Placenta growth factor and vascular endothelial growth factor are co-expressed during early embryonic development

A Single Trophoblast Layer Acts as the Gatekeeper at the Endothelial-Hematopoietic Crossroad in the Placenta

During embryonic development the placental vasculature acts as a major hematopoietic niche, where endothelial to hematopoietic transition ensures emergence of hematopoietic stem cells (HSCs). However, the molecular mechanisms that regulate the placental hematoendothelial niche are poorly understood. Using a parietal trophoblast giant cell (TGC)-specific knockout mouse model and single-cell RNA-sequencing, we show that the paracrine factors secreted by the TGCs are critical in the development of this niche. Disruptions in the TGC-specific paracrine signaling leads to the loss of HSC population and the concomitant expansion of a KDR+/DLL4+/PROM1+ hematoendothelial cell-population in the placenta. Combining single-cell transcriptomics and receptor-ligand pair analyses, we also define the parietal TGC-dependent paracrine signaling network and identify Integrin signaling as a fundamental regulator of this process. Our study elucidates novel mechanisms by which non-autonomous signaling from the primary parietal TGCs maintain the delicate placental hematopoietic-angiogenic balance and ensures embryonic and extraembryonic development.

Hemostasis in the Pregnant Woman, the Placenta, the Fetus, and the Newborn Infant

The hemostasis system is composed of procoagulant, anticoagulant, and fibrinolytic proteins that interact with endothelial and blood cells and with each other in a complex system of checks and balances to maintain blood flow while preventing both hemorrhage and thrombosis. Pregnancy is a unique physiological state in which biological alterations predispose both mother and fetus to both bleeding and clotting. The placenta is a vascular interface for maternal and fetal blood exchange which predisposes the mother to hemorrhage. Maternal hemostasis presents a compensatory hypercoagulability including elevated factor VIII, von Willebrand factor, fibrinogen and thrombin generation, decreased thrombin regulation with resistance to activated protein C and decreased free protein S, and decreased fibrinolysis with increased plasminogen activator inhibitors. The placental vascular surface is of fetal trophoblastic origin that derives many characteristics of endothelium but differs in that tissue factor is constitutively expressed. Ontogeny of fetal hemostasis is characteristic. Platelets, von Willebrand factor, factor VIII, and fibrinogen are expressed and mature early in gestation, while vitamin K-dependent and contact factors exhibit delayed development. The fetal hemostatic system has a decreased capacity to generate or regulate thrombin, resulting in a fragile balance with little capacity to compensate under stress conditions, particularly in the infant born prematurely. Dysfunction of the maternal/placental/fetal unit gives rise to gestational disorders including preeclampsia, fetal growth restriction, placental abruption, and premature delivery. Knowledge of normal hemostasis levels and function are critical to evaluate bleeding or clotting syndromes in the pregnant woman and her fetus or newborn infant.

PlGF Immunological Impact during Pregnancy

During pregnancy, the mother’s immune system has to tolerate the persistence of paternal alloantigens without affecting the anti-infectious immune response. Consequently, several mechanisms aimed at preventing allograft rejection, occur during a pregnancy. In fact, the early stages of pregnancy are characterized by the correct balance between inflammation and immune tolerance, in which proinflammatory cytokines contribute to both the remodeling of tissues and to neo-angiogenesis, thus, favoring the correct embryo implantation. In addition to the creation of a microenvironment able to support both immunological privilege and angiogenesis, the trophoblast invades normal tissues by sharing the same behavior of invasive tumors. Next, the activation of an immunosuppressive phase, characterized by an increase in the number of regulatory T (Treg) cells prevents excessive inflammation and avoids fetal immuno-mediated rejection. When these changes do not occur or occur incompletely, early pregnancy failure follows. All these events are characterized by an increase in different growth factors and cytokines, among which one of the most important is the angiogenic growth factor, namely placental growth factor (PlGF). PlGF is initially isolated from the human placenta. It is upregulated during both pregnancy and inflammation. In this review, we summarize current knowledge on the immunomodulatory effects of PlGF during pregnancy, warranting that both innate and adaptive immune cells properly support the early events of implantation and placental development. Furthermore, we highlight how an alteration of the immune response, associated with PlGF imbalance, can induce a hypertensive state and lead to the pre-eclampsia (PE).

Association between fertility treatments and early placentation markers

INTRODUCTION

Pregnancies resulting from fertility treatments are at higher risk of placenta-mediated complications. Hence, we aimed to estimate the association between fertility treatment and levels of first-trimester markers of placentation.

METHODS

We conducted a cohort study in an academic center from 03/2011 to 12/2014. Adult nulliparous women with singleton pregnancies were recruited between 11 ^+ 0 and 13 ^+ 6 weeks of gestation. Data on maternal characteristics, medical history, and pregnancies conceived through fertility treatments (whether ovulation agents, insemination or assisted reproductive technologies) were collected. Maternal serum concentrations of PlGF, sFlt-1, PAPP-A, AFP, and free β-hCG were obtained, and notches and UtA-PI were measured using Doppler ultrasound. Mean Multiple of the Medians (MoM) and frequencies were computed to estimate the mean differences (MD) or risk ratios (RR) comparing fertility treatment to spontaneous pregnancies.

RESULTS

427 (9%) pregnancies out of 4815 were conceived through fertility treatments, using ovulation agents (n = 233, 5%), insemination (n = 174, 4%) and/or assisted reproductive technologies (n = 85, 2%). The latter were associated with significantly lower log₁₀PAPP-A MoM (adjusted MD: -0.02, 95%CI: -0.04 to -0.01), lower log₁₀PlGF MoM (adjusted MD: -0.04, 95%CI: -0.06 to -0.01) and higher log₁₀free β-hCG MoM (adjusted MD: 0.05, 95%CI: 0.01 to 0.09) compared to spontaneous pregnancies. Ovulation agents and insemination were associated with the presence of notches (adjusted RR: 1.24, 95%CI: 1.14 to 1.35; and 1.27, 95%CI: 1.15 to 1.42, respectively) and higher log₁₀UtA-PI MoM (adjusted MD: 0.16, 95%CI: 0.08 to 0.24; and 0.17, 95%CI: 0.07 to 0.27, respectively) than spontaneous pregnancies.

CONCLUSION

Fertility treatments are associated with significant variations in markers of placentation.

Maternal high-fat diet sex-specifically alters placental morphology and transcriptome in rats: Assessment by next-generation sequencing

INTRODUCTION

Maternal nutrition is an extremely important health issue. We evaluated the impact of maternal high fat diet (HFD) on pregnancy outcomes, elucidated how the rat placenta and fetus respond to diet manipulation based on fetal sex, and identified candidate genes and pathways.

METHODS

Rats were fed a normal or HFD diet for 10 weeks before conception and during gestation. The placenta was collected on gestational day 21 and sexed. Placental histology was analyzed and placental candidate genes and pathways were identified using whole-genome RNA next-generation sequencing.

RESULTS

Pup weights in both sexes from HFD dams were reduced. The weight of the placenta from the HFD group was also decreased in both sexes, but changes in placental layer distributions were only significant for female fetuses. Maternal HFD altered the placental transcriptome in a sex-specific manner. Activation of the placental renin-angiotensin system (RAS) by maternal HFD was associated with fetal growth restriction in both fetal sexes.

CONCLUSIONS

The placenta reacts to maternal HFD by altering the placental layer distribution and gene expression in a sex-specific manner. The male placenta in late gestation is thought to exhibit greater plasticity relative to the female placenta; however, fetuses of both sexes exhibited similar growth restriction. Our data reveal an association between the placental RAS and HFD-induced fetal growth restriction.

Identification of potential target genes associated with the reversion of androgen-dependent skeletal muscle atrophy

Muscle wasting or atrophy is extensively associated with human systemic diseases including diabetes, cancer, and kidney failure. Accumulating evidence from transcriptional profiles has noted that a common set of genes, termed atrogenes, is modulated in atrophying muscles. However, the transcriptional changes that trigger the reversion or attenuation of muscle atrophy have not been characterized at the molecular level until now. Here, we applied cDNA microarrays to investigate the transcriptional response of androgen-sensitive Levator ani muscle (LA) during atrophy reversion. Most of the differentially expressed genes behaved as atrogenes and responded to castration-induced atrophy. However, seven genes (APLN, DUSP5, IGF1, PIK3IP1, KLHL38, PI15, and MKL1) did not respond to castration but instead responded exclusively to testosterone replacement. Considering that almost all proteins encoded by these genes are associated with the reversion of atrophy and may function as regulators of cell proliferation/growth, our results provide new perspectives on the existence of anti-atrogenes.

Loss of placental growth factor ameliorates maternal hypertension and preeclampsia in mice

Preeclampsia remains a clinical challenge due to its poorly understood pathogenesis. A prevailing notion is that increased placental production of soluble fms-like tyrosine kinase-1 (sFlt-1) causes the maternal syndrome by inhibiting proangiogenic placental growth factor (PlGF) and VEGF. However, the significance of PlGF suppression in preeclampsia is uncertain. To test whether preeclampsia results from the imbalance of angiogenic factors reflected by an abnormal sFlt-1/PlGF ratio, we studied PlGF KO (Pgf-/-) mice and noted that the mice did not develop signs or sequelae of preeclampsia despite a marked elevation in circulating sFLT-1. Notably, PlGF KO mice had morphologically distinct placentas, showing an accumulation of junctional zone glycogen. We next considered the role of placental PlGF in an established model of preeclampsia (pregnant catechol-O-methyltransferase-deficient [COMT-deficient] mice) by generating mice with deletions in both the Pgf and Comt genes. Deletion of placental PlGF in the context of COMT loss resulted in a reduction in maternal blood pressure and increased placental glycogen, indicating that loss of PlGF might be protective against the development of preeclampsia. These results identify a role for PlGF in placental development and support a complex model for the pathogenesis of preeclampsia beyond an angiogenic factor imbalance.

Murine embryos exposed to human endometrial MSCs-derived extracellular vesicles exhibit higher VEGF/PDGF AA release, increased blastomere count and hatching rates

Endometrial Mesenchymal Stromal Cells (endMSCs) are multipotent cells with immunomodulatory and pro-regenerative activity which is mainly mediated by a paracrine effect. The exosomes released by MSCs have become a promising therapeutic tool for the treatment of immune-mediated diseases. More specifically, extracellular vesicles derived from endMSCs (EV-endMSCs) have demonstrated a cardioprotective effect through the release of anti-apoptotic and pro-angiogenic factors. Here we hypothesize that EV-endMSCs may be used as a co-adjuvant to improve in vitro fertilization outcomes and embryo quality. Firstly, endMSCs and EV-endMSCs were isolated and phenotypically characterized for in vitro assays. Then, in vitro studies were performed on murine embryos co-cultured with EV-endMSCs at different concentrations. Our results firstly demonstrated a significant increase on the total blastomere count of expanded murine blastocysts. Moreover, EV-endMSCs triggered the release of pro-angiogenic molecules from embryos demonstrating an EV-endMSCs concentration-dependent increase of VEGF and PDGF-AA. The release of VEGF and PDGF-AA by the embryos may indicate that the beneficial effect of EV-endMSCs could be mediating not only an increase in the blastocyst’s total cell number, but also may promote endometrial angiogenesis, vascularization, differentiation and tissue remodeling. In summary, these results could be relevant for assisted reproduction being the first report describing the beneficial effect of human EV-endMSCs on embryo development.

Molecular Regulation of Sprouting Angiogenesis

The term angiogenesis arose in the 18th century. Several studies over the next 100 years laid the groundwork for initial studies performed by the Folkman laboratory, which were at first met with some opposition. Once overcome, the angiogenesis field has flourished due to studies on tumor angiogenesis and various developmental models that can be genetically manipulated, including mice and zebrafish. In addition, new discoveries have been aided by the ability to isolate primary endothelial cells, which has allowed dissection of various steps within angiogenesis. This review will summarize the molecular events that control angiogenesis downstream of biochemical factors such as growth factors, cytokines, chemokines, hypoxia-inducible factors (HIFs), and lipids. These and other stimuli have been linked to regulation of junctional molecules and cell surface receptors. In addition, the contribution of cytoskeletal elements and regulatory proteins has revealed an intricate role for mobilization of actin, microtubules, and intermediate filaments in response to cues that activate the endothelium. Activating stimuli also affect various focal adhesion proteins, scaffold proteins, intracellular kinases, and second messengers. Finally, metalloproteinases, which facilitate matrix degradation and the formation of new blood vessels, are discussed, along with our knowledge of crosstalk between the various subclasses of these molecules throughout the text. Compr Physiol 8:153-235, 2018.

The fibrinolysis inhibitor α2-antiplasmin restricts lymphatic remodelling and metastasis in a mouse model of cancer

Remodelling of lymphatic vessels in tumours facilitates metastasis to lymph nodes. The growth factors VEGF-C and VEGF-D are well known inducers of lymphatic remodelling and metastasis in cancer. They are initially produced as full-length proteins requiring proteolytic processing in order to bind VEGF receptors with high affinity and thereby promote lymphatic remodelling. The fibrinolytic protease plasmin promotes processing of VEGF-C and VEGF-D in vitro, but its role in processing them in cancer was unknown. Here we explore plasmin's role in proteolytically activating VEGF-D in vivo, and promoting lymphatic remodelling and metastasis in cancer, by co-expressing the plasmin inhibitor α₂-antiplasmin with VEGF-D in a mouse tumour model. We show that α₂-antiplasmin restricts activation of VEGF-D, enlargement of intra-tumoural lymphatics and occurrence of lymph node metastasis. Our findings indicate that the fibrinolytic system influences lymphatic remodelling in tumours which is consistent with previous clinicopathological observations correlating fibrinolytic components with cancer metastasis.

Placental growth factor: What hematologists need to know

Although first identified in placenta, the angiogenic factor known as placental growth factor (PlGF) can be widely expressed in ischemic or damaged tissues. Recent studies have indicated that PlGF is a relevant factor in the pathobiology of blood diseases including hemoglobinopathies and hematologic malignancies. Therapies for such blood diseases may one day be based upon these and ongoing investigations into the role of PlGF in sickle cell disease, acute and chronic leukemias, and complications related to hematopoietic cell transplantation. In this review, we summarize recent studies regarding the potential role of PlGF in blood disorders and suggest avenues for future research.

[Histological hanges in the placenta and vascularization of its villi in early- and late-onset preeclampsia]

AIM

to make a comparative histological study of the placenta and a morphometric analysis of its terminal villi in early- and late-onset preeclampsia.

MATERIAL AND METHODS

Placentae from patients whose pregnancy had been complicated by the development of early- (n=26) or late-onset (n=84) preeclampsia were examined. A control group comprised placentae from 28 patients with physiological pregnancy and no extragenital diseases. The authors made a comparative histological study of placental tissue and a morphometric analysis of the terminal villi using the sections immunohistochemically stained for CD31.

RESULTS

It was determined that there was a preponderance of branching angiogenesis in the preeclamptic chorionic villi and an increase in the number of syncytial nodules and microcysts in the septae in late-onset preeclampsia. Morphometric analysis of immunohistochemical placental specimens established a reduction in the sizes and vascularization indicators of terminal villi that determine the development of placental hypoxia and are more pronounced in cases of early-onset preeclampsia.

Placenta: the forgotten organ

The placenta sits at the interface between the maternal and fetal vascular beds where it mediates nutrient and waste exchange to enable in utero existence. Placental cells (trophoblasts) accomplish this via invading and remodeling the uterine vasculature. Amazingly, despite being of fetal origin, trophoblasts do not trigger a significant maternal immune response. Additionally, they maintain a highly reliable hemostasis in this extremely vascular interface. Decades of research into how the placenta differentiates itself from embryonic tissues to accomplish these and other feats have revealed a previously unappreciated level of complexity with respect to the placenta's cellular composition. Additionally, novel insights with respect to roles played by the placenta in guiding fetal development and metabolism have sparked a renewed interest in understanding the interrelationship between fetal and placental well-being. Here, we present an overview of emerging research in placental biology that highlights these themes and the importance of the placenta to fetal and adult health.

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.

Development of the hemochorial maternal vascular spaces in the placenta through endothelial and vasculogenic mimicry

The maternal vasculature within the placenta in primates and rodents is unique because it is lined by fetal cells of the trophoblast lineage and not by maternal endothelial cells. In addition to trophoblast cells that invade the uterine spiral arteries that bring blood into the placenta, other trophoblast subtypes sit at different levels of the vascular space. In mice, at least five distinct subtypes of trophoblast cells have been identified which engage maternal endothelial cells on the arterial and venous frontiers of the placenta, but which also form the channel-like spaces within it through a process analogous to formation of blood vessels (vasculogenic mimicry). These cells are all large, post-mitotic trophoblast giant cells. In addition to assuming endothelial cell-like characteristics (endothelial mimicry), they produce dozens of different hormones that are thought to regulate local and systemic maternal adaptations to pregnancy. Recent work has identified distinct molecular pathways in mice that regulate the morphogenesis of trophoblast cells on the arterial and venous sides of the vascular circuit that may be analogous to specification of arterial and venous endothelial cells.

Embryonic stem cell-derived trophoblast differentiation: a comparative review of the biology, function, and signaling mechanisms

The development of the placenta is imperative for successful pregnancy establishment, yet the earliest differentiation events of the blastocyst-derived trophectoderm that forms the placenta remain difficult to study in humans. Human embryonic stem cells (hESC) display a unique ability to form trophoblast cells when induced to differentiate either by the addition of exogenous BMP4 or by the formation of cellular aggregates called embryoid bodies. While mouse trophoblast stem cells (TSC) have been isolated from blastocyst outgrowths, mouse ESC do not spontaneously differentiate into trophoblast cells. In this review, we focus on addressing the similarities and differences between mouse TSC differentiation and hESC-derived trophoblast differentiation. We discuss the functional and mechanistic diversity that is found in different species models. Of central importance are the unique signaling events that trigger downstream gene expression that create specific cellular fate decisions. We support the idea that we must understand the nuances that hESC differentiation models display so that investigators can choose the appropriate model system to fit experimental needs.

Alcohol-induced premature permeability in mouse placenta-yolk sac barriers in vivo

OBJECTIVE

Acute alcohol exposure induces malformation and malfunction of placenta-yolk sac tissues in rodents, reducing the labyrinth zone in the placenta and altering the permeability and fluidity of the cell membrane. During normal mouse placentation the cells line up in an optimal way to form a hemotrichorial placenta where layers II and III are connected through gap junctions. These act as molecular sieves that limit the passage of large molecules. PlGF is a developmentally regulated protein that controls the passage of molecules in the vasculosyncytial membranes and media of large blood vessels in the placental villi. In addition to the chorioallontoic placenta, rodents also have another type of placenta that consists of Reichert's membrane within the trophoblast cell layer on the maternal side and the parietal endodermal cells on the embryonic site. This forms a separate materno-fetal transport system. We study here whether alcohol affects these two placental barriers, leading to placental malfunction that in turn diminishes the nutrient supply to the embryo.

STUDY DESIGN

CD-1 mice received two intraperitoneal injections of 3 g/kg ethanol at 4 h intervals at 8.75 days post coitum (dpc). The placentas were collected on 9.5, 11.5 and 14.5 dpc and used for histopathological protein studies. Hemotrichorial cell layer structure interactions through connective tissue and gap junction were analyzed by electron microscopy. The permeability of the feto-maternal barrier was visualized with Evans Blue.

RESULTS

VEGF, a permeability inducer, was found to be up-regulated in the mouse placenta after acute alcohol exposure, and permeability was also affected by altered structures in the barriers that separate the feto-maternal blood circulation which destroyed the gap junctions in the hemotrichorial cell layer, reduced the thickness of Reichert's membrane and interfered with with Reichert's trophoblast/Reichert's parietal interaction. These defects together could have caused the permeability malfunction of the placenta-yolk sac tissues as visualized and quantified here by Evans Blue leakage.

CONCLUSIONS

An altered PlGF/VEGF ratio together with barrier malformation may contribute to placental malfunction by altering the permeability of the feto-maternal barriers. Further studies are needed in order to show whether premature permeability is involved in the intrauterine growth restriction observed in human FAS embryos.

The discovery of placenta growth factor and its biological activity

Angiogenesis is a complex biological phenomenon crucial for a correct embryonic development and for post-natal growth. In adult life, it is a tightly regulated process confined to the uterus and ovary during the different phases of the menstrual cycle and to the heart and skeletal muscles after prolonged and sustained physical exercise. Conversly, angiogenesis is one of the major pathological changes associated with several complex diseases like cancer, atherosclerosis, arthritis, diabetic retinopathy and age-related macular degeneration. Among the several molecular players involved in angiogenesis, some members of VEGF family, VEGF-A, VEGF-B and placenta growth factor (PlGF), and the related receptors VEGF receptor 1 (VEGFR-1, also known as Flt-1) and VEGF receptor 2 (VEGFR-2, also known as Flk-1 in mice and KDR in human) have a decisive role. In this review, we describe the discovery and molecular characteristics of PlGF, and discuss the biological role of this growth factor in physiological and pathological conditions.

Placenta accreta: pathogenesis of a 20th century iatrogenic uterine disease

Placenta accreta refers to different grades of abnormal placental attachment to the uterine wall, which are characterised by invasion of trophoblast into the myometrium. Placenta accreta has only been described and studied by pathologists for less than a century. The fact that the first detailed description of a placenta accreta happened within a couple of decades of major changes in the caesarean surgical techniques is highly suggestive of a direct relationship between prior uterine surgery and abnormal placenta adherence. Several concepts have been proposed to explain the abnormal placentation in placenta accreta including a primary defect of the trophoblast function, a secondary basalis defect due to a failure of normal decidualization and more recently an abnormal vascularisation and tissue oxygenation of the scar area. The vast majority of placenta accreta are found in women presenting with a previous history of caesarean section and a placenta praevia. Recent epidemiological studies have also found that the strongest risk factor for placenta praevia is a prior caesarean section suggesting that a failure of decidualization in the area of a previous uterine scar can have an impact on both implantation and placentation. Ultrasound studies of uterine caesarean section scar have shown that large and deep myometrial defects are often associated with absence of re-epithelialisation of the scar area. These findings support the concept of a primary deciduo-myometrium defect in placenta accreta, exposing the myometrium and its vasculature below the junctional zone to the migrating trophoblast. The loss of this normal plane of cleavage and the excessive vascular remodelling of the radial and arcuate arteries can explain the in-vivo findings and the clinical consequence of placenta accreta. Overall these data support the concept that abnormal decidualization and trophoblastic changes of the placental bed in placenta accreta are secondary to the uterine scar and thus entirely iatrogenic.

Placental growth factor contributes to bronchial neutrophilic inflammation and edema in allergic asthma

Placental growth factor (PlGF) and its receptor vascular endothelial growth factor receptor 1 (VEGFR1) play an important role in pathological conditions related to angiogenesis, vascular leakage, and inflammation. This study investigated their contributions to inflammation and the formation of edema in allergic asthma. The expression of PlGF and VEGFR1 was measured in induced sputum of patients with asthma (n = 11) and healthy subjects (n = 11), and in bronchial biopsies of house dust mite (HDM)-allergic patients stimulated with HDM allergens. The effects of the endonasal administration of human PlGF-2 and PlGF deficiency on inflammation and edema were evaluated in a murine model of allergic asthma. The migration of human neutrophils in response to hPlGF-2 was tested in vitro. The expression of PlGF and VEGFR1 was significantly higher in the sputum of patients with asthma, and in Der p 1-induced PlGF in biopsies from HDM-allergic patients. PlGF was increased in the bronchi of ovalbumin (OVA)-challenged mice compared with control mice (65 ± 17 pg/mg versus 18 ± 1 pg/mg, respectively; P < 0.01), and VEGFR1 was expressed in bronchial epithelium, endothelium (control mice), and inflammatory cells (OVA-challenged mice). The endonasal instillation of hPlGF-2 in wild-type, OVA-challenged mice led to an increase in bronchial neutrophils, lung tissue wet/dry ratio, and IL-17. PlGF-deficient mice showed lower numbers of BAL-infiltrating neutrophils, a reduced lung wet/dry ratio, and lower production of IL-17, macrophage inflammatory protein-2, and granulocyte chemotactic protein-2/LPS-induced chemokine compared with wild-type, OVA-challenged mice. hPlGF-2 induced the migration of human neutrophils in vitro in a VEGFR1-dependent way. PlGF and its receptor VEGFR1 are up-regulated in allergic asthma and play a proinflammatory role by inducing tissue edema, and increasing tissue neutrophilia and the production of IL-17.

Localization of C-Fos-Induced Growth Factor (Figf) mRNA Expression in the Mouse Uterus during Implantation

The purpose of this study was to characterize the localization of Figf mRNA in the mouse uterus during embryo implantation. Strong Figf mRNA hybridization signals were seen in the primary decidual zone just after the onset of implantation from Days 4.5–6.5. On Day 7.5, this expression continued around the concept us, but in addition we observed high expression of Figf mRNA in the endothelial cells that line the forming vascular sinusoids in the lateral me some trial decidua. Interestingly, on Days 8.5 this high expression continued in the endothelial cells of sinusoids in the lateral me some trial decidual tissue but not in the decidual cells surrounding the concept us. As implantation and placental development finished, Figf mRNA expression remained in the endothelial cells of the sinusoids and spiral arterioles of the decidua basalis. Interestingly, Flt4 mRNA was localized to the endothelial cells lining the sinusoids that form during implantation. Since the endothelial cells of the me some trial sinusoids exhibit a high level of proliferation, we speculate that FIGF-FLT4 signaling may play a role in their formation and function during implantation. This work will provide a basis for further research on the potential role of FIGF-FLT4 signaling in endometrial angiogenesis during implantation in mice.

Placental growth factor regulates cardiac adaptation and hypertrophy through a paracrine mechanism

RATIONALE

Paracrine growth factor-mediated crosstalk between cardiac myocytes and nonmyocytes in the heart is critical for programming adaptive cardiac hypertrophy in which myocyte size, capillary density, and the extracellular matrix function coordinately.

OBJECTIVE

To examine the role that placental growth factor (PGF) plays in the heart as a paracrine regulator of cardiac adaptation to stress stimulation.

METHODS AND RESULTS

PGF is induced in the heart after pressure-overload stimulation, where it is expressed in both myocytes and nonmyocytes. We generated cardiac-specific and adult inducible PGF-overexpressing transgenic mice and analyzed Pgf(-/-) mice to examine the role that this factor plays in cardiac disease and paracrine signaling. Although PGF transgenic mice did not have a baseline phenotype or a change in capillary density, they did exhibit a greater cardiac hypertrophic response, a greater increase in capillary density, and increased fibroblast content in the heart in response to pressure-overload stimulation. PGF transgenic mice showed a more adaptive type of cardiac growth that was protective against signs of failure with pressure overload and neuroendocrine stimulation. Antithetically, Pgf(-/-) mice rapidly died of heart failure within 1 week of pressure overload, they showed an inability to upregulate angiogenesis, and they showed significantly less fibroblast activity in the heart. Mechanistically, we show that PGF does not have a direct effect on cardiomyocytes but works through endothelial cells and fibroblasts by inducing capillary growth and fibroblast proliferation, which secondarily support greater cardiac hypertrophy through intermediate paracrine growth factors such as interleukin-6.

CONCLUSIONS

PGF is a secreted factor that supports hypertrophy and cardiac function during pressure overload by affecting endothelial cells and fibroblasts that in turn stimulate and support the myocytes through additional paracrine factors.

Placental vasculogenesis is regulated by keratin-mediated hyperoxia in murine decidual tissues

The mammalian placenta represents the interface between maternal and embryonic tissues and provides nutrients and gas exchange during embryo growth. Recently, keratin intermediate filament proteins were found to regulate embryo growth upstream of the mammalian target of rapamycin pathway through glucose transporter relocalization and to contribute to yolk sac vasculogenesis through altered bone morphogenetic protein 4 signaling. Whether keratins have vital functions in extraembryonic tissues is not well understood. Here, we report that keratins are essential for placental function. In the absence of keratins, we find hyperoxia in the decidual tissue directly adjacent to the placenta, because of an increased maternal vasculature. Hyperoxia causes impaired vasculogenesis through defective hypoxia-inducible factor 1α and vascular endothelial growth factor signaling, resulting in invagination defects of fetal blood vessels into the chorion. In turn, the reduced labyrinth, together with impaired gas exchange between maternal and embryonic blood, led to increased hypoxia in keratin-deficient embryos. We provide evidence that keratin-positive trophoblast secretion of prolactin-like protein a (Prlpa) and placental growth factor (PlGF) during decidualization are altered in the absence of keratins, leading to increased infiltration of uterine natural killer cells into placental vicinity and increased vascularization of the maternal decidua. Our findings suggest that keratin mutations might mediate conditions leading to early pregnancy loss due to hyperoxia in the decidua.

Accreta complicating complete placenta previa is characterized by reduced systemic levels of vascular endothelial growth factor and by epithelial-to-mesenchymal transition of the invasive trophoblast

OBJECTIVE

We sought to characterize serum angiogenic factor profile of women with complete placenta previa and determine if invasive trophoblast differentiation characteristic of accreta, increta, or percreta shares features of epithelial-to-mesenchymal transition.

STUDY DESIGN

We analyzed gestational age-matched serum samples from 90 pregnant women with either complete placenta previa (n = 45) or uncomplicated pregnancies (n = 45). Vascular endothelial growth factor (VEGF), placental growth factor, and soluble form of fms-like-tyrosine-kinase-1 were immunoassayed. VEGF and phosphotyrosine immunoreactivity was surveyed in histological specimens relative to expression of vimentin and cytokeratin-7.

RESULTS

Women with previa and invasive placentation (accreta, n = 5; increta, n = 6; percreta, n = 2) had lower systemic VEGF (invasive previa: median 0.8 [0.02-3.4] vs control 6.5 [2.7-10.5] pg/mL, P = .02). VEGF and phosphotyrosine immunostaining predominated in the invasive extravillous trophoblasts that coexpressed vimentin and cytokeratin-7, an epithelial-to-mesenchymal transition feature and tumorlike cell phenotype.

CONCLUSION

Lower systemic free VEGF and a switch of the interstitial extravillous trophoblasts to a metastable cell phenotype characterize placenta previa with excessive myometrial invasion.

Adenoviral delivery of VEGF121 early in pregnancy prevents spontaneous development of preeclampsia in BPH/5 mice

An imbalance in circulating proangiogenic and antiangiogenic factors is postulated to play a causal role in preeclampsia (PE). We have described an inbred mouse strain, BPH/5, which spontaneously develops a PE-like syndrome including late-gestational hypertension, proteinuria, and poor feto-placental outcomes. Here we tested the hypothesis that an angiogenic imbalance during pregnancy in BPH/5 mice leads to the development of PE-like phenotypes in this model. Similar to clinical findings, plasma from pregnant BPH/5 showed reduced levels of free vascular endothelial growth factor (VEGF) and placental growth factor (PGF) compared to C57BL/6 controls. This was paralleled by a marked decrease in VEGF protein and Pgf mRNA in BPH/5 placentae. Surprisingly, antagonism by the soluble form of the FLT1 receptor (sFLT1) did not appear to be the cause of this reduction, as sFLT1 levels were unchanged or even reduced in BPH/5 compared to controls. Adenoviral-mediated delivery of VEGF(121) (Ad-VEGF) via tail vein at embryonic day 7.5 normalized both the plasma-free VEGF levels in BPH/5 and restored the in vitro angiogenic capacity of serum from these mice. Ad-VEGF also reduced the incidence of fetal resorptions and prevented the late-gestational spike in blood pressure and proteinuria observed in BPH/5. These data underscore the importance of dysregulation of angiogenic factors in the pathogenesis of PE and suggest the potential utility of early proangiogenic therapies in treating this disease.

Function of IRE1 alpha in the placenta is essential for placental development and embryonic viability

Inositol requiring enzyme-1 (IRE1), a protein located on the endoplasmic reticulum (ER) membrane, is highly conserved from yeast to humans. This protein is activated during ER stress and induces cellular adaptive responses to the stress. In mice, IRE1alpha inactivation results in widespread developmental defects, leading to embryonic death after 12.5 days of gestation. However, the cause of this embryonic lethality is not fully understood. Here, by using in vivo imaging analysis and conventional knockout mice, respectively, we showed that IRE1alpha was activated predominantly in the placenta and that loss of IRE1alpha led to reduction in vascular endothelial growth factor-A and severe dysfunction of the labyrinth in the placenta, a highly developed tissue of blood vessels. We also used a conditional knockout strategy to demonstrate that IRE1alpha-deficient embryos supplied with functionally normal placentas can be born alive. Fetal liver hypoplasia thought to be responsible for the embryonic lethality of IRE1alpha-null mice was virtually absent in rescued IRE1alpha-null pups. These findings reveal that IRE1alpha plays an essential function in extraembryonic tissues and highlight the relationship of physiological ER stress and angiogenesis in the placenta during pregnancy in mammals.

Vasoactivity to and endogenous release of vascular endothelial growth factor in the in vitro perfused human placental lobule from pregnancies complicated by preeclampsia

Vascular endothelial growth factor (VEGF) is a potent, physiologically relevant, vasodilator of the human term fetoplacental vasculature of placental lobules from normal pregnancy. There is evidence that VEGF and its receptors are dysregulated in preeclampsia (PE). Here, we used dual perfusion of the human placental lobule to test the hypothesis that the VEGF vasodilatory effect on the fetoplacental circulation is altered in PE and examined how vascular responsiveness relates to circulating levels of free VEGF in fetal sera in this disease. Umbilical cord sera and fetal venous perfusate concentrations of free VEGF from pregnancies complicated with PE were significantly lower compared to the normal group (P<0.05 and P<0.01, respectively). There was elevated in vitro placental release of the sequestrating soluble receptor, sVEGFR-1, into the fetal-side perfusate with PE compared to the normal group (P<0.05). The umbilical sera PlGF-1 level was higher by an order of magnitude in the fetal circulation in PE compared to normal pregnancy (P<0.0001), with the placenta appearing to contribute appreciably to these levels. Placental net contribution to maternal systemic free VEGF levels appeared to be negligible in both groups. sVEGFR-1 levels were elevated in the maternal-side venous perfusate with PE compared to the normal pregnancy (P<0.01). Perfused lobules from PE pregnancy exhibited an enhanced fetoplacental vasodilatory response to exogenous VEGF (P<0.001), with a longer recovery time (P<0.05), compared to the normal control group. Extrapolation of our combined functional and biochemical data suggests that a decrease in the in vivo circulating levels of free VEGF in PE is likely to contribute to compromised fetoplacental vascular patency in this disease.

The discovery of the placental growth factor and its role in angiogenesis: a historical review

The placental growth factor (PlGF) is an angiogenic protein belonging to the vascular endothelial growth factor (VEGF) family, which was discovered in 1991 by an Italian scientist, Maria Graziella Persico. Dr Persico cloned and purified PlGF and determined its structure by crystallography resolution. Furthermore, she identified VEGF receptor-1 (VEGFR-1) as the receptor for PlGF, and in collaboration with Dr Peter Carmeliet in Leuven, she generated evidence that loss of PlGF does not affect development, reproduction, or postnatal life. PlGF is expressed primarily in the placenta and is up-regulated in several pathological conditions, although its role is still controversial. Some data in literature reported that PlGF enhances pathological angiogenesis by initiating a cross-talk between VEGFR-1 and VEGFR-2, whereas other studies did not confirm these findings. Regarding the potential therapeutic employment of PlGF, recent evidence has shown that an anti-PlGF antibody may act as a potent antiangiogenic agent, and that it has the advantage of minor toxicity when combined with anti-VEGF strategies.

Adverse adipose phenotype and hyperinsulinemia in gravid mice deficient in placental growth factor

Pregnancy-induced metabolic changes are regulated by signals from an expanded adipose organ. Placental growth factor (PlGF), acting through vascular endothelial growth factor receptor-1, may be among those signals. There is a steep rise in circulating PlGF during normal pregnancy, which is repressed in gravidas who develop preeclampsia. PlGF-deficiency in mice impairs adipose vascularization and development. Here we studied young-adult PlGF-deficient (PlGF(-/-)) and wild-type mice on a high-fat diet in the nongravid state and at embryonic day (E) 13.5 or E18.5 of gestation. Litter size and weight were normal, but E18.5 placentas were smaller in PlGF(-/-) pregnancies. PlGF(-/-) mice showed altered intraadipose dynamics, with the following: 1) less blood vessels and fewer brown, uncoupling protein (UCP)-1-positive, adipocytes in white sc and perigonadal fat compartments and 2) white adipocyte hypertrophy. The mRNA expression of beta(3)-adrenergic receptors, peroxisome proliferator-activated receptor-gamma coactivator-1alpha, and UCP-1 was decreased accordingly. Moreover, PlGF(-/-) mice showed hyperinsulinemia. Pregnancy-associated changes were largely comparable in PlGF(-/-) and wild-type dams. They included expanded sc fat compartments and adipocyte hypertrophy, whereas adipose expression of key angiogenesis/adipogenesis (vascular endothelial growth factor receptor-1, peroxisome proliferator-activated receptor-gamma(2)) and thermogenesis (beta(3)-adrenergic receptors, peroxisome proliferator-activated receptor-gamma coactivator-1alpha, and UCP-1) genes was down-regulated; circulating insulin levels gradually increased during pregnancy. In conclusion, reduced adipose vascularization in PlGF(-/-) mice impairs adaptive thermogenesis in favor of energy storage, thereby promoting insulin resistance and hyperinsulinemia. Pregnancy adds to these changes by PlGF-independent mechanisms. Disturbed intraadipose dynamics is a novel mechanism to explain metabolic changes in late pregnancy in general and preeclamptic pregnancy in particular.

Placental growth factor-1 attenuates vascular endothelial growth factor-A-dependent tumor angiogenesis during beta cell carcinogenesis

Members of the vascular endothelial growth factor (VEGF) family are critical players in angiogenesis and lymphangiogenesis. Although VEGF-A has been shown to exert fundamental functions in physiologic and pathologic angiogenesis, the exact role of the VEGF family member placental growth factor (PlGF) in tumor angiogenesis has remained controversial. To gain insight into PlGF function during tumor angiogenesis, we have generated transgenic mouse lines expressing human PlGF-1 in the beta cells of the pancreatic islets of Langerhans (Rip1PlGF-1). In single-transgenic Rip1PlGF-1 mice, intra-insular blood vessels are found highly dilated, whereas islet physiology is unaffected. Upon crossing of these mice with the Rip1Tag2 transgenic mouse model of pancreatic beta cell carcinogenesis, tumors of double-transgenic Rip1Tag2;Rip1PlGF-1 mice display reduced growth due to attenuated tumor angiogenesis. The coexpression of transgenic PlGF-1 and endogenous VEGF-A in the beta tumor cells of double-transgenic animals causes the formation of low-angiogenic hPlGF-1/mVEGF-A heterodimers at the expense of highly angiogenic mVEGF-A homodimers resulting in diminished tumor angiogenesis and reduced tumor infiltration by neutrophils, known to contribute to the angiogenic switch in Rip1Tag2 mice. The results indicate that the ratio between the expression levels of two members of the VEGF family of angiogenic factors, PlGF-1 and VEGF-A, determines the overall angiogenic activity and, thus, the extent of tumor angiogenesis and tumor growth.

Genetic Deletion of Placenta Growth Factor in Mice Alters Uterine NK Cells

Placenta growth factor (PlGF; formerly PGF), a vascular endothelial growth factor gene family member, is expressed in human implantation sites by maternal uterine NK (uNK) and fetal trophoblast cells. Lower than normal concentrations of blood and urinary PlGF have been associated with impending onset of pre-eclampsia, a hypertensive disease of late human gestation characterized by limited intravascular trophoblast invasion. In pregnant rodents, delivery of the PlGF antagonist sFlt-1 or S-endoglin induces pre-eclampsia-like lesions. Mice genetically deleted in PlGF reproduce, but neither their implantation sites nor their uNK cell development are described. We combined real-time PCR of endometrium from nonpregnant and gestation day (gd)6-18 C57BL6/J (B6) mice with immunohistology to analyze PlGF expression in normal mouse pregnancy. To estimate the significance of uNK cell-derived PlGF, PlGF message was quantified in mesometrial decidua from pregnant alymphoid Rag2 null/common gamma chain null mice and in laser capture-microdissected B6 uNK cells. Histopathologic consequences from PlGF deletion were also characterized in the implantation sites from PlGF null mice. In B6, decidual PlGF expression rose between gd8-16. uNK cells were among several types of cells transcribing PlGF in decidualized endometrium. Immature uNK cells, defined by their low numbers of cytoplasmic granules, were the uNK cells displaying the greatest number of transcripts. PlGF deletion promoted the early differentiation high numbers of binucleate uNK cells (gd8) but had no other significant, morphometrically detectable impact on implantation sites. Thus, in mice, PlGF plays an important role in successful uNK cell proliferation and/or differentiation.

Shared and disparate components of the pathophysiologies of fetal growth restriction and preeclampsia

Intrauterine growth restriction (IUGR) and preeclampsia differ in their association with maternal disease but share a similar placental pathology. Moreover, mothers who have had pregnancies complicated by preeclampsia or IUGR are at elevated later-life cardiovascular risk. Why, then, do some women develop IUGR and others develop preeclampsia? In this clinical opinion, based on a review of the literature, we hypothesize that both women experiencing preeclampsia and IUGR enter pregnancy with some degree of endothelial dysfunction, a lesion that predisposes to shallow placentation. In our opinion, preeclampsia develops when abnormal placentation, through the mediator of elevated circulating cytokines, interacts with maternal metabolic syndrome, comprised of adiposity, insulin resistance/hyperglycemia, hyperlipidemia, and coagulopathy. IUGR develops in the absence of antenatal metabolic syndrome. Among these women, the baby is affected by shallow placentation but the mother does not develop clinically apparent disease. This conceptualization provides a testable framework for future etiologic studies of preeclampsia and IUGR.

Maternal medicine: Morphometric placental villous and vascular abnormalities in early- and late-onset pre-eclampsia with and without fetal growth restriction

OBJECTIVE

To evaluate placental morphology in pregnancies complicated by early- and late-onset pre-eclampsia (PET) with and without fetal growth restriction (FGR) using stereological techniques.

DESIGN

A total of 69 pregnant women were studied. Twenty women had pregnancies complicated by PET, 17 by FGR and 16 by both PET and FUR; the remaining 16 were from gestational-age-matched controls. Each group was further classified into early onset (<34 weeks) and late onsets (>34 weeks) based on gestational ages.

SETTING

NPIMR at Northwick Park and St Marks Hospital.

POPULATION

placentae from pregnant women.

METHODS

Formalin-fixed, wax-embedded sections stained with anti-CD34 antibodies and counterstained with haematoxylin.

MAIN OUTCOME MEASURES

Volumes, surface areas, lengths, diameters and shape factors of the villous tissues and fetal vasculature in the intermediate and terminal villi of all the groups studied.

RESULTS

Terminal villi volume and surface area were compromised in early-onset PET cases, late-onset PET had no impact on peripheral villi or vasculature features. The morphology of the vascular and villous subcomponents in the intermediate and terminal villi was significantly influenced by late-onset FGR, whereas early-onset FGR caused a reduction in placental weight. Length estimates were not influenced by PET, FGR or age of onset. Intermediate arteriole shape factor was significantly reduced in late-onset FGR.

CONCLUSIONS

Isolated early-onset PET was associated with abnormal placental morphology, but placentas from late-onset PET were morphologically similar to placentas from gestational-age-matched controls, confirming the existence of two subsets of this condition and supporting the hypothesis that late-onset PET is a maternal disorder and not a placental disease.

Essential role of B-Raf in ERK activation during extraembryonic development

The kinases of the Raf family have been intensively studied as activators of the mitogen-activated protein kinase kinase/extra-cellular signal-regulated kinase (ERK) module in regulated and deregulated proliferation. Genetic evidence that Raf is required for ERK activation in vivo has been obtained in lower organisms, which express only one Raf kinase, but was hitherto lacking in mammals, which express more than one Raf kinase. Ablation of the two best studied Raf kinases, B-Raf and Raf-1, is lethal at midgestation in mice, hampering the detailed study of the essential functions of these proteins. Here, we have combined conventional and conditional gene ablation to show that B-Raf is essential for ERK activation and for vascular development in the placenta. B-Raf-deficient placentae show complete absence of phosphorylated ERK and strongly reduced HIF-1alpha and VEGF levels, whereas all these parameters are normal in Raf-1-deficient placentae. In addition, neither ERK phosphorylation nor development are affected in B-raf-deficient embryos that are born alive obtained by epiblast-restricted gene inactivation. The data demonstrate that B-Raf plays a nonredundant role in ERK activation during extraembyronic mammalian development in vivo.

Isolated placental vessel response to vascular endothelial growth factor and placenta growth factor in normal and growth-restricted pregnancy

Vascular endothelial growth factor (VEGF) and placenta growth factor (PlGF) cause vasodilation. We examined the vasomotor response of isolated placental vessels to VEGF and PlGF in normal (group I) and intrauterine growth retardation (IUGR)-complicated pregnancy (group II). Rings of vessels were prepared in vitro and mounted on the vessel myograph plunged in tissue bath. The magnitude of dilation to increased doses of VEGF and PlGF has been studied. VEGF is a more potent vasodilator than PlGF. Both, VEGF- and PlGF-induced vasorelaxation was diminished in the IUGR (group II) nearly by half, compared to control (group I). Relative placental nitric oxide deficiency, or decreased sensitivity to VEGF and PlGF may contribute to the development of high impedance fetoplacental circulation.

Expression of placenta growth factor is regulated by both VEGF and hyperglycaemia via VEGFR-2

Placenta growth factor (PlGF) has been implicated in both physiological and pathological angiogenesis; however, little is known about what regulates its expression. In this study, retinal microvascular endothelial cells and pericytes were exposed to varying concentrations of VEGF and glucose and PlGF expression measured by RT-PCR and Western blotting. Both PlGF mRNA and protein were observed in unstimulated microvascular endothelial cells with only weak expression in pericytes. In endothelial cells, VEGF (100 ng/ml) and glucose (15 mM) induced an increase in expression of PlGF at both the mRNA and protein level while no effect was observed for pericytes. The increase in PlGF expression could be totally abolished by blocking VEGFR-2, and in the case of glucose by neutralising VEGF. VEGF-stimulated PlGF expression was largely inhibited by PD 98059, an inhibitor of mitogen-activated protein kinase (MAPK) and partially by GF 109203X, an inhibitor of protein kinase C (PKC), indicating that VEGF up-regulates PlGF expression via the MAPK signalling pathway and partially through PKC. Taken together, our findings suggest that VEGF orchestrates the contribution of PlGF in angiogenesis via more than one intracellular pathway and that hyperglycaemia, as occurs in diabetes, is an important regulator of PlGF expression via VEGF up-regulation.

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.

A critical role of placental growth factor in the induction of inflammation and edema formation

Angiogenesis is a prominent feature of a number of inflammatory human diseases, including rheumatoid arthritis, psoriasis, and cutaneous delayed-type hypersensitivity (DTH) reactions. Up-regulation of placental growth factor (PlGF), a member of the vascular endothelial growth factor (VEGF) family, has been found in several conditions associated with pathologic angiogenesis; however, its distinct role in the control of angiogenesis has remained unclear. To directly investigate the biologic function of PlGF in cutaneous inflammation and angiogenesis, DTH reactions were investigated in the ear skin of wild-type mice, of PlGF-deficient mice, and of transgenic mice with targeted overexpression of human PlGF-2 in epidermal keratinocytes, driven by a keratin 14 promoter expression construct. Chronic transgenic delivery of PlGF-2 to murine epidermis resulted in a significantly increased inflammatory response, associated with more pronounced vascular enlargement, edema, and inflammatory cell infiltration than seen in wild-type mice. Conversely, PlGF deficiency resulted in a diminished and abbreviated inflammatory response, together with a reduction of inflammatory angiogenesis and edema formation. VEGF expression was up-regulated at a comparable level in the inflamed skin of all genotypes. These findings reveal that placental growth factor plays a critical role in the control of cutaneous inflammation, and they suggest inhibition of PlGF bioactivity as a potential new approach for anti-inflammatory therapy.

Loss of placental growth factor protects mice against vascular permeability in pathological conditions

Vascular leakage contributes to numerous disorders but only a limited number of molecules have been demonstrated to modulate permeability of the vessel wall. The vascular endothelial growth factor (VEGF) is a potent inducer of vascular leakage. Previous studies demonstrated that exogenous administration of placental growth factor (PlGF), a homologue of VEGF, stimulates vascular permeability but the role of endogenous PlGF in plasma extravasation during pathological conditions remains unknown. We recently generated PlGF deficient (PlGF(-/-)) mice and demonstrated that loss of PlGF impaired pathological angiogenesis by attenuating the response to VEGF. Here, we demonstrate that absence of PlGF reduces vascular leakage induced by skin wounding, allergens, and neurogenic inflammation. These findings suggest that inhibition of PlGF might be an attractive tool to reduce vascular leakage in various diseases.

Vascular endothelial growth factor ligands and receptors that regulate human cytotrophoblast survival are dysregulated in severe preeclampsia and hemolysis, elevated liver enzymes, and low platelets syndrome

Human placental development combines elements of tumorigenesis and vasculogenesis. The organ's specialized epithelial cells, termed cytotrophoblasts, invade the uterus where they reside in the interstitial compartment. They also line uterine arteries and veins. During invasion, ectodermally derived cytotrophoblasts undergo pseudovasculogenesis, switching their adhesion molecule repertoire to mimic that of vascular cells. Failures in this transformation accompany the pregnancy complication preeclampsia. Here, we used a combination of in situ and in vitro analyses to characterize the cell's expression of vascular endothelial growth factor (VEGF) family ligands and receptors, key regulators of conventional vasculogenesis and angiogenesis. Cytotrophoblast differentiation and invasion during the first and second trimesters of pregnancy were associated with down-regulation of VEGF receptor (VEGFR)-2. Invasive cytotrophoblasts in early gestation expressed VEGF-A, VEGF-C, placental growth factor (PlGF), VEGFR-1, and VEGFR-3 and, at term, VEGF-A, PlGF, and VEGFR-1. In vitro the cells incorporated VEGF-A into the surrounding extracellular matrix; PlGF was secreted. We also found that cytotrophoblasts responded to the VEGF ligands they produced. Blocking ligand binding significantly decreased their expression of integrin alpha1, an adhesion molecule highly expressed by endovascular cytotrophoblasts, and increased apoptosis. In severe preeclampsia and hemolysis, elevated liver enzymes, and low platelets syndrome, immunolocalization on tissue sections showed that cytotrophoblast VEGF-A and VEGFR-1 staining decreased; staining for PlGF was unaffected. Cytotrophoblast secretion of the soluble form of VEGFR-1 in vitro also increased. Together, the results of this study showed that VEGF family members regulate cytotrophoblast survival and that expression of a subset of family members is dysregulated in severe forms of preeclampsia.

Placental development: lessons from mouse mutants

The placenta is the first organ to form during mammalian embryogenesis. Problems in its formation and function underlie many aspects of early pregnancy loss and pregnancy complications in humans. Because the placenta is critical for survival, it is very sensitive to genetic disruption, as reflected by the ever-increasing list of targeted mouse mutations that cause placental defects. Recent studies of mouse mutants with disrupted placental development indicate that signalling interactions between the placental trophoblast and embryonic cells have a key role in placental morphogenesis. Furthering our understanding of mouse trophoblast development should provide novel insights into human placental function.

Synergism between vascular endothelial growth factor and placental growth factor contributes to angiogenesis and plasma extravasation in pathological conditions

Vascular endothelial growth factor (VEGF) stimulates angiogenesis by activating VEGF receptor-2 (VEGFR-2). The role of its homolog, placental growth factor (PlGF), remains unknown. Both VEGF and PlGF bind to VEGF receptor-1 (VEGFR-1), but it is unknown whether VEGFR-1, which exists as a soluble or a membrane-bound type, is an inert decoy or a signaling receptor for PlGF during angiogenesis. Here, we report that embryonic angiogenesis in mice was not affected by deficiency of PlGF (Pgf-/-). VEGF-B, another ligand of VEGFR-1, did not rescue development in Pgf-/- mice. However, loss of PlGF impaired angiogenesis, plasma extravasation and collateral growth during ischemia, inflammation, wound healing and cancer. Transplantation of wild-type bone marrow rescued the impaired angiogenesis and collateral growth in Pgf-/- mice, indicating that PlGF might have contributed to vessel growth in the adult by mobilizing bone-marrow-derived cells. The synergism between PlGF and VEGF was specific, as PlGF deficiency impaired the response to VEGF, but not to bFGF or histamine. VEGFR-1 was activated by PlGF, given that anti-VEGFR-1 antibodies and a Src-kinase inhibitor blocked the endothelial response to PlGF or VEGF/PlGF. By upregulating PlGF and the signaling subtype of VEGFR-1, endothelial cells amplify their responsiveness to VEGF during the 'angiogenic switch' in many pathological disorders.

The growth promoting effects of bFGF, PD-ECGF and VEGF on cultured postimplantation rat embryos deprived of serum fractions

Serum components in which embryos are cultured in vitro are very important for normal embryonic development. In this study, rat serum was fractionated using Macrosep filters to study the effect of a single growth factor. The fractionated serum, both that containing only material greater than 30 kDa molecular weight (> 30 kDa) and that from which material between 30 kDa and 50 kDa had been removed (< 30 kDa+ > 50 kDa), caused significant embryonic growth retardation. Addition of different concentrations of basic fibroblast growth factor (bFGF, 18 kDa), vascular endothelial growth factor (VEGF, 45 kDa) and platelet-derived endothelial growth factor (PD-ECGF, 45 kDa), to fractionated serum (bFGF to > 30 kDa serum and VEGF or PD-ECGF to < 30 kDa+ > 50 kDa serum) partially restored embryonic growth and development according to a morphological scoring system and protein assay. This restoration was clear by all criteria, as well as in yolk sac vascularisation and heart development. The growth promoting effects of all 3 factors were significant but did not reach the level seen in embryos grown in whole rat serum. The effect of these growth factors was also investigated on anembryonic yolk sac development using a concentration for which maximum whole embryonic growth was seen (128 ng/ml bFGF, 1.6 ng/ml VEGF and 4 ng/ml PD-ECGF), and significant anembryonic yolk sac development was found. These findings suggest that the angiogenic factors may have a growth promoting effect on total embryonic development and vascularisation.