Transfer of a prion strain to different hosts leads to emergence of strain variants

Several lines of evidence suggest that various cofactors may be required for prion replication. PrP binds to polyanions, and RNAs were shown to promote the conversion of PrP C into PrP Sc in vitro . In the present study, we investigated strain-specific differences in RNA requirement during in vitro conversion and the potential role of RNA as a strain-specifying component of infectious prions. We found that RNase treatment impairs PrP Sc -converting activity of 9 murine prion strains by protein misfolding cyclic amplification (PMCA) in a strain-specific fashion. While the addition of RNA restored PMCA conversion efficiency, the effect of synthetic polynucleotides or DNA was strain dependent, showing a different promiscuity of prion strains in cofactor utilization. The biological properties of RML propagated by PMCA under RNA-depleted conditions were compared to those of brain-derived and PMCA material generated in the presence of RNA. Inoculation of RNA-depleted RML in Tga20 mice resulted in an increased incidence of a distinctive disease phenotype characterized by forelimb paresis. However, this abnormal phenotype was not conserved in wild-type mice or upon secondary transmission. Immunohistochemical and cell panel assay analyses of mouse brains did not reveal significant differences between mice injected with the different RML inocula. We conclude that replication under RNA-depleted conditions did not modify RML prion strain properties. Our study cannot, however, exclude small variations of RML properties that would explain the abnormal clinical phenotype observed. We hypothesize that RNA molecules may act as catalysts of prion replication and that variable capacities of distinct prion strains to utilize different cofactors may explain strain-specific dependency upon RNA.

Section: Discussionmentioning

confidence: 99%

Strain-Specific Role of RNAs in Prion Replication

Saá

Sferrazza

Ottenberg

et al. 2012

“…This may be explained by selective pressures applied during cross-species transmission (71,73). Possibly the GPIneg-22L and C57-22L stocks might contain a variety of strains (74,75), and inoculation into a new host species might allow outgrowth and adaptation of a new strain. Interestingly, the low level of glycosylation found in GPIneg-22L appeared to be conserved following transmission to tg66 mice (Fig.…”

Section: Figmentioning

confidence: 99%

Increased Infectivity of Anchorless Mouse Scrapie Prions in Transgenic Mice Overexpressing Human Prion Protein

Race

Phillips

Meade-White

et al. 2015

Prion protein (PrP) is found in all mammals, mostly as a glycoprotein anchored to the plasma membrane by a C-terminal glycosylphosphatidylinositol (GPI) linkage. Following prion infection, host protease-sensitive prion protein (PrPsen or PrPC) is converted into an abnormal, disease-associated, protease-resistant form (PrPres). Biochemical characteristics, such as the PrP amino acid sequence, and posttranslational modifications, such as glycosylation and GPI anchoring, can affect the transmissibility of prions as well as the biochemical properties of the PrPres generated. Previous in vivo studies on the effects of GPI anchoring on prion infectivity have not examined cross-species transmission. In this study, we tested the effect of lack of GPI anchoring on a species barrier model using mice expressing human PrP. In this model, anchorless 22L prions derived from tg44 mice were more infectious than 22L prions derived from C57BL/10 mice when tested in tg66 transgenic mice, which expressed wild-type anchored human PrP at 8-to 16-fold above normal. Thus, the lack of the GPI anchor on the PrPres from tg44 mice appeared to reduce the effect of the mouse-human PrP species barrier. In contrast, neither source of prions induced disease in tgRM transgenic mice, which expressed human PrP at 2-to 4-fold above normal. IMPORTANCE Prion protein (PrP) is found in all mammals, usually attached to cells by an anchor molecule called GPI. Following prion infection, PrP is converted into a disease-associated form (PrPres). While most prion diseases are species specific, this finding is not consistent, and species barriers differ in strength. The amino acid sequence of PrP varies among species, and this variability affects prion species barriers. However, other PrP modifications, including glycosylation and GPI anchoring, may also influence cross-species infectivity. We studied the effect of PrP GPI anchoring using a mouse-to-human species barrier model. Experiments showed that prions produced by mice expressing only anchorless PrP were more infectious than prions produced in mice expressing anchored PrP. Thus, the lack of the GPI anchor on prions reduced the effect of the mouse-human species barrier. Our results suggest that prion diseases that produce higher levels of anchorless PrP may pose an increased risk for cross-species infection. P rion diseases, also known as transmissible spongiform encephalopathies (TSEs), are fatal neurodegenerative diseases that occur in many mammals, including humans. Central to all prion diseases is the conversion of the normal host prion protein (PrPsen or PrPC) into an abnormal, protease-resistant form (PrPres) associated with disease. In previous studies, PrPres and infectivity were generated concurrently in a cell-free in vitro system, proving that live cells were not required for formation of new prion infectivity in a cell-free in vitro system (1-4), a finding which supported the role of PrPres as the infectious prion agent (5). During the course of prion disease, repeated conversion of P...

“…While we did not determine whether low levels of HY TME persist in this study, taken together, these results suggest that the blocking strain can inhibit, but not extinguish, superinfecting strain conversion. In this model, altering the conditions of prion formation can lead to the emergence of different strains (64)(65)(66)(67)(68).…”

Section: Transsynaptic Neuronal Transport Of Prpmentioning

confidence: 99%

Incongruity between Prion Conversion and Incubation Period following Coinfection

Langenfeld

Shikiya

Kincaid

et al. 2016

When multiple prion strains are inoculated into the same host, they can interfere with each other. Strains with long incubation periods can suppress conversion of strains with short incubation periods; however, nothing is known about the conversion of the long-incubation-period strain during strain interference. To investigate this, we inoculated hamsters in the sciatic nerve with long-incubation-period strain 139H prior to superinfection with the short-incubation-period hyper (HY) strain of transmissible mink encephalopathy (TME). First, we found that 139H is transported along the same neuroanatomical tracks as HY TME, adding to the growing body of evidence indicating that PrP Sc favors retrograde transneuronal transport. In contrast to a previous report, we found that 139H interferes with HY TME infection, which is likely due to both strains targeting the same population of neurons following sciatic nerve inoculation. Under conditions where 139H blocked HY TME from causing disease, the strainspecific properties of PrP Sc corresponded with the strain that caused disease, consistent with our previous findings. In the groups of animals where incubation periods were not altered, we found that the animals contained a mixture of 139H and HY TME PrP Sc . This finding expands the definition of strain interference to include conditions where PrP Sc formation is altered yet disease outcome is unaltered. Overall, these results contradict the premise that prion strains are static entities and instead suggest that strain mixtures are dynamic regardless of incubation period or clinical outcome of disease. IMPORTANCEPrions can exist as a mixture of strains in naturally infected animals, where they are able to interfere with the conversion of each other and to extend incubation periods. Little is known, however, about the dynamics of strain conversion under conditions where incubation periods are not affected. We found that inoculation of the same animal with two strains can result in the alteration of conversion of both strains under conditions where the resulting disease was consistent with infection with only a single strain. These data challenge the idea that prion strains are static and suggests that strain mixtures are more dynamic than previously appreciated. This observation has significant implications for prion adaptation. P rion diseases are transmissible neurodegenerative diseases of animals, including humans, with no known effective treatment. Prion diseases of animals include scrapie of sheep and goats, chronic wasting disease of cervids, bovine spongiform encephalopathy of cattle, and transmissible mink encephalopathy (TME) of ranch-raised mink. Prion diseases of humans include kuru of the Fore people of Papua New Guinea, Creutzfeldt-Jakob disease (CJD), Gerstmann-Sträussler-Scheinker syndrome, and fatal familial insomnia (1-8). Human prion diseases are unique in biology in that they can have infectious, familial, or sporadic etiologies. Interestingly, brain material from all three etiologies is infecti...