中药调控双酚A诱发大鼠性早熟的表观遗传学机制探讨

The key mechanism of central precocious puberty onset is the advanced occurrence of the increased pulsatile hypothalamic GnRH release，hypothalamic kisspeptin encoded by Kiss-1 gene is a key factor of regulating GnRH neurons and an "information relay" that mediates the environmental factors interfering with puberty onset, and the two genes mentioned above is affected by the epigenetic mechanism. The epigenetics is also one of mechanisms by which environmental factors regulate puberty onset. Bisphenol A (BPA) which humans are the most widely exposed to is one of environmental endocrine disturbs (EEDs) and a trigger of precocious puberty, and it can affect gene expression by epigenetics. Our past studies indicate that Chinese traditional medicine can antagonize rats' precocious puberty induced by bisphenol A, yet if it is achieved by epigenetic mechanism is not well-known. In our research the female offspring of female rats exposed to bisphenol A in pregnancy or lactation will be used to observe the gene methylation and histone modification of hypothalamic Kiss-1 and GnRH gene during puberty onset to explore the epigenetic mechanism of BPA's inducing precocious puberty, and then the female offspring above are administrated to Chinese traditional medicine to clarify if it can antagonize rats' precocious puberty induced by bisphenol A by regulating two genes expression through epigenetics in order to deeply reveal its therapeutic mechanism of precocious puberty.

下丘脑GnRH脉冲性释放增多提前出现是真性性早熟的关键，Kisspeptin是调节GnRH神经元的关键因子，也是环境因素干扰青春期发育的“信息中继站”，由Kiss-1基因编码，两基因表达受表观遗传调控，表观遗传也是近年来发现的环境因素影响青春期启动的重要机制之一。双酚A是人类暴露最多的环境内分泌干扰物（EEDs），可通过表观遗传干扰基因表达，也可调节Kisspeptin、GnRH基因表达，是性早熟的诱因之一。课题组发现:中药可拮抗双酚A诱发大鼠性早熟，但是否通过表观遗传学实现不明确。本研究通过母鼠双酚A灌胃法使子代雌鼠在孕期、哺乳期暴露于双酚A，观察子代雌鼠青春期启动时下丘脑Kiss-1、GnRH基因表达中表观遗传学（DNA甲基化，组蛋白修饰）的变化，揭示双酚A诱发性早熟的机制，并给予中药干预，观察中药是否通过表观遗传调节两基因表达以此拮抗EEDs诱发性早熟，深入揭示中药治疗性早熟的机制。

世界范围内的流调显示近一个世纪儿童青春期发育的时相逐渐提前，性早熟的发病率逐渐增多，可能与环境污染与改变以及儿童营养健康状况改善等密切相关。性早熟对儿童身、心健康均可产生不良影响，也增加成年后代谢性疾病、乳腺癌等的发病风险，对性早熟发病原因、机理及防治仍是热点。环境内分泌干扰物（EED）是性早熟常见的诱因之一，此类物质诱发性早熟的机制不明确，本研究以性征发育研究明确的SD雌性大鼠作为研究对象，以人群中广泛暴露的BPA作为环境内分泌干扰物的代表，深入探讨环境内分泌干扰物诱发性早熟的机制，以及滋阴泻火中药治疗性早熟的机制。本次研究发现：生命发育早期（孕期、哺乳期）BPA（0-40 mg/kg·d）暴露可使下丘脑-垂体-性腺轴（HPG）提前激活而诱发性早熟；且此效应与暴露剂量成正相关；高浓度BPA暴露（20-40mg/Kg）在促进早发育的同时，还会导致性腺发育异常以及高雄激素症；低、中、高剂量新生期BPA暴露可导致大鼠下丘脑GnRH、Kiss1表达在mRNA及蛋白层面均明显增高，由此激活HPG轴；BPA暴露导致下丘脑kiss1、GnRH基因表达的机制通过改变下丘脑Kiss1基因启动子区域组蛋白的修饰而实现，或与改变Kiss1基因某些特定CpG位点甲基化水平有一定的关系；也可能与通过下丘脑脂质代谢相关的信号通路间接调节了Kiss、GnRH基因的表达而实现；滋阴泻火中药可以拮抗大鼠BPA暴露诱发的青春期发育提前。本次研究发现即使低剂量的EED对儿童HPG的影响亦不可忽视,且BPA诱发HPG启动的机制可能通过其本身的弱性激素效应，也可能通过表观遗传效应或脂质代谢途径等多靶点途径实现，这对于儿童乃至妇女保健以及疾病的预防具有一定的指导意义。中药可以拮抗BPA诱发性早熟这一现象，进一步完善了中医药治疗儿童性早熟的机制研究。