Restoration of Progranulin Expression Rescues Cortical Neuron Generation in Induced Pluripotent Stem Cell Model of Frontotemporal Dementia

To understand how haploinsufficiency of progranulin (PGRN) protein causes frontotemporal dementia (FTD), we created induced pluripotent stem cells (iPSC) from patients carrying the GRNIVS1+5G>C mutation (FTD-iPSCs). FTD-iPSCs were fated to cortical neurons, the cells most affected in FTD and known to express PGRN. Although generation of neuroprogenitors was unaffected, their further differentiation into neurons, especially CTIP2-, FOXP2- or TBR1-TUJ1 double positive cortical neurons, was significantly decreased in FTD-neural progeny. Zinc finger nuclease-mediated introduction of PGRN cDNA into the AAVS1 locus corrected defects in cortical neurogenesis, demonstrating that PGRN haploinsufficiency causes inefficient cortical neuron generation. RNAseq analysis confirmed reversal of altered gene expression profile following genetic correction. Wnt signaling pathway, one of the top defective pathways in FTD-iPSC-derived neurons coupled with its reversal following genetic correction, makes it an important candidate. Therefore, we demonstrate for the first time that PGRN haploinsufficiency hampers corticogenesis in vitro.