Publications

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 (PrP C ) 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 PrP C expression after using of mimic technology on cell culture. In addition, RT-qPCR was performed to analyzed miR519a-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 PrP C . 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.

JTD Keywords: Activation, Alzheimer's disease, Biomarke, Brain, Cellular prion protein, Developmental expression, Gen, Micrornas, Plasma, Prpc, Tau-aggregation

Background Cellular prion protein (PrP(C)) is a cell surface GPI-anchored protein, usually known for its role in the pathogenesis of human and animal prionopathies. However, increasing knowledge about the participation of PrP(C) in prion pathogenesis contrasts with puzzling data regarding its natural physiological role. PrP(C) is expressed in a number of tissues, including at high levels in the nervous system, especially in neurons and glial cells, and while previous studies have established a neuroprotective role, conflicting evidence for a synaptic function has revealed both reduced and enhanced long-term potentiation, and variable observations on memory, learning, and behavior. Such evidence has been confounded by the absence of an appropriate knock-out mouse model to dissect the biological relevance of PrP(C), with some functions recently shown to be misattributed to PrP(C) due to the presence of genetic artifacts in mouse models. Here we elucidate the role of PrP(C) in the hippocampal circuitry and its related functions, such as learning and memory, using a recently available strictly co-isogenic Prnp(0/0) mouse model (Prnp(ZH3/ZH3)). Results We performed behavioral and operant conditioning tests to evaluate memory and learning capabilities, with results showing decreased motility, impaired operant conditioning learning, and anxiety-related behavior in Prnp(ZH3/ZH3) animals. We also carried in vivo electrophysiological recordings on CA3-CA1 synapses in living behaving mice and monitored spontaneous neuronal firing and network formation in primary neuronal cultures of Prnp(ZH3/ZH3) vs wildtype mice. PrP(C) absence enhanced susceptibility to high-intensity stimulations and kainate-induced seizures. However, long-term potentiation (LTP) was not enhanced in the Prnp(ZH3/ZH3) hippocampus. In addition, we observed a delay in neuronal maturation and network formation in Prnp(ZH3/ZH3) cultures. Conclusion Our results demonstrate that PrP(C) promotes neuronal network formation and connectivity. PrP(C) mediates synaptic function and protects the synapse from excitotoxic insults. Its deletion may underlie an epileptogenic-susceptible brain that fails to perform highly cognitive-demanding tasks such as associative learning and anxiety-like behaviors.

JTD Keywords: anxiety, behavior, cellular prion protein, epilepsy, hippocampus, Anxiety, Behavior, Cellular prion protein, Developmental expression, Epilepsy, Gene-expression, Hippocampus, Kainate-induced seizures, Lacking, Ltp, Memory, Messenger-rna, Motor behavior, Mouse, Prp

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 GSK3?, 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 GSK3? 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 GSK3? 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 GSK3?. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

JTD Keywords: alternative splicing, alzheimer's disease, alzheimers-disease, alzheimer’s disease, amyloid-beta, cellular prion protein, frontotemporal dementia, glycogen-synthase kinase-3, gsk3 beta, gsk3?, gsk3β, messenger-rna, microtubule-associated protein tau, neurofibrillary tangles, progressive supranuclear palsy, promotes neuronal differentiation, stem-cells, tauopathies, Alternative splicing, Alzheimer’s disease, Cellular prion protein, Gsk3?, Microtubule-associated protein tau, Tauopathies

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.

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

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..

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

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.

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

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.

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

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.

JTD Keywords: Cellular prion protein, Neurotoxicity, Truncated prion protein

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.

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

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.

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

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.

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