Direct programming of neural progenitors into medium spiny neurons by transcription factor transfection

Huntington’s disease is an autosomal dominant neurological disease caused by an elongated CAG repeat in exon 1 of the huntingtin gene. There is currently no cure and treatments are limited. The genetic mutation causes selective cell death of the medium spiny neurons which reside in the striatum of the basal ganglia. Current disease models don’t necessarily recapitulate all aspects of the human disease and so alternatives are needed. The advent of induced pluripotent stem cells (iPSC), has allowed for HD patient specific pluripotent stem cells to be derived, hence differentiation of these cells in vitro could provide a disease model for drug testing and investigation of disease pathology. Current protocols for differentiation of pluripotent stem cells into medium spiny neurons (MSNs) are often inconsistent and lead to low yields of MSNs. Directing differentiation through forced expression of transcription factors has been used to differentiate neurons from fibroblasts and pluripotent stem cells, often with increased efficiency. Utilising transcription factors vital in post-mitotic MSN development, this study has aimed to produce MSNs in vitro, by transfection of transcription factors or combinations thereof in a multicistronic plasmid into ventral forebrain neural progenitors. This study has involved the cloning and expression of 5 different transcription factors important in MSN development in iPSC-derived neural progenitors. Two of these transcription factors; NOLZ1 (ZNF503) and ISL1 were further investigated for their ability to differentiate neural progentiroes into MSNs. This study showed that transfection of ISL1 enabled differentiation of neurons to produce a higher proportion of cells resembling MSNs, characterised by co-expression of the MSN markers DARPP32 and CTIP2 and expressing FOXP1. The combination of NOLZ1 and ISL1 in transfection improved functional maturation of neurons, becoming increasingly spontaneously active and increased excitability, as well as responding to GABA and NMDA, with dopamine D1 agonist enhancement of NMDA currents