CGG repeat expansion in NOTCH2NLC causes mitochondrial dysfunction and progressive neurodegeneration in Drosophila model

Proc Natl Acad Sci U S A. 2022 Oct 11;119(41):e2208649119. doi: 10.1073/pnas.2208649119. Epub 2022 Oct 3.


Neuronal intranuclear inclusion disease (NIID) is a neuromuscular/neurodegenerative disease caused by the expansion of CGG repeats in the 5' untranslated region (UTR) of the NOTCH2NLC gene. These repeats can be translated into a polyglycine-containing protein, uN2CpolyG, which forms protein inclusions and is toxic in cell models, albeit through an unknown mechanism. Here, we established a transgenic Drosophila model expressing uN2CpolyG in multiple systems, which resulted in progressive neuronal cell loss, locomotor deficiency, and shortened lifespan. Interestingly, electron microscopy revealed mitochondrial swelling both in transgenic flies and in muscle biopsies of individuals with NIID. Immunofluorescence and immunoelectron microscopy showed colocalization of uN2CpolyG with mitochondria in cell and patient samples, while biochemical analysis revealed that uN2CpolyG interacted with a mitochondrial RNA binding protein, LRPPRC (leucine-rich pentatricopeptide repeat motif-containing protein). Furthermore, RNA sequencing (RNA-seq) analysis and functional assays showed down-regulated mitochondrial oxidative phosphorylation in uN2CpolyG-expressing flies and NIID muscle biopsies. Finally, idebenone treatment restored mitochondrial function and alleviated neurodegenerative phenotypes in transgenic flies. Overall, these results indicate that transgenic flies expressing uN2CpolyG recapitulate key features of NIID and that reversing mitochondrial dysfunction might provide a potential therapeutic approach for this disorder.

Keywords: idebenone treatment; mitochondrial oxidative phosphorylation defects; neuronal intranuclear inclusion disease; polyG; transgenic Drosophila model.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 5' Untranslated Regions
  • Animals
  • Animals, Genetically Modified
  • Drosophila* / genetics
  • Intranuclear Inclusion Bodies / genetics
  • Intranuclear Inclusion Bodies / pathology
  • Leucine / genetics
  • Mitochondria / genetics
  • Mitochondria / pathology
  • Neurodegenerative Diseases* / genetics
  • Neurodegenerative Diseases* / pathology
  • RNA-Binding Proteins / genetics
  • Trinucleotide Repeat Expansion / genetics


  • 5' Untranslated Regions
  • RNA-Binding Proteins
  • Leucine

Supplementary concepts

  • Neuronal intranuclear inclusion disease