Guanylyl cyclase/natriuretic peptide receptor-A signaling antagonizes phosphoinositide hydrolysis, Ca(2+) release, and activation of protein kinase C

The RAAS Goodfellas in Cardiovascular System

In the last two decades, the study of the renin-angiotensin-aldosterone system (RAAS) has revealed a counterregulatory protective axis. This protective arm is characterized by ACE2/Ang 1-7/MasR and Ang 1-9 that largely counteracts the classic arm of the RAAS mediated by ACE/Ang II/AT1R/aldosterone and plays an important role in the prevention of inflammation, oxidative stress, hypertension, and cardiovascular remodeling. A growing body of evidence suggests that enhancement of this counterregulatory arm of RAAS represents an important therapeutic approach to facing cardiovascular comorbidities. In this review, we provide an overview of the beneficial effects of ACE2, Ang 1-7/MasR, and Ang 1-9 in the context of oxidative stress, vascular dysfunction, and organ damage.

MasR and pGCA receptor activation protects primary vascular smooth muscle cells and endothelial cells against oxidative stress via inhibition of intracellular calcium

Cardiovascular diseases (CVDs) are associated with vascular smooth muscle cell (VSMC) and endothelial cell (EC) damage. Angiotensin1-7 (Ang1-7) and B-type natriuretic peptide (BNP) are responsible for vasodilation and regulation of blood flow. These protective effects of BNP are primarily mediated by the activation of sGCs/cGMP/cGKI pathway. Conversely, Ang1-7 inhibits Angiotensin II-induced contraction and oxidative stress via Mas receptor activation. Thus, the aim of the study was to determine the effect of co-activation of MasR and particulate guanylate cyclase receptor (pGCA) pathways by synthesized novel peptide (NP) in oxidative stress-induced VSMCs and ECs. MTT and Griess reagent assay kits were used for the standardization of the oxidative stress (H₂ O₂ ) induced model in VSMCs. The expression of targeted receptors in VSMC was done by RT-PCR and Western blot analysis. Protective effect of NP in VSMC and EC was determined by immunocytochemistry, FACS analysis, and Western blot analysis. Underlying mechanisms of EC-dependent VSMC relaxation were done by determining downstream mRNA gene expression and intracellular calcium imaging of cells. Synthesized NP significantly improved oxidative stress-induced injury in VSMCs. Remarkably, the actions of NP were superior to that of the Ang1-7 and BNP alone. Further, a mechanistic study in VSMC and EC suggested the involvement of upstream mediators of calcium inhibition for the therapeutic effect. NP is reported to possess vascular protective activities and is also involved in the improvement of endothelial damage. Moreover, it is highly effective than that of individual peptides BNP and Ang1-7 and therefore it may represent a promising strategy for CVDs.

Guanylyl cyclase/natriuretic peptide receptor-A: Identification, molecular characterization, and physiological genomics

The natriuretic peptides (NPs) hormone family, which consists mainly of atrial, brain, and C-type NPs (ANP, BNP, and CNP), play diverse roles in mammalian species, ranging from renal, cardiac, endocrine, neural, and vascular hemodynamics to metabolic regulations, immune responsiveness, and energy distributions. Over the last four decades, new data has transpired regarding the biochemical and molecular compositions, signaling mechanisms, and physiological and pathophysiological functions of NPs and their receptors. NPs are incremented mainly in eliciting natriuretic, diuretic, endocrine, vasodilatory, and neurological activities, along with antiproliferative, antimitogenic, antiinflammatory, and antifibrotic responses. The main locus responsible in the biological and physiological regulatory actions of NPs (ANP and BNP) is the plasma membrane guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA), a member of the growing multi-limbed GC family of receptors. Advances in this field have provided tremendous insights into the critical role of Npr1 (encoding GC-A/NPRA) in the reduction of fluid volume and blood pressure homeostasis, protection against renal and cardiac remodeling, and moderation and mediation of neurological disorders. The generation and use of genetically engineered animals, including gene-targeted (gene-knockout and gene-duplication) and transgenic mutant mouse models has revealed and clarified the varied roles and pleiotropic functions of GC-A/NPRA in vivo in intact animals. This review provides a chronological development of the biochemical, molecular, physiological, and pathophysiological functions of GC-A/NPRA, including signaling pathways, genomics, and gene regulation in both normal and disease states.

Natriuretic Peptides—New Targets for Neurocontrol of Blood Pressure via Baroreflex Afferent Pathway

Natriuretic peptides (NPs) induce vasodilation, natriuresis, and diuresis, counteract the renin–angiotensin–aldosterone system and autonomic nervous system, and are key regulators of cardiovascular volume and pressure homeostasis. Baroreflex afferent pathway is an important reflex loop in the neuroregulation of blood pressure (BP), including nodose ganglion (NG) and nucleus tractus solitarius (NTS). Dysfunction of baroreflex would lead to various hypertensions. Here, we carried out functional experiments to explore the effects of NPs on baroreflex afferent function. Under physiological and hypertensive condition (high-fructose drinking-induced hypertension, HFD), BP was reduced by NPs through NG microinjection and baroreflex sensitivity (BRS) was enhanced via acute intravenous NPs injection. These anti-hypertensive effects were more obvious in female rats with the higher expression of NPs and its receptor A/B (NPRA/NPRB) and lower expression of its receptor C (NPRC). However, these effects were not as obvious as those in HFD rats compared with the same gender control group, which is likely to be explained by the abnormal expression of NPs and NPRs in the hypertensive condition. Our data provide additional evidence showing that NPs play a crucial role in neurocontrol of BP regulation via baroreflex afferent function and may be potential targets for clinical management of metabolic-related hypertension.

Effects of cGMP/Akt/GSK-3β signaling pathway on atrial natriuretic peptide secretion in rabbits with rapid atrial pacing

Atrial natriuretic peptide (ANP) plays a pivotal role in the regulation of the cardiovascular system. The ANP level increases during atrial fibrillation (AF), suggesting that AF may provoke ANP secretion, but its potential mechanism is still unclear. In the present study, the potential mechanisms of rapid atrial pacing (RAP) regulating ANP secretion was explored. Rabbits were subjected to burst RAP, ANP secretion increased whereas cyclic guanosine monophosphate (cGMP) concentrations decreased during RAP. The p-Akt and p-GSK-3β levels decreased in atrial tissues. Natriuretic peptide receptor A (NPR-A) protein and particulate guanylate cyclase (PGC) activity were detected. The sensitivity of NPR-A to ANP decreased, leading to the decrease of PGC activity. Also, the isolated atrial perfusion system were made in the rabbit model, cGMP was shown to inhibit ANP secretion, and the Akt inhibitor LY294002 (LY) and GSK-3β inhibitor SB216763 (SB) attenuated the inhibitory effects of cGMP on ANP secretion and enhanced the inhibitory effects of cGMP on atrial dynamics. In conclusion, NPR-A interacts with ANP to regulate PGC expression, and influence the expression of cGMP during RAP, which involves in the Akt/GSK-3β signaling pathway. From the aforementioned points we conclude that cGMP regulates ANP secretion by the Akt/GSK-3β signaling pathway during atrial pacing.

Moderate Aerobic Training Inhibits Middle-Aged Induced Cardiac Calcineurin-NFAT Signaling by Improving TGF-ß, NPR-A, SERCA2, and TRPC6 in Wistar Rats

OBJECTIVE

The purpose of this study was to investigate the effect of moderate-intensity training on the calcineurin/ nuclear factor of activated t-cells (NFAT) pathway and factors affecting it in the middle-age Wistar rats.

MATERIALS AND METHODS

In this experimental study, 40 young (n=10, 4-month-old) and middle-aged (n=30, 13-15 months old) Wistar rats were included in this experimental study. All young and 10 middle-aged rats did not training and served as a control comparision; while the remaining 20 middle-aged rats were trained at moderate intensity for 4-weeks (n=10) or 8-weeks (n=10) on a treadmill (speed: 16 m/minutes, slope: 0%, distance: 830 m, duration: 54 minutes).

RESULTS

Calcineurin tissue expression was increased in the middle-aged control rats compared to the young control rats (P=0.001). Expression of sarco/endoplasmic reticulum Ca²⁺-ATPase (SERC2A), natriuretic peptide receptor-A (NPR-A), phospholamban (PLB), plasma membrane Ca²⁺ ATPase (PMCA4b), and p-AKT was significantly decreased in the heart tissue of middle-aged control compared to the young control rats (P=0.001). Furthermore, transforming growth factor beta (TGF-β), including transient receptor potential canonical 6 (TRPC6), were up-regulated in the heart tissue of middle-aged control compared to the young control rats (P=0.001). However, aerobic training inhibited this pathway and reversed all changes in the trained middle-aged rats.

CONCLUSION

Aerobic training effectively inhibited the calcineurin/NFATc pathway and modulated intracellular Ca²⁺ levels at least partially by restoring NPR-A, SERCA2, p-PLB, and p-AKT, and decreasing TRPC6 and TGF-β levels.

Blockade of the natriuretic peptide clearance receptor attenuates proteinuria in a mouse model of focal segmental glomerulosclerosis

Glomerular podocytes play a key role in proteinuric diseases. Accumulating evidence suggests that cGMP signaling has podocyte protective effects. The major source of cGMP generation in podocytes is natriuretic peptides. The natriuretic peptide clearance receptor (NPRC) binds and degrades natriuretic peptides. As a result, NPRC inhibits natriuretic peptide-induced cGMP generation. To enhance cGMP generation in podocytes, we blocked natriuretic peptide clearance using the specific NPRC ligand ANP(4-23). We then studied the effects of NPRC blockade in both cultured podocytes and in a mouse transgenic (TG) model of focal segmental glomerulosclerosis (FSGS) created in our laboratory. In this model, a single dose of the podocyte toxin puromycin aminonucleoside (PAN) causes robust albuminuria in TG mice, but only mild disease in non-TG animals. We found that natriuretic peptides protected cultured podocytes from PAN-induced apoptosis, and that ANP(4-23) enhanced natriuretic peptide-induced cGMP generation in vivo. PAN-induced heavy proteinuria in vehicle-treated TG mice, and this increase in albuminuria was reduced by treatment with ANP(4-23). Treatment with ANP(4-23) also reduced the number of mice with glomerular injury and enhanced urinary cGMP excretion, but these differences were not statistically significant. Systolic BP was similar in vehicle and ANP(4-23)-treated mice. These data suggest that: 1. Pharmacologic blockade of NPRC may be useful for treating glomerular diseases such as FSGS, and 2. Treatment outcomes might be improved by optimizing NPRC blockade to inhibit natriuretic peptide clearance more effectively.

Molecular Signaling Mechanisms and Function of Natriuretic Peptide Receptor-A in the Pathophysiology of Cardiovascular Homeostasis

The discovery of atrial, brain, and C-type natriuretic peptides (ANP, BNP, and CNP) and their cognate receptors has greatly increased our knowledge of the control of hypertension and cardiovascular homeostasis. ANP and BNP are potent endogenous hypotensive hormones that elicit natriuretic, diuretic, vasorelaxant, antihypertrophic, antiproliferative, and antiinflammatory effects, largely directed toward the reduction of blood pressure (BP) and cardiovascular diseases (CVDs). The principal receptor involved in the regulatory actions of ANP and BNP is guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA), which produces the intracellular second messenger cGMP. Cellular, biochemical, molecular, genetic, and clinical studies have facilitated understanding of the functional roles of natriuretic peptides (NPs), as well as the functions of their receptors, and signaling mechanisms in CVDs. Transgenic and gene-targeting (gene-knockout and gene-duplication) strategies have produced genetically altered novel mouse models and have advanced our knowledge of the importance of NPs and their receptors at physiological and pathophysiological levels in both normal and disease states. The current review describes the past and recent research on the cellular, molecular, genetic mechanisms and functional roles of the ANP-BNP/NPRA system in the physiology and pathophysiology of cardiovascular homeostasis as well as clinical and diagnostic markers of cardiac disorders and heart failure. However, the therapeutic potentials of NPs and their receptors for the diagnosis and treatment of cardiovascular diseases, including hypertension, heart failure, and stroke have just begun to be expanded. More in-depth investigations are needed in this field to extend the therapeutic use of NPs and their receptors to treat and prevent CVDs.

Atrial Natriuretic Peptide31-67: A Novel Therapeutic Factor for Cardiovascular Diseases

The characterization of the cardiac hormone atrial natriuretic peptide (ANP_99–126), synthesized and secreted predominantly by atrial myocytes under stimulation by mechanical stretch, has established the heart as an endocrine organ with potent natriuretic, diuretic, and vasodilating actions. Three additional distinct polypeptides resulting from proteolytic cleavage of proANP have been identified in the circulation in humans. The mid-sequence proANP fragment 31–67 (also known as proANP_31–67) has unique potent and prolonged diuretic and natriuretic properties. In this review, we report the main effects of this circulating hormone in different tissues and organs, and its mechanisms of actions. We further highlight recent evidence on the cardiorenal protective actions of chronic supplementation of synthetic proANP_31–67 in preclinical models of cardiorenal disease. Finally, we evaluate the use of proANP_31–67 as a new therapeutic strategy to repair end-organ damage secondary to hypertension, diabetes mellitus, renal diseases, obesity, heart failure, and other morbidities that can lead to impaired cardiac function and structure.

Nutrient sensing in Leishmania: Flagellum and cytosol

Parasites are by definition organisms that utilize resources from a host to support their existence, thus, promoting their ability to establish long-term infections and disease. Hence, sensing and acquiring nutrients for which the parasite and host compete is central to the parasitic mode of existence. Leishmania are flagellated kinetoplastid parasites that parasitize phagocytic cells, principally macrophages, of vertebrate hosts and the alimentary tract of sand fly vectors. Because nutritional supplies vary over time within both these hosts and are often restricted in availability, these parasites must sense a plethora of nutrients and respond accordingly. The flagellum has been recognized as an "antenna" that plays a core role in sensing environmental conditions, and various flagellar proteins have been implicated in sensing roles. In addition, these parasites exhibit non-flagellar intracellular mechanisms of nutrient sensing, several of which have been explored. Nonetheless, mechanistic details of these sensory pathways are still sparse and represent a challenging frontier for further experimental exploration.

The therapeutic effect of B-type natriuretic peptides in acute decompensated heart failure

B-type natriuretic peptide (BNP) exhibits roles in natriuresis and diuresis, making it an ideal drug that may aid in diuresing a fluid-overloaded patient with poor or worsening renal function. Several randomized clinical trials have tested the hypothesis that infusions of pharmacological doses of BNP to acute heart failure (HF) patients may enhance decongestion and preserve renal function in this clinical setting. Unfortunately, none of these have demonstrated beneficial outcomes. The current challenge for BNP research in acute HF lies in addressing a failure of concept and a reluctance to abandon an ineffective research model. Future success will necessitate a detailed understanding of the mechanism of action of BNP, as well as better integration of basic and clinical science.

Sacubitril/Valsartan Decreases Cardiac Fibrosis in Left Ventricle Pressure Overload by Restoring PKG Signaling in Cardiac Fibroblasts

Background Heart failure (HF) is invariably accompanied by development of cardiac fibrosis, a form of scarring that increases muscular tissue rigidity and decreases cardiac contractility. Cardiac fibrosis arises from a pathological attempt to repair tissue damaged during maladaptive remodeling. Treatment options to block or reverse fibrosis have proven elusive. Neprilysin is an endopeptidase that degrades vasoactive peptides, including atrial natriuretic peptide. Thus, neprilysin inhibition reduces hypertension, ultimately limiting maladaptive cardiac remodeling. LCZ696, which consists of an angiotensin receptor blocker (valsartan [VAL]) and a neprilysin inhibitor (sacubitril [SAC]), was shown to be well tolerated and significantly reduced the risk of death and hospitalization in HF patients with reduced ejection fraction. We hypothesized that SAC/VAL directly inhibits fibroblast activation and development of pathological fibrosis. Methods and Results We used a mouse model of left ventricle pressure overload coupled to in vitro studies in primary mouse and human cardiac fibroblasts (CFs) to study the impact of SAC/VAL on CF activation and cardiac fibrosis. SAC/VAL significantly ameliorated pressure overload-induced cardiac fibrosis by blocking CF activation and proliferation, leading to functional improvement. Mechanistically, the beneficial impact of SAC/VAL at least partially stemmed from restoration of PKG (protein kinase G) signaling in HF patient-derived CF, which inhibited Rho activation associated with myofibroblast transition. Conclusions This study reveals that SAC/VAL acts directly on CF to prevent maladaptive cardiac fibrosis and dysfunction during pressure overload-induced hypertrophy and suggests that SAC/VAL should be evaluated as a direct antifibrotic therapeutic for conditions such as HF with preserved ejection fraction.

Expression and Secretion of an Atrial Natriuretic Peptide in Beige-Like 3T3-L1 Adipocytes

The browning of white adipose tissue (beige adipocytes) stimulates energy expenditure. Omega-3 fatty acids have been shown to induce thermogenic action in adipocytes via G-protein coupled receptor 120 (GPR120). Atrial natriuretic peptide (ANP) is a peptide hormone that plays the role of maintaining normal blood pressure in kidneys to inhibit Na⁺ reuptake. Recently, ANP was found to induce adipocyte browning by binding to NPR1, an ANP receptor. However, the expression of ANP in adipocytes has not yet been studied. Therefore, in this study, we investigate the expression of ANP in beige-like adipocytes induced by docosahexaenoic acids (DHA), T3, or a PPAR agonist, rosiglitazone. First, we found that brown adipocyte-specific genes were upregulated in beige-like adipocytes. DHA promoted ANP expression in beige-like cells, whereas DHA-induced ANP expression was abolished by GPR120 knockout. ANP secretion of beige-like adipocytes was increased via PKC/ERK1/2 signaling in the GPR120 pathway. Furthermore, ANP secreted from beige-like adipocytes acted on HEK-293 cells, the recipient cells, leading to increased cGMP activity. After the NPR1 knockdown of HEK-293 cells, cGMP activity was not changed. Taken together, our findings indicate that beige-like adipocytes induce ANP secretion, which may contribute to improving obesity-associated metabolic disease.

Pharmacokinetics and intraocular pressure-lowering activity of TAK-639, a novel C-type natriuretic peptide analog, in rabbit, dog, and monkey

TAK-639 is a topical, 9-amino acid, synthetic, C-type natriuretic peptide analog in development for the treatment of primary open-angle glaucoma and ocular hypertension. This study investigated the impact of TAK-639 on intraocular pressure (IOP), the levels of TAK-639 in aqueous humor, and the pharmacokinetic/pharmacodynamic relationship of TAK-639 following topical ocular administration to normotensive female Dutch belted rabbits, beagle dogs, and cynomolgus monkeys. In the IOP studies, rabbits (n = 6/group) and dogs (n = 8/group) received a single topical ocular dose of TAK-639 0.03%, 0.1%, 0.3%, or 0.6% in the right eye and vehicle in the left eye; monkeys (n = 8/group) received TAK-639 0.1%, 0.3%, 0.6%, 0.9%, or 1.2% in the right eye only. IOP was measured pre dose and at various time points from 0.5 to 24 h post dose for rabbits, and 1-48 h post dose for dogs and monkeys. To assess exposure in aqueous humor, another set of animals received a single ocular dose of TAK-639 0.03%, 0.1%, 0.3%, or 0.6% (rabbits, n = 20/group; dogs, n = 14/group) or TAK-639 0.3%, 0.6%, or 1.2% (monkeys, n = 10/group) in both eyes. Aqueous humor and plasma were collected at the same post dose time points at which IOP was measured. Aqueous humor and plasma TAK-639 concentrations were measured by liquid chromatography-mass spectrometry, and pharmacokinetic parameters were estimated with non-compartmental analysis. Topical ocular administration of TAK-639 resulted in a dose-dependent decrease in IOP, with maximum mean decreases in IOP ranging from -8.90% to -34.4% in the rabbit, from -16.5% to -26.4% in the dog, and from -3.43% to -13.5% in the monkey. The duration of the IOP-lowering effect was 12 h in the rabbit and monkey and 48 h in the dog. TAK-639 exposure in aqueous humor (both maximum concentration and area under the curve) was also dose dependent, with maximum concentration ranging from 0.152 to 93.6 ng/mL (0.03% and 0.6% doses, respectively) in rabbits, 0.490-13.8 ng/mL (0.03% and 0.3% doses, respectively) in dogs, and 1.16-18.1 ng/mL (0.3% and 1.2% doses, respectively) in monkeys. The pharmacokinetic/pharmacodynamic profile, when fitted to an inhibitory sigmoidal model, demonstrated that TAK-639 exposure in aqueous humor correlated well with IOP reduction in these species. The TAK-639 exposure in aqueous humor at half maximal IOP reduction (EC₅₀) was lower in monkey and dog than in rabbit (0.2 and 0.4 vs. 2.0 ng/mL, respectively). In plasma, quantifiable concentrations of TAK-639 were low and detectable predominantly at early time points. In conclusion, in rabbit, dog, and monkey, a single topical ocular drop of TAK-639 had a significant IOP-lowering effect that correlated well with increases in TAK-639 levels in aqueous humor and resulted in minimal systemic exposure of TAK-639.

Elevated plasma cyclic guanosine monophosphate may explain greater efferent arteriolar tone in adults with longstanding type 1 diabetes: A brief report

Cyclic guanosine monophosphate (cGMP) influences intrarenal hemodynamics in animal models, but the relationship between cGMP and renal function in adults with type 1 diabetes (T1D) remains unclear. In this study, plasma cGMP correlated with efferent arteriolar resistance, effective renal plasma flow, and renal vascular resistance in adults with T1D.

Hyperlipidemias and Obesity

The organs require oxygen and other types of nutrients (amino acids, sugars, and lipids) to function, the heart consuming large amounts of fatty acids for oxidation and adenosine triphosphate (ATP) generation.

C-Type Natriuretic Peptide Ameliorates Lipopolysaccharide-Induced Cardiac Dysfunction in Rats with Pulmonary Arterial Hypertension

Lipopolysaccharide induces rapid deterioration of cardiac function in rats with pulmonary arterial hypertension. It was desired to investigate if this cardiac dysfunction could be treated by C-type natriuretic peptide. Rat pulmonary arterial hypertension was induced by intraperitoneal injection of monocrotaline. Hemodynamics and cardiac function were measured by pressure-volume (P-V) catheter before and after the rats were treated with lipopolysaccharide and C-type natriuretic peptide. Cyclic guanosine 3',5'-monophosphate (cGMP) level was determined by enzyme-linked immunosorbent assay analysis. After the rats were injected with low-dose lipopolysaccharide, they experienced left ventricle systolic function deterioration. Administration of C-type natriuretic peptide improved hemodynamics and left ventricle systolic function. cGMP level was elevated after C-type natriuretic peptide treatment. C-type natriuretic peptide could ameliorate lipopolysaccharide-induced cardiac dysfunction and restore hemodynamic deterioration in rats with pulmonary arterial hypertension.

Upregulation of Myocardial and Vascular Phosphodiesterase 9A in A Model of Atherosclerotic Cardiovascular Disease

Atherosclerosis is strongly associated with cardiac dysfunction and heart failure. Besides microvascular dysfunction and diminishment of the cardiac nitric oxide-Protein Kinase G (NO-PKG) pathway, recent evidence suggests that phosphodiesterase 9A (PDE9A) enzyme has an unfavorable role in pathological changes. Here, we characterized a rabbit model that shows cardiac dysfunction as a result of an atherogenic diet, and examined the myocardial PDE9A signaling. Rabbits were divided into Control (normal diet) and HC (atherogenic diet) groups. Cardiac function was evaluated by echocardiography. Vascular function was assessed, along with serum biomarkers. Histological stains were conducted, expression of selected proteins and cyclic guanosine monophosphate (cGMP) levels were determined. Signs of diastolic dysfunction were shown in HC animals, along with concentric hypertrophy and interstitial fibrosis. Endothelial function was diminished in HC rabbits, along with marked reduction in the aortic lumen, and increased left ventricle outflow tract (LVOT) pressures. A significant increase was shown in myocardial PDE9A levels in HC animals with unchanged vasodilator-stimulated phosphoprotein (VASP) phosphorylation and cGMP levels. Upregulation of PDE9A may be associated with early stage of cardiac dysfunction in atherosclerotic conditions. Since PDE9A is involved in cGMP degradation and in deactivation of the cardioprotective PKG signaling pathway, it may become an encouraging target for future investigations in atherosclerotic diseases.

Molecular mechanisms underlying the neuroprotective role of atrial natriuretic peptide in experimental acute ischemic stroke

Along with its role in regulating blood pressure and fluid homeostasis, the natriuretic peptide system could be also part of an endogenous protective mechanism against brain damage. We aimed to assess the possibility that exogenous atrial natriuretic peptide (ANP) could protect against acute ischemic stroke, as well as the molecular mechanisms involved. Three groups of rats subjected to transient middle cerebral artery occlusion (tMCAO, intraluminal filament technique, 60 min) received intracerebroventricular vehicle, low-dose ANP (0.5 nmol) or high-dose ANP (2.5 nmol), at 30 min reperfusion. Neurofunctional condition, and brain infarct and edema volumes were measured at 24 h after tMCAO. Apoptotic cell death and expression of natriuretic peptide receptors (NPR-A and NPR-C), K⁺ channels (K_ATP, K_V and BK_Ca), and PI3K/Akt and MAPK/ERK1/2 signaling pathways were analyzed. Significant improvement in neurofunctional status, associated to reduction in infarct and edema volumes, was shown in the high-dose ANP group. As to the molecular mechanisms analyzed, high-dose ANP: 1) reduced caspase-3-mediated apoptosis; 2) did not modify the expression of NPR-A and NPR-C, which had been downregulated by the ischemic insult; 3) induced a significant reversion of ischemia-downregulated K_ATP channel expression; and 4) induced a significant reversion of ischemia-upregulated pERK2/ERK2 expression ratio. In conclusion, ANP exerts a significant protective role in terms of both improvement of neurofunctional status and reduction in infarct volume. Modulation of ANP on some molecular mechanisms involved in ischemia-induced apoptotic cell death (K_ATP channels and MAPK/ERK1/2 signaling pathway) could account, at least in part, for its beneficial effect. Therefore, ANP should be considered as a potential adjunctive neuroprotective agent improving stroke outcome after successful reperfusion interventions.

Molecular and genetic aspects of guanylyl cyclase natriuretic peptide receptor-A in regulation of blood pressure and renal function

Natriuretic peptides (NPs) exert diverse effects on several biological and physiological systems, such as kidney function, neural and endocrine signaling, energy metabolism, and cardiovascular function, playing pivotal roles in the regulation of blood pressure (BP) and cardiac and vascular homeostasis. NPs are collectively known as anti-hypertensive hormones and their main functions are directed toward eliciting natriuretic/diuretic, vasorelaxant, anti-proliferative, anti-inflammatory, and anti-hypertrophic effects, thereby, regulating the fluid volume, BP, and renal and cardiovascular conditions. Interactions of NPs with their cognate receptors display a central role in all aspects of cellular, biochemical, and molecular mechanisms that govern physiology and pathophysiology of BP and cardiovascular events. Among the NPs atrial and brain natriuretic peptides (ANP and BNP) activate guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA) and initiate intracellular signaling. The genetic disruption of Npr1 (encoding GC-A/NPRA) in mice exhibits high BP and hypertensive heart disease that is seen in untreated hypertensive subjects, including high BP and heart failure. There has been a surge of interest in the NPs and their receptors and a wealth of information have emerged in the last four decades, including molecular structure, signaling mechanisms, altered phenotypic characterization of transgenic and gene-targeted animal models, and genetic analyses in humans. The major goal of the present review is to emphasize and summarize the critical findings and recent discoveries regarding the molecular and genetic regulation of NPs, physiological metabolic functions, and the signaling of receptor GC-A/NPRA with emphasis on the BP regulation and renal and cardiovascular disorders.

Immunolocalization of natriuretic peptides and their receptors in goat (Capra hircus) heart

Natriuretic peptides are structurally similar, but genetically distinct, hormones that participate in cardiovascular homeostasis by regulating blood and extracellular fluid volume and blood pressure. We investigated the distribution of natriuretic peptides and their receptors in goat (Capra hircus) heart tissue using the peroxidase-anti-peroxidase (PAP) immunohistochemical method. Strong staining of atrial natriuretic peptide (ANP) was observed in atrial cardiomyocytes, while strong staining for brain natriuretic peptide (BNP) was observed in ventricular cardiomyocytes. Slightly stronger cytoplasmic C-type natriuretic peptide (CNP) immunostaining was detected in the ventricles compared to the atria. Natriuretic peptide receptor-A (NPR-A) immunoreactivity was more prominent in the atria, while natriuretic peptide receptor-B (NPR-B) immunoreactivity was stronger in the ventricles. Cytoplasmic natriuretic peptide receptor-C (NPR-C) immunoreactivity was observed in both the atria and ventricles, although staining was more prominent in the ventricles. ANP immunoreactivity ranged from weak to strong in endothelial and vascular smooth muscle cells. Endothelial cells exhibited moderate to strong BNP immunoreactivity, while vascular smooth cells displayed weak to strong staining. Endothelial cells exhibited weak to strong cytoplasmic CNP immunoreactivity. Vascular smooth muscle cells were labeled moderately to strongly for CNP. Weak to strong cytoplasmic NPR-A immunoreactivity was found in the endothelial cells and vascular smooth muscle cells stained weakly to moderately for NPR-A. Endothelial and vascular smooth cells exhibited weak to strong cytoplasmic NPR-B immunoreactivity. Moderate to strong NPR-C immunoreactivity was observed in the endothelial and smooth muscle cells. Small gender differences in the immunohistochemical distribution of natriuretic peptides and receptors were observed. Our findings suggest that endothelial cells, vascular smooth cells and cardiomyocytes express both natriuretic peptides and their receptors.

Regulation, signalling and functions of hormonal peptides in pulmonary vascular remodelling during hypoxia

Hypoxic state affects organism primarily by decreasing the amount of oxygen reaching the cells and tissues. To adjust with changing environment organism undergoes mechanisms which are necessary for acclimatization to hypoxic stress. Pulmonary vascular remodelling is one such mechanism controlled by hormonal peptides present in blood circulation for acclimatization. Activation of peptides regulates constriction and relaxation of blood vessels of pulmonary and systemic circulation. Thus, understanding of vascular tone maintenance and hypoxic pulmonary vasoconstriction like pathophysiological condition during hypoxia is of prime importance. Endothelin-1 (ET-1), atrial natriuretic peptide (ANP), and renin angiotensin system (RAS) function, their receptor functioning and signalling during hypoxia in different body parts point them as disease markers. In vivo and in vitro studies have helped understanding the mechanism of hormonal peptides for better acclimatization to hypoxic stress and interventions for better management of vascular remodelling in different models like cell, rat, and human is discussed in this review.

A Novel Role for Brain Natriuretic Peptide: Inhibition of IL-1β Secretion via Downregulation of NF-kB/Erk 1/2 and NALP3/ASC/Caspase-1 Activation in Human THP-1 Monocyte

Interleukin-1β (IL-1β) is a pleiotropic cytokine and a crucial mediator of inflammatory and immune responses. IL-1β processing and release are tightly controlled by complex pathways such as NF-kB/ERK1/2, to produce pro-IL-1β, and NALP3/ASC/Caspase-1 inflammasome, to produce the active secreted protein. Dysregulation of both IL-1β and its related pathways is involved in inflammatory/autoimmune disorders and in a wide range of other diseases. Identifying molecules modulating their expression is a crucial need to develop new therapeutic agents. IL-1β is a strong regulator of Brain Natriuretic Peptide (BNP), a hormone involved in cardiovascular homeostasis by guanylyl cyclase Natriuretic Peptide Receptor (NPR-1). An emerging role of BNP in inflammation and immunity, although proposed, remains largely unexplored. Here, we newly demonstrated that, in human THP-1 monocytes, LPS/ATP-induced IL-1β secretion is strongly inhibited by BNP/NPR-1/cGMP axis at all the molecular mechanisms that tightly control its production and release, NF-kB, ERK 1/2, and all the elements of NALP3/ASC/Caspase-1 inflammasome cascade, and that NALP3 inflammasome inhibition is directly related to BNP deregulatory effect on NF-kB/ERK 1/2 activation. Our findings reveal a novel potent anti-inflammatory and immunomodulatory role for BNP and open new alleys of investigation for a possible employment of this endogenous agent in the treatment of inflammatory/immune-related and IL-1β/NF-kB/ERK1/2/NALP3/ASC/Caspase-1-associated diseases.

Atrial natriuretic peptide regulates adipose tissue accumulation in adult atria

The abundance of epicardial adipose tissue (EAT) is associated with atrial fibrillation (AF), the most frequent cardiac arrhythmia. However, both the origin and the factors involved in EAT expansion are unknown. Here, we found that adult human atrial epicardial cells were highly adipogenic through an epithelial-mesenchymal transition both in vitro and in vivo. In a genetic lineage tracing the WT1^CreERT2+/-Rosa^tdT+/- mouse model subjected to a high-fat diet, adipocytes of atrial EAT derived from a subset of epicardial progenitors. Atrial myocardium secretome induces the adipogenic differentiation of adult mesenchymal epicardium-derived cells by modulating the balance between mesenchymal Wingless-type Mouse Mammary Tumor Virus integration site family, member 10B (Wnt10b)/β-catenin and adipogenic ERK/MAPK signaling pathways. The adipogenic property of the atrial secretome was enhanced in AF patients. The atrial natriuretic peptide secreted by atrial myocytes is a major adipogenic factor operating at a low concentration by binding to its natriuretic peptide receptor A (NPRA) receptor and, in turn, by activating a cGMP-dependent pathway. Hence, our data indicate cross-talk between EAT expansion and mechanical function of the atrial myocardium.

Biomarkers for monitoring chemotherapy-induced cardiotoxicity

Cardiotoxicity, including acute and late-onset cardiotoxicity, is a well-known adverse effect of many types of antitumor agents. Early identification of patients with cardiotoxicity is important to ensure prompt treatment and minimize toxic effects. The etiology of chemotherapy-induced cardiotoxicity is multifactorial. Traditional methods for assessment of chemotherapy-induced cardiotoxicity typically involve serial measurements of cardiac function via multi-modality imaging techniques. Typically, however, significant left ventricular dysfunction has already occurred when cardiotoxicity is detected by imaging techniques. Biomarkers, most importantly cardiac natriuretic peptides and troponins, are promising markers for identifying patients potentially at risk for clinical heart failure symptoms. This review summarizes the recent progress in clinical utilization of biomarkers for early diagnosis of acute cardiotoxicity and for prediction of late-onset cardiotoxicity. We also discuss the conflicting results of different studies and the association of results with study design.

Atrial natriuretic peptide down-regulates LPS/ATP-mediated IL-1β release by inhibiting NF-kB, NLRP3 inflammasome and caspase-1 activation in THP-1 cells

Atrial natriuretic peptide (ANP) is an hormone/paracrine/autocrine factor regulating cardiovascular homeostasis by guanylyl cyclase natriuretic peptide receptor (NPR-1). ANP plays an important role also in regulating inflammatory and immune systems by altering macrophages functions and cytokines secretion. Interleukin-1β (IL-1β) is a potent pro-inflammatory cytokine involved in a wide range of biological responses, including the immunological one. Unlike other cytokines, IL-1β production is rigorously controlled. Primarily, NF-kB activation is required to produce pro-IL-1β; subsequently, NALP3 inflammasome/caspase-1 activation is required to cleave pro-IL-1β into the active secreted protein. NALP3 is a molecular platform capable of sensing a large variety of signals and a major player in innate immune defense. Due to their pleiotropism, IL-1β and NALP3 dysregulation is a common feature of a wide range of diseases. Therefore, identifying molecules regulating IL-1β/NALP3/caspase-1 expression is an important step in the development of new potential therapeutic agents. The aim of our study was to evaluate the effect of ANP on IL-1β/NALP3/caspase-1 expression in LPS/ATP-stimulated human THP1 monocytes. We provided new evidence of the direct involvement of ANP/NPR-1/cGMP axis on NF-kB/NALP3/caspase-1-mediated IL-1β release and NF-kB-mediated pro-IL-1β production. In particular, ANP inhibited both NF-kB and NALP3/caspase-1 activation leading to pro- and mature IL-1β down-regulation. Our data, pointing out a modulatory role of this endogenous peptide on IL-1β release and on NF-kB/NALP3/caspase-1 activation, indicate an important anti-inflammatory and immunomodulatory effect of ANP via these mechanisms. We suggest a possible employment of ANP for the treatment of inflammatory/immune-related diseases and IL-1β/NALP3-associated disorders, affecting millions of people worldwide.

Differential expression and regulation of anti-hypertrophic genes Npr1 and Npr2 during β-adrenergic receptor activation-induced hypertrophic growth in rats

We sought to determine the effect of chronic activation of β-adrenergic receptor (β-AR) on the left ventricular (LV) expression profile of Npr1 and Npr2 (coding for NPR-A and NPR-B, respectively) genes, and the functional activity of these receptors in adult Wistar rat hearts. The Npr1 gene expression was markedly reduced (3.5-fold), while the Npr2 gene expression was up regulated (4-fold) in Isoproterenol (ISO)-treated heart as compared with controls. A gradual reduction in NPR-A protein (3-fold), cGMP levels (75%) and a steady increased expression of NPR-B protein (4-fold), were noticed in ISO hearts. Further, in-vitro membranes assay shows that NPR-A dependent guanylyl cyclase (GC) activity was down-regulated (2-fold), whereas NPR-B dependent GC activity was increased (5-fold) in ISO treated hearts. Atenolol treatment normalized the altered expression of Npr1 and Npr2 genes. In conclusion, the chronic β-AR activation differentially regulates Npr1 and Npr2 genes in the heart. Npr1 down regulation is positively associated with the development of left ventricular hypertrophy (LVH) in ISO rats.

Brain natriuretic peptide constitutively downregulates P2X3 receptors by controlling their phosphorylation state and membrane localization

BACKGROUND

ATP-gated P2X3 receptors are important transducers of nociceptive stimuli and are almost exclusively expressed by sensory ganglion neurons. In mouse trigeminal ganglion (TG), P2X3 receptor function is unexpectedly enhanced by pharmacological block of natriuretic peptide receptor-A (NPR-A), outlining a potential inhibitory role of endogenous natriuretic peptides in nociception mediated by P2X3 receptors. Lack of change in P2X3 protein expression indicates a complex modulation whose mechanisms for downregulating P2X3 receptor function remain unclear.

RESULTS

To clarify this process in mouse TG cultures, we suppressed NPR-A signaling with either siRNA of the endogenous agonist BNP, or the NPR-A blocker anantin. Thus, we investigated changes in P2X3 receptor distribution in the lipid raft membrane compartment, their phosphorylation state, as well as their function with patch clamping. Delayed onset of P2X3 desensitization was one mechanism for the anantin-induced enhancement of P2X3 activity. Anantin application caused preferential P2X3 receptor redistribution to the lipid raft compartment and decreased P2X3 serine phosphorylation, two phenomena that were not interdependent. An inhibitor of cGMP-dependent protein kinase and siRNA-mediated knockdown of BNP mimicked the effect of anantin.

CONCLUSIONS

We demonstrated that in mouse trigeminal neurons endogenous BNP acts on NPR-A receptors to determine constitutive depression of P2X3 receptor function. Tonic inhibition of P2X3 receptor activity by BNP/NPR-A/PKG pathways occurs via two distinct mechanisms: P2X3 serine phosphorylation and receptor redistribution to non-raft membrane compartments. This novel mechanism of receptor control might be a target for future studies aiming at decreasing dysregulated P2X3 receptor activity in chronic pain.

Endocytosis and Trafficking of Natriuretic Peptide Receptor-A: Potential Role of Short Sequence Motifs

The targeted endocytosis and redistribution of transmembrane receptors among membrane-bound subcellular organelles are vital for their correct signaling and physiological functions. Membrane receptors committed for internalization and trafficking pathways are sorted into coated vesicles. Cardiac hormones, atrial and brain natriuretic peptides (ANP and BNP) bind to guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA) and elicit the generation of intracellular second messenger cyclic guanosine 3',5'-monophosphate (cGMP), which lowers blood pressure and incidence of heart failure. After ligand binding, the receptor is rapidly internalized, sequestrated, and redistributed into intracellular locations. Thus, NPRA is considered a dynamic cellular macromolecule that traverses different subcellular locations through its lifetime. The utilization of pharmacologic and molecular perturbants has helped in delineating the pathways of endocytosis, trafficking, down-regulation, and degradation of membrane receptors in intact cells. This review describes the investigation of the mechanisms of internalization, trafficking, and redistribution of NPRA compared with other cell surface receptors from the plasma membrane into the cell interior. The roles of different short-signal peptide sequence motifs in the internalization and trafficking of other membrane receptors have been briefly reviewed and their potential significance in the internalization and trafficking of NPRA is discussed.