Psg18 is specifically expressed in follicle-associated epithelium

Interaction of Pregnancy-Specific Glycoprotein 1 With Integrin Α5β1 Is a Modulator of Extravillous Trophoblast Functions

Human pregnancy-specific glycoproteins (PSGs) serve immunomodulatory and pro-angiogenic functions during pregnancy and are mainly expressed by syncytiotrophoblast cells. While PSG mRNA expression in extravillous trophoblasts (EVTs) was reported, the proteins were not previously detected. By immunohistochemistry and immunoblotting, we show that PSGs are expressed by invasive EVTs and co-localize with integrin 5. In addition, we determined that native and recombinant PSG1, the most highly expressed member of the family, binds to 51 and induces the formation of focal adhesion structures resulting in adhesion of primary EVTs and EVT-like cell lines under 21% oxygen and 1% oxygen conditions. Furthermore, we found that PSG1 can simultaneously bind to heparan sulfate in the extracellular matrix and to 51 on the cell membrane. Wound healing assays and single-cell movement tracking showed that immobilized PSG1 enhances EVT migration. Although PSG1 did not affect EVT invasion in the in vitro assays employed, we found that the serum PSG1 concentration is lower in African-American women diagnosed with early-onset and late-onset preeclampsia, a pregnancy pathology characterized by shallow trophoblast invasion, than in their respective healthy controls only when the fetus was a male; therefore, the reduced expression of this molecule should be considered in the context of preeclampsia as a potential therapy.

Development of intestinal M cells and follicle-associated epithelium is regulated by TRAF6-mediated NF-κB signaling

TRAF6 is essential for RANK-mediated NF-κB activation and is involved in the development of several types of cells. Kanaya et al. demonstrate that RANK–TRAF6-mediated NF-κB is essential for the development of M cells and FAE.

M cells are located in the follicle-associated epithelium (FAE) that covers Peyer’s patches (PPs) and are responsible for the uptake of intestinal antigens. The differentiation of M cells is initiated by receptor activator of NF-κB. However, the intracellular pathways involved in M cell differentiation are still elusive. In this study, we demonstrate that the NF-κB pathway activated by RANK is essential for M cell differentiation using in vitro organoid culture. Overexpression of NF-κB transcription factors enhances the expression of M cell–associated molecules but is not sufficient to complete M cell differentiation. Furthermore, we evaluated the requirement for tumor necrosis factor receptor–associated factor 6 (TRAF6). Conditional deletion of TRAF6 in the intestinal epithelium causes a complete loss of M cells in PPs, resulting in impaired antigen uptake into PPs. In addition, the expression of FAE-associated genes is almost silenced in TRAF6-deficient mice. This study thus demonstrates the crucial role of TRAF6-mediated NF-κB signaling in the development of M cells and FAE.

Food Intake Affects Sperm-Egg Fusion Through the GIP/PSG17 Axis in Mice

In addition to overeating, starvation also reduces fecundity in mammals. However, little is known about the molecular mechanisms linking food intake to fertility, especially in males. Gastric inhibitory polypeptide (GIP), which is released from intestinal K-cells after meal ingestion, stimulates insulin secretion from pancreatic β-cells through the action of incretin and has several extrapancreatic effects. Here, we identified GIP receptor (Gipr) expression in mouse spermatids. Microarray analysis revealed that pregnancy-specific glycoprotein 17 (Psg17), a potential CD9-binding partner, was significantly decreased in GIP receptor-knockout (Gipr-/-) testes. Glycosylphosphatidylinositol-anchored PSG17 was expressed on the surface of acrosome-reacted sperm, and Gipr-/- sperm led to a lower fertilization rate in vitro, compared with that of Gipr+/+ sperm, both in the absence and presence of the zona pellucida. Plasma GIP concentrations and Psg17 messenger RNA (mRNA) were immediately increased in the testis after a single meal, whereas ingestion of a chronic high-fat diet markedly decreased Gipr and Psg17 mRNA. These results suggest that reduced GIP signaling, by decreased GIP levels or the downregulation of Gipr, is associated with the reduction of fecundity due to starvation or overeating. Thus, proper regulation of GIP signaling in the testis could be a potential unique therapeutic target for male infertility in obese and diabetic individuals.

Pregnancy-specific glycoprotein expression in normal gastrointestinal tract and in tumors detected with novel monoclonal antibodies

Pregnancy-specific glycoproteins (PSGs) are immunoglobulin superfamily members related to the carcinoembryonic antigen-related cell adhesion molecule (CEACAM) family and are encoded by 10 genes in the human. They are secreted at high levels by placental syncytiotrophoblast into maternal blood during pregnancy, and are implicated in immunoregulation, thromboregulation, and angiogenesis. To determine whether PSGs are expressed in tumors, we characterized 16 novel monoclonal antibodies to human PSG1 and used 2 that do not cross-react with CEACAMs to study PSG expression in tumors and in the gastrointestinal (GI) tract using tissue arrays and immunohistochemistry. Staining was frequently observed in primary squamous cell carcinomas and colonic adenocarcinomas and was correlated with the degree of tumor differentiation, being largely absent from metastatic samples. Staining was also observed in normal oesophageal and colonic epithelium. PSG expression in the human and mouse GI tract was confirmed using quantitative RT-PCR. However, mRNA expression was several orders of magnitude lower in the GI tract compared to placenta. Our results identify a non-placental site of PSG expression in the gut and associated tumors, with implications for determining whether PSGs have a role in tumor progression, and utility as tumor biomarkers.

Identification of novel genes selectively expressed in the follicle-associated epithelium from the meta-analysis of transcriptomics data from multiple mouse cell and tissue populations

The follicle-associated epithelium (FAE) overlying the Peyer's patches and the microfold cells (M cells) within it are important sites of antigen transcytosis across the intestinal epithelium. Using a meta-analysis approach, we identified a transcriptional signature that distinguished the FAE from a large collection of mouse cells and tissues. A co-expressed cluster of 21 FAE-specific genes was identified, and the analysis of the transcription factor binding site motifs in their promoter regions indicated that these genes shared an underlying transcriptional programme. This cluster contained known FAE- (Anxa10, Ccl20, Psg18 and Ubd) and M-cell-specific (Gp2) genes, suggesting that the others were novel FAE-specific genes. Some of these novel candidate genes were expressed highly by the FAE and M cells (Calcb, Ces3b, Clca2 and Gjb2), and others only by the FAE (Ascl2, Cftr, Fgf15, Gpr133, Kcna1, Kcnj15, Mycl1, Pgap1 and Rps6kl). We also identified a subset of novel FAE-related genes that were induced in the intestinal epithelium after receptor activator of nuclear factor (NF)-κB ligand stimulation. These included Mfge8 which was specific to FAE enterocytes. This study provides new insight into the FAE transcriptome. Further characterization of the candidate genes identified here will aid the identification of novel regulators of cell function in the FAE.

Murine pregnancy-specific glycoprotein 23 induces the proangiogenic factors transforming-growth factor beta 1 and vascular endothelial growth factor a in cell types involved in vascular remodeling in pregnancy

Haemochorial placentation is a unique physiological process in which the fetal trophoblast cells remodel the maternal decidual spiral arteries to establish the fetoplacental blood supply. Pregnancy-specific glycoproteins (PSGs) are members of the carcinoembryonic antigen family. PSGs are produced by the placenta of rodents and primates and are secreted into the bloodstream. PSG23 is one of 17 members of the murine PSG family (designated PSG16 to PSG32). Previous studies determined that PSGs have immunoregulatory functions due to their ability to modulate macrophage cytokine secretion. Here we show that recombinant PSG23 induces transforming growth factor (TGF) beta1, TGFB1, and vascular endothelial growth factor A (VEGFA) in primary murine macrophages and the macrophage cell line RAW 264.7 cells. In addition, we identified new cell types that responded to PSG23 treatment. Dendritic cells, endothelial cells, and trophoblasts, which are involved in maternal vasculature remodeling during pregnancy, secreted TGFB1 and VEGFA in response to PSG23. PSG23 showed cross-reactivity with human cells, including human monocytes and the trophoblast cell line, HTR-8/SVneo cells. We analyzed the binding of PSG23 to the tetraspanin CD9, the receptor for PSG17, and found that CD9 is not essential for PSG23 binding and activity in macrophages. Overall these studies show that PSGs can modulate the secretion of important proangiogenic factors, TGFB1 and VEGFA, by different cell types involved in the development of the placenta.