Expression of ADAMTS-4 by chondrocytes in the surface zone of human osteoarthritic cartilage is regulated by epigenetic DNA de-methylation
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The two major aggrecanases involved in osteoarthritis (OA) are ADAMTS-4 and ADAMTS-5. Knock-out studies suggested that ADAMTS-5, but not ADAMTS-4, is the major aggrecanase in murine OA. However, studies of human articular cartilage suggest that ADAMTS-4 also contributes to aggrecan degradation in human OA. This study investigated ADAMTS-4 in human OA. While ADAMTS-4 was virtually absent in control cartilage, numerous ADAMTS-4 immuno-positive chondrocytes were present in OA cartilage and their numbers increased with disease severity. RT-PCR confirmed expression, especially in the surface zone. DNA methylation was lost at specific CpG sites in the ADAMTS-4 promoter in OA chondrocytes, suggesting that the increased gene expression was more than a simple up-regulation, but involved loss of DNA methylation at specific CpG sites, resulting in a heritable and permanent expression of ADAMTS-4 in OA chondrocytes. These results suggest that ADAMTS-4 is epigenetically regulated and plays a role in aggrecan degradation in human OA.
KeywordsADAMTS-4 Osteoarthritis DNA methylation Gene expression Immunocytochemistry Histology
This study was supported by grant no. 43747 from the Wessex Medical Trust. All authors thank the Orthopaedic Surgeons of Southampton General Hospital, especially Mr. Simon Tilley and Mr. Ben Bolland, for supplying the femoral heads following joint replacement surgery. We are grateful to Miss Wai Mun Loo for contributing Fig. 2j and k. We also gratefully acknowledge funding by the Wessex Medical Trust and all the “Great Hip & Knee” Walkers without whom this research would not have been possible. Last, but not least, the excellent editing by Dr. Felix Bronner, University of Connecticut Health Center, is also much appreciated.
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