Relative Abundance of apoE and Aβ1–42 Associated with Abnormal Prion Protein Differs between Creutzfeldt-Jakob Disease Subtypes

Aggregated
and protease-resistant mammalian prion protein (PrPSc)
is the primary protein component of infectious prions.
Enriched PrPSc preparations are often used to study the
mechanisms that underly prion disease. However, most enrichment procedures
are relatively nonspecific and tend to yield significant amounts of
non-PrPSc components including various proteins that could
confound functional and structural studies. It is thus important to
identify these proteins and assess their potential relevance to prion
pathogenesis. Following proteinase K treatment and phosphotungstic
acid precipitation of brain homogenate, we have used mass spectrometry
to analyze the protein content of PrPSc isolated from prion-infected
mice, multiple cases of sporadic Creutzfeldt-Jakob disease (sCJD),
and human growth hormone associated cases of iatrogenic CJD (iCJD).
Creatine kinase was the primary protein contaminant in all PrPSc samples, while many of the other proteins identified were
also found in non-CJD controls, which suggests that they are not CJD
specific. Interestingly, the Alzheimer’s disease associated
peptide amyloid β 1–42 (Aβ1–42) was identified
in the majority of the sCJD cases as well as non-CJD age-matched controls,
while apoliprotein E was found in greater abundance in the sCJD cases.
By contrast, while some of the iCJD cases showed evidence of higher
molecular weight Aβ oligomers, monomeric Aβ1–42
peptide was not detected by immunoblot, and only one case had significant
levels of apolipoprotein E. Our data are consistent with the age-associated
deposition of Aβ1–42 in older sporadic CJD and non-CJD
patients and suggest that both apolipoprotein E and Aβ1–42
abundance can differ depending upon the type of CJD.

聚集型抗蛋白酶哺乳动物朊蛋白（PrPSc, protease-resistant mammalian prion protein）是传染性朊病毒的主要蛋白组分。富集的PrPSc制剂常被用于研究朊病毒疾病的潜在发病机制。然而，多数富集流程相对缺乏特异性，往往会残留大量非PrPSc成分，包括多种可能干扰功能与结构研究的蛋白。因此，鉴定这些污染蛋白并评估其与朊病毒致病过程的潜在关联至关重要。
本研究对脑组织匀浆进行蛋白酶K（proteinase K）处理与磷钨酸（phosphotungstic acid）沉淀后，采用质谱（mass spectrometry）分析法对来自朊病毒感染小鼠、多例散发性克雅氏病（sCJD, sporadic Creutzfeldt-Jakob disease）患者以及人生长激素相关医源性克雅氏病（iCJD, iatrogenic CJD）病例中分离得到的PrPSc的蛋白组成进行了分析。
所有PrPSc样本中的主要蛋白污染物均为肌酸激酶；其余多数鉴定出的蛋白也在非克雅氏病对照样本中被检出，提示这些蛋白并非克雅氏病特异性标志物。
值得注意的是，阿尔茨海默病相关肽段β淀粉样蛋白1-42（Aβ1–42, amyloid β 1–42）在多数sCJD病例以及年龄匹配的非克雅氏病对照样本中均被检出；而载脂蛋白E（apolipoprotein E）在sCJD病例中的丰度更高。
与之形成对比的是，尽管部分iCJD病例存在高分子量Aβ寡聚体的证据，但免疫印迹法未检测到单体型Aβ1–42肽段，且仅1例iCJD病例中存在高水平的载脂蛋白E。
本研究数据与老年散发性克雅氏病及非克雅氏病患者体内Aβ1–42的年龄相关性沉积特征相符，同时提示载脂蛋白E与Aβ1–42的丰度可能因克雅氏病的类型而异。