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del Rio, Jose A., Ferrer, Isidre, (2020). Potential of microfluidics and lab-on-chip platforms to improve understanding of “prion-like” protein assembly and behavior Frontiers in Bioengineering and Biotechnology 8, 570692

Human aging is accompanied by a relevant increase in age-associated chronic pathologies, including neurodegenerative and metabolic diseases. The appearance and evolution of numerous neurodegenerative diseases is paralleled by the appearance of intracellular and extracellular accumulation of misfolded proteins in affected brains. In addition, recent evidence suggests that most of these amyloid proteins can behave and propagate among neural cells similarly to infective prions. In order to improve understanding of the seeding and spreading processes of these “prion-like” amyloids, microfluidics and 3D lab-on-chip approaches have been developed as highly valuable tools. These techniques allow us to monitor changes in cellular and molecular processes responsible for amyloid seeding and cell spreading and their parallel effects in neural physiology. Their compatibility with new optical and biochemical techniques and their relative availability have increased interest in them and in their use in numerous laboratories. In addition, recent advances in stem cell research in combination with microfluidic platforms have opened new humanized in vitro models for myriad neurodegenerative diseases affecting different cellular targets of the vascular, muscular, and nervous systems, and glial cells. These new platforms help reduce the use of animal experimentation. They are more reproducible and represent a potential alternative to classical approaches to understanding neurodegeneration. In this review, we summarize recent progress in neurobiological research in “prion-like” protein using microfluidic and 3D lab-on-chip approaches. These approaches are driven by various fields, including chemistry, biochemistry, and cell biology, and they serve to facilitate the development of more precise human brain models for basic mechanistic studies of cell-to-cell interactions and drug discovery.

Keywords: Lab-On-Chip, Amyloid propagation, Microfluidics, Fibril, Seeding, Spreading, Prion-like, Prionoid

Gavín, Rosalina, Lidón, Laia, Ferrer, Isidre, del Río, José Antonio, (2020). The quest for cellular prion protein functions in the aged and neurodegenerating brain Cells 9, (3), 591

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.

Keywords: Prion, Tau, Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, Neuroprotection

Lidón, Laia, Vergara, Cristina, Ferrer, Isidro, Hernández, Félix, Ávila, Jesús, del Rio, Jose A., Gavín, Rosalina, (2020). Tau protein as a new regulator of cellular prion protein transcription Molecular Neurobiology 57, (10), 4170-4186

Cellular prion protein (PrPC) is largely responsible for transmissible spongiform encephalopathies (TSEs) when it becomes the abnormally processed and protease resistant form PrPSC. Physiological functions of PrPC include protective roles against oxidative stress and excitotoxicity. Relevantly, PrPC downregulates tau levels, whose accumulation and modification are a hallmark in the advance of Alzheimer's disease (AD). In addition to the accumulation of misfolded proteins, in the initial stages of AD-affected brains display both increased reactive oxygen species (ROS) markers and levels of PrPC. However, the factors responsible for the upregulation of PrPC are unknown. Thus, the aim of this study was to uncover the different molecular actors promoting PrPC overexpression. In order to mimic early stages of AD, we used β-amyloid-derived diffusible ligands (ADDLs) and tau cellular treatments, as well as ROS generation, to elucidate their particular roles in human PRNP promoter activity. In addition, we used specific chemical inhibitors and site-specific mutations of the PRNP promoter sequence to analyze the contribution of the main transcription factors involved in PRNP transcription under the analyzed conditions. Our results revealed that tau is a new modulator of PrPC expression independently of ADDL treatment and ROS levels. Lastly, we discovered that the JNK/c-jun-AP-1 pathway is involved in increased PRNP transcription activity by tau but not in the promoter response to ROS.

Keywords: Alzheimer’s disease, Cellular prion protein, Promoter, Tau, Tauopathies

Del Río, J. A., Ferrer, Isidre, Gavín, R., (2018). Role of cellular prion protein in interneuronal amyloid transmission Progress in Neurobiology 165-167, 87-102

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 (PrPC) binding has been a focus of interest in Alzheimer’s disease (AD). At the molecular level, β-amyloid/PrPC interaction takes place in two differently charged clusters of PrPC. In addition to β-amyloid, participation of PrPC in α-synuclein binding and brain spreading also appears to be relevant in α-synucleopathies. This review summarizes current knowledge about PrPC as a putative receptor for amyloid proteins and the physiological consequences of these interactions..

Keywords: Cellular prion protein, Amyloid, Proteinaceous species, ‘prion-like’ spreading, Spreading, Neurodegeneration

Matamoros-Angles, A., Gayosso, L. M., Richaud-Patin, Y., Di Domenico, A., Vergara, C., Hervera, A., Sousa, A., Fernández-Borges, N., Consiglio, A., Gavín, R., López de Maturana, R., Ferrer, Isidro, López de Munain, A., Raya, A., Castilla, J., Sánchez-Pernaute, R., Del Río, J. A., (2018). iPS cell cultures from a Gerstmann-Sträussler-Scheinker patient with the Y218N PRNP mutation recapitulate tau pathology Molecular Neurobiology 55, (4), 3033-3048

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.

Keywords: Cellular prion protein, Gerstmann-Sträussler-Scheinker, Induced pluripotent stem cells, Tau

Pallarès, Irantzu, de Groot, Natalia S., Iglesias, Valentín, Sant'Anna, Ricardo, Biosca, Arnau, Fernàndez-Busquets, Xavier, Ventura, Salvador, (2018). Discovering putative prion-like proteins in Plasmodium falciparum: A computational and experimental analysis Frontiers in Microbiology 9, Article 1737

Prions are a singular subset of proteins able to switch between a soluble conformation and a self-perpetuating amyloid state. Traditionally associated with neurodegenerative diseases, increasing evidence indicates that organisms exploit prion-like mechanisms for beneficial purposes. The ability to transit between conformations is encoded in the so-called prion domains, long disordered regions usually enriched in glutamine/asparagines residues. Interestingly, Plasmodium falciparum, the parasite that causes the most virulent form of malaria, is exceptionally rich in proteins bearing long Q/N-rich sequence stretches, accounting for roughly 30% of the proteome. This biased composition suggests that these protein regions might correspond to prion-like domains (PrLDs) and potentially form amyloid assemblies. To investigate this possibility, we performed a stringent computational survey for Q/N-rich PrLDs on P. falciparum. Our data indicate that ~10% of P. falciparum protein sequences have prionic signatures, and that this subproteome is enriched in regulatory proteins, such as transcription factors and RNA-binding proteins. Furthermore, we experimentally demonstrate for several of the identified PrLDs that, despite their disordered nature, they contain inner short sequences able to spontaneously self-assemble into amyloid-like structures. Although the ability of these sequences to nucleate the conformational conversion of the respective full-length proteins should still be demonstrated, our analysis suggests that, as previously described for other organisms, prion-like proteins might also play a functional role in P. falciparum.

Keywords: Plasmodium, Protein aggregation, Amyloid, Prion, Q-N-rich sequences, Protein Disorder

Mata, Agata, Urrea, Laura, Vilches, Silvia, Llorens, Franc, Thüne, Katrin, Espinosa, Juan-Carlos, Andréoletti, Olivier, Sevillano, Alejandro M., Torres, Juan María, Requena, Jesús Rodríguez, Zerr, Inga, Ferrer, Isidro, Gavín, Rosalina, del Río, José Antonio, (2017). Reelin expression in Creutzfeldt-Jakob disease and experimental models of transmissible spongiform encephalopathies Molecular Neurobiology 54, (8), 6412-6425

Reelin is an extracellular glycoprotein involved in key cellular processes in developing and adult nervous system, including regulation of neuronal migration, synapse formation, and plasticity. Most of these roles are mediated by the intracellular phosphorylation of disabled-1 (Dab1), an intracellular adaptor molecule, in turn mediated by binding Reelin to its receptors. Altered expression and glycosylation patterns of Reelin in cerebrospinal and cortical extracts have been reported in Alzheimer’s disease. However, putative changes in Reelin are not described in natural prionopathies or experimental models of prion infection or toxicity. With this is mind, in the present study, we determined that Reelin protein and mRNA levels increased in CJD human samples and in mouse models of human prion disease in contrast to murine models of prion infection. However, changes in Reelin expression appeared only at late terminal stages of the disease, which prevent their use as an efficient diagnostic biomarker. In addition, increased Reelin in CJD and in in vitro models does not correlate with Dab1 phosphorylation, indicating failure in its intracellular signaling. Overall, these findings widen our understanding of the putative changes of Reelin in neurodegeneration.

Keywords: Reelin, Creutzfeldt-Jakob disease, Dab-1, Cellular prion protein

Vilches, S., Vergara, C., Nicolás, O., Mata, A., Del Río, J. A., Gavín, R., (2016). Domain-specific activation of death-associated intracellular signalling cascades by the cellular prion protein in neuroblastoma cells Molecular Neurobiology 53, (7), 4438–4448

The biological functions of the cellular prion protein remain poorly understood. In fact, numerous studies have aimed to determine specific functions for the different protein domains. Studies of cellular prion protein (PrPC) domains through in vivo expression of molecules carrying internal deletions in a mouse Prnp null background have provided helpful data on the implication of the protein in signalling cascades in affected neurons. Nevertheless, understanding of the mechanisms underlying the neurotoxicity induced by these PrPC deleted forms is far from complete. To better define the neurotoxic or neuroprotective potential of PrPC N-terminal domains, and to overcome the heterogeneity of results due to the lack of a standardized model, we used neuroblastoma cells to analyse the effects of overexpressing PrPC deleted forms. Results indicate that PrPC N-terminal deleted forms were properly processed through the secretory pathway. However, PrPΔF35 and PrPΔCD mutants led to death by different mechanisms sharing loss of alpha-cleavage and activation of caspase-3. Our data suggest that both gain-of-function and loss-of-function pathogenic mechanisms may be associated with N-terminal domains and may therefore contribute to neurotoxicity in prion disease. Dissecting the molecular response induced by PrPΔF35 may be the key to unravelling the physiological and pathological functions of the prion protein.

Keywords: Cellular prion protein, Neurotoxicity, Truncated prion protein

del Río, J. A., Gavín, R., (2016). Functions of the cellular prion protein, the end of Moore's law, and Ockham's razor theory Prion , 10, (1), 25-40

Since its discovery the cellular prion protein (encoded by the Prnp gene) has been associated with a large number of functions. The proposed functions rank from basic cellular processes such as cell cycle and survival to neural functions such as behavior and neuroprotection, following a pattern similar to that of Moore's law for electronics. In addition, particular interest is increasing in the participation of Prnp in neurodegeneration. However, in recent years a redefinition of these functions has begun, since examples of previously attributed functions were increasingly re-associated with other proteins. Most of these functions are linked to so-called “Prnp-flanking genes” that are close to the genomic locus of Prnp and which are present in the genome of some Prnp mouse models. In addition, their role in neuroprotection against convulsive insults has been confirmed in recent studies. Lastly, in recent years a large number of models indicating the participation of different domains of the protein in apoptosis have been uncovered. However, after more than 10 years of molecular dissection our view is that the simplest mechanistic model in PrPC-mediated cell death should be considered, as Ockham's razor theory suggested.

Keywords: Neurodegeneration, Prion, PrP

Requena, J. R., Kristensson, K., Korth, C., Zurzolo, C., Simmons, M., Aguilar-Calvo, P., Aguzzi, A., Andreoletti, O., Benestad, S. L., Böhm, R., Brown, K., Calgua, B., del Río, J. A., Espinosa, J. C., Girones, R., Godsave, S., Hoelzle, L. E., Knittler, M. R., Kuhn, F., Legname, G., Laeven, P., Mabbott, N., Mitrova, E., Müller-Schiffmann, A., Nuvolone, M., Peters, P. J., Raeber, A., Roth, K., Schmitz, M., Schroeder, B., Sonati, T., Stitz, L., Taraboulos, A., Torres, J. M., Yan, Z. X., Zerr, I., (2016). The Priority position paper: Protecting Europe's food chain from prions Prion , 10, (3), 165-181

Bovine spongiform encephalopathy (BSE) created a global European crisis in the 1980s and 90s, with very serious health and economic implications. Classical BSE now appears to be under control, to a great extent as a result of a global research effort that identified the sources of prions in meat and bone meal (MBM) and developed new animal-testing tools that guided policy. Priority ( was a European Union (EU) Framework Program 7 (FP7)-funded project through which 21 European research institutions and small and medium enterprises (SMEs) joined efforts between 2009 and 2014, to conduct coordinated basic and applied research on prions and prion diseases. At the end of the project, the Priority consortium drafted a position paper ( position paper) with its main conclusions. In the present opinion paper, we summarize these conclusions. With respect to the issue of re-introducing ruminant protein into the feed-chain, our opinion is that sustaining an absolute ban on feeding ruminant protein to ruminants is essential. In particular, the spread and impact of non-classical forms of scrapie and BSE in ruminants is not fully understood and the risks cannot be estimated. Atypical prion agents will probably continue to represent the dominant form of prion diseases in the near future in Europe. Atypical L-type BSE has clear zoonotic potential, as demonstrated in experimental models. Similarly, there are now data indicating that the atypical scrapie agent can cross various species barriers. More epidemiological data from large cohorts are necessary to reach any conclusion on the impact of its transmissibility on public health. Re-evaluations of safety precautions may become necessary depending on the outcome of these studies. Intensified searching for molecular determinants of the species barrier is recommended, since this barrier is key for important policy areas and risk assessment. Understanding the structural basis for strains and the basis for adaptation of a strain to a new host will require continued fundamental research, also needed to understand mechanisms of prion transmission, replication and how they cause nervous system dysfunction and death. Early detection of prion infection, ideally at a preclinical stage, also remains crucial for development of effective treatment strategies.

Keywords: Atypical BSE, Atypical scrapie, BSE, CJD, Prion, Scrapie

Moles, Ernest, Valle-Delgado, Juan José, Urbán, Patricia, Azcárate, Isabel G., Bautista, José M., Selva, Javier, Egea, Gustavo, Ventura, Salvador, Fernàndez-Busquets, Xavier, (2015). Possible roles of amyloids in malaria pathophysiology Future Science OA , 1, (2), FSO43

The main therapeutic and prophylactic tools against malaria have been locked for more than a century in the classical approaches of using drugs targeting metabolic processes of the causing agent, the protist Plasmodium spp., and of designing vaccines against chosen antigens found on the parasite’s surface. Given the extraordinary resources exhibited by Plasmodium to escape these traditional strategies, which have not been able to free humankind from the scourge of malaria despite much effort invested in them, new concepts have to be explored in order to advance toward eradication of the disease. In this context, amyloid-forming proteins and peptides found in the proteome of the pathogen should perhaps cease being regarded as mere anomalous molecules. Their likely functionality in the pathophysiology of Plasmodium calls for attention being paid to them as a possible Achilles’ heel of malaria. Here we will give an overview of Plasmodium-encoded amyloid-forming polypeptides as potential therapeutic targets and toxic elements, particularly in relation to cerebral malaria and the blood–brain barrier function. We will also discuss the recent finding that the genome of the parasite contains an astonishingly high proportion of prionogenic domains.

Keywords: Amyloids, Intrinsically unstructured proteins, Malaria, Prions

Vergara, C., Ordóñez-Gutiérrez, L., Wandosell, F., Ferrer, Isidro, del Río, J. A., Gavín, R., (2015). Role of PrPC expression in tau protein levels and phosphorylation in alzheimer's disease evolution Molecular Neurobiology 51, (3), 1206-1220

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 (PrPC) 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 PrPC expression in the development of AD, and a putative relationship between PrPC and tau processing is emerging. However, the role of tau/PrPC interaction in AD is poorly understood. In this study, we show increased susceptibility to Aβ-derived diffusible ligands (ADDLs) in neuronal primary cultures from PrPC knockout mice, compared to wild-type, which correlates with increased tau expression. Moreover, we found increased PrPC 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 PrPC 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.

Keywords: Aβ oligomers, Alzheimer's disease, Cellular prion protein, Microtubule-associated protein tau

Llorens, Franc, Zafar, Saima, Ansoleaga, Belén, Shafiq, Mohsin, Blanco, Rosi, Carmona, Marga, Grau-Rivera, Oriol, Nos, Carlos, Gelpí, Ellen, del Río, José Antonio, Zerr, Inga, Ferrer, Isidre, (2015). Subtype and regional regulation of prion biomarkers in sporadic Creutzfeldt-Jakob disease Neuropathology and Applied Neurobiology , 41, (5), 631-645

Aims Creutzfeldt-Jakob disease (CJD) is a rapid progressive neurological disease leading to dementia and death. Prion biomarkers are altered in the cerebrospinal fluid (CSF) of CJD patients, but the pathogenic mechanisms underlying these alterations are still unknown. The present study examined prion biomarker levels in the brain and CSF of sporadic CJD (sCJD) cases and their correlation with neuropathological lesion profiles. Methods The expression levels of 14-3-3, Tau, phospho-Tau and α-synuclein were measured in the CSF and brain of sCJD cases in a subtype- and region-specific manner. In addition, the activity of prion biomarker kinases, the expression levels of CJD hallmarks and the most frequent neuropathological sCJD findings were analysed. Results Prion biomarkers levels were increased in the CSF of sCJD patients; however, correlations between mRNA, total protein and their phosphorylated forms in brain were different. The observed downregulation of the main Tau kinase, GSK3, in sCJD brain samples may help to explain the differential phospho-Tau/Tau ratios between sCJD and other dementias in the CSF. Importantly, CSF biomarkers levels do not necessarily correlate with sCJD neuropathological findings. Interpretation Present findings indicate that prion biomarkers levels in sCJD tissues and their release into the CSF are differentially regulated following specific modulated responses, and suggest a functional role for these proteins in sCJD pathogenesis.

Keywords: Creutzfeldt-Jakob disease, Prion Protein, Cerebrospinal fluid, Prion Biomarkers, disease subtype, Glycogen synthase kinase 3

Ordoñez-Gutiérrez, L., Torres, J. M., Gavín, R., Antón, M., Arroba-Espinosa, A. I., Espinosa, J. C., Vergara, C., del Río, J. A., Wandosell, F., (2013). Cellular prion protein modulates β-amyloid deposition in aged APP/PS1 transgenic mice Neurobiology of Aging , 34, (12), 2793-2804

Alzheimer's disease and prion diseases are neuropathological disorders that are caused by abnormal processing and aggregation of amyloid and prion proteins. Interactions between amyloid precursor protein (APP) and PrPc proteins have been described at the neuron level. Accordingly to this putative interaction, we investigated whether β-amyloid accumulation may affect prion infectivity and, conversely, whether different amounts of PrP may affect β-amyloid accumulation. For this purpose, we used the APPswe/PS1dE9 mouse line, a common model of Alzheimer's disease, crossed with mice that either overexpress (Tga20) or that lack prion protein (knock-out) to generate mice that express varying amounts of prion protein and deposit β-amyloid. On these mouse lines, we investigated the influence of each protein on the evolution of both diseases. Our results indicated that although the presence of APP/PS1 and β-amyloid accumulation had no effect on prion infectivity, the accumulation of β-amyloid deposits was dependent on PrPc, whereby increasing levels of prion protein were accompanied by a significant increase in β-amyloid aggregation associated with aging.

Keywords: Aging, Amyloid, Neurodegeneration, Prion, Signaling

Llorens, F., Carulla, P., Villa, A., Torres, J. M., Fortes, P., Ferrer, Isidro, Del Río, J. A., (2013). PrPC regulates epidermal growth factor receptor function and cell shape dynamics in Neuro2a cells Journal of Neurochemistry , 127, (1), 124-138

The prion protein (PrP) plays a key role in prion disease pathogenesis. Although the misfolded and pathologic variant of this protein (PrPSC) has been studied in depth, the physiological role of PrPC remains elusive and controversial. PrPC is a cell-surface glycoprotein involved in multiple cellular functions at the plasma membrane, where it interacts with a myriad of partners and regulates several intracellular signal transduction cascades. However, little is known about the gene expression changes modulated by PrPC in animals and in cellular models. In this article, we present PrPC-dependent gene expression signature in N2a cells and its implication in the most overrepresented functions: cell cycle, cell growth and proliferation, and maintenance of cell shape. PrPC over-expression enhances cell proliferation and cell cycle re-entrance after serum stimulation, while PrPC silencing slows down cell cycle progression. In addition, MAP kinase and protein kinase B (AKT) pathway activation are under the regulation of PrPC in asynchronous cells and following mitogenic stimulation. These effects are due in part to the modulation of epidermal growth factor receptor (EGFR) by PrPC in the plasma membrane, where the two proteins interact in a multimeric complex. We also describe how PrPC over-expression modulates filopodia formation by Rho GTPase regulation mainly in an AKT-Cdc42-N-WASP-dependent pathway.

Keywords: Cell signaling, Cellular prion protein, Filopodia, Gene expression, Microarray, Proliferation

Llorens, F., Del Rio, J. A., (2012). Unraveling the neuroprotective mechanisms of PrPC in excitotoxicity Prion , 6, (3), 245-251

Knowledge of the natural roles of cellular prion protein (PrPC) is essential to an understanding of the molecular basis of prion pathologies. This GPIanchored protein has been described in synaptic contacts, and loss of its synaptic function in complex systems may contribute to the synaptic loss and neuronal degeneration observed in prionopathy. In addition, Prnp knockout mice show enhanced susceptibility to several excitotoxic insults, GABAA receptor-mediated fast inhibition was weakened, LTP was modified and cellular stress increased. Although little is known about how PrPC exerts its function at the synapse or the downstream events leading to PrPCmediated neuroprotection against excitotoxic insults, PrPC has recently been reported to interact with two glutamate receptor subunits (NR2D and GluR6/7). In both cases the presence of PrPC blocks the neurotoxicity induced by NMDA and Kainate respectively. Furthermore, signals for seizure and neuronal cell death in response to Kainate in Prnp knockout mouse are associated with JNK3 activity, through enhancing the interaction of GluR6 with PSD-95. In combination with previous data, these results shed light on the molecular mechanisms behind the role of PrPC in excitotoxicity. Future experimental approaches are suggested and discussed.

Keywords: Prion protein, Excitotoxicity, Neuroprotection, Glutamate receptors, Synapse, prionopathy

Carulla, Patricia, Bribian, Ana, Rangel, Alejandra, Gavin, Rosalina, Ferrer, Isidro, Caelles, Carme, Antonio del Rio, Jose, Llorens, Franc, (2011). Neuroprotective role of PrP(C) against kainate-induced epileptic seizures and cell death depends on the modulation of JNK3 activation by GluR6/7-PSD-95 binding Molecular Biology of the Cell , 22, (17), 3041-3054

Cellular prion protein (PrP(C)) is a glycosyl-phosphatidylinositol-anchored glycoprotein. When mutated or misfolded, the pathogenic form (PrP(SC)) induces transmissible spongiform encephalopathies. In contrast, PrP(C) has a number of physiological functions in several neural processes. Several lines of evidence implicate PrP(C) in synaptic transmission and neuroprotection since its absence results in an increase in neuronal excitability and enhanced excitotoxicity in vitro and in vivo. Furthermore, PrP(C) has been implicated in the inhibition of N-methyl-D-aspartic acid (NMDA)-mediated neurotransmission, and prion protein gene (Prnp) knockout mice show enhanced neuronal death in response to NMDA and kainate (KA). In this study, we demonstrate that neurotoxicity induced by KA in Prnp knockout mice depends on the c-Jun N-terminal kinase 3 (JNK3) pathway since Prnp(%) Jnk3(%) mice were not affected by KA. Pharmacological blockage of JNK3 activity impaired PrP(C)-dependent neurotoxicity. Furthermore, our results indicate that JNK3 activation depends on the interaction of PrP(C) with postsynaptic density 95 protein (PSD-95) and glutamate receptor 6/7 (GluR6/7). Indeed, GluR6-PSD-95 interaction after KA injections was favored by the absence of PrP(C). Finally, neurotoxicity in Prnp knockout mice was reversed by an AMPA/KA inhibitor (6,7-dinitroquinoxaline-2,3-dione) and the GluR6 antagonist NS-102. We conclude that the protection afforded by PrP(C) against KA is due to its ability to modulate GluR6/7-mediated neurotransmission and hence JNK3 activation.

Keywords: Ischemic brain-injury, Prion protein PrP(C), Stress-inducible protein-1, Synaptic plasticity, Neurite outgrowth, Signaling module, Caspase-3 activation, Organotypic cultures, Cerebral-ischemia

Gavín, R., Ferrer, Isidro, del Río, J. A., (2010). Involvement of Dab1 in APP processing and [beta]-amyloid deposition in sporadic Creutzfeldt-Jakob patients Neurobiology of Disease , 37, (2), 324-329

Alzheimer's disease and prion pathologies (e.g., Creutzfeldt-Jakob disease (CJD)) display profound neural lesions associated with aberrant protein processing and extracellular amyloid deposits. Dab1 has been implicated in the regulation of amyloid precursor protein (APP), but a direct link between human prion diseases and Dab1/APP interactions has not been published. Here we examined this putative relationship in 17 cases of sporadic CJD (sCJD) post-mortem. Biochemical analyses of brain tissue revealed two groups, which also correlated with PrPsc types 1 and 2. One group with PrPsc type 1 showed increased Dab1 phosphorylation and lower [beta]CTF production with an absence of A[beta] deposition. The second sCJD group, which carried PrPsc type 2, showed lower levels of Dab1 phosphorylation and [beta]CTF production, and A[beta] deposition. Thus, the present observations suggest a correlation between Dab1 phosphorylation, A[beta] deposition and PrPsc type in sCJD.

Keywords: Prionopathies, Amyloid plaques, Alzheimer's disease, Dab1

Nicolas, O., Gavin, R., Del Rio, J. A., (2009). New insights into cellular prion protein (PrPc) functions: The "ying and yang" of a relevant protein Brain Research Reviews , 61, (2), 170-184

The conversion of cellular prion protein (PrPc) a GPI-anchored protein, into a protease-K-resistant and infective form (generally termed PrPsc) is mainly responsible for Transmissible Spongiform Encephalopathies (TSEs), characterized by neuronal degeneration and progressive loss of basic brain functions. Although PrPc is expressed by a wide range of tissues throughout the body, the complete repertoire of its functions has not been fully deter-mined. Recent studies have confirmed its participation in basic physiological processes such as cell proliferation and the regulation of cellular homeostasis. Other studies indicate that PrPc interacts with several molecules to activate signaling cascades with a high number of cellular effects. To deter-mine PrPc functions, transgenic mouse models have been generated in the last decade. In particular, mice lacking specific domains of the PrPc protein have revealed the contribution of these domains to neurodegenerative processes. A dual role of PrPc has been shown, since most authors report protective roles for this protein while others describe pro-apoptotic functions. in this review, we summarize new findings on PrPc functions, especially those related to neural degeneration and cell signaling.

Keywords: Prion, Doppel, Shadoo, Cell death, Cell proliferation, Cell differentiation

Rangel, A., Madroñal, N., Gruart i Massó, A., Gavin,, Llorens, Sumoy, Torres, Delgado-Gar, Del Rio, J. A., (2009). Regulation of GABA(A) and glutamate receptor expression, synaptic facilitation and long-term potentiation in the hippocampus of prion mutant mice PLoS ONE 4, (10), e7592 (1-14)

Background: Prionopathies are characterized by spongiform brain degeneration, myoclonia, dementia, and periodic electroencephalographic (EEG) disturbances. The hallmark of prioniopathies is the presence of an abnormal conformational isoform (PrPsc) of the natural cellular prion protein (PrPc) encoded by the Prnp gene. Although several roles have been attributed to PrPc, its putative functions in neuronal excitability are unknown. Although early studies of the behavior of Prnp knockout mice described minor changes, later studies report altered behavior. To date, most functional PrPc studies on synaptic plasticity have been performed in vitro. To our knowledge, only one electrophysiological study has been performed in vivo in anesthetized mice, by Curtis and coworkers. They reported no significant differences in paired-pulse facilitation or LTP in the CA1 region after Schaffer collateral/commissural pathway stimulation. Methodology/Principal Findings: Here we explore the role of PrPc expression in neurotransmission and neural excitability using wild-type, Prnp 2/2 and PrPc-overexpressing mice (Tg20 strain). By correlating histopathology with electrophysiology in living behaving mice, we demonstrate that both Prnp 2/2 mice but, more relevantly Tg20 mice show increased susceptibility to KA, leading to significant cell death in the hippocampus. This finding correlates with enhanced synaptic facilitation in paired-pulse experiments and hippocampal LTP in living behaving mutant mice. Gene expression profiling using IlluminaTM microarrays and Ingenuity pathways analysis showed that 129 genes involved in canonical pathways such as Ubiquitination or Neurotransmission were co-regulated in Prnp 2/2 and Tg20 mice. Lastly, RT-qPCR of neurotransmission-related genes indicated that subunits of GABAA and AMPA-kainate receptors are co-regulated in both Prnp 2/2 and Tg20 mice. Conclusions/Significance: Present results demonstrate that PrPc is necessary for the proper homeostatic functioning of hippocampal circuits, because of its relationships with GABAA and AMPA-Kainate neurotransmission. New PrPc functions have recently been described, which point to PrPc as a target for putative therapies in Alzheimer’s disease. However, our results indicate that a ‘‘gain of function’’ strategy in Alzheimer’s disease, or a ‘‘loss of function’’ in prionopathies, may impair PrPc function, with devastating effects. In conclusion, we believe that present data should be taken into account in the development of future therapies.

Keywords: Prions, Prionopathies, Natural cellular prion protein (PrPc), Hippocampus, GABA (A) receptor, Glutamate Receptor

Bravo, R., Arimon, M., Valle-Delgado, J. J., Garcia, R., Durany, N., Castel, S., Cruz, M., Ventura, S., Fernàndez-Busquets, X., (2008). Sulfated polysaccharides promote the assembly of amyloid beta(1-42) peptide into stable fibrils of reduced cytotoxicity Journal of Biological Chemistry , 283, (47), 32471-32483

The histopathological hallmarks of Alzheimer disease are the self-aggregation of the amyloid beta peptide (A beta) in extracellular amyloid fibrils and the formation of intraneuronal Tau filaments, but a convincing mechanism connecting both processes has yet to be provided. Here we show that the endogenous polysaccharide chondroitin sulfate B (CSB) promotes the formation of fibrillar structures of the 42-residue fragment, A beta(1-42). Atomic force microscopy visualization, thioflavin T fluorescence, CD measurements, and cell viability assays indicate that CSB-induced fibrils are highly stable entities with abundant beta-sheet structure that have little toxicity for neuroblastoma cells. We propose a wedged cylinder model for A beta(1-42) fibrils that is consistent with the majority of available data, it is an energetically favorable assembly that minimizes the exposure of hydrophobic areas, and it explains why fibrils do not grow in thickness. Fluorescence measurements of the effect of different A beta(1-42) species on Ca2+ homeostasis show that weakly structured nodular fibrils, but not CSB-induced smooth fibrils, trigger a rise in cytosolic Ca2+ that depends on the presence of both extracellular and intracellular stocks. In vitro assays indicate that such transient, local Ca2+ increases can have a direct effect in promoting the formation of Tau filaments similar to those isolated from Alzheimer disease brains.

Keywords: AFM, Alzheimers-disease, Chondroitin sulfate, Heparan-sulfate, Lipid-bilayers, Beta-peptide, In-vitro, Neurodegenerative diseases, Extracellular-matrix, Prion protein