围生期接触环境雌激素双酚A诱发雄鼠性早熟及其分子机制的研究

Sexual precocity is a growth and development disorder accompanying by the advancement of the puberty. Environmental estrogens, estrogenic chemicals in the environment, were showed to have close relationships with the early-onset puberty. Bisphenol A (BPA), which has a similar structure with diethylstilbestrol (DES), is the main representative of phenolic environmental estrogens. The previous results of our lab for the first time demonstrate that perinatal exposure (from gestation day 10 through lactation day 7) to the environmental dose of BPA (2μg/kg/d) can increase the weigh of testis and the number of elongating spermatids compared to control male rat at PND 35, which suggest BPA can advance the puberty of male rats. Spermatogenesis and sperm maturation are regulated by the FSH/LH and T in the hypothalamic-pituitary-testicular axis (HPT axis) and the gene expression in the germ cells. On this basis, using molecular-biological and pharmacological approaches, this project will focus on: (1) clarify the effect of perinatal exposure to BPA on the activation of GnRH neurons, and the synthesis and release of FSH/LH and T; (2) explain the roles of BPA-induced reproductive endocrine alternation on the mitosis and meiosis of germ cells; (3) discuss the influences of BPA exposure on epigenetic modification of spermatogenesis and sperm maturation associated genes, then clarify the molecular mechanisms underlying BPA-induced testicular development and the onset of spermatogenesis at puberty. The results of this study will provide the theoretical basis and tactics for prevention and treatment of sexual precocity.

性早熟是一种生长发育异常现象，表现为青春期特征提前出现。外环境中的雌激素样化合物-环境雌激素被认为与性早熟的发生密切相关。双酚A(bisphenol A, BPA)结构与己烯雌酚相似，是酚类环境雌激素的主要代表。本室前期研究首次发现，围生期(胚胎第10天至出生后第7天)接触低剂量BPA(2μg/kg/d)能够引起子代雄鼠青春期睾丸重量增加和精子细胞提前出现。精子的发生和成熟主要受到下丘脑-垂体-睾丸轴上促性腺激素和雄激素的调控以及生精细胞内固有基因的调节。基于此，本课题的研究焦点是(1)明确围生期BPA暴露对下丘脑GnRH神经元的青春期启动、促性腺激素和雄激素产生和释放的影响；(2)阐述BPA扰乱生殖内分泌功能对生精过程中有丝分裂和减数分裂的作用；(3)探讨BPA对精子发生和成熟相关基因表观遗传的影响。通过阐明环境雌激素致睾丸发育和精子发生提前的分子机制，为性早熟的预防和治疗提供理论依据。

早期研究已报道，胚胎期低剂量BPA暴露可引起子代雌鼠性早熟。但有关BPA暴露对雄性子代性早熟影响的研究甚少。本研究首先发现，围生期(胚胎第10天至出生后第7天)接触低剂量BPA(2μg/kg/d)能够引起子代雄鼠青春期睾丸重量增加和精子细胞提前出现。进一步的实验结果表明，青春期前BPA-雄鼠血浆FSH和LH水平都显著升高，LH脉冲频率明显加快；GnRH mRNA水平明显增加；ARC-kiss1 mRNA水平明显增加。这些结果表明BPA暴露通过激活ARC-kiss肽神经元提前启动HPT轴。同时研究还发现，BPA暴露增强了PND21 KLm和Cys-TE（Sertoli细胞特异性基因）以及c-fos和Jun-B（减数分裂相关基因）等基因的表达，而且表达增强可以被GPR-54拮抗剂P234阻断。而且FSH水平的升高和精子发生的提前均可被阻断。这些结果表明围生期环境剂量BPA暴露可以提高kiss1表达提前激活GnRH神经元，进而通过FSH-Sertoli细胞促进精子细胞的减数分裂。. 另外，本课题还发现将种植前胚胎（胚胎第1天至第5天）暴露于低剂量BPA(20μg/kg/d)可以阻碍青春期至成年期睾丸的发育，同时伴有睾酮水平的长期下降。深入的研究发现种植前BPA暴露可以通过降低StAR启动子区H3和H3K14乙酰化进而长久抑制StAR的表达并最终抑制睾酮水平。该结果说明植入前BPA暴露可以通过特异性地降低StAR 启动子区乙酰化水平长期降低睾酮水平进而延缓睾丸的发育。