VE-cadherin expression allows identification of a new class of hematopoietic stem cells within human embryonic liver.

Edification of the human hematopoietic system during development is characterized by the production of waves of hematopoietic cells separated in time, formed in distinct embryonic sites (ie, yolk sac, truncal arteries including the aorta, and placenta). The embryonic liver is a major hematopoietic organ wherein hematopoietic stem cells (HSCs) expand, and the future, adult-type, hematopoietic cell hierarchy becomes established. We report herein the identification of a new, transient, and rare cell population in the human embryonic liver, which coexpresses VE-cadherin, an endothelial marker, CD45, a pan-hematopoietic marker, and CD34, a common endothelial and hematopoietic marker. This population displays an outstanding self-renewal, proliferation, and differentiation potential, as detected by in vitro and in vivo hematopoietic assays compared with its VE-cadherin negative counterpart. Based on VE-cadherin expression, our data demonstrate the existence of 2 phenotypically and functionally separable populations of multipotent HSCs in the human embryo, the VE-cadherin(+) one being more primitive than the VE-cadherin(-) one, and shed a new light on the hierarchical organization of the embryonic liver HSC compartment.

Human Fetal Liver Mesenchymal Stem Cell-Derived Exosomes Impair Natural Killer Cell Function.

Mesenchymal stem cells (MSCs) are powerful immunomodulators that regulate the diverse functions of immune cells involved in allogeneic reactions, such as T cells and natural killer (NK) cells, through cell-cell contact or secreted factors. Exosomes secreted by MSCs may be involved in their regulatory functions, providing new therapeutic tools. Here, we showed that fetal liver (FL) MSC-derived exosomes inhibit proliferation, activation, and cytotoxicity of NK cells. Exosomes bearing latency associated peptide (LAP), TGFß, and thrombospondin 1 (TSP1), a regulatory molecule for TGFß, induced downstream TGFß/Smad2/3 signaling in NK cells. The inhibition of TGFß, using a neutralizing anti-TGFß antibody, restored NK proliferation, differentiation, and cytotoxicity, demonstrating that FL-MSC-derived exosomes exert their inhibition on NK cell function via TGFß. These results suggest that FL-MSC-derived exosomes regulate NK cell functions through exosome-associated TGFß.

VE-Cadherin and ACE Co-Expression Marks Highly Proliferative Hematopoietic Stem Cells in Human Embryonic Liver.

Despite advances to engineer transplantable hematopoietic stem and progenitor cells (HSPCs) for research and therapy, an in-depth characterization of the developing human hematopoietic system is still lacking. The human embryonic liver is at the crossroad of several hematopoietic sites and harbors a complex hematopoietic hierarchy, including the first actively dividing HSPCs that will further seed the definitive hematopoietic organs. However, few are known about the phenotypic and functional HSPC organization operating at these stages of development. In this study, using a combination of four endothelial and hematopoietic surface markers, that is, the endothelial-specific marker vascular endothelial-cadherin (Cdh5, CD144), the pan-leukocyte antigen CD45, the hemato-endothelial marker CD34, and the angiotensin-converting enzyme (ACE, CD143), we identified distinct HSPC subsets, and among them, a population co-expressing the four markers that uniquely harbored an outstanding proliferation potential both ex vivo and in vivo. Moreover, we traced back this population to the yolk sac (YS) and aorta-gonad-mesonephros (AGM) sites of hematopoietic emergence. Taken together, our data will help to identify human HSPC self-renewal and amplification mechanisms for future cell therapies.

Differential expression of E-cadherin, ß-catenin, and Lewis x between invasive hydatidiform moles and post-molar choriocarcinomas.

Trophoblast cell adhesion and migration are carefully coordinated during normal placental development. We have compared the expression of three adhesion molecules, E-cadherin, ß-catenin, and Lewis x, by immunohistochemistry during normal trophoblast differentiation, and in hydatidiform moles and choriocarcinomas. Both E-cadherin and ß-catenin were expressed in normal placenta cytotrophoblast, and this expression decreased with trophoblast maturation. E-cadherin was mainly localized along the contact between cytotrophoblast and syncytiotrophoblast, which indicates its role in the differentiation of the syncytial layer. Lewis x disappeared progressively during differentiation of normal villous vessels, and was expressed in molar pregnancies. Interestingly, whereas choriocarcinomas were not, or poorly, stained, invasive hydatidiform moles (invHMs) strongly expressed Lewis x in vascular structures. This observation correlated well with E-cadherin and ß-catenin expression and suggests that these three markers are associated with the invasive transformation. The presence of robust endothelial structures in invHMs could also explain their ability to maintain organized villous architecture (contrary to metastatic choriocarcinomas) during their invasion of extrauterine tissues such as the lung or the brain after dissemination through the blood flow. In our hands, Lewis x appeared to be a new, reliable marker that can be used to clearly distinguish invHMs from choriocarcinomas.

Activity and tissue distribution of splice variants of alpha6-fucosyltransferase in human embryogenesis.

The product of the FUT8 gene transfers an alpha1-6 fucose on the innermost N-acetylglucosamine of the chitobiose core of N-glycans. Northern blot analysis shows four main transcripts of 3.0, 3.3, 3.9, and 4.2 kb in the embryo. The larger forms around 4-kb decrease in fetus and adult. Fourteen embryo transcripts of FUT8 were cloned. Twelve exons comprising two new 5'untranslated-exons (A and B) and two new 3'UT-ends (L1 and L2) and the complete genomic organization of the FUT8 gene (330 kb) are described. Transcripts starting with the 5'UT-exon A are always associated with exons C and D. Exon B initiates another series of transcripts associated to exon C and D or directly to exon D. A third series of transcripts starts at exon C. The data suggest an expression of FUT8 regulated by three different promoters, starting transcription in exons A, B, or C. The A or C series are better expressed than the B series. After transfection with these cDNA constructs the transcripts with 5'UT-exons A or C have higher expression of FUT8 transcripts and higher alpha6-fucosyltransferase activity, whereas the activity of the B series is about two-thirds lower for both parameters, suggesting that exon B reduces the expression of the transcripts.