Triploid human embryonic stem cells derived from tripronuclear zygotes displayed pluripotency and trophoblast differentiation ability similar to the diploid human embryonic stem cells

Comparison of Four Protocols for In Vitro Differentiation of Human Embryonic Stem Cells into Trophoblast Lineages by BMP4 and Dual Inhibition of Activin/Nodal and FGF2 Signaling

Human embryonic stem cells (hESCs) cultured in media containing bone morphogenic protein 4 (BMP4; B) differentiate into trophoblast-like cells. Supplementing media with inhibitors of activin/nodal signaling (A83-01) and of fibroblast growth factor 2 (PD173074) suppresses mesoderm and endoderm formation and improves specification of trophoblast-like lineages, but with variable effectiveness. We compared differentiation in four BMP4-containing media: mTeSR1-BMP4 only, mTeSR1-BAP, basal medium with BAP (basal-BAP), and a newly defined medium, E7-BAP. These media variably drive early differentiation towards trophoblast-like lineages with upregulation of early trophoblast markers CDX2 and KRT7 and downregulation of pluripotency markers (OCT4 and NANOG). As expected, based on differences between media in FGF2 and its inhibitors, downregulation of mesendoderm marker EOMES was variable between media. By day 7, only hESCs grown in E7-BAP or basal-BAP expressed HLA-G protein, indicating the presence of cells with extravillous trophoblast characteristics. Expression of HLA-G and other differentiation markers (hCG, KRT7, and GCM1) was highest in basal-BAP, suggesting a faster differentiation in this medium, but those cultures were more inhomogeneous and still expressed some endodermal and pluripotency markers. In E7-BAP, HLA-G expression increased later and was lower. There was also a low but maintained expression of some C19MC miRNAs, with more CpG hypomethylation of the ELF5 promoter, suggesting that E7-BAP cultures differentiate slower along the trophoblast lineage. We conclude that while all protocols drive differentiation into trophoblast lineages with varying efficiency, they have advantages and disadvantages that must be considered when selecting a protocol for specific experiments.

Generation, genomic characterization, and differentiation of triploid human embryonic stem cells

Humans are diploid organisms, and triploidy in human embryos is responsible for ∼10% of spontaneous miscarriages. Surprisingly, some pregnancies proceed to triploid newborns that suffer from many neuro-developmental disorders. To investigate the impact of triploidy on human development, we generate triploid human embryonic stem cells (hESCs) by fusing isogenic haploid and diploid hESCs. Comparison of the transcriptome, methylome, and genome-wide replication timing shows general similarity between diploid and triploid hESCs. However, triploid cells have a larger volume than diploid cells, demonstrating decreased surface-area-to-volume ratio. This leads to a significant downregulation of cell surface ion channel genes, which are more essential in neural progenitors than in undifferentiated cells, leading to inhibition of differentiation, and it affects the neuronal differentiation ability of triploid hESCs, both in vitro and in vivo. Notably, our research establishes a platform to study triploidy in humans and points to their pathology as observed in triploid embryos.

Stem Cell-Based Trophoblast Models to Unravel the Genetic Causes of Human Miscarriages

Miscarriage affects approximately 15% of clinically recognized pregnancies, and 1-3% of couples experience pregnancy loss recurrently. Approximately 50-60% of miscarriages result from chromosomal abnormalities, whereas up to 60% of euploid recurrent abortions harbor variants in candidate genes. The growing number of detected genetic variants requires an investigation into their role in adverse pregnancy outcomes. Since placental defects are the main cause of first-trimester miscarriages, the purpose of this review is to provide a survey of state-of-the-art human in vitro trophoblast models that can be used for the functional assessment of specific abnormalities/variants implicated in pregnancy loss. Since 2018, when primary human trophoblast stem cells were first derived, there has been rapid growth in models of trophoblast lineage. It has been found that a proper balance between self-renewal and differentiation in trophoblast progenitors is crucial for the maintenance of pregnancy. Different responses to aneuploidy have been shown in human embryonic and extra-embryonic lineages. Stem cell-based models provide a powerful tool to explore the effect of a specific aneuploidy/variant on the fetus through placental development, which is important, from a clinical point of view, for deciding on the suitability of embryos for transfer after preimplantation genetic testing for aneuploidy.

Derivation of human triploid trophoblast stem cells

PURPOSE

Human trophoblast stem cells (hTSCs) are counterparts of the precursor cells of the placenta and are valuable cell models for the study of placental development and the pathogenesis of placental diseases. The aim of this work was to establish a triploid human TSC (hTSC^3PN) derived from the tripronuclear embryos, which are clinically discarded but readily available, for potential applications in basic placental research and disease modeling.

METHODS

Eighteen tripronuclear human zygotes from IVF were collected and cultured for 5-6 days. Five high-quality blastocysts were harvested and were individually cultured in hTSC medium. Finally, two hTSC lines were established after 10 days and could be passaged stably.

RESULTS

The karyotyping analysis showed that hTSC^3PN contained three sets of chromosomes. And the hTSC^3PN exhibited typical features of hTSCs, with the ability to differentiate into two trophoblast lineages: extravillous cytotrophoblasts (EVTs) and syncytiotrophoblasts (STs). In addition, the hTSC^3PN can mimic some vital features of trophoblast, including hormone secretion and invasion. Further studies showed that the proliferation and differentiation of hTSC^3PN were reduced compared with normal hTSCs, which may be related to the disturbed metabolic signaling in hTSC^3PN.

CONCLUSIONS

We established the triploid hTSC lines derived from tripronuclear embryos, which provides a potentially useful research model in vitro to study human placental biology and diseases.

Mesenchymal Stem/Stromal-Like Cells from Diploid and Triploid Human Embryonic Stem Cells Display Different Gene Expression Profiles

Background:

hESCs-MSCs open a new insight into future cell therapy applications, due to their unique characteristics, including immunomodulatory features, proliferation, and differentiation.

Methods:

Herein, hESCs-MSCs were characterized by IF technique with CD105 and FIBRONECTIN as markers and FIBRONECTIN, VIMENTIN, CD10, CD105, and CD14 genes using RT-PCR technique. FACS was performed for CD44, CD73, CD90, and CD105 markers. Moreover, these fibroblast-like cells, due to multipotent characteristics, differentiated to the osteoblast.

Results:

MSCs were derived from diploid and triploid hESC lines using sequential 3D and 2D cultures and characterized with the specific markers. IF showed the expression of FIBRONECTIN and CD105 in hESCs-MSCs. Flow cytometry data indicated no significant difference in the expression of MSC markers after 6 and 13 passages. Interestingly, gene expression profiles revealed slight differences between MSCs from diploid and triploid hESCs. The hESCs-MSCs displayed osteogenic differentiation capacity, which was confirmed by Alizarin red staining.

Conclusion:

Our findings reveal that both diploid and triploid hESC lines are capable of forming MSCs; however, there are some differences in their gene expression profiles. Generation of MSCs from hESCs, as a non-invasive procedure in large scale, will lend itself for the future cell-based therapeutic applications.

Specification of trophoblast from embryonic stem cells exposed to BMP4

Trophoblast (TB) comprises the outer cell layers of the mammalian placenta that make direct contact with the maternal uterus and, in species with a highly invasive placenta, maternal blood. It has its origin as trophectoderm, a single epithelial layer of extra-embryonic ectoderm that surrounds the embryo proper at the blastocyst stage of development. Here, we briefly compare the features of TB specification and determination in the mouse and the human. We then review research on a model system that has been increasingly employed to study TB emergence, namely the BMP4 (bone morphogenetic protein-4)-directed differentiation of human embryonic stem cells (ESCd), and discuss why outcomes using it have proved so uneven. We also examine the controversial aspects of this model, particularly the issue of whether or not the ESCd represents TB at all. Our focus here has been to explore similarities and potential differences between the phenotypes of ESCd, trophectoderm, placental villous TB, and human TB stem cells. We then explore the role of BMP4 in the differentiation of human pluripotent cells to TB and suggest that it converts the ESC into a totipotent state that is primed for TB differentiation when self-renewal is blocked. Finally we speculate that the TB formed from ESC is homologous to the trophectoderm-derived, invasive TB that envelopes the implanting conceptus during the second week of pregnancy.

Attempts for Generation of Embryonic Stem Cells from Human Embryos Following In Vitro Embryo Twinning

In vitro embryo twinning can be used to increase the number of the human embryos available for production of human embryonic stem cell (hESC) lines. The aim of this study was to generate hESCs following the production of the twin embryos by in vitro embryo splitting procedures. In total 21 chromosomally abnormal (three pronuclei) embryos underwent in vitro embryo twinning and were allowed to develop to the blastocyst stage. As a result, 42 twin embryos were obtained, of which 24 developed to blastocyst stage. Using micromanipulation technique, the zona-free blastocysts were recovered and plated onto mitotically inactivated Yazd human foreskin fibroblast (Batch18; YhFF#18) feeder layers in microdrops. After 3 to 5 days of blastocyst culture onto human foreskin fibroblast feeder layers, the hESC-like outgrowths were passaged onto new feeders in microdrops. The initial outgrowths of hESC-like cells were generated, and cells were proliferated, passaged, and some of them expressed hESC and trophoblastic markers; however, no cell lines were established. This might be due to the low cell number and poor quality of inner cell mass within these twin blastocysts. In vitro embryo twinning by increasing the number of the human embryos could be useful in the future for the generation of new pluripotent stem cell lines. However, the challenge remains to optimize the methods.

Stem cell insights into human trophoblast lineage differentiation

BACKGROUND

The human placenta is vital for fetal development, yet little is understood about how it forms successfully to ensure a healthy pregnancy or why this process is inadequate in 1 in 10 pregnancies, leading to miscarriage, intrauterine growth restriction or preeclampsia. Trophoblasts are placenta-specific epithelial cells that maximize nutrient exchange. All trophoblast lineages are thought to arise from a population of trophoblast stem cells (TSCs). However, whilst the isolation of murine TSC has led to an explosion in understanding murine placentation, the isolation of an analogous human TSC has proved more difficult. Consequently, alternative methods of studying human trophoblast lineage development have been employed, including human embryonic stem cells (hESCs), induced pluripotent stem cells (iPS) and transformed cell lines; but what do these proxy models tell us about what is happening during early placental development?

OBJECTIVE AND RATIONALE

In this systematic review, we evaluate current approaches to understanding human trophoblast lineage development in order to collate and refine these models and inform future approaches aimed at establishing human TSC lines.

SEARCH METHODS

To ensure all relevant articles were analysed, an unfiltered search of Pubmed, Embase, Scopus and Web of Science was conducted for 25 key terms on the 13th May 2016. In total, 47 313 articles were retrieved and manually filtered based on non-human, non-English, non-full text, non-original article and off-topic subject matter. This resulted in a total of 71 articles deemed relevant for review in this article.

OUTCOMES

Candidate human TSC populations have been identified in, and isolated from, both the chorionic membrane and villous tissue of the placenta, but further investigation is required to validate these as 'true' human TSCs. Isolating human TSCs from blastocyst trophectoderm has not been successful in humans as it was in mice, although recently the first reported TSC line (USFB6) was isolated from an eight-cell morula. In lieu of human TSC lines, trophoblast-like cells have been induced to differentiate from hESCs and iPS. However, differentiation in these model systems is difficult to control, culture conditions employed are highly variable, and the extent to which they accurately convey the biology of 'true' human TSCs remains unclear, particularly as a consensus has not been met among the scientific community regarding which characteristics a human TSC must possess.

WIDER IMPLICATIONS

Human TSC models have the potential to revolutionize our understanding of trophoblast differentiation, allowing us to make significant gains in understanding the underlying pathology of pregnancy disorders and to test potential therapeutic interventions on cell function in vitro. In order to do this, a collaborative effort is required to establish the criteria that define a human TSC to confirm the presence of human TSCs in both primary isolates and to determine how accurately trophoblast-like cells derived from current model systems reflect trophoblast from primary tissue. The in vitro systems currently used to model early trophoblast lineage formation have provided insights into early human placental formation but it is unclear whether these trophoblast-like cells are truly representative of primary human trophoblast. Consequently, continued refinement of current models, and standardization of culture protocols is essential to aid our ability to identify, isolate and propagate 'true' human TSCs from primary tissue.