Satellite Cell Content in Different Muscle Regions Following Volumetric Muscle Loss Injury

Volumetric muscle loss (VML) refers to the loss of a significant portion of skeletal muscle tissue, which cannot regenerate through the body's natural repair mechanisms. Satellite cells play a crucial role in muscle regeneration due to their ability to proliferate, migrate to injured areas, and fuse with other cells or muscle fibers to repair or create new tissue. PURPOSE: This study examined the satellite cell distribution in different regions of VML-injured muscle to understand their response to trauma. METHODS: Four adult male Lewis rats (3-4 months old) underwent a surgical procedure where a 6mm full-thickness biopsy punch created a VML injury in the middle third of the tibialis anterior (TA) muscle in the left hindlimb. The uninjured right hindlimb served as a control. After 6 weeks, TA muscles from both hindlimbs were collected and processed for immunohistochemistry. Satellite cells were identified using Pax7, Laminin, and DAPI staining, and images were collected from three regions of the injured muscle: the defect (injury site), the border (tissue surrounding the defect), and the distal region (farther from the injury). These images were then compared to the uninjured control muscle. RESULTS: Satellite cell content in the border region (0.04062±0.0150 Pax7+ cells/mm²) was significantly higher than in the defect, distal, or control regions (p=0.0028). There were no differences in satellite cell content between the defect (0.007764±0.0039 Pax7+ cells/mm²), distal (0.01002±0.0031 Pax7+ cells/mm²), and control (0.00746±0.0037 Pax7+ cells/mm²) regions (p=0.9). CONCLUSION: These results suggest that VML injuries fail to regenerate because satellite cells accumulate in the border region and do not migrate into the defect area, where they could generate new muscle fibers. This may be due to the removal of the extracellular matrix, which deprives the satellite cells of structural support needed for migration. Therefore, regenerative therapies should focus on adding both satellite cells and extracellular matrix to improve muscle regeneration following VML.