The endothelium but not the syncytiotrophoblast of human placenta expresses caveolae.

The human placenta is a complex specialized structure that mediates the interchange of molecules, ions, and gases between maternal and foetal circulation. We have investigated the distribution and expression of caveolae/caveolin in the placenta. Using immunochemical, immunocytochemical, and ultrastructural methods, we show that the placenta expresses caveolin-1 and caveolin-2, which are marker proteins for caveolae. These proteins and caveolae were expressed at high levels in endothelium of placental capillaries and in endothelial and smooth muscle cells of larger vessels. In addition, fibroblasts in areas of the placenta with high connective tissue content also expressed caveolin. However, we were unable to detect these proteins or caveolae-like structures in the syncytiotrophoblast layer or in cytotrophoblasts. These results have important implications for further understanding placental biology and for the role of caveolae in cell regulation in this organ.