Xiangzhu Xiao

A Novel Human Disease with Abnormal Prion Protein Sensitive to Protease

To report a novel prion disease characterized by distinct histopathological and immunostaining features, and associated with an abnormal isoform of the prion protein (PrP) that, contrary to the common prion diseases, is predominantly sensitive to protease digestion.

Variably protease-sensitive prionopathy: a new sporadic disease of the prion protein

The objective of the study is to report 2 new genotypic forms of protease‐sensitive prionopathy (PSPr), a novel prion disease described in 2008, in 11 subjects all homozygous for valine at codon 129 of the prion protein (PrP) gene (129VV). The 2 new PSPr forms affect individuals who are either homozygous for methionine (129MM) or heterozygous for methionine/valine (129MV).

Insoluble aggregates and protease-resistant conformers of prion protein in uninfected human brains.

Aggregated prion protein (PrPSc), which is detergent-insoluble and partially proteinase K (PK)-resistant, constitutes the major component of infectious prions that cause a group of transmissible spongiform encephalopathies in animals and humans. PrPSc derives from a detergent-soluble and PK-sensitive cellular prion protein (PrPC) through an α-helix to β-sheet transition. This transition confers on the PrPSc molecule unique physicochemical and biological properties, including insolubility in nondenaturing detergents, an enhanced tendency to form aggregates, resistance to PK digestion, and infectivity, which together are regarded as the basis for distinguishing PrPSc from PrPC. Here we demonstrate, using sedimentation and size exclusion chromatography, that small amounts of detergent-insoluble PrP aggregates are present in uninfected human brains. Moreover, PK-resistant PrP core fragments are detectable following PK treatment. This is the first study that provides experimental evidence supporting the hypothesis that there might be silent prions lying dormant in normal human brains.

Amyloid-β42 Interacts Mainly with Insoluble Prion Protein in the Alzheimer Brain

The prion protein (PrP) is best known for its association with prion diseases. However, a controversial new role for PrP in Alzheimer disease (AD) has recently emerged. In vitro studies and mouse models of AD suggest that PrP may be involved in AD pathogenesis through a highly specific interaction with amyloid-β (Aβ42) oligomers. Immobilized recombinant human PrP (huPrP) also exhibited high affinity and specificity for Aβ42 oligomers. Here we report the novel finding that aggregated forms of huPrP and Aβ42 are co-purified from AD brain extracts. Moreover, an anti-PrP antibody and an agent that specifically binds to insoluble PrP (iPrP) co-precipitate insoluble Aβ from human AD brain. Finally, using peptide membrane arrays of 99 13-mer peptides that span the entire sequence of mature huPrP, two distinct types of Aβ binding sites on huPrP are identified in vitro. One specifically binds to Aβ42 and the other binds to both Aβ42 and Aβ40. Notably, Aβ42-specific binding sites are localized predominantly in the octapeptide repeat region, whereas sites that bind both Aβ40 and Aβ42 are mainly in the extreme N-terminal or C-terminal domains of PrP. Our study suggests that iPrP is the major PrP species that interacts with insoluble Aβ42 in vivo. Although this work indicated the interaction of Aβ42 with huPrP in the AD brain, the pathophysiological relevance of the iPrP/Aβ42 interaction remains to be established.

PrP conformational transitions alter species preference of a PrP-specific antibody

The epitope of the 3F4 antibody most commonly used in human prion disease diagnosis is believed to consist of residues Met-Lys-His-Met (MKHM) corresponding to human PrP-(109–112). This assumption is based mainly on the observation that 3F4 reacts with human and hamster PrP but not with PrP from mouse, sheep, and cervids, in which Met at residue 112 is replaced by Val. Here we report that, by brain histoblotting, 3F4 did not react with PrP of uninfected transgenic mice expressing elk PrP; however, it did show distinct immunoreactivity in transgenic mice infected with chronic wasting disease. Compared with human PrP, the 3F4 reactivity with the recombinant elk PrP was 2 orders of magnitude weaker, as indicated by both Western blotting and surface plasmon resonance. To investigate the molecular basis of these species- and conformer-dependent preferences of 3F4, the epitope was probed by peptide membrane array and antigen competition experiments. Remarkably, the 3F4 antibody did not react with MKHM but reacted strongly with KTNMK (corresponding to human PrP-(106–110)), a sequence that is also present in cervids, sheep, and cattle. 3F4 also reacted with elk PrP peptides containing KTNMKHV. We concluded that the minimal sequence for the 3F4 epitope consists of residues KTNMK, and the species- and conformer-dependent preferences of 3F4 arise largely from the interactions between Met112 (human PrP) or Val115 (cervid PrP) and adjacent residues.

Accessibility of a critical prion protein region involved in strain recognition and its implications for the early detection of prions

Abstract.Human prion diseases are characterized by the accumulation in the brain of proteinase K (PK)-resistant prion protein designated PrP27-30 detectable by the 3F4 antibody against human PrP109-112. We recently identified a new PK-resistant PrP species, designated PrP*20, in uninfected human and animal brains. It was preferentially detected with the 1E4 antibody against human PrP 97-108 but not with the anti-PrP 3F4 antibody, although the 3F4 epitope is adjacent to the 1E4 epitope in the PrP*20 molecule. The present study reveals that removal of the N-terminal amino acids up to residue 91 significantly increases accessibility of the 1E4 antibody to PrP of brains and cultured cells. In contrast to cells expressing wild-type PrP, cells expressing pathogenic mutant PrP accumulate not only PrP*20 but also a small amount of 3F4-detected PK-resistant PrP27-30. Remarkably, during the course of human prion disease, a transition from an increase in 1E4-detected PrP*20 to the occurrence of the 3F4-detected PrP27-30 was observed. Our study suggests that an increase in the level of PrP*20 characterizes the early stages of prion diseases.

Sequence-dependent prion protein misfolding and neurotoxicity.

Prion diseases are neurodegenerative disorders caused by misfolding of the normal prion protein (PrP) into a pathogenic “scrapie” conformation. To better understand the cellular and molecular mechanisms that govern the conformational changes (conversion) of PrP, we compared the dynamics of PrP from mammals susceptible (hamster and mouse) and resistant (rabbit) to prion diseases in transgenic flies. We recently showed that hamster PrP induces spongiform degeneration and accumulates into highly aggregated, scrapie-like conformers in transgenic flies. We show now that rabbit PrP does not induce spongiform degeneration and does not convert into scrapie-like conformers. Surprisingly, mouse PrP induces weak neurodegeneration and accumulates small amounts of scrapie-like conformers. Thus, the expression of three highly conserved mammalian prion proteins in transgenic flies uncovered prominent differences in their conformational dynamics. How these properties are encoded in the amino acid sequence remains to be elucidated.

Glycoform-Selective Prion Formation in Sporadic and Familial Forms of Prion Disease

The four glycoforms of the cellular prion protein (PrPC) variably glycosylated at the two N-linked glycosylation sites are converted into their pathological forms (PrPSc) in most cases of sporadic prion diseases. However, a prominent molecular characteristic of PrPSc in the recently identified variably protease-sensitive prionopathy (VPSPr) is the absence of a diglycosylated form, also notable in familial Creutzfeldt-Jakob disease (fCJD), which is linked to mutations in PrP either from Val to Ile at residue 180 (fCJDV180I) or from Thr to Ala at residue 183 (fCJDT183A). Here we report that fCJDV180I, but not fCJDT183A, exhibits a proteinase K (PK)-resistant PrP (PrPres) that is markedly similar to that observed in VPSPr, which exhibits a five-step ladder-like electrophoretic profile, a molecular hallmark of VPSPr. Remarkably, the absence of the diglycosylated PrPres species in both fCJDV180I and VPSPr is likewise attributable to the absence of PrPres glycosylated at the first N-linked glycosylation site at residue 181, as in fCJDT183A. In contrast to fCJDT183A, both VPSPr and fCJDV180I exhibit glycosylation at residue 181 on di- and monoglycosylated (mono181) PrP prior to PK-treatment. Furthermore, PrPV180I with a typical glycoform profile from cultured cells generates detectable PrPres that also contains the diglycosylated PrP in addition to mono- and unglycosylated forms upon PK-treatment. Taken together, our current in vivo and in vitro studies indicate that sporadic VPSPr and familial CJDV180I share a unique glycoform-selective prion formation pathway in which the conversion of diglycosylated and mono181 PrPC to PrPSc is inhibited, probably by a dominant-negative effect, or by other co-factors.

Transmission Characteristics of Variably Protease-Sensitive Prionopathy

This disease is transmissible and thus an authentic prion disease.

Structural Determinants of Phenotypic Diversity and Replication Rate of Human Prions

The infectious pathogen responsible for prion diseases is the misfolded, aggregated form of the prion protein, PrPSc. In contrast to recent progress in studies of laboratory rodent-adapted prions, current understanding of the molecular basis of human prion diseases and, especially, their vast phenotypic diversity is very limited. Here, we have purified proteinase resistant PrPSc aggregates from two major phenotypes of sporadic Creutzfeldt-Jakob disease (sCJD), determined their conformational stability and replication tempo in vitro, as well as characterized structural organization using recently emerged approaches based on hydrogen/deuterium (H/D) exchange coupled with mass spectrometry. Our data clearly demonstrate that these phenotypically distant prions differ in a major way with regard to their structural organization, both at the level of the polypeptide backbone (as indicated by backbone amide H/D exchange data) as well as the quaternary packing arrangements (as indicated by H/D exchange kinetics for histidine side chains). Furthermore, these data indicate that, in contrast to previous observations on yeast and some murine prion strains, the replication rate of sCJD prions is primarily determined not by conformational stability but by specific structural features that control the growth rate of prion protein aggregates.