Angiotensin II and angiotensin-(1-7) decrease sFlt1 release in normal but not preeclamptic chorionic villi: an in vitro study

BACKGROUND

During preeclampsia, placental angiogenesis is impaired. Factors released from the placenta including vascular endothelial growth factor (VEGF), placental growth factor (PLGF), soluble VEGF receptor 1 (sFlt1), and soluble endoglin (sEng) are regulatory molecules of placental development and function. While the renin angiotensin system has been shown to regulate angiogenic factors in other research fields, these mechanisms have not been extensively studied during pregnancy.

METHODS

We evaluated the effects of angiotensin II (Ang II) and angiotensin-(1-7) [Ang-(1-7)] on the release of VEGF, PLGF, sFlt1, and sEng from placental chorionic villi (CV). CV were collected from nulliparous third-trimester normotensive and preeclamptic subjects. CV were incubated for 0, 2, 4, and 16 hours with or without Ang II (1 nM and 1 microM) or Ang-(1-7) (1 nM and 1 microM). The release of VEGF, PLGF, sFlt1, sEng, lactate dehydrogenase (LDH), and human placenta lactogen (HPL) was measured by ELISA.

RESULTS

The release of sFlt1, PLGF, sEng from normal and preeclamptic CV increased over time. Release of sFlt1 and sEng was significantly higher from preeclamptic CV. VEGF was below the detectable level of the assay in normal and preeclamptic CV. After 2 hours, sFlt1 release from normal CV was significantly inhibited with Ang II (1 nM and 1 microM) and Ang-(1-7) (1 nM and 1 microM). There was a time-dependent increase in HPL indicating that the CV were functioning normally.

CONCLUSIONS

Our study demonstrates a critical inhibitory role of angiotensin peptides on sFlt1 in normal pregnancy. Loss of this regulation in preeclampsia may allow sFlt1 to increase resulting in anti-angiogenesis and end organ damage in the mother.

Insulin-like Growth Factors-I and -II and Insulin-like Growth Factor Binding Protein-1 during normal pregnancy: pattern of secretion and correlation with other placental hormones

OBJECTIVES

To describe pattern of secretion of insulin-like growth factor (IGF)-I, IGF-II, IGF binding protein (IGFBP)-1 and their correlation with each other and major placental hormones during normal pregnancy.

DESIGN

Longitudinal study.

SETTING

Academic Institutions and a Tertiary Care Maternity Hospital.

PARTICIPANTS

Healthy women with singleton uncomplicated pregnancies (N = 35).

MEASUREMENTS

Serum levels of IGF-I, IGF-II, IGFBP-1, chorionic gonadotrophin (HCG), placental lactogen (HPL), prolactin, oestradiol and progesterone were studied thrice during the antenatal period and within 24 h of delivery.

RESULTS

IGF-I, IGFBP-1, HPL, prolactin, oestradiol and progesterone increased and HCG decreased significantly with advancing gestation (Repeated measures ANOVA: P < 0.01 to 0.0001). IGF-II levels were not significantly affected by period of gestation. Significant negative correlations (multiple regression analysis) were seen between IGFBP-1 and prolactin at 28 +/- 2 (P = 0.0226) and 36 +/- 2 (P = 0.0417) weeks of amenorrhoea (WOA) and between oestradiol and IGF-II at 36 +/- 2 WOA (P = 0.037). Prolactin and IGF-I at 14 +/- 2 WOA (P = 0.0225) and progesterone and IGFBP-1 at 28 +/- 2 WOA (P = 0.0216) correlated positively.

CONCLUSIONS

Maternal IGF-I and IGFBP-1 but not IGF-II significantly increase as pregnancy advances. Components of the IGF system regulate or are affected by some of the placental hormones and the effects vary with the period of gestation.

[Clinicopathologic analysis of uterine epithelioid trophoblastic tumor]

OBJECTIVE

To study the clinicopathologic features, immunophenotype, differential diagnosis and prognosis of uterine epithelioid trophoblastic tumor(ETT).

METHODS

From 2000 to 2007, 5 ETTs cases were diagnosed in the affiliated Women's Hospital, School of Medicine, Zhejiang University. The pathologic characteristics and immunophenotype of the tumors were analyzed by histological examination and immunohistochemistry of CK18, p63, inhibin-alpha, HCG, HPL, PLAP and Ki-67. The clinical prognostic factors were evaluated based on a following-up data with a period of 11 - 50 months.

RESULTS

The overall prevalence of ETT was 0.48% among all the gestational trophoblastic diseases patients received in the same period. Five ETT patients were in the reproductive ages with a median of 33 years. Histologically, the tumor showed an invasive, nodular growth consisting of uniform mononuclear trophoblastic cells. There were zones of hyaline material in the tumour nests. Necrosis was commonly seen with a characteristic geographic pattern. Immunohistochemically, all cases displayed a diffuse CK18 and p63 positivity, to be either positive focally or negative for HCG, HPL and PLAP staining. Inhibin-alpha staining was positive or negative either in the 5 cases. Two patients died of the tumour relapse: one died after 1 year with the tumor having a high mitotic activity (averagely 15 mitotic figures per 10 high-power fields), and the other died of lung metastasis 2 years after the diagnosis.

CONCLUSIONS

ETT is a rare trophoblastic disease with distinct clinicopathological features and immunostaining patterns. A high mitotic index and lung metastasis are indicators for an unfavorable prognosis.

Effects of cadmium on the expression of placental lactogens and Pit-1 genes in the rat placental trophoblast cells

Cadmium is an endocrine disrupter (ED) with detrimental effects on mammalian reproduction. The placenta is a primary target for cadmium toxicity during pregnancy. Very little of this metal crosses the placenta to the fetus, and consequently it accumulates in high concentrations in the placenta. Cadmium affects on steroid synthesis and has estrogen- and androgen-like activities. In this study, we investigated the toxic effects of cadmium on placental trophoblast cells as well as the mRNA levels of placental lactogens (PLs), which are under the control of estrogen and play a pivotal role during pregnancy. Pregnant F344 Fisher rats were injected subcutaneously with 0, 0.2, and 2.0mg/kg BW/day of cadmium (CdCl(2)) dissolved in saline from days 11 to 19 of pregnancy and were sacrificed on day 20. The mRNA levels of the PL-Iv and -II genes and Pit-1alpha and beta isotype genes, the trans-acting factor of PLs, were analyzed by Northern blot hybridization and reverse transcription-polymerase chain reaction, respectively. The frequency of the placental trophoblast cells was observed histochemically. Developmental data and apoptotic chromosomal DNA fragmentation of placental cells were also observed. The mRNA levels of PL-Iv and -II were reduced in a dose-dependent manner by cadmium. The mRNA levels of the Pit-1alpha and beta isotype genes were also reduced by cadmium. In the uterus-conjugated region of the placental junctional zone, the frequency rates of trophoblast cells were lower in the cadmium-treated groups than in the control group. High-dose cadmium exposure (2.0mg) induced not only the reduction of trophoblast cell frequency but also apoptotic chromosomal DNA fragmentation in the junctional zone of the placenta. Developmental metrics such as placental and fetal weights and a number of live fetuses, decreased, while a numbers of resorptions, dead fetuses, and post-implantation losses increased significantly (p<0.05) in the cadmium-treated groups compared to the control. These data suggested that cadmium inhibits the expression of PL genes and reduces the number of trophoblast cells in the rat placenta via an estrogen-like activity, leading to significant toxic effects on placental growth and physiological function in rats.

Effects of prenatal tobacco exposure on gene expression profiling in umbilical cord tissue

Maternal smoking doubles the risk of delivering a low birth weight infant. The purpose of this study was to analyze differential gene expression in umbilical cord tissue as a function of maternal smoking, with an emphasis on growth-related genes. We recruited 15 pregnant smokers and 15 women who never smoked during pregnancy to participate. RNA was isolated from umbilical cord tissue collected and snap frozen at the time of delivery. Microarray analysis was performed using the Affymetrix GeneChip Scanner 3000. Six hundred seventy-eight probes corresponding to 545 genes were differentially expressed (i.e. had an intensity ratio > +/- 1.3 and a corrected significance value p < 0.005) in tissue obtained from smokers versus nonsmokers. Genes important for fetal growth, angiogenesis, or development of connective tissue matrix were upregulated among smokers. The most highly upregulated gene was CSH1, a somatomammotropin gene. Two other somatomammotropin genes (CSH2 and CSH-L1) were also upregulated. The most highly downregulated gene was APOBEC3A; other downregulated genes included those that may be important in immune and barrier protection. Validation of the three somatomammotropin genes showed a high correlation between qPCR and microarray expression. We conclude that maternal smoking may be associated with altered gene expression in the offspring.

Induction of central leptin resistance in hyperphagic pseudopregnant rats by chronic prolactin infusion

Pregnancy in rats is associated with hyperphagia, increased fat deposition, and elevated plasma leptin concentrations. Elevated leptin would be expected to inhibit food intake, but hypothalamic leptin resistance develops around midpregnancy, allowing hyperphagia to be maintained and excess energy to be stored as fat in preparation for future metabolic demands of lactation. To investigate the hormonal mechanisms inducing leptin resistance during pregnancy, the anorectic response to leptin was examined during pseudopregnancy. Pseudopregnant rats have identical hormonal profiles to early pregnancy, but no placenta formation, allowing differentiation of maternal and placental hormone effects on appetite. To investigate the effect of leptin on food intake, d-9 pseudopregnant rats were injected with leptin (4 microg) via an intracerebroventricular (icv) cannula, and then food intake was measured 24 h later. Pseudopregnant rats were hyperphagic but had normal anorectic responses to leptin. We therefore hypothesized that a longer exposure time to high concentrations of progesterone might be required to mimic the leptin resistance that occurs on d 14 of pregnancy. Pseudopregnant rats were given progesterone to prolong pseudopregnancy beyond the time that leptin resistance develops during pregnancy. However, rats remained responsive to icv leptin. To model the placental lactogen secretion that occurs during pregnancy, pseudopregnant rats were given progesterone and chronic icv ovine prolactin infusion. Central icv injection of leptin had no effect on food intake in pseudopregnant rats receiving chronic ovine prolactin. These results suggest that chronically high lactogen levels, secreted by the placenta during the second half of pregnancy, induce central leptin resistance.

Lactogens promote beta cell survival through JAK2/STAT5 activation and Bcl-XL upregulation

One of the goals in the treatment for diabetes is to enhance pancreatic beta cell function, proliferation, and survival. This study explores the role of lactogenic hormones, prolactin (PRL) and placental lactogen (PL), in beta cell survival. We have previously shown that transgenic mice expressing mouse placental lactogen-1 (mPL1) in beta cells under the rat insulin II promoter (RIP) are resistant to the diabetogenic and cytotoxic effects of streptozotocin (STZ) in vivo. The current study demonstrates that lactogens protect rat insulinoma (INS-1) cells and primary mouse beta cells against two distinct beta cell death inducers, STZ and dexamethasone (DEX), in vitro. Further, we identify the mechanism through which lactogens protect beta cells against DEX-induced death. The signaling pathway mediating this protective effect is the janus-activated-kinase-2/signal transducer and activator of transcription-5 (JAK2/STAT5) pathway. This is demonstrated in INS-1 cells and primary mouse beta cells using three separate approaches, pharmacological inhibitors, JAK2-specific siRNAs and a dominant-negative STAT5 mutant. Furthermore, lactogens specifically and significantly increase the anti-apoptotic protein Bcl-XL in insulinoma cells and mouse islets. Bcl-XL-specific siRNA significantly inhibits lactogen-mediated protection against DEX-induced beta cell death. We believe this is the first direct demonstration of lactogens mediating their protective effect through the JAK2/STAT5 pathway in the beta cell and through Bcl-XL in any cell type.

Trophogram, an immunohistochemistry-based algorithmic approach, in the differential diagnosis of trophoblastic tumors and tumorlike lesions

Recent histopathologic and molecular studies of trophoblastic cells in the normal placenta and in a variety of trophoblastic diseases have revealed that the latter recapitulate the differentiation of normal trophoblast in the early developing placenta. This new knowledge, especially the identification and characterization of the protein markers expressed in human trophoblast, not only helps elucidate the pathogenesis of trophoblastic lesions but also provides a repertoire of immunohistochemical markers that may facilitate the diagnosis of various trophoblastic diseases. This article reviews the recent advances in the trophoblast-associated markers that have been reported to be useful in the differential diagnosis of trophoblastic tumors and tumorlike lesions. Moreover, a "trophogram," which is a stepwise and rational immunohistochemistry-based approach, will be introduced. The trophogram may prove to be useful in assisting the differential diagnosis of various trophoblastic diseases in diagnostic pathology.

Lysyl Oxidase Interacts with Hormone Placental Lactogen and Synergistically Promotes Breast Epithelial Cell Proliferation and Migration

Lysyl oxidase (LOX), an extracellular amine oxidase, catalyzes the cross-linking of collagen and elastin. LOX has been also shown to play an essential role in promoting the invasive and metastatic potential of breast tumor cells. However, the LOX-interacting factors in these processes are not known. In this study, we identified placental lactogen (PL), a member of the growth hormone/prolactin hormone family, as a LOX-interacting partner using yeast two-hybrid screens. PL is normally only expressed in placental syncytiotrophoblasts, but PL genes are amplified and expressed in a high percentage of invasive ductal breast carcinomas. We confirmed LOX-PL interactions using far Western and solid phase binding assays. In activity assays, PL was not a substrate or inhibitor of LOX. We further demonstrated that PL is expressed in breast tumor epithelial cells and detected LOX-PL interactions by coimmunoprecipitation in invasive breast cancer cells. In MCF-10A normal breast epithelial cells stably expressing LOX, PL, or both, LOX had no effect on cell proliferation, PL alone increased proliferation by 49%, and coexpression of LOX and PL led to a 121% increase in cell proliferation. Unlike in tumor cells, LOX did not induce a more migratory phenotype in MCF-10A cells; nor did PL. However, their coexpression resulted in a 240% increase in cell migration, suggesting that these interactions may be highly relevant to the transition of epithelial cells toward a migratory phenotype during the development and progression of breast carcinoma and a significant role for LOX-PL interactions in epithelial cell behavior.

[Clinicopathologic study of tumors of intermediate trophoblasts]

OBJECTIVE

To study the clinicopathologic features and immunophenotype of placental site trophoblastic tumor (PSTT) and epithelioid trophoblastic tumor (ETT).

METHODS

During the period from 1959 to 2005, a total of 1012 cases of gestational trophoblastic disease were diagnosed in Beijing Obstetrics and Gynecology Hospital. Six cases of PSTT and a case of ETT were retrieved from the archives of Beijing Obstetrics and Gynecology Hospital. Immunohistochemical study for cytokeratin 18, human chorionic gonadotropin (hCG), human placental lactogen (hPL), Mel-CAM (CD146), placental-like alkaline phosphatase (PLAP), epithelial membrane antigen (EMA), inhibin-alpha and proliferative cell nuclear antigen (PCNA) were performed. The morphologic features and immunohistochemical findings were compared with those of the controlled group which consisted of 20 cases of early gestational villi with decidua basalis and 20 cases of hydatidiform moles with implantation site.

RESULTS

The mean age of patients with PSTT was 32.4, while the age of patients with ETT was 36. Major clinical findings included irregular vaginal bleeding and amenorrhea. Preoperative serum hCG level varied from normal to moderately elevated. Serum testosterone level was raised in 1 case. Uterine curettage could achieve an accurate pathologic diagnosis in 60% of cases. ETT involved mainly the lower uterine segment and endocervix. Histologically, PSTT cells permeated between the myometrial fibers and vessels either individually or connecting in cords or sheets in a manner reminiscent of the implantation site reaction. ETT composed of a relatively uniform population of mononuclear trophoblastic cells, clumping together in nests as the cell islets associating with eosinophilic, fibrillary and hyaline material and necrotic debris, forming a "geographic map" like pattern. Immunohistochemical study for hPL, hCG, Mel-CAM (CD146) and PLAP was most helpful for the differential diagnosis. The duration of follow-up varied from 14 months to 19 years. One case of PSTT developed metastasis in pancreas, 5 months after the operation. The remaining patients survived without tumor recurrence.

CONCLUSIONS

PSTT is a tumor of implantation site intermediate trophoblasts while ETT differentiates towards chorionic-type intermediate trophoblasts. The different pathologic features and immunophenotype observed were closely related with the difference in tumor cell differentiation. An accurate pathologic diagnosis of the uterine curettage material is important for the clinical management. According to the limited follow-up data available, the clinical behavior of ETT is seemed similar to that of PSTT.

Structural and mechanistic studies on the inhibition of the hypoxia-inducible transcription factor hydroxylases by tricarboxylic acid cycle intermediates

In humans both the levels and activity of the alpha-subunit of the hypoxia-inducible transcription factor (HIF-alpha) are regulated by its post-translation hydroxylation as catalyzed by iron- and 2-oxoglutarate (2OG)-dependent prolyl and asparaginyl hydroxylases (PHD1-3 and factor-inhibiting HIF (FIH), respectively). One consequence of hypoxia is the accumulation of tricarboxylic acid cycle intermediates (TCAIs). In vitro assays were used to assess non-2OG TCAIs as inhibitors of purified PHD2 and FIH. Under the assay conditions, no significant FIH inhibition was observed by the TCAIs or pyruvate, but fumarate, succinate, and isocitrate inhibited PHD2. Mass spectrometric analyses under nondenaturing conditions were used to investigate the binding of TCAIs to PHD2 and supported the solution studies. X-ray crystal structures of FIH in complex with Fe(II) and fumarate or succinate revealed similar binding modes for each in the 2OG co-substrate binding site. The in vitro results suggest that the cellular inhibition of PHD2, but probably not FIH, by fumarate and succinate may play a role in the Warburg effect providing that appropriate relative concentrations of the components are achieved under physiological conditions.

Effect of leptin on the regulation of placental hormone secretion in cultured human placental cells

Placenta is an important source of leptin during pregnancy that contributes to the high plasma leptin levels in pregnant women. Leptin and its functional receptors are synthesized in trophoblast cells that, in turn, secrete gestational hormones supporting a paracrine or autocrine role for leptin in the endocrine activity of the placenta. In the present study we examined the effect of leptin on in vitro release of gestational hormones (human chorionic gonadotropin (hCG), human placental lactogen (hPL), progesterone, estrogens and testosterone) by human term placental cells in culture. Placentas at term were obtained immediately after delivery from mothers with uncomplicated pregnancies. Progesterone, hCG, hPL, estradiol, estrone, estriol and testosterone levels were measured by different assays in culture media of cells maintained in monolayer culture after incubation for 12, 24, 48 or 72 h with leptin or placebo. Incubation with leptin did not modify hCG, hPL, progesterone, estriol and estrone secretion for any of the doses and times assayed. However, leptin led to a dose-dependent decrease in estradiol release. This effect was observed when treatment with recombinant human leptin spanned from 12 to 72 h. At this time an increase in testosterone levels was observed in leptin-treated cells versus placebo. These results indicate that leptin can be considered a gestational hormone implied in the endocrine function of the placenta, with an important role in control of the production of steroid reproductive hormones in placental cells in vitro.

Expression profiling of mouse placental lactogen II and its correlative genes using a cDNA microarray analysis in the developmental mouse placenta

The placenta is a highly differentiated organ essential for embryonic growth and development. In order to search for key molecules that are associated with mouse placental lactogen II (mPL-II) gene expression, we applied mouse cDNA microarray analysis to RNAs extracted from placentae on days 10, 12, 14, 16 and 18 of pregnancy. Changes in gene expression were categorized between days 10 and 12, 12 and 14, 14 and 16 and 16 and 18 of pregnancy. After microarray analysis, which had a minimum detectable fold change for differential expression of 2, we selected 10 genes, Apoa2, Apoc2, Ceacam14, Creg1, Fmo1, Igf2, Slc2a1, Spink3, Spi1-1 and Tpbpa, exhibiting a expression pattern similar to the mPL-II gene. Furthermore, we performed real-time PCR analysis and in situ hybridization (ISH) to find correlative expression genes for the mPL-II gene. From these results, we identified a resemblance in gene expression between mPL-II and Igf2 and selected these genes for performance of double-fluorescence immunohistochemical staining. We colocalized these proteins in labyrinthine trophoblast cells. These results strongly suggest that the expression of mPL-II and Igf2 is highly related to placental development in mice. This large-scale identification of genes regulated during placentogenesis assists in further elucidation of the molecular basis of extraembryonic development and function.

Molecular analysis of circulating RNA in plasma

Circulating RNA in plasma and serum is a newly developed area for molecular diagnosis. To date, increasing numbers of studies show that plasma and serum RNA could serve as both tumor- and fetal-specific markers for cancer detection and prenatal diagnosis, respectively. Recently, by introducing the highly sensitive one-step real-time quantitative reverse-transcription (RT)-polymerase chain reaction (PCR), these potentially valuable RNA species, which often only exist at low concentrations in plasma and serum, can now be readily detected and quantified. Following the successful quantification of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA in plasma of normal individuals, several placenta-derived mRNA species, including the mRNA transcripts of human placental lactogen (hPL), the beta-subunit of human chorionic gonadotropin (betahCG), and corticotropin-releasing hormone (CRH) were also quantified in plasma of pregnant women. These circulating placental RNA species have provided the fetal-polymorphism-independent markers for prenatal diagnosis. The achievement in detecting the placental RNA in maternal plasma represents a significant step toward the development of RNA markers for noninvasive prenatal gene expression profiling. This detection technique can be extended to access a wide range of disease conditions, such as cancer and trauma. The one-step, real-time quantitative RT-PCR is a highly sensitive and specific, yet practically simple, RNA detection technique. This powerful technology may allow the practical employment of circulating RNA in the high-throughput clinical screening and monitoring applications.

Syncytiotrophoblastic vesicles in placental intervillous space

OBJECTIVE

This study was undertaken to investigate the origin and function of vesicles found in the intervillous space.

STUDY DESIGN

A retrospective study was performed by using placental sections of different gestational ages. The number of vesicles was counted in each section of gestational age groups. Immunohistochemical staining for beta-human chorionic gonadotropin (beta-hCG) and human placental lactogen (hPL) was conducted to confirm the origin of vesicles.

RESULTS

Staining for beta-hCG and hPL was prominent in vesicles separating from syncytiotrophoblast into the intervillous space. The numbers of vesicles were not significantly different in gestational age groups of 42 to 30 weeks and all vesicles disappeared in 9- to 5-week groups. Large vesicles tended to show degeneration and disintegration in the intervillous space.

CONCLUSION

The vesicles containing beta-hCG and hPL suggest a different secretory mechanism of syncytiotrophoblast.

C-Reactive Protein Production in Term Human Placental Tissue

OBJECTIVE

C-reactive protein (CRP) is a marker of systemic inflammation. Recently, it has been shown that CRP is present in amniotic fluid and fetal urine, and that elevated levels are associated with adverse pregnancy outcome. However, the precise source of amniotic fluid CRP, its regulation, and function during pregnancy is still a matter of debate. The present in vivo and in vitro studies were designed to investigate the production of CRP in human placental tissues.

MATERIAL AND METHODS

Ten paired blood samples from peripheral maternal vein (MV), umbilical cord artery (UA) and umbilical vein (UV) were collected from women with elective caesarean sections at term. The placental protein accumulation capacity of hCG, hPL, leptin and CRP was compared with the dual in vitro perfusion method of an isolated cotyledon of human term placentae and quantified by ELISA. Values for accumulation (release) were calculated as total accumulation of maternal and fetal circuits normalized for tissue weight and duration of perfusion. For gene expression, RNA was extracted from placental tissue and reverse transcribed. RT-PCR and real-time PCR were performed using specific primers.

RESULTS

The median (range) CRP level was significantly different between UA and UV [50.1 ng/ml (12.1-684.6) vs. 61 ng/ml (16.9-708.1)]. The median (range) difference between UV and UA was 9.3 ng/ml (2.2-31.6). A significant correlation was found between MV CRP and both UA and UV CRP levels. Median (range) MV CRP levels [2649 ng/ml (260.1-8299)] were 61.2 (6.5-96.8) fold higher than in the fetus. In vitro, the total accumulation rates (mean+/-SD) were 31+/-13 (mU/g/min, hCG), 1.16+/-0.19 (microg/g/min, hPL), 4.71+/-1.91 (ng/g/min, CRP), and 259+/-118 (pg/g/min, leptin). mRNA for hCG, hPL and leptin was detectable using conventional RT-PCR, while CRP mRNA could only be demonstrated by applying real-time RT-PCR. In the perfused tissue the transcript levels for the four proteins were comparable to those detected in the native control tissue.

CONCLUSIONS

Our results demonstrate that the human placenta produces and releases CRP mainly into the maternal circulation similarly to other analyzed placental proteins under in vitro conditions. Further studies are needed to explore the exact role of placental CRP during pregnancy.

Crystal Structure and Site 1 Binding Energetics of Human Placental Lactogen

In primates, placental lactogen (PL) is a pituitary hormone with fundamental roles during pregnancy involving fetal growth, metabolism, and stimulating lactation in the mother. Human placental lactogen (hPL) is highly conserved with human growth hormone (hGH) and both hormones bind to the hPRLR extracellular domain (ECD), the first step in receptor homodimerization, in a Zn2+-dependent manner. A modified surface plasmon resonance method was developed to measure the kinetics for hPL and hGH binding to the hPRLR ECD, with and without Zn2+ and showed that hPL has about a tenfold higher affinity for the hPRLR ECD1 than hGH. The crystal structure of the free state of hPL has been determined to 2.0 A resolution showing the molecule possesses an overall structure similar to other long chain four-helix bundle cytokines. Comparison of the free hPL structure with the 1:1 complex structure of hGH bound to the hPRLR ECD1 suggests that two surface loops undergo conformational changes >10 A upon binding. An 18 residue Ala-scan was used to characterize the binding energy epitope for the site 1 interface of hPL. Individual alanine substitutions at five positions reduced binding affinity by a DeltaDeltaG > or = 3 kcal mol(-1). A comparison of the hPL site 1 epitope with that previously determined for hGH indicates contributions of individual residues track reasonably well between hPL and hGH. In particular, residues involved in the zinc-binding site and Lys172 constitute the principal binding determinants for both hormones. However, several residues that are identical between hPL and hGH contribute quite differently to the binding of the hPRLR ECD1. Additionally, the overall magnitudes of the DeltaDeltaG changes observed from the Ala-scan of hPL were markedly larger than those determined in the comparative scan of hGH to the hPRLR ECD1. The structural and biophysical data presented here show that subtle changes in the structural context of an interaction can lead to significantly different effects at the individual residue level.

The Transcription Factor PLA-1/SKN-1A is Expressed in Human Placenta and Regulates the Placental Lactogen-3 Gene Expression

Here we report the selective expression of two POU transcription factor genes, PLA-1 and OCT-1, in human placenta and choriocarcinoma cell lines JAR, JEG-3 and BeWo. Pla-1 protein binds to a POU-consensus DNA sequence in the human placental lactogen-3 (PL-3) promoter and it is capable of trans-activating its transcription up to 18-fold. Other tissue-specific or ubiquitous POU transcription factors such as Pit-1/GHF-1 or Oct-1 showed none or low levels of trans-activation of the PL-3 promoter. In addition, we identified an unique and highly charged region in the N-terminal portion of Pla-1 protein required for full trans-activation of the PL-3 promoter.

Src family kinases play multiple roles in differentiation of trophoblasts from human term placenta

Tyrosine phosphorylation plays a major role in controlling many biological processes in different cell types. Src family kinases (SFKs) are one of the most studied groups of tyrosine kinases and can mediate a variety of signalling pathways. However, little is known about the expression of SFKs in human term placenta and their implication in trophoblast differentiation. Therefore, we examined the expression profile of SFK members over time in culture and their implication in differentiation. In vitro, freshly isolated cytotrophoblast cells, cultured in 10% fetal bovine serum (FBS), spontaneously aggregate and fuse to form multinucleated cells that resemble phenotypically mature syncytiotrophoblasts, that concomitantly produce human chorionic gonadotropin (hCG) and human placental lactogen (hPL). In this study, we showed that trophoblasts expressed all SFK members and some of them are expressed as different splice variants. Moreover, using real-time PCR, this study showed two different expression profiles of SFKs in human trophoblasts during culture. In addition, the protein level and phosphorylation status of Src were evaluated using specific antibodies. Src was rapidly phosphorylated at Tyr-416 and dephosphorylated at Tyr-527 after FBS addition. Surprisingly, inhibition of SFKs by 4-amino-5-(4-chlorophenyl)-7-(t-butyl) pyrazolo[3,4-d] pyrimidine (PP2) or herbimycin A had different effects on trophoblast differentiation. While herbimycin A inhibited morphological and hormonal differentiation, PP2 stimulated hormonal differentiation and inhibited cell adhesion and spreading with no effect on cell fusion. In summary, this study showed that SFKs play different roles in trophoblast differentiation, probably depending on SFK members activated. Thus, this study increases our knowledge and understanding of pathology related to impaired trophoblast differentiation such as pre-eclampsia and trophoblast neoplasm.

Evaluation of beta-cell replication in mice transgenic for hepatocyte growth factor and placental lactogen: comprehensive characterization of the G1/S regulatory proteins reveals unique involvement of p21cip

We hypothesized that combined transgenic overexpression of hepatocyte growth factor (HGF) and placental lactogen in islets would lead to even greater increases in beta-cell mass and replication than either growth factor alone. This did not occur, suggesting that beta-cell replication is saturable or subject to molecular restraint. We therefore performed the first comprehensive G(1)/S cell cycle survey in islets, cataloguing the broad range of kinases, cyclins, and kinase inhibitors that control the G(1)/S transition in islets from normal, HGF, placental lactogen, and doubly transgenic mice. Many of the G(1)/S checkpoint regulators (E2Fs; pRb; p107; p130; cyclins D(1),(2),(3), A, and E; cdk-2; cdk-4; p15; p16; p18; p19; p21; p27; MDM2; p53; c-Myc; and Egr-1) are present in the murine islet. Most of these proteins were unaltered by overexpression of HGF or placental lactogen, either alone or in combination. In contrast, p21(cip) was uniquely, dramatically, and reproducibly upregulated in placental lactogen and HGF islets. p21(cip) was also present in, and upregulated in, proliferating human islets, localizing specifically in beta-cells and translocating to the nucleus on mitogenic stimulation. Homozygous p21(cip) loss releases islets from growth inhibition, markedly enhancing proliferation in response to HGF and placental lactogen.

Effect of IPs, cAMP, and cGMP on the hPL and hCG secretion from human term placenta

The acute control of human placental lactogen (hPL) and chorionic gonadotrophin (hCG) secretion by the placenta remains elusive. The in vitro release of both hormones can be stimulated by calcium inflow and by albumin. To investigate the placental secretory response to putative ligand(s) present in the maternal circulation, we evaluated the coupling of the hPL and hCG releases from term placenta with intracellular signaling pathways. Addition of NaF, forskolin or sodium nitroprusside, activators of the inositol phosphates (IPs), cAMP and cGMP pathways, significantly increased their respective messengers in villous explants but failed to affect the hPL and hCG releases from syncytiotrophoblast. By contrast, albumin did not modify the IPs, cAMP and cGMP villous content but significantly stimulated the placental hormonal release. These data suggest that the hPL and hCG secretion is not regulated through the IPs, cAMP and cGMP signaling pathways.

Temporospatial expression of placental lactogen and prolactin-related protein-1 genes in the bovine placenta and uterus during pregnancy

The anatomical location of binucleate cells (BNC) influences protein expression but not steroid synthesis in ruminants. In order to determine if BNC in disparate locations differentially express bovine placental lactogen (bPL) and prolactin-related protein-1 (bPRP-1), we quantitated bPL and bPRP-1 transcripts in placentomal (cotyledonary, caruncular) and interplacentomal (intercotyledonary, intercaruncular) tissues throughout pregnancy in the bovine using real-time reverse transcription PCR (RT-PCR) and in situ hybridization. Levels of both bPL and bPRP-1 transcripts at peri-implantation were significantly higher (P < 0.01) in the fetal membrane than in caruncular and intercaruncular tissues. Thereafter, mRNA for these related proteins demonstrated different spatial as well as temporal patterns of expression. Levels of bPRP-1 transcripts peaked at day 60 of pregnancy. Between day 60 and 100, bPRP-1 transcripts fell by approximately sevenfold (P < 0.01) in cotyledonary and intercotyledonary tissues, and fourfold in caruncular (P < 0.01) tissue. Levels of bPRP-1 transcripts remained low in the cotyledonary, intercotyledonary, and caruncular tissues until peripartum. In contrast, bPL expression in placentomes increased with progression of gestation (P < 0.01), but decreased in interplacentomal tissue around peripartum. To conclude, disparate patterns of bPRP-1 and bPL genes are transcribed in the placentomal and interplacentomal tissues during gestation in the bovine, suggesting that these prolactin-like hormones serve distinct functions and are regulated differently in the uteroplacental unit in this species.

Hepatocyte nuclear factor-3alpha binding at P sequences of the human growth hormone locus is associated with pituitary repressor function

The human GH family consists of five genes, including the placental chorionic somatomammotropins (CS), within a single locus on chromosome 17. Based on nuclease sensitivity, the entire GH/CS locus is accessible in pituitary chromatin, yet only GH-N is expressed. Previously, we reported a P sequence element (263P) capable of repressing placental CS-A promoter activity in transfected pituitary (GC) cells, and our data indicated a possible role for nuclear factor-1 (NF-1) and regulatory factor X1 in this repression. In this study we show the formation of two independent pituitary complexes in vitro: a repressor complex containing NF-1 and a nonfunctional complex containing regulatory factor X1. In vitro repressor function is stabilized by the presence of P sequence element C (PSE-C), downstream of the previously characterized PSE-A and PSE-B. Repressor function is also dependent on an intact Pit-1 binding site in the CS-A promoter. EMSAs with PSE-C reveal binding of the hepatocyte nuclear factor-3/forkhead (HNF-3/fkh) family of transcription factors in rat pituitary GC cells. This observation is extended to human pituitary tissue, where HNF-3alpha's association with P sequences is confirmed by chromatin immunoprecipitation. Furthermore, protein-protein interactions between HNF-3alpha and NF-1 family members are demonstrated. These results identify HNF-3alpha as an additional member of the pituitary P sequence regulatory complex, implicating it in tissue-specific expression of the human GH/CS family.