Schizophrenia-Relevant DISC1 Interruption Alters Wnt Signaling and Cell Fate in Human iPSC-Derived Neurons

Abstract

The advent of human induced pluripotent stem cell (iPSC) technology has allowed for unprecedented investigation into the pathophysiology of human neurological and psychiatric diseases. Use of human iPSC-derived neural cells to study disease is complicated by the genetic heterogeneity of cell lines and diversity of differentiation protocols. Here, I address issues surrounding neuropsychiatric disease modeling with human iPSCs.

Dozens of published protocols exist to differentiate iPSCs into forebrain neuronal cultures. Among the factors that distinguish these methods are: use of small molecules, monolayer vs. aggregate culture, choice of plating substrates, method of NPC isolation, and glial co-culture. Each of these factors is evaluated here, creating a resource that directly compares a variety of differentiation procedures. The most efficient and reproducible method was an embryoid aggregate differentiation protocol, including aggregate plating onto a Matrigel substrate, enzymatic neural rosette selection, and neuronal dissociation and plating onto Matrigel.

This optimized protocol is used to model a schizophrenia-relevant mutation in human neural cells. Genetic and clinical association studies have identified disrupted-in-schizophrenia 1 (DISC1) as a strong candidate risk gene for major mental illness. DISC1 was initially associated with mental illness upon the discovery that its coding sequence is interrupted by a balanced chr(1;11) translocation in a Scottish family, in which the translocation cosegregates with psychiatric disorders. I investigate the functional and biochemical consequences of DISC1 interruption in human neurons using TALENs or CRISPR-Cas9 to introduce DISC1 frameshift mutations into iPSCs. I show that disease-relevant DISC1 targeting results in decreased DISC1 protein expression by nonsense-mediated decay, increases baseline Wnt signaling in neural progenitor cells, and causes a shift in neural cell fate. DISC1-dependent Wnt signaling and cell fate changes can be reversed by antagonizing the Wnt pathway during a critical window in neural progenitor development. These experiments suggest that DISC1-disruption increases Wnt signaling, which alters the balance and identity of neural progenitors, thereby subtly modifying cell fate.

These studies evaluate the use of multiple differentiation procedures in neural disease modeling, shed light on the roles of DISC1 during human brain development, and further our understanding of the pathogenesis of major mental illness.