Identification of disulfiram as a secretase-modulating compound with beneficial effects on Alzheimer's disease hallmarks

ADAM10 is a metalloproteinase acting on the amyloid precursor protein (APP) as an alpha-secretase in neurons. Its enzymatic activity results in secretion of a neuroprotective APP cleavage product (sAPP-alpha) and prevents formation of the amyloidogenic A-beta peptides, major hallmarks of Alzheimer’s disease (AD). Elevated ADAM10 levels appeared to contribute to attenuation of A-beta-plaque formation and learning and memory deficits in AD mouse models. Therefore, it has been assumed that ADAM10 might represent a valuable target in AD therapy. Here we screened a FDA-approved drug library and identified disulfiram as a novel ADAM10 gene expression enhancer. Disulfiram increased ADAM10 production as well as sAPP-alpha in SH-SY5Y human neuronal cells and additionally prevented A-beta aggregation in an in vitro assay in a dose-dependent fashion. In addition, acute disulfiram treatment of Alzheimer model mice induced ADAM10 expression in peripheral blood cells, reduced plaque-burden in the dentate gyrus and ameliorated behavioral deficits. Alcohol-dependent patients are subjected to disulfiram-treatment to discourage alcohol-consumption. In such patients, enhancement of ADAM10 by disulfiram-treatment was demonstrated in peripheral blood cells. Our data suggest that disulfiram could be repurposed as an ADAM10 enhancer and AD therapeutic. However, efficacy and safety has to be analyzed in Alzheimer patients in the future.

Alzheimer's disease in the gut-Major changes in the gut of 5xFAD model mice with ApoA1 as potential key player

Alzheimer's disease (AD) affects around 33 million people worldwide, which makes it the most prominent form of dementia. The main focus of AD research has been on the central nervous system (CNS) for long, but in recent years, the gut gained more attention. The intestinal tract is innervated by the enteric nervous system (ENS), built of numerous different types of neurons showing great similarity to neurons of the CNS. It already has been demonstrated that the amyloid precursor protein, which plays a major role in AD pathology, is also expressed in these cells. We analyzed gut tissue of AD model mice (5xFAD) and the respective wild-type littermates at different pathological stages: pre-pathological, early pathological and late pathological. Our results show significant difference in function of the intestine of 5xFAD mice as compared to wild-type mice. Using a pathway array detecting 84 AD-related gene products, we found ApoA1 expression significantly altered in colon tissue of 5xFAD mice. Furthermore, we unveil ApoA1's beneficial impact on cell viability and calcium homeostasis of cultured enteric neurons of 5xFAD animals. With this study, we demonstrate that the intestine is altered in AD-like pathology and that ApoA1 might be one key player within the gut.

The Synthetic Retinoid Acitretin Increases IL-6 in the Central Nervous System of Alzheimer Disease Model Mice and Human Patients

These days, the important role of retinoids in adult brain functionality and homeostasis is well accepted and has been proven by genomic as well as non-genomic mechanisms. In the healthy brain, numerous biological processes, e.g., cell proliferation, neurogenesis, dendritic spine formation as well as modulation of the immune system, have been attributed to retinoid signaling. This, together with the finding that retinoid metabolism is impaired in Alzheimer's disease (AD), led to preclinical and early clinical testing of natural and synthetic retinoids as innovative pharmaceuticals with multifactorial properties. Acitretin, an aromatic retinoid, was found to exert an anti-amyloidogenic effect in mouse models for AD as well as in human patients by stimulating the alpha-secretase ADAM10. The lipophilic drug was already demonstrated to easily pass the blood brain barrier after i.p. administration and evoked increased nest building capability in the 5xFAD mouse model. Additionally, we analyzed the immune-modulatory capacity of acitretin via a multiplex array in the 5xFAD mouse model and evaluated some of our findings in human CSF derived from a pilot study using acitretin. Although several serum analytes did not display changes, Interleukin-6 (IL-6) was found to be significantly increased in both-mouse and human neural material. This demonstrates that acitretin exerts an immune stimulatory effect-besides the alpha-secretase induction-which could impact the alleviation of learning and memory disabilities observed in the mouse model.

Dietary Wheat Amylase Trypsin Inhibitors Impact Alzheimer's Disease Pathology in 5xFAD Model Mice

Wheat amylase trypsin inhibitors (ATIs) represent a common dietary protein component of gluten-containing cereals (wheat, rye, and barley). They act as toll-like receptor 4 ligands, and are largely resistant to intestinal proteases, eliciting a mild inflammatory response within the intestine after oral ingestion. Importantly, nutritional ATIs exacerbated inflammatory bowel disease and features of fatty liver disease and the metabolic syndrome in mice. For Alzheimer’s disease (AD), both inflammation and altered insulin resistance are major contributing factors, impacting onset as well as progression of this devastating brain disorder in patients. In this study, we evaluated the impact of dietary ATIs on a well-known rodent model of AD (5xFAD). We assessed metabolic, behavioral, inflammatory, and microbial changes in mice consuming different dietary regimes with and without ATIs, consumed ad libitum for eight weeks. We demonstrate that ATIs, with or without a gluten matrix, had an impact on the metabolism and gut microbiota of 5xFAD mice, aggravating pathological hallmarks of AD. If these findings can be translated to patients, an ATI-depleted diet might offer an alternative therapeutic option for AD and warrants clinical intervention studies.

Transcriptional repression of the ectodomain sheddase ADAM10 by TBX2 and potential implication for Alzheimer's disease

BACKGROUND

The ADAM10-mediated cleavage of transmembrane proteins regulates cellular processes such as proliferation or migration. Substrate cleavage by ADAM10 has also been implicated in pathological situations such as cancer or Morbus Alzheimer. Therefore, identifying endogenous molecules, which modulate the amount and consequently the activity of ADAM10, might contribute to a deeper understanding of the enzyme's role in both, physiology and pathology.

METHOD

To elucidate the underlying cellular mechanism of the TBX2-mediated repression of ADAM10 gene expression, we performed overexpression, RNAi-mediated knockdown and pharmacological inhibition studies in the human neuroblastoma cell line SH-SY5Y. Expression analysis was conducted by e.g. real-time RT-PCR or western blot techniques. To identify the binding region of TBX2 within the ADAM10 promoter, we used luciferase reporter assay on deletion constructs and EMSA/WEMSA experiments. In addition, we analyzed a TBX2 loss-of-function Drosophila model regarding the expression of ADAM10 orthologs by qPCR. Furthermore, we quantified the mRNA level of TBX2 in post-mortem brain tissue of AD patients.

RESULTS

Here, we report TBX2 as a transcriptional repressor of ADAM10 gene expression: both, the DNA-binding domain and the repression domain of TBX2 were necessary to effect transcriptional repression of ADAM10 in neuronal SH-SY5Y cells. This regulatory mechanism required HDAC1 as a co-factor of TBX2. Transcriptional repression was mediated by two functional TBX2 binding sites within the core promoter sequence (- 315 to - 286 bp). Analysis of a TBX2 loss-of-function Drosophila model revealed that kuzbanian and kuzbanian-like, orthologs of ADAM10, were derepressed compared to wild type. Vice versa, analysis of cortical brain samples of AD-patients, which showed reduced ADAM10 mRNA levels, revealed a 2.5-fold elevation of TBX2, while TBX3 and TBX21 levels were not affected.

CONCLUSION

Our results characterize TBX2 as a repressor of ADAM10 gene expression and suggest that this regulatory interaction is conserved across tissues and species.