Combined findings of FDG-PET and arterial spin labeling in sporadic Creutzfeldt-Jakob disease

ABSTRACT

Sporadic Creutzfeldt-Jakob disease (sCJD) is a fatal progressive neurodegenerative disease. Multimodal approaches, including electroencephalogram, diffusion-weighted imaging (DWI) of brain MRI, and cerebrospinal fluid biomarkers, have been applied to increase the diagnostic accuracy of sCJD. Although previous studies suggested DWI could be the most useful modality for sCJD diagnosis, whether metabolism changes underlying in sCJD are still poorly understood. To the best of our knowledge, there are only one case using the technique of arterial spin labeling (ASL) to detection and follow-up of perfusion changes in CJD. Herein, we described a 71-year-old woman presented with progressive cognitive decline, behavioral and psychological symptoms for two months. The patient died one month later after her admission. As far as we know, this is the first report using the combination of fluorodeoxyglucose positron emission tomography and ASL to explore the metabolism changes in sCJD. Our case exemplifies the difficulty clinicians may face in the diagnosis of sCJD.     

Non-functioning chaperonin GroEL stimulates protein aggregation

To clarify the role of chaperones in the development of amyloid diseases, the interaction of the chaperonin GroEL with misfolded proteins and recombinant prions has been studied. The efficiency of the chaperonin-assisted folding of denatured glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was shown to be decreased in the presence of prions. Prions are capable of binding to GroEL immobilized on Sepharose, but this does not prevent the interaction between GroEL and other denatured proteins. The size of individual proteins (GroEL, GAPDH, and the recombinant prion) and aggregates formed after their mixing have been determined by the dynamic light scattering analysis. It was shown that at 25°C, the non-functioning chaperonin (equimolar mixture of GroEL and GroES in the absence of Mg-ATP) bound prion yielding large aggregates (greater than 400 nm). The addition of Mg-ATP decreased significantly the size of the aggregates to 70–80 nm. After blocking of one of the chaperonin active sites by oxidized denatured GAPDH, the aggregate size increased to 1200 nm, and the addition of Mg-ATP did not prevent the aggregation. These data indicate the significant role of chaperonins in the formation of amyloid structures and demonstrate the acceleration of aggregation in the presence of functionally inactive chaperonins. The suggested model can be used for the analysis of the efficiency of antiaggregants in the system containing chaperonins.     

13C, 15N Resonance Assignment of Parts of the HET-s Prion Protein in its Amyloid Form

The partial ¹⁵N and ¹³C solid-state NMR resonance assignment of the HET-s prion protein fragment 218–289 in its amyloid form is presented. It is based on experiments measured at MAS frequencies in the range of 20–40 kHz using exclusively adiabatic polarization-transfer schemes. The resonance assignment within each residue is based on two-dimensional ¹³C––¹³C correlation spectra utilizing the DREAM mixing scheme. The sequential linking of the assigned residues used a set of two- and three-dimensional ¹⁵N––¹³C correlation experiments. Almost all cross peaks visible in the spectra are assigned, but only resonances from 43 of the 78 amino-acid residues could be detected. The missing residues are thought to be highly disordered and/or highly dynamic giving rise to broad resonance lines that escaped detection in the experiments applied. The line widths of the observed resonances are narrow and comparable to line widths observed in micro-crystalline samples. The 43 assigned residues are located in two fragments of about 20 residues. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Irreversible formation of intermediate BSA oligomers requires and induces conformational changes

Understanding the relation between protein conformational changes and aggregation, and the physical mechanisms leading to such processes, is of primary importance, due to its direct relation to a vast class of severe pathologies. Growing evidence also suggests that oligomeric intermediates, which may occur early in the aggregation pathway, can be themselves pathogenic. The possible cytotoxicity of oligomers of non-disease-associated proteins adds generality to such suggestion and to the interest of studies of oligomer formation. Here we study the early stages of aggregation of Bovine Serum Albumin (BSA), a non pathogenic protein which has proved to be a useful model system. Dynamic light scattering and circular dichroism measurements in kinetic experiments following step-wise temperature rises, show that the "intermediate" form, which initiates large-scale aggregation, is the result of structural and conformational changes and concurrent formation of oligomers, of average size in the range of 100-200 A. Two distinct thresholds are observed. Beyond the first one oligomerization starts and causes partial irreversibility of conformational changes. Beyond the second threshold, additional secondary structural changes occurring in proteins being recruited progress on the same time scale of oligomerization. The concurrent behavior causes a mutual stabilization of oligomerization, and of structural and conformational changes, evidenced by a progressive increase of their irreversibility. This process interaction appears to be pivotal in producing irreversible oligomers.     

The role of pH on instability and aggregation of sickle hemoglobin solutions

Understanding the physical basis of protein aggregation covers strong physical and biomedical interests. Sickle hemoglobin (HbS) is a point-mutant form of normal human adult hemoglobin (HbA). It is responsible for the first identified "molecular disease," as its propensity to aggregation is responsible for sickle cell disease. At moderately higher than physiological pH value, this propensity is inhibited: The rate of aggregate nucleation becomes exceedingly small and solubility after polymerization increases. These order-of-magnitude effects on polymer nucleation rates and concurrent relatively modest changes of solubility after polymerization are here shown to be related to both pH-induced changes of location and shape of the liquid-liquid demixing (LLD) region. This allows establishment of a self-consistent contact between the thermodynamics of the solution as such (i.e., the LLD region), the kinetics of fiber nucleation, the theory of percolation, and the thermodynamics of gelation. The observed pH-induced changes are largely attributable to strong perturbations of hydrophobic hydration configurations and related free energy by electric charges. Similar mechanisms of effective control of aggregate nucleation rates by means of agents such as cosolutes, pH, salts, and additives, shifting the LLD and associated regions of anomalous fluctuations, promise to be relevant to the whole field of protein aggregation pathologies.     

Huntington toxicity in yeast model depends on polyglutamine aggregation mediated by a prion-like protein Rnq1

The cause of Huntington's disease is expansion of polyglutamine (polyQ) domain in huntingtin, which makes this protein both neurotoxic and aggregation prone. Here we developed the first yeast model, which establishes a direct link between aggregation of expanded polyQ domain and its cytotoxicity. Our data indicated that deficiencies in molecular chaperones Sis1 and Hsp104 inhibited seeding of polyQ aggregates, whereas ssa1, ssa2, and ydj1-151 mutations inhibited expansion of aggregates. The latter three mutants strongly suppressed the polyQ toxicity. Spontaneous mutants with suppressed aggregation appeared with high frequency, and in all of them the toxicity was relieved. Aggregation defects in these mutants and in sis1-85 were not complemented in the cross to the hsp104 mutant, demonstrating an unusual type of inheritance. Since Hsp104 is required for prion maintenance in yeast, this suggested a role for prions in polyQ aggregation and toxicity. We screened a set of deletions of nonessential genes coding for known prions and related proteins and found that deletion of the RNQ1 gene specifically suppressed aggregation and toxicity of polyQ. Curing of the prion form of Rnq1 from wild-type cells dramatically suppressed both aggregation and toxicity of polyQ. We concluded that aggregation of polyQ is critical for its toxicity and that Rnq1 in its prion conformation plays an essential role in polyQ aggregation leading to the toxicity.     

A two population model of prion transport through a tunnelling nanotube

This article develops a two prion population model that simulates prion trafficking between an infected dendritic cell and a neuron. The situation when the two cells are connected by a tunnelling nanotube (TNT) is simulated. Two mechanisms of prion transport are considered: lateral diffusion in the TNT membrane and active actin-dependent transport inside endocytic vesicles that are propelled by myosin Va molecular motors. Analytical solutions describing prion concentrations and fluxes are obtained. Numerical results are compared with those predicted by a single prion population model that relies on a single reaction–diffusion equation and accounts for the two modes of prion transport in an effective way.     

Exosomes: A Bubble Ride for Prions?

In certain cell types, endosomal multivesicular bodies may fuse with the cell surface in an exocytic manner. During this process, the small 50-90-nm-diameter vesicles contained in their lumen are released into the extracellular environment. The released vesicles are called exosomes. Exosome secretion can be used by cells to eject molecules targeted to intraluminal vesicles of multivesicular bodies, but particular cell types exploit exosomes as intercellular communication devices for transfer of proteins and lipids between cells. The molecular composition of exosomes is determined by sorting events within endosomes that occur concomitantly with the generation of intraluminal vesicles. As other raft-associated components, the glycosylphosphatidylinositol-linked prion protein transits through multivesicular bodies. Recent findings in non-neuronal cell models indicate prion protein association with secreted exosomes. Thus, exosomes could constitute vehicles for transmission of the infectious prion protein, bypassing cell-cell contact in the dissemination of prions.     

Video camera count of burrow‐dwelling fairy prions,sooty shearwaters,and tuatara on Takapourewa (Stephens Island), New Zealand

Abstract

Video camera technology is an increasingly common tool in the study of burrow‐dwelling animals. A camera used to observe the inhabitants of narrow burrows on Takapourewa (Cook Strait, New Zealand) is described. Population densities (animals per m²) of up to 1.1 for fairy prions {Pachyptila turtur), 0.06 for sooty shearwaters (Puffinus griseus), and 0.15 for tuatara (Sphenodon punctatus) were estimated in four different habitats. These data are similar to other estimates collected in more labour intensive studies on the island, and provide baseline information for future conservation work on Takapourewa.