EXPRESSION OF INTEGRINS BY HUMAN TROPHOBLAST AND DIFFERENTIAL ADHESION TO LAMININ OR FIBRONECTIN

The process of placental implantation involves a series of transformations of trophoblast from a single polarized epithelial layer resting on a basement membrane (villous trophoblast), to cellular aggregates (trophoblast columns) which ultimately disperse to invade uterine decidua as individual celts (interstitial trophoblast). Such tissue re-modelling is associated with changes in the constituents of the extracellular matrix and in the expression of matrix receptors by the cells, the most relevant being the family of integrins which bind to laminin and fibronectin. In this study we show, by immunohistology and flow cytometry, a gradual loss of laminin receptors with the concomitant acquisition of fibronectin receptors as trophoblast is transformed from the villous phenotype, through the cell columns, into the extravillous population. The pattern of staining for the alpha5, alpha6, beta1 and beta4 subunits indicates that the integrins expressed by trophoblast are predominantly the alpha5beta1 and the alpha6beta4 heterodimers. We have also shown that isolated trophoblast cells assume a flattened, sessile phenotype when cultured on laninin but exhibit a more spreading, motile morphology when plated on fibronectin. In addition, numerous multinucleated giant cells are observed on a fibronectin substrate. Our data suggest that the relative expression of laminin and fibronectin receptors may determine the morphology and behaviour of trophoblast during the process of implantation.