title: Motoneuronal and muscle-selective removal of ALS-related misfolded proteins.
abstract: ALS (amyotrophic lateral sclerosis), a fatal motoneuron (motor neuron) disease, occurs in clinically indistinguishable sporadic (sALS) or familial (fALS) forms. Most fALS-related mutant proteins identified so far are prone to misfolding, and must be degraded in order to protect motoneurons from their toxicity. This process, mediated by molecular chaperones, requires proteasome or autophagic systems. Motoneurons are particularly sensitive to misfolded protein toxicity, but other cell types such as the muscle cells could also be affected. Muscle-restricted expression of the fALS protein mutSOD1 (mutant superoxide dismutase 1) induces muscle atrophy and motoneuron death. We found that several genes have an altered expression in muscles of transgenic ALS mice at different stages of disease. MyoD, myogenin, atrogin-1, TGFβ1 (transforming growth factor β1) and components of the cell response to proteotoxicity [HSPB8 (heat shock 22kDa protein 8), Bag3 (Bcl-2-associated athanogene 3) and p62] are all up-regulated by mutSOD1 in skeletal muscle. When we compared the potential mutSOD1 toxicity in motoneuron (NSC34) and muscle (C2C12) cells, we found that muscle ALS models possess much higher chymotryptic proteasome activity and autophagy power than motoneuron ALS models. As a result, mutSOD1 molecular behaviour was found to be very different. MutSOD1 clearance was found to be much higher in muscle than in motoneurons. MutSOD1 aggregated and impaired proteasomes only in motoneurons, which were particularly sensitive to superoxide-induced oxidative stress. Moreover, in muscle cells, mutSOD1 was found to be soluble even after proteasome inhibition. This effect could be associated with a higher mutSOD1 autophagic clearance. Therefore muscle cells seem to manage misfolded mutSOD1 more efficiently than motoneurons, thus mutSOD1 toxicity in muscle may not directly depend on aggregation.
authors.affiliation: ‡Dipartimento di Neurologia e Laboratorio di Neuroscienze, IRCCS Istituto Auxologico Italiano, 20133 Milan, Italy.
authors.forename: Valeria
authors.initials: V
authors.lastname: Crippa
authors.forename: Mariarita
authors.initials: M
authors.lastname: Galbiati
authors.forename: Alessandra
authors.initials: A
authors.lastname: Boncoraglio
authors.forename: Paola
authors.initials: P
authors.lastname: Rusmini
authors.forename: Elisa
authors.initials: E
authors.lastname: Onesto
authors.forename: Elisa
authors.initials: E
authors.lastname: Giorgetti
authors.forename: Riccardo
authors.initials: R
authors.lastname: Cristofani
authors.forename: Arianna
authors.initials: A
authors.lastname: Zito
authors.forename: Angelo
authors.initials: A
authors.lastname: Poletti
authors.forename: Angela
authors.initials: A
authors.lastname: Poletti
mesh_terms: D000690:Amyotrophic Lateral Sclerosis / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D000818:Animals; D006801:Humans; D009046:Motor Neurons / Q000378:metabolism* / Q000473:pathology; D009132:Muscles / Q000378:metabolism* / Q000473:pathology; D017510:Protein Folding; D013482:Superoxide Dismutase / Q000737:chemistry / Q000378:metabolism*; D000072105:Superoxide Dismutase-1
chemical_list: C000606290:SOD1 protein, human; C000606291:Sod1 protein, mouse; D013482:Superoxide Dismutase; D000072105:Superoxide Dismutase-1