Delayed angiogenesis and VEGF production in CCR2−/− mice during impaired skeletal muscle regeneration

Abstract

The regulation of vascular endothelial growth factor (VEGF) levels and angiogenic events during skeletal muscle regeneration remains largely unknown. This study examined angiogenesis, VEGF levels, and muscle regeneration after cardiotoxin (CT)-induced injury in mice lacking the CC chemokine receptor 2 (CCR2). Muscle regeneration was significantly decreased in CCR2−/− mice as was the early accumulation of macrophages after injury. In both mouse strains, tissue VEGF was similar at baseline (no injections) and significantly decreased at day 3 post-CT. Tissue VEGF in wild-type (WT) mice was restored within 7 days postinjury but remained significantly reduced in CCR2−/− mice until day 21. Capillary density (capillaries/mm2) within regenerating muscle was maximal in WT mice at day 7 and double that of baseline muscle. In comparison, maximal capillary density in CCR2−/− mice occurred at 21 days postinjury. Maximal capillary density developed concurrent with the restoration of tissue VEGF in both strains. A highly significant, inverse relationship existed between the size of regenerated muscle fibers and capillaries per square millimeter. Although this relationship was comparable in WT and CCR2−/− animals, there was a significant decrease in the magnitude of this response in the absence of CCR2, reflecting the observation that regenerated muscle fiber size in CCR2−/− mice was only 50% of baseline at 42 days postinjury, whereas WT mice had attained baseline fiber size by day 21. Thus CCR2-dependent events in injured skeletal muscle, including impaired macrophage recruitment, contribute to restoration of tissue VEGF levels and the dynamic processes of capillary formation and muscle regeneration.

Regulatory interactions between muscle and the immune system during muscle regeneration

“…Instead of the stereotypic inflammatory response in acutely injured muscle, CTX-injected muscles in CCR2-null mutant mice showed a greatly reduced invasion of macrophages into the injury site, while neutrophil numbers were elevated for a prolonged period (80). In addition, injured muscles in CCR2 mutants showed persistent necrosis of muscle fibers and a slowed growth of fiber diameter at the injury site.…”

“…As in other tissues, Ly6Cϩ/F4/80-neutrophils are the first responders and begin to appear at elevated numbers within 2 h of muscle damage, typically peaking in concentration between 6 and 24 h postinjury and then rapidly declining in numbers. Following the onset of neutrophil invasion, phagocytic macrophages begin to invade, reaching significantly elevated concentrations at about 24 h postinjury and continue to increase in numbers until about 2 days postinjury, when their numbers begin to decline sharply (8,16,26,80,98,109,117). Their invasion precedes the elevation of a population of nonphagocytic macrophages that reaches peak concentrations in the muscle at about 4 days postinjury but remains significantly elevated for many days (Fig.…”

Vascular endothelial growth factor is highly expressed in muscle tissue of patients with polymyositis and patients with dermatomyositis

“…VEGF is able to enhance myoblast migration in vitro and prevent apoptosis of myoblasts in cell culture and in skeletal muscle following ischemia (42). In addition, impaired muscle regeneration was observed in mice during delayed angiogenesis and low-level VEGF production (43). Maximal capillary density postinjury was observed concomitant with the restoration of tissue VEGF (43).…”

“…In addition, impaired muscle regeneration was observed in mice during delayed angiogenesis and low-level VEGF production (43). Maximal capillary density postinjury was observed concomitant with the restoration of tissue VEGF (43). This might indicate that growing, regenerating muscle fibers have an increased need for nutrient delivery, which can be accomplished by increased capillary density.…”

Regulation of myogenic stem cell behaviour by vessel cells: The "ménage à trois" of satellite cells, periendothelial cells and endothelial cells

“…26 Inversely, in mice exhibiting delay and impairment of muscle regeneration (CCR2 -/-mice), VEGF level is decreased until day 21, time of restoration of maximal capillary density. 27 The authors showed that maximal capillary density developed concurrent with the restoration of tissue VEGF, and observed an inverse relationship between the size of regenerated muscle fibres and the number of capillaries. 27 These studies indicates the existence of VEGF-dependent mechanisms at work in the dynamic processes of capillary formation and muscle regeneration.…”