Huntington’s disease (HD) is a neurodegenerative disease that involves a complex combination of psychiatric, cognitive and motor impairments. Synaptic dysfunction has been implicated in HD pathogenesis. However, the mechanisms have not been clearly delineated. Synaptic vesicular zinc is closely linked to modulating synaptic transmission and maintaining cognitive ability. It is significant to assess zinc homeostasis for further revealing the pathogenesis of synaptic dysfunction and cognitive impairment in HD. Histochemical staining by autometallography indicated that synaptic vesicular zinc was decreased in the hippocampus, cortex and striatum of N171-82Q HD transgenic mice. Analyses by immunohistochemistry, Western blot and RT-PCR found that the expression of zinc transporter 3 (ZnT3) required for transport of zinc into synaptic vesicles was obviously reduced in these three brain regions of the HD mice aged from 14 to 20 weeks and BHK cells expressing mutant huntingtin. Significantly, dual-luciferase reporter gene and chromatin immunoprecipitation assays demonstrated that transcription factor Sp1 could activate ZnT3 transcription via its binding to the GC boxes in ZnT3 promoter. Moreover, mutant huntingtin was found to inhibit the binding of Sp1 to the promoter of ZnT3 and down-regulate ZnT3 expression, and the decline in ZnT3 expression could be ameliorated through overexpression of Sp1. This is first study to reveal a significant loss of synaptic vesicular zinc and a decline in ZnT3 transcriptional activity in the HD transgenic mice. Our work sheds a novel mechanistic insight into pathogenesis of HD that mutant huntingtin down-regulates expression of ZnT3 through inhibiting binding of Sp1 to the promoter of ZnT3 gene, causing disruption of synaptic vesicular zinc homeostasis. Disrupted vesicular zinc ultimately leads to early synaptic dysfunction and cognitive deficits in HD. It is also suggested that maintaining normal synaptic vesicular zinc concentration is a potential therapeutic strategy for HD.

中文翻译：

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亨廷顿病转基因小鼠大脑中锌转运蛋白 ZnT3 转录活性和突触囊泡锌的破坏。

亨廷顿病 (HD) 是一种神经退行性疾病，涉及精神、认知和运动障碍的复杂组合。突触功能障碍与 HD 发病机制有关。然而，机制尚未明确描述。突触囊泡锌与调节突触传递和维持认知能力密切相关。评估锌稳态对于进一步揭示 HD 中突触功能障碍和认知障碍的发病机制具有重要意义。自动金相组织化学染色表明，N171-82Q HD 转基因小鼠的海马、皮质和纹状体中突触囊泡锌减少。通过免疫组织化学分析，Western blot和RT-PCR发现，在14-20周龄的HD小鼠和表达突变亨廷顿蛋白的BHK细胞的这三个脑区，锌转运到突触小泡所需的锌转运蛋白3（ZnT3）的表达明显降低。值得注意的是，双荧光素酶报告基因和染色质免疫沉淀测定表明，转录因子 Sp1 可以通过与 ZnT3 启动子中的 GC 盒结合来激活 ZnT3 转录。此外，发现突变亨廷顿蛋白抑制Sp1与ZnT3启动子的结合并下调ZnT3的表达，并且通过Sp1的过表达可以改善ZnT3表达的下降。这是第一项揭示 HD 转基因小鼠突触囊泡锌显着丧失和 ZnT3 转录活性下降的研究。我们的工作揭示了 HD 发病机制的新机制见解，即突变亨廷顿蛋白通过抑制 Sp1 与 ZnT3 基因启动子的结合来下调 ZnT3 的表达，从而破坏突触泡状锌稳态。被破坏的囊泡锌最终导致 HD 的早期突触功能障碍和认知缺陷。还建议维持正常的突触小泡锌浓度是 HD 的潜在治疗策略。