title: Endothelial cells influence the osteogenic potential of bone marrow stromal cells.
abstract: BACKGROUND
  Improved understanding of the interactions between bone cells and endothelial cells involved in osteogenesis should aid the development of new strategies for bone tissue engineering. The aim of the present study was to determine whether direct communication between bone marrow stromal cells (MSC) and human umbilical vein endothelial cells (EC) could influence the osteogenic potential of MSC in osteogenic factor-free medium.
  
  
  METHODS
  After adding EC to MSC in a direct-contact system, cell viability and morphology were investigated with the WST assay and immunostaining. The effects on osteogenic differentiation of adding EC to MSC was systematically tested by the using Superarray assay and results were confirmed with real-time PCR.
  
  
  RESULTS
  Five days after the addition of EC to MSC in a ratio of 1:5 (EC/MSC) significant increases in cell proliferation and cellular bridges between the two cell types were detected, as well as increased mRNA expression of alkaline phosphatase (ALP). This effect was greater than that seen with addition of osteogenic factors such as dexamethasone, ascorbic acid and beta-glycerophosphate to the culture medium. The expression of transcription factor Runx2 was enhanced in MSC incubated with osteogenic stimulatory medium, but was not influenced by induction with EC. The expression of Collagen type I was not influenced by EC but the cells grown in the osteogenic factor-free medium exhibited higher expression than those cultured with osteogenic stimulatory medium.
  
  
  CONCLUSIONS
  These results show that co-culturing of EC and MSC for 5 days influences osteogenic differentiation of MSC, an effect that might be independent of Runx2, and enhances the production of ALP by MSC.
authors.affiliation: Department of Clinical Dentistry-Center for Clinical Dental Research, University of Bergen, Norway. Ying.xue@uib.no
authors.forename: Ying
authors.initials: Y
authors.lastname: Xue
authors.forename: Zhe
authors.initials: Z
authors.lastname: Xing
authors.forename: Sølve
authors.initials: S
authors.lastname: Hellem
authors.forename: Kristina
authors.initials: K
authors.lastname: Arvidson
authors.forename: Kamal
authors.initials: K
authors.lastname: Mustafa
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D001698:Biomedical Engineering; D001854:Bone Marrow Cells / Q000166:cytology*; D018929:Cell Culture Techniques / Q000379:methods; D002470:Cell Survival; D002478:Cells, Cultured; D018920:Coculture Techniques; D050659:Core Binding Factor Alpha 1 Subunit / Q000378:metabolism; D004730:Endothelium, Vascular / Q000378:metabolism; D006801:Humans; D008954:Models, Biological; D010012:Osteogenesis / Q000502:physiology*; D017154:Stromal Cells / Q000166:cytology*; D013997:Time Factors; D014471:Umbilical Veins / Q000166:cytology
chemical_list: D050659:Core Binding Factor Alpha 1 Subunit; C493709:RUNX2 protein, human; D000469:Alkaline Phosphatase