The prepared tau exon-specific antibodies revealed distinct profiles of tau in CSF of the patients with Creutzfeldt-Jakob disease

Screening of tau protein kinase inhibitors in a tauopathy-relevant cell-based model of tau hyperphosphorylation and oligomerization

Tauopathies are a class of neurodegenerative disorders characterized by abnormal deposition of post-translationally modified tau protein in the human brain. Tauopathies are associated with Alzheimer's disease (AD), chronic traumatic encephalopathy (CTE), and other diseases. Hyperphosphorylation increases tau tendency to aggregate and form neurofibrillary tangles (NFT), a pathological hallmark of AD. In this study, okadaic acid (OA, 100 nM), a protein phosphatase 1/2A inhibitor, was treated for 24h in mouse neuroblastoma (N2a) and differentiated rat primary neuronal cortical cell cultures (CTX) to induce tau-hyperphosphorylation and oligomerization as a cell-based tauopathy model. Following the treatments, the effectiveness of different kinase inhibitors was assessed using the tauopathy-relevant tau antibodies through tau-immunoblotting, including the sites: pSer202/pThr205 (AT8), pThr181 (AT270), pSer202 (CP13), pSer396/pSer404 (PHF-1), and pThr231 (RZ3). OA-treated samples induced tau phosphorylation and oligomerization at all tested epitopes, forming a monomeric band (46-67 kDa) and oligomeric bands (170 kDa and 240 kDa). We found that TBB (a casein kinase II inhibitor), AR and LiCl (GSK-3 inhibitors), cyclosporin A (calcineurin inhibitor), and Saracatinib (Fyn kinase inhibitor) caused robust inhibition of OA-induced monomeric and oligomeric p-tau in both N2a and CTX culture. Additionally, a cyclin-dependent kinase 5 inhibitor (Roscovitine) and a calcium chelator (EGTA) showed contrasting results between the two neuronal cultures. This study provides a comprehensive view of potential drug candidates (TBB, CsA, AR, and Saracatinib), and their efficacy against tau hyperphosphorylation and oligomerization processes. These findings warrant further experimentation, possibly including animal models of tauopathies, which may provide a putative Neurotherapy for AD, CTE, and other forms of tauopathy-induced neurodegenerative diseases.

Profiles of 14-3-3 and Total Tau in CSF Samples of Chinese Patients of Different Genetic Prion Diseases

Background

The abnormal alterations of proteins 14-3-3 and tau in cerebrospinal fluid (CSF) are widely used for the diagnosis of sporadic Creutzfeldt-Jakob disease (sCJD), while the situations of CSF biomarkers in genetic prion diseases (gPrDs), particularly in Chinese gPrDs patients, have not been well documented.

Methods

Here, with the help of commercial 14-3-3 and total tau ELISA kits, we evaluated the levels of proteins 14-3-3 and tau in the CSF samples of 140 Chinese patients of 14 different types of gPrDs.

Results

We found that CSF 14-3-3 ELISA values in the patients with P102L GSS and D178N FFI were remarkably low, while those in the patients with T188K, E196A, and E200K gCJD were relatively high. Linear correlation assays identified a positive correlation between positive rate in Western blot (WB) and ELISA values of CSF 14-3-3. ELISA assays for total tau in CSF samples identified relatively high levels in the cases of T188K, E196A, and E200K gCJD (median: 133840.81, 159992.80, and 153342.92 AU/ml), but relatively low levels in those of P102L GSS and D178N FFI (median: 64397.77 and 43856.79 AU/ml).

Conclusion

These data illustrate heterogeneous profiles of CSF 14-3-3 and tau in various types of gPrDs, depending on the differences in the mutations in PRNP.

Remarkable increases of α1-antichymotrypsin in brain tissues of rodents during prion infection

α1-Antichymotrypsin (α1-ACT) belongs to a kind of acute-phase inflammatory protein. Recently, such protein has been proved exist in the amyloid deposits which is the hallmark of Alzheimer's disease, but limitedly reported in prion disease. To estimate the change of α1-ACT during prion infection, the levels of α1-ACT in the brain tissues of scrapie agents 263K-, 139A- and ME7-infected rodents were analyzed, respectively. Results shown that α1-ACT levels were significantly increased in the brain tissues of the three kinds of scrapie-infected rodents, displaying a time-dependent manner during prion infection. Immunohistochemistry assays revealed the increased α1-ACT mainly accumulated in some cerebral regions of rodents infected with prion, such as cortex, thalamus and cerebellum. Immunofluorescent assays illustrated ubiquitously localization of α1-ACT with GFAP positive astrocytes, Iba1-positive microglia and NeuN-positive neurons. Moreover, double-stained immunofluorescent assays and immunohistochemistry assays using series of brain slices demonstrated close morphological colocalization of α1-ACT signals with that of PrP and PrP^Sc in the brain slices of 263K-infected hamster. However, co-immunoprecipitation does not identify any detectable molecular interaction between the endogenous α1-ACT and PrP either in the brain homogenates of 263K-infected hamsters or in the lysates of prion-infected cultured cells. Our data here imply that brain α1-ACT is increased abnormally in various scrapie-infected rodent models. Direct molecular interaction between α1-ACT and PrP seems not to be essential for the morphological colocalization of those two proteins in the brain tissues of prion infection.

The Levels of Tau Isoforms Containing Exon-2 and Exon-10 Segments Increased in the Cerebrospinal Fluids of the Patients with Sporadic Creutzfeldt-Jakob Disease

The alteration of protein tau in the cerebrospinal fluid (CSF) of Creutzfeldt-Jakob disease (CJD) has been widely evaluated, possessing a significant diagnostic value for CJD. With the biotin-labeled tau-exon-specific mAbs, direct ELISA methods were established and the levels of tau isoforms containing exon-2 and exon-10 segments in CSF of the patients with various human prion diseases and in brain tissues of scrapie-infected animals were evaluated. The results showed that the levels of tau, especially containing four repeats in microtubule binding domain, were increased in the CSF samples of the patients with sporadic CJD (sCJD). Using the unlabeled (cold) mixed exon-specific mAbs, a competitive tau ELISA was conducted based on a commercial tau kit. It revealed that the majority of the increased tau in the CSF of sCJD cases was derived from the tau isoforms with exon-2 and exon-10 segments. Increases of CSF tau isoforms with exon-2 and exon-10 segments were also observed in the patients of E200K and T188K genetic CJD (gCJD), but not in the cases of fatal familiar insomnia (FFI). The increasing levels of tau isoforms with exon-2 and exon-10 segments in the group of sCJD correlated well with the positive 14-3-3 in CSF. Additionally, the similar alterative profiles of tau isoforms with exon-2 and exon-10 segments were also observed in the brain tissues of scrapie-infected rodents and a sCJD patient. Our data here propose the tau isoforms with exon-2 and exon-10 segments increase in CSF of sCJD and some types of gCJD, which may help to understand the physiological metabolism and pathological significance of various tau isoforms in the pathogenesis of prion diseases.

Preparation of human tau exon-2- and -10-specific monoclonal antibodies for the recognition of brain tau proteins in various mammals

The aggregations of tau protein in brain tissue have been described in a large number of neurodegenerative diseases; however, due to the lack of tau isoform- or exon-specific antibodies, the exact situations under which various brain tau isoforms can be found and their exact contributions during disease progression remain unknown. Therefore, in this study, we prepared tau exon-specific monoclonal antibodies (mAbs) that recognize different mammalian tau isoforms. Briefly, 3 Balb/c mice were separately immunized (3 mice per antigen) with the recombinant GST-fusion proteins, GST-tE2 and GST-tE10. Two hybridoma cell lines, 4A8 and 3E12, secreting antibodies against human tau exon-2 and -10 were established using the hybridoma technique. The sensitivity and specificity of the prepared mAbs were evaluated using indirect ELISA and western blot analysis. The ability of the prepared mAbs, 4A8 and 3E12, to recognize endogenous tau protein in the brain tissues of various mammals was estimated by immunoprecipitation. Based on the results of various verification methods, we found that the prepared mAbs, 4A8 and 3E12, not only specifically reacted with the individual recombinant GST tau exon fusion proteins, but also correctly recognized the recombinant human tau isoforms containing respective exon sequences, as shown by western blot analysis. Furthermore, western blot analysis and immunoprecipitation assays verified that the mAbs, 4A8 and 3E12, recognized endogenous tau proteins in human brain tissue, as well as tau proteins in a series of mammalian tissues, including goat, bovine, rabbit, hamster and mouse. Thus, in the present study, using the hybridoma technique, we successfully prepared the mAbs, 4A8 against tau exon-2 and 3E12 against tau exon-10, which provide useful tools for determining potential alternations of tau isoforms in neurodegenerative diseases.

Death or secretion? The demise of a plausible assumption about CSF-tau in Alzheimer Disease?

Our recent identification of an exosomal route for tau protein secretion¹ marks a key similarity between tau and other aggregation-prone proteins implicated in neurodegenerative disease pathogenesis and is to some extent congruent with the popular idea that tau pathology spreads between neurons via a “prionlike” template-mediated protein misfolding mechanism in AD and other tauopathies. However, the observation that much of the phosphotau in CSF samples from early AD patients is exosomal (and thus likely to have been secreted) calls into question a very widely held and plausible assumption - the idea that the elevated CSF-tau in AD is due to the passive release and accumulation of tau in the CSF as a consequence of widespread neuronal death. Here we examine this issue directly and explore some of the broader implications of this study for our understanding of AD pathogenesis and the prospects for improving its diagnosis and treatment.

Comparative peptidome analyses of the profiles of the peptides ranging from 1-10 KD in CSF samples pooled from probable sporadic CJD and non-CJD patients

The shotgun strategy applying tandem mass spectrometry has been widely used to identify the proteins that are differentially distributed among diseases for its high reliability and efficiency. To find out the potential difference of protein profiles in cerebrospinal fluids (CSF) between Creutzfeldt-Jakob disease (CJD) and non-CJD patients, especially in the fraction ranging from 1-10 KD, the CSF samples of 40 probable sporadic CJD (sCJD) patients, 32 non-CJD cases with dementia and 17 non-CJD cases without dementia were separately pooled and enriched by the magnetic beads based weak cation exchange chromatography (MB-WCX). After trypsin digestion, each enriched CSF was separated and identified by RP-HPLC-ESI-QTOF MS/MS. In total, 42, 53 and 47 signals of proteins were identified in the pooled CSF fraction less than 10 KD of probable sCJD, non-CJD with dementia and non-CJD without dementia, respectively. Compared with that of probable sCJD, the similarity of CSF protein profiles of non-CJD with dementia (76.2%) were higher than that of non-CJD without dementia (57.1%). Nine CSF proteins were found to be specially observed in probable sCJD group. Those data may help to select the potential biomarkers for diagnosis of CJD. Additionally, further studies of the small segments of cellular proteins in CSF of CJD patients may also provide scientific clues for understanding the neuropathogenesis of TSEs.

Dysfunction of microtubule-associated proteins of MAP2/tau family in Prion disease

The aggregation of PrP (Sc) is thought to be crucial for the neuropathology of prion diseases. A growing body of evidence demonstrates that the perturbation of the microtubule network contributes to PrP (Sc) -mediated neurodegeneration. Microtubules are a component of the cytoskeleton and play a central role in organelle transport, axonal elongation and cellular architecture in neurons. The polymerization, stabilization, arrangement of microtubules can be modulated by interactions with a series of microtubule-associated proteins (MAPs). Recent studies have proposed the abnormal alterations of two major microtubule-associated proteins, tau and MAP2, in the brain tissues of naturally occurred and experimental human and animal prion diseases. Increased total tau protein and hyperphosphorylation of tau at multiple residues are observed at the terminal stage of prion disease. The abnormal aggregation of tau protein disturbs its binding ability to microtubules and affects the microtubule dynamic. Significantly downregulated MAP2 is detected in the brain tissues of scrapie-infected hamsters and PrP106-126 treated cells, which corresponds well with the remarkably low levels of tubulin. In conclusion, dysfunction of MAP2/tau family leads to disruption of microtubule structure and impairment of axonal transport, and eventually triggers apoptosis in neurons, which becomes an essential pathway for prion to induce the neuropathology.

Is tau ready for admission to the prion club?

Aggregation-prone proteins associated with neurodegenerative disease, such as α synuclein and β amyloid, now appear to share key prion-like features with mammalian prion protein, such as the ability to recruit normal proteins to aggregates and to translocate between neurons. These features may shed light on the genesis of stereotyped lesion development patterns in conditions such as Alzheimer disease and Lewy Body dementia. We discuss the qualifications of tau protein as a possible "prionoid" mediator of lesion spread based on recent characterizations of the secretion, uptake and transneuronal transfer of human tau isoforms in a variety of tauopathy models, and in human patients. In particular, we consider (1) the possibility that prionoid behavior of misprocessed tau in neurodegenerative disease may involve other aggregation-prone proteins, including PrP itself, and (2) whether "prionlike" tau lesion propagation might include mechanisms other than protein-protein templating.

Protein modification by dicarbonyl molecular species in neurodegenerative diseases

Neurodegeneration results from abnormalities in cerebral metabolism and energy balance within neurons, astrocytes, microglia, or microvascular endothelial cells of the blood-brain barrier. In Alzheimer's disease, β-amyloid is considered the primary contributor to neuropathology and neurodegeneration. It now is believed that certain systemic diseases, such as diabetes mellitus, can contribute to neurodegeneration through the effects of chronic hyperglycemia/insulin resistance resulting in protein glycation, oxidative stress and inflammation within susceptible brain regions. Here, we present an overview of research focusing on the role of protein glycation, oxidative stress, and inflammation in the neurodegenerative process. Of special interest in this paper is the effect of methylglyoxal (MGO), a cytotoxic byproduct of glucose metabolism, elevated in neurodegenerative disease, and diabetes mellitus, on cerebral protein function and oxidative stress. How MGO interacts with amino acid residues within β-amyloid, and small peptides within the brain, is also discussed in terms of the affect on protein function.