Postsynaptic scaffold proteins in health and disease Dr. Jonathan Hanley

Transcription

1 Postsynaptic Scaffold Proteins in Health and Disease 1 School of Biochemistry University of Bristol, UK Talk outline Introduction to synapses, their plasticity and molecular organization Focus on excitatory synapses Focus on GRIP, PSD 95 and SHANK Alzheimer s disease, ASD, schizophrenia, ischaemia 2 The brain 3 1

2 The synapse neurons in the brain Communicate via synapses Allow neurons to form circuits/networks 5 The synapse (2) The most fundamental processing unit in the brain Synapses are subject to very precise regulation This depends on the specific stimulation at that synapse, and also the physiological /biochemical state of the neuron Synaptic plasticity underlies learning and memory Many neurological diseases are synaptopathies Hippocampal neuron stained with PSD-95 antibody Excitatory and inhibitory synapses Inhibitory GABA and glycine GABA A R, GlyR Dendritic shaft/soma Excitatory Glutamate AMPAR, NMDAR, KAR Dendritic spines 6 van Spronsen and Hoogenraad 2010 Curr Neurol Neurosci Rep.10:

3 Postsynaptic scaffold proteins at CNS GABAergic synapses Gephyrin: Core scaffold Clusters GABA A R and GlyR Binds F-actin and microtubules Luscher and Keller Pharmacology and Therapeutics 102: Postsynaptic scaffold proteins at CNS GABAergic synapses (2) 8 Collybistin: Cdc42 GEF (Guanine nucleotide Exchange Factor) Regulates membrane targeting of gephyrin Interacts with neuroligin Luscher and Keller Pharmacology and Therapeutics 102: Postsynaptic scaffold proteins at CNS GABAergic synapses (3) 9 Dystrophin -glycoprotein complex: At a subset of inhibitory synapses Can cluster independently of receptors and gephyrin Interacts with neuroligin Luscher and Keller Pharmacology and Therapeutics 102:

4 Postsynaptic scaffold proteins at CNS glutamatergic synapses TARP Feng and Zhang, Nature Reviews Neuroscience Comparison of complexity at inhibitory and excitatory synapses Excitatory Inhibitory 11 Renner et al., Current Opinion in Neurobiology 18: Synaptic strength Strong synapse Weak synapse glu - glu - glu - glu - 12 Lots of AMPARs Fewer AMPARs 4

5 AMPA receptor trafficking Lateral diffusion Lateral diffusion PSD scaffold Exocytosis Endocytosis Recycling 13 Degradation AMPAR trafficking in synaptic plasticity glu- P P Ca 2+ Long-term potentiation (LTP) 14 SAP97 PSD-95 MyoV Recycling GRIP PSD-95 AP2 PICK1 Long-term depression (LTD) Degradation Endocytosis NMDAR GluR1/2 GluR2/3 Dendritic spines More AMPARs, bigger PSD, bigger spine Spine size and shape influence diffusion of molecules 15 van Spronsen and Hoogenraad 2010 Curr Neurol Neurosci Rep.10:

6 Spine shape influences diffusion of synaptic proteins and signalling factors 16 Lee et al., (2012). Neural Plasticity 2012, Dendritic spines (2) Very dynamic Actin-rich structures LTP and LTD inducing stimuli influence actin polymerisation and depolymerisation (respectively) Leads to spine growth/shrinkage 17 Spines shrink and grow during plasticity by changes in actin polymerisation 18 Tada and Sheng Current Opinion in Neurobiology, 16:

7 Postsynaptic scaffold proteins at CNS glutamatergic synapses TARP 19 Feng and Zhang, Nature Reviews Neuroscience GRIP (Glutamate Receptor Interacting Protein) Interact with GluA2/3 subunits of AMPARs Family of proteins 2 genes, also splice variants Multi-PDZ, hence multiple interactors Not tightly associated with the PSD GRIP1 % identity GRIP2 % identity ABP V PDZ 1 PDZ 2 PDZ 3 PDZ 4 PDZ 5 PDZ 6 PDZ V PDZ 1 PDZ 2 PDZ 3 PDZ 4 PDZ 5 PDZ 6 PDZ PDZ 1 PDZ 2 PDZ 3 PDZ 4 PDZ 5 PDZ 6 20 Based on: Dong et al., Journal of Neuroscience 19: GRIP family protein interactions MT5- Sec8 SNARE NEEP21 AMPAR MMP liprin-α PICK1 PDZ 1 PDZ 2 PDZ 3 PDZ 4 PDZ 5 PDZ 6 PDZ 7 KIF5 N-PRAP PIKE ephrin/ephr GRASP-1 21 Trafficking NEEP21 PICK1 Sec8 KIF5 liprin-α SNARE Intracellular signaling GRASP-1 PIKE liprin-α Plasma membrane proteins AMPAR ephrin/ephr N-PRAP MT5-matrix metalloprotease 7

8 Role of GRIP and interactors in AMPAR trafficking 22 Anggono and Huganir, Current Opinion in Neurobiology, 22: PSD-95 Major constituent of the PSD Interacts with NMDARs directly, and with AMPARs via TARPs (Transmembrane AMPAR Regulatory Proteins) The MAGUK protein family (Membrane Associated Guanylate Kinase) Regulates AMPAR synaptic localisation Brings signalling components close to Ca 2+ source and to substrates 23 Modified from Zheng et al., The Neuroscientist 17: Regulation of AMPAR synaptic localization by PSD-95 i) The slot hypothesis PSD-95 molecules define a potential AMPAR position in the PSD Number of PSD-95 molecules in a synapse is dynamically regulated - Palmitoylation, ubiquitination, phosphorylation Interaction of TARPs with PSD-95 also regulated TARP 24 8

9 Regulation of AMPAR synaptic localization by PSD-95 (2) ii) Lateral mobility Via TARPs, PSD-95 restricts AMPAR lateral mobility AMPAR-TARP interaction is maintained as a tight complex Scope for regulation of TARP-PSD-95 interaction 25 Bats et al., Neuron 53: iii) Regulation of synaptic plasticity Regulation of PSD-95 localisation at PSD can control synaptic AMPAR number Palmitoylation stabilises PSD-95 at PSD PSD-95 polyubiquitination leads to degradation Ser 295 (JNK) phosphorylation stabilizes PSD-95 at PSD Ser 73 (CaMKII) phosphorylation destabilizes PSD-95 at PSD 26 Xu et al., Current Opinion in Neurobiology, 21: Iasevoli et al Neurochemical Research 38: 1-22 AMPARs freed up from PSD-95 scaffold Diffuse in plane of plasma membrane Internalised at endocytic zones 9

10 PSD-95 as a signaling scaffold 28 PSD-95 as a signaling scaffold (2) 29 Kalirin 7 is a Rac GEF Mediates NMDAR-dependent signaling to control actin polymerisation Hence regulates dendritic spine morphology PSD-95 as a signaling scaffold (3) SynGAP = Ras GAP; SPAR = Rap GAP Regulate Ras and Rap signaling and consequently MAP kinase pathways Variety of effects on AMPAR trafficking and spine morphology 30 10

11 PSD-95 as a signaling scaffold (4) nnos = neuronal Nitric Oxide Synthase Involved in synapse and spine formation, but also cell death nnos activation is Ca 2+ /CaM dependent and also regulated by CaMKII 31 PSD-95 as a signaling scaffold (5) 32 SH3-GK domain interacts with AKAP79/150 (A-Kinase Anchoring Protein) PKA, PKC and calcineurin bind AKAP79/150 This interaction is required for LTD Shank proteins SH3 and multiple ankyrin repeat domains (aka ProSAP Proline-rich synapse-associated protein) Shank 1-3 Large multi-domain scaffold proteins Interface between PSD and actin cytoskeleton Numerous roles in organizing the spine molecular architecture 33 11

12 Shank protein-interaction sites α-fodrin GKAP, β-pix Cortactin, IRSp53 Homer Grabrucker et al., Trends in Cell Biology 21, Scaffolding proteins in neurological disease Dementia (e.g. Alzheimer s disease) Autism Spectrum Disorders (ASD, e.g. autism or Asperger syndrome) Schizophrenia Brain ischaemia (e.g. stroke) Putative lifetime trajectory of dendritic spine number 35 Penzes et al., Nature Neuroscience 14, Alzheimer s disease PSD-95, GKAP and Shank3 decreased in AD cortex β-amyloid causes NMDA receptor-dependent degradation of PSD-95 This would initially cause loss of AMPARs, mglurs May cause synapse loss associated with AD 36 12

13 Autism spectrum disorders Many genes implicated in ASD encode PSD proteins Include Shank2/3 and their interactors e.g. InsG3680 results in premature stop codon SNP in GRIP1 GluA2 binding region Increases GluA2 interaction and hence surface expression 37 Schizophrenia Expression of several PSD proteins affected Shank3 mutations also associated with this disorder e.g. C3349T also results in truncated C-terminus Numerous PSD-95 de novo mutations associated with the disorder PSD-95 expression is reduced in prefrontal cortex of schizophrenic patients 38 Brain ischemia (e.g. stroke) Loss of oxygen and glucose supply to neurons Loss of ionic gradients across neuronal membranes Excessive glutamate release Delayed cell death (~2 days following insult) Hippocampal CA1 neurons particularly vulnerable 39 Johnston et al Lancet Neurol10:

14 PSD-95 (2) Disrupting GluN2-PSD-95 reduces infarct after stroke Disease process involvesover-activation of a normal physiological pathway PSD-95 links NMDAR over-excitation to apoptosis pathways via nnos 40 Tymianski, Nature Neuroscience 14: GRIP Synaptic AMPARs basally contain GluA2 GluA2-containing AMPARs are Ca 2+ impermeable Oxygen/glucose deprivation leads to rapid switch to GluA2-lacking AMPARs PICK1 and GRIP bind GluA2 and regulate trafficking 41 Liu and Zukin Trends in Neurosciences 30: Summary Synapses are the most fundamental processing unit in the brain Modifications of synaptic strength underlie the formation of neuronal networks, which represent cognitive processes Precise regulation of synaptic structure and function is crucial for normal cognition Scaffold proteins are at the core of synaptic organization and are therefore critical to cognitive function Mutations in scaffold proteins can lead to neurological disease 42 14

15 Acknowledgements