Mechanisms of prion-induced neurodegeneration

Prion-induced ferroptosis is facilitated by RAC3

Prions are infectious agents that initiate transmissible spongiform encephalopathies, causing devastating neuronal destruction in Creutzfeldt-Jakob and Kuru disease. Rapid cell death depends on presence of the endogenous prion protein PrPC, but its mechanistic contribution to pathogenesis is unclear. Here we investigate the molecular role of PrPC, reactive oxygen species and lipid metabolism in ferroptosis susceptibility, a regulated cell death process characterized by lipid peroxidation. We discover that elevated expression of the cellular prion PrPC creates a relaxed oxidative milieu that favors accumulation of unsaturated long-chain phospholipids responsible for ferroptotic death. This condition is sustained by the luminal protein glutathione peroxidase 8, which detoxifies reactive species produced by protein misfolding. Consequently, both PrPC and infectious Creutzfeldt-Jakob disease (CJD) prions trigger ferroptotic markers and sensitization. This lethality is further enhanced by RAC3, a small GTPase. Depletion of RAC3 is observed solely in pathologically afflicted cortices in CJD patients, revealing a synergistic modulation of lipids and reactive species that drives ferroptosis susceptibility. Together, the results show that PrPC initially suppresses oxidative stress, attenuates cellular defenses, and establishes a systemic vulnerability to the ferroptotic cascade. These results provide insight into the mechanism underlying regulation of ferroptosis in prion diseases and highlight potential therapeutic targets for diseases involving dysregulated cell death processes.

Creutzfeldt-Jakob disease: A comprehensive review of current understanding and research

Creutzfeldt-Jakob Disease (CJD) is one of the sample prion diseases that have characteristic features of rapidly progressive neurodegenerative disease manifested by psychomotor changes, some of which include cognitive dysfunction, motor disorder, and behavioral abnormalities. In general, this brief review will assist in elucidating the clinical features and onset, causes, diagnostic challenges, and therapeutic possibilities of CJD. It is classified into sporadic, hereditary, and acquired forms, and affection is identified as linked to the different prion varieties and genetic profiles. The disease process of CJD consists of the deposition of misfolded prions in the brain that causes apoptosis and the subsequent morphological features in the form of spongiform changes. Diagnostic strategies have changed; presently, one can see imaging methods, diagnosis through CSF biomarkers, and genetic-based diagnosis. At this time, there is no cure for CJD; therefore, management and treatment aim at supporting the patient and alleviating the signs and symptoms of the disease. As per our discussion, this review sought to accustom the readers with recent studies conducted, diagnostic advancements, and probable therapeutic approaches, pointing to the general index that more research is needed to fight CJD.

The PINK1/Parkin pathway of mitophagy exerts a protective effect during prion disease

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.

Prion Protein Octarepeat Domain Forms Transient β-Sheet Structures upon Residue-Specific Binding to Cu(II) and Zn(II) Ions

Misfolding of the cellular prion protein (PrP^C) is associated with the development of fatal neurodegenerative diseases called transmissible spongiform encephalopathies (TSEs). Metal ions appear to play a crucial role in PrP^C misfolding. PrP^C is a combined Cu(II) and Zn(II) metal-binding protein, where the main metal-binding site is located in the octarepeat (OR) region. Thus, the biological function of PrP^C may involve the transport of divalent metal ions across membranes or buffering concentrations of divalent metal ions in the synaptic cleft. Recent studies have shown that an excess of Cu(II) ions can result in PrP^C instability, oligomerization, and/or neuroinflammation. Here, we have used biophysical methods to characterize Cu(II) and Zn(II) binding to the isolated OR region of PrP^C. Circular dichroism (CD) spectroscopy data suggest that the OR domain binds up to four Cu(II) ions or two Zn(II) ions. Binding of the first metal ion results in a structural transition from the polyproline II helix to the β-turn structure, while the binding of additional metal ions induces the formation of β-sheet structures. Fluorescence spectroscopy data indicate that the OR region can bind both Cu(II) and Zn(II) ions at neutral pH, but under acidic conditions, it binds only Cu(II) ions. Molecular dynamics simulations suggest that binding of either metal ion to the OR region results in the formation of β-hairpin structures. As the formation of β-sheet structures can be a first step toward amyloid formation, we propose that high concentrations of either Cu(II) or Zn(II) ions may have a pro-amyloid effect in TSE diseases.

Mouse models of chronic wasting disease: A review

Animal models are essential tools for investigating and understanding complex prion diseases like chronic wasting disease (CWD), an infectious prion disease of cervids (elk, deer, moose, and reindeer). Over the past several decades, numerous mouse models have been generated to aid in the advancement of CWD knowledge and comprehension. These models have facilitated the investigation of pathogenesis, transmission, and potential therapies for CWD. Findings have impacted CWD management and disease outcomes, though much remains unknown, and a cure has yet to be discovered. Studying wildlife for CWD effects is singularly difficult due to the long incubation time, subtle clinical signs at early stages, lack of convenient in-the-field live testing methods, and lack of reproducibility of a controlled laboratory setting. Mouse models in many cases is the first step to understanding the mechanisms of disease in a shortened time frame. Here, we provide a comprehensive review of studies with mouse models in CWD research. We begin by reviewing studies that examined the use of mouse models for bioassays for tissues, bodily fluids, and excreta that spread disease, then address routes of infectivity and infectious load. Next, we delve into studies of genetic factors that influence protein structure. We then move on to immune factors, possible transmission through environmental contamination, and species barriers and differing prion strains. We conclude with studies that make use of cervidized mouse models in the search for therapies for CWD.

Seeing Neurodegeneration in a New Light Using Genetically Encoded Fluorescent Biosensors and iPSCs

Neurodegenerative diseases present a progressive loss of neuronal structure and function, leading to cell death and irrecoverable brain atrophy. Most have disease-modifying therapies, in part because the mechanisms of neurodegeneration are yet to be defined, preventing the development of targeted therapies. To overcome this, there is a need for tools that enable a quantitative assessment of how cellular mechanisms and diverse environmental conditions contribute to disease. One such tool is genetically encodable fluorescent biosensors (GEFBs), engineered constructs encoding proteins with novel functions capable of sensing spatiotemporal changes in specific pathways, enzyme functions, or metabolite levels. GEFB technology therefore presents a plethora of unique sensing capabilities that, when coupled with induced pluripotent stem cells (iPSCs), present a powerful tool for exploring disease mechanisms and identifying novel therapeutics. In this review, we discuss different GEFBs relevant to neurodegenerative disease and how they can be used with iPSCs to illuminate unresolved questions about causes and risks for neurodegenerative disease.

Investigating neurological symptoms of infectious diseases like COVID-19 leading to a deeper understanding of neurodegenerative disorders such as Parkinson's disease

Apart from common respiratory symptoms, neurological symptoms are prevalent among patients with COVID-19. Research has shown that infection with SARS-CoV-2 accelerated alpha-synuclein aggregation, induced Lewy-body-like pathology, caused dopaminergic neuron senescence, and worsened symptoms in patients with Parkinson's disease (PD). In addition, SARS-CoV-2 infection can induce neuroinflammation and facilitate subsequent neurodegeneration in long COVID, and increase individual vulnerability to PD or parkinsonism. These findings suggest that a post-COVID-19 parkinsonism might follow the COVID-19 pandemic. In order to prevent a possible post-COVID-19 parkinsonism, this paper reviewed neurological symptoms and related findings of COVID-19 and related infectious diseases (influenza and prion disease) and neurodegenerative disorders (Alzheimer's disease, PD and amyotrophic lateral sclerosis), and discussed potential mechanisms underlying the neurological symptoms and the relationship between the infectious diseases and the neurodegenerative disorders, as well as the therapeutic and preventive implications in the neurodegenerative disorders. Infections with a relay of microbes (SARS-CoV-2, influenza A viruses, gut bacteria, etc.) and prion-like alpha-synuclein proteins over time may synergize to induce PD. Therefore, a systematic approach that targets these pathogens and the pathogen-induced neuroinflammation and neurodegeneration may provide cures for neurodegenerative disorders. Further, antiviral/antimicrobial drugs, vaccines, immunotherapies and new therapies (e.g., stem cell therapy) need to work together to treat, manage or prevent these disorders. As medical science and technology advances, it is anticipated that better vaccines for SARS-CoV-2 variants, new antiviral/antimicrobial drugs, effective immunotherapies (alpha-synuclein antibodies, vaccines for PD or parkinsonism, etc.), as well as new therapies will be developed and made available in the near future, which will help prevent a possible post-COVID-19 parkinsonism in the 21st century.

Synthesis, insecticidal activity, and mode of action of novel imidazopyridine mesoionic derivatives containing an amido group

BACKGROUND

In our previous work, we applied a new synthetic strategy to design and synthesize a series of imidazopyridine mesoionic derivatives with an ester group. The newly synthesized compounds had excellent insecticidal activity against aphids; however, insecticidal activity against planthoppers was less than satisfactory. In the present study, we designed and synthesized a series of novel imidazopyridine mesoionic compounds, containing an amido group, and these compounds were found to have improved insecticidal activity against planthoppers.

RESULTS

The bioassay results demonstrated that most of the target compounds had moderate-to-good insecticidal activity against Sogatella furcifera, and some exhibited good-to-excellent insecticidal activity against Aphis craccivora. Among them, compound C6 had the highest insecticidal activity against S. furcifera and A. craccivora, with LC₅₀ values of 10.5 and 2.09 μg mL^-1 , respectively. Proteomic results suggested that the differentially expressed proteins mainly were enriched in the nervous system-related pathways after compound C6 treatment. Enzymatic assay results showed that compound C6 and triflumezopyrim had a certain inhibitory effect on acetylcholinesterase. Molecular docking and real-time quantitative PCR results indicated that compound C6 not only may act on the nicotinic acetylcholine receptor, but also may interact with the α4 and β1 subunits of this receptor.

CONCLUSION

The results reported here contribute to the development of new mesoionic insecticides and further our understanding of the mode-of-action of imidazopyridine mesoionic derivatives. © 2022 Society of Chemical Industry.

Early Stages of RNA-Mediated Conversion of Human Prions

Prion diseases are characterized by the conversion of prion proteins from a PrPC fold into a disease-causing PrPSC form that is self-replicating. A possible agent to trigger this conversion is polyadenosine RNA, but both mechanism and pathways of the conversion are poorly understood. Using coarse-grained molecular dynamic simulations we study the time evolution of PrPC over 600 μs. We find that both the D178N mutation and interacting with polyadenosine RNA reduce the helicity of the protein and encourage formation of segments with strand-like motifs. We conjecture that these transient β-strands nucleate the conversion of the protein to the scrapie conformation PrPSC.

Lack of the immune adaptor molecule SARM1 accelerates disease in prion infected mice and is associated with increased mitochondrial respiration and decreased expression of NRF2

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 (SARM1^KO) 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 SARM1^KO 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 SARM1^KO 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.

Calcineurin Controls Cellular Prion Protein Expression in Mouse Astrocytes

Prion diseases arise from the conformational conversion of the cellular prion protein (PrP^C) into a self-replicating prion isoform (PrP^Sc). Although this process has been studied mostly in neurons, a growing body of evidence suggests that astrocytes express PrP^C and are able to replicate and accumulate PrP^Sc. Currently, prion diseases remain incurable, while downregulation of PrP^C represents the most promising therapy due to the reduction of the substrate for prion conversion. Here we show that the astrocyte-specific genetic ablation or pharmacological inhibition of the calcium-activated phosphatase calcineurin (CaN) reduces PrP^C expression in astrocytes. Immunocytochemical analysis of cultured CaN-KO astrocytes and isolation of synaptosomal compartments from the hippocampi of astrocyte-specific CaN-KO (ACN-KO) mice suggest that PrP^C is downregulated both in vitro and in vivo. The downregulation occurs without affecting the glycosylation of PrP^C and without alteration of its proteasomal or lysosomal degradation. Direct assessment of the protein synthesis rate and shotgun mass spectrometry proteomics analysis suggest that the reduction of PrP^C is related to the impairment of global protein synthesis in CaN-KO astrocytes. When WT-PrP and PrP-D177N, a mouse homologue of a human mutation associated with the inherited prion disease fatal familial insomnia, were expressed in astrocytes, CaN-KO astrocytes showed an aberrant localization of both WT-PrP and PrP-D177N variants with predominant localization to the Golgi apparatus, suggesting that ablation of CaN affects both WT and mutant PrP proteins. These results provide new mechanistic details in relation to the regulation of PrP expression in astrocytes, suggesting the therapeutic potential of astroglial cells.

New Synthetic Method and Insecticidal Activities of Novel Imidazopyridine Mesoionic Derivatives Containing an Ester Group

To develop novel insecticides with high efficiency, a new mode of action, and safety to nontarget organisms and the environment, a series of imidazopyridine mesoionic compounds containing an ester group have been designed and synthesized via a new synthetic method discovered by our group. The bioactivity results showed that most of the target compounds exhibited significant insecticidal activities against Aphis craccivora, and some of them showed moderate insecticidal activities against Sogatella furcifera. Among them, compounds C2, C4-C11, and D3 showed excellent insecticidal activities against A. craccivora (LC₅₀ values were lower than 4.5 μg/mL), which were superior to those of pymetrozine (LC₅₀ = 6.19 μg/mL) and triflumezopyrim (LC₅₀ = 4.68 μg/mL). Remarkably, the insecticidal activity of compound C9 was 5.9-fold greater than that of triflumezopyrim with an LC₅₀ value of 0.8 μg/mL. Proteomics and molecular docking results indicated that compound C9 may affect the nervous system of A. craccivora and act on nicotinic acetylcholine receptors like triflumezopyrim.

Metals in ALS TDP-43 Pathology

Amyotrophic lateral sclerosis (ALS), Alzheimer's disease, Parkinson's disease and similar neurodegenerative disorders take their toll on patients, caregivers and society. A common denominator for these disorders is the accumulation of aggregated proteins in nerve cells, yet the triggers for these aggregation processes are currently unknown. In ALS, protein aggregation has been described for the SOD1, C9orf72, FUS and TDP-43 proteins. The latter is a nuclear protein normally binding to both DNA and RNA, contributing to gene expression and mRNA life cycle regulation. TDP-43 seems to have a specific role in ALS pathogenesis, and ubiquitinated and hyperphosphorylated cytoplasmic inclusions of aggregated TDP-43 are present in nerve cells in almost all sporadic ALS cases. ALS pathology appears to include metal imbalances, and environmental metal exposure is a known risk factor in ALS. However, studies on metal-to-TDP-43 interactions are scarce, even though this protein seems to have the capacity to bind to metals. This review discusses the possible role of metals in TDP-43 aggregation, with respect to ALS pathology.

Impact of COVID-19 Pandemic on Patients With Neurodegenerative Diseases

COVID-19 pandemic has already produced great impacts on global health security and social-economy. Elderly, particularly those with underlying diseases, are suffering from higher fatality rate. Neurodegenerative diseases are a group of incurable neurological disorders of loss of neuron and/or myelin sheath, which affect hundreds of millions of elderly populations and usually need long-term care. Older population is one of the most vulnerable to COVID-19 pandemic. In this report, we reviewed the current status of COVID-19 on the patients with several neurodegenerative diseases, particularly Alzheimer’s disease, Parkinson’s disease, prion disease, and amyotrophic lateral sclerosis. Meanwhile, the potential mechanisms of SARS-CoV-2 infection in the pathogenesis of neurodegenerative diseases were also summarized.

Prion peptide-mediated calcium level alteration governs neuronal cell damage through AMPK-autophagy flux

BACKGROUND

The distinctive molecular structure of the prion protein, PrPsc, is established only in mammals with infectious prion diseases. Prion protein characterizes either the transmissible pathogen itself or a primary constituent of the disease. Our report suggested that prion protein-mediated neuronal cell death is triggered by the autophagy flux. However, the alteration of intracellular calcium levels, AMPK activity in prion models has not been described. This study is focused on the effect of the changes in intracellular calcium levels on AMPK/autophagy flux pathway and PrP (106-126)-induced neurotoxicity.

METHODS

Western blot and Immunocytochemistry was used to detect AMPK and autophagy-related protein expression. Flow cytometry and a TdT-mediated biotin-16-dUTP nick-end labeling (TUNEL) assay were used to detect the percentage of apoptotic cells. Calcium measurement was employed using fluo-4 by confocal microscope.

RESULTS

We examined the effect of calcium homeostasis alterations induced by human prion peptide on the autophagy flux in neuronal cells. Treatment with human prion peptide increased the intracellular calcium concentration and induced cell death in primary neurons as well as in a neuronal cell line. Using pharmacological inhibitors, we showed that the L-type calcium channel is involved in the cellular entry of calcium ions. Inhibition of calcium uptake prevented autophagic cell death and reduction in AMP-activated protein kinase (AMPK) activity induced by human prion peptide.

CONCLUSION

Our data demonstrated that prion peptide-mediated calcium inflow plays a pivotal role in prion peptide-induced autophagic cell death, and reduction in AMPK activity in neurons. Altogether, our results suggest that calcium influx might play a critical role in neurodegenerative diseases, including prion diseases. Video Abstract.

RNA-seq and network analysis reveal unique glial gene expression signatures during prion infection

Background

Prion diseases and prion-like disorders, including Alzheimer’s disease and Parkinson’s disease, are characterized by gliosis and accumulation of misfolded aggregated host proteins. Ablating microglia in prion-infected brain by treatment with the colony-stimulating factor-1 receptor (CSF-1R) inhibitor, PLX5622, increased accumulation of misfolded prion protein and decreased survival time.

Methods

To better understand the role of glia during neurodegeneration, we used RNA-seq technology, network analysis, and hierarchical cluster analysis to compare gene expression in brains of prion-infected versus mock-inoculated mice. Comparisons were also made between PLX5622-treated prion-infected mice and untreated prion-infected mice to assess mechanisms involved in disease acceleration in the absence of microglia.

Results

RNA-seq and network analysis suggested that microglia responded to prion infection through activation of integrin CD11c/18 and did not adopt the expression signature associated with other neurodegenerative disease models. Instead, microglia acquired an alternative molecular signature late in the disease process. Furthermore, astrocytes expressed a signature pattern of genes which appeared to be specific for prion diseases. Comparisons were also made with prion-infected mice treated with PLX5622 to assess the impact of microglia ablation on astrocyte gene expression during prion infection. In the presence of microglia, a unique mix of transcripts associated with A1- and A2-reactive astrocytes was increased in brains of prion-infected mice. After ablation of microglia, this reactive astrocyte expression pattern was enhanced. Thus, after prion infection, microglia appeared to decrease the overall A1/A2-astrocyte responses which might contribute to increased survival after infection.

Conclusions

RNA-seq analysis indicated dysregulation of over 300 biological processes within the CNS during prion disease. Distinctive microglia- and astrocyte-associated expression signatures were identified during prion infection. Furthermore, astrogliosis and the unique astrocyte-associated expression signature were independent of microglial influences. Astrogliosis and the unique astrocyte-associated gene expression pattern were increased when microglia were ablated. Our findings emphasize the potential existence of alternative pathways for activating the A1/A2 paradigm in astrocytes during neurodegenerative disease.

Aggregation of biologically important peptides and proteins: inhibition or acceleration depending on protein and metal ion concentrations

The process of aggregation of proteins and peptides is dependent on the concentration of proteins, and the rate of aggregation can be altered by the presence of metal ions, but this dependence is not always a straightforward relationship. In general, aggregation does not occur under normal physiological conditions, yet it can be induced in the presence of certain metal ions. However, the extent of the influence of metal ion interactions on protein aggregation has not yet been fully comprehended. A consensus has thus been difficult to reach because the acceleration/inhibition of the aggregation of proteins in the presence of metal ions depends on several factors such as pH and the concentration of the aggregated proteins involved as well as metal concentration level of metal ions. Metal ions, like Cu2+, Zn2+, Pb2+ etc. may either accelerate or inhibit aggregation simply because the experimental conditions affect the behavior of biomolecules. It is clear that understanding the relationship between metal ion concentration and protein aggregation will prove useful for future scientific applications. This review focuses on the dependence of the aggregation of selected important biomolecules (peptides and proteins) on metal ion concentrations. We review proteins that are prone to aggregation, the result of which can cause serious neurodegenerative disorders. Furthering our understanding of the relationship between metal ion concentration and protein aggregation will prove useful for future scientific applications, such as finding therapies for neurodegenerative diseases.

Quantitative prediction of electronic absorption spectra of copper(II)-bioligand systems: Validation and applications

The visible region of the electronic absorption spectra of Cu(II) complexes was studied by time-dependent density functional theory (TD-DFT). The performance of twelve functionals in the prediction of absorption maxima (λ_max) was tested on eleven compounds with different geometry, donors and charge. The ranking of the functionals for λ_max was determined in terms of mean absolute percent deviation (MAPD) and standard deviation (SD) and it is as follows: BHandHLYP > M06 ≫ CAM-B3LYP ≫ MPW1PW91 ~ B1LYP ~ BLYP > HSE06 ~ B3LYP > B3P86 ~ ω-B97x-D ≫ TPSSh ≫ M06-2X (MAPD) and BHandHLYP > M06 ~ HSE06 > ω-B97x-D ~ CAM-B3LYP ~ MPW1PW91 > B1LYP ~ B3LYP > B3P86 > BLYP ≫ TPSSh ≫ M06-2X (SD). With BHandHLYP functional the MAPD is 3.1% and SD is 2.3%, while with M06 the MAPD is 3.7% and SD is 3.7%. The protocol validated in the first step of the study was applied to: i) calculate the number of transitions in the spectra and relate them to the geometry of Cu(II) species; ii) determine the coordination of axial water(s); iii) predict the electronic spectra of the systems where Cu(II) is bound to human serum albumin (HSA) and to the regions 94-97 and 108-112 of prion protein (PrP). The results indicate that the proposed computational protocol allows a successful prediction of the electronic spectra of Cu(II) species and to relate an experimental spectrum to a specific structure.

PrP (58-93) peptide from unstructured N-terminal domain of human prion protein forms amyloid-like fibrillar structures in the presence of Zn2+ ions

Many transition metal ions modulate the aggregation of different amyloid peptides. Substoichiometric zinc concentrations can inhibit aggregation, while an excess of zinc can accelerate the formation of cytotoxic fibrils. In this study, we report the fibrillization of the octarepeat domain to amyloid-like structures. Interestingly, this self-assembling process occurred only in the presence of Zn(ii) ions. The formed peptide aggregates are able to bind amyloid specific dyes thioflavin T and Congo red. Atomic force microscopy and transmission electron microscopy revealed the formation of long, fibrillar structures. X-ray diffraction and Fourier transform infrared spectroscopy studies of the formed assemblies confirmed the presence of cross-β structure. Two-component analysis of synchrotron radiation SAXS data provided the evidence for a direct decrease in monomeric peptide species content and an increase in the fraction of aggregates as a function of Zn(ii) concentration. These results could shed light on Zn(ii) as a toxic agent and on the metal ion induced protein misfolding in prion diseases.

Axonal changes in experimental prion diseases recapitulate those following constriction of postganglionic branches of the superior cervical ganglion: a comparison 40 years later

The major neurological feature of prion diseases is a neuronal loss accomplished through either apoptosis or autophagy. In this review, I compared axonal alterations in prion diseases to those described 40 years earlier as a result of nerve ligation. I also demonstrated that autophagic vacuoles and autophagosomes are a major part of dystrophic neurites. Furthermore, I summarized the current status of the autophagy in prion diseases and hypothesize, that spongiform change may originate from the autophagic vacuoles. This conclusion should be supported by other methods, in particular laser confocal microscopy.

We observed neuronal autophagic vacuoles in different stages of formation, and our interpretation of the ‘maturity’ of their formation may or may not equate to actual developmental stages. Initially, a part of the neuronal cytoplasm was sequestrated within double or multiple membranes (phagophores) and often exhibited increased electron-density. The intracytoplasmic membranes formed labyrinth-like structures that suggest a multiplication of those membranes. The autophagic vacuoles then expand and eventually, a vast area of the cytoplasm was transformed into a merging mass of autophagic vacuoles. Margaret R. Matthews published a long treatise in the Philosophical Transactions of the Royal Society of London in which she had described in great detail the ultrastructure of postganglionic branches of the superior cervical ganglion in the rat following ligation of them. The earliest changes observed by Matthews between 6 h to 2 days in the proximal stump were distensions of proximal axons. Analogously, in our models, an increased number of ‘regular’ (round) and ‘irregular’ MVB and some autophagic vacuoles were observed collectively, both processes were similar.

DFT Protocol for EPR Prediction of Paramagnetic Cu(II) Complexes and Application to Protein Binding Sites

With the aim to provide a general protocol to interpret electron paramagnetic resonance (EPR) spectra of paramagnetic copper(II) coordination compounds, density functional theory (DFT) calculations of spin Hamiltonian parameters g and A for fourteen Cu(II) complexes with different charges, donor sets, and geometry were carried out using ORCA software. The performance of eleven functionals was tested, and on the basis of the mean absolute percent deviation (MAPD) and standard deviation (SD), the ranking of the functionals for Az is: B3LYP > B3PW91 ~ B3P86 > PBE0 > CAM-B3LYP > TPSSh > BH and HLYP > B2PLYP > MPW1PW91 > ω-B97x-D >> M06; and for gz is: PBE0 > BH and HLYP > B2PLYP > ω-B97x-D > B3PW91~B3LYP~B3P86 > CAM-B3LYP > TPSSh~MPW1PW91 >> M06. With B3LYP the MAPD with respect to A z exp t l is 8.6% with a SD of 4.2%, while with PBE0 the MAPD with respect to g z exp t l is 2.9% with a SD of 1.1%. The results of the validation confirm the fundamental role of the second order spin-orbit contribution to Az. The computational procedure was applied to predict the values of gz and Az of the adducts formed by Cu(II) with albumin and two fragments of prion protein, 106–126 and 180–193.

The cellular and pathologic prion protein

The cellular prion protein, PrP^C, is a small, cell surface glycoprotein with a function that is currently somewhat ill defined. It is also the key molecule involved in the family of neurodegenerative disorders called transmissible spongiform encephalopathies, which are also known as prion diseases. The misfolding of PrP^C to a conformationally altered isoform, designated PrP^TSE, is the main molecular process involved in pathogenesis and appears to precede many other pathologic and clinical manifestations of disease, including neuronal loss, astrogliosis, and cognitive loss. PrP^TSE is also believed to be the major component of the infectious "prion," the agent responsible for disease transmission, and preparations of this protein can cause prion disease when inoculated into a naïve host. Thus, understanding the biochemical and biophysical properties of both PrP^C and PrP^TSE, and ultimately the mechanisms of their interconversion, is critical if we are to understand prion disease biology. Although entire books could be devoted to research pertaining to the protein, herein we briefly review the state of knowledge of prion biochemistry, including consideration of prion protein structure, function, misfolding, and dysfunction.

Mutations Alter RNA-Mediated Conversion of Human Prions

Prion diseases are connected with self-replication and self-propagation of misfolded proteins. The rate-limiting factor is the formation of the initial seed. We have recently studied the early stages in the conversion between functional PrP^C and the infectious scrapie PrP^SC form, triggered by the binding of RNA. Here, we study how this process is modulated by the prion sequence. We focus on residues 129 and 178, which are connected to the hereditary neurodegenerative disease fatal familial insomnia.

Prion protein inhibits fast axonal transport through a mechanism involving casein kinase 2

Prion diseases include a number of progressive neuropathies involving conformational changes in cellular prion protein (PrP^c) that may be fatal sporadic, familial or infectious. Pathological evidence indicated that neurons affected in prion diseases follow a dying-back pattern of degeneration. However, specific cellular processes affected by PrP^c that explain such a pattern have not yet been identified. Results from cell biological and pharmacological experiments in isolated squid axoplasm and primary cultured neurons reveal inhibition of fast axonal transport (FAT) as a novel toxic effect elicited by PrP^c. Pharmacological, biochemical and cell biological experiments further indicate this toxic effect involves casein kinase 2 (CK2) activation, providing a molecular basis for the toxic effect of PrP^c on FAT. CK2 was found to phosphorylate and inhibit light chain subunits of the major motor protein conventional kinesin. Collectively, these findings suggest CK2 as a novel therapeutic target to prevent the gradual loss of neuronal connectivity that characterizes prion diseases.

Copper- and Zinc-Promoted Interdomain Structure in the Prion Protein: A Mechanism for Autoinhibition of the Neurotoxic N-Terminus

The function of the cellular prion protein (PrP^C), while still poorly understood, is increasingly linked to its ability to bind physiological metal ions at the cell surface. PrP^C binds divalent forms of both copper and zinc through its unstructured N-terminal domain, modulating interactions between PrP^C and various receptors at the cell surface and ultimately tuning downstream cellular processes. In this chapter, we briefly discuss the molecular features of copper and zinc uptake by PrP^C and summarize evidence implicating these metal ions in PrP-mediated physiology. We then focus our review on recent biophysical evidence revealing a physical interaction between the flexible N-terminal and globular C-terminal domains of PrP^C. This interdomain cis interaction is electrostatic in nature and is promoted by the binding of Cu²⁺ and Zn²⁺ to the N-terminal octarepeat domain. These findings, along with recent cellular studies, suggest a mechanism whereby NC interactions serve to regulate the activity and/or toxicity of the PrP^C N-terminus. We discuss this potential mechanism in relation to familial prion disease mutations, lethal deletions of the PrP^C central region, and neurotoxicity induced by certain globular domain ligands, including bona fide prions and toxic amyloid-β oligomers.

Small-molecule PET Tracers for Imaging Proteinopathies

In this chapter, we provide a review of the challenges and advances in developing successful PET imaging agents for 3 major types of aggregated amyloid proteins: amyloid-beta (Aβ), tau, and alpha-synuclein (α-syn). These 3 amyloids are involved in the pathogenesis of a variety of neurodegenerative diseases, referred to as proteinopathies or proteopathies, that include Alzheimer disease, Lewy body dementias, multiple system atrophy, and frontotemporal dementias, among others. In the Introduction section, we briefly discuss the history of amyloid in neurodegenerative diseases and describe why progress in developing effective imaging agents has been hampered by the failure of crystallography to provide definitive ligand-protein interactions for rational radioligand design efforts. Instead, the field has relied on largely serendipitous, trial-and-error methods to achieve useful and specific PET amyloid imaging tracers for Aβ, tau, and α-syn deposits. Because many of the proteopathies involve more than 1 amyloid protein, it is important to develop selective PET tracers for the different amyloids to help assess the relative contribution of each to total amyloid burden. We use Pittsburgh compound B to illustrate some of the critical steps in developing a potent and selective Aβ PET imaging agent. Other selective Aβ and tau PET imaging compounds have followed similar pathways in their developmental processes. Success for selective α-syn PET imaging agents has not been realized yet, but work is ongoing in multiple laboratories throughout the world. In the tau sections, we provide background regarding 3-repeat (3R) and 4-repeat (4R) tau proteins and how they can affect the binding of tau radioligands in different tauopathies. We review the ongoing efforts to assess the properties of tau ligands, which are useful in 3R, 4R, or combined 3R-4R tauopathies. Finally, we describe in the α-syn sections recent attempts to develop selective tracers to image α-synucleinopathies.

An In Vivo 11C-(R)-PK11195 PET and In Vitro Pathology Study of Microglia Activation in Creutzfeldt-Jakob Disease

Microgliosis is part of the immunobiology of Creutzfeldt-Jakob disease (CJD). This is the first report using ¹¹C-(R)-PK11195 PET imaging in vivo to measure 18 kDa translocator protein (TSPO) expression, indexing microglia activation, in symptomatic CJD patients, followed by a postmortem neuropathology comparison. One genetic CJD (gCJD) patient, two sporadic CJD (sCJD) patients, one variant CJD (vCJD) patient (mean ± SD age, 47.50 ± 15.95 years), and nine healthy controls (mean ± SD age, 44.00 ± 11.10 years) were included in the study. TSPO binding potentials were estimated using clustering and parametric analyses of reference regions. Statistical comparisons were run at the regional and at the voxel-wise levels. Postmortem evaluation measured scrapie prion protein (PrP^Sc) immunoreactivity, neuronal loss, spongiosis, astrogliosis, and microgliosis. ¹¹C-(R)-PK11195-PET showed a significant TSPO overexpression at the cortical level in the two sCJD patients, as well as thalamic and cerebellar involvement; very limited parieto-occipital activation in the gCJD case; and significant increases at the subcortical level in the thalamus, basal ganglia, and midbrain and in the cerebellum in the vCJD brain. Along with misfolded prion deposits, neuropathology in all patients revealed neuronal loss, spongiosis and astrogliosis, and a diffuse cerebral and cerebellar microgliosis which was particularly dense in thalamic and basal ganglia structures in the vCJD brain. These findings confirm significant microgliosis in CJD, which was variably modulated in vivo and more diffuse at postmortem evaluation. Thus, TSPO overexpression in microglia activation, topography, and extent can vary in CJD subtypes, as shown in vivo, possibly related to the response to fast apoptotic processes, but reaches a large amount at the final disease course.

Lysosomal Quality Control in Prion Diseases

Prion diseases are transmissible, familial or sporadic. The prion protein (PrP), a normal cell surface glycoprotein, is ubiquitously expressed throughout the body. While loss of function of PrP does not elicit apparent phenotypes, generation of misfolded forms of the protein or its aberrant metabolic isoforms has been implicated in a number of neurodegenerative disorders such as scrapie, kuru, Creutzfeldt-Jakob disease, fatal familial insomnia, Gerstmann-Sträussler-Scheinker and bovine spongiform encephalopathy. These diseases are all phenotypically characterised by spongiform vacuolation of the adult brain, hence collectively termed as late-onset spongiform neurodegeneration. Misfolded form of PrP (PrP^Sc) and one of its abnormal metabolic isoforms (the transmembrane ^CtmPrP) are known to be disease-causing agents that lead to progressive loss of structure or function of neurons culminating in neuronal death. The aberrant forms of PrP utilise and manipulate the various intracellular quality control mechanisms during pathogenesis of these diseases. Amongst these, the lysosomal quality control machinery emerges as one of the primary targets exploited by the disease-causing isoforms of PrP. The autophagosomal-lysosomal degradation pathway is adversely affected in multiple ways in prion diseases and may hence be regarded as an important modulator of neurodegeneration. Some of the ESCRT pathway proteins have also been shown to be involved in the manifestation of disease phenotype. This review discusses the significance of the lysosomal quality control pathway in affecting transmissible and familial types of prion diseases.