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The PINK1/Parkin pathway of mitophagy has been implicated in the pathogenesis of Parkinson's disease. In prion diseases, a transmissible neurodegenerative disease caused by the misfolded and infectious prion protein (PrPSc), expression of both PINK1 and Parkin are elevated, suggesting that PINK1/Parkin mediated mitophagy may also play a role in prion pathogenesis. Using mice in which expression of either PINK1 (PINK1KO) or Parkin (ParkinKO) has been ablated, we analyzed the potential role of PINK1 and Parkin in prion pathogenesis. Prion infected PINK1KO and ParkinKO mice succumbed to disease more rapidly (153 and 150 days, respectively) than wild-type control C57Bl/6 mice (161 days). Faster incubation times in PINK1KO and ParkinKO mice did not correlate with altered prion pathology in the brain, altered expression of proteins associated with mitochondrial dynamics, or prion-related changes in mitochondrial respiration. However, the expression level of mitochondrial respiration Complex I, a major site for the formation of reactive oxygen species (ROS), was higher in prion infected PINK1KO and ParkinKO mice when compared to prion infected control mice. Our results demonstrate a protective role for PINK1/Parkin mitophagy during prion disease, likely by helping to minimize ROS formation via Complex I, leading to slower prion disease progression. [ABSTRACT FROM AUTHOR]

Prion diseases are transmissible, fatal neurologic diseases that include Creutzfeldt-Jakob Disease (CJD) in humans, chronic wasting disease (CWD) in cervids, bovine spongiform encephalopathy (BSE) in cattle and scrapie in sheep. Prions are extremely difficult to inactivate and established methods to reduce prion infectivity are often dangerous, caustic, expensive, or impractical. Identifying viable and safe methods for treating prion contaminated materials is important for hospitals, research facilities, biologists, hunters, and meat-processors. For three decades, some prion researchers have used a phenolic product called Environ LpH (eLpH) to inactivate prions. ELpH has been discontinued, but a similar product, Wex-cide 128, containing the similar phenolic chemicals as eLpH is now available. In the current study, we directly compared the anti-prion efficacy of eLpH and Wex-cide 128 against prions from four different species (hamster 263K, cervid CWD, mouse 22L and human CJD). Decontamination was performed on either prion infected brain homogenates or prion contaminated steel wires and mouse bioassay was used to quantify the remaining prion infectivity. Our data show that both eLpH and Wex-cide 128 removed 4.0–5.5 logs of prion infectivity from 22L, CWD and 263K prion homogenates, but only about 1.25–1.50 logs of prion infectivity from human sporadic CJD. Wex-cide 128 is a viable substitute for inactivation of most prions from most species, but the resistance of CJD to phenolic inactivation is a concern and emphasizes the fact that inactivation methods should be confirmed for each target prion strain. [ABSTRACT FROM AUTHOR]

Accumulation of insoluble aggregates of infectious, partially protease-resistant prion protein (PrPD) generated via the misfolding of protease sensitive prion protein (PrPC) into the same infectious conformer, is a hallmark of prion diseases. Aggregated PrPD is taken up and degraded by cells, a process likely involving changes in aggregate structure that can be monitored by accessibility of the N-terminus of full-length PrPD to cellular proteases. We therefore tracked the protease sensitivity of full-length PrPD before and after cellular uptake for two murine prion strains, 22L and 87V. For both strains, PrPD aggregates were less stable following cellular uptake with increased accessibility of the N-terminus to cellular proteases across most aggregate sizes. However, a limited size range of aggregates was able to better protect the N-termini of full-length PrPD, with the N-terminus of 22L-derived PrPD more protected than that of 87V. Interestingly, changes in aggregate structure were associated with minimal changes to the protease-resistant core of PrPD. Our data show that cells destabilize the aggregate quaternary structure protecting PrPD from proteases in a strain-dependent manner, with structural changes exposing protease sensitive PrPD having little effect on the protease-resistant core, and thus conformation, of aggregated PrPD. [ABSTRACT FROM AUTHOR]

The properties of infectious prions and the pathology of the diseases they cause are dependent upon the unique conformation of each prion strain. How the pathology of prion disease correlates with different strains and genetic backgrounds has been investigated via in vivo assays, but how interactions between specific prion strains and cell types contribute to the pathology of prion disease has been dissected more effectively using in vitro cell lines. Observations made through in vivo and in vitro assays have informed each other with regard to not only how genetic variation influences prion properties, but also how infectious prions are taken up by cells, modified by cellular processes and propagated, and the cellular components they rely on for persistent infection. These studies suggest that persistent cellular infection results from a balance between prion propagation and degradation. This balance may be shifted depending upon how different cell lines process infectious prions, potentially altering prion stability, and how fast they can be transported to the lysosome. Thus, in vitro studies have given us a deeper understanding of the interactions between different prions and cell types and how they may influence prion disease phenotypes in vivo. [ABSTRACT FROM AUTHOR]

Transmissible spongiform encephalopathies (TSEs), or prion diseases, are neurodegenerative diseases that affect many mammalian species. Some examples include bovine spongiform encephalopathy (BSE) in cattle, scrapie in sheep and goats, Creutzfeldt-Jakob [...]

Prion diseases are a group of fatal, transmissible neurodegenerative diseases of mammals. In the brain, axonal loss and neuronal death are prominent in prion infection, but the mechanisms remain poorly understood. Sterile alpha and heat/Armadillo motif 1 (SARM1) is a protein expressed in neurons of the brain that plays a critical role in axonal degeneration. Following damage to axons, it acquires an NADase activity that helps to regulate mitochondrial health by breaking down NAD+, a molecule critical for mitochondrial respiration. SARM1 has been proposed to have a protective effect in prion disease, and we hypothesized that it its role in regulating mitochondrial energetics may be involved. We therefore analyzed mitochondrial respiration in SARM1 knockout mice (SARM1KO) and wild-type mice inoculated either with prions or normal brain homogenate. Pathologically, disease was similar in both strains of mice, suggesting that SARM1 mediated axonal degradation is not the sole mechanism of axonal loss during prion disease. However, mitochondrial respiration was significantly increased and disease incubation time accelerated in prion infected SARM1KO mice when compared to wild-type mice. Increased levels of mitochondrial complexes II and IV and decreased levels of NRF2, a potent regulator of reactive oxygen species, were also apparent in the brains of SARM1KO mice when compared to wild-type mice. Our data suggest that SARM1 slows prion disease progression, likely by regulating mitochondrial respiration, which may help to mitigate oxidative stress via NRF2. [ABSTRACT FROM AUTHOR]

Protease-sensitive prion protein (PrPc) can be converted to protease-resistant forms that are analogous to scrapie-associated prion protein (PrPSc) in a cell-free system that contains purified components. This conversion is preferential and needs the presence of preexisting PrPSc, proving that PrPSc is obtained from specific PrPc-PrPSc interactions. The PrPSc formation mechanism is central in the transmissible spongiform encephalopathies pathogenesis.

The preparation of amyloid fibrils by using a pathogenic prion protein peptide which could be influenced to yield fibrils with novel ultrastructural properties by changing the physical microenvironment is presented.

Prion protein (PrPC) is a protease-sensitive and soluble cell surface glycoprotein expressed in almost all mammalian cell types. PrPSc, a protease-resistant and insoluble form of PrPC, is the causative agent of prion diseases, fatal and transmissible neurogenerative diseases of mammals. Prion infection is initiated via either ingestion or inoculation of PrPSc or when host PrPC stochastically refolds into PrPSc. In either instance, the early events that occur during prion infection remain poorly understood. We have used transgenic mice expressing mouse PrPC tagged with a unique antibody epitope to monitor the response of host PrPC to prion inoculation. Following intracranial inoculation of either prion-infected or uninfected brain homogenate, we show that host PrPC can accumulate both intra-axonally and within the myelin membrane of axons suggesting that it may play a role in axonal loss following brain injury. Moreover, in response to the inoculation host PrPC exhibits an increased insolubility and protease resistance similar to that of PrPSc, even in the absence of infectious prions. Thus, our results raise the possibility that damage to the brain may be one trigger by which PrPC stochastically refolds into pathogenic PrPSc leading to productive prion infection. [ABSTRACT FROM AUTHOR]

Prions, characterized by self-propagating protease-resistant prion protein (PrP) conformations, are agents causing prion disease. Recent studies generated several such self-propagating protease-resistant recombinant PrP (rPrP-res) conformers. While some cause prion disease, others fail to induce any pathology. Here we showed that although distinctly different, the pathogenic and non-pathogenic rPrP-res conformers were similarly recognized by a group of conformational antibodies against prions and shared a similar guanidine hydrochloride denaturation profile, suggesting a similar overall architecture. Interestingly, two independently generated non-pathogenic rPrP-res were almost identical, indicating that the particular rPrP-res resulted from cofactor-guided PrP misfolding, rather than stochastic PrP aggregation. Consistent with the notion that cofactors influence rPrP-res conformation, the propagation of all rPrP-res formed with phosphatidylglycerol/RNA was cofactor-dependent, which is different from rPrP-res generated with a single cofactor, phosphatidylethanolamine. Unexpectedly, despite the dramatic difference in disease-causing capability, RT-QuIC assays detected large increases in seeding activity in both pathogenic and non-pathogenic rPrP-res inoculated mice, indicating that the non-pathogenic rPrP-res is not completely inert in vivo. Together, our study supported a role of cofactors in guiding PrP misfolding, indicated that relatively small structural features determine rPrP-res’ pathogenicity, and revealed that the in vivo seeding ability of rPrP-res does not necessarily result in pathogenicity. [ABSTRACT FROM AUTHOR]

Sporadic Creutzfeldt-Jakob disease (sCJD) is the most prevalent of the human prion diseases, which are fatal and transmissible neurodegenerative diseases caused by the infectious prion protein (PrPSc). The origin of sCJD is unknown, although the initiating event is thought to be the stochastic misfolding of endogenous prion protein (PrPC) into infectious PrPSc. By contrast, human growth hormone-associated cases of iatrogenic CJD (iCJD) in the United Kingdom (UK) are associated with exposure to an exogenous source of PrPSc. In both forms of CJD, heterozygosity at residue 129 for methionine (M) or valine (V) in the prion protein gene may affect disease phenotype, onset and progression. However, the relative contribution of each PrPC allotype to PrPSc in heterozygous cases of CJD is unknown. Using mass spectrometry, we determined that the relative abundance of PrPSc with M or V at residue 129 in brain specimens from MV cases of sCJD was highly variable. This result is consistent with PrPC containing an M or V at residue 129 having a similar propensity to misfold into PrPSc thus causing sCJD. By contrast, PrPSc with V at residue 129 predominated in the majority of the UK human growth hormone associated iCJD cases, consistent with exposure to infectious PrPSc containing V at residue 129. In both types of CJD, the PrPSc allotype ratio had no correlation with CJD type, age at clinical onset, or disease duration. Therefore, factors other than PrPSc allotype abundance must influence the clinical progression and phenotype of heterozygous cases of CJD. [ABSTRACT FROM AUTHOR]

Prion diseases such as Creutzfeldt-Jakob disease in humans, bovine spongiform encephalopathy in cattle, and scrapie in sheep are fatal neurodegenerative diseases for which there is no effective treatment. The pathology of these diseases involves the conversion of a protease sensitive form of the cellular prion protein (PrPC) into a protease resistant infectious form (PrPsc or PrPres). Both in vitro (cell culture and cell free conversion assays) and in vivo (animal) studies have demonstrated the strong dependence of this conversion process on protein sequence homology between the initial prion inoculum and the host’s own cellular prion protein. The presence of non-homologous (heterologous) proteins is often inhibitory to this conversion process. We hypothesize that the presence of heterologous prion proteins from one species might therefore constitute an effective treatment for prion disease in another species. To test this hypothesis, we infected mice intracerebrally with murine adapted RML-Chandler scrapie and treated them with heterologous prion protein (purified bacterially expressed recombinant hamster prion protein) or vehicle alone. Treated animals demonstrated reduced disease associated pathology, decreased accumulation of protease-resistant disease-associated prion protein, with delayed onset of clinical symptoms and motor deficits. This was concomitant with significantly increased survival times relative to mock-treated animals. These results provide proof of principle that recombinant hamster prion proteins can effectively and safely inhibit prion disease in mice, and suggest that hamster or other non-human prion proteins may be a viable treatment for prion diseases in humans. [ABSTRACT FROM AUTHOR]

Prion diseases are a heterogeneous class of fatal neurodegenerative disorders associated with misfolding of host cellular prion protein (PrPC) into a pathological isoform, termed PrPSc. Prion diseases affect various mammals, including humans, and effective treatments are not available. Prion diseases are distinguished from other protein misfolding disorders - such as Alzheimer's or Parkinson's disease - in that they are infectious. Prion diseases occur sporadically without any known exposure to infected material, and hereditary cases resulting from rare mutations in the prion protein have also been documented. The mechanistic underpinnings of prion and other neurodegenerative disorders remain poorly understood. Various proteomics techniques have been instrumental in early PrPSc detection, biomarker discovery, elucidation of PrPSc structure and mapping of biochemical pathways affected by pathogenesis. Moving forward, proteomics approaches will likely become more integrated into the clinical and research settings for the rapid diagnosis and characterization of prion pathogenesis. [ABSTRACT FROM AUTHOR]

Prion diseases are characterized by the conversion of the soluble protease-sensitive host-encoded prion protein (PrPC) into its aggregated, protease-resistant, and infectious isoform (PrPSc). One of the earliest events occurring in cells following exposure to an exogenous source of prions is the cellular uptake of PrPSc. It is unclear how the biochemical properties of PrPSc influence its uptake, although aggregate size is thought to be important. Here we show that for two different strains of mouse prions, one that infects cells (22L) and one that does not (87V), a fraction of PrPSc associated with distinct sedimentation properties is preferentially taken up by the cells. However, while the fraction of PrPSc and the kinetics of uptake were similar for both strains, PrPSc derived from the 87V strain was disaggregated more rapidly than that derived from 22L. The increased rate of PrPSc disaggregation did not correlate with either the conformational or aggregate stability of 87V PrPSc, both of which were greater than those of 22L PrPSc. Our data suggest that the kinetics of disaggregation of PrPSc following cellular uptake is independent of PrPSc stability but may be dependent upon some component of the PrPSc aggregate other than PrP. Rapid disaggregation of 87V PrPSc by the cell may contribute, at least in part, to the inability of 87V to infect cells in vitro. [ABSTRACT FROM AUTHOR]

In most forms of prion disease, infectivity is present primarily in the central nervous system or immune system organs such as spleen and lymph node. However, a transgenic mouse model of prion disease has demonstrated that prion infectivity can also be present as amyloid deposits in heart tissue. Deposition of infectious prions as amyloid in human heart tissue would be a significant public health concern. Although abnormal disease-associated prion protein (PrPSc) has not been detected in heart tissue from several amyloid heart disease patients, it has been observed in the heart tissue of a patient with sporadic Creutzfeldt-Jakob Disease (sCJD), the most common form of human prion disease. In order to determine whether prion infectivity can be found in heart tissue, we have inoculated formaldehyde fixed brain and heart tissue from two sCJD patients, as well as prion protein positive fixed heart tissue from two amyloid heart disease patients, into transgenic mice overexpressing the human prion protein. Although the sCJD brain samples led to clinical or subclinical prion infection and deposition of PrPSc in the brain, none of the inoculated heart samples resulted in disease or the accumulation of PrPSc. Thus, our results suggest that prion infectivity is not likely present in cardiac tissue from sCJD or amyloid heart disease patients. [ABSTRACT FROM AUTHOR]

During prion infection, the normal, protease-sensitive conformation of prion protein (PrPC) is converted via seeded polymerization to an abnormal, infectious conformation with greatly increased protease-resistance (PrPSc). In vitro, protein misfolding cyclic amplification (PMCA) uses PrPSc in prion-infected brain homogenates as an initiating seed to convert PrPC and trigger the self-propagation of PrPSc over many cycles of amplification. While PMCA reactions produce high levels of protease-resistant PrP, the infectious titer is often lower than that of brain-derived PrPSc. More recently, PMCA techniques using bacterially derived recombinant PrP (rPrP) in the presence of lipid and RNA but in the absence of any starting PrPSc seed have been used to generate infectious prions that cause disease in wild-type mice with relatively short incubation times. These data suggest that lipid and/or RNA act as cofactors to facilitate the de novo formation of high levels of prion infectivity. Using rPrP purified by two different techniques, we generated a self-propagating protease-resistant rPrP molecule that, regardless of the amount of RNA and lipid used, had a molecular mass, protease resistance and insolubility similar to that of PrPSc. However, we were unable to detect prion infectivity in any of our reactions using either cell-culture or animal bioassays. These results demonstrate that the ability to self-propagate into a protease-resistant insoluble conformer is not unique to infectious PrP molecules. They suggest that the presence of RNA and lipid cofactors may facilitate the spontaneous refolding of PrP into an infectious form while also allowing the de novo formation of self-propagating, but non-infectious, rPrP-res. [ABSTRACT FROM AUTHOR]

The secreted cochaperone STI1 triggers activation of protein kinase A (PKA) and ERK1/2 signaling by interacting with the cellular prion (PrPC) at the cell surface, resulting in neuroprotection and increased neuritogenesis. Here, we investigated whether STI1 triggers PrPC trafficking and tested whether this process controls PrPC-dependent signaling. We found that STI1, but not a STI1 mutant unable to bind PrPC, induced PrPC endocytosis. STI1-induced signaling did not occur in cells devoid of endogenous PrPC; however, heterologous expression of PrPC reconstituted both PKA and ERK1/2 activation. In contrast, a PrPC mutant lacking endocytic activity was unable to promote ERK1/2 activation induced by STI1, whereas it reconstituted PKA activity in the same condition, suggesting a key role of endocytosis in the former process. The activation of ERK1/2 by STI1 was transient and appeared to depend on the interaction of the two proteins at the cell surface or shortly after internalization. Moreover, inhibition of dynamin activity by expression of a dominant-negative mutant caused the accumulation and colocalization of these proteins at the plasma membrane, suggesting that both proteins use a dynamin-dependent internalization pathway. These results show that PrPC endocytosis is a necessary step to modulate STI1-dependent ERK1/2 signaling involved in neuritogenesis. [ABSTRACT FROM AUTHOR]

Prion diseases are transmissible neurodegenerative disorders characterized by the accumulation in the CNS of the protease-resistant prion protein (PrPres), a structurally misfolded isoform of its physiological counterpart PrPsen. Both neuropathogenesis and prion infectivity are related to PrPres formation. Here, we report that the nonpsychoactive cannabis constituent cannabidiol (CBD) inhibited PrPres accumulation in both mouse and sheep scrapie-infected cells, whereas other structurally related cannabinoid analogs were either weak inhibitors or noninhibitory. Moreover, after intraperitoneal infection with murine scrapie, peripheral injection of CBD limited cerebral accumulation of PrPres and significantly increased the survival time of infected mice. Mechanistically, CBD did not appear to inhibit PrPres accumulation via direct interactions with PrP, destabilization of PrPres aggregates, or alteration of the expression level or subcellular localization of PrPsen. However, CBD did inhibit the neurotoxic effects of PrPres and affected PrPres-induced microglial cell migration in a concentration-dependent manner. Our results suggest that CBD may protect neurons against the multiple molecular and cellular factors involved in the different steps of the neurodegenerative process, which takes place during prion infection. When combined with its ability to target the brain and its lack of toxic side effects, CBD may represent a promising new anti-prion drug. [ABSTRACT FROM AUTHOR]

The scrapie prion protein isoform, PrPSc, is a prion-associated marker that seeds the conformational conversion and polymerization of normal protease-sensitive prion protein (PrP-sen). This seeding activity allows ultrasensitive detection of PrPSc using cyclical sonicated amplification (PMCA) reactions and brain homogenate as a source of PrP-sen. Here we describe a much faster seeded polymerization method (rPrP-PMCA) which detects ≥50 ag of hamster PrPSc (≈0.003 lethal dose) within 2–3 d. This technique uses recombinant hamster PrP-sen, which, unlike brain-derived PrP-sen, can be easily concentrated, mutated and synthetically tagged. We generated protease-resistant recombinant PrP fibrils that differed from spontaneously initiated fibrils in their proteolytic susceptibility and by their infrared spectra. This assay could discriminate between scrapie-infected and uninfected hamsters using 2-μl aliquots of cerebral spinal fluid. This method should facilitate the development of rapid, ultrasensitive prion assays and diagnostic tests, in addition to aiding fundamental studies of structure and mechanism of PrPSc formation. [ABSTRACT FROM AUTHOR]

Transmissible spongiform encephalopathy (TSE) diseases are characterized by the accumulation in brain of an abnormal protease-resistant form of the host-encoded prion protein (PrP), PrP-res. PrP-res conformation differs among TSE agents derived from various sources, and these conformational differences are thought to influence the biological characteristics of these agents. In this study, we introduced deletions into the flexible N-terminal region of PrP (residues 34-124) and investigated the effect of this region on the conformation of PrP-res generated in an in vitro cell-free conversion assay. PrP deleted from residues 34 to 99 generated 12-16-kDa protease-resistant bands with intact C termini but variable N termini. The variable N termini were the result of exposure of new protease cleavage sites in PrP-res between residues 130 and 157, suggesting that these new cleavage sites were caused by alterations in the conformation of the PrP-res generated. Similarly truncated 12-16-kDa PrP bands were also identified in brain homogenates from mice infected with mouse-passaged hamster scrapie as well as in the cellfree conversion assay using conditions that mimicked the hamster/mouse species barrier to infection. Thus, by its effects on PrP-res conformation, the flexible N-terminal region of PrP seemed to influence TSE pathogenesis and cross-species TSE transmission. [ABSTRACT FROM AUTHOR]