Nitric oxide synthase regulatory sites. Phosphorylation by cyclic AMP-dependent protein kinase, protein kinase C, and calcium/calmodulin protein kinase; identification of flavin and calmodulin binding sites

Induction of Nitric Oxide and Its Role in Facial Nerve Regeneration According to the Method of Facial Nerve Injury

Nitric oxide (NO) is an important molecule in cell communication that also plays an important role in many biological processes. Given the dual role of NO in nerve degeneration and regeneration after facial nerve injury, we sought to delve deeper into its role through a systematic literature review. A comprehensive review of the literature employing SCOPUS, PubMed, Cochrane Library, EMBASE, and Google Scholar databases was conducted to evaluate the induction and role of NO in neurodegeneration and regeneration after facial nerve injury. From the 20 papers ultimately reviewed, the central findings were that neuronal nitric oxide synthase(nNOS), endothelial nitric oxide synthase (eNOS), and induced nitric oxide synthase (iNOS) increased or decreased depending on the method of facial nerve damage, damaged area, harvested area, and animal age, and were correlated with degeneration and regeneration of the facial nerve. Research conducted on rats and mice demonstrated that NO, nNOS, eNOS, and iNOS play significant roles in nerve regeneration and degeneration. However, the relationship between nerve damage and NO could not be defined by a simple causal relationship. Instead, the involvement of NOS depends on the type of nerve cell, source of NO, timing, and location of expression, age of the target animal, and proximity of the damage location to the brainstem. Consequently, nNOS, eNOS, and iNOS expression levels and functions may vary significantly.

Silva H, P. de Carvalho R, Ventura ALM, Calaza KC, Silveira MS, Kubrusly RCC, de Melo Reis RA. The Healthy and Diseased Retina Seen through Neuron-Glia Interactions

The retina is the sensory tissue responsible for the first stages of visual processing, with a conserved anatomy and functional architecture among vertebrates. To date, retinal eye diseases, such as diabetic retinopathy, age-related macular degeneration, retinitis pigmentosa, glaucoma, and others, affect nearly 170 million people worldwide, resulting in vision loss and blindness. To tackle retinal disorders, the developing retina has been explored as a versatile model to study intercellular signaling, as it presents a broad neurochemical repertoire that has been approached in the last decades in terms of signaling and diseases. Retina, dissociated and arranged as typical cultures, as mixed or neuron- and glia-enriched, and/or organized as neurospheres and/or as organoids, are valuable to understand both neuronal and glial compartments, which have contributed to revealing roles and mechanisms between transmitter systems as well as antioxidants, trophic factors, and extracellular matrix proteins. Overall, contributions in understanding neurogenesis, tissue development, differentiation, connectivity, plasticity, and cell death are widely described. A complete access to the genome of several vertebrates, as well as the recent transcriptome at the single cell level at different stages of development, also anticipates future advances in providing cues to target blinding diseases or retinal dysfunctions.

Non-canonical nitric oxide signalling and DNA methylation: Inflammation induced epigenetic alterations and potential drug targets

DNA methylation controls DNA accessibility to transcription factors and other regulatory proteins, thereby affecting gene expression and hence cellular identity and function. As epigenetic modifications control the transcriptome, epigenetic dysfunction is strongly associated with pathological conditions and ageing. The development of pharmacological agents that modulate the activity of major epigenetic proteins are in pre-clinical development and clinical use. However, recent publications have identified novel redox-based signalling pathways, and therefore novel drug targets, that may exert epigenetic effects. This review will discuss the recent developments in nitric oxide (NO) signalling on DNA methylation as well as potential epigenetic drug targets that have emerged from the intersection of inflammation/redox biology and epigenetic regulation.

Nitric Oxide Synthase Blockade Impairs Spontaneous Calcium Activity in Mouse Primary Hippocampal Culture Cells

Oscillation of intracellular calcium concentration is a stable phenomenon that affects cellular function throughout the lifetime of both electrically excitable and non-excitable cells. Nitric oxide, a gaseous secondary messenger and the product of nitric oxide synthase (NOS), affects intracellular calcium dynamics. Using mouse hippocampal primary cultures, we recorded the effect of NOS blockade on neuronal spontaneous calcium activity. There was a correlation between the amplitude of spontaneous calcium events and the number of action potentials (APs) (Spearman R = 0.94). There was a linear rise of DAF-FM fluorescent emission showing an increase in NO concentration with time in neurons (11.9 ± 1.0%). There is correlation between the integral of the signal from DAF-FM and the integral of the spontaneous calcium event signal from Oregon Green 488 (Spearman R = 0.58). Blockade of NOS affected the parameters of the spontaneous calcium events studied (amplitude, frequency, integral, rise slope and decay slope). NOS blockade by Nw-Nitro-L-arginine suppressed the amplitude and frequency of spontaneous calcium events. The NOS blocker 3-Bromo-7-Nitroindazole reduced the frequency but not the amplitude of spontaneous calcium activity. Blockade of the well-known regulator of NOS, calcineurin with cyclosporine A reduced the integral of calcium activity in neurons. The differences and similarities in the effects on the parameters of spontaneous calcium effects caused by different blockades of NO production help to improve understanding of how NO synthesis affects calcium dynamics in neurons.

The Role of Macula Densa Nitric Oxide Synthase 1 Beta Splice Variant in Modulating Tubuloglomerular Feedback

Abnormalities in renal electrolyte and water excretion may result in inappropriate salt and water retention, which facilitates the development and maintenance of hypertension, as well as acid-base and electrolyte disorders. A key mechanism by which the kidney regulates renal hemodynamics and electrolyte excretion is via tubuloglomerular feedback (TGF), an intrarenal negative feedback between tubules and arterioles. TGF is initiated by an increase of NaCl delivery at the macula densa cells. The increased NaCl activates luminal Na-K-2Cl cotransporter (NKCC2) of the macula densa cells, which leads to activation of several intracellular processes followed by the production of paracrine signals that ultimately result in a constriction of the afferent arteriole and a tonic inhibition of single nephron glomerular filtration rate. Neuronal nitric oxide (NOS1) is highly expressed in the macula densa. NOS1β is the major splice variant and accounts for most of NO generation by the macula densa, which inhibits TGF response. Macula densa NOS1β-mediated modulation of TGF responses plays an essential role in control of sodium excretion, volume and electrolyte hemostasis, and blood pressure. In this article, we describe the mechanisms that regulate macula densa-derived NO and their effect on TGF response in physiologic and pathologic conditions. © 2023 American Physiological Society. Compr Physiol 13:4215-4229, 2023.

Role of the macula densa sodium glucose cotransporter type 1-neuronal nitric oxide synthase-tubuloglomerular feedback pathway in diabetic hyperfiltration

An increase of glomerular filtration rate (GFR) is a common observation in early diabetes and is considered a key risk factor for subsequent kidney injury. However, the mechanisms underlying diabetic hyperfiltration have not been fully clarified. Here, we tested the hypothesis that macula densa neuronal nitric oxide synthase (NOS1) is upregulated via sodium glucose cotransporter type 1 (SGLT1) in diabetes, which then inhibits tubuloglomerular feedback (TGF) promoting glomerular hyperfiltration. Therefore, we examined changes in cortical NOS1 expression and phosphorylation, nitric oxide production in the macula densa, TGF response, and GFR during the early stage of insulin-deficient (Akita) diabetes in wild-type and macula densa-specific NOS1 knockout mice. A set of sophisticated techniques including microperfusion of juxtaglomerular apparatus in vitro, micropuncture of kidney tubules in vivo, and clearance kinetics of plasma fluorescent-sinistrin were employed. Complementary studies tested the role of SGLT1 in SGLT1 knockout mice and explored NOS1 expression and phosphorylation in kidney biopsies of cadaveric donors. Diabetic mice had upregulated macula densa NOS1, inhibited TGF and elevated GFR. Macula densa-selective NOS1 knockout attenuated the diabetes-induced TGF inhibition and GFR elevation. Additionally, deletion of SGLT1 prevented the upregulation of macula densa NOS1 and attenuated inhibition of TGF in diabetic mice. Furthermore, the expression and phosphorylation levels of NOS1 were increased in cadaveric kidneys of diabetics and positively correlated with blood glucose as well as estimated GFR in the donors. Thus, our findings demonstrate that the macula densa SGLT1-NOS1-TGF pathway plays a crucial role in the control of GFR in diabetes.

Knockout of Macula Densa Neuronal Nitric Oxide Synthase Increases Blood Pressure in db/db Mice

[Figure: see text].

Neurophysiologic implications of neuronal nitric oxide synthase

The molecular and chemical properties of neuronal nitric oxide synthase (nNOS) have made it a key mediator in many physiological functions and signaling transduction. The NOS monomer is inactive, but the dimer form is active. There are three forms of NOS, which are neuronal (nNOS), inducible (iNOS), and endothelial (eNOS) nitric oxide synthase. nNOS regulates nitric oxide (NO) synthesis which is the mechanism used mostly by neurons to produce NO. nNOS expression and activation is regulated by some important signaling proteins, such as cyclic adenosine monophosphate (cAMP) response element-binding protein (CREB), calmodulin (CaM), heat shock protein 90 (HSP90)/HSP70. nNOS-derived NO has been implicated in modulating many physiological functions, such as synaptic plasticity, learning, memory, neurogenesis, etc. In this review, we have summarized recent studies that have characterized structural features, subcellular localization, and factors that regulate nNOS function. Finally, we have discussed the role of nNOS in the developing brain under a wide range of physiological conditions, especially long-term potentiation and depression.

The heart is lost without the hypothalamus

Neuroanatomic and functional studies show the paraventricular (PVN) of the hypothalamus to have a central role in the autonomic control that supports cardiovascular regulation. Direct and indirect projections from the PVN preautonomic neurons to the sympathetic preganglionic neurons in the spinal cord modulate sympathetic activity. The preautonomic neurons of the PVN adjust their level of activation in response to afferent signals arising from peripheral viscerosensory receptors relayed through the nucleus tractus solitarius. The prevailing sympathetic tone is a balance between excitatory and inhibitory influences that arises from the preautonomic PVN neurons. Under physiologic conditions, tonic sympathetic inhibition driven by a nitric oxide-γ-aminobutyric acid-mediated mechanism is dominant, but in pathologic situation such as heart failure there is a switch from inhibition to sympathoexcitation driven by glutamate and angiotensin II. Angiotensin II, reactive oxygen species, and hypoxia as a result of myocardial infarction/ischemia alter the tightly regulated posttranslational protein-protein interaction of CAPON (carboxy-terminal postsynaptic density protein ligand of neuronal nitric oxide synthase (NOS1)) and PIN (protein inhibitor of NOS1) signaling mechanism. Within the preautonomic neurons of the PVN, the disruption of CAPON and PIN signaling leads to a downregulation of NOS1 expression and reduced NO bioavailability. These data support the notion that CAPON-PIN dysregulation of NO bioavailability is a major contributor to the pathogenesis of sympathoexcitation in heart failure.

New Mechanism for the Sex Differences in Salt-Sensitive Hypertension: The Role of Macula Densa NOS1β-Mediated Tubuloglomerular Feedback

Females are relatively resistant to salt-sensitive hypertension than males, but the mechanisms are not completely elucidated. We recently demonstrated a decisive role of macula densa neuronal NOS1β (nitric oxide synthase β)-mediated tubuloglomerular feedback (TGF) in the long-term control of glomerular filtration rate, sodium excretion, and blood pressure. In the present study, we hypothesized that the macula densa NOS1β-mediated TGF mechanism is different between male and female, thereby contributing to the sexual dimorphism of salt-sensitive hypertension. We used microperfusion, micropuncture, clearance of fluorescein isothiocyanate-inulin, and radio telemetry to examine the sex differences in the changes of macula densa NOS1β expression and activity, TGF response, natriuresis, and blood pressure after salt loading in wild-type and macula densa-specific NOS1 knockout mice. In wild-type mice, a high-salt diet induced greater increases in macula densa NOS1β expression and phosphorylation at Ser 1417, greater nitric oxide generation by the macula densa, and more inhibition in TGF response in vitro and in vivo in females than in males. Additionally, the increases of glomerular filtration rate, urine flow rate, and sodium excretion in response to an acute volume expansion were significantly greater in females than in males. The blood pressure responses to angiotensin II plus a high-salt diet were significantly less in females than in males. In contrast, these sex differences in TGF, natriuretic response, and blood pressure were largely diminished in knockout mice. In conclusion, macula densa NOS1β-mediated TGF is a novel and important mechanism for the sex differences in salt-sensitive hypertension.

High-Protein Diet-Induced Glomerular Hyperfiltration Is Dependent on Neuronal Nitric Oxide Synthase β in the Macula Densa via Tubuloglomerular Feedback Response

It is well known that high protein intake increases glomerular filtration rate. Evidence from several studies indicated that NO and tubuloglomerular feedback (TGF) mediate the effect. However, a recent study with a neuronal NO synthase-α knockout model refuted this mechanism and concluded that neither neuronal NO synthase nor TGF response is involved in the protein-induced hyperfiltration. To examine the discrepancy, this study tested a hypothesis that neuronal NO synthase-β in the macula densa mediates the high-protein diet-induced glomerular hyperfiltration via TGF mechanism. We examined the effects of high protein intake on NO generation at the macula densa, TGF response, and glomerular filtration rate in wild-type and macula densa-specific neuronal NO synthase KO mice. In wild-type mice, high-protein diet increased kidney weight, glomerular filtration rate, and renal blood flow, while reduced renal vascular resistance. TGF response in vivo and in vitro was blunted, and NO generation in the macula densa was increased following high-protein diet, associated with upregulations of neuronal NO synthase-β expression and phosphorylation at Ser1417. In contrast, these high-protein diet-induced changes in NO generation at the macula densa, TGF response, renal blood flow, and glomerular filtration rate in wild-type mice were largely attenuated in macula densa-specific neuronal NO synthase KO mice. In conclusion, we demonstrated that high-protein diet-induced glomerular hyperfiltration is dependent on neuronal NO synthase β in the macula densa via TGF response.

Dopamine Receptor Blockade Attenuates Purinergic P2X4 Receptor-Mediated Prepulse Inhibition Deficits and Underlying Molecular Mechanisms

Sensorimotor gating refers to the ability to filter incoming sensory information in a stimulus-laden environment and disruption of this physiological process has been documented in psychiatric disorders characterized by cognitive aberrations. The effectiveness of current pharmacotherapies for treatment of sensorimotor gating deficits in the patient population still remains controversial. These challenges emphasize the need to better understand the biological underpinnings of sensorimotor gating which could lead to discovery of novel drug targets for therapeutic intervention. Notably, we recently reported a role for purinergic P2X4 receptors (P2X4Rs) in regulation of sensorimotor gating using prepulse inhibition (PPI) of acoustic startle reflex. P2X4Rs are ion channels gated by adenosine-5′-triphosphate (ATP). Ivermectin (IVM) induced PPI deficits in C57BL/6J mice in a P2X4R-specific manner. Furthermore, mice deficient in P2X4Rs [P2X4R knockout (KO)] exhibited PPI deficits that were alleviated by dopamine (DA) receptor antagonists demonstrating an interaction between P2X4Rs and DA receptors in PPI regulation. On the basis of these findings, we hypothesized that increased DA neurotransmission underlies IVM-mediated PPI deficits. To test this hypothesis, we measured the effects of D1 and D2 receptor antagonists, SCH 23390 and raclopride respectively and D1 agonist, SKF 82958 on IVM-mediated PPI deficits. To gain mechanistic insights, we investigated the interaction between IVM and dopaminergic drugs on signaling molecules linked to PPI regulation in the ventral striatum. SCH 23390 significantly attenuated the PPI disruptive effects of IVM to a much greater degree than that of raclopride. SKF 82958 failed to potentiate IVM-mediated PPI disruption. At the molecular level, modulation of D1 receptors altered IVM’s effects on dopamine and cyclic-AMP regulated phosphoprotein of 32 kDa (DARPP-32) phosphorylation. Additionally, IVM interacted with the DA receptors antagonists and SKF 82958 in phosphorylation of Ca²⁺/calmodulin kinase IIα (CaMKIIα) and its downstream target, neuronal nitric oxide synthase (nNOS). Current findings suggest an involvement for D1 and D2 receptors in IVM-mediated PPI disruption via modulation of DARPP-32, CaMKIIα and nNOS. Taken together, the findings suggest that stimulation of P2X4Rs can lead to DA hyperactivity and disruption of information processing, implicating P2X4Rs as a novel drug target for treatment of psychiatric disorders characterized by sensorimotor gating deficits.

Critical Roles of Carbon Monoxide and Nitric Oxide in Ca2+ Signaling for Insulin Secretion in Pancreatic Islets

AIMS

Glucagon-like peptide-1 (GLP-1) increases intracellular Ca²⁺ concentrations, resulting in insulin secretion from pancreatic β-cells through the sequential production of Ca²⁺ mobilizing messengers nicotinic acid adenine dinucleotide phosphate (NAADP) and cyclic ADP-ribose (cADPR). We previously found that NAADP activates the neuronal type of nitric oxide (NO) synthase (nNOS), the product of which, NO, activates guanylyl cyclase to produce cyclic guanosine monophosphate (cGMP), which, in turn, induces cADPR formation. Our aim was to explore the relationship between Ca²⁺ signals and gasotransmitters formation in insulin secretion in β-cells upon GLP-1 stimulation.

RESULTS

We show that NAADP-induced cGMP production by nNOS activation is dependent on carbon monoxide (CO) formation by heme oxygenase-2 (HO-2). Treatment with exogenous NO and CO amplifies cGMP formation, Ca²⁺ signal strength, and insulin secretion, whereas this signal is impeded when exposed to combined treatment with NO and CO. Furthermore, CO potentiates cGMP formation in a dose-dependent manner, but higher doses of CO inhibited cGMP formation. Our data with regard to zinc protoporphyrin, a HO inhibitor, and HO-2 knockdown, revealed that NO-induced cADPR formation and insulin secretion are dependent on HO-2. Consistent with this observation, the administration of NO or CO donors to type 2 diabetic mice improved glucose tolerance, but the same did not hold true when both were administered concurrently.

INNOVATION

Our research reveals the role of two gas transmitters, CO and NO, for Ca²⁺ second messengers formation in pancreatic β-cells.

CONCLUSION

These results demonstrate that CO, the downstream regulator of NO, plays a role in bridging the gap between the Ca²⁺ signaling messengers during insulin secretion in pancreatic β-cells.

Calcium ion implicitly modulates the adsorption ability of ion-dependent type II antifreeze proteins on an ice/water interface: a structural insight

Ca²⁺modulates the dynamics of ion-dependent type II AFP to efficiently adsorb on ice surface with high degree of specificity.

Generation and characterization of functional phosphoserine-incorporated neuronal nitric oxide synthase holoenzyme

Phosphorylation is an important pathway for the regulation of nitric oxide synthase (NOS) at the posttranslational level. However, the molecular underpinnings of NOS regulation by phosphorylations remain unclear to date, mainly because of the problems in making a good amount of active phospho-NOS proteins. Herein, we have established a system in which recombinant rat nNOS holoprotein can be produced with site-specific incorporation of phosphoserine (pSer) at residue 1412, using a specialized bacterial host strain for pSer incorporation. The pSer1412 nNOS protein demonstrates UV-Vis, far-UV CD and fluorescence spectral properties that are identical to those of nNOS overexpressed in other bacterial strains. The protein is also functional, possessing normal NO production and NADPH oxidation activities in the presence of abundant substrate L-Arg. Conversely, the rate of FMN-heme interdomain electron transfer (IET) in pSer1412 nNOS is considerably lower than that of wild-type (wt) nNOS, while the phosphomimetic S1142E mutant possesses similar electron transfer kinetics to that of wt. The successful incorporation and high yield of pSer1412 into rat nNOS and the significant change in the IET kinetics upon the phosphorylation demonstrate a highly useful method for incorporating native phosphorylation sites as a substantial improvement to commonly used phosphomimetics.

Calcineurin and Its Role in Synaptic Transmission

Calcineurin (CaN) is a serine/threonine phosphatase widely expressed in different cell types and structures including neurons and synapses. The most studied role of CaN is its involvement in the functioning of postsynaptic structures of central synapses. The role of CaN in the presynaptic structures of central and peripheral synapses is less understood, although it has generated a considerable interest and is a subject of a growing number of studies. The regulatory role of CaN in synaptic vesicle endocytosis in the synapse terminals is actively studied. In recent years, new targets of CaN have been identified and its role in the regulation of enzymes and neurotransmitter secretion in peripheral neuromuscular junctions has been revealed. CaN is the only phosphatase that requires calcium and calmodulin for activation. In this review, we present details of CaN molecular structure and give a detailed description of possible mechanisms of CaN activation involving calcium, enzymes, and endogenous and exogenous inhibitors. Known and newly discovered CaN targets at pre- and postsynaptic levels are described. CaN activity in synaptic structures is discussed in terms of functional involvement of this phosphatase in synaptic transmission and neurotransmitter release.

Intraventricular infusion of quinolinic acid impairs spatial learning and memory in young rats: a novel mechanism of lead-induced neurotoxicity

Background

Lead (Pb), a heavy metal, and quinolinic acid (QA), a metabolite of the kynurenine pathway of tryptophan metabolism, are known neurotoxicants. Both Pb and QA impair spatial learning and memory. Pb activates astrocytes and microglia, which in turn induce the synthesis of QA. We hypothesized increased QA production in response to Pb exposure as a novel mechanism of Pb-neurotoxicity.

Methods

Two experimental paradigms were used. In experiment one, Wistar rat pups were exposed to Pb via their dams’ drinking water from postnatal day 1 to 21. Control group was given regular water. In the second protocol, QA (9 mM) or normal saline (as Vehicle Control) was infused into right lateral ventricle of 21-day old rats for 7 days using osmotic pumps. Learning and memory were assessed by Morris water maze test on postnatal day 30 or 45 in both Pb- and QA-exposed rats. QA levels in the Pb exposed rats were measured in blood by ELISA and in the brain by immunohistochemistry on postnatal days 45 and 60. Expression of various molecules involved in learning and memory was analyzed by Western blot. Means of control and experimental groups were compared with two-way repeated measure ANOVA (learning) and t test (all other variables).

Results

Pb exposure increased QA level in the blood (by ~ 58%) and increased (p < 0.05) the number of QA-immunoreactive cells in the cortex, and CA1, CA3 and dentate gyrus regions of the hippocampus, compared to control rats. In separate experiments, QA infusion impaired learning and short-term memory similar to Pb. PSD-95, PP1, and PP2A were decreased (p < 0.05) in the QA-infused rats, whereas tau phosphorylation was increased, compared to vehicle infused rats.

Conclusion

Putting together the results of the two experimental paradigms, we propose that increased QA production in response to Pb exposure is a novel mechanism of Pb-induced neurotoxicity.

The other side of the coin: Hypersociability

Affiliative social motivation and behavior, that is, sociability that includes attachment, prosocial behavior (sharing, caring and helping) and empathy (the ability to understand and share the feelings of others), has high variability in the human population, with a portion of people outside of the normal range. While psychiatric disorders and autism spectrum disorders are typically associated with a deficit in social behavior, the opposite trait of hypersociability and indiscriminate friendliness are exhibited by individual with specific neurodevelopmental disorders and following early adverse care. Here we discuss both genetic and environmental factors that cause or increase the risk for developing pathological hypersociability from human to rodent models.

Modulation of nNOSser852 phosphorylation and translocation by PKA/PP1 pathway in endothelial cells

Neuronal nitric oxide synthase (nNOS) is now considered an important player in vascular function. It has a protective role in atherosclerosis and hypertension. However, despite its importance, little is known about the mechanisms that regulate its activity in vascular cells. Here we explore the mechanisms by which nNOS is activated in endothelium. We evaluated aorta relaxation response and phosphorylation of nNOS during protein phosphatases 1 and 2 (PP1 and PP2) inhibition, in eNOS silenced mice. PP1 translocation and interaction between the nuclear inhibitor of PP1 (NIPP1) and PP1 was evaluated in endothelial EA.hy926 cells. We demonstrate here that acetylcholine (Ach)-induced relaxation is completely abolished by nNOS inhibition in eNOS silenced mice aorta which also decreased NO and H₂O₂ concentrations. ACh induced dephosphorylation of nNOS^ser852 in aorta after 20 min stimulation. Endothelial cells also showed a decrease in nNOS^ser852 phosphorylation during 20 min of ACh stimulation. PP2 inhibition had no effect on Ach-induced nNOS^Ser852 dephosphorylation in endothelial cells and did not modify Ach-induced vasodilation in aorta from eNOS silenced mice. Non-selective PP1/PP2 inhibition prevented nNOSSer852 dephosphorylation in endothelial cells and prevented Ach-induced vasodilation in eNOS silenced mice. ACh induced time-dependent PP1 and NIPP1 dissociation and PP1 translocation to cytoplasm. Protein kinase A (PKA) inhibition abolished PP1 translocation and further nNOS^ser852 dephosphorylation. In addition, 8-Br-cAMP reduced NIPP1/PP1 interaction, stimulated PP1 translocation and nNOS^ser852 dephosphorylation. Moreover, PKA Inhibition led to a decreased nNOS translocation to perinuclear region. Taken together, our results elucidate a mechanism whereby PP1 is activated by a cAMP/PKA-dependent pathway, leading to dephosphorylation of nNOS^ser852 and subsequent NO and possible H₂O₂ production resulting in endothelium-dependent vascular relaxation.

DA Negatively Regulates IGF-I Actions Implicated in Cognitive Function via Interaction of PSD95 and nNOS in Minimal Hepatic Encephalopathy

Insulin-like growth factor I (IGF-I) has been positively correlated with cognitive ability. Cognitive decline in minimal hepatic encephalopathy (MHE) was shown to be induced by elevated intracranial dopamine (DA). The beneficial effect of IGF-I signaling in MHE remains unknown. In this study, we found that IGF-I content was reduced in MHE rats and that IGF-I administration mitigated cognitive decline of MHE rats. A protective effect of IGF-I on the DA-induced interaction between postsynaptic density protein 95 (PSD95) and neuronal nitric oxide synthase (nNOS) was found in neurons. Ribosomal S6 protein kinase (RSK) phosphorylated nNOS in response to IGF-I by recruiting extracellular signal-regulated kinase (ERK1/2). In turn, DA inactivated the ERK1/2/RSK pathway and stimulated the PSD95–nNOS interaction by downregulating IGF-I. Inhibition of the interaction between PSD95 and nNOS ameliorated DA-induced memory impairment. As DA induced deficits in the ERK1/2/RSK pathway and the interaction between PSD95 and nNOS in MHE brains, IGF-I administration exerted a protective effect via interruption of the interaction between PSD95 and nNOS. These results suggest that IGF-I antagonizes DA-induced cognitive loss by disrupting PSD95–nNOS interactions in MHE.

Shear-Induced Nitric Oxide Production by Endothelial Cells

We present a biochemical model of the wall shear stress-induced activation of endothelial nitric oxide synthase (eNOS) in an endothelial cell. The model includes three key mechanotransducers: mechanosensing ion channels, integrins, and G protein-coupled receptors. The reaction cascade consists of two interconnected parts. The first is rapid activation of calcium, which results in formation of calcium-calmodulin complexes, followed by recruitment of eNOS from caveolae. The second is phosphorylation of eNOS by protein kinases PKC and AKT. The model also includes a negative feedback loop due to inhibition of calcium influx into the cell by cyclic guanosine monophosphate (cGMP). In this feedback, increased nitric oxide (NO) levels cause an increase in cGMP levels, so that cGMP inhibition of calcium influx can limit NO production. The model was used to predict the dynamics of NO production by an endothelial cell subjected to a step increase of wall shear stress from zero to a finite physiologically relevant value. Among several experimentally observed features, the model predicts a highly nonlinear, biphasic transient behavior of eNOS activation and NO production: a rapid initial activation due to the very rapid influx of calcium into the cytosol (occurring within 1-5 min) is followed by a sustained period of activation due to protein kinases.

The endocannabinoid system: 'NO' longer anonymous in the control of nitrergic signalling?

The endocannabinoid system (ECS) is a key cellular signalling system that has been implicated in the regulation of diverse cellular functions. Importantly, growing evidence suggests that the biological actions of the ECS may, in part, be mediated through its ability to regulate the production and/or release of nitric oxide, a ubiquitous bioactive molecule, which functions as a versatile signalling intermediate. Herein, we review and discuss evidence pertaining to ECS-mediated regulation of nitric oxide production, as well as the involvement of reactive nitrogen species in regulating ECS-induced signal transduction by highlighting emerging work supporting nitrergic modulation of ECS function. Importantly, the studies outlined reveal that interactions between the ECS and nitrergic signalling systems can be both stimulatory and inhibitory in nature, depending on cellular context. Moreover, such crosstalk may act to maintain proper cell function, whereas abnormalities in either system can undermine cellular homoeostasis and contribute to various pathologies associated with their dysregulation. Consequently, future studies targeting these signalling systems may provide new insights into the potential role of the ECS–nitric oxide signalling axis in disease development and/or lead to the identification of novel therapeutic targets for the treatment of nitrosative stress-related neurological, cardiovascular, and metabolic disorders.

Post-translational regulation of neuronal nitric oxide synthase: implications for sympathoexcitatory states

INTRODUCTION

Nitric oxide (NO) synthesized via neuronal nitric oxide synthase (nNOS) plays a significant role in regulation/modulation of autonomic control of circulation. Various pathological states are associated with diminished nNOS expression and blunted autonomic effects of NO in the central nervous system (CNS) including heart failure, hypertension, diabetes mellitus, chronic renal failure etc. Therefore, elucidation of the molecular mechanism/s involved in dysregulation of nNOS is essential to understand the pathogenesis of increased sympathoexcitation in these diseased states. Areas covered: nNOS is a highly regulated enzyme, being regulated at transcriptional and posttranslational levels via protein-protein interactions and modifications viz. phosphorylation, ubiquitination, and sumoylation. The enzyme activity of nNOS also depends on the optimal concentration of substrate, cofactors and association with regulatory proteins. This review focuses on the posttranslational regulation of nNOS in the context of normal and diseased states within the CNS. Expert opinion: Gaining insight into the mechanism/s involved in the regulation of nNOS would provide novel strategies for manipulating nNOS directed therapeutic modalities in the future, including catalytically active dimer stabilization and protein-protein interactions with intracellular protein effectors. Ultimately, this is expected to provide tools to improve autonomic dysregulation in various diseases such as heart failure, hypertension, and diabetes.

The Expression of NP847 and Sox2 after TBI and Its Influence on NSCs

The proliferation and differentiation of neural stem cells (NSCs) is important for neural regeneration after cerebral injury. Here, for the first time, we show that phosphorylated (p)-ser847-nNOS (NP847), rather than nNOS, may play a major role in NSC proliferation after traumatic brain injury (TBI). Western blot results demonstrated that the expression of NP847 and Sox2 in the hippocampus is up-regulated after TBI, and they both peak 3 days after brain injury. In addition, an immunofluorescence experiment indicated that NP847 and Sox2 partly co-localize in the nuclei of NSCs after TBI. Further immunoprecipitation experiments found that NP847 and Sox2 can directly interact with each other in NSCs. Moreover, in an OGD model of NSCs, NP847 expression is decreased, which is followed by the down-regulation of Sox2. Interestingly, in this study, we did not observe changes in the expression of nNOS in the OGD model. Further research data suggest that the NP847-Sox2 complex may play a major role in NSCs through the Shh/Gli signaling pathway in a CaMKII-dependent manner after brain injury.

Relevance of peroxynitrite formation and 3-nitrotyrosine on spermatozoa physiology

HIGHLIGHTS

Male fertility decline has been attributed, in part, to increased oxidative stress.Here we will focus on spermatozoa ROS, namely O2•-, NO and ONOO- and their contribution to protein tyrosine nitration, namely by 3-NT formation.An in depth review will be made on the methods used to detect protein oxidation.Detecting 3-NT in sperm proteins will have a crucial clinical impact, namely on the follow up of anti-oxidant therapies.

ABSTRACT

Infertility is a clinical condition that affects around 15% of reproductive-aged couples worldwide. Around half of these cases are due to male factors, the most owing to idiopathic causes. The increase of reactive oxygen species (ROS), which leads to oxidative stress (OS), has been discussed in the last years as a possible cause of male idiopathic infertility. Superoxide anion (O2 •-) and nitric oxide (NO) can react with each other contributing to the formation of peroxynitrite (ONOO-). This molecule can then act on spermatozoa proteins, leading to nitration of protein tyrosines - addition of a nitro (NO2) group - that is then manifested by the formation of 3-nitrotyrosine (3-NT). In turn, 3-NT may be responsible for the alteration or inactivation of the protein function.This review will focus on the description of spermatozoa ROS, namely O2 •-, NO and ONOO- and in their contribution to protein tyrosine nitration, namely by 3-NT formation. Previous results about the effect of ONOO- and 3-NT in spermatozoa will be presented, as well as, the methods that can be performed to detect the protein oxidation by these species. The impact of measuring, at the clinical level, 3-NT, considered a marker of OS, in spermatozoa will be discussed.

REVIEW ■ : Nitric Oxide: Actions and Pathological Roles

Nitric oxide is a unique biological messenger molecule. It mediates, in part, the immune functions of mac rophages ; it is produced by endothelial cells to mediate blood vessel relaxation; and it also serves as a neurotransmitter in the central and peripheral nervous system. Endothelial nitric oxide synthase and neuronal nitric oxide synthase are thought to be primarily constitutive, with activation induced by calcium entry into cells in the absence of protein synthesis, whereas the macrophage nitric oxide synthase is inducible with large increases in new nitric oxide synthase protein synthesis after immune stimulation. The molecular targets of nitric oxide are expanding, as are its physiological and pathophysiological roles in the nervous system. Nitric oxide may regulate neurotransmitter release, and it may play a key role in nervous system morpho genesis and synaptic plasticity and regulate gene expression. Under conditions of excessive formation, nitric oxide is emerging as an important neurotoxin in a variety of disorders of the nervous system. The Neuro scientist 1:7-18, 1995

Dexras1 a unique ras-GTPase interacts with NMDA receptor activity and provides a novel dissociation between anxiety, working memory and sensory gating

Dexras1 is a novel GTPase that acts at a confluence of signaling mechanisms associated with psychiatric and neurological disease including NMDA receptors, NOS1AP and nNOS. Recent work has shown that Dexras1 mediates iron trafficking and NMDA-dependent neurodegeneration but a role for Dexras1 in normal brain function or psychiatric disease has not been studied. To test for such a role, mice with germline knockout (KO) of Dexras1 were assayed for behavioral abnormalities as well as changes in NMDA receptor subunit protein expression. Because Dexras1 is up-regulated during stress or by dexamethasone treatment, we included measures associated with emotion including anxiety and depression. Baseline anxiety-like measures (open field and zero maze) were not altered, nor were depression-like behavior (tail suspension). Measures of memory function yielded mixed results, with no changes in episodic memory (novel object recognition) but a significant decrement on working memory (T-maze). Alternatively, there was an increase in pre-pulse inhibition (PPI), without concomitant changes in either startle amplitude or locomotor activity. PPI data are consistent with the direction of change seen following exposure to dopamine D2 antagonists. An examination of NMDA subunit expression levels revealed an increased expression of the NR2A subunit, contrary to previous studies demonstrating down-regulation of the receptor following antipsychotic exposure (Schmitt et al., 2003) and up-regulation after exposure to isolation rearing (Turnock-Jones et al., 2009). These findings suggest a potential role for Dexras1 in modulating a selective subset of psychiatric symptoms, possibly via its interaction with NMDARs and/or other disease-related binding-partners. Furthermore, data suggest that modulating Dexras1 activity has contrasting effects on emotional, sensory and cognitive domains.

Properties of Taurine Release in Glucose-Free Media in Hippocampal Slices from Developing and Adult Mice

The release of preloaded [(3)H]taurine from hippocampal slices from developing 7-day-old and young adult 3-month-old mice was studied in a superfusion system in the absence of glucose. These hypoglycemic conditions enhanced the release at both ages, the effect being markedly greater in developing mice. A depolarizing K(+) concentration accentuated the release, which indicates that it was partially mediated by exocytosis. The anion channel blockers were inhibitory, witnessing the contribution of ion channels. NO-generating agents fomented the release as a sign of the participation of excitatory amino acid receptors. The other second messenger systems were apparently less efficient. The much greater taurine release could be a reason for the well-known greater tolerance of developing nervous tissue to lack of glucose.

The prelimbic cortex muscarinic M₃ receptor-nitric oxide-guanylyl cyclase pathway modulates cardiovascular responses in rats

The prelimbic cortex (PL), a limbic structure, sends projections to areas involved in the control of cardiovascular responses. Stimulation of the PL with acetylcholine (ACh) evokes depressor and tachycardiac responses mediated by local PL muscarinic receptors. Early studies demonstrated that stimulation of muscarinic receptors induced nitric oxide (NO) synthesis and cyclic guanosine cyclic monophosphate (cGMP) formation. Hence, this study investigates which PL muscarinic receptor subtype is involved in the cardiovascular response induced by ACh and tests the hypothesis that cardiovascular responses caused by muscarinic receptor stimulation in the PL are mediated by local NO and cGMP formation. PL pretreatment with J104129 (an M3 receptor antagonist) blocked the depressor and tachycardiac response evoked by injection of ACh into the PL. Pretreatment with either pirenzepine (an M1 receptor antagonist) or AF-DX 116 (an M2 and M4 receptor antagonist) did not affect cardiovascular responses evoked by ACh. Moreover, similarly to the antagonism of PL M3 receptors, pretreatment with N(ω)-propyl-L-arginine (an inhibitor of neuronal NO synthase), carboxy-PTIO(S)-3-carboxy-4-hydroxyphenylglicine (an NO scavenger), or 1H-[1,2,4]oxadiazolol-[4,3-a]quinoxalin-1-one (a guanylate cyclase inhibitor) blocked both the depressor and the tachycardiac response evoked by ACh. The current results demonstrate that cardiovascular responses evoked by microinjection of ACh into the PL are mediated by local activation of the M3 receptor-NO-guanylate cyclase pathway.

PACAP induces plasticity at autonomic synapses by nAChR-dependent NOS1 activation and AKAP-mediated PKA targeting

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a pleiotropic neuropeptide found at synapses throughout the central and autonomic nervous system. We previously found that PACAP engages a selective G-protein coupled receptor (PAC1R) on ciliary ganglion neurons to rapidly enhance quantal acetylcholine (ACh) release from presynaptic terminals via neuronal nitric oxide synthase (NOS1) and cyclic AMP/protein kinase A (PKA) dependent processes. Here, we examined how PACAP stimulates NO production and targets resultant outcomes to synapses. Scavenging extracellular NO blocked PACAP-induced plasticity supporting a retrograde (post- to presynaptic) NO action on ACh release. Live-cell imaging revealed that PACAP stimulates NO production by mechanisms requiring NOS1, PKA and Ca(2+) influx. Ca(2+)-permeable nicotinic ACh receptors composed of α7 subunits (α7-nAChRs) are potentiated by PKA-dependent PACAP/PAC1R signaling and were required for PACAP-induced NO production and synaptic plasticity since both outcomes were drastically reduced following their selective inhibition. Co-precipitation experiments showed that NOS1 associates with α7-nAChRs, many of which are perisynaptic, as well as with heteromeric α3*-nAChRs that generate the bulk of synaptic activity. NOS1-nAChR physical association could facilitate NO production at perisynaptic and adjacent postsynaptic sites to enhance focal ACh release from juxtaposed presynaptic terminals. The synaptic outcomes of PACAP/PAC1R signaling are localized by PKA anchoring proteins (AKAPs). PKA regulatory-subunit overlay assays identified five AKAPs in ganglion lysates, including a prominent neuronal subtype. Moreover, PACAP-induced synaptic plasticity was selectively blocked when PKA regulatory-subunit binding to AKAPs was inhibited. Taken together, our findings indicate that PACAP/PAC1R signaling coordinates nAChR, NOS1 and AKAP activities to induce targeted, retrograde plasticity at autonomic synapses. Such coordination has broad relevance for understanding the control of autonomic synapses and consequent visceral functions.

Tetrahydrobiopterin in cardiovascular health and disease

Tetrahydrobiopterin (BH4) functions as a cofactor for several important enzyme systems, and considerable evidence implicates BH4 as a key regulator of endothelial nitric oxide synthase (eNOS) in the setting of cardiovascular health and disease. BH4 bioavailability is determined by a balance of enzymatic de novo synthesis and recycling, versus degradation in the setting of oxidative stress. Augmenting vascular BH4 levels by pharmacological supplementation has been shown in experimental studies to enhance NO bioavailability. However, it has become more apparent that the role of BH4 in other enzymatic pathways, including other NOS isoforms and the aromatic amino acid hydroxylases, may have a bearing on important aspects of vascular homeostasis, inflammation, and cardiac function. This article reviews the role of BH4 in cardiovascular development and homeostasis, as well as in pathophysiological processes such as endothelial and vascular dysfunction, atherosclerosis, inflammation, and cardiac hypertrophy. We discuss the therapeutic potential of BH4 in cardiovascular disease states and attempt to address how this modulator of intracellular NO-redox balance may ultimately provide a powerful new treatment for many cardiovascular diseases.

Say "no" to spinal cord injury: is nitric oxide an option for therapeutic strategies?

PURPOSE

a literature review was made to investigate the role of nitric oxide (NO) in spinal cord injury, a pathological condition that leads to motor, sensory, and autonomic deficit. Besides, we were interested in potential therapeutic strategies interfering with NO mechanism of secondary damage.

MATERIALS

A literature search using PubMed Medline database has been performed.

RESULTS

excessive NO production after spinal cord injury promotes oxidative damage perpetuating the injury causing neuronal loss at the injured site and in the surrounding area.

CONCLUSION

different therapeutic approaches for contrasting or avoiding NO secondary damage have been studied, these include nitric oxide synthase inhibitors, compounds that interfere with inducible NO synthase expression, and molecules working as antioxidant. Further studies are needed to explain the neuroprotective or cytotoxic role of the different isoforms of NO synthase and the other mediators that take part or influence the NO cascade. In this way, it would be possible to find new therapeutic targets and furthermore to extend the experimentation to humans.

A pivotal role for tryptophan 447 in enzymatic coupling of human endothelial nitric oxide synthase (eNOS): effects on tetrahydrobiopterin-dependent catalysis and eNOS dimerization

Tetrahydrobiopterin (BH4) is a required cofactor for the synthesis of NO by NOS. Bioavailability of BH4 is a critical factor in regulating the balance between NO and superoxide production by endothelial NOS (eNOS coupling). Crystal structures of the mouse inducible NOS oxygenase domain reveal a homologous BH4-binding site located in the dimer interface and a conserved tryptophan residue that engages in hydrogen bonding or aromatic stacking interactions with the BH4 ring. The role of this residue in eNOS coupling remains unexplored. We overexpressed human eNOS W447A and W447F mutants in novel cell lines with tetracycline-regulated expression of human GTP cyclohydrolase I, the rate-limiting enzyme in BH4 synthesis, to determine the importance of BH4 and Trp-447 in eNOS uncoupling. NO production was abolished in eNOS-W447A cells and diminished in cells expressing W447F, despite high BH4 levels. eNOS-derived superoxide production was significantly elevated in W447A and W447F versus wild-type eNOS, and this was sufficient to oxidize BH4 to 7,8-dihydrobiopterin. In uncoupled, BH4-deficient cells, the deleterious effects of W447A mutation were greatly exacerbated, resulting in further attenuation of NO and greatly increased superoxide production. eNOS dimerization was attenuated in W447A eNOS cells and further reduced in BH4-deficient cells, as demonstrated using a novel split Renilla luciferase biosensor. Reduction of cellular BH4 levels resulted in a switch from an eNOS dimer to an eNOS monomer. These data reveal a key role for Trp-447 in determining NO versus superoxide production by eNOS, by effects on BH4-dependent catalysis, and by modulating eNOS dimer formation.

Vasorelaxant action of an ethylacetate fraction of Euphorbia humifusa involves NO-cGMP pathway and potassium channels

ETHNOPHARMACOLOGICAL RELEVANCE

Euphorbia humifusa Willd. (EH) is an important traditional Chinese medicine that has commonly been used for treating bacillary dysentery and enteritis in many Asian countries for thousands of years. EH has a wide variety of pharmacological actions such as antioxidant, hypotensive, and hypolipidemic effects. However, the mechanisms involved are to be defined.

AIM OF THE STUDY

The present study was performed to evaluate the cardiovascular effects of EH in rats.

MATERIALS AND METHODS

Methanol extract of EH (MEH) and ethylacetate fraction of the MEH (EEH) was examined for their vascular relaxant effects in phenylephrine-precontracted aortic rings. Effects of EEH on systolic blood pressure and heart rate were tested in Sprague-Dawley rats.

RESULTS

MEH and EEH induced vasorelaxation in a concentration-dependent manner. Endothelium-denudation abolished the EEH-induced vasorelaxation. Pretreatment of the endothelium-intact aortic rings with N(G)-nitro-L-arginine methylester (L-NAME) and 1H-[1,2,4]-oxadiazolo-[4,3-α]-quinoxalin-1-one (ODQ) significantly inhibited the EEH-induced vasorelaxation. EEH increased cGMP levels of the aortic rings in a concentration-dependent manner and the effect was blocked by L-NAME or ODQ. Extracellular Ca(2+) depletion and treatments with thapsigargin, Gd(3+), and 2-aminoethyl diphenylborinate significantly attenuated the EEH-induced vasorelaxation. Wortmannin markedly attenuated the EEH-induced vasorelaxation. In addition, tetraethylammonium, iberiotoxin, and charybdotoxin, but not apamin, attenuated the EEH-induced vasorelaxation. Glibenclamide, indomethacin, atropine, and propranolol had no effects on the EEH-induced vasorelaxation. Furthermore, EEH decreased systolic blood pressure and heart rate in a concentration-dependent manner in rats.

CONCLUSIONS

The present study demonstrates that EEH induces endothelium-dependent vasorelaxation via eNOS-NO-cGMP signaling through the modification of intracellular Ca(2+), Ca(2+) entry, and large- and intermediate-conductance KCa channel homeostasis. The data also suggest that the Akt-eNOS pathway is involved in the EEH-induced vasorelaxation. EEH induces hypotension and bradycardia in vivo.

Nitric oxide in cerebral vasospasm: theories, measurement, and treatment

In recent decades, a large body of research has focused on the role of nitric oxide (NO) in the development of cerebral vasospasm (CV) following subarachnoid hemorrhage (SAH). Literature searches were therefore conducted regarding the role of NO in cerebral vasospasm, specifically focusing on NO donors, reactive nitrogen species, and peroxynitrite in manifestation of vasospasm. Based off the assessment of available evidence, two competing theories are reviewed regarding the role of NO in vasospasm. One school of thought describes a deficiency in NO due to scavenging by hemoglobin in the cisternal space, leading to an NO signaling deficit and vasospastic collapse. A second hypothesis focuses on the dysfunction of nitric oxide synthase, an enzyme that synthesizes NO, and subsequent generation of reactive nitrogen species. Both theories have strong experimental evidence behind them and hold promise for translation into clinical practice. Furthermore, NO donors show definitive promise for preventing vasospasm at the angiographic and clinical level. However, NO augmentation may also cause systemic hypotension and worsen vasospasm due to oxidative distress. Recent evidence indicates that targeting NOS dysfunction, for example, through erythropoietin or statin administration, also shows promise at preventing vasospasm and neurotoxicity. Ultimately, the role of NO in neurovascular disease is complex. Neither of these theories is mutually exclusive, and both should be considered for future research directions and treatment strategies.

Phosphorylation of neuronal nitric oxide synthase at Ser1412 in the dentate gyrus of rat brain after transient forebrain ischemia

We previously demonstrated that calmodulin-dependent protein kinase IIα (CaM-KIIα) phosphorylates nNOS at Ser(847) in the hippocampus after forebrain ischemia; this phosphorylation attenuates NOS activity and might contribute to resistance to post-ischemic damage. We also revealed that cyclic AMP-dependent protein kinase (PKA) could phosphorylate nNOS at Ser(1412)in vitro. In this study, we focused on chronological and topographical changes in the phosphorylation of nNOS at Ser(1412) after rat forebrain ischemia. The hippocampus and adjacent cortex were collected at different times, up to 24h, after 15min of forebrain ischemia. NOS was partially purified from crude samples using ADP agarose gel. Neuronal NOS, phosphorylated (p)-nNOS at Ser(1412), PKA, and p-PKA at Thr(197) were studied in the rat hippocampus and cortex using Western blot analysis and immunohistochemistry. Western blot analysis revealed that p-nNOS at Ser(1412) significantly increased between 1 and 6h after reperfusion in the hippocampus, but not in the cortex. PKA was cosedimented with nNOS by ADP agarose gel. Immunohistochemistry revealed that phosphorylation of nNOS at Ser(1412) and PKA at Thr(197) occurred in the subgranular layer of the dentate gyrus. Forebrain ischemia might thereby induce temporary activation of PKA at Thr(197), which then phosphorylates nNOS at Ser(1412) in the subgranular layer of the dentate gyrus.

Involvement of N-methyl-D-aspartate glutamate receptor and nitric oxide in cardiovascular responses to dynamic exercise in rats

Dynamic exercise evokes sustained cardiovascular responses, which are characterized by arterial pressure and heart rate increases. Although it is well accepted that there is central nervous system mediation of cardiovascular adjustments during exercise, information on the role of neural pathways and signaling mechanisms is limited. It has been reported that glutamate, by acting on NMDA receptors, evokes the release of nitric oxide through activation of neuronal nitric oxide synthase (nNOS) in the brain. In the present study, we tested the hypothesis that NMDA receptors and nNOS are involved in cardiovascular responses evoked by an acute bout of exercise on a rodent treadmill. Moreover, we investigated possible central sites mediating control of responses to exercise through the NMDA receptor-nitric oxide pathway. Intraperitoneal administration of the selective NMDA glutamate receptor antagonist dizocilpine maleate (MK-801) reduced both the arterial pressure and heart rate increase evoked by dynamic exercise. Intraperitoneal treatment with the preferential nNOS inhibitor 7-nitroindazole reduced exercise-evoked tachycardiac response without affecting the pressor response. Moreover, treadmill running increased NO formation in the medial prefrontal cortex (MPFC), bed nucleus of the stria teminalis (BNST) and periaqueductal gray (PAG), and this effect was inhibited by systemic pretreatment with MK-801. Our findings demonstrate that NMDA receptors and nNOS mediate the tachycardiac response to dynamic exercise, possibly through an NMDA receptor-NO signaling mechanism. However, NMDA receptors, but not nNOS, mediate the exercise-evoked pressor response. The present results also provide evidence that MPFC, BNST and PAG may modulate physiological adjustments during dynamic exercise through NMDA receptor-NO signaling.

Effects of male silkworm pupa powder on the erectile dysfunction by chronic ethanol consumption in rats

Erectile dysfunction (ED) is a highly prevalent disorder that affects millions of men worldwide. ED is now considered an early manifestation of atherosclerosis, and consequently, a precursor of systemic vascular disease. This study was designed to investigate the effects of male silkworm pupa powder (SWP) on the levels of nitric oxide synthase (NOS) expression, nitrite, and glutathione (GSH); lipid peroxidation; libido; and erectile response of the corpus cavernosum of the rat penis. We induced ED in the study animals by oral administration of 20% ethanol over 8 weeks. The SWP-treated male rats were divided into 3 groups that were orally administered 200, 400, and 800 mg/kg. The libido of the SWP-administered male rats was higher than that of the ethanol control group. In addition, the erectile response of the corpus cavernosum was restored in males on SWP administration, to a level similar to that of the normal group without ED. The testosterone concentration did not increase significantly. The lipid peroxidation in the corpus cavernosum of the male rats administered SWP decreased significantly. In contrast, compared to the ethanol group, SWP-administered male rats showed increased GSH levels in the corpus cavernosum. The level of nitrite and NOS expression in the corpus cavernosum of SWP-administered male rats increased significantly. These results indicated that SWP effectively restored ethanol-induced ED in male rats.

Vasodilatory effects of ethanol extract of Radix Paeoniae Rubra and its mechanism of action in the rat aorta

ETHNOPHARMACOLOGICAL RELEVANCE

Radix Paeoniae Rubra (RPR) is an important traditional Chinese medicine (TCM) commonly used in clinic for a long history in China. RPR is the radix of either Paeonia lactiflora Pall. or Paeonia veitchii Lynch. RPR has a wide variety of pharmacological actions such as anti-thrombus, anti-coagulation, and anti-atherosclerotic properties, protecting heart and liver. However, the mechanisms involved are to be defined.

AIM OF THE STUDY

The aim of the present study was to define the effect of Paeonia lactiflora Pall. extracts on vascular tension and responsible mechanisms in rat thoracic aortic rings.

MATERIALS AND METHODS

Ethanol extract of Paeonia lactiflora Pall. (EPL) was examined for their vascular relaxant effects in isolated phenylephrine-precontracted rat thoracic aorta.

RESULTS

EPL induced relaxation of the phenylephrine-precontracted aortic rings in a concentration-dependent manner. Vascular relaxation induced by EPL was significantly inhibited by removal of the endothelium or pretreatment of the rings with N(G)-nitro-L-arginine methylester (L-NAME) or 1H-[1,2,4]-oxadiazolo-[4,3-α]-quinoxalin-1-one (ODQ). Extracellular Ca²⁺ depletion or diltiazem significantly attenuated EPL-induced vasorelaxation. Modulators of the store-operated Ca²⁺ entry (SOCE), thapsigargin, 2-aminoethyl diphenylborinate and Gd³⁺, and an inhibitor of Akt, wortmannin, markedly attenuated the EPL-induced vasorelaxation. Further, the EPL-induced vasorelaxation was significantly attenuated by pretreatment with tetraethylammonium, a non-selective K(Ca) channels blocker, or glibenclamide, an ATP-sensitive K⁺ channels inhibitor, respectively. Inhibition of cyclooxygenases with indomethacin, and adrenergic and muscarinic receptors blockade had no effects on the EPL-induced vasorelaxation.

CONCLUSIONS

The present study suggests that EPL relaxes vascular smooth muscle via endothelium-dependent and Akt- and SOCE-eNOS-cGMP-mediated pathways through activation of both K(Ca) and K(ATP) channels and inhibition of L-type Ca²⁺ channels.

Inhibition of the adrenomedullin/nitric oxide signaling pathway in early diabetic retinopathy

The nitric oxide (NO) signaling pathway is integrally involved in visual processing and changes in the NO pathway are measurable in eyes of diabetic patients. The small peptide adrenomedullin (ADM) can activate a signaling pathway to increase the enzyme activity of neuronal nitric oxide synthase (nNOS). ADM levels are elevated in eyes of diabetic patients and therefore, ADM may play a role in the pathology of diabetic retinopathy. The goal of this research was to test the effects of inhibiting the ADM/NO signaling pathway in early diabetic retinopathy. Inhibition of this pathway decreased NO production in high-glucose retinal cultures. Treating diabetic mice with the PKC β inhibitor ruboxistaurin for 5 weeks lowered ADM mRNA levels and ADM-like immunoreactivity and preserved retinal function as assessed by electroretinography. The results of this study indicate that inhibiting the ADM/NO signaling pathway prevents neuronal pathology and functional losses in early diabetic retinopathy.

Biliverdin inhibits Toll-like receptor-4 (TLR4) expression through nitric oxide-dependent nuclear translocation of biliverdin reductase

The cellular response to an inflammatory stressor requires a proinflammatory cellular activation followed by a controlled resolution of the response to restore homeostasis. We hypothesized that biliverdin reductase (BVR) by binding biliverdin (BV) quells the cellular response to endotoxin-induced inflammation through phosphorylation of endothelial nitric oxide synthase (eNOS). The generated NO, in turn, nitrosylates BVR, leading to nuclear translocation where BVR binds to the Toll-like receptor-4 (TLR4) promoter at the Ap-1 sites to block transcription. We show in macrophages that BV-induced eNOS phosphorylation (Ser-1177) and NO production are mediated in part by Ca(2+)/calmodulin-dependent kinase kinase. Furthermore, we show that BVR is S-nitrosylated on one of three cysteines and that this posttranslational modification is required for BVR-mediated signaling. BV-induced nuclear translocation of BVR and inhibition of TLR4 expression is lost in macrophages derived from Enos(-/-) mice. In vivo in mice, BV provides protection from acute liver damage and is dependent on the availability of NO. Collectively, we elucidate a mechanism for BVR in regulating the inflammatory response to endotoxin that requires eNOS-derived NO and TLR4 signaling in macrophages.

Brain GLP-1 signaling regulates femoral artery blood flow and insulin sensitivity through hypothalamic PKC-δ

OBJECTIVE

Glucagon-like peptide 1 (GLP-1) is a gut-brain hormone that regulates food intake, energy metabolism, and cardiovascular functions. In the brain, through a currently unknown molecular mechanism, it simultaneously reduces femoral artery blood flow and muscle glucose uptake. By analogy to pancreatic β-cells where GLP-1 activates protein kinase C (PKC) to stimulate insulin secretion, we postulated that PKC enzymes would be molecular targets of brain GLP-1 signaling that regulate metabolic and vascular function.

RESEARCH DESIGN AND METHODS

We used both genetic and pharmacological approaches to investigate the role of PKC isoforms in brain GLP-1 signaling in the conscious, free-moving mouse simultaneous with metabolic and vascular measurements.

RESULTS

In normal wild-type (WT) mouse brain, the GLP-1 receptor (GLP-1R) agonist exendin-4 selectively promotes translocation of PKC-δ (but not -βII, -α, or -ε) to the plasma membrane. This translocation is blocked in Glp1r(-/-) mice and in WT mice infused in the brain with exendin-9, an antagonist of the GLP-1R. This mechanism coordinates both blood flow in the femoral artery and whole-body insulin sensitivity. Consequently, in hyperglycemic, high-fat diet-fed diabetic mice, hypothalamic PKC-δ activity was increased and its pharmacological inhibition improved both insulin-sensitive metabolic and vascular phenotypes.

CONCLUSIONS

Our studies show that brain GLP-1 signaling activates hypothalamic glucose-dependent PKC-δ to regulate femoral artery blood flow and insulin sensitivity. This mechanism is attenuated during the development of experimental hyperglycemia and may contribute to the pathophysiology of type 2 diabetes.

Involvement of adenosine A2A receptors in engulfment-dependent apoptotic cell suppression of inflammation

Efficient execution of apoptotic cell death followed by efficient clearance mediated by professional macrophages is a key mechanism in maintaining tissue homeostasis. Removal of apoptotic cells usually involves three central elements: 1) attraction of phagocytes via soluble "find me" signals, 2) recognition and phagocytosis via cell surface-presenting "eat me" signals, and 3) suppression or initiation of inflammatory responses depending on additional innate immune stimuli. Suppression of inflammation involves both direct inhibition of proinflammatory cytokine production and release of anti-inflammatory factors, which all contribute to the resolution of inflammation. In the current study, using wild-type and adenosine A(2A) receptor (A2AR) null mice, we investigated whether A2ARs, known to mediate anti-inflammatory signals in macrophages, participate in the apoptotic cell-mediated immunosuppression. We found that macrophages engulfing apoptotic cells release adenosine in sufficient amount to trigger A2ARs, and simultaneously increase the expression of A2ARs, as a result of possible activation of liver X receptor and peroxisome proliferators activated receptor δ. In macrophages engulfing apoptotic cells, stimulation of A2ARs suppresses the NO-dependent formation of neutrophil migration factors, such as macrophage inflammatory protein-2, using the adenylate cyclase/protein kinase A pathway. As a result, loss of A2ARs results in elevated chemoattractant secretion. This was evident as pronounced neutrophil migration upon exposure of macrophages to apoptotic cells in an in vivo peritonitis model. Altogether, our data indicate that adenosine is one of the soluble mediators released by macrophages that mediate engulfment-dependent apoptotic cell suppression of inflammation.