Synaptic Protein Interaction Network Disruptions Suggest Convergence Among Autism Mouse Models

Background: Mutations in genes expressed at the glutamate synapse are commonly reported in autism genetic studies. Moreover, mouse models of autism often show disruptions of glutamatergic transmission and excitatory/inhibitory balance, even when the gene under study is not localized to the synapse.  These data suggest that disruption of glutamatergic transmission may be a central component of many different genetic and environmental causes of autism.

Objectives: Use quantitative multiplex immunoprecipitation to identify convergent molecular pathways at the glutamate synapse in different genetic and environmental models of autism.

Methods: In order to test this synaptic hypothesis of autism pathogenesis, we have assembled a quantitative multiplex immunoprecipitation (QMI) assay to measure dynamic protein-protein interaction networks at the glutamate synapse in mouse models of autism.  The QMI assay immunoprecipitates a given protein onto a microbead substrate, and quantifies the abundance of co-immunoprecipitated proteins in shared complexes using fluorescently tagged antibodies read by a flow cytometer.  Currently, we can simultaneously measure 225 binary protein combinations.

Results: Using QMI, we have analyzed several independent genetic and environmental mouse models of autism and quantified the differences in the synaptic protein interaction network in the hippocampus and frontal cortex.  Our results show that when one synaptic protein is deleted (e.g. Shank3), the abundance of many seemingly unrelated protein complexes is affected (e.g. a complex containing Neuroligin3 and GRIN1).  By comparing protein network changes in different mouse models using graph-theory-based techniques, we are beginning to identify a set of proteins in shared complexes that are altered in multiple models of autism. 

Conclusions: We predict that a better understanding of both levels of individual protein abundance and, critically, the interactions among synaptic proteins, will enable the identification of convergent molecular pathways in different models of autism, and allow the classification of biologically relevant sub-groups of the disorder.