Extracellular matrix components of the placental extravillous trophoblast: immunocytochemistry and ultrastructural distribution

Abstract

Invasive extravillous trophoblast cells of the human placenta are embedded in a self-secreted extracellular matrix, the matrix-type fibrinoid. The ultrastructure and molecular composition of the matrix-type fibrinoid of the term human placenta were studied by transmission electron microscopy and immunogold labelling. We used antibodies directed against different matrix proteins such as collagen type IV, laminin, vitronectin, heparan sulfate, various fibronectin isoforms, and against the oncofetal blood group antigen, "i". Immunogold labelling patterns of matrix proteins are the basis for the subdivision of the trophoblast-derived matrix-type fibrinoid into mosaic-like patches of structurally and immunocytochemically different compartments. Firstly, fine granular patches with structural similarities to basal lamina material are composed solely of collagen type IV and laminin. Secondly, an ultrastructurally amorphous glossy substance shows reactivity with antibodies against heparan sulfate and vitronectin. A third type of patches, fine fibrillar networks embedded in the above-mentioned glossy matrix, are reactive with antibodies against normal fibronectin isoforms (IST-4, IST-6, IST-9) and oncofetal isoforms (BC-1, FDC-6). The blood group precursor antigen "i" was not only expressed on the surfaces of the extravillous trophoblast cells but was associated with the fibronectin-positive fibrils. In conclusion, within this extracellular matrix, clear compartments of different composition can be distinguished from each other. Glycosylation with "i" in this matrix may be involved in immunological masking, thus preventing rejection of placenta and fetus.

The anatomy of the normal placenta

“…Fibrinoid can be found at the intervillous surface of the chorionic and basal plates, encasing or partly covering placental villi, or in the depth of the basal plate. During the last decade fibrinoid was investigated regarding origin and composition resulting in a new classification of two subtypes, fibrin-type fibrinoid and matrix-type fibrinoid 29 57 – 59…”

“…Matrix-type fibrinoid is a secretion product of extravillous trophoblasts containing all kinds of extracellular matrix proteins such as oncofetal fibronectin, tenascin, collagen IV, laminin and cellular fibronectins as well as heparane sulphate and vitronectin, fibrillin and merosin 57 59 62 – 65…”

First trimester human placenta prevents breast cancer cell attachment to the matrix: The role of extracellular matrix

“…During implantation, the placenta manipulates the surrounding ECM composition and structure . EVT cells that invade the uterine wall secrete ECM proteins and proteinases (e.g., matrix metalloproteinase 2 (MMP2) and MMP9), which degrade the maternal matrix . The elimination of BCCL specifically from the proximity of placental implantation sites suggests that a special ECM structure/composition prevents their attachment.…”

Relevance of Syndecan-1 in the Trophoblastic BeWo Cell Syncytialization

“…There are some reports on the possible ways through which syndecans regulate the cellular function. In humans, trophoblast, and epithelial cells, syndecans support cell adhesion via binding of adhesion molecules such as fibronectins, collagens and thrombospondin 34,38 . Additionally, syndecan expressed on the apical surface of the syncytiotrophoblast, through binding with growth factors may help in establishing feto‐maternal communication 18 .…”