Recombinant mouse prion protein (recMoPrP) produced in Escherichia coli was polymerized into amyloid fibrils that represent a subset of β sheet–rich structures. Fibrils consisting of recMoPrP(89–230) were inoculated intracerebrally into transgenic (Tg) mice expressing MoPrP(89–231). The mice developed neurologic dysfunction between 380 and 660 days after inoculation. Brain extracts showed protease-resistant PrP by Western blotting; these extracts transmitted disease to wild-type FVB mice and Tg mice overexpressing PrP, with incubation times of 150 and 90 days, respectively. Neuropathological findings suggest that a novel prion strain was created. Our results provide compelling evidence that prions are infectious proteins.

There is growing concern that bovine spongiform encephalopathy (BSE) may have passed from cattle to humans. We report here that transgenic (Tg) mice expressing bovine (Bo) prion protein (PrP) serially propagate BSE prions and that there is no species barrier for transmission from cattle to Tg(BoPrP) mice. These same mice were also highly susceptible to a new variant of Creutzfeldt-Jakob disease (nvCJD) and natural sheep scrapie. The incubation times (Ϸ250 days), neuropathology, and disease-causing PrP isoforms in Tg(BoPrP)Prnp 0/0 mice inoculated with nvCJD and BSE brain extracts were indistinguishable and differed dramatically from those seen in these mice injected with natural scrapie prions. Our findings provide the most compelling evidence to date that prions from cattle with BSE have infected humans and caused fatal neurodegeneration.

We report that branched polyamines, including polyamidoamide dendimers, polypropyleneimine, and polyethyleneimine, are able to purge PrP Sc , the protease-resistant isoform of the prion protein, from scrapie-infected neuroblastoma (ScN2a) cells in culture. The removal of PrP Sc by these compounds depends on both the concentration of branched polymer and the duration of exposure. Chronic exposure of ScN2a cells to low noncytotoxic concentrations of branched polyamines for 1 wk reduced PrP Sc to an undetectable level, a condition that persisted at least 3 wk after removal of the compound. Structure-activity analysis revealed that a high surface density of primary amino groups is required for polyamines to eliminate PrP Sc effectively from cells. The removal of PrP Sc by branched polyamines is attenuated by chloroquine in living cells, and exposure of scrapie-infected brain extracts with branched polyamines at acidic pH rendered the PrP Sc susceptible to protease in vitro, suggesting that endosomes or lysozomes may be the site of action. Our studies suggest that branched polyamines might be useful therapeutic agents for treatment of prion diseases and perhaps a variety of other degenerative disorders.neurodegeneration ͉ protein conformation P rion diseases are a group of fatal neurodegenerative disorders that can occur in hereditary, sporadic, and infectious forms (1). These illnesses occur in humans and a variety of other animals (2). Prions are infectious proteins. The normal cellular form of the prion protein (PrP), designated PrP C , contains three ␣-helices and has little ␤-sheet; in contrast, the protein of the prions, denoted the scrapie form of PrP (PrP Sc ), is rich in ␤-sheet structure. The accumulation of PrP Sc in the central nervous system precedes neurologic dysfunction accompanied by neuronal vacuolation and astrocytic gliosis.The spectrum of human prion diseases includes kuru (3), Creutzfeldt-Jakob disease (CJD) (4), Gerstmann-Sträussler-Scheinker disease, fatal familial insomnia (5, 6), and a new form of human prion disease, new variant CJD (nvCJD), which has emerged in Great Britain and France (7-9). Several lines of evidence have suggested a link between the nvCJD outbreak and a preceding epidemic of bovine spongiform encephalopathy (7,(10)(11)(12). Although it is too early to predict the number of nvCJD cases that might eventually arise in Great Britain and elsewhere (8), it is clear that effective therapeutics for prion diseases are urgently needed. Unfortunately, although a number of compounds including amphotericins, sulfated polyanions, Congo red dye, and anthracycline antibiotics, have been reported as prospective therapeutic agents (13-16), all have demonstrated only modest potential to impede prion propagation, and none have been shown to effect the removal of preexisting prions from an infected host.Here we report that noncytotoxic concentrations of branched polyamines can rapidly eliminate PrP Sc from chronically infected ScN2a cells. These compounds appear to act by stimulating normal ...