Prions: health scare and biological challenge

α-synuclein as an emerging pathophysiological biomarker of Alzheimer's disease

INTRODUCTION

α-syn aggregates represent the pathological hallmark of synucleinopathies as well as a frequent copathology (almost 1/3 of cases) in AD. Recent research indicates a potential role of α-syn species, measured in CSF with conventional analytical techniques, in the differential diagnosis between AD and synucleinopathies (such as DLB). Pioneering studies report the detection of α-syn in blood, however, conclusive investigations are controversial. Ultrasensitive seed amplification techniques, enabling the selective quantification of α-syn seeds, may represent an effective solution to identify the α-syn component in AD and facilitate a biomarker-guided stratification.

AREAS COVERED

We performed a PubMed-based review of the latest findings on α-syn-related biomarkers for AD, focusing on bodily fluids. A dissertation on the role of ultrasensitive seed amplification assays, detecting α-syn seeds from different biological samples, was conducted.

EXPERT OPINION

α-syn may contribute to progressive AD neurodegeneration through cross-seeding especially with tau protein. Ultrasensitive seed amplification techniques may support a biomarker-drug co-development pathway and may be a pathophysiological candidate biomarker for the evolving ATX(N) system to classify AD and the spectrum of primary NDDs. This would contribute to a precise approach to AD, aimed at implementing disease-modifying treatments.

Structural and Functional Insights into α-Synuclein Fibril Polymorphism

Abnormal accumulation of aggregated α-synuclein (α-Syn) is seen in a variety of neurodegenerative diseases, including Parkinson's disease (PD), multiple system atrophy (MSA), dementia with Lewy body (DLB), Parkinson's disease dementia (PDD), and even subsets of Alzheimer's disease (AD) showing Lewy-body-like pathology. These synucleinopathies exhibit differences in their clinical and pathological representations, reminiscent of prion disorders. Emerging evidence suggests that α-Syn self-assembles and polymerizes into conformationally diverse polymorphs in vitro and in vivo, similar to prions. These α-Syn polymorphs arising from the same precursor protein may exhibit strain-specific biochemical properties and the ability to induce distinct pathological phenotypes upon their inoculation in animal models. In this review, we discuss clinical and pathological variability in synucleinopathies and several aspects of α-Syn fibril polymorphism, including the existence of high-resolution molecular structures and brain-derived strains. The current review sheds light on the recent advances in delineating the structure-pathogenic relationship of α-Syn and how diverse α-Syn molecular polymorphs contribute to the existing clinical heterogeneity in synucleinopathies.

Pathogenesis, detection, and control of scrapie in sheep

In sheep, scrapie is a fatal neurologic disease that is caused by a misfolded protein called a prion (designated PrP^Sc). The normal cellular prion protein (PrP^C) is encoded by an endogenous gene, PRNP, that is present in high concentrations within the CNS. Although a broad range of functions has been described for PrP^C, its entire range of functions has yet to be fully elucidated. Accumulation of PrP^Sc results in neurodegeneration. The PRNP gene has several naturally occurring polymorphisms, and there is a strong correlation between scrapie susceptibility and PRNP genotype. The cornerstone of scrapie eradication programs is the selection of scrapie-resistant genotypes to eliminate classical scrapie. Transmission of classical scrapie in sheep occurs during the prenatal and periparturient periods when lambs are highly susceptible. Initially, the scrapie agent is disseminated throughout the lymphoid system and into the CNS. Shedding of the scrapie agent occurs before the onset of clinical signs. In contrast to classical scrapie, atypical scrapie is believed to be a spontaneous disease that occurs in isolated instances in older animals within a flock. The agent that causes atypical scrapie is not considered to be naturally transmissible. Transmission of the scrapie agent to species other than sheep, including deer, has been experimentally demonstrated as has the transmission of nonscrapie prion agents to sheep. The purpose of this review is to outline the current methods for diagnosing scrapie in sheep and the techniques used for studying the pathogenesis and host range of the scrapie agent. Also discussed is the US scrapie eradication program including recent updates.

Cardiomyopathy associated with Ceutzfeld-Jakob disease: a diagnosis of exclusion: a case report

Background

Creutzfeldt–Jakob disease (CJD), the most common prion disease in humans, is primarily known for its adverse neurological impact and inevitable mortality. Data regarding myocardial involvement in CJD are scarce.

Case summary

A 54-year-old female patient, presented with progressive effort dyspnoea, was diagnosed with unexplained non-ischaemic cardiomyopathy. An extensive cardiac work-up including cardiac magnetic resonance imaging (MRI) did not reveal any underlying aetiology. Simultaneously, the patient developed involuntary limb movements and progressive cognitive decline. Thalamic high-signal abnormalities on diffusion-weighted images were apparent on brain MRI. Based on these findings, she was subsequently referred to a neurology department, where she suddenly died the day after her admission. Brain autopsy demonstrated spongiform encephalopathy. A genetic analysis performed to her son revealed a mutation in the PRNP gene; all of these were consistent with CJD.

Discussion

This case describes the clinical association of CJD and cardiomyopathy and the diagnosis prion-induced cardiomyopathy by exclusion. It is not inconceivable that the coexistence of these two clinical entities may be related to genetic expression and contemporaneously deposition of infectious prions in myocardial muscle and brain tissue. Awareness of this possible association could be of important public-safety concern, and merits further collaborative cardiac-neurological work-up to elucidate this phenotype among patients with unexplained cardiomyopathy with neurological symptoms that resemble CJD.

α-Synuclein misfolding and aggregation: Implications in Parkinson's disease pathogenesis

α-Synuclein (α-Syn) has been extensively studied for its structural and biophysical properties owing to its pathophysiological role in Parkinson's disease (PD). Lewy bodies and Lewy neurites are the pathological hallmarks of PD and contain α-Syn aggregates as their major component. It was therefore hypothesized that α-Syn aggregation is actively associated with PD pathogenesis. The central role of α-Syn aggregation in PD is further supported by the identification of point mutations in α-Syn protein associated with rare familial forms of PD. However, the correlation between aggregation propensities of α-Syn mutants and their association with PD phenotype is not straightforward. Recent evidence suggested that oligomers, formed during the initial stages of aggregation, are the potent neurotoxic species causing cell death in PD. However, the heterogeneous and unstable nature of these oligomers limit their detailed characterization. α-Syn fibrils, on the contrary, are shown to be the infectious agents and propagate in a prion-like manner. Although α-Syn is an intrinsically disordered protein, it exhibits remarkable conformational plasticity by adopting a range of structural conformations under different environmental conditions. In this review, we focus on the structural and functional aspects of α-Syn and role of potential factors that may contribute to the underlying mechanism of synucleinopathies. This information will help to identify novel targets and develop specific therapeutic strategies to combat Parkinson's and other protein aggregation related neurodegenerative diseases.

Review: PrP 106-126 - 25 years after

A quarter of a century ago, we proposed an innovative approach to study the pathogenesis of prion disease, one of the most intriguing biomedical problems that remains unresolved. The synthesis of a peptide homologous to residues 106-126 of the human prion protein (PrP106-126), a sequence present in the PrP amyloid protein of Gerstmann-Sträussler-Scheinker syndrome patients, provided a tractable tool for investigating the mechanisms of neurotoxicity. Together with several other discoveries at the beginning of the 1990s, PrP106-126 contributed to underpin the role of amyloid in the pathogenesis of protein-misfolding neurodegenerative disorders. Later, the role of oligomers on one hand and of prion-like spreading of pathology on the other further clarified mechanisms shared by different neurodegenerative conditions. Our original report on PrP106-126 neurotoxicity also highlighted a role for programmed cell death in CNS diseases. In this review, we analyse the prion research context in which PrP106-126 first appeared and the advances in our understanding of prion disease pathogenesis and therapeutic perspectives 25 years later.

Esterification of PQQ Enhances Blood-Brain Barrier Permeability and Inhibitory Activity against Amyloidogenic Protein Fibril Formation

Several neurodegenerative diseases have a common pathophysiology where selective damage to neurons results from the accumulation of amyloid oligomer proteins formed via fibrilization. Considering that the formation of amyloid oligomers leads to cytotoxicity, the development of chemical compounds that are able to effectively cross the blood-brain barrier (BBB) and inhibit this conversion to oligomers and/or fibrils is essential for neurodegenerative disease therapy. We previously reported that pyrroloquinoline quinone (PQQ) prevented aggregation and fibrillation of α-synuclein, amyloid β_1-42 (Aβ_1-42), and mouse prion protein. To develop a novel drug against neurodegenerative diseases based on PQQ, it is necessary to improve the insufficient BBB permeability of PQQ. Here, we show that an esterified compound of PQQ, PQQ-trimethylester (PQQ-TME), has twice the BBB permeability than PQQ in vitro. Moreover, PQQ-TME exhibited greater inhibitory activity against fibrillation of α-synuclein, Aβ_1-42, and prion protein. These results indicated that esterification of PQQ could be a useful approach in developing a novel PQQ-based amyloid inhibitor.

Bone regeneration with a collagen model polypeptides/α-tricalcium phosphate sponge in a canine tibia defect model

INTRODUCTION

We evaluated the effects of synthesized collagen model polypeptides consisting of a proline-hydroxyproline-glycine (poly(PHG)) sequence combined with porous alpha-tricalcium phosphate (α-TCP) particles on bone formation in a canine tibia defect model.

MATERIALS AND METHODS

The porous α-TCP particles were mixed with a poly(PHG) solution, and the obtained sponge was then cross-linked and characterized by x-ray diffraction and scanning electron microscopy. Tibia defects were analyzed in 12 healthy beagles using microcomputed tomography and histological evaluation.

RESULTS

At 2 and 4 weeks, the volume density of new bone was higher in the poly(PHG)/α-TCP group than in poly(PHG) alone group (P < 0.05); however, there was no difference at 8 weeks (P > 0.05). Histological evaluation at 4 weeks after implantation revealed that the poly(PHG) had degraded, and newly formed bone was present on the surface of the α-TCP particles. At 8 weeks, continuous cortical bone formation with a Haversian structure covered the top of the bone defects in both groups.

CONCLUSION

This study demonstrates that the composite created using porous α-TCP particles and poly(PHG) is sufficiently adaptable for treating bone defects.

The cell biology of prion-like spread of protein aggregates: mechanisms and implication in neurodegeneration

The misfolding and aggregation of specific proteins is a common hallmark of many neurodegenerative disorders, including highly prevalent illnesses such as Alzheimer's and Parkinson's diseases, as well as rarer disorders such as Huntington's and prion diseases. Among these, only prion diseases are ‘infectious’. By seeding misfolding of the PrPC (normal conformer prion protein) into PrPSc (abnormal disease-specific conformation of prion protein), prions spread from the periphery of the body to the central nervous system and can also be transmitted between individuals of the same or different species. However, recent exciting data suggest that the transmissibility of misfolded proteins within the brain is a property that goes way beyond the rare prion diseases. Evidence indicates that non-prion aggregates [tau, α-syn (α-synuclein), Aβ (amyloid-β) and Htt (huntingtin) aggregates] can also move between cells and seed the misfolding of their normal conformers. These findings have enormous implications. On the one hand they question the therapeutical use of transplants, and on the other they indicate that it may be possible to bring these diseases to an early arrest by preventing cell-to-cell transmission. To better understand the prion-like spread of these protein aggregates it is essential to identify the underlying cellular and molecular factors. In the present review we analyse and discuss the evidence supporting prion-like spreading of amyloidogenic proteins, especially focusing on the cellular and molecular mechanisms and their significance.

Biochemical aspects of dementias

Alzheimer's disease, frontotemporal dementia, dementia with Lewy bodies, and prion diseases are age-related neurodegenerative disorders associated with a progressive decline of cognitive brain functions. Due to the increase in prevalence rates, and the rising costs associated with clinical and social care, treatments designed to prevent or reverse these diseases are urgently needed. The most common major biochemical characteristic of these neurodegenerative diseases is the deposition of abnormal protein aggregates in brain. The decryption of the mechanisms of aggregation and associated neurotoxicity may reveal new therapeutic targets, which will enable treatment for these devastating conditions.

Construction and characterization of a tissue-engineered oral mucosa equivalent based on a chitosan-fish scale collagen composite

This study was designed to (1) assess the in vitro biocompatibility of a chitosan-collagen composite scaffold (C3) constructed by blending commercial chitosan and tilapia scale collagen with oral mucosa keratinocytes, (2) histologically and immunohistochemically characterize an ex vivo-produced oral mucosa equivalent constructed using the C3 (EVPOME-C), and (3) compare EVPOME-C with oral mucosa constructs utilizing AlloDerm® (EVPOME-A), BioMend® Extend™ (EVPOME-B), and native oral mucosa. C3 scaffold had a well-developed fibril network and a sufficiently small porosity to prevent keratinocytes from growing inside the scaffold after cell-seeding. The EVPOME oral mucosa constructs were fabricated in a chemically defined culture system. After culture at an air-liquid interface, EVPOME-C and EVPOME-B had multilayered epithelium with keratinization, while EVPOME-A had a more organized stratified epithelium. Ki-67 and p63 immunolabeled cells in the basal layer of all EVPOMEs suggested a regenerative ability. Compared with native oral mucosa, the keratin 15 and 10/13 expression patterns in all EVPOMEs showed a less-organized differentiation pattern. In contrast to the β1-integrin and laminin distribution in EVPOME-A and native oral mucosa, the subcellular deposition in EVPOME-C and EVPOME-B indicated that complete basement membrane formation failed. These findings demonstrated that C3 has a potential application for epithelial tissue engineering and provides a new potential therapeutic device for oral mucosa regenerative medicine.

Effects on bone regeneration when collagen model polypeptides are combined with various sizes of alpha-tricalcium phosphate particles

We evaluated the effects on bone formation of combining synthesized collagen model polypeptides consisting of a Pro-Hyp-Gly [poly(PHG)] sequence and alpha-tricalcium phosphate (α-TCP) particles with various median sizes (large: 580.8 μm; small: 136.2 μm; or large and small mixed: 499.3 μm) in a skull defect model in mini-pigs. Quantitative image analyses for the volume density (VD) of new bone revealed that the VD in each α-TCP group was significantly higher than that in the poly(PHG) control group, with the mixed group showing the highest VD among all the groups at 4 weeks after implantation. Histological assessments revealed that the small α-TCP particles were almost completely degraded at 8 weeks. At 12 weeks, all sizes of α-TCP particles were completely degraded and remodeling of the lamellar bone was observed. The present findings suggest that particle size may influence the success of bone formation in defects.

Molecular interaction of TPPP with PrP antagonized the CytoPrP-induced disruption of microtubule structures and cytotoxicity

Background

Tubulin polymerization promoting protein/p25 (TPPP/p25), known as a microtubule-associated protein (MAP), is a brain-specific unstructured protein with a physiological function of stabilizing cellular microtubular ultrastructures. Whether TPPP involves in the normal functions of PrP or the pathogenesis of prion disease remains unknown. Here, we proposed the data that TPPP formed molecular complex with PrP. We also investigated its influence on the aggregation of PrP and fibrillization of PrP106–126 in vitro, its antagonization against the disruption of microtubule structures and cytotoxicity of cytosolic PrP in cells, and its alternation in the brains of scrapie-infected experimental hamsters.

Methodology/Principal Findings

Using pull-down and immunoprecipitation assays, distinct molecular interaction between TPPP and PrP were identified and the segment of TPPP spanning residues 100–219 and the segment of PrP spanning residues 106–126 were mapped as the regions responsible for protein interaction. Sedimentation experiments found that TPPP increased the aggregation of full-length recombinant PrP (PrP23–231) in vitro. Transmission electron microscopy and Thioflavin T (ThT) assays showed that TPPP enhanced fibril formation of synthetic peptide PrP106–126 in vitro. Expression of TPPP in the cultured cells did not obviously change the microtubule networks observed by a tubulin-specific immunofluorescent assay and cell growth features measured by CCK8 tests, but significantly antagonized the disruption of microtubule structures and rescued the cytotoxicity caused by the accumulation of cytosolic PrP (CytoPrP). Furthermore, Western blots identified that the levels of the endogenous TPPP in the brains of scrapie-infected experimental hamsters were significantly reduced.

Conclusion/Significance

Those data highlight TPPP may work as a protective factor for cells against the damage effects of the accumulation of abnormal forms of PrPs, besides its function as an agent for dynamic stabilization of microtubular ultrastructures.

Lack of a-disintegrin-and-metalloproteinase ADAM10 leads to intracellular accumulation and loss of shedding of the cellular prion protein in vivo

Background

The cellular prion protein (PrP^C) fulfils several yet not completely understood physiological functions. Apart from these functions, it has the ability to misfold into a pathogenic scrapie form (PrP^Sc) leading to fatal transmissible spongiform encephalopathies. Proteolytic processing of PrP^C generates N- and C-terminal fragments which play crucial roles both in the pathophysiology of prion diseases and in transducing physiological functions of PrP^C. A-disintegrin-and-metalloproteinase 10 (ADAM10) has been proposed by cell culture experiments to be responsible for both shedding of PrP^C and its α-cleavage. Here, we analyzed the role of ADAM10 in the proteolytic processing of PrP^C in vivo.

Results

Using neuron-specific Adam10 knockout mice, we show that ADAM10 is the sheddase of PrP^C and that its absence in vivo leads to increased amounts and accumulation of PrP^C in the early secretory pathway by affecting its posttranslational processing. Elevated PrP^C levels do not induce apoptotic signalling via p53. Furthermore, we show that ADAM10 is not responsible for the α-cleavage of PrP^C.

Conclusion

Our study elucidates the proteolytic processing of PrP^C and proves a role of ADAM10 in shedding of PrP^C in vivo. We suggest that ADAM10 is a mediator of PrP^C homeostasis at the plasma membrane and, thus, might be a regulator of the multiple functions discussed for PrP^C. Furthermore, identification of ADAM10 as the sheddase of PrP^C opens the avenue to devising novel approaches for therapeutic interventions against prion diseases.

Association of tissue lineage and gene expression: conservatively and differentially expressed genes define common and special functions of tissues

BACKGROUND

Embryogenesis is the process by which the embryo is formed, develops, and establishes developmental hierarchies of tissues. The recent advance in microarray technology made it possible to investigate the tissue specific patterns of gene expression and their relationship with tissue lineages. This study is focused on how tissue specific functions, tissue lineage, and cell differentiation are correlated, which is essential to understand embryonic development and organism complexity.

RESULTS

We performed individual gene and gene set based analysis on multiple tissue expression data, in association with the classic topology of mammalian fate maps of embryogenesis. For each sub-group of tissues on the fate map, conservatively, differentially and correlatively expressed genes or gene sets were identified. Tissue distance was found to correlate with gene expression divergence. Tissues of the ectoderm or mesoderm origins from the same segments on the fate map shared more similar expression pattern than those from different origins. Conservatively expressed genes or gene sets define common functions in a tissue group and are related to tissue specific diseases, which is supported by results from Gene Ontology and KEGG pathway analysis. Gene expression divergence is larger in certain human tissues than in the mouse homologous tissues.

CONCLUSION

The results from tissue lineage and gene expression analysis indicate that common function features of neighbor tissue groups were defined by the conservatively expressed genes and were related to tissue specific diseases, and differentially expressed genes contribute to the functional divergence of tissues. The difference of gene expression divergence in human and mouse homologous tissues reflected the organism complexity, i.e. distinct neural development levels and different body sizes.

Biomolecular Structure and Modeling: Problem and Application Perspective

The experimental progress described in the previous chapter has been accompanied by an increasing desire to relate the complex three-dimensional (3D) shapes of biomolecules to their biological functions and interactions with other molecular systems. Structural biology, computational biology, genomics, proteomics, bioinformatics, chemoinformatics, and others are natural partner disciplines in such endeavors.

PrP expression, PrPSc accumulation and innervation of splenic compartments in sheep experimentally infected with scrapie

Background

In prion disease, the peripheral expression of PrP^C is necessary for the transfer of infectivity to the central nervous system. The spleen is involved in neuroinvasion and neural dissemination in prion diseases but the nature of this involvement is not known. The present study undertook the investigation of the spatial relationship between sites of PrP^Sc accumulation, localisation of nerve fibres and PrP^C expression in the tissue compartments of the spleen of scrapie-inoculated and control sheep.

Methodology/Principal Findings

Laser microdissection and quantitative PCR were used to determine PrP mRNA levels and results were compared with immunohistochemical protocols to distinguish PrP^C and PrP^Sc in tissue compartments of the spleen. In sheep experimentally infected with scrapie, the major sites of accumulation of PrP^Sc in the spleen, namely the lymphoid nodules and the marginal zone, expressed low levels of PrP mRNA. Double immunohistochemical labelling for PrP^Sc and the pan-nerve fibre marker, PGP, was used to evaluate the density of innervation of splenic tissue compartments and the intimacy of association between PrP^Sc and nerves. Some nerve fibres were observed to accompany blood vessels into the PrP^Sc-laden germinal centres. However, the close association between nerves and PrP^Sc was most apparent in the marginal zone. Other sites of close association were adjacent to the wall of the central artery of PALS and the outer rim of germinal centres.

Conclusions/Significance

The findings suggest that the degree of PrP^Sc accumulation does not depend on the expression level of PrP^C. Though several splenic compartments may contribute to neuroinvasion, the marginal zone may play a central role in being the compartment with most apparent association between nerves and PrP^Sc.

The biodegradability of poly(Pro-Hyp-Gly) synthetic polypeptide and the promotion of a dermal wound epithelialization using a poly(Pro-Hyp-Gly) sponge

Collagens are widely used in medical applications, but animal-derived collagens have several drawbacks, such as low thermal stability, nonspecific cell attachment, and susceptibility to contamination by infectious pathogens, such as prions, which may transfect humans. We have previously reported the chemical synthesis of polypeptides consisting of a Pro-Hyp-Gly sequence and the high thermostability of their triple-helical structure. To clarify the biomaterial characteristics of the poly(Pro-Hyp-Gly) polypeptide, we assessed its biodegradability and its capability for skin regeneration. Eight weeks after implantation, a poly(Pro-Hyp-Gly) freeze-dried sponge embedded subcutaneously into a rat dorsal area degraded at the same rate as Terudermis, which is made from bovine type I atelocollagen and is used as an artificial dermis. Surprisingly, compared with Terudermis, the poly(Pro-Hyp-Gly) sponge significantly promoted epithelialization of a full-thickness wound on a rabbit's ear pad. This chemically synthesized polypeptide may be useful as a scaffold for tissue engineering and tissue regeneration.

Beta-secretase: structure, function, and evolution

The most popular current hypothesis is that Alzheimer's disease (AD) is caused by aggregates of the amyloid peptide (Abeta), which is generated by cleavage of the Abeta protein precursor (APP) by beta-secretase (BACE-1) followed by gamma-secretase. BACE-1 cleavage is limiting for the production of Abeta, making it a particularly good drug target for the generation of inhibitors that lower Abeta. A landmark discovery in AD was the identification of BACE-1 (a.k.a. Memapsin-2) as a novel class of type I transmembrane aspartic protease. Although BACE-2, a homologue of BACE-1, was quickly identified, follow up studies using knockout mice demonstrated that BACE-1 was necessary and sufficient for most neuronal Abeta generation. Despite the importance of BACE-1 as a drug target, development has been slow due to the incomplete understanding of its function and regulation and the difficulties in developing a brain penetrant drug that can specifically block its large catalytic pocket. This review summarizes the biological properties of BACE-1 and attempts to use phylogenetic perspectives to understand its function. The article also addresses the challenges in discovering a selective drug-like molecule targeting novel mechanisms of BACE-1 regulation.

Molecular mechanisms of prion pathogenesis

Prion diseases are infectious neurodegenerative diseases occurring in humans and animals with an invariably lethal outcome. One fundamental mechanistic event in prion diseases is the aggregation of aberrantly folded prion protein into large amyloid plaques and fibrous structures associated with neurodegeneration. The cellular prion protein (PrPC) is absolutely required for disease development, and prion knockout mice are not susceptible to prion disease. Prions accumulate not only in the central nervous system but also in lymphoid organs, as shown for new variant and sporadic Creutzfeldt-Jakob patients and for some animals. To date it is largely accepted that prions consist primarily of PrPSc, a misfolded and aggregated beta-sheet-rich isoform of PrPC. However, PrPSc may or may not be completely congruent with the infectious moiety. Here, we discuss the molecular mechanisms leading to neurodegeneration, the role of the immune system in prion pathogenesis, and the existence of prion strains that appear to have different tropisms and biochemical characteristics.

Application of a novel in vitro selection technique to isolate and characterise high affinity DNA aptamers binding mammalian prion proteins

Clinical diagnosis and research into transmissible spongiform encephalopathies are hampered by the lack of sufficiently sensitive and specific reagents able to adequately detect the normal cellular form of the prion protein, PrP(C), and the pathological isoform, PrP(Sc). In order to provide such reagents, we applied Systematic Evolution of Ligands by EXponential enrichment (SELEX) against a recombinant murine prion protein, to select single-stranded DNA ligands (aptamers) of high affinity. The SELEX protocol and subsequent aptamer characterisation employed protein immobilisation/partitioning using nickel-complexed magnetic particles and a novel SYBR Green-mediated quantitative real-time PCR technique. Following eight rounds of selection, the enriched aptamer pool was cloned and 24 clones sequenced. Seven of these were 'orphan' clones and the remainder were grouped into three separate T-rich families. All but four of the aptamer clones exhibited specific binding to the murine prion protein and the majority also bound to human and ovine prion proteins. Dissociation constants (K(d)) ranged from 18 to 79 nM. Flow cytometry with fluorescein-labelled aptamers confirmed that binding to cells was dependent on the expression of PrP(C). Preliminary studies also indicate that a trivalent aptamer pool is capable of binding the pathological isoform PrP(Sc) following guanidinium denaturation.

A potential blood test for transmissible spongiform encephalopathies by detecting carbohydrate-dependent aggregates of PrPres-like proteins in scrapie-Infected hamster plasma

PrPres has rarely been detected in blood (except in leukocytes) even in diseased animal models that are known to contain a large amount of PrPres in infected tissues. It seems likely that PrPres detection in blood is difficult because of the low titer of infectious material within the blood. Here, we demonstrate the detection of proteinase K-resistant 3F4-reactive protein in the plasma of scrapie-infected hamsters but not in the plasma of mock-infected hamsters by partial purification using a novel method termed "acidic SDS precipitation," in conjunction with a highly sensitive chemiluminescence detection system used to show the presence of PrP at a concentration equivalent to 1.4x10(-9) g of brain homogenate or 1.5x10(-12) g (6.5x10(-17) mol) of rPrP by conventional Western blotting. The 3F4-reactive proteins in scrapie-infected hamster plasma often resulted in multiple Mw protein bands occurring at higher Mw positions than the position of the di-glycosyl PrP molecule. Mixing scrapie-infected hamster brain homogenate with mock-infected hamster plasma resulted in the formation of similar Mw positions for multiple 3F4-reactive proteins. Predigestion of carbohydrate side chains from the proteins in the plasma or brain homogenate before mixing resulted in failure to obtain these multiple 3F4-reactive proteins. These observations indicate that PrPres aggregated with other proteins in the plasma through carbohydrate side chains and was successfully detected in the plasma of scrapie-infected hamsters. Counterparts in these aggregates with PrPres-like proteins in scHaPl are not known but any that exist should resist the PK digestion.

Cellular prion protein regulates beta-secretase cleavage of the Alzheimer's amyloid precursor protein

Proteolytic processing of the amyloid precursor protein (APP) by beta-secretase, beta-site APP cleaving enzyme (BACE1), is the initial step in the production of the amyloid beta (Abeta) peptide, which is involved in the pathogenesis of Alzheimer's disease. The normal cellular function of the prion protein (PrP(C)), the causative agent of the transmissible spongiform encephalopathies such as Creutzfeldt-Jakob disease in humans, remains enigmatic. Because both APP and PrP(C) are subject to proteolytic processing by the same zinc metalloproteases, we tested the involvement of PrP(C) in the proteolytic processing of APP. Cellular overexpression of PrP(C) inhibited the beta-secretase cleavage of APP and reduced Abeta formation. Conversely, depletion of PrP(C) in mouse N2a cells by siRNA led to an increase in Abeta peptides secreted into the medium. In the brains of PrP knockout mice and in the brains from two strains of scrapie-infected mice, Abeta levels were significantly increased. Two mutants of PrP, PG14 and A116V, that are associated with familial human prion diseases failed to inhibit the beta-secretase cleavage of APP. Using constructs of PrP, we show that this regulatory effect of PrP(C) on the beta-secretase cleavage of APP required the localization of PrP(C) to cholesterol-rich lipid rafts and was mediated by the N-terminal polybasic region of PrP(C) via interaction with glycosaminoglycans. In conclusion, this is a mechanism by which the cellular production of the neurotoxic Abeta is regulated by PrP(C) and may have implications for both Alzheimer's and prion diseases.

M1 and M3 muscarinic receptors control physiological processing of cellular prion by modulating ADAM17 phosphorylation and activity

The cellular prion protein (PrP(c)) undergoes a physiological processing yielding the N-terminal fragment referred to as N1, the production of which can be constitutive or protein kinase C regulated. We show that activation of endogenous muscarinic receptors by carbachol and by the M1-selective agonist AF267B increases N1 recovery in an atropine-sensitive manner, in mouse embryonic primary neurons. To identify the muscarinic receptor subtype involved, we used human embryonic kidney HEK293 (HEK) cells stably overexpressing M1, M2, M3, or M4 receptor subtype. Carbachol and the selective M1 agonist AF267B dose dependently increased N1 release by HEK-M3 and HEK-M1 cells, respectively, whereas carbachol did not modify N1 production by HEK-M2 or HEK-M4 cells. We demonstrate that the increase of N1 was not attributable to modified trafficking to the membrane of either PrP(c) or the disintegrin metalloproteases ADAM10 or ADAM17. Furthermore, we establish that carbachol affects the overall phosphorylation of ADAM17 on its threonine and tyrosine but not serine residues, whereas levels of phosphorylated ADAM9 were not affected. Interestingly, carbachol also increases the hydrolysis of the fluorimetric substrate JMV2770, which mimicked the sequence encompassing the N1 site cleavage and was shown previously to behave as an ADAM protease substrate. Mutations of threonine 735 but not of tyrosine 702 of the ADAM17 cytoplasmic tail abolishes the carbachol-induced increase of N1, ADAM17 phosphorylation, and JMV2770-hydrolyzing activity in M1- and M3-expressing HEK293 cells. Thus, our data provide strong evidence that muscarinic receptor activation increases the physiological processing of PrP(c) by upregulating the phosphorylation state and activity of ADAM17 protease.

Pharmacokinetics and distribution of clioquinol in golden hamsters

Clioquinol (5-chloro-7-iodo-8-quinolinol) is a zinc and copper chelator that can dissolve amyloid deposits and may be beneficial in Alzheimer's disease. Prion diseases are also degenerative CNS disorders characterised by amyloid deposits. The pharmacokinetics and tissue distribution of drugs active against prions may clarify their targets of action. We describe the pharmacokinetics of clioquinol in hamster plasma, spleen and brain after single and repeated oral or intraperitoneal administration (50 mg kg(-1)), as well as after administration with the diet. A single intraperitoneal administration led to peak plasma clioquinol concentrations after 15 min (Tmax), followed by a decay with an apparent half-life of 2.20 +/- 1.1 h. After oral administration, Tmax was reached after 30 min and was followed by a similar process of decay; the AUC(0-last) was 16% that recorded after intraperitoneal administration. The Cmax and AUC values in spleen after a single administration were about 65% (i.p.) and 25% (p.o.) those observed in blood; those in liver were 35% (p.o.) those observed in blood and those in brain were 20% (i.p.) and 10% (p.o.) those observed in plasma. After repeated oral doses, the plasma, brain and spleen concentrations were similar to those observed at the same times after a single dose. One hour after intraperitoneal dosing, clioquinol was also found in the ventricular CSF. Clioquinol was also given with the diet; its morning and afternoon concentrations were similar, and matched those after oral administration. No toxicity was found after chronic administration. Our results indicate that clioquinol, after oral administration with the diet, reaches concentrations in brain and peripheral tissues (particularly spleen) that can be considered effective in preventing prion accumulation, but are at least ten times lower than those likely to cause toxicity.

Study on interaction between microtubule associated protein tau and prion protein

Microtubule-associated protein tau is considered to play roles in many neurodegenerative diseases including some transmissible spongiform encephalopathies. To address the possible molecular linkage of prion protein (PrP) and tau, a GST-fusion segment of human tau covering the three-repeat region and various PrP segments was used in the tests of GST pull-down and immunoprecipitation. We found tau protein interacted with various style prion proteins such as native prion protein (PrPc) or protease-resistant isoform (PrPSc). Co-localization signals of tau and PrP were found in the CHO cell tranfected with both PrP and tau gene. The domain of interaction with tau was located at N-terminal of PrP (residues 23 to 91). The evidence of molecular interactions between PrP and tau protein highlights a potential role of tau in the biological function of PrP and the pathogenesis of TSEs.

Group I mGluR signaling in BSE-infected bovine-PrP transgenic mice

Abnormalities of synapses and impaired synaptic transmission appear to be crucial in the pathogenesis of prion diseases. Excitotoxic mechanisms have been postulated as a major cause of neurodegeneration in these conditions. In this line, previous studies have shown abnormal group 1 metabotropic glutamate receptor signaling in Creutzfeldt-Jakob disease (CJD). In the present study, we have examined this pathway by western blotting in the cerebral cortex of bovine-spongiform encephalopathy (BSE)-infected bovine-PrP transgenic mice at different days post-inoculation (dpi). Activation of post-synaptic metabotropic glutamate receptor 1 (mGluR1) promotes phospholipase Cbeta1 (PLCbeta1) activation which may activate, in turn, protein kinase C (PKC), which regulates gene expression. Densitometric analysis of the western blot bands revealed no differences in the protein levels of (mGluR1) through time, but demonstrated decreased levels of PLCbeta1 and protein kinase C delta (nPKCdelta) at 270dpi, at the time when mice showed neurological deficits accompanied by neuropathological changes and PrPres deposition in the brain. The present results show, for the first time impairment of the mGluR1/PLCbeta1/PKCdelta pathway signaling with disease-progression in a murine model of BSE.

Adenosine A1 Receptor Protein Levels and Activity Is Increased in the Cerebral Cortex in Creutzfeldt-Jakob Disease and in Bovine Spongiform Encephalopathy-Infected Bovine-PrP Mice

Prion diseases are characterized by neuronal loss, astrocytic gliosis, spongiform change, and abnormal protease-resistant prion protein (PrP) deposition. Creutzfeldt-Jakob disease (CJD) is the most prevalent human prion disease, whereas scrapie and bovine spongiform encephalopathy (BSE) are the most common animal prion diseases. Several candidates have been proposed as mediators of degeneration in prion diseases, one of them glutamate. Recent studies have shown reduced metabotropic glutamate receptor/phospholipase C signaling in the cerebral cortex in CJD, suggesting that this important neuromodulator and neuroprotector pathway is attenuated in CJD. Adenosine is involved in the regulation of different metabolic processes under physiological and pathologic conditions. Adenosine function is mediated by adenosine receptors, which are categorized into 4 types: A1, A2A, A2B, and A3. A1Rs are G-protein-coupled receptors that induce the inhibition of adenylyl cyclase activity. The most dramatic inhibitory actions of adenosine receptors are on the glutamatergic system. For these reasons, we examined the levels of A1Rs in the frontal cortex of 12 patients with CJD and 6 age-matched controls and in BSE-infected bovine-PrP transgenic mice (BoPrP-Tg110 mice) at different postincubation times to address modifications in A1Rs with disease progression. A significant increase in the protein levels of A1Rs was found in the cerebral cortex in CJD and in the murine BSE model at advanced stages of the disease and coincidental with the appearance of PrP expression. In addition, the activity of A1Rs was analyzed by in vitro assays with isolated membranes of the frontal cortex in CJD. Increased activity of the receptor, as revealed by the decreased forskolin-stimulated cAMP production in response to the A1R agonists cyclohexyl adenosine and cyclopentyl adenosine, was observed in CJD cases when compared with controls. Finally, mRNA A1R levels were similar in CJD and control cases, thus suggesting abnormal A1R turnover or dysregulation of raft-associated signaling pathways in CJD. These results show, for the first time, sensitization of A1Rs in prion diseases.

Prion diseases and the gastrointestinal tract

The gastrointestinal (GI) tract plays a central role in the pathogenesis of transmissible spongiform encephalopathies. These are human and animal diseases that include bovine spongiform encephalopathy, scrapie and Creutzfeldt-Jakob disease. They are uniformly fatal neurological diseases, which are characterized by ataxia and vacuolation in the central nervous system. Although they are known to be caused by the conversion of normal cellular prion protein to its infectious conformational isoform (PrPsc) the process by which this isoform is propagated and transported to the brain remains poorly understood. M cells, dendritic cells and possibly enteroendocrine cells are important in the movement of infectious prions across the GI epithelium. From there, PrPsc propagation requires B lymphocytes, dendritic cells and follicular dendritic cells of Peyer's patches. The early accumulation of the disease-causing agent in the plexuses of the enteric nervous system supports the contention that the autonomic nervous system is important in disease transmission. This is further supported by the presence of PrPsc in the ganglia of the parasympathetic and sympathetic nerves that innervate the GI tract. Additionally, the lymphoreticular system has been implicated as the route of transmission from the gut to the brain. Although normal cellular prion protein is found in the enteric nervous system, its role has not been characterized. Further research is required to understand how the cellular components of the gut wall interact to propagate and transmit infectious prions to develop potential therapies that may prevent the progression of transmissible spongiform encephalopathies.

Determination of 5-chloro-7-iodo-8-quinolinol (clioquinol) in plasma and tissues of hamsters by high-performance liquid chromatography and electrochemical detection

This paper describes a method of determining clioquinol levels in hamster plasma and tissue by means of HPLC and electrochemical detection. Clioquinol was separated on a Nucleosil C18 300 mm x 3.9 mm i.d. 7 microm column at 1 ml/min using a phosphate/citrate buffer 0.1M (400 ml) with 600 ml of a methanol:acetonitrile (1:1, v/v) mobile phase. The retention times of clioquinol and the IS were, respectively, 11.6 and 8.1 min; the quantitation limit (CV>8%) was 5 ng/ml in plasma and 10 ng/ml in tissues. The intra- and inter-assay accuracies of the method were more than 95%, with coefficients of variation between 3.0 and 7.7%, and plasma and tissue recovery rates of 72-77%. There was a linear response to clioquinol 5-2000 ng/ml in plasma, and 10-1000 ng/g in tissues. The method is highly sensitive and selective, makes it possible to study the pharmacokinetics of plasma clioquinol after oral administration and the distribution of clioquinol in tissues, and could be used to monitor plasma clioquinol levels in humans.

Pathogenesis and prevalence of variant Creutzfeldt-Jakob disease

In the late 1980s and early 1990s, there was widespread exposure of the UK population to bovine spongiform encephalopathy (BSE)-contaminated food products, which has led to over 150 deaths from variant Creutzfeldt-Jakob disease (vCJD). Although the pathogenesis in humans is not fully understood, data from animal models and, to a lesser extent, patients with vCJD suggest that oral exposure to BSE is rapidly followed by accumulation of PrP(res) in gut-associated lymphoid tissue, then, after haematogenous spread, throughout the lymphoreticular system. Spread to the central nervous system may not occur for several years, but blood from individuals in the pre-clinical phase appears to be able to transmit disease. The incidence of vCJD has remained low and is in decline, but it is known from iatrogenic CJD and kuru that human prion disease can have incubation periods of up to 40 years. Cases of vCJD are therefore likely to occur for many more years and alternative phenotypes may develop in individuals with different PRNP genotypes to those seen to date. Studies in transgenic mice have shown that sub-clinical infection is frequent following oral exposure to BSE and a study looking at the accumulation of PrP in anonymized human lymphoid tissue samples found positive cases. There are likely to be a number of asymptomatic 'carriers' of disease within the UK and although it is unclear whether these individuals will develop clinical disease, there is a potential for iatrogenic spread to others. These uncertainties highlight the importance of developing a reliable blood test for vCJD and the continued need for surveillance.

Prion protein-related proteins from zebrafish are complex glycosylated and contain a glycosylphosphatidylinositol anchor

A hallmark of prion diseases in mammals is a conformational transition of the cellular prion protein (PrP(C)) into a pathogenic isoform termed PrP(Sc). PrP(C) is highly conserved in mammals, moreover, genes of PrP-related proteins have been recently identified in fish. While there is only little sequence homology to mammalian PrP, PrP-related fish proteins were predicted to be modified with N-linked glycans and a C-terminal glycosylphosphatidylinositol (GPI) anchor. We biochemically characterized two PrP-related proteins from zebrafish in cultured cells and show that both zePrP1 and zeSho2 are imported into the endoplasmic reticulum and are post-translationally modified with complex glycans and a C-terminal GPI anchor.

The role of chaperones in Parkinson's disease and prion diseases

The etiologies of neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, polyglutamine diseases, or prion diseases may be diverse; however, aberrations in protein folding, processing, and/or degradation are common features of these entities, implying a role of quality control systems, such as molecular chaperones and the ubiquitin-proteasome pathway. There is substantial evidence for a causal role of protein misfolding in the pathogenic process coming from neuropathology, genetics, animal modeling, and biophysics. The presence of protein aggregates in all neurodegenerative diseases gave rise to the hypothesis that protein aggregates, be it intracellular or extracellular deposits, may perturb the cellular homeostasis and disintegrate neuronal function (Table 1). More recently, however, an increasing number of studies have indicated that protein aggregates are not toxic per se and might even serve a protective role by sequestering misfolded proteins. Specifically, experimental models of polyglutamine diseases, Alzheimer's disease, and Parkinson's disease revealed that the appearance of aggregates can be dissociated from neuronal toxicity, while misfolded monomers or oligomeric intermediates seem to be the toxic species. The unique features of molecular chaperones to assist in the folding of nascent proteins and to prevent stress-induced misfolding was the rationale to exploit their effects in different models of neurodegenerative diseases. This chapter concentrates on two neurodegenerative diseases, Parkinson's disease and prion diseases, with a special focus on protein misfolding and a possible role of molecular chaperones.

KDEL-tagged anti-prion intrabodies impair PrP lysosomal degradation and inhibit scrapie infectivity

Transmissible spongiform encephalopathy or prion diseases are fatal neurodegenerative disorders characterized by the conversion of the cellular prion protein (PrPC) into the infectious scrapie isoform (PrPSc). We have recently demonstrated that anti-prion intrabodies targeted to the lumen of the endoplasmic reticulum provide a simple and effective means to inhibit the transport of PrPC to the cell surface. Here, we report that they completely block the traffic of mature full-length PrPC molecules, impair prion lysosomal degradation, and interfere with the early phase of scrapie formation. Since anti-prion intrabodies efficiently block PrPSc accumulation in vitro, we investigated whether they could also antagonize scrapie infectivity in vivo. We found that mice intracerebrally injected with KDEL-8H4-NGF-differentiated PC12 cells infected with scrapie neither develop scrapie clinical signs nor brain damage. Furthermore, no protease-resistant PrPSc is detectable in brains of inoculated animals. These results indicate that anti-prion intrabody strategy may be effective against prion infection.

Oxidation, glycoxidation, lipoxidation, nitration, and responses to oxidative stress in the cerebral cortex in Creutzfeldt-Jakob disease

Gel electrophoresis and Western blotting of frontal cortex homogenates have been carried out in sporadic Creutzfeldt-Jakob disease (CJD) cases and age-matched controls to gain understanding of the expression of glycation-end products (AGEs). N-Carboxymethyl-lysine (CML) and N-carboxyethyl-lysine (CEL) were used as markers of glycoxidation; 4-hydroxynonenal (4-HNE) and malondialdehyde-lysine (MDAL) as markers of lipoxidation; and nitrotyrosine (N-tyr) and neuronal, endothelial and inducible nitric oxide synthase (nNOS, eNos and iNos) as markers of protein nitration and as sources of NO production, respectively. Age receptor (RAGE) and Cu/Zn superoxide dismutase (SOD1) and Mn superoxide dismutase (SOD2) expression levels were also examined. The results showed a significant increase in the expression levels of AGE (p<0.05), CEL (p<0.001), RAGE (p<0.05), HNE-modified proteins (p<0.01), nNOS, iNOS and eNOS (p<0.01 and p<0.05, respectively), N-tyr (p<0.05), and SOD1 (p<0.05) and SOD2 (p<0.05). No relationship was observed between PrP genotype, PrP type, PrP burden, and expression levels of oxidative stress markers. The present findings demonstrate oxidative, glycoxidative, lipoxidative and nitrative protein damage, accompanied by increased oxidative responses, in the cerebral cortex in sporadic CJD. These results provide support for the concept that oxidative stress may have important implications in the pathogenesis of prion diseases.

Synthesis of poly(Pro-Hyp-Gly)(n) by direct poly-condensation of (Pro-Hyp-Gly)(n), where n=1, 5, and 10, and stability of the triple-helical structure

Pro-Hyp-Gly is a characteristic amino acid sequence found in fibrous collagens, and (Pro-Hyp-Gly)(10), which has been widely used as a collagen-model peptide, forms a stable triple-helical structure. Here, we synthesized polypeptides consisting of the Pro-Hyp-Gly sequence by direct poly-condensation of (Pro-Hyp-Gly)(n), where n=1, 5, and 10, using 1-hydroxybenzotriazole and 1-ethyl-3-(3-dimethyl-aminopropyl)-carbodiimide hydrochloride in both phosphate buffer (pH=7.4) and dimethylsulfoxide (DMSO) solutions for 48 h at 20 degrees C. The reaction of (Pro-Hyp-Gly)(5) and (Pro-Hyp-Gly)(10) in DMSO successfully gave polypeptides with molecular weights over 10,000, whereas low molecular weight products were obtained by reaction in phosphate buffer (pH=7.4). In contrast, Pro-Hyp-Gly at a concentration of 50 mg/mL in phosphate buffer (pH=7.4) gave polypeptides with molecular weights over 10,000. The Fourier transform infrared (FTIR) and (1)H nuclear magnetic resonance (NMR) spectra of poly(Pro-Hyp-Gly)(10) revealed that the polymerization of (Pro-Hyp-Gly)(10) described in this report had no side reactions. Each polypeptide obtained shows a collagen-like triple-helical structure, and the triple-helical structures of poly(Pro-Hyp-Gly) and poly(Pro-Hyp-Gly)(10) were stable up to T=80 degrees C, which suggests that the high molecular weight promotes stability of the triple-helical structure, in addition to the high Hyp content. Furthermore, transmission electron microscopy (TEM) observations show that poly(Pro-Hyp-Gly)(10) aggregates to form nanofiber-like structures about 10 nm in width, which suggests that a Pro-Hyp-Gly repeating sequence contains enough information for triple-helix formation, and for subsequent nanofiber-like structure formation.

Nonlinear Optical Studies of the Agricultural Antibiotic Morantel Interacting with Silica/Water Interfaces

It is now known that the untreated discharge of pharmaceuticals into the environment can impact human health and development and lead to increased drug resistance in biota. Here, we present the first direct interface-specific studies that address the mobility of the widely used agricultural antibiotic morantel, which is commonly present in farm runoff. Surface-bound morantel was spectroscopically identified using second harmonic generation (SHG) via a two-photon resonance of its n-pi* transition and in the C-H stretching region by vibrational sum frequency generation (VSFG). Resonantly enhanced SHG adsorption isotherm measurements carried out at the silica/water interface between 6 x 10(-7) and 5 x 10(-5) M morantel concentration result in a free energy of adsorption of 42(2) kJ/mol at pH 7. Finally, real-time tracking of morantel interaction with the silica/water interface shows that the binding events are fully reversible, consistent with its high mobility in silica-rich soil environments. This work thus indicates that pharmaceuticals discharged into the environment can enter the groundwater supply of municipal water systems, at which point their removal is challenging. In addition, the high mobility of morantel in silica-rich soil environments could lead to developing increased interaction of this antibiotic with target organisms, which could respond by increased drug resistance.

The disintegrin ADAM9 indirectly contributes to the physiological processing of cellular prion by modulating ADAM10 activity

The cellular prion protein (PrP(c)) is physiologically cleaved in the middle of its 106-126 amino acid neurotoxic region at the 110/111 downward arrow112 peptidyl bond, yielding an N-terminal fragment referred to as N1. We recently demonstrated that two disintegrins, namely ADAM10 and ADAM17 (TACE, tumor necrosis factor alpha converting enzyme) participated in both constitutive and protein kinase C-regulated generation of N1, respectively. These proteolytic events were strikingly reminiscent of those involved in the so-called "alpha-secretase pathway" that leads to the production of secreted sAPPalpha from betaAPP. We show here, by transient and stable transfection analyses, that ADAM9 also participates in the constitutive secretion of N1 in HEK293 cells, TSM1 neurons, and mouse fibroblasts. Decreasing endogenous ADAM9 expression by an antisense approach drastically reduces both N1 and sAPPalpha recoveries. However, we establish that ADAM9 was unable to increase N1 and sAPPalpha productions after transient transfection in fibroblasts depleted of ADAM10. Accordingly, ADAM9 is unable to cleave a fluorimetric substrate of membrane-bound alpha-secretase activity in ADAM10(-/-) fibroblasts. However, we establish that co-expression of ADAM9 and ADAM10 in ADAM10-deficient fibroblasts leads to enhanced membrane-bound and released fluorimetric substrate hydrolyzing activity when compared with that observed after ADAM10 cDNA transfection alone in ADAM10(-/-) cells. Interestingly, we demonstrate that shedded ADAM10 displays the ability to cleave endogenous PrP(c) in fibroblasts. Altogether, these data provide evidence that ADAM9 is an important regulator of the physiological processing of PrP(c) and betaAPP but that this enzyme acts indirectly, likely by contributing to the shedding of ADAM10. ADAM9 could therefore represent, besides ADAM10, another potential therapeutic target to enhance the breakdown of the 106-126 and Abeta toxic domains of the prion and betaAPP proteins.

Combined pharmacological, mutational and cell biology approaches indicate that p53-dependent caspase 3 activation triggered by cellular prion is dependent on its endocytosis

We have previously established that cellular prion PrP(c) elicited p53-dependent caspase 3 activation in various transfected cells and primary cultured neurons. Although we showed that PrP(c) modulates p53 expression at both transcriptional and post-transcriptional levels, it remained unclear as to whether cellular prion signals at the membrane to trigger intracellular messages or if prion proapoptotic activity necessitated its translocation into the cytoplasm. Here, we compare the processing and cell death-related functions of PrP(c) with those of a mutated PrP(c) protein (N-3F4 MoPrP(c)) in which three basic N-terminal residues responsible for PrP(c) internalization had been mutated. As expected, N-3F4 MoPrP(c) remains exclusively located at the membrane, whereas PrP(c) partitions between membrane-associated and intracellular compartments, but both, proteins undergo constitutive and protein kinase C-regulated disintegrin-mediated proteolysis, leading to N1 fragment production. Unlike PrP(c), N-3F4 MoPrP(c) expression does not induce caspase 3 activation after stimulation by staurosporine and was inert on p53 expression and promoter transactivation in both human cells and TSM1 mouse neurons. Interestingly, PrP(c)-induced caspase 3 activation was closely linked to its endocytosis. This phenotype was enhanced by proteasomal inhibition and prevented by sucrose treatment. Accordingly, immunohistochemical analysis showed that protection towards degradation increased intracellular PrP(c)-like immunoreactivity, while sucrose treatments fully abolished PrP(c) intracellular expression and co-localization with transferrin. Altogether, we, establish here, using combined biochemical, mutational and cell biology approaches, that the caspase 3 activation associated with cellular prion is closely related to its ability to undergo endocytosis. This is, to our knowledge, the first direct description of an endocytosis-dependent PrP(c)-associated function.