Endogenous Aß peptide promote Aß oligomerization tendency of spiked synthetic Aß in Alzheimer's disease plasma.

Alzheimer's disease (AD) is the most common form of age-associated dementia. Several studies have predicted that AD is caused by the production and deposition of the ß-amyloid peptide (Aß) in the brain, which is one of pathologic hallmarks of AD. In particular, Aß oligomers are reportedly the most toxic and pathogenic of other peptide forms. We previously developed Multimer Detection System-Oligomeric Amyloid-ß (MDS-OAß), a technique for measuring Aß oligomerization in plasma to diagnose AD. Here, we clarified the molecular sizes of oligomers that can be detected by the MDS and investigated differences in plasma spiking with a synthetic Aß peptide in the plasma of AD patients and individuals with non-AD neurological conditions. To determine Aß oligomer sizes detectable by MDS, size exclusion chromatography (SEC) was first performed on incubated samples of synthetic Aß42 peptides. As a result, no MDS signals were observed for the Aß42 monomer fractions, but strong signals were found for oligomers of 7-35-mers long. Also, an amplified luminescent proximity homogeneous assay-linked immunoassay (AlphaLISA) was used to confirm that synthetic Aß peptides not only recruited endogenous Aß in plasma but also induced significantly stronger seeding in AD plasma than in healthy control plasma. In addition, the absence of the MDS signals in Aß-depleted plasma confirmed that the increased oligomerization tendency in AD plasma is dependent on the presence of endogenous Aß in plasma. Therefore, the MDS-OAß measurement of oligomerization differences in plasma after incubation with spiked synthetic Aß peptides has significant potential in AD diagnosis.

C-Src-mediated phosphorylation of δ-catenin increases its protein stability and the ability of inducing nuclear distribution of ß-catenin.

Although δ-catenin was first considered as a brain specific protein, strong evidence of δ-catenin overexpression in various cancers, including prostate cancer, has been accumulated. Phosphorylation of δ-catenin by Akt and GSK3ß has been studied in various cell lines. However, tyrosine phosphorylation of δ-catenin in prostate cancer cells remains unknown. In the current study, we demonstrated that Src kinase itself phosphorylates δ-catenin on its tyrosine residues in prostate cancer cells and further illustrated that Y1073, Y1112 and Y1176 of δ-catenin are predominant sites responsible for tyrosine phosphorylation mediated by c-Src. Apart from c-Src, other Src family kinases, including Fgr, Fyn and Lyn, can also phosphorylate δ-catenin. We also found that c-Src-mediated Tyr-phosphorylation of δ-catenin increases its stability via decreasing its affinity to GSK3ß and enhances its ability of inducing nuclear distribution of ß-catenin through interrupting the integrity of the E-cadherin. Taken together, these results indicate that c-Src can enhance the oncogenic function of δ-catenin in prostate cancer cells.

Mitochondrial Complex I Inhibition Accelerates Amyloid Toxicity.

Alzheimer's disease (AD) is neurodegenerative disease, characterized by the progressive decline of memory, cognitive functions, and changes in personality. The major pathological features in postmortem brains are neurofibrillary tangles and amyloid beta (Aß) deposits. The majority of AD cases are sporadic and age-related. Although AD pathogenesis has not been established, aging and declining mitochondrial function has been associated. Mitochondrial dysfunction has been observed in AD patients' brains and AD mice models, and the mice with a genetic defect in mitochondrial complex I showed enhanced Aß level in vivo. To elucidate the role of mitochondrial complex I in AD, we used SH-SY5Y cells transfected with DNA constructs expressing human amyloid precursor protein (APP) or human Swedish APP mutant (APP-swe). The expression of APP-swe increased the level of Aß protein in comparison with control. When complex I was inhibited by rotenone, the increase of ROS level was remarkably higher in the cells overexpressing APP-swe compared to control. The number of dead cell was significantly increased in APP-swe-expressing cells by complex I inhibition. We suggest that complex I dysfunction accelerate amyloid toxicity and mitochondrial complex I dysfunction in aging may contribute to the pathogenesis of sporadic AD.

TREM2 promotes Aß phagocytosis by upregulating C/EBPα-dependent CD36 expression in microglia.

TREM2 plays a critical role in the alleviation of Alzheimer's disease by promoting Aß phagocytosis by microglia, but the detailed molecular mechanism underlying TREM2-induced direct phagocytic activity of Aß remains to be revealed. We found that learning and memory functions were improved in aged TREM2 TG mice, with the opposite effects in KO mice. The amount of phagocytosed Aß was significantly reduced in the primary microglia of KO mice. CD36 expression in primary microglia was greater in TG than in WT mice but was substantially decreased in KO mice. The expression of C/EBPα, an upstream transcriptional activator of CD36, was also elevated in primary microglia of TG mice but decreased in KO mice. The transcription of CD36 was markedly increased by TREM2 overexpression, and this effect was suppressed by a mutation of the C/EBPα binding site on the CD36 promoter. The TREM2-induced expression of CD36 and C/EBPα was inhibited by treatment with PI3K/AKT signaling blockers, and phosphorylation of AKT was elevated in TREM2-overexpressing BV2 cells. The present study provides evidence that TREM2 is required for preventing loss of memory and learning in Alzheimer's disease by regulating C/EBPα-dependent CD36 expression and the consequent Aß phagocytosis.