Prions from Sporadic Creutzfeldt-Jakob Disease Patients Propagate as Strain Mixtures

Abstract

Sporadic Creutzfeldt-Jakob disease (sCJD) cases are currently classified according to the methionine/valine polymorphism at codon 129 of the PRNP gene and the proteinase K-digested abnormal prion protein (PrPres) isoform identified by Western blotting (type 1 or type 2). Converging evidence led to the view that MM/MV1, VV/MV2, and VV1 and MM2 sCJD cases are caused by distinct prion strains. However, in a significant proportion of sCJD patients, both type 1 and type 2 PrPres were reported to accumulate in the brain, which raised questions about the diversity of sCJD prion strains and the coexistence of two prion strains in the same patient. In this study, a panel of sCJD brain isolates (n = 29) that displayed either a single or mixed type 1/type 2 PrPres were transmitted into human-PrP-expressing mice (tgHu). These bioassays demonstrated that two distinct prion strains (M1CJD and V2CJD) were associated with the development of sCJD in MM1/MV1 and VV2/MV2 patients. However, in about 35% of the investigated VV and MV cases, transmission results were consistent with the presence of both M1CJD and V2CJD strains, including in patients who displayed a “pure” type 1 or type 2 PrPres. The use of a highly sensitive prion in vitro amplification technique that specifically probes the V2CJD strain revealed the presence of the V2CJD prion in more than 80% of the investigated isolates, including isolates that propagated as a pure M1CJD strain in tgHu. These results demonstrate that at least two sCJD prion strains can be present in a single patient. IMPORTANCE sCJD occurrence is currently assumed to result from spontaneous and stochastic formation of a misfolded PrP nucleus in the brains of affected patients. This original nucleus then recruits and converts nascent PrPC into PrPSc, leading to the propagation of prions in the patient’s brain. Our study demonstrates the coexistence of two prion strains in the brains of a majority of the 23 sCJD patients investigated. The relative proportion of these sCJD strains varied both between patients and between brain areas in a single patient. These findings strongly support the view that the replication of an sCJD prion strain in the brain of a patient can result in the propagation of different prion strain subpopulations. Beyond its conceptual importance for our understanding of prion strain properties and evolution, the sCJD strain mixture phenomenon and its frequency among patients have important implications for the development of therapeutic strategies for prion diseases.

Sensitive protein misfolding cyclic amplification of sporadic Creutzfeldt–Jakob disease prions is strongly seed and substrate dependent

“…A similar in vivo observation was also reported after transmission to the same TgMet mice used in our study 49 and confirmed by Cassard et al . after the propagation of MV2 and VV2 sCJD prions from the brain of 10 different patients with confirmed sCJD in a very similar TgMet line 14 . However, in Bishop et al study completed by the recent results from Cassard et al, type-1 sCJD subtypes transmitted to HuVV mice maintained their initial type-1 PrP res signature, which in this respect contrasts with our current in vitro observations.…”

Improving the Predictive Value of Prion Inactivation Validation Methods to Minimize the Risks of Iatrogenic Transmission With Medical Instruments

“…Human prions did not escape the rule. Sporadic and vCJD prions propagate without species barrier in mice transgenic for human PrP, in the absence of mismatch at polymorphic codon 129 (Bishop et al, 2010;Beringue et al, 2012;Chapuis et al, 2016;Jaumain et al, 2016;Cassard et al, 2020). These models, -in the absence of cell models propagating human prions -, allow a relatively rapid, inexpensive, and large production of potentially biologically cloned and well-characterized humanized prions with respect to pathogenesis, strain type and infectivity titers.…”

“…At least six distinct strain types are described according to their transmission properties in transgenic mice expressing human PrP. Starting from the most prevalent cases in the population, these strains are classified as MM1/MV1, VV2, MV2, VV1, cortical-MM2, thalamic-MM2 strains (Bishop et al, 2010;Moda et al, 2012;Chapuis et al, 2016;Jaumain et al, 2016;Cassard et al, 2020). Co-propagation of MM1 and VV2 strains has been observed in a significant proportion of sporadic CJD patients (Cassard et al, 2020).…”

“…(D) PrP Sc assemblies (C i ) dilution in PMCA buffer tends to displace a detailed-balance toward the formation of smaller objects here termed C 1 , which are assimilated to suPrP (Igel-Egalon et al, 2017). 2014; Bougard et al, 2016;Concha-Marambio et al, 2016;Cassard et al, 2020); (2) The PrP C substrate can be optimized. The higher the PrP C concentration, the higher the sensitivity achieved (Mays et al, 2009;Moudjou et al, 2014Moudjou et al, , 2016, which lends support for the use of brain from transgenic mice overexpressing PrP C .…”

“…Phenotypically, prion strains encode unique stereotypical biological traits including the time course to disease, neuropathological features and tropism for specific brain regions or lymphoid organs (Bruce, 2003;Collinge and Clarke, 2007;Beringue et al, 2008b;Weissmann et al, 2011). Co-propagation of strains has been observed, notably in CJD (Cassard et al, 2020) and sheep scrapie (Le Dur et al, 2017;Huor et al, 2019). PrP Sc structural polymorphism is mostly considered as between strain polymorphism.…”