C-type natriuretic peptide (CNP): The cardiovascular system and beyond.

C-type natriuretic peptide (CNP) represents the 'local' member of the natriuretic peptide family, functioning in an autocrine or paracrine capacity to modulate a hugely diverse portfolio of physiological processes. Whilst the best-characterised of these regulatory roles are in the cardiovascular system, akin to its predominantly endocrine siblings atrial (ANP) and brain (BNP) natriuretic peptides, CNP governs many additional, unrelated mechanisms including bone growth, gamete maturation, auditory processing, and neuronal integrity. Furthermore, there is currently great interest in mimicking the biological activity of CNP for therapeutic gain in many of these disparate organ systems. Herein, we provide an overview of the physiology, pathophysiology and pharmacology of CNP in both cardiovascular and non-cardiovascular settings.

Auto/Paracrine C-Type Natriuretic Peptide/Cyclic GMP Signaling Prevents Endothelial Dysfunction.

Endothelial dysfunction is cause and consequence of cardiovascular diseases. The endothelial hormone C-type natriuretic peptide (CNP) regulates vascular tone and the vascular barrier. Its cGMP-synthesizing guanylyl cyclase-B (GC-B) receptor is expressed in endothelial cells themselves. To characterize the role of endothelial CNP/cGMP signaling, we studied mice with endothelial-selective GC-B deletion. Endothelial EC GC-B KO mice had thicker, stiffer aortae and isolated systolic hypertension. This was associated with increased proinflammatory E-selectin and VCAM-1 expression and impaired nitric oxide bioavailability. Atherosclerosis susceptibility was evaluated in such KO and control littermates on Ldlr (low-density lipoprotein receptor)-deficient background fed a Western diet for 10 weeks. Notably, the plaque areas and heights within the aortic roots were markedly increased in the double EC GC-B/Ldlr KO mice. This was accompanied by enhanced macrophage infiltration and greater necrotic cores, indicating unstable plaques. Finally, we found that EC GC-B KO mice had diminished vascular regeneration after critical hind-limb ischemia. Remarkably, all these genotype-dependent changes were only observed in female and not in male mice. Auto/paracrine endothelial CNP/GC-B/cGMP signaling protects from arterial stiffness, systolic hypertension, and atherosclerosis and improves reparative angiogenesis. Interestingly, our data indicate a sex disparity in the connection of diminished CNP/GC-B activity to endothelial dysfunction.

Pre-IVM with C-type natriuretic peptide promotes mitochondrial biogenesis of bovine oocytes via activation of CREB.

The aim of this study was to evaluate the effects of C-type natriuretic peptide (CNP) treatment prior to in vitro maturation (IVM) on mitochondria biogenesis in bovine oocyte matured in vitro and explore the related causes. The results showed that treatment with CNP before IVM significantly improved mitochondrial content, elevated the expression of genes related to mitochondria biogenesis, and increased the protein levels of phosphorylation of cAMP-response element binding protein (p-CREB) in bovine oocytes following IVM. However, further studies revealed that treatment with CNP before IVM could not increased the protein levels of p-CREB in bovine oocytes when natriuretic peptide receptor 2 activities was inhibited using the relative specific inhibitor Gö6976. In addition, treatment with CNP before IVM could not improved mitochondrial content or elevated the expression of genes related to mitochondria biogenesis in bovine oocytes when CREB activities was abolished using the specific inhibitor 666-15. In summary, these results provide evidence that treatment of bovine oocytes with CNP before IVM promotes mitochondrial biogenesis in vitro, possibly by activating CREB.

C-type natriuretic peptide/cGMP/FoxO3 signaling attenuates hyperproliferation of pericytes from patients with pulmonary arterial hypertension.

Pericyte dysfunction, with excessive migration, hyperproliferation, and differentiation into smooth muscle-like cells contributes to vascular remodeling in Pulmonary Arterial Hypertension (PAH). Augmented expression and action of growth factors trigger these pathological changes. Endogenous factors opposing such alterations are barely known. Here, we examine whether and how the endothelial hormone C-type natriuretic peptide (CNP), signaling through the cyclic guanosine monophosphate (cGMP) -producing guanylyl cyclase B (GC-B) receptor, attenuates the pericyte dysfunction observed in PAH. The results demonstrate that CNP/GC-B/cGMP signaling is preserved in lung pericytes from patients with PAH and prevents their growth factor-induced proliferation, migration, and transdifferentiation. The anti-proliferative effect of CNP is mediated by cGMP-dependent protein kinase I and inhibition of the Phosphoinositide 3-kinase (PI3K)/AKT pathway, ultimately leading to the nuclear stabilization and activation of the Forkhead Box O 3 (FoxO3) transcription factor. Augmentation of the CNP/GC-B/cGMP/FoxO3 signaling pathway might be a target for novel therapeutics in the field of PAH.

Haemodynamic, hormonal and renal actions of osteocrin in normal sheep.

Osteocrin (OSTN) is an endogenous protein sharing structural similarities with the natriuretic peptides [NPs; atrial (ANP), B-type (BNP) and C-type (CNP) NP], which are hormones known for their crucial role in maintaining pressure/volume homeostasis. Osteocrin competes with the NPs for binding to the receptor involved in their clearance (NPR-C). In the present study, having identified, for the first time, the major circulating form of OSTN in human and ovine plasma, we examined the integrated haemodynamic, endocrine and renal effects of vehicle-controlled incremental infusions of ovine proOSTN (83-133) and its metabolism in eight conscious normal sheep. Incremental i.v. doses of OSTN produced stepwise increases in circulating concentrations of the peptide, and its metabolic clearance rate was inversely proportional to the dose. Osteocrin increased plasma levels of ANP, BNP and CNP in a dose-dependent manner, together with concentrations of their intracellular second messenger, cGMP. Increases in plasma cGMP were associated with progressive reductions in arterial pressure and central venous pressure. Plasma cAMP, renin and aldosterone were unchanged. Despite significant increases in urinary cGMP levels, OSTN administration was not associated with natriuresis or diuresis in normal sheep. These results support OSTN as an endogenous ligand for NPR-C in regulating plasma concentrations of NPs and associated cGMP-mediated bioactivity. Collectively, our findings support a role for OSTN in maintaining cardiovascular homeostasis.

Neprilysin Inhibition Promotes Skeletal Growth via the CNP/NPR-B Pathway.

C-type natriuretic peptide (CNP) plays a crucial role in enhancing endochondral bone growth and holds promise as a therapeutic agent for impaired skeletal growth. To overcome CNP's short half-life, we explored the potential of dampening its clearance system. Neprilysin (NEP) is an endopeptidase responsible for catalyzing the degradation of CNP. Thus, we investigated the effects of NEP inhibition on skeletal growth by administering sacubitril, a NEP inhibitor, to C57BL/6 mice. Remarkably, we observed a dose-dependent skeletal overgrowth phenotype in mice treated with sacubitril. Histological analysis of the growth plate revealed a thickening of the hypertrophic and proliferative zones, mirroring the changes induced by CNP administration. The promotion of skeletal growth observed in wild-type mice treated with sacubitril was nullified by the knockout of cartilage-specific natriuretic peptide receptor B (NPR-B). Notably, sacubitril promoted skeletal growth in mice only at 3 to 4 weeks of age, a period when endogenous CNP and NEP expression was higher in the lumbar vertebrae. Additionally, sacubitril facilitated endochondral bone growth in organ culture experiments using tibial explants from fetal mice. These findings suggest that NEP inhibition significantly promotes skeletal growth via the CNP/NPR-B pathway, warranting further investigations for potential applications in people with short stature.

The Rectal Gland of the Shark: The Road to Understanding the Mechanism and Regulation of Transepithelial Chloride Transport.

Pictured, described, and speculated on, for close to 400 years, the function of the rectal gland of elasmobranchs remained unknown. In the late 1950s, Burger discovered that the rectal gland of Squalus acanthias secreted an almost pure solution of sodium chloride, isosmotic with blood, which could be stimulated by volume expansion of the fish. Twenty five years later, Stoff discovered that the secretion of the gland was mediated by adenyl cyclase. Studies since then have shown that vasoactive intestinal peptide (VIP) is the neurotransmitter responsible for activating adenyl cyclase; however, the amount of circulating VIP does not change in response to volume expansion. The humoral factor involved in activating the secretion of the gland is C-type natriuretic peptide, secreted from the heart in response to volume expansion. C-type natriuretic peptide circulates to the gland where it stimulates the release of VIP from nerves within the gland, but it also has a direct effect, independent of VIP. Sodium, potassium, and chloride are required for the gland to secrete, and the secretion of the gland is inhibited by ouabain or furosemide. The current model for the secretion of chloride was developed from this information. Basolateral NaKATPase maintains a low intracellular concentration of sodium, which establishes the large electrochemical gradient for sodium directed into the cell. Sodium moves from the blood into the cell (together with potassium and chloride) down this electrochemical gradient, through a coupled sodium, potassium, and two chloride cotransporter (NKCC1). On activation, chloride moves from the cell into the gland lumen, down its electrical gradient through apical cystic fibrosis transmembrane regulator. The fall in intracellular chloride leads to the phosphorylation and activation of NKCC1 that allows more chloride into the cell. Transepithelial sodium secretion into the lumen is driven by an electrical gradient through a paracellular pathway. The aim of this review was to examine the history of the origin of this model for the transport of chloride and suggest that it is applicable to many epithelia that transport chloride, both in resorptive and secretory directions.

Efficiency of C-type natriuretic peptide on improvement of Iraqi local ram's epididymal sperms.

Background: Fertility plays a great role in animal reproduction since high-quality semen improves sheep industry reproduction. The current worldwide data revealed the close relation of C-type natriuretic peptide (CNP) to the reproductive function of rams. Aims: Evaluation of the effect of CNP on cooled sperms using traditional and molecular assays. Methods: Totally, of 20 testicular samples were collected, processed to obtain the semen samples, and divided into two parts; one was treated with a suitable dose of CNP, and the other served as a control. Sperm samples of both groups were cooled for 3 days and tested at 0, 24, 48, and 72 hours. Results: The findings revealed that the suitable dose of CNP-treated sperms was 0.01 × 10-13. Values of individual motility, live sperms, and sperm concentration were reduced significantly in CNP-24h, CNP-48h, and CNP-72h when compared to control; however, abnormal sperms were increased in both control and CNP groups at 24, 48, and 72 hours when compared to values of 0 hour. Concerning turbidmetric analysis, a significant reduction in values of lag time was observed in CNP when compared to control at all times of cooling intervals. In both CNP and control groups, motility index was decreased at 24, 48, and 72 hours when compared to 0 hour. For velocity, significant increases were shown in CNP compared with control at all cooling intervals. However, values of both groups were increased significantly at 24, 48, and 72 hours times when compared to 0 hour. Fraction of rapidly moving sperm of CNP was elevated at 0 hour and decreased at 24, 48, and 72 hours when compared to control. Expression of the hNPR-B gene was reduced gradually in sperms of CNP and control groups at times of cooling intervals. Conclusion: To the best of our knowledge, this first Iraqi study targets the effect of CNP on epididymal sperms of rams. However, changes that occur after excessive CNP exposure remain unclear, and the toxicological profile of CNP requires furthermore supplements.

C-type natriuretic peptide improves maternally aged oocytes quality by inhibiting excessive PINK1/Parkin-mediated mitophagy.

The overall oocyte quality declines with aging, and this effect is strongly associated with a higher reactive oxygen species (ROS) level and the resultant oxidative damage. C-type natriuretic peptide (CNP) is a well-characterized physiological meiotic inhibitor that has been successfully used to improve immature oocyte quality during in vitro maturation. However, the underlying roles of CNP in maternally aged oocytes have not been reported. Here, we found that the age-related reduction in the serum CNP concentration was highly correlated with decreased oocyte quality. Treatment with exogenous CNP promoted follicle growth and ovulation in aged mice and enhanced meiotic competency and fertilization ability. Interestingly, the cytoplasmic maturation of aged oocytes was thoroughly improved by CNP treatment, as assessed by spindle/chromosome morphology and redistribution of organelles (mitochondria, the endoplasmic reticulum, cortical granules, and the Golgi apparatus). CNP treatment also ameliorated DNA damage and apoptosis caused by ROS accumulation in aged oocytes. Importantly, oocyte RNA-seq revealed that the beneficial effect of CNP on aged oocytes was mediated by restoration of mitochondrial oxidative phosphorylation, eliminating excessive mitophagy. CNP reversed the defective phenotypes in aged oocytes by alleviating oxidative damage and suppressing excessive PINK1/Parkin-mediated mitophagy. Mechanistically, CNP functioned as a cAMP/PKA pathway modulator to decrease PINK1 stability and inhibit Parkin recruitment. In summary, our results demonstrated that CNP supplementation constitutes an alternative therapeutic approach for advanced maternal age-related oocyte deterioration and may improve the overall success rates of clinically assisted reproduction in older women.

A Redesigned Method for CNP-Synchronized In Vitro Maturation Inhibits Oxidative Stress and Apoptosis in Cumulus-Oocyte Complexes and Improves the Developmental Potential of Porcine Oocytes.

In vitro embryo production depends on high-quality oocytes. Compared with in vivo matured oocytes, in vitro oocytes undergo precocious meiotic resumption, thus compromising oocyte quality. C-type natriuretic peptide (CNP) is a follicular factor maintaining meiotic arrest. Thus, CNP-pretreatment has been widely used to improve the in vitro maturation (IVM) of oocytes in many species. However, the efficacy of this strategy has remained unsatisfactory in porcine oocytes. Here, by determining the functional concentration and dynamics of CNP in inhibiting spontaneous meiotic resumption, we improved the current IVM system of porcine oocytes. Our results indicate that although the beneficial effect of the CNP pre-IVM strategy is common among species, the detailed method may be largely divergent among them and needs to be redesigned specifically for each one. Focusing on the overlooked role of cumulus cells surrounding the oocytes, we also explore the mechanisms relevant to their beneficial effect. In addition to oocytes per se, the enhanced anti-apoptotic and anti-oxidative gene expression in cumulus cells may contribute considerably to improved oocyte quality. These findings not only emphasize the importance of screening the technical parameters of the CNP pre-IVM strategy for specific species, but also highlight the critical supporting role of cumulus cells in this promising strategy.

The FSH-mTOR-CNP signaling axis initiates follicular antrum formation by regulating tight junction, ion pumps, and aquaporins.

The initial formation of the follicular antrum (iFFA) serves as a dividing line between gonadotropin-independent and gonadotropin-dependent folliculogenesis, enabling the follicle to sensitively respond to gonadotropins for its further development. However, the mechanism underlying iFFA remains elusive. Herein, we reported that iFFA is characterized by enhanced fluid absorption, energy consumption, secretion, and proliferation and shares a regulatory mechanism with blastula cavity formation. By use of bioinformatics analysis, follicular culture, RNA interference, and other techniques, we further demonstrated that the tight junction, ion pumps, and aquaporins are essential for follicular fluid accumulation during iFFA, as a deficiency of any one of these negatively impacts fluid accumulation and antrum formation. The intraovarian mammalian target of rapamycin-C-type natriuretic peptide pathway, activated by follicle-stimulating hormone, initiated iFFA by activating tight junction, ion pumps, and aquaporins. Building on this, we promoted iFFA by transiently activating mammalian target of rapamycin in cultured follicles and significantly increased oocyte yield. These findings represent a significant advancement in iFFA research, further enhancing our understanding of folliculogenesis in mammals.

The oocyte cumulus complex regulates mouse sperm migration in the oviduct.

As the time of ovulation draws near, mouse spermatozoa move out of the isthmic reservoir, which is a prerequisite for fertilization. However, the molecular mechanism remains unclear. The present study revealed that mouse cumulus cells of oocytes-cumulus complexes (OCCs) expressed transforming growth factor-ß ligand 1 (TGFB1), whereas ampullary epithelial cells expressed the TGF-ß receptors, TGFBR1 and TGFBR2, and all were upregulated by luteinizing hormone (LH)/human chorionic gonadotropin (hCG). OCCs and TGFB1 increased natriuretic peptide type C (NPPC) expression in cultured ampullae via TGF-ß signaling, and NPPC treatment promoted spermatozoa moving out of the isthmic reservoir of the preovulatory oviducts. Deletion of Tgfb1 in cumulus cells and Tgfbr2 in ampullary epithelial cells blocked OCC-induced NPPC expression and spermatozoa moving out of the isthmic reservoir, resulting in compromised fertilization and fertility. Oocyte-derived paracrine factors were required for promoting cumulus cell expression of TGFB1. Therefore, oocyte-dependent and cumulus cell-derived TGFB1 promotes the expression of NPPC in oviductal ampulla, which is critical for sperm migration in the oviduct and subsequent fertilization.

C Type Natriuretic Peptide Receptor Activation Inhibits Sodium Channel Activity in Human Aortic Endothelial Cells by Activating the Diacylglycerol-Protein Kinase C Pathway.

The C-type natriuretic peptide receptor (NPRC) is expressed in many cell types and binds all natriuretic peptides with high affinity. Ligand binding results in the activation or inhibition of various intracellular signaling pathways. Although NPRC ligand binding has been shown to regulate various ion channels, the regulation of endothelial sodium channel (EnNaC) activity by NPRC activation has not been studied. The objective of this study was to investigate mechanisms of EnNaC regulation associated with NPRC activation in human aortic endothelial cells (hAoEC). EnNaC protein expression and activity was attenuated after treating hAoEC with the NPRC agonist cANF compared to vehicle, as demonstrated by Western blotting and patch clamping studies, respectively. NPRC knockdown studies using siRNA's corroborated the specificity of EnNaC regulation by NPRC activation mediated by ligand binding. The concentration of multiple diacylglycerols (DAG) and the activity of protein kinase C (PKC) was augmented after treating hAoEC with cANF compared to vehicle, suggesting EnNaC activity is down-regulated upon NPRC ligand binding in a DAG-PKC dependent manner. The reciprocal cross-talk between NPRC activation and EnNaC inhibition represents a feedback mechanism that presumably is involved in the regulation of endothelial function and aortic stiffness.

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.

Efficacy of vosoritide in the treatment of achondroplasia.

Achondroplasia is the commonest form of dwarfism and results from a mutation in the fibroblast growth factor receptor 3 (FGFR3) gene on chromosome 4p16.3. The mutation is at nucleotide 1138 resulting in a G-to-A transition (134934.0001). This condition is characterized by full penetration meaning that everyone with this genetic mutation will exhibit the phenotypic characteristics of achondroplasia. It is a gain-of function mutation that causes increased inhibition of cartilage formation. C-type natriuretic peptide (CNP) acts on the growth plate through the natriuretic peptide receptor-B (NPR-B) causing the transformation of guanosine 5'-triphosphate into cyclic guanosine monophosphate. However, CNP cannot be used in the treatment of achondroplasia because it is rapidly degraded by neutral endopeptidase. Vosoritide is a modified recombinant human CNP and has a half-life 10 times that of CNP. Clinical trials have demonstrated that vosoritide is effective in significantly increasing the annualized growth velocity in children with achondroplasia before the fusion of the epiphyses.

Guanylyl Cyclase-B Dependent Bone Formation in Mice is Associated with Youth, Increased Osteoblasts, and Decreased Osteoclasts.

C-type natriuretic peptide (CNP) activation of guanylyl cyclase-B (GC-B) catalyzes the synthesis of cGMP in chondrocytes and osteoblasts. Elevated cGMP stimulates long bone growth, and inactivating mutations in CNP or GC-B reduce cGMP, which causes dwarfism. GC-B7E/7E mice that express a GC-B mutant that cannot be inactivated by dephosphorylation exhibit increased CNP-dependent GC-B activity, which increases bone length, as well as bone mass and strength. Importantly, how GC-B increases bone mass is not known. Here, we injected 12-week-old, wild type mice once daily for 28 days with or without BMN-111 (Vosoritide), a proteolytically resistant CNP analog. We found that BMN-111 treated mice had elevated levels of osteocalcin and collagen 1 C-terminal telopeptide (CTX) as well as increased osteoblasts and osteoclasts. In BMN-111 injected mice, tibial mRNAs for Rank ligand and osteoprotegrin were increased and decreased, respectively, whereas sclerostin mRNA was elevated 400-fold, consistent with increased osteoclast activity and decreased osteoblast activity. Mineral apposition rates and trabecular bone mass were not elevated in response to BMN-111. Because 9-week-old male GC-B7E/7E mice have increased bone mass but do not exhibit increased mineral apposition rates, we examined 4-week-old male GC-B7E/7E mice and found that these animals had increased serum osteocalcin, but not CTX. Importantly, tibias from these mice had 37% more osteoblasts, 26% fewer osteoclasts as well as 36% and 40% higher mineral apposition and bone formation rates, respectively. We conclude that GC-B-dependent bone formation is coupled to an early juvenile process that requires both increased osteoblasts and decreased osteoclasts.

The loading of C-type natriuretic peptides improved hemocompatibility and vascular regeneration of electrospun poly(ε-caprolactone) grafts.

As a result of thrombosis or intimal hyperplasia, synthetic artificial vascular grafts had a low success rate when they were used to replace small-diameter arteries (inner diameter < 6 mm). C-type natriuretic peptides (CNP) have anti-thrombotic effects, and can promote endothelial cell (EC) proliferation and inhibit vascular smooth muscle cell (SMC) over-growth. In this study, poly(ε-caprolactone) (PCL) vascular grafts loaded with CNP (PCL-CNP) were constructed by electrospinning. The PCL-CNP grafts were able to continuously release CNP at least 25 days in vitro. The results of scanning electron microscopy (SEM) and mechanical testing showed that the loading of CNP did not change the microstructure and mechanical properties of the PCL grafts. In vitro blood compatibility analysis displayed that PCL-CNP grafts could inhibit thrombin activity and reduce platelet adhesion and activation. In vitro cell experiments demonstrated that PCL-CNP grafts activated ERK1/2 and Akt signaling in human umbilical vein endothelial cells (HUVECs), as well as increased cyclin D1 expression, enhanced proliferation and migration, and increased vascular endothelial growth factor (VEGF) secretion and nitric oxide (NO) production. The rabbit arteriovenous (AV)-shunt ex vitro indicated that CNP loading significantly improved the antithrombogenicity of PCL grafts. The assessment of vascular grafts in rat abdominal aorta implantation model displayed that PCL-CNP grafts promoted the regeneration of ECs and contractile SMCs, modulated macrophage polarization toward M2 phenotype, and enhanced extracellular matrix remodeling. These findings confirmed for the first time that loading CNP is an effective approach to improve the hemocompatibility and vascular regeneration of synthetic vascular grafts. STATEMENT OF SIGNIFICANCE: Small-diameter (< 6 mm) vascular grafts (SDVGs) have not been made clinically available due to their prevalence of thrombosis, limited endothelial regeneration and intimal hyperplasia. The incorporation of bioactive molecules into SDVGs serves as an effective solution to improve hemocompatibility and endothelialization. In this study, for the first time, we loaded C-type natriuretic peptides (CNP) into PCL grafts by electrospunning and confirmed the effectiveness of loading CNP on improving the hemocompatibility and vascular regeneration of artificial vascular grafts. Regenerative advantages included enhancement of endothelialization, modulation of macrophage polarization toward M2 phenotypes, and improved contractile smooth muscle cell regeneration. Our investigation brings attention to CNP as a valuable bioactive molecule for modifying cardiovascular biomaterial.

C-type natriuretic peptide and its contribution to bone growth.

INTRODUCTION AND OBJECTIVE: The expression of the C-type natriuretic peptide (CNP) gene has been detected in the growth cartilage of the long bones and vertebrae. This article provides an overview of the role of CNP in bone growth and presents the results of the authors' research on the concentration of the NTproCNP and its relationship with growth velocity and bone markers in healthy school-age children. MATERIAL AND METHODS: The study involved 75 girls and 59 boys aged from 9.0-11.8 years (mean 10.29±0.74). Body weight, height and lower limb length were measured, and blood samples were collected twice at six-month intervals. In the first serum sample, the concentrations of NTproCNP, C-terminal propeptide type I (CICP), C-terminal telopeptide type I collagen (ICTP) osteocalcin (OC) and bone-specific alkaline phosphatase (BAP) were determined. In the second sample, NTproCNP concentration was assessed. RESULTS: During the six-month follow-up period, the increase in body height and weight of girls was greater than boys (p<0.000; p=0.003, respectively). While during the first examination the concentration of NTproCNP in girls and boys was similar, during the second examination it was higher in girls than in boys (p=0.04). Weak positive correlations between the increase in body height and NTproCNP, CICP, BAP as well as OC were found. There were no correlations between NTproCNP and the bone markers. CONCLUSIONS: The results suggest that NTproCNP concentration depends on growth velocity in children. There is increasing evidence that a better knowledge of CNP biology contributes to a better understanding of bone growth mechanisms.

Molecular Mechanism of Induction of Bone Growth by the C-Type Natriuretic Peptide.

The skeletal development process in the body occurs through sequential cellular and molecular processes called endochondral ossification. Endochondral ossification occurs in the growth plate where chondrocytes differentiate from resting, proliferative, hypertrophic to calcified zones. Natriuretic peptides (NPTs) are peptide hormones with multiple functions, including regulation of blood pressure, water-mineral balance, and many metabolic processes. NPTs secreted from the heart activate different tissues and organs, working in a paracrine or autocrine manner. One of the natriuretic peptides, C-type natriuretic peptide-, induces bone growth through several mechanisms. This review will summarize the knowledge, including the newest discoveries, of the mechanism of CNP activation in bone growth.

C-type natriuretic peptide facilitates autonomic Ca2+ entry in growth plate chondrocytes for stimulating bone growth.

The growth plates are cartilage tissues found at both ends of developing bones, and vital proliferation and differentiation of growth plate chondrocytes are primarily responsible for bone growth. C-type natriuretic peptide (CNP) stimulates bone growth by activating natriuretic peptide receptor 2 (NPR2) which is equipped with guanylate cyclase on the cytoplasmic side, but its signaling pathway is unclear in growth plate chondrocytes. We previously reported that transient receptor potential melastatin-like 7 (TRPM7) channels mediate intermissive Ca2+ influx in growth plate chondrocytes, leading to activation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) for promoting bone growth. In this report, we provide evidence from experiments using mutant mice, indicating a functional link between CNP and TRPM7 channels. Our pharmacological data suggest that CNP-evoked NPR2 activation elevates cellular cGMP content and stimulates big-conductance Ca2+-dependent K+ (BK) channels as a substrate for cGMP-dependent protein kinase (PKG). BK channel-induced hyperpolarization likely enhances the driving force of TRPM7-mediated Ca2+ entry and seems to accordingly activate CaMKII. Indeed, ex vivo organ culture analysis indicates that CNP-facilitated bone growth is abolished by chondrocyte-specific Trpm7 gene ablation. The defined CNP signaling pathway, the NPR2-PKG-BK channel-TRPM7 channel-CaMKII axis, likely pinpoints promising target proteins for developing new therapeutic treatments for divergent growth disorders.