Expression of Na+/I- symporter and pendred syndrome genes in trophoblast cells

Placental iodide transport is critical for the fetal thyroid function, but the molecular mechanisms of this transport are not understood. The expressi on of two recently identified iodide transporters, namely the sodium/iodide symporter (NIS) and pendrin, the product of the gene responsible for the P endred syndrome (PDS), was studied using real-time kinetic quantitative PCR and immunohistochemistry 1) in placental tissues collected at different ge stational ages and 2) in primary cultures of villous cytotrophoblast cells (VCT) that differentiate and fuse over 2-3 days in vitro to form villous sy ncytiotrophoblast (VSCT) cells. Both NIS and PDS genes are expressed in placenta, albeit at low levels comp ared with those in thyroid tissue. NIS gene expression in placental samples from first trimester and term pregnancies was similar. In contrast, the ex pression of PDS gene was higher in term than in first trimester pregnancy s amples. In vitro, NIS gene was expressed at a high level in VCT obtained fr om first trimester pregnancy, and its expression decreased by 3- to 4-fold during the differentiation of VCT in VSCT. Expression of NIS was lower (up to 30-fold) in VCT obtained in placental samples from third trimester than from first trimester pregnancy. In contrast, the expression of PDS gene was low in VCT and increased by 5- to 10-fold during VSCT formation; this was observed in cells isolated from placental samples of both first trimester a nd term pregnancies. Immunohistochemical analysis showed that NIS protein w as present on the entire membrane of VCT, whereas pendrin was mainly locate d at the brush border membrane of VSCT, facing the mother. In conclusion, 1 ) NIS and PDS genes are differently expressed in the placenta during gestat ion; and 2)whereas pendrin is expressed at the brush border membrane of syn cytiotrophoblast cells, NIS protein is mainly located in the cytotrophoblas t layer.