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Nat Med. 2018 Mar;24(3):313-325. doi: 10.1038/nm.4490. Epub 2018 Feb 5.

Haploinsufficiency leads to neurodegeneration in C9ORF72 ALS/FTD human induced motor neurons.

Author information

1
Department of Stem Cell Biology and Regenerative Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California, USA.
2
Eli and Edythe Broad CIRM Center for Regenerative Medicine and Stem Cell Research at USC, Los Angeles, California, USA.
3
Zilkha Neurogenetic Institute, Keck School of Medicine of the University of Southern California, Los Angeles, California, USA.
4
Department of Physiology and Biophysics, Keck School of Medicine, University of Southern California, Los Angeles, California, USA.
5
Department of Pathology, Stanford University School of Medicine, Stanford, California, USA.
6
Jefferson Weinberg ALS Center, Vickie and Jack Farber Institute for Neuroscience, Department of Neuroscience, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
7
Department of Translational Neuroscience, Brain Center Rudolf Magnus, University Medical Center Utrecht, Utrecht, the Netherlands.
8
DRVision Technologies, LLC, Bellvue, Washington, USA.
9
Icagen Corporation, Oro Valley, Arizona, USA.
10
Verge Genomics, San Francisco, California, USA.
11
Department of Psychiatry and Behavioral Sciences, Keck School of Medicine, University of Southern California, Los Angeles, California, USA.
12
National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA.
13
Department of Neurology, University Medical Center Utrecht, Utrecht, the Netherlands.

Abstract

An intronic GGGGCC repeat expansion in C9ORF72 is the most common cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), but the pathogenic mechanism of this repeat remains unclear. Using human induced motor neurons (iMNs), we found that repeat-expanded C9ORF72 was haploinsufficient in ALS. We found that C9ORF72 interacted with endosomes and was required for normal vesicle trafficking and lysosomal biogenesis in motor neurons. Repeat expansion reduced C9ORF72 expression, triggering neurodegeneration through two mechanisms: accumulation of glutamate receptors, leading to excitotoxicity, and impaired clearance of neurotoxic dipeptide repeat proteins derived from the repeat expansion. Thus, cooperativity between gain- and loss-of-function mechanisms led to neurodegeneration. Restoring C9ORF72 levels or augmenting its function with constitutively active RAB5 or chemical modulators of RAB5 effectors rescued patient neuron survival and ameliorated neurodegenerative processes in both gain- and loss-of-function C9ORF72 mouse models. Thus, modulating vesicle trafficking was able to rescue neurodegeneration caused by the C9ORF72 repeat expansion. Coupled with rare mutations in ALS2, FIG4, CHMP2B, OPTN and SQSTM1, our results reveal mechanistic convergence on vesicle trafficking in ALS and FTD.

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