Alzheimer's disease amyloid beta and prion protein amyloidogenic peptides promote macrophage survival,DNA synthesis and enhanced proliferative response to CSF-1 (M-CSF)

Microglial cells, macrophage-lineage cells in the brain, are increased in amyloid-containing plaques in Alzheimer’s disease (AD) and in the lesions of prion diseases. Recent studies suggest that microglia have a central role in turnover of amyloid in these diseases. We report here that synthetic amyloid beta (Aβ) 1-42 and prion protein (PrP) 106-126 peptides promote macrophage survival; they also induce macrophage DNA synthesis, particularly in the presence of sub-optimal concentrations of the growth factor, macrophage-colony stimulating factor (M-CSF or CSF-1). These responses are proposed to provide a means to increase brain microglia/macrophage numbers thereby enhancing subsequent inflammatory/immune responses. These fibrillogenic peptides join the list of aggregates having these effects on macrophages, indicating the generality of this type of response.     

Genotype frequencies at codon 129 of the Prion Protein Gene in Brazil: implications in susceptibility to variant Creutzfeldt--Jakob disease compared to European and Asian populations

A polymorphism at codon 129 of the prion protein gene has been shown to confer genetic susceptibility to prion diseases, and to influence the epidemic course of variant Creutzfeldt--Jakob disease. We employed a PCR-endonuclease digestion-based assay to investigate this genetic trait in Brazil, and then compared our results to previously published data from several European and Asian countries.Financial Support: Fundacao de Amparo a Pesquisa do Estado de São Paulo -- FAPESP     

The metabolism of glycosaminoglycans is impaired in prion diseases

It is well established that the conversion of PrP(C) to PrP(Sc) is the key event in prion disease biology. In addition, several lines of evidence suggest that glycosaminoglycans (GAGs) and in particular heparan sulfate (HS) may play a role in the PrP(C) to PrP(Sc) conversion process. It has been proposed that PrP(Sc) accumulation in prion diseases may induce aberrant activation of lysosomal activity, which has been shown to result in neurodegeneration in a number of diseases, especially lysosomal storage disorders. Among such diseases, only the ones resulting from defects in GAGs degradation are accompanied by secretion of large amounts of GAG metabolites in urine. In this work, we show that GAGs are secreted in the urine of prion-infected animals and humans, and surprisingly, also in the urine of mice ablated for the PrP gene. We hypothesize that both the presence of PrP(Sc) or the absence of PrP(C) may alter the metabolism of GAGs.     

Pathogenesis of prion diseases

Prion diseases are rare neurological disorders that may be of genetic or infectious origin, but most frequently occur sporadically in humans. Their outcome is invariably fatal. As the responsible pathogen, prions have been implicated. Prions are considered to be infectious particles that represent mainly, if not solely, an abnormal, protease-resistant isoform of a cellular protein, the prion protein or PrP^C. As in other neurodegenerative diseases, aggregates of misfolded protein conformers are deposited in the CNS of affected individuals. Pathogenesis of prion diseases comprises mainly two equally important, albeit essentially distinct, topics: first, the mode, spread, and amplification of infectivity in acquired disease, designated as peripheral pathogenesis. In this field, significant advances have implicated an essential role of lymphoid tissues for peripheral prion replication, before a likely neural spread to the CNS. The second is the central pathogenesis, dealing, in addition to spread and replication of prions within the CNS, with the mechanisms of nerve cell damage and death. Although important roles for microglial neurotoxicity, oxidative stress, and complement activation have been identified, we are far from complete understanding, and therapeutic applications in prion diseases still need to be developed.     

Effective antigen-retrieval method for immunohistochemical detection of abnormal isoform of prion proteins in animals

For immunohistochemistry of the prion diseases, several pretreatment methods to enhance the immunoreactivity of human and animal abnormal proteinase-resistant prion protein (PrP^Sc) on the tissue sections have been employed. The method of 121°C hydrated autoclaving pretreatment or the combination method of 121°C hydrated autoclaving with a certain chemical reagent (formic acid or proteinase K, etc) are now widely used. We found that an improved hydrated autoclaving method at 135°C, more effectively enhanced PrP^Sc immunoreactivity for the antibodies recognizing the linear epitope. In addition, this method was more effective for the long-term fixation samples as compared with other previous methods. However, this modified method could not retrieve PrP^Sc antigenic epitopes composed of conformational structures or several discontinuous epitopes. We describe the comparative studies between our improved method and other antigen-retrieval procedures reported previously. Based on the differences of reaction among the antibodies, we also discuss the mechanisms of the hydrated autoclaving methods to retrieve PrP^Sc immunoreactivity.     

GFP-tagged prion protein is correctly localized and functionally active in the brains of transgenic mice

Prion diseases result from conversion of PrPC, a neuronal membrane glycoprotein of unknown function, into PrPSc, an abnormal conformer that is thought to be infectious. To facilitate analysis of PrP distribution in the brain, we have generated transgenic mice in which a PrP promoter drives expression of PrP-EGFP, a fusion protein consisting of enhanced green fluorescent protein inserted adjacent to the glycolipid attachment site of PrP. We find that PrP-EGFP in the brain is glycosylated and glycolipid-anchored and is localized to the surface membrane and the Golgi apparatus of neurons. Like endogenous PrP, PrP-EGFP is concentrated in synapse-rich regions and along axon tracts. PrP-EGFP is functional in vivo, since it ameliorates the cerebellar neurodegeneration induced by a truncated form of PrP. These observations clarify uncertainties in the cellular localization of PrPC in brain, and they establish PrP-EGFP transgenic mice as useful models for further studies of prion biology.     

Clusterin solubility and aggregation in Creutzfeldt-Jakob disease

Prion protein (PrP^C) is a glycolipid-anchored cell membrane syaloglycoprotein that localizes in presynaptic membranes. PrP has the property of aggregating into amyloid fibrils and being deposited in the brains in cases with transmissible encephalopathies (TSEs), when PrP^C is converted into abnormal protease-resistant PrP (PrP^RES). Clusterin is a heterodimeric glycoprotein, the expression of which is enhanced in astrocytes in association with punctate-type PrP^RES deposits during TSE progression. In addition, clusterin co-localizes in PrP^RES plaques in several human TSEs, including Creutzfeldt-Jakob disease (CJD). Clusterin is up-regulated in the cerebral cortex and cerebellum in CJD as revealed by DNA micro-array technology. Clusterin expression was examined in seven sporadic cases of CJD (codon 129 genotype, PrP type: 4 MM1, 1 MV1, 1 MV2, 1 VV2) and three age-matched controls by immunohistochemistry, Western blotting and solubility. In addition to small punctate clusterin deposition in the neuropil, single- and double-labeling immunohistochemistry disclosed clusterin localization in PrP^RES plaques, which predominated in the cerebellum of cases MV1, MV2 and VV2. Moreover, clusterin in plaques, but not punctate clusterin deposits, was resistant to protease digestion, as revealed in tissue sections pre-incubated with proteinase K. Clusterin in CJD, but not clusterin in control brains, was partially resistant to protease digestion in Western blots of total brain homogenates immunostained with anti-clusterin antibodies, which were processed in parallel with Western blots to PrP, without and with pre-incubation with proteinase K. Protein aggregation was analyzed in brain homogenates subjected to several solvents. PrP was recovered in the deoxycholate fraction in control and CJD cases, but in the SDS fraction only in CJD, thus indicating differences in PrP solubility between CJD and controls. Clusterin was recovered in the cytosolic, deoxycholate and SDS fraction in both CJD and control cases, but only clusterin from CJD was recovered in the urea-soluble fraction and, especially, in the remaining pellet. These findings demonstrate the capacity of clusterin to form aggregates and interact with PrP^RES aggregates. The implications of this property are not known, but it can be suggested that clusterin participates in PrP clustering and sequestration, thus modifying PrP toxicity in CJD.     

Transmission of prion disease

The transmission of bovine spongiform encephalopathy to humans as variant Creutzfeldt‐Jakob disease (vCJD) has focused public attention on how prion diseases are transmitted and how prions reach the brain after exposure. Prion diseases are characterised by transmissibility and neuropathological features of gliosis, neuronal loss and microscopic vacuoles, termed spongiosis. The principal component of prions is the glycoprotein PrP^Sc, which is a conformational modified isoform of the normal membrane protein PrP^C. How are prions transmitted and how do prions find their way once they have been ingested? Prion models in mouse and hamster point to lymphoreticular cells which support an early replication phase of prions before reaching the central nervous system via peripheral nerves. Whilst some key players seem to have been identified so far, the mechanisms of prion propagation to the brain are still not fully understood. Seemingly contradictory results have led to some confusion and have provoked discussion.     

建议将Prion的中文名定为"朊毒"

近年来,由于疯牛病在西欧大量传播,并引发人类的克-雅氏病,因此其病原体"Prion"引起了全球的高度重视.然而,Prion尚未有正式的中文定名,迄今在国内发表的文章中使用的Prion译名有近10种.为了尽量准确地表达Prusiner创用"Prion"一词的原意,中国科学院院士、病毒学家毛江森教授建议,将Prion的中文名定为"朊毒".--编者摘