FIBROBLAST GROWTH FACTOR-II (FGF-S) IS PRESENT IN MATERNAL AND CORD SERUM, AND IN THE MOTHER IS ASSOCIATED WITH A BINDING-PROTEIN IMMUNOLOGICALLY RELATED TO THE FGF RECEPTOR-1

Fibroblast growth factor-2 (FGF-2) is expressed in human fetal tissues and placenta. We, therefore, determined whether FGF-2 appeared in either fetal or maternal circulations during normal pregnancies [fetuses appropriate for gestational age (AGA)] or those complicated by fetal growth restriction (small for gestational age). Cordocentesis was performed, and matched maternal blood was collected between 19-39 weeks gestation, whereas maternal and cord blood and amniotic fluid (AF) were collected at term. FGF-2 was extracted from maternal serum (MS), cord serum (CS), and AF by heparin-Sepharose affinity chromatography and subjected to Western blot analysis or quantified by specific RIA. Western blot analysis of MS, CS, and AF revealed, in each case, a single immunoreactive FGF-2 species of 18 kilodaltons (kDa), although this was not present in nonpregnant serum. In AGA pregnancies, immunoreactive FGF-2 was present in MS from at least 18 weeks gestation and rose to maximum values at the end of second trimester (weeks 28-31; mean +/- SEM, 342 +/- 62 pmol/L), but by term had declined (weeks 40-42; 104 +/- 24 pmol/L). In CS, FGF-2 immunoreactivity was highest at weeks 18-20 of gestation (662 +/- 144 pmol/L), but thereafter, slowly declined to term (weeks 40-42; 119 +/- 28 pmo/L). Immunoreactive FGF-2 levels in MS and CS of small for gestational age pregnancies in the second trimester tended to be lower than those in AGA pregnancies, but differences were not statistically significant. AF also contained immunoreactive FGF-2 at term (91 +/- 35 pmol/L). Neutral gel chromatography on Sephadex G-200 revealed that FGF-2 immunoreactivity eluted as a broad peak with an apparent molecular size of 55-160 kDa. These same fractions contained peptides of 55-60, 90-95, and 120-130 kDa, which were recognized by antisera against the extracellular domain of the high affinity FGF receptor, FGFR1, after Western blot. Ligand blot analysis of the same nitrocellulose filters using I-125-labeled FGF-2 revealed that the 55- to 60-kDa species specifically bound FGF-2. This binding species was not recognized during Western blot analysis using an antiserum raised against the intracellular tyrosine kinase domain of FGFR1, suggesting that it represents a truncated receptor form. Similar FGFR1 immunoreactive species were present in nonpregnant female and male sera, but were barely detectable in term CS or AF. These results suggest that soluble FGF-2 is present in MS, CS, and AF, and that in MS, this circulates in complex with a binding protein(s) related to the extracellular domain of the high affinity receptor, FGFR1.