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Sublytic terminal complement attack on myotubes decreases the expression of mRNAs encoding muscle-specific proteins
1Department of Pathology, University of Maryland School of Medicine, Baltimore, USA.
Journal of Neurochemistry
|April 1, 1997
Summary
The complement C5b-9 complex impairs muscle gene expression by increasing mRNA decay and reducing transcription. This finding suggests a role for C5b-9 in inflammatory muscle disorders like myasthenia gravis.
Area of Science:
- Immunology
- Molecular Biology
- Muscle Physiology
Background:
- The complement system, particularly the C5b-9 complex, is implicated in the pathogenesis of myasthenia gravis.
- Previous studies noted altered muscle-specific gene expression in experimental models of this autoimmune muscle disease.
Purpose of the Study:
- To investigate the impact of sublytic complement C5b-9 on gene expression in differentiated C2C12 myotubes.
- To elucidate the mechanisms by which C5b-9 affects muscle-specific gene expression, including mRNA stability and transcription.
Main Methods:
- C5b-9 complexes were generated using C7-deficient serum with or without C7.
- Northern blot analysis was used to quantify mRNA levels of specific muscle genes (alpha-actin, troponin I, acetylcholine receptor alpha, muscle aldolase A, HSP83).
- Luciferase reporter assays were employed to assess the effect of C5b-9 on muscle gene transcription using troponin promoter constructs.
Main Results:
- Sublytic C5b-9 significantly decreased mRNA levels for alpha-actin, troponin I, acetylcholine receptor alpha, and muscle aldolase A within 2 hours.
- C5b-9 exposure led to enhanced mRNA decay, particularly for acetylcholine receptor alpha (half-life > 8 hours).
- C5b-9 reduced luciferase activity by 50% in myotubes transfected with troponin promoter-luciferase constructs, indicating transcriptional inhibition, and increased c-jun mRNA while decreasing myoD mRNA.
Conclusions:
- Sublytic C5b-9 inhibits muscle-specific gene expression through both accelerated mRNA decay and reduced transcriptional activity.
- These findings highlight a potential pathogenic role for the complement C5b-9 complex in immune-mediated inflammatory muscle disorders, including myasthenia gravis.