptor expression. Reductions in NO may be mediating their effects on blood pressure via glutamatergic and angiotenergic-mediated mechanisms.…”