Tau Exon 10 Inclusion by PrPC through Downregulating GSK3β Activity

Tau protein is largely responsible for tauopathies, including Alzheimer's disease (AD), where it accumulates in the brain as insoluble aggregates. Tau mRNA is regulated by alternative splicing, and inclusion or exclusion of exon 10 gives rise to the 3R and 4R isoforms respectively, whose balance is physiologically regulated. In this sense, one of the several factors that regulate alternative splicing of tau is GSK3β, whose activity is inhibited by the cellular prion protein (PrPC), which has different physiological functions in neuroprotection and neuronal differentiation. Moreover, a relationship between PrPC and tau expression levels has been reported during AD evolution. For this reason, in this study we aimed to analyze the role of PrPC and the implication of GSK3β in the regulation of tau exon 10 alternative splicing. We used AD human samples and mouse models of PrPC ablation and tau overexpression. In addition, we used primary neuronal cultures to develop functional studies. Our results revealed a paralleled association between PrPC expression and tau 4R isoforms in all models analyzed. In this sense, reduction or ablation of PrPC levels induces an increase in tau 3R/4R balance. More relevantly, our data points to GSK3β activity downstream from PrPC in this phenomenon. Our results indicate that PrPC plays a role in tau exon 10 inclusion through the inhibitory capacity of GSK3β

Disease-specific changes in Reelin protein and mRNA in neurodegenerative diseases

Reelin is an extracellular glycoprotein that modulates neuronal function and synaptic plasticity in the adult brain. Decreased levels of Reelin activity have been postulated as a key factor during neurodegeneration in Alzheimer's disease (AD) and in aging. Thus, changes in levels of full-length Reelin and Reelin fragments have been revealed in cerebrospinal fluid (CSF) and in post-mortem brains samples of AD patients with respect to non-AD patients. However, conflicting studies have reported decreased or unchanged levels of full-length Reelin in AD patients compared to control (nND) cases in post-mortem brains and CSF samples. In addition, a compelling analysis of Reelin levels in neurodegenerative diseases other than AD is missing. In this study, we analyzed brain levels of RELN mRNA and Reelin protein in post-mortem frontal cortex samples from different sporadic AD stages, Parkinson's disease with dementia (PDD), and Creutzfeldt-Jakob disease (sCJD), obtained from five different Biobanks. In addition, we measured Reelin protein levels in CSF samples of patients with mild cognitive impairment (MCI), dementia, or sCJD diagnosis and a group of neurologically healthy cases. The results indicate an increase in RELN mRNA in the frontal cortex of advanced stages of AD and in sCJD(I) compared to controls. This was not observed in PDD and early AD stages. However, Reelin protein levels in frontal cortex samples were unchanged between nND and advanced AD stages and PDD. Nevertheless, they decreased in the CSF of patients with dementia in comparison to those not suffering with dementia and patients with MCI. With respect to sCJD, there was a tendency to increase in brain samples in comparison to nND and to decrease in the CSF with respect to nND. In conclusion, Reelin levels in CSF cannot be considered as a diagnostic biomarker for AD or PDD. However, we feel that the CSF Reelin changes observed between MCI, patients with dementia, and sCJD might be helpful in generating a biomarker signature in prodromal studies of unidentified dementia and sCJD

Regulación de la expresión de PrPc como elemento clave en las modificaciones de tau en la enfermedad de Alzheimer

[spa] La presente tesis doctoral se inició en septiembre de 2016 como continuación del estudio ya realizado en los años previos durante el desarrollo del trabajo de fin de grado en el curso 2014- 2015 y el trabajo de fin de máster en el curso 2015-2016. El proyecto está enmarcado en la línea de investigación del grupo del Dr. José Antonio del Río en el Instituto de Bioingeniería de Cataluña (IBEC) llevada a cabo por la Dra. Rosalina Gavín. Se basa en el análisis del papel que ejerce la proteína priónica celular (PrPC) en la enfermedad de Alzheimer y sus implicaciones en la neuroprotección del sistema nervioso. Estudios anteriores a mi vinculación demostraron algunas de las funciones que presenta la PrPC tanto a nivel patológico en las denominadas prionopatías, como a nivel fisiológico mediante el estudio de modelos animales de ratón carentes de PrPC. Del mismo modo, también se investigó acerca del péptido beta amiloide, uno de los responsables del desarrollo de la enfermedad, y se valoró el uso terapéutico de γ-péptidos derivados de prolina para evitar la acumulación aberrante de péptido beta amiloide en el cerebro. Sin embargo, mi tesis doctoral se centra en otro de los rasgos neuropatológicos característicos de la enfermedad, la proteína tau. Concretamente el trabajo realizado trata de comprender los principales mecanismos de regulación por los que tau y PrPC están interconectados en el contexto de la enfermedad de Alzheimer. Por un lado, nos propusimos como objetivo identificar los factores que impulsan a una mayor expresión de PrPC en estadios iniciales de la enfermedad y, por otro lado, aquellas condiciones que hacen decaer sus niveles en fases más avanzadas. De esta manera, se ampliará el conocimiento de las posibles moléculas que en un futuro puedan servir de diana terapéutica. Además, otro de los objetivos ha sido el de analizar la intervención de PrPC en procesos de modificación de la proteína tau que tienen gran relevancia en múltiples enfermedades neurodegenerativas como son las taupatías. Por ello, en esta tesis se resumirán los datos conocidos y los últimos avances de la enfermedad de Alzheimer y las dos proteínas mencionadas anteriormente, tau y PrPC, así como se aportará nueva información que se recoge en dos publicaciones adjuntas en el Anexo. La primera de las publicaciones corresponde al trabajo del Capítulo 1, mientras que el Capítulo 2 se encuentra en preparación para ser publicado

The quest for cellular prion protein functions in aged and neurodegenerative brain

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

<span style="color:black">miR-519a-3p, found to regulate cellular prion protein during Alzheimer’s disease pathogenesis, as a biomarker of asymptomatic stages. </span>

Clinical relevance of miRNAs as biomarkers is growing due to their stability and detection in biofluids. In this, diagnosis at asymptomatic stages of Alzheimer's disease (AD) remains a challenge since it can only be made at autopsy according to Braak NFT staging. Achieving the objective of detecting AD at early stages would allow possible therapies to be addressed before the onset of cognitive impairment. Many studies have determined that the expression pattern of some miRNAs is dysregulated in AD patients, but to date, none has been correlated with downregulated expression of cellular prion protein (PrPC) during disease progression. That is why, by means of cross studies of miRNAs up-regulated in AD with in silico identification of potential miRNAs-binding to 3'UTR of human PRNP gene, we selected miR-519a-3p for our study. Then, in vitro experiments were carried out in two ways. First, we validated miR-519a-3p target on 3'UTR-PRNP, and second, we analyzed the levels of PrPC expression after using of mimic technology on cell culture. In addition, RT-qPCR was performed to analyzed miR-519a-3p expression in human cerebral samples of AD at different stages of disease evolution. Additionally, samples of other neurodegenerative diseases such as other non-AD tauopathies and several synucleinopathies were included in the study. Our results showed that miR-519a-3p overlaps with PRNP 3'UTR in vitro and promotes downregulation of PrPC. Moreover, miR-519a-3p was found to be up-regulated exclusively in AD samples from stage I to VI, suggesting its potential use as a novel label of preclinical stages of the disease