Source genotype influence on cross species transmission of transmissible spongiform encephalopathies evaluated by RT-QuIC

Aqueous extraction of formalin-fixed paraffin-embedded tissue and detection of prion disease using real-time quaking-induced conversion

OBJECTIVE

The goal of the research presented here is to determine if methods previously developed for the aqueous extraction of PrPSc from formalin-fixed paraffin-embedded tissue (FFPET) are applicable to the detection PrPSc by real-time quaking induced conversion (RT-QuIC). Previous work has utilized aqueous extraction of FFPET for detection of transmissible spongiform encephalopathies (TSEs) utilizing western blot and ELISA. This research extends the range of suitable methods for detection of TSEs in FFPET to RT-QuIC, which is arguably the most sensitive method to detect TSEs.

RESULTS

We found complete agreement between the TSE status and the results from RT-QuIC seeded with the aqueous extract of FFPET samples. The method affords the diagnostic assessment TSE status by RT-QuIC of FFPET without the use of organic solvents that would otherwise create a mixed chemical-biological waste for disposal.

Scrapie versus Chronic Wasting Disease in White-Tailed Deer

White-tailed deer are susceptible to scrapie (WTD scrapie) after oronasal inoculation with the classical scrapie agent from sheep. Deer affected by WTD scrapie are difficult to differentiate from deer infected with chronic wasting disease (CWD). To assess the transmissibility of the WTD scrapie agent and tissue phenotypes when further passaged in white-tailed deer, we oronasally inoculated wild-type white-tailed deer with WTD scrapie agent. We found that WTD scrapie and CWD agents were generally similar, although some differences were noted. The greatest differences were seen in bioassays of cervidized mice that exhibited significantly longer survival periods when inoculated with WTD scrapie agent than those inoculated with CWD agent. Our findings establish that white-tailed deer are susceptible to WTD scrapie and that the presence of WTD scrapie agent in the lymphoreticular system suggests the handling of suspected cases should be consistent with current CWD guidelines because environmental shedding may occur.

Hofmeister Effect in RT-QuIC Seeding Activity of Chronic Wasting Disease Prions

Chronic wasting disease (CWD) is a transmissible spongiform encephalopathy (TSE) that causes a fatal neurodegenerative disease in cervids. Cases of CWD are rapidly increasing in North America among wild and farmed cervid populations, and potential for zoonotic transmission is not yet determined. Therefore, in order to manage the disease, it is imperative to devise a system that can detect CWD during its early phases to prevent spread to new captive herds through introduction of CWD-affected animals into otherwise CWD-free herds. Real-time quaking-induced conversion (RT-QuIC) assays have been applied to detect the presence of disease-associated prions from various samples in both animals and humans. In this study, we have tested the use of five Hofmeister anions that range from weakly hydrating to strongly hydrating: Na₃citrate, Na₂SO₄, NaCl, NaI, and NaClO₄ in RT-QuIC reactions for CWD seeding activity using different recombinant prion proteins as substrates. This work shows how the ionic environment of the RT-QuIC reaction can enhance or diminish the seeding activity. The use of Na₂SO₄ or NaI as the sodium salt for RT-QuIC using bank vole recombinant prion substrate for the detection of CWD using brain samples reduces the lag time to detect with reasonable specificity. For detection of the CWD in fecal samples, only NaI showed comparable reduction in lag time relative to NaCl but required reduced temperature to alleviate spontaneous fibril formation in negative control samples. Selection of the proper ion environment and recombinant prion protein substrate will make RT-QuIC a powerful diagnostic tool for early detection of CWD prions, further supporting CWD surveillance in wild and captive cervids.

Role of donor genotype in RT-QuIC seeding activity of chronic wasting disease prions using human and bank vole substrates

Chronic wasting disease is a transmissible spongiform encephalopathy of cervids. This fatal neurodegenerative disease is caused by misfolding of the cellular prion protein (PrPC) to pathogenic conformers (PrPSc), and the pathogenic forms accumulate in the brain and other tissues. Real-time Quaking Induced Conversion (RT-QuIC) can be used for the detection of prions and for prion strain discrimination in a variety of biological tissues from humans and animals. In this study, we evaluated how either PrPSc from cervids of different genotypes or PrPSc from different sources of CWD influence the fibril formation of recombinant bank vole (BV) or human prion proteins using RT-QuIC. We found that reaction mixtures seeded with PrPSc from different genotypes of white-tailed deer or reindeer brains have similar conversion efficiency with both substrates. Also, we observed similar results when assays were seeded with different sources of CWD. Thus, we conclude that the genotypes of all sources of CWD used in this study do not influence the level of conversion of PrPC to PrPSc.

PAD-Beads enrichment enhances detection of PrPSc using real-time quaking-induced conversion

Objective

Scrapie is a transmissible spongiform encephalopathy (TSE) that naturally occurs in sheep and goats. This fatal neurodegenerative disease results from misfolding of the normal cellular prion protein (PrP^C) to a pathogenic prion protein form (PrP^Sc). This pathogenic form, PrP^Sc, accumulates in the brain and lymphoid tissues. The presence of PrP^Sc can be detected by an in vitro conversion assay known as real-time quaking induced conversion (RT-QuIC). RT-QuIC has been used to detect PrP^Sc in a variety of biological tissues from brains to fluids. While this technique is both rapid and sensitive, enhancing the detection of prions would be valuable in the diagnostic laboratories.

Results

In this study, we assessed whether PrP^Sc detection sensitivity of RT-QuIC can be increased by enriching PrP^Sc in scrapie tissue homogenates using commercially available aggregated protein binding ligands coated magnetic beads (PAD-Beads). Coupling of RT-QuIC to PAD-Beads based cleanup allowed detection of PrP^Sc rapidly and without dilution of scrapie sheep brain homogenates prior to RT-QuIC. The PAD-Beads sample pretreatment step prior to RT-QuIC is a useful enhancement in the diagnosis of TSEs.