title: Anabolic and catabolic responses of human articular chondrocytes to varying oxygen percentages.
abstract: BACKGROUND
  Oxygen is a critical parameter proposed to modulate the functions of chondrocytes ex-vivo as well as in damaged joints. This article investigates the effect of low (more physiological) oxygen percentage on the biosynthetic and catabolic activity of human articular chondrocytes (HAC) at different phases of in vitro culture.
  
  
  METHODS
  HAC expanded in monolayer were cultured in pellets for two weeks (Phase I) or up to an additional two weeks (Phase II). In each Phase, cells were exposed to 19% or 5% oxygen. Resulting tissues and culture media were assessed to determine amounts of produced/released proteoglycans and collagens, metalloproteinases (MMPs), collagen degradation products and collagen fibril organization using biochemical, (immuno)-histochemical, gene expression and scanning electron microscopy analyses. In specific experiments, the hypoxia-inducible factor-1alpha (HIF-1alpha) inhibitor cadmium chloride was supplemented in the culture medium to assess the involvement of this pathway.
  
  
  RESULTS
  Independent from the oxygen percentage during expansion, HAC cultured at 5% O(2) (vs 19% O(2)) during Phase I accumulated higher amounts of glycosaminoglycans and type II collagen and expressed reduced levels of MMP-1 and MMP-13 mRNA and protein. Switching to 19% oxygen during Phase II resulted in reduced synthesis of proteoglycan and collagen, increased release of MMPs, accumulation of type II collagen fragments and higher branching of collagen fibrils. In contrast, reducing O(2) during Phase II resulted in increased proteoglycan and type II collagen synthesis and reduced expression and release of MMP-13 mRNA and protein. Supplementation of cadmium chloride during differentiation culture at 5% O(2) drastically reduced the up-regulation of type II collagen and the down-regulation of MMP-1 mRNA.
  
  
  CONCLUSIONS
  The application of more physiologic oxygen percentage during specific phases of differentiation culture enhanced the biosynthetic activity and reduced the activity of catabolic enzymes implicated in cartilage breakdown. Modulation of the oxygen percentage during HAC culture may be used to study pathophysiological events occurring in osteoarthritis and to enhance properties of in vitro engineered cartilaginous tissues.
authors.affiliation: Department of Surgery, University Hospital Basel, Hebelstrasse 20, Basel, 4031, Switzerland.
authors.forename: Simon
authors.initials: S
authors.lastname: Ströbel
authors.forename: Marko
authors.initials: M
authors.lastname: Loparic
authors.forename: David
authors.initials: D
authors.lastname: Wendt
authors.forename: Andreas D
authors.initials: AD
authors.lastname: Schenk
authors.forename: Christian
authors.initials: C
authors.lastname: Candrian
authors.forename: Raija L P
authors.initials: RL
authors.lastname: Lindberg
authors.forename: Florina
authors.initials: F
authors.lastname: Moldovan
authors.forename: Andrea
authors.initials: A
authors.lastname: Barbero
authors.forename: Ivan
authors.initials: I
authors.lastname: Martin
mesh_terms: D000328:Adult; D000368:Aged; D002122:Calcium Chloride / Q000494:pharmacology; D002358:Cartilage, Articular / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D002478:Cells, Cultured; D019902:Chondrocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D024043:Collagen Type II / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects; D004359:Drug Therapy, Combination; D005260:Female; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000037:antagonists & inhibitors / Q000378:metabolism; D008297:Male; D020781:Matrix Metalloproteinase 1 / Q000235:genetics / Q000378:metabolism; D053509:Matrix Metalloproteinase 13 / Q000235:genetics / Q000378:metabolism; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000378:metabolism / Q000473:pathology; D010100:Oxygen / Q000494:pharmacology*; D011509:Proteoglycans / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism
chemical_list: D024043:Collagen Type II; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D011509:Proteoglycans; D012333:RNA, Messenger; D053509:Matrix Metalloproteinase 13; D020781:Matrix Metalloproteinase 1; D002122:Calcium Chloride; D010100:Oxygen