Detection and cellular localization of plasma membrane-associated and cytoplasmic fatty acid-binding proteins in human placenta

The aim of this study was to investigate location and the types of membrane-associated and cytoplasmic fatty acid-binding proteins in human placental trophoblasts using monospecific polyclonal antibodies. Western blot analysis demonstrated the presence of multiple membrane and cytoplasmic fatty acid transport/binding proteins in human placenta. In addition to previously reported placental membrane fatty acid-binding (p-FABPpm, 40 kDa), fatty acid translocase (FAT, 88 kDa) and fatty acid transport protein (FATP, 62 kDa) were detected in both microvillous and basal membranes of the human placenta. Among the cytoplasmic proteins, heart (H) and liver (L) type FABP were detected in the cytosol of the human placental primary trophoblasts as well as in human placental choriocarcinoma (BeWo) cells. The immunoreactivity of epidermal type (E)-FABP was not detected in trophoblasts or BeWo cells despite its presence in human placental cytosol. Location of FAT and FATP on the both sides of the bipolar placental cells may favour transport of free fatty acids (FFA) pool in both directions i.e. from the mother to the fetus and vice versa. However, p-FABPpm, because of its exclusive location on the microvillous membranes, may favour the unidirectional flow of maternal plasma long-chain polyunsaturated fatty acids present in the FFA pool to the fetus, due to binding specificity for these fatty acids. Although the roles of these proteins in placental fatty acid uptake and metabolism are yet to be understood fully, their complex interaction may be involved in the uptake of maternal FFA by the placenta for delivery to the fetus.