Activity Of PrP Research Articles

To Evaluate the Antimicrobial Activity of PRP and PRF with and without Nanosilver.

To evaluate the antimicrobial activity of PRP and PRF with and without nanosilver. The materials were tested in powdered form is nanosilver. The nanosilver particles was mixed to form with PRP and PRF so as to placed in a wells followed the groups are experimental groups; Group I: PRP + nanosilver particles, Group II: PRF + nanosilver and control group: PRP and PRF and normal saline. Silver nanoparticles was tested at concentrations of 50 μ gram per mL. The powder was prepared for each group with identical amount of the powder (milligram/mg) and then mixed with 1 milliliter liquid. The plates are then incubated at 37°C under appropriate atmospheric conditions (80% N2, 10% CO2, 10% H2) for 24 hours, 48 hours, and 72 hours under anaerobic conditions in a CO2 incubator. The diameters of the zones of bacterial and fungal growth inhibition around the wells containing the test substances are then recorded after the period of incubation. The inhibitory zone determined in millimeter by measuring scale the shortest distance between the outer margin of the well and initial microbial as well as fungal growth. The experiments were performed 20 times and the mean and standard deviations of the inhibitory zones were calculated. Platelet rich fibrin is mixed with nanosilver particles showed higher antimicrobial efficacy than platelet rich plasma with nanosilver and simple platelet rich plasma and platelet rich fibrin are equivalent when it is placed against the anaerobic bacteria E.faecalis and yeast like fungi Candida albicans, respectively. Groups presented with antimicrobial efficacy in this order- Group IV > Group II > Group III > Group I.

BIO26: Engineering Anti-platelet polymers for regenerative cardiovascular applications

Thrombogenesis is the main failure cause of implantable cardiovascular devices. Thrombus formation not only occludes devices but exacerbates immune responses responsible for foreign body reaction. Biodegradable polymers modified with anticoagulating moieties represent a strategy to overcome these limitations. Herein, we propose the use of a novel polyester urethane urea (PEUU) with pendant carboxyl groups for functionalization with different anti-platelet deposition molecules. PEUU was synthesized from PCL (Polycaprolactone), 1,4-diisocyanatobutane and putrescine, and then chemically oxidized to introduce carboxyl groups in the polymer backbone (PEUU-COOH). PEUU-COOH was functionalized in-situ with Polyethyleneimine mW 400 (PEI), 4 arm Polyethylene Glycol (PEG-4-Arm-NH2), seleno-L-cystine, heparin sodium and fondaporinux as anti-platelet deposition molecules. After solvent casting, functionalization was confirmed via Fourier-transformed infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Metabolic activity (MTT) and hemolysis assays were performed to validate biocompatibility. Anti-platelet activity of PRP exposed films was examined via a platelet aggregation assay, through an activation assay via lactate dehydrogenase (LDH), and by surface imaging with scanning electron microscopy (SEM). Whole-blood clotting time quantification assay was carried out to evaluate anticogulating properties. Upon oxidation, PEUU exhibited COOH pendant groups that were successfully employed to conjugate the anti-platelet molecules, obtaining homogeneous films. Overall cytotoxicity was below 20% and the hemolysis was below 5%, suggesting high biocompatibility and hemocompatibility. The most potent anticoagulant activity was obtained for heparin-functionalized materials followed by PEG-4-Arm-NH2 and PEI. Surprisingly, Seleno-L-cystine and Fondaporinux showed no anti-platelet activity. Results indicate that the polymers introduced here are a promising strategy to avoid thrombogenesis in vascular grafts.

Pure Platelet and Leukocyte-Platelet-Rich Plasma for Regenerative Medicine in Orthopedics-Time- and Preparation-Dependent Release of Growth Factors and Effects on Synovial Fibroblasts: A Comparative Analysis.

Intra-articular injections of autologous platelet concentrates are considered capable to enhance the healing of cartilage lesions, alleviate joint inflammation, and relieve other musculoskeletal pathological conditions. The aim of this study was to analyze the soluble fractions obtained from platelet-rich plasma (pure- and leukocyte-PRP) to compare time- and preparation-dependent modifications of growth factor concentrations and the supporting activity of the two preparations on synovial fibroblast growth and hyaluronic acid (HA) production in vitro. The release kinetics of FGF-2, SDF-1, VEGF, HGF, EGF, PD GF-AB/BB, IGF-1, VCAM-1, and TGF-β isoforms were followed up to 168 h after PRP activation, and their amounts were determined by multiplex-beads immunoassay. Synovial cell growth and supernatant HA production were respectively analyzed by Alamar Blue assay and ELISA. Time-dependent modifications grouped molecules in three peculiar patterns: one reaching the highest concentrations within 18 h and decreasing afterwards, another progressively increasing up to 168 h, and the last peaking at the central time points. Synovial fibroblast growth in response to L-PRP and P-PRP revealed differences over time and among added concentrations. Both preparations displayed a preserved supporting capacity of HA synthesis.

Dual Bioactivity of Angiotensin Converting Enzyme Inhibition and Antioxidant Novel Tripeptides from Sipunculus nudus L. and Their Related Mechanism Analysis for Antihypertention

The pathogenesis of hypertension is related to many factors including active angiotensin-I-converting enzyme (ACE) and excess reactive oxygen species (ROS), the combination of ACE inhibition and antioxidant activity in one compound might be useful for the treatment of hypertension. Sipunculus nudus L contain high protein content, which can be used as a valuable raw material to prepare bio-active peptides. In this study, two novel tripeptides, LPK and PRP, with dual bioactivity of ACE inhibition and antioxidant were purified and identified from the worm. The antioxidant activities of LPK and PRP are dose-dependent, including 2,2-diphenyl-1-picrylhydrazyl (DPPH), superoxide anion and hydroxyl radical scavenging activities. Moreover, the antioxidant activity of PRP was stronger than that of LPK. In addition, LPK and PRP also show higher ACE inhibitory activity, with IC50 of 6.54 and 0.42 mM, respectively. Molecular docking simulation showed that both the peptides could interact with the active ACE sites via hydrogen bonds, which can reduce the production of Ang II, thereby; LPK and PRP treatment could decrease Ang II-triggered superoxide production, and meanwhile, the peptides treatment could directly remove excess reactive oxygen species. The above-mentioned advantageous effects appeared to involve the stress of the RAS and scavenging ROS, both were benefit to treat hypertension. This research showed that LPK and PRP had potential to be developed as antihypertension agents, which might be a new strategy for high value utilization of Sipunculus nudus L as functional food material.

Aptamer-Induced-Dimerization Strategy Attenuates AβO Toxicity through Modulating the Trophic Activity of PrPC Signaling

Current therapeutic strategies for Alzheimer's disease (AD) mainly focus on amyloid β oligomer (AβO) formation or clearance. However, most of them have failed to yield good clinical results. There is an urgent need to explore an alternative therapeutic target for AD treatments. Recent studies have indicated that the cellular prion protein (PrPC) is one of the cell-surface receptors of AβO that mediates related neurotoxicity. Besides, as a neuroprotective protein, the dimerization of PrPC seems to be critical for its trophic activity. We presume that modulating PrPC receptor activity could be another potential approach to abrogate AβO toxicity. In the present work, using an aptamer-induced dimerization (AID) strategy, we enforce PrPC dimerization and modulate its neurotrophic signaling. The AID strategy can attenuate AβO toxic action by (i) interfering with AβO-PrPC interaction and promoting neuroprotective shedding of PrPC; (ii) preventing the AβO-induced mitochondrial dysfunction and the caspase-3-induced apoptosis; and (iii) reducing the secretion of inflammatory cytokines and relieving the neuroinflammation microenvironment. Our findings suggest that the strategy targeting PrPC signaling may shed light on validating new therapeutic strategies in AD.

Regenerative effect of platelet-rich plasma in the murine ischemic limbs

AimsThe purpose of this study was to investigate the effect of PPRP (pure PRP) and LPRP (PRP with leukocytes) on recovery from limb ischemia and on expression of growth factors involved in angiogenesis, myogenesis and fibrogenesis. Material and methodsPPRP and LPRP prepared by centrifugation were added to cultures of C2C12 and NIH3T3 cells (1 or 10% PRPs) to evaluate alterations in cell metabolism and expression of growth factors by MTT, ELISA and RT-qPCR, respectively. To evaluate in vivo regenerative effects, PRPs were injected into the ischemic limbs of BALB/c mice and muscle mass/strength and histomorphometry were evaluated after 30 days. Key findingsMice treated with PRPs after limb ischemia showed an increase in the size of myofibers and muscle strength, reduced fibrosis and adipocytes, and decreased capillary density and necrosis scores compared to untreated mice. In cell culture, serum deprivation reduced the viability of C2C12 and NIH3T3 cells to about 50%, but the addition of 1% PRPs completely recovered this loss. Both PRPs, downregulated most of the tested genes; however, angiogenic gene Vegfa in C2C12 and the fibrogenic genes Col1a1 and Col3a1 in NIH3T3 cells were upregulated by LPRP. SignificancePPRP and LPRP had similar effects in regulation of genes involved in angiogenesis, myogenesis and fibrogenesis. However, the presence of leucocytes did not significantly affect regenerative activities of PRP in the ischemic limb.

Platelet-Rich Plasma: Fundamentals and Clinical Applications

AbstractPlatelet-rich plasma (PRP) is perhaps the most widely studied of the biologic therapies, with an ever-growing body of evidence supporting its safety and efficacy in decreasing inflammation and pain and promoting healing in the setting of both nonoperative and operative treatments. PRP is produced by the centrifugation of whole blood, isolating its constituent parts based on their unique densities. These density gradients can be selectively harvested so as to obtain different concentrations of various blood product components, such as platelets and leukocytes. A precise and consistent method for describing the essential characteristics of different PRP formulations is critical for both practical and research purposes. The concentration of platelets, method of activation, and the total number of red blood cells (RBCs), white blood cells (WBCs), and neutrophils relative to baseline values are all of particular importance in accurately describing a PRP formulation. The biologic activity of PRP is manifold: platelet α granules promote the release of various growth factors, including vascular endothelial growth factor and tissue growth factor β, while inflammation is modulated through inhibition of the nuclear factor-κB pathway. PRP has been convincingly shown to be efficacious in the setting of patellar tendinopathies, knee osteoarthritis, and lateral epicondylitis. In fact, several recent randomized controlled trials have demonstrated the superiority of PRP over both corticosteroids and hyaluronic acid in treating knee OA-related symptoms. There is also substantial promise for the utility of PRP in treating partial hamstring tears and as an adjunct to rotator cuff (RC) repair, especially in the setting of small- to medium-sized tears, where it appears to exert substantial analgesic effects and promote enhanced rates of RC repair healing.

Comparison and Investigation of Exosomes Derived from Platelet-Rich Plasma Activated by Different Agonists

PRP-Exos are nanoscale cup-shaped vesicles that carry a variety of proteins, mRNAs, microRNAs, and other bioactive substances. PRP-Exos can be formed through several induction pathways, which determine their molecular profiles and facilitate their tailormade participation in intercellular communication. Currently, little is known on how the PRP-Exos activation method influences the quality and quantity of PRP-Exos. The present study aims to observe and analyze the number, profile, and growth factors of PRP-Exos through TEM, Nanoflow, and WB after PRP activation and compare the difference in function of PRP-Exos on HUVECs, with different stimuli (calcium gluconate, thrombin, or both). We found that PRP activated with both thrombin and calcium gluconate harvested the highest concentration of exosomes [(7.16 ± 0.46) × 1010 particles/ml], compared to thrombin group [(4.87 ± 0.15) × 1010 particles/ml], calcium gluconate group [(5.85 ± 0.43) × 1010 particles/ml], or saline group [(7.52 ± 0.19) × 109 particles/ml], respectively (P < 0.05) via Nanoflow analysis. The WB analysis showed that cytokines (VEGF, PDGFBB, bFGF, TGF-β) are differentially encapsulated in PRP-Exos, depending on the PRP stimulus, in which the mixture-PRP-Exos yielded the highest concentration of cytokines. In the function assay of PRP-Exos on HUVECs, the mixture-PRP-Exos promoted HUVECs proliferation, increased HUVECs migration, promoted the formation of vessel-like by HUVECs via the AKT ERK signal pathway more dramatically, compared with other groups. In summary, our studies showed that PRP activated by the mixture of calcium gluconate and thrombin harvested the best quality of exosomes which had the top biological functions. This study provides a protocol for selecting appropriate PRP activators to obtain high-quality exosomes for future applications.

Structural Features of Heparin and Its Interactions With Cellular Prion Protein Measured by Surface Plasmon Resonance.

Self-propagating form of the prion protein (PrPSc) causes many neurodegenerative diseases, such as Creutzfeldt-Jakob disease (CJD) and Gerstmann-Straussler-Scheinker syndrome (GSS). Heparin is a highly sulfated linear glycosaminoglycan (GAG) and is composed of alternating D-glucosamine and L-iduronic acid or D-glucuronic acid sugar residues. The interactions of heparin with various proteins in a domain-specific or charged-dependent manner provide key roles on many physiological and pathological processes. While GAG-PrP interactions had been previously reported, the specific glycan structures that facilitate interactions with different regions of PrP and their binding kinetics have not been systematically investigated. In this study, we performed direct binding surface plasmon resonance (SPR) assay to characterize the kinetics of heparin binding to four recombinant murine PrP constructs including full length (M23–230), a deletion mutant lacking the four histidine-containing octapeptide repeats (M23–230 Δ59–90), the isolated N-terminal domain (M23–109), and the isolated C-terminal domain (M90–230). Additionally, we found the specific structural determinants required for GAG binding to the four PrP constructs with chemically defined derivatives of heparin and other GAGs by an SPR competition assay. Our findings may be instrumental in developing designer GAGs for specific targets within the PrP to fine-tune biological and pathophysiological activities of PrP.

Altered Domain Structure of the Prion Protein Caused by Cu2+ Binding and Functionally Relevant Mutations: Analysis by Cross-Linking, MS/MS, and NMR

The cellular isoform of the prion protein (PrPC) serves as precursor to the infectious isoform (PrPSc), and as a cell-surface receptor, which binds misfolded protein oligomers as well as physiological ligands such as Cu2+ ions. PrPC consists of two domains: a flexible N-terminal domain and a structured C-terminal domain. Both the physiological and pathological functions of PrP depend on intramolecular interactions between these two domains, but the specific amino acid residues involved have proven challenging to define. Here, we employ a combination of chemical cross-linking, mass spectrometry, NMR, molecular dynamics simulations, and functional assays to identify residue-level contacts between the N- and C-terminal domains of PrPC. We also determine how these interdomain contacts are altered by binding of Cu2+ ions and by functionally relevant mutations. Our results provide a structural basis for interpreting both the normal and toxic activities of PrP.

The effect of combination therapy on critical-size bone defects using non-activated platelet-rich plasma and adipose-derived stem cells.

Non-activated platelet-rich plasma (nPRP) slowly releases growth factors that induce bone regeneration. Adipose tissue-derived stem cells (ASCs) are also known to induce osteoblast differentiation. In this study, we investigated the combined effect of nPRP and ASC treatment compared with single therapy on bone regeneration. Thirty New Zealand white rabbits with 15 × 15mm2 calvarial defects were randomly divided into four treatment groups: control, nPRP, ASC, or nPRP + ASC groups. For treatment, rabbits received a collagen sponge (Gelfoam®) saturated with 1ml normal saline (controls), 1ml non-activated PRP (nPRP group), 2 × 106 ASCs (ASCs group), or 2 × 106 ASCs plus l ml nPRP (nPRP + ASCs group). After 16weeks, bone volume and new bone surface area were measured, using three-dimensional computed tomography and digital photography. Bone regeneration was also histologically analyzed. Bone surface area in the nPRP group was significantly higher than both the control and ASC groups (p < 0.001 and p < 0.01, respectively). The percentage of regenerated bone surface area in the nPRP + ASC group was also significantly higher than the corresponding ratios in the control group (p < 0.001). The volume of new bone in the nPRP group was increased compared to the controls (p < 0.05). Our results demonstrate that slow-releasing growth factors from nPRP did not influence ASC activation in this model of bone healing. PRP activation is important for the success of combination therapy using nPRP and ASCs.

PR708: The antimicrobial activity of PRP, PRF and CGF ‐ a review

PR708: The antimicrobial activity of PRP, PRF and CGF ‐ a review

Evaluación del efecto del plasma rico en plaquetas en diferentes tiempos y concentraciones sobre la viabilidad de fibroblastos de ligamento periodontal y osteoblastos / Evaluation of Platelet-Rich Plasma Effect at different times and concentrations ...

&lt;strong&gt;ABSTRACT&lt;em&gt;. Background:&lt;/em&gt;&lt;/strong&gt;&lt;em&gt; &lt;/em&gt;Growth factors used in health treatments can be obtained from a first-generation source called platelet-rich plasma. The variety of protocols to prepare PRP produces variable results regarding PRP activation time and its effects on cell proliferation and viability. &lt;strong&gt;&lt;em&gt;Purpose:&lt;/em&gt;&lt;/strong&gt;&lt;em&gt; &lt;/em&gt;To evaluate proliferation and cell viability of periodontal ligament fibroblasts and osteoblasts stimulated with PRP in several concentrations and times after PRP activation. &lt;strong&gt;&lt;em&gt;Methods:&lt;/em&gt;&lt;/strong&gt; An in vitro study was carried out using periodontal ligament fibroblast and osteoblast cell cultures. PRP from venous blood of a healthy adult was prepared through centrifugation and activated with 10 % CaCl&lt;sub&gt;2&lt;/sub&gt;. The effect on cell proliferation after application of 1 %, 3 %, and 5% PRP and platelet-poor plasma was evaluated at 0, 12, 24, 48, and 72 hours after activation through MTS. The control group consisted of culture that did not receive any treatment. Data were analyzed using Chi square, Fisher, and McNemar tests. &lt;strong&gt;&lt;em&gt;Results:&lt;/em&gt;&lt;/strong&gt;&lt;em&gt; &lt;/em&gt;The cell viability assay showed statistically significant differences between the experimental and the control groups. Cell viability increased in cells treated with 5 % PRP 24 hours after activation (p=0.05). &lt;strong&gt;&lt;em&gt;Conclusions:&lt;/em&gt;&lt;/strong&gt;&lt;em&gt; &lt;/em&gt;Fibroblast and osteoblast cell lines tended to be more viable 24 hours after activation with 5% PRP.

Extraction optimization and characterization of polysaccharide antioxidants from &lt;i&gt;Pinellia ternata&lt;/i&gt; (Thunb) Breit rhizome

Purpose: To investigate the optimum extraction conditions of polysaccharides from Pinellia Rhizoma (PRP) and their antioxidant activities. Methods: Response surface methodology (RSM) was applied to optimize the water extraction conditions of PRP by Box-Benhnken design (BBD). A high performance liquid chromatography (HPLC) method was performed for determining the monosaccharide composition, while a high performance gel permeation chromatography (HPGPC) method was established for determining the molecular weight distribution of PRP. In addition, scavenging DPPH and superoxide anion radical scavenging assays were used to evaluate the antioxidant activities of PRP. Results: As a result, the optimum extraction conditions of PRP were as follows: extraction time, 103 min; solid-liquid ratio, 24 g/mL; and extraction no., 3. Under these conditions, the maximum extraction yield of PRP was 2.47 %, which matched the optimum value (2.55 %) predicted by RSM. The results of HPLC analysis suggest that the monosaccharide composition of PRP was mannose (Man), galactose acid (Gal acid), galactose (Gal), glucose (Glc), and arabinose (Ara) in molar ratios of 5.76:2.20:2.64:4.57:1, respectively, and the molecular weight ranged from 13592 to 445065. Furthermore, PRP showed marked antioxidant activities with the highest DPPH free radical scavenging rate of 71.5 % and O 2- free radical scavenging rate of 87.5 % at a concentration of 10 mg/mL. Conclusion: RSM is a rapid and effective statistical technique for optimizing conditions for PRP extraction. Furthermore, PRP is a potential natural source of antioxidants. Keywords: Pinellia rhizoma , Polysaccharides Optimization extraction, Monosaccharide composition, Antioxidant activity

Inhibitory activities of platelet-rich and platelet-poor plasma on the growth- of pathogenic bacteria

The utility and efficacy of novel materials in tissue regeneration and antimicrobial therapy are contingent upon the employment of either blood derivatives rich in platelets or platelet-poor-plasma (PPP). This effect is largely mediated by the increased or decreased concentration of platelets in the plasma. The current study aimed to analyze and evaluate the impact of platelet-rich (PRP) or PPP on inhibiting the growth of human pathogenic bacteria and compare their effects with those of chloramphenicol and penicillin. In the current comparative study, PRP-1 was generated using 1-step blood centrifugation method; whereas, for PRP-2 and PPP the 2-step centrifugation protocol was used. The antimicrobial activity of PRP-1, 2, and PPP were tested on Staphylococcus aureus, Escherichia coli, Klebsiella pneumonia, Pseudomonas aeruginosa, Streptococcus agalactiae, Staphylococcus epidermidis, Shigella sp. and Serratia sp. Well diffusion and serial micro-dilution methods were used for this purpose. Chloramphenicol and penicillin susceptibility were tested using the disk diffusion method. While whole blood (WB) and PPP had no discernible impact on the growth parameters of any of the bacteria tested in the current study, PRP-1 reduced the growth rate of a few selected strains. In addition, while PRP-2 clearly inhibited the growth of Shigella sp., E. coli, S. aureus, S. agalactiae, and S. epidermidis, it had no impact on the growth of K. pneumoniae, P. aeruginosa, and Serratia sp. It can be claimed that there is a strong correlation between the concentration of platelets and the antibacterial activity of PRP.

Temporal Resolution of Misfolded Prion Protein Transport, Accumulation, Glial Activation, and Neuronal Death in the Retinas of Mice Inoculated with Scrapie

Currently, there is a lack of pathological landmarks to describe the progression of prion disease invivo. Our goal was to use an experimental model to determine the temporal relationship between the transport of misfolded prion protein (PrP(Sc)) from the brain to the retina, the accumulation of PrP(Sc) in the retina, the response of the surrounding retinal tissue, and loss of neurons. Retinal samples from mice inoculated with RML scrapie were collected at 30, 60, 90, 105, and 120 days post inoculation (dpi) or at the onset of clinical signs of disease (153 dpi). Retinal homogenates were tested for prion seeding activity. Antibody staining was used to assess accumulation of PrP(Sc) and the resulting response of retinal tissue. Loss of photoreceptors was used as a measure of neuronal death. PrP(Sc) seeding activity was first detected in all samples at 60 dpi. Accumulation of PrP(Sc) and coincident activation of retinal glia were first detected at 90 dpi. Activation of microglia was first detected at 105 dpi, but neuronal death was not detectable until 120 dpi. Our results demonstrate that by using the retina we can resolve the temporal separation between several key events in the pathogenesis of prion disease.

Quantitative Real-Time Quaking-Induced Conversion Allows Monitoring of Disease-Modifying Therapy in the Urine of Prion-Infected Mice.

Prion diseases are fatal neurodegenerative diseases characterized by accumulation of the pathogenic prion protein PrP in the brain. We established quantitative real-time quaking-induced conversion for the measurement of minute amounts of PrP in body fluids such as urine. Using this approach, we monitored the efficacy of antiprion therapy by quantifying the seeding activity of PrP from the brain and urine of mice after prion infection. We found that the aggregation inhibitor anle138b decreased the levels of PrP in the brain and urine. Importantly, variations of PrP levels in the urine closely corresponded to those in the brain. Our findings indicate that quantification of urinary PrP enables measurement of prion disease progression in body fluids and can substitute for immunodetection in brain tissue. We expect PrP quantification biologic fluids (such as urine and cerebrospinal fluid) with quantitative real-time quaking-induced conversion to emerge as a valuable noninvasive diagnostic tool for monitoring disease progression and the efficacy of therapeutic approaches in animal studies and human clinical trials of prion diseases. Moreover, highly sensitive methods for quantifying pathologic aggregate seeds might provide novel molecular biomarkers for other neurodegenerative diseases that may involve prion-like mechanisms (protein aggregation and spreading), such as Alzheimer disease and Parkinson disease.

Prion Protein Promotes Kidney Iron Uptake via Its Ferrireductase Activity

Brain iron-dyshomeostasis is an important cause of neurotoxicity in prion disorders, a group of neurodegenerative conditions associated with the conversion of prion protein (PrP(C)) from its normal conformation to an aggregated, PrP-scrapie (PrP(Sc)) isoform. Alteration of iron homeostasis is believed to result from impaired function of PrP(C) in neuronal iron uptake via its ferrireductase activity. However, unequivocal evidence supporting the ferrireductase activity of PrP(C) is lacking. Kidney provides a relevant model for this evaluation because PrP(C) is expressed in the kidney, and ∼370 μg of iron are reabsorbed daily from the glomerular filtrate by kidney proximal tubule cells (PT), requiring ferrireductase activity. Here, we report that PrP(C) promotes the uptake of transferrin (Tf) and non-Tf-bound iron (NTBI) by the kidney in vivo and mainly NTBI by PT cells in vitro. Thus, uptake of (59)Fe administered by gastric gavage, intravenously, or intraperitoneally was significantly lower in PrP-knock-out (PrP(-/-)) mouse kidney relative to PrP(+/+) controls. Selective in vivo radiolabeling of plasma NTBI with (59)Fe revealed similar results. Expression of exogenous PrP(C) in immortalized PT cells showed localization on the plasma membrane and intracellular vesicles and increased transepithelial transport of (59)Fe-NTBI and to a smaller extent (59)Fe-Tf from the apical to the basolateral domain. Notably, the ferrireductase-deficient mutant of PrP (PrP(Δ51-89)) lacked this activity. Furthermore, excess NTBI and hemin caused aggregation of PrP(C) to a detergent-insoluble form, limiting iron uptake. Together, these observations suggest that PrP(C) promotes retrieval of iron from the glomerular filtrate via its ferrireductase activity and modulates kidney iron metabolism.

Regulation of PrP(C) signaling and processing by dimerization.

The cellular prion protein (PrPC) is a glycosylphosphatidylinositol (GPI)-anchored protein present at the cell surface. PrPC N-terminal moiety is intrinsically disordered and is able to interact with a variety of ligands. Physiological ligands have neurotrophic activity, whilst others, including protein toxic oligomers, have neurotoxic functions. These two opposite activities involve different interacting partners and result from different PrPC-activated signaling pathways. Remarkably, PrPC may be inactivated either by physiological endoproteolysis and release of the N-terminal domain, or by ectodomain shedding. Ligand-induced PrPC dimerization or enforced dimerization of PrPC indicate that PrPC dimerization represents an important molecular switch for both intracellular signaling and inactivation by the release of PrPC N-terminal domain or shedding. In this review, we summarize evidence that cell surface receptor activity of PrPC is finely regulated by dimerization.

PDK1 decreases TACE-mediated α-secretase activity and promotes disease progression in prion and Alzheimer's diseases

α-secretase-mediated cleavage of amyloid precursor protein (APP) precludes formation of neurotoxic amyloid-β (Aβ) peptides, and α-cleavage of cellular prion protein (PrP(C)) prevents its conversion into misfolded, pathogenic prions (PrP(Sc)). The mechanisms leading to decreased α-secretase activity in Alzheimer's and prion disease remain unclear. Here, we find that tumor necrosis factor-α-converting enzyme (TACE)-mediated α-secretase activity is impaired at the surface of neurons infected with PrP(Sc) or isolated from APP-transgenic mice with amyloid pathology. 3-phosphoinositide-dependent kinase-1 (PDK1) activity is increased in neurons infected with prions or affected by Aβ deposition and in the brains of individuals with Alzheimer's disease. PDK1 induces phosphorylation and caveolin-1-mediated internalization of TACE. This dysregulation of TACE increases PrP(Sc) and Aβ accumulation and reduces shedding of TNF-α receptor type 1 (TNFR1). Inhibition of PDK1 promotes localization of TACE to the plasma membrane, restores TACE-dependent α-secretase activity and cleavage of APP, PrP(C) and TNFR1, and attenuates PrP(Sc)- and Aβ-induced neurotoxicity. In mice, inhibition or siRNA-mediated silencing of PDK1 extends survival and reduces motor impairment following PrP(Sc) infection and in APP-transgenic mice reduces Alzheimer's disease-like pathology and memory impairment.