title: Differential expression of Flk-1 and Flt-1 in rat skeletal muscle in response to chronic ischaemia: favourable effect of muscle activity.
abstract: To determine the involvement of vascular endothelial growth factor (VEGF) and its receptors Flk-1 and Flt-1 in capillary growth in ischaemic skeletal muscle, extensor digitorum longus muscles from hindlimbs of Sprague-Dawley rats were studied at 1, 2 and 5 week intervals after iliac artery ligation. Muscle VEGF protein levels (as determined by Western-blot analysis) increased only after 2 (60%) and 5 (80%) weeks, with more capillaries positively immunostained for VEGF than in control muscles. Ischaemia-induced angiogenesis was gradual, with capillary proliferation at 1 and 2 weeks and capillary:fibre ratio increased 20% after 5 weeks. This was associated with an initial doubling of Flk-1 protein after 1 week that declined below control levels by 5 weeks, whereas Flt-1 expression was elevated more than 40% at all time points. During more sustained ischaemia (femoral ligation 3 weeks after iliac ligation), VEGF protein level at 5 weeks was even higher, but Flt-1 and Flk-1 were unchanged from control levels and no capillary growth occurred. Intermittent electrical stimulation (10 Hz, 7x15 min/day) of these ischaemic muscles between weeks 3-5 did not elevate VEGF further, but increased Flk-1 by 32%, decreased Flt-1 by 71%, and led to significant capillary growth. These results demonstrate that during chronic muscle ischaemia Flk-1 and Flt-1 are regulated differentially and that electrical stimulation of ischaemic muscles can promote angiogenesis via Flk-1 up-regulation. Even when ischaemic muscle VEGF levels are high, capillary growth appears to be dependent on the presence of Flk-1.
authors.affiliation: School of Sport and Exercise Sciences, University of Birmingham, Birmingham B15 2TT, UK. M.Milkiewicz@bham.ac.uk
authors.forename: Malgorzata
authors.initials: M
authors.lastname: Milkiewicz
authors.forename: Olga
authors.initials: O
authors.lastname: Hudlicka
authors.forename: Julie
authors.initials: J
authors.lastname: Verhaeg
authors.forename: Stuart
authors.initials: S
authors.lastname: Egginton
authors.forename: Margaret D
authors.initials: MD
authors.lastname: Brown
mesh_terms: D000818:Animals; D015153:Blotting, Western / Q000379:methods; D002196:Capillaries; D004558:Electric Stimulation; D016228:Endothelial Growth Factors / Q000032:analysis / Q000378:metabolism; D016326:Extracellular Matrix Proteins / Q000032:analysis / Q000378:metabolism*; D006614:Hindlimb; D007150:Immunohistochemistry / Q000379:methods; D036341:Intercellular Signaling Peptides and Proteins / Q000032:analysis / Q000378:metabolism; D007511:Ischemia / Q000378:metabolism*; D008222:Lymphokines / Q000032:analysis / Q000378:metabolism; D008297:Male; D018482:Muscle, Skeletal / Q000098:blood supply* / Q000378:metabolism*; D009389:Neovascularization, Pathologic; D051381:Rats; D017207:Rats, Sprague-Dawley; D042461:Vascular Endothelial Growth Factor A; D040281:Vascular Endothelial Growth Factor Receptor-1; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000032:analysis / Q000378:metabolism*; D042442:Vascular Endothelial Growth Factors
chemical_list: D016228:Endothelial Growth Factors; D016326:Extracellular Matrix Proteins; D036341:Intercellular Signaling Peptides and Proteins; D008222:Lymphokines; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; C501164:Flt1 protein, rat; D040281:Vascular Endothelial Growth Factor Receptor-1; D040301:Vascular Endothelial Growth Factor Receptor-2