Spread of scrapie by contact in mice

Drug resistance confounding prion therapeutics

There is not a single pharmaceutical that halts or even slows any neurodegenerative disease. Mounting evidence shows that prions cause many neurodegenerative diseases, and arguably, scrapie and Creutzfeldt-Jakob disease prions represent the best therapeutic targets. We report here that the previously identified 2-aminothiazoles IND24 and IND81 doubled the survival times of scrapie-infected, wild-type mice. However, mice infected with Rocky Mountain Laboratory (RML) prions, a scrapie-derived strain, and treated with IND24 eventually exhibited neurological dysfunction and died. We serially passaged their brain homogenates in mice and cultured cells. We found that the prion strain isolated from IND24-treated mice, designated RML[IND24], emerged during a single passage in treated mice. Although RML prions infect both the N2a and CAD5 cell lines, RML[IND24] prions could only infect CAD5 cells. When passaged in CAD5 cells, the prions remained resistant to high concentrations of IND24. However, one passage of RML[IND24] prions in untreated mice restored susceptibility to IND24 in CAD5 cells. Although IND24 treatment extended the lives of mice propagating different prion strains, including RML, another scrapie-derived prion strain ME7, and chronic wasting disease, it was ineffective in slowing propagation of Creutzfeldt-Jakob disease prions in transgenic mice. Our studies demonstrate that prion strains can acquire resistance upon exposure to IND24 that is lost upon passage in mice in the absence of IND24. These data suggest that monotherapy can select for resistance, thus intermittent therapy with mixtures of antiprion compounds may be required to slow or stop neurodegeneration.

Three scrapie prion isolates exhibit different accumulation patterns of the prion protein scrapie isoform

To investigate the molecular basis of prion diversity, we inoculated transgenic mice expressing the Syrian hamster prion protein (PrP) with three distinct prion isolates. We compared the three isolates designated Sc237, 139H, and Me7H in Tg(SHaPrP)7 mice with clinical signs of scrapie because the incubation times with these mice are considerably shorter than the times found with hamsters. Each prion isolate produced a distinctive pattern of the scrapie isoform of PrP (PrPSc) accumulation, as determined by histoblotting, a technique developed for the regional mapping of PrPSc deposition. The PrPSc pattern with the Me7H isolate was particularly interesting because it appeared to be confined to the hypothalamus and related structures--including the interstitial nucleus of the stria terminalis, the paraventricular nucleus of the thalamus, and periaqueductal grey. Additionally, the regions of PrPSc accumulation remained highly restricted, even though the incubation time for Me7H scrapie was significantly longer than with Sc237 and 139H isolates. Neuropathological changes characterized by neuronal vacuolation and astrocytic gliosis were confined to those regions where PrPSc accumulated. These findings argue that the cell-specific propagation of prion isolates may be responsible for different properties exhibited by each of the isolates.