Simple and Fast Assay for Apolipoprotein E Phenotyping and Glycotyping: Discovering Isoform-Specific Glycosylation in Plasma and Cerebrospinal Fluid.
Simple and Fast Assay for Apolipoprotein E Phenotyping and Glycotyping: Discovering Isoform-Specific Glycosylation in Plasma and Cerebrospinal Fluid.
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DOI：
10.3233/jad-200203
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Nedelkov D
中科院分区：
文献类型：
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作者：
Hu Y;Meuret C;Go S;Yassine HN;Nedelkov D
载脂蛋白E β 4等位基因（APOE 4）增加阿尔茨海默病（AD）发病风险的机制尚未完全阐明。在脑脊液（CSF）中，apoE被严重糖基化。通过新开发的质谱免疫分析（MSIA）测定，确定APOE基因型对CSF和血浆中apoE蛋白亚型相对丰度及其特异性糖基化模式的影响。分析了一组非痴呆老年个体（n = 22）的血浆和CSF中的总糖基化和亚型特异性糖基化，该组个体由纯合的β 3和β 4或杂合的β 3/β 4、β 2/β 3或β 2/β 4携带者组成。 用唾液酸酶处理后，进一步证实了聚糖结构。在杂合子个体中，血浆中的apoE 3/E2、E4/E2和E4/E3亚型比率均显著低于CSF。对于所有个体，在血浆中观察到单个O-连接聚糖，而在CSF中观察到每个apoE两个聚糖（相同类型）。对于所有apoE亚型，CSF中的糖基化apoE与总apoE的比值均高于血浆。在血浆和CSF中，观察到从apoE 2> apoE 3> apoE 4降低糖基化的趋势。与其他亚型相比，apoE 4中CSF中二级糖基化百分比的差异显著更大。新的MSIA apoE检测方法可有效区分血浆和CSF中的apoE亚型和糖型。ApoE 4是CSF中主要的同种型，糖基化程度最低。通过MSIA评估apoE异构体特异性糖基化可能有助于阐明脑apoE代谢和AD风险。
The mechanisms of how APOE ɛ4 allele (APOE4) increases the risk of Alzheimer’s disease (AD) pathology have not been fully elucidated. In cerebrospinal fluid (CSF), apoE is heavily glycosylated. To determine the impact of APOE genotype on the relative abundance of apoE protein isoforms and their specific glycosylation patterns in CSF and plasma via a newly developed mass spectrometric immunoassay (MSIA) assay. Total glycosylation and isoform-specific glycosylation were analyzed in plasma and CSF from a group of non-demented older individuals (n = 22), consisting of homozygous ɛ3 and ɛ4 or heterozygous ɛ3/ɛ4, ɛ2/ɛ3, or ɛ2/ɛ4 carriers. The glycan structures were further confirmed after treatment with sialidase. In heterozygous individuals, the apoE3/E2, E4/E2, and E4/E3 isoform ratios were all significantly lower in plasma compared to CSF. For all individuals, a single O-linked glycan was observed in plasma, while two glycans (of the same type) per apoE were observed in CSF. The ratio of glycosylated to total apoE was greater in CSF compared to plasma for all apoE isoforms. In plasma and CSF, a trend of decreasing glycosylation was observed from apoE2 > apoE3 > apoE4. The difference in the percentage of secondary glycosylation in CSF was significantly greater in apoE4 compared to the other isoforms. The new MSIA apoE assay robustly distinguishes among apoE isoforms and glycoforms in plasma and CSF. ApoE4 is the predominant isoform and least glycosylated in CSF. Assessing apoE isoform-specific glycosylation by MSIA may help clarify brain apoE metabolism and AD risk.