Proteasomes remain intact, but show early focal alteration in their composition in a mouse model of amyotrophic lateral sclerosis

• Published in: Journal of neurochemistry 2008-06, Vol.105 (6), p.2353-2366
• Main Authors: Kabashi, Edor, Agar, Jeffrey N, Hong, Yu, Taylor, David M, Minotti, Sandra, Figlewicz, Denise A, Durham, Heather D
• Format: Article
• Language: English
• Subjects: Alanine - genetics; Amyotrophic lateral sclerosis; Amyotrophic Lateral Sclerosis - enzymology; Amyotrophic Lateral Sclerosis - genetics; Amyotrophic Lateral Sclerosis - pathology; Animals; Biochemistry; Biological and medical sciences; Cerebrospinal fluid. Meninges. Spinal cord; Cu/Zn-superoxide dismutase; Cu/Zn-superoxide dismutase 1; Degenerative and inherited degenerative diseases of the nervous system. Leukodystrophies. Prion diseases; Disease Models, Animal; Glycine - genetics; Humans; Medical sciences; Mice; Mice, Transgenic; motor neuron disease; Mutation; Nervous system (semeiology, syndromes); Neurology; Proteasome Endopeptidase Complex - genetics; Proteasome Endopeptidase Complex - metabolism; protein aggregates; protein aggregation; Protein folding; proteolysis; Rodents; Spinal Cord - enzymology; Spinal Cord - pathology; Superoxide Dismutase - genetics; Superoxide Dismutase - metabolism; ubiquitin-proteasome pathway; Ubiquitination
• ISSN: 0022-3042; 1471-4159
• DOI: 10.1111/j.1471-4159.2008.05317.x

In amyotrophic lateral sclerosis caused by mutations in Cu/Zn-superoxide dismutase (SOD1), altered solubility and aggregation of the mutant protein implicates failure of pathways for detecting and catabolizing misfolded proteins. Our previous studies demonstrated early reduction of proteasome-mediated proteolytic activity in lumbar spinal cord of SOD1G⁹³A transgenic mice, tissue particularly vulnerable to disease. The purpose of this study was to identify any underlying abnormalities in proteasomal structure. In lumbar spinal cord of pre-symptomatic mice [postnatal day 45 (P45) and P75], normal levels of structural 20S α subunits were incorporated into 20S/26S proteasomes; however, proteasomal complexes separated by native gel electrophoresis showed decreased immunoreactivity with antibodies to β3, a structural subunit of the 20S proteasome core, and β5, the subunit with chymotrypsin-like activity. This occurred prior to increase in β5i immunoproteasomal subunit. mRNA levels were maintained and no association of mutant SOD1 with proteasomes was identified, implicating post-transcriptional mechanisms. mRNAs also were maintained in laser captured motor neurons at a later stage of disease (P100) in which multiple 20S proteins are reduced relative to the surrounding neuropil. Increase in detergent-insoluble, ubiquitinated proteins at P75 provided further evidence of stress on mechanisms of protein quality control in multiple cell types prior to significant motor neuron death.