A Novel PRNP Y218N Mutation in Gerstmann-Sträussler-Scheinker Disease With Neurofibrillary Degeneration

Tau oligomers impair memory and synaptic plasticity through the cellular prion protein

Deposition of abnormally phosphorylated tau aggregates is a central event leading to neuronal dysfunction and death in Alzheimer's disease (AD) and other tauopathies. Among tau aggregates, oligomers (TauOs) are considered the most toxic. AD brains show significant increase in TauOs compared to healthy controls, their concentration correlating with the severity of cognitive deficits and disease progression. In vitro and in vivo neuronal TauO exposure leads to synaptic and cognitive dysfunction, but their mechanisms of action are unclear. Evidence suggests that the cellular prion protein (PrPC) may act as a mediator of TauO neurotoxicity, as previously proposed for β-amyloid and α-synuclein oligomers. To investigate whether PrPC mediates TauO detrimental activities, we compared their effects on memory and synaptic plasticity in wild type (WT) and PrPC knockout (Prnp0/0) mice. Intracerebroventricular injection of TauOs significantly impaired recognition memory in WT but not in Prnp0/0 mice. Similarly, TauOs inhibited long-term potentiation in acute hippocampal slices from WT but not Prnp0/0 mice. Surface plasmon resonance indicated a high-affinity binding between TauOs and PrPC with a KD of 20-50 nM. Immunofluorescence analysis of naïve and PrPC-overexpressing HEK293 cells exposed to TauOs showed a PrPC dose-dependent association of TauOs with cells over time, and their co-localization with PrPC on the plasma membrane and in intracellular compartments, suggesting PrPC-may play a role in TauO internalization. These findings support the concept that PrPC mediates the detrimental activities of TauOs through a direct interaction, suggesting that targeting this interaction might be a promising therapeutic strategy for AD and other tauopathies.

Genetic prion diseases presenting as frontotemporal dementia: clinical features and diagnostic challenge

Background

To elucidate the clinical and ancillary features of genetic prion diseases (gPrDs) presenting with frontotemporal dementia (FTD) to aid early identification.

Methods

Global data of gPrDs presenting with FTD caused by prion protein gene mutations were collected from literature review and our records. Fifty-one cases of typical FTD and 136 cases of prion diseases admitted to our institution were included as controls. Clinical and ancillary data of the different groups were compared.

Results

Forty-nine cases of gPrDs presenting with FTD were identified. Compared to FTD or prion diseases, gPrDs presenting with FTD were characterized by earlier onset age (median 45 vs. 61/60 years, P < 0.001, P < 0.001) and higher incidence of positive family history (81.6% vs. 27.5/13.2%, P < 0.001, P < 0.001). Furthermore, GPrDs presenting with FTD exhibited shorter duration (median 5 vs. 8 years) and a higher rate of parkinsonism (63.7% vs. 9.8%, P < 0.001), pyramidal signs (39.1% vs. 7.8%, P = 0.001), mutism (35.9% vs. 0%, P < 0.001), seizures (25.8% vs. 0%, P < 0.001), myoclonus (22.5% vs. 0%, P < 0.001), and hyperintensity on MRI (25.0% vs. 0, P < 0.001) compared to FTD. Compared to prion diseases, gPrDs presenting with FTD had a longer duration of symptoms (median 5 vs. 1.1 years, P < 0.001), higher rates of frontotemporal atrophy (89.7% vs. 3.3%, P < 0.001), lower rates of periodic short-wave complexes on EEG (0% vs. 30.3%, P = 0.001), and hyperintensity on MRI (25.0% vs. 83.0%, P < 0.001). The frequency of codon 129 Val allele in gPrDs presenting with FTD was significantly higher than that reported in the literature for gPrDs in the Caucasian and East Asian populations (33.3% vs. 19.2%/8.0%, P = 0.005, P < 0.001).

Conclusions

GPrDs presenting with FTD are characterized by early-onset, high incidence of positive family history, high frequency of the Val allele at codon 129, overlapping symptoms with prion disease and FTD, and ancillary features closer to FTD. PRNP mutations may be a rare cause in the FTD spectrum, and PRNP genotyping should be considered in patients with these features.

Alterations of Striatal Subregions in a Prion Protein Gene V180I Mutation Carrier Presented as Frontotemporal Dementia With Parkinsonism

Objective

To explore the roles of striatal subdivisions in the pathogenesis of frontotemporal dementia with parkinsonism (FTDP) in a patient resulting from prion protein gene (PRNP) mutation.

Methods

This patient received clinical interviews and underwent neuropsychological assessments, genetic testing, [18F]-fluorodeoxyglucose positron emission tomography ([18F]-FDG PET)/MRI, and [18F]-dihydrotetrabenazine positron emission tomography ([18F]-DTBZ PET)/CT. Region-of-interest analysis was conducted concerning metabolism, and dopamine transport function between this patient and 12 controls, focusing on the striatum subregions according to the Oxford-GSK-Imanova Striatal Connectivity Atlas.

Results

A 64-year-old man initially presented with symptoms of motor dysfunction and subsequently behavioral and personality changes. FTDP was initially suspected. Sequence analysis disclosed a valine to isoleucine at codon 180 in PRNP. Compared to controls, this patient had a severe reduction (> 2SD) of standard uptake value ratio (SUVR) in the limbic and executive subregions but relative retention of metabolism in rostral motor and caudal motor subregions using [18F]-FDG PET/MRI, and the SUVR decreased significantly across the striatal in [18F]-DTBZ PET/CT, especially in the rostral motor and caudal motor subregions.

Conclusion

The alteration of frontal striatal loops may be involved in cognitive impairment in FTDP, and the development of parkinsonism in FTDP may be primarily due to the involvement of the presynaptic nigrostriatal loops in PRNP V180I mutation.

Description of the first Spanish case of Gerstmann-Sträussler-Scheinker disease with A117V variant: clinical, histopathological and biochemical characterization

Gerstmann–Sträussler–Scheinker disease (GSS) is a rare neurodegenerative illness that belongs to the group of hereditary or familial Transmissible Spongiform Encephalopathies (TSE). Due to the presence of different pathogenic alterations in the prion protein (PrP) coding gene, it shows an enhanced proneness to misfolding into its pathogenic isoform, leading to prion formation and propagation. This aberrantly folded protein is able to induce its conformation to the native counterparts forming amyloid fibrils and plaques partially resistant to protease degradation and showing neurotoxic properties. PrP with A117V pathogenic variant is the second most common genetic alteration leading to GSS and despite common phenotypic and neuropathological traits can be defined for each specific variant, strikingly heterogeneous manifestations have been reported for inter-familial cases bearing the same pathogenic variant or even within the same family. Given the scarcity of cases and their clinical, neuropathological, and biochemical variability, it is important to characterize thoroughly each reported case to establish potential correlations between clinical, neuropathological and biochemical hallmarks that could help to define disease subtypes. With that purpose in mind, this manuscript aims to provide a detailed report of the first Spanish GSS case associated with A117V variant including clinical, genetic, neuropathological and biochemical data, which could help define in the future potential disease subtypes and thus, explain the high heterogeneity observed in patients suffering from these maladies.

Extracellular Prion Protein Aggregates in Nine Gerstmann–Sträussler–Scheinker Syndrome Subjects with Mutation P102L: A Micromorphological Study and Comparison with Literature Data

Gerstmann–Sträussler–Scheinker syndrome (GSS) is a hereditary neurodegenerative disease characterized by extracellular aggregations of pathological prion protein (PrP) forming characteristic plaques. Our study aimed to evaluate the micromorphology and protein composition of these plaques in relation to age, disease duration, and co-expression of other pathogenic proteins related to other neurodegenerations. Hippocampal regions of nine clinically, neuropathologically, and genetically confirmed GSS subjects were investigated using immunohistochemistry and multichannel confocal fluorescent microscopy. Most pathognomic prion protein plaques were small (2–10 µm), condensed, globous, and did not contain any of the other investigated proteinaceous components, particularly dystrophic neurites. Equally rare (in two cases out of nine) were plaques over 50 µm having predominantly fibrillar structure and exhibit the presence of dystrophic neuritic structures; in one case, the plaques also included bulbous dystrophic neurites. Co-expression with hyperphosphorylated protein tau protein or amyloid beta-peptide (Aβ) in GSS PrP plaques is generally a rare observation, even in cases with comorbid neuropathology. The dominant picture of the GSS brain is small, condensed plaques, often multicentric, while presence of dystrophic neuritic changes accumulating hyperphosphorylated protein tau or Aβ in the PrP plaques are rare and, thus, their presence probably constitutes a trivial observation without any relationship to GSS development and progression.

Homozygous R136S mutation in PRNP gene causes inherited early onset prion disease

BACKGROUND

More than 40 pathogenic heterozygous PRNP mutations causing inherited prion diseases have been identified to date. Recessive inherited prion disease has not been described to date.

METHODS

We describe the clinical and neuropathological data of inherited early-onset prion disease caused by the rare PRNP homozygous mutation R136S. In vitro PrPSc propagation studies were performed using recombinant-adapted protein misfolding cyclic amplification technique. Brain material from two R136S homozygous patients was intracranially inoculated in TgMet129 and TgVal129 transgenic mice to assess the transmissibility of this rare inherited form of prion disease.

RESULTS

The index case presented symptoms of early-onset dementia beginning at the age of 49 and died at the age of 53. Neuropathological evaluation of the proband revealed abundant multicentric PrP plaques and Western blotting revealed a ~ 8 kDa protease-resistant, unglycosylated PrPSc fragment, consistent with a Gerstmann-Sträussler-Scheinker phenotype. Her youngest sibling suffered from progressive cognitive decline, motor impairment, and myoclonus with onset in her late 30s and died at the age of 48. Genetic analysis revealed the presence of the R136S mutation in homozygosis in the two affected subjects linked to homozygous methionine at codon 129. One sibling carrying the heterozygous R136S mutation, linked to homozygous methionine at codon 129, is still asymptomatic at the age of 74. The inoculation of human brain homogenates from our index case and an independent case from a Portuguese family with the same mutation in transgenic mice expressing human PrP and in vitro propagation of PrPSc studies failed to show disease transmissibility.

CONCLUSION

In conclusion, biallelic R136S substitution is a rare variant that produces inherited early-onset human prion disease with a Gerstmann-Sträussler-Scheinker neuropathological and molecular signature. Even if the R136S variant is predicted to be "probably damaging", heterozygous carriers are protected, at least from an early onset providing evidence for a potentially recessive pattern of inheritance in human prion diseases.

On the role of the cellular prion protein in the uptake and signaling of pathological aggregates in neurodegenerative diseases

Neurodegenerative disorders are associated with intra- or extra-cellular deposition of aggregates of misfolded insoluble proteins. These deposits composed of tau, amyloid-β or α-synuclein spread from cell to cell, in a prion-like manner. Novel evidence suggests that the circulating soluble oligomeric species of these misfolded proteins could play a major role in pathology, while insoluble aggregates would represent their protective less toxic counterparts. Recent convincing data support the proposition that the cellular prion protein, PrP^C, act as a toxicity-inducing receptor for amyloid-β oligomers. As a consequence, several studies focused their investigations to the role played by PrP^C in binding other protein aggregates, such as tau and α-synuclein, for its possible common role in mediating toxic signalling. The biological relevance of PrP^C as key ligand and potential mediator of toxicity for multiple proteinaceous aggregated species, prions or PrP^Sc included, could lead to relevant therapeutic implications. Here we describe the structure of PrP^C and the proposed interplay with its pathological counterpart PrP^Sc and then we recapitulate the most recent findings regarding the role of PrP^C in the interaction with aggregated forms of other neurodegeneration-associated proteins.

The role of the cellular prion protein in the uptake and toxic signaling of pathological neurodegenerative aggregates

Neurodegenerative disorders are invariably associated with intra- or extra-cellular deposition of aggregates composed of misfolded insoluble proteins. These deposits composed of tau, amyloid-β or α-synuclein spread from cell to cell, in a prion-like manner. Emerging evidence suggests that the circulating soluble species of these misfolded proteins (usually referred as oligomers) could play a major role in pathology, while insoluble aggregates would represent their protective less toxic counterparts. Convincing data support the hypothesis that the cellular prion protein, PrP^C, act as a toxicity-transducing receptor for amyloid-β oligomers. As a consequence, several studies extended investigations to the role played by PrP^C in binding aggregates of proteins other than Aβ, such as tau and α-synuclein, for its possible common role in mediating toxic signaling. A better characterization of the biological relevance of PrP^C as key ligand and potential mediator of toxicity for multiple proteinaceous aggregated species, prions or PrP^Sc included, would bring relevant therapeutic implications. Here we will first describe the structure of the prion protein and the hypothesized interplay with its pathological counterpart PrP^Sc and then we will recapitulate the most relevant discoveries regarding the role of PrP^C in the interaction with aggregated forms of other neurodegeneration-associated proteins.

The Quest for Cellular Prion Protein Functions in the Aged and Neurodegenerating Brain

Cellular (also termed ‘natural’) prion protein has been extensively studied for many years for its pathogenic role in prionopathies after misfolding. However, neuroprotective properties of the protein have been demonstrated under various scenarios. In this line, the involvement of the cellular prion protein in neurodegenerative diseases other than prionopathies continues to be widely debated by the scientific community. In fact, studies on knock-out mice show a vast range of physiological functions for the protein that can be supported by its ability as a cell surface scaffold protein. In this review, we first summarize the most commonly described roles of cellular prion protein in neuroprotection, including antioxidant and antiapoptotic activities and modulation of glutamate receptors. Second, in light of recently described interaction between cellular prion protein and some amyloid misfolded proteins, we will also discuss the molecular mechanisms potentially involved in protection against neurodegeneration in pathologies such as Alzheimer’s, Parkinson’s, and Huntington’s diseases.

Atomic insights into the effects of pathological mutants through the disruption of hydrophobic core in the prion protein

Destabilization of prion protein induces a conformational change from normal prion protein (PrPC) to abnormal prion protein (PrPSC). Hydrophobic interaction is the main driving force for protein folding, and critically affects the stability and solvability. To examine the importance of the hydrophobic core in the PrP, we chose six amino acids (V176, V180, T183, V210, I215, and Y218) that make up the hydrophobic core at the middle of the H2-H3 bundle. A few pathological mutants of these amino acids have been reported, such as V176G, V180I, T183A, V210I, I215V, and Y218N. We focused on how these pathologic mutations affect the hydrophobic core and thermostability of PrP. For this, we ran a temperature-based replica-exchange molecular dynamics (T-REMD) simulation, with a cumulative simulation time of 28 μs, for extensive ensemble sampling. From the T-REMD ensemble, we calculated the protein folding free energy difference between wild-type and mutant PrP using the thermodynamic integration (TI) method. Our results showed that pathological mutants V176G, T183A, I215V, and Y218N decrease the PrP stability. At the atomic level, we examined the change in pair-wise hydrophobic interactions from valine-valine to valine-isoleucine (and vice versa), which is induced by mutation V180I, V210I (I215V) at the 180th-210th (176th-215th) pair. Finally, we investigated the importance of the π-stacking between Y218 and F175.

Novel prion mutation (p.Tyr225Cys) in a Korean patient with atypical Creutzfeldt-Jakob disease

Background: A novel prion variant, PRNP p.Tyr225Cys (c.674A>G; p.Y225C), was identified in an atypical Creutzfeldt–Jakob disease (CJD) patient. The patient had a 5-year history of progressive cognitive impairment with speech and gait disturbances. From the basic neurological examination at his first hospital visit, rigidity and myoclonic jerks in all limbs were observed without focal weakness. Electroencephalogram showed the diffuse slow continuous delta activity in the bilateral cerebral hemisphere. Magnetic resonance imaging revealed abnormalities in the brain, such as cortical signal changes and edema in the frontotemporoparietal lobes and the basal ganglia. Cerebrospinal fluid 14–3-3 protein analysis showed a weakly positive signal. Family history remained unclear, but the patient’s mother and sister were diagnosed with cognitive impairment but both refused genetic testing.

Methods: Targeted next generation sequencing (NGS) was performed on 50 genes, involved in different neurodegeneratives diseases, such as Alzheimer's, Parkinson's, frontotemporal dementia or prion diseases. In silico analyses and structure predictions were performed on the potential patohgenic mutations.

Results: NGS and standard sequencing revealed the novel PRNP p.Tyr225Cys mutation in the patient. Structure predictions revealed that this may make the helix more flexible. In addition, the extra cysteine residue in TM-III of prion protein may result in disturbances of natural disulfide bond.

Conclusion: Hence, the pathogenicity of PRNP p.Tyr225Cys was not fully confirmed at present, and its penetrance was suggested to be low. However, its possible pathogenic nature in prion diseases cannot be ignored, since Tyr/Cys exchange could disturb the helix dynamics and contribute to conformational alteration and disease progression.

Detection of tau in Gerstmann-Sträussler-Scheinker disease (PRNP F198S) by [18F]Flortaucipir PET

This study aimed to determine the pattern of [¹⁸F]flortaucipir uptake in individuals affected by Gerstmann-Sträussler-Scheinker disease (GSS) associated with the PRNP F198S mutation. The aims were to: 1) determine the pattern of [¹⁸F]flortaucipir uptake in two GSS patients; 2) compare tau distribution by [¹⁸F]flortaucipir PET imaging among three groups: two GSS patients, two early onset Alzheimer’s disease patients (EOAD), two cognitively normal older adults (CN); 3) validate the PET imaging by comparing the pattern of [¹⁸F]flortaucipir uptake, in vivo, with that of tau neuropathology, post-mortem. Scans were processed to generate standardized uptake value ratio (SUVR) images. Regional [¹⁸F]flortaucipir SUVR was extracted and compared between GSS patients, EOADs, and CNs. Neuropathology and tau immunohistochemistry were carried out post-mortem on a GSS patient who died 9 months after the [¹⁸F]flortaucipir scan. The GSS patients were at different stages of disease progression. Patient A was mildly to moderately affected, suffering from cognitive, psychiatric, and ataxia symptoms. Patient B was moderately to severely affected, suffering from ataxia and parkinsonism accompanied by psychiatric and cognitive symptoms. The [¹⁸F]flortaucipir scans showed uptake in frontal, cingulate, and insular cortices, as well as in the striatum and thalamus. Uptake was greater in Patient B than in Patient A. Both GSS patients showed greater uptake in the striatum and thalamus than the EOADs and greater uptake in all evaluated regions than the CNs. Thioflavin S fluorescence and immunohistochemistry revealed that the anatomical distribution of tau pathology is consistent with that of [¹⁸F]flortaucipir uptake. In GSS patients, the neuroanatomical localization of pathologic tau, as detected by [¹⁸F]flortaucipir, suggests correlation with the psychiatric, motor, and cognitive symptoms. The topography of uptake in PRNP F198S GSS is strikingly different from that seen in AD. Further studies of the sensitivity, specificity, and anatomical patterns of tau PET in diseases with tau pathology are warranted.

An autopsy report of three kindred in a Gerstmann-Sträussler-Scheinker disease P105L family with a special reference to prion protein, tau, and beta-amyloid

INTRODUCTION

Gerstmann-Sträussler-Scheinker disease P105L (GSS105) is a rare variant of GSS caused by a point mutation of the prion protein (PrP) gene at codon 105 (proline to leucine substitution). It is clinically characterized by spastic paraparesis and dementia and histopathologically defined by PrP-plaques in the brain. This report describes a clinicopathological analysis of three autopsied kindred from a Japanese GSS105 family, plus a topological analysis of PrP, hyperphosphorylated tau (p-tau), and beta-amyloid (Aβ).

METHODS

Using paraffin-embedded sections, we applied histology and single- and multiple-labeling immunohistochemistry for PrP, p-tau, and Aβ to the three cases. Comparative semi-quantitative analyses of tissue injuries and PrP-plaques were also employed.

RESULTS

Case 1 (45 years old (yo)) and Case 2 (56 yo) are sisters, and Case 3 (49 yo) is the son of Case 2. Case 1 and Case 2 presented with spastic paraparesis followed by dementia, whereas Case 3 presented, not with spastic paraparesis, but with psychiatric symptoms. In Case 1 and Case 2, the brain showed tissue injuries with many PrP-plaques in the cerebral cortices, and the pyramidal tract showed myelin loss/pallor. In Case 3, the brain was least degenerated with a number of PrP-plaques; however, the pyramidal tract remained intact. In addition, p-tau was deposited in all cases, where p-tau was present in or around PrP-plaques. By double-labeling immunohistochemistry, the colocalization of p-tau with PrP-plaques was confirmed. Moreover in Case 2, Aβ was deposited in the cerebral cortices. Interestingly, not only p-tau but also Aβ was colocalized with PrP-plaques. In all cases, both three repeat tau and four repeat tau were associated with PrP-plaques.

CONCLUSIONS

The clinicopathological diversity of GSS105, which is possible even in the same family, was ascertained. Not only p-tau but also Aβ could be induced by PrP ("secondary degeneration"), facilitating the kaleidoscopic symptoms of GSS.

Genetic PrP Prion Diseases

Genetic prion diseases (gPrDs) caused by mutations in the prion protein gene (PRNP) have been classified as genetic Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker disease, or fatal familial insomnia. Mutations in PRNP can be missense, nonsense, and/or octapeptide repeat insertions or, possibly, deletions. These mutations can produce diverse clinical features. They may also show varying ancillary testing results and neuropathological findings. Although the majority of gPrDs have a rapid progression with a short survival time of a few months, many also present as ataxic or parkinsonian disorders, which have a slower decline over a few to several years. A few very rare mutations manifest as neuropsychiatric disorders, with systemic symptoms that include gastrointestinal disorders and neuropathy; these forms can progress over years to decades. In this review, we classify gPrDs as rapid, slow, or mixed types based on their typical rate of progression and duration, and we review the broad spectrum of phenotypes manifested by these diseases.

iPS Cell Cultures from a Gerstmann-Sträussler-Scheinker Patient with the Y218N PRNP Mutation Recapitulate tau Pathology

Gerstmann-Sträussler-Scheinker (GSS) syndrome is a fatal autosomal dominant neurodegenerative prionopathy clinically characterized by ataxia, spastic paraparesis, extrapyramidal signs and dementia. In some GSS familiar cases carrying point mutations in the PRNP gene, patients also showed comorbid tauopathy leading to mixed pathologies. In this study we developed an induced pluripotent stem (iPS) cell model derived from fibroblasts of a GSS patient harboring the Y218N PRNP mutation, as well as an age-matched healthy control. This particular PRNP mutation is unique with very few described cases. One of the cases presented neurofibrillary degeneration with relevant Tau hyperphosphorylation. Y218N iPS-derived cultures showed relevant astrogliosis, increased phospho-Tau, altered microtubule-associated transport and cell death. However, they failed to generate proteinase K-resistant prion. In this study we set out to test, for the first time, whether iPS cell-derived neurons could be used to investigate the appearance of disease-related phenotypes (i.e, tauopathy) identified in the GSS patient.

Role of cellular prion protein in interneuronal amyloid transmission

Several studies have indicated that certain misfolded amyloids composed of tau, β-amyloid or α-synuclein can be transferred from cell to cell, suggesting the contribution of mechanisms reminiscent of those by which infective prions spread through the brain. This process of a 'prion-like' spreading between cells is also relevant as a novel putative therapeutic target that could block the spreading of proteinaceous aggregates throughout the brain which may underlie the progressive nature of neurodegenerative diseases. The relevance of β-amyloid oligomers and cellular prion protein (PrP^C) binding has been a focus of interest in Alzheimer's disease (AD). At the molecular level, β-amyloid/PrP^C interaction takes place in two differently charged clusters of PrP^C. In addition to β-amyloid, participation of PrP^C in α-synuclein binding and brain spreading also appears to be relevant in α-synucleopathies. This review summarizes current knowledge about PrP^C as a putative receptor for amyloid proteins and the physiological consequences of these interactions.

Dominantly inherited prion protein cerebral amyloidoses - a modern view of Gerstmann-Sträussler-Scheinker

Among genetically determined neurodegenerative diseases, the dominantly inherited prion protein cerebral amyloidoses are characterized by deposition of amyloid in cerebral parenchyma or blood vessels. Among them, Gerstmann-Sträussler-Scheinker disease has been the first to be described. Their clinical, neuropathologic, and molecular phenotypes are distinct from those observed in Creutzfeldt-Jakob disease (CJD) and related spongiform encephalopathies. It is not understood why specific mutations in the prion protein gene (PRNP) cause cerebral amyloidosis and others cause CJD. A significant neurobiologic event in these amyloidoses is the frequent coexistence of prion amyloid with tau neurofibrillary pathology, a phenomenon suggesting that similar pathogenetic mechanisms may be shared among different diseases in the sequence of events occurring in the cascade from amyloid formation to tau aggregation. This chapter describes the clinical, neuropathologic, and biochemical phenotypes associated with each of the PRNP mutations causing an inherited cerebral amyloidosis and emphasizes the variability of phenotypes.

Sisyphus in Neverland

The study of life and living organisms and the way in which these interact and organize to form social communities have been central to my career. I have been fascinated by biology, neurology, and neuropathology, but also by history, sociology, and art. Certain current historical, political, and social events, some occurring proximally but others affecting people in apparently distant places, have had an impact on me. Epicurus, Seneca, and Camus shared their philosophical positions which I learned from. Many scientists from various disciplines have been exciting sources of knowledge as well. I have created a world of hypothesis and experiments but I have also got carried away by serendipity following unexpected observations. It has not been an easy path; errors and wanderings are not uncommon, and opponents close to home much more abundant than one might imagine. Ambition, imagination, resilience, and endurance have been useful in moving ahead in response to setbacks. In the end, I have enjoyed my dedication to science and I am grateful to have glimpsed beauty in it. These are brief memories of a Spanish neuropathologist born and raised in Barcelona, EU.

Different Complicated Brain Pathologies in Monozygotic Twins With Gerstmann-Sträussler-Scheinker Disease

Gerstmann-Sträussler-Scheinker disease (GSS) is an autosomal, dominantly inherited prion disease. In this study, we present different complicated brain pathologies determined postmortem of monozygotic GSS twin sisters. Case 1 showed cerebellar ataxia at the age of 58 years, and died at 66 years. Case 2 became symptomatic at the age of 75 years, and died at 79 years. There was a 17-year difference in the age of onset between the twins. Postmortem examination revealed numerous prion protein (PrP) plaques in the brains of both cases. The spongiform change and brain atrophy in case 1 were more severe compared with those in case 2. Western-blot analysis identified proteinase-resistant PrP (PrPres) at the molecular weight of 21-30 kDa and 8 kDa in the twins. Gel filtration revealed that PrPres was mainly composed of PrP oligomer. PrPres signal patterns were similar between the twins. Additionally, case 1 showed α-synucleinopathy and case 2 showed Alzheimer disease pathology. These different proteinopathies were involved in the amyloid plaque formations of both cases. The degree of GSS pathology was mainly related to disease duration. The amyloid plaque formations could be decorated by concomitant neuropathological changes such as α-synucleinopathy and tauopathy.

Generation of a new infectious recombinant prion: a model to understand Gerstmann-Sträussler-Scheinker syndrome

Human transmissible spongiform encephalopathies (TSEs) or prion diseases are a group of fatal neurodegenerative disorders that include Kuru, Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker syndrome (GSS), and fatal familial insomnia. GSS is a genetically determined TSE caused by a range of mutations within the prion protein (PrP) gene. Several animal models, based on the expression of PrPs carrying mutations analogous to human heritable prion diseases, support that mutations might predispose PrP to spontaneously misfold. An adapted Protein Misfolding Cyclic Amplification methodology based on the use of human recombinant PrP (recPMCA) generated different self-propagating misfolded proteins spontaneously. These were characterized biochemically and structurally, and the one partially sharing some of the GSS PrP^Sc molecular features was inoculated into different animal models showing high infectivity. This constitutes an infectious recombinant prion which could be an invaluable model for understanding GSS. Moreover, this study proves the possibility to generate recombinant versions of other human prion diseases that could provide a further understanding on the molecular features of these devastating disorders.

Genetic prion disease: Experience of a rapidly progressive dementia center in the United States and a review of the literature

Although prion diseases are generally thought to present as rapidly progressive dementias with survival of only a few months, the phenotypic spectrum for genetic prion diseases (gPrDs) is much broader. The majority have a rapid decline with short survival, but many patients with gPrDs present as slowly progressive ataxic or parkinsonian disorders with progression over a few to several years. A few very rare mutations even present as neuropsychiatric disorders, sometimes with systemic symptoms such as gastrointestinal disorders and neuropathy, progressing over years to decades. gPrDs are caused by mutations in the prion protein gene (PRNP), and have been historically classified based on their clinicopathological features as genetic Jakob-Creutzfeldt disease (gJCD), Gerstmann-Sträussler-Scheinker (GSS), or Fatal Familial Insomnia (FFI). Mutations in PRNP can be missense, nonsense, and octapeptide repeat insertions or a deletion, and present with diverse clinical features, sensitivities of ancillary testing, and neuropathological findings. We present the UCSF gPrD cohort, including 129 symptomatic patients referred to and/or seen at UCSF between 2001 and 2016, and compare the clinical features of the gPrDs from 22 mutations identified in our cohort with data from the literature, as well as perform a literature review on most other mutations not represented in our cohort. E200K is the most common mutation worldwide, is associated with gJCD, and was the most common in the UCSF cohort. Among the GSS-associated mutations, P102L is the most commonly reported and was also the most common at UCSF. We also had several octapeptide repeat insertions (OPRI), a rare nonsense mutation (Q160X), and three novel mutations (K194E, E200G, and A224V) in our UCSF cohort. © 2016 Wiley Periodicals, Inc.

Quantifying prion disease penetrance using large population control cohorts

More than 100,000 genetic variants are reported to cause Mendelian disease in humans, but the penetrance-the probability that a carrier of the purported disease-causing genotype will indeed develop the disease-is generally unknown. We assess the impact of variants in the prion protein gene (PRNP) on the risk of prion disease by analyzing 16,025 prion disease cases, 60,706 population control exomes, and 531,575 individuals genotyped by 23andMe Inc. We show that missense variants in PRNP previously reported to be pathogenic are at least 30 times more common in the population than expected on the basis of genetic prion disease prevalence. Although some of this excess can be attributed to benign variants falsely assigned as pathogenic, other variants have genuine effects on disease susceptibility but confer lifetime risks ranging from <0.1 to ~100%. We also show that truncating variants in PRNP have position-dependent effects, with true loss-of-function alleles found in healthy older individuals, a finding that supports the safety of therapeutic suppression of prion protein expression.

Hereditary Human Prion Diseases: an Update

Prion diseases in humans are neurodegenerative diseases which are caused by an accumulation of abnormal, misfolded cellular prion protein known as scrapie prion protein (PrP^Sc). Genetic, acquired, or spontaneous (sporadic) forms are known. Pathogenic mutations in the human prion protein gene (PRNP) have been identified in 10-15 % of CJD patients. These mutations may be single point mutations, STOP codon mutations, or insertions or deletions of octa-peptide repeats. Some non-coding mutations and new mutations in the PrP gene have been identified without clear evidence for their pathogenic significance. In the present review, we provide an updated overview of PRNP mutations, which have been documented in the literature until now, describe the change in the DNA, the family history, the pathogenicity, and the number of described cases, which has not been published in this complexity before. We also provide a description of each genetic prion disease type, present characteristic histopathological features, and the PrP^Sc isoform expression pattern of various familial/genetic prion diseases.

Different misfolding mechanisms converge on common conformational changes: human prion protein pathogenic mutants Y218N and E196K

Prion diseases are caused by misfolding and aggregation of the prion protein (PrP). Pathogenic mutations such as Y218N and E196K are known to cause Gerstmann-Sträussler-Scheinker syndrome and Creutzfeldt-Jakob disease, respectively. Here we describe molecular dynamics simulations of these mutant proteins to better characterize the detailed conformational effects of these sequence substitutions. Our results indicate that the mutations disrupt the wild-type native PrP(C) structure and cause misfolding. Y218N reduced hydrophobic packing around the X-loop (residues 165-171), and E196K abolished an important wild-type salt bridge. While differences in the mutation site led PrP mutants to misfold along different pathways, we observed multiple traits of misfolding that were common to both mutants. Common traits of misfolding included: 1) detachment of the short helix (HA) from the PrP core; 2) exposure of side chain F198; and 3) formation of a nonnative strand at the N-terminus. The effect of the E196K mutation directly abolished the wild-type salt bridge E196-R156, which further destabilized the F198 hydrophobic pocket and HA. The Y218N mutation propagated its effect by increasing the HB-HC interhelical angle, which in turn disrupted the packing around F198. Furthermore, a nonnative contact formed between E221 and S132 on the S1-HA loop, which offered a direct mechanism for disrupting the hydrophobic packing between the S1-HA loop and HC. While there were common misfolding features shared between Y218N and E196K, the differences in the orientation of HB and HC and the X-loop conformation might provide a structural basis for identifying different prion strains.

Role of PrP(C) Expression in Tau Protein Levels and Phosphorylation in Alzheimer's Disease Evolution

Alzheimer's disease (AD) is characterized by the presence of amyloid plaques mainly consisting of hydrophobic β-amyloid peptide (Aβ) aggregates and neurofibrillary tangles (NFTs) composed principally of hyperphosphorylated tau. Aβ oligomers have been described as the earliest effectors to negatively affect synaptic structure and plasticity in the affected brains, and cellular prion protein (PrP(C)) has been proposed as receptor for these oligomers. The most widely accepted theory holds that the toxic effects of Aβ are upstream of change in tau, a neuronal microtubule-associated protein that promotes the polymerization and stabilization of microtubules. However, tau is considered decisive for the progression of neurodegeneration, and, indeed, tau pathology correlates well with clinical symptoms such as dementia. Different pathways can lead to abnormal phosphorylation, and, as a consequence, tau aggregates into paired helical filaments (PHF) and later on into NFTs. Reported data suggest a regulatory tendency of PrP(C) expression in the development of AD, and a putative relationship between PrP(C) and tau processing is emerging. However, the role of tau/PrP(C) interaction in AD is poorly understood. In this study, we show increased susceptibility to Aβ-derived diffusible ligands (ADDLs) in neuronal primary cultures from PrP(C) knockout mice, compared to wild-type, which correlates with increased tau expression. Moreover, we found increased PrP(C) expression that paralleled with tau at early ages in an AD murine model and in early Braak stages of AD in affected individuals. Taken together, these results suggest a protective role for PrP(C) in AD by downregulating tau expression, and they point to this protein as being crucial in the molecular events that lead to neurodegeneration in AD.

A matter of life, death and diseases: mitochondria from a proteomic perspective

Mitochondria are highly ordered, integrated organelles that energize cellular activities and contribute to programmed death by initiating disciplined apoptotic cascades. This review seeks to clarify our understanding of mitochondrial structural-functional integrity beyond the resolved nuclear genome by unraveling the dynamic mitochondrial proteome and elucidating proteome/genome interplay. The roles of mechanochemical coupling between mitoskeleton and cytoskeleton and crosstalk with other organelles in orchestrating cellular outcomes are explained. The authors also review the modulation of mitochondrial-related oxidative stress on apoptosis and cancer development and the context is applied to interpret pathogenetic events in neurodegenerative disorders and cardiovascular diseases. The accumulated proteomics evidence is used to describe the integral role that mitochondria play and how they influence other intracellular organelles. Possible mitochondrial-targeted therapeutic interventions are also discussed.

Interaction between misfolded PrP and the ubiquitin-proteasome system in prion-mediated neurodegeneration

Prion diseases are associated with the conformational conversion of cellular prion protein (PrP(C)) to pathological β-sheet isoforms (PrP(Sc)), which is the infectious agent beyond comprehension. Increasing evidence indicated that an unknown toxic gain of function of PrP(sc) underlies neuronal death. Conversely, strong evidence indicated that cellular prion protein might be directly cytotoxic by mediating neurotoxic signaling of β-sheet-rich conformers independent of prion replication. Furthermore, the common properties of β-sheet-rich isoform such as PrP(Sc) and β amyloid protein become the lynchpin that interprets the general pathological mechanism of protein misfolding diseases. Dysfunction of the ubiquitin-proteasome system (UPS) has been implicated in various protein misfolding diseases. However, the mechanisms of this impairment remain unknown in many cases. In prion disease, prion-infected mouse brains have increased levels of ubiquitin conjugates, which correlate with decreased proteasome function. Both PrP(C) and PrP(Sc) accumulate in cells after proteasome inhibition, which leads to increased cell death. A direct interaction between 20S core particle and PrP isoforms was demonstrated. Here we review the ability of misfolded PrP and UPS to affect each other, which might contribute to the pathological features of prion-mediated neurodegeneration.

Prion disease: a tale of folds and strains

Research on prions, the infectious agents of devastating neurological diseases in humans and animals, has been in the forefront of developing the concept of protein aggregation diseases. Prion diseases are distinguished from other neurodegenerative diseases by three peculiarities. First, prion diseases, in addition to being sporadic or genetic like all other neurodegenerative diseases, are infectious diseases. Animal models were developed early on (a long time before the advent of transgenic technology), and this has made possible the discovery of the prion protein as the infectious agent. Second, human prion diseases have true equivalents in animals, such as scrapie, which has been the subject of experimental research for many years. Variant Creutzfeldt-Jakob disease (vCJD) is a zoonosis caused by bovine spongiform encephalopathy (BSE) prions. Third, they show a wide variety of phenotypes in humans and animals, much wider than the variants of any other sporadic or genetic neurodegenerative disease. It has now become firmly established that particular PrP(Sc) isoforms are closely related to specific human prion strains. The variety of human prion diseases, still an enigma in its own right, is a focus of this article. Recently, a series of experiments has shown that the concept of aberrant protein folding and templating, first developed for prions, may apply to a variety of neurodegenerative diseases. In the wake of these discoveries, the term prion has come to be used for Aβ, α-synuclein, tau and possibly others. The self-propagation of alternative conformations seems to be the common denominator of these "prions," which in future, in order to avoid confusion, may have to be specified either as "neurodegenerative prions" or "infectious prions."

Divergent clinical and neuropathological phenotype in a Gerstmann-Sträussler-Scheinker P102L family

OBJECTIVES

Gerstmann-Sträussler-Scheinker syndrome belongs to the genetic prion diseases being associated with mutations in the prion protein gene (PRNP). The most common is the point mutation at codon 102, leading to the substitution of proline to leucine (P102L). Previous reports have indicated a phenotypic heterogeneity among individuals with this mutation. Here, we describe the clinical and pathological phenotype in members of the first Finnish kindred with the P102L mutation in the PNRP gene.

MATERIALS AND METHODS

Genetic and clinical information was available in five members of a family, while a systematic histologic and immunohistochemical assessment of the post-mortem brain was carried out in three.

RESULTS

Clinical presentation, disease duration and the clinical phenotype (ataxia vs dementia) varied between patients. There was a significant correlation between clinical symptoms and the neuroanatomical distribution of prion protein-immunoreactive aggregates, i.e. subtentorial predominance in ataxia vs cortical predominance in dementia. A significant concomitant Alzheimer is disease-related pathology was observed in the brain of one patient with dementia as onset symptom.

CONCLUSIONS

This is the first Scandinavian family carrying the P102L mutation in the PRNP gene. Gerstmann-Sträussler-Scheinker syndrome should be considered in the differential diagnosis when handling with patients with ataxia and/or dementia of unclear aetiology.

Squirrel monkeys (Saimiri sciureus) infected with the agent of bovine spongiform encephalopathy develop tau pathology

Squirrel monkeys (Saimiri sciureus) were infected experimentally with the agent of classical bovine spongiform encephalopathy (BSE). Two to four years later, six of the monkeys developed alterations in interactive behaviour and cognition and other neurological signs typical of transmissible spongiform encephalopathy (TSE). At necropsy examination, the brains from all of the monkeys showed pathological changes similar to those described in variant Creutzfeldt-Jakob disease (vCJD) of man, except that the squirrel monkey brains contained no PrP-amyloid plaques typical of that disease. Constant neuropathological features included spongiform degeneration, gliosis, deposition of abnormal prion protein (PrP(TSE)) and many deposits of abnormally phosphorylated tau protein (p-Tau) in several areas of the cerebrum and cerebellum. Western blots showed large amounts of proteinase K-resistant prion protein in the central nervous system. The striking absence of PrP plaques (prominent in brains of cynomolgus macaques [Macaca fascicularis] with experimentally-induced BSE and vCJD and in human patients with vCJD) reinforces the conclusion that the host plays a major role in determining the neuropathology of TSEs. Results of this study suggest that p-Tau, found in the brains of all BSE-infected monkeys, might play a role in the pathogenesis of TSEs. Whether p-Tau contributes to development of disease or appears as a secondary change late in the course of illness remains to be determined.

An overview of human prion diseases

Prion diseases are transmissible, progressive and invariably fatal neurodegenerative conditions associated with misfolding and aggregation of a host-encoded cellular prion protein, PrP^C. They have occurred in a wide range of mammalian species including human. Human prion diseases can arise sporadically, be hereditary or be acquired. Sporadic human prion diseases include Cruetzfeldt-Jacob disease (CJD), fatal insomnia and variably protease-sensitive prionopathy. Genetic or familial prion diseases are caused by autosomal dominantly inherited mutations in the gene encoding for PrP^C and include familial or genetic CJD, fatal familial insomnia and Gerstmann-Sträussler-Scheinker syndrome. Acquired human prion diseases account for only 5% of cases of human prion disease. They include kuru, iatrogenic CJD and a new variant form of CJD that was transmitted to humans from affected cattle via meat consumption especially brain. This review presents information on the epidemiology, etiology, clinical assessment, neuropathology and public health concerns of human prion diseases. The role of the PrP encoding gene (PRNP) in conferring susceptibility to human prion diseases is also discussed.

Frequency distribution of PRNP polymorphisms in the Pakistani population

Prion diseases are neurodegenerative conditions caused by misfolding of a normal host-encoded prion protein (PrPC) into pathogenic scrapie prion protein (PrPSc). In human prion diseases, the M129V prion protein polymorphism is known to confer susceptibility to the disease, determines PrPSc conformation and alters clinicopathological phenotypes. To date, all clinicopathologically confirmed cases of a variant form of Cruetzfeldt-Jacob disease (vCJD) have been 129MM homozygotes. There is also predominance of 129MM homozygotes in sporadic CJD (sCJD). No information regarding prion disorders is available from Pakistan. Although only invasive procedures like brain biopsy can confirm the diagnosis of prion disorders, testing a corresponding human population for variation in the prion protein gene (PRNP) may provide some insights into the presence of these disorders in a locality. The current study therefore aimed at exploring the genetic susceptibility of Pakistani population to CJD. A total of 909 unrelated individuals including 221 hemophiliacs representing all 4 major provinces of Pakistan were screened for M129V polymorphism and insertions or deletions of octapeptide repeats (OPRIs/OPRDs) using Polymerase Chain Reaction coupled with Restriction Fragment Length Polymorphism (PCR-RFLP). Concordance of the results of some PCR-RFLP reactions was also confirmed by dideoxy automated Sanger sequencing. The frequencies of M129V alleles (129M and 129V) and genotypes (129MM, 129MV and 129VV) were found in all 909 individuals to be 0.7101, 0.2899, 0.5270, 0.3663 and 0.1067, respectively. Deletion of 1 octapeptide repeat (1-OPRD) was detected in heterozygous state in PRNP of 10 individuals and in homozygous state in 1 individual. An insertion of 3 octapeptide repeats (3-OPRI) was found in 1 individual and an insertion of 1 octapeptide repeat (1-OPRI) in two individuals. Both 3-OPRI and 1-OPRI were present in heterozygous state and were linked to 129M allele. There were no significant χ2 differences between M129V allelic and genotypic frequencies of healthy individuals and hemophiliacs. However, M129V allelic and genotypic frequencies differed significantly between Pakistani population and East Asian and Western populations. Non-significant χ2 differences between M129V frequencies of healthy individuals and hemophiliacs suggest that individuals manifesting single gene disorders may provide naturally randomized samples for studies aiming at surveying the genetic variation. The combined excess of 129MM and 129VV homozygosity and the presence of 3-OPRI in 1 individual imply that Pakistani population is susceptible to prion disorders. Cases of prion disorders may exist in Pakistan, albeit at lower annual prevalence than other countries where life expectancy is greater than 65 years.

Gerstmann-Straüssler-Scheinker PRNP P102L-129V mutation

Neuropathological and biochemical studies in a case of Gerstmann-Straüssler-Scheinker disease bearing the PRNP P102L-129V mutation showed numerous multicentric PrPres in the cerebral cortex, striatum, thalamus and cerebellum, PrPres globular deposits in the anterior and posterior horns of the spinal cord, and multiple granular PrPres deposits in the grey and white matter of the encephalon and spinal cord. Western blots with antiPrPres antibodies revealed several weak bands ranging from 36 to 66 kDa, weak bands of 29 and 24 kDa, a strong band of about 20 kDa, a low band of molecular weight around 15 kDa and a weaker band of about 7 kDa. Spongiform degeneration was absent. Hyper-phosphorylated 3R and 4R tau occurred in dystrophic neurites surrounding PrPres plaques, neuropil threads and, to a lesser degree, in the form of neurofibrillary tangles. Gel electrophoresis of sarkosyl-insoluble fractions and western blotting with anti-phospho-tau antibodies showed a pattern similar to that seen in Alzheimer disease cases run in parallel. Dystrophic neurites in the vicinity of PrPres plaques were enriched in voltage dependent anion channel thus suggesting abnormal accumulation of mitochondria. These changes were associated with increased oxidative damage in neurons and astrocytes, Finally, increased expression of active stress kinases, that have the capacity to phosphorylate tau in vitro, p38 (p-38-P) and SAPK/ JNK (SAPK/JNK-P) was found in cell processes surrounding PrP plaques. Together, these observations provide evidences of mitochondrial abnormalities, and increased oxidative stress damage and oxidative stress responses in GSS bearing the PRNP P102L-129V mutation.