title: Expression of the dermatomyositis autoantigen Mi-2 in regenerating muscle.
abstract: OBJECTIVE
  Autoantibodies against the chromatin remodeler Mi-2 are found in a distinct subset of patients with dermatomyositis (DM). Previous quantitative immunoblotting experiments demonstrated that Mi-2 protein levels are up-regulated in DM muscle. This study was undertaken to define the population of cells expressing high levels of Mi-2 in DM muscle and to explore the regulation and functional role of Mi-2 during muscle regeneration.
  
  
  METHODS
  The expression of Mi-2 was analyzed by immunofluorescence microscopy in human muscle biopsy specimens. In an experimental mouse model, cardiotoxin was used to induce muscle injury and repair, and expression of Mi-2 during muscle regeneration was studied in this model by immunofluorescence and immunoblotting analyses. In addition, a cell culture system of muscle differentiation was utilized to artificially modulate Mi-2 levels during proliferation and differentiation of myoblasts.
  
  
  RESULTS
  In human DM muscle tissue, increased Mi-2 expression was found preferentially in the myofibers within fascicles affected by perifascicular atrophy, particularly in the centralized nuclei of small perifascicular muscle fibers expressing markers of regeneration. In injured mouse muscle tissue, Mi-2 levels were dramatically and persistently up-regulated during muscle regeneration in vivo. Premature silencing of Mi-2 with RNA interference in vitro resulted in accelerated myoblast differentiation.
  
  
  CONCLUSIONS
  Expression of Mi-2 is markedly up-regulated during muscle regeneration in a mouse model of muscle injury and repair. It is also up-regulated in human DM myofibers expressing markers of regeneration. Results of the in vitro studies indicate that this protein may play a role in modulating the kinetics of myoblast differentiation. Our findings thus suggest that high levels of Mi-2 expression in muscle biopsy tissue from patients with DM reflect the presence of incompletely differentiated muscle cells.
authors: Johns Hopkins Bayview, Johns Hopkins Myositis Center, Johns Hopkins University School of Medicine, Baltimore, Maryland 21224, USA. amammen@jhmi.edu
authors: Andrew L
authors: AL
authors: Mammen
authors: Livia A
authors: LA
authors: Casciola-Rosen
authors: John C
authors: JC
authors: Hall
authors: Lisa
authors: L
authors: Christopher-Stine
authors: Andrea M
authors: AM
authors: Corse
authors: Antony
authors: A
authors: Rosen
mesh_terms: D000818:Animals; D001323:Autoantibodies / Q000097:blood*; D001324:Autoantigens / Q000276:immunology*; D054715:Cardiotoxins / Q000633:toxicity; D002454:Cell Differentiation; D002478:Cells, Cultured; D003882:Dermatomyositis / Q000139:chemically induced / Q000276:immunology* / Q000473:pathology; D004195:Disease Models, Animal; D006801:Humans; D056245:Mi-2 Nucleosome Remodeling and Deacetylase Complex / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018482:Muscle, Skeletal / Q000187:drug effects / Q000473:pathology / Q000502:physiology*; D032446:Myoblasts / Q000166:cytology / Q000378:metabolism; D012038:Regeneration / Q000187:drug effects / Q000502:physiology*
chemical_list: D001323:Autoantibodies; D001324:Autoantigens; C115323:CHD4 protein, human; D054715:Cardiotoxins; C045760:Mi-2 antibodies; D056245:Mi-2 Nucleosome Remodeling and Deacetylase Complex