Cell culture models of human trophoblast--primary culture of trophoblast--a workshop report

Dynamic modeling of uteroplacental blood flow in IUGR indicates vortices and elevated pressure in the intervillous space - a pilot study

Ischemic placental disease is a concept that links intrauterine growth retardation (IUGR) and preeclampsia (PE) back to insufficient remodeling of uterine spiral arteries. The rheological consequences of insufficient remodeling of uterine spiral arteries were hypothesized to mediate the considerably later manifestation of obstetric disease. However, the micro-rheology in the intervillous space (IVS) cannot be examined clinically and rheological animal models of the human IVS do not exist. Thus, an in silico approach was implemented to provide in vivo inaccessible data. The morphology of a spiral artery and the inflow region of the IVS were three-dimensionally reconstructed to provide a morphological stage for the simulations. Advanced high-end supercomputing resources were used to provide blood flow simulations at high spatial resolution. Our simulations revealed turbulent blood flow (high-velocity jets and vortices) combined with elevated blood pressure in the IVS and increased wall shear stress at the villous surface in conjunction with insufficient spiral artery remodeling only. Post-hoc histological analysis of uterine veins showed evidence of increased trophoblast shedding in an IUGR placenta. Our data support that rheological alteration in the IVS is a relevant mechanism linking ischemic placental disease to altered structural integrity and function of the placenta.

Molecular Cross-Talk at the Feto-Maternal Interface

Molecular cross-talk at the feto-maternal interface occurs between many different cell types, including uterine leukocytes, extravillous trophoblast cells, and uterine spiral arteries, is essential for the establishment and maintenance of pregnancy. This review concentrates on human pregnancy and examines three main areas in which cross-talk occurs; immune tolerance, regulation of extravillous trophoblast invasion, and remodeling of the uterine spiral arteries.

Vaccine-Derived Neutralizing Antibodies to the Human Cytomegalovirus gH/gL Pentamer Potently Block Primary Cytotrophoblast Infection

Human cytomegalovirus (HCMV) elicits neutralizing antibodies (NAb) of various potencies and cell type specificities to prevent HCMV entry into fibroblasts (FB) and epithelial/endothelial cells (EpC/EnC). NAb targeting the major essential envelope glycoprotein complexes gB and gH/gL inhibit both FB and EpC/EnC entry. In contrast to FB infection, HCMV entry into EpC/EnC is additionally blocked by extremely potent NAb to conformational epitopes of the gH/gL/UL128/130/131A pentamer complex (PC). We recently developed a vaccine concept based on coexpression of all five PC subunits by a single modified vaccinia virus Ankara (MVA) vector, termed MVA-PC. Vaccination of mice and rhesus macaques with MVA-PC resulted in a high titer and sustained NAb that blocked EpC/EnC infection and lower-titer NAb that inhibited FB entry. However, antibody function responsible for the neutralizing activity induced by the MVA-PC vaccine is uncharacterized. Here, we demonstrate that MVA-PC elicits NAb with cell type-specific neutralization potency and antigen recognition pattern similar to human NAb targeting conformational and linear epitopes of the UL128/130/131A subunits or gH. In addition, we show that the vaccine-derived PC-specific NAb are significantly more potent than the anti-gH NAb to prevent HCMV spread in EpC and infection of human placental cytotrophoblasts, cell types thought to be of critical importance for HCMV transmission to the fetus. These findings further validate MVA-PC as a clinical vaccine candidate to elicit NAb that resembles those induced during HCMV infection and provide valuable insights into the potency of PC-specific NAb to interfere with HCMV cell-associated spread and infection of key placental cells.

IMPORTANCE

As a consequence of the leading role of human cytomegalovirus (HCMV) in causing permanent birth defects, developing a vaccine against HCMV has been assigned a major public health priority. We have recently introduced a vaccine strategy based on a widely used, safe, and well-characterized poxvirus vector platform to elicit potent and durable neutralizing antibody (NAb) responses targeting the HCMV envelope pentamer complex (PC), which has been suggested as a critical component for a vaccine to prevent congenital HCMV infection. With this work, we confirm that the NAb elicited by the vaccine vector have properties that are similar to those of human NAb isolated from individuals chronically infected with HCMV. In addition, we show that PC-specific NAb have potent ability to prevent infection of key placental cells that HCMV utilizes to cross the fetal-maternal interface, suggesting that NAb targeting the PC may be essential to prevent HCMV vertical transmission.

Paracrine and epigenetic control of trophectoderm differentiation from human embryonic stem cells: the role of bone morphogenic protein 4 and histone deacetylases

Our understanding of paracrine and epigenetic control of trophectoderm (TE) differentiation is limited by available models of preimplantation human development. Simple, defined media for selective TE differentiation of human embryonic stem cells (hESCs) were developed, enabling mechanistic studies of early placental development. Paracrine requirements of preimplantation human development were evaluated with hESCs by measuring lineage-specific transcription factor expression levels in single cells and morphological transformation in response to selected paracrine and epigenetic modulators. Bone morphogenic protein 4 (BMP4) addition to feeder-free pluripotent stem cells on matrigel frequently formed CDX2-positive TE. However, BMP4 or activin A inhibition alone also produced a mix of mesoderm and extraembryonic endoderm under these conditions. Further, BMP4 failed to form TE from adherent hESC maintained in standard feeder-dependent monolayers. Given that the efficiency and selectivity of BMP4-induced TE depended on medium components, we developed a basal medium containing insulin and heparin. In this medium, BMP4 induction of TE was dose dependent and with activin A inhibition by SB431542 (SB), approached 100% of cells. This paracrine stimulation of pluripotent cells transformed colony morphology from a cuboidal to squamous epithelium quantitatively on day 3, and produced significant multinucleated syncytiotrophoblasts by day 8. Addition of trichostatin A, a histone deacetylase (HDAC) inhibitor, reduced HDAC3, histone H3K9 methylation, and slowed differentiation in a dose-dependent manner. Modulators of BMP4- or HDAC-dependent signaling might adversely influence the timing and viability of early blastocyst developed in vitro. Since blastocyst development is synchronized to uterine receptivity, epigenetic regulators of TE differentiation might adversely affect implantation in vivo.

In vitro study on human trophoblast cells infected with HCMV

Human trophoblast cells were isolated and cultured in vitro in order to investigate possible pathogenesis of intrauterine infection caused by HCMV. Trophoblast cells were obtained by compound enzymes digestion and discontinuous percoll gradient. Cells and purity were identified by using immunocytochemistry assay with anti-CK7, Vim and beta-hCG antibodies. HCMV AD169 strain replication in isolated trophoblast cells and cell apoptosis were detected at different time points post infection (p.i.). The results showed that highly purified trophoblast cells were obtained. Specific virus replication was increased dramatically at the 24th h p.i., and then increased slowly during 48 h and 72 h. Apoptosis rate of trophoblast cells infected with HCMV was (34.68+/-3.14)% at 24th h p.i., while that in control group was (15.32+/-2.34)% (P<0.05). It was suggested that highly purified trophoblast cells can be isolated by the simplified cell purification method. HCMV can infect human trophoblast cells, and be quickly replicated, resulting in the accelerated apoptosis of human trophoblast cells during early time.

Characterization and expression of netrin-1 and its receptors UNC5B and DCC in human placenta

Netrins are a family of proteins that mediate axonal guidance in the central nervous system (CNS). In addition to the CNS, netrins are involved in cell adhesion, motility, proliferation, differentiation, and survival. Because these processes occur in the placenta, we raised the question of whether netrin-1 is expressed by placental cells during development. In the present study, we analyzed the spatial and temporal distribution of netrin-1 and its two receptors, DCC (deleted in colorectal cancer) and UNC5B (uncoordinated-5 homolog) in human placenta using RT-PCR, Western blotting, and immunohistochemistry analysis. We demonstrated the presence of the proteins and transcripts of netrin-1 and its receptors in placenta and cytotrophoblasts. Furthermore, using immunohistochemistry, we localized endogenous netrin-1 protein staining to villous and extravillous cytotrophoblasts, and secreted netrin-1 outside the syncytiotrophoblasts. The DCC receptor was localized to syncytiotrophoblasts and invasive extravillous cytotrophoblasts during the first trimester and at term. On the other hand, the UNC5B receptor was localized to villous and extravillous cytotrophoblasts proximal to anchoring areas during the first trimester. At term, UNC5B was observed in decidual cells and weakly in extravillous cells. The discrete pattern of netrin-1 and netrin-1 receptor distribution suggested that netrin-1 protein functions might vary with its localization in the placenta and probably with time of gestation.

Increased TLR4 expression in murine placentas after oral infection with periodontal pathogens

Maternal periodontitis has emerged as a putative risk factor for preterm births in humans. The periodontitis-associated dental biofilm is thought to serve as an important source of oral bacteria and related virulence factors that hematogenously disseminate and affect the fetoplacental unit; however the underlying biological mechanisms are yet to be fully elucidated. This study hypothesized that an oral infection with the human periodontal pathogens Campylobacter rectus and Porphyromonas gingivalis is able to induce fetal growth restriction, placental inflammation and enhance Toll-like receptors type 4 (TLR4) expression in a murine pregnancy model. Female Balb/C mice (n = 40) were orally infected with C. rectus and/or P. gingivalis over a 16-week period and mated once/week. Pregnant mice were sacrificed at embryonic day (E) 16.5 and placentas were collected and analyzed for TLR4 mRNA levels and qualitative protein expression by real-time PCR and immunofluorescence. TLR4 mRNA expression was found to be increased in the C. rectus-infected group (1.98 +/- 0.886-fold difference, P < 0.01, ANOVA) compared to controls. Microscopic analysis of murine placentas showed enhanced immunofluorescence of TLR4 in trophoblasts, mainly in the placental labyrinth layer. Also, combined oral infection with C. rectus and P. gingivalis significantly reduced the overall fecundity compared to controls (16.7% vs. 75%, infected vs. non-infected mice respectively, P = 0.03, Kaplan-Meier). The results supported an enhanced placental TLR4 expression after oral infection with periodontal pathogens. The TLR4 pathway has been implicated in the pathogenesis of preterm births; therefore the abnormal regulation of placental TLR4 may give new insights into how maternal periodontitis and periodontal pathogens might be linked to placental inflammation and preterm birth pathogenesis.

Protein tyrosine phosphatase interacting protein 51 (PTPIP51) mRNA expression and localization and its in vitro interacting partner protein tyrosine phosphatase 1B (PTP1B) in human placenta of the first, second, and third trimester

The cellular localization of protein tyrosine phosphatase 51 (PTPIP51) and its in vitro interacting partner protein tyrosine phosphatase 1B (PTP1B) was studied in human placentae of different gestational stages. The expression of PTPIP51 protein and mRNA was observed in the syncytiotrophoblast and cytotrophoblast layer of placentae from the first, second, and third trimesters. In contrast, PTP1B expression was restricted to the syncytiotrophoblast during all gestational stages. Cells of the cytotrophoblasts and parts of the syncytiotrophoblasts expressing high amounts of PTPIP51 were found to execute apoptosis as shown by TdT-mediated dUTP-biotin nick end labeling assay, cytokeratin 18f, and caspase 3 expression. PTPIP51 could also be traced in the endothelium and smooth muscle cells of placental arterial and venous vessels, identified by double immunostainings with antibodies directed against van Willebrand factor and alpha-smooth muscle actin. Some of these cells showing a high PTPIP51 reactivity were Ki67 positive, indicating proliferation. Additionally, a small population of placental CD14-positive macrophages and mesenchymal cells within the villous stroma were detected as PTPIP51 positive. Our data suggest that both proteins, PTPIP51 and PTP1B, play a role in differentiation and apoptosis of the cytotrophoblast and syncytiotrophoblast, respectively. Moreover, PTPIP51 may also serve as a cellular signaling partner in angiogenesis and vascular remodeling.

Culture of mature trophoblastic giant cells from bovine placentomes

The mostly binucleate trophoblast giant cells (TGC) found in bovine placentomes, in addition to synthesizing and releasing hormones play an important role in fetal development and maternal adaptation to pregnancy. Placentomes from early gestation were collected, and for isolation of mature TGC, three cellular disaggregation methods, mechanical (MECH), enzymatic by trypsin (TRYP) or collagenase (COLL) were compared to each other. Further on, the cell survival in culture medium (DMEM) supplemented with either 10% fetal calf serum (FCS) or 10% serum replacement (SR) on culture plates free of any substrate was evaluated over a period of 90 days by trypan blue exclusion. The cells were further characterized by HOECHST 33342 nuclear staining, and immunocytochemical staining with monoclonal antibodies against vimentin and cytokeratin. A mean total rate of TGC survival of 82.56% was recorded. Statistical analysis showed significantly higher survival rates after enzymatic disaggregation with COLL (86.23%) than following MECH (80.38%) or TRYP (80.91%) treatment. Supplementation of DMEM with FCS resulted in significantly higher cellular survival rates (87.13%) when compared to the addition of SR (77.73%). Analysis of the influence of both, disaggregation method and medium supplementation on TGC survival revealed statistically significant differences between the following groups: MECH-SR (71.09%) was significantly lower than all other groups; TRYP-SR (78.03%) was significantly different from all other groups; TRYP-FCS (83.43%) and COLL-SR (84.08%) were significantly lower than MECH-FCS (89.98%) which together with COLL-FCS (88.25%) showed the highest cellular survival rate. In summary, our results show that TGC isolated from early gestation placentomes may be viable for more than 90 days of culture. However, whether these TGC produce placental lactogen throughout this period has yet to be determined.

Effect of low oxygen concentrations on trophoblast-like cell line invasion

The applicability of trophoblast-like cell lines to the study of trophoblast function has been widely debated. The present study investigated the effect of oxygen on the invasiveness, apoptosis, proliferation and secreted proteases of four different trophoblast cell lines; HTR-8/SVneo, SGHPL-4, JEG3 and JAR. All experiments were performed at 20% and 3% oxygen for 24, 48 and 72h. Immunostaining for integrins alpha1, alpha6 and beta3, cytokeratin 7 and HLA-G was used to determine the phenotype of the different cell lines. Invasion was assessed using the Matrigel invasion assay. Immunostaining for M30 and Ki67 determined levels of apoptosis and proliferation, respectively. Gelatin and casein/plasminogen zymography were performed on conditioned media to determine levels of secreted matrix metalloproteinase (MMP) 2 and MMP9 and urokinase plasminogen activator (uPA), respectively. None of the cell lines immunostained for all markers normally expressed by extravillous trophoblast cells. Invasiveness of HTR-8/SVneo and JEG3 cells cultured in 3% oxygen was increased after 24h but was inhibited by 72h in culture. Invasion of SGHPL-4 cells was inhibited after culture in 3% oxygen for 24h. Invasion by JAR cells was not affected by changes in oxygen concentration. The different cell lines also displayed different responses to culture period in 3% oxygen with respect to apoptosis, proliferation and secreted proteases. Care should be taken before results obtained using cell lines as a model for EVT are extrapolated to extravillous trophoblast cell behaviour in vivo.

Identification of antibodies against HAI-1 and integrin alpha6beta4 as immunohistochemical markers of human villous cytotrophoblast

Syncytiotrophoblast and invasive extravillous trophoblast arise from a common stem cell, namely villous cytotrophoblast, but have very different characteristics. The study of the differentiation process relies on the availability of suitable markers for these different cell types of developing placenta. In this work, we have produced monoclonal antibodies that are specific to human villous cytotrophoblast. Monoclonal antibody (MAb) MG2 was specific to villous cytotrophoblast across gestation, and recognizes hepatocyte growth factor activator inhibitor type 1. MAb MD10 stained villous cytotrophoblast across gestation and also some endothelial cells, particularly in the second or third trimester. MAb MD10 recognizes human integrin alpha6beta4. As a test for specificity, the novel MAbs were also used for staining of frozen tissue from human colon carcinoma. The results show that the two antibodies can be used as tools to study human villous cytotrophoblasts and also human tumors. The MG2 antibody seems most specific and promising for the study of various aspects of human villous cytotrophoblast.

Three-dimensional growth of extravillous cytotrophoblasts promotes differentiation and invasion

Human trophoblast research relies on a combination of in vitro models, including isolated primary cultures, explant cultures, and trophoblast cell lines. In the present study, we have utilized the rotating wall vessel (RWV) bioreactor to generate a three-dimensional (3-D) model of human placentation for the study of cytotrophoblast (CTB) invasion. The RWV supported the growth of the human CTB cell line SGHPL-4 and allowed for the formation of complex, multilayered 3-D aggregates that were morphologically, phenotypically, and functionally distinct from SGHPL-4 monolayers. The cells cultured three-dimensionally differentiated into an aggressively invasive cell population characterized by the upregulation of matrix metalloproteinase-2 (MMP-2), MMP-3, MMP-9 and urokinase-type plasminogen activator (uPA) secretion and activation. Microarray analysis of the 3-D and 2-D cultured cells revealed increased expression in the 3-D cells of various genes that are known mediators of invasion, including MT1-MMP, PECAM-1 and L-selectin, as well as genes not previously associated with CTB differentiation such as MMP-13 and MT5-MMP. These results were verified by quantitative real-time PCR. These findings suggest that when cultured in 3-D, SGHPL-4 cells closely mimic differentiating in utero CTBs, providing a novel approach for the in vitro study of the molecular mechanisms that regulate CTB differentiation and invasion.

Endocrine cell lines from the placenta

Cell-lines derived from human placenta and chorion have been used extensively to model the endocrine functions of human trophoblast. In general terms, the endocrine functions of the primary cells and tissues are at least partially replicated within the cell-lines, suggesting that they may be used as appropriate models. There are, however, two major provisos that compromise this generalisation. Firstly, the endocrine function of placenta represents a complex interaction between cytotrophoblast, syncytiotrophoblast and multiple regulators, so a single cell population digested from the normal environment is unlikely to represent this. Secondly, the characterisation of primary trophoblast populations and of cell-lines is incomplete, complicating the assignment of functions to trophoblast populations. Despite these difficulties, useful information has been obtained from the available cell-lines, regardless of whether they have arisen spontaneously, been transformed in vitro, or derived from cancers in vivo.

Functional proteomics of neurokinin B in the placenta indicates a novel role in regulating cytotrophoblast antioxidant defences

Neurokinin B (NKB) has recently been demonstrated to be secreted from the placenta in abnormally high amounts in preeclampsia (PE) and to cause hypertension in rats, suggesting it may be a mediator of some pathophysiological features of PE. It is also known that NKB receptors exist in the placenta. To determine the effect of high levels of NKB on the placenta, we have performed proteomics on five separate preparations of cultured purified human term cytotrophoblast cells. The results showed a statistically significant decrease in 20 proteins, of which five were unknown proteins. Proteins important in antioxidant defenses that decreased were thioredoxin, cyclophilin A, cytokeratin 1, and peroxiredoxin 5. Two proteins that inhibit intravascular anticoagulation, cytokeratin 1 and annexin 11 were also decreased. Pathways involving pro-inflammatory cytokine activation of NF-kappa B are opposed by Raf kinase inhibitor protein, which was also decreased. Cofilin 1, a protein involved in defense against bacteria, was also decreased. Among other proteins that were suppressed by NKB were proteasome proteins, desmoplakin, and calgizzarin. Western blots confirmed the decrease in cytokeratin 1 and cyclophilin A protein after NKB exposure. In PE, there is reduced antioxidant activity and increased intravascular coagulation. The findings that high levels of NKB, similar to those observed in PE, can impair these two classes of activity support the hypothesis that high NKB levels may contribute to the pathogenesis of PE.

Evaluation of Cytokeratin 7 as an accurate intracellular marker with which to assess the purity of human placental villous trophoblast cells by flow cytometry

Villous trophoblast cells (TC) obtained from first trimester and term human placentae after trypsin/Percoll gradient isolation were immunodepleted of contaminant cells. The level of purity was assessed by the intracellular expression of the pan trophoblast marker cytokeratin-7 (CK7) and comparisons were made with the GB25 trophoblast-specific (cytotrophoblast+syncytiotrophoblast) cell surface marker. The presence of contaminating cells was traced with intracellular vimentin, or cell surface CD2, CD36, and CD163 markers and evaluated by flow cytometric analysis. The pattern of CK7 expression by trophoblast cells was also analyzed by immunofluorescence microscopy. Most batches of TC from first trimester or term placentae (92+/-3% and 96+/-2%, respectively) showed a high percentage of CK7 expressing cells, with less than 2% contaminating vimentin positive cells. In some batches of TC with a lower percentage (65+/-4%) of CK7-expressing cells, no vimentin was found, but a low percentage of CD36-expressing cells was evidenced, with no presence of CD2, and/or CD163-expressing cells. The intracellular CK7 signal correlated significantly with that of GB25 (p<0.05) cell surface expression in TC of term placentae. The choriocarcinoma BeWo and Jar cell lines also showed high levels (>92%) of CK7-expressing cells. Conversely, the control U87 astrocytoma cell line showed a high percentage (>90%) of vimentin but no CK7-expressing cells. These results provide evidence that the mutually exclusive pattern of intracellular CK7/vimentin expression of human TC can be used for evaluation by flow cytometry of the purity of primary human trophoblast cells.

Large Variability of Trophoblast Gene Expression Within and Between Human Normal Term Placentae

Human placenta extracts are widely used in clinical and fundamental research, particularly to study the hormonal and exchange functions of the placenta. However, very little is known about the distribution of the main hormone mRNAs in the placenta as a whole. Total placenta extracts are heterogeneous in their cellular components, as they contain material of both fetal and maternal origin, and in their structure. Results vary greatly depending upon the location of the biopsy and the number of biopsies performed. We used real-time quantitative RT-PCR to determine whether transcripts corresponding to the main hormones secreted by the human placenta (e.g. hCG, HPL and PGH) are equally distributed within and between term placentae. We also measured cytokeratin 7 transcripts, which are specifically expressed in the trophoblast, and transcripts corresponding to nuclear receptors PPARgamma and RXRalpha. A comparison of the results obtained with 12 different samples from each of four normal term placentae revealed that the amounts of transcripts differ considerably within and between each placenta. This emphasizes the need to study large numbers of samples when looking for significant differences in gene expression.

Predominant Intracellular Expression of CXCR4 and CCR5 in Purified Primary Trophoblast Cells from First Trimester and Term Human Placentae

PROBLEM

The aim of the present study was to define the expression of CXCR4 and CCR5 on non-cultured non-stimulated primary human trophoblast cells (TCs) immediately after their immunopurification.

METHOD OF STUDY

We have evaluated by flow cytometric analysis and immunofluorescence, highly purified primary TCs prepared from first trimester (8.2 +/- 0.3 weeks, n = 15) and term (Caesarean section, n = 10) placentae for the cell surface and intracellular expression of CXCR4 and CCR5.

RESULTS

There was a high level of individual variability for CXCR4 and CCR5 expression between trophoblast batches. In first trimester and term placentae TCs, we found a greater number of TCs preparations expressing intracellular CXCR4 than CCR5 (P < 0.05). Both receptors were predominantly localized in the intracellular compartment of TCs, whatever if isolated from first trimester or term placentae.

CONCLUSIONS

The functional consequences of the predominance of CXCR4 expression and of cellular addressing are briefly discussed.

Demonstration of a tissue factor pathway inhibitor 2 messenger RNA synthesis by pure villous cytotrophoblast cells isolated from term human placentas

Tissue factor pathway inhibitor 2 (TFPI-2), a Kunitz-type proteinase inhibitor, might play an important role during placenta growth by regulating trophoblast invasion and differentiation. Many TFPI-2 transcripts have been detected in syncytiotrophoblast cells, but conflicting results have been reported concerning TFPI-2 synthesis by the cytotrophoblast. To address this issue, we developed a method to isolate pure preparations of human villous cytotrophoblast cells from normal term placentas, and the synthesis of tissue factor, TFPI-1, and TFPI-2 mRNAs was then evaluated. Cells were isolated by trypsin-DNase-EDTA digestion, followed by Percoll gradient separation and immunodepletion of human leukocyte antigen-positive cells. The quality of villous cytotrophoblast cells was verified by electron microscopy. Purity of cell preparations was assessed by labeling cells with GB25, a monoclonal antibody specific to villous trophoblast cells, and by checking the absence of contaminating cells using anti-CD9 antibody. The lack of hCG, CD32 mRNA, and tissue factor mRNA also indicated the absence of contaminating cells. Using competitive reverse transcription polymerase chain reaction, we showed that freshly isolated villous cytotrophoblast cells synthesized significant levels of TFPI-1 mRNA and larger amounts of TFPI-2 mRNA. TFPI-1 and TFPI-2 mRNA synthesis remained unchanged when cytotrophoblast cells were cultured in complete medium and evolved as a multinucleated syncytiotrophoblast. These results indicate that the villous cytotrophoblast and syncytiotrophoblast are both important sites of TFPI-2 synthesis in the human placenta. This study also indicates that tissue factor detection should be used systematically to check the purity of cytotrophoblast cell preparations because it allows detection of contamination by monocytes/macrophages and by syncytial fragments.

A positive immunoselection method to isolate villous cytotrophoblast cells from first trimester and term placenta to high purity

We developed a method for isolating highly pure villous cytotrophoblast cells from first trimester and term placenta that excludes extravillous trophoblast and syncytiotrophoblast fragments. The method is based on positive immunoselection using an antibody (mAb C76/18) reacting with hepatocyte growth factor activator inhibitor 1, HAI-1, a membrane antigen on villous cytotrophoblast. As a comparison, we also immunopurified cells using an antibody against CD105, present on syncytiotrophoblast and some extravillous trophoblast cells. The isolates were characterized by flow cytometry. HAI-1-positive cells from first trimester and term placentae were highly pure (>98 per cent cytokeratin 7-positive) mononuclear trophoblast cells. These isolations were contaminated with only very small percentages of vimentin and CD45-positive cells. HAI-1-positive trophoblast cells lacked CD105 and also HLA class I, a marker for extravillous trophoblast. In culture HAI-1-positive cells adhered, displayed an epithelial morphology, and survived for more than three days. In contrast, CD105-positive cell fractions from first trimester placenta were a heterogeneous mixture of mononuclear and multinuclear elements consisting of syncytiotrophoblast fragments, extravillous trophoblast cells, as well as around 5 per cent non-trophoblastic contaminants. In conclusion, the positive immunoselection method using antibody C76/18 yielded highly pure villous cytotrophoblast cells devoid of elements derived from syncytiotrophoblast or extravillous trophoblast.

Trophoblast apoptosis in human placenta at term as detected by expression of a cytokeratin 18 degradation product of caspase

CONTEXT

Apoptosis occurs in the normal placenta. The monoclonal antibody M30 is directed against a novel epitope of cytokeratin 18 (CK18) that is formed by caspase cleavage early in the apoptotic cascade, and this antibody may therefore be useful for evaluating trophoblast apoptosis.

OBJECTIVE

We undertook the present study to evaluate the use of monoclonal antibody M30 to assess trophoblast apoptosis in placenta at term.

METHODS

We stained paraffin-embedded placental tissues from 15 deliveries at term with M30. We compared positive M30 staining and CK18 staining (as detected by a monoclonal antibody directed against CK18) of trophoblasts in serial slides. We also compared apoptotic rates as detected by M30 and TUNEL (terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling) in 7 of the placentas.

RESULTS

In fields of villous tissue, most M30-positive cells were CK18-positive syncytiotrophoblasts. Approximately half of M30-positive cells occurred as focal positive staining in the syncytial layer, and half occurred as abundant staining of syncytiotrophoblasts in areas with increased intervillous or perivillous fibrinoid. We found very few M30-positive cells in villous stroma. In decidual/basal plate tissues, most (two thirds) of the M30-positive cells were CK18-positive extravillous trophoblasts, whereas one third were syncytiotrophoblasts of anchoring villi. Since TUNEL detects apoptosis in both epithelial and nonepithelial cells, more cells were positively stained with TUNEL than with M30 in some tissue fields. However, our observations suggest that M30 was more sensitive than TUNEL in recognizing apoptotic trophoblasts and had less nonspecific staining than TUNEL.

CONCLUSION

We recommend the use of monoclonal antibody M30 for apoptosis studies in placental tissues. This antibody is easy to handle, the staining obtained seems specific, and the nonspecific staining seems negligible.

Characterization of trophoblast cell isolations by a modified flow cytometry assay

The purity of isolated trophoblast cells is an important checkpoint in in vitro studies on the human placenta. Maintaining viability of primary cells for a prolonged period, or achieving cell proliferation in primary cell cultures, is often a matter of concern. In this paper we present a method for characterizing the purity of isolated trophoblast cells based on the expression of cytoskeletal proteins, as well as for assessing their cell cycle status, by flow cytometry. We show that after a simple permeabilization and fixation step in 70 per cent methanol, staining for cytokeratin 7 and vimentin could discriminate between trophoblast cells and contaminating populations. The method was applicable to trophoblast cells both from villous and extravillous origin. By staining the proliferation-related antigen Ki-67 and DNA, information was gained about the cell cycle status and viability of freshly isolated and cultured villous trophoblast cells. This method may help to quickly and quantitatively characterize preparations of isolated trophoblast, as well as to search for culture conditions favouring long-term survival and proliferation.

Expression of a cytokeratin 18 neo-epitope is a specific marker for trophoblast apoptosis in human placenta

In epithelial cells the caspase-mediated cleavage of cytokeratin 18 during apoptosis leads to the formation of a specific neo-epitope, recognized by the antibody M30. To test whether this antibody can be used as a specific marker for apoptotic trophoblast, we have stained serial sections of villi and junctional zone of first and third trimester human placenta with antibodies against cytokeratins 7 and 18, and against active caspase 3, with M30 and with the TUNEL reaction. Comparison of M30 immunoreactivities with TUNEL positivity and immunoreactivities for cytokeratins 7 and 18 clearly demonstrates that M30 specifically labels late apoptotic trophoblast cells. This finding is supported by the fact that in trophoblast, M30 immunoreactivities largely overlap with those for active caspase 3. As compared to the TUNEL test, the M30 immune reaction appears to be a highly reproducible marker for apoptotic trophoblast. This antibody stains a larger number of cells within the apoptosis cascade as compared to the TUNEL reaction, since cytokeratin 18 cleavage starts earlier than cleavage of DNA and since endonuclease activation can be bypassed in some trophoblast cells. The data suggest that M30 is superior to the TUNEL reaction as a marker for the detection of trophoblast apoptosis since it is easier to handle, more specific for apoptosis and less prone to artifacts.