SWIR Fluorescence Imaging In Vivo Monitoring and Evaluating Implanted M2 Macrophages in Skeletal Muscle Regeneration

Skeletal muscle has a robust regeneration ability that is impaired by severe injury, disease, and aging, resulting in a decline in skeletal muscle function. Therefore, improving skeletal muscle regeneration is a key challenge in treating skeletal muscle-related disorders. Owing to their significant role in tissue regeneration, implantation of M2 macrophages (M2Mø) has great potential for improving skeletal muscle regeneration. Here, we present a short-wave infrared (SWIR) fluorescence imaging technique to obtain more in vivo information for an in-depth evaluation of the skeletal muscle regeneration effect after M2Mø transplantation. SWIR fluorescence imaging was employed to track implanted M2Mø in the injured skeletal muscle of mouse models. It is found that the implanted M2Mø accumulated at the injury site for two weeks. Then, SWIR fluorescence imaging of blood vessels showed that M2Mø implantation could improve the relative perfusion ratio on day 5 (1.09 ± 0.09 vs 0.85 ± 0.05; p = 0.01) and day 9 (1.38 ± 0.16 vs 0.95 ± 0.03; p = 0.01) post-injury, as well as augment the degree of skeletal muscle regeneration on day 13 post-injury. Finally, multiple linear regression analyses determined that post-injury time and relative perfusion ratio could be used as predictive indicators to evaluate skeletal muscle regeneration. These results provide more in vivo details about M2Mø in skeletal muscle regeneration and confirm that M2Mø could promote angiogenesis and improve the degree of skeletal muscle repair, which will guide the research and development of M2Mø implantation to improve skeletal muscle regeneration.