Expression of matrix metalloproteinases during murine chorioallantoic placenta maturation

Involvement of metalloproteinase and nitric oxide synthase/nitric oxide mechanisms in early decidual angiogenesis-vascularization of normal and experimental pathological mouse placenta related to maternal alcohol exposure

Successful pregnancy for optimal fetal growth requires adequate early angiogenesis and remodeling of decidual spiral arterioles during placentation. Prior to the initiation of invasion and endothelial replacement by trophoblasts, interactions between decidual stromal cells and maternal leukocytes, such as uterine natural killer cells and macrophages, play crucial roles in the processes of early maternal vascularization, such as proliferation, apoptosis, migration, differentiation, and matrix and vessel remodeling. These placental angiogenic events are highly dependent on the coordination of several mechanisms at the early maternal-fetal interface, and one of them is the expression and activity of matrix metalloproteinases (MMPs) and endothelial nitric oxide synthases (NOSs). Inadequate balances of MMPs and nitric oxide (NO) are involved in several placentopathies and pregnancy complications. Since alcohol consumption during gestation can affect fetal growth associated with abnormal placental development, recently, we showed, in a mouse model, that perigestational alcohol consumption up to organogenesis induces fetal malformations related to deficient growth and vascular morphogenesis of the placenta at term. In this review, we summarize the current knowledge of the early processes of maternal vascularization that lead to the formation of the definitive placenta and the roles of angiogenic MMP and NOS/NO mechanisms during normal and altered early gestation in mice. Then, we propose hypothetical defective decidual cellular and MMP and NOS/NO mechanisms involved in abnormal decidual vascularization induced by perigestational alcohol consumption in an experimental mouse model. This review highlights the important roles of decidual cells and their MMP and NOS balances in the physiological and pathophysiological early maternal angiogenesis-vascularization during placentation in mice.

Placenta-specific lncRNA 1600012P17Rik is expressed in spongiotrophoblast and glycogen trophoblast cells of mouse placenta

A few long noncoding RNAs (long ncRNAs, lncRNAs) exhibit trophoblast cell type-specific expression patterns and functional roles in mouse placenta. However, the cell- and stage-specific expression patterns and functions of most placenta-derived lncRNAs remain unclear. In this study, we explored mouse placenta-associated lncRNAs using a combined bioinformatic and experimental approach. We used the FANTOM5 database to survey lncRNA expression in mouse placenta and found that 1600012P17Rik (MGI: 1919275, designated P17Rik), a long intergenic ncRNA, was the most highly expressed lncRNA at gestational day 17. Polymerase chain reaction analysis confirmed that P17Rik was exclusively expressed in placenta and not in any of the adult organs examined in this study. In situ hybridization analysis revealed that it was highly expressed in spongiotrophoblast cells and to a lesser extent in glycogen trophoblast cells, including migratory glycogen trophoblast cells invading the decidua. Moreover, we found that it is a polyadenylated lncRNA localized mainly to the cytoplasm of these trophoblast cells. As these trophoblast cells also expressed the neighboring protein-coding gene, pappalysin 2 (Pappa2), we investigated the effects of P17Rik on Pappa2 expression using Pappa2-expressing MC3T3-E1 cells and found that P17Rik transfection increased the messenger RNA (mRNA) and protein levels of Pappa2. These results indicate that mouse placenta-specific lncRNA P17Rik modulates the expression of the neighboring protein-coding gene Pappa2 in spongiotrophoblast and glycogen trophoblast cells of mouse placenta during late gestation.

Comparative matrix metalloproteinase-2 and -9 expression and activity during endotheliochorial and hemochorial trophoblastic invasiveness

To establish a functional placenta, its development needs adequate trophoblastic invasiveness. The intricate and complex morphological and molecular aspects regulating trophoblastic invasion during endotheliochorial placentation of domestic carnivores and their similarities and differences with the hemochorial placenta are still poorly understood. During placentation processes, from the time of implantation, trophoblast cells invade the uterine endometrium where they achieve extensive degradation and remodeling of extracellular matrix components; in this process, matrix metalloproteinases (MMPs), particularly MMP-2 and 9, have an essential role in rebuilding, cell migration, and invasiveness. This review provides an overview of comparative trophoblast invasive events and the expression and activity of MMP-2 and 9 during endotheliochorial and hemochorial placentation, emphasizing dog and mouse placental models. Understanding of trophoblastic invasiveness in two models of placentation, the intermediately invasive domestic carnivore endotheliochorial placenta, and the more highly invasive mouse hemochorial placenta, contributes to deepen knowledge of the trophoblast invasive processes and their diverse and complex human placental alterations, such as preeclampsia.

Activities of matrix metalloproteinase-2 and -9 in amniotic fluid at parturition in mares with normal and high-risk pregnancy

The matrix metalloproteinases (MMPs) are a family of enzymes involved in extracellular matrix remodeling. MMPs are secreted in a latent form and activated by local and infiltrating cells. MMP-2 and -9 are the most studied in reproduction and have been detected in bovine, ovine, equine and human placenta. There is only one study on MMPs in the equine amniotic fluid (AF) reporting a decrease in the activity of MMP-2 in case of premature delivery. The aim of this study was focused on MMP-2 and -9 activity in AF collected at parturition from mares with normal or high-risk pregnancy. High-risk pregnancy was defined as a history of premature udder development/lactation, increase of combined thickness of the uterus and placenta, vulvar discharge and/or mare's systemic illness. The diagnosis of placental insufficiency was confirmed retrospectively after macroscopic and histopatologic examination of the placenta. AF was collected by needle puncture of the amnion within 5 min after its appearance through the vulva. The activity of MMP-2 and -9 was analyzed by in-gel zymography allowing the evaluation of both latent and active forms. Twenty mares with normal pregnancy (group 1) and 8 mares with high-risk pregnancy (group 2) were included. All mares in group 2 had a high-risk pregnancy with a diagnosis of placental insufficiency associated with placental villous hypoplasia, placentitis or placental edema. The bands relative to latent and active forms of MMP-2 were clearly visible in both groups and the activity of latent (P = 0.010) and active (P = 0.004) forms was lower in the AF samples of group 2. The band of the latent form of MMP-9 was visible in 17/20 samples of group 1, while it was completely absent in all samples of group 2. In contrast, the band of the active form was clearly visible and with a greater activity in AF samples of group 2 (P = 0.002). Placental dysfunction seems to induce a lower MMP-2 activity and a higher MMP-9 activity through the release of pro-inflammatory cytokines. Because fetal pulmonary secretions are a likely source of gelatinases in AF during late gestation, the increased MMP-9 activity could be related to fetal distress. These data provide a starting point to better understand the role of MMPs in equine pregnancy, although it should be confirmed in a larger and more homogeneous population of mares with high-risk pregnancy.

New insights into the roles of CUL1 in mouse placenta development

CULLIN1 (CUL1) protein, as a scaffold protein in Skp1-CUL1-F box (SCF) E3 ligases complex, was reported involved in different cellular functions to regulate the early embryonic development. In our previous study, we have demonstrated that CUL1 promote trophoblast cell invasion at the maternal-fetal interface in human and the CUL1 protein significantly decreased in preeclampsia (PE) placenta, but how CUL1 involved in placentation is still obscure. Due to the embryo lethal in CUL1 knockout mice, the lentivirus mediated placenta-specific CUL1 knockdown mice model was constructed to uncover the potential role of CUL1 in placentation. In this study, CUL1 was first detected in mouse placenta. CUL1 mainly expressed in trophoblast giant cell at E9.5, and spongiotrophoblast at E11.5 and E13.5 by using immunohistochemistry and int situ hybridization. In lentivirus mediated placenta specific mouse model, the number of implanted embryos was reduced in CUL1 shRNA group at E13.5 and E18.5 compared to control group. Based on the morphological analysis of histologic staining, we observed that spongiotrophoblast layer is expanded, fetal angiogenesis in labyrinth was obstructed and fetus blood cells were accumulated in vessels. These results indicated that decreased expression of CUL1 affect placentation of mice, which give new insights into the cause of gestational diseases, but the exactly mechanism still needs further study.

Differential expression and activity of matrix metalloproteinases 2 and 9 in canine early placenta

The zonary and endotheliochorial dog placenta is the most invasive placenta of carnivores. The importance of matrix metalloproteinases (MMP) in placenta invasiveness has been determined in several mammals including species with haemochorial, epitheliochorial and endotheliochorial placentation. Regarding the latter, the expression of MMP enzymes has been studied in the cat and the mature canine placenta. The aim of this study was to analyse the expression and activity of MMP-2 and MMP-9 in the early dog placenta. Placentae from 18 to 30 days of pregnancy were collected from four bitches. Two placentae from each bitch were analysed. Placental tissue from one uterine horn was fixed in formaldehyde for immunohistochemistry, while marginal haematoma, labyrinth, non-implantative and implantative endometrium from the contralateral horn were immediately frozen in dry ice for the analysis of MMP expression (Western blot [WB]) and activity (zymography). MMP-2 and MMP-9 were evidenced in the labyrinth, maternal glands and marginal haematoma; this finding was directly correlated with levels of MMP expression by WB, and with the activity of MMP-2, mainly in the haematoma (the area of major remodelling of tissues). Thus, although MMP-9 is well expressed in the early canine placenta, it is not active. Given the important role of MMPs for invasiveness, maternal-foetal angiogenesis and the establishment of a correct foetal nutrition, the results are consistent with the findings in other species in which the MMP-2 activation precedes the MMP-9 one in early placentation.

Differences in extracellular matrix remodeling in the placenta of mares that retain fetal membranes and mares that deliver fetal membranes physiologically

INTRODUCTION

In mammals, placenta separation at term may involve degradation of the extracellular matrix by matrix metalloproteinases (MMPs). The activity of MMPs is modulated by TIMPs. We hypothesized that the placentas of mares that deliver fetal membranes physiologically and those that retain fetal membranes (FMR) differ in terms of histology; mRNA expression of MMP-2 and MMP-9; protein expression of MMP-2, MMP-9, and TIMP-2; and the potential activity of both MMPs.

METHODS

Placenta biopsies were taken from mares (n = 9; 4 FMR, 5 controls) immediately after foal expulsion. Retention was defined as failure to expel all fetal membranes within 3 h of expulsion. All mares were monitored for time of expulsion. The degree of allantochorial/endometrial adhesion was determined in FMR mares, and biopsies from all mares were histologically examined. mRNA expression, protein immunolocalization, protein amount and potential enzyme activity were determined with RT-PCR, immunohistochemistry, Western Blotting and zymography, respectively.

RESULTS

FMR mares had strong to extremely strong allantochorial/endometrial adhesion, and significantly more connective tissue in the allantochorial villi than controls. The range of MMP-2 mRNA expression levels was more than 13 times greater in FMR mares than in controls. Protein content of both MMPs and TIMP-2 differed significantly between groups. The range of potential MMP-2 and MMP-9 activity was larger in FMR mares, and MMP-2 potential activity was 1.4 times higher in controls (P = 0.02).

DISCUSSION

These results indicate differences in extracellular matrix remodeling in FMR mares and controls, and suggest dysregulation of MMP expression and activation in FMR mares.

Matrix metalloproteinase-9 deficiency phenocopies features of preeclampsia and intrauterine growth restriction

The pregnancy complication preeclampsia (PE), which occurs in approximately 3% to 8% of human pregnancies, is characterized by placental pathologies that can lead to significant fetal and maternal morbidity and mortality. Currently, the only known cure is delivery of the placenta. As the etiology of PE remains unknown, it is vital to find models to study this common syndrome. Here we show that matrix metalloproteinase-9 (MMP9) deficiency causes physiological and placental abnormalities in mice, which mimic features of PE. As with the severe cases of this syndrome, which commence early in gestation, MMP9-null mouse embryos exhibit deficiencies in trophoblast differentiation and invasion shortly after implantation, along with intrauterine growth restriction or embryonic death. Reciprocal embryo transfer experiments demonstrated that embryonic MMP9 is a major contributor to normal implantation, but maternal MMP9 also plays a role in embryonic trophoblast development. Pregnant MMP9-null mice bearing null embryos exhibited clinical features of PE as VEGF dysregulation and proteinuria accompanied by preexisting elevated blood pressure and kidney pathology. Thus, our data show that fetal and maternal MMP9 play a role in the development of PE and establish the MMP9-null mice as a much-needed model to study the clinical course of this syndrome.

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

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

Matrix metalloproteinase expression and activity in trophoblast-decidual tissues at organogenesis in CF-1 mouse

During early placentation, matrix metalloproteinases (MMPs) play important roles in decidualization, trophoblast migration, invasion, angiogenesis, vascularization and extracellular matrix (ECM) remodeling of the endometrium. The aim of our study was to analyze the localization, distribution and differential expression of MMP-2 and -9 in the organogenic implantation site and to evaluate in vivo and in vitro decidual MMP-2 and -9 activities on day 10 of gestation in CF-1 mouse. Whole extracts for Western blotting of organogenic E10-decidua expressed MMP-2 and -9 isoforms. MMP-2 immunoreactivity was found in a granular and discrete pattern in ECM of mesometrial decidua (MD) near maternal blood vessels and slightly in non-decidualized endometrium (NDE). Immunoexpression of MMP-9 was also detected in NDE, in cytoplasm of decidual cells and ECM of vascular MD, in trophoblastic area and in growing antimesometrial deciduum. Gelatin zymography showed that MMP-9 activity was significantly lower in CM compared to the active form of direct (not cultured) and cultured decidua. The decidual active MMP-9 was significantly higher than the active MMP-2. These results show differential localization, protein expression and enzymatic activation of MMPs, suggesting specific roles for MMP-2 and MMP-9 in decidual and trophoblast tissues related to organogenic ECM remodeling and vascularization during early establishment of mouse placentation.

Gene expression profiling of bovine peripartal placentomes: detection of molecular pathways potentially involved in the release of foetal membranes

The mechanisms underlying detachment of foetal membranes after birth in cows are still unclear. To address this problem in a systematic manner, we performed the first holistic transcriptome study of bovine placentomes antepartum (AP;n=4 cows) and intrapartum (IP;n=4 cows) using Affymetrix GeneChip Bovine Genome Arrays. Three placentomes were extracted from each cow, and tissue samples from the contact zones of the placentomes (foeto-maternal units) were recovered by systematic random sampling and processed for RNA extraction and for stereological quantification of cellular composition. Statistical analysis of microarray data (false discovery rate 1%) revealed 759 mRNAs with at least twofold higher levels in the samples of the AP group, whereas 514 mRNAs showed higher levels in the IP group. The differentially expressed genes were classified according to biological processes and molecular functions using the Functional Annotation Clustering tool of the DAVID Bioinformatics Resources. Genes with higher mRNA levels in the AP group were nearly completely related to mitotic cell cycle and tissue differentiation. During parturition, a complete shift occurred because the genes with higher mRNA levels in IP were nearly all related to three different physiological processes/complexes: i) apoptosis, ii) degradation of extra cellular matrix and iii) innate immune response, which play a fundamental role in placental detachment. These results are an excellent basis for future studies investigating the molecular basis of retained foetal membranes.

Endopolyploid and proliferating trophoblast cells express different patterns of intracellular cytokeratin and glycogen localization in the rat placenta

The presence of keratin intermediate filaments is a characteristic of trophoblast differentiation. Meantime, their intracellular localization in the functionally different subtypes of placental trophoblast is poorly investigated in rodent, whereas their placentae are being broadly investigated in recent years as a model of the feto-maternal interaction. The purpose was to study the intracellular distribution of cytokeratin filaments in correlation with glycogen deposits, both being important constituents of the trophoblast cells in rat placenta. Different rat trophoblast cell populations exhibited different patterns of cytokeratin immunolocalization. The most intensive immunostaining was observed in the highly endopolyploid SGTCs (secondary giant trophoblast cells) at the border with decidua basalis. The most prominent cytokeratin-positive threads were found at the periphery of cytoplasm and in the extensive system of cytoplasmic sprouts by which the SGTC connect each other. Similar cytokeratin intensity and distribution was detected in the TSC (trabecular spongiotrophoblast cells) of the junctional zone of placenta that line the lacunae with the maternal blood. Clusters of highly proliferative pre-glycogen as well as glycogen cells showed some weaker cytokeratin signals mostly in the perinuclear and peripheral zones of cytoplasm. At the 11.5th to the 13.5th day of gestation, the interstitial and endovascular invasive endopolyploid TGTCs (tertiary giant trophoblast cells) prove the intensive cytokeratin staining throughout the cytoplasm and its sprouts. Meantime, the TGTCs were glycogen negative. By contrast, glycogen was heavily accumulated in the glycogen cells that belong both to the junctional zone of placenta and the cuff of the central arterial channel underlying the monolayer of endovascularly invading TGTCs. Thus, the TGTCs that are first to penetrate into the depth of the uterine wall do not contain glycogen but are accompanied by the glycogen-rich cells. The SGTC also contained the prominent deposits of glycogen at the periphery of cytoplasm and in the cytoplasmic sprouts. At the 16th day of gestation, an extensive interstitial invasion of the cytokeratin-positive glycogen trophoblast cells from the junctional zone was observed. The patterns of cytokeratin and glycogen intracellular localization are specific for each subtype of the rat trophoblast; that is, most probably, accounted for by the functional diversity of different trophoblast populations, i.e. patterns of invasion/phagocytosis and their involvement in a barrier at the feto-maternal interface.

Concomitant lack of MMP9 and uPA disturbs physiological tissue remodeling

Urokinase-type plasminogen activator (uPA) and matrix metalloproteinase-9 (MMP9, gelatinase B) have separately been recognized to play important roles in various tissue remodeling processes. In this study, we demonstrate that deficiency for MMP9 in combination with ablation of either uPA- or tissue-type plasminogen activator (tPA)-catalyzed plasminogen activation is critical to accomplish normal gestation in mice. Gestation was also affected by simultaneous lack of MMP9 and the uPA receptor (uPAR). Interestingly, uPA-deficiency additionally exacerbated the effect of MMP9-deficiency on bone growth and an additive effect caused by combined lack in MMP9 and uPA was observed during healing of cutaneous wounds. By comparison, MMP9-deficiency combined with absence of either tPA or uPAR resulted in no significant effect on wound healing, indicating that the role of uPA during wound healing is independent of uPAR, when MMP9 is absent. Notably, compensatory upregulation of uPA activity was seen in wounds from MMP9-deficient mice. Taken together, these studies reveal essential functional dependency between MMP9 and uPA during gestation and tissue repair.

Mammalian Llgl2 is necessary for proper branching morphogenesis during placental development

Cell polarity plays a critical role in the development of all metazoans; however, the mechanisms of cell polarity and the specific role of cell polarity pathways in mammalian organisms are still poorly understood. Lethal giant larvae (Lgl) is an apical-basal polarity gene identified in Drosophila, where it functions as a tumor suppressor controlling self-renewal and differentiation of progenitor cells. There are two orthologs of Lgl in mammalian genomes: Llgl1 and Llgl2. While mammalian Lgls are assumed to be tumor suppressor genes, little is known about their function in vivo. Here we report the functional analysis of murine Llgl2. We generated Llgl2(-/-) mice and found that Llgl2 functions as a polarity protein required for proper branching morphogenesis during placental development. Llgl2(-/-) pups are born as runts but quickly catch up in size and grow into normal-size adults. Surprisingly, no prominent phenotypes or spontaneous tumors were observed in adult Llgl2(-/-) mice. Analyses of placental trophoblasts reveal a critical role for Llgl2 in cell polarization and polarized cell invasion. We conclude that mammalian Llgl2 is required for proper polarized invasion of trophoblasts and efficient branching morphogenesis during placental development, but, unlike its Drosophila ortholog, it does not function as a canonical tumor suppressor gene.

MMP9 is protective against lethal inflammatory mass lesions in the mouse colon

The family of matrix metalloproteinases (MMPs) is responsible for extracellular matrix degradation during physiological and pathophysiological tissue remodeling processes such as embryogenesis, tissue repair and cancer progression. Despite these important roles of MMPs, inhibition or ablation of individual members of the MMP family in animal models have been shown to have little effect. It has been speculated that this results from a functional overlap between individual MMPs and (as-yet-unclassified) functional overlaps between MMPs and other protease systems. We here present genetic data showing that concomitant ablation of MMP9 (gelatinase B) and the serine protease plasmin results in lethal inflammatory mass lesions in the colon. These lesions possessed several histological attributes that are characteristic of mucosal prolapse seen in humans, and they were found to be associated with splenomegaly, enlarged mesenteric lymph nodes, decreased thymus size and altered populations of circulating immune cells. A time-course study provided evidence that the massive lymphoid hyperplasia and reactive changes were secondary to discrete fibrinous lesions also observed in mice only deficient for plasminogen (Plg), the zymogen for plasmin. These data demonstrate a non-appreciated vital protective role for MMP9 in the absence of Plg.

Oxidative stress promotes the increase of matrix metalloproteinases-2 and -9 activities in the feto-placental unit of diabetic rats

Maternal diabetes increases the risk of congenital malformations, placental dysfunction and diseases in both the neonate and the offspring's later life. Oxidative stress has been involved in the etiology of these abnormalities. Matrix metalloproteases (MMPs), involved in multiple developmental pathways, are increased in the fetus and placenta from diabetic experimental models. As oxidants could be involved in the activation of latent MMPs, we investigated a putative relationship between MMPs activities and oxidative stress in the feto-placental unit of diabetic rats at midgestation. We found that H2O2 enhanced and that superoxide dismutase (SOD) reduced MMPs activities in the maternal side of the placenta and in the fetuses from control and diabetic rats. MMPs were not modified by oxidative status in the fetal side of the placenta. Lipid peroxidation was enhanced in the maternal and fetal sides of the placenta and in the fetus from diabetic rats when compared to controls, and gradually decreased from the maternal placental side to the fetus in diabetic animals. The activities of the antioxidant enzymes SOD and catalase were decreased in the maternal placental side, catalase activity was enhanced in the fetal placental side and both enzymes were increased in the fetuses from diabetic rats when compared to controls. Our data demonstrate changes in the oxidative balance and capability of oxidants to upregulate MMPs activity in the feto-placental unit from diabetic rats, a basis to elucidate links between oxidative stress and alterations in the developmental pathways in which MMPs are involved.

Placental and embryonic growth restriction in mice with reduced function epidermal growth factor receptor alleles

Embryos lacking an epidermal growth factor receptor (EGFR) exhibit strain-specific defects in placental development that can result in mid-gestational embryonic lethality. To determine the level of EGFR signaling required for normal placental development, we characterized congenic strains homozygous for the hypomorphic Egfr(wa2) allele or heterozygous for the antimorphic Egfr(Wa5) allele. Egfr(wa2) homozygous embryos and placentas exhibit strain-dependent growth restriction at 15.5 days post-coitus while Egfr(Wa5) heterozygous placentas are only slightly reduced in size with no effect on embryonic growth. Egfr(wa2) homozygous placentas have a reduced spongiotrophoblast layer in some strains, while spongiotrophoblasts and glycogen cells are almost completely absent in others. Our results demonstrate that more EGFR signaling occurs in Egfr(Wa5) heterozygotes than in Egfr(wa2) homozygotes and suggest that Egfr(wa2) homozygous embryos model EGFR-mediated intrauterine growth restriction in humans. We also consistently observed differences between strains in wild-type placenta and embryo size as well as in the cellular composition and expression of trophoblast cell subtype markers and propose that differential expression in the placenta of Glut3, a glucose transporter essential for normal embryonic growth, may contribute to strain-dependent differences in intrauterine growth restriction caused by reduced EGFR activity.

Impaired placental neovascularization in mice with pregnancy-associated hypertension

Preeclampsia is a serious disorder that may result in severe morbidity and mortality for mother and fetus, and it is thought that the placental dysfunction is important in the pathogenesis of preeclampsia. As the model of preeclampsia, we previously generated a transgenic mouse model that developed pregnancy-associated hypertension (PAH) by mating females expressing human angiotensinogen with males expressing human renin. In PAH mice, maternal blood pressure started to rise from days 12 to 13 of gestation (E12-13) to term (E19-20), which is accompanied by the fetal intrauterine growth retardation and systemic maternal disorders including proteinuria and convulsion. To understand the pathology of the complications in PAH mice that overlap with those in human preeclampsia, we analyzed the PAH placenta sequentially from the onset of hypertension to the term of delivery. In PAH placenta, histological analysis revealed that the microvessel densities of fetal vasculature at term were significantly lower than those of normal placenta, and the majority of terminal vessels of PAH placenta were lacking for pericytes and basement membrane. The interaction between fetal vasculature and maternal blood canal at labyrinth of PAH placenta was morphologically distorted, and the expression patterns of key molecules in neovascularization of PAH placenta were distinct from those of normal placenta during pregnancy. In addition, maternal plasma level of soluble form of vascular endothelial growth factor receptor-1 (sVEGFR-1) was significantly increased in PAH at E19. Furthermore, in uteroplacental site, in situ proteolytic activity of PAH mice was suppressed from E16 to term compared to that of normal pregnancy, and the expression of matrix metalloproteinase-2 mRNA was strikingly downregulated at E16 in PAH mice. Collective data suggest that the impairments of fetoplacental neovascularization and uteroplacental remodeling contribute to the development of complications in PAH.

Loss of Cited2 affects trophoblast formation and vascularization of the mouse placenta

Cited2 is widely expressed in the developing embryo and in extraembryonic tissues including the placenta. Gene expression can be induced by a number of factors; most notably by the hypoxia inducible transcription factor, HIF1, under low oxygen conditions. Cited2 encodes for a transcriptional co-factor that in vitro can act as both a positive and negative regulator of transcription. This function is due to its interaction with CBP/p300 and appears to depend on whether Cited2 enables CBP/p300 to interact with the basic transcriptional machinery, or if its binding prevents such an interaction from occurring. Here, we report a novel function for Cited2 in placenta formation, following gene deletion in mouse. In the absence of Cited2 the placenta and embryo are significantly small from 12.5 and 14.5 dpc respectively, and death occurs in utero. Cited2 null placentas have fewer differentiated trophoblast cell types; specifically there is a reduction in trophoblast giant cells, spongiotrophoblasts and glycogen cells. In addition, the fetal vasculature of the placenta is disorganised and there are fewer anastomosing capillaries. Given that Cited2 is expressed in both trophoblasts and the fetal vasculature, the observed defects fit well with the sites of gene expression. We conclude that Cited2 is required for normal placental development and vascularisation, and hence for embryo viability.

Hypoxia inhibits differentiation of lineage-specific Rcho-1 trophoblast giant cells

Defects in placental development lead to pregnancies at risk for miscarriage and intrauterine growth retardation and are associated with preeclampsia, a leading cause of maternal death and premature birth. In preeclampsia, impaired placental formation has been associated with alterations in a specific trophoblast lineage, the invasive trophoblast cells. In this study, an RT-PCR Trophoblast Gene Expression Profile previously developed by our laboratory was utilized to examine the lineage-specific gene expression of the rat Rcho-1 trophoblast cell line. Our results demonstrated that Rcho-1 cells represent an isolated, trophoblast population committed to the giant cell lineage. RT-PCR analysis revealed that undifferentiated Rcho-1 cells expressed trophoblast stem cell marker, Id2, and trophoblast giant cell markers. On differentiation, Rcho-1 cells downregulated Id2 and upregulated Csh1, a marker of the trophoblast giant cell lineage. Neither undifferentiated nor differentiated Rcho-1 cells expressed spongiotrophoblast marker Tpbpa or labyrinthine markers Esx1 and Tec. Differentiating Rcho-1 cells in hypoxia did not alter the expression of lineage-specific markers; however, hypoxia did inhibit the downregulation of the trophoblast stem cell marker Id2. Differentiation in hypoxia also blocked the induction of CSH1 protein. In addition, hypoxia inhibited stress fiber formation and abolished the induction of palladin, a protein associated with stress fiber formation and focal adhesions. Thus, Rcho-1 cells can be maintained as a proliferative, lineage-specific cell line that is committed to the trophoblast giant cell lineage on differentiation in both normoxic and hypoxic conditions; however, hypoxia does inhibit aspects of trophoblast giant cell differentiation at the molecular, morphological, and functional levels.

Progressive loss of the spongiotrophoblast layer of Birc6/Bruce mutants results in embryonic lethality

We have generated a mouse line with a mutant allele of the mouse Bruce/Birc6 gene induced by gene trap mutagenesis. Based on its structural features, Bruce is a member of the family of apoptosis inhibitor proteins (IAPs). This mutation leads to a truncated transcript and protein and results in a complete loss of the wildtype Bruce protein. Bruce mutant mice die from a progressive loss of their placental spongiotrophoblast layer between day 11.5 and 14.5 of embryonic development. The cause of the Bruce homozygous mutant phenotype is a lack of proliferation of spongiotrophoblast cells in the developing placenta. In contrast to in vitro data, which indicate a function for Bruce in apoptosis inhibition, the in vivo results presented here suggest instead a role for Bruce in cell division.

Differential roles of renin and angiotensinogen in the feto-maternal interface in the development of complications of pregnancy

We previously identified a transgenic mouse model that developed pregnancy-associated hypertension (PAH) and intrauterine growth restriction (IUGR) by mating females expressing human angiotensinogen (hANG) with males expressing human renin (hRN). These phenotypic defects were not observed in the opposite type of mating combination, despite the feto-placental overexpression of hRN and hANG detected in both types of crossbreeding. Detailed analysis of transgene localization in the labyrinth and its permeability to the maternal circulation revealed that hRN produced in trophoblast giant cells was secreted into the maternal circulation, whereas hANG, produced in chorionic trophoblasts and trophoblastic epithelium, was undetectable in the maternal plasma, probably due to their distinct spatial and temporal expression in labyrinth. These results demonstrated that PAH and IUGR could be mediated by feto-placental hRN through its permeability to the maternal circulation, not by feto-placental hANG production. Furthermore, overexpression of maternally derived hANG in decidua and spiral arteries of pregnant females with PAH and IUGR raises the possibility of local activation of the renin-angiotensin system and its pathophysiological effects on placental hypoperfusion in complications of pregnancy. This study provides in vivo evidence that the cell-specific expression of RN and ANG in the feto-maternal interface impacts their differential roles in pregnancy.

Serine protease HtrA1 is developmentally regulated in trophoblast and uterine decidual cells during placental formation in the mouse

Development of a hemochorial placenta involves trophoblast proliferation, differentiation, and invasion into the uterus to promote blood flow to the embryo. Trophoblast invasion is tightly controlled by expression of specific proteases in the trophoblast and highly coordinated activities in the uterus. One uterine event essential for placentation is the developmentally regulated formation and regression of the decidua. In mice, decidual regression takes place in a temporal- and spatial-specific manner that is coordinated with placental development. In this study, we identified that the serine protease HtrA1 (high temperature requirement factor A1) was specifically expressed in differentiated trophoblast cells, especially the giant cells, during the early stages of placental development. A high level of HtrA1 expression was also detected in decidua capsularis specifically at the decidual-trophoblast interface where active involution occurs. Thus, we have identified a previously unknown role for HtrA1 as a protease potentially important for trophoblast differentiation/invasion and uterine decidual regression during placental development.

Different molecular mechanisms underlie placental overgrowth phenotypes caused by interspecies hybridization, cloning, andEsx1mutation

To obtain a deeper insight into the genes and gene networks involved in the development of placentopathies, we have assessed global gene expression in three different models of placental hyperplasia caused by interspecies hybridization (IHPD), cloning by nuclear transfer, and mutation of the Esx1 gene, respectively. Comparison of gene expression profiles of approximately 13,000 expressed sequence tags (ESTs) identified specific subsets of genes with changed expression levels in IHPD, cloned, and Esx1 mutant placentas. Of interest, only one gene of known function and one EST of unknown function were found common to all three placentopathies; however, a significant number of ESTs were common to IHPD and cloned placentas. In contrast, only one gene was shared between IHPD and Esx1 mutant, and cloned and Esx1 mutant placentas, respectively. These genes common to different abnormal placental growth genotypes are likely to be important in the occurrence of placentopathy.

A functional overlap of plasminogen and MMPs regulates vascularization during placental development

Both plasminogen activators and matrix metalloproteinases (MMPs) have been implicated in a variety of developmental processes in the mouse during embryo implantation and placentation. We show here that pharmacological treatment of plasminogen-deficient mice with the broad spectrum MMP inhibitor galardin leads to a high rate of embryonic lethality. Implantation sites from plasminogen-deficient galardin-treated mice at 7.5 days post coitus (dpc) showed delay in both decidualization and invasion of maternal vessels into the decidua. At 8.5 dpc, half of the embryos were runted and still at the developmental stage of a 7.5 dpc embryo. Most embryos that escaped these initial defects eventually died, probably from defective vascularization and development of the labyrinth layer of the placenta, although a direct role on embryo development cannot be ruled out. These results demonstrate that the combination of MMPs and plasminogen is essential for the proper development of the placenta. Plasminogen deficiency alone and galardin treatment alone had much less effect and there was a pronounced synergism on both placental vascularization and embryonic lethality, indicating a functional overlap between plasminogen and MMPs.

Effect of high concentrations of glucose on differentiation of rat trophoblast cells in vitro

AIMS/HYPOTHESIS

Previous studies have shown that diabetic placentas are characterized by structural and biochemical anomalies, including defects in the differentiation of trophoblasts. In this study, the Rcho-1 cell line was used to investigate the impact of high glucose concentrations on different markers of differentiation of rat trophoblast cells in giant cells (endoreduplication, invasive phenotype and endocrine phenotype).

MATERIALS

Rcho-1 cells were incubated for 12 days in medium supplemented with different concentrations of glucose and 10% horse serum to optimize differentiation. The cells were examined for the proportion of nuclei showing signs of apoptosis. The effect of high glucose was investigated on the endoreduplication process, on invasive phenotype (secretion of gelatinase B) and on endocrine phenotype (expression of placental lactogen I (PL-I) and II (PL-II) and progesterone secretion).

RESULTS

Apoptosis was not induced by high glucose in Rcho-1. The number of cells was higher in the cultures exposed to high glucose (p<0.05) and their nuclei contained more DNA compared with control cells (p<0.001), while their nuclear size was smaller (p<0.001). Gelatinase B secretion increased during differentiation but no difference was found when gelatinase B secretion from trophoblasts exposed to high glucose was compared with the control cells. Rcho-1 cell cultures showed an increase in PL-I and PL-II mRNA expressions during differentiation and which was not affected by high glucose. Progesterone secretion increased during differentiation in control cultures. However, this increase was abolished when trophoblasts were cultured in high glucose.

CONCLUSIONS/INTERPRETATION

Our data suggest that high glucose influences the endoreduplication process and the steroidogenesis during differentiation of rattrophoblasts.

Matrix metalloproteinases mediate the dismantling of mesenchymal structures in the tadpole tail during thyroid hormone-induced tail resorption

It has been suggested that a family of tissue remodelling enzymes called matrix metalloproteinases (MMPs) play a causal role in the process of tail resorption during thyroid hormone-induced metamorphosis of the anuran tadpole; however, this hypothesis has never been directly substantiated. We cloned two new Xenopus MMPs, gelatinase A (MMP-2) and MT3-MMP (MMP-16), and the MMP inhibitor TIMP-2. These clones were used along with several others to perform a comprehensive expression study. We show that all MMPs and TIMP-2 are dramatically induced in the resorbing tail during spontaneous metamorphosis and are spatially coexpressed, primarily in the remodelling mesenchymal tissues. By Northern blotting, we show that all the examined MMPs/TIMP-2 are also induced by treatment of organ-cultured tails with thyroid hormone (T(3)). Using the organ culture model, we provide the first direct evidence that MMPs are required for T(3)-induced tail resorption by showing that a synthetic inhibitor of MMP activity/expression can specifically retard the resorption process. By gelatin zymography, we also show T(3) induction of a fifth MMP, preliminarily identified as gelatinase B (GelB; MMP-9). Moreover, T(3) not only induces MMP/TIMP expression but also MMP activation, and we provide evidence that TIMP-2 participates in the latter process. These findings suggest that MMPs and TIMPs act in concert to effect the dismantling of mesenchymal structures during T(3)-induced metamorphic tadpole tail resorption.

Coordinated induction of extracellular proteolysis systems during experimental autoimmune encephalomyelitis in mice

Plasminogen activators (PAs) and matrix metalloproteinases (MMPs) are considered to play an important role in the pathogenesis of multiple sclerosis. Experimental autoimmune encephalomyelitis (EAE) is widely used as an animal model of multiple sclerosis. Whereas several studies have addressed the expression of various MMPs and their inhibitors in the pathogenesis of EAE, the expression of the molecules of the PA system during EAE has not been reported previously. The present study was undertaken to investigate the expression of the molecules of the PA system (tPA, uPA, PAI-1, uPAR, LRP), as well as several members of the MMP family and their inhibitors in the course of actively induced EAE in BALB/c mice. During clinical EAE, the PA system was up-regulated in the central nervous system at several levels. Induction of expression of tPA and PAI-1 transcripts was detected in activated astrocytes in the white matter. Inflammatory cells expressed uPA receptor, uPAR. In situ zymography demonstrated the presence of increased tPA and uPA activities in the areas of the inflammatory damage. Accumulation of fibrin, fibronectin, and vitronectin immunoreactivity was seen in perivascular matrices of symptomatic animals. In addition, transcription of MT1-MMP and metalloelastase (in inflammatory cells), and TIMP-1 (in activated astrocytes) was induced during EAE. Increased gelatinolytic activity was detected at the sites of inflammatory cell accumulation by in situ zymography of fluorescently labeled gelatin; substrate gel zymography identified the up-regulated gelatinolytic activity as gelatinase B. Overall, our study demonstrates concurrent induction of PA and MMP systems during active EAE, supporting further the concept that the neuroinflammatory damage in EAE involves altered balance between multiple extracellular proteases and their inhibitors.

Placental development: lessons from mouse mutants

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

Acute food restriction increases collagen breakdown and phagocytosis by mature decidual cells of mice

An ultrastructural study was undertaken on antimesometrial mature decidual tissue of fed and food-restricted mice, on day 9 of pregnancy. The mean ad libitum food intake was established on mice from the 8th till the 9th day of pregnancy. Fed mice were used as controls. Experimental animals were divided into two groups: one was allowed to feed 25% of normal diet and the other 50%. Extracellular collagen fibrils were scarce in fed animals and conspicuous in food restriction. Granular electron-dense deposits and filamentous aggregates of disintegrating collagen fibrils were observed in all food-deprived mice but were rarely noted in fed animals. Intracellular vacuolar structures exhibited other typical cross-banded collagen immersed in finely granular electron-translucent material (clear vacuole) or electron-dense material containing collagen fibrils with a faint periodicity (dark vacuole). The clear and dark vacuoles were scarce in fed animals and evident in food-restricted mice, mainly in those 25% food restricted. Although collagen breakdown may be part of the normal process of decidual tissue remodelling our results suggest that it is enhanced in food-restricted animals. Thus it seems that collagen breakdown is a normal mechanism that may be regulated by the food intake of the pregnant animal.

Screening for genes involved in tissue invasion based on placenta formation and cancer cell lines with low and high metastatic potential

During the formation of placenta, trophoblast cells vigorously invade maternal uterine tissues, sharing many features with the invasion of cancers. We applied RNA differential display to placenta tissues from 8.5 to 17.5 days post-coitus (dpc) ICR mice, and isolated 188 cDNA fragments expressed differentially. Among the 25 known cDNA fragments thus far analyzed, six cDNAs have been reported to be relevant to tumor invasion and/or metastasis. Furthermore, 11 of 20 unknown cDNAs isolated showed differential expression between the pairs of cancer cell lines with low and high metastatic potential, indicating potential usefulness of the present two-step approach.

Coexpression of cytokeratin and vimentin in mice trophoblastic giant cells

Trophoblastic giant cells reach their maximum size and exhibit a conspicuous synthetic and invasive activity during mouse placentation. The cytoskeleton, given the complex functions of the cells, shows a well-developed network of intermediate filament proteins. Immunohistochemistry combined with confocal and conventional immunofluorescence studies of intermediate filaments proteins cytokeratin and vimentin were performed in mice trophoblastic giant cells on days 9-11 of pregnancy. Specimens were fixed in phosphate-buffered formaldehyde and tissues were processed for routine paraffin embedding. Trophoblastic giant cells from antimesometrial, lateral or mesometrial uterine regions, through days 9-11 of pregnancy, expressed the same staining with both immunoperoxidase and immunofluorescent techniques. Cytokeratin filamentous structures were intensely immunoreactive and were detected throughout the cells cytoplasm; a few cells exhibited strongest fluorescence in the peripheral cytoplasm. Vimentin-positive staining was often distributed throughout the cells cytoplasm, most frequently and more intensely in the peripheral region; in some cells, it was present only in the peripheral regions. It is probable that expression of vimentin in midpregnancy trophoblastic giant cells may be associated with the rapid and conspicuous increase in size and synthetic activity of the cells and also with phagocytosis of degraded materials and invasion of decidual tissue.