Neurotoxicity of prion peptides mimicking the central domain of the cellular prion protein

The physiological functions of PrP(C) remain enigmatic, but the central domain, comprising highly conserved regions of the protein may play an important role. Indeed, a large number of studies indicate that synthetic peptides containing residues 106-126 (CR) located in the central domain (CD, 95-133) of PrP(C) are neurotoxic. The central domain comprises two chemically distinct subdomains, the charge cluster (CC, 95-110) and a hydrophobic region (HR, 112-133). The aim of the present study was to establish the individual cytotoxicity of CC, HR and CD. Our results show that only the CD peptide is neurotoxic. Biochemical, Transmission Electron Microscopy and Atomic Force Microscopy experiments demonstrated that the CD peptide is able to activate caspase-3 and disrupt the cell membrane, leading to cell death

iPS cell cultures from a Gerstmann-Straussler-Scheinker patient with the Y218N PRNP mutation recapitulate tau pathology

Gerstmann-Straussler-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

Papel regulador de la proteína priónica celular en la enfermedad de Alzheimer y uso de gamma-péptidos como potenciales agentes terapéuticos

[spa] La enfermedad de Alzheimer (EA) es la forma más común de demencia. Afecta, actualmente, a más de 30 millones de personas en todo el mundo, causando un gran impacto socioeconómico que aumenta año tras año con unos 7,7 millones de nuevos casos por año. La enfermedad de caracteriza por un deterioro cognitivo y cambios conductuales. A nivel patofisiológico se caracteriza por la acumulación del péptido beta-amiloide (Aß), y la proteína tau. La proteína tau es una proteína que se une a tubulina, estabilizando los microtúbulos y ayudando a su polimerización. En la enfermedad, la proteína se hiperfosforila, desestabilizando los microtúbulos por un lado, y auto-agregándose para formar filamentos helicoidales pareados y finalmente los ovillos neurofibrilares. La proteína precursora amiloide (APP), en la enfermedad, es procesada por beta- y gamma-secretasas, resultando en la formación del péptido beta-amiloide, en la vía amiloidogénica. Este péptido agrega dando lugar a las placas amiloides. Se ha descrito que los oligómeros, un estadio de agregación intermedio, son las formas más tóxicas, y que PrPC, que sea demostrado que se une con elevada afinidad a los oligómeros de Aß, podría ser un receptor y mediador de la toxicidad causada por éstos. PrPC es conocida por su participación en las enfermedades espongiformes transmisibles (EETs), en su forma patogénica llamada PrPSc, que se acumula en el cerebro formando agregados, aunque también se han encontrado agregados amiloides en estas enfermedades y una disminución de los niveles de PrPC. Esta proteína participa en procesos como la neuritogénesis o la transmisión sináptica, y hay evidencias de que podría tener una función neuroprotectora en el cerebro. Esta tesis doctoral aborda la participación de PrPC en la EA, des de diferentes puntos de vista, tanto en la acumulación del péptido Aß, como en la fosforilación de tau. Nuestros datos apuntan a una posible función neuroprotectora por parte de PrPC. Por un lado, hemos observado que PrPC podría regular la fosforilación de tau modulando los niveles de expresión de ésta, que se produce debido a los oligómeros de Aß, de forma específica, y no por los agregados insolubles y fibrilares. También hemos visto que, una sobreexpresión de PrPC correlaciona tanto con un aumento de la fosforilación de tau como con un aumento del depósito de Aß, apuntando a una posible pérdida de esta función neuroprotectora. También hemos estudiado la relación entre el péptido Aß y PrPC desde la perspectiva de las enfermedades espongiformes. Hay evidencias de PrPC regula los niveles de Aß en la EA, y debido a la presencia de agregados amiloides, y a una disminución de los niveles de PrPC en las EETs, nos planteamos el papel del depósito de Aß en la infectividad del prión. Nuestros resultados apuntan a que estos depósitos no afectan a la infectividad. Por último, a nivel terapéutico, existen tratamientos paliativos para la EA enfocados en compensar el desequilibrio en diferentes neurotransmisores como la acetilcolina o el glutamato. Estos tratamientos no consiguen frenar el avance de la enfermedad. Aunque muchas alternativas de diferentes clases están ahora en diferentes fases clínicas, algunas de ellas han presentado efectos secundarios como meningoencefalitis, y otras no han conseguido mejorar los síntomas en pacientes respecto a grupos control con placebo. Esta tesis aborda una posible alternativa a los tratamientos anti-amiloides actuales. A partir del screening de una librería de gamma-péptidos derivados de prolina, hemos identificado un candidato con propiedades relacionadas con la neuritogénesis, y una disminución de los niveles de Aß, por la modulación de la beta-secretasa BACE1.[eng] Alzheimer’s disease (AD) is the most common form of dementia. Nowadays, it affects more than 30 million people worldwide. The disease is characterised by cognitive impairment and behavioural changes. At the pathophysiological level, it is characterised by the accumulation of beta-amyloid peptide (Aß), and tau protein. Tau protein interacts with tubulin, stabilizing the microtubules and taking part in their polymerization. In the disease, the protein becomes hyperphosphorylated destabilizing the microtubules, and self-aggregates to form paired helical filaments (PHF), and later neurofibrillary tangles (NFT). The amyloid precursor protein (APP), in the disease is processed by beta- and gamma-secretases, resulting in the formation of Aß peptide, in the amyloidogenic pathway, that aggregates forming amyloid plaques. It has been described that oligomeric forms, an intermediate aggregation state, are the most toxic species, and PrPC, that has been described of as having high affinity for Aß oligomers, could be a receptor and a mediator of their toxicity. PrPC is known for its participation in transmissible spongiform diseases (TSEs), in its pathogenic form called PrPSc, that accumulates in the brain forming aggregates, although amyloid aggregates and a decrease in PrPC levels have also been found. This protein takes part in processes like neuritogenesis or synaptic transmission, and there are evidences that it could have a neuroprotective role in the brain. We have studied the participation of PrPC in AD, in the accumulation Aß, as well as in tau phosphorylation. Our results point to a possible neuroprotective function of PrPC. On the one hand, we have observed that PrPC would regulate tau phosphorylation, caused by oligomeric forms of Aß specifically, and not by insoluble and fibrillary aggregates, by modulating tau expression levels. We have also seen that an overexpression of PrPC correlates with an increase in tau phosphorylation but also with an increase in Aß deposit, pointing to a possible loss of its neuroprotective function. We have also studied the relation between Aß and PrPC, in TSEs. There are evidences that PrPC regulates Aß levels in AD, and, as there are amyloid aggregates and a decrease in PrPC levels in TSEs, we addressed the role of Aß deposit in prion infectivity. Our results suggest that those deposits do not affect infectivity. Finally, from a therapeutic point of view, there are only palliative treatments for AD, focused on compensating neurotransmitters that are not well regulated in the brain, like acetylcholine or glutamate. Although there are a lot of alternatives in different clinical phases, some of them showed secondary effects like meningoencephalitis, while others did not improve symptoms in patients. In this work, we suggest an alternative from the screening of a library formed by proline-derived gamma-peptides, from which we have identified a candidate with properties related with neuritogenesis, and a decrease in Aß levels by modulating beta-secretasa BACE1

Funcions de les molècules associades a la mielina i la proteïna priònica cel•lular (PrPc) en neurodegeneració (Malaltia d’Alzheimer) i neuroinflamació (Esclerosi Múltiple)

Les proteïnes associades a la mielina (MAIS), Nogo-A, MAG i OMgp, són molècules que presenten una capacitat inhibitòria molt important per el recreixement axonal i la neuroreparació després de lesió. No obstant des de fa anys les seves funcions han estat ampliades i s’han involucrat en diferents processos degeneratius del sistema nerviós o en processos neuroinflamatoris del sistema nerviós central i el perifèric com ara l'Escleresi Múltiple (MS). La base neurobiològica d’indicadors moleculars que són responsables del dany axonal en MS segueixen sense estar plenament descrits. Recentment s’ha publicat que el mecanisme de senyalització Nogo-A pot regir els primers canvis de la desmielinització immunomediada del sistema nerviós central en el model animal de MS, l’encefalomielitis autoimmune experimental (EAE). De la mateixa forma la proteïna priònica cel•lular és una proteïna que s’ha associat majoritàriament a malalties espongiformes, però que recentment s’ha vinculat (no sense controvèrsia) amb la seva possible relació amb la Malaltia d'Alzheimer (AD), ja que seria capaç de reclutar els oligòmers d’Aβ (ADDLs), els quals correlacionen millor amb el grau de demència, i amb els que interacciona directament, actuant així com un possible mediador de la fosforilació de tau en la malaltia. No obstant, les funcions de les MAIS i de la PrPc en aquests models de la malaltia no estan clarament definits i, per altra banda, es desconeixen els mecanismes de senyalització implicats, no descartant de forma clara el component neural i l’immune.Myelin associated proteins (MAIS), Nogo-A, MAG and OMgp, are molecules that have a great inhibitory capacity which is very important for the axonal regrowth and neurorepair after injury. However, their functions have been increased and have been involved in different degenerative processes of the nervous system or in neuroinflamatory processes of the central nervous system (CNS) and peripheral nervous system (PNS) like Multiple Sclerosis (MS). The neurologic basis of molecular markers that are responsible of the axonal injury in MS, are still not fully described. Recently, it has basis of molecular markers that are responsible of the axonal injury in MS, are still not fully described. Recently, it has been published that the mechanism of Nogo-A signalling can trigger the first changes in the loss of myelin in the CNS in the animal model of MS, called Experimental Autoimmune Encephalomyelitis (EAE). Moreover, the Cellular Prion the animal model of MS, called Experimental Autoimmune Encephalomyelitis (EAE). Moreover, the Cellular Prion Protein (PrPc) has been mostly associated with spongiform diseases. Recently it has been connected with Alzheimer’s Disease (AD), being able to interact directly with β-Amyloid oligomers, which correlate better with the degree of the Disease (AD), being able to interact directly with β-Amyloid oligomers, which correlate better with the degree of the disease, and may act as a mediator in the phosphorylation of Tau in AD. Nevertheless, the functions of MAIS and PrPc in those models of disease are not clearly understood, and, on the other hand, the mechanisms implied in the signalling are unknown