Mechanical impact induces cartilage degradation via mitogen activated protein kinases.
OBJECTIVE
To determine the activation of Mitogen activated protein (MAP) kinases in and around cartilage subjected to mechanical damage and to determine the effects of their inhibitors on impaction-induced chondrocyte death and cartilage degeneration.


METHODS
The phosphorylation of MAP kinases was examined with confocal microscopy and immunoblotting. The effects of MAP kinase inhibitors on impaction-induced chondrocyte death and proteoglycan (PG) loss were determined with fluorescent microscopy and 1, 9-Dimethyl-Methylene Blue (DMMB) assay. The expression of catabolic genes at mRNA levels was examined with quantitative real-time PCR.


RESULTS
Early p38 activation was detected at 20 min and 1h post-impaction. At 24h, enhanced phosphorylation of p38 and extracellular signal-regulated protein kinase (ERK)1/2 was visualized in chondrocytes from in and around impact sites. The phosphorylation of p38 was increased by 3.0-fold in impact sites and 3.3-fold in adjacent cartilage. The phosphorylation of ERK-1 was increased by 5.8-fold in impact zone and 5.4-fold in adjacent cartilage; the phosphorylation of ERK-2 increased by 4.0-fold in impacted zone and 3.6-fold in adjacent cartilage. Furthermore, the blocking of p38 pathway did not inhibit impaction-induced ERK activation. The inhibition of p38 or ERK pathway significantly reduced injury-related chondrocyte death and PG losses. Quantitative Real-time PCR analysis revealed that blunt impaction significantly up-regulated matrix metalloproteinase (MMP)-13, Tumor necrosis factor (TNF)-α, and ADAMTS-5 expression.


CONCLUSIONS
These findings implicate p38 and ERK mitogen activated protein kinases (MAPKs) in the post-injury spread of cartilage degeneration and suggest that the risk of post-traumatic osteoarthritis (PTOA) following joint trauma could be decreased by blocking their activities, which might be involved in up-regulating expressions of MMP-13, ADAMTS-5, and TNF-α.
Ding
L
L
Department of Orthopaedics and Rehabilitation, University of Iowa Hospitals and Clinics, Iowa City, Iowa 52242, USA.
Heying
E
E
Nicholson
N
N
Stroud
N J
NJ
Homandberg
G A
GA
Buckwalter
J A
JA
Guo
D
D
Martin
J A
JA
D000818:Animals; D002358:Cartilage, Articular / Q000201:enzymology / Q000293:injuries* / Q000378:metabolism*; D002417:Cattle; D016923:Cell Death / Q000187:drug effects / Q000502:physiology; D002470:Cell Survival / Q000502:physiology; D019902:Chondrocytes / Q000201:enzymology / Q000502:physiology; D004195:Disease Models, Animal; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D015151:Immunoblotting; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D011509:Proteoglycans / Q000032:analysis; D013314:Stress, Mechanical; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D011509:Proteoglycans; D048049:Extracellular Signal-Regulated MAP Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases
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