Effect of transforming growth factor-β on the plasminogen activator system in cultured first trimester human cytotrophoblasts

Abstract

Plasminogen activators (PAs) play an important role in facilitating trophoblast invasion of the uterus and in the maintenance of blood fluidity within the placental intervillous spaces. We previously found that transforming growth factor-β (TGF-β), produced mainly by the decidua, inhibits first trimester trophoblast invasiveness at least partly via induction of tissue inhibitor of metalloproteinases-1 production and secretion by the trophoblasts. The present study examined whether TGF- β 1 affects PA and plasminogen activator inhibitor-1 (PAI-1 ) production by cultured human cytotrophoblasts. Immortalized first trimester human cytotrophoblasts (HTR-8/SVneo) were cultured in the absence or presence of TGF- β 1 (0–10 ng/ml) for 24 h, after which the levels of urokinase-type PA (uPA), PAI-1 and uPA activity in the serum-free conditioned media were determined by enzyme-linked immunosorbent assay (ELISA), protein zymography, and a chromogenic uPA activity assay. Cellular PAI-1 mRNA levels were also determined in cultures following a 24-h incubation with a single dose (5 ng/ml) of TGF- β 1. Presence of TGF- β 1 at 1 ng/ml resulted in a greater than 12-fold reduction in the levels of total uPA as determined by ELISA. Furthermore, released uPA activity levels in similar cultures incubated with 5 ng/ml of TGF- β 1 were reduced to 35 per cent of control values. In contrast, cultures incubated with as little as 0.1 ng/ml TGF-β exhibited a 63 per cent increase in the levels of secreted PAI-1 protein. Similarly, both the 2.2- and 3.0-kb PAI-1 cellular mRNA species were elevated in trophoblast cells incubated with 5 ng/ml TGF- β 1 when compared with control cells. Thus, it appears that the reduced uPA activity observed in the cultures incubated with TGF- β 1 is due to reduced secretion of uPA and increased PAI-1 production and secretion. These results suggest that TGF-β may also exert its anti-invasive effect by down-regulating trophoblast-derived PA activity. Through its effects on the PA system, TGF-β may also play an indirect role in the regulation of uteroplacental blood flow.