title: Chondrocyte autophagy is stimulated by HIF-1 dependent AMPK activation and mTOR suppression.
abstract: The goal of the study is to examine the relationship between the sensor molecules, Hypoxia Inducible Factor-1 (HIF-1), AMP activated Protein Kinase (AMPK) and mammalian Target of Rapamycin (mTOR) in chondrocyte survival and autophagy. We showed that chondrocytes expressed the energy sensor AMPK-1 and that activation increased with maturation. In addition, we showed that thapsigargin treatment activated AMPK and autophagy in a HIF-1-dependent manner. Using serum-starved AMPK-silenced cells, we demonstrated that AMPK was required for the induction of the autophagic response. We also noted a change in chondrocyte sensitivity to apoptogens, due to activation of caspase-8 and cleavage and activation of the pro-apoptotic protein, BID. To test the hypothesis that AMPK signaling directly promoted autophagy, we inhibited AMPK activity in mTOR silenced cells and showed that while mTOR suppression induced autophagy, AMPK inhibition did not block this activity. Based on these findings, it is concluded that because of the micro-environmental changes experienced by the chondrocyte, autophagy is activated by AMPK in a HIF-1-dependent manner.
authors.affiliation: Department of Orthopedic Surgery, Thomas Jefferson University, Philadelphia, PA 19107, USA.
authors.forename: Jolene
authors.initials: J
authors.lastname: Bohensky
authors.forename: Serge
authors.initials: S
authors.lastname: Leshinsky
authors.forename: Vickram
authors.initials: V
authors.lastname: Srinivas
authors.forename: Irving M
authors.initials: IM
authors.lastname: Shapiro
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001343:Autophagy / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D002470:Cell Survival; D019902:Chondrocytes / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D020868:Gene Silencing; D006132:Growth Plate / Q000166:cytology / Q000201:enzymology; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D058570:TOR Serine-Threonine Kinases; D019284:Thapsigargin / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; C497443:Hif1a protein, mouse; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D047908:Intracellular Signaling Peptides and Proteins; D034741:RNA, Small Interfering; D019284:Thapsigargin; C546843:mTOR protein, mouse; C548179:Prkaa1 protein, mouse; D017346:Protein Serine-Threonine Kinases; D058570:TOR Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; D002118:Calcium