Tau Accumulation via Reduced Autophagy Mediates GGGGCC Repeat Expansion-Induced Neurodegeneration in Drosophila Model of ALS
Xue Wen 1 • Ping An 1 • Hexuan Li 1 • Zijian Zhou1 • Yimin Sun 1 • Jian Wang 1 • Lixiang Ma 2 • Boxun Lu 1
1 Neurology Department at Huashan Hospital, State Key Laboratory of Medical Neurobiology and Ministry of Education Frontiers Center for Brain Science, School of Life Sciences, Fudan University, Shanghai 200438, China
2 Department of Anatomy, Histology and Embryology, School of Basic Medical Sciences, Fudan University, Shanghai 200032, China
Abstract
Expansions of trinucleotide or hexanucleotide repeats lead to several neurodegenerative disorders, including Huntington disease [caused by expanded CAG repeats (CAGr) in the HTT gene], and amyotrophic lateral sclerosis [ALS, possibly caused by expanded GGGGCC repeats (G4C2r) in the C9ORF72 gene], of which the molecular mechanisms remain unclear. Here, we demonstrated that lowering the Drosophila homologue of tau protein (dtau) significantly rescued in vivo neurodegeneration, motor performance impairments, and the shortened life-span in Drosophila expressing expanded CAGr or expanded G4C2r. Expression of human tau (htau4R) restored the disease-related phenotypes that had been mitigated by the loss of dtau, suggesting an evolutionarily-conserved role of tau in neurodegeneration. We further revealed that G4C2r expression increased tau accumulation by inhibiting autophagosome–lysosome fusion, possibly due to lowering the level of BAG3, a regulator of autophagy and tau. Taken together, our results reveal a novel mechanism by which expanded G4C2r causes neurodegeneration via an evolutionarily-conserved mechanism. Our findings provide novel autophagy-related mechanistic insights into C9ORF72-ALS and possible entry points to disease treatment.
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