Tomosyns attenuate SNARE assembly and synaptic depression by binding to VAMP2-containing template complexes.

Tomosyns are widely thought to attenuate membrane fusion by competing with synaptobrevin-2/VAMP2 for SNARE-complex assembly. Here, we present evidence against this scenario. In a novel mouse model, tomosyn-1/2 deficiency lowered the fusion barrier and enhanced the probability that synaptic vesicles fuse, resulting in stronger synapses with faster depression and slower recovery. While wild-type tomosyn-1m rescued these phenotypes, substitution of its SNARE motif with that of synaptobrevin-2/VAMP2 did not. Single-molecule force measurements indeed revealed that tomosyn's SNARE motif cannot substitute synaptobrevin-2/VAMP2 to form template complexes with Munc18-1 and syntaxin-1, an essential intermediate for SNARE assembly. Instead, tomosyns extensively bind synaptobrevin-2/VAMP2-containing template complexes and prevent SNAP-25 association. Structure-function analyses indicate that the C-terminal polybasic region contributes to tomosyn's inhibitory function. These results reveal that tomosyns regulate synaptic transmission by cooperating with synaptobrevin-2/VAMP2 to prevent SNAP-25 binding during SNARE assembly, thereby limiting initial synaptic strength and equalizing it during repetitive stimulation.

The complementary roles of VAMP-2, -3, and -7 in platelet secretion and function.

Platelet secretion requires Soluble N-ethylmaleimide Sensitive Attachment Protein Receptors (SNAREs). Vesicle SNAREs/Vesicle-Associated Membrane Proteins (v-SNAREs/VAMPs) on granules and t-SNAREs in plasma membranes mediate granule release. Platelet VAMP heterogeneity has complicated the assessment of how/if each is used and affects hemostasis. To address the importance of VAMP-7 (V7), we analyzed mice with global deletions of V3 and V7 together or platelet-specific deletions of V2, V3, and global deletion of V7. We measured the kinetics of cargo release, and its effects on three injury models to define the context-specific roles of these VAMPs. Loss of V7 minimally affected dense and α granule release but did affect lysosomal release. V3-/-7-/- and V2Δ3Δ7-/- platelets showed partial defects in α and lysosomal release; dense granule secretion was unaffected. In vivo assays showed that loss of V2, V3, and V7 caused no bleeding or occlusive thrombosis. These data indicate a role for V7 in lysosome release that is partially compensated by V3. V7 and V3, together, contribute to α granule release, however none of these deletions affected hemostasis/thrombosis. Our results confirm the dominance of V8. When it is present, deletion of V2, V3, or V7 alone or in combination minimally affects platelet secretion and hemostasis.

What did we know? V8 is the primary VAMP isoform for platelet granule secretion, but V2 and V3 play compensatory roles.V3 is important for platelet endocytosis.V7 plays a minimal role in secretion and does not affect hemostasis.What did we discover? The loss of both V3 and V7 increases α and lysosomal secretion defects.Platelet-specific deletion of V2 and V3 with global V7-deletion causes defective α and lysosomal release.Secretion deficiencies in V3^−/−7^−/− and V2^Δ3^Δ7^−/− have no effect on hemostasis or thrombosis.What is the impact? We show that endosomal v-SNAREs (V3 and V7) play minor roles in secretion.V3^−/−7^−/− and platelet-specific V2^Δ3^Δ7^−/− mice are viable and will be valuable in in vivo studies of membrane trafficking.

Identification of residues critical for the extension of Munc18-1 domain 3a.

BACKGROUND: Neurotransmitter release depends on the fusion of synaptic vesicles with the presynaptic membrane and is mainly mediated by SNARE complex assembly. During the transition of Munc18-1/Syntaxin-1 to the SNARE complex, the opening of the Syntaxin-1 linker region catalyzed by Munc13-1 leads to the extension of the domain 3a hinge loop, which enables domain 3a to bind SNARE motifs in Synaptobrevin-2 and Syntaxin-1 and template the SNARE complex assembly. However, the exact mechanism of domain 3a extension remains elusive. RESULTS: Here, we characterized residues on the domain 3a hinge loop that are crucial for the extension of domain 3a by using biophysical and biochemical approaches and electrophysiological recordings. We showed that the mutation of residues T323/M324/R325 disrupted Munc13-1-mediated SNARE complex assembly and membrane fusion starting from Munc18-1/Syntaxin-1 in vitro and caused severe defects in the synaptic exocytosis of mouse cortex neurons in vivo. Moreover, the mutation had no effect on the binding of Synaptobrevin-2 to isolated Munc18-1 or the conformational change of the Syntaxin-1 linker region catalyzed by the Munc13-1 MUN domain. However, the extension of the domain 3a hinge loop in Munc18-1/Syntaxin-1 was completely disrupted by the mutation, leading to the failure of Synaptobrevin-2 binding to Munc18-1/Syntaxin-1. CONCLUSIONS: Together with previous results, our data further support the model that the template function of Munc18-1 in SNARE complex assembly requires the extension of domain 3a, and particular residues in the domain 3a hinge loop are crucial for the autoinhibitory release of domain 3a after the MUN domain opens the Syntaxin-1 linker region.

Altered Distribution of SNARE Proteins in Primary Neurons Exposed to Different Alpha-Synuclein Proteoforms.

Growing evidence indicates that the pathological alpha-synuclein (α-syn) aggregation in Parkinson's disease (PD) and dementia with Lewy bodies (DLB) starts at the synapses. Physiologic α-syn is involved in regulating neurotransmitter release by binding to the SNARE complex protein VAMP-2 on synaptic vesicles. However, in which way the SNARE complex formation is affected by α-syn pathology remains unclear. In this study, primary cortical neurons were exposed to either α-syn monomers or preformed fibrils (PFFs) for different time points and the effect on SNARE protein distribution was analyzed with a novel proximity ligation assay (PLA). Short-term exposure to monomers or PFFs for 24 h increased the co-localization of VAMP-2 and syntaxin-1, but reduced the co-localization of SNAP-25 and syntaxin-1, indicating a direct effect of the added α-syn on SNARE protein distribution. Long-term exposure to α-syn PFFs for 7 d reduced VAMP-2 and SNAP-25 co-localization, although there was only a modest induction of ser129 phosphorylated (pS129) α-syn. Similarly, exposure to extracellular vesicles collected from astrocytes treated with α-syn PFFs for 7 d influenced VAMP-2 and SNAP-25 co-localization despite only low levels of pS129 α-syn being formed. Taken together, our results demonstrate that different α-syn proteoforms have the potential to alter the distribution of SNARE proteins at the synapse.

Structural Mechanism of Soluble N-ethylmaleimide-Sensitive Factor Attachment Protein Receptor Complex Assembly in Lipid Bilayers Revealed by Solid-State NMR.

Synaptic vesicle fusion is mediated by soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins, including synaptobrevin-2 (Syb-2), syntaxin-1 (Syx-1), and SNAP-25. However, it remains controversial whether the formation of thoroughly contacted α-helical bundle from the SNARE motifs to the end of the transmembrane domains (TMDs) is necessary for SNARE-mediated membrane fusion. In this study, we characterized the conformation of Syb-2 in different assembly states using a combination of dipolar- and scalar-based solid-state NMR experiments in lipid bilayers. Our spectral analysis revealed a highly dynamic nature of the Syb-2 TMD with considerable α-helical contents. Chemical shift perturbation and mutational analysis indicated that the coupling between Syb-2 and Syx-1 TMDs mediated by residue Gly-100 of Syb-2 together with high mobility of the C-terminal segment of Syb-2 TMD are required for inner membrane merger. Our results provide new insights into the role of the Syb-2 TMD in driving membrane fusion, which improves the current understanding of the structural mechanism of SNARE complex assembly. This study highlights the significance of membrane environments in elucidating the mechanism of membrane proteins.

Vesicle-associated membrane protein 2 is a cargo-selective v-SNARE for a subset of GPCRs.

Vesicle fusion at the plasma membrane is critical for releasing hormones and neurotransmitters and for delivering the cognate G protein-coupled receptors (GPCRs) to the cell surface. The SNARE fusion machinery that releases neurotransmitters has been well characterized. In contrast, the fusion machinery that delivers GPCRs is still unknown. Here, using high-speed multichannel imaging to simultaneously visualize receptors and v-SNAREs in real time in individual fusion events, we identify VAMP2 as a selective v-SNARE for GPCR delivery. VAMP2 was preferentially enriched in vesicles that mediate the surface delivery of µ opioid receptor (MOR), but not other cargos, and was required selectively for MOR recycling. Interestingly, VAMP2 did not show preferential localization on MOR-containing endosomes, suggesting that v-SNAREs are copackaged with specific cargo into separate vesicles from the same endosomes. Together, our results identify VAMP2 as a cargo-selective v-SNARE and suggest that surface delivery of specific GPCRs is mediated by distinct fusion events driven by distinct SNARE complexes.

Separation of Single Core and Multicore Lytic Granules by Subcellular Fractionation and Immunoisolation.

Subcellular fractionation is an important tool used to separate intracellular organelles, structures or proteins. Here, we describe a stepwise protocol to isolate two types of lytic granules, multicore (MCG), and single core (SCG), from primary murine CTLs. We used cell disruption by nitrogen cavitation followed by separation of organelles via discontinuous sucrose density gradient centrifugation. Immunoisolation with a Synaptobrevin 2 antibody attached to magnetic beads was then used to harvest Synaptobrevin 2 positive granules for immunoblotting, mass spectrometry, electron, and light microscopy.

Citicoline ameliorates arsenic-induced hepatotoxicity and diabetes in mice by overexpression of VAMP2, PPAR-γ, As3MT, and SIRT3.

The use of arsenic in arsenic-based pesticides has been common in many countries in the past and today. There is considerable evidence linking arsenic exposure to hepatotoxicity and diabetes. Destructive phenomena such as hepatic oxidative stress and inflammation can interfere with glucose uptake and insulin function. In the present study, the antioxidant, anti-inflammatory, and molecular mechanism of citicoline against sodium arsenite-induced hepatotoxicity and glucose intolerance were investigated in mice. Citicoline improved glucose tolerance impaired by sodium arsenite. Citicoline increased the hepatic activity of catalase, superoxide dismutase, and glutathione peroxidase enzymes. Moreover, we found that citicoline prevents an increase in the levels of thiobarbituric acid reactive substances. Citicoline reduced levels of caspase 3, tumor necrosis factor-alpha, and interleukin 6 in sodium arsenite intoxicated groups. It was shown that citicoline increased the expression of arsenite methyltransferase, vesicle-associated membrane protein 2, peroxisome proliferator-activated receptor gamma, and sirtuin 3 to combat sodium arsenite toxicity. Citicoline reduced glucose intolerance, which was disrupted by sodium arsenite, by affecting the pancreatic and extra-pancreatic pathways involved in insulin production, secretion, and action. Based on our results, citicoline can be considered a modulating agent against arsenic-induced hepatotoxicity and hyperglycemia. Considering the relationship between arsenic exposure and the occurrence of side effects such as liver toxicity and diabetes, it is necessary to monitor and awareness of arsenic residues from sources such as drinking water.

Synaptic biomarkers in the cerebrospinal fluid associate differentially with classical neuronal biomarkers in patients with Alzheimer's disease and frontotemporal dementia.

BACKGROUND: Loss of synaptic functionality has been recently identified as an early-stage indicator of neurological diseases. Consequently, monitoring changes in synaptic protein levels may be relevant for observing disease evolution or treatment responses in patients. Here, we have studied the relationship between fluid biomarkers of neurodegeneration and synaptic dysfunction in patients with Alzheimer's disease (AD), frontotemporal dementia (FTD), and subjective cognitive decline (SCD). METHODS: The exploratory cohort consisted of cerebrospinal fluid (CSF) samples (n = 60) from patients diagnosed with AD (n = 20), FTD (n = 20), and SCD (n = 20) from the Amsterdam Dementia Cohort. We developed two novel immunoassays for the synaptic proteins synaptosomal-associated protein-25 (SNAP25) and vesicle-associated membrane protein-2 (VAMP2). We measured the levels of these biomarkers in CSF, in addition to neuronal pentraxin-2 (NPTX2), glutamate ionotropic receptor-4 (GluR4), and neurogranin (Ng) for this cohort. All in-house immunoassays were validated and analytically qualified prior to clinical application. CSF neurogranin (Ng) was measured using a commercially available ELISA. RESULTS: This pilot study indicated that SNAP25, VAMP2, and Ng may not be specific biomarkers for AD as their levels were significantly elevated in patients with both AD and FTD compared to SCD. Moreover, the strength of the correlations between synaptic proteins was lower in the AD and FTD clinical groups compared to SCD. SNAP25, VAMP2, and Ng correlated strongly with each other as well as with total Tau (Tau) and phosphorylated Tau (PTau) in all three clinical groups. However, this correlation was weakened or absent with NPTX2 and GluR4. None of the synaptic proteins correlated to neurofilament light (NfL) in any clinical group. CONCLUSION: The correlation of the synaptic biomarkers with CSF Tau and PTau but the lack thereof with NfL implies that distinct pathological pathways may be involved in synaptic versus axonal degeneration. Our results reflect the diversity of synaptic pathology in neurodegenerative dementias.

A synthetic organelle approach to probe SNARE-mediated membrane fusion in a bacterial host.

In vivo and in vitro assays, particularly reconstitution using artificial membranes, have established the role of synaptic soluble N-Ethylmaleimide-sensitive attachment protein receptors (SNAREs) VAMP2, Syntaxin-1A, and SNAP-25 in membrane fusion. However, using artificial membranes requires challenging protein purifications that could be avoided in a cell-based assay. Here, we developed a synthetic biological approach based on the generation of membrane cisternae by the integral membrane protein Caveolin in Escherichia coli and coexpression of SNAREs. Syntaxin-1A/SNAP-25/VAMP-2 complexes were formed and regulated by SNARE partner protein Munc-18a in the presence of Caveolin. Additionally, Syntaxin-1A/SNAP-25/VAMP-2 synthesis provoked increased length of E. coli only in the presence of Caveolin. We found that cell elongation required SNAP-25 and was inhibited by tetanus neurotoxin. This elongation was not a result of cell division arrest. Furthermore, electron and super-resolution microscopies showed that synaptic SNAREs and Caveolin coexpression led to the partial loss of the cisternae, suggesting their fusion with the plasma membrane. In summary, we propose that this assay reconstitutes membrane fusion in a simple organism with an easy-to-observe phenotype and is amenable to structure-function studies of SNAREs.

Interneuronal In Vivo Transfer of Synaptic Proteins.

Neuron-to-neuron transfer of pathogenic α-synuclein species is a mechanism of likely relevance to Parkinson's disease development. Experimentally, interneuronal α-synuclein spreading from the low brainstem toward higher brain regions can be reproduced by the administration of AAV vectors encoding for α-synuclein into the mouse vagus nerve. The aim of this study was to determine whether α-synuclein's spreading ability is shared by other proteins. Given α-synuclein synaptic localization, experiments involved intravagal injections of AAVs encoding for other synaptic proteins, ß-synuclein, VAMP2, or SNAP25. Administration of AAV-VAMP2 or AAV-SNAP25 caused robust transduction of either of the proteins in the dorsal medulla oblongata but was not followed by interneuronal VAMP2 or SNAP25 transfer and caudo-rostral spreading. In contrast, AAV-mediated ß-synuclein overexpression triggered its spreading to more frontal brain regions. The aggregate formation was investigated as a potential mechanism involved in protein spreading, and consistent with this hypothesis, results showed that overexpression of ß-synuclein, but not VAMP2 or SNAP25, in the dorsal medulla oblongata was associated with pronounced protein aggregation. Data indicate that interneuronal protein transfer is not a mere consequence of increased expression or synaptic localization. It is rather promoted by structural/functional characteristics of synuclein proteins that likely include their tendency to form aggregate species.

Immunolocalization of vesicular glutamate transporter 2 and exocytosis-related proteins in afferent nerve endings innervating taste buds in the rat incisive papilla.

The present study aimed to investigate the immunolocalization of vesicular glutamate transporter (VGLUT) 1 and 2, and proteins associated with exocytosis, i.e., core components of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor complex (synaptosomal-associated protein of 25 kDa, syntaxin 1, and vesicle-associated membrane protein 2) and synaptotagmin-1 (Syt1), in incisive papillary taste buds of rats using double-indirect immunofluorescence. No VGLUT1 immunoreactivity was observed, whereas VGLUT2-immunoreactive punctate products were closely associated with guanine nucleotide-binding protein G(t) subunit α3-immmunoreactive cells in taste buds. VGLUT2 was immunolocalized in P2X3 purinoceptor-expressing afferent nerve endings. Synaptosomal-associated protein of 25 kDa, syntaxin 1, and vesicle-associated membrane protein 2 were immunolocalized in nerve endings containing VGLUT2-immunoreactive products as well as a few cells in taste buds. VGLUT2 was co-immunolocalized in some intragemmal nerve endings immunoreactive for Syt1, a calcium sensor implicated in vesicle membrane fusion. The present results suggest that afferent nerve endings innervating incisive taste buds release glutamate by exocytosis to modulate taste cell function.

Functional and Pathological Effects of α-Synuclein on Synaptic SNARE Complexes.

α-Synuclein is an abundant protein at the neuronal synapse that has been implicated in Parkinson's disease for over 25 years and characterizes the hallmark pathology of a group of neurodegenerative diseases now known as the synucleinopathies. Physiologically, α-synuclein exists in an equilibrium between a synaptic vesicle membrane-bound α-helical multimer and a cytosolic largely unstructured monomer. Through its membrane-bound state, α-synuclein functions in neurotransmitter release by modulating several steps in the synaptic vesicle cycle, including synaptic vesicle clustering and docking, SNARE complex assembly, and homeostasis of synaptic vesicle pools. These functions have been ascribed to α-synuclein's interactions with the synaptic vesicle SNARE protein VAMP2/synaptobrevin-2, the synaptic vesicle-attached synapsins, and the synaptic vesicle membrane itself. How α-synuclein affects these processes, and whether disease is due to loss-of-function or gain-of-toxic-function of α-synuclein remains unclear. In this review, we provide an in-depth summary of the existing literature, discuss possible reasons for the discrepancies in the field, and propose a working model that reconciles the findings in the literature.

Localization of SNARE proteins in the brain and corpus allatum of Bombyx mori.

Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) make up the core machinery that mediates membrane fusion. SNAREs, syntaxin, synaptosome-associated protein (SNAP), and synaptobrevin form a tight SNARE complex that brings the vesicle and plasma membranes together and is essential for membrane fusion. The cDNAs of SNAP-25, VAMP2, and Syntaxin 1A from Bombyx mori were inserted into a plasmid, transformed into Escherichia coli, and purified. We then produced antibodies against the SNAP-25, VAMP2, and Syntaxin 1A of Bombyx mori of rabbits and rats, which were used for immunohistochemistry. Immunohistochemistry results revealed that the expression of VAMP2 was restricted to neurons in the pars intercerebralis (PI), dorsolateral protocerebrum (DL), and central complex (CX) of the brain. SNAP-25 was restricted to neurons in the PI and the CX of the brain. Syntaxin 1A was restricted to neurons in the PI and DL of the brain. VAMP2 co-localized with SNAP-25 in the CX, and with Syntaxin 1A in the PI and DL. VAMP2, SNAP-25, and Syntaxin 1A are present in the CA. Bombyxin-immunohistochemical reactivities (IRs) of brain and CA overlapped with VAMP2-, SNAP-25, and Syntaxin 1A-IRs. VAMP2 and Syntaxin 1A are present in the prothoracicotropic hormone (PTTH)-secretory neurons of the brain.

Energetics, kinetics, and pathways of SNARE assembly in membrane fusion.

Fusion of transmitter-containing vesicles with plasma membranes at the synaptic and neuromuscular junctions mediates neurotransmission and muscle contractions, respectively, thereby underlying all thoughts and actions. The fusion process is driven by the coupled folding and assembly of three synaptic SNARE proteins--syntaxin-1 and SNAP-25 on the target plasma membrane (t-SNAREs) and VAMP2 on the vesicular membrane (v-SNARE) into a four-helix bundle. Their assembly is chaperoned by Munc18-1 and many other proteins to achieve the speed and accuracy required for neurotransmission. However, the physiological pathway of SNARE assembly and its coupling to membrane fusion remains unclear. Here, we review recent progress in understanding SNARE assembly and membrane fusion, with a focus on results obtained by single-molecule manipulation approaches and electric recordings of single fusion pores. We describe two pathways of synaptic SNARE assembly, their associated intermediates, energetics, and kinetics. Assembly of the three SNAREs in vitro begins with the formation of a t-SNARE binary complex, on which VAMP2 folds in a stepwise zipper-like fashion. Munc18-1 significantly alters the SNARE assembly pathway: syntaxin-1 and VAMP2 first bind on the surface of Munc18-1 to form a template complex, with which SNAP-25 associates to conclude SNARE assembly and displace Munc18-1. During membrane fusion, multiple trans-SNARE complexes cooperate to open a dynamic fusion pore in a manner dependent upon their copy number and zippering states. Together, these results demonstrate that stepwise and cooperative SNARE assembly drive stagewise membrane fusion.

Propofol attenuates kinesin-mediated axonal vesicle transport and fusion.

Propofol is a widely used general anesthetic, yet the understanding of its cellular effects is fragmentary. General anesthetics are not as innocuous as once believed and have a wide range of molecular targets that include kinesin motors. Propofol, ketamine, and etomidate reduce the distances that Kinesin-1 KIF5 and Kinesin-2 KIF3 travel along microtubules in vitro. These transport kinesins are highly expressed in the CNS, and their dysfunction leads to a range of human pathologies including neurodevelopmental and neurodegenerative diseases. While in vitro data suggest that general anesthetics may disrupt kinesin transport in neurons, this hypothesis remains untested. Here we find that propofol treatment of hippocampal neurons decreased vesicle transport mediated by Kinesin-1 KIF5 and Kinesin-3 KIF1A ∼25-60%. Propofol treatment delayed delivery of the KIF5 cargo NgCAM to the distal axon. Because KIF1A participates in axonal transport of presynaptic vesicles, we tested whether prolonged propofol treatment affects synaptic vesicle fusion mediated by VAMP2. The data show that propofol-induced transport delay causes a significant decrease in vesicle fusion in distal axons. These results are the first to link a propofol-induced delay in neuronal trafficking to a decrease in axonal vesicle fusion, which may alter physiological function during and after anesthesia.

CNS myelination requires VAMP2/3-mediated membrane expansion in oligodendrocytes.

Myelin is required for rapid nerve signaling and is emerging as a key driver of CNS plasticity and disease. How myelin is built and remodeled remains a fundamental question of neurobiology. Central to myelination is the ability of oligodendrocytes to add vast amounts of new cell membrane, expanding their surface areas by many thousand-fold. However, how oligodendrocytes add new membrane to build or remodel myelin is not fully understood. Here, we show that CNS myelin membrane addition requires exocytosis mediated by the vesicular SNARE proteins VAMP2/3. Genetic inactivation of VAMP2/3 in myelinating oligodendrocytes caused severe hypomyelination and premature death without overt loss of oligodendrocytes. Through live imaging, we discovered that VAMP2/3-mediated exocytosis drives membrane expansion within myelin sheaths to initiate wrapping and power sheath elongation. In conjunction with membrane expansion, mass spectrometry of oligodendrocyte surface proteins revealed that VAMP2/3 incorporates axon-myelin adhesion proteins that are collectively required to form nodes of Ranvier. Together, our results demonstrate that VAMP2/3-mediated membrane expansion in oligodendrocytes is indispensable for myelin formation, uncovering a cellular pathway that could sculpt myelination patterns in response to activity-dependent signals or be therapeutically targeted to promote regeneration in disease.

Ferroportin-dependent ferroptosis induced by ellagic acid retards liver fibrosis by impairing the SNARE complexes formation.

Chronic liver injury causing liver fibrosis is a major cause of morbidity and mortality worldwide. Targeting the suppression of hepatic stellate cell (HSC) activation is recognized as an effective strategy for the treatment of liver fibrosis. Ellagic acid (EA), a natural polyphenol product isolated from fruits and vegetables, possesses many biological functions. Here, EA exerts its antifibrotic activity by inducing ferroptotic cell death of activated HSCs, which is accompanied by redox-active iron accumulation, lipid peroxidation, and GSH depletion in CCl4 mice and human LX-2 cells. The specific ferroptosis inhibitor ferrostatin-1 prevented EA-induced ferroptotic cell death. Mechanistically, EA impairs the formation of vesicle-associated membrane protein 2 (VAMP2)/syntaxin 4 and VAMP2/synaptosome-associated protein 23 complexes by suppressing VAMP2 expression by enhancing its degradation in a proteasome-dependent pathway. This leads to the impairment of ferroportin (FPN, an iron exporter) translocation and intracellular iron extrusion. Interestingly, VAMP2 overexpression inhibits the role of EA in blocking FPN translocation and increasing intracellular ferritin content (an iron storage marker). In contrast, VAMP2 knockdown shows a synergistic effect on EA-mediated ferroptotic events in both HSCs. Additionally, HSC-specific overexpression of VAMP2 impaired EA-induced HSC ferroptosis in mouse liver fibrosis, and HSC-specific VAMP2 knockdown increased the inhibitory effect of EA on fibrosis. Taken together, our data suggest that the natural product EA exerts its antifibrotic effects by inducing FPN-dependent ferroptosis of HSCs by disrupting the formation of SNARE complexes, and EA will hopefully serve as a prospective compound for liver fibrosis treatment.

Syntaxin 7 contributes to breast cancer cell invasion by promoting invadopodia formation.

Invasion in various cancer cells requires coordinated delivery of signaling proteins, adhesion proteins, actin-remodeling proteins and proteases to matrix-degrading structures called invadopodia. Vesicular trafficking involving SNAREs plays a crucial role in the delivery of cargo to the target membrane. Screening of 13 SNAREs from the endocytic and recycling route using a gene silencing approach coupled with functional assays identified syntaxin 7 (STX7) as an important player in MDA-MB-231 cell invasion. Total internal reflection fluorescence microscopy (TIRF-M) studies revealed that STX7 resides near invadopodia and co-traffics with MT1-MMP (also known as MMP14), indicating a possible role for this SNARE in protease trafficking. STX7 depletion reduced the number of invadopodia and their associated degradative activity. Immunoprecipitation studies revealed that STX7 forms distinct SNARE complexes with VAMP2, VAMP3, VAMP7, STX4 and SNAP23. Depletion of VAMP2, VAMP3 or STX4 abrogated invadopodia formation, phenocopying what was seen upon lack of STX7. Whereas depletion of STX4 reduced MT1-MMP level at the cell surfaces, STX7 silencing significantly reduced the invadopodia-associated MT1-MMP pool and increased the non-invadosomal pool. This study highlights STX7 as a major contributor towards the invadopodia formation during cancer cell invasion. This article has an associated First Person interview with the first author of the paper.

circ_CSNK1E modulates airway smooth muscle cells proliferation and migration via miR-34a-5p/VAMP2 axis in asthma.

BACKGROUND: Excessive proliferation and migration of airway smooth muscle cells (ASMCs) directly lead to airway remodeling in asthma. However, the role of circular RNAs (circRNAs) in airway remodeling remains unclear. This study aimed to investigate the regulatory role and mechanism of circ_CSNK1E in ASMCs proliferation and migration. METHODS: In this study, RNA-sequencing was used to analyze cicRNAs expression in asthma samples. ASMCs were treated with 25 ng/ml PDGF-BB to establish a model of asthma in vitro. Then, we used RT-qPCR to assess circRNAs, microRNAs (miRNAs) and messenger RNAs (mRNAs) expression. Besides, CCK-8, colony formation, wound healing and transwell chamber assays were carried out to explore cell proliferation and migration. Subcellular localization assay was used to detect the location of circRNA. Next, bioinformatics, luciferase reporter and RIP assays were performed to evaluate the relationship among circ_CSNK1E, miRNA-34a-5p and VAMP2. RESULTS: circ_CSNK1E expression was found to be significantly up-regulated in asthma samples and PDGF-BB-induced ASMCs. Functional experiments revealed that inhibition of circRNA_CSNK1E suppressed proliferation and migration of ASMCs stimulated by PDGF-BB. Next, we found that circRNA_CSNK1E served as a sponge for miR-34a-5p in ASMCs, and miR-34a-5p mimic suppressed proliferation and migration of ASMCs. Moreover, VAMP2 was confirmed as a direct target of miR-34a-5p. At last, inhibition of circRNA_CSNK1E suppressed proliferation and migration of ASMCs stimulated by PDGF-BB through miR-34a-5p/VAMP2 axis. CONCLUSION: Collectively, these findings clarified the importance of circ_CSNK1E/miRNA-34a-5p/VAMP2 axis for the proliferation and migration of ASMCs. These indicated that inhibition of circ_CSNK1E might be a potential target for the treatment of airway remodeling in asthma.