Exosomes Secreted by Human Placenta Carry Functional Fas Ligand and TRAIL Molecules and Convey Apoptosis in Activated Immune Cells, Suggesting Exosome-Mediated Immune Privilege of the Fetus

Abstract

Apoptosis is crucially important in mediating immune privilege of the fetus during pregnancy. We investigated the expression and in vitro apoptotic activity of two physiologically relevant death messengers, the TNF family members Fas ligand (FasL) and TRAIL in human early and term placentas. Both molecules were intracellularly expressed, confined to the late endosomal compartment of the syncytiotrophoblast, and tightly associated to the generation and secretion of placental exosomes. Using immunoelectron microscopy, we show that FasL and TRAIL are expressed on the limiting membrane of multivesicular bodies where, by membrane invagination, intraluminal microvesicles carrying membranal bioactive FasL and TRAIL are formed and released in the extracellular space as exosomes. Analyzing exosomes secreted from placental explant cultures, to our knowledge, we demonstrate for the first time that FasL and TRAIL are clustered on the exosomal membrane as oligomerized aggregates ready to form death-inducing signaling complex. Consistently, placental FasL- and TRAIL-carrying exosomes triggered apoptosis in Jurkat T cells and activated PBMC in a dose-dependent manner. Limiting the expression of functional FasL and TRAIL to exosomes comprise a dual benefit: 1) storage of exosomal FasL and TRAIL in multivesicular bodies is protected from proteolytic cleavage and 2) upon secretion, delivery of preformed membranal death molecules by exosomes rapidly triggers apoptosis. Our results suggest that bioactive FasL- and TRAIL-carrying exosomes, able to convey apoptosis, are secreted by the placenta and tie up the immunomodulatory and protective role of human placenta to its exosome-secreting ability.

CD4+VEGFR1HIGH T cell as a novel Treg subset regulates inflammatory bowel disease in lymphopenic mice

“…55 Some papers have reported that microRNA-containing or Fas ligand-expressing exosomes from Tregs or other tissues could mediate effector T-cell apoptosis. [56][57][58] Taken together, CD4 1 VEGFR1 high T-cell-mediated suppression might be exerted in various ways depending on the microenvironment, so that further studies to identify soluble factor(s) responsible for the suppressive activity should be considered under various circumstances. IBD is a chronic and relapsing inflammatory disorder and one of the CD4 1 T-cell-mediated autoimmune diseases.…”

Placenta-derived exosomes: potential biomarkers of preeclampsia

“…Alternatively, the direct quantification of placenta-derived exosomes from total purified exosomes using PLAP as a placenta-specific marker has been achieved. [79][80][81][82][83][84][85] In contrast to immunocapture methods, this method eliminates inaccuracies attributed to the lower exosomal yield obtained using immunocapture techniques. However, the direct quantification of placentaderived exosomes in maternal circulation is largely dependent on the purity of the exosomal fraction.…”

“…Exosomes usually contain a variety of molecules that are native to the originating cell and enriched with endosome-associated protein markers, such as tetraspanins (CD63, CD81, CD82, CD9, CD37), HSP70, RAB proteins, ALIX, TSG101, endocytic proteins, and cell-specific proteins, which provide information regarding their cellular origin. 95 Pregnancyassociated exosomes have been found to contain a number of membrane-bound protein markers, such as NKGD2 ligands, 96 FasL, 82,83 TRAIL, 82 and syncytin 1, 97 which suggests that placenta-derived exosomes play a key role in maintaining maternal-fetal tolerance (Figure 4). Other specific pregnancy-associated exosomal proteins, such as TGFβ, indicate that placenta-derived exosomes are involved in the control of STB growth, proliferation and differentiation.…”

“…[79][80][81] Alternative technologies, such as analytical size-exclusion chromatography and immunoaffinity capture, 82,83 for the isolation of PLAP + exosomes from maternal circulation have been shown elsewhere; however, these methods, especially the latter, result in analytical challenges with regard to the reproducibility and precision of the quantification of placentaderived exosomes in maternal circulation. Alternatively, the direct quantification of placenta-derived exosomes from total purified exosomes using PLAP as a placenta-specific marker has been achieved.…”

Extracellular presence/release of galectins from HTR-8/SVneo extravillous trophoblast cells*

“…It is of interest to note that EVT cell invasion is increased by both gal-1 (Kolundzic et al, 2011b) and EVs from cytotrophoblast cells grown in a hypoxic environment (Salomon et al, 2013). Both gal-1 (Blois et al, 2007;Tirado-Gonzalez et al, 2013) and placental EVs (Stenqvist et al, 2013;Mincheva-Nilsson and Baranov, 2014;Tannetta et al, 2014) are involved in immunoregulation during pregnancy. As for gal-3 and gal-8, their role in trophoblasts is still unresolved.…”