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Epitope Fingerprinting for Recognition of the Polyclonal Serum Autoantibodies of Alzheimer's Disease.

ABSTRACT: Autoantibodies (aAb) associated with Alzheimer's disease (AD) have not been sufficiently characterized and their exact involvement is undefined. The use of information technology and computerized analysis with phage display technology was used, in the present research, to map the epitope of putative self-antigens in AD patients. A 12-mer random peptide library, displayed on M13 phages, was screened using IgG from AD patients with two repetitions. Seventy-one peptides were isolated; however, only 10 were positive using the Elisa assay technique (Elisa Index > 1). The results showed that the epitope regions of the immunoreactive peptides, identified by phage display analysis, were on the exposed surfaces of the proteins. The putative antigens MAST1, Enah, MAO-A, X11/MINT1, HGF, SNX14, ARHGAP 11A, APC, and CENTG3, which have been associated with AD or have functions in neural tissue, may indicate possible therapeutic targets.

SUBMITTER: de Oliveira-Junior LC

PROVIDER: S-EPMC4568325 | biostudies-literature | 2015

REPOSITORIES: biostudies-literature

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Epitope Fingerprinting for Recognition of the Polyclonal Serum Autoantibodies of Alzheimer's Disease.

de Oliveira-Júnior Luiz Carlos LC Araújo Santos Fabiana de Almeida Fde A Goulart Luiz Ricardo LR Ueira-Vieira Carlos C

BioMed research international 20150831

Autoantibodies (aAb) associated with Alzheimer's disease (AD) have not been sufficiently characterized and their exact involvement is undefined. The use of information technology and computerized analysis with phage display technology was used, in the present research, to map the epitope of putative self-antigens in AD patients. A 12-mer random peptide library, displayed on M13 phages, was screened using IgG from AD patients with two repetitions. Seventy-one peptides were isolated; however, only ...[more]

PMID: 26417591

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Project description:Background: Recent efforts have described an immunogenic component to the pathobiology of Alzheimer's disease (AD) and Parkinson's disease (PD). However, current methods of studying fluid autoantibodies, such as enzyme-linked immunosorbent assays and immunohistochemistry, are hypothesis-driven and not optimal for discovering new autoantibody biomarkers by proteome-wide screening. Recently, we developed a general mass spectrometry-based approach to identify tissue-specific autoantibodies in serum, at a proteome-wide level. In this study, we adapted the method to explore novel autoantibody biomarkers in the cerebrospinal fluid (CSF) of AD and PD patients. Methods: CSF samples were obtained from 10 headache control individuals, 10 AD patients and 10 PD patients. Antibodies present in the CSF were isolated by immobilization to protein-G magnetic beads. These antibodies were incubated with a brain tissue extract, prepared from frontal cortex, pons, cerebellum and brain stem. Protein antigens captured by the protein-G magnetic bead-bound antibodies were digested with trypsin and analyzed using mass spectrometry. Autoantibody candidates were selected by 1) detection in one or less individuals of the control group and 2) identification in at least half of the patient groups. Results: There were 16 putative autoantibody biomarkers selected from the AD group. Glia-derived nexin autoantibody was detected in eight of ten AD patients and was absent in the control group. Other AD pathology-related targets were also identified, such as actin-interaction protein, quinone oxidoreductase, sushi repeat-containing protein, metalloproteinase inhibitor 2, IP3 receptor 1 and sarcoplasmic/endoplasmic reticulum calcium ATPase 2. An additional eleven autoantibody targets were also identified in the present experiment, although their link to AD is not clear. No autoantibodies in the PD group satisfied our selection criteria. Conclusion: Our unbiased mass spectrometry method was able to detect new putative CSF autoantibody biomarkers of AD. Further investigation into the involvement of humoral autoimmunity in AD and PD pathobiology may be warranted.

Project description:Systemic sclerosis (SSc) is a severe chronic autoimmune disease with high morbidity and mortality. Sera of patients with SSc contain a large variety of autoantibody (aab) reactivities. Among these are functionally active aab that bind to G protein-coupled receptors (GPCR) such as C-X-C motif chemokine receptor 3 (CXCR3) and 4 (CXCR4). Aab binding to the N-terminal portion of these two GPCRs have been shown to be associated with slower disease progression in SSc, especially deterioration of lung function. Aabs binding to GPCRs exhibit functional activities by stimulating or inhibiting GPCR signaling. The specific functional activity of aabs crucially depends on the epitopes they bind to. To identify the location of important epitopes on CXCR3 recognized by aabs from SSc patients, we applied an array of 36 overlapping 18-20mer peptides covering the entire CXCR3 sequence, comparing epitope specificity of SSc patient sera (N?=?32, with positive reactivity with CXCR3) to healthy controls (N?=?30). Binding of SSc patient and control sera to these peptides was determined by ELISA. Using a Bayesian model approach, we found increased binding of SSc patient sera to peptides corresponding to intracellular epitopes within CXCR3, while the binding signal to extracellular portions of CXCR3 was found to be reduced. Experimentally determined epitopes showed a good correspondence to those predicted by the ABCpred tool. To verify these results and to translate them into a novel diagnostic ELISA, we combined the peptides that represent SSc-associated epitopes into a single ELISA and evaluated its potential to discriminate SSc patients (N?=?31) from normal healthy controls (N?=?47). This ELISA had a sensitivity of 0.61 and a specificity of 0.85. Our data reveals that SSc sera preferentially bind intracellular epitopes of CXCR3, while an extracellular epitope in the N-terminal domain that appears to be target of aabs in healthy individuals is not bound by SSc sera. Based upon our results, we could devise a novel ELISA concept that may be helpful for monitoring of SSc patients.

Project description:BackgroundAlzheimer's disease (AD) is caused by many intertwining pathologies involving metabolic aberrations. Patients with metabolic syndrome (MetS) generally show hyperglycemia and dyslipidemia, which can lead to the formation of aldehydic adducts such as acrolein on peptides in the brain and blood. However, the pathogenesis from MetS to AD remains elusive.MethodsAn AD cell model expressing Swedish and Indiana amyloid precursor protein (APP-Swe/Ind) in neuro-2a cells and a 3xTg-AD mouse model were used. Human serum samples (142 control and 117 AD) and related clinical data were collected. Due to the involvement of MetS in AD, human samples were grouped into healthy control (HC), MetS-like, AD with normal metabolism (AD-N), and AD with metabolic disturbance (AD-M). APP, amyloid-beta (Aß), and acrolein adducts in the samples were analyzed using immunofluorescent microscopy, histochemistry, immunoprecipitation, immunoblotting, and/or ELISA. Synthetic Aß1-16 and Aß17-28 peptides were modified with acrolein in vitro and verified using LC-MS/MS. Native and acrolein-modified Aß peptides were used to measure the levels of specific autoantibodies IgG and IgM in the serum. The correlations and diagnostic power of potential biomarkers were evaluated.ResultsAn increased level of acrolein adducts was detected in the AD model cells. Furthermore, acrolein adducts were observed on APP C-terminal fragments (APP-CTFs) containing Aß in 3xTg-AD mouse serum, brain lysates, and human serum. The level of acrolein adducts was correlated positively with fasting glucose and triglycerides and negatively with high-density lipoprotein-cholesterol, which correspond with MetS conditions. Among the four groups of human samples, the level of acrolein adducts was largely increased only in AD-M compared to all other groups. Notably, anti-acrolein-Aß autoantibodies, especially IgM, were largely reduced in AD-M compared to the MetS group, suggesting that the specific antibodies against acrolein adducts may be depleted during pathogenesis from MetS to AD.ConclusionsMetabolic disturbance may induce acrolein adduction, however, neutralized by responding autoantibodies. AD may be developed from MetS when these autoantibodies are depleted. Acrolein adducts and the responding autoantibodies may be potential biomarkers for not only diagnosis but also immunotherapy of AD, especially in complication with MetS.

Dataset Information

Epitope Fingerprinting for Recognition of the Polyclonal Serum Autoantibodies of Alzheimer's Disease.

Publications

Epitope Fingerprinting for Recognition of the Polyclonal Serum Autoantibodies of Alzheimer's Disease.

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