Expression of variant luteinizing hormone/chorionic gonadotropin receptors and degradation of chorionic gonadotropin in human chorionic villous macrophages.

Human gonads and non-gonadal organs/tissues express luteinizing hormone/chorionic gonadotropin (LH/CG) receptors. This study aimed to identify the LH/CG receptors and to clarify their function in human placental chorionic villous macrophages. Macrophages as well as syncytiotrophoblasts of human chorionic villous tissues were immunohistochemically positive for LH/CG receptor throughout gestation. By reverse transcription-nested polymerase chain reaction methods, villous macrophages were shown to express a variant type of LH/CG receptor, the sequencing of which revealed a deletion of exon 9. For experiments in vitro, a monocyte-macrophage cell line, THP-1, was transfected with vector alone, wild-type LH/CG receptor, and exon 9-deleted LH/CG receptor after phorbol 12-myristate 13-acetate (PMA) treatment. Non-PMA-treated THP-1 cells transfected with vector alone were also examined. THP-1 cells expressed exon 9-deleted LH/CG receptor after treatment with PMA. After the cells of the four groups were cultured in medium containing intact human CG (hCG), the concentrations of hCG and its beta-core fragment (beta-CF) were measured in the supernatant of the culture medium and in the cell cytosol. Time-dependent hCG uptake was observed in both non-PMA-treated and PMA-treated THP-1 cells, suggesting that the variant receptor is not directly involved in the ingestion of hCG. The degradation of hCG and excretion of beta-CF were progressed in PMA-treated cells but not in the un-treated cells. In the cell cytosol, the ratio of beta-CF and hCG concentrations (beta-CF/hCG) was significantly higher in the PMA-treated cells than in non-PMA-treated cells; however, it did not differ between the PMA-treated cells transfected with exon 9-deleted receptor and those transfected with vector alone. Macrophages may express the variant receptor in order to recognize the intracytoplasmic hCG and transport it to the lysosome. Among the two PMA-treated cells, the ratio was lower in those transfected with wild-type receptor. The expression of the variant receptor may modulate the degradation of hCG but be reduced by expression of the wild-type receptor in its lacking macrophages. Our data suggest a potentially important role for exon 9-deleted LH/CG receptors expressed in human placental villous macrophages in the local metabolism of hCG.