title: In vitro osteogenic potential of human mesenchymal stem cells is predicted by Runx2/Sox9 ratio.
abstract: BACKGROUND
  Runx2 is one of the most studied transcription factors expressed in mesenchymal stem cells (MSCs) upon their commitment toward an osteogenic differentiation. During endochondral bone formation in vivo, Sox9 directly interacts with Runx2 and represses its activity; however, the role of Sox9 in direct osteogenesis in vitro has been largely overlooked.
  
  
  METHODS
  Bone marrow-derived human MSCs (hMSCs) were cultured in vitro either in the control or osteogenic medium supplemented with dexamethasone (DEX). To further investigate the role of Sox9 in direct osteogenesis in vitro, hMSCs were treated with Sox9 siRNA.
  
  
  RESULTS
  We show here that Sox9 is the key early indicator during in vitro osteogenic differentiation of hMSCs. Osteogenic induction leads to a significant decrease of Sox9 gene and protein expression by day 7. Treatment of hMSCs with Sox9 siRNA enhanced mineralization in vitro, suggesting that downregulation of Sox9 is involved in direct osteogenesis. siRNA knockdown of Sox9 did not in itself induce osteogenesis in the absence of DEX, indicating that other factors are still required.
  
  
  CONCLUSIONS
  Screening of not preselected donors of different ages and gender (n=12) has shown that the Runx2/Sox9 ratio on day 7 is correlated to the (45)Ca incorporation on day 28. The impact of Sox9 downregulation in the mineralization of human MSCs in vitro indicates a so far unprecedented role of Sox9 as a major regulator of direct osteogenesis. We propose that the Runx2/Sox9 ratio is a promising, early, in vitro screening method for osteogenicity of human MSCs.
authors: 1 AO Research Institute Davos , Davos Platz, Switzerland .
authors: Claudia
authors: C
authors: Loebel
authors: Ewa M
authors: EM
authors: Czekanska
authors: Marco
authors: M
authors: Bruderer
authors: Gian
authors: G
authors: Salzmann
authors: Mauro
authors: M
authors: Alini
authors: Martin J
authors: MJ
authors: Stoddart
mesh_terms: D000328:Adult; D000368:Aged; D050659:Core Binding Factor Alpha 1 Subunit / Q000235:genetics / Q000378:metabolism*; D003907:Dexamethasone / Q000494:pharmacology; D015536:Down-Regulation / Q000187:drug effects; D018274:Electroporation; D005260:Female; D006801:Humans; D008297:Male; D059630:Mesenchymal Stem Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008875:Middle Aged; D010012:Osteogenesis / Q000187:drug effects / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D055758:SOX9 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D014019:Tissue Donors; D055815:Young Adult
chemical_list: D050659:Core Binding Factor Alpha 1 Subunit; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D055758:SOX9 Transcription Factor; D003907:Dexamethasone