RESUMEN

Synaptotagmin-1 is a synaptic vesicle transmembrane protein that senses calcium influx via its tandem C2-domains, triggering synchronous neurotransmitter release. Disruption to SYT1 is associated with neurodevelopmental disorders, highlighting the importance of identifying high-quality research reagents to enhance understanding of Synaptotagmin-1 in health and disease. Here we have characterized thirteen Synaptotagmin-1 commercial antibodies for western blot, immunoprecipitation, immunofluorescence and flow cytometry using a standardized experimental protocol based on comparing read-outs in knockout cell lines and isogenic parental controls. These studies are part of a larger, collaborative initiative seeking to address antibody reproducibility issues by characterizing commercially available antibodies for human proteins and publishing the results openly as a resource for the scientific community. While use of antibodies and protocols vary between laboratories, we encourage readers to use this report as a guide to select the most appropriate antibodies for their specific needs.

Asunto(s)

Anticuerpos , Western Blotting , Citometría de Flujo , Técnica del Anticuerpo Fluorescente , Inmunoprecipitación , Sinaptotagmina I , Sinaptotagmina I/inmunología , Sinaptotagmina I/metabolismo , Humanos , Citometría de Flujo/métodos , Inmunoprecipitación/métodos , Técnica del Anticuerpo Fluorescente/métodos , Anticuerpos/inmunología

RESUMEN

Synaptotagmin-1 (Syt1) is a calcium sensor that regulates synaptic vesicle fusion in synchronous neurotransmitter release. Syt1 interacts with negatively charged lipids and the SNARE complex to control the fusion event. However, it remains incompletely understood how Syt1 mediates Ca2+-trigged synaptic vesicle fusion. Here, we discovered that Syt1 undergoes liquid-liquid phase separation (LLPS) to form condensates both in vitro and in living cells. Syt1 condensates play a role in vesicle attachment to the PM and efficiently recruit SNAREs and complexin, which may facilitate the downstream synaptic vesicle fusion. We observed that Syt1 condensates undergo a liquid-to-gel-like phase transition, reflecting the formation of Syt1 oligomers. The phase transition can be blocked or reversed by Ca2+, confirming the essential role of Ca2+ in Syt1 oligomer disassembly. Finally, we showed that the Syt1 mutations causing Syt1-associated neurodevelopmental disorder impair the Ca2+-driven phase transition. These findings reveal that Syt1 undergoes LLPS and a Ca2+-sensitive phase transition, providing new insights into Syt1-mediated vesicle fusion.

Asunto(s)

Calcio , Vesículas Sinápticas , Sinaptotagmina I , Sinaptotagmina I/metabolismo , Sinaptotagmina I/genética , Calcio/metabolismo , Humanos , Animales , Vesículas Sinápticas/metabolismo , Multimerización de Proteína , Proteínas SNARE/metabolismo , Proteínas SNARE/genética , Transición de Fase , Mutación/genética , Células HEK293 , Fusión de Membrana , Proteínas Adaptadoras del Transporte Vesicular/metabolismo , Proteínas Adaptadoras del Transporte Vesicular/genética , Separación de Fases

RESUMEN

Acute kidney injury (AKI) is common and an independent risk factor for mortality in patients with paraquat (PQ) poisoning. Currently, no specific antidote is available. Synaptotagmin-1 (SYT1) has been identified as a key protein that facilitates PQ efflux in PQ-resistant A549 cells, thereby preventing PQ-induced lung injury. However, the protective effect of STY1 on PQ-induced AKI remains to be elucidated. This study exposed human kidney 2 (HK-2) cells overexpressing SYT1 to PQ. These cells exhibited significantly lower levels of growth inhibition, reactive oxygen species production, early apoptosis, and PQ accumulation compared to the parent HK-2 cells. Transcriptomic screening and Western blot analysis revealed that SYT1 overexpression significantly promoted the expression of glucose transporter 2 (GLUT2). Inhibition of GLUT2 completely abolished the protective effects of SYT1 overexpression in HK-2 cells and restored intracellular PQ concentrations. Further immunoprecipitation-shotgun and RNA interference experiments revealed that SYT1 binds to and stabilizes the protein SERPINE1 mRNA-binding protein 1 (SERBP1), enhancing the stability of GLUT2 mRNA and its protein levels. In summary, SYT1 antagonizes PQ intracellular accumulation and prevents nephrocyte toxicity by up-regulating SERBP1/GLUT2 expression. This study identifies a potential target for the treatment of PQ-induced AKI.

Asunto(s)

Transportador de Glucosa de Tipo 2 , Paraquat , Sinaptotagmina I , Regulación hacia Arriba , Humanos , Paraquat/toxicidad , Sinaptotagmina I/metabolismo , Sinaptotagmina I/genética , Regulación hacia Arriba/efectos de los fármacos , Línea Celular , Transportador de Glucosa de Tipo 2/metabolismo , Transportador de Glucosa de Tipo 2/genética , Proteínas de Unión al ARN/metabolismo , Proteínas de Unión al ARN/genética , Apoptosis/efectos de los fármacos , Especies Reactivas de Oxígeno/metabolismo , Lesión Renal Aguda/metabolismo , Lesión Renal Aguda/inducido químicamente , Lesión Renal Aguda/patología

RESUMEN

We previously reported the presence of P2X3 purinoceptors (P2X3)-expressing subserosal afferent nerve endings consisting of net- and basket-like nerve endings in the rat gastric antrum. These nerve endings may morphologically be vagal mechanoreceptors activated by antral peristalsis. The present study investigated immunoreactivities for vesicular glutamate transporter (VGLUT) 1 and VGLUT2 as well as exocytosis-related proteins, i.e., core components of the SNARE complex (SNAP25, Stx1, and VAMP2) and synaptotagmin-1 (Syt1), in whole-mount preparations of the rat gastric antrum using double immunofluorescence. VGLUT1 immunoreactivity was not detected, whereas VGLUT2 immunoreactivity was observed in P2X3-immunoreactive subserosal nerve endings composed of both net- and basket-like endings. In net-like nerve endings, intense VGLUT2 immunoreactivity was localized in polygonal bulges of reticular nerve fibers and peripheral axon terminals. Furthermore, intense immunoreactivities for SNAP25, Stx1, and VAMP2 were localized in net-like nerve endings. Intense immunoreactivities for VAMP2 and Syt1 were observed in VGLUT2-immunoreactive net-like nerve endings. In basket-like nerve endings, VGLUT2 immunoreactivity was localized in pleomorphic terminal structures and small bulges surrounding the subserosal ganglion, whereas immunoreactivities for SNAP25, Stx1, and VAMP2 were weak in these nerve endings. VGLUT2-immunoreactive basket-like nerve endings were weakly immunoreactive for VAMP2 and Syt1. These results suggest that subserosal afferent nerve endings release glutamate by exocytosis mainly from net-like nerve endings to modulate their mechanoreceptor function.

Asunto(s)

Exocitosis , Ácido Glutámico , Terminaciones Nerviosas , Antro Pilórico , Receptores Purinérgicos P2X3 , Proteína 2 de Transporte Vesicular de Glutamato , Animales , Masculino , Ratas , Ácido Glutámico/metabolismo , Inmunohistoquímica , Terminaciones Nerviosas/metabolismo , Antro Pilórico/inervación , Antro Pilórico/metabolismo , Ratas Wistar , Receptores Purinérgicos P2X3/metabolismo , Proteína 25 Asociada a Sinaptosomas/metabolismo , Sinaptotagmina I/metabolismo , Sintaxina 1/metabolismo , Proteína 2 de Membrana Asociada a Vesículas/metabolismo , Proteína 1 de Transporte Vesicular de Glutamato/metabolismo , Proteína 2 de Transporte Vesicular de Glutamato/metabolismo

RESUMEN

We examined the role of protein tyrosine phosphatase receptor sigma (PTPRS) in the context of Alzheimer's disease and synaptic integrity. Publicly available datasets (BRAINEAC, ROSMAP, ADC1) and a cohort of asymptomatic but "at risk" individuals (PREVENT-AD) were used to explore the relationship between PTPRS and various Alzheimer's disease biomarkers. We identified that PTPRS rs10415488 variant C shows features of neuroprotection against early Tau pathology and synaptic degeneration in Alzheimer's disease. This single nucleotide polymorphism correlated with higher PTPRS transcript abundance and lower p(181)Tau and GAP-43 levels in the CSF. In the brain, PTPRS protein abundance was significantly correlated with the quantity of two markers of synaptic integrity: SNAP25 and SYT-1. We also found the presence of sexual dimorphism for PTPRS, with higher CSF concentrations in males than females. Male carriers for variant C were found to have a 10-month delay in the onset of AD. We thus conclude that PTPRS acts as a neuroprotective receptor in Alzheimer's disease. Its protective effect is most important in males, in whom it postpones the age of onset of the disease.

Asunto(s)

Enfermedad de Alzheimer , Biomarcadores , Polimorfismo de Nucleótido Simple , Sinapsis , Proteínas tau , Anciano , Anciano de 80 o más Años , Femenino , Humanos , Masculino , Persona de Mediana Edad , Enfermedad de Alzheimer/líquido cefalorraquídeo , Enfermedad de Alzheimer/patología , Enfermedad de Alzheimer/genética , Enfermedad de Alzheimer/metabolismo , Biomarcadores/líquido cefalorraquídeo , Encéfalo/metabolismo , Encéfalo/patología , Proteínas Tirosina Fosfatasas Clase 2 Similares a Receptores/genética , Proteínas Tirosina Fosfatasas Clase 2 Similares a Receptores/metabolismo , Sinapsis/metabolismo , Sinapsis/patología , Proteína 25 Asociada a Sinaptosomas/metabolismo , Proteína 25 Asociada a Sinaptosomas/genética , Proteína 25 Asociada a Sinaptosomas/líquido cefalorraquídeo , Sinaptotagmina I/metabolismo , Sinaptotagmina I/genética , Proteínas tau/líquido cefalorraquídeo , Proteínas tau/metabolismo

RESUMEN

Migrasomes, organelles crucial for cell communication, undergo distinct stages of nucleation, maturation, and expansion. The regulatory mechanisms of migrasome formation, particularly through biological cues, remain largely unexplored. This study reveals that calcium is essential for migrasome formation. Furthermore, we identify that Synaptotagmin-1 (Syt1), a well-known calcium sensor, is not only enriched in migrasomes but also indispensable for their formation. The calcium-binding ability of Syt1 is key to initiating migrasome formation. The recruitment of Syt1 to migrasome formation sites (MFS) triggers the swelling of MFS into unstable precursors, which are subsequently stabilized through the sequential recruitment of tetraspanins. Our findings reveal how calcium regulates migrasome formation and propose a sequential interaction model involving Syt1 and Tetraspanins in the formation and stabilization of migrasomes.

Asunto(s)

Calcio , Vesículas Extracelulares , Sinaptotagmina I , Animales , Humanos , Calcio/metabolismo , Señalización del Calcio , Comunicación Celular , Orgánulos/metabolismo , Sinaptotagmina I/metabolismo , Sinaptotagmina I/genética , Tetraspaninas/metabolismo , Tetraspaninas/genética , Vesículas Extracelulares/metabolismo , Ratones , Línea Celular , Células Madre Embrionarias/citología , Células Madre Embrionarias/metabolismo

RESUMEN

Synaptotagmin-1 (Syt-1) is a calcium sensing protein that is resident in synaptic vesicles. It is well established that Syt-1 is essential for fast and synchronous neurotransmitter release. However, the role of Ca2+ and phospholipid binding in the function of Syt-1, and ultimately in neurotransmitter release, is unclear. Here, we investigate the binding of Ca2+ to Syt-1, first in the absence of lipids, using native mass spectrometry to evaluate individual binding affinities. Syt-1 binds to one Ca2+ with a KD ∼ 45 µM. Each subsequent binding affinity (n ≥ 2) is successively unfavorable. Given that Syt-1 has been reported to bind anionic phospholipids to modulate the Ca2+ binding affinity, we explored the extent that Ca2+ binding was mediated by selected anionic phospholipid binding. We found that phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) and dioleoylphosphatidylserine (DOPS) positively modulated Ca2+ binding. However, the extent of Syt-1 binding to phosphatidylinositol 3,5-bisphosphate (PI(3,5)P2) was reduced with increasing [Ca2+]. Overall, we find that specific lipids differentially modulate Ca2+ binding. Given that these lipids are enriched in different subcellular compartments and therefore may interact with Syt-1 at different stages of the synaptic vesicle cycle, we propose a regulatory mechanism involving Syt-1, Ca2+, and anionic phospholipids that may also control some aspects of vesicular exocytosis.

Asunto(s)

Calcio , Fosfolípidos , Sinaptotagmina I , Calcio/metabolismo , Exocitosis/fisiología , Neurotransmisores/metabolismo , Fosfolípidos/metabolismo , Transmisión Sináptica/fisiología , Vesículas Sinápticas/metabolismo , Sinaptotagmina I/metabolismo , Animales , Ratas

RESUMEN

Despite decades of intense study, the molecular basis of asynchronous neurotransmitter release remains enigmatic. Synaptotagmin (syt) 7 and Doc2 have both been proposed as Ca2+ sensors that trigger this mode of exocytosis, but conflicting findings have led to controversy. Here, we demonstrate that at excitatory mouse hippocampal synapses, Doc2α is the major Ca2+ sensor for asynchronous release, while syt7 supports this process through activity-dependent docking of synaptic vesicles. In synapses lacking Doc2α, asynchronous release after single action potentials is strongly reduced, while deleting syt7 has no effect. However, in the absence of syt7, docked vesicles cannot be replenished on millisecond timescales. Consequently, both synchronous and asynchronous release depress from the second pulse onward during repetitive activity. By contrast, synapses lacking Doc2α have normal activity-dependent docking, but continue to exhibit decreased asynchronous release after multiple stimuli. Moreover, disruption of both Ca2+ sensors is non-additive. These findings result in a new model whereby syt7 drives activity-dependent docking, thus providing synaptic vesicles for synchronous (syt1) and asynchronous (Doc2 and other unidentified sensors) release during ongoing transmission.

Asunto(s)

Sinapsis , Vesículas Sinápticas , Sinaptotagminas , Animales , Ratones , Potenciales de Acción , Calcio/metabolismo , Exocitosis , Neurotransmisores , Sinapsis/metabolismo , Transmisión Sináptica , Vesículas Sinápticas/metabolismo , Sinaptotagmina I/metabolismo , Sinaptotagminas/metabolismo , Proteínas de Unión al Calcio/metabolismo , Proteínas del Tejido Nervioso/metabolismo

RESUMEN

Synaptotagmin-1 (Syt1) is a presynaptic calcium sensor with two calcium binding domains, C2A and C2B, that triggers action potential-induced synchronous neurotransmitter release, while suppressing asynchronous and spontaneous release. We identified a de novo missense mutation (P401L) in the C2B domain in a patient with developmental delay and autistic symptoms. Expressing the orthologous mouse mutant (P400L) in cultured Syt1 null mutant neurons revealed a reduction in dendrite outgrowth with a proportional reduction in synapses. This was not observed in single Syt1PL-rescued neurons that received normal synaptic input when cultured in a control network. Patch-clamp recordings showed that spontaneous miniature release events per synapse were increased more than 500% in Syt1PL-rescued neurons, even beyond the increased rates in Syt1 KO neurons. Furthermore, action potential-induced asynchronous release was increased more than 100%, while synchronous release was unaffected. A similar shift to more asynchronous release was observed during train stimulations. These cellular phenotypes were also observed when Syt1PL was overexpressed in wild type neurons. Our findings show that Syt1PL desynchronizes neurotransmission by increasing the readily releasable pool for asynchronous release and reducing the suppression of spontaneous and asynchronous release. Neurons respond to this by shortening their dendrites, possibly to counteract the increased synaptic input. Syt1PL acts in a dominant-negative manner supporting a causative role for the mutation in the heterozygous patient. We propose that the substitution of a rigid proline to a more flexible leucine at the bottom of the C2B domain impairs clamping of release by interfering with Syt1's primary interface with the SNARE complex. This is a novel cellular phenotype, distinct from what was previously found for other SYT1 disease variants, and points to a role for spontaneous and asynchronous release in SYT1-associated neurodevelopmental disorder.

Asunto(s)

Mutación Missense , Trastornos del Neurodesarrollo , Neuronas , Neurotransmisores , Transmisión Sináptica , Sinaptotagmina I , Sinaptotagmina I/metabolismo , Sinaptotagmina I/genética , Humanos , Animales , Ratones , Transmisión Sináptica/fisiología , Trastornos del Neurodesarrollo/genética , Trastornos del Neurodesarrollo/metabolismo , Neuronas/metabolismo , Neurotransmisores/metabolismo , Sinapsis/metabolismo , Potenciales de Acción/fisiología , Masculino , Ratones Noqueados , Femenino , Técnicas de Placa-Clamp/métodos

RESUMEN

Synaptic dysfunction is a core component of the pathophysiology of schizophrenia. However, the genetic risk factors and molecular mechanisms related to synaptic dysfunction are still not fully understood. The Stonin 2 (STON2) gene encodes a major adaptor for clathrin-mediated endocytosis (CME) of synaptic vesicles. In this study, we showed that the C-C (307Pro-851Ala) haplotype of STON2 increases the susceptibility to schizophrenia and examined whether STON2 variations cause schizophrenia-like behaviors through the regulation of CME. We found that schizophrenia-related STON2 variations led to protein dephosphorylation, which affected its interaction with synaptotagmin 1 (Syt1), a calcium sensor protein located in the presynaptic membrane that is critical for CME. STON2307Pro851Ala knockin mice exhibited deficits in synaptic transmission, short-term plasticity, and schizophrenia-like behaviors. Moreover, among seven antipsychotic drugs, patients with the C-C (307Pro-851Ala) haplotype responded better to haloperidol than did the T-A (307Ser-851Ser) carriers. The recovery of deficits in Syt1 sorting and synaptic transmission by acute administration of haloperidol effectively improved schizophrenia-like behaviors in STON2307Pro851Ala knockin mice. Our findings demonstrated the effect of schizophrenia-related STON2 variations on synaptic dysfunction through the regulation of CME, which might be attractive therapeutic targets for treating schizophrenia-like phenotypes.

Asunto(s)

Esquizofrenia , Transmisión Sináptica , Sinaptotagmina I , Animales , Femenino , Humanos , Masculino , Ratones , Antipsicóticos/farmacología , Antipsicóticos/uso terapéutico , Endocitosis/efectos de los fármacos , Técnicas de Sustitución del Gen , Predisposición Genética a la Enfermedad , Haloperidol/farmacología , Haplotipos , Fosforilación , Transporte de Proteínas , Esquizofrenia/metabolismo , Esquizofrenia/genética , Sinapsis/metabolismo , Sinapsis/efectos de los fármacos , Transmisión Sináptica/efectos de los fármacos , Vesículas Sinápticas/metabolismo , Sinaptotagmina I/metabolismo , Sinaptotagmina I/genética

RESUMEN

Synaptotagmin (syt) 1, a Ca2+ sensor for synaptic vesicle exocytosis, functions in vivo as a multimer. Syt1 senses Ca2+ via tandem C2-domains that are connected to a single transmembrane domain via a juxtamembrane linker. Here, we show that this linker segment harbors a lysine-rich, intrinsically disordered region that is necessary and sufficient to mediate liquid-liquid phase separation (LLPS). Interestingly, condensate formation negatively regulates the Ca2+-sensitivity of syt1. Moreover, Ca2+ and anionic phospholipids facilitate the observed phase separation, and increases in [Ca2+]i promote the fusion of syt1 droplets in living cells. Together, these observations suggest a condensate-mediated feedback loop that serves to fine-tune the ability of syt1 to trigger release, via alterations in Ca2+ binding activity and potentially through the impact of LLPS on membrane curvature during fusion reactions. In summary, the juxtamembrane linker of syt1 emerges as a regulator of syt1 function by driving self-association via LLPS.

Asunto(s)

Vesículas Sinápticas , Sinaptotagmina I , Sinaptotagmina I/metabolismo , Vesículas Sinápticas/metabolismo , Separación de Fases , Membrana Celular/metabolismo , Transmisión Sináptica , Calcio/metabolismo

RESUMEN

Protein structure prediction has emerged as a core technology for understanding biomolecules and their interactions. Here, we combine homology-based structure prediction with molecular phylogenetic analysis to study the evolution of electrostatic membrane binding among the vertebrate synaptotagmin-like protein (Slp) family. Slp family proteins play key roles in the membrane trafficking of large dense-core secretory vesicles. Our previous experimental and computational study found that the C2A domain of Slp-4 (also called granuphilin) binds with high affinity to anionic phospholipids in the cytoplasmic leaflet of the plasma membrane through a large positively charged protein surface centered on a cluster of phosphoinositide-binding lysine residues. Because this surface contributes greatly to Slp-4 C2A domain membrane binding, we hypothesized that the net charge on the surface might be evolutionarily conserved. To test this hypothesis, the known C2A sequences of Slp-4 among vertebrates were organized by class (from mammalia to pisces) using molecular phylogenetic analysis. Consensus sequences for each class were then identified and used to generate homology structures, from which Poisson-Boltzmann electrostatic potentials were calculated. For comparison, homology structures and electrostatic potentials were also calculated for the five human Slp protein family members. The results demonstrate that the charge on the membrane-binding surface is highly conserved throughout the evolution of Slp-4, and more highly conserved than many individual residues among the human Slp family paralogs. Such molecular phylogenetic-driven computational analysis can help to describe the evolution of electrostatic interactions between proteins and membranes which are crucial for their function.

Asunto(s)

Proteínas de Unión al Calcio , Glicoproteínas de Membrana , Animales , Humanos , Filogenia , Proteínas de Unión al Calcio/metabolismo , Electricidad Estática , Glicoproteínas de Membrana/química , Sinaptotagmina I/metabolismo , Secuencia de Aminoácidos , Proteínas del Tejido Nervioso/química , Estructura Terciaria de Proteína , Calcio/metabolismo

RESUMEN

Insulin secretion depends on the Ca2+-regulated fusion of granules with the plasma membrane. A recent model of Ca2+-triggered exocytosis in secretory cells proposes that lipids in the plasma membrane couple the calcium sensor Syt1 to the membrane fusion machinery (Kiessling et al., 2018). Specifically, Ca2+-mediated binding of Syt1's C2 domains to the cell membrane shifts the membrane-anchored SNARE syntaxin-1a to a more fusogenic conformation, straightening its juxtamembrane linker. To test this model in live cells and extend it to insulin secretion, we enriched INS1 cells with a panel of lipids with different acyl chain compositions. Fluorescence lifetime measurements demonstrate that cells with more disordered membranes show an increase in fusion efficiency, and vice versa. Experiments with granules purified from INS1 cells and recombinant SNARE proteins reconstituted in supported membranes confirmed that lipid acyl chain composition determines SNARE conformation and that lipid disordering correlates with increased fusion. Addition of Syt1's C2AB domains significantly decreased lipid order in target membranes and increased SNARE-mediated fusion probability. Strikingly, Syt's action on both fusion and lipid order could be partially bypassed by artificially increasing unsaturated phosphatidylserines in the target membrane. Thus, plasma membrane lipids actively participate in coupling Ca2+/synaptotagmin-sensing to the SNARE fusion machinery in cells.

Asunto(s)

Células Secretoras de Insulina , Fusión de Membrana , Lípidos de la Membrana/metabolismo , Proteínas SNARE/metabolismo , Células Secretoras de Insulina/metabolismo , Membrana Celular/metabolismo , Sinaptotagmina I/química , Sinaptotagmina I/metabolismo , Exocitosis , Proteínas Recombinantes/metabolismo , Calcio/metabolismo

RESUMEN

Synaptotagmin-1 and synaptotagmin-7 are two prominent calcium sensors that regulate exocytosis in neuronal and neuroendocrine cells. Upon binding calcium, both proteins partially penetrate lipid bilayers that bear anionic phospholipids, but the specific underlying mechanisms that enable them to trigger exocytosis remain controversial. Here, we examine the biophysical properties of these two synaptotagmin isoforms and compare their interactions with phospholipid membranes. We discover that synaptotagmin-1-membrane interactions are greatly influenced by membrane order; tight packing of phosphatidylserine inhibits binding due to impaired membrane penetration. In contrast, synaptotagmin-7 exhibits robust membrane binding and penetration activity regardless of phospholipid acyl chain structure. Thus, synaptotagmin-7 is a super-penetrator. We exploit these observations to specifically isolate and examine the role of membrane penetration in synaptotagmin function. Using nanodisc-black lipid membrane electrophysiology, we demonstrate that membrane penetration is a critical component that underlies how synaptotagmin proteins regulate reconstituted, exocytic fusion pores in response to calcium.

Asunto(s)

Calcio , Sinaptotagmina I , Sinaptotagminas/metabolismo , Calcio/metabolismo , Sinaptotagmina I/metabolismo , Exocitosis/fisiología , Membrana Celular/metabolismo , Proteínas de Unión al Calcio/metabolismo , Fosfolípidos/metabolismo

RESUMEN

MicroRNAs (miRNAs) are important post-transcriptional factors involved in the regulation of gene expression and play crucial roles in biological processes related to milk fat metabolism. Our previous study revealed that miR-19a expression was significantly higher in the mammary epithelial cells of high-milk fat cows than in those of low-milk fat cows. However, the precise molecular mechanisms underlying these differences remain unclear. In this study, we found a high expression of miR-19a in the mammary tissues of dairy cows. The regulatory effects of miR-19a on bovine mammary epithelial cells (BMECs) were analyzed using cell counting kit-8 and 5-ethynyl-2'-deoxyuridine assays, which demonstrated that miR-19a significantly inhibited BMEC proliferation. Transfection of the miR-19a mimic into BMECs significantly upregulated the expression of milk fat marker genes LPL, SCAP, and SREBP1, promoting triglyceride (TG) synthesis and lipid droplet formation, whereas the miR-19a inhibitor exhibited the opposite function. TargetScan and miRWalk predictions revealed that synaptotagmin 1 (SYT1) is a target gene of miR-19a. A dual luciferase reporter gene assay, RT-qPCR, and western blot analyses revealed that miR-19a directly targets the 3'-untranslated region (UTR) of SYT1 and negatively regulates SYT1 expression. Functional validation revealed that overexpression of SYT1 in BMECs significantly downregulated the expression of LPL, SCAP, and SREBP1, and inhibited TG synthesis and lipid droplet formation. Conversely, the knockdown of SYT1 had the opposite effect. Altogether, miR-19a plays a crucial role in regulating the proliferation and differentiation of BMECs and regulates biological processes related to TG synthesis and lipid droplet formation by suppressing SYT1 expression. These findings provide a strong foundation for further research on the functional mechanisms underlying milk fat metabolism in dairy cows.

Asunto(s)

MicroARNs , Leche , Femenino , Bovinos , Animales , Leche/metabolismo , Sinaptotagmina I/genética , Sinaptotagmina I/metabolismo , Triglicéridos/metabolismo , Glándulas Mamarias Animales/metabolismo , MicroARNs/genética , MicroARNs/metabolismo , Células Epiteliales/metabolismo , Regiones no Traducidas 3'/genética

RESUMEN

Exocytosis and endocytosis are essential physiological processes and are of prime importance for brain function. Neurotransmission depends on the Ca2+-triggered exocytosis of synaptic vesicles (SVs). In neurons, exocytosis is spatiotemporally coupled to the retrieval of an equal amount of membrane and SV proteins by compensatory endocytosis. How exocytosis and endocytosis are balanced to maintain presynaptic membrane homeostasis and, thereby, sustain brain function is essentially unknown. We combine mouse genetics with optical imaging to show that the SV calcium sensor Synaptotagmin 1 couples exocytic SV fusion to the endocytic retrieval of SV membranes by promoting the local activity-dependent formation of the signaling lipid phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) at presynaptic sites. Interference with these mechanisms impairs PI(4,5)P2-triggered SV membrane retrieval but not exocytic SV fusion. Our findings demonstrate that the coupling of SV exocytosis and endocytosis involves local Synaptotagmin 1-induced lipid signaling to maintain presynaptic membrane homeostasis in central nervous system neurons.

Asunto(s)

Vesículas Sinápticas , Sinaptotagmina I , Animales , Ratones , Endocitosis/fisiología , Exocitosis/fisiología , Lípidos , Transmisión Sináptica , Vesículas Sinápticas/metabolismo , Sinaptotagmina I/genética , Sinaptotagmina I/metabolismo

RESUMEN

Caspase-11 (Casp-11) is known to induce pyroptosis and defends against cytosol-invading bacterial pathogens, but its regulation remains poorly defined. Here, we identified extended synaptotagmin 1 (E-Syt1), an endoplasmic reticulum protein, as a key regulator of Casp-11 oligomerization and activation. Macrophages lacking E-Syt1 exhibited reduced production of interleukin-1ß (IL-1ß) and impaired pyroptosis upon cytosolic lipopolysaccharide (LPS) delivery and cytosol-invasive bacterial infection. Moreover, cleavage of Casp-11 and its downstream substrate gasdermin D were significantly diminished in ESyt1-/- macrophages. Upon LPS stimulation, E-Syt1 underwent oligomerization and bound to the p30 domain of Casp-11 via its synaptotagmin-like mitochondrial lipid-binding protein (SMP) domain. E-Syt1 oligomerization and its interaction with Casp-11 facilitated Casp-11 oligomerization and activation. Notably, ESyt1-/- mice were susceptible to infection by cytosol-invading bacteria Burkholderia thailandensis while being resistant to LPS-induced endotoxemia. These findings collectively suggest that E-Syt1 may serve as a platform for Casp-11 oligomerization and activation upon cytosolic LPS sensing.

Asunto(s)

Caspasas , Lipopolisacáridos , Animales , Ratones , Caspasa 1/metabolismo , Caspasas/metabolismo , Citosol/metabolismo , Inflamasomas/metabolismo , Lipopolisacáridos/farmacología , Lipopolisacáridos/metabolismo , Macrófagos/metabolismo , Sinaptotagmina I/metabolismo

RESUMEN

Extended-synaptotagmin 1 (E-Syt1) is an endoplasmic reticulum membrane protein that is involved in cellular lipid transport. Our previous study identified E-Syt1 as a key factor for the unconventional protein secretion of cytoplasmic proteins in liver cancer, such as protein kinase C delta (PKCδ); however, it is unclear whether E-Syt1 is involved in tumorigenesis. Here, we showed that E-Syt1 contributes to the tumorigenic potential of liver cancer cells. E-Syt1 depletion significantly suppressed the proliferation of liver cancer cell lines. Database analysis revealed that E-Syt1 expression is a prognostic factor for hepatocellular carcinoma (HCC). Immunoblot analysis and cell-based extracellular HiBiT assays showed that E-Syt1 was required for the unconventional secretion of PKCδ in liver cancer cells. Furthermore, deficiency of E-Syt1 suppressed the activation of insulin-like growth factor 1 receptor (IGF1R) and extracellular-signal-related kinase 1/2 (Erk1/2), both of which are signaling pathways mediated by extracellular PKCδ. Three-dimensional sphere formation and xenograft model analysis revealed that E-Syt1 knockout significantly decreased tumorigenesis in liver cancer cells. These results provide evidence that E-Syt1 is critical for oncogenesis and is a therapeutic target for liver cancer.

Asunto(s)

Carcinoma Hepatocelular , Neoplasias Hepáticas , Humanos , Sinaptotagmina I/metabolismo , Carcinoma Hepatocelular/genética , Neoplasias Hepáticas/genética , Línea Celular , Carcinogénesis

RESUMEN

Synaptotagmin 9 (SYT9) is a tandem C2 domain Ca2+ sensor for exocytosis in neuroendocrine cells; its function in neurons remains unclear. Here, we show that, in mixed-sex cultures, SYT9 does not trigger rapid synaptic vesicle exocytosis in mouse cortical, hippocampal, or striatal neurons, unless it is massively overexpressed. In striatal neurons, loss of SYT9 reduced the frequency of spontaneous neurotransmitter release events (minis). We delved into the underlying mechanism and discovered that SYT9 was localized to dense-core vesicles that contain substance P (SP). Loss of SYT9 impaired SP release, causing the observed decrease in mini frequency. This model is further supported by loss of function mutants. Namely, Ca2+ binding to the C2A domain of SYT9 triggered membrane fusion in vitro, and mutations that disrupted this activity abolished the ability of SYT9 to regulate both SP release and mini frequency. We conclude that SYT9 indirectly regulates synaptic transmission in striatal neurons by controlling SP release.SIGNIFICANCE STATEMENT Synaptotagmin 9 (SYT9) has been described as a Ca2+ sensor for dense-core vesicle (DCV) exocytosis in neuroendocrine cells, but its role in neurons remains unclear, despite widespread expression in the brain. This article examines the role of SYT9 in synaptic transmission across cultured cortical, hippocampal, and striatal neuronal preparations. We found that SYT9 regulates spontaneous neurotransmitter release in striatal neurons by serving as a Ca2+ sensor for the release of the neuromodulator substance P from DCVs. This demonstrates a novel role for SYT9 in neurons and uncovers a new field of study into neuromodulation by SYT9, a protein that is widely expressed in the brain.

Asunto(s)

Sustancia P , Vesículas Sinápticas , Animales , Ratones , Sinaptotagminas/metabolismo , Sustancia P/metabolismo , Vesículas Sinápticas/metabolismo , Transmisión Sináptica/fisiología , Neuronas/metabolismo , Exocitosis , Neurotransmisores/metabolismo , Sinaptotagmina I/metabolismo , Calcio/metabolismo

RESUMEN

The integrity of ER-mitochondria appositions ensures transfer of ions and phospholipids (PLs) between these organelles and exerts crucial effects on mitochondrial bioenergetics. Malfunctions within the ER-mitochondria contacts altering lipid trafficking homeostasis manifest in diverse pathologies, but the molecular effectors governing this process remain ill-defined. Here, we report that PERK promotes lipid trafficking at the ER-mitochondria contact sites (EMCS) through a non-conventional, unfolded protein response-independent, mechanism. PERK operates as an adaptor for the recruitment of the ER-plasma membrane tether and lipid transfer protein (LTP) Extended-Synaptotagmin 1 (E-Syt1), within the EMCS. In resting cells, the heterotypic E-Syt1-PERK interaction endorses transfer of PLs between the ER and mitochondria. Weakening the E-Syt1-PERK interaction or removing the lipid transfer SMP-domain of E-Syt1, compromises mitochondrial respiration. Our findings unravel E-Syt1 as a PERK interacting LTP and molecular component of the lipid trafficking machinery of the EMCS, which critically maintains mitochondrial homeostasis and fitness.

Asunto(s)

Mitocondrias , Membranas Mitocondriales , Fosfolípidos , Sinaptotagmina I , eIF-2 Quinasa , Humanos , Transporte Biológico , eIF-2 Quinasa/metabolismo , Metabolismo de los Lípidos , Mitocondrias/metabolismo , Fosfolípidos/metabolismo , Sinaptotagmina I/metabolismo , Membranas Mitocondriales/metabolismo