Shank3 and the Par polarity complex in neurodevelopmental disorders

Project Summary Autism Spectrum Disorders (ASD) and schizophrenia are two distinct neurodevelopmental disorders with certain shared symptoms. Yet the underlying synaptic mechanisms leading to these distinct and shared behavioral phenotypes remain elusive. Both disorders show a strong genetic component, and recent studies have pointed to a number of shared genes that are mutated in both ASD and schizophrenia. One of the most prominent monogenic genes for both disorders is SHANK3, which encodes a synaptic scaffolding protein. However, the mechanisms by which Shank3 mutations differentially affect synaptic functions are still unclear. A recent study in epithelial cells shows Shank2 interacts with the partitioning-defective (Par) polarity complex, which includes Par3, Par6 and atypical PKC (aPKC). Consistent with this, our preliminary data show that Shank3 interacts with aPKC in vivo, and this interaction is reduced in the Par3 conditional knockout hippocampus. Interestingly, we found that aPKC activation is reduced in Shank3 ASD-associated InsG3680 mutant mouse brains, while an overactivation of aPKC is observed in Shank3 schizophrenia-associated R1117X mutant brains. Thus, we hypothesize that Shank3 targets the Par polarity complex to synapses and regulates its activation. ASD- and schizophrenia-associated Shank3 mutations will result in differential dysregulation of aPKC activation, leading to distinct changes in synaptic plasticity and behavioral defects. In the first aim, we will test the hypothesis that dendritic spine structural plasticity is differentially affected by Shank3 ASD and schizophrenia mutants through dysregulated activation of aPKC. In Aim 2, we will test the hypothesis that dysregulation of aPKC activation in Shank3 mutants leads to altered AMPA receptor (AMPAR) trafficking and nanodomain localization at the spine surface. Our studies will utilize advanced molecular imaging techniques, including ?STED super resolution imaging, FRET and FRAP live cell imaging, combined with two-photon glutamate uncaging-induced dendritic spine structural plasticity. We will also complement these imaging approaches with biochemical analyses in SHANK3 ASD and schizophrenia- associated mutant knockin mouse models. Together, our proposed studies will establish a mechanistic link between Shank3 and the Par polarity complex in regulating synaptic plasticity in neurodevelopmental disorders including ASD and schizophrenia. As Par3 is genetically linked to ASD, schizophrenia, and high cognitive performance, our studies will shed light on the role of a Shank3-Par polarity signaling complex in cognitive defects in neurodevelopmental disorders.