"Meiosis arrester" C-natriuretic peptide directly stimulates oocyte mtDNA accumulation and is implicated in aging-associated oocyte mtDNA loss.

C-natriuretic peptide (CNP) is the central regulator of oocyte meiosis progression, thus coordinating synchronization of oocyte nuclear-cytoplasmic maturation. However, whether CNP can independently regulate cytoplasmic maturation has been long overlooked. Mitochondrial DNA (mtDNA) accumulation is the hallmark event of cytoplasmic maturation, but the mechanism underlying oocyte mtDNA replication remains largely elusive. Herein, we report that CNP can directly stimulate oocyte mtDNA replication at GV stage, and deficiency of follicular CNP may contribute largely to lower mtDNA copy number in in vitro matured oocytes. The mechanistic study showed that cAMP-PKA-CREB1 signaling cascade underlies the regulatory role of CNP in stimulating mtDNA replication and upregulating related genes. Of interest, we also report that CNP-NPR2 signaling is inhibited in aging follicles, and this inhibition is implicated in lower mtDNA copy number in oocytes from aging females. Together, our study provides the first direct functional link between follicular CNP and oocyte mtDNA replication, and identifies its involvement in aging-associated mtDNA loss in oocytes. These findings, not only update the current knowledge of the functions of CNP in coordinating oocyte maturation but also present a promising strategy for improving in vitro fertilization outcomes of aging females.

The CR9 element is a novel mechanical load-responsive enhancer that regulates natriuretic peptide genes expression.

Enhancers regulate gene expressions in a tissue- and pathology-specific manner by altering its activities. Plasma levels of atrial and brain natriuretic peptides, encoded by the Nppa and Nppb, respectively, and synthesized predominantly in cardiomyocytes, vary depending on the severity of heart failure. We previously identified the noncoding conserved region 9 (CR9) element as a putative Nppb enhancer at 22-kb upstream from the Nppb gene. However, its regulatory mechanism remains unknown. Here, we therefore investigated the mechanism of CR9 activation in cardiomyocytes using different kinds of drugs that induce either cardiac hypertrophy or cardiac failure accompanied by natriuretic peptides upregulation. Chronic treatment of mice with either catecholamines or doxorubicin increased CR9 activity during the progression of cardiac hypertrophy to failure, which is accompanied by proportional increases in Nppb expression. Conversely, for cultured cardiomyocytes, doxorubicin decreased CR9 activity and Nppb expression, while catecholamines increased both. However, exposing cultured cardiomyocytes to mechanical loads, such as mechanical stretch or hydrostatic pressure, upregulate CR9 activity and Nppb expression even in the presence of doxorubicin. Furthermore, the enhancement of CR9 activity and Nppa and Nppb expressions by either catecholamines or mechanical loads can be blunted by suppressing mechanosensing and mechanotransduction pathways, such as muscle LIM protein (MLP) or myosin tension. Finally, the CR9 element showed a more robust and cell-specific response to mechanical loads than the -520-bp BNP promoter. We concluded that the CR9 element is a novel enhancer that responds to mechanical loads by upregulating natriuretic peptides expression in cardiomyocytes.

Epigenetic control of natriuretic peptides: implications for health and disease.

The natriuretic peptides (NPs) family, including a class of hormones and their receptors, is largely known for its beneficial effects within the cardiovascular system to preserve regular functions and health. The concentration level of each component of the family is of crucial importance to guarantee a proper control of both systemic and local cardiovascular functions. A fine equilibrium between gene expression, protein secretion and clearance is needed to achieve the final optimal level of NPs. To this aim, the regulation of gene expression and translation plays a key role. In this regard, we know the existence of fine regulatory mechanisms, the so-called epigenetic mechanisms, which target many genes at either the promoter or the 3'UTR region to inhibit or activate their expression. The gene encoding ANP (NPPA) is regulated by histone modifications, DNA methylation, distinct microRNAs and a natural antisense transcript (NPPA-AS1) with consequent implications for both health and disease conditions. Notably, ANP modulates microRNAs on its own. Histone modifications of BNP gene (NPPB) are associated with several cardiomyopathies. The proBNP processing is regulated by miR30-GALNT1/2 axis. Among other components of the NPs family, CORIN, NPRA, NPRC and NEP may undergo epigenetic regulation. A better understanding of the epigenetic control of the NPs family will allow to gain more insights on the pathological basis of common cardiovascular diseases and to identify novel therapeutic targets. The present review article aims to discuss the major achievements obtained so far with studies on the epigenetic modulation of the NPs family.

Assessment of causality of natriuretic peptides and atrial fibrillation and heart failure: a Mendelian randomization study in the FINRISK cohort.

AIMS: Natriuretic peptides are extensively studied biomarkers for atrial fibrillation (AF) and heart failure (HF). Their role in the pathogenesis of both diseases is not entirely understood and previous studies several single-nucleotide polymorphisms (SNPs) at the NPPA-NPPB locus associated with natriuretic peptides have been identified. We investigated the causal relationship between natriuretic peptides and AF as well as HF using a Mendelian randomization approach. METHODS AND RESULTS: N-terminal pro B-type natriuretic peptide (NT-proBNP) (N = 6669), B-type natriuretic peptide (BNP) (N = 6674), and mid-regional pro atrial natriuretic peptide (MR-proANP) (N = 6813) were measured in the FINRISK 1997 cohort. N = 30 common SNPs related to NT-proBNP, BNP, and MR-proANP were selected from studies. We performed six Mendelian randomizations for all three natriuretic peptide biomarkers and for both outcomes, AF and HF, separately. Polygenic risk scores (PRSs) based on multiple SNPs were used as genetic instrumental variable in Mendelian randomizations. Polygenic risk scores were significantly associated with the three natriuretic peptides. Polygenic risk scores were not significantly associated with incident AF nor HF. Most cardiovascular risk factors showed significant confounding percentages, but no association with PRS. A causal relation except for small causal betas is unlikely. CONCLUSION: In our Mendelian randomization approach, we confirmed an association between common genetic variation at the NPPA-NPPB locus and natriuretic peptides. A strong causal relationship between natriuretic peptides and incidence of AF as well as HF at the community-level was ruled out. Therapeutic approaches targeting natriuretic peptides will therefore very likely work through indirect mechanisms.

Tuscany Sangiovese grape juice imparts cardioprotection by regulating gene expression of cardioprotective C-type natriuretic peptide.

PURPOSE: A regular intake of red grape juice has cardioprotective properties, but its role on the modulation of natriuretic peptides (NPs), in particular of C-type NP (CNP), has not yet been proven. The aims were to evaluate: (1) in vivo the effects of long-term intake of Tuscany Sangiovese grape juice (SGJ) on the NPs system in a mouse model of myocardial infarction (MI); (2) in vitro the response to SGJ small RNAs of murine MCEC-1 under physiological and ischemic condition; (3) the activation of CNP/NPR-B/NPR-C in healthy human subjects after 7 days' SGJ regular intake. METHODS: (1) C57BL/6J male and female mice (n = 33) were randomly subdivided into: SHAM (n = 7), MI (n = 15) and MI fed for 4 weeks with a normal chow supplemented with Tuscany SGJ (25% vol/vol, 200 µl/per day) (MI + SGJ, n = 11). Echocardiography and histological analyses were performed. Myocardial NPs transcriptional profile was investigated by Real-Time PCR. (2) MCEC-1 were treated for 24 h with a pool of SGJ small RNAs and cell viability under 24 h exposure to H2O2 was evaluated by MTT assay. (3) Human blood samples were collected from seven subjects before and after the 7 days' intake of Tuscany SGJ. NPs and miRNA transcriptional profile were investigated by Real-Time PCR in MCEC-1 and human blood. RESULTS: Our experimental data, obtained in a multimodal pipeline, suggest that the long-term intake of SGJ promotes an adaptive response of the myocardium to the ischemic microenvironment through the modulation of the cardiac CNP/NPR-B/NPR-C system. CONCLUSIONS: Our results open new avenue in the development of functional foods aimed at enhancing cardioprotection of infarcted hearts through action on the myocardial epigenome.

Palmitic acid induces guanylin gene expression through the Toll-like receptor 4/nuclear factor-κB pathway in rat macrophages.

Recently, we showed that double-transgenic rats overexpressing guanylin (Gn), a bioactive peptide, and its receptor, guanylyl cyclase-C (GC-C), specifically in macrophages demonstrate an antiobesity phenotype and low-expression levels of proinflammatory cytokines in the mesenteric fat even when fed a high-fat diet. Here, we examined the levels and mechanism of Gn and GC-C transcription following saturated fatty acid and lipopolysaccharide (LPS), an activator of Toll-like receptor 4 (TLR4), exposure by using the NR8383 macrophage cell line. In addition, the levels of guanylin and cGMP were increased by addition of either palmitic acid or LPS. Next, we investigated the interaction of the gene transcription and nuclear factor-κB (NF-κB) by using an NF-κB inhibitor and chromatin immunoprecipitation assay. We showed that palmitic acid induced Gn gene expression via TLR4 and NF-κB. Moreover, we demonstrated that NF-κB binding to the Gn promoter was responsible for the induction of gene transcription by palmitic acid or LPS. Our results indicate that saturated fatty acids such as palmitic acid activate Gn gene expression via the NF-κB pathway, raising the possibility that the activated Gn-GC-C system may contribute to the inhibition of high-fat diet-induced proinflammatory cytokines in macrophages.

Comprehensive Study of the Proteome and Transcriptome of the Venom of the Most Venomous European Viper: Discovery of a New Subclass of Ancestral Snake Venom Metalloproteinase Precursor-Derived Proteins.

The nose-horned viper, its nominotypical subspecies Vipera ammodytes ammodytes ( Vaa), in particular, is, medically, one of the most relevant snakes in Europe. The local and systemic clinical manifestations of poisoning by the venom of this snake are the result of the pathophysiological effects inflicted by enzymatic and nonenzymatic venom components acting, most prominently, on the blood, cardiovascular, and nerve systems. This venom is a very complex mixture of pharmacologically active proteins and peptides. To help improve the current antivenom therapy toward higher specificity and efficiency and to assist drug discovery, we have constructed, by combining transcriptomic and proteomic analyses, the most comprehensive library yet of the Vaa venom proteins and peptides. Sequence analysis of the venom gland cDNA library has revealed the presence of messages encoding 12 types of polypeptide precursors. The most abundant are those for metalloproteinase inhibitors (MPis), bradykinin-potentiating peptides (BPPs), and natriuretic peptides (NPs) (all three on a single precursor), snake C-type lectin-like proteins (snaclecs), serine proteases (SVSPs), P-II and P-III metalloproteinases (SVMPs), secreted phospholipases A2 (sPLA2s), and disintegrins (Dis). These constitute >88% of the venom transcriptome. At the protein level, 57 venom proteins belonging to 16 different protein families have been identified and, with SVSPs, sPLA2s, snaclecs, and SVMPs, comprise ∼80% of all venom proteins. Peptides detected in the venom include NPs, BPPs, and inhibitors of SVSPs and SVMPs. Of particular interest, a transcript coding for a protein similar to P-III SVMPs but lacking the MP domain was also found at the protein level in the venom. The existence of such proteins, also supported by finding similar venom gland transcripts in related snake species, has been demonstrated for the first time, justifying the proposal of a new P-IIIe subclass of ancestral SVMP precursor-derived proteins.

Natriuretic peptides appeared after their receptors in vertebrates.

BACKGROUND: In mammals, the natriuretic system contains three natriuretic peptides, NPPA, NPPB and NPPC, that bind to three transmembrane receptors, NPR1, NPR2 and NPR3. The natriuretic peptides are known only in vertebrates. In contrast, the receptors have orthologs in all the animal taxa and in plants. However, in non-vertebrates, these receptors do not have natriuretic properties, and most of their ligands are unknown. How was the interaction of the NP receptors and the NP established in vertebrates? Do natriuretic peptides have orthologs in non-vertebrates? If so, what was the function of the interaction? How did that function change? If not, are the NP homologous to ancestral NPR ligands? Or did the receptor's binding pocket completely change during evolution? METHODS: In the present study, we tried to determine if the pairs of natriuretic receptors and their ligands come from an ancestral pair, or if the interaction only appeared in vertebrates. Alignments, modeling, docking, research of positive selection, and motif research were performed in order to answer this question. RESULTS: We discovered that the binding pocket of the natriuretic peptide receptors was completely remodeled in mammals. We found several peptides in non vertebrates that could be related to human natriuretic peptides, but a set of clues, as well as modeling and docking analysis, suggest that the natriuretic peptides undoubtedly appeared later than their receptors during animal evolution. We suggest here that natriuretic peptide receptors in non vertebrates bind to other ligands. CONCLUSIONS: The present study further support that vertebrate natriuretic peptides appeared after their receptors in the tree of life. We suggest the existence of peptides that resemble natriuretic peptides in non-vertebrate species, that might be the result of convergent evolution.

Renoguanylin stimulates apical CFTR translocation and decreases HCO3- secretion through PKA activity in the Gulf toadfish (Opsanus beta).

The guanylin peptides - guanylin, uroguanylin and renoguanylin (RGN) - are endogenously produced hormones in teleost fish enterocytes that are activators of guanylyl cyclase-C (GC-C) and are potent modulators of intestinal physiology, particularly in seawater teleosts. Most notably, they reverse normal net ion-absorbing mechanisms that are vital to water absorption, an important process for seawater teleost survival. The role of guanylin-peptide stimulation of the intestine remains unclear, but it is hypothesized to facilitate the removal of solids from the intestine by providing fluid to enable their removal by peristalsis. The present study used one member of this group of peptides - RGN - to provide evidence for the prominent role that protein kinase A (PKA) plays in mediating the effects of guanylin-peptide stimulation in the posterior intestine of the Gulf toadfish (Opsanus beta). Protein kinase G was found to not mediate the intracellular effects of RGN, despite previous evidence showing that GC-C activation leads to higher cyclic guanosine monophosphate formation. RGN reversed the absorptive short-circuit current and increased conductance in the Gulf toadfish intestine. These effects are correlated to increased trafficking of the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel to the apical membrane, which is negated by PKA inhibition. Moreover, RGN decreased HCO3- secretion, likely by limiting apical HCO3-/Cl- exchange (possibly by reducing SLC26a6 activity), a reduction that was enhanced by PKA inhibition. RGN seems to alter PKA activity in the posterior intestine to recruit CFTR to the apical membrane and reduce HCO3- secretion.

Natriuretic peptide system regulation in granulosa cells during follicle deviation and ovulation in cattle.

Natriuretic peptides (NPs) are known to regulate reproductive events in polyovulatory species, but their function and regulation in monovulatory species remain to be fully characterized. Using a well-established in vivo model, we found that bovine granulosa cells from follicles near the deviation stage express mRNA for the three NP receptors (NPR1, NPR2 and NPR3), but not for NP precursors (NPPA, NPPB and NPPC). The abundance of NPR3 mRNA was higher in dominant compared to subordinate follicles at the expected time of follicular deviation. After deviation, mRNA for all NP receptors was significantly more abundant in the dominant follicle. Intrafollicular inhibition of oestrogen receptors downregulated NPR1 mRNA in dominant follicles. In granulosa cells from preovulatory follicles, NPPC mRNA increased at 3 and 6 h after systemic GnRH treatment, but decreased at 12 and 24 h to similar levels observed in samples collected at 0 h. After GnRH treatment, NPR1 mRNA was upregulated at 24 h, NPR3 mRNA gradually decreased after 3 h, while NPR2 mRNA was not regulated. The mRNA expression of the enzyme FURIN increased at 24 h after GnRH treatment. These findings revealed that the expression of mRNA encoding important components of the NP system is regulated in bovine granulosa cells during follicular deviation and in response to GnRH treatment, which suggests a role of NP system in the modulation of these processes in monovulatory species.

Theoretical structural characterization of lymphoguanylin: A potential candidate for the development of drugs to treat gastrointestinal disorders.

Guanylin peptides (GPs) are small cysteine-rich peptide hormones involved in salt absorption, regulation of fluids and electrolyte homeostasis. This family presents four members: guanylin (GN), uroguanylin (UGN), lymphoguanylin (LGN) and renoguanylin (RGN). GPs have been used as templates for the development of drugs for the treatment of gastrointestinal disorders. Currently, LGN is the only GP with only one disulfide bridge, making it a remarkable member of this family and a potential drug template; however, there is no structural information about this peptide. In fact, LGN is predicted to be highly disordered and flexible, making it difficult to obtain structural information using in vitro methods. Therefore, this study applied a series of 1µs molecular dynamics simulations in order to understand the structural behavior of LGN, comparing it to the C115Y variant of GN, which shows the same Cys to Tyr modification. LGN showed to be more flexible than GN C115Y. While the negatively charged N-terminal, despite its repellent behavior, seems to be involved mainly in pH-dependent activity, the hydrophobic core showed to be the determinant factor in LGN's flexibility, which could be essential in its activity. These findings may be determinant in the development of new medicines to help in the treatment of gastrointestinal disorders. Moreover, our investigation of LGN structure clarified some issues in the structure-activity relationship of this peptide, providing new knowledge of guanylin peptides and clarifying the differences between GN C115Y and LGN.

The Role of Biomarkers in Detection of Cardio-toxicity.

The goal of this paper is to review the current literature on the role of biomarkers in the detection and management of patients with cardio-oncologic disease. The role of biomarker surveillance in patients with known cardiac disease, as a result of chemotherapy or with the potential to develop cardio-toxicity, will be discussed. In addition, the studies surrounding sub-clinical cardiac toxicity monitoring during therapy, identification of high-risk patients prior to therapy, and tailoring oncologic therapies to potential biomarker risk profiles are reviewed. Based on evidence, to date, troponin and natriuretic peptides have the greatest potential to detect sub-clinical cardiac dysfunction and even tailor therapy to prevent progression based on biomarker profiles. Finally, future directions for potential utilization of novel biomarkers for the improvement of care of patients in the field of cardio-oncology are discussed.

[Natriuretic peptide precursor C coding gene contributes to zebrafish angiogenesis].

This study aimed to investigate the expression of the natriuretic peptide precursor C coding gene nppc and its role in angiogenesis during embryonic period of the zebrafish. Whole mount in situ hybridization was performed to detect the expression pattern of nppc. nppc specific morpholino and nppc mRNA were injected respectively into the one-cell stage embryo to specifically knock-down and rescue the expression of nppc in Tg (flk1:GFP) and Tg (fli1a:nGFP) transgenic lines. The morphology and endothelial cell number of intersegmental vessel (ISV) were analyzed after imaging using the laser scanning confocal microscope. The results revealed that nppc was expressed in the brain, heart and vasculature of zebrafish larvae at 24 and 48 hours post-fertilization (hpf). Knock-down of nppc affected the development of ISV. Endothelial cell number was reduced after the knock-down of nppc. These results suggest that nppc controls zebrafish angiogenesis by affecting the endothelial cell proliferation and migration.

Guanylin and uroguanylin are produced by mouse intestinal epithelial cells of columnar and secretory lineage.

Guanylin (GN) and uroguanylin (UGN), through activation of guanylyl cyclase C (GCC), serve to control intestinal fluid homeostasis. Both peptides are produced in the intestinal epithelium, but their cellular origin has not been fully charted. Using quantitative PCR and an improved in situ hybridization technique (RNAscope), we have assessed the expression of GN (Guca2a), UGN (Guca2b), and GCC (Gucy2c) in mouse intestine. In the crypts of Lieberkühn, expression of Guca2a and Guca2b was restricted to cells of secretory lineage, at the crypt's base, and to a region above, previously identified as a common origin of cellular differentiation. In this compartment, comparatively uniform levels of Guca2a and Guca2b expression were observed throughout the length of the gut. In contrast, Guca2a and Guca2b expression in the villus-surface region was more variable, and reflected the distinct, but overlapping expression pattern observed previously. Accordingly, in jejunum and ileum, Guca2a and Guca2b were abundantly expressed by enterocytes, whereas in colon only Guca2a transcript was found in the surface region. In duodenum, only low levels of Guca2b transcript were observed in columnar cells, and Guca2a expression was restricted entirely to cells of the secretory lineage. Gucy2c was shown to be expressed relatively uniformly along the rostrocaudal and crypt-villus axes and was also found in the duodenal glands. Our study reveals novel aspects of the cellular localization of the GCC signaling axis that, apart from its role in the regulation of fluid balance, link it to pH regulation, cell cycle control, and host defense.

Structural impact analysis of missense SNPs present in the uroguanylin gene by long-term molecular dynamics simulations.

The guanylate cyclase activator 2B, also known as uroguanylin, is part of the guanylin peptide family, which includes peptides such as guanylin and lymphoguanylin. The guanylin peptides could be related to sodium absorption inhibition and water secretion induction and their dysfunction may be related to various pathologies such as chronic renal failure, congestive heart failure and nephrotic syndrome. Besides, uroguanylin point mutations have been associated with essential hypertension. However, currently there are no studies on the impact of missense SNPs on uroguanylin structure. This study applied in silico SNP impact prediction tools to evaluate the impact of uroguanylin missense SNPs and to filter those considered as convergent deleterious, which were then further analyzed through long-term molecular dynamics simulations of 1µs of duration. The simulations suggested that all missense SNPs considered as convergent deleterious caused some kind of structural change to the uroguanylin peptide. Additionally, four of these SNPs were also shown to cause modifications in peptide flexibility, possibly resulting in functional changes.

Uroguanylin levels in intestine and plasma are regulated by nutritional status in a leptin-dependent manner.

PURPOSE: Uroguanylin (UGN) is a 16 amino acid peptide produced mainly by intestinal epithelial cells. Nutrients intake increases circulating levels of prouroguanylin that is processed and converted to UGN to activate the guanylyl cyclase 2C receptor (GUCY2C). Given that the UGN-GUCY2C system has been proposed as a novel gut-brain endocrine axis regulating energy balance, the aim of the present study was to investigate the regulation of UGN protein levels in duodenum and circulating levels in lean and obese mice under different nutritional conditions and its potential interaction with leptin. METHODS: Swiss, C57BL/6 wild-type and ob/ob male adult mice under different nutritional conditions were used: fed ad libitum standard diet (control); 48 h fasting (fasted); 48 h fasting followed by 24 h of feeding (refed); and fed high-fat diet (45 %) during 10 weeks. In addition, peripheral leptin administration was performed. Intestinal uroguanylin expression was studied by Western blot analysis; plasma levels were measured by ELISA. RESULTS: Food deprivation significantly reduced plasma UGN levels, which were correlated with the lower protein levels of UGN in duodenum. These effects were reverted after refeeding and leptin challenge. Consistently, in ob/ob mice UGN expression was decreased, whereas leptin treatment up-regulated UGN levels in duodenum in these genetically modified mice compared to WT. Diet-induced obese mice displayed increased UGN levels in intestine and plasma in comparison with lean mice. CONCLUSIONS: Our findings suggest that UGN levels are correlated with energy balance status and that the regulation of UGN by nutritional status is leptin-dependent.

Privileged frameworks from snake venom.

Venom as a form of chemical prey capture is a key innovation that has underpinned the explosive radiation of the advanced snakes (Caenophidia). Small venom proteins are often rich in disulfide bonds thus facilitating stable molecular scaffolds that present key functional residues on the protein surface. New toxin types are initially developed through the venom gland over-expression of normal body proteins, their subsequent gene duplication and diversification that leads to neofunctionalisation as random mutations modify their structure and function. This process has led to preferentially selected (privileged) cysteine-rich scaffolds that enable the snake to build arrays of toxins many of which may lead to therapeutic products and research tools. This review focuses on cysteine-rich small proteins and peptides found in snake venoms spanning natriuretic peptides to phospholipase enzymes, while highlighting their three-dimensional structures and biological functions as well as their potential as therapeutic agents or research tools.

Tail wags the dog: activity of krait natriuretic peptide is determined by its C-terminal tail in a natriuretic peptide receptor-independent manner.

Natriuretic peptides (NPs) are potent vasoactive hormones, which maintain pressure-volume homoeostasis. Snake venom NPs exhibit distinct biological activity compared with mammalian NPs due to subtle changes in their sequences. We recently identified a new NP from krait venom (KNP), with an unusual 38-residue long C-terminal tail, which has a propensity to form an α-helix. KNP mediates vasodilation via NP receptor (NPR) independent mechanisms on pre-contracted aortic strips in contrast with classical NPs. The infusion of KNP in anaesthetized rats resulted in a prolonged and sustained drop in blood pressure (BP) and heart rate (HR) with no renal effects in contrast with mammalian counterparts. Deletion mutant studies have revealed the presence of two functional segments in KNP, namely Ring and Helix. Although the Ring interacts with NPR, its contribution to the activity of KNP is shown to be negligible as both KNP and Helix elicit equipotent endothelium-dependent vasorelaxation. Further, KNP and Helix signalled through endothelial nitric oxide (NO) to mediate NPR-independent vasodilation. Thus, KNP exhibits non-canonical characteristics through its C-terminal tail, despite a functional NP ring. The present study has altered the paradigm of NP biology through the understanding of structure-function relationships and may serve as a lead for the design of novel hypotensive agents.

The differential role of renoguanylin in osmoregulation and apical Cl-/HCO3- exchange activity in the posterior intestine of the Gulf toadfish (Opsanus beta).

The guanylin family of peptides are effective regulators of intestinal physiology in marine teleosts. In the distal intestinal segments, they inhibit or reverse fluid absorption by inhibiting the absorptive short-circuit current (Isc). The present findings demonstrate that mRNA from guanylin and uroguanylin, as well as at least one isoform of the guanylin peptide receptor, apical guanylyl cyclase-C (GC-C), was highly expressed in the intestine and rectum of the Gulf toadfish (Opsanus beta). In the posterior intestine, GC-C, as well as the cystic fibrosis transmembrane conductance regulator and basolateral Na(+)/K(+)/2Cl(-) cotransporter, which comprise a Cl(-)-secretory pathway, were transcriptionally upregulated in 60 parts per thousand (ppt). The present study also shows that, in intestinal tissues from Gulf toadfish held in 35 ppt, renoguanylin (RGN) expectedly causes net Cl(-) secretion, inhibits both the absorptive Isc and fluid absorption, and decreases HCO3(-) secretion. Likewise, in intestinal tissues from Gulf toadfish acclimated to 60 ppt, RGN also inhibits the absorptive Isc and fluid absorption but to an even greater extent, corresponding with the mRNA expression data. In contrast, RGN does not alter Cl(-) flux and, instead, elevates HCO3(-) secretion in the 60-ppt group, suggesting increased apical Cl(-)/HCO3(-) exchange activity by SLC26a6. Overall, these findings reinforce the hypotheses that the guanylin peptide system is important for salinity acclimatization and that the secretory response could facilitate the removal of solids, such as CaCO3 precipitates, from the intestine.

Guanylin-Guanylyl cyclase-C signaling in macrophages regulates mesenteric fat inflammation induced by high-fat diet.

Guanylin (Gn), a bioactive peptide, and its receptor, guanylyl cyclase-C (GC-C), are primarily present in the intestine and maintain homeostasis in body fluids. Recently, rats whose macrophages overexpress Gn and GC-C were found to be resistant to diet-induced obesity. Considering that obesity is strongly related to a chronic inflammatory state in white adipose tissues, it is possible that Gn-GC-C macrophages contribute to the regulation of inflammation. In the present study, we investigated the inflammatory state of mesenteric fat in rats transgenic for both Gn and GC-C (double-transgenic [dTg] rats) by evaluating the levels of cyclic guanosine monophosphate (cGMP), a second messenger of Gn-GC-C, cGMP-dependent protein kinase (PKG), and phosphorylated vasodilator-stimulated phosphoprotein (VASP), a target protein of PKG. The levels of cGMP in dTg rats was higher than in WT rats fed the same diet. Although there were no significant differences in levels of PKG and phosphorylated VASP between WT and dTg rats fed a standard diet (STD), these levels in dTg rats fed a high fat diet (HFD) were markedly increased compared with levels in HFD WT rats. Furthermore, mRNA levels of proinflammatory factors in mesenteric fat were lower in HFD dTg rats than in HFD WT rats and were similar to levels in STD WT and dTg rats. These results indicate that the Gn-GC-C system in macrophages regulates the cGMP-PKG-VASP pathway and controls obesity through the downregulation of proinflammatory factors.