Mechanistic Contribution of Defective Presynaptic Cargo Transport to the Autism-linked Pathogenesis

Authors

• GJ Xiong
• YX Xie
• T Sun
• XT Cheng
• N Huang
• MY Lin
• SN Li
• ZH Sheng

Abstract

The formation, maintenance, and remodeling of synapses require targeted delivery of newly synthesized presynaptic cargoes from the soma to synapses. We previously identified syntabulin as a kinesin KIF5 adaptor that mediates axonal transport of active zone (AZ) precursors from the soma to presynaptic terminals, which is essential for synapse formation in developing neurons and synapse maintenance and remodeling in matured neurons. Autism spectrum disorders (ASDs) are highly inheritable neurodevelopmental disorders characterized by impaired social interaction, reduced communication, and increased repetitive behaviors. Mutations of genes that control synapses formation and maturation are emerging to be an important cellular basis of ASDs. It remains elusive whether impaired axonal transport of presynaptic proteins affects synapse formation and maturation and thus contributes to autism pathogenesis. Interestingly, a genetic study of ASD patients identified a de-novo syntabulin variant that changes a conserved residue within the KIF5-binding domain. We confirmed that this mutation impairs the syntabulin-KIF5 interaction. Syntabulin gene locates on 8q23.2 within the autism susceptibility loci 8q22-24. Thus, there is an urgent need to establish whether de-novo syntabulin variants are associated with the autism pathogenesis. To address this, we generated Nestin-Cre; syntabulinloxP/loxP conditional knock out (cKO) mice in which syntabulin is null in the brain since the embryonic stage. Time-lapse imaging shows that hippocampal neurons of syntabulin cKO mice display impaired axonal transport of AZ precursors from the soma to developing presynaptic boutons and reduced mature synapse density. Electron microscopy study reveals synapse loss of mature excitatory synapses and a decrease in docking vesicles per synapse in cKO hippocampus CA1 neurons. Moreover, syntabulin cKO mice show reduced frequency of miniature excitatory postsynaptic currents and impaired long-term synaptic plasticity in hippocampal Schaffer collateral–CA1 synapses. Consequently, the syntabulin cKO mice exhibit core autism-like traits including defective social recognition, reduced ultrasonic vocalizations, increased repetitive behavior, and impaired spatial learning and memory. Our study establishes for the first time that defective axonal transport contributes to the pathogenesis associated with synaptic and behavioral abnormalities in mice that bear similarities to autism patients, thus providing new cellular targets for therapeutic intervention.

Scientific Focus Area: Neuroscience

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