Monoclonal antibodies that target pathological assemblies of Aβ

Modeling Late-Onset Sporadic Alzheimer's Disease through BMI1 Deficiency

Late-onset sporadic Alzheimer's disease (AD) is the most prevalent form of dementia, but its origin remains poorly understood. The Bmi1/Ring1 protein complex maintains transcriptional repression of developmental genes through histone H2A mono-ubiquitination, and Bmi1 deficiency in mice results in growth retardation, progeria, and neurodegeneration. Here, we demonstrate that BMI1 is silenced in AD brains, but not in those with early-onset familial AD, frontotemporal dementia, or Lewy body dementia. BMI1 expression was also reduced in cortical neurons from AD patient-derived induced pluripotent stem cells but not in neurons overexpressing mutant APP and PSEN1. BMI1 knockout in human post-mitotic neurons resulted in amyloid beta peptide secretion and deposition, p-Tau accumulation, and neurodegeneration. Mechanistically, BMI1 was required to repress microtubule associated protein tau (MAPT) transcription and prevent GSK3beta and p53 stabilization, which otherwise resulted in neurodegeneration. Restoration of BMI1 activity through genetic or pharmaceutical approaches could represent a therapeutic strategy against AD.

TDP-43 inhibitory peptide alleviates neurodegeneration and memory loss in an APP transgenic mouse model for Alzheimer's disease

Alzheimer's disease (AD) is the leading cause of dementia in the elderly, characterized clinically by progressive decline in cognitive function and neuropathologically by the presence of senile plaques and neuronal loss in the brain. While current drugs for AD are always employed as symptomatic therapies with variable benefits, there is no treatment to delay its progression or halt neurodegeneration. TAR DNA-binding protein 43 (TDP-43) proteinopathy has increasingly been implicated as a prominent histopathological feature of AD and related dementias. Our recent studies have implicated mitochondria as critical targets of TDP-43 neurotoxicity. Here, we demonstrate that the suppression of mitochondrial-associated TDP-43 protects against neuronal loss and behavioral deficits in 5XFAD transgenic mice recapitulating AD-related phenotypes. In AD patients and 5XFAD mice, the level of TDP-43 is increased in mitochondria, and TDP-43 highly co-localizes with mitochondria in brain neurons exhibiting TDP-43 proteinopathy. Chronic administration of a TDP-43 mitochondrial localization inhibitory peptide, PM1, significantly alleviates TDP-43 proteinopathy, mitochondrial abnormalities, microgliosis and even neuronal loss without effect on amyloid plaque load in 12-month-old 5XFAD mice well after the onset of symptoms. Additionally, PM1 also improves the cognitive and motor function in 12-month-old 5XFAD mice and completely prevents the onset of mild cognitive impairment in 6-month-old 5XFAD mice. These data indicate that mitochondria-associated TDP-43 is likely involved in AD pathogenesis and that the inhibitor of mitochondria-associated TDP-43 may be a valuable drug to treat underlying AD.

A Rationally Designed Humanized Antibody Selective for Amyloid Beta Oligomers in Alzheimer's Disease

Advances in the understanding of Alzheimer’s disease (AD) suggest that pathogenesis is not directly related to plaque burden, but rather to soluble toxic amyloid-beta oligomers (AßO). Therapeutic antibodies targeting Aß monomers and/or plaque have shown limited efficacy and dose-limiting adverse events in clinical trials. These findings suggest that antibodies capable of selectively neutralizing toxic AßO may achieve improved efficacy and safety. To this end, we generated monoclonal antibodies against a conformational Aß epitope predicted by computational modeling to be presented on toxic AßO but not monomers or fibrils. The resulting lead antibody, PMN310, showed the desired AßO-selective binding profile. In vitro, PMN310 inhibited AßO propagation and toxicity. In vivo, PMN310 prevented AßO-induced loss of memory formation and reduced synaptic loss and inflammation. A humanized version (huPMN310) compared favorably to other Aß-directed antibodies showing a lack of adverse event-associated binding to Aß deposits in AD brains, and greater selective binding to AßO-enriched AD brain fractions that contain synaptotoxic Aß species. Systemic administration of huPMN310 in mice resulted in brain exposure and kinetics comparable to those of other therapeutic human monoclonal antibodies. Greater selectivity for AßO and the potential to safely administer high doses of huPMN310 are expected to result in enhanced safety and therapeutic potency.

The Amyloid-β Oligomer Hypothesis: Beginning of the Third Decade

The amyloid-β oligomer (AβO) hypothesis was introduced in 1998. It proposed that the brain damage leading to Alzheimer’s disease (AD) was instigated by soluble, ligand-like AβOs. This hypothesis was based on the discovery that fibril-free synthetic preparations of AβOs were potent CNS neurotoxins that rapidly inhibited long-term potentiation and, with time, caused selective nerve cell death (Lambert et al., 1998). The mechanism was attributed to disrupted signaling involving the tyrosine-protein kinase Fyn, mediated by an unknown toxin receptor. Over 4,000 articles concerning AβOs have been published since then, including more than 400 reviews. AβOs have been shown to accumulate in an AD-dependent manner in human and animal model brain tissue and, experimentally, to impair learning and memory and instigate major facets of AD neuropathology, including tau pathology, synapse deterioration and loss, inflammation, and oxidative damage. As reviewed by Hayden and Teplow in 2013, the AβO hypothesis “has all but supplanted the amyloid cascade.” Despite the emerging understanding of the role played by AβOs in AD pathogenesis, AβOs have not yet received the clinical attention given to amyloid plaques, which have been at the core of major attempts at therapeutics and diagnostics but are no longer regarded as the most pathogenic form of Aβ. However, if the momentum of AβO research continues, particularly efforts to elucidate key aspects of structure, a clear path to a successful disease modifying therapy can be envisioned. Ensuring that lessons learned from recent, late-stage clinical failures are applied appropriately throughout therapeutic development will further enable the likelihood of a successful therapy in the near-term.

Does Intraneuronal Accumulation of Carboxyl-terminal Fragments of the Amyloid Precursor Protein Trigger Early Neurotoxicity in Alzheimer’s Disease?

Background:

Alzheimer’s disease (AD) is associated with extracellular accumulation and aggregation of amyloid β (Aβ) peptides ultimately seeding in senile plaques. Recent data show that their direct precursor C99 (βCTF) also accumulates in AD-affected brain as well as in AD-like mouse models. C99 is consistently detected much earlier than Aβ, suggesting that this metabolite could be an early contributor to AD pathology. C99 accumulates principally within endolysosomal and autophagic structures and its accumulation was described as both a consequence and one of the causes of endolysosomalautophagic pathology, the occurrence of which has been documented as an early defect in AD. C99 was also accompanied by C99-derived C83 (αCTF) accumulation occurring within the same intracellular organelles. Both these CTFs were found to dimerize leading to the generation of higher molecular weight CTFs, which were immunohistochemically characterized in situ by means of aggregate-specific antibodies.

Discussion:

Here, we discuss studies demonstrating a direct link between the accumulation of C99 and C99-derived APP-CTFs and early neurotoxicity. We discuss the role of C99 in endosomal-lysosomalautophagic dysfunction, neuroinflammation, early brain network alterations and synaptic dysfunction as well as in memory-related behavioral alterations, in triple transgenic mice as well as in newly developed AD animal models.

Conclusion:

This review summarizes current evidence suggesting a potential role of the β -secretasederived APP C-terminal fragment C99 in Alzheimer’s disease etiology

Neonatal infection leads to increased susceptibility to Aβ oligomer-induced brain inflammation, synapse loss and cognitive impairment in mice

Harmful environmental stimuli during critical stages of development can profoundly affect behavior and susceptibility to diseases. Alzheimer disease (AD) is the most frequent neurodegenerative disease, and evidence suggest that inflammatory conditions act cumulatively, contributing to disease onset. Here we investigated whether infection early in life can contribute to synapse damage and cognitive impairment induced by amyloid-β oligomers (AβOs), neurotoxins found in AD brains. To this end, wild-type mice were subjected to neonatal (post-natal day 4) infection by Escherichia coli (1 × 10⁴ CFU/g), the main cause of infection in low-birth-weight premature infants in the US. E. coli infection caused a transient inflammatory response in the mouse brain starting shortly after infection. Although infected mice performed normally in behavioral tasks in adulthood, they showed increased susceptibility to synapse damage and memory impairment induced by low doses of AβOs (1 pmol; intracerebroventricular) in the novel object recognition paradigm. Using in vitro and in vivo approaches, we show that microglial cells from E. coli-infected mice undergo exacerbated activation when exposed to low doses of AβOs. In addition, treatment of infected pups with minocycline, an antibiotic that inhibits microglial pro-inflammatory polarization, normalized microglial response to AβOs and restored normal susceptibility of mice to oligomer-induced cognitive impairment. Interestingly, mice infected with by E. coli (1 × 10⁴ CFU/g) during adolescence (post-natal day 21) or adulthood (post-natal day 60) showed normal cognitive performance even in the presence of AβOs (1 pmol), suggesting that only infections at critical stages of development may lead to increased susceptibility to amyloid-β-induced toxicity. Altogether, our findings suggest that neonatal infections can modulate microglial response to AβOs into adulthood, thus contributing to amyloid-β-induced synapse damage and cognitive impairment.

A novel crosslinking protocol stabilizes amyloid β oligomers capable of inducing Alzheimer's-associated pathologies

Amyloid β oligomers (AβOs) accumulate early in Alzheimer's disease (AD) and experimentally cause memory dysfunction and the major pathologies associated with AD, for example, tau abnormalities, synapse loss, oxidative damage, and cognitive dysfunction. In order to develop the most effective AβO-targeting diagnostics and therapeutics, the AβO structures contributing to AD-associated toxicity must be elucidated. Here, we investigate the structural properties and pathogenic relevance of AβOs stabilized by the bifunctional crosslinker 1,5-difluoro-2,4-dinitrobenzene (DFDNB). We find that DFDNB stabilizes synthetic Aβ in a soluble oligomeric conformation. With DFDNB, solutions of Aβ that would otherwise convert to large aggregates instead yield solutions of stable AβOs, predominantly in the 50-300 kDa range, that are maintained for at least 12 days at 37°C. Structures were determined by biochemical and native top-down mass spectrometry analyses. Assayed in neuronal cultures and i.c.v.-injected mice, the DFDNB-stabilized AβOs were found to induce tau hyperphosphorylation, inhibit choline acetyltransferase, and provoke neuroinflammation. Most interestingly, DFDNB crosslinking was found to stabilize an AβO conformation particularly potent in inducing memory dysfunction in mice. Taken together, these data support the utility of DFDNB crosslinking as a tool for stabilizing pathogenic AβOs in structure-function studies.

Kalirin-7 prevents dendritic spine dysgenesis induced by amyloid beta-derived oligomers

Synapse degeneration and dendritic spine dysgenesis are believed to be crucial early steps in Alzheimer's disease (AD), and correlate with cognitive deficits in AD patients. Soluble amyloid beta (Aβ)-derived oligomers, also termed Aβ-derived diffusible ligands (ADDLs), accumulate in the brain of AD patients and play a crucial role in AD pathogenesis. ADDLs bind to mature hippocampal neurons, induce structural changes in dendritic spines and contribute to neuronal death. However, mechanisms underlying structural and toxic effects are not fully understood. Here, we report that ADDLs bind to cultured mature cortical pyramidal neurons and induce spine dysgenesis. ADDL treatment induced the rapid depletion of kalirin-7, a brain-specific guanine-nucleotide exchange factor for the small GTPase Rac1, from spines. Kalirin-7 is a key regulator of dendritic spine morphogenesis and maintenance in forebrain pyramidal neurons and here we show that overexpression of kalirin-7 prevents ADDL-induced spine degeneration. Taken together, our results suggest that kalirin-7 may play a role in the early events leading to synapse degeneration, and its pharmacological activation may prevent or delay synapse pathology in AD.

Exercise-linked FNDC5/irisin rescues synaptic plasticity and memory defects in Alzheimer's models

Defective brain hormonal signaling has been associated with Alzheimer’s disease (AD), a disorder characterized by synapse and memory failure. Irisin is an exercise-induced myokine released upon cleavage of membrane-bound precursor protein FNDC5, also expressed in the hippocampus. Here we show that FNDC5/irisin levels are reduced in AD hippocampi and cerebrospinal fluid, and in experimental AD models. Knockdown of brain FNDC5/irisin impaired long-term potentiation and novel object recognition memory in mice. Conversely, boosting brain levels of FNDC5/irisin rescued synaptic plasticity and memory in AD mouse models. Peripheral overexpression of FNDC5/irisin rescued memory impairment, whereas blockade of either peripheral or brain FNDC5/irisin attenuated the neuroprotective actions of physical exercise on synaptic plasticity and memory in AD mice. By showing that FNDC5/irisin is an important mediator of the beneficial effects of exercise in AD models, our findings place FNDC5/irisin as a novel agent capable of opposing synapse failure and memory impairment in AD.

Integrative approach to sporadic Alzheimer's disease: deficiency of TYROBP in cerebral Aβ amyloidosis mouse normalizes clinical phenotype and complement subnetwork molecular pathology without reducing Aβ burden

Integrative gene network approaches enable new avenues of exploration that implicate causal genes in sporadic late-onset Alzheimer's disease (LOAD) pathogenesis, thereby offering novel insights for drug-discovery programs. We previously constructed a probabilistic causal network model of sporadic LOAD and identified TYROBP/DAP12, encoding a microglial transmembrane signaling polypeptide and direct adapter of TREM2, as the most robust key driver gene in the network. Here, we show that absence of TYROBP/DAP12 in a mouse model of AD-type cerebral Aβ amyloidosis (APP^KM670/671NL/PSEN1^Δexon9) recapitulates the expected network characteristics by normalizing the transcriptome of APP/PSEN1 mice and repressing the induction of genes involved in the switch from homeostatic microglia to disease-associated microglia (DAM), including Trem2, complement (C1qa, C1qb, C1qc, and Itgax), Clec7a and Cst7. Importantly, we show that constitutive absence of TYROBP/DAP12 in the amyloidosis mouse model prevented appearance of the electrophysiological and learning behavior alterations associated with the phenotype of APP^KM670/671NL/PSEN1^Δexon9 mice. Our results suggest that TYROBP/DAP12 could represent a novel therapeutic target to slow, arrest, or prevent the development of sporadic LOAD. These data establish that the network pathology observed in postmortem human LOAD brain can be faithfully recapitulated in the brain of a genetically manipulated mouse. These data also validate our multiscale gene networks by demonstrating how the networks intersect with the standard neuropathological features of LOAD.

Methods for Structural Analysis of Amyloid Fibrils in Misfolding Diseases

Many proteins and peptides are able to self-assemble in solution in vitro and in vivo to form amyloid-like fibrils. These fibrils share common structural characteristics. In order for a fibril to be characterized as amyloid, it is expected to fit certain criteria including the composition of cross-β. Here we describe how the formation of amyloid fibrils can be characterized in vitro using a variety of methods including circular dichroism and intrinsic tyrosine/tryptophan fluoresence to follow conformational changes; Thioflavin and/or ThS assembly to monitor nucleation and growth; transmission electron microscopy to visualize fibrillar morphology and X-ray fiber diffraction to examine cross-β structure.

Evidence of intraneuronal Aβ accumulation preceding tau pathology in the entorhinal cortex

Growing evidence gathered from transgenic animal models of Alzheimer's disease (AD) indicates that the intraneuronal accumulation of amyloid-β (Aβ) peptides is an early event in the AD pathogenesis, producing cognitive deficits before the deposition of insoluble plaques. Levels of soluble Aβ are also a strong indicator of synaptic deficits and concurrent AD neuropathologies in post-mortem AD brain; however, it remains poorly understood how this soluble amyloid pool builds within the brain in the decades leading up to diagnosis, when a patient is likely most amenable to early therapeutic interventions. Indeed, characterizing early intracellular Aβ accumulation in humans has been hampered by the lack of Aβ-specific antibodies, variability in the quality of available human brain tissue and the limitations of conventional microscopy. We therefore sought to investigate the development of the intraneuronal Aβ pathology using extremely high-quality post-mortem brain material obtained from a cohort of non-demented subjects with short post-mortem intervals and processed by perfusion-fixation. Using well-characterized monoclonal antibodies, we demonstrate that the age-dependent intraneuronal accumulation of soluble Aβ is pervasive throughout the entorhinal cortex and hippocampus, and that this phase of the amyloid pathology becomes established within AD-vulnerable regions before the deposition of Aβ plaques and the formation of tau neurofibrillary tangles. We also show for the first time in post-mortem human brain that Aβ oligomers do in fact accumulate intraneuronally, before the formation of extracellular plaques. Finally, we validated the origin of the Aβ-immunopositive pool by resolving Aβ- and APP/CTF-immunoreactive sites using super resolution structured illumination microscopy. Together, these findings indicate that the lifelong accrual of intraneuronal Aβ may be a potential trigger for downstream AD-related pathogenic events in early disease stages.

Neurodegenerative Diseases: Regenerative Mechanisms and Novel Therapeutic Approaches

Regeneration refers to regrowth of tissue in the central nervous system. It includes generation of new neurons, glia, myelin, and synapses, as well as the regaining of essential functions: sensory, motor, emotional and cognitive abilities. Unfortunately, regeneration within the nervous system is very slow compared to other body systems. This relative slowness is attributed to increased vulnerability to irreversible cellular insults and the loss of function due to the very long lifespan of neurons, the stretch of cells and cytoplasm over several dozens of inches throughout the body, insufficiency of the tissue-level waste removal system, and minimal neural cell proliferation/self-renewal capacity. In this context, the current review summarized the most common features of major neurodegenerative disorders; their causes and consequences and proposed novel therapeutic approaches.

A Rational Structured Epitope Defines a Distinct Subclass of Toxic Amyloid-beta Oligomers

Oligomers of amyloid-β (AβO) are deemed key in synaptotoxicity and amyloid seeding of Alzheimer's disease (AD). However, the heterogeneous and dynamic nature of AβO and inadequate markers for AβO subtypes have stymied effective AβO identification and therapeutic targeting in vivo. We identified an AβO-subclass epitope defined by differential solvent orientation of the lysine 28 side chain in a constrained loop of serine-asparagine-lysine (cSNK), rarely displayed in molecular dynamics simulations of monomer and fibril ensembles. A mouse monoclonal antibody targeting AβO^cSNK recognizes ∼50-60 kDa SDS-resistant soluble Aβ assemblages in AD brain and prolongs the lag phase of Aβ aggregation in vitro. Acute peripheral infusion of a murine IgG1 anti-AβO^cSNK in two AD mouse models reduced soluble brain Aβ aggregates by 20-30%. Chronic cSNK peptide immunization of APP/PS1 mice engendered an anti-AβO^cSNK IgG1 response without epitope spreading to Aβ monomers or fibrils and was accompanied by preservation of global PSD95 expression and improved cued fear memory. Our data indicate that the oligomer subtype AβO^cSNK participates in synaptotoxicity and propagation of Aβ aggregation in vitro and in vivo.

Molecular Recognition between Aβ-Specific Single-Domain Antibody and Aβ Misfolded Aggregates

Aβ is the toxic amyloid polypeptide responsible for Alzheimer's disease (AD). Prevention and elimination of the Aβ misfolded aggregates are the promising therapeutic strategies for the AD treatments. Gammabody, the Aβ-Specific Single-domain (VH) antibody, recognizes Aβ aggregates with high affinity and specificity and reduces their toxicities. Employing the molecular dynamics simulations, we studied diverse gammabody-Aβ recognition complexes to get insights into their structural and dynamic properties and gammabody-Aβ recognitions. Among many heterogeneous binding modes, we focused on two gammabody-Aβ recognition scenarios: recognition through Aβ β-sheet backbone and on sidechain surface. We found that the gammabody primarily uses the complementarity-determining region 3 (CDR3) loop with the grafted Aβ sequence to interact with the Aβ fibril, while CDR1/CDR2 loops have very little contact. The gammabody-Aβ complexes with backbone binding mode are more stable, explaining the gammabody's specificity towards the C-terminal Aβ sequence.

Plasma Oligomeric Beta Amyloid in Alzheimer's Disease with History of Agent Orange Exposure

BACKGROUND AND PURPOSE

During the Vietnam War, many Korean soldiers were exposed to Agent Orange. Until now, there existed only limited evidence of association between exposure to Agent Orange and Alzheimer's disease (AD). The main pathological feature of AD is brain amyloidosis. To explore the pathophysiological characteristic of AD with Agent Orange exposure, we compared newly developed amyloid beta (Aβ) oligomer levels in plasma between AD with Agent Orange exposure and without exposure.

METHODS

We recruited 48 AD patients with Agent Orange exposure and 66 AD patients without Agent Orange. Using the Multimer Detection System technique, which was based on an enzyme-linked immunosorbent assay, we measured Aβ oligomers in the plasma of study subjects.

RESULTS

Compared to normal control patients, plasma Aβ oligomer levels were higher in AD patients regardless of history of Agent Orange exposure. However, AD patients with Agent Orange exposure showed higher plasma Aβ oligomer levels than AD patients without Agent Orange.

DISCUSSION

This study showed higher plasma Aβ oligomer levels in AD patients with Agent Orange exposure compared to AD patients without Agent Orange. This finding suggests the possibility of a different pathophysiology of AD patients with Agent Orange exposure from AD patients without Agent Orange.

Stabilization of a Membrane-Associated Amyloid-β Oligomer for Its Validation in Alzheimer's Disease

We have recently reported on the preparation of a membrane-associated β-barrel Pore-Forming Aβ42 Oligomer (βPFO_Aβ42). It corresponds to a stable and homogeneous Aβ42 oligomer that inserts into lipid bilayers as a well-defined pore and adopts a specific structure with characteristics of a β-barrel arrangement. As a follow-up of this work, we aim to establish βPFO_Aβ42's relevance in Alzheimer's disease (AD). However, βPFO_Aβ42 is formed under dodecyl phosphocholine (DPC) micelle conditions-intended to mimic the hydrophobic environment of membranes-which are dynamic. Consequently, dilution of the βPFO_Aβ42/DPC complex in a detergent-free buffer leads to dispersion of the DPC molecules from the oligomer surface, leaving the oligomer without the hydrophobic micelle belt that stabilizes it. Since dilution is required for any biological test, transfer of βPFO_Aβ42 from DPC micelles into another hydrophobic biomimetic membrane environment, that remains associated with βPFO_Aβ42 even under high dilution conditions, is a requisite for the validation of βPFO_Aβ42 in AD. Here we describe conditions for exchanging DPC micelles with amphipols (APols), which are amphipathic polymers designed to stabilize membrane proteins in aqueous solutions. APols bind in an irreversible but non-covalent manner to the hydrophobic surface of membrane proteins preserving their structure even under extreme dilution conditions. We tested three types of APols with distinct physical-chemical properties and found that the βPFO_Aβ42/DPC complex can only be trapped in non-ionic APols (NAPols). The characterization of the resulting βPFO_Aβ42/NAPol complex by biochemical tools and structural biology techniques allowed us to establish that the oligomer structure is maintained even under high dilution. Based on these findings, this work constitutes a first step towards the in vivo validation of βPFO_Aβ42 in AD.

The Anti-Prion Antibody 15B3 Detects Toxic Amyloid-β Oligomers

15B3 is a monoclonal IgM antibody that selectively detects pathological aggregates of the prion protein (PrP). We report the unexpected finding that 15B3 also recognizes oligomeric but not monomeric forms of amyloid-β (Aβ)42, an aggregating peptide implicated in the pathogenesis of Alzheimer's disease (AD). The 15B3 antibody: i) inhibits the binding of synthetic Aβ42 oligomers to recombinant PrP and neuronal membranes; ii) prevents oligomer-induced membrane depolarization; iii) antagonizes the inhibitory effects of oligomers on the physiological pharyngeal contractions of the nematode Caenorhabditis elegans; and iv) counteracts the memory deficits induced by intracerebroventricular injection of Aβ42 oligomers in mice. Thus this antibody binds to pathologically relevant forms of Aβ, and offers a potential research, diagnostic, and therapeutic tool for AD.

Mesenchymal stem cells and cell-derived extracellular vesicles protect hippocampal neurons from oxidative stress and synapse damage induced by amyloid-β oligomers

Alzheimer's disease (AD) is a disabling and highly prevalent neurodegenerative condition, for which there are no effective therapies. Soluble oligomers of the amyloid-β peptide (AβOs) are thought to be proximal neurotoxins involved in early neuronal oxidative stress and synapse damage, ultimately leading to neurodegeneration and memory impairment in AD. The aim of the current study was to evaluate the neuroprotective potential of mesenchymal stem cells (MSCs) against the deleterious impact of AβOs on hippocampal neurons. To this end, we established transwell cocultures of rat hippocampal neurons and MSCs. We show that MSCs and MSC-derived extracellular vesicles protect neurons against AβO-induced oxidative stress and synapse damage, revealed by loss of pre- and postsynaptic markers. Protection by MSCs entails three complementary mechanisms: 1) internalization and degradation of AβOs; 2) release of extracellular vesicles containing active catalase; and 3) selective secretion of interleukin-6, interleukin-10, and vascular endothelial growth factor to the medium. Results support the notion that MSCs may represent a promising alternative for cell-based therapies in AD.

Deficiency of TYROBP, an adapter protein for TREM2 and CR3 receptors, is neuroprotective in a mouse model of early Alzheimer's pathology

Conventional genetic approaches and computational strategies have converged on immune-inflammatory pathways as key events in the pathogenesis of late onset sporadic Alzheimer’s disease (LOAD). Mutations and/or differential expression of microglial specific receptors such as TREM2, CD33, and CR3 have been associated with strong increased risk for developing Alzheimer’s disease (AD). DAP12 (DNAX-activating protein 12)/TYROBP, a molecule localized to microglia, is a direct partner/adapter for TREM2, CD33, and CR3. We and others have previously shown that TYROBP expression is increased in AD patients and in mouse models. Moreover, missense mutations in the coding region of TYROBP have recently been identified in some AD patients. These lines of evidence, along with computational analysis of LOAD brain gene expression, point to DAP12/TYROBP as a potential hub or driver protein in the pathogenesis of AD. Using a comprehensive panel of biochemical, physiological, behavioral, and transcriptomic assays, we evaluated in a mouse model the role of TYROBP in early stage AD. We crossed an Alzheimer’s model mutant APP^KM670/671NL/PSEN1^Δexon9(APP/PSEN1) mouse model with Tyrobp^−/− mice to generate AD model mice deficient or null for TYROBP (APP/PSEN1; Tyrobp^+/− or APP/PSEN1; Tyrobp^−/−). While we observed relatively minor effects of TYROBP deficiency on steady-state levels of amyloid-β peptides, there was an effect of Tyrobp deficiency on the morphology of amyloid deposits resembling that reported by others for Trem2^−/− mice. We identified modulatory effects of TYROBP deficiency on the level of phosphorylation of TAU that was accompanied by a reduction in the severity of neuritic dystrophy. TYROBP deficiency also altered the expression of several AD related genes, including Cd33. Electrophysiological abnormalities and learning behavior deficits associated with APP/PSEN1 transgenes were greatly attenuated on a Tyrobp-null background. Some modulatory effects of TYROBP on Alzheimer’s-related genes were only apparent on a background of mice with cerebral amyloidosis due to overexpression of mutant APP/PSEN1. These results suggest that reduction of TYROBP gene expression and/or protein levels could represent an immune-inflammatory therapeutic opportunity for modulating early stage LOAD, potentially leading to slowing or arresting the progression to full-blown clinical and pathological LOAD.

A human scFv antibody that targets and neutralizes high molecular weight pathogenic amyloid-β oligomers

Brain accumulation of soluble oligomers of the amyloid-β peptide (AβOs) is increasingly considered a key early event in the pathogenesis of Alzheimer's disease (AD). A variety of AβO species have been identified, both in vitro and in vivo, ranging from dimers to 24mers and higher order oligomers. However, there is no consensus in the literature regarding which AβO species are most germane to AD pathogenesis. Antibodies capable of specifically recognizing defined subpopulations of AβOs would be a valuable asset in the identification, isolation, and characterization of AD-relevant AβO species. Here, we report the characterization of a human single chain antibody fragment (scFv) denoted NUsc1, one of a number of scFvs we have identified that stringently distinguish AβOs from both monomeric and fibrillar Aβ. NUsc1 readily detected AβOs previously bound to dendrites in cultured hippocampal neurons. In addition, NUsc1 blocked AβO binding and reduced AβO-induced neuronal oxidative stress and tau hyperphosphorylation in cultured neurons. NUsc1 further distinguished brain extracts from AD-transgenic mice from wild type (WT) mice, and detected endogenous AβOs in fixed AD brain tissue and AD brain extracts. Biochemical analyses indicated that NUsc1 targets a subpopulation of AβOs with apparent molecular mass greater than 50 kDa. Results indicate that NUsc1 targets a particular AβO species relevant to AD pathogenesis, and suggest that NUsc1 may constitute an effective tool for AD diagnostics and therapeutics.

Production of Monoclonal Antibodies to Pathologic β-sheet Oligomeric Conformers in Neurodegenerative Diseases

We describe a novel approach to produce conformational monoclonal antibodies selected to specifically react with the β-sheet secondary structure of pathological oligomeric conformers, characteristic of many neurodegenerative diseases. Contrary to past and current efforts, we utilize a mammalian non-self-antigen as an immunogen. The small, non-self peptide selected was covalently polymerized with glutaraldehyde until it reached a high β-sheet secondary structure content, and species between 10–100kDa that are immunogenic, stable and soluble (p13Bri). Inoculation of p13Bri in mice elicited antibodies to the peptide and the β-sheet secondary structure conformation. Hybridomas were produced and clones selected for their reactivity with at least two different oligomeric conformers from Alzheimer’s, Parkinson and/or Prion diseases. The resulting conformational monoclonals are able to detect pathological oligomeric forms in different human neurodegenerative diseases by ELISA, immunohistochemistry and immunoblots. This technological approach may be useful to develop tools for detection, monitoring and treatment of multiple misfolding disorders.

Cross Talk Between Brain Innate Immunity and Serotonin Signaling Underlies Depressive-Like Behavior Induced by Alzheimer's Amyloid-β Oligomers in Mice

Considerable clinical and epidemiological evidence links Alzheimer's disease (AD) and depression. However, the molecular mechanisms underlying this connection are largely unknown. We reported recently that soluble Aβ oligomers (AβOs), toxins that accumulate in AD brains and are thought to instigate synapse damage and memory loss, induce depressive-like behavior in mice. Here, we report that the mechanism underlying this action involves AβO-induced microglial activation, aberrant TNF-α signaling, and decreased brain serotonin levels. Inactivation or ablation of microglia blocked the increase in brain TNF-α and abolished depressive-like behavior induced by AβOs. Significantly, we identified serotonin as a negative regulator of microglial activation. Finally, AβOs failed to induce depressive-like behavior in Toll-like receptor 4-deficient mice and in mice harboring a nonfunctional TLR4 variant in myeloid cells. Results establish that AβOs trigger depressive-like behavior via a double impact on brain serotonin levels and microglial activation, unveiling a cross talk between brain innate immunity and serotonergic signaling as a key player in mood alterations in AD.

SIGNIFICANCE STATEMENT

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the main cause of dementia in the world. Brain accumulation of amyloid-β oligomers (AβOs) is a major feature in the pathogenesis of AD. Although clinical and epidemiological data suggest a strong connection between AD and depression, the underlying mechanisms linking these two disorders remain largely unknown. Here, we report that aberrant activation of the brain innate immunity and decreased serotonergic tonus in the brain are key players in AβO-induced depressive-like behavior in mice. Our findings may open up new possibilities for the development of effective therapeutics for AD and depression aimed at modulating microglial function.

Neuroprotective astrocyte-derived insulin/insulin-like growth factor 1 stimulates endocytic processing and extracellular release of neuron-bound Aβ oligomers

Synaptopathy underlying memory deficits in Alzheimer's disease (AD) is increasingly thought to be instigated by toxic oligomers of the amyloid beta peptide (AβOs). Given the long latency and incomplete penetrance of AD dementia with respect to Aβ pathology, we hypothesized that factors present in the CNS may physiologically protect neurons from the deleterious impact of AβOs. Here we employed physically separated neuron-astrocyte cocultures to investigate potential non-cell autonomous neuroprotective factors influencing AβO toxicity. Neurons cultivated in the absence of an astrocyte feeder layer showed abundant AβO binding to dendritic processes and associated synapse deterioration. In contrast, neurons in the presence of astrocytes showed markedly reduced AβO binding and synaptopathy. Results identified the protective factors released by astrocytes as insulin and insulin-like growth factor-1 (IGF1). The protective mechanism involved release of newly bound AβOs into the extracellular medium dependent upon trafficking that was sensitive to exosome pathway inhibitors. Delaying insulin treatment led to AβO binding that was no longer releasable. The neuroprotective potential of astrocytes was itself sensitive to chronic AβO exposure, which reduced insulin/IGF1 expression. Our findings support the idea that physiological protection against synaptotoxic AβOs can be mediated by astrocyte-derived insulin/IGF1, but that this protection itself is vulnerable to AβO buildup.

The contribution of biophysical and structural studies of protein self-assembly to the design of therapeutic strategies for amyloid diseases

Many neurodegenerative disorders, including Alzheimer's, Parkinson's and the prion diseases, are characterized by a conformational conversion of normally soluble proteins or peptides into pathological species, by a process of misfolding and self-assembly that leads ultimately to the formation of amyloid fibrils. Recent studies support the idea that multiple intermediate species with a wide variety of degrees of neuronal toxicity are generated during such processes. The development of a high level of knowledge of the nature and structure of the pathogenic amyloid species would significantly enhance efforts to underline the molecular origins of these disorders and also to develop both accurate diagnoses and effective therapeutic interventions for these types of conditions. In this review, we discuss recent biophysical and structural information concerning different types of amyloid aggregates and the way in which such information can guide rational therapeutic approaches designed to target specific pathogenic events that occur during the development of these highly debilitating and increasingly common diseases.

Astrocyte Transforming Growth Factor Beta 1 Protects Synapses against Aβ Oligomers in Alzheimer's Disease Model

Alzheimer's disease (AD) is characterized by progressive cognitive decline, increasingly attributed to neuronal dysfunction induced by amyloid-β oligomers (AβOs). Although the impact of AβOs on neurons has been extensively studied, only recently have the possible effects of AβOs on astrocytes begun to be investigated. Given the key roles of astrocytes in synapse formation, plasticity, and function, we sought to investigate the impact of AβOs on astrocytes, and to determine whether this impact is related to the deleterious actions of AβOs on synapses. We found that AβOs interact with astrocytes, cause astrocyte activation and trigger abnormal generation of reactive oxygen species, which is accompanied by impairment of astrocyte neuroprotective potential in vitro We further show that both murine and human astrocyte conditioned media (CM) increase synapse density, reduce AβOs binding, and prevent AβO-induced synapse loss in cultured hippocampal neurons. Both a neutralizing anti-transforming growth factor-β1 (TGF-β1) antibody and siRNA-mediated knockdown of TGF-β1, previously identified as an important synaptogenic factor secreted by astrocytes, abrogated the protective action of astrocyte CM against AβO-induced synapse loss. Notably, TGF-β1 prevented hippocampal dendritic spine loss and memory impairment in mice that received an intracerebroventricular infusion of AβOs. Results suggest that astrocyte-derived TGF-β1 is part of an endogenous mechanism that protects synapses against AβOs. By demonstrating that AβOs decrease astrocyte ability to protect synapses, our results unravel a new mechanism underlying the synaptotoxic action of AβOs in AD.SIGNIFICANCE STATEMENT Alzheimer's disease is characterized by progressive cognitive decline, mainly attributed to synaptotoxicity of the amyloid-β oligomers (AβOs). Here, we investigated the impact of AβOs in astrocytes, a less known subject. We show that astrocytes prevent synapse loss induced by AβOs, via production of transforming growth factor-β1 (TGF-β1). We found that AβOs trigger morphological and functional alterations in astrocytes, and impair their neuroprotective potential. Notably, TGF-β1 reduced hippocampal dendritic spine loss and memory impairment in mice that received intracerebroventricular infusions of AβOs. Our results describe a new mechanism underlying the toxicity of AβOs and indicate novel therapeutic targets for Alzheimer's disease, mainly focused on TGF-β1 and astrocytes.

Unraveling Prion Protein Interactions with Aptamers and Other PrP-Binding Nucleic Acids

Transmissible spongiform encephalopathies (TSEs) are a group of neurodegenerative disorders that affect humans and other mammals. The etiologic agents common to these diseases are misfolded conformations of the prion protein (PrP). The molecular mechanisms that trigger the structural conversion of the normal cellular PrP (PrP^C) into the pathogenic conformer (PrP^Sc) are still poorly understood. It is proposed that a molecular cofactor would act as a catalyst, lowering the activation energy of the conversion process, therefore favoring the transition of PrP^C to PrP^Sc. Several in vitro studies have described physical interactions between PrP and different classes of molecules, which might play a role in either PrP physiology or pathology. Among these molecules, nucleic acids (NAs) are highlighted as potential PrP molecular partners. In this context, the SELEX (Systematic Evolution of Ligands by Exponential Enrichment) methodology has proven extremely valuable to investigate PrP–NA interactions, due to its ability to select small nucleic acids, also termed aptamers, that bind PrP with high affinity and specificity. Aptamers are single-stranded DNA or RNA oligonucleotides that can be folded into a wide range of structures (from harpins to G-quadruplexes). They are selected from a nucleic acid pool containing a large number (10¹⁴–10¹⁶) of random sequences of the same size (~20–100 bases). Aptamers stand out because of their potential ability to bind with different affinities to distinct conformations of the same protein target. Therefore, the identification of high-affinity and selective PrP ligands may aid the development of new therapies and diagnostic tools for TSEs. This review will focus on the selection of aptamers targeted against either full-length or truncated forms of PrP, discussing the implications that result from interactions of PrP with NAs, and their potential advances in the studies of prions. We will also provide a critical evaluation, assuming the advantages and drawbacks of the SELEX (Systematic Evolution of Ligands by Exponential Enrichment) technique in the general field of amyloidogenic proteins.

Amyloid-β oligomers transiently inhibit AMP-activated kinase and cause metabolic defects in hippocampal neurons

AMP-activated kinase (AMPK) is a key player in energy sensing and metabolic reprogramming under cellular energy restriction. Several studies have linked impaired AMPK function to peripheral metabolic diseases such as diabetes. However, the impact of neurological disorders, such as Alzheimer disease (AD), on AMPK function and downstream effects of altered AMPK activity on neuronal metabolism have been investigated only recently. Here, we report the impact of Aβ oligomers (AβOs), synaptotoxins that accumulate in AD brains, on neuronal AMPK activity. Short-term exposure of cultured rat hippocampal neurons or ex vivo human cortical slices to AβOs transiently decreased intracellular ATP levels and AMPK activity, as evaluated by its phosphorylation at threonine residue 172 (AMPK-Thr(P)¹⁷²). The AβO-dependent reduction in AMPK-Thr(P)¹⁷² levels was mediated by glutamate receptors of the N-methyl-d-aspartate (NMDA) subtype and resulted in removal of glucose transporters (GLUTs) from the surfaces of dendritic processes in hippocampal neurons. Importantly, insulin prevented the AβO-induced inhibition of AMPK. Our results establish a novel toxic impact of AβOs on neuronal metabolism and suggest that AβO-induced, NMDA receptor-mediated AMPK inhibition may play a key role in early brain metabolic defects in AD.

Interaction of amyloid-β (Aβ) oligomers with neurexin 2α and neuroligin 1 mediates synapse damage and memory loss in mice

Brain accumulation of the amyloid-β protein (Aβ) and synapse loss are neuropathological hallmarks of Alzheimer disease (AD). Aβ oligomers (AβOs) are synaptotoxins that build up in the brains of patients and are thought to contribute to memory impairment in AD. Thus, identification of novel synaptic components that are targeted by AβOs may contribute to the elucidation of disease-relevant mechanisms. Trans-synaptic interactions between neurexins (Nrxs) and neuroligins (NLs) are essential for synapse structure, stability, and function, and reduced NL levels have been associated recently with AD. Here we investigated whether the interaction of AβOs with Nrxs or NLs mediates synapse damage and cognitive impairment in AD models. We found that AβOs interact with different isoforms of Nrx and NL, including Nrx2α and NL1. Anti-Nrx2α and anti-NL1 antibodies reduced AβO binding to hippocampal neurons and prevented AβO-induced neuronal oxidative stress and synapse loss. Anti-Nrx2α and anti-NL1 antibodies further blocked memory impairment induced by AβOs in mice. The results indicate that Nrx2α and NL1 are targets of AβOs and that prevention of this interaction reduces the deleterious impact of AβOs on synapses and cognition. Identification of Nrx2α and NL1 as synaptic components that interact with AβOs may pave the way for development of novel approaches aimed at halting synapse failure and cognitive loss in AD.

Memantine reduces the production of amyloid-β peptides through modulation of amyloid precursor protein trafficking

Memantine, an uncompetitive glutamatergic N-methyl-D-aspartate (NMDA) receptor antagonist, is widely used as medication for the treatment of Alzheimer's disease (AD). It has been reported that memantine reduces amyloid-β peptide (Aβ) levels in both neuronal cultures and in brains of animal models of AD. However, the underlying mechanism of these effects is unclear. Here we examined the effect of memantine on Aβ production. Memantine was administered to 9-month-old Tg2576 mice, a transgenic mouse model of AD, at 10 or 20mg/kg/day in drinking water for 1 month. Memantine significantly reduced the amounts of both CHAPS-soluble and CHAPS-insoluble Aβ in the brains of Tg2576 mice. Memantine at 10mg/kg/day for 1 month also reduced the levels of insoluble Aβ42 in the brains of aged F344 rats. Moreover, memantine reduced Aβ and sAPPβ levels in conditioned media from rat primary cortical cultures without affecting the enzymatic activities of α-secretase, β-secretase, or γ-secretase. Notably, in a cell-surface biotinylation assay, memantine increased the amount of amyloid precursor protein (APP) at the cell surface without changing the total amount of APP. Collectively, our results indicate that chronic treatment with memantine reduces the levels of Aβ both in AD models and in aged animals, and that memantine affects the endocytosis pathway of APP, which is required for β-secretase-mediated cleavage. This leads to a reduction in Aβ production. These results suggest that memantine reduces Aβ production and plaque deposition through the regulation of intracellular trafficking of APP.

Intraneuronal aggregation of the β-CTF fragment of APP (C99) induces Aβ-independent lysosomal-autophagic pathology

Endosomal-autophagic-lysosomal (EAL) dysfunction is an early and prominent neuropathological feature of Alzheimers’s disease, yet the exact molecular mechanisms contributing to this pathology remain undefined. By combined biochemical, immunohistochemical and ultrastructural approaches, we demonstrate a link between EAL pathology and the intraneuronal accumulation of the β-secretase-derived βAPP fragment (C99) in two in vivo models, 3xTgAD mice and adeno-associated viral-mediated C99-infected mice. We present a pathological loop in which the accumulation of C99 is both the effect and causality of impaired lysosomal-autophagic function. The deleterious effect of C99 was found to be linked to its aggregation within EAL-vesicle membranes leading to disrupted lysosomal proteolysis and autophagic impairment. This effect was Aβ independent and was even exacerbated when γ-secretase was pharmacologically inhibited. No effect was observed in inhibitor-treated wild-type animals suggesting that lysosomal dysfunction was indeed directly linked to C99 accumulation. In some brain areas, strong C99 expression also led to inflammatory responses and synaptic dysfunction. Taken together, this work demonstrates a toxic effect of C99 which could underlie some of the early-stage anatomical hallmarks of Alzheimer’s disease pathology. Our work also proposes molecular mechanisms likely explaining some of the unfavorable side-effects associated with γ-secretase inhibitor-directed therapies.

A critical role for the self-assembly of Amyloid-β1-42 in neurodegeneration

Amyloid β1-42 (Aβ1-42) plays a central role in Alzheimer’s disease. The link between structure, assembly and neuronal toxicity of this peptide is of major current interest but still poorly defined. Here, we explored this relationship by rationally designing a variant form of Aβ1-42 (vAβ1-42) differing in only two amino acids. Unlike Aβ1-42, we found that the variant does not self-assemble, nor is it toxic to neuronal cells. Moreover, while Aβ1-42 oligomers impact on synaptic function, vAβ1-42 does not. In a living animal model system we demonstrate that only Aβ1-42 leads to memory deficits. Our findings underline a key role for peptide sequence in the ability to assemble and form toxic structures. Furthermore, our non-toxic variant satisfies an unmet demand for a closely related control peptide for Aβ1-42 cellular studies of disease pathology, offering a new opportunity to decipher the mechanisms that accompany Aβ1-42-induced toxicity leading to neurodegeneration.

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.

Effective anti-Alzheimer Aβ therapy involves depletion of specific Aβ oligomer subtypes

BACKGROUND

Recent studies have implicated specific assembly subtypes of β-amyloid (Aβ) peptide, specifically soluble oligomers (soAβ) as disease-relevant structures that may underlie memory loss in Alzheimer disease. Removing existing soluble and insoluble Aβ assemblies is thought to be essential for any attempt at stabilizing brain function and slowing cognitive decline in Alzheimer disease. IV immunoglobulin (IVIg) therapies have been shown to contain naturally occurring polyclonal antibodies that recognize conformational neoepitopes of soluble or insoluble Aβ assemblies including soAβ. These naturally occurring polyclonal antibodies have been suggested to underlie the apparent clinical benefits of IVIg. However, direct evidence linking anti-Aβ antibodies to the clinical bioactivity of IVIg has been lacking.

METHODS

Five-month-old female Dutch APP E693Q mice were treated for 3 months with neat IVIg or with IVIg that had been affinity-depleted over immobilized Aβ conformers in 1 of 2 assembly states. Memory was assessed in a battery of tests followed by quantification of brain soAβ levels using standard anti-soAβ antibodies.

RESULTS

We provide evidence that NU4-type soAβ (NU4-soAβ) assemblies accumulate in the brains of Dutch APP E693Q mice and are associated with defects in memory, even in the absence of insoluble Aβ plaques. Memory benefits were associated with depletion from APP E693Q mouse brain of NU4-soAβ and A11-soAβ but not OC-type fibrillar Aβ oligomers.

CONCLUSIONS

We propose that targeting of specific soAβ assembly subtypes may be an important consideration in the therapeutic and/or prophylactic benefit of anti-Aβ antibody drugs.

Rifampicin is a candidate preventive medicine against amyloid-β and tau oligomers

Amyloid-β, tau, and α-synuclein, or more specifically their soluble oligomers, are the aetiologic molecules in Alzheimer's disease, tauopathies, and α-synucleinopathies, respectively. These proteins have been shown to interact to accelerate each other's pathology. Clinical studies of amyloid-β-targeting therapies in Alzheimer's disease have revealed that the treatments after disease onset have little benefit on patient cognition. These findings prompted us to explore a preventive medicine which is orally available, has few adverse effects, and is effective at reducing neurotoxic oligomers with a broad spectrum. We initially tested five candidate compounds: rifampicin, curcumin, epigallocatechin-3-gallate, myricetin, and scyllo-inositol, in cells expressing amyloid precursor protein (APP) with the Osaka (E693Δ) mutation, which promotes amyloid-β oligomerization. Among these compounds, rifampicin, a well-known antibiotic, showed the strongest activities against the accumulation and toxicity (i.e. cytochrome c release from mitochondria) of intracellular amyloid-β oligomers. Under cell-free conditions, rifampicin inhibited oligomer formation of amyloid-β, tau, and α-synuclein, indicating its broad spectrum. The inhibitory effects of rifampicin against amyloid-β and tau oligomers were evaluated in APPOSK mice (amyloid-β oligomer model), Tg2576 mice (Alzheimer's disease model), and tau609 mice (tauopathy model). When orally administered to 17-month-old APPOSK mice at 0.5 and 1 mg/day for 1 month, rifampicin reduced the accumulation of amyloid-β oligomers as well as tau hyperphosphorylation, synapse loss, and microglial activation in a dose-dependent manner. In the Morris water maze, rifampicin at 1 mg/day improved memory of the mice to a level similar to that in non-transgenic littermates. Rifampicin also inhibited cytochrome c release from the mitochondria and caspase 3 activation in the hippocampus. In 13-month-old Tg2576 mice, oral rifampicin at 0.5 mg/day for 1 month decreased amyloid-β oligomer accumulation, tau hyperphosphorylation, synapse loss, and microglial activation, but not amyloid deposition. Rifampicin treatment to 14-15-month-old tau609 mice at 0.5 and 1 mg/day for 1 month also reduced tau oligomer accumulation, tau hyperphosphorylation, synapse loss, and microglial activation in a dose-dependent fashion, and improved the memory almost completely at 1 mg/day. In addition, rifampicin decreased the level of p62/sequestosome-1 in the brain without affecting the increased levels of LC3 (microtubule-associated protein light chain 3) conversion, suggesting the restoration of autophagy-lysosomal function. Considering its prescribed dose and safety in humans, these results indicate that rifampicin could be a promising, ready-to-use medicine for the prevention of Alzheimer's disease and other neurodegenerative diseases.

Peripherally administered sera antibodies recognizing amyloid-β oligomers mitigate Alzheimer's disease-like pathology and cognitive decline in aged 3× Tg-AD mice

Active and passive immunotherapy targeting amyloid-β (Aβ) may be the most promising strategy to prevent or treat Alzheimer's disease (AD). Previously, immunization with the recombinant 6Aβ15-T antigen generated robust anti-Aβ serum antibodies that strongly recognized Aβ42 oligomers in different mice, markedly reduced the amyloid burden, and improved behavioral performance of immunized older AD mice. Here, we further determined that these anti-6Aβ15-T serum antibodies from different strains of mice displayed anti-Aβ antibody responses against the same epitopes in the Aβ1-15 region. Peripheral administration of anti-6Aβ15-T serum antibodies was also effective to mitigate AD-like pathology and cognitive decline in aged 3× Tg-AD mice. Specifically, the levels of Aβ and tau in the brains of 3× Tg-AD mice were significantly reduced after passive immunotherapy, which seemed necessary or beneficial to ameliorate memory impairment. In addition, our results showed that this immunotherapy also prevented presynaptic dynamin 1 degradation, which might help to further protect synaptic functions and allow functional recovery of cognition. Moreover, immunization with 6Aβ15-T in rabbits induced a similar antibody response as that in mice, and the rabbit serum antibodies reacted strongly with Aβ42 oligomers and inhibited oligomer-mediated neurotoxicity. We concluded that passive immunization with Aβ42 oligomer conformation-sensitive anti-6Aβ15-T serum antibodies is effective in providing potentially therapeutic effects in aged 3× Tg-AD mice by reducing Aβ and tau.

Unexpected partial correction of metabolic and behavioral phenotypes of Alzheimer's APP/PSEN1 mice by gene targeting of diabetes/Alzheimer's-related Sorcs1

Introduction

Insulin resistance and type 2 diabetes mellitus (T2D) are associated with increased risk for cognitive impairment, Alzheimer’s disease (AD) and vascular dementia. SORCS1 encodes a protein-sorting molecule genetically linked to both T2D and AD. The association of SORCS1 with both AD and T2D is sexually dimorphic in humans, with both disease associations showing more robust effects in females. Based on published evidence that manipulation of the mouse genome combining multiple genes related to cerebral amyloidosis, to T2D, or both, might provide novel mouse models with exacerbated amyloid and/or diabetes phenotypes, we assessed memory, glucose homeostasis, and brain biochemistry and pathology in male and female wild-type, Sorcs1 -/-, APP/PSEN1, and Sorcs1 -/- X APP/PSEN1 mice.

Results

Male mice with either the APP/PSEN1 or Sorcs1 -/- genotype displayed earlier onset and persistent impairment in both learning behavior and glucose homeostasis. Unlike prior examples in the literature, the behavioral and metabolic abnormalities in male mice were not significantly exacerbated when the two disease model mice (Sorcs1 -/- models T2D; APP/PSEN1 models AD) were crossed. However, female Sorcs1 -/- X APP/PSEN1 mice exhibited worse metabolic dysfunction than Sorcs1 -/- knockout mice and worse memory than wild-type mice. The deletion of Sorcs1 from APP/PSEN1 mutant mice led to no obvious changes in brain levels of total or oligomeric amyloid-beta (Aβ) peptide.

Conclusions

In general, unexpectedly, there was a trend for gene targeting of Sorcs1-/- to partially mitigate, not exacerbate, the metabolic and amyloid pathologies. These results indicate that crossing AD model mice and T2D model mice may not always cause exacerbation of both the amyloidosis phenotype and the metabolic phenotype and highlight the unexpected pitfalls of creating mixed models of disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s40478-016-0282-y) contains supplementary material, which is available to authorized users.

Solvent exposure of Tyr10 as a probe of structural differences between monomeric and aggregated forms of the amyloid-β peptide

Aggregation of amyloid-β (Aβ) peptides is a characteristic pathological feature of Alzheimer's disease. We have exploited the relationship between solvent exposure and intrinsic fluorescence of a single tyrosine residue, Tyr10, in the Aβ sequence to probe structural features of the monomeric, oligomeric and fibrillar forms of the 42-residue Aβ1-42. By monitoring the quenching of Tyr10 fluorescence upon addition of water-soluble acrylamide, we show that in Aβ1-42 oligomers this residue is solvent-exposed to a similar extent to that found in the unfolded monomer. By contrast, Tyr10 is significantly shielded from acrylamide quenching in Aβ1-42 fibrils, consistent with its proximity to the fibrillar cross-β core. Furthermore, circular dichroism measurements reveal that Aβ1-42 oligomers have a considerably lower β-sheet content than the Aβ1-42 fibrils, indicative of a less ordered molecular arrangement in the former. Taken together these findings suggest significant differences in the structural assembly of oligomers and fibrils that are consistent with differences in their biological effects.

Detection of oligomers and fibrils of α-synuclein by AIEgen with strong fluorescence

We report a fluorophore, TPE-TPP, with AIE characteristics which is utilized as a fluorescence probe to monitor the α-synuclein (α-Syn) fibrillation process. Compared with ThT, TPE-TPP shows a higher sensitivity in the detection of α-Syn oligomers as well as fibrils with a stronger fluorescence. The performance of TPE-TPP was evaluated using fluorescence, AFM, dot blot, and SEC.

Validation and Characterization of a Novel Peptide That Binds Monomeric and Aggregated β-Amyloid and Inhibits the Formation of Neurotoxic Oligomers

Although the formation of β-amyloid (Aβ) deposits in the brain is a hallmark of Alzheimer disease (AD), the soluble oligomers rather than the mature amyloid fibrils most likely contribute to Aβ toxicity and neurodegeneration. Thus, the discovery of agents targeting soluble Aβ oligomers is highly desirable for early diagnosis prior to the manifestation of a clinical AD phenotype and also more effective therapies. We have previously reported that a novel 15-amino acid peptide (15-mer), isolated via phage display screening, targeted Aβ and attenuated its neurotoxicity (Taddei, K., Laws, S. M., Verdile, G., Munns, S., D'Costa, K., Harvey, A. R., Martins, I. J., Hill, F., Levy, E., Shaw, J. E., and Martins, R. N. (2010) Neurobiol. Aging 31, 203-214). The aim of the current study was to generate and biochemically characterize analogues of this peptide with improved stability and therapeutic potential. We demonstrated that a stable analogue of the 15-amino acid peptide (15M S.A.) retained the activity and potency of the parent peptide and demonstrated improved proteolytic resistance in vitro (stable to t = 300 min, c.f. t = 30 min for the parent peptide). This candidate reduced the formation of soluble Aβ42 oligomers, with the concurrent generation of non-toxic, insoluble aggregates measuring up to 25-30 nm diameter as determined by atomic force microscopy. The 15M S.A. candidate directly interacted with oligomeric Aβ42, as shown by coimmunoprecipitation and surface plasmon resonance/Biacore analysis, with an affinity in the low micromolar range. Furthermore, this peptide bound fibrillar Aβ42 and also stained plaques ex vivo in brain tissue from AD model mice. Given its multifaceted ability to target monomeric and aggregated Aβ42 species, this candidate holds promise for novel preclinical AD imaging and therapeutic strategies.

Structural, morphological, and functional diversity of amyloid oligomers

Protein misfolding and aggregation are known to play a crucial role in a number of important human diseases (Alzheimer's, Parkinson's, prion, diabetes, cataracts, etc.) as well as in a multitude of physiological processes. Protein aggregation is a highly complex process resulting in a variety of aggregates with different structures and morphologies. Oligomeric protein aggregates (amyloid oligomers) are formed as both intermediates and final products of the aggregation process. They are believed to play an important role in many protein aggregation-related diseases, and many of them are highly cytotoxic. Due to their instability and structural heterogeneity, information about structure, mechanism of formation, and physiological effects of amyloid oligomers is sparse. This review attempts to summarize the existing information on the major properties of amyloid oligomers.

Effects of Aβ exposure on long-term associative memory and its neuronal mechanisms in a defined neuronal network

Amyloid beta (Aβ) induced neuronal death has been linked to memory loss, perhaps the most devastating symptom of Alzheimer’s disease (AD). Although Aβ-induced impairment of synaptic or intrinsic plasticity is known to occur before any cell death, the links between these neurophysiological changes and the loss of specific types of behavioral memory are not fully understood. Here we used a behaviorally and physiologically tractable animal model to investigate Aβ-induced memory loss and electrophysiological changes in the absence of neuronal death in a defined network underlying associative memory. We found similar behavioral but different neurophysiological effects for Aβ 25-35 and Aβ 1-42 in the feeding circuitry of the snail Lymnaea stagnalis. Importantly, we also established that both the behavioral and neuronal effects were dependent upon the animals having been classically conditioned prior to treatment, since Aβ application before training caused neither memory impairment nor underlying neuronal changes over a comparable period of time following treatment.

Prion-Protein-interacting Amyloid-β Oligomers of High Molecular Weight Are Tightly Correlated with Memory Impairment in Multiple Alzheimer Mouse Models

Alzheimer disease (AD) is characterized by amyloid-β accumulation, with soluble oligomers (Aβo) being the most synaptotoxic. However, the multivalent and unstable nature of Aβo limits molecular characterization and hinders research reproducibility. Here, we characterized multiple Aβo forms throughout the life span of various AD mice and in post-mortem human brain. Aβo exists in several populations, where prion protein (PrP(C))-interacting Aβo is a high molecular weight Aβ assembly present in multiple mice and humans with AD. Levels of PrP(C)-interacting Aβo match closely with mouse memory and are equal or superior to other Aβ measures in predicting behavioral impairment. However, Aβo metrics vary considerably between mouse strains. Deleting PrP(C) expression in mice with relatively low PrP(C)-interacting Aβo (Tg2576) results in partial rescue of cognitive performance as opposed to complete recovery in animals with a high percentage of PrP(C)-interacting Aβo (APP/PSEN1). These findings highlight the relative contributions and interplay of Aβo forms in AD.