title: Autophagy modulates osteoarthritis-related gene expression in human chondrocytes.
abstract: OBJECTIVE
  Autophagy, an evolutionarily conserved process for the bulk degradation of cytoplasmic components, serves as a cell survival mechanism. The purpose of this study was to elucidate the role of autophagy in human chondrocytes and pathophysiology of osteoarthritis (OA).
  
  
  METHODS
  Autophagy in articular cartilage and primary chondrocytes was assessed using antibodies for the autophagy markers light chain 3 and beclin 1. The states of autophagy under catabolic and nutritional stresses were examined. We also examined the effects of inhibition or induction of autophagy under stimulation with interleukin-1β. Autophagy was inhibited by small interfering RNA targeting ATG5, and autophagy was induced by rapamycin. The effects of inhibition or induction of autophagy were examined by real-time polymerase chain reaction for aggrecan, COL2A1, MMP13, and ADAMTS5 messenger RNA. To further examine the mechanism of autophagy regulation in OA human chondrocytes, we investigated whether autophagy modulates apoptosis and reactive oxygen species (ROS).
  
  
  RESULTS
  Autophagy was increased in OA chondrocytes and cartilage. Catabolic and nutritional stresses increased autophagy. In addition, the inhibition of autophagy caused OA-like gene expression changes, while the induction of autophagy prevented them. Furthermore, the inhibition of autophagy increased the amount of cleaved poly(ADP-ribose) polymerase and cleaved caspase 9, while the induction of autophagy inhibited these increases. ROS activity was also decreased by induction of autophagy.
  
  
  CONCLUSIONS
  These observations suggested that increased autophagy is an adaptive response to protect cells from stresses, and that autophagy regulates OA-like gene expression changes through the modulation of apoptosis and ROS. Further studies about autophagy in chondrocytes will provide novel insights into the pathophysiology of OA.
authors.affiliation: Kobe University Graduate School of Medicine, Kobe, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Sasaki
authors.forename: Koji
authors.initials: K
authors.lastname: Takayama
authors.forename: Takehiko
authors.initials: T
authors.lastname: Matsushita
authors.forename: Kazunari
authors.initials: K
authors.lastname: Ishida
authors.forename: Seiji
authors.initials: S
authors.lastname: Kubo
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Matsumoto
authors.forename: Norifumi
authors.initials: N
authors.lastname: Fujita
authors.forename: Shinya
authors.initials: S
authors.lastname: Oka
authors.forename: Masahiro
authors.initials: M
authors.lastname: Kurosaka
authors.forename: Ryosuke
authors.initials: R
authors.lastname: Kuroda
mesh_terms: D000368:Aged; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism; D001343:Autophagy / Q000502:physiology*; D000071186:Beclin-1; D002358:Cartilage, Articular / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D019902:Chondrocytes / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D005260:Female; D015870:Gene Expression / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D008297:Male; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism; D020370:Osteoarthritis, Knee / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D020123:Sirolimus / Q000494:pharmacology
chemical_list: D051017:Apoptosis Regulatory Proteins; C491997:BECN1 protein, human; D000071186:Beclin-1; C477012:MAP1LC3A protein, human; D008565:Membrane Proteins; D008869:Microtubule-Associated Proteins; D034741:RNA, Small Interfering; D020123:Sirolimus