Localization of endoglin, a transforming growth factor-β binding protein, and of CD44 and integrins in placenta during the first trimester of pregnancy

S St-Jacques, M Forte, SJ Lye… - Biology of …, 1994 - academic.oup.com
S St-Jacques, M Forte, SJ Lye, M Letarte
Biology of reproduction, 1994academic.oup.com
Endoglin is an integral membrane glycoprotein that binds transforming growth factor-β1
(TGFβ1) with high affinity and is predominantly expressed on human endothelial cells.
Characterization of this homodimeric protein from human term placenta has shown that it is
particularly abundant on the syncytiotrophoblast. Immunofluorescence staining of sections of
first trimester placenta now reveals that endoglin is found at even higher levels on the
syncytiotrophoblast of samples ranging from 6 to 12 wk of gestation. Very low levels are …
Abstract
Endoglin is an integral membrane glycoprotein that binds transforming growth factor-β1 (TGFβ1) with high affinity and is predominantly expressed on human endothelial cells. Characterization of this homodimeric protein from human term placenta has shown that it is particularly abundant on the syncytiotrophoblast. Immunofluorescence staining of sections of first trimester placenta now reveals that endoglin is found at even higher levels on the syncytiotrophoblast of samples ranging from 6 to 12 wk of gestation. Very low levels are observed on the undifferentiated cytotrophoblast cells that can be identified by their expression of the α6β4 integrin, a receptor for laminin. Within the villi, blood vessels and stromal cells are negative for endoglin but positive for α1β1 integrin, a receptor for collagens and laminin. Stromal cells also express CD44, a hyaluronic acid receptor. Of particular interest is the up-regulation of endoglin expression in the transition from polarized undifferentiated to non-polarized intermediate cytotrophoblasts (CTB) as the cells align in columns to invade the uterus. This occurs in parallel with the acquisition of α5β1 integrin (fibronectin receptor) and precedes the loss of α6;β4 integrin. CD44 and α1β1 integrin are noticeably absent from the CTB within the columns but are expressed at very high levels throughout the placental bed. Endoglin is undetectable within the decidua; thus, intermediate CTB that have invaded the placental bed express α5β1 integrin and cytokeratins but not endoglin. Our studies suggest that the expression of the TGFβ binding protein endoglin is critical to placental development. It is low on CTB, transiently increased on intermediate trophoblast cells within the columns, and induced and maintained at high levels on syncytiotrophoblast throughout pregnancy.
Oxford University Press