Nucleolin: a cell portal for viruses, bacteria, and toxins.

The main localization of nucleolin is the nucleolus, but this protein is present in multiple subcellular sites, and it is unconventionally secreted. On the cell surface, nucleolin acts as a receptor for various viruses, some bacteria, and some toxins. Aim of this review is to discuss the characteristics that make nucleolin able to act as receptor or co-receptor of so many and different pathogens. The important features that emerge are its multivalence, and its role as a bridge between the cell surface and the nucleus. Multiple domains, short linear motifs and post-translational modifications confer and modulate nucleolin ability to interact with nucleic acids, with proteins, but also with carbohydrates and lipids. This modular multivalence allows nucleolin to participate in different types of biomolecular condensates and to move to various subcellular locations, where it can act as a kind of molecular glue. It moves from the nucleus to the cell surface and can accompany particles in the reverse direction, from the cell surface into the nucleus, which is the destination of several pathogens to manipulate the cell in their favour.

Structural Integrity of Nucleolin Is Required to Suppress TDP-43-Mediated Cytotoxicity in Yeast and Human Cell Models.

The Transactivating response (TAR) element DNA-binding of 43 kDa (TDP-43) is mainly implicated in the regulation of gene expression, playing multiple roles in RNA metabolism. Pathologically, it is implicated in amyotrophic lateral sclerosis and in a class of neurodegenerative diseases broadly going under the name of frontotemporal lobar degeneration (FTLD). A common hallmark of most forms of such diseases is the presence of TDP-43 insoluble inclusions in the cell cytosol. The molecular mechanisms of TDP-43-related cell toxicity are still unclear, and the contribution to cell damage from either loss of normal TDP-43 function or acquired toxic properties of protein aggregates is yet to be established. Here, we investigate the effects on cell viability of FTLD-related TDP-43 mutations in both yeast and mammalian cell models. Moreover, we focus on nucleolin (NCL) gene, recently identified as a genetic suppressor of TDP-43 toxicity, through a thorough structure/function characterization aimed at understanding the role of NCL domains in rescuing TDP-43-induced cytotoxicity. Using functional and biochemical assays, our data demonstrate that the N-terminus of NCL is necessary, but not sufficient, to exert its antagonizing effects on TDP-43, and further support the relevance of the DNA/RNA binding central region of the protein. Concurrently, data suggest the importance of the NCL nuclear localization for TDP-43 trafficking, possibly related to both TDP-43 physiology and toxicity.

Perturbations of the Proteome and of Secreted Metabolites in Primary Astrocytes from the hSOD1(G93A) ALS Mouse Model.

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease whose pathophysiology is largely unknown. Despite the fact that motor neuron (MN) death is recognized as the key event in ALS, astrocytes dysfunctionalities and neuroinflammation were demonstrated to accompany and probably even drive MN loss. Nevertheless, the mechanisms priming astrocyte failure and hyperactivation are still obscure. In this work, altered pathways and molecules in ALS astrocytes were unveiled by investigating the proteomic profile and the secreted metabolome of primary spinal cord astrocytes derived from transgenic ALS mouse model overexpressing the human (h)SOD1(G93A) protein in comparison with the transgenic counterpart expressing hSOD1(WT) protein. Here we show that ALS primary astrocytes are depleted of proteins-and of secreted metabolites-involved in glutathione metabolism and signaling. The observed increased activation of Nf-kB, Ebf1, and Plag1 transcription factors may account for the augmented expression of proteins involved in the proteolytic routes mediated by proteasome or endosome-lysosome systems. Moreover, hSOD1(G93A) primary astrocytes also display altered lipid metabolism. Our results provide novel insights into the altered molecular pathways that may underlie astrocyte dysfunctionalities and altered astrocyte-MN crosstalk in ALS, representing potential therapeutic targets to abrogate or slow down MN demise in disease pathogenesis.

Regulation of Endoplasmic Reticulum-Mitochondria Tethering and Ca2+ Fluxes by TDP-43 via GSK3ß.

Mitochondria-ER contacts (MERCs), tightly regulated by numerous tethering proteins that act as molecular and functional connections between the two organelles, are essential to maintain a variety of cellular functions. Such contacts are often compromised in the early stages of many neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS). TDP-43, a nuclear protein mainly involved in RNA metabolism, has been repeatedly associated with ALS pathogenesis and other neurodegenerative diseases. Although TDP-43 neuropathological mechanisms are still unclear, the accumulation of the protein in cytoplasmic inclusions may underlie a protein loss-of-function effect. Accordingly, we investigated the impact of siRNA-mediated TDP-43 silencing on MERCs and the related cellular parameters in HeLa cells using GFP-based probes for MERCs quantification and aequorin-based probes for local Ca2+ measurements, combined with targeted protein and mRNA profiling. Our results demonstrated that TDP-43 down-regulation decreases MERCs density, thereby remarkably reducing mitochondria Ca2+ uptake after ER Ca2+ release. Thorough mRNA and protein analyses did not highlight altered expression of proteins involved in MERCs assembly or Ca2+-mediated ER-mitochondria cross-talk, nor alterations of mitochondrial density and morphology were observed by confocal microscopy. Further mechanistic inspections, however, suggested that the observed cellular alterations are correlated to increased expression/activity of GSK3ß, previously associated with MERCs disruption.

Microglia in Prion Diseases: Angels or Demons?

Prion diseases are rare transmissible neurodegenerative disorders caused by the accumulation of a misfolded isoform (PrPSc) of the cellular prion protein (PrPC) in the central nervous system (CNS). Neuropathological hallmarks of prion diseases are neuronal loss, astrogliosis, and enhanced microglial proliferation and activation. As immune cells of the CNS, microglia participate both in the maintenance of the normal brain physiology and in driving the neuroinflammatory response to acute or chronic (e.g., neurodegenerative disorders) insults. Microglia involvement in prion diseases, however, is far from being clearly understood. During this review, we summarize and discuss controversial findings, both in patient and animal models, suggesting a neuroprotective role of microglia in prion disease pathogenesis and progression, or-conversely-a microglia-mediated exacerbation of neurotoxicity in later stages of disease. We also will consider the active participation of PrPC in microglial functions, by discussing previous reports, but also by presenting unpublished results that support a role for PrPC in cytokine secretion by activated primary microglia.

The prion protein regulates glutamate-mediated Ca2+ entry and mitochondrial Ca2+ accumulation in neurons.

The cellular prion protein (PrPC) whose conformational misfolding leads to the production of deadly prions, has a still-unclarified cellular function despite decades of intensive research. Following our recent finding that PrPC limits Ca2+ entry via store-operated Ca2+ channels in neurons, we investigated whether the protein could also control the activity of ionotropic glutamate receptors (iGluRs). To this end, we compared local Ca2+ movements in primary cerebellar granule neurons and cortical neurons transduced with genetically encoded Ca2+ probes and expressing, or not expressing, PrPC Our investigation demonstrated that PrPC downregulates Ca2+ entry through each specific agonist-stimulated iGluR and after stimulation by glutamate. We found that, although PrP-knockout (KO) mitochondria were displaced from the plasma membrane, glutamate addition resulted in a higher mitochondrial Ca2+ uptake in PrP-KO neurons than in their PrPC-expressing counterpart. This was because the increased Ca2+ entry through iGluRs in PrP-KO neurons led to a parallel increase in Ca2+-induced Ca2+ release via ryanodine receptor channels. These data thus suggest that PrPC takes part in the cell apparatus controlling Ca2+ homeostasis, and that PrPC is involved in protecting neurons from toxic Ca2+ overloads.

ALS-Associated SOD1(G93A) Decreases SERCA Pump Levels and Increases Store-Operated Ca2+ Entry in Primary Spinal Cord Astrocytes from a Transgenic Mouse Model.

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder characterized by the selective death of motor neurons (MNs), probably by a combination of cell- and non-cell-autonomous processes. The past decades have brought many important insights into the role of astrocytes in nervous system function and disease, including the implication in ALS pathogenesis possibly through the impairment of Ca2+-dependent astrocyte-MN cross-talk. In this respect, it has been recently proposed that altered astrocytic store-operated Ca2+ entry (SOCE) may underlie aberrant gliotransmitter release and astrocyte-mediated neurotoxicity in ALS. These observations prompted us to a thorough investigation of SOCE in primary astrocytes from the spinal cord of the SOD1(G93A) ALS mouse model in comparison with the SOD1(WT)-expressing controls. To this purpose, we employed, for the first time in the field, genetically-encoded Ca2+ indicators, allowing the direct assessment of Ca2+ fluctuations in different cell domains. We found increased SOCE, associated with decreased expression of the sarco-endoplasmic reticulum Ca2+-ATPase and lower ER resting Ca2+ concentration in SOD1(G93A) astrocytes compared to control cells. Such findings add novel insights into the involvement of astrocytes in ALS MN damage.

The Link of the Prion Protein with Ca2+ Metabolism and ROS Production, and the Possible Implication in Aß Toxicity.

The cellular prion protein (PrPC) is an ubiquitous cell surface protein mostly expressed in neurons, where it localizes to both pre- and post-synaptic membranes. PrPC aberrant conformers are the major components of mammalian prions, the infectious agents responsible for incurable neurodegenerative disorders. PrPC was also proposed to bind aggregated misfolded proteins/peptides, and to mediate their neurotoxic signal. In spite of long-lasting research, a general consensus on the precise pathophysiologic mechanisms of PrPC has not yet been reached. Here we review our recent data, obtained by comparing primary neurons from PrP-expressing and PrP-knockout mice, indicating a central role of PrPC in synaptic transmission and Ca2+ homeostasis. Indeed, by controlling gene expression and signaling cascades, PrPC is able to optimize glutamate secretion and regulate Ca2+ entry via store-operated channels and ionotropic glutamate receptors, thereby protecting neurons from threatening Ca2+ overloads and excitotoxicity. We will also illustrate and discuss past and unpublished results demonstrating that Aß oligomers perturb Ca2+ homeostasis and cause abnormal mitochondrial accumulation of reactive oxygen species by possibly affecting the PrP-dependent downregulation of Fyn kinase activity.

Absolute quantification of myosin heavy chain isoforms by selected reaction monitoring can underscore skeletal muscle changes in a mouse model of amyotrophic lateral sclerosis.

Skeletal muscle fibers contain different isoforms of myosin heavy chain (MyHC) that define distinctive contractile properties. In light of the muscle capacity to adapt MyHC expression to pathophysiological conditions, a rapid and quantitative assessment of MyHC isoforms in small muscle tissue quantities would represent a valuable diagnostic tool for (neuro)muscular diseases. As past protocols did not meet these requirements, in the present study we applied a targeted proteomic approach based on selected reaction monitoring that allowed the absolute quantification of slow and fast MyHC isoforms in different mouse skeletal muscles with high reproducibility. This mass-spectrometry-based method was validated also in a pathological specimen, by comparison of the MyHC expression profiles in different muscles from healthy mice and a genetic mouse model of amyotrophic lateral sclerosis (ALS) expressing the SOD1(G93A) mutant. This analysis showed that terminally ill ALS mice have a fast-to-slow shift in the fiber type composition of the tibialis anterior and gastrocnemius muscles, as previously reported. These results will likely open the way to accurate and rapid diagnoses of human (neuro)muscular diseases by the proposed method. Graphical Abstract Methods for myosin heavy chain (MyHC) quantification: a comparison of classical methods and selected reaction monitoring (SRM)-based mass spectrometry approaches.

Age-dependent neuromuscular impairment in prion protein knockout mice.

INTRODUCTION: The cellular prion protein (PrP(C) ) is commonly recognized as the precursor of prions, the infectious agents of the fatal transmissible spongiform encephalopathies, or prion diseases. Despite extensive effort, the physiological role of PrP(C) is still ambiguous. Evidence has suggested that PrP(C) is involved in different cellular functions, including peripheral nerve integrity and skeletal muscle physiology. METHODS: We analyzed the age-dependent influence of PrP(C) on treadmill test-based aerobic exercise capacity and on a series of morphological and metabolic parameters using wild-type and genetically modified mice of different ages expressing, or knockout (KO) for, PrP(C) . RESULTS: We found that aged PrP-KO mice displayed a reduction in treadmill performance compared with PrP-expressing animals, which was associated with peripheral nerve demyelination and alterations of skeletal muscle fiber type. CONCLUSION: PrP-KO mice have an age-dependent impairment of aerobic performance as a consequence of specific peripheral nerve and muscle alterations.

Essential Oil Molecules Can Break the Loop of Oxidative Stress in Neurodegenerative Diseases.

Essential oils (EOs) are mixtures of volatile compounds, extracted from aromatic plants, with multiple activities including antioxidant and anti-inflammatory ones. EOs are complex mixtures easy to find on the market and with low costs. In this mini narrative review, we have collected the results of in vitro and in vivo studies, which tested these EOs on validated models of neurodegeneration and in particular of the two main neurodegenerative diseases (NDs) that afflict humans: Alzheimer's and Parkinson's. Since EO compositions can vary greatly, depending on the environmental conditions, plant cultivar, and extraction methods, we focused our attention to studies involving single EO molecules, and in particular those that have demonstrated the ability to cross the blood-brain barrier. These single EO molecules, alone or in defined mixtures, could be interesting new therapies to prevent or slow down oxidative and inflammatory processes which are common mechanisms that contribute to neuronal death in all NDs.

Secreted Metabolome of ALS-Related hSOD1(G93A) Primary Cultures of Myocytes and Implications for Myogenesis.

Amyotrophic lateral sclerosis (ALS) is a motor neuron (MN) disease associated with progressive muscle atrophy, paralysis, and eventually death. Growing evidence demonstrates that the pathological process leading to ALS is the result of multiple altered mechanisms occurring not only in MNs but also in other cell types inside and outside the central nervous system. In this context, the involvement of skeletal muscle has been the subject of a few studies on patients and ALS animal models. In this work, by using primary myocytes derived from the ALS transgenic hSOD1(G93A) mouse model, we observed that the myogenic capability of such cells was defective compared to cells derived from control mice expressing the nonpathogenic hSOD1(WT) isoform. The correct in vitro myogenesis of hSOD1(G93A) primary skeletal muscle cells was rescued by the addition of a conditioned medium from healthy hSOD1(WT) myocytes, suggesting the existence of an in trans activity of secreted factors. To define a dataset of molecules participating in such safeguard action, we conducted comparative metabolomic profiling of a culture medium collected from hSOD1(G93A) and hSOD1(WT) primary myocytes and report here an altered secretion of amino acids and lipid-based signaling molecules. These findings support the urgency of better understanding the role of the skeletal muscle secretome in the regulation of the myogenic program and mechanisms of ALS pathogenesis and progression.

Pllans-II: Unveiling the Action Mechanism of a Promising Chemotherapeutic Agent Targeting Cervical Cancer Cell Adhesion and Survival Pathways.

Despite advances in chemotherapeutic drugs used against cervical cancer, available chemotherapy treatments adversely affect the patient's quality of life. For this reason, new molecules from natural sources with antitumor potential and few side effects are required. In previous research, Pllans-II, a phospholipase A2 type-Asp49 from Porthidium lansbergii lansbergii snake venom, has shown selective attack against the HeLa and Ca Ski cervical cancer cell lines. This work suggests that the cytotoxic effect generated by Pllans-II on HeLa cells is triggered without affecting the integrity of the cytoplasmic membrane or depolarizing the mitochondrial membranes. The results allow us to establish that cell death in HeLa is related to the junction blockage between α5ß1 integrins and fibronectin of the extracellular matrix. Pllans-II reduces the cells' ability of adhesion and affects survival and proliferation pathways mediated by intracellular communication with the external environment. Our findings confirmed Pllans-II as a potential prototype for developing a selective chemotherapeutic drug against cervical cancer.

SOD1 in ALS: Taking Stock in Pathogenic Mechanisms and the Role of Glial and Muscle Cells.

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder characterized by the loss of motor neurons in the brain and spinal cord. While the exact causes of ALS are still unclear, the discovery that familial cases of ALS are related to mutations in the Cu/Zn superoxide dismutase (SOD1), a key antioxidant enzyme protecting cells from the deleterious effects of superoxide radicals, suggested that alterations in SOD1 functionality and/or aberrant SOD1 aggregation strongly contribute to ALS pathogenesis. A new scenario was opened in which, thanks to the generation of SOD1 related models, different mechanisms crucial for ALS progression were identified. These include excitotoxicity, oxidative stress, mitochondrial dysfunctions, and non-cell autonomous toxicity, also implicating altered Ca2+ metabolism. While most of the literature considers motor neurons as primary target of SOD1-mediated effects, here we mainly discuss the effects of SOD1 mutations in non-neuronal cells, such as glial and skeletal muscle cells, in ALS. Attention is given to the altered redox balance and Ca2+ homeostasis, two processes that are strictly related with each other. We also provide original data obtained in primary myocytes derived from hSOD1(G93A) transgenic mice, showing perturbed expression of Ca2+ transporters that may be responsible for altered mitochondrial Ca2+ fluxes. ALS-related SOD1 mutants are also responsible for early alterations of fundamental biological processes in skeletal myocytes that may impinge on skeletal muscle functions and the cross-talk between muscle cells and motor neurons during disease progression.

Cellular prion protein is implicated in the regulation of local Ca2+ movements in cerebellar granule neurons.

The cellular prion protein (PrP(C)) is a cell-surface glycoprotein mainly expressed in the CNS. The structural conversion of PrP(C) generates the prion, the infectious agent causing transmissible spongiform encephalopathies, which are rare and fatal diseases affecting animals and humans. Despite decades of intensive research, the mechanism of prion-associated neurodegeneration and the physiologic role of PrP(C) are still obscure. Recent evidence, however, supports the hypothesis that PrP(C) may be involved in the control of Ca(2+) homeostasis. Given the universal significance of Ca(2+) as an intracellular messenger for both the life and death of cells, this possibility may help explain the complex, often controversial, dataset accumulated on PrP(C) physiology, and the events leading to prion-associated neuronal demise. In this study, we have compared local Ca(2+) movements in cerebellar granule neurons (CGN) derived from wild-type (WT), or PrP-knockout (KO), mice, by means of the Ca(2+)-sensitive photo-probe, aequorin, genetically targeted to specific intracellular domains and delivered to CGN by lentiviral vectors. The use of an aequorin that localizes to the cytosolic domains proximal to the plasma membrane has allowed us to demonstrate that there was a dramatic increase of store-operated Ca(2+) entry in PrP-KO CGN compared to WT neurons. Notably, this phenotype was rescued upon restoring PrP(C) expression. The Ca(2+)-phenotype of PrP-KO neurons can in part be explained by the lower expression of two major Ca(2+)-extruding proteins, namely the plasma membrane and the sarco-endoplasmic reticulum Ca(2+)-ATPases. The lower sarco-endoplasmic reticulum Ca(2+)-ATPase content may also contribute to explain why PrP-KO CGN accumulated less Ca(2+) in the endoplasmic reticulum than the WT counterpart.

The cellular prion protein is expressed in olfactory sensory neurons of adult mice but does not affect the early events of the olfactory transduction pathway.

A conformational conversion of the cellular prion protein (PrP(C)) is now recognized as the causal event of fatal neurodegenerative disorders, known as prion diseases. In spite of long-lasting efforts, however, the physiological role of PrP(C) remains unclear. It has been reported that PrP(C) is expressed in various areas of the olfactory system, including the olfactory epithelium, but its precise localization in olfactory sensory neurons (OSNs) is still debated. Here, using immunohistochemistry tools, we have reinvestigated the expression and localization of PrP(C) in the olfactory epithelium of adult congenic mice expressing different PrP(C) amounts, that is, wild-type, PrP-knockout, and transgenic PrP(C)-overexpressing animals. We found that PrP(C) was expressed in OSNs, in which, however, it was unevenly distributed, being detectable at low levels in cell bodies, dendrites and apical layer, and more abundantly in axons. We also studied the involvement of PrP(C) in the response of the olfactory epithelium to odorants, by comparing the electro-olfactograms of the 3 mouse lines subjected to different stimulation protocols. We found no significant difference between the 3 PrP genotypes, supporting previous reports that exclude a direct action of PrP(C) in the early signal transduction activity of the olfactory epithelium.

Nucleolin Rescues TDP-43 Toxicity in Yeast and Human Cell Models.

TDP-43 is a nuclear protein involved in pivotal processes, extensively studied for its implication in neurodegenerative disorders. TDP-43 cytosolic inclusions are a common neuropathologic hallmark in amyotrophic lateral sclerosis (ALS) and related diseases, and it is now established that TDP-43 misfolding and aggregation play a key role in their etiopathology. TDP-43 neurotoxic mechanisms are not yet clarified, but the identification of proteins able to modulate TDP-43-mediated damage may be promising therapeutic targets for TDP-43 proteinopathies. Here we show by the use of refined yeast models that the nucleolar protein nucleolin (NCL) acts as a potent suppressor of TDP-43 toxicity, restoring cell viability. We provide evidence that NCL co-expression is able to alleviate TDP-43-induced damage also in human cells, further supporting its beneficial effects in a more consistent pathophysiological context. Presented data suggest that NCL could promote TDP-43 nuclear retention, reducing the formation of toxic cytosolic TDP-43 inclusions.

Cross-talk between PDGF and S1P signalling elucidates the inhibitory effect and potential antifibrotic action of the immunomodulator FTY720 in activated HSC-cultures.

Platelet-derived growth factor (PDGF) has been shown to be essential in the activation of hepatic stellate cells (HSCs), contributing to the onset and development of hepatic fibrosis. Recently, sphingosine-1-phosphate (S1P) has been shown to be a mitogen and stimulator of chemotaxis also for HSCs. Since it has been demonstrated in several cell types that cross-talk between PDGF and S1P signalling pathways occurs, our aim was to investigate the potential antifibrotic effect of FTY720, whose phosphorylated form acts as a potent S1P receptor (S1PR) modulator, on HSCs. FTY720 inhibits cell proliferation and migration after PDGF stimulation on HSCs in a concentration range between 0.1 and 1 muM. By using compounds that block S1P signalling (PTX and VPC23019), we assessed that FTY720 also acts in an S1P receptor-independent way by decreasing the level of tyrosine phosphorylation of PDGF receptor, with subsequent inhibition of the PDGF signalling pathway. In addition, inhibition of sphingosine kinase2 (SphK2), which is responsible for FTY720 phosphorylation, by DMS/siRNA unveils a mechanism of action irrespective of its phosphorylation, in particular decreasing the level of S1P(1) on the plasma membrane. These findings led us to hypothesize a potential use of FTY720 as a potential antifibrotic drug for further clinical application.

Enzymatic labelling of snake venom phospholipase A2 toxins.

Almost all animal venoms contain secretory phospholipases A2 (PLA2s), 14 kDa disulfide-rich enzymes that hydrolyze membrane phospholipids at the sn-2 position, releasing lysophospholipids and fatty acids. These proteins, depending on their sequence, show a wide variety of biochemical, toxic and pharmacological effects and deserve to be studied for their numerous possible applications, and to improve antivenom drugs. The cellular localization and activity of a protein can be studied by conjugating it with a tag. In this work, we applied an enzymatic labelling method, using Streptomyces mobaraense transglutaminase, on three snake venom PLA2s: a recombinant neuro- and myotoxic group I PLA2 from Notechis scutatus scutatus, and two myotoxic group II PLA2s from Bothrops asper - one of them a natural catalytically inactive variant. We demonstrate that TGase can be used to produce active mono- or bi-derivatives of these three PLA2s modified at specific Lys residues, and that all three of these proteins, conjugated with fluorescent peptides, are internalized in primary myotubes.

The Prion Protein Regulates Synaptic Transmission by Controlling the Expression of Proteins Key to Synaptic Vesicle Recycling and Exocytosis.

The cellular prion protein (PrPC), whose misfolded conformers are implicated in prion diseases, localizes to both the presynaptic membrane and postsynaptic density. To explore possible molecular contributions of PrPC to synaptic transmission, we utilized a mass spectrometry approach to quantify the release of glutamate from primary cerebellar granule neurons (CGN) expressing, or deprived of (PrP-KO), PrPC, following a depolarizing stimulus. Under the same conditions, we also tracked recycling of synaptic vesicles (SVs) in the two neuronal populations. We found that in PrP-KO CGN these processes decreased by 40 and 60%, respectively, compared to PrPC-expressing neurons. Unbiased quantitative mass spectrometry was then employed to compare the whole proteome of CGN with the two PrP genotypes. This approach allowed us to assess that, relative to the PrPC-expressing counterpart, the absence of PrPC modified the protein expression profile, including diminution of some components of SV recycling and fusion machinery. Subsequent quantitative RT-PCR closely reproduced proteomic data, indicating that PrPC is committed to ensuring optimal synaptic transmission by regulating genes involved in SV dynamics and neurotransmitter release. These novel molecular and cellular aspects of PrPC add insight into the underlying mechanisms for synaptic dysfunctions occurring in neurodegenerative disorders in which a compromised PrPC is likely to intervene.