The antibody aducanumab reduces Aβ plaques in Alzheimer’s disease

Pharmacological and Toxicological Properties of the Potent Oral γ-Secretase Modulator BPN-15606

Alzheimer’s disease (AD) is characterized neuropathologically by an abundance of 1) neuritic plaques, which are primarily composed of a fibrillar 42-amino-acid amyloid-β peptide (Aβ), as well as 2) neurofibrillary tangles composed of aggregates of hyperphosporylated tau. Elevations in the concentrations of the Aβ42 peptide in the brain, as a result of either increased production or decreased clearance, are postulated to initiate and drive the AD pathologic process. We initially introduced a novel class of bridged aromatics referred tγ-secretase modulatoro as γ-secretase modulators that inhibited the production of the Aβ42 peptide and to a lesser degree the Aβ40 peptide while concomitantly increasing the production of the carboxyl-truncated Aβ38 and Aβ37 peptides. These modulators potently lower Aβ42 levels without inhibiting the γ-secretase–mediated proteolysis of Notch or causing accumulation of carboxyl-terminal fragments of APP. In this study, we report a large number of pharmacological studies and early assessment of toxicology characterizing a highly potent γ-secretase modulator (GSM), (S)-N-(1-(4-fluorophenyl)ethyl)-6-(6-methoxy-5-(4-methyl-1H-imidazol-1-yl)pyridin-2-yl)-4-methylpyridazin-3-amine (BPN-15606). BPN-15606 displayed the ability to significantly lower Aβ42 levels in the central nervous system of rats and mice at doses as low as 5–10 mg/kg, significantly reduce Aβ neuritic plaque load in an AD transgenic mouse model, and significantly reduce levels of insoluble Aβ42 and pThr181 tau in a three-dimensional human neural cell culture model. Results from repeat-dose toxicity studies in rats and dose escalation/repeat-dose toxicity studies in nonhuman primates have designated this GSM for 28-day Investigational New Drug-enabling good laboratory practice studies and positioned it as a candidate for human clinical trials.

AAV-mediated expression of anti-tau scFvs decreases tau accumulation in a mouse model of tauopathy

Ising et al. report expression of anti-tau scFvs in the brain of a mouse model of tauopathy by AAV-mediated gene transfer. Treated mice show markedly decreased tau hyperphosphorylation and detergent-soluble tau species. Therefore, the F_c domain is not required to mediate effects in tauopathy.

Tauopathies are characterized by the progressive accumulation of hyperphosphorylated, aggregated forms of tau. Our laboratory has previously demonstrated that passive immunization with an anti-tau antibody, HJ8.5, decreased accumulation of pathological tau in a human P301S tau-expressing transgenic (P301S-tg) mouse model of frontotemporal dementia/tauopathy. To investigate whether the F_c domain of HJ8.5 is required for the therapeutic effect, we engineered single-chain variable fragments (scFvs) derived from HJ8.5 with variable linker lengths, all specific to human tau. Based on different binding properties, we selected two anti-tau scFvs and tested their efficacy in vivo by adeno-associated virus–mediated gene transfer to the brain of P301S-tg mice. The scFvs significantly reduced levels of hyperphosphorylated, aggregated tau in brain tissue of P301S-tg mice, associated with a decrease in detergent-soluble tau species. Interestingly, these mice showed substantial levels of scFvs in the cerebrospinal fluid without significant effects on total extracellular tau levels. Therefore, our study provides a novel strategy for anti-tau immunotherapeutics that potentially limits a detrimental proinflammatory response.

UB-311, a novel UBITh® amyloid β peptide vaccine for mild Alzheimer's disease

Introduction

A novel amyloid β (Aβ) synthetic peptide vaccine (UB-311) has been evaluated in a first-in-human trial with patients of mild-to-moderate Alzheimer's disease. We describe translational research covering vaccine design, preclinical characterization, and phase-I clinical trial with supportive outcome that advances UB-311 into an ongoing phase-II trial.

Methods

UB-311 is constructed with two synthetic Aβ_1–14–targeting peptides (B-cell epitope), each linked to different helper T-cell peptide epitopes (UBITh^®) and formulated in a Th2-biased delivery system. The hAPP751 transgenic mouse model was used to perform the proof-of-concept study. Baboons and macaques were used for preclinical safety, tolerability, and immunogenicity evaluation. Patients with mild-to-moderate Alzheimer's disease (AD) were immunized by intramuscular route with 3 doses of UB-311 at weeks 0, 4, and 12, and monitored until week 48. Safety and immunogenicity were assessed per protocol, and preliminary efficacy was analyzed by Alzheimer's Disease Assessment Scale–Cognitive Subscale (ADAS-Cog), Mini–Mental State Examination (MMSE), and Alzheimer's Disease Cooperative Study–Clinician's Global Impression of Change (ADCS-CGIC).

Results

UB-311 covers a diverse genetic background and facilitates strong immune response with high responder rate. UB-311 reduced the levels of Aβ_1–42 oligomers, protofibrils, and plaque load in hAPP751 transgenic mice. Safe and well-tolerated UB-311 generated considerable site-specific (Aβ_1–10) antibodies across all animal species examined. In AD patients, UB-311 induced a 100% responder rate; injection site swelling and agitation were the most common adverse events (4/19 each). A slower rate of increase in ADAS-Cog from baseline to week 48 was observed in the subgroup of mild AD patients (MMSE ≥ 20) compared with the moderate AD subgroup, suggesting that UB-311 may have a potential of cognition improvement in patients with early stage of Alzheimer's dementia.

Discussion

The UBITh^® platform can generate a high-precision molecular vaccine with high responder rate, strong on-target immunogenicity, and a potential of cognition improvement, which support UB-311 for active immunotherapy in early-to-mild AD patients currently enrolled in a phase-II trial (NCT02551809).

Microfluidic neural probes: in vivo tools for advancing neuroscience

Microfluidic neural probes hold immense potential as in vivo tools for dissecting neural circuit function in complex nervous systems. Miniaturization, integration, and automation of drug delivery tools open up new opportunities for minimally invasive implants. These developments provide unprecedented spatiotemporal resolution in fluid delivery as well as multifunctional interrogation of neural activity using combined electrical and optical modalities. Capitalizing on these unique features, microfluidic technology will greatly advance in vivo pharmacology, electrophysiology, optogenetics, and optopharmacology. In this review, we discuss recent advances in microfluidic neural probe systems. In particular, we will highlight the materials and manufacturing processes of microfluidic probes, device configurations, peripheral devices for fluid handling and packaging, and wireless technologies that can be integrated for the control of these microfluidic probe systems. This article summarizes various microfluidic implants and discusses grand challenges and future directions for further developments.

Old Maids: Aging and Its Impact on Microglia Function

Microglia are highly active and vigilant housekeepers of the central nervous system that function to promote neuronal growth and activity. With advanced age, however, dysregulated inflammatory signaling and defects in phagocytosis impede their ability to perform the most essential of homeostatic functions, including immune surveillance and debris clearance. Microglial activation is one of the hallmarks of the aging brain and coincides with age-related neurodegeneration and cognitive decline. Age-associated microglial dysfunction leads to cellular senescence and can profoundly alter the response to sterile injuries and immune diseases, often resulting in maladaptive responses, chronic inflammation, and worsened outcomes after injury. Our knowledge of microglia aging and the factors that regulate age-related microglial dysfunction remain limited, as the majority of pre-clinical studies are performed in young animals, and human brain samples are difficult to obtain quickly post-mortem or in large numbers. This review outlines the impact of normal aging on microglial function, highlights the potential mechanisms underlying age-related changes in microglia, and discusses how aging can shape the recovery process following injury.

The role of histidines in amyloid β fibril assembly

Low pH has a strong stabilising effect on the fibrillar assembly of amyloid β, which is associated with Alzheimer's disease. The stabilising effect is already pronounced at pH 6.0, suggesting that protonation of histidines might mediate this effect. Through the systematic substitution of the three native histidines in Aβ for alanines, we have evaluated their role in fibril stability. Using surface plasmon resonance, we show that at neutral pH the fibrillar forms of all His-Ala variants are destabilised by a factor of 4-12 compared to wild-type Aβ. However, none of the His-Ala Aβ variants impair the stabilising effect of the fibril at low pH.

Alzheimer's disease in people with Down's syndrome: the prospects for and the challenges of developing preventative treatments

People with Down's syndrome (DS) are at high risk for developing Alzheimer's disease (AD) at a relatively young age. This increased risk is not observed in people with intellectual disabilities for reasons other than DS and for this reason it is unlikely to be due to non-specific effects of having a neurodevelopmental disorder but, instead, a direct consequence of the genetics of DS (trisomy 21). Given the location of the amyloid precursor protein (APP) gene on chromosome 21, the amyloid cascade hypothesis is the dominant theory accounting for this risk, with other genetic and environmental factors modifying the age of onset and the course of the disease. Several potential therapies targeting the amyloid pathway and aiming to modify the course of AD are currently being investigated, which may also be useful for treating AD in DS. However, given that the neuropathology associated with AD starts many years before dementia manifests, any preventative treatment must start well before the onset of symptoms. To enable trials of such interventions, plasma, CSF, brain, and retinal biomarkers are being studied as proxy early diagnostic and outcome measures for AD. In this systematic review, we consider the prospects for the development of potential preventative treatments of AD in the DS population and their evaluation.

New drugs in psychiatry: focus on new pharmacological targets

The approval of psychotropic drugs with novel mechanisms of action has been rare in recent years. To address this issue, further analysis of the pathophysiology of neuropsychiatric disorders is essential for identifying new pharmacological targets for psychotropic medications. In this report, we detail drug candidates being examined as treatments for psychiatric disorders. Particular emphasis is placed on agents with novel mechanisms of action that are being tested as therapies for depression, schizophrenia, or Alzheimer’s disease. All of the compounds considered were recently approved for human use or are in advanced clinical trials. Drugs included here are new antipsychotic medications endowed with a preferential affinity at dopamine D3 receptor (cariprazine) or at glutamatergic or cannabinoid receptors, as well as vortioxetine, a drug approved for managing the cognitive deficits associated with major depression. New mechanistic approaches for the treatment of depression include intravenous ketamine or esketamine or intranasal esketamine. As for Alzheimer’s disease, the possible value of passive immunotherapy with agents such as aducanumab is considered to be a potential disease-modifying approach that could slow or halt the progressive decline associated with this devastating disorder.

Aromatherapy and Aromatic Plants for the Treatment of Behavioural and Psychological Symptoms of Dementia in Patients with Alzheimer's Disease: Clinical Evidence and Possible Mechanisms

The treatment of agitation and aggression, typical Behavioural and Psychological Symptoms of Dementia (BPSDs) of Alzheimer's Disease (AD), is one of the most complicated aspects of handling patients suffering from dementia. Currently, the management of these symptoms often associated with an increased pain perception, which notably reduces the patients' quality of life (QoL), relies on the employment of antipsychotic drugs. Unfortunately, the use of these pharmacological agents has some limits: in the long term, they do not result in being equally effective as in the first weeks of treatment and they present important side effects. Therefore, there is growing interest, supported by clinical evidence, in aromatherapy for the control of agitation, aggression, and psychotic symptoms. Some molecular mechanisms have been proposed to explain the behavioural effects of essential oils, as the whole phytocomplex or the single components, but important basic research effort is still needed. For this reason, rigorous preclinical studies are necessary in order to understand the pharmacological basis of aromatherapy in the treatment of BPSDs and to widen the cluster of effective essential oils in pharmacotherapeutic practice.

A novel pathway for amyloids self-assembly in aggregates at nanomolar concentration mediated by the interaction with surfaces

A limitation of the amyloid hypothesis in explaining the development of neurodegenerative diseases is that the level of amyloidogenic polypeptide in vivo is below the critical concentration required to form the aggregates observed in post-mortem brains. We discovered a novel, on-surface aggregation pathway of amyloidogenic polypeptide that eliminates this long-standing controversy. We applied atomic force microscope (AFM) to demonstrate directly that on-surface aggregation takes place at a concentration at which no aggregation in solution is observed. The experiments were performed with the full-size Aβ protein (Aβ42), a decapeptide Aβ(14-23) and α-synuclein; all three systems demonstrate a dramatic preference of the on-surface aggregation pathway compared to the aggregation in the bulk solution. Time-lapse AFM imaging, in solution, show that over time, oligomers increase in size and number and release in solution, suggesting that assembled aggregates can serve as nuclei for aggregation in bulk solution. Computational modeling performed with the all-atom MD simulations for Aβ(14-23) peptide shows that surface interactions induce conformational transitions of the monomer, which facilitate interactions with another monomer that undergoes conformational changes stabilizing the dimer assembly. Our findings suggest that interactions of amyloidogenic polypeptides with cellular surfaces play a major role in determining disease onset.

ErbB2 regulates autophagic flux to modulate the proteostasis of APP-CTFs in Alzheimer's disease

Proteolytic processing of amyloid precursor protein (APP) C-terminal fragments (CTFs) by γ-secretase underlies the pathogenesis of Alzheimer's disease (AD). An RNA interference screen using APP-CTF [99-residue CTF (C99)]- and Notch-specific γ-secretase interaction assays identified a unique ErbB2-centered signaling network that was predicted to preferentially govern the proteostasis of APP-C99. Consistently, significantly elevated levels of ErbB2 were confirmed in the hippocampus of human AD brains. We then found that ErbB2 effectively suppressed autophagic flux by physically dissociating Beclin-1 from the Vps34-Vps15 complex independent of its kinase activity. Down-regulation of ErbB2 by CL-387,785 decreased the levels of C99 and secreted amyloid-β in cellular, zebrafish, and mouse models of AD, through the activation of autophagy. Oral administration of an ErbB2-targeted CL-387,785 for 3 wk significantly improves the cognitive functions of APP/presenilin-1 (PS1) transgenic mice. This work unveils a noncanonical function of ErbB2 in modulating autophagy and establishes ErbB2 as a therapeutic target for AD.

Dissociable diffusion MRI patterns of white matter microstructure and connectivity in Alzheimer's disease spectrum

Recent efforts using diffusion tensor imaging (DTI) have documented white matter (WM) alterations in Alzheimer's disease (AD). The full potential of whole-brain DTI, however, has not been fully exploited as studies have focused on individual microstructural indices independently. In patients with AD (n = 79), mild (MCI, n = 55) and subjective (SCI, n = 30) cognitive impairment, we applied linked independent component analysis (LICA) to model inter-subject variability across five complementary DTI measures (fractional anisotropy (FA), axial/radial/mean diffusivity, diffusion tensor mode), two crossing fiber measures estimated using a multi-compartment crossing-fiber model reflecting the volume fraction of the dominant (f1) and non-dominant (f2) diffusion orientation, and finally, connectivity density obtained from full-brain probabilistic tractography. The LICA component explaining the largest data variance was highly sensitive to disease severity (AD < MCI < SCI) and revealed widespread coordinated decreases in FA and f1 with increases in all diffusivity measures in AD. Additionally, it reflected regional coordinated decreases and increases in f2, mode and connectivity density, implicating bidirectional alterations of crossing fibers in the fornix, uncinate fasciculi, corpus callosum and major sensorimotor pathways. LICA yielded improved diagnostic classification performance compared to univariate region-of-interest features. Our results document coordinated WM microstructural and connectivity alterations in line with disease severity across the AD continuum.

Affibody molecules as engineered protein drugs

Affibody molecules can be used as tools for molecular recognition in diagnostic and therapeutic applications. There are several preclinical studies reported on diagnostic and therapeutic use of this molecular class of alternative scaffolds, and early clinical evidence is now beginning to accumulate that suggests the Affibody molecules to be efficacious and safe in man. The small size and ease of engineering make Affibody molecules suitable for use in multispecific constructs where AffiMabs is one such that offers the option to potentiate antibodies for use in complex disease.

Validation of the Semiquantitative Static SUVR Method for 18F-AV45 PET by Pharmacokinetic Modeling with an Arterial Input Function

Increased brain uptake of ¹⁸F-AV45 visualized by PET is a key biomarker for Alzheimer disease (AD). The SUV ratio (SUVR) is widely used for quantification, but is subject to variability based on choice of reference region and changes in cerebral blood flow. Here we validate the SUVR method against the gold standard volume of distribution (V_T) to assess cross-sectional differences in plaque load. Methods: Dynamic 60-min ¹⁸F-AV45 (291 ± 67 MBq) and 1-min ¹⁵O-H₂O (370 MBq) scans were obtained in 35 age-matched elderly subjects, including 10 probable AD, 15 amnestic mild cognitive impairment (aMCI), and 10 cognitively healthy controls (HCs). ¹⁸F-AV45 V_T was determined from 2-tissue-compartment modeling using a metabolite-corrected plasma input function. Static SUVR was calculated at 50-60 min after injection, using either cerebellar gray matter (SUVR_CB) or whole subcortical white matter (SUVR_WM) as the reference. Additionally, whole cerebellum, pons, centrum semiovale, and a composite region were examined as alternative references. Blood flow was quantified by ¹⁵O-H₂O SUV. Data are presented as mean ± SEM. Results: There was rapid metabolization of ¹⁸F-AV45, with only 35% of unchanged parent remaining at 10 min. Compared with V_T, differences in cortical Aβ load between aMCI and AD were overestimated by SUVR_WM (+4% ± 2%) and underestimated by SUVR_CB (-10% ± 2%). V_T correlated better with SUVR_WM (Pearson r: from 0.63 for posterior cingulate to 0.89 for precuneus, P < 0.0001) than with SUVR_CB (Pearson r: from 0.51 for temporal lobe [P = 0.002] to 0.82 for precuneus [P < 0.0001]) in all tested regions. Correlation results for the alternative references were in between those for CB and WM. ¹⁵O-H₂O data showed that blood flow was decreased in AD compared with aMCI in cortical regions (-5% ± 1%) and in the reference regions (CB, -9% ± 8%; WM, -8% ± 8%). Conclusion: Increased brain uptake of ¹⁸F-AV45 assessed by the simplified static SUVR protocol does not truly reflect Aβ load. However, SUVR_WM is better correlated with V_T and more closely reflects V_T differences between aMCI and AD than SUVR_CB.

Cerebrospinal fluid biomarkers for Alzheimer's disease in Down syndrome

Down syndrome (DS), present in nearly six million people, is associated with an extremely high risk to develop Alzheimer's disease (AD). Amyloid-β and tau pathology are omnipresent from age 40 years onward, but clinical symptoms do not appear in all DS individuals. Dementia diagnostics is complex in this population, illustrating the great need for predictive biomarkers. Although blood biomarkers have not yet proven useful, cerebrospinal fluid (CSF) biomarkers (low amyloid-β42, high t-tau, and high p-tau) effectively contribute to AD diagnoses in the general population and are increasingly used in clinical practice. Surprisingly, CSF biomarkers have been barely evaluated in DS. Breaking the taboo on CSF analyses would finally allow for the elucidation of its utility in (differential) diagnoses and staging of disease severity. A sensitive and specific biomarker profile for AD in DS would be of paramount importance to daily care, adaptive caregiving, and specific therapeutic interventions.

Integrated analysis of genetic, behavioral, and biochemical data implicates neural stem cell-induced changes in immunity, neurotransmission and mitochondrial function in Dementia with Lewy Body mice

We previously demonstrated that transplantation of murine neural stem cells (NSCs) can improve motor and cognitive function in a transgenic model of Dementia with Lewy Bodies (DLB). These benefits occurred without changes in human α-synuclein pathology and were mediated in part by stem cell-induced elevation of brain-derived neurotrophic factor (BDNF). However, instrastriatal NSC transplantation likely alters the brain microenvironment via multiple mechanisms that may synergize to promote cognitive and motor recovery. The underlying neurobiology that mediates such restoration no doubt involves numerous genes acting in concert to modulate signaling within and between host brain cells and transplanted NSCs. In order to identify functionally connected gene networks and additional mechanisms that may contribute to stem cell-induced benefits, we performed weighted gene co-expression network analysis (WGCNA) on striatal tissue isolated from NSC- and vehicle-injected wild-type and DLB mice. Combining continuous behavioral and biochemical data with genome wide expression via network analysis proved to be a powerful approach; revealing significant alterations in immune response, neurotransmission, and mitochondria function. Taken together, these data shed further light on the gene network and biological processes that underlie the therapeutic effects of NSC transplantation on α-synuclein induced cognitive and motor impairments, thereby highlighting additional therapeutic targets for synucleinopathies.

Subcortical Shape Changes, Hippocampal Atrophy and Cortical Thinning in Future Alzheimer's Disease Patients

Efficacy of future treatments depends on biomarkers identifying patients with mild cognitive impairment at highest risk for transitioning to Alzheimer's disease. Here, we applied recently developed analysis techniques to investigate cross-sectional differences in subcortical shape and volume alterations in patients with stable mild cognitive impairment (MCI) (n = 23, age range 59–82, 47.8% female), future converters at baseline (n = 10, age range 66–84, 90% female) and at time of conversion (age range 68–87) compared to group-wise age and gender matched healthy control subjects (n = 23, age range 61–81, 47.8% female; n = 10, age range 66–82, 80% female; n = 10, age range 68–82, 70% female). Additionally, we studied cortical thinning and global and local measures of hippocampal atrophy as known key imaging markers for Alzheimer's disease. Apart from bilateral striatal volume reductions, no morphometric alterations were found in cognitively stable patients. In contrast, we identified shape alterations in striatal and thalamic regions in future converters at baseline and at time of conversion. These shape alterations were paralleled by Alzheimer's disease like patterns of left hemispheric morphometric changes (cortical thinning in medial temporal regions, hippocampal total and subfield atrophy) in future converters at baseline with progression to similar right hemispheric alterations at time of conversion. Additionally, receiver operating characteristic curve analysis indicated that subcortical shape alterations may outperform hippocampal volume in identifying future converters at baseline. These results further confirm the key role of early cortical thinning and hippocampal atrophy in the early detection of Alzheimer's disease. But first and foremost, and by distinguishing future converters but not patients with stable cognitive abilities from cognitively normal subjects, our results support the value of early subcortical shape alterations and reduced hippocampal subfield volumes as potential markers for the early detection of Alzheimer's disease.

Islet amyloid polypeptide: Another key molecule in Alzheimer's pathogenesis?

Recent epidemiological evidence reveals that patients suffering from type 2 diabetes mellitus (T2DM) often experience a significant decline in cognitive function, and approximately 70% of those cases eventually develop Alzheimer's disease (AD). Although several pathological processes are shared by AD and T2DM, the exact molecular mechanisms connecting these two diseases are poorly understood. Aggregation of human islet amyloid polypeptide (hIAPP), the pathological hallmark of T2DM, has also been detected in brain tissue and is associated with cognitive decline and AD development. In addition, hIAPP and amyloid β protein (Aβ) share many biophysical and physiological properties as well as exert similar cytotoxic mechanisms. Therefore, it is important to examine the possible role of hIAPP in the pathogenesis of AD. In this article, we introduce the basics on this amyloidogenic protein. More importantly, we discuss the potential mechanisms of hIAPP-induced AD development, which will be beneficial for proposing novel and feasible strategies to optimize AD prevention and/or treatment in diabetics.

Protein-Remodeling Factors As Potential Therapeutics for Neurodegenerative Disease

Protein misfolding is implicated in numerous neurodegenerative disorders including amyotrophic lateral sclerosis, Parkinson's disease, Alzheimer's disease, and Huntington's disease. A unifying feature of patients with these disorders is the accumulation of deposits comprised of misfolded protein. Aberrant protein folding can cause toxicity through a loss or gain of protein function, or both. An intriguing therapeutic approach to counter these disorders is the application of protein-remodeling factors to resolve these misfolded conformers and return the proteins to their native fold and function. Here, we describe the application of protein-remodeling factors to alleviate protein misfolding in neurodegenerative disease. We focus on Hsp104, Hsp110/Hsp70/Hsp40, NMNAT, and HtrA1, which can prevent and reverse protein aggregation. While many of these protein-remodeling systems are highly promising, their activity can be limited. Thus, engineering protein-remodeling factors to enhance their activity could be therapeutically valuable. Indeed, engineered Hsp104 variants suppress neurodegeneration in animal models, which opens the way to novel therapeutics and mechanistic probes to help understand neurodegenerative disease.

The prion model for progression and diversity of neurodegenerative diseases

The neuropathology of different neurodegenerative diseases begins in different brain regions, and involves distinct brain networks. Evidence indicates that transcellular propagation of protein aggregation, which is the basis of prion disease, might underlie the progression of pathology in neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and Huntington's disease. The prion model predicts specific patterns of neuronal vulnerability and network involvement on the basis of the conformation of pathological proteins. Indeed, evidence indicates that self-propagating aggregate conformers, or so-called strains, are associated with distinct neuropathological syndromes. The extension of this hypothesis to our understanding of common neurodegenerative disorders can suggest new therapeutic approaches, such as immunotherapy and small molecules, to block transcellular propagation, and new diagnostic tools to detect early evidence of disease.

Designer protein disaggregases to counter neurodegenerative disease

Protein misfolding and aggregation unify several devastating neurodegenerative disorders, including Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. There are no effective therapeutics for these disorders and none that target the reversal of the aberrant protein misfolding and aggregation that cause disease. Here, I showcase important advances to define, engineer, and apply protein disaggregases to mitigate deleterious protein misfolding and counter neurodegeneration. I focus on two exogenous protein disaggregases, Hsp104 from yeast and gene 3 protein from bacteriophages, as well as endogenous human protein disaggregases, including: (a) Hsp110, Hsp70, Hsp40, and small heat-shock proteins; (b) HtrA1; and (c) NMNAT2 and Hsp90. I suggest that protein-disaggregase modalities can be channeled to treat numerous fatal and presently incurable neurodegenerative diseases.

Clearance of cerebral Aβ in Alzheimer's disease: reassessing the role of microglia and monocytes

Deficiency in cerebral amyloid β-protein (Aβ) clearance is implicated in the pathogenesis of the common late-onset forms of Alzheimer’s disease (AD). Accumulation of misfolded Aβ in the brain is believed to be a net result of imbalance between its production and removal. This in turn may trigger neuroinflammation, progressive synaptic loss, and ultimately cognitive decline. Clearance of cerebral Aβ is a complex process mediated by various systems and cell types, including vascular transport across the blood–brain barrier, glymphatic drainage, and engulfment and degradation by resident microglia and infiltrating innate immune cells. Recent studies have highlighted a new, unexpected role for peripheral monocytes and macrophages in restricting cerebral Aβ fibrils, and possibly soluble oligomers. In AD transgenic (ADtg) mice, monocyte ablation or inhibition of their migration into the brain exacerbated Aβ pathology, while blood enrichment with monocytes and their increased recruitment to plaque lesion sites greatly diminished Aβ burden. Profound neuroprotective effects in ADtg mice were further achieved through increased cerebral recruitment of myelomonocytes overexpressing Aβ-degrading enzymes. This review summarizes the literature on cellular and molecular mechanisms of cerebral Aβ clearance with an emphasis on the role of peripheral monocytes and macrophages in Aβ removal.

Diagnostic pathology of Alzheimer's disease from routine microscopy to immunohistochemistry and experimental correlations

The absence of any histologic correlate for Alzheimer's disease despite its commonness and severe clinical sequelae may offers clues to its etiology. Recent evidence strongly suggests that the central event of this disease is the hyperphosphorylation of neuronal tau protein and not the beta amyloid precipitates. In each case, essential and soluble neuronal proteins derivatives form insoluble aggregates that can readily be detected by immunohistochemistry using antibodies specific for the misfolded proteins. Immunohistochemistry also demonstrates that neurons with hyperphosphorylated tau protein are viable. Experimental evidence using neuronal cell cultures suggests that the affected neurons in Alzheimer's disease may have undergone molecular changes that include accumulation of anti-apopotic proteins MCL1 and cFLIP that do not allow the cell to undergo programmed cell death but, rather, to "immortalize" and thus accumulate hyperphosphorylated tau protein in the neuronal cell body and beta amyloid in downstream dendrites. We describe a simplified protocol to demonstrate such changes based on tagged LNA modified microRNA/antimicroRNA oligomers and cell cultures. Co-expression showed that the tagged antimiR-512 strongly localized with the markedly up-regulated proteins MCL1 and cFLIP with concomitant accumulation of hyperphosphorylated tau protein. The data underscore to the anatomic pathologist that the diagnosis of Alzheimer's disease is best accomplished by simple immunohistochemistry tests correlated to the clinical history and the key role pathologists can play in understanding the cause of the disease.

Optimal Reference Region to Measure Longitudinal Amyloid-β Change with 18F-Florbetaben PET

Accurate measurement of changes in amyloid-β (Aβ) deposition over time is important in longitudinal studies, particularly in anti-Aβ therapeutic trials. To achieve this, the optimal reference region (RR) must be selected to reduce variance of Aβ PET measurements, allowing early detection of treatment efficacy. The aim of this study was to determine the RR that allows earlier detection of subtle Aβ changes using ¹⁸F-florbetaben PET. Methods: Forty-five patients with mild cognitive impairment (mean age ± SD, 72.69 ± 6.54 y; 29 men/16 women) who underwent up to 3 ¹⁸F-florbetaben scans were included. Baseline scans were visually classified as high (Aβ+) or low (Aβ-) amyloid. Six cortical regions were quantified using a standardized region-of-interest atlas applied to the spatially normalized gray matter image obtained from segmentation of the baseline T1-weighted volumetric MRI. Four RRs (cerebellar gray matter [CGM], whole cerebellum [WCER], pons, and subcortical white matter [SWM]) were studied. The SUV ratio (SUVR) for each RR was calculated by dividing cortex activity by RR activity, with a composite SUVR averaged over 6 cortical regions. SUVR increase from baseline to 1 and 2 y, and percentage Aβ deposition per year, were assessed across Aβ+ and Aβ- groups. Results: SUVs for any RR were not significantly different over time. Percentage Aβ accumulation per year derived from composite SUVR was 0.10 ± 1.72 (Aβ-) and 1.36 ± 1.98 (Aβ+) (P = 0.02) for CGM and 0.13 ± 1.47 and 1.32 ± 1.75 (P = 0.01), respectively, for WCER. Compared with baseline, the composite SUVR increase in Aβ+ scans was significantly larger than in Aβ- scans at 1 y (P = 0.04 [CGM]; P = 0.03 [WCER]) and 2 y (P = 0.02 [CGM]; P = 0.01 [WCER]) using these 2 RRs. Significant SUVR changes using the pons as the RR were detected only at 2 y (P = 0.46 [1 y], P = 0.001 [2 y]). SUVR using the SWM as the RR showed no significant differences at either follow-up (P = 0.39 [1 y], P = 0.09 [2 y]). Conclusion: RR selection influences reliable early measurement of Aβ changes over time. Compared with SWM and pons, which do not fulfil the RR requirements and have limited sensitivity to detect Aβ changes, cerebellar RRs are recommended for ¹⁸F-florbetaben PET because they allow earlier detection of Aβ accumulation.

Microglia Function in the Central Nervous System During Health and Neurodegeneration

Microglia are resident cells of the brain that regulate brain development, maintenance of neuronal networks, and injury repair. Microglia serve as brain macrophages but are distinct from other tissue macrophages owing to their unique homeostatic phenotype and tight regulation by the central nervous system (CNS) microenvironment. They are responsible for the elimination of microbes, dead cells, redundant synapses, protein aggregates, and other particulate and soluble antigens that may endanger the CNS. Furthermore, as the primary source of proinflammatory cytokines, microglia are pivotal mediators of neuroinflammation and can induce or modulate a broad spectrum of cellular responses. Alterations in microglia functionality are implicated in brain development and aging, as well as in neurodegeneration. Recent observations about microglia ontogeny combined with extensive gene expression profiling and novel tools to study microglia biology have allowed us to characterize the spectrum of microglial phenotypes during development, homeostasis, and disease. In this article, we review recent advances in our understanding of the biology of microglia, their contribution to homeostasis, and their involvement in neurodegeneration. Moreover, we highlight the complexity of targeting microglia for therapeutic intervention in neurodegenerative diseases.

Therapeutic Potential of Secreted Amyloid Precursor Protein APPsα

Cleavage of the amyloid precursor protein (APP) by α-secretase generates an extracellularly released fragment termed secreted APP-alpha (APPsα). Not only is this process of interest due to the cleavage of APP within the amyloid-beta sequence, but APPsα itself has many physiological properties that suggest its great potential as a therapeutic target. For example, APPsα is neurotrophic, neuroprotective, neurogenic, a stimulator of protein synthesis and gene expression, and enhances long-term potentiation (LTP) and memory. While most early studies have been conducted in vitro, effectiveness in animal models is now being confirmed. These studies have revealed that either upregulating α-secretase activity, acutely administering APPsα or chronic delivery of APPsα via a gene therapy approach can effectively treat mouse models of Alzheimer's disease (AD) and other disorders such as traumatic head injury. Together these findings suggest the need for intensifying research efforts to harness the therapeutic potential of this multifunctional protein.

Immune Regulation of Antibody Access to Neuronal Tissues

This review highlights recent advances in how the innate and adaptive immune systems control the blood-brain barrier (BBB) and the blood-nerve barrier (BNB). Interferons and TAM receptors play key roles in innate immune control of the BBB. Cells of the adaptive immune system, particularly CD4⁺ T cells, take distinct routes to enter neural tissues and mediate immune surveillance. Furthermore, T cell-mediated opening of the BBB and the BNB is crucial to allow antibody access and thereby block the replication of neurotropic viruses. Such novel insights gained from basic research provide key foundations for future design of therapeutic strategies - enabling antibody access to the brain may be key to cancer immunotherapy and to the use of vaccines against neurodegenerative conditions such as Alzheimer's disease.

Preclinical Alzheimer's disease: A systematic review of the cohorts underlying the concept

Preclinical Alzheimer's disease (AD) is a relatively recent concept describing an entity characterized by the presence of a pathophysiological biomarker signature characteristic for AD in the absence of specific clinical symptoms. There is rising interest in the scientific community to define such an early target population mainly because of failures of all recent clinical trials despite evidence of biological effects on brain amyloidosis for some compounds. A conceptual framework has recently been proposed for this preclinical phase of AD. However, few data exist on this silent stage of AD. We performed a systematic review to investigate how the concept is defined across studies. The review highlights the substantial heterogeneity concerning the three main determinants of preclinical AD: "normal cognition," "cognitive decline," and "AD pathophysiological signature." We emphasize the need for a harmonized nomenclature of the preclinical AD concept and standardized population-based and case-control studies using unified operationalized criteria.

In vivo Evidence for Therapeutic Properties of Cannabidiol (CBD) for Alzheimer's Disease

Alzheimer's disease (AD) is a debilitating neurodegenerative disease that is affecting an increasing number of people. It is characterized by the accumulation of amyloid-β and tau hyperphosphorylation as well as neuroinflammation and oxidative stress. Current AD treatments do not stop or reverse the disease progression, highlighting the need for new, more effective therapeutics. Cannabidiol (CBD) is a non-psychoactive phytocannabinoid that has demonstrated neuroprotective, anti-inflammatory and antioxidant properties in vitro. Thus, it is investigated as a potential multifunctional treatment option for AD. Here, we summarize the current status quo of in vivo effects of CBD in established pharmacological and transgenic animal models for AD. The studies demonstrate the ability of CBD to reduce reactive gliosis and the neuroinflammatory response as well as to promote neurogenesis. Importantly, CBD also reverses and prevents the development of cognitive deficits in AD rodent models. Interestingly, combination therapies of CBD and Δ⁹-tetrahydrocannabinol (THC), the main active ingredient of cannabis sativa, show that CBD can antagonize the psychoactive effects associated with THC and possibly mediate greater therapeutic benefits than either phytocannabinoid alone. The studies provide “proof of principle” that CBD and possibly CBD-THC combinations are valid candidates for novel AD therapies. Further investigations should address the long-term potential of CBD and evaluate mechanisms involved in the therapeutic effects described.

Brain barriers and brain fluid research in 2016: advances, challenges and controversies

This editorial highlights some of the advances that occurred in relation to brain barriers and brain fluid research in 2016. It also aims to raise some of the attendant controversies and challenges in such research.

Alzheimer's disease: experimental models and reality

Experimental models of Alzheimer's disease (AD) are critical to gaining a better understanding of pathogenesis and to assess the potential of novel therapeutic approaches. The most commonly used experimental animal models are transgenic mice that overexpress human genes associated with familial AD (FAD) that result in the formation of amyloid plaques. However, AD is defined by the presence and interplay of both amyloid plaques and neurofibrillary tangle pathology. The track record of success in AD clinical trials thus far has been very poor. In part, this high failure rate has been related to the premature translation of highly successful results in animal models that mirror only limited aspects of AD pathology to humans. A greater understanding of the strengths and weakness of each of the various models and the use of more than one model to evaluate potential therapies would help enhance the success of therapy translation from preclinical studies to patients. In this review, we summarize the pathological features and limitations of the major experimental models of AD, including transgenic mice, transgenic rats, various physiological models of sporadic AD and in vitro human cell culture models.

Apolipoprotein E metabolism and functions in brain and its role in Alzheimer's disease

PURPOSE OF REVIEW

APOE4 genotype is the strongest genetic risk factor for Alzheimer's disease. Prevailing evidence suggests that amyloid β plays a critical role in Alzheimer's disease. The objective of this article is to review the recent findings about the metabolism of apolipoprotein E (ApoE) and amyloid β and other possible mechanisms by which ApoE contributes to the pathogenesis of Alzheimer's disease.

RECENT FINDINGS

ApoE isoforms have differential effects on amyloid β metabolism. Recent studies demonstrated that ApoE-interacting proteins, such as ATP-binding cassette A1 (ABCA1) and LDL receptor, may be promising therapeutic targets for Alzheimer's disease treatment. Activation of liver X receptor and retinoid X receptor pathway induces ABCA1 and other genes, leading to amyloid β clearance. Inhibition of the negative regulators of ABCA1, such as microRNA-33, also induces ABCA1 and decreases the levels of ApoE and amyloid β. In addition, genetic inactivation of an E3 ubiquitin ligase, myosin regulatory light chain interacting protein, increases LDL receptor levels and inhibits amyloid accumulation. Although amyloid β-dependent pathways have been extensively investigated, there have been several recent studies linking ApoE with vascular function, neuroinflammation, metabolism, synaptic plasticity, and transcriptional regulation. For example, ApoE was identified as a ligand for a microglial receptor, TREM2, and studies suggested that ApoE may affect the TREM2-mediated microglial phagocytosis.

SUMMARY

Emerging data suggest that ApoE affects several amyloid β-independent pathways. These underexplored pathways may provide new insights into Alzheimer's disease pathogenesis. However, it will be important to determine to what extent each mechanism contributes to the pathogenesis of Alzheimer's disease.

T cell responses in the central nervous system

T cells are required for immune surveillance of the central nervous system (CNS); however, they can also induce severe immunopathology in the context of both viral infections and autoimmunity. The mechanisms that are involved in the priming and recruitment of T cells to the CNS are only partially understood, but there has been renewed interest in this topic since the 'rediscovery' of lymphatic drainage from the CNS. Moreover, tissue-resident memory T cells have been detected in the CNS and are increasingly recognized as an autonomous line of host defence. In this Review, we highlight the main mechanisms that are involved in the priming and CNS recruitment of CD4⁺ T cells, CD8⁺ T cells and regulatory T cells. We also consider the plasticity of T cell responses in the CNS, with a focus on viral infection and autoimmunity.

APOE Genotype Differentially Modulates Effects of Anti-Aβ, Passive Immunization in APP Transgenic Mice

Background

APOE genotype is the foremost genetic factor modulating β-amyloid (Aβ) deposition and risk of sporadic Alzheimer’s disease (AD). Here we investigated how APOE genotype influences response to anti-Aβ immunotherapy.

Methods

APP_SW/PS1_dE9 (APP) transgenic mice with targeted replacement of the murine Apoe gene for human APOE alleles received 10D5 anti-Aβ or TY11-15 isotype control antibodies between the ages of 12 and 15 months.

Results

Anti-Aβ immunization decreased both the load of fibrillar plaques and the load of Aβ immunopositive plaques in mice of all APOE backgrounds. Although the relative reduction in parenchymal Aβ plaque load was comparable across all APOE genotypes, APP/ε4 mice showed the greatest reduction in the absolute Aβ plaque load values, given their highest baseline. The immunization stimulated phagocytic activation of microglia, which magnitude adjusted for the post-treatment plaque load was the greatest in APP/ε4 mice implying association between the ε4 allele and impaired Aβ phagocytosis. Perivascular hemosiderin deposits reflecting ensued microhemorrhages were associated with vascular Aβ (VAβ) and ubiquitously present in control mice of all APOE genotypes, although in APP/ε3 mice their incidence was the lowest. Anti-Aβ immunization significantly reduced VAβ burden but increased the number of hemosiderin deposits across all APOE genotypes with the strongest and the weakest effect in APP/ε2 and APP/ε3 mice, respectively.

Conclusions

Our studies indicate that APOE genotype differentially modulates microglia activation and Aβ plaque load reduction during anti-Aβ immunotherapy. The APOE ε3 allele shows strong protective effect against immunotherapy associated microhemorrhages; while, conversely, the APOE ε2 allele increases risk thereof.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-017-0156-1) contains supplementary material, which is available to authorized users.

Astrocytic transporters in Alzheimer's disease

Astrocytes play a fundamental role in maintaining the health and function of the central nervous system. Increasing evidence indicates that astrocytes undergo both cellular and molecular changes at an early stage in neurological diseases, including Alzheimer's disease (AD). These changes may reflect a change from a neuroprotective to a neurotoxic phenotype. Given the lack of current disease-modifying therapies for AD, astrocytes have become an interesting and viable target for therapeutic intervention. The astrocyte transport system covers a diverse array of proteins involved in metabolic support, neurotransmission and synaptic architecture. Therefore, specific targeting of individual transporter families has the potential to suppress neurodegeneration, a characteristic hallmark of AD. A small number of the 400 transporter superfamilies are expressed in astrocytes, with evidence highlighting a fraction of these are implicated in AD. Here, we review the current evidence for six astrocytic transporter subfamilies involved in AD, as reported in both animal and human studies. This review confirms that astrocytes are indeed a viable target, highlights the complexities of studying astrocytes and provides future directives to exploit the potential of astrocytes in tackling AD.

Aberrant proteolytic processing and therapeutic strategies in Alzheimer disease

Amyloid-β peptide (Aβ) and tau are major components of senile plaques and neurofibrillary tangles, respectively, deposited in the brains of Alzheimer disease (AD) patients. Aβ is derived from amyloid-β precursor protein that is sequentially cleaved by two aspartate proteases, β- and γ-secretases. Secreted Aβ is then catabolized by several proteases. Several lines of evidence suggest that accumulation of Aβ by increased production or decreased degradation induces the tau-mediated neuronal toxicity and symptomatic manifestations of AD. Thus, the dynamics of cerebral Aβ, called as "Aβ economy", would be the mechanistic basis of AD pathogenesis. Partial loss of γ-secretase activity leads to the increased generation of toxic Aβ isoforms, indicating that activation of γ-secretase would provide a beneficial effect for AD. After extensive discovery and development efforts, BACE1, which is a β-secretase enzyme, has emerged as a prime drug target for lowering brain Aβ levels. Recent studies revealed the decreased clearance of Aβ in sporadic AD patients, suggesting the importance of the catabolic mechanism in the pathogenesis of AD. I will discuss with these proteolytic mechanisms involved in the regulation of Aβ economy, and development of effective treatment and diagnostics for AD.

Comparison of Efficacy of Preventive and Therapeutic Vaccines Targeting the N Terminus of β-Amyloid in an Animal Model of Alzheimer's Disease

Previously, we reported that Alzheimer's disease (AD) epitope vaccines (EVs) composed of N-terminal β-amyloid (Aβ42) B cell epitope fused with universal foreign T helper (Th) epitope(s) were immunogenic, potent, and safe in different amyloid precursor protein (APP) transgenic mice with early AD-like pathology. However, developing an effective therapeutic vaccine is much more challenging, especially when a self-antigen such as Aβ42 is a target. Here, we directly compare the efficacy of anti-Aβ42 antibodies in Tg2576 mice with low or high levels of AD-like pathology at the start of immunizations: 6-6.5 months for preventive vaccinations and 16-19 months for therapeutic vaccinations. EV in a preventive setting induced high levels of anti-Aβ antibodies, significantly reducing pathologic forms of Aβ in the brains of Tg2576 mice. When used therapeutically for immunesenescent Tg2576 mice, EV induced low levels of antibodies not sufficient for clearing of AD-like pathology. Separately, we demonstrated that EV was also not effective in 11-11.5-month-old Tg2576 mice with moderate AD-like pathology. However, we augmented the titers of anti-Aβ antibodies in transgenic (Tg) mice of the same age possessing the pre-existing memory Th cells and detected a significant decrease in diffuse and core plaques in cortical regions compared to control animals along with improved novel object recognition performance.

Atomic structures of fibrillar segments of hIAPP suggest tightly mated β-sheets are important for cytotoxicity

hIAPP fibrils are associated with Type-II Diabetes, but the link of hIAPP structure to islet cell death remains elusive. Here we observe that hIAPP fibrils are cytotoxic to cultured pancreatic β-cells, leading us to determine the structure and cytotoxicity of protein segments composing the amyloid spine of hIAPP. Using the cryoEM method MicroED, we discover that one segment, 19-29 S20G, forms pairs of β-sheets mated by a dry interface that share structural features with and are similarly cytotoxic to full-length hIAPP fibrils. In contrast, a second segment, 15-25 WT, forms non-toxic labile β-sheets. These segments possess different structures and cytotoxic effects, however, both can seed full-length hIAPP, and cause hIAPP to take on the cytotoxic and structural features of that segment. These results suggest that protein segment structures represent polymorphs of their parent protein and that segment 19-29 S20G may serve as a model for the toxic spine of hIAPP.