Atrial natriuretic factor and related peptide hormones

Multilimbed membrane guanylate cyclase signaling system, evolutionary ladder

One monumental discovery in the field of cell biology is the establishment of the membrane guanylate cyclase signal transduction system. Decoding its fundamental, molecular, biochemical, and genetic features revolutionized the processes of developing therapies for diseases of endocrinology, cardio-vasculature, and sensory neurons; lastly, it has started to leave its imprints with the atmospheric carbon dioxide. The membrane guanylate cyclase does so via its multi-limbed structure. The inter-netted limbs throughout the central, sympathetic, and parasympathetic systems perform these functions. They generate their common second messenger, cyclic GMP to affect the physiology. This review describes an historical account of their sequential evolutionary development, their structural components and their mechanisms of interaction. The foundational principles were laid down by the discovery of its first limb, the ACTH modulated signaling pathway (the companion monograph). It challenged two general existing dogmas at the time. First, there was the question of the existence of a membrane guanylate cyclase independent from a soluble form that was heme-regulated. Second, the sole known cyclic AMP three-component-transduction system was modulated by GTP-binding proteins, so there was the question of whether a one-component transduction system could exclusively modulate cyclic GMP in response to the polypeptide hormone, ACTH. The present review moves past the first question and narrates the evolution and complexity of the cyclic GMP signaling pathway. Besides ACTH, there are at least five additional limbs. Each embodies a unique modular design to perform a specific physiological function; exemplified by ATP binding and phosphorylation, Ca²⁺-sensor proteins that either increase or decrease cyclic GMP synthesis, co-expression of antithetical Ca²⁺ sensors, GCAP1 and S100B, and modulation by atmospheric carbon dioxide and temperature. The complexity provided by these various manners of operation enables membrane guanylate cyclase to conduct diverse functions, exemplified by the control over cardiovasculature, sensory neurons and, endocrine systems.

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.

Ligand-Dependent Downregulation of Guanylyl Cyclase/Natriuretic Peptide Receptor-A: Role of miR-128 and miR-195

Cardiac hormones act on the regulation of blood pressure (BP) and cardiovascular homeostasis. These hormones include atrial and brain natriuretic peptides (ANP, BNP) and activate natriuretic peptide receptor-A (NPRA), which enhance natriuresis, diuresis, and vasorelaxation. In this study, we established the ANP-dependent homologous downregulation of NPRA using human embryonic kidney-293 (HEK-293) cells expressing recombinant receptor and MA-10 cells harboring native endogenous NPRA. The prolonged pretreatment of cells with ANP caused a time- and dose-dependent decrease in ¹²⁵I-ANP binding, Guanylyl cyclase (GC) activity of receptor, and intracellular accumulation of cGMP leading to downregulation of NPRA. Treatment with ANP (100 nM) for 12 h led to an 80% decrease in ¹²⁵I-ANP binding to its receptor, and BNP decreased it by 62%. Neither 100 nM c-ANF (truncated ANF) nor C-type natriuretic peptide (CNP) had any effect. ANP (100 nM) treatment also decreased GC activity by 68% and intracellular accumulation cGMP levels by 45%, while the NPRA antagonist A71915 (1 µM) almost completely blocked ANP-dependent downregulation of NPRA. Treatment with the protein kinase G (PKG) stimulator 8-(4-chlorophenylthio)-cGMP (CPT-cGMP) (1 µM) caused a significant increase in ¹²⁵I-ANP binding, whereas the PKG inhibitor KT 5823 (1 µM) potentiated the effect of ANP on the downregulation of NPRA. The transfection of miR-128 significantly reduced NPRA protein levels by threefold compared to control cells. These results suggest that ligand-dependent mechanisms play important roles in the downregulation of NPRA in target cells.

Functional Analysis of Bronchopulmonary Dysplasia-Related Neuropeptides in Preterm Infants and miRNA-Based Diagnostic Model Construction

Background

Bronchopulmonary dysplasia (BPD) has a high mortality rate. This study was aimed at identifying and analysing the risk factors associated with BPD using bioinformatic and mechanical analyses and establishing a predictive model to assess the risk of BPD in preterm infants.

Methods

We identified differentially expressed RNAs via the intersection of miRNAs between datasets. Online analysis tools were used to predict genes targeted by differentially expressed miRNAs (DEmiRNAs) and to generate and visualise competing endogenous RNA (ceRNA) coexpression networks. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were subsequently performed on the DEmiRNAs. In addition, an intersection analysis was performed on mRNA and neuropeptide-related genes in the ceRNA network. DEmiRNAs associated with BPD and those involved in ceRNA networks were used to establish a diagnostic prediction model. The GSE108604 dataset was used as a validation set to verify the model.

Results

A total of 26 DEmiRNAs were identified from the tracheal aspirates (TAs) of patients with BPD and healthy controls. In addition, a total of 1076 DEmRNAs were obtained from the GSE8586 dataset. Functional enrichment analysis of DEmRNAs revealed an abnormal reduction in mitochondrial-related activity and cellular responses to oxidative stress in patients with BPD. The neuropeptide-related genes OPRL1 and NPPA were found to be upregulated in BPD samples. Eventually, hsa-miR-1258, hsa-miR-298, hsa-miR-483-3p, and hsa-miR-769-5p were screened out and used to establish the prediction model. Calibration curves and detrended correspondence analysis (DCA) revealed that the model had good clinical applicability.

Conclusions

The prediction model provided a simple method for individualised assessment, early diagnosis, and prevention of BPD risk in preterm infants.

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.

Gender difference of association between plasma N-terminal pro-atrial natriuretic peptide and metabolic syndrome

PURPOSE

The natriuretic peptides (NPs) system, and mainly atrial natriuretic peptide (ANP), plays a key role in human metabolism and cardiometabolic disorders. Due to differences in NP levels and in prevalence of metabolic syndrome (MetS) between men and women, we aimed to explore the gender difference of association between N-terminal pro-atrial natriuretic peptide (NT-proANP) and MetS in a general population in China.

METHODS

Participants' weight, height, waist circumference, blood pressure, plasma NT-proANP, and other traditional biomarkers were measured. Multivariate logistic regression models were used to determine the association between plasma NT-proANP and MetS, and the odds ratio (OR) and 95% confidence interval (CI) were calculated for men and women, respectively.

RESULTS

Among 2203 participants, 1361 (61.78%) were women, 687(30.77%) participants had MetS, and the average age was 53 years. Women had a higher level of NT-proANP than men. However, adjusted logistic regression demonstrated that men in the upper quartile group of NT-proANP had 0.60 (95% CI 0.39-0.92) times the risk of having MetS, while women in the upper quartile group had 1.10 (95% CI 0.77-1.56) times the risk of having MetS compared to the lower quartile group. Furthermore, with the increase of the level of NT-proANP, the ORs showed a declining trend in men (P = 0.017), but it was not statistically significant among women (P = 0.700).

CONCLUSIONS

There are gender differences in the relationship between NT-proANP and MetS, while an inverse association between plasma NT-proANP and MetS in men suggests that higher levels of NT-proANP may be a protective factor for MetS.

UMBRELLA protocol: systematic reviews of multivariable biomarker prognostic models developed to predict clinical outcomes in patients with heart failure

BACKGROUND

Heart failure (HF) is a chronic and common condition with a rising prevalence, especially in the elderly. Morbidity and mortality rates in people with HF are similar to those with common forms of cancer. Clinical guidelines highlight the need for more detailed prognostic information to optimise treatment and care planning for people with HF. Besides proven prognostic biomarkers and numerous newly developed prognostic models for HF clinical outcomes, no risk stratification models have been adequately established. Through a number of linked systematic reviews, we aim to assess the quality of the existing models with biomarkers in HF and summarise the evidence they present.

METHODS

We will search MEDLINE, EMBASE, Web of Science Core Collection, and the prognostic studies database maintained by the Cochrane Prognosis Methods Group combining sensitive published search filters, with no language restriction, from 1990 onwards. Independent pairs of reviewers will screen and extract data. Eligible studies will be those developing, validating, or updating any prognostic model with biomarkers for clinical outcomes in adults with any type of HF. Data will be extracted using a piloted form that combines published good practice guidelines for critical appraisal, data extraction, and risk of bias assessment of prediction modelling studies. Missing information on predictive performance measures will be sought by contacting authors or estimated from available information when possible. If sufficient high quality and homogeneous data are available, we will meta-analyse the predictive performance of identified models. Sources of between-study heterogeneity will be explored through meta-regression using pre-defined study-level covariates. Results will be reported narratively if study quality is deemed to be low or if the between-study heterogeneity is high. Sensitivity analyses for risk of bias impact will be performed.

DISCUSSION

This project aims to appraise and summarise the methodological conduct and predictive performance of existing clinically homogeneous HF prognostic models in separate systematic reviews.Registration: PROSPERO registration number CRD42019086990.

The Protective Role of Natriuretic Peptide Receptor 2 against High Salt Injury in the Renal Papilla

Mutations in natriuretic peptide receptor 2 (Npr2) gene cause a rare form of short-limbed dwarfism, but its physiological effects have not been well studied. Human and mouse genetic data suggest that Npr2 in the kidney plays a role in salt homeostasis. Herein, we described anatomic changes within renal papilla of Npr2 knockout (Npr2-/-) mice. Dramatic reduction was found in diuresis, and albuminuria was evident after administration of 1% NaCl in drinking water in Npr2-/- and heterozygous (Npr2+/-) mice compared with their wild-type (Npr2+/+) littermates. There was indication of renal epithelial damage accompanied by high numbers of red blood cells and inflammatory cells (macrophage surface glycoproteins binding to galectin-3) and an increase of renal epithelial damage marker (T-cell Ig and mucin domain 1) in Npr2-/- mice. Addition of 1% NaCl tended to increase apoptotic cells (cleaved caspase 3) in the renal papilla of Npr2-/- mice. In vitro, genetic silencing of the Npr2 abolished protective effects of C-type natriuretic peptide, a ligand for Npr2, against death of M-1 kidney epithelial cells exposed to 360 mmol/L NaCl. Finally, significantly lower levels of expression of the NPR2 protein were detected in renal samples of hypertensive compared with normotensive human subjects. Taken together, these findings suggest that Npr2 is essential to protect renal epithelial cells from high concentrations of salt and prevent kidney injury.

Genetic Ablation and Guanylyl Cyclase/Natriuretic Peptide Receptor-A: Impact on the Pathophysiology of Cardiovascular Dysfunction

Mice bearing targeted gene mutations that affect the functions of natriuretic peptides (NPs) and natriuretic peptide receptors (NPRs) have contributed important information on the pathogenesis of hypertension, kidney disease, and cardiovascular dysfunction. Studies of mice having both complete gene disruption and tissue-specific gene ablation have contributed to our understanding of hypertension and cardiovascular disorders. These phenomena are consistent with an oligogenic inheritance in which interactions among a few alleles may account for genetic susceptibility to hypertension, renal insufficiency, and congestive heart failure. In addition to gene knockouts conferring increased risks of hypertension, kidney disorders, and cardiovascular dysfunction, studies of gene duplications have identified mutations that protect against high blood pressure and cardiovascular events, thus generating the notion that certain alleles can confer resistance to hypertension and heart disease. This review focuses on the intriguing phenotypes of Npr1 gene disruption and gene duplication in mice, with emphasis on hypertension and cardiovascular events using mouse models carrying Npr1 gene knockout and/or gene duplication. It also describes how Npr1 gene targeting in mice has contributed to our knowledge of the roles of NPs and NPRs in dose-dependently regulating hypertension and cardiovascular events.

Procholecystokinin expression and processing in cardiac myocytes

The mammalian heart is by now an established endocrine organ whose myocytes in a regulated manner release atrial and ventricular natriuretic peptides (ANP and BNP). But like other hormone-producing cells in classic endocrine organs, the cardiac myocytes also express genes of additional peptide hormones. One such hormone gene is that of the well-known pleiotropic gut-brain peptide system, cholecystokinin (CCK), which is expressed at mRNA and protein levels in both atrial and ventricular cardiac myocytes. The posttranslational processing of proCCK in the myocytes, however, deviates substantially from that of other CCK-producing cells. Hence, the predominant cardiac proCCK product is devoid of the N-terminal 1-24 fragment, and besides O-sulfated at three C-terminal tyrosyl residues (Y₇₆, Y₉₀, and Y₉₂). Moreover, carboxyamidated CCK peptides are present only in very low trace amounts (≤0.1%) in comparison with the truncated and triple-sulfated proCCK fragment. The present review first summarizes present knowledge about the wide-spread expression of the CCK system in mammals, and then discusses the possible function and biomarker role of the specific cardiac proCCK variant. The review concludes that the many unsettled questions about the specific cardiac expression cascade as well as the functional and diagnostic roles of cardiac CCK are worth pursuing.

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.

Biomarkers, myocardial fibrosis and co-morbidities in heart failure with preserved ejection fraction: an overview

The prevalence of heart failure with preserved ejection fraction (HFpEF) is steadily increasing. Its diagnosis remains difficult and controversial and relies mostly on non-invasive echocardiographic detection of left ventricular diastolic dysfunction and elevated filling pressures. The large phenotypic heterogeneity of HFpEF from pathophysiologic al underpinnings to clinical manifestations presents a major obstacle to the development of new therapies targeted towards specific HF phenotypes. Recent studies suggest that natriuretic peptides have the potential to improve the diagnosis of early HFpEF, but they still have significant limitations, and the cut-off points for diagnosis and prognosis in HFpEF remain open to debate. The purpose of this review is to present potential targets of intervention in patients with HFpEF, starting with myocardial fibrosis and methods of its detection. In addition, co-morbidities are discussed as a means to treat HFpEF according to cut-points of biomarkers that are different from usual. Biomarkers and approaches to co-morbidities may be able to tailor therapies according to patients' pathophysiological needs. Recently, soluble source of tumorigenicity 2 (sST2), growth differentiation factor 15 (GDF-15), galectin-3, and other cardiac markers have emerged, but evidence from large cohorts is still lacking. Furthermore, the field of miRNA is a very promising area of research, and further exploration of miRNA may offer diagnostic and prognostic applications and insight into the pathology, pointing to new phenotype-specific therapeutic targets.

Midregional proatrial natriuretic peptide improves risk stratification after ischemic stroke

Objective

To validate midregional proatrial natriuretic peptide (MR-proANP) for outcome prediction and diagnosis of cardioembolic stroke etiology compared to established clinical variables.

Methods

In this prospective multicenter cohort study, we quantified MR-proANP levels in ischemic stroke patients within 24 hours of onset. Primary outcome measures were 90-day mortality, unfavorable functional outcome (modified Rankin Scale score >2), and cardioembolic stroke etiology diagnosed during hospitalization.

Results

Of 788 included patients, 783 completed their 90-day follow-up, and 118 patients (15%) died. After full adjustment, MR-proANP levels were associated with 90-day mortality (adjusted hazard ratio 6.12, 95% confidence interval [CI] 2.36–15.84, p = 0.01) and functional outcome (adjusted odds ratio [aOR] 2.46, 95% CI 1.05–5.74, p = 0.038). For mortality prediction, adding MR-proANP to the regression model increased its discriminatory accuracy, and the continuous net reclassification index (cNRI) was 49% (95% CI 26%–78%, p < 0.001). For functional outcome, there was no significant improvement in discrimination or reclassification. Cardioembolic stroke etiology and the diagnosis of atrial fibrillation at hospital discharge were associated with MR-proANP with an aOR of 2.10 (95% CI 1.11–3.97, p = 0.02) and 18.35 (95% CI 7.94–42.45, p < 0.001), respectively. The cNRI of MR-proANP for cardioembolic stroke etiology was not significant, as opposed to atrial fibrillation (78%, 95% CI 60%–89%, p < 0.001). MR-proANP levels ≥289 pmol/L had a specificity of 86% and sensitivity of 48% for the diagnosis of atrial fibrillation.

Conclusion

MR-proANP is a newly validated blood biomarker providing additional prognostic information for mortality after stroke. Higher MR-proANP levels were associated with cardioembolic stroke etiology and, even more strongly, atrial fibrillation.

Association between plasma proANP and hyperuricemia in Chinese Han women: a cross-sectional study

Background:

Association between pro-atrial natriuretic peptide (proANP) and hyperuricemia has not yet been investigated in population. This study aimed to examine the association in Chinese Han women.

Methods:

We measured plasma proANP, serum uric acid, and other traditional biomarkers in 1360 women older than 30 years residing in the Gusu district of Suzhou City. Association between plasma proANP and hyperuricemia was analyzed in women aged ≥45 years and those aged <45 years, respectively.

Results:

In women aged ≥45 years, the odds ratio (OR) [95% confidence interval (CI)] of hyperuricemia with high proANP (over the median) was 0.57 (0.34–0.97) compared to those with low proANP (p=0.040). After adjustment for age and other potential covariates, a high plasma proANP was associated with a decreased risk of hyperuricemia in women aged ≥45 years (OR 0.40; 95% CI, 0.19–0.84), when the highest and lowest categories were compared. In contrast, there was no association between plasma proANP and hyperuricemia in women aged <45 years. We did not observe a significant interaction between age and proANP (pinteraction=0.113). Sensitivity analyses further confirmed these age-specific findings.

Conclusions:

Plasma proANP was significantly and inversely associated with hyperuricemia in Chinese Han women aged ≥45 years. This study suggests that an increased plasma proANP should be a protective factor of hyperuricemia among middle-aged and old women.

Plasma proANP1-98 levels are positively associated with central obesity: A cross-sectional study in a general population of China

BACKGROUND

Atrial natriuretic peptide (ANP) and its prohormone activating enzyme are associated with central obesity, suggesting there may be a potential relationship between proANP_1-98 and central obesity. However, the association is still lack of population-based evidence. We explored the association in a general population of China.

METHODS

We measured plasma proANP_1-98, waist circumference and other traditional biomarkers in 2203 participants aged≥30y. Multivariate logistic regression models were used to determine the association between plasma proANP_1-98 and central obesity, and odds ratio (OR) and 95% confidence interval (CI) were calculated.

RESULTS

High proANP_1-98 was significantly associated with increased risk of central obesity in participants, and the multivariate adjusted OR (95% CI) of central obesity associated with the second, third and fourth quartiles of proANP_1-98 were 1.33 (1.03-1.72), 1.69 (1.31-2.19) and 1.76 (1.35-2.29), respectively, compared with the lowest quartile of proANP_1-98. There was a dose-response relationship between proANP_1-98 and risk of central obesity among the participants (P_trend<0.001). Sensitivity analyses further confirmed these associations. Adding proANP_1-98 to a model containing conventional risk factors improved discriminatory power of central obesity (as shown by significant improvement in continuous NRI and IDI).

CONCLUSIONS

Contrary to known reduced ANP levels in central obesity, we found that plasma proANP_1-98 was positively associated with central obesity, suggesting that elevated plasma proANP_1-98 may be a marker or a risk factor for central obesity.

Discovery and dimeric approach of novel Natriuretic Peptide Receptor A (NPR-A) agonists

Novel agonists of the Natriuretic Peptide Receptor A (NPR-A) were obtained through random screening and subsequent structural modification of triazine derivatives. The key structural feature to improve in vitro activity was the dimerization of triazine monomer derivatives. The non peptide derivative 7c and 13a showed highly potent NPR-A agonistic activity in vitro and diuretic activity in vivo. These results implied that non-peptidic small molecules open the possibility of new therapy for congestive heart failure.

Misexpression of Tbx18 in cardiac chambers of fetal mice interferes with chamber-specific developmental programs but does not induce a pacemaker-like gene signature

Initiation of cardiac excitation depends on a specialized group of cardiomyocytes at the venous pole of the heart, the sinoatrial node (SAN). The T-box transcription factor gene Tbx18 is expressed in the SAN myocardium and is required for formation of a large portion of the pacemaker. Previous studies suggested that Tbx18 is also sufficient to reprogram ventricular cardiomyocytes into SAN cells in rat, guinea-pig and pig hearts. To evaluate the consequences of misexpression of Tbx18 for imposing a nodal phenotype onto chamber myocardial cells in fetal mice, we used two independent conditional approaches with chamber-specific cre driver lines and an Hprt(Tbx18) misexpression allele. Myh6-Cre/+;Hprt(Tbx18/y) mice developed dilated atria with thickened walls, reduced right ventricles and septal defects that resulted in reduced embryonic and post-natal survival. Tagln-Cre/+;Hprt(Tbx18/y) mice exhibited slightly smaller hearts with rounded trabeculae that supported normal embryonic survival. Molecular analyses showed that the SAN gap junction and ion channel profile was not ectopically induced in chamber myocardium but the working myocardial gene program was partially inhibited in atria and ventricles of both misexpression models. Left atrial expression of Pitx2 was strongly repressed in Myh6-Cre/+;Hprt(Tbx18/y) embryos. We conclude that exclusion of Tbx18 expression from the developing atria and (right) ventricle is important to achieve normal cardiac left-right patterning and myocardial differentiation, and that Tbx18 is not sufficient to induce full SAN differentiation of chamber cardiomyocytes in fetal mice.

Role of FQQI motif in the internalization, trafficking, and signaling of guanylyl-cyclase/natriuretic peptide receptor-A in cultured murine mesangial cells

Binding of the cardiac hormone atrial natriuretic peptide (ANP) to transmembrane guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA), produces the intracellular second messenger cGMP in target cells. To delineate the critical role of an endocytic signal in intracellular sorting of the receptor, we have identified a FQQI (Phe(790), Gln(791), Gln(792), and Ile(793)) motif in the carboxyl-terminal region of NPRA. Mouse mesangial cells (MMCs) were transiently transfected with the enhanced green fluorescence protein (eGFP)-tagged wild-type (WT) and mutant constructs of eGFP-NPRA. The mutation FQQI/AAAA, in the eGFP-NPRA cDNA sequence, markedly attenuated the internalization of mutant receptors by almost 49% compared with the WT receptor. Interestingly, we show that the μ1B subunit of adaptor protein-1 binds directly to a phenylalanine-based FQQI motif in the cytoplasmic tail of the receptor. However, subcellular trafficking indicated that immunofluorescence colocalization of the mutated receptor with early endosome antigen-1 (EEA-1), lysosome-associated membrane protein-1 (LAMP-1), and Rab 11 marker was decreased by 57% in early endosomes, 48% in lysosomes, and 42% in recycling endosomes, respectively, compared with the WT receptor in MMCs. The receptor containing the mutated motif (FQQI/AAAA) also produced a significantly decreased level of intracellular cGMP during subcellular trafficking than the WT receptor. The coimmunoprecipitation assay confirmed a decreased level of colocalization of the mutant receptor with subcellular compartments during endocytic processes. The results suggest that the FQQI motif is essential for the internalization and subcellular trafficking of NPRA during the hormone signaling process in intact MMCs.

Effect of natriuretic peptides on cerebral artery blood flow in healthy volunteers

The natriuretic peptides (NPs), atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP), have vasoactive functions that concern humans and most animals, but their specific effects on cerebral circulation are poorly understood. We therefore examined the responsiveness of cerebral arteries to different doses of the natriuretic peptides in animals and humans. We conducted a dose-response experiment in guinea pigs (in vitro) and a double-blind, three-way cross-over study in healthy volunteers (in vivo). In the animal experiment, we administered cumulative doses of NPs to pre-contracted segments of cerebral arteries. In the main study, six healthy volunteers were randomly allocated to receive two intravenous doses of ANP, BNP or CNP, respectively, over 20 min on three separate study days. We recorded blood flow velocity in the middle cerebral artery (VMCA) by transcranial Doppler. In addition, we measured temporal and radial artery diameters, headache response and plasma concentrations of the NPs. In guinea pigs, ANP and BNP but not CNP showed significant dose-dependent relaxation of cerebral arteries. In healthy humans, NP infusion had no effect on mean VMCA, and we found no difference in hemodynamic responses between the NPs. Furthermore, natriuretic peptides did not affect temporal and radial artery diameters or induce headache. In conclusion, natriuretic peptides in physiological and pharmacological doses do not affect blood flow velocity in the middle cerebral artery or dilate extracerebral arteries in healthy volunteers.

New medical therapies for heart failure

Heart failure (HF) can rightfully be called the epidemic of the 21(st) century. Historically, the only available medical treatment options for HF have been diuretics and digoxin, but the capacity of these agents to alter outcomes has been brought into question by the scrutiny of modern clinical trials. In the past 4 decades, neurohormonal blockers have been introduced into clinical practice, leading to marked reductions in morbidity and mortality in chronic HF with reduced left ventricular ejection fraction (LVEF). Despite these major advances in pharmacotherapy, our understanding of the underlying disease mechanisms of HF from epidemiological, clinical, pathophysiological, molecular, and genetic standpoints remains incomplete. This knowledge gap is particularly evident with respect to acute decompensated HF and HF with normal (preserved) LVEF. For these clinical phenotypes, no drug has been shown to reduce long-term clinical event rates substantially. Ongoing developments in the pharmacotherapy of HF are likely to challenge our current best-practice algorithms. Novel agents for HF therapy include dual-acting neurohormonal modulators, contractility-enhancing agents, vasoactive and anti-inflammatory peptides, and myocardial protectants. These novel compounds have the potential to enhance our armamentarium of HF therapeutics.

Subcellular trafficking of guanylyl cyclase/natriuretic peptide receptor-A with concurrent generation of intracellular cGMP

Atrial natriuretic peptide (ANP) modulates blood pressure and fluid volume by activation of natriuretic peptide receptor-A (NPRA). Immunofluorescence (IF) studies reveal that NPRA is internalized and redistributed into subcellular compartments with concurrent production of cGMP.

Atrial natriuretic peptide (ANP) activates guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA), which lowers blood pressure and blood volume. The objective of the present study was to visualize internalization and trafficking of enhanced GFP (eGFP)-tagged NPRA (eGFP–NPRA) in human embryonic kidney-293 (HEK-293) cells, using immunofluorescence (IF) and co-immunoprecipitation (co-IP) of eGFP–NPRA. Treatment of cells with ANP initiated rapid internalization and co-localization of the receptor with early endosome antigen-1 (EEA-1), which was highest at 5 min and gradually decreased within 30 min. Similarly, co-localization of the receptor was observed with lysosome-associated membrane protein-1 (LAMP-1); however, after treatment with lysosomotropic agents, intracellular accumulation of the receptor gradually increased within 30 min. Co-IP assays confirmed that the localization of internalized receptors occurred with subcellular organelles during the endocytosis of NPRA. Rab 11, which was used as a recycling endosome (Re) marker, indicated that ∼20% of receptors recycled back to the plasma membrane. ANP-treated cells showed a marked increase in the IF of cGMP, whereas receptor was still trafficking into the intracellular compartments. Thus, after ligand binding, NPRA is rapidly internalized and trafficked from the cell surface into endosomes, Res and lysosomes, with concurrent generation of intracellular cGMP.

Regional heterogeneity of expression of renal NPRs, TonEBP, and AQP-2 mRNAs in rats with acute kidney injury

To understand the pathophysiology of ischemia/reperfusion (I/R) - induced acute kidney injury (AKI), the present study defined changes in renal function, plasma renotropic hormones and its receptors in the kidney 2, 5, or 7 days after 45 min-renal ischemia in rats. Blood urea nitrogen, plasma creatinine, and osmolarity increased 2 days after I/R injury and tended to return to control level 7 days after I/R injury. Decreased renal function tended to return to control level 5 days after I/R injury. However, plasma concentrations of atrial natriuretic peptide and renin did not change. In control kidney, natriuretic peptide receptor (NPR)-A, -B and -C mRNAs were highly expressed in medulla (ME), inner cortex (IC), and outer cortex (OC), respectively, and tonicity-responsive enhancer binding protein (TonEBP), auqaporin-2 (AQP-2) and eNOS mRNAs were highly expressed in ME. NPR-A and -B mRNA expressions were markedly decreased 2 days after I/R injury. On 5 days after I/R injury, NPR-A mRNA expression increased in OC and recovered to control level in IC but not in ME. NPR-B mRNA expression was increased in OC, and recovered to control level in IC and ME. NPR-C mRNA expression was markedly decreased in OC 2 and 5 days after I/R injury. TonEBP, APQ-2 and eNOS mRNA expressions were markedly decreased 2 days after I/R injury and did not recover in ME 7 days after I/R injury. Therefore, we suggest that there is a regional heterogeneity of regulation of renal NPRs, TonEBP, and APQ-2 mRNA in AKI.

Systemic, but not cardiomyocyte-specific, deletion of the natriuretic peptide receptor guanylyl cyclase A increases cardiomyocyte number in neonatal mice

Guanylyl cyclase A (GC-A), the receptor for atrial and B-type natriuretic peptides, is implicated in the regulation of blood pressure and cardiac growth. We used design-based stereological methods to examine the effect of GC-A inactivation on cardiomyocyte volume, number and subcellular composition in postnatal mice at day P2. In mice with global, systemic GC-A deletion, the cardiomyocyte number was significantly increased, demonstrating that hyperplasia is the main cause for the increase in ventricle weight in these early postnatal animals. In contrast, conditional, cardiomyocyte-restricted inactivation of GC-A had no significant effect on ventricle weight or cardiomyocyte number. The mean volume of cardiomyocytes and the myocyte-related volumes of the four major cell organelles (myofibrils, mitochondria, nuclei and sarcoplasm) were similar between genotypes. Taken together, systemic GC-A deficiency induces cardiac enlargement based on a higher number of normally composed and sized cardiomyocytes early after birth, whereas cardiomyocyte-specific GC-A abrogation is not sufficient to induce cardiac enlargement and has no effect on number, size and composition of cardiomyocytes. We conclude that postnatal cardiac hyperplasia in mice with global GC-A inactivation is provoked by systemic alterations, e.g., arterial hypertension. Direct GC-A-mediated effects in cardiomyocytes seem not to be involved in the regulation of myocyte proliferation at this early stage.

Increased plasma concentrations of midregional proatrial natriuretic Peptide is associated with risk of cardiorenal dysfunction in type 1 diabetes

BACKGROUND

To examine possible associations between midregional proatrial natriuretic peptide (MR-proANP) and diabetic complications at baseline and risk of mortality and end-stage renal disease (ESRD) during follow-up in type 1 diabetes.

METHODS

Observational study including 667 patients, with plasma MR-proANP measured at baseline. Complications were defined as micro- (n = 168) or macroalbuminuria (n = 190) (urinary albumin excretion rate (UAER) 30-299 or ≥ 300 mg/24h), previous cardiovascular disease (CVD) (n = 143), cardiac autonomic dysfunction (heart rate variability < 11 beats/min) (n = 369), and retinopathy (n = 523). Adjustments included gender, age, systolic blood pressure, estimated glomerular filtration rate (eGFR), UAER, HbA1c, total cholesterol, 24-hour urinary sodium excretion (24h-U(Na)), body mass index, daily insulin dose, antihypertensive treatment, and smoking in linear regression analyses and analysis of covariance models. Development of ESRD (dialysis, renal transplantation, or GFR/eGFR < 15 ml/min/1.73 m(2)) and mortality was recorded through national registers.

RESULTS

The cohort included 293 (44%) females, aged 55 ± 13 years. Plasma MR-proANP (median (interquartile)) was 74.7 (49.2-116.8) pmol/L. Adjusted, MR-proANP correlated positively with age and UAER and negatively with eGFR, 24h-U(Na), total cholesterol, and HbA1c (P < 0.05). Moreover, MR-proANP levels increased with albuminuria degree and were higher in patients with previous CVD (P ≤ 0.001), but similar in patients with or without autonomic dysfunction or retinopathy (P ≥ 0.076). During follow-up (3.5 (3.1-4.0) years), higher MR-proANP concentrations predicted ESRD and mortality combined (n = 35) adjusted for gender, age, systolic blood pressure, eGFR, and previous CVD (hazard ratio per 1SD increase in logANP: 2.8 (1.6-4.7; P < 0.001)).

CONCLUSIONS

Increased plasma MR-proANP was associated with impaired renal function, increased albuminuria, and previous CVD. Moreover, MR-proANP concentrations were associated with increased risk of development of ESRD and mortality combined during follow-up.

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

Thus far, three related natriuretic peptides (NPs) and three distinct sub-types of cognate NP receptors have been identified and characterized based on the specific ligand binding affinities, guanylyl cyclase activity, and generation of intracellular cGMP. Atrial and brain natriuretic peptides (ANP and BNP) specifically bind and activate guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA), and C-type natriuretic peptide (CNP) shows specificity to activate guanylyl cyclase/natriuretic peptide receptor-B (GC-B/NPRB). All three NPs bind to natriuretic peptide receptor-C (NPRC), which is also known as clearance or silent receptor. The NPRA is considered the principal biologically active receptor of NP family; however, the molecular signaling mechanisms of NP receptors are not well understood. The activation of NPRA and NPRB produces the intracellular second messenger cGMP, which serves as the major signaling molecule of all three NPs. The activation of NPRB in response to CNP also produces the intracellular cGMP; however, at lower magnitude than that of NPRA, which is activated by ANP and BNP. In addition to enhanced accumulation of intracellular cGMP in response to all three NPs, the levels of cAMP, Ca²⁺ and inositol triphosphate (IP₃) have also been reported to be altered in different cells and tissue types. Interestingly, ANP has been found to lower the concentrations of cAMP, Ca²⁺, and IP₃; however, NPRC has been proposed to increase the levels of these metabolic signaling molecules. The mechanistic studies of decreased and/or increased levels of cAMP, Ca²⁺, and IP₃ in response to NPs and their receptors have not yet been clearly established. This review focuses on the signaling mechanisms of ANP/NPRA and their biological effects involving an increased level of intracellular accumulation of cGMP and a decreased level of cAMP, Ca²⁺, and IP₃ in different cells and tissue systems.

Porcine natriuretic peptide type B (pNPPB) maintains mouse oocyte meiotic arrest via natriuretic peptide receptor 2 (NPR2) in cumulus cells

In mouse ovarian follicles, the oocyte is maintained in meiotic prophase arrest by natriuretic peptide type C (NPPC) acting via its cognate receptor, natriuretic peptide receptor 2 (NPR2). As there is a marked species difference in the receptor selectivity of the natriuretic peptide family, this study examined the functional effect of other natriuretic peptides, type A (NPPA) and type B (NPPB), acting via NPR2 on mouse-oocyte meiotic arrest. The results by quantitative, reverse-transcriptase PCR showed that Npr2 was the predominant natriuretic peptide receptor transcript, and that Npr1 and Npr3 mRNA levels were negligible in cumulus cells isolated from equine chorionic gonadotropin (eCG)-primed, immature female mice. While NPPA and NPPB from human and rat had no effect on oocyte maturation, porcine NPPB (pNPPB) maintained oocyte meiotic arrest in a dose-dependent manner. Furthermore, pNPPB-mediated meiotic arrest and cGMP production could be completely blocked by the NPR2 inhibitor sphingosine-1-phosphate (S1P). Neither the NPR1 antagonist anantin or Npr1 knockout had an effect on pNPPB-mediated meiotic arrest. Thus, pNPPB can functionally maintain mouse-oocyte meiotic arrest by the receptor NPR2 of cumulus cells. These findings demonstrate that pNPPB may be used as a probe to identify the essential amino acid sequences for activation of NPR2.

Psychosocial correlates of atrial natriuretic peptide: a marker of vascular health

BACKGROUND

Psychosocial factors have been associated with cardiovascular outcomes, but few studies have examined the association between psychosocial function and natriuretic peptides.

PURPOSE

The purpose of this study is to determine the predictive value of hostility, anger, and social support in relation to atrial natriuretic peptide (ANP), a marker of vascular health, among middle-aged men.

METHODS

One hundred twenty-one men (mean age = 39.8 years, SD = 4.1) underwent assessments of ANP and completed the Cook-Medley Hostility Scale, the Spielberger State-Trait Anger Scale, and the Interview Schedule for Social Interaction.

RESULTS

Higher levels of hostility (β = 0.22 [95 % CI 0.04, 0.40], P = 0.032) and trait anger (β = 0.18 [95 % CI 0.01, 0.37], P = 0.044) were associated with greater ANP levels. In contrast, higher perceived social support was also associated with lower ANP levels, (β = -0.19 [95 % CI -0.05, -0.41], P = 0.010).

CONCLUSIONS

Psychosocial factors, including hostility, anger, and social support, are associated with varying ANP levels among middle-aged men, independent of cardiovascular and behavioral risk factors.

The heart in obesity-hypertension

There is growing recognition that obesity is reaching epidemic proportions throughout the world. In adults, obesity is associated with increased cardiovascular morbidity and mortality. A series of endocrine, metabolic and hemodynamic mechanisms have been responsible for the development of obesity-hypertension. These mechanisms include: a suppressed biologic activity and availability of natriuretic peptide, increased sympathetic adrenergic activity, release of angiotensin ll from adipocytes and activation of the renin-angiotensin-aldosterone system, leptin resistance, chronic hyperleptinemia and hyperinsulinemia. The systemic hemodynamic profile of obesity includes high intravascular volume, increased cardiac output and inappropriately normal peripheral resistance. The cardiovascular adaptations to these changes include changes in vascular responsiveness and concentric-eccentric left ventricular hypertrophy, and may be responsible for increased risk of congestive heart failure, arrhythmia and sudden death.

Plasma membrane guanylate cyclase is a multimodule transduction system

This minireview highlights the studies which suggest that guanylate cyclase is a single-component transducing system, containing distinct signaling modules in a single membrane-spanning protein. A guanylate cyclase signaling model is proposed which envisions the following sequential events: (1) a signal is initiated by the binding of the hormone to the ligand binding module; (2) the signal is potentiated by ATP at ARM; and (3) the amplified signal is finally transduced at the catalytic site. All of these signaling steps together constitute a switch, which when turned on, generates the second messenger cyclic GMP.

Biomarkers and diagnostics in heart failure

Heart failure (HF) biomarkers have dramatically impacted the way HF patients are evaluated and managed. B-type natriuretic peptide (BNP) and N-terminal proBNP (NT-proBNP) are the gold standard biomarkers in determining the diagnosis and prognosis of HF, and studies on natriuretic peptide-guided HF management look promising. An array of additional biomarkers has emerged, each reflecting different pathophysiological processes in the development and progression of HF: myocardial insult, inflammation and remodeling. Novel biomarkers, such as mid-regional pro atrial natriuretic peptide (MR-proANP), mid-regional pro adrenomedullin (MR-proADM), highly sensitive troponins, soluble ST2 (sST2), growth differentiation factor (GDF)-15 and Galectin-3, show potential in determining prognosis beyond the established natriuretic peptides, but their role in the clinical care of the patient is still partially defined and more studies are needed. This article is part of a Special Issue entitled: Heart failure pathogenesis and emerging diagnostic and therapeutic interventions.

Emerging Roles of Natriuretic Peptides and their Receptors in Pathophysiology of Hypertension and Cardiovascular Regulation

Thus far, three related natriuretic peptides (NPs) and three distinct receptors have been identified, which have advanced our knowledge towards understanding the control of high blood pressure, hypertension, and cardiovascular disorders to a great extent. Biochemical and molecular studies have been advanced to examine receptor function and signaling mechanisms and the role of second messenger cGMP in pathophysiology of hypertension, renal hemodynamics, and cardiovascular functions. The development of gene-knockout and gene-duplication mouse models along with transgenic mice have provided a framework for understanding the importance of the antagonistic actions of natriuretic peptides receptor in cardiovascular events at the molecular level. Now, NPs are considered as circulating markers of congestive heart failure, however, their therapeutic potential for the treatment of cardiovascular diseases such as hypertension, renal insufficiency, cardiac hypertrophy, congestive heart failure, and stroke has just begun to unfold. Indeed, the alternative avenues of investigations in this important are need to be undertaken, as we are at the initial stage of the molecular therapeutic and pharmacogenomic implications.

Treatment of Obese Female and MaleSHHF/Mcc-facpRats with Antihypertensive Drugs, Nifedipine and Enalapril: Effects on Body Weight, Fat Distribution, Insulin Resistance and Systolic Pressure

Little is known about the effects of common antihypertensive drugs in obese, insulin-resistant females. Nine-month-old obese female SHHF/Mcc-fa(cp) rats that received either nifedipine, a calcium channel antagonist, or enalapril, an angiotensin-converting-enzyme inhibitor, for three months were compared with untreated SHHF/Mcc-fa(cp) rats (controls). After one month, nifedipine significantly decreased body weight in obese females compared to either enalapril or controls. After three months of treatment, total, abdominal, and subcutaneous fat masses were decreased in obese females given nifedipine compared to either enalapril or controls. Enalapril treatment was associated with a redistribution of fat mass from abdominal to subcutaneous depots. Nifedipine reduced plasma triglyceride and fasting glucose levels and improved insulin response to an oral glucose load in obese females, whereas enalapril did not appear to affect glycemic control. Systolic pressure was not significantly decreased until after two months of treatment with nifedipine or three months of treatment with enalapril in obese females and may have coincided with improvement in insulin-resistance. Similarly, plasma atrial natriuretic peptide concentrations were significantly lower in obese females given nifedipine. To determine how obese males responded to a calcium channel antagonist, six-month-old obese male SHHF/Mcc-fa(cp) rats were treated for three months with either nifedipine or placebo (controls). Nifedipine-treated obese males showed a mild but significant decrease in weight gain that was due to a decrease in fat deposition in both subcutaneous and abdominal depots and systolic blood pressure was significantly reduced after one month of treatment. Nifedipine did not affect other plasma biochemical parameters in obese males. In conclusion, nifedipine improved systolic pressure and glycemic control in obese female SHHF/Mcc-fa(cp) rats, effects that may be associated with a marked loss in body weight and fat mass and improved lipid metabolism. Nifedipine-treated obese males exhibited only a diminished weight gain that was not associated with changes in diabetic characteristics.

Guanylyl cyclase/natriuretic peptide receptor-A signaling antagonizes the vascular endothelial growth factor-stimulated MAPKs and downstream effectors AP-1 and CREB in mouse mesangial cells

Along with its natriuretic, diuretic, and vasodilatory properties, atrial natriuretic peptide (ANP), and its guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA) exhibit an inhibitory effect on cell growth and proliferation. However, the signaling pathways mediating this inhibition are not well understood. The objective of this study was to determine the effect of ANP-NPRA system on mitogen-activated protein kinases (MAPKs) and the downstream proliferative transcription factors involving activating protein-1 (AP-1) and cAMP-response element binding protein (CREB) in agonist-stimulated mouse mesangial cells (MMCs). We found that ANP inhibited vascular endothelial growth factor (VEGF)-stimulated phosphorylation of MAPKs (Erk1, Erk2, JNK, and p38), to a greater extent in NPRA-transfected cells (50-60 %) relative to vector-transfected cells (25-30 %). The analyses of the phosphorylated transcription factors revealed that ANP inhibited VEGF-stimulated activation of CREB, and the AP-1 subunits (c-jun and c-fos). Gel shift assays demonstrated that ANP inhibited VEGF-stimulated AP-1 and CREB DNA-binding ability by 67 and 62 %, respectively. The addition of the protein kinase G (PKG) inhibitor, KT-5823, restored the VEGF-stimulated activation of MAPKs, AP-1, and CREB, demonstrating the integral role of cGMP/PKG signaling in NPRA-mediated effects. Our results delineate the underlying mechanisms through which ANP-NPRA system exerts an inhibitory effect on MAPKs and down-stream effector molecules, AP-1, and CREB, critical for cell growth and proliferation.

Hormonal control of mammalian oocyte meiosis at diplotene stage

Mammalian oocytes grow and undergo meiosis within ovarian follicles. Fully grown oocytes are arrested at the first meiotic prophase by a mural granulosa origin "arrester" until a surge of luteinizing hormone (LH) from the pituitary at the mid-cycle stimulates the immature oocyte to resume meiosis. Recent evidence indicates that natriuretic peptide precursor type C (NPPC) produced by mural granulosa cells stimulates the generation of cyclic guanosine 3',5'-monophosphate (cGMP) by cumulus cell natriuretic peptide receptor 2 (NPR2), which diffuses into oocyte via gap junctions and inhibits oocyte phosphodiesterase 3A (PDE3A) activity and cyclic adenosine 3',5'-monophosphate (cAMP) hydrolysis and maintains meiotic arrest with a high intraoocyte cAMP level. This cAMP is generated through the activity of the Gs G-protein by the G-protein-coupled receptor, GPR3 and GPR12, and adenylyl cyclases (ADCY) endogenous to the oocyte. Further studies suggest that endocrine hormones, such as follicle-stimulating hormone (FSH), LH, 17β-estradiol (E2) and oocyte-derived paracrine factors (ODPFs), participate in oocyte meiosis possibly by the regulation of NPPC and/or NPR2. A detailed investigation of NPPC and NPR2 expression in follicle cells will elucidate the precise molecular mechanisms of gonadotropins, and control the arrest as well as resumption of meiosis.

Guanylyl cyclase / atrial natriuretic peptide receptor-A: role in the pathophysiology of cardiovascular regulation

Atrial natriuretic factor (ANF), also known as atrial natriuretic peptide (ANP), is an endogenous and potent hypotensive hormone that elicits natriuretic, diuretic, vasorelaxant, and anti-proliferative effects, which are important in the control of blood pressure and cardiovascular events. One principal locus involved in the regulatory action of ANP and brain natriuretic peptide (BNP) is guanylyl cyclase / natriuretic peptide receptor-A (GC-A/NPRA). Studies on ANP, BNP, and their receptor, GC-A/NPRA, have greatly increased our knowledge of the control of hypertension and cardiovascular disorders. Cellular, biochemical, and molecular studies have helped to delineate the receptor function and signaling mechanisms of NPRA. Gene-targeted and transgenic mouse models have advanced our understanding of the importance of ANP, BNP, and GC-A/NPRA in disease states at the molecular level. Importantly, ANP and BNP are used as critical markers of cardiac events; however, their therapeutic potentials for the diagnosis and treatment of hypertension, heart failure, and stroke have just begun to be realized. We are now just at the initial stage of molecular therapeutics and pharmacogenomic advancement of the natriuretic peptides. More investigations should be undertaken and ongoing ones be extended in this important field.

The functional genomics of guanylyl cyclase/natriuretic peptide receptor-A: perspectives and paradigms

The cardiac hormones atrial natriuretic peptide and B-type natriuretic peptide (brain natriuretic peptide) activate guanylyl cyclase (GC)-A/natriuretic peptide receptor-A (NPRA) and produce the second messenger cGMP. GC-A/NPRA is a member of the growing family of GC receptors. The recent biochemical, molecular and genomic studies on GC-A/NPRA have provided important insights into the regulation and functional activity of this receptor protein, with a particular emphasis on cardiac and renal protective roles in hypertension and cardiovascular disease states. The progress in this field of research has significantly strengthened and advanced our knowledge about the critical roles of Npr1 (coding for GC-A/NPRA) in the control of fluid volume, blood pressure, cardiac remodeling, and other physiological functions and pathological states. Overall, this review attempts to provide insights and to delineate the current concepts in the field of functional genomics and signaling of GC-A/NPRA in hypertension and cardiovascular disease states at the molecular level.

Genetic regulation of the growth plate

The epiphyseal growth plate consists of a layer of cartilage present only during the growth period and vanishes soon after puberty in long bones. It is divided to three well-defined zones, from epiphyses; resting, proliferative, and hypertrophic zones. Chondrocyte proliferation and differentiation and subsequent bone formation in this cartilage are controlled by various endocrine, autocrine, and paracrine factors which finally results into elimination of the cartilaginous tissue and promotion of the epiphyseal fusion. As chondrocytes differentiate from round, quiescent, and single structure to flatten and proliferative and then large and terminally differentiated, they experience changes in their gene expression pattern which allow them to transform from cartilaginous tissue to bone. This review summarizes the literature in this area and shortly describes different factors that affect growth plate cartilage both at the local and systemic levels. This may eventually help us to develop new treatment strategies of different growth disorders.

Cystatin C increases in cardiac injury: a role in extracellular matrix protein modulation

AIMS

Numerous lines of evidence suggest a role of oxidative stress in initiation and progression of heart failure. We identify novel pathways of oxidative stress in cardiomyocytes using proteomic technology.

METHODS AND RESULTS

Cardiomyocytes and cardiac fibroblasts isolated from rat hearts were treated with sublethal doses of H(2)O(2) for detection of secreted protein factors in the conditioned media by mass spectrometry-based proteomics. Comparison between the two cell types leads to the finding that H(2)O(2) caused an elevated cystatin C protein in the conditioned medium from cardiomyocytes. When cardiomyopathy was induced in mice by chronic administration of doxorubicin, elevated cystatin C protein was detected in the plasma. Myocardial ischaemia by left anterior descending coronary artery occlusion causes an increase in the level of cystatin C protein in the plasma. In myocardial tissue from the ischaemic area, an increase in cystatin C correlates with the inhibition of cathepsin B activity and accumulation of fibronectin and collagen I/III. Overexpressing cystatin C gene or exposing fibroblasts to cystatin C protein results in an inhibition of cathepsin B and accumulation of fibronectin and collagen I/III.

CONCLUSION

Oxidants induce elevated cystatin C production from CMCs. Cystatin C plays a role in cardiac extracellular matrix remodelling.

Glial cells as sources and targets of natriuretic peptides

Natriuretic peptides and their receptors are widely expressed in mammalian CNS and increasing evidence implicates them in the regulation of neural development, synaptic transmission and processing of information, and neuroprotection. Although the peptides have been mainly localized in neuronal populations they are also produced in glial cells. Astroglia and microglia also express functional natriuretic peptide receptors that can regulate important physiological responses. In this article we review evidence on the localization of natriuretic peptides and their receptors in astroglial and microglial cells and summarize data supporting the participation of this signalling system in neuron-glia and glia-brain blood vessel communication relevant to CNS function.