Transmissibility of H-Type Bovine Spongiform Encephalopathy to Hamster PrP Transgenic Mice

Influence of Interspecies Transmission of Atypical Bovine Spongiform Encephalopathy Prions to Hamsters on Prion Characteristics

Bovine spongiform encephalopathy (BSE) is a prion disease in cattle and is classified into the classical type (C-BSE) and two atypical BSEs, designated as high type (H-BSE) and low type (L-BSE). These classifications are based on the electrophoretic migration of the proteinase K-resistant core (PrP^res) of the disease-associated form of the prion protein (PrP^d). In a previous study, we succeeded in transmitting the H-BSE prion from cattle to TgHaNSE mice overexpressing normal hamster cellular PrP (PrP^C). Further, Western blot analysis demonstrated that PrP^res banding patterns of the H-BSE prion were indistinguishable from those of the C-BSE prion in TgHaNSE mice. In addition, similar PrP^res glycoprofiles were detected among H-, C-, and L-BSE prions in TgHaNSE mice. Therefore, to better understand atypical BSE prions after interspecies transmission, H-BSE prion transmission from TgHaNSE mice to hamsters was investigated, and the characteristics of classical and atypical BSE prions among hamsters, wild-type mice, and mice overexpressing bovine PrP^C (TgBoPrP) were compared in this study using biochemical and neuropathological methods. Identical PrP^res banding patterns were confirmed between TgHaNSE mice and hamsters in the case of all three BSE prion strains. However, these PrP^res banding patterns differed from those of TgBoPrP and wild-type mice infected with the H-BSE prion. In addition, glycoprofiles of TgHaNSE mice and hamsters infected with the L-BSE prion differed from those of TgBoPrP mice infected with the L-BSE prion. These data indicate that the PrP^C amino acid sequences of new host species rather than other host environmental factors may affect some molecular aspects of atypical BSE prions. Although three BSE prion strains were distinguishable based on the neuropathological features in hamsters, interspecies transmission modified some molecular properties of atypical BSE prions, and these properties were indistinguishable from those of C-BSE prions in hamsters. Taken together, PrP^res banding patterns and glycoprofiles are considered to be key factors for BSE strain typing. However, this study also revealed that interspecies transmission could sometimes influence these characteristics.

Prion Strains and Transmission Barrier Phenomena

Several experimental evidences show that prions are non-conventional pathogens, which physical support consists only in proteins. This finding raised questions regarding the observed prion strain-to-strain variations and the species barrier that happened to be crossed with dramatic consequences on human health and veterinary policies during the last 3 decades. This review presents a focus on a few advances in the field of prion structure and prion strains characterization: from the historical approaches that allowed the concept of prion strains to emerge, to the last results demonstrating that a prion strain may in fact be a combination of a few quasi species with subtle biophysical specificities. Then, we will focus on the current knowledge on the factors that impact species barrier strength and species barrier crossing. Finally, we present probable scenarios on how the interaction of strain properties with host characteristics may account for differential selection of new conformer variants and eventually species barrier crossing.

Experimental Infection of Cattle With a Novel Prion Derived From Atypical H-Type Bovine Spongiform Encephalopathy

H-type bovine spongiform encephalopathy (H-BSE) is an atypical form of BSE in cattle. During passaging of H-BSE in transgenic bovinized (TgBoPrP) mice, a novel phenotype of BSE, termed BSE-SW emerged and was characterized by a short incubation time and host weight loss. To investigate the biological and biochemical properties of the BSE-SW prion, a transmission study was conducted in cattle, which were inoculated intracerebrally with brain homogenate from BSE-SW-infected TgBoPrP mice. The disease incubation period was approximately 15 months. The animals showed characteristic neurological signs of dullness, and severe spongiform changes and a widespread, uniform distribution of disease-associated prion protein (PrP^Sc) were observed throughout the brain of infected cattle. Immunohistochemical PrP^Sc staining of the brain revealed the presence of intraglial accumulations and plaque-like deposits. No remarkable differences were identified in vacuolar lesion scores, topographical distribution patterns, and staining types of PrP^Sc in the brains of BSE-SW- vs H-BSE-infected cattle. PrP^Sc deposition was detected in the ganglia, vagus nerve, spinal nerve, cauda equina, adrenal medulla, and ocular muscle. Western blot analysis revealed that the specific biochemical properties of the BSE-SW prion, with an additional 10- to 12-kDa fragment, were well maintained after transmission. These findings indicated that the BSE-SW prion has biochemical properties distinct from those of H-BSE in cattle, although clinical and pathologic features of BSW-SW in cattle are indistinguishable from those of H-BSE. The results suggest that the 2 infectious agents, BSE-SW and H-BSE, are closely related strains.

Intra- and Interspecies Transmission of Atypical BSE - What Can We Learn from It?

After the detection of the first cases of atypical bovine spongiform encephalopathy (BSE) more than ten years ago, the etiology, pathogenesis and agent distribution of these novel BSE forms in cattle were completely unknown. Many studies have been performed in the meantime to elucidate the pathogenic mechanisms of these diseases. A wealth of data has been accumulated regarding the distribution of the abnormal isoform of the prion protein, PrP^Sc, in tissues of affected cattle, confirming the general restriction of the PrP^Sc and agent distribution to the central and peripheral nervous system, albeit at slightly higher levels as compared to classical BSE. However, due to lack of data, the assumptions regarding the spontaneous etiology of both atypical BSE forms (H-BSE and L-BSE) and also the origin of the classical BSE epidemic are still mainly speculative. By performing subpassage experiments of both the atypical BSE forms in a variety of conventional and transgenic mice and Syrian Gold hamsters, we aimed to improve our understanding of the strain stability of these BSE forms. It turned out that under these experimental conditions, both the atypical BSE forms may alter their phenotypes and become indistinguishable from classical BSE. Information about the classical and atypical BSE strain characteristics help to improve our understanding of the correlation between all three BSE forms.