Complex patterns of ADAM12 mRNA and protein splice variants in the human placenta

Role of ADAM and ADAMTS Disintegrin and Metalloproteinases in Normal Pregnancy and Preeclampsia

Normal pregnancy (NP) involves intricate processes starting with egg fertilization, proceeding to embryo implantation, placentation and gestation, and culminating in parturition. These pregnancy-related processes require marked uteroplacental and vascular remodeling by proteolytic enzymes and metalloproteinases. A disintegrin and metalloproteinase (ADAM) and ADAM with thrombospondin motifs (ADAMTS) are members of the zinc-dependent family of proteinases with highly conserved protein structure and sequence homology, which include a pro-domain, and a metalloproteinase, disintegrin and cysteine-rich domain. In NP, ADAMs and ADAMTS regulate sperm-egg fusion, embryo implantation, trophoblast invasion, placental angiogenesis and spiral arteries remodeling through their ectodomain proteolysis of cell surface cytokines, cadherins and growth factors as well as their adhesion with integrins and cell-cell junction proteins. Preeclampsia (PE) is a serious complication of pregnancy characterized by new-onset hypertension (HTN) in pregnancy (HTN-Preg) at or after 20 weeks of gestation, with or without proteinuria. Insufficient trophoblast invasion of the uterine wall, inadequate expansive remodeling of the spiral arteries, reduced uteroplacental perfusion pressure, and placental ischemia/hypoxia are major initiating events in the pathogenesis of PE. Placental ischemia/hypoxia increase the release of reactive oxygen species (ROS), which lead to aberrant expression/activity of certain ADAMs and ADAMTS. In PE, abnormal expression/activity of specific ADAMs and ADAMTS that function as proteolytic sheddases could alter proangiogenic and growth factors, and promote the release of antiangiogenic factors and inflammatory cytokines into the placenta and maternal circulation leading to generalized inflammation, endothelial cell injury and HTN-Preg, renal injury and proteinuria, and further decreases in uteroplacental blood flow, exaggeration of placental ischemia, and consequently fetal growth restriction. Identifying the role of ADAMs and ADAMTS in NP and PE has led to a better understanding of the underlying molecular and vascular pathways, and advanced the potential for novel biomarkers for prediction and early detection, and new approaches for the management of PE.

Role of EZH2-mediated H3K27me3 in placental ADAM12-S expression: implications for fetoplacental growth

BACKGROUND

Enhancer of zeste homolog 2 (EZH2)-mediated histone 3 lysine 27 trimethylation (H3K27me3) is a transcription silencing mark, which is indispensable for cell lineage specification at the early blastocyst stage. This epigenetic repression is maintained in placental cytotrophoblasts but is lifted when cytotrophoblasts differentiate into syncytiotrophoblasts. However, the physiological impact of this lift remains elusive. Here, we investigated whether lifting EZH2-mediated H3K27me3 during syncytialization upregulates the expression of a short secretory isoform of a disintegrin and metalloprotease 12 (ADAM12-S), a well-recognized placenta-derived protease that cleaves insulin-like growth factor binding protein 3 to increase insulin-like growth factor (IGF) bioavailability for the stimulation of fetoplacental growth. The transcription factor and the upstream signal involved were also explored.

METHODS

Human placenta tissue and cultured primary human placental cytotrophoblasts were utilized to investigate the role of EZH2-mediated H3K27me3 in ADAM12-S expression and the associated transcription factor and upstream signal during syncytialization. A mouse model was used to examine whether inhibition of EZH2-mediated H3K27me3 regulates placental ADAM12-S expression and fetoplacental growth.

RESULTS

EZH2 and ADAM12 are distributed primarily in villous cytotrophoblasts and syncytiotrophoblasts, respectively. Increased ADAM12-S expression, decreased EZH2 expression, and decreased EZH2/H3K27me3 enrichment at the ADAM12 promoter were observed during syncytialization. Knock-down of EZH2 further increased ADAM12-S expression in trophoblasts. Syncytialization was also accompanied by increased STAT5B expression and phosphorylation as well as its enrichment at the ADAM12 promoter. Knock-down of STAT5B attenuated ADAM12-S expression during syncytialization. Epidermal growth factor (EGF) was capable of inducing ADAM12-S expression via stimulation of STAT5B expression and phosphorylation during syncytialization. Mouse studies revealed that administration of an EZH2 inhibitor significantly increased ADAM12-S levels in maternal blood and fetoplacental weights along with decreased H3K27me3 abundance and increased ADAM12-S expression in the placenta.

CONCLUSIONS

Lifting EZH2-mediated H3K27me3 increases ADAM12-S expression during syncytialization with the participation of EGF-activated STAT5B, which may lead to elevation of ADAM12-S level in maternal blood resulting in increased IGF bioavailability for the stimulation of fetoplacental growth in pregnancy. Our studies suggest that the role of EZH2-mediated H3K27me3 may switch from cell lineage specification at the early blastocyst stage to regulation of fetoplacental growth in later gestation.

Molecular characteristics of established trophoblast-derived cell lines

INTRODUCTION

Research on human placental development and function lacks a conclusive in vivo model. To investigate the intracellular molecular mechanisms in trophoblast cells, different cell lines have been established during the last decades. So far, none of these accomplishes all features of primary trophoblast, thus their suitability as well as the transferability of the results has been discussed. The aim of this study is to assess molecular markers and features matching different trophoblast subpopulations in trophoblastic cell lines to provide orientation on their suitability and relevance for distinct research questions.

METHODS

The commonly used trophoblastic cell lines, BeWo, JEG-3, HTR-8/SVneo, AC1-M59, AC1-M32, ACH-3P and Swan71 were selected. qPCR and immunoblotting were used to determine expression of characteristic molecular markers. C14MC, C19MC and miR-371-3 miRNA expression were investigated by real time PCR. Proliferation, migration and network stabilization assays were performed. Hormone secretion was determined by chemiluminescent-immunoassays. DNA profiles were obtained by Short Tandem Repeat (STR)-genotyping.

RESULTS

Immortalized cell lines differ from choriocarcinoma-derived ones in the expression of HLA-G, E-cadherin, N-cadherin, VE-cadherin, cadherin-11, cytokeratin 7, vimentin, ADAM12 and PRG2. Compared to choriocarcinoma-derived cell lines, expression of C19MC and hormone secretion were almost absent in immortalized cell lines. Conversely, they express C14MC and exhibit higher migration and network stabilization.

DISCUSSION

The data presented will help justify the use of a cell line to evaluate distinct features of trophoblast biology and pathology. In general, characteristics and markers of choriocarcinoma derived cell lines seem to be more similar to in vivo trophoblast than immortalized cell lines and thus might be regarded as more suitable models.

Identification of ADAM12 as a Novel Basigin Sheddase

The transmembrane glycoprotein basigin, a member of the immunoglobulin superfamily, stimulates matrix metalloproteinase (MMP)-mediated extracellular matrix (ECM) degradation and thereby drives cancer cell invasion. Basigin is proteolytically shed from the cell surface and high concentrations of soluble basigin in the blood dictates poor prognosis in cancer patients. A positive correlation between basigin and a disintegrin and metalloproteinase (ADAM)-12 in serum from prostate cancer patients has been reported. Yet, the functional relevance of this correlation is unknown. Here, we show that ADAM12 interacts with basigin and cleaves it in the juxtamembrane region. Specifically, overexpression of ADAM12 increases ectodomain shedding of an alkaline phosphatase-tagged basigin reporter protein from the cell surface. Moreover, CRISPR/Cas9-mediated knockout of ADAM12 in human HeLa carcinoma cells results in reduced shedding of the basigin reporter, which can be rescued by ADAM12 re-expression. We detected endogenous basigin fragments, corresponding to the expected size of the ADAM12-generated ectodomain, in conditioned media from ADAM12 expressing cancer cell-lines, as well as serum samples from a healthy pregnant donor and five bladder cancer patients, known to contain high ADAM12 levels. Supporting the cancer relevance of our findings, we identified several cancer-associated mutations in the basigin membrane proximal region. Subsequent in vitro expression showed that some of these mutants are more prone to ADAM12-mediated shedding and that the shed ectodomain can enhance gelatin degradation by cancer cells. In conclusion, we identified ADAM12 as a novel basigin sheddase with a potential implication in cancer.

ADAM12-directed ectodomain shedding of E-cadherin potentiates trophoblast fusion

Trophoblasts, placental cells of epithelial lineage, undergo extensive differentiation to form the cellular components of the placenta. Trophoblast progenitor cell differentiation into the multinucleated syncytiotrophoblast is a key developmental process required for placental function, where defects in syncytiotrophoblast formation and turnover associate with placental pathologies and link to poor pregnancy outcomes. The cellular and molecular processes governing syncytiotrophoblast formation are poorly understood, but require the activation of pathways that direct cell fusion. The protease, A Disintegrin and Metalloproteinase 12 (ADAM12), controls cell fusion in myoblasts and is highly expressed in the placenta localizing to multiple trophoblast populations. However, the importance of ADAM12 in regulating trophoblast fusion is unknown. Here, we describe a function for ADAM12 in regulating trophoblast fusion. Using two distinct trophoblast models of cell fusion, we show that ADAM12 is dynamically upregulated and is under the transcriptional control of protein kinase A. siRNA-directed loss of ADAM12 impedes spontaneous fusion of primary cytotrophoblasts, whereas overexpression of the secreted variant, ADAM12S, potentiates cell fusion in the Bewo trophoblast cell line. Mechanistically, both ectopic and endogenous levels of ADAM12 were shown to control trophoblast fusion through E-cadherin ectodomain shedding and remodeling of intercellular boundaries. This study describes a novel role for ADAM12 in placental development, specifically highlighting its importance in controlling the differentiation of villous cytotrophoblasts into multinucleated cellular structures. Moreover, this work identifies E-cadherin as a novel ADAM12 substrate, and highlights the significance that cell adhesion molecule ectodomain shedding has in normal development.

The Elsevier Trophoblast Research Award Lecture: Importance of metzincin proteases in trophoblast biology and placental development: a focus on ADAM12

Placental development is a highly regulated process requiring signals from both fetal and maternal uterine compartments. Within this complex system, trophoblasts, placental cells of epithelial lineage, form the maternal-fetal interface controlling nutrient, gas and waste exchange. The commitment of progenitor villous cytotrophoblasts to differentiate into diverse trophoblast subsets is a fundamental process in placental development. Differentiation of trophoblasts into invasive stromal- and vascular-remodeling subtypes is essential for uterine arterial remodeling and placental function. Inadequate placentation, characterized by defects in trophoblast differentiation, may underlie the earliest cellular events driving pregnancy disorders such as preeclampsia and fetal growth restriction. Molecularly, invasive trophoblasts acquire characteristics defined by profound alterations in cell-cell and cell-matrix adhesion, cytoskeletal reorganization and production of proteolytic factors. To date, most studies have investigated the importance of the matrix metalloproteinases (MMPs) and their ability to efficiently remodel components of the extracellular matrix (ECM). However, it is now becoming clear that besides MMPs, other related proteases regulate trophoblast invasion via mechanisms other than ECM turnover. In this review, we will summarize the current knowledge on the regulation of trophoblast invasion by members of the metzincin family of metalloproteinases. Specifically, we will discuss the emerging roles that A Disintegrin and Metalloproteinases (ADAMs) play in placental development, with a particular focus on the ADAM subtype, ADAM12.

A disintegrin and metalloproteinase 12 (ADAM12) localizes to invasive trophoblast, promotes cell invasion and directs column outgrowth in early placental development

During pregnancy, stromal- and vascular-remodeling trophoblasts serve critical roles in directing placental development acquiring pro-invasive characteristics. The A Disintegrin and Metalloproteinase (ADAM) family of multifunctional proteins direct cellular processes across multiple organ systems via their intrinsic catalytic, cell adhesive and intracellular signaling properties. ADAM12, existing as two distinct splice variants (ADAM12L and ADAM12S), is highly expressed in the human placenta and promotes cell migration and invasion in several tumor cell lines; however, its role in trophoblast biology is unknown. In this study, ADAM12 was localized to anchoring trophoblast columns in first trimester placentas and to highly invasive extracellular matrix-degrading trophoblasts in placental villous explants. The importance of ADAM12 in directing trophoblast invasion was tested using loss-of and gain-of-function strategies, where siRNA-directed knockdown of ADAM12 inhibited trophoblast cell invasion while over-expression promoted migration and invasion in two trophoblastic cell models. In placental villous explant cultures, siRNA-directed loss of ADAM12 significantly dampened trophoblast column outgrowth. Additionally, we provide functional evidence for the ADAM12S variant in promoting trophoblast invasion and column outgrowth through a mechanism requiring its catalytic activity. This is the first study to assign a function for ADAM12 in trophoblast biology, where ADAM12 may play a central role regulating the behavior of invasive trophoblast subsets in early pregnancy. This study also underlines the importance of ADAM12L and ADAM12S in directing cell motility in normal developmental processes outside of cancer, specifically highlighting a potentially important function of ADAM12S in directing early placental development.

Where polarity meets fusion: role of Par6 in trophoblast differentiation during placental development and preeclampsia

Trophoblast cell fusion is a prerequisite for proper human placental development. Herein we examined the contribution of Par6 (Partitioning defective protein 6), a key regulator of cell polarity, to trophoblast cell fusion in human placental development. During early placentation, Par6 localized to nuclei of cytotrophoblast cells but with advancing gestation Par6 shifted its localization to the cytoplasm and apical brush border of the syncytium. Exposure of primary isolated trophoblasts to 3% O(2) resulted in elevated Par6 expression, maintenance of tight junction marker ZO-1 at cell boundaries, and decreased fusogenic syncytin 1 expression compared with cells cultured at 20% O(2). Treatment of choriocarcinoma BeWo cells with forskolin, a known inducer of fusion, increased syncytin 1 expression but decreased that of Par6 and ZO-1. Par6 overexpression in the presence of forskolin maintained ZO-1 at cell boundaries while decreasing syncytin 1 levels. In contrast, silencing of Par6 disrupted ZO-1 localization at cell boundaries and altered the expression and distribution of acetylated α-tubulin. Par6 expression was elevated in preeclamptic placentas relative to normotensive preterm controls and Par6 located to trophoblast cells expressing ZO-1. Together, our data indicate that Par6 negatively regulates trophoblast fusion via its roles on tight junctions and cytoskeleton dynamics and provide novel insight into the contribution of this polarity marker in altered trophoblast cell fusion typical of preeclampsia.

The role of ADAM-mediated shedding in vascular biology

Within the vasculature the disintegrins and metalloproteinases (ADAMs) 8, 9, 10, 12, 15, 17, 19, 28 and 33 are expressed on endothelial cells, smooth muscle cells and on leukocytes. As surface-expressed proteases they mediate cleavage of vascular surface molecules at an extracellular site close to the membrane. This process is termed shedding and leads to the release of a soluble substrate ectodomain thereby critically modulating the biological function of the substrate. In the vasculature several surface molecules undergo ADAM-mediated shedding including tumour necrosis factor (TNF) α, interleukin (IL) 6 receptor α, L-selectin, vascular endothelial (VE)-cadherin, the transmembrane CX3C-chemokine ligand (CX3CL) 1, Notch, transforming growth factor (TGF) and heparin-binding epidermal growth factor (HB-EGF). These substrates play distinct roles in vascular biology by promoting inflammation, permeability changes, leukocyte recruitment, resolution of inflammation, regeneration and/or neovascularisation. Especially ADAM17 and ADAM10 are capable of cleaving many substrates with diverse function within the vasculature, whereas other ADAMs have a more restricted substrate range. Therefore, targeting ADAM17 or ADAM10 by pharmacologic inhibition or gene knockout not only attenuates the inflammatory response in animal models but also affects tissue regeneration and neovascularisation. Recent discoveries indicate that other ADAMs (e.g. ADAM8 and 9) also play important roles in vascular biology but appear to have more selective effects on vascular responses (e.g. on neovascularisation only). Although, targeting of ADAM17 and ADAM10 in inflammatory diseases is still a promising approach, temporal and spatial as well as substrate-specific inhibition approaches are required to minimise undesired side effects on vascular cells.