Cellular Phenotypes in Human iPSC-Derived Neurons from a Genetic Model of Autism Spectrum Disorder

Abstract

Summary A deletion or duplication in the 16p11.2 region is associated with neurodevelopmental disorders including autism spectrum disorder and schizophrenia. In addition to clinical characteristics, carriers of the 16p11.2 copy number variant (CNV) manifest opposing neuroanatomical phenotypes, e.g. macrocephaly in deletion carriers (16pdel) and microcephaly in duplication carriers (16pdup). Using fibroblasts obtained from 16pdel and 16pdup carriers, we generated induced pluripotent stem cells (iPSCs) and differentiated them into neurons to identify causal cellular mechanisms underlying neurobiological phenotypes. Our study revealed increased soma size and dendrite length in 16pdel neurons and reduced neuronal size and dendrite length in 16pdup neurons. Functional properties of iPSC-derived neurons corroborated aspects of these contrasting morphological differences that may underlie brain size. Interestingly, both 16pdel and 16pdup neurons displayed reduced synaptic density, suggesting that distinct mechanisms may underlie brain size and neuronal connectivity at this locus.

Overexpression of CD47 is associated with brain overgrowth in 16p11.2 deletion syndrome

“…We acknowledge that while the sample sizes in this study are small (but comparable to other iPSC studies modeling subtypes of psychiatric disorders) [26][27][28]56 , they would benefit from including more patients with 16p11.2 deletion and/or other disorders with defined macrocephaly. Validating these findings in postmortem brain tissue in 16p11.2 deletion individuals with brain overgrowth would also be valuable, though this resource is limited and constrained by the fact that most brain banks worldwide do not have head circumference or brain volume data tagged with postmortem human brain tissue.…”

“…Recent work has shown that CD47 plays a critical role in regulating synaptic pruning during early brain development 22 , providing further support that the same pathways can go awry in neurodevelopmental disorders. While a number of studies are beginning to show changes in NPC proliferation 26,28 and neuronal size 27 associated with autism with brain enlargement, these studies focused on changes in gray matter and have only investigated molecular and cellular mechanisms in cultures in vitro [26][27][28] . We demonstrate that CD47 is upregulated in two distinct cell types (NPCs and OPCs) at particular stages of development in 16p11.2 deletion syndrome, leading to suppressed phagocytosis both in vitro and in vivo.…”

“…Increases in gray matter volume have been associated with brain enlargement in 16p11.2 deletion carriers with macrocephaly 24,25 . Increases in neural progenitor cell (NPC) proliferation and neuronal cell size have been associated with brain overgrowth using iPSC models of ASD with macrocephaly or 16p11.2 CNV iPSCs, respectively 26,27 . Using iPSC modeling in two-and three-dimensional systems, recent work has shown that the critical period during which gene networks become dysregulated in autism with macrocephaly occurs early at the neural stem cell stage prior to further differentiation and maturation into neurons 28 .…”

Alterations in neuronal physiology, development, and function associated with a common duplication of chromosome 15 involving CHRNA7

“…In recent years, we and others have characterized cellular phenotypes linked to neurodevelopmental disorders, either in patient iPSC-derived neurons or after introduction of a pathogenic mutation into control iPSCs using CRISPR/Cas9-based gene editing. iPSC-based studies have been conducted to characterize syndromic forms of ASD, de novo cases, and instances where either monogenic or polygenic contributors to disease are indicated (10)(11)(12)(13)(14). These studies identified potential contributors to disease, including alterations in gene expression, differential regulation of developmental signaling pathways, and impairment of neurogenesis and synaptogenesis (11)(12)(13)(15)(16)(17)(18).…”

“…iPSC-based studies have been conducted to characterize syndromic forms of ASD, de novo cases, and instances where either monogenic or polygenic contributors to disease are indicated (10)(11)(12)(13)(14). These studies identified potential contributors to disease, including alterations in gene expression, differential regulation of developmental signaling pathways, and impairment of neurogenesis and synaptogenesis (11)(12)(13)(15)(16)(17)(18). In addition to identifying phenotypes linked to affectation, some of these studies found specific, disorder-linked targets that were amenable to pharmacological rescue (10,19,20).…”