Wnt通路在百草枯及代森锰所致多巴胺能神经损伤中的作用及机制的研究

Parkinson’s disease (PD) is a kind of progressive and irreversible nervous system disease which is characterized by the damage of dopaminergic (DA) neurons. Recent studies have shown that one exposed to environmental toxicants during his/her early life can lead to dysfunction of some neural protective genes and subsequently progressive degeneration of DA neurons when he/she grown up or aged. Our previous study has shown that exposure to paraquat in development period can lead to DA neurons injury through down-regulating the expression of nuclear receptor-related factor 1 (Nuur1) whose precursors’ proliferation and differentiation are under the regulation of Wnt signaling. Therefore, we hypothesized that Wnt signaling is involved in regulating the differentiation of DA neurons during early life exposure to environmental toxicants; the Wnt signaling and related gene expression changes were continuously exist and would play a key role in the DA neurons injuries in response to environmental stimuli or aged. In the present study, two pesticides paraquat and maneb were selected as representative environmental toxicants because they can causes classic symptoms of PD. In vitro cell culture and in vivo animal experiment were designed in this study, and gene overexpression and RNA interference were used to detect how Wnt signaling regulating the differentiation and maturation of DA’ precursors, and therefore to explore the mechanism by which early life exposure to environmental toxicants cause late onset of DA injuries. Thus, the present study is hopefully to provide some new theoretical bases for clinical screening of the preventive or therapeutic targets for some degenerative diseases.

帕金森病（PD）是以多巴胺(DA)能神经元受损为主要特征的一类神经退行性疾病。最近研究表明生命早期暴露环境毒物可致成年/老年某些神经元保护基因功能障碍，引起进展性DA能神经元变性。我们前期研究发现，发育期接触百草枯使核受体相关因子1（Nurr1）的表达下调，导致DA能神经元受损。Nurr1前体物质的增生和分化受Wnt通路调节，因此我们假设，生命早期接触环境毒物可通过Wnt通路影响DA能神经元分化，这种影响持续存在，并在成年/老年期受到环境/年龄等因素的刺激时再次发挥关键调控作用导致DA能神经元损伤。本研究以引起典型类PD症状的环境毒物百草枯和代森锰为研究工具，利用基因过表达和RNA干扰等技术，以控制 DA 能神经元前体细胞分化和成熟的Wnt通路为切入点，结合细胞培养和动物试验的方法探讨生命早期接触环境毒物对DA 能神经损伤的机制，为人类某些神经退行性病的预防及治疗提供新的理论依据和靶点。

本研究以引起典型类PD症状的环境毒物百草枯（PQ）和代森锰为研究工具，以控制 DA 能神经元前体细胞分化和成熟的Wnt通路为切入点来探讨生命早期接触环境毒物对DA 能神经损伤的机制。研究结果表明：联合应用PQ和代森锰能抑制SH-SY5Y细胞的增殖和分化，使细胞内Wnt1、核受体相关因子1（Nurr1）和酪氨酸羟化酶（TH）表达下调，Wnt5a表达上调。用SiRNA抑制Wnt1表达后，其下游Nurr1和TH表达均下调，Wnt5a表达上调。说明Wnt 通路在Nurr1诱导的DA能神经元损伤中起到了重要作用。体内实验研究进一步表明孕期和哺乳期联合暴露PQ和代森锰能使断乳后的大鼠Wnt1基因表达下调，Wnt5a表达上调，Nurr1和TH的表达下调，Wnt通路的这种表达失调一直持续到了成年期。同时成年期的仔鼠再次暴露PQ时，大鼠的行为能力和纹状体内DA含量与未暴露组相比，其下降的更为显著。说明神经发育的关键期联合暴露PQ和代森锰不仅导致DA能神经元受损还加重了DA能神经元对外界环境的易感性。