Signal transduction and biological function of placenta growth factor in primary human trophoblast

Long non-coding RNA ARAP1-AS1 contributes to cell proliferation and migration in clear cell renal cell carcinoma via the miR-361-3p/placental growth factor axis

Clear cell renal cell carcinoma (ccRCC) is an aggressive malignancy with a poor prognosis. Therefore, investigating the molecular mechanism of ccRCC is important for ccRCC treatment. Here, we aimed to explore the effect of the long non-coding RNA ARAP1-AS1/miR-361-3p/PGF axis on ccRCC. The expression of lncRNA ARAP1-AS1, miR-361-3p, and placental growth factor (PGF) in ccRCC cells was verified by real-time quantitative PCR (RT-qPCR). The influence of the ARAP1-AS1/miR-361-3p/PGF axis on ccRCC cells was identified using the Cell Counting Kit-8 (CCK-8) assay, colony formation assay, flow cytometry, and wound healing assay. The interaction between ARAP1-AS1, miR-361-3p, and PGF was confirmed by bioinformatics analysis and luciferase assay. The results showed that the levels of ARAP1-AS1 and PGF increased in ccRCC cells, while miR-361-3p expression decreased. Cell functional experiments showed that cell proliferation and migration were inhibited by silencing ARAP1-AS1 or PGF, while miR-361-3p inhibitor or PGF overexpression could relieve the inhibitory effect of silencing ARAP1-AS1 on ccRCC cells. Moreover, ARAP1-AS1 sponges miR-361-3p to increase PGF expression. In conclusion, our study revealed that ARAP1-AS1 enhanced the malignancy of ccRCC cells by regulating the miR-361-3p/PGF axis.

Placental Growth Factor and Adverse Obstetric Outcomes in a Mixed-Risk Cohort of Women Screened for Preeclampsia in the First Trimester of Pregnancy

OBJECTIVE

The study aimed to investigate the association between placental growth factor (PlGF) and adverse obstetric outcomes in a mixed-risk cohort of pregnant women screened for preeclampsia (PE) in the first trimester.

METHODS

We included women with singleton pregnancies screened for PE between April 2014 and September 2016. Outcome data were retrieved from the New South Wales Perinatal Data Collection (NSW PDC) by linkage to the prenatal cohort. Adverse outcomes were defined as spontaneous preterm birth (sPTB) before 37-week gestation, birth weight (BW) below the 3rd centile, PE, gestational hypertension (GH), stillbirth, and neonatal death.

RESULTS

The cohort consisted of 11,758 women. PlGF multiple of the median (MoM) was significantly associated with maternal sociodemographic characteristics (particularly smoking status and parity) and all biomarkers used in the PE first trimester screening model (notably pregnancy-associated plasma protein A MoM and uterine artery pulsatility index [PI] MoM). Low levels of PlGF (<0.3 MoM and <0.5 MoM) were independently associated with sPTB, low BW, PE, GH, and a composite adverse pregnancy outcome score, with odds ratios between 1.81 and 4.44 on multivariable logistic regression analyses.

CONCLUSIONS

Low PlGF MoM levels are independently associated with PE and a range of other adverse pregnancy outcomes. Inclusion of PlGF should be considered in future models screening for adverse pregnancy outcomes in the first trimester.

Effect of Placental Growth Factor on Trophoblast-Endothelial Cell Interactions In Vitro

Placental growth factor (PlGF) is an important angiogenic factor which has an emerging role in the clinical management of suspected preeclampsia. The role of PlGF in normal placental development is not completely understood and it is uncertain whether PlGF influences trophoblast and endothelial cell interactions central to uterine spiral artery remodelling, especially in variable oxygen conditions. A two-cell model of endovascular invasion was used. Tissue culture plates were coated with Matrigel™, on which fluorescent-labelled uterine microvascular endothelial cells (1 × 10⁵/well) and HTR8/SVNeo cells were co-cultured (1 × 10⁵/well) for 20 h. Co-cultures were treated with recombinant human PlGF (rhPlGF) (10 or 100 ng/mL) and incubated at either 21% O₂ or 2% O₂. Images were captured by fluorescence microscopy and analysed using ImageJ (n = 7). Data was analysed using SPSSv24. Treatment with rhPlGF did not improve integration in co-cultures irrespective of oxygen conditions but increased proliferation in 2% O₂ of both trophoblast and endothelial cells. Expression of angiogenic factors VEGF, sFLT-1, PlGF and CXCL12 in both co-cultures and in isolated trophoblast cells was not altered by rhPlGF treatment. Expression of TLR-3 mRNA in co-cultures was increased by rhPlGF 100 ng/mL at 21% O₂ (p = 0.03). PlGF contributes to trophoblast and endothelial cell proliferation in the setting of physiological hypoxia but does not influence trophoblast and endothelial cell interactions in an in vitro model of spiral artery remodelling. Upregulation of TLR-3 expression in co-cultures may indicate a role for PlGF in the placental inflammatory response.

The physiology of intrapartum fetal compromise at term

Uterine contractions in labor result in a 60% reduction in uteroplacental perfusion, causing transient fetal and placental hypoxia. A healthy term fetus with a normally developed placenta is able to accommodate this transient hypoxia by activation of the peripheral chemoreflex, resulting in a reduction in oxygen consumption and a centralization of oxygenated blood to critical organs, namely the heart, brain, and adrenals. Providing there is adequate time for placental and fetal reperfusion between contractions, these fetuses will be able to withstand prolonged periods of intermittent hypoxia and avoid severe hypoxic injury. However, there exists a cohort of fetuses in whom abnormal placental development in the first half of pregnancy results in failure of endovascular invasion of the spiral arteries by the cytotrophoblastic cells and inadequate placental angiogenesis. This produces a high-resistance, low-flow circulation predisposing to hypoperfusion, hypoxia, reperfusion injury, and oxidative stress within the placenta. Furthermore, this renders the placenta susceptible to fluctuations and reduction in uteroplacental perfusion in response to external compression and stimuli (as occurs in labor), further reducing fetal capillary perfusion, placing the fetus at risk of inadequate gas/nutrient exchange. This placental dysfunction predisposes the fetus to intrapartum fetal compromise. In the absence of a rare catastrophic event, intrapartum fetal compromise occurs as a gradual process when there is an inability of the fetal heart to respond to the peripheral chemoreflex to maintain cardiac output. This may arise as a consequence of placental dysfunction reducing pre-labor myocardial glycogen stores necessary for anaerobic metabolism or due to an inadequate placental perfusion between contractions to restore fetal oxygen and nutrient exchange. If the hypoxic insult is severe enough and long enough, profound multiorgan injury and even death may occur. This review provides a detailed synopsis of the events that can result in placental dysfunction, how this may predispose to intrapartum fetal hypoxia, and what protective mechanisms are in place to avoid hypoxic injury.

First Trimester Screening for Fetal Aneuploidies Using Placental Growth Factor: The Great Obstetrical Syndrome (GOS) Study

OBJECTIVE

This study sought to estimate the ability of first trimester maternal serum placental growth factor (PlGF) to identify fetal aneuploidies.

METHODS

A prospective cohort study of singleton pregnancy at 11 to 13 weeks was conducted. Maternal serum PlGF concentration was measured using BRAHMS PlGF plus KRYPTOR automated assays (Thermo Scientific BRAHMS, Hennigsdorf, Germany). PlGF and nuchal translucency were log-transformed and reported as multiples of the median (MoM) adjusted for crown-rump length. Detection rates were calculated using receiver-operator characteristic curves.

RESULTS

The study observed 21 cases of fetal aneuploidies (0.4%) out of 4765 participants. Trisomy 21 (13 cases; 0.85 MoM; interquartile range [IQR] 0.80-0.93), trisomy 18 (two cases; 0.77 MoM; IQR 0.66-0.87) and trisomy 13 (two cases; 0.68 MoM; IQR 0.61-0.75) were associated with low PlGF concentrations. The low PlGF values observed in the cases of monosomy X (two cases; 0.85 MoM; IQR 0.82-0.88, P = 0.05), triploidy (0.78 MoM, P = 0.11), and 47,XX,i(22)(p10) (0.18 MoM, P = 0.08) were not statistically different from the controls. A model including maternal age, nuchal translucency, and PlGF could have identified all (95% CI 83%-100%) cases of trisomy 21 and six of the other fetal aneuploidies (75%) at a false-positive rate of 9%.

CONCLUSION

Low first trimester PlGF is associated with an increased risk of fetal aneuploidy. PlGF combined with first trimester ultrasound (nuchal translucency, uterine artery Doppler, and early fetal anatomy) could identify not only women at high risk for preeclampsia, but also fetuses at high risk of aneuploidy for optimal further testing (non-invasive testing for common aneuploidy screening or chorionic villus sampling for full screening and diagnosis).

First-Trimester Placental Growth Factor for the Prediction of Preeclampsia in Nulliparous Women: The Great Obstetrical Syndromes Cohort Study

BACKGROUND

First-trimester maternal serum markers have been associated with preeclampsia (PE). We aimed to evaluate the performance of first-trimester placental growth factor (PlGF) for the prediction of PE in nulliparous women.

SUBJECTS AND METHODS

We conducted a prospective cohort study of nulliparous women with singleton pregnancy at 11-13 weeks. Maternal serum PlGF concentration was measured using B·R·A·H·M·S PlGFplus KRYPTOR automated assays and reported in multiple of the median adjusted for gestational age. We used proportional hazard models, along with receiver operating characteristic curves and areas under the curve (AUC).

RESULTS

Out of 4,652 participants, we observed 232 (4.9%) cases of PE including 202 (4.3%) term and 30 (0.6%) preterm PE. PlGF was associated with the risk of term (AUC = 0.61, 95% confidence interval [CI] 0.57-0.65) and preterm PE (AUC = 0.73, 95% CI 0.64-0.83). The models were improved with the addition of maternal characteristics (AUC for term PE 0.66, 95% CI 0.62-0.71; AUC for preterm PE 0.81, 95% CI 0.72-0.91; p < 0.01). At a false-positive rate of 10%, PlGF combined with maternal characteristics could have predicted 26% of term and 55% of preterm PE. The addition of pregnancy-associated plasma protein A did not significantly improve the prediction models.

CONCLUSION

First-trimester PlGF combined with maternal characteristics is useful to predict preterm PE in nulliparous women.

Systematic review of maternal Placental Growth Factor levels in late pregnancy as a predictor of adverse intrapartum and perinatal outcomes

AIM

This systematic review evaluates the utility of maternal Placental Growth Factor (PlGF) when measured in late pregnancy (>20 weeks) as a predictor of adverse obstetric and perinatal outcomes.

METHODS

Pubmed and Embase were searched using the term "placental growth factor" in combination with relevant perinatal outcomes. Studies were included if they measured PlGF levels in pregnant women after 20 + 0 weeks gestation and reported relevant adverse obstetric or perinatal outcomes related to placental insufficiency (excluding pre-eclampsia).

RESULTS

Twenty-six studies were eligible for inclusion with 21 studies investigating the relationship between PlGF and small for gestational age (SGA) and 7 studies investigating PlGF for the prediction of other adverse perinatal outcomes. In all studies, maternal PlGF levels were significantly lower in the SGA group compared to controls. Other outcomes investigated included caesarean section (CS) for fetal compromise, low Apgar score, neonatal intensive care unit (NICU) admission, neonatal acidosis, stillbirth, and intrapartum fetal compromise. The results generally showed a significant association between low PlGF levels and CS for fetal compromise, NICU admission and stillbirth.

CONCLUSION

Low maternal PlGF levels in late pregnancy are strongly associated with SGA. Findings across studies were variable in relation to PlGF and the prediction of other adverse intrapartum and perinatal outcomes, however there was a consistent association between low PlGF levels and CS for fetal compromise, NICU admission and stillbirth. This review suggests that the use of PlGF for the prediction of adverse outcomes is promising. Its predictive value may potentially be enhanced if used in combination with other biomarkers or biophysical measures of fetal well-being.

Placental growth factor and pre-eclampsia

Placental growth factor (PlGF) is an increasingly important molecule in the prediction, diagnosis and treatment of pre-eclampsia. It has pro-angiogenic effects on the feto-placental circulation and supports trophoblast growth. Mechanisms by which PlGF expression is regulated continue to be investigated. Low circulating PlGF precedes the manifestation of clinical disease in pre-eclamptic pregnancies and intrauterine growth restriction. This suggests that low PlGF is a marker of abnormal placentation, but it remains uncertain whether this is a cause or consequence. Prediction of pre-eclampsia using PlGF is promising and may assist in the targeting of resources to women at highest risk of adverse pregnancy outcomes. Promisingly, experimental animal models of pre-eclampsia have been successfully treated with supplemental PlGF. Treatment of pre-eclampsia with PlGF is a potential therapeutic option requiring further exploration. This review focuses specifically on the role of PlGF in normal and pathological placental development and in the clinical management of pre-eclampsia.

Dlx3 and GCM-1 functionally coordinate the regulation of placental growth factor in human trophoblast-derived cells

Placental growth factor (PGF) is abundantly expressed by trophoblast cells within human placentae and is important for trophoblast development and placental vascularization. Circulating maternal serum levels of PGF are dynamically upregulated across gestation in normal pregnancies, whereas low circulating levels and placental production of PGF have been implicated in the pathogenesis of preeclampsia and other gestational diseases. However, the underlying molecular mechanism of regulating PGF expression in the human placenta remains poorly understood. In this study, we demonstrated that transcription factors Distal-less 3 (DLX3) and Glial cell missing-1 (GCM1) were both sufficient and required for PGF expression in human trophoblast-derived cells by overexpression and knockdown approaches. Surprisingly, while DLX3 and GCM1 were both positive regulators of PGF, co-overexpression of DLX3 and GCM1 led to an antagonist effect on PGF expression on the endogenous gene and a luciferase reporter. Further, deletion and site-directed mutagenesis studies identified a novel regulatory element on the PGF promoter mediating both DLX3- and GCM1-dependent PGF expression. This regulatory region was also found to be essential for the basal activity of the PGF promoter. Finally, Chromatin-immunoprecipitation (ChIP) assays revealed colocalization of DLX3 and GCM1 at the identified regulatory region on the PGF promoter. Taken together, our studies provide important insights into intrinsic regulation of human placental PGF expression through the functional coordination of DLX3 and GCM1, and are likely to further the understanding of pathogenesis of PGF dysregulation in preeclampsia and other disease conditions.

Mapping out p38MAPK

To generate new hypotheses, sometimes a "systems" approach is needed. In this review, I focus on the mitogen-activated kinase p38 because it has been recently shown to play an important role in the developmental programing and senescence of normal and stressed reproductive tissues. What follows is an overview of (i) pathways of p38 activation and their involvement in basic biological processes, (ii) evidence that p38 is involved in the homeostasis of reproductive tissues, (iii) how focus on p38 can be incorporated into investigation of normal and stressed pregnancies. Existence of excellent reviews will be mentioned as well as relevant animal models.

Intrauterine administration of human chorionic gonadotropin does not improve pregnancy and life birth rates independently of blastocyst quality: a randomised prospective study

BACKGROUND

Successful embryo implantation depends on a well-timed maternal-embryonic crosstalk. Human chorionic gonadotropin (hCG) secreted by the embryo is known to play a key role in this process and to trigger a complex signal transduction cascade allowing the apposition, attachment, and invasion of the embryo into the decidualized uterus. Production of hCG was reported to be dependent on blastocyst quality and several articles suggested that intrauterine hCG injection increases pregnancy and implantation rates in IVF patients. However, no study has as yet analysed birth rates as final outcome. Our objective was to determine whether clinical outcome after blastocyst transfer can be improved by intrauterine injection of hCG and whether this is dependent on blastocyst quality.

METHODS

A prospective randomised study was conducted in two settings. In cohort A, hCG application was performed two days before blastocyst transfer. In cohort B, the administration of hCG occurred just prior to embryo transfer on day 5. For both cohorts, patients were randomised to either intrauterine hCG application or to the control group that received culture medium. Clinical outcome was analysed according to blastocyst quality of transferred embryos.

RESULTS

The outcome of 182 IVF-cycles (cohort A) and 1004 IVF-cycles (cohort B) was analysed. All patients received a fresh autologous blastocyst transfer on day five. Primary outcomes were pregnancy rates (PR), clinical pregnancy rates (cPR), miscarriage rates (MR), and live birth rates (LBR). No improvement of clinical outcome after intrauterine hCG administration on day 3 (cohort A) or day 5 (cohort B) was found, independently of blastocyst quality transferred. The final outcome in cohort A: LBR after transfer of top blastocysts was 50.0 % with hCG and 53.3 % in the control group. With non-top blastocysts, LBR of 17.1 % (hCG) and 18.2 % (control) were observed (n.s.). In cohort B, LBR with top blastocysts was 53.3 % (hCG) and 48.4 % (control), with non-top blastocysts it came to 28.7 % (hCG) and 35.0 % (control). The differences between the groups were statistically not significant. Furthermore, we investigated a possible benefit of hCG administration in correlation with female age. In both age groups (<38 years and ≥ 38 years) we found similar LBR after treatment with hCG vs. medium. A LBR of 47.1 % vs. 48.7 % was obtained in the younger group and 26.6 % vs. 30.8 % in the older group.

CONCLUSIONS

In contrast to previous studies indicating a substantial benefit from intrauterine hCG application in cleavage stage embryo transfers, in our study we could not find any evidence for improvement of clinical outcome in blastocyst transfer cycles, neither with top nor with non-top quality morphology.

Gestational loss and growth restriction by angiogenic defects in placental growth factor transgenic mice

OBJECTIVE

Angiogenesis is an important biological process during development, reproduction, and in immune responses. Placental growth factor (PlGF) is a member of vascular endothelial growth factor that is critical for angiogenesis and vasculogenesis. We generated transgenic mice overexpressing PlGF in specifically T cells using the human CD2-promoter to investigate the effects of PlGF overexpression.

APPROACH AND RESULTS

Transgenic mice were difficult to obtain owing to high lethality; for this reason, we investigated why gestational loss occurred in these transgenic mice. Here, we report that placenta detachment and inhibition of angiogenesis occurred in PlGF transgenic mice during the gestational period. Moreover, even when transgenic mice were born, their growth was restricted.

CONCLUSIONS

Conclusively, PlGF overexpression prevents angiogenesis by inhibiting Braf, extracellular signal-regulated kinase activation, and downregulation of HIF-1α in the mouse placenta. Furthermore, it affected regulatory T cells, which are important for maintenance of pregnancy.

Interaction of mesenchymal stem cells with fibroblast-like synoviocytes via cadherin-11 promotes angiogenesis by enhanced secretion of placental growth factor

Bone marrow-derived mesenchymal stem cells (MSC) exist in the synovium of patients with rheumatoid arthritis (RA), yet the role of MSC in RA is elusive. Placental growth factor (PlGF) expression is increased in RA synovial fluids, and blocking of PlGF attenuates progression of arthritis in mice. In this study, we observed that PlGF induced chemotaxis of MSC in a dose-dependent manner, which was blocked by anti-vascular endothelial growth factor receptor-1 peptide. MSC exposed to PlGF elicited increased phosphorylation of Akt and p38 MAPK. PlGF-mediated chemotaxis was inhibited by PI3K inhibitor (LY294002) and p38 MAPK inhibitor (SB203580), but not by ERK1/2 inhibitor (PD98059). Fibroblast-like synoviocytes (FLS) constitutively produced PlGF, but MSC released negligible amounts of PlGF. Of note, when FLS of RA patients and MSC were cocultured, PlGF production by FLS was significantly increased; such an increase was dependent on the number of added MSC. Moreover, coculture conditioned medium promoted chemotaxis of MSC and increased angiogenesis in Matrigel plugs assay, and these were suppressed by preincubation of the medium with anti-PlGF Ab. Transwell experiments revealed that MSC to FLS contact was required for the increase in PlGF production by coculture. Cadherin-11 was expressed both in FLS and MSC, and small interfering RNA knockdown of cadherin-11 in FLS significantly abrogated the enhanced PlGF production under coculture conditions. These data indicate that increased levels of PlGF in RA joints could induce the migration of MSC to the synovium, and interaction of migrated MSC with FLS via cadherin-11 may contribute to angiogenesis and chronic synovitis by enhancing the secretion of PlGF.

Increased angiogenic factor secretion by decidual natural killer cells from pregnancies with high uterine artery resistance alters trophoblast function

STUDY QUESTION

Are the concentrations of factors secreted by decidual natural killer (dNK) cells from pregnancies at high risk of poor spiral artery remodelling different to those secreted from pregnancies at low risk?

SUMMARY ANSWER

Expression levels of PLGF, sIL-2R, endostatin and angiogenin were significantly increased by dNK cells from high-risk pregnancies, and angiogenin and endostatin were found to alter trophoblast function.

WHAT IS KNOWN ALREADY

During early pregnancy, maternal uterine spiral arteries are remodelled from small diameter, low-flow, high-resistance vessels into larger diameter, higher flow vessels, with low-resistance. This change is essential for the developing fetus to obtain sufficient oxygen and nutrients. dNK cells have been implicated in this process.

STUDY DESIGN, SIZE, DURATION

dNK cells were isolated from first trimester terminations of pregnancies (obtained with local ethical approval) screened for normal- or high-resistance index, indicative of cases least (<1%) and most (>21%) likely to have developed pre-eclampsia had the pregnancy not been terminated (n = 18 each group). Secreted factors and the effects of these on the trophoblast cell line, SGHPL-4, were assessed in vitro.

PARTICIPANTS/MATERIALS, SETTING, METHODS

A multiplex assay was used to assess dNK cell-secreted factors. SGHPL-4 cell functions were assessed using time-lapse microscopy, 3D invasion assays, endothelial-like tube formation ability and western blot analysis.

MAIN RESULTS AND THE ROLE OF CHANCE

The expression levels of PLGF (P < 0.01), sIL-2R (P < 0.01), endostatin (P < 0.05) and angiogenin (P < 0.05) were significantly increased by dNK cells from high-risk pregnancies. Endostatin significantly decreased SGHPL-4 invasion (P < 0.05), SGHPL-4 tube formation (P < 0.05) and SGHPL-4 Akt^ser473 phosphorylation (P < 0.05). Angiogenin significantly decreased SGHPL-4 invasion (P < 0.05), but increased SGHPL-4 tube formation (P < 0.01) and decreased SGHPL-4 Akt^ser473 phosphorylation (P < 0.05).

LIMITATIONS, REASONS FOR CAUTION

The culture of dNK cells and protein concentrations in vitro may not fully represent the in vivo situation. Although SGHPL-4 cells are extravillous trophoblast derived, further studies would be needed to confirm the roles of angiogenin and endostatin in vivo.

WIDER IMPLICATIONS OF THE FINDINGS

The altered expression of secreted factors of dNK cells may contribute to pregnancy disorders associated with poor spiral artery remodelling.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the Wellcome Trust (project reference 091550). R.F. was a recipient of a PhD studentship from the Division of Biomedical Sciences, St. George's, University of London. The authors have no conflict of interests.

Effect of zeranol on expression of apoptotic and cell cycle proteins in murine placentae

Mycotoxins are chemicals produced by fungus and many of them are toxic to humans. Zeranol is a mycotoxin used to promote growth in cattle in North America; yet such a practice draws concern about the residual compound in meat in European countries. In the present study, the toxicity of zeranol was tested in a mouse model for reproduction. Pregnant ICR mice were given p.o. daily doses of zeranol at 0, 1, 10, 100mg/kg for 4 days (from E13.5 to E16.5). Increased rates of fetal resorption at late gestation (E17.5) and preterm birth (<E18.5) were observed in mice treated with zeranol. The apparent factors causing these perinatal conditions were subsequently investigated. Perturbation of cell death or proliferation-related proteins might deter the growth and maintenance of the placentae, and the subsequent fetal resorption and preterm birth. Placental tissue isolated from pregnant mice at E17.5 showed that the expressions of Cdk2 and 4, Cyclin D1 and Bcl-xL were reduced in zeranol-treatment groups. The downregulations might signify growth or maintenance failure in the placentae. Furthermore, reduction in the signaling proteins Erk-1/2 in the placentae could trigger the decrease in the cell cycle/apoptosis proteins. In addition, relaxin is associated with preterm labor. An increase in placental Relaxin-1 expression could also contribute to early delivery in this study. Result of the current study suggested that exposure to zeranol might introduce adverse effect in pregnancy.

Thrombophilic-type placental pathologies and skeletal growth delay following maternal administration of angiostatin4.5 in mice

During placentation, the concentration of fibrinous deposits on the surfaces of maternal vasculature plays a role in villous development and has been strongly implicated in the pathophysiology of human fetal growth restriction (FGR). Fibrinous deposits are conspicuous sites of platelet aggregation where there is local activation of the hemostatic cascade. During activation of the hemostatic cascade, a number of pro- and antiangiogenic agents may be generated at the cell surface, and an imbalance in these factors may contribute to the placental pathology characteristic of FGR. We tested the hypothesis that angiostatin(4.5) (AS(4.5)), a cleavage fragment of plasminogen liberated at the cell surface, is capable of causing FGR in mice. Increased maternal levels of AS(4.5) in vivo result in reproducible placental pathology, including an altered vascular compartment (both in decidual and labyrinthine layers) and increased apoptosis throughout the placenta. In addition, there is significant skeletal growth delay and conspicuous edema in fetuses from mothers that received AS(4.5). Maternally generated AS(4.5), therefore, can access maternal placental vasculature and have a severe effect on placental architecture and inhibit fetal development in vivo. These findings strongly support the hypothesis that maternal AS(4.5) levels can influence placental development, possibly by directly influencing trophoblast turnover in the placenta, and contribute to fetal growth delay in mice.

Nicotine restores endothelial dysfunction caused by excess sFlt1 and sEng in an in vitro model of preeclamptic vascular endothelium: a possible therapeutic role of nicotinic acetylcholine receptor (nAChR) agonists for preeclampsia

OBJECTIVE

In this study we tested the hypothesis that nicotine restores proangiogenic functions to endothelial cells pretreated with soluble fms-like tyrosine kinase 1 and/or soluble endoglin.

STUDY DESIGN

Wound healing assay and tube formation assay were performed using human umbilical vein endothelial cells treated with nicotine (10(-9) to 10(-6) M), and with various combinations of soluble fms-like tyrosine kinase 1 (100 ng/mL), soluble endoglin (100 ng/mL), and nicotine (10(-7) M). Enzyme-linked immunosorbent assay was performed to measure vascular endothelial growth factor, placental growth factor, and transforming growth factor-beta1 concentrations in the conditioned media treated with nicotine (10(-9) to 10(-6) M).

RESULTS

Nicotine significantly facilitated endothelial migration and tube formation. By contrast, soluble fms-like tyrosine kinase 1 and/or soluble endoglin suppressed these endothelial functions. Nicotine restored these soluble fms-like tyrosine kinase 1 and/or soluble endoglin-reduced endothelial functions. Placental growth factor, but not transforming growth factor-beta1, production was significantly stimulated by the presence of nicotine. Vascular endothelial growth factor was undetectable.

CONCLUSION

Our results suggest a possible mechanism for the protective effects of cigarette smoking against preeclampsia, thus proposing a therapeutic potential of nicotine or other nicotinic acetylcholine receptor agonists for preeclampsia.

Regulation of trophoblast migration and survival by a novel neural regeneration peptide

Although placental trophoblast migration is tightly controlled in an autocrine/paracrine manner, the nature of chemoattractive factors facilitating and directing this biological activity remains largely elusive. Neural regeneration peptides (NRP), a recently discovered peptide family, stimulate neuronal migration, differentiation and survival of post-natal neurons within the murine central nervous system. Based on the neural-repair related activities of these peptides and parallels between neuronal and placental cell behaviour patterns, this study postulated that they play a role in placental development, in particular trophoblast migration and survival and investigated the role of a newly discovered NRP motif (NNZ-4920), which exhibits about 70% homology to the mouse NRP motif sequence and is homologous to a 13-mer fragment within the N-terminus of human CAPS2, in trophoblast migration and survival regulation. NNZ-4920 significantly enhanced trophoblast migration by 51% (P<0.01) compared with controls and protected against stress induced by serum withdrawal and tumour necrosis factor-alpha/interferon-gamma treatment, at femtomolar concentrations, with efficacy similar to epidermal growth factor. CAPS2 expression was detected in purified term trophoblast and decidual cells. In conclusion, the placenta may be a source of NRP-related gene expression. Its encoded peptide products exert biological effects on term trophoblast migration and survival in vitro.

Hypoxia increases placenta growth factor expression in human myocardium and cultured neonatal rat cardiomyocytes

BACKGROUND

Placenta growth factor (PlGF) plays an important role in pathologic angiogenesis and is believed to be an independent biomarker in patients with coronary artery disease. However, little is known regarding the regulation of PlGF expression in heart tissue.

METHODS

We determined expression changes in PlGF and its receptor, VEGFR1, in normal and abnormal biopsies from human cardiac allografts and in cardiomyocytes cultured under hypoxia or cyclical stretch conditions.

RESULTS

Human donor myocardium and biopsies from allografts without fibrin deposits expressed PlGF and VEGFR1 mRNA. Biopsies (n = 7) with myocardial fibrin, elevated serum cardiac troponin I titers (p < 0.03) and cellular infiltrates (p < 0.05) expressed 1.6-fold more PlGF mRNA than biopsies from allografts without fibrin (n = 11; p < 0.05). PlGF protein was localized in cardiomyocytes, extracellular matrix and some microvessels in areas with fibrin deposition. VEGFR1 mRNA expression was not different between groups. Cultured neonatal rat cardiomyocytes constitutively expressed PlGF/VEGFR1 under normoxia. PlGF expression was increased 3.88 +/- 0.62-fold after 12 hours (n = 6; p </= 0.05) and 3.64 +/- 0.41-fold after 24 hours of hypoxia (n = 6; p <or= 0.05). Shorter periods of hypoxia, conditioned media from hypoxic cells and cyclical stretch did not significantly alter PlGF or VEGFR1 expression.

CONCLUSIONS

Cardiomyocyte PIGF expression is upregulated by hypoxia in vitro and its expression increases significantly in allografts with myocardial damage. Collectively, these results provide important temporal and spatial evidence that endogenous PlGF may facilitate cardiac healing after myocardial hypoxia/ischemia.

Potential markers of preeclampsia--a review

Preeclampsia is a leading cause of maternal and fetal/neonatal mortality and morbidity worldwide. The early identification of patients with an increased risk for preeclampsia is therefore one of the most important goals in obstetrics. The availability of highly sensitive and specific physiologic and biochemical markers would allow not only the detection of patients at risk but also permit a close surveillance, an exact diagnosis, timely intervention (e.g. lung maturation), as well as simplified recruitment for future studies looking at therapeutic medications and additional prospective markers. Today, several markers may offer the potential to be used, most likely in a combinatory analysis, as predictors or diagnostic tools. We present here the current knowledge on the biology of preeclampsia and review several biochemical markers which may be used to monitor preeclampsia in a future, that, we hope, is not to distant from today.

Plasma soluble vascular endothelial growth factor receptor-1 concentration is elevated prior to the clinical diagnosis of pre-eclampsia

OBJECTIVE

Accumulating evidence suggests that the balance between vascular endothelial growth factor (VEGF), placental growth factor (PIGF), and their receptors is important for effective vasculogenesis, angiogenesis, and placental development. Recently, the soluble form of VEGFR-1 (sVEGFR-1), an antagonist to VEGF and PIGF, has been implicated in the pathophysiology of pre-eclampsia. Plasma sVEGFR-1 concentration is elevated in pre-eclampsia at the time of clinical diagnosis and correlates with the severity of the disease. The purpose of this study was to determine whether the concentrations of sVEGFR-1 in plasma of pre-eclamptic patients change prior to the clinical manifestations of the disease.

METHODS

A longitudinal case-control study was conducted in normal pregnant women (n = 44) and patients with pre-eclampsia (n = 44). Blood sampling was performed at six intervals: (1) 7-16 weeks; (2) 16-24 weeks; (3) 24-28 weeks; (4)28-32 weeks; (5) 32-36 weeks; and (6) more than 37 weeks of gestation. To examine the relationship between plasmasVEGFR-1 concentration and interval to clinical diagnosis of pre-eclampsia, plasma samples of pre-eclamptic patients at different gestational ages were stratified according to the interval from blood sampling to clinical development of the disease into five groups: (1) at clinical manifestation; (2) 2-5 weeks; (3) 6-10 weeks; (4) 11-16 weeks; and (5) 17-25 weeks before clinical manifestations. Plasma concentrations of sVEGFR-1 were determined by enzyme-linked immunoassay. Parametric statistics and repeated measure procedures were used for the analysis.

RESULTS

The mean plasma sVEGFR-1 concentration in pre-eclamptic patients before the clinical manifestation of the disease was significantly higher than in normal pregnant women at 24-28, 28-32, and 32-37 weeks of gestation (p = 0.02,p < 0.001, and p < 0.001, respectively). In contrast, no significant differences in the mean plasma sVEGFR-1 concentration between patients with pre-eclampsia and normal pregnant women were observed both at 7-16 weeks and 16-24 weeks of gestation (p= 0.1 and p= 0.9). Similarly, the mean plasma sVEGFR-1 concentration was significantly higher in pre-eclamptic patients than in normal pregnant women at clinical manifestation, at 2-5 weeks (mean 3.8 weeks), and at 6-10 weeks (mean 8.2 weeks) prior to the development of clinical pre-eclampsia (p < 0.001, p < 0.001, and p = 0.002,respectively). Among patients with early-onset pre-eclampsia (defined as gestational age of 34 weeks or less), the mean plasma sVEGFR-1 concentration was significantly higher in pre-eclampsia (before clinical diagnosis) than in normal pregnant women at 24-28 (mean 26.4) weeks of gestation (p = 0.008). In contrast, among patients with the late-onset disease(defined as gestational age of more than 34 weeks), plasma sVEGFR-1 concentration in pre-clinical pre-eclampsia was significantly higher than in normal pregnant women at 28-32 (mean 30.2) weeks of gestation (p < 0.001).

CONCLUSIONS

Plasma sVEGFR-1 concentration is elevated in pre-eclampsia prior to the clinical diagnosis of the disease. This elevation began 6-10 weeks prior to the clinical manifestations, and the increase was more pronounced at 2-5 weeks before the diagnosis, as well as at clinical presentation. Furthermore, in early-onset pre-eclampsia, plasma concentration ofsVEGFR-1 is elevated earlier than the late-onset disease.

Compartmentalizing VEGF-induced ERK2/1 signaling in placental artery endothelial cell caveolae: a paradoxical role of caveolin-1 in placental angiogenesis in vitro

On vascular endothelial growth factor (VEGF) stimulation, both VEGF R1 and R2 receptors were phosphorylated in ovine fetoplacental artery endothelial (oFPAE) cells. Treatment with VEGF stimulated both time- and dose-dependent activation of ERK2/1 in oFPAE cells. VEGF-induced ERK2/1 activation was mediated by VEGFR2, but not VEGFR1, and was linked to intracellular calcium, protein kinase C, and Raf-1. VEGF stimulated oFPAE cell proliferation, migration, and tube formation in vitro. Blockade of ERK2/1 pathway attenuated VEGF-induced cell proliferation and tube formation but failed to inhibit migration in oFPAE cells. Disruption of caveolae by cholesterol depletion with methyl-beta-cyclodextrin or by down-regulation of its structural protein caveolin-1 blunted VEGF-induced ERK2/1 activation, proliferation, and tube formation in oFPAE cells, indicating an essential role of integral caveolae in these VEGF-induced responses. Adenoviral overexpression of caveolin-1 and addition of a caveolin scaffolding domain peptide also inhibited VEGF-stimulated ERK2/1 activation, cell proliferation, and tube formation in oFPAE cells. Furthermore, molecules comprising the ERK2/1 signaling module, including VEGFR2, protein kinase Calpha, Raf-1, MAPK kinase 1/2, and ERK2/1, resided with caveolin-1 in caveolae. VEGF transiently stimulated ERK2/1 activation in the caveolae similarly as in intact cells. Caveolae disruption greatly diminished ERK2/1 activation by VEGF in oFPAE cell caveolae. We conclude that caveolae function as a platform for compartmentalizing the VEGF-induced ERK2/1 signaling module. Caveolin-1 and caveolae play a paradoxical role in regulating VEGF-induced ERK2/1 activation and in vitro angiogenesis as evidenced by the similar inhibitory effects of down-regulation and overexpression of caveolin-1 and disruption of caveolae in oFPAE cells.

Abnormalities of IGF-I signaling in the pathogenesis of diseases of the bone, brain, and fetoplacental unit in humans

IGF-I action is essential for the regulation of tissue formation and remodeling, bone growth, prenatal growth, brain development, and muscle metabolism. Cellular effects of IGF-I are mediated through the IGF-I receptor, a transmembrane tyrosine kinase that phosphorylates intracellular substrates, resulting in the activation of multiple intracellular signaling cascades. Dysregulation of IGF-I actions due to impairment in the postreceptor signaling machinery may contribute to multiple diseases in humans. This article will review current information on IGF-I signaling and illustrate recent results demonstrating how impaired IGF-I signaling and action may contribute to the pathogenesis of human diseases, including osteoporosis, neurodegenerative disorders, and reduced fetal growth in utero.

Placenta growth factor induces 5-lipoxygenase-activating protein to increase leukotriene formation in sickle cell disease

Individuals with sickle cell disease (SCD) have increased inflammation, a high incidence of airway hyperreactivity (AH), and increased circulating leukotrienes (LT). We show that expression of 5-lipoxygenase and 5-lipoxygenase activating protein (FLAP), key catalytic molecules in the LT pathway, were significantly increased in peripheral blood mononuclear cells (MNCs) in patients with SCD, compared with healthy controls. Placenta growth factor (PlGF), elaborated from erythroid cells, activated MNC and THP-1 monocytic cells to induce LT production. PlGF-mediated increased FLAP mRNA expression occurred via activation of phosphoinositide-3 (PI-3) kinase, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, and hypoxia inducible factor-1alpha (HIF-1alpha). HIF-1alpha small interfering RNA (siRNA) reduced PlGF-induced FLAP expression. FLAP promoter-driven luciferase constructs demonstrated that PlGF-mediated luciferase induction was abrogated upon mutation of HIF-1alpha response element (HRE), but not the nuclear factor-kappaB (NF-kappaB) site in the FLAP promoter; a finding confirmed by chromatin immunoprecipitation (ChIP) analysis. PlGF also increased HIF-1alpha binding to the HRE in the FLAP promoter. Therefore, it is likely that the intrinsically elevated levels of PlGF in SCD subjects contribute to increased LT, which in turn, mediate both inflammation and AH. Herein, we identify a mechanism of increased LT in SCD and show HIF-1alpha as a hypoxia-independent target of PlGF. These studies provide new avenues to ameliorate these complications.

CXCL10/IP-10: a missing link between inflammation and anti-angiogenesis in preeclampsia?

OBJECTIVE

Interferon (IFN)-gamma inducible protein, CXCL10/IP-10, is a member of the CXC chemokine family with pro-inflammatory and anti-angiogenic properties. This chemokine has been proposed to be a key link between inflammation and angiogenesis. The aim of this study was to determine whether preeclampsia and delivery of a small for gestational age (SGA) neonate are associated with changes in maternal serum concentration of CXCL10/IP-10.

STUDY DESIGN

This cross-sectional study included patients in the following groups: (1) non-pregnant women (N = 49); (2) women with normal pregnancies (N = 89); (3) patients with preeclampsia (N = 100); and (4) patients who delivered an SGA neonate (N = 78). SGA was defined as birth weight below the 10th percentile. Maternal serum concentrations of CXCL10/IP-10 were measured by sensitive immunoassay. Non-parametric statistics were used for analysis.

RESULTS

(1) Patients with normal pregnancies had a significantly higher median serum concentration of CXCL10/IP-10 than non-pregnant women (median 116.1 pg/mL, range 40.7-1314.3 vs. median 90.3 pg/mL, range 49.2-214.7, respectively; p = 0.002); (2) no significant correlation was found between maternal serum concentration of CXCL10/IP-10 and gestational age (between 19 and 38 weeks); (3) there were no differences in median serum CXCL10/IP-10 concentrations between patients who delivered an SGA neonate and those with normal pregnancies (median 122.4 pg/mL, range 37.3-693.5 vs. median 116.1 pg/mL, range 40.7-1314.3, respectively; p > 0.05); (4) patients with preeclampsia had a higher median serum concentration of CXCL10/IP-10 than normal pregnant women (median 156.4 pg/mL, range 47.4-645.9 vs. median 116.1 pg/mL, range 40.7-1314.3, respectively; p < 0.05); (5) patients with preeclampsia had a higher median concentration of CXCL10/IP-10 than those who delivered an SGA neonate (median 156.4 pg/mL, range 47.4-645.9 vs. median 122.4 pg/mL, range 37.3-693.5, respectively; p < 0.05).

CONCLUSIONS

Patients with preeclampsia have significantly higher serum concentrations of CXCL10/IP-10 than both normal pregnant women and mothers who have SGA neonates. These results are likely to reflect an anti-angiogenic state as well as an enhanced systemic inflammatory response in patients with preeclampsia. Alternatively, since preeclampsia and SGA share several mechanisms of disease, it is possible that a higher concentration of this chemokine may contribute to the clinical presentation of preeclampsia in patients with a similar intrauterine insult.

Glial cell missing 1 regulates placental growth factor (PGF) gene transcription in human trophoblast

Placental growth factor (PGF, previously known as PlGF) is prominently expressed by trophoblasts in human placenta, whereas most nontrophoblast cells express low levels of PGF mRNA under normal physiological conditions. We have shown that hypoxia decreases PGF expression in the trophoblast, but little is known about transcriptional regulation of PGF gene expression. We sought to determine promoter regions of the human PGF gene that contribute to its restricted high constitutive expression in the trophoblast. Overlapping putative promoter regions of human PGF gene encompassing 2-1.5 kb were cloned into reporter vectors and co-transfected into trophoblast and nontrophoblast cell lines. Promoter activity generated by a 2-1.5-kb clone was significantly higher in trophoblasts than in nontrophoblasts. Selective deletion mutants showed that a clone encompassing the PGF (2-828/++34) region generated promoter activity similar to the 2-1.5-kb region in the trophoblast. However, deletion of another 131 bp from this subclone (2-698/++34) resulted in significantly less promoter activity in the trophoblast. The (2-828/2-698) region significantly enhanced activity of a minimal promoter construct in trophoblast but not in nontrophoblast cells, suggesting that this region contributes to regulating PGF transcription in the trophoblast. Site-directed mutagenesis of a glial cell missing 1 (GCM1) motif in the 131-bp region significantly decreased enhancer activity in the trophoblast. Furthermore, overexpression of GCM1 significantly increased PGF 2-1.5-kb promoter activity and PGF mRNA expression in trophoblast and nontrophoblast cells. Forced overexpression of GCM1 restored PGF expression in the hypoxic trophoblast. These data support a functional role for GCM1 contributing to constitutively high trophoblast PGF expression and is the first direct evidence of an oxygen-responsive, trophoblast-specific transcription factor contributing to the regulation of PGF expression.

Analysis of the gene regulatory program induced by the homeobox transcription factor distal-less 3 in mouse placenta

Dlx3, a homeodomain transcription factor, is essential for placental development in the mouse. The Dlx3(-/-) mouse embryo dies at embryonic d 9.5-10 putatively due to placental failure. To develop a more comprehensive understanding of the gene profile regulated by Dlx3, microarray analysis was used to determine differences in gene expression within the placenta of Dlx3(+/+) and Dlx3(-/-) mice. Array analysis revealed differential expression of 401 genes, 33 genes in which signal to log ratio values of null/wild-type were lower than -0.5 or higher than 0.5. To corroborate these findings, quantitative real-time PCR was used to confirm differential expression for 11 genes, nine of which displayed reduced expression and two with enhanced expression in the Dlx3(-/-) mouse. Loss of Dlx3 resulted in a marked reduction (>60%) in mRNA expression of placental growth factor (Pgf), a member of the vascular endothelial growth factor family. Consistent with these results, Pgf secretion from placental explants tended to be reduced in the Dlx3(-/-) mice, compared with wild type. To investigate mechanisms of Dlx3 regulation of Pgf gene transcription, we cloned 5.2 kb of the Pgf 5' flanking sequence for use in reporter gene assays. Expression of the Pgf promoter luciferase reporter containing at least three Dlx3 binding sites was increased markedly by overexpression of Dlx3 supporting the conclusion that Dlx3 may have a direct effect on Pgf promoter activity. These studies provide a novel view of the transcriptome regulated by Dlx3 in mouse placenta. Dlx3 is specifically required for full expression and secretion of Pgf in vivo. Moreover, in vitro studies support the conclusion that Dlx3 is sufficient to directly modulate expression of the Pgf gene promoter in placental cells.

Circulating Angiogenic Factors and Placental Abruption

OBJECTIVE

Abnormalities in circulating angiogenic factors have been reported in diseases of abnormal placentation, such as preeclampsia and intrauterine growth restriction. Our objective was to determine whether circulating angiogenic factors are altered in another placental vascular disease, abruptio placentae.

METHODS

In a nested case-control study of nulliparous pregnancies, we examined levels of placental growth factor (PlGF) and soluble fms-like tyrosine kinase 1 (sFlt-1) in serum collected prospectively from 31 women who later developed placental abruption and from 31 normal control subjects. All serum specimens were collected before the onset of hypertension or abruption and before labor or delivery. Serum angiogenic factors were compared within 3 gestational age windows: early (20 weeks or less), middle (21-32 weeks), and late (33 weeks or more) pregnancy.

RESULTS

During early pregnancy women who developed placental abruption had lower PlGF and higher sFlt-1 concentrations and higher sFlt-1/PlGF ratios than women with normal pregnancies. In mid-pregnancy these differences became greater, reaching statistical significance for PlGF concentration (431 versus 654 pg/mL, P<.01) and the sFlt-1/PlGF ratio (25.3 versus 2.5, P<.01). When the women with placental abruption were subdivided into those who did (n=10) and those who did not (n=21) develop preeclampsia or gestational hypertension, significant alterations in angiogenic factors were noted only in women who later developed hypertension in pregnancy. Among these women, PlGF concentrations were decreased in mid-pregnancy (160 versus 723 pg/mL, P<.001), and the mid-pregnancy sFlt-1/PlGF ratio was increased (70.1 versus 2.3, P=.001).

CONCLUSION

Serum levels of the proangiogenic factor PlGF were decreased, and those of the antiangiogenic ratio sFlt-1/PlGF were increased in nulliparous women who subsequently developed hypertension and placental abruption.

Maternal nutrient restriction upregulates growth signaling pathways in the cotyledonary artery of cow placentomes

This study evaluated the role of MAPK/ERK1/2 and/or PI3-K/Akt signaling pathways in modulating bovine placentomal vascularity in response to maternal nutrient restriction. Beef cows were randomly assigned to control fed (Control, n=15, 100% of requirements) or nutrient restricted (NR, n=15, 50% requirements) diets from day 30 to day 125 of gestation. Ten cows from each dietary group were necropsied on day 125 (approximately 45% gestation), and the remaining cows in each diet group were then fed control diets and necropsied on day 250 (approximately 90% gestation). At day 125 of gestation, NR cows exhibited increased (P=0.06) COT vascularity, improved (P<0.05) placentome efficiency (fetal weight/placentomal weight), and increased (P<0.05) phosphorylated Akt and ERK1/2 in COT arteries compared to Control cows. By day 250, however, treatment differences in COT vascularity and phosphorylated Akt and ERK1/2 in COT arteries were lost. On both gestational days, no treatment difference was observed in the levels of phosphorylated Akt or ERK1/2 in CAR arteries. CAR vascularity was similar across treatment on day 125, but tended to be greater (P<0.10) in NR than Control cows on day 250. These data suggest that conceptuses react to an early gestational nutrient restriction by up-regulating COT growth signaling pathways associated with angiogenesis, and that these compensations do not persist to term.

Evidence supporting that the excess of the sVEGFR-1 concentration in maternal plasma in preeclampsia has a uterine origin

BACKGROUND

Preeclampsia has been considered an anti-angiogenic state. Two factors have been implicated in the genesis of this state: soluble vascular endothelial growth factor receptor-1 (sVEGFR-1) and placental growth factor (PlGF). Indeed, the concentrations of PlGF, an angiogenic factor, are lower in preeclampsia than in normal pregnancy, while the opposite is the case for the anti-angiogenic factor, sVEGFR-1. The source of the excess sVEGFR-1 has not yet been determined. Since the placenta could be a source of sVEGFR-1, we conducted a study to determine whether there is a gradient in the plasma concentration of sVEGFR-1 and PlGF between the uterine vein and the antecubital vein in both patients with preeclampsia and normal pregnant women.

METHODS

A cross-sectional study was performed to determine the plasma concentrations of sVEGFR-1 and PlGF in the uterine and antecubital vein of patients with preeclampsia (n = 9) and normal pregnant women at term (n = 9). Plasma samples were collected from antecubital and uterine veins at the time of cesarean section. The concentrations of sVEGFR-1 and PlGF were determined using specific enzyme-linked immunoassays. The differences of plasma concentrations of sVEGFR-1 and PlGF between uterine and antecubital veins in both groups were compared by paired t-tests.

RESULTS

Patients with preeclampsia had a significantly higher mean plasma concentration of sVEGFR-1 in the uterine vein than in the antecubital vein (uterine vein: mean 13,675 +/- 5,684 pg/ml vs. antecubital vein: mean 10,234 +/- 4,700 pg/ml; paired t-tests, p = 0.04). In contrast, among normal pregnant women at term, there was no significant difference in plasma concentrations of sVEGFR-1 between the uterine and antecubital veins (uterine vein: mean 1,918 +/- 665 pg/ml vs. antecubital vein: mean 1,750 +/- 475 pg/ml; paired t-tests, p = 0.1). The mean plasma concentration of sVEGFR-1, either in the antecubital or uterine vein, was significantly higher in preeclampsia than in normal pregnancy (unpaired t-tests; both p < 0.001). There was no significant difference in the mean plasma concentration of PlGF between the uterine and the antecubital veins in both the preeclamptic (uterine vein, mean +/- SD: 129 +/- 106 pg/ml vs. antecubital vein, mean +/- SD: 82 +/- 43 pg/ml; paired t-tests, p = 0.2) and normal pregnancy groups (uterine vein, mean +/- SD: 331 +/- 254 pg/ml vs. antecubital vein, mean +/- SD: 319 +/- 259 pg/ml; paired t-tests, p = 0.4). The mean plasma concentration of PlGF, either in the uterine or antecubital vein, was lower in preeclampsia than in normal pregnancy (unpaired t-tests; p = 0.008 and 0.02 respectively).

CONCLUSIONS

Plasma concentration of sVEGFR-1 was higher in the uterine vein than in the antecubital vein in women with preeclampsia. This provides evidence supporting the concept that the uterus is a potential source of the excess circulating sVEGFR-1 concentration in preeclamptic women.

The role of apoptosis in the regulation of trophoblast survival and differentiation during pregnancy

Apoptosis is important for normal placental development, but it may also be involved in the pathophysiology of pregnancy-related diseases. Normal placental development is dependent upon the differentiation and invasion of the trophoblast, the main cellular component of the placenta. Trophoblast apoptosis increases in normal placentas as gestation proceeds, and a greater incidence of trophoblast apoptosis has been observed in pregnancies complicated by preeclampsia or intrauterine growth retardation (IUGR). In response to different stimuli, apoptosis may be initiated extrinsically by the death receptor pathway or intrinsically by the mitochondrial pathway. The central executioners of apoptosis are the caspases, which cleave numerous vital cellular proteins to affect the apoptotic cascade. By inhibiting caspase activation, several endogenous inhibitors, including flice-like inhibitory proteins (FLIPs), inhibitors of apoptosis (IAPs), and antiapoptotic Bcl-2 family members, can prevent further propagation of the death signal. Macrophages present at the maternal-fetal interface may also contribute to trophoblast survival by removing apoptotic cells and producing cytokines and growth factors, which influence the progression of the apoptotic cascade. This review focuses on the role of apoptosis in trophoblast development and differentiation, the molecular mechanisms by which normal trophoblast apoptosis can occur, and how it is regulated to prevent excessive trophoblast apoptosis and possible pregnancy complications.

Multiple anti-apoptotic pathways stimulated by EGF in cytotrophoblasts

Epidermal growth factor (EGF) reduces apoptosis in primary cytotrophoblast (CT) in culture through two separate pathways: the extracellular signal related kinase (ERK) 1/2 and phosphatidyl inositol 3-kinase (PI-3 kinase) paths. Whether other pathways are involved in survival signalling is unknown. We here show that the c-Jun NH2 terminal kinase (JNK) and the mitogen activated kinase (MAPK) p38 are also activated by EGF as seen by increases in JNK and p38 phosphorylation. However, inhibition of JNK phosphorylation with the specific inhibitor SP600125 increases apoptosis in a manner refractory to the addition of EGF but inhibition of p38 phosphorylation with its specific inhibitor SB 203580 does not increase apoptosis. EGF also activates sphingosine kinase-1 (SPHK-1), which converts sphingosine to sphingosine-1-phosphate, and its inhibition with dimethyl sphingosine (DMS) increased trophoblast death. Inhibition of SPHK-1 also did not affect EGF stimulated phosphorylation of PI-3 kinase, Akt, ERK1/2 or p38 but inhibition of PI-3 kinase with a specific inhibitor LY294002 partly (40%) inhibited the EGF-stimulated increase in SPHK-1 activity. We conclude that, in addition to the PI-3 kinase and ERK1/2 pathways, EGF acts through its receptor to stimulate JNK, p38 and SPHK-1 pathways, but that the JNK and SPHK-1, and not the p38, pathways are involved in suppressing apoptosis. This information provides evidence that EGF stimulates survival along multiple pathways that differ in trophoblast and other cell types.

Hypoxia-induced increase in soluble Flt-1 production correlates with enhanced oxidative stress in trophoblast cells from the human placenta

OBJECTIVE

Placental trophoblast cells (TCs) produce soluble Flt-1 (sFlt-1). Hypoxia induces placental oxidative stress and modulates trophoblast function. The aim of this study was to investigate whether hypoxia mediates TC sFlt-1 production and whether increased sFlt-1 production correlates with increased oxidative stress in placental TCs.

METHODS

Placentas were obtained immediately after delivery from normal pregnant women (n = 8). Placental TCs were isolated by Dispase digestion of villous tissue and purified by Percoll gradient centrifugation. Isolated TCs were cultured under normoxia (21% O2: 5% CO2/95% air) and hypoxia (2% O2/5% CO2/93% N2) conditions for 3 days in vitro. TC productions of sFlt-1, VEGF, and PlGF were measured by enzyme-linked immunosorbent assay (ELISA). Lipid peroxide production and superoxide dismutase (CuZn-SOD) levels were evaluated. Messenger RNA expressions of Flt-1, VEGF and PlGF were determined by RT-PCR. Messenger RNA expressions for superoxide dismutase (CuZn-SOD) and heme oxygenase-1 (HO-1) were also determined. Data are expressed as mean +/- SE. A p level less than 0.05 was considered statistically different.

RESULTS

Our results show that sFlt-1 production was significantly increased by TCs cultured under hypoxia condition that correlates with increased lipid peroxide production. We also found that under hypoxia condition: (1) the ratio of PlGF/VEGF production was reversed; (2) the ratio of lipid peroxides to superoxide dismutase production was increased. The increased mRNA expressions for Flt-1 and VEGF and the decreased mRNA expression for PlGF in TCs were consistent with the protein productions under hypoxia condition.

CONCLUSION

We concluded that upregulation of sFlt-1 and unbalanced PlGF/VEGF production associated with increased oxidative stress are consequences of hypoxia in placental TCs. Our results suggest that placental TCs are major sources of sFlt-1 and VEGF levels in the maternal circulation in women with preeclampsia.

The expression of apoptosis related genes in the first trimester human placenta using a short term in vitro model

Using in vitro model for studying the induction and inhibition of spontaneous apoptosis in human first trimester placental villi, mediated by the free radical scavenger SOD, we have examined the expression of bcl-xL, bax, Caspase-3 and PARP (Poly ADP-ribosyl). An increase in apoptosis was associated with activation of PARP and an increase and activation of Caspase-3. There was no significant change in bcl-x or bax. Therefore bcl-x and bax do not appear to have a significant role in apoptosis in the first trimester in vitro. Cleavage of Caspase-3 rather than transcriptional regulation appears to be the main determinant of Caspase-3 activity in first trimester placental villi.

Activated peripheral blood mononuclear cells induce p44/42 mitogen-activated protein kinase phosphorylation in trophoblast-like JAR cells

Mammalian pregnancy bears many similarities to transplantation, since the fetus is semi-allogenic to mother. Thus, mammals have developed numerous mechanisms to protect the developing fetus from maternal immunologic recognition and attack. We have previously shown that human choriocarcinoma JAR cells, which resemble first trimester trophoblasts, regulate several important mRNAs in activated peripheral blood mononuclear cells (PBMC). We now provide further evidence that communication between maternal and fetal tissues is bi-directional, and that activation of PBMC leads to activation of specific signaling pathways in JAR cells. Activated PBMC were co-cultured with JAR cells for specific time intervals, after which JAR cells were lysed and subjected to western blotting for activated forms of the JNK, Erk 1-2, and p38 mitogen-activated protein kinases (MAPK). Phosphorylation of Erk 1-2, but not JNK or p38, was induced in co-cultures of PBMC and JAR cells. These results were also obtained when JAR cells were incubated with conditioned medium from activated, but not resting, PBMC. Results were confirmed using specific MAPK reporter constructs, using luciferase activity as a measure of Elk-1 phosphorylation. Erk 1-2 phosphorylation was not required for JAR cells to inhibit IL-2 production in activated PBMC. Addition of the specific MAPK inhibitor UO126 to JAR cells prior to the addition of activated PBMC to the cultures did not abolish the capacity of JAR cells to inhibit IL-2 mRNA expression in PBMC. We conclude that there is likely to be significant bi-directional signaling between leukocytes and trophoblasts at the maternal-fetal interface. We propose the existence of a delicate maternal-fetal immunologic homeostasis based on these experimental results.

Identification of Placenta Growth Factor Determinants for Binding and Activation of Flt-1 Receptor

Placenta growth factor (PlGF) belongs to the vascular endothelial growth factor (VEGF) family and represents a key regulator of angiogenic events in pathological conditions. PlGF exerts its biological function through the binding and activation of the seven immunoglobulin-like domain receptor Flt-1, also known as VEGFR-1. Here, we report the first detailed mutagenesis studies that provide a basis for understanding molecular recognition between PlGF-1 and Flt-1, highlighting some of the residues that are critical for receptor recognition. Mutagenesis analysis, performed on the basis of a structural model of interaction between PlGF and the minimal binding domain of Flt-1, has led to the identification of several PlGF-1 residues involved in Flt-1 recognition. The two negatively charged residues, Asp-72 and Glu-73, located in the beta3-beta4 loop, are critical for Flt-1 binding. Other mutations, which bring about a significant decrease in PlGF binding activity, are Gln-27, located in the N-terminal alpha-helix, and Pro-98 and Tyr-100 on the beta6 strand. The mutation of one of the two glycosylated residues of PlGF, Asn-84, generates a PlGF variant with reduced binding activity. This indicates that, unlike in VEGF, glycosylation plays an important role in Flt-1 binding. The double mutation of residues Asp-72 and Glu-73 generates a PlGF variant unable to bind and activate the receptor molecules on the cell surface. This variant failed to induce in vitro capillary-like tube formation of primary endothelial cells or neo-angiogenesis in an in vivo chorioallantoic membrane assay.

Deferential Regulation of Placenta Growth Factor (PlGF)-Mediated Signal Transduction in Human Primary Term Trophoblast and Endothelial Cells

Increasing evidence supports that many common obstetrical complications may involve the disruption of normal placental and/or uterine vascular function. Placenta growth factor (PlGF) is an angiogenic factor that is abundantly expressed in the placenta, with primary site of synthesis being trophoblast. Receptors for PlGF include products of the fms-like tyrosine kinase (flt-1) gene which is expressed in several cell types including endothelial cells and trophoblast. PlGF activation of flt-1 in trophoblast induces the stress activated protein kinase (SAPK) signal transduction pathways, JNK (c-Jun-N-Terminal Kinase) and p38, with little induction of the extracellular signal-regulated protein kinase (ERK)-1/2 pathways. In contrast, PlGF induces strong ERK-1/2 activation, but little JNK or p38 responses in human umbilical vein endothelial cells (HUVEC). To better understand the biochemical functions of PlGF in trophoblast, we studied upstream signal regulatory molecules to determine those that are responsible for directing the divergent PlGF signal transduction responses in these cell types. PlGF induced similar activation of Nck and PLC-gamma in trophoblast and HUVEC. In marked contrast, SHP-2 and Gab2 were strongly activated by PlGF in endothelial cells but not trophoblast. These results suggest a general role for Nck and PLC-gamma in mediating PlGF signal transduction responses independent of the different downstream MAPK pathways activated. However, SHP-2 and Gab2 are regulatory molecules involved in the PlGF induction of different terminal pathways in HUVEC and trophoblast.

Determinants of Placental Vascularity

PROBLEM

Vascular growth during implantation and placentation is critical for successful gestation and it is thought that vascular insufficiencies during placentation contribute to a number of obstetrical complications. However, relatively little is known regarding the regulation of angiogenesis in the placenta.

METHOD OF STUDY

We review literature concerning the potential significance of inadequate placental vascularity as a contributor to the obstetrical complications of spontaneous abortion, fetal growth restriction and preeclampsia. Gene expression assays were used to compare fluctuations of placenta growth factor (PlGF) and PlGF receptor expression in normal and preeclamptic trophoblast in vitro.

RESULTS

Studies have shown that common obstetrical complications manifest altered placental vascularity. Both intrinsic defects (gene knockouts) and extrinsic factors (O(2) tension, cytokines, etc) may be responsible for the defects. Some of these factors have been shown to influence trophoblast vascular endothelial growth factor (VEGF)/PlGF expression suggesting this particular family of angiogenic proteins play an important role in placental angiogenesis.

CONCLUSION

Placental vascularization reflects a complex interaction of regulatory factors. Understanding the regulation of vascular growth in the placenta will provide much needed insight into placenta-related vascular insufficiencies.

Evidence of a novel isoform of placenta growth factor (PlGF-4) expressed in human trophoblast and endothelial cells

Placenta growth factor (PlGF), a homodimeric glycoprotein that is homologous to vascular endothelial growth factor (VEGF), is mitogenic to endothelial cells and protects trophoblast from apoptosis. Alternative splicing of mature mRNA gives rise to three known isoforms of PlGF. PlGF is expressed by human trophoblast during normal pregnancy, however, it is not known which isoforms are produced. We have utilized RT-PCR to characterize PlGF isoform expression in normal human trophoblast and umbilical vein endothelial cells (HUVEC). Our results show that PlGF-1, PlGF-2, and PlGF-3 isoforms are expressed by trophoblast and HUVECs. In addition, both cell types also express a novel variant of PlGF, tentatively termed PlGF-4, which has not been previously reported. PlGF-4 consists of the same sequence of PlGF-3, plus the heparin binding domain previously thought to be present only in PlGF-2. Presence of the heparin binding domain in PlGF-4 suggests that this variant would remain cell membrane-associated and thus could influence trophoblast and endothelial cells in an autocrine manner.

Mechanism of monocyte activation and expression of proinflammatory cytochemokines by placenta growth factor

Monocytes from patients with sickle cell disease (SCD) are in an activated state. However, the mechanism of activation of monocytes in SCD is not known. Our studies showed that placenta growth factor (PlGF) activated monocytes and increased mRNA levels of cytokines (tumor necrosis factor-alpha [TNF-alpha] and interleukin-1beta [IL-1beta]) and chemokines (monocyte chemotactic protein-1 [MCP-1], IL-8, and macrophage inflammatory protein-1beta [MIP-1beta]) in both normal monocytes and in the THP-1 monocytic cell line. This increase in mRNA expression of cytochemokines was also reflected in monocytes derived from subjects with SCD. We studied the PlGF-mediated downstream cellular signaling events that caused increased transcription of inflammatory cytochemokines and chemotaxis of THP-1 monocytes. PlGF-mediated cytochemokine mRNA and protein expression was inhibited by PD98059 and wortmannin, inhibitors of mitogen-activated protein kinase kinase (MAPK/MEK) kinase and phosphatidylinositol-3 (PI3) kinase, respectively, but not by SB203580, a p38 kinase inhibitor. PlGF caused a time-dependent transient increase in phosphorylation of extracellular signal-regulated kinase-1/2 (ERK-1/2), which was completely inhibited by wortmannin, indicating that activation of PI3 kinase preceded MEK activation. PlGF also induced transient phosphorylation of AKT. MEK and PI3 kinase inhibitors and antibody to Flt-1 abrogated PlGF-induced chemotaxis of THP-1 monocytes. Overexpression of a dominant-negative AKT or a dominant-negative PI3 kinase p85 subunit in THP-1 monocytes attenuated the PlGF-mediated phosphorylation of ERK-1/2, cytochemokine secretion, and chemotaxis. Taken together, these data show that activation of monocytes by PlGF occurs via activation of Flt-1, which results in activation of PI3 kinase/AKT and ERK-1/2 pathways. Therefore, we propose that increased levels of PlGF in circulation play an important role in the inflammation observed in SCD via its effects on monocytes.

Preventing pathological regression of blood vessels

Oxygen administration to premature infants suppresses retinal VEGF expression and results in the catastrophic vessel loss associated with retinopathy of prematurity. A study investigating the development of the retinal vasculature in mice (see related article on pages 50–57) demonstrates that specific activation of VEGF receptor-1 by placental growth factor-1 protects against oxygen-induced vessel loss without stimulating vascular proliferation and neovascularization.