Wang Shanshan, Ichinomiya Taiga, Savchenko Paul, Devulapalli Swetha, Wang Dongsheng, Beltz Gianna, Saito Takashi, Saido Takaomi C, Wagner Steve L, Patel Hemal H, Head Brian P
Veterans Affairs San Diego Healthcare System, San Diego, CA, United States.
Department of Anesthesia, University of California, San Diego, San Diego, CA, United States.
Front Mol Neurosci. 2022 Jul 29;15:909989. doi: 10.3389/fnmol.2022.909989. eCollection 2022.
Mitochondria play a crucial role in Alzheimer's disease (AD) onset and progression. Traditional transgenic AD mouse models which were widely used in the past decades share a common limitation: The overexpression of APP and overproduction of amyloid-beta (Aβ) are accompanied by other APP peptide fragments, which could introduce artificial and non-clinically relevant phenotypes. Here, we performed an in-depth and time-resolved behavioral and metabolic characterization of a clinically relevant AD mouse model engineered to express normal physiological levels of APP harboring humanized Swedish (K670N/M671L), Beyreuther/Iberian (I716F), and Arctic (E693G) mutations ( ), termed APP knock-in (APPKI) mice. Our result showed that APPKI mice exhibited fear learning deficits at 6-m age and contextual memory deficit at 12-m age. Histopathological analysis revealed mild amyloidosis (6E10) accompanied by microgliosis (Iba1) as early as 3 months, which progressed significantly together with significant astrocytosis at 6 and 12 m. We further analyzed hippocampal mitochondrial dysfunction by multiple assays, while 3-m APPKI mice brain mitochondrial function remains a similar level as WT mice. Significant mitochondrial dysfunction characterized by decreased ATP production and higher membrane potential with subsequent overproduction of reactive oxygen species (ROS) was observed in mitochondria isolated from 7-m APPKI mice hippocampal tissue. Morphologically, these mitochondria were larger in volume with a decreased level of mitochondrial fusion protein mitofusin-2 (MFN2). At 12 months, APPKI mice exhibit a significantly decreased total mitochondrial oxygen consumption rate (OCR) in isolated hippocampal mitochondria detected by high-resolution respirometry. These data indicate early mitochondrial dysfunction in the brain at pre-symptomatic age in the mice, which may play a key role in the progression of the disease. Moreover, the identified behavioral and bioenergetic alterations in this clinically relevant AD mouse model provide a valuable tool to optimize the temporal component for therapeutic interventions to treat AD.
线粒体在阿尔茨海默病（AD）的发病和进展中起着至关重要的作用。过去几十年广泛使用的传统转基因AD小鼠模型有一个共同的局限性：APP的过度表达和淀粉样β蛋白（Aβ）的过量产生伴随着其他APP肽片段，这可能会引入人为的、与临床无关的表型。在此，我们对一种临床相关的AD小鼠模型进行了深入的、时间分辨的行为和代谢特征分析，该模型经工程改造后表达携带人源化瑞典（K670N/M671L）、拜罗伊特/伊比利亚（I716F）和北极（E693G）突变的正常生理水平的APP（ ），称为APP基因敲入（APPKI）小鼠。我们的结果表明，APPKI小鼠在6月龄时表现出恐惧学习缺陷，在12月龄时表现出情境记忆缺陷。组织病理学分析显示，早在3个月时就出现了轻度淀粉样变性（6E10）并伴有小胶质细胞增生（Iba1），在6个月和12个月时显著进展，同时伴有明显的星形细胞增生。我们通过多种检测方法进一步分析了海马体线粒体功能障碍，而3月龄APPKI小鼠脑线粒体功能与野生型小鼠保持相似水平。在从7月龄APPKI小鼠海马组织分离的线粒体中观察到以ATP产生减少和膜电位升高以及随后活性氧（ROS）过量产生为特征的显著线粒体功能障碍。从形态学上看，这些线粒体体积更大，线粒体融合蛋白线粒体融合素2（MFN2）水平降低。在12个月时，通过高分辨率呼吸测定法检测发现，APPKI小鼠分离的海马体线粒体中的总线粒体氧消耗率（OCR）显著降低。这些数据表明，在该小鼠模型的症状前年龄，大脑中就出现了早期线粒体功能障碍，这可能在疾病进展中起关键作用。此外，在这个临床相关的AD小鼠模型中确定的行为和生物能量改变为优化治疗AD的治疗干预的时间成分提供了一个有价值的工具。
