Assorted effects of TGFbeta and chondroitinsulfate on p38 and ERK1/2 activation levels in human articular chondrocytes stimulated with LPS.
OBJECTIVE
Inadequate cellular response of chondrocytes to stress frequently terminates in osteoarthritis (OA). Adequate response is fundamentally modulated by concerted cytokine signaling events, directing degradation and synthesis of cartilage on articular surfaces where and whenever necessary. Transforming growth factor (TGF)beta is a prominent mediator in cartilage anabolism, although particular catabolic activities are occasionally reported. Clearly, before the TGFbeta signal gets through to the gene regulatory machinery, cross talk with modulators occurs.


METHODS
We tested the hypothesis whether chondroitinsulfate (CS) modulates cell signaling. TGFbeta and/or soluble CS was added to human articular chondrocytes (HACs) and activation of p38 and extracellular signal related kinase (ERK)1/2 was determined by immunoblot analysis. Expression levels of mRNA of matrix metalloproteinase (MMP)-2, -3 and -13 were determined by real-time polymerase chain reaction (PCR).


RESULTS
No significant effects were observed unless cells were stimulated with lipopolysaccharide (LPS), invigorating catabolic metabolism in chondrocytes. LPS effects, however, were profoundly modulated by TGFbeta, CS and both applied in combination. Most prominent, the silencing of p38 stress signal by CS was superimposable to that of TGFbeta. Phospho-ERK1/2 levels were raised by TGFbeta three-fold over LPS induced levels. In contrast, CS treatment, alone or combined with TGFbeta, reduced phosphorylation significantly below LPS induced levels. Finally, suppression of LPS induced MMP-13 mRNA levels resulted with CS.


CONCLUSIONS
Soluble CS modulates signaling events in chondrocytes concurrent with MMP-13 down regulation. The effects observed suggest a feedback signaling mechanism cross talking with TGFbeta-signal pathways and may serve an explanation, on the cellular level, for the beneficial effects found in clinical studies with pharmacologic application of CS.
Holzmann
J
J
Zentrum Physiology and Pathophysiology, A-1090 Wien, Währingerstr. 10/13, Austria.
Brandl
N
N
Zemann
A
A
Schabus
R
R
Marlovits
S
S
Cowburn
R
R
Huettinger
M
M
D002358:Cartilage, Articular / Q000166:cytology / Q000201:enzymology*; D002478:Cells, Cultured; D019902:Chondrocytes / Q000201:enzymology*; D002809:Chondroitin Sulfates / Q000378:metabolism*; D017364:Collagenases / Q000378:metabolism; D004789:Enzyme Activation / Q000502:physiology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D015870:Gene Expression; D006801:Humans; D008070:Lipopolysaccharides / Q000378:metabolism; D053509:Matrix Metalloproteinase 13; D020778:Matrix Metalloproteinase 2 / Q000378:metabolism; D019278:Matrix Metalloproteinase 3 / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*
D008070:Lipopolysaccharides; D016212:Transforming Growth Factor beta; D002809:Chondroitin Sulfates; D048049:Extracellular Signal-Regulated MAP Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048051:p38 Mitogen-Activated Protein Kinases; D017364:Collagenases; C507079:MMP13 protein, human; D053509:Matrix Metalloproteinase 13; D019278:Matrix Metalloproteinase 3; D020778:Matrix Metalloproteinase 2