Expression of Adrenomedullin by Human Placental Cytotrophoblasts and Choriocarcinoma JAr Cells

Adrenomedullin is a multifunctional peptide expressed in a variety of tissues. This study was conducted to investigate the expression of adrenomedullin and its mRNA by human trophoblasts and the possible existence of adrenomedullin receptor in those cells. Human placentas in all three trimesters were obtained from patients undergoing therapeutic abortions and deliveries. Total RNA was extracted from placental trophoblastic tissues and JAr choriocarcinoma cells, and the expression of adrenomedullin mRNA was determined by RT-PCR. Immunohistochemical analysis was performed by the avidin/biotin immunoperoxidase method using a specific antibody to adrenomedullin. The secretion of adrenomedullin by JAr cells cultured in medium containing [35S]cysteine-[35S]methionine was determined by immunoprecipitation followed by PAGE. The presence of adrenomedullin receptor in JAr cells was examined using a binding assay with [125I]rat adrenomedullin. Adrenomedullin mRNA was expressed by human placental trophoblastic tissues in all three trimesters and by JAr cells. Immunohistochemical analysis revealed that adrenomedullin is expressed by cytotrophoblasts in placentas in all three trimesters, but not by syncytiotrophoblasts. The expression of adrenomedullin in the cytotrophoblast was most abundant in first trimester placenta and became less abundant during the course of pregnancy. JAr cells synthesized and secreted immunoreactive adrenomedullin. Binding assay with [125I]rat adrenomedullin demonstrated specific binding of adrenomedullin to JAr cells, indicating the existence of a specific receptor for adrenomedullin in trophoblastic cells. Adrenomedullin is transcribed and secreted by cytotrophoblastic cells that possess adrenomedullin receptor. Adrenomedullin may play a potential role as an autocrine/paracrine factor in the growth of cytotrophoblasts, especially in early gestation.