Tissue transglutaminase at embryo-maternal interface

Hypoxia and inflammation conditions differentially affect the expression of tissue transglutaminase spliced variants and functional properties of extravillous trophoblast cells

PROBLEM

Persistent hypoxia and inflammation beyond early pregnancy are involved in a bad outcome because of defective trophoblast invasiveness. Tissue transglutaminase (TG2) coregulates several cell functions. An aberrant expression and/or transamidation activity could contribute to placental dysfunction.

METHOD OF STUDY

The first-trimester trophoblast cell line (Swan-71) was used to study TG2 expression and cell functions in the absence or presence of inflammatory cytokines (TNF-α, IL-1β) or chemical hypoxia (CoCl₂ ). We analyzed The concentration of cytokines in the supernatant by ELISA; Cell migration by scratch assay; NF-κB activation by detection of nuclear p65 by immunofluorescence or flow cytometry using a Swan-71 NF-κB-hrGFP reporter cell line. Tissue transglutaminase expression was analyzed by immunoblot and confocal microscopy. Expression of spliced mRNA variants of tissue transglutaminase was analyzed by RT-PCR. Transamidation activity was assessed by flow cytometry using 5-(biotinamido)-pentylamine substrate.

RESULTS

Chemical hypoxia and TGase inhibition, but not inflammatory stimuli, decreased Swan-71 migration. IL-6 production was also decreased by chemical hypoxia, but increased by inflammation. Intracellular TGase activity was increased by all stimuli, but NF-κB activation was observed only in the presence of proinflammatory cytokines. TG2 expression was decreased by CoCl₂ and TNF-α. Translocation of TG2 and p65 to nuclei was observed only with TNF-α, without colocalization. Differential relative expression of spliced variants of mRNA was observed between CoCl₂ and inflammatory stimuli.

CONCLUSION

The observed decrease in total TG2 expression and relative increase in short variants under hypoxia conditions could contribute to impaired trophoblast invasion and impact on pregnancy outcome.

Tissue Transglutaminase Impairs HTR-8/SVneo Trophoblast Cell Invasion via the PI3K/AKT Signaling Pathway

OBJECTIVES

The pathogenesis of preeclampsia (PE) is associated with impaired trophoblast invasion, which results in placental insufficiency. Our earlier studies demonstrated that tissue transglutaminase (tTG) is highly expressed in human PE serum. However, whether tTG participates in trophoblast invasion remains unclear. The aim of the present study was to determine the role and mechanism of tTG in regulating matrix metalloproteinase (MMP)-2/MMP-9 expression to reduce trophoblast invasiveness in PE.

METHODS

HTR-8/SVneo cells were transfected with a lentivirus vector and small interfering RNA targeting tTG. The protein level was detected by Western blotting. Cell proliferation and apoptosis were assessed by MTS and flow cytometry assays, respectively. Cell invasion was investigated by Transwell assay. In addition, the influence of tTG on PI3K and AKT mRNA levels in HTR-8/SVneo cells was evaluated using reverse transcription-quantitative PCR.

RESULTS

tTG-overexpression inhibited HTR-8/SVneo cell proliferation and invasion and promoted apoptosis. In addition, upregulation of tTG induced an increase of PI3K and phosphorylated AKT and a decrease of MMP-2 and MMP-9 expression. tTG-knockdown significantly promoted the proliferation and invasion of HTR-8/SVneo cells and inhibited the apoptosis. Furthermore, the PI3K expression level was reduced, and the MMP-2/MMP-9 protein levels were increased.

CONCLUSION

Taken together, the present study demonstrated that tTG-overexpression inhibited HTR-8/SVneo cell invasion via reducing the expression of MMP-2 and MMP-9 by activating PI3K/AKT signaling pathway, which may lead to the occurrence or development of PE. The present data provide new insights into modulation of tTG expression as a potential therapeutic target for PE.

Proteomic sift through serum and endometrium profiles unraveled signature proteins associated with subdued fertility and dampened endometrial receptivity in women with polycystic ovary syndrome

The objective of this study is to discern the proteomic differences responsible for hampering the receptivity of endometrium and subduing the fertility of females with polycystic ovary syndrome in analogy to healthy fertile females. This study was designed in collaboration with Hakeem Abdul Hameed Centenary Hospital affiliated to Jamia Hamdard, New Delhi, India. Serum samples were taken from infertile PCOS subjects (n = 6) and fertile control subjects (n = 6) whereas endometrial tissue samples were recruited from ovulatory PCOS (n = 4), anovulatory PCOS (n = 4) and normal healthy fertile control subjects (n = 4) for proteomic studies. Additionally, endometrial biopsies from healthy fertile control (n = 8), PCOS with infertility (n = 6), unexplained infertility (n = 3) and endometrial hyperplasia (n = 3) were taken for validation studies. Anthropometric, biochemical and hormonal evaluation was done for all the subjects enrolled in this study. Protein profiles were generated through 2D-PAGE and differential proteins analyzed with PD-QUEST software followed by identification with MALDI-TOF MS protein mass fingerprinting. Validation of identified proteins was done through RT-PCR relative expression analysis. Protein profiling of serum revealed differential expression of proteins involved in transcriptional regulation, embryogenesis, DNA repair, decidual cell ploidy, immunomodulation, intracellular trafficking and degradation processes. Proteins involved in cell cycle regulation, cellular transport and signaling, DNA repair, apoptotic processes and mitochondrial metabolism were found to be differentially expressed in endometrium. The findings of this study revealed proteins that hold strong candidature as potential drug targets to regulate the cellular processes implicating infertility and reduced receptivity of endometrium in women with polycystic ovary syndrome.

Transglutaminase Activity Determines Nuclear Localization of Serotonin Immunoreactivity in the Early Embryos of Invertebrates and Vertebrates

Serotonin (5-HT) is a key player in many physiological processes in both the adult organism and developing embryo. One of the mechanisms for 5-HT-mediated effects is covalent binding of 5-HT to the target proteins catalyzed by transglutaminases (serotonylation). Despite the implication in a variety of physiological processes, the involvement of serotonylation in embryonic development remains unclear. Here we tested the hypothesis that 5-HT serves as a substrate for transglutaminase-mediated transamidation of the nuclear proteins in the early embryos of both vertebrates and invertebrates. For this, we demonstrated that the level of serotonin immunoreactivity (5-HT-ir) in cell nuclei increases upon the elevation of 5-HT concentration in embryos of sea urchins, mollusks, and teleost fish. Consistently, pharmacological inhibition of transglutaminase activity resulted in the reduction of both brightness and nuclear localization of anti-5-HT staining. We identified specific and bright 5-HT-ir within nuclei attributed to a subset of different cell types: ectodermal and endodermal, macro- and micromeres, and blastoderm. Western blot and dot blot confirmed the presence of 5-HT-ir epitopes in the normal embryos of all the species examined. The experimental elevation of 5-HT level led to the enhancement of 5-HT-ir-related signal on blots in a species-specific manner. The obtained results demonstrate that 5-HT is involved in transglutaminase-dependent monoaminylation of nuclear proteins and suggest nuclear serotonylation as a possible regulatory mechanism during early embryonic development. The results reveal that this pathway is conserved in the development of both vertebrates and invertebrates.

Magnetic Resonance Imaging Reveals Distinct Roles for Tissue Transglutaminase and Factor XIII in Maternal Angiogenesis During Early Mouse Pregnancy

OBJECTIVE

The early embryo implantation is characterized by enhanced uterine vascular permeability at the site of blastocyst attachment, followed by extracellular-matrix remodeling and angiogenesis. Two TG (transglutaminase) isoenzymes, TG2 (tissue TG) and FXIII (factor XIII), catalyze covalent cross-linking of the extracellular-matrix. However, their specific role during embryo implantation is not fully understood. Approach and Results: For mapping the distribution as well as the enzymatic activities of TG2 and FXIII towards blood-borne and resident extracellular-matrix substrates, we synthetized selective and specific low molecular weight substrate analogs for each of the isoenzymes. The implantation sites were challenged by genetically modifying the trophoblast cells in the outer layer of blastocysts, to either overexpress or deplete TG2 or FXIII, and the angiogenic response was studied by dynamic contrast-enhanced-magnetic resonance imaging. Dynamic contrast-enhanced-magnetic resonance imaging revealed a decrease in the permeability of decidual vasculature surrounding embryos in which FXIII were overexpressed in trophoblast cell. Reduction in decidual blood volume fraction was demonstrated when either FXIII or TG2 were overexpressed in embryonic trophoblast cell and was elevated when trophoblast cell was depleted of FXIII. These results were corroborated by histological analysis.

CONCLUSIONS

In this study, we report on the isoenzyme-specific roles of TG2 and FXIII during the early days of mouse pregnancy and further reveal their involvement in decidual angiogenesis. Our results reveal an important magnetic resonance imaging-detectable function of embryo-derived TG2 and FXIII on regulating maternal angiogenesis during embryo implantation in mice.Visual Overview: An online visual overview is available for this article.

Effects of dietary quercetin on female fertility in mice: implication of transglutaminase 2

Use of the dietary supplement quercetin is on the rise. Because previous studies imply an inhibitory effect of quercetin on male fertility, we explored the effects of this flavonoid on fertility in female mice. Birth outcomes, and ovarian morphology in 4-week-old offspring, were assessed in mice receiving dietary quercetin (5mgkg^-1day^-1) for 9 months during two breeding periods: from 2 to 6 months (prime reproductive age) and 8 to11 months of age. Quercetin increased birth spacing, leading to a 60% reduction in the number of litters, but enhanced folliculogenesis in ovaries of female offspring. While in young females quercetin caused an almost 70% increase in litter size, in older animals this effect was reversed. Consistent with the inhibitory activity of quercetin on the enzyme transglutaminase 2 (TG2), genetic ablation of TG2 in mice mirrors the effects of quercetin on birth outcomes and follicular development. Further, TG2-null mice lack responsiveness to quercetin ingestion. Our study shows for the first time that dietary quercetin can cause reduced reproductive potential in female mice and implies that TG2 may regulate ovarian ageing.

Potential roles of metalloproteinases of endometrium-derived exosomes in embryo-maternal crosstalk during implantation

During embryo implantation, crosstalk between the endometrial epithelium and the blastocyst, especially the trophoblasts, is a prerequisite for successful implantation. During this crosstalk, various molecular and functional changes occur to promote synchrony between the embryo and the endometrium as well as the uterine cavity microenvironment. In the past few years, growing evidence has shown that endometrium-derived exosomes play pivotal roles in the embryonic-maternal crosstalk during implantation, although the exact mechanism of this crosstalk has yet to be determined. The presence of metalloproteinases has been reported in endometrium-derived exosomes, implying the importance of these enzymes in exosome-based crosstalk. Thus, in this review, we describe the potential roles of the metalloproteinases of endometrium-derived exosomes in promoting embryo attachment and implantation. This study could provide a better understanding of the potential roles of exosomal metalloproteinases in embryo implantation and pave the way for developing novel exosome-based regulatory agents to support early pregnancy.

Biological functionalities of transglutaminase 2 and the possibility of its compensation by other members of the transglutaminase family

Transglutaminase 2 (TG2) is the most widely distributed and most abundantly expressed member of the transglutaminase family of enzymes, a group of intracellular and extracellular proteins that catalyze the Ca²⁺-dependent posttranslational modification of proteins. It is a unique member of the transglutaminase family owing to its specialized biochemical, structural and functional elements, ubiquitous tissue distribution and subcellular localization, and substrate specificity. The broad substrate specificity of TG2 and its flexible interaction with numerous other gene products may account for its multiple biological functions. In addition to the classic Ca²⁺-dependent transamidation of proteins, which is a hallmark of transglutaminase enzymes, additional Ca²⁺-independent enzymatic and nonenzymatic activities of TG2 have been identified. Many such activities have been directly or indirectly implicated in diverse cellular physiological events, including cell growth and differentiation, cell adhesion and morphology, extracellular matrix stabilization, wound healing, cellular development, receptor-mediated endocytosis, apoptosis, and disease pathology. Given the wide range of activities of the transglutaminase gene family it has been suggested that, in the absence of active versions of TG2, its function could be compensated for by other members of the transglutaminase family. It is in the light of this assertion that we review, herein, TG2 activities and the possibilities and premises for compensation for its absence.

Effect of single post-ovulatory administration of levonorgestrel on gene expression profile during the receptive period of the human endometrium

The hypothesis that levonorgestrel (LNG) used as an emergency contraceptive interferes with endometrial receptivity remains unproven. We compared the endometrial gene expression profile during the receptive period after administering a single dose of LNG 1.5 mg or placebo on day 1 of the luteal phase. An endometrial biopsy was done on day LH+7 or LH+8 and samples were taken from seven volunteers, each one contributing with one cycle treated with placebo and another with LNG. The expression of 20 383 genes was determined using cDNA microarrays. Real-time RT-PCR was used 1) to confirm the differences found in DNA microarray analysis and 2) to determine the effect of LNG on transcript levels of C3, C4BPα, COX2, MAOA, S100A4, and SERPINB9, known to be upregulated during receptivity, and on cPLA2α, JAK1, JNK1, CTSL1, and GSTP1, known to respond to mifepristone. Additional endometrial biopsies were done during the pre-receptive (LH+3) and receptive (LH+7) period and samples were taken from eight untreated volunteers in order to determine the changes associated with acquisition of receptivity of 14 genes. Mean levels of PAEP, TGM2, CLU, IGF2, and IL6ST mRNAs increased after administering LNG while those of HGD, SAT1, EVA1, LOC90133, ANXA1, SLC25A29, CYB5A, CRIP1, and SLC39A14 decreased. Except for the level of ANXA1 transcript, all changes remained within the range observed in untreated controls, and none of the transcripts responding to mifepristone changed in response to LNG. Post-ovulatory administration of LNG caused minimal changes in gene expression profiling during the receptive period. Neither the magnitude nor the nature or direction of the changes endorses the hypothesis that LNG interferes with endometrial receptivity.

Extracellular transglutaminase 2 has a role in cell adhesion, whereas intracellular transglutaminase 2 is involved in regulation of endothelial cell proliferation and apoptosis

OBJECTIVE

Transglutaminase 2 (TG2) is a multifunctional protein with an important role in vascular biology, where it is involved in cell-matrix interaction, cell attachment and cell population expansion. In efforts to elucidate the role of TG2 in endothelial cell biology, in this study, we measured several endothelial cell characteristics in cells where TG2 was specifically knocked down by RNAi.

MATERIALS AND METHODS

The effect of small interfering RNA (siRNA)-TG2 on human umbilical vein endothelial cells was studied. Adhesion and cell viability were assessed by chemical reduction of MTT, and cell proliferation was analysed by flow cytometry. Apoptosis was evaluated by annexin V/PI dual staining and protein expression level was assayed by western blotting.

RESULTS

We found that siRNA-TG2 reduced endothelial cell number, lead to cell adhesion deficiency, cell cycle arrest in G₁ phase and induction of apoptosis. Our results show that exogenously added TG2 could reverse loss of adhesion but did not overcome the defect in cell proliferation, nor could it inhibit siRNA-TG2-induced apoptosis.

CONCLUSION

We conclude that TG2 loss in endothelial cells causes reduction in cell number as a result of cell cycle arrest, flaws in adhesion and induction of apoptosis. Our results imply that reduction in cell number and increased apoptosis in response to TG2 silencing is independent of the cell adhesion process. Altogether, our findings underline the significance of TG2 in endothelial cell cycle progression and cell survival, in vitro.

Polymerization of insulin-like growth factor-binding protein-1 (IGFBP-1) potentiates IGF-I actions in placenta

Insulin-like growth factor (IGF)-binding protein-1 (IGFBP-1), the main secretory protein of decidua that binds to IGFs and has been shown to inhibit or stimulate IGFs' bioactivities. Polymerization, one of the posttranslational modifications of IGFBP-1, has been shown to lead to loss of inhibiting effect of IGFBP-1 on IGF-I actions. The current studies were undertaken to elucidate the effects of steroid hormones on IGFBP-1 polymerization in trophoblast cell cultures. Placental tissues were obtained during legal, elective procedures of termination of pregnancy performed between 7 and 10 weeks of gestation, and primary trophoblast cells were separated. IGFBP-1 polymerization was analyzed by SDS-PAGE and immunoblotting. IGFBP-1 was polymerized when IGFBP-1 was added to trophoblast cell cultures. Polymerization of IGFBP-1 was inhibited by the addition of anti-tissue transglutaminase antibody into the culture media. There was an increase in the intensity of polymerized IGFBP-1 bands with the addition of medroxyprogesterone acetate (MPA), while no such difference was observed upon treatment with estradiol. MPA also increased the expression of tissue transglutaminase on trophoblast cell membranes. IGF-I stimulated trophoblast cell migration, while IGFBP-1 inhibited this IGF-I-induced trophoblast response. Addition of MPA attenuated the inhibitory effects of IGFBP-1 on IGF-I-induced trophoblast cell migration. IGFBP-1 was polymerized by tissue transglutaminase on the cell surface of trophoblasts, and MPA increased tissue transglutaminase expression on the cell surface and facilitated IGFBP-1 polymerization. These results suggest that progesterone might facilitate polymerization of decidua-secreted IGFBP-1 and increase IGF-I actions at feto-maternal interface, thereby stimulating trophoblast invasion of maternal uterus.

Separation of the molecular forms of the insulin-like growth factor (IGF)-Binding proteins by affinity chromatography

Association of IGFBP-1, IGFBP-2 and IGFBP-3 with other proteins in human serum and placental cell membranes was investigated using affinity chromatography matrix with immobilized antibodies. Circulating IGFBP-1 was found to be predominantly bound to alpha(2)-macroglobulin and not in the binary complex with its ligand, IGFBP-2 complexes and/or polymers were detected, which was not acknowledged before, and IGFBP-3 molecular forms were differentiated into those that form binary/ternary complexes and those that form stable associations with other serum proteins. As for placental membranes, both IGFBP-1 dimers and high molecular mass IGFBP-1 associations, most probably with alpha(2)-macroglobulin, were recognized and resolved.

IGFBP-1 forms associated with placental cell membranes

Fetal growth in utero depends on the proper development and function of the placenta. Insulin-like growth factors (IGFs) are critically involved in placental development. During pregnancy, an IGF-binding protein, IGFBP-1, which is produced by maternal decidua, plays an important role in the control of the bioavailability of IGFs. It has recently been proposed that cleavage of decidual IGFBP-1 by matrix metalloproteases is a novel mechanism in the control of placental development. The presence of IGFBP-1 in solubilized placental cell membranes, i.e. its association with the membranes, was detected in an earlier work. Herein, it is shown that IGFBP-1 from the solubilized membranes forms dimers, as well as high molecular mass complexes. IGFBP-1 dimers preferably contain the non-phosphorylated form of IGFBP-1. The high molecular mass forms are polymers of IGFBP-1 or its complexes with other membrane proteins. Dimerization of IGFBP-1, together with its association with the placental cell membrane, could serve as an additional mechanism of the regulation of IGF availability to the type 1 IGF receptors.

The membrane-spanning domain of CD98 heavy chain promotes alpha(v)beta3 integrin signals in human extravillous trophoblasts

CD98 heavy chain (CD98hc) is expressed highly in developing human placental trophoblast. CD98hc is an amino acid transporter and is thought to function in cell fusion, adhesion, and invasion by interacting with integrins. In invasive extravillous trophoblast, alpha(v)beta(3) integrin is expressed in a temporally and spatially specific manner, which prompted us to investigate the potential role of CD98hc in signal transduction of alpha(v)beta(3) integrin. Immunocytochemistry of extravillous trophoblast derived from human placenta revealed that CD98hc colocalized with alpha(v)beta(3) integrin and with alpha(v)beta(3)-associated cytoplasmic proteins including paxillin, vinculin, and focal adhesion kinase. Coimmunoprecipitation of CD98hc and its mutants revealed that the transmembrane domain of CD98hc is necessary for the association of CD98hc with alpha(v)beta(3) integrin. When CD98hc negative liver cells (FLC4) were stably transfected with CD98hc and the extracellular domain of CD98hc was cross-linked by anti-CD98 antibody, FLC4 cells binding affinity to fibronectin and cell motility increased. The anti-CD98 antibody cross-linking promoted actin stress fiber formation and activation of signal transduction downstream of RhoA GTPase, and elevated the phosphorylation of focal adhesion kinase, paxillin, and protein kinase B. Pretreatment of transfected FLC4 cells with specific inhibitors for alpha(v)beta(3)integrin, phosphatidylinositol 3-kinase, and RhoA diminished these effects caused by anti-CD98 antibody cross-linking. These results suggest that notoriously invasive activity of extravillous trophoblast is mediated by CD98hc, which promotes alpha(v)beta(3) integrin-dependent signals.

Secretory role for human uterodomes (pinopods): secretion of LIF

The differentiation of human endometrial epithelium is a dynamic event, which occurs throughout the menstrual cycle in preparation for pregnancy. The appearance of uterodomes (pinopods) in this regard was first introduced in rodents with an established pinocytotic function, whereas little evidence was available in humans in this context. This study was undertaken to identify the potential physiological roles of uterodomes in the implantation process. To address this, endometrial biopsies from early, mid- and late luteal phases of the menstrual cycle of 23 fertile female patients with regular menses were used. Scanning and transmission electron microscopies (SEM and TEM) as well as immunofluorescence and immunogold TEM were performed to study the morphological changes and the expression pattern of leukaemia inhibitory factor (LIF) at uterodomes. Our results illustrated a high level of LIF expression in the human uterodomes, which was colocalized with the well-known biochemical markers of exocytosis, including syntaxin-1, 25-kDa synaptosomal protein (SNAP-25) and vesicle-associated membrane protein-2 (VAMP-2). Our morphological and immunocytochemical findings illustrated a secretory function for human uterodomes for the first time. In conclusion, this novel function for uterodomes provides an important clue in detection of their physiological function(s) during the process of the plasma membrane transformation.