Coordinated maturation of neurons and synapses in the adolescent human neocortex

About This Grant

PROJECT SUMMARY / ABSTRACT During childhood and adolescence, tightly orchestrated processes profoundly restructure synaptic connectivity and neuronal physiology in the human neocortex. Defects in this maturation underlie childhood neurodevelopmental disorders including autism, but a key gap exists in our knowledge of these cellular, synaptic, and circuit changes in the juvenile human neocortex. We hypothesize that the postnatal maturation of distinct synapse subclasses and active neuronal properties is central to human neocortical circuit function, and that these processes are impaired in autism. To test this, we have developed a robust pipeline to retrieve and analyze specimens that must be resected during pediatric neurosurgical procedures to access deep epileptic foci, vascular malformations, or brain tumors. Due to comorbidity between autism and epilepsy, about 30% of these patients also have an autism diagnosis. In our preliminary results, we find that human neocortical glutamatergic synapses cluster into at least five distinct subclasses based on receptor content, and that this subclass composition diverges across postnatal ages and across species. We further find that active neuronal properties including spike rate adaptation increase through human adolescence, driven by elevation in BK-type calcium-activated potassium channels, and that these active physiology properties are reduced in children with autism. The proposed study will define the maturation of juvenile human neocortical neurons and synapses in individuals with and without autism in three specific aims. First, we will use conjugate array tomography to delineate human synapse subclasses based on molecular composition and ultrastructure and determine if a distinctive subclass that we have identified, which is enriched in AMPA- and NMDA-type glutamate receptors, emerges in adolescence. Second, we will use whole-cell physiology recording and single-cell transcriptomics (Patch-Seq) in human brain slices to determine if active physiology properties and synaptic plasticity of human neocortical neurons change through childhood and adolescence and if these changes are impaired in autism. Third, we will knock out synaptic proteins linked to autism and neurodevelopment using CRISPR in human brain slice cultures to determine if adolescent maturation of specific, human-enriched synapse subclasses is impaired. These aims are propelled by three key innovations: a novel definition of functionally interpretable synapse subclasses based on single-synapse analysis, an extraordinary pipeline between Stanford University and Lucile Packard Children’s hospital to rapidly access pediatric neurosurgical specimens, and a system for causal manipulation of synaptic proteins in human brain slice cultures. When completed, this study will yield key insight into the fundamental principles governing postnatal human neocortical maturation, and how this maturation is impaired in autism.