Oxidation of Helix-3 Methionines Precedes the Formation of PK Resistant PrPSc

While elucidating the peculiar epitope of the α-PrP mAb IPC2, we found that PrPSc exhibits the sulfoxidation of residue M213 as a covalent signature. Subsequent computational analysis predicted that the presence of sulfoxide groups at both Met residues 206 and 213 destabilize the α-fold, suggesting oxidation may facilitate the conversion of PrPC into PrPSc. To further study the effect of oxidation on prion formation, we generated pAbs to linear PrP peptides encompassing the Helix-3 region, as opposed to the non-linear complexed epitope of IPC2. We now show that pAbs, whose epitopes comprise Met residues, readily detected PrPC, but could not recognize most PrPSc bands unless they were vigorously reduced. Next, we showed that the α-Met pAbs did not recognize newly formed PrPSc, as is the case for the PK resistant PrP present in lines of prion infected cells. In addition, these reagents did not detect intermediate forms such as PK sensitive and partially aggregated PrPs present in infected brains. Finally, we show that PrP molecules harboring the pathogenic mutation E200K, which is linked to the most common form of familial CJD, may be spontaneously oxidized. We conclude that the oxidation of methionine residues in Helix-3 represents an early and important event in the conversion of PrPC to PrPSc. We believe that further investigation into the mechanism and role of PrP oxidation will be central in finally elucidating the mechanism by which a normal cell protein converts into a pathogenic entity that causes fatal brain degeneration.This work has been supported by grants from the Israeli Science foundation and The Israeli Ministry of Health (RG) as well as grants BFU2009-07971 from the Ministerio de Ciencia e Innovación (MG) and PI101209 from the Fundación Cien (MG)

Targeting of prion-infected lymphoid cells to the central nervous system accelerates prion infection

BACKGROUND: Prions, composed of a misfolded protein designated PrP(Sc), are infectious agents causing fatal neurodegenerative diseases. We have shown previously that, following induction of experimental autoimmune encephalomyelitis, prion-infected mice succumb to disease significantly earlier than controls, concomitant with the deposition of PrP(Sc) aggregates in inflamed white matter areas. In the present work, we asked whether prion disease acceleration by experimental autoimmune encephalomyelitis results from infiltration of viable prion-infected immune cells into the central nervous system. METHODS: C57Bl/6 J mice underwent intraperitoneal inoculation with scrapie brain homogenates and were later induced with experimental autoimmune encephalomyelitis by inoculation of MOG(35-55) in complete Freund's adjuvant supplemented with pertussis toxin. Spleen and lymph node cells from the co-induced animals were reactivated and subsequently injected into naïve mice as viable cells or as cell homogenates. Control groups were infected with viable and homogenized scrapie immune cells only with complete Freund's adjuvant. Prion disease incubation times as well as levels and sites of PrP(Sc) deposition were next evaluated. RESULTS: We first show that acceleration of prion disease by experimental autoimmune encephalomyelitis requires the presence of high levels of spleen PrP(Sc). Next, we present evidence that mice infected with activated prion-experimental autoimmune encephalomyelitis viable cells succumb to prion disease considerably faster than do mice infected with equivalent cell extracts or other controls, concomitant with the deposition of PrP(Sc) aggregates in white matter areas in brains and spinal cords. CONCLUSIONS: Our results indicate that inflammatory targeting of viable prion-infected immune cells to the central nervous system accelerates prion disease propagation. We also show that in the absence of such targeting it is the load of PrP(Sc) in the inoculum that determines the infectivity titers for subsequent transmissions. Both of these conclusions have important clinical implications as related to the risk of prion disease contamination of blood products

Fatal Prion Disease in a Mouse Model of Genetic E200K Creutzfeldt-Jakob Disease

Genetic prion diseases are late onset fatal neurodegenerative disorders linked to pathogenic mutations in the prion protein-encoding gene, PRNP. The most prevalent of these is the substitution of Glutamate for Lysine at codon 200 (E200K), causing genetic Creutzfeldt-Jakob disease (gCJD) in several clusters, including Jews of Libyan origin. Investigating the pathogenesis of genetic CJD, as well as developing prophylactic treatments for young asymptomatic carriers of this and other PrP mutations, may well depend upon the availability of appropriate animal models in which long term treatments can be evaluated for efficacy and toxicity. Here we present the first effective mouse model for E200KCJD, which expresses chimeric mouse/human (TgMHu2M) E199KPrP on both a null and a wt PrP background, as is the case for heterozygous patients and carriers. Mice from both lines suffered from distinct neurological symptoms as early as 5–6 month of age and deteriorated to death several months thereafter. Histopathological examination of the brain and spinal cord revealed early gliosis and age-related intraneuronal deposition of disease-associated PrP similarly to human E200K gCJD. Concomitantly we detected aggregated, proteinase K resistant, truncated and oxidized PrP forms on immunoblots. Inoculation of brain extracts from TgMHu2ME199K mice readily induced, the first time for any mutant prion transgenic model, a distinct fatal prion disease in wt mice. We believe that these mice may serve as an ideal platform for the investigation of the pathogenesis of genetic prion disease and thus for the monitoring of anti-prion treatments

Methionine Sulfoxides on Prion Protein Helix-3 Switch on the α-Fold Destabilization Required for Conversion

BACKGROUND: The conversion of the cellular prion protein (PrP(C)) into the infectious form (PrP(Sc)) is the key event in prion induced neurodegenerations. This process is believed to involve a multi-step conformational transition from an alpha-helical (PrP(C)) form to a beta-sheet-rich (PrP(Sc)) state. In addition to the conformational difference, PrP(Sc) exhibits as covalent signature the sulfoxidation of M213. To investigate whether such modification may play a role in the misfolding process we have studied the impact of methionine oxidation on the dynamics and energetics of the HuPrP(125-229) alpha-fold. METHODOLOGY/PRINCIPAL FINDINGS: Using molecular dynamics simulation, essential dynamics, correlated motions and signal propagation analysis, we have found that substitution of the sulfur atom of M213 by a sulfoxide group impacts on the stability of the native state increasing the flexibility of regions preceding the site of the modification and perturbing the network of stabilizing interactions. Together, these changes favor the population of alternative states which maybe essential in the productive pathway of the pathogenic conversion. These changes are also observed when the sulfoxidation is placed at M206 and at both, M206 and M213. CONCLUSIONS/SIGNIFICANCE: Our results suggest that the sulfoxidation of Helix-3 methionines might be the switch for triggering the initial alpha-fold destabilization required for the productive pathogenic conversion

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements