Circulating levels of placental proteins, placental protein 5 (PP5), placental lactogen and Schwangerschafts-protein 1 (SP1), in antepartum eclampsia

Increased placental expression of Placental Protein 5 (PP5) / Tissue Factor Pathway Inhibitor-2 (TFPI-2) in women with preeclampsia and HELLP syndrome: Relevance to impaired trophoblast invasion?

INTRODUCTION

Placental Protein 5 (PP5)/Tissue Factor Pathway Inhibitor-2 (TFPI-2) is an extracellular matrix-associated protein mainly expressed by the syncytiotrophoblast that may regulate trophoblast invasion. Our aim was to study placental PP5/TFPI-2 expression and its relation to placental pathology in various forms of preeclampsia and HELLP syndrome.

METHODS

Placental and maternal blood specimens were collected at the time of delivery from the same women in the following groups: 1) early controls; 2) early preeclampsia; 3) early preeclampsia with HELLP syndrome; 4) late controls; and 5) late preeclampsia. After histopathological examination, placental specimens were immunostained with polyclonal anti-PP5/TFPI-2 antibody on Western blot and tissue microarray immunohistochemistry. Placental PP5/TFPI-2 immunoscores were assessed manually and with a semi-automated method. Maternal sera were immunoassayed for PP5/TFPI-2.

RESULTS

PP5/TFPI-2 was localized to the cytoplasm of syncytiotrophoblast. Manual and semi-automated PP5/TFPI-2 immunoscores were higher in early preeclampsia with or without HELLP syndrome but not in late preeclampsia than in respective controls. In patients with preeclampsia, the correlation of placental PP5/TFPI-2 expression with maternal vascular malperfusion score of the placenta was positive while it was negative with birthweight and placental weight. Maternal serum PP5/TFPI-2 concentration was higher in early preeclampsia and it tended to be higher in early preeclampsia with HELLP syndrome than in early controls.

DISCUSSION

Our findings suggest that an increased placental PP5/TFPI-2 expression may be associated with abnormal placentation in early preeclampsia, with or without HELLP syndrome.

Specific expression of PP5/TFPI2 mRNA by syncytiotrophoblasts in human placenta as revealed by in situ hybridization

Placental protein 5 (PP5) is a placenta-derived glycoprotein with serine proteinase-inhibiting activity. To date its physiological functions have not been well elucidated. Recently, cDNA sequence analysis revealed that PP5 belongs to the Kunitz-type proteinase inhibitor family and it is identical to tissue factor pathway inhibitor-2 (TFPI-2), homologous to TFPI. Northern blot analysis demonstrated that placental tissue is extremely rich in the transcripts. This study localized PP5/TFPI-2 mRNA in placental tissues at three different gestational periods using in situ hybridization. PP5/TFPI-2 mRNA was specifically detected in syncytiotrophoblast at any gestational period examined, suggesting that syncytiotrophoblast is the principal production site of PP5/TFPI-2 in developing placental tissues. This mRNA expression pattern of PP5/TFPI-2 is quite different from that of TFPI, which is mainly found in vascular endothelial cells. The results indicated possible roles of PP5/TFPI-2 in the trophoblast differentiation and in the maintenance of intervillous blood flow. Also, Northern analysis demonstrated no or little expression of PP5/TFPI-2 in four choriocarcinoma cell lines, in contrast to its abundant expression in syncytiotrophoblast.

Hypertension in pregnancy: changes in activin A maternal serum concentration

Human placenta is the major source of activin A in maternal circulation. The aim of the present study was to evaluate maternal activin A serum concentration in pregnant women with chronic hypertension (n = 14), pregnancy-induced hypertension (n = 10) or pre-eclampsia (n = 16). In the group of pregnant women with chronic hypertension and of healthy pregnant women (n = 10) activin A was measured in samples collected longitudinally throughout gestation. Using a specific two-site enzyme-linked immunosorbent assay, it has been possible to measure maternal serum activin A concentration. In addition, the effect of recombinant human activin A administration on mean arterial pressure and heart rate in female rats have been also investigated. Mean +/- SEM of maternal serum activin A concentration in pre-eclamptic women (57.4 +/- 28.3 ng/ml), was significantly higher than in women with pregnancy-induced hypertension (14.8 +/- 10.5 ng/ml), chronic hypertension (10.3 +/- 5.4 ng/ml) or healthy control women (9.2 +/- 9.4 ng/ml) (P < 0.01). Serum activin A levels evaluated 2 weeks after anti-hypertensive treatment were not significantly different in pre-eclamptic women. Moreover, when exogenous recombinant human activin A was administered in female rats arterial pressure or frequency of heart rate did not change. The present study showed that maternal serum activin A concentration is abnormally high in patients with pre-eclampsia. Thus, since the patients with chronic hypertension or pregnancy-induced hypertension have activin A concentration in the normal range of values, activin A may be a prognostic marker of hypertension in pregnancy.

Plasma corticotrophin-releasing factor (CRF) in abnormal pregnancy

Maternal plasma levels of cortiocotrophin-releasing factor (CRF) have been measured in abnormal pregnancy states to assess their potential as biochemical markers for at-risk pregnancies. CRF levels were not significantly altered in patients with hydatidiform mole, polyhydramnios or diabetes. CRF levels were elevated in pregnancies complicated by accidental antepartum haemorrhage at 28 weeks (P less than 0.03) but not for the rest of the third trimester. In twin pregnancies CRF levels were significantly raised throughout the third trimester (28-32 weeks, P less than 0.01; 34-36 weeks, P less than 0.001). In patients with pregnancy-induced hypertension (28 weeks, P less than 0.001; 32-36 weeks, P less than 0.001; and 38-40 weeks, P less than 0.01), preterm labour and premature rupture of the membranes (28 weeks, P less than 0.004; 30-32 weeks, P less than 0.002; and 34-36 weeks, P less than 0.001), CRF levels were significantly raised and in some patients levels were elevated 11 weeks before the onset of signs or symptoms. These observations raise the possibility that maternal CRF measurement may be of use as a predictive indicator of certain at-risk pregnancies.

Dramatic increase of placental protein 5 levels following injection of small doses of heparin

In the course of an investigation on the effects of thyroid releasing hormone in pregnant women we noted a dramatic increase in the levels of placental protein 5 (PP5) in maternal blood. This increase ranged from 10 times to over 40 times the basal levels. Further study showed that the rise was associated with the use of heparin to maintain the patency of the cannula through which the samples were collected. Furthermore, the phenomenon appeared to be systemic rather than local, and may well be due to a direct effect of heparin on PP5 secretion by the placenta.