Michel Brémont (1953–2020)

International audienceNo abstract availabl

The C-terminal domain of Salmonid Alphavirus nonstructural protein 2 (nsP2) is essential and sufficient to block RIG-I pathway induction and interferon-mediated antiviral response.

International audienceSalmonid alphavirus (SAV) is an atypical alphavirus, which has a considerable impact on salmon and trout farms. Unlike other alphaviruses such as the chikungunya virus, SAV is transmitted without an arthropod vector, and does not cause cell shut-off during infection. The mechanisms by which SAV escapes the host immune system remain unknown. By studying the role of SAV proteins on the RIG-I signaling cascade, the first line of defense of the immune system during infection, we demonstrated that non-structural protein 2 (nsP2) effectively blocks the induction of type I interferon (IFN). This inhibition, independent of the protease activity carried by nsP2, occurs downstream of IRF3 which is the transcription factor allowing the activation of the IFN promoter and its expression. The inhibitory effect of nsP2 on the RIG-I pathway depends on the localization of nsP2 in the host cell nucleus which is linked to two nuclear localization sequences (NLS) located in its C-terminal part. The C-terminal domain of nsP2 by itself is sufficient and necessary to block IFN induction. Mutation of the NLS of nsP2 is deleterious to the virus. Finally, nsP2 does not interact with IRF3, indicating that its action is possible through a targeted interaction within discrete areas of chromatin, as suggested by its punctate distribution observed in the nucleus. These results therefore demonstrate a major role for nsP2 in the control by SAV of the host cell's innate immune response. Importance The global consumption of fish continues to rise and the future demand cannot be met by capture fisheries alone due to limited stocks of wild fish. Aquaculture is currently the world's fastest growing food production sector with an annual growth rate of 6-8 %. Recurrent outbreaks of SAV result in significant economic losses with serious environmental consequences on wild stocks. While the clinical and pathological signs of SAV infection are fairly well known, the molecular mechanisms involved are poorly described. In the present study, we focus on the non-structural protein nsP2 and characterize a specific domain containing nuclear localization sequences that are critical for the inhibition of the host innate immune response mediated by the RIG-I pathway

Deciphering the Fine-Tuning of the Retinoic Acid-Inducible Gene-I Pathway in Teleost Fish and Beyond

International audienceInterferons are the first lines of defense against viral pathogen invasion during the early stages of infection. Their synthesis is tightly regulated to prevent excessive immune responses and possible deleterious effects on the host organism itself. The RIG-I-like receptor signaling cascade is one of the major pathways leading to the production of interferons. This pathway amplifies danger signals and mounts an appropriate innate response but also needs to be finely regulated to allow a rapid return to immune homeostasis. Recent advances have characterized different cellular factors involved in the control of the RIG-I pathway. This has been most extensively studied in mammalian species; however, some inconsistencies remain to be resolved. The IFN system is remarkably well conserved in vertebrates and teleost fish possess all functional orthologs of mammalian RIG-I-like receptors as well as most downstream signaling molecules. Orthologs of almost all mammalian regulatory components described to date exist in teleost fish, such as the widely used zebrafish, making fish attractive and powerful models to study in detail the regulation and evolution of the RIG-I pathway

LA PROTÉINE NON STRUCTURALE 2 (NSP2) DE L'ALPHAVIRUS DE SALMONIDÉS BLOQUE LA RÉPONSE INTERFÉRON INDUITE PAR RIG-I

International audienceL’alphavirus de salmonidés (SAV) a un impact considérable sur les élevages de saumons et de truites. Les épidémies récurrentes de SAV entraînent des pertes économiques importantes avec de sérieuses conséquences environnementales sur les stocks sauvages. Les vaccins disponibles n’ont pas montré une efficacité suffisante pour stopper la circulation de ce virus dans les élevages, notamment en Norvège, plus gros producteur européen de saumon, où des infections ont été signalées dans plus de 150 fermes en 2019. Si les signes cliniques et pathologiques de l’infection sont assez bien connus, les mécanismes moléculaires impliqués sont quant à eux peu décrits. Le SAV est un alphavirus atypique. Il se transmet sans vecteur arthropode, se réplique à basse température, et n’entraine pas de shut-off cellulaire lors de l’infection. A la différence d’autres alphavirus, tel que le virus Chikungunya, les mécanismes permettant au SAV d’échapper au système immunitaire de l’hôte restent inconnus. En étudiant le rôle des protéines du SAV sur la cascade de signalisation RIG-I, première ligne de défense du système immunitaire lors d’une infection, nous avons démontré que la protéine non-structurale 2 (nsP2) bloque très efficacement l’induction d’interféron de type I (IFN1). Cette inhibition, indépendante de l’activité protéase portée par nsP2, à lieu en aval d’IRF3 qui est le facteur de transcription permettant l’activation du promoteur de l’IFN1 ainsi que son expression. Le blocage de la cascade RIG-I dépend de la localisation de nsP2 dans le noyau de la cellule hôte grâce aux deux séquences d’adressage nucléaire (NLS) situées dans sa partie C-terminale. Ce domaine C-terminal de nsP2 est à lui seul suffisant et nécessaire pour bloquer l’induction d’IFN1. La mutation des NLS de la protéine nsP2 est délétère pour le virus. Enfin, nsP2 n’interagit pas avec IRF3, indiquant que son action est possible par une interaction ciblée avec des zones discrètes de la chromatine, comme le suggère le marquage ponctiforme détecté dans le noyau. Ces résultats démontrent donc un rôle majeur de nsP2 pour le contrôle par le SAV de la réponse l’immunitaire innée de la cellule hôte, et que le blocage de la cascade RIG-I est possible grâce à des interactions spécifiques entre cette protéine virale et des régions de l’ADN impliquées dans l’expression de l’interféron de type 1

Attenuated infectious hematopoietic necrosis virus with rearranged gene order as potential vaccine

The genome of infectious hematopoietic necrosis virus (IHNV), a salmonid novirhabdovirus, has been engineered to modify the gene order and to evaluate the impact on a possible attenuation of the virus in vitro and in vivo. By reverse genetics, eight recombinant IHNVs (rIHNVs), termed NxGy according to the respective positions of the nucleoprotein (N) and glycoprotein (G) genes along the genome, have been recovered. All rIHNVs have been fully characterized in vitro for their cytopathic effects, kinetics of replication, and profiles of viral gene transcription. These rIHNVs are stable through up to 10 passages in cell culture. Following bath immersion administration of the various rIHNVs to juvenile trout, some of the rIHNVs were clearly attenuated (N2G3, N2G4, N3G4, and N4G1). The position of the N gene seems to be one of the most critical features correlated to the level of viral attenuation. The induced immune response potential in fish was evaluated by enzyme-linked immunosorbent spot assay (ELISPOT) and seroneutralization assays. The recombinant virus N2G3 induced a strong antibody response in immunized fish and conferred 86% of protection against wild-type IHNV challenge in trout, thus representing a promising starting point for the development of a live attenuated vaccine candidate. IMPORTANCE In Europe, no vaccines are available against infectious hematopoietic necrosis virus (IHNV), one of the major economic threats in fish aquaculture. Live attenuated vaccines are conditioned by a sensible balance between attenuation and pathogenicity. Moreover, nonsegmented negative-strain RNA viruses (NNSV) are subject to a transcription gradient dictated by the order of the genes in their genomes. With the perspective of developing a vaccine against IHNV, we engineered various recombinant IHNVs with reordered genomes in order to artificially attenuate the virus. Our results validate the gene rearrangement approach as a potent and stable attenuation strategy for fish novirhabdovirus and open a new perspective for design of vaccines against other NNSV

The effects of Curcuma longa and curcumin on reproductive systems

Objective. Curcuma longa (C. longa) was used in some countries such as China and India for various medicinal purposes. Curcumin, the active component of C. longa, is commonly used as a coloring agent in foods, drugs, and cosmetics. C. longa and curcumin have been known to act as antioxidant, anti-inflammatory, anti-mutagen, and anti-carcinogenic agents. Th e attempt of the present review was to give an effort on a detailed literature survey concentrated on the protective effects of C. longa and curcumin on the reproductive organs activity. Methods. The databases such as, PubMed, Web of Science, Google Scholar, Scopus, and Iran- Medex, were considered. The search terms were “testis” or “ovary” and “Curcuma longa”, “curcumin”, “antioxidant effect”, “anti-inflammatory effect” and “anti-cancer effect”. Results. C. longa and curcumin inhibited the production of the tumor necrosis factor-α (TNF-α) and prostaglandin E2 (PGE2) and increased the caspases (3, 8 and 9) activities in HL-60 prostate cancer. Furthermore, C. longa and curcumin suppressed the vascular endothelial growth factor (VEGF), phosphorylated signal transducers and activators of the transcription 3 (STAT) and matrix metalloproteinase-9 (MMP-9) in ovarian cancer cell line. Conclusion. C. longa and curcumin might decrease the risk of cancer and other malignant diseases in the reproductive system. C. longa and curcumin have a protective effect on the reproductive organs activity such as, anti-inflammatory, anti-apoptotic, and antioxidant effects in normal cells but showed pro-apoptotic effects in the malignant cells. Therefore, different effects of C. longa and curcumin are dependent on the doses and the type of cells used in various models studied

Zebrafish ( Danio rerio ) larvae as a model for real‐time studies of propagating VHS virus infection, tissue tropism and neutrophil activity

International audienceViral haemorrhagic septicaemia virus (VHSV) is a negative-sense single-stranded RNA virus that infects more than 140 different fish species. In this study, zebrafish larvae were employed as in vivo model organisms to investigate progression of disease, the correlation between propagation of the infection and irreversibility of disease, cell tropism and in situ neutrophil activity towards the VHSV-infected cells. A recombinant VHSV strain, encoding "tomato" fluorescence (rVHSV-Tomato), was used in zebrafish to be able to follow the progress of the infection in the live host in real-time. Two-day-old zebrafish larvae were injected into the yolk sac with the recombinant virus. The virus titre peaked 96 hr post-infection in zebrafish larvae kept at 18 degrees C, and correlated with 33% mortality and high morbidity among the larvae. By utilizing the transgenic zebrafish line Tg(fli1:GFP)(y1) with fluorescently tagged endothelial cells, we were able to demonstrate that the virus initially infected endothelial cells lining the blood vessels. By observing the rVHSV-Tomato infection in the neutrophil reporter zebrafish line Tg(MPX:eGFP)(i114) , we inferred that only a subpopulation of the neutrophils responded to the virus infection. We conclude that the zebrafish larvae are suitable for real-time studies of VHS virus infections, allowing in vivo dissection of host-virus interactions at the whole organism level

MAVS joue un rôle majeur dans l'induction de la réponse immunitaire innée contre les virus ARN et ADN chez le poisson

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Fish genotype significantly influences susceptibility of juvenile rainbow trout, Oncorhynchus mykiss (Walbaum), to waterborne infection with infectious salmon anaemia virus

International audienc

Susceptibility of juvenile rainbow trout to ISAV waterborne infection greatly depends upon fish genotype

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