Myoglobin over-expression attenuates angiogenic response in hindlimb ischemia in mice

Myoglobin is expressed exclusively in striated skeletal muscles and has been implicated in nitric oxide scavenging. Accumulating data suggest a critical role for nitric oxide in both the endogenous and therapeutic angiogenic response to ischemia. A clear role for myoglobin in ischemic skeletal muscle is uncertain. We hypothesized that myoglobin overexpression has an adverse impact on the angiogenic response to ischemia.

Muscle-specific myoglobin over-expressing transgenic mice (MbTG, n = 11), wild type littermates (WT, n = 23) underwent unilateral femoral artery ligation and excision. Laser doppler perfusion imaging was used to monitor changes in hindlimb perfusion before surgery and weekly after surgery up to 28 days. Tissue ischemia was assessed by a necrosis incidence. Upon termination of the experiment (28 days after surgery), skeletal muscles (gastrocnemius, and tibialis anterior) were harvested, the distal part of the muscle was frozen and embedded for histology study, the proximal part was used either to detect vascular endothelial growth factor (VEGF) level with enzyme-linked immunosorbent assays (ELISA) or to determine the proliferation (proliferating cell nuclear antigen (PCNA)) and apoptosis (Bax, and Bcl-2) condition in ischemic muscle by Western blotting. Capillaries were stained with endothelial phosphate alkaline staining and vascular density was expressed in capillaries/fiber.

The recovery of perfusion in MbTG mice was similar to that of WT mice on day 7 (0.485 +/- 0.095 vs 0.500 +/- 0.084) but was significantly less on day 14 (0.536 +/- 0.086 vs 0.623 +/- 0.077, P < 0.05), day 21 (0.588 +/- 0.082 vs 0.684 +/- 0.068, P < 0.01) and day 28 (0.606 +/- 0.079 vs 0.733 +/- 0.093, P < 0.01). The necrosis incidence was higher in MbTG than in WT (54.5% vs 21.6%). Vascular density was less in MbTG compared with that in WT (gastrocnemius 0.19 +/- 0.08 vs 0.30 +/- 0.08, P < 0.05; tibialis anterior 0.22 +/- 0.11 vs 0.33 +/- 0.04, P < 0.05). With ischemic injury, the VEGF level was increased in both MbTG and WT (45.2% and 20.4%, respectively). Western blotting showed that after hindlimb ischemia the proliferation was similar in both MbTG and WT, however, apoptosis was increased in MbTG relative to WT, shown as more expression of Bax and less expression of Bcl-2.

An increase in expression of myoglobin protein in skeletal muscle reduces the endogenous perfusion recovery following surgically induced hind-limb ischemia.