Signal transduction and metabolism in chondrocytes is modulated by lactoferrin.
OBJECTIVE
Activation of granulocytes causes a considerable rise in the concentration of lactoferrin (Lf) in synovial fluid (SF). We here investigate consequences thereof on signal transduction and the balance between catabolic and anabolic metabolism in chondrocytes.


METHODS
Signal transduction was analysed in cultured chondrocytes by immunodetection of mitogen activated protein kinases (MAPK) and analysis of Smad2 translocation to the nucleus. Expression levels of matrix metalloproteinases (MMPs) and of aggrecan were measured by reverse-transcription-PCR. The proteolytic activity of MMPs was ascertained by zymography. Expression of the low-density-lipoprotein-receptor-related-protein-1 (LRP-1), a Lf receptor for signalling, was assayed by immunohistochemistry in cartilage and in cultured chondrocytes by immunoblotting.


RESULTS
We found LRP-1 expressed in dedifferentiated chondrocytes in culture and in cartilage tissue preferentially on the articular surface where it can encounter Lf within SF. Lf stimulated proliferation of chondrocytes, comparable to transforming growth factor-beta1 (TGFbeta1) and activated p38 and the extracellular-signal regulated-kinases 1/2 (ERK1/2) within minutes. Surprisingly, Lf induced nuclear Smad2 translocation, a signal pathway ascribed to TGFbeta receptor activation. Lf significantly increased the levels of catabolic indicators such as MMP1, MMP2, MMP3 and MMP13 and inhibited aggrecan synthesis.


CONCLUSIONS
Lf is a robust regulator of chondrocyte metabolism, comparable to TGFbeta1. The catabolic influence together with the proliferative stimulus indicates a function as an early phase cytokine, enhancing MMPs, necessary for degradation of damaged tissue and stimulating proliferation of chondrocytes, necessary for reconstruction.
Brandl
N
N
Medical University of Vienna, Center Physiology and Pathophysiology, Vienna, Austria.
Zemann
A
A
Kaupe
I
I
Marlovits
S
S
Huettinger
P
P
Goldenberg
H
H
Huettinger
M
M
D053674:Aggrecans / Q000378:metabolism; D002358:Cartilage, Articular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D019902:Chondrocytes / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D007781:Lactoferrin / Q000494:pharmacology*; D026503:Low Density Lipoprotein Receptor-Related Protein-1 / Q000378:metabolism; D020782:Matrix Metalloproteinases / Q000378:metabolism*; D020929:Mitogen-Activated Protein Kinase Kinases / Q000032:analysis* / Q000276:immunology; D011506:Proteins / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects*; D051899:Smad2 Protein / Q000032:analysis
D053674:Aggrecans; C514519:LDLR-related protein 1A, human; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D011506:Proteins; C497782:SMAD2 protein, human; D051899:Smad2 Protein; D020929:Mitogen-Activated Protein Kinase Kinases; D007781:Lactoferrin; D020782:Matrix Metalloproteinases