Human keratinocytes express cellular prion-related protein in vitro and during inflammatory skin diseases

Collagen Mimicry with a Short Collagen Model Peptide

Mimicking triple helix and fibrillar network of collagen through collagen model peptide(CMP) with short GPO tripeptide repeats is a great challenge. Herein, a minimalistic CMP comprising only five GPO repeats [(GPO)5 ] is presented. This novel approach involves the fusion of ultrashort peptide with the synergetic power of π-system and β-sheet formation to short CMP (GPO)5 . Accordingly, a hydrogel-forming, fluorenylmethoxycarbonyl (Fmoc)-functionalized ultrashort peptide (NFGAIL) is fused at the N-terminus and phenylalanine at the C-terminus of (GPO)5 (Fmoc-NFGAIL-(GPO)5 -F-COOH, FmP-5GPO). At room temperature, it forms a robust triple helix in aqueous buffer solution and has a relatively high melting point of 35 °C. The fluorenyl motif stabilizes the triple helix by aromatic π-π interactions as in its absence, triple helix is not formed. NFGAIL, which forms a β-sheet, also aids in triple helix stabilization via intermolecular hydrogen bonding and hydrophobic interactions. FmP-5GPO forms highly entangled nanofibrils with a micrometer length, which have excellent cell viability. The achievement of stable triple helix and fibrils in such a short CMP(FmP-5GPO) sequence is a challenging feat, and its significance in CMP-based biomaterials is undeniable. The present strategy highlights the potential for developing new CMP sequences through intelligent tuning of fusion peptides and GPO repeats.

The Multifaceted Functions of Prion Protein (PrPC) in Cancer

The cellular prion protein (PrPC) is a glycoprotein anchored to the cell surface by glycosylphosphatidylinositol (GPI). PrPC is expressed both in the brain and in peripheral tissues. Investigations on PrPC's functions revealed its direct involvement in neurodegenerative and prion diseases, as well as in various physiological processes such as anti-oxidative functions, copper homeostasis, trans-membrane signaling, and cell adhesion. Recent findings have revealed the ectopic expression of PrPC in various cancers including gastric, melanoma, breast, colorectal, pancreatic, as well as rare cancers, where PrPC promotes cellular migration and invasion, tumor growth, and metastasis. Through its downstream signaling, PrPC has also been reported to be involved in resistance to chemotherapy and tumor cell apoptosis. This review summarizes the variance of expression of PrPC in different types of cancers and discusses its roles in their development and progression, as well as its use as a potential target to treat such cancers.

Persistent ER stress causes GPI anchor deficit to convert a GPI-anchored prion protein into pro-PrP via the ATF6-miR449c-5p-PIGV axis

Endoplasmic reticulum (ER) stress and unfolded protein response are cells' survival strategies to thwart disruption of proteostasis. Tumor cells are continuously being challenged by ER stress. The prion protein, PrP, normally a glycosylphosphatidylinositol (GPI)-anchored protein exists as a pro-PrP retaining its GPI-peptide signal sequence in human pancreatic ductal cell adenocarcinoma (PDAC). Higher abundance of pro-PrP indicates poorer prognosis in PDAC patients. The reason why PDAC cells express pro-PrP is unknown. Here, we report that persistent ER stress causes conversion of GPI-anchored PrP to pro-PrP via a conserved ATF6-miRNA449c-5p-PIGV axis. Mouse neurons and AsPC-1, a PDAC cell line, express GPI-anchored PrP. However, continuous culture of these cells with the ER stress inducers thapsigargin or brefeldin A results in the conversion of a GPI-anchored PrP to pro-PrP. Such a conversion is reversible; removal of the inducers allows the cells to re-express a GPI-anchored PrP. Mechanistically, persistent ER stress increases the abundance of an active ATF6, which increases the level of miRNA449c-5p (miR449c-5p). By binding the mRNA of PIGV at its 3'-UTRs, miR449c-5p suppresses the level of PIGV, a mannosyltransferase pivotal in the synthesis of the GPI anchor. Reduction of PIGV leads to disruption of the GPI anchor assembly, causing pro-PrP accumulation and enhancing cancer cell migration and invasion. The importance of ATF6-miR449c-5p-PIGV axis is recapitulated in PDAC biopsies as the higher levels of ATF6 and miR449c-5p and lower levels of PIGV are markers of poorer outcome for patients with PDAC. Drugs targeting this axis may prevent PDAC progression.

Cell secretomes for wound healing and tissue regeneration: Next generation acellular based tissue engineered products

Wound represents a significant socioeconomic burden for both affected individuals and as a whole healthcare system. Accordingly, stem cells have garnered attention due to their differentiation capacity and ability to aid tissue regeneration by releasing biologically active molecules, found in the cells’ cultivated medium which known as conditioned medium (CM) or secretomes. This acellular approach provides a huge advantage over conventional treatment options, which are mainly used cellular treatment at wound closure. Interestingly, the secretomes contained the cell-secreted proteins such as growth factors, cytokines, chemokines, extracellular matrix (ECM), and small molecules including metabolites, microvesicles, and exosomes. This review aims to provide a general view on secretomes and how it is proven to have great potential in accelerating wound healing. Utilizing the use of secretomes with its secreted proteins and suitable biomaterials for fabrications of acellular skin substitutes can be promising in treating skin loss and accelerate the healing process.

PIWIL-2 and piRNAs are regularly expressed in epithelia of the skin and their expression is related to differentiation

PIWI proteins play multiple roles in germline stem cell maintenance and self-renewal. PIWI-interacting RNAs (piRNAs) associate with PIWI proteins, form effector complexes and maintain genome integrity and function in the regulation of gene expression by epigenetic modifications. Both are involved in cancer development. In this study, we investigated the expression of PIWIL-2 and piRNAs in normal human skin and epithelial tumors and its regulation during keratinocyte (KC) differentiation. Immunohistochemistry showed that PIWIL-2 was regularly expressed in the epidermis and adnexal tissue with strongest expression in sebaceous glands. Cell culture studies revealed an association of PIWIL-2 expression with the state of differentiated KC. In contrast, the PIWIL-2 expression pattern did not correlate with stem cell compartments or malignancy. piRNAs were consistently detected in KC in vitro by next-generation sequencing and the expression levels of numerous piRNAs were regulated during KC differentiation. Epidermal piRNAs were predominantly derived from processed snoRNAs (C/D-box snoRNAs), tRNAs and protein coding genes. Our data indicate that components of the PIWIL-2-piRNA pathway are present in epithelial cells of the skin and are regulated in the context of KC differentiation, suggesting a role of somatic gene regulation. However, putative roles in the maintenance of stem cell compartments or the development of malignancy in the skin were not supported by this study.

Transgene Biocontainment Strategies for Molecular Farming

Advances in plant synthetic biology promise to introduce novel agricultural products in the near future. 'Molecular farms' will include crops engineered to produce medications, vaccines, biofuels, industrial enzymes, and other high value compounds. These crops have the potential to reduce costs while dramatically increasing scales of synthesis and provide new economic opportunities to farmers. Current transgenic crops may be considered safe given their long-standing use, however, some applications of molecular farming may pose risks to human health and the environment. Unwanted gene flow from engineered crops could potentially contaminate the food supply, and affect wildlife. There is also potential for unwanted gene flow into engineered crops which may alter their ability to produce compounds of interest. Here, we briefly discuss the applications of molecular farming and explore the various genetic and physical methods that can be used for transgene biocontainment. As yet, no technology can be applied to all crop species, such that a combination of approaches may be necessary. Effective biocontainment is needed to enable large scale molecular farming.

Binding between Prion Protein and Aβ Oligomers Contributes to the Pathogenesis of Alzheimer's Disease

A plethora of evidence suggests that protein misfolding and aggregation are underlying mechanisms of various neurodegenerative diseases, such as prion diseases and Alzheimer's disease (AD). Like prion diseases, AD has been considered as an infectious disease in the past decades as it shows strain specificity and transmission potential. Although it remains elusive how protein aggregation leads to AD, it is becoming clear that cellular prion protein (PrP^C) plays an important role in AD pathogenesis. Here, we briefly reviewed AD pathogenesis and focused on recent progresses how PrP^C contributed to AD development. In addition, we proposed a potential mechanism to explain why infectious agents, such as viruses, conduce AD pathogenesis. Microbe infections cause Aβ deposition and upregulation of PrP^C, which lead to high affinity binding between Aβ oligomers and PrP^C. The interaction between PrP^C and Aβ oligomers in turn activates the Fyn signaling cascade, resulting in neuron death in the central nervous system (CNS). Thus, silencing PrP^C expression may turn out be an effective treatment for PrP^C dependent AD.

First clinical experience with a new injectable recombinant human collagen scaffold combined with autologous platelet-rich plasma for the treatment of lateral epicondylar tendinopathy (tennis elbow)

BACKGROUND

Lateral epicondylitis is a tendinopathy of the common extensor origin at the elbow. When traditional conservative treatment fails, more effective therapies are needed. Vergenix Soft Tissue Repair (STR) Matrix (CollPlant Ltd., Ness-Ziona, Israel) is an injectable gel composed of cross-linked bioengineered recombinant human type I collagen combined with autologous platelet-rich plasma (STR/PRP). The complex forms a collagen-fibrin matrix that promotes cell migration and tissue repair. Based on positive outcomes from preclinical trials, this study is the first clinical trial of STR/PRP on tendinopathy. We hypothesized that STR/PRP would be a safe and effective treatment for lateral epicondylar tendinopathy.

METHODS

Patients with chronic lateral epicondylitis underwent treatment with STR/PRP. Outcome assessment included grip strength, functional disability, and changes in sonographic tendon appearance for up to 6 months after treatment.

RESULTS

The study enrolled 40 patients. No systemic or local severe adverse events were reported. Clinical evaluation revealed an improvement in the mean Patient-Rated Tennis Elbow Evaluation score from 64.8 before treatment and showed a 59% reduction at 6 months. The 12-Item Short-Form Health Survey questionnaire showed improvement from a mean score of 30.7 to 37.7 at the final follow-up. Grip strength increased from 28.8 kg at baseline to 36.8 kg at 6 months. Improvements in sonographic tendon appearance were evident among 68% of patients.

CONCLUSION

STR/PRP is a safe treatment that effectively induces clinically significant improvements in elbow symptoms and general well-being as well as objective measures of strength and imaging of the common extensor tendon within 6 months of treatment of elbow tendinopathy recalcitrant to standard treatments.

Prion Protein Family Contributes to Tumorigenesis via Multiple Pathways

A wealth of evidence suggests that proteins from prion protein (PrP) family contribute to tumorigenesis in many types of cancers, including pancreatic ductal adenocarcinoma (PDAC), breast cancer, glioblastoma, colorectal cancer, gastric cancer, melanoma, etc. It is well documented that PrP is a biomarker for PDAC, breast cancer, and gastric cancer. However, the underlying mechanisms remain unclear. The major reasons for cancer cell-caused patient death are metastasis and multiple drug resistance, both of which connect to physiological functions of PrP expressing in cancer cells. PrP enhances tumorigenesis by multiple pathways. For example, PrP existed as pro-PrP in most of the PDAC cell lines, thus increasing cancer cell motility by binding to cytoskeletal protein filamin A (FLNa). Using PDAC cell lines BxPC-3 and AsPC-1 as model system, we identified that dysfunction of glycosylphosphatidylinositol (GPI) anchor synthesis machinery resulted in the biogenesis of pro-PrP. In addition, in cancer cells without FLNa expression, pro-PrP can modify cytoskeleton structure by affecting cofilin/F-actin axis, thus influencing cancer cell movement. Besides pro-PrP, we showed that GPI-anchored unglycosylated PrP can elevate cell mobility by interacting with VEGFR2, thus stimulating cell migration under serum-free condition. Besides affecting cancer cell motility, overexpressed PrP or doppel (Dpl) in cancer cells has been shown to increase cell proliferation, multiple drug resistance, and angiogenesis, thus, proteins from PrP gene family by affecting important processes via multiple pathways for cancer cell growth exacerbating tumorigenesis.

Recombinant mouse prion protein alone or in combination with lipopolysaccharide alters expression of innate immunity genes in the colon of mice

The objectives of this study were to test whether recombinant mouse (mo)PrP alone or in combination with LPS or under simulated endotoxemia would affect expression of genes related to host inflammatory and antimicrobial responses. To test our hypotheses colon tissues were collected from 16 male mice (FVB/N strain) and mounted in an Ussing chamber. Application of moPrP to the mucosal side of the colon affected genes related to TLR- and NLR- signaling and antimicrobial responses. When LPS was added on the mucosal side of the colon, genes related to TLR, Nlrp3 inflammasome, and iron transport proteins were over-expressed. Addition of LPS to the serosal side of the colon up-regulated genes related to TLR- and NLR-signaling, Nlrp3 inflammasome, and a chemokine. Treatment with both moPrP and LPS to the mucosal side of the colon upregulated genes associated with TLR, downstream signal transduction (DST), inflammatory response, attraction of dendritic cells to the site of inflammation, and the JNK-apoptosis pathway. Administration of moPrP to the mucosal side and LPS to the serosal side of the colon affected genes related to TLR- and NLR-signaling, DST, apoptosis, inflammatory response, cytokines, chemokines, and antimicrobial peptides. Overall this study suggests a potential role for moPrP as an endogenous 'danger signal' associated with activation of colon genes related to innate immunity and antibacterial responses.

Induction of cellular prion protein (PrPc) under hypoxia inhibits apoptosis caused by TRAIL treatment

Hypoxia decreases cytotoxic responses to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) protein. Cellular prion protein (PrPc) is regulated by HIF-1α in neurons. We hypothesized that PrPc is involved in hypoxia-mediated resistance to TRAIL-induced apoptosis. We found that hypoxia induced PrPc protein and inhibited TRAIL-induced apoptosis. Thus silencing of PrPc increased TRAIL-induced apoptosis under hypoxia. Overexpression of PrPc protein using an adenoviral vector inhibited TRAIL-induced apoptosis. In xenograft model in vivo, shPrPc transfected cells were more sensitive to TRAIL-induced apoptosis than in shMock transfected cells. Molecular chemo-therapy approaches based on the regulation of PrPc expression need to address anti-tumor function of TRAIL under hypoxia. Molecular chemo-therapy approaches based on the regulation of PrPc expression need to address anti-tumor function of TRAIL under hypoxia.

Prion protein and cancers

The normal cellular prion protein, PrP(C) is a highly conserved and widely expressed cell surface glycoprotein in all mammals. The expression of PrP is pivotal in the pathogenesis of prion diseases; however, the normal physiological functions of PrP(C) remain incompletely understood. Based on the studies in cell models, a plethora of functions have been attributed to PrP(C). In this paper, we reviewed the potential roles that PrP(C) plays in cell physiology and focused on its contribution to tumorigenesis.

Human collagen produced in plants: more than just another molecule

Consequential to its essential role as a mechanical support and affinity regulator in extracellular matrices, collagen constitutes a highly sought after scaffolding material for regeneration and healing applications. However, substantiated concerns have been raised with regard to quality and safety of animal tissue-extracted collagen, particularly in relation to its immunogenicity, risk of disease transmission and overall quality and consistency. In parallel, contamination with undesirable cellular factors can significantly impair its bioactivity, vis-a-vis its impact on cell recruitment, proliferation and differentiation. High-scale production of recombinant human collagen Type I (rhCOL1) in the tobacco plant provides a source of an homogenic, heterotrimeric, thermally stable "virgin" collagen which self assembles to fine homogenous fibrils displaying intact binding sites and has been applied to form numerous functional scaffolds for tissue engineering and regenerative medicine. In addition, rhCOL1 can form liquid crystal structures, yielding a well-organized and mechanically strong membrane, two properties indispensable to extracellular matrix (ECM) mimicry. Overall, the shortcomings of animal- and cadaver-derived collagens arising from their source diversity and recycled nature are fully overcome in the plant setting, constituting a collagen source ideal for tissue engineering and regenerative medicine applications.

A lympho-follicular microenvironment is required for pathological prion protein deposition in chronically inflamed tissues from scrapie-affected sheep

In sheep scrapie, pathological prion protein (PrP^Sc) deposition occurs in the lymphoreticular and central nervous systems. We investigated PrP^Sc distribution in scrapie-affected sheep showing simultaneous evidence of chronic lymphofollicular, lymphoproliferative/non-lymphofollicular, and/or granulomatous inflammations in their mammary gland, lung, and ileum. To do this, PrP^Sc detection was carried out via immunohistochemistry and Western Blotting techniques, as well as through inflammatory cell immunophenotyping. Expression studies of gene coding for biological factors modulating the host’s inflammatory response were also carried out. We demonstrated that ectopic PrP^Sc deposition occurs exclusively in the context of lymphofollicular inflammatory sites, inside newly formed and well-organized lymphoid follicles harboring follicular dendritic cells. On the contrary, no PrP^Sc deposition was detected in granulomas, even when they were closely located to newly formed lymphoid follicles. A significantly more consistent expression of lymphotoxin α and β mRNA was detected in lymphofollicular inflammation compared to the other two types, with lymphotoxin α and β signaling new lymphoid follicles’ formation and, likely, the occurrence of ectopic PrP^Sc deposition inside them. Our findings suggest that, in sheep co-affected by scrapie and chronic inflammatory conditions, only newly formed lymphoid follicles provide a suitable micro-environment that supports the scrapie agent’s replication in inflammatory sites, with an increased risk of prion shedding through body secretions/excretions.

Pro-prion binds filamin A, facilitating its interaction with integrin beta1, and contributes to melanomagenesis

Filamin A (FLNA) is an integrator of cell mechanics and signaling. The spreading and migration observed in FLNA sufficient A7 melanoma cells but not in the parental FLNA deficient M2 cells have been attributed to FLNA. In A7 and M2 cells, the normal prion (PrP) exists as pro-PrP, retaining its glycosylphosphatidyl-inositol (GPI) anchor peptide signal sequence (GPI-PSS). The GPI-PSS of PrP has a FLNA binding motif and binds FLNA. Reducing PrP expression in A7 cells alters the spatial distribution of FLNA and organization of actin and diminishes cell spreading and migration. Integrin β1 also binds FLNA. In A7 cells, FLNA, PrP, and integrin β1 exist as two independent, yet functionally linked, complexes; they are FLNA with PrP or FLNA with integrin β1. Reducing PrP expression in A7 cells decreases the amount of integrin β1 bound to FLNA. A PrP GPI-PSS synthetic peptide that crosses the cell membrane inhibits A7 cell spreading and migration. Thus, in A7 cells FLNA does not act alone; the binding of pro-PrP enhances association between FLNA and integrin β1, which then promotes cell spreading and migration. Pro-PrP is detected in melanoma in situ but not in melanocyte. Invasive melanoma has more pro-PrP. The binding of pro-PrP to FLNA, therefore, contributes to melanomagenesis.

The fatal attraction between pro-prion and filamin A: prion as a marker in human cancers

Pancreatic cancer is the fourth leading cancer causing deaths in the USA, with more than 30,000 deaths per year. The overall median survival for all pancreatic cancer is 6 months and the 5-year survival rate is less than 10%. This dismal outcome reflects the inefficacy of the chemotherapeutic agents, as well as the lack of an early diagnostic marker. A protein known as prion (PrP) is expressed in human pancreatic cancer cell lines. However, in these cell lines, the PrP is incompletely processed and exists as pro-PrP. The pro-PrP binds to a molecule inside the cell, filamin A (FLNa), which is an integrator of cell signaling and mechanics. The binding of pro-PrP to FLNa disrupts the normal functions of FLNa, altering the cell's cytoskeleton and signal transduction machineries. As a result, the tumor cells grow more aggressively. Approximately 40% of patients with pancreatic cancer express PrP in their cancer. These patients have significantly shorter survival compared with patients whose pancreatic cancers lack PrP. Therefore, expression of pro-PrP and its binding to FLNa provide a growth advantage to pancreatic cancers. In this article, we discuss the following points: the biology of PrP, the consequences of binding of pro-PrP to FLNa in pancreatic cancer, the detection of pro-PrP in other cancers, the potential of using pro-PrP as a diagnostic marker, and prevention of the binding between pro-PrP and FLNa as a target for therapeutic intervention in cancers.

The fatal attraction between pro-prion and filamin A: prion as a marker in human cancers

Pancreatic cancer is the fourth leading cancer causing deaths in the USA, with more than 30,000 deaths per year. The overall median survival for all pancreatic cancer is 6 months and the 5-year survival rate is less than 10%. This dismal outcome reflects the inefficacy of the chemotherapeutic agents, as well as the lack of an early diagnostic marker. A protein known as prion (PrP) is expressed in human pancreatic cancer cell lines. However, in these cell lines, the PrP is incompletely processed and exists as pro-PrP. The pro-PrP binds to a molecule inside the cell, filamin A (FLNa), which is an integrator of cell signaling and mechanics. The binding of pro-PrP to FLNa disrupts the normal functions of FLNa, altering the cell's cytoskeleton and signal transduction machineries. As a result, the tumor cells grow more aggressively. Approximately 40% of patients with pancreatic cancer express PrP in their cancer. These patients have significantly shorter survival compared with patients whose pancreatic cancers lack PrP. Therefore, expression of pro-PrP and its binding to FLNa provide a growth advantage to pancreatic cancers. In this article, we discuss the following points: the biology of PrP, the consequences of binding of pro-PrP to FLNa in pancreatic cancer, the detection of pro-PrP in other cancers, the potential of using pro-PrP as a diagnostic marker, and prevention of the binding between pro-PrP and FLNa as a target for therapeutic intervention in cancers.

Detection of PrPSc in lung and mammary gland is favored by the presence of Visna/maedi virus lesions in naturally coinfected sheep

There are few reports on the pathogenesis of scrapie (Sc) and Visna/maedi virus (VMV) coinfections. The aim of this work was to study in vivo as well as post mortem both diseases in 91 sheep. Diagnosis of Sc and VMV infections allowed the distribution of animals into five groups according to the presence (+) or absence (−) of infection by Sc and VMV: Sc−/VMV−, Sc−/VMV+, Sc+/VMV− and Sc+/VMV+. The latter was divided into two subgroups, with and without VMV-induced lymphoid follicle hyperplasia (LFH), respectively. In both the lung and mammary gland, PrP^Sc deposits were found in the germinal center of hyperplasic lymphoid follicles in the subgroup of Sc+/VMV+ having VMV-induced LFH. This detection was always associated with (and likely preceded by) PrP^Sc observation in the corresponding lymph nodes. No PrP^Sc was found in other VMV-associated lesions. Animals suffering from scrapie had a statistically significantly lower mean age than the scrapie free animals at the time of death, with no apparent VMV influence. ARQ/ARQ genotype was the most abundant among the 91 ewes and the most frequent in scrapie-affected sheep. VMV infection does not seem to influence the scrapie risk group distribution among animals from the five groups established in this work. Altogether, these data indicate that certain VMV-induced lesions can favor PrP^Sc deposits in Sc non-target organs such as the lung and the mammary gland, making this coinfection an interesting field that warrants further research for a better comprehension of the pathogenesis of both diseases.

Antimicrobial activity of human prion protein is mediated by its N-terminal region

Background

Cellular prion-related protein (PrP^c) is a cell-surface protein that is ubiquitously expressed in the human body. The multifunctionality of PrP^c, and presence of an exposed cationic and heparin-binding N-terminus, a feature characterizing many antimicrobial peptides, made us hypotesize that PrP^c could exert antimicrobial activity.

Methodology and Principal Findings

Intact recombinant PrP exerted antibacterial and antifungal effects at normal and low pH. Studies employing recombinant PrP and N- and C-terminally truncated variants, as well as overlapping peptide 20mers, demonstrated that the antimicrobial activity is mediated by the unstructured N-terminal part of the protein. Synthetic peptides of the N-terminus of PrP killed the Gram-negative bacteria Escherichia coli and Pseudomonas aeruginosa, and the Gram-positive Bacillus subtilis and Staphylococcus aureus, as well as the fungus Candida parapsilosis. Fluorescence studies of peptide-treated bacteria, paired with analysis of peptide effects on liposomes, showed that the peptides exerted membrane-breaking effects similar to those seen after treatment with the “classical” human antimicrobial peptide LL-37. In contrast to LL-37, however, no marked helix induction was detected for the PrP-derived peptides in presence of negatively charged (bacteria-mimicking) liposomes. PrP furthermore showed an inducible expression during wounding of human skin ex vivo and in vivo, as well as stimulation of keratinocytes with TGF-α in vitro.

Conclusions

The demonstration of an antimicrobial activity of PrP, localisation of its activity to the N-terminal and heparin-binding region, combined with results showing an increased expression of PrP during wounding, indicate that PrPs could have a previously undisclosed role in host defense.

Rationale for diagnosing human prion disease

Human prion diseases (PrD) like Creutzfeldt-Jakob disease (CJD) include sporadic, acquired and familial neurodegenerative disorders. The central events in the neuropathological process of PrDs are severe neuronal loss, spongiform change and accumulation of abnormal prion protein (PrPSc). The latter is a conformational variant of the host-encoded cellular PrP (PrPC), a copper-binding protein. The physiological role of PrPC is debated. Definitive diagnosis of PrD is based on post mortem demonstration of PrPSc by immunohistochemistry or Western blot. Mutations in the PrP gene (PRNP), the polymorphic site at codon 129, and the molecular characteristic of protease resistant PrP influence the phenotype. Clinical symptoms, cranial MRI scan, EEG and investigation of 14-3-3 protein in cerebrospinal fluid (CSF) suggest a diagnosis of probable CJD. Variant CJD, related to bovine spongiform encephalopathy, shows a different clinical course, symmetrical high intensity MRI signal in the pulvinar, presence of PrPSc in tonsil biopsy tissue, and a lower sensitivity of CSF 14-3-3 protein compared to sporadic CJD. Future possibilities in diagnosis of PrDs include either the demonstration of PrPSc in body fluids or disease associated changes in laboratory variables or gene expression.

Quantitative and qualitative analysis of cellular prion protein (PrP(C)) expression in bovine somatic tissues

The host encoded cellular prion protein (PrP(C)) is an N-linked glycoprotein tethered to the cell membrane by a glycophosphatidylinositol (GPI) anchor. Under certain conditions, PrP(C) can undergo conversion into a conformationally-altered isoform (PrP(Sc)) widely believed to be the pathogenic agent of transmissible spongiform encephalopathies (TSEs). Understanding the tissue-specific expression of PrP(C) is crucial considering that cells expressing high levels of PrP(C) bear a risk for conversion and accumulation of PrP(Sc). In the present study, fifteen bovine somatic tissues were analyzed for PrP(C) expression by quantitative western blot and immunohistochemistry. Quantitative western blot analysis revealed highest expression of PrP(C) in cerebellum, obex and spinal cord. Intermediate levels were detected in thymus, intestine, nerve, heart and spleen, and lower levels in lung, muscle, kidney, lymph node, skin, pancreas and liver. Immunohistochemical analysis detected intense cellular-specific PrP(C) staining in neurons, thymocytes and lymphocytes. PrP(C) was also detected in the enteric wall, pancreatic islets of langerhans, myocardium, pulmonary alveolar sacs, renal glomeruli and dermal epithelial cells. This study demonstrated the quantitatively varied, wide-spread, tissue- and cell-specific expression pattern of PrP(C) in bovine somatic tissues. The importance of this study is to lay the foundation for understanding the tissue-specific expression of PrP(C) and to consider the potential participation of more bovine tissues in the transmission of BSE infection.

Physiology of the prion protein

Prion diseases are transmissible spongiform encephalopathies (TSEs), attributed to conformational conversion of the cellular prion protein (PrP(C)) into an abnormal conformer that accumulates in the brain. Understanding the pathogenesis of TSEs requires the identification of functional properties of PrP(C). Here we examine the physiological functions of PrP(C) at the systemic, cellular, and molecular level. Current data show that both the expression and the engagement of PrP(C) with a variety of ligands modulate the following: 1) functions of the nervous and immune systems, including memory and inflammatory reactions; 2) cell proliferation, differentiation, and sensitivity to programmed cell death both in the nervous and immune systems, as well as in various cell lines; 3) the activity of numerous signal transduction pathways, including cAMP/protein kinase A, mitogen-activated protein kinase, phosphatidylinositol 3-kinase/Akt pathways, as well as soluble non-receptor tyrosine kinases; and 4) trafficking of PrP(C) both laterally among distinct plasma membrane domains, and along endocytic pathways, on top of continuous, rapid recycling. A unified view of these functional properties indicates that the prion protein is a dynamic cell surface platform for the assembly of signaling modules, based on which selective interactions with many ligands and transmembrane signaling pathways translate into wide-range consequences upon both physiology and behavior.

Neuronal and astrocytic cells, obtained after differentiation of human neural GFAP-positive progenitors, present heterogeneous expression of PrPc

PrP(c) is a cellular isoform of the prion protein with an unknown normal function. One of the putative physiological roles of this protein is its involvement in cell differentiation. Recently, in vitro and in vivo studies showed that GFAP-positive cells have characteristics of stem/progenitor cells that generate neurons and glia. We used an in vitro model of human neurogenesis from GFAP-positive progenitor cells to study the expression of PrP(c) during neural differentiation. Semi-quantitative multiplex-PCR assay and Western blot analysis revealed a significant increase of PRNP expression level in differentiated cells compared to undifferentiated cell population. As determined by immunocytochemistry followed by a quantitative image analysis, the PrP(c) level increased significantly in neuronal cells and did not increase significantly in glial cells. Of note, glial and neuronal cells showed a very large heterogeneity of PrP(c) expression. Our results provide the basis for studying the role of PrP(c) in cell differentiation and neurogenesis from human GFAP-positive progenitor cells.

Differential expression of calcium-related genes in gastric cancer cells transfected with cellular prion protein

The prion protein (PrPC) has a primary role in the pathogenesis of transmissible spongiform encephalopathies, which causes prion disorders partially due to Ca2+ dysregulation. In our previous work, we found that overexpressed PrPC in gastric cancer was involved in apoptosis, cell proliferation, and metastasis of gastric cancer. To better understand how PrPC acts in gastric cancer, a human microarray was performed to select differentially regulated genes that correlate with the biological function of PrPC. The microarray data were analyzed and revealed 3798 genes whose expression increased at least 2-fold in gastric cancer cells transfected with PrPC. These genes encode proteins involved in several aspects of cell biology, among which, we specially detected molecules related to calcium, especially the S100 calcium-binding proteins, and found that PrPC upregulates S100A1, S100A6, S100B, and S100P but downregulates CacyBP in gastric cancer cells. We also found that intracellular Ca2+ levels in cells transfected with PrPC increased, whereas these levels decreased in knockdowns of these cells. Taken together, PrPC might increase intracellular Ca2+, partially through calcium-binding proteins, or PrPC might upregulate the expression of S100 proteins, partially through stimulating the intracellular calcium level in gastric cancer. Though the underlying mechanisms need further exploration, this study provides a new insight into the role of PrPC in gastric cancer and enriches our knowledge of prion protein.

Accumulation of pathological prion protein PrPSc in the skin of animals with experimental and natural scrapie

Prion infectivity and its molecular marker, the pathological prion protein PrP^Sc, accumulate in the central nervous system and often also in lymphoid tissue of animals or humans affected by transmissible spongiform encephalopathies. Recently, PrP^Sc was found in tissues previously considered not to be invaded by prions (e.g., skeletal muscles). Here, we address the question of whether prions target the skin and show widespread PrP^Sc deposition in this organ in hamsters perorally or parenterally challenged with scrapie. In hamsters fed with scrapie, PrP^Sc was detected before the onset of symptoms, but the bulk of skin-associated PrP^Sc accumulated in the clinical phase. PrP^Sc was localized in nerve fibres within the skin but not in keratinocytes, and the deposition of PrP^Sc in skin showed no dependence from the route of infection and lymphotropic dissemination. The data indicated a neurally mediated centrifugal spread of prions to the skin. Furthermore, in a follow-up study, we examined sheep naturally infected with scrapie and detected PrP^Sc by Western blotting in skin samples from two out of five animals. Our findings point to the skin as a potential reservoir of prions, which should be further investigated in relation to disease transmission.

Transmissible spongiform encephalopathies (TSEs), or prion diseases, are fatal neurodegenerative diseases affecting the central nervous system. According to the prion hypothesis, TSEs are caused by proteinaceous infectious particles (“prions”) that consist essentially of PrP^Sc, an aberrant form of the prion protein with a pathologically altered folding and/or aggregation structure. Scrapie of sheep, chronic wasting disease (CWD) of deer, bovine spongiform encephalopathy (BSE) of cattle, and variant Creutzfeldt-Jakob disease (vCJD) of humans are prominent examples of acquired prion diseases. To further pinpoint the peripheral tissues that could serve as reservoirs of prions in the mammalian body and from which these pathogens could be potentially disseminated into the environment and transmitted to other individuals, we examined the skin of hamsters perorally challenged with scrapie and of naturally infected scrapie sheep for the presence of PrP^Sc. We show that PrP^Sc can accumulate in the skin at late stages of incubation, and that the protein is located primarily in small nerve fibres within this organ. The question of whether the skin may also provide a reservoir for prions in CWD, BSE, or vCJD, and the role of the skin in relation to the natural transmission of scrapie in the field needs further investigation.

Human cellular prion protein hPrPC is sorted to the apical membrane of epithelial cells

Propagation of the scrapie isoform of the prion protein (PrP(Sc)) depends on the expression of endogenous cellular prion (PrP(C)). During oral infection, PrP(Sc) propagates, by conversion of the PrP(C) to PrP(Sc), from the gastrointestinal tract to the nervous system. Intestinal epithelium could serve as the primary site for PrP(C) conversion. To investigate PrP(C) sorting in epithelia cells, we have generated both a green fluorescent protein (EGFP) or hemagglutinin (HA) tagged human PrP(C) (hPrP(C)). Combined molecular, biochemical, and single living polarized cell imaging characterizations suggest that hPrP(C) is selectively targeted to the apical side of Madin-Darby canine kidney (MDCKII) and of intestinal epithelia (Caco2) cells.

Expression of the prion protein gene (PRNP) and cellular prion protein (PrPc) in cattle and sheep fetuses and maternal tissues during pregnancy

We investigated the expression of prion protein gene both on mRNA and protein levels in bovine and ovine female reproductive organs during gestation and various tissues of their fetuses. The fetal tissues of both species included brain, cotyledon, heart, intestine, kidney, liver, lung, and muscle. In cattle, prion protein gene (PRNP) transcripts were detected by semiquantitative RT-PCR in reproductive tissues such as ovary, oviduct, endometrium, myometrium, follicles, and granulosa cells. In various tissues of 2-month-old fetuses, higher expression levels were found in brain and cotyledon compared to the other tissues. To detect the expression of the gene transcript in in vivo preimplantation embryos and 1-month-old fetuses, real-time PCR was performed showing that the level of gene expression in zygote stage was significantly higher (p < or = 0.05) than that of the other stages. Sheep were categorized as resistant (RI) or high susceptible (R5) to scrapie according to their PRNP genotype. In both genotype groups, the PRNP mRNA was detectable in all tissues studied including ovary, oviduct, endometrium, myometrium, and caruncle of ewes and all tissues of 2-month-old fetuses of both groups. Comparison between reproductive organs demonstrates the highest expression level in caruncle tissue of R1 ewes, whereas the level was high in brain and low in liver of both R1 and R5 fetuses. In addition, real-time RT-PCR was performed in immature oocytes, mature oocytes, in vivo embryos at morula stage, and 1-month-old fetuses. The results showed that the relative expression levels of the ovine PRNP mRNA in mature oocytes and morula stage embryos were significantly lower than those in immature oocytes and 1-month-old fetuses (p < or = 0.05). Western blot analyses revealed the immunoreactive bands corresponding to the cellular prion protein (PrPc) in all maternal and fetal tissues examined of both cattle and sheep. Moreover, immunohistochemical staining implicated localization of the PrPc in ovarian cortex and ovarian medulla of both species. However, PrPc was not detected in oocyte, granulosa cells, theca cells, and corpus luteum in this study.

Developmental expression of PrP in the post-implantation embryo

Since prion protein (PrP) mRNA and PrP(C) expression levels in transgenic (Tg) mice using the CosSHa.tet vector correlate well with the PrP transgene copy, we constructed Prnp-LacZ Tg animals expressing beta-galactosidase that was inserted into the CosSHa.tet vector. The CosSHa.tet vector was created from a large PrP cosmid clone in which the PrP open reading frame was deleted. In the developing nervous system, the beta-galactosidase marker was not expressed in the neural progenitors of the mitotically active ventricular zone. It is first expressed in cells that have ceased proliferating, migrated radially from the ventricular zone, and differentiated into neurons in the intermediate layer. At E11.5 p.c., motor neurons in the ventral neural tube clearly express the marker transgene. Expression in dorsal neural tube neurons is observed at later stages, after their differentiation. These results indicate that Prnp gene expression in the nervous system begins in post-mitotic neural cells that have undergone neuronal differentiation. This pattern of Prnp expression in the nervous system appears to persist throughout the adult life of mammals.

Myiasis as a risk factor for prion diseases in humans

Prion diseases are transmissible spongiform encephalopathies of humans and animals. The oral route is clearly associated with some prion diseases, according to the dissemination of bovine spongiform encephalopathy (BSE or mad cow disease) in cattle and kuru in humans. However, other prion diseases such as scrapie (in sheep) and chronic wasting disease (CWD) (in cervids) cannot be explained in this way and are probably more associated with a pattern of horizontal transmission in both domestic and wild animals. The skin and mucous membranes are a potential target for prion infections because keratinocytes and lymphocytes are susceptible to the abnormal infective isoform of the prion protein. Iatrogenic transmission of Creutzfeldt-Jakob disease (CJD) was also recognized after corneal transplants in humans and scrapie was successfully transmitted to mice after ocular instillation of infected brain tissue, confirming that these new routes could also be important in prion infections. Some ectoparasites have been proven to harbour prion rods in laboratory experiments. Prion rods were identified in both fly larvae and pupae; adult flies are also able to express prion proteins. The most common causes of myiasis in cattle and sheep, closely related animals with previous prion infections, are Hypoderma bovis and Oestrus ovis, respectively. Both species of flies present a life cycle very different from human myiasis, as they have a long contact with neurological structures, such as spinal canal and epidural fat, which are potentially rich in prion rods. Ophthalmomyiases in humans is commonly caused by both species of fly larvae worldwide, providing almost direct contact with the central nervous system (CNS). The high expression of the prion protein on the skin and mucosa and the severity of the inflammatory response to the larvae could readily increase the efficiency of transmission of prions in both animals and humans.

Cellular prion protein promotes invasion and metastasis of gastric cancer

Cellular prion protein (PrPc) is a glycosylphosphatidylinositol (GPI) -anchored membrane protein that is highly conserved in mammalian species. PrPc has the characteristics of adhesive molecules and is thought to play a role in cell adhesion and membrane signaling. Here we investigated the possible role of PrPc in the process of invasiveness and metastasis in gastric cancers. PrPc was found to be highly expressed in metastatic gastric cancers compared to nonmetastatic ones by immunohistochemical staining. PrPc significantly promoted the adhesive, invasive, and in vivo metastatic abilities of gastric cancer cell lines SGC7901 and MKN45. PrPc also increased promoter activity and the expression of MMP11 by activating phosphorylated ErK1/2 in gastric cancer cells. MEK inhibitor PD98059 and MMP11 antibody (Ab) significantly inhibited in vitro invasive and in vivo metastatic abilities induced by PrPc. N-terminal fragment (amino acid 24-90) was suggested to be an indispensable region for signal transduction and invasion-promoting function of PrPc. Taken together, the present work revealed a novel function of PrPc that the existence of N-terminal region of PrPc could promote the invasive and metastatic abilities of gastric cancer cells at least partially through activation of MEK/ERK pathway and consequent transactivation of MMP11.

Aggravation of ischemic brain injury by prion protein deficiency: Role of ERK-1/-2 and STAT-1

The cellular isoform of prion protein, PrPc, may confer neuroprotection in the brain, according to recent studies. To elucidate the role of PrPc in stroke pathology, we subjected PrPc-knockout (Prnp(0/0)), wild-type and PrPc-transgenic (tga20) mice to 30 min of intraluminal middle cerebral artery occlusion, followed by 3, 24 or 72 h reperfusion, and examined how PrPc levels influence brain injury and cell signaling. In immunohistochemical experiments and Western blots, we show that PrPc expression is absent in the brains of Prnp(0/0) mice, detectable in wild-type controls and approximately 4.0-fold elevated in tga20 mice. We provide evidence that PrPc deficiency increases infarct size by approximately 200%, while transgenic PrPc restores tissue viability, albeit not above levels in wild-type animals. To elucidate the mechanisms underlying Prnp(0/0)-induced injury, we performed Western blots, which revealed increased activities of ERK-1/-2, STAT-1 and caspase-3 in ischemic brains of Prnp(0/0)mice. Our data suggest a role of cytosolic signaling pathways in Prnp(0/0)-induced cell death.

Risk analysis of ectoparasites acting as vectors for chronic wasting disease

Prion diseases are rare neurodegenerative diseases of humans and animals with a lethal evolution. Animal prion infections, such as chronic wasting disease (CWD) and scrapie (sheep) have shown a pattern of horizontal transmission. CWD is an endemic disease that has been affecting thousands of domestic and wild cervids in US for the last three decades. The mode of contamination is not known, although direct contact between infected and non-infected animals via saliva, urine and feces have been considered. Increasing spread of CWD has raised concerns about the potential transmission to humans and the conversion of human prion protein by CWD-associated prions has been demonstrated in laboratory experiments. Fly larvae exposed to brain infected material were able to readily transmit scrapie to hamsters. Prion rods were identified in both larvae and fly pupae. New lines of evidence confirmed that adult flies are also able to express prion proteins. The most prevalent species of myiasis in cattle, sheep and wild cervids (Hypoderma spp.) present a very different life cycle from human myiasis, with a long contact with neurologic structures, such as the spinal canal and epidural fat, that are potentially rich in prion rods. Considering the huge amount of fly larvae that affects each animal, it is important to discuss the possibility that these ectoparasites could theoretically act as reservoirs and vectors for CWD and other prion diseases. It is critical to recognize all the possible factors involved in CWD transmission since ectoparasites could be handled in an easier way than the environmental persistence of infectious prions.

Prion protein accumulation and neuroprotection in hypoxic brain damage

The function of the normal conformational isoform of prion protein, PrP(C), remains unclear although lines of research have suggested a role in the cellular response to oxidative stress. Here we investigate the expression of PrP(C) in hypoxic brain tissues to examine whether PrP(C) is in part regulated by neuronal stress. Cases of adult cerebral ischemia and perinatal hypoxic-ischemic injury in humans were compared with control tissues. PrP(C) immunoreactivity accumulates within neuronal processes in the penumbra of hypoxic damage in adult brain, and within neuronal soma in cases of perinatal hypoxic-ischemic injury, and in situ hybridization analysis suggests an up-regulation of PrP mRNA during hypoxia. Rodents also showed an accumulation of PrP(C) in neuronal soma within the penumbra of ischemic lesions. Furthermore, the infarct size in PrP-null mice was significantly greater than in the wild type, supporting the proposed role for PrP(C) in the neuroprotective adaptive cellular response to hypoxic injury.

cDNA representational difference analysis of ileal Peyer’s patches in lambs after oral inoculation with scrapie

cDNA representational difference analysis (RDA) was used to study gene expression profiles in the ileal Peyer's patch of a lamb 1 week after oral inoculation with the scrapie agent. Twenty-five differentially expressed cDNA fragments were identified and cloned. Sequence analysis indicated seven novel gene sequences. Other clones shared sequence homology with genes encoding ribosomal and mitochondrial proteins, the translation initiation factor EIF4GII and the bovine pancreatic thread protein. Reverse Northern was used to confirm the differential expression in another four lambs inoculated with scrapie and the tissue distribution of the novel genes was examined using Northern blot analysis.

Vaccinia virus pathogenicity in atopic dermatitis is caused by allergen-induced immune response that prevents the antiviral cellular and humoral immunity

Atopic dermatitis (AD) serves as a contraindication for the immunization of AD patients with a live vaccinia virus (VV) vaccine. The antiallergen IgE interacts with the Fc receptors (FcepsilonRI) on dendritic cell (DC) membranes and with allergen molecules. The immunological events that lead to AD disease, the activation of the T-helper 2 (Th2) immune response, the synthesis of the cytokines IL-4, IL-5, IL-13, and the inhibition of the T-helper 1 (Th1) damage the capacity of the host to develop anti-VV cytotoxic cells (CTLs). In the presence of Th2-derived cytokine IL-4 in the AD skin and the synthesis of VV proteins that interfere recruitment of DCs by host cytokines, the VV can cause a generalized infection. Conceptually, new VV recombinants may be needed for human immunization. Such VV recombinants should lack the genes that interfere with the host immune system and express a mutated human IL-4 cytokine gene that will prevent negative regulatory mechanisms. Such improved VV recombinants may be used to express genes from pathogenic viruses.

Stimulation of cellular prion protein expression by TSH in human thyrocytes

The cellular isoform of prion protein (PrP(C)) is a cell-surface glycosyl-phosphatidylinositol-anchored protein which is ubiquitously expressed on the cell membrane. It may function as a cell receptor or as a cell adhesion molecule. Thyroid follicles, obtained from patients with Graves' disease at thyroidectomy, were cultured in F-12/RPMI-1640 medium supplemented with 0.5% fetal bovine serum and bovine thyroid stimulating hormone (bTSH). Northern blot analyses revealed that bTSH increased the steady-state expression levels of PrP mRNA in a time- and dose-dependent manner. This increase was reproduced by dibutyryl-cAMP and 12-decanoylphorbol-13-acetate. The mRNA expression was greater in thyroid follicles in suspension culture than in thyrocytes cultured in a monolayer. These findings suggest that TSH stimulates PrP mRNA expression in thyrocytes through the protein kinase A and C pathways. The greater mRNA expression in thyroid follicles than in monolayer cells suggests that PrP(C) may be involved in structure formation or maintenance of thyroid follicles.

Could ectoparasites act as vectors for prion diseases?

Prion diseases are rare neurodegenerative diseases of humans and animals with a lethal evolution. Several cell types found on the human skin, including keratinocytes, fibroblasts and lymphocytes, are susceptible to the abnormal infective isoform of the prion protein, which transforms the skin to produce a potential target for prion infection. Iatrogenic transmission of Creutzfeldt-Jakob disease was also recognized after corneal transplants in humans, and scrapie was successfully transmitted to mice after ocular instillation of infected brain tissue, confirming that these new routes, as well as cerebral inoculation and oral ingestion, could be important in prion infections. Animal prion infections, such as scrapie (sheep) and "mad cow disease" (cattle), have shown a pattern of horizontal transmission in farm conditions and several ectoparasites have been shown to harbor prion rods in laboratory experiments. Fly larvae and mites were exposed to brain-infected material and were readily able to transmit scrapie to hamsters. New lines of evidence have confirmed that adult flies are also able to express prion proteins. Because ocular and cerebral myiases and mite infestation are not rare worldwide, and most cases are caused by fly larvae or hay mites that usually affect sheep and cattle, it is important to discuss the possibility that these ectoparasites could eventually act as reservoirs and/or vectors for prion diseases.

Organ distribution of prion proteins in variant Creutzfeldt-Jakob disease

In this article we give an overview of the transmissible spongiform encephalopathies, with emphasis on the evidence for the distribution of abnormal prions in tissues. The normal prion protein is distributed ubiquitously throughout human body tissues. Endogenous expression of the normal prion protein, as well as auxiliary proteins, plays a part in accumulation of the abnormal prion protein. As exemplified by variant Creutzfeldt-Jakob disease (vCJD) the abnormal prion protein can accumulate in the host lymphoid system, in particular the follicular dendritic cells. The route for the disease-related prion neuroinvasion is likely to involve the peripheral nervous system. An alternative route may involve blood constituents. Both animal studies and studies on vCJD patients suggest a potential for abnormal prion distribution in several peripheral tissues other than the lymphoreticular system. In human beings the abnormal prion has been reported in the brain, tonsils, spleen, lymph node, retina, and proximal optic nerve. Infectivity, although present in peripheral tissues, is at lower levels than in the central nervous system (CNS). Animal models suggest that the growth of infectivity in the CNS is likely to be gradual with maximum values during the clinical phase of disease. That tissues may harbour the abnormal prion, at different levels of infectivity, during the incubation period of the disease raises concerns of iatrogenic transmission of the disease either after surgery, blood transfusion, or accidental organ transplantation from donors in the preclinical phase of the disease.

Doenças priônicas: avaliação dos riscos envolvidos na utilização de produtos de origem bovina

Os príons são proteínas que se mostram capazes de auto-replicação apesar de, para isso, alterar o metabolismo celular. São responsáveis por inúmeras doenças em animais e no ser humano (doenças priônicas), todas elas fatais. Essas moléstias apresentam enorme variabilidade quanto ao período de incubação, de alguns meses a 40 anos. Os príons acumulam-se e destroem os neurônios, provocando quadros conhecidos como encefalopatias espongiosiformes. Discute-se a apresentação clínica, epidemiológica e histórica das doenças priônicas. O foco maior de discussão recai, no entanto, na possibilidade teórica da transmissão iatrogênica dos príons por meio das formulações tópicas que utilizam ceramidas (cerebrosídeos) ou placenta de origem bovina, assim como pelo risco representado por alguns procedimentos dermatológicos, como transplantes da pele e implantes de colágeno.

Neuropathology of prion diseases

In prion diseases, neuropathology has remained the most important tool to give a definite diagnosis, and neuropathological research has contributed significantly to our current pathogenetic understanding. Immunohistochemistry for the disease-associated prion protein (PrP(Sc)) is indispensable for the neuropathological confirmation of prion diseases. The amount and distribution of PrP(Sc) deposits do not always correlate with type and severity of local tissue damage. PrP(Sc) deposition occurs only where neuronal parenchyma is present; in scarred infarctions with prominent gliosis, PrP(Sc) does not accumulate. Early, severe and selective loss affects a subset of inhibitory GABAergic neurons both in human and experimental prion diseases. The central pathogenetic cascade includes oxidative stress to neurons and their apoptosis. New patterns of PrP(Sc) immunoreactivity include granular ganglionic and tiny adaxonal PrP(Sc) deposits in peripheral nervous tissue, and dendritic cells and macrophages in vessel walls, suggesting that mobile haematogenous cells may be involved in spread of prions.

A possible role of keratinocytes of skin and mucous membranes in prion propagation and transmission

Prion diseases or transmissible spongiform encephalopathies are lethal neurodegenerative diseases caused by proteinaceous agents that consist of an abnormal form of a host protein designated PrP and are devoid of nucleic acids. In laboratory settings these diseases are usually transmitted by intracerebral or peripheral inoculation. In the field they have been shown to be transmitted by uptake of contaminated food but in most instances the route of transmission remains obscure. Both nervous and lymphatic tissues in peripheral organs have been implicated in the spread and propagation of prions. The exact sites of uptake and initial propagation of the infectious agents have not yet been determined, however. As the expression of PrPc is required for the propagation of the infectious agent the search for peripheral cells positive for PrPc may reveal potential routes of entry and transmission. Recently epidermal and mucosal keratinocytes have been found to express PrPc. These data together with the recent finding that epithelial cells are able to support prion replication in vitro suggest that keratinocytes might play a role in the pathogenesis and/or transmission of prion diseases.

Prions in dermatology

Prion diseases are uncommon fatal neurodegenerative disorders that have gained scientific importance as a result of the emergence of new forms of these diseases in both animals and humans. Prions appear to be composed principally or entirely of abnormal isoforms of a host-encoded glycoprotein. There is substantial scientific evidence to support the notion that bovine spongiform encephalopathy ("mad cow disease") has affected humans. Recent studies have demonstrated that prions can adhere easily to metal surfaces, and normal sterilization procedures are not likely to completely inactivate them. Iatrogenic transmission of prion diseases, such as Creutzfeldt-Jakob disease, was recognized after corneal transplantations, dura mater grafts, neurosurgical procedures, and the use of human hormones (growth hormone and gonadotropin). Although bovine collagen has long been recognized as a safe and biocompatible material, dermatologists should be aware of the theoretical potential for prion transmission when materials from bovine origin and products obtained from cultured cells fed with fetal or newborn calf serum are used.

Expression of cellular prion-related protein by murine Langerhans cells and keratinocytes

Transmissible spongiform encephalopathies are characterized by the accumulation of a proteinase-resistant isoform of the cellular prion-related protein (PrP(c)) within the central nervous system (CNS). The accumulation of scrapie-associated PrP (PrP(Sc)) within cells of the lymphoreticular system prior to its accumulation in the CNS is regarded as important for the development of neurological diseases after peripheral inoculation. Little, however, is known as to which cells are the targets for peripheral inoculation. Here, the presence of PrP(c) on murine Langerhans cells (LC), dendritic cells in the skin and mucosa, and keratinocytes (KC) is demonstrated by immunohistochemical staining, Western-blotting and FACS analysis. The expression of PrP(c) mRNA in freshly purified LC and KC was also detected by reverse transcriptase-polymerase chain reaction. The expression of PrP(c) on LC was slightly increased during culture. These data suggest that LC and KC may be the targets for peripheral infection with prions.

Nonneuronal cellular prion protein

The normal cellular prion protein (PrP(c)) is a membrane sialoglycoprotein of unknown function having the unique property of adopting an abnormal tertiary conformation. The pathological conformer PrP(sc) would be the agent of transmissible spongiform encephalopathies or prion diseases. They include scrapie and bovine spongiform encephalopathy in animals and Creutzfeldt-Jakob disease in humans. The conversion of PrP(c) into PrP(sc) in the brain governs the clinical phenotype of the disease. However, the three-dimensional structure change of PrP(c) can also take place outside the central nervous system, in nonneuronal cells particularly of lymphoid tissue where the agent replicates. In natural infection, PrP(c) in nonneuronal cells of peripheral extracerebral organs may play a key role as the receptor required to enable the entry of the infectious agent into the host. In the present review we have undertaken a first evaluation of compelling data concerning the PrP(c)-expressing cells of nonneuronal origin present in cerebral and extracerebral tissues. The analysis of tissue, cellular, and subcellular localization of PrP(c) may help us better understand the biological function of PrP(c) and provide some information on physiopathological processes underlying prion diseases.

Self prion protein peptides are immunogenic in Lewis rats

Prion diseases are caused by abnormal folding of the prion protein. The paradigm is that the prion protein is not immunogenic because the immune system must be tolerant to such a self protein. In an attempt to identify immunogenic prion peptides, we immunized Lewis rats with peptides that fitted the MHC class II RT1.B(1)motif. Both humoral and cellular immunity to the prion peptides were obtained without any harmful effects to young animals. However, when 8-month-old rats were immunized, a sixth (6/36) of the rats developed severe skin inflammation with concomitant hair loss. These findings suggest that immunity to self-prion peptides can be readily induced in Lewis rats and that this immune response may have pathogenic consequences in older rats.

Cellular prion protein status in sheep: tissue-specific biochemical signatures

Expression of the cellular prion protein PrP(C) is sine qua none for the development of transmissible spongiform encephalopathy and thus for the accumulation of the illness-associated conformer PrP(Sc). Therefore, the tissue distribution of PrP(C) at the protein level in both quantitative and qualitative terms was investigated. PrP(C) was quantified using a two-site enzyme immunometric assay which was calibrated with purified ovine recombinant prion protein (rPrP). The most PrP(C)-rich tissue was the brain, followed by the lungs, skeletal muscle, heart, uterus, thymus and tongue, which contained between 20- and 50-fold less PrP(C) than the brain. The PrP(C) content of these tissues seems to be comparable between sheep. Other organs, however, showed different, but low, levels of the protein depending on the animal examined. This was also the case for tissues from the gastrointestinal tract. The tissue containing the lowest concentration of PrP(C) was shown to be the liver, where PrP(C) was found to be between 564- and 16000-fold less abundant than in the brain. PrP(C) was concentrated from crude cellular extracts by immunoprecipitation using several monoclonal and polyclonal anti-ovine PrP antibodies. Interestingly, it was observed that the isoform profile of PrP(C) was tissue-specific. The most atypical electrophoretic profile of PrP(C) was found in the skeletal muscle, where two polypeptides of 32 and 35 kDa were detected.

Microglia and prion disease

Gliosis is one of the hallmarks of the prion diseases. Prion diseases are fatal neurodegenerative conditions of low incidence made famous by both the hypothesis that a protein acts as the infectious agent without involvement of nucleic acid and the speculative idea that a disease of cattle, BSE, has spread to humans from the ingestion of prion-infected beef. Despite these unproved hypotheses, the aetiology of the prion diseases remains unsolved. The rapid degenerative course of the disease is preceded by a long incubation period with little or no symptoms. The rapid neurodegeneration in the disease follows from increased deposition of an abnormal isoform of a normal neuronal protein. Co-incident with the appearance of this abnormal protein is the activation of large numbers of microglia. Studies in cell culture with both the abnormal prion protein and a peptide-mimic suggest that neuronal degeneration occurs because of two concurrent effects. First, there is a reduction in neuronal resistance to toxic insults and, second, there is an increase in the production of toxic substances such as reactive oxygen species by microglia and a decrease in glutamate clearance by astrocytes. Microglia activated by the abnormal form of the prion protein also release cytokines, which stimulate changes in astrocytes such as proliferation. The implication of this is that microglia may play a major role in initiating the pathological changes in prion disease. This review discusses the role of microglia in these changes.