Demyelination in brain cell aggregate cultures, induced by a monoclonal antibody against the myelin/oligodendrocyte glycoprotein (MOG).

Previous work has shown that aggregate cultures prepared from fetal rat telencephalon and grown in a chemically defined medium offer a useful model to study developmental processes such as myelin synthesis. Since compact myelin is formed in these cultures, we investigated the possibility to use this culture system to study demyelinating mechanisms. In particular, we examined the effect of a monoclonal antibody (8-18C5) directed against the myelin/oligodendrocyte glycoprotein (MOG). We found that addition of anti-MOG antibodies and complement to aggregate cultures led to a highly significant decrease in myelin basic protein (MBP) content and 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP) specific activity. These results indicate that, in our culture system, anti-MOG antibodies have a strong demyelinating effect.

Simultaneous LC-MS/MS quantification of P-glycoprotein and cytochrome P450 probe substrates and their metabolites in DBS and plasma.

BACKGROUND: An LC-MS/MS method has been developed for the simultaneous quantification of P-glycoprotein (P-gp) and cytochrome P450 (CYP) probe substrates and their Phase I metabolites in DBS and plasma. P-gp (fexofenadine) and CYP-specific substrates (caffeine for CYP1A2, bupropion for CYP2B6, flurbiprofen for CYP2C9, omeprazole for CYP2C19, dextromethorphan for CYP2D6 and midazolam for CYP3A4) and their metabolites were extracted from DBS (10 µl) using methanol. Analytes were separated on a reversed-phase LC column followed by SRM detection within a 6 min run time. RESULTS: The method was fully validated over the expected clinical concentration range for all substances tested, in both DBS and plasma. The method has been successfully applied to a PK study where healthy male volunteers received a low dose cocktail of the here described P-gp and CYP probes. Good correlation was observed between capillary DBS and venous plasma drug concentrations. CONCLUSION: Due to its low-invasiveness, simple sample collection and minimal sample preparation, DBS represents a suitable method to simultaneously monitor in vivo activities of P-gp and CYP.

Impact of genetic polymorphisms in cytomegalovirus glycoprotein B on outcomes in solid-organ transplant recipients with cytomegalovirus disease.

BACKGROUND:It is unknown whether specific viral polymorphisms affect in vivo therapeutic response in patients with cytomegalovirus (CMV) disease. Polymorphisms in the CMV glycoprotein B (gB) gene allow discrimination of 4 distinct genotypes (gB1-gB4). We assessed the influence of gB genotypes on the clinical and virologic outcome of CMV disease. METHODS:Solid-organ transplant recipients enrolled in a multicenter trial of CMV disease treatment (VICTOR study) were included in this study. CMV gB genotyping was performed using quantitative real-time polymerase chain reaction at day 0 (start of antiviral therapy). RESULTS:Among 239 patients with CMV disease, the prevalence of gB strain types was 26% for gB1, 10% for gB2, 10% for gB3, and 5% for gB4, whereas mixed infections were present in 49%. Donor-seropositive/recipient-seropositive patients were more likely to have mixed gB infection than donor-seropositive/recipient-seronegative patients (40% vs. 12%; P = .001). Median baseline viral loads were higher and time to viral eradication was longer ( P = .006 and P = .026 , respectively) for mixed infection versus infection with a single genotype. In a multivariate model, mixed gB infection was a significant predictor of failure to eradicate virus by day 21 (mixed vs single genotype; odds ratio, 2.66; 95% confidence interval, 1.31-5.38; P = .007 ) after controlling for baseline viral load, CMV serostatus at baseline, ganciclovir resistance, and antiviral treatment. No effect of gB genotype was seen on virologic or clinical CMV recurrence. CONCLUSIONS:No specific gB genotype appears to confer a specific CMV virulence advantage. However, mixed gB genotype infections are associated with higher viral loads and delayed viral clearance.

Viral envelope glycoprotein processing by proprotein convertases.

The proprotein convertases (PCs) are a family of nine mammalian enzymes that play key roles in the maintenance of cell homeostasis by activating or inactivating proteins via limited proteolysis under temporal and spatial control. A wide range of pathogens, including major human pathogenic viruses can hijack cellular PCs for their own purposes. In particular, productive infection with many enveloped viruses critically depends on the processing of their fusion-active viral envelope glycoproteins by cellular PCs. Based on their crucial role in virus-host interaction, PCs can be important determinants for viral pathogenesis and represent promising targets of therapeutic antiviral intervention. In the present review we will cover basic aspects and recent developments of PC-mediated maturation of viral envelope glycoproteins of selected medically important viruses. The molecular mechanisms underlying the recognition of PCs by viral glycoproteins will be described, including recent findings demonstrating differential PC-recognition of viral and cellular substrates. We will further discuss a possible scenario how viruses during co-evolution with their hosts adapted their glycoproteins to modulate the activity of cellular PCs for their own benefit and discuss the consequences for virus-host interaction and pathogenesis. Particular attention will be given to past and current efforts to evaluate cellular PCs as targets for antiviral therapeutic intervention, with emphasis on emerging highly pathogenic viruses for which no efficacious drugs or vaccines are currently available.

Inhibition of glial cell proinflammatory activities by peroxisome proliferator-activated receptor gamma agonist confers partial protection during antimyelin oligodendrocyte glycoprotein demyelination in vitro.

Peroxisome proliferator-activated receptor gamma (PPAR-gamma) is a member of the nuclear hormone superfamily originally characterized as a regulator of adipocyte differentiation and lipid metabolism. In addition, PPAR-gamma has important immunomodulatory functions. If the effect of PPAR-gamma's activation in T-cell-mediated demyelination has been recently demonstrated, nothing is known about the role of PPAR-gamma in antibody-induced demyelination in the absence of T-cell interactions and monocyte/macrophage activation. Therefore, we investigated PPAR-gamma's involvement by using an in vitro model of inflammatory demyelination in three-dimensional aggregating rat brain cell cultures. We found that PPAR-gamma was not constitutively expressed in these cultures but was strongly up-regulated following demyelination mediated by antibodies directed against myelin oligodendrocyte glycoprotein (MOG) in the presence of complement. Pioglitazone, a selective PPAR-gamma agonist, partially protected aggregates from anti-MOG demyelination. Heat shock responses and the expression of the proinflammatory cytokine tumor necrosis factor-alpha were diminished by pioglitazone treatment. Therefore, pioglitazone protection seems to be linked to an inhibition of glial cell proinflammatory activities following anti-MOG induced demyelination. We show that PPAR-gamma agonists act not only on T cells but also on antibody-mediated demyelination. This may represent a significant benefit in treating multiple sclerosis patients.

Cell surface expression of a functional rubella virus E1 glycoprotein by addition of a GPI anchor.

Rubella virus (RV) envelope glycoproteins E1 and E2 are targeted to the Golgi as heterodimers. While E2 contains a transmembrane Golgi retention signal, E1 is arrested in a pre-Golgi compartment in the absence of E2, and appears to require heterodimerization in order to reach the Golgi. Various forms of E1 with deletions in the ectodomain or lacking the cytoplasmic (CT) and transmembrane (TM) domains, as well as the 29 C-terminal amino acid residues of the ectodomain were also retained intracellularly. We therefore investigated the possibility of targetting E1 to the plasma membrane by addition of a glycosylphosphatidylinositol (GPI) anchor. We found that E1GPI was transported to the cell surface where it retained the hemadsorption activity characteristic of the wild-type E1/E2 heterodimer. Furthermore, coexpression of a mammalian GPI-specific phospholipase D (GPI-PLD) resulted in the release of E1GPI and in constitutive expression of a soluble form of E1. This study thus demonstrates that the GPI anchor has a dominant effect over the E1 pre-Golgi retention signal and that E1 is sufficient for hemadsorption.

Isoelectric focusing of alpha-1 acid glycoprotein (orosomucoid) in immobilized pH-gradients with 8M urea: detection of its desialylated variants using an alkaline phosphatase-linked secondary antibody system.

A method allowing a clear separation of the different variants of desialylated alpha 1-acid glycoprotein (orosomucoid) has been developed using isoelectric focusing in immobilized pH gradients, supplemented with 8 M urea and 2% v/v 2-mercaptoethanol. Immunoblotting with two antibody-steps afforded high sensitivity and permitted the detection of about 700 pg of alpha 1-acid glycoprotein in a 20 microL plasma sample diluted 1:28 672. A one year old bloodstrain, kept at room temperature, could easily be phenotyped.

Carcinoembryonic antigen (CEA): demonstration of a partial identity between CEA and a normal glycoprotein.

The carcinoembryonic antigen of the human digestive tract (CEA), described by Gold as a glycoprotein specific for digestive carcinomatous and foetal tissues, was found to have common antigenic determinants with a glycoprotein of smaller size extracted from normal adult tissues. This observation suggests that only a part of the CEA molecule carries the onco-foetal specificity. It also has practical implications regarding the radioimmunoassay for CEA used for the diagnosis of certain carcinomas.

Ezrin-Radixin-Moesin-binding Sequence of PSGL-1 Glycoprotein Regulates Leukocyte Rolling on Selectins and Activation of Extracellular Signal-regulated Kinases.

P-selectin glycoprotein ligand-1 (PSGL-1) mediates the capture (tethering) of free-flowing leukocytes and subsequent rolling on selectins. PSGL-1 interactions with endothelial selectins activate Src kinases and spleen tyrosine kinase (Syk), leading to α(L)β(2) integrin-dependent leukocyte slow rolling, which promotes leukocyte recruitment into tissues. In addition, but through a distinct pathway, PSGL-1 engagement activates ERK. Because ezrin, radixin and moesin proteins (ERMs) link PSGL-1 to actin cytoskeleton and because they serve as adaptor molecules between PSGL-1 and Syk, we examined the role of PSGL-1 ERM-binding sequence (EBS) on cell capture, rolling, and signaling through Syk and MAPK pathways. We carried out mutational analysis and observed that deletion of EBS severely reduced 32D leukocyte tethering and rolling on L-, P-, and E-selectin and slightly increased rolling velocity. Alanine substitution of Arg-337 and Lys-338 showed that these residues play a key role in supporting leukocyte tethering and rolling on selectins. Importantly, EBS deletion or Arg-337 and Lys-338 mutations abrogated PSGL-1-induced ERK activation, whereas they did not prevent Syk phosphorylation or E-selectin-induced leukocyte slow rolling. These studies demonstrate that PSGL-1 EBS plays a critical role in recruiting leukocytes on selectins and in activating the MAPK pathway, whereas it is dispensable to phosphorylate Syk and to lead to α(L)β(2)-dependent leukocyte slow rolling.

Envelope glycoprotein of arenaviruses.

Arenaviruses include lethal human pathogens which pose serious public health threats. So far, no FDA approved vaccines are available against arenavirus infections, and therapeutic options are limited, making the identification of novel drug targets for the development of efficacious therapeutics an urgent need. Arenaviruses are comprised of two RNA genome segments and four proteins, the polymerase L, the envelope glycoprotein GP, the matrix protein Z, and the nucleoprotein NP. A crucial step in the arenavirus life-cycle is the biosynthesis and maturation of the GP precursor (GPC) by cellular signal peptidases and the cellular enzyme Subtilisin Kexin Isozyme-1 (SKI-1)/Site-1 Protease (S1P) yielding a tripartite mature GP complex formed by GP1/GP2 and a stable signal peptide (SSP). GPC cleavage by SKI-1/S1P is crucial for fusion competence and incorporation of mature GP into nascent budding virion particles. In a first part of our review, we cover basic aspects and newer developments in the biosynthesis of arenavirus GP and its molecular interaction with SKI-1/S1P. A second part will then highlight the potential of SKI-1/S1P-mediated processing of arenavirus GPC as a novel target for therapeutic intervention to combat human pathogenic arenaviruses.

Binding of d-methadone, l-methadone, and dl-methadone to proteins in plasma of healthy volunteers: role of the variants of alpha 1-acid glycoprotein.

The plasma concentrations of alpha 1-acid glycoprotein (AAG), albumin, triglycerides, cholesterol, and total proteins, as well as the plasma binding of racemic, d-methadone, and l-methadone were measured in 45 healthy subjects. The AAG phenotypes and the concentrations of AAG variants were also determined. The measured free fractions for racemic, d-methadone, and l-methadone were, respectively, 12.7% +/- 3.3%, 10.0% +/- 2.9%, and 14.2% +/- 3.2% (mean +/- SD). A significant correlation was obtained between the binding ratio (B/F) for dl-methadone and the total AAG concentration (r = 0.724; p less than 0.001). A multiple stepwise regression analysis showed that AAG was the main explanatory variable for the binding of the racemate. When concentrations of AAG variants were considered, a significant correlation was obtained between the binding ratio of dl-methadone and orosomucoid2 A concentration (r = 0.715; p less than 0.001), a weak correlation between dl-methadone and orosomucoid1 S concentration (r = 0.494; p less than 0.001), and no correlation between dl-methadone and orosomucoid1 F1 concentration (r = 0.049; not significant). Similar findings were obtained with the enantiomers. This study shows the importance of considering not only total AAG but also concentrations of AAG variants when measuring the binding of methadone and possibly of other drugs in plasma.

Characterization of SKI-1/S1P-mediated processing of Arenavirus glycoprotein precursors

Arenaviruses are rodent-born world-wide distributed negative strand RNA viruses that comprise a number of important human pathogens including Lassa virus (LASV) which causes more than 3 00'000 infections annually in Western Africa. Lymphocytic choriomeningitis virus (LCMV) is the prototypic member of the arenavirus family, which is divided in two major subgroups according to serological properties and geographical distribution, the Old World and New World arenaviruses. The envelope glycoprotein precursors (GPCs) of arenaviruses have to undergo proteolytic processing to acquire biological function and to be incorporated into progeny virions. A cellular enzyme is responsible for this processing: the Subtilisin Kexin Isozyme-1 or Site-1 protease (SKI- 1/S1P). In this thesis we have studied the relationship between SKI-1/S1P and the envelope GPs of arenaviruses. In a first project, we investigated the molecular interactions between SKI-1/SIP and arenavirus GPCs. Using SKI-1/SIP mutants, we confirmed previously published observations locating LCMV GPC and LASV GPC processing in the Late Golgi/TGN and ER/cis-Golgi, respectively. A single mutation in the cleavage site of LCMV was sufficient to re-locate SKI- 1/SIP-mediated processing from the late Golgi/TGN to the ER/cis-Golgi. We then demonstrated that the transmembrane domain, the C-terminal tail and the phosphorylation sites of SKI-1/S1P are dispensable for GPC processing. Additionally we identified a SKI- 1/S1P mutant defective for autoprocessing at site Β, B' that was selectively impaired in processing of viral GPCs but not cellular substrates. We also showed that a soluble variant of SKI-1/SIΡ was unable to cleave envelope GPs at the cell surface when added in the culture medium. This study highlighted a new target for small molecule inhibitors that would specifically impair GPC but not cellular substrate processing. In a second project, we identified and characterized two residues: LASV GPC Y253 and SKI-1/S1P Y285 that are important for the SKI-1/SIP-mediated LASV GPC cleavage. An alignment of GPC sequences revealed a conserved aromatic residue in P7 position in the GPCs of Old World and Clade C of New World arenaviruses. Mutations in GPC at position P7 impaired processing efficiency. In SKI-1/S1P, mutating Y285 into A negatively affected processing of substrates containing aromatic residues in P7, without affecting others. This property could be used to develop specific drugs targeting SKI-1/SIP-mediated cleavage of LASV GPC without affecting cellular substrates. As a third project we studied the role of the SKI-1/SIP-mediated processing and the unusual stable signal peptide (SSP) for the folding and secretion of soluble forms of the ectodomain of LASV and LCMV glycoproteins. We provide evidence that the transmembrane domain and the cytosolic tail are crucial for the stability of the prefusion conformation of arenavirus GP and that the SSP is required for transport and processing of full-length GP, but not the soluble ectodomain per se. Taken together, these results will lead to a better understanding of the complex interactions between arenavirus GPCs and SKI-1/S IP, paving the avenue for the development of novel anti-arenaviral therapeutics. - Les Arenavirus sont des virus à ARN négatif distribués mondialement et portés par les rongeurs. Cette famille de virus comprend des virus hautement pathogènes pour l'homme comme le virus de Lassa (LASV) qui cause plus de 300Ό00 infections par année en Afrique de l'Ouest. Le virus de la chorioméningite lymphocytaire (LCMV) est le représentant de cette famille qui est divisée en deux sous-groupes selon des critères sérologiques et de distributions géographiques: arenavirus du Nouveau et de l'Ancien monde. Les glycoprotéines d'enveloppe de ces virus (GPCs) doivent être clivées pour être incorporées dans le virus et ainsi lui permettre d'être infectieux. Une enzyme cellulaire est responsable de ce clivage : la Subtilisin Kexin Isozyme-1 ou protéase Site-1 (SKI-l/SlP). Dans cette thèse, nous avons étudié la relation entre cette enzyme cellulaire et les GPs des arenavirus. Dans un premier temps, nous avons étudié les interactions moléculaires entre SKI- 1/S1P et GPC. A l'aide de mutants de SKI-l/SlP, nous avons confirmé des résultats précédemment publiés montrant que les glycoprotéines d'enveloppe de LASV sont clivés dans le réticulum endoplasmique/cis-Golgi alors que celles de LCMV sont clivées dans le Golgi tardif/TGN. Une seule mutation dans le site de clivage de la glycoprotéine de LCMV est suffisante pour changer le compartiment cellulaire dans lequel est clivée cette glycoprotéine. Ensuite, nous avons démontré que le domaine transmembranaire, la partie cytosolique C-terminale ainsi que les sites de phosphorylations de cette enzyme ne sont pas indispensables pour permettre le clivage de GPC. De plus, nous avons identifié un mutant de SKI-l/SlP dans lequel Γ autoprocessing au site B,B' est impossible, incapable de cliver GPC mais toujours pleinement fonctionnelle envers ses substrats cellulaires. Nous avons également démontré qu'une forme soluble de SKI-l/SlP ajoutée dans le milieu de culture n'est pas capable de couper GPC à la surface de la cellule. Cette étude a défini une nouvelle cible potentielle pour un médicament qui inhiberait le clivage des glycoprotéines des arenavirus sans affecter les processus normaux de la cellule. Dans un second project, nous avons identifié deux acides aminés, LASV GPC Y253 et SKI-l/SlP Y285, qui sont important pour le clivage de LASV GPC. Un alignement des séquences de clivage des GPCs a montré qu'un résidu aromatique est conservé en position P7 du site de clivage chez tous les arenavirus de l'Ancien monde et dans le clade C des arenavirus du Nouveau monde. Une mutation de cet acide aminée dans GPC réduit l'efficacité de clivage par SKI-l/SlP. Mutation de la tyrosine 285 de SKI-l/SlP en alanine affecte négativement le clivage des substrats contenant un résidu aromatique en position P7 sans affecter les autres. Cette propriété pourrait être utilisée pour le développement de médicaments spécifiques ciblant le clivage de GPC. Finalement, nous avons étudié le rôle du processing accomplit par SKI-l/SlP et du signal peptide pour le pliage et la sécrétion de formes solubles des glycoprotéines de LASV et LCMV. Nous avons montré que le domaine transmembranaire et la partie cytosolique de GP sont crucials pour la stabilité de la conformation pre-fusionnelle des GPs et que SSP est nécessaire pour le transport et le processing de GP, mais pas de son ecto-domaine soluble. En conclusion, les résultats obtenus durant cette thèse permettrons de mieux comprendre les interactions complexes entre SKI-l/SlP et les glycoprotéines des arenavirus, ouvrant le chemin pour le développement de nouveaux médicaments anti-arénaviraux.

Antiviral activity of a small-molecule inhibitor of arenavirus glycoprotein processing by the cellular site 1 protease.

Arenaviruses merit interest as clinically important human pathogens and include several causative agents, chiefly Lassa virus (LASV), of hemorrhagic fever disease in humans. There are no licensed LASV vaccines, and current antiarenavirus therapy is limited to the use of ribavirin, which is only partially effective and is associated with significant side effects. The arenavirus glycoprotein (GP) precursor GPC is processed by the cellular site 1 protease (S1P) to generate the peripheral virion attachment protein GP1 and the fusion-active transmembrane protein GP2, which is critical for production of infectious progeny and virus propagation. Therefore, S1P-mediated processing of arenavirus GPC is a promising target for therapeutic intervention. To this end, we have evaluated the antiarenaviral activity of PF-429242, a recently described small-molecule inhibitor of S1P. PF-429242 efficiently prevented the processing of GPC from the prototypic arenavirus lymphocytic choriomeningitis virus (LCMV) and LASV, which correlated with the compound's potent antiviral activity against LCMV and LASV in cultured cells. In contrast, a recombinant LCMV expressing a GPC whose processing into GP1 and GP2 was mediated by furin, instead of S1P, was highly resistant to PF-429242 treatment. PF-429242 did not affect virus RNA replication or budding but had a modest effect on virus cell entry, indicating that the antiarenaviral activity of PF-429242 was mostly related to its ability to inhibit S1P-mediated processing of arenavirus GPC. Our findings support the feasibility of using small-molecule inhibitors of S1P-mediated processing of arenavirus GPC as a novel antiviral strategy.