Prominent pancreatic endocrinopathy and altered control of food intake disrupt energy homeostasis in prion diseases.

Prion diseases are fatal neurodegenerative diseases that can induce endocrinopathies. The basis of altered endocrine function in prion diseases is not well understood, and the purpose of this study was to investigate the spatiotemporal relationship between energy homeostasis and prion infection in hamsters inoculated with either the 139H strain of scrapie agent, which induces preclinical weight gain, or the HY strain of transmissible mink encephalopathy (TME), which induces clinical weight loss. Temporal changes in body weight, feed, and water intake were measured as well as both non-fasted and fasted concentrations of serum glucose, insulin, glucagon, beta-ketones, and leptin. In 139H scrapie-infected hamsters, polydipsia, hyperphagia, non-fasted hyperinsulinemia with hyperglycemia, and fasted hyperleptinemia were found at preclinical stages and are consistent with an anabolic syndrome that has similarities to type II diabetes mellitus and/or metabolic syndrome X. In HY TME-infected hamsters, hypodipsia, hypersecretion of glucagon (in both non-fasted and fasted states), increased fasted beta-ketones, fasted hypoglycemia, and suppressed non-fasted leptin concentrations were found while feed intake was normal. These findings suggest a severe catabolic syndrome in HY TME infection mediated by chronic increases in glucagon secretion. In both models, alterations of pancreatic endocrine function were not associated with PrP(Sc) deposition in the pancreas. The results indicate that prominent endocrinopathy underlies alterations in body weight, pancreatic endocrine function, and intake of food. The prion-induced alterations of energy homeostasis in 139H scrapie- or HY TME-infected hamsters could occur within areas of the hypothalamus that control food satiety and/or within autonomic centers that provide neural outflow to the pancreas.

Accessibility of a critical prion protein region involved in strain recognition and its implications for the early detection of prions.

Human prion diseases are characterized by the accumulation in the brain of proteinase K (PK)-resistant prion protein designated PrP27 - 30 detectable by the 3F4 antibody against human PrP109 - 112. We recently identified a new PK-resistant PrP species, designated PrP*20, in uninfected human and animal brains. It was preferentially detected with the 1E4 antibody against human PrP 97 - 108 but not with the anti-PrP 3F4 antibody, although the 3F4 epitope is adjacent to the 1E4 epitope in the PrP*20 molecule. The present study reveals that removal of the N-terminal amino acids up to residue 91 significantly increases accessibility of the 1E4 antibody to PrP of brains and cultured cells. In contrast to cells expressing wild-type PrP, cells expressing pathogenic mutant PrP accumulate not only PrP*20 but also a small amount of 3F4-detected PK-resistant PrP27 - 30. Remarkably, during the course of human prion disease, a transition from an increase in 1E4-detected PrP*20 to the occurrence of the 3F4-detected PrP27 - 30 was observed. Our study suggests that an increase in the level of PrP*20 characterizes the early stages of prion diseases.

Adaptation and selection of prion protein strain conformations following interspecies transmission of transmissible mink encephalopathy.

Interspecies transmission of the transmissible spongiform encephalopathies (TSEs), or prion diseases, can result in the adaptation and selection of TSE strains with an expanded host range and increased virulence such as in the case of bovine spongiform encephalopathy and variant Creutzfeldt-Jakob disease. To investigate TSE strain adaptation, we serially passaged a biological clone of transmissible mink encephalopathy (TME) into Syrian golden hamsters and examined the selection of distinct strain phenotypes and conformations of the disease-specific isoform of the prion protein (PrP(Sc)). The long-incubation-period drowsy (DY) TME strain was the predominate strain, based on the presence of its strain-specific PrP(Sc) following interspecies passage. Additional serial passages in hamsters resulted in the selection of the hyper (HY) TME PrP(Sc) strain-dependent conformation and its short incubation period phenotype unless the passages were performed with a low-dose inoculum (e.g., 10(-5) dilution), in which case the DY TME clinical phenotype continued to predominate. For both TME strains, the PrP(Sc) strain pattern preceded stabilization of the TME strain phenotype. These findings demonstrate that interspecies transmission of a single cloned TSE strain resulted in adaptation of at least two strain-associated PrP(Sc) conformations that underwent selection until one type of PrP(Sc) conformation and strain phenotype became predominant. To examine TME strain selection in the absence of host adaptation, hamsters were coinfected with hamster-adapted HY and DY TME. DY TME was able to interfere with the selection of the short-incubation HY TME phenotype. Coinfection could result in the DY TME phenotype and PrP(Sc) conformation on first passage, but on subsequent passages, the disease pattern converted to HY TME. These findings indicate that during TSE strain adaptation, there is selection of a strain-specific PrP(Sc) conformation that can determine the TSE strain phenotype.

Methods for studying prion protein (PrP) metabolism and the formation of protease-resistant PrP in cell culture and cell-free systems. An update.

Transmissible spongiform encephalopathies (TSE) or prion diseases result in aberrant metabolism of prion protein (PrP) and the accumulation of a protease-resistant, insoluble, and possibly infectious form of PrP, PrP-res. Studies of PrP biosynthesis, intracellular trafficking, and degradation has been studied in a variety of tissue culture cells. Pulse-chase metabolic labeling studies in scrapie-infected cells indicated that PrP-res is made posttranslationally from an apparently normal protease-sensitive precursor, PrP-sen, after the latter reaches the cell surface. Cell-free reactions have provided evidence that PrP-res itself can induce the conversion of PrP-sen to PrP-res in a highly species- and strain-specific manner. These studies have shed light on the mechanism of PrP-res formation and suggest molecular bases for TSE species barrier effects and agent strain propagation.

Strain-dependent differences in beta-sheet conformations of abnormal prion protein.

Strain diversity in the transmissible spongiform encephalopathies (TSEs) has been proposed to be determined by variations in the conformation of the abnormal, protease-resistant form of prion protein (PrP-res). We have investigated whether infection of hamsters with three TSE strains resulted in the formation of PrP-res with different conformations using limited proteinase K (PK) digestion and infrared spectroscopy. PrP-res isolated from the brains of hamsters infected with the hyper (HY), drowsy (DY), and 263K TSE strains yielded similar SDS-polyacrylamide gel electrophoresis profiles prior to PK treatment. However, after limited digestion with PK, the PrP-res from the DY strain exhibited a fragmentation pattern that was distinct from that of the other two strains. Infrared spectra of HY and 263K PrP-res each had major absorption bands in the amide I region at 1626 and 1636 cm-1 both prior to and after digestion with PK. These bands were not evident in the DY PrP-res spectra, which had a unique band at 1629-1630 cm-1 and stronger band intensity at both 1616 and 1694-1695 cm-1. Because absorbances from 1616 to 1636 cm-1 of protein infrared spectra are attributed primarily to beta-sheet structures, these findings indicate that the conformations of HY and 263K PrP-res differ from DY PrP-res at least in structural regions with beta-sheet secondary structure. These results support the hypothesis that strain-specific PrP-res conformers can self-propagate by converting the normal prion protein to the abnormal conformers that induce phenotypically distinct TSE diseases.

Astrocyte-specific expression of hamster prion protein (PrP) renders PrP knockout mice susceptible to hamster scrapie.

Transmissible spongiform encephalopathies are characterized by spongiosis, astrocytosis and accumulation of PrPSc, an isoform of the normal host protein PrPC. The exact cell types responsible for agent propagation and pathogenesis are still uncertain. To determine the possible role of astrocytes, we generated mice devoid of murine PrP but expressing hamster PrP transgenes driven by the astrocyte-specific GFAP promoter. After inoculation with hamster scrapie, these mice accumulated infectivity and PrPSc to high levels, developed severe disease after 227 +/- 5 days and died 7 +/- 4 days later. Therefore, astrocytes could play an important role in scrapie pathogenesis, possibly by an indirect toxic effect on neurons. Interestingly, mice expressing the same transgenes but also endogenous murine PrP genes propagated infectivity without developing disease.

In situ formation of protease-resistant prion protein in transmissible spongiform encephalopathy-infected brain slices.

The transmissible spongiform encephalopathies (TSEs) comprise a group of fatal neurodegenerative diseases that are characterized by the conversion of the normal host cellular prion protein (PrPC), to the abnormal protease-resistant prion protein isoform (PrP-res). It has been proposed, though not proven, that the infectious TSE agent consists solely of PrP-res and that PrP-res-induced conformational conversion of PrPC to additional PrP-res represents agent replication. In this study we demonstrate in situ conversion of protease-sensitive PrPC to PrP-res in TSE-infected brain slices. One step in this process is the binding of soluble PrPC to endogenous PrP-res deposits. The newly formed PrP-res associated with the slices in a pattern that correlated with the pre-existing brain distribution of PrP-res. Punctate in situ PrP conversion was observed in brain regions containing PrP-res amyloid plaques, and a more dispersed conversion product was detected in areas containing diffuse PrP-res deposits. These studies provide direct evidence that PrP-res formation involves the incorporation of soluble PrPC into both nonfibrillar and fibrillar PrP-res deposits in TSE-infected brain. Our findings suggest that the in situ PrP conversion reaction leads to additional polymerization of endogenous PrP-res aggregates and is analogous to the process of PrP-res fibril and subfibril growth in vivo.

Neuron-specific expression of a hamster prion protein minigene in transgenic mice induces susceptibility to hamster scrapie agent.

To study the effect of cell type-restricted hamster PrP expression on susceptibility to the hamster scrapie agent, we generated transgenic mice using a 1 kb hamster cDNA clone containing the 0.76 kb HPrP open reading frame under control of the neuron-specific enolase promoter. In these mice, expression of HPrP was detected only in brain tissue, with highest levels found in neurons of the cerebellum, hippocampus, thalamus, and cerebral cortex. These transgenic mice were susceptible to infection by the 263K strain of hamster scrapie with an average incubation period of 93 days, compared to 72 days in normal hamsters. In contrast, nontransgenic mice were not susceptible to this agent. These results indicate that neuron-specific expression of the 1 kb HPrP minigene including the HPrP open-reading frame is sufficient to mediate susceptibility to hamster scrapie, and that HPrP expression in nonneuronal brain cells is not necessary to overcome the TSE species barrier.

Inhibition of murine retrovirus-induced neurodegeneration in the spinal cord by explant culture.

The neurovirulent chimeric mouse ecotropic retrovirus FrCasE causes a rapid neurodegenerative disease of the central nervous system (CNS) characterized by the appearance of spongiform lesions in motor areas 10 days after neonatal inoculation. To study the details of the pathogenic process, we examined the ability of an ex vivo spinal cord model to recapitulate disease. Organotypic spinal cord slice cultures were established from IRW mice 7 days after neonatal inoculation. This corresponds to a time when virus expression in the CNS is first detectable but spongiform changes have yet to evolve. Infectivity associated with these cultures peaked at 7 days in vitro and persisted at this level for 6 weeks. FrCasE infection of the spinal cord slices was primarily found associated with microglial cells. Infection of neurons, astrocytes, oligodendroglia, and endothelial cells was not observed; however, significant astrogliosis was found. Despite the presence of extensive microglial infection in close association with spinal motor neurons in organotypic cultures, no virus-specific spongiform degenerative changes were observed. These results suggest that removal of motor neurons from the developing CNS, despite maintaining the local cytoarchitectural relationships, prevents the virus from eliciting its pathological effects. Possible reasons for the interruption of lesion development are discussed.

Non-genetic propagation of strain-specific properties of scrapie prion protein.

The infectious agents causing scrapie and other transmissible spongiform encephalopathies have been postulated to consist solely of the protease-resistant form of prion protein (PrPSc). One unprecedented requirement of the protein-only model is that the 'inheritance' of pathogen strain differences must be mediated by stable variations in PrPSc structure, rather than mutations in an agent-specific nucleic acid. Strain differences in PrPSc structure have been described for the hyper (HY) and drowsy (DY) strains of hamster transmissible mink encephalopathy (TME), a scrapie-like disease originating in mink. Although HY and DY PrPSc are both post-translationally derived from the precursor prion protein (PrPC) they are cleaved at different amino-terminal sites by proteinase K (ref. 8). Here we investigate whether this strain-specific property of PrPSc is transmitted to PrPC during formation of new PrPSc. PrPSc from the HY and DY TME strains converted the protease-sensitive PrPC into two distinct sets of protease-resistant PrP products in a cell-free system. These data provide evidence that self-propagation of PrPSc polymers with distinct three-dimensional structures could be the molecular basis of scrapie strains.

Distinct PrP properties suggest the molecular basis of strain variation in transmissible mink encephalopathy.

The molecular basis of strain variation in scrapie diseases is unknown. The only identified component of the agent is the posttranslationally modified host prion protein (PrPSc). The biochemical and physical properties of PrP from two strains of transmissible mink encephalopathy (TME), called hyper (HY) and drowsy (DY), were compared to investigate if PrP heterogeneity could account for strain diversity. The degradation rate of PrPTME digested with proteinase K was found to be strain specific and correlated with inactivation of the TME titer. Edman protein sequencing revealed that the major N-terminal end of HY PrPTME commenced at least 10 amino acid residues prior to that of DY PrPTME after digestion with proteinase K. Analysis of the brain distribution of PrPTME exhibited a strain-specific pattern and localization of PrPTME to the perikarya of specific neuron populations. Our findings are consistent with HY and DY PrPTME having distinct protein conformations and/or strain-specific ligand interactions that influence PrPTME properties. We propose that PrPTME conformation could play a role in targeting TME strains to different neuron populations in which strain-specific formation occurs. These data are consistent with the idea that PrPTME protein structure determines the molecular basis of strain variation.

Transmissible mink encephalopathy species barrier effect between ferret and mink: PrP gene and protein analysis.

Experimental infection of transmissible mink encephalopathy (TME) in two closely related mustelids, black ferret (Mustela putorius furo) and mink (Mustela visa), revealed differences in their susceptibility to the TME agent. When challenged with the Stetsonville TME agent, a longer incubation period was observed in ferrets (28 to 38 months) than mink (4 months). Western blot analysis of ferret and mink prion proteins (PrP) demonstrated no detectable differences between the proteins. Northern blot analysis of ferret brain RNA indicated that PrP mRNA abundance is similar in infected and uninfected individuals. We amplified the PrP coding region from ferret DNA using the polymerase chain reaction and compared the deduced amino acid sequence of the ferret PrP gene with the mink PrP gene. This comparison revealed six silent base changes and two amino acid changes between mink and ferret: Phe-->Lys at codon 179 and Arg-->Gln at codon 224, respectively. These changes may indicate the region of PrP that is responsible for the species barrier effect between mink and ferret.

Physicochemical and biological characterizations of distinct strains of the transmissible mink encephalopathy agent.

Inoculation of the Stetsonville, Wisconsin source of transmissible mink encephalopathy (TME) into Syrian hamsters has identified two strains of the TME agent having distinct biological properties and producing disease-specific prion proteins (PrPTME) having different physicochemical properties. Although several strains of the sheep scrapie agent have been identified in Great Britain, this is the first indication that agents producing transmissible spongiform encephalopathies in the United States also are capable of producing distinct strains.

Epidemiologic and experimental studies on transmissible mink encephalopathy.

Transmissible mink encephalopathy (TME) is a rare foodborne disease of ranch-raised mink produced by an as yet unidentified contaminated feed ingredient. Because of the clinicopathologic similarities to scrapie and the indistinguishable physicochemical properties of their transmissible agents, it was initially assumed that TME was caused by feeding mink scrapie-infected sheep. However, subsequent studies testing the oral susceptibility of mink to scrapie were unsuccessful. Epidemiologic investigations of individual incidents of TME have not identified an association between the occurrence of disease and the feeding of any particular ingredient. However, there are two incidents in which the rancher was confident that sheep were not fed. The most recent of these was in Stetsonville, Wisconsin in 1985 where the meat portion of the diet was composed almost exclusively of downer dairy cows. To examine the possibility that cattle may have been the source of infection on the Stetsonville ranch, mink brain was experimentally inoculated intracerebrally into two Holstein steers. Both of these animals developed fatal spongiform encephalopathies 18 and 19 months after inoculation. These findings are compatible with the Stetsonville incident of TME being caused by feeding mink infected cattle tissue and they suggest the presence of an unrecognized BSE-like disease in the United States. Further experimental studies on the Stetsonville source of TME have identified two distinct strains of the transmissible agent in Syrian hamsters. These strains vary in length of incubation period, clinical signs, endstage brain infectivity titre, and pathogenicity for mink.(ABSTRACT TRUNCATED AT 250 WORDS)

Biochemical and physical properties of the prion protein from two strains of the transmissible mink encephalopathy agent.

Transmissible mink encephalopathy (TME) has been transmitted to Syrian golden hamsters, and two strains of the causative agent, HYPER (HY) and DROWSY (DY), have been identified that have different biological properties. During scrapie, a TME-like disease, an endogenous cellular protein, the prion protein (PrPC), is modified (to PrPSc) and accumulates in the brain. PrPSc is partially resistant to proteases and is claimed to be an essential component of the infectious agent. Purification and analysis of PrP from hamsters infected with the HY and DY TME agent strains revealed differences in properties of PrPTME sedimentation in N-lauroylsarcosine, sensitivity to digestion with proteinase K, and migration in polyacrylamide gels. PrPC and HY PrPTME can be distinguished on the basis of their relative solubilities in detergent and protease sensitivities. PrPTME from DY-infected brain tissue shared solubility characteristics of PrP from both uninfected and HY-infected tissue. Limited protease digestion of PrPTME revealed strain-specific migration patterns upon polyacrylamide gel electrophoresis. Prolonged proteinase K treatment or N-linked deglycosylation of PrPTME did not eliminate such differences but demonstrated the PrPTME from DY-infected brain was more sensitive to protease digestion than HY PrPTME. Antigenic mapping of PrPTME with antibodies raised against synthetic peptides revealed strain-specific differences in immunoreactivity in a region of the amino-terminal end of PrPTME containing amino acid residues 89 to 103. These findings indicate that PrPTME from the two agent strains, although originating from the same host, differ in composition, conformation, or both. We conclude that PrPTME from the HY and DY strains undergo different posttranslational modifications that could explain differences in the biochemical properties of PrPTME from the two sources. Whether these strain-specific posttranslational events are directly responsible for the distinct biological properties of the HY and DY agent strains remains to be determined.

Identification of two biologically distinct strains of transmissible mink encephalopathy in hamsters.

Experimental transmission of the Stetsonville, Wisconsin, U.S.A. source of transmissible mink encephalopathy (TME) to outbred Syrian golden hamsters resulted in two distinct syndromes, termed hyper (HY) and drowsy (DY), that diverge by the third hamster passage. The syndromes differed with respect to clinical signs, incubation period, brain titre, brain lesion profile and pathogenicity in mink. HY hamster TME had an incubation period of 65 +/- 1 days and was characterized by clinical signs of hyperaesthesia and cerebellar ataxia. Lethargy and the absence of hyperexcitability or cerebellar ataxia were representative of DY hamster TME which had an incubation period of 168 +/- 2 days. At endstage, HY and DY infected animals had brain titres of 10(9.5) LD50/g and 10(7.4) LD50/g of tissue, respectively, indicating that the replication kinetics of these two strains is different. Hamster TME passaged back into mink revealed that only DY retained mink pathogenicity. This suggests that the DY agent is the major mink pathogen in the Stetsonville TME source that is also pathogenic in hamsters after a long incubation period. The HY agent is likely to be a minor component of the original TME mink brain that replicates more rapidly than DY agent in hamsters, but alone is non-pathogenic in mink. The presence of the HY and DY strains of agent that retain their biological characteristics on repeated hamster passage in the Stetsonville TME source requires that the informational molecule encoding these transmissible agents has the capacity to account for this biological diversity.

Epidemiological and experimental studies on a new incident of transmissible mink encephalopathy.

Epidemiological investigation of a new incident of transmissible mink encephalopathy (TME) in Stetsonville, Wisconsin, U.S.A. in 1985 revealed that the mink rancher had never fed sheep products to his mink but did feed them large amounts of products from fallen or sick dairy cattle. To investigate the possibility that this occurrence of TME may have resulted from exposure to infected cattle, two Holstein bull calves were injected intracerebrally with mink brain from the Stetsonville ranch. Each bull developed a fatal spongiform encephalopathy 18 and 19 months after inoculation, respectively, and both bovine brains passaged back into mink were highly pathogenic by either intracerebral or oral inoculation. These results suggest the presence of a previously unrecognized scrapie-like infection in cattle in the United States.

Cadmium-resistant mutant of Bacillus subtilis 168 with reduced cadmium transport.

Cd2+ and Mn2+ accumulation was studied with wild-type Bacillus subtilis 168 and a Cd2+-resistant mutant. After 5 min of incubation in the presence of 0.1 microM 109Cd2+ or 54Mn2+, both strains accumulated comparable amounts of 54Mn2+, while the sensitive cells accumulated three times more 109Cd2+ than the Cd2+-resistant cells did. Both 54Mn2+ and 109Cd2+ uptake, which apparently occur by the same transport system, demonstrated cation specificity; 20 microM Mn2+ or Cd2+ (but not Zn2+) inhibited the uptake of 0.1 microM 109Cd2+ or 54Mn2+. 54Mn2+ and 109Cd2+ uptake was energy dependent and temperature sensitive, but 109Cd2+ uptake in the Cd2+-resistant strain was only partially inhibited by an uncoupler or by a decrease in temperature. 109Cd2+ uptake in the sensitive strain followed Michaelis-Menten kinetics with a Km of 1.8 microM Cd2+ and a Vmax of 1.5 mumol/min X g (dry weight); 109Cd2+ uptake in the Cd2+-resistant strain was not saturable. The apparent Km value for the saturable component of 109Cd2+ uptake by the Cd2+-resistant strain was very similar to that of the sensitive strain, but the Vmax was 25 times lower than the Vmax for the sensitive strain. The Km and Vmax for 54Mn2+ uptake by both strains were very similar. Cd2+ inhibition of 54Mn2+ uptake had an apparent Ki of 3.4 and 21.5 microM Cd2+ for the sensitive and Cd2+-resistant strains, respectively. Mn2+ had an apparent Ki of 1.2 microM Mn2+ for inhibition of 109Cd2+ uptake by the sensitive strain, but the Cd2+-resistant strain had no defined Ki value for inhibition of Cd2+ uptake by Mn2+.