Spatial and Temporal Distribution of Tie-1 and Tie-2 During Very Early Development of the Human Placenta

Evaluation of Vasculogenic Factors in the Developing Embryo at Weeks Five and Seven With a Special Focus on CD133 and TIE2 Markers

Background Human embryo vasculogenesis (blood vessel development starting from endothelial precursors) includes the ability of mesenchymal cells and pluripotent stem cells to differentiate into endothelial cells. Quantification of endothelial progenitor cells is difficult to assess during the early steps of human embryo development due to several factors, especially due to the paucity of human embryo tissue which is usually discarded after early-stage pregnancy abortive methods. CD133 (Promimin-1) is a general marker of progenitor cells, but combined with other endothelial markers such as CD34, it may identify endothelial progenitor cells during embryonic development. CD34 immunohistochemistry was previously performed by our team to identify human embryo capillaries and comparatively assess microvessel density between different human embryonic tissues. TIE2 is an angiopoietin receptor strongly involved in the newly formed blood vessel maturation due to its expression in some mesenchymal precursors for future pericytes. CD34 assesses the presence of endothelial cells but its single use does not evaluate the endothelial progenitor state as CD133 may do nor vessel maturation as TIE2 may do. Data about the dynamics of CD133/TIE2 expression in the early stages of human embryo development are scarce. Hence, in this study, we aimed to comparatively assess the dynamic of CD133+ endothelial precursors and TIE2 expression on five and seven-week-old human embryonic tissues with a special emphasis on their expression on embryonic vascular beds. Methodology CD133 and TIE2 immunohistochemistry was performed on five and seven-week-old human embryonic tissues followed by their quantification using the Qu Path digital image analysis (DIA) automated method. Results CD133 and TIE2 showed divergent patterns of expression during the initial phases of human embryonic development, specifically in the vascular endothelium of tiny capillaries. The expression of CD133 in endothelial cells lining the perfused lumen gradually decreased from five to seven-week-old embryos. It remained expressed with greater intensity in cells located at the tip of the vascular bud that emerged into pre-existing capillaries. TIE2 was much more specific than CD133, being restricted to the level of the vascular endothelium; therefore, it was easier to quantify using digital image analysis. The endothelium of the embryonic aorta was an exception to the divergent expression, as CD133 and TIE2 were consistently co-expressed in the seven-week-old embryo. The Qu Path DIA assessment increased the accuracy of CD133 and TIE2 evaluation, being the first time they were quantified by using automated software and not manually. Conclusions High heterogeneity of CD133 and TIE2 was observed between five and seven-week-old embryonic tissues as well as between different embryonic regions from the same gestational age. The unique finding of CD133/TIE2 co-expression persistence inside aortic endothelium needs further studies to elucidate the role of this co-expression.

Identification of downstream targets and signaling pathways of long non-coding RNA NR_002794 in human trophoblast cells

Preeclampsia (PE) is a huge threat to pregnant women. Our previous study demonstrated that long non-coding RNA (lncRNA) NR_002794 was highly expressed in placentas of PE patients and could regulate the phenotypes of trophoblast cells. However, the downstream regulatory mechanisms of NR_002794 remain unknown. In this text, some potential downstream targets or signaling pathways of NR_002794 were identified through RNA sequencing (RNA-seq) and bioinformatics analysis in SWAN71 trophoblast cells. Western blot assay demonstrated that NR_002794 inactivated protein kinase B (AKT) and extracellular signal-regulated kinase 1/2 (ERK1/2) pathways and activated cell apoptotic signaling in SWAN71 cells. Both RNA-seq and reverse transcription-quantitative PCR (RT-qPCR) outcomes showed that NR_002794 up-regulation could notably inhibit the expression of C-C motif chemokine ligand 4 like 2 (CCL4L2), interleukin 15 receptor subunit alpha (IL15RA), interleukin 32 (IL32), and tyrosine kinase with immunoglobulin-like and EGF-like domains 1 (TIE1), while NR_002794 knockdown induced these gene expressions in SWAN71 cells. CCK-8, BrdU, Transwell, wound healing, and flow cytometry analyses showed that NR_002794 inhibited cell proliferation and migration and induced cell apoptosis through down-regulating TIE1 in SWAN71 cells. In conclusion, lncRNA NR_002794 could exert its functions by regulating AKT and ERK1/2 pathways and TIE1 expression in human trophoblast cells.

Effect of Maternal Obesity in Mice on IL-6 Levels and Placental Endothelial Cell Homeostasis

Obesity during pregnancy is a known health risk for mother and child. Since obesity is associated with increased inflammatory markers, our objectives were to determine interleukin-6 (IL-6) levels in obese mice and to examine the effect of IL-6 on placental endothelial cells. Placentas, blood, and adipose tissue of C57BL/6N mice, kept on high fat diet before and during pregnancy, were harvested at E15.5. Serum IL-6 levels were determined and endothelial cell markers and IL-6 expression were measured by qRT-PCR and western blot. Immunostaining was used to determine surface and length densities of fetal capillary profiles and placental endothelial cell homeostasis. Human placental vein endothelial cells were cultured and subjected to proliferation, apoptosis, senescence, and tube formation assays after stimulation with hyperIL-6. Placental endothelial cell markers were downregulated and the percentage of senescent endothelial cells was higher in the placental exchange zone of obese dams and placental vascularization was strongly reduced. Additionally, maternal IL-6 serum levels and IL-6 protein levels in adipose tissue were increased. Stimulation with hyperIL-6 provoked a dose dependent increase of senescence in cultured endothelial cells without any effects on proliferation or apoptosis. Diet-induced maternal obesity led to an IUGR phenotype accompanied by increased maternal IL-6 serum levels. In the placenta of obese dams, this may result in a disturbed endothelial cell homeostasis and impaired fetal vasculature. Cell culture experiments confirmed that IL-6 is capable of inducing endothelial cell senescence.

The role of Hofbauer cells on the pathogenesis of early pregnancy loss

INTRODUCTION

Hofbauer cells (HC) are the placental macrophages that play a significant role in many important placental events. The aim of this retrospective study is to investigate the role of HC in the pathogenesis of early pregnancy loss (EPL).

METHODS

The slides were obtained from archival blocks of missed abortion (MA, n = 15) and blighted ovum (BO, n = 15) cases. Unwanted pregnancies materials constituted the control group (n = 15). HC and endothelial cells were identified using immunohistochemical methods. HC were counted under light microscope. The extent of villous vasculature was evaluated using two methods; the Chalkey method and microvessel scoring.

RESULTS

The mean number of villous HC was found to be significantly higher in both MA and BO groups in contrast to the control group. MA group also showed a higher number of HC in comparison with the BO group. Higher microvessel scoring was also found in MA group in contrast to other two groups. Chalkey method revealed no significant difference in the extent of villous vasculature for the control group in comparison with MA and BO.

DISCUSSION

As we identified relatively low quantity of HC in BO associated with defective vasculature, we hypothesize that an inadequate microvessel formation after hypoxic insult can explain the pathogenesis of BO. We believe that HC are increased in MA due to their divergent roles on immunity and inflammation.

CONCLUSION

We therefore conclude that HC may be of biological importance in the pathogenesis of EPL.

Angiogenic factors in preeclampsia and related disorders

During fetal development, the human placenta undergoes high levels of both angiogenesis and vasculogenesis. Additionally, the developing placenta undergoes a process of vascular mimicry (referred to as pseudovasculogenesis) as cytotrophoblasts convert from an epithelial to an endothelial phenotype. The initiation, maturation, and maintenance of the placental vasculature are of critical importance. Failure to do so can lead to adverse obstetric outcomes such as preeclampsia and/or intrauterine growth restriction (IUGR). Furthermore, the foundation of many aspects of adult health is laid in utero. In this context, normal placental function is not only critical for normal fetal development but can also permanently influence long-term health and disease. Understanding the mechanisms that regulate placental vasculogenesis and angiogenesis is therefore of critical importance. This chapter will focus on placental vascular development with a particular emphasis on the role of angiogenic factors in the pathogenesis of the maternal syndrome of preeclampsia and related disorders.

The paracrinology of tubal ectopic pregnancy

As part of successful human reproduction, the Fallopian tube must provide a suitable environment for pre-implantation development of the embryo and for efficient transport of the embryo to the uterus for implantation. These functions are coordinated by paracrine interactions between tubal epithelial, smooth muscle and immune cells and the cells of the developing embryo. Alterations in these signals can lead to a tubal microenvironment encouraging of embryo implantation and to dysregulated tubal motility, ultimately resulting in inappropriate and early implantation of the embryo in the Fallopian tube. Here, we highlight novel and emerging concepts in tubal physiology and pathobiology, such as the induction of a receptive phenotype within the Fallopian tube, leading to ectopic implantation. Chlamydia trachomatis infection is a risk factor for tubal ectopic pregnancy. Activation of toll-like receptor 2 (TLR-2) in the Fallopian tube epithelium, by C. trachomatis has recently been demonstrated, leading to the dysregulation of factors involved in implantation and smooth muscle contractility, such as prokineticins (PROK), activin A and interleukin 1 (IL-1). The Fallopian tube has also recently been shown to harbour a unique population of immune cells, compared to the endometrium. In addition, the complement of immune cells in the Fallopian tube has been reported to be altered in Fallopian tube from women with ectopic pregnancy. There are increasing data suggesting that vascularisation of the Fallopian tube, by the embryo during ectopic pregnancy, differs from that initiated in the uterus during normal pregnancy. This too, is likely the result of paracrine signals between the embryo and the tubal microenvironment.

Significant decrease in maternal serum concentrations of angiopoietin-1 and -2 after delivery

OBJECTIVE

To characterize the physiological distribution of angiopoietins (Ang)-1 and Ang-2 and soluble endothelial cell-specific tyrosine kinase receptor-2 (Tie-2) at term and following delivery.

DESIGN

A prospective, descriptive study.

SETTING

Helsinki University Central Hospital.

POPULATION

Twenty healthy term pregnant women undergoing elective cesarean delivery and their newborns.

METHODS

The concentrations were analysed by enzyme-linked immunosorbent assay in maternal antepartum and the first postpartum day sera, umbilical serum, amniotic fluid and maternal and newborn urine.

MAIN OUTCOME MEASURES

Concentrations of Ang-1, Ang-1 and Tie-2. Results. Concentrations of maternal serum Ang-1 and Ang-2 decreased after delivery {[median (range)]: Ang-1, from 33 (25-51) to 30 (18-49) ng/mL, p= 0.017; and Ang-2, from 5.4 (1.8-18) to 1.4 (0.7-4.6) ng/mL, p < 0.0001}, whereas Tie-2 concentrations remained stable [23 (13-41) vs. 25 (14-29) ng/mL, p= 0.107]. Compared with maternal antepartum serum, umbilical serum concentrations of Ang-1 [46 (28-59) ng/mL, p < 0.0001] and Tie-2 [45 (21-71) ng/mL, p < 0.0001] were higher and those of Ang-2 similar [5.4 (1.8-18) vs. 4.2 (2.9-6.0) ng/mL; p= 0.067]. Low concentrations of Ang-1 [1.2 (0.1-2.2) ng/mL], Ang-2 [1.1 (0.3-4.1) ng/mL] and Tie-2 [0.4 (0.08-0.9) ng/mL] were observed in amniotic fluid, but they were undetectable in newborn urine and in most of the maternal urine samples.

CONCLUSIONS

Maternal Ang-1 and Ang-2 concentrations decreased following delivery. Umbilical concentrations of Ang-1 and Tie-2 were higher than the maternal concentrations.

Low VEGF expression in conceptus material and maternal serum AFP and β-hCG levels as indicators of defective angiogenesis in first-trimester miscarriages

OBJECTIVE

The aims of this study were to assess the relationship between early miscarriages and vascular endothelial growth factor (VEGF) expression and to determine the serum levels of first-trimester maternal alpha-fetoprotein (AFP) and human chorionic gonadotropin (β-hCG) as markers of angiogenesis and predictors of abortion and intrauterine fetal loss.

MATERIAL AND METHODS

The present study was a prospective, single-center, randomized controlled clinical trial. Ninety-five women who were 6-10 weeks pregnant between May and June 2010 were included in the study. The subjects were divided into three groups, i.e., incomplete abortion (IA) (n=31), intrauterine death (IU-D) (n=32) and control (elective pregnancy termination) (n=32). Feto-placental materials were compared based on immune staining for VEGF in the pathology laboratory, and maternal serum samples were tested in the hormone laboratory.

RESULTS

Serum β-hCG levels in the patient groups were significantly lower than the controls (p=0.001). The serum AFP level was lower than the controls in the IA group while it was higher than the controls in the IU-D (p=0.016). Immunohistochemistry showed that the cytotrophoblast, syncytiotrophoblast and endometrial gland epithelium were weakly stained for VEGF in the patient groups (IA and IU-D) in comparison to the control group (p=0.06, p=0.028, p=0.006).

CONCLUSION

Early pregnancy losses are related to insufficient angiogenesis, and maternal serum AFP and β-hCG can be used as markers of angiogenesis in the first trimester.

Jab1 expression is associated with TGF-β1 signaling in chronic rhinosinusitis and nasal polyposis

Jab1, which is a fifth component of COP9 signalosome, plays an essential role in cell growth and proliferation. Jab1 is also shown to regulate transforming growth factor-beta (TGF-β) signaling in carcinoma cells. The aim of the present study was to investigate the expression and the correlation of Jab1 and TGF-β1 in chronic rhinosinusitis and nasal polyposis. Here, we show the elevated expression of Jab1 and TGF-β1 in diseased mucosa without nasal polyps and a correlation between Jab1 and TGF-β1 expression. Forty-six samples (26 patients with nasal polyps, 10 patients with chronic rhinosinusitis and 10 control subjects) were included to this study. Immunohistochemistry and Western blotting were performed for the assessment of Jab1 and TGF-β1 localization and the expression of proteins. Double staining of both proteins showed that Jab1 and TGF-β1 were colocalized in the epithelium, inflammatory cells and the vascular endothelium of nasal mucosa. There was a significant increase in the expression of TGF-β1 and Jab1 in patients without nasal polyps and a significant decrease in patients with nasal polyps compared to controls. Moreover, correlation was detected between the expression of Jab1 and TGF-β1 in chronic rhinosinusitis and nasal polyposis. Our results demonstrate that chronic rhinosinusitis is characterized by elevated expression of Jab1 and TGF-β1 compared to nasal polyposis and Jab1 may play a vital role in the pathogenesis of both chronic rhinosinusitis and nasal polyposis.

Developmental expression of p97/VCP (Valosin-containing protein) and Jab1/CSN5 in the rat testis and epididymis

BACKGROUND

The ubiquitin proteasome system (UPS) is a key player in regulating many cellular processes via proteasomal degradation of ubiquitinated proteins. Recently published data show that Jab1/CSN5 interacts with p97/VCP and controls the ubiquitination status of proteins bound to p97/VCP in mouse and human cells. However, coexpression of p97/VCP and Jab1/CSN5 in the developing rat testis and epididymis has not previously been studied.

METHODS

Testicular and epididymal tissues from 5-, 15-, 30-, and 60-day-old rats were examined by immunohistochemistry and Western blotting. Colocalisation of proteins was determined by immunofluorescence microscopy.

RESULTS

In the 5-day-old rat testis, p97/VCP and Jab1/CSN5 were specifically expressed in gonocytes. The expression of p97/VCP and Jab1/CSN5 significantly increased at day 15 and was found in spermatogonia, Sertoli cells and spermatocytes. In 30- and 60-day-old rat testes, p97/VCP indicated moderate to strong expression in Sertoli cells, spermatogonia, round and elongating spermatids. However, moderate to weak expression was observed in spermatocytes. Jab1/CSN5 showed strong expression in spermatogonia and spermatocytes, while relatively moderate expression was observed in round and elongating spermatids in 30- and 60-day-old rat testes. In contrast, in the epididymis, the expression of both proteins gradually increased from 5 to 60 days of age. After rats reached 2 weeks of age, the expression of both proteins was mostly restricted to the basal and principal cells of the caput epididymis.

CONCLUSIONS

Our study suggests that p97/VCP and Jab1/CSN5 could be an important part of the UPS in the developing rat testis and epididymis and that both proteins may be involved in the regulation of spermatogenesis and epididymal epithelial functions.

Vasculogenesis and angiogenesis in the endometrium during menstrual cycle and implantation

Blood vessels develop via two subsequent processes, vasculogenesis and angiogenesis, both being of crucial importance during menstrual cycle and implantation. These processes are also involved in the development of the fetal and placental vasculatures. During vasculogenesis, formation of the earliest primitive capillaries is achieved by in situ differentiation of hemangiogenic stem cells that are derived from pluripotent mesenchymal cells. The subsequent process, angiogenesis, is characterized by development of new vessels from already existing vessels, and is a well coordinated process initiated by stimulation of various growth factors. Vasculogenesis and angiogenesis are important and complex processes involving extensive interplay between cells and growth factors. The development, maturation and maintenance of the vascular network are necessary for successful hemochorial placentation as well as normal embryonic development and growth. In this review, we outline the basic mechanisms of vasculogenesis and angiogenesis in the endometrium during the menstrual cycle and different stages of implantation, and consider how this data can be applied to human pregnancy. Recent studies have shown that during the initiation steps of implantation, angiogenic factors trigger vasculogenesis and angiogenesis. Different inducers and stimulators affect angiogenesis and vasculogenesis by directly or indirectly stimulating proliferation, differentiation and migration of endothelial or respective precursor cells. As a conclusion, understanding the mechanisms of angiogenesis and the roles of angiogenic factors during the menstrual cycle and implantation may provide new insights and possible approaches for embryo implantation and healthy pregnancy.

The human placenta is a hematopoietic organ during the embryonic and fetal periods of development

We studied the potential role of the human placenta as a hematopoietic organ during embryonic and fetal development. Placental samples contained two cell populations-CD34(++)CD45(low) and CD34(+)CD45(low)-that were found in chorionic villi and in the chorioamniotic membrane. CD34(++)CD45(low) cells express many cell surface antigens found on multipotent primitive hematopoietic progenitors and hematopoietic stem cells. CD34(++)CD45(low) cells contained colony-forming units culture (CFU-C) with myeloid and erythroid potential in clonogenic in vitro assays, and they generated CD56(+) natural killer cells and CD19(+)CD20(+)sIgM(+) B cells in polyclonal liquid cultures. CD34(+)CD45(low) cells mostly comprised erythroid- and myeloid-committed progenitors, while CD34(-) cells lacked CFU-C. The placenta-derived precursors were fetal in origin, as demonstrated by FISH using repeat-sequence chromosome-specific probes for X and Y. The number of CD34(++)CD45(low) cells increased with gestational age, but their density (cells per gram of tissue) peaked at 5-8 wk, decreasing more than sevenfold at the onset of the fetal phase (9 wk of gestation). In addition to multipotent progenitors, the placenta contained myeloid- and erythroid-committed progenitors indicative of active in situ hematopoiesis. These data suggest that the human placenta is an important hematopoietic organ, raising the possibility of banking placental hematopoietic stem cells along with cord blood for transplantation.

HOXA13 Is essential for placental vascular patterning and labyrinth endothelial specification

In eutherian mammals, embryonic growth and survival is dependent on the formation of the placenta, an organ that facilitates the efficient exchange of oxygen, nutrients, and metabolic waste between the maternal and fetal blood supplies. Key to the placenta's function is the formation of its vascular labyrinth, a series of finely branched vessels whose molecular ontogeny remains largely undefined. In this report, we demonstrate that HOXA13 plays an essential role in labyrinth vessel formation. In the absence of HOXA13 function, placental endothelial cell morphology is altered, causing a loss in vessel wall integrity, edema of the embryonic blood vessels, and mid-gestational lethality. Microarray analysis of wild-type and mutant placentas revealed significant changes in endothelial gene expression profiles. Notably, pro-vascular genes, including Tie2 and Foxf1, exhibited reduced expression in the mutant endothelia, which also exhibited elevated expression of genes normally expressed in lymphatic or sinusoidal endothelia. ChIP analysis of HOXA13–DNA complexes in the placenta confirmed that HOXA13 binds the Tie2 and Foxf1 promoters in vivo. In vitro, HOXA13 binds sequences present in the Tie2 and Foxf1 promoters with high affinity (K_d = 27–42 nM) and HOXA13 can use these bound promoter regions to direct gene expression. Taken together, these findings demonstrate that HOXA13 directly regulates Tie2 and Foxf1 in the placental labyrinth endothelia, providing a functional explanation for the mid-gestational lethality exhibited by Hoxa13 mutant embryos as well as a novel transcriptional program necessary for the specification of the labyrinth vascular endothelia.

Defects in placental development are a common cause of mid-gestational lethality. Key to the placenta's function is its vascular labyrinth, a series of finely branched vessels that facilitate the efficient exchange of gases, nutrients, and metabolic waste between the maternal and fetal blood supplies. In this study, we identify a novel role for the transcription factor HOXA13 in formation of the placental vascular labyrinth. In the absence of HOXA13 function, labyrinth vessel branching and endothelial specification is compromised, causing mid-gestational lethality due to placental insufficiency. Analysis of the genes affected by the loss of HOXA13 function revealed significant reductions in the expression of several pro-vascular genes, including Tie2 and Foxf1. Analysis of the Tie2 and Foxf1 promoters confirmed that HOXA13 binds sites present in each promoter with high affinity in the placenta, and in vitro, HOXA13 can use these bound sequences to regulate gene expression. These results suggest that Tie2 and Foxf1 are direct transcriptional targets of HOXA13 in the developing placental labyrinth, providing a novel transcriptional pathway to consider when examining pathologies of the placenta and placental insufficiency, as well as the evolutionary mechanisms required for the emergence of the vascular placenta in eutherian mammals.

Angiogenesis in implantation

PROBLEM

Implantation failure and early pregnancy loss are common following natural conceptions and they are particularly important clinical hurdles to overcome following assisted reproduction attempts. The importance of adequate vascular development and maintenance during implantation has recently become a major focus of investigation.

MATERIALS AND METHODS

Review of current published literature was undertaken to summerize the cells and cell products that regulate tissue vascularity during implantation.

RESULTS

Vascular development at the maternal fetal interface can be regulated by a number of different cell types; two principal candidates are trophoblast and natural killer cells. A wide range of soluble factors, some with well established angiogenic functions as well as other more novel factors, can contribute to vascular development and maintenance at the maternal-fetal interface.

CONCLUSIONS

Robust vascular development occurs during implantation and early placentation of normal pregnancies. Studies to define the extent and mechanisms by which defects in vascularity contribute to human implantation failure and early miscarriage need to be undertaken.

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.

Sequential Steps During Vasculogenesis and Angiogenesis in the Very Early Human Placenta

Development of blood vessels takes place via two subsequent processes, vasculogenesis and angiogenesis. During vasculogenesis, formation of first blood vessels is achieved by differentiation of hemangiogenic stem cells from pluripotent mesenchymal cells, while during angiogenesis new blood vessels form from already existing vessels. The combination of our data with those from the literature leads us to depict the chronological steps of cell differentiation in the mesenchymal core of placental villi during vasculogenesis and angiogenesis. This current opinion will focus on the temporal and spatial expression of VEGF and its receptors VEGFR-1 and VEGFR-2, and the angiopoietin receptors Tie-1 and Tie-2 in parallel to vascular maturation in human placental villi during very early stages of placental development. There is evidence that the interplay of a variety of growth factors secreted from different cell types during development is needed to trigger as well as maintain placental vasculogenesis and angiogenesis.