title: Activation of AMP-activated protein kinase decreases receptor activator of NF-κB ligand expression and increases sclerostin expression by inhibiting the mevalonate pathway in osteocytic MLO-Y4 cells.
abstract: BACKGROUND
  AMP-activated protein kinase (AMPK) plays important roles in bone metabolism; however, little is known about its role in osteocytes. This study investigated the effects of AMPK activation on the expression of receptor activator of NF-κB ligand (RANKL) and sclerostin in osteocytes.
  
  
  RESULTS
  Real-time PCR showed that AMPK activation by 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) significantly decreased the expression of Rankl in a dose- and time-dependent manner and significantly increased the expression of Sost, the gene encoding sclerostin, in osteocytic MLO-Y4 cells. Western blotting confirmed that AICAR decreased RANKL protein levels and increased sclerostin levels. In addition, suppression of AMPKα1 by siRNA significantly increased the expression of Rankl on 4 days after the transfection of siRNA, while Sost expression was not changed. Simvastatin, an inhibitor of HMG-CoA reductase, significantly decreased Rankl expression and increased Sost expression in MLO-Y4 cells. Supplementation with mevalonate or geranylgeranyl pyrophosphate, which are downstream metabolites of HMG-CoA reductase, significantly reversed the effects of AICAR.
  
  
  CONCLUSIONS
  These findings indicated that AMPK regulated RANKL and sclerostin expression through the mevalonate pathway in osteocytes.
authors.affiliation: Internal Medicine 1, Shimane University Faculty of Medicine, 89-1, Enya-cho, Izumo 693-8501, Shimane, Japan. Electronic address: pinyan@med.shimane-u.ac.jp.
authors.forename: Maki
authors.initials: M
authors.lastname: Yokomoto-Umakoshi
authors.affiliation: Internal Medicine 1, Shimane University Faculty of Medicine, 89-1, Enya-cho, Izumo 693-8501, Shimane, Japan. Electronic address: ippei.k@med.shimane-u.ac.jp.
authors.forename: Ippei
authors.initials: I
authors.lastname: Kanazawa
authors.affiliation: Internal Medicine 1, Shimane University Faculty of Medicine, 89-1, Enya-cho, Izumo 693-8501, Shimane, Japan. Electronic address: atakeno@med.shimane-u.ac.jp.
authors.forename: Ayumu
authors.initials: A
authors.lastname: Takeno
authors.affiliation: Internal Medicine 1, Shimane University Faculty of Medicine, 89-1, Enya-cho, Izumo 693-8501, Shimane, Japan. Electronic address: ken1nai@med.shimane-u.ac.jp.
authors.forename: Ken-ichiro
authors.initials: K
authors.lastname: Tanaka
authors.affiliation: Internal Medicine 1, Shimane University Faculty of Medicine, 89-1, Enya-cho, Izumo 693-8501, Shimane, Japan. Electronic address: mnotsu25@med.shimane-u.ac.jp.
authors.forename: Masakazu
authors.initials: M
authors.lastname: Notsu
authors.affiliation: Internal Medicine 1, Shimane University Faculty of Medicine, 89-1, Enya-cho, Izumo 693-8501, Shimane, Japan. Electronic address: sugimoto@med.shimane-u.ac.jp.
authors.forename: Toshitsugu
authors.initials: T
authors.lastname: Sugimoto
mesh_terms: D055372:AMP-Activated Protein Kinases; D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002460:Cell Line; D015536:Down-Regulation; D004789:Enzyme Activation; D006023:Glycoproteins / Q000378:metabolism*; D036341:Intercellular Signaling Peptides and Proteins; D008798:Mevalonic Acid / Q000378:metabolism*; D051379:Mice; D010011:Osteocytes / Q000166:cytology / Q000378:metabolism*; D053245:RANK Ligand; D015398:Signal Transduction
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D006023:Glycoproteins; D036341:Intercellular Signaling Peptides and Proteins; D053245:RANK Ligand; C486030:Sost protein, mouse; D055372:AMP-Activated Protein Kinases; D008798:Mevalonic Acid
keywords: AMP-activated protein kinase; Mevalonate pathway; Osteocyte; RANKL; Sclerostin