Denervation dynamically regulates integrin alpha7 signaling pathways and microscopic structures in rats
Feng-Chou Tsai1, Man-Hui Pai, Chong-Chi Chiu
1Center for Mathematical Biology, Graduate Institute of Clinical Medicine, College of Medicine, Taipei Medical University, and Department of Surgery, Taipei Medical University Hospital, Taipei, Taiwan.
Background:
Peripheral nerve injury causes serious problems in orthopedic and plastic surgeries. Cell adhesion molecules such as integrin alpha7 provoke cell binding and signaling pathways within myofibers. Expression profiles of integrin alpha7 signaling pathways and the molecule's microscopic structure were assessed to investigate the long-term dynamic changes in denervated rat skeletal muscle.
Methods:
A denervated rat skeletal muscle model was established by severing the sciatic nerve for 1 week, 2 weeks, 4 weeks, 8 weeks, 12 weeks, 20 weeks, and 26 weeks. Molecular expressions were investigated by mRNA and Western blot. The structural alterations were detected by immunohistochemistry, scanning electron microscopy, and transmission electron microscopy.
Results:
The denervated muscle atrophy presented the following dynamic molecular alterations: an initial increase around postdenervation in week (PIW) 8 and then a subsequent decay of integrin alpha7, integrin downstream signaling pathway (Ras or Raf or, ERK1/2), Akt, cleaved caspase-3, fast myosin heavy chain (MHC), beta actin, and RhoA. We demonstrated that the expressions of multiple signaling molecules were highly upregulated at PIW 8 (p<0.01). Scanning electron microscopy findings of the surface textures of myofibers showed more severe damage at PIW 8 and subsequently became smoother. Inner structures of myofibers separated with discontinuity on transmission electron microscopy examinations.
Conclusion:
Our novel finding showed that time-series alterations of integrin alpha7 signaling molecules and surface microstructures in the long-term denervated rat skeletal muscle are biphasic and coherently dynamic. Persisted p-Akt elevation suggested that denervated muscle may regenerate if reinnervation or other treatment was performed.
Insights
Peripheral nerve injury impacts skeletal muscle, with integrin alpha7 signaling showing biphasic changes. Persistently elevated p-Akt suggests potential for muscle regeneration with treatment.
Area of Science:
- Cellular and Molecular Biology
- Regenerative Medicine
- Skeletal Muscle Physiology
Background:
- Peripheral nerve injury poses significant challenges in reconstructive surgeries.
- Integrin alpha7 plays a role in cell adhesion and signaling within myofibers.
- Understanding long-term changes in denervated muscle is crucial.
Purpose of the Study:
- To investigate the dynamic, long-term changes in integrin alpha7 signaling pathways and microstructures in denervated rat skeletal muscle.
- To correlate molecular expression profiles with structural alterations over time.
Main Methods:
- Established a rat model of sciatic nerve transection with analysis at multiple time points (1-26 weeks).
- Utilized mRNA and Western blot for molecular expression analysis.
- Employed immunohistochemistry, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) for structural assessment.
Main Results:
- Denervated muscle exhibited biphasic alterations in integrin alpha7 and downstream signaling molecules (Ras, Raf, ERK1/2, Akt, cleaved caspase-3, MHC, beta actin, RhoA), with peak upregulation at 8 weeks post-denervation.
- SEM revealed severe myofiber surface damage at 8 weeks, followed by smoothing.
- TEM showed discontinuity in the inner structures of myofibers.
Conclusions:
- Integrin alpha7 signaling molecules and myofiber microstructures display coherent, biphasic dynamic changes in long-term denervated muscle.
- Sustained p-Akt levels indicate a potential for muscle regeneration contingent upon reinnervation or therapeutic intervention.
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