The clinicopathological phenotypes of sporadic Creutzfeldt-Jakob disease (sCJD) correlate with the allelotypes (M or V) of the polymorphic codon 129 of the human prion protein (PrP) gene and the electrophoretic mobility patterns of abnormal prion protein (PrP Sc ). Transmission of sCJD prions to mice expressing human PrP with a heterologous genotype (referred to as cross-sequence transmission) results in prolonged incubation periods. We previously reported that cross-sequence transmission can generate a new prion strain with unique transmissibility, designated a traceback phenomenon. To verify experimentally the traceback of sCJD-VV2 prions, we inoculated sCJD-VV2 prions into mice expressing human PrP with the 129M/M genotype. These 129M/M mice showed altered neuropathology and a novel PrP Sc type after a long incubation period. We then passaged the brain homogenate from the 129M/M mouse inoculated with sCJD-VV2 prions into other 129M/M or 129V/V mice. Despite cross-sequence transmission, 129V/V mice were highly susceptible to these prions compared to the 129M/M mice. The neuropathology and PrP Sc type of the 129V/V mice inoculated with the 129M/M mouse-passaged sCJD-VV2 prions were identical to those of the 129V/V mice inoculated with sCJD-VV2 prions. Moreover, we generated for the first time a type 2 PrP Sc -specific antibody in addition to type 1 PrP Sc -specific antibody and discovered that drastic changes in the PrP Sc subpopulation underlie the traceback phenomenon. Here, we report the first direct evidence of the traceback in prion infection.

Atypical bovine spongiform encephalopathy (BSE) has recently been identified in Europe, North America, and Japan. It is classified as H-type and L-type BSE according to the molecular mass of the disease-associated prion protein (PrPSc). To investigate the topographical distribution and deposition patterns of immunolabeled PrPSc, H-type BSE isolate was inoculated intracerebrally into cattle. H-type BSE was successfully transmitted to 3 calves, with incubation periods between 500 and 600 days. Moderate to severe spongiform changes were detected in the cerebral and cerebellar cortices, basal ganglia, thalamus, and brainstem. H-type BSE was characterized by the presence of PrP-immunopositive amyloid plaques in the white matter of the cerebrum, basal ganglia, and thalamus. Moreover, intraglial-type immunolabeled PrPSc was prominent throughout the brain. Stellate-type immunolabeled PrPSc was conspicuous in the gray matter of the cerebral cortex, basal ganglia, and thalamus, but not in the brainstem. In addition, PrPSc accumulation was detected in the peripheral nervous tissues, such as trigeminal ganglia, dorsal root ganglia, optic nerve, retina, and neurohypophysis. Cattle are susceptible to H-type BSE with a shorter incubation period, showing distinct and distinguishable phenotypes of PrPSc accumulation.

BackgroundSporadic Creutzfeldt-Jakob disease is classified according to the genotype at polymorphic codon 129 (M or V) of the prion protein (PrP) gene and the type (1 or 2) of abnormal isoform of PrP (PrPSc) in the brain. The most complicated entity in the current classification system is MV2, since it shows wide phenotypic variations, i.e., MV2 cortical form (MV2C), MV2 with kuru plaques (MV2K), or a mixed form (MV2K + C). To resolve their complicated pathogenesis, we performed a comprehensive analysis of the three MV2 subgroups based on histopathological, molecular, and transmission properties.ResultsIn histopathological and molecular analyses, MV2C showed close similarity to MM2 cortical form (MM2C) and could be easily discriminated from the other MV2 subgroups. By contrast, MV2K and MV2K + C showed the same molecular type and the same transmission type, and the sole difference between MV2K and MV2K + C was the presence of cortical pathology characteristic of MV2C/MM2C. The remarkable molecular feature of MV2K or MV2K + C was a mixture of type 2 PrPSc and intermediate type PrPSc, which shows intermediate electrophoretic mobility between types 1 and 2 PrPSc. Modeling experiments using PrP-humanized mice indicated that MV2K contains a mixture of intermediate type PrPSc with the 129M genotype (Mi PrPSc) and type 2 PrPSc with the 129V genotype (V2 PrPSc) that originated from V2 PrPSc, whereas MV2C + K may also contain type 2 PrPSc with the 129M genotype and cortical pathology (M2C PrPSc) that lacks infectivity to the PrP-humanized mice in addition to Mi and V2 PrPSc.ConclusionsTaken together, the present study suggests that the phenotypic heterogeneity of MV2 stems from their different PrPSc origin(s).

Two normally occurring polymorphisms of the human PRNP gene, methionine (M)/valine (V) at codon 129 and glutamic acid (E)/lysine (K) at codon 219, can affect the susceptibility to prion diseases. It has long been recognized that 129M/M homozygotes are overrepresented in sporadic Creutzfeldt-Jakob disease (CJD) patients and variant CJD patients, whereas 219E/K heterozygotes are absent in sporadic CJD patients. In addition to these pioneering findings, recent progress in experimental transmission studies and worldwide surveillance of prion diseases have identified novel relationships between the PRNP polymorphisms and the prion disease susceptibility. For example, although 219E/K heterozygosity confers resistance against the development of sporadic CJD, this genotype is not entirely protective against acquired forms (iatrogenic CJD and variant CJD) or genetic forms (genetic CJD and Gerstmann-Sträussler-Scheinker syndrome) of prion diseases. In addition, 129M/V heterozygotes predispose to genetic CJD caused by a pathogenic PRNP mutation at codon 180. These findings show that the effects of the PRNP polymorphisms may be more complicated than previously thought. This review aims to summarize recent advances in our knowledge about the influence of the PRNP polymorphisms on the prion disease susceptibility.

It has been assumed that the agent causing BSE in cattle is a uniform strain (classical BSE); however, different neuropathological and molecular phenotypes of BSE (atypical BSE) have been recently reported. We demonstrated the successful transmission of L-type-like atypical BSE detected in Japan (BSE/JP24 isolate) to cattle. Based on the incubation period, neuropathological hallmarks, and molecular properties of the abnormal host prion protein, the characteristics of BSE/JP24 prion were apparently distinguishable from the classical BSE prion and closely resemble those of bovine amyloidotic spongiform encephalopathy prion detected in Italy.

BackgroundPrions, infectious agents associated with prion diseases such as Creutzfeldt-Jakob disease in humans, bovine spongiform encephalopathy (BSE) in cattle, and scrapie in sheep and goats, are primarily comprised of PrPSc, a protease-resistant misfolded isoform of the cellular prion protein PrPC. Protein misfolding cyclic amplification (PMCA) is a highly sensitive technique used to detect minute amounts of scrapie PrPSc. However, the current PMCA technique has been unsuccessful in achieving good amplification in cattle. The detailed distribution of PrPSc in BSE-affected cattle therefore remains unknown.Methodology/Principal FindingsWe report here that PrPSc derived from BSE-affected cattle can be amplified ultra-efficiently by PMCA in the presence of sulfated dextran compounds. This method is capable of amplifying very small amounts of PrPSc from the saliva, palatine tonsils, lymph nodes, ileocecal region, and muscular tissues of BSE-affected cattle. Individual differences in the distribution of PrPSc in spleen and cerebrospinal fluid samples were observed in terminal-stage animals. However, the presence of PrPSc in blood was not substantiated in the BSE-affected cattle examined.Conclusions/SignificanceThe distribution of PrPSc is not restricted to the nervous system and can spread to peripheral tissues in the terminal disease stage. The finding that PrPSc could be amplified in the saliva of an asymptomatic animal suggests a potential usefulness of this technique for BSE diagnosis. This highly sensitive method also has other practical applications, including safety evaluation or safety assurance of products and byproducts manufactured from bovine source materials.

A case of L-type-like atypical bovine spongiform encephalopathy was detected in 14-year-old Japanese black beef cattle (BSE/ JP24). To clarify the biological and biochemical properties of the prion in BSE/JP24, we performed a transmission study with wildtype mice and bovinized transgenic mice (TgBoPrP). The BSE/ JP24 prion was transmitted to TgBoPrP mice with the incubation period of 199.7 ± 3.4 days, which was shorter than that of classical BSE (C-BSE) (223.5 ± 13.5 days). Further, C-BSE was transmitted to wild-type mice with the incubation period of about 409 days, whereas BSE/JP24 prion inoculated mice showed no clinical signs up to 649 days. Severe vacuolation and a widespread and uniform distribution of PrP Sc were pathologically observed in the brain of BSE/JP24 prion affected TgBoPrP mice. The molecular weight and glycoform ratio of PrP Sc in BSE/JP24 were different from those in C-BSE, and PrP Sc in BSE/JP24 exhibited weaker proteinase K resistance than that in C-BSE. These findings revealed that the BSE/JP24 prion has distinct biological and biochemical properties reported for that of C-BSE. Interestingly, a shorter incubation period was observed at the subsequent passage of the BSE/JP24 prion to TgBoPrP mice (152.2 ± 3.1 days). This result implies that BSE/JP24 prion has newly emerged and showed the possibility that L-type BSE prion might be classified into multiple strains.

Dura mater graft-associated Creutzfeldt-Jakob disease (dCJD) can be divided into two subgroups that exhibit distinct clinical and neuropathological features, with the majority represented by a non-plaque-type of dCJD (np-dCJD) and the minority by a plaque-type of dCJD (p-dCJD). The two distinct phenotypes of dCJD had been considered to be unrelated to the genotype (methionine, M or valine, V) at polymorphic codon 129 of the PRNP gene or type (type 1 or type 2) of abnormal isoform of prion protein (PrPSc) in the brain, while these are major determinants of clinicopathological phenotypes of sporadic CJD (sCJD). The reason for the existence of two distinct subgroups in dCJD had remained elusive. Recent progress in research of the pathogenesis of dCJD has revealed that two distinct subgroups of dCJD are caused by infection with different PrPSc strains from sCJD, i.e., np-dCJD caused by infection with sCJD-MM1/MV1, and p-dCJD caused by infection with sCJD-VV2 or -MV2. These studies have also revealed previously unrecognized problems as follows: (i) the numbers of p-dCJD patients may increase in the future, (ii) the potential risks of secondary infection from dCJD, particularly from p-dCJD, may be considerable, and (iii) the effectiveness of the current PrPSc decontamination procedures against the PrPSc from p-dCJD is uncertain. To prevent secondary infection from p-dCJD, the establishment of effective decontamination procedures is an urgent issue. In this review, we summarize the past and future problems surrounding dCJD.