Autocrine Regulation of Inducible Nitric-oxide Synthase in Macrophages by Atrial Natriuretic Peptide

Abstract

Atrial natriuretic peptide (ANP), a cardiovascular hormone, has been shown to inhibit synthesis of nitric oxide in lipopolysaccharide (LPS)-activated mouse bone marrow-derived macrophages via activation of its guanylate cyclase-coupled receptor. The goal of the present study was to elucidate the potential sites of inducible nitric-oxide synthase (iNOS) regulation affected by ANP and revealed the following. 1) ANP and dibutyryl-cGMP did not inhibit catalytic iNOS activity measured by the conversion rate of L-[ H]arginine to L-[ H]citrulline in homogenates of LPS-treated cells. 2) Pretreatment of cells with ANP dose-dependently reduced the LPS-induced L-[3 H]citrulline production that has been shown to be due to reduced iNOS protein levels detected by Western blot. 3) ANP does not alter the ratio of catalytically active iNOS dimer versus inactive iNOS monomer considered to be a major post-translational regulatory mechanism for the enzyme. 4) Macrophages exposed to ANP display decreased LPS-induced iNOS mRNA levels. 5) Importantly, two basic mechanisms seem to be responsible for this observation, i.e. ANP specifically induced acceleration of iNOS mRNA decay and ANP reduced binding activity of NF-B, the transcription factor predominantly responsible for LPS-induced iNOS expression in murine macrophages. Moreover, 6) ANP acts via an autocrine mechanism since recently ANP was shown to be secreted by LPS-activated macrophages, and we demonstrated here that LPS-induced NO synthesis was increased after blocking the binding of endogenous ANP by a receptor antagonist. These observations suggest ANP as a new autocrine macrophage factor regulating NO synthesis both transcriptionally and post-transcriptionally. ANP may help to balance NO production of activated macrophages and thus may allow successful immune response without adverse effects on host cells.

Regulation of an inwardly rectifying K+channel by nitric oxide in cultured human proximal tubule cells

“…In contrast to nNOS and eNOS, the activity of iNOS is independent of intracellular Ca 2ϩ , and its mRNA expression is enhanced by lipopolysaccharide or cytokines (19,37,38). Interestingly, several investigators reported that ANP affected NO production probably by modulating expression of iNOS mRNA in human proximal tubule cells (5,24) or mouse macrophages (13,14). However, the present study showed that hANP activated the channel even when the NOS inhibitor or ODQ was present in the bath.…”

Atrial Natriuretic Peptide Polarizes Human Dendritic Cells Toward a Th2-Promoting Phenotype Through Its Receptor Guanylyl Cyclase-Coupled Receptor A

“…Recent evidence has suggested that ANP also influences the functions of immune cells: ANP stimulates migration of human neutrophils (7), inhibits proliferation of rat thymocytes (8), enhances human NK cell cytotoxicity (9), and inhibits NO and TNF-␣ production of murine macrophages (10,11). The last effect may be related to the previous observation that ANP could attenuate ischemia-reperfusion injury of the liver via GC-A (12).…”

“…Taken together, it is strongly suggested that the observation described in this study has certain physiological relevance. Considering that GC-A is expressed on macrophages (2) and DCs as we report but not on monocytes, ANP is likely to exert its immunoregulatory actions in tissue microenvironments, where the paracrine or autocrine mechanism of ANP may take place (2,10). Further studies are required to define the roles of ANP and GC-A in immune regulation in vivo and to better understand the cross-talk between the reno-cardiovascular system and the immune system.…”

Selective up-regulation of PDE1B2 upon monocyte-to-macrophage differentiation

“…This effect is well established in neutrophils and has been suggested to be the case for macrophages (54,55). cGMP in macrophages has been shown to modulate inflammatory processes, such as inducible NO synthase induction (56,57) and TNF-␣ release (58)(59)(60)(61). Also, it is known that intracellular calcium transients are important modulators of macrophage (62)(63)(64) function.…”