Effect of hypoxia and endothelial loss on vascular smooth muscle cell responsiveness to VEGF-A: role of flt-1/VEGF-receptor-1.
OBJECTIVE
The influence of hypoxia and endothelial loss on the responsiveness of vascular smooth muscle cells (VSMCs) to vascular endothelial growth factor (VEGF-A) was tested.


RESULTS
Exposure to hypoxia induced a potentiation of cultured cell proliferation in response to either the agonist for the VEGF receptor 1 (flt-1) placental growth factor (PlGF-1) or to VEGF-A. This effect was mediated by the mitogen activated protein kinase (MAPK) cascade, since it was inhibited by the MAPK kinase inhibitor PD98059 and by the farnesyl transferase inhibitor II. Accordingly, PlGF-1 activated extracellular signal-regulated kinase(1/2). In rat aortic rings deprived of endothelium and cultured in three-dimensional fibrin gels, an increased sprouting of tubular structures in response to VEGF-A was observed only under hypoxia. Studies on rat aorta preparations revealed an endothelium-dependent vasorelaxation in response to either VEGF-A or PlGF1, which was reversed to a contractile response in endothelium-deprived preparations exposed to hypoxia. Western blot and immunohistochemistry of endothelium-deprived preparations exposed to hypoxia showed flt-1 receptor expression in all medial cells. Conversely, flt-1 mRNA, of endothelium-deprived aortic preparations and of tubular structures, was unchanged by hypoxia.


CONCLUSIONS
These findings demonstrate that experimental conditions mimicking pathological vascular injury can make VSMCs responsive to VEGF-A through the induction of functional flt-1 receptors.
Parenti
Astrid
A
Department of Preclinical and Clinical Pharmacology, University of Florence, Viale G. Pieraccini 6, Italy.
Brogelli
Laura
L
Filippi
Sandra
S
Donnini
Sandra
S
Ledda
Fabrizio
F
D000818:Animals; D001011:Aorta; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D016228:Endothelial Growth Factors / Q000235:genetics / Q000494:pharmacology*; D004730:Endothelium, Vascular / Q000293:injuries* / Q000378:metabolism; D016326:Extracellular Matrix Proteins / Q000235:genetics / Q000502:physiology*; D000860:Hypoxia / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000293:injuries* / Q000378:metabolism; D018919:Neovascularization, Physiologic; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D042461:Vascular Endothelial Growth Factor A; D040281:Vascular Endothelial Growth Factor Receptor-1; D014661:Vasoconstriction
D016228:Endothelial Growth Factors; D016326:Extracellular Matrix Proteins; D012333:RNA, Messenger; D042461:Vascular Endothelial Growth Factor A; C501164:Flt1 protein, rat; D040281:Vascular Endothelial Growth Factor Receptor-1; D020928:Mitogen-Activated Protein Kinases