Accumulation of Phosphorylated β-Catenin Enhances ROS-Induced Cell Death in Presenilin-Deficient Cells

Presenilin (PS) is involved in many cellular events under physiological and pathological conditions. Previous reports have revealed that PS deficiency results in hyperproliferation and resistance to apoptotic cell death. In the present study, we investigated the effects of PS on β-catenin and cell mortality during serum deprivation. Under these conditions, PS1/PS2 double-knockout MEFs showed aberrant accumulation of phospho-β-catenin, higher ROS generation, and notable cell death. Inhibition of β-catenin phosphorylation by LiCl reversed ROS generation and cell death in PS deficient cells. In addition, the K19/49R mutant form of β-catenin, which undergoes normal phosphorylation but not ubiquitination, induced cytotoxicity, while the phosphorylation deficient S37A β-catenin mutant failed to induce cytotoxicity. These results indicate that aberrant accumulation of phospho-β-catenin underlies ROS-mediated cell death in the absence of PS. We propose that the regulation of β-catenin is useful for identifying therapeutic targets of hyperproliferative diseases and other degenerative conditions

The novel RAGE interactor PRAK is associated with autophagy signaling in Alzheimer’s disease pathogenesis

BACKGROUND: The receptor for advanced glycation end products (RAGE) has been found to interact with amyloid β (Aβ). Although RAGE does not have any kinase motifs in its cytosolic domain, the interaction between RAGE and Aβ triggers multiple cellular signaling involved in Alzheimer’s disease (AD). However, the mechanism of signal transduction by RAGE remains still unknown. Therefore, identifying binding proteins of RAGE may provide novel therapeutic targets for AD. RESULTS: In this study, we identified p38-regulated/activated protein kinase (PRAK) as a novel RAGE interacting molecule. To investigate the effect of Aβ on PRAK mediated RAGE signaling pathway, we treated SH-SY5Y cells with monomeric form of Aβ. We demonstrated that Aβ significantly increased the phosphorylation of PRAK as well as the interaction between PRAK and RAGE. We showed that knockdown of PRAK rescued mTORC1 inactivation induced by Aβ treatment and decreased the formation of Aβ-induced autophagosome. CONCLUSIONS: We provide evidence that PRAK plays a critical role in AD pathology as a key interactor of RAGE. Thus, our data suggest that PRAK might be a potential therapeutic target of AD involved in RAGE-mediated cell signaling induced by Aβ. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s13024-016-0068-5) contains supplementary material, which is available to authorized users

Genome instability in Alzheimer disease

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder and the most common form of dementia. Autosomal dominant, familial AD (fAD) is very rare and caused by mutations in amyloid precursor protein (APP), presenilin-1 (PSEN-1), and presenilin-2 (PSEN-2) genes. The pathogenesis of sporadic AD (sAD) is more complex and variants of several genes are associated with an increased lifetime risk of AD. Nuclear and mitochondrial DNA integrity is pivotal during neuronal development, maintenance and function. DNA damage and alterations in cellular DNA repair capacity have been implicated in the aging process and in age-associated neurodegenerative diseases, including AD. These findings are supported by research using animal models of AD and in DNA repair deficient animal models. In recent years, novel mechanisms linking DNA damage to neuronal dysfunction have been identified and have led to the development of noninvasive treatment strategies. Further investigations into the molecular mechanisms connecting DNA damage to AD pathology may help to develop novel treatment strategies for this debilitating disease. Here we provide an overview of the role of genome instability and DNA repair deficiency in AD pathology and discuss research strategies that include genome instability as a componen

Rac1 changes the substrate specificity of gamma-secretase between amyloid precursor protein and Notch1

Beta amyloid peptide is generated from amyloid precursor protein (APP) by proteolytic cleavage of beta- and gamma-secretases, and plays a critical role in the pathogenesis of Alzheimer's disease. Since gamma-secretase cleaves several proteins including APP and Notch in a number of cell types, it is important to understand the conditions determining gamma-secretase substrate specificity. In the present study, inhibition of Rac1 attenuated gamma-secretase activity for APP, resulting in decreased production of the APP intracellular domain but accumulated C-terminal fragments (APP-CTF). In contrast, Rac1 inhibitor, NSC23766 increased production of the Notch1 intracellular domain but slightly decreased the ectodomain-shed form of Notch1 (NotchDeltaE). To elucidate the mechanism underlying these observations, we performed co-immunoprecipitation experiments to analyze the interaction between Rac1 and presenilin1 (PS1), a component of the gamma-secretase complex. Inhibition of Rac1 enhanced its interaction with PS1. Under the same condition, PS1 interacted more strongly with NotchDeltaE than with APP-CTF. Our results suggested that PS1 determines the preferred substrate for gamma-secretase between APP and Notch1, depending on the activation status of Rac1

The novel RAGE interactor PRAK is associated with autophagy signaling in Alzheimers disease pathogenesis

Background The receptor for advanced glycation end products (RAGE) has been found to interact with amyloid β (Aβ). Although RAGE does not have any kinase motifs in its cytosolic domain, the interaction between RAGE and Aβ triggers multiple cellular signaling involved in Alzheimers disease (AD). However, the mechanism of signal transduction by RAGE remains still unknown. Therefore, identifying binding proteins of RAGE may provide novel therapeutic targets for AD. Results In this study, we identified p38-regulated/activated protein kinase (PRAK) as a novel RAGE interacting molecule. To investigate the effect of Aβ on PRAK mediated RAGE signaling pathway, we treated SH-SY5Y cells with monomeric form of Aβ. We demonstrated that Aβ significantly increased the phosphorylation of PRAK as well as the interaction between PRAK and RAGE. We showed that knockdown of PRAK rescued mTORC1 inactivation induced by Aβ treatment and decreased the formation of Aβ-induced autophagosome. Conclusions We provide evidence that PRAK plays a critical role in AD pathology as a key interactor of RAGE. Thus, our data suggest that PRAK might be a potential therapeutic target of AD involved in RAGE-mediated cell signaling induced by Aβ

Aβ-induced degradation of BMAL1 and CBP leads to circadian rhythm disruption in Alzheimers disease

Background Patients with Alzheimers disease (AD) frequently experience disruption of their circadian rhythms, but whether and how circadian clock molecules are perturbed by AD remains unknown. AD is an age-related neurological disorder and amyloid-β (Aβ) is one of major causative molecules in the pathogenesis of AD. Results In this study, we investigated the role of Aβ in the regulation of clock molecules and circadian rhythm using an AD mouse model. These mice exhibited altered circadian behavior, and altered expression patterns of the circadian clock genes, Bmal1 and Per2. Using cultured cells, we showed that Aβ induces post-translational degradation of the circadian clock regulator CBP, as well as the transcription factor BMAL1, which forms a complex with the master circadian transcription factor CLOCK. Aβ-induced degradation of BMAL1 and CBP correlated with the reduced binding of transcription factors to the Per2 promoter, which in turn resulted in disruptions to PER2 protein expression and the oscillation of Per2 mRNA levels. Conclusions Our results elucidate the underlying mechanisms for disrupted circadian rhythm in AD

ABeta-induced degradation of BMAL1 and CBP leads to circadian rhythm disruption in Alzheimer's disease

Background: Patients with Alzheimer's disease (AD) frequently experience disruption of their circadian rhythms, but whether and how circadian clock molecules are perturbed by AD remains unknown. AD is an age-related neurological disorder and amyloid-β (Aβ) is one of major causative molecules in the pathogenesis of AD. Results: In this study, we investigated the role of Aβ in the regulation of clock molecules and circadian rhythm using an AD mouse model. These mice exhibited altered circadian behavior, and altered expression patterns of the circadian clock genes, Bmal1 and Per2. Using cultured cells, we showed that Aβ induces post-translational degradation of the circadian clock regulator CBP, as well as the transcription factor BMAL1, which forms a complex with the master circadian transcription factor CLOCK. Aβ-induced degradation of BMAL1 and CBP correlated with the reduced binding of transcription factors to the Per2 promoter, which in turn resulted in disruptions to PER2 protein expression and the oscillation of Per2 mRNA levels. Conclusions: Our results elucidate the underlying mechanisms for disrupted circadian rhythm in AD. © 2015 Song et al.; licensee BioMed Central.1

Phospho-β-catenin was accumulated in PS dKO MEFs under serum deprivation conditions.

<p>(A) β-catenin was accumulated in PS dKO MEFs, not in PS WT under normal and serum deprivation conditions. β-actin served as a loading control. (B) PS WT and PS dKO MEFs were incubated in growth media or DMEM for 30 hr, followed by immunofluorescent staining. PS dKO MEFs in DMEM labeled more brightly against anti-phospho-β-catenin (S33, 37, T41) antibody. The white bar represents 200 µm. (C) PS dKO MEFs were incubated w/wo 10 mM LiCl or 200 µM trolox in DMEM for 30 hr and labeled with phospho-β-catenin (S33, 37, T41)-specific antibody (Red). Many cells contained phosphorylated forms of β-catenin in DMEM- and trolox-treated PS dKO MEFs by fluorescence microscopy. But, LiCl-treated PS dKO MEFs stained weakly. DAPI staining was used to visualize cell nuclei (Blue). The white bar represents 200 µm. (D) Western blot analysis showed that LiCl effectively decreased phosphorylation of β-catenin at the S33, 37, and T41 sites without altering total β-catenin or β-actin levels. However, trolox-treated cells showed similar levels of phospho-β-catenin compared with DMEM alone.</p

PS dKO MEFs are vulnerable to serum deprivation-induced cell death.

<p>(A) Western blot analysis of nicastrin and PS1 showing that PS dKO MEFs prevent nicastrin maturation. hPS1 MEFs were rescued PS1 and nicastrin maturation. Calnexin served as a loading control for membrane fractions. Filled and blank arrows indicate mature and immature nicastrin, respectively. Filled and blank arrowheads indicate full-length PS1 and PS1-CTF, respectively. (B) LDH release assay showing that PS dKO MEFs are injured by serum deprivation-induced stress. All MEFs were incubated DMEM media without serum for 36 hr. The graph represents (%) of positive control. Data are means±SEM values of three independent experiments. * represents significant differences from PS WT MEFs. ***P<0.001. # represents significant differences from PS dKO MEFs. ###P<0.001.</p