Cryo-EM Analysis of Ribosomal Defects in C9ORF72-Associated Frontotemporal Dementia and ALS

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Abstract Frontotemporal dementia (FTD), caused by atrophy of frontal and/or anterior temporal lobes, is the second most common form of dementia after Alzheimer’s disease. FTD patients often show changes in personality, loss of empathy and disinhibition, or language impairment and movement deficits. The most common genetic cause of FTD is a GGGGCC (G4C2) repeat expansion in the first intron of the C9ORF72 gene. The sense and antisense repeat RNAs are translated into 5 different dipeptide repeat (DPR) proteins that are observed in C9ORF72 patient brain neurons. Among them, poly(GR) and poly(PR) are most toxic but it remains largely unknown which specific molecular and structural mechanisms of action underly their neurotoxicity. In this R21 project, we will examine the high-resolution structural mechanisms of poly(GR) and poly(PR) production by the ribosome, the underlying cis-inhibition of translation by expanded G4C2 repeats and DPR proteins, and translation dysregulation directly in FTD patient neurons. By discovering the molecular mechanisms of C9ORF72-caused FTD and further developing tools for high-resolution structural biology in neurons, our project may open new directions in neuroscience research and therapeutics development of other molecular pathologies underlying dementia.