title: Osmolarity determines the in vitro chondrogenic differentiation capacity of progenitor cells via nuclear factor of activated T-cells 5.
abstract: BACKGROUND
  Previous studies have shown that human articular chondrocytes in vitro are osmolarity-responsive and increase matrix synthesis under cartilage-specific physiological osmolarity. The effects of increased osmolarity on chondrogenesis of progenitor cells in vitro are largely unknown. We therefore aimed to elucidate whether hyperosmolarity facilitates their chondrogenic differentiation and whether Nfat5 is involved.
  
  
  METHODS
  ATDC5 cells and human bone marrow stem cells (hBMSCs) were differentiated in the chondrogenic lineage in control and increased osmolarity conditions. Chondrogenic outcome was measured by gene- and protein expression analysis. RNAi was used to determine the role of Nfat5 in chondrogenic differentiation under normal and increased osmolarity.
  
  
  RESULTS
  Increasing the osmolarity of differentiation medium with 100mOsm resulted in significantly increased chondrogenic marker expression (Col2a1, Col10a1, Acan, Sox9, Runx2 and GAGs) during chondrogenic differentiation of the two chondroprogenitors, ATDC5 and hBMSCs. Nfat5 knockdown under both control and increased osmolarity affected chondrogenic differentiation and suppressed the osmolarity-induced chondrogenic induction. Knockdown of Nfat5 in early differentiation significantly decreased early Sox9 expression, whereas knockdown of Sox9 in early differentiation did not affect early Nfat5 expression.
  
  
  CONCLUSIONS
  Increasing the osmolarity of chondrogenic culture media by 100mOsm significantly increased chondrogenic gene expression during the course of chondrogenic differentiation of progenitor cells. Nfat5 may be involved in regulating chondrogenic differentiation of these cells under both normal and increased osmolarities and might regulate chondrogenic differentiation through influencing early Sox9 expression.
authors.affiliation: Department of Orthopaedic Surgery, CAPHRI school for public health and primary care, Maastricht University Medical Center, P.O. Box 5800, 6202 AZ, Maastricht, The Netherlands. marjolein.caron@maastrichtuniversity.nl
authors.forename: Marjolein M J
authors.initials: MM
authors.lastname: Caron
authors.forename: Anna E
authors.initials: AE
authors.lastname: van der Windt
authors.forename: Pieter J
authors.initials: PJ
authors.lastname: Emans
authors.forename: Lodewijk W
authors.initials: LW
authors.lastname: van Rhijn
authors.forename: Holger
authors.initials: H
authors.lastname: Jahr
authors.forename: Tim J M
authors.initials: TJ
authors.lastname: Welting
mesh_terms: D001483:Base Sequence; D002356:Cartilage / Q000166:cytology*; D002454:Cell Differentiation; D002460:Cell Line; D049109:Cell Proliferation; D017931:DNA Primers; D006801:Humans; D009994:Osmolar Concentration; D016133:Polymerase Chain Reaction; D034622:RNA Interference; D013234:Stem Cells / Q000166:cytology*; D014157:Transcription Factors / Q000502:physiology*
chemical_list: D017931:DNA Primers; C118125:NFAT5 protein, human; D014157:Transcription Factors