title: High-magnitude mechanical strain inhibits the differentiation of bone-forming rat calvarial progenitor cells.
abstract: OBJECTIVE
  Orthodontic tooth movement occurs during the bone remodeling induced by therapeutic mechanical strain. It is important to investigate the relation between the strength of mechanical stress and bone formation activity. The aim of this study was to determine the effect of high-magnitude mechanical strain on bone formation in detail.
  
  
  METHODS
  Osteoblast-like cells isolated from fetal rat calvariae were loaded with 18% cyclic tension force (TF) for 48 h. To phenotypically investigate the effect of TF, we measured the number and the size of bone nodules stained by von Kossa technique on day 21 after cell seeding and determined the calcium content of bone nodules on day 14. Furthermore, we examined the gene expression of BMP-2, Runx2 and Msx2, which are important factors for bone nodule formation, on days 1, 4 and 7 after TF loading.
  
  
  RESULTS
  The maximum bone nodule size in the control group was 1620 and 719 μm in the TF group. Furthermore, the mean number of bone nodules sized over 360 μm in the TF group was significantly decreased compared to the control group. The calcium content was also significantly decreased to 42% by TF loading. The mRNA expression of BMP-2, Runx2 and Msx2 was decreased 1 and 4 days after TF loading.
  
  
  CONCLUSIONS
  The differentiation of bone forming progenitor cells into bone nodule forming cells was inhibited by TF due to the decreased expression of bone formation related factors such as BMP-2, Runx2 and Msx2.
authors.affiliation: Department of Orthodontics .
authors.forename: Rena
authors.initials: R
authors.lastname: Fushiki
authors.forename: Kotoe
authors.initials: K
authors.lastname: Mayahara
authors.forename: Mai
authors.initials: M
authors.lastname: Ogawa
authors.forename: Yasuyo
authors.initials: Y
authors.lastname: Takahashi
authors.forename: Yoko
authors.initials: Y
authors.lastname: Karasawa
authors.forename: Niina
authors.initials: N
authors.lastname: Tsurumachi
authors.forename: Takahiko
authors.initials: T
authors.lastname: Tamura
authors.forename: Noriyoshi
authors.initials: N
authors.lastname: Shimizu
mesh_terms: D000818:Animals; D000943:Antigens, Differentiation / Q000096:biosynthesis; D002454:Cell Differentiation; D005786:Gene Expression Regulation; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012886:Skull / Q000166:cytology / Q000378:metabolism*; D013234:Stem Cells / Q000166:cytology / Q000378:metabolism*; D013314:Stress, Mechanical
chemical_list: D000943:Antigens, Differentiation
keywords: BMP-2; bone nodule; differentiation; mechanical strain; osteoblast