3xTg-AD mice show intraneuronal Aβ accumulation and memory disturbances before extracellular Aβ deposition. Our data demonstrating improvement of memory function of 3xTg-AD mice with decreases in intraneuronal Aβ and p-tau levels by APO treatment strongly suggest that intraneuronal Aβ is an important therapeutic target and APO will be a novel drug for AD.

Amyloid-β protein (Aβ) accumulates in the neurons of Alzheimer's disease (AD) patients at an early stage of the disease. Recently, we found that Aβ with a toxic turn at positions 22 and 23 accumulates in neurons in AD brain. Here, we studied the accumulation of Aβ, toxic turn Aβ and high-molecular-weight Aβ oligomers in presenilin 1 (PS1) gene-transfected SH-SY5Y cells as well as in the brains of 3xTg-AD mice and AD patients. Immunostaining revealed that accumulation of toxic turn Aβ was promoted in G384A- and I143T-mutant PS1-transfected cells and further enhanced by co-transfection of cells with the Aβ-precursor protein (AβPP) gene. In contrast, accumulation of high-molecular-weight Aβ oligomers was promoted in mutant PS1 cells but attenuated by co-transfection of cells with the AβPP gene. Toxic turn Aβ was detected in the neurons of 3xTg-AD mice aged 2 months, when the mice were cognitively unimpaired. In contrast, high-molecular-weight Aβ oligomers were detected in the neurons of 7-month-old mice, when memory dysfunction is apparent. Furthermore, immunostaining and western blotting for Rab4, Rab6 and GRP78 revealed increased levels of these proteins in mutant PS1 cells and their accumulation in the neurons of 3xTg-AD mice. Remarkably, GRP78 immunoreactivity was increased at 2 months of age. Double-label immunostaining of AD brain revealed an apparent association between toxic turn Aβ and GRP78, an endoplasmic reticulum (ER) stress marker. Intraneuronal accumulation of toxic turn Aβ may be associated with ER stress in the brains of AD model mice and AD patients at an early stage.

Amyloid-β protein (Aβ) accumulates in the neurons of Alzheimer's disease (AD) patients at an early stage of the disease. Recently, we found that Aβ with a toxic turn at positions 22 and 23 accumulates in neurons in AD brain. Here, we studied the accumulation of Aβ, toxic turn Aβ and high-molecular-weight Aβ oligomers in presenilin 1 (PS1) gene-transfected SH-SY5Y cells as well as in the brains of 3xTg-AD mice and AD patients. Immunostaining revealed that accumulation of toxic turn Aβ was promoted in G384A- and I143T-mutant PS1-transfected cells and further enhanced by co-transfection of cells with the Aβ-precursor protein (AβPP) gene. In contrast, accumulation of high-molecular-weight Aβ oligomers was promoted in mutant PS1 cells but attenuated by co-transfection of cells with the AβPP gene. Toxic turn Aβ was detected in the neurons of 3xTg-AD mice aged 2 months, when the mice were cognitively unimpaired. In contrast, high-molecular-weight Aβ oligomers were detected in the neurons of 7-month-old mice, when memory dysfunction is apparent. Furthermore, immunostaining and western blotting for Rab4, Rab6 and GRP78 revealed increased levels of these proteins in mutant PS1 cells and their accumulation in the neurons of 3xTg-AD mice. Remarkably, GRP78 immunoreactivity was increased at 2 months of age. Double-label immunostaining of AD brain revealed an apparent association between toxic turn Aβ and GRP78, an endoplasmic reticulum (ER) stress marker. Intraneuronal accumulation of toxic turn Aβ may be associated with ER stress in the brains of AD model mice and AD patients at an early stage.

No abstract

Apomorphine hydrochloride (APO) is known to be a dopamine receptor agonist, and has recently been found to be a novel drug for Alzheimer's disease (AD). We found that APO treatment ameliorated oxidative stress in an AD mouse model and specifically attenuated the hydrogen peroxide-induced p53-related apoptosis in the SH-SY5Y neuroblastoma cell line. To further understand the mechanism behind this action, we investigated the actions of APO on intracellular redox systems, such as the glutathione cycle and catalase. We studied the effects of specific inhibitors for glutathione peroxidase (GPx), glutathione reductase (GR), and catalase (BCNU, MCS, and ATZ, respectively) on the effects of APO. Treatments with MCS or BCNU, but not ATZ, significantly attenuated the protective effects of APO. Interestingly, APO treatment elevated GPx activity, but did not increase the expression of the GPx1 protein. Although BCNU treatment attenuated APO effects, GR activity was not elevated by APO treatment. The same effects were observed in primary neuronal cultures. In addition, treatment with dopamine D1, D2, D3 and D4 receptor antagonists did not counteract the protective action of APO. Thus, APO may enhance GPx activity through dopamine receptor-independent pathways.