Related Experiment Video
Updated: Mar 6, 2026
Induction of Acute Skeletal Muscle Regeneration by Cardiotoxin Injection
Published on: January 1, 2017
Pattern of cardiotoxin-induced muscle remodeling in distinct TLR-4 deficient mouse strains
Eustáquio Luiz Paiva-Oliveira1,2, Rafael Ferreira da Silva1,2, Maria Bellio3
1Department of Immunobiology, Institute of Biology, Fluminense Federal University, Niterói, Rio de Janeiro, 24 020 141, Brazil.
Abstract:
Tissue damage triggers innate immune response mediated by Toll-like receptor 4 (TLR) that recognizes endogenous host danger molecules associated with cell death and tissue inflammation, although the precise role of TLR-4 signaling in muscle tissue repair is still uncertain. Previously, we observed that TLR-4 exerted a protective effect preventing excessive muscular damage induced by Bothrops jararacussu crude venom. This study aimed to evaluate the involvement of TLR-4 at early stages of muscular tissue remodeling in distinct mouse strains after injection of purified snake venom. Muscular injury was induced by injection of 25 µl (0.05 mg/ml) of cardiotoxin (CTX) from Naja mossambica in the gastrocnemius muscle of C3H/HeN (wild-type); C3H/HeJ mice that express a non-functional TLR-4 receptor, C57BL/6 and Tlr4 -/- (B6 background) mice. Comparing to control, Tlr4 -/- mice presented at early stages (3 DPI) of muscle injury mild inflammation with low MMP-9 activity, scarce macrophage infiltration and premature change to anti-inflammatory phenotype, low TNF-α mRNA levels and reduced myogenin expression, with low regeneration and tissue remodeling. The presence of more Ly6Cneg macrophages in Tlr4 -/- mice at 3 DPI indicates that TLR-4 may influence the differentiation into Ly6Cneg or likely affect proliferation of such cells in the muscle. The present study shows that TLR-4 deficiency and genetic background influence the outcome of muscular tissue repair in aseptic lesions and yet still maintaining some level of signaling in the TLR4-mutant mice.
Insights
Toll-like receptor 4 (TLR-4) plays a crucial role in muscle tissue repair. TLR-4 deficiency in mice impairs early muscle regeneration and remodeling following injury, impacting inflammation and macrophage activity.
Area of Science:
- Immunology
- Muscle Regeneration
- Molecular Biology
Background:
- Tissue damage activates the innate immune system via Toll-like receptor 4 (TLR-4), which recognizes danger molecules.
- The exact role of TLR-4 signaling in muscle tissue repair remains unclear, though previous studies suggest a protective effect against venom-induced damage.
- Understanding TLR-4's function is critical for developing strategies to enhance muscle healing.
Purpose of the Study:
- To investigate the involvement of TLR-4 in the early stages of muscle tissue remodeling.
- To compare the effects of TLR-4 deficiency on muscle repair across different mouse strains after cardiotoxin-induced injury.
Main Methods:
- Induction of muscular injury using cardiotoxin (CTX) from Naja mossambica in the gastrocnemius muscle.
- Utilized distinct mouse strains: C3H/HeN (wild-type), C3H/HeJ (non-functional TLR-4), C57BL/6, and Tlr4-/- (B6 background).
- Assessed early stages (3 days post-injection) of muscle injury, evaluating inflammation, macrophage infiltration, MMP-9 activity, TNF-α mRNA, and myogenin expression.
Main Results:
- Tlr4-/- mice exhibited mild inflammation, reduced MMP-9 activity, and scarce macrophage infiltration at 3 days post-injury compared to controls.
- These mice showed a premature shift to an anti-inflammatory phenotype, with lower TNF-α mRNA levels and reduced myogenin expression.
- Tlr4-/- mice displayed impaired muscle regeneration and tissue remodeling, with altered Ly6Cneg macrophage populations, suggesting TLR-4 influences macrophage differentiation or proliferation.
Conclusions:
- TLR-4 deficiency significantly impacts the early phases of aseptic muscle tissue repair.
- Genetic background and TLR-4 status influence the outcome of muscle regeneration and remodeling.
- TLR-4 signaling is essential for effective inflammatory responses and cellular processes driving muscle repair.
