Neprilysin overexpression inhibits plaque formation but fails to reduce pathogenic Abeta oligomers and associated cognitive deficits in human amyloid precursor protein transgenic mice

Aβ∗56 is a stable oligomer that impairs memory function in mice

Amyloid-β (Aβ) oligomers consist of fibrillar and non-fibrillar soluble assemblies of the Aβ peptide. Aβ∗56 is a non-fibrillar Aβ assembly that is linked to memory deficits. Previous studies did not decipher specific forms of Aβ present in Aβ∗56. Here, we confirmed the memory-impairing characteristics of Aβ∗56 and extended its biochemical characterization. We used anti-Aβ(1-x), anti-Aβ(x-40), anti-Aβ(x-42), and A11 anti-oligomer antibodies in conjunction with western blotting, immunoaffinity purification, and size-exclusion chromatography to probe aqueous brain extracts from Tg2576, 5xFAD, and APP/TTA mice. In Tg2576, Aβ∗56 is a ∼56-kDa, SDS-stable, A11-reactive, non-plaque-dependent, water-soluble, brain-derived oligomer containing canonical Aβ(1-40). In 5xFAD, Aβ∗56 is composed of Aβ(1-42), whereas in APP/TTA, it contains both Aβ(1-40) and Aβ(1-42). When injected into the hippocampus of wild-type mice, Aβ∗56 derived from Tg2576 mice impairs memory. The unusual stability of this oligomer renders it an attractive candidate for studying relationships between molecular structure and effects on brain function.

Downregulation of Dickkopf-3, a Wnt antagonist elevated in Alzheimer's disease, restores synapse integrity and memory in a disease mouse model

Increasing evidence supports a role for deficient Wnt signaling in Alzheimer's disease (AD). Studies reveal that the secreted Wnt antagonist Dickkopf-3 (DKK3) colocalizes to amyloid plaques in AD patients. Here, we investigate the contribution of DKK3 to synapse integrity in healthy and AD brains. Our findings show that DKK3 expression is upregulated in the brains of AD subjects and that DKK3 protein levels increase at early stages in the disease. In hAPP-J20 and hAPPNL-G-F/NL-G-F mouse AD models, extracellular DKK3 levels are increased and DKK3 accumulates at dystrophic neuronal processes around plaques. Functionally, DKK3 triggers the loss of excitatory synapses through blockade of the Wnt/GSK3β signaling with a concomitant increase in inhibitory synapses via activation of the Wnt/JNK pathway. In contrast, DKK3 knockdown restores synapse number and memory in hAPP-J20 mice. Collectively, our findings identify DKK3 as a novel driver of synaptic defects and memory impairment in AD.

IM-MS and ECD-MS/MS Provide Insight into Modulation of Amyloid Proteins Self-Assembly by Peptides and Small Molecules

Neurodegenerative proteinopathies are characterized by formation and deposition of misfolded, aggregated proteins in the nervous system leading to neuronal dysfunction and death. It is widely believed that metastable oligomers of the offending proteins, preceding the fibrillar aggregates found in the tissue, are the proximal neurotoxins. There are currently almost no disease-modifying therapies for these diseases despite an active pipeline of preclinical development and clinical trials for over two decades, largely because studying the metastable oligomers and their interaction with potential therapeutics is notoriously difficult. Mass spectrometry (MS) is a powerful analytical tool for structural investigation of proteins, including protein-protein and protein-ligand interactions. Specific MS tools have been useful in determining the composition and conformation of abnormal protein oligomers involved in proteinopathies and the way they interact with drug candidates. Here, we analyze critically the utilization of ion-mobility spectroscopy-MS (IM-MS) and electron-capture dissociation (ECD) MS/MS for analyzing the oligomerization and conformation of multiple amyloidogenic proteins. We also discuss IM-MS investigation of their interaction with two classes of compounds developed by our group over the last two decades: C-terminal fragments derived from the 42-residue form of amyloid β-protein (Aβ42) and molecular tweezers. Finally, we review the utilization of ECD-MS/MS for elucidating the binding sites of the ligands on multiple proteins. These approaches are readily applicable to future studies addressing similar questions and hold promise for facilitating the development of successful disease-modifying drugs against neurodegenerative proteinopathies.

Aβ*56 is a stable oligomer that correlates with age-related memory loss in Tg2576 mice

Amyloid-β (Aβ) oligomers consist of fibrillar and non-fibrillar soluble assemblies of the Aβ peptide. Tg2576 human amyloid precursor protein (APP)-expressing transgenic mice modeling Alzheimer's disease produce Aβ*56, a non-fibrillar Aβ assembly that has been shown by several groups to relate more closely to memory deficits than plaques. Previous studies did not decipher specific forms of Aβ present in Aβ*56. Here, we confirm and extend the biochemical characterization of Aβ*56. We used anti-Aβ(1-x), anti-Aβ(x-40), and A11 anti-oligomer antibodies in conjunction with western blotting, immunoaffinity purification, and size-exclusion chromatography to probe aqueous brain extracts from Tg2576 mice of different ages. We found that Aβ*56 is a ∼56-kDa, SDS-stable, A11-reactive, non-plaque-related, water-soluble, brain-derived oligomer containing canonical Aβ(1-40) that correlates with age-related memory loss. The unusual stability of this high molecular-weight oligomer renders it an attractive candidate for studying relationships between molecular structure and effects on brain function.

Treadmill Exercise Reduces Neuroinflammation, Glial Cell Activation and Improves Synaptic Transmission in the Prefrontal Cortex in 3 × Tg-AD Mice

Physical exercise improves memory and cognition in physiological aging and Alzheimer's disease (AD), but the mechanisms remain poorly understood. Here, we test the hypothesis that Aβ oligomer accumulation, neuroinflammation, and glial cell activation may lead to disruption of synaptic transmission in the prefrontal cortex of 3 × Tg-AD Mice, resulting in impairment of learning and memory. On the other hand, treadmill exercise could prevent the pathogenesis and exert neuroprotective effects. Here, we used immunohistochemistry, western blotting, enzyme-linked immunosorbent assay, and slice electrophysiology to analyze the levels of GSK3β, Aβ oligomers (Aβ dimers and trimers), pro-inflammatory cytokines (IL-1β, IL-6, and TNFα), the phosphorylation of CRMP2 at Thr514, and synaptic currents in pyramidal neurons in the prefrontal cortex. We show that 12-week treadmill exercise beginning in three-month-old mice led to the inhibition of GSK3β kinase activity, decreases in the levels of Aβ oligomers, pro-inflammatory cytokines (IL-1β, IL-6, and TNFα), and the phosphorylation of CRMP2 at Thr514, reduction of microglial and astrocyte activation, and improvement of excitatory and inhibitory synaptic transmission of pyramidal neurons in the prefrontal cortex of 3 × Tg-AD Mice. Thus, treadmill exercise reduces neuroinflammation, glial cell activation and improves synaptic transmission in the prefrontal cortex in 3 × Tg-AD mice, possibly related to the inhibition of GSK3β kinase activity.

Disruption of the grid cell network in a mouse model of early Alzheimer's disease

Early-onset familial Alzheimer’s disease (AD) is marked by an aggressive buildup of amyloid beta (Aβ) proteins, yet the neural circuit operations impacted during the initial stages of Aβ pathogenesis remain elusive. Here, we report a coding impairment of the medial entorhinal cortex (MEC) grid cell network in the J20 transgenic mouse model of familial AD that over-expresses Aβ throughout the hippocampus and entorhinal cortex. Grid cells showed reduced spatial periodicity, spatial stability, and synchrony with interneurons and head-direction cells. In contrast, the spatial coding of non-grid cells within the MEC, and place cells within the hippocampus, remained intact. Grid cell deficits emerged at the earliest incidence of Aβ fibril deposition and coincided with impaired spatial memory performance in a path integration task. These results demonstrate that widespread Aβ-mediated damage to the entorhinal-hippocampal circuit results in an early impairment of the entorhinal grid cell network.

It remains poorly understood how the onset of Alzheimer’s disease affects spatial cognition. Here, the authors report that spatial coding in grid cells deteriorates over time in a mouse model of Alzheimer’s disease during the early stages of pathology while place cell and head direction coding remain intact.

Extracellular Vesicles Released from Neprilysin Gene-Modified Human Umbilical Cord-Derived Mesenchymal Stem Cell Enhance Therapeutic Effects in an Alzheimer's Disease Animal Model

Alzheimer's disease (AD) animal studies have reported that mesenchymal stem cells (MSCs) have therapeutic effects; however, clinical trial results are controversial. Neprilysin (NEP) is the main cleavage enzyme of β-amyloid (Aβ), which plays a major role in the pathology and etiology of AD. We evaluated whether transplantation of MSCs with NEP gene modification enhances the therapeutic effects in an AD animal model and then investigated these pathomechanisms. We manufactured NEP gene-enhanced human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) and intravenously transplanted them in Aβ_1-42-injected AD animal models. We compared the differences in behavioral tests and immunohistochemical assays between four groups: normal, Aβ_1-42 injection, naïve hUC-MSCs, and NEP-enhanced hUC-MSCs. Both naïve and NEP-enhanced hUC-MSC groups showed significant improvements in memory compared to the Aβ_1-42 injection group. There was no significant difference between naïve and NEP-enhanced hUC-MSC groups. There was a significant decrease in Congo red, BACE-1, GFAP, and Iba-1 and a significant increase in BDNF, NeuN, and NEP in both hUC-MSC groups compared to the Aβ_1-42 injection group. Among them, BDNF, NeuN, GFAP, Iba-1, and NEP showed more significant changes in the NEP-enhanced hUC-MSC group than in the naïve group. After stem cell injection, stem cells were not found. Extracellular vesicles (EVs) were equally observed in the hippocampus in the naïve and NEP-enhanced hUC-MSC groups. However, the EVs of NEP-enhanced hUC-MSCs contained higher amounts of NEP as compared to the EVs of naïve hUC-MSCs. Thus, hUC-MSCs affect AD animal models through stem cell-released EVs. Although there was no significant difference in cognitive function between the hUC-MSC groups, NEP-enhanced hUC-MSCs had superior neurogenesis and anti-inflammation properties compared to naïve hUC-MSCs due to increased NEP in the hippocampus by enriched NEP-possessing EVs. NEP gene-modified MSCs that release an increased amount of NEP within EVs may be a promising therapeutic option in AD treatment.

Cardiovascular Outcomes with Sacubitril-Valsartan in Heart Failure: Emerging Clinical Data

One of the defining features of heart failure (HF) is neurohormonal activation. The renin-angiotensin-aldosterone-system (RAAS) and sympathetic nervous system (SNS) cause vasoconstriction and fluid retention and, in response, the secretion of natriuretic peptides (NPs) from volume and pressure-overloaded myocardium promotes vasodilation and diuresis. Inhibition of the RAAS with either angiotensin-converting enzyme inhibitors (ACEI) or angiotensin receptor blockers (ARB) has been the cornerstone of medical treatment for HF with a reduced ejection fraction (HFrEF) but, until recently, it was unclear how the beneficial effects of NPs may be augmented in patients with HF. Neprilysin, a metalloproteinase widely distributed throughout the body, plays a role in degrading the gross excess of circulating NPs in patients with HF. Early studies of neprilysin inhibition suggested possible physiological benefits. In 2014, the PARADIGM-HF trial found that sacubitril-valsartan, a combination of the ARB valsartan, and the neprilysin inhibitor sacubitril, was superior to enalapril in patients with HFrEF, reducing the relative risk of cardiovascular (CV) death or first hospitalisation with HF by 20%. Almost half of the patients with HF symptoms have a “preserved” ejection fraction (HFpEF); however, the PARAGON-HF study found that sacubitril-valsartan in patients with LVEF ≥45% had no effect on CV death or first and recurrent hospitalisations with HF compared to valsartan. Guidelines across the world have changed to include sacubitril-valsartan for patients with HFrEF yet, nearly 6 years after PARADIGM-HF, there is still uncertainty as to when and in whom sacubitril-valsartan should be started. Furthermore, there may yet be subsets of patients with HFpEF who might benefit from treatment with sacubitril-valsartan. This review will describe the mechanisms behind the outcome benefit of sacubitril-valsartan in patients with HFrEF and to consider its future role in the management of patients with HF.

MCF7 Spheroid Development: New Insight about Spatio/Temporal Arrangements of TNTs, Amyloid Fibrils, Cell Connections, and Cellular Bridges

Human breast adenocarcinoma cells (MCF7) grow in three-dimensional culture as spheroids that represent the structural complexity of avascular tumors. Therefore, spheroids offer a powerful tool for studying cancer development, aggressiveness, and drug resistance. Notwithstanding the large amount of data regarding the formation of MCF7 spheroids, a detailed description of the morpho-functional changes during their aggregation and maturation is still lacking. In this study, in addition to the already established role of gap junctions, we show evidence of tunneling nanotube (TNT) formation, amyloid fibril production, and opening of large stable cellular bridges, thus reporting the sequential events leading to MCF7 spheroid formation. The variation in cell phenotypes, sustained by dynamic expression of multiple proteins, leads to complex networking among cells similar to the sequence of morphogenetic steps occurring in embryogenesis/organogenesis. On the basis of the observation that early events in spheroid formation are strictly linked to the redox homeostasis, which in turn regulate amyloidogenesis, we show that the administration of N-acetyl-l-cysteine (NAC), a reactive oxygen species (ROS) scavenger that reduces the capability of cells to produce amyloid fibrils, significantly affects their ability to aggregate. Moreover, cells aggregation events, which exploit the intrinsic adhesiveness of amyloid fibrils, significantly decrease following the administration during the early aggregation phase of neutral endopeptidase (NEP), an amyloid degrading enzyme.

Cathepsin D regulates cerebral Aβ42/40 ratios via differential degradation of Aβ42 and Aβ40

BACKGROUND

Cathepsin D (CatD) is a lysosomal protease that degrades both the amyloid β-protein (Aβ) and the microtubule-associated protein, tau, and has been genetically linked to late-onset Alzheimer disease (AD). Here, we sought to examine the consequences of genetic deletion of CatD on Aβ proteostasis in vivo and to more completely characterize the degradation of Aβ42 and Aβ40 by CatD.

METHODS

We quantified Aβ degradation rates and levels of endogenous Aβ42 and Aβ40 in the brains of CatD-null (CatD-KO), heterozygous null (CatD-HET), and wild-type (WT) control mice. CatD-KO mice die by ~ 4 weeks of age, so tissues from younger mice, as well as embryonic neuronal cultures, were investigated. Enzymological assays and surface plasmon resonance were employed to quantify the kinetic parameters (K_M, k_cat) of CatD-mediated degradation of monomeric human Aβ42 vs. Aβ40, and the degradation of aggregated Aβ42 species was also characterized. Competitive inhibition assays were used to interrogate the relative inhibition of full-length human and mouse Aβ42 and Aβ40, as well as corresponding p3 fragments.

RESULTS

Genetic deletion of CatD resulted in 3- to 4-fold increases in insoluble, endogenous cerebral Aβ42 and Aβ40, exceeding the increases produced by deletion of an insulin-degrading enzyme, neprilysin or both, together with readily detectable intralysosomal deposits of endogenous Aβ42-all by 3 weeks of age. Quite significantly, CatD-KO mice exhibited ~ 30% increases in Aβ42/40 ratios, comparable to those induced by presenilin mutations. Mechanistically, the perturbed Aβ42/40 ratios were attributable to pronounced differences in the kinetics of degradation of Aβ42 vis-à-vis Aβ40. Specifically, Aβ42 shows a low-nanomolar affinity for CatD, along with an exceptionally slow turnover rate that, together, renders Aβ42 a highly potent competitive inhibitor of CatD. Notably, the marked differences in the processing of Aβ42 vs. Aβ40 also extend to p3 fragments ending at positions 42 vs. 40.

CONCLUSIONS

Our findings identify CatD as the principal intracellular Aβ-degrading protease identified to date, one that regulates Aβ42/40 ratios via differential degradation of Aβ42 vs. Aβ40. The finding that Aβ42 is a potent competitive inhibitor of CatD suggests a possible mechanistic link between elevations in Aβ42 and downstream pathological sequelae in AD.

The Toxicity and Polymorphism of β-Amyloid Oligomers

It is widely accepted that β-amyloid oligomers (Aβos) play a key role in the progression of Alzheimer's disease (AD) by inducing neuron damage and cognitive impairment, but Aβos are highly heterogeneous in their size, structure and cytotoxicity, making the corresponding studies tough to carry out. Nevertheless, a number of studies have recently made remarkable progress in the describing the characteristics and pathogenicity of Aβos. We here review the mechanisms by which Aβos exert their neuropathogenesis for AD progression, including receptor binding, cell membrane destruction, mitochondrial damage, Ca2+ homeostasis dysregulation and tau pathological induction. We also summarize the characteristics and pathogenicity such as the size, morphology and cytotoxicity of dimers, trimers, Aβ*56 and spherical oligomers, and suggest that Aβos may play a different role at different phases of AD pathogenesis, resulting in differential consequences on neuronal synaptotoxicity and survival. It is warranted to investigate the temporal sequence of Aβos in AD human brain and examine the relationship between different Aβos and cognitive impairment.

Amyloidosis is associated with thicker myelin and increased oligodendrogenesis in the adult mouse brain

In Alzheimer's disease, amyloid plaque formation is associated with the focal death of oligodendrocytes and soluble amyloid β impairs the survival of oligodendrocytes in vitro. However, the response of oligodendrocyte progenitor cells (OPCs) to early amyloid pathology remains unclear. To explore this, we performed a histological, electrophysiological, and behavioral characterization of transgenic mice expressing a pathological form of human amyloid precursor protein (APP), containing three single point mutations associated with the development of familial Alzheimer's disease (PDGFB‐APP^Sw.Ind, also known as J20 mice). PDGFB‐APP^Sw.Ind transgenic mice had impaired survival from weaning, were hyperactive by 2 months of age, and developed amyloid plaques by 6 months of age, however, their spatial memory remained intact over this time course. Hippocampal OPC density was normal in P60‐P180 PDGFB‐APP^Sw.Ind transgenic mice and, by performing whole‐cell patch‐clamp electrophysiology, we found that their membrane properties, including their response to kainate (100 µM), were largely normal. However, by P100, the response of hippocampal OPCs to GABA was elevated in PDGFB‐APP^Sw.Ind transgenic mice. We also found that the nodes of Ranvier were shorter, the paranodes longer, and the myelin thicker for hippocampal axons in young adult PDGFB‐APP^Sw.Ind transgenic mice compared with wildtype littermates. Additionally, oligodendrogenesis was normal in young adulthood, but increased in the hippocampus, entorhinal cortex, and fimbria of PDGFB‐APP^Sw.Ind transgenic mice as pathology developed. As the new oligodendrocytes were not associated with a change in total oligodendrocyte number, these cells are likely required for cell replacement.

N-Terminal Truncated Aβ4-42 Is a Substrate for Neprilysin Degradation in vitro and in vivo

In sporadic Alzheimer's disease (AD), an imbalance between production and clearance of amyloid-β (Aβ) peptides seems to account for enhanced Aβ accumulation. The metalloprotease neprilysin (NEP) is an important Aβ degrading enzyme as shown by a variety of in vitro and in vivo studies. While the degradation of full-length Aβ peptides such as Aβ1-40 and Aβ1-42 is well established, it is less clear whether NEP is also capable of degrading N-terminally truncated Aβ species such as the common variant Aβ4-42. In the present report, we confirmed the degradation of Aβ4-x species by neprilysin using in vitro digestion and subsequent analysis using gel-based assays and mass spectrometry. By crossing Tg4-42 mice expressing only Aβ4-42 peptides with homozygous NEP-knock-out mice (NEP-/-), we were able to demonstrate that NEP deficiency increased hippocampal intraneuronal Aβ levels and aggravated neuron loss in the Tg4-42 transgenic mouse model of AD.

Neuroprotective Effects of Salidroside in a Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD), the most common form of dementia worldwide, is characterized by pathological hallmarks like β-amyloid peptide (Aβ) and clinical manifestations including cognitive impairment, psychiatry disorders, and behavioral changes. Salidroside (Sal) extracted from Rhodiola rosea L. showed protective effects against Aβ-induced neurotoxicity in a Drosophila AD model in our previous research. In the present study, daily doses of Sal were administered to APP/PS1 mice, a mouse model of AD, and several parameters were tested, including behavioral performance, Aβ status, levels of synapse-related proteins, and levels of PI3K/Akt targets of mTOR cell signaling pathway proteins. The behavioral testing showed an improvement in locomotor activity in the APP/PS1 mice after the administration of Sal. Treatment with Sal decreased both the soluble and insoluble Aβ levels and increased the expression of PSD95, NMDAR1, and calmodulin-dependent protein kinase II. The phosphatidylinositide PI3K/Akt/mTOR signaling was upregulated, which was in accordance with the above improvements from Sal treatment. Our findings suggested that Sal may protect the damaged synapses of the neurons in the APP/PS1 mice.

Extracellular Vesicles as a Neprilysin Delivery System Memory Improvement in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative brain disorder which has no effective treatment yet due to the blood barrier in the brain that limits the drugs with the potential of disease improvement. Extracellular vesicles (EVs) are biocompatible nanoparticles with a lipid membrane. These vesicles are secreted from various cells such as mesenchymal stem cells (MSCs) and can pass through biological barriers for transfer of information such as signals or be used as carriers for various proteins like Neprilysin (NEP). NEP is an active enzyme in the clearance of abnormal aggregated beta-amyloid sheets in the brain. In the present study, we used EVs to carry NEP for memory improvement in Alzheimer's disease. For this purpose, bone marrow MSCs were isolated from rat femur. Stemness evaluation of established cells was characterized by differentiation potency and specific markers with flowcytometry. EVs were isolated from MSCs supernatant by ultracentrifugation and analyzed by scanning electron microscopy (SEM), dynamic light scattering (DLS) and western blotting. EVs were loaded with NEP by freeze-thaw cycle and then administrated intranasally in a rat model of the AD for 14 days. Our findings showed EV-loaded NEP caused a decrease in IL-1beta and also BAX but an increase in BCL2 expression level in the rat brain. Altogether, these data showed that EV-loaded NEP can improve brain-related behavioural function which may be mediated through the regulation of inflammation and apoptosis. These findings suggest that EV-loaded NEP can be considered as a potential drug delivery system for the improvement of AD.

Exploring the Mitochondrial Degradome by the TAILS Proteomics Approach in a Cellular Model of Parkinson's Disease

Parkinson’s disease (PD) is the second most frequent neurodegenerative disease worldwide and the availability of early biomarkers and novel biotargets represents an urgent medical need. The main pathogenetic hallmark of PD is the specific loss of nigral dopaminergic neurons, in which mitochondrial dysfunction plays a crucial role. Mitochondrial proteases are central to the maintenance of healthy mitochondria and they have recently emerged as drug targets. However, an exhaustive characterization of these enzymes and their targets is still lacking, due to difficulties in analyzing proteolytic fragments by bottom-up proteomics approaches. Here, we propose the “mitochondrial dimethylation-TAILS” strategy, which combines the isolation of mitochondria with the enrichment of N-terminal peptides to analyze the mitochondrial N-terminome. We applied this method in a cellular model of altered dopamine homeostasis in neuroblastoma SH-SY5Y cells, which recapitulates early steps of PD pathogenesis. The main aim was to identify candidate mitochondrial proteases aberrantly activated by dopamine dysregulation and their cleaved targets. The proposed degradomics workflow was able to improve the identification of mitochondrial proteins if compared to classical shotgun analysis. In detail, 40% coverage of the mitochondrial proteome was obtained, the sequences of the transit peptides of two mitochondrial proteins were unveiled, and a consensus cleavage sequence for proteases involved in the processing of mitochondrial proteins was depicted. Mass spectrometry proteomics data have been submitted to ProteomeXchange with the identifier PXD013900. Moreover, sixty-one N-terminal peptides whose levels were affected by dopamine treatment were identified. By an in-depth analysis of the proteolytic peptides included in this list, eleven mitochondrial proteins showed altered proteolytic processing. One of these proteins (i.e., the 39S ribosomal protein L49 – MRPL49) was cleaved by the neprilysin protease, already exploited in clinics as a biotarget. We eventually demonstrated a mitochondrial subcellular localization of neprilysin in human cells for the first time. Collectively, these results shed new light on mitochondrial dysfunction linked to dopamine imbalance in PD and opened up the possibility to explore the mitochondrial targets of neprilysin as candidate biomarkers.

Co-Administration of TiO2 Nanowired Mesenchymal Stem Cells with Cerebrolysin Potentiates Neprilysin Level and Reduces Brain Pathology in Alzheimer's Disease

Neprilysin (NPL), the rate-limiting enzyme for amyloid beta peptide (AβP), appears to play a crucial role in the pathogenesis of Alzheimer's disease (AD). Since mesenchymal stem cells (MSCs) and/or cerebrolysin (CBL, a combination of neurotrophic factors and active peptide fragments) have neuroprotective effects in various CNS disorders, we examined nanowired delivery of MSCs and CBL on NPL content and brain pathology in AD using a rat model. AD-like symptoms were produced by intraventricular (i.c.v.) administration of AβP (1-40) in the left lateral ventricle (250 ng/10 μl, once daily) for 4 weeks. After 30 days, the rats were examined for NPL and AβP concentrations in the brain and related pathology. Co-administration of TiO2-nanowired MSCs (10⁶ cells) with 2.5 ml/kg CBL (i.v.) once daily for 1 week after 2 weeks of AβP infusion significantly increased the NPL in the hippocampus (400 pg/g) from the untreated control group (120 pg/g; control 420 ± 8 pg/g brain) along with a significant decrease in the AβP deposition (45 pg/g from untreated control 75 pg/g; saline control 40 ± 4 pg/g). Interestingly, these changes were much less evident when the MSCs or CBL treatment was given alone. Neuronal damages, gliosis, and myelin vesiculation were also markedly reduced by the combined treatment of TiO2, MSCs, and CBL in AD. These observations are the first to show that co-administration of TiO2-nanowired CBL and MSCs has superior neuroprotective effects in AD probably due to increasing the brain NPL level effectively, not reported earlier.

Current and Emerging Pharmacological Targets for the Treatment of Alzheimer's Disease

No cure or disease-modifying therapy for Alzheimer's disease (AD) has yet been realized. However, a multitude of pharmacological targets have been identified for possible engagement to enable drug discovery efforts for AD. Herein, we review these targets comprised around three main therapeutic strategies. First is an approach that targets the main pathological hallmarks of AD: amyloid-β (Aβ) oligomers and hyperphosphorylated tau tangles which primarily focuses on reducing formation and aggregation, and/or inducing their clearance. Second is a strategy that modulates neurotransmitter signaling. Comprising this strategy are the cholinesterase inhibitors and N-methyl-D-aspartate receptor blockade treatments that are clinically approved for the symptomatic treatment of AD. Additional targets that aim to stabilize neuron signaling through modulation of neurotransmitters and their receptors are also discussed. Finally, the third approach comprises a collection of 'sensitive targets' that indirectly influence Aβ or tau accumulation. These targets are proteins that upon Aβ accumulation in the brain or direct Aβ-target interaction, a modification in the target's function is induced. The process occurs early in disease progression, ultimately causing neuronal dysfunction. This strategy aims to restore normal target function to alleviate Aβ-induced toxicity in neurons. Overall, we generally limit our analysis to targets that have emerged in the last decade and targets that have been validated using small molecules in in vitro and/or in vivo models. This review is not an exhaustive list of all possible targets for AD but serves to highlight the most promising and critical targets suitable for small molecule drug intervention.

CSF pro-orexin and amyloid-β38 expression in Alzheimer's disease and frontotemporal dementia

There is an unmet need for markers that can stratify different forms and subtypes of dementia. Because of similarities in clinical presentation, it can be difficult to distinguish between Alzheimer's disease (AD) and frontotemporal dementia (FTD). Using a multiplex targeted proteomic LC-MS/MS platform, we aimed to identify cerebrospinal fluid proteins differentially expressed between patients with AD and FTD. Furthermore analysis of 2 confirmed FTD genetic subtypes carrying progranulin (GRN) and chromosome 9 open reading frame 72 (C9orf72) mutations was performed to give an insight into the differing pathologies of these forms of FTD. Patients with AD (n = 13) demonstrated a significant (p < 0.007) 1.24-fold increase in pro-orexin compared to FTD (n = 32). Amyloid beta-38 levels in patients with AD were unaltered but demonstrated a >2-fold reduction (p < 0.0001) in the FTD group compared to controls and a similar 1.83-fold reduction compared to the AD group (p < 0.001). Soluble TREM2 was elevated in both dementia groups but did not show any difference between AD and FTD. A further analysis comparing FTD subgroups revealed slightly lower levels of proteins apolipoprotein E, CD166, osteopontin, transthyretin, and cystatin C in the GRN group (n = 9) compared to the C9orf72 group (n = 7). These proteins imply GRN FTD elicits an altered inflammatory response to C9orf72 FTD.

Amylin in Alzheimer's disease: Pathological peptide or potential treatment?

Alzheimer's disease (AD) is a neurodegenerative disease for which we currently lack effective treatments or a cure. The pancreatic peptide hormone amylin has recently garnered interest as a potential pharmacological target for the treatment of AD. A number of studies have demonstrated that amylin and amylin analogs like the FDA-approved diabetes drug pramlintide can reduce amyloid burden in the brain and improve cognitive symptoms of AD. However, other data suggest that amylin may have pathological effects in AD due to its propensity to misfold and aggregate under certain conditions. Here, the literature supporting a beneficial versus harmful role of amylin in AD is reviewed. Additionally, several critical gaps in the literature are discussed, such as our limited understanding of the amylin system during aging and in disease states, as well as complexities of amylin receptor signaling and of changing pathophysiology during AD progression that might underlie the seemingly conflicting or contradictory results in the amylin/AD literature. This article is part of the Special Issue entitled 'Metabolic Impairment as Risk Factors for Neurodegenerative Disorders.'

Stimulating the Activity of Amyloid-Beta Degrading Enzymes: A Novel Approach for the Therapeutic Manipulation of Amyloid-Beta Levels

Alzheimer's disease is a debilitating neurological disease placing significant burden on health care budgets around the world. It is widely believed that accumulation of amyloid-beta (Aβ) in the brain is a key event that initiates neurodegeneration, thus the clearance of Aβ from brain could be a key therapeutic strategy. Aβ exists in an equilibrium in healthy individuals, and recent research would suggest that dysfunction in the clearance pathways is the driving force behind its accumulation. One mechanism of clearance is proteolytic degradation by enzymes, and increasing the expression of these enzymes in animal models of Alzheimer's disease has indeed shown promising results. This approach could be challenging to translate into the clinic given the likely need for genetic manipulation. We hypothesize that stimulating the activity of these enzymes (as opposed to increasing expression) through pharmacological agents will enhance degradation or at least prevent amyloid deposition, and is therefore another potentially novel avenue to manipulate Aβ levels for therapeutic purposes. We discuss the recent research supporting this hypothesis as well as possible drawbacks to this approach.

DNA methylation level of the neprilysin promoter in Alzheimer's disease brains

Neprilysin (NEP), a membrane-bound metalloprotease, has been shown to play an essential role in the clearance of amyloid beta (Aβ) peptides. Previous studies have reported that NEP expression is downregulated in the normal aging brain as well as in the Alzheimer's disease (AD) brain, providing evidence that the downregulation of NEP expression contributes to the age-dependent deposition of Aβ-containing plaques, a pathological hallmark of AD. However, the mechanisms underlying the downregulation remain unclear. In this study, we explored the relationship between DNA methylation status of CpG islands in the NEP promoter and its expression level in AD brains. We performed pyrosequencing analyses to detect the DNA methylation level in 31 postmortem AD brains and 40 normal control brains. All 30 CpG sites showed no clear difference in methylation level. To further focus on methylation changes specific to neuronal cells, we performed methylation array experiments using neuronal nuclei from postmortem brains and found no clear difference in the methylation level between AD and normal control samples. Our detailed analyses, with a substantial number of brain samples, provide the first convincing evidence that DNA methylation of the NEP promoter is not involved in AD development and progression.

Early changes in hyppocampal neurogenesis induced by soluble Ab1-42 oligomers

Alzheimer's disease is characterized by the loss of neurons, the accumulation of intracellular neurofibrillary tangles and extracellular amyloid plaques in the brain. However, there are contradicting data on differences in neurogenesis at the onset of the disease or before the formation of amyloid plaques. As awareness of the importance of the pre-symptom phase in neurodegenerative diseases grows in the context of early diagnosis and pathogenesis, we analyzed the critical periods of adult hippocampal neurogenesis at an early stage under the action of soluble Ab1-42 beta-amyloid. The proliferation, migration and neuronal cells survival were evaluated in mice with an injection of soluble amyloid beta-oligomers. It was found that the injection of Ab1-42 oligomers causes a decrease in cell proliferation in the mouse hippocampus. Despite the preservation of the neuroblast pool in animals after beta-amyloid injection, the process of radial migration is disrupted, and an increase in apoptosis in the neurogenic niche was revealed. Thus, our results demonstrate damage of neurogenesis critical stages: the progenitor cells, neuroblast migration, the integration of immature neurons, and the survival of neurons under application of soluble beta-amyloid oligomers. The obtained data indicate decline in proliferation rate in the subgranular zone, that is accompanied by ectopic differentiation and disturbed migration, producing, apparently, abnormal neurons that have lower survival rates. That could lead to a decrease in mature neurons numbers and the number of cells in the granular layer of the dentate gyrus.

Nanoscale Dynamics of Amyloid β-42 Oligomers As Revealed by High-Speed Atomic Force Microscopy

Amyloid β-protein (Aβ) oligomers are emerging as potent neurotoxic species in Alzheimer's disease pathogenesis. Detailed characterization of oligomer structure and dynamics is necessary to develop oligomer-specific therapeutic agents. However, oligomers exist transiently, which complicates their structural analysis. One approach to mitigate these problems has been photochemical cross-linking of native oligomers. In these states, the oligomers can be isolated and purified for physical and chemical studies. Here we characterized the structure of isolated cross-linked Aβ42 trimers, pentamers, and heptamers with atomic force microscopy (AFM) imaging and probed their dynamics in solution using time-lapse high-speed AFM. This technique enables visualization of the structural dynamics of the oligomers at nanometer resolution on a millisecond time scale. Results demonstrate that cross-linked pentamers and heptamers are very dynamic fluctuating between a compact single-globular and multiglobular assemblies. Trimers remain in their single-globular geometry that elongates adopting an ellipsoidal shape. Biological significance of oligomers dynamics is discussed.

Alzheimer's disease as oligomeropathy

Alzheimer's disease (AD) is the most common age-related neurodegenerative disorder and is characterized by pathological aggregates of amyloid β-protein (Aβ) and tau protein. On the basis of genetic evidence, biochemical data, and animal models, Aβ has been suggested to be responsible for the pathogenesis of AD (the amyloid hypothesis). Aβ molecules tend to aggregate to form oligomers, protofibrils, and mature fibrils. Although mature fibrils in the final stage have been thought to be the cause of AD pathogenesis, recent studies using synthetic Aβ peptides, a cell culture model, Aβ precursor protein transgenic mice models, and human samples, such as cerebrospinal fluids and postmortem brains of AD patients, suggest that pre-fibrillar forms (oligomers of Aβ) are more deleterious than are extracellular fibril forms. Based on this recent evidence showing that oligomers have a central role in the pathogenesis of AD, the term "oligomeropathy" could be used to define AD and other protein-misfolding diseases. In this review, I discuss recent developments in the "oligomer hypothesis" including our research findings regarding the pathogenesis of AD.

A novel Alzheimer's disease drug candidate targeting inflammation and fatty acid metabolism

Background

CAD-31 is an Alzheimer’s disease (AD) drug candidate that was selected on the basis of its ability to stimulate the replication of human embryonic stem cell-derived neural precursor cells as well as in APPswe/PS1ΔE9 AD mice. To move CAD-31 toward the clinic, experiments were undertaken to determine its neuroprotective and pharmacological properties, as well as to assay its therapeutic efficacy in a rigorous mouse model of AD.

Results

CAD-31 has potent neuroprotective properties in six distinct nerve cell assays that mimic toxicities observed in the old brain. Pharmacological and preliminary toxicological studies show that CAD-31 is brain-penetrant and likely safe. When fed to old, symptomatic APPswe/PS1ΔE9 AD mice starting at 10 months of age for 3 additional months in a therapeutic model of the disease, there was a reduction in the memory deficit and brain inflammation, as well as an increase in the expression of synaptic proteins. Small-molecule metabolic data from the brain and plasma showed that the major effect of CAD-31 is centered on fatty acid metabolism and inflammation. Pathway analysis of gene expression data showed that CAD-31 had major effects on synapse formation and AD energy metabolic pathways.

Conclusions

All of the multiple physiological effects of CAD-31 were favorable in the context of preventing some of the toxic events in old age-associated neurodegenerative diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s13195-017-0277-3) contains supplementary material, which is available to authorized users.

Sacubitril/valsartan: beyond natriuretic peptides

Natriuretic peptides, especially B-type natriuretic peptide (BNP), have primarily been regarded as biomarkers in heart failure (HF). However, they are also possible therapeutic agents due to their potentially beneficial physiological effects. The angiotensin receptor-neprilysin inhibitor, sacubitril/valsartan, simultaneously augments the natriuretic peptide system (NPS) by inhibiting the enzyme neprilysin (NEP) and inhibits the renin-angiotensin-aldosterone system (RAAS) by blocking the angiotensin II receptor. It has been shown to improve mortality and hospitalisation outcomes in patients with HF due to left ventricular systolic dysfunction. The key advantage of sacubitril/valsartan has been perceived to be its ability to augment BNP, while its other effects have largely been overlooked. This review highlights the important effects of sacubitril/valsartan, beyond just the augmentation of BNP. First we discuss how NPS physiology differs between healthy individuals and those with HF by looking at mechanisms like the overwhelming effects of RAAS on the NPS, natriuretic peptide receptor desensitisation and absolute natriuretic deficiency. Second, this review explores other hormones that are augmented by sacubitril/valsartan such as bradykinin, substance P and adrenomedullin that may contribute to the efficacy of sacubitril/valsartan in HF. We also discuss concerns that sacubitril/valsartan may interfere with amyloid-β homeostasis with potential implications on Alzheimer's disease and macular degeneration. Finally, we explore the concept of 'autoinhibition' which is a recently described observation that humans have innate NEP inhibitory capability when natriuretic peptide levels rise above a threshold. There is speculation that autoinhibition may provide a surge of natriuretic and other vasoactive peptides to rapidly reverse decompensation. We contend that by pre-emptively inhibiting NEP, sacubitril/valsartan is inducing this surge earlier during decompensation, resulting in the better outcomes observed.

Safety of the neprilysin/renin-angiotensin system inhibitor LCZ696

Objectives

The combined neprilysin/rennin-angiotensin system inhibitor sacubitril/valsartan (LCZ696) has shown its superiority over ACEI/ARB therapy. In view of the existing concern of its adverse effects, we aimed to provide evidence of the safety of the new drug.

Results

A total of 6 randomized trials with 11,821 subjects were included in this analysis. No significant differences were found in any adverse effects between LCZ696 and ACEI/ARB or placebo groups. LCZ696 significantly decreased the risks of serious adverse events and death compared with ACEI/ARB. LCZ696 also significantly decrease the risk of discontinuation of treatment for any adverse event no matter compared with ACEI/ARB or a placebo. LCZ696 significantly increased the risk of angioedema and dizziness, while it decreased the risk of renal dysfunction and bronchitis. There was no difference for hypotension, hyperkalemia, cough, upper respiratory tract inflammation, diarrhoea, back pain, nasopharyngitis, headache and influenza between the LCZ696 group and the ACEI/ARB group.

Materials and Methods

A meta-analysis of eligible studies that used LCZ696 in heart failure and hypertension was performed. Embase, PubMed and the Cochrane Library were searched for randomized controlled trials (RCTs) with data on any adverse effects, serious adverse events, discontinuation of treatment for any adverse event, death, angioedema, hypotension, hyperkalemia, and other adverse effects to perform this meta-analysis.

Conclusions

In addition to the beneficial effect of LCZ696 on end point events, the available evidences showed that LCZ696 was associated with less drug-risks than a placebo and ACEI/ARB.

Exogenous expression of Drp1 plays neuroprotective roles in the Alzheimer's disease in the Aβ42 transgenic Drosophila model

Background

Alzheimer's disease (AD) is one of the most common neurodegenerative disorders. Recent studies have shown that mitochondrial dysfunction is a causative factor of AD. Drp1 (Dynamin-related protein 1), a regulator of mitochondrial fission, shows neuroprotective effects on Parkinson’s disease. In this study, we investigate the effect and mechanism of Drp1 on Aβ42 transgenic Drosophila.

Methods

Elav-gal4/UAS>Aβ42 transgenic Drosophila model was constructed using Elav-gal4 promoter. The effects of Drp1 on the lifespan, motor ability and neuronal degeneration of the transgenic Drosophila were explored by over-expressing Drp1 in the Aβ42 transgenic Drosophila. ATP levels in the brain tissues of Aβ42 transgenic Drosophila were detected using high performance liquid chromatography (HPLC).

Results

Exogenous expression of Drp1 promoted crawling ability, reduced the levels of ATP in Drosophila brain and suppressed the neuronal degeneration.

Conclusion

The protective effect of Drp1 on the Aβ42 transgenic Drosophila was achieved by protecting the mitochondrial function, suggesting that Drp1 may be a potential therapeutic strategies for AD.

The amyloid-β oligomer Aβ*56 induces specific alterations in neuronal signaling that lead to tau phosphorylation and aggregation

Oligomeric forms of amyloid-forming proteins are believed to be the principal initiating bioactive species in many neurodegenerative disorders, including Alzheimer's disease (AD). Amyloid-β (Aβ) oligomers are implicated in AD-associated phosphorylation and aggregation of the microtubule-associated protein tau. To investigate the specific molecular pathways activated by different assemblies, we isolated various forms of Aβ from Tg2576 mice, which are a model for AD. We found that Aβ*56, a 56-kDa oligomer that is detected before patients develop overt signs of AD, induced specific changes in neuronal signaling. In primary cortical neurons, Aβ*56 interacted with N-methyl-d-aspartate receptors (NMDARs), increased NMDAR-dependent Ca²⁺ influx, and consequently increased intracellular calcium concentrations and the activation of Ca²⁺-dependent calmodulin kinase IIα (CaMKIIα). In cultured neurons and in the brains of Tg2576 mice, activated CaMKIIα was associated with increased site-specific phosphorylation and missorting of tau, both of which are associated with AD pathology. In contrast, exposure of cultured primary cortical neurons to other oligomeric Aβ forms (dimers and trimers) did not trigger these effects. Our results indicate that distinct Aβ assemblies activate neuronal signaling pathways in a selective manner and that dissecting the molecular events caused by each oligomer may inform more effective therapeutic strategies.

Regulation of Synaptic Amyloid-β Generation through BACE1 Retrograde Transport in a Mouse Model of Alzheimer's Disease

Amyloid-β (Aβ) peptides play a key role in synaptic damage and memory deficits in the early pathogenesis of Alzheimer's disease (AD). Abnormal accumulation of Aβ at nerve terminals leads to synaptic pathology and ultimately to neurodegeneration. β-site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1) is the major neuronal β-secretase for Aβ generation. However, the mechanisms regulating BACE1 distribution in axons and β cleavage of APP at synapses remain largely unknown. Here, we reveal that dynein-Snapin-mediated retrograde transport regulates BACE1 trafficking in axons and APP processing at presynaptic terminals. BACE1 is predominantly accumulated within late endosomes at the synapses of AD-related mutant human APP (hAPP) transgenic (Tg) mice and patient brains. Defective retrograde transport by genetic ablation of snapin in mice recapitulates late endocytic retention of BACE1 and increased APP processing at presynaptic sites. Conversely, overexpressing Snapin facilitates BACE1 trafficking and reduces synaptic BACE1 accumulation by enhancing the removal of BACE1 from distal AD axons and presynaptic terminals. Moreover, elevated Snapin expression via stereotactic hippocampal injections of adeno-associated virus particles in mutant hAPP Tg mouse brains decreases synaptic Aβ levels and ameliorates synapse loss, thus rescuing cognitive impairments associated with hAPP mice. Altogether, our study provides new mechanistic insights into the complex regulation of BACE1 trafficking and presynaptic localization through Snapin-mediated dynein-driven retrograde axonal transport, thereby suggesting a potential approach of modulating Aβ levels and attenuating synaptic deficits in AD.SIGNIFICANCE STATEMENT β-Site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1) trafficking and synaptic localization significantly influence its β secretase activity and amyloid-β (Aβ) production. In AD brains, BACE1 is accumulated within dystrophic neurites, which is thought to augment Aβ-induced synaptotoxicity by Aβ overproduction. However, it remains largely unknown whether axonal transport regulates synaptic APP processing. Here, we demonstrate that Snapin-mediated retrograde transport plays a critical role in removing BACE1 from presynaptic terminals toward the soma, thus reducing synaptic Aβ production. Adeno-associated virus-mediated Snapin overexpression in the hippocampus of mutant hAPP mice significantly decreases synaptic Aβ levels, attenuates synapse loss, and thus rescues cognitive deficits. Our study uncovers a new pathway that controls synaptic APP processing by enhancing axonal BACE1 trafficking, thereby advancing our fundamental knowledge critical for ameliorating Aβ-linked synaptic pathology.

Network abnormalities and interneuron dysfunction in Alzheimer disease

The function of neural circuits and networks can be controlled, in part, by modulating the synchrony of their components' activities. Network hypersynchrony and altered oscillatory rhythmic activity may contribute to cognitive abnormalities in Alzheimer disease (AD). In this condition, network activities that support cognition are altered decades before clinical disease onset, and these alterations predict future pathology and brain atrophy. Although the precise causes and pathophysiological consequences of these network alterations remain to be defined, interneuron dysfunction and network abnormalities have emerged as potential mechanisms of cognitive dysfunction in AD and related disorders. Here, we explore the concept that modulating these mechanisms may help to improve brain function in these conditions.

Neuregulin 1 improves cognitive deficits and neuropathology in an Alzheimer's disease model

Several lines of evidence suggest that neuregulin 1 (NRG1) signaling may influence cognitive function and neuropathology in Alzheimer’s disease (AD). To test this possibility, full-length type I or type III NRG1 was overexpressed via lentiviral vectors in the hippocampus of line 41 AD mouse. Both type I and type III NRG1 improves deficits in the Morris water-maze behavioral task. Neuropathology was also significantly ameliorated. Decreased expression of the neuronal marker MAP2 and synaptic markers PSD95 and synaptophysin in AD mice was significantly reversed. Levels of Aβ peptides and plaques were markedly reduced. Furthermore, we showed that soluble ectodomains of both type I and type III NRG1 significantly increased expression of Aβ-degrading enzyme neprilysin (NEP) in primary neuronal cultures. Consistent with this finding, immunoreactivity of NEP was increased in the hippocampus of AD mice. These results suggest that NRG1 provides beneficial effects in candidate neuropathologic substrates of AD and, therefore, is a potential target for the treatment of AD.

Aβ-Degrading Proteases: Therapeutic Potential in Alzheimer Disease

The amyloid β-protein (Aβ) plays an indispensable role in the pathogenesis of Alzheimer disease (AD). Aβ is subject to proteolytic degradation by a diverse array of peptidases and proteinases, known collectively as Aβ-degrading proteases (AβDPs). A growing number of AβDPs have been identified that impact Aβ powerfully and in a surprising variety of ways. As such, AβDPs hold considerable therapeutic potential for the treatment and/or prevention of AD. Here, we critically review the relative merits of therapeutic strategies targeting AβDPs compared with current Aβ-lowering strategies focused on immunotherapies and pharmacological modulation of Aβ-producing enzymes. Several innovative advances have increased considerably the feasibility of delivering AβDPs to the brain or enhancing their activity in a non-invasive manner. We argue that therapies targeting AβDPs offer numerous potential advantages that should be explored through continued research into this promising field.

A Study of Aβ Oligomers in the Temporal Cortex and Cerebellum of Patients with Neuropathologically Confirmed Alzheimer's Disease Compared to Aged Controls

BACKGROUND/AIMS

Investigations of Aβ oligomers in neuropathologically confirmed Alzheimer's disease (AD) are still scarce. We report neurohistopathological and biochemical analyses using antibodies against tau and amyloid β (Aβ) pathology.

METHODS

Thirty elderly AD patients and 43 age-matched controls with or without deposition of amyloid plaques (AP) were analyzed by immunohistochemistry. In 21 cases with available fresh tissue, Western blots were also performed. Neuropathological analysis included quantitative assessment of neurofibrillary tangles (NFT), AP and Aβ oligomer densities in the mesial temporal cortex (TC).

RESULTS

NFT, fibrillar amyloid and Aβ oligomeric deposit densities were significantly higher in AD patients than in controls. There was no relationship between oligomeric Aβ densities and Braak NFT staging scores. Furthermore, Aβ oligomer expression was closely correlated with Aβ plaques in the TC. By Western blot, Aβ oligomers were observed in AD patients, in plaque-free controls, in 1 'tangle-only AD' case, as well as in the cerebellum. A band near 55 kDa was the only Western blot signal that was significantly increased in the TC of AD patients compared to controls as well as less expressed in the cerebellum.

CONCLUSION

These results suggest that a putative dodecamer, near 55 kDa, may contribute to AD vulnerability of the TC.

X-ray Crystallographic Structures of a Trimer, Dodecamer, and Annular Pore Formed by an Aβ17-36 β-Hairpin

High-resolution structures of oligomers formed by the β-amyloid peptide Aβ are needed to understand the molecular basis of Alzheimer’s disease and develop therapies. This paper presents the X-ray crystallographic structures of oligomers formed by a 20-residue peptide segment derived from Aβ. The development of a peptide in which Aβ_17–36 is stabilized as a β-hairpin is described, and the X-ray crystallographic structures of oligomers it forms are reported. Two covalent constraints act in tandem to stabilize the Aβ_17–36 peptide in a hairpin conformation: a δ-linked ornithine turn connecting positions 17 and 36 to create a macrocycle and an intramolecular disulfide linkage between positions 24 and 29. An N-methyl group at position 33 blocks uncontrolled aggregation. The peptide readily crystallizes as a folded β-hairpin, which assembles hierarchically in the crystal lattice. Three β-hairpin monomers assemble to form a triangular trimer, four trimers assemble in a tetrahedral arrangement to form a dodecamer, and five dodecamers pack together to form an annular pore. This hierarchical assembly provides a model, in which full-length Aβ transitions from an unfolded monomer to a folded β-hairpin, which assembles to form oligomers that further pack to form an annular pore. This model may provide a better understanding of the molecular basis of Alzheimer’s disease at atomic resolution.

NET amyloidogenic backbone in human activated neutrophils

Activated human neutrophils produce a fibrillar DNA network [neutrophil extracellular traps (NETs)] for entrapping and killing bacteria, fungi, protozoa and viruses. Our results suggest that the neutrophil extracellular traps show a resistant amyloidogenic backbone utilized for addressing reputed proteins and DNA against the non-self. The formation of amyloid fibrils in neutrophils is regulated by the imbalance of reactive oxygen species (ROS) in the cytoplasm. The intensity and source of the ROS signal is determinant for promoting stress-associated responses such as amyloidogenesis and closely related events: autophagy, exosome release, activation of the adrenocorticotrophin hormone/α-melanocyte-stimulating hormone (ACTH/α-MSH) loop and synthesis of specific cytokines. These interconnected responses in human activated neutrophils, that have been evaluated from a morphofunctional and quantitative viewpoint, represent primitive, but potent, innate defence mechanisms. In invertebrates, circulating phagocytic immune cells, when activated, show responses similar to those described previously for activated human neutrophils. Invertebrate cells within endoplasmic reticulum cisternae produce a fibrillar material which is then assembled into an amyloidogenic scaffold utilized to convey melanin close to the invader. These findings, in consideration to the critical role played by NET in the development of several pathologies, could explain the structural resistance of these scaffolds and could provide the basis for developing new diagnostic and therapeutic approaches in immunomediated diseases in which the innate branch of the immune system has a pivotal role.

Increasing the Receptor Tyrosine Kinase EphB2 Prevents Amyloid-β-induced Depletion of Cell Surface Glutamate Receptors by a Mechanism That Requires the PDZ-binding Motif of EphB2 and Neuronal Activity

Diverse lines of evidence suggest that amyloid-β (Aβ) peptides causally contribute to the pathogenesis of Alzheimer disease (AD), the most frequent neurodegenerative disorder. However, the mechanisms by which Aβ impairs neuronal functions remain to be fully elucidated. Previous studies showed that soluble Aβ oligomers interfere with synaptic functions by depleting NMDA-type glutamate receptors (NMDARs) from the neuronal surface and that overexpression of the receptor tyrosine kinase EphB2 can counteract this process. Through pharmacological treatments and biochemical analyses of primary neuronal cultures expressing wild-type or mutant forms of EphB2, we demonstrate that this protective effect of EphB2 depends on its PDZ-binding motif and the presence of neuronal activity but not on its kinase activity. We further present evidence that the protective effect of EphB2 may be mediated by the AMPA-type glutamate receptor subunit GluA2, which can become associated with the PDZ-binding motif of EphB2 through PDZ domain-containing proteins and can promote the retention of NMDARs in the membrane. In addition, we show that the Aβ-induced depletion of surface NMDARs does not depend on several factors that have been implicated in the pathogenesis of Aβ-induced neuronal dysfunction, including aberrant neuronal activity, tau, prion protein (PrP^C), and EphB2 itself. Thus, although EphB2 does not appear to be directly involved in the Aβ-induced depletion of NMDARs, increasing its expression may counteract this pathogenic process through a neuronal activity- and PDZ-dependent regulation of AMPA-type glutamate receptors.

Targeting protein aggregation for the treatment of degenerative diseases

The aggregation of specific proteins is hypothesized to underlie several degenerative diseases, which are collectively known as amyloid disorders. However, the mechanistic connection between the process of protein aggregation and tissue degeneration is not yet fully understood. Here, we review current and emerging strategies to ameliorate aggregation-associated degenerative disorders, with a focus on disease-modifying strategies that prevent the formation of and/or eliminate protein aggregates. Persuasive pharmacological and genetic evidence now supports protein aggregation as the cause of postmitotic tissue dysfunction or loss. However, a more detailed understanding of the factors that trigger and sustain aggregate formation and of the structure-activity relationships underlying proteotoxicity is needed to develop future disease-modifying therapies.

Failure of perivascular drainage of β-amyloid in cerebral amyloid angiopathy

In Alzheimer's disease, amyloid-β (Aβ) accumulates as insoluble plaques in the brain and deposits in blood vessel walls as cerebral amyloid angiopathy (CAA). The severity of CAA correlates with the degree of cognitive decline in dementia. The distribution of Aβ in the walls of capillaries and arteries in CAA suggests that Aβ is deposited in the perivascular pathways by which interstitial fluid drains from the brain. Soluble Aβ from the extracellular spaces of gray matter enters the basement membranes of capillaries and drains along the arterial basement membranes that surround smooth muscle cells toward the leptomeningeal arteries. The motive force for perivascular drainage is derived from arterial pulsations combined with the valve effect of proteins present in the arterial basement membranes. Physical and biochemical changes associated with arteriosclerosis, aging and possession of apolipoprotein E4 genotype lead to a failure of perivascular drainage of soluble proteins, including Aβ. Perivascular cells associated with arteries and the lymphocytes recruited in the perivenous spaces contribute to the clearance of Aβ. The failure of perivascular clearance of Aβ may be a major factor in the accumulation of Aβ in CAA and may have significant implications for the design of therapeutics for the treatment of Alzheimer's disease.

Chronic Anatabine Treatment Reduces Alzheimer's Disease (AD)-Like Pathology and Improves Socio-Behavioral Deficits in a Transgenic Mouse Model of AD

Anatabine is a minor tobacco alkaloid, which is also found in plants of the Solanaceae family and displays a chemical structure similarity with nicotine. We have shown previously that anatabine displays some anti-inflammatory properties and reduces microgliosis and tau phosphorylation in a pure mouse model of tauopathy. We therefore investigated the effects of a chronic oral treatment with anatabine in a transgenic mouse model (Tg PS1/APPswe) of Alzheimer's disease (AD) which displays pathological Aβ deposits, neuroinflammation and behavioral deficits. In the elevated plus maze, Tg PS1/APPswe mice exhibited hyperactivity and disinhibition compared to wild-type mice. Six and a half months of chronic oral anatabine treatment, suppressed hyperactivity and disinhibition in Tg PS1/APPswe mice compared to Tg PS1/APPswe receiving regular drinking water. Tg PS1/APPswe mice also elicited profound social interaction and social memory deficits, which were both alleviated by the anatabine treatment. We found that anatabine reduces the activation of STAT3 and NFκB in the vicinity of Aβ deposits in Tg PS1/APPswe mice resulting in a reduction of the expression of some of their target genes including Bace1, iNOS and Cox-2. In addition, a significant reduction in microgliosis and pathological deposition of Aβ was observed in the brain of Tg PS1/APPswe mice treated with anatabine. This is the first study to investigate the impact of chronic anatabine treatment on AD-like pathology and behavior in a transgenic mouse model of AD. Overall, our data show that anatabine reduces β-amyloidosis, neuroinflammation and alleviates some behavioral deficits in Tg PS1/APPswe, supporting further exploration of anatabine as a possible disease modifying agent for the treatment of AD.

Distinctive RNA expression profiles in blood associated with Alzheimer disease after accounting for white matter hyperintensities

BACKGROUND

Defining the RNA transcriptome in Alzheimer Disease (AD) will help understand the disease mechanisms and provide biomarkers. Though the AD blood transcriptome has been studied, effects of white matter hyperintensities (WMH) were not considered. This study investigated the AD blood transcriptome and accounted for WMH.

METHODS

RNA from whole blood was processed on whole-genome microarrays.

RESULTS

A total of 293 probe sets were differentially expressed in AD versus controls, 5 of which were significant for WMH status. The 288 AD-specific probe sets classified subjects with 87.5% sensitivity and 90.5% specificity. They represented 188 genes of which 29 have been reported in prior AD blood and 89 in AD brain studies. Regulated blood genes included MMP9, MME (Neprilysin), TGFβ1, CA4, OCLN, ATM, TGM3, IGFR2, NOV, RNF213, BMX, LRRN1, CAMK2G, INSR, CTSD, SORCS1, SORL1, and TANC2.

CONCLUSIONS

RNA expression is altered in AD blood irrespective of WMH status. Some genes are shared with AD brain.

A combination Alzheimer's therapy targeting BACE1 and neprilysin in 5XFAD transgenic mice

BACKGROUND

Accumulating evidence indicates that partial inhibition of β-site APP-cleaving enzyme 1 (BACE1), which initiates amyloid-β (Aβ) production, mitigates Alzheimer's disease (AD)-like pathologies and memory deficits in a battery of transgenic mouse models. However, our previous investigations suggest that therapeutic BACE1 suppression may be beneficial only if targeted on earlier stages of AD and encounter dramatic reductions in efficacy during disease progression. This study was designed to test the possibility that a combination approach, aimed at inhibiting BACE1 and boosting neprilysin (a major Aβ-degrading enzyme) activities, may be able to mechanistically overcome the limited efficacy of anti-Aβ therapy in advanced AD.

RESULTS

After crossbreeding between BACE1 heterozygous knockout (BACE1(+/-)), neprilysin transgenic (NEP) and 5XFAD mice, we analyzed the resultant mice at 12 months of age when 5XFAD controls showed robust amyloid-β (Aβ) accumulation and elevation of BACE1 expression (~2 folds). Although haploinsufficiency lowered BACE1 expression by ~50% in concordance with reduction in gene copy number, profound β-amyloidosis, memory deficits and cholinergic neuron death were no longer rescued in BACE1(+/-) · 5XFAD mice concomitant with their persistently upregulated BACE1 (i.e., equivalent to wild-type control levels). Notably, neprilysin overexpression not only prevented Aβ accumulation but also suppressed the translation initiation factor eIF2α-associated elevation of BACE1 and lowered levels of the β-secretase-cleaved C-terminal fragment of APP (C99) in NEP · 5XFAD mice. Interestingly, these markers for β-amyloidogenesis in BACE1(+/-) · NEP · 5XFAD mice were further reduced to the levels reflecting a combination of single BACE1 allele ablation and the abolishment of translational BACE1 upregulation. However, since neprilysin overexpression was striking (~8-fold relative to wild-type controls), memory impairments, cholinergic neuronal loss and β-amyloidosis were similarly prevented in NEP · 5XFAD and BACE1(+/-) · NEP · 5XFAD mice.

CONCLUSIONS

Our findings indicate that robust overexpression of neprilysin is sufficient to ameliorate AD-like phenotypes in aged 5XFAD mice. We also found that Aβ-degrading effects of overexpressed neprilysin can block deleterious BACE1-elevating mechanisms that accelerate Aβ production, warranting further study to test whether interventions moderately activating neprilysin may be useful for boosting the limited efficacy of therapeutic BACE1 inhibition in treating AD with established Aβ pathology.

Toxic oligomer species of amyloid-β in Alzheimer's disease, a timing issue

A decade following the paradigm-shifting concept that endogenous forms of soluble, non-fibrillar amyloid-β (Aβ) might constitute the major bioactive entity causing synaptic loss and cognitive decline in Alzheimer's disease (AD), our understanding of these oligomeric species still remains conspicuously superficial. The current lack of direct evaluation tools for each endogenous Aβ oligomer hampers our ability to readily address crucial question such as: (i) where they form and accumulate?; (ii) when they first appear in human brains and body fluids?; (iii) what is the longitudinal expression of these putative toxins during the course of the disease?; (iv) and how do these soluble Aβ assemblies alter synaptic and neuronal function in the brain? Despite these limitations, indirect ex vivo measurement and isolation from biological specimens has been possible and have allowed parsing out intrinsic differences between putative endogenous Aβ oligomers. In this review, I integrated recent findings and extrapolated emerging hypotheses derived from these studies with the hope to provide a clarified view on the putative role of endogenous Aβ oligomers in AD, with a particular emphasis on the timing at which these soluble species might act in the aging and diseased brain.