The human placenta: a model for tenascin expression.

Tenascin is a large glycoprotein of the extracellular matrix. Previous reports have demonstrated that it is associated with epithelial-mesenchymal interfaces and is expressed during embryonic and tumour development, wound healing, cell proliferation and it may be involved in immunomodulation. The human placenta shows numerous features related to these aspects. We have investigated the presence of tenascin in the human placenta throughout pregnancy by immunohistochemistry. We used monoclonal (mAb) and polyclonal (pAb) antibodies to tenascin, a mAb to fibrin, a pAb to fibrinogen, and the mAb Ki-67 as proliferation marker. Tenascin was highly expressed in the mesenchymal villi which are considered the basis of growth and differentiation of the villous trees. Moreover, fibrinoid deposits at the surfaces of the villous trees were always separated from the fetal stroma by tenascin. The stroma of villi encased in fibrinoid was also positive for tenascin. This glycoprotein was also expressed in the villous stroma directly apposed to cell islands and cell columns. In the proximal portions of both epithelial structures, cytotrophoblast was Ki-67 positive. These data show that tenascin is expressed during the development of the placenta, particularly in the mesenchymal villi, cell islands and cell columns. These structures are considered to be the proliferating units of the villous trees. Tenascin underlying fibrinoid deposits suggests that it also participates in repair mechanisms. Thus, in the human placenta tenascin expression can be correlated with villous growth, cell proliferation, and fibrinoid deposition. Its role in immunoprotection of fetal tissues in areas where syncytiotrophoblast as barrier is missing or damaged is discussed.     

The human placenta as a target tissue for glucagon

Glucagon's effect on the placenta was studied in cultured human term trophoblast and in homogenized term and first-trimester placentas. In studies with cultured term trophoblast, glucagon stimulated the generation of cyclic AMP and estradiol secretion and inhibited placental lactogen secretion. Incubation of homogenates of term and of first-trimester placenta with 0.5 mM dibutyryl cAMP revealed a marked decrease of pyruvate kinase activity. Glucagon produced a similar decrease in first-trimester homogenates, but failed to affect term placentas. The present demonstration of the placenta as a target tissue for glucagon suggests an active contribution of the trophoblast to energy metabolism during pregnancy.     

The human placenta: a novel source of inhibin

Human placental extracts contain inhibin bioactivity and immunoactivity giving dose response curves parallel to a human follicular fluid inhibin standard. Inhibin bioactivity in vitro was neutralised by preincubation of extracts with antisera raised to pure bovine inhibin. Umbilical cord blood from term infants contained immunoactivity. Human placental inhibin differs from human ovarian inhibin in terms of its biological: immunological ratio.     

Fibulin-5 expression in the human placenta

Fibulin-5 is a secreted extracellular matrix glycoprotein and displays a diverse panel of biological functions, which can be segregated into elastogenic as well as extra-elastogenic functions. While elastogenic functions of fibulin-5 include essential roles in early steps of elastic fibre assembly, extra-elastogenic functions are widespread. Depending on the cell type used, fibulin-5 mediates cell adherence via a subset of integrins, antagonizes angiogenesis and inhibits migration as well as proliferation of endothelial and smooth muscle cells. In this study, we focused on the spatiotemporal expression of fibulin-5 in the human placenta. With progressing gestation, placental fibulin-5 expression increased from first trimester towards term. At term, placental fibulin-5 mRNA expression is lower when compared with other well-vascularized organs such as lung, kidney, heart, uterus and testis. In first trimester, placenta immunohistochemistry localized fibulin-5 in villous cytotrophoblasts and extravillous cytotrophoblasts of the proximal cell column. In term placenta, fibulin-5 was detected in the endothelial basement membrane and adventitia-like regions of vessels in the chorionic plate and stem villi. Cell culture experiments with the villous trophoblast-derived cell line BeWo showed that fibulin-5 expression was downregulated during functional differentiation and intercellular fusion. Moreover, cultivation of BeWo cells under low oxygen conditions impaired intercellular fusion and upregulated fibulin-5 expression. The spatiotemporal shift from the trophoblast compartment in first trimester to the villous vasculature at term suggests a dual role of fibulin-5 in human placental development.     

HLA-G in the human placenta: expression and potential functions

HLA-G is a non-classical class I molecule specifically expressed in the placenta, suggesting that it might have a physiological function at the materno-foetal interface. The structural characteristics of HLA-G, the placental pattern of expression and the functional properties of this class Ib glycoprotein in vitro are described and evaluated in the context of pregnancy. The possible anti-viral function of HLA-G, its modulatory role of natural killer cell activity and its likely non-immunological functions are discussed.     

Regulation of tenascin expression in bone

Tenascins regulate cell interaction with the surrounding pericellular matrix. Within bone, tenascins C and W influence osteoblast adhesion and differentiation, although little is known about the regulation of tenascin expression. In this study we examined the effect of osteogenic differentiation, bone morphogenetic protein (BMP) and Wnt growth factors, and mechanical loading on tenascin expression in osteogenic cells. Osteogenic differentiation increased tenascin C (TnC), and decreased tenascin W (TnW), expression. Both growth factors and mechanical loading increased both TnC and TnW expression, albeit via distinct signaling mechanisms. Both BMP-2 and Wnt5a induction of tenascin expression were mediated by MAP kinases. These data establish a role for BMP, Wnts, and mechanical loading in the regulation of tenascin expression in osteoblasts.     

The regulation of human corticotrophin-releasing hormone gene expression in the placenta

Corticotrophin-releasing hormone (CRH) is a 41 amino acid neuropeptide that is expressed in the hypothalamus and the human placenta. Placental CRH production has been linked to the determination of gestational length in the human. Although encoded by a single copy gene, CRH expression in the placenta is regulated differently to the hypothalamus. Glucocorticoids stimulate CRH promoter activity in the placenta but inhibit it's activity in the hypothalamus, via mechanisms involving different regions of the CRH promoter. We discuss how various stimuli alter CRH promoter activity and why these responses are unique to the placenta.     

The human placenta exhibits a unique transcriptomic void

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Differences in gene expression between first and third trimester human placenta: a microarray study

Background

The human placenta is a rapidly developing organ that undergoes structural and functional changes throughout the pregnancy. Our objectives were to investigate the differences in global gene expression profile, the expression of imprinted genes and the effect of smoking in first and third trimester normal human placentas.

Materials and Methods

Placental samples were collected from 21 women with uncomplicated pregnancies delivered at term and 16 healthy women undergoing termination of pregnancy at 9–12 weeks gestation. Placental gene expression profile was evaluated by Human Genome Survey Microarray v.2.0 (Applied Biosystems) and real-time polymerase chain reaction.

Results

Almost 25% of the genes spotted on the array (n = 7519) were differentially expressed between first and third trimester placentas. Genes regulating biological processes involved in cell proliferation, cell differentiation and angiogenesis were up-regulated in the first trimester; whereas cell surface receptor mediated signal transduction, G-protein mediated signalling, ion transport, neuronal activities and chemosensory perception were up-regulated in the third trimester. Pathway analysis showed that brain and placenta might share common developmental routes. Principal component analysis based on the expression of 17 imprinted genes showed a clear separation of first and third trimester placentas, indicating that epigenetic modifications occur throughout pregnancy. In smokers, a set of genes encoding oxidoreductases were differentially expressed in both trimesters.

Conclusions

Differences in global gene expression profile between first and third trimester human placenta reflect temporal changes in placental structure and function. Epigenetic rearrangements in the human placenta seem to occur across gestation, indicating the importance of environmental influence in the developing feto-placental unit.     

The pig: a model for human infectious diseases

An animal model to study human infectious diseases should accurately reproduce the various aspects of disease. Domestic pigs (Sus scrofa domesticus) are closely related to humans in terms of anatomy, genetics and physiology, and represent an excellent animal model to study various microbial infectious diseases. Indeed, experiments in pigs are much more likely to be predictive of therapeutic treatments in humans than experiments in rodents. In this review, we highlight the numerous advantages of the pig model for infectious disease research and vaccine development and document a few examples of human microbial infectious diseases for which the use of pigs as animal models has contributed to the acquisition of new knowledge to improve both animal and human health.     

The regulation of human corticotrophin-releasing hormone gene expression in the placenta.

Corticotrophin-releasing hormone (CRH) is a 41 amino acid neuropeptide that is expressed in the hypothalamus and the human placenta. Placental CRH production has been linked to the determination of gestational length in the human. Although encoded by a single copy gene, CRH expression in the placenta is regulated differently to the hypothalamus. Glucocorticoids stimulate CRH promoter activity in the placenta but inhibit it's activity in the hypothalamus, via mechanisms involving different regions of the CRH promoter. We discuss how various stimuli alter CRH promoter activity and why these responses are unique to the placenta.     

Towards a rational modeling for the human placenta

An attempt is made to provide a general framework sufficient of handling analytically typical questions concerned with a physiological functioning of a human placenta. The principles of mechanics and thermodynamics, as they apply to a continuum theory of mixtures, are the essential tools in constructing the model. In general terms, it is assumed that each point of the placenta space is simultaneously occupied by placenta tissue, fetal blood, and maternal blood. These three constituents are allowed to interact mechanically, chemically, and thermally. One of the basic features of the model is its capability of providing quantitative information on the deformation of the placenta tissue and the pressure distribution of the fetal and maternal blood. Effects of inertia, deformation, and changes of shape and weight of the placenta during gestation are also taken into account.     

The expression of tenascin by neural crest cells and glia.

The extracellular matrix glycoprotein tenascin is concentrated in both the embryo and adult in regions where cell motility is taking place. For example, during avian neural crest morphogenesis tenascin is concentrated in the rostral half of the sclerotome, precisely where the neural crest cells themselves are found. Previous in vitro studies indicated that somite cells were the source of this tenascin, implying a role for tenascin in directing the ventral migration of neural crest cells and thus the establishment of the periodic arrangement of the PNS. In this study, we have used a cDNA probe to identify the source of tenascin found along the pathways of the neural crest using in situ hybridization. In tissue sections, individual cells found along the neural crest migratory pathways, both before entering the somites and within the somites, are strongly labelled by the tenascin cDNA. In vitro neural crest cells are more strongly labelled with the tenascin probe than somite cells. Finally, western blotting has been used to identify tenascin in culture medium conditioned by neural crest cells. This indicates that neural crest cells themselves are the source of much of the tenascin found lining their migratory pathways, and that interactions with somite cells may not be needed to induce the expression of tenascin. We have also studied the distribution of tenascin mRNA in the developing spinal cord and spinal ganglia. At embryonic days 7 and 10, tenascin cDNA hybridizes within cells that appear to be migrating from the ependymal layer to the white matter, as well as within cells in the dorsal roots.(ABSTRACT TRUNCATED AT 250 WORDS)     

Alcoholism: protein expression profiles in a human hippocampal model

It is well known that chronic, excessive consumption of alcohol can cause brain damage/structural changes in the regions important for neurocognitive function. Some of the damages are permanent, while others are reversible. Molecular mechanisms underlying alcohol-induced and/or -related brain damage are largely unknown, although it is generally believed that three factors (ethanol, nutritious and hepatic factors) play important roles. Recently, we have been employing a high-throughput proteomics technology to investigate several alcohol-sensitive brain regions from uncomplicated and hepatic cirrhosis-complicated alcoholics to understand the mechanisms of alcohol effects on the CNS at the level of protein expression. The changes of protein expression profiles in the hippocampus of alcoholic subjects were firstly demonstrated using 2D gel electrophoresis-based proteomics. Protein expression profiles identified in the hippocampus of alcoholic subjects were significantly different from those previously identified by our group in other brain regions of the same alcoholic cases, possibly indicating that these different brain regions react differently to chronic alcohol ingestion at the level of protein expression. Identified changes of protein expression associated with astrocyte and oxidative stress may indicate the possibility that increased levels of CNS ammonia and reactive oxygen species induced by alcoholic mild hepatic damage/dysfunction could cause selective damage in astrocytes of the hippocampus. Although our data did not demonstrate any evidence of direct alcohol effects to induce the alteration of protein expression in association with brain damage, high-throughput neuroproteomics approaches have proved to have the potential to dissect the mechanisms of complex brain disorders. Proteomics studies on human hippocampus, an important region for neurocognitive function and psychiatric illnesses (e.g., Alzheimer’s disease, alcoholism and schizophrenia) are still sparse, and further investigation is warranted to understand the underlying mechanisms.     

Alcoholism: protein expression profiles in a human hippocampal model

It is well known that chronic, excessive consumption of alcohol can cause brain damage/structural changes in the regions important for neurocognitive function. Some of the damages are permanent, while others are reversible. Molecular mechanisms underlying alcohol-induced and/or -related brain damage are largely unknown, although it is generally believed that three factors (ethanol, nutritious and hepatic factors) play important roles. Recently, we have been employing a high-throughput proteomics technology to investigate several alcohol-sensitive brain regions from uncomplicated and hepatic cirrhosis-complicated alcoholics to understand the mechanisms of alcohol effects on the CNS at the level of protein expression. The changes of protein expression profiles in the hippocampus of alcoholic subjects were firstly demonstrated using 2D gel electrophoresis-based proteomics. Protein expression profiles identified in the hippocampus of alcoholic subjects were significantly different from those previously identified by our group in other brain regions of the same alcoholic cases, possibly indicating that these different brain regions react differently to chronic alcohol ingestion at the level of protein expression. Identified changes of protein expression associated with astrocyte and oxidative stress may indicate the possibility that increased levels of CNS ammonia and reactive oxygen species induced by alcoholic mild hepatic damage/dysfunction could cause selective damage in astrocytes of the hippocampus. Although our data did not demonstrate any evidence of direct alcohol effects to induce the alteration of protein expression in association with brain damage, high-throughput neuroproteomics approaches have proved to have the potential to dissect the mechanisms of complex brain disorders. Proteomics studies on human hippocampus, an important region for neurocognitive function and psychiatric illnesses (e.g., Alzheimer's disease, alcoholism and schizophrenia) are still sparse, and further investigation is warranted to understand the underlying mechanisms.     

Endogenous heparin-binding lectin activity in human placenta: purification and developmental expression

Human placental extracts contain a herapin-inhibitable lectin activity. The lectin, which closely resembles those from chicken and rat tissues, was purified by heparin-affinity chromatography. It shares many properties with the previously reported lectins, including hapten specificity, molecular weight of monomers, and immunological cross-reactivity. Sections from different stages of placental development, stained by immunohistochemistry procedures using lectin-specific antibody, showed that the lectin was initially present only in cytotrophoblasts of early first trimester villi. Later in the first trimester, both cytotrophoblasts and syncytiotrophoblasts were stained positively for lectin. From second trimester to term, the lectin was seen only in syncytiotrophoblasts.     

Extracellular matrix-dependent regulation of angiogenin expression in human placenta

Knowledge of the rapidly developing hierarchy of controls affecting vascular development in placenta is required to understand how the growth factors and their receptor-mediated signals actually produce vessels. At the cell biological level, these events clearly require stable interactions between the cells, and cells with the surrounding ECM. The objective of the study was to understand the role of integrins and ECM on the expression and secretion of angiogenin in placentas and from trophoblasts in culture. Functionally active term placental explant culture and trophoblast cultures were used to demonstrate the differential secretion profile of angiogenin and real-time quantitative RT-PCR to demonstrate the mRNA expression in the presence or absence of ECM proteins. In this study, a significant increase in expression and secretion of angiogenin occurred in the presence of vitronectin (VN) and fibronectin (FN). Using antibody-blocking experiments it was also demonstrated that the angiogenin secretion is mediated by placental integrins, alpha(V)beta3 and alpha5beta1. In addition, exposure to hypoxic conditions resulted in diminished angiogenin secretion in the presence of both ECMs suggesting that angiogenin expression in the presence of ECM is modulated by local O2 concentration. In conclusion, this study provides evidence for the regulatory role of ECM and integrins on the mRNA expression and secretion of angiogenin in human placenta. ECMs may have a pivotal role in enhancing secretion of this peptide necessary for placental angiogenesis and provides the impetus as additional targets for the control of angiogenesis in pathological pregnancy.     

Amino acid sequence of mouse tenascin and differential expression of two tenascin isoforms during embryogenesis

We have isolated cDNA clones for mouse tenascin and analyzed expression of tenascin mRNAs during embryonic development of the kidney and gut. The deduced amino acid sequence of the mouse tenascin cDNAs shows a modular structure of repeats similar to chicken and human tenascin. In mouse there are 14.5 cysteine-rich repeats with similarity to the EGF repeat, followed by several repeats with similarity to the type III repeat of fibronectin. A longer variant contains 13 fibronectin type III repeats, whereas a shorter splice variant of mouse tenascin lacks the 5 type III repeats that occur directly after the fifth repeat in the longer variant. Contrary to the chicken and human sequences, mouse tenascin does not contain an RGD sequence in the third type III repeat implicated in cell attachment, or in any other positions. In Northern hybridizations to RNA from primary embryonic fibroblasts, the cDNA clone M 20/1 detects two mRNAs with sizes close to 6 and 8 kb. This, and the other data presented here suggest that the two major mouse tenascin polypeptides arise through an alternative RNA splicing. The two major mRNAs are differentially expressed during development. The 8-kb mRNA is more prominent than the 6-kb mRNA throughout prenatal kidney development, but during postnatal development the ratio of the two mRNAs changes. A different expression pattern is seen in the developing gut where the 6-kb mRNA predominates during embryogenesis with the 8-kb mRNA appearing later. The mRNA data of the developing gut correspond with previous protein data, which showed that the shorter Mr 210,000 polypeptide predominates during earlier developmental stages and the larger Mr 260,000 polypeptide appears later in the embryonic gut (Aufderheide, E., and P. Ekblom. 1988. J. Cell Biol. 107:2341-2349).     

Sulfate transport in human placenta: further evidence for a sodium-independent mechanism

Sulfate transport in isolated placental brush-border membrane vesicles has properties consistent with an anion exchange process. To ascertain the relevance of this finding to sulfate accumulation by the fetus and placenta in vivo, we examined sulfate transport in human placental tissue slices, comparing sulfate uptake with that of a non-metabolizable amino acid marker, alpha-aminoisobutyrate (AIB). In contrast to AIB, which was actively concentrated from physiological media, sulfate uptake by the placenta slice was concentrative only in the absence of sodium and at low pH. Uptake of sulfate reached a steady state after 60 min. It was blocked by DIDS (4,4'-diisothiocyanostilbene-2,2'-disulfonate), a specific inhibitor of anion transport, but not by ouabain. We found no evidence for Na(+)-dependent uptake of sulfate in incubated placental tissue. It seems unlikely that Na(+)-dependent sulfate transport by the placenta can be responsible for net sulfate accumulation by the human fetus.