Synaptic nanostructure and dysfunction in neurodevelopmental disorders

PROJECT SUMMARY Neurodevelopmental disorders are a serious health problem affecting more than 3% of children worldwide. More than 1,000 genetic variants in synaptic proteins are linked to neurodevelopmental disorders such as autism spectrum disorder (ASD) and schizophrenia. While the symptoms of these disorders differ, each of them affects transmission between synapses in the brain, altering how information is passed throughout the neural network. To understand what causes these disorders and how to treat them, researchers are striving to learn the mechanism behind how these genetic variations affect synaptic function at the cellular and molecular level. This study aims to help answer foundational questions about synaptic transmission using the emerging framework of macromolecular assemblies. Transmitting information efficiently from one synapse to another requires transcellular nanocolumns (TNCs). TNCs span the synaptic cleft and align the neurotransmitter release site of one neuron with the receptors on a neighboring neuron. Unfortunately, the arrangement of components within these TNCs remains unclear. This makes it challenging to determine whether disease-causing mutations disrupt functional TNC formation. This proposal employs an innovative, multidisciplinary approach that combines cutting-edge cryogenic electron tomography (cryo-ET), biochemical methods, mass spectrometry, cell imaging and electrophysiological recordings to generate a nanoscale, macromolecular blueprint of synaptic transmission. Our central hypothesis is that synaptic proteins form subsynaptic PSD nanoblocks, receptor nanodomains and cleft adhesion molecule pairs as key building components for TNC alignment and activity dependent re-organization, which is critical for regulating synaptic transmission and plasticity. Toward proving this hypothesis, the authors have already used cryo-ET on cultured primary neurons, induced human neurons, and isolated nerve terminals to directly visualize the nanoscale organization of TNCs in near native state. These efforts have provided the first molecular-resolution information on such TNC assemblies. Advancing from that success, we will utilize two independent yet complementary aims to establish the sub-10 nm resolution structure of TNCs in healthy physiology and diseases: (1) investigate the molecular architecture, composition, and assembly of postsynaptic nanoblocks, (2) determine the in situ structures of synaptic adhesion molecular pairs and glutamate receptors, then investigate their organization within the synaptic cleft and their alignment with PSD nanoblocks. This research will significantly advance scientific understanding of the molecular architecture, dynamics, and functions of synaptic nanostructures, particularly TNCs. This knowledge will enable development of new therapeutics that target nanoscale structures.