Cells of the metrial gland: their relation to trophoblast cells and reproductive characteristics

Data on the origin, morphology and function of metrial gland cells are reviewed. Characteristic features of metrial gland cells are the availability of numerous eosinophilic granules lying near two round or oval nuclei and peripheral zone of the cytoplasm, generally devoid of organelles. This zone can generate pseudopodia-like projections. The notable peculiarity of metrial gland cells involves their ability to penetrate into blood vessels, to migrate towards the embryo, and to achieve the ectoplacental cone. The majority of metrial gland cells is accumulated in the decidua basalis zone where the tertiary trophoblast cells usually migrate. The metrial gland cells seem to constitute a cell population analogous to that of decidual cells. Data on the protective role of metrial gland cells are discussed. The metrial gland cells are proven to be polyploid. Polyploid nuclei are found both in mononucleate and binucleate cells. Acytokinetic mitosis is presumably a way leading to polyploidization of metrial gland cells.     

The differentiation of the decidua and the distribution of metrial gland cells in the pregnant mouse uterus

Summary A study was made with the light microscope of the cellular changes involved in the formation of the decidua in the pregnant mouse uterus up to day 11 of pregnancy. The differentiation sequence was similar to that found by previous workers but the morphology and development of the basal zone is described in more detail. In addition, the morphology of glycogen rich cells in an area termed the lateral decidual zone is described. The distribution of granulated metrial gland cells and their precursors is described. These cells are first found in the uterine stroma before the blastocyst has implanted. Later they occur in the decidua and in the circular smooth muscle zone beneath the mesometrial triangle prior to the formation of the metrial gland. Granulated metrial gland cells are also found in the maternal blood spaces of the implantation site.     

Glycogen-containing cells in the maternal and embryonic portions of the placenta in the rat and the common vole Microtus subarvalis

Differentiation sequences and further transfiguration of glycogen-rich cells during placenta development were investigated for the rat and field vole Microtus subarvalis (11-20 day gestation). The presence of glycogen is a characteristic feature of decidual cells located in the region of lateral sinusoids, as well as of metrial gland cells, secondary giant trophoblast cells and trophoblast cells in the connective zone of placenta. Glycogen-containing metrial gland cells and trophoblast cells of connective zone of placenta are found to underlie the layer of tertiary giant trophoblast cells that cover the wall of the central arteria. Thus, both maternal and embryo-derived glycogen-containing cells always accompany the tertiary giant trophoblast cells that penetrate deeply into the maternal part of placenta but do not contain glycogen. In the field vole placenta the cells of peripheral trophoblast subpopulation of the connective zone of placenta attaching to the decidua basalis are stained by PAS-reaction more intensely than deeply situated ones. These data, as well as other phenomena revealed here, show that maternal and trophoblastic cells attaching to each other in placenta contain, as a rule glycogen. Glycogen cells in rat placenta and trophoblast cells of peripheral subpopulation of connective zone of placenta are similar in many respects. In this connection, a possible protective role of glycogen-containing cells, that probably favour the co-existence of maternal and embryo-derived cells in placenta, is discussed.     

In situ localization and characterization of bone marrow-derived cells in the decidua of normal murine pregnancy.

The study reported here was designed to examine the in situ distribution and characteristics of hemopoietically derived decidual cells during normal pregnancy in mice prenatally reconstituted with bone marrow cells carrying a transgenic marker. Bone marrow cells from a transgenic CD-1 strain (CD-1 beta; carrying 1000 copies of beta-globin genes in tandem) were injected into the yolk sac of Day 17 conventional CD-1 embryos. The pregnant females were allowed to deliver normally, and the female offspring raised to puberty were mated with CD-1 males and then killed on Day 12 of gestation. The extent of chimerism in sections of their spleens, uteri, and other organs was evaluated by in situ hybridization of the sections with a biotinylated cDNA probe specific for the beta-globin genes followed by avidin-biotin-peroxidase staining. Tissue controls were provided by CD-1 beta and CD-1 mice, respectively. Tissues were also processed without the application of the probe or with the application of biotinylated lambda DNA as specificity controls. Reconstituted mice exhibited variable degrees of hemopoietic chimerism as indicated by labeling of their splenic lymphocytes (18-54%; mean 42%) as well as hemopoietic cells in other organs. Variable cellular labeling was also noted in their decidua basalis and metrial glands. Labeled cells in these tissues were identified as typical decidual cells, macrophages, and granulated metrial gland (GMG) cells. Labeling of typical decidual cells varied extensively among implantation sites in the same chimera, the average labeling ranging from 17% to 33% (mean 24%) in various chimeras. Labeling was also noted in GMG cells, lymphocytes, and some decidual cells migrating out of metrial gland explants after 24-h culture. The non-pregnant uterus of a chimeric mouse revealed significant labeling of endometrial stromal cells indicative of their hemopoietic origin. These results revealed a hemopoietic origin of certain typical decidual cells and GMG cells identified in situ during normal murine pregnancy and a hemopoietic origin of certain endometrial stromal cells that may represent precursors of decidual cells. The precise timing of the predecidual stem cell migration from the bone marrow to the uterus remains to be defined.     

Immunosuppressor activity of rat endometrial granulated cells and their differentiation

Natural killer and natural suppressor activities of the rat endometrial granulated cells were assayed on day 13 of pregnancy or pseudopregnancy. Metrial gland granulated cells were used as endometrial granulated cells. The natural killer activities of metrial gland granulated cells and other cells were determined by means of Hashimoto-Sudo test with K562 cells as targets. The estimation of natural killer activity included removal of the cells sticking to glass from a suspension of material gland granulated cells. Cytochemically, metrial gland granulated cells were identified by the presence of PAS-positive granules in the cytoplasm after treatment of the cells with diastase and identification of a specific antigen with the help of specific antisera. The natural killer activity of metrial gland granulated cells was twice weaker than that of splenocytes from the same pregnant or pseudopregnant females. The level of natural killer activity was proportional to the content of metrial gland granulated cells in a cell system. These data suggest that the natural killer activity of metrial gland granulated cells is realized via their contact with cell targets. Natural killer and suppressor activities were determined simultaneously for metrial gland granulated cells and splenocytes of the same rat with common cell targets. When estimating the nuclear suppressor activity of metrial gland granulated cells, the splenocytes of the same rat were used as an effector in a natural killer test. Various amounts of metrial gland granulated cells were added to the effector : target system at a ratio of 50:1. The natural suppressor activity of metrial gland granulated cells did not depend on the amount of metrial gland granulated cells present in a natural killer system. After fractionation in a Percoll gradient, the highest natural killer activity was recorded in a 30% Percoll fraction. The highest and lowest natural suppressor activities were recorded in 30% and 60% Percoll fractions, respectively. The culture medium was characterized by natural suppressor activity as well. The differences in mean areas of metrial gland granulated cells in 30 and 60% Percoll fractions between the pregnant (144.7 +/- 13.4 and 75.0 +/- 12.5 microm2, respectively) and pseudopregnant (97.5 +/- 4.9 and 69.2 +/- 3.5 microm2) females were reliable. The natural killer activity was estimated in all studied 23 samples of metrial gland granulated cells, among which 18 (79.6 +/- 7.8%) displayed the natural suppressor activity as well. The absence of natural suppressor activity in five samples was combined with the absence of this activity in their culture medium and with a reduction in the mean area of metrial gland granulated cells in 30% Percoll fraction to 109.1 +/- 5.2 microm2. The data obtained confirm the known data on a low activity of metrial gland granulated cells and demonstrated for the first time the natural suppressor activity of these cells. It was concluded that the natural suppressor activity of metrial gland granulated cells is due to their differentiation from metrial gland granulated cells with natural killer activity.     

Decidualisation: origin and role of associated cells

Proliferation of peri- and subluminal stroma following a stimulus from the blastocyst leads to the appearance of decidual cells in the mammalian endometrium. Decidualisation can also be elicited by artificial stimuli in pseudopregnant animals. A variety of histophysiological reactions accompany decidualisation and distinct morphological features characterize decidual cells localized in the antimesometrial and mesometrial area. Granulated metrial gland cells, arising in the endometrium of decidualising uterus, form a separate class of cells and become prominent in the mesometrial triangle as pregnancy advances. This review deals with factors related to induction of decidualisation; structural characteristics of decidual and metrial gland cells; the origin and postulated roles of decidualisation-associated cells. The functional role of decidual and metrial gland cells is discussed in relation to their structural complexity and recent observations on the haemopoietic origin of these cells.     

The structure and differentiation of granulated metrial gland cells of the pregnant mouse uterus

Summary A study was made with the light and electron microscopes of the granulated metrial gland cells of the decidua basalis of the pregnant mouse uterus, up to day 11 of pregnancy. The granulated metrial gland cells are large, up to 50 in diameter, mono- or binucleate and the glycogen rich cytoplasm typically contains many large glycoprotein granules which may be up to 5 in diameter. Morphological evidence is described in support of a lymphocyte-like cell being the precursor to the granulated metrial gland cell. This differentiation sequence is similar to that already proposed in the rat but differences between the ultrastructure of the mature metrial gland cells of rats and mice were noted.     

Immunosuppressor activity of rat endometrial granulated cells and their differentiation

Natural killer and natural suppressor activities of the rat endometrial granulated cells were assayed on days 13 and 14 of pregnancy or pseudopregnancy. Metrial gland granulated cells were used as endometrial granulated cells. The natural killer activities of metrial gland granulated cells and other cells were determined by means of Hashimoto-Sudo test with K562 cells as targets. The estimation of natural killer activity included removal of the cells sticking to glass from a suspension of material gland granulated cells. Cytochemically, metrial gland granulated cells were identified by the presence of PAS-positive granules in the cytoplasm after treatment of the cells with diastase and identification of a specific antigen with the help of specific antisera. The natural killer activity of metrial gland granulated cells was twice weaker than that of splenocytes from the same pregnant or pseudopregnant females. The level of natural killer activity was proportional to the content of metrial gland granulated cells in a cell system. These data suggest that the natural killer activity of metrial gland granulated cells is realized via their contact with cell targets. Natural killer and suppressor activities were determined simultaneously for metrial gland granulated cells and splenocytes of the same rat with common cell targets. When estimating the natural suppressor activity of metrial gland granulated cells, the splenocytes of the same rat were used as an effector in a natural killer test. Various amounts of metrial gland granulated cells were added to the effector: target system at a ratio of 50 : 1. The natural suppressor activity of metrial gland granulated cells did not depend on the amount of metrial gland granulated cells present in a natural killer system. After fractionation in a Percoll gradient, the highest natural killer activity was recorded in a 60% Percoll fraction. The highest and lowest natural suppressor activities were recorded in 30% and 60% Percoll fractions, respectively. The culture medium was characterized by natural suppressor activity as well. The differences in mean areas of metrial gland granulated cells in 30 and 60% Percoll fractions between the pregnant (144.7 ± 13.4 and 75.0 ± 12.5 µm², respectively) and pseudopregnant (97.5 ± 4.9 and 69.2 ± 3.5 µm², respectively) females were reliable. The natural killer activity was estimated in all studied 23 samples of metrial gland granulated cells, among which 18 (79.6 ± 7.8%) displayed the natural suppressor activity as well. The absence of natural suppressor activity in five samples was combined with the absence of this activity in their culture medium and with a reduction in the mean area of metrial gland granulated cells in 30% Percoll fraction to 109 ± 5 µm². The data obtained confirm the known data on a low killer activity of metrial gland granulated cells and demonstrated for the first time the natural suppressor activity of these cells. It was concluded that the natural suppressor activity of metrial gland granulated cells is due to their differentiation from metrial gland granulated cells with natural killer activity.Translated from Ontogenez, Vol. 36, No. 1, 2005, pp. 26–34.Original Russian Text Copyright © 2005 by Podporina, Mikhailov.     

Time course of the differentiation of granulated metrial gland cells in chimeric mice

Granulated metrial gland (GMG) cell differentiation was examined in deciduomata in lethally irradiated mice which had been reconstituted with rat bone marrow. The time at which the bone marrow reconstitution was carried out was varied in relation to the time of initiating the decidual reaction. GMG cells were examined at various times after bone marrow transplantation to determine whether they had the morphology which characterised them as being derived from host or donor stem cells. Differentiation of donor type GMG cells was seen within the first week after transplantation and occurred even when the bone marrow was transplanted two days after initiating the decidual response.     

Characterization of murine decidual natural killer (NK) cells and their relevance to the success of pregnancy

The identification of lytic cells in 6.5-day to 9.5-day murine decidua as NK cells has been extended. The cells with natural killer (NK) activity in early decidua were nonphagocytic and heterogeneous in size as assessed by velocity sedimentation at unit gravity. The numbers of lytic cells were reduced by treatment with anti-asialo GM1 in vivo and they were absent from the decidua of bg/bg mice. Thus, decidual NK cells were not distinct from NK cells in other tissues. The decline in the levels of decidual NK activity as pregnancy progressed was attributed to their regulation by other cells present in decidua by midgestation. The development of NK activity in decidua was dependent upon the presence of an embryo, however, decidual NK cells were not essential for successful pregnancy because viable offspring were obtained from mice lacking decidual NK activity. It was shown that NK cells from either spleen or decidua were unlikely to cause damage to embryos during the first half of pregnancy as freshly dissociated 9.5- and 11.5-day embryonic cells resisted NK lysis. Furthermore, blastocysts were not damaged by coincubation with splenic or decidual NK cells and were viable upon subsequent embryo transfer. These studies indicate that decidual NK cells are not essential for successful pregnancy and are not necessarily detrimental to early embryos. It is suggested that decidual NK cells may play other nonimmunological roles during embryonic development.     

孕酮对人早孕子宫蜕膜细胞活性肾素分泌的调节

子宫蜕膜是肾素产生的主要部位,肾素包括活性与非活性肾素,活性肾素可使血管紧张素原水解生成血管紧张素Ⅰ,继而调节血管紧张素Ⅱ的表达。实验表明：（１）妊娠早期（孕５～９周）,人子宫蜕膜活性肾素的含量随妊娠周龄增加而升高,孕８周时可达６３３７±１２８４ＡⅠｎｇ／ｇｗｗ·ｈ－１;（２）早孕子宫蜕膜组织活性肾素占总肾素量的１／４;（３）孕酮可调节蜕膜细胞活性肾素的合成与分泌。人早孕子宫蜕膜组织中存在高水平的活性肾素,性类固醇激素可调节蜕膜细胞活性肾素的表达,可以认为,子宫局部肾素血管紧张素系统在妊娠过程中发挥了重要作用。     

Synergistic induction of apoptosis in primary rat decidual cells by INF-gamma and TNF

In the rat, in response to blastocyst implantation, stromal cells of the endometrium proliferate and differentiate into decidual cells, forming the decidua. After reaching its maximum development, the decidua undergoes regression. This phenomenon appears to be due to an active process involving apoptosis. As there is sparse knowledge concerning the mechanisms of induction of decidual cell death, the potential role of cytokines present in the uterine environment during pregnancy, such as tumor necrosis factor (TNF) and interferon-gamma (INF-gamma) was explored in primary cultures of rat decidual cells. The effects of these factors upon cellular viability, nuclear morphologic alterations, expression, and enzymatic activities of the effector caspases-3/7 were evaluated. The results obtained demonstrated that in contrast to TNF, which did not induce any alteration, INF-gamma and in association with TNF caused a decrease in cell viability and an increase in the appearance of apoptotic bodies in a time-dependent manner that was augmented in the co-presence of TNF. An increase in caspase-3/7 activities after 12 hr of TNF/INF-gamma treatment was also observed. These findings suggest that INF-gamma expressed in the uterine environment may play an important role in regulating apoptosis through potential synergistic mechanisms with TNF and thereby modulate decidual stability and regression during pregnancy.     

Expression of mRNA encoding insulin‐like growth factors I and II by uterine tissues and placenta during pregnancy in the rat

The uterus and the placenta synthesize insulin‐like growth factors (IGFs) and insulin‐like binding proteins (IGFBPs). These growth factors are implicated in processes of proliferation and differentiation that occur in the uterus. To determine the patterns of expression of IGFs during rat pregnancy we used in situ hybridization with digoxigenin labeled probes on uterus from day 7 to day 16 of pregnancy. In early gestation days (7–8) both IGF mRNAs showed similar tissue distribution with relative abundance in the stroma and circular muscle layer. On days 11 and 12 expression for IGF‐I mRNA was found in the mesometrial decidua and metrial gland and in the ectoplacental cone while clear expression of IGF‐II mRNA could only be found in the latter. On days 13 and 14, expression for IGF‐I mRNA could be detected in the mesometrial decidua and metrial gland but no expression was observed for IGF‐II mRNA. A gradient of IGF‐I mRNA expression could be observed in the placenta on day 16, with the trophoblastic cells of the basal zone expressing the signal with stronger intensity than in the labyrinthine zone. For IGF‐II mRNA the highest expression was associated with the labyrinthine zone. Endovascular trophoblast was positive for both mRNAs. The spatial and temporal patterns of expression suggests a role for IGFs in the process of decidualization as well as in the establishment, growth and differentiation of the various trophoblast cells of the placenta. Mol. Reprod. Dev. 53:294–305, 1999. © 1999 Wiley‐Liss, Inc.     

Acetylesterase isoenzymes in rat uterus and placenta

The occurrence of acetylesterase activity in the uterus and placenta of the rat has been investigated using a general histochemical simultaneous coupling technique after separation on polyacrylamide gradient gels. apart from a complex band associated with serum esterases which was demonstrated in all the tissues studied, several other isoenzyme bands were demonstrable in differing degrees in the yolk sac and the virgin uterus. Two of these bands were evident in metrial gland up to day 16 of pregnancy, and a third became present by day 17. Unlike the other two bands, this new band did not seem to be associated with the large granules of the granulated metrial gland cells. None of these bands were detected in trophoblast. The metrial gland isoenzymes reacted as well at acid pH as at neutral pH. The yolk sac isoenzymes reacted either as well or slightly better at acid pH, and one extra band was demonstrable under acid conditions.     

Murine granulated metrial gland cells at uterine implantation sites are natural killer lineage cells

Granulated metrial gland (GMG) cells, a population of morphologically distinct, bone marrow-derived cells in murine decidua that react with mAb 4H12, are shown in this report to express NK-specific Ag and to become cytolytic to the NK cell target YAC-1 when cultured in the lymphokine IL-2. When 1-mm3 explants of 8-day decidual tissue were cultured with IL-2, large numbers of 4H12+ GMG cells migrated out of the tissue. Migration was dependent on the amount of IL-2 used. This explant technique was used to isolate a pure population of GMG cells. The migratory activated GMG cells were phenotypically 4H12+, NK1.1+, LGL-1+/-, CD3-, and MAC-1-. Furthermore, the IL-2-activated GMG cells killed YAC-1 but not P815 cells in a 4-h 51Cr-release cytotoxicity assay. 4H12+ GMG cells from collagenase-digested decidual tissue also were analyzed for the presence of NK lineage Ag by flow cytometry and shown to coexpress the NK-associated Ag NK1.1 and ASGM1 but not the T cell Ag CD3 or macrophage Ag MAC-1 or F4/80. GMG cells isolated by collagenase digestion did not express LGL-1, an Ag associated with lytic NK cells. Our results demonstrate that GMG cells express Ag and functions characteristic of NK cells, and thus GMG cells can be assigned to the NK lineage. The possible relevance of NK cells at implantation sites is discussed.     

Expression of vascular endothelial growth factor by granulated metrial gland cells in pregnant murine uteri

Granulated metrial gland (GMG) cells are a characteristic uterine component belonging to a natural killer cell lineage. This study is aimed at revealing their kinetic and spatial relationship with vascular growth during pregnancy and the expression of vascular endothelial growth factor (VEGF). GMG cells and blood vessels were identified by periodic-acid-Schiff-reagent (PAS)-stained granules and positive staining for factor-VIII-related antigen, respectively. GMG cells were widely distributed in the decidua and metrial gland and showed a numerical increase with a peak at day 13 in parallel with the increase of vascular density. Preceding the maximal vascular development at day 13, microvessels with a narrow lumen representative of neovascularization prevailed at days 7-9, and the VEGF content in the decidua/metrial gland was significantly elevated at days 7-13 concurrently with mRNA expression. By immunolight microscopy combined with PAS staining, GMG cells with PAS-stained granules were positive for VEGF. Immunoelectron microscopy demonstrated that immunoreactions were diffuse in the cytoplasm but not localized in the granules. In contrast, fibroblast-like stromal cells were negative. These data indicate that GMG cells express VEGF and may play inducing roles in uterine neovascularization during pregnancy.     

Developmental expression of adenosine deaminase in placental tissues of the early postimplantation mouse embryo and uterine stroma

In this study, we have investigated the distribution of adenosine deaminase (ADA) in embryonic, extra-embryonic, and decidual tissues of the developing mouse embryo. ADA catalyzes a key step in purine metabolism converting adenosine to inosine. ADA specific activity (nmol/min/micrograms protein) was present at low levels in the embryo-decidual unit during the first 2 days of postimplantation development but then increased starting late on Day 6 of gestation (Day 0 plug). By Day 9, ADA specific activity was 80-fold higher than on Day 6. A histochemical staining method for ADA activity was applied to cryostat sections of the implantation site. The developmental increase localized primarily to the trophoblast/antimesometrial decidua interface between Days 7 and 9 of gestation, and decidua basalis and the metrial gland by Day 11. Immunofluorescent staining with sheep anti-mouse ADA antiserum confirmed the presence of ADA antigenicity in tissues forming the maternal/fetal interface. ADA specific activity was 19-fold higher in homogenates of the Day 11 decidua/parietal yolk sac than in the thymus, a tissue generally thought of as ADA-rich. High levels of ADA activity and immunoreactivity were also detected in the embryonal plasma during organogenesis, but the embryo proper showed only low levels. These results indicate that ADA is tightly regulated within tissues forming the maternal/fetal interface during early postimplantation stages of development.     

Specificity of purified monoacylglycerol lipase, palmitoyl-CoA hydrolase, palmitoyl-carnitine hydrolase, and nonspecific carboxylesterase from rat liver microsomes

The comparative substrate specificities of five purified serine hydrolases from rat liver microsomes have been investigated, especially their action upon natural lipoids. All enzymes had high carboxylesterase activities with simple aliphatic and aromatic esters and thioesters. The broad pH optima were in the range of pH 6-10. Synthetic amides were less potent substrates. The hydrolytic activities towards palmitoyl-CoA and monoacyl glycerols were generally high, whereas phospholipids and palmitoyl carnitine were cleaved at moderate rates. Acetyl-CoA, acetyl carnitine, and ceramides were not cleaved at all. The closely related hydrolases with the highest isoelectric points (pI 6.2 and 6.4) were most active with palmitoyl-CoA and palmitoyl glycerol. One of these enzymes might also be responsible for the low cholesterol oleate-hydrolyzing capacity of rat liver microsomes. Among the other hydrolases, that with pI 6.0 showed significant activities with simple butyric acid esters, 1-octanoyl glycerol, and octanoylamide. The esterase with pI 5.6 had the relatively highest activities with palmitoyl carnitine and lysophospholipids. The purified enzyme with pI 5.2 showed some features of the esterase pI 5.6, but generally had lower specific activities, except with 4-nitrophenyl acetate. The lipoid substrates competitively inhibited the arylesterase activity of the enzymes. The varying activities of the individual hydrolases were influenced in parallel by a variety of inhibitors, indicating that the purified hydrolases possessed a relatively broad specificity and were not mixtures of more specific enzymes. The nomenclature of the purified hydrolases is discussed.