Cellular systems for the identification of pathological pathways in Huntington’s disease

Huntington’s disease (HD) is an incurable, neurodegenerative disorder and a member of the polyQ diseases group. HD is characterized by cell loss, mostly GABAergic medium spiny neurons, in the striatum and cortex. The genetic defect of the disease is an abnormal number of tri-nucleotide CAG repeats in the Huntingtin (HTT) gene, which encodes a polyglutamine (polyQ) expansion. These polyQ tracts lead to HTT protein misfolding and aggregation.

While the genetic mutation causing HD has been identified over 25 years ago, the pathologic mechanisms underlying HD are still not clear. In order to elucidate the pathological pathways involved in HD, we established different cell lines to track polyQ aggregate formation/clearance using a genome-wide CRISPR/Cas9-based loss-of-function screen. Comparing RNA-seqing polyQ-containing versus polyQ-less iPSC-derived neuronal progenitor cells, we identified several candidates involved in polyQ biology. In addition, using genome-wide CRISPR screens for the formation of polyQ aggregates in cells which express polyQ-GFP but which lack aggregates, we identified several candidates involved in aggregate formation. Our platform enables an unbiased discovery of polyQ disease relevant pathways, identifying both factors involved in aggregate formation, as well as factors involved in aggregate clearance.