Indirect immunofluorescent localization of prolactin to the cytoplasm of decidua and trophoblast cells in human placental membranes at term

Human predecidual stromal cells are mesenchymal stromal/stem cells and have a therapeutic effect in an immune-based mouse model of recurrent spontaneous abortion

Background

Human decidual stromal cells (DSCs) are involved in the maintenance and development of pregnancy, in which they play a key role in the induction of immunological maternal–fetal tolerance. Precursors of DSCs (preDSCs) are located around the vessels, and based on their antigen phenotype, previous studies suggested a relationship between preDSCs and mesenchymal stromal/stem cells (MSCs). This work aimed to further elucidate the MSC characteristics of preDSCs.

Methods

We established 15 human preDSC lines and 3 preDSC clones. Physiological differentiation (decidualization) of these cell lines and clones was carried out by in vitro culture with progesterone (P4) and cAMP. Decidualization was confirmed by the change in cellular morphology and prolactin (PRL) secretion, which was determined by enzyme immunoassay of the culture supernatants. We also studied MSC characteristics: (1) In mesenchymal differentiation, under appropriate culture conditions, these preDSC lines and clones differentiated into adipocytes, osteoblasts, and chondrocytes, and differentiation was confirmed by cytochemical assays and RT-PCR. (2) The expression of stem cell markers was determined by RT-PCR. (3) Cloning efficiency was evaluated by limited dilution. (4) Immunoregulatory activity in vivo was estimated in DBA/2-mated CBA/J female mice, a murine model of immune-based recurrent abortion. (5) Survival of preDSC in immunocompetent mice was analyzed by RT-PCR and flow cytometry.

Results

Under the effect of P4 and cAMP, the preDSC lines and clones decidualized in vitro: the cells became rounder and secreted PRL, a marker of physiological decidualization. PreDSC lines and clones also exhibited MSC characteristics. They differentiated into adipocytes, osteoblasts, and chondrocytes, and preDSC lines expressed stem cell markers OCT-4, NANOG, and ABCG2; exhibited a cloning efficiency of 4 to 15%; significantly reduced the embryo resorption rate (P < 0.001) in the mouse model of abortion; and survived for prolonged periods in immunocompetent mice. The fact that 3 preDSC clones underwent both decidualization and mesenchymal differentiation shows that the same type of cell exhibited both DSC and MSC characteristics.

Conclusions

Together, our results confirm that preDSCs are decidual MSCs and suggest that these cells are involved in the mechanisms of maternal–fetal immune tolerance.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1284-z) contains supplementary material, which is available to authorized users.

Calcium Homeostasis in Human Placenta: Role of Calcium‐Handling Proteins

The human placenta is a transitory organ, representing during pregnancy the unique connection between the mother and her fetus. The syncytiotrophoblast represents the specialized unit in the placenta that is directly involved in fetal nutrition, mainly involving essential nutrients, such as lipids, amino acids, and calcium. This ion is of particular interest since it is actively transported by the placenta throughout pregnancy and is associated with many roles during intrauterine life. At term, the human fetus has accumulated about 25-30 g of calcium. This transfer allows adequate fetal growth and development, since calcium is vital for fetal skeleton mineralization and many cellular functions, such as signal transduction, neurotransmitter release, and cellular growth. Thus, there are many proteins involved in calcium homeostasis in the human placenta.

Life Cycle of Decidual Cells

The decisive events in the development of decidual cells (DC) are presented through examples of human and rodent decidua. Human decidua is formed by large decidual cells (LDC), endometrial granulated cells (eGC), and small decidual cells. The LDC form the main type of decidual membranes, which determine the morphological characteristics of the decidua as a tissue. Immediate precursor cells of LDC are located below the basement membrane of the uterine epithelium before and during implantation. At the next stage of differentiation, LDC acquire a spindle-like shape. Rodent LDC form an epithelium-like structure with gland properties at the terminal stage of differentiation. The single-cell structure of human decidua is a derivative of the epithelial organization of rodent decidua. Spindle-like rat LDC are characterized by a high level of protein, RNA, and DNA synthesis and by intensive proliferation. At the beginning of pregnancy, a cell proliferation predominates over cell loss. By Days 12-13 of rat pregnancy LDC loss reaches 80% per day. Terminally differentiated LDC (tLDC) disappear from decidua due to apoptosis. Apoptosis of tLDC and the exhaustion of their precursors account for the disappearance of LDC in the middle of rat pregnancy. Human term decidua is composed of living cells. Human LDC (hLDC) comprise the largest part of human decidual cells (hLDC). hLDC account for 60-90% of hDC but their relative amount can decrease to 35% in the case of significant cell loss under unfavorable conditions. A decrease of LDC is not accompanied by DC proliferation. The lack of ability of decidua to compensate for DC loss suggests DC is a growing type of cell population without cambial cells. LDC function largely by blebbing and budding. Human and rat endometrial granulated cells (eGC) are characterized by a low level of natural killer (NK) activity and a high level of natural suppressor (NS) activity. The combination of NK and NS properties is characteristic of the eGC immunoregulatory function. Other functions of decidua include control of inflammation and trophoblast growth and expansion in the uterus. The life span of decidual cells is limited by pregnancy.

Factors regulating interaction between trophoblast and human endometrium

Implantation is a crucial step in human reproduction. Disturbances of this process are responsible for pregnancy failure after both in vivo and in vitro fertilization. The endometrium provides the implanting embryo with a unique substratum where the embryo communicates with biochemical signals, attaches itself, penetrates and grows without blood circulation. The highly proliferative phase of the cytotrophoblast, during early human embryogenesis, may be due to endogenous production of growth factors that may establish autocrine/short range paracrine stimulator loops which explain the tumor-like properties of these tissues. Endometrial BM penetration and stroma invasion may be due to the proteolytic capability of the human embryo. It is suggested that collagenase and the urokinase-like plasminogen activator are responsible for this activity. To clarify the molecular mechanisms involved in human embryo implantation several models are suggested: culture of blastocysts, culture of endometrial cells, and endometrial explant co-culture. Human blastocysts cultured with whole perfused human uteri make it possible to recognize some aspects of the entire implantation process and give us the possibility of improving the benefits provided by new technologies in reproductive medicine and reducing embryonic loss at an early stage.

Observation of production of immunoactive prolactin by normal human connective tissue in cell culture

Data from our in vitro studies indicate a new source of prolactin (PRL)-like activity, normal human connective tissue. Fascial cells from primary culture and subsequent passages produced an extracellular antigen which specifically reacted in a radioimmunoassay RIA developed to detect human pituitary PRL. An initial peak or first surge of fascial PRL-like activity occurred between 4 and 15 d in primary culture. Ibuprofen, cytotoxic levels of 0.01% azide, or 7.5 mM EDTA and medium lacking serum [fetal bovine serum (FBS)] significantly (P less than or equal to 0.05) reduced PRL-like activity levels, whereas female steroids, 257 to 342 milliosmolarity, 1 to 3.6 mg/ml glucose, 2 to 20% FBS, and dialyzed FBS (MWCO approximately 1 kDa) were without effect. Optimum production of PRL-like activity occurred at pH 7.3. A second surge began after 18 d and continued until passage indicating that perhaps two populations of cells produced PRL-like activity in primary culture. Production of PRL-like activity by cells from early passages (1 and 2) became detectable at confluence, was serum-dependent, showed two patterns (tonic, rising to plateau), and averaged 3.2 fg.cell-1.3 d-1 feed interval. Cells from late passages showed morphologic damage from repetitive trypsinization, aging, and reduced production of PRL-like activity with aberrant production pattern. Production of PRL-like activity was maintained in an unusual long-term culture. These in vitro studies demonstrate the most recently recognized and ubiquitous source of human extrapituitary PRL or PRL-like activity, normal connective tissue (fascia).

Basement membrane components in normal hyperplastic and neoplastic endometrium

The major basement membrane (BM) components, laminin and type IV collagen, were studied by immunochemistry in normal, hyperplastic, and neoplastic endometrium. By immunoperoxidase technique, proliferative and secretive endometrium showed capillary and epithelial cell basement membranes with linear staining with antibodies to both laminin and type IV collagen. Immunostaining of laminin and type IV collagen showed that capillaries were surrounded by a continuous perivascular sheath of these matrices in specimens of adenomatous hyperplasia and in nearly all specimens of endometrial adenocarcinoma. Laminin and type IV collagen were found to accumulate around glandular epithelial cells of adenomatous hyperplastic endometrium, but in several specimens these linear surrounding formations were defective and discontinuous. In several areas of well-differentiated endometrial adenocarcinomas BM-like structures were found around glandular epithelial cells as shadows without staining for laminin and type IV collagen. These basement membrane components accumulate around stromal cells to encircle each cell with a gradual, progressive, and cyclic process depending on the phase of the menstrual cycle. Laminin and type IV collagen were clearly detected around stromal cells at days 20 to 22 of the menstrual cycle and more thickly at days 26 to 28. The accumulation of these matrices around stromal cells is a progesterone/progestin-related process. In the well-differentiated adenocarcinoma a mid-term treatment with progestin (Danatrol Maggioni-Winthrop, SPA, Milan, Italy) was found to be effective on laminin and type IV collagen accumulation around stromal cells.

Early human pregnancy in vitro utilizing an artificially perfused uterus

The penetration of luminal epithelium in the uterine cavity represents the crucial event that triggers the failure of embryo implant, thus limiting the possibility of fertility control. The purpose of our study was to implant a human blastocyst, cultured in vitro, into a human uterus extracorporeally perfused with an oxygenated medium. For this purpose, human blastocysts, collected from patients who underwent IVF program because of irreparable tubal infertility, were injected under the luminal epithelium of human perfused uteri. Light and electron microscopy showed that human blastocyst can successfully undergo the stage of implantation and trophoblastic invasion in 52 hours of extracorporeal perfusion.

Studies on endometrial cells in human pregnancy by monoclonal antibodies

By immunizing mice with endometrial cells from pregnant women, we obtained two hybridoma clones, 9D3 (IgG1) and 9E3 (IgG3), secreting monoclonal antibodies (MoAbs) that selectively stained endometrial stromal cells having prolactin in their cytoplasm, but did not stain glandular epithelium nor small lymphoid cells. From examination of tissues, cells and cell lines, it was found that 9E3 antigen was broadly distributed among various mesenchymal cells, while 9D3 antigen was distributed on a more restricted spectrum of mesenchymal cells, skin basal cells and a promonocytic cell line (U937). Neither of these antibodies stained peripheral blood cells, bone marrow cells or endometrium of the proliferating phase. Furthermore, 9D3 MoAb reacted with all melanoma cell lines and squamous cell lines examined. The antigenic molecule that was recognized by 9D3 MoAb had a molecular weight of 94,000.

Immunohistochemical localization of follicle-stimulating hormone, luteinizing hormone, growth hormone, adrenocorticotrophic hormone and prolactin in the human placenta

The sites of localization of luteinizing hormone (LH), follicle-stimulating hormone (FSH), growth hormone (GH), adrenocorticotrophic hormone (ACTH) and prolactin (PRL) within placental tissues have been studied by an immunoperoxidase technique. The syncytiotrophoblast is the sole significant site of localization of LH, FSH, GH and ACTH; PRL is found both in syncytiotrophoblast and in decidual cells. It is highly probable that the sites of localization of these peptide hormones represents their sites of synthesis in the placenta and thus that the syncytiotrophoblast is the sole site of synthesis of LH, FSH, LH and ACTH. PRL appears to be synthesized both in syncytiotrophoblast and decidua, but the latter is probably not the major site of synthesis of this hormone. Whether these placental peptide hormones have any physiological role to play during pregnancy or whether the placental capacity to synthesize such hormones is an atavistic phenomenon of no functional importance is currently a moot point.

Identification of the mRNA coding for prolactin in the human decidua

Total RNAs extracted from amnion, chorion and decidua of the human second trimester placentas were translated in the cell-free translation system, followed by immunoprecipitation with antiserum to human prolactin (Prl) and electrophoresis in sodium dodecyl sulfate slab gel. A single immunospecific protein with an apparent molecular weight of approximately 25,500, about 3000 daltons larger than authentic Prl, was formed only with RNA from decidua, and it competed with unlabeled Prl but not with unlabeled human placental lactogen (hPL) for binding to the antibody. The electrophoretic patterns of the fragments formed by partial enzymatic proteolysis of it and authentic Prl were similar.

Placental hormones: I. Immunofluorescence studies of the localization of chorionic gonadotrophin, placental lactogen and prolactin in human and rat placenta and in the endometrium of pregnant rats

Chorionic gonadotrophin (CG), placental lactogen (PL) and prolactin (PRL) were localized in sections of human and rat placenta using the indirect immunofluorescence technique. Antisera were absorbed with homologous and unrelated antigens by affinity chromatography or complexed with their respective antigens. To exclude binding of IgG and immune complexes to Fc-receptor in chorionic tissue, thus leading to erroneous results, sections were preincubated with an excess of rat IgG. The results indicate that, in the human placenta, human CG (hCG) and human PL (hPL) can be identified in the syncytiotrophoblast. Using antibodies to hPRL fluorescence was found in giant cells within the cytotrophoblastic islands in the intervillous space and in cytotrophoblastic cells within placental septa. In the rat placenta rat PL (rPL) and rat PRL (rPRL) could be identified in the giant cells of the basal zone. Furthermore rPRL/rPL was localized in the endometrium and adjacent decidial cells of rat pregnancy. No staining of chorionic cells was detected using antibodies against hCG and bLH, which cross-reacted with rLH. These experiments provide further evidence that the rat placenta is unlikely to produce a CG/LH-like hormone.

Maternal serum hormone changes during abortion induced with 9-deoxo-16, 16-dimethyl-9-methylene prostaglandin E2

Serum hormone levels in women undergoing successful first and second trimester abortions induced by 9-deoxo-16, 16-dimethyl-9-methylene prostaglandin E2 vagitories have been measured. Significantly decreased levels of prolactin (p less than 0.01) and TSH (p less than 0.05) were seen in both groups of women but the drop appeared sooner, within two hours, in first trimester abortions. Regardless of gestational length there was a significant decrease in serum human chorionic gonadotropin (hCG) (p less than 0.01) concentrations in maternal serum six hours into treatment. In the second trimester abortions total estriol, alpha-fetoprotein and lactoplacental hormone hPL were analysed in maternal serum but the levels did not change over the eight hour investigation period. It is speculated that the PGE2-derivative most likely affects the maternal pituitary secretion of prolactin and TSH, possibly via direct or indirect interference with TRH mechanism(s).

Prolactin binding sites on human chorion-decidua tissue

An effective procedure has been developed and utilized to demonstrate the presence of prolactin receptors on the plasma membranes of human chorion-decidua cells. Particulate fractions from human chorion-decidua sedimenting between 1,500 and 45,000 x g display optimal binding of 215I-labeled ovine prolactin when incubated at a membrane protein concentration of 200 micrograms per assay tube for 2 hours at 22 degrees C. Specific binding was increased by pretreatment of the membrane particles with 5M magnesium chloride to remove endogenous prolactin. These receptors show binding parameters (affinity, 0.92 x 10(9) L/mode; capacity, approximately 80 fmoles/mg) similar to those of lactogenic receptors in the rabbit mammary gland and, the rabbit and rat liver. The presence of prolactin receptors in human chorion-decidua suggests that may play a role in mediating local action(s) of prolactin such as involvement in the decidualization reaction or in maintaining fetal osmoregulation.

Study on maternal, fetal and amniotic prolactin in gestational diabetic women, at term

In order to determine whether prolactin secretion was affected in diabetic pregnancy, maternal, fetal and amniotic fluid prolactin (PRL) concentrations were measured in gestational non treated diabetic women at parturition. Amniotic fluid PRL levels, though higher than those in maternal and fetal serum, were significantly lower than those of the controls (p less than 0.005); no case of respiratory distress syndrome or congenital malformation was found at birth.

The regulation in vitro of placental release of human chorionic gonadotropin, placental lactogen, and prolactin: effects of an adrenergic beta-receptor agonist and antagonist

An experimental model for the study of placental tissue release of hormones has been explored. It has been shown that the trophoblast in Ringer-glucose solution releases human placental lactogen (hPL) and chorionic gonadotropin (hCG) in a time- (10 to 180 minutes) and temperature- (4 degrees and 37 degrees C) dependent manner. The adrenergic beta-receptor agonist terbutaline caused an increase in hCG secretion but did not affect hPL. With a mixed trophoblast/decidua preparation, prolactin release was not found to be time and temperature related. Terbutaline increased prolactin release and timolol decreased it. The data suggest tha adrenergic mechanisms are involved in hCG and prolactin secretion from the placenta.

Serum prolactin levels and immunohistochemical localization of prolactin in trophoblastic disease

The circulating levels of chorionic gonadotropin, pregnancy specific beta-I-glycoprotein, prolactin and oestradiol were estimated by radioimmunoassay in 219 serum samples from 18 patients with choriocarcinoma and 45 samples from 8 patients with hydatidiform mole. Prolactin and oestradiol concentrations were higher in samples which also contained trophoblastic markers. This difference was also seen in patients with choriocarcinoma and it was not due to chemotherapy, since the difference between hCG positive and hCG negative samples was maintained during chemotherapy. Prolactin was found by immunoperoxidase technique in the syncytiotrophoblast of normal placenta throughout gestation, and also in hydatidiform mole, invasive mole and choriocarcinoma. It is suggested that the malignant syncytiotrophoblast may contribute to circulating prolactin levels either by direct secretion of prolactin or by oestrogen stimulation of the pituitary.