Reduced autophagy upon C9ORF72 loss synergizes with dipeptide repeat protein toxicity in G4C2 repeat expansion disorders

EMBO J. 2020 Feb 17;39(4):e100574. doi: 10.15252/embj.2018100574. Epub 2020 Jan 13.


Expansion of G4C2 repeats within the C9ORF72 gene is the most common cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Such repeats lead to decreased expression of the autophagy regulator C9ORF72 protein. Furthermore, sense and antisense repeats are translated into toxic dipeptide repeat (DPR) proteins. It is unclear how these repeats are translated, and in which way their translation and the reduced expression of C9ORF72 modulate repeat toxicity. Here, we found that sense and antisense repeats are translated upon initiation at canonical AUG or near-cognate start codons, resulting in polyGA-, polyPG-, and to a lesser degree polyGR-DPR proteins. However, accumulation of these proteins is prevented by autophagy. Importantly, reduced C9ORF72 levels lead to suboptimal autophagy, thereby impairing clearance of DPR proteins and causing their toxic accumulation, ultimately resulting in neuronal cell death. Of clinical importance, pharmacological compounds activating autophagy can prevent neuronal cell death caused by DPR proteins accumulation. These results suggest the existence of a double-hit pathogenic mechanism in ALS/FTD, whereby reduced expression of C9ORF72 synergizes with DPR protein accumulation and toxicity.

Keywords: C9ORF72; RAN translation; amyotrophic lateral sclerosis; autophagy; neurodegeneration.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amyotrophic Lateral Sclerosis / genetics*
  • Amyotrophic Lateral Sclerosis / pathology
  • Autophagy*
  • C9orf72 Protein / genetics*
  • C9orf72 Protein / metabolism
  • Cell Death
  • DNA Repeat Expansion
  • Dipeptides / genetics
  • Dipeptides / toxicity*
  • Frontotemporal Dementia / genetics*
  • Frontotemporal Dementia / pathology
  • HEK293 Cells
  • Humans
  • Neurons / pathology
  • Proteins / genetics
  • Proteins / toxicity


  • C9orf72 Protein
  • C9orf72 protein, human
  • Dipeptides
  • Proteins

Supplementary concepts

  • Frontotemporal Dementia With Motor Neuron Disease