Age‐related impeded regeneration of mouse minced anterior tibial muscle

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Abstract
The effect of increasing age on the completeness of anterior tibial muscle regeneration from autotransplants of minced muscle has been studied in Swiss Webster and C57/B6J mice aged 18 to 120 days. A progressively declining capability to regenerate new myofibers was associated with a decreasing phagocytic clearance of implanted myofiber debris. Concurrently, there was decreased presumptive myoblast proliferation and new myofiber formation. The importance of age‐related host factors, including nonspecific macrophage activity, in muscle mince regeneration was demonstrated by: (1) the successful regeneration of muscle in hetero‐transplanted muscle minces from older mice implanted in younger animals and (2) the failure of muscle regeneration when the reverse experiment was performed in syngeneic animals. Heterologous striated muscle from the diaphragm regenerated in the bed of the excised anterior tibial muscle, whereas heterologous cardiac muscle failed to regenerate as expected because of the absence of satellite cells. The failure of phagocytic clearance of implanted myofiber mince and concurrent retardation of regeneration suggests a major age‐related nonimmune role of phagocytic macrophages in the early stages of regeneration of anterior tibial muscle from isotopic minced muscle implants.