EVIDENCE FOR THE EXISTENCE OF A NOVEL PREGNANCY-ASSOCIATED SOLUBLE VARIANT OF THE VASCULAR ENDOTHELIAL GROWTH-FACTOR RECEPTOR, FLT-1

Angiogenesis is essential in physiological processes including ovulati on, implantation and pregnancy. One of the most potent regulators is t he cytokine vascular endothelial growth factor (VEGF). We provide evid ence for a novel pregnancy-associated soluble variant of the VEGF rece ptor Flt-1. VEGF ranged from undetectable to 157.3 pg/ml (mean 49.9 pg /ml, SD 48.4 pg/ml) in plasma samples from normal volunteers (n = 10), but was undetectable in plasma from pregnant women (n = 12) and amnio tic fluid (n = 10). Recoveries of spiked VEGF were poor in pregnancy-r elated samples, indicating the presence of VEGF-binding activity which was confirmed using biosensor and chromatographic techniques. Partial purification and protein sequencing indicated a novel soluble form of Flt-1 with a subunit size of 150 kDa. Normally present as a multimeri c structure of similar to 400-550 kDa, complexes of 600-700 kDa were f ormed following binding of multiple VEGF molecules. Reverse transcript ase polymerase chain reaction of Flt-1 in placenta, amnion, chorion, h uman umbilical vein endothelial cells and cord blood samples produced bands of the predicted sizes but failed to identify any additional RNA species, and possible reasons for this are discussed. Soluble Flt-1 m ay be important in regulating the actions of VEGF in angiogenesis and trophoblast invasion and may have therapeutic implications in diseases with inappropriate angiogenesis such as proliferative retinopathies a nd cancer.