Transforming growth factor alpha suppression of articular chondrocyte phenotype and Sox9 expression in a rat model of osteoarthritis.
OBJECTIVE
To define the roles of transforming growth factor alpha (TGFalpha) in cartilage degradation.


METHODS
Primary rat articular chondrocytes and articular osteochondral explants were cultured with TGFalpha to assess the effects of TGFalpha on chondrocyte physiology and phenotype.


RESULTS
TGFalpha altered chondrocyte morphology through reorganization of the actin cytoskeleton and formation of stress fibers. Expression of anabolic genes, including aggrecan, type II collagen, and cartilage link protein, was reduced in response to TGFalpha. Proliferation of chondrocytes and formation of articular chondrocyte clusters was stimulated by TGFalpha. Expression of matrix metalloproteinase 13 and cathepsin C was increased by TGFalpha. We demonstrated the down-regulation of Sox9 messenger RNA and protein levels by TGFalpha. This was associated with reduced levels of phosphorylated and total SOX9 in cartilage explants upon TGFalpha treatment. In contrast, another growth factor identified in our microarrays, Kitl, had no effects on the chondrocyte parameters tested. To examine correlations between the increased levels of TGFalpha in experimental knee osteoarthritis (OA) with the levels of TGFalpha in humans with knee OA, a microarray analysis of mRNA from 13 normal and 12 late-stage OA cartilage samples was performed. Seven OA samples showed TGFA mRNA levels similar to those in the normal controls, but expression was markedly increased in the other 5 OA samples. These data confirm that TGFA transcript levels are increased in a subset of patients with OA.


CONCLUSIONS
This study adds TGFalpha to the list of dysregulated cytokines present in degrading cartilage in OA. Since TGFalpha inhibits articular chondrocyte anabolic capacity, increases catabolic factors, and contributes to the development of chondrocyte clusters, TGFalpha may be a potential target for therapeutic strategies in the treatment of OA.
Appleton
C Thomas G
CT
University of Western Ontario, London, Ontario, Canada.
Usmani
Shirine E
SE
Bernier
Suzanne M
SM
Aigner
Thomas
T
Beier
Frank
F
D000368:Aged; D000818:Animals; D002358:Cartilage, Articular / Q000276:immunology / Q000473:pathology; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D019902:Chondrocytes / Q000187:drug effects / Q000473:pathology* / Q000502:physiology; D004195:Disease Models, Animal; D015870:Gene Expression / Q000187:drug effects / Q000276:immunology; D006609:High Mobility Group Proteins / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000276:immunology* / Q000473:pathology / Q000503:physiopathology*; D010641:Phenotype; D010766:Phosphorylation / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D055758:SOX9 Transcription Factor; D019089:Stem Cell Factor / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism; D016211:Transforming Growth Factor alpha / Q000378:metabolism* / Q000494:pharmacology
D006609:High Mobility Group Proteins; D055758:SOX9 Transcription Factor; C527932:SOX9 protein, human; D019089:Stem Cell Factor; D014157:Transcription Factors; D016211:Transforming Growth Factor alpha