Brain region-specific disruption of Shank3 in mice reveals a dissociation for cortical and striatal circuits in autism-related behaviors

Alexandra L Bey,Aaron J Towers,Haidun Yan,Yilin Yang,Rebecca L Passman,Yong-Hui Jiang,Lara J Duffney,Erin Gaidis,William C Wetsel,Xiaoming Wang,Xinyu Cao,Henry H Yin,Samuel W Hulbert,Namsoo Kim,Ramona M Rodriguiz

doi:10.1038/s41398-018-0142-6

Abstract

We previously reported a new line of Shank3 mutant mice which led to a complete loss of Shank3 by deleting exons 4−22 (Δe4−22) globally. Δe4−22 mice display robust ASD-like behaviors including impaired social interaction and communication, increased stereotypical behavior and excessive grooming, and a profound deficit in instrumental learning. However, the anatomical and neural circuitry underlying these behaviors are unknown. We generated mice with Shank3 selectively deleted in forebrain, striatum, and striatal D1 and D2 cells. These mice were used to interrogate the circuit/brain-region and cell-type specific role of Shank3 in the expression of autism-related behaviors. Whole-cell patch recording and biochemical analyses were used to study the synaptic function and molecular changes in specific brain regions. We found perseverative exploratory behaviors in mice with deletion of Shank3 in striatal inhibitory neurons. Conversely, self-grooming induced lesions were observed in mice with deletion of Shank3 in excitatory neurons of forebrain. However, social, communicative, and instrumental learning behaviors were largely unaffected in these mice, unlike what is seen in global Δe4−22 mice. We discovered unique patterns of change for the biochemical and electrophysiological findings in respective brain regions that reflect the complex nature of transcriptional regulation of Shank3. Reductions in Homer1b/c and membrane hyper-excitability were observed in striatal loss of Shank3. By comparison, Shank3 deletion in hippocampal neurons resulted in increased NMDAR-currents and GluN2B-containing NMDARs. These results together suggest that Shank3 may differentially regulate neural circuits that control behavior. Our study supports a dissociation of Shank3 functions in cortical and striatal neurons in ASD-related behaviors, and it illustrates the complexity of neural circuit mechanisms underlying these behaviors.

Highlights

Despite significant advances in identifying genetic defects in patients diagnosed with autism spectrum disorder (ASD), the anatomical basis and underlying neural circuit mechanisms that contribute to its core symptoms remain elusive[1,2]
Generation of conditional Shank[3] knockout (KO) mice Since it has been hypothesized that cortico-striatal circuits underlie ASD-like behaviors, we crossed the recently generated transgenic mouse with loxP sites flanking Shank[3] exons 4−22 (e4−22flox/flox) to mice expressing Cre recombinase to disrupt the expression of Shank[3] in cortical or striatal regions (Fig. 1a)
We found that NEX-Cre Shank3 floxed mice (NEX)-Shank[3] mice had a tendency for increased selfgrooming but with significant variability (p = 0.086); altered self-grooming was not observed in Dlx5/ 6-Shank[3], Drd1-Cre Shank3 floxed mice (Drd1)-Shank[3], or Drd2-Cre Shank3 floxed mice (Drd2)-Shank[3] mice that targeted the basal ganglia for Shank[3] disruption (Fig. 2e)

Summary

Introduction

Despite significant advances in identifying genetic defects in patients diagnosed with autism spectrum disorder (ASD), the anatomical basis and underlying neural circuit mechanisms that contribute to its core symptoms remain elusive[1,2]. These limitations represent a critical gap in our understanding of the disorder and hinder our ability to develop therapies targeting specific molecular or neural circuit abnormalities that underlie the condition. Human imaging studies of individuals affected by ASD have identified a pattern of morphological changes affecting many brain regions including the frontal cortex, hippocampus, amygdala, and striatum[3,4]. While several studies have found correlations between corticostriatal imaging phenotypes and repetitive behaviors[15,21], limitations in technique, heterogeneity of patient populations, and inability to perform direct manipulations limit our ability to demonstrate causality between the anatomical and behavioral manifestations of the disorder

Methods

Results

Conclusion