title: Autophagy regulates TNFα-mediated joint destruction in experimental arthritis.
abstract: OBJECTIVE
  Autophagy is a homeostatic process to recycle dispensable and damaged cell organelles. Dysregulation of autophagic pathways has recently been implicated in the pathogenesis of various diseases. Here, we investigated the role of autophagy during joint destruction in arthritis.
  
  
  METHODS
  Autophagy in osteoclasts was analysed in vitro and ex vivo by transmission electron microscopy, Western blotting and immunohistochemistry for Beclin1 and Atg7. Small molecule inhibitors, LysMCre-mediated knockout of Atg7 and lentiviral overexpression of Beclin1 were used to modulate autophagy in vitro and in vivo. Osteoclast differentiation markers were quantified by real-time PCR. The extent of bone and cartilage destruction was analysed in human tumour necrosis factor α transgenic (hTNFα tg) mice after adoptive transfer with myeloid specific Atg7-deficient bone marrow.
  
  
  RESULTS
  Autophagy was activated in osteoclasts of human rheumatoid arthritis (RA) showing increased expression of Beclin1 and Atg7. TNFα potently induced the expression of autophagy-related genes and activated autophagy in vitro and in vivo. Activation of autophagy by overexpression of Beclin1-induced osteoclastogenesis and enhanced the resorptive capacity of cultured osteoclasts, whereas pharmacologic or genetic inactivation of autophagy prevented osteoclast differentiation. Arthritic hTNFα tg mice transplanted with Atg7(fl/fl)×LysMCre(+) bone marrow cells (BMC) showed reduced numbers of osteoclasts and were protected from TNFα-induced bone erosion, proteoglycan loss and chondrocyte death.
  
  
  CONCLUSIONS
  These findings demonstrate that autophagy is activated in RA in a TNFα-dependent manner and regulates osteoclast differentiation and bone resorption. We thus provide evidence for a central role of autophagy in joint destruction in RA.
authors.affiliation: Department of Internal Medicine III and Institute for Clinical Immunology, University of Erlangen-Nuremberg, Erlangen, Germany.
authors.forename: Neng-Yu
authors.initials: NY
authors.lastname: Lin
authors.forename: Christian
authors.initials: C
authors.lastname: Beyer
authors.forename: Andreas
authors.initials: A
authors.lastname: Giessl
authors.forename: Trayana
authors.initials: T
authors.lastname: Kireva
authors.forename: Carina
authors.initials: C
authors.lastname: Scholtysek
authors.forename: Stefan
authors.initials: S
authors.lastname: Uderhardt
authors.forename: Luis Enrique
authors.initials: LE
authors.lastname: Munoz
authors.forename: Clara
authors.initials: C
authors.lastname: Dees
authors.forename: Alfiya
authors.initials: A
authors.lastname: Distler
authors.forename: Stefan
authors.initials: S
authors.lastname: Wirtz
authors.forename: Gerhard
authors.initials: G
authors.lastname: Krönke
authors.forename: Brian
authors.initials: B
authors.lastname: Spencer
authors.forename: Oliver
authors.initials: O
authors.lastname: Distler
authors.forename: Georg
authors.initials: G
authors.lastname: Schett
authors.forename: Jörg H W
authors.initials: JH
authors.lastname: Distler
mesh_terms: D019264:Adoptive Transfer; D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000235:genetics; D001169:Arthritis, Experimental / Q000276:immunology* / Q000473:pathology*; D001343:Autophagy / Q000276:immunology*; D000071193:Autophagy-Related Protein 7; D000071186:Beclin-1; D015415:Biomarkers; D016026:Bone Marrow Transplantation; D001862:Bone Resorption / Q000276:immunology / Q000473:pathology; D004195:Disease Models, Animal; D007596:Joints / Q000473:pathology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D046529:Microscopy, Electron, Transmission; D008869:Microtubule-Associated Proteins / Q000235:genetics; D010010:Osteoclasts / Q000276:immunology / Q000473:pathology / Q000648:ultrastructure; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000276:immunology*
chemical_list: D051017:Apoptosis Regulatory Proteins; C502661:Atg7 protein, mouse; D000071186:Beclin-1; C115010:Becn1 protein, mouse; D015415:Biomarkers; D008869:Microtubule-Associated Proteins; D014409:Tumor Necrosis Factor-alpha; D000071193:Autophagy-Related Protein 7