Sublytic terminal complement attack on myotubes decreases the expression of mRNAs encoding muscle-specific proteins
Related Experiment Video
Updated: Sep 27, 2026
Cryosectioning of Contiguous Regions of a Single Mouse Skeletal Muscle for Gene Expression and Histological Analyses
Published on: December 12, 2016
1Department of Pathology, University of Maryland School of Medicine, Baltimore, USA.
Abstract:
Activation of inflammatory and cytotoxic complement effectors that include the C5b-9 complex plays an important pathogenic role in myasthenia gravis, an inflammatory autoimmune disease of the muscle. Altered muscle-specific gene expression has been observed in experimental myasthenic rats. In this study, we have examined the effect of sublytic C5b-9 on myotubes differentiated from C2C12 myoblasts, by generating C5b-9 with C7-deficient serum with or without C7. Within 2 h, C7-deficient serum plus C7, compared with C7-deficient serum alone, induced markedly decreased levels of mRNAs encoding alpha-actin, troponin I slow twitch isoform, acetylcholine receptor alpha, and muscle aldolase A, whereas the heat shock protein 83 mRNA level remained constant, by northern analysis. Because the half-life of the acetylcholine receptor alpha was estimated to be > 8 h, the C5b-9 effect was, in part, due to enhanced mRNA decay. Because C5b-9 also induced c-jun mRNA and reduced the myoD mRNA level, a possible inhibition of muscle gene transcription by C5b-9 was examined in myotubes transfected with troponin promoter-luciferase gene constructs. Luciferase activity was reduced to 50% in response to C5b-9 at 2 h. Thus, C5b-9 appears to inhibit the muscle-specific gene expression by stimulating mRNA decay and by decreasing the transcription process. The data also indicate a possible pathogenic role of C5b-9 in immune-mediated inflammatory muscle disorders in which complement activation has been implicated.
Insights
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.
Related Concept Videos
01:26Cross-bridge Cycle
01:21Satellite Stem Cells and Muscular Dystrophy
01:26Chemical Synapses
Because chemical synapses depend on the release of neurotransmitter molecules from synaptic vesicles to pass on their signal, there is an approximately one millisecond delay between when the axon potential reaches the presynaptic terminal and when the neurotransmitter leads to opening of postsynaptic ion channels. Additionally, this signaling is...
01:29Neuromuscular Junction And Blockade
01:26Chemical Synapses
Because chemical synapses depend on the release of neurotransmitter molecules from synaptic vesicles to pass on their signal, there is an approximately one millisecond delay between when the axon potential reaches the presynaptic terminal and when the neurotransmitter leads to opening of postsynaptic ion channels. Additionally, this signaling is...
01:22Myasthenia Gravis ll: Pathophysiology