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.

Mood disorders are highly prevalent and heterogenous mental illnesses with devastating rates of mortality and treatment resistance. The molecular basis of those conditions involves complex interplay between genetic and environmental factors. Currently, there are no objective procedures for diagnosis, prognosis and personalization of patients\' treatment. There is an urgent need to search for novel molecular targets for biomarkers in mood disorders. Cellular prion protein (PrPc) is infamous for its potential to convert its insoluble form, leading to neurodegeneration in Creutzfeldt-Jacob disease. Meanwhile, in its physiological state, PrPc presents neuroprotective features and regulates neurotransmission and synaptic plasticity. The aim of this study is to integrate the available knowledge about molecular mechanisms underlying the impact of PrPc on the pathophysiology of mood disorders. Our review indicates an important role of this protein in regulation of cognitive functions, emotions, sleep and biological rhythms, and its deficiency results in depressive-like behavior and cognitive impairment. PrPc plays a neuroprotective role against excitotoxicity, oxidative stress and inflammation, the main pathophysiological events in the course of mood disorders. Research indicates that PrPc may be a promising biomarker of cognitive decline. There is an urgent need of human studies to elucidate its potential utility in clinical practice.

Prion diseases are fatal neurodegenerative disorders characterized by the conversion of the cellular prion protein (PrPC) into a misfolded prion form, which is believed to disrupt the cellular membranes. However, the exact mechanisms underlying prion toxicity, including the formation of membrane pores, are not fully understood. The prion protein consists of two domains: a globular domain (GD) and a flexible N-terminus (FT) domain. Although a proximal polybasic amino acid (FT(23-31) sequence of FT is a prerequisite for cellular membrane permeabilization, other functional domain regions may modulate its effects. Through single-channel electrical recordings and cryo-electron microscopy (cryo-EM), we discovered that the FT(23-50) fragment forms pore-shaped oligomers and plays a dominant role in membrane permeabilization within the full-length mouse prion protein (mPrP(23-230)). In contrast, the FT(51-110) domain or the C-terminal domain downregulate the channel activity of FT(23-50) and mPrP(23-230). The addition of prion mimetic antibody, POM1 significantly amplifies mPrP(23-230) membrane permeabilization, whereas POM1_Y104A, a mutant that binds to PrP but cannot elicit toxicity, has a negligible effect on membrane permeabilization. Additionally, the anti-N-terminal antibody POM2 or Cu2+ binds to the FT domain, subsequently enhancing the FT(23-110) channel activity. Importantly, our setup provides a novel approach without an external fused protein to examine the channel activity of truncated PrP in the lipid membranes. We therefore propose that the primary N-terminal residues are essential for membrane permeabilization, while other functional segments of PrP play a vital role in modulating the pathological effects of PrP-mediated neurotoxicity.

Alternative α- and β-cleavage events in the cellular prion protein (PrPC) central region generate fragments with distinct biochemical features that affect prion disease pathogenesis, but the assignment of precise cleavage positions has proven challenging. Exploiting mouse transgenic models expressing wild-type (WT) PrPC and an octarepeat region mutant allele (S3) with increased β-fragmentation, cleavage sites were defined using LC-MS/MS in conjunction with N-terminal enzymatic labeling and chemical in-gel acetylation. Our studies profile the net proteolytic repertoire of the adult brain, as deduced from defining hundreds of proteolytic events in other proteins, and position individual cleavage events in PrPC α- and β-target areas imputed from earlier, lower resolution methods; these latter analyses established site heterogeneity, with six cleavage sites positioned in the β-cleavage region of WT PrPC and nine positions for S3 PrPC. Regarding α-cleavage, aside from reported N-termini at His110 and Val111, we identified a total of five shorter fragments in the brain of both mice lines. We infer that aminopeptidase activity in the brain could contribute to the ragged N-termini observed around PrPC\'s α- and β-cleavage sites, with this work providing a point of departure for further in vivo studies of brain proteases.

The cellular prion protein (PrPC) is required for skeletal muscle function. Here, we report that a higher level of PrPC accumulates in the cytoplasm of the skeletal muscle of six myopathy patients compared to controls. PrPC inhibits skeletal muscle cell autophagy, and blocks myoblast differentiation. PrPC selectively binds to a subset of miRNAs during myoblast differentiation, and the colocalization of PrPC and miR-214-3p was observed in the skeletal muscle of six myopathy patients with excessive PrPC. We demonstrate that PrPC is overexpressed in skeletal muscle cells under pathological conditions, inhibits muscle cell differentiation by physically interacting with a subset of miRNAs, and selectively recruits these miRNAs into its phase-separated condensate in living myoblasts, which in turn enhances liquid-liquid phase separation of PrPC, promotes pathological aggregation of PrP, and results in the inhibition of autophagy-related protein 5-dependent autophagy and muscle bundle formation in myopathy patients characterized by incomplete muscle regeneration.

Oligomers formed from monomers of the amyloid β-protein (Aβ) are thought to be central to the pathogenesis of Alzheimer\'s disease (AD). Unsurprisingly for a complex disease, current mouse models of AD fail to fully mimic the clinical disease in humans. Moreover, results obtained in a given mouse model are not always reproduced in a different model. Cellular prion protein (PrPC) is now an established receptor for Aβ oligomers. However, studies of the Aβ-PrPC interaction in different mouse models have yielded contradictory results. Here we performed a longitudinal study assessing a range of biochemical and histological features in the commonly used J20 and APP-PS1 mouse models. Our analysis demonstrated that PrPC ablation had no effect on amyloid accumulation or oligomer production. However, we found that APP-PS1 mice had higher levels of oligomers, that these could bind to recombinant PrPC, and were recognised by the OC antibody which distinguishes parallel, in register fibrils. On the other hand, J20 mice had a lower level of Aβ oligomers, which did not interact with PrPC when tested in vitro and were OC-negative. These results suggest the two mouse models produce diverse Aβ assemblies that could interact with different targets, highlighting the necessity to characterise the conformation of the Aβ oligomers concomitantly with the toxic cascade elicited by them. Our results provide an explanation for the apparent contradictory results found in APP-PS1 mice and the J20 mouse line in regards to Aβ toxicity mediated by PrPC.

The cellular prion protein (PrPC) is well-known for its involvement, under its pathogenic protease-resistant form (PrPSc), in a group of neurodegenerative diseases, known as prion diseases. PrPC is expressed in nervous system, as well as in other peripheral organs, and has been found overexpressed in several types of solid tumors. Notwithstanding, studies in recent years have disclosed an emerging role for PrPC in various cancer associated processes. PrPC has high binding affinity for 37/67 kDa laminin receptor (RPSA), a molecule that acts as a key player in tumorigenesis, affecting cell growth, adhesion, migration, invasion and cell death processes. Recently, we have characterized at cellular level, small molecules able to antagonize the direct PrPC binding to RPSA and their intracellular trafficking. These findings are very crucial considering that the main function of RPSA is to modulate key events in the metastasis cascade. Elucidation of the role played by PrPC/RPSA interaction in regulating tumor development, progression and response to treatment, represents a very promising challenge to gain pathogenetic information and discover novel specific biomarkers and/or therapeutic targets to be exploited in clinical settings. This review attempts to convey a detailed description of the complexity surrounding these multifaceted proteins from the perspective of cancer hallmarks, but with a specific focus on the role of their interaction in the control of proliferation, migration and invasion, genome instability and mutation, as well as resistance to cell death controlled by autophagic pathway.

Currently, no effective therapeutics exist for the treatment of incurable neurodegenerative diseases such as Alzheimer\'s disease (AD). The cellular prion protein (PrPC) acts as a high-affinity receptor for amyloid beta oligomers (AβO), a main neurotoxic species mediating AD pathology. The interaction of AβO with PrPC subsequently activates Fyn tyrosine kinase and neuroinflammation. Herein, we used our previously developed peptide aptamer 8 (PA8) binding to PrPC as a therapeutic to target the AβO-PrP-Fyn axis and prevent its associated pathologies. Our in vitro results indicated that PA8 prevents the binding of AβO with PrPC and reduces AβO-induced neurotoxicity in mouse neuroblastoma N2a cells and primary hippocampal neurons. Next, we performed in vivo experiments using the transgenic 5XFAD mouse model of AD. The 5XFAD mice were treated with PA8 and its scaffold protein thioredoxin A (Trx) at a 14.4 µg/day dosage for 12 weeks by intraventricular infusion through Alzet® osmotic pumps. We observed that treatment with PA8 improves learning and memory functions of 5XFAD mice as compared to Trx-treated 5XFAD mice. We found that PA8 treatment significantly reduces AβO levels and Aβ plaques in the brain tissue of 5XFAD mice. Interestingly, PA8 significantly reduces AβO-PrP interaction and its downstream signaling such as phosphorylation of Fyn kinase, reactive gliosis as well as apoptotic neurodegeneration in the 5XFAD mice compared to Trx-treated 5XFAD mice. Collectively, our results demonstrate that treatment with PA8 targeting the AβO-PrP-Fyn axis is a promising and novel approach to prevent and treat AD.

Prion diseases are a novel class of infectious disease based in the misfolding of the cellular prion protein (PrPC) into a pathological, self-propagating isoform (PrPSc). These fatal, untreatable neurodegenerative disorders affect a variety of species causing scrapie in sheep and goats, bovine spongiform encephalopathy (BSE) in cattle, chronic wasting disease (CWD) in cervids, and Creutzfeldt-Jacob disease (CJD) in humans. Of the animal prion diseases, CWD is currently regarded as the most significant threat due its ongoing geographical spread, environmental persistence, uptake into plants, unpredictable evolution, and emerging evidence of zoonotic potential. The extensive efforts to manage CWD have been largely ineffective, highlighting the need for new disease management tools, including vaccines. Development of an effective CWD vaccine is challenged by the unique biology of these diseases, including the necessity, and associated dangers, of overcoming immune tolerance, as well the logistical challenges of vaccinating wild animals. Despite these obstacles, there has been encouraging progress towards the identification of safe, protective antigens as well as effective strategies of formulation and delivery that would enable oral delivery to wild cervids. In this review we highlight recent strategies for antigen selection and optimization, as well as considerations of various platforms for oral delivery, that will enable researchers to accelerate the rate at which candidate CWD vaccines are developed and evaluated.

This study investigated whether melatonin (Mel) would promote cisplatin to suppress the proliferation and growth of bladder cancer (BC) cells by inhibiting cellular prion protein (PrPC)-mediated cell stress and cell proliferation signaling. An immunohistochemical staining of tissue arrays from BC patients demonstrated that the PrPC expression was significantly upregulated from stage I to III BC (p < 0.0001). The BC cellline of T24 was categorized into G1 (T24), G2 (T24 + Mel/100 μM), G3 (T24+cisplatin/6 μM), G4 (PrPC overexpression in T24 (i.e., PrPC-OE-T24)), G5 (PrPC-OE-T24+Mel), and G6 (PrPC-OE-T24+cisplatin). When compared with a human uroepithelial cell line (SV-HUC-1), the cellular viability/wound healing ability/migration rate were significantly increased in T24 cells (G1) and further significantly increased in PrPC-OE-T24 cells (G4); and they were suppressed in Mel (G2/G5) or cisplatin (G3/G6) treatment (all p < 0.0001). Additionally, the protein expressions of cell proliferation (PI3K/p-Akt/p-m-TOR/MMP-9/PrPC), cell cycle/mitochondrial functional integrity (cyclin-D1/clyclin-E1/ckd2/ckd4/mitochondrial-cytochrome-C/PINK1), and cell stress (RAS/c-RAF/p-MEK1/2, p-ERK1/2) markers showed a similar pattern of cell viability among the groups (all p < 0.001). After the BC cell line of UMUC3 was implanted into nude mouse backs, by day 28 mthe BC weight/volume and the cellular levels of PrPC/MMP-2/MMP-9 were significantly, gradually reduced from groups one to four (all p < 0.0001). The protein expressions of cell proliferation (PI3K/p-Akt/p-m-TOR/MMP-9/PrPC), cell cycle/mitophagy (cyclin-D1/clyclin-E1/ckd2/ckd4/PINK1), and cell stress (RAS/c-RAF/p-MEK1,2/p-ERK1,2) signaling were significantly, progressively reduced from groups one to four, whereas the protein expressions of apoptotic (Mit-Bax/cleaved-caspase-3/cleaved-PARP) and oxidative stress/mitochondrial damaged (NOX-1/NOX-2/cytosolic-cytochrome-C/p-DRP1) markers expressed an opposite pattern of cell proliferation signaling among the groups (all p < 0.0001). Mel-cisplatin suppressed BC cell growth/proliferation via inhibiting the PrPC in upregulating the cell proliferation/cell stress/cell cycle signaling.