Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by memory loss and personality changes, eventually leading to dementia. The pathological hallmarks of AD are senile plaques and neurofibrillary tangles, which comprise abnormally aggregated β-amyloid peptide (Aβ) and hyperphosphorylated tau protein. To develop preventive, diagnostic, and therapeutic strategies for AD, it is essential to establish animal models that recapitulate the pathophysiological process of AD. In this review, we will summarize the advantages and limitations of various mouse models of AD, including transgenic, knock-in, and injection models based on Aβ and tau. We will also discuss other mouse models based on neuroinflammation because recent genetic studies have suggested that microglia are crucial in the pathogenesis of AD. Although each mouse model has its advantages and disadvantages, further research on AD pathobiology will lead to the establishment of more accurate mouse models, and accelerate the development of innovative therapeutics.

Astrocytes are among the most abundant cells in the brain and are implicated in the clearance of brain Ab via their regulation of the blood-brain barrier, glymphatic system, and proteolytic degradation. The cellular morphology and activity of astrocytes are modulated by several molecules, including x3 polyunsaturated fatty acids, such as docosahexaenoic acid, which is one of the most abundant lipids in the brain, via the G protein-coupled receptor GPR120/FFAR4. In this study, we analyzed the role of GPR120 signaling in the Ab-degrading activity of astrocytes. Treatment with the selective antagonist upregulated the matrix metalloproteinase (MMP) inhibitor-sensitive Ab-degrading activity in primary astrocytes. Moreover, the inhibition of GPR120 signaling increased the levels of Mmp2 and Mmp14 mRNAs, and decreased the expression levels of tissue inhibitor of metalloproteinases 3 (Timp3) and Timp4, suggesting that GPR120 negatively regulates the astrocyte-derived MMP network. Finally, the intracerebral injection of GPR120-specific antagonist substantially decreased the levels of TBS-soluble Ab in male AD model mice, and this effect was canceled by the coinjection of an MMP inhibitor. These data indicate that astrocytic GPR120 signaling negatively regulates the Ab-degrading activity of MMPs.

Amyloid-β (Aβ) deposition in the brain parenchyma is one of the pathological hallmarks of Alzheimer disease (AD). We have previously identified amyloid precursor protein (APP)669-711 (a.k.a. Aβ(-3)-40) in human plasma using immunoprecipitation combined with matrix-assisted laser desorption ionization time-of-flight mass spectrometry (IP-MALDI-MS). Furthermore, we found that the level of a composite biomarker, i.e., a combination of APP669-711/Aβ1-42 ratio and Aβ1-40/Aβ1-42 ratio in human plasma, correlates with the amyloid PET status of AD patients. However, the production mechanism of APP669-711 has remained unclear. Using in vitro and in vivo assays, we identified A Disintegrin and Metalloproteinase with a Thrombospondin type 1 motif, type 4 (ADAMTS4) as a responsible enzyme for APP669-711 production. ADAMTS4 cleaves APP directly to generate the C-terminal stub c102, which is subsequently proteolyzed by γ-secretase to release APP669-711. Genetic knockout of ADAMTS4 reduced the production of endogenous APP669-711 by 30% to 40% in cultured cells as well as mouse plasma, irrespectively of Aβ levels. Finally, we found that the endogenous murine APP669-711/Aβ1-42 ratio was increased in aged AD model mice, which shows Aβ deposition as observed in human patients. These data suggest that ADAMTS4 is involved in the production of APP669-711, and a plasma biomarker determined by IP-MALDI-MS can be used to estimate the level of Aβ deposition in the brain of mouse models.

Background Amyloid‐β peptide (Aβ) is deposited in the brains of Alzheimer disease (AD) patients, and proteolytically derived from its precursor protein, APP. APP669‐711 (a.k.a. Aβ(‐3)‐40) is a novel APP‐derived peptide detected in the plasma using immunoprecipitation‐matrix‐assisted laser desorption ionization‐time‐of‐flight mass spectrometry (IP‐MS). We have reported that the composite plasma biomarker, which is combination of APP669‐711/Aβ1‐42 ratio and Aβ1‐40/ Aβ1‐42 ratio, surrogates the accumulation of Aβ in brain (Kaneko et al., Proc Jpn Acad Ser B Phys Biol Sci. 2014; Nakamura et al., Nature 2018). However, the mechanism of APP669‐711 production is largely unclear. Method We analyzed the effects of several inhibitors and genetic knockouts on the production of APP699‐711 in cultured cells. Result Endogenous APP669‐711 was detected in the conditioned medium of BE2‐(C), Neuro2a and A549 cells by IP‐MS. Pharmacological experiments revealed that APP669‐711 is generated by sequential cleavages by GM6001‐sensitive metalloprotease at 669 site and γ‐secretase. Based on the preferences of the substrate sequence, we focused on ADAMTS4, which is the secreted metalloprotease with thrombospondin motif. Overexpression of ADAMTS4 resulted in the overproduction of APP669‐711, which was diminished by the catalytically inactivating mutation (i.e., E362A). Furthermore, endogenous APP669‐711 production was decreased in ADAMTS4 knockout cells. Conclusion These results indicate that ADAMTS4 is involved in the production pathway of APP669‐711, a novel plasma biomarker for Aβ deposition in the brain.

Background:We have previously identified APP669-711 (a.k.a. Aβ(-3)-40) in human plasma using immunoprecipitation combined with matrix-assisted laser desorption ionization time-of-flight mass spectrometry (IP-MALDI-MS) (Kaneko et al., Proc Jpn Acad Ser B Phys Biol Sci. 2014). Our assay has revealed that the composite biomarker, which is a combination of APP669-711/Aβ1-42 ratio and Aβ1-40/ Aβ1-42 ratio in human plasma, correlates with amyloid PET status (Nakamura et al., Nature 2018).However, the significance of these peptide ratios in an APP/PS1 mouse model of Alzheimer's disease has been unclear. In this study, we investigated the levels of Aβrelated peptides including APP669-711 in plasma samples from the model mouse. Method:We prepared plasma samples from young (2 months of age) and old (23-25 months of age) APP/PS1 mice expressing both APP bearing the Swedish mutation and PSEN1 harboring ΔE9 mutation, and cultured supernatants of HEK293 cells. Mouse plasma samples and cultured supernatants were measured by IP-MALDI-MS.Result: Human APP669-711 was detected in cultured supernatant of HEK293 cells overexpressing human wild-type APP but not human APP with the Swedish mutation. This result indicated that two amino acid substitutions (i.e., Swedish mutation) near the APP669 site inhibited the APP669 cleavage and the production of APP669-711 from the transgene of APP/PS1 mice. Then we focused on mouse endogenous murine Aβ-related peptides in the evaluation of plasma biomarker for the amyloid deposition in the brains of APP/PS1 mice. The analysis of APP/PS1 mouse plasma showed that murine APP669-711/Aβ1-42 and APP669-711/Aβ1-40 ratios were increased in old mice with plaques compared to young mice without them. However, the murine Aβ1-40/Aβ1-42 ratio was not changed between old and young mice. Conclusion:These results suggested that the APP669-711/Aβ1-42 ratio is a common biomarker for the amyloid plaque pathology in humans and APP/PS1 mice. Also, we revealed the possibility that the APP669-711/Aβ1-40 ratio is a biomarker specific for the brain Aβ deposition in APP/PS1 mice. These biomarkers can be useful tools to study lifestyle intervention and drug development for the prevention of amyloid deposition using the model mouse.