Hypoxia promotes the differentiated human articular chondrocyte phenotype through SOX9-dependent and -independent pathways.
The chondrocyte is solely responsible for synthesis and maintenance of the resilient articular cartilage matrix that gives this load-bearing tissue its mechanical integrity. When the differentiated cell phenotype is lost, the matrix becomes compromised and cartilage function begins to fail. We have recently shown that hypoxia promotes the differentiated phenotype through hypoxia-inducible factor 2alpha (HIF-2alpha)-mediated SOX9 induction of the main matrix genes. However, to date, only a few genes have been shown to be SOX9 targets, while little is known about SOX9-independent regulators. We therefore performed a detailed microarray study to address these issues. Analysis involved 35 arrays on chondrocytes obtained from seven healthy, non-elderly human cartilage samples. Genes were selected that were down-regulated with serial passage in culture (as this causes loss of the differentiated phenotype) and subsequently up-regulated in hypoxia. The importance of key findings was further probed using the technique of RNA interference on these human articular chondrocytes. Our results show that hypoxia has a broader beneficial effect on the chondrocyte phenotype than has been previously described. Of special note, we report new hypoxia-inducible and SOX9-regulated genes, Gdf10 and Chm-I. In addition, Mig6 and InhbA were induced by hypoxia, predominantly via HIF-2alpha, but were not regulated by SOX9. Therefore, hypoxia, and more specifically HIF-2alpha, promotes both SOX9-dependent and -independent factors important for cartilage homeostasis. HIF-2alpha may therefore represent a new and promising therapeutic target for cartilage repair.
Lafont
Jérôme E
JE
Kennedy Institute of Rheumatology, Faculty of Medicine, Imperial College London, 1 Aspenlea Road, London W6 8LH, United Kingdom.
Talma
Sonia
S
Hopfgarten
Christine
C
Murphy
Christopher L
CL
D000293:Adolescent; D000328:Adult; D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism; D055398:Bone Morphogenetic Protein 3; D019485:Bone Morphogenetic Proteins / Q000096:biosynthesis; D002358:Cartilage, Articular / Q000166:cytology / Q000378:metabolism*; D002454:Cell Differentiation / Q000502:physiology*; D015687:Cell Hypoxia / Q000502:physiology; D002478:Cells, Cultured; D002648:Child; D019902:Chondrocytes / Q000166:cytology / Q000378:metabolism*; D005109:Extracellular Matrix / Q000378:metabolism; D005260:Female; D020869:Gene Expression Profiling; D055413:Growth Differentiation Factor 10; D006609:High Mobility Group Proteins / Q000378:metabolism*; D006801:Humans; D028322:Inhibin-beta Subunits / Q000096:biosynthesis; D036341:Intercellular Signaling Peptides and Proteins / Q000096:biosynthesis; D008297:Male; D008875:Middle Aged; D020411:Oligonucleotide Array Sequence Analysis; D055758:SOX9 Transcription Factor; D014157:Transcription Factors / Q000378:metabolism*; D015854:Up-Regulation / Q000502:physiology*; D000099162:Endothelial PAS Domain-Containing Protein 1
D051792:Basic Helix-Loop-Helix Proteins; D055398:Bone Morphogenetic Protein 3; D019485:Bone Morphogenetic Proteins; D055413:Growth Differentiation Factor 10; D006609:High Mobility Group Proteins; D028322:Inhibin-beta Subunits; D036341:Intercellular Signaling Peptides and Proteins; D055758:SOX9 Transcription Factor; D014157:Transcription Factors; D000099162:Endothelial PAS Domain-Containing Protein 1; C525757:BMP3 protein, human; C525785:GDF10 protein, human; C527932:SOX9 protein, human; C103008:inhibin beta A subunit