Research on the Correlations between Autonomic Nerve Activity and Cardiac Function and Consciousness Level during and after Open Heart Surgery

科学研究費補助金研究成果報告書研究種目: 一般研究(C)研究期間: 1993～1994課題番号: 05671115研究代表者: 田畑 良宏（滋賀医科大学・医学部・助教授）研究分担者: 松野 修一（滋賀医科大学・医学部・助手

Early Postnatal Exposure to a Low Dose of Decabromodiphenyl Ether Affects Expression of Androgen and Thyroid Hormone Receptor-Alpha and Its Splicing Variants in Mouse Sertoli Cells

<div><p>Decabromodiphenyl ether (decaBDE) adversely affects reproduction and development. Our previous study showed that postnatal exposure to a low dose of decaBDE (0.025 mg/kg body weight/day) by subcutaneous injection on postnatal days (PNDs) 1 through 5 leads to reductions in testicular size and number of Sertoli cells and sperm, while higher dose of decaBDE (2.5 mg/kg body weight/day) had no significant differences about these. In the present study, we examined the molecular mechanism of these effects on mouse testes following postnatal exposure to a low decaBDE dose. We hypothesized that postnatal exposure to decaBDE may alter levels of serum thyroid hormones (THs) and testosterone, or the level of TH receptor alpha (<i>Thra</i>) transcripts and its splicing variants and androgen receptor (<i>Ar</i>) in Sertoli cells, adversely affecting spermatogenesis. To test this hypothesis, we examined serum TH and testosterone levels and the levels of transcripts of the <i>Ar, Thra</i> and its splicing variants, and <i>Thra</i> splicing factors (<i>Hnrnpa1</i>, <i>Srsf1</i>, and <i>Hnrnph1</i>) with qPCR in isolated mouse Sertoli cells exposed postnatally to decaBDE (0.025, 0.25, and 2.5 mg/kg). Levels of serum testosterone and transcripts encoding <i>Ar</i>, <i>Thra</i>, and its variant, <i>Thra1,</i> declined significantly in Sertoli cells of mice exposed to 0.025 mg decaBDE/kg. No significant differences in serum TH level or <i>Thra2, Hnrnph1</i>, or <i>Srsf1</i> transcript levels were observed between control and decaBDE-exposed mice. However, the <i>Thra1</i>:<i>Thra2</i> and <i>Hnrnpa1</i>:<i>Srsf1</i> ratios were altered in Sertoli cells of mice exposed to 0.025 mg decaBDE/kg but not in cells exposed to 0.25 or 2.5 mg decaBDE/kg. These results indicate that postnatal exposure to a low dose of decaBDE on PNDs 1 through 5 lowers the testosterone level and the levels of <i>Ar</i> and <i>Thra</i> transcripts in Sertoli cells, accompanied by an imbalance in the ratios of <i>Thra</i> splicing variants, resulting in smaller testicular size and impaired spermatogenesis.</p></div

Levels of <i>Thra</i> and <i>Ar</i> transcripts in isolated Sertoli cells.

<p>Levels of transcripts of <i>Thra</i> (A), <i>Thra1</i> (B), <i>Thra2</i> (C), and <i>Ar</i> (D) were measured using qPCR in control and decaBDE-exposed isolated Sertoli cells cultured for 1 week. Transcript expression was normalized to the level of <i>Actb</i> transcript expression and is shown as the ratio relative to <i>Actb</i> compared with the control (set as a value of 1.0). Each value is the mean ± SD of 6-9 samples per group. *<i>P</i><0.05 compared with the control.</p

Serum testosterone levels in control and decaBDE-exposed mice.

<p>Testosterone levels in the serum of control and decaBDE-exposed mice were measured by ELISA. Each value is the mean ± SD of 6 samples per group. *<i>P</i><0.05 compared with the control.</p

Serum TH levels in control and decaBDE-exposed mice.

<p>Total T₃ (A), total T₄ (B), FT₃ (C) and FT₄ (D) levels in the serum of control and decaBDE-exposed mice were measured by ELISA. Each value is the mean ± SD of 6 samples per group.</p

Possible mechanism following early postnatal exposure to a low dose of decaBDE (0.025 mg/kg) in mouse testis.

<p>Early postnatal exposure to decaBDE from PND 1 to 5 causes to reduce serum testosterone level and <i>Ar</i> transcript levels in Sertoli cells, resulting in smaller testes size, reduced sperm count and a lower number of Sertoli cells, as well as decreased transcript levels of <i>Thra</i> and its splicing variant, <i>Thra1,</i> and an imbalance in the expression ratios of <i>Thra1</i>:<i>Thra2</i> and <i>Hnrnpa1</i>:<i>Srsf1</i> (gray box). It remains unknown if these latter changes are related to smaller testes size, reduced sperm count and lower number of Sertoli cells (dotted line).</p