Role of hypoxia-inducible factor 1 alpha in the integrity of articular cartilage in murine knee joints.
BACKGROUND
Chondrocytes have to withstand considerable hypoxic conditions within the avascular articular cartilage. The present study investigated the effects of inhibiting or stabilizing hypoxia-inducible factor (HIF)-1 alpha by 2-methoxyestradiol or dimethyloxaloylglycine on the progression of osteoarthritis in murine knee joints.


METHODS
2-Methoxyestradiol was injected six times over a period of 2 weeks into the left knee joint of Balb/C mice. Joints were assessed by histochemical and immunohistochemical methods, 3 weeks and 12 weeks following the first injection. Dimethyloxaloylglycine, an inhibitor of HIF-degrading prolyl-hydroxylases, was injected into the left knee joints of STR/ORT mice once a week over the entire period of 12 weeks. Right knee joints that received a saline solution served as controls. In addition, the effects of dimethyloxaloylglycine on HIF-1 target gene expression and on collagen metabolism were analyzed in vitro.


RESULTS
Injection of 2-methoxyestradiol led to osteoarthritic changes in the treated knee joints of Balb/C mice. The first signs of osteophyte formation were observed in the knee joints after 3 weeks, followed by progressive destruction of the articular cartilage at 12 weeks that was not, however, accompanied by inflammatory reactions. Injection of dimethyloxaloylglycine could not prevent severe osteoarthritis that spontaneously developed in the knee joints of STR/ORT mice. In chondrocyte cultures, administration of dimethyloxaloylglycine resulted in an upregulation of Sox9 expression. Such a stimulatory effect was not observed, however, for the expression of type II collagen, which might be the indirect consequence of intracellular collagen retention observed by immunofluorescence or of increased expression of IL-1 beta and IL-6.


CONCLUSIONS
Induction of osteoarthritis by 2-methoxyestradiol demonstrates the importance of HIF-1 in maintaining the integrity of hypoxic articular cartilage. Stabilization of HIF-1 by dimethyloxaloylglycine, however, was not of therapeutic value, since this nonselective prolyl-hydroxylase inhibitor also interferes with proper collagen metabolism and induces the expression of catabolic cytokines.
Gelse
Kolja
K
Division of Orthopaedic Rheumatology, University of Erlangen-Nuremberg, Rathsberger Strasse 57, Erlangen 91054, Germany. kolja.gelse@web.de
Pfander
David
D
Obier
Simon
S
Knaup
Karl X
KX
Wiesener
Michael
M
Hennig
Friedrich F
FF
Swoboda
Bernd
B
D000077584:2-Methoxyestradiol; D000600:Amino Acids, Dicarboxylic / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis; D002358:Cartilage, Articular / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D015687:Cell Hypoxia / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D019902:Chondrocytes / Q000187:drug effects / Q000378:metabolism*; D016207:Cytokines / Q000096:biosynthesis / Q000187:drug effects; D004958:Estradiol / Q000031:analogs & derivatives / Q000633:toxicity; D005260:Female; D005455:Fluorescent Antibody Technique; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000187:drug effects / Q000378:metabolism*; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D007719:Knee Joint / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008807:Mice, Inbred BALB C; D020370:Osteoarthritis, Knee / Q000139:chemically induced / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050257:Tubulin Modulators / Q000633:toxicity
D000600:Amino Acids, Dicarboxylic; D016207:Cytokines; C497443:Hif1a protein, mouse; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D050257:Tubulin Modulators; D004958:Estradiol; D000077584:2-Methoxyestradiol; C040947:oxalylglycine
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