The Proteome of the Dentate Terminal Zone of the Perforant Path Indicates Presynaptic Impairment in Alzheimer Disease
The Proteome of the Dentate Terminal Zone of the Perforant Path Indicates Presynaptic Impairment in Alzheimer Disease
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DOI：
10.1074/mcp.ra119.001737
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发表时间：
2020-01-01
影响因子：
7
通讯作者：
Frykman, Susanne
中科院分区：
文献类型：
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作者：
Haytural, Hazal;Mermelekas, Georgios;Frykman, Susanne
突触功能障碍是阿尔茨海默病（AD）的早期致病事件。因此，维持健康的神经传递对于减缓或阻止认知能力下降至关重要。为了寻找可能在突触功能障碍中发挥作用的蛋白质，我们研究了富含兴奋性突触的高度脆弱的海马区域的蛋白质组。我们深入的蛋白质组学分析表明 AD 中突触前信号传导受损。使用免疫组织化学，我们证实 AD 中复合蛋白-1、复合蛋白-2 和突触旋转蛋白-1 的水平显着降低。突触功能障碍是阿尔茨海默病 (AD) 的早期致病事件，导致网络紊乱和认知能力下降。有些突触比其他突触更脆弱，包括穿通路径的突触，它为海马体提供主要的兴奋性输入。为了阐明这些突触功能障碍的分子机制，我们对穿通路径的齿状末端区域进行了探索性蛋白质组学研究。齿状回分子层外三分之二（穿通路径突触所在的位置）是从五名 AD 受试者和五名对照者身上进行显微解剖的。将显微解剖的组织溶解并用胰蛋白酶消化。每个样品中的肽都用不同的同量异位标签标记，合并在一起并通过高分辨率等电聚焦预分级为 72 个级分。然后通过液相色谱-质谱法分析每个级分。我们量化了 7322 种蛋白质的相对表达水平，其中 724 种蛋白质在 AD 中表现出显着改变的水平。我们使用富集和通路分析进行的全面数据分析强烈表明，突触前信号传导（例如胞吐作用和突触小泡循环过程）在 AD 的该区域受到严重干扰，而突触后蛋白质则保持不变。在显着改变的蛋白质中，我们选择了三种下调幅度最大的突触蛋白质； Complexin-1、complexin-2 和 synaptogyrin-1，使用由 6 个 AD 病例和 8 个对照病例组成的新队列进行进一步验证。免疫组织化学染色的半定量分析证实，AD 齿状回外三分之二分子层中的complexin-1、complexin-2 和 synaptogyrin-1 水平降低。我们深入的蛋白质组学分析提供了关于 AD 相关突触功能障碍潜在分子机制的广泛知识，并支持疾病早期阶段突触前改变比突触后改变更重要。所鉴定的特定突触蛋白有可能用于阻止 AD 中的突触功能障碍。
Synaptic dysfunction is an early pathogenic event in Alzheimer disease (AD). Hence the maintenance of healthy neurotransmission becomes crucial to slow or halt cognitive decline. In search of identifying proteins that could play a role in synaptic dysfunction, we studied the proteome of a highly vulnerable hippocampal region that is enriched in excitatory synapses. Our in-depth proteomic analysis suggests an impaired presynaptic signaling in AD. Using immunohistochemistry, we verified significantly reduced levels of complexin-1, complexin-2, and synaptogyrin-1 in AD.Synaptic dysfunction is an early pathogenic event in Alzheimer disease (AD) that contributes to network disturbances and cognitive decline. Some synapses are more vulnerable than others, including the synapses of the perforant path, which provides the main excitatory input to the hippocampus. To elucidate the molecular mechanisms underlying the dysfunction of these synapses, we performed an explorative proteomic study of the dentate terminal zone of the perforant path. The outer two-thirds of the molecular layer of the dentate gyrus, where the perforant path synapses are located, was microdissected from five subjects with AD and five controls. The microdissected tissues were dissolved and digested by trypsin. Peptides from each sample were labeled with different isobaric tags, pooled together and pre-fractionated into 72 fractions by high-resolution isoelectric focusing. Each fraction was then analyzed by liquid chromatography-mass spectrometry. We quantified the relative expression levels of 7322 proteins, whereof 724 showed significantly altered levels in AD. Our comprehensive data analysis using enrichment and pathway analyses strongly indicated that presynaptic signaling, such as exocytosis and synaptic vesicle cycle processes, is severely disturbed in this area in AD, whereas postsynaptic proteins remained unchanged. Among the significantly altered proteins, we selected three of the most downregulated synaptic proteins; complexin-1, complexin-2 and synaptogyrin-1, for further validation, using a new cohort consisting of six AD and eight control cases. Semi-quantitative analysis of immunohistochemical staining confirmed decreased levels of complexin-1, complexin-2 and synaptogyrin-1 in the outer two-thirds of the molecular layer of the dentate gyrus in AD. Our in-depth proteomic analysis provides extensive knowledge on the potential molecular mechanism underlying synaptic dysfunction related to AD and supports that presynaptic alterations are more important than postsynaptic changes in early stages of the disease. The specific synaptic proteins identified could potentially be targeted to halt synaptic dysfunction in AD.