STEROIDOGENESIS AND HORMONE ACTION IN THE TESTIS
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(100) ESTRADIOL INCREASES PROLIFERATIVE CAPACITY OF IMMATURE RAT LEYDIG CELLS.
Ge, Ren-Shan1, Akingbemi, Benson1, Sottas, Chantal1, Hardy, Matthew1, 1 Center for Biomedical Research, New York, NY
ABSTRACT- Aromatase, the enzyme that catalyzes synthesis of the natural estrogen 17-estradiol (E2), and estrogen receptor proteins (ER and ER) are expressed in the male reproductive tract and specifically in Leydig cells. Thus, Leydig cells are subject to estrogen action. ER ( and ) expression levels are highest in developing Leydig cells at the time of greatest mitotic activity in this cell type. The aim of the present study was to evaluate the direct effects of estrogen on Leydig cell proliferation at different developmental stages: progenitor (PLC) from 21-, immature (ILC) from 35-, and adult Leydig cells (ALC) from 90-day old Sprague Dawley rats. Leydig cell proliferative capacities were measured by 3H-thymidine incorporation after exposure to different E2 concentrations (range: 10 nM to 1000 nM) in vitro. At low doses, 10 and 50 nM, E2 significantly inhibited proliferation of progenitor Leydig cells but this effect was absent at higher doses. On the other hand, E2 caused dose-dependent increases in thymidine incorporation (cpm/103 cells) by immature Leydig cells: 1.6 ± 0.1, 1.9 ± 0.2*, 1.9 ± 0.1*, 3.4 ± 0.2*, 3.4 ± 0.2*, and 7.1 ± 0.3* at 0, 10, 50, 250, 500, 1000 nM (*p < 0.001 compared to control untreated cells). Adult Leydig cells did not incorporate thymidine to any significant extent. The steady-state mRNA levels for the two ER subtypes were measured in purified Leydig cells at 21, 35, and 90 days of age. ER expression was low and detectable only in progenitor Leydig cells. However, Leydig cells at all stages expressed ER mRNA, and levels were highest at the immature stage. When normalized to ribosomal protein S16 mRNA as internal control, the values were 1.68 for PLC, 2.65 for ILC, and 1.64 for ALC. Increased ER expression is known to enhance estrogen signaling. In summary, these observations indicate that estrogen may have a regulatory role in Leydig cell proliferation during development. They also suggest that exposures to environmental agents with estrogenic activity have the potential to alter the rates of Leydig cell mitosis. There are implications for Leydig cell hyperplasia because increased E2 production in transgenic mice overexpressing the aromatase gene induces Leydig cell tumors. Supported by NIH HD 32588 and ES 10233.
KEY WORDS: estrogen, estrogen receptor isoforms, Leydig cell, proliferation