The PSD-95/nNOS complex: new drugs for depression?

The emerging role of nitric oxide in the synaptic dysfunction of vascular dementia

With an increase in global aging, the number of people affected by cerebrovascular diseases is also increasing, and the incidence of vascular dementia-closely related to cerebrovascular risk-is increasing at an epidemic rate. However, few therapeutic options exist that can markedly improve the cognitive impairment and prognosis of vascular dementia patients. Similarly in Alzheimer's disease and other neurological disorders, synaptic dysfunction is recognized as the main reason for cognitive decline. Nitric oxide is one of the ubiquitous gaseous cellular messengers involved in multiple physiological and pathological processes of the central nervous system. Recently, nitric oxide has been implicated in regulating synaptic plasticity and plays an important role in the pathogenesis of vascular dementia. This review introduces in detail the emerging role of nitric oxide in physiological and pathological states of vascular dementia and summarizes the diverse effects of nitric oxide on different aspects of synaptic dysfunction, neuroinflammation, oxidative stress, and blood-brain barrier dysfunction that underlie the progress of vascular dementia. Additionally, we propose that targeting the nitric oxide-sGC-cGMP pathway using certain specific approaches may provide a novel therapeutic strategy for vascular dementia.

Complement C1q/C3-CR3 signaling pathway mediates abnormal microglial phagocytosis of synapses in a mouse model of depression

BACKGROUND

Both functional brain imaging studies and autopsy reports have indicated the presence of synaptic loss in the brains of depressed patients. The activated microglia may dysfunctionally engulf neuronal synapses, leading to synaptic loss and behavioral impairments in depression. However, the mechanisms of microglial-synaptic interaction under depressive conditions remain unclear.

METHODS

We utilized lipopolysaccharide (LPS) to induce a mouse model of depression, examining the effects of LPS on behaviors, synapses, microglia, microglial phagocytosis of synapses, and the C1q/C3-CR3 complement signaling pathway. Additionally, a C1q neutralizing antibody was employed to inhibit the C1q/C3-CR3 signaling pathway and assess its impact on microglial phagocytosis of synapses and behaviors in the mice.

RESULTS

LPS administration resulted in depressive and anxiety-like behaviors, synaptic loss, and abnormal microglial phagocytosis of synapses in the hippocampal dentate gyrus (DG) of mice. We found that the C1q/C3-CR3 signaling pathway plays a crucial role in this abnormal microglial activity. Treatment with the C1q neutralizing antibody moderated the C1q/C3-CR3 pathway, leading to a decrease in abnormal microglial phagocytosis, reduced synaptic loss, and improved behavioral impairments in the mice.

CONCLUSIONS

The study suggests that the C1q/C3-CR3 complement signaling pathway, which mediates abnormal microglial phagocytosis of synapses, presents a novel potential therapeutic target for depression treatment.

Phosphoproteomics implicates glutamatergic and dopaminergic signalling in the antidepressant-like properties of the iron chelator deferiprone

BACKGROUND

Current antidepressants have limitations due to insufficient efficacy and delay before improvement in symptoms. Polymorphisms of the serotonin transporter (5-HTT) gene have been linked to depression (when combined with stressful life events) and altered response to selective serotonergic reuptake inhibitors. We have previously revealed the antidepressant-like properties of the iron chelator deferiprone in the 5-HTT knock-out (KO) mouse model of depression. Furthermore, deferiprone was found to alter neural activity in the prefrontal cortex of both wild-type (WT) and 5-HTT KO mice.

METHODS

In the current study, we examined the molecular effects of acute deferiprone treatment in the prefrontal cortex of both genotypes via phosphoproteomics analysis.

RESULTS

In WT mice treated with deferiprone, there were 22 differentially expressed phosphosites, with gene ontology analysis implicating cytoskeletal proteins. In 5-HTT KO mice treated with deferiprone, we found 33 differentially expressed phosphosites. Gene ontology analyses revealed phosphoproteins that were predominantly involved in synaptic and glutamatergic signalling. In a drug-naïve cohort (without deferiprone administration), the analysis revealed 21 differentially expressed phosphosites in 5-HTT KO compared to WT mice. We confirmed the deferiprone-induced increase in tyrosine hydroxylase serine 40 residue phosphorylation (pTH-Ser40) (initially revealed in our phosphoproteomics study) by Western blot analysis, with deferiprone increasing pTH-Ser40 expression in WT and 5-HTT KO mice.

CONCLUSION

As glutamatergic and synaptic signalling are dysfunctional in 5-HTT KO mice (and are the target of fast-acting antidepressant drugs such as ketamine), these molecular effects may underpin deferiprone's antidepressant-like properties. Furthermore, dopaminergic signalling may also be involved in deferiprone's antidepressant-like properties.

Reperfusion and cytoprotective agents are a mutually beneficial pair in ischaemic stroke therapy: an overview of pathophysiology, pharmacological targets and candidate drugs focusing on excitotoxicity and free radical

Stroke is the second-leading cause of death and the leading cause of disability in much of the world. In particular, China faces the greatest challenge from stroke, since the population is aged quickly. In decades of clinical trials, no neuroprotectant has had reproducible efficacy on primary clinical end points, because reperfusion is probably a necessity for neuroprotection to be clinically beneficial. Fortunately, the success of thrombolysis and endovascular thrombectomy has taken us into a reperfusion era of acute ischaemic stroke (AIS) therapy. Brain cytoprotective agents can prevent detrimental effects of ischaemia, and therefore 'freeze' ischaemic penumbra before reperfusion, extend the time window for reperfusion therapy. Because reperfusion often leads to reperfusion injury, including haemorrhagic transformation, brain oedema, infarct progression and neurological worsening, cytoprotective agents will enhance the efficacy and safety of reperfusion therapy by preventing or reducing reperfusion injuries. Therefore, reperfusion and cytoprotective agents are a mutually beneficial pair in AIS therapy. In this review, we outline critical pathophysiological events causing cell death within the penumbra after ischaemia or ischaemia/reperfusion in the acute phase of AIS, focusing on excitotoxicity and free radicals. We discuss key pharmacological targets for cytoprotective therapy and evaluate the recent advances of cytoprotective agents going through clinical trials, highlighting multitarget cytoprotective agents that intervene at multiple levels of the ischaemic and reperfusion cascade.

Downregulation of Preso protects against ischemic/reperfusion-mediated neuronal injury through regulating PSD95-nNOS/YAP pathways

Cerebral ischemic/reperfusion (I/R) injury has become a great challenge harming patients' life. This study aims to explore the regulatory role of Preso during cerebral I/R injury and to elucidate the potential mechanism. Here, we established a middle cerebral artery occlusion/reperfusion (MCAO/IR) rat model and an oxygen-glucose deprivation/reoxygenation (OGD/R)-mediated PC12 cell model to evaluate the expression and role of Preso following cerebral I/R injury. Histopathological injury and infarct size were assessed by hematoxylin and eosin (HE) and 2,3,5-Triphenyltertrazolium chloride (TTC) staining. Double immunofluorescence staining was performed to assess neuronal apoptosis in brain tissues. Cell counting kit-8 (CCK-8) and flow cytometry were performed to evaluate cell viability and apoptosis, respectively. The reactive oxygen species (ROS) and nitric oxide (NO) levels were detected using their respective detection kits, and the expression of corresponding proteins was examined adopting Western blot. The results showed that Preso was upregulated in OGD/R-induced PC12 cells and MCAO rats. Preso knockdown significantly reduced OGD/R-caused viability loss, apoptosis and oxidative stress in PC12 cells, and reduced infarct size, attenuated histological injury, and inhibited apoptosis and oxidative stress in the brain tissues from MCAO rats, as well as inhibiting the expression of postsynaptic density protein-95 (PSD95) and nitric oxide synthase (nNOS) and repressing YAP phosphorylation in vitro. In addition, the protective role of Preso knockdown against cerebral I/R injury was partly strengthened by IC87201, the nNOS/PSD95 interaction inhibitor, or weakened by Verteporfin (Vert), an inhibitor of YAP. In conclusion, Perso knockdown might exert a protective role against cerebral I/R injury via regulating PSD95-nNOS and YAP pathways, providing a potential therapeutic target for the treatment of ischemic stroke.

Depressive-like behavior and impaired synaptic plasticity in the prefrontal cortex as later consequences of prenatal hypoxic-ischemic insult in rats

Perinatal hypoxia-ischemia (HI) is a leading cause of morbidity and mortality among newborns. Infants with HI encephalopathy may experience lasting consequences, such as depression, in adulthood. In this study, we examined depressive-like behavior, neuronal population, and markers of monoaminergic and synaptic plasticity in the prefrontal cortex (PFC) of adolescent rats subjected to a prenatal HI model. Pregnant rats underwent a surgery in which uterine and ovarian blood flow was blocked for 45 min at E18 (HI procedure). Sham-operated subjects were also generated (SH procedure). Behavioral tests were conducted on male and female pups from P41 to P43, and animals were histologically processed or dissected for western blotting at P45. We found that the HI groups consumed less sucrose in the sucrose preference test and remained immobile for longer periods in the forced swim test. Additionally, we observed a significant reduction in neuronal density and PSD95 levels in the HI group, as well as a smaller number of synaptophysin-positive cells. Our results underscore the importance of this model in investigating the effects of HI-induced injuries, as it reproduces an increase in depressive-like behavior and suggests that the HI insult affects circuits involved in mood modulation.

Ovariectomy Exacerbates Acute Ethanol-Induced Tachycardia: Role of Nitric Oxide and NMDA Receptors in the Rostral Ventrolateral Medulla

Ethanol consumption influences cardiovascular functions. In humans, acute consumption of ethanol causes dose-dependent tachycardia. Our previous study showed that ethanol-induced tachycardia might involve decreased nitric oxide (NO) signaling in the brain’s medulla. NMDA receptors, another important target of ethanol, are one of the upstream signals of nitric oxide. Reports showed the modulation of NMDA receptor function by estrogen or estrogen receptors. The present study aims to examine the hypothesis that depletion of estrogen by ovariectomy (OVX) might modulate ethanol-induced tachycardia by regulating NMDA receptor function and NO signaling in the cardiovascular regulatory nucleus of the brain. Ethanol (3.2 g/kg, 40% v/v, 10 mL/kg) or saline (10 mL/kg) was administered by oral gavage in sham or OVX female Sprague-Dawley (SD) rats. The blood pressure (BP) and heart rate (HR) were measured using the tail-cuff method. The levels of phosphoserine 896 of the GluN1 subunit (pGluN1-serine 896) and NMDA GluN1 subunits (GluN1) were determined by immunohistochemistry. The expressions of nitric oxide synthase (NOS) and estrogen receptors in the tissue were measured by Western blotting. Nitric oxide contents were measured as total nitrate-nitrite by colorimetric assay kit. In a 2-h observation, there was no significant change in BP between the saline and ethanol groups. However, compared with saline, ethanol caused an increase in HR (tachycardia) in sham control or OVX rats. Interestingly, ethanol produced more significant tachycardia in the OVX group than in the sham control group. Nitric oxide levels were lower in the area of the rostral ventrolateral medulla (RVLM) 60 min following ethanol administration in OVX compared with sham control, without significant changes in the expression of NOS and estrogen receptors (ERα and ERβ). In addition, a decrease in the immunoreactivity of pGluN1-serine 896, without significant changes in GluN1, was found in neurons of RVLM 40 min following ethanol administration in OVX compared with sham control. Our results suggest that depletion of estradiol (E2) by OVX might exacerbate the tachycardia following ethanol administration, the underlying mechanism of which might be associated with decreased NMDA receptor function and NO level in the RVLM.

Disrupting the nNOS/NOS1AP interaction in the medial prefrontal cortex impairs social recognition and spatial working memory in mice

The neuronal isoform of nitric oxide synthase (nNOS) and its interacting protein NOS1AP have been linked to several mental disorders including schizophrenia and depression. An increase in the interaction between nNOS and NOS1AP in the frontal cortex has been suggested to contribute to the emergence of these disorders. Here we aimed to uncover whether disruption of their interactions in the frontal cortex leads to mental disorder endophenotypes. Targeting the medial prefrontal cortex (mPFC), we stereotaxically injected wild-type C57BL/6J mice with recombinant adeno-associated virus (rAAV) expressing either full-length NOS1AP, the nNOS binding region of NOS1AP (i.e. NOS1AP_396-503), or the nNOS amino-terminus (i.e. nNOS_1-133), which was shown to disrupt the interaction of endogenous nNOS with PSD-95. We tested these mice in a comprehensive behavioural battery, assessing different endophenotypes related to mental disorders. We found no differences in anxiety-related and exploratory behaviours. Likewise, social interaction was comparable in all groups. However, social recognition was impaired in NOS1AP and NOS1AP_396-503 mice. These mice, as well as mice overexpressing nNOS_1-133 also displayed impaired spatial working memory (SWM) capacity, while spatial reference memory (SRM) remained intact. Finally, mice overexpressing NOS1AP and nNOS_1-133, but not NOS1AP_396-503, failed to habituate to the startling pulses in an acoustic startle response (ASR) paradigm, though we found no difference in overall startle intensity or prepulse inhibition (PPI) of the ASR. Our findings indicate a distinct role of NOS1AP/nNOS/PSD-95 interactions in the mPFC to contribute to specific endophenotypic changes observed in different mental disorders.

Effects of electroconvulsive therapy on nitrosative stress and oxidative DNA damage parameters in patients with a depressive episode

BACKGROUND

Few studies have investigated the relationship between electroconvulsive therapy (ECT) and markers of nitrosative stress and oxidative DNA damage.

OBJECTIVE

The aim of this study is to examine changes in nitrosative stress and oxidative DNA damage in patients with a depressive episode treated with ECT.

METHODS

The current study included 48 patients with a depressive episode treated with ECT and 30 healthy control participants. First, the serum nitrosative stress markers of nitric oxide (NO•), nitric oxide synthase (NOS), and peroxynitrite (ONOO-) and the oxidative DNA damage marker 8-hydroxy-2'-deoxyguanosine (8-OHdG) were compared between the study and control groups. These parameters were also compared pre- and post-treatment for the study group.

RESULTS

NO•, NOS, and ONOO- levels were significantly higher in patients with depressive disorder (DD) than in the control group. NO• and NOS levels significantly decreased in the ECT group after treatment while 8-OHdG levels significantly increased.

CONCLUSIONS

The study findings suggest that ECT may have reduced nitrosative stress levels while increasing oxidative DNA damage. More research is now needed to better understand the issue.KEY POINTSNitrosative stress levels can increase in patients with depressive disorder.Electroconvulsive therapy may reduce nitrosative stress while increasıng oxidative DNA damage.These results suggest that nitrosative stress plays an important role in the mechanism of action of electroconvulsive therapy.

Antidepressant-like effect of Ganoderma lucidum spore polysaccharide-peptide mediated by upregulation of prefrontal cortex brain-derived neurotrophic factor

A 28-kDa polysaccharide-peptide (PGL) with antidepressant-like activities was isolated from spores of the mushroom Ganoderma lucidum. It was unadsorbed on DEAE-cellulose. Its internal amino acid sequences manifested pronounced similarity with proteins from the mushrooms Lentinula edodes and Agaricus bisporus. The monosaccharides present in 28-kDa PGL comprised predominantly of glucose (over 90%) and much fewer galactose, mannose residues, and other residues. PGL manifested antidepressant-like activities as follows. It enhanced viability and DNA content in corticosterone-injured PC12 cells(a cell line derived from a pheochromocytoma of the rat adrenal medulla with an embryonic origin from the neural crest containing a mixture of neuroblastic cells and eosinophilic cells) and reduced LDH release. A single acute PGL treatment shortened the duration of immobility of mice in both tail suspension and forced swimming tests. PGL treatment enhanced sucrose preference and shortened the duration of immobility in mice exposed to chronic unpredictable mild stress (CUMS). Chronic PGL treatment reversed the decline in mouse brain serotonin and norepinephrine levels but did not affect dopamine levels. PGL decreased serum corticosterone levels and increased BDNF mRNA and protein levels and increased synapsin I and PSD95 levels in the prefrontal cortex. This effect was completely blocked by pretreatment with the BDNF antagonist K252a, indicating that PGL increased synaptic proteins in a BDNF-dependent manner.Key points• An antidepressive polysaccharide-peptide PGL was isolated from G. lucidum spores.• PGL protected PC12 nerve cells from the toxicity of corticosterone.• PGL upregulated BDNF expression and influenced key factors in the prefrontal cortex.

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.

Synthesis of Novel Pyrido[1,2-c]pyrimidine Derivatives with 6-Fluoro-3-(4-piperidynyl)-1,2-benzisoxazole Moiety as Potential SSRI and 5-HT1A Receptor Ligands

Two series of novel 4-aryl-2H-pyrido[1,2-c]pyrimidine (6a–i) and 4-aryl-5,6,7,8-tetrahydropyrido[1,2-c]pyrimidine (7a–i) derivatives were synthesized. The chemical structures of the new compounds were confirmed by ¹H and ¹³C NMR spectroscopy and ESI-HRMS spectrometry. The affinities of all compounds for the 5-HT_1A receptor and serotonin transporter protein (SERT) were determined by in vitro radioligand binding assays. The test compounds demonstrated very high binding affinities for the 5-HT_1A receptor of all derivatives in the series (6a–i and 7a–i) and generally low binding affinities for the SERT protein, with the exception of compounds 6a and 7g. Extended affinity tests for the receptors D₂, 5-HT_2A, 5-HT₆ and 5-HT₇ were conducted with regard to selected compounds (6a, 7g, 6d and 7i). All four compounds demonstrated very high affinities for the D₂ and 5-HT_2A receptors. Compounds 6a and 7g also had high affinities for 5-HT₇, while 6d and 7i held moderate affinities for this receptor. Compounds 6a and 7g were also tested in vivo to identify their functional activity profiles with regard to the 5-HT_1A receptor, with 6a demonstrating the activity profile of a presynaptic agonist. Metabolic stability tests were also conducted for 6a and 6d.

Inhibition of phosphodiesterase-4 suppresses HMGB1/RAGE signaling pathway and NLRP3 inflammasome activation in mice exposed to chronic unpredictable mild stress

Inhibition of phosphodiesterase-4 (PDE4) produces robust anti-inflammatory and antidepressant-like effects in multiple animal models. However, the detailed mechanisms have not been well studied. Receptor for advanced glycation endproducts (RAGE) and inflammasome activation are implicated in the etiology of depression. Here, we aimed to investigate the involvement of RAGE and nucleotide-binding domain (NOD)-like receptor protein 3 (NLRP3) inflammasome in the antidepressant-like effects of PDE4 inhibition in mice. We found that inhibition of PDE4 by roflupram (ROF, 0.5, and 1.0 mg/kg, i.g.) exerted antidepressant-like effects in mice subjected to chronic unpredictable mild stress (CUMS). Simultaneously, ROF inhibited CUMS-induced microglial activation and restored the morphology of microglial cells in the hippocampus, as evidenced by reduced total process length, area, volume, number of branching points, number of terminal points and total sholl intersections of microglia. ROF also decreased the expression of ionized calcium-binding adapter molecule-1 and the level of interleukin-1β. Western blot analysis showed that PDE4 inhibition suppressed the high-mobility group box 1 protein (HMGB1)/RAGE signaling pathway, as the levels of HMGB1, RAGE, toll-like receptor 4, phosphorylated p38 mitogen-activated protein kinase, and nuclear factor κ-B were decreased in both hippocampus and cortex in mice after treatment with ROF. Moreover, ROF also attenuated the protein levels of NLRP3, the apoptosis-associated speck-like protein containing (ASC), and cysteine-requiring aspartate protease-1 (Caspase-1), which are key proteins in the NLRP3-mediated inflammasome signaling pathway. In summary, these results demonstrate that the down-regulation of HMGB1/RAGE signaling pathway and inflammasome suppression possibly contribute to the antidepressant-like effects of PDE4 inhibitors. And, ROF has potential as a candidate drug in the treatment of depression.

Antidiabetic Drug Metformin Ameliorates Depressive-Like Behavior in Mice with Chronic Restraint Stress via Activation of AMP-Activated Protein Kinase

Depression is one of the most prevalent neuropsychiatric disorders in modern society. However, traditional drugs, such as monoaminergic agents, have defect showing lag response requiring several weeks to months. Additionally, these drugs have limited efficacy and high resistance rates in patients with depression. Thus, there is an urgent need to develop novel drugs or approaches for the treatment of depression. Here, using biochemical, pharmacological, genetic and behavioral methods, we demonstrate that metformin imparts a fast-acting antidepressant-like effect in naïve mice as well as stressed mice subjected to chronic restraint stress model. Moreover, inhibition of AMP-activated protein kinase (AMPK) activity by compound C or knock down of hippocampal AMPKα occluded the antidepressant-like effect induced by metformin. Our results suggest that metformin may be a viable therapeutic drug for the treatment of stress-induced depression via activation of AMPK.

Effects of brazilein on PSD-95 protein expression and neurological recovery in mice after sciatic nerve injury

PURPOSE

To evaluate the local nerve myelin recovery and the expression of PSD-95 protein and mRNA in the L4-L6 segment of the spinal cord after applying Brazilein to sciatic nerve injury BALB/c mice model and investigate the regulatory effects of Brazilein on myelin recovery after peripheral nerve injury.

METHODS

A total of 160 BALB/c mice were selected to establish the unilateral sciatic nerve injury model and randomly divided into four groups: saline blank control, Brazilein high-dose, medium-dose, and low-dose. Mice were assessed at different time points (1 w, 2 w, 4 w, 8 w) after sciatic nerve injury for the sciatic functional index (SFI) and sciatic nerve function recovery of the injured side by myelin Luxol Fast Blue (LFB) staining of the sciatic nerve. In addition, immunohistochemistry, real time-PCR, and Western blot were used to detect the PSD-95 expression in the spinal cord L4-L6 segments of the injured sciatic nerve at each time point.

RESULTS

The results of SFI and sciatic nerve function recovery, as well as, myelin LFB staining of the injured side indicated that all indexes of the Brazilein middle- and high-dose groups were significantly better than the low-dose and blank control groups at each time point. The PSD-95 expression in the L4-L6 segment of the spinal cord was statistically lower in the high- and medium-dose groups than in the low-dose and blank control groups at 1 w, 2 w, and 4 w, while the differences between the groups were not significant at 8 w.

CONCLUSION

Brazilein inhibits PSD-95 activation in the corresponding segment of sciatic nerve spinal cord in BALB/c mice after sciatic nerve injury, thereby inhibiting the excessive expression of free radicals and promoting myelin regeneration.

Spatial quantification of the synaptic activity phenotype across large populations of neurons with Markov random fields

Motivation

The collective and co-ordinated synaptic activity of large neuronal populations is relevant to neuronal development as well as a range of neurological diseases. Quantification of synaptically-mediated neuronal signalling permits further downstream analysis as well as potential application in target validation and in vitro screening assays. Our aim is to develop a phenotypic quantification for neuronal activity imaging data of large populations of neurons, in particular relating to the spatial component of the activity.

Results

We extend the use of Markov random field (MRF) models to achieve this aim. In particular, we consider Bayesian posterior densities of model parameters in Gaussian MRFs to directly model changes in calcium fluorescence intensity rather than using spike trains. The basis of our model is defining neuron 'neighbours' by the relative spatial positions of the neuronal somata as obtained from the image data whereas previously this has been limited to defining an artificial square grid across the field of view and spike binning. We demonstrate that our spatial phenotypic quantification is applicable for both in vitro and in vivo data consisting of thousands of neurons over hundreds of time points. We show how our approach provides insight beyond that attained by conventional spike counting and discuss how it could be used to facilitate screening assays for modifiers of disease-associated defects of communication between cells.

Availability and implementation

We supply the MATLAB code and data to obtain all of the results in the paper.

Supplementary information

Supplementary data are available at Bioinformatics online.

Emerging Themes in PDZ Domain Signaling: Structure, Function, and Inhibition

Post-synaptic density-95, disks-large and zonula occludens-1 (PDZ) domains are small globular protein-protein interaction domains widely conserved from yeast to humans. They are composed of ∼90 amino acids and form a classical two α-helical/six β-strand structure. The prototypical ligand is the C-terminus of partner proteins; however, they also bind internal peptide sequences. Recent findings indicate that PDZ domains also bind phosphatidylinositides and cholesterol. Through their ligand interactions, PDZ domain proteins are critical for cellular trafficking and the surface retention of various ion channels. In addition, PDZ proteins are essential for neuronal signaling, memory, and learning. PDZ proteins also contribute to cytoskeletal dynamics by mediating interactions critical for maintaining cell-cell junctions, cell polarity, and cell migration. Given their important biological roles, it is not surprising that their dysfunction can lead to multiple disease states. As such, PDZ domain-containing proteins have emerged as potential targets for the development of small molecular inhibitors as therapeutic agents. Recent data suggest that the critical binding function of PDZ domains in cell signaling is more than just glue, and their binding function can be regulated by phosphorylation or allosterically by other binding partners. These studies also provide a wealth of structural and biophysical data that are beginning to reveal the physical features that endow this small modular domain with a central role in cell signaling.

Spontaneously hypertensive rats exhibit higher sensitivity to ethanol-induced hypotensive effects: Role of NMDA receptors and nitric oxide in rostral ventrolateral medulla

Intake of ethanol (alcohol) affects cardiovascular function. Acute ethanol intake has been shown to lower blood pressure (BP) in hypertensive patients. The present study was undertaken to examine the effects and mechanisms of acute administration of ethanol on BP in hypertensive and normotensive rats. Ethanol was given by intraperitoneal (i.p.) injection in male spontaneously hypertensive rats (SHRs) and the normotensive Wistar-Kyoto rats (WKYs). BP responses were measured in free-moving conscious rats or in urethane-anesthetized rats. Inhibitors were applied by bilateral microinjection into the rostral ventrolateral medulla (RVLM). Nitric oxide (NO•) levels and glutamate levels were determined by nitrate and nitrite (NOx) analyzer and HPLC-ECD, respectively. Intraperitoneal (i.p.) injection of ethanol (1.6 g/kg) caused a significant decrease in BP in free-moving or in anesthetized SHRs but not in WKYs. A higher dose (3.2 g/kg) of ethanol decreased BP in both SHRs and WKYs, although the depressor responses in SHRs occurred significantly earlier than those in WKYs. The blood ethanol concentrations 60 min after injection were similar in SHRs and WKYs. Bilateral microinjection of nitric oxide synthase (NOS) inhibitors or glutamatergic NMDA receptor antagonists into the RVLM 5 min after administration of ethanol significantly inhibited the ethanol-induced depressor effects in SHRs. The levels of NOx and glutamate release in the RVLM following ethanol administration and the NOx content in the RVLM areas 30 min after administration were significantly increased in SHRs, but not in WKYs. Our results showed that SHRs were more sensitive to ethanol-induced hypotensive effects than WKYs because of augmentation of ethanol-induced expression of the glutamatergic NMDA receptor/NO• signal in the RVLM of SHRs.

Inhibitors of the NMDA-Nitric Oxide Signaling Pathway Protect Against Neuronal Atrophy and Synapse Loss Provoked by l-alpha Aminoadipic Acid-treated Astrocytes

The impact of treating astrocytes with the astrocytic toxin l-alpha amino adipic acid (L-AAA) on neuronal outgrowth, complexity and synapse formation was assessed, using a model of astrocyte-neuronal interaction. Treatment of rat primary cortical neurons with conditioned media (CM) derived from astrocytes treated with L-AAA reduced neuronal complexity and synapse formation. L-AAA provoked a reduction in the expression of glial fibrillary acid protein (GFAP) and a reduction in ATP-linked mitochondrial respiration in astrocytic cells. As the NMDA-R/PSD-95/NOS signaling pathway is implicated in regulating the structural plasticity of neurons, treatment of neuronal cultures with the neuronal nitric oxide synthase (nNOS) inhibitor 1-[2-(trifluoromethyl)phenyl] imidazole (TRIM) [100 nM] was assessed and observed to protect against L-AAA-treated astrocytic CM-induced reduction in neuronal complexity and synapse loss. Treatment with the NMDA-R antagonist ketamine protected against the CM-induced loss of synapse formation whereas the novel PSD-95/nNOS inhibitors 2-((1H-benzo[d] [1,2,3]triazol-5-ylamino) methyl)-4,6-dichlorophenol (IC87201) and 4-(3,5-dichloro-2-hydroxy-benzylamino)-2-hydroxybenzoic acid (ZL006) protected against synapse loss with partial protection against reduced neurite outgrowth. Furthermore, L-AAA delivery to the pre-limbic cortex (PLC) of mice was found to increase dendritic spine density and treatment with ZL006 reduced this effect. In summary, L-AAA-induced astrocyte impairment leads to a loss of neuronal complexity and synapse loss in vitro and increased dendritic spine density in vivo that may be reversed by inhibitors of the NMDA-R/PSD-95/NOS pathway. The results have implications for understanding astrocytic-neuronal interaction and the search for drug candidates that may provide therapeutic approaches for brain disorders associated with astrocytic histopathology.

A surface magnetic imprinted polymers as artificial receptors for selective and efficient capturing of new neuronal nitric oxide synthase-post synaptic density protein-95 uncouplers

In this work, surface magnetic molecularly imprinted polymers (SMMIPs) were synthesized and used as artificial receptors in the dispersive magnetic solid phase extraction (DMSPE) for capturing potential neuronal nitric oxide synthase-post synaptic density protein-95 (nNOS-PSD-95) uncouplers, which is known as neuroprotection against stroke. Factors that affected selective separation and adsorption of the artificial receptors, such as the amount of template, the types of functional monomer and porogen solvents, and the molar ratio of template/functional monomer/cross-linker were optimized. The artificial receptors were also characterized using fourier transformed infrared, scanning electron microscope, thermal gravimetric analysis and physical property measurement systems. Multiple interactions between template and SMMIPs led to larger binding capacities, faster binding kinetics, quicker separation abilities and more efficient selectivity than the surface magnetic nonimprinted polymers (SMNIPs). The SMMIPs were successfully applied to capture potential nNOS-PSD-95 uncouplers from complex samples, and eight compounds were seized and confirmed rapidly when combined with HPLC and MS. The detection of the new nNOS-PSD-95 uncouplers ranged from 0.001 to 1.500 mg/mL with correlation coefficients of 0.9990-0.9995. The LOD and LOQ were 0.10-0.68 μg/mL and 0.47-2.11 μg/mL, respectively. The neuroprotective effect and co-immunoprecipitation test in vitro revealed that Emodin-1-O-β-d-glucoside, Rhaponticin, Gnetol and 2,3,5,4'-Tetrahydroxystilbene-2-O-β-d-glucoside have neuroprotective and uncoupling activities, and that they may be the new uncouplers of nNOS-PSD-95.

Regional Specific Modulation of Stress-Induced Neuronal Activation Associated with the PSD95/NOS Interaction Inhibitor ZL006 in the Wistar Kyoto Rat

BACKGROUND

To determine brain areas involved in the antidepressant-related behavioral effects of the selective neuronal nitric oxide synthase inhibitor 1-(2-Trifluoro-methyl-phenyl) imidazole (TRIM) and experimental test compound 4-((3,5-dichloro-2-hydroxybenzyl)amino)-2-hydroxybenzoic acid (ZL006), an inhibitor of the PSD of 95 kDa/neuronal nitric oxide synthase interaction in the N-methyl-D-aspartic acid receptor signalling pathway, regional specific expression of the neuronal activation marker c-FOS was assessed following exposure to the forced swimming test in the Wistar Kyoto rat.

METHODS

Wistar Kyoto rats were subjected to a 15-minute swim pretest (pre-forced swimming test) period on day 1. At 24, 5, and 1 hour prior to the 5-minute test, which took place 24 hours following the pre-forced swimming test, animals were treated with TRIM (50 mg/kg; i.p.), ZL006 (10 mg/kg; i.p.), or saline vehicle (1 mL/kg i.p). Behavior was recorded during both pretest and test periods.

RESULTS

Both TRIM and ZL006 decreased immobility time in Wistar Kyoto rats in the forced swimming test. Exposure to the forced swimming test increased c-FOS immunoreactivity in the lateral septum, paraventricular nucleus of the hypothalamus, periaqueductal grey, dentate gyrus, and ventral CA1 of the hippocampus compared with non-forced swimming test-exposed controls. Forced swimming test-induced c-FOS immunoreactivity was further increased in the lateral septum, periaqueductal gray, and paraventricular nucleus of the hypothalamus following treatment with TRIM or ZL006. By contrast, forced swimming test-induced c-FOS immunoreactivity was reduced in dorsal dentate gyrus and ventral CA1 following treatment with TRIM or ZL006. Exposure to the forced swimming test resulted in an increase in NADPH diaphorase staining in the paraventricular nucleus of the hypothalamus. This forced swimming test-induced increase was attenuated following treatment with ZL006 and points to the paraventricular nucleus as a brain region where ZL006 acts to attenuate forced swimming test-induced neuronal nitric oxide synthase activity while concomitantly regulating region specific neuronal activation associated with an antidepressant-related response.

CONCLUSIONS

This study identified a pattern of enhanced and reduced forced swimming test-related c-FOS immunoreactivity indicative of a regulated network where inhibition of nitric oxide coupled to the N-methyl-D-aspartic acid receptor leads to activation of the lateral septum, periaqueductal gray, and paraventricular nucleus of the hypothalamus with concomitant inhibition of the hippocampus.

Delineation of molecular pathway activities of the chronic antidepressant treatment response suggests important roles for glutamatergic and ubiquitin-proteasome systems

The aim of this study was to identify molecular pathways related to antidepressant response. We administered paroxetine to the DBA/2J mice for 28 days. Following the treatment, the mice were grouped into responders or non-responders depending on the time they spent immobile in the forced swim test. Hippocampal metabolomics and proteomics analyses revealed that chronic paroxetine treatment affects glutamate-related metabolite and protein levels differentially in the two groups. We found significant differences in the expression of N-methyl-d-aspartate receptor and neuronal nitric oxide synthase proteins between the two groups, without any significant alterations in the respective transcript levels. In addition, we found that chronic paroxetine treatment altered the levels of proteins associated with the ubiquitin-proteasome system (UPS). The soluble guanylate cyclase-β1, proteasome subunit α type-2 and ubiquitination levels were also affected in peripheral blood mononuclear cells from antidepressant responder and non-responder patients suffering from major depressive disorder. We submit that the glutamatergic system and UPS have a crucial role in the antidepressant treatment response in both mice and humans.

Whole-exome sequencing of individuals from an isolated population implicates rare risk variants in bipolar disorder

Bipolar disorder affects about 1% of the world's population, and its estimated heritability is about 75%. Only few whole genome or whole-exome sequencing studies in bipolar disorder have been reported, and no rare coding variants have yet been robustly identified. The use of isolated populations might help finding variants with a recent origin, more likely to have drifted to higher frequency by chance. Following this approach, we investigated 28 bipolar cases and 214 controls from the Faroe Islands by whole exome sequencing, and the results were followed-up in a British sample of 2025 cases and 1358 controls. Seventeen variants in 16 genes in the single-variant analysis, and 3 genes in the gene-based statistics surpassed exome-wide significance in the discovery phase. The discovery findings were supported by enrichment analysis of common variants from genome-wide association studies (GWAS) data and interrogation of protein-protein interaction networks. The replication in the British sample confirmed the association with NOS1 (missense variant rs79487279) and NCL (gene-based test). A number of variants from the discovery set were not present in the replication sample, including a novel PITPNM2 missense variant, which is located in a highly significant schizophrenia GWAS locus. Likewise, PIK3C2A identified in the gene-based analysis is located in a combined bipolar and schizophrenia GWAS locus. Our results show support both for existing findings in the literature, as well as for new risk genes, and identify rare variants that might provide additional information on the underlying biology of bipolar disorder.

Serine 707 of APPL1 is Critical for the Synaptic NMDA Receptor-Mediated Akt Phosphorylation Signaling Pathway

Accumulating evidence indicates that the synaptic activation of N-methyl-D-aspartate receptors (NMDARs) has a neuroprotective effect on neurons. Our previous study demonstrated that APPL1 (adaptor protein containing pleckstrin homology domain, phosphotyrosine-binding domain, and leucine zipper motif) mediates the synaptic activity-dependent activation of PI3K-Akt signaling via coupling this pathway with NMDAR-PSD95 (postsynaptic density protein 95) complexes. However, the molecular mechanism underlying this process is still unknown. In the present study, we investigated the interaction of APPL1 with PSD95 using co-immunocytochemical staining and western blotting. We found that the PDZ2 domain of PSD95 is a binding partner of APPL1. Furthermore, we identified serine 707 of APPL1, a predicted phosphorylation site within the PDZ-binding motif at the C-terminus, as critical for the binding of APPL1 to PSD95, as well as for activation of the Akt signaling pathway during synaptic activity. This suggests that serine 707 of APPL1 is a potential phosphorylation site and may be involved in regulating the neuroprotective Akt signaling pathway that depends on synaptic NMDAR activity.

Research progress in NOS1AP in neurological and psychiatric diseases

Nitric Oxide Synthase 1 Adaptor Protein (NOS1AP, previously named CAPON) was firstly identified in rat brain in 1998. Structurally, NOS1AP consists of a phosphotyrosine-binding (PTB) domain at its N-terminal and a PDZ (PSD-95/discs-large/ZO-1) ligand motif at its C-terminal. The PTB domain of NOS1AP mediates the interactions with Dexras1, scribble, and synapsins. The PDZ ligand motif of NOS1AP binds to the PDZ domain of NOS1, the enzyme responsible for nitric oxide synthesis in the nervous system. NOS1AP is implicated in Dexras1 activation, neuronal nitric oxide production, Hippo pathway signaling, and dendritic development through the association with these important partners. An increasing body of evidence is pointing to the significant roles of NOS1AP in excitotoxic neuronal damage, traumatic nervous system injury, bipolar disorder, and schizophrenia. However, the study progress in NOS1AP in neurological or psychiatric diseases, has not been systematically reviewed. Here we introduce the expression, structure, and isoforms of NOS1AP, then summarize the physiological roles of NOS1AP, and discuss the relationships between NOS1AP alterations and the pathophysiology of some neurological and psychiatric disorders. The review will promote the further investigation of NOS1AP in brain disorders and the development of drugs targeting the NOS1AP PTB domain or PDZ-binding motif in the future.

Interaction of NOS1AP with the NOS-I PDZ domain: Implications for schizophrenia-related alterations in dendritic morphology

Schizophrenia involves morphological brain changes, including changes in synaptic plasticity and altered dendritic development. Amongst the most promising candidate molecules for schizophrenia are neuronal nitric oxide (NO) synthase (NOS-I, also known as nNOS) and its adapter protein NOS1AP (previously named CAPON). However, the precise molecular mechanisms by which NOS-I and NOS1AP affect disease pathology remain to be resolved. Interestingly, overexpression of NOS1AP affects dendritic morphology, possibly through increased association with the NOS-I PDZ domain. To investigate the effect of NOS1AP on dendritic morphology we overexpressed different NOS1AP isoforms, NOS1AP deletion mutants and the aminoterminal 133 amino acids of NOS-I (NOS-IN133) containing an extended PDZ domain. We examined the interaction of the overexpressed constructs with endogenous NOS-I by co-immunoprecipitation and the consequences of increased NOS-I/NOS1AP PDZ interaction in primary cultures of hippocampal and cortical neurons from C57BL/6J mice. Neurons overexpressing NOS1AP isoforms or deletion mutants showed highly altered spine morphology and excessive growth of filopodia-like protrusions. Sholl analysis of immunostained primary cultured neurons revealed that dendritic branching was mildly affected by NOS1AP overexpression. Our results hint towards an involvement of NOS-I/NOS1AP interaction in the regulation of dendritic spine plasticity. As altered dendritic spine development and filopodial outgrowth are important neuropathological features of schizophrenia, our findings may provide insight into part of the molecular mechanisms involved in brain morphology alterations observed in schizophrenia. As the NOS-I/NOS1AP interface can be targeted by small molecules, our findings ultimately might help to develop novel treatment strategies for schizophrenia patients.

Source memory in rats is impaired by an NMDA receptor antagonist but not by PSD95-nNOS protein-protein interaction inhibitors

Limitations of preclinical models of human memory contribute to the pervasive view that rodent models do not adequately predict therapeutic efficacy in producing cognitive impairments or improvements in humans. We used a source-memory model (i.e., a representation of the origin of information) we developed for use in rats to evaluate possible drug-induced impairments of both spatial memory and higher order memory functions in the same task. Memory impairment represents a major barrier to use of NMDAR antagonists as pharmacotherapies. The scaffolding protein postsynaptic density 95kDa (PSD95) links NMDARs to the neuronal enzyme nitric oxide synthase (nNOS), which catalyzes production of the signaling molecule nitric oxide (NO). Therefore, interrupting PSD95-nNOS protein-protein interactions downstream of NMDARs represents a novel therapeutic strategy to interrupt NMDAR-dependent NO signaling while bypassing unwanted side effects of NMDAR antagonists. We hypothesized that the NMDAR antagonist MK-801 would impair source memory. We also hypothesized that PSD95-nNOS inhibitors (IC87201 and ZL006) would lack the profile of cognitive impairment associated with global NMDAR antagonists. IC87201 and ZL006 suppressed NMDA-stimulated formation of cGMP, a marker of NO production, in cultured hippocampal neurons. MK-801, at doses that did not impair motor function, impaired source memory under conditions in which spatial memory was spared. Thus, source memory was more vulnerable than spatial memory to impairment. By contrast, PSD95-nNOS inhibitors, IC87201 and ZL006, administered at doses that are behaviorally effective in rats, spared source memory, spatial memory, and motor function. Thus, PSD95-nNOS inhibitors are likely to exhibit favorable therapeutic ratios compared to NMDAR antagonists.

Z-guggulsterone negatively controls microglia-mediated neuroinflammation via blocking IκB-α-NF-κB signals

Induction of pro-inflammatory factors is one of the characteristics of microglial activation and can be regulated by numerous active agents extracted from plants. Suppression of pro-inflammatory factors is beneficial to alleviate neuroinflammation. Z-guggulsterone, a compound extracted from the gum resin of the tree commiphora mukul, exhibits numerous anti-inflammatory effects. However, the role and mechanism of Z-guggulsterone in pro-inflammatory responses in microglia remains unclear. This study addressed this issue in in vitro murine microglia and in vivo neuroinflammation models. Results showed that Z-guggulsterone reduced inducible nitric oxide (iNOS) protein expression as well as nitric oxide (NO), tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) production in LPS-stimulated BV-2 cells. Z-guggulsterone also reduced the mRNA level of iNOS, TNF-α, and IL-6. Mechanistic studies revealed that Z-guggulsterone attenuated the LPS-induced degradation of inhibitor κ B-α (IκB-α) as well as the LPS-induced nuclear translocation of nuclear factor-κB (NF-κB). Z-guggulsterone, however, failed to reduce the LPS-induced increase in NF-κB phosphorylation level. These major findings were ascertained in primary microglia where the LPS-induced increases in iNOS expression, NO content, and IκB-α degradation were diminished by Z-guggulsterone treatment. In a mouse model of neuroinflammation, Z-guggulsterone exhibited significant anti-inflammatory effects, which were exemplified by the attenuation of microglial activation and neuroinflammation-induced behavioral abnormalities in Z-guggulsterone-treated mice. Taken together, these studies demonstrate that Z-guggulsterone attenuates the LPS-mediated induction of pro-inflammatory factors in microglia via inhibition of IκB-α-NF-κB signals, providing evidence to uncover the potential role of Z-guggulsterone in neuroinflammation-associated disorder therapies.

Association of NOS1AP variants and depression phenotypes in schizophrenia

BACKGROUND

The nitric oxide synthase 1 adaptor protein gene (NOS1AP) has previously been recognised as a schizophrenia susceptibility gene due to its role in glutamate neurotransmission. The gene is believed to inhibit nitric oxide (NO) production activated by the N-methyl-d-aspartate (NMDA) receptor and reduced NO levels have been observed in schizophrenia patients. However, association studies investigating NOS1AP and schizophrenia have produced inconsistent results, most likely because schizophrenia is a clinically heterogeneous disorder. This study aims to investigate the association between NOS1AP variants and defined depression phenotypes of schizophrenia.

METHODS

Nine NOS1AP SNPs, rs1415259, rs1415263, rs1858232, rs386231, rs4531275, rs4656355, rs4657178, rs6683968 and rs6704393 were genotyped in 235 schizophrenia subjects screened for various phenotypes of depression.

RESULT

One NOS1AP SNP (rs1858232) was associated with the broad diagnosis of schizophrenia and eight SNPs were associated with depression related phenotypes within schizophrenia. The rs1415259 SNP showed strong association with sleep dysregulation phenotypes of depression.

CONCLUSION

Results suggest that NOS1AP variants are associated with various forms of depression in schizophrenia and are more prevalent in males.

LIMITATION

Schizophrenia is a clinically heterogeneous disease that can vary greatly between different ethnic and geographic populations so our observations should be viewed with caution until they are independently replicated, particularly in larger patient cohorts.

Neuronal nitric oxide synthase (NOS1) and its adaptor, NOS1AP, as a genetic risk factors for psychiatric disorders

Nitric oxide (NO) is a gaseous transmitter produced by nitric oxide synthases (NOSs). The neuronal isoform (NOS-I, encoded by NOS1) is the main source of NO in the central nervous system (CNS). Animal studies suggest that nitrinergic dysregulation may lead to behavioral abnormalities. Unfortunately, the large number of animal studies is not adequately reflected by publications concerning humans. These include post-mortem studies, determination of biomarkers, and genetic association studies. Here, we review the evidence for the role of NO in psychiatric disorders by focusing on the human NOS1 gene as well as biomarker studies. Owing to the complex regulation of NOS1 and the varying function of NOS-I in different brain regions, no simple, unidirectional association is expected. Rather, the 'where, when and how much' of NO formation is decisive. Present data, although still preliminary and partially conflicting, suggest that genetically driven reduced NO signaling in the prefrontal cortex is associated with schizophrenia and cognition. Both NOS1 and its interaction partner NOS1AP have a role therein. Also, reduced NOS1 expression in the striatum determined by a length polymorphism in a NOS1 promoter (NOS1 ex1f-VNTR) goes along with a variety of impulsive behaviors. An association of NOS1 with mood disorders, suggested by animal models, is less clear on the genetic level; however, NO metabolites in blood may serve as biomarkers for major depression and bipolar disorder. As the nitrinergic system comprises a relevant target for pharmacological interventions, further studies are warranted not only to elucidate the pathophysiology of mental disorders, but also to evaluate NO function as a biomarker.

Bacopa monnieri Extract (CDRI-08) Modulates the NMDA Receptor Subunits and nNOS-Apoptosis Axis in Cerebellum of Hepatic Encephalopathy Rats

Hepatic encephalopathy (HE), characterized by impaired cerebellar functions during chronic liver failure (CLF), involves N-methyl-D-aspartate receptor (NMDAR) overactivation in the brain cells. Bacopa monnieri (BM) extract is a known neuroprotectant. The present paper evaluates whether BM extract is able to modulate the two NMDAR subunits (NR2A and NR2B) and its downstream mediators in cerebellum of rats with chronic liver failure (CLF), induced by administration of 50 mg/kg bw thioacetamide (TAA) i.p. for 14 days, and in the TAA group rats orally treated with 200 mg/kg bw BM extract from days 8 to 14. NR2A is known to impart neuroprotection and that of NR2B induces neuronal death during NMDAR activation. Neuronal nitric oxide synthase- (nNOS-) apoptosis pathway is known to mediate NMDAR led excitotoxicity. The level of NR2A was found to be significantly reduced with a concomitant increase of NR2B in cerebellum of the CLF rats. This was consistent with significantly enhanced nNOS expression, nitric oxide level, and reduced Bcl2/Bax ratio. Moreover, treatment with BM extract reversed the NR2A/NR2B ratio and also normalized the levels of nNOS-apoptotic factors in cerebellum of those rats. The findings suggest modulation of NR2A and NR2B expression by BM extract to prevent neurochemical alterations associated with HE.

Biochemical investigations of the mechanism of action of small molecules ZL006 and IC87201 as potential inhibitors of the nNOS-PDZ/PSD-95-PDZ interactions

ZL006 and IC87201 have been presented as efficient inhibitors of the nNOS/PSD-95 protein-protein interaction and shown great promise in cellular experiments and animal models of ischemic stroke and pain. Here, we investigate the proposed mechanism of action of ZL006 and IC87201 using biochemical and biophysical methods, such as fluorescence polarization (FP), isothermal titration calorimetry (ITC), and (1)H-(15)N HSQC NMR. Our data show that under the applied in vitro conditions, ZL006 and IC87201 do not interact with the PDZ domains of nNOS or PSD-95, nor inhibit the nNOS-PDZ/PSD-95-PDZ interface by interacting with the β-finger of nNOS-PDZ. Our findings have implications for further medicinal chemistry efforts of ZL006, IC87201 and analogues, and challenge the general and widespread view on their mechanism of action.

Novel 4-aryl-pyrido[1,2-c]pyrimidines with dual SSRI and 5-HT(1A) activity. Part 5

A series of novel 4-aryl-pyrido[1,2-c]pyrimidine derivatives containing a 1-(2-quinoline)piperazine moiety was synthesized. The chemical structure of new compounds was confirmed by FT-IR, (1)H NMR, (13)C NMR and HRMS spectra as well as elemental analysis. Affinity of the novel pyrido[1,2-c]pyrimidine derivatives for 5-HT1A, 5-HT2A receptors and serotonin transporter (SERT) was evaluated in an in vitro radioligand binding assay. Tested compounds showed moderate to high affinity for 5-HT1AR and SERT and low affinity for 5-HT2AR. Selected ligands were subjected to in vivo tests, such as induced hypothermia and the forced swimming test in mice, which determined presynaptic agonistic activity of the ligands 8d, 8e, 9d and 9e and presynaptic antagonistic activity of the ligands 8a, 8b, 9a, 9b. Additionally, metabolic stability evaluation was performed for selected ligands, proving that a para-substitution in the 4-aryl-pyrido[1,2-c]pyrimidine moiety leads to an increase in stability, whereas a substitution in the ortho-position lowers the stability.

Targeting protein-protein interactions with trimeric ligands: high affinity inhibitors of the MAGUK protein family

PDZ domains in general, and those of PSD-95 in particular, are emerging as promising drug targets for diseases such as ischemic stroke. We have previously shown that dimeric ligands that simultaneously target PDZ1 and PDZ2 of PSD-95 are highly potent inhibitors of PSD-95. However, PSD-95 and the related MAGUK proteins contain three consecutive PDZ domains, hence we envisioned that targeting all three PDZ domains simultaneously would lead to more potent and potentially more specific interactions with the MAGUK proteins. Here we describe the design, synthesis and characterization of a series of trimeric ligands targeting all three PDZ domains of PSD-95 and the related MAGUK proteins, PSD-93, SAP-97 and SAP-102. Using our dimeric ligands targeting the PDZ1-2 tandem as starting point, we designed novel trimeric ligands by introducing a PDZ3-binding peptide moiety via a cysteine-derivatized NPEG linker. The trimeric ligands generally displayed increased affinities compared to the dimeric ligands in fluorescence polarization binding experiments and optimized trimeric ligands showed low nanomolar inhibition towards the four MAGUK proteins, thus being the most potent inhibitors described. Kinetic experiments using stopped-flow spectrometry showed that the increase in affinity is caused by a decrease in the dissociation rate of the trimeric ligand as compared to the dimeric ligands, likely reflecting the lower probability of simultaneous dissociation of all three PDZ ligands. Thus, we have provided novel inhibitors of the MAGUK proteins with exceptionally high affinity, which can be used to further elucidate the therapeutic potential of these proteins.

Pannexin1 as a novel cerebral target in pathogenesis of hepatic encephalopathy

Hepatic encephalopathy (HE) represents a nervous system disorder caused due to liver dysfunction. HE is broadly classified as acute/overt and moderate-minimal HE. Since HE syndrome severely affects quality of life of the patients and it may be life threatening, it is important to develop effective therapeutic strategy against HE. Mainly ammonia neurotoxicity is considered accountable for HE. Increased level of ammonia in the brain activates glutamate-NMDA (N-methyl-D-aspartate) receptor (NMDAR) pathway leading to Ca(2+) influx, energy deficit and oxidative stress in the post synaptic neurons. Moreover, NMDAR blockage has been found to be a poor therapeutic option, as this neurotransmitter receptor plays important role in maintaining normal neurophysiology of the brain. Thus, searching new molecular players in HE pathogenesis is of current concern. There is an evolving concept about roles of the trans-membrane channels in the pathogenesis of a number of neurological complications. Pannexin1 (Panx1) is one of them and has been described to be implicated in stroke, epilepsy and ischemia. Importantly, the pathogenesis of these complications relates to some extent with NMDAR over activation. Thus, it is speculated that HE pathogenesis might also involve Panx1. Indeed, some recent observations in the animal models of HE provide support to this argument. Since opening of Panx1 channel is mostly associated with the neuronal dysfunctions, down regulation of this channel could serve as a relevant therapeutic strategy without producing any serious side effects. In the review article an attempt has been made to summarize the current information on implication of Panx1 in the brain disorders and its prospects for being examined as pharmacological target in HE pathogenesis.

Neuronal nitric oxide synthase (NOS1) polymorphisms interact with financial hardship to affect depression risk

There is increasing evidence that genetic factors have a role in differential susceptibility to depression in response to severe or chronic adversity. Studies in animals suggest that nitric oxide (NO) signalling has a key role in depression-like behavioural responses to stress. This study investigated whether genetic variation in the brain-expressed nitric oxide synthase gene NOS1 modifies the relationship between psychosocial stress and current depression score. We recruited a population sample of 1222 individuals who provided DNA and questionnaire data on symptoms and stress. Scores on the List of Life-Threatening Experiences (LTE) questionnaire for the last year and self-rated current financial hardship were used as measures of recent/ongoing psychosocial stress. Twenty SNPs were genotyped. Significant associations between eight NOS1 SNPs, comprising two regional haplotypes, and current depression score were identified that survived correction for multiple testing when current financial hardship was used as the interaction term. A smaller three-SNP haplotypes (rs10507279, rs1004356 and rs3782218) located in a regulatory region of NOS1 showed one of the strongest effects, with the A-C-T haplotype associating with higher depression scores at low adversity levels but lower depression scores at higher adversity levels (p=2.3E-05). These results suggest that NOS1 SNPs interact with exposure to economic and psychosocial stressors to alter individual's susceptibility to depression.

Mechanisms of NOS1AP action on NMDA receptor-nNOS signaling

NMDA receptors (NMDAR) are glutamate-gated calcium channels that play pivotal roles in fundamental aspects of neuronal function. Dysregulated receptor function contributes to many disorders. Recruitment by NMDARs of calcium-dependent enzyme nNOS via PSD95 is seen as a key contributor to neuronal dysfunction. nNOS adaptor protein (NOS1AP), originally described as a competitor of PSD95:nNOS interaction, is regarded an inhibitor of NMDAR-driven nNOS function. In conditions of NMDAR hyperactivity such as excitotoxicity, one expects NOS1AP to be neuroprotective. Conditions of NMDAR hypoactivity, as thought to occur in schizophrenia, might be exacerbated by NOS1AP. Indeed GWAS have implicated NOS1AP and nNOS in schizophrenia. Several studies now indicate NOS1AP can mediate rather than inhibit NMDAR/nNOS-dependent responses, including excitotoxic signaling. Yet the concept of NOS1AP as an inhibitor of nNOS predominates in studies of human disease genetics. Here we review the experimental evidence to evaluate this apparent controversy, consider whether the known functions of NOS1AP might defend neurons against NMDAR dysregulation and highlight specific areas for future investigation to shed light on the functions of this adaptor protein.

Metaplastic effects of subanesthetic ketamine on CA1 hippocampal function

Ketamine is a non-competitive N-methyl-d-aspartate receptor (NMDAR) antagonist of interest in neuropsychiatry. In the present studies, we examined the effects of subanesthetic, low micromolar ketamine on excitatory postsynaptic potentials (EPSPs), population spikes (PSs) and synaptic plasticity in the CA1 region of rat hippocampal slices. Ketamine acutely inhibited NMDAR-mediated synaptic responses with half-maximal effects near 10 μM. When administered for 15-30 min at 1-10 μM, ketamine had no effect on baseline dendritic AMPA receptor-mediated EPSPs, but persistently enhanced somatic EPSPs in the pyramidal cell body layer and augmented PS firing. Acute low micromolar ketamine also had no effect on the induction of long-term potentiation (LTP) but blocked long-term depression (LTD). Following 30 min administration of 1-10 μM ketamine, however, a slowly developing and persistent form of LTP inhibition was observed that took two hours following ketamine washout to become manifest. This LTP inhibition did not result from prolonged or enhanced NMDAR inhibition during drug washout. Effects of low ketamine on somatic EPSPs and LTP were not mimicked by a high ketamine concentration that completely inhibited NMDARs, and both of these effects were blocked by co-administration of low ketamine with a low concentration of the competitive NMDAR antagonist, 2-amino-5-phosphonovalerate or inhibitors of nitric oxide synthase. These results indicate that concentrations of ketamine relevant to psychotropic and psychotomimetic effects have complex metaplastic effects on hippocampal function that involve activation of unblocked NMDARs during ketamine exposure.

Protein interacting with C-kinase 1 (PICK1) binding promiscuity relies on unconventional PSD-95/discs-large/ZO-1 homology (PDZ) binding modes for nonclass II PDZ ligands

PDZ domain proteins control multiple cellular functions by governing assembly of protein complexes. It remains unknown why individual PDZ domains can bind the extreme C terminus of very diverse binding partners and maintain selectivity. By employing NMR spectroscopy, together with molecular modeling, mutational analysis, and fluorescent polarization binding experiments, we identify here three structural mechanisms explaining why the PDZ domain of PICK1 selectively binds >30 receptors, transporters, and kinases. Class II ligands, including the dopamine transporter, adopt a canonical binding mode with promiscuity obtained via differential packing in the binding groove. Class I ligands, such as protein kinase Cα, depend on residues upstream from the canonical binding sequence that are likely to interact with flexible loop residues of the PDZ domain. Finally, we obtain evidence that the unconventional ligand ASIC1a has a dual binding mode involving a canonical insertion and a noncanonical internal insertion with the two C-terminal residues forming interactions outside the groove. Together with an evolutionary analysis, the data show how unconventional binding modes might evolve for a protein recognition domain to expand the repertoire of functionally important interactions.

Acidic pH increases cGMP accumulation through the OGR1/phospholipase C/Ca(2+)/neuronal NOS pathway in N1E-115 neuronal cells

Neuronal NO synthase (nNOS)-mediated cGMP accumulation has been shown to affect a variety of neuronal cell activities, regardless of whether they are detrimental or beneficial, depending on the amount of their levels, under the physiological and pathological situations. In the present study, we examined the role of proton-sensing G protein-coupled receptors (GPCRs), which have been identified as new pH sensors, in the acidic pH-induced nNOS/cGMP activity in N1E-115 neuronal cells. In this cell line, ovarian cancer G protein-coupled receptor 1 (OGR1) and G protein-coupled receptor 4 (GPR4) mRNAs are expressed. An extracellular acidic pH increased cGMP accumulation, which was inhibited by nNOS-specific inhibitors. Acidic pH also activated phospholipase C/Ca(2+) pathways and Akt-induced phosphorylation of nNOS at S1412, both of which have been shown to be critical regulatory mechanisms for nNOS activation. The acidic pH-induced activation of the phospholipase C/Ca(2+) pathway, but not Akt/nNOS phosphorylation, was inhibited by small interfering RNA specific to OGR1 and YM-254890, an inhibitor of Gq/11 proteins, in association with the inhibition of cGMP accumulation. Moreover cGMP accumulation was inhibited by 2-aminoethoxydiphenyl borate, an inhibitor of inositol 1,4,5-trisphosphate channel; however, it was not by wortmannin, a phosphatidylinositol 3-kinase inhibitor, which inhibited Akt/nNOS phosphorylation. In conclusion, acidic pH stimulates cGMP accumulation preferentially through the OGR1/Gq/11 proteins/phospholipase C/Ca(2+)/nNOS in N1E-115 neuronal cells. Akt-mediated phosphorylation of nNOS, however, does not appreciably contribute to the acidification-induced accumulation of cGMP.

Molecular mechanisms of neuronal nitric oxide synthase in cardiac function and pathophysiology

Neuronal nitric oxide synthase (nNOS or NOS1) is the major endogenous source of myocardial nitric oxide (NO), which facilitates cardiac relaxation and modulates contraction. In the healthy heart it regulates intracellular Ca(2+), signalling pathways and oxidative homeostasis and is upregulated from early phases upon pathogenic insult. nNOS plays pivotal roles in protecting the myocardium from increased oxidative stress, systolic/diastolic dysfunction, adverse structural remodelling and arrhythmias in the failing heart. Here, we show that the downstream target proteins of nNOS and underlying post-transcriptional modifications are shifted during disease progression from Ca(2+)-handling proteins [e.g. PKA-dependent phospholamban phosphorylation (PLN-Ser(16))] in the healthy heart to cGMP/PKG-dependent PLN-Ser(16) with acute angiotensin II (Ang II) treatment. In early hypertension, nNOS-derived NO is involved in increases of cGMP/PKG-dependent troponin I (TnI-Ser(23/24)) and cardiac myosin binding protein C (cMBP-C-Ser(273)). However, nNOS-derived NO is shown to increase S-nitrosylation of various Ca(2+)-handling proteins in failing myocardium. The spatial compartmentation of nNOS and its translocation for diverse binding partners in the diseased heart or various nNOS splicing variants and regulation in response to pathological stress may be responsible for varied underlying mechanisms and functions. In this review, we endeavour to outline recent advances in knowledge of the molecular mechanisms mediating the functions of nNOS in the myocardium in both normal and diseased hearts. Insights into nNOS gene regulation in various tissues are discussed. Overall, nNOS is an important cardiac protector in the diseased heart. The dynamic localization and various mediating mechanisms of nNOS ensure that it is able to regulate functions effectively in the heart under stress.

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.

Aquaporin-4 knockout exacerbates corticosterone-induced depression by inhibiting astrocyte function and hippocampal neurogenesis

AIMS

The predominant expression of aquaporin-4 (AQP4) in the brain implies that this water channel may be involved in a range of brain disorders. This study was designed to investigate the role of AQP4 in the pathogenesis of depression, and related possible biological mechanism.

METHODS AND RESULTS

Wild-type (AQP4(+/+) ) and AQP4 knockout (AQP4(-/-) ) mice were given daily subcutaneous injections of corticosterone (20 mg/kg) for consecutive 21 days. Forced swimming test (FST) and tail suspension test (TST) showed longer immobility times in corticosterone-treated AQP4(-/-) genotype, indicating AQP4 knockout exacerbated depressive-like behaviors in mice. Using immunohistological staining, western blot, and enzyme-linked immunosorbent assay (ELISA), we found a significant loss of astrocytes, aggravated downregulation of excitatory amino acid transporter 2 (EAAT2), synapsin-1, and glial cell line-derived neurotrophic factor (GDNF) in the hippocampus of AQP4(-/-) mice. Moreover, even less hippocampal neurogenesis was identified in corticosterone-treated AQP4(-/-) mice in vivo and hippocampus-derived adult neural stem cells (ANSCs) in vitro.

CONCLUSIONS

The present findings suggest AQP4 involves the pathogenesis of depression by modulating astrocytic function and adult neurogenesis, highlighting a novel profile of AQP4 as a potential target for the treatment for depression.

The role of nitric oxide in pre-synaptic plasticity and homeostasis

Since the observation that nitric oxide (NO) can act as an intercellular messenger in the brain, the past 25 years have witnessed the steady accumulation of evidence that it acts pre-synaptically at both glutamatergic and GABAergic synapses to alter release-probability in synaptic plasticity. NO does so by acting on the synaptic machinery involved in transmitter release and, in a coordinated fashion, on vesicular recycling mechanisms. In this review, we examine the body of evidence for NO acting as a retrograde factor at synapses, and the evidence from in vivo and in vitro studies that specifically establish NOS1 (neuronal nitric oxide synthase) as the important isoform of NO synthase in this process. The NOS1 isoform is found at two very different locations and at two different spatial scales both in the cortex and hippocampus. On the one hand it is located diffusely in the cytoplasm of a small population of GABAergic neurons and on the other hand the alpha isoform is located discretely at the post-synaptic density (PSD) in spines of pyramidal cells. The present evidence is that the number of NOS1 molecules that exist at the PSD are so low that a spine can only give rise to modest concentrations of NO and therefore only exert a very local action. The NO receptor guanylate cyclase is located both pre- and post-synaptically and this suggests a role for NO in the coordination of local pre- and post-synaptic function during plasticity at individual synapses. Recent evidence shows that NOS1 is also located post-synaptic to GABAergic synapses and plays a pre-synaptic role in GABAergic plasticity as well as glutamatergic plasticity. Studies on the function of NO in plasticity at the cellular level are corroborated by evidence that NO is also involved in experience-dependent plasticity in the cerebral cortex.

Small-molecule inhibitors at the PSD-95/nNOS interface have antidepressant-like properties in mice

Previous studies have demonstrated that nitric oxide (NO) synthase inhibitors are as efficacious as tricyclic antidepressants in preclinical antidepressant screening procedures and in attenuating behavioural deficits associated with animal models of depression. The N-methyl-D-aspartate receptor (NMDA-R) complex gates Ca(2+), which interacts with calmodulin to subsequently activate NO synthase. We hypothesised that uncoupling neuronal nitric oxide synthase (nNOS) from the NMDA-R through the scaffolding protein postsynaptic density protein 95 (PSD-95) would produce behavioural antidepressant effects similar to NO synthase inhibitors. Small-molecule inhibitors of the PSD-95/nNOS interaction, IC87201 (0.01-2 mg/kg) and ZL006 (10 mg/kg) were tested for antidepressant properties in tests of antidepressant activity namely the tail suspension and forced swim tests in mice. We now report that IC87201 and ZL006 produce antidepressant-like responses in the forced swimming test (FST) and tail suspension test (TST) following a single administration in mice. By contrast to the tricyclic antidepressant imipramine (25 mg/kg), the effects are not observed 1 h following drug administration but are apparent 24 and 72 h later. Furthermore prior exposure to the TST or FST is required in order to observe the antidepressant-related activity. Similar delayed and sustained antidepressant-like effects were observed following TRIM (50 mg/kg) and ketamine (30 mg/kg) in the TST. The antidepressant-like effects of ZL006 also generalise to IC87201 in the TST. IC87201 was devoid of effects on locomotor activity and step-through latency in the passive avoidance cognition test. These data support the hypothesis that targeting the PSD-95/nNOS interaction downstream of NMDA-R produces antidepressant effects and may represent a novel class of therapeutics for major depressive disorders.