Optical control of network formation in stem cell-derived neurons

Michigan State University, East Lansing MI

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Abstract

? DESCRIPTION (provided by applicant): Neuronal loss is responsible for the profoundly devastating effects of neurological injury and disease for millions of patients worldwide, and the central nervous system has little capacity for self-repair. Regeneration of damaged neural circuitry with stem cell-derived neurons is a promising approach to the problem, particularly given the discovery that pluripotent stem cells can be derived by reprogramming a patient's own skin cells (induced pluripotent stem cells, iPSCs). However, functional integration of stem cell-derived neurons with host tissue continues to be a challenge met with few successes, and the field requires new and better tools to control stem cell fate and connectivity. We propose new optical methods to enable the construction of defined neural networks, where light is used to pattern specific neuronal subtypes and selectively connect them with target cell types. The approach uses a recently-described photosensitive bacterial transcription factor to drive gene expression as well as optogenetic control of neuronal spiking to selectively strengthen or weaken connections between specific populations of neurons. To demonstrate proof-of-concept, the project begins with a functional characterization of rat iPSC-derived neurons and subsequently generates pilot data to demonstrate the feasibility of using spatiotemporal patterns of light-activated gene expression and channel gating to build neural networks. For optical control of connectivity, the frequencies and patterns of stimulation are adopted from literature demonstrating either elimination or stabilization of synapses in mature neurons following optogenetic stimulation. For light-driven gene expression, the photosensitive transcription factor is delivered via recombinant replication-defective retroviruses with broad-spectrum neural promoters. Results are validated through a combination of whole-cell electrophysiology, identification of synaptic markers with immunohistochemistry, and spatially patterned optical induction of fluorescent reporter gene expression. These proof-of-concept studies will establish new protocols to control connectivity between specific neuronal populations with light, with the future potential to use a modified light-activated transcription factor to determine subtype specification. This will lay the foundation to use optical stimulation to define the identity and connectivity of neurons derived from stem cells, giving new tools to construct and reconstruct neural circuitry in vitro and in vivo in future work.