Aspects of human fetoplacental vasculogenesis and angiogenesis. II. Changes during normal pregnancy

Resident Endothelial Progenitor Cells From Human Placenta Have Greater Vasculogenic Potential Than Circulating Endothelial Progenitor Cells From Umbilical Cord Blood

Endothelial colony-forming cells (ECFCs) isolated from umbilical cord blood (CBECFCs) are highly proliferative and form blood vessels in vivo. The purpose of this investigation was to isolate and characterize a population of resident ECFCs from the chorionic villi of term human placenta and provide a comparative analysis of their proliferative and vasculogenic potential with CBECFCs. ECFCs were isolated from umbilical cord blood and chorionic villi from placentas obtained by caesarean deliveries. Placental ECFCs (PECFCs) expressed CD144, CD31, CD105, and KDR and were negative for CD45 and CD34, consistent with other ECFC phenotypes. PECFCs were capable of 28.6 ± 6.0 population doublings before reaching senescence (vs. 47.4 ± 3.2 for CBECFCs, p < 0.05, n = 4). In single cell assays, 46.5 ± 1.2% underwent at least one division (vs. 51.0 ± 1.8% of CBECFCs, p = 0.07, n = 6), and of those dividing PECFCs, 71.8 ± 0.9% gave rise to colonies of >500 cells (highly proliferative potential clones) over 14 days (vs. 69.4 ± 0.7% of CBECFCs, p = 0.07, n = 9). PECFCs formed 5.2 ± 0.8 vessels/mm(2) in collagen/fibronectin plugs implanted into non-obese diabetic/severe combined immunodeficient (NOD/SCID) mice, whereas CBECFCs formed only 1.7 ± 1.0 vessels/mm(2) (p < 0.05, n = 4). This study demonstrates that circulating CBECFCs and resident PECFCs are identical phenotypically and contain equivalent quantities of high proliferative potential clones. However, PECFCs formed significantly more blood vessels in vivo than CBECFCs, indicating that differences in vasculogenic potential between circulating and resident ECFCs exist.

Maternal angiogenic profile in pregnancies that remain normotensive

OBJECTIVE

We sought to determine if maternal characteristics are associated with angiogenic profile in the first and second trimester of normotensive pregnancies.

STUDY DESIGN

Circulating levels of maternal placental like growth factor (PlGF), soluble fms-like tyrosine kinase receptor (sFlt1), and soluble endoglin (sEng) were measured in serum samples collected during the first (median 11.3 weeks) and second trimester (median 17.1 weeks) of 182 normotensive pregnancies. Diastolic blood pressure (DBP), systolic blood pressure (SBP), and mean arterial pressure (MAP) were measured at the same visits when samples were collected to measure angiogenic factors. Linear regression analysis was used to examine associations of the angiogenic measures with maternal characteristics. The association between blood pressure measures and concentrations of angiogenic factors was evaluated using Spearman correlation and linear regression analysis.

RESULTS

In adjusted analyses, nulliparous women had higher sFlt1 concentrations in both first (p=0.06) and second (p=0.001) trimester. Higher BMI was associated with greater sFlt1 concentrations in both the first (p=0.004) and second trimester (p=0.008), but significantly lower sEng concentrations in both trimesters (p=0.002 for first trimester and p=0.0009 for second). Nulliparity and higher BMI also were associated with higher sFlt1/PLGF anti-angiogenic ratios in both first (p=0.05 and p=0.007, respectively) and second trimesters (p=0.003 and p=0.02, respectively). First trimester sFlt1 levels were weakly correlated with first trimester SBP (r(s)=0.18, p=0.03) and MAP (r(s)=0.16, p=0.04). Second trimester sEng levels were inversely associated with second trimester MAP (r(s)=-0.17, p=0.05). Including blood pressure measures in the linear regression models did not change the reported associations of angiogenic factors with maternal characteristics.

CONCLUSIONS

These results demonstrate that even early in normotensive pregnancies maternal characteristics are associated with variations in angiogenic profile across this population.

Placental expression of endothelial and inducible nitric oxide synthase and nitric oxide levels in patients with HELLP syndrome

OBJECTIVE

To determine placental gene expression of endothelial and inducible nitric oxide synthases and measure nitric oxide levels in patients with hemolysis, elevated liver enzyme levels, and low platelet count syndrome.

STUDY DESIGN

Preterm placentas were obtained from 15 patients with hemolysis, elevated liver enzyme levels, and low platelet count syndrome and 30 controls matched for age, parity, and gestational age. mRNA levels were evaluated by real-time polymerase chain reaction, whereas nitric oxide and peroxynitrite production was measured by a commercially available kit.

RESULTS

Placental gene expression of inducible nitric oxide and endothelial nitric oxide synthases were significantly lower in the hemolysis, elevated liver enzyme levels, and low platelet count syndrome group than in controls, whereas nitric oxide and peroxynitrite production were significantly higher in hemolysis, elevated liver enzyme levels, and low platelet count syndrome compared with controls.

CONCLUSION

The reduced endothelial nitric oxide and inducible nitric oxide synthases gene expression in women with hemolysis, elevated liver enzyme levels, and low platelet count syndrome may indicate extreme placental dysfunction that is unable to compensate the endothelial derangement and the related hypertension. The higher nitric oxide formation found in hemolysis, elevated liver enzyme levels, and low platelet count syndrome placentas could be explained as a counteraction to the impaired fetoplacental perfusion, typical of the syndrome.

MicroRNA array and microarray evaluation of endometrial receptivity in patients with high serum progesterone levels on the day of hCG administration

BACKGROUND

To determine the effect of higher progesterone (P) level on endometrial receptivity.

METHODS

This was a prospective analysis conducted in the Reproductive Medical Center of Peking University Third Hospital. All patients received IVF treatment and canceled embryo transfer in the same cycle and were divided into group 1 (normal P; 7 patients) and group 2 (elevated P; 12 patients). Endometrial biopsies were performed 6 days after oocyte retrieval. The global miRNA and mRNA gene expressions in endometrial biopsies were investigated with a V4.0 miRNA probe and 22 K Human Genome Array. Fold ratios were derived to compare gene regulation between the groups. Spp1 and Ang gene expression was selected to verify the array results by RT-PCR and the protein expression of osteopontin and VEGF was determined using an immunohistochemical method.

RESULTS

There were 4 miRNA (all down-regulated) and 22 mRNA (13 up-regulated and 9 down-regulated) exhibiting differential expression between the groups on the microRNA and microarray chips. miRNA-451, Spp1, and Ang expression in RT-PCR verified the array results. Osteopontin and VEGF were also shown to have positive expression in the endometrium.

CONCLUSIONS

Data from microRNA and microarray analysis suggests dissimilar endometrial receptivity in patients with high P levels on the day of hCG, and elevated osteopontin and decreased VEGF had poor pregnancy rates.

Umbilical artery Doppler in the assessment of fetal growth restriction

Antepartum fetal surveillance with Doppler ultrasound of umbilical artery has shown significant diagnostic efficacy in identifying fetal compromise in pregnancies complicated with fetal growth restriction (FGR). Its effectiveness in decreasing perinatal mortality has been shown by randomized clinical trials (Level I evidence). This test is the only antepartum fetal test that has shown this level of effectiveness and should be the standard of practice in managing FGR (Level A recommendation). The overall management considerations should encompass other standard fetal monitoring tests (Level B and C recommendations).

Effect of gestational diabetes on maternal artery function

Endothelial dysfunction has been observed systemically in women with gestational diabetes (GDM). Important cardiovascular adaptations occur during pregnancy, including enhanced endothelium-dependent vasodilation in systemic and uterine arteries, which are necessary to ensure the health of both mother and fetus. The effects of GDM, however, on uterine artery function and the possible mechanisms that mediate endothelial dysfunction remain unknown. The aim of this study was to utilize a mouse model of GDM to investigate (a) effects on uteroplacental flow, (b) endothelial function of uterine and mesenteric arteries, and (c) possible mechanisms of any dysfunction observed. Pregnant mice heterozygous for a leptin receptor mutation (Lepr(db) (/+); He) spontaneously develop GDM and were compared to wild-type (WT) mice at day 18.5 of gestation. Uterine artery flow was assessed using ultrasound biomicroscopy. Uterine and mesenteric artery function was assessed using wire myography. Arterial superoxide production was measured using oxidative fluorescence microphotography. In vivo uteroplacental perfusion was impaired in mice with GDM, indicated by a significant increase in uterine artery resistance index. Maximal endothelium-dependent relaxation to methacholine was significantly impaired in mesenteric arteries from mice with GDM, while sensitivity was significantly reduced in uterine arteries. Both uterine and mesenteric arteries from mice with GDM exhibited a greater dependence on nitric oxide and increased superoxide production compared with those from mice with a healthy pregnancy. A significant source of superoxide in GDM mice was uncoupled nitric oxide synthase. These changes may contribute to the development of some of the fetal and maternal complication associated with GDM.

Multifocal chorangiomatosis

Multifocal chorangiomatosis (MC) is an uncommon villous capillary lesion sharing some features with villous chorangiosis and placental chorangioma. We prospectively identified 53 cases of MC among 5429 consecutively accessioned placentas of >20 weeks gestation over a 10-year period. Two gestational age (GA)-matched controls were selected for each case from the same cohort and a case control analysis of associated clinical and pathologic features was performed. Multifocal chorangiomatosis was seen at all GAs but was most frequent in very preterm placentas (<32 weeks). Avascular villi, villous chorangiosis, and distal villous immaturity were each seen in approximately half of placentas with MC. Other common placental findings included concentric narrowing of fetal villous arterioles, villous edema, and dysmorphic villi. Only one case had an associated placental chorangioma. Maternal factors significantly associated with MC were advanced maternal age, non-African-American ancestry, nonprimigravid status, and >5 previous pregnancies. Infants with placental MC had a significantly increased prevalence of congenital anomalies. Multifocal chorangiomatosis was subcategorized as extensive versus patchy based on the size of the largest focus (> versus < ×2 microscopic field). Fetuses with extensive MC, when compared with patchy MC, were more likely to have congenital anomalies and stillbirth and to be large for GA. Paradoxically, those with patchy MC were more likely to be small for GA. The results of this study suggest that MC may represent an abnormal proliferation of the paravascular capillary net in proximal villi related to fetoplacental developmental anomalies and abnormal fetal blood flow.

Placental-derived mesenchyme influences chorionic gonadotropin and progesterone secretion of human embryonic stem cell-derived trophoblasts

Studies of early placental development in humans are difficult because of limitations on experimental material availability from the perimplantation period. We used a coculture system to determine the effects of various effector cell types on trophoblast differentiation. Enhanced green fluorescent protein (EGFP)-expressing H1 human embryonic stem cells were used in co-suspension with human term placental fibroblasts (TPFs) and dermal fibroblasts (CI2F) to form combination embryoid bodies (EBs), with the goal of recapitulating placental morphogenesis through incorporation of placental mesenchymal cells. Overall, the results demonstrated that when using mesenchymal cells for EB preparation from term placentas (TPF), combination EB-derived trophoblasts secrete higher levels of human chorionic gonadotropin (hCG) and progesterone compared to EBs made without effector cells, whereas there was no effect of dermal fibroblasts. This is due to the secretory activity of the EB-derived trophoblasts and not due to the number of differentiated trophoblasts per EB, demonstrating that nontrophoblast cells of the placenta can influence trophoblast endocrine activity.

Intrauterine growth restriction and placental angiogenesis

BACKGROUND

Vascular endothelial growth factor (VEGF), basic-fibroblast growth factor (b-FGF), and endothelial nitric oxide synthase (eNOS) are factors that take part in placental angiogenesis. They are highly expressed during embryonic and fetal development, especially in the first trimester. In this study, we aimed to investigate the role of placental angiogenesis in the development of intrauterine growth restriction (IUGR) by comparing the levels of expression of VEGF-A, b-FGF, and eNOS in normal-term pregnancy and IUGR placentas.

METHODS

The expression of VEGF-A, b-FGF, and eNOS was studied using the avidin-biotin-peroxidase method in placental tissues diagnosed as normal (n = 55) and IUGR (n = 55). Results were evaluated in a semi-quantitative manner.

RESULTS

The expression of all the markers was significantly higher (p < 0.001) in cytotrophoblasts, syncytiotrophoblasts, extravillous trophoblasts, vascular smooth muscle cells, chorionic villous stromal cells, and villous vascular endothelial cells of the IUGR placentas when compared with those collected from normal-term pregnancies.

CONCLUSION

Increased expression of VEGF-A, b-FGF, and eNOS may be the result of inadequate uteroplacental perfusion, supporting the proposal that abnormal angiogenesis plays a role in the pathophysiology of IUGR.

Estrogen regulation of placental angiogenesis and fetal ovarian development during primate pregnancy

During human and nonhuman primate pregnancy, an extensive blood vessel network is established within the villous placenta to support fetal growth and follicles develop within the fetal ovary to provide a pool of oocytes for reproductive function in adulthood. These two important developmental events occur in association with a progressive increase in placental estrogen production and levels. This review will describe the developmental processes required for placental vascularization and fetal follicular maturation and recent studies which show that estrogen has an important role in regulating these events.

Dysregulation of angiopoietins is associated with placental malaria and low birth weight

Background

Placental malaria (PM) is associated with adverse pregnancy outcomes including low birth weight (LBW). However, the precise mechanisms by which PM induces LBW are poorly defined. Based on the essential role of angiopoietin (ANG)-1 and -2 in normal placental vascular development, we hypothesized that PM may result in the dysregulation of angiopoietins and thereby contribute to LBW outcomes.

Methods and Findings

In a mouse model of PM, we show that Plasmodium berghei ANKA infection of pregnant mice resulted in dysregulated angiopoietin levels and fetal growth restriction. PM lead to decreased ANG-1, increased ANG-2, and an elevated ratio of ANG-2/ANG-1 in the placenta and the serum. These observations were extended to malaria-exposed pregnant women: In a study of primigravid women prospectively followed over the course of pregnancy, Plasmodium falciparum infection was associated with a decrease in maternal plasma ANG-1 levels (P = 0.031) and an increase in the ANG-2:ANG-1 ratio (P = 0.048). ANG-1 levels recovered with successful treatment of peripheral parasitemia (P = 0.010). In a cross-sectional study of primigravidae at delivery, angiopoietin dysregulation was associated with PM (P = 0.002) and LBW (P = 0.041). Women with PM who delivered LBW infants had increased ANG-2:ANG-1 ratios (P = 0.002) compared to uninfected women delivering normal birth weight infants.

Conclusions

These data support the hypothesis that dysregulation of angiopoietins is associated with PM and LBW outcomes, and suggest that ANG-1 and ANG-2 levels may be clinically informative biomarkers to identify P. falciparum-infected mothers at risk of LBW deliveries.

Maternal and fetal microvasculature in sheep placenta at several stages of gestation

Maternal and fetal microvasculature was studied in ewes at days 50, 90 and 130 of gestation using microvascular corrosion casting and scanning electron microscopy. Microvascular corrosion casts of caruncles at day 50 were cup-shaped with a centrally located cavity. Branches of radial arteries entered the caruncle from its base and ramified on the maternal surface of the caruncle. Stem arteries broke into an extensive mesh of capillaries forming crypts on the fetal surface. The architecture of the caruncle at day 90 was similar to what was found at day 50 but the vascularity and the depth of the crypts increased in correspondence to increased branching of fetal villi. The substance of the caruncle was thicker at day 130 compared with day 50, with no remarkable difference compared with day 90. Capillary sinusoids of irregular form and diameter were observed on the fetal surface of the caruncle at all stages. These sinusoids may reduce blood flow resistance and subsequently increase transplacental exchange capacity. A microvascular corrosion cast of the cotyledon was cup-shaped with wide and narrow sides. Cotyledonary vessels entered and left the cotyledon from the narrow side. A cotyledonary artery gave proximal collateral branches immediately after entering the cotyledon and then further branched to supply the remaining portion of the cotyledon. Vessel branches broke into a mesh of capillaries forming the fetal vascular villi. Fetal villi that were nearest to the center of the cotyledon were the longest. Capillaries forming villi were in the form of a web-like mesh, were irregular in size and had sinusoidal dilations. The architecture of the cotyledon at day 90 was similar to day 50, but the vascularity increased. Branching of the fetal villi became more abundant. This extensive branching presumably allows a higher degree of invasion and surface contact to maternal tissues. At day 130, the distal portions of the fetal villi showed low ridges and troughs to increase the surface area for diffusion. Branching of fetal villi appears to influence the elaboration of maternal crypts in all stages of gestation. However, correspondence between crypts and villi is restricted to distal portions of fetal villi.

Novel pathways for implantation and establishment and maintenance of pregnancy in mammals

Uterine receptivity to implantation varies among species, and involves changes in expression of genes that are coordinate with attachment of trophectoderm to uterine lumenal and superficial glandular epithelia, modification of phenotype of uterine stromal cells, silencing of receptors for progesterone and estrogen, suppression of genes for immune recognition, alterations in membrane permeability to enhance conceptus-maternal exchange of factors, angiogenesis and vasculogenesis, increased vascularity of the endometrium, activation of genes for transport of nutrients into the uterine lumen, and enhanced signaling for pregnancy recognition. Differential expression of genes by uterine epithelial and stromal cells in response to progesterone, glucocorticoids, prostaglandins and interferons may influence uterine receptivity to implantation in mammals. Uterine receptivity to implantation is progesterone-dependent; however, implantation is preceded by loss of expression of receptors for progesterone (PGR) so that progesterone most likely acts via PGR-positive stromal cells throughout pregnancy. Endogenous retroviruses expressed by the uterus and/or blastocyst also affect implantation and placentation in various species. Understanding the roles of the variety of hormones, growth factors and endogenous retroviral proteins in uterine receptivity for implantation is essential to enhancing reproductive health and fertility in humans and domestic animals.

Angiogenesis in differentiated placental multipotent mesenchymal stromal cells is dependent on integrin alpha5beta1

Human placental multipotent mesenchymal stromal cells (hPMSCs) can be isolated from term placenta, but their angiogenic ability and the regulatory pathways involved are not known. hPMSCs were shown to express integrins α_v, α₄, α₅, β₁, β₃, and β₅ and could be induced to differentiate into cells expressing endothelial markers. Increases in cell surface integrins α₅ and β₁, but not α₄, α_vβ₃, or α_vβ₅, accompanied endothelial differentiation. Vascular endothelial growth factor-A augmented the effect of fibronectin in enhancing adhesion and migration of differentiated hPMSC through integrin α₅β₁, but not α_vβ₃ or α_vβ₅. Formation of capillary-like structures in vitro from differentiated cells was inhibited by pre-treatment with function-blocking antibodies to integrins α₅ and β₁. When hPMSCs were seeded onto chick chorioallantoic membranes (CAM), human von Willebrand factor-positive cells were observed to engraft in the chick endothelium. CAMs transplanted with differentiated hPMSCs had a greater number of vessels containing human cells and more incorporated cells per vessel compared to CAMs transplanted with undifferentiated hPMSCs, and overall angiogenesis was enhanced more by the differentiated cells. Function-blocking antibodies to integrins α₅ and β₁ inhibited angiogenesis in the CAM assay. These results suggest that differentiated hPMSCs may contribute to blood vessel formation, and this activity depends on integrin α₅β₁.

Analysis of placenta vascularization in patients with uterine altered artery Doppler flow velocity exams

BACKGROUND

One of the frequent questions in obstetric practice is to determine placental vascular changes that may account for abnormal Doppler flow velocity alterations in maternal uterine vessels from women and fetuses without pregnancy pathology.

METHODS

A retrospective morphometric study was realized using 27 placentas from patients submitted for Doppler flow velocity exam during pregnancy. The placentas were morphologically examined using hematoxylin-eosin staining. Measurements of villi were made with the use of a video camera coupled to a common light microscope and a computer with automatic image analyzing software.

RESULTS

Of the 27 placentas, 13 (48%) were of patients showing unaltered Doppler and 14 (52%) showing altered Doppler. The number of stem villi vessels was significantly larger in the placentas of patients with Doppler exam alterations (P = 0.003). This group also presented greater stem villi vessel thickness, although without significant difference. The number of intermediary and terminal villi vessels was greater in the placentas of patients with altered Doppler exams (P < 0.001), and a greater terminal villi area was observed in these cases (P < 0.001).

CONCLUSION

The morphological proof that uterine artery Doppler flow velocity exam alterations are associated with placental vascular alterations demonstrates the importance of this exam during prenatal care, even in the absence of maternal-fetal alterations.

Vasodilator factors in the systemic and local adaptations to pregnancy

We postulate that an orchestrated network composed of various vasodilatory systems participates in the systemic and local hemodynamic adaptations in pregnancy. The temporal patterns of increase in the circulating and urinary levels of five vasodilator factors/systems, prostacyclin, nitric oxide, kallikrein, angiotensin-(1-7) and VEGF, in normal pregnant women and animals, as well as the changes observed in preeclamptic pregnancies support their functional role in maintaining normotension by opposing the vasoconstrictor systems. In addition, the expression of these vasodilators in the different trophoblastic subtypes in various species supports their role in the transformation of the uterine arteries. Moreover, their expression in the fetal endothelium and in the syncytiotrophoblast in humans, rats and guinea-pigs, favour their participation in maintaining the uteroplacental circulation. The findings that sustain the functional associations of the various vasodilators, and their participation by endocrine, paracrine and autocrine regulation of the systemic and local vasoactive changes of pregnancy are abundant and compelling. However, further elucidation of the role of the various players is hampered by methodological problems. Among these difficulties is the complexity of the interactions between the different factors, the likelihood that experimental alterations induced in one system may be compensated by the other players of the network, and the possibility that data obtained by manipulating single factors in vitro or in animal studies may be difficult to translate to the human. In addition, the impossibility of sampling the uteroplacental interface along normal pregnancy precludes obtaining longitudinal profiles of the various players. Nevertheless, the possibility of improving maternal blood pressure regulation, trophoblast invasion and uteroplacental flow by enhancing vasodilation (e.g. L-arginine, NO donors, VEGF transfection) deserves unravelling the intricate association of vasoactive factors and the systemic and local adaptations to pregnancy.

No correlation between ultrasound placental grading at 31-34 weeks of gestation and a surrogate estimate of organ function at term obtained by stereological analysis

We test the experimental hypothesis that early changes in the ultrasound appearance of the placenta reflect poor or reduced placental function. The sonographic (Grannum) grade of placental maturity was compared to placental function as expressed by the morphometric oxygen diffusive conductance of the villous membrane. Ultrasonography was used to assess the Grannum grade of 32 placentas at 31-34 weeks of gestation. Indications for the scans included a history of previous fetal abnormalities, previous fetal growth problems or suspicion of IUGR. Placentas were classified from grade 0 (most immature) to grade III (most mature). We did not exclude smokers or complicated pregnancies as we aimed to correlate the early appearance of mature placentas with placental function. After delivery, microscopical fields on formalin-fixed, trichrome-stained histological sections of each placenta were obtained by multistage systematic uniform random sampling. Using design-based stereological methods, the exchange surface areas of peripheral (terminal and intermediate) villi and their fetal capillaries and the arithmetic and harmonic mean thicknesses of the villous membrane (maternal surface of villous trophoblast to adluminal surface of vascular endothelium) were estimated. An index of the variability in thickness of this membrane, and an estimate of its oxygen diffusive conductance, were derived secondarily as were estimates of the mean diameters and total lengths of villi and fetal capillaries. Group comparisons were drawn using analysis of variance. We found no significant differences in placental volume or composition or in the dimensions or diffusive conductances of the villous membrane. Subsequent exclusion of smokers did not alter these main findings. Grannum grades at 31-34 weeks of gestation appear not to provide reliable predictors of the functional capacity of the term placenta as expressed by the surrogate measure, morphometric diffusive conductance.

Chapter 10. Methods for evaluating uteroplacental angiogenesis and their application using animal models

In this chapter, we present some of the compelling evidence confirming the importance of placental angiogenesis to fetal growth and development in normal and compromised pregnancies. We then describe the methodology that has been used to evaluate placental angiogenesis throughout pregnancy, including both the practical methods used to obtain reliable samples of the placental microcirculation as well as computerized methods used to analyze and reconstruct it. We then briefly describe the changes in placental angiogenesis and function in the models of normal and compromised pregnancy that we have used, and conclude with what we have learned from these studies and what we believe are the larger questions remaining.

Decreased expression of pigment epithelium derived factor (PEDF), an inhibitor of angiogenesis, in placentas of unexplained stillbirths

Normal placental vascular development depends upon the complex interactions between angiogenic inducers and inhibitors within the placenta. Alterations within the placental microenvironment can promote an imbalance in angiogenic mediators which may be associated with adverse perinatal outcomes. The purpose of this study was to investigate the placentas of infants with unexplained stillbirth as compared to live-born infants and to determine whether alterations in angiogenic inducer vascular endothelial growth factor (VEGF) or inhibitor pigment epithelium-derived factor (PEDF) are associated with altered angiogenesis, vascular remodeling and stillbirth. Placentas of 22 unexplained stillbirths and 44 age-matched live-born controls were scored for microvascular density (MVD), vasculopathy and microvascular permeability. A subset was scored for expression of angiogenic inducer VEGF and inhibitor pigment epithelium-derived factor. Stillborn placentas demonstrated higher MVD than controls (mean+SD: 116.6+/-46.3 v. 60.8+/-13.5, respectively, p<0.001). Vasculopathy was present in 10/22 (45%) stillbirths compared to 0/44 (0%) controls (p<0.001); increased vascular permeability was present in 15/22 (68%) cases and 5/44 (11%) controls (p<0.001). PEDF expression was significantly lower in stillborn placentas (1.7+/-0.3) than live-born controls (3.6+/-0.8, p<0.01) while VEGF expression was similar (3.3+/-0.7 v. 3.7+/-0.4, respectively, p>0.05). In conclusion, we found that unexplained stillbirth is associated with loss of angiogenic inhibitor PEDF, vasculopathy and heightened angiogenesis in the placenta.

Modeling the variability of shapes of a human placenta

BACKGROUND

Placentas are generally round/oval in shape, but "irregular" shapes are common. In the Collaborative Perinatal Project data, irregular shapes were associated with lower birth weight for placental weight, suggesting variably shaped placentas have altered function.

METHODS

(I) Using a 3D one-parameter model of placental vascular growth based on Diffusion Limited Aggregation (an accepted model for generating highly branched fractals), models were run with a branching density growth parameter either fixed or perturbed at either 5-7% or 50% of model growth. (II) In a data set with detailed measures of 1207 placental perimeters, radial standard deviations of placental shapes were calculated from the umbilical cord insertion, and from the centroid of the shape (a biologically arbitrary point). These two were compared to the difference between the observed scaling exponent and the Kleiber scaling exponent (0.75), considered optimal for vascular fractal transport systems. Spearman's rank correlation considered p<0.05 significant.

RESULTS

(I) Unperturbed, random values of the growth parameter created round/oval fractal shapes. Perturbation at 5-7% of model growth created multilobate shapes, while perturbation at 50% of model growth created "star-shaped" fractals. (II) The radial standard deviation of the perimeter from the umbilical cord (but not from the centroid) was associated with differences from the Kleiber exponent (p=0.006).

CONCLUSIONS

A dynamical DLA model recapitulates multilobate and "star" placental shapes via changing fractal branching density. We suggest that (1) irregular placental outlines reflect deformation of the underlying placental fractal vascular network, (2) such irregularities in placental outline indicate sub-optimal branching structure of the vascular tree, and (3) this accounts for the lower birth weight observed in non-round/oval placentas in the Collaborative Perinatal Project.

Human fetal placental endothelial cells have a mature arterial and a juvenile venous phenotype with adipogenic and osteogenic differentiation potential

Growing interest in the sources of origin of blood vessel related diseases has led to an increasing knowledge about the heterogeneity and plasticity of endothelial cells lining arteries and veins. So far, most of these studies were performed on animal models. Here, we hypothesized that the plasticity of human fetal endothelial cells depends on their vascular bed of origin i.e. vein or artery and further that the differences between arterial and venous endothelial cells would extend to phenotype and genotype. We established a method for the isolation of fetal arterial and venous endothelial cells from the human placenta and studied the characteristics of both cell types. Human placental arterial endothelial cells (HPAEC) and human placental venous endothelial cells (HPVEC) express classical endothelial markers and differ in their phenotypic, genotypic, and functional characteristics: HPAEC are polygonal cells with a smooth surface growing in loose arrangements and forming monolayers with classical endothelial cobblestone morphology. They express artery-related genes (hey-2, connexin 40, depp) and more endothelial-associated genes than HPVEC. Functional testing demonstrated that vascular endothelial growth factors (VEGFs) induce a higher proliferative response on HPAEC, whereas placental growth factors (PlGFs) are only effective on HPVEC. HPVEC are spindle-shaped cells with numerous microvilli at their surface. They grow closely apposed to each other, form fibroblastoid swirling patterns at confluence and have shorter generation and population doubling times than HPAEC. HPVEC overexpress development-associated genes (gremlin, mesenchyme homeobox 2, stem cell protein DSC54) and show an enhanced differentiation potential into adipocytes and osteoblasts in contrast to HPAEC. These data provide collective evidence for a juvenile venous and a more mature arterial phenotype of human fetal endothelial cells. The high plasticity of the fetal venous endothelial cells may reflect their role as tissue-resident endothelial progenitors during embryonic development with a possible benefit for regenerative cell therapy.

Physiological distribution of placental growth factor and soluble Flt-1 in early pregnancy

OBJECTIVE

To examine the distribution of placental growth factor (PlGF), vascular endothelial growth factor (VEGF) and soluble VEGF receptor-1 (sFlt-1) in maternal and embryonic fluid compartments in early pregnancy.

METHOD

The concentrations of PlGF, VEGF and sFlt-1 were measured in coelomic fluid and maternal serum from 16 singleton pregnancies at 7.0-9.3 weeks. In six cases, amniotic fluid was also examined.

RESULTS

The median concentration of PlGF was 14.1 (range 8.9-27.6) pg/mL in maternal serum, 13.9 (range 9.5-31.4) pg/mL in coelomic fluid and 8.9 (range 3.9-15.3) pg/mL in amniotic fluid. The concentration of PlGF increased between 7.0 and 9.3 weeks in maternal serum (p = 0.001) and decreased in coelomic and amniotic fluid (p = 0.001). The median concentration of sFlt-1 was 8561 (range 6724-10 673) pg/mL in coelomic fluid, 523 (range 244-986) pg/mL in maternal serum, 30 (range 12-83) pg/mL in amniotic fluid (p = 0.0001), and it did not change significantly with gestation. VEGF was undetectable in most of the samples, and therefore, no further analysis was performed.

CONCLUSION

PlGF and sFlt-1 are present in the maternal and fetal fluid compartments in very early pregnancy, and their distribution is consistent with their site of production and the local conditions of transport.

Vasculogenesis and angiogenesis in the IUGR placenta

Placenta vascular formation is important for fetal growth and development. Proper development of the placenta ensures the exchange of oxygen/nutrients and blood flow necessary for fetal growth. In this chapter, we will discuss the processes of vasculogenesis, angiogenesis, and pseudovasculogenesis during placental development and in pregnancies complicated by intrauterine growth restriction. Some of the factors controlling these processes include oxygen, the VEGF family of growth factors, and their receptors. Disruption in the balance of these controlling factors may explain the vascular malformations seen in pregnancies complicated by intrauterine growth restriction.

Regulation of placental villous angiopoietin-1 and -2 expression by estrogen during baboon pregnancy

We recently showed an increase in vascular endothelial growth factor (VEGF), decrease in angiopoietin-1 (Ang-1) and unaltered Ang-2 expression by the villous placenta with advancing baboon pregnancy. Moreover, placental VEGF expression was increased by estrogen in early pregnancy. In the present study, we determined whether placental Ang-1 and Ang-2 are regulated by estrogen. Ang-1 and Ang-2 mRNA and protein were determined by RT-PCR and immunocytochemistry in the placenta of baboons on Day 60 of gestation (term is 184 days) after administration of estrogen precursor androstenedione on Days 25-59 or on Day 54 after acute estradiol administration. Chronic androstenedione treatment increased serum estradiol levels three-fold (P < 0.001) and decreased (P < 0.05) villous cytotrophoblast Ang-1 mRNA to a level (0.36 +/- 0.08 relative to 18S rRNA) that was one-third of that in untreated animals (0.98 +/- 0.26). Within 2 hr of estradiol administration, cytotrophoblast Ang-1 mRNA was decreased to a level (0.24 +/- 0.05) one-fifth (P < 0.05) of that in untreated animals (1.14 +/- 0.23). However, Ang-2 mRNA levels were unaltered. Ang-1, Ang-2 and estrogen receptors alpha and beta protein were localized within villous cytotrophoblasts providing a mechanism for estrogen action at this site. In summary, estrogen increased VEGF, decreased Ang-1, and had no effect on Ang-2 expression within placental cytotrophoblasts during early baboon pregnancy. We propose that the estrogen-dependent differential regulation of these angioregulatory factors underpins the unique pattern of neovascularization established within the villous placenta during primate pregnancy.

Twin-to-twin transfusion syndrome: an antiangiogenic state?

OBJECTIVE

An imbalanced chronic blood flow between the donor and recipient twin through placental vascular anastomoses is the accepted pathophysiology of twin-to-twin transfusion syndrome (TTTS). Vascular endothelial growth factor receptor-1 (VEGFR-1) mRNA is overexpressed only in the syncytiotrophoblast of the donor twin in some cases of TTTS. This study was conducted to determine maternal plasma concentrations of placental growth factor (PlGF), soluble VEGFR-1, and soluble endoglin (s-Eng) in monochorionic-diamniotic pregnancies with and without TTTS.

STUDY DESIGN

This case-control study included monochorionic-diamniotic pregnancies between 16-26 weeks with and without TTTS. Maternal plasma concentrations of PlGF, sVEGFR-1, and s-Eng were determined with ELISA. A P value < .05 was considered statistically significant.

RESULTS

Patients with TTTS had higher median plasma concentrations of s-Eng (14.8 ng/mL vs 7.8 ng/mL; P < .001) and sVEGFR-1 (6383.1 pg/mL vs 3220.1 pg/mL; P < .001]; and lower median plasma concentrations of PlGF (115.5 pg/mL vs 359.3 pg/mL; P = .002) than those without TTTS.

CONCLUSION

We propose that an antiangiogenic state may be present in some cases of TTTS.

Angiogenic, hyperpermeability and vasodilator network in utero-placental units along pregnancy in the guinea-pig (Cavia porcellus)

BACKGROUND

The angiogenic and invasive properties of the cytotrophoblast are crucial to provide an adequate area for feto-maternal exchange. The present study aimed at identifying the localization of interrelated angiogenic, hyperpermeability and vasodilator factors in the feto-maternal interface in pregnant guinea-pigs.

METHODS

Utero-placental units were collected from early to term pregnancy. VEGF, Flt-1, KDR, B2R and eNOS were analyzed by immunohistochemistry, and the intensity of the signals in placenta and syncytial streamers was digitally analysed. Flt1 and eNOS content of placental homogenates was determined by western blotting. Statistical analysis used one-way analysis of variance and Tukey's Multiple Comparison post-hoc test.

RESULTS

In the subplacenta, placental interlobium and labyrinth VEGF, Flt-1, KDR, B2R and eNOS were expressed in all stages of pregnancy. Syncytial streamers in all stages of gestation, and cytotrophoblasts surrounding myometrial arteries in early and mid pregnancy - and replacing the smooth muscle at term - displayed immunoreactivity for VEGF, Flt-1, KDR, eNOS and B2R. In partly disrupted mesometrial arteries in late pregnancy cytotrophoblasts and endothelial cells expressed VEGF, Flt-1, KDR, B2R and eNOS. Sections incubated in absence of the first antibody, or in presence of rabbit IgG fraction and mouse IgG serum, yielded no staining. According to the digital analysis, Flt-1 increased in the placental interlobium in days 40 and 60 as compared to day 20 (P = 0.016), and in the labyrinth in day 60 as compared to days 20 and 40 (P = 0.026), while the signals for VEGF, KDR, B2R, and eNOS showed no variations along pregnancy. In syncytial streamers the intensity of VEGF immunoreactivity was increased in day 40 in comparison to day 20 (P = 0.027), while that of B2R decreased in days 40 and 60 as compared to day 20 (P = 0.011); VEGF, Flt-1, KDR, B2R and eNOS expression showed no variations. Western blots for eNOS and Flt-1 in placental homogenates showed no significant temporal differences along pregnancy.

CONCLUSION

The demonstration of different angiogenic, hyperpermeability and vasodilator factors in the same cellular protagonists of angiogenesis and invasion in the pregnant guinea-pig, supports the presence of a functional network, and strengthens the argument that this species provides an adequate model to understand human pregnancy.

Maternal asthma and placental morphometry: effects of severity, treatment and fetal sex

Asthma is the most common respiratory disease to complicate pregnancy. Although adverse effects on the fetus have been documented, there is a paucity of information regarding the effects of asthma, and its treatment, on placental morphology. The aim of this study was to test for volumetric differences in placental composition between non-asthmatic pregnancies and those associated with maternal asthma grouped according to asthma severity and glucocorticoid (GC) treatment. Each placenta was weighed and random samples of tissue were fixed in formalin-saline, embedded in wax and analysed by design-based stereology. Volume densities of parenchymal compartments (peripheral villi and maternal intervillous space) and residual non-parenchyma were estimated by test point counting and converted to absolute volumes by taking into account placental size. Relative and absolute lengths of villi and capillaries were also estimated and used to derive secondary quantities related to villous capillarization and maturation. Between-group comparisons were drawn by two-way analysis of variance with group and fetal sex as the principal factors. Compared to non-asthmatic controls, asthmatics had reduced absolute volumes of fetal capillaries which was most marked in those with moderate/severe asthma and those using low and high doses of inhaled GCs. Changes in the total length and mean cross-sectional area of capillaries and peripheral villi were also observed. Lengths were greater in mild asthmatics and lowest in those with high GC usage. Calibre areas were lower in mild asthmatics and villous calibres in the high GC group were greater than those in asthmatics not taking GCs. Those making greatest use of inhaled GCs also had villi which were hypovascularized in terms of capillary:villus length ratios. The findings suggest that the morphometric differences in fetoplacental vascularity are likely to be due to the effects of asthma and use of inhaled GCs rather than the effects of maternal or fetal hypoxic stress.

Fetal growth restriction: pathogenic mechanisms

Complex genetic and environmental mechanisms of maternal, fetal and placental origin regulate fetal growth and may contribute to fetal growth restriction (FGR). The somatotrophic regulatory factors include IGF-I, IGF-II, the IGF binding proteins (IGFBP) 1-6, IGF receptors 1 and 2, and the IGFBP specific proteases. Abnormal remodeling of utero-placental arteries and abnormal fetal-placental angiogenesis has also been implicated in FGR. The underlying molecular mediators include vascular endothelial growth factor (VEGF), placental growth factor (PlGF), VEGF receptors, VEGF binding proteins, and numerous other agents working through multiple pathways many of which still remain unknown. Expression of these major angiogenic factors appears to be regulated by local oxygen partial pressure. Future investigations may resolve many of these issues not only adding to the clarity of our understanding of the mechanisms of growth restriction but also improving clinical management.

A stereological perspective on placental morphology in normal and complicated pregnancies

Stereology applied to randomly-generated thin sections allows minimally-biased and economical quantitation of the 3D structure of the placenta from molecular to whole-organ levels. With these sampling and estimation tools, it is possible to derive global quantities (tissue volumes, interface surface areas, tubule lengths and particle numbers), average values (e.g. mean cell size or membrane thickness), spatial relationships (e.g. between compartments and immunoprobes) and functional potential (e.g. diffusive conductance). This review indicates ways in which stereology has been used to interpret the morphology of human and murine placentas including the processes of villous growth, trophoblast differentiation, vascular morphogenesis and diffusive transport. In human placenta, global quantities have shown that villous maturation involves differential growth of fetal capillaries and increases in endothelial cell number. Villous trophoblast is a continuously renewing epithelium and, through much of gestation, exhibits a steady state between increasing numbers of nuclei in cytotrophoblast (CT) and syncytiotrophoblast (ST). The epithelium gradually becomes thinner because its surface expands at a faster rate than its volume. These changes help to ensure that placental diffusing capacity matches the growth in fetal mass. Comparable events occur in the murine placenta. Some of these processes are perturbed in complicated pregnancies: 1) fetoplacental vascular growth is compromised in pregnancies accompanied by maternal asthma, 2) changes in trophoblast turnover occur in pre-eclampsia and intrauterine growth restriction, and 3) uteroplacental vascular development is impoverished, but diffusive transport increases, in pregnant mice exposed to particulate urban air pollution. Finally, quantitative immunoelectron microscopy now permits more rigorous analysis of the spatial distributions of interesting molecules between subcellular compartments or shifts in distributions following experimental manipulation.

Hofbauer Cells in Early Human Placenta: Possible Implications in Vasculogenesis and Angiogenesis

The stroma of the placental villi contain numerous macrophages, so-called Hofbauer cells which are of mesenchymal origin and are thought to function in many processes. Although there are many studies concerning placental vasculogenesis and angiogenesis, there has been a lack of evidence on the possible roles of Hofbauer cells in these processes. In this study we hypothesized that Hofbauer cell locations and numbers might be correlated with the vascular structures within the placental villi core and therefore may be implicated to play roles in placental vasculogenesis and angiogenesis. Placental tissues were obtained from normal first-trimester pregnancies. Tissues were prepared for light microscopic investigations. Double immunohistochemistry staining with CD31/PECAM1 and CD68 was applied to placental tissues. In placental villous core, majority of the Hofbauer cells were found to be either in close contact with angiogenic cell cords and primitive vascular tubes or located in between them. Moreover, the number of Hofbauer cells and vasculogenic structures were found to be significantly correlated. The findings of this study suggest for the first time that Hofbauer cells might be involved in the processes of vasculogenesis and angiogenesis in the placenta.

Vasculogenesis and angiogenesis in the early human placenta

Vasculogenesis and angiogenesis are two consecutive processes during blood vessel development in the human placenta. While vasculogenesis, which is the formation of first blood vessels, is achieved by differentiation of pluripotent mesenchymal cells into haemangiogenic stem cells. The subsequent step, angiogenesis, is characterized by development of new vessels from already existing vessels. In this review, we aim to give an overview of vasculogenesis and angiogenesis during the first trimester of human placental development. Recent studies have shown that at the very early stages of placental development, cytotrophoblasts trigger vasculogenesis and angiogenesis, whereas as pregnancy progresses Hofbauer and stromal cells take over the task of triggering blood vessel development. Important growth factors in this scenario are the vascular endothelial growth factor (VEGF) family and their receptors, as well as Tie-1 and Tie-2. This review depicts the molecular and morphological steps of vasculogenesis and angiogenesis, which can give further insights into human placental development and maturation disorders.

Human type 2 17 beta-hydroxysteroid dehydrogenase mRNA and protein distribution in placental villi at mid and term pregnancy

BACKGROUND

During human pregnancy, the placental villi produces high amounts of estradiol. This steroid is secreted by the syncytium, which is directly in contact with maternal blood. Estradiol has to cross placental foetal vessels to reach foetal circulation. The enzyme 17beta-hydroxysteroid dehydrogenase type 2 (17beta-HSD2) was detected in placental endothelial cells of foetal vessels inside the villi. This enzyme catalyzes the conversion of estradiol to estrone, and of testosterone to androstenedione. It was proposed that estradiol level into foetal circulation could be regulated by 17beta-HSD2.

METHODS

We obtained placentas from 10 to 26 6/7 weeks of pregnancy from women undergoing voluntary termination of pregnancy, term placentas were collected after normal spontaneous vaginal deliveries. We quantified 17beta-HSD2 mRNA levels in mid-gestation and term human placenta by RT-QPCR. We produced a new anti-17beta-HSD2 antibody to study its spatio-temporal expression by immunohistochemistry. We also compared steroid levels (testosterone, estrone and estradiol) and 17beta-HSD2 mRNA and protein levels between term placenta and endometrium.

RESULTS

High 17beta-HSD2 mRNA and protein levels were found in both mid-gestation and term placentas. However, we showed that 17beta-HSD2 mRNA levels increase by 2.27 fold between mid-gestation and term. This period coincides with a transitional phase in the development of the villous vasculature. In mid-gestation placenta, high levels of 17beta-HSD2 were found in mesenchymal villi and immature intermediate villi, more precisely in endothelial cells of the stromal channel. At term, high levels of 17beta-HSD2 were found in the numerous sinusoidal capillaries of terminal villi. 17beta-HSD2 mRNA and protein levels in term placentas were respectively 25.4 fold and 30 to 60 fold higher than in the endometrium. Steroid levels were also significantly higher in term placenta than in the endometrium.

CONCLUSION

The spatial and temporal expression of 17beta-HSD2 in the placenta during pregnancy and the comparison of 17beta-HSD2 expression and steroid levels between placental villi and endometrium are compatible with a role in the modulation of active and inactive forms of estrogens. Our observations strongly support the hypothesis that 17beta-HSD2 acts as a barrier decreasing estradiol secretion rates in the foetal circulation.

Placental villous vascular endothelial growth factor expression and vascularization after estrogen suppression during the last two-thirds of baboon pregnancy

We have recently shown that placental cytotrophoblast vascular endothelial growth factor (VEGF) expression and vessel density were increased by elevating estrogen and decreased by suppressing estrogen in early baboon pregnancy. The present study determined whether the elevation in estrogen which occurs in the last two-thirds of baboon pregnancy also has a role in the regulation of placental villous VEGF expression and angiogenesis. Placentas were obtained on day 170 of gestation (term, 184 days) from baboons untreated or treated with the aromatase inhibitor CGS 20267 or CGS 20267 plus estradiol daily on days 30-169. Serum estradiol levels in CGS 20267-treated baboons were decreased (P < 0.001) by 95%, however, placental cytotrophoblast VEGF mRNA levels (means +/- SE, attomoles/microg RNA) were similar in untreated (25,807 +/- 5,873), CGS 20267-treated (23,900 +/- 1,940) and CGS 20267 plus estradiol-treated (26,885 +/- 2,569) baboons. VEGF mRNA levels in the syncytiotrophoblast (2,008 +/- 405) and inner villous stromal cell (1,724 +/- 287) fractions of untreated baboons also were not altered by CGS 20267. However, whole villous VEGF mRNA levels in CGS 20267-treated baboons (18,590 +/- 2,315) were 4-fold greater (P < 0.001) than in untreated animals and restored to normal by estradiol. Percent vascularized area (15.88 +/- 0.88%) and vessel density (1,375 +/- 71/mm(2)) of the villous placenta in untreated animals were not altered by estrogen deprivation. We propose that villous cytotrophoblasts lose their responsivity to estrogen and that placental villous cytotrophoblast VEGF expression and angiogenesis are regulated by estrogen in a cell- and gestational age-specific manner, and that factors other than estrogen maintain VEGF expression in the last two-thirds of pregnancy.

Moderate maternal nutrient restriction, but not glucocorticoid administration, leads to placental morphological changes in the baboon (Papio sp.)

The aims of the present study were to describe the ontogeny of spatial relationships between placental components in baboons and to investigate alterations in these indices following (1) moderate maternal nutrient restriction and (2) administration of glucocorticoids to pregnant baboons. We investigated the effects of glucocorticoids since they have been shown to play a role in the altered fetal growth that accompanies maternal nutrient restriction. Glucocorticoids are also given to pregnant women who threaten premature labor to accelerate fetal lung maturation. A third aim was to compare our findings to those in similar conditions in human pregnancy. Volumetric placental development in the baboon was similar to that in the human, although growth of fetal capillaries was slower over the second half of gestation in baboon than in human placentas. Intervillous space (IVS) and villous star volumes were halved at the end of gestation compared to the middle of gestation, as described in the human placenta. When mothers were fed 70% of feed eaten by controls fed ad libitum, placental volumetric structure was unchanged at mid-gestation but was altered by the end of gestation when placental weight, but not fetal weight or length, was decreased. At the end of gestation villous volume and surface area, capillary surface area, and the villous isomorphic coefficient were all decreased, In contrast, IVS hydraulic diameter was increased. All parameters were similar in pregnancies with male and female fetuses, with the exception of fetal capillary volume, which was unchanged in pooled samples and those from male fetuses, but decreased in pregnancies with female fetuses. Glucocorticoid administration during the second half of gestation did not produce any changes in the measured indices of placental composition. In summary, these changes in placental structure, associated with maternal nutrient restriction, would all act to decrease placental transport of nutrients. The influence of MNR on villous capillarization depends on fetal gender.