Classical bovine spongiform encephalopathy and chronic wasting disease:two sides of the prion coin

Transmissible spongiform encephalopathies(TSEs)are a group of progressive and ultimately fatal neurologic diseases of man and animals,all resulting from the propagated misfolding of the host's normal cellular prion protein.These diseases can be spontaneous,heritable,anthropogenic/iatrogenic,or in some cases horizontally transmissible,and include such notable TSEs as bovine spongiform encephalopathy(BSE)of cattle and chronic wasting disease(CWD)of cervids.Although they are both unequivocally protein misfolding disorders,they differ markedly in their pathogenesis,transmissibility,and zoonotic potential.While the BSE epidemic has largely abated over the past three decades following global feed bans on ruminant meat and bone meal,CWD,which is readily transmitted through various forms of excreta,has rapidly expanded from its original endemic zone to encompass much of North America,along with recently identified foci in Scandinavia.Most importantly,although the classical form of BSE has proven transmissible to humans consuming contaminated beef or beef products,so far there have been no conclusive reports on the zoonotic transmission of cWD to humans.The underlying basis for these differences-whether host or agent directed-are not well understood,though may be due to inherent differences in the three-dimensional structure of the misfolded BSE or CWD prion proteins or the expression levels and tissue distribution of respective cellular prion proteins.With the uncontrolled geographic spread of CWD,it is imperative that we improve our understanding of the factors governing prion disease pathogenesis,transmission,and zoonotic potential.

Impacts of bovine spongiform encephalopathy and avian influenza on U.S. meat demand

This paper examines the U.S. meat demand impacts of the announced outbreaks of bovine spongiform encephalopathy（BSE） and avian influenza（AI）. Findings indicate that beef and chicken demand was negatively affected by BSE and AI disease outbreaks. Specifically, in the short run, U.S. consumers shift demand due to both outbreaks but more so due to domestic disease outbreaks than for outbreaks occurring overseas-the impact of U.S. AI outbreaks is about 0.5% for beef and the impact of U.S. BSE cases is around –0.42% for beef and 0.4% for pork, respectively. Regarding the BSE shock on meat demand, there is a high rate of beef demand adjusted from disturbance to the long-run equilibrium and a lower adjustment rate for chicken demand because of the repeated outbreaks of AI worldwide. In the long run, information related to severe, persistently recurring overseas animal disease outbreaks changes U.S. consumers＇ meat consumption patterns. Although effects of animal diseases on U.S. meat demand were statistically significant, the magnitudes were small-the impact of WHO reported human death numbers for AI is 0.005% for beef, –0.002% for pork, and –0.006% for chicken and the impact of U.S. BSE cases is 1.1% for pork and –0.7% for chicken.

Progress on low susceptibility mechanisms of transmissible spongiform encephalopathies

Transmissible spongiform encephalopathies （TSEs）, also known as prion diseases, are a group of fatal neurodegenerative diseases detected in a wide range of mammalian species. The ＂protein-only＂ hypothesis of TSE suggests that prions are transmissible particles devoid of nucleic acid and the primary pathogenic event is thought to be the conversion of cellular prion protein （PrPc） into the disease-associated isoform （prpSc）. According to susceptibility to TSEs, animals can be classified into susceptible species and low susceptibility species. In this review we focus on several species with low susceptibility to TSEs： dogs, rabbits, horses and buffaloes. We summarize recent studies into the characteristics of low susceptibility regarding protein structure, and biochemical and genetic properties.

Inducing prion protein shedding as a neuroprotective and regenerative approach in pathological conditions of the brain:from theory to facts

In the last decades,the role of the prion protein(PrP) in neurodegenerative diseases has been intensively investigated,initially in prion diseases of humans(e.g., Creutzfeldt-J akob disease) and animals(e.g.,scrapie in sheep,chronic wasting disease in deer and elk,or "mad cow disease" in cattle).Templated misfolding of physiological cellular prion protein(PrPC) into an aggregation-prone isoform(termed PrP "Scrapie"(PrPSc)),self-re plication and spreading of the latter inside the brain and to peripheral tissues,and the associated formation of infectious proteopathic seeds(termed "prions")are among the essential pathogenic mechanisms underlying this group of fatal and transmissible spongiform encephalopathies.Late r,key roles of the correctly folded PrPCwere identified in more common human brain diseases(such as Alzheimer s disease or Parkinson’s disease) associated with the misfolding and/or accumulation of other proteins(such as amyloid-β,tau or α-synuclein,respectively).PrPChas also been linked with n euro protective and regenerative functions,for instance in hypoxic/ischemic conditions such as stroke.However,despite a mixed "bouquet" of suggested functions,our understanding of pathological and,especially,physiological roles played by PrPCin the brain and beyond is ce rtainly incomplete.Interactions with various other proteins at the cell surfa ce or within intracellular compartments may account for the functional diversity linked with PrPC.Moreover,conserved endogenous proteolytic processing of PrPCgenerates seve ral defined PrPCfragments,possibly holding intrinsic functions in physiological and pathological conditions,thus making the "true and complete biology" of this protein more complicated to be elucidated.Here,we focus on one of those released PrPCfragments,namely shed PrP(sPrP),generated by a membrane-proximate ADAM10-mediated cleavage event at the cell surfa ce.Similar to other soluble PrP fragments(such as the N1 fragment representing PrP’s released N-terminal tail upon the major α-cleavage event)or expe rimentally employed recombinant PrP,sPrP is being suggested to act n euro protective in Alzheimer’s disease and other protein misfolding diseases.Seve ral lines of evidence on extracellular PrPC(fragments) suggest that induction of PrPCrelease co uld be a future therapeutic option in various brain disorders.Our recent identification of a substrate-specific approach to stimulate the shedding by ADAM 10,based on ligands binding to cell surface PrPC,may further set the stage for research into this direction.

Protein folding pathology in domestic animals

Fibrillar proteins form structural elements of cells and the extracellular matrix. Pathological lesions, of fibrillar microanatomical structures, or secondary fibrillar changes in globular proteins are well known. A special group concerns histologically amorphous deposits, amyloid. The major characteristics of amyloid are: apple green birefringence after Congo red staining of histological sections, and non-branching 7–10 nm thick fibrils on electron microscopy revealing a high content of cross beta pleated sheets. About 25 different types of amyloid have been characterised. In animals, AA-amyloid is the most frequent type. Other types of amyloid in animals represent: AIAPP (in cats), AApoAI, AApoAII, localised AL-amyloid, amyloid in odontogenic or mammary tumors and amyloid in the brain. In old dogs Aβ and in sheep APrPsc-amyloid can be encountered. AA-amyloidosis is a systemic disorder with a precursor in blood, acute phase serum amyloid A (SAA). In chronic inflammatory processes AA-amyloid can be deposited. A rapid crystallization of SAA to amyloid fibrils on small beta-sheeted fragments, the ‘amyloid enhancing factor’ (AEF), is known and the AEF has been shown to penetrate the enteric barrier. Amyloid fibrils can aggregate from various precursor proteins in vitro in particular at acidic pH and when proteolytic fragments are formed. Molecular chaperones influence this process. Tissue data point to amyloid fibrillogenesis in lysosomes and near cell surfaces. A comparison can be made of the fibrillogenesis in prion diseases and in enhanced AA-amyloidosis. In the reactive form, acute phase SAA is the supply of the precursor protein, whereas in the prion diseases, cell membrane proteins form a structural source. Aβ-amyloid in brain tissue of aged dogs showing signs of dementia forms a canine counterpart of senile dementia of the Alzheimer type (ccSDAT) in man. Misfolded proteins remain potential food hazards. Developments concerning prevention of amyloidogenesis and therapy of amyloid deposits are shortly commented.

Correlation between the Insertion/Deletion Mutations of Prion Protein Gene and BSE Susceptibility and Milk Performance in Dairy Cows

Objective To investigate the 23 bp and 12 bp insertion/deletion(indel)mutations within the bovine prion protein(PRNP)gene in Chinese dairy cows,and to detect the associations of two indel mutations with BSE susceptibility and milk performance.Methods Based on bovine PRNP gene sequence,two pairs of primers for testing the 23 bp and 12 bp indel mutations were designed.The PCR amplification and agarose electrophoresis were carried out to distinguish the different genotypes within the mutations.Moreover,based on previous data from other cattle breeds and present genotypic and allelic frequencies of two indels mutations in this study,the corrections between the two indel mutations and BSE susceptibility were tested,as well as the relationships between the mutations and milk performance traits were analyzed in this study based on the statistical analyses.Results In the analyzed Chinese Holstein population,the frequencies of two"del"alleles in 23 bp and 12 bp indel muations were more frequent.The frequency of haplotype of 23del-12del was higher than those of 23del-12ins and 23ins-12del.From the estimated r2and D’values,two indel polymorphisms were linked strongly in the Holstein population(D’=57.5%,r2=0.257).Compared with the BSE-affected cattle populations from the reported data,the significant differences of genotypic and allelic frequencies were found among present Holstein and some BSE-affected populations(P<0.05 or P<0.01).Similarly,there were significant frequency distribution differences of genotypes and alleles among Chinese Holstein and several previous reported healthy dairy cattle(P<0.05 or P<0.01).Moreover,association of genotype and combined genotypes of two indel polymorphisms with milk performance and resistant mastitis traits were analyzed in Holstein population,but no significant differences were found(P>0.05).Conclusions These observations revealed that the influence of two indel mutations within the bovine PRNP gene on BSE depended on the breed and they did not affect the milk production traits,which layed the foundation for future selection of resistant animals,and for improving health conditions for dairy breeding against BSE in China.

Dynamic Analyses of PrP and PrP^(Sc) in Brain Tissues of Golden Hamsters Infected With Scrapie Strain 263K Revealed Various PrP Forms

Objective To expatiate dynamic changes in hamsters infected with scrapie strain 263K, to observe the presence and aggravation of various forms of PrP and PrPSc during incubation period, and to probe primarily the relationship between the onset of clinic manifestations and the presence of different PrPSc forms. Methods Hamster-adapted scrapie strain 263K was intracerebrally inoculated into hamsters. Different forms of PrP and PrPSc were monitored dynamically by Western blot and immuno-histochemical assays. The presence of scrapie-associated fibril (SAF) was assayed by electron microscopy analysis (EM) and immune-golden EM. Results PrPSc was initially detected in the brain tissues of the animals in 20 days post-inoculation by immunohistochemistry and 40 days with Western blot. Quantitative evaluations revealed that the amounts of PrP and PrPSc in brain tissues increased along with the incubation. Several high and low molecular masses of PrP were seen in the brains of the long-life span infected animals. Deglycosylation assays identified that the truncated PrP in the infected brains showed similar glycosylation patterns as the full-length PrP. The presence of short fragments was seemed to relate with the onset of clinical conditions. Conclusion These results indicate that infectious agents exist and accumulate in central nerve system prior to the onset of the illness. Various molecular patterns of PrPSc may indwell in brain tissues during the infection.