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Prion Biology and Diseases

by Stanley B. Prusiner

Cold Spring Harbor Laboratory Press; 2nd edition

800 pages

A Prion-related diseases constitute a unique category of illnesses that can be inherited, infectious, or sporadic. The ongoing saga of efforts to unravel the pathogenesis of prion diseases is one of the most fascinating accounts in recent medical science. This group of diseases seems to have dispelled two long-held convictions: that nucleic acids are always needed to encode biologic information transmitted from generation to generation, and that a protein of a given amino acid sequence can give rise only to one tertiary structure of biologic importance. Prion Biology and Diseases provides an authoritative review of the work on prions. The book is an essential introduction for anyone embarking on prion research and is also a useful reference for those already working in this field.

The prion, or proteinaceous infectious particle, is thought to be responsible for a wide range of diseases characterized clinically by dementia and neuropathologically by neuronal loss, spongiform change, astrocytosis, and varying degrees of amyloid deposition. Prion diseases in humans include Creutzfeldt-Jakob disease, fatal familial insomnia, Gerstmann-Straussler disease, and kuru; diseases in animals include scrapie and bovine spongiform encephalopathy. The cause of these diseases is thought to be a conformational change in a normal cellular protein, PrP(sup C), which is transformed into an infectious protein called PrP(sup Sc) (the superscript Sc denotes scrapie). PrP(sup Sc) does not differ from PrP(sup C) in its amino acid sequence or post-translational modifications; unlike PrP(sup C), however, PrP(sup Sc) is insoluble and resistant to proteinase K digestion, and it has a larger (beta)-sheet content and a propensity to aggregate into fibrils.

Although prion diseases in humans have thus far been rare, they are among the best-characterized "conformational diseases." Hence, the mechanisms of and potential therapeutic approaches to prion diseases may be relevant to more common conformational disorders, such as Alzheimer's disease (in which the amyloid (beta)-peptide is deposited as amyloid), Parkinson's disease (involving (alpha)-synuclein deposition in Lewy bodies), and the many neurodegenerative conditions associated with increased CAG repeats (e.g., Huntington's disease). Another reason for the importance of prion diseases is the recent reports of the transmission of bovine spongiform encephalopathy to humans through contaminated meat and bone meal, a topic that is well reviewed in this book. Evidence suggests that bovine spongiform encephalopathy has crossed the species barrier and now infects humans, resulting in new-variant Creutzfeldt-Jakob disease. It is unclear whether these cases mark the beginning of a human epidemic in Europe similar to that of bovine spongiform encephalopathy or whether the number of cases will remain small, as occurred with iatrogenic Creutzfeldt-Jakob disease after exposure to cadaveric growth hormone.

Many questions about prions remain unanswered, and for the most part, they are thoroughly examined in this book. An important issue is the basis for prion strains. There are many distinct isolates of prions, each associated with a specific incubation time and with specific neuropathological and Western blot features. If the protein-only hypothesis is correct, then each PrP(sup Sc) strain has a different abnormal conformation. Another unanswered question concerns "protein X." Prusiner and his colleagues have hypothesized that there is a species-specific protein that facilitates the unfolding of PrP(sup C) and its refolding into nascent PrP(sup Sc). Similar to the nucleic acid some suggest is associated with the infectivity of prions, this protein remains unidentified. The concept of protein X as a "pathological chaperone" is similar to the proposed role of apolipoprotein E4 in Alzheimer's disease. An issue that also needs to be resolved is the inability to develop synthetic or recombinant PrP(sup Sc) that is infectious in vivo -- a crucial requirement for the final proof of the protein-only hypothesis.

This book is a testament to the tremendous contributions of Prusiner and his collaborators in the field of prion research. The majority of the 17 chapters are coauthored by Prusiner or one or more of his collaborators. The information is very well organized and consistent. Until the final questions about prions are answered, however, this will continue to be an area of great controversy

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