Importance of a syndapin-mediated interconnection of cytoskeleton and membrane trafficking for neuronal structure, function and plasticity
Final Report Abstract
Synaptic transmission relies on effective and accurate compensatory endocytosis. F-BAR proteins such as syndapin I serve as membrane curvature sensors and/or inducers and thereby support membrane remodelling processes. As their in vivo functions urgently awaited disclosure, we successfully generated syndapin I loss-of-function models both in zebrafish and mice. Our data demonstrate that the F-BAR protein syndapin I is crucial for proper brain function. Syndapin I KO mice suffer from seizures, a phenotype consistent with excessive hippocampal network activity. Loss of syndapin I causes defects in presynaptic membrane trafficking processes, which are especially evident under high-capacity retrieval conditions, accumulation of endocytic intermediates, loss of synaptic vesicle size control, impaired activity-dependent synaptic vesicle retrieval and defective synaptic activity. Detailed molecular analyses demonstrate that syndapin I plays an important role in the recruitment of all dynamin isoforms, central players in vesicle fission reactions, to the membrane. Thus, syndapin I acts as pivotal membrane anchoring factor for dynamins during regeneration of synaptic vesicles. Our phenotypical analyses of syndapin I KO mice thus highlight the functional importance of syndapin I for proper synaptic vesicle formation in hippocampal and retinal synapses, for proper hippocampal network activity and for proper function of the mammalian brain as such. Insights into mechanisms coordinating membrane remodeling, local actin nucleation, and postsynaptic scaffolding during postsynapse formation are important for understanding vertebrate brain function. Gene knockout and RNAi in individual neurons reveal that the F-BAR protein syndapin I is furthermore a crucial postsynaptic coordinator in formation of excitatory synapses. Syndapin I deficiency caused significant reductions of synapse and dendritic spine densities. These syndapin I functions reflected direct, SH3 domain–mediated associations and functional interactions with ProSAP1/Shank2. They furthermore required F-BAR domain-mediated membrane binding. Ultrahigh-resolution imaging of specifically membrane-associated, endogenous syndapin I at membranes of freeze-fractured neurons revealed that membrane-bound syndapin I preferentially occurred in spines and formed clusters at distinct postsynaptic membrane subareas. Postsynaptic syndapin I deficiency led to reduced frequencies of miniature excitatory postsynaptic currents, i.e., to defects in synaptic transmission phenocopying ProSAP1/Shank2 KO, and impairments in proper synaptic ProSAP1/Shank2 distribution. Syndapin I–enriched membrane nanodomains thus seem to be important spatial cues and organizing platforms, shaping dendritic membrane areas into synaptic compartments. Synaptic plasticity involves surface level alterations of GluA1-containing AMPA receptors. Our analyses identify syndapin I as core component for hippocampal synaptic plasticity at the molecular, cellular, electrophysiological and behavioral level. Syndapin I KO resulted in impaired activity-dependent internalization of endogenous GluA1 and GluA2 and highlights a central role for syndapin I in multiple forms of LTD. Strikingly, already in absence of LTD-inducing stimuli, spatial localization and surface clustering of GluA1 and GluA2 were impaired upon syndapin I KO. Our work thereby unravels fundamental molecular aspects of hippocampal synaptic plasticity, as syndapin I is a central player driving synaptic availability and fine-tuning of GluA1 during synaptic plasticity. Interestingly, our analyses furthermore revealed an additional crucial role of syndapin I in inhibitory neurotransmitter receptor organization. Glycine receptors mediate inhibitory neurotransmission in spinal cord and brainstem. Our studies detected a direct interaction of syndapin I with the large intracellular loop of the β subunit of the glycine receptor and also a role of syndapin I in the organization and anchoring of synaptic glycine receptors. In summary, our investigations on different levels ranging from molecules to whole organisms have led to a deeper understanding of pre- and postsynaptic organization and membrane trafficking processes as well as the function of syndapin I therein and have furthermore provided important new insights into the molecular mechanisms of neurotransmission and synaptic plasticity including their physiological relevance.
Publications
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(2009). F-BAR proteins of the syndapin family shape the plasma membrane and are crucial for neuromorphogenesis. J. Neurosci. 29, 13715-13727
Dharmalingam E, Haeckel A, Pinyol R, Schwintzer L, Koch D, Kessels MM, Qualmann B
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(2011). Let's go bananas: revisiting the endocytic BAR code. EMBO J. 30, 3501-3515
Qualmann B, Koch D, Kessels MM
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(2011). Proper synaptic vesicle formation and neuronal network activity critically rely on syndapin I. EMBO J. 30, 4955-4969
Koch D, Spiwoks-Becker I, Sabanov V, Sinning A, Dugladze T, Stellmacher A, Ahuja R, Grimm J, Schüler S, Müller A, Angenstein F, Ahmed T, Diesler A, Moser M, Tom Dieck S, Spessert R, Boeckers TM, Fässler R, Hübner CA, Balschun D, Gloveli T, Kessels MM, Qualmann B
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(2011). The functions of the actin nucleator Cobl in cellular morphogenesis critically depend on syndapin I. EMBO J. 30, 3147-3159
Schwintzer L, Koch N, Ahuja R, Grimm J, Kessels MM, Qualmann B
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(2013). Ciliated sensory hair cell formation and function require the F-BAR protein syndapin I and the WH2 domain-based actin nucleator Cobl. J. Cell Sci. 126: 196-208
Schüler S, Hauptmann J, Perner B, Kessels MM, Englert C, Qualmann B
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(2013). FMRP regulates actin filament organization via the armadillo protein p0071. RNA 19, 1483-1496
Nolze A, Schneider J, Keil R, Lederer M, Hüttelmaier S, Kessels MM, Qualmann B, Hatzfeld M
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(2014). ProSAP1 and membrane nanodomain-associated syndapin I promote postsynapse formation and function. J. Cell Biol. 205, 197-215
Schneider K, Seemann E, Liebmann L, Ahuja R, Koch D, Westermann M, Hübner CA, Kessels MM, Qualmann B
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(2014). Proteomic analysis of glycine receptor β subunit (GlyRβ)-interacting proteins: evidence for syndapin I regulating synaptic glycine receptors. J. Biol. Chem. 289, 11396-11409
del Pino I, Koch D, Schemm R, Qualmann B, Betz H, Paarmann I
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(2015). Cooperative functions of the two F-BAR proteins Cip4 and Nostrin in the regulation of E-cadherin in epithelial morphogenesis. J. Cell Sci.128, 499-515
Zobel T, Brinkmann K, Koch N, Schneider K, Seemann E, Fleige A, Qualmann B, Kessels MM, Bogdan S
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(2015). Different functional modes of BAR domain proteins in formation and plasticity of mammalian postsynapses. J. Cell Sci. 128, 3177-3185
Kessels MM, Qualmann B
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(2018). Cobl-like promotes actin filament formation and dendritic branching using only a single WH2 domain. J. Cell Biol. 217, 211-230
Izadi M, Schlobinski D, Lahr M, Schwintzer L, Qualmann B, Kessels MM
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(2018). The Na+/H+ Exchanger Nhe1 Modulates Network Excitability via GABA Release. Cereb. Cortex
Bocker HT, Heinrich T, Liebmann L, Hennings JC, Seemann E, Gerth M, Jakovcevski I, Preobraschenski J, Kessels MM, Westermann M, Isbrandt D, Jahn R, Qualmann B, Hübner CA
