Impaired 26S Proteasome Assembly Precedes Neuronal Loss in Mutant UBQLN2 Rats

Int J Mol Sci. 2021 Apr 21;22(9):4319. doi: 10.3390/ijms22094319.


Proteasomal dysfunction is known to be associated with amyotrophic lateral sclerosis and frontotemporal degeneration (ALS/FTD). Our previous reports have shown that a mutant form of ubiquilin-2 (UBQLN2) linked to ALS/FTD leads to neurodegeneration accompanied by accumulations of the proteasome subunit Rpt1 in transgenic rats, but the precise pathogenic mechanisms of how this mutation impairs the proteasome remains to be elucidated. Here, we reveal that this UBQLN2 mutation in rats disrupted the proteasome integrity prior to neurodegeneration, that it dissociated the 26S proteasome in vitro, and that its depletion did not affect 26S proteasome assembly. During both disease progression and in an age-dependent manner, we found that proteasome subunits were translocated to the nucleus, including both of the 20S core particles (PSMA1 and PSMB7) and the 19S regulatory particles (Rpt1 and Rpn1), suggesting that defective proteasome function may result from the proteasome-subunit mislocalization. Taken together, the present data demonstrate that impaired proteasome assembly is an early event in the pathogenesis of UBQLN2-associated neurodegeneration in mutant UBQLN2 rats.

Keywords: ALS; FTD; UBQLN2; proteasome; protein aggregation; rat.

MeSH terms

  • Amyotrophic Lateral Sclerosis / genetics
  • Amyotrophic Lateral Sclerosis / metabolism
  • Amyotrophic Lateral Sclerosis / physiopathology*
  • Animals
  • Cysteine Endopeptidases
  • Disease Models, Animal
  • Frontotemporal Dementia / genetics
  • Frontotemporal Dementia / metabolism
  • Frontotemporal Dementia / physiopathology*
  • Mutation*
  • Neurons / metabolism
  • Neurons / physiology*
  • Proteasome Endopeptidase Complex / metabolism*
  • Protein Aggregation, Pathological
  • Rats
  • Rats, Transgenic
  • Ubiquitins / genetics*
  • Ubiquitins / metabolism


  • Ubiquitins
  • Ubqln2 protein, rat
  • Cysteine Endopeptidases
  • PSMB7 protein, rat
  • Proteasome Endopeptidase Complex
  • ATP dependent 26S protease

Supplementary concepts

  • Frontotemporal Dementia With Motor Neuron Disease