Early Cellular, Molecular, Morphological and Behavioral Changes in the Humanized Amyloid-Beta-Knock-In Mouse Model of Late-Onset Alzheimer’s Disease

Abstract

The purpose of our study is to investigate early cellular, molecular, morphological and behavioral changes in humanized amyloid-beta-knock-in (hAbKI) mice. Using seven-month-old homozygous hAbKI mice, we studied behavioral phenotype parameters, including spatial learning and memory (Morris Water Maze), locomotor activity (open field), working memory (Y-maze) and motor coordination (rotarod); mRNA abundance, protein levels, soluble amyloid-beta 40 and 42 levels and regional immunoreactivities of key markers of mitochondrial dynamics, mitochondrial biogenesis, synaptic health, mitophagy and autophagy; mitochondrial function and using transmission electron microscopy & Golgi–Cox staining, we assessed mitochondrial morphology and dendritic spines. Our extensive behavioral analysis revealed that seven-month-old hAbKI mice showed impairments in motor coordination, reduced locomotor and exploration activities, impairments in working memory and spatial learning and memory. Our mRNA and protein analyses revealed the increased expression of mitochondrial-fission genes and reduced expression of mitochondrial-fusion, mitochondrial-biogenesis, synaptic, autophagy and mitophagy genes in seven-month-old hAbKI mice. An immunofluorescence analysis revealed altered immunoreactivities and agreed with the immunoblot results. Transmission-electron-microscopy data revealed increased mitochondrial fragmentation and reduced mitochondrial length in both hippocampal and cortical tissues of seven-month-old hAbKI mice and mitochondrial function defective. A Golgi–Cox-staining analysis revealed reduced dendritic spines in both cerebral cortices and hippocampi of hAbKI mice. Soluble amyloid-beta (1–40 and 1–42) were detected in three-month-old hAbKI mice and progressively increased in seven-month-old mice. These observations suggest that the human amyloid-beta peptide is sufficient to cause behavioral, mitochondrial, synaptic and ultrastructural changes in seven-month-old hAbKI mice. Our study findings also suggest that hAbKI mice might serve as a model for preclinical studies of preventive therapies.

Are mitophagy enhancers therapeutic targets for Alzheimer’s disease?

“…These and other observations [ 128 , 129 ] strongly suggest mitophagy enhancers are promising drugs to treat patients with AD and other tauopathies. However, these drugs need to be tested carefully using mouse models, particularly recently developed humanized Abeta knock-in (hAbKI) mice that express human amyloid beta peptide and exhibit late-onset AD features [ 130 , 131 ]. Currently, we are several mitophagy enhancers in late-onset hAbKI mice.…”

A Combination Therapy of Urolithin A+EGCG Has Stronger Protective Effects than Single Drug Urolithin A in a Humanized Amyloid Beta Knockin Mice for Late-Onset Alzheimer’s Disease

“…A recent behavioral study of 7-month-old hAbKI mice revealed defects in motor coordination, locomotor activity, spatial and learning/working memory [ 41 ]. Our current study findings of the behavioral phenotype are improved in urolithin A and a combination of urolithin A+EGCG-treated hAbKI mice; however, protective effects are stronger in combination treatment.…”

“…Our recent study of 7-month-old homozygous hAbKI mice revealed that hAbKI mice showed behavioral impairments in motor coordination, reduced locomotor and exploration activities, and impairments in working memory and spatial learning and memory [ 41 ]. The mRNA and protein analyses revealed the increased expression of mitochondrial fission genes and reduced expression of mitochondrial-fusion, mitochondrial biogenesis, synaptic, autophagy and mitophagy genes in hAbKI mice.…”

“…Reduced dendritic spines were observed in both the cerebral cortices and hippocampi of hAbKI mice. Soluble Aβ40 and Aβ42 were detected at 3 months of age and progressively increased in 7-month-old hAbKI mice [ 41 ]. These observations suggest that early behavioral, cellular, molecular, synaptic, dendritic and mitochondrial changes occur in hAbKI mice of late-onset AD.…”

“…We assessed behavioral changes using the Y-maze, open field, rotarod and Morris water maze and also assessed mRNA and protein levels of mitochondrial dynamics, biogenesis, mitophagy and synaptic genes and cell survival; assessed mitochondrial structure and dendritic spines in 7-month-old hAbKI mice treated with urolithin A and urolithin A+EGCG. Since we reported the findings of 7-month-old hAbKI mice in comparison to WT control mice earlier [ 41 ], in the current study, we compared the data between urolithin A and a combination treatment of urolithin A+EGCG with hAbKI mice.…”