Expression of Vascular Endothelial Growth Factor and Vascular Endothelial Growth Factor Receptor-2 (KDR/Flk-1) in Ischemic Skeletal Muscle and Its Regeneration

Abstract

Vascular endothelial growth factor (VEGF) is a hypoxia-inducible endothelial cell mitogen and survival factor. Its receptor VEGFR-2 (KDR/Flk-1) mediates these effects. We studied the expression of VEGF and VEGFR-2 in ischemic human and rabbit skeletal muscle by immunohistochemistry and in situ hybridization. Human samples were obtained from eight lower limb amputations because of acute or chronic critical ischemia. In chronically ischemic human skeletal muscle VEGF and VEGFR-2 expression was restricted to atrophic and regenerating skeletal myocytes, whereas in acutely ischemic limbs VEGF and VEGFR-2 were expressed diffusely in the affected muscle. Hypoxia-inducible factor-1alpha was associated with VEGF and VEGFR-2 expression both in acute and chronic ischemia but not in regeneration. Hindlimb ischemia was induced in 20 New Zealand White rabbits by excising the femoral artery. Magnetic resonance imaging and histological sections revealed extensive ischemic damage in the thigh and leg muscles of ischemic rabbit hindlimbs with VEGF expression similar to acute human lower limb ischemia. After 1 and 3 weeks of ischemia VEGF expression was restricted to regenerating myotubes and by 6 weeks regeneration and expression of VEGF was diminished. VEGFR-2 expression was co-localized with VEGF expression in regenerating myotubes. Macrophages and an increased number of capillaries were associated with areas of ischemic muscle expressing VEGF and VEGFR-2. In conclusion, two patterns of VEGF and VEGFR-2 expression in human and rabbit ischemic skeletal muscle are demonstrated. In acute skeletal muscle ischemia VEGF and VEGFR-2 are expressed diffusely in the affected muscle. In chronic skeletal muscle ischemia and in skeletal muscle recovering from ischemia VEGF and VEGFR-2 expression are restricted to atrophic and regenerating muscle cells suggesting the operation of an autocrine pathway that may promote survival and regeneration of myocytes.

Phosphorylated KDR expression in endometrial cancer cells relates to HIF1α/VEGF pathway and unfavourable prognosis

“…Upregulation of VEGF and KDR, which is paralleled by HIF1a expression, has also been recorded in rabbit skeletal muscle during acute hypoxia. 36 KDR is also induced by hypoxia in choroid-retinal endothelial (RF/6A) cells. 37 In any case, the co-expression of pKDR with the HIF1a downstream genes may be an additional reason for the unfavourable prognosis noted in tumours with pKDR expression.…”

Angiogenic Actions of Angiopoietin-1 Require Endothelium-Derived Nitric Oxide

“…The cornea is normally avascular and thus unlikely to express angiogenic factors, whereas in the ischemic hindlimb model, tissue hypoxia results in up-regulation of angiogenic factors and their receptors. 36 Matrigel is derived from tumor basement membrane and contains low concentrations of multiple growth factors, possibly providing a suitable background to support the angiogenic actions of Ang1.…”

Adaptive Myogenesis under Hypoxia

“…The myogenic differentiation of myoblasts is highly orchestrated by a family of myogenic regulatory factors (MRFs), such as myoD, myogenin, myf5, and MRF4 in collaboration with the E2A gene products (E12 or E47) and/or the myogenic enhancing factors (6, 41, 53). Although a plethora of information on the embryonic development of muscle exists, there is still a lack of clear understanding of how postnatal myogenic satellite cells are regulated during muscle regeneration, especially by their microenvironment.Tissue ischemia in myocardium and skeletal muscle results in hypoxia and elevates the expression of the hypoxia-inducible transcription factor HIF-1␣ and its downstream gene, VEGF (32,40). Although ischemic tissue is exposed to hypoxia and decreased nutritional supply, cells will alter their metabolism, proliferation, and differentiation programs in response to hypoxia alone.…”