School of Forensic Medicine, China Medical University, Shenyang, Liaoning, People's Republic of China.
J Neurosci Res. 2012 Dec;90(12):2237-46. doi: 10.1002/jnr.23121. Epub 2012 Sep 18.
The neurotoxins paraquat (PQ) and dopamine (DA or 6-OHDA) cause apoptosis of dopaminergic neurons in the substantia nigra pars compacta (SNpc), reproducing an important pathological feature of Parkinson's disease (PD). Secretogranin III (SCG3), a member of the multifunctional granin family, plays a key role in neurotransmitter storage and transport and in secretory granule biogenesis, which involves the uptake of exogenous toxins and endogenous "toxins" in neuroendocrine cells. However, the molecular mechanisms of neurotoxin-induced apoptosis in dopaminergic neurons and the role of SCG3-associated signaling pathways in neuroendocrine regulation are unclear. To address this, we used PQ- and DA-induced apoptosis in SH-SY5Y human dopaminergic cells as an in vitro model to investigate the association between SCG3 expression level and apoptosis. SCG3 was highly expressed in SH-SY5Y cells, and SCG3 mRNA and protein levels were dramatically decreased after PQ treatment. Apoptosis induced by PQ is associated with caspase activation and decreased SCG3 expression, and restoration of SCG3 expression is observed after treatment with caspase inhibitors. Overexpressed SCG3 in nonneuronal cells and endogenous SCG3 in SH-SY5Y cells are cleaved into specific fragments by recombinant caspase-3 and -7, but the fragments were not detected in PQ-treated SH-SY5Y cells. Therefore, SCG3 may be involved in apoptosis signal transduction as a caspase substrate, leading to loss of its original biological functions. In addition, SCG3 may be a pivotal component of the neuroendocrine pathway and play an important role in neuronal communication and neurotransmitter release, possibly representing a new potential target in the course of PD pathogenesis.
百草枯（PQ）和多巴胺（DA 或 6-OHDA）会导致黑质致密部（SNpc）中的多巴胺能神经元凋亡，复制了帕金森病（PD）的一个重要病理特征。神经分泌颗粒蛋白 III（SCG3）是多功能颗粒蛋白家族的一员，在神经递质储存和运输以及分泌颗粒发生中发挥关键作用，涉及到神经内分泌细胞中外源毒素和内源性“毒素”的摄取。然而，多巴胺能神经元中神经毒素诱导的细胞凋亡的分子机制以及与 SCG3 相关的信号通路在神经内分泌调节中的作用尚不清楚。为了解决这个问题，我们使用 PQ 和 DA 诱导的 SH-SY5Y 人多巴胺能细胞凋亡作为体外模型，研究了 SCG3 表达水平与凋亡之间的关系。SCG3 在 SH-SY5Y 细胞中高度表达，PQ 处理后 SCG3 mRNA 和蛋白水平显著降低。PQ 诱导的凋亡与半胱天冬酶激活和 SCG3 表达减少有关，用半胱天冬酶抑制剂处理后观察到 SCG3 表达的恢复。在非神经元细胞中过表达的 SCG3 和 SH-SY5Y 细胞中的内源性 SCG3 被重组的 caspase-3 和 -7 切割成特定的片段，但在 PQ 处理的 SH-SY5Y 细胞中未检测到这些片段。因此，SCG3 可能作为半胱天冬酶的底物参与凋亡信号转导，导致其原有生物学功能丧失。此外，SCG3 可能是神经内分泌途径的关键组成部分，在神经元通讯和神经递质释放中发挥重要作用，可能代表 PD 发病机制过程中的一个新的潜在靶点。
