SNAP-25/syntaxin 1A complex functionally modulates neurotransmitter gamma-aminobutyric acid reuptake

Neuronal exposure induces neurotransmitter signaling and synaptic mediators in tumors early in brain metastasis

BACKGROUND

Brain metastases (BM) are responsible for neurological decline and poor overall survival. Although the pro-metastatic roles of glial cells, and the acquisition of neuronal attributes in established BM tumors have been described, there are no studies that investigate the initial interplay between neurons and brain-seeking tumor cells. The aim of this study was to characterize early tumor-neuron interactions and the induced CNS-adaptive changes in tumor cells prior to macro-colonization.

METHODS

Utilizing pure neuronal cultures and brain-naïve and patient-derived BM tumor cells, we surveyed the early induction of mediators of neurotransmitter (NT) and synaptic signaling in breast and lung tumor cells. Reliance on microenvironmental GABA in breast-to-brain metastatic cells (BBMs) was assessed in vitro and in vivo.

RESULTS

Co-culture with neurons induces early expression of classical NT receptor genes (HTR4, GRIA2, GRIN2B, GRM4, GRM8, DRD1) and neuronal synaptic mediators (CNR1, EGR2, ARC, NGFR, NRXN1) in breast and lung cancer cells. NT-dependent classification of tumor cells within the neuronal niche shows breast cancer cells become GABAergic responsive brain metastases (GRBMs) and transition from relying on autocrine GABA, to paracrine GABA from adjacent neurons; while autocrine Dopaminergic breast and lung tumor cells persist. In vivo studies confirm reliance on paracrine GABA is an early CNS-acclimation strategy in breast cancer. Moreover, neuronal contact induces early resurgence in Reelin expression in tumor cells through epigenetic activation, facilitating CNS adaptation.

CONCLUSION

Tumor-neuron interactions allow for CNS-adaptation early in the course of brain metastasis.

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.

Regulation of Glutamate, GABA and Dopamine Transporter Uptake, Surface Mobility and Expression

Neurotransmitter transporters limit spillover between synapses and maintain the extracellular neurotransmitter concentration at low yet physiologically meaningful levels. They also exert a key role in providing precursors for neurotransmitter biosynthesis. In many cases, neurons and astrocytes contain a large intracellular pool of transporters that can be redistributed and stabilized in the plasma membrane following activation of different signaling pathways. This means that the uptake capacity of the brain neuropil for different neurotransmitters can be dynamically regulated over the course of minutes, as an indirect consequence of changes in neuronal activity, blood flow, cell-to-cell interactions, etc. Here we discuss recent advances in the mechanisms that control the cell membrane trafficking and biophysical properties of transporters for the excitatory, inhibitory and modulatory neurotransmitters glutamate, GABA, and dopamine.

Heteromeric Solute Carriers: Function, Structure, Pathology and Pharmacology

Solute carriers form one of three major superfamilies of membrane transporters in humans, and include uniporters, exchangers and symporters. Following several decades of molecular characterisation, multiple solute carriers that form obligatory heteromers with unrelated subunits are emerging as a distinctive principle of membrane transporter assembly. Here we comprehensively review experimentally established heteromeric solute carriers: SLC3-SLC7 amino acid exchangers, SLC16 monocarboxylate/H⁺ symporters and basigin/embigin, SLC4A1 (AE1) and glycophorin A exchanger, SLC51 heteromer Ost α-Ost β uniporter, and SLC6 heteromeric symporters. The review covers the history of the heteromer discovery, transporter physiology, structure, disease associations and pharmacology - all with a focus on the heteromeric assembly. The cellular locations, requirements for complex formation, and the functional role of dimerization are extensively detailed, including analysis of the first complete heteromer structures, the SLC7-SLC3 family transporters LAT1-4F2hc, b^0,+AT-rBAT and the SLC6 family heteromer B⁰AT1-ACE2. We present a systematic analysis of the structural and functional aspects of heteromeric solute carriers and conclude with common principles of their functional roles and structural architecture.

Structure and Gating Dynamics of Na+/Cl- Coupled Neurotransmitter Transporters

Neurotransmitters released at the neural synapse through vesicle exocytosis are spatiotemporally controlled by the action of neurotransmitter transporters. Integral membrane proteins of the solute carrier 6 (SLC6) family are involved in the sodium and chloride coupled uptake of biogenic amine neurotransmitters including dopamine, serotonin, noradrenaline and inhibitory neurotransmitters including glycine and γ-amino butyric acid. This ion-coupled symport works through a well-orchestrated gating of substrate through alternating-access, which is mediated through movements of helices that resemble a rocking-bundle. A large array of commercially prescribed drugs and psychostimulants selectively target neurotransmitter transporters thereby modulating their levels in the synaptic space. Drug-induced changes in the synaptic neurotransmitter levels can be used to treat depression or neuropathic pain whereas in some instances prolonged usage can lead to habituation. Earlier structural studies of bacterial neurotransmitter transporter homolog LeuT and recent structure elucidation of the Drosophila dopamine transporter (dDAT) and human serotonin transporter (hSERT) have yielded a wealth of information in understanding the transport and inhibition mechanism of neurotransmitter transporters. Computational studies based on the structures of dDAT and hSERT have shed light on the dynamics of varied components of these molecular gates in affecting the uphill transport of neurotransmitters. This review seeks to address structural dynamics of neurotransmitter transporters at the extracellular and intracellular gates and the effect of inhibitors on the ligand-binding pocket. We also delve into the effect of additional factors including lipids and cytosolic domains that influence the translocation of neurotransmitters across the membrane.

Silencing of Syntaxin 1A in the Dopaminergic Neurons Decreases the Activity of the Dopamine Transporter and Prevents Amphetamine-Induced Behaviors in C. elegans

The dopamine transporter (DAT) is a cell membrane protein whose main function is to reuptake the dopamine (DA) released in the synaptic cleft back into the dopaminergic neurons. Previous studies suggested that the activity of DAT is regulated by allosteric proteins such as Syntaxin-1A and is altered by drugs of abuse such as amphetamine (Amph). Because Caenorhabditis elegans expresses both DAT (DAT-1) and Syntaxin-1A (UNC-64), we used this model system to investigate the functional and behavioral effects caused by lack of expression of unc-64 in cultured dopaminergic neurons and in living animals. Using an inheritable RNA silencing technique, we were able to knockdown unc-64 specifically in the dopaminergic neurons. This cell-specific knockdown approach avoids the pleiotropic phenotypes caused by knockout mutations of unc-64 and ensures the transmission of dopaminergic specific unc-64 silencing to the progeny. We found that, similarly to dat-1 knockouts and dat-1 silenced lines, animals with reduced unc-64 expression in the dopaminergic neurons did not respond to Amph treatment when tested for locomotor behaviors. Our in vitro data demonstrated that in neuronal cultures derived from animals silenced for unc-64, the DA uptake was reduced by 30% when compared to controls, and this reduction was similar to that measured in neurons isolated from animals silenced for dat-1 (40%). Moreover, reduced expression of unc-64 in the dopaminergic neurons significantly reduced the DA release elicited by Amph. Because in C. elegans DAT-1 is the only protein capable to reuptake DA, these data show that reduced expression of unc-64 in the dopaminergic neurons decreases the capability of DAT in re-accumulating synaptic DA. Moreover, these results demonstrate that decreased expression of unc-64 in the dopaminergic neurons abrogates the locomotor behavior induced by Amph. Taken together these data suggest that Syntaxin-1A plays an important role in both functional and behavioral effects caused by Amph.

SNARE proteins in membrane trafficking

SNAREs are the core machinery mediating membrane fusion. In this review, we provide an update on the recent progress on SNAREs regulating membrane fusion events, especially the more detailed fusion processes dissected by well-developed biophysical methods and in vitro single molecule analysis approaches. We also briefly summarize the relevant research from Chinese laboratories and highlight the significant contributions on our understanding of SNARE-mediated membrane trafficking from scientists in China.

SLC6A1 gene involvement in susceptibility to attention-deficit/hyperactivity disorder: A case-control study and gene-environment interaction

Attention-deficit/hyperactivity disorder (ADHD) is an early onset childhood neurodevelopmental disorder with an estimated heritability of approximately 76%. We conducted a case-control study to explore the role of the SLC6A1 gene in ADHD. The genotypes of eight variants were determined using Sequenom MassARRAY technology. The participants in the study were 302 children with ADHD and 411 controls. ADHD symptoms were assessed using the Conners Parent Symptom Questionnaire. In our study, rs2944366 was consistently shown to be associated with the ADHD risk in the dominant model (odds ratio [OR]=0.554, 95% confidence interval [CI]=0.404-0.760), and nominally associated with Hyperactive index score (P=0.027). In addition, rs1170695 has been found to be associated with the ADHD risk in the addictive model (OR=1.457, 95%CI=1.173-1.809), while rs9990174 was associated with the Hyperactive index score (P=0.010). Intriguingly, gene-environmental interactions analysis consistently revealed the potential interactions of rs1170695 with blood lead (P_mul=0.044) to modify the ADHD risk. Expression quantitative trait loci analysis suggested that these positive single nucleotide polymorphisms (SNPs) may mediate SLC6A1 gene expression. Therefore, our results suggest that selected SLC6A1 gene variants may have a significant effect on the ADHD risk.

Chronic Cerebral Hypoperfusion Induced Synaptic Proteome Changes in the rat Cerebral Cortex

Chronic cerebral hypoperfusion (CCH) evokes mild cognitive impairment (MCI) and contributes to the progression of vascular dementia and Alzheimer's disease (AD). How CCH induces these neurodegenerative processes that may spread along the synaptic network and whether they are detectable at the synaptic proteome level of the cerebral cortex remains to be established. In the present study, we report the synaptic protein changes in the cerebral cortex after stepwise bilateral common carotid artery occlusion (BCCAO) induced CCH in the rat. The occlusions were confirmed with magnetic resonance angiography 5 weeks after the surgery. Synaptosome fractions were prepared using sucrose gradient centrifugation from cerebral cortex dissected 7 weeks after the occlusion. The synaptic protein differences between the sham operated and CCH groups were analyzed with label-free nanoUHPLC-MS/MS. We identified 46 proteins showing altered abundance due to CCH. In particular, synaptic protein and lipid metabolism, as well as GABA shunt-related proteins showed increased while neurotransmission and synaptic assembly-related proteins showed decreased protein level changes in CCH rats. Protein network analysis of CCH-induced protein alterations suggested the importance of increased synaptic apolipoprotein E (APOE) level as a consequence of CCH. Therefore, the change in APOE level was confirmed with Western blotting. The identified synaptic protein changes would precede the onset of dementia-like symptoms in the CCH model, suggesting their importance in the development of vascular dementia.

A Central Small Amino Acid in the VAMP2 Transmembrane Domain Regulates the Fusion Pore in Exocytosis

Exocytosis depends on cytosolic domains of SNARE proteins but the function of the transmembrane domains (TMDs) in membrane fusion remains controversial. The TMD of the SNARE protein synaptobrevin2/VAMP2 contains two highly conserved small amino acids, G₁₀₀ and C₁₀₃, in its central portion. Substituting G₁₀₀ and/or C₁₀₃ with the β-branched amino acid valine impairs the structural flexibility of the TMD in terms of α-helix/β-sheet transitions in model membranes (measured by infrared reflection-absorption or evanescent wave spectroscopy) during increase in protein/lipid ratios, a parameter expected to be altered by recruitment of SNAREs at fusion sites. This structural change is accompanied by reduced membrane fluidity (measured by infrared ellipsometry). The G₁₀₀V/C₁₀₃V mutation nearly abolishes depolarization-evoked exocytosis (measured by membrane capacitance) and hormone secretion (measured biochemically). Single-vesicle optical (by TIRF microscopy) and biophysical measurements of ATP release indicate that G₁₀₀V/C₁₀₃V retards initial fusion-pore opening, hinders its expansion and leads to premature closure in most instances. We conclude that the TMD of VAMP2 plays a critical role in membrane fusion and that the structural mobility provided by the central small amino acids is crucial for exocytosis by influencing the molecular re-arrangements of the lipid membrane that are necessary for fusion pore opening and expansion.

Molecular basis for the interaction of the mammalian amino acid transporters B0AT1 and B0AT3 with their ancillary protein collectrin

Many solute carrier 6 (SLC6) family transporters require ancillary subunits to modify their expression and activity. The main apical membrane neutral amino acid transporters in mouse intestine and kidney, B(0)AT1 and B(0)AT3, require the ancillary protein collectrin or ACE2 for plasma membrane expression. Expression and activity of SLC6 neurotransmitter transporters are modulated by interaction with syntaxin 1A. Utilizing monocarboxylate-B(0)AT1/3 fusion constructs, we discovered that collectrin is also necessary for B(0)AT1 and B(0)AT3 catalytic function. Syntaxin 1A and syntaxin 3 inhibit the membrane expression of B(0)AT1 by competing with collectrin for access. A mutagenesis screening approach identified residues on trans-membrane domains 1α, 5, and 7 on one face of B(0)AT3 as a key region involved in interaction with collectrin. Mutant analysis established residues that were involved in collectrin-dependent functions as follows: plasma membrane expression of B(0)AT3, catalytic activation, or both. These results identify a potential binding site for collectrin and other SLC6 ancillary proteins.

P2Y1 receptor inhibits GABA transport through a calcium signalling-dependent mechanism in rat cortical astrocytes

Astrocytes express a variety of purinergic (P2) receptors, involved in astrocytic communication through fast increases in [Ca(2+) ]i . Of these, the metabotropic ATP receptors (P2Y) regulate cytoplasmic Ca(2+) levels through the PLC-PKC pathway. GABA transporters are a substrate for a number of Ca(2+) -related kinases, raising the possibility that calcium signalling in astrocytes impact the control of extracellular levels of the major inhibitory transmitter in the brain. To access this possibility we tested the influence of P2Y receptors upon GABA transport into astrocytes. Mature primary cortical astroglial-enriched cultures expressed functional P2Y receptors, as evaluated through Ca(2+) imaging, being P2Y1 the predominant P2Y receptor subtype. ATP (100 μM, for 1 min) caused an inhibition of GABA transport through either GAT-1 or GAT-3 transporters, decreasing the Vmax kinetic constant. ATP-induced inhibition of GATs activity was still evident in the presence of adenosine deaminase, precluding an adenosine-mediated effect. This, was mimicked by a specific agonist for the P2Y1,12,13 receptor (2-MeSADP). The effect of 2-MeSADP on GABA transport was blocked by the P2 (PPADS) and P2Y1 selective (MRS2179) receptor antagonists, as well as by the PLC inhibitor (U73122). 2-MeSADP failed to inhibit GABA transport in astrocytes where intracellular calcium had been chelated (BAPTA-AM) or where calcium stores were depleted (α-cyclopiazonic acid, CPA). In conclusion, P2Y1 receptors in astrocytes inhibit GABA transport through a mechanism dependent of P2Y1 -mediated calcium signalling, suggesting that astrocytic calcium signalling, which occurs as a consequence of neuronal firing, may operate a negative feedback loop to enhance extracellular levels of GABA.

Gamma aminobutyric acid transporter subtype 1 gene knockout mice: a new model for attention deficit/hyperactivity disorder

Attention deficit/hyperactivity disorder (ADHD) is characterized by hyperactivity, impaired sustained attention, impulsivity, and is usually accompanied by varying degrees of learning difficulties and lack of motor coordination. However, the pathophysiology and etiology of ADHD remain inconclusive so far. Our previous studies have demonstrated that the gamma aminobutyric acid transporter subtype 1 (GAT1) gene knockout (ko) mouse (gat1-/-) is hyperactive and exhibited impaired memory performance in the Morris water maze. In the current study, we found that the gat1-/- mice showed low levels of attentional focusing and increased impulsivity. In addition, the gat1-/- mice displayed ataxia characterized by defects in motor coordination and balance skills. The hyperactivity in the ko mice was reduced by both methylphenidate and amphetamine. Collectively, these results suggest that GAT1 ko mouse is a new animal model for ADHD studying and GAT1 may be a new target to treat ADHD.

Endogenous SNAP-25 regulates native voltage-gated calcium channels in glutamatergic neurons

In addition to its primary role as a fundamental component of the SNARE complex, SNAP-25 also modulates voltage-gated calcium channels (VGCCs) in various overexpression systems. Although these studies suggest a potential negative regulatory role of SNAP-25 on VGCC activity, the effects of endogenous SNAP-25 on native VGCC function in neurons are unclear. In the present study, we investigated the VGCC properties of cultured glutamatergic and GABAergic rat hippocampal neurons. Glutamatergic currents were dominated by P/Q-type channels, whereas GABAergic cells had a dominant L-type component. Also, glutamatergic VGCC current densities were significantly lower with enhanced inactivation rates and shifts in the voltage dependence of activation and inactivation curves compared with GABAergic cells. Silencing endogenous SNAP-25 in glutamatergic neurons did not alter P/Q-type channel expression or localization but led to increased VGCC current density without changes in the VGCC subtype proportions. Isolation of the P/Q-type component indicated that increased current in the absence of SNAP-25 was correlated with a large depolarizing shift in the voltage dependence of inactivation. Overexpressing SNAP-25 in GABAergic neurons reduced current density without affecting the VGCC subtype proportion. Accordingly, VGCC current densities in glutamatergic neurons from Snap-25(+/-) mice were significantly elevated compared with wild type glutamatergic neurons. Overall, this study demonstrates that endogenous SNAP-25 negatively regulates native VGCCs in glutamatergic neurons which could have important implications for neurological diseases associated with altered SNAP-25 expression.

SAT1, A Glutamine Transporter, is Preferentially Expressed in GABAergic Neurons

Subsets of GABAergic neurons are able to maintain high frequency discharge patterns, which requires efficient replenishment of the releasable pool of GABA. Although glutamine is considered a preferred precursor of GABA, the identity of transporters involved in glutamine uptake by GABAergic neurons remains elusive. Molecular analyses revealed that SAT1 (Slc38a1) features system A characteristics with a preferential affinity for glutamine, and that SAT1 mRNA expression is associated with GABAergic neurons. By generating specific antibodies against SAT1 we show that this glutamine carrier is particularly enriched in GABAergic neurons. Cellular SAT1 distribution resembles that of GAD67, an essential GABA synthesis enzyme, suggesting that SAT1 can be involved in translocating glutamine into GABAergic neurons to facilitate inhibitory neurotransmitter generation.

Heterogeneity of glutamatergic and GABAergic release machinery in cerebral cortex: analysis of synaptogyrin, vesicle-associated membrane protein, and syntaxin

To define whether cortical glutamatergic and GABAergic release machineries can be differentiated on the basis of the nature and amount of proteins they express, we studied the degree of co-localization of synaptogyrin (SGYR) 1 and 3, vesicle-associated membrane protein (VAMP) 1 and 2, syntaxin (STX) 1A and 1B in vesicular glutamate transporter (VGLUT)1-, VGLUT2- and vesicular GABA transporter (VGAT)-positive (+) puncta and synaptic vesicles in the rat cerebral cortex. Co-localization studies showed that SGYR1 and 3 were expressed in about 90% of VGLUT1+, 70% of VGLUT2+ and 80% of VGAT+ puncta; VAMP1 was expressed in approximately 45% of VGLUT1+, 55% of VGLUT2+, and 80% of VGAT+ puncta; VAMP2 in about 95% of VGLUT1+, 75% of VGLUT2+, and 80% of VGAT+ puncta; STX1A in about 65% of VGLUT1+, 30% of VGLUT2+, and 3% of VGAT+ puncta, and STX1B in approximately 45% of VGLUT1+, 35% of VGLUT2+, and 70% of VGAT+ puncta. Immunoisolation studies showed that while STX1A was completely segregated and virtually absent from VGAT synaptic vesicles, STX1B, VAMP1/VAMP2, SGYR1/SGYR3 showed a similar pattern with the highest expression in VGLUT1 immunoisolated vesicles and the lowest in VGAT immunoisolated vesicles. Moreover, we studied the localization of STX1B at the electron microscope and found that a population of axon terminals forming symmetric synapses were STX1B-positive.These results extend our previous observations on the differential expression of presynaptic proteins involved in neurotransmitter release in GABAergic and glutamatergic terminals and indicate that heterogeneity of glutamatergic and GABAergic release machinery can be contributed by both the presence or absence of a given protein in a nerve terminal and the amount of protein expressed by synaptic vesicles.

Proteomic screen for multiprotein complexes in synaptic plasma membrane from rat hippocampus by blue native gel electrophoresis and tandem mass spectrometry

Neuronal synapses are specialized sites for information exchange between neurons. Many diseases, such as addiction and mood disorders, likely result from altered expression of synaptic proteins, or altered formation of synaptic complexes involved in neurotransmission or neuroplasticity. A detailed description of native multiprotein complexes in synaptic plasma membranes (PM) is therefore essential for understanding biological mechanisms and disease processes. For the first time in this study, two-dimensional Blue Native/SDS-PAGE electrophoresis, combined with tandem mass spectrometry, was used to screen multiprotein complexes in synaptic plasma membranes from rat hippocampus. As a result, 514 unique proteins were identified, of which 36% were integral membrane proteins. In addition, 19 potentially novel and known heterooligomeric multiprotein complexes were found, such as the SNARE and ATPase complexes. A potentially novel protein complex, involving syntaxin, synapsin I and Na+/K+ ATPase alpha-1, was further confirmed by co-immunoprecipitation and immunofluorescence staining. As demonstrated here, Blue Native-PAGE is a powerful tool for the separation of hydrophobic membrane proteins. The combination of Blue Native-PAGE and mass spectrometry could systematically identify multiprotein complexes.

Altered expression of genes involved in ATP biosynthesis and GABAergic neurotransmission in the ventral prefrontal cortex of suicides with and without major depression

The prefrontal cortex is believed to play a major role in depression and suicidal behavior through regulation of cognition, memory, recognition of emotion, and anxiety-like states, with numerous post-mortem studies documenting a prefrontal serotonergic dysregulation considered to be characteristic of depressive psychopathology. This study was carried out to detect changes in gene expression associated with both suicide and major depression using oligonucleotide microarrays (Affymetrix HG-U133 chip set) summarizing expression patterns in primarily ventral regions of the prefrontal cortex (BA44, 45, 46 and 47). A total of 37 male subjects were included in this study, of which 24 were suicides (depressed suicides=16, nondepressed suicides=8) and 13 were matched controls. All subjects were clinically characterized by means of psychological autopsies using structured interviews. Unique patterns of differential expression were validated in each of the cortical regions evaluated, with group-specific changes highlighting the involvement of several key neurobiological pathways that have been implicated in both suicide and depression. An overrepresentation of factors involved in cell cycle control and cell division (BA44), transcription (BA44 and 47) and myelination (BA46) was seen in gene ontology analysis of differentially expressed genes, which also highlights changes in the expression of genes involved in ATP biosynthesis and utilization across all areas. Gene misexpression in BA46 was most pronounced between the two suicide groups, with many significant genes involved in GABAergic neurotransmission. The pronounced misexpression of genes central to GABAergic signaling and astrocyte/oligodendrocyte function provides further support for a central glial pathology in depression and suicidal behavior.

Genetic and expression analyses reveal elevated expression of syntaxin 1A ( STX1A) in high functioning autism

Autism is a pervasive developmental disorder diagnosed in early childhood. Abnormalities of serotonergic neurotransmission have been reported in autism. Serotonin transporter (5-HTT), which modulates serotonin levels, is a major therapeutic target in autism. Therefore, factors that regulate 5-HTT expression might be implicated in autism. One candidate 5-HTT-regulatory protein is the presynaptic protein, syntaxin 1A (STX1A). We examined the association of STX1A with autism in a trio association study using DNA samples from 249 AGRE trios with autistic probands. Only male probands were selected, since autism is more prevalent among males. The probands of 102 trios had IQ>70, and were considered as high functioning autism (HFA). In transmission disequilibrium test (TDT) analysis, rs2293485 (p=0.034) and rs4717806 (p=0.033) showed nominal associations with HFA; modest haplotype association was also observed. The SNPs that showed associations were related to early developmental abnormalities (ADI-R_D). We further compared STX1A mRNA expression in the lymphocytes of drug-naive HFA patients (n=12) and age- and sex-matched controls (n=13). STX1A expression in the HFA group was significantly higher (p=0.001) than that of controls. Thus, we suggest a possible role of STX1A in the pathogenesis of HFA. During early childhood, there is a period of high brain serotonin synthesis that is disrupted in autistic children; STX1A might influence the serotonergic system during this stage of neurodevelopment, as implied by the association with ADI-R_D.

Syntaxin 1A interaction with the dopamine transporter promotes amphetamine-induced dopamine efflux

The soluble N-ethylmaleimide-sensitive factor attachment protein receptor protein syntaxin 1A (SYN1A) interacts with and regulates the function of transmembrane proteins, including ion channels and neurotransmitter transporters. Here, we define the first 33 amino acids of the N terminus of the dopamine (DA) transporter (DAT) as the site of direct interaction with SYN1A. Amphetamine (AMPH) increases the association of SYN1A with human DAT (hDAT) in a heterologous expression system (hDAT cells) and with native DAT in murine striatal synaptosomes. Immunoprecipitation of DAT from the biotinylated fraction shows that the AMPH-induced increase in DAT/SYN1A association occurs at the plasma membrane. In a superfusion assay of DA efflux, cells overexpressing SYN1A exhibited significantly greater AMPH-induced DA release with respect to control cells. By combining the patch-clamp technique with amperometry, we measured DA release under voltage clamp. At -60 mV, a physiological resting potential, AMPH did not induce DA efflux in hDAT cells and DA neurons. In contrast, perfusion of exogenous SYN1A (3 microM) into the cell with the whole-cell pipette enabled AMPH-induced DA efflux at -60 mV in both hDAT cells and DA neurons. It has been shown recently that Ca2+/calmodulin-dependent protein kinase II (CaMKII) is activated by AMPH and regulates AMPH-induced DA efflux. Here, we show that AMPH-induced association between DAT and SYN1A requires CaMKII activity and that inhibition of CaMKII blocks the ability of exogenous SYN1A to promote DA efflux. These data suggest that AMPH activation of CaMKII supports DAT/SYN1A association, resulting in a mode of DAT capable of DA efflux.

Induction of insulin secretion in engineered liver cells by nitric oxide

BACKGROUND

Type 1 Diabetes Mellitus results from an autoimmune destruction of the pancreatic beta cells, which produce insulin. The lack of insulin leads to chronic hyperglycemia and secondary complications, such as cardiovascular disease. The currently approved clinical treatments for diabetes mellitus often fail to achieve sustained and optimal glycemic control. Therefore, there is a great interest in the development of surrogate beta cells as a treatment for type 1 diabetes. Normally, pancreatic beta cells produce and secrete insulin only in response to increased blood glucose levels. However in many cases, insulin secretion from non-beta cells engineered to produce insulin occurs in a glucose-independent manner. In the present study we engineered liver cells to produce and secrete insulin and insulin secretion can be stimulated via the nitric oxide pathway.

RESULTS

Expression of either human insulin or the beta cell specific transcription factors PDX-1, NeuroD1 and MafA in the Hepa1-6 cell line or primary liver cells via adenoviral gene transfer, results in production and secretion of insulin. Although, the secretion of insulin is not significantly increased in response to high glucose, treatment of these engineered liver cells with L-arginine stimulates insulin secretion up to three-fold. This L-arginine-mediated insulin release is dependent on the production of nitric oxide.

CONCLUSION

Liver cells can be engineered to produce insulin and insulin secretion can be induced by treatment with L-arginine via the production of nitric oxide.