Research Projects

Nucleotide repeat expansions cause more than fifty human diseases, most of which primarily affect the nervous system. Expanded repeat RNAs can be translated into toxic peptides through a non-canonical translation inhiation process known as repeat-associated non-AUG (RAN) translation. A hexanucleotide ‘GGGGCC’ repeat expansion in the C9orf72 gene is the major genetic cause of both Amyotrophic Lateral Sclerosis and Frontotemporal Dementia (C9orf72-associated ALS/FTD). Expanded G4C2 repeat RNA can sequester cellular RNA-binding proteins (RBPs) into nuclear foci and can undergo RAN translation to produce dipeptide repeat proteins (DPRs: glycine-alanine [GA], glycine-proline [GP], and glycine-arginine [GR] from the sense strand; proline-arginine [PR], and proline-alanine [PA] peptides). While RAN translation is an important phenomenon contributing to disease, it is a highly inefficient process, and the amount of RAN-translated dipeptide products is not very high. This indicates other processes related to RAN translation may also contribute to the disease. Recently it was found that, presumably due to translational frameshifting, a chimeric DPR is produced from the ‘GGGGCC’ repeat RNA that may contribute to the severe outcome of ALS/FTD as opposed to homogenous DPR. In our previous work, using chemical probing and deep sequencing, we determined the GGGGCC repeat RNA structure, which promotes RAN translation in vivo. Based on the initial outcomes of the previous project, now I propose to determine how ‘GGGGCC’ repeat RNA folding may lead to ribosome stalling, collision, and frameshifting to produce toxic chimeric peptides and determine neuronal cell fate decisions. Further, we propose to utilize a dual targeting of dipeptide repeat toxicity. First, we will employ RNA G-quadruplex targeting small molecules to inhibit dipeptide repeats and chimeric DPR productions. In parallel, we will use an engineered molecular chaperone to directly counter toxic repeat peptides produced through RAN translation to mitigate DPR toxicity in C9orf72-associated ALS/FTD.