Hypoxia Promotes the Production and Inhibits the Destruction of Human Articular Cartilage
Article first published online: 23 APR 2013
Copyright © 2013 by the American College of Rheumatology
Arthritis & Rheumatism
Volume 65, Issue 5, pages 1302–1312, May 2013
How to Cite
Thoms, B. L., Dudek, K. A., Lafont, J. E. and Murphy, C. L. (2013), Hypoxia Promotes the Production and Inhibits the Destruction of Human Articular Cartilage. Arthritis & Rheumatism, 65: 1302–1312. doi: 10.1002/art.37867
- Issue published online: 23 APR 2013
- Article first published online: 23 APR 2013
- Accepted manuscript online: 17 JAN 2013 03:40PM EST
- Manuscript Accepted: 8 JAN 2013
- Manuscript Received: 28 SEP 2012
- Arthritis Research UK
- Kennedy Institute of Rheumatology Trust, UK
To determine the effects of hypoxia on both anabolic and catabolic pathways of metabolism in human articular cartilage and to elucidate the roles played by hypoxia-inducible factors (HIFs) in these responses.
Normal human articular cartilage from a range of donors was obtained at the time of above-the-knee amputations due to sarcomas not involving the joint space. Fresh cartilage tissue explants and isolated cells were subjected to hypoxia and treatment with interleukin-1α. Cell transfections were performed on isolated human chondrocytes.
Using chromatin immunoprecipitation, we found that hypoxia induced cartilage production in human tissue explants through direct binding of HIF-2α to a specific site in the master-regulator gene SOX9. Importantly, hypoxia also suppressed spontaneous and induced destruction of human cartilage in explant culture. We found that anticatabolic responses were predominantly mediated by HIF-1α. Manipulation of the hypoxia-sensing pathway through depletion of HIF-targeting prolyl hydroxylase–containing protein 2 (PHD-2) further enhanced cartilage responses as compared to hypoxia alone. Hypoxic regulation of tissue-specific metabolism similar to that in human cartilage was observed in pig, but not mouse, cartilage.
We found that resident chondrocytes in human cartilage are exquisitely adapted to hypoxia and use it to regulate tissue-specific metabolism. Our data revealed that while fundamental regulators, such as SOX9, are key molecules both in mice and humans, the way in which they are controlled can differ. This is all the more important since it is upstream regulators such as this that need to be directly targeted for therapeutic benefit. HIF-specific hydroxylase PHD-2 may represent a relevant target for cartilage repair.