Genetic mutations underlying familial Alzheimer’s disease (AD) were identified decades ago, but the field is still in search of transformative therapies for patients. While mouse models based on overexpression of mutated transgenes have yielded key insights in mechanisms of disease, those models are subject to artifacts, including random genetic integration of the transgene, ectopic expression and non-physiological protein levels. The genetic engineering of novel mouse models using knock-in approaches addresses some of those limitations. With mounting evidence of the role played by microglia in AD, high-dimensional approaches to phenotype microglia in those models are critical to refine our understanding of the immune response in the brain. We engineered a novel App knock-in mouse model (AppSAA) using homologous recombination to introduce three disease-causing coding mutations (Swedish, Arctic and Austrian) to the mouse App gene. Amyloid-β pathology, neurodegeneration, glial responses, brain metabolism and behavioral phenotypes were characterized in heterozygous and homozygous AppSAA mice at different ages in brain and/ or biofluids. Wild type littermate mice were used as experimental controls. We used in situ imaging technologies to define the whole-brain distribution of amyloid plaques and compare it to other AD mouse models and human brain pathology. To further explore the microglial response to AD relevant pathology, we isolated microglia with fibrillar Aβ content from the brain and performed transcriptomics and metabolomics analyses and in vivo brain imaging to measure energy metabolism and microglial response. Finally, we also characterized the mice in various behavioral assays. Leveraging multi-omics approaches, we discovered profound alteration of diverse lipids and metabolites as well as an exacerbated disease-associated transcriptomic response in microglia with high intracellular Aβ content. The AppSAA knock-in mouse model recapitulates key pathological features of AD such as a progressive accumulation of parenchymal amyloid plaques and vascular amyloid deposits, altered astroglial and microglial responses and elevation of CSF markers of neurodegeneration. Those observations were associated with increased TSPO and FDG-PET brain signals and a hyperactivity phenotype as the animals aged. Our findings demonstrate that fibrillar Aβ in microglia is associated with lipid dyshomeostasis consistent with lysosomal dysfunction and foam cell phenotypes as well as profound immuno-metabolic perturbations, opening new avenues to further investigate metabolic pathways at play in microglia responding to AD-relevant pathogenesis. The in-depth characterization of pathological hallmarks of AD in this novel and open-access mouse model should serve as a resource for the scientific community to investigate disease-relevant biology.

中文翻译：

---

新颖的 App 敲入小鼠模型显示了淀粉样蛋白病理学的关键特征，并揭示了小胶质细胞的深刻代谢失调

家族性阿尔茨海默病 (AD) 的基因突变在几十年前就已被发现，但该领域仍在寻找针对患者的变革性疗法。虽然基于突变转基因过度表达的小鼠模型已经对疾病机制产生了重要的见解，但这些模型受到伪影的影响，包括转基因的随机遗传整合、异位表达和非生理蛋白质水平。使用敲入方法的新型小鼠模型的基因工程解决了其中一些局限性。随着越来越多的证据表明小胶质细胞在 AD 中发挥的作用，对这些模型中小胶质细胞表型的高维方法对于完善我们对大脑免疫反应的理解至关重要。我们利用同源重组设计了一种新型 App 敲入小鼠模型 (AppSAA)，将三种致病编码突变（瑞典语、北极语和奥地利语）引入到小鼠 App 基因中。在不同年龄的杂合子和纯合子 AppSAA 小鼠的大脑和/或生物液中对淀粉样蛋白-β 病理学、神经变性、神经胶质反应、脑代谢和行为表型进行了表征。使用野生型同窝小鼠作为实验对照。我们使用原位成像技术来定义淀粉样斑块的全脑分布，并将其与其他 AD 小鼠模型和人脑病理学进行比较。为了进一步探索小胶质细胞对 AD 相关病理的反应，我们从大脑中分离出含有纤维状 Aβ 的小胶质细胞，并进行转录组学和代谢组学分析以及体内脑成像，以测量能量代谢和小胶质细胞反应。最后，我们还在各种行为测定中对小鼠进行了表征。利用多组学方法，我们发现细胞内 Aβ 含量高的小胶质细胞中多种脂质和代谢物发生了深刻的变化，并且与疾病相关的转录组反应加剧。AppSAA 敲入小鼠模型概括了 AD 的关键病理特征，例如实质淀粉样斑块和血管淀粉样蛋白沉积的逐渐积累、星形胶质细胞和小胶质细胞反应的改变以及脑脊液神经变性标记物的升高。这些观察结果与随着动物衰老而增加的 TSPO 和 FDG-PET 脑信号以及多动表型有关。我们的研究结果表明，小胶质细胞中的纤维状 Aβ 与脂质稳态失衡有关，与溶酶体功能障碍和泡沫细胞表型以及深刻的免疫代谢扰动一致，为进一步研究小胶质细胞响应 AD 相关发病机制的代谢途径开辟了新途径。在这种新颖且开放的小鼠模型中对 AD 病理特征的深入表征应成为科学界研究疾病相关生物学的资源。