Figure 7.

Cytotrophoblasts produce the same repertoire of VEGF family members in vivo and in vitro. Cytotrophoblasts (CTBs) isolated from human placentas were examined for their production of VEGF mRNA (A) and protein (B and C). mRNA, purified from cells before they were plated (0 hours) and after 12 hours of culture on a Matrigel substrate, was analyzed by Northern blot hybridization. First (I) and second (II) trimester samples expressed approximately equal amounts of RNAs encoding VEGF-A and VEGF-C; VEGF-B mRNA levels were much lower and VEGF-D was not detected (A, left). Isolated placental fibroblasts also produced VEGF-A and VEGF-C mRNAs and low levels of VEGF-B mRNA. In contrast, cytotrophoblasts, not fibroblasts, produced PlGF mRNA (A, right). Cytotrophoblast production of VEGF-A and PlGF was assessed by ELISA (B). No VEGF-A was detected in conditioned medium from either first, second, or third (III) trimester cytotrophoblasts that were plated on Matrigel substrates, whereas all of the choriocarcinoma cell lines produced amounts of this growth factor that were easily detected by ELISA (B, left). In contrast, PlGF was secreted by both cytotrophoblasts and choriocarcinoma cells (B, right). The ELISA data in B are the means and standard deviations of three experiments. If the cells were plated on a laminin substrate instead of Matrigel, approximately equal amounts of VEGF-A partitioned in the cell and conditioned medium (CM) fractions as determined by immunoblotting (C). The isoforms produced by cytotrophoblasts migrated more slowly than recombinant VEGF₁₆₅.