Interactions between wild-type and mutant prion proteins modulate neurodegeneration in transgenic mice.

201

207

On passaging synthetic prions, two isolates emerged with incubation times differing by nearly 100 days. Using conformational-stability assays, we determined the guanidine hydrochloride (Gdn⅐HCl) concentration required to denature 50% of disease-causing prion protein (PrP Sc ) molecules, denoted as the [Gdn⅐HCl]1/2 value. For the two prion isolates enciphering shorter and longer incubation times, [Gdn⅐HCl]1/2 values of 2.9 and 3.7 M, respectively, were found. Intrigued by this result, we measured the conformational stabilities of 30 prion isolates from synthetic and naturally occurring sources that had been passaged in mice. When the incubation times were plotted as a function of the [Gdn⅐HCl] 1/2 values, a linear relationship was found with a correlation coefficient of 0.93. These findings demonstrate that (i) less stable prions replicate more rapidly than do stable prions, and (ii) a continuum of PrP Sc structural states enciphers a multitude of incubation-time phenotypes. Our data argue that cellular machinery must exist for propagating a large number of different PrP Sc conformers, each of which enciphers a distinct biological phenotype as reflected by a specific incubation time. The biophysical explanation for the unprecedented plasticity of PrP Sc remains to be determined.conformational stability ͉ memory ͉ strain ͉ synthetic prions ͉ tertiary structure

Section: Methodsmentioning

confidence: 99%

Continuum of prion protein structures enciphers a multitude of prion isolate-specified phenotypes

Legname

Nguyen

Peretz

et al. 2006

201

207

“…Tissue from Tg(MCK-SHaPrP)8775͞Prnp 0/0 mice (Tg, transgenic; MCK, muscle creatine kinase; SHa, Syrian hamster), which express SHaPrP, were assayed in Syrian hamsters (25,26). Tissues from Tg(␣-actinMoPrP)6906͞Prnp 0/0 (Mo, mouse) and Tg(TTR-MoPrP)8332͞ Prnp 0/0 mice (TTR, transthyretin), which express mouse PrP, were assayed in Tg(MoPrP)4053͞FVB mice, a Tg line that overexpresses mouse Prnp a (27). The relationship between incubation time and prion titer for Tg(MoPrP)4053͞FVB, using the RML prion strain, is log titer (ID 50 units͞g) ϭ 1 ϩ 32.189⅐e (Ϫ0.0278⅐(mean inc. time (days) ) (23).…”

Section: Methodsmentioning

confidence: 99%

Prions in skeletal muscle

Bosque

Ryou²,

Telling³

et al. 2002

142

107

Here we report that mouse skeletal muscle can propagate prions and accumulate substantial titers of these pathogens. We found both high prion titers and the disease-causing isoform of the prion protein (PrP Sc ) in the skeletal muscle of wild-type mice inoculated with either the Me7 or Rocky Mountain Laboratory strain of murine prions. Particular muscles accumulated distinct levels of PrP Sc , with the highest levels observed in muscle from the hind limb. To determine whether prions are produced or merely accumulate intramuscularly, we established transgenic mice expressing either mouse or Syrian hamster PrP exclusively in muscle. Inoculating these mice intramuscularly with prions resulted in the formation of high titers of nascent prions in muscle. In contrast, inoculating mice in which PrP expression was targeted to hepatocytes resulted in low prion titers. Our data demonstrate that factors in addition to the amount of PrP expressed determine the tropism of prions for certain tissues. That some muscles are intrinsically capable of accumulating substantial titers of prions is of particular concern. Because significant dietary exposure to prions might occur through the consumption of meat, even if it is largely free of neural and lymphatic tissue, a comprehensive effort to map the distribution of prions in the muscle of infected livestock is needed. Furthermore, muscle may provide a readily biopsied tissue from which to diagnose prion disease in asymptomatic animals and even humans.

“…The discovery that mutations in the PrP gene cause inherited prion disease in humans (2), which is transmissible to laboratory animals (3)(4)(5), and the generation of infectious prions in transgenic (Tg) mice expressing mutant PrP assert that prions are devoid of nucleic acid (6)(7)(8). Furthermore, the recent demonstration that prion diversity can be enciphered in the conformation of PrP Sc no longer demands a scrapie-specific nucleic acid to explain the existence of strains of prions (9,10) That the cellular isoform of PrP (PrP C ) interacts with PrP Sc during the formation of nascent PrP Sc was surmised from Tg mouse studies where mice expressing a Syrian hamster (SHa) PrP transgene were susceptible to SHa prions (11).…”

mentioning

confidence: 99%

Evidence for protein X binding to a discontinuous epitope on the cellular prion protein during scrapie prion propagation

Kaneko

Zulianello

Scott

et al. 1997

468

420

Studies on the transmission of human (Hu) prions to transgenic (Tg) mice suggested that another molecule provisionally designated protein X participates in the formation of nascent scrapie isoform of prion protein (PrP Sc ). We report the identification of the site at which protein X binds to the cellular isoform of PrP (PrP C ) using scrapieinfected mouse (Mo) neuroblastoma cells transfected with chimeric Hu͞MoPrP genes even though protein X has not yet been isolated. Substitution of a Hu residue at position 214 or 218 prevented PrP Sc formation. The side chains of these residues protrude from the same surface of the C-terminal ␣-helix and form a discontinuous epitope with residues 167 and 171 in an adjacent loop. Substitution of a basic residue at positions 167, 171, or 218 also prevented PrP Sc formation: at a mechanistic level, these mutant PrPs appear to act as ''dominant negatives'' by binding protein X and rendering it unavailable for prion propagation. Our findings seem to explain the protective effects of basic polymorphic residues in PrP of humans and sheep and suggest therapeutic and prophylactic approaches to prion diseases.