Particulate Guanylyl Cyclase Research Articles

Designer Natriuretic Peptides for Heart Failure

The endogenous natriuretic peptides ANP, BNP and CNP, via particulate guanylyl cyclase (GC) receptors and the second messenger cyclic guanosine monophosphate (cGMP), are potent activators of key signaling pathways. Emerging research suggests that in human disease such as heart failure (HF) these natriuretic peptides (NP), which possess broad pleiotropic protective properties, may be deficient or may be released by the heart as abnormal molecular forms with reduced pGC activating properties. Therefore, novel NP/GC/cGMP therapies and innovative NP peptide delivery systems are being developed. CD-NP (cenderitide) represents a new class of NP, which we call designer NPs which was designed at Mayo Clinic. CD-NP represents the most clinically advanced of the designer NPs that is now in clinical trials for HF. CD-NP was uniquely designed to co-activate both the GC-A receptor to which ANP and BNP bind as well as GC-B to which CNP binds. Thus it has the unique ability to optimally activate the entire NP/GC receptor family. Clinical trials are now underway to chronically deliver CD-NP by a subcutaneous patch pump simulating the strategy for chronic insulin administration to reduce rehospitalization for HF. Other innovative delivery systems also include oral delivery and gene delivery. As increasing evidence supports the key role of hypertension especially resistant hypertension as a cause of HF, we also will discuss our second designer NP which is named MANP which functions as a super ANP and a pure GC-A agonist. Motivated by genetic studies that human hypertension may be linked in part to an ANP deficiency; MANP serves as a potent natriuretic, aldosterone suppressing and blood pressure lowering peptide, which goes beyond native ANP. Importantly, it may be delivered chronically both by subcutaneous, oral and novel nanotechnologies permitting enhanced hypertension control, which goes beyond conventional anti-hypertensive agents. Thus, designer NPs hold the promise as novel treatments as well as preventive strategies for HF resulting in a reduction in the burden of cardiovascular disease.

The Natriuretic Peptide Receptors NPR-A and NPR-B Are Differentially Regulation by Extracellular Matrix Proteins

BackgroundCardiac fibroblasts (CFs) regulate myocardial remodeling by proliferating, differentiating, and secreting extra-cellular matrix proteins (ECMs). Natriuretic peptides (NPs) are anti-fibrotic, inhibiting collagen production, augmenting matrix metalloproteinases, and suppressing CF proliferation. Recently, we demonstrated that the ECM proteins fibronectin (FN) and Collagen IV (Col IV) augmented production of BNP's second messenger cGMP in CFs, supporting crosstalk between these ECM components and BNP involving its particulate guanylyl cyclase receptor, NPR-A. The goal of this investigation was to assess whether CNP and CNP-like peptides, which signal through the NPR-B receptor, are also affected by the ECM.MethodsHuman CFs were cultured as previously described on ECM coated or non-coated plates. Cyclic GMP assays were done as previously reported.ResultsAs previously observed, BNP in vitro induced a dose dependent increase in cGMP which was augmented by FN and Col IV (p<0.05) that was abrogated by NPR-A antibody blockade. In contrast, activation of cGMP by two known active forms of CNP, CNP-22 and CNP-53 which bind to NPR-B, were not affected by ECM presence. Interestingly, the designer peptide CD-NP, known to signal through both NPR-A and NPR-B demonstrated an increase in cGMP with FN and Col IV similar to that observed with BNP.ConclusionOur data suggests that NPR-A activation is augmented by ECM while NPR-B activation is not which may be important in understanding the physiological role of these cGMP receptors in the regulation of myocardial remodeling and guiding natriuretic peptide based therapeutics in its inhibition. Interestingly, the CNP-like chimeric in CF's demonstrates properties of BNP supporting its unique role as an anti-fibrotic therapeutic. BackgroundCardiac fibroblasts (CFs) regulate myocardial remodeling by proliferating, differentiating, and secreting extra-cellular matrix proteins (ECMs). Natriuretic peptides (NPs) are anti-fibrotic, inhibiting collagen production, augmenting matrix metalloproteinases, and suppressing CF proliferation. Recently, we demonstrated that the ECM proteins fibronectin (FN) and Collagen IV (Col IV) augmented production of BNP's second messenger cGMP in CFs, supporting crosstalk between these ECM components and BNP involving its particulate guanylyl cyclase receptor, NPR-A. The goal of this investigation was to assess whether CNP and CNP-like peptides, which signal through the NPR-B receptor, are also affected by the ECM. Cardiac fibroblasts (CFs) regulate myocardial remodeling by proliferating, differentiating, and secreting extra-cellular matrix proteins (ECMs). Natriuretic peptides (NPs) are anti-fibrotic, inhibiting collagen production, augmenting matrix metalloproteinases, and suppressing CF proliferation. Recently, we demonstrated that the ECM proteins fibronectin (FN) and Collagen IV (Col IV) augmented production of BNP's second messenger cGMP in CFs, supporting crosstalk between these ECM components and BNP involving its particulate guanylyl cyclase receptor, NPR-A. The goal of this investigation was to assess whether CNP and CNP-like peptides, which signal through the NPR-B receptor, are also affected by the ECM. MethodsHuman CFs were cultured as previously described on ECM coated or non-coated plates. Cyclic GMP assays were done as previously reported. Human CFs were cultured as previously described on ECM coated or non-coated plates. Cyclic GMP assays were done as previously reported. ResultsAs previously observed, BNP in vitro induced a dose dependent increase in cGMP which was augmented by FN and Col IV (p<0.05) that was abrogated by NPR-A antibody blockade. In contrast, activation of cGMP by two known active forms of CNP, CNP-22 and CNP-53 which bind to NPR-B, were not affected by ECM presence. Interestingly, the designer peptide CD-NP, known to signal through both NPR-A and NPR-B demonstrated an increase in cGMP with FN and Col IV similar to that observed with BNP. As previously observed, BNP in vitro induced a dose dependent increase in cGMP which was augmented by FN and Col IV (p<0.05) that was abrogated by NPR-A antibody blockade. In contrast, activation of cGMP by two known active forms of CNP, CNP-22 and CNP-53 which bind to NPR-B, were not affected by ECM presence. Interestingly, the designer peptide CD-NP, known to signal through both NPR-A and NPR-B demonstrated an increase in cGMP with FN and Col IV similar to that observed with BNP. ConclusionOur data suggests that NPR-A activation is augmented by ECM while NPR-B activation is not which may be important in understanding the physiological role of these cGMP receptors in the regulation of myocardial remodeling and guiding natriuretic peptide based therapeutics in its inhibition. Interestingly, the CNP-like chimeric in CF's demonstrates properties of BNP supporting its unique role as an anti-fibrotic therapeutic. Our data suggests that NPR-A activation is augmented by ECM while NPR-B activation is not which may be important in understanding the physiological role of these cGMP receptors in the regulation of myocardial remodeling and guiding natriuretic peptide based therapeutics in its inhibition. Interestingly, the CNP-like chimeric in CF's demonstrates properties of BNP supporting its unique role as an anti-fibrotic therapeutic.

Designer natriuretic peptides for heart failure: advanced in clinical development

Background The increasing burden of heart failure (HF) is a major unmet need for new therapeutics. No new drug has been approved for HF for over a decade. The natriuretic peptides as endogenous activators of particulate guanylyl cyclase (GC) receptors represent an unparalleled opportunity for novel therapeutic agents for HF. Specifically, the GC-A receptor activated by ANP and BNP and GCB activation by CNP mediate beneficial pleiotropic actions, which include natriuresis, vasodilatation, suppression of the renin-angiotensin-aldosterone system, inhibition of cardiomyocyte hypertrophy, retardation of fibrosis and improvement in ventricular function and structure.

Do prostanoids or nitric oxide mediate sensitization of the von Bezold–Jarisch reflex by B‐type natriuretic peptide?

1. Cardiac natriuretic peptides act on cardiopulmonary chemoreceptor afferents to enhance the von Bezold-Jarisch reflex (BJR). Activity of the natriuretic peptide particulate guanylyl cyclase receptor is essential for full expression of the BJR. Whether natriuretic peptides act directly on cardiac afferents or they require another intermediate factor(s) for their effects on the BJR is unknown. Endogenous candidates tested as possible intermediates in the present study were prostanoids and nitric oxide (NO), plausible endogenous chemical mediators of cardiac chemoreflex activity. 2. Dose-dependent BJR bradycardia was evoked by the 5-HT(3) receptor agonist, phenylbiguanide (range 5-89 μg/kg), in conscious instrumented adult sheep (n = 6). The influence of B-type natriuretic peptide (BNP; the most potent of the natriuretic peptides) on the BJR was assessed before and after blockade of prostanoids (using indomethacin, 1 mg/kg per h i.v.) or nitric oxide (using N-nitro-l-arginine (NOLA), 3 mg/kg bolus, then 3 mg/kg per h infusion i.v.). 3. On their own, indomethacin and NOLA did not significantly alter the BJR, showing that prostanoids and NO are not essential endogenous mediators of the BJR. As shown in previous studies, BNP (10 pmol/kg per min i.v.) infusion enhanced the BJR by 85 ± 36%, P < 0.05. When the production of either prostanoids or nitric oxide was inhibited, BNP still enhanced the BJR. 4. The present study provides evidence that BNP does not require the activity or influence of prostaglandins or NO for its sensitising effects on the BJR. We propose that natriuretic peptides act directly on cardiac afferents, in synergy with 5-HT(3) agonists, to facilitate the BJR.

Altered regulation of renal nitric oxide and atrial natriuretic peptide systems in angiotensin II-induced hypertension

The present study was aimed to determine whether there is an altered role of local nitric oxide (NO) and atrial natriuretic peptide (ANP) systems in the kidney in association with the angiotensin (Ang) II-induced hypertension. Male Sprague–Dawley rats were used. Ang II (100 ng·min − 1 ·kg − 1 ) was infused through entire time course. Thirteenth day after beginning the regimen, kidneys were taken. The protein expression of NO synthase (NOS) and nitrotyrosine was determined by semiquantitative immunoblotting. The mRNA expression of components of ANP system was determined by real-time polymerase chain reaction. The activities of soluble and particulate guanylyl cyclases were determined by the amount of cGMP generated in responses to sodium nitroprusside and ANP, respectively. There developed hypertension and decreased creatinine clearance in the experimental group. The protein expression of eNOS, nNOS and nitrotyrosine was increased in the cortex, while that of iNOS remained unaltered. The urinary excretion of NO increased in Ang II-induced hypertensive rats. The catalytic activity of soluble guanylyl cyclase was blunted in the glomerulus in Ang II-induced hypertensive rats. The mRNA expression of ANP was increased in Ang II-induced hypertensive rats. Neither the expression of NPR-A nor that of NPR-C was changed. The protein expression of neutral endopeptidase was decreased and the activity of particulate guanylyl cyclase was blunted in the glomerulus and papilla in Ang II-induced hypertensive rats. In conclusion, the synthesis of NO and ANP was increased in the kidney of Ang II-induced hypertension, while stimulated cGMP response was blunted. These results suggest desensitization of guanylyl cyclase in the kidney of Ang II-induced hypertensive rats, which may contribute to the associated renal vasoconstriction and hypertension.

Cyclic GMP signaling in rat urinary bladder, prostate, and epididymis: tissue-specific changes with aging and in response to Leydig cell depletion

Aging of the male reproductive system leads to changes in endocrine signaling and is frequently associated with the emergence of prostate hyperplasia and bladder dysfunctions. Recent reports highlight prostate and bladder as promising targets for therapeutic interventions with inhibitors of the cyclic GMP (cGMP)-degrading phosphodiesterase 5 (PDE5). However, the cGMP signaling system in these organs is as yet poorly characterized, and the possibility of age-related alterations has not been addressed. This study investigates key proteins of cGMP pathways in bladder, prostate, and epididymis of young (3 months) and old (23-24 months) Wistar rats. Local differences in the abundance of PDE5, soluble guanylyl cyclase (sGC) and particulate guanylyl cyclases (GC-A, GC-B), endothelial nitric oxide synthase, and cGMP-dependent protein kinase I (PRKG1 (cGKI)) revealed pronounced tissue-specific peculiarities. Although cGMP-generating enzymes were not affected by age in all organs, we recognized age-related decreases of PDE5 expression in bladder and a selective diminishment of membrane-associated PRKG1 in epididymis. In disagreement with published data, all cGMP pathway proteins including PDE5 are poorly expressed in prostate. However, prostatic PRKG1 expression increases with aging. Androgen withdrawal during temporary Leydig cell elimination induced a massive (>12-fold) upregulation of PRKG1 in prostate but not in other (penis and epididymis) androgen-dependent organs. These findings identify PRKG1 as a key androgen-sensitive signaling protein in prostate of possible importance for growth regulation. The elucidated effects may have significance for age-associated pathologies in the male lower-urinary tract.

Consideration of Natriuretic Peptide Receptor C

To The Editor: With interest, we read the recent article by Castro et al,1 and the corresponding editorial,2 in Circulation Research , in which the authors find differential regulation of cGMP produced by particulate guanylyl cyclase (pGC) compared with that produced by soluble guanylyl cyclase (sGC). This work by experts in the field provides strong evidence …

Presence of dendroaspis natriuretic peptide and its binding to NPR-A receptor in rabbit kidney

Natriuretic peptides help to maintain sodium and fluid volume homeostasis in a healthy cardio-renal environment. Since the identification of Dendroaspis natriuretic peptide (DNP) as a new member of the natriuretic peptide family, DNP has been considered as an important regulator of natriuresis and dieresis. The present study was undertaken to investigate the presence of immunoreactive Dendroaspis natriuretic peptide (DNP) and its specific receptor in rabbit. DNP was detected in heart, kidney, liver, brain, and plasma by radioimmunoassay (RIA). DNP contents of cardiac atrium and ventricle, renal cortex and medulla, liver, and brain were 1.42±0.15, 1.06±0.08, 2.55±0.21, 1.81±0.16, 1.36±0.22, and 0.69±0.15pg/mg of wet weight, respectively. The concentration of DNP in plasma was 235.44±15.44pg/ml. By quantitative in vitro receptor autoradiography, specific 125I-DNP binding sites were revealed in glomeruli, interlobular artery, acuate artery, vasa recta bundle, and inner medulla of the kidney with an apparent dissociation constant (Kd) of 0.29±0.05, 0.36±0.03, 0.84±0.19, 1.18±0.23, and 10.91±1.59nM, respectively. Basal rate of 3′, 5′-cyclic guanosine monophosphate (cGMP) production by particulate guanylyl cyclase (GC) activation of glomerular membranes was basally 13.40±1.70pmol/mg protein/min. DNP caused an increment of cGMP production in similar magnitude to that caused by ANP, BNP, and urodilatin, while the production of cGMP by CNP was significantly lower than that by DNP. Our results show that plasma levels of DNP were higher when compared to other tissues. DNP produces cGMP via the NPR-A receptor subtype in the kidney, similarly to ANP and BNP, suggesting that plasma DNP could have similar functions as ANP and BNP.

17β-Estradiol Elevates cGMP and, via Plasma Membrane Recruitment of Protein Kinase GIα, Stimulates Ca2+ Efflux from Rat Hepatocytes

Rapid non-genomic effects of 17beta-estradiol, the principal circulating estrogen, have been observed in a wide variety of cell types. Here we investigate rapid signaling effects of 17beta-estradiol in rat hepatocytes. We show that, above a threshold concentration of 1 nm, 17beta-estradiol, but not 17alpha-estradiol, stimulates particulate guanylyl cyclase to elevate cGMP, which through activation and plasma membrane recruitment of protein kinase G isoform Ialpha, stimulates plasma membrane Ca(2+)-ATPase-mediated Ca(2+) efflux from rat hepatocytes. These effects are extremely rapid in onset and are mimicked by a membrane-impermeant 17beta-estradiol-BSA conjugate, suggesting that 17beta-estradiol acts at the extracellular face of the plasma membrane. We also show that 17beta-estradiol binds specifically to the intact hepatocyte plasma membrane through an interaction that is competed by an excess of atrial natriuretic peptide but also shows many similarities to the pharmacological characteristics of the putative gamma-adrenergic receptor. We, therefore, propose that the observed rapid signaling effects of 17beta-estradiol are mediated either through the guanylyl cyclase A receptor for atrial natriuretic peptide or through the gamma-adrenergic receptor, which is either itself a transmembrane guanylyl cyclase or activates a transmembrane guanylyl cyclase through cross-talk signaling.

Agonist-Specific Compartmentation of cGMP Action in Myometrium

Nitric oxide relaxes myometrium in a cGMP-independent manner. Although cGMP activates its cognate kinase, this is not required for the inhibitory effect of nitric oxide. Thus, nitric oxide-mediated cGMP elevation does not enjoy the same set of substrates as it does in other smooth muscles. To further understand the regulation of relaxation of uterine muscle by cGMP, we have studied the actions of peptide-mediated cGMP action in guinea pig myometrium. We used both functional and biochemical studies of the action of the particulate guanylyl cyclase activator uroguanylin and its receptor, particulate guanylyl cyclase type C, to address the relationship between cGMP elevation acting in the membrane signaling domain to that of the nonmembrane region of the cell. Uroguanylin relaxed oxytocin-induced contractions in a dose-dependent fashion only in pregnant myometrium. Both relaxation and cGMP accumulation after uroguanylin stimulation were blocked by the putative particulate guanylyl cyclase type C inhibitors 2-chloro-ATP and isatin (1H-indole-2,3-dione), but not by the soluble guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-A]quinoxalin-1-one (ODQ). Uroguanylin stimulated cGMP accumulation only in the pregnant myometrium. Caveolin-1 expression increased in pregnancy toward term. In the caveolin-1-containing membrane domain, uroguanylin, but not the nitric-oxide donor, led to the elevation of cGMP that was insensitive to ODQ. Particulate guanylyl cyclase C was expressed and prouroguanylin was detected in pregnant myometrium. We conclude that a uroguanylin-particulate cyclase-cGMP relaxation pathway is present and cGMP is compartmented in myometrium. The agonist-mediated selectivity of relaxation to cGMP is of fundamental pharmacological interest in understanding signal transduction in smooth muscle.

A New Signal From B-Type Natriuretic Peptide in ST-Elevation Myocardial Infarction

A New Signal From B-Type Natriuretic Peptide in ST-Elevation Myocardial Infarction

Different effects of soluble and particulate guanylyl cyclases on expression of inflammatory cytokines in rat peripheral blood mononuclear cells

Inflammation involves the cooperation of various cells and biologically active molecules. An important intracellular messenger molecule participating in the regulation of the process is cyclic GMP (cGMP), which is synthesized by guanylyl cyclases (GCs). The GC family comprises cytosolic (soluble) and membrane-bound (particulate) enzymes. The aim of this study was to determine whether and how the synthesis of cGMP by various forms of GC affects the expression of inflammatory cytokines depending on the activity of the transcription factors NF-κB (nuclear factor-κB) and AP-1 (activator protein-1). We established that in rat peripheral blood mononuclear cells (PBMCs), synthesis of cGMP was elevated by sodium nitroprusside (SNP), the activator of soluble GC, and by atrial natriuretic peptide (ANP) and C-type natriuretic peptide (CNP), the activators of particulate GC-A and GC-B, respectively. Stimulation of various GCs differently affected the expressions of the cytokines IL-1β, IL-6, and TNF-α in control cells and in cells activated by bacterial endotoxin (LPS). In control PBMCs their expression was elevated by stimulation of soluble, but not particulate, GC. SNP caused an increase in NF-κB activity, but had no influence on the activity of AP-1. The cells treated with LPS decreased the expressions of IL-1β, IL-6, and TNF-α in response to stimulation of particulate GC-A, but not other guanylyl cyclases. This inhibitory effect was a result of suppression of the activities of NF-κB and AP-1. Both effects that of SNP and of ANP, were cGMP dependent, as shown using its membrane-permeable analog 8-Br-cGMP. The implementation of specific inhibitors showed that the stimulatory effect of SNP was mediated by soluble GC and cGMP-dependent protein kinase (PKG-I). However, PKG-I was not involved in the inhibition of NF-κB and AP-1 activities by ANP in LPS-activated cells. Taken together, these results for the first time indicate that various GCs and various cGMP-dependent signaling pathways can modulate the activity of AP-1 and/or NF-κB and thus affect the expressions of IL-1β, IL-6, and TNF-α, which play important roles in the development of inflammation.

C‐type natriuretic peptide regulation of guanosine‐3′,5′‐cyclic monophosphate production in human endothelial cells

In vascular smooth muscle cells, relaxant actions of guanosine--3',5'-cyclic monophosphate (cGMP) are well recognized, but there is increasing evidence that cGMP also plays regulatory roles in vascular endothelium. However, the autacoid and endocrine mechanisms controlling cGMP production in endothelium are not well understood. The objective of these studies was to examine the mechanisms of cGMP accumulation in human umbilical vein endothelial cells (HUVEC) in response to natriuretic peptides. Expression in HUVEC of natriuretic peptide receptors, particulate guanylyl cyclases (GC)-A and GC-B, was confirmed by RT-PCR and Western blot analysis. In the presence of the phosphodiesterase inhibitor IBMX 500 microM, 3 h incubation of HUVEC with B-type natriuretic peptide (BNP) (preferential GC-A agonist) or C-type natriuretic peptide (CNP) (preferential GC-B agonist) stimulated concentration-dependent increases in cGMP production. At 10 and 100 nM, we observed two to three-fold greater potency of CNP compared to BNP. In the absence of IBMX, CNP-stimulated cGMP accumulation was significantly less than cGMP accumulation in response to sodium nitroprusside 1 mM. This greater sensitivity of GC-B-derived cGMP to phosphodiesterases suggests compartmentalization of two pools of cGMP from particulate and soluble guanylyl cyclases. Although CNP 100 nM and 1 microM was observed to increase nitrite + nitrate (stable metabolites of NO) production in HUVEC two-fold above basal level, the soluble guanylyl cyclase inhibitor ODQ 10 microM did not significantly modify CNP-stimulated cGMP accumulation suggesting that endothelial actions of CNP may be NO-independent. In conclusion, these studies indicate functional signaling by natriuretic peptides in endothelial cells, supporting possible roles of these mediators in regulating endothelial cell function.

Determination of cyclic GMP concentration using a gold nanoparticle-modified optical fiber

Guanosine 3′,5′-cyclic monophosphate (cGMP) produced from guanosine triphosphate (GTP) via soluble or particulate guanylyl cyclase (GC) is an important second messenger for signal transduction within cells. The currently used methods of measuring cGMP including radioimmunoassay and enzyme immunoassay involve the use of radioisotopes or tracers. To develop a cGMP assay that is label-free, non-radioactive, able to detect cGMP directly, and highly specific and sensitive, we used a gold nanoparticle-modified optical fiber (GNOF) conjugated with anti-cGMP antiserum to determine cGMP concentration based on localized surface plasmon resonance (LSPR). The optimal antisera dilution and incubation time for preparing the probe are 1:250 and 2 h, respectively. The sensor shows detection ranges of 0.0025–0.1 and 0.1–100 pmol/ml for acetylated cGMP and cGMP, respectively. The sensitivity for measuring acetylated cGMP is three orders of magnitude higher than that for cGMP. In addition, the biosensor can be stored at 4 °C up to 4 week without losing sensitivity significantly.

Atrial Natriuretic Peptide Regulates Ca2+ Channel in Early Developmental Cardiomyocytes

BackgroundCardiomyocytes derived from murine embryonic stem (ES) cells possess various membrane currents and signaling cascades link to that of embryonic hearts. The role of atrial natriuretic peptide (ANP) in regulation of membrane potentials and Ca2+ currents has not been investigated in developmental cardiomyocytes.Methodology/Principal FindingsWe investigated the role of ANP in regulating L-type Ca2+ channel current (ICaL) in different developmental stages of cardiomyocytes derived from ES cells. ANP decreased the frequency of action potentials (APs) in early developmental stage (EDS) cardiomyocytes, embryonic bodies (EB) as well as whole embryo hearts. ANP exerted an inhibitory effect on basal ICaL in about 70% EDS cardiomyocytes tested but only in about 30% late developmental stage (LDS) cells. However, after stimulation of ICaL by isoproterenol (ISO) in LDS cells, ANP inhibited the response in about 70% cells. The depression of ICaL induced by ANP was not affected by either Nω, Nitro-L-Arginine methyl ester (L-NAME), a nitric oxide synthetase (NOS) inhibitor, or KT5823, a cGMP-dependent protein kinase (PKG) selective inhibitor, in either EDS and LDS cells; whereas depression of ICaL by ANP was entirely abolished by erythro-9-(2-Hydroxy-3-nonyl) adenine (EHNA), a selective inhibitor of type 2 phosphodiesterase(PDE2) in most cells tested.Conclusion/SignificancesTaken together, these results indicate that ANP induced depression of action potentials and ICaL is due to activation of particulate guanylyl cyclase (GC), cGMP production and cGMP-activation of PDE2 mediated depression of adenosine 3′, 5′–cyclic monophophate (cAMP)–cAMP-dependent protein kinase (PKA) in early cardiomyogenesis.

Natriuretic Peptides: New Players in Energy Homeostasis

In this issue of Diabetes , Miyashita et al. (1) provide compelling new evidence that natriuretic peptides (NPs) play a key role in the regulation of body weight and energy metabolism. In a series of complementary experiments, the investigators show that the NP–cyclic guanosine monophosphate (cGMP) signaling system increases the capacity for fat oxidation, activates mitochondrial biogenesis, and prevents the deleterious effects of a high-fat diet (HFD). NPs are not new players in metabolic regulation. Since the discovery of atrial natriuretic peptide (ANP) in 1980 (2), a large body of work has highlighted the multifaceted roles of NPs in the regulation of blood volume and arterial pressure. NPs are members of a family of structurally similar but genetically distinct endogenous peptide hormones. The NP family consists of at least three mammalian peptides: atrial-, brain-, and C-type (ANP, BNP, and CNP, respectively) (3). ANP and BNP preferentially bind to a particulate guanylyl cyclase (GC) receptor called GC-A, whereas CNP is the physiological ligand for GC-B (4). Through their diuretic, vasodilatory, and antimitogenic properties, the NPs play an important role in the regulation of cardiovascular, renal, and endocrine homeostasis (3–5). New findings by Miyashita et al. convincingly demonstrate that the NP-cGMP system also plays a role in the regulation of fatty acid metabolism and body weight regulation (Fig. 1). The researchers generated a series of mouse models to investigate. BNP transgenic mice, which overexpress BNP in the liver at supraphysiological levels (>100-fold compared with resting level), tended to be leaner than wild-type mice. When challenged with HFD, these mice resisted diet-induced obesity and insulin resistance. They had lower total body fat, increased whole-body oxygen consumption and fat …

CATALYTIC RECEPTORS

CATALYTIC RECEPTORS

Altered regulation of renal nitric oxide, atrial natriuretic peptide and cyclooxygenase systems in aldosterone escape in rats

The present study was aimed to determine whether there is an altered role of local nitric oxide (NO), atrial natriuretic peptide (ANP) and cyclooxygenase (COX) systems in the kidney in association with the aldosterone escape. Male Sprague–Dawley rats were used. Aldosterone (200 μg/day) was infused through entire time course. The control group was kept on a low sodium diet (0.02 mEq/day), and the experimental group was supplied with a higher sodium diet (2.0 mEq/day). Four days after beginning the regimen, the kidneys were taken. The protein expression of NO synthase (NOS) and COX isoforms was determined by semiquantitative immunoblotting. The mRNA expression of components of ANP system was determined by real-time polymerase chain reaction. The activities of soluble and particulate guanylyl cyclases were determined by the amount of cGMP generated in responses to sodium nitroprusside and ANP, respectively. There developed aldosterone escape in the experimental group. Accordingly, the renal content and the urinary excretion of NO increased. The expression of nNOS was increased in the inner medulla. Neither the expression of eNOS nor that of iNOS was changed. The expression and the catalytic activity of soluble guanylyl cyclase remained unaltered. The mRNA expression of ANP was increased. Neither the expression of NPR-A or NPR-C nor the activity of particulate guanylyl cyclase was altered in the papilla. The protein expression of COX-2 was increased in the inner medulla, while that of COX-1 remained unchanged. In conclusion, the upregulation of nNOS, ANP, and COX-2 may be causally related with the aldosterone escape.

C-type natriuretic peptide (CNP) is a bifurcation factor for sensory neurons

Neuronal circuits are shaped during development by the coordinated action of guidance factors and signals that regulate axonal branching. Unlike guidance cues, the molecules and signaling cascades that underlie axonal branching remain to be resolved. Here we show that the secreted molecule C-type natriuretic peptide (CNP) induces a cGMP signaling cascade via its receptor particulate guanylyl cyclase Npr2 which is essential for sensory axon bifurcation at the dorsal root entry zone (DREZ) of the spinal cord. In contrast, another form of sensory axon branching-collateral formation-is not affected by this pathway. We also demonstrate that cGMP signaling via the nitric oxide-stimulated soluble guanylyl cyclase system (NO-GC) is dispensable for sensory axon branching. Functionally, the bifurcation error in CNP mutant mice is maintained at mature stages and results in a reduced input on secondary neurons as detected by patch-clamp recordings.

B-Type Natriuretic Peptide: Endogenous Regulator of Myocardial Structure, Biomarker and Therapeutic Target

B-type natriuretic peptide (BNP), initially identified in brain tissues, is now recognized as a key cardiac hormone. Numerous studies over the last decade have demonstrated that both exogenous and endogenous BNP prevent left ventricular (LV) hypertrophy in experimental settings, largely via activation of particulate guanylyl cyclase (pGC)-coupled receptors. BNP represents somewhat of a paradox, in that upregulation of BNP expression is widely used as a diagnostic marker for LV hypertrophy, diastolic dysfunction and heart failure in the clinic. We and others have postulated that BNP serves as an endogenous brake on the LV myocardium, seeking to curb the runaway train of signaling pathways that drive the progression from LV hypertrophy though remodeling, heart failure and death. This review summarizes the mechanisms of BNP's antihypertrophic actions, the role for cyclic GMP-mediated inhibition of pro-hypertrophic signaling, and BNP's impact on LV function. The improved understanding of the mechanisms of BNP regulation of LV hypertrophy and function that has emerged from both the experimental and clinical experience with this peptide provides new insight into the potential that BNP pharmacotherapy still offers for patients with LV hypertrophy.