Idiopathic Autism: Cellular and Molecular Phenotypes in Pluripotent Stem Cell-Derived Neurons

Abstract

Autism spectrum disorder is a complex neurodevelopmental disorder whose pathophysiology remains elusive as a consequence of the unavailability for study of patient brain neurons; this deficit may potentially be circumvented by neural differentiation of induced pluripotent stem cells. Rare syndromes with single gene mutations and autistic symptoms have significantly advanced the molecular and cellular understanding of autism spectrum disorders, however, in aggregate they only represent a fraction of all cases of autism. In an effort to define the cellular and molecular phenotypes in human neurons of non-syndromic autism we generated induced pluripotent stem cells (iPSCs) from three male autism spectrum disorder patients who had no identifiable clinical syndromes, and their unaffected male siblings and subsequently differentiated these patient-specific stem cells into electrophysiologically active neurons. iPSC-derived neurons from these autistic patients displayed decreases in the frequency and kinetics of spontaneous excitatory postsynaptic currents relative to controls, as well as significant decreases in Na+ and inactivating K+ voltage-gated currents. Moreover, whole-genome microarray analysis of gene expression identified 161 unique genes that were significantly differentially expressed in autistic patients iPSCs-derived neurons (> two-fold, FDR < 0·05). These genes were significantly enriched for processes related to synaptic transmission, such as neuroactive ligand-receptor signaling and extracellular matrix interactions, and were enriched for genes previously associated with autism spectrum disorder. Our data demonstrate aberrant voltage-gated currents and underlying molecular changes related to synaptic function in iPSCs-derived neurons from individuals with idiopathic autism as compared to unaffected siblings controls.

Human in vitro models for understanding mechanisms of autism spectrum disorder

“…Two kinds of genetic modeling have been performed using cells either from individuals whose genetic contributions are unknown or undefined, so called idiopathic [59,60,[112][113][114][115][116][117][118][119][120], or from individuals harboring major effect mutations that are presumed causal or which have been engineered to carry these mutations. These mutations include ASD-associated CNVs such as 15q11q13 deletion (Angelman syndrome) [121] and duplication (Dup15q syndrome) [122], 22q11.2 deletion (DiGeorge syndrome) [123,124], 16p11.2 deletion and duplication [125], and 15q13.3 deletion [126], as well as single-gene mutations including SHANK3 [127][128][129][130], CHD8 [131,132], NRXN1 [133][134][135][136][137], NLGN4 [138], EHMT1 (Kleefstra syndrome) [139], PTCHD1-AS [140], UBE3A (Angelman's syndrome) [141], and CACNA1C (Timothy syndrome) [142] (summarized in Table 1).…”

“…Dysregulation in neuronal differentiation and synaptic and dendritic deficits may underlie the decreased spontaneous activity and decreased excitability found in many studies. These are often observed in neurons derived from individuals with idiopathic forms of ASD [112,116,167], as well as from individuals with genetically defined forms of ASD such as SHANK3 [127,130], 16p11.2 deletion and duplication [125], Angelman syndrome [121], Dup15q syndrome [122], NRXN1 mutations [133,135,137], and PTCHD1-AS [140]. Decreases in spontaneous neuronal activity were also found in five out of ten genes associated with ASD when mutations were introduced into neurons derived from typically developing individuals (ATRX, AFF2, KCNQ2, SCN2A, and ASTN2; see Table 1 for the full list of genes tested) [147].…”

Enriched expression of genes associated with autism spectrum disorders in human inhibitory neurons

“…Because of the extensive genetic heterogeneity in ASD, investigators have carried out transcriptomic studies in postmortem samples or ASD patient-derived neural samples with the goals of finding common pathways and cellular processes dysregulated in ASD brains or neural samples 34-40 . We thus decided to study whether differentially expressed genes (DEGs) in molecular studies carried out between ASD and control subjects exhibited similar cell type-biased expression patterns as ASD candidate genes identified from genetic studies.…”

“…Differentially expressed genes in blood 35 were also detected by GEO2R and defined as p<0.05. Gene lists from other brain-related samples, including postmortem cortices (“Cortex2” 36 and “Cortex3” 37 ), induced pluripotent stem cell (iPSC)-derived cerebral organoids (“Organoid”) 38 , neural progenitor cells (NPC) 39 , and neurons (“Neuronl” 39 and “Neuron2” 40 ), were obtained from the original papers.…”

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

“…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).…”