Discriminating α-synuclein strains in Parkinson's disease and multiple system atrophy.

Synucleinopathies are neurodegenerative diseases that are associated with the misfolding and aggregation of α-synuclein, including Parkinson's disease, dementia with Lewy bodies and multiple system atrophy1. Clinically, it is challenging to differentiate Parkinson's disease and multiple system atrophy, especially at the early stages of disease2. Aggregates of α-synuclein in distinct synucleinopathies have been proposed to represent different conformational strains of α-synuclein that can self-propagate and spread from cell to cell3-6. Protein misfolding cyclic amplification (PMCA) is a technique that has previously been used to detect α-synuclein aggregates in samples of cerebrospinal fluid with high sensitivity and specificity7,8. Here we show that the α-synuclein-PMCA assay can discriminate between samples of cerebrospinal fluid from patients diagnosed with Parkinson's disease and samples from patients with multiple system atrophy, with an overall sensitivity of 95.4%. We used a combination of biochemical, biophysical and biological methods to analyse the product of α-synuclein-PMCA, and found that the characteristics of the α-synuclein aggregates in the cerebrospinal fluid could be used to readily distinguish between Parkinson's disease and multiple system atrophy. We also found that the properties of aggregates that were amplified from the cerebrospinal fluid were similar to those of aggregates that were amplified from the brain. These findings suggest that α-synuclein aggregates that are associated with Parkinson's disease and multiple system atrophy correspond to different conformational strains of α-synuclein, which can be amplified and detected by α-synuclein-PMCA. Our results may help to improve our understanding of the mechanism of α-synuclein misfolding and the structures of the aggregates that are implicated in different synucleinopathies, and may also enable the development of a biochemical assay to discriminate between Parkinson's disease and multiple system atrophy.

Two structurally defined Aß polymorphs promote different pathological changes in susceptible mice.

Misfolded Aß is involved in the progression of Alzheimer's disease (AD). However, the role of its polymorphic variants or conformational strains in AD pathogenesis is not fully understood. Here, we study the seeding properties of two structurally defined synthetic misfolded Aß strains (termed 2F and 3F) using in vitro and in vivo assays. We show that 2F and 3F strains differ in their biochemical properties, including resistance to proteolysis, binding to strain-specific dyes, and in vitro seeding. Injection of these strains into a transgenic mouse model produces different pathological features, namely different rates of aggregation, formation of different plaque types, tropism to specific brain regions, differential recruitment of Aß40 /Aß42 peptides, and induction of microglial and astroglial responses. Importantly, the aggregates induced by 2F and 3F are structurally different as determined by ssNMR. Our study analyzes the biological properties of purified Aß polymorphs that have been characterized at the atomic resolution level and provides relevant information on the pathological significance of misfolded Aß strains.

Erythrocyte adenosine A2B receptor prevents cognitive and auditory dysfunction by promoting hypoxic and metabolic reprogramming.

Hypoxia drives aging and promotes age-related cognition and hearing functional decline. Despite the role of erythrocytes in oxygen (O2) transport, their role in the onset of aging and age-related cognitive decline and hearing loss (HL) remains undetermined. Recent studies revealed that signaling through the erythrocyte adenosine A2B receptor (ADORA2B) promotes O2 release to counteract hypoxia at high altitude. However, nothing is known about a role for erythrocyte ADORA2B in age-related functional decline. Here, we report that loss of murine erythrocyte-specific ADORA2B (eAdora2b-/-) accelerates early onset of age-related impairments in spatial learning, memory, and hearing ability. eAdora2b-/- mice display the early aging-like cellular and molecular features including the proliferation and activation of microglia and macrophages, elevation of pro-inflammatory cytokines, and attenuation of hypoxia-induced glycolytic gene expression to counteract hypoxia in the hippocampus (HIP), cortex, or cochlea. Hypoxia sufficiently accelerates early onset of cognitive and cochlear functional decline and inflammatory response in eAdora2b-/- mice. Mechanistically, erythrocyte ADORA2B-mediated activation of AMP-activated protein kinase (AMPK) and bisphosphoglycerate mutase (BPGM) promotes hypoxic and metabolic reprogramming to enhance production of 2,3-bisphosphoglycerate (2,3-BPG), an erythrocyte-specific metabolite triggering O2 delivery. Significantly, this finding led us to further discover that murine erythroblast ADORA2B and BPGM mRNA levels and erythrocyte BPGM activity are reduced during normal aging. Overall, we determined that erythrocyte ADORA2B-BPGM axis is a key component for anti-aging and anti-age-related functional decline.

Adaptive selection of a prion strain conformer corresponding to established North American CWD during propagation of novel emergent Norwegian strains in mice expressing elk or deer prion protein.

Prions are infectious proteins causing fatal, transmissible neurodegenerative diseases of animals and humans. Replication involves template-directed refolding of host encoded prion protein, PrPC, by its infectious conformation, PrPSc. Following its discovery in captive Colorado deer in 1967, uncontrollable contagious transmission of chronic wasting disease (CWD) led to an expanded geographic range in increasing numbers of free-ranging and captive North American (NA) cervids. Some five decades later, detection of PrPSc in free-ranging Norwegian (NO) reindeer and moose marked the first indication of CWD in Europe. To assess the properties of these emergent NO prions and compare them with NA CWD we used transgenic (Tg) and gene targeted (Gt) mice expressing PrP with glutamine (Q) or glutamate (E) at residue 226, a variation in wild type cervid PrP which influences prion strain selection in NA deer and elk. Transmissions of NO moose and reindeer prions to Tg and Gt mice recapitulated the characteristic features of CWD in natural hosts, revealing novel prion strains with disease kinetics, neuropathological profiles, and capacities to infect lymphoid tissues and cultured cells that were distinct from those causing NA CWD. In support of strain variation, PrPSc conformers comprising emergent NO moose and reindeer CWD were subject to selective effects imposed by variation at residue 226 that were different from those controlling established NA CWD. Transmission of particular NO moose CWD prions in mice expressing E at 226 resulted in selection of a kinetically optimized conformer, subsequent transmission of which revealed properties consistent with NA CWD. These findings illustrate the potential for adaptive selection of strain conformers with improved fitness during propagation of unstable NO prions. Their potential for contagious transmission has implications for risk analyses and management of emergent European CWD. Finally, we found that Gt mice expressing physiologically controlled PrP levels recapitulated the lymphotropic properties of naturally occurring CWD strains resulting in improved susceptibilities to emergent NO reindeer prions compared with over-expressing Tg counterparts. These findings underscore the refined advantages of Gt models for exploring the mechanisms and impacts of strain selection in peripheral compartments during natural prion transmission.

PMCA for ultrasensitive detection of prions and to study disease biology.

The emergence of a novel class of infectious agent composed exclusively of a misfolded protein (termed prions) has been a challenge in modern biomedicine. Despite similarities on the behavior of prions with respect to conventional pathogens, the many uncertainties regarding the biology and virulence of prions make them a worrisome paradigm. Since prions do not contain nucleic acids and rely on a very different way of replication and spreading, it was necessary to invent a novel technology to study them. In this article, we provide an overview of such a technology, termed protein misfolding cyclic amplification (PMCA), and summarize its many applications to detect prions and understand prion biology.

Accurate Detection of α-Synuclein Seeds in Cerebrospinal Fluid from Isolated Rapid Eye Movement Sleep Behavior Disorder and Patients with Parkinson's Disease in the DeNovo Parkinson (DeNoPa) Cohort.

BACKGROUND: Misfolded α-synuclein (αSyn) aggregates (αSyn-seeds) in cerebrospinal fluid (CSF) are biomarkers for synucleinopathies such as Parkinson's disease (PD). αSyn-seeds have been detected in prodromal cases with isolated rapid eye movement sleep behavior disorder (iRBD). OBJECTIVES: The objective of this study was to determine the accuracy of the αSyn-seed amplification assay (αS-SAA) in a comprehensively characterized cohort with a high proportion of PD and iRBD CSF samples collected at baseline. METHODS: We used a high-throughput αS-SAA to analyze 233 blinded CSF samples from 206 participants of the DeNovo Parkinson Cohort (DeNoPa) (113 de novo PD, 64 healthy controls, 29 iRBD confirmed by video polysomnography). Results were compared with the final diagnosis, which was determined after up to 10 years of longitudinal clinical evaluations, including dopamine-transporter-single-photon emission computed tomography (DAT-SPECT) at baseline, CSF proteins, Movement Disorder Society-Unified Parkinson's Disease Rating Scale, and various cognitive and nonmotor scales. RESULTS: αS-SAA detected αSyn-seeds in baseline PD-CSF with 98% accuracy. αSyn-seeds were detected in 93% of the iRBD cases. αS-SAA results showed higher agreement with the final than the initial diagnosis, as 14 patients were rediagnosed as non-αSyn aggregation disorder. For synucleinopathies, αS-SAA showed higher concordance with the final diagnosis than DAT-SPECT. Statistically significant correlations were found between assay parameters and disease progression. CONCLUSIONS: Our results confirm αS-SAA accuracy at the first clinical evaluation when a definite diagnosis is most consequential. αS-SAA conditions reported here are highly sensitive, enabling the detection of αSyn-seeds in CSF from iRBD just months after the first symptoms, suggesting that αSyn-seeds are present in the very early prodromal phase of synucleinopathies. Therefore, αSyn-seeds are clear risk markers for synuclein-related disorders, but not for time of phenoconversion. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

The clock modulator Nobiletin mitigates astrogliosis-associated neuroinflammation and disease hallmarks in an Alzheimer's disease model.

Alzheimer's disease (AD) is a devastating neurodegenerative disorder, and there is a pressing need to identify disease-modifying factors and devise interventional strategies. The circadian clock, our intrinsic biological timer, orchestrates various cellular and physiological processes including gene expression, sleep, and neuroinflammation; conversely, circadian dysfunctions are closely associated with and/or contribute to AD hallmarks. We previously reported that the natural compound Nobiletin (NOB) is a clock-enhancing modulator that promotes physiological health and healthy aging. In the current study, we treated the double transgenic AD model mice, APP/PS1, with NOB-containing diets. NOB significantly alleviated ß-amyloid burden in both the hippocampus and the cortex, and exhibited a trend to improve cognitive function in these mice. While several systemic parameters for circadian wheel-running activity, sleep, and metabolism were unchanged, NOB treatment showed a marked effect on the expression of clock and clock-controlled AD gene expression in the cortex. In accordance, cortical proteomic profiling demonstrated circadian time-dependent restoration of the protein landscape in APP/PS1 mice treated with NOB. More importantly, we found a potent efficacy of NOB to inhibit proinflammatory cytokine gene expression and inflammasome formation in the cortex, and immunostaining further revealed a specific effect to diminish astrogliosis, but not microgliosis, by NOB in APP/PS1 mice. Together, these results underscore beneficial effects of a clock modulator to mitigate pathological and cognitive hallmarks of AD, and suggest a possible mechanism via suppressing astrogliosis-associated neuroinflammation.

Preventive and therapeutic reduction of amyloid deposition and behavioral impairments in a model of Alzheimer's disease by whole blood exchange.

Alzheimer's disease (AD) is the major form of dementia in the elderly population. The main neuropathological changes in AD patients are neuronal death, synaptic alterations, brain inflammation, and the presence of cerebral protein aggregates in the form of amyloid plaques and neurofibrillary tangles. Compelling evidence suggests that the misfolding, aggregation, and cerebral deposition of amyloid-beta (Aß) plays a central role in the disease. Thus, prevention and removal of misfolded protein aggregates is considered a promising strategy to treat AD. In the present study, we describe that the development of cerebral amyloid plaques in a transgenic mice model of AD (Tg2576) was significantly reduced by 40-80% through exchanging whole blood with normal blood from wild type mice having the same genetic background. Importantly, such reduction resulted in improvement in spatial memory performance in aged Tg2576 mice. The exact mechanism by which blood exchange reduces amyloid pathology and improves memory is presently unknown, but measurements of Aß in plasma soon after blood exchange suggest that mobilization of Aß from the brain to blood may be implicated. Our results suggest that a target for AD therapy may exist in the peripheral circulation, which could open a novel disease-modifying intervention for AD.

Crossing the species barrier by PrP(Sc) replication in vitro generates unique infectious prions.

Prions are unconventional infectious agents composed exclusively of misfolded prion protein (PrP(Sc)), which transmits the disease by propagating its abnormal conformation to the cellular prion protein (PrP(C)). A key characteristic of prions is their species barrier, by which prions from one species can only infect a limited number of other species. Here, we report the generation of infectious prions by interspecies transmission of PrP(Sc) misfolding by in vitro PMCA amplification. Hamster PrP(C) misfolded by mixing with mouse PrP(Sc) generated unique prions that were infectious to wild-type hamsters, and similar results were obtained in the opposite direction. Successive rounds of PMCA amplification result in adaptation of the in vitro-produced prions, in a process reminiscent of strain stabilization observed upon serial passage in vivo. Our results indicate that PMCA is a valuable tool for the investigation of cross-species transmission and suggest that species barrier and strain generation are determined by the propagation of PrP misfolding.

Plasma Exchange Reduces Aß Levels in Plasma and Decreases Amyloid Plaques in the Brain in a Mouse Model of Alzheimer's Disease.

Alzheimer's disease (AD) is the most common type of dementia, characterized by the abnormal accumulation of protein aggregates in the brain, known as neurofibrillary tangles and amyloid-ß (Aß) plaques. It is believed that an imbalance between cerebral and peripheral pools of Aß may play a relevant role in the deposition of Aß aggregates. Therefore, in this study, we aimed to evaluate the effect of the removal of Aß from blood plasma on the accumulation of amyloid plaques in the brain. We performed monthly plasma exchange with a 5% mouse albumin solution in the APP/PS1 mouse model from 3 to 7 months old. At the endpoint, total Aß levels were measured in the plasma, and soluble and insoluble brain fractions were analyzed using ELISA. Brains were also analyzed histologically for amyloid plaque burden, plaque size distributions, and gliosis. Our results showed a reduction in the levels of Aß in the plasma and insoluble brain fractions. Interestingly, histological analysis showed a reduction in thioflavin-S (ThS) and amyloid immunoreactivity in the cortex and hippocampus, accompanied by a change in the size distribution of amyloid plaques, and a reduction in Iba1-positive cells. Our results provide preclinical evidence supporting the relevance of targeting Aß in the periphery and reinforcing the potential use of plasma exchange as an alternative non-pharmacological strategy for slowing down AD pathogenesis.

Prion Dissemination through the Environment and Medical Practices: Facts and Risks for Human Health.

Prion diseases are a group of fatal, infectious neurodegenerative disorders affecting various species of mammals, including humans. The infectious agent in these diseases, termed prion, is composed exclusively of a misfolded protein that can spread and multiply in the absence of genetic materials. In this article, we provide an overview of the mechanisms of prion replication, interindividual transmission, and dissemination in communities. In particular, we review the potential role of the natural environment in prion transmission, including the mechanisms and pathways for prion entry and accumulation in the environment as well as its roles in prion mutation, adaptation, evolution, and transmission. We also discuss the transmission of prion diseases through medical practices, scientific research, and use of biological products. Detailed knowledge of these aspects is crucial to limit the spreading of existing prion diseases as well as to prevent the emergence of new diseases with possible catastrophic consequences for public health.

North American and Norwegian Chronic Wasting Disease Prions Exhibit Different Potential for Interspecies Transmission and Zoonotic Risk.

BACKGROUND: Chronic wasting disease (CWD) is a rapidly spreading prion disorder affecting various species of wild and captive cervids. The risk that CWD poses to cohabiting animals or more importantly to humans is largely unknown. METHODS: In this study, we investigated differences in the capacity of CWD isolates obtained from 6 different cervid species to induce prion conversion in vitro by protein misfolding cyclic amplification. We define and quantify spillover and zoonotic potential indices as the efficiency by which CWD prions sustain prion generation in vitro at expenses of normal prion proteins from various mammals and human, respectively. RESULTS: Our data suggest that reindeer and red deer from Norway could be the most transmissible CWD prions to other mammals, whereas North American CWD prions were more prone to generate human prions in vitro. CONCLUSIONS: Our results suggest that Norway and North American CWD prions correspond to different strains with distinct spillover and zoonotic potentials.

Alpha-Synuclein Oligomers and Neurofilament Light Chain Predict Phenoconversion of Pure Autonomic Failure.

OBJECTIVE: To explore the role of alpha-synuclein (αSyn) oligomers and neurofilament light chain (NfL) in cerebrospinal fluid (CSF) of patients with pure autonomic failure (PAF) as markers of future phenoconversion to multiple system atrophy (MSA). METHODS: Well-characterized patients with PAF (n = 32) were enrolled between June 2016 and February 2019 at Mayo Clinic Rochester and followed prospectively with annual visits to determine future phenoconversion to MSA, Parkinson's disease (PD), or dementia with Lewy bodies (DLB). ELISA was utilized to measure NfL and protein misfolding cyclic amplification (PMCA) to detect αSyn oligomers in CSF collected at baseline. RESULTS: Patients were followed for a median of 3.9 years. Five patients converted to MSA, 2 to PD, and 2 to DLB. NfL at baseline was elevated only in patients who later developed MSA, perfectly separating those from future PD and DLB converters as well as non-converters. ASyn-PMCA was positive in all but two cases (94%). The PMCA reaction was markedly different in five samples with maximum fluorescence and reaction kinetics previously described in MSA patients; all of these patients later developed MSA. INTERPRETATION: αSyn-PMCA is almost invariably positive in the CSF of patients with PAF establishing this condition as α-synucleinopathy. Both NfL and the magnitude and reaction kinetics of αSyn PMCA faithfully predict which PAF patients will eventually phenoconvert to MSA. This finding has important implications not only for prognostication, but also for future trials of disease modifying therapies, allowing for differentiation of MSA from Lewy body synucleinopathies before motor symptoms develop. ANN NEUROL 2021;89:1212-1220.

Transmission of cerebral amyloid pathology by peripheral administration of misfolded Aß aggregates.

Previous reports showed that brain Aß amyloidosis can be induced in animal models by exogenous administration of pre-formed aggregates. To date, only intra-peritoneal and intra-venous administrations are described as effective means to peripherally accelerate brain Aß amyloidosis by seeding. Here, we show that cerebral accumulation of Aß can be accelerated after exposing mouse models of Alzheimer's disease (AD) to Aß seeds by different peripheral routes of administration, including intra-peritoneal and intra-muscular. Interestingly, animals receiving drops of brain homogenate laden with Aß seeds in the eyes were efficiently induced. On the contrary, oral administration of large quantities of brain extracts from aged transgenic mice and AD patients did not have any effect in brain pathology. Importantly, pathological induction by peripheral administration of Aß seeds generated a large proportion of aggregates in blood vessels, suggesting vascular transport. This information highlights the role of peripheral tissues and body fluids in AD-related pathological changes.

Uptake, Retention, and Excretion of Infectious Prions by Experimentally Exposed Earthworms.

Prions are proteinaceous infectious agents that can be transmitted through various components of the environment, including soil particles. We found that earthworms exposed to prion-contaminated soil can bind, retain, and excrete prions, which remain highly infectious. Our results suggest that earthworms potentially contribute to prion disease spread in the environment.

Alpha-Synuclein Oligomers and Neurofilament Light Chain in Spinal Fluid Differentiate Multiple System Atrophy from Lewy Body Synucleinopathies.

OBJECTIVE: To explore the role of alpha-synuclein (αSyn) oligomers and neurofilament light chain (NFL) in cerebrospinal fluid (CSF) as markers of early multiple system atrophy (MSA) and to contrast findings with Lewy body synucleinopathies. METHODS: In a discovery cohort of well-characterized early MSA patients (n = 24) and matched healthy controls (CON, n = 14), we utilized enzyme-linked immunosorbent assay to measure NFL and protein misfolding cyclic amplification (PMCA) to detect αSyn oligomers in CSF. We confirmed findings in a separate prospectively enrolled cohort of patients with early MSA (n = 38), Parkinson disease (PD, n = 16), and dementia with Lewy bodies (DLB, n = 13), and CON subjects (n = 15). RESULTS: In the discovery cohort, NFL was markedly elevated in MSA patients, with perfect separation from CON. αSyn-PMCA was nonreactive in all CON, whereas all MSA samples were positive. In the confirmatory cohort, NFL again perfectly separated MSA from CON, and was significantly lower in PD and DLB compared to MSA. PMCA was again nonreactive in all CON, and positive in all but 2 MSA cases. All PD and all but 2 DLB samples were also positive for αSyn aggregates but with markedly different reaction kinetics from MSA; aggregation occurred later, but maximum fluorescence was higher, allowing for perfect separation of reactive samples between MSA and Lewy body synucleinopathies. INTERPRETATION: NFL and αSyn oligomers in CSF faithfully differentiate early MSA not only from CON but also from Lewy body synucleinopathies. The findings support the role of these markers as diagnostic biomarkers, and have important implications for understanding pathophysiologic mechanisms underlying the synucleinopathies. ANN NEUROL 2020;88:503-512.

Multiple system atrophy-associated oligodendroglial protein p25α stimulates formation of novel α-synuclein strain with enhanced neurodegenerative potential.

Pathology consisting of intracellular aggregates of alpha-Synuclein (α-Syn) spread through the nervous system in a variety of neurodegenerative disorders including Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy. The discovery of structurally distinct α-Syn polymorphs, so-called strains, supports a hypothesis where strain-specific structures are templated into aggregates formed by native α-Syn. These distinct strains are hypothesised to dictate the spreading of pathology in the tissue and the cellular impact of the aggregates, thereby contributing to the variety of clinical phenotypes. Here, we present evidence of a novel α-Syn strain induced by the multiple system atrophy-associated oligodendroglial protein p25α. Using an array of biophysical, biochemical, cellular, and in vivo analyses, we demonstrate that compared to α-Syn alone, a substoichiometric concentration of p25α redirects α-Syn aggregation into a unique α-Syn/p25α strain with a different structure and enhanced in vivo prodegenerative properties. The α-Syn/p25α strain induced larger inclusions in human dopaminergic neurons. In vivo, intramuscular injection of preformed fibrils (PFF) of the α-Syn/p25α strain compared to α-Syn PFF resulted in a shortened life span and a distinct anatomical distribution of inclusion pathology in the brain of a human A53T transgenic (line M83) mouse. Investigation of α-Syn aggregates in brain stem extracts of end-stage mice demonstrated that the more aggressive phenotype of the α-Syn/p25α strain was associated with an increased load of α-Syn aggregates based on a Förster resonance energy transfer immunoassay and a reduced α-Syn aggregate seeding activity based on a protein misfolding cyclic amplification assay. When injected unilaterally into the striata of wild-type mice, the α-Syn/p25α strain resulted in a more-pronounced motoric phenotype than α-Syn PFF and exhibited a "tropism" for nigro-striatal neurons compared to α-Syn PFF. Overall, our data support a hypothesis whereby oligodendroglial p25α is responsible for generating a highly prodegenerative α-Syn strain in multiple system atrophy.

(De)stabilization of Alpha-Synuclein Fibrillary Aggregation by Charged and Uncharged Surfactants.

Parkinson's disease (PD) is the second most common neurodegenerative disorder. An important hallmark of PD involves the pathological aggregation of proteins in structures known as Lewy bodies. The major component of these proteinaceous inclusions is alpha (α)-synuclein. In different conditions, α-synuclein can assume conformations rich in either α-helix or ß-sheets. The mechanisms of α-synuclein misfolding, aggregation, and fibrillation remain unknown, but it is thought that ß-sheet conformation of α-synuclein is responsible for its associated toxic mechanisms. To gain fundamental insights into the process of α-synuclein misfolding and aggregation, the secondary structure of this protein in the presence of charged and non-charged surfactant solutions was characterized. The selected surfactants were (anionic) sodium dodecyl sulphate (SDS), (cationic) cetyltrimethylammonium chloride (CTAC), and (uncharged) octyl ß-D-glucopyranoside (OG). The effect of surfactants in α-synuclein misfolding was assessed by ultra-structural analyses, in vitro aggregation assays, and secondary structure analyses. The α-synuclein aggregation in the presence of negatively charged SDS suggests that SDS-monomer complexes stimulate the aggregation process. A reduction in the electrostatic repulsion between N- and C-terminal and in the hydrophobic interactions between the NAC (non-amyloid beta component) region and the C-terminal seems to be important to undergo aggregation. Fourier transform infrared spectroscopy (FTIR) measurements show that ß-sheet structures comprise the assembly of the fibrils.

Prion disease is accelerated in mice lacking stress-induced heat shock protein 70 (HSP70).

Prion diseases are a group of incurable neurodegenerative disorders that affect humans and animals via infection with proteinaceous particles called prions. Prions are composed of PrPSc, a misfolded version of the cellular prion protein (PrPC). During disease progression, PrPSc replicates by interacting with PrPC and inducing its conversion to PrPSc As PrPSc accumulates, cellular stress mechanisms are activated to maintain cellular proteostasis, including increased protein chaperone levels. However, the exact roles of several of these chaperones remain unclear. Here, using various methodologies to monitor prion replication (i.e. protein misfolding cyclic amplification and cellular and animal infectivity bioassays), we studied the potential role of the molecular chaperone heat shock protein 70 (HSP70) in prion replication in vitro and in vivo Our results indicated that pharmacological induction of the heat shock response in cells chronically infected with prions significantly decreased PrPSc accumulation. We also found that HSP70 alters prion replication in vitro More importantly, prion infection of mice lacking the genes encoding stress-induced HSP70 exhibited accelerated prion disease progression compared with WT mice. In parallel with HSP70 being known to respond to endogenous and exogenous stressors such as heat, infection, toxicants, and ischemia, our results indicate that HSP70 may also play an important role in suppressing or delaying prion disease progression, opening opportunities for therapeutic intervention.