BASIC FIBROBLAST GROWTH FACTOR-INDUCED ANGIOGENIC PHENOTYPE IN MOUSE ENDOTHELIUM - A STUDY OF AORTIC AND MICROVASCULAR ENDOTHELIAL-CELL LINES

The mouse is the most commonly used species for in vivo studies on ang iogenesis related to tumor development. Yet, to the best of our knowle dge, very few reports on the in vitro interaction of the angiogenic ba sic fibroblast growth factor (bFGF) with mouse endothelial cells are a vailable. Three mouse endothelial cell lines originated from aorta (MA ECs), brain capillaries (MBECs), and heart capillaries (MHECs) were ch aracterized for endothelial phenotypic markers, in vivo tumorigenic ac tivity, and the capacity to respond in vitro to bFGF. These cells expr ess angiotensin-converting enzyme, acetylated LDL receptor, constituti ve endothelial nitric oxide synthase, and vascular cell adhesion molec ule-1 and bind Griffonia simplicifolia-I lectin. When injected subcuta neously in nude mice, MAECs induced the appearance of slow-growing vas cular lesions reminiscent of epithelioid hemangioendothelioma, whereas MBEC xenografts grew rapidly, showing Kaposi's sarcoma-like morpholog ical features. No lesions were induced by injection of MHECs. MAECs, M BECs, and MHECs expressed both low-affinity heparan sulfate bFGF-bindi ng sites and high-affinity tyrosine kinase receptors (FGFRs) on their surfaces. In particular, MAECs expressed FGFR-2/bek mRNA, whereas micr ovascular MBECs and MHECs expressed FGFR-1/flg mRNA. According, bFGF i nduced a mitogenic response and the phosphorylation of extracellular s ignal-regulated kinase-2 in all the cell lines. In contrast, upregulat ion of urokinase-type plasminogen activator expression was observed in bFGF-treated microvascular MBECs and MHECs but not in MAECs. Also, bF GF-treated MBECs and MHECs but not MAECs invaded a three-dimensional f ibrin gel and formed hollow, capillary-like structures. The relevance of the modifications of the fibrinolytic balance of mouse microvascula r endothelium in bFGF-induced angiogenesis was validated in vivo by a gelatin-sponge assay in which the plasmin inhibitors tranexamic acid a nd epsilon-aminocaproic acid given to mice in the drinking water inhib ited neovascularization induced by the growth factor. In conclusion, d ifferences in response to bFGF exist between large-vessel MAECs and mi crovascular MBECs and MHECs. Both in vitro and in vivo data point to a role of the profibrinolytic phenotype induced by bFGF in microvascula r endothelial cells during mouse angiogenesis. Our observations make t hese endothelial cell lines suitable for further studies on mouse endo thelium during angiogenesis and in angioproliferative diseases.