DEVELOPING A CLINCALLY RELEVANT ISOGENIC CELL LINE OF HUNTINGTON’S DISEASE

Abstract

Huntington’s Disease (HD) is a neurodegenerative disease caused by a CAG expansion in exon 1 of the HTT gene. The age of symptom onset is inversely correlated with the length of the CAG tract. CAA interruptions in the CAG tract have a protective effect, delaying the onset of symptoms despite still coding for a glutamine residue. Evidence suggests that genes outside of the CAG expansion also contribute to differences in age of symptom onset. To improve our knowledge of disease, a clinically relevant model system is necessary. Here, we identify that many model systems use overexpressed protein that fails to adhere to the stoichiometry of an endogenous system. Many systems also use CAG expansions beyond what would be seen in a clinical case of HD or do not appropriately account for the influence of other genes. TruHD fibroblast cells immortalized with human telomerase reverse transcriptase are derived from patient samples and have a stable genome. Here, we discuss attempts to develop isogenic cell lines by editing TruHD cells to have different CAG repeats. While we were unsuccessful in isolating clones carrying the desired edit, future researchers can use this work as a guide to navigate the successful creation of isogenic cells. We can compare phenotypes between pre and post edited cells to see how they change with a new CAG length in an otherwise stable genetic background. We also discuss the successful editing of TruHD cells with a CAG to CAA base edit to introduce a CAA interruption in diseased cells. We discuss how to propagate these cells for future research to compare pre and post edited cells to better understand the protective action of CAA interruptions.