Selective activation of the B natriuretic peptide receptor by C-type natriuretic peptide (CNP)

Functional and structural characterization of a novel member of the natriuretic family of peptides from the venom ofPseudocerastes persicus

A novel peptide, PNP (Pseudocerastes persicus natriuretic peptide), was isolated from the venom of the Iranian viper P. persicus. Amino acid sequencing revealed that the 37-residue peptide belongs to the family of natriuretic peptides. The physiological effects of intra-venously PNP infused into anesthetized rats on urine flow, sodium excretion and blood pressure were comparable to those of atrial natriuretic peptide (ANP). In PC12 cells that were treated with either PNP, ANP, or C-type natriuretic peptide, PNP induced a similar cGMP response as ANP. Since PC12 cells only express the natriuretic peptide receptor (NPR)-A receptor we conclude that PNP binds to the NPR-A receptor. The solution conformation of PNP was characterized using (1)H nuclear magnetic resonance spectroscopy and indicates a high degree of conformational flexibility.

Structure, Regulation, and Function of Mammalian Membrane Guanylyl Cyclase Receptors, With a Focus on Guanylyl Cyclase-A

Besides soluble guanylyl cyclase (GC), the receptor for NO, there are at least seven plasma membrane enzymes that synthesize the second-messenger cGMP. All membrane GCs (GC-A through GC-G) share a basic topology, which consists of an extracellular ligand binding domain, a short transmembrane region, and an intracellular domain that contains the catalytic (GC) region. Although the presence of the extracellular domain suggests that all these enzymes function as receptors, specific ligands have been identified for only three of them (GC-A through GC-C). GC-A mediates the endocrine effects of atrial and B-type natriuretic peptides regulating arterial blood pressure and volume homeostasis and also local antihypertrophic actions in the heart. GC-B is a specific receptor for C-type natriuretic peptide, having more of a paracrine function in vascular regeneration and endochondral ossification. GC-C mediates the effects of guanylin and uroguanylin on intestinal electrolyte and water transport and on epithelial cell growth and differentiation. GC-E and GC-F are colocalized within the same photoreceptor cells of the retina and have an important role in phototransduction. Finally, the functions of GC-D (located in the olfactory neuroepithelium) and GC-G (expressed in highest amounts in lung, intestine, and skeletal muscle) are completely unknown. This review discusses the structure and functions of membrane GCs, with special emphasis on the physiological endocrine and cardiac functions of GC-A, the regulation of hormone-dependent GC-A activity, and the relevance of alterations of the atrial natriuretic peptide/GC-A system to cardiovascular diseases.

Regulation of the guanylyl cyclase-B receptor by alternative splicing

Guanylyl cyclase-B (GC-B) is a single transmembrane receptor that binds C-type natriuretic peptide (CNP). The ligand/receptor appears critical in the regulation of cell proliferation and differentiation where it acts as an adversary of mitogenic signaling pathways. We have isolated three guanylyl cyclase-B isoforms generated from a single gene by alternative splicing and termed them GC-B1, GC-B2, and GC-B3. GC-B1 is full-length and responds maximally to CNP, GC-B2 contains a 25-amino acid deletion in the protein kinase homology domain, and GC-B3 only retains a part of the extracellular ligand-binding domain. GC-B2 binds CNP, but the ligand fails to activate the cyclase, while GC-B3 fails to bind ligand. When GC-B2 or GC-B3 is expressed coincident with GC-B1, they act as dominant negative isoforms by virtue of blocking formation of active GC-B1 homodimers. Relative expression levels of GC-B1, GC-B2, and GC-B3 vary across tissues and as a function of in vitro culture; the relative amount of GC-B2 to GC-B1 is repressed in cultured smooth muscle cells relative to endogenous ratios in the medial layer cells of the aorta. Thus, GC-B isoform levels can be independently regulated. Given that the splice variants serve as dominant negative forms, these will serve as regulators of the full-length GC-B.

Four functionally distinct C-type natriuretic peptides found in fish reveal evolutionary history of the natriuretic peptide system

Natriuretic peptides (NPs) are major cardiovascular and osmoregulatory hormones in vertebrates. Although tetrapods generally have three subtypes, atrial NP (ANP), B-type NP (BNP), and C-type NP (CNP), some teleosts lack BNP, and sharks and hagfish have only one NP. Thus, NPs have diverged during fish evolution, possibly reflecting changes in osmoregulatory systems. In this study, we found, by cDNA cloning, four distinct CNPs (1 through 4) in the medaka (Oryzias latipes) and puffer fish (Takifugu rubripes), although to our knowledge no more than two CNPs have been isolated from a vertebrate species. Predicted mature CNP-1 was most similar, and CNP-4 was most dissimilar, to mammalian CNPs. However, synthetic CNP-4 most potently activated OlGC1, a medaka CNP-specific receptor (NPR-B) expressed in cultured cells, whereas CNP-1 and CNP-3 most activated OlGC7 and OlGC2, two medaka homologues of the ANP/BNP receptor (NPR-A), respectively. Linkage mapping in medaka followed by comparative genomic analyses among fishes and humans located four CNP genes in separate medaka chromosomes corresponding to human chromosomes 1, 2, 12, and 17. From conserved synteny, the following evolutionary history of NPs was evoked: (i) four CNP genes were generated by chromosomal duplications before the divergence of elasmobranchs; (ii) the CNP-3 gene generated ANP and BNP genes through tandem duplication before the divergence of tetrapods and teleosts; (iii) CNP-1 and -2 genes were retained in the teleost lineage but not in the tetrapod lineage; (iv) the CNP-3 gene disappeared from the tetrapod lineage after divergence of amphibians; and (v) the CNP-4 gene is retained in humans as CNP.

Atrial natriuretic peptide expression is increased in rat cerebral cortex following spreading depression: possible contribution to sd-induced neuroprotection

Cortical spreading depression (CSD) is characterised by slowly propagating waves of cellular depolarization and depression and involves transient changes in blood flow, ion balance and metabolism. In cerebral ischaemia, peri-infarct CSD-like depolarization potentiates infarct growth, whereas preconditioning with a CSD episode protects against subsequent ischaemic insult. Thus, many of the long-lasting molecular changes that occur in CSD-affected tissue are presumed to be part of a 'neuroprotective cascade.' 3',5'-Cyclic guanosine monophosphate (cGMP) has been shown to be a neuroprotective mediator and the nitric oxide system, which increases cGMP production by soluble guanylate cyclase, is up-regulated by CSD. Atrial and C-type natriuretic peptide (ANP/CNP) are present in cerebral cortex and their actions are mediated via particulate guanylate cyclase receptors and cGMP production. Therefore, in further efforts to characterise the role of cGMP-related systems in CSD and neuroprotection, this study investigated possible changes in cortical natriuretic peptide expression following acute, unilateral CSD in rats. Using in situ hybridisation, significant 20-80% increases in ANP mRNA were detected in layers II and VI of ipsilateral cortex at 6 h and 1-14 days after CSD. Ipsilateral cortical levels were again equivalent to control contralateral values after 28 days. Assessment of cortical concentrations of ANP immunoreactivity by radioimmunoassay revealed a significant 57% increase at 7 days after CSD. Despite using a sensitive signal-amplification protocol, authentic ANP-like immunostaining was readily detected in subcortical nerve fibres, but was not reliably detected in normal or CSD-affected neocortex, suggesting the presence of very low levels, and/or active or differential processing of the peptide. Cortical CNP mRNA levels are not altered by CSD, indicating the specificity of the observed effects.Overall, these novel findings demonstrate a prolonged increase in cortical ANP expression after an acute episode of CSD. The overlap between the described time course of CSD-induced protection against ischaemic insult and demonstrated increases in ANP levels, suggest that ANP (like nitric oxide) may contribute to CSD-induced neuroprotection, via effects on cGMP production and other signal-transduction pathways.

Gene expression, secretion, and autocrine action of C-type natriuretic peptide in cultured adult rat cardiac fibroblasts

C-type natriuretic peptide (CNP), the third member of the natriuretic peptide family, is known to be synthesized in the central nervous system and vascular endothelial cells, in contrast to atrial natriuretic peptide and brain natriuretic peptide. However, there have been no studies concerning CNP production in cultured cardiac cells. Here, we examined the production and the local effect of CNP in cultured ventricular cells. Under serum-free conditions, adult rat cardiac fibroblasts secreted immunoreactive CNP time dependently. TGF-beta1, basic fibroblast growth factor, and endothelin-1 significantly stimulated CNP secretion. Northern blot analysis detected significant expressions of CNP and its specific receptor (guanylyl cyclase-B) mRNA in cardiac fibroblasts. CNP stimulated intracellular cGMP production in fibroblasts more intensely than atrial and brain natriuretic peptides. CNP inhibited both DNA and collagen syntheses of cardiac fibroblasts, and these inhibitory effects by CNP were stronger than by atrial and brain natriuretic peptides. The inhibition by CNP of DNA and collagen syntheses was reproduced by a cGMP analog, 8-bromo cGMP. The present findings demonstrate that CNP is synthesized in and secreted from cardiac fibroblasts and suggest that CNP has a suppressive effect on fibroblast proliferation and extracellular matrix production, probably via the guanylyl cyclase-B-mediated cGMP-dependent process. CNP produced by cardiac fibroblasts may play a role as an autocrine regulator against excessive cardiac fibrosis.

The neurobiology and control of anxious states

Fear is an adaptive component of the acute "stress" response to potentially-dangerous (external and internal) stimuli which threaten to perturb homeostasis. However, when disproportional in intensity, chronic and/or irreversible, or not associated with any genuine risk, it may be symptomatic of a debilitating anxious state: for example, social phobia, panic attacks or generalized anxiety disorder. In view of the importance of guaranteeing an appropriate emotional response to aversive events, it is not surprising that a diversity of mechanisms are involved in the induction and inhibition of anxious states. Apart from conventional neurotransmitters, such as monoamines, gamma-amino-butyric acid (GABA) and glutamate, many other modulators have been implicated, including: adenosine, cannabinoids, numerous neuropeptides, hormones, neurotrophins, cytokines and several cellular mediators. Accordingly, though benzodiazepines (which reinforce transmission at GABA(A) receptors), serotonin (5-HT)(1A) receptor agonists and 5-HT reuptake inhibitors are currently the principle drugs employed in the management of anxiety disorders, there is considerable scope for the development of alternative therapies. In addition to cellular, anatomical and neurochemical strategies, behavioral models are indispensable for the characterization of anxious states and their modulation. Amongst diverse paradigms, conflict procedures--in which subjects experience opposing impulses of desire and fear--are of especial conceptual and therapeutic pertinence. For example, in the Vogel Conflict Test (VCT), the ability of drugs to release punishment-suppressed drinking behavior is evaluated. In reviewing the neurobiology of anxious states, the present article focuses in particular upon: the multifarious and complex roles of individual modulators, often as a function of the specific receptor type and neuronal substrate involved in their actions; novel targets for the management of anxiety disorders; the influence of neurotransmitters and other agents upon performance in the VCT; data acquired from complementary pharmacological and genetic strategies and, finally, several open questions likely to orientate future experimental- and clinical-research. In view of the recent proliferation of mechanisms implicated in the pathogenesis, modulation and, potentially, treatment of anxiety disorders, this is an opportune moment to survey their functional and pathophysiological significance, and to assess their influence upon performance in the VCT and other models of potential anxiolytic properties.

Atrial natriuretic peptides elevate cyclic GMP levels in primary cultures of rat ependymal cells

The aim of this study was to examine the effect of atrial natriuretic peptides on primary cultures of ependymal cells, as measured by changes in intracellular levels of cyclic GMP. Incubation of ependymal cells with rat atrial natriuretic peptide-(1-28) (rANP) elicited a 30-fold increase in ependymal cGMP content within 1 min and more than a 100-fold increase within 10 min to a plateau value of approximately 30 pmol/mg protein. The C-type natriuretic peptide (CNP) elicited a similar increase in cGMP levels; however the maximal effect was observed within 1 min and the levels subsequently dropped by 90% to a low plateau within 10 min. A comparison of the concentration-response curves for rANP, human ANP-(1-28) (hANP) and CNP showed that rANP, hANP and CNP had similar effects, with regards to elevation of cGMP levels at high concentrations, but with differing EC50 values. These results demonstrate the presence of a heterogenous population of functional ANP receptors i n cultured ependymalcells suggesting that ANP may regulate specific ependymal cell activity.

C-type natriuretic peptide of rainbow trout (Oncorhynchus mykiss): primary structure and vasorelaxant activities

Natriuretic peptides (NPs) play important roles in osmoregulatory and cardiovascular systems of vertebrates. For functional studies of NPs, rainbow trout (Oncorhynchus mykiss), a euryhaline fish, is an interesting model. The information on homologous NPs of salmonid fish is, however, still incomplete with respect to C-type NP (CNP). In this study, we isolated cDNAs encoding the precursor of CNP from the brain of trout. Predicted mature CNP (CNP-22) sequence was identical to that of killifish Fundulus heteroclitus, and only one amino acid was different from that of the eel Anguilla japonica, demonstrating a greater conservation among different teleost species than is found with atrial NP (ANP) and ventricular NP (VNP). While the preprosegment of trout CNP retained 57% similarity to the eel sequence, similarities were low to those of sharks and tetrapods. The major site of expression identified by RT-PCR was the brain with minor expression in the atrium. The putative mature CNP-22 was synthesized and its biological activity was compared with other trout NPs (ANP and VNP) using trout ventral aorta, efferent branchial and celiacomesenteric arteries and anterior cardinal vein in vitro. Synthetic trout CNP-22 relaxed all pre-contracted vessels with potencies comparable to trout ANP and VNP.

The therapeutic effect of natriuretic peptides in heart failure; differential regulation of endothelial and inducible nitric oxide synthases

The abnormal regulation of nitric oxide synthase activity represents an underlying feature of heart failure. Increased peripheral vascular resistance, and decreased renal function may be in part related to impaired endothelium-dependent nitric oxide (NO) synthesis. Paradoxically, the chronic production of NO by inducible nitric oxide synthase (iNOS) in heart failure exerts deleterious effects on ventricular contractility, and circulatory function. Consequently, pharmacologically improving endothelium-dependent NO synthesis and the concomitant inhibition of iNOS activity would be therapeutically advantageous. Interestingly, natriuretic peptides have been shown to differentially regulate endothelial NOS (eNOS) and iNOS activity. Moreover, in both patients and animal models of heart failure, pharmacologically increasing plasma natriuretic peptide levels ameliorated vascular tone, renal function, and ventricular contractility. Based on these observations, the following review will explore whether the therapeutic benefit of the natriuretic peptide system in heart failure may occur in part via the amelioration of endothelium-dependent NO synthesis, and the concomitant inhibition of cytokine-mediated iNOS expression.

Lysophosphatidic acid inhibits C-type natriuretic peptide activation of guanylyl cyclase-B

C-type natriuretic peptide (CNP), found in endothelial cells, chondrocytes, and neurons, binds its cognate transmembrane receptor, natriuretic peptide receptor-B (NPR-B/GC-B), and stimulates the synthesis of the intracellular signaling molecule, cGMP. The known physiologic consequences of this binding event are vasorelaxation, inhibition of cell proliferation, and the stimulation of long bone growth. Here we report that 10% fetal bovine serum markedly reduced CNP-dependent cGMP elevations in NIH3T3 fibroblast. The purified serum components platelet-derived growth factor and lysophosphatidic acid (LPA) mimicked the effect of serum on CNP-dependent cGMP elevations, but the latter factor resulted in the most dramatic reductions. The LPA-dependent inhibition was rapid and dose dependent, having t(1/2) and IC(50) values of approximately 5 min and 3.0 micro M LPA, respectively. The decreased cGMP concentrations resulted from reduced CNP-dependent NPR-B guanylyl cyclase activity that did not require losses in receptor protein or activation of protein kinase C, indicating a previously undescribed desensitization pathway. These data suggest that NPR-B is repressed by LPA and that one mechanism by which LPA exerts its effects is through the heterologous desensitization of the CNP/NPR-B/cGMP pathway. We hypothesize that cross-talk between the LPA and CNP signaling pathway maximizes the response of fibroblasts in the wound-healing process.

Natriuretic peptides suppress protein kinase C activity to reduce evoked dopamine efflux from pheochromocytoma (PC12) cells

The observation that natriuretic peptides and protein kinase C activators influence evoked neurotransmitter efflux by diametrically opposed mechanisms prompted an investigation of the influence of natriuretic peptides on protein kinase C activity and the potential involvement of this pathway in neuromodulatory responses to natriuretic peptides. C-Type natriuretic peptide attenuated both evoked dopamine efflux and protein kinase C activity in a concentration-dependent manner consistent with a 10% diminution in protein kinase C activity producing a 4.6-6.2% reduction in evoked dopamine efflux. The ability of C-type natriuretic peptide to suppress evoked dopamine efflux was abolished by treatment with the protein kinase C inhibitors chelerythrine (10 micro M) and staurosporine (10 nM). Both chelerythrine and staurosporine attenuated protein kinase C activity at the concentrations used. The natriuretic peptide C receptor (NPR-C) appeared to mediate the attenuation of protein kinase C activity, because the effect was mimicked by a pentadecapeptide fragment of the NPR-C, and the effect of C-type natriuretic peptide was attenuated by an antibody generated against the same region of the receptor. These data suggest that C-type natriuretic peptide attenuates neurotransmitter efflux by a mechanism involving suppression of neuronal protein kinase C activity via an interaction with the NPR-C.

Vasopressin-dependent inhibition of the C-type natriuretic peptide receptor, NPR-B/GC-B, requires elevated intracellular calcium concentrations

Natriuretic peptides bind their cognate cell surface guanylyl cyclase receptors and elevate intracellular cGMP concentrations. In vascular smooth muscle cells, this results in the activation of the type I cGMP-dependent protein kinase and vasorelaxation. In contrast, pressor hormones like arginine-vasopressin, angiotensin II, and endothelin bind serpentine receptors that interact with G(q) and activate phospholipase Cbeta. The products of this enzyme, diacylglycerol and inositol trisphosphate, activate the conventional and novel forms of protein kinase C (PKC) and elevate intracellular calcium concentrations, respectively. The latter response results in vasoconstriction, which opposes the actions of natriuretic peptides. Previous reports have shown that pressor hormones inhibit natriuretic peptide receptors NPR-A or NPR-B in a variety of different cell types. Although the mechanism for this inhibition remains unknown, it has been universally accepted that PKC is an obligatory component of this pathway primarily because pharmacologic activators of PKC mimic the inhibitory effects of these hormones. Here, we show that in A10 vascular smooth muscle cells, neither chronic PKC down-regulation nor specific PKC inhibitors block the AVP-dependent desensitization of NPR-B even though both processes block PKC-dependent desensitization. In contrast, the cell-permeable calcium chelator, BAPTA-AM (1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, tetraacetoxymethyl ester), abrogates the AVP-dependent desensitization of NPR-B, and ionomycin, a calcium ionophore, mimics the AVP effect. These data show that the inositol trisphosphate/calcium arm of the phospholipase C pathway mediates the desensitization of a natriuretic peptide receptor in A10 cells. In addition, we report that CNP attenuates AVP-dependent elevations in intracellular calcium concentrations. Together, these data reveal a dominant role for intracellular calcium in the reciprocal regulation of these two important vasoactive signaling systems.

Characterization of VIP and PACAP receptors in cultured rat penis corpus cavernosum smooth muscle cells and their interaction with guanylate cyclase-B receptors

Penile corpus cavernosum smooth muscle relaxation can be induced by both cyclic AMP and cyclic GMP-elevating agents, but possible interactions between these two signalling pathways are still poorly understood. Using in vitro cultured rat penile corpus cavernosum smooth muscle (CCSM) cells, we have characterized the local expression and functional activities of receptors for the cAMP-elevating peptides, PACAP and VIP, and for the cGMP-elevating peptides, CNP and ANP. Stimulation of the cells with various concentrations of PACAP(-27/-38) or VIP resulted in rapid and dose-dependent increases in cyclic AMP levels. RT-PCR analyses revealed gene expression of PAC(1) and VPAC(2) but not of VPAC(1) receptors in the cells. The natriuretic peptide, CNP, and the nitric oxide donor, sodium nitroprusside, were capable of enhancing cyclic GMP formation, indicating the presence of membrane-associated in addition to soluble guanylate cyclase (sGC) activities in these cells. Findings that cyclic GMP formation was preferentially activated by CNP but not by the related peptide, ANP, were consistent with RT-PCR analyses, demonstrating gene expression of the CNP receptor, GC-B, but not of the ANP receptor, GC-A, in these cells. Prior exposure of the cells to 10(-8) M PACAP resulted in a marked down-regulation of GC-B activity, whereas sGC was not affected. These findings provide functional and molecular evidence for the presence of three receptors, PAC(1), VPAC(2) and GC-B, involved in cyclic nucleotide signalling in penile CCSM cells. The observed cross-talk of the PACAP/VIP receptors with GC-B but not with sGC may have implications for the therapy of erectile dysfunction.

A single-nucleotide polymorphism in C-type natriuretic peptide gene may be associated with hypertension

We conducted an association study between genetic variants of C-type natriuretic peptide gene (CNP) and hypertension in a Japanese population. We found four genetic variants, two in the promoter region, one missense mutation, and one in the 3'-untranslated region (3'-UTR), and genotyped all four variants in 2,006 subjects recruited from the Suita study. One of the variants, G2628A in 3'-UTR, was found to be associated with blood pressure. Multiple logistic analyses indicated that the genotype of the G2628A polymorphism (GG=1, GA+AA=2) (p=0.0034), sex (p=0.0288), alcohol consumption (p=0.0002), age (p<0.0001), and body mass index (p<0.0001) were predictors of hypertension. The odds ratio of the GA+AA genotype over the GG genotype for hypertension was 1.40 (p=0.0034, 95% confidence interval (CI) 1.12-1.75). Multiple logistic analyses in a younger subpopulation aged below 65 years indicated that the odds ratio of the GA+AA genotype over the GG genotype for hypertension was 1.58 (p=0.0024, 95%CI 1.18-2.12). Thus, the CNP G2628A polymorphism made an even greater contribution to hypertension in the younger subpopulation.

Brain natriuretic peptide: role in cardiovascular and volume homeostasis

The identification of natriuretic peptides as key regulators of natriuresis and vasodilatation, and the appreciation that their secretion is under the control of cardiac hemodynamic and neurohumoral factors, has caused wide interest. The natriuretic peptides are structurally similar, but genetically distinct peptides that have diverse actions on cardiovascular, renal, and endocrine homeostasis. Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are of myocardial cell origin, while cardiac natriuretic peptide (CNP) is of endothelial origin. ANP and BNP bind to the natriuretic peptide receptor (NPR-A) which, via 3' 5'-cyclic guanosine monophosphate (cGMP), mediates natriuresis, vasodialation, renin inhibition, and antimitogenic properties. CNP lacks natriuretic action but possesses vasodilating and growth inhibiting effects via the guanyl cyclase linked natriuretic peptide-B (NPR-B) receptor. All three peptides are cleared by natriuretic peptide-C receptor (NPR-C) and degraded by neutral endopeptidase, both of which are widely expressed in kidney, lung, and vascular wall. Recently, a fourth member of the natriuretic peptide, dendroaspsis natriuretic peptide (DNP) has been reported to be present in human plasma and atrial myocardium.

Postnatal changes in inhibitory effect of C-type natriuretic peptide on secretion of ANP

To define developmental changes in atrial natriuretic peptide (ANP) secretion and in the cross talk between C-type natriuretic peptide (CNP) and ANP, we performed experiments in isolated perfused nonbeating cardiac atria isolated from rabbits between 1 and 8 wk of age. Changes in atrial pressure resulted in increases in atrial volume that rose with age and reached the peak value at 4 wk. A rise in volume change increased ANP secretion with concomitant translocation of extracellular fluid (ECF) into the atrial lumen, which increased with age and reached the peak value at 4 wk. The positive relationship between stretch-induced ANP secretion and ECF translocation shifted upward and leftward with age. CNP suppressed stretch-induced ANP secretion in the 8-wk-old group but not in the 2- and 4-wk-old groups without differences in ECF translocation and atrial volume. Therefore, the ANP secretion in terms of ECF translocation was markedly suppressed by CNP in the 8-wk-old group but not in the 2- and 4-wk-old groups. The production of cGMP by CNP in atrial tissue membranes was markedly attenuated in young rabbits. However, 8-bromo-cGMP suppressed stretch-induced ANP secretion in 2- and 8-wk-old groups. Natriuretic peptide receptor-B mRNA was similar in both groups. Therefore, we conclude that the inhibitory effect of CNP on atrial ANP secretion is developmentally regulated, being absent during normal cardiac development in young animals and intact in adult animals.

The nitric oxide releasing agent sodium nitroprusside modulates cocaine-induced immediate early gene expression in rat brain

The nitric oxide (NO)/cGMP pathway triggers key events in synaptic phenomena involved in learning and memory. Using in situ hybridization, the present report demonstrates that NO released by sodium nitroprusside regulates egr-1, c-fos, and junB immediate early gene expression in rat forebrain. These genes, which are rapidly and transiently induced in response to diverse extracellular stimulation, coordinate alterations in gene expression underlying neuronal plasticity. Intracerebroventricular injection of sodium nitroprusside induced immediate early gene expression, which was highest in the nucleus accumbens. On the other hand, sodium nitroprusside abolished the cocaine-induced early gene expression in the dopaminergic projection fields nucleus accumbens, caudate-putamen, and frontal cortex. Further studies are warranted to explore the potential of the NO/cGMP/cGMP-dependent protein kinase pathway to modify cocaine-related behavioral effects.

Conformations of platypus venom C-type natriuretic peptide in aqueous solution and sodium dodecyl sulfate micelles

Nuclear magnetic resonance spectroscopy was used to investigate the conformations of the platypus venom C-type natriuretic peptide A (OvCNPa) in aqueous solutions and in solutions containing sodium dodecyl sulfate (SDS) micelles. The chemically synthesized OvCNPa showed a substantial decrease in flexibility in aqueous solution at 10 degrees C, allowing the observation of medium- and long-range nuclear Overhauser enhancement (NOE) connectivities. Three-dimensional structures calculated using these data showed flexible and reasonably well-defined regions, the locations of which were similar in the two solvents. In aqueous solution, the linear part that spans residues 3-14 was basically an extended conformation while the cyclic portion, defined by residues 23-39, contained a series of beta-turns. The overall shape of the cyclic portion was similar to that observed for an atrial natriuretic peptide (ANP) variant in aqueous solution. OvCNPa adopted a different conformation in SDS micelles wherein the N-terminal region, defined by residues 2-10, was more compact, characterised by turns and a helix, while the cyclic region had turns and an overall shape that was fundamentally different from those structures observed in aqueous solution. The hydrophobic cluster, situated at the centre of the ring of the structure in aqueous solution, was absent in the structure in the presence of SDS micelles. Thus, OvCNPa interacts with SDS micelles and can possibly form ion-channels in cell membranes.

A novel missense mutation of exon 3 in the type A human natriuretic peptide receptor gene: possible association with essential hypertension

The natriuretic peptide (NP) family is involved in regulation of blood pressure and fluid volume. We recently characterized the exon/intron organization of the human type A NP receptor (hNPRA) gene. The aim of this study was to isolate the genetic markers according to the organization of this gene, and to study the association between this gene and essential hypertension. Using polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) analysis, we identified a novel missense mutation, M3411, consisting of a methionine (ATG) to isoleucine (ATC) substitution at nucleotide 1023 in exon 3. Computer-aided three-dimensional structural analysis suggested that M341 exists in the loop between two alpha-helices, and that the mutation may influence receptor activities by altering the conformation of the alpha-helices. We performed an association study of the mutation in 210 essential hypertension (EH) patients and 210 normotensive controls. The overall distribution of alleles was not significantly different between the control and EH groups. However, the C/C homozygous genotype was found only in the EH group. The ratio of plasma brain natriuretic peptide (BNP)/mean blood pressure of the C/C genotype was significantly higher than that of the G/G genotype or the G/C genotype. We conclude that the significance of homozygous M3411 mutation in exon 3 is worth investigating for its possible association with EH.

Discovery of a natriuretic peptide family and their clinical application

The identification of atrial natriuretic peptide (ANP) induced an explosive series of studies on the new peptide involved in control of the circulation, both in the basic and clinical fields. During the first decade of ANP research surprising progress has been made, revealing that the heart is an endocrine organ regulating the circulation system. ANP has been developed as a diagnostic tool and as a therapeutic drug for cardiac failure. In the second decade, brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) were identified, unveiling new profiles of this peptide family. Although BNP is also a circulating hormone that shares a common receptor with ANP, it is different from ANP in its' synthesis and secretion. Plasma concentration of BNP reflects the severity of heart failure in patients in a dramatic fashion, much moreso than ANP. Thus, BNP has been developed as a powerful diagnostic tool for cardiovascular diseases. The third congener, CNP, having a receptor of its own, was initially thought to function only in the brain. CNP was subsequently found to be produced from vascular endothelial cells and macrophages, indicating that CNP is a local regulator and also an antiproliferative factor in the vascular cell system, rather than a circulating hormone. Trials for the clinical application of CNP have also been discussed.

Identification of the atrial natriuretic factor-RICreceptor subtype (B-clone) in cultured rat aortic smooth muscle cells

The present report demonstrates the presence in cultured rat aortic smooth muscle cells of a natriuretic factor receptor subtype with a specificity typical of the ANF-R1C (B-clone) receptor subtype. To prove the existence of this receptor subtype in this cell line we show that pCNP-(82-103) is the most potent activator of the intrinsic guanylate cyclase activity, and that [125I]pCNP-(82-103) binds to a specific receptor subtype which is insensitive to the ANF-R2 specific ligand, C-ANF. The investigation of its binding characteristics show the rank potency order of the natriuretic factors in competing for pCNP binding to be pCNP greater than pBNP greater than rANF. Furthermore it was possible to covalently photolabel this receptor subtype with underivatized]125I]pCNP and show that it is composed of a single subunit of 130 kDa with very high specificity for pCNP.

Expression and control of C-type natriuretic peptide in rat vascular smooth muscle cells

C-type natriuretic peptide (CNP) is a member of the natriuretic peptide family mainly distributed in the central nervous system. CNP is also produced and secreted by the endothelium and inhibits vascular smooth muscle cell proliferation. We have reported that endothelial damage stimulates only transiently vascular smooth muscle cell proliferation in arteries due to the development of an autocrine neointimal system for CNP that modulates neointimal growth. The present study demonstrates the production and secretion of CNP in rat vascular smooth muscle cells in the absence of endothelium. In addition, these cells express atrial natriuretic peptide (ANP) and the natriuretic peptide receptors A, B, and C. The production and secretion of CNP in vascular smooth muscle cells is stimulated by transforming growth factor-beta, whereas basic fibroblast growth factor plays an inhibitory role. These data show that ANP and mainly CNP are coexpressed with the natriuretic peptide receptors in rat vascular smooth muscle cells. This provides evidence for a vascular natriuretic peptide autocrine system of physiological relevance in these cells.

Dendroaspis natriuretic peptide-like immunoreactivity and its regulation in rat aortic vascular smooth muscle

Dendroaspis natriuretic peptide (DNP) is a recently isolated 38 amino acid peptide that shares structural and functional properties with the other members of the natriuretic peptide family. The present study demonstrates the presence of DNP-like immunoreactivity in sections of rat aorta, carotid artery and renal vasculature and tubules. DNP-like immunoreactivity was detected in culture aortic vascular smooth muscle cells and medium and is regulated by endothelin-1, angiotensin II and sodium nitroprusside but not by transforming growth factor-beta. Our observations indicate that DNP elicits a marked inhibitory effect on DNA synthesis in culture rat aortic vascular smooth muscle cells.

Differential responses of newborn pulmonary arteries and veins to atrial and C-type natriuretic peptides

Atrial natriuretic peptide (ANP) and C-type natriuretic peptide (CNP) are important dilators of the pulmonary circulation during the perinatal period. We compared the responses of pulmonary arteries (PA) and veins (PV) of newborn lambs to these peptides. ANP caused a greater relaxation of PA than of PV, and CNP caused a greater relaxation of PV than of PA. RIA showed that ANP induced a greater increase in cGMP content of PA than CNP. In PV, ANP and CNP caused a similar moderate increase in cGMP content. Receptor binding study showed more specific binding sites for ANP than for CNP in PA and more for CNP than for ANP in PV. Relative quantitative RT-PCR for natriuretic peptide receptor A (NPR-A) and B (NPR-B) mRNAs show that, in PA, NPR-A mRNA is more prevalent than NPR-B mRNA, whereas, in PV, NPR-B mRNA is more prevalent than NPR-A mRNA. In conclusion, in the pulmonary circulation, arteries are the major site of action for ANP, and veins are the major site for CNP. Furthermore, the differences in receptor abundance and the involvement of a cGMP-independent mechanism may contribute to the heterogeneous effects of the natriuretic peptides in PA and PV of newborn lambs.

C-type natriuretic peptide system in rabbit colon

C-type natriuretic peptide (CNP) is mainly distributed in the brain and vascular endothelium and is considered to act as a local regulator in many tissues. The present study was aimed to determine the presence of CNP system and its biological function in rabbit colon. The serial dilution curves of tissue extracts were parallel to the standard curve of CNP-22. With gel permeation chromatography and reverse-phase HPLC, the major immunoreactive peak of CNP was observed at the same elution time corresponding to the synthetic CNP-53. The concentration of CNP in the mucosal layer of colon was 212.49 +/- 30.44 pg/g tissue wet weight (n = 7), which was significantly higher than that in the muscular layer. The presence of CNP mRNA was also detected by RT-PCR and Southern blot analysis. Production of cGMP by the activation of particulate guanylyl cyclase stimulated by BNP and CNP was higher in membranes obtained from the muscular layer than from mucosal layer. More cGMP was produced by CNP than by ANP. Both natriuretic peptide receptor-A and -B mRNAs were detected by RT-PCR and specific binding sites to 125I-[Tyr(0)]-CNP-22 were mainly localized to the muscular layer. Synthetic CNP inhibited basal tension, frequency and amplitude of basal motility of taenia coli of the right colon. This study showing the presence of CNP system and its biological function in colon suggests that endogenous CNP synthesized in the mucosal layer may have a paracrine function as a local regulator of colonic motility.

Proliferative actions of natriuretic peptides on neuroblastoma cells. Involvement of guanylyl cyclase and non-guanylyl cyclase pathways

To identify neural tumor cell lines that could be used as models to study growth-related natriuretic peptide actions, we determined the effects of these peptides on the proliferation of human and rodent neuroblastoma cell lines. Subnanomolar concentrations of atrial natriuretic peptide (ANP) and type C natriuretic peptide (CNP) stimulated proliferation in all four cell lines. These actions were associated with cGMP elevation and were blocked by a protein kinase G inhibitor. These data imply the involvement of guanylyl cyclase (GC)-coupled natriuretic receptors. However, higher concentrations of ANP and CNP, and low concentrations of des-[Gln(18),Ser(19),Gly(20),Leu(21),Gly(22)]-ANP(4-23)-NH(2) (desANP(4-23)) (analog for NPR-C receptor) exerted antiproliferative actions in three of the cell lines. These effects were insensitive to a protein kinase G inhibitor and to HS-142-1, suggesting that growth-inhibitory actions involved a non-GC receptor. They did not appear to involve cAMP, protein kinase A, protein kinase C, or calcium mobilization but were abolished when constitutive mitogen-activated protein kinase activity was inhibited. Radioligand binding experiments revealed the presence of a uniform class of binding sites in NG108 cells and multiple binding sites in Neuro2a cells. Northern and reverse transcriptase-polymerase chain reaction analyses revealed differential gene expression for NPR-A/B/C in NG108 and Neuro2a cells. The results indicate that natriuretic peptides stimulate neuroblastoma cell proliferation through type NPR-A/B (GC) receptors. Higher concentrations of ANP and CNP exerted a mitogen-activated protein kinase-dependent antiproliferative action mediated by a non-GC receptor that interacts with desANP(4-23) with relatively high affinity.

Atrial natriuretic peptide-like immunoreactivity in neurons and astrocytes of human cerebellum and inferior olivary complex

Atrial natriuretic peptide (ANP) has previously been localized in areas of mammalian brain associated with olfaction, cardiovascular function, and fluid/electrolyte homeostasis. Despite the presence of several types of natriuretic peptide receptors in mammalian cerebellum, neither intrinsic nor extrinsic sources of the natriuretic peptides have been described. In this report we describe the immunohistochemical localization of both intrinsic and extrinsic sources for ANP in human cerebellum. ANP-like immunoreactivity (ANP-LIR) was observed in climbing fibers in the cerebellar molecular layer that probably originated from isolated immunopositive neurons of the inferior olivary complex. Intrinsic sources of ANP-LIR included small subpopulations of protoplasmic and fibrous astrocytes and Bergmann glia, as well as Golgi and Lugaro neurons of the granule cell layer. These results suggest that, in addition to its presumptive roles in local vasoregulation, ANP may serve as a modulator of the activity of Purkinje neurons.

Attenuation of inhibitory effect of CNP on the secretion of ANP from hypertrophied atria

It has been shown that atrial natriuretic peptide (ANP) influences proliferation of cardiac cells. To define the possible role of C-type natriuretic peptide (CNP) in cardiac hypertrophy, the influence of CNP on the secretion of ANP was studied with the use of perfused nonbeating atria from monocrotaline-treated rats. Increases in atrial volume caused proportional increases in ANP secretion that were markedly suppressed by CNP (10(-6) M) in nonhypertrophied left atria and control right atria but not in hypertrophied right atria. However, increases in atrial volume and mechanically stimulated extracellular fluid (ECF) translocation by CNP were similar to those in the control group. Therefore, the secretion of ANP in terms of ECF translocation was decreased by CNP in nonhypertrophied left and control right atria but not in hypertrophied atria. However, the inhibitory effect of 8-bromo-cGMP on the secretion of ANP was observed in both atria. The cGMP productions from perfused hypertrophied atria and their membranes exposed to CNP were significantly lower than those from nonhypertrophied atria. No significant difference in natriuretic peptide receptor-B transcript was found. Therefore, attenuation of the inhibitory effect of CNP on the ANP secretion in hypertrophied atria may be due to lack of cGMP production. The results showing the relief of CNP-induced negative inhibition of ANP secretion by atrial hypertrophy suggest that CNP may be a contributing factor to delay the development of cardiac hypertrophy.

C-type natriuretic peptide (CNP) regulates cocaine-induced dopamine increase and immediate early gene expression in rat brain

The neuropeptide C-type natriuretic peptide (CNP) is the primary biologically active natriuretic peptide in brain. Using in situ hybridization, the present report demonstrates that CNP regulates egr-1, c-fos and junB immediate early gene expression in rat brain. In the frontal cortex, CNP induced immediate early gene expression whereas it inhibited dose-dependently the cocaine-induced early gene expression in the dopaminergic projection fields nucleus accumbens and caudate-putamen. CNP may produce its effect directly on dopaminergic neurons because we found that its receptor, guanylyl cyclase GC-B, was expressed in the mesencephalon where dopaminergic neurons originate, as well as in their projection fields. The inhibition by CNP of the early gene expression elicited by cocaine in the caudate-putamen is correlated with a CNP-evoked decrease in cocaine-induced rise in extracellular dopamine, measured by in vivo microdialysis experiments. The significance of the inhibition of cocaine-induced dopamine release and early gene induction by the endogenous peptide CNP is demonstrated by data indicating that CNP reduced the cocaine-induced spontaneous locomotor activation. By inhibiting dopaminergic neuronal activity, CNP represents a potential negative regulator of related behavioural effects of cocaine.

Gestational regulation of the gene expression of C-type natriuretic peptide in mouse reproductive and embryonic tissue

C-Type natriuretic peptide (CNP) is a vasoactive hormone and the endothelial component of the natriuretic peptide system. We examined the expression of CNP in mouse reproductive organs and embryos at different stages of gestation. Pregnant mice were killed and embryos were dissected on gestational days 9.5, 12.5, 15.5, 18.5 postconceptionem (pc) and at term. Nonpregnant mice were used as controls. Total RNA was isolated from placenta, ovaries, myometrium and from head and trunk of embryos and neonates. CNP-mRNA was quantified by ribonuclease-protection assay (RPA). Uterine CNP-mRNA concentrations increase during pregnancy up to the sevenfold concentration, whereas in the ovaries these levels decrease to 10% compared to nonpregnant controls. In the placenta, a peak of CNP expression has been observed around day 15.5 pc, whereby placenta showed the strongest CNP signals. CNP-mRNA concentrations in embryos are gestational age-dependent with a high level at day 9.5 pc in head and trunk. These results indicate that CNP has a regulatory function in pregnancy and embryonic development.

Evidence for a novel natriuretic peptide receptor that prefers brain natriuretic peptide over atrial natriuretic peptide

Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) exert their physiological actions by binding to natriuretic peptide receptor A (NPRA), a receptor guanylate cyclase (rGC) that synthesizes cGMP in response to both ligands. The family of rGCs is rapidly expanding, and it is plausible that there might be additional, as yet undiscovered, rGCs whose function is to provide alternative signalling pathways for one or both of these peptides, particularly given the low affinity of NPRA for BNP. We have investigated this hypothesis, using a genetically modified (knockout) mouse in which the gene encoding NPRA has been disrupted. Enzyme assays and NPRA-specific Western blots performed on tissues from wild-type mice demonstrate that ANP-activated cGMP synthesis provides a good index of NPRA protein expression, which ranges from maximal in adrenal gland, lung, kidney, and testis to minimal in heart and colon. In contrast, immunoreactive NPRA is not detectable in tissues isolated from NPRA knockout animals and ANP- and BNP-stimulatable GC activities are markedly reduced in all mutant tissues. However, testis and adrenal gland retain statistically significant, high-affinity responses to BNP. This residual response to BNP cannot be accounted for by natriuretic peptide receptor B, or any other known mammalian rGC, suggesting the presence of a novel receptor in these tissues that prefers BNP over ANP.

Molecular cloning of natriuretic peptide receptor A from bullfrog (Rana catesbeiana) brain and its functional expression

A comparative study of natriuretic peptide receptor (NPR) was performed by cloning the NPR-A receptor subtype from the bullfrog (Rana catesbeiana) brain and analyzing its functional expression. Like other mammalian NPR-A receptors, the bullfrog NPR-A receptor consists of an extracellular ligand binding domain, a hydrophobic transmembrane domain, a kinase-like domain and a guanylate cyclase domain. Sequence comparison among the bullfrog and mammalian receptors revealed a relatively low ( approximately 45%) similarity in the extracellular domain compared to a very high similarity ( approximately 92%) in the cytoplasmic regulatory and catalytic domains. Expression of NPR-A mRNA was detected in various bullfrog tissues including the brain, heart, lung, kidney and liver; highest levels were observed in lung. Functional expression of the receptor in COS-7 cells revealed that frog atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) elicited cyclic guanosine 3'5'-monophosphate production by stimulating the receptor in a dose-dependent manner from 10(-10) M concentrations. Rat ANP was also effective in stimulating the frog receptor whereas rat BNP and porcine BNP were less responsive to the receptor. On the other hand, frog C-type natriuretic peptide (CNP) as well as porcine CNP stimulated the receptor only at high concentrations (10(-7) M). This clearly indicates that the bullfrog receptor is a counterpart of mammalian NPR-A, and is specific for ANP or BNP but not for CNP.

Natriuretic peptides stimulate steroidogenesis in the fetal rat testis

To study the regulation of fetal testicular steroidogenesis in the rat, we examined effects of members of the natriuretic peptide family, that is, atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP), on testosterone production of dispersed Leydig cells of rat fetuses at Embryonic Day (E) 18.5. All three peptides stimulated testosterone production, with significant effect at concentrations > or =1 x 10(-8) mol/L of ANP, > or =1 x 10(-9) mol/L of BNP, and > or =1 x 10(-6) mol/L of CNP. Likewise, receptors for all three peptides (i.e., NPR-A, NPR-B, and NPR-C) were expressed in the fetal testis as early as E15.5. The natriuretic peptides had no effect on cAMP production by fetal Leydig cells. When tested in combination with two other peptides previously shown to stimulate fetal testicular steroidogenesis, vasoactive intestinal peptide and pituitary adenylate cyclase-stimulating polypeptide (PACAP-27), the combined effects did not differ significantly from the maximum effect with any one of the peptides alone. In conclusion, our present findings provide both functional and molecular evidences for NPR-A, NPR-B, and NPR-C in the fetal testis. Because ANP has previously been detected in fetal plasma and we now demonstrate the expression of BNP and CNP in fetal testes, these findings indicate involvement of the natriuretic peptides in endocrine and paracrine regulation during the early phase of fetal testicular steroidogenesis at E15.5--19.5 (i.e., before the onset of pituitary LH secretion).

Blockade of the natriuretic peptide receptor guanylyl cyclase-A inhibits NF-kappaB activation and alleviates myocardial ischemia/reperfusion injury

Acute myocardial infarction (AMI) remains the leading cause of death in developed countries. Although reperfusion of coronary arteries reduces mortality, it is associated with tissue injury. Endothelial P-selectin-mediated infiltration of neutrophils plays a key role in reperfusion injury. However, the mechanism of the P-selectin induction is not known. Here we show that infarct size after ischemia/reperfusion was significantly smaller in mice lacking guanylyl cyclase-A (GC-A), a natriuretic peptide receptor. The decrease was accompanied by decreases in neutrophil infiltration in coronary endothelial P-selectin expression. Pretreatment with HS-142-1, a GC-A antagonist, also decreased infarct size and P-selectin induction in wild-type mice. In cultured endothelial cells, activation of GC-A augmented H2O2-induced P-selectin expression. Furthermore, ischemia/reperfusion-induced activation of NF-kappaB, a transcription factor that is known to promote P-selectin expression, is suppressed in GC-A-deficient mice. These results suggest that inhibition of GC-A alleviates ischemia/reperfusion injury through suppression of NF-kappaB-mediated P-selectin induction. This novel, GC-A-mediated mechanism of ischemia/reperfusion injury may provide the basis for applying GC-A blockade in the clinical treatment of reperfusion injury.

C-type natriuretic peptide system in rabbit oviduct

C-type natriuretic peptide (CNP), a third member of the natriuretic peptide family, is known to be distributed mainly in brain and vascular endothelium and is considered to act as a local regulator in many tissues. The purpose of this study was to determine the presence of CNP system and its biological function in rabbit oviduct. The serial dilution curve of tissue extracts was parallel to the standard curve of CNP((1-22)) and a major peak of molecular profile of tissue extracts by HPLC was CNP((1-53)). mRNA of CNP which was the same size as positive control was also detected by Southern blot analysis. CNP increased the production of 3',5'-cyclic guanosine monophosphate (cGMP) in the purified membrane of oviduct, which was more in membranes derived from the isthmic portion than in the ampullar portion. The presence of mRNAs of natriuretic peptide receptor-A (NPR-A) and NPR-B was demonstrated by RT-PCR. Synthetic CNP((1-22)) inhibited both frequency and amplitude of basal motility of oviduct in a dose-dependent manner. The inhibitory effect of CNP on the basal motility was more potent in the isthmic portion than in the ampullar portion. These results demonstrate the presence of CNP system in the oviduct and regional differences in motility inhibition by CNP between isthmic and ampullar portions. Therefore, these findings suggest the possible existence of a CNP system that may exert a local regulator of basal motility, either alone or in concert with other hormones.

Molecular and biochemical characterization of a CNP-sensitive guanylyl cyclase in bovine tracheal smooth muscle

Muscarinic activation of bovine tracheal smooth muscle (BTSM) is involved in cyclic guanosine monophosphate (cGMP) production mediated through soluble (sGC) and membrane-bound (mGC) guanylyl cyclases. A muscarinic- and NaCl-sensitive mGC exists in BTSM regulated by muscarinic receptors coupled to G proteins. To identify the mGCs expressed in BTSM, reverse transcriptase/polymerase chain reaction (RT-PCR) from total RNA was performed using degenerate oligonucleotides for amplification of a region conserved among GC catalytic domains. Cloning of amplification products revealed that 76% of all BTSM GC transcripts corresponded to the sGC beta1 subunit and 24% to the B-type (C-type NP 1-22 [CNP]-sensitive) GC receptor. cGMP production by BTSM membrane and soluble fractions confirmed that sGC activity is 3-fold with respect to mGC activity. RT-PCR using specific oligonucleotides revealed that A (atrial NP-sensitive) and C (guanylin-sensitive) mGC subtypes are also expressed in BTSM. Stimulation of basal plasma membrane GC activity by CNP was higher than that by ANP, whereas guanylin showed no effect, indicating that CNP-sensitive guanylyl cyclase (GC-B) is the predominant functional BTSM mGC subtype. Strong adenosine triphosphate inhibition of CNP-stimulated mGC activity supports the finding that the tracheal mGC isoform belongs to the natriuretic peptide-sensitive mGCs. Additionally, CNP was able to reverse the chloride inhibition of BTSM mGC activity, suggesting that this is a novel G protein-coupled GC-B receptor.

Systematic screening of type B human natriuretic peptide receptor gene polymorphisms and association with essential hypertension

C-type natriuretic peptide (CNP) dilates arteries, lowers blood pressure and inhibits proliferation of vascular smooth muscle cells via the type B natriuretic peptide receptor (NPRB). The CNP-NPRB system may play a crucial role in the development of cardiovascular disease. We recently determined the structure of the human NPRB gene. In the present study, our objectives are to identify the polymorphisms of the NPRB gene and investigate the association of this gene with essential hypertension (EH). We used the polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) technique to study the NPRB gene polymorphism, and conducted an association study using a novel polymorphic marker. PCR-SSCP analysis of all 22 exons was done in 90 subjects, and abnormally-migrating bands were observed in the analyses of exon 11 and intron 18. Direct sequencing of these DNA fragments revealed the following sequence alterations: a C to T transition at nucleotide (nt) 2077 in exon 11 and a 9-bp insertion/deletion (I/D) in intron 18. PCR-restriction fragment length polymorphism analysis (PCR-RFLP) was developed to detect the C2077T transition. PCR-RFLP analyses of healthy subjects revealed that the C2077T polymorphism had complete linkage to GT repeats in intron 2 reported previously. The I/D polymorphism was identified by polyacrylamide gel electrophoresis, and it was not linked to any known polymorphic alleles of this gene. Therefore, the possible association between the I/D polymorphism and EH was investigated. A total of 123 individuals with EH and 123 age-matched normotensive control subjects were studied. Overall distributions of allele frequencies in the two groups were not significantly different. Although the I/D polymorphism in intron 18 of the NPRB gene was not associated with EH, the results of this study, which identified two novel polymorphisms in the human NPRB gene, will facilitate further genetic analysis of this gene and cardiovascular disease.

Enhanced expression and release of C-type natriuretic peptide in freshwater eels

C-type natriuretic peptide (CNP) is recognized as a paracrine factor acting locally in the brain and periphery. To assess the role of CNP in teleost fish, a cDNA encoding a CNP precursor was initially cloned from the eel brain. CNP message subsequently detected by ribonuclease protection assay, using the cDNA as probe, was most abundant in the brain followed by liver, gut, gills, and heart. Expression was generally higher in freshwater (FW) than in seawater (SW) eels, but not in the brain. Plasma CNP concentration measured by a newly developed homologous radioimmunoassay for eel CNP was higher in FW than in SW eels. The CNP concentration was also higher in the heart of FW eels but not in the brain. These results show that CNP is abundantly synthesized in peripheral tissues of FW eels and secreted constitutively into the circulation. Therefore, CNP is a circulating hormone as well as a paracrine factor in eels. Together with our previous demonstration that CNP-specific receptor expression is enhanced in FW eels, it appears that CNP is a hormone important for FW adaptation. Because atrial NP (ANP) promotes SW adaptation in eels, CNP and ANP, despite high sequence identity, appear to have opposite effects on environmental adaptation of the euryhaline fish.

C-type natriuretic peptide induces redifferentiation of vascular smooth muscle cells with accelerated reendothelialization

We recently reported that C-type natriuretic peptide (CNP) occurs in vascular endothelial cells and acts as a vascular-type natriuretic peptide. In the present study, we stimulated the cGMP cascade in proliferating smooth muscle cells (SMCs), in which particulate guanylate cyclase-B, the specific receptor for CNP, is predominantly expressed, by use of an adenovirus encoding rat CNP cDNA (Ad.CNP). In the Ad.CNP-treated cultured SMCs, CNP caused the growth inhibition of SMCs at G(1) phase with an early increase of p21(CIP1/WAF1) expression and subsequent upregulation of p16(INK4a). The expression of smooth muscle myosin heavy chain-2, which is the molecular marker of highly differentiated SMCs, was reinduced in the Ad.CNP-treated SMCs. The Ad.CNP-treated SMCs also reexpressed particulate guanylate cyclase-A, which shows high affinity to atrial and brain natriuretic peptide and is exclusively expressed in well-differentiated SMCs. CNP, which was overexpressed in rabbit femoral arteries in vivo at the time of balloon injury, significantly suppressed neointimal formation. Furthermore, an enhancement of the expression of smooth muscle myosin heavy chain-2 occurred in the residual neointima. In addition, early regeneration of endothelial cells was observed in the Ad.CNP-infected group. Thus, stimulation of cGMP cascade in proliferating dedifferentiated SMCs can induce growth inhibition and redifferentiation of SMCs with accelerated reendothelialization.

Natriuretic peptide signalling: molecular and cellular pathways to growth regulation

The natriuretic peptides (NPs) constitute a family of polypeptide hormones that regulate mammalian blood volume and blood pressure. The ability of the NPs to modulate cardiac hypertrophy and cell proliferation as well is now beginning to be recognized. The NPs interact with three membrane-bound receptors, all of which contain a well-characterized extracellular ligand-binding domain. The R1 subclass of NP receptors (NPR-A and NPR-B) contains a C-terminal guanylyl cyclase domain and is responsible for most of the NPs downstream actions through their ability to generate cGMP. The R2 subclass lacks an obvious catalytic domain and functions primarily as a clearance receptor. This review focuses on the signal transduction pathways initiated by ligand binding and other factors that help to determine signalling specificities, including allosteric factors modulating cGMP generation, receptor desensitization, the activation and function of cGMP-dependent protein kinase (PKG), and identification of potential nuclear or cytoplasmic targets such as the mitogen-activated protein kinase signalling (MAPK) cascade. The inhibition of cardiac growth and hypertrophy may be an important but underappreciated action of the NP signalling system.

Dwarfism and early death in mice lacking C-type natriuretic peptide

Longitudinal bone growth is determined by endochondral ossification that occurs as chondrocytes in the cartilaginous growth plate undergo proliferation, hypertrophy, cell death, and osteoblastic replacement. The natriuretic peptide family consists of three structurally related endogenous ligands, atrial, brain, and C-type natriuretic peptides (ANP, BNP, and CNP), and is thought to be involved in a variety of homeostatic processes. To investigate the physiological significance of CNP in vivo, we generated mice with targeted disruption of CNP (Nppc(-/-) mice). The Nppc(-/-) mice show severe dwarfism as a result of impaired endochondral ossification. They are all viable perinatally, but less than half can survive during postnatal development. The skeletal phenotypes are histologically similar to those seen in patients with achondroplasia, the most common genetic form of human dwarfism. Targeted expression of CNP in the growth plate chondrocytes can rescue the skeletal defect of Nppc(-/-) mice and allow their prolonged survival. This study demonstrates that CNP acts locally as a positive regulator of endochondral ossification in vivo and suggests its pathophysiological and therapeutic implication in some forms of skeletal dysplasia.

Alpha-helical-corticotropin-releasing hormone reverses anxiogenic effects of C-type natriuretic peptide in rats

Previously we have shown that atrial natriuretic peptide (ANP) has anxiolytic-like properties after intraperitoneal, intracerebroventricular and intraamygdala infusion in rats. Since C-type natriuretic peptide (CNP) exerts endocrine and behavioral effects opposing those of ANP, we characterized the behavioral properties of CNP after icv infusion in rats by their performance in the elevated plus maze with and without the corticotropin-releasing hormone (CRH) antagonist alpha-helical-CRH (alpha-CRH). Low CNP doses of 0.05 microg icv or 0.1 microg icv did not significantly influence the behavior of rats in the plus maze. At higher doses (0.5 microg, 2 microg, 5 microg icv) CNP had distinct anxiogenic properties. Our hypothesis that corticotropin-releasing hormone (CRH) is involved, which elicits anxiety-like behavior, was examined by icv coadministration of alpha-CRH, an antagonist at CRH-1 and CRH-2-receptors. Icv alpha-CRH alone had no intrinsic anxiolytic properties at a dose of 25 microg. The anxiogenic effects of 2 microg CNP icv seen in the plus maze were entirely blocked by alpha-CRH. Directly after exposition ACTH and corticosterone levels did not differ between the groups, but after 30 min ACTH levels were significantly higher in the CNP-treated group compared to alpha-CRH/CNP-treated animals. Corticosterone was found significantly lowered in the alpha-CRH/saline group compared to the CNP treated group but not compared to saline controls. Our data suggest opposing effects of CNP and ANP on anxiety-related behavior and neuroendocrine regulation in rats, which appear to be mediated via different receptor occupation and brain regions, and by a CRH-dependent mechanism.

Three dimensional atomic model and experimental validation for the ATP-Regulated Module (ARM) of the atrial natriuretic factor receptor guanylate cyclase

Atrial natriuretic factor (ANF) receptor guanylate cyclase (ANF-RGC) is a single chain transmembrane-spanning protein, containing both ANF binding and catalytic activities. ANF binding to the extracellular receptor domain activates the cytosolic catalytic domain, generating the second messenger cyclic GMP. Obligatory in this activation process is an intervening transduction step, which is regulated by the binding of ATP to the cyclase. The partial structural motif of the ATP binding domain of the cyclase has been elucidated and has been termed ATP Regulatory Module (ARM). The crystal structures of the tyrosine kinase domains of the human insulin receptor and haematopoietic cell kinase were used to derive a homology-based model of the ARM domain of ANF-RGC. The model identifies the precise configuration of the ATP-binding pocket in the ARM domain, accurately represents its ATP-dependent features, and shows that the ATP-dependent transduction phenomenon is a two-step mechanism. In the first step, ATP binds to its pocket and changes its configuration; in the second step, via an unknown protein kinase, it phosphorylates the cyclase for its full activation.

Organ-specific mRNA distribution of C-type natriuretic peptide in neonatal and adult mice

C-type natriuretic peptide (CNP) is described as an endothelium-derived vasodilator and a growth inhibitor of vascular smooth muscle cells. In the present study, CNP mRNA was quantified by RNase-protection assay to elucidate organ distribution of CNP in neonatal and adult mice. In adult mice, the highest CNP expressions were detected in uterus and ovary, which exceeded the CNP concentrations of forebrain and brainstem. In contrast, neonatal mice showed highest CNP-mRNA levels in forebrain and brainstem with lower levels in skin, tongue, heart, lung, thymus, skeletal muscle, liver, kidney, stomach, and skull. Thus, CNP-expression pattern diminishes during postnatal development. The observation that the expression level of CNP mRNA is 2.2-fold higher in the adult forebrain compared to the neonatal forebrain allows a comparison between all neonatal and adult organs.

Cyclosporine impairs the guanylyl cyclase activity of the natriuretic peptide receptor in the glomerulus

In order to elucidate the involvement of the atrial natriuretic peptide (ANP) and its receptor (natriuretic peptide receptor; NPR) system in cyclosporine-induced nephrotoxicity, we investigated the cyclosporine A (CsA)-induced changes in characteristics of the NPR/guanylyl cyclase system in the glomerulus and inner medulla of the rat kidney. CsA was administered intramuscularly to rats for 2 weeks (CsA group). Particulate guanylyl cyclase activity was measured in glomerular and inner medullary membranes. For receptor characteristics, quantitative in vitro receptor autoradiography was performed. The guanylyl cyclase activity in the glomerulus from the CsA group was attenuated compared with that from the control. However, the activity in the inner medulla was not affected by CsA treatment. Direct application of CsA to normal glomerular membrane completely abolished the ANP-induced guanylyl cyclase activation. Binding studies, using(125)I-ANP, revealed that B(max)was decreased in the CsA group, while K(d)was not affected in the glomerulus. However, in the inner medulla, neither B(max)nor K(d)was affected by CsA treatment. CsA did not displace the(125)I-ANP bindings to NPRs in the normal rat kidney. Local tissue ANP as well as plasma ANP concentration in both groups was not significantly different. These results indicate that CsA impairs the guanylyl cyclase activity mainly in the glomerulus by the decrease in NPR population and/or by direct inhibition, suggesting that the ANP/NPR system might be involved in CsA-induced nephrotoxicity.

Three dimensional atomic model and experimental validation for the ATP-Regulated Module (ARM) of the atrial natriuretic factor receptor guanylate cyclase

Atrial natriuretic factor (ANF) receptor guanylate cyclase (ANF-RGC) is a single chain transmembrane-spanning protein, containing both ANF binding and catalytic activities. ANF binding to the extracellular receptor domain activates the cytosolic catalytic domain, generating the second messenger cyclic GMP. Obligatory in this activation process is an intervening transduction step, which is regulated by the binding of ATP to the cyclase. The partial structural motif of the ATP binding domain of the cyclase has been elucidated and has been termed ATP Regulatory Module (ARM). The crystal structures of the tyrosine kinase domains of the human insulin receptor and haematopoietic cell kinase were used to derive a homology-based model of the ARM domain of ANF-RGC. The model identifies the precise configuration of the ATP-binding pocket in the ARM domain, accurately represents its ATP-dependent features, and shows that the ATP-dependent transduction phenomenon is a two-step mechanism. In the first step, ATP binds to its pocket and changes its configuration; in the second step, via an unknown protein kinase, it phosphorylates the cyclase for its full activation.