The molar vesicle fluid contains the beta-core fragment of human chorionic gonadotropin

Human chorionic gonadotropin induces human macrophages to form intracytoplasmic vacuoles mimicking Hofbauer cells in human chorionic villi

The most characteristic morphological feature of macrophages in the stroma of placental villi, known as Hofbauer cells, is their highly vacuolated appearance. They also show positive immunostaining for human chorionic gonadotropin (hCG) and express messenger ribonucleic acid of the luteinizing hormone/chorionic gonadotropin receptor with a deletion of exon 9 (LH/CG-R Δ9). Maternal hCG enters fetal plasma through the mesenchyme of the placental villi and promotes male sexual differentiation in early pregnancy; therefore, excess hCG may induce aberrant genital differentiation and hCG must be adjusted at the fetomaternal interface. We hypothesized that hCG is regulated by Hofbauer cells and that their peculiar vacuoles are involved in a cell-specific function. To assess the morphological modification and expression of LH/CG-R Δ9 in human macrophages after hCG exposure, the present study examined phorbol 12-myristate 13-acetate (PMA)-treated THP-1 cells, a human monocyte-macrophage cell line. hCG induced transient vacuole formation in PMA-treated THP-1 cells, morphologically mimicking Hofbauer cells. Immunocytochemistry showed that PMA-treated THP-1 cells incorporated hCG but not luteinizing hormone or follicle-stimulating hormone. Western blotting analyses demonstrated that PMA-treated THP-1 cells expressed an immunoreactive 60-kDa protein, designated as endogenous LH/CG-R Δ9. hCG induced a transient reduction in the LH/CG-R Δ9, which was synchronous with the appearance of cytoplasmic vacuoles. In conclusion, human macrophages regulating hCG via cytoplasmic LH/CG-R Δ9 mimic the morphological characteristics of Hofbauer cells. Their vacuoles may be associated with their cell-specific function to protect the fetus from exposure to excess maternal hCG during pregnancy.

Human chorionic villous macrophages as a fetal biological shield from maternal chorionic gonadotropin

In addition to its most well characterized biological role in the rescue and maintenance of corpus luteum function, human chorionic gonadotropin (hCG) also stimulates the onset of fetal gonadal steroidogenesis. However, excess hCG is teratogenic to fetal gonadal tissues, and therefore hCG must be tightly regulated. Although there is an anatomical barrier between the fetal vessels and maternal blood, other mechanisms may regulate hCG levels. In the present study, we investigated whether human chorionic villous macrophages degraded maternal hCG. Isolated human macrophages incorporated and degraded hCG in a time-dependent manner. Human placental villous macrophages and phorbol myristate acetate (PMA)-treated THP-1 cells expressed the gene encoding an exon 9-deleted form of the luteinizing hormone/chorionic gonadotropin (LH/CG) receptor; expression of the full-length receptor was not determined. While both PMA-treated or untreated THP-1 cells could uptake hCG into their cytoplasms, hCG degradation and excretion of its byproducts only progressed in PMA-treated THP-1 cells. In conclusion, hCG internalization and degradation are different processes in macrophages that protect fetal gonadogenesis from excess hCG. The exon 9-deleted LH/CG receptor, but not the full-length receptor, is involved in the degradation of cytoplasmic hCG by organ-specific, dominant-negative interactions.

The human chorionic gonadotropin molecule from patients with trophoblastic diseases has a high thyrotropic activity but is less active in the ovary

To examine the pathogenesis of hyperthyroidism in women with trophoblastic diseases, the biological activity of human chorionic gonadotropin (hCG) molecules in women with normal pregnancy (n = 85) and in women with trophoblastic diseases (vesicular mole, n = 30; and choriocarcinoma, n = 12) was compared. Hyperthyroidism (thyroid stimulating hormone (TSH) < 0.3 mIU/l) was observed more frequently in women with trophoblastic diseases. All the sera were then subjected to Chinese hamster ovary cells transfected with the human TSH receptor (CHO-hTSHr cells) and cAMP production was compared. Sera from the women with choriocarcinoma showed the highest cAMP production. Interestingly, significant correlation between serum hCG level and cAMP production in CHO-hTSHr cells was observed only in women with trophoblastic disease. All the sera were then applied to CHO cells transfected with hCG/luteinizing hormone (LH) receptor (CHO-hCG/LHr cells). In contrast to the findings with the TSH receptor, sera from the women with normal pregnancy showed the highest cAMP production in these cells. Correlation between serum hCG level and cAMP production in CHO-hCG/LHr cells was significant only in normal pregnancy. These results indicate that the hCG molecule from women with trophoblastic diseases displays enhanced thyrotropic activity.