Role for Striatal Glutaminergic Signaling in Decreased Risk Assessment in Autism Mouse Models
The genetic etiology of Autism Spectrum Disorder (ASD) is composed of hundreds of genes, and it is expected that these genes affect common molecular mechanisms responsible for ASD-related behavior. In addition to the core autism phenotypes, individuals diagnosed with ASD often display anxiety and impulsivity However, the molecular drivers of these behaviors are unknown.
Using multiple genetic mouse models of ASD, we aimed to determine the relationship between anxiety and impulsivity, and to determine the molecular mechanisms responsible for these behaviors.
We performed locomotion, anxiety-related and risk-assessment (RA) behavioral and molecular experimentation on four mouse models of ASD: Shank3 KO, CNTNAP2 KO, Chr16p11.2del, and BTBR mice. We performed Open Field (OF), Dark Light (DL), and Elevated Plus Maze (EPM). We extracted RNA from the striatum of all four mouse models, and their controls, and performed whole throughput RNA sequencing (RNA-seq) on all samples. We then performed Weighted Gene Coexpression Network Analysis (WGCNA) on the RNA-seq data, and correlated co-expressed genes to the behavior of the knockout animals. We further analyzed the WGCNA data to locate hubs of gene products that could be used as potential therapeutic targets. Finally, we performed in-vivo pharmacological intervention to target these hubs, and affect behavior in the mic models.
In behavioral experiments, the CNTNAP2 KO, Shank3 KO and Chr16del models displayed reduced anxiety-like behavior, which correlates with reduced risk-assessing behavior in the EPM and DL test. In the OF, all four mouse models expressed locomotion deficits. The WGCNA analysis of the striatal transcriptome revealed one distinct module of co-expressed genes that had a significant correlation with the risk-assessment behavior both in the EPM and DL, and subsequent PPI analysis of this genetic module revealed a cluster of hubs dominated by Glur4 and Glur5 glutamate receptors. Western blot analysis performed on the synaptosomes of the Shank3 KO mouse model's striatum revealed a significantly reduction of Glur4. We therefore acutely injected the AMPA and Kainate antagonist NBQX into the striatum of C57 and Shank3 KO animals via cannulas. The C57 mice expressed reduced Anxiety-like and risk assessment behavior both in the EPM and DL, while no changes were observed in the OF. Interestingly, the Shank3 KO mice treated with NBQX showed additional decrease in anxiety-like and RA behavior in the EPM, and reduced RA behavior in the DL test and no changes in the OF. These results validate our bioinformatic analysis.
Our study has determined that there is significantly decreased risk assessment in multiple autism mouse models. Furthermore, the molecular and pharmacological data implicate striatal glutaminergic-signalling as a potential molecular driver of decreased risk assessment. These results suggest a mechanism driving increased impulsivity and decreased awareness of risk in individuals diagnosed with ASD.