title: Osteoblast differentiation is functionally associated with decreased AMP kinase activity.
abstract: Osteoblasts, originating from mesenchymal stem cells, play a pivotal role in bone formation and mineralization. Several transcription factors including runt-related transcription factor 2 (Runx2) have been reported to be essential for osteoblast differentiation, whereas the cytoplasmic signal transduction pathways controlling the differentiation process have not been fully elucidated. AMP-activated protein kinase (AMPK) is a serine-threonine kinase generally regarded as a key regulator of cellular energy homeostasis, polarity, and division. Recent lines of evidence have indicated that the activity of the catalytic alpha subunit of AMPK is regulated through its phosphorylation by upstream AMPK kinases (AMPKKs) including LKB1. Here, we explored the role of AMPK in osteoblast differentiation using in vitro culture models. Phosphorylation of AMPKalpha was significantly decreased during osteoblastic differentiation in both primary osteoblasts and MC3T3-E1, a mouse osteoblastic cell line. Conversely, the terminal differentiation of primary osteoblasts and MC3T3-E1 cells, represented by matrix mineralization, was significantly inhibited by glucose restriction and stimulation with metformin, both of which are known activators of AMPK. Matrix mineralization of MC3T3-E1 cells was also inhibited by the forced expression of a constitutively active form of AMPKalpha. Metformin significantly inhibited gene expression of Runx2 along with osteoblast differentiation markers including osteocalcin (Ocn), bone sialo protein (Bsp), and osteopontin (Opn). Thus, our present data indicate that differentiation of osteoblasts is functionally associated with decreased AMPK activity.
authors.affiliation: Department of Oral Biochemistry, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima, Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Kasai
authors.forename: Kenjiro
authors.initials: K
authors.lastname: Bandow
authors.forename: Hiraku
authors.initials: H
authors.lastname: Suzuki
authors.forename: Norika
authors.initials: N
authors.lastname: Chiba
authors.forename: Kyoko
authors.initials: K
authors.lastname: Kakimoto
authors.forename: Tomokazu
authors.initials: T
authors.lastname: Ohnishi
authors.forename: Shin-ichiro
authors.initials: S
authors.lastname: Kawamoto
authors.forename: Eiichi
authors.initials: E
authors.lastname: Nagaoka
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Matsuguchi
mesh_terms: D041721:3T3-L1 Cells; D055372:AMP-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D017667:Adipocytes / Q000166:cytology; D000469:Alkaline Phosphatase / Q000378:metabolism; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002113:Calcification, Physiologic / Q000187:drug effects; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology*; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D050659:Core Binding Factor Alpha 1 Subunit / Q000235:genetics; D015870:Gene Expression / Q000187:drug effects / Q000235:genetics; D005947:Glucose / Q000172:deficiency / Q000494:pharmacology; D007004:Hypoglycemic Agents / Q000494:pharmacology; D058574:Integrin-Binding Sialoprotein; D008687:Metformin / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D010006:Osteoblasts / Q000166:cytology* / Q000378:metabolism; D015675:Osteocalcin / Q000235:genetics; D053495:Osteopontin / Q000235:genetics; D010766:Phosphorylation / Q000187:drug effects; D012265:Ribonucleotides / Q000494:pharmacology; D012795:Sialoglycoproteins / Q000235:genetics; D014162:Transfection
chemical_list: D050659:Core Binding Factor Alpha 1 Subunit; D007004:Hypoglycemic Agents; C546872:Ibsp protein, mouse; D058574:Integrin-Binding Sialoprotein; D012265:Ribonucleotides; C493716:Runx2 protein, mouse; D012795:Sialoglycoproteins; C506896:Spp1 protein, mouse; D015675:Osteocalcin; D053495:Osteopontin; D000620:Aminoimidazole Carboxamide; D008687:Metformin; D055372:AMP-Activated Protein Kinases; D000469:Alkaline Phosphatase; C031143:AICA ribonucleotide; D005947:Glucose