血红素缺乏在铅致神经发育毒性中的作用研究

Lead (Pb) exposure decreased the activity of ALAD and increased the activity of HO-1 in neural system prompted that Pb exposure could induce heme deficiency. The deficiency of heme results in serious neurodevelopmental damage which can be also observed in Pb-exposed neural system, such as reduction of neurotrophic factors expression, abnormal neurons differentiation, neurons dysfunction and even apoptosis. However, it is unkown that the role of heme deficiency in Pb-induced developmental neurotoxicity. Our previous study indicated that Pb treatment decreased the levels of synapsins and neurotrophic factors in nerve cells, which could be relieved while heme was supplemented. Therefore, we take the opinion that heme deficiency participates into the process of Pb-induced developmental neurotoxicity. In this current research, we will firstly explore the mechanism of Pb-induced heme deficiency in fetal rats, rat neural stem cells and SH-SY5Y cells. Then, we will study whether heme supplement can provide the protective effects against Pb-induced developmental neurotoxicity during the process of neural stem cells differentiate to mature neurons. Finally, we will investigate the protective role of heme for Pb-induced developmental neurotoxicity through increasing the heme level by intervening in the synthesis, transportation and degradation of heme in SH-SY5Y cells. This study will help to illuminate the process and mechanism of developmental neurotoxicity induced by Pb, and will provide scientific evidence for heme as a novel intervention site against Pb-induced developmental neurotoxicity.

研究发现铅在神经系统中可致ALAD酶活性降低和HO-1酶活性升高，提示其可导致血红素缺乏。血红素缺乏与铅诱导的神经发育毒性有众多相似之处，均可导致神经营养因子水平降低，神经元分化异常、功能紊乱甚至凋亡等。然血红素缺乏是否参与铅致神经发育毒性过程还未可知。前期研究发现铅暴露导致神经元突触蛋白及神经营养因子水平显著下降，这一现象在补充血红素后得以改善。据此，本研究提出铅暴露导致神经细胞血红素缺乏，后者参与铅致神经发育毒性过程。本研究拟在胎鼠、大鼠神经干细胞及SH-SY5Y细胞中探索铅致血红素缺乏的机制；然后在神经干细胞分化为成熟神经元过程中探讨补充血红素是否对铅致神经发育毒性具有保护作用；最后通过干预SH-SY5Y细胞血红素合成、运输或降解过程来提高血红素水平，明确血红素对铅致神经发育毒性的保护作用。本研究的完成将有助于阐明铅致神经发育毒性的过程和机制，并为血红素作为潜在干预位点提供科学依据。

铅对发育期神经系统的影响非常严重，可导致儿童智力低下、听力损伤、生长发育迟缓、行为障碍、记忆力减退等，因此明确铅致神经发育毒性机制并进行有效的干预是亟需解决的问题。既往研究发现铅在神经系统中可致ALAD酶活性降低和HO-1酶活性升高，提示铅暴露可致神经细胞血红素缺乏。血红素缺乏与铅诱导的神经发育毒性有众多相似之处，然其是否参与铅致神经发育毒性过程还未可知。本研究利用补充血红素和基因编辑敲降BACH1干预血红素代谢的方法，探讨血红素缺乏在铅致神经发育毒性中的作用，发现：1.PbAc在大鼠神经干细胞和SH-SY5Y细胞中导致血红素合成过程中的ALAD酶活性显著降低，同时介导血红素分解的HO-1酶活性显著升高；2.补充Hemin在分化SH-SY5Y细胞中缓解PbAc诱导的ATP产生减少和氧化磷酸化（OXPHOS）水平降低，并抑制PbAc诱导的糖酵解；3.Hemin缓解PbAc对分化的SH-SY5Y细胞轴突生长和突触蛋白表达的抑制；4.PbAc促进分化的SH-SY5Y细胞中BACH1的表达，而Hemin抑制铅诱导的BACH1表达增加；5.敲降BACH1在分化的SH-SY5Y细胞中缓解PbAc诱导的线粒体OXPHOS水平降低和ATP产生减少，抑制PbAc诱导的糖酵解；6.敲降BACH1促进分化的SH-SY5Y细胞中线粒体OXPHOS相关亚基的表达；7.敲降BACH1缓解PbAc对分化的SH-SY5Y细胞轴突生长和突触形成的抑制作用，对铅致分化神经元生长和突触损伤具有保护作用。综上，本研究发现，铅暴露通过抑制血红素合成和促进血红素降解导致神经元中血红素水平下降，Hemin通过抑制铅诱导的BACH1的表达进而维持神经元线粒体呼吸功能，对分化神经元的生长和突触形成具有保护作用。本研究进一步阐明了铅致神经发育毒性机制，同时为血红素作为潜在干预位点提供了科学依据。