Anabolic and catabolic responses of human articular chondrocytes to varying oxygen percentages
1 Departments of Surgery and of Biomedicine, University Hospital Basel, Hebelstrasse 20, Basel, 4031, Switzerland
2 M.E. Müller Institute for Structural Biology, Biozentrum University of Basel, Klingelbergstrasse 50/70, Basel, 4056, Switzerland
3 Department of Orthopaedic Surgery and Traumatology, Ospedale Regionale di Lugano, Via Tesserete 46, Lugano, 6900, Switzerland
4 Departments of Biomedicine and Neurology, University Hospital Basel, Hebelstrasse 20, Basel, 4031, Switzerland
5 Faculty of Dentistry and CHU Sainte-Justine, University of Montreal, 3175 Côte Sainte-Catherine, Montreal, H3T1C5, Canada
Arthritis Research & Therapy 2010, 12:R34 doi:10.1186/ar2942Published: 2 March 2010
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.
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-1α (HIF-1α) inhibitor cadmium chloride was supplemented in the culture medium to assess the involvement of this pathway.
Independent from the oxygen percentage during expansion, HAC cultured at 5% O2 (vs 19% O2) 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 O2 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% O2 drastically reduced the up-regulation of type II collagen and the down-regulation of MMP-1 mRNA.
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.