Pharmacological Regulation of Neural Circuit Formation in hIPSC-Derived Neurons and ‘Mini-Brains’
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Date
2018-07-20
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Authors
Rudisill, Taylor Lee
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East Carolina University
Abstract
Emerging evidence suggests that altered neural connectivity, particularly at the level of synaptic connections, contributes to the pathology of many neurodevelopmental and neurodegenerative diseases. For instance, post-mortem Autistic patient brain samples have increased numbers of excitatory to inhibitory synaptic connections, referred to as an E/I imbalance [42]. Contrastingly, post-mortem brain samples from patients diagnosed with Alzheimer's disease have decreased numbers of synaptic connections [42]. In order to understand the mechanisms that underlie the formation of these synaptic circuits, we develop 3-D human cortical organoids ('mini-brains') from human-induced pluripotent stem cells (hIPSCs). Previous research demonstrates that rearrangements of the actomyosin cytoskeleton drive neural circuit formation, in particular the development and maturation of actin-enriched spines at excitatory synapses. This thesis work investigates how pharmacological regulation of actomyosin activity affects neuronal connectivity during neurite formation in 2-D and excitatory synapse formation in 3-D 'mini-brains'. The Rho-Kinase (ROCK) inhibitor, Y-27632, both inhibits non-muscle myosin II (NM-II) and leads to a corresponding increase in Rac-driven actin polymerization. In 2-D, Y-27632 promotes neurite formation. Specifically, Y-27632 increases the number, length, and branching of neurites in hIPSC-derived neurons. Furthermore, Y-27632 increases neurite persistence, while decreasing neurite protrusion and retraction rates. However, in 3-D, acute Y-27632 treatment increases excitatory synapse area, consistent with an increase in Rac-driven actin polymerization [39]. Thus, Y-27632 increases both neurite outgrowth and excitatory synapse formation and may serve as a potential therapeutic for neurodegenerative diseases associated with synapse loss such as Alzheimer's disease. This study demonstrates the need for physiologically-relevant brain models, such as 3-D cortical organoids, to assess the impact of drug therapies on developing neural circuits to potentially treat neurodevelopmental and neurodegenerative disorders.