The Uterine Spiral Arteries In Human Pregnancy: Facts and Controversies

Uterine spiral arteries play a vital role in supplying nutrients to the placenta and fetus, and for this purpose they are remodelled into highly dilated vessels by the action of invading trophoblast (physiological change). Knowledge of the mechanisms of these changes is relevant for a better understanding of pre-eclampsia and other pregnancy complications which show incomplete spiral artery remodelling. Controversies still abound concerning different steps in these physiological changes, and several of these disagreements are highlighted in this review, thereby suggesting directions for further research. First, a better definition of the degree of decidua- versus trophoblast-associated remodelling may help to devise a more adequate terminology. Other contestable issues are the vascular plugging and its relation with oxygen, trophoblast invasion from the outside or the inside of the vessels (intravasation versus extravasation), the impact of haemodynamics on endovascular migration, the replacement of arterial components by trophoblast, maternal tissue repair mechanisms and the role of uterine natural killer (NK) cells. Several of these features may be disturbed in complicated pregnancies, including the early decidua-associated vascular remodelling, vascular plugging and haemodynamics. The hyperinflammatory condition of pre-eclampsia may be responsible for vasculopathies such as acute atherosis, although the overall impact of such lesions on placental function is far from clear. Several features of the human placental bed are mirrored by processes in other species with haemochorial placentation, and studying such models may help to illuminate poorly understood aspects of human placentation.

Mathias Duval on Placental Development in Mice and Rats

Mathias Duval (1844-1907) was one of the pioneers in elucidating the intricate placental histology of different mammalian groups, notably the rodents. Using a well-dated series of mouse conceptuses, he described in detail the successive steps in placental development, and for confirmation he included observations on a (undated) collection of rat specimens. Not only was he able to identify correctly the different extra-embryonic cell layers, but he was also the first to recognize trophoblast invasion in rodents. Not all his interpretations are still valid, however. Re-reading his extensive and detailed work "Le placenta des rongeurs" (1890-1892) confronts us with still existing gaps in our present understanding of placental development, notably the morphogenesis of the different placental layers and the differentiation of invasive trophoblast. His understanding of uteroplacental blood flow was still limited, and he failed to recognize the complexity of the maternal decidua and its vasculature, which is essential for correctly understanding the pathways and extent of trophoblast invasion. Although Duval was active in promoting Darwin's evolutionary ideas, he refrained from extrapolating too quickly his findings in rodents to other mammalian groups including humans. In his view detailed histological studies on complete series of specimens had to come first, and thus provide a firm basis for a proper understanding of placental function and evolution.

Differential effects of inducers of syncytialization and apoptosis on BeWo and JEG-3 choriocarcinoma cells

BACKGROUND

The interactions of trophoblasts with the cytokine network at the fetomaternal interface determine the pathway the cell undertakes, e.g. proliferation, differentiation and apoptosis.

METHODS

We used cultures of fusigenic BeWo and non-fusigenic JEG-3 choriocarcinoma cells to study the effects of inducers of syncytialisation (forskolin) and apoptosis [tumour necrosis factor-alpha (TNFalpha)] on differentiation, viability, proliferation and apoptosis.

RESULTS

E-cadherin immunostaining showed that syncytium formation was confined to BeWo and not JEG-3 cells, while secretion of hCG was promoted by forskolin in both cell types implying a 'dissociation' between morphological and biochemical differentiation. Forskolin also had differential effects on cell viability (MTT reduction test) and proliferation (Ki67 immunostaining with MIB-1 monoclonal antibody), both decreasing in BeWo and increasing in JEG-3 cells. TNFalpha increased apoptosis (cytokeratin neo-epitope immunostaining with M30 monoclonal antibody) in both cell types, an effect which was blocked by epidermal growth factor selectively in JEG-3 cells.

CONCLUSION

Our results suggest that the differential responses of BeWo and JEG-3 cells to inducers of syncytialization and apoptosis might be related to their fusigenic capacity. Caution is needed when extrapolating results obtained by these models to normal trophoblast populations. However, we speculate that these models can help identify key factors involved in trophoblast differentiation at the placental bed.

Endovascular trophoblast invasion and associated structural changes in uterine spiral arteries of the pregnant rat

The involvement of endovascular trophoblast in fibrinoid deposition, replacement of the endothelium and vascular smooth muscle breakdown is studied in spiral arteries of the mesometrial triangle from day 15 to day 21 of rat pregnancy, by examining arterial cross sections after staining for cytokeratin, PAS, CD31 and alpha-actin. From day 15 to day 18 of pregnancy, fibrinoid deposition underneath the endovascular trophoblast increases gradually, whereas the amount of endovascular trophoblast in invaded arteries remains constant. CD31 staining is significantly reduced in sub-ET (= underlying the endovascular trophoblast) as compared to extra-ET (= outside the endovascular trophoblast) and no-ET (= non-invaded arterial sections) at each time-point of pregnancy examined (P < 0.005 and P < 0.0005 at each day of pregnancy), whereas alpha-actin staining is reduced both in sub-ET and in extra-ET as compared to no-ET. During pregnancy, CD31 staining in sub-ET initially declines, but increases significantly on day 21 (P < 0.001 versus d20) suggesting re-endothelialization of the vascular wall. In conclusion, changes in spiral arteries of pregnant rats reveal striking similarities with physiological changes seen in human pregnancy, thus emphasizing the usefulness of this species as an experimental model for studying normal and complicated pregnancies in humans.

The placental bed in pregnancies complicated by primary antiphospholipid syndrome

Pregnancy in women with primary antiphospholipid syndrome (APS) is frequently associated with placental insufficiency leading to intrauterine growth restriction (IUGR)+/-fetal death, pre-eclampsia, placental abruption, premature delivery or thrombosis. The aim of this study was to investigate the placental bed in APS pregnancies for evidence of impaired trophoblast invasion, endothelial cell activation (ECA) and macrophage infiltration.

METHODS

Biopsies from the presumed site of the placental bed were obtained from 12 women with treated primary APS and 16 controls. Immunohistochemical methods were employed to investigate expression of cytokeratin (trophoblasts), alpha-actin (smooth muscle), CD68 (macrophages) and VCAM-1 (as marker of ECA). Fibrinoid and elastin distribution and expression were determined by periodic acid/Schiff and orcein stain, respectively.

RESULTS

Three APS pregnancies developed IUGR, one with concurrent pre-eclampsia. Eight of 12 APS biopsies were confirmed to be from the placental bed; one patient failed to meet APS criteria and was excluded from analysis; six included spiral arteries in the biopsy; 11 of 16 controls' biopsies were from the placental bed. APS biopsies had a higher concentration of inflammatory cells (p=0.0001), particularly macrophages (p=0.014). Three APS biopsies showed necrosis with hyperplastic vessels; one demonstrated arterial thromboses, but none had profound vasculopathy/atherosis or ECA.

CONCLUSION

Inflammatory mechanisms in the placental bed may contribute to APS pregnancy complications.

Interstitial trophoblast invasion in the decidua and mesometrial triangle during the last third of pregnancy in the rat

Like other species with haemochorial placentation, pregnant rats show marked invasion of the uterine wall by trophoblast. While an endovascular pathway of invasion has been recognized for a long time, only recently, by application of cytokeratin immunostaining, the existence of an interstitial pathway of invasion has been established. Interstitial invasion is mainly effected by glycogen cell-like trophoblast arising from glycogen cell islands of the trophospongium opening up into the decidua, and from glycogen cell sheaths surrounding the intraplacental maternal arterial channels which are connected with the spiral arteries in decidua and mesometrial triangle. Quantitative evaluation of interstitial invasion in both maternal compartments was carried out on days 15-21, using PAS staining and cytokeratin and alpha-actin immunostaining for detecting trophoblast and defining maternal tissue compartments. Measurements of compartment size, cytokeratin-positive areas and invasion extent were performed using the KS400 image analysis system. A distinct pattern of interstitial trophoblast invasion emerged, starting from central decidual areas around the maternal arterial channels, and mushrooming into the mesometrial triangle reaching a peak at day 18, followed by gradual regression of the invaded areas. These measurements may serve as a basis for further experiments to evaluate factors which may influence the depth of trophoblast invasion.

Thomas Huxley and the rat placenta in the early debates on evolution

The 19th century debates on mammalian classification in the light of the new evolutionary thinking led to controversies between Thomas Huxley and Richard Owen concerning the value of the placenta as a representative key organ. As a main point in his argument, Huxley provided a detailed description of a sectioned rat placenta, highlighting the importance of decidualization of the uterus as an argument supporting an evolutionary relationship between rodents, insectivores and primates, an idea hotly contested by Owen. In addition, he illustrated and correctly interpreted the maternal blood supply from uterus to placenta in striking detail. During the succeeding decades the key role of trophoblast in placenta formation was discovered, and the decidua became neglected in later comparative studies. Nevertheless, at the present time trophoblast-decidual interaction is regarded as an extremely important feature of placental development in both primates and rodents, and Huxley can therefore rightfully be considered as an early pioneer in placental research.

Alpha-2 Macroglobulin Controls Trophoblast Positioning in Mouse Implantation Sites

In humans, functional deficiency of alpha-2M is not known, implying alpha 2M is essential for gestational success. Mice, deficient in two members of the alpha-2 Macroglobulin (alpha 2M) family, i.e. alpha-2 macroglobulin (MAM) and murinoglobulin-1 (MUG-1) are viable, fertile and phenotypically normal, unless stressed (Am J Pathol, 155 (1999), 983). Here, we analysed implantation sites in MAM(-/-)/MUG-1(-/-)mice during pregnancy, a strong physiological stressor. Despite some post-implantation fetal loss, mean litter size was comparable to congenic C57Bl/6J (B6) mice, but MAM(-/-)/MUG-1(-/-)pups were significantly lighter and the sex ratio was skewed towards males. Implantation sites appeared histologically normal up to gestational day (gd) 8. By gd 10, extensive over-development of trophoblasts was evident, accompanied by relative deficits in decidua, in the mural mesometrial lymphoid aggregates of pregnancy and in uterine Natural Killer cells. At gd 10-12, decidual spiral arteries were dilated but abnormally cuffed by trophoblasts that extended anomalously, for midgestation, to the myometrial circular smooth muscle. Ultrastructurally, trophoblasts in the mesometrial decidua made intimate contact with endothelial cells that were shedding membrane fragments. These findings demonstrate that alpha 2M, and thereby proteinases and/or cytokines whose bio-availability is regulated by alpha 2M, exert significant decidual regulation on trophoblast invasion.

Matrix metalloproteinases-2 and -9 and their endogenous tissue inhibitors in tissue remodeling after sealing of the fetal membranes in a sheep model of fetoscopic surgery

OBJECTIVES

We studied collagen plugging of the fetoscopic access site in an in vivo fetal lamb model for fetoscopic surgery and possible role for matrix metalloproteinase (MMP)-2 and -9 and tissue inhibitors (TIMPs).

METHODS

Eight ewes had fetoscopic balloon occlusion of the trachea as an experimental treatment for congenital diaphragmatic hernia between days 88 and 99 of gestation (term 145 days) with sampling of amniotic, allantoic, and tracheal fluid. Nonoperated cotwins were used as controls. The fetoscopy port was closed using a collagen plug. Ten days (range 9-12) later, fluids were sampled and plug sites collected for histologic analysis. Activity of MMP-2 (72 kDa, gelatinase A) and MMP-9 (92 kDa, gelatinase B) was determined in the fluids by zymography and secretion of TIMPs (27-30 kDa; TIMP-1, glycosylated TIMP-3 and TIMP-4, 24 kDa; unglycosylated TIMP-3, 21 kDa; TIMP-2) by reverse zymography and quantified by densitometric analysis.

RESULTS

No pregnancy was complicated by amniorhexis or preterm labor. At cesarean, normal volumes of amniotic and allantoic fluid were present in all cases. Histology of the plug sites revealed good integration of the collagen plug without complete restoration of membrane integrity. MMP-2, MMP-9, and TIMPs were detected in all fluids. In the operated animals, significantly (P <.05) higher activity of MMP-9 was found in amniotic fluid, with lower concentrations of TIMPs in allantoic fluid (P <.01). Tracheal occlusion was associated with a significant (P <.02) increase in both MMP-2 and -9 in tracheal fluid.

CONCLUSION

Collagen plugging of the fetoscopic access port sites in sheep resulted in functionally effective sealing of the fetal membranes. Changes in MMP-2, MMP-9, and TIMPs suggest an active remodeling of both the fetal lung and the fetal membranes.

Differential effects of IL-11 on rat blastocysts and decidua during the peri-implantation period

PROBLEM

To study effects of interleukin-11 (IL-11) on blastocyst development and decidualization.

METHOD OF STUDY

Rats, injected with buffer (C) or IL-11 [1 mg/kg/day = high dose (HD), 60 microg/kg/week = low dose (LD)-1, 30 microg/kg twice a week = low dose (LD)-2] were made pregnant or pseudopregnant to obtain blastocysts or deciduomata.

RESULTS

As compared with C, more LD-2 blastocysts hatched in culture, while hatching and attachment of HD blastocysts was decreased. Blastocysts from untreated rats in IL-11 supplemented medium (4 ng/mL) demonstrated increased hatching and attachment. The weight of the decidualized uterus in HD and LD-2 pseudopregnant rats was reduced as compared with C and LD- 1. On deciduomata sections from IL-11 treated rats, the area inside the uterine muscle layer was reduced, and mitotic over pycnotic indices were increased in the anti-mesometrial area and decreased in the mesometrial area.

CONCLUSIONS

Low doses of IL-11 improve hatching and attachment of blastocysts, but both high and low doses impair decidualization.

Downregulation of placental syncytin expression and abnormal protein localization in pre-eclampsia

Development of placentation and successful pregnancy depend on co-ordinated interactions between the maternal decidua and myometrium, and the invasive properties of the fetal trophoblast. Syncytin, a protein encoded by the envelope gene of a recently identified human endogenous defective retrovirus, HERV-W, is highly expressed in placental tissue. Previously, we have shown that the major site of syncytin expression is the placental syncytiotrophoblast, a fused multinuclear syncytium originating from cytotrophoblast cells. Here we present the first evidence that in pre-eclampsia, syncytin gene expression levels are dramatically reduced. Additionally, immunohistochemical examination of normal placentae and placentae from women with pre-eclampsia reveals that the syncytin protein in placental tissue from women with pre-eclampsia is localized improperly to the apical syncytiotrophoblast microvillous membrane as opposed to its normal location on the basal syncytiotrophoblast cytoplasmic membrane. Our previous results suggest that syncytin may mediate placental cytotrophoblast fusion in vivo and may play an important role in human placental morphogenesis. The present study suggests that altered expression of the syncytin gene, and altered cellular location of its protein product, may contribute to the aetiology of pre-eclampsia.

An organ-culture for in vitro evaluation of fetal membrane healing capacity

OBJECTIVES

We aimed to set up an organ culture of human amniochorion to evaluate fetal membrane repair capacity following surgical trauma.

METHODS

Fetal membranes were collected from four patients, during elective caesarean section at term. Explants were traumatised at the centre and cultured on collagen support material for a total of 12 days. Viability was assessed by light microscopy and proliferation by detection of 5-Bromo-2' deoxy-Uridine (BrdU) incorporation and immunohistochemistry. Wound healing capacity was assessed trough photographic documentation every 2 days.

RESULTS

Cultures showed good survival for 12 days. Increased cellularity, survival and proliferations were observed at the borders of the cultures in contrast to the central trauma site. During the 12 days observation period, no significant closure of the membrane defect could be demonstrated.

CONCLUSION

This organ culture system represents a new model for the study of human fetal membrane repair. Despite good survival and localised proliferation, no obvious closure of a surgically created defect was observed in the described culture conditions.

Uterine haemodynamics as a possible driving force for endovascular trophoblast migration in the placental bed

Uteroplacental vascular adaptation during pregnancy depends on retrograde endovascular migration of trophoblast in the uterine spiral arteries and their subsequent incorporation into the vessel wall. In the human, this migration process occurs in a step-wise fashion, starting with plugging of the distal ends of the arteries, followed by migration into the decidual and, after several weeks' delay, into the myometrial segments. The hypothesis is put forward that haemodynamical forces play an important regulatory role in this process. A mechanical signal transduction system should then be present within the trophoblastic cells to trigger their rheotactic behaviour. Since the condition of preeclampsia is characterized by restricted colonization of spiral arteries by trophoblast, the implications of this proposed regulatory system on the pathogenesis of the disease are considered.

Cytotoxic effects of tumour necrosis factor (TNF)-alpha and interferon-gamma on cultured human trophoblast are modulated by fibronectin

Tumour necrosis factor (TNF)-alpha and interferon (IFN)-gamma, produced by maternal inflammatory cells, may compromise trophoblast survival at the trophoblast-maternal interface and notably in the placental bed which is invaded by trophoblast. Extracellular matrix components, e.g. fibronectin, may enhance trophoblast survival. A possible protective effect of fibronectin against toxic effects of TNF-alpha and IFN-gamma was investigated in cultured trophoblasts isolated from six human term placentas, grown on uncoated and fibronectin-coated plastics. IFN-gamma and increasing doses of TNF-alpha resulted in decreasing viability of trophoblast on uncoated as well as fibronectin-coated dishes, as shown by 3-[4, 5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assays, but for each TNF/IFN treatment condition viability on fibronectin was higher (P < 0.001). Epidermal growth factor (EGF), a growth factor reported to protect against TNF-alpha/IFN-gamma induced toxicity, resulted in further increased viability, but not if IFN-gamma was included in the treatment. EGF caused increased fibronectin secretion into the medium (P < 0.001), and double cytokeratin/fibronectin immunostaining confirmed the trophoblastic nature of fibronectin secreting cells. We conclude that fibronectin increases viability, but does not completely abolish the cytotoxic action of TNF-alpha and IFN-gamma on trophoblast. The protective effect of EGF may be related to stimulation of fibronectin secretion by trophoblast.

Growth characteristics of diabetic rat ectoplacental cones in vivo and in vitro

AIMS/HYPOTHESIS

To investigate the outgrowth of the ectoplacental cone in diabetic rats in vivo and in vitro.

METHODS

Female Wistar rats were injected intraperitoneally with streptozotocin (75 mg/kg body weight, n = 15), or with control buffer (n = 27) 3 days before mating. On day 9 (day 1 = copulation plug) decidual swellings were weighed and the volume and mitotic index of the embryo and ectoplacental cone were estimated. Also, ectoplacental cones were cultured either in the presence of decidual cells from pseudopregnant diabetic rats or in high glucose concentration media. Cultures were evaluated by the daily outgrowth and by the proportion of giant cells and proliferating cells on day 5.

RESULTS

In diabetic rats on day 9, the weight of the decidual swellings and the mitotic index in the ectoplacental cone were lower compared with controls (p < 0.0001 and p < 0.05, respectively). In vitro, control ectoplacental cones in the presence of decidual cells from diabetic rats showed a slight reduction in outgrowth on day 3 and 5 of culture. Outgrowth of diabetic ectoplacental cones in high glucose concentration medium was impaired on day 1 (p < 0.0005) compared with control ectoplacental cones in control medium, and on day 1 and 2 (both p < 0.005) compared with control ectoplacental cones in high glucose concentration medium. In control medium, the outgrowth of diabetic ectoplacental cones was impaired on day 1 (p < 0.05), compared with control ectoplacental cones. Proliferation was stimulated in diabetic ectoplacental cone cultures.

CONCLUSION/INTERPRETATION

These data suggest that the outgrowth of diabetic ectoplacental cones is impaired by high glucose concentrations.

Effects of interleukin 11 (IL-11) on early post-implantation development of the rat

The development of embryos, trophoblast and decidua of IL-11-treated rats were examined in vivo, while ectoplacental cones (EPC) were studied in vitro. Female Wistar rats were injected daily with buffer (C), 1 mg/kg IL-11 (HD) daily or 30 microgram/kg (LD) IL-11 twice a week. On day 9 of pregnancy, embryonic tissue volume was reduced in IL-11-treated animals, but EPC volume was elevated, compared to controls. Mitotic indices were reduced in embryos (P<0.05 for LD, P<0.001 for HD) and in EPCs of both groups. Pycnotic indices were elevated in LD (NS) and HD (P<0.05) embryos, but decreased in EPCs of the LD group (P<0.01). Morphological abnormalities were observed in decidua, embryo and trophoblast. In HD, EPC attachment was impaired after 1 day culture but proliferation was stimulated after 5 days. Defective decidualization in IL-11 treated rats may therefore result in abnormal development of embryo and trophoblast.

Matrix metalloproteinases -2 and -9 and their endogenous tissue inhibitors in fetal membrane repair following fetoscopy in a rabbit model

The cellular mechanisms underlying fetal membrane repair are poorly understood. Matrix metalloproteinases (MMP) and the endogenous tissue inhibitors of metalloproteinases (TIMP) play a key role in the control of turnover of extracellular matrix in fetal membranes at normal parturition and preterm prelabour rupture of the fetal membranes (PPROM). The time course of secretion of MMP-2 (72 kDa, gelatinase A) and MMP-9 (92 kDa, gelatinase B) and TIMP into extra-embryonic coelomic, allantoic and amniotic fluids in a rabbit model was examined. Furthermore, to evaluate their role in fetal membrane repair, the changes induced by fetoscopy at mid-gestation (23 days; gestation length is 32 days) were investigated. Zymography showed predominantly secretion of latent MMP-2 at 18, 23 and 30 days of gestation in all gestational compartments. Reverse zymography detected a broad range of TIMP activity with molecular weights of 27-30 kDa (TIMP-1, glycosylated TIMP-3 and TIMP-4), 24 kDa (unglycosylated TIMP-3) and 21 kDa (TIMP-2). Following fetoscopy, both MMP-2 and TIMP increased significantly in amniotic fluid and extra-embryonic coelomic fluid, but not in allantoic fluid, as demonstrated by densitometric analyses. These findings indicate a modulating role for MMP and TIMP in the repair processes following a surgically induced fetal membrane defect.

Maternal serum levels of macrophage colony-stimulating factor are associated with adverse pregnancy outcome

OBJECTIVE

The aim of this study was the measurement of maternal serum levels of M-CSF throughout pregnancy, in a low risk obstetrical population, to examine the relationship of M-CSF and pregnancy outcome.

STUDY DESIGN

Maternal serum was obtained at various stages of pregnancy and post partum, M-CSF levels were measured by ELISA, pertinent clinical data tabulated, and pregnancy outcome was determined.

RESULTS

In 564 pregnancies studied, 22% of 260 nulliparous pregnancies and 10% of 304 multiparous pregnancies were hypertensive. Preeclampsia occurred in 1.5% of nulliparous and in 1% of the multiparous women. In apparently normal pregnancies with good outcome, M-CSF levels rose throughout pregnancy. No cases of preeclampsia occurred if maternal serum M-CSF levels increased more than 100% throughout pregnancy.

CONCLUSIONS

This study suggests that absolute levels and relative changes in maternal serum M-CSF levels during pregnancy are associated with adverse pregnancy outcomes.

Successful sealing of fetoscopic access sites with collagen plugs in the rabbit model

OBJECTIVE

The aim of this study was to evaluate the efficacies of various plugging techniques in sealing the membrane defect created by fetoscopy in the rabbit at midgestation.

STUDY DESIGN

Fetoscopy was performed in pregnant rabbits at 23 days' gestation (term, 32 days' gestation). In group 1 fetal sacs were left unclosed (positive control group, n = 24). In group 2 injection with commercially available extracellular matrix (Matrigel; BD Labware, Bedford, Mass) was performed and a myometrial suture was inserted (n = 23). In group 3 the entry site was plugged with collagen (Colgen; Inter-Phar, Paris, France) combined with a myometrial suture (n = 22). At 30 days' gestation the membrane integrity, amniotic fluid presence, and fetal lung/body weight ratios were assessed. The plugging site was examined histologically.

RESULTS

The use of suture and collagen plugs (group 3) resulted in functional restoration of membrane integrity with preservation of amniotic fluid and normal fetal lung/body weight ratio at term in 82% of cases, compared with 42% in the positive control group (group 1; P <.05). Histologic examination revealed entrapment of membranes between the plug and the myometrium but no anatomic repair of the membranes. The use of suture and extracellular matrix (group 2) did not achieve better results than those seen in group 1 (positive control group).

CONCLUSION

Collagen plugs achieved functional sealing of fetoscopic access sites in a rabbit model and prevented oligohydramnios and pulmonary hypoplasia.