title: Extracellular signal-regulated kinase 1/2 is involved in ascorbic acid-induced osteoblastic differentiation in periodontal ligament cells.
abstract: BACKGROUND
  Periodontal ligament (PDL) cells possess osteoblast-like properties and play key roles in periodontal regeneration. Previously, we have reported that ascorbic acid promotes the osteoblastic differentiation of PDL cells by modulating the type I collagen-integrin interaction. However, the signaling pathway activated following collagen-integrin interaction is still unclear. In this study, we examined the involvement of extracellular signal-regulated kinase (ERK)1/2 in the expression of osteoblastic marker genes such as the osteoblast-specific transcriptional factor runt-related transcription factor 2 (Runx2), alkaline phosphatase (ALP), and osteocalcin (OCN) in PDL cells.
  
  
  METHODS
  PDL cells were cultured on a conventional or type I collagen-coated dish in the presence or absence of ascorbic acid and examined for ALP activity and osteoblastic marker genes. For detection of ERK1/2, cells were plated on a petri (non-adhesive) dish or type I collagen-coated dish, and Western blot analysis was performed. The effect of the ERK1/2 inhibitor on osteoblastic marker gene expression was examined.
  
  
  RESULTS
  Ascorbic acid increased gene expression of Runx2, ALP, and OCN. A combination of ascorbic acid and type I collagen remarkably upregulated Runx2, ALP, and OCN gene expression and ALP activity. Western blot analysis revealed an increased level of ERK1/2 phosphorylation in cells plated on type I collagen. An ERK1/2 inhibitor suppressed ascorbic acid-induced ALP and OCN gene expression, whereas Runx2 was not affected in PDL cells.
  
  
  CONCLUSIONS
  These results indicate that ERK1/2 is involved in ascorbic acid-induced osteoblastic differentiation during PDL cell attachment to type I collagen.
authors.affiliation: Periodontology, Department of Hard Tissue Engineering, Graduate School, Tokyo Medical and Dental University, Tokyo, Japan. mimori.peri@tmd.ac.jp
authors.forename: Kaori
authors.initials: K
authors.lastname: Mimori
authors.forename: Motohiro
authors.initials: M
authors.lastname: Komaki
authors.forename: Kengo
authors.initials: K
authors.lastname: Iwasaki
authors.forename: Isao
authors.initials: I
authors.lastname: Ishikawa
mesh_terms: D000328:Adult; D000469:Alkaline Phosphatase / Q000096:biosynthesis / Q000235:genetics; D001205:Ascorbic Acid / Q000494:pharmacology; D015153:Blotting, Western; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D024042:Collagen Type I / Q000502:physiology; D050659:Core Binding Factor Alpha 1 Subunit / Q000096:biosynthesis / Q000235:genetics; D005260:Female; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D016023:Integrins / Q000502:physiology; D020935:MAP Kinase Signaling System; D008297:Male; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000502:physiology*; D010006:Osteoblasts / Q000166:cytology*; D015675:Osteocalcin / Q000096:biosynthesis / Q000235:genetics; D010513:Periodontal Ligament / Q000166:cytology* / Q000201:enzymology; D016133:Polymerase Chain Reaction; D015854:Up-Regulation
chemical_list: D024042:Collagen Type I; D050659:Core Binding Factor Alpha 1 Subunit; D005419:Flavonoids; D016023:Integrins; C493709:RUNX2 protein, human; D015675:Osteocalcin; D019950:Mitogen-Activated Protein Kinase 1; D000469:Alkaline Phosphatase; D001205:Ascorbic Acid; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one