School of Pharmacy, University of Wisconsin-Madison, Madison, WI 53705, United States.
Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53705, United States.
J Proteomics. 2022 Apr 15;257:104507. doi: 10.1016/j.jprot.2022.104507. Epub 2022 Feb 3.
Alzheimer's disease (AD) is the most common form of dementia and one of the leading causes of death in the United States. In the past decades, extensive efforts have been devoted to biomarker discovery for early diagnosis and treatment of AD. Herein, this study aims to quantify clusterin (CLU) and apolipoprotein E (APOE) in blood samples from AD patients and evaluate these two proteins as potential biomarkers in AD diagnosis. In-house synthesized 5-plex isotopic N,N-dimethyl leucine (iDiLeu) tags were used to label target peptide standards at different concentrations to construct standard curves. Our study revealed that the levels of CLU and APOE exhibited clear differences in male vs. female AD groups but not in male vs. female non-AD groups. In contrast, the levels of serum CLU and APOE did not show statistically significant differences in the AD groups and non-AD groups. Principal component analysis (PCA) with CLU and APOE showed some separation between the AD and non-AD participants. Significance: Dissecting CLU and APOE heterogeneity in AD pathogenesis may therefore facilitate delineating the pathological relevance for sex-related pathways, leading to personalized medicine in the future. Collectively, this study introduces a cost-effective absolute quantitative proteomics strategy for target protein quantitation and lays the foundation for future investigation of CLU and APOE as potential biomarkers for AD. SIGNIFICANCE STATEMENT: As blood-based biomarkers for AD diagnosis are cost-effective and introduce less invasiveness, discovery and validation of biomarkers in the blood samples of AD patients have become a hot topic in Alzheimer's and dementia research. Thus far, amyloid β (Aβ), total-tau and phosphorylated tau (p-tau) in blood show great accuracy and specificity in diagnosis of AD. However, the underlying mechanism of AD pathology remains to be elusive and complex. Besides these well studied proteins, many other proteins, such as clusterin (CLU) and apolipoprotein E (APOE) have also been found to be related to AD development. It has been implicated that these two proteins are involved in Aβ clearance and deposition. In this study, we measure the absolute concentrations of these two proteins in blood and shed some light on the potential roles of CLU and APOE in AD pathology. Dissecting CLU and APOE heterogeneity in AD pathogenesis may therefore facilitate delineating the pathological relevance for specific pathways between different genders, leading to personalized medicine in the future. Collectively, this study introduces a cost-effective absolute quantitative proteomics strategy for target protein quantitation and lays the foundation for future investigation of CLU and APOE as potential biomarkers for AD.
阿尔茨海默病（AD）是最常见的痴呆症形式，也是美国的主要死亡原因之一。在过去的几十年中，人们致力于发现生物标志物，以实现 AD 的早期诊断和治疗。在此，本研究旨在定量检测 AD 患者血液样本中的载脂蛋白 E（APOE）和簇蛋白（CLU），并评估这两种蛋白作为 AD 诊断的潜在生物标志物。本研究采用内合成的 5 plex 同位素 N,N-二甲基亮氨酸（iDiLeu）标签，以不同浓度标记目标肽标准品，构建标准曲线。我们的研究表明，CLU 和 APOE 的水平在男性 AD 组和女性 AD 组之间存在明显差异，但在男性非 AD 组和女性非 AD 组之间没有差异。相比之下，AD 组和非 AD 组的血清 CLU 和 APOE 水平没有统计学差异。用 CLU 和 APOE 进行主成分分析（PCA）显示 AD 组和非 AD 组之间有一定的分离。意义：因此，剖析 AD 发病机制中 CLU 和 APOE 的异质性，可能有助于阐明性别相关通路的病理相关性，从而为未来的个体化医疗奠定基础。综上所述，本研究提出了一种具有成本效益的靶向蛋白定量绝对定量蛋白质组学策略，为 CLU 和 APOE 作为 AD 潜在生物标志物的进一步研究奠定了基础。意义：作为 AD 诊断的基于血液的生物标志物，具有成本效益且侵入性较小，因此在 AD 患者的血液样本中发现和验证生物标志物已成为阿尔茨海默病和痴呆症研究的热门话题。迄今为止，血液中的淀粉样蛋白β（Aβ）、总 tau 和磷酸化 tau（p-tau）在 AD 诊断中具有很高的准确性和特异性。然而，AD 病理的潜在机制仍然难以捉摸和复杂。除了这些研究充分的蛋白质外，许多其他蛋白质，如簇蛋白（CLU）和载脂蛋白 E（APOE），也与 AD 发展有关。有研究表明，这两种蛋白参与 Aβ的清除和沉积。在这项研究中，我们测量了这两种蛋白在血液中的绝对浓度，并对 CLU 和 APOE 在 AD 病理中的潜在作用有了一些了解。因此，剖析 AD 发病机制中 CLU 和 APOE 的异质性，可能有助于阐明性别相关通路的病理相关性，从而为未来的个体化医疗奠定基础。综上所述，本研究提出了一种具有成本效益的靶向蛋白定量绝对定量蛋白质组学策略，为 CLU 和 APOE 作为 AD 潜在生物标志物的进一步研究奠定了基础。
