Can induced pluripotent stem cells from frontotemporal dementia be used to characterize mechanisms underlying progranulin haploinsufficiency mediated neurodegeneration?

Frontotemporal dementia (FTD) is a neurodegenerative disease, leading to behavioral changes and language difficulties. Unlike other forms of dementia, FTD generally affects younger people and is heritable in many cases, with mutations in three genes (GRN, MAPT and C9orf72) explaining the majority of genetic cases. Autosomal dominant loss-of-function mutations in progranulin (GRN) induce haploinsufficiency of the protein and are associated with up to one third of all genetic FTD cases worldwide. However, in the rare event of homozygous loss of GRN, patients present with the strikingly different phenotype of neuronal ceroid lipofuscinosis. The study of GRN mutations has been hampered by the lack of overt signs of neurodegeneration in heterozygous Grn rodent models. Induced pluripotent stem cell (iPSC) technology offers an interesting alternative to create mutation-specific models and investigate the effects of GRN haploinsufficiency.

In this manuscript, I describe the development a series of genome engineered hiPSC models that enable further study of the specific contribution of the GRN mutation to GRN-linked neurodegeneration. I seamlessly inserted the GRNIVS1+5G>C gene mutation into a normal donor iPSC line and created patient iPSC lines that conditionally overexpress a copy of the GRN gene with the aim to create a flexible, inducible correction of the GRN haploinsufficiency. Functional characterization of patient-derived GRN haploinsufficient iPSC, revealed possible cytoskeletal dysfunction. Transcriptome analysis of patient-derived and engineered GRN mutant neuronal progeny supported this possibility by revealing a disease-related transcriptional signature of reduced expression of extracellular matrix and cytoskeletal components. Investigating patient-derived and genome engineered GRNIVS1+5G>C PSC and cortical neurons, therefore unequivocally links disease related phenotypes to GRN haploinsufficiency. 

A key feature of neurons, is their electrophysiological activity. Investigating electrophysiological activity by standard methods however, is time-consuming and restricted in throughput. With the aim to improve maturation of neuronal cultures, I examined the effect of nanotopography on neuronal PSC progeny and it’s applicability in microelectrode arrays (MEA). This lead to the development of a novel tool to investigate neurodegeneration.