title: Chaperone-mediated autophagy components are upregulated in sporadic inclusion-body myositis muscle fibres.
abstract: OBJECTIVE
  Sporadic inclusion-body myositis (s-IBM) is an age-associated degenerative muscle disease. Characteristic features are muscle-fibre vacuolization and intramuscle-fibre accumulations of multiprotein aggregates, which may result from the demonstrated impairments of the 26S proteasome and autophagy. Chaperone-mediated autophagy (CMA) is a selective form of lysosomal degradation targeting proteins carrying the KFERQ motif. Lysosome-associated membrane protein type 2A (LAMP2A) and the heat-shock cognate protein 70 (Hsc70) constitute specific CMA components. Neither CMA components nor CMA activity has been studied in normal or disease human muscle, to our knowledge.
  
  
  METHODS
  We studied CMA components by immunocytochemistry, immunoblots, real-time PCR and immunoprecipitation in: (a) 16 s-IBM, nine aged-matched normal and nine disease control muscle biopsies; and (b) cultured human muscle fibres (CHMFs) with experimentally inhibited activities of either the 26S proteasome or autophagy.
  
  
  RESULTS
  Compared with age-matched controls, in s-IBM muscle, LAMP2A and Hsc70 were on a given transverse section accumulated as aggregates in approximately 5% of muscle fibres, where they (a) colocalized with each other and α-synuclein (α-syn), a CMA-targeted protein; and (b) were bound to each other and to α-syn by immunoprecipitation. By immunoblots, LAMP2A was increased sevenfold P < 0.001 and Hsc70 2.6-fold P < 0.05. LAMP2A mRNA was increased 4.4-fold P < 0.001 and Hsc70 mRNA 1.9-fold P < 0.05. In CHMFs inhibition of either the 26S proteasome or autophagy induced CMA, evidenced by a significant increase of both LAMP2A and Hsc70.
  
  
  CONCLUSIONS
  Our study demonstrates, for the first time, up-regulation of CMA components in s-IBM muscle, and it provides further evidence that altered protein degradation is likely an important pathogenic aspect in s-IBM.
authors: USC Neuromuscular Center, Department of Neurology, University of Southern California Keck School of Medicine, Good Samaritan Hospital, Los Angeles, CA, USA.
authors: M
authors: M
authors: Cacciottolo
authors: A
authors: A
authors: Nogalska
authors: C
authors: C
authors: D'Agostino
authors: W K
authors: WK
authors: Engel
authors: V
authors: V
authors: Askanas
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001343:Autophagy / Q000502:physiology*; D005260:Female; D006801:Humans; D008247:Lysosomes / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D008875:Middle Aged; D018832:Molecular Chaperones / Q000378:metabolism*; D018485:Muscle Fibers, Skeletal / Q000378:metabolism* / Q000473:pathology; D018979:Myositis, Inclusion Body / Q000378:metabolism* / Q000473:pathology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D015854:Up-Regulation / Q000502:physiology; D051844:alpha-Synuclein / Q000378:metabolism
chemical_list: D008565:Membrane Proteins; D018832:Molecular Chaperones; D012333:RNA, Messenger; D051844:alpha-Synuclein; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease
keywords: autophagy; chaperone-mediated autophagy; cultured human muscle fibres; protein degradation; sporadic inclusion-body myositis; α-synuclein