Peptide aptamer-mediated modulation of prion protein α-cleavage as treatment strategy for prion and other neurodegenerative diseases

正Despite intensive research,most neurodegenerative diseases cannot be cured and for some of them no treatment is available to increase survival or quality of life.Among the latter are prion diseases,fatal and transmissible neurodegenerative diseases of humans and other animals.Exam-     

Disease‐specific particles without prion protein in prion diseases – phenomenon or epiphenomenon?

The search for the cause of transmissible spongiform encephalopathies (TSEs) has a long and tortuous history. In a recent paper, 25-nm virus-like particles were identified that were consistently observed in cell cultures infected with Creutzfeldt-Jakob disease (CJD) and scrapie; they are similar to, or even identical with, the virus-like tubulovesicular structures (TVS) found in experimental scrapie as early as in 1968, and subsequently in all naturally occurring and experimentally induced TSEs. These particles have been viewed with caution by the scientific community because of the unverified or uninterpretable record of virus-like structures reported over the years in TSEs. TVS are spherical or tubular particles of approximate diameter 25-37 nm. They are smaller than synaptic vesicles, but larger than many particulate structures of the central nervous system, such as glycogen granules. Their electron density is higher compared with synaptic vesicles, and in experimental murine scrapie, they form paracrystalline arrays. None of these observations distinguish between TVS as an entity critical to the infectious process, or as a highly specific ultrastructural epiphenomenon, but their consistent presence in all TSEs demands further research.     

Cellular prion protein participates in amyloid-β transcytosis across the blood-brain barrier

The blood-brain barrier (BBB) facilitates amyloid-β (Aβ) exchange between the blood and the brain. Here, we found that the cellular prion protein (PrP(c)), a putative receptor implicated in mediating Aβ neurotoxicity in Alzheimer's disease (AD), participates in Aβ transcytosis across the BBB. Using an in vitro BBB model, [(125)I]-Aβ(1-40) transcytosis was reduced by genetic knockout of PrP(c) or after addition of a competing PrP(c)-specific antibody. Furthermore, we provide evidence that PrP(c) is expressed in endothelial cells and, that monomeric Aβ(1-40) binds to PrP(c). These observations provide new mechanistic insights into the role of PrP(c) in AD.     

Colocalization of prion protein and β protein in the same amyloid plaques in patients with Gerstmann-Sträussler Syndrome

Summary We examined paraffin-embedded brain sections from three patients with Creutzfeldt-Jakob disease (CJD) and four patients with Gerstmann-Sträussler syndrome (GSS) who also had protein deposits in the brains. Immunostaining using anti-prion protein (PrP) and anti- protein coupled with formic acid pretreatment, revealed PrP deposits and protein deposits, respectively. In all four GSS patients examined, sequential double immunostaining and single immunostaining in serial sections or simultaneous double immunofluorescence revealed the colocalization of PrP and protein in the same amyloid plaques. The plaques labeled with both antibodies were designated as -PrP plaques. Small kuru plaques of less than 15 m in diameter were rarely found to coexist with deposits. The percentages of -PrP plaques in larger kuru plaques were not constant among the four GSS patients. The colocalization patterns of both deposits were observed as being roughly of two types as follows: (1) diffuse protein deposits located around the PrP core; and (2) a protein core and PrP core simultaneously existing in one amyloid plaque. Under an electron microscope, we were able to confirm the presence of both protein and PrP in a single plaque in four GSS patients older than 60 years old. In contrast, no colocalization of either deposits was seen in the amyloid plaque core fractions of a young GSS patient who had no protein deposits, even at the electron microscopic level. Therefore, the colocalization of both proteins in a single plaque is believed to be age-related and incidental in GSS patients but suggests a similar morphogenesis of both amyloid deposits.Supported in part by a Grant-in-Aid for Scientific Research (02454245, 03454171) from the Ministry of Education, Science and Culture of Japan     

Analysis of the polymorphic prion protein gene codon 129 in idiopathic Parkinson’s disease

Summary. Idiopathic Parkinson’s disease (IPD) is a neurodegenerative disorder of unknown aetiology. Histopathological similarities between IPD and Creutzfeldt-Jakob prion disease (CJD) have been suggested. Homozygosity at polymorphic prion protein gene codon 129 (PRNP129) is a risk factor for developing CJD. Therefore we investigated a putative genetic link between CJD and IPD by studying PRNP129 genotype segregation in 81 patients with IPD. We did not ascertain a different PRNP129 genotype distribution in IPD patients compared to healthy Germans. We found a significant difference in PRNP129 genotype in dependence of the clinical predominance type of IPD. Patients with tremor-dominant IPD presented less frequent a methionine homozygosis at PRNP129 than hypokinetic-rigid IPD patients (30% versus 62.5%; p < 0.033). In conclusion, genotype distribution at codon 129 is obviously not essential in determining IPD. But our results may provide first evidence of an association between certain PRNP129 polymorphisms and the clinical presentation of IPD. Both authors contributed equally to this work Present addresses: Institute of Reconstructive Neurobiology, Hertie Foundation, University of Bonn, Sigmund-Freud-Strasse 25, 53105 Bonn, Germany; Schering AG, Clinical Development CNS, Sellerstrasse 31, 13342 Berlin, Germany     

Mutant prion protein D202N associated with familial prion disease is retained in the endoplasmic reticulum and forms ‘curly’ intracellular aggregates

Transmissible Spongiform Encephalopathies are fatal neurodegenerative disorders of humans and animals that are familial, sporadic, and infectious in nature. Familial disorders of humans include Gerstmann–Straussler–Scheinker disease (GSS), familial Creutzfeldt–Jakob disease (CJD), and fatal familial insomnia, and result from point mutations in the prion protein gene. Although neurotoxicity in familial cases is believed to result from a spontaneous change in conformation of mutant prion protein (PrP) to the pathogenic PrP-scrapie (PrP^Sc) form, emerging evidence indicates otherwise. We have investigated the processing and metabolism of mutant PrP D202N (PrP^202N) in cell models to elucidate possible mechanisms of cytotoxicity. In this report, we demonstrate that PrP^202N expressed in human neuroblastoma cells fails to achieve a mature conformation following synthesis and accumulates in the endoplasmic reticulum as ‘curly’ aggregates. In addition, PrP^202N cells show increased sensitivity to free radicals, indicating that neuronal susceptibility to oxidative damage may account for the neurotoxicity observed in cases of GSS resulting from PrP D202N mutation. Yaping Gu and Susamma Verghese contributed equally.     

Saccharomyces cerevisiae in neuroscience:how unicellular organism helps to better understand prion protein?

The baker's yeast Saccharomyces(S.)cerevisiae is a single-celled eukaryotic model organism widely used in research on life sciences.Being a unicellular organism,S.cerevisiae has some evident limitations in application to neuroscience.However,yeast prions are extensively studied and they are known to share some hallmarks with mammalian prion protein or other amyloidogenic proteins found in the pathogenesis of Alzheimer's,Parkinson's,or Huntington's diseases.Therefore,the yeast S.cerevisiae has been widely used for basic research on aggregation properties of proteins in cellulo and on their propagation.Recently,a yeast-based study revealed that some regions of mammalian prion protein and amyloidβ1–42 are capable of induction and propagation of yeast prions.It is one of the examples showing that evolutionarily distant organisms share common mechanisms underlying the structural conversion of prion proteins making yeast cells a useful system for studying mammalian prion protein.S.cerevisiae has also been used to design novel screening systems for anti-prion compounds from chemical libraries.Yeastbased assays are cheap in maintenance and safe for the researcher,making them a very good choice to perform preliminary screening before further characterization in systems engaging mammalian cells infected with prions.In this review,not only classical red/white colony assay but also yeast-based screening assays developed during last year are discussed.Computational analysis and research carried out using yeast prions force us to expect that prions are widely present in nature.Indeed,the last few years brought us several examples indicating that the mammalian prion protein is no more peculiar protein–it seems that a better understanding of prion proteins nature-wide may aid us with the treatment of prion diseases and other amyloid-related medical conditions.     

Microglia is a component of the prion protein amyloid plaque in the Gerstmann-Sträussler-Scheinker syndrome

Summary The microglial cell has been demonstrated as component of the cerebral amyloid plaque of Alzheimer's disease. Involvement of microglia in plaques of another cerebral amyloidosis, the Gerstmann-Sträussler-Scheinker syndrome (GSS), has found little attention. We examine here the presence of microglia in GSS plaques by immunohistochemistry and transmission electron microscopy. Paraffin sections from five brains of patients with GSS were immunolabelled with antibodies against prion protein, A4/ amyloid protein, ferritin, leukocyte common antigen, HLA-DR, CD 68, and the MAC387 epitope for microglia and monocytes/macrophages; microglia was also labelled with the Ricinus communis agglutinin-1 lectin. Such (immuno)labelling demonstrated many delicate cell processes and occasional somata within and around prion protein plaques in all GSS brains. Microglial immunoreactivity was strongest with anti-ferritin and variable with anti-macrophage antibodies. Ultrastructural examination of brain tissue from one autopsy and one biopsy of GSS identified microglial cells in close proximity of amyloid plaque fibrils. Our observations demonstrate microglia as an important component of the amyloid plaque in GSS and suggest a major role for microglia in processing and deposition, or at least organization, of prion protein amyloid. Thus, plaques in both transmissible and nontransmissible cerebral amyloidoses seem to develop via similar pathogenetic mechanisms, irrespective of differences in etiology and molecular composition of the amyloid.Supported in part by the Austrian Fund for the Advancement of Scientific Research (P8196-MED). This study is part of the EC BIOMED I Project The human prion diseases led by H. Budka     

Is there a role for cellular prion protein in intrathymic T cell differentiation and migration?

The cellular prion protein (PrP(C)) is expressed in the nervous and immune systems. Functionally, PrP(C) has been suggested to participate in neuron survival, neuritogenesis and T lymphocyte activation. Moreover, PrP(C) interaction with laminin influences neuronal adhesion and neurite extension. Nevertheless, so far the physiological role of PrP(C) has not been completely elucidated, particularly in the immune system. The aim of the study was to evaluate the possible participation of PrP(C) in intrathymic T cell development. We evaluated T cell differentiation markers in thymocytes and peripheral lymphocytes, as well as thymocyte death in PrP(C)-null or PrP(C)-overexpressing (Tga20) mice, compared to wild-type controls. In these same animals, we ascertained laminin-driven thymocyte migration. Compared to controls, only marginal differences were found in PrP(C)-null animals. However, Tga20 mice exhibited a severe thymic hypoplasia, with 10-20% lymphocytes compared to wild-type counterparts. In particular, the frequency of CD4+CD8+ cells was largely reduced, and this was accompanied by a dramatic increase in the frequency of CD4-CD8- thymocytes, which could be as high as 60-65% of the whole-cell suspensions. Moreover, Tga20 mice exhibited an increase in thymocyte death, comprising the CD4+CD8+, as well as CD4+ and CD8+ single-positive cells. Additionally, laminin-driven migration was largely impaired in Tga20 mice, in which we also found a significant decrease in total T lymphocytes in the spleen and lymph nodes. Our results show that PrP(C) overexpression alters intrathymic T cell development, a defect that likely has a negative impact in the formation of the T cell peripheral pool.     

The epsilon isoform of 14-3-3 protein is a component of the prion protein amyloid deposits of Gerstmann-Sträussler-Scheinker disease

The 14-3-3 proteins are highly conserved, ubiquitous molecules involved in a variety of biologic events, such as transduction pathway modulation, cell cycle control, and apoptosis. Seven isoforms have been identified that are abundant in the brain, preferentially localized in neurons. Remarkable increases in 14-3-3 are seen in the cerebrospinal fluid of patients with Creutzfeldt-Jakob disease (CJD), and it has been found in pathologic inclusions of several neurodegenerative diseases. Moreover, the zeta isoform has been detected in prion protein (PrP) amyloid deposits of CJD patients. To further investigate the cerebral distribution of 14-3-3 in prion-related encephalopathies, we carried out an immunohistochemical and biochemical analysis of brain tissue from patients with Gerstmann-Str?ussler-Scheinker disease (GSS) and sporadic, familial and acquired forms of CJD, using specific antibodies against the seven 14-3-3 isoforms. The study showed a strong immunoreactivity of PrP amyloid plaques of GSS patients for the 14-3-3 epsilon isoform, but not for the other isoforms. The epsilon isoform of 14-3-3 was not found in PrP deposits of CJD. These results indicate that the epsilon isoform of 14-3-3 is a component of PrP amyloid deposits of GSS and suggest that this is the sole 14-3-3 isoform specifically involved in the neuropathologic changes associated with this disorder.     

Aβ inhibition of ionic conductance in mouse basal forebrain neurons is dependent upon the cellular prion protein PrPC

Current therapies for Alzheimer's disease (AD) address a loss of cholinergic neurons, while accumulation of neurotoxic amyloid β (Aβ) peptide assemblies is thought central to molecular pathogenesis. Overlaps may exist between prionopathies and AD wherein Aβ oligomers bind to the cellular prion protein PrP(C) and inhibit synaptic plasticity in the hippocampus (Laurén et al., 2009). Here we applied oligomeric Aβ to neurons with different PrP (Prnp) gene dosage. Whole-cell recordings were obtained from dissociated neurons of the diagonal band of Broca (DBB), a cholinergic basal forebrain nucleus. In wild-type (wt) mice, Aβ???? evoked a concentration-dependent reduction of whole-cell outward currents in a voltage range between -30 and +30 mV; reduction occurred through a combined modulation of a suite of potassium conductances including the delayed rectifier (I(K)), the transient outward (I(A)), and the iberiotoxin-sensitive (calcium-activated potassium, I(C)) currents. Inhibition was not seen with Aβ???? peptide, while Aβ????-induced responses were reduced by application of anti-PrP antibody, attenuated in cells from Prnp?/? hemizygotes, and absent in Prnp?/? homozygotes. Similarly, amyloidogenic amylin peptide depressed DBB whole-cell currents in DBB cells from wt mice, but not Prnp?/? homozygotes. While prior studies give broad support for a neuroprotective function for PrP(C), our data define a latent pro-pathogenic role in the presence of amyloid assemblies.     

Novel prion protein gene mutation at codon 196 (E196A) in a septuagenarian with Creutzfeldt–Jakob disease

Creutzfeldt–Jakob disease (CJD) is a rare and rapidly progressive neurodegenerative disease of the central nervous system, which may occur in inherited, acquired (variant and iatrogenic), or spontaneous (sporadic) forms. We report a 76-year-old Chinese man with CJD found to have a novel mutation in the prion protein gene (PRNP). The 14-3-3 protein was positive in the cerebrospinal fluid; diffusion-weighted MRI revealed ribbon-like high signal intensity in the bilateral cortices; and electroencephalography showed typical periodic synchronous discharge. CJD was diagnosed based on characteristic clinical manifestations. Interestingly, a point mutation of PRNP at codon 196 (E196A: GAG → GCG) was detected. In conclusion, we identified a patient with CJD with a novel PRNP mutation, which expands the spectrum of PRNP mutations in CJD.     

Cerebral amyloid angiopathy with co-localization of prion protein and beta-amyloid in an 85-year-old patient with sporadic Creutzfeldt–Jakob disease

We report on an 85-year-old woman with hypertensive cerebral arteriolosclerosis who presented with rapidly progressive encephalopathy leading to death within 4 months. Magnetic resonance imaging showed mild cortical atrophy consistent with her age and diffuse leukoaraiosis. Her CSF 14–3–3 protein was positive. Neuropathology showed severe spongiform change and gliosis in the grey matter and immunohistochemistry revealed diffuse prion protein deposition in a predominant synaptic pattern. She had no family history of neurological disorder and genotyping did not show any prion protein gene mutation, in keeping with a diagnosis of sporadic Creutzfeldt–Jakob disease. There was also diffuse amyloid angiopathy involving the cortical and leptomeningeal arterioles of the cerebral hemispheres and cerebellum and the capillaries of the grey matter. The amyloid angiopathy expressed beta-amyloid but also prion protein and double immunostaining confirmed co-localization of both proteins in many vessel walls. Alzheimer’s type pathology was restricted to a few diffuse beta-amyloid plaques in the entorhinal cortex and rare tangles in the hippocampus. Deposition of prion protein in cerebral vessels has been reported in a single case of stop codon 145 mutation of the PRNP gene. Co-localization of beta-amyloid and prion protein in the same amyloid plaque has been described in elderly patients with Creutzfeldt–Jakob or Gerstmann–Sträussler–Scheinker diseases but only exceptionally in cerebral amyloid angiopathy. In this patient, hypertensive cerebrovascular disease may have contributed to the failure to eliminate both proteins from the brain.     

Spongiform encephalopathy in transgenic mice expressing a point mutation in the β2-α2 loop of the prion protein

Transmissible spongiform encephalopathies are fatal neurodegenerative diseases attributed to misfolding of the cellular prion protein, PrP(C), into a β-sheet-rich, aggregated isoform, PrP(Sc). We previously found that expression of mouse PrP with the two amino acid substitutions S170N and N174T, which result in high structural order of the β2-α2 loop in the NMR structure at pH 4.5 and 20°C, caused transmissible de novo prion disease in transgenic mice. Here we report that expression of mouse PrP with the single-residue substitution D167S, which also results in a structurally well ordered β2-α2 loop at 20°C, elicits spontaneous PrP aggregation in vivo. Transgenic mice expressing PrP(D167S) developed a progressive encephalopathy characterized by abundant PrP plaque formation, spongiform change, and gliosis. These results add to the evidence that the β2-α2 loop has an important role in intermolecular interactions, including that it may be a key determinant of prion protein aggregation.     

Hyperphosphorylated tau deposition parallels prion protein burden in a case of Gerstmann-Sträussler-Scheinker syndrome P102L mutation complicated with dementia

Hyperphosphorylated tau (p-tau) deposition has been documented in a limited population of patients with Gerstmann-Str?ussler-Scheinker syndrome (GSS) with particular point mutations of the prion protein (PrP) gene. Although its pathogenesis is only poorly understood, p-tau in GSS is known to be identical to that in Alzheimer's disease (AD). We conducted immunohistochemical and quantitative image studies on the brain from a 44-year-old man with a 7-year history of dementia, diagnosed as having GSS with a point mutation of the PrP gene at codon 102 (GSS102), the commonest mutation in GSS. Severe spongiform degeneration and numerous PrP plaques were disclosed in the cerebral cortices and hippocampus, consistent with the diagnosis. However, rarely described in GSS102, prominent p-tau deposits as pretangles, neurofibrillary tangles and degenerating neurites were demonstrated adjacent to or around PrP plaques. beta-Amyloid protein (Abeta) plaques were generally sparse and appeared invariably to be of a diffuse type. Double-labeling immunohistochemistry yielded co-localization of p-tau with PrP but not with Abeta. Most PrP plaques did not contain Abeta. These results excluded a diagnosis of concomitant AD. Quantitative analysis on a fractional area density of immunoreactive pixels demonstrated that burdens of PrP and p-tau but not Abeta were significantly correlated. These results suggest that p-tau deposition in this GSS102 is secondarily induced by PrP but not by Abeta (secondary tauopathy). Our study also suggests that p-tau deposition might be a more common phenomenon in long-standing GSS.     

Neuropathological features of a case with schizophrenia and prion protein gene P102L mutation before onset of Gerstmann-Sträussler-Scheinker disease

Gerstmann-Sträussler-Scheinker disease (GSS) is a hereditary transmissible spongiform encephalopathy associated with prion protein gene mutation P102L. The age of onset is roughly restricted to around the sixth decade; however, it is unclear whether the disease-specific pathology of GSS is already evident in the pre-clinical stage. We had a chance to examine an autopsy case with PRNP P102L mutation. The patient had died at 50 years of age before the clinical symptoms of GSS had appeared; neither neuronal loss, gliosis nor spongiform change was found anywhere in the brain. Immunohistochemistry failed to detect any deposition of prion protein. It is thus considered that amyloid plaque formation in GSS probably develops in a relatively rapid fashion compared with Alzheimer's disease. Although the patient suffered from schizophrenia, no significant pathological changes were detected except for astrocytic inclusion bodies in the cerebral cortex. The nature and significance of the inclusion bodies, which are not observed in patients with GSS, remain unclear.     

散发性Creutzfeldt-Jakob病患者10例prion基因研究

目的 检测10例Creutzfeldt-Jakob病（CJD）患者prion基因（PRNP）外显子突变情况.方法 抽取患者外周静脉血,提取DNA,PCR法扩增PRNP外显子后直接测序,并用限制性内切酶Nsp Ⅰ检测PRNP 129位点密码子基因型.结果 2例肯定CJD患者中,1例PRNP检测未见异常,另1例PRNP第729碱基G被C取代（729G→C）,使编码prion第211个氨基酸的密码子GAG变成了GAC,翻译后第211个氨基酸由谷氨酸变为天冬氨酸（E211D）.8例很可能CJD患者中,2例PRNP第751碱基G被A取代（751G→A）,使编码prion第219个氨基酸的密码子GAG变成了AAG,翻译后第219个氨基酸由谷氨酸变为赖氨酸（E219K）.10例CJD患者PRNP 129位点密码子基因型都是甲硫氨酸纯合型.结论 1例肯定CJD患者的prion基因外显子存在一种新的点突变E211D,这很可能是导致遗传prion病发生的原因.2例很可能CJD患者的prion基因突变E219K,与M129V同属于基因多态性,而不是致病原因.prion基因检测有助于prion病的诊断.