Chen-Fang Dong

Human tau protein forms complex with PrP and some GSS- and fCJD-related PrP mutants possess stronger binding activities with tau in vitro.

Microtubule associated protein tau is considered to play roles in some types of human transmissible spongiform encephalopathies (TSE). In this study, the full-length and several truncated human tau proteins were expressed from E. coli and purified. Using GST pull down, co-immunoprecipitation assay and tau-coated ELISA, the molecular interaction between tau protein and PrP was confirmed in the context of the full-length human tau. The N terminus (amino acids 1–91) and tandem repeats region (amino acids 186–283) of tau protein were responsible for the interaction with PrP. The octapeptide repeats within PrP directly affected the binding activity of PrP with tau. GSS-related mutant PrP102L and fCJD- related mutants with two and seven extra octarepeats showed more active binding capacity with tau than wild-type PrP. The molecular interactions between PrP and tau protein highlight a potential role of tau in the biological function of PrP and the pathogenesis of TSE.

Changes of tau profiles in brains of the hamsters infected with scrapie strains 263 K or 139 A possibly associated with the alteration of phosphate kinases

BackgroundPhospho-tau deposition has been described in a rare genetic human prion disease, Gerstmann-Sträussler-Scheinker syndrome, but is not common neuropathological picture for other human and animal transmissible spongiform encephalopathies (TSEs). This study investigated the possible changes of tau and phosphorylated tau (p-tau, at Ser396, Ser404, and Ser202/Thr205) in scrapie experimental animals.MethodsThe profiles of tau and p-tau (p-tau, at Ser396, Ser404, and Ser202/Thr205) in the brain tissues of agents 263K- or 139A-infected hamsters were evaluated by Western blots and real-time PCR. Meanwhile, the transcriptional and expressive levels of GSK3β and CDK5 in the brains were tested.ResultsThe contents of total tau and p-tau at Ser202/Thr205 increased, but p-tau at Ser396 and Ser404 decreased at the terminal stages, regardless of scrapie strains. Transcriptional levels of two tau isoforms were also increased. Additionally, it showed higher CDK5, but lower GSK3β transcriptional and expressive levels in the brains of scrapie-infected animals. Analysis of brain samples collected from different times after inoculated with agent 263 K revealed that the changes of tau profiles and phosphate kinases were time-relative events.ConclusionThese data suggest that changes of profiles of p-tau at Ser396, Ser404 and Ser202/Thr205 are illness-correlative phenomena in TSEs, which may arise of the alteration of phosphate kinases. Alteration of tau, p-tau (Ser396, Ser404, and Ser202/Thr205), GSK3β and CDK5 were either intermediate or consequent events in TSE pathogenesis and proposed the potential linkage of these bioactive proteins with the pathogenesis of prion diseases.

Cytosolic PrP induces apoptosis of cell by disrupting microtubule assembly.

Prion protein (PrP) is able to bind with tubulin and to interfere with the formation of microtubule. To investigate the influence of accumulation of cytosolic PrP in cytoplasm on microtubule, plasmid pcDNA3.1-PrP23-230 expressing human PrP23-230 was introduced into HeLa cells. Immunoprecipitation assays identified the molecular interaction between cytosolic PrP and cellular tubulin. Confocal microscopy showed the co-localization of the expressed cytosolic PrP with tubulin in cytoplasm. Immunofluorescent assays of tubulin illustrated remarkable disruption of microtubular structures in the cells accumulated with cytosolic PrP. Meanwhile, the expressed cytosolic PrP significantly reduced cell viability and induced cell apoptosis. The amounts of microtubule protein in the cells expressing cytosolic PrP were decreased. Moreover, the levels of endogenous tubulin in the brain tissues of scrapie-infected hamsters were significantly lower than that of normal one. It highlights a close linkage between disruption of microtubule framework and cell death caused by abnormal presence of cellular PrP in cytoplasm. The association of apoptosis with microtubule-disrupting activity caused by cytosolic PrP may further provide insight into the unresolved biological function of PrP in the neurons.

Elevated levels of tau protein in cerebrospinal fluid of patients with probable Creutzfeldt-Jakob disease.

Introduction:A definitive diagnosis of Creutzfeldt–Jakob disease (CJD) can only be made by neuropathologic examination and demonstration of typical pathologic changes and the pathologic prion protein in central nervous tissues. This study investigated the diagnostic sensitivity and specificity of the microtubule-association protein tau in cerebrospinal fluid (CSF) from Chinese patients with sporadic CJD. Methods:Two hundred two CSF samples from clinically suspected patients with sporadic CJD were analyzed for tau protein by enzyme-linked immunosorbent assay and for the signal transduction regulatory protein 14-3-3 protein by immunoblot. Results:Remarkably increased levels of tau protein and increased incidence of 14-3-3 positivity were observed in probable CJD, when compared with possible CJD and others. With a threshold of 1400 pg/mL, tau determination showed a sensitivity of 90% and a specificity of 94% for the diagnosis of probable CJD. The combination of raised tau and positive 14-3-3 increased the specificity but slightly reduced the sensitivity. Statistical analysis indicated that the raised level of tau positively correlated with the presence of 14-3-3 in CSF but not with other main clinical features, eg, age, gender, clinical manifestations and sampling time. Conclusions:These data suggest that Chinese patients with probable CJD have similar increased levels of tau in the CSF as in Caucasian patients. Measurement of CSF tau will be another potential technique for antemortem CJD diagnosis.

Tumor necrosis factor-α of Red nucleus involved in the development of neuropathic allodynia.

The pro-inflammatory cytokine tumor necrosis factor-α (TNF-α) is associated with the generation of inflammatory and neuropathic pain. The current study aims to investigate the expression of TNF-α in the brain of rats with spared nerve injury (SNI), a neuropathic pain model with the lesion of common peroneal and tibial nerves. Two weeks following SNI, the immunohistochemical results identified that the expression level of TNF-α in the Red nucleus (RN) of SNI rats was apparently higher than that of sham-operated rats. To further study the roles of TNF-α in the development of neuropathic pain, different doses of anti-TNF-α antibody (20, 2.0 and 0.2 μg/ml) were microinjected into the RN contralateral to the nerve injury side of SNI rats. The results showed that the 50% paw withdrawal threshold (von Frey test) of SNI rats were increased by 20 and 2.0 μg/ml anti-TNF-α antibody as compared with that of the basic value and control groups (P<0.05), the analgesic effect lasted for 50 and 30 min, respectively. However, no significant analgesic effect was observed after 0.2 μg/ml antibody was microinjected into the RN. These results suggest that the TNF-α of RN is involved in the development of neuropathic allodynia in SNI rats.

Different expression patterns of CK2 subunits in the brains of experimental animals and patients with transmissible spongiform encephalopathies.

To address the possible alteration of casein kinase 2 (CK2) in transmissible spongiform encephalopathies (TSEs), the levels and patterns of CK2 in the brain tissues of hamsters or C57BL mice inoculated intracerebrally with scrapie agents 263K or 139A were evaluated by Western blots, followed by quantitative analysis. Specific semi-quantitative RT-PCR for evaluating the mRNA transcripts of CK2 subunits was performed in parallel. Compared with normal animals, the levels of CK2α and CK2β in the brains of infected hamsters and mice were significantly decreased, regardless of which scrapie agent was. However, the expression of CK2α′ or CK2α′/CK2α′′ in the animals infected with agents 263K or 139A was considerably increased. Furthermore, decreases of CK2α and CK2β and increases of CK2α′/CK2α′′ were observed in cerebella homogenates from one familial Creutzfeldt-Jakob disease (fCJD) case and one fatal familial insomnia (FFI) case. These results suggest that alterations of CK2 subunits in brains are illness-correlative phenomena in TSEs and indicate a potential linkage of CK2 changes with the pathogenesis of prion diseases.

PrP mutants with different numbers of octarepeat sequences are more susceptible to the oxidative stress

One of the physiological functions of cellular prion protein (PrPC) is believed to work as a cellular resistance to oxidative stress, in which the octarepeats region within PrP plays an important role. However, the detailed mechanism is less clear. In this study, the expressing plasmids of wild-type PrP (PrP-PG5) and various PrP mutants containing 0 (PrP-PG0), 9 (PrP-PG9) and 12 (PrP-PG12) octarepeats were generated and PrP proteins were expressed both in E. coli and in mammalian cells. Protein aggregation and formation of carbonyl groups were clearly seen in the recombinant PrPs expressed from E. coli after treatment of H2O2. MTT and trypan blue staining assays revealed that the cells expressing the mutated PrPs within octarepeats are less viable than the cells expressing wild-type PrP. Statistically significant high levels of intracellular free radicals and low levels of glutathione peroxidase were observed in the cells transfected with plasmids containing deleted or inserted octarepeats. Remarkably more productions of carbonyl groups were detected in the cells expressing PrPs with deleted and inserted octarepeats after exposing to H2O2. Furthermore, cells expressing wild-type PrP showed stronger resistant activity to the challenge of H2O2 at certain extent than the mutated PrPs and mock. These data provided the evidences that the octarepeats number within PrP is critical for maintaining its activity of antioxidation. Loss of its protective function against oxidative stress may be one of the possible pathways for the mutated PrPs to involve in the pathogenesis of familial Creutzfeldt-Jacob diseases.

Manganese-induced changes of the biochemical characteristics of the recombinant wild-type and mutant PrPs.

Manganese may play some roles in the pathogenesis of prion diseases. In this study, recombinant human wild-type (WT) PrP and PrP mutants with deleted or inserted octarepeats were exposed to manganese, and their biochemical and biophysical characteristics were evaluated by proteinase K (PK) digestion, sedimentation experiments, transmission electron microscopy and circular dichroism. It demonstrated that incubation of manganese remarkably increased PK-resistances, protein aggregations and β-sheet contents of the PrPs. Moreover, the PrP mutants of inserted or deleted octarepeats were much vulnerable to the influence of manganese, which showed obviously more aggregation and higher β-sheet content than that of WT-PrP. It highlights that the effect of manganese on the PrP seems to lie on the incorrectness of the octarepeats numbers. The association of the octarepeats number of PrP with manganese may further provide insight into the unresolved biological function of PrP in the neurons.

Sensitive detection of PrPSc by Western blot assay based on streptomycin sulphate precipitation.

Transmissible spongiform encephalopathies, also termed prion diseases, are fatal neurodegenerative disorders that affect both humans and animals, which are characterized by presences of protease‐resistance disease‐associated prion protein (PrPSc) in brains. In the present study, we optimized the Western blot assay for PrPSc with a precipitation procedure of streptomycin sulphate. After incubated with suitable amount of streptomycin sulphate, the detective sensitivity for PrPSc was remarkably improved. The precipitation of PrPSc was obviously influenced by pH value in the solution. Employs of PrPSc stock sample into various mimic specimens, including normal hamster brain homogenate, human cerebrospinal fluid and urine, demonstrated that streptomycin precipitation markedly increased the detective sensitivity of PrPSc, regardless in low concentration or in large volume. In addition, the PrPSc from a human brain tissue of familiar Creutzfeldt–Jakob disease (fCJD) was efficiently precipitated with streptomycin sulphate. As a sensitive, specific, rapid and flexible protocol for PrPSc, the protocol in this study has the potential, alone or combined with other techniques, to detect low levels of PrPSc in the specimens not only from central nerve system, but also from peripheral organs or fluids.

The propagation of hamster-adapted scrapie PrPSc can be enhanced by reduced pyridine nucleotide in vitro.

Transmissible spongiform encephalopathies (TSEs), or prion diseases, are fatal neurodegenerative disorders caused by an infectious agent termed a prion, which can convert normal cellular prion protein (PrPC) into a pathologically misfolded isoform (PrPSc). Taking advantage of protein misfolding cyclic amplification (PMCA), a series of experiments was conducted to investigate the possible influences of pyridine nucleotides on the propagation activities of hamster‐adapted scrapie agents 263K and 139A in vitro using normal hamster brain homogenates and recombinant hamster PrP as the substrates. The results showed that PrPSc from both scrapie agent 263K‐ and 139A‐infected brains propagated more efficiently in PMCA with the addition of reduced NADPH, showing an obvious dose‐dependent enhancement. Reduced NADH also prompted PrPSc propagation, whereas NADP, NAD and vitamin C failed. Moreover, following incubation with NADPH, recombinant hamster PrP could be efficiently converted into the proteinase K‐resistant form when exposed to the trace of PrPSc from infected hamsters. Our data provide evidence that the reduced pyridine nucleotide plays an important role in the propagation of prion and this process seems to target PrPC molecules.