The Par Polarity Complex and Shank3 in dendritic spine dynamics: Mechanistic insights into synaptic plasticity, cognition, and neurodevelopmental disorders
Creators: name: Voglewede, Mikayla Marie
Publisher: name: No Publisher Supplied
Year: 2024

description: The morphogenesis and plasticity of dendritic spines are associated with synaptic strength, learning, and memory. Dendritic spines are highly compartmentalized structures, which makes proteins involved in cellular polarization and membrane compartmentalization likely candidates regulating their formation and maintenance. Indeed, recent studies suggest polarity proteins help form and maintain dendritic spines by compartmentalizing the spine neck and head. Here, we use mouse models to investigate the role of the Par polarity complex in dendritic spines and cognition. We also examine the role of Shank3 in neurodevelopmental disorders and its interaction with the Par complex proteins. The Par3 polarity protein is critical for subcellular compartmentalization in different developmental processes. Variants of PARD3, encoding PAR3, are associated with intelligence and neurodevelopmental disorders. However, the role of Par3 in glutamatergic synapse formation and cognitive functions in vivo remains unknown. Here, we show that forebrain-specific Par3 conditional knockout leads to increased long, thin dendritic spines in vivo. In addition, we observed a decrease in the amplitude of miniature excitatory postsynaptic currents. Surprisingly, loss of Par3 in vivo enhances hippocampal-dependent spatial learning and memory and repetitive behavior. Phosphoproteomic analysis revealed proteins regulating cytoskeletal dynamics are significantly dysregulated downstream of Par3. Mechanistically, we found Par3 deletion causes increased Rac1 activation and dysregulated microtubule dynamics through CAMSAP2. Together, our data reveal an unexpected role for Par3 as a molecular gatekeeper in regulating the pool of immature dendritic spines, a rate-limiting step of learning and memory, through modulating Rac1 activation and microtubule dynamics in vivo. Abnormalities in dendritic spines are often found in neurodevelopmental disorders. Autism Spectrum Disorders (ASD) and schizophrenia are distinct neurodevelopmental disorders that share certain symptoms and genetic components. Recent studies have identified the synaptic scaffolding protein Shank3 as a leading candidate gene for both disorders. Mutations in the SHANK3 gene have been linked to both ASD and schizophrenia; however, how patient-derived mutations affect the structural plasticity of dendritic spines during brain development is unknown. Here we use live two photon in vivo imaging to examine dendritic spine structural plasticity in mice with SHANK3 mutations associated with ASD and schizophrenia. We identified shared and distinct phenotypes in dendritic spine morphogenesis and plasticity in the ASD-associated InsG3680 mutant mice and the schizophrenia-associated R1117X mutant mice. No significant changes in dendritic arborization were observed in either mutant, raising the possibility that synaptic dysregulation may be a key contributor to the behavioral defects previously reported in these mice. We further investigated the molecular mechanisms mediating the dendritic spine abnormalities in these Shank3 mutants. We show that Shank3 forms a complex with atypical protein kinase C (aPKC) in vivo, an interaction that is preserved in the R1117X mutant. In vitro, R1117X and InsG3680 mutants both shuttle Shank3 and aPKC towards the nucleus away from polarity protein Par3. In vivo, we use synaptosomal fractionation to determine that R1117X but not InsG3680 alters aPKC activity and PKCι/λ localization. Both mutations mislocalize Homer1 while InsG3680 also reduces synaptic PSD-95 levels. These findings shed light on how patient-linked mutations in SHANK3 affect dendritic spine dynamics and the Par polarity complex in the developing brain, which provides insight into the synaptic basis for the distinct phenotypes observed in ASD and schizophrenia.