Cellular junctions on the free surface of human placental syncytium

Syncytiotrophoblast of Placentae from Women with Zika Virus Infection Has Altered Tight Junction Protein Expression and Increased Paracellular Permeability

The cytotrophoblast of human placenta transitions into an outer multinucleated syncytiotrophoblast (STB) layer that covers chorionic villi which are in contact with maternal blood in the intervillous space. During pregnancy, the Zika virus (ZIKV) poses a serious prenatal threat. STB cells are resistant to ZIKV infections, yet placental cells within the mesenchyme of chorionic villi are targets of ZIKV infection. We seek to determine whether ZIKV can open the paracellular pathway of STB cells. This route is regulated by tight junctions (TJs) which are present in the uppermost portion of the lateral membranes of STB cells. We analyzed the paracellular permeability and expression of E-cadherin, occludin, JAMs -B and -C, claudins -1, -3, -4, -5 and -7, and ZO-1, and ZO-2 in the STB of placentae from ZIKV-infected and non-infected women. In ZIKV-infected placentae, the pattern of expression of TJ proteins was preserved, but the amount of claudin-4 diminished. Placentae from ZIKV-infected women were permeable to ruthenium red, and had chorionic villi with a higher mean diameter and Hofbauer hyperplasia. Finally, ZIKV added to the basolateral surface of a trophoblast cell line reduced the transepithelial electrical resistance. These results suggest that ZIKV can open the paracellular pathway of STB cells.

Hypoxia-induced and HIF1α-VEGF-mediated tight junction dysfunction in choriocarcinoma cells: Implications for preeclampsia

INTRODUCTION

Accumulated data indicate that placental hypoxia is implicated in the pathogenesis of preeclampsia (PE). Tight junction (TJ) is important structure that sustains normal placental barrier function, its dysregulation under hypoxia has been observed. This study was designed to explore hypoxia-induced TJ dysfunction in trophoblast cells and its possible involvement in PE pathophysiology.

METHODS

Choriocarcinoma cells were grown in a monolayer and treated with cobalt chloride (CoCl₂) to induce hypoxia. TJ architecture was assessed using transmission electron microscopy, and locations of TJ proteins were determined by immunofluorescence. TJ functions were assessed by transepithelial electrical resistance (TER) and increased cell paracellular permeability (CPP), and the expression of TJ-related proteins, HIF-1α and VEGF was measured.

RESULTS

The TJ functions of trophoblast cells were significantly altered by hypoxia; TER decreased and CPP increased in a time- and concentration-dependent manner. Significant alterations in TJ protein expression and increases in HIF1α and VEGF expression were observed in hypoxic cells, and these effects were attenuated by pretreatment with YC-1. Moreover, corresponding changes in TJ protein expression were also detected in preeclamptic placentas.

CONCLUSION

These data demonstrate that trophoblast cells undergo significant changes in TJ protein expression under hypoxic conditions and highlight the potential significance of the HIF1α-VEGF axis in the regulation of TJ structure and function in the preeclamptic placenta.

Calcium Homeostasis in Human Placenta: Role of Calcium‐Handling Proteins

The human placenta is a transitory organ, representing during pregnancy the unique connection between the mother and her fetus. The syncytiotrophoblast represents the specialized unit in the placenta that is directly involved in fetal nutrition, mainly involving essential nutrients, such as lipids, amino acids, and calcium. This ion is of particular interest since it is actively transported by the placenta throughout pregnancy and is associated with many roles during intrauterine life. At term, the human fetus has accumulated about 25-30 g of calcium. This transfer allows adequate fetal growth and development, since calcium is vital for fetal skeleton mineralization and many cellular functions, such as signal transduction, neurotransmitter release, and cellular growth. Thus, there are many proteins involved in calcium homeostasis in the human placenta.

Ultrastructure of the normal human placenta

In this review, the ultrastructure of the normal human chorionic villus is examined and illustrated. The outer covering of trophoblast, comprising the generative cytotrophoblast and the multinucleated syncytiotrophoblast which is derived from it, is described, including such features as the microvillous surface, vesicles and vacuoles, endoplasmic reticulum and secretory droplets. The structure, composition, development and inclusions of the trophoblastic basement membrane are discussed, and the ultrastructure of the various components of the stroma, including reticulum cells, fibroblasts, Hofbauer cells, capillaries and the non-cellular matrix are illustrated and described, with special reference to their inter-relationships and function.

The distribution of intermediate filament proteins, actin and desmoplakins in human placental tissue as revealed by polyclonal and monoclonal antibodies

The distribution of intermediate filament proteins (cytokeratin, vimentin, desmin), actin, and desmoplakins in various placental compartments was studied by immunofluorescence microscopy using polyclonal and monoclonal antibodies. Trophoblast cells (cytotrophoblast, syncytiotrophoblast, isolated trophoblast cells, trophoblastic giant cells) were strongly stained by all types of cytokeratin antibodies. Antibodies to desmoplakins revealed the presence of desmosomes at all membranes, except the basal membrane of cytotrophoblast cells, and at the basal as well as the lumen-oriented membrane of the syncytiotrophoblast. After disappearance of the cytotrophoblast cell layer the distribution of desmosomes in the syncytiotrophoblast was unaltered. Isolated trophoblast cells contained desmosomes around their entire circumference. Amnion epithelial cells were heterogeneous with respect to cytokeratin composition as revealed, for example, by polyclonal antibodies with a broad range of cytokeratin reactivity and by monoclonal antibodies to cytokeratin No. 18. With the latter, a heterogeneous staining of amnion epithelial cells was achieved. Desmosomes (spots reactive with desmoplakin antibodies) were present at the lateral membranes of the amnion epithelial cells. In addition, vimentin filaments were coexpressed in these cells. Large vessels of the chorionic plate and stem villi showed thick walls consisting of vimentin-, desmin- and actin-positive cells. They were surrounded by mantles rich in vimentin-, desmin- and actin-positive cells, resembling myofibroblasts. This indicates that these cells may play a role in villous contractility and modulation of the intervillous space with effect on both maternal and fetal placental circulation.