Proteomic analysis of host brain components that bind to infectious particles in Creutzfeldt-Jakob disease

Abstract

Transmissible encephalopathies (TSEs), such as Creutzfeldt-Jakob disease (CJD) and scrapie, are caused by infectious agents that provoke strain-specific patterns of disease. Misfolded host prion protein (PrP-res amyloid) is believed to be the causal infectious agent. However, particles that are stripped of PrP retain both high infectivity and viral proteins not detectable in uninfected mouse controls. We here detail host proteins bound with FU-CJD agent infectious brain particles by proteomic analysis. More than 98 proteins were differentially regulated, and 56 FU-CJD exclusive proteins were revealed after PrP, GFAP, C1q, ApoE, and other late pathologic response proteins were removed. Stripped FU-CJD particles revealed HSC70 (144× the uninfected control), cyclophilin B, an FU-CJD exclusive protein required by many viruses, and early endosome-membrane pathways known to facilitate viral processing, replication, and spread. Synaptosomal elements including synapsin-2 (at 33×) and AP180 (a major FU-CJD exclusive protein) paralleled the known ultrastructural location of 25 nm virus-like TSE particles and infectivity in synapses. Proteins without apparent viral or neurodegenerative links (copine-3), and others involved in viral-induced protein misfolding and aggregation, were also identified. Human sCJD brain particles contained 146 exclusive proteins, and heat shock, synaptic, and viral pathways were again prominent, in addition to Alzheimer, Parkinson, and Huntington aggregation proteins. Host proteins that bind TSE infectious particles can prevent host immune recognition and contribute to prolonged cross-species transmissions (the species barrier). Our infectious particle strategy, which reduces background sequences by >99%, emphasizes host targets for new therapeutic initiatives. Such therapies can simultaneously subvert common pathways of neurodegeneration.

Keywords: Amyloid; Chaperones; Early endosomes; Microbiology; Synapses; Viral transit.

Fig. 1

Sequential steps in the rapid isolation of p18 FU-CJD brain particles showing a blot with gold-stained proteins on left panel and corresponding PrP/PrP-res in the right panel. Cytosol from non-detergent treated homogenates was first separated from nuclei and membrane-myelin components and cleared of lysosomes at 10,000g to yield s10 supernatant with >90% of the starting brain infectivity. RNAse added to s10 is seen at double arrows, and subsequent generation of the p18 shows reduced contaminating RNAse. The p18, treated with high PK (++ lanes, residual PK at arrow) which reduced proteins to barely visible amounts despite the high CE load, and PrP was not visible after 2hr PK (<0.05% of starting PrP); this 0.05% signal at ∼29kd is typical of non-specific binding of PrP antibody to PK. The 4 hr sample analyzed had verified high infectivity as previously detailed (14). Standard lower PrP-res bands are seen in lane 2′ and molecular weight markers are indicated.