Amyloid-beta antibody binding to cerebral amyloid angiopathy fibrils and risk for amyloid-related imaging abnormalities

Therapeutic antibodies have been developed to target amyloid-beta (Aβ), and some of these slow the progression of Alzheimer's disease (AD). However, they can also cause adverse events known as amyloid-related imaging abnormalities with edema (ARIA-E). We investigated therapeutic Aβ antibody binding to cerebral amyloid angiopathy (CAA) fibrils isolated from human leptomeningeal tissue to study whether this related to the ARIA-E frequencies previously reported by clinical trials. The binding of Aβ antibodies to CAA Aβ fibrils was evaluated in vitro using immunoprecipitation, surface plasmon resonance, and direct binding assay. Marked differences in Aβ antibody binding to CAA fibrils were observed. Solanezumab and crenezumab showed negligible CAA fibril binding and these antibodies have no reported ARIA-E cases. Lecanemab showed a low binding to CAA fibrils, consistent with its relatively low ARIA-E frequency of 12.6%, while aducanumab, bapineuzumab, and gantenerumab all showed higher binding to CAA fibrils and substantially higher ARIA-E frequencies (25-35%). An ARIA-E frequency of 24% was reported for donanemab, and its binding to CAA fibrils correlated with the amount of pyroglutamate-modified Aβ present. The findings of this study support the proposal that Aβ antibody-CAA interactions may relate to the ARIA-E frequency observed in patients treated with Aβ-based immunotherapies.

Altered amyloid-β structure markedly reduces gliosis in the brain of mice harboring the Uppsala APP deletion

Deposition of amyloid beta (Aβ) into plaques is a major hallmark of Alzheimer's disease (AD). Different amyloid precursor protein (APP) mutations cause early-onset AD by altering the production or aggregation properties of Aβ. We recently identified the Uppsala APP mutation (APPUpp), which causes Aβ pathology by a triple mechanism: increased β-secretase and altered α-secretase APP cleavage, leading to increased formation of a unique Aβ conformer that rapidly aggregates and deposits in the brain. The aim of this study was to further explore the effects of APPUpp in a transgenic mouse model (tg-UppSwe), expressing human APP with the APPUpp mutation together with the APPSwe mutation. Aβ pathology was studied in tg-UppSwe brains at different ages, using ELISA and immunohistochemistry. In vivo PET imaging with three different PET radioligands was conducted in aged tg-UppSwe mice and two other mouse models; tg-ArcSwe and tg-Swe. Finally, glial responses to Aβ pathology were studied in cell culture models and mouse brain tissue, using ELISA and immunohistochemistry. Tg-UppSwe mice displayed increased β-secretase cleavage and suppressed α-secretase cleavage, resulting in AβUpp42 dominated diffuse plaque pathology appearing from the age of 5-6 months. The γ-secretase cleavage was not affected. Contrary to tg-ArcSwe and tg-Swe mice, tg-UppSwe mice were [11C]PiB-PET negative. Antibody-based PET with the 3D6 ligand visualized Aβ pathology in all models, whereas the Aβ protofibril selective mAb158 ligand did not give any signals in tg-UppSwe mice. Moreover, unlike the other two models, tg-UppSwe mice displayed a very faint glial response to the Aβ pathology. The tg-UppSwe mouse model thus recapitulates several pathological features of the Uppsala APP mutation carriers. The presumed unique structural features of AβUpp42 aggregates were found to affect their interaction with anti-Aβ antibodies and profoundly modify the Aβ-mediated glial response, which may be important aspects to consider for further development of AD therapies.

A light at the end of the tunnel - from mutation identification to a potential treatment for Alzheimer's disease

Recent advances have driven the development of immunotherapies that act by either promoting or suppressing a patient's immune system to treat inflammation, autoimmune disease, cardiovascular disease, infectious diseases, and several cancers. In addition, research conducted over the past 25 years has identified therapeutic targets and indicated that immunotherapy could be used to treat Alzheimer's disease (AD). Despite a number of setbacks, this approach has now led to the development of the first disease-modifying treatments for this devastating disease. A key neuropathological feature of AD is the accumulation of a ~40-amino acid peptide known as amyloid β (Aβ) in the brain and cerebrovasculature. Our detection of an Aβ precursor protein mutation that caused early-onset AD in a Swedish family by enhancing Aβ protofibril formation sharpened the focus on soluble Aβ aggregates (oligomers and protofibrils) as viable therapeutic targets. Initial studies developed and tested a mouse monoclonal antibody (mAb158) with specific conformation-dependent binding to these soluble Aβ aggregates. Treatment with mAb158 selectively reduced Aβ protofibrils in the brain and cerebrospinal fluid of a transgenic mouse model of AD. A humanized version of mAb158 (lecanemab) subsequently entered clinical trials. Based on promising Phase 2 data showing plaque clearance and reduced cognitive decline, a Phase 3 trial found that lecanemab slowed decline on the primary cognitive endpoint by 27% over 18 months and also produced positive effects on secondary clinical endpoints and key biomarkers. In July 2023, the FDA granted lecanemab a full approval, and this therapeutic antibody will be marketed as Leqembi®. This represents a significant advance for patients with AD, although many challenges remain. In particular, it is now more important than ever to identify individuals who are vulnerable to AD, so that treatment can be initiated at an early stage in the disease process.

The interwoven fibril-like structure of amyloid-beta plaques in mouse brain tissue visualized using super-resolution STED microscopy

BACKGROUND

Standard neuropathologic analysis of Alzheimer's brain relies on traditional fluorescence microscopy, which suffers from limited spatial resolution due to light diffraction. As a result, it fails to reveal intricate details of amyloid plaques. While electron microscopy (EM) offers higher resolution, its extensive sample preparation, involving fixation, dehydration, embedding, and sectioning, can introduce artifacts and distortions in the complex brain tissue. Moreover, EM lacks molecular specificity and has limited field of view and imaging depth.

RESULTS

In our study, we employed super-resolution Stimulated Emission Depletion (STED) microscopy in conjunction with the anti-human APP recombinant antibody 1C3 fluorescently labelled with DyLightTM633 (1C3-DyLight633). This combination allowed us to visualize amyloidogenic aggregates in vitro and in brain sections from a 17-month-old 3×Tg-AD mouse with sub-diffraction limited spatial resolution. Remarkably, we achieved a spatial resolution of 29 nm in vitro and 62 nm in brain tissue sections, surpassing the capabilities of conventional confocal microscopy by 5-10 times. Consequently, we could discern individual fibrils within plaques, an achievement previously only possible with EM.

CONCLUSIONS

The utilization of STED microscopy represents a groundbreaking advancement in the field, enabling researchers to delve into the characterization of local mechanisms that underlie Amyloid (Aβ) deposition into plaques and their subsequent clearance. This unprecedented level of detail is especially crucial for comprehending the etiology of Alzheimer's disease and developing the next generation of anti-amyloid treatments. By facilitating the evaluation of drug candidates and non-pharmacological interventions aiming to reduce amyloid burden, STED microscopy emerges as an indispensable tool for driving scientific progress in Alzheimer's research.

Reduction of brain stem pathology and transient amelioration of early cognitive symptoms in transgenic mice treated with a monoclonal antibody against α-synuclein oligomers/protofibrils

Immunotherapy against alpha-synuclein (α-syn) is a promising novel treatment strategy for Parkinson's disease (PD) and related α-synucleinopathies. We have previously shown that systemic treatment with the monoclonal oligomer/protofibril-selective antibody mAb47 targeting cytotoxic α-syn leads to reduced central nervous system levels of such species as well as an indication of reduced late-stage symptoms in aged (Thy-1)-h[A30P] α-syn transgenic mice. Here, we performed an early-onset long-term treatment study with this antibody to evaluate effects on brain pathology and behavioral outcomes in the same mouse model. Compared to the placebo group, the treatment strongly reduced phosphorylated α-syn (pS129 α-syn) pathology in the upper brain stem. Moreover, a preserved recognition memory and risk assessment behavior could be seen in antibody-treated mice at six months of age, even although these effects were no longer significant at eleven months of age. Importantly, no evidence of inflammatory responses or other potential toxic effects was seen with the treatment. Taken together, this study supports the strategy to target α-syn oligomers/protofibrils with monoclonal antibodies to counteract early symptoms and slow down the progression of PD and other α-synucleinopathies.

The amyloid-β pathway in Alzheimer's disease: a plain language summary

WHAT IS THIS SUMMARY ABOUT?

This plain language summary of an article published in Molecular Psychiatry, reviews the evidence supporting the role of the amyloid-β (Aβ) pathway and its dysregulation in Alzheimer's disease (AD), and highlights the rationale for drugs targeting the Aβ pathway in the early stages of the disease.

WHY IS THIS IMPORTANT?

Aβ is a protein fragment (or peptide) that exists in several forms distinguished by their size, shape/structure, degree of solubility and disease relevance. The accumulation of Aβ plaques is a hallmark of AD. However, smaller, soluble aggregates of Aβ - including Aβ protofibrils - also play a role in the disease. Because Aβ-related disease mechanisms are complex, the diagnosis, treatment and management of AD should be reflective of and guided by up-to-date scientific knowledge and research findings in this area. This article describes the Aβ protein and its role in AD, summarizing the evidence showing that altered Aβ clearance from the brain may lead to the imbalance, toxic buildup and misfolding of the protein - triggering a cascade of cellular, molecular and systematic events that ultimately lead to AD.

WHAT ARE THE KEY TAKEAWAYS?

The physiological balance of brain Aβ levels in the context of AD is complex. Despite many unanswered questions, mounting evidence indicates that Aβ has a central role in driving AD progression. A better understanding of the Aβ pathway biology will help identify the best therapeutic targets for AD and inform treatment approaches.

Lecanemab, Aducanumab, and Gantenerumab - Binding Profiles to Different Forms of Amyloid-Beta Might Explain Efficacy and Side Effects in Clinical Trials for Alzheimer's Disease

Immunotherapy against amyloid-beta (Aβ) is a promising option for the treatment of Alzheimer's disease (AD). Aβ exists as various species, including monomers, oligomers, protofibrils, and insoluble fibrils in plaques. Oligomers and protofibrils have been shown to be toxic, and removal of these aggregates might represent an effective treatment for AD. We have characterized the binding properties of lecanemab, aducanumab, and gantenerumab to different Aβ species with inhibition ELISA, immunodepletion, and surface plasmon resonance. All three antibodies bound monomers with low affinity. However, lecanemab and aducanumab had very weak binding to monomers, and gantenerumab somewhat stronger binding. Lecanemab was distinctive as it had tenfold stronger binding to protofibrils compared to fibrils. Aducanumab and gantenerumab preferred binding to fibrils over protofibrils. Our results show different binding profiles of lecanemab, aducanumab, and gantenerumab that may explain clinical results observed for these antibodies regarding both efficacy and side effects.

Mutation analysis of disease causing genes in patients with early onset or familial forms of Alzheimer's disease and frontotemporal dementia

Background

Most dementia disorders have a clear genetic background and a number of disease genes have been identified. Mutations in the tau gene (MAPT) lead to frontotemporal dementia (FTD), whereas mutations in the genes for the amyloid-β precursor protein (APP) and the presenilins (PSEN1, PSEN2) cause early-onset, dominantly inherited forms of Alzheimer’s disease (AD).

Even if mutations causing Mendelian forms of these diseases are uncommon, elucidation of the pathogenic effects of such mutations have proven important for understanding the pathogenic processes. Here, we performed a screen to identify novel pathogenic mutations in known disease genes among patients undergoing dementia investigation.

Results

Using targeted exome sequencing we have screened all coding exons in eleven known dementia genes (PSEN1, PSEN2, APP, MAPT, APOE, GRN, TARDBP, CHMP2B, TREM2, VCP and FUS) in 102 patients with AD, FTD, other dementia diagnoses or mild cognitive impairment.

We found three AD patients with two previously identified pathogenic mutations in PSEN1 (Pro264Leu and Met146Val). In this screen, we also identified the recently reported APP mutation in two siblings with AD. This mutation, named the Uppsala mutation, consists of a six amino acid intra-amyloid β deletion.

In addition, we found several potentially pathogenic mutations in PSEN2, FUS, MAPT, GRN and APOE. Finally, APOE ε4 was prevalent in this patient group with an allele frequency of 54%.

Conclusions

Among the 102 screened patients, we found two disease causing mutations in PSEN1 and one in APP, as well as several potentially pathogenic mutations in other genes related to neurodegenerative disorders. Apart from giving important information to the clinical investigation, the identification of disease mutations can contribute to an increased understanding of disease mechanisms.

ABBV-0805, a novel antibody selective for soluble aggregated α-synuclein, prolongs lifespan and prevents buildup of α-synuclein pathology in mouse models of Parkinson's disease

A growing body of evidence suggests that aggregated α-synuclein, the major constituent of Lewy bodies, plays a key role in the pathogenesis of Parkinson's disease and related α-synucleinopathies. Immunotherapies, both active and passive, against α-synuclein have been developed and are promising novel treatment strategies for such disorders. Here, we report on the humanization and pharmacological characteristics of ABBV-0805, a monoclonal antibody that exhibits a high selectivity for human aggregated α-synuclein and very low affinity for monomers. ABBV-0805 binds to a broad spectrum of soluble aggregated α-synuclein, including small and large aggregates of different conformations. Binding of ABBV-0805 to pathological α-synuclein was demonstrated in Lewy body-positive post mortem brains of Parkinson's disease patients. The functional potency of ABBV-0805 was demonstrated in several cellular assays, including Fcγ-receptor mediated uptake of soluble aggregated α-synuclein in microglia and inhibition of neurotoxicity in primary neurons. In vivo, the murine version of ABBV-0805 (mAb47) displayed significant dose-dependent decrease of α-synuclein aggregates in brain in several mouse models, both in prophylactic and therapeutic settings. In addition, mAb47 treatment of α-synuclein transgenic mice resulted in a significantly prolonged survival. ABBV-0805 selectively targets soluble toxic α-synuclein aggregates with a picomolar affinity and demonstrates excellent in vivo efficacy. Based on the strong preclinical findings described herein, ABBV-0805 has been progressed into clinical development as a potential disease-modifying treatment for Parkinson's disease.

The Amyloid-β Pathway in Alzheimer's Disease

Breakthroughs in molecular medicine have positioned the amyloid-β (Aβ) pathway at the center of Alzheimer's disease (AD) pathophysiology. While the detailed molecular mechanisms of the pathway and the spatial-temporal dynamics leading to synaptic failure, neurodegeneration, and clinical onset are still under intense investigation, the established biochemical alterations of the Aβ cycle remain the core biological hallmark of AD and are promising targets for the development of disease-modifying therapies. Here, we systematically review and update the vast state-of-the-art literature of Aβ science with evidence from basic research studies to human genetic and multi-modal biomarker investigations, which supports a crucial role of Aβ pathway dyshomeostasis in AD pathophysiological dynamics. We discuss the evidence highlighting a differentiated interaction of distinct Aβ species with other AD-related biological mechanisms, such as tau-mediated, neuroimmune and inflammatory changes, as well as a neurochemical imbalance. Through the lens of the latest development of multimodal in vivo biomarkers of AD, this cross-disciplinary review examines the compelling hypothesis- and data-driven rationale for Aβ-targeting therapeutic strategies in development for the early treatment of AD.

Novel multivalent design of a monoclonal antibody improves binding strength to soluble aggregates of amyloid beta

Background

Amyloid-β (Aβ) immunotherapy is a promising therapeutic strategy in the fight against Alzheimer’s disease (AD). A number of monoclonal antibodies have entered clinical trials for AD. Some of them have failed due to the lack of efficacy or side-effects, two antibodies are currently in phase 3, and one has been approved by FDA. The soluble intermediate aggregated species of Aβ, termed oligomers and protofibrils, are believed to be key pathogenic forms, responsible for synaptic and neuronal degeneration in AD. Therefore, antibodies that can strongly and selectively bind to these soluble intermediate aggregates are of great diagnostic and therapeutic interest.

Methods

We designed and recombinantly produced a hexavalent antibody based on mAb158, an Aβ protofibril-selective antibody. The humanized version of mAb158, lecanemab (BAN2401), is currently in phase 3 clinical trials for the treatment of AD. The new designs involved recombinantly fusing single-chain fragment variables to the N-terminal ends of mAb158 antibody. Real-time interaction analysis with LigandTracer and surface plasmon resonance were used to evaluate the kinetic binding properties of the generated antibodies to Aβ protofibrils. Different ELISA setups were applied to demonstrate the binding strength of the hexavalent antibody to Aβ aggregates of different sizes. Finally, the ability of the antibodies to protect cells from Aβ-induced effects was evaluated by MTT assay.

Results

Using real-time interaction analysis with LigandTracer, the hexavalent design promoted a 40-times enhanced binding with avidity to protofibrils, and most of the added binding strength was attributed to the reduced rate of dissociation. Furthermore, ELISA experiments demonstrated that the hexavalent design also had strong binding to small oligomers, while retaining weak and intermediate binding to monomers and insoluble fibrils. The hexavalent antibody also reduced cell death induced by a mixture of soluble Aβ aggregates.

Conclusion

We provide a new antibody design with increased valency to promote binding avidity to an enhanced range of sizes of Aβ aggregates. This approach should be general and work for any aggregated protein or repetitive target.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40035-021-00258-x.

The Uppsala APP deletion causes early onset autosomal dominant Alzheimer's disease by altering APP processing and increasing amyloid β fibril formation

Point mutations in the amyloid precursor protein gene (APP) cause familial Alzheimer's disease (AD) by increasing generation or altering conformation of amyloid β (Aβ). Here, we describe the Uppsala APP mutation (Δ690-695), the first reported deletion causing autosomal dominant AD. Affected individuals have an age at symptom onset in their early forties and suffer from a rapidly progressing disease course. Symptoms and biomarkers are typical of AD, with the exception of normal cerebrospinal fluid (CSF) Aβ42 and only slightly pathological amyloid-positron emission tomography signals. Mass spectrometry and Western blot analyses of patient CSF and media from experimental cell cultures indicate that the Uppsala APP mutation alters APP processing by increasing β-secretase cleavage and affecting α-secretase cleavage. Furthermore, in vitro aggregation studies and analyses of patient brain tissue samples indicate that the longer form of mutated Aβ, AβUpp1-42_Δ19-24, accelerates the formation of fibrils with unique polymorphs and their deposition into amyloid plaques in the affected brain.

Heparanase overexpression impedes perivascular clearance of amyloid-β from murine brain: relevance to Alzheimer's disease

Defective amyloid-β (Aβ) clearance from the brain is a major contributing factor to the pathophysiology of Alzheimer's disease (AD). Aβ clearance is mediated by macrophages, enzymatic degradation, perivascular drainage along the vascular basement membrane (VBM) and transcytosis across the blood-brain barrier (BBB). AD pathology is typically associated with cerebral amyloid angiopathy due to perivascular accumulation of Aβ. Heparan sulfate (HS) is an important component of the VBM, thought to fulfill multiple roles in AD pathology. We previously showed that macrophage-mediated clearance of intracortically injected Aβ was impaired in the brains of transgenic mice overexpressing heparanase (Hpa-tg). This study revealed that perivascular drainage was impeded in the Hpa-tg brain, evidenced by perivascular accumulation of the injected Aβ in the thalamus of Hpa-tg mice. Furthermore, endogenous Aβ accumulated at the perivasculature of Hpa-tg thalamus, but not in control thalamus. This perivascular clearance defect was confirmed following intracortical injection of dextran that was largely retained in the perivasculature of Hpa-tg brains, compared to control brains. Hpa-tg brains presented with thicker VBMs and swollen perivascular astrocyte endfeet, as well as elevated expression of the BBB-associated water-pump protein aquaporin 4 (AQP4). Elevated levels of both heparanase and AQP4 were also detected in human AD brain. These findings indicate that elevated heparanase levels alter the organization and composition of the BBB, likely through increased fragmentation of BBB-associated HS, resulting in defective perivascular drainage. This defect contributes to perivascular accumulation of Aβ in the Hpa-tg brain, highlighting a potential role for heparanase in the pathogenesis of AD.

A randomized, double-blind, phase 2b proof-of-concept clinical trial in early Alzheimer's disease with lecanemab, an anti-Aβ protofibril antibody

BACKGROUND

Lecanemab (BAN2401), an IgG1 monoclonal antibody, preferentially targets soluble aggregated amyloid beta (Aβ), with activity across oligomers, protofibrils, and insoluble fibrils. BAN2401-G000-201, a randomized double-blind clinical trial, utilized a Bayesian design with response-adaptive randomization to assess 3 doses across 2 regimens of lecanemab versus placebo in early Alzheimer's disease, mild cognitive impairment due to Alzheimer's disease (AD) and mild AD dementia.

METHODS

BAN2401-G000-201 aimed to establish the effective dose 90% (ED90), defined as the simplest dose that achieves ≥90% of the maximum treatment effect. The primary endpoint was Bayesian analysis of 12-month clinical change on the Alzheimer's Disease Composite Score (ADCOMS) for the ED90 dose, which required an 80% probability of ≥25% clinical reduction in decline versus placebo. Key secondary endpoints included 18-month Bayesian and frequentist analyses of brain amyloid reduction using positron emission tomography; clinical decline on ADCOMS, Clinical Dementia Rating-Sum-of-Boxes (CDR-SB), and Alzheimer's Disease Assessment Scale-Cognitive Subscale (ADAS-Cog14); changes in CSF core biomarkers; and total hippocampal volume (HV) using volumetric magnetic resonance imaging.

RESULTS

A total of 854 randomized subjects were treated (lecanemab, 609; placebo, 245). At 12 months, the 10-mg/kg biweekly ED90 dose showed a 64% probability to be better than placebo by 25% on ADCOMS, which missed the 80% threshold for the primary outcome. At 18 months, 10-mg/kg biweekly lecanemab reduced brain amyloid (-0.306 SUVr units) while showing a drug-placebo difference in favor of active treatment by 27% and 30% on ADCOMS, 56% and 47% on ADAS-Cog14, and 33% and 26% on CDR-SB versus placebo according to Bayesian and frequentist analyses, respectively. CSF biomarkers were supportive of a treatment effect. Lecanemab was well-tolerated with 9.9% incidence of amyloid-related imaging abnormalities-edema/effusion at 10 mg/kg biweekly.

CONCLUSIONS

BAN2401-G000-201 did not meet the 12-month primary endpoint. However, prespecified 18-month Bayesian and frequentist analyses demonstrated reduction in brain amyloid accompanied by a consistent reduction of clinical decline across several clinical and biomarker endpoints. A phase 3 study (Clarity AD) in early Alzheimer's disease is underway.

TRIAL REGISTRATION

Clinical Trials.gov NCT01767311 .

Characterization of monomeric and soluble aggregated Aβ in Down's syndrome and Alzheimer's disease brains

The major characteristics of Alzheimer's disease (AD) are amyloid plaques, consisting of aggregated beta amyloid (Aβ) peptides, together with tau pathology (tangles, neuropil treads and dystrophic neurites surrounding the plaques), in the brain. Down's syndrome (DS) individuals are at increased risk to develop AD-type pathology; most DS individuals have developed substantial pathology already at the age of 40. DS individuals have an extra copy of chromosome 21, harbouring the amyloid precursor protein gene (APP). Our aim was to investigate the Aβ peptide pattern in DS and AD brains to investigate differences in their amyloid deposition and aggregation, respectively. Cortical tissue from patients with DS (with amyloid pathology), sporadic AD and controls were homogenized and fractionated into TBS (water soluble) and formic acid (water insoluble) fractions. Immunoprecipitation (IP) was performed using a variety of antibodies targeting different Aβ species including oligomeric Aβ. Mass spectrometry was then used to evaluate the presence of Aβ species in the different patient groups. A large number of Aβ peptides were identified including Aβ1-X, 2-X, 3-X, 4-X, 5-X, 11-X, and Aβ peptides extended N terminally of the BACE1 cleavage site and ending at amino 15 in the Aβ sequence APP/Aβ(-X to 15), as well as peptides post-translationally modified by pyroglutamate formation. Most Aβ peptides had higher abundance in AD and DS compared to controls, except the APP/Aβ(-X to 15) peptides which were most abundant in DS followed by controls and AD. Furthermore, the abundancies of AβX-40 and AβX-34 were increased in DS compared with AD. Aβ1-40, Aβ1-42, and Aβ4-42 were identified as the main constitutes of protofibrils (IP'd using mAb158) and higher relative Aβ1-42 signals were obtained compared with samples IP'd with 6E10 + 4G8, indicating that the protofibrils/oligomers were enriched with peptides ending at amino acid 42. All Aβ peptides found in AD were also present in DS indicating similar pathways of Aβ peptide production, degradation and accumulation, except for APP/Aβ(-X to 15). Likewise, the Aβ peptides forming protofibrils/oligomers in both AD and DS were similar, implying the possibility that treatment with clinical benefit in sporadic AD might also be beneficial for subjects with DS.

Fluorine-18-Labeled Antibody Ligands for PET Imaging of Amyloid-β in Brain

Antibodies are attractive as radioligands due to their outstanding specificity and high affinity, but their inability to cross the blood-brain barrier (BBB) limits their use for CNS targets. To enhance brain distribution, amyloid-β (Aβ) antibodies were fused to a transferrin receptor (TfR) antibody fragment, enabling receptor mediated transport across the BBB. The aim of this study was to label these bispecific antibodies with fluorine-18 and use them for Aβ PET imaging. Bispecific antibody ligands RmAb158-scFv8D3 and Tribody A2, both targeting Aβ and TfR, were functionalized with trans-cyclooctene (TCO) groups and conjugated with ¹⁸F-labeled tetrazines through an inverse electron demand Diels-Alder reaction performed at ambient temperature. ¹⁸F-labeling did not affect antibody binding in vitro, and initial brain uptake was high. Conjugates with the first tetrazine variant ([¹⁸F]T1) displayed high uptake in bone, indicating extensive defluorination, a problem that was resolved with the second and third tetrazine variants ([¹⁸F]T2 and [¹⁸F]T3). Although the antibody ligands' half-life in blood was too long to optimally match the physical half-life of fluorine-18 (t_1/2 = 110 min), [¹⁸F]T3-Tribody A2 PET seemed to discriminate transgenic mice (tg-ArcSwe) with Aβ deposits from wild-type mice 12 h after injection. This study demonstrates that ¹⁸F-labeling of bispecific, brain penetrating antibodies is feasible and, with further optimization, could be used for CNS PET imaging.

Discovery of rare variants associated with blood pressure regulation through meta-analysis of 1.3 million individuals

Genetic studies of blood pressure (BP) to date have mainly analyzed common variants (minor allele frequency > 0.05). In a meta-analysis of up to ~1.3 million participants, we discovered 106 new BP-associated genomic regions and 87 rare (minor allele frequency ≤ 0.01) variant BP associations (P < 5 × 10-8), of which 32 were in new BP-associated loci and 55 were independent BP-associated single-nucleotide variants within known BP-associated regions. Average effects of rare variants (44% coding) were ~8 times larger than common variant effects and indicate potential candidate causal genes at new and known loci (for example, GATA5 and PLCB3). BP-associated variants (including rare and common) were enriched in regions of active chromatin in fetal tissues, potentially linking fetal development with BP regulation in later life. Multivariable Mendelian randomization suggested possible inverse effects of elevated systolic and diastolic BP on large artery stroke. Our study demonstrates the utility of rare-variant analyses for identifying candidate genes and the results highlight potential therapeutic targets.

Aβ and tau prion-like activities decline with longevity in the Alzheimer's disease human brain

The hallmarks of Alzheimer's disease (AD) are the accumulation of Aβ plaques and neurofibrillary tangles composed of hyperphosphorylated tau. We developed sensitive cellular assays using human embryonic kidney-293T cells to quantify intracellular self-propagating conformers of Aβ in brain samples from patients with AD or other neurodegenerative diseases. Postmortem brain tissue from patients with AD had measurable amounts of pathological Aβ conformers. Individuals over 80 years of age had the lowest amounts of prion-like Aβ and phosphorylated tau. Unexpectedly, the longevity-dependent decrease in self-propagating tau conformers occurred in spite of increasing amounts of total insoluble tau. When corrected for the abundance of insoluble tau, the ability of postmortem AD brain homogenates to induce misfolded tau in the cellular assays showed an exponential decrease with longevity, with a half-life of about one decade over the age range of 37 to 99 years. Thus, our findings demonstrate an inverse correlation between longevity in patients with AD and the abundance of pathological tau conformers. Our cellular assays can be applied to patient selection for clinical studies and the development of new drugs and diagnostics for AD.

[Alzheimer's disease - the most common cause of dementia]

Alzheimer's disease is the most common cause of dementia. As many as 250,000 people in Sweden will have a dementia disease in 2050. The »amyloid cascade hypothesis« is a common model which explains how β-amyloid affects the function of the nerve cells. Alzheimer's disease has a long-lasting course and can present in typical and atypical forms. CSF analyses for »core AD CSF biomarkers« and synaptic proteins have been available for clinical diagnostics. PET scanning can detect either β-amyloid or tau aggregates in the brain of living humans. Current Alzheimer's disease therapy is based on two classes of cognition-enhancing drugs: acetylcholinesterase inhibitor and NMDA-receptor antagonist, which delays cognitive decline in most patients. The latest clinical development of potential therapy for Alzheimer's is active or passive immunotherapy against brain β-amyloid and tau, where several studies have shown varying but promising treatment effects. Non-pharmacological interventions in patients with AD aim to delay the loss of mental abilities, helping people to be independent in everyday life for as long as possible, and to increase their well-being and quality of life.

Improved Differential Diagnosis of Alzheimer's Disease by Integrating ELISA and Mass Spectrometry-Based Cerebrospinal Fluid Biomarkers

Background:

Alzheimer’s disease (AD) is diagnosed based on a clinical evaluation as well as analyses of classical biomarkers: Aβ₄₂, total tau (t-tau), and phosphorylated tau (p-tau) in cerebrospinal fluid (CSF). Although the sensitivities and specificities of the classical biomarkers are fairly good for detection of AD, there is still a need to develop novel biochemical markers for early detection of AD.

Objective:

We explored if integration of novel proteins with classical biomarkers in CSF can better discriminate AD from non-AD subjects.

Methods:

We applied ELISA, mass spectrometry, and multivariate modeling to investigate classical biomarkers and the CSF proteome in subjects (n = 206) with 76 AD patients, 74 mild cognitive impairment (MCI) patients, 11 frontotemporal dementia (FTD) patients, and 45 non-dementia controls. The MCI patients were followed for 4–9 years and 21 of these converted to AD, whereas 53 remained stable.

Results:

By combining classical CSF biomarkers with twelve novel markers, the area of the ROC curves (AUROCS) of distinguishing AD and MCI/AD converters from non-AD were 93% and 96%, respectively. The FTDs and non-dementia controls were identified versus all other groups with AUROCS of 96% and 87%, respectively.

Conclusions:

Integration of new and classical CSF biomarkers in a model-based approach can improve the identification of AD, FTD, and non-dementia control subjects.

Longitudinal cognitive decline in autosomal-dominant Alzheimer's disease varies with mutations in APP and PSEN1 genes

The purpose was to compare longitudinal cognitive changes in APP and PSEN1 gene mutation carriers and noncarriers from four autosomal-dominant Alzheimer's disease (ADAD) families across preclinical and early clinical stages of disease. Carriers (n = 34) with four different mutations (PSEN1_M146V, PSEN1_H163Y, APP_SWE, and APP_ARC) and noncarriers (n = 41) were followed up longitudinally with repeated cognitive assessments starting many years before the expected clinical onset. The relationship between cognition and years to expected clinical onset, education, age, and type of mutation was analyzed using mixed-effects models. Results showed an education-dependent and time-related cognitive decline with linear and quadratic predictors in mutation carriers. Cognitive decline began close to the expected clinical onset and was relatively rapid afterward in PSEN1 mutation carriers, whereas decline was slower and started earlier than 10 years before expected clinical onset in APP mutation carriers. In noncarriers, the decline was minimal across time in accordance with normal aging. These results suggest that phenotypes for onset and rate of cognitive decline vary with PSEN1 and APP genes, suggesting a behavioral heterogeneity in ADAD.

Genetic meta-analysis of diagnosed Alzheimer's disease identifies new risk loci and implicates Aβ, tau, immunity and lipid processing

Risk for late-onset Alzheimer's disease (LOAD), the most prevalent dementia, is partially driven by genetics. To identify LOAD risk loci, we performed a large genome-wide association meta-analysis of clinically diagnosed LOAD (94,437 individuals). We confirm 20 previous LOAD risk loci and identify five new genome-wide loci (IQCK, ACE, ADAM10, ADAMTS1, and WWOX), two of which (ADAM10, ACE) were identified in a recent genome-wide association (GWAS)-by-familial-proxy of Alzheimer's or dementia. Fine-mapping of the human leukocyte antigen (HLA) region confirms the neurological and immune-mediated disease haplotype HLA-DR15 as a risk factor for LOAD. Pathway analysis implicates immunity, lipid metabolism, tau binding proteins, and amyloid precursor protein (APP) metabolism, showing that genetic variants affecting APP and Aβ processing are associated not only with early-onset autosomal dominant Alzheimer's disease but also with LOAD. Analyses of risk genes and pathways show enrichment for rare variants (P = 1.32 × 10-7), indicating that additional rare variants remain to be identified. We also identify important genetic correlations between LOAD and traits such as family history of dementia and education.

Antibody-Based In Vivo PET Imaging Detects Amyloid-β Reduction in Alzheimer Transgenic Mice After BACE-1 Inhibition

Visualization of amyloid-β (Aβ) pathology with PET has become an important tool for making a specific clinical diagnosis of Alzheimer disease (AD). However, the available amyloid PET radioligands, such as ¹¹C-Pittsburgh compound B, reflect levels of insoluble Aβ plaques but do not capture soluble and protofibrillar Aβ forms. Furthermore, the plaque load appears to be fairly static during clinical stages of AD and may not be affected by Aβ-reducing treatments. The aim of the present study was to investigate whether a novel PET radioligand based on an antibody directed toward soluble aggregates of Aβ can be used to detect changes in Aβ levels during disease progression and after treatment with a β-secretase (BACE-1) inhibitor. Methods: One set of transgenic mice (tg-ArcSwe, a model of Aβ pathology) aged between 7 and 16 mo underwent PET with the Aβ protofibril-selective radioligand ¹²⁴I-RmAb158-scFv8D3 (where RmAb is recombinant mouse monoclonal antibody and scFv is single-chain variable fragment) to follow progression of Aβ pathology in the brain. A second set of tg-ArcSwe mice, aged 10 mo, were treated with the BACE-1 inhibitor NB-360 for 3 mo and compared with an untreated control group. A third set of tg-ArcSwe mice, also aged 10 mo, underwent PET as a baseline group. Brain tissue was isolated after PET to determine levels of Aβ by ELISA and immunohistochemistry. Results: The concentration of ¹²⁴I-RmAb158-scFv8D3, as measured in vivo with PET, increased with age and corresponded well with the ex vivo autoradiography and Aβ immunohistochemistry results. Mice treated with NB-360 showed significantly lower in vivo PET signals than untreated animals and were similar to the baseline animals. The decreased ¹²⁴I-RmAb158-scFv8D3 concentrations in NB-360-treated mice, as quantified with PET, corresponded well with the decreased Aβ levels measured in postmortem brain. Conclusion: Several treatments for AD are in phase 2 and 3 clinical trials, but the possibility of studying treatment effects in vivo on the important, nonfibrillar, forms of Aβ is limited. This study demonstrated the ability of the Aβ protofibril-selective radioligand ¹²⁴I-RmAb158-scFv8D3 to follow disease progression and detect treatment effects with PET imaging in tg-ArcSwe mice.

Efficient clearance of Aβ protofibrils in AβPP-transgenic mice treated with a brain-penetrating bifunctional antibody

Background

Amyloid-β (Aβ) immunotherapy is one of the most promising disease-modifying strategies for Alzheimer’s disease (AD). Despite recent progress targeting aggregated forms of Aβ, low antibody brain penetrance remains a challenge. In the present study, we used transferrin receptor (TfR)-mediated transcytosis to facilitate brain uptake of our previously developed Aβ protofibril-selective mAb158, with the aim of increasing the efficacy of immunotherapy directed toward soluble Aβ protofibrils.

Methods

Aβ protein precursor (AβPP)-transgenic mice (tg-ArcSwe) were given a single dose of mAb158, modified for TfR-mediated transcytosis (RmAb158-scFv8D3), in comparison with an equimolar dose or a tenfold higher dose of unmodified recombinant mAb158 (RmAb158). Soluble Aβ protofibrils and total Aβ in the brain were measured by enzyme-linked immunosorbent assay (ELISA). Brain distribution of radiolabeled antibodies was visualized by positron emission tomography (PET) and ex vivo autoradiography.

Results

ELISA analysis of Tris-buffered saline brain extracts demonstrated a 40% reduction of soluble Aβ protofibrils in both RmAb158-scFv8D3- and high-dose RmAb158-treated mice, whereas there was no Aβ protofibril reduction in mice treated with a low dose of RmAb158. Further, ex vivo autoradiography and PET imaging revealed different brain distribution patterns of RmAb158-scFv8D3 and RmAb158, suggesting that these antibodies may affect Aβ levels by different mechanisms.

Conclusions

With a combination of biochemical and imaging analyses, this study demonstrates that antibodies engineered to be transported across the blood-brain barrier can be used to increase the efficacy of Aβ immunotherapy. This strategy may allow for decreased antibody doses and thereby reduced side effects and treatment costs.

The Aβ protofibril selective antibody mAb158 prevents accumulation of Aβ in astrocytes and rescues neurons from Aβ-induced cell death

Background

Currently, several amyloid beta (Aβ) antibodies, including the protofibril selective antibody BAN2401, are in clinical trials. The murine version of BAN2401, mAb158, has previously been shown to lower the levels of pathogenic Aβ and prevent Aβ deposition in animal models of Alzheimer’s disease (AD). However, the cellular mechanisms of the antibody’s action remain unknown. We have recently shown that astrocytes effectively engulf Aβ₄₂ protofibrils, but store rather than degrade the ingested Aβ aggregates. In a co-culture set-up, the incomplete degradation of Aβ₄₂ protofibrils by astrocytes results in increased neuronal cell death, due to the release of extracellular vesicles, containing N-truncated, neurotoxic Aβ.

Methods

The aim of the present study was to investigate if the accumulation of Aβ in astrocytes can be affected by the Aβ protofibril selective antibody mAb158. Co-cultures of astrocytes, neurons, and oligodendrocytes, derived from embryonic mouse cortex, were exposed to Aβ₄₂ protofibrils in the presence or absence of mAb158.

Results

Our results demonstrate that the presence of mAb158 almost abolished Aβ accumulation in astrocytes. Consequently, mAb158 treatment rescued neurons from Aβ-induced cell death.

Conclusion

Based on these findings, we conclude that astrocytes may play a central mechanistic role in anti-Aβ immunotherapy.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1134-4) contains supplementary material, which is available to authorized users.

CRISPR/Cas9 Mediated Disruption of the Swedish APP Allele as a Therapeutic Approach for Early-Onset Alzheimer's Disease

The APPswe (Swedish) mutation in the amyloid precursor protein (APP) gene causes dominantly inherited Alzheimer’s disease (AD) as a result of increased β-secretase cleavage of the amyloid-β (Aβ) precursor protein. This leads to abnormally high Aβ levels, not only in brain but also in peripheral tissues of mutation carriers. Here, we selectively disrupted the human mutant APP^SW allele using CRISPR. By applying CRISPR/Cas9 from Streptococcus pyogenes, we generated allele-specific deletions of either APP^SW or APP^WT. As measured by ELISA, conditioned media of targeted patient-derived fibroblasts displayed an approximate 60% reduction in secreted Aβ. Next, coding sequences for the APP^SW-specific guide RNA (gRNA) and Cas9 were packaged into separate adeno-associated viral (AAV) vectors. Site-specific indel formation was achieved both in primary neurons isolated from APP^SW transgenic mouse embryos (Tg2576) and after co-injection of these vectors into hippocampus of adult mice. Taken together, we here present proof-of-concept data that CRISPR/Cas9 can selectively disrupt the APP^SW allele both ex vivo and in vivo—and thereby decrease pathogenic Aβ. Hence, this system may have the potential to be developed as a tool for gene therapy against AD caused by APPswe and other point mutations associated with increased Aβ.

Increased Levels of Extracellular Microvesicle Markers and Decreased Levels of Endocytic/Exocytic Proteins in the Alzheimer's Disease Brain

BACKGROUND

Alzheimer's disease (AD) is a chronic neurodegenerative disorder accounting for more than 50% of all dementia cases. AD neuropathology is characterized by the formation of extracellular plaques and intracellular neurofibrillary tangles consisting of aggregated amyloid-β and tau, respectively. The disease mechanism has only been partially elucidated and is believed to also involve many other proteins.

OBJECTIVE

This study intended to perform a proteomic profiling of post mortem AD brains and compare it with control brains as well as brains from other neurological diseases to gain insight into the disease pathology.

METHODS

Here we used label-free shotgun mass spectrometry to analyze temporal neocortex samples from AD, other neurological disorders, and non-demented controls, in order to identify additional proteins that are altered in AD. The mass spectrometry results were verified by antibody suspension bead arrays.

RESULTS

We found 50 proteins with altered levels between AD and control brains. The majority of these proteins were found at lower levels in AD. Pathway analyses revealed that several of the decreased proteins play a role in exocytic and endocytic pathways, whereas several of the increased proteins are related to extracellular vesicles. Using antibody-based analysis, we verified the mass spectrometry results for five representative proteins from this group of proteins (CD9, HSP72, PI42A, TALDO, and VAMP2) and GFAP, a marker for neuroinflammation.

CONCLUSIONS

Several proteins involved in exo-endocytic pathways and extracellular vesicle functions display altered levels in the AD brain. We hypothesize that such changes may result in disturbed cellular clearance and a perturbed cell-to-cell communication that may contribute to neuronal dysfunction and cell death in AD.

Erratum: Sequence data and association statistics from 12,940 type 2 diabetes cases and controls

This corrects the article DOI: 10.1038/sdata.2017.179.

Sequence data and association statistics from 12,940 type 2 diabetes cases and controls

To investigate the genetic basis of type 2 diabetes (T2D) to high resolution, the GoT2D and T2D-GENES consortia catalogued variation from whole-genome sequencing of 2,657 European individuals and exome sequencing of 12,940 individuals of multiple ancestries. Over 27M SNPs, indels, and structural variants were identified, including 99% of low-frequency (minor allele frequency [MAF] 0.1-5%) non-coding variants in the whole-genome sequenced individuals and 99.7% of low-frequency coding variants in the whole-exome sequenced individuals. Each variant was tested for association with T2D in the sequenced individuals, and, to increase power, most were tested in larger numbers of individuals (>80% of low-frequency coding variants in ~82 K Europeans via the exome chip, and ~90% of low-frequency non-coding variants in ~44 K Europeans via genotype imputation). The variants, genotypes, and association statistics from these analyses provide the largest reference to date of human genetic information relevant to T2D, for use in activities such as T2D-focused genotype imputation, functional characterization of variants or genes, and other novel analyses to detect associations between sequence variation and T2D.

Alpha-synuclein oligomer-selective antibodies reduce intracellular accumulation and mitochondrial impairment in alpha-synuclein exposed astrocytes

Background

Due to its neurotoxic properties, oligomeric alpha-synuclein (α-syn) has been suggested as an attractive target for passive immunization against Parkinson’s disease (PD). In mouse models of PD, antibody treatment has been shown to lower the levels of pathogenic α-syn species, including oligomers, although the mechanisms of action remain unknown. We have previously shown that astrocytes rapidly engulf α-syn oligomers that are intracellularly stored, rather than degraded, resulting in impaired mitochondria.

Methods

The aim of the present study was to investigate if the accumulation of α-syn in astrocytes can be affected by α-syn oligomer-selective antibodies. Co-cultures of astrocytes, neurons, and oligodendrocytes were derived from embryonic mouse cortex and exposed to α-syn oligomers or oligomers pre-incubated with oligomer-selective antibodies.

Results

In the presence of antibodies, the astrocytes displayed an increased clearance of the exogenously added α-syn, and consequently, the α-syn accumulation in the culture was markedly reduced. Moreover, the addition of antibodies rescued the astrocytes from the oligomer-induced mitochondrial impairment.

Conclusions

Our results demonstrate that oligomer-selective antibodies can prevent α-syn accumulation and mitochondrial dysfunction in cultured astrocytes.

An Expanded Genome-Wide Association Study of Type 2 Diabetes in Europeans

To characterize type 2 diabetes (T2D)-associated variation across the allele frequency spectrum, we conducted a meta-analysis of genome-wide association data from 26,676 T2D case and 132,532 control subjects of European ancestry after imputation using the 1000 Genomes multiethnic reference panel. Promising association signals were followed up in additional data sets (of 14,545 or 7,397 T2D case and 38,994 or 71,604 control subjects). We identified 13 novel T2D-associated loci (P < 5 × 10^-8), including variants near the GLP2R, GIP, and HLA-DQA1 genes. Our analysis brought the total number of independent T2D associations to 128 distinct signals at 113 loci. Despite substantially increased sample size and more complete coverage of low-frequency variation, all novel associations were driven by common single nucleotide variants. Credible sets of potentially causal variants were generally larger than those based on imputation with earlier reference panels, consistent with resolution of causal signals to common risk haplotypes. Stratification of T2D-associated loci based on T2D-related quantitative trait associations revealed tissue-specific enrichment of regulatory annotations in pancreatic islet enhancers for loci influencing insulin secretion and in adipocytes, monocytes, and hepatocytes for insulin action-associated loci. These findings highlight the predominant role played by common variants of modest effect and the diversity of biological mechanisms influencing T2D pathophysiology.

Efficient and inexpensive transient expression of multispecific multivalent antibodies in Expi293 cells

BACKGROUND

Immunotherapy is a very fast expanding field within drug discovery and, hence, rapid and inexpensive expression of antibodies would be extremely valuable. Antibodies are, however, difficult to express. Multifunctional antibodies with additional binding domains further complicate the expression. Only few protocols describe the production of tetravalent bispecific antibodies and all with limited expression levels..

METHODS

Here, we describe a protocol that can produce functional tetravalent, bispecific antibodies at around 22 mg protein/l to a low cost. The expression system is based on the Expi293 cells, which have been adapted to grow in denser cultures than HEK293 cells and gives higher expression yields. The new protocol transfects the Expi293 cells with PEI (which has a negligible cost).

RESULTS

The protocol has been used to generate multiple variants of tetra- and hexavalent bispecific antibodies with yields of around 22 mg protein/l within 10 days. All materials are commercially available and the implementation of the protocol is inexpensive and straightforward. The bispecific antibodies generated in our lab were capable of binding to all antigens with similar affinity as the original antibody. Two of the bispecific antibodies have also been used in transgenic mice as positron emission tomography (PET) ligands to successfully detect amyloid-beta (Aβ) aggregates in vivo.

CONCLUSIONS

This protocol is the first describing transfection of the human Expi293 cells with PEI. It can be used to generate functional multi-specific antibodies in high amounts. The use of biological drugs, and in particular multispecific antibodies, is rapidly increasing, hence improved protocols such as the one presented here are highly valuable.

Cognitive function in very old men does not correlate to biomarkers of Alzheimer's disease

Background

The Alzheimer’s disease (AD) brain displays atrophy with amyloid-β (Aβ) and tau deposition, whereas decreased Aβ42 and increased tau are measured in cerebrospinal fluid (CSF). The aim of this study was to relate cognitive performance to the degree of brain atrophy, CSF biomarker levels and neuropathology in a cohort of aged men.

Methods

Fifty-eight 86–92-year-old men from the Uppsala Longitudinal Study of Adult Men (ULSAM) cohort underwent cognitive testing, brain computed tomography and lumbar puncture. Atrophy was graded with established scales. Concentrations of CSF Aβ42, t-tau and p-tau were measured by ELISA. Thirteen brains were examined post mortem.

Results

Forty-six of the individuals were considered non-demented, whereas twelve were diagnosed with dementia, either at baseline (n = 4) or during follow-up (n = 8). When comparing subjects with and without dementia, there were no differences in the degree of atrophy, although the mini mental state examination (MMSE) scoring correlated weakly with the degree of medial temporal atrophy (MTA) (p = 0.04). Moreover, the CSF biomarker levels did not differ significantly between healthy (n = 27) and demented (n = 8) subjects (median values 715 vs 472 pg/ml for Aβ42, 414 vs 427 pg/ml for t-tau and 63 vs 60 pg/ml for p-tau). Similarly, there were no differences in the biomarker levels between individuals with mild (n = 24) and severe (n = 11) MTA (median values 643 vs 715 pg/ml for Aβ42, 441 vs 401 pg/ml for t-tau and 64 vs 53 pg/ml for p-tau). Finally, the neuropathological changes did not correlate with any of the other measures.

Conclusion

In this cohort of aged men only a weak correlation could be seen between cognitive performance and MTA, whereas the various neuroradiological, biochemical and neuropathological measures did not correlate with each other. Thus, AD biomarkers seem to be less informative in subjects of an advanced age.

Rare coding variants in PLCG2, ABI3, and TREM2 implicate microglial-mediated innate immunity in Alzheimer's disease

We identified rare coding variants associated with Alzheimer's disease in a three-stage case-control study of 85,133 subjects. In stage 1, we genotyped 34,174 samples using a whole-exome microarray. In stage 2, we tested associated variants (P < 1 × 10-4) in 35,962 independent samples using de novo genotyping and imputed genotypes. In stage 3, we used an additional 14,997 samples to test the most significant stage 2 associations (P < 5 × 10-8) using imputed genotypes. We observed three new genome-wide significant nonsynonymous variants associated with Alzheimer's disease: a protective variant in PLCG2 (rs72824905: p.Pro522Arg, P = 5.38 × 10-10, odds ratio (OR) = 0.68, minor allele frequency (MAF)cases = 0.0059, MAFcontrols = 0.0093), a risk variant in ABI3 (rs616338: p.Ser209Phe, P = 4.56 × 10-10, OR = 1.43, MAFcases = 0.011, MAFcontrols = 0.008), and a new genome-wide significant variant in TREM2 (rs143332484: p.Arg62His, P = 1.55 × 10-14, OR = 1.67, MAFcases = 0.0143, MAFcontrols = 0.0089), a known susceptibility gene for Alzheimer's disease. These protein-altering changes are in genes highly expressed in microglia and highlight an immune-related protein-protein interaction network enriched for previously identified risk genes in Alzheimer's disease. These genetic findings provide additional evidence that the microglia-mediated innate immune response contributes directly to the development of Alzheimer's disease.

A Low-Frequency Inactivating AKT2 Variant Enriched in the Finnish Population Is Associated With Fasting Insulin Levels and Type 2 Diabetes Risk

To identify novel coding association signals and facilitate characterization of mechanisms influencing glycemic traits and type 2 diabetes risk, we analyzed 109,215 variants derived from exome array genotyping together with an additional 390,225 variants from exome sequence in up to 39,339 normoglycemic individuals from five ancestry groups. We identified a novel association between the coding variant (p.Pro50Thr) in AKT2 and fasting plasma insulin (FI), a gene in which rare fully penetrant mutations are causal for monogenic glycemic disorders. The low-frequency allele is associated with a 12% increase in FI levels. This variant is present at 1.1% frequency in Finns but virtually absent in individuals from other ancestries. Carriers of the FI-increasing allele had increased 2-h insulin values, decreased insulin sensitivity, and increased risk of type 2 diabetes (odds ratio 1.05). In cellular studies, the AKT2-Thr50 protein exhibited a partial loss of function. We extend the allelic spectrum for coding variants in AKT2 associated with disorders of glucose homeostasis and demonstrate bidirectional effects of variants within the pleckstrin homology domain of AKT2.

Rapid amyloid-β oligomer and protofibril accumulation in traumatic brain injury

Deposition of amyloid-β (Aβ) is central to Alzheimer's disease (AD) pathogenesis and associated with progressive neurodegeneration in traumatic brain injury (TBI). We analyzed predisposing factors for Aβ deposition including monomeric Aβ40, Aβ42 and Aβ oligomers/protofibrils, Aβ species with pronounced neurotoxic properties, following human TBI. Highly selective ELISAs were used to analyze N-terminally intact and truncated Aβ40 and Aβ42, as well as Aβ oligomers/protofibrils, in human brain tissue, surgically resected from severe TBI patients (n = 12; mean age 49.5 ± 19 years) due to life-threatening brain swelling/hemorrhage within one week post-injury. The TBI tissues were compared to post-mortem AD brains (n = 5), to post-mortem tissue of neurologically intact (NI) subjects (n = 4) and to cortical biopsies obtained at surgery for idiopathic normal pressure hydrocephalus patients (iNPH; n = 4). The levels of Aβ40 and Aβ42 were not elevated by TBI. The levels of Aβ oligomers/protofibrils in TBI were similar to those in the significantly older AD patients and increased compared to NI and iNPH controls (P < 0.05). Moreover, TBI patients carrying the AD risk genotype Apolipoprotein E epsilon3/4 (APOE ε3/4; n = 4) had increased levels of Aβ oligomers/protofibrils (P < 0.05) and of both N-terminally intact and truncated Aβ42 (P < 0.05) compared to APOE ε3/4-negative TBI patients (n = 8). Neuropathological analysis showed insoluble Aβ aggregates (commonly referred to as Aβ plaques) in three TBI patients, all of whom were APOE ε3/4 carriers. We conclude that soluble intermediary Aβ aggregates form rapidly after TBI, especially among APOE ε3/4 carriers. Further research is needed to determine whether these aggregates aggravate the clinical short- and long-term outcome in TBI.

Large-scale genome-wide analysis identifies genetic variants associated with cardiac structure and function

BACKGROUND

Understanding the genetic architecture of cardiac structure and function may help to prevent and treat heart disease. This investigation sought to identify common genetic variations associated with inter-individual variability in cardiac structure and function.

METHODS

A GWAS meta-analysis of echocardiographic traits was performed, including 46,533 individuals from 30 studies (EchoGen consortium). The analysis included 16 traits of left ventricular (LV) structure, and systolic and diastolic function.

RESULTS

The discovery analysis included 21 cohorts for structural and systolic function traits (n = 32,212) and 17 cohorts for diastolic function traits (n = 21,852). Replication was performed in 5 cohorts (n = 14,321) and 6 cohorts (n = 16,308), respectively. Besides 5 previously reported loci, the combined meta-analysis identified 10 additional genome-wide significant SNPs: rs12541595 near MTSS1 and rs10774625 in ATXN2 for LV end-diastolic internal dimension; rs806322 near KCNRG, rs4765663 in CACNA1C, rs6702619 near PALMD, rs7127129 in TMEM16A, rs11207426 near FGGY, rs17608766 in GOSR2, and rs17696696 in CFDP1 for aortic root diameter; and rs12440869 in IQCH for Doppler transmitral A-wave peak velocity. Findings were in part validated in other cohorts and in GWAS of related disease traits. The genetic loci showed associations with putative signaling pathways, and with gene expression in whole blood, monocytes, and myocardial tissue.

CONCLUSION

The additional genetic loci identified in this large meta-analysis of cardiac structure and function provide insights into the underlying genetic architecture of cardiac structure and warrant follow-up in future functional studies.

FUNDING

For detailed information per study, see Acknowledgments.

Decreased HHV-6 IgG in Alzheimer's Disease

Human herpesviruses have previously been implicated in the pathogenesis of Alzheimer's disease (AD) but whether they are causal, facilitating, or confounding factors is yet to be established. A total of 50 AD subjects and 52 non-demented (ND) controls were analyzed in a multiplex assay for IgG reactivity toward herpes simplex virus (HSV), varicella zoster virus (VZV), cytomegalovirus (CMV), and human herpesvirus 6 (HHV-6). The HHV-6 IgG reactivity was significantly lower in AD subjects compared to ND controls, whereas there were no differences in HSV, VZV, or CMV antibody levels between the groups. Analysis of peripheral blood mononuclear cells with a subtype-specific HHV-6 PCR revealed no signs of reactivation, as AD and ND subjects presented with comparable HHV-6 DNA levels in PBMCs, and all positive samples were of subtype B. Whether HHV-6 is a factor in AD remains to be elucidated in future studies.

A bispecific Tribody PET radioligand for visualization of amyloid-beta protofibrils - a new concept for neuroimaging

Antibodies are highly specific for their target molecules, but their poor brain penetrance has restricted their use as PET ligands for imaging of targets within the CNS. The aim of this study was to develop an antibody-based radioligand, using the Tribody^TM format, for PET imaging of soluble amyloid-beta (Aβ) protofibrils, which are suggested to cause neurodegeneration in Alzheimer's disease. Antibodies, even when expressed in smaller engineered formats, are large molecules that do not enter the brain in sufficient amounts for imaging purposes. Hence, their transport across the blood-brain barrier (BBB) needs to be facilitated, for example through interaction with the transferrin receptor (TfR). Thus, a Fab fragment of the TfR antibody 8D3 was fused with two single chain variable fragments (scFv) of the Aβ protofibril selective antibody mAb158. Five Tribody^TM proteins (A1-A5) were generated with different linkers between the Fab-8D3 and scFv-158. All proteins bound to TfR and Aβ protofibrils in vitro. Three of the proteins (A1-A3) were radiolabeled with iodine-125 and studied ex vivo in wild-type (wt) and transgenic mice overexpressing human Aβ. The systemic pharmacokinetics were similar with half-lives in blood of around 9h for all three ligands. Brain concentrations at 2h were around 1% of the injected dose per gram brain tissue, which is similar to what is observed for small molecular radioligands and at least 10-fold higher than antibodies in general. At 72h, transgenic mice showed higher concentrations of radioactivity in the brain than wt mice (12, 15- and 16-fold for A1, A2 and A3 respectively), except in the cerebellum, an area largely devoid of Aβ pathology. A3 was then labelled with iodine-124 for in vivo positron emission tomography (PET) imaging. Brain concentrations were quantified in six different regions showing a clear distinction both quantitatively and visually between wt and transgenic mice and a good correlation with Aβ pathology. We have thus produced a recombinant, bispecific protein, actively transported into the brain, for PET imaging within the CNS. In a longer perspective, this technique may enable imaging of other proteins involved in neurodegenerative diseases for which imaging agents are completely lacking today.

Bivalent Brain Shuttle Increases Antibody Uptake by Monovalent Binding to the Transferrin Receptor

The blood-brain barrier (BBB) is an obstacle for antibody passage into the brain, impeding the development of immunotherapy and antibody-based diagnostics for brain disorders. In the present study, we have developed a brain shuttle for active transport of antibodies across the BBB by receptor-mediated transcytosis. We have thus recombinantly fused two single-chain variable fragments (scFv) of the transferrin receptor (TfR) antibody 8D3 to the light chains of mAb158, an antibody selectively binding to Aβ protofibrils, which are involved in the pathogenesis of Alzheimer's disease (AD). Despite the two TfR binders, a monovalent interaction with TfR was achieved due to the short linkers that sterically hinder bivalent binding to the TfR dimer. The design enabled efficient receptor-mediated brain uptake of the fusion protein. Two hours after administration, brain concentrations were 2-3% of the injected dose per gram brain, comparable to small molecular drugs and 80-fold higher than unmodified mAb158. After three days, fusion protein concentrations in AD transgenic mouse brains were 9-fold higher than in wild type mice, demonstrating high in vivo specificity. Thus, our innovative recombinant design markedly increases mAb158 brain uptake, which makes it a strong candidate for improved Aβ immunotherapy and as a PET radioligand for early diagnosis and evaluation of treatment effect in AD. Moreover, this approach could be applied to any target within the brain.

Mapping of Surface-Exposed Epitopes of In Vitro and In Vivo Aggregated Species of Alpha-Synuclein

Aggregated alpha-synuclein is the main component of Lewy bodies, intraneuronal deposits observed in Parkinson’s disease and dementia with Lewy bodies. The objective of the study was to identify surface-exposed epitopes of alpha-synuclein in vitro and in vivo formed aggregates. Polyclonal immunoglobulin Y antibodies were raised against short linear peptides of the alpha-synuclein molecule. An epitope in the N-terminal region (1–10) and all C-terminal epitopes (90–140) were found to be exposed in an indirect enzyme-linked immunosorbent assay (ELISA) using recombinant monomeric, oligomeric, and fibrillar alpha-synuclein. In a phospholipid ELISA, the N-terminus and mid-region of alpha-synuclein (i.e., 1–90) were associated with phosphatidylserine and thus occluded from antibody binding. The antibodies that reacted most strongly with epitopes in the in vitro aggregates (i.e., 1–10 and epitopes between positions 90–140) also labeled alpha-synuclein inclusions in brains from transgenic (Thy-1)-h[A30P] alpha-synuclein mice and Lewy bodies and Lewy neurites in brains of patients with alpha-synucleinopathies. However, differences in reactivity were observed with the C-terminal antibodies when brain tissue from human and transgenic mice was compared. Taken together, the study shows that although similar epitopes are exposed in both in vitro and in vivo formed alpha-synuclein inclusions, structural heterogeneity can be observed between different molecular species.