ProCNP and CNP are expressed primarily in male genital organs

C-type natriuretic peptide (CNP) in the paraventricular nucleus-mediated renal sympatho-inhibition

Volume reflex produces sympatho-inhibition that is mediated by the hypothalamic paraventricular nucleus (PVN). However, the mechanisms for the sympatho-inhibitory role of the PVN and the neurochemical factors involved remain to be identified. In this study, we proposed C-type natriuretic peptide (CNP) as a potential mediator of this sympatho-inhibition within the PVN. Microinjection of CNP (1.0 μg) into the PVN significantly decreased renal sympathetic nerve activity (RSNA) (-25.8% ± 1.8% vs. -3.6% ± 1.5%), mean arterial pressure (-15.0 ± 1.9 vs. -0.1 ± 0.9 mmHg) and heart rate (-23.6 ± 3.5 vs. -0.3 ± 0.9 beats/min) compared with microinjection of vehicle. Picoinjection of CNP significantly decreased the basal discharge of extracellular single-unit recordings in 5/6 (83%) rostral ventrolateral medulla (RVLM)-projecting PVN neurons and in 6/13 (46%) of the neurons that were not antidromically activated from the RVLM. We also observed that natriuretic peptide receptor type C (NPR-C) was present on the RVLM projecting PVN neurons detected by dual-labeling with retrograde tracer. Prior NPR-C siRNA microinjection into the PVN significantly blunted the decrease in RSNA to CNP microinjections into the PVN. Volume expansion-mediated reduction in RSNA was significantly blunted by prior administration of NPR-C siRNA into the PVN. These results suggest a potential role for CNP within the PVN in regulating RSNA, specifically under physiological conditions of alterations in fluid balance.

Effect of C-Type Natriuretic Peptide (CNP) on Spermatozoa Maturation in Adult Rat Epididymis

C-type natriuretic peptide (CNP) is highly expressed in male reproductive tissues, such as the epididymis. The aim of this study is to explore the role of CNP in the maturation of rat epididymal spermatozoa. First, the expression levels of CNP and its specific natriuretic peptide receptor-B (NPR-B) were detected in various tissues of rats and epididymis at different stages after birth. Then a castrated rat model was established to analyze the relationship between testosterone and CNP/NPR-B expression in the epididymis. Finally, CNP and different inhibitors (NPR-B inhibitors, cGMP inhibitors) were used to incubate epididymal sperm in vitro to examine sperm mobility and expression of sperm maturation-related factors. The results showed CNP/NPR-B mRNAs were expressed in all tissues of rats, but were extremely highly expressed in male genital ducts (seminal vesicle, prostate and epididymis). The expression of CNP/NPR-B in epididymis was the highest at birth and the fifth week after birth. In the epididymis, CNP/NPR-B were highly expressed in the caput and located in the epididymal epithelial cells. After castration, the expression of CNP/NPR-B decreased sharply and was restored quickly after testosterone supplementation. In vitro, CNP could significantly promote the acquisition of epididymal sperm motility through the NPR-B/cGMP pathway and induce the expression of sperm maturation-related factors (such as Bin1b, Catsper 1, Dnah17, Fertilin). This study shows that CNP plays a role in epididymal sperm maturation. The mechanism of CNP is to promote the acquisition of epididymal sperm fluidity through the NPR-B/cGMP signaling pathway and also to regulate sperm maturation-related genes. Moreover, the expression of CNP/NPR-B was regulated by testosterone.

Review A State of Natriuretic Peptide Deficiency

Measurement of natriuretic peptides (NPs) has proven its clinical value as biomarker, especially in the context of heart failure (HF). In contrast, a state partial NP deficiency appears integral to several conditions in which lower NP concentrations in plasma presage overt cardiometabolic disease. Here, obesity and type 2 diabetes have attracted considerable attention. Other factors - including age, sex, race, genetics, and diurnal regulation - affect the NP "armory" and may leave some individuals more prone to development of cardiovascular disease. The molecular maturation of NPs has also proven complex with highly variable O-glycosylation within the biosynthetic precursors. The relevance of this regulatory step in post-translational propeptide maturation has recently become recognized in biomarker measurement/interpretation and cardiovascular pathophysiology. An important proportion of people appear to have reduced effective net NP bioactivity in terms of receptor activation and physiological effects. The state of NP deficiency, then, both entails a potential for further biomarker development and could also offer novel pharmacological possibilities. Alleviating the state of NP deficiency before development of overt cardiometabolic disease in selected patients could be a future path for improving precision medicine.

C-Type Natriuretic Peptide (CNP) Could Improve Sperm Motility and Reproductive Function of Asthenozoospermia

This study is to analyze the effect of C-type natriuretic peptide (CNP) on sperm motility of asthenozoospermia and explore the influence mechanism of CNP on the reproductive system and sperm motility. Our results showed that the concentration of CNP in asthenospermia patients’ semen was lower than in normal people’s. The motility of sperm could be improved markedly by CNP and 8-Br-cGMP, while the effect of CNP was inhibited by NPR-B antagonist and KT5823. In the asthenozoospermia mouse model induced by CTX, CNP injection could improve sperm motility in the epididymis, alleviate tissue damage in the testes and epididymis, and increase testosterone levels. The asthenospermia mouse model showed high activity of MDA and proinflammatory factors (TNF-α, IL-6), as well as low expression of antioxidants (SOD, GSH-Px, CAT) in the testis and epididymis, but this situation could be significantly ameliorated after being treated with CNP. Those studies indicated that the concentration of CNP in the semen of asthenospermia patients is lower than in normal people and could significantly promote sperm motility through the NPR-B/cGMP pathway. In the asthenospermia mouse model induced by CTX, CNP can alleviate the damage of cyclophosphamide to the reproductive system and sperm motility. The mechanism may involve increasing testosterone and reducing ROS and proinflammatory factors to damage the tissue and sperm.

C-Type Natriuretic Peptide Plays an Anti-Inflammatory Role in Rat Epididymitis Induced by UPEC

Human epididymitis is mainly caused by retrograde urinary tract infection with uropathogenic Escherichia coli (UPEC). This disease is an important factor (accounting for 20-30%) causing male infertility. C-type natriuretic peptide (CNP), a protein composed of 22 amino acids, is proved to play an immunoregulatory role in respiratory and cardiovascular systems. CNP is expressed extremely high in the epididymis, but whether CNP plays the same role in acute epididymitis is unclear. At first, we established an acute caput epididymitis model in rats with UPEC and treated them with CNP to measure inflammatory damage. Then RNA-seq transcriptome technology was used to reveal potential signal pathways. Secondly, the turbidity and activity of UPEC were assessed using a microplate reader and the amount of UPEC by agar plates after incubation with CNP. Thirdly, macrophages in caput epididymis were tested by immunohistochemistry (IHC). Meanwhile, lipopolysaccharide (LPS) with or without CNP was used to stimulate the macrophage (RAW264.7) in vitro and to detect the expression level of pro-inflammatory factors. Finally, the macrophage (RAW264.7) was treated with CNP, 8-Br-cGMP [cyclic guanosinc monophosphate (cGMP) analog] and KT5823 [protein kinase G (PKG) inhibitor], and the expression level of nuclear factor-k-gene binding (NF-kB) signal pathway was examined. The results showed that the damage of epididymis induced by UPEC as well as the pro-inflammatory factors could be alleviated significantly with CNP treatment. CNP could inhibit the activity and numbers of bacteria in both in vivo and in vitro experiments. Moreover, CNP repressed the invasion, and the expression of pro-inflammatory factors (such as NF-kB, IL-1β, IL-6, TNF-α) in macrophages and its effect could be inhibited by KT5823. Therefore, we drew a conclusion from the above experiments that CNP alleviates the acute epididymitis injury induced by UPEC. On one hand, CNP could inhibit the growth of UPEC. On the other hand, CNP could decrease invasion and inflammatory reaction of macrophages; the mechanism was involved in inhibiting NF-kB signal pathway through the cGMP/PKG in macrophages. This research would open up the possibility of using CNP as a potential treatment for epididymitis.

Sperm Functional Genome Associated With Bull Fertility

Bull fertility is an important economic trait in sustainable cattle production, as infertile or subfertile bulls give rise to large economic losses. Current methods to assess bull fertility are tedious and not totally accurate. The massive collection of functional data analyses, including genomics, proteomics, metabolomics, transcriptomics, and epigenomics, helps researchers generate extensive knowledge to better understand the unraveling physiological mechanisms underlying subpar male fertility. This review focuses on the sperm phenomes of the functional genome and epigenome that are associated with bull fertility. Findings from multiple sources were integrated to generate new knowledge that is transferable to applied andrology. Diverse methods encompassing analyses of molecular and cellular dynamics in the fertility-associated molecules and conventional sperm parameters can be considered an effective approach to determine bull fertility for efficient and sustainable cattle production. In addition to gene expression information, we also provide methodological information, which is important for the rigor and reliability of the studies. Fertility is a complex trait influenced by several factors and has low heritability, although heritability of scrotal circumference is high and that it is a known fertility maker. There is a need for new knowledge on the expression levels and functions of sperm RNA, proteins, and metabolites. The new knowledge can shed light on additional fertility markers that can be used in combination with scrotal circumference to predict the fertility of breeding bulls. This review provides a comprehensive review of sperm functional characteristics or phenotypes associated with bull fertility.

Circulating products of C-type natriuretic peptide and links with organ function in health and disease

Paracrine actions of CNP and rapid degradation at source severely limit study of CNP's many roles in vivo. However provided sensitive and validated assays are used, there is increasing evidence that low concentrations of bioactive CNP in plasma, and the readily detectable concentrations of the bio-inactive processed product of proCNP (aminoterminal proCNP), can be used to advance understanding of the hormone's role in pathophysiology. Provided renal function is normal, concordant changes in both CNP and NTproCNP reflect change in tissue production of proCNP whereas change in CNP alone results from altered rates of bioactive CNP degradation and are reflected in the ratio of NTproCNP to CNP. As already shown in juveniles, where plasma concentration of CNP products are higher and are associated with concurrent endochondral bone growth, measurements of plasma CNP products in mature adults have potential to clarify organ response to stress and injury. Excepting the role of CNP in fetal-maternal welfare, this review examines evidence linking plasma CNP products with function of a wide range of tissues in adults, including the impact of extraneous factors such as nutrients, hormone therapy and exercise.

Cross comparison of seminal plasma proteins from cattle and buffalo (Bubalus bubalis)

The objective of this study was to evaluate seminal plasma proteins from cattle and buffalo (Bubalus bubalis), to identify differences between related species. Sixteen buffaloes and 16 cattle between 30 and 60 months of age were used. Semen collection was performed by electroejaculation, followed by macroscopic and microscopic subjective analyses. After analysis, the samples were centrifuged at 800 g for 10 min, and the supernatant (seminal plasma) was recentrifuged at 10,000 g for 30 min at 4°C. The total protein concentration was determined by the Bradford method, and the proteins were digested in solution for mass spectrometry (nLC-MS/MS). Multivariate statistical analysis was used to evaluate the proteomics results by non-hierarchical clustering the considering exponentially modified protein abundance index (emPAI). Principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) were used for clustering. Proteomics identified 78 proteins, and multivariate analysis showed 4 that were over-expressed in buffaloes (cystatin C, prosaposin, peptide YY and keratin type II cytoskeletal 5) and 9 in cattle (spermadhesin-1, seminal plasma protein PDC-109, ribonuclease 4, metalloproteinase inhibitor 2, acrosin inhibitor 1, seminal ribonuclease, C-type natriuretic peptide, angiogenin-1 and osteopontin). Among the proteins identified in seminal plasma, the C-type natriuretic peptide and metalloproteinase inhibitors were described for the first time in buffaloes. Some protease inhibitors were found over-expressed in buffaloes, and important proteins in seminal plasma of cattle were not identified or were found at lower expression levels in buffaloes, which can contribute to reproductive performance in this species.

Spatiotemporal expression patterns of natriuretic peptides in rat testis and epididymis during postnatal development

Natriuretic peptide (NP) family is composed of atrial, brain and C-type NP (NPPA, NPPB and NPPC). Here, we aimed to investigate NP expression in testis and epididymis during postnatal development. NPPA expression was observed in gonocytes at prepubertal period but in only spermatocytes in pachytene and leptotene/zygotene stage at pubertal period. In prepubertal and pubertal periods, we detected NPPB expression in only Leydig cells. However, NPPC expression was detected in all of the gonocytes and Sertoli cells, spermatocytes and some interstitial cells in prepubertal and pubertal periods. In postpubertal and mature periods, NPPA and NPPB staining were detected in Leydig cells, elongated and round spermatids but not in spermatogonia and spermatocytes. However, we observed NPPC expression in all cells of the seminiferous tubules and Leydig cells in the postpubertal and mature periods. Epididymal epithelium showed intense NPPC expression during postnatal period but weak NPPA and NPPB expression in prepubertal and pubertal periods. The expression of three NPs in the testis significantly increased after puberty. In conclusion, puberty had a significant effect on NP expression in testis. Unlike NPPA and NPPB, expression of NPPC in all cells of the seminiferous tubule suggests that NPPC is effective in each step of spermatogenesis.

Discovery of O-glycans on atrial natriuretic peptide (ANP) that affect both its proteolytic degradation and potency at its cognate receptor

Atrial natriuretic peptide (ANP) is a peptide hormone that in response to atrial stretch is secreted from atrial myocytes into the circulation, where it stimulates vasodilatation and natriuresis. ANP is an important biomarker of heart failure where low plasma concentrations exclude cardiac dysfunction. ANP is a member of the natriuretic peptide (NP) family, which also includes the B-type natriuretic peptide (BNP) and the C-type natriuretic peptide. The proforms of these hormones undergo processing to mature peptides, and for proBNP, this process has previously been demonstrated to be regulated by O-glycosylation. It has been suggested that proANP also may undergo post-translational modifications. Here, we conducted a targeted O-glycoproteomics approach to characterize O-glycans on NPs and demonstrate that all NP members can carry O-glycans. We identified four O-glycosites in proANP in the porcine heart, and surprisingly, two of these were located on the mature bioactive ANP itself. We found that one of these glycans is located within a conserved sequence motif of the receptor-binding region, suggesting that O-glycans may serve a function beyond intracellular processing and maturation. We also identified an O-glycoform of proANP naturally occurring in human circulation. We demonstrated that site-specific O-glycosylation shields bioactive ANP from proteolytic degradation and modifies potency at its cognate receptor in vitro Furthermore, we showed that ANP O-glycosylation attenuates acute renal and cardiovascular ANP actions in vivo The discovery of novel glycosylated ANP proteoforms reported here significantly improves our understanding of cardiac endocrinology and provides important insight into the etiology of heart failure.

Natriuretic Peptides and Normal Body Fluid Regulation

Natriuretic peptides are structurally related, functionally diverse hormones. Circulating atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are delivered predominantly by the heart. Two C-type natriuretic peptides (CNPs) are paracrine messengers, notably in bone, brain, and vessels. Natriuretic peptides act by binding to the extracellular domains of three receptors, NPR-A, NPR-B, and NPR-C of which the first two are guanylate cyclases. NPR-C is coupled to inhibitory proteins. Atrial wall stress is the major regulator of ANP secretion; however, atrial pressure changes plasma ANP only modestly and transiently, and the relation between plasma ANP and atrial wall tension (or extracellular volume or sodium intake) is weak. Absence and overexpression of ANP-related genes are associated with modest blood pressure changes. ANP augments vascular permeability and reduces vascular contractility, renin and aldosterone secretion, sympathetic nerve activity, and renal tubular sodium transport. Within the physiological range of plasma ANP, the responses to step-up changes are unimpressive; in man, the systemic physiological effects include diminution of renin secretion, aldosterone secretion, and cardiac preload. For BNP, the available evidence does not show that cardiac release to the blood is related to sodium homeostasis or body fluid control. CNPs are not circulating hormones, but primarily paracrine messengers important to ossification, nervous system development, and endothelial function. Normally, natriuretic peptides are not powerful natriuretic/diuretic hormones; common conclusions are not consistently supported by hard data. ANP may provide fine-tuning of reno-cardiovascular relationships, but seems, together with BNP, primarily involved in the regulation of cardiac performance and remodeling. © 2017 American Physiological Society. Compr Physiol 8:1211-1249, 2018.

Early synergistic interactions between the HPV16‑E7 oncoprotein and 17β-oestradiol for repressing the expression of Granzyme B in a cervical cancer model

Although high-risk human papillomavirus (HR‑HPV) infection has a prominent role in the aetiology of cervical cancer (CC), sex steroid hormones may also be involved in this process; however, the cooperation between oestrogen and HR‑HPV in the early stages of cervical carcinogenesis is poorly understood. Since 17β-oestradiol (E2) and the HPV type 16‑E7 oncoprotein induce CC in transgenic mice, a microarray analysis was performed in the present study to generate global gene expression profiles from 2‑month‑old FVB (non‑transgenic) and K14E7 (transgenic) mice who were left untreated or were treated for 1 month with E2. Upregulation of cancer-related genes that have not been previously reported in the context of CC, including glycerophosphodiester phosphodiesterase domain containing 3, interleukin 1 receptor type II, natriuretic peptide type C, MGAT4 family member C, lecithin-retinol acyltransferase (phosphatidylcholine-retinol-O-acyltransferase) and glucoside xylosyltransferase 2, was observed. Notably, upregulation of the serine (or cysteine) peptidase inhibitor clade B member 9 gene and downregulation of the Granzyme gene family were observed; the repression of the Granzyme B pathway may be a novel mechanism of immune evasion by cancer cells. The present results provide the basis for further studies on early biomarkers of CC risk and synergistic interactions between HR‑HPV and oestrogen.

NT-proCNP as a new indicator of asthenozoospermia

PURPOSE

C-type natriuretic peptide (CNP) is a proinflammatory peptide. The highest concentration of CNP is found in male reproductive organs. This study aims to analyze the role of N-terminal C-type natriuretic propeptide (NT-proCNP) as a new indicator of asthenozoospermia.

MATERIAL/METHODS

Semen was collected after 3-5 days of sexual abstinence from 86 men. The participants were between 25 and 38 years old, 51 of which had asthenozoospermia and 35 of which had normal sperm motility. Semen was analyzed for the concentrations of NT-proCNP, spermatozoa, percentages of live sperm, and sperm exhibiting a specific type of movement. The laboratory tests and analyses were performed using accepted methods and under appropriate conditions.

RESULTS

A significant difference in the concentration and motility of spermatozoa was observed between the focus and control groups. The concentration of spermatozoa in the focus group was significantly lower than in the control group (median: 38.5 vs. 69.8mln/ml [p=0.016] respectively). The progressive motility of spermatozoa demonstrated a significantly lower performance in the focus group than in the control group (median: 10.4% vs. 45% respectively). The concentration of NT-proCNP was significantly higher in the focus group (median: 29.1 vs. 17.9pmol/l; p<0.001). The Area under the Receiver Operating Characteristic (AUROC) curve for the concentration of NT-proCNP - as an indicator of asthenozoospermia - was 0.733. Participants with a concentration of NT-proCNP higher than 28.8pmol/l had asthenozoospermia with 52.9% sensitivity and 94.3% specificity.

CONCLUSIONS

NT-proCNP - an indicator of inflammatory reaction - should be evaluated as an indicator of asthenozoospermia.

Protective Effect of Dietary Ghrelin-Containing Salmon Stomach Extract on Mortality and Cardiotoxicity in Doxorubicin-Induced Mouse Model of Heart Failure

Ghrelin exhibits a cardioprotective effect. We examined whether orally administered ghrelin-containing salmon stomach extract (sSE) instead of chemically synthesized ghrelin protects against doxorubicin (DOX)-induced cardiotoxicity in mice. Mice were divided into four groups: (i) the control, (ii) DOX groups were fed a control diet (AIN-93G), (iii) the sSE, and (iv) DOX + sSE groups were fed a 10% sSE diet (AIN-93G + 10% sSE). After a 4-week pretreatment of sSE, DOX or saline was administered to the corresponding groups by intraperitoneal injection. The groups fed the 10% sSE diet consumed significantly more food than the groups fed the control diet before the DOX injection. No mortality was observed in the DOX + sSE group, whereas 40% (2 of 5) mortality was observed in the DOX group. Compared with the DOX group, levels of ascites and plasma cardiac troponin I improved in the DOX + sSE group. Significantly lesser DOX-induced collagen accumulation was observed in the left heart ventricle of the DOX group than in that of the DOX + sSE group. These results suggest that the dietary ghrelin contained in sSE mimics synthetic ghrelin in cardioprotective effect. Ghrelin in sSE (45 pmol/g) and the food intake-stimulating effect of sSE may explain, at least in part, the protective effect of orally administered teleost ghrelin.

Role of C-type natriuretic peptide in the function of normal human sperm

C-type natriuretic peptide (CNP) is a newly discovered type of local regulatory factor that mediates its biological effects through the specific, membrane-bound natriuretic peptide receptor-B (NPR-B). Recent studies have established that CNP is closely related to male reproductive function. The aims of this study were to determine the distribution of CNP/NPR-B in human ejaculated spermatozoa through different methods (such as immunolocalization, real time polymerase chain reaction and Western Blot), and then to evaluate the influence of CNP on sperm function i n vitro, such as motility and acrosome reaction. Human semen samples were collected from consenting donors who met the criteria of the World Health Organization for normozoospermia. Our results show that the specific receptor NPR-B of CNP is localized in the acrosomal region of the head and the membrane of the front-end tail of the sperm, and there is no signal of CNP in human sperm. Compared with the control, CNP can induce a significant dose-dependent increase in spermatozoa motility and acrosome reaction. In summary, CNP/NPR-B can affect sperm motility and acrosome reaction, thus regulating the reproductive function of males. CNP may be a new key factor in regulating sperm function.

Brain-specific natriuretic peptide receptor-B deletion attenuates high-fat diet-induced visceral and hepatic lipid deposition in mice

C-type natriuretic peptide (CNP) and its receptor, natriuretic peptide receptor-B (NPR-B), are abundantly distributed in the hypothalamus. To explore the role of central CNP/NPR-B signaling in energy regulation, we generated mice with brain-specific NPR-B deletion (BND mice) by crossing Nestin-Cre transgenic mice and mice with a loxP-flanked NPR-B locus. Brain-specific NPR-B deletion prevented body weight gain induced by a high-fat diet (HFD), and the mesenteric fat and liver weights were significantly decreased in BND mice fed an HFD. The decreased liver weight in BND mice was attributed to decreased lipid accumulation in the liver, which was confirmed by histologic findings and lipid content. Gene expression analysis revealed a significant decrease in the mRNA expression levels of CD36, Fsp27, and Mogat1 in the liver of BND mice, and uncoupling protein 2 mRNA expression was significantly lower in the mesenteric fat of BND mice fed an HFD than in that of control mice. This difference was not observed in the epididymal or subcutaneous fat. Although previous studies reported that CNP/NPR-B signaling inhibits SNS activity in rodents, SNS is unlikely to be the underlying mechanism of the metabolic phenotype observed in BND mice. Taken together, CNP/NPR-B signaling in the brain could be a central factor that regulates visceral lipid accumulation and hepatic steatosis under HFD conditions. Further analyses of the precise mechanisms will enhance our understanding of the contribution of the CNP/NPR-B system to energy regulation.

C-type natriuretic peptide ameliorates pulmonary fibrosis by acting on lung fibroblasts in mice

Background

Pulmonary fibrosis has high rates of mortality and morbidity; however, no effective pharmacological therapy has been established. C-type natriuretic peptide (CNP), a member of the natriuretic peptide family, selectively binds to the transmembrane guanylyl cyclase (GC)-B receptor and exerts anti-inflammatory and anti-fibrotic effects in various organs through vascular endothelial cells and fibroblasts that have a cell-surface GC-B receptor. Given the pathophysiological importance of fibroblast activation in pulmonary fibrosis, we hypothesized that the anti-fibrotic and anti-inflammatory effects of exogenous CNP against bleomycin (BLM)-induced pulmonary fibrosis were exerted in part by the effect of CNP on pulmonary fibroblasts.

Methods

C57BL/6 mice were divided into two groups, CNP-treated (2.5 μg/kg/min) and vehicle, to evaluate BLM-induced (1 mg/kg) pulmonary fibrosis and inflammation. A periostin-CNP transgenic mouse model exhibiting CNP overexpression in fibroblasts was generated and examined for the anti-inflammatory and anti-fibrotic effects of CNP via fibroblasts in vivo. Additionally, we assessed CNP attenuation of TGF-β-induced differentiation into myofibroblasts by using immortalized human lung fibroblasts stably expressing GC-B receptors. Furthermore, to investigate whether CNP acts on human lung fibroblasts in a clinical setting, we obtained primary-cultured fibroblasts from surgically resected lungs of patients with lung cancer and analyzed levels of GC-B mRNA transcription.

Results

CNP reduced mRNA levels of the profibrotic cytokines interleukin (IL)-1β and IL-6, as well as collagen deposition and the fibrotic area in lungs of mice with bleomycin-induced pulmonary fibrosis. Furthermore, similar CNP effects were observed in transgenic mice exhibiting fibroblast-specific CNP overexpression. In cultured-lung fibroblasts, CNP treatment attenuated TGF-β–induced phosphorylation of Smad2 and increased mRNA and protein expression of α-smooth muscle actin and SM22α, indicating that CNP suppresses fibroblast differentiation into myofibroblasts. Furthermore, human lung fibroblasts from patients with or without interstitial lung disease substantially expressed GC-B receptor mRNA.

Conclusions

These data suggest that CNP ameliorates bleomycin-induced pulmonary fibrosis by suppressing TGF-β signaling and myofibroblastic differentiation in lung fibroblasts. Therefore, we propose consideration of CNP for clinical application to pulmonary fibrosis treatment.

C-type natriuretic peptide and its precursor: potential markers in human prostate cancer

AIM

Seminal plasma offer a more organ-specific matrix for markers in prostatic disease. We hypothesized that C-type natriuretic peptide (CNP) expression may constitute such a new target.

METHODS

Patients with benign prostatic hyperplasia, clinically localized and metastatic prostate cancer were examined for CNP and CNP precursor (proCNP) concentrations in blood and seminal plasma. Furthermore, CNP and the CNP receptor (NPR-B) mRNA contents in tissue from prostate and seminal vesicles were analyzed by qPCR.

RESULTS

CNP and NPR-B concentrations decreased with increasing tumor burden (p = 0.0027 and p = 0.0096, respectively). In contrast, seminal plasma CNP and proCNP concentrations were markedly increased with increased tumor burden (p < 0.0001 and p < 0.0001, respectively).

CONCLUSION

CNP/proCNP could be new markers in human prostate cancer.

Exogenous C-type natriuretic peptide infusion ameliorates unilateral ureteral obstruction-induced tubulointerstitial fibrosis in rats

Although many experimental therapeutic roles for C-type natriuretic peptide (CNP) have been documented in the field of cardiovascular and pulmonary-vascular disease, the therapeutic uses of CNP to nephropathies are not as well documented. In this study, we established a rat model of unilateral ureteral obstruction (UUO) to observe the beneficial effects of CNP on tubulointerstitial fibrosis (TIF). In UUO rats, CNP administration induced a significant increase in plasma CNP levels, and caused a significant decrease in blood urea nitrogen and creatinine levels. In addition, CNP infusion also alleviated the pathological lesions and collagen IV accumulation in the obstructed kidneys through downregulation of tissue inhibitor of metalloproteinase-1 (TIMP-1) and TIMP-2 expression. In conclusion, exogenous CNP infusion can ameliorate UUO-induced TIF in rats. However, the use of CNP as a therapeutic agent requires further evaluation before being considered for human TIF.

Time-lapse imaging as a tool to investigate contractility of the epididymal duct--effects of cGMP signaling

The well orchestrated function of epididymal smooth muscle cells ensures transit of spermatozoa through the epididymal duct during which spermatozoa acquire motility and fertilizing capacity. Relaxation of smooth muscle cells is mediated by cGMP signaling and components of this pathway are found within the male reproductive tract. Whereas contractile function of caudal parts of the rat epididymal duct can be examined in organ bath studies, caput and corpus regions are fragile and make it difficult to mount them in an organ bath. We developed an ex vivo time-lapse imaging-based approach to investigate the contractile pattern in these parts of the epididymal duct. Collagen-embedding allowed immobilization without impeding contractility or diffusion of drugs towards the duct and therefore facilitated subsequent movie analyses. The contractile pattern was made visible by placing virtual sections through the acquired image stack to track wall movements over time. By this, simultaneous evaluation of contractile activity at different positions of the observed duct segment was possible. With each contraction translating into a spike, drug-induced alterations in contraction frequency could be assessed easily. Peristaltic contractions were also detectable and throughout all regions in the proximal epididymis we found regular spontaneous contractile activity that elicited movement of intraluminal contents. Stimulating cGMP production by natriuretic peptide ANP or inhibiting degradation of cGMP by the phosphodiesterase 5 inhibitor sildenafil significantly reduced contractile frequency in isolated duct segments from caput and corpus. RT-PCR analysis after laser-capture microdissection localized the corresponding molecules to the smooth muscle layer of the duct. Our time-lapse imaging approach proved to be feasible to assess contractile function in all regions of the epididymal duct under near physiological conditions and provides a tool to evaluate acute (side) effects of drugs and to investigate various signaling pathways.

Neutral endopeptidase (CD10) is abundantly expressed in the epididymis and localized to a distinct population of epithelial cells--its relevance for CNP degradation

Neutral endopeptidase (NEP, metallo-endopeptidase EC 3.4.24.11; enkephalinase, neprilysin, CD10, CALLA) represents a major regulator of bioactivity of natriuretic peptides. C-type natriuretic peptide (CNP) is present in high levels in epididymis and seminal plasma. However, detailed expression pattern and CNP-related function of NEP in the epididymis are unknown. Comparison of NEP protein levels in various organs revealed an extremely high expression in human and mouse epididymis. NEP was localized exclusively to apical (luminal) parts of epithelial cells. In man, strong NEP-immunoreactivity was associated with epithelia of efferent ducts and the epididymal duct including stereocilia. Segment-by-segment analysis in mouse revealed a distinct distribution along the epididymal duct. We also found the CNP receptor guanylyl cyclase B (GC-B) in epithelial cells of the epididymal duct. Two different NEP inhibitors decreased CNP degradation and increased CNP/GC-B-induced cGMP production by epididymal membranes, suggesting a functional involvement of NEP. Data indicate an important, previously neglected, role of NEP for regulation of luminal factors in the epididymis and suggest a novel role for CNP/GC-B in the epididymal epithelium, presumably in context of local water balance.

Cardiac C-type natriuretic peptide gene expression and plasma concentrations in neonatal piglets

BACKGROUND

C-type natriuretic peptide (CNP) is a member of the natriuretic peptide family. Cardiac ANP and BNP expressions are firmly established, whereas CNP expression in the mammalian heart remains controversial. In the present report, we used a porcine model of the neonatal period with high expressions of cardiac ANP and BNP in order to elucidate the cardiac CNP expression profile.

METHODS

Plasma and cardiac tissue were obtained from newborn piglets during the first 72 h of life. The chamber-specific CNP mRNA contents were quantified by real-time PCR analysis. The proCNP concentrations in plasma and cardiac tissue extracts were quantified by a porcine-specific radioimmunoassay.

RESULTS

Cardiac CNP mRNA contents (n=24) were low compared to sites of known expression, where porcine seminal vesicle CNP mRNA contents were 200-fold higher. In addition, plasma proCNP concentrations in the newborn piglets (n=44) were exceedingly low compared to proANP concentrations (5.3 pmol/L (3.2-8.6) vs. 3438 pmol/L (2790-5418), p<0.0001). The proCNP concentrations in atrial tissue extracts were barely detectable (≤0.06 pmol/g) (n=2) compared to ventricular proANP (130 pmol/g (101-159)) and atrial proANP (12,303 pmol/g (10,623-15,412)).

CONCLUSION

Our data show that the heart is not a major source of circulating proCNP in neonatal piglets.

C-type natriuretic peptide transcriptomic profiling increases in human leukocytes of patients with chronic heart failure as a function of clinical severity

The aim of this study was to evaluate the transcriptomic profiling of C-type natriuretic peptide (CNP) and of its specific receptor, NPR-B in human leukocytes of heart failure (HF) patients as a function of clinical severity, assessing the possible changes with respect to healthy subjects (C). mRNA expression was evaluated by Real-Time PCR and total RNA was extracted from leukocytes of C (n=8) and of HF patients (NYHA I-II, n=7; NYHA III-IV, n=13) with PAXgene Blood RNA Kit. Significantly higher levels of CNP mRNA expression were found in HF patients as a function of clinical severity (C=0.23±0.058, NYHA I-II=0.47±0.18, NYHA III-IV=2.58±0.71, p=0.005 C vs NYHA III-IV, p=0.017 NYHA I-II vs NYHA III-IV) and NPR-B transcript levels resulted down-regulated in HF patients with higher NYHA class (C=2.2±0.61, NYHA I-II=2.76±0.46, NYHA III-IV=0.29±0.13, p=0.001 C vs NYHA III-IV, p<0.0001 NYHA I-II vs NYHA III-IV). A significant negative correlation between CNP and NPR-B mRNA expression (r=0.5, p=0.03) was also observed. These results suggest a co-regulation of NPR-B and CNP expression supporting the relevance of this receptor in human disease characterized by a marked inflammatory/immune component and suggesting the possibility of manipulating inflammation via pharmacological agents selective for this receptor.

Phosphodiesterase 5 (PDE5) inhibition, ANP and NO rapidly reduce epididymal duct contractions, but long-term PDE5 inhibition in vivo does not

Contractility of the peritubular smooth muscle layer ensures the transit of immotile spermatozoa through the epididymal duct to acquire their fertilizing capacity. Atrial natriuretic peptide (ANP) and nitric oxide (NO) affect contractility via cGMP signals that are controlled by phosphodiesterases (PDEs). Sildenafil inhibits the cGMP-hydrolyzing PDE5 and thereby promotes relaxation of smooth muscle cells. While sildenafil is increasingly used in young patients for the treatment of pulmonary hypertension, virtually no knowledge exists about PDEs in the epididymis. Western blotting, immunohistochemistry and RT-PCR analyses after laser capture microdissection localized PDE5 to smooth muscle cells, but not to epithelial cells, of the epididymal duct in man and rat. Sildenafil, ANP and NO significantly slowed spontaneous contractions of rat epididymal duct segments in organ bath studies. Sildenafil effects were additive to ANP and NO. Long-term exposure to sildenafil in vivo did not change the PDE5 expression or the observed contractility pattern with the rapid relaxing response toward ANP, NO and sildenafil. Data demonstrate that PDE5 is an important member of cGMP signaling pathways regulating the finely orchestrated process of epididymal duct contractility and suggest, however, that in the epididymis side effects of therapeutically used sildenafil are unlikely.

B-type natriuretic peptide: from posttranslational processing to clinical measurement

BACKGROUND

Plasma cardiac natriuretic peptides and peptide fragments from their molecular precursors are markers of heart disease. Clinical studies have defined the current diagnostic utility of these markers, whereas biochemical elucidation of peptide structure and posttranslational processing has revealed new plasma peptide forms of potential clinical use.

CONTENT

Natriuretic propeptide structures undergo variable degrees of endo- and exoproteolytic cleavages as well as amino acid modifications, which leave the plasma phase of the peptides highly heterogeneous and dependent on cardiac pathophysiology and capacity. An ongoing characterization of the molecular heterogeneity may not only help us to appreciate the biosynthetic capacity of the endocrine heart but may also lead to the discovery of new and more disease-specific targets for future molecular diagnosis.

SUMMARY

Peptides derived from pro-atrial natriuretic peptide and pro-B-type natriuretic peptide are useful plasma markers in heart failure. New data have defined cardiac myocytes as competent endocrine cells in posttranslational processing and cellular secretion.

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

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

The role of C-type natriuretic peptide in rat testes during spermatogenesis

C-type natriuretic peptide (CNP) is a 22-amino acid peptide and act as a local paracrine or autocrine regulator. There is growing evidence that CNP is involved in male reproductive processes. To investigate the role of CNP during spermatogenesis, we measured the mRNA expression of CNP and its specific membrane-bound natriuretic peptide receptor-B (NPR-B) using real-time RT-PCR in the testes of normal rats on different postnatal days. After that spermatogenesis dysfunction model induced by ornidazole was established with the aim to study the correlation of CNP with spermatogenic dysfunction. Then, Sertoli cells from 18- to 22-day-old healthy male rats were cultured in the presence of different CNP concentrations (1×10(-6), 1×10(-7) and 1×10(-8) mol l(-1)), and the mRNA expression levels of androgen-binding protein, inhibin B and transferrin were examined at 0 min, 30 min, 1 h, 2 h, 4 h, 8 h, 12 h, 24 h and 48 h. During the postnatal development of rat testes, the highest mRNA expression levels of CNP and NPR-B were found at postnatal D(0), and the levels then declined gradually, with a second CNP peak at postnatal D(35). In the ornidazole-induced infertile rat testes, CNP gene expression was lower than in the uninduced rats (P<0.05), while NPR-B gene expression was greater (P<0.05). In cultured Sertoli cells, supplementation with CNP stimulated the gene expression of androgen-binding protein/inhibin B/transferrin, particularly at 12 h, and 1×10(-7) mol l(-1) CNP had the highest upregulation effect. The gene expression levels of CNP/NPR-B in rat testes at different postnatal stages and in infertile rat testes indicated that CNP may participate in the physiology and/or pathology related to spermatogenesis. Moreover, CNP regulated endocrine function in Sertoli cells. Taken together, these results showed that CNP is closely tied to spermatogenesis.

Practical application of natriuretic peptides in paediatric cardiology

It is still uncertain if cardiac natriuretic peptides are useful biomarkers in paediatric cardiology. In this review we identify four clinical scenarios in paediatric cardiology, where clinical decision-making can be difficult, and where we feel the paediatric cardiologists need additional diagnostic tools. Natriuretic peptide measurements could be that extra tool. We discuss and suggest N-terminal pro-B-type natriuretic peptide and B-type natriuretic peptide reference intervals for children without cardiovascular disease and cut-off points for the four specific paediatric heart conditions. We conclude that in premature neonates with persistent arterial ducts; in teenagers with tetralogy of Fallot and pulmonary regurgitation; and in children with heart transplants and potential allograft rejection cardiac peptides can provide the clinician with additional information, but in children with atrial septal defects the peptides are not helpful in guiding treatment or follow-up.

C-type natriuretic-derived peptides as biomarkers in human disease

The natriuretic peptide system comprises three structurally related peptides: atrial natriuretic peptide, B-type natriuretic peptide and C-type natriuretic peptide. In circulation, they play an important endocrine role in the regulation of cardiovascular homeostasis by maintaining blood pressure and extracellular fluid volume. Atrial natriuretic peptide and B-type natriuretic peptide have gained considerable diagnostic interest as biomarkers in cardiovascular disease. By contrast, C-type natriuretic peptide has not yet been ascribed a role in human diagnostics. This perspective aims at recapitulating the present biochemical and clinical issues concerning C-type natriuretic peptide measurement in plasma as a potential biomarker.

Biosynthesis of cardiac natriuretic peptides

Cardiac-derived peptide hormones were identified more than 25 years ago. An astonishing amount of clinical studies have established cardiac natriuretic peptides and their molecular precursors as useful markers of heart disease. In contrast to the clinical applications, the biogenesis of cardiac peptides has only been elucidated during the last decade. The cellular synthesis including amino acid modifications and proteolytic cleavages has proven considerably more complex than initially perceived. Consequently, the elimination phase of the peptide products in circulation is not yet well characterized. An ongoing characterization of the molecular heterogeneity will help appreciate the biosynthetic capacity of the endocrine heart and could introduce new diagnostic possibilities. Notably, different biosynthetic products may not be equal markers of the same pathophysiological processes. An inefficient post-translational prohormone maturation will also affect the biology of the cardiac natriuretic peptide system. This review aims at summarizing the myocardial synthesis of natriuretic peptides focusing on B-type natriuretic peptide, where new data has disclosed cardiac myocytes as highly competent endocrine cells. The structurally related atrial natriuretic peptide will be mentioned where appropriate, whereas C-type natriuretic peptide will not be considered as a cardiac peptide of relevance in mammalian physiology.

Regional release and clearance of C-type natriuretic peptides in the human circulation and relation to cardiac function

Production and clearance of plasma C-type natriuretic peptide (CNP) and amino terminal (NT)-proCNP immunoreactivity in the human circulation remain poorly characterized. Accordingly, we have measured arterial and venous concentrations of CNP and NT-proCNP across multiple tissue beds during cardiac catheterization in 120 subjects (age: 64.2+/-9.0 years; 73% men) investigated for cardiovascular disorders. The heart, head and neck, and musculoskeletal tissues made the clearest contributions to both plasma CNP and NT-proCNP (P<0.05). Net release of NT-proCNP was also observed from hepatic tissue (P<0.001). Negative arteriovenous gradients for CNP were observed across renal, hepatic, and pulmonary tissue (P<0.05), indicating net clearance, whereas no tissue-specific site of NT-proCNP clearance was identified. Age, mean pulmonary artery pressure, left ventricular end diastolic pressure, Brandt score of myocardial jeopardy, and troponin I were independent predictors of circulating CNP levels in multivariable analysis. Sex and kidney function were independently predictive of arterial NT-proCNP. The proportional step-up of CNP (+60%) across the heart was less than for brain natriuretic peptide (+123%) but greater than for NT-pro-brain natriuretic peptide (NT-proBNP) (+36%) and NT-proCNP (+42%; P<0.001 for all). We conclude that cardiac and head and neck tissue are important sources of CNP. Circulating CNP but not NT-proCNP concentrations are related to cardiac hemodynamic load and ischemic burden. Although cardiac release is most evident, multiple additional tissues release NT-proCNP immunoreactivity without evidence for an organ-specific site for NT-proCNP degradation. Taken together, differences in magnitude and direction of transorgan gradients for CNP compared with NT-proCNP suggest net generalized cosecretion with differing mechanisms of clearance.

C-type natriuretic peptide in prostate cancer

C-type natriuretic peptide (CNP) is expressed in the male reproductive organs in pigs. To examine whether the human prostate also expresses the CNP gene, we measured CNP and N-terminal proCNP in prostate cancer tissue extracts and performed immunohistochemical biopsy staining. Additionally, proCNP-derived peptides were quantitated in plasma from patients with prostate cancer. Blood was collected from healthy controls and patients before surgery for localized prostate cancer. Tissue extracts were prepared from tissue biopsies obtained from radical prostatectomy surgery. N-terminal proCNP, proCNP (1-50) and CNP were measured in plasma and tissue extracts. Biopsies were stained for CNP-22 and N-terminal proCNP. Tissue extracts from human prostate cancer contained mostly N-terminal proCNP [median 5.3 pmol/g tissue (range 1.0-12.9)] and less CNP [0.14 pmol/g tissue (0.01-1.34)]. Immunohistochemistry demonstrated the presence of the peptides in prostatic epithelial cells. The N-terminal proCNP concentrations in plasma were marginally lower in patients with localized prostate cancer compared with control subjects [13.8 pmol/l (11.0-17.2) vs. 15.1 pmol/l (10.4-23.2), p=0.002] but not enough to justify the use of N-terminal proCNP as a cancer marker. Further research is needed to establish whether measurement of proCNP-derived peptides may offer clinical information.