Distinct Functions of Syntaxin-1 in Neuronal Maintenance, Synaptic Vesicle Docking, and Fusion in Mouse Neurons

Brain insulin resistance triggers early onset Alzheimer disease in Down syndrome

Dysregulation of insulin signaling pathway with reduced downstream neuronal survival and plasticity mechanisms is a fundamental abnormality observed in Alzheimer's disease (AD) brain. This phenomenon, known as brain insulin resistance, is associated with poor cognitive performance and is driven by the uncoupling of insulin receptor (IR) from its direct substrate (IRS1). Considering that Down syndrome (DS) and AD neuropathology share many common features, we investigated metabolic aspects of neurodegeneration, i.e., brain insulin resistance, in DS and whether it would contribute to early onset AD in DS population. Changes of levels and activation of main brain proteins belonging to the insulin signaling pathway (i.e., IR, IRS1, PTEN, GSK3β, PKCζ, AS160, GLUT4) were evaluated. Furthermore, we analyzed whether changes of these proteins were associated with alterations of: (i) proteins regulating brain energy metabolism; (ii) APP cleavage; and (ii) regulation of synaptic plasticity mechanisms in post-mortem brain samples collected from people with DS before and after the development of AD pathology (DSAD) compared with their age-matched controls. We found that DS cases were characterized by key markers of brain insulin resistance (reduced IR and increased IRS1 inhibition) early in life. Furthermore, downstream from IRS1, an overall uncoupling among the proteins of insulin signaling was observed. Dysregulated brain insulin signaling was associated with reduced hexokinase II (HKII) levels and proteins associated with mitochondrial complexes levels as well as with reduced levels of syntaxin in DS cases. Tellingly, these alterations precede the development of AD neuropathology and clinical presentations in DS. We propose that markers of brain insulin resistance rise earlier with age in DS compared with the general population and may contribute to the cognitive impairment associated with the early development of AD in DS.

3β, 6β-dichloro-5-hydroxy-5α-cholestane facilitates neuronal development through modulating TrkA signaling regulated proteins in primary hippocampal neuron

Potentiating neuritogenesis through pharmacological intervention might hold therapeutic promise in neurodegenerative disorders and acute brain injury. Here, we investigated the novel neuritogenic potentials of a steroidal chlorohydrin, 3β, 6β-dichloro-5-hydroxy-5α-cholestane (hereafter, SCH) and the change in cellular proteome to gain insight into the underlying mechanism of its neurotrophic activity in hippocampal neurons. Morphometric analysis showed that SCH promoted early neuronal differentiation, dendritic arborization and axonal maturation. Proteomic and bioinformatic analysis revealed that SCH induced upregulation of several proteins, including those associated with neuronal differentiation and development. Immunocytochemical data further indicates that SCH-treated neurons showed upregulation of Hnrnpa2b1 and Map1b, validating their proteomic profiles. In addition, a protein-protein interaction network analysis identified TrkA as a potential target connecting most of the upregulated proteins. The neurite outgrowth effect of SCH was suppressed by TrkA inhibitor, GW441756, verifying TrkA-dependent activity of SCH, which further supports the connection of TrkA with the upregulated proteins. Also, the computational analysis revealed that SCH interacts with the NGF-binding domain of TrkA through Phe327 and Asn355. Collectively, our findings provide evidence that SCH promotes neuronal development via upregulating TrkA-signaling proteins and suggest that SCH could be a promising therapeutic agent in the prevention and treatment of neurodegenerative disorders.

SNARE Complex-Associated Proteins and Alcohol

Alcohol addiction causes major health problems throughout the world, causing numerous deaths and incurring a huge economic burden to society. To develop an intervention for alcohol addiction, it is necessary to identify molecular target(s) of alcohol and associated molecular mechanisms of alcohol action. The functions of many central and peripheral synapses are impacted by low concentrations of ethanol (EtOH). While the postsynaptic targets and mechanisms are studied extensively, there are limited studies on the presynaptic targets and mechanisms. This article is an endeavor in this direction, focusing on the effect of EtOH on the presynaptic proteins associated with the neurotransmitter release machinery. Studies on the effects of EtOH at the levels of gene, protein, and behavior are highlighted in this article.

Synaptojanin and Endophilin Mediate Neck Formation during Ultrafast Endocytosis

Ultrafast endocytosis generates vesicles from the plasma membrane as quickly as 50 ms in hippocampal neurons following synaptic vesicle fusion. The molecular mechanism underlying the rapid maturation of these endocytic pits is not known. Here we demonstrate that synaptojanin-1, and its partner endophilin-A, function in ultrafast endocytosis. In the absence of synaptojanin or endophilin, the membrane is rapidly invaginated, but pits do not become constricted at the base. The 5-phosphatase activity of synaptojanin is involved in formation of the neck, but 4-phosphatase is not required. Nevertheless, these pits are eventually cleaved into vesicles; within a 30-s interval, synaptic endosomes form and are resolved by clathrin-mediated budding. Then synaptojanin and endophilin function at a second step to aid with the removal of clathrin coats from the regenerated vesicles. These data together suggest that synaptojanin and endophilin can mediate membrane remodeling on a millisecond timescale during ultrafast endocytosis.

Extenuation of in utero toxic effects of MeHg in the developing neurons by Fisetin via modulating the expression of synaptic transmission and plasticity regulators in hippocampus of the rat offspring

The neurotoxic environmental contaminant, methylmercury (MeHg), has shown to have detrimental effects on the developing brain when exposed during gestation. We have shown in our earlier studies that gestational administration of 3,3',4',7-Tetrahydroxyflavone or Fisetin reduces the toxic effects of MeHg in the developing rat brain. The current study has pivoted to study the mechanism behind the mitigating action of Fisetin against prenatal MeHg exposure induced neurotoxicity. Negligible data is available about the toxicity targets of MeHg in the developing brain. Studies have exhibited that MeHg exposure cause toxic effects on synaptic transmission and plasticity in the offspring brain. Hence, we aimed to study the effect of Fisetin on MeHg induced alterations in the expressions of regulatory genes and proteins involved in synaptic plasticity and transmission. Pregnant rats were grouped according to the type of oral administration as, (i) Control, (ii) MeHg (1.5 mg/kg b. w.), (iii) MeHg + Fisetin (30 mg/kg b. w.) and (iv) Fisetin (30 mg/kg b. w). Maternal administration of Fisetin prevented MeHg exposure induced downregulation of neurogranin (Nrgn), dendrin (Ddn), Syntaxin 1 A (Stx1a), Lin-7 homolog A (Lin7a), Complexin-2 (Cplx2) and Exocyst complex component 8 (Exoc8) genes in the offspring rat. Fisetin also prevented MeHg exposure induced downregulation of brain derived neurotrophic factor (BDNF), Glial-cell derived neurotrophic factor (GDNF) protein expressions and hampered reactive astrogliosis in the hippocampus of F₁ generation rats. Hence, through this study, we conclude that Fisetin modulates the expression of regulatory genes and proteins involved in synaptic transmission and plasticity and extenuates MeHg neurotoxicity in the developing rat brain.

Syntaxin 3, but not syntaxin 4, is required for mast cell-regulated exocytosis, where it plays a primary role mediating compound exocytosis

Mast cells (MCs) participate in allergy, inflammation, and defense against pathogens. They release multiple immune mediators via exocytosis, a process that requires SNARE proteins, including syntaxins (Stxs). The identity of the Stxs involved in MC exocytosis remains controversial. Here, we studied the roles of Stx3 and -4 in fully developed MCs from conditional knockout mice by electrophysiology and EM, and found that Stx3, and not Stx4, is crucial for MC exocytosis. The main defect seen in Stx3-deficient MCs was their inability to engage multigranular compound exocytosis, while leaving most single-vesicle fusion events intact. We used this defect to show that this form of exocytosis is not only required to accelerate MC degranulation but also essential to achieve full degranulation. The exocytic defect was severe but not absolute, indicating that an Stx other than Stx3 and -4 is also required for exocytosis in MCs. The removal of Stx3 affected only regulated exocytosis, leaving other MC effector responses intact, including the secretion of cytokines via constitutive exocytosis. Our in vivo model of passive systemic anaphylaxis showed that the residual exocytic function of Stx3-deficient MCs was sufficient to drive a full anaphylactic response in mice.

Lithium Improves Dopamine Neurotransmission and Increases Dopaminergic Protein Abundance in the Striatum after Traumatic Brain Injury

Experimental models of traumatic brain injury (TBI) recapitulate secondary injury sequela and cognitive dysfunction reported in patients afflicted with a TBI. Impairments in neurotransmission are reported in multiple brain regions in the weeks following experimental TBI and may contribute to behavioral dysfunction. Formation of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex is an important mechanism for neurotransmitter exocytosis. We previously showed that lithium treatment attenuated hippocampal decreases in α-synuclein and VAMP2, enhanced SNARE complex formation, and improved cognitive performance after TBI. However, the effect of TBI on striatal SNARE complex formation is not known. We hypothesized lithium treatment would attenuate TBI-induced impairments in evoked dopamine release and increase the abundance of synaptic proteins associated with dopamine neurotransmission. The current study evaluated the effect of lithium (1 mmol/kg/day) administration on striatal evoked dopamine neurotransmission, SNARE complex formation, and proposed actions of lithium, including inhibition of GSK3β, assessment of synaptic marker protein abundance, and synaptic proteins important for dopamine synthesis and transport following controlled cortical impact (CCI). Sprague-Dawley rats were subjected to CCI or sham injury and treated daily with lithium chloride or vehicle for 7 days post-injury. We provide novel evidence that CCI reduces SNARE protein and SNARE complex abundance in the striatum at 1 week post-injury. Lithium administration improved evoked dopamine release and increased the abundance of α-synuclein, D2 receptor, and phosphorylated tyrosine hydroxylase in striatal synaptosomes post-injury. These findings show that lithium treatment attenuated dopamine neurotransmission deficits and increased the abundance of synaptic proteins important for dopamine signaling after TBI.

Syntaxin-1/TI-VAMP SNAREs interact with Trk receptors and are required for neurotrophin-dependent outgrowth

SNARE proteins are essential components of the machinery that regulates vesicle trafficking and exocytosis. Their role is critical for the membrane-fusion processes that occur during neurotransmitter release. However, research in the last decade has also unraveled the relevance of these proteins in membrane expansion and cytoskeletal rearrangements during developmental processes such as neuronal migration and growth cone extension and attraction. Neurotrophins are neurotrophic factors that are required for many cellular functions throughout the brain, including neurite outgrowth and guidance, synaptic formation, and plasticity. Here we show that neurotrophin Trk receptors form a specific protein complex with the t-SNARE protein Syntaxin 1, both in vivo and in vitro. We also demonstrate that blockade of Syntaxin 1 abolishes neurotrophin-dependent growth of axons in neuronal cultures and decreases exocytotic events at the tip of axonal growth cones. 25-kDa soluble N-ethylmaleimide-sensitive factor attachment protein and Vesicle-associated membrane protein 2 do not participate in the formation of this SNARE complex, while tetanus neurotoxin-insensitive vesicle-associated membrane protein interacts with Trk receptors; knockdown of this (v) SNARE impairs Trk-dependent outgrowth. Taken together, our results support the notion that an atypical SNARE complex comprising Syntaxin 1 and tetanus neurotoxin-insensitive vesicle-associated membrane protein is required for axonal neurotrophin function.

The unfolding landscape of the congenital myasthenic syndromes

Congenital myasthenic syndromes (CMS) are heterogeneous disorders in which the safety margin of neuromuscular transmission is impaired by one or more specific mechanisms. Since the advent of next-generation sequencing methods, the discovery of novel CMS targets and phenotypes has proceeded at an accelerated rate. Here, we review the current classification of CMS and describe our findings in five of these targets identified and investigated in our laboratory in the past 5 years. Defects in LRP4 hinder synaptic development and maintenance; the defects in PREPL are predicted to diminish filling of the synaptic vesicle with acetylcholine; and defects in SNAP25, Munc13-1, and synaptotbrevin-1 impede synaptic vesicle exocytosis.

Syntaxins on granules promote docking of granules via interactions with munc18

SNAREs and SNARE-binding accessory proteins are believed to be central molecular components of neurotransmitter release, although the precise sequence of molecular events corresponding to distinct physiological states is unclear. The mechanism of docking of vesicles to the plasma membrane remains elusive, as the anchoring protein residing on vesicles is unknown. Here I show that targeting small amounts of syntaxin to granules by transmembrane domain alteration leads to a substantial enhancement of syntaxin clustering beneath granules, as well as of morphological granule docking. The effect was abolished without munc18 and strongly reduced by removal of the N-terminal peptide in the syntaxin mutant. Thus, in contrast to the current paradigm, I demonstrate that syntaxin acts from the vesicular membrane, strongly facilitating docking of vesicles, likely via interaction of its N-peptide with munc18. Docking was assayed by quantifying the syntaxin clusters beneath granules, using two-color Total Internal Reflectance Fluorescence microscopy in live PC-12 cells and confirmed by electron microscopy. Hereby, I propose a new model of vesicle docking, wherein munc18 bridges the few syntaxin molecules residing on granules to the syntaxin cluster on the plasma membrane, suggesting that the number of syntaxins on vesicles determines docking and conceivably fusion probability.

SNARE complex in axonal guidance and neuroregeneration

Through complex mechanisms that guide axons to the appropriate routes towards their targets, axonal growth and guidance lead to neuronal system formation. These mechanisms establish the synaptic circuitry necessary for the optimal performance of the nervous system in all organisms. Damage to these networks can be repaired by neuroregenerative processes which in turn can re-establish synapses between injured axons and postsynaptic terminals. Both axonal growth and guidance and the neuroregenerative response rely on correct axonal growth and growth cone responses to guidance cues as well as correct synapses with appropriate targets. With this in mind, parallels can be drawn between axonal regeneration and processes occurring during embryonic nervous system development. However, when studying parallels between axonal development and regeneration many questions still arise; mainly, how do axons grow and synapse with their targets and how do they repair their membranes, grow and orchestrate regenerative responses after injury. Major players in the cellular and molecular processes that lead to growth cone development and movement during embryonic development are the Soluble N-ethylamaleimide Sensitive Factor (NSF) Attachment Protein Receptor (SNARE) proteins, which have been shown to be involved in axonal growth and guidance. Their involvement in axonal growth, guidance and neuroregeneration is of foremost importance, due to their roles in vesicle and membrane trafficking events. Here, we review the recent literature on the involvement of SNARE proteins in axonal growth and guidance during embryonic development and neuroregeneration.

Vesicle release site organization at synaptic active zones

Information transfer between nerve cells (neurons) forms the basis of behavior, emotion, and survival. Signal transduction from one neuron to another occurs at synapses, and relies on both electrical and chemical signal propagation. At chemical synapses, incoming electrical action potentials trigger the release of chemical neurotransmitters that are sensed by the connected cell and here reconverted to an electrical signal. The presynaptic conversion of an electrical to a chemical signal is an energy demanding, highly regulated process that relies on a complex, evolutionarily conserved molecular machinery. Here, we review the biophysical characteristics of this process, the current knowledge of the molecules operating in this reaction and genetic specializations that may have evolved to shape inter-neuronal signaling.

Transcellular Nanoalignment of Synaptic Function

At each of the brain's vast number of synapses, the presynaptic nerve terminal, synaptic cleft, and postsynaptic specialization form a transcellular unit to enable efficient transmission of information between neurons. While we know much about the molecular machinery within each compartment, we are only beginning to understand how these compartments are structurally registered and functionally integrated with one another. This review will describe the organization of each compartment and then discuss their alignment across pre- and postsynaptic cells at a nanometer scale. We propose that this architecture may allow for precise synaptic information exchange and may be modulated to contribute to the remarkable plasticity of brain function.

Transcellular Nanoalignment of Synaptic Function

At each of the brain's vast number of synapses, the presynaptic nerve terminal, synaptic cleft, and postsynaptic specialization form a transcellular unit to enable efficient transmission of information between neurons. While we know much about the molecular machinery within each compartment, we are only beginning to understand how these compartments are structurally registered and functionally integrated with one another. This review will describe the organization of each compartment and then discuss their alignment across pre- and postsynaptic cells at a nanometer scale. We propose that this architecture may allow for precise synaptic information exchange and may be modulated to contribute to the remarkable plasticity of brain function.

Motor cortex excitability in seizure-free STX1B mutation carriers with a history of epilepsy and febrile seizures

OBJECTIVE

Mutations in STX1B encoding the presynaptic protein syntaxin-1B are associated with febrile seizures with or without epilepsy. It is unclear to what extent these mutations are linked to abnormalities of cortical glutamatergic or GABAergic neurotransmission. We explored this question using single- and paired-pulse transcranial magnetic stimulation (TMS) excitability markers.

METHODS

We studied nine currently asymptomatic adult STX1B mutation carriers with history of epilepsy and febrile seizures, who had been seizure-free for at least eight years without antiepileptic drug treatment, and ten healthy age-matched controls. Resting motor threshold (RMT), and input-output curves of motor evoked potential (MEP) amplitude, short-interval intracortical inhibition (SICI, marker of GABA_Aergic excitability) and intracortical facilitation (ICF, marker of glutamatergic excitability) were tested.

RESULTS

RMT, and input-output curves of MEP amplitude, SICI and ICF revealed no significant differences between STX1B mutation carriers and healthy controls.

CONCLUSIONS

Findings suggest normal motor cortical GABA_Aergic and glutamatergic excitability in currently asymptomatic STX1B mutation carriers.

SIGNIFICANCE

TMS measures of motor cortical excitability show utility in demonstrating normal excitability in adult STX1B mutation carriers with history of seizures.

Lateral Fluid Percussion Injury Impairs Hippocampal Synaptic Soluble N-Ethylmaleimide Sensitive Factor Attachment Protein Receptor Complex Formation

Traumatic brain injury (TBI) and the activation of secondary injury mechanisms have been linked to impaired cognitive function, which, as observed in TBI patients and animal models, can persist for months and years following the initial injury. Impairments in neurotransmission have been well documented in experimental models of TBI, but the mechanisms underlying this dysfunction are poorly understood. Formation of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex facilitates vesicular docking and neurotransmitter release in the synaptic cleft. Published studies highlight a direct link between reduced SNARE complex formation and impairments in neurotransmitter release. While alterations in the SNARE complex have been described following severe focal TBI, it is not known if deficits in SNARE complex formation manifest in a model with reduced severity. We hypothesized that lateral fluid percussion injury (lFPI) reduces the abundance of SNARE proteins, impairs SNARE complex formation, and contributes to impaired neurobehavioral function. To this end, rats were subjected to lFPI or sham injury and tested for acute motor performance and cognitive function at 3 weeks post-injury. lFPI resulted in motor impairment between 1 and 5 days post-injury. Spatial acquisition and spatial memory, as assessed by the Morris water maze, were significantly impaired at 3 weeks after lFPI. To examine the effect of lFPI on synaptic SNARE complex formation in the injured hippocampus, a separate cohort of rats was generated and brains processed to evaluate hippocampal synaptosomal-enriched lysates at 1 week post-injury. lFPI resulted in a significant reduction in multiple monomeric SNARE proteins, including VAMP2, and α-synuclein, and SNARE complex abundance. The findings in this study are consistent with our previously published observations suggesting that impairments in hippocampal SNARE complex formation may contribute to neurobehavioral dysfunction associated with TBI.

Early Golgi Abnormalities and Neurodegeneration upon Loss of Presynaptic Proteins Munc18-1, Syntaxin-1, or SNAP-25

The loss of presynaptic proteins Munc18-1, syntaxin-1, or SNAP-25 is known to produce cell death, but the underlying features have not been compared experimentally. Here, we investigated these features in cultured mouse CNS and DRG neurons. Side-by-side comparisons confirmed massive cell death, before synaptogenesis, within 1-4 DIV upon loss of t-SNAREs (syntaxin-1, SNAP-25) or Munc18-1, but not v-SNAREs (synaptobrevins/VAMP1/2/3 using tetanus neurotoxin (TeNT), also in TI-VAMP/VAMP7 knock-out (KO) neurons). A condensed cis-Golgi was the first abnormality observed upon Munc18-1 or SNAP-25 loss within 3 DIV. This phenotype was distinct from the Golgi fragmentation observed in apoptosis. Cell death was too rapid after syntaxin-1 loss to study Golgi abnormalities. Syntaxin-1 and Munc18-1 depend on each other for normal cellular levels. We observed that endogenous syntaxin-1 accumulates at the Golgi of Munc18-1 KO neurons. However, expression of a non-neuronal Munc18 isoform that does not bind syntaxin-1, Munc18-3, in Munc18-1 KO neurons prevented cell death and restored normal cis-Golgi morphology, but not synaptic transmission or syntaxin-1 targeting. Finally, we observed that DRG neurons are the only Munc18-1 KO neurons that do not degenerate in vivo or in vitro In these neurons, cis-Golgi abnormalities were less severe, with no changes in Golgi shape. Together, these data demonstrate that cell death upon Munc18-1, syntaxin-1, or SNAP-25 loss occurs via a degenerative pathway unrelated to the known synapse function of these proteins and involving early cis-Golgi abnormalities, distinct from apoptosis.SIGNIFICANCE STATEMENT This study provides new insights in a neurodegeneration pathway triggered by the absence of specific proteins involved in synaptic transmission (syntaxin-1, Munc18-1, SNAP-25), whereas other proteins involved in the same molecular process (synaptobrevins, Munc13-1/2) do not cause degeneration. Massive cell death occurs in cultured neurons upon depleting syntaxin-1, Munc18-1, and/or SNAP-25, well before synapse formation. This study characterizes several relevant cellular phenotypes, especially early cis-Golgi abnormalities, distinct from abnormalities observed during apoptosis, and rules out several other phenotypes as causal (defects in syntaxin-1 targeting and synaptic transmission). As proteins, such as syntaxin-1, Munc18-1, or SNAP-25, modulate α-synuclein neuropathy and/or are dysregulated in Alzheimer's disease, understanding this type of neurodegeneration may provide new links between synaptic defects and neurodegeneration in humans.

Defining the transcriptomic landscape of the developing enteric nervous system and its cellular environment

BACKGROUND

Motility and the coordination of moving food through the gastrointestinal tract rely on a complex network of neurons known as the enteric nervous system (ENS). Despite its critical function, many of the molecular mechanisms that direct the development of the ENS and the elaboration of neural network connections remain unknown. The goal of this study was to transcriptionally identify molecular pathways and candidate genes that drive specification, differentiation and the neural circuitry of specific neural progenitors, the phox2b expressing ENS cell lineage, during normal enteric nervous system development. Because ENS development is tightly linked to its environment, the transcriptional landscape of the cellular environment of the intestine was also analyzed.

RESULTS

Thousands of zebrafish intestines were manually dissected from a transgenic line expressing green fluorescent protein under the phox2b regulatory elements [Tg(phox2b:EGFP) ^w37 ]. Fluorescence-activated cell sorting was used to separate GFP-positive phox2b expressing ENS progenitor and derivatives from GFP-negative intestinal cells. RNA-seq was performed to obtain accurate, reproducible transcriptional profiles and the unbiased detection of low level transcripts. Analysis revealed genes and pathways that may function in ENS cell determination, genes that may be identifiers of different ENS subtypes, and genes that define the non-neural cellular microenvironment of the ENS. Differential expression analysis between the two cell populations revealed the expected neuronal nature of the phox2b expressing lineage including the enrichment for genes required for neurogenesis and synaptogenesis, and identified many novel genes not previously associated with ENS development. Pathway analysis pointed to a high level of G-protein coupled pathway activation, and identified novel roles for candidate pathways such as the Nogo/Reticulon axon guidance pathway in ENS development.

CONCLUSION

We report the comprehensive gene expression profiles of a lineage-specific population of enteric progenitors, their derivatives, and their microenvironment during normal enteric nervous system development. Our results confirm previously implicated genes and pathways required for ENS development, and also identify scores of novel candidate genes and pathways. Thus, our dataset suggests various potential mechanisms that drive ENS development facilitating characterization and discovery of novel therapeutic strategies to improve gastrointestinal disorders.

Lithium increases hippocampal SNARE protein abundance after traumatic brain injury

Rodent models of traumatic brain injury (TBI) reproduce secondary injury sequela and cognitive impairments observed in patients afflicted by a TBI. Impaired neurotransmission has been reported in the weeks following experimental TBI, and may be a contributor to behavioral dysfunction. The soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex, the machinery facilitating vesicular docking and fusion, is a highly-conserved mechanism important for neurotransmission. Following TBI, there is a reduction in both the formation of the SNARE complex and the abundance of multiple SNARE proteins, including the chaperone protein cysteine string protein α (CSPα). Treatment with lithium in naïve rats reportedly increases the expression of CSPα. In the context of TBI, brain-injured rats treated with lithium exhibit improved outcome in published reports, but the mechanisms underlying the improvement are poorly understood. The current study evaluated the effect of lithium administration on the abundance of SNARE proteins and SNARE complex formation, hemispheric tissue loss, and neurobehavioral performance following controlled cortical impact (CCI). Sprague Dawley rats were subjected to CCI or sham injury, and treated daily with lithium chloride or vehicle for up to 14days. Administration of lithium after TBI modestly improved spatial memory at 14days post-injury. Semi-quantitative immunoblot analysis of hippocampal lysates revealed that treatment with lithium attenuated reductions in key SNARE proteins and SNARE complex formation at multiple time points post-injury. These findings highlight that treatment with lithium increased the abundance of synaptic proteins that facilitate neurotransmission and may contribute to improved cognitive function after TBI.

Beyond the SNARE: Munc18-1 chaperones α-synuclein

Early infantile epileptic encephalopathy (EIEE)-associated mutations in MUNC18-1 cause Munc18-1 misfolding and cellular aggregation. In this issue, Chai et al. (2016. J. Cell Biol http://dx.doi.org/10.1083/jcb.201512016) find that Munc18-1 is a molecular chaperone for α-synuclein and that aggregated Munc18-1 EIEE-causing mutants promote α-synuclein aggregation.

Loss of MUNC13-1 function causes microcephaly, cortical hyperexcitability, and fatal myasthenia

Objective:

To identify the molecular basis of a fatal syndrome of microcephaly, cortical hyperexcitability, and myasthenia.

Methods:

We performed clinical and in vitro microelectrode studies of neuromuscular transmission, examined neuromuscular junctions cytochemically and by electron microscopy (EM), and searched for mutations by Sanger and exome sequencing.

Results:

Neuromuscular transmission was severely compromised by marked depletion of the readily releasable pool of quanta, but the probability of quantal release was normal. Cytochemical and EM studies revealed normal endplate architecture. Exome sequencing identified a homozygous nonsense mutation in the N-terminal domain of MUNC13-1 (UNC13A) truncating the protein after 101 residues.

Conclusions:

Loss of Munc13-1 function predicts that syntaxin 1B is consigned to a nonfunctional closed state; this inhibits cholinergic transmission at the neuromuscular junction and glutamatergic transmission in the brain. Inactivation of syntaxin 1B likely accounts for the patient's cortical hyperexcitability because mutations of syntaxin 1B cause febrile seizures with or without epilepsy, haploinsufficiency of the STX1B is associated with myoclonic astatic epilepsy, and antisense knockdown of stx1b in zebrafish larvae elicits epileptiform discharges. A very recent publication also shows that syntaxin 1B has a separate obligatory role for maintenance of developing and mature neurons and illustrates impaired brain development in syntaxin 1A/1B double knockout mice. We therefore attribute our patient's microcephaly to the truncating homozygous Munc13-1 mutation that consigns syntaxin 1B to a permanently closed nonfunctional state akin to a knockout.