Maternal Blood Vessels Research Articles

Light and Scanning Electron Microscopic Study on the Blood Vascular System of the Donkey Placenta

The donkey placenta is diffuse and epitheliochorial with numerous microplacentomes consisting of a fetal microcotyledonary and a maternal microcaruncular part. The microplacentomal vasculature during the last third of pregnancy has been investigated by light microscopy in comparison to scanning electron microscopy of the materno-fetal contact surface and corrosion casts of blood vessels after plastic instillation from either the microcotyledonary or the microcaruncular side, and, for the first time in a perissodactyle, from both sides. Morphological data were semiquantitatively evaluated. The supplying parts of both, the microcotyledonary and the microcaruncular vascular system are strictly proximo-distally oriented, thus reaching the capillary systems or working parts in the shortest way possible. The straight course of the vasculature, particularly on the fetal side, suggests the occurrence of venulo-arteriolar back diffusion. The fetal capillary system consists of convolutes confronting the maternal septal capillary complexes in a countercurrent way. This materno-fetal blood flow interrelationship is highly efficient in terms of placental exchange, which is further supported (1) by dilations and increasing coiling of the fetal venular capillary limbs in particular and (2) by a decrease in the interhaemal distance from 12.5 to 7.2 microm between the two capillary systems. Besides the countercurrent blood flow interrelationship, some maternal branch arterioles reach the septal capillary system from the maternally oriented pole of the microplacentome or microcaruncle, respectively, resulting in the less efficient crosscurrent blood flow. Hence, in the donkey placenta fetal and maternal blood vessels meet in a mix of countercurrent and crosscurrent flow patterns.

Maternal diabetes affects specific extracellular matrix components during placentation

During embryo implantation, invasive trophoblast cells mediate embryo invasion into the decidualized stroma, forming a rich network of lacunae that connect the embryonic tissues to the maternal blood vessels. Placentation is probably guided by the composition and organization of the endometrial extracellular matrix. Certain pathological conditions that occur during pregnancy, including diabetes, have been linked to abnormal placental morphology and consequent fetal morbidity. We used immunoperoxidase techniques to identify members of the collagen, proteoglycan and glycoprotein families in the various compartments of the rat placenta and to determine whether experimentally induced diabetes affects placental morphology and alters the distribution of these molecules during pregnancy. Single injections of alloxan (40 mg kg(-1) i.v.) were used to induce diabetes on day 2 of pregnancy in Wistar rats. Placentas were collected on days 14, 17, and 20. Type I and III collagen, as well as the proteoglycans decorin and biglycan, were found to be distributed throughout the placentas of control and diabetic rats. In both groups, laminin expression decreased at the end of pregnancy. In contrast, fibronectin was detected in the labyrinth region of diabetic rats at all gestational stages studied, whereas it was detected only at term pregnancy in the placentas of control rats. These results show for the first time that some extracellular matrix molecules are modulated during placental development. However, as diabetic rats presented increased fibronectin deposition exclusively in the labyrinth region, we speculate that diabetes alters the microenvironment at the maternal-fetal interface, leading to developmental abnormalities in the offspring.

Stage-specific Integration of Maternal and Embryonic Peroxisome Proliferator-activated Receptor δ Signaling Is Critical to Pregnancy Success

Successful pregnancy depends on well coordinated developmental events involving both maternal and embryonic components. Although a host of signaling pathways participate in implantation, decidualization, and placentation, whether there is a common molecular link that coordinates these processes remains unknown. By exploiting genetic, molecular, pharmacological, and physiological approaches, we show here that the nuclear transcription factor peroxisome proliferator-activated receptor (PPAR) delta plays a central role at various stages of pregnancy, whereas maternal PPARdelta is critical to implantation and decidualization, and embryonic PPARdelta is vital for placentation. Using trophoblast stem cells, we further elucidate that a reciprocal relationship between PPARdelta-AKT and leukemia inhibitory factor-STAT3 signaling pathways serves as a cell lineage sensor to direct trophoblast cell fates during placentation. This novel finding of stage-specific integration of maternal and embryonic PPARdelta signaling provides evidence that PPARdelta is a molecular link that coordinates implantation, decidualization, and placentation crucial to pregnancy success. This study is clinically relevant because deferral of on time implantation leads to spontaneous pregnancy loss, and defective trophoblast invasion is one cause of preeclampsia in humans.

Vascular Arrangement and Ultrastructure of the European Eelpout Zoarces viviparus Ovary: Implications for Maternal–Embryonic Exchange

The structural basis for exchange between maternal serum and ovarian fluid in the viviparous teleost Zoarces viviparus was investigated. Casts of the ovarian vasculature showed that blood supply to the ovary is initially directed to the follicular appendages lining the ovarian wall through thick-walled muscular arteries running along the ovary wall and within the follicular appendages. The follicles had a rich capillary network with diffusion distances between maternal blood and ovarian fluid comparable to those found for gill epithelia, suggesting this is the primary site of gas exchange between maternal plasma and ovarian fluid. Follicular capillary beds were continuous with those in the ovary wall and were eventually drained by the ovarian and intestinal venous systems. The barrier between ovarian fluid and maternal blood consisted of the endothelial cells of the maternal blood vessels and a layer of epithelial cells lining the ovarian lumen, with an intermittent layer of loose connective fibers. Junctional complexes between cells were predominantly anchoring junctions with the occurrence of occasional occluding junctions, supporting the possibility of paracellular transport from maternal serum to ovarian fluid of small molecular weight compounds. Heavy investment in keratin filaments suggests that follicles are tissues of high structural integrity. Evidence for protein synthesis in the ovarian lining was found in the form of Golgi apparatus and rough endoplasmic reticulum. Although numerous cytoplasmic vacuoles and secretory granules were present in both epithelial and endothelial cells, the fate of synthesized protein remains to be determined.

Differences in placental structure during gestation associated with large and small pig fetuses1,2

The efficiency of nutrient transport from the pregnant female pig to the developing fetus depends on the size and function of the placenta. It has been reported that maternal and fetal blood vessels are arranged in a cross-countercurrent arrangement within placental microscopic folds. Thus, the blood supplies are in close apposition to each other within these microscopic folds, and maternal and fetal blood flows in approximately opposite directions perpendicular to the plane of the placenta. This arrangement indicates that the width of the microscopic folds influences placental efficiency. The objective of this study was to determine whether differences in pig placental microscopic fold development are associated with differences in fetal size or are influenced by selection for ovulation rate or uterine capacity. Gilts from a randomly selected control line, a line selected for ovulation rate, and a line selected for uterine capacity were slaughtered, and uterine wall samples were collected within the placentas associated with the largest and smallest fetuses in each litter on d 45, 65, 85, and 105 of gestation. The uterine wall samples were processed for histology and analyzed using computer-assisted morphometry. Average width of the placental folds and average width of the placental stroma above the folds were measured. To measure fold complexity, the length of the epithelial bilayer for a given length of placenta was also measured. The width of the folded bilayer increased significantly from d 65 to 105 and was greater in placentas associated with small fetuses compared with large fetuses on d 105 of gestation. In contrast, the width of the placental stroma above the folded bilayer decreased with gestation and decreased more rapidly in placenta associated with the smallest compared with the largest fetus. These results indicate that the width of the microscopic folds of the placental trophoblast/endometrial epithelial bilayer is increased in placenta associated with small fetuses, which we hypothesize will increase the surface area for interaction between maternal and fetal blood supplies, thus improving placental efficiency in response to reduced placental size.

Upregulation of Soluble Vascular Endothelial Growth Factor Receptor 1 Contributes to Angiogenesis Defects in the Placenta of α 2B -Adrenoceptor–Deficient Mice

Alpha2-adrenoceptors are essential presynaptic regulators of norepinephrine release from sympathetic nerves. Previous studies in mice with targeted deletions in the 3 alpha2-adrenoceptor genes have indicated that these receptors are essential for embryonic development. In the present study, we searched for the alpha2-adrenoceptor subtype(s) involved in placental development and its molecular mechanism using mice carrying targeted deletions in alpha2-adrenoceptor genes. Congenic alpha2B-adrenoceptor-deficient mice (Adra2b-/-) developed a defect in fetal and maternal vessel formation in the placenta labyrinth at embryonic day 10.5. This defect was accompanied by reduced endothelial cell proliferation and decreased extracellular signal-regulated kinase 1/2 phosphorylation levels in Adra2b-/- as compared with Adra2b+/+ placentae. Microarray analysis of wild-type and mutant placentae (maternal genotype Adra2b+/-) revealed 179 genes, which were significantly up- or downregulated >1.5-fold in alpha2B-deficient placentae. The type 1 receptor for vascular endothelial growth factor (Flt1), which is coexpressed with alpha2B-adrenoceptors in spongiotrophoblast and giant cells of the placenta, was found to be 2.3-fold upregulated in alpha2B-deficient placentae. Neutralization of Flt1 and its soluble splice variant sFlt1 by a specific antibody in vivo prevented the vascular defect in alpha2B-deficient placentae at embryonic day 10.5. Thus, alpha2B-adrenoceptors are essential to suppress antiangiogenic (s)Flt1 in spongiotrophoblasts to control the coordinated formation of a vascular labyrinth of fetal and maternal blood vessels in the murine placenta during development.

PROGRANULIN IS EXPRESSED DURING MINK EMBRYO IMPLANTATION AND PLACENTA FORMATION

The mink is a seasonal breeder displaying embryonic diapause, comprising an arrest in embryo development at the blastocyst stage. Resumption of development and initiation of implantation are controlled by photoperiod and hypophysial prolactin secretion. We are using the mink as a model to study the pre- and post- implantation molecular events in the embryos by terminating diapause with exogenous prolactin treatment. Progranulin is a secretory glycoprotein which was previously shown to be involved in embryo hatching prior to implantation, and to be expressed in placental tissues in the mouse. By in situ hybridization and immunohistochemistry, we sought to determine the distribution of progranulin expression in the mink uterus around the time of embryo implantation. Following the resumption of embryonic development, the luminal and glandular epithelium of the activated uterus exhibit strong expression of progranulin mRNA and protein. The day of implantation, the cytotrophoblast and the transformed glandular epithelium show a marked staining for both progranulin mRNA and protein. During the formation of the trophoblastic villi, the expression of progranulin transcripts and protein is particularly strong in the cytotrophoblast cells. When the labyrinth is vascularized by the embryonic and maternal blood vessels, progranulin expression is evident in the cytotrophoblast, the syncytiotrophoblast, in the maternal hypertrophied endothelial cells, as well as in the glandular epithelium of the glandular zone of the mink endotheliochorial placenta. This evidence suggests that progranulin plays an important role in embryo implantation and development of the mink endotheliochorial placenta. Supported by a grant from the Natural Sciences and Engineering Research Council to B.D. Murphy. (poster)

Effects of uteroplacental restriction on the relaxin-family receptors, Lgr7 and Lgr8, in the uterus of late pregnant rats

The peptide hormone relaxin stimulates uterine growth and endometrial angiogenesis and inhibits myometrial contractions in a variety of species. The receptor for relaxin is a leucine-rich repeat containing G-protein-coupled receptor Lgr7 (RXFP1) that is highly expressed in the myometrium of late pregnant mice, with a significant decrease in receptor density observed at term. The present study first compared the expression of Lgr7 with another relaxin-family receptor Lgr8 (RXFP2) in the uterus and placenta of late pregnant rats. The uterus was separated into endometrial and myometrial components, and the myometrium into fetal and non-fetal sites, for further analysis. We then assessed the response of these receptors to uteroplacental restriction (UPR). Expression of the Lgr7 gene was significantly higher in the uterus compared with the placenta. Within the uterus, on Day 20 of gestation, there was equivalent expression of Lgr7 in fetal and non-fetal sites of the myometrium, as well as in the endometrium v. myometrium. The second receptor investigated, Lgr8, was also expressed in the endometrium and myometrium, but at significantly lower levels than Lgr7. Bilateral ligation of the maternal uterine blood vessels on Day 18 of gestation resulted in uteroplacental restriction, a decrease in fetal weight and litter size, and a significant upregulation in uterine, but not placental, Lgr7 and Lgr8 gene expression in UPR animals compared with controls. These data suggest that both relaxin family receptors are upregulated in response to a reduction in uteroplacental blood flow in rats.

Autotaxin Stabilizes Blood Vessels and Is Required for Embryonic Vasculature by Producing Lysophosphatidic Acid

Autotaxin (ATX) is a cancer-associated motogen that has multiple biological activities in vitro through the production of bioactive small lipids, lysophosphatidic acid (LPA). ATX and LPA are abundantly present in circulating blood. However, their roles in circulation remain to be solved. To uncover the physiological role of ATX we analyzed ATX knock-out mice. In ATX-null embryos, early blood vessels appeared to form properly, but they failed to develop into mature vessels. As a result ATX-null mice are lethal around embryonic day 10.5. The phenotype is much more severe than those of LPA receptor knock-out mice reported so far. In cultured allantois explants, neither ATX nor LPA was angiogenic. However, both of them helped to maintain preformed vessels by preventing disassembly of the vessels that was not antagonized by Ki16425, an LPA receptor antagonist. In serum from heterozygous mice both lysophospholipase D activity and LPA level were about half of those from wild-type mice, showing that ATX is responsible for the bulk of LPA production in serum. The present study revealed a previously unassigned role of ATX in stabilizing vessels through novel LPA signaling pathways.

Comparative Placentation and Animal Models: Patterns of Trophoblast Invasion – A Workshop Report

Keywords: Epitheliochorial placentation; Endotheliochorial placentation; Haemochorial placentation; Placenta;TrophoblastINTRODUCTIONThe degree of trophoblast invasion is very variable betweenspecies [1]. However, the factors influencing it, and benefitsderiving from it, are little understood. In the epitheliochorialplacentation of pig, camel, and horse, trophoblast microvilliinterdigitate with those of the maternal uterine epithelium,and there is no trophoblast invasion as such. One modificationof this is synepitheliochorial placentation where some special-ised trophoblast cells detach and migrate through to the mater-nal epithelium and fuse with it, as is seen in ovine and bovineplacentae. Another is the trophoblast girdle cell invasion intothe endometrium to form the cups in the early horse placenta.In endotheliochorial placentation there is some invasion intothe maternal stroma, stopping short at maternal blood vessels,while the most invasive form is haemochorial, found in human,rodent, bat and other species, where the maternal endotheliumis stripped away so that the trophoblast is in direct contactwith maternal blood. There is at present some controversyabout which form is the most primitive and what evolutionarypressures influenced the development of the different placentaltypes [2,3].In order to understand these systems and their relevance tohuman pregnancy, it is important to examine the modes of pla-centation of various other species. The contributors to thisworkshop covered many different facets of this subject aswell as a wide range of animals, from the elephant to themouse.CONTRASTING PATTERNS OF TROPHOBLASTINVASION IN THE RAT AND MOUSER. Pijnenborg discussed work done with L. Vercruysse, andshowed how, as in the human, both rat and mouse have twopathways of trophoblast invasion, a vascular and an interstitialpathway. Vascular invasion in the mouse is limited to the de-cidua, and follows a perivascular route, showing gradual re-placement of the endothelium from the outside. Vascularsmooth muscle is absent in decidua, and much thinned inthe noninvaded mesometrial triangle. The remodelling istherefore independent of trophoblast. Areas of intense vascularremodelling are associated with high numbers of uterine natu-ral killer (uNK) cells which, when underdeveloped, allow peri-vascular trophoblast invasion into the distal decidua [4],suggesting a possible reciprocal relationship between tropho-blast invasion and uNK cell distribution. In contrast, vascularinvasion in the rat extends into the mesometrial triangle, isendovascular, and is followed by endothelial replacementfrom the inside, while the thinned vascular smooth muscle layershows severe fragmentation [5]. In the mesometrial triangle ofdeciduomata (without trophoblast) vascular smooth muscleshows similar thinning as in mice. Further muscle breakdownin placental sites of the rat is clearly associated with tropho-blast. In the rat, uNK distribution is more associated withthe spiral arteries than in the mouse, but might have a similarfunction in initial vascular remodelling. Rat spiral arterychanges include fibrinoid deposition between trophoblast andvessel wall and, as in the human, re-endothelialization aftermural incorporation of invaded trophoblast. Interstitial inva-sion follows vascular invasion and arises from trophospongialglycogen cells in both species. However, deep interstitial inva-sion beyond the decidua occurs only in the rat, extending intothe mesometrial triangle from day 16 and filling most of itfrom day 18 onwards [6].

Effects of IL-1 beta on RT1-A/RT1-DM at the maternal-fetal interface during pregnancy in rats

Interleukin-1 (IL-1beta) beta and major histocompatibility complex (MHC) play an important role during pregnancy. Expression of non-classical class MHC II RT1-DM antigen and classical class MHC I RT1-A antigen induced by IL-1beta was examined by Northern blotting, Western blotting and immunohistochemistry. IL-1beta treatment significantly increased the expression of RT1-A and RT1-DM in early and mid pregnancy. In late pregnancy, expression of RT1-DM significantly increased in uteri and decreased in placenta. Immunohistochemical studies indicated that, in early pregnancy, RT1-DM protein mainly localized to luminal and glandular uterine epithelium, and RT1-A was present in deciduas basalis, outer layer of luminal epithelium and glandular epithelium. During mid and late pregnancy, RT1-DM was present in maternal blood vessels and syncytiotrophoblast of labyrinthine zone, and RT1-A was present in maternal blood vessels and trophoblastic epithelium of the labyrinthine layers. These findings show that exogenous IL-1beta affects expression of RT1-DM and RT1-A and does not affect the localization of corresponding molecules during pregnancy.

Localization of Vascular Endothelial Growth Factor (VEGF) and its Receptors VEGFR-1 and VEGFR-2 in Bovine Placentomes from Implantation Until Term

Interactions of vascular endothelial growth factor (VEGF) with its receptors VEGFR-1 and VEGFR-2 promoting angiogenesis have been described in placentation of human, mink and pig. The bovine placenta is multiplex, villous and synepitheliochorial due to migratory trophoblast giant cells (TGC). To determine the role of VEGF in bovine implantation and placentation, placentomes and interplacentomal areas from 33 cows from early implantation until near term were evaluated by immunohistochemistry. VEGF immunoreactivity was detected in fetal and maternal blood vessel tissues during implantation and throughout gestation, and in preimplantatory trophoblast cells and uterine epithelium. After implantation the immunoreaction was confined to TGC and uterine epithelium. An antibody against bovine VEGF revealed a strong reactivity in the stroma of maternal caruncular septa in early and mid-gestation, which distinctly decreased near term. In interplacentomal areas, VEGF was found in luminal and glandular epithelia as well as in trophoblast, with distinctly higher reactivity in giant cells. VEGFR-1 was observed in trophoblast and uterine epithelium around implantation. Later, in definite placentomes, VEGFR-1 was localized in TGC near the chorionic plate and in maternal endothelial cells in the center of the placentome. VEGFR-1 and VEGFR-2 were co-localized in uterine epithelium and trophoblast as well as in blood vessel tissue and uterine glands. The presence of VEGF, VEGFR-1 and VEGFR-2 at the feto-maternal interface and in vasculature indicates that in the bovine VEGF may have (1) classic functions in angiogenesis and vascular permeability, (2) growth factor properties, facilitating feto-maternal exchange via paracrine action, (3) chemotactic activity on capillary endothelium, and (4) an autocrine influence on TGC migratory activity.

Expression of phosphodiesterase 5 in maternal and fetal sheep

Ovine pregnancy is associated with elevated levels of nitric oxide. Nitric oxide stimulates cyclic guanosine monophosphate (cGMP), which results in vascular smooth muscle relaxation/vasodilation. Phosphodiesterase type 5 regulates cGMP in the urogenital track. The present study was designed to determine message expression of phosphodiesterase type 5 in the myometrium, uterine vessels, and placentome of the sheep and phosphodiesterase type 5 protein expression in the maternal and fetal placentome. Tissue was collected from 5 nonpregnant and 5 pregnant anesthetized animals (gestational day = 134 +/- 4) and frozen at -80 degrees C. Optimized reverse transcription-polymerase chain reaction was performed on all tissues, and immunohistochemistry was performed on the placentome only. Phosphodiesterase type 5 messenger ribonucleic acid levels were significantly higher in the myometrium and placentome, compared with the maternal blood vessels. Phosphodiesterase type 5 protein was immuno-localized to the vascular smooth muscle of the maternal vessels, stroma, and placental capsule only. Although phosphodiesterase type 5 messenger ribonucleic acid was present in the fetal placenta, phosphodiesterase type 5 protein was expressed only in maternally derived placental tissue. This suggests that regulation of cGMP levels and vascular tone in the umbilical circulation differs from the uterine circulation.

Fibroblast Growth Factor (FGF)-1, FGF2, FGF7 and FGF Receptors are Uniformly Expressed in Trophoblast Giant Cells During Restricted Trophoblast Invasion in Cows

The bovine placenta is characterized by a limited invasion of trophoblast giant cells (TGC). In contrast to mononuclear trophoblast cells (MTC), TGC are non-polarized cells, which migrate and fuse with single uterine epithelial cells throughout gestation. Fibroblast growth factors (FGF) were shown to be associated with the migratory activity of cells, cell differentiation and angiogenesis, and due to its localization in trophoblast cells were proposed as important regulating factors in hemochorial placentae of rodents and humans, and the (syn)epitheliochorial placenta of pig and sheep. Since migrating bovine TGC are of epithelial origin, but exhibit similarities to mesenchymal cells we hypothesize that the restricted trophoblast invasion in cattle is characterized by a specific FGF expression pattern. Therefore, the spatiotemporal expression of specific FGF factor:receptor pairs, either acting on cells of mesenchymal origin or on epithelial cells was examined in bovine placental tissues throughout gestation and prepartum by immunohistochemistry, semiquantitative RT-PCR and in situ hybridization. FGF1 protein was found in trophoblast, caruncular epithelium (CE) and stroma (CS), stroma of chorionic villi (SCV), and in fetal and maternal blood vessels. FGF2 signals dominated in maternal vascular endothelia (VE), immature TGC, and MTC, whereas staining in other cell types was clearly weaker. FGF7 protein was detected in fetal and maternal blood vessel as well as in immature TGC and MTC predominantly at the chorionic plate. FGFR immunoreaction was localized in immature TGC, MTC, and to a clearly lesser extent in CS, CE and fetal and maternal blood vessels. Mature TGC stained negatively for all examined factors and FGFR. The corresponding mRNAs specific for FGF1, -2, -7, total FGFR, and FGFR2 isoforms IIIb and IIIc were colocalized in immature TGC, whereas hybridization was substantially lower in CE and absent in CS, SCV and mature TGC throughout gestation, but switched to CS and VE immediately prepartum. Semiquantitative RT-PCR revealed higher mRNA levels for FGF1, FGFR, and FGFR2IIIc in cotyledons compared to caruncles (p<0.05), whereas it was the opposite with FGF2 (p<0.001). FGF7 and FGFR2IIIb mRNA levels did not differ between caruncles and cotyledons. Significant changes (p<0.05) of mRNA levels related to gestational age were found for FGF1 and FGFR2IIIc, but not for FGF2, -7, total FGFR, and FGFR2IIIb. The specific localization of all examined FGF family members in TGC suggests that TGC, apart from their classical function as producers of hormonal products, play other important roles in the regulation of bovine placentomal growth, differentiation and angiogenesis.

Extracellular Matrix Components and Matrix Degrading Enzymes in the Feline Placenta during Gestation

In the endotheliochorial placenta of the cat, the maternal surface epithelium and parts of the connective tissue have to be removed to bring the fetal blood vessels in close contact to the maternal capillaries. The composition of the extracellular matrix (ECM) in the feline uterus is not known and it is still not clear if and which parts of the maternal ECM persist during gestation in the placental labyrinth. We demonstrated various extracellular matrix components (collagen types I, III, IV, and laminin) and matrix metalloproteinases (MMP-1, -2, -13) using immunohistochemistry and studied the distribution of intermediate filaments (vimentin, cytokeratin) and alpha-smooth muscle actin (SMA) in the placental girdle on specimens of different stages of gestation. Collagen types I and III were mainly present in the fetal chorionic lamellae whereas diminished in the maternal placental labyrinth part. Collagen IV and laminin were expressed in fetal basement membranes and mesenchyme. Maternal endothelial cells and stromal cells showed a positive immunoreaction for anti-collagen type IV and laminin. MMP-2 was identified in the maternal stroma, including decidual cells. Endothelia of maternal blood vessels within the labyrinth contained MMP-1, -2 and -13, probably associated with angiogenesis. In the trophoblast MMP-1 and -13 were demonstrated. Maternal stem vessels were accompanied by a thick layer of syncytiotrophoblast. Around these vessels, collagen type I and SMA were present in a periendothelial region between the endothelium and the trophoblast. These findings indicate that a strictly regulated balance between ECM deposition and ECM degradation in the feline placental labyrinth is necessary for proper placental development and function.

The Expression of Insulin-like Growth Factor and Insulin-like Growth Factor Binding Protein mRNAs in Mouse Placenta

Insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs) are paracrine regulators of tissue growth and development, and are expressed at the sites of biological action. To study the role of the IGFs and IGFBPs in mouse placental development, we determined the temporal and spatial expression patterns of the mRNAs at embryonic days 10.5 to 18.5 by in situ hybridization. IGF-II mRNA was expressed strongly in mesoderm and fetal blood vessels of early placenta and in labyrinthine trophoblast of later placenta. In the junctional zone, IGF-II mRNA was expressed first in spongiotrophoblasts, later strongly in glycogen cells and variably in giant cells. IGFBP-2 mRNA was expressed weakly in spongiotrophoblasts and glycogen cells. IGFBP-2, -5 and -6 mRNAs were detected in the stroma of the metrial gland. Myometrium expressed IGFBP-2 mRNA strongly, IGFBP-6 mRNA moderately and IGFBP-5 mRNA weakly. The endothelium of maternal blood vessels in decidua expressed IGFBP-3 and -5 mRNAs, and some deeper vessels expressed IGFBP-4 mRNA. In the yolk sac, IGF-II mRNA was expressed in endoderm and mesoderm, whereas IGFBP-1, -2 and -4 mRNAs were expressed only in endoderm, and IGFBP-4 mRNA in mesoderm. Strong expression of IGF-II mRNA in glycogen cells suggests a role in the autocrine/paracrine regulation of invasion. Similar to rat and guinea pig, but in contrast to man and primates, IGFBP mRNAs, except IGFBP-4, were not expressed in mouse decidua. However, IGFBP-3, -4 and -5 mRNAs were expressed in endothelium of maternal blood vessels, and IGFBP-2 and -6 mRNAs in myometrium, where IGFBPs may play a critical role in regulating trophoblast invasion. These findings suggest possible biological roles of the peptides at the feto-maternal interface.

Placentation in the Mexican lizard Sceloporus mucronatus (Squamata: Phrynosomatidae)

We used light microscopy to study placental structure of the lizard Sceloporus mucronatus throughout 6 months of embryonic development. Three stages of placental development could be assigned to embryos based on the arrangement of the extraembryonic membranes. A highly vascular choriovitelline placenta was present in the embryonic hemisphere and a nonvascular bilaminar omphalopleure covered most of the abembryonic hemisphere of the egg during embryonic Stages 10-28. A chorioallantoic placenta replaced the choriovitelline placenta by embryonic Stage 29 and an omphaloplacenta covered the abembryonic hemisphere at this stage. The combination of these two placental types occurred in Stage 29-36 embryos. The final stage of placentation, embryonic Stages 37-40, was characterized by an omphalallantoic placenta in the abembryonic hemisphere and a chorioallantoic placenta in the embryonic hemisphere of the egg. The choriovitelline and chorioallantoic placentae are well vascularized, with closely apposed maternal and embryonic blood vessels. These structures are the most likely sites of respiratory exchange. In contrast, the omphaloplacenta and omphalallantoic placentae contain cuboidal or columnar epithelia and these structures may function in histotrophic exchange. Placentation of S. mucronatus is similar to that of predominantly lecithotrophic species in other squamate lineages suggesting that the evolution of this placental morphology is a response to similar factors and is independent of phylogeny.

210. Localisation of insulin-like growth factor-II (IGF-II) and its receptor in early murine pregnancy: a role in placentation and angiogenesis in the decidua?

The highly invasive activity of the human placenta is tightly regulated by a variety of growth factors and other molecules. Contrary to the dominant view, recent data suggests that IGF-II, upon binding to the IGF2R, can stimulate an intracellular signalling pathway.1 Evidence in humans and mice suggests that IGF-II and the IGF2R are important regulators of placental growth; however, to date they have not yet been localised to early murine implantation sites. This study provides a photo micrographic account of early placental development and the decidual vasculature in the mouse, and localises IGF-II and the IGF2R from days 5.5 to 10.5 of pregnancy. During early pregnancy, the decidua displays a paucity of blood vessels, which appear to undergo angiogenesis, so that by day 10.5 the decidua has become a highly vascularized structure, with an extensive network of dilated vessels that presumably enable maximal blood supply to the placenta. Unlike humans, murine trophoblast cells do not invade the endometrium individually, but remain in close contact with the main giant cell layer. The trophoblast giant cells (TGCs) are the outermost cell type of the murine placenta and maternal blood spaces beneath this layer are not lined by endothelium. Due to their location, TGCs appear to play a direct role in displacing this endothelium and therefore may play a role in the transformation into trophoblast lined maternal blood spaces. IGF-II and its receptor were present throughout early pregnancy in the conceptus and maternal decidua supporting their role as regulators of fetal and placental development. Most interesting, however, was their association with the developing maternal blood vessels in the mesometrial decidua. It seems likely that in mice the maternal vessels are remodelled by a variety of locally derived molecules. By association, IGF-II and its receptor are likely candidates. (1)McKinnon T, et al. (2001). Stimulation of human extravillous trophoblast migration by IGF-II is mediated by IGF type 2 receptor involving inhibitory G protein(s) and phosphorylation of MAPK. J. Clin. Endocrinol. Metab. 86(8), 3665–3674.

The Placenta

The human placenta is a discoid organ that has a hemochorial relationship with the mother. That is to say, the trophoblast that covers the villi is in direct contact with the maternal blood. Transfer of substances has to traverse the syncytiotrophoblast, cytotrophoblast, villous basement membrane, fetal capillary bed, and its endothelium. Although the placenta is the most available tissue, it is the least thoroughly investigated organ, and many aspects of its control still are unknown. Especially deficient is our knowledge of the genetic control of its many functions. The placenta also has a different imprinting pattern (paternal imprinting) from that of the embryo. The prevailing sentiment is that once delivery has occurred, it is a superfluous tissue that only needs to be discarded. There are many reasons, however, that knowledge of placental pathology can aid materially in a better understanding of newborns who have anomalies or neonatal problems. Further, a detailed examination of the placenta at birth can provide a better insight into prenatal life and its possible disturbances than is possible from notes in the history of the patient. The shape of the placenta is extremely variable (Fig. 1), probably due to placental location, its interaction with the endometrium, and uterine shape. The placenta implants anywhere in the uterus, but most commonly, it is in an anterior or posterior location. Much less often it is on the fundus. The shape often can be understood best by considering the history of its implantation. The reason for a specific shape can be derived further from the frequently aberrant shapes of twin placentas where competition for space in the uterus, a phenomenon that has been termed “trophotropism,” can be inferred to have existed. This term was used initially in attempts to explain the placental features in the uncommon event of a placenta …

Human cytomegalovirus interleukin-10 downregulates metalloproteinase activity and impairs endothelial cell migration and placental cytotrophoblast invasiveness in vitro.

At the uterine-placental interface, fetal cytotrophoblasts invade the decidua, breach maternal blood vessels, and form heterotypic contacts with uterine microvascular endothelial cells. In early gestation, differentiating- invading cytotrophoblasts produce high levels of matrix metalloproteinase 9 (MMP-9), which degrades the extracellular matrix and increases the invasion depth. By midgestation, when invasion is complete, MMP levels are reduced. Cytotrophoblasts also produce human interleukin-10 (hIL-10), a pleiotropic cytokine that modulates immune responses, helping to protect the fetal hemiallograft from rejection. Human cytomegalovirus (CMV) is often detected at the uterine-placental interface. CMV infection impairs cytotrophoblast differentiation and invasion, altering the expression of the cell adhesion and immune molecules. Here we report that infection with a clinical CMV strain, VR1814, but not a laboratory strain, AD169, downregulates MMP activity in uterine microvascular endothelial cells and differentiating-invading cytotrophoblasts. Infected cytotrophoblasts expressed CMV IL-10 (cmvIL-10) mRNA and secreted the viral cytokine, which upregulated hIL-10. Functional analyses showed that cmvIL-10 treatment impaired migration in endothelial cell wounding assays and cytotrophoblast invasion of Matrigel in vitro. Comparable changes occurred in cells that were exposed to recombinant hIL-10 or cmvIL-10. Our results show that cmvIL-10 decreases MMP activity and dysregulates the cell-cell and/or cell-matrix interactions of infected cytotrophoblasts and endothelial cells. Reduced MMP activity early in placental development could impair cytotrophoblast remodeling of the uterine vasculature and eventually restrict fetal growth in affected pregnancies.