[Cyclic nucleotide phosphodiesterases: therapeutic targets in cardiac hypertrophy and failure]. / Les phosphodiestérases des nucléotides cycliques - Cibles thérapeutiques dans l'hypertrophie et l'insuffisance cardiaques.

Cyclic nucleotide phosphodiesterases (PDEs) modulate neurohormonal regulation of cardiac function by degrading cAMP and cGMP. In cardiomyocytes, multiple isoforms of PDEs with different enzymatic properties and subcellular locally regulate cyclic nucleotide levels and associated cellular functions. This organisation is severely disrupted during hypertrophy and heart failure (HF), which may contribute to disease progression. Clinically, PDE inhibition has been seen as a promising approach to compensate for the catecholamine desensitisation that accompanies heart failure. Although PDE3 inhibitors such as milrinone or enoximone can be used clinically to improve systolic function and relieve the symptoms of acute CHF, their chronic use has proved detrimental. Other PDEs, such as PDE1, PDE2, PDE4, PDE5, PDE9 and PDE10, have emerged as potential new targets for the treatment of HF, each with a unique role in local cyclic nucleotide signalling pathways. In this review, we describe cAMP and cGMP signalling in cardiomyocytes and present the different families of PDEs expressed in the heart and their modifications in pathological cardiac hypertrophy and HF. We also review results from preclinical models and clinical data indicating the use of specific PDE inhibitors or activators that may have therapeutic potential in CI.

Title: Les phosphodiestérases des nucléotides cycliques - Cibles thérapeutiques dans l'hypertrophie et l'insuffisance cardiaques. Abstract: Les phosphodiestérases des nucléotides cycliques (PDE) modulent la régulation neuro-hormonale de la fonction cardiaque en dégradant l'AMPc et le GMPc. Dans les cardiomyocytes, de multiples isoformes de PDE, aux propriétés enzymatiques et aux localisations subcellulaires différentes, régulent localement les niveaux de nucléotides cycliques et les fonctions cellulaires associées. Cette organisation est fortement perturbée au cours de l'hypertrophie et de l'insuffisance cardiaque à fraction d'éjection réduite (IC), ce qui peut contribuer à la progression de la maladie. Sur le plan clinique, l'inhibition des PDE a été considérée comme une approche prometteuse pour compenser la désensibilisation aux catécholamines qui accompagne l'IC. Bien que des inhibiteurs de la PDE3, tels que la milrinone ou l'énoximone, puissent être utilisés cliniquement pour améliorer la fonction systolique et soulager les symptômes de l'IC aiguë, leur utilisation chronique s'est avérée préjudiciable. D'autres PDE, telles que les PDE1, PDE2, PDE4, PDE5, PDE9 et PDE10, sont apparues comme de nouvelles cibles potentielles pour le traitement de l'IC, chacune ayant un rôle unique dans les voies de signalisation locales des nucléotides cycliques. Dans cette revue, nous décrivons la signalisation de l'AMPc et du GMPc dans les cardiomyocytes et présentons les différentes familles de PDE exprimées dans le cœur ainsi que leurs modifications dans l'hypertrophie cardiaque pathologique et dans l'IC. Nous évaluons également les résultats issus de modèles précliniques ainsi que les données cliniques indiquant l'utilisation d'inhibiteurs ou d'activateurs de PDE spécifiques qui pourraient avoir un potentiel thérapeutique dans l'IC.

Theophylline-induced endothelium-dependent vasodilation is mediated by increased nitric oxide release and phosphodiesterase inhibition in rat aorta.

This study aimed to examine the endothelial dependence of vasodilation induced by the phosphodiesterase inhibitor theophylline in isolated rat thoracic aortas and elucidate the underlying mechanism, with emphasis on endothelial nitric oxide (NO). The effects of various inhibitors and endothelial denudation on theophylline-induced vasodilation, and the effect of theophylline on vasodilation induced by NO donor sodium nitroprusside, cyclic guanosine monophosphate (cGMP) analog bromo-cGMP, and ß-agonist isoproterenol in endothelium-denuded aorta were examined. The effects of theophylline and sodium nitroprusside on cGMP formation were also examined. We examined the effect of theophylline on endothelial nitric oxide synthase (eNOS) phosphorylation and intracellular calcium levels. Theophylline-induced vasodilation was greater in endothelium-intact aortas than that in endothelium-denuded aortas. The NOS inhibitor, NW-nitro-L-arginine methyl ester; non-specific guanylate cyclase (GC) inhibitor, methylene blue; and NO-sensitive GC inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a] quinoxalin-1-one inhibited theophylline-induced vasodilation in endothelium-intact aortas. Theophylline increased the vasodilation induced by sodium nitroprusside, bromo-cGMP, and isoproterenol. Theophylline increased cGMP formation in endothelium-intact aortas, and sodium nitroprusside-induced cGMP formation in endothelium-denuded aortas. Moreover, theophylline increased stimulatory eNOS (Ser1177) phosphorylation and endothelial calcium levels, but decreased the phosphorylation of inhibitory eNOS (Thr495). These results suggested that theophylline-induced endothelium-dependent vasodilation was mediated by increased endothelial NO release and phosphodiesterase inhibition.

Dynamics of intracellular cGMP during chemotaxis in Dictyostelium cells.

Cyclic guanosine 3',5'-monophosphate (cGMP) is a ubiquitous important second messenger involved in various physiological functions. Here, intracellular cGMP (cGMPi) was visualized in chemotactic Dictyostelium cells using the fluorescent probe, D-Green cGull. When wild-type cells were stimulated with a chemoattractant, fluorescence transiently increased, but guanylate cyclase-null cells did not show a change in fluorescence, suggesting that D-Green cGull is a reliable indicator of cGMPi. In the aggregation stage, the responses of cGMPi propagated in a wave-like fashion from the aggregation center. The oscillation of the cGMPi wave was synchronized almost in phase with those of other second messengers, such as the intracellular cAMP and Ca2+. The phases of these waves preceded those of the oscillations of actomyosin and cell velocity, suggesting that these second messengers are upstream of the actomyosin and chemotactic migration. An acute increase in cGMPi concentration released from membrane-permeable caged cGMP induced a transient shuttle of myosin II between the cytosol and cell cortex, suggesting a direct link between cGMP signaling and myosin II dynamics.

Pharmacodynamic properties for inhibition of cAMP- and cGMP elimination by pentoxifylline remain unaltered in vitro during hypothermia.

BACKGROUND: Rewarming from hypothermia is associated with severe complications, one of which is hypothermia-induced cardiac dysfunction. This condition is characterized by decreased cardiac output accompanied by increased total peripheral resistance. This contributes to mortality rate approaching 40%. Despite this, no pharmacological interventions are recommended for these patients below 30 °C. Raising the intracellular levels of cAMP and/or cGMP, through PDE3- and PDE5-inhibitors respectively, have showed the ability to alleviate hypothermia-induced cardiac dysfunction in vivo. Drugs that raise levels of both cAMP and cGMP could therefore prove beneficial in patients suffering from hypothermia-induced cardiac dysfunction. METHODS: The unselective PDE-inhibitor pentoxifylline was investigated to determine its ability to reach the intracellular space, inhibit PDE3 and PDE5 and inhibit cellular efflux of cAMP and cGMP at temperatures 37, 34, 30, 28, 24 and 20 °C. Recombinant human PDE-enzymes and human erythrocytes were used in the experiments. IC50-values were calculated at all temperatures to determine temperature-dependent changes. RESULTS: At 20 °C, the IC50-value for PDE5-mediated enzymatic breakdown of cGMP was significantly increased compared to normothermia (IC50: 39.4 µM ± 10.9 µM vs. 7.70 µM ± 0.265 µM, p-value = 0.011). No other significant changes in IC50-values were observed during hypothermia. CONCLUSIONS: This study shows that pentoxifylline has minimal temperature-dependent pharmacodynamic changes, and that it can inhibit elimination of both cAMP and cGMP at low temperatures. This can potentially be effective treatment of hypothermia-induced cardiac dysfunction. TRIAL REGISTRATION: Not applicable.

IGFBP7-AS1 is a p53-responsive long noncoding RNA downregulated by Epstein-Barr virus that contributes to viral tumorigenesis.

Epstein-Barr virus (EBV) is closely related to the development of several malignancies, such as B-cell lymphoma (B-CL), by the mechanism through which these malignancies develop remains largely unknown. We previously observed downregulation of the long noncoding RNA (lncRNA) IGFBP7-AS1 in response to EBV infection. However, the role of IGFBP7-AS1 in EBV-associated cancers has not been clarified. Here, we found that expression of IGFBP7-AS1, as well as its sense gene IGFBP7, is decreased in EBV-positive B-CL cells and clinical tissues. IGFBP7-AS1 stabilizes IGFBP7 mRNA by forming a duplex based on their overlapping regions. The tumour suppressor p53 transcriptionally activates IGFBP7-AS1 expression by binding to the promoter region of the lncRNA gene. The IGFBP7-AS1 expression is able to be rescued in EBV-positive cells in wild-type (wt) p53-dependent manner. IGFBP7-AS1 inhibits the proliferation and promotes the apoptosis of B-CL cells. Moreover, tumorigenic properties due to the depletion of IGFBP7-AS1 were restored by exogenous expression of IGFBP7 or wt-p53. Furthermore, the functional p53/IGFBP7-AS1/IGFBP7 axis facilitates apoptosis by suppressing the production and secretion of the NPPB signal peptide and further regulating the cGMP-PKG signalling pathway. This study demonstrates that EBV promotes tumorigenesis, particularly in B-CL progression, by downregulating the novel p53-responsive lncRNA IGFBP7-AS1.

Protein kinase G phosphorylates the Alzheimer's disease-associated tau protein at distinct Ser/Thr sites.

Intraneuronal accumulation of hyperphosphorylated tau is a pathological hallmark of several neurodegenerative disorders, including Alzheimer's disease. Phosphorylation plays a crucial role in modulating the tau-microtubule interaction and the ability of the protein to aggregate, but despite efforts during the past decades, the real identity of the kynases involved in vivo remains uncertain. Here, for the first time, we demonstrate that the cGMP-dependent protein kinase G (PKG) phosphorylates tau in both in vitro and in vivo models. More intriguingly, we provide evidence that PKG phosphorylates tau at Ser214 but not at Ser202, a condition that could reduce the pathological aggregation of the protein shifting tau from a pro-aggregant to a neuroprotective anti-aggregant conformation.

Possible protective effect of TNF-α inhibition and triad NO/cGMP/VEGF activation on gastric ulcer in rats.

Peptic ulcers are one of the world's major gastrointestinal disorders, embracing both gastric and duodenal ulcers, and affecting 10% of the world population. The current study aimed to investigate the possible protective effect of tadalafil and pentoxifylline (PTX) on indomethacin-induced peptic ulcers. Male albino rats were divided into five groups: control group; ulcerated group; Indomethacin + Tadalafil, in which animals were pretreated with tadalafil orally before indomethacin; Indomethacin+ PTX, in which animals were pretreated with PTX orally before indomethacin; and Indomethacin + Tadafil + PTX. Indomethacin treatment revealed histopathological changes and ulcer scoring and ulcer index were markedly increased. Serum levels of prostaglandin and heme oxygenase-1 were significantly decreased. The ulcerogenic also induced marked oxidative stress as evident from the increased malondialdehyde, decreased in gastric glutathione content and superoxide dismutase activity, while the gastric myeloperoxidase was increased. Gastric nitric oxide content was decreased and the expression of vascular endothelial growth factor was downregulated while the tumor necrosis factor α (TNF-α) level was dramatically increased. Pretreatment of the ulcerative group by either tadalafil or PTX or their combination improved all these pathological changes. Tadalafil or PTX may have a role in protecting gastric mucosa damage caused by indomethacin which may be useful in the future for the treatment of gastric ulceration.

Atrial Natriuretic Peptide Improves Neurite Outgrowth from Spiral Ganglion Neurons In Vitro through a cGMP-Dependent Manner.

The spiral ganglion neurons (SGNs) are the primary afferent neurons in the spiral ganglion (SG), while their degeneration or loss would cause sensorineural hearing loss. As a cardiac-derived hormone, atrial natriuretic peptide (ANP) plays a critical role in cardiovascular homeostasis through binding to its functional receptors (NPR-A and NPR-C). ANP and its receptors are widely expressed in the mammalian nervous system where they could be implicated in the regulation of multiple neural functions. Although previous studies have provided direct evidence for the presence of ANP and its functional receptors in the inner ear, their presence within the cochlear SG and their regulatory roles during auditory neurotransmission and development remain largely unknown. Based on our previous findings, we investigated the expression patterns of ANP and its receptors in the cochlear SG and dissociated SGNs and determined the influence of ANP on neurite outgrowth in vitro by using organotypic SG explants and dissociated SGN cultures from postnatal rats. We have demonstrated that ANP and its receptors are expressed in neurons within the cochlear SG of postnatal rat, while ANP may promote neurite outgrowth of SGNs via the NPR-A/cGMP/PKG pathway in a dose-dependent manner. These results indicate that ANP would play a role in normal neuritogenesis of SGN during cochlear development and represents a potential therapeutic candidate to enhance regeneration and regrowth of SGN neurites.

Synaptic vesicle traffic is supported by transient actin filaments and regulated by PKA and NO.

Synaptic vesicles (SVs) can be pooled across multiple synapses, prompting questions about their dynamic allocation for neurotransmission and plasticity. We find that the axonal traffic of recycling vesicles is not supported by ubiquitous microtubule-based motility but relies on actin instead. Vesicles freed from synaptic clusters undergo ~1 µm bouts of active transport, initiated by nearby elongation of actin filaments. Long distance translocation arises when successive bouts of active transport were linked by periods of free diffusion. The availability of SVs for active transport can be promptly increased by protein kinase A, a key player in neuromodulation. Vesicle motion is in turn impeded by shutting off axonal actin polymerization, mediated by nitric oxide-cyclic GMP signaling leading to inhibition of RhoA. These findings provide a potential framework for coordinating post-and pre-synaptic strength, using retrograde regulation of axonal actin dynamics to mobilize and recruit presynaptic SV resources.

Molecular mechanisms and cellular functions of cGAS-STING signalling.

The cGAS-STING signalling axis, comprising the synthase for the second messenger cyclic GMP-AMP (cGAS) and the cyclic GMP-AMP receptor stimulator of interferon genes (STING), detects pathogenic DNA to trigger an innate immune reaction involving a strong type I interferon response against microbial infections. Notably however, besides sensing microbial DNA, the DNA sensor cGAS can also be activated by endogenous DNA, including extranuclear chromatin resulting from genotoxic stress and DNA released from mitochondria, placing cGAS-STING as an important axis in autoimmunity, sterile inflammatory responses and cellular senescence. Initial models assumed that co-localization of cGAS and DNA in the cytosol defines the specificity of the pathway for non-self, but recent work revealed that cGAS is also present in the nucleus and at the plasma membrane, and such subcellular compartmentalization was linked to signalling specificity of cGAS. Further confounding the simple view of cGAS-STING signalling as a response mechanism to infectious agents, both cGAS and STING were shown to have additional functions, independent of interferon response. These involve non-catalytic roles of cGAS in regulating DNA repair and signalling via STING to NF-κB and MAPK as well as STING-mediated induction of autophagy and lysosome-dependent cell death. We have also learnt that cGAS dimers can multimerize and undergo liquid-liquid phase separation to form biomolecular condensates that could importantly regulate cGAS activation. Here, we review the molecular mechanisms and cellular functions underlying cGAS-STING activation and signalling, particularly highlighting the newly emerging diversity of this signalling pathway and discussing how the specificity towards normal, damage-induced and infection-associated DNA could be achieved.

Combinatorial roles of mitochondria and cGMP/PKG pathway in the generation of neuronal free Zn2+ under the presence of nitric oxide.

BACKGROUND: Nitric oxide (NO), which possesses both protective and toxic properties, has been observed to have a complicated biphasic character within various types of tissues, including neuronal cells. NO was also found to cause the increase of another important signaling molecular Zn (termed as NZR). The molecular mechanism of NZR has been extensively investigated, but the source of Zn is present of a major candidate that is yet to be answered. The NO-protein kinase G (PKG) pathway, mitochondria, and metallothioneins (MTs), are all proposed to be the individual source of NZR. However, this hypothesis remains inconclusive. In this study, we examined the function of PKG signaling cascades, the mitochondria storage, and MT-1 during NZR of living PC12 cells. METHODS: We applied live-cell imaging in combination with pharmacological inhibitors and activators as well as in vitro Zn assay to dissect the functions of the above candidates in NZR. RESULTS: Two mechanisms, namely, mitochondria as the only Zn source and the opening of NO-PKG-dependent mitochondrial ATP-sensitive potassium channels (mKATP) as the key to releasing NO-induced increase in mitochondrial Zn, were proven to be the two critical paths of NZR in neuronal-related cells. CONCLUSION: This new finding provides a reasonable explanation to previously existing and contradictory conclusions regarding the function of mitochondria/mKATP and PKG signaling on the molecular mechanism of NZR.

Legionella quorum sensing meets cyclic-di-GMP signaling.

Bacterial gene regulation occurs through complex networks, wherein linear systems respond to intracellular or extracellular cues and engage on vivid crosstalk. The ubiquitous water-borne bacterium Legionella pneumophila colonizes various distinct environmental niches ranging from biofilms to protozoa, and - as an 'accidental' pathogen - the human lung. Consequently, L. pneumophila gene regulation evolved to integrate a broad spectrum of different endogenous and exogenous signals. Endogenous signals produced and detected by L. pneumophila comprise the quorum sensing autoinducer LAI-1 (3-hydroxypentadecane-4-one) and c-di-GMP. As an exogenous cue, nitric oxide controls the c-di-GMP regulatory network of L. pneumophila. The Legionella quorum sensing (Lqs) system regulates virulence, motility and natural competence of L. pneumophila. The Lqs system is linked to c-di-GMP signaling through the pleiotropic transcription factor LvbR, which also regulates the architecture of L. pneumophila biofilms. In this review, we highlight recent insights into the crosstalk of Legionella quorum sensing and c-di-GMP signaling.

Blood pressure lowering effect and vascular activity of Phyllanthus niruri extract: The role of NO/cGMP signaling pathway and ß-adrenoceptor mediated relaxation of isolated aortic rings.

ETHNOPHARMACOLOGICAL RELEVANCE: Phyllanthus niruri have a long history of use in the traditional treatment of various ailments including hypertension. Literature reports have indicated that it is a potent antihypertensive herbal medication used traditionally. AIM OF THE STUDY: This study was carried out to investigate the antihypertensive and vasodilatory activity of four solvents extracts of P. niruri namely; petroleum ether (PEPN), chloroform (CLPN), methanol (MEPN) and water (WEPN), with the aim of elucidating the mechanism of action and identifying the phytochemical constituents. MATERIALS AND METHODS: Male Spontaneous Hypertensive Rats (SHRs) were given oral gavage of P. niruri extract daily for two weeks and the blood pressure was recorded in vivo. We also determine the vasodilation effect of the extracts on rings of isolated thoracic aorta pre-contracted with phenylephrine (PE, 1 µM). Endothelium-intact or endothelium-denuded aorta rings were pre-incubated with various antagonists like 1H-[1,2,4] oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ, 10 µM) and Methylene blue (MB 10 µM), sGC inhibitors; Nω-Nitro-L-arginine methyl ester hydrochloride (L-NAME, 10 µM) a nitric oxide synthase (NOS) inhibitor; atropine (10 µM), a cholinergic receptor blocker; indomethacin (10 µM), a cyclooxygenase inhibitor and various K+ channel blockers such as glibenclamide (10 µM) and tetraethyl ammonium (TEA 10 µM) for mechanism study. RESULTS: SHRs receiving P. niruri extracts showed a significant decrease in their blood pressure (BP) when compared to the baseline value, with PEPN being more potent. The extracts (0.125-4 mg/mL) also induced vasorelaxation on endothelium-intact aorta rings. PEPN elicited the most potent maximum relaxation effect (Rmax). Mechanism assessment of PEPN showed that its relaxation effect is significantly suppressed in endothelium-denuded aorta rings. Pre-incubation of aorta rings with atropine, L-NAME, ODQ, indomethacin, and propranolol also significantly attenuated its relaxation effect. Conversely, incubation with TEA and glibenclamide did not show a significant effect on PEPN-induced relaxation. CONCLUSION: This study indicates that the antihypertensive activity of P. niruri extract is mediated by vasoactive phytoconstituents that dilate the arterial wall via endothelium-dependent pathways and ß-adrenoceptor activity which, in turn, cause vasorelaxation and reduce blood pressure.

c-di-GMP Arms an Anti-σ to Control Progression of Multicellular Differentiation in Streptomyces.

Streptomyces are our primary source of antibiotics, produced concomitantly with the transition from vegetative growth to sporulation in a complex developmental life cycle. We previously showed that the signaling molecule c-di-GMP binds BldD, a master repressor, to control initiation of development. Here we demonstrate that c-di-GMP also intervenes later in development to control differentiation of the reproductive hyphae into spores by arming a novel anti-σ (RsiG) to bind and sequester a sporulation-specific σ factor (σWhiG). We present the structure of the RsiG-(c-di-GMP)2-σWhiG complex, revealing an unusual, partially intercalated c-di-GMP dimer bound at the RsiG-σWhiG interface. RsiG binds c-di-GMP in the absence of σWhiG, employing a novel E(X)3S(X)2R(X)3Q(X)3D motif repeated on each helix of a coiled coil. Further studies demonstrate that c-di-GMP is essential for RsiG to inhibit σWhiG. These findings reveal a newly described control mechanism for σ-anti-σ complex formation and establish c-di-GMP as the central integrator of Streptomyces development.

Mechanical Stimuli Affect Escherichia coli Heat-Stable Enterotoxin-Cyclic GMP Signaling in a Human Enteroid Intestine-Chip Model.

Modeling host-pathogen interactions with human intestinal epithelia using enteroid monolayers on permeable supports (such as Transwells) represents an alternative to animal studies or use of colon cancer-derived cell lines. However, the static monolayer model does not expose epithelial cells to mechanical forces normally present in the intestine, including luminal flow and serosal blood flow (shear force) or peristaltic forces. To determine the contribution of mechanical forces in the functional response of human small intestine to a virulence factor of a pathogenic intestinal bacterium, human jejunal enteroids were cultured as monolayers in microengineered fluidic-based Organ-Chips (Intestine-Chips) exposed to enterotoxigenic Escherichia coli heat-stable enterotoxin A (ST) and evaluated under conditions of static fluid, apical and basolateral flow, and flow plus repetitive stretch. Application of flow increased epithelial cell height and apical and basolateral secretion of cyclic GMP (cGMP) under baseline, unstimulated conditions. Addition of ST under flow conditions increased apical and basolateral secretion of cGMP relative to the level under static conditions but did not enhance intracellular cGMP accumulation. Cyclic stretch did not have any significant effect beyond that contributed by flow. This study demonstrates that fluid flow application initiates changes in intestinal epithelial cell characteristics relative to those of static culture conditions under both baseline conditions and with exposure to ST enterotoxin and suggests that further investigations of the application of these mechanical forces will provide insights into physiology and pathophysiology that more closely resemble intact intestine than study under static conditions.

Vasorelaxation elicited by endogenous and exogenous hydrogen sulfide in mouse mesenteric arteries.

H2S causes vasorelaxation however there is considerable heterogeneity in the reported pharmacological mechanism of this effect. This study examines the contribution of endogenously released H2S in the regulation of vascular tone and the mechanism of H2S-induced vasorelaxation in small resistance-like arteries. Mesenteric arteries from C57 and eNOS-/- mice were mounted in myographs to record isometric force. Vasorelaxation responses to NaHS were examined in the presence of various inhibitors of vasorelaxation pathways. Expression and activity of the H2S-producing enzyme, cystathionine-γ-lyase (CSE), were also examined. CSE was expressed in vascular smooth muscle and perivascular adipose cells from mouse mesenteric artery. The substrate for CSE, L-cysteine, caused a modest vasorelaxation (35%) in arteries from C57 mice and poor vasorelaxation (10%) in arteries from eNOS-/- mice that was sensitive to the CSE inhibitor DL-propargylglycine. The fast H2S donor, NaHS, elicited a full and biphasic vasorelaxation response in mesenteric arteries (EC50 (1) 8.7 µM, EC50 (2) 0.6 mM), which was significantly inhibited in eNOS-/- vessels (P < 0.05), unaffected by endothelial removal, or blockers at any point in the NO via soluble guanylate cyclase and cGMP (NO-sGC-cGMP) vasorelaxation pathway. Vasorelaxation to NaHS was significantly inhibited by blocking K+ channels of the KCa and KV subtypes and the Cl-/HCO3- exchanger (P < 0.05). Further experiments showed that NaHS can significantly inhibit voltage-gated Ca2+ channel function (P < 0.05). The vasorelaxant effect of H2S in small resistance-like arteries is complex, involving eNOS, K+ channels, Cl-/HCO3- exchanger, and voltage-gated Ca2+ channels. CSE is present in the smooth muscle and periadventitial adipose tissue of these resistance-like vessels and can be activated to cause modest vasorelaxation under these in vitro conditions.

Chemotaxis and cyclic-di-GMP signalling control surface attachment of Escherichia coli.

Attachment to surfaces is an important early step during bacterial infection and during formation of submerged biofilms. Although flagella-mediated motility is known to be important for attachment of Escherichia coli and other bacteria, implications of motility regulation by cellular signalling remain to be understood. Here, we show that motility largely promotes attachment of E. coli, including that mediated by type 1 fimbriae, by allowing cells to reach, get hydrodynamically trapped at and explore the surface. Inactivation or inhibition of the chemotaxis signalling pathway improves attachment by suppressing cell reorientations and thereby increasing surface residence times. The attachment is further enhanced by deletion of genes encoding the cyclic diguanosine monophosphate (c-di-GMP)-dependent flagellar brake YcgR or the diguanylate cyclase DgcE. Such increased attachment in absence of c-di-GMP signalling is in contrast to its commonly accepted function as a positive regulator of the sessile state. It is apparently due to the increased swimming speed of E. coli in absence of YcgR-mediated motor control, which strengthens adhesion mediated by the type 1 fimbriae. Thus, both signalling networks that regulate motility of E. coli also control its engagement with both biotic and abiotic surfaces, which has likely implications for infection and biofilm formation.

LuxR-Type Regulator AclR1 of Azorhizobium caulinodans Regulates Cyclic di-GMP and Numerous Phenotypes in Free-Living and Symbiotic States.

LuxR-type regulators play important roles in transcriptional regulation in bacteria and control various biological processes. A genome sequence analysis showed the existence of seven LuxR-type regulators in Azorhizobium caulinodans ORS571, an important nitrogen-fixing bacterium in both its free-living state and in symbiosis with its host, Sesbania rostrata. However, the functional mechanisms of these regulators remain unclear. In this study, we identified a LuxR-type regulator that contains a cheY-homologous receiver (REC) domain in its N terminus and designated it AclR1. Interestingly, phylogenetic analysis revealed that AclR1 exhibited relatively close evolutionary relationships with MalT/GerE/FixJ/NarL family proteins. Functional analysis of an aclR1 deletion mutant (ΔaclR1) in the free-living state showed that AclR1 positively regulated cell motility and flocculation but negatively regulated exopolysaccharide production, biofilm formation, and second messenger cyclic diguanylate (c-di-GMP)-related gene expression. In the symbiotic state, the ΔaclR1 mutant was defective in competitive colonization and nodulation on host plants. These results suggested that AclR1 could provide bacteria with the ability to compete effectively for symbiotic nodulation. Overall, our results show that the REC-LuxR-type regulator AclR1 regulates numerous phenotypes both in the free-living state and during host plant symbiosis.

Associations Between the Cyclic Guanosine Monophosphate Pathway and Cardiovascular Risk Factors: MESA.

Background cGMP mediates numerous cardioprotective functions and is a potential therapeutic target for cardiovascular disease. Preclinical studies suggest that plasma cGMP is reflective of natriuretic peptide stimulation. Epidemiologic associations between cGMP and natriuretic peptide, as well as cardiovascular disease risk factors, are unknown. Methods and Results We measured plasma cGMP in 542 men and 496 women free of cardiovascular disease and heart failure in MESA (Multi-Ethnic Study of Atherosclerosis). Cross-sectional associations of N-terminal pro-B type natriuretic peptide, sex hormones, and cardiovascular disease/heart failure risk factors with log(cGMP) were analyzed using multivariable linear regression models. Mean (SD) cGMP was 4.7 (2.6) pmol/mL, with no difference between the sexes. After adjusting for cardiovascular risk factors, N-terminal pro-B type natriuretic peptide was significantly positively associated with cGMP (P<0.05). Higher blood pressure and lower estimated glomerular filtration rate were associated with higher cGMP (P<0.05). Triglyceride levels, total/high-density lipoprotein cholesterol ratio, presence of diabetes mellitus, and the homeostatic model assessment of insulin resistance were inversely associated with cGMP (P<0.05). Among women, free testosterone and dehydroepiandrosterone were inversely associated with cGMP, while sex hormone binding globulin was positively associated (P<0.05). Conclusions In a community-cohort, plasma cGMP was associated with natriuretic peptide signaling. Higher blood pressure and greater renal dysfunction were positively associated with cGMP, while adverse metabolic risk factors were inversely associated. Increased androgenicity in postmenopausal women was inversely associated with cGMP. These novel associations further our understanding of the role of cGMP in a general population.

Cyclic nucleotide-dependent relaxation in human umbilical vessels.

Umbilical vessels have a low sensitivity to dilate, and this property is speculated to have physiological implications. We aimed to investigate the different relaxing responses of human umbilical arteries (HUAs) and veins (HUVs) to agonists acting through the cAMP and cGMP pathways. Vascular rings were suspended in organ baths for isometric force measurement. Following precontraction with the thromboxane prostanoid (TP) receptor agonist U44069, concentration-response curves to the nitric oxide (NO) donor sodium nitroprusside (SNP), the soluble guanylate cyclase (sGC) stimulator BAY 41-2272, the adenylate cyclase (AC) activator forskolin, the ß-adrenergic receptor agonists isoproterenol (ADRB1), salmeterol (ADRB2), and BRL37344 (ADRB3), and the phosphodiesterase (PDE) inhibitors milrinone (PDE3), rolipram (PDE4), and sildenafil (PDE5) were performed. None of the tested drugs induced a relaxation higher than 30% of the U44069-induced tone. Rings from HUAs and HUVs showed a similar relaxation to forskolin, SNP, PDE inhibitors, and ADRB agonists. BAY 41-2272 was significantly more efficient in relaxing veins than arteries. ADRB agonists evoked weak relaxations (< 20%), which were impaired in endothelium-removed vessels or in the presence of the NO synthase inhibitor L-NAME, sGC inhibitor ODQ. PKA and PKG inhibitors impaired ADBR1-mediated relaxation but did not affect ADRB2-mediated relaxation. ADRB3-mediated relaxation was impaired by PKG inhibition in HUAs and by PKA inhibition in HUVs. Although HUA and HUV rings were relaxed by BRL37344, immunohistochemistry and RT-qPCR analysis showed that, compared to ADRB1 and ADRB2, ADRB3 receptors are weakly or not expressed in umbilical vessels. In conclusion, our study confirmed the low relaxing capacity of HUAs and HUVs from term infants. ADRB-induced relaxation is partially mediated by endothelium-derived NO pathway in human umbilical vessels.