TNF-alpha/TNFRI in primary and immortalized first trimester cytotrophoblasts

During the first trimester of pregnancy endogenous expression of tumour necrosis factor (TNF)-alpha has been detected in villous, as well as in proliferating and invading extravillous, trophoblasts suggesting that the protein could be involved in trophoblast differentiation. To gain insights into the putative role of the TNF-alpha signalling pathway, we investigated expression of its receptors, TNFR I and II, in first trimester placentae and early trophoblasts, and studied the influence of the cytokine on cell proliferation and apoptosis. ELISA and RT-PCR revealed secretion/expression of TNFRI protein/mRNA in immortalized ED27 cells and purified first trimester cytotrophoblasts, while soluble TNFRII was undetectable in cell culture supernatants. In agreement, immunohistochemical analyses of first trimester placentae showed that TNFRI is localized to the villous cyto- and syncytiotrophoblast, to the proliferating cytotrophoblasts of the cell islands and cell columns, as well as to extravillous cells invading decidual tissue. TNFRII, however, was absent in early trophoblast populations. Interleukin (IL)-1 and phorbol 12-myristate 13-acetate (PMA) induced shedding of TNFRI from ED27 and primary cells suggesting that under inflammatory conditions the soluble receptor protein may protect from cytotoxic effects of TNF-alpha. Upon incubation with increasing amounts of TNF-alpha no significant changes in DNA-content or cell numbers were found, suggesting that the cytokine does not augment proliferation of primary cytotrophoblasts. High doses of TNF-alpha, however, provoked growth arrest in ED27 cells as evaluated by cell counting, but did not induce necrosis/apoptosis as was assessed by TUNEL assay. In first trimester cells addition of elevated amounts of TNF-alpha resulted in the appearance of TUNEL-positive cells and an increase in caspase-3 enzyme activity suggesting that the TNF-alpha-dependent apoptotic cascade is executed in a portion of the early cytotrophoblasts.

Hypoxia downregulates continuous and interleukin-1-induced expression of human chorionic gonadotropin in choriocarcinoma cells

The effects of hypoxia on JEG-3, BeWo, and JAr cells were investigated and it was demonstrated that choriocarcinoma cells can be used as a model to study the molecular mechanism of hypoxia-mediated repression of human chorionic gonadotropin (hCG). Cells were maintained under hypoxia (3.5 per cent O2) for 72 h without loss of variability, as demonstrated by the fact that 93-98 per cent of the cells excluded trypan blue. Up to 48 h, cell growth was not significantly influenced by hypoxia, and analysis by flow cytometry did not reveal major changes in cell cycle distribution. JEG-3, BeWo, and JAr cells which were grown for 48 h under hypoxia secreted 81, 67, and 71 per cent less hCG than cells cultivated under normoxic conditions. The extent of hCG reduction was dependent on the oxygen concentration. Moreover, release of the hormone from hypoxic JAr cells was not stimulated upon addition of interleukin-1 (IL-1). Treatment of JEG-3 cells with methotrexate (MTX) led to a 4.3-fold augmentation in hCG secretion and to an increase in the amount of G0/G1 cells. However, when cells were cultured in the presence of MTX and hypoxia, hCG secretion decreased 10-fold and beta hCG mRNA declined to almost undetectable levels suggesting that downregulation of beta hCG mRNA is the major cause of diminished hCG release under hypoxic conditions.

Interleukin-1 stimulates tumor necrosis factor-alpha (TNF-alpha) release from cytotrophoblastic BeWo cells independently of induction of the TNF-alpha mRNA

Constitutive tumor necrosis factor-alpha expression (TNF-alpha) has been detected in first trimester trophoblast cells and differentiated syncytiotrophoblasts. However, molecules which induce TNF-alpha release from these cells and their mechanism of action have not been defined. We show for the first time that interleukin-1 (IL-1), a regulator of trophoblast development, induces TNF-alpha expression in proliferating cytotrophoblastic cells and purified term trophoblasts. Both IL-1alpha and beta stimulate TNF-alpha release from BeWo cells and TNF-alpha mRNA was transiently expressed. In growth-arrested/differentiated BeWo cells TNF-alpha mRNA was detectable without inducer, however, in the presence of IL-1beta TNF-alpha secretion was weakly stimulated compared to proliferating cells. Cycloheximide strongly increased IL-1beta-induced TNF-alpha mRNA concentration indicating that de novo protein synthesis is not required for TNF-alpha gene expression. However, treatment with cycloheximide did not prevent IL-1beta-stimulated release of TNF-alpha, indicating that the cytokine can regulate TNF-alpha secretion at a posttranslational level, independently of TNF-alpha mRNA induction. Besides demonstration of this novel mechanism of IL-1-stimulated TNF-alpha expression, our data indicate an important role of IL-1 in TNF-alpha production of cytotrophoblastic cells.