STEM CELL MODELS OF BIPOLAR DISORDER - A DEVELOPMENTAL PERSPECTIVE

Abstract A major challenge in understanding human neuropsychiatric disorders is the lack of viable cells and tissues for analysis. Patient-derived induced pluripotent stem cells (iPSC) offer the opportunity to examine the full complement of neural tissues to identify underlying disease mechanisms. Increasingly considered to have a neurodevelopmental basis, to study Bipolar Disorder (BP), we have derived and characterized iPSC from fibroblasts obtained from undiagnosed Controls (C) and patients with BP, and have coaxed them to form neurons and glial cells. Using microarray analysis of BP and unaffected control iPSC neurons, we previously identified differences in neuronal lineage allocation between groups, with BP neurons favoring differentiation of ventral MGE derivatives and Control neurons forming dorsal cortical precursors. To determine the developmental basis of these observations we employed microarray analysis, identifying 59 miRNAs that were significantly dysregulated in BP iPSC neurons. We have validated 5 miRNAs that were elevated and 3 miRNAs that were lower in BP derived neurons. GO pathway analysis of miRNAs significantly elevated in BP derived neurons indicate that these miRNAs regulate a wide variety of cellular processes, including proliferation, cell junction and extracellular matrix organization, chromatin modification, mRNA processing, and carbohydrate metabolism. We use a luciferase assay to validate the targets of these miRNAs, which will then be overexpressed in iPSC derived cells to determine their effects on neuronal behavior. To determine if our results are restricted to neurons we examined differences in the behavior of astrocytes derived from BP and C individuals. After differentiation as astrospheres, precursors were passaged and expanded in FGF-2 and EGF producing a population of astrocytes which were positive for the glial precursor marker CD44. Expression of S100beta, and the glutamate transporters EAAT1 and EAAT2 were markedly lower in BP astrocytes, and cell doubling times at early passage number were greater in BP cells. These differences in gene expression and behavior suggest that BP astrocytes are functionally distinct from control astrocytes. Current investigations are in progress to examine gliotransmitter expression and behaviors in co-culture. We have identified differences in calcium signaling in BP vs C neurons; BP neurons are more active than those derived from Control patients. Remarkably, lithium pre-treatment significantly reduced calcium transients and wave amplitude in BP neurons to Control levels, providing a tractable model system to examine the response of iPSC-derived neurons to pathway perturbagens and treatments involved in BP. One of those is ketamine, which we are applying to brain organoids derived from iPSC to determine their response to this therapeutic. Additional work is examining the effects of increased CACNA1C expression associated with the AA allele of rs1006737 -- the strongest and most replicated association with bipolar disorder -- in neuronal differentiation and function. AA carrier BP cells are undergoing gene editing to revert the mutant genotype to GG, and their calcium signaling and differentiation potential assessed. The overarching goal of our research is to identify novel disease phenotypes and mechanisms involved in bipolar disorder, with the long term goal of improving treatment.