Highly infectious prions are not directly neurotoxic

Iryna Benilova,Adam Wenborn,John Collinge,Christian Schmidt,Michael Wiggins De Oliveira,Madeleine Reilly,Jonathan D F Wadsworth,Cassandra Terry,Aline T Marinho,Emmanuel Risse,Huda Al-Doujaily,Malin K Sandberg,Parmjit S Jat

doi:10.1073/pnas.2007406117

Abstract

Prions are infectious agents which cause rapidly lethal neurodegenerative diseases in humans and animals following long, clinically silent incubation periods. They are composed of multichain assemblies of misfolded cellular prion protein. While it has long been assumed that prions are themselves neurotoxic, recent development of methods to obtain exceptionally pure prions from mouse brain with maintained strain characteristics, and in which defined structures-paired rod-like double helical fibers-can be definitively correlated with infectivity, allowed a direct test of this assertion. Here we report that while brain homogenates from symptomatic prion-infected mice are highly toxic to cultured neurons, exceptionally pure intact high-titer infectious prions are not directly neurotoxic. We further show that treatment of brain homogenates from prion-infected mice with sodium lauroylsarcosine destroys toxicity without diminishing infectivity. This is consistent with models in which prion propagation and toxicity can be mechanistically uncoupled.

Highlights

Prion diseases are fatal transmissible neurodegenerative conditions affecting humans and a range of other mammalian species [1, 2]
We show that treatment of brain homogenates from prion-infected mice with sodium lauroylsarcosine (≥2% [wt/vol] final concentration) destroys toxicity without reducing the prion infectivity titer, thereby clearly demonstrating that infectious prion assemblies can be uncoupled from neurotoxicity
We isolated prions from the brains of clinically sick mice that had been intracerebrally inoculated with the Rocky Mountain Laboratory (RML) prion strain using an established method to isolate exceptionally pure high-titer prions [20]

Summary

Introduction

Prion diseases are fatal transmissible neurodegenerative conditions affecting humans and a range of other mammalian species [1, 2]. We have previously demonstrated that, following an initial phase of exponential prion propagation in vivo, which is not ratelimited by PrPC expression level, infective titer reaches a plateau level, and the duration of this plateau phase to clinical onset is inversely proportional to PrPC expression level [15] During this plateau phase there is accumulation of protease-sensitive diseaserelated forms of PrP at a rate linearly proportional to the PrPC expression level [14]. This model proposes that infectious prions are themselves not toxic but that a pathway switch to production of PrPL once a plateau level of infectivity is reached is responsible for the synaptotoxicity and neurodegeneration that leads to clinical onset [3, 14, 15] This model is supported by the recognition of subclinical prion infections where animals may live a normal life span despite harboring high prion titers in their brains [16,17,18,19]. The advances reported here will facilitate isolation of the neurotoxic PrP species and its structural characterization

Methods

Results

Conclusion