Figure 1
Three dimensional structure of PrPC solved by (A) nuclear magnetic resonance (PDB code 1QM1) and (B) X-ray diffraction (PDB code 1I4M).
DOI: https://doi.org/10.4414/smw.2016.14354
Since Stanley Prusiner proposed the “protein only” hypothesis three decades ago [1], research in the field of transmissible spongiform encephalopathies (TSEs), a group of fatal neurodegenerative disorders affecting several mammalian species including humans, has been focused mainly on the misfolded prion protein PrPSc, widely accepted as the causal agent. Human prion diseases (which include Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker disease and familial fatal insomnia among others [2]) and animal prion diseases (such as scrapie in sheep and goats [3], chronic wasting disease in cervids [4], bovine spongiform encephalopathy in cattle [5] or transmissible mink encephalopathy [6]) all share some common features including spongiform degeneration of the central nervous system (CNS), amyloid plaque formation, neuronal loss and reactive gliosis [7]. All those pathological hallmarks were linked through the “protein only” hypothesis to the presence in the CNS of a 27 to 30 KDa protease-resistant protein named PrP27-30 or PrPSc (scrapie-associated prion protein), a derivative of the single gene encoded, protease sensitive, 30–35 KDa cell-surface glycoprotein known as PrPC (cellular prion protein) [8, 9].
Compelling evidence from the last three decades clearly shows that TSEs develop as a result of a poorly understood misfolding event that converts the PrPC to PrPSc, which is found aggregated, is protease resistant and able to induce its aberrant conformation in PrPC, leading to its accumulation in the CNS [1]. Depending on the source of PrPSc, prion disorders can be classified as infectious if the PrPSc is acquired from external sources, genetic if the PrPSc is produced internally due to disease associated mutations in the PrP encoding gene, or sporadic if the PrPSc is formed as a result of spontaneous misfolding of the wild type PrPC [10–12]. TSEs can manifest as phenotypically distinct diseases in animals that share identical PrP sequences, known to be caused by different PrPSc conformers, named strains [13–15]. How these distinct pathogenic isoforms emerge has been difficult to understand and fit within both Prusiner’s theory and the mechanistic rules governing the variable ability of interspecies transmission of the different prion strains [16, 17].
Despite all the knowledge gathered in more than three decades of research and the general understanding of the pathological processes, the molecular mechanisms remain elusive, making it difficult to develop rational therapeutic strategies for this group of incurable diseases. Specifically, the central process of TSEs, the conversion of PrPC to PrPSc, together with the strain diversity and interspecies transmission, are all structurally determined [18, 19], so to definitively solve the three-dimensional structure of all the proteins involved would be a great step forward towards the design of new rational strategies that could interfere with prion propagation and disease progression. However, it must be stressed that several compounds interfering with the pathological process have been found by phenotypic screening on in vitro and in vivo model systems, regardless of structural features. This is the case for compounds such as pentosan polysulphate [20, 21] or other sulphated glycans [22, 23] that prevented PrPSc accumulation in cell culture and prolonged survival times in mice models [24]. Similarly, some amyloid-binding sulphonated dyes, such as Congo red [25], suramin [26] or curcumin [27], have long been known to inhibit PrPSc accumulation. Cyclic tetrapyrroles, compounds with a highly conjugated planar ring system that bind transition metal ions, were also reported to inhibit PrPSc accumulation in vitro and prolong survival times upon early administration in vivo [28, 29]. A possible mechanism of action has been recently described at a single-molecule level using force spectroscopy [30]. Other anti-prion compounds worth mentioning include tetracyclic compounds [31, 32] and lysosomotropic compounds such as quinacrine, chlorpromazine and quinine [33–35]. However the use of many of the molecules listed is hampered by severe adverse effects or poor blood-brain barrier permeability, among other disadvantages, leading to the design of derivative compounds that may solve these problems and enhance their antiprion activity.
Although all these, and several other compounds, were discovered in the absence of structural knowledge about PrP isoforms, a better understanding at the molecular level of the interactions between the compounds and PrPC or PrPSc would be highly valuable for a more rational optimisation or derivative design. Other strategies will be only briefly described, as this review is mainly focused on therapeutic approaches that could derive from new structural insights on the central event of TSEs, the misfolding of PrP. Some of the most interesting approaches for the treatment of TSEs that do not involve direct interaction with PrP and thus could be developed regardless of structural features include: (i) perturbation of lipid rafts for PrPC sequestration or redistribution [36–40]; (ii) suppression of PrPC expression through siRNAs [41, 42]; (iii) targeting accessory molecules or pathways to conversion [43–47]; (iv) enhancing PrPSc clearance [48–50]; and (v) use of neuroprotective agents as symptomatic treatment [51–53].
However, in this review article we intend to offer an overview of what is known about prion architecture and how the limited structural information available has been used in the quest for remedies for these devastating disorders.
The PrPC is the only element involved in the central process of PrPC to PrPSc conversion that has been structurally characterised at a high resolution level (fig. 1). Although several models have been proposed during recent years, neither PrPC/PrPSc interactions nor the PrPSc fibril structure have been solved yet, and the lack of knowledge is clearly proven by the strikingly different molecular models suggested (table 1).
Figure 1
Three dimensional structure of PrPC solved by (A) nuclear magnetic resonance (PDB code 1QM1) and (B) X-ray diffraction (PDB code 1I4M).
The cellular form of PrP is a cell membrane protein, generally found in lipid rafts, which is comprised of an unstructured N-terminal and a globular C-terminal domain. The latter consists of three α-helices, and a β-sheet formed by two antiparallel β-strands that during its maturation undergo a few posttranslational modifications such as glycosylphosphatidylinositol (GPI anchor) attachment, addition of up to two N-linked glycans and the formation of a disulphide bond that connects the C-terminal α-helices [54–59]. Despite the detailed structural information available, the physiological role of the C-terminal domain remains uncertain and many different functions have been proposed, such as copper regulation [60, 61], signal transduction [62, 63], immune system modulation [64–66], programmed cell death inhibition [67, 68] and so on. Nonetheless, some of the previously suspected functions of PrP are being reassigned to other proteins. Some robust studies seem to confirm its role in neuroprotection and myelin maintenance [69], finally starting to separate the wheat from the chaff in the large number of functions attributed to PrPC.
Even though it is widely accepted that PrP misfolding is the central event in disease pathogenesis [70], the exact mechanism by which the misfolding occurs or even the exact composition of the protein form causing the prion disease has not yet been identified [71]. Hereditary or familial forms of the disease clearly establish that some single point mutations, mostly located in the globular domain of the PrP, as well as insertions or deletions found in other regions, increase the tendency to misfold [72–78]. Similarly, several monoclonal antibodies known to bind to specific motifs of the globular domain are able to prevent prion disease in animals [79–82]. Knowledge of PrPC structure, as well as studies that indicate that different regions of the protein are critical for the initial misfolding steps [83–87], have led to the rational design of strategies for PrPC stabilisation. Although initial attempts to stabilise PrPC were made with well-known molecular chaperones [88] or compounds previously found to bind PrPC regardless its structure [28, 89–93], descriptive and structural studies on PrP mutants [94] and the binding sites for PrPC-stabilising compounds are proving useful for the detection of key regions and design of new therapeutic strategies. This is the case with some recent studies, where PrPs with distinct pathological point mutations [95] or protective polymorphisms [96, 97] were analysed in depth to reveal their structural basis, in order to counteract or mimic their effect. This is in line with the search for point mutations or polymorphic variants that increase the thermodynamic stability of PrPC [98]. Most of the research done on PrPC-stabilising compounds is still based on chemical modification of drugs previously found effective in model systems or structure-activity studies with large chemical derivative libraries [34, 99–103]. It should be noted that the latter studies can be performed without any knowledge of the structural arrangement of PrPC. However, very promising approaches based on knowledge of PrPC structure and in silico modelling [104], such as the NAGARA tool developed by Ma and collaborators, are leading the way to the new era of rational drug design [105].
One of the big unsolved questions concerning PrPC to PrPSc conversion is the molecular mechanism by which PrPSc induces its aberrant conformation in PrPC. Models mimicking this phenomenon in vitro have clearly shown the selective binding of both isoforms of PrP [106], and further studies on PrPC/PrPSc binding and interspecies transmission revealed some putative interaction sites [106–110]. However, the prion strain diversity and the many different putative binding sites found suggest that interaction between isoforms is mechanistically complex and highly precise. There are two main theoretical models describing this phenomenon: heterodimer polymerisation [111], in which conformational conversion to PrPSc is templated by contact with monomeric PrPSc, and autocatalytic seeded polymerisation [112], in which conversion is induced by polymeric PrPSc. Blocking this PrPC/PrPSc interaction with molecules that bind either to PrPC or PrPSc is an important therapeutic target where the lack of structural details impedes the design of rational strategies. Thus, proper identification of interacting sites and detailed mechanistic description of this process are of vital importance. Some molecules have been found to interfere in this process, among which dominant negative inhibition strategies stand out. These approaches are based on the addition of heterologous PrPC or PrP fragments known to be poorly convertible through interspecies transmissibility studies or through the finding of protective PrP variants [107, 113, 114]. Moreover, other rational approaches are based on computational searches of chemical compounds that mimic the spatial orientation and polymorphisms of the key PrP residues that confer dominant negative inhibition [115].
Apart from therapeutic actions against PrPC/PrPSc interaction, actions on the neurotoxic PrP species and PrPSc disaggregation or degradation need to be considered. Again, the detailed molecular mechanisms behind prion-induced neurotoxicity, PrPSc structure and aggregate clearance are still unsolved, impeding the rational design of treatments focused on reduction of toxicity, blockade of PrPSc fibril growth or enhanced aggregate degradation. Concerning neurotoxicity, compelling evidence indicates that fibrillar PrPSc deposition is not directly linked to neurodegeneration and to the existence of oligomeric species associated with toxicity [71, 116, 117]. However, the great variety of misfolded oligomeric forms detected hinders identification of the really toxic and infectious ones, impeding any therapeutic action against them. Furthermore, how these unknown neurotoxic forms of PrP exert their effect on the nerve cells is another open question, although several mechanisms have been proposed, such as induction of apoptosis by activation of the complement pathway [118], by formation of pores in the cell membranes [119, 120], by specific modulation of N-methyl-D-aspartate (NMDA) receptors [121] or by inhibition of the proteasome [122]. The importance of accurately assessing the cytotoxic mechanism was highlighted by the toxicity induced by some antiprion monoclonal antibodies through binding to certain epitopes on the PrPC [123, 124]. This suggests a possible role for PrPC in the neurotoxic pathway and that, until this pathway is properly characterised, any therapeutic strategy based on molecules binding to PrPC is potentially toxic. Protein homeostasis is also known to be altered in disorders caused by protein misfolding, and some evidence indicates that its impairment might be an early mediator of prion-induced neurodegeneration through repression of global protein expression or activation of pro-apoptotic pathways. In this case, therapeutic efforts are targeted on components involved in those pathways, regardless of the structural features of the PrP species inducing neurodegeneration [124–128].
Finally, the last unsolved mystery related to PrPC/PrPSc conversion that could contribute to the development of rational therapies is the three-dimensional structure of the PrPSc aggregates. Despite being a research topic of tremendous importance in order to reach a complete understanding of the prion diseases and one of the first entities associated with the pathology, its difficult purification, insolubility and aggregated state have limited the reliable structural data obtained. Hopefully, infectious recombinant prion generation in in vitro systems may soon help to overcome some of these issues related to sample amount and purity, allowing the acquisition of high-resolution structural data [129]. The variety of biophysical techniques applied to the resolution PrPSc aggregate structure has yielded equally variable data and thus led to the publication of several different molecular models (table 1) [130–139]. Such differing models as the parallel in-register extended β-sheet model with no α-helix proposed by Cobb [130] and the β-solenoid modelled by Wille [131] illustrate the controversy surrounding the real structure of infectious prions. Moreover, none of the molecular models proposed fits entirely with all the experimental structural data available [140], although they could be partially correct or even describe different possible arrangements for misfolded PrP, highlighting the tremendous importance of an accurate identification of infectious versus noninfectious PrP polymers that are definitely generated in vitro [141] and may also be present in vivo. Given the lack of reliable structural information, it is not yet possible to design rational therapeutic candidates at the PrPSc level, although some interesting strategies have been proposed that take advantage of the limited structural information available. This is the case for rational vaccine design based on disease-associated epitopes through identification of PrP regions exclusively exposed in its misfolded conformation [142], which illustrates the advantage of even partial structural information. But with a few exceptions, compounds promoting fibril stabilisation or clearance have been mainly found through screening for amyloid-binding compounds or structure-based design of their derivatives, with poorly understood mechanisms of action [143–146]. Compounds that are known to be effective against other protein misfolding-related disorders that share some pathological features with prion diseases [147–151] have also become an important source of anti-amyloidogenic compounds [152–154]. However, many of the compounds tested had blood-brain barrier permeability issues, toxicity or strain specificity problems that hindered their clinical application. The strain specificity of some apparently successful compounds, clearly shown by Berry and collaborators [155], is alarming as it suggests that a general treatment for prion disorders might be impossible unless structural differences between strains are described in detail. Moreover, prions have been shown to acquire drug resistance under selection pressure of antiprion compounds, probably through slightly different structural variants already present as subvariants of the strains or “quasi species” [156–158]. This poses a problem not just for therapy development but also for the structural study of prions that seem to appear as a heterogeneous structural mix. Although other interesting therapeutic approaches have been explored and are being developed that do not require PrPSc structural knowledge, such as engineering disaggregases [159, 160], and inducing expression of kinases [161, 162] and heparanases [21, 163], direct actions against PrPSc imply the need for reliable structural models of the infectious and neurotoxic agent.
Altogether, this overview of the current knowledge on mechanistic data about prion pathogenesis and the possibilities opened for rational therapy design states clearly the urgent need of accurate molecular models that would enable a significant step forward in the treatment of these still incurable diseases.
| Table 1: Main features of different structural models proposed for the three dimensional structure of PrPSc. (Adapted from reference [73]). | |||
| Model | Description | Acceptance | Reference |
| Four-stranded β-sheet with two α-helices | Based on a truncated version of PrPSc (108–218) constructed by combining computational techniques and experimental data from the secondary structures of PrPSc from CD and FTIR studies. It suggests a four-stranded β-sheet that conserves two C-terminal α-helices. | Recent experimental observations do not support the interpretation of FTIR measurements on which this model was based. | [132] |
| Antiparallel intertwined β-helix | Molecular modelling of possible β-helical structures is based on primary sequence arrangement, assignment of conformations based on established examples of β-helical conformations and potential tertiary anti-parallel conformations. This results in strands of antiparallel β-sheets projected from an antiparallel intertwined core that expands into eight β-strands. | The height of eight β-strands predicted by this model is in contradiction with the X-fibre diffraction results [131]. | [133] |
| Parallel β-helix | Characterisation with electron crystallography of two infectious variants of the prion protein, two dimensional crystals of truncated PrPSc (27–30) and a miniprion (PrPSc106) that indicate the existence of a parallel β-helix in the core. Given the low resolution of the technique, they could be left-handed or right-handed parallel β-helices. | Recent experimental observations do not support the presence of C-terminal α-helices that this model predicted. | [134] |
| Five-stranded β-sheet with C-terminal α-helices | Model based on sequence analysis and X-ray diffraction data on recombinant PrP that suggests a dimerisation mechanism. It was modelled from the human TATA-box binding protein structure, which is a five-stranded β-sheet that in the case of PrP conserves the C-terminal α-helices. | Recent experimental observations do not support the presence of the C-terminal α-helices. | [135] |
| Spiral model | Molecular dynamics simulation was used to model the structural change of a recombinant PrP at acidic pH. This resulted in a spiral model where the original α-helices from PrPC are conserved and up to four β-strands are also formed. A fibrillary structure was proposed where the β-strands angles are not perpendicular to the fibril axis. | X-ray fibre diffraction data [131] is incompatible with β-strand angles not perpendicular to the fibril axis. Moreover the high α-helical content does not fit with FTIR and limited proteolysis data. | [136] |
| Left-handed β-helix “Govaerts” | Based on the previous parallel β-helix model and higher resolution electron micrographs of the same two-dimensional crystals of truncated PrPSc (27–30) and miniprion (PrPSc106). It shows a crystal composed of trimeric cells and results in a left-handed β-helical model with the C-terminal conserving the α-helix. | Recent experimental observations do not support the presence of the C-terminal α-helices. | [137] |
| Left-handed β-helix “Stork” | Molecular dynamics was applied to study the stability of small polyglutamine β-helices in solution. Based on these findings, a β-helical model was proposed. The model contains a sequence alignment different from the model proposed by Govaerts et al, but similar in many other features. | Recent experimental observations do not support the presence of the C-terminal α-helices. | [138] |
| Two rung β-helix | Based on previous left-handed β-helix models and using molecular dynamics, the β-helical structural model was refined and a more stable arrangement proposed. Unlike the previous models, instead of four β-helical rungs per PrP monomer, a fibril composed by two rung monomers was suggested. This model is denser, with a tighter packing of helices and half of the height per monomer. | The height per monomer proposed does not match with that observed in X-ray diffraction studies [131] and the presence of α-helices at the C-terminal is also no longer supported by recent experimental data. | [139] |
| Parallel in-register β-sheet structure | Site-directed spin-labelling and electron paramagnetic resonance spectroscopy were used to study a recombinant PrP amyloid, showing a parallel, in-register β-sheet structure, where each monomer accounts for 4.8 Å of the fibril height. | It does not fit with the X-ray diffraction data, which indicates repeating units in the fibril that are 19.2 Å high [131]. | [130] |
| CD = circular dichroism; FTIR = Fourier transform infrared spectroscopy; PrP = prion protein; PrPSc = scrapie-associated prion protein | |||
1 Prusiner SB. Novel proteinaceous infectious particles cause scrapie. Science. 1982;216:136–44.
2 Collinge J. Prion diseases of humans and animals: their causes and molecular basis. Annu Rev Neurosci. 2001;24:519–550.
3 Jeffrey M, Gonzalez L. Classical sheep transmissible spongiform encephalopathies: pathogenesis, pathological phenotypes and clinical disease. Neuropathol Appl Neurobiol. 2007;33:373–94.
4 Williams ES, Young S. Spongiform encephalopathies in Cervidae. Rev Sci Tech. 1992;11:551–67.
5 Bradley R, Collee JG, Liberski PP. Variant CJD (vCJD) and bovine spongiform encephalopathy (BSE): 10 and 20 years on: part 1. Folia Neuropathol. 2006;44:93–101.
6 Marsh RF, Hadlow WJ. Transmissible mink encephalopathy. Rev Sci Tech. 1992;11:539–50.
7 Soto C, Satani N. The intricate mechanisms of neurodegeneration in prion diseases. Trends Mol Med. 2011;17:14–24.
8 Bolton DC, Mckinley MP, Prusiner SB. Identification of a protein that purifies with the scrapie prion. Science. 1982;218:1309–11.
9 Oesch B, Westaway D, Walchli M, Mckinley MP, Kent SB, Aebersold R, et al. A cellular gene encodes scrapie PrP 27–30 protein. Cell. 1985;40:735–46.
10 Gajdusek C, Gibbs C, Alpers M. Experimental transmission of kuru-like syndrome to chimpanzees. Nature. 1966; 209: 794–6.
11 Masters CL, Gajdusek DC, Gibbs CJ, Jr. The familial occurrence of Creutzfeldt-Jakob disease and Alzheimer's disease. Brain. 1981;104:535–58.
12 Hsiao KK, Cass C, Schellenberg GD, Bird T, Devine-Gage E, Wisniewski H, et al. A prion protein variant in a family with the telencephalic form of Gerstmann-Straussler-Scheinker syndrome. Neurology. 1991;41:681–4.
13 Bruce ME. TSE strain variation. Br Med Bull. 2003;66:99–108.
14 Kascsak RJ, Rubenstein R, Merz PA, Carp RI, Robakis NK, Wisniewski HM, et al. Immunological comparison of scrapie-associated fibrils isolated from animals infected with four different scrapie strains. J Virol. 1986;59:676–83.
15 Kascsak RJ, Rubenstein R, Carp RI. Evidence for biological and structural diversity among scrapie strains. Curr Top Microbiol Immunol. 1991;172:139–52.
16 Bruce M, Chree A, Mconnell I, Foster J, Pearson G, Fraser H. Transmission of bovine spongiform encephalopathy and scrapie to mice: strain variation and the species barrier. Philos Trans R Soc Lond B Biol Sci. 1994;343:405–11.
17 Kocisko DA, Priola SA, Raymond GJ, Chesebro B, Lansbury PT, Jr., Caughey B. Species specificity in the cell-free conversion of prion protein to protease-resistant forms: a model for the scrapie species barrier. Proc Natl Acad Sci U S A. 1995;92:3923–7.
18 Prusiner SB, Scott MR, Dearmond SJ, Cohen FE. Prion protein biology. Cell. 1998;93:337–48.
19 Saijo E, Hughson AG, Raymond GJ, Suzuki A, Horiuchi M, Caughey B. PrPSc-Specific Antibody Reveals C-terminal Conformational Differences between Prion Strains. J Virol. 2016;90:4905–13.
20 Caughey B, Raymond GJ. Sulfated polyanion inhibition of scrapie-associated PrP accumulation in cultured cells. J Virol. 1993;67:643–50.
21 Gabizon R, Meiner Z, Halimi M, Ben-Sasson SA. Heparin-like molecules bind differentially to prion-proteins and change their intracellular metabolic fate. J Cell Physiol. 1993;157:319–25.
22 Doh-ura K, Kuge T, Uomoto M, Nishizawa K, Kawasaki Y, Iha M. Prophylactic effect of dietary seaweed Fucoidan against enteral prion infection. Antimicrob Agents Chemother. 2007;51:2274–7.
23 Engelstein R, Ovadia H, Gabizon R. Copaxone interferes with the PrP Sc-GAG interaction. Eur J Neurol. 2007;14:877–84.
24 Farquhar C, Dickinson A, Bruce M. Prophylactic potential of pentosan polysulphate in transmissible spongiform encephalopathies. Lancet. 1999;353:117.
25 Caughey B, Race RE. Potent inhibition of scrapie-associated PrP accumulation by congo red. J Neurochem. 1992;59:768–71.
26 Ladogana A, Casaccia P, Ingrosso L, Cibati M, Salvatore M, Xi YG, et al. Sulphate polyanions prolong the incubation period of scrapie-infected hamsters. J Gen Virol. 1992;73(3):661–5.
27 Caughey B, Raymond LD, Raymond GJ, Maxson L, Silveira J, Baron GS. Inhibition of protease-resistant prion protein accumulation in vitro by curcumin. J Virol. 2003;77:5499–502.
28 Caughey WS, Raymond LD, Horiuchi M, Caughey B. Inhibition of protease-resistant prion protein formation by porphyrins and phthalocyanines. Proc Natl Acad Sci U S A. 1998;95:12117–22.
29 Priola SA, Raines A, Caughey W. Prophylactic and therapeutic effects of phthalocyanine tetrasulfonate in scrapie-infected mice. J Infect Dis. 2003;188:699–705.
30 Gupta AN, Neupane K, Rezajooei N, Cortez LM, Sim VL, Woodside MT. Pharmacological chaperone reshapes the energy landscape for folding and aggregation of the prion protein. Nat Commun. 2016;7:12058.
31 Forloni G, Iussich S, Awan T, Colombo L, Angeretti N, Girola L, et al. Tetracyclines affect prion infectivity. Proc Natl Acad Sci U S A. 2002;99:10849–54.
32 Guo YJ, Han J, Yao HL, Zhang BY, Gao JM, Zhang J, et al. Treatment of scrapie pathogen 263K with tetracycline partially abolishes protease-resistant activity in vitro and reduces infectivity in vivo. Biomed Environ Sci. 2007;20:198–202.
33 Doh-Ura K, Iwaki T, Caughey B. Lysosomotropic agents and cysteine protease inhibitors inhibit scrapie-associated prion protein accumulation. J Virol. 2000;74:4894–7.
34 Korth C, May BC, Cohen FE, Prusiner SB. Acridine and phenothiazine derivatives as pharmacotherapeutics for prion disease. Proc Natl Acad Sci U S A. 2001;98:9836–41.
35 Ryou C, Legname G, Peretz D, Craig JC, Baldwin MA, Prusiner SB. Differential inhibition of prion propagation by enantiomers of quinacrine. Lab Invest. 2003;83:837–43.
36 Taraboulos A, Scott M, Semenov A, Avrahami D, Laszlo L, Prusiner SB. Cholesterol depletion and modification of COOH-terminal targeting sequence of the prion protein inhibit formation of the scrapie isoform. J Cell Biol. 1995;129:121–32. Erratum in: J Cell Bio.l 1995 Jul;130(2):501.
37 Mangé A, Nishida N, Milhavet O, Mcmahon HE, Casanova D, Lehmann S. Amphotericin B inhibits the generation of the scrapie isoform of the prion protein in infected cultures. J Virol. 2000;74:3135–40.
38 Klingenstein R, Lober S, Kujala P, Godsave S, Leliveld SR, Gmeiner P, et al. Tricyclic antidepressants, quinacrine and a novel, synthetic chimera thereof clear prions by destabilizing detergent-resistant membrane compartments. J Neurochem. 2006;98:748–59.
39 Gilch S, Kehler C, Schatzl HM. The prion protein requires cholesterol for cell surface localization. Mol Cell Neurosci. 2006;31:346–53.
40 Kempster S, Bate C, Williams A. Simvastatin treatment prolongs the survival of scrapie-infected mice. Neuroreport. 2007;18:479–82.
41 Tilly G, Chapuis J, Vilette D, Laude H, Vilotte JL. Efficient and specific down-regulation of prion protein expression by RNAi. Biochem Biophys Res Commun. 2003;305:548–51.
42 Pfeifer A, Eigenbrod S, Al-Khadra S, Hofmann A, Mitteregger G, Moser M, et al. Lentivector-mediated RNAi efficiently suppresses prion protein and prolongs survival of scrapie-infected mice. J Clin Invest. 2006;116:3204–10.
43 Leucht C, Simoneau S, Rey C, Vana K, Rieger R, Lasmezas CI et al. The 37 kDa/67 kDa laminin receptor is required for PrP(Sc) propagation in scrapie-infected neuronal cells. EMBO Rep. 2003;4:290–5.
44 Bate C, Reid S, Williams A. Phospholipase A2 inhibitors or platelet-activating factor antagonists prevent prion replication. J Biol Chem. 2004;279:36405–11.
45 Ertmer A, Gilch S, Yun SW, Flechsig E, Klebl B, Stein-Gerlach M, et al. The tyrosine kinase inhibitor STI571 induces cellular clearance of PrPSc in prion-infected cells. J Biol Chem. 2004;279:41918–27.
46 Yun SW, Ertmer A, Flechsig E, Gilch S, Riederer P, Gerlach M, et al. The tyrosine kinase inhibitor imatinib mesylate delays prion neuroinvasion by inhibiting prion propagation in the periphery. J Neurovirol. 2007;13:328–37.
47 Zuber C, Mitteregger G, Schuhmann N, Rey C, Knackmuss S, Rupprecht W, et al. Delivery of single-chain antibodies (scFvs) directed against the 37/67 kDa laminin receptor into mice via recombinant adeno-associated viral vectors for prion disease gene therapy. J Gen Virol. 2008;89:2055–61.
48 Supattapone S, Nguyen HO, Cohen FE, Prusiner SB, Scott MR. Elimination of prions by branched polyamines and implications for therapeutics. Proc Natl Acad Sci U S A. 1999;96:14529–34.
49 Winklhofer KF, Tatzelt J. Cationic lipopolyamines induce degradation of PrPSc in scrapie-infected mouse neuroblastoma cells. Biol Chem. 2000;381:463–9.
50 Bera A, Nandi PK. Biological polyamines inhibit nucleic-acid-induced polymerisation of prion protein. Arch Virol. 2007;152:655–68.
51 Otto M, Cepek L, Ratzka P, Doehlinger S, Boekhoff I, Wiltfang J, et al. Efficacy of flupirtine on cognitive function in patients with CJD: A double-blind study. Neurology. 2004;62:714–8.
52 Dirikoc S, Priola SA, Marella M, Zsurger N, Chabry J. Nonpsychoactive cannabidiol prevents prion accumulation and protects neurons against prion toxicity. J Neurosci. 2007;27:9537–44.
53 Kimata A, Nakagawa H, Ohyama R, Fukuuchi T, Ohta S, Suzuki T,, et al. New series of antiprion compounds: pyrazolone derivatives have the potent activity of inhibiting protease-resistant prion protein accumulation. J Med Chem. 2007;50:5053–6.
54 Hay B, Barry RA, Lieberburg I, Prusiner SB, Lingappa VR. Biogenesis and transmembrane orientation of the cellular isoform of the scrapie prion protein Mol Cell Biol. 1987;7:914–20. Erratum in: Mol Cell Biol. 1987;7(5):2035.
55 Stahl N, Borchelt DR, Hsiao K, Prusiner SB. Scrapie prion protein contains a phosphatidylinositol glycolipid. Cell. 1987;51:229–40.
56 Haraguchi T, Fisher S, Olofsson S, Endo T, Groth D, Tarentino A, et al. Asparagine-linked glycosylation of the scrapie and cellular prion proteins. Arch Biochem Biophys. 1989;274:1–13.
57 Harris DA, Huber MT, Van Dijken P, Shyng SL, Chait BT, Wang R. Processing of a cellular prion protein: identification of N- and C-terminal cleavage sites. Biochemistry. 1993;32:1009–16.
58 Riek R, Hornemann S, Wider G, Glockshuber R, Wuthrich K. NMR characterization of the full-length recombinant murine prion protein, mPrP(23–231). FEBS Lett. 1997;413:282–8.
59 Zahn R, Liu A, Luhrs T, Riek R, Von Schroetter C, Lopez Garcia F, et al. NMR solution structure of the human prion protein. Proc Natl Acad Sci U S A. 2000;97:145–50.
60 Colling SB, Collinge J, Jefferys JG. Hippocampal slices from prion protein null mice: disrupted Ca(2+)-activated K+ currents. Neurosci Lett. 1996;209:49–52.
61 Jackson GS, Murray I, Hosszu LL, Gibbs N, Waltho JP, Clarke AR, et al. Location and properties of metal-binding sites on the human prion protein. Proc Natl Acad Sci U S A. 2001;98:8531–5.
62 Mouillet-Richard S, Ermonval M, Chebassier C, Laplanche JL, Lehmann S, Launay JM, et al. Signal transduction through prion protein. Science. 2000;289:1925–8.
63 Chiarini LB, Freitas AR, Zanata SM, Brentani RR, Martins VR, Linden R. Cellular prion protein transduces neuroprotective signals. EMBO J. 2002;21:3317–26.
64 Mattei V, Garofalo T, Misasi R, Circella A, Manganelli V, Lucania G, et al. Prion protein is a component of the multimolecular signaling complex involved in T cell activation. FEBS Lett. 2004;560:14–8.
65 De Almeida CJ, Chiarini LB, Da Silva JP, Pm ES, Martins MA, Linden R. The cellular prion protein modulates phagocytosis and inflammatory response. J Leukoc Biol. 2005;77:238–46.
66 Bainbridge J, Walker KB. The normal cellular form of prion protein modulates T cell responses. Immunol Lett. 2005;96:147–50.
67 Kuwahara C, Takeuchi AM, Nishimura T, Haraguchi K, Kubosaki A, Matsumoto Y, et al. Prions prevent neuronal cell-line death. Nature. 1999;400:225–6.
68 Bounhar Y, Zhang Y, Goodyer CG, Leblanc A. Prion protein protects human neurons against Bax-mediated apoptosis. J Biol Chem. 2001;276:39145–9.
69 Bremer J, Baumann F, Tiberi C, Wessig C, Fischer H, Schwarz P, et al. Axonal prion protein is required for peripheral myelin maintenance. Nat Neurosci. 2010;13:310–8.
70 Bueler H, Aguzzi A, Sailer A, Greiner RA, Autenried P, Aguet M, et al. Mice devoid of PrP are resistant to scrapie. Cell. 1993;73:1339–47.
71 Singh J, Udgaonkar JB. Molecular Mechanism of the Misfolding and Oligomerization of the Prion Protein: Current Understanding and Its Implications. Biochemistry. 2015;54:4431–42.
72 Van Der Kamp MW, Daggett V. The consequences of pathogenic mutations to the human prion protein. Protein Eng Des Sel. 2009;22:461–8.
73 Beck JA, Mead S, Campbell TA, Dickinson A, Wientjens DP, Croes EA, et al. Two-octapeptide repeat deletion of prion protein associated with rapidly progressive dementia. Neurology. 2001;57:354–6.
74 Goldfarb LG, Brown P, McCombie WR, Goldgaber D, Swergold GD, Wills PR, et al. Transmissible familial Creutzfeldt-Jakob disease associated with five, seven, and eight extra octapeptide coding repeats in the PRNP gene. Proc Natl Acad Sci U S A. 1991;88:10926–30.
75 Liemann S, Glockshuber R. Influence of amino acid substitutions related to inherited human prion diseases on the thermodynamic stability of the cellular prion protein. Biochemistry. 1999;38:3258–67.
76 Swietnicki W, Petersen RB, Gambetti P, Surewicz WK. Familial mutations and the thermodynamic stability of the recombinant human prion protein. J Biol Chem. 1998;273:31048–52.
77 Cappai R, Stewart L, Jobling MF, Thyer JM, White AR, Beyreuther K, et al. Familial prion disease mutation alters the secondary structure of recombinant mouse prion protein: implications for the mechanism of prion formation. Biochemistry. 1999;38:3280–4.
78 Apetri AC, Surewicz WK. Kinetic intermediate in the folding of human prion protein. J Biol Chem. 2002;277:44589–92.
79 Heppner FL, Musahl C, Arrighi I, Klein MA, Rulicke T, Oesch B et al. Prevention of scrapie pathogenesis by transgenic expression of anti-prion protein antibodies. Science. 2001;294:178–82.
80 Peretz D, Williamson RA, Kaneko K, Vergara J, Leclerc E, Schmitt-Ulms G, et al. Antibodies inhibit prion propagation and clear cell cultures of prion infectivity. Nature. 2001;412:739–43.
81 White AR, Enever P, Tayebi M, Mushens R, Linehan J, Brandner S, et al. Monoclonal antibodies inhibit prion replication and delay the development of prion disease. Nature. 2003;422:80–3.
82 Antonyuk SV, Trevitt CR, Strange RW, Jackson GS, Sangar D, Batchelor M, et al. Crystal structure of human prion protein bound to a therapeutic antibody. Proc Natl Acad Sci U S A. 2009;106:2554–8.
83 Chakroun N, Fornili A, Prigent S, Kleinjung J, Dreiss CA, Rezaei H, et al. Decrypting Prion Protein Conversion into a β-Rich Conformer by Molecular Dynamics. J Chem Theory Comput. 2013;9:2455–65.
84 Chen J, Thirumalai D. Helices 2 and 3 are the initiation sites in the PrP(C) –> PrP(SC) transition. Biochemistry. 2013;52:310–9.
85 Morrissey MP, Shakhnovich EI. Evidence for the role of PrP(C) helix 1 in the hydrophilic seeding of prion aggregates. Proc Natl Acad Sci U S A. 1999;96:11293–8.
86 Campos SR, Machuqueiro M, Baptista AM. Constant-pH molecular dynamics simulations reveal a beta-rich form of the human prion protein. J Phys Chem B. 2010;114:12692–700.
87 Ziegler J, Sticht H, Marx UC, Müller W, Rösch P, Schwarzinger S. CD and NMR studies of prion protein (PrP) helix 1. Novel implications for its role in the PrPC–>PrPSc conversion process. J Biol Chem. 2003; 278: 50175-50181.
88 Tatzelt J, Prusiner SB, Welch WJ. Chemical chaperones interfere with the formation of scrapie prion protein. EMBO J. 1996;15:6363–73.
89 Caughey B, Brown K, Raymond GJ, Katzenstein GE, Thresher W. Binding of the protease-sensitive form of PrP (prion protein) to sulfated glycosaminoglycan and congo red [corrected]. J Virol. 1994;68:2135–41.
90 Kocisko DA, Caughey B. Searching for anti-prion compounds: cell-based high-throughput in vitro assays and animal testing strategies. Methods Enzymol. 2006;412:223–34.
91 Kocisko DA, Bertholet N, Moore RA, Caughey B, Vaillant A. Identification of prion inhibitors by a fluorescence-polarization-based competitive binding assay. Anal Biochem. 2007;363:154–6.
92 Lee KS, Raymond LD, Schoen B, Raymond GJ, Kett L, Moore RA, et al. Hemin interactions and alterations of the subcellular localization of prion protein. J Biol Chem. 2007;282:36525–33.
93 Nicoll AJ, Trevitt CR, Tattum MH, Risse E, Quarterman E, Ibarra AA, et al. Pharmacological chaperone for the structured domain of human prion protein. Proc Natl Acad Sci U S A. 2010;107:17610–5.
94 Meli M, Gasset M, Colombo G. Dynamic diagnosis of familial prion diseases supports the beta2-alpha2 loop as a universal interference target. PLoS One. 2011;6:e19093.
95 Hadzi S, Ondracka A, Jerala R, Hafner-Bratkovic I. Pathological mutations H187R and E196K facilitate subdomain separation and prion protein conversion by destabilization of the native structure. FASEB J. 2015;29:882–93.
96 Biljan I, Giachin G, Ilc G, Zhukov I, Plavec J, Legname G. Structural basis for the protective effect of the human prion protein carrying the dominant-negative E219K polymorphism. Biochem J. 2012;446:243–51.
97 Asante EA, Smidak M, Grimshaw A, Houghton R, Tomlinson A, Jeelani A, et al. A naturally occurring variant of the human prion protein completely prevents prion disease. Nature. 2015;522:478–81.
98 Kong Q, Mills JL, Kundu B, Li X, Qing L, Surewicz K, et al. Thermodynamic stabilization of the folded domain of prion protein inhibits prion infection in vivo. Cell Rep. 2013;4:248–54.
99 Ouidja MO, Petit E, Kerros ME, Ikeda Y, Morin C, Carpentier G, et al. Structure-activity studies of heparan mimetic polyanions for anti-prion therapies. Biochem Biophys Res Commun. 2007;363:95–100.
100 Guo K, Mutter R, Heal W, Reddy TR, Cope H, Pratt S et al. Synthesis and evaluation of a focused library of pyridine dicarbonitriles against prion disease. Eur J Med Chem. 2008;43:93–106.
101 Thompson MJ, Borsenberger V, Louth JC, Judd KE, Chen B. Design, synthesis, and structure-activity relationship of indole-3-glyoxylamide libraries possessing highly potent activity in a cell line model of prion disease. J Med Chem. 2009;52:7503–11.
102 Venko K, Zuperl S, Novic M. Prediction of antiprion activity of therapeutic agents with structure-activity models. Mol Divers. 2014;18:133–48.
103 Nguyen PH, Hammoud H, Halliez S, Pang Y, Evrard J, Schmitt M, et al. Structure-activity relationship study around guanabenz identifies two derivatives retaining antiprion activity but having lost α2-adrenergic receptor agonistic activity. ACS Chem Neurosci. 2014;5:1075–82.
104 Hosokawa-Muto J, Kamatari YO, Nakamura HK, Kuwata K. Variety of antiprion compounds discovered through an in silico screen based on cellular-form prion protein structure: Correlation between antiprion activity and binding affinity. Antimicrob Agents Chemother. 2009;53:765–71.
105 Ma B, Yamaguchi K, Fukuoka M, Kuwata K. Logical design of anti-prion agents using NAGARA. Biochem Biophys Res Commun. 2016;469:930–5.
106 Horiuchi M, Caughey B. Specific binding of normal prion protein to the scrapie form via a localized domain initiates its conversion to the protease-resistant state. EMBO J. 1999;18:3193–203.
107 Horiuchi M, Priola SA, Chabry J, Caughey B. Interactions between heterologous forms of prion protein: binding, inhibition of conversion, and species barriers. Proc Natl Acad Sci U S A. 2000;97:5836–41.
108 Solforosi L, Bellon A, Schaller M, Cruite JT, Abalos GC, Williamson RA. Toward molecular dissection of PrPC-PrPSc interactions. J Biol Chem. 2007;282:7465–71.
109 Turnbaugh JA, Unterberger U, Saa P, Massignan T, Fluharty BR, Bowman FP, et al. The N-terminal, polybasic region of PrP(C) dictates the efficiency of prion propagation by binding to PrP(Sc). J Neurosci. 2012;32:8817–30.
110 Kurt TD, Bett C, Fernandez-Borges N, Joshi-Barr S, Hornemann S, Rulicke T, et al. Prion transmission prevented by modifying the beta2-alpha2 loop structure of host PrPC. J Neurosci. 2014;34:1022–7.
111 Caughey B, Kocisko DA, Raymond GJ, Lansbury PT, Jr. Aggregates of scrapie-associated prion protein induce the cell-free conversion of protease-sensitive prion protein to the protease-resistant state. Chem Biol. 1995; 2: 807–17.
112 Come JH, Fraser PE, Lansbury PT, Jr. A kinetic model for amyloid formation in the prion diseases: importance of seeding. Proc Natl Acad Sci U S A. 1993;90:5959–63.
113 Priola SA, Caughey B, Race RE, Chesebro B. Heterologous PrP molecules interfere with accumulation of protease-resistant PrP in scrapie-infected murine neuroblastoma cells. J Virol. 1994;68:4873–8.
114 Holscher C, Delius H, Burkle A. Overexpression of nonconvertible PrPc delta114–121 in scrapie-infected mouse neuroblastoma cells leads to trans-dominant inhibition of wild-type PrP(Sc) accumulation. J Virol. 1998;72:1153–9.
115 Perrier V, Wallace AC, Kaneko K, Safar J, Prusiner SB, Cohen FE. Mimicking dominant negative inhibition of prion replication through structure-based drug design. Proc Natl Acad Sci U S A. 2000;97:6073–8.
116 Silveira JR, Raymond GJ, Hughson AG, Race RE, Sim VL, Hayes SF, et al. The most infectious prion protein particles. Nature. 2005 437:257–61.
117 Simoneau S, Rezaei H, Sales N, Kaiser-Schulz G, Lefebvre-Roque M, Vidal C, et al. In vitro and in vivo neurotoxicity of prion protein oligomers. PLoS Pathog. 2007;3:e125.
118 Erlich P, Dumestre-Perard C, Ling WL, Lemaire-Vieille C, Schoehn G, Arlaud GJ, et al. Complement protein C1q forms a complex with cytotoxic prion protein oligomers. J Biol Chem. 285:19267–76.
119 Bahadi R, Farrelly PV, Kenna BL, Kourie JI, Tagliavini F, Forloni G, et al. Channels formed with a mutant prion protein PrP(82-146) homologous to a 7-kDa fragment in diseased brain of GSS patients. Am J Physiol Cell Physiol. 2003;285:C862–72.
120 Chich JF, Chapuis C, Henry C, Vidic J, Rezaei H, Noinville S. Vesicle permeabilization by purified soluble oligomers of prion protein: a comparative study of the interaction of oligomers and monomers with lipid membranes. J Mol Biol. 397:1017–30.
121 Khosravani H, Zhang Y, Tsutsui S, Hameed S, Altier C, Hamid J, et al. Prion protein attenuates excitotoxicity by inhibiting NMDA receptors. J Gen Physiol. 2008;131:i5.
122 Kristiansen M, Deriziotis P, Dimcheff DE, Jackson GS, Ovaa H, Naumann H, et al. Disease-associated prion protein oligomers inhibit the 26S proteasome. Mol Cell. 2007;26:175–88.
123 Reimann RR, Sonati T, Hornemann S, Herrmann US, Arand M, Hawke S, et al. Differential Toxicity of Antibodies to the Prion Protein. PLoS Pathog. 2016;12:e1005401.
124 Solforosi L, Criado JR, Mcgavern DB, Wirz S, Sanchez-Alavez M, Sugama S, et al. Cross-linking cellular prion protein triggers neuronal apoptosis in vivo. Science. 2004;303:1514–6.
125 Halliday M, Radford H, Sekine Y, Moreno J, Verity N, Le Quesne J, et al. Partial restoration of protein synthesis rates by the small molecule ISRIB prevents neurodegeneration without pancreatic toxicity. Cell Death Dis. 2015;6:e1672.
126 Mckinnon C, Goold R, Andre R, Devoy A, Ortega Z, Moonga J, et al. Prion-mediated neurodegeneration is associated with early impairment of the ubiquitin-proteasome system. Acta Neuropathol. 2016;131:411–25.
127 Moreno JA, Radford H, Peretti D, Steinert JR, Verity N, Martin MG, et al. Sustained translational repression by eIF2α-P mediates prion neurodegeneration. Nature. 2012;485:507–11.
128 Lefebvre-Roque M, Kremmer E, Gilch S, Zou WQ, Feraudet C, Gilles CM, et al. Toxic effects of intracerebral PrP antibody administration during the course of BSE infection in mice. Prion. 2007;1:198–206.
129 Wang F, Wang X, Yuan CG, Ma J. Generating a prion with bacterially expressed recombinant prion protein. Science. 2010;327:1132–5.
130 Cobb NJ, Sonnichsen FD, Mchaourab H, Surewicz WK. Molecular architecture of human prion protein amyloid: a parallel, in-register beta-structure. Proc Natl Acad Sci U S A. 2007;104:18946–51.
131 Wille H, Bian W, Mcdonald M, Kendall A, Colby DW, Bloch L, et al. Natural and synthetic prion structure from X-ray fiber diffraction. Proc Natl Acad Sci U S A. 2009; 106: 16990–5.
132 Huang Z, Prusiner SB, Cohen FE. Scrapie prions: a three-dimensional model of an infectious fragment. Fold Des. 1996;1:13–9.
133 Downing DT, Lazo ND. Molecular modelling indicates that the pathological conformations of prion proteins might be beta-helical. Biochem J. 1999;343Pt 2:453–60.
134 Wille H, Michelitsch MD, Guenebaut V, Supattapone S, Serban A, Cohen FE, et al. Structural studies of the scrapie prion protein by electron crystallography. Proc Natl Acad Sci U S A. 2002;99:3563–8.
135 Mornon JP, Prat K, Dupuis F, Boisset N, Callebaut I. Structural features of prions explored by sequence analysis. II. A PrP(Sc) model. Cell Mol Life Sci. 2002;59:2144–54.
136 Demarco ML, Daggett V. From conversion to aggregation: protofibril formation of the prion protein. Proc Natl Acad Sci U S A. 2004;101:2293–8.
137 Govaerts C, Wille H, Prusiner SB, Cohen FE. Evidence for assembly of prions with left-handed beta-helices into trimers. Proc Natl Acad Sci U S A. 2004;101:8342–7.
138 Stork M, Giese A, Kretzschmar HA, Tavan P. Molecular dynamics simulations indicate a possible role of parallel beta-helices in seeded aggregation of poly-Gln. Biophys J. 2005;88:2442–51.
139 Langedijk JP, Fuentes G, Boshuizen R, Bonvin AM. Two-rung model of a left-handed beta-helix for prions explains species barrier and strain variation in transmissible spongiform encephalopathies. J Mol Biol. 2006;360:907–20.
140 Requena JR, Wille H. The structure of the infectious prion protein: experimental data and molecular models. Prion. 2014;8:60–6.
141 Noble GP, Wang DW, Walsh DJ, Barone JR, Miller MB, Nishina KA, et al. A Structural and Functional Comparison Between Infectious and Non-Infectious Autocatalytic Recombinant PrP Conformers. PLoS Pathog. 2015;11:e1005017.
142 Marciniuk K, Maattanen P, Taschuk R, Airey TD, Potter A, Cashman NR et al. Development of a multivalent, PrP(Sc)-specific prion vaccine through rational optimization of three disease-specific epitopes. Vaccine. 2014; 32: 1988–97.
143 Webb S, Lekishvili T, Loeschner C, Sellarajah S, Prelli F, Wisniewski T, et al. Mechanistic insights into the cure of prion disease by novel antiprion compounds. J Virol. 2007;81:10729–41.
144 Margalith I, Suter C, Ballmer B, Schwarz P, Tiberi C, Sonati T, et al. Polythiophenes inhibit prion propagation by stabilizing prion protein (PrP) aggregates. J Biol Chem. 2012;287:18872–87.
145 Mays CE, Joy S, Li L, Yu L, Genovesi S, West FG, et al. Prion inhibition with multivalent PrPSc binding compounds. Biomaterials. 2012;33:6808–22.
146 Herrmann US, Schütz AK, Shirani H, Huang D, Saban D, Nuvolone M, et al. Structure-based drug design identifies polythiophenes as antiprion compounds. Sci Transl Med. 2015;7:299.
147 Lundmark K, Westermark GT, Nystrom S, Murphy CL, Solomon A, Westermark P. Transmissibility of systemic amyloidosis by a prion-like mechanism. Proc Natl Acad Sci U S A. 2002;99:6979–84. Erratum in: Proc Natl Acad Sci U S A. 2003 Mar 18;100(6):3543.
148 Meyer-Luehmann M, Coomaraswamy J, Bolmont T, Kaeser S, Schaefer C, Kilger E, et al. Exogenous induction of cerebral beta-amyloidogenesis is governed by agent and host. Science. 2006;313:1781–4.
149 Eisele YS, Bolmont T, Heikenwalder M, Langer F, Jacobson LH, Yan ZX, et al. Induction of cerebral beta-amyloidosis: intracerebral versus systemic Abeta inoculation. Proc Natl Acad Sci U S A. 2009;106:12926–31.
150 Luk KC, Song C, O'brien P, Stieber A, Branch JR, Brunden KR, et al. Exogenous alpha-synuclein fibrils seed the formation of Lewy body-like intracellular inclusions in cultured cells. Proc Natl Acad Sci U S A. 2009;106:20051–6.
151 Kordower JH, Chu Y, Hauser RA, Freeman TB, Olanow CW. Lewy body-like pathology in long-term embryonic nigral transplants in Parkinson's disease. Nat Med. 2008;14:504–6.
152 Cortez LM, Campeau J, Norman G, Kalayil M, Van Der Merwe J, Mckenzie D, et al. Bile Acids Reduce Prion Conversion, Reduce Neuronal Loss, and Prolong Male Survival in Models of Prion Disease. J Virol. 2015;89:7660–72.
153 Kumar J, Namsechi R, Sim VL. Structure-Based Peptide Design to Modulate Amyloid Beta Aggregation and Reduce Cytotoxicity. PLoS One. 2015;10:e0129087.
154 Lam HT, Graber MC, Gentry KA, Bieschke J. Stabilization of alpha-Synuclein Fibril Clusters Prevents Fragmentation and Reduces Seeding Activity and Toxicity. Biochemistry. 2016;55:675–85.
155 Berry DB, Lu D, Geva M, Watts JC, Bhardwaj S, Oehler A, et al. Drug resistance confounding prion therapeutics. Proceedings of the National Academy of Sciences of the United States of America. 2013;110.
156 Ghaemmaghami S, Ahn M, Lessard P, Giles K, Legname G, Dearmond SJ, et al. Continuous quinacrine treatment results in the formation of drug-resistant prions. PLoS Pathog. 2009;5:e1000673.
157 Oelschlegel A, Weissmann C. Acquisition of Drug Resistance and Dependence by Prions. PLoS Pathog. 2013;9:e1003158.
158 Kawasaki Y, Kawagoe K, Chen CJ, Teruya K, Sakasegawa Y, Doh-Ura K. Orally administered amyloidophilic compound is effective in prolonging the incubation periods of animals cerebrally infected with prion diseases in a prion strain-dependent manner. J Virol. 2007;81:12889–98.
159 Jackrel ME, Shorter J. Engineering enhanced protein disaggregases for neurodegenerative disease. Prion. 2015;9:90–109.
160 Chernoff YO, Lindquist SL, Ono B, Inge-Vechtomov SG, Liebman SW. Role of the chaperone protein Hsp104 in propagation of the yeast prion-like factor [psi+]. Science. 1995;268:880–4.
161 Wang H, Tian C, Fan XY, Chen LN, Lv Y, Sun J, et al. Polo-like kinase 3 (PLK3) mediates the clearance of the accumulated PrP mutants transiently expressed in cultured cells and pathogenic PrP(Sc) in prion infected cell line via protein interaction. Int J Biochem Cell Biol. 2015;62:24–35.
162 Wang ZY, Shi Q, Wang SB, Tian C, Xu Y, Guo Y, et al. Co-expressions of casein kinase 2 (CK2) subunits restore the down-regulation of tubulin levels and disruption of microtubule structures caused by PrP mutants. J Mol Neurosci. 2013;50:14–22.
163 Kovalchuk Ben-Zaken O, Nissan I, Tzaban S, Taraboulos A, Zcharia E, Matzger S, et al. Transgenic over-expression of mammalian heparanase delays prion disease onset and progression. Biochem Biophys Res Commun. 2015;464:698–704.
Acknowledgments:The authors are grateful for the support from IKERBasque foundation, Dr. Jesús R. Requena (CIMUS, University of Santiago de Compostela) for useful discussion and Theresa Haran for careful language revision.
Disclosure statement: This work was financially supported by a national grant from Spain (AGL2015-65046-C2-1-R) and a Basque government grant (2014111157). No other potential conflict of interest relevant to this article was reported.