Mechanisms of toxicity in C9FTLD/ALS

• Published in: Acta neuropathologica Vol. 127; no. 3; pp. 359 - 376
• Main Authors: Gendron, Tania F., Belzil, Veronique V., Zhang, Yong-Jie, Petrucelli, Leonard
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.03.2014; Springer; Springer Nature B.V
• Subjects: Amyotrophic lateral sclerosis; Amyotrophic Lateral Sclerosis - genetics; Amyotrophic Lateral Sclerosis - metabolism; Amyotrophic Lateral Sclerosis - pathology; Animals; Binding proteins; Brain - metabolism; Brain - pathology; C9orf72 Protein; Disease; DNA Repeat Expansion; Epigenetic inheritance; Epigenetics; Frontotemporal Lobar Degeneration - genetics; Frontotemporal Lobar Degeneration - metabolism; Frontotemporal Lobar Degeneration - pathology; Genetic translation; Humans; Kinases; Medicine; Medicine & Public Health; Neurodegenerative Diseases - genetics; Neurodegenerative Diseases - metabolism; Neurodegenerative Diseases - pathology; Neurosciences; Pathology; Protein binding; Proteins; Proteins - genetics; Proteins - metabolism; Review; RNA; RNA - metabolism; Spinal cord; Spinal Cord - metabolism; Spinal Cord - pathology; Toxicity; Bidirectional transcription; Epigenetics; Expanded repeat; Repeat-associated non-ATG translation; Amyotrophic lateral sclerosis; Frontotemporal lobar degeneration; C9ORF72; RNA foci
• ISSN: 0001-6322; 1432-0533
• DOI: 10.1007/s00401-013-1237-z

A hexanucleotide repeat expansion within a non-coding region of the C9ORF72 gene is the most common mutation causative of frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS). Elucidating how this bidirectionally transcribed G 4 C 2 ·C 4 G 2 expanded repeat causes “C9FTLD/ALS” has since become an important goal of the field. Likely pathogenic mechanisms include toxicity induced by repeat-containing RNAs, and loss of C9orf72 function due to epigenetic changes resulting in decreased C9ORF72 mRNA expression. With regards to the former, sense and antisense transcripts of the expanded repeat aberrantly interact with various RNA-binding proteins and form discrete nuclear structures, termed RNA foci. These foci have the capacity to sequester select RNA-binding proteins, thereby impairing their function. (G 4 C 2 ) exp and (C 4 G 2 ) exp transcripts also succumb to an alternative fate: repeat-associated non-ATG (RAN) translation. This unconventional mode of translation, which occurs in the absence of an initiating codon, results in the abnormal production of poly(GA), poly(GP), poly(GR), poly(PR) and poly(PA) peptides, collectively referred to as C9RAN proteins. C9RAN proteins form neuronal inclusions throughout the central nervous system of C9FTLD/ALS patients and may contribute to disease pathogenesis. This review aims to summarize the important findings from studies examining mechanisms of disease in C9FTLD/ALS, and will also highlight some of the many questions in need of further investigation.