Nitric oxide regulates adenylyl cyclase activity in rat striatal membranes

Localization of MIF-II on mammalian spermatozoa: A study revealing its structure, function and motility inhibitory pathway

Motility of spermatozoa is a crucial factor for determining semen quality. Here we report motility inhibitory factor (MIF-II) from goat epididymal plasma, revealing its structure, function, localization and motility inhibitory pathway. Structural characterization with MALDI revealed novelty of this protein while circular dichroism data confirmed its alpha helical nature. Higher dilutions of MIF-II antibody increased cauda sperm motility and induced immature/immotile caput sperm motility as tested microscopically. Higher number of sperm cells and lower dilutions of antibody induced agglutination in cauda sperm showing surface localization. Indirect immuno-fluorescence showed MIF-II localization throughout the caput sperm surface which relocated more towards acrosomal region with maturation. ELISA assay revealed gradual increase and decrease in concentration of MIF-II in epididymal plasma and plasma membrane respectively from caput to cauda. Signaling cascade that leads to sperm motility inhibition elevates nitric oxide levels through cAMP dependent pathway. MIF-II treatment doesn't alter sperm surface morphology. Expression pattern of MIF-II during epididymal maturation goes hand-in-hand with gaining motility potential as well as dormancy of spermatozoa before ejaculation. Both MIF-II and its antibody inhibit fertilization in-vitro thus expected to open new gateway for future male infertility and contraceptive development research.

Cardiac cAMP: production, hydrolysis, modulation and detection

Cyclic adenosine 3′,5′-monophosphate (cAMP) modulates a broad range of biological processes including the regulation of cardiac myocyte contractile function where it constitutes the main second messenger for β-adrenergic receptors' signaling to fulfill positive chronotropic, inotropic and lusitropic effects. A growing number of studies pinpoint the role of spatial organization of the cAMP signaling as an essential mechanism to regulate cAMP outcomes in cardiac physiology. Here, we will briefly discuss the complexity of cAMP synthesis and degradation in the cardiac context, describe the way to detect it and review the main pharmacological arsenal to modulate its availability.

Production of nitric oxide by carp (Cyprinus carpio L.) kidney leukocytes is regulated by cyclic 3',5'-adenosine monophosphate

The inducible nitric oxide synthase (iNOS) plays a central role in the inflammatory reactions that follow infection or tissue damage. Induction of nitric oxide (NO) synthesis by bacterial lipopolysaccharide (LPS) depends on activation of G protein-coupled receptors in mammals. Thus, it was our intention to evaluate whether similar mechanisms are involved in iNOS activation in fish leukocytes. Therefore, the participation of membrane-bound receptors which activate effectors via G proteins has been confirmed using the G protein inhibitor suramin. Furthermore, the NO produced by iNOS performs both beneficial and detrimental actions. It is thus conceivable that regulatory mechanisms exist which control the timing and intensity of NO production by iNOS in order to outweigh protective effects against detrimental ones. The second messenger cAMP produced by adenylyl cyclases (ACs) plays a key role in the regulation of many cellular functions. Since cAMP signaling inhibits numerous immunological reactions, studies have been carried out to determine whether cAMP-dependent pathways could inhibit NO production by carp leukocytes as well. To measure cellular responses such as NO production by carp leukocytes derived from head and trunk kidneys treatments were performed with the cAMP elevating agents forskolin and dibutyryl-cAMP (db-cAMP) prior to stimulation with Aeromonas hydrophila. Pharmacological studies in stimulated kidney leukocytes showed that increased intracellular cAMP levels lead to reduced NO formation. This reduction of NO production was not due to decreased cell numbers, since a tetrazolium dye-based assay revealed no reduction of cell viability by cyclic nucleotide elevating agents. Thus, our data provide evidence that the AC/cAMP signaling pathway is well established in carp leukocytes. Cyclic AMP leads to type II immune response. We provide evidence that the predominant AC in fish leukocytes is a particulate enzyme due to its sensitivity to forskolin. Treatment of leukocytes with agents increasing intracellular cAMP gave clear evidence for participation of this cyclic nucleotide in immune signaling.

Regulatory properties of adenylate cyclases type 5 and 6: A progress report

Adenylate cyclases (AC) type 5 and 6 comprise the calcium-inhibited family of adenylate cyclase isoforms. Here we review recent discoveries in the regulation of AC5 and AC6 with a focus on posttranslational modifications including glycosylation, nitrosylation, and phosphorylation by the cyclic AMP-dependent protein kinase (PKA), protein kinase C (PKC), and Raf1. We also describe novel signaling interactions such as Galpha(q)-mediated potentiation of AC6 activation. Novel regulators of AC5 and AC6, including small molecules and proteins that physically interact with AC5 and AC6 such as snapin, regulator of G protein signaling 2 (RGS2), protein associated with myc (PAM), and caveolin peptides are discussed. We also describe several recent studies that demonstrate the usefulness of transgenic or adenoviral overexpression of AC5 and AC6 in models for disease states such as cardiovascular hypertrophy. The discovery of novel regulatory mechanisms for AC5 and AC6 and their potential role in crucial physiological processes provide new avenues for research into therapeutic interventions targeting the cyclic AMP pathway.

S-nitrosothiols modulate G protein-coupled receptor signaling in a reversible and highly receptor-specific manner

Background

Recent studies indicate that the G protein-coupled receptor (GPCR) signaling machinery can serve as a direct target of reactive oxygen species, including nitric oxide (NO) and S-nitrosothiols (RSNOs). To gain a broader view into the way that receptor-dependent G protein activation – an early step in signal transduction – might be affected by RSNOs, we have studied several receptors coupling to the G_i family of G proteins in their native cellular environment using the powerful functional approach of [³⁵S]GTPγS autoradiography with brain cryostat sections in combination with classical G protein activation assays.

Results

We demonstrate that RSNOs, like S-nitrosoglutathione (GSNO) and S-nitrosocysteine (CysNO), can modulate GPCR signaling via reversible, thiol-sensitive mechanisms probably involving S-nitrosylation. RSNOs are capable of very targeted regulation, as they potentiate the signaling of some receptors (exemplified by the M2/M4 muscarinic cholinergic receptors), inhibit others (P2Y₁₂ purinergic, LPA₁lysophosphatidic acid, and cannabinoid CB₁ receptors), but may only marginally affect signaling of others, such as adenosine A₁, μ-opioid, and opiate related receptors. Amplification of M2/M4 muscarinic responses is explained by an accelerated rate of guanine nucleotide exchange, as well as an increased number of high-affinity [³⁵S]GTPγS binding sites available for the agonist-activated receptor. GSNO amplified human M4 receptor signaling also under heterologous expression in CHO cells, but the effect diminished with increasing constitutive receptor activity. RSNOs markedly inhibited P2Y₁₂ receptor signaling in native tissues (rat brain and human platelets), but failed to affect human P2Y₁₂ receptor signaling under heterologous expression in CHO cells, indicating that the native cellular signaling partners, rather than the P2Y₁₂ receptor protein, act as a molecular target for this action.

Conclusion

These in vitro studies show for the first time in a broader general context that RSNOs are capable of modulating GPCR signaling in a reversible and highly receptor-specific manner. Given that the enzymatic machinery responsible for endogenous NO production is located in close proximity with the GPCR signaling complex, especially with that for several receptors whose signaling is shown here to be modulated by exogenous RSNOs, our data suggest that GPCR signaling in vivo is likely to be subject to substantial, and highly receptor-specific modulation by NO-derived RSNOs.

Down-regulation of nitrergic transmission in the rat striatum after chronic nigrostriatal deafferentation

Dopamine and NO are physiological stimulators of synthesis of cAMP and cGMP, respectively, and NO synthase-containing interneurons in the striatum are physiologically activated by dopamine-containing neurons in the substantia nigra. This study investigated whether lesioning dopamine neurons has multiple consequences in the striatum consistent with the reported sensitization of cAMP synthesis, including alteration of the NO-cGMP pathway and phosphodiesterase-dependent metabolism of cyclic nucleotides. The substantia nigra of adult Sprague-Dawley rats was unilaterally lesioned with 6-hydroxydopamine. Two months later, we determined expression of NO synthase and evaluated cGMP and cAMP levels of intact and deafferented striatum. Moreover, we evaluated cAMP- and cGMP-phosphodiesterase activities in basal conditions and after Ca2+-calmodulin stimulation and determined the expression of the phosphodiesterase-1B isoform and the levels of phosphodiesterase-1B mRNA. Using immunocytochemistry we characterized the distribution of NO synthase and phosphodiesterase-1B within striatal neurons. In the dopamine-deafferented striatum, NO synthase levels were decreased by 42% while NO synthase-immunopositive intrastriatal fibres but not NO synthase neuronal bodies were reduced in number. In the deafferented striatum basal cGMP levels were reduced, and cAMP levels were increased, but cGMP-phosphodiesterase and cAMP-phosphodiesterase activities were both increased in basal and Ca2+-calmodulin-stimulated conditions. Accordingly, phosphodiesterase-1B expression and phosphodiesterase-1B mRNA were upregulated while a large population of medium-sized striatal neurons showed increased phosphodiesterase-1B immunoreactivity. Dopamine deafferentation led to a complex down-regulation of the NO-cGMP pathway in the striatum and to an up-regulation of phosphodiesterase-1B-dependent cyclic nucleotide metabolism, showing new aspects of neuronal plasticity in experimental hemiparkinsonism.

Nitric oxide agents and apomorphine-induced rat behaviors

BACKGROUND

Nitric oxide (NO) may alter dopamine release in the brain. Activation of D2-dopamine receptors may suppress NO synthase, and inhibition of NO synthase prevents behaviors induced by psychostimulants. We have investigated the modulatory actions of the precursor of NO synthesis (L-arginine) and the broad-spectrum NO synthesis inhibitor NG-nitro-L-arginine methyl ester (L-NAME) on apomorphine-induced behaviors in the rat.

METHODS

Apomorphine was injected subcutaneously, and behaviors induced by the drug were examined in the presence or absence of intracerebroventricular administration of L-arginine and L-NAME.

RESULTS

Our data indicate that L-arginine or L-NAME treatment decreased licking and yawning, but not penile erection induced by apomorphine.

CONCLUSION

Apomorphine-induced behaviors may be modulated by NO levels.

Nitric oxide influences the maturation of cumulus cell-enclosed mouse oocytes cultured in spontaneous maturation medium and hypoxanthine-supplemented medium through different signaling pathways

Nitric oxide (NO) has been recently shown to act with a dual action in mouse oocyte meiotic maturation depending on its concentration, but the mechanism(s) through which it influences oocyte maturation has not been fully clarified to date. The purpose of this study was to test the hypothesis that different signaling mechanisms exist for NO-stimulated and NO-inhibited in vitro maturation of meiosis in cumulus cell-enclosed oocytes (CEOs) from PMSG-primed immature female mice. CEOs were cultured in both spontaneous maturation model and hypoxanthine (HX) arrested model to investigate the mechanism(s). Sodium nitroprusside (SNP, an NO donor) at a concentration of 1mM delayed significantly germinal vesical breakdown (GVBD) during the first 5 h of incubation period and further inhibited the formation of first polar body (PB1) at the end of 24 h of incubation. While SNP, at a concentration of 10 microM, stimulated significantly the meiotic maturation of oocytes by overcoming the inhibition of HX. Methinine blue (MB, 10 microM) or 1-H-[1,2,4] oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ, 10 microM)), two soluble guanylate cyclase (sGC) inhibitors, could reverse SNP-inhibited spontaneous oocyte maturation, but had no effect on SNP-stimulated meiotic maturation in the presence of HX. 8-Br-cGMP (1mM), a cell-permeating cGMP analogue, demonstrated a significant inhibitory effect on both spontaneous meiotic maturation and HX-arrested meiotic maturation. The delay effect of SNP on GVBD occurrence was similar to that of forskolin (6 microM, an adenylate cyclase stimulator) and rolipram (250 microM, a phosphodiesterase 4 inhibitor), two cAMP elevating reagents. Both forskolin and rolipram reversed significantly the SNP-stimulated meiotic maturation, but did not reverse the SNP-inhibited spontaneous meiotic maturation. Cilostamide (1 microM), the selective inhibitor of phosphodiestrase 3 (PDE3), could mimic the inhibitory effect of HX on the spontaneous meiotic maturation in CEOs and this inhibitory effect could also be reversed by SNP (10 microM). Moreover, sphingosine (3 microM), a protein kinase C (PKC) inhibitor, blocked the SNP-inhibited spontaneous meiotic maturation, but did not block the SNP-stimulated meiotic maturation. Clearly, these results suggest that pathway differences are present between SNP-inhibited spontaneous meiotic maturation and SNP-stimulated meiotic maturation of mouse oocytes.

Cytokine-stimulated nitric oxide production inhibits adenylyl cyclase and cAMP-dependent secretion in cholangiocytes

BACKGROUND & AIMS

The biliary epithelium is involved both in bile production and in the inflammatory/reparative response to liver damage. Recent data indicate that inflammatory aggression to intrahepatic bile ducts results in chronic progressive cholestasis.

METHODS

To understand the effects of nitric oxide on cholangiocyte secretion and biliary tract pathophysiology we have investigated: (1) the effects of proinflammatory cytokines on NO production and expression of the inducible nitric oxide synthase (NOS2), (2) the effects of NO on cAMP-dependent secretory mechanisms, and (3) the immunohistochemical expression of NOS2 in a number of human chronic liver diseases.

RESULTS

Our results show that: (1) tumor necrosis factor (TNF)-alpha, and interferon (IFN)-gamma, synergically stimulate NO production in cultured cholangiocytes through an increase in NOS2 gene and protein expression; (2) micromolar concentrations of NO inhibit forskolin-stimulated cAMP production by adenylyl cyclase (AC), cyclic adenosine monophosphate (cAMP)-dependent fluid secretion, and cAMP-dependent Cl(-) and HCO(3)(-) transport mediated by cystic fibrosis transmembrane conductance regulator (CFTR) and anion exchanger isoform 2, respectively; (3) cholestatic effects of NO and of proinflammatory cytokines are prevented by NOS-2 inhibitors and by agents (manganese(III)-tetrakis(4-benzoic acid)porphyrin [MnTBAP], urate, trolox) able to block the formation of reactive nitrogen oxide species (RNOS); (4) NOS2 expression is increased significantly in the biliary epithelium of patients with primary sclerosing cholangitis (PSC).

CONCLUSIONS

Our findings show that proinflammatory cytokines stimulate the biliary epithelium to generate NO, via NOS2 induction, and that NO causes ductular cholestasis by a RNOS-mediated inhibition of AC and of cAMP-dependent HCO(3)(-) and Cl(-) secretory mechanisms. This pathogenetic sequence may contribute to ductal cholestasis in inflammatory cholangiopathies.

Nitric oxide and the other cyclic nucleotide

Nitric oxide (NO) participates in the regulation of the daily activities of cells as well as in cytotoxic events. Elucidating the mechanism(s) by which NO carries out its diverse functions has been the goal of numerous laboratories. In the cardiovascular system, evidence indicates that NO mediates its effects via an activation of soluble guanylyl cyclase (sGC). In other tissues, it is not clear if sGC is an exclusive target for NO or what the functions of cGMP might be. It is also unlikely that the diversity of NO actions is explained solely by changes in cGMP. This review focuses on the evidence that NO modulates cAMP signalling, with specific attention to the effects of NO on adenylyl cyclase (AC) as the target of NO regulation.

Adenylyl cyclase types I and VI but not II and V are selectively inhibited by nitric oxide

Adenylyl cyclase (AC) isoforms catalyze the synthesis of 3',5'-cyclic AMP from ATP. These isoforms are critically involved in the regulation of gene transcription, metabolism, and ion channel activity among others. Nitric oxide (NO) is a gaseous product whose synthesis from L-arginine is catalyzed by the enzyme NO synthase. It has been well established that NO activates the enzyme guanylyl cyclase, but little has been reported on the effects of NO on other important second messengers, such as AC. In the present study, the effects of sodium nitroprusside (SNP), a nitric oxide-releasing compound, on COS-7 cells transfected with plasmids containing AC types I, II, V and VI were evaluated. Total inhibition (approximately 98.5%) of cAMP production was observed in COS-7 cells transfected with the AC I isoform and previously treated with SNP (10 mM) for 30 min, when stimulated with ionomycin. A high inhibition (approximately 76%) of cAMP production was also observed in COS-7 cells transfected with the AC VI isoform and previously treated with SNP (10 mM) for 30 min, when stimulated with forskolin. No effect on cAMP production was observed in cells transfected with AC isoforms II and V.