Generation and Partial Characterization of Rabbit Monoclonal Antibody to Pyroglutamate Amyloid-β3-42 (pE3-Aβ)

Expression and immunogenicity analysis of the capsid proteins of porcine circovirus types 2 to 4

Porcine circovirus (PCV) comprises four types, PCV1, PCV2, PCV3, and PCV4, which belong to the Circovirus genus of the family Circoviridae. PCV1 is nonpathogenic, whereas PCV2, PCV3, and PCV4 can infect pigs and cause disease. However, due to a lack of experimental evidence, whether vaccines based on PCV capsid (Cap) can induce cross-reactivity against PCVs remains controversial. In this study, recombinant truncated capsids (rCaps) of PCV2, PCV3, and PCV4 were highly and efficiently expressed and purified, followed by the development and evaluation of antibodies against PCVs. The results showed that monovalent and trivalent antigens based on the recombinant Caps had adequate immunogenicity to stimulate specific antibodies against the corresponding protein and virus. Furthermore, antisera prepared from the recombinant Caps also cross-reacted with different PCVs. Therefore, recombinant proteins can be used as candidate antigens to develop vaccines and ELISA diagnostic kits. In addition, the antibodies prepared in this study are promising candidates for the simultaneous prevention and treatment of PCVs in the clinic.

The amyloid plaque proteome in early onset Alzheimer's disease and Down syndrome

Amyloid plaques contain many proteins in addition to beta amyloid (Aβ). Previous studies examining plaque-associated proteins have shown these additional proteins are important; they provide insight into the factors that drive amyloid plaque development and are potential biomarkers or therapeutic targets for Alzheimer's disease (AD). The aim of this study was to comprehensively identify proteins that are enriched in amyloid plaques using unbiased proteomics in two subtypes of early onset AD: sporadic early onset AD (EOAD) and Down Syndrome (DS) with AD. We focused our study on early onset AD as the drivers of the more aggressive pathology development in these cases is unknown and it is unclear whether amyloid-plaque enriched proteins differ between subtypes of early onset AD. Amyloid plaques and neighbouring non-plaque tissue were microdissected from human brain sections using laser capture microdissection and label-free LC-MS was used to quantify the proteins present. 48 proteins were consistently enriched in amyloid plaques in EOAD and DS. Many of these proteins were more significantly enriched in amyloid plaques than Aβ. The most enriched proteins in amyloid plaques in both EOAD and DS were: COL25A1, SMOC1, MDK, NTN1, OLFML3 and HTRA1. Endosomal/lysosomal proteins were particularly highly enriched in amyloid plaques. Fluorescent immunohistochemistry was used to validate the enrichment of four proteins in amyloid plaques (moesin, ezrin, ARL8B and SMOC1) and to compare the amount of total Aβ, Aβ40, Aβ42, phosphorylated Aβ, pyroglutamate Aβ species and oligomeric species in EOAD and DS. These studies showed that phosphorylated Aβ, pyroglutamate Aβ species and SMOC1 were significantly higher in DS plaques, while oligomers were significantly higher in EOAD. Overall, we observed that amyloid plaques in EOAD and DS largely contained the same proteins, however the amount of enrichment of some proteins was different in EOAD and DS. Our study highlights the significant enrichment of many proteins in amyloid plaques, many of which may be potential therapeutic targets and/or biomarkers for AD.

Innate immunity stimulation via CpG oligodeoxynucleotides ameliorates Alzheimer's disease pathology in aged squirrel monkeys

Alzheimer's disease is the most common cause of dementia and the only illness among the top 10 causes of death for which there is no disease-modifying therapy. The failure rate of clinical trials is very high, in part due to the premature translation of successful results in transgenic mouse models to patients. Extensive evidence suggests that dysregulation of innate immunity and microglia/macrophages plays a key role in Alzheimer's disease pathogenesis. Activated resident microglia and peripheral macrophages can display protective or detrimental phenotypes depending on the stimulus and environment. Toll-like receptors (TLRs) are a family of innate immune regulators known to play an important role in governing the phenotypic status of microglia. We have shown in multiple transgenic Alzheimer's disease mouse models that harnessing innate immunity via TLR9 agonist CpG oligodeoxynucleotides (ODNs) modulates age-related defects associated with immune cells and safely reduces amyloid plaques, oligomeric amyloid-β, tau pathology, and cerebral amyloid angiopathy (CAA) while promoting cognitive benefits. In the current study we have used a non-human primate model of sporadic Alzheimer's disease pathology that develops extensive CAA-elderly squirrel monkeys. The major complications in current immunotherapeutic trials for Alzheimer's disease are amyloid-related imaging abnormalities, which are linked to the presence and extent of CAA; hence, the prominence of CAA in elderly squirrel monkeys makes them a valuable model for studying the safety of the CpG ODN-based concept of immunomodulation. We demonstrate that long-term use of Class B CpG ODN 2006 induces a favourable degree of innate immunity stimulation without producing excessive or sustained inflammation, resulting in efficient amelioration of both CAA and tau Alzheimer's disease-related pathologies in association with behavioural improvements and in the absence of microhaemorrhages in aged elderly squirrel monkeys. CpG ODN 2006 has been well established in numerous human trials for a variety of diseases. The present evidence together with our earlier, extensive preclinical research, validates the beneficial therapeutic outcomes and safety of this innovative immunomodulatory approach, increasing the likelihood of CpG ODN therapeutic efficacy in future clinical trials.

Correlation of pyroglutamate amyloid β and ptau Ser202/Thr205 levels in Alzheimer's disease and related murine models

Senile plaques frequently contain Aβ-pE(3), a N-terminally truncated Aβ species that is more closely linked to AD compared to other Aβ species. Tau protein is highly phosphorylated at several residues in AD, and specifically phosphorylation at Ser202/Thr205 is known to be increased in AD. Several studies suggest that formation of plaques and tau phosphorylation might be linked to each other. To evaluate if Aβ-pE(3) and ptau Ser202/Thr205 levels correlate in human and transgenic AD mouse models, we analyzed human cortical and hippocampal brain tissue of different Braak stages as well as murine brain tissue of two transgenic mouse models for levels of Aβ-pE(3) and ptau Ser202/Thr205 and correlated the data. Our results show that Aβ-pE(3) formation is increased at early Braak stages while ptau Ser202/Thr205 mostly increases at later stages. Further analyses revealed strongest correlations between the two pathologies in the temporal, frontal, cingulate, and occipital cortex, however correlation in the hippocampus was weaker. Evaluation of murine transgenic brain tissue demonstrated a slow but steady increase of Aβ-pE(3) from 6 to 12 months of age in the cortex and hippocampus of APP_SL mice, and a very early and strong Aβ-pE(3) increase in 5xFAD mice. ptau Ser202/Thr205 levels increased at the age of 9 months in APP_SL mice and at 6 months in 5xFAD mice. Our results show that Aβ-pE(3) and ptau Ser202/Thr205 levels strongly correlate in human as well as murine tissues, suggesting that tau phosphorylation might be amplified by Aβ-pE(3).

Enhanced accumulation of N-terminally truncated Aβ with and without pyroglutamate-11 modification in parvalbumin-expressing GABAergic neurons in idiopathic and dup15q11.2-q13 autism

Autism, the most frequent neurodevelopmental disorder of a very complex etiopathology, is associated with dysregulation of cellular homeostatic mechanisms, including processing of amyloid-β precursor protein (APP). Products of APP processing — N-terminally truncated amyloid-β peptide (N-tr-Aβ) species — are accumulated in autism in neurons and glia in the cortex, cerebellum, and subcortical structures of the brain. This process in neurons is correlated with increased oxidative stress. Because abnormally high levels of N-tr-Aβ are detected in only a fraction of neurons in the prefrontal cortex, we applied immunocytochemical staining and confocal microscopy in autopsy brain material from idiopathic and chromosome 15q11.2-q13 duplication (dup-15) autism to measure the load of N-tr-Aβ in the cells and synapses and to identify the subpopulation of neurons affected by these pathophysiological processes. The peptides accumulated in autism are N-terminally truncated; therefore, we produced a new antibody against Aβ truncated at N-terminal amino acid 11 modified to pyroglutamate to evaluate the presence and distribution of this peptide species in autism. We also quantified and characterized the oligomerization patterns of the Aβ-immunoreactive peptides in autism and control frozen brain samples. We provide morphological evidence, that in idiopathic and dup-15 autism, accumulation of N-tr-Aβ with and without pyroglutamate-11 modified N-terminus affects mainly the parvalbumin-expressing subpopulation of GABAergic neurons. N-tr-Aβ peptides are accumulated in neurons’ cytoplasm and nucleus as well as in GABAergic synapses. Aβ peptides with both C-terminus 40 and 42 were detected by immunoblotting in frozen cortex samples, in the form of dimers and complexes of the molecular sizes of 18-24kD and 32-34kD. We propose that deposition of N-tr-Aβ specifically affects the functions of the parvalbumin-expressing GABAergic neurons and results in a dysregulation of brain excitatory–inhibitory homeostasis in autism. This process may be the target of new therapies.

Novel monoclonal antibody 3B8 specifically recognizes pyroglutamate-modified amyloid β 3-42 peptide in brain of AD patients and 3xTg-AD transgenic mice

In addition to the full-length beta-amyloid peptides (Aβ 1-40/42), several Aβ variants, truncated at their N- or C-termini and bearing different post-translational modifications, have been detected in the brain of Alzheimer´s disease (AD) patients. AβN3(pE), an Aβ peptide bearing an amino-terminal pyroglutamate at position 3, is a significant constituent of intracellular, extracellular and vascular Aβ deposits in brain tissue from individuals with AD and Down syndrome. Pioneering immunotherapy studies have primarily focused on the full-length Aβ peptide, disregarding the presence of N-truncated/modified species. However, in recent years, increasing attention has been directed towards AβN3(pE), in both pre-clinical studies and clinical trials. In the present study, we generated and characterized an anti-AβN3(pE) mouse monoclonal antibody (3B8) that recognizes amyloid aggregates in brain tissue from AD patients and in 3xTg-AD transgenic mice. To identify the epitope recognized by 3B8, a library of random heptapeptides fused to the minor coat protein of M13 phage was screened. Results from screening, along with those from ELISA assays against distinct Aβ fragments, suggest recognition of two conformational epitopes present in AβN3(pE) and Aβ 3-42, regardless of the glutamate-pyroglutamate modification. The novel 3B8 antibody may be useful in future therapeutic and diagnostic applications for AD.

Protein Substrates for Reaction Discovery: Site-Selective Modification with Boronic Acid Reagents

Chemical modification of natural proteins must navigate difficult selectivity questions in a complex polyfunctional aqueous environment, within a narrow window of acceptable conditions. Limits on solvent mixtures, pH, and temperature create challenges for most synthetic methods. While a protein's complex polyfunctional environment undoubtedly creates challenges for traditional reactions, we wondered if it also might create opportunities for pursuing new bioconjugation reactivity directly on protein substrates. This Account describes our efforts to date to discover and develop new and useful reactivity for protein modification by starting from an open-ended screen of potential transition-metal catalysts for boronic acid reactivity with a model protein substrate. By starting from a broad screen, we were hoping to take advantage of the very many potential reactive sites on even a small model protein. And perhaps more importantly, whole proteins as reaction screening substrates might exhibit uniquely reactive local environments, the results of a dense combination of functional groups that would be nearly impossible to mimic in a small-molecule context. This effort has resulted in the discovery of four new protein modification reactions with boronic acid reagents, including a remarkable modification of specific backbone N-H bonds. This histidine-directed Chan-Lam coupling, based on specific proximity of an imidazole and two amide groups, is one important example of powerful reactivity that depends on a combination of functional groups that proteins make possible. Other bioconjugation reactions uncovered include a three-component tyrosine metalation with rhodium(III), a nickel-catalyzed cysteine arylation, and an unusual ascorbate-mediated oxidative process for N-terminal modification. The remarkably broad scope of reactivity types encountered in this work is a testament to the breadth of boronic acid reactivity. It is also a demonstration of the diverse reactivities that are possible by the combined alteration of boronic acid structure and metal promoter. The discovery of specific backbone modification chemistry has been a broadly empowering reactivity. Pyroglutamate, a naturally occurring posttranslational modification, exhibits remarkably high reactivity in histidine-directed backbone modification, which allows us to treat pyroglutamate as a reactive bioorthogonal handle that is readily incorporated into proteins of interest by natural machinery. In another research direction, the development of a vinylogous photocleavage system has allowed us to view backbone modification as a photocaging modification which is released by exposure to light.

Recent advancements toward therapeutic vaccines against Alzheimer's disease

INTRODUCTION

Alzheimer's disease (AD) is a devastating neurodegenerative disease characterized by protein aggregates of amyloid β (Aβ) and tau. These proteins have normal physiological functions, but in AD, they undergo a conformational change and aggregate as toxic oligomeric and fibrillar species with a high β-sheet content.

AREAS COVERED

Active and passive immunotherapeutic approaches are among the most attractive methods for targeting misfolded Aβ and tau. Promising preclinical testing of various immunotherapeutic approaches has yet to translate to cognitive benefits in human clinical trials. Knowledge gained from these past failures has led to the development of second-generation Aβ-active immunotherapies, anti-Aβ monoclonal antibodies targeting a wide array of Aβ conformations, and to a number of immunotherapies targeting pathological tau. This review covers the more recent advances in vaccine development for AD from 2016 to present.

EXPERT COMMENTARY

Due to the complex pathophysiology of AD, greatest clinical efficacy will most likely be achieved by concurrently targeting the most toxic forms of both Aβ and tau.