Differential Regulation and Function of the Fas/Fas Ligand System in Human Trophoblast Cells1

Abstract

Trophoblast rejection, which is characterized by increased apoptosis, is mediated by T helper (Th)-1, or proinflammatory, cytokines, whereas Th-2, or anti-inflammatory, cytokines confer immune protection and facilitate implantation. We investigated the role of both types of cytokines on the expression and function of the Fas/Fas ligand (FasL) apoptotic pathway in trophoblast cells. First-trimester human trophoblast primary-culture cells as well as A3 and HTR/8 trophoblast cell lines were treated with proinflammatory cytokines such as interferon-gamma (IFN-gamma) and tumor necrosis factor alpha (TNFalpha) and with the anti-inflammatory cytokines interleukin (IL)-6 and IL-10. Sensitivity to Fas-mediated apoptosis was measured using an activating anti-Fas monoclonal antibody. Cell viability was evaluated using the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) and CellTiter 96 assay. Fas/FasL mRNA and protein expression levels were determined using reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analysis, respectively. Trophoblast cells normally express FasL, but low levels of Fas, and they are resistant to Fas-mediated apoptosis. IFN-gamma and TNFalpha promote Fas expression and sensitivity, whereas IL-6 and IL-10 increase the resistance of trophoblast cells to Fas-mediated apoptosis. Furthermore, IL-10 treatment activates FLICE-like inhibitory protein (FLIP), a downstream inhibitor of Fas apoptotic signaling. Although trophoblast cells express Fas, susceptibility to Fas does not necessarily correlate with its expression. In this study, we demonstrate that Th-2 cytokines increase the resistance of trophoblast cells to Fas-mediated apoptosis either by inhibiting Fas expression or by inducing FLIP activation. This "trophoblast-cytokine-Fas/FasL triad" determines the ability of the Fas/FasL system to regulate trophoblast viability and, consequently, the success or failure of pregnancy.

Maternal serum of women with pre-eclampsia reduces trophoblast cell viability: evidence for an increased sensitivity to Fas-mediated apoptosis

“…Indeed, increased concentrations of pro-inflammatory cytokines, such as TNF-a and interleukin (IL)-1 receptor antagonist, have been reported in pre-eclampsia [62][63][64] . Some of these cytokines have been shown to activate apoptotic genes, such as the Fas/FasL system 65,66 and Bcl-2 26 in trophoblast, leading to aberrant placental invasion, function and rejection. In a recent study, we demonstrated that antiinflammatory cytokines (IL-10 and IL-6) increased the resistance of trophoblast cells to Fas-mediated apoptosis, either by inhibiting Fas expression or by inducing Flice Like Inhibitory Protein (Flip) activation.…”

“…In a recent study, we demonstrated that antiinflammatory cytokines (IL-10 and IL-6) increased the resistance of trophoblast cells to Fas-mediated apoptosis, either by inhibiting Fas expression or by inducing Flice Like Inhibitory Protein (Flip) activation. On the other hand, pro-inflammatory cytokines (TNF-a and interferon-g) increase trophoblast sensitivity to Fasmediated apoptosis 65 . In this study, we found that serum from pre-eclamptic patients rendered the trophoblast more sensitive to Fas-mediated apoptosis, suggesting that this biological effect may be mediated by pro-inflammatory cytokines which have been reported to be increased in the plasma/serum of women with pre-eclampsia.…”

XAF1 Mediates Tumor Necrosis Factor-α-induced Apoptosis and X-linked Inhibitor of Apoptosis Cleavage by Acting through the Mitochondrial Pathway

“…First Trimester Primary Trophoblast Cell Isolation and Culture-Primary trophoblast cells were isolated from first trimester placentas as previously described (2,3). Isolated first trimester trophoblast cells were cultured at 37°C/5% CO 2 in Dulbecco's modified Eagle's medium supplemented with 10% human serum (Gemini Bio-Products, Woodland, CA).…”

“…The Fas/Fas ligand system represents one of the most common and well characterized TNF death receptor apoptotic pathways. Despite expressing both Fas and Fas ligand, trophoblast cells isolated from first trimester placentas are resistant to Fas-mediated apoptosis under normal conditions (1)(2)(3). However, in contrast to Fas ligand-induced apoptosis, first trimester trophoblast cells have been shown to be sensitive to TNF-␣-mediated apoptosis (1,2,4,5).…”

“…Despite expressing both Fas and Fas ligand, trophoblast cells isolated from first trimester placentas are resistant to Fas-mediated apoptosis under normal conditions (1)(2)(3). However, in contrast to Fas ligand-induced apoptosis, first trimester trophoblast cells have been shown to be sensitive to TNF-␣-mediated apoptosis (1,2,4,5). Since both Fas and TNF-R1, the death receptor that mediates TNF-␣-induced apoptosis (6,7), share several components of the intracellular apoptotic cascade, it is unknown how first trimester trophoblast cells remain resistant to Fas but sensitive to TNF-␣-induced apoptosis.…”