Human in vitro models for understanding mechanisms of autism spectrum disorder.

Early brain development is a critical epoch for the development of autism spectrum disorder (ASD). In vivo animal models have, until recently, been the principal tool used to study early brain development and the changes occurring in neurodevelopmental disorders such as ASD. In vitro models of brain development represent a significant advance in the field. Here, we review the main methods available to study human brain development in vitro and the applications of these models for studying ASD and other psychiatric disorders. We discuss the main findings from stem cell models to date focusing on cell cycle and proliferation, cell death, cell differentiation and maturation, and neuronal signaling and synaptic stimuli. To be able to generalize the results from these studies, we propose a framework of experimental design and power considerations for using in vitro models to study ASD. These include both technical issues such as reproducibility and power analysis and conceptual issues such as the brain region and cell types being modeled

The iPSC perspective on schizophrenia

Over a decade of schizophrenia research using human induced pluripotent stem cell (iPSC)-derived neural models has provided substantial data describing neurobiological characteristics of the disorder in vitro. Simultaneously, translation of the results into general mechanistic concepts underlying schizophrenia pathophysiology has been trailing behind. Given that modeling brain function using cell cultures is challenging, the gap between the in vitro models and schizophrenia as a clinical disorder has remained wide. In this review, we highlight reproducible findings and emerging trends in recent schizophrenia-related iPSC studies. We illuminate the relevance of the results in the context of human brain development, with a focus on processes coinciding with critical developmental periods for schizophrenia.Peer reviewe

MicroRNA Dysregulation in Neuropsychiatric Disorders and Cognitive Dysfunction

MicroRNAs (miRNAs) are evolutionarily-conserved small non-coding RNAs that are important posttranscriptional regulators of gene expression. Genetic Variants may cause microRNA dysregulation and the concomitant aberrant target expression. The dysregulation of one or a few targets may in turn lead to functional consequences ranging from phenotypic variations to disease conditions. In this thesis, I present our studies of mouse models of two human genetic variants - a rare copy number variant (CNV), 22q11.2 microdeletions, and a common single nucleotide polymorphism (SNP), BDNF Val66Met. 22q11.2 microdeletions result in specific cognitive deficits and high risk to develop schizophrenia. Analysis of Df(16)A+/- mice, which model this microdeletion, revealed abnormalities in the formation of neuronal dendrites and spines as well as microRNA dysregulation in brain. We show a drastic reduction of miR- 185, which resides within the 22q11.2 locus, to levels more than expected by a hemizygous deletion and demonstrate that this reduction impairs dendritic and spine development. miR-185 targets and represses, through an evolutionary conserved target site, a previously unknown inhibitor of these processes that resides in the Golgi apparatus. Sustained derepression of this inhibitor after birth represents the most robust transcriptional disturbance in the brains of Df(16)A+/- mice and could affect the formation and maintenance of neural circuits. Reduction of miR-185 also has milder effects on the expression of a group of Golgi-related genes. One the other hand, BNDF Val66Met results in impaired activity-dependent secretion of BDNF from neuronal terminals and affects episodic memory and affective behaviors. We found a modest reduction of miR-146b which causes derepression of mRNA and/or protein levels of a few targets. Our findings add to the growing evidence of the pivotal involvement of miRNAs in the development of neuropsychiatric disorders and cognitive dysfunction. In addition, the identification of key players in miRNA dysregulation has implications for both basic and translational research in psychiatric disorders and cognitive dysfunction

The 22q11.2 region regulates presynaptic gene-products linked to schizophrenia

How the 22q11.2 deletion predisposes to psychiatric disease is unclear. Here, the authors examine living human neuronal cells and show that 22q11.2 regulates the expression of genes linked to autism during early development, and genes linked to schizophrenia and synaptic biology in neurons. It is unclear how the 22q11.2 deletion predisposes to psychiatric disease. To study this, we generated induced pluripotent stem cells from deletion carriers and controls and utilized CRISPR/Cas9 to introduce the heterozygous deletion into a control cell line. Here, we show that upon differentiation into neural progenitor cells, the deletion acted in trans to alter the abundance of transcripts associated with risk for neurodevelopmental disorders including autism. In excitatory neurons, altered transcripts encoded presynaptic factors and were associated with genetic risk for schizophrenia, including common and rare variants. To understand how the deletion contributed to these changes, we defined the minimal protein-protein interaction network that best explains gene expression alterations. We found that many genes in 22q11.2 interact in presynaptic, proteasome, and JUN/FOS transcriptional pathways. Our findings suggest that the 22q11.2 deletion impacts genes that may converge with psychiatric risk loci to influence disease manifestation in each deletion carrier.Peer reviewe

The Perspectives of Early Diagnosis of Schizophrenia Through the Detection of Epigenomics-Based Biomarkers in iPSC-Derived Neurons

The lack of early diagnostic biomarkers for schizophrenia greatly limits treatment options that deliver therapeutic agents to affected cells at a timely manner. While previous schizophrenia biomarker research has identified various biological signals that are correlated with certain diseases, their reliability and practicality as an early diagnostic tool remains unclear. In this article, we discuss the use of atypical epigenetic and/or consequent transcriptional alterations (ETAs) as biomarkers of early-stage schizophrenia. Furthermore, we review the viability of discovering and applying these biomarkers through the use of cutting-edge technologies such as human induced pluripotent stem cell (iPSC)-derived neurons, brain models, and single-cell level analyses. Copyright © 2021 Lee, Seo, Jeong, Lee and Lee.1

Modeling psychiatric disorders: from genomic findings to cellular phenotypes

Major programs in psychiatric genetics have identified 4150 risk loci for psychiatric disorders. These loci converge on a small number of functional pathways, which span conventional diagnostic criteria, suggesting a partly common biology underlying schizophrenia, autism and other psychiatric disorders. Nevertheless, the cellular phenotypes that capture the fundamental features of psychiatric disorders have not yet been determined. Recent advances in genetics and stem cell biology offer new prospects for cell-based modeling of psychiatric disorders. The advent of cell reprogramming and induced pluripotent stem cells (iPSC) provides an opportunity to translate genetic findings into patient-specific in vitro models. iPSC technology is less than a decade old but holds great promise for bridging the gaps between patients, genetics and biology. Despite many obvious advantages, iPSC studies still present multiple challenges. In this expert review, we critically review the challenges for modeling of psychiatric disorders, potential solutions and how iPSC technology can be used to develop an analytical framework for the evaluation and therapeutic manipulation of fundamental disease processes

Investigating functional and genetic interactions underlying schizophrenia risk in 22q11.2 Deletion Syndrome

22q11.2 Deletion Syndrome (22q11.2DS) is a genetic disorder caused by a hemizygous deletion at chromosome 22q11.2. It is the most common chromosomal microdeletion and the strongest known molecular genetic risk factor associated with schizophrenia. However, the underlying mechanisms that lead to this neuropsychiatric risk remain largely unknown. The work in this thesis sought to investigate possible genetic and functional mechanisms that contribute to schizophrenia risk in 22q.11.2DS. Potential schizophrenia candidate and disease modifier genes from within and outside of the 22q11.2 deletion region were explored. From within the deletion, DGCR8 was initially selected as a gene of interest due to its key role in the microRNA biogenesis pathway and therefore gene expression regulation. Additional candidate genes were identified by assessing gene co-expression during fetal development in relation to DGCR8 and predicated of loss of function and happloinsuffiency intolerance, leading to the selection of HIRA and ZDHHC8. Transcriptome wide association studies were performed in disease relevant tissues to identify schizophrenia modifier genes outside of the deletion by comparing 22q11.2DS patients with and without schizophrenia. However, this analysis identified no significant differences in gene expression. CRISPR/Cas9 genome editing technology was utilised to knockout DGCR8 in human embryonic stem cells. Mutant lines were generated and differentiated into cortical neuroprogenitor cells to investigate the role of DGCR8 in neurodevelopment. This work provided further evidence that DGCR8 knockout lines derived from human embryonic stem cells may not be a viable method of modelling due to genomic instability, lack of protein reduction and so insufficient disease recapitulation. Finally, a lentiviral based CRISPR/Cas9 system in human neuroprogenitor cells (hNPCs) was established. Genetic manipulation of DGCR8 in hNPCs further indicated a relationship between DGCR8 and TBR1 in cortical development. This thesis combines bioinformatic and cellular approaches to provide a basis for investigation of mechanisms underlying schizophrenia risk in 22q11.2DS