Acute injury of skeletal muscle damages myofibers, microvessels, and supporting tissue components. To restore the structural and functional integrity of intact muscle, each tissue component must regenerate. In adult skeletal muscle, resident muscle stem cells (satellite cells) efficiently regenerate myofibers within 10 days post injury (dpi) and microvascular integrity recovers by 21 dpi. However, the requirement for crosstalk between regenerating myofibers and microvessels is poorly understood. We tested the hypothesis that myofiber regeneration is necessary for revascularization and restoration of microvascular integrity. To ablate satellite cells and impair myofiber regeneration, we studied male and female mice (age, ~4 mo) in which tamoxifen-dependent Cre recombination induced the expression of diphtheria toxin in quiescent satellite cells, killing them prior to injury. For acute muscle injury, the gluteus maximus muscle (GM) was injected with BaCl2 (1.2%, 75 µL). Microvascular perfusion and permeability were evaluated by injecting fluorescent dextrans (70 amp; 155 kDa) into the circulation during intravital imaging of the GM at defined timepoints following injury. Despite the absence of myofiber regeneration, sprouting angiogenesis was robust and capillary perfusion was restored within 7 dpi, as observed in wild-type mice. However, the permeability barrier of nascent microvessels was compromised as shown by profuse leakage of both fluorescent dextrans. At 21 dpi, the absence of regenerated myofibers was accompanied by sustained inflammation and myosteatosis. Areas of ectopic adipocyte accumulation were hypervascular and localized around venules. Adjacent areas contained empty myofiber “sheaths” which were underperfused; residual microvascular networks exhibited pruning. These findings suggest that, following acute injury of adult skeletal muscle, revascularization occurs in the absence of myogenesis but is defective and nascent vessels are unstable. We conclude that myofiber regeneration is essential to recovering a functionally intact microcirculation following muscle injury.
