Protein kinase A-dependent neuronal nitric oxide synthase activation mediates the enhancement of baroreflex response by adrenomedullin in the nucleus tractus solitarii of rats

Network analysis of S-nitrosylated synaptic proteins demonstrates unique roles in health and disease

Nitric oxide can covalently modify cysteine thiols on target proteins to alter that protein's function in a process called S-nitrosylation (SNO). S-nitrosylation of synaptic proteins plays an integral part in neurotransmission. Here we review the function of the SNO-proteome at the synapse and whether clusters of SNO-modification may predict synaptic dysfunction associated with disease. We used a systematic search strategy to concatenate SNO-proteomic datasets from normal human or murine brain samples. Identified SNO-modified proteins were then filtered against proteins reported in the Synaptome Database, which provides a detailed and experimentally verified annotation of all known synaptic proteins. Subsequently, we performed an unbiased network analysis of all known SNO-synaptic proteins to identify clusters of SNO proteins commonly involved in biological processes or with known disease associations. The resulting SNO networks were significantly enriched in biological processes related to metabolism, whereas significant gene-disease associations were related to Schizophrenia, Alzheimer's, Parkinson's and Huntington's disease. Guided by an unbiased network analysis, the current review presents a thorough discussion of how clustered changes to the SNO-proteome influence health and disease.

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.

GLP-2 Regulation of Dietary Fat Absorption and Intestinal Chylomicron Production via Neuronal Nitric Oxide Synthase (nNOS) Signaling

Postprandial dyslipidemia is a metabolic condition commonly associated with insulin-resistant states, such as obesity and type 2 diabetes. It is characterized by the overproduction of intestinal chylomicron particles and excess atherogenic chylomicron remnants in circulation. We have previously shown that glucagon-like peptide 2 (GLP-2) augments dietary fat uptake and chylomicron production in insulin-resistant states; however, the underlying mechanisms remain unclear. Previous studies have implicated nitric oxide (NO) in the absorptive actions of GLP-2. In this study, we report a novel role for neuronal NO synthase (nNOS)-mediated NO generation in lipid uptake and chylomicron formation based on studies in C57BL/6J mice, nNOS-/- mice, and Syrian golden hamsters after intraduodenal and oral fat administration. GLP-2 treatment in wild-type (WT) mice significantly increased postprandial lipid accumulation and circulating apolipoprotein B48 protein levels, while these effects were abolished in nNOS-/- mice. nNOS inhibition in Syrian golden hamsters and protein kinase G (PKG) inhibition in WT mice also abrogated the effect of GLP-2 on postprandial lipid accumulation. These studies demonstrate a novel mechanism in which nNOS-generated NO is crucial for GLP-2-mediated lipid absorption and chylomicron production in both mouse and hamster models. Overall, our data implicate an nNOS-PKG-mediated pathway in GLP-2-mediated stimulation of dietary fat absorption and intestinal chylomicron production.

Intertwined associations between oxidative and nitrosative stress and endocannabinoid system pathways: Relevance for neuropsychiatric disorders

The endocannabinoid system (ECS) appears to regulate metabolic, cardiovascular, immune, gastrointestinal, lung, and reproductive system functions, as well as the central nervous system. There is also evidence that neuropsychiatric disorders are associated with ECS abnormalities as well as oxidative and nitrosative stress pathways. The goal of this mechanistic review is to investigate the mechanisms underlying the ECS's regulation of redox signalling, as well as the mechanisms by which activated oxidative and nitrosative stress pathways may impair ECS-mediated signalling. Cannabinoid receptor (CB)1 activation and upregulation of brain CB2 receptors reduce oxidative stress in the brain, resulting in less tissue damage and less neuroinflammation. Chronically high levels of oxidative stress may impair CB1 and CB2 receptor activity. CB1 activation in peripheral cells increases nitrosative stress and inducible nitric oxide (iNOS) activity, reducing mitochondrial activity. Upregulation of CB2 in the peripheral and central nervous systems may reduce iNOS, nitrosative stress, and neuroinflammation. Nitrosative stress may have an impact on CB1 and CB2-mediated signalling. Peripheral immune activation, which frequently occurs in response to nitro-oxidative stress, may result in increased expression of CB2 receptors on T and B lymphocytes, dendritic cells, and macrophages, reducing the production of inflammatory products and limiting the duration and intensity of the immune and oxidative stress response. In conclusion, high levels of oxidative and nitrosative stress may compromise or even abolish ECS-mediated redox pathway regulation. Future research in neuropsychiatric disorders like mood disorders and deficit schizophrenia should explore abnormalities in these intertwined signalling pathways.

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.

Adrenomedullin increases cAMP accumulation and BDNF expression in rat DRG and spinal motor neurons

Objectives

Adrenomedullin (AM) has high expression in the spinal cord. In this study, we investigated the expression of AM and its receptor components, including calcitonin receptor-like receptor (CLR) and receptor activity modifying proteins (RAMPs) in dorsal root ganglion (DRG) and spinal motor (SM) neurons. Furthermore, the effects of AM on cAMP/cAMP response element-binding protein (CREB), AKT/glycogen synthase kinase-3 beta (GSK-3β) signaling pathways, and expressions of brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) were evaluated.

Materials and Methods

Rat embryonic DRG and SM neurons were isolated, purified, and cultured. Real-time PCR was used to assess expressions of AM, CLR, and RAMPs. cAMP levels, p-CREB, BDNF, and NT-3 were determined using an enzyme-linked immunosorbent assay. p-AKT and p-GSK-3β levels were determined by western blotting. Real-time PCR showed expressions of AM, CLR, RAMP2, and RAMP3 in both DRG and SM neurons.

Results

AM increased cAMP accumulation and p-CREB levels in DRG and SM neurons. AM increased p-AKT and p-GSK-3β in DRG, but not SM neurons. AM significantly increased BDNF expression in both DRG and SM neurons. There was also an increase in NT-3 level in both DRG and SM neurons, which is statistically significant in SM neurons.

Conclusion

These results showed both DRG and SM neurons are targets of AM actions in the spinal cord. An increase in BDNF expression by AM in both DRG and SM neurons suggests the possible beneficial role of AM in protecting, survival, and regeneration of sensory and motor neurons.

A new mechanism for the sex differences in angiotensin II-induced hypertension: the role of macula densa NOS1β-mediated tubuloglomerular feedback

Females are protected against the development of angiotensin II (ANG II)-induced hypertension compared with males, but the mechanisms have not been completely elucidated. In the present study, we hypothesized that the effect of ANG II on the macula densa nitric oxide (NO) synthase 1β (NOS1β)-mediated tubuloglomerular feedback (TGF) mechanism is different between males and females, thereby contributing to the sexual dimorphism of ANG II-induced hypertension. We used microperfusion, micropuncture, clearance of FITC-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 (BP) after a 2-wk ANG II infusion in wild-type and macula densa-specific NOS1 knockout mice. In wild-type mice, ANG II induced higher expression of macula densa NOS1β, greater NO generation by the macula densa, and a lower TGF response in vitro and in vivo in females than in males; the increases of glomerular filtration rate, urine flow rate, and Na⁺ excretion in response to an acute volume expansion were significantly greater and the BP responses to ANG II were significantly less in females than in males. In contrast, these sex differences in the effects of ANG II on TGF, natriuretic response, and BP were largely diminished in knockout mice. In addition, tissue culture of human kidney biopsies (renal cortex) with ANG II resulted in a greater increase in NOS1β expression in females than in males. In conclusion, macula densa NOS1β-mediated TGF is a novel and important mechanism for the sex differences in ANG II-induced hypertension.

Role of neuronal nitric oxide synthase on cardiovascular functions in physiological and pathophysiological states

This review describes and summarizes the role of neuronal nitric oxide synthase (nNOS) on the central nervous system, particularly on brain regions such as the ventrolateral medulla (VLM) and the periaqueductal gray matter (PAG), and on blood vessels and the heart that are involved in the regulation and control of the cardiovascular system (CVS). Furthermore, we shall also review the functional aspects of nNOS during several physiological, pathophysiological, and clinical conditions such as exercise, pain, cerebral vascular accidents or stroke and hypertension. For example, during stroke, a cascade of molecular, neurochemical, and cellular changes occur that affect the nervous system as elicited by generation of free radicals and nitric oxide (NO) from vulnerable neurons, peroxide formation, superoxides, apoptosis, and the differential activation of three isoforms of nitric oxide synthases (NOSs), and can exert profound effects on the CVS. Neuronal NOS is one of the three isoforms of NOSs, the others being endothelial (eNOS) and inducible (iNOS) enzymes. Neuronal NOS is a critical homeostatic component of the CVS and plays an important role in regulation of different systems and disease process including nociception. The functional and physiological roles of NO and nNOS are described at the beginning of this review. We also elaborate the structure, gene, domain, and regulation of the nNOS protein. Both inhibitory and excitatory role of nNOS on the sympathetic autonomic nervous system (SANS) and parasympathetic autonomic nervous system (PANS) as mediated via different neurotransmitters/signal transduction processes will be explored, particularly its effects on the CVS. Because the VLM plays a crucial function in cardiovascular homeostatic mechanisms, the neuroanatomy and cardiovascular regulation of the VLM will be discussed in conjunction with the actions of nNOS. Thereafter, we shall discuss the up-to-date developments that are related to the interaction between nNOS and cardiovascular diseases such as hypertension and stroke. Finally, we shall focus on the role of nNOS, particularly within the PAG in cardiovascular regulation and neurotransmission during different types of pain stimulus. Overall, this review focuses on our current understanding of the nNOS protein, and provides further insights on how nNOS modulates, regulates, and controls cardiovascular function during both physiological activity such as exercise, and pathophysiological conditions such as stroke and hypertension.

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.

Macula Densa SGLT1-NOS1-Tubuloglomerular Feedback Pathway, a New Mechanism for Glomerular Hyperfiltration during Hyperglycemia

BACKGROUND

Glomerular hyperfiltration is common in early diabetes and is considered a risk factor for later diabetic nephropathy. We propose that sodium-glucose cotransporter 1 (SGLT1) senses increases in luminal glucose at the macula densa, enhancing generation of neuronal nitric oxide synthase 1 (NOS1)-dependent nitric oxide (NO) in the macula densa and blunting the tubuloglomerular feedback (TGF) response, thereby promoting the rise in GFR.

METHODS

We used microperfusion, micropuncture, and renal clearance of FITC-inulin to examine the effects of tubular glucose on NO generation at the macula densa, TGF, and GFR in wild-type and macula densa-specific NOS1 knockout mice.

RESULTS

Acute intravenous injection of glucose induced hyperglycemia and glucosuria with increased GFR in mice. We found that tubular glucose blunts the TGF response in vivo and in vitro and stimulates NO generation at the macula densa. We also showed that SGLT1 is expressed at the macula densa; in the presence of tubular glucose, SGLT1 inhibits TGF and NO generation, but this action is blocked when the SGLT1 inhibitor KGA-2727 is present. In addition, we demonstrated that glucose increases NOS1 expression and NOS1 phosphorylation at Ser1417 in mouse renal cortex and cultured human kidney tissue. In macula densa-specific NOS1 knockout mice, glucose had no effect on NO generation, TGF, and GFR.

CONCLUSIONS

We identified a novel mechanism of acute hyperglycemia-induced hyperfiltration wherein increases in luminal glucose at the macula densa upregulate the expression and activity of NOS1 via SGLT1, blunting the TGF response and promoting glomerular hyperfiltration.

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.

Expression of adrenomedullin in rats after spinal cord injury and intervention effect of recombinant human erythropoietin

The expression of adrenomedullin (ADM) in injured tissue of rat spinal cord was observed and the effect of recombinant human erythropoietin was analyzed. A total of 45 Sprague-Dawley rats were selected and divided into 3 equal groups including, a sham-operation group in which rats received an excision of vertebral plate; a spinal cord injury model group and a recombinant human erythropoietin group in which rats with spinal cord injury received a caudal vein injection of 300 units recombinant human erythropoietin after injury. Hematoxylin and eosin staining was performed to observe the spinal cord injury conditions. Immunohistochemical staining was performed to observe the expression of ADM. Pathologic changes in the group of recombinant human erythropoietin at various times were significantly less severe than those in the group of spinal cord injury model. The expression of ADM was increased particularly in the group of recombinant human erythropoietin (P<0.01). The improved Tarlov scores of the group of spinal cord injury model and the group of recombinant human erythropoietin were lower than those of the sham-operation group at 3, 6 and 9 days (P<0.01). Thus, the recombinant human erythropoietin is capable of alleviating the secondary injury of spinal cord. One of the mechanisms may be achieved by promoting the increase of ADM expression.

Near infrared radiation protects against oxygen-glucose deprivation-induced neurotoxicity by down-regulating neuronal nitric oxide synthase (nNOS) activity in vitro

Near infrared radiation (NIR) has been shown to be neuroprotective against neurological diseases including stroke and brain trauma, but the underlying mechanisms remain poorly understood. In the current study we aimed to investigate the hypothesis that NIR may protect neurons by attenuating oxygen-glucose deprivation (OGD)-induced nitric oxide (NO) production and modulating cell survival/death signaling. Primary mouse cortical neurons were subjected to 4 h OGD and NIR was applied at 2 h reoxygenation. OGD significantly increased NO level in primary neurons compared to normal control, which was significantly ameliorated by NIR at 5 and 30 min post-NIR. Neither OGD nor NIR significantly changed neuronal nitric oxide synthase (nNOS) mRNA or total protein levels compared to control groups. However, OGD significantly increased nNOS activity compared to normal control, and this effect was significantly diminished by NIR. Moreover, NIR significantly ameliorated the neuronal death induced by S-Nitroso-N-acetyl-DL-penicillamine (SNAP), a NO donor. Finally, NIR significantly rescued OGD-induced suppression of p-Akt and Bcl-2 expression, and attenuated OGD-induced upregulation of Bax, BAD and caspase-3 activation. These results suggest NIR may protect against OGD at least partially through reducing NO production by down-regulating nNOS activity, and modulating cell survival/death signaling.

Chloroquine-induced scratching is mediated by NO/cGMP pathway in mice

Chloroquine (CQ), a 4-aminoquinoline drug, has long been used in the treatment and prevention of malaria. However its side effect generalized pruritus contributes to treatment failures, and consequently results in the development of chloroquine resistant strains of Plasmodium falciparum. It was proposed that the administration of CQ correlated with increase in nitric oxide (NO) production. Nitric oxide is involved in some pruritic disorders such as atopic dermatitis, psoriasis and scratching behavior evoked by pruritogens like substance P. Therefore, the aim of this study was to investigate the involvement of NO/cGMP pathway in CQ-induced scratching in mice. Scratching behaviors were recorded by a camera after intradermal (ID) injection of CQ in the shaved rostral back of the mice. The results obtained show that CQ elicited scratching in a dose-dependent manner with a peak effective dose of 400μg/site. Injection of non-specific NOS inhibitor, N-nitro-l-arginine methyl ester or neuronal NOS selective inhibitor and 7-nitroindazole, reduced CQ-induced scratching significantly. On the other hand, administration of aminoguanidine as inducible NOS inhibitor has no inhibitory effect on this behavior. Also, injection of l-arginine as a precursor of NO significantly increased this response. Conversely, accumulation of cGMP by sildenafil as a selective phosphodiesterase type 5 inhibitor, potentiated the scratching behavior by CQ. This study therefore shows that CQ-induced scratching behavior is mediated by the NO/cGMP pathway.

Cardiac sympathetic afferent reflex response to intermedin microinjection into paraventricular nucleus is mediated by nitric oxide and γ-amino butyric acid in hypertensive rats

Intermedin (IMD) is a member of calcitonin/calcitonin gene-related peptide (CGRP) and involves in the regulation of cardiovascular function in both peripheral tissues and central nervous system (CNS). Paraventricular nucleus (PVN) of hypothalamus is an important site in the control of cardiac sympathetic afferent reflex (CSAR) which participates in sympathetic over-excitation of hypertension. The aim of this study is to investigate whether IMD in the PVN is involved in the inhibition of CSAR and its related mechanism in hypertension. Rats were subjected to two-kidney one-clip (2K1C) surgery to induce renovascular hypertension or sham-operation (Sham). Acute experiments were carried out four weeks later under anesthesia. The CSAR was evaluated with the renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) responses to the epicardial application of capsaicin. The RSNA and MAP were recorded in sinoaortic-denervated, cervical-vagotomized and anesthetized rats. Bilateral PVN microinjection of IMD (25 pmol) caused greater decrease in the CSAR in 2K1C rats than in Sham rats, which was prevented by pretreatment with adrenomedullin (AM) receptor antagonist AM22-52, non-selective nitric oxide (NO) synthase (NOS) inhibitor l-NAME or γ-amino butyric acid (GABA)B receptor blocker CGP-35348. PVN pretreatment with CGRP receptor antagonist CGRP8-37 or GABAA receptor blocker gabazine had no significant effect on the CSAR response to IMD. AM22-52, l-NAME and CGP-35348 in the PVN could increase CSAR in Sham and 2K1C rats. These data indicate that IMD in the PVN inhibits CSAR via AM receptor, and both NO and GABA in the PVN involve in the effect of IMD on CSAR in Sham and renovascular hypertensive rats.

Protein kinase D interacts with neuronal nitric oxide synthase and phosphorylates the activatory residue serine 1412

Neuronal Nitric Oxide Synthase (nNOS) is the biosynthetic enzyme responsible for nitric oxide (·NO) production in muscles and in the nervous system. This constitutive enzyme, unlike its endothelial and inducible counterparts, presents an N-terminal PDZ domain known to display a preference for PDZ-binding motifs bearing acidic residues at -2 position. In a previous work, we discovered that the C-terminal end of two members of protein kinase D family (PKD1 and PKD2) constitutes a PDZ-ligand. PKD1 has been shown to regulate multiple cellular processes and, when activated, becomes autophosphorylated at Ser⁹¹⁶, a residue located at -2 position of its PDZ-binding motif. Since nNOS and PKD are spatially enriched in postsynaptic densities and dendrites, the main objective of our study was to determine whether PKD1 activation could result in a direct interaction with nNOS through their respective PDZ-ligand and PDZ domain, and to analyze the functional consequences of this interaction. Herein we demonstrate that PKD1 associates with nNOS in neurons and in transfected cells, and that kinase activation enhances PKD1-nNOS co-immunoprecipitation and subcellular colocalization. However, transfection of mammalian cells with PKD1 mutants and yeast two hybrid assays showed that the association of these two enzymes does not depend on PKD1 PDZ-ligand but its pleckstrin homology domain. Furthermore, this domain was able to pull-down nNOS from brain extracts and bind to purified nNOS, indicating that it mediates a direct PKD1-nNOS interaction. In addition, using mass spectrometry we demonstrate that PKD1 specifically phosphorylates nNOS in the activatory residue Ser¹⁴¹², and that this phosphorylation increases nNOS activity and ·NO production in living cells. In conclusion, these novel findings reveal a crucial role of PKD1 in the regulation of nNOS activation and synthesis of ·NO, a mediator involved in physiological neuronal signaling or neurotoxicity under pathological conditions such as ischemic stroke or neurodegeneration.

Brain stem NOS and ROS in neural mechanisms of hypertension

SIGNIFICANCE

There is now compelling evidence to substantiate the notion that by depressing baroreflex regulation of blood pressure and augmenting central sympathetic outflow through their actions on the nucleus tractus solitarii (NTS) and rostral ventrolateral medulla (RVLM), brain stem nitric oxide synthase (NOS) and reactive oxygen species (ROS) are important contributing factors to neural mechanisms of hypertension. This review summarizes our contemporary views on the impact of NOS and ROS in the NTS and RVLM on neurogenic hypertension, and presents potential antihypertensive strategies that target brain stem NOS/ROS signaling.

RECENT ADVANCES

NO signaling in the brain stem may be pro- or antihypertensive depending on the NOS isoform that generates this gaseous moiety and the site of action. Elevation of the ROS level when its production overbalances its degradation in the NTS and RVLM underlies neurogenic hypertension. Interventional strategies with emphases on alleviating the adverse actions of these molecules on blood pressure regulation have been investigated.

CRITICAL ISSUES

The pathological roles of NOS in the RVLM and NTS in neural mechanisms of hypertension are highly complex. Likewise, multiple signaling pathways underlie the deleterious roles of brain-stem ROS in neurogenic hypertension. There are recent indications that interactions between brain stem ROS and NOS may play a contributory role.

FUTURE DIRECTIONS

Given the complicity of action mechanisms of brain-stem NOS and ROS in neural mechanisms of hypertension, additional studies are needed to identify the most crucial therapeutic target that is applicable not only in animal models but also in patients suffering from neurogenic hypertension.

Anti-hypertrophic and anti-oxidant effect of beta3-adrenergic stimulation in myocytes requires differential neuronal NOS phosphorylation

RATIONALE

Stimulation of β3-adrenoreceptors (β3-AR) blunts contractility and improves chronic left ventricular function in hypertrophied and failing hearts in a neuronal nitric oxide synthase (nNOS) dependent manner. nNOS can be regulated by post-translational modification of stimulatory phosphorylation residue Ser1412 and inhibitory residue Ser847. However, the role of phosphorylation of these residues in cardiomyocytes and β3-AR protective signaling has yet to be explored.

OBJECTIVE

We tested the hypothesis that β3-AR regulation of myocyte stress requires changes in nNOS activation mediated by differential nNOS phosphorylation.

METHODS AND RESULTS

Endothelin (ET-1) or norepinephrine induced hypertrophy in rat neonatal ventricular cardiomyocytes (NRVMs) was accompanied by increased β3-AR gene expression. Co-administration of the β3-AR agonist BRL-37433 (BRL) reduced cell size and reactive oxygen species (ROS) generation, while augmenting NOS activity. BRL-dependent augmentation of NOS activity and ROS suppression due to NE were blocked by inhibiting nNOS (L-VNIO). BRL augmented nNOS phosphorylation at Ser1412 and dephosphorylation at Ser847. Cells expressing constitutively dephosphorylated Ser1412A or phosphorylated Ser847D nNOS mutants displayed reduced nNOS activity and a lack of BRL modulation. BRL also failed to depress ROS from NE in cells with nNOS-Ser847D. Inhibiting Akt decreased BRL-induced nNOS-Ser1412 phosphorylation and NOS activation, whereas Gi/o blockade blocked BRL-regulation of both post-translational modifications, preventing enhancement of NOS activity and ROS reduction. BRL resulted in near complete dephosphorylation of Ser847 and a moderate rise in Ser1412 phosphorylation in mouse myocardium exposed to chronic pressure-overload.

CONCLUSION

β3-AR regulates myocardial NOS activity and ROS via activation of nNOS involving reciprocal changes in phosphorylation at two regulatory sites. These data identify a novel and potent anti-oxidant and anti-hypertrophic pathway due to nNOS post-translational modification that is coupled to β3-AR receptor stimulation.

Neuronal nitric oxide synthase inhibition attenuates the development of L-DOPA-induced dyskinesia in hemi-Parkinsonian rats

Long-term treatment with the dopamine precursor levodopa (l-DOPA) frequently induces dyskinesia in Parkinson's disease patients, which is a major complication of this therapy. Previous studies using animal models show that repeated administration of l-DOPA results in alterations of some signaling molecules, including ΔFosB, phospho-DARPP32 and phosoho-GluA1 (also referred to as GluR1 or GluR-A) AMPA receptor subunits. Moreover, an in vivo microdialysis study showed that l-DOPA increases nitric oxide (NO) production in the striatum. However, it is not known whether NO is involved in the development of dyskinesia. The present study examined the effects of NOS inhibitors on the development of l-DOPA-induced dyskinesia in the rats. Dyskinesia symptoms were triggered by daily administration of l-DOPA for 3-4weeks in unilateral 6-hydroxydopamine lesioned rats. Repeated treatments, 30min prior l-DOPA administration, of the nonselective NOS inhibitor, N(G)-nitro-l-arginine methyl ester, and the nNOS inhibitor 7-nitroindazole, but not the inducible NOS inhibitor aminoguanidine, attenuated the development of l-DOPA-induced dyskinesia. In agreement with the behavioral analysis, 7-nitroindazole reduced the l-DOPA-induced increases in ΔFosB, phospho-DARPP32 and phospho-GluA1 AMPA receptor subunit levels in the striatum of 6-hydroxydopamine-lesioned rats. Furthermore, aminoguanidine did not affect ΔFosB or phospho-GluA1 AMPA receptor subunit levels. These findings suggest that nNOS-derived NO is involved in the development of l-DOPA-induced dyskinesia through a post-synaptic mechanism.