Department of Cell Biology, Capital Medical University, Beijing 100069, China.
Biochimie. 2012 Mar;94(3):617-27. doi: 10.1016/j.biochi.2011.09.013. Epub 2011 Sep 22.
Extracellular cysteine (Cys)/cystine (CySS) redox potential (E(h)) has been shown to regulate diverse biological processes, including enzyme catalysis, gene expression, and signaling pathways for cell proliferation and apoptosis, and is sensitive to aging, smoking, and other host factors. However, the effects of extracellular Cys/CySS redox on the nervous system remain unknown. In this study, we explored the role of extracellular Cys/CySS E(h) in metabotropic glutamate receptor 5 (mGlu5) activation to understand the mechanism of its regulation of nerve cell growth and activation. We showed that the oxidized Cys/CySS redox state (0 mV) in C6 glial cells induced a significant increase in mGlu5-mediated phosphorylation of extracellular signal-regulated kinase (ERK), blocked by an inhibitor of mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (MEK), U0126, a nonpermeant alkylating agent, 4-acetamide-4'-maleimidylstilbene-2,2'-disulfonic acid (AMS), and a specific mGlu5 antagonist, 2-methyl-6-(phenylethynyl)pyridine (MPEP), respectively. ERK phosphorylation under oxidized extracellular Cys/CySS E(h) was confirmed in mGlu5-overexpressed human embryonic kidney 293 (HEK293) cells. Oxidized extracellular Cys/CySS E(h) also stimulated the generation of intracellular reactive oxygen species (ROS) involved in the phosphorylation of ERK by mGlu5. Moreover, activation of mGlu5 by oxidized extracellular Cys/CySS E(h) was found to affect expression of NF-κB and inducible nitric oxide synthase (iNOS). The results also showed that extracellular Cys/CySS E(h) involved in the activation of mGlu5 controlled cell death and cell activation in neurotoxicity. In addition, plasma Cys/CySS E(h) was found to be associated with the process of Parkinson's disease (PD) in a rotenone-induced rat model of PD together with dietary deficiency and supplementation of sulfur amino acid (SAA). The effects of extracellular Cys/CySS E(h) on SAA dietary deficiency in the rotenone-induced rat model of PD was almost blocked by MPEP pretreatment, further indicating that oxidized extracellular Cys/CySS E(h) plays a role in mGlu5 activity. Taken together, the results indicate that mGlu5 can be activated by extracellular Cys/CySS redox in nerve cells, which possibly contributes to the process of PD. These in vitro and in vivo findings may aid in the development of potential new nutritional strategies that could assist in slowing the degeneration of PD.
细胞外半胱氨酸 (Cys)/胱氨酸 (CySS) 氧化还原电势 (Eh) 已被证明可调节多种生物学过程，包括酶催化、基因表达以及细胞增殖和凋亡的信号通路，并且对半胱氨酸/CySS 氧化还原对外界环境因素（如老化、吸烟等）较为敏感。然而，细胞外 Cys/CySS 氧化还原对神经系统的影响仍不清楚。在本研究中，我们探讨了细胞外 Cys/CySS Eh 在代谢型谷氨酸受体 5 (mGlu5) 激活中的作用，以了解其调节神经细胞生长和激活的机制。结果表明，C6 神经胶质细胞中氧化的 Cys/CySS 氧化还原状态 (0 mV) 可显著增加 mGlu5 介导的细胞外信号调节激酶 (ERK) 的磷酸化，这一过程可被丝裂原活化蛋白激酶 (MAPK)/细胞外信号调节激酶 (ERK) 抑制剂 U0126、非穿透性烷化剂 4-乙酰氨基-4'-亚甲二氧基苯乙腈 (AMS) 和特定的 mGlu5 拮抗剂 2-甲基-6-(苯乙炔基)吡啶 (MPEP) 阻断。在 mGlu5 过表达的人胚肾 293 (HEK293) 细胞中也证实了氧化的细胞外 Cys/CySS Eh 可诱导 ERK 磷酸化。氧化的细胞外 Cys/CySS Eh 还可刺激涉及 mGlu5 激活的细胞内活性氧 (ROS) 的生成，从而磷酸化 ERK。此外，研究发现，氧化的细胞外 Cys/CySS Eh 通过 mGlu5 激活可影响 NF-κB 和诱导型一氧化氮合酶 (iNOS) 的表达。结果还表明，细胞外 Cys/CySS Eh 参与 mGlu5 的激活可控制神经毒性中的细胞死亡和细胞激活。此外，在鱼藤酮诱导的帕金森病 (PD) 大鼠模型中，发现血浆 Cys/CySS Eh 与 PD 过程有关，包括饮食缺乏和硫氨基酸 (SAA) 补充。MPEP 预处理几乎阻断了细胞外 Cys/CySS Eh 在鱼藤酮诱导的 PD 大鼠模型中对 SAA 饮食缺乏的影响，进一步表明氧化的细胞外 Cys/CySS Eh 可调节 mGlu5 活性。综上所述，这些结果表明，神经细胞中的细胞外 Cys/CySS 氧化还原可激活 mGlu5，这可能有助于 PD 的发生。这些体外和体内研究结果可能有助于开发新的潜在营养策略，从而有助于减缓 PD 的退化。
