Placental localization of human pregnancy--associated plasma proteins

Biochemical Screening for Fetal Trisomy 21: Pathophysiology of Maternal Serum Markers and Involvement of the Placenta

It is now well established that maternal serum markers are often abnormal in fetal trisomy 21. Their determination is recommended for prenatal screening and pregnancy follow-up. However, mechanisms leading to abnormal maternal serum levels of such markers are still debated. Our objective was to help clinicians and scientists unravel the pathophysiology of these markers via a review of the main studies published in this field, both in vivo and in vitro, focusing on the six most widely used markers (hCG, its free subunit hCGβ, PAPP-A, AFP, uE3, and inhibin A) as well as cell-free feto-placental DNA. Analysis of the literature shows that mechanisms underlying each marker's regulation are multiple and not necessarily directly linked with the supernumerary chromosome 21. The crucial involvement of the placenta is also highlighted, which could be defective in one or several of its functions (turnover and apoptosis, endocrine production, and feto-maternal exchanges and transfer). These defects were neither constant nor specific for trisomy 21, and might be more or less pronounced, reflecting a high variability in placental immaturity and alteration. This explains why maternal serum markers can lack both specificity and sensitivity, and are thus restricted to screening.

A Novel Diagnostic Biomarker, PZP, for Detecting Colorectal Cancer in Type 2 Diabetes Mellitus Patients Identified by Serum-Based Mass Spectrometry

Background: Growing evidence has confirmed that populations with type 2 diabetes mellitus (T2DM) have an increasing risk of developing colorectal cancer (CRC). Thus, convenient and effective screening strategies for CRC should be developed for the T2DM population to increase the detection rate of CRC.

Methods: Twenty serum samples extracted from five healthy participants, five T2DM patients, five CRC patients and five T2DM patients with CRC (T2DM + CRC) were submitted to data-independent acquisition mass spectrometry (DIA-MS) analysis to discover unique differentially altered proteins (DAPs) for CRC in patients with T2DM. Then, the diagnostic value of pregnancy zone protein (PZP) was validated by ELISA analysis in the validated cohort.

Results: Based on DIA-MS analysis, we found eight unique proteins specific to T2DM patients with CRC. Among these proteins, four proteins showed different expression between the T2DM + CRC and T2DM groups, and PZP exhibited the largest difference. Next, the diagnostic value of serum PZP was validated by ELISA analysis with an AUC of 0.713. Moreover, the combination of PZP, CA199 and CEA exhibited encouraging diagnostic value, and the AUC reached 0.916.

Conclusion: Overall, our current research implied that PZP could be regarded as a newfound serum biomarker for CRC medical diagnosis in T2DM patients.

Aggrephagy Deficiency in the Placenta: A New Pathogenesis of Preeclampsia

Aggrephagy is defined as the selective degradation of aggregated proteins by autophagosomes. Protein aggregation in organs and cells has been highlighted as a cause of multiple diseases, including neurodegenerative diseases, cardiac failure, and renal failure. Aggregates could pose a hazard for cell survival. Cells exhibit three main mechanisms against the accumulation of aggregates: protein refolding by upregulation of chaperones, reduction of protein overload by translational inhibition, and protein degradation by the ubiquitin-proteasome and autophagy-lysosome systems. Deletion of autophagy-related genes reportedly contributes to intracellular protein aggregation in vivo. Some proteins recognized in aggregates in preeclamptic placentas include those involved in neurodegenerative diseases. As aggregates are derived both intracellularly and extracellularly, special endocytosis for extracellular aggregates also employs the autophagy machinery. In this review, we discuss how the deficiency of aggrephagy and/or macroautophagy leads to poor placentation, resulting in preeclampsia or fetal growth restriction.

Activated α2-macroglobulin binding to cell surface GRP78 induces trophoblastic cell fusion

The villous cytotrophoblastic cells have the ability to fuse and differentiate, forming the syncytiotrophoblast (STB). The syncytialisation process is essential for placentation. Nevertheless, the mechanisms involved in cell fusion and differentiation are yet to be fully elucidated. It has been suggested that cell surface glucose-regulated protein 78 (GRP78) was involved in this process. In multiple cancer cells, cell membrane-located GRP78 has been reported to act as a receptor binding to the active form of α₂-macroglobulin (α₂M*), activating thus several cellular signalling pathways implicated in cell growth and survival. We hypothesised that GRP78 interaction with α₂M* may also activate signalling pathways in trophoblastic cells, which, in turn, may promote cell fusion. Here, we observed that α₂M mRNA is highly expressed in trophoblastic cells, whereas it is not expressed in the choriocarcinoma cell line BeWo. We thus took advantage of forskolin-induced syncytialisation of BeWo cells to study the effect of exogenous α₂M* on syncytialisation. We first demonstrated that α₂M* induced trophoblastic cell fusion. This effect is dependent on α₂M*-GRP78 interaction, ERK1/2 and CREB phosphorylation, and unfolded protein response (UPR) activation. Overall, these data provide novel insights into the signalling molecules and mechanisms regulating trophoblastic cell fusion.

Spliceosome protein EFTUD2 is upregulated in the trophoblast of spontaneous miscarriage and hydatidiform mole

BACKGROUND

Elongation factor Tu GTP binding domain containing 2 (EFTUD2) is an alternative splicing factor that modulates cell differentiation and activation processes. EFTUD2 is known to modulate immune responses and mutation of the EFTUD2-gene lead to fetal malformation. Little is known about its expression and role in normal and disturbed first trimester pregnancy.

PATIENTS AND METHODS

We investigated the expression of EFTUD2 in placental tissue obtained from patients with normal (n = 14), spontaneous miscarriage (n = 15) and molar (n = 14) pregnancy by immunohistochemistry. The expression of EFTUD2 was correlated on the protein level with known immune modulatory proteins like pregnancy zone protein (PZP) and in addition with human chorionic gonadotropin (hCG). Furthermore, we analysed the EFTUD2 and PZP expression in vitro after stimulation of the chorioncarcinoma cell line JEG-3 with hCG.

RESULTS

EFTUD2 is significantly upregulated in the syncytiotrophoblast of spontaneous miscarriage (p = 0.003) and molar pregnancy (p = 0.003) compared to week of gestation-adjusted normal first trimester placentas. PZP is negatively correlated (p = 0.021) to EFTUD2 in the syncytiotrophoblast and is therefore significantly downregulated in miscarriage (p = 0.028) and mole pregnancy (p = 0.006). In addition, hCG is positively correlated to EFTUD2 in mole pregnancy. The addition of hCG to chorioncarcinoma cell lines JEG-3 in vitro stimulated EFTUD2 expression in these cells (p = 0.027).

CONCLUSION

Regulation of alternative splicing seems crucial for a successful ongoing pregnancy. The up-regulated elongation factor EFTUD2 may have a critical role in miscarriage.

Human PZP and common marmoset A2ML1 as pregnancy related proteins

While pregnancy-related proteins (PRP) are known to contribute to immunotolerance during pregnancy, their significance to development of invasive placenta is unclear. We compared PRP expression in humans and the common marmoset (Callithrix jacchus), a new-world monkey. Invasive placenta was observed at the maternal-foetal interface of marmoset placenta from green fluorescent protein (GFP)-expressing foetus and wild type mother. The pregnancy zone protein (PZP) and alpha-2 macroglobulin-like 1 (A2ML1) proteins exhibited the most prominent increase in expression during the second trimester in humans and marmoset, respectively. In humans, PZP accumulated at the maternal-foetal interface and A2ML1 accumulated in the amnion. Similarly, A2ML1 mRNA was detected in marmoset placenta. These proteins belong to the A2M family of protease inhibitors, and both PZP and A2ML1 share around 90% homology between human and marmoset and have highly conserved structures. However, the protease-reacting bait regions of the proteins had lower homology (56.8–60.7% in proteins) relative to the rest of the sequence. Notably, the cleavage site of a proinflammatory proline-endopeptidase was preserved in human PZP and marmoset A2ML1. These proteins contain multiple sites that are cleaved by proteases involving proline-endopeptidase. Systemic regulation of these A2M family proteins may be important in animals with invasive placenta.

Screening and Identification of Pregnancy Zone Protein and Leucine-Rich Alpha-2-Glycoprotein as Potential Serum Biomarkers for Early-Onset Myocardial Infarction using Protein Profile Analysis

PURPOSE

The present study aims to discover novel serum biomarkers of early-onset myocardial infarction (MI) using proteomic analysis.

EXPERIMENTAL DESIGN

In the first stage, the iTRAQ-coupled LC-MS/MS technique is utilized to investigate protein profiles of patients with early-onset MI. In the second stage, these candidate proteins are validated using ELISA.

RESULTS

A total of 538 proteins are quantified, with pregnancy zone protein (PZP), leucine-rich α-2-glycoprotein (LRG) and Apolipoprotein C-I (Apo C-I) being upregulated and Apolipoprotein A-I (Apo A-I) and Apolipoprotein A-IV (Apo A-IV) downregulated in early-onset MI patients. Results from the validation stage demonstrate that the serum concentrations of PZP and LRG are significantly increased in the early-onset MI group. The correlation between the concentrations of C-reactive protein (CRP) and the two candidate biomarkers is positive. Area under the curve values used to diagnose early-onset MI for LRG and PZP are 0.939 and 0.874, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Five differential serum proteins are identified in early-onset MI using proteomic analysis. Lipoprotein-related biomarkers further demonstrate the close relationship between lipid metabolism and the disease. Inflammation-associated LRG and PZP may be novel biomarkers of the disease. In addition, changes in these proteins may partly reveal the possible mechanisms in the pathogenesis and pathophysiology of early-onset MI.

The proteolytic activity of pregnancy-associated plasma protein-A is potentially regulated by stanniocalcin-1 and -2 during human ovarian follicle development

STUDY QUESTION

Is the proteolytic activity of pregnancy-associated plasma protein-A (PAPP-A) regulated by the stanniocalcins (STC1 and STC2) during human follicle maturation?

SUMMARY ANSWER

The STCs and PAPP-A show similar expression by immunohistochemistry in developing follicles, and regulation of PAPP-A proteolytic activity is suggested by the identification of inhibited protein complexes between PAPP-A and STC1 or STC2 in human follicular fluid (FF).

WHAT IS KNOWN ALREADY

The insulin-like growth factor (IGF)-regulating proteinase PAPP-A is secreted by the granulosa cells of estrogen-dominant follicles and is involved in follicle growth. STC1 and STC2 have recently been identified as novel PAPP-A inhibitors, and their expression in non-human mammalian ovaries has previously been observed.

STUDY DESIGN, SIZE, DURATION

The proteolytic activity of PAPP-A in human follicular fluid was assessed, and the interaction between PAPP-A and the STCs in human ovarian tissues and follicular fluid was analyzed using immunoassays. From 21 women, matched pairs of follicular fluid were obtained from one follicle just prior to final maturation of follicles with human chorionic gonadotrophin (hCG), and from another follicle in connection with oocyte aspiration after hCG treatment. Ovarian tissues were obtained from women having one ovary removed for fertility preservation by cryopreservation prior to gonadotoxic treatment.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The concentration and activity of PAPP-A were determined in all samples of follicular fluid. Furthermore, to investigate PAPP-A regulation during follicle development, immunohistochemical staining of PAPP-A, STC1, and STC2 was performed on pre-antral and antral human follicles. To attempt the demonstration of native complexes between PAPP-A and the STCs, immunoprecipitation from a pool of human follicular fluid was performed.

MAIN RESULTS AND THE ROLE OF CHANCE

The concentration of PAPP-A antigen in follicular fluid increased upon stimulation of ovulation with hCG (P < 0.02), but at the same time, PAPP-A activity was decreased. PAPP-A, STC1, and STC2 were localized together in primordial, late primary, and antral follicles, indicating that complex formation is possible in ovarian tissue. Covalent PAPP-A:STC2 and non-covalent PAPP-A:STC1 complexes were immunoprecipitated from follicular fluid, documenting for the first time native inhibited complexes between PAPP-A and the STCs.

LIMITATIONS, REASONS FOR CAUTION

We have demonstrated the presence of native complexes between PAPP-A and the STCs in the human ovary, indicating STC-mediated PAPP-A proteolytic inhibition. Further investigation is required to extend this principle to other tissues.

WIDER IMPLICATIONS OF THE FINDINGS

Our data suggest that the STCs contribute to PAPP-A regulation during folliculogenesis and support a general model in which STC1 and STC2 are regulators of mammalian IGF activity through inhibition of PAPP-A. We suggest that future functional studies take both PAPP-A and the STCs into consideration.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by grants from the Novo Nordisk Foundation, and the Danish Council for Independent Research. No competing interests declared.

Myocardial and Peripheral Ischemia Causes an Increase in Circulating Pregnancy-Associated Plasma Protein-A in Non-atherosclerotic, Non-heparinized Pigs

The usefulness of circulating pregnancy-associated plasma protein-A (PAPP-A) as a biomarker for acute coronary syndrome (ACS) is widely debated. We used the pig as a model to assess PAPP-A dynamics in the setting of myocardial ischemia. Induction of myocardial ischemia by ligation of the left anterior descending (LAD) coronary artery caused a systemic rise in PAPP-A. However, the ischemic myocardium was excluded as the source of PAPP-A. Interestingly, induction of ischemia in peripheral tissues by ligation of the left femoral artery caused a systemic rise in PAPP-A originating from the left hind limb. This is the first study to demonstrate PAPP-A elevations in the absence of atherosclerosis or heparin during myocardial ischemia. Our findings thus add to the current discussion of the usefulness of PAPP-A as a biomarker for ACS.

Pregnancy-associated plasma protein-A and the vulnerable plaque

For more than a decade, pregnancy-associated plasma protein-A (PAPP-A) has been examined for its relation to acute coronary syndrome (ACS) and the vulnerable plaque. This review summarizes the current knowledge of plasma PAPP-A in relation to nonpregnant individuals focusing on patients with ACS, discusses its use as a possible biomarker for diagnosis and prognosis in ACS, briefly describes the challenges in different assay technologies and describes the effect of heparin administration on PAPP-A concentrations in plasma.

First trimester maternal serum placental growth factor levels in twin pregnancies

BACKGROUND

An understanding of the normal behavior of biochemical markers in twin pregnancies is necessary in order to offer prenatal screening to this subgroup. This study investigates the levels of first trimester maternal serum placental growth factor (PlGF) in twin and singleton pregnancies.

METHODS

The PlGF concentrations were measured by an automated assay in the first trimester maternal serum of 440 dichorionic twin, 116 monochorionic twin, and 607 singleton pregnancy samples thawed from frozen storage.

RESULTS

The PlGF concentrations in singleton levels were predicted by gestational age, maternal ethnicity, and smoking status. Following the correction for these variables, PlGF levels were, on average, 41% higher in dichorionics, but only 16% higher in monochorionics, compared to singleton pregnancies.

CONCLUSIONS

First trimester maternal serum PlGF levels are increased in twin pregnancies compared with singleton pregnancies, but to less of an extent than is common with other screening markers, especially in monochorionic twins.

Pregnancy-associated plasma protein (PAPP)-A expressed in the mammary gland controls epithelial cell proliferation and differentiation

Lactation is an important event in all-mammalian species. To investigate the role of pregnancy-associated plasma protein (PAPP)-A in lactogenesis, we determined (i) PAPP-A expression in mouse mammary glands and (ii) the biological functions of PAPP-A in mammary epithelial cells. PAPP-A mRNA level was low during early mid pregnancy and increased during mid-late pregnancy, and then slightly decreased during lactation. Cell proliferation signals, but not differentiation, increased PAPP-A mRNA expression in HC11 mammary epithelial cells. Treatment of recombinant PAPP-A protein stimulated HC11 cell proliferation and suppressed the expression of β-casein mRNA, which is one of the milk proteins and cell differentiation marker. Surprisingly, in forcing expression experiment, PAPP-A increased β-casein mRNA expression. Our data suggest that PAPP-A has different roles on intracellular expressing and extracellular treatment to mammary epithelial cells. Taken together, in early pregnancy, circulating PAPP-A protein might be supplied from other organs and stimulates mammary gland growth. In contrast, during mid-late pregnancy, local PAPP-A expression begins and enhances cell differentiation within mammary epithelial cell.

Biomarkers in pre-eclampsia: a novel approach to early detection of the disease

Pre-eclampsia is a unique disorder of human pregnancy with a great impact on maternal and perinatal morbidity and mortality worldwide and especially in developing countries. The aetiology is still unknown and the pathophysiology of the disease is the subject of extensive investigation. Recently, much of the interest of the investigators for the prediction of pre-eclampsia has been aimed at measurable manifestations of abnormal placentation, endothelial dysfunction and feto-maternal unit perfusion. Biomarkers constitute a novel approach to an early detection of the disease. Low maternal serum levels of PAPP-A and PP13 early in pregnancy are predictive for emerging pre-eclampsia. On the other hand, increased levels of homocysteine, ADMA, sEng, leptin and sFlt-1 in the 1st trimester, signal the onset of the disease later in pregnancy. After the onset of pre-eclampsia, increased serum levels of PAPP-A, ADMA, homocysteine and sFlt-1 are associated with the severity of the disease. The identification of biomarkers which can contribute to the early detection of pre-eclampsia is essential. It could then be possible to apply better surveillance and treatment protocols in such patients.

Performance of free β-human chorionic gonadotrophin (free β-hCG) and pregnancy associated plasma protein-A (PAPP-A) analysis between Delfia Xpress and AutoDelfia systems in The Netherlands

: The VU University Medical Center (VUmc) was the first hospital in the Netherlands to introduce the Delfia Xpress for the analysis of free β-human chorionic gonadotrophin (β-hCG) and pregnancy associated plasma protein-A (PAPP-A) in the first trimester screening program for Down syndrome. Since then, others have implemented this system. In this study, we tested the equality of measurements for free β-hCG and PAPP-A between Delfia Xpress systems and one AutoDelfia system.

: A total of 40 serum samples were aliquoted and stored at –20°C. Samples were analyzed by six Delfia Xpress systems and one AutoDelfia system over a time period of 2 years.

: The relationships between free β-hCG and PAPP-A were excellent for the different Delfia Xpress systems (r>0.99, p<0.0001). For PAPP-A, the agreement between the main system at VUmc and five other systems was linear with slopes between 0.99 and 1.06. Similarly, agreement for free β-hCG was linear with slopes between 0.99 and 1.09. Likewise, agreement for PAPP-A and free β-hCG was excellent for the AutoDelfia vs. the main Delfia Xpress at the VUmc (r>0.99, p<0.0001). For both PAPP-A and free β-hCG, the relationships were linear with slopes of 1.08 and 1.07.

: We demonstrate an excellent agreement for the analysis of PAPP-A and free β-hCG between Delfia Xpress systems and one AutoDelfia system.

Clin Chem Lab Med 2009;47:222–6.

Placenta-derived, cellular messenger RNA expression in the maternal blood of preeclamptic women

OBJECTIVE

To perform gene expression profiling and real-time quantitative reverse-transcription polymerase chain reaction (PCR) analysis to identify biomarkers of preeclampsia in cellular messenger RNA (mRNA) from maternal blood.

METHODS

We performed a microarray analysis with five maternal blood samples from women with preeclampsia and five matched control subjects. Up-regulated gene expression was further analyzed through reverse-transcription PCR analysis with 28 consecutive blood samples from women affected with preeclampsia and 29 controls.

RESULTS

Both pregnancy-specific beta1 glycoprotein and trophoblast glycoprotein were selected based on microarray analysis. Reverse-transcription PCR analysis detected significantly increased mRNA concentrations among women in the preeclampsia group. When stratified according to mild or severe preeclampsia, 19.2-fold and 41.8-fold increases in pregnancy-specific beta1 glycoprotein and 8.3-fold and 10.6-fold increases in trophoblast glycoprotein were observed, respectively. Among women with hemolysis, elevated liver enzymes, and low platelet count syndrome, 51.6-fold and 13.1-fold increases in pregnancy-specific beta1 glycoprotein and trophoblast glycoprotein were observed, respectively. In the preeclampsia group, pregnancy-specific beta1 glycoprotein correlated with severity of proteinuria (P<.001) and systolic blood pressure (P=.01).

CONCLUSION

The mRNA expression of pregnancy-specific beta1 glycoprotein and trophoblast glycoprotein is up-regulated in cells circulating within blood from women with preeclampsia, and pregnancy-specific beta1 glycoprotein expression is positively correlated with the clinical severity of preeclampsia.

LEVEL OF EVIDENCE

II.

Functions of alpha 2 macroglobulins in pregnancy

The alpha 2 macroglobulins (A2M) are a family of abundant plasma proteins produced predominantly by the mammalian liver. Pregnancy zone proteins (PZP) of humans and rats are A2M family members that bind a wide variety of macromolecules including the important pregnancy-associated molecules such as vascular endothelial growth factor, placenta growth factor and glycodelin (also called PP14). Recently, a mouse gene analogous to PZP (A2M of pregnancy or A2Mp) was cloned. A2Mp has a unique pattern of expression in reproductive and cardiovascular tissues and, unexpectedly, is not expressed by liver. Since changes in heart function and remodeling of renal and uterine vasculature are amongst the earliest maternal responses to pregnancy, the product of the A2Mp gene has been postulated to systemically regulate these changes. A2Ms with and without non-covalently bound ligands also down regulate immune cell activation but promote immune cell migration, additional features associated with gestational success. Here, we review the A2M gene families of mice and humans, the predicted structural relationships between A2M and its pregnancy induced forms and the postulated roles for this gene family in normal pregnancy.

Characterization of a Murine Alpha 2 Macroglobulin Gene Expressed in Reproductive and Cardiovascular Tissue1

Full-length cDNA for a mouse gene A2-macroglobulin induced by pregnancy (A2mp) was cloned from mesometrial decidua at Gestation Day 10. The 4622-base pair cDNA encodes a protein of 1473 AA with >70% sequence identity and all typical domains of other A2M-family members in humans and rodents, despite unique absence of hepatic expression. The bait region is most distinct and has the greatest sequence similarity with rat acute-phase A2m. Northern blotting, reverse transcription and real-time-PCR, and in situ hybridization studies using C57Bl/6 mice revealed uterine induction of A2mp during decidualization and strong, midgestational association with modifying spiral arteries. Ovaries, testes, lactating mammary glands, heart, and kidney were the only additional organs with A2mp expression that was localized to granulosa and cumulus cells in secondary follicles; primary seminiferous epithelium, including Sertoli cells, mammary alveolar, and ductal epithelium; cardiac endothelium; and renal collecting tubules, respectively. Infusion of native human A2M into pregnant alymphoid or interferon-gamma gene-ablated mice overcame blocks to pregnancy-induced spiral artery modification in these strains. Activated human A2M was also effective, suggesting mechanisms independent of proteinase inhibition. Identification of cytokines, growth factors, or other molecules bound to A2MP should provide new insights into decidualization, spiral artery modification, and cardiovascular adaptation to pregnancy.

Maternal serum pregnancy-associated plasma protein-A and free β-human chorionic gonadotrophin in pregnancies conceived with fresh and frozen-thawed embryos fromin vitro fertilization and intracytoplasmic sperm injection

OBJECTIVE

Maternal serum pregnancy-associated plasma protein-A (PAPP-A) and free beta-human chorionic gonadotrophin (beta-hCG) are useful markers in the screening of Down syndrome in the first trimester. We investigated the effect of intracytoplasmic sperm injection (ICSI), freezing and thawing of embryos on the levels of these two analytes in assisted reproduction pregnancies.

METHODS

We recruited 149 women who conceived after assisted reproduction with fresh embryos (92 from conventional IVF and 57 from ICSI), 85 women who conceived with frozen-thawed embryos (54 from conventional IVF and 31 from ICSI) and 401 women with spontaneous conceptions as controls. The concentrations of PAPP-A and free beta-hCG were measured between 10 and 14 weeks and were converted to multiples of medians (MoM) for comparisons.

RESULTS

Median PAPP-A MoMs were significantly reduced in ICSI pregnancies in the fresh and frozen-thawed embryo subgroups (0.70 and 0.66 MoM respectively) and in the IVF fresh embryo subgroups (0.83 MoM), as compared to controls (1.00 MoM). Free beta-hCG MoM was significantly reduced in the IVF fresh embryos subgroup (0.87 MoM), but not in the other three subgroups.

CONCLUSION

Further studies for exploring the underlying pathophysiology and adjustment in the marker levels for screening of Down syndrome are warranted in pregnancies conceived after assisted reproduction.

Pregnancy zone protein is a carrier and modulator of placental protein-14 in T-cell growth and cytokine production

A successful pregnancy can only occur when the maternal immune system fails to attack the allogeneic fetus. Two plasma proteins with described immunoregulatory activities, pregnancy zone protein (PZP) and placental protein-14 (PP14; also known as glycodelin-A), increase dramatically during pregnancy, prompting us to examine their potential role in mediating fetal protection. First, we demonstrated that both native PZP and its receptor-recognized monoamine-activated form (MA-PZP) bound non-covalently and specifically to PP14, exhibiting K(d) values greater than 3 microM, as determined by surface plasmon resonance. Our evidence further suggests that PZP is potentially a more effective carrier of PP14 than its relative alpha2-macroglobulin. Second, we found that T-cell activation, as measured by increased proliferation and IL-2 production, was inhibited by either PZP or PP14 in a dose-dependent manner. However, when PZP and PP14 were combined, they acted synergistically to inhibit T cell proliferation and IL-2 production. Interestingly, the combination of PZP and PP14 had little effect on the production of T(H)2 cytokine, IL-4. Based upon these findings, we hypothesize that PZP and PP14 form a stable complex in the plasma of pregnant women and together act synergistically to selectively modulate T-cell activation. Mechanistically, this activity appears to be independent of the PZP receptor (CD91) or PZP's anti-proteinase activity.

Differential regulation of pregnancy associated plasma protein (PAPP)-A during pregnancy in human and mouse

Serum IGFBP-4 proteolytic activity increases dramatically during human pregnancy and is mainly attributed to the pregnancy-associated plasma protein-A (PAPP-A). To understand the regulation and actions of PAPP-A in vivo, we evaluated the utility of a mouse model system. Serum from day-9 and day-17 pregnant mice and age-matched controls was tested for IGFBP-4 proteolytic activity using recombinant mouse IGFBP-4 as the substrate. Surprisingly, IGFBP-4 proteolytic activity in mouse pregnancy serum (mPS) was not significantly different from that of non-pregnancy serum (mNPS). Addition of IGF-II to mPS or mNPS at a dose sufficient to increase IGFBP-4 proteolysis by human PS failed to enhance IGFBP-4 proteolysis. PAPP-A neutralization antibody did not inhibit IGFBP-4 proteolysis by mPS or mNPS, but completely blocked IGFBP-4 proteolytic activity in human PS (hPS, mouse osteoblast conditioned medium, and mouse amniotic fluid). To determine whether the lack of PAPP-A activity in mPS was due to low expression of PAPP-A in the placenta, we cloned a mouse genomic DNA, which contained 1 kb of the entire exon 2 coding sequence and 2.5 kb of the flanking intron sequences. The exon 2-coded mouse and human PAPP-A shared 86% amino acid sequence identity. RT-PCR analysis revealed that the PAPP-A mRNA level in mouse placenta was lower compared to that in human placenta by at least two orders of magnitude. PAPP-A expression was also lower in mouse placenta compared to those in mouse kidney, osteoblasts, and bone marrow stromal cells.

CONCLUSIONS

(1) Serum IGFBP-4 proteolytic activity is differentially regulated by pregnancy in human and mouse. (2) The lack of an increase in serum IGFBP-4 proteolytic activity during mouse pregnancy is due to the low level of PAPP-A expression in the placenta.

Identification and regulation of the IGFBP-4 protease and its physiological inhibitor in human trophoblasts and endometrial stroma: evidence for paracrine regulation of IGF-II bioavailability in the placental bed during human implantation

The IGF family plays an important role in implantation and placental physiology. IGF-II is abundantly expressed by placental trophoblasts, and IGF binding protein (IGFBP)-4, a potent inhibitor of IGF actions, is the second most abundant IGFBP in the placental bed, expressed exclusively by the maternal decidua. Proteolysis of IGFBP-4 results in decreased affinity for IGF peptides, thereby enhancing IGF actions. In the current study, we have identified the IGFBP-4 protease and its inhibitor in human trophoblast and decidualized endometrial stromal cell cultures, and we have investigated their regulation in an effort to understand control of IGF-II bioavailability at the placental-decidual interface in human implantation. IGFBP-4 protease activity was detected in conditioned media (CM) from human trophoblasts and decidualized endometrial stromal cells using (125)I-IGFBP-4 substrate. Identification of the IGFBP-4 protease as pregnancy-associated plasma protein-A (PAPP-A) was confirmed by specific immunoinhibition and immunodepletion of the IGFBP-4 protease activity with specific PAPP-A antibodies. The IGFBP-4 protease activity was IGF-II-dependent in trophoblast CM. In decidualized stromal CM, PAPP-A/IGFBP-4 protease activity was also IGF-II-dependent, but was evident only when IGF-II was added in molar excess of the predominant IGFBP in decidualized stromal cell CM, IGFBP-1, supporting bioavailable IGF-II as a key cofactor of IGFBP-4 proteolysis by PAPP-A. Cultured first and second trimester human trophoblasts (n = 5) secreted PAPP-A into CM with mean +/- SEM levels of 172.4 +/- 32.8 mIU/liter.10(5) cells, determined by specific ELISA. PAPP-A in trophoblast CM (n = 3) and did not change in the presence of IGF-II (1-100 ng/ml). Cultured human endometrial stromal cells (n = 4) secreted low levels of PAPP-A (6.25 +/- 3.6 mIU/liter.10(5) cells). A physiological inhibitor of PAPP-A, the proform of eosinophil major basic protein (proMBP), was detected in trophoblast CM at levels of 1853 +/- 308 mIU/liter.10(5) cells, determined by specific ELISA, and was nearly undetectable in CM of human endometrial stromal cells. Upon in vitro decidualization of endometrial stromal cells with progesterone, PAPP-A levels in CM increased nearly 9-fold without a concomitant change in proMBP. In contrast to the experiments with trophoblasts, IGF-II and the IGF analogues, Leu(27) IGF-II, and Des (1-6) IGF-II, resulted in a dose-dependent decrease of PAPP-A levels in decidualized endometrial stromal CM by 70-90%, and a dose-dependent increase in proMBP of 14- to 41-fold. The data demonstrate conclusively that the IGF-II-dependent IGFBP-4 protease of human trophoblast and decidual origin is PAPP-A. Furthermore, the differential regulation of decidual PAPP-A and proMBP by insulin-like peptides supports a role for trophoblast-derived IGF-II as a paracrine regulator of these maternal decidual products that have the potential to regulate IGF-II bioavailability at the trophoblast-decidual interface. Overall, the data underscore potential roles for a complex family of enzyme (PAPP-A), substrate (IGFBP-4), inhibitor (proMBP), and cofactor (IGF-II) in the placental bed during human implantation.

Highly specific monoclonal antibody demonstrates that pregnancy-specific glycoprotein (PSG) is limited to syncytiotrophoblast in human early and term placenta

Pregnancy specific glycoproteins (PSG) in humans constitute a family of 11 closely related glycoproteins (PSG1-8, PSG11-13) of unknown function(s), which are produced in large amounts by the placenta. As a step toward understanding the biology of PSG, specific monoclonal antibodies (mAbs) against PSG were developed and used to investigate the ultrastructural localization of PSG in the early and term placenta and in first trimester decidua. One mAb, BAP-3, was found to react with all six individually expressed PSGs representing five alternatively spliced forms, but not with any of the seven expressed members of the carcinoembryonic antigen (CEA) subfamily. The BAP-3 epitope is located in the PSG B2 domain. Using the BAP-3 mAb, PSGs were found to be expressed exclusively by the syncytiotrophoblast of first trimester and term villi. The intensity of the staining was much higher in early than in term placenta. All three main cellular compartments involved in the biosynthesis pathway of secreted proteins, i.e. rough endoplasmic reticulum, the Golgi complex and secretory vesicles, were stained for PSG. A second PSG-reactive mAb, BAP-1, also stained the apical plasma membrane of some glandular epithelial cells in first trimester decidua in addition to syncytiotrophoblast. This staining was most likely due to cross-reactivity with biliary glycoprotein (BGP).

Isolation and characterization of circulating complex between human pregnancy-associated plasma protein-A and proform of eosinophil major basic protein

The plasma protein previously known as pregnancy associated plasma protein-A (PAPP-A) and believed to contain only one kind of polypeptide chain has recently been shown to be a complex containing two different chains in equimolar amounts. One of the chains is now defined as the PAPP-A subunit, and the other has been identified as the proform of eosinophil major basic protein (proMBP) (Oxvig et al. (1993) J. Biol. Chem. 268, 12243-12246). A procedure for large scale preparation of the circulating complex (PAPP-A/proMBP) from pooled pregnancy serum is described. The amino acid and carbohydrate compositions of the isolated reduced and carboxymethylated PAPP-A (199 kDa) and proMBP subunits (38 kDa), and of the intact PAPP-A/proMBP have been determined. The PAPP-A and proMBP subunits contain 13.4% (w/w) and 38.6% (w/w) carbohydrate, respectively, and the intact complex contains 17.4% (w/w) carbohydrate. The PAPP-A subunit contains N-bound carbohydrate groups. In contrast, the proMBP subunit contains both N- and O-bound groups as well as glycosaminoglycan, previously found among plasma proteins only in inter-alpha-trypsin inhibitor and pre-alpha-trypsin inhibitor. It is shown that PAPP-A/proMBP can competitively inhibit human leucocyte elastase (KI = (5-10) x 10(-9) M) at an ionic strength of 0.075, but the inhibition is negligible at ionic strengths greater than 0.15. Human cathepsin G is also competitively inhibited (KI approx. 1 x 10(-6) M). The inhibition of both enzymes is most likely due to interactions with the glycosaminoglycan moiety of PAPP-A/proMBP. It is concluded that PAPP-A/proMBP is neither a potent nor a specific inhibitor of human leucocyte elastase.

Biochemical properties, activities, and presence in biologic fluids of eosinophil granule major basic protein

The existence of a proform of MBP is predicted from the sequence of MBP cDNA clones. ProMBP has been purified from the supernatants of CHO cells transfected with cDNA encoding prepro MBP. Purification involved heparin-Sepharose affinity purification followed by two sequential size fractionation steps over Sephadex G-100 and yielded proMBP with a molecular mass of 33 kd. Recombinant proMBP from the heparin-Sepharose column was subjected to isoelectric focusing followed by SDS-PAGE and Western blot analysis. The results indicated that most of the 33 kd form of proMBP focused predominantly between pI 4.2 and 5.1, with a major peak at a pI of approximately 4.9. Analyses of the carbohydrates associated with the purified 33 kd form of recombinant proMBP indicated the addition of 4856 to 5150 Da by carbohydrates characteristic of the complex type. Consistent with the hypothesis that the function of the propiece is to neutralize MBP toxicity during granule processing, proMBP lacked MBP cytostimulatory properties and actually blocked the effect of MBP in two different systems, basophil histamine release and neutrophil activation. In addition, as a measure of toxicity, proMBP did not inhibit protein synthesis, whereas MBP markedly reduced protein synthesis. The mechanisms by which MBP exerts its actions both as a cytostimulant and as a toxin are not known; however, it is known that cationic MBP readily reacts with acidic lipids. Using artificial liposomes as targets, MBP caused a disordering of the lipid bilayer membrane, resulting in fusion and lysis. Therefore, MBP may act both as a cytostimulant and as a toxin because of its marked cationicity and its ability to disorder lipid membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

Pregnancy-associated plasma protein A levels in maternal serum, extraembryonic coelomic and amniotic fluids in the first trimester

First trimester maternal serum levels of pregnancy-associated plasma protein A(PAPP-P) are reduced in women with a Down's syndrome pregnancy. We have examined the concentration of this molecule in the amniotic (AF) and extra-embryonic coelomic (EECF) fluids surrounding the developing fetus. Maternal serum levels of PAPP-A were elevated in all samples and steadily rose from a median of 480 mIU/1 at 8 weeks to a median of 6375 mIU/1 at 14 weeks gestation. Levels of PAPP-A were low in EECF and undetectable in the AF until 14 weeks gestation. This pattern of distribution is in contrast to that of most other trophoblast-associated antigens. This may reflect PAPP-A physiology and its specific production by the syncytiotrophoblast.

Ultrastructural localization of pregnancy-specific beta 1-glycoprotein (SP1) and cathepsin B in villi of early placenta of the macaque

Pregnancy-specific beta 1-glycoprotein (SP1) is found in maternal serum very early in gestation in both human and non-human primates. As judged by light microscopic immunocytochemistry, the major source of SP1 is the syncytial trophoblast, but little is known of the subcellular localization of SP1 indicative of the cellular pathway involved in secretion of the hormone. To study subcellular distribution of SP1, we used electron microscopic immunocytochemistry carried out on macaque placental villi from early (3-4 weeks) gestation. Both light and electron microscopic results confirmed localization confined to syncytial trophoblast in the villi. Within syncytial trophoblast labeling was predominantly over small granules in the apical cytoplasm. The Golgi complex also showed labeling, and light labeling was associated with the endoplasmic reticulum. For comparison, we also localized cathepsin B, a lysosomal protease. By way of contrast this enzyme was localized primarily in large cytoplasmic granules. The results are consistent with a secretory pathway including synthesis in the ER, processing by the Golgi complex, and exocytotic release into maternal blood in the intervillous space.

Cloning of the complete gene for carcinoembryonic antigen: analysis of its promoter indicates a region conveying cell type-specific expression

Carcinoembryonic antigen (CEA) is a widely used tumor marker, especially in the surveillance of colonic cancer patients. Although CEA is also present in some normal tissues, it is apparently expressed at higher levels in tumorous tissues than in corresponding normal tissues. As a first step toward analyzing the regulation of expression of CEA at the transcriptional level, we have isolated and characterized a cosmid clone (cosCEA1), which contains the entire coding region of the CEA gene. A close correlation exists between the exon and deduced immunoglobulin-like domain borders. We have determined a cluster of transcriptional starts for CEA and the closely related nonspecific cross-reacting antigen (NCA) gene and have sequenced their putative promoters. Regions of sequence homology are found as far as approximately 500 nucleotides upstream from the translational starts of these genes, but farther upstream they diverge completely. In both cases we were unable to find classic TATA or CAAT boxes at their expected positions. To characterize the CEA and NCA promoters, we carried out transient transfection assays with promoter-indicator gene constructs in the CEA-producing adenocarcinoma cell line SW403, as well as in nonproducing HeLa cells. A CEA gene promoter construct, containing approximately 400 nucleotides upstream from the translational start, showed nine times higher activity in the SW403 than in the HeLa cell line. This indicates that cis-acting sequences which convey cell type-specific expression of the CEA gene are contained within this region.

Cloning of the complete gene for carcinoembryonic antigen: analysis of its promoter indicates a region conveying cell type-specific expression

Carcinoembryonic antigen (CEA) is a widely used tumor marker, especially in the surveillance of colonic cancer patients. Although CEA is also present in some normal tissues, it is apparently expressed at higher levels in tumorous tissues than in corresponding normal tissues. As a first step toward analyzing the regulation of expression of CEA at the transcriptional level, we have isolated and characterized a cosmid clone (cosCEA1), which contains the entire coding region of the CEA gene. A close correlation exists between the exon and deduced immunoglobulin-like domain borders. We have determined a cluster of transcriptional starts for CEA and the closely related nonspecific cross-reacting antigen (NCA) gene and have sequenced their putative promoters. Regions of sequence homology are found as far as approximately 500 nucleotides upstream from the translational starts of these genes, but farther upstream they diverge completely. In both cases we were unable to find classic TATA or CAAT boxes at their expected positions. To characterize the CEA and NCA promoters, we carried out transient transfection assays with promoter-indicator gene constructs in the CEA-producing adenocarcinoma cell line SW403, as well as in nonproducing HeLa cells. A CEA gene promoter construct, containing approximately 400 nucleotides upstream from the translational start, showed nine times higher activity in the SW403 than in the HeLa cell line. This indicates that cis-acting sequences which convey cell type-specific expression of the CEA gene are contained within this region.

A baboon model for pregnancy-associated antigens (PAPP-A, PP5, PP14)

By radioimmunoassays established on human derived antigens, PAPP-A, PP5 and PP14 immunoreactivity was detected in placental extracts and blood of pregnant baboons. None of the serial dilution curves suggested parallelism between respective human and baboon samples. Based on slopes of regressed logit-log transformed binding data, PAPP-A demonstrated the greatest degree of interspecies immunological crossreactivity. PP14 showed the least conservation of antigenic determinants. Physicochemical characterization on heparin, zinc chelate and bovine thrombin affinity matrices could not distinguish human from baboon-derived antigens. As in the human, baboon PAPP-A and PP5 were not detected in blood of male or non-pregnant animals. PP14 was detected in baboon follicular fluid, and only PP5 immunoreactivity was measured in culture media of baboon embryos. Of the three antigens, PAPP-A was detected in pregnant baboons at about 61 days gestation, that is, 4 weeks before PP5 and PP14. With the exception of PP14 which attained peak concentration at 118 days of pregnancy, PAPP-A and PP5 concentrations were greatest at term. In conjunction with physicochemical and immunological criteria, these physiological kinetics clearly support a role for developing a baboon model to serve for further studies into feto-maternal signals, particularly antigens such as PAPP-A and PP5.

Clearance pattern of maternal serum pregnancy specific beta 1-glycoprotein after treatment in active and regressed tubal pregnancy

The clearance pattern of maternal serum pregnancy specific beta 1-glycoprotein (SP1) was studied in 16 cases of tubal pregnancy (9 active and 7 regressed) after 12, 24, 48, 72, 96, 120 and 192 h following surgery. The mean values of the hormone in both groups showed a statistically highly significant difference in all measurements before and after treatment (P less than 0.001), but they followed the same exponential regression pattern. The half-life of SP1 in active tubal pregnancies after salpingectomy was 36.2 h and in regressed tubal pregnancies after salpingostomy was 37.5 h.

Maternal levels of pregnancy-specific beta 1-glycoprotein (SP-1) are elevated in pregnancies affected by Down's syndrome

Concentrations of pregnancy-specific beta 1-glycoprotein (SP-1) were measured in maternal blood and amniotic fluid of patients with a trisomic fetus and compared with that of a cytogenetically normal fetus at weeks 16-19 of pregnancy. The SP-1 concentrations were significantly elevated in the sera of women with a Down's syndrome fetus, whereas amniotic fluid levels were only slightly increased. It is suggested that high levels of maternal SP-1 in the second trimester of pregnancy may be a valuable indicator in the prenatal detection of fetal trisomy 21.

Receptors for alpha 2-macroglobulin- and pregnancy zone protein-proteinase complexes in the human placental syncytiotrophoblast

Receptors for complexes between alpha 2-macroglobulin (alpha 2M) and proteinases (e.g. trypsin) were identified and characterized in the human placenta. The receptors also bound the complex formed between pregnancy zone protein (PZP) and chymotrypsin, although with slightly lower affinity, whereas binding of alpha 2M or PZP in their native forms was negligible. Treatment with methylamine to cleave the internal thiol esters caused an increase in binding affinity of alpha 2M to the level of alpha 2M-trypsin but only a minor increase in the affinity of PZP. Chorionic villi prepared from normal full-term placentae were approximately half occupied by endogenous alpha 2M or PZP complexes. These ligands, as well as prebound 125I-labelled alpha 2M-trypsin, were rapidly removed by the addition of 5 mM EDTA. Binding was similar in villi from eight-week and full-term placentae. Autoradiography showed that labelled alpha 2M-trypsin was associated with the syncytiotrophoblast. The kinetics of 125I-labelled alpha 2M-trypsin binding at 4 degrees C was similar in isolated villi and microvillous membranes. Association was slow, with apparent equilibrium by about 16 h. Dissociation of prebound tracer was slow but markedly accelerated in the presence of unlabelled ligand at a saturating concentration. The concentration-dependence of binding at equilibrium yielded a non-linear Scatchard plot. Most of the binding of ligand at tracer concentration was accounted for by high-affinity receptors with a dissociation constant (Kd) of about 50 pM. The content of high-affinity receptors in one placenta was estimated as approximately 125 pmol, i.e., a significant fraction of the total receptor population in the pregnant woman.

Potential role of pregnancy-associated plasma protein-A in human reproduction

By radioimmunoassay, pregnancy-associated plasma protein-A (PAPP-A) was undetectable in matched follicular and luteal phase serum samples (n = 17) or in the peripheral circulation of normal males (n = 17). However, seminal plasma (91.5%), cervical mucus (100%) and pre-ovulatory follicular fluid (99.6%) were consistently PaPP-A positive. In addition to PAPP-A, four circulating protease inhibitors (PIs) were detected in pooled seminal plasma whereas pooled follicular fluid contained an additional six. Follicular concentrations of serum PIs were inversely related to molecular size. By contrast, PAPP-A formed a positive concentration gradient across the blood-reproductive tract barrier suggesting PAPP-A production within the reproductive tract. A minor proportion (1.7%) of ejaculated spermatozoa were coated with PAPP-A, as demonstrated by direct immunofluorescence. Since PAPP-A specifically inhibits leucocyte elastase, it is suggested that PAPP-A coated spermatozoa were "selected" to overcome localized phagocytic-proteolytic degradation. The physiological significance of these findings are discussed in relation to human reproduction.

Immunolocalization of alpha and beta chains of human chorionic gonadotropin, placental lactogen and pregnancy-specific beta-glycoprotein in term placenta by a touch preparation method

Touch preparations of human placenta yield cells retaining antigenic reactivity to immunoperoxidase stains for alpha and beta chains of human chorionic gonadotropin, placental lactogen, and pregnancy-specific beta glycoprotein. This method is a rapid and simple alternative to conventional frozen and paraffin-embedded sections for detection of placental peptides.

New placental proteins: chemistry, physiology and clinical use

In the past decade, several new placental proteins have been isolated and studied. The 'pregnancy-specific' beta 1-glycoprotein (SP1) is a major placental product with unusual physicochemical properties that has been extensively investigated, but its biological function remains uncertain. Pregnancy-associated plasma protein A (PAPP-A), a glycoprotein of mol. wt 400,000, has effects in vitro on the coagulation and complement cascades, probably by its properties of protease inhibition. Placental protein 5 (PP5) may be involved in the coagulation and fibrinolytic systems, and in follicle maturation and semen liquefaction. 'Placental protein 12' (PP12) is not a product of the placenta at all; it appears to be produced in the female genital tract under the influence of progesterone and may also be produced by proliferating liver cells. Further study may reveal new roles for these placental proteins beyond their traditional roles as tumour markers.

Comparison of different antibody preparations against pregnancy-associated plasma protein-A (PAPP-A) for use in localization and immunoassay studies

Four antibody preparations against pregnancy-associated plasma protein (PAPP-A) were compared in order to find an explanation for the contradictory results published on tissue localization, clinical usefulness and biological function of PAPP-A. One of the preparations studied was a rabbit anti-PAPP-A antiserum which has been offered for general scientific use (Bischof et al. 1979). Only the IgG fraction of anti-PAPP-A antisera which appeared to be monospecific and had been further absorbed with fetal connective tissue gave specific uniform staining of the cytoplasm of the syncytiotrophoblast exclusively. Circulating PAPP-A could not be detected by RIA employing this IgG preparation in the non-pregnant state, or before 18 days after conception. Circulating PAPP-A could be detected in all seven pregnant women studied within 4 weeks after conception. Identical results were obtained with a commercially available IgG fraction against PAPP-A.

Pulsatile secretion of pregnancy-associated plasma protein-A (PAPP-A) in non-pregnant women

No changes in PAPP-A levels could be detected when plasma samples were obtained every second day throughout the entire menstrual cycle in three healthy women. But when measured every 30 min throughout 12 consecutive hours, in four healthy women, PAPP-A followed a pulsatile pattern which may originate in the endometrium since no PAPP-A pulses were detected in a long-term hysterectomized woman, or in two men. The pulses were not related to levels of oestradiol, progesterone, FSH or LH.

Immunohistochemical aspects of immunological cross-reaction and masking of epitopes for localization studies on pregnancy-associated plasma protein A

The influence of antibody absorption procedures and proteolytic pre-treatment of formaldehyde-fixed placental tissue on the localization of pregnancy-associated plasma protein A by immunoperoxidase technique was examined. Apparently monospecific IgG fraction of the anti-plasma protein applied directly on fixed tissue resulted in staining of connective tissue and a thin apical rim of the syncytiotrophoblast. Further absorption of the antibody with foetal connective tissue abolished this staining reaction. Pre-treatment of the fixed placental tissue with trypsin prior to application of the antibody, which had been absorbed with connective tissue, resulted in staining within the cytoplasm of the syncytiotrophoblast exclusively. Identical staining was seen when this IgG preparation was used directly on frozen placental tissue. The results point to the importance of the specificity of the antibody preparations and of proteolytic unmasking of epitopes when fixed tissues are used for localization studies of pregnancy-associated plasma protein A by immunoperoxidase technique.

In vitro release of pregnancy-associated plasma protein-A (PAPP-A) by human endometrial cells

Evidence has now accumulated to sustain the idea that pregnancy-associated plasma protein-A (PAPP-A) is not pregnancy specific: it can be localized immunohistochemically in nonpregnant human endometrium. Thus, it was of interest to see if a primary cell culture of human endometrial cells was capable of producing PAPP-A. Immunoreactive PAPP-A-like material was detected in the culture medium of glandular as well as stromal cells. The presence of PAPP-A in endometrial culture medium was specific and could not be attributed to a nonspecific protease effect on the tracer used in radioimmunoassay. The production rate of PAPP-A by stromal cells could be enhanced by the addition of medroxyprogesterone acetate (MPA). Estradiol (E2) alone or in combination with MPA did not modify the production rate of PAPP-A. The production rate of PAPP-A by glandular cells remained unchanged after treatment with MPA and/or E2. These results confirm that in nonpregnant women PAPP-A is a progesterone-dependent protein produced by the endometrium.

In vitro production of pregnancy-associated plasma protein-A (PAPP-A) by trophoblastic cells

Pregnancy-associated plasma protein-A (PAPP-A) a high molecular weight glycoprotein, is found in high concentration in the maternal circulation during pregnancy. Immunohistochemically, PAPP-A can be localized in the trophoblast and in the decidua. Short term cultures of trophoblastic and decidual explants produce PAPP-A in vitro. It was thus of interest to see if long term cultures of primary monolayers of human trophoblast cells were capable of producing PAPP-A. Under our in vitro conditions, trophoblastic monolayers were producing both PAPP-A and beta hCG. During the first 3 days of culture PAPP-A levels increased in the medium whereas beta hCG levels decreased. The production of both proteins could be inhibited by cycloheximide. These results strongly suggest that the trophoblast is a source of PAPP-A in vivo.

Progesterone dependence and extratrophoblastic origin of pregnancy-associated plasma protein-A (PAPP-A) in early pregnancy

Pregnancy-associated plasma protein-A (PAPP-A) is a macromolecular glycoprotein produced in increasing concentration as pregnancy advances. PAPP-A is not specific to pregnancy since measurable levels have been found in non-pregnant females and in males. In non-pregnant females, PAPP-A is probably produced by the endometrium. The origin of PAPP-A in pregnant women is still controversial. In-vitro trophoblast and decidual explants both produce PAPP-A. So far, it is not known if the same applies to the in-vivo situation and to what extent these two tissues contribute to the circulating levels of PAPP-A. This study compares the circulating concentrations of PAPP-A and beta-hCG and progesterone in different pathological situations. In hydatidiform moles, beta-hCG levels are very high demonstrating an intense trophoblastic activity, whereas PAPP-A levels remain in the normal range. With spontaneous abortions, beta-hCG levels decline to very low values whereas PAPP-A continues to increase. These observations furnish indirect evidence for a major contribution to circulating PAPP-A levels by extratrophoblastic sites. Furthermore, PAPP-A levels decrease after administration of an anti-progesterone (RU486) either in-vivo or in-vitro. This is considered as a proof that PAPP-A levels in early pregnancy are progesterone dependent.