Human megakaryocytes and platelets contain the estrogen receptor β and androgen receptor (AR): Testosterone regulates AR expression

Gender differences in vascular thromboses are well known, and there is evidence that platelets may be involved in these differences and that sex hormones affect platelet function. We characterized the expression of the estrogen receptor α (ER α), estrogen receptor β (ER β), progesterone receptor (PR), and androgen receptor (AR) in the megakaryocyte lineage. Megakaryocytes generated ex vivo from normal human CD34⁺ stem cells contained RNA for ER β and AR, which increased with cell differentiation. Platelets and human erythroleukemia (HEL) cells also contained ER β and AR transcripts. No ER α or PR messenger RNA or protein was detected in the megakaryocyte lineage. Immunofluorescence microscopy showed that ER β protein was present in glycoprotein (GP) IIb⁺ megakaryocytes and the HEL megakaryocytic cell line in a predominantly cytoplasmic location. AR showed a cytoplasmic and nuclear distribution in GPIIb⁺ and GPIIb^- cells derived from CD34⁺ cells and in HEL cells. Western immunoblotting confirmed the presence of ER β and AR in platelets. Megakaryocyte and HEL AR expression was up-regulated by 1, 5, and 10 nmol/L testosterone, but down-regulated by 100 nmol/L testosterone. These findings indicate a regulated ability of megakaryocytes to respond to testosterone and suggest a potential mechanism through which sex hormones may mediate gender differences in platelet function and thrombotic diseases. (C) 2000 by The American Society of Hematology.