The cartilage chondrolytic mechanism of fibronectin fragments involves MAP kinases: comparison of three fragments and native fibronectin.
OBJECTIVE
To define the role of mitogen activated protein (MAP) kinases in fibronectin fragment (Fn-f) mediated matrix metalloproteinase (MMP) upregulation and damage to bovine cartilage and to compare activities of three Fn-fs with native fibronectin (Fn), which is inactive in terms of cartilage damage.


METHODS
Bovine chondrocytes were cultured with three Fn-fs, an amino-terminal 29-kDa, a gelatin-binding 50-kDa and a central 140-kDa Fn-f or native Fn at concentrations from 0.01 to 1 microM, concentrations lower than those found in osteoarthritis synovial fluids. Lysates were probed for activation of MAP kinases, extracellular signal-regulated kinase 1/2 (ERK1/2), p38 and stress activated protein kinase/c-jun N-terminal kinase (SAPK/JNK). Confocal fluorescent microscopy was used to visualize movement of activated kinases. Kinase inhibitors were tested for their abilities to block Fn-f mediated protein upregulation of MMP-3 and MMP-13 and Fn-f induced depletion of cartilage proteoglycan (PG) from cultured explants.


RESULTS
The 29-kDa, the most potent Fn-f in terms of cartilage damage, enhanced phosphorylation of ERK1/2, p38 and JNK1/2 within a 1-h incubation while the 50 and 140-kDa Fn-fs required up to 4 h for maximal activity and native Fn was only minimally active toward p38 and JNK, but did strongly activate ERK1/2. The activated kinases displayed a distribution toward the nuclear membrane and within the nucleus. MAP kinase inhibitors markedly decreased Fn-f mediated upregulation of MMP-3 or MMP-13 and Fn-f mediated cartilage PG depletion.


CONCLUSIONS
These results suggest that Fn-fs upregulate MMP-3 and MMP-13 in bovine chondrocytes through MAP kinases and that kinase inhibitors afford protection against this degenerative pathway.
Ding
L
L
Department of Biochemistry and Molecular Biology, University of North Dakota, School of Medicine and Health Sciences, Grand Forks, ND 58202, United States.
Guo
D
D
Homandberg
G A
GA
D000818:Animals; D002356:Cartilage / Q000378:metabolism*; D002417:Cattle; D002478:Cells, Cultured; D019902:Chondrocytes / Q000378:metabolism* / Q000502:physiology; D005353:Fibronectins / Q000378:metabolism*; D020782:Matrix Metalloproteinases / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism*
D005353:Fibronectins; D010446:Peptide Fragments; D020928:Mitogen-Activated Protein Kinases; D020782:Matrix Metalloproteinases