Department of Cell Biology, Emory University, Atlanta, United States
Nancy Zhang
Department of Cell Biology, Emory University, Atlanta, United States
Elke Braems
Department of Neurosciences, Experimental Neurology and Leuven Brain Institute, KU Leuven, Leuven, Belgium; Center for Brain & Disease Research, Laboratory of Neurobiology, VIB, Campus Gasthuisberg, Leuven, Belgium
Department of Cell Biology, Emory University, Atlanta, United States
Keena Yin
Department of Cell Biology, Emory University, Atlanta, United States
Seneshaw Asress
Department of Neurology, Emory University, Atlanta, United States
Kara Heeren
Department of Neurosciences, Experimental Neurology and Leuven Brain Institute, KU Leuven, Leuven, Belgium; Center for Brain & Disease Research, Laboratory of Neurobiology, VIB, Campus Gasthuisberg, Leuven, Belgium
Anwesha Banerjee
Department of Cell Biology, Emory University, Atlanta, United States
Emma Davis
Department of Cell Biology, Emory University, Atlanta, United States
Samantha L Schwartz
Department of Biochemistry, Emory University, Atlanta, United States
Graeme L Conn
Department of Biochemistry, Emory University, Atlanta, United States
Gary J Bassell
Department of Cell Biology, Emory University, Atlanta, United States
Ludo Van Den Bosch
Department of Neurosciences, Experimental Neurology and Leuven Brain Institute, KU Leuven, Leuven, Belgium; Center for Brain & Disease Research, Laboratory of Neurobiology, VIB, Campus Gasthuisberg, Leuven, Belgium
GGGGCC (G4C2) hexanucleotide repeat expansion in the C9ORF72 gene is the most common genetic cause of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). The repeat is bidirectionally transcribed and confers gain of toxicity. However, the underlying toxic species is debated, and it is not clear whether antisense CCCCGG (C4G2) repeat expanded RNAs contribute to disease pathogenesis. Our study shows that C9ORF72 antisense C4G2 repeat expanded RNAs trigger the activation of the PKR/eIF2α-dependent integrated stress response independent of dipeptide repeat proteins that are produced through repeat-associated non-AUG-initiated translation, leading to global translation inhibition and stress granule formation. Reducing PKR levels with either siRNA or morpholinos mitigates integrated stress response and toxicity caused by the antisense C4G2 RNAs in cell lines, primary neurons, and zebrafish. Increased phosphorylation of PKR/eIF2α is also observed in the frontal cortex of C9ORF72 FTD/ALS patients. Finally, only antisense C4G2, but not sense G4C2, repeat expanded RNAs robustly activate the PKR/eIF2α pathway and induce aberrant stress granule formation. These results provide a mechanism by which antisense C4G2 repeat expanded RNAs elicit neuronal toxicity in FTD/ALS caused by C9ORF72 repeat expansions.
