Phenotypic assays for β-amyloid in mouse embryonic stem cell-derived neurons

O-GlcNAcylation Inhibits Endocytosis of Amyloid Precursor Protein by Decreasing Its Localization in Lipid Raft Microdomains

Like protein phosphorylation, O-GlcNAcylation is a common post-translational protein modification. We already reported that O-GlcNAcylation of amyloid precursor protein (APP) in response to insulin signaling reduces neurotoxic amyloid-β (Aβ) production via inhibition of APP endocytosis. Internalized APP is delivered to endosomes and lysosomes where Aβ is produced. However, the molecular mechanism involved in the effect of APP O-GlcNAcylation on APP trafficking remains unknown. To investigate the relationship between APP O-GlcNAcylation and APP endocytosis, we tested the effects of insulin on neuroblastoma SH-SY5Y cells overexpressing APP and BACE1, and cultured rat hippocampal neurons. The present study showed that APP O-GlcNAcylation translocated APP from lipid raft to non-raft microdomains in the plasma membrane by using immunocytochemistry and discontinuous sucrose gradients method. By using the biotinylation method, we also found that APP preferentially underwent endocytosis from lipid rafts and that the amount of internalized APP from lipid rafts was specifically reduced by O-GlcNAcylation. These results indicate that O-GlcNAcylation can regulate lipid raft-dependent APP endocytosis via translocation of APP into non-raft microdomains. Our findings showed a new functional role of O-GlcNAcylation for the regulation of APP trafficking, offering new mechanistic insight for Aβ production.

Identifying Anti-prion Chemical Compounds Using a Newly Established Yeast High-Throughput Screening System

Prion-like protein aggregation underlies the pathology of a group of fatal neurodegenerative diseases in humans, including Alzheimer's disease (AD), Parkinson's disease, amyotrophic lateral sclerosis, and transmissible spongiform encephalopathy. At present, few high-throughput screening (HTS) systems are available for anti-prion small-molecule identification. Here we describe an innovative phenotypic HTS system in yeast that allows for efficient identification of chemical compounds that eliminate the yeast prion [SWI⁺]. We show that some identified anti-[SWI⁺] compounds can destabilize other non-[SWI⁺] prions, and their antagonizing effects can be prion- and/or variant specific. Intriguingly, among the identified hits are several previously identified anti-PrP^Sc compounds and a couple of US Food and Drug Administration-approved drugs for AD treatment, validating the efficacy of this HTS system. Moreover, a few hits can reduce proteotoxicity induced by expression of several pathogenic mammalian proteins. Thus, we have established a useful HTS system for identifying compounds that can potentially antagonize prionization and human proteinopathies.

Activation of transient receptor potential melastatin 7 (TRPM7) channel increases basal autophagy and reduces amyloid β-peptide

Cerebral accumulation of amyloid β-peptide (Aβ), which is produced from amyloid precursor protein (APP), is the primary cause of Alzheimer's disease (AD). Autophagy recycles cellular components and digests intracellular components including Aβ. The Ca²⁺- and Mg²⁺-permeable transient receptor potential melastatin 7 (TRPM7) channel underlies the constitutive Ca²⁺ influx in some cells. Since we already reported that TRPM7 channel-mediated Ca²⁺ influx regulates basal autophagy, we hypothesize that the activation of TRPM7 channel could increase basal autophagy and consequently decrease Aβ. In this study, we showed that naltriben (NTB), a specific TRPM7 channel activator, induced Ca²⁺ influx and activated autophagic signaling in neuroblastoma SH-SY5Y cells. NTB also promoted co-localization of LC3 and APP, and reduced Aβ. Furthermore, we found that an early-onset familial AD-associated presenilin1 ΔE9 (PS1 ΔE9) mutant cells had attenuated basal autophagy. NTB was able to recover autophagy and decrease Aβ in PS1 ΔE9 cells. Our results show that the activating TRPM7 channel may prevent AD-related Aβ neuropathology via modulating Ca²⁺-regulated basal autophagy.

Drug repositioning approaches for the discovery of new therapeutics for Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia and represents one of the highest unmet needs in medicine today. Drug development efforts for AD have been encumbered by largely unsuccessful clinical trials in the last decade. Drug repositioning, a process of discovering a new therapeutic use for existing drugs or drug candidates, is an attractive and timely drug development strategy especially for AD. Compared with traditional de novo drug development, time and cost are reduced as the safety and pharmacokinetic properties of most repositioning candidates have already been determined. A majority of drug repositioning efforts for AD have been based on positive clinical or epidemiological observations or in vivo efficacy found in mouse models of AD. More systematic, multidisciplinary approaches will further facilitate drug repositioning for AD. Some experimental approaches include unbiased phenotypic screening using the library of available drug collections in physiologically relevant model systems (e.g. stem cell-derived neurons or glial cells), computational prediction and selection approaches that leverage the accumulating data resulting from RNA expression profiles, and genome-wide association studies. This review will summarize several notable strategies and representative examples of drug repositioning for AD.

Induced Pluripotent Stem Cells Derived from Alzheimer's Disease Patients: The Promise, the Hope and the Path Ahead

The future hope of generated induced pluripotent stem cells (iPS cells) from Alzheimer’s disease patients is multifold. Firstly, they may help to uncover novel mechanisms of the disease, which could lead to the development of new and unprecedented drugs for patients and secondly, they could also be directly used for screening and testing of potential new compounds for drug discovery. In addition, in the case of familial known mutations, these cells could be targeted by use of advanced gene-editing techniques to correct the mutation and be used for future cell transplantation therapies. This review summarizes the work so far in regards to production and characterization of iPS cell lines from both sporadic and familial Alzheimer’s patients and from other iPS cell lines that may help to model the disease. It provides a detailed comparison between published reports and states the present hurdles we face with this new technology. The promise of new gene-editing techniques and accelerated aging models also aim to move this field further by providing better control cell lines for comparisons and potentially better phenotypes, respectively.

The 14th International Conference on Alzheimer's Drug Discovery, 9 - 10 September 2013, in Jersey City, New Jersey

The following conference was the 14th International Conference on Alzheimer's Drug Discovery held 9 - 10 September 2013, in Jersey City, NJ. The conference attracted about 140 attendees with 49% from academia, 36% from industry and private practice, 10% from nonprofit organizations and 2% from the government. The meeting had two plenary speakers that kicked off each morning of the conference and then two sessions each day to cover different aspects of Alzheimer's disease drug discovery. There were sessions on neuroprotection, mitochondrial function, biomarkers, ApoE, tau and protein clearance. The conference was organized by the Alzheimer's Drug Discovery Foundation (ADDF) with all of the presenters supported by grants awarded by the ADDF. The conference had financial support from the pharmaceutical companies Merck & Co., Eli Lilly & Co. and Pfizer, Inc. Friends, exhibitors and media partners also helped financially support the conference.