Characterization of natural antigen-specific antibodies from naïve sturgeon serum

In this study, we isolated and characterized natural antibodies found in serum samples from Bester sturgeon (Huso huso × Acipenser ruthenus). Natural antibodies specifically detected hen egg lysozyme (HEL), keyhole limpet hemocyanin (KLH), and several species of pathogenic bacteria. Interestingly, we detected no antibodies with similar specificity in serum samples from rainbow trout (Oncorhynchus mykiss) or from Japanese flounder (Paralichthys olivaceus). Binding capacity of the sturgeon natural serum antibodies increased slightly at 7 months compared to 3 months after hatching. Antigen-specific antibodies against KLH, Aeromonas hydrophila and Streptococcus iniae were affinity-fractionated from naive sera of Bester sturgeon; specific detection of the corresponding antigens was observed. We conclude that Bester sturgeon are capable of generating unique natural antibodies including those that are pathogen-specific.

A proteolytic method for evaluating O-GlcNAcylation on proteins of similar molecular weight to antibody heavy chain after immunoprecipitation

Investigating a protein of interest that runs at the same molecular weight as antibody heavy chain is a frequent deterrent to its evaluation by immunoprecipitation. Methods of minimizing the detection of the immunoprecipitating antibody are available. However, these still present a barrier to evaluating if intracellular proteins are modified by the O-GlcNAc post-translation protein modification due to interfering glycosylation on antibodies. IdeZ protease specifically cleaves antibody at the hinge region, allowing collapse of the antibody fragments to 25 kDa after denaturation. Thus, this proteolytic method uniquely allows evaluation of O-GlcNAcylation of proteins of interest formerly obscured by antibody heavy chain.

Immunoprecipitation of Acetyl-lysine And Western Blotting of Long-chain acyl-CoA Dehydrogenases and Beta-hydroxyacyl-CoA Dehydrogenase in Palmitic Acid Treated Human Renal Tubular Epithelial Cells

As one of the main energy metabolism organs, kidney has been proved to have high energy requirements and are more inclined to fatty acid metabolism as the main energy source. Long-chain acyl-CoA dehydrogenases (LCAD) and beta-hydroxyacyl-CoA dehydrogenase (beta-HAD), key enzymes involved in fatty acid oxidation, has been identified as the substrate of acetyltransferase GCN5L1 and deacetylase Sirt3. Acetylation levels of LCAD and beta-HAD regulate its enzymes activity and thus affect fatty acid oxidation rate. Moreover, immunoprecipitation is a key assay for the detection of LCAD and beta-HAD acetylation levels. Here we describe a protocol of immunoprecipitation of acetyl-lysine and western blotting of LCAD and beta-HAD in palmitic acid treated HK-2 cells (human renal tubular epithelial cells). The scheme provides the readers with clear steps so that this method could be applied to detect the acetylation level of various proteins.

In Vivo Crosslinking of Histone and RNA-Binding Proteins

Protein-protein interactions are essential in various cellular processes including regulation of gene expression, formation of protein complexes, and cellular signaling transduction. In particular, several proteins in the nucleus interact to regulate transcription and RNA splicing. These protein-protein interactions are short and weak and occur through transient processes, making it difficult to identify these interactions. In addition, detection of interacting partners in vitro using cell lysates cannot provide complete information due to the loss of spatial organization and changes in protein modification. Here we describe an in vivo crosslinking technique using disuccinimidyl suberate (DSS), which is useful to capture and stabilize proteins to analyze the interacting proteins.

Anti-Myelin Proteolipid Protein Peptide Monoclonal Antibodies Recognize Cell Surface Proteins on Developing Neurons and Inhibit Their Differentiation

Using a panel of monoclonal antibodies (mAbs) to myelin proteolipid protein (PLP) peptides, we found that in addition to CNS myelin, mAbs to external face but not cytoplasmic face epitopes immunostained neurons in immature human CNS tissues and in adult hippocampal dentate gyrus and olfactory bulbs, that is neural stem cell niches (NSCN). To explore the pathobiological significance of these observations, we assessed the mAb effects on neurodifferentiation in vitro. The mAbs to PLP 50-69 (IgG1κ and IgG2aκ), and 178-191 and 200-219 (both IgG1κ) immunostained live cell surfaces and inhibited neurite outgrowth of E18 rat hippocampal precursor cells and of PC12 cells, which do not express PLP. Proteins immunoprecipitated from PC12 cell extracts and captured by mAb-coated magnetic beads were identified by GeLC-MS/MS. Each neurite outgrowth-inhibiting mAb captured a distinct set of neurodifferentiation molecules including sequence-similar M6 proteins and other unrelated membrane and extracellular matrix proteins, for example integrins, Eph receptors, NCAM-1, and protocadherins. These molecules are expressed in adult human NSCN and are implicated in the pathogenesis of many chronic CNS disease processes. Thus, diverse anti-PLP epitope autoantibodies may inhibit neuronal precursor cell differentiation via multispecific recognition of cell surface molecules thereby potentially impeding endogenous neuroregeneration in NSCN and in vivo differentiation of exogenous neural stem cells.

CD11d is a novel antigen on chicken leukocytes

In life sciences, antibodies are among the most commonly used tools for identifying, tracking, quantifying and isolating molecules, mainly proteins. However, it has recently become clear that antibodies often fall short with respect to specificity and selectivity and in many cases target proteins are not even known. When commercial availability of antibodies is scarce, e.g. for targeting proteins from farm animals, researchers face additional challenges: they often have to rely on cross-reactive antibodies, which are poorly characterized for their exact target, their actual cross-reactivity and the desired application. In this study, we aimed at identifying the true target of mouse monoclonal antibody 8F2, which was generated against chicken PBMC and used for decades in research, while it's actual target molecule remained unknown. We used 8F2 antibody for immunoprecipitation in chicken PBMC and subsequently identified its true target as CD11d, which was never described in chicken lymphocytes before, by quantitative LC-MSMS. The most abundant interactor of CD11d was identified as integrin beta 2. The existence of this alpha integrin was therefore clearly proven on protein level and provides a first basis to further assess the role of CD11d in chickens in future studies. Data are available via ProteomeXchange with identifier PXD017248. SIGNIFICANCE: Our studies determined CD11d as the true target of a previously uncharacterized mouse monoclonal antibody 8F2, generated against chicken peripheral blood derived mononuclear cells (PBMC). This is therefore now first member of alpha integrins in chickens, that existence was now clearly identified on protein level. The additional identification of CD11d interactors provides information on integrin-dependent regulation of signaling networks, allowing further functional studies.

The leucine-rich repeat domain of human peroxidasin 1 promotes binding to laminin in basement membranes

Human peroxidasin 1 (PXDN) is a homotrimeric multidomain heme peroxidase and essential for tissue development and architecture. It has a biosynthetic function and catalyses the hypobromous acid-mediated formation of specific covalent sulfilimine (SN) bonds, which cross-link type IV collagen chains in basement membranes. Currently, it is unknown whether and which domain(s) [i.e. leucine-rich repeat domain (LRR), immunoglobulin domains, peroxidase domain, von Willebrand factor type C domain] of PXDN interact with the polymeric networks of the extracellular matrix (ECM), and how these interactions integrate and regulate the enzyme's cross-linking activity, without imparting oxidative damage to the ECM. In this study, we probed the interactions of four PXDN constructs with different domain compositions with components of a basement membrane extract by immunoprecipitation. Strong binding of the LRR-containing construct was detected with the major ECM protein laminin. Analysis of these interactions by surface plasmon resonance spectroscopy revealed similar kinetics and affinities of binding of the LRR-containing construct to human and murine laminin-111, with calculated dissociation constants of 1.0 and 1.5 μM, respectively. The findings are discussed with respect to the recently published in-solution structures of the PXDN constructs and the proposed biological role of this peroxidase.

Identification of novel interacting partners of the NEDD4 ubiquitin ligase in mouse testis

Posttranslational modification by ubiquitination targets proteins for degradation, recycling, stabilization or altered trafficking, and as such can alter cellular signaling pathways. The substrate specificity of this multistep process is controlled by ubiquitin ligases, including those of the HECT domain-containing NEDD4 family. In the testis, ubiquitination of many proteins contributes to organ development and maturation of spermatozoa and NEDD4 is known to be important in the control of spermatogonial stem cell homeostasis. However, a comprehensive understanding of NEDD4 substrates in testis development is lacking. Here we demonstrate high expression of Nedd4 in somatic cells of the mouse testis and in the murine Leydig cell-like cell line TM3. Immunoprecipitation of NEDD4 tagged with GFP at either the amino or carboxyl terminus was subjected to proteomic analysis for interacting proteins. We identified a substantial list of potential interaction partners, including known NEDD4 substrates, proteins involved in ubiquitination and proteins important for testis development and spermatogenesis. We confirmed the interaction of NEDD4 with a subset of these putative interacting proteins, validating the integrity of the dataset. These potential interactors may be further explored to reveal important roles of NEDD4-mediated ubiquitination in the testis. SIGNIFICANCE: Ubiquitination is important for testis development and function, and NEDD4 is known to ubiquitinate various proteins to affect cellular signaling and development, including those implicated in spermatogenesis. However, substrates of NEDD4 that are important during testis development remain to be identified. Here we report NEDD4 expression in the developing testis and TM3 testicular cell line. This study identifies a substantial list of NEDD4 interacting proteins in the TM3 testicular cell line, with validation of some of these interactions. Hence, this provides novel NEDD4 targets that may contribute to testis development and function that may be further explored.

Identification of host cell proteins that interact with the M protein of porcine epidemic diarrhea virus

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Interaction of PEDV M protein with host cellular proteins eIF3L, CDC42 and Rab11A was confirmed.

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PEDV replication may be regulated by eIF3L expression.

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218 host cell proteins were designated putative PEDV M protein interacting proteins.

Porcine epidemic diarrhea virus (PEDV) is a coronavirus that causes severe diarrhea in pigs of all ages and a high fatality rate in neonates. The PEDV membrane protein (M) plays crucial roles in viral assembly, viral budding and host immune regulation, most likely by interacting with host cell proteins that have yet to be identified. In this study, co-immunoprecipitation (Co-IP) using an M-specific monoclonal antibody, coupled with LC-MS/MS, was employed to identify M protein-interacting proteins in PEDV-infected cells. Three viral proteins (S, E and ORF3) and 218 host cell proteins were identified as putative M-interacting partners. Bioinformatic analysis showed that the identified host cell proteins were related to 131 signal pathways and 10 biological processes. In addition, interaction between translation initiation factor 3(eIF3L) and M protein was validated by Co-IP. Down-regulation of eIF3L expression significantly increased viral production, which suggests that eIF3L could be a negative regulator in PEDV replication. This interactome study of the PEDV M protein will serve to clarify its function during viral replication.

Immunoprecipitation for the Analysis of Macromolecular Complexes in Trypanosoma cruzi

Immunoprecipitation is a helpful tool to assess interactions between proteins and proteins or nucleic acids (DNA or RNA). Its principle consists in capturing and enriching one or multiple target proteins from a complex sample with a specific antibody conjugated to a solid matrix and isolating the RNA and/or protein molecules associated to those target(s) group of proteins that can be further identified by advanced techniques such as RNA-seq and/or mass spectrometry. Since this technique allows for identifying, mapping, and checking new protein-protein and protein-RNA interactions, its use is very convenient in situations where many proteins remain with their functions uncharacterized, as is the case of the protozoan Trypanosoma cruzi. Here we describe a protocol that is based on the cryogrinding method for cell lysis and the use of antibodies conjugated to magnetic beads to capture and purify protein complexes in a robust and efficient way.

Towards mechanized biparametric ceruloplasmin assay

Two analytical strategies for determination of both biocatalytic activity and concentration of ceruloplasmin conditions have been proposed. For this purpose, two constructions of fully-mechanized Multicommutated Flow Analysis (MCFA) systems were designed. The versatility of solenoid pumps and valves arrangement enabled to construct both manifolds using similar flow units, taking into account the different requirements for each method. In the case of ceruloplasmin catalytic activity assay, the kinetic measurements with the use of p-phenylenediamine and hydrogen peroxide were performed. The optimization process was focused on the selection of substrate and oxidizer concentration, incubation time as well as solving the issue of substrate autoxidation. It led to the development of the flow bioanalytical system characterized by following analytical parameters: LOD - 0.07 U mL^{- 1}, LOQ - 0.38 U mL^-1, RSD ≤6% with 8 μL consumption of human serum. In turn, for examination of ceruloplasmin concentration, the light-scattering detector was used in MCFA system adapted for immunoprecipitation measurements. In this case, the use of potentiator (polyethylene glycol) turned out to be necessary to obtain satisfactory analytical signals. Such a method allowed to obtain 35 measurements per hour with LOD and LOQ of 0.9 mg L^-1 and 3.2 mg L^-1, respectively. The usefulness of both MCFA systems was successfully examined by performing analyses of real human serum samples.

Scaffold attachment factor B: distribution and interaction with ERα in the rat brain

Scaffold attachment factor (SAFB) 1 and its homologue SAFB2 are multifunctional proteins that are involved in various cellular mechanisms, including chromatin organization and transcriptional regulation, and are also corepressors of estrogen receptor alpha (ERα). Both SAFBs are expressed at high levels in the brain. However, the distributions of SAFB1 and SAFB2 have yet to be characterized in detail and it is unclear whether both proteins interact with ERα in the brain. In this study, we investigated the expression and distribution of both SAFBs and their interaction with ERα in adult male rat brain. Immunohistochemical staining showed that SAFB1 and SAFB2 have a similar distribution pattern and are widely expressed throughout the brain. Double-fluorescence immunohistochemical and immunocytochemical analyses in primary cultures showed that the two SAFB proteins are localized in nuclei of neurons, astrocytes, and oligodendrocytes. Of note, SAFB2 was also found in cytoplasmic regions in these cell lineages. Both SAFB proteins were also expressed in ERα-positive cells in the medial preoptic area (MPOA) and arcuate and ventromedial hypothalamic nuclei. Co-immunoprecipitation experiments revealed that both SAFB proteins from the MPOA reciprocally interact with endogenous ERα. These results indicate that, in addition to a role in basal cellular function in the brain, the SAFB proteins may serve as ERα corepressors in hormone-sensitive regions.

Assessing Self-interaction of Mammalian Nuclear Proteins by Co-immunoprecipitation

Protein-protein interactions constitute the molecular foundations of virtually all biological processes. Co-immunoprecipitation (CoIP) experiments are probably the most widely used method to probe both heterotypic and homotypic protein-protein interactions. Recent advances in super-resolution microscopy have revealed that several nuclear proteins such as transcription factors are spatially distributed into local high-concentration clusters in mammalian cells, suggesting that many nuclear proteins self-interact. These observations have further underscored the need for orthogonal biochemical approaches for testing if self-association occurs, and if so, what the mechanisms are. Here, we describe a CoIP protocol specifically optimized to test self-association of endogenously tagged nuclear proteins (self-CoIP), and to evaluate the role of nucleic acids in such self-interaction. This protocol has proven reliable and robust in our hands, and it can be used to test both homotypic and heterotypic (CoIP) protein-protein interactions.

Mass Spectrometry-Based Analysis of TRPP2 Phosphorylation

Differential phosphorylation of proteins is a key regulatory mechanism in biology. Immunoprecipitation-coupled mass spectrometry facilitates the targeted analysis of transient receptor ion potential channel polycystin-2 (TRPP2) phosphorylation. However, empirical testing is required to optimize experimental conditions for immunoprecipitation and mass spectrometry. Here, we present a detailed workflow for the reliable analysis of endogenous TRPP2 phosphorylation in differentiated renal epithelial cells.

Monitoring MHC Ubiquitination by MARCH Ubiquitin Ligases

Ubiquitination is a reversible process that controls the intracellular transport of many transmembrane molecules. Ubiquitination of MHC I, MHC II, and CD1a by different members of the MARCH family of E3 ubiquitin ligases is a key event in the regulation of the potent immunostimulatory properties of activated dendritic cells. We describe here methods to monitor and quantify the ubiquitination levels of these different antigen presentation molecules and its impact on their cell surface accumulation.

Quantitative Mass Spectrometric Assay of Whole and CNBr-Cleaved Amyloid-β Peptides in Human Brain

Various amyloid-β (Aβ) peptides accumulate in brain in Alzheimer's disease, and the amounts of specific peptide variants may have pathological significance. The quantitative determination of these variants is challenging because losses inevitably occur during tissue processing and analysis. This report describes the use of stable-isotope-labeled Aβ peptides as internal standards for quantitative mass spectrometric assays, and the use of cyanogen bromide (CNBr) to remove C-terminal residues beyond Met35. The removal of residues beyond Met35 reduces losses due to aggregation, and facilitates the detection of post-translationally modified Aβ peptides. Results from 8 human brain samples suggest that the tissue concentrations of the 42-residue Aβ peptide tend to be similar in different patients. Concentrations of the 40-residue Aβ peptide are more variable, and may be greater or lesser than the 42-residue peptide. The concentration of the CNBr cleavage product closely matches the sum of the 40-residue and 42-residue peptide concentrations, indicating that these two Aβ peptides account for most of the C-terminal variants in these patients. CNBr treatment facilitated the detection of post-translational modifications such as pyroglutamyl and hexose-modified Aβ peptides.

Double-Stranded RNA Pull-Down to Characterize Viral Replication Complexes in Plants

Plant RNA viruses are obligate intracellular parasites that hijack specific cellular membranes to replicate their genomes in what are commonly known as viral replication complexes (VRC). These contain host- and virus-encoded proteins and viral RNA. Double-stranded RNA (dsRNA) is a mandatory intermediate of RNA replication and a hallmark feature of VRCs. We have recently developed a method to isolate viral dsRNA and its associated proteins through pull-down of an ectopically expressed dsRNA-binding protein (B2:GFP) from infected Arabidopsis thaliana plants. After mass spectrometry analysis to identify the dsRNA-associated proteins, resulting candidate proteins of interest are tagged with a red fluorescent protein and their subcellular localization in relation to VRCs is assessed by transient expression within leaves of B2:GFP-transgenic Nicotiana benthamiana plants. In this chapter we describe in detail these experimental procedures to allow investigators to characterize the replication complexes of their plant RNA virus of interest.

Detection of Phosphorylation on Immunoprecipitates from Total Protein Extracts of Arabidopsis thaliana Seedlings

Phosphorylation is a versatile posttranslational modification that can regulate the localization, stability, and conformation of proteins; protein-protein interactions; and enzyme activities. Phosphorylation of plasma membrane proteins, for example, can serve as recognition signals for ubiquitin ligases and hence can trigger its endocytic degradation. Key determinants of protein phosphorylation are kinases and phosphatases that are spatiotemporally regulated to phosphorylate or dephosphorylate specific target proteins. To understand the dynamics and regulatory mechanisms of protein phosphorylation, it is essential to analyze the phosphorylation status of the proteins and identify phosphorylation sites as well as the modifying enzymes. In this chapter, we describe methods that can be used for the detection of phosphoproteins that are immunoprecipitated from Arabidopsis total extracts.

Immunoprecipitation of DNA:RNA Hybrids Using the S9.6 Antibody

Formation of DNA:RNA hybrids or R-loops contributes to numerous biologic processes. The development of the S9.6 antibody makes the analysis of R-Loops (DNA:RNA hybrids) possible through immunoprecipitation. Here, we describe the isolation of DNA:RNA hybrid structures using the S9.6 antibody. Using this protocol, both the DNA and RNA binding partners of the R-loop can be analyzed via qPCR, whole genome sequencing, or other methods.

Back-Pyrophosphorylation Assay to Detect In Vivo InsP7-Dependent Protein Pyrophosphorylation in Mammalian Cells

Protein pyrophosphorylation involves the transfer of a high-energy β-phosphate from inositol pyrophosphates, such as diphosphoinositol pentakisphosphate (InsP₇) to phosphorylated serine residues. Over a decade of research has established several proteins, involved in diverse physiological processes, as substrates of InsP₇-mediated pyrophosphorylation. However, the need for detection of this posttranslational modification on endogenous proteins is paramount. "Back-pyrophosphorylation" is a simple technique to test whether a native protein undergoes InsP₇-mediated pyrophosphorylation inside cells. The basis of this technique relies on the fact that a target protein isolated from cells with lower InsP₇ levels exists in a hypo-pyrophosphorylated form as compared to the same protein isolated from cells with normal InsP₇ levels. Hence, when radiolabeled InsP₇ is added to a target protein immunoprecipitated from both these cell types, the hypopyrophosphorylated protein accepts a higher amount of radiolabeled phosphate when compared to the protein isolated from wild-type cells. This chapter provides detailed methods to identify an InsP₇ target protein and conduct a back-pyrophosphorylation assay on a target protein immunoprecipitated from cells with normal versus reduced InsP₇ levels, to confirm its endogenous pyrophosphorylation status.

Immunoprecipitation methods to identify S-glutathionylation in target proteins

S-glutathionylation is a reversible post-translational modification of proteins that generate a mixed disulfide between glutathione to thiolate anion of cysteine residues in target proteins. In the last ten years, S-glutathionylation has been extensively studied since it represents the cellular response to oxidative stress, in physiological as well as pathological conditions. This modification may be a protective mechanism from irreversible oxidative damage and, on the other hand, may modulate protein folding and function. Due to the importance of S-glutathionylation in cellular redox signaling, various methods have been developed to identify S-gluthationylated proteins. Herein, we describe two easy methods to recognized S-glutathionylation of a target protein after oxidative stress in cellular extracts based on different immunoprecipitation procedures. The immunoprecipitation assay allows the capture of one glutathionylated protein using a specific antibody that binds to the target protein. The presence of S-glutathionylation in the immunoprecipitated protein is identified using anti-glutathione antibody. The second type of approach is based on the detection of the glutathionylated protein with biotin/streptavidin technique. After different steps of protection of non-oxidized thiolic groups and reduction of S-glutathionylated groups, the newly-formed protein free-thiols are labeled with biotin-GSH. The modified protein can be isolate with streptavidin-beads and recognized using an antibody against target protein. •S-glutathionylation is a reversible post-translational modification of proteins that recently has been emerged as important signaling in the redox regulation of protein function.•Both methods to identify glutathionylated proteins are economic, easy and do not require particular equipment.•The setups of both methods guarantee high reproducibility.

Cross-linking Proteomics Indicates Effects of Simvastatin on the TLR2 Interactome and Reveals ACTR1A as a Novel Regulator of the TLR2 Signal Cascade

Toll-like receptor 2 (TLR2) is a pattern recognition receptor that, upon ligation by microbial molecules, interacts with other proteins to initiate pro-inflammatory responses by the cell. Statins (hydroxymethylglutaryl coenzyme A reductase inhibitors), drugs widely prescribed to reduce hypercholesterolemia, are reported to have both pro- and anti-inflammatory effects upon cells. Some of these responses are presumed to be driven by effects on signaling proteins at the plasma membrane, but the underlying mechanisms remain obscure. We reasoned that profiling the effect of statins on the repertoire of TLR2-interacting proteins might provide novel insights into the mechanisms by which statins impact inflammation. In order to study the TLR2 interactome, we designed a coimmunoprecipitation (IP)-based cross-linking proteomics study. A hemagglutinin (HA)-tagged-TLR2 transfected HEK293 cell line was used to precipitate the TLR2 interactome upon cell exposure to the TLR2 agonist Pam3CSK4 and simvastatin, singly and in combination. To stabilize protein interactors, we used two different chemical cross-linkers with different spacer chain lengths. Proteomic analysis revealed important combinatorial effects of simvastatin and Pam3CSK4 on the TLR2 interactome. After stringent data filtering, we identified alpha-centractin (ACTR1A), an actin-related protein and subunit of the dynactin complex, as a potential interactor of TLR2. The interaction was validated using biochemical methods. RNA interference studies revealed an important role for ACTR1A in induction of pro-inflammatory cytokines. Taken together, we report that statins remodel the TLR2 interactome, and we identify ACTR1A, a part of the dynactin complex, as a novel regulator of TLR2-mediated immune signaling pathways.

Evaluation of a novel particle-based assay for detection of autoantibodies in idiopathic inflammatory myopathies

BACKGROUND

Myositis specific antibodies (MSA) represent not only important diagnostic tools for idiopathic inflammatory myopathies (IIM), but also help to stratify patients into subsets with particular clinical features, treatment responses, and disease outcome. Consequently, standardization of MSA is of high importance. Although many laboratories rely on protein immunoprecipitation (IP) for the detection of MSA, IP standardization is challenging and therefore reliable alternatives are mandatory. Recently, we identified significant variation between IP and line immunoassay (LIA) for the detection of MSA and myositis associated antibodies. In this study we aimed to compare the results from our previous study to the results obtained with a novel fully automated particle-based technology for the detection of MSA and MAA.

METHODS

A total of 54 sera from patients with idiopathic inflammatory myopathy (IIM) were tested using three methods: IP, LIA (Euroimmun, Germany) and a novel particle-based multi-analyte technology (PMAT, Inova Diagnostics, US, research use only). The analysis focused on antibodies to EJ, SRP, Jo-1, NXP-2, MDA5, TIF1-γ, and Mi-2.

RESULTS

Significant variations were observed among all methods. Overall, the novel PMAT assays showed slightly better correlation with IP, but the kappa agreement was strongly dependent on the antibody tested. When the results obtained from IP were used as reference for receiver operating characteristic (ROC) curve analysis, good discrimination and a high area under the curve (AUC) value were found for PMAT (AUC = 0.83, 95% confidence interval, CI 0.70-0.95) which was significantly higher (p = .0332) than the LIA method (AUC = 0.70, 95% CI 0.56-0.84).

CONCLUSION

The novel PMAT used to detect a spectrum of MSA in IIM represents a potential alternative to IP and other diagnostic assays. Additional studies based on larger cohorts are needed to fully assess the performance of the novel PMAT system for the detection of autoantibodies in myositis.

A soluble truncated tau species related to cognitive dysfunction and caspase-2 is elevated in the brain of Huntington's disease patients

Huntington’s disease (HD) is a progressive neurodegenerative disease. Involuntary movements, cognitive impairment and psychiatric disturbance are the major clinical manifestations, and gradual atrophy and selective neuronal loss in the striatum and cerebral cortex are the pathologic hallmarks. HD is caused by expanded CAG trinucleotide repeats at the N-terminus of IT15 that encodes the huntingtin (HTT) protein, though the molecular mechanisms through which the mutant HTT (mHTT) exerts toxic effects remain obscure. Members of the caspase family, including caspase-2 (Casp2), play an important role in HD pathogenesis. Genetic ablation of Casp2 ameliorates cognitive and motor deficits of HD mice, though the molecular targets of Casp2 are still unclear. It is well established that the microtubule-associated protein tau potentiates cognitive dysfunction in a variety of neurodegenerative disorders, including HD. Our recent study indicates that Casp2-catalyzed tau cleavage at aspartate 314 (tau 2N4R isoform numbering system) mediates synaptotoxicity, cognitive deficits and neurodegeneration in cellular and mouse models of frontotemporal dementia; further, levels of Δtau314, the soluble, N-terminal cleavage product, are elevated in individuals with mild cognitive impairment and Alzheimer’s disease, compared with cognitively normal individuals. Here, we identified the presence of Δtau314 proteins in the striatum (caudate nucleus) and prefrontal cortex (Brodmann’s area 8/9) of human subjects, and showed that in both structures, levels of Casp2 and Δtau314 proteins correlate well, and both proteins are higher in HD patients than non-HD individuals. Our findings advance our understanding of the contribution of Casp2-mediated Δtau314 production to HD pathogenesis.

A simplified and sensitive immunoprecipitation mass spectrometry protocol for the analysis of amyloid-beta peptides in brain tissue

In the field of Alzheimer's disease, there is an urgent need for novel analytical tools to identify disease-specific biomarkers and to evaluate therapeutics. Preclinical trials commonly employ amyloid beta (Aβ) peptide signatures as a read-out. In this paper, we report a simplified and detailed protocol for robust immunoprecipitation of Aβ in brain tissue prior to mass spectrometric detection exemplified by a study using transgenic mice. The established method employed murine monoclonal and rabbit polyclonal antibodies and was capable of yielding well-reproducible peaks of high intensity with low background signal intensities corresponding to various Aβ forms.