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Expression of specific matrix metalloproteinases in inflammatory myopathies
B C Kieseier1, C Schneider, J M Clements
1Department of Neurology, Karl Franzens University, Graz, Austria. bc.kieseier@kfunigraz.ac.at
Abstract:
The family of matrix metalloproteinases (MMPs) comprises endopeptidases that are capable of degrading all extracellular matrix components. Given these actions, it is conceivable that MMPs may play a pathogenic role in inflammatory myopathies. These immune-mediated disorders are characterized by the invasion of mononuclear phagocytes and T lymphocytes and the loss of muscle fibres. We examined whether specific MMPs and their natural inhibitors (tissue inhibitors of metalloproteinases; TIMPs) are expressed in muscle during acute inflammatory attacks by studying muscle biopsies obtained from patients diagnosed as having polymyositis, dermatomyositis, sporadic inclusion body myositis and, for comparison, from cases of various muscular dystrophies. Quantitative polymerase chain reaction analysis revealed significantly elevated mRNA expression of interstitial collagenase (MMP-1) and gelatinase B (MMP-9) in polymyositis and dermatomyositis and to a lesser extent in inclusion body myositis, whereas the level of expression of TIMPs remained unchanged in comparison with controls. Increased mRNA levels were associated with enhanced enzyme expression, as determined by immunoblotting, gelatin zymography and in situ zymography. Immunohistochemically, MMP-1 could be localized around the sarcolemma of diseased muscle fibres and to cells resembling fibroblasts, whereas MMP-9 seemed to be expressed primarily by invading T lymphocytes. Raised levels of MMPs could not be detected in the sera of affected patients, emphasizing the crucial action of MMPs in the inflamed muscle. Our results imply a pathogenic role for specific MMPs in the genesis of inflammatory myopathies, and open new strategies for therapeutic intervention.
Insights
Matrix metalloproteinases (MMPs) are elevated in inflammatory myopathies, suggesting a pathogenic role. MMPs are involved in muscle fiber damage, indicating potential therapeutic targets for these immune-mediated disorders.
Area of Science:
- Biochemistry
- Immunology
- Neurology
Background:
- Matrix metalloproteinases (MMPs) degrade extracellular matrix components.
- Inflammatory myopathies involve immune cell invasion and muscle fiber loss.
- MMPs may contribute to the pathology of inflammatory myopathies.
Purpose of the Study:
- To investigate the expression of MMPs and their inhibitors (TIMPs) in muscle biopsies from patients with inflammatory myopathies.
- To determine the role of specific MMPs in the pathogenesis of polymyositis, dermatomyositis, and inclusion body myositis.
Main Methods:
- Quantitative polymerase chain reaction (qPCR) to analyze mRNA expression of MMPs and TIMPs.
- Immunoblotting, gelatin zymography, and in situ zymography to assess enzyme levels and activity.
- Immunohistochemistry to localize MMP expression within muscle tissue.
Main Results:
- Significantly elevated mRNA and protein levels of interstitial collagenase (MMP-1) and gelatinase B (MMP-9) were found in polymyositis and dermatomyositis.
- MMP-1 localized around diseased muscle fibers, while MMP-9 was primarily expressed by infiltrating T lymphocytes.
- TIMP levels remained unchanged, and elevated MMPs were not detected in patient sera.
Conclusions:
- Specific MMPs, particularly MMP-1 and MMP-9, play a pathogenic role in inflammatory myopathies.
- These findings suggest that MMPs are crucial in the inflamed muscle environment.
- Targeting MMPs could offer new therapeutic strategies for inflammatory myopathies.