Altered MICOS Morphology and Mitochondrial Ion Homeostasis Contribute to Poly(GR) Toxicity Associated with C9-ALS/FTD

Cell Rep. 2020 Aug 4;32(5):107989. doi: 10.1016/j.celrep.2020.107989.


Amyotrophic lateral sclerosis (ALS) manifests pathological changes in motor neurons and various other cell types. Compared to motor neurons, the contribution of the other cell types to the ALS phenotypes is understudied. G4C2 repeat expansion in C9ORF72 is the most common genetic cause of ALS along with frontotemporal dementia (C9-ALS/FTD), with increasing evidence supporting repeat-encoded poly(GR) in disease pathogenesis. Here, we show in Drosophila muscle that poly(GR) enters mitochondria and interacts with components of the Mitochondrial Contact Site and Cristae Organizing System (MICOS), altering MICOS dynamics and intra-subunit interactions. This impairs mitochondrial inner membrane structure, ion homeostasis, mitochondrial metabolism, and muscle integrity. Similar mitochondrial defects are observed in patient fibroblasts. Genetic manipulation of MICOS components or pharmacological restoration of ion homeostasis with nigericin effectively rescue the mitochondrial pathology and disease phenotypes in both systems. These results implicate MICOS-regulated ion homeostasis in C9-ALS pathogenesis and suggest potential new therapeutic strategies.

Keywords: C9-ALS/FTD; DPR; K(+)/H(+) antiporter; MICOS; Mic27/Apool; Opa1; cristae junction; mitochondrial K(+) homeostasis; muscle; nigericin.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amyotrophic Lateral Sclerosis / genetics*
  • Animals
  • Animals, Genetically Modified
  • C9orf72 Protein / genetics*
  • DNA Repeat Expansion*
  • Drosophila Proteins / metabolism
  • Drosophila melanogaster / genetics
  • Drosophila melanogaster / ultrastructure
  • Fibroblasts / metabolism
  • Fibroblasts / pathology
  • Frontotemporal Dementia / genetics*
  • HEK293 Cells
  • HeLa Cells
  • Homeostasis*
  • Humans
  • Ions
  • Male
  • Mitochondria, Muscle / metabolism*
  • Mitochondria, Muscle / ultrastructure
  • Mitochondrial Proteins / metabolism*
  • Nigericin / pharmacology
  • Protein Binding


  • C9orf72 Protein
  • Drosophila Proteins
  • Ions
  • Mitochondrial Proteins
  • Nigericin