Insulin-like growth factor-I messenger ribonucleic acid in the developing human placenta and in term placenta of diabetics

Differential expression of leukemia inhibitory factor and insulin like growth factor-1 between normal pregnancies, partial hydatidiform moles and complete hydatidiform moles

INTRODUCTION

Leukemia inhibitory factor (LIF) and insulin like growth factor-1 (IGF-1) are two of the most important growth factors mediating trophoblast actions. We hypothesized that the localization and expression patterns of LIF and IGF-1 in partial and complete hydatidiform moles (HM) compared with normal first trimester placentas may provide an understanding of the proliferative processes in HMs.

METHODS

The study population included curettage material of women diagnosed as complete or partial HM as a result of histopathological and immunohistochemical examination (complete HM group, n = 8; partial HM group, n = 8) and women undergoing dilatation&curettage for unwanted pregnancies (control group, n = 8). Expression of LIF and IGF-1 among placental cell groups was evaluated immunohistochemically and given a score depending on immunostaining intensity.

RESULTS

In normal chorionic villi strong expression of LIF and IGF-1 was present. Both LIF and IGF-1 expressions were weaker in the chorionic villi of complete HMs. In complete mole decidua there was a significant decrease in glandular and endothelial IGF-1 expression along with a decrease in decidual cell LIF expression compared to normal first trimester decidua. LIF expression in extravillous trophoblasts was stronger in complete molar placentas compared to normal placentas.

DISCUSSION

LIF and IGF-1 are important regulators of trophoblast proliferation and invasion. Differential expression of LIF and IGF-1 in molar trophoblasts and chorionic villi might have a role in regulation of trophoblasts in complete moles. Decreased expression of glandular IGF-1 and decidual LIF might be related to the decidual changes during trophoblastic proliferation and invasion of decidua in complete HMs.

Data Mining of Determinants of Intrauterine Growth Retardation Revisited Using Novel Algorithms Generating Semantic Maps and Prototypical Discriminating Variable Profiles

OBJECTIVES

Intra-uterine growth retardation is often of unknown origin, and is of great interest as a "Fetal Origin of Adult Disease" has been now well recognized. We built a benchmark based upon a previously analysed data set related to Intrauterine Growth Retardation with 46 subjects described by 14 variables, related with the insulin-like growth factor system and pro-inflammatory cytokines, namely interleukin-6 and tumor necrosis factor-α.

DESIGN AND METHODS

We used new algorithms for optimal information sorting based on the combination of two neural network algorithms: Auto-contractive Map and Activation and Competition System. Auto-Contractive Map spatializes the relationships among variables or records by constructing a suitable embedding space where 'closeness' among variables or records reflects accurately their associations. The Activation and Competition System algorithm instead works as a dynamic non linear associative memory on the weight matrices of other algorithms, and is able to produce a prototypical variable profile of a given target.

RESULTS

Classical statistical analysis, proved to be unable to distinguish intrauterine growth retardation from appropriate-for-gestational age (AGA) subjects due to the high non-linearity of underlying functions. Auto-contractive map succeeded in clustering and differentiating completely the conditions under study, while Activation and Competition System allowed to develop the profile of variables which discriminated the two conditions under study better than any other previous form of attempt. In particular, Activation and Competition System showed that ppropriateness for gestational age was explained by IGF-2 relative gene expression, and by IGFBP-2 and TNF-α placental contents. IUGR instead was explained by IGF-I, IGFBP-1, IGFBP-2 and IL-6 gene expression in placenta.

CONCLUSION

This further analysis provided further insight into the placental key-players of fetal growth within the insulin-like growth factor and cytokine systems. Our previous published analysis could identify only which variables were predictive of fetal growth in general, and identified only some relationships.

Artificial Neural Networks, and Evolutionary Algorithms as a systems biology approach to a data-base on fetal growth restriction

One of the specific aims of systems biology is to model and discover properties of cells, tissues and organisms functioning. A systems biology approach was undertaken to investigate possibly the entire system of intra-uterine growth we had available, to assess the variables of interest, discriminate those which were effectively related with appropriate or restricted intrauterine growth, and achieve an understanding of the systems in these two conditions. The Artificial Adaptive Systems, which include Artificial Neural Networks and Evolutionary Algorithms lead us to the first analyses. These analyses identified the importance of the biochemical variables IL-6, IGF-II and IGFBP-2 protein concentrations in placental lysates, and offered a new insight into placental markers of fetal growth within the IGF and cytokine systems, confirmed they had relationships and offered a critical assessment of studies previously performed.

Maternal-placental insulin-like growth factor (IGF) signaling and its importance to normal embryo-fetal development

As background for an antibody-based therapeutic program against the IGF receptor, we undertook a review of available information on the early pregnancy-specific regulation and localization of IGFs, IGF-binding proteins (BPs), IGFBP-specific proteases, and the type 1 IGF receptor relative to placental maintenance, function of placental nutrient transporters, placental cellular differentiation/turnover/apoptosis, and critical hormone signaling needed to maintain pregnancy. Possible adverse outcomes of altered IGF signaling include prenatal loss, fetal growth retardation, and maldevelopment are also discussed. It appears that the IGF axes in both the conceptus and mother are important for normal embryo-fetal growth. Thus, all molecules (i.e., both small and large) that disrupt the IGF axis could be expected to have some degree of fetal consequences.

Colony stimulating factor-1 (CSF-1) in pregnancy

Uterine growth factors appear to play a role in the regulation of pregnancy. One of these, colony stimulating factor-1 (CSF-1), synthesized by the uterine epithelium under the control of female sex steroids, has been shown to have important functions both before implantation and during the formation of the placenta. In the female reproductive tract the CSF-1 receptor, the product of the c-fms proto-oncogene, is expressed in decidual cells, trophoblasts and macrophages, indicating that these cells are the primary targets for CSF-1. This article reviews the biology of CSF-1 during gestation as well as the possible involvement of CSF-1 and its receptor in the aetiology of gynaecological tumours.

Placental determinants of fetal growth: identification of key factors in the insulin-like growth factor and cytokine systems using artificial neural networks

BACKGROUND

Changes and relationships of components of the cytokine and IGF systems have been shown in placenta and cord serum of fetal growth restricted (FGR) compared with normal newborns (AGA). This study aimed to analyse a data set of clinical and biochemical data in FGR and AGA newborns to assess if a mathematical model existed and was capable of identifying these two different conditions in order to identify the variables which had a mathematically consistent biological relevance to fetal growth.

METHODS

Whole villous tissue was collected at birth from FGR (N = 20) and AGA neonates (N = 28). Total RNA was extracted, reverse transcribed and then real-time quantitative (TaqMan) RT-PCR was performed to quantify cDNA for IGF-I, IGF-II, IGFBP-1, IGFBP-2 and IL-6. The corresponding proteins with TNF-alpha in addition were assayed in placental lysates using specific kits. The data were analysed using Artificial Neural Networks (supervised networks), and principal component analysis and connectivity map.

RESULTS

The IGF system and IL-6 allowed to predict FGR in approximately 92% of the cases and AGA in 85% of the cases with a low number of errors. IGF-II, IGFBP-2, and IL-6 content in the placental lysates were the most important factors connected with FGR. The condition of being FGR was connected mainly with the IGF-II placental content, and the latter with IL-6 and IGFBP-2 concentrations in placental lysates.

CONCLUSION

These results suggest that further research in humans should focus on these biochemical data. Furthermore, this study offered a critical revision of previous studies. The understanding of this system biology is relevant to the development of future therapeutical interventions possibly aiming at reducing IL-6 and IGFBP-2 concentrations preserving IGF bioactivity in both placenta and fetus.

Immunolocalization of insulin-like growth factor I (IGF-I) during preimplantation in rat uterus

OBJECTIVE

The aim of this study was to determine the insulin-like growth factor (IGF-I) immunolocalization in rat uterus at preimplantation period.

DESIGN

The tissue samples were examined from pregnant animals between gestational day 1 and 5 using immunocytochemistry.

RESULTS

While both the uterine luminal epithelium and the glandular epithelium were stained strongly from gestational day 1 - 3 by IGF-I antibody, the IGF-I immunoreactivity was moderate in myometrium and capillary endothelium. At this period, the IGF-I immunoreactivity was weakly present in a few endometrial stromal cells. At day 4, while IGF-I immunostaining intensity was particularly decreased in the basal domains of uterine luminal epithelium and glandular epithelium, it was similar to the first 3 days of gestation in myometrium and capillary endothelium. The endometrial vascularization and the number of stromal cells immunoreacting with IGF-I increased. The differentiation of stromal cells into decidual cells was seen at gestational day 5 and IGF-I was strongly expressed in the decidualizing cells. The IGF-I immunoreactivity in uterine luminal epithelium and glandular epithelium was similar to gestational day 4. IGF-I immunoreactivity was strongly detected in all of endometrial stromal cells.

CONCLUSION

These results indicate that IGF-I expression in the rat uterus changes in the early pregnancy process and increase toward to day when implantation will be initiated.

Altered placental and fetal expression of IGFs and IGF-binding proteins associated with intrauterine growth restriction in fetal sheep during early and mid-pregnancy

The insulin-like growth factors (IGFs) are postulated to be altered in association with the development of intrauterine growth restriction (IUGR). The present studies examined placental and fetal hepatic mRNA concentration of components of the IGF system at two time points (55 and 90 d gestational age, dGA; Term 147 dGA) in a hyperthermia (HT)-induced sheep model of placental insufficiency-IUGR. Maternal plasma insulin and IGF-I were constant at 55 and 90 dGA and were unaffected by treatment. Umbilical vein insulin concentrations tended to be reduced at 90 dGA following HT exposure. Caruncle IGF-I mRNA was increased at 90 dGA in HT placentae (p < 0.05), while cotyledon concentrations were constant over gestation and unaltered by treatment. In control cotyledons, IGF-II mRNA concentration increased (p < 0.01) and IGFBP-3 decreased between 55 and 90 dGA (p < 0.01). Cotyledon IGF-II and caruncle IGFBP-4 mRNA were elevated at 55 dGA in HT placentae compared with control (p < 0.01 and p < 0.05 respectively). Fetal hepatic IGF-I, IGFBP-2, -3 and -4 concentrations rose over gestation (p < 0.05), but there were no treatment effects. These data suggest that changes in placental IGF expression in early and mid gestation may predispose the pregnancy to placental insufficiency, resulting in inadequate substrate supply to the developing fetus later in gestation.

Interleukin-6 and insulin-like growth factor system relationships and differences in the human placenta and fetus from the 35th week of gestation

The integrity of the insulin-like growth factor (IGF) system is essential for normal fetal growth. Cytokine and IGF-IGFBP relationships have been shown in specific tissues, but it is unknown whether these occur in the placenta. We aimed to assess possible differences in the IGF system depending on gestational age (GA) from week 35 to 40, and to study relationships of IL-6 with components of the IGF system in the placenta and newborn infant. We followed 32 normal births and collected whole villous tissue and cord serum. Total RNA was extracted from the placenta samples, reverse transcribed and then real-time quantitative (TaqMan) RT-PCR was performed to quantify cDNA for IGF-I, IGF-II, IGFBP-1, IGFBP-2 and IL-6. The corresponding proteins were assayed in placenta lysates and cord serum using specific commercial kits. Two groups of subjects (Group 1, 35-37 weeks GA, N=12 and Group 2, 38-40 weeks GA, N=20) were studied. In placenta, IGF-I mRNA was more abundant than IGF-II mRNA at all times and together with IGFBP-1mRNA were less expressed at term. IGFBP-2 and IL-6 mRNAs were higher after week 37 GA. IL-6 and IGFBP-2 gene expression were closely related. The corresponding proteins showed similar differences to the genes but IGF-I was undetectable in the lysates, whereas IGF-II was abundant. IGFBP-2 concentrations were very high and greater than those of IGFBP-1. In the newborn, no difference was seen in any cord serum protein after week 35 GA. IGFBP-1 was negatively correlated with parameters of neonatal size. In conclusion, this study reports new insights into IL-6, IGF-IGFBP relationships within the human placenta and shows the importance of comparing subjects with the same GA.

Immunohistochemical localization of ECE-1 in the human placenta

Over the last several years, endothelin (ET-1) has emerged as an important mediator in the pathogenesis of pre-eclampsia and preterm labour, as well as in the normal function of gestational tissues. While the distribution of ET and its binding sites in the human placenta have been well studied, much less has so far been reported about the distribution of placental ET-1 processing enzymes. By immunohistochemical analysis and immunofluorescence, endothelin-converting enzyme-1 (ECE-1), the enzyme that synthesizes ET-1, is localized to five distinct cell populations in the human placenta: (1) the endothelial cells lining the maternal basal plate blood vessels, (2) the intermediate trophoblasts, (3) the endothelial cells lining the chorionic villous blood vessels, (4) the chorionic villous stromal cells and (5) the chorionic villous trophoblasts. The localization of ECE-1 corresponds with the previously reported distribution of ET-1 in the human placenta and is in accordance with the function of this enzyme in regulating vascular tone through synthesis of ET-1. The abundance of ECE-1 in the basal plate is consistent with a second possible function of this enzyme in affecting uterine contractions. ECE-1 may serve as a target for prognosis and therapy in states of pathologically altered vascular tone and/or altered myometrial smooth muscle tone in gestation.

Studies on the localization of 5-hydroxytryptamine and its receptors in human placenta

The localization of 5-hydroxytryptamine (5-HT) and its receptors in human placenta was studied under light and electron microscopy using immunohistochemistry and in situ hybridization. The syncytiotrophoblast, cytotrophoblast, stromal cells and decidual cells in human placentae all appeared to be 5-HT immunoreactive. The 5-HT immunoreactive material was distributed in cytoplasm with negative nuclei. The 5-HT immunoreactive material was also found in capillary endothelium. Trophoblast cells cultured in serum-free medium also showed 5-HT immunoreactivity in the cytoplasm. Fetal white blood cells and both syncytiotrophoblast and cytotrophoblast in human placenta showed 5-HT receptor immunoreactivity and 5-HT1A receptor mRNA hybridized signal was also detected in cytoplasm. The stromal cells and capillary endothelium in placental villi and maternal decidual cells all showed 5-HT receptor immunoreactivity in cytoplasm. The small flattened vesicles and large dense cored vesicles within trophoblast cells showed electron-dense 5-HT receptor immunoreactivity using immunoelectron microscopy. These results suggest that human placenta may not only produce 5-HT but also be a 5-HT target organ, and that 5-HT may not only play roles in placental development and pregnancy maintenance by paracrine and autocrine interactions but may also take part in regulating fetal development.

Expression of the insulin-like growth factors and their receptors in term placentas: a comparison between normal and IUGR births

Intrauterine growth retardation (IUGR) is defined as growth retarded to be below the tenth centile. The insulin-like growth factors and their receptors are implicated in pre- and postnatal growth and development, and it is believed that alteration in their activity may contribute to IUGR. In this study nine normal and nine intrauterine growth retarded births were followed and term placentas examined for expression of the insulin-like growth factors and their receptors. It was found that the expression of insulin-like growth factor 1 (IGF1), insulin-like growth factor 2 (IGF2), and the insulin, IGF1 and IGF2 receptor transcripts (IGF1R and IGF2R, respectively) was present in all term placentas examined. Expression of insulin was not detected. Quantitative polymerase chain reaction (PCR) was used to compare transcription levels in term placentas from normal with IUGR births. There was no significant difference in the levels of transcripts for IGF1, insulin receptor, or IGF2R between normal and IUGR term placentas. However, the IUGR term placentas had significantly higher levels of IGF2 and IGF1R expression compared with the normal term placentas. The increase in the transcription of IGF2 and IGF1R in IUGR term placentas may represent a counter regulatory mechanism in response to the growth retardation.

Type I insulin-like growth factor receptors in the BeWo choriocarcinoma cell (b30 clone) during cell differentiation

The expression of insulin-like growth factor (IGF) receptors in the differentiating human trophoblast was studied using the b30 clone of the BeWo choriocarcinoma cell line (BeWob30) as a model system. This clonally derived cell line differentiates over 48-72 h, in culture, to form syncytiotrophoblasts when intracellular cAMP levels are elevated by exposure to 100 microM forskolin (FSK). IGF receptors were studied at various times during the differentiation process by measuring the specific binding of [125I]-IGF-I and [125I]-IGF-II to attached cells. First, [125I]-IGF-I bound to a single class of binding sites in the untreated cells (KD approximately 1-2 x 10-10 M) that exhibited binding specificity characteristic of the type I IGF receptor (IGF-I > or = IGF-II > > Insulin). FSK treatment resulted in a two- to threefold increase in the number of these binding sites. Increased receptor expression was observed as early as 24 h after FSK treatment and remained elevated for at least 72 h. Next, [125I]-IGF-II bound to two classes of binding sites in the untreated cells, a high-affinity (KD approximately 2.5 x 10(-10) M), low-capacity site and a low-affinity (KD approximately 6 x 10(-9) M), high-capacity site. The Bmax and KD of the high-affinity site suggested that it represented the type I IGF receptor. Competition studies revealed that 15-20 per cent of total [125I]-IGF-II binding only was sensitive to IGF-I competition in the untreated cells. After FSK treatment, however, unlabelled IGF-I inhibited 60-70 per cent of specific [125I]-IGF-II binding. Scatchard analysis revealed a two- to fourfold increase in the number of both binding sites with no change in their respective binding affinities. Cross-linking analysis demonstrated that [125I]-IGF-II bound to two structurally distinct binding sites in the untreated BeWob30 cell consistent with both the type I and II IGF receptors. After FSK treatment, however, there was an increase in the relative amount of [125I]-IGF-II associated with the higher affinity type I IGF receptor. The BeWob30 cells expressed no insulin receptors at any stage of differentiation. These data demonstrate that the BeWob30 choriocarcinoma cell line expresses both type I and II IGF receptors. Induction of cell differentiation is associated with an increase in type I IGF receptors expressed at the cell surface. These receptors bind IGF-II with high-affinity, providing additional binding capacity for locally available IGF-II. These data are consistent with specific roles for the type I IGF receptor in regulating differentiated trophoblast cell function. Furthermore, the early rise in type I IGF receptor number suggests they may play a regulatory role in the differentiation process itself.

Decreased expression of placental growth hormone in intrauterine growth retardation

During normal pregnancy, the levels of placental GH in the maternal circulation increase significantly until 35 wk of gestation. We have previously shown that these levels are significantly reduced in cases of intrauterine growth retardation (IUGR). To better understand the basis of this observation, we have studied the expression of placental GH in placentas from normal births (n = 6) and births with IUGR (n = 5). In situ hybridization histochemistry was used to determine the mean number of cells per area expressing this message, as well as the mean level of specific mRNA per cell. We have found that the mean mRNA signal level per cell of placental GH did not differ between normal or IUGR placentas. However, the mean number of cells/ area expressing this mRNA was significantly greater in normal placentas compared with IUGR placentas (normal 12.8 +/- 0.9 cells/unit area, IUGR 4.9 +/- 2.4 cells/unit area, analysis of variance: p < 0.004). These data suggest that the decreased levels of placental GH in the maternal circulation in IUGR are not due only to the reduced size of the placenta, but also to changes in the placental tissue which result in a reduced number of cells per area that are capable of producing this peptide.

Growth promoting peptides in diabetic and non-diabetic pregnancy: interactions with trophoblastic receptors and serum carrier proteins

Infantile macrosomia in diabetic pregnancy (DP) is commonly attributed to fetal hyperinsulinism. However, insulin-like growth factors in the mother and the fetus, their binding proteins and their placental receptors may also play roles in the process of fetal overgrowth. We measured levels of maternal and cord serum IGF-I, IGF-II, C-peptide, IGFBP-1, IGFBP-2 and IGFBP-3 in 8 White Class B insulin dependent DP and 8 non-diabetic pregnancies (NP). These results were correlated with the concentration and affinity of placental trophoblastic membrane receptors (TR) for insulin (IN), IGF-I and IGF-II as well as with infant and placenta weights and maternal body mass indices. Significant respective differences between the diabetic and non-diabetic groups were found in mean infant weight, 4248 +/- 114 vs 3555 +/- 119 g (p < 0.001), placental weight 765 +/- 51 vs 575 +/- 24 g (p < 0.01), maternal body mass index 32.8 +/- 3.8 vs 21.3 +/- 1.2 (p < 0.02), cord serum IGF-I 136.8 +/- 6.6 vs 85.9 +/- 5.7 ng/ml (p < 0.01), cord serum C-peptide 18.7 +/- 3.5 vs 9.0 +/- 1.7 ng/ml (p < 0.025), cord serum IGFBP-1 21.9 +/- 4.7 vs 133.2 +/- 43.2 ng/ml (p < 0.025), cord serum IGFBP-2 672.0 +/- 76 vs 1206 +/- 220 ng/ml (p < 0.05) and cord serum IGFBP-3 11.5 +/- 1.0 vs 5.6 +/- 0.6 ng/ml (p < 0.001). No significant differences were found between DP and NP with respect to cord serum IGF-II, maternal serum IGF-I, IGF-II, C-peptide, IGFBP-1, IGFBP-2 and IGFBP-3, and the concentration and affinity of TR for IN, IGF-I and IGF-II. Analysis of variance revealed an interaction between infant weight and the weight of the placenta (p < 0.01), cord IGF-I (p < 0.02), cord C-peptide (p < 0.01) and cord IGFBP-3 (p < 0.01). Regression analysis revealed significant correlations of cord IGF-I with cord values of IGFBP-2 (r = -0.52, p = 0.04) and IGFBP-3 (r = 0.66, p < 0.005). Maternal serum IGF-I significantly correlated only with maternal IGFBP-3 (r = 0.65, p < 0.01). These results suggest that increased fetal production of insulin and IGF-I may contribute to the development of infantile macrosomia in DP. Concomitant changes in fetal production of IGFBPs, particularly IGFBP-2 and IGFBP-3, may modulate the action of insulin and IGFs. The lack of change in number or binding affinity of placental trophoblastic receptors for insulin, IGF-I and IGF-II tends to exclude a significant regulatory role of these receptors in the production of fetal macrosomia.

Dose-related effect of IGF-I on placental prostanoid release

Prostanoids play an important role throughout all of pregnancy and during the initiation and progress of labor. The human placenta at term produces large quantities of prostanoids, yet little is known of the factors regulating their biosynthesis. In a previous study we observed that insulin-like growth factor I (IGF-I) specifically inhibits thromboxane B2 (TxB2) and prostaglandin F2 alpha (PGF2 alpha) from human term placental explants. In these studies we have defined the dose-related action of IGF-I on the release of placental prostanoids. With use of a perifusion system, the basal release of prostaglandin E2 (PGE2), PGF2 alpha, TxB2 and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) from human term placental explants increased from the fifth hour in culture, while the release of 13,14-dihydro-15-keto-PGF2 alpha (PGFM) remained constant. The addition of IGF-I (5.2-83.3 ng/mL) to the perifusing medium effected an inhibition of TxB2 and PGF2 alpha. The release of TxB2 was inhibited in a dose-related fashion from the initiation of IGF-I treatment and throughout the five hours of treatment, whereas the inhibition of PGF2 alpha was significant only at a dose of 83.3 ng/mL of IGF-I. Yet, the release of 6-keto-PGF1 alpha, PGE2, or PGFM was not altered by any dose of IGF-I studied. Because both TxB2 and PGF2 alpha are vasoconstrictors, we have proposed that IGF-I may enhance vasodilation in the placenta. Therefore, IGF-I may allow for increased blood flow, thus affecting the maintenance of pregnancy and the supply of nutrients available for the growth of the fetus.

Epidermal growth factor receptor and human fetoplacental development

Alteration of placental development directly interferes with fetal growth. Epidermal growth factor (EGF) plays a major role in placental implantation, growth and differentiation. EGF acts on its placental target cells, i.e. the trophoblasts, via a specific receptor (EGFR) which belongs to the tyrosine kinase receptor family. Abundant placental EGF receptors are located in the brush border at the fetomaternal interface. EGFR expression is modulated by trophoblast differentiation and by hormones or toxic substances such as smoke. Interestingly, in microvilli purified from placentae of infants with intrauterine growth retardation (IUGR) a decrease or absence of tyrosine kinase activity is observed. This suggests that an alteration of EGFR biological activity might interfere with the fetoplacental unit development.

Human cytotrophoblast invasion is up-regulated by epidermal growth factor: evidence that paracrine factors modify this process

Formation of the human placenta requires a subset of cytotrophoblast stem cells to acquire an invasive phenotype. We examined the effect on cytotrophoblast invasiveness of growth factors that control the differentiation of other cells. Exogenous TGF-beta 1, PDGF-AA, PDGF-BB, and TNF-alpha affected neither cell morphology nor the rate of cytotrophoblast invasion in vitro. In contrast, addition of EGF to first trimester cytotrophoblast cultures produced dramatic changes in morphology and a severalfold increase in invasive capacity. The effects of EGF on later gestation cytotrophoblasts, whose invasive capacity is diminished, were much less pronounced. Next we investigated whether cytotrophoblasts themselves produce ligands that interact with the EGF receptor. A radioimmunoassay and a radioreceptor assay failed to detect EGF receptor ligands in cytotrophoblast-conditioned medium. Likewise, by RT-PCR cytotrophoblasts expressed neither EGF nor TGF-alpha mRNA. In contrast, EGF receptor mRNA was expressed and its protein levels remained constant during the experiment. Immunolocalization using F(ab') fragments of an anti-human EGF antibody failed to detect this growth factor in the chorionic villus. We conclude that maternal ligands that interact with the EGF receptor could play an important role by up-regulating trophoblast invasion, particularly during the early stages of pregnancy.

Endothelin: potential role in development and disease

Endothelin is a vasoconstrictor substance, initially isolated from porcine endothelial cell supernatant, which has a structure different from any other mammalian peptide. An extensive array of biological activities has been ascribed to endothelin which, besides having unrivaled vasoconstrictive effects, modulates neurotransmission, regulates other hormones and neurotransmitters, and also has potent hyperplastic/hypertrophic effects. These observations have suggested important roles for endothelin in pathophysiological conditions and also in normal development. Inhibition of endothelin activity can decrease vasoconstriction associated with pathophysiological settings. Inhibition of endothelin activity also decreases mitogenesis and therefore cellular proliferation and growth, thereby supporting a role for endothelin in processes which are an integral part of normal development.

Differential expression of insulin-like growth factor-II in specific regions of the late (post day 9.5) murine placenta

Insulin-like growth factor-II (IGF-II) expression has been implicated as a major determinant of fetal size during murine pregnancy. It remains unclear whether expression in the fetus, the placenta, or both is the overriding factor controlling growth. To gain further understanding of the placental contribution, we mapped IGF-II expression in the fetal vascular and trophoblastic portions of the late murine placenta (day 9.5-18.5). We found that, as in the fetus itself, vasculogenic mesenchyme, in this case derived from the allantois, was the strongest expressor of IGF-II. Trophoblast, on the other hand, while expressing somewhat less IGF-II, showed a dynamic pattern of IGF-II expression, which reflected its continuing differentiation during late pregnancy. Initially (days 9.5 and 12.5), the spongiotrophoblast, which is homologous to the cytotrophoblast columns and shell in early human pregnancy, strongly expressed IGF-II. Later, expression in the spongiotrophoblast was down-regulated as a new population, the so-called glycogen cells, emerged within the spongiotrophoblast (day 12.5-15.5) and went on to invade the mesometrial decidua. Glycogen cells, which are homologous to human intermediate trophoblast, strongly expressed IGF-II. Trophoblast lining the area of maternal-fetal exchange, the labyrinth, on the other hand, maintained a constitutive lower level of IGF-II expression throughout late pregnancy.

Effect of IGF-1 on placental prostanoid production

Prostanoids play an important role throughout all of pregnancy and during the initiation and progress of labor. The human placenta, at term, produces large quantities of prostanoids, yet little is known of the steps regulating their biosynthesis. In these studies, the effect of IGF-I on the release of placental prostanoids was investigated. The basal release of prostaglandin E (PGE), prostaglandin F (PGF), thromboxane (TxB2) and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) increased from the fifth hour in culture, while the release of 13, 14-dihydro-15-keto-PGF2 alpha (PGFM) remained constant and hCG release decreased. The addition of IGF-I (10(-8) M) to the perfusing medium effected an inhibition of TxB2 and PGF within two and one-half hours of exposure. However, the release of PGE, PGFM, 6-keto-PGF1 alpha or hCG was not altered by IGF-I. Because both TxB2 and PGF are vaso-constrictors, we have proposed that IGF-I may enhance vasodilation in the placenta. Therefore, IGF-I may allow increased blood flow, thus affecting the maintenance of pregnancy and supply of nutrients for the growth of the fetus.

Syncytiotrophoblastic localization of the human growth hormone variant mRNA in the placenta

The hGH/hCS genes, clustered on chromosome 17 in the 5' to 3' order GH-N, CS-L, CS-A, GH-V and CS-B, show a high degree of sequence identity. The expression product of the GH-V gene is the placental growth hormone, which replaces pituitary GH in maternal blood throughout pregnancy. By means of mRNA competitive hybridization using 32P-labelled and unlabelled 30 bases long oligonucleotides, we first optimized specific hybridization conditions. In situ hybridization was then performed to locate the GH-V mRNA encoding placental growth hormone. The hGH-V gene appears expressed in the placental syncytiotrophoblast. Unlike the CS-A and CS-B genes (both encoding hPL) which are expressed uniformly in the syncytiotrophoblast, the GH-V mRNA is located in a few syncytiotrophoblast cells only.

Regulation of the aromatase activity of human placental cytotrophoblasts by insulin, insulin-like growth factor-I, and -II

Studies to be reviewed were stimulated by the clinical observation, albeit controversial, that diabetic pregnancy may be associated with lower serum oestrogen levels than nondiabetic pregnancy. Pregnant diabetic women are usually intensively treated with insulin to maintain euglycemia, frequently resulting in peripheral hyperinsulinemia. The placenta, which is the primary source of oestrogens during pregnancy, would be exposed to this elevation in circulating insulin levels. Similarly, insulin-like growth factors (IGFs), which are synthesized and secreted by placental tissues and could influence placental function in an autocrine or paracrine fashion, may be elevated in diabetic pregnancy. We will review studies, which show that (i) insulin, insulin-like growth factor-I (IGF-I), and -II inhibit the aromatase activity of human cytotrophoblasts, (ii) these peptides can inhibit aromatase by activation of their respective receptors, and (iii) the potency of IGF-II in suppressing aromatase greatly exceeds that of either insulin or IGF-I. Finally, evidence will be reviewed, which suggests that inositol-glycan mediators ('second messengers') serve as the signal transduction system for insulin's inhibition of aromatase activity. Hence, placental exposure to increased concentrations of insulin and/or IGFs in the pregnant diabetic woman may result in inhibition of aromatase activity and decreased serum oestrogen levels.

Transgenic strategies in reproductive endocrinology

The present discussion surveys some of the recently published studies utilizing transgenic strategies to address questions in reproductive endocrinology. Beginning with a brief introduction of the transgenic method itself, the following areas are covered: 1. Sexual development and Müllerian-inhibiting substance; 2. Hypogonadal mice and hypothalamic GnRH; 3. The GnRH neuron: generation of immortalized rare cell types; 4. Glycoprotein hormones: immortalized cells, development and evolution; 5. Growth hormone and reproduction; and, 6. Gestation and the insulin-like growth factors. In each section, the discussion attempts to be integrative with respect to the significance of the results to physiological, cellular and molecular biology. We believe this approach is appropriate, as transgenic science itself is necessarily an integration of all of these levels of investigation and participation from those working at all levels is needed.

Acidic fibroblast growth factor and heart development. Role in myocyte proliferation and capillary angiogenesis

Proliferative growth of the ventricular myocyte (cardiomyocyte) is primarily limited to fetal and early neonatal periods of development. In concert with the neonatal "transition" from proliferative to hypertrophic growth, ventricular remodeling of the nonmyocyte compartment is characterized by increased extracellular matrix synthesis/deposition and capillary angiogenesis. A role for locally generated and bioactive ventricular acidic fibroblast growth factor (aFGF) in these processes is proposed and substantiated by the following: 1) colocalization of aFGF peptide and fibroblast growth factor receptor (flg) transcripts to the developing fetal cardiomyocyte by immunohistochemistry, immunoelectron microscopy, and in situ hybridization, 2) continued localization of aFGF peptide and transcripts to the neonatal/mature cardiomyocyte, and 3) localization of flg immunoreactivity and transcripts to specific neonatal ventricular nonmuscle cell types. Specific ventricular cell types at distinct developmental stages appear to be responsive to ventricular myocyte-derived aFGF (myocytes in the fetal heart and nonmyocytes/endothelial cells in the neonatal heart). These data indicate that expression of aFGF and one of its receptors (flg) are most pronounced in the fetal to early neonatal ventricle, the presence of both suggesting an autocrine/paracrine growth regulatory function. As the animal matures, ventricular capillary angiogenesis may be facilitated by "release" of cardiomyocyte-derived fibroblast growth factors into the surrounding extracellular space/matrix functioning as a "paracrine" angiogenic stimuli. Therefore, the results of our study suggest that myocyte-derived aFGF may function to increase the fetal ventricular cardiomyocyte population in absolute number as well as to facilitate the subsequent increase in capillary angiogenesis that occurs during cardiomyocyte maturation and ventricular remodeling.

Spatial distribution of active genes implicated in the regulation of insulin-like growth factor stimulatory loops in human decidual and placental tissue of first-trimester pregnancy

We have previously shown that the insulin-like growth factor-2 (IGF-2) gene is partially coexpressed with the IGF-1 and -2 receptor genes in proliferative cytotrophoblasts of the human extraembryonic tissue. Here we show that high levels of IGF-2 gene expression are not restricted to the embryonic tissue but can also be found in the decidua compacta. The IGF-2 gene is thus expressed at high levels in the mesenchymal stroma of the decidua to establish potentially short-range communication with primarily IGF-1 receptor-positive mesenchymal stroma cells. Conversely, the glandular and surface epithelia coexpress the IGF-1 receptor and IGF-1 genes, while the IGF-2 gene is not detected above background levels. The potential control mechanisms of these cell-cell signalling pathways were investigated by the analysis of the spatial distribution of active IGF binding proteins (IGFBP) genes. The IGFBP-3 gene is coexpressed with the IGF-2 gene in proliferative cytotrophoblasts of the embryonic placenta. While active IGFBP-1 and -2 genes in our hands cannot be detected in the embryonic placenta, all three IGFBP genes are expressed in complex and overlapping patterns in the decidua compacta. The results are discussed in terms of how the various IGFBP genes may operate in different cell types to restrict IGF local stimulatory pathways.

Transforming growth factor-beta 1 in heart development

Defined biochemical stimuli regulating neonatal ventricular myocyte (cardiomyocyte) development have not been established. Since cardiomyocytes stop proliferating during the first 3-5 days of age in the rodent, locally generated 'anti-proliferative' and/or differentiation signals can be hypothesized. The transforming growth factor-beta (TGF-beta) family of peptides are multifunctional regulators of proliferation and differentiation of many different cell types. We have determined in neonatal and maturing rat hearts that TGF-beta 1 gene expression occurs in pups of both normotensive (Wistar Kyoto, WKY) and hypertrophy-prone rats (spontaneously hypertensive, SHR). TGF-beta 1 transcript levels were readily apparent in total ventricular RNA from SHR pups within 1 day of age and elevated in 3-7 day old WKY and SHR hearts when cardiomyocyte proliferation indices are diminished. TGF-beta 1 transcript levels remain at a 'relatively' high level throughout maturation and into adulthood in both strains. Further, TGF-beta 1 transcripts were localized to cardiomyocytes of neonatal rat ventricular tissue sections by in situ hybridization. Immunoreactive TGF-beta was co-localized to the intracellular compartment of neonatal cardiomyocytes at the light and electron microscopic level. In vitro analysis using primary cultures of fetal and neonatal cardiomyocytes indicated that TGF-beta s inhibit mitogen stimulated DNA synthesis and thymidine incorporation. From these data, we propose that locally generated TGF-beta s may act as autocrine and/or paracrine regulators of cardiomyocyte proliferation and differentiation as intrinsic components of a multifaceted biochemical regulatory process governing heart development.

Gonadotropins induce accumulation of insulin-like growth factor I mRNA in pig granulosa cells in vitro

Pig granulosa cells have been shown to synthesize insulin-like growth factor (IGF) I peptide in vitro, and this expression is regulated by gonadotropins via the cAMP pathway. By hybridizing an IGF I cDNA probe with total RNA isolated from pig granulosa cells cultured in vitro, we show that these cells contain two IGF I transcripts of about 0.9 kb and 9 kb in size. Treatment of the cells with gonadotropins (follicle-stimulating hormone, luteinizing hormone) or cAMP agonists (dibutyryl-cAMP, forskolin) induces an accumulation of the transcripts which can be abolished by transcriptional inhibitors, but not by translational inhibitors. We thus provide new evidence that pig granulosa cells are a site of IGF I synthesis, and we conclude that (1) gonadotropins increase IGF I mRNA levels; (2) the accumulation of IGF I mRNA results from an increased transcription; (3) the stimulation of IGF I gene transcription does not require ongoing protein synthesis; (4) these effects of follicle-stimulating hormone can be mimicked by cAMP agonists.

Loss of tumorigenicity of rat glioblastoma directed by episome-based antisense cDNA transcription of insulin-like growth factor I

Malignant glioma is the most common brain tumor. The molecular basis of glioma tumorigenicity has not been defined. Cultured glioma cells accumulate high levels of insulin-like growth factor I (IGF-I) transcripts. We asked whether IGF-I expression is coupled to tumorigenicity, using a combined in vivo/in vitro system employing antisense RNA for IGF-I. An antisense IGF-I expression construct in an expression vector that incorporates Epstein-Barr virus replicative signals and the ZnSO4-inducible metallothionein I transcriptional promoter was assembled. Stable glioma transfectants were derived from C6 glioma cells, which constitutively express IGF-I. B-104 neuroblastoma cells, derived originally from the same tumor but not expressing IGF-I, were also transfected as controls. In the absence of ZnSO4, the C6 transfectants expressed high levels of IGF-I mRNA and protein as detected by in situ hybridization and immunocytochemistry, respectively. Addition of ZnSO4 in the culture medium resulted in high levels of antisense transcript accumulation and dramatically decreased levels of endogenous IGF-I mRNA and IGF-I protein. Subcutaneous injection of either nontransfected C6 parental cells or C6 cells transfected with vector without IGF-I sequences into rats resulted in large tumors after 2 weeks, as did transfected and nontransfected B-104 cells. However, the rats injected with transfected C6 cells yielded no tumors after 40 weeks of observation. Two weeks after injection of the transfected C6 cells a small cyst was apparent in six rats. Histologic sections revealed a few glioma cells infiltrated by a large number of mononuclear cells. No infiltration of mononuclear cells was apparent in the glioma tumors resulting from injection of parental (nontransfected) cells, suggesting that the parental cells, but not the antisense IGF-I transfectants, escape the host immune response.

Amino acid transport by the cultured human placental trophoblast: effect of insulin on AIB transport

Insulin responsiveness in the human placenta is controversial. This study evaluated insulin stimulation of alpha-aminoisobutyric acid (AIB) uptake in cultured human placental trophoblasts. Both Na(+)-dependent and -independent components of AIB uptake were present in cultured trophoblasts. Na(+)-dependent AIB uptake was significantly stimulated by insulin in a time-dependent manner, as early as 2 h, with a maximum at 12 h of continuous exposure to hormone. Insulin treatment for 4 h increased both the initial uptake rate and the final intracellular concentration. Stimulation was dependent on insulin concentration, with significant stimulation beginning at 10(-9) M. Insulin treatment increased maximum velocity but not the Michaelis constant. Approximately 75% of basal (unstimulated) AIB uptake was inhibited by 10 mM alpha-methylaminoisobutyric acid (MeAIB). The insulin-stimulated increment above basal AIB uptake was completely inhibited by 10 mM MeAIB. Cycloheximide treatment significantly reduced basal and stimulated AIB uptake, although a significant response to insulin persisted. Na(+)-dependent AIB uptake was also stimulated by glucagon, dexamethasone, and 8-bromoadenosine 3',5'-cyclic monophosphate, but not by vasopressin. This study further characterizes amino acid uptake by the human placenta and demonstrates that the Na(+)-dependent component of AIB uptake by the cultured trophoblasts is stimulated by physiological concentrations of insulin.

In vitro growth rate of placental fibroblasts is developmentally regulated

Placental cells of mesenchymal origin were used to study the regulation of fetal growth at the cellular level. A significant difference in the in vitro growth rates of placental fibroblasts was observed as a function of gestational age. Cells derived from 10-19-wk placentae exhibited proliferative rates two to three times greater than cells derived from 7-9-wk placentae (16-30 h vs. 30-60 h, P less than 0.001). The proliferation rate remained stable throughout multiple passages in culture. Additionally, these two groups of cell strains exhibited marked differences in their responsiveness to mitogenic stimuli. Using maximal effective concentrations, insulin-like growth factor I interacted synergistically with epidermal growth factor and fibroblast growth factor to stimulate DNA synthesis in cells derived from 10-19-wk placentae. By contrast, the interaction of insulin-like growth factor 1 with epidermal growth factor and fibroblast growth factor exhibited significantly less synergy in 7-9-wk cells. These findings argue that the accelerated growth rate of human fetal cells results primarily from developmental events intrinsic to the cells and is associated with enhanced responsiveness to the mitogenic action of peptide growth factors.

Insulin-like growth factor-II (IGF-II) and IGF binding proteins in human endometrium

The insulin-like growth factor autocrine/paracrine system is believed to play a role in steroid-mediated endometrial differentiation. It is constituted of the mitogenic peptides (IGF-I and IGF-II), membrane receptors, and a family of high-affinity binding proteins (IGFBPs) that regulate the actions of the IGFs at their target cells. We have investigated expression of the mRNAs encoding the three major IGFBPs (IGFBP-1, IGFBP-2, and IGFBP-3) in human endometrium and have found, by Northern analysis, differential expression of all three mRNAs in secretory compared to proliferative endometrium, different steroidal milieux. IGF-II mRNAs were also detected in secretory endometrium. Finally, we found that human endometrial stromal cells in culture synthesize and secrete IGFBP-2 and IGFBP-3, and that the synthesis of IGFBP-2 is regulated by steroid hormones.

Comparative aspects of conceptus signals for maternal recognition of pregnancy

Maintenance of corpus luteum (CL) function is essential for establishment of pregnancy in mammals. Estrogens from pig conceptuses (embryo and associated membranes) initiate events that, with prolactin, redirect secretion of the uterine luteolytic hormone prostaglandin F2 alpha (PGF) from an endocrine (to uterine veins) to an exocrine (to uterine lumen) direction to prevent luteolysis. Ovine conceptuses secrete ovine trophoblast protein-1 (oTP-1), which exhibits high amino acid sequence relatedness with alpha II interferons (IFN alpha II) and inhibits synthesis of endometrial receptors for oxytocin and uterine production of luteolytic pulses of PGF. Estrogens and oTP-1 are local antiluteolytic signals to endometrium, whereas human chorionic gonadotrophin (hCG) appears to have a direct luteotrophic effect on CL. A progestational endometrium secretes proteins that serve as growth factors, transport proteins, regulatory proteins and enzymes, as well as transporting nutrients into the uterine lumen to support conceptus development.

Preparation of fibroblast-free cytotrophoblast cultures utilizing differential expression of the CD9 antigen

The leukemia-associated antigen CD9 is present on a variety of normal cells, with apparent variable expression on normal human fibroblasts. In this study, we demonstrate by immunoperoxidase staining and direct binding studies that the CD9 antigen is uniformly expressed on normal human fibroblasts grown from first trimester and term placenta, embryonic fetal fibroblasts, and from human adult and fetal skin fibroblasts. Higher CD9 expression was present on fetal cells. CD9 antigen was not present on trophoblast. Over 99% of fibroblasts could be absorbed onto antibody to the CD9 antigen conjugated to magnetic beads. By applying this selective immunoadsorption of fibroblasts to term placental cytotrophoblast preparations, we demonstrated that fibroblast contamination could be nearly completely eliminated. This is a novel technique for purifying primary trophoblast cultures and may have wider applicability in cell culture of other cell types.

Expression of the insulin-like and platelet-derived growth factor genes in human uterine tissues

The human uterus repeatedly exhibits cyclic biochemical and cytological changes during the reproductive period of life. These changes are the result of a well-characterized endocrine network involving the hypothalamus, pituitary, and ovary. The exact nature of the mechanism(s) by which the sex steroids act on the uterus remains to be elucidated. Possible local mediators of hormonal action on the uterus include polypeptide growth factors. Using the method of RNA transfer blot hybridization, we have analyzed tissue samples from the cycling human endometrium and tissue samples of human myometrium and myometrial benign tumor (leiomyoma) for the presence of platelet-derived growth factor (PDGF) and insulin-like growth factor (IGF) RNA. All the uterine tissues examined possessed RNA for PDGF-B chain and IGF-I and -II. Two transcripts were observed for PDGF-B chain, four were observed for IGF-I, and eight were observed for IGF-II. Overall, the relative abundance of PDGF-B chain RNA was consistent in all of the uterine tissues examined. In contrast, IGF RNA relative abundance varied. IGF-I RNA was highest in late proliferative stage endometrium, and IGF-II RNA was highest in early proliferative stage endometrium. Both IGF-I and IGF-II RNAs were greater in amount of leiomyoma than in myometrium. The increased IGF-I RNA in late proliferative-stage human endometrium correlates with the known elevation of estradiol secretion by the ovary and the increased concentration of uterine estradiol receptors during this stage of the menstrual cycle.(ABSTRACT TRUNCATED AT 250 WORDS)

Localization of platelet-derived endothelial cell growth factor in human placenta and purification of an alternatively processed form

Platelet-derived endothelial cell growth factor (PD-ECGF) was purified to homogeneity from human term placenta, an organ characterized by extensive angiogenesis. N-terminal amino acid sequencing revealed that placental PD-ECGF was proteolytically processed at Thr-6, in contrast to PD-ECGF purified from human platelets, which is processed at Ala-11. The purified factor stimulated porcine aortic endothelial cells as well as two choriocarcinoma cell lines. Immunohistochemical staining revealed that PD-ECGF was present in the connective tissue cells of the placenta. The possibility that PD-ECGF is involved in the development of the placenta is discussed.

Insulin-like growth factors and neonatal cardiomyocyte development: ventricular gene expression and membrane receptor variations in normotensive and hypertensive rats

Defined factors regulating or influencing mammalian ventricular myocyte (cardiomyocyte) development are not known at this time. During early neonatal ventricular growth, cardiomyocytes begin a 'transition phase' of development toward cellular maturation (hypertrophy) that entails terminal proliferation and cellular binucleation. Insulin-like growth factor-I and -II (IGFs) are believed to play a major role in mammalian postnatal and fetal growth, possibly functioning in local environments which facilitate autocrine or paracrine tissue growth characteristics. Therefore, we examined the expression of the IGF genes and their corresponding membrane receptors in ventricles of normotensive and spontaneously hypertensive (SHR) rat pups during the first 7-14 days of age. We have determined: (1) by receptor crosslinking that neonatal ventricular membranes possess type 1 and type 2 IGF receptors; (2) by receptor binding analysis that type 1 IGF receptor concentration is elevated between days 1-7 in the SHR and shows an age-related decline in concentration and an increase in affinity in both strains; (3) by Northern blot analysis that neonatal rat ventricular tissue expresses primarily IGF-II RNA transcripts of 3.6, 2.3 and 1.7 kilobases (kb) in size, with low levels of IGF-I transcripts detected; (4) by slot-blot hybridization that SHR ventricles contain higher levels of IGF-II transcripts at 3 days of age; and (5) localized the IGF transcripts to ventricular myocytes by tissue in situ hybridization. These observations support a role for cardiomyocyte-produced IGFs that may be locally produced and act in an autocrine or paracrine fashion to modulate cardiomyocyte growth and maturation in the developing rat heart. Because both IGF receptor and IGF RNA transcript parameters differed in SHR hearts, genetically predisposed to hypertrophy, a potentially important biochemical alteration may be associated with the fetal/neonatal growth abnormalities of the developing heart in this rat strain.