Protease-Sensitive Conformers in Broad Spectrum of Distinct PrP ^Sc Structures in Sporadic Creutzfeldt-Jakob Disease Are Indicator of Progression Rate

Abstract

The origin, range, and structure of prions causing the most common human prion disease, sporadic Creutzfeldt-Jakob disease (sCJD), are largely unknown. To investigate the molecular mechanism responsible for the broad phenotypic variability of sCJD, we analyzed the conformational characteristics of protease-sensitive and protease-resistant fractions of the pathogenic prion protein (PrP ^Sc) using novel conformational methods derived from a conformation-dependent immunoassay (CDI). In 46 brains of patients homozygous for polymorphisms in the PRNP gene and exhibiting either Type 1 or Type 2 western blot pattern of the PrP ^Sc, we identified an extensive array of PrP ^Sc structures that differ in protease sensitivity, display of critical domains, and conformational stability. Surprisingly, in sCJD cases homozygous for methionine or valine at codon 129 of the PRNP gene, the concentration and stability of protease-sensitive conformers of PrP ^Sc correlated with progression rate of the disease. These data indicate that sCJD brains exhibit a wide spectrum of PrP ^Sc structural states, and accordingly argue for a broad spectrum of prion strains coding for different phenotypes. The link between disease duration, levels, and stability of protease-sensitive conformers of PrP ^Sc suggests that these conformers play an important role in the pathogenesis of sCJD.

Author Summary

Sporadic Creutzfeldt-Jakob disease (sCJD) is the most common human prion disease worldwide. This neurodegenerative disease, which is transmissible and invariably fatal, is characterized by the accumulation of an abnormally folded isoform (PrP ^Sc) of a host-encoded protein (PrP ^C), predominantly in the brain. Most researchers believe that PrP ^Sc is the infectious agent and five or six subtypes of sCJD have been identified. Whether or not these subtypes represent distinct strains of sCJD prions is debated in the context of the extraordinary variability of sCJD phenotypes, frequent co-occurrence of different PrP ^Sc fragments in the same brain, and the fact that up to 90% of protease-sensitive PrP ^Sc eludes the conventional analysis because it is destroyed by protease treatment. Using novel conformational methods, we identified within each clinical and pathological category an array of PrP ^Sc structures that differ in protease-sensitivity, display of critical domains, and conformational stability. Each of these features offers evidence of a distinct conformation. The link between the rate at which the disease progresses, on the one hand, and the concentration and stability of protease-sensitive conformers of PrP ^Sc on the other, suggests that these conformers play an important role in how the disease originates and progresses.