Synaptic Interactome Mining Reveals p140Cap as a New Hub for PSD Proteins Involved in Psychiatric and Neurological Disorders

Annalisa Alfieri,Yohann Couté,Alessandro Morellato,Isabella Russo,Elisabetta Menna,Elisabetta Boeri Erba,Joseph D Buxbaum,Ugo Ala,Michela Matteoli,Paola Defilippi,Alfredo Brusco,Emilia Turco,J Douglas Armstrong,Silvia De Rubeis,Oksana Sorokina,Costanza Angelini,Annie Adrait,Colin Mclean

doi:10.3389/fnmol.2017.00212

Abstract

Altered synaptic function has been associated with neurological and psychiatric conditions including intellectual disability, schizophrenia and autism spectrum disorder (ASD). Amongst the recently discovered synaptic proteins is p140Cap, an adaptor that localizes at dendritic spines and regulates their maturation and physiology. We recently showed that p140Cap knockout mice have cognitive deficits, impaired long-term potentiation (LTP) and long-term depression (LTD), and immature, filopodia-like dendritic spines. Only a few p140Cap interacting proteins have been identified in the brain and the molecular complexes and pathways underlying p140Cap synaptic function are largely unknown. Here, we isolated and characterized the p140Cap synaptic interactome by co-immunoprecipitation from crude mouse synaptosomes, followed by mass spectrometry-based proteomics. We identified 351 p140Cap interactors and found that they cluster to sub complexes mostly located in the postsynaptic density (PSD). p140Cap interactors converge on key synaptic processes, including transmission across chemical synapses, actin cytoskeleton remodeling and cell-cell junction organization. Gene co-expression data further support convergent functions: the p140Cap interactors are tightly co-expressed with each other and with p140Cap. Importantly, the p140Cap interactome and its co-expression network show strong enrichment in genes associated with schizophrenia, autism, bipolar disorder, intellectual disability and epilepsy, supporting synaptic dysfunction as a shared biological feature in brain diseases. Overall, our data provide novel insights into the molecular organization of the synapse and indicate that p140Cap acts as a hub for postsynaptic complexes relevant to psychiatric and neurological disorders.

Highlights

Mutations in genes encoding synaptic proteins have been associated with several brain disorders, including schizophrenia, autism spectrum disorder (ASD) and developmental delay/intellectual disability (DD/ID) (De Rubeis et al, 2014; Fromer et al, 2014; Deciphering Developmental Disorders, 2015)
These data indicate that the p140Cap immunoprecipitation is highly specific, making these samples suitable for the identification of p140Cap interactors by mass spectrometry (MS)
Our work is the first comprehensive proteomic analysis of the synaptic interactome of p140Cap, which is indispensable for dendritic spine initiation and maturation and forms of hippocampal synaptic plasticity (Repetto et al, 2014)

Summary

Introduction

Mutations in genes encoding synaptic proteins have been associated with several brain disorders, including schizophrenia, autism spectrum disorder (ASD) and developmental delay/intellectual disability (DD/ID) (De Rubeis et al, 2014; Fromer et al, 2014; Deciphering Developmental Disorders, 2015). Amongst the recently discovered synaptic proteins is p140Cap/SNIP (Chin et al, 2000; Di Stefano et al, 2004), a scaffolding protein localized in dendritic spines (Jaworski et al, 2009) and encoded by the SRCIN1 gene. Acute down-regulation of p140Cap in primary hippocampal neurons reduces the number of mushroom spines and proportionally increases the number of dendritic filopodia (Jaworski et al, 2009; Tomasoni et al, 2013), a defect in synaptic maturation that can be observed in p140Cap knockout (KO) mice (Repetto et al, 2014). P140Cap KO mice show impairments in object recognition, suggestive of defects in memory consolidation and retrieval cognitive defects (Repetto et al, 2014)

Methods

Results

Conclusion