Konstantinos Xanthopoulos

Methionine Sulfoxides on PrPSc: A Prion-Specific Covalent Signature

Prion diseases are fatal neurodegenerative disorders believed to be transmitted by PrP (Sc), an aberrant form of the membrane protein PrP (C). In the absence of an established form-specific covalent difference, the infectious properties of PrP (Sc) were uniquely ascribed to the self-perpetuation properties of its aberrant fold. Previous sequencing of the PrP chain isolated from PrP(27-30) showed the oxidation of some methionine residues; however, at that time, these findings were ascribed to experimental limitations. Using the unique recognition properties of alphaPrP mAb IPC2, protein chemistry, and state of the art mass spectrometry, we now show that while a large fraction of the methionine residues in brain PrP (Sc) are present as methionine sulfoxides this modification could not be found on brain PrP (C) as well as on its recombinant models. In particular, the pattern of oxidation of M213 with respect to the glycosylation at N181 of PrP (Sc) differs both within and between species, adding another diversity factor to the structure of PrP (Sc) molecules. Our results pave the way for the production of prion-specific reagents in the form of antibodies against oxidized PrP chains which can serve in the development of both diagnostic and therapeutic strategies. In addition, we hypothesize that the accumulation of PrP (Sc) and thereafter the pathogenesis of prion disease may result from the poor degradation of oxidized aberrantly folded PrP.

Immunization with recombinant prion protein leads to partial protection in a murine model of TSEs through a novel mechanism

Transmissible spongiform encephalopathies are neurodegenerative diseases, which despite fervent research remain incurable. Immunization approaches have shown great potential at providing protection, however tolerance effects hamper active immunization protocols. In this study we evaluated the antigenic potential of various forms of recombinant murine prion protein and estimated their protective efficacy in a mouse model of prion diseases. One of the forms tested provided a significant elongation of survival interval. The elongation was mediated via an acute depletion of mature follicular dendritic cells, which are associated with propagation of the prion infectious agent in the periphery and in part to the development of humoral immunity against prion protein. This unprecedented result could offer new strategies for protection against transmissible encephalopathies as well as other diseases associated with follicular dendritic cells.

Species and Strain Glycosylation Patterns of PrPSc

Background A key event in transmissible spongiform encephalopathies (TSEs) is the conversion of the soluble, protease-sensitive glycosylated prion protein (PrPC) to an abnormally structured, aggregated and partially protease-resistant isoform (PrPSc). Both PrP isoforms bear two potential glycosylation sites and thus in a typical western blot with an anti-PrP antibody three distinct bands appear, corresponding to the di-, mono- or unglycosylated forms of the protein. The relative intensity and electrophoretic mobility of the three bands are characteristic of each TSE strain and have been used to discriminate between them. Methodology/Principal Findings In the present study we used lectin-based western blotting to evaluate possible variations in composition within sugar chains carried by PrPSc purified from subjects affected with different TSEs. Our findings indicate that in addition to the already well-documented differences in electrophoretic mobility and amounts of the glycosylated PrPSc forms, TSE strains also vary in the abundance of specific N-linked sugars of the PrPSc protein. Conclusions/Significance These results imply that PrP glycosylation might fine-tune the conversion of PrPC to PrPSc and could play an accessory role in the appearance of some of the characteristic features of TSE strains. The differences in sugar composition could also be used as an additional tool for discrimination between the various TSEs.

Tissue plasminogen activator in brain tissues infected with transmissible spongiform encephalopathies

Prion propagation involves conversion of host PrP(C) to a disease-related isoform, PrP(Sc), which accumulates during disease and is the principal component of the transmissible agent. Proteolysis seems to play an important role in PrP metabolism. Plasminogen, a serine protease precursor, has been shown to interact with PrP(Sc). Plasminogen can be proteolytically activated by tissue plasminogen activator (tPA). Recent reports imply a crosstalk between tPA-mediated plasmin activation and PrP. In our study, both tPA activity and tPA gene expression were found elevated in TSE-infected brains as compared to their normal counterparts. Furthermore, it was proved that PrP(Sc), in contrast to PrP(C), could not be degraded by plasmin. In addition, it was observed that TSE symptoms and subsequent death of plasminogen-deficient and tPA-deficient scrapie challenged mice preceded that of wild-type controls. Our data imply that enhanced tPA activity observed in prion infected brains may reflect a neuro-protective response.

Inactivation of CYLD in intestinal epithelial cells exacerbates colitis-associated colorectal carcinogenesis - a short report

PurposeCYLD is a tumor suppressor that has been linked to the development of various human malignancies, including colon cancer. The tumor-suppressing function of CYLD is associated with its deubiquitinating activity, which maps to the carboxyl-terminal region of the protein. In the present study we evaluated the role of intestinal epithelial CYLD in colitis-associated cancer using a conditional mouse CYLD inactivation model.MethodsIn order to evaluate the role of CYLD in intestinal epithelial carcinogenesis, mice (IEC-CyldΔ9 mice) that carry a mutation that eliminates the deubiquitinating domain of CYLD in intestinal epithelial cells (IEC) were generated by crossing Villin-Cre transgenic mice to previously generated mice carrying a loxP-flanked Cyld exon 9 (Cyldflx9 mice).ResultsWe found that IEC-CyldΔ9 mice did not present spontaneous intestinal abnormalities up to one year of age. However, upon challenge with a combination of genotoxic (AOM) and pro-inflammatory (DSS) agents we found that the number of adenomas in the IEC-CyldΔ9 mice was dramatically increased compared to the control mice. Inactivation of CYLD in intestinal epithelial cells did not affect the classical nuclear factor-kappaB (NF-κB) and c-Jun kinase (JNK) activation pathways under physiological conditions, suggesting that these pathways do not predispose CYLD-deficient intestinal epithelia to colorectal cancer development before the onset of genotoxic and/or pro-inflammatory stress.ConclusionsOur findings underscore a critical tumor-suppressing role for functional intestinal epithelial CYLD in colitis-associated carcinogenesis. CYLD expression and its associated pathways in intestinal tumors may be exploited for future prognostic and therapeutic purposes.

Homogenous photocatalytic decontamination of prion infected stainless steel and titanium surfaces

Prions are notorious for their extraordinary resistance to traditional methods of decontamination, rendering their transmission a public health risk. Iatrogenic Creutzfeldt–Jakob disease (iCJD) via contaminated surgical instruments and medical devices has been verified both experimentally and clinically. Standard methods for prion inactivation by sodium hydroxide or sodium hypochlorite have failed, in some cases, to fully remove prion infectivity, while they are often impractical for routine applications. Prion accumulation in peripheral tissues and indications of human-to-human bloodborne prion transmission, highlight the need for novel, efficient, yet user-friendly methods of prion inactivation. Here we show both in vitro and in vivo that homogenous photocatalytic oxidation, mediated by the photo-Fenton reagent, has the potential to inactivate the pathological prion isoform adsorbed on metal substrates. Photocatalytic oxidation with 224 μg mL−1 Fe3+, 500 μg mL−1 h−1 H2O2, UV-A for 480 min lead to 100% survival in golden Syrian hamsters after intracranial implantation of stainless steel wires infected with the 263K prion strain. Interestingly, photocatalytic treatment of 263K infected titanium wires, under the same experimental conditions, prolonged the survival interval significantly, but failed to eliminate infectivity, a result that we correlate with the increased adsorption of PrPSc on titanium, in comparison to stainless steel. Our findings strongly indicate that our, user- and environmentally friendly protocol can be safely applied to the decontamination of prion infected stainless steel surfaces.

Inhibition of PrP(Sc) formation in scrapie infected N2a cells by 5,7,8-trimethyl-3,4-dihydro-2H-1,4-benzoxazine derivatives.

Prion diseases are fatal, neurodegenerative diseases characterized by the structural conversion of the normal, cellular prion protein, PrPC into an abnormally structured, aggregated and partially protease-resistant isoform, termed PrPSc. Although substantial research has been directed toward development of therapeutics targeting prions, there is still no curative treatment for the disease. Benzoxazines are bicyclic heterocyclic compounds possessing several pharmaceutically important properties, including neuroprotection and reactive oxygen species scavenging. In an effort to identify novel inhibitors of prion formation, several 5,7,8-trimethyl-1,4-benzoxazine derivatives were evaluated in vitro for their effectiveness on the expression levels of normal PrPC and its conversion to the abnormal isoforms of PrPSc in a scrapie-infected cell culture model. The most potent compound was 2-(4-methoxyphenyl)-5,7,8-trimethyl-3,4-dihydro-2H-1,4-benzoxazine, with a diminishing effect on the formation of PrPSc, thus establishing a class of compounds with a promising therapeutic use against prion diseases.

Cerebrospinal fluid neurofilament light in suspected sporadic Creutzfeldt-Jakob disease

Sporadic Creutzfeldt-Jakob disease (sCJD) is the most common form of human prion disease. It is invariably fatal and displays a short clinical disease stage. The key event in sCJD is the propagation of a beta-sheet rich conformer of the physiological PrPC protein, known as PrPSc. Neuropathological disease characteristics include gliosis, neuronal loss and spongiform degeneration; disease clinical manifestations refer to mental and visual disabilities, cognitive impairment, gait or limb ataxia, myoclonus and mutism. Definite sCJD diagnosis requires post-mortem brain material histopathological examination. However, highly certain pre-mortem differential diagnosis is desired to exclude other treatable disorders and to reduce disease transmission risks. Detection and/or quantification of cerebrospinal fluid (CSF) biomarkers reflecting neuronal damage and PrPC misfolding in the diseased brain significantly enhance pre-mortem diagnosis. Previously established and newly identified biomarkers are used towards this direction. Increased CSF Neurofilament light chain (NFL) concentrations have been reported in several neurological disorders, including prion diseases. In the present study, we analyzed CSF NFL levels in two independent patient cohorts, consisting of highly suspected sCJD cases that were further classified as sCJD or non-CJD according to established diagnostic criteria. CSF NFL concentrations were increased in sCJD compared to non-CJD cases in both cohorts (area under the curve (with 95% confidence interval) equal to 0.89 (0.82 to 0.97) and 0.86 (0.77 to 0.96), respectively. CSF NFL was associated neither to age nor to sex but correlated with total-tau concentrations in both cohorts. Overall, our data provide independent validation of CSF NFL utility in sCJD differential diagnosis.

MicroRNA Alterations in the Brain and Body Fluids of Humans and Animal Prion Disease Models: Current Status and Perspectives

Prion diseases are transmissible progressive neurodegenerative conditions characterized by rapid neuronal loss accompanied by a heterogeneous neuropathology, including spongiform degeneration, gliosis and protein aggregation. The pathogenic mechanisms and the origins of prion diseases remain unclear on the molecular level. Even though neurodegenerative diseases, including prion diseases, represent distinct entities, their pathogenesis shares a number of features including disturbed protein homeostasis, an overload of protein clearance pathways, the aggregation of pathological altered proteins, and the dysfunction and/or loss of specific neuronal populations. Recently, direct links have been established between neurodegenerative diseases and miRNA dysregulated patterns. miRNAs are a class of small non-coding RNAs involved in the fundamental post-transcriptional regulation of gene expression. Studies of miRNA alterations in the brain and body fluids in human prion diseases provide important insights into potential miRNA-associated disease mechanisms and biomarker candidates. miRNA alterations in prion disease models represent a unique tool to investigate the cause-consequence relationships of miRNA dysregulation in prion disease pathology, and to evaluate the use of miRNAs in diagnosis as biomarkers. Here, we provide an overview of studies on miRNA alterations in human prion diseases and relevant disease models, in relation to pertinent studies on other neurodegenerative diseases.

Immunobiology of Prion Diseases

Prion diseases are invariably lethal neurodegenerative diseases, associated with the structural conversion of the cellular isoform of the prion protein to its pathological, disease-associated isoform. The cellular isoform of the prion protein is highly conserved and virtually ubiquitously expressed; nevertheless, its physiological role remains unclear. Mounting evidence suggests its involvement in the regulation and function of the immune system. At the same time, the immune system is heavily involved in the pathogenesis of the diseases, playing a major role in the peripheral replication of the infectious agent and spread toward the central nervous system. On the other hand, immunotherapies are among the most promising means of intervention. This chapter deals with these fascinating and sometimes contrasting aspects of prion biology, with an emphasis on the immunization protocols developed for prophylaxis and treatment of prion diseases.