Synaptic Vesicle Docking: Sphingosine Regulates Syntaxin1 Interaction with Munc18

Department of Molecular and Developmental Genetics, VIB, Leuven, Belgium.
PLoS ONE (Impact Factor: 3.53). 02/2009; 4(4):e5310. DOI: 10.1371/journal.pone.0005310
Source: PubMed

ABSTRACT Consensus exists that lipids must play key functions in synaptic activity but precise mechanistic information is limited. Acid sphingomyelinase knockout mice (ASMko) are a suitable model to address the role of sphingolipids in synaptic regulation as they recapitulate a mental retardation syndrome, Niemann Pick disease type A (NPA), and their neurons have altered levels of sphingomyelin (SM) and its derivatives. Electrophysiological recordings showed that ASMko hippocampi have increased paired-pulse facilitation and post-tetanic potentiation. Consistently, electron microscopy revealed reduced number of docked vesicles. Biochemical analysis of ASMko synaptic membranes unveiled higher amounts of SM and sphingosine (Se) and enhanced interaction of the docking molecules Munc18 and syntaxin1. In vitro reconstitution assays demonstrated that Se changes syntaxin1 conformation enhancing its interaction with Munc18. Moreover, Se reduces vesicle docking in primary neurons and increases paired-pulse facilitation when added to wt hippocampal slices. These data provide with a novel mechanism for synaptic vesicle control by sphingolipids and could explain cognitive deficits of NPA patients.

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Available from: Maria Dolores Ledesma, Aug 15, 2015
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    • "There is increasing evidence to support a role for sphingolipids in neurotransmitter release ((Colombaioni and Garcia-Gil, 2004) and see (Brailoiu et al., 2002; Camoletto et al., 2009; Darios et al., 2009; Kanno et al., 2010)). Sphingosine was shown to activate the synaptic vesicle protein synaptobrevin leading to SNARE complex formation which is involved in membrane fusion. "
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    ABSTRACT: The synaptic vesicle (SV) cycle includes exocytosis of vesicles loaded with a neurotransmitter such as glutamate, coordinated recovery of SVs by endocytosis, refilling of vesicles, and subsequent release of the refilled vesicles from the presynaptic bouton. SV exocytosis is tightly linked with endocytosis, and variations in the number of vesicles, and/or defects in the refilling of SVs, will affect the amount of neurotransmitter available for release (Sudhof, 2004). There is increasing interest in the roles synaptic vesicle lipids and lipid metabolizing enzymes play in this recycling. Initial emphasis was placed on the role of polyphosphoinositides in SV cycling as outlined in a number of reviews (Lim and Wenk, 2009, Martin, 2012, Puchkov and Haucke, 2013, Rohrbough and Broadie, 2005). Other lipids are now recognized to also play critical roles. For example, PLD1 (Humeau et al., 2001, Rohrbough and Broadie, 2005) and some DGKs ((Miller et al., 1999, Nurrish et al., 1999) play roles in neurotransmission which is consistent with the critical roles for phosphatidic acid (PtdOH) and diacylglycerol (DAG) in the regulation of SV exo/endocytosis (Cremona et al., 1999, Exton, 1994, Huttner and Schmidt, 2000, Lim and Wenk, 2009, Puchkov and Haucke, 2013, Rohrbough and Broadie, 2005). PLD generates phosphatidic acid by catalyzing the hydrolysis of phosphatidylcholine (PtdCho) and in some systems this PtdOH is de-phosphorylated to generate DAG. In contrast, DGK catalyzes the phosphorylation of DAG thereby converting it into PtdOH. While both enzymes are poised to regulate the levels of DAG and PtdOH, therefore, they both lead to the generation of PtdOH and could have opposite effects on DAG levels. This is particularly important for SV cycling as PtdOH and DAG are both needed for evoked exocytosis (Lim and Wenk, 2009, Puchkov and Haucke, 2013, Rohrbough and Broadie, 2005). Two lipids and their involved metabolic enzymes, two sphingolipids have also been implicated in exocytosis: sphingosine (Camoletto et al., 2009, Chan et al., 2012, Chan and Sieburth, 2012, Darios et al., 2009, Kanno et al., 2010, Rohrbough et al., 2004) and sphingosine-1-phosphate (Chan, Hu, 2012, Chan and Sieburth, 2012, Kanno, Nishizaki, 2010). Finally a number of reports have focused on the somewhat less well studies roles of sphingolipids and cholesterol in SV cycling. In this report, we review the recent understanding of the roles PLDs, DGKs, and DAG lipases, as well as sphingolipids and cholesterol play in synaptic vesicle cycling.
    Advances in Biological Regulation 09/2014; 57. DOI:10.1016/j.jbior.2014.09.010
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    • "In general, our results unveil PI(4,5)P2 modulation as a new therapeutic target for NPA and provides a potential pharmacological strategy based on the use of drugs that increase the PLCγ/PI(4,5)P2 signaling pathway, illustrated here through the adding of MARCKS peptide. Recently, we could demonstrate such contribution to the cognitive decay occurring in the aged brain, which could be rescued as well by intracerebral delivery of MARCKS (Camoletto et al., 2009). On the other hand the cause of the disease, high SM in the CNS as well as in other organs, is upstream MARCKS/PI(4,5)P2/PLCγ pathway, making this treatment beneficial but not therapeutical for the treatment of NPA disease. "
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    ABSTRACT: Niemann-Pick disease type A (NPDA) is a fatal disease due to mutations in the acid sphingomyelinase (ASM) gene, which triggers the abnormal accumulation of sphingomyelin (SM) in lysosomes and the plasma membrane of mutant cells. Although the disease affects multiple organs, the impact on the brain is the most invalidating feature. The mechanisms responsible for the cognitive deficits characteristic of this condition are only partially understood. Using mice lacking the ASM gene (ASMKO), a model system in NPDA research, we here report that high sphingomyelin levels in mutant neurons lead to low synaptic levels of phosphoinositide PI(4,5)P2 and reduced activity of its hydrolyzing phosphatase PLCγ, which are key players in synaptic plasticity events. In addition, mutant neurons have reduced levels of membrane-bound MARCKS, a protein required for PI(4,5)P2 membrane clustering and hydrolysis. Intracerebroventricular infusion of a peptide that mimics the effector domain of MARCKS increases the content of PI(4,5)P2 in the synaptic membrane and ameliorates behavioral abnormalities in ASMko mice.
    Neurobiology of Disease 09/2014; 73. DOI:10.1016/j.nbd.2014.09.008 · 5.20 Impact Factor
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    • "The concentration of sphingosine in cells is estimated to be $5 lM (Blom et al., 2006) and may increase under various pathological conditions (for example: Alzheimer disease, 2-fold (He et al., 2010); Nieman-Pick type A disease, 4–5-fold (Camoletto et al., 2009) and after consumption of alcohol, 3-fold (Dasgupta et al., 2007). Darios and coworkers demonstrated, that sphingosine facilitates the formation of ternary SNARE complexes in vitro, in a dose-dependent manner, with an EC 50 $ 10 lM (Darios et al., 2009). "
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