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Progressive aggregation despite chaperone associations of a mutant SOD1-YFP in transgenic mice that develop ALS.

Recent studies suggest that superoxide dismutase 1 (SOD1)-linked amyotrophic lateral sclerosis results from destabilization and misfolding of mutant forms of this abundant cytosolic enzyme. Here, we have tracked the expression and fate of a misfolding-prone human SOD1, G85R, fused to YFP, in a line of transgenic G85R SOD1-YFP mice. These mice, but not wild-type human SOD1-YFP transgenics, developed lethal paralyzing motor symptoms at 9 months. In situ RNA hybridization of spinal cords revealed predominant expression in motor neurons in spinal cord gray matter in all transgenic animals. Concordantly, G85R SOD-YFP was diffusely fluorescent in motor neurons of animals at 1 and 6 months of age, but at the time of symptoms, punctate aggregates were observed in cell bodies and processes. Biochemical analyses of spinal cord soluble extracts indicated that G85R SOD-YFP behaved as a misfolded monomer at all ages. It became progressively insoluble at 6 and 9 months of age, associated with presence of soluble oligomers observable by gel filtration. Immunoaffinity capture and mass spectrometry revealed association of G85R SOD-YFP, but not WT SOD-YFP, with the cytosolic chaperone Hsc70 at all ages. In addition, 3 Hsp110's, nucleotide exchange factors for Hsp70s, were captured at 6 and 9 months. Despite such chaperone interactions, G85R SOD-YFP formed insoluble inclusions at late times, containing predominantly intermediate filament proteins. We conclude that motor neurons, initially "compensated" to maintain the misfolded protein in a soluble state, become progressively unable to do so.

Pubmed ID: 19171884

Authors

  • Wang J
  • Farr GW
  • Zeiss CJ
  • Rodriguez-Gil DJ
  • Wilson JH
  • Furtak K
  • Rutkowski DT
  • Kaufman RJ
  • Ruse CI
  • Yates JR
  • Perrin S
  • Feany MB
  • Horwich AL

Journal

Proceedings of the National Academy of Sciences of the United States of America

Publication Data

February 3, 2009

Associated Grants

  • Agency: NIDDK NIH HHS, Id: R37 DK042394
  • Agency: Howard Hughes Medical Institute, Id:

Mesh Terms

  • Amyotrophic Lateral Sclerosis
  • Animals
  • Glial Fibrillary Acidic Protein
  • Luminescent Proteins
  • Mice
  • Mice, Transgenic
  • Molecular Chaperones
  • Motor Neurons
  • Nucleic Acid Hybridization
  • Solubility
  • Spinal Cord
  • Superoxide Dismutase
  • Ubiquitin