Dexras1: a G protein specifically coupled to neuronal nitric oxide synthase via CAPON

Recessive variants in the intergenic NOS1AP-C1orf226 locus cause monogenic kidney disease responsive to anti-proteinuric treatment

In genetic disease, an accurate expression landscape of disease genes and faithful animal models will enable precise genetic diagnoses and therapeutic discoveries, respectively. We previously discovered that variants in NOS1AP , encoding nitric oxide synthase 1 (NOS1) adaptor protein, cause monogenic nephrotic syndrome (NS). Here, we determined that an intergenic splice product of N OS1AP / Nos1ap and neighboring C1orf226/Gm7694 , which precludes NOS1 binding, is the predominant isoform in mammalian kidney transcriptional and proteomic data. Gm7694 -/- mice, whose allele exclusively disrupts the intergenic product, developed NS phenotypes. In two human NS subjects, we identified causative NOS1AP splice variants, including one predicted to abrogate intergenic splicing but initially misclassified as benign based on the canonical transcript. Finally, by modifying genetic background, we generated a faithful mouse model of NOS1AP -associated NS, which responded to anti-proteinuric treatment. This study highlights the importance of intergenic splicing and a potential treatment avenue in a mendelian disorder.

Rasd1 is involved in white matter injury through neuron-oligodendrocyte communication after subarachnoid hemorrhage

AIMS

Rasd1 has been reported to be correlated with neurotoxicity, metabolism, and rhythm, but its effect in case of subarachnoid hemorrhage (SAH) remained unclear. White matter injury (WMI) and ferroptosis participate in the early brain injury (EBI) after SAH. In this work, we have investigated whether Rasd1 can cause ferroptosis and contribute to SAH-induced WMI.

METHODS

Lentivirus for Rasd1 knockdown/overexpression was administrated by intracerebroventricular (i.c.v) injection at 7 days before SAH induction. SAH grade, brain water content, short- and long-term neurobehavior, Western blot, real-time PCR, ELISA, biochemical estimation, immunofluorescence, diffusion tensor imaging (DTI), and transmission electron microscopy (TEM) were systematically performed. Additionally, genipin, a selective uncoupling protein 2(UCP2) inhibitor, was used in primary neuron and oligodendrocyte co-cultures for further in vitro mechanistic studies.

RESULTS

Rasd1 knockdown has improved the neurobehavior, glia polarization, oxidative stress, neuroinflammation, ferroptosis, and demyelination. Conversely, Rasd1 overexpression aggravated these changes by elevating the levels of reactive oxygen species (ROS), inflammatory cytokines, MDA, free iron, and NCOA4, as well as contributing to the decrease of the levels of UCP2, GPX4, ferritin, and GSH mechanistically. According to the in vitro study, Rasd1 can induce oligodendrocyte ferroptosis through inhibiting UCP2, increasing reactive oxygen species (ROS), and activating NCOA4-mediated ferritinophagy.

CONCLUSIONS

It can be concluded that Rasd1 exerts a modulated role in oligodendrocytes ferroptosis in WMI following SAH.

"NO" Time in Fear Response: Possible Implication of Nitric-Oxide-Related Mechanisms in PTSD

Post-traumatic stress disorder (PTSD) is a psychiatric condition characterized by persistent fear responses and altered neurotransmitter functioning due to traumatic experiences. Stress predominantly affects glutamate, a neurotransmitter crucial for synaptic plasticity and memory formation. Activation of the N-Methyl-D-Aspartate glutamate receptors (NMDAR) can trigger the formation of a complex comprising postsynaptic density protein-95 (PSD95), the neuronal nitric oxide synthase (nNOS), and its adaptor protein (NOS1AP). This complex is pivotal in activating nNOS and nitric oxide (NO) production, which, in turn, activates downstream pathways that modulate neuronal signaling, including synaptic plasticity/transmission, inflammation, and cell death. The involvement of nNOS and NOS1AP in the susceptibility of PTSD and its comorbidities has been widely shown. Therefore, understanding the interplay between stress, fear, and NO is essential for comprehending the maintenance and progression of PTSD, since NO is involved in fear acquisition and extinction processes. Moreover, NO induces post-translational modifications (PTMs), including S-nitrosylation and nitration, which alter protein function and structure for intracellular signaling. Although evidence suggests that NO influences synaptic plasticity and memory processing, the specific role of PTMs in the pathophysiology of PTSD remains unclear. This review highlights pathways modulated by NO that could be relevant to stress and PTSD.

The Physiological Function of nNOS-Associated CAPON Proteins and the Roles of CAPON in Diseases

In this review, the structure, isoform, and physiological role of the carboxy-terminal PDZ ligand of neuronal nitric oxide synthase (CAPON) are summarized. There are three isoforms of CAPON in humans, including long CAPON protein (CAPON-L), short CAPON protein (CAPON-S), and CAPON-S' protein. CAPON-L includes three functional regions: a C-terminal PDZ-binding motif, carboxypeptidase (CPE)-binding region, and N-terminal phosphotyrosine (PTB) structural domain. Both CAPON-S and CAPON-S' only contain the C-terminal PDZ-binding motif. The C-terminal PDZ-binding motif of CAPON can bind with neuronal nitric oxide synthase (nNOS) and participates in regulating NO production and neuronal development. An overview is given on the relationship between CAPON and heart diseases, diabetes, psychiatric disorders, and tumors. This review will clarify future research directions on the signal pathways related to CAPON, which will be helpful for studying the regulatory mechanism of CAPON. CAPON may be used as a drug target, which will provide new ideas and solutions for treating human diseases.

Nitric Oxide: Physiological Functions, Delivery, and Biomedical Applications

Nitric oxide (NO) is a gaseous molecule that has a central role in signaling pathways involved in numerous physiological processes (e.g., vasodilation, neurotransmission, inflammation, apoptosis, and tumor growth). Due to its gaseous form, NO has a short half-life, and its physiology role is concentration dependent, often restricting its function to a target site. Providing NO from an external source is beneficial in promoting cellular functions and treatment of different pathological conditions. Hence, the multifaceted role of NO in physiology and pathology has garnered massive interest in developing strategies to deliver exogenous NO for the treatment of various regenerative and biomedical complexities. NO-releasing platforms or donors capable of delivering NO in a controlled and sustained manner to target tissues or organs have advanced in the past few decades. This review article discusses in detail the generation of NO via the enzymatic functions of NO synthase as well as from NO donors and the multiple biological and pathological processes that NO modulates. The methods for incorporating of NO donors into diverse biomaterials including physical, chemical, or supramolecular techniques are summarized. Then, these NO-releasing platforms are highlighted in terms of advancing treatment strategies for various medical problems.

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.

Dexras1 Induces Dysdifferentiation of Oligodendrocytes and Myelin Injury by Inhibiting the cAMP-CREB Pathway after Subarachnoid Hemorrhage

White matter damage (WMD), one of the research hotspots of subarachnoid hemorrhage (SAH), mainly manifests itself as myelin injury and oligodendrocyte differentiation disorder after SAH, although the specific mechanism remains unclear. Dexamethasone-induced Ras-related protein 1(Dexras1) has been reported to be involved in nervous system damage in autoimmune encephalitis and multiple sclerosis. However, whether Dexras1 participates in dysdifferentiation of oligodendrocytes and myelin injury after SAH has yet to be examined, which is the reason for creating the research content of this article. Here, intracerebroventricular lentiviral administration was used to modulate Dexras1 levels in order to determine its functional influence on neurological injury after SAH. Immunofluorescence, transmission electron microscopy, and Western blotting methods, were used to investigate the effects of Dexras1 on demyelination, glial cell activation, and differentiation of oligodendrocyte progenitor cells (OPCs) after SAH. Primary rat brain neurons were treated with oxyhemoglobin to verify the association between Dexras1 and cAMP-CREB. The results showed that Dexras1 levels were significantly increased upon in vivo SAH model, accompanied by OPC differentiation disturbances and myelin injury. Dexras1 overexpression significantly worsened OPC dysdifferentiation and myelin injury after SAH. In contrast, Dexras1 knockdown ameliorated myelin injury, OPC dysdifferentiation, and glial cell activation. Further research of the underlying mechanism discovered that the cAMP-CREB pathway was inhibited after Dexras1 overexpression in the in vitro model of SAH. This study is the first to confirm that Dexras1 induced oligodendrocyte dysdifferentiation and myelin injury after SAH by inhibiting the cAMP-CREB pathway. This present research may reveal novel therapeutic targets for the amelioration of brain injury and neurological dysfunction after SAH.

Ketamine alleviating depressive-like behaviors is associated with regulation of nNOS–CAPON–Dexras1 complex in chronic unpredictable mild stress rats

Background

A growing number of studies have demonstrated that ketamine induces rapid and sustained antidepressant action. Neuronal nitric oxide synthase (nNOS) signaling has been explored for the treatment of neuropsychiatric disorders for decades. But the effect of ketamine on nNOS signaling is poorly understood. The aim of the present study was to investigate the effect of ketamine on nNOS signaling in a chronic unpredictable mild stress (CUMS) model of depression.

Methods

Forty-eight rats were randomly divided into four groups: the control group of healthy rats (group C), the healthy rats treated with ketamine 10 mg/kg for 3 days (group CK), the rats model of stress-induced depression group (group D), and the depressed group treated with ketamine 10 mg/kg for 3 days (group DK). The sucrose preference test and open field test were used to assess behavioral changes. Immunohistochemistry, immunofluorescence, and real-time PCR analysis were carried out to measure the expression of nNOS, CAPON, and Dexras1 in the prefrontal cortex (PFC) of the CUMS rats.

Results

Compared with healthy rats, the total distance traveled, the rearing counts, the sucrose preference percentage (SPP), and CAPON and Dexras1 expression in the PFC significantly decreased, while nNOS expression increased in CUMS rats. After treating with ketamine, the total distance traveled, the rearing counts, the SPP, and CAPON and Dexras1 expression significantly increased, while nNOS expression significantly decreased.

Conclusion

The results indicated that ketamine improved the depressive behavior of rats, which may be related to the reduced nNOS expression and enhanced CAPON and Dexras1 expression.

Protein S-Nitrosation: Biochemistry, Identification, Molecular Mechanisms, and Therapeutic Applications

Protein S-nitrosation (SNO), a posttranslational modification (PTM) of cysteine (Cys) residues elicited by nitric oxide (NO), regulates a wide range of protein functions. As a crucial form of redox-based signaling by NO, SNO contributes significantly to the modulation of physiological functions, and SNO imbalance is closely linked to pathophysiological processes. Site-specific identification of the SNO protein is critical for understanding the underlying molecular mechanisms of protein function regulation. Although careful verification is needed, SNO modification data containing numerous functional proteins are a potential research direction for druggable target identification and drug discovery. Undoubtedly, SNO-related research is meaningful not only for the development of NO donor drugs but also for classic target-based drug design. Herein, we provide a comprehensive summary of SNO, including its origin and transport, identification, function, and potential contribution to drug discovery. Importantly, we propose new views to develop novel therapies based on potential protein SNO-sourced targets.

Functional diversity in the RAS subfamily of small GTPases

RAS small GTPases regulate important signalling pathways and are notorious drivers of cancer development and progression. While most research to date has focused on understanding and addressing the oncogenic potential of three RAS oncogenes: HRAS, KRAS, and NRAS; the full RAS subfamily is composed of 35 related GTPases with diverse cellular functions. Most remain deeply understudied despite strong evolutionary conservation. Here, we highlight a group of 17 poorly characterized RAS GTPases that are frequently down-regulated in cancer and evidence suggests may function not as oncogenes, but as tumour suppressors. These GTPases remain largely enigmatic in terms of their cellular function, regulation, and interaction with effector proteins. They cluster within two families we designate as 'distal-RAS' (D-RAS; comprised of DIRAS, RASD, and RASL10) and 'CaaX-Less RAS' (CL-RAS; comprised of RGK, NKIRAS, RERG, and RASL11/12 GTPases). Evidence of a tumour suppressive role for many of these GTPases supports the premise that RAS subfamily proteins may collectively regulate cellular proliferation.

Association of nitric oxide synthase 1 adaptor protein gene polymorphisms with schizophrenia in a Chinese Han population

INTRODUCTION

Previous studies have analyzed the association between nitric oxide synthase 1 adaptor protein (NOS1AP) polymorphisms and schizophrenia; however, the results were inconsistent and there was a lack of evidence in a larger sample of Chinese Han population.

SUBJECTS AND METHODS

We decided to determine the association between four NOS1AP single-nucleotide polymorphisms (i.e., rs1858232A/G, rs4531275C/T, rs4657178C/T, and rs6704393C/T) and schizophrenia in northern Chinese Han population (350 patients and 522 controls) using restriction fragment length polymorphism.

RESULTS

Between schizophrenia group and healthy group, the genotype and allele frequencies for rs1858232A/G differed significantly (χ ² = 6.256, 4.145; P = 0.044, 0.045), but neither genotype nor allele frequencies of rs4531275C/T differed significantly. The genotype frequencies for rs4657178C/T and rs6704393C/T differed significantly (χ ² = 19.782, 12.683; P < 0.01, P = 0.002) between schizophrenia group and healthy group. In the gender-specific analysis, we found statistically significant difference in genotype frequencies between patients and controls in both subgroups for rs4657178C/T (χ ² = 9.356, 9.585; P = 0.009, 0.008). There was also a significant difference in the genotype frequency between patients and controls in male subgroup for rs6704393C/T (χ ² = 8.800, P = 0.012). In the haplotype analysis, only the TCT haplotype frequency of rs6704393C/T, rs4531275C/T, and rs4657178C/T differed significantly between patients and controls in total population (χ ² = 5.215, P = 0.022).

IN CONCLUSION

Individuals with G allele of rs1858232A/G and C allele of rs4657178C/T which may be risk factors for schizophrenia should be given more attention, and also to individuals with the TCT haplotype, who are more likely to have schizophrenia. These results provide novel evidence for an association between NOS1AP polymorphisms and schizophrenia.

Organic mercury solid phase chemoselective capture for proteomic identification of S-nitrosated proteins and peptides

Cysteine S-nitrosation mediates NO signaling and protein function under pathophysiological conditions. Herein, we provide a detailed protocol regarding the organic mercury chemoselective enrichment of S-nitrosated proteins and peptides. We discuss key aspects of the enrichment strategy and provide technical tips for the best performance of the experimental protocol.

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.

Hippocampal overexpression of NOS1AP promotes endophenotypes related to mental disorders

BACKGROUND

Nitric oxide synthase 1 adaptor protein (NOS1AP; previously named CAPON) is linked to the glutamatergic postsynaptic density through interaction with neuronal nitric oxide synthase (nNOS). NOS1AP and its interaction with nNOS have been associated with several mental disorders. Despite the high levels of NOS1AP expression in the hippocampus and the relevance of this brain region in glutamatergic signalling as well as mental disorders, a potential role of hippocampal NOS1AP in the pathophysiology of these disorders has not been investigated yet.

METHODS

To uncover the function of NOS1AP in hippocampus, we made use of recombinant adeno-associated viruses to overexpress murine full-length NOS1AP or the NOS1AP carboxyterminus in the hippocampus of mice. We investigated these mice for changes in gene expression, neuronal morphology, and relevant behavioural phenotypes.

FINDINGS

We found that hippocampal overexpression of NOS1AP markedly increased the interaction of nNOS with PSD-95, reduced dendritic spine density, and changed dendritic spine morphology at CA1 synapses. At the behavioural level, we observed an impairment in social memory and decreased spatial working memory capacity.

INTERPRETATION

Our data provide a mechanistic explanation for a highly selective and specific contribution of hippocampal NOS1AP and its interaction with the glutamatergic postsynaptic density to cross-disorder pathophysiology. Our findings allude to therapeutic relevance due to the druggability of this molecule.

FUNDING

This study was funded in part by the DFG, the BMBF, the Academy of Finland, the NIH, the Japanese Society of Clinical Neuropsychopharmacology, the Ministry of Education of the Russian Federation, and the European Community.

Biological Mechanisms of S-Nitrosothiol Formation and Degradation: How Is Specificity of S-Nitrosylation Achieved?

The modification of protein cysteine residues underlies some of the diverse biological functions of nitric oxide (NO) in physiology and disease. The formation of stable nitrosothiols occurs under biologically relevant conditions and time scales. However, the factors that determine the selective nature of this modification remain poorly understood, making it difficult to predict thiol targets and thus construct informatics networks. In this review, the biological chemistry of NO will be considered within the context of nitrosothiol formation and degradation whilst considering how specificity is achieved in this important post-translational modification. Since nitrosothiol formation requires a formal one-electron oxidation, a classification of reaction mechanisms is proposed regarding which species undergoes electron abstraction: NO, thiol or S-NO radical intermediate. Relevant kinetic, thermodynamic and mechanistic considerations will be examined and the impact of sources of NO and the chemical nature of potential reaction targets is also discussed.

Dorsal Hippocampus to Infralimbic Cortex Circuit is Essential for the Recall of Extinction Memory

Posttraumatic stress disorder subjects usually show impaired recall of extinction memory, leading to extinguished fear relapses. However, little is known about the neural mechanisms underlying the impaired recall of extinction memory. We show here that the activity of dorsal hippocampus (dHPC) to infralimbic (IL) cortex circuit is essential for the recall of fear extinction memory in male mice. There were functional neural projections from the dHPC to IL. Using optogenetic manipulations, we observed that silencing the activity of dHPC-IL circuit inhibited recall of extinction memory while stimulating the activity of dHPC-IL circuit facilitated recall of extinction memory. "Impairment of extinction consolidation caused by" conditional deletion of extracellular signal-regulated kinase 2 (ERK2) in the IL prevented the dHPC-IL circuit-mediated recall of extinction memory. Moreover, silencing the dHPC-IL circuit abolished the effect of intra-IL microinjection of ERK enhancer on the recall of extinction memory. Together, we identify a dHPC to IL circuit that mediates the recall of extinction memory, and our data suggest that the dysfunction of dHPC-IL circuit and/or impaired extinction consolidation may contribute to extinguished fear relapses.

Tracing the path of inhaled nitric oxide: Biological consequences of protein nitrosylation

Nitric oxide (NO) is a comprehensive regulator of vascular and airway tone. Endogenous NO produced by nitric oxide synthases regulates multiple signaling cascades, including activation of soluble guanylate cyclase to generate cGMP, relaxing smooth muscle cells. Inhaled NO is an established therapy for pulmonary hypertension in neonates, and has been recently proposed for the treatment of hypoxic respiratory failure and acute respiratory distress syndrome due to COVID-19. In this review, we summarize the effects of endogenous and exogenous NO on protein S-nitrosylation, which is the selective and reversible covalent attachment of a nitrogen monoxide group to the thiol side chain of cysteine. This posttranslational modification targets specific cysteines based on the acid/base sequence of surrounding residues, with significant impacts on protein interactions and function. S-nitrosothiol (SNO) formation is tightly compartmentalized and enzymatically controlled, but also propagated by nonenzymatic transnitrosylation of downstream protein targets. Redox-based nitrosylation and denitrosylation pathways dynamically regulate the equilibrium of SNO-proteins. We review the physiological roles of SNO proteins, including nitrosohemoglobin and autoregulation of blood flow through hypoxic vasodilation, and pathological effects of nitrosylation including inhibition of critical vasodilator enzymes; and discuss the intersection of NO source and dose with redox environment, in determining the effects of protein nitrosylation.

Nitric Oxide and S-Nitrosylation in Cardiac Regulation: G Protein-Coupled Receptor Kinase-2 and β-Arrestins as Targets

Cardiac diseases including heart failure (HF), are the leading cause of morbidity and mortality globally. Among the prominent characteristics of HF is the loss of β-adrenoceptor (AR)-mediated inotropic reserve. This is primarily due to the derangements in myocardial regulatory signaling proteins, G protein-coupled receptor (GPCR) kinases (GRKs) and β-arrestins (β-Arr) that modulate β-AR signal termination via receptor desensitization and downregulation. GRK2 and β-Arr2 activities are elevated in the heart after injury/stress and participate in HF through receptor inactivation. These GPCR regulators are modulated profoundly by nitric oxide (NO) produced by NO synthase (NOS) enzymes through S-nitrosylation due to receptor-coupled NO generation. S-nitrosylation, which is NO-mediated modification of protein cysteine residues to generate an S-nitrosothiol (SNO), mediates many effects of NO independently from its canonical guanylyl cyclase/cGMP/protein kinase G signaling. Herein, we review the knowledge on the NO system in the heart and S-nitrosylation-dependent modifications of myocardial GPCR signaling components GRKs and β-Arrs.

Ferroptosis Is Regulated by Mitochondria in Neurodegenerative Diseases

BACKGROUND

Neurodegenerative diseases are characterized by a gradual decline in motor and/or cognitive function caused by the selective degeneration and loss of neurons in the central nervous system, but their pathological mechanism is still unclear. Previous research has revealed that many forms of cell death, such as apoptosis and necrosis, occur in neurodegenerative diseases. Research in recent years has noticed that there is a new type of cell death in neurodegenerative diseases: ferroptosis. An increasing body of literature provides evidence for an involvement of ferroptosis in neurodegenerative diseases.

SUMMARY

In this article, we review a new form of cell death in neurodegenerative diseases: ferroptosis. Ferroptosis is defined as an iron-dependent form of regulated cell death, which occurs through the lethal accumulation of lipid-based reactive oxygen species when glutathione-dependent lipid peroxide repair systems are compromised. Several salient and established features of neurodegenerative diseases (including lipid peroxidation and iron dyshomeostasis) are consistent with ferroptosis, which means that ferroptosis may be involved in the progression of neurodegenerative diseases. In addition, as the center of energy metabolism in cells, mitochondria are also closely related to the regulation of iron homeostasis in the nervous system. At the same time, neurodegenerative diseases are often accompanied by degeneration of mitochondrial activity. Mitochondrial damage has been found to be involved in lipid peroxidation and iron dyshomeostasis in neurodegenerative diseases. Key Messages: Based on the summary of the related mechanisms of ferroptosis, we conclude that mitochondrial damage may affect neurodegenerative diseases by regulating many aspects of ferroptosis, including cell metabolism, iron dyshomeostasis, and lipid peroxidation.

Dexras1 plays a pivotal role in maintaining the equilibrium between adipogenesis and osteogenesis

BACKGROUND

Chronic steroid treatment causes an increase in visceral adiposity and osteoporosis. It is believed that steroids may alter a balance between differentiation of mesenchymal stem cells (MSCs) into either adipocytes or osteoblasts; however, the detailed molecular mechanisms are unclear. We previously identified Dexras1 as a critical factor that potentiates adipogenesis in response to glucocorticoids. Thus, in this study, we investigated the role of Dexras1 in maintaining the balance between chronic steroid treatment-associated adipogenesis and osteoporosis.

MATERIAL AND METHODS

We treated wild type (WT) and Dexras1 knockout (KO) mice with dexamethasone for five weeks followed by 60% HFD for additional two weeks with dexamethasone. The changes of glucocorticoid-induced body weight gain and osteoporosis were analyzed. Bone marrow derived stromal cells (BMSCs) and mouse embryonic fibroblasts (MEFs) extracted from WT and Dexras1 KO mice, as well as MC3T3-E1 pre-osteoblasts and osteoclasts differentiated from RAW264.7 were analyzed to further define the role of Dexras1 in osteoblasts and osteoclasts.

RESULTS

Dual-energy X-ray absorptiometry and micro-computed tomography analyses in murine femurs revealed that Dexras1 deficiency was associated with increased osteogenesis, concurrent with reduced adipogenesis. Furthermore, Dexras1 deficiency promoted osteogenesis of BMSCs and MEFs in vitro, suggesting that Dexras1 deficiency prevents steroid-induced osteoporosis. We also observed that Dexras1 downregulated SMAD signaling pathways, which reduced the osteogenic differentiation capacity of pre-osteoblast MC3T3-E1 cells into mature osteoblasts.

CONCLUSION

We propose that Dexras1 is critical for maintaining the equilibrium between adipogenesis and osteogenesis upon steroid treatment.

nNOS-CAPON blockers produce anxiolytic effects by promoting synaptogenesis in chronic stress-induced animal models of anxiety

BACKGROUND AND PURPOSE

Anxiety disorder is a common mental health disorder. However, there are few safe and fast-acting anxiolytic drugs available that can treat anxiety disorder. We previously demonstrated that the interaction of neuronal NOS (nNOS) with its carboxy-terminal PDZ ligand (CAPON) is involved in regulating anxiety-related behaviours. Here, we further investigated the anxiolytic effects of nNOS-CAPON disruptors in chronic stress-induced anxiety in animals.

EXPERIMENTAL APPROACH

Mice were intravenously treated with nNOS-CAPON disruptors, ZLc-002 or Tat-CAPON12C, at the last week of chronic mild stress (CMS) exposure. We also infused corticosterone (CORT) into the hippocampus of mice to model anxiety behaviours and also delivered ZLc-002 or Tat-CAPON12C on the last week of chronic CORT treatment via pre-implanted cannula. Anxiety-related behaviours were examined using elevated plus maze, open field, novelty-suppressed feeding and light-dark (LD) tests. The level of nNOS-CAPON interaction was determined by co-immunoprecipitation (CO-IP) and proximity ligation assay (PLA). The neural mechanisms underlying the behavioural effects of nNOS-CAPON uncoupling in anxiety animal models were assessed by western blot, immunofluorescence and Golgi-Cox staining.

KEY RESULTS

ZLc-002 and Tat-CAPON12C reversed CMS- or CORT-induced anxiety-related behaviours. ZLc-002 and Tat-CAPON12C increased synaptogenesis along with improved dendritic remodelling in CMS mice or CORT-treated cultured neurons. Meanwhile, blocking nNOS-CAPON interaction significantly activated the cAMP response element-binding protein (CREB)-brain-derived neurotrophic factor (BDNF) pathway, which is associated with synaptic plasticity.

CONCLUSION AND IMPLICATIONS

Collectively, these results provide evidence for the anxiolytic effects of nNOS-CAPON uncouplers and their underlying mechanisms in anxiety disorders.

Hepatic nitric oxide synthase 1 adaptor protein regulates glucose homeostasis and hepatic insulin sensitivity in obese mice depending on its PDZ binding domain

BACKGROUND

NOS1AP is an adaptor protein and its SNP rs12742393 was associated with type 2 diabetes (T2D). However, it remains uncertain whether NOS1AP plays a role in regulation of insulin sensitivity. Hepatic insulin resistance contributed to the development of T2D. Here, our investigation was focused on whether NOS1AP is involved in the regulation of hepatic insulin sensitivity and its underlying mechanisms.

METHODS

Liver specific NOS1AP condition knockout (CKO) and NOS1AP overexpression mice were generated and given a high fat diet. SNPs of NOS1AP gene were genotyped in 86 human subjects.

FINDINGS

NOS1AP protein is expressed in human and mouse liver. CKO mice exhibited impaired pyruvate, glucose and insulin tolerance, and increased lipid deposits in the liver. Conversely, NOS1AP overexpression in livers of obese mice improved pyruvate and/or glucose, and insulin tolerance, and attenuated liver lipid accumulation. Moreover, hepatocytes from CKO mice exhibited an elevated glucose production and mRNA expressions of Pc and Pck1. Overexpression of NOS1AP potentiated insulin-stimulated activation of IR/Akt in livers from obese mice. The insulin sensitizing effect of NOS1AP could be mimicked by overexpression of C-terminal domain of NOS1AP in ob/ob mice. Furthermore, NOS1AP overexpression in liver significantly inhibited p38 MAPK phosphorylation, and maintained ER homeostasis through p-eIF2a-ATF4-CHOP pathway. Subjects with rsl2742393 of NOS1AP have higher risk to develop hepatic steatosis.

INTERPRETATION

Our data demonstrate a novel role of NOS1AP in regulating hepatic insulin sensitivity and p38 MAPK inactivation in obese mice, which makes NOS1AP a potential therapeutic target for the prevention and treatment of T2D. FUND: This work was supported by the National Natural Science Foundation of China (81670707, 31340072) (to C. Wang), and National Basic Research Program of China (Nation 973 Program) (2011CB504001) (to W. Jia).

Systematic Meta-Analysis of the Association Between a Common NOS1AP Genetic Polymorphism, the QTc Interval, and Sudden Death

Contemporary studies have identified rs10494366 in the nitric oxide synthase 1 adaptor protein (NOS1AP) gene as a new genetic marker in modulating the QT interval and sudden cardiac death (SCD) in general populations. However, the conclusions were not coincident. Therefore, we conducted for the first time a system evaluation of the relativity of rs10494366, the QT interval, and sudden death by meta-analysis. In our study, the meta-analysis displayed the GG genotype of rs10494366 correlated with the QT interval in women with no heterogeneity, and in diabetes mellitus (DM) patients with minor heterogeneity. In the Caucasian population, the correlation of rs10494366 and sudden death was significant. The heterogeneity referred to the relevance between rs10494366 and sudden death in the Asian population. In conclusion, the minor allele of rs10494366 may have an impact on the QT interval in women or DM patients and may have a potential role in sudden death in the Caucasian population.

Dexras1 Deletion and Iron Chelation Promote Neuroprotection in Experimental Optic Neuritis

Dysregulation of iron metabolism, and resultant cytotoxicity, has been implicated in the pathogenesis of multiple sclerosis (MS) and other neurodegenerative processes. Iron accumulation promotes cytotoxicity through various mechanisms including oxidative stress and glutamate toxicity, and occurs in both MS patients and in the experimental autoimmune encephalomyelitis (EAE) model of MS. Divalent Metal Transporter1, a major iron importer in cells, is stimulated by signaling of Dexras1, a small G protein member of the Ras family. Dexras1 is activated by S-nitrosylation by nitric oxide (NO) produced by either inducible nitric oxide synthase in activated microglia/macrophages or neuronal nitric oxide synthase in neurons. Here we show Dexras1 exacerbates oxidative stress-induced neurodegeneration in experimental optic neuritis, an inflammatory demyelinating optic nerve condition that occurs in MS and EAE. Dexras1 deletion, as well as treatment with the iron chelator deferiprone, preserves vision and attenuates retinal ganglion cell (RGC) and axonal loss during EAE optic neuritis. These results suggest that iron entry triggered by NO-activated Dexras1 signaling is a potential mechanism of neuronal death in experimental optic neuritis. The current data suggest modulation of Dexras1 signaling and iron chelation are potential novel treatment strategies for optic neuritis and MS, and possibly other optic neuropathies as well.

Protein S-Nitrosylation: Determinants of Specificity and Enzymatic Regulation of S-Nitrosothiol-Based Signaling

SIGNIFICANCE

Protein S-nitrosylation, the oxidative modification of cysteine by nitric oxide (NO) to form protein S-nitrosothiols (SNOs), mediates redox-based signaling that conveys, in large part, the ubiquitous influence of NO on cellular function. S-nitrosylation regulates protein activity, stability, localization, and protein-protein interactions across myriad physiological processes, and aberrant S-nitrosylation is associated with diverse pathophysiologies. Recent Advances: It is recently recognized that S-nitrosylation endows S-nitroso-protein (SNO-proteins) with S-nitrosylase activity, that is, the potential to trans-S-nitrosylate additional proteins, thereby propagating SNO-based signals, analogous to kinase-mediated signaling cascades. In addition, it is increasingly appreciated that cellular S-nitrosylation is governed by dynamically coupled equilibria between SNO-proteins and low-molecular-weight SNOs, which are controlled by a growing set of enzymatic denitrosylases comprising two main classes (high and low molecular weight). S-nitrosylases and denitrosylases, which together control steady-state SNO levels, may be identified with distinct physiology and pathophysiology ranging from cardiovascular and respiratory disorders to neurodegeneration and cancer.

CRITICAL ISSUES

The target specificity of protein S-nitrosylation and the stability and reactivity of protein SNOs are determined substantially by enzymatic machinery comprising highly conserved transnitrosylases and denitrosylases. Understanding the differential functionality of SNO-regulatory enzymes is essential, and is amenable to genetic and pharmacological analyses, read out as perturbation of specific equilibria within the SNO circuitry.

FUTURE DIRECTIONS

The emerging picture of NO biology entails equilibria among potentially thousands of different SNOs, governed by denitrosylases and nitrosylases. Thus, to elucidate the operation and consequences of S-nitrosylation in cellular contexts, studies should consider the roles of SNO-proteins as both targets and transducers of S-nitrosylation, functioning according to enzymatically governed equilibria.

Dysregulation of stress systems and nitric oxide signaling underlies neuronal dysfunction in Alzheimer's disease

Stress is a multimodal response involving the coordination of numerous body systems in order to maximize the chance of survival. However, long term activation of the stress response results in neuronal oxidative stress via reactive oxygen and nitrogen species generation, contributing to the development of depression. Stress-induced depression shares a high comorbidity with other neurological conditions including Alzheimer's disease (AD) and dementia, often appearing as one of the earliest observable symptoms in these diseases. Furthermore, stress and/or depression appear to exacerbate cognitive impairment in the context of AD associated with dysfunctional catecholaminergic signaling. Given there are a number of homologous pathways involved in the pathophysiology of depression and AD, this article will highlight the mechanisms by which stress-induced perturbations in oxidative stress, and particularly NO signaling, contribute to neurodegeneration.

Effects of Long Form of CAPON Overexpression on Glioma Cell Proliferation are Dependent on AKT/mTOR/P53 Signaling

Background: CAPON has two isoforms in human brain: long form of CAPON (CAPON-L) and short form of CAPON (CAPON-S). Recent studies have indicated the involvement of CAPON in tumor cell growth. We aimed to reveal the role of the two CAPON isoforms in the proliferation of glioma cells in this study. Materials and Methods: Lentivirus-mediated stable cell lines with CAPON-L or CAPON-S overexpression were established in U87 and U251 glioma cells. Cell counting kit-8 and colony formation assays were used to evaluate cell proliferation. Western blot analysis of cell cycle-related proteins and flow cytometry were performed to analyze cell cycle progression. Some important molecules of the AKT/mTOR pathway and P53 were also measured by Western blot analysis. Results: Overexpression of CAPON-L showed a significantly inhibitory role in U251 cells, while it exhibited a promoting role in U87 cells. Consistently, overexpressing CAPON-L impeded the cell cycle progression and down-regulated the expression levels of Cyclin D1, CDK4 and CDK6 in U251 cells, whereas it up-regulated the CDK6 level in U87 cells. The overexpression of CAPON-L significantly decreased the phosphorylation and/or total levels of AKT, mTOR and S6 in U251 cells, while it did not affect these signaling molecules in U87 cells, except for a significant increase in the phosphorylation of AKT at Thr-308 site. Transfecting constitutively active AKT (myr-AKT) partially reversed the decreased phosphorylation of AKT and S6 in the CAPON-L-overexpressing U251 cells. In addition, we found a significant decrease in the wild-type P53 level in the CAPON-L-overexpressing U87 cells. The overexpression of CAPON-S also inhibited cell proliferation, blocked cell cycle progression, and decreased the AKT/mTOR pathway activity in U251 cells. Conclusion: The effects of CAPON-L overexpression on glioma cell proliferation are dependent on the AKT/mTOR/P53 activity. The overexpression of CAPON inhibits U251 cell proliferation through the AKT/mTOR signaling pathway, while overexpressing CAPON-L promoted U87 cell proliferation, possibly through down-regulating the P53 level.

Neuronal nitric oxide synthase and affective disorders

Affective disorders including major depressive disorder (MDD), bipolar disorder (BPD), and general anxiety affect more than 10% of population in the world. Notably, neuronal nitric oxide synthase (nNOS), a downstream signal molecule of N-methyl-D-aspartate receptors (NMDARs) activation, is abundant in many regions of the brain such as the prefrontal cortex (PFC), hippocampus, amygdala, dorsal raphe nucleus (DRN), locus coeruleus (LC), and hypothalamus, which are closely associated with the pathophysiology of affective disorders. Decreased levels of the neurotransmitters including 5-hydroxytryptamine or serotonin (5-HT), noradrenalin (NA), and dopamine (DA) as well as hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis are common pathological changes of MDD, BPD, and anxiety. Increasing data suggests that nNOS in the hippocampus play a crucial role in the etiology of MDD whereas nNOS-related dysregulation of the nitrergic system in the LC is closely associated with the pathogenesis of BPD. Moreover, hippocampal nNOS is implicated in the role of serotonin receptor 1 A (5-HTR1 A) in modulating anxiety behaviors. Augment of nNOS and its carboxy-terminal PDZ ligand (CAPON) complex mediate stress-induced anxiety and disrupting the nNOS-CAPON interaction by small molecular drug generates anxiolytic effect. To date, however, the function of nNOS in affective disorders is not well reviewed. Here, we summarize works about nNOS and its signal mechanisms implicated in the pathophysiology of affective disorders. On the basis of this review, it is suggested that future research should more fully focus on the role of nNOS in the pathomechanism and treatment of affective disorders.

Role of estrogen and RAS signaling in repeated implantation failure

In humans, hormonal regulation is crucial for the preparation of uterine environment leading to either successful implantation or menstrual cycle. Estrogen is a pivotal female steroid hormone that regulates the uterine dynamics along with progesterone in the estrous and menstrual cycles in humans. Estrogen signals act via nuclear estrogen receptor or membrane-bound receptor. The membrane-bound estrogen receptor plays a crucial role in the rapid response of estrogen in the uterine epithelium. Recently, RASD1 has received attention as a novel signal transducer of estrogen in various systems including female reproductive organs. In this review, we discuss the regulation of estrogen and RASD1 signaling in the uterus and also provide insights into RAS as a novel signaling molecule in repeated implantation failure.

Computational Structural Biology of S-nitrosylation of Cancer Targets

Nitric oxide (NO) plays an essential role in redox signaling in normal and pathological cellular conditions. In particular, it is well known to react in vivo with cysteines by the so-called S-nitrosylation reaction. S-nitrosylation is a selective and reversible post-translational modification that exerts a myriad of different effects, such as the modulation of protein conformation, activity, stability, and biological interaction networks. We have appreciated, over the last years, the role of S-nitrosylation in normal and disease conditions. In this context, structural and computational studies can help to dissect the complex and multifaceted role of this redox post-translational modification. In this review article, we summarized the current state-of-the-art on the mechanism of S-nitrosylation, along with the structural and computational studies that have helped to unveil its effects and biological roles. We also discussed the need to move new steps forward especially in the direction of employing computational structural biology to address the molecular and atomistic details of S-nitrosylation. Indeed, this redox modification has been so far an underappreciated redox post-translational modification by the computational biochemistry community. In our review, we primarily focus on S-nitrosylated proteins that are attractive cancer targets due to the emerging relevance of this redox modification in a cancer setting.

Hippocampal nuclear factor kappa B accounts for stress-induced anxiety behaviors via enhancing neuronal nitric oxide synthase (nNOS)-carboxy-terminal PDZ ligand of nNOS-Dexras1 coupling

Anxiety disorders are associated with a high social burden worldwide. Recently, increasing evidence suggests that nuclear factor kappa B (NF-κB) has significant implications for psychiatric diseases, including anxiety and depressive disorders. However, the molecular mechanisms underlying the role of NF-κB in stress-induced anxiety behaviors are poorly understood. In this study, we show that chronic mild stress (CMS) and glucocorticoids dramatically increased the expression of NF-κB subunits p50 and p65, phosphorylation and acetylation of p65, and the level of nuclear p65 in vivo and in vitro, implicating activation of NF-κB signaling in chronic stress-induced pathological processes. Using the novelty-suppressed feeding (NSF) and elevated-plus maze (EPM) tests, we found that treatment with pyrrolidine dithiocarbamate (PDTC; intra-hippocampal infusion), an inhibitor of NF-κB, rescued the CMS- or glucocorticoid-induced anxiogenic behaviors in mice. Microinjection of PDTC into the hippocampus reversed CMS-induced up-regulation of neuronal nitric oxide synthase (nNOS), carboxy-terminal PDZ ligand of nNOS (CAPON), and dexamethasone-induced ras protein 1 (Dexras1) and dendritic spine loss of dentate gyrus (DG) granule cells. Moreover, over-expression of CAPON by infusing LV-CAPON-L-GFP into the hippocampus induced nNOS-Dexras1 interaction and anxiety-like behaviors, and inhibition of NF-κB by PDTC reduced the LV-CAPON-L-GFP-induced increases in nNOS-Dexras1 complex and anxiogenic-like effects in mice. These findings indicate that hippocampal NF-κB mediates anxiogenic behaviors, probably via regulating the association of nNOS-CAPON-Dexras1, and uncover a novel approach to the treatment of anxiety disorders.

nNOS-CAPON interaction mediates amyloid-β-induced neurotoxicity, especially in the early stages

In neurons, increased protein–protein interactions between neuronal nitric oxide synthase (nNOS) and its carboxy‐terminal PDZ ligand (CAPON) contribute to excitotoxicity and abnormal dendritic spine development, both of which are involved in the development of Alzheimer's disease. In models of Alzheimer's disease, increased nNOS–CAPON interaction was detected after treatment with amyloid‐β in vitro, and a similar change was found in the hippocampus of APP/PS1 mice (a transgenic mouse model of Alzheimer's disease), compared with age‐matched background mice in vivo. After blocking the nNOS–CAPON interaction, memory was rescued in 4‐month‐old APP/PS1 mice, and dendritic impairments were ameliorated both in vivo and in vitro. Furthermore, we demonstrated that S‐nitrosylation of Dexras1 and inhibition of the ERK–CREB–BDNF pathway might be downstream of the nNOS–CAPON interaction.

Developmental Alcohol Exposure Impairs Activity-Dependent S-Nitrosylation of NDEL1 for Neuronal Maturation

Neuronal nitric oxide synthase is involved in diverse signaling cascades that regulate neuronal development and functions via S-Nitrosylation-mediated mechanism or the soluble guanylate cyclase (sGC)/cyclic guanosine monophosphate (cGMP) pathway activated by nitric oxide. Although it has been studied extensively in vitro and in invertebrate animals, effects on mammalian brain development and underlying mechanisms remain poorly understood. Here we report that genetic deletion of "Nos1" disrupts dendritic development, whereas pharmacological inhibition of the sGC/cGMP pathway does not alter dendritic growth during cerebral cortex development. Instead, nuclear distribution element-like (NDEL1), a protein that regulates dendritic development, is specifically S-nitrosylated at cysteine 203, thereby accelerating dendritic arborization. This post-translational modification is enhanced by N-methyl-D-aspartate receptor-mediated neuronal activity, the main regulator of dendritic formation. Notably, we found that disruption of S-Nitrosylation of NDEL1 mediates impaired dendritic maturation caused by developmental alcohol exposure, a model of developmental brain abnormalities resulting from maternal alcohol use. These results highlight S-Nitrosylation as a key activity-dependent mechanism underlying neonatal brain maturation and suggest that reduction of S-Nitrosylation of NDEL1 acts as a pathological factor mediating neurodevelopmental abnormalities caused by maternal alcohol exposure.

Dexras1 is a homeostatic regulator of exercise-dependent proliferation and cell survival in the hippocampal neurogenic niche

Adult hippocampal neurogenesis is highly responsive to exercise, which promotes the proliferation of neural progenitor cells and the integration of newborn granule neurons in the dentate gyrus. Here we show that genetic ablation of the small GTPase, Dexras1, suppresses exercise-induced proliferation of neural progenitors, alters survival of mitotic and post-mitotic cells in a stage-specific manner, and increases the number of mature newborn granule neurons. Dexras1 is required for exercise-triggered recruitment of quiescent neural progenitors into the cell cycle. Pharmacological inhibition of NMDA receptors enhances SGZ cell proliferation in wild-type but not dexras1-deficient mice, suggesting that NMDA receptor-mediated signaling is dependent on Dexras1. At the molecular level, the absence of Dexras1 abolishes exercise-dependent activation of ERK/MAPK and CREB, and inhibits the upregulation of NMDA receptor subunit NR2A, bdnf, trkB and vegf-a expression in the dentate gyrus. Our study reveals Dexras1 as an important stage-specific regulator of exercise-induced neurogenesis in the adult hippocampus by enhancing pro-mitogenic signaling to neural progenitor cells and modulating cell survival.

Nitric oxide signalling in cardiovascular health and disease

Nitric oxide (NO) signalling has pleiotropic roles in biology and a crucial function in cardiovascular homeostasis. Tremendous knowledge has been accumulated on the mechanisms of the nitric oxide synthase (NOS)-NO pathway, but how this highly reactive, free radical gas signals to specific targets for precise regulation of cardiovascular function remains the focus of much intense research. In this Review, we summarize the updated paradigms on NOS regulation, NO interaction with reactive oxidant species in specific subcellular compartments, and downstream effects of NO in target cardiovascular tissues, while emphasizing the latest developments of molecular tools and biomarkers to modulate and monitor NO production and bioavailability.

Rasd1 is an estrogen-responsive immediate early gene and modulates expression of late genes in rat anterior pituitary cells

Dexamethasone-induced Ras-related protein 1 (Rasd1) is a member of the Ras superfamily of monomeric G proteins that have a regulatory function in signal transduction. Here we investigated the role of Rasd1 in regulating estrogen-induced gene expression in primary cultures of rat anterior pituitary cells. Rasd1 mRNA expression in anterior pituitary cells decreased after treatment with forskolin or serum and increased after treatment with 17β-estradiol (E2). Increases in Rasd1 mRNA expression occurred as early as 0.5 h after E2 treatment, peaked at 1 h and were sustained for as long as 96 h. This rapid and profound increase in Rasd1 mRNA expression induced by E2 was also seen in GH4C1 cells, an estrogen receptor-positive somatolactotroph cell line. Among pituitary estrogen-responsive late genes studied, basal mRNA expression of Pim3 and Igf1 genes was decreased by RNA interference-mediated knockdown of Rasd1 expression, whereas basal expression of the Giot1 gene was increased. Moreover, Rasd1 knockdown enhanced stimulation of Pim3 mRNA expression and attenuated inhibition of Fosl1 mRNA expression 24 h after E2 treatment. These changes in mRNA expression were accompanied by enhanced activity of promoters containing CRE, AP-1 and SRE binding sequences. These results suggest that Rasd1 is an estrogen-responsive immediate early gene and modulates E2 induction of at least several late genes in anterior pituitary cells.

Dynamics of nitric oxide controlled by protein complex in bacterial system

Nitric oxide (NO) plays diverse and significant roles in biological processes despite its cytotoxicity, raising the question of how biological systems control the action of NO to minimize its cytotoxicity in cells. As a great example of such a system, we found a possibility that NO-generating nitrite reductase (NiR) forms a complex with NO-decomposing membrane-integrated NO reductase (NOR) to efficiently capture NO immediately after its production by NiR in anaerobic nitrate respiration called denitrification. The 3.2-Å resolution structure of the complex of one NiR functional homodimer and two NOR molecules provides an idea of how these enzymes interact in cells, while the structure may not reflect the one in cells due to the membrane topology. Subsequent all-atom molecular dynamics (MD) simulations of the enzyme complex model in a membrane and structure-guided mutagenesis suggested that a few interenzyme salt bridges and coulombic interactions of NiR with the membrane could stabilize the complex of one NiR homodimer and one NOR molecule and contribute to rapid NO decomposition in cells. The MD trajectories of the NO diffusion in the NiR:NOR complex with the membrane showed that, as a plausible NO transfer mechanism, NO released from NiR rapidly migrates into the membrane, then binds to NOR. These results help us understand the mechanism of the cellular control of the action of cytotoxic NO.

Subcellular Targeting of Nitric Oxide Synthases Mediated by Their N-Terminal Motifs

From a catalytic point of view, the three mammalian nitric oxide synthases (NOSs) function in an almost identical way. The N-terminal oxygenase domain catalyzes the conversion of l-arginine to l-citrulline plus ·NO in two sequential oxidation steps. Once l-arginine binds to the active site positioned above the heme moiety, two consecutive monooxygenation reactions take place. In the first step, l-arginine is hydroxylated to make Nω-hydroxy-l-arginine in a process that requires 1 molecule of NADPH and 1 molecule of O₂ per mol of l-arginine reacted. In the second step, Nω-hydroxy-l-arginine, never leaving the active site, is oxidized to ·NO plus l-citrulline and 1 molecule of O₂ and 0.5 molecules of NADPH are consumed. Since nitric oxide is an important signaling molecule that participates in a number of biological processes, including neurotransmission, vasodilation, and immune response, synthesis and release of ·NO in vivo must be exquisitely regulated both in time and in space. Hence, NOSs have evolved introducing in their amino acid sequences subcellular targeting motifs, most of them located at their N-termini. Deletion studies performed on recombinant, purified NOSs have revealed that part of the N-terminus of all three NOS can be eliminated with the resulting mutant enzymes still being catalytically active. Likewise, NOS isoforms lacking part of their N-terminus when transfected in cells render mislocalized, active proteins. In this review we will comment on the current knowledge of these subcellular targeting signals present in nNOS, iNOS, and eNOS.

Rapid expression of RASD1 is regulated by estrogen receptor-dependent intracellular signaling pathway in the mouse uterus

Dexamethasone-induced RAS-related protein 1 (RASD1) is a signaling protein that is involved in various cellular processes. In a previous study, we found that RASD1 expression was down-regulated in the uterine endometrium of repeated implantation failure patients. The study aim was to determine whether RASD1 is expressed in the endometrium of mouse uterus and how it is regulated by steroid hormones during the estrous cycle. In this study, we investigated RASD1 expression and regulation in an ovariectomized female mouse model. Rasd1 mRNA was highly expressed in mouse reproductive tissues, including the uterus. Rasd1 expression was detected exclusively in the endometrial epithelium at the proestrus stage of the estrous cycle. Rasd1 expression in uteri increased with administration of estradiol, but not progesterone. Its expression was rapidly induced within 2 h after E₂ treatment. Pretreatment with ICI 182,780, an estrogen receptor antagonist, reduced RASD1 protein expression. In addition, we identified that rapid expression of Rasd1 was mediated by the estrogen intracellular signaling including both p38-mitogen-activated protein kinase and the extracellular signal-regulated kinase. These findings suggest that RASD1 acts as a novel signaling molecule and plays an important role in regulating dynamic uterine remodeling during the estrous cycle in the uterus.

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

INTRODUCTION

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

Nitrosothiol formation and S-nitrosation signaling through nitric oxide synthases

Nitric oxide (NO) is a gaseous signaling molecule impacting many biological pathways. NO is produced in mammals by three nitric oxide synthase (NOS) isoforms: neuronal (nNOS), endothelial (eNOS), and inducible (iNOS). nNOS and eNOS produce low concentrations of NO for paracrine signaling; NO produced and released from one cell diffuses to a neighboring cell where it binds and activates soluble guanylyl cyclase (sGC). iNOS produces high concentrations of NO using NO toxicity to amplify the innate immune response. Recent work has also defined protein cysteine S-nitrosation as a pathway of sGC-independent NO signaling. Though many studies have shown that S-nitrosation regulates the activity of NOS isoforms and other proteins in vivo, many issues need to be resolved to establish S-nitrosation as a viable signaling mechanism. Several chemical mechanisms result in S-nitrosation including transition metal-catalyzed pathways, NO oxidation followed by thiolate reaction, and thiyl radical recombination with NO. Once formed, nitrosothiols can be transferred between cellular cysteine residues via transnitrosation reactions. However, it is largely unclear how these chemical processes result in selective S-nitrosation of specific cellular cysteine residues. S-nitrosation site selectivity may be imparted via direct interactions or colocalization with NOS isoforms that focus chemical or transnitrosation mechanisms of nitrosothiol formation or transfer. Here, we discuss chemical mechanisms of nitrosothiol formation, S-nitrosation of NOS isoforms, and potential S-nitrosation signaling cascades resulting from NOS S-nitrosation.

Reactive Oxygen Species: Physiological and Physiopathological Effects on Synaptic Plasticity

In the mammalian central nervous system, reactive oxygen species (ROS) generation is counterbalanced by antioxidant defenses. When large amounts of ROS accumulate, antioxidant mechanisms become overwhelmed and oxidative cellular stress may occur. Therefore, ROS are typically characterized as toxic molecules, oxidizing membrane lipids, changing the conformation of proteins, damaging nucleic acids, and causing deficits in synaptic plasticity. High ROS concentrations are associated with a decline in cognitive functions, as observed in some neurodegenerative disorders and age-dependent decay of neuroplasticity. Nevertheless, controlled ROS production provides the optimal redox state for the activation of transductional pathways involved in synaptic changes. Since ROS may regulate neuronal activity and elicit negative effects at the same time, the distinction between beneficial and deleterious consequences is unclear. In this regard, this review assesses current research and describes the main sources of ROS in neurons, specifying their involvement in synaptic plasticity and distinguishing between physiological and pathological processes implicated.

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.

Array-based molecular karyotyping in fetuses with isolated brain malformations identifies disease-causing CNVs

Background

The overall birth prevalence for congenital malformations of the central nervous system (CNS) among Europeans may be as high as 1 in 100 live births. The etiological factors remain largely unknown. The aim of this study was to detect causative copy number variations (CNVs) in fetuses of terminated pregnancies with prenatally detected isolated brain malformations.

Methods

Array-based molecular karyotyping was performed in a cohort of 35 terminated fetuses with isolated CNS malformations. Identified putative disease-causing CNVs were confirmed using quantitative polymerase chain reaction or multiplex ligation-dependent probe amplification.

Results

Based on their de novo occurrence and/or their established association with congenital brain malformations, we detected five disease-causing CNVs in four fetuses involving chromosomal regions 6p25.1-6p25.3 (FOXC1), 6q27, 16p12.3, Xp22.2-Xp22.32 (MID1), and Xp22.32-Xp22.33. Furthermore, we detected a probably disease-causing CNV involving chromosomal region 3p26.3 in one fetus, and in addition, we detected 12 CNVs in nine fetuses of unknown clinical significance. All CNVs except for two were absent in 1307 healthy in-house controls (frequency <0.0008). Each of the two CNVs present in in-house controls was present only once (frequency = 0.0008). Furthermore, our data suggests the involvement of CNTN6 and KLHL15 in the etiology of agenesis of the corpus callosum, the involvement of RASD1 and PTPRD in Dandy-Walker malformation, and the involvement of ERMARD in ventriculomegaly.

Conclusions

Our study suggests that CNVs play an important role in the etiology of isolated brain malformations.

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.

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

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