Departments of Pathology, New York University School of Medicine, New York, NY, 10016, USA.
Departments of Psychiatry, New York University School of Medicine, 550 First Avenue, New York, NY, 10016, USA.
Transl Neurodegener. 2022 Jun 1;11(1):30. doi: 10.1186/s40035-022-00303-3.
The molecular heterogeneity of Alzheimer's amyloid-β (Aβ) deposits extends well beyond the classic Aβ1-40/Aβ1-42 dichotomy, substantially expanded by multiple post-translational modifications that increase the proteome diversity. Numerous truncated fragments consistently populate the brain Aβ peptidome, and their homeostatic regulation and potential contribution to disease pathogenesis are largely unknown. Aβ4-x peptides have been reported as major components of plaque cores and the limited studies available indicate their relative abundance in Alzheimer's disease (AD).
Immunohistochemistry was used to assess the topographic distribution of Aβ4-x species in well-characterized AD cases using custom-generated monoclonal antibody 18H6-specific for Aβ4-x species and blind for full-length Aβ1-40/Aβ1-42-in conjunction with thioflavin-S and antibodies recognizing Aβx-40 and Aβx-42 proteoforms. Circular dichroism, thioflavin-T binding, and electron microscopy evaluated the biophysical and aggregation/oligomerization properties of full-length and truncated synthetic homologues, whereas stereotaxic intracerebral injections of monomeric and oligomeric radiolabeled homologues in wild-type mice were used to evaluate their brain clearance characteristics.
All types of amyloid deposits contained the probed Aβ epitopes, albeit expressed in different proportions. Aβ4-x species showed preferential localization within thioflavin-S-positive cerebral amyloid angiopathy and cored plaques, strongly suggesting poor clearance characteristics and consistent with the reduced solubility and enhanced oligomerization of their synthetic homologues. In vivo clearance studies demonstrated a fast brain efflux of N-terminally truncated and full-length monomeric forms whereas their oligomeric counterparts-particularly of Aβ4-40 and Aβ4-42-consistently exhibited enhanced brain retention.
The persistence of aggregation-prone Aβ4-x proteoforms likely contributes to the process of amyloid formation, self-perpetuating the amyloidogenic loop and exacerbating amyloid-mediated pathogenic pathways.
阿尔茨海默病淀粉样β（Aβ）沉积物的分子异质性远不止于经典的 Aβ1-40/Aβ1-42 二分法，大量的翻译后修饰大大增加了蛋白质组的多样性。许多截断片段始终存在于大脑 Aβ肽组中，但其内稳态调节及其对疾病发病机制的潜在贡献在很大程度上仍是未知的。Aβ4-x 肽已被报道为斑块核心的主要成分，并且现有有限的研究表明它们在阿尔茨海默病（AD）中的相对丰度。
使用针对 Aβ4-x 物种的定制生成的单克隆抗体 18H6 ，结合噻唑黄素-S 和识别 Aβx-40 和 Aβx-42 蛋白水解物的抗体，通过免疫组织化学评估在经过充分特征描述的 AD 病例中 Aβ4-x 物种的拓扑分布。圆二色性、噻唑黄素-T 结合和电子显微镜评估全长和截断合成同源物的生物物理和聚集/寡聚特性，而单体和寡聚放射性标记同源物的立体定向脑内注射在野生型小鼠中用于评估其脑清除特性。
所有类型的淀粉样沉积物都包含探测到的 Aβ表位，尽管表达比例不同。Aβ4-x 物种在噻唑黄素-S 阳性的脑淀粉样血管病和有核斑块内表现出优先定位，强烈表明清除特性差，与合成同源物的溶解度降低和增强的寡聚化一致。体内清除研究表明，N 端截断和全长单体形式具有快速的脑流出，而其寡聚体形式 - 特别是 Aβ4-40 和 Aβ4-42 - 则一致表现出增强的脑保留。
易于聚集的 Aβ4-x 蛋白水解物的持续存在可能有助于淀粉样形成过程，自我维持淀粉样形成循环并加剧淀粉样介导的致病途径。
