Stability of BSE infectivity towards heat treatment even after proteolytic removal of prion protein

Jan P M Langeveld,Jason Shih,Michael Beekes,Umberto Agrimi,Achim Thomzig,Romolo Nonno,Michele A Di Bari,Aart Davidse,Laura Pirisinu,Martin H Groschup,Olivier Andréoletti,Dieter Becher,Anne Balkema-Buschmann

doi:10.1186/s13567-021-00928-8

Abstract

The unconventional infectious agents of transmissible spongiform encephalopathies (TSEs) are prions. Their infectivity co-appears with PrPSc, aberrant depositions of the host’s cellular prion protein (PrPC). Successive heat treatment in the presence of detergent and proteolysis by a keratinase from Bacillus licheniformis PWD-1 was shown before to destroy PrPSc from bovine TSE (BSE) and sheep scrapie diseased brain, however data regarding expected reduction of infectivity were still lacking. Therefore, transgenic Tgbov XV mice which are highly BSE susceptible were used to quantify infectivity before and after the bovine brain treatment procedure. Also four immunochemical analyses were applied to compare the levels of PrPSc. After heating at 115 °C with or without subsequent proteolysis, the original BSE infectivity of 106.2–6.4 ID50 g−1 was reduced to a remaining infectivity of 104.6–5.7 ID50 g−1 while strain characteristics were unaltered, even after precipitation with methanol. Surprisingly, PrPSc depletion was 5–800 times higher than the loss of infectivity. Similar treatment was applied on other prion strains, which were CWD1 in bank voles, 263 K scrapie in hamsters and sheep PG127 scrapie in tg338 ovinized mice. In these strains however, infectivity was already destroyed by heat only. These findings show the unusual heat resistance of BSE and support a role for an additional factor in prion formation as suggested elsewhere when producing prions from PrPC. Leftover material in the remaining PrPSc depleted BSE preparation offers a unique substrate for searching additional elements for prion infectivity and improving our concept about the nature of prions.

Highlights

Prions are infectious agents of transmissible spongiform encephalopathies (TSEs) or prion diseases [1]
In this study we investigated whether our P rPSc removal from bovine spongiform encephalopathy (BSE) infected cow brain using heating at 115 °C and enzymatic proteolysis goes together with removal of infectivity in the highly sensitive transgenic Tgbov XV mice expressing bovine PrP
PrPSc digestion in heat treated cattle brain Heating alone in the presence of 2% sarkosyl at 115 °C of homogenates prepared from brain tissue of a British confirmed BSE cow with clinical signs did not lead to significant loss of PrPSc immunoreactivity (Figure 1B, cfr. lane 4 with lanes 1–3) as was previously shown [22]

Summary

Introduction

Prions are infectious agents of transmissible spongiform encephalopathies (TSEs) or prion diseases [1]. Langeveld et al Vet Res (2021) 52:59 the presence of P rPC is a prerequisite for TSE infection was presented from PrP-less mice, goats and cells, and by the production of infectivity from recombinantly expressed and purified PrP [6,7,8,9,10,11,12,13,14] Another argument for the validity of the role of PrP in the agent is the close relation between susceptibility/resistance in e.g. sheep, goats and humans and genetic polymorphisms in the PRNP coding region [15,16,17]. From observations with bovine spongiform encephalopathy (BSE) inoculated in in-bred wildtype mice it was even postulated that an additional unidentified agent may be essential for transmission while PrPSc would be involved in species adaptation [21].1

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Results

Conclusion