Rôle de la polarisation M2 des macrophages dans le contrôle d'infections fongiques et parasitaires : implication des récepteurs nucléaires PPARgamma et LRH-1 et des récepteurs lectine de type C

Les macrophages, cellules clés de la réponse immune innée, possèdent une remarquable plasticité phénotypique et fonctionnelle qui leur permet de s'adapter aux différents signaux présents dans leur microenvironnement. Parmi ces éléments, l'état inflammatoire général et métabolique de l'individu, ainsi que la présence d'agents étrangers potentiellement pathogènes vont influencer l'état de polarisation des macrophages. Dans ce travail de thèse, nous nous sommes plus particulièrement intéressés à deux types de facteurs environnementaux (i) le diabète de type 2, caractérisé par une inflammation à bas bruit et une susceptibilité accrue aux infections fongiques (ii) une infection parasitaire, la leishmaniose viscérale. Nous avons montré qu'une insulino-résistance engendrée par un régime hyperlipidique induit une polarisation inflammatoire M2b des macrophages associée à une susceptibilité accrue à une infection candidosique gastro-intestinale. Nous avons ensuite démontré que des ligands du récepteur nucléaire PPAR? orientent la polarisation M2b vers un phénotype M2a, efficace pour l'élimination de Candida albicans. Cette différenciation est caractérisée par la surexpression des récepteurs membranaires Dectine-1 et Mannose (MR), deux récepteurs lectine de type C impliqués dans l'internalisation de cette levure par le macrophage et dans la production d'intermédiaires réactifs de l'oxygène. Ce travail est publié dans PLoS One 2010 Sep 20;5(9):e12828. doi: 10.1371/journal.pone.0012828. Ainsi, approfondir les voies de signalisation conduisant à l'activation de PPARgamma présente un intérêt thérapeutique majeur. Lors de ce travail de thèse, nous nous sommes intéressés au récepteur nucléaire LRH-1, connu pour réguler l'expression d'enzymes impliquées dans la synthèse de dérivés d'acides gras, ligands potentiels de PPARgamma. Nous avons démontré l'implication de LRH-1 dans la polarisation M2. LRH-1 serait impliqué dans la production de ligands endogènes de PPARgamma et ainsi dans son activation. Nous avons également montré que les souris déficientes pour LRH-1 spécifiquement dans les macrophages présentent une susceptibilité accrue aux infections candidosiques avec des fonctions microbicides associées à la polarisation M2 altérées. Ces résultats suggèrent que LRH-1 pourrait être une nouvelle cible thérapeutique dans le traitement des infections fongiques en favorisant la production de ligands de PPARgamma et une polarisation M2 bénéfique pour l'hôte. Ce travail est actuellement en cours de soumission. Dans la deuxième partie de ce travail, nous avons étudié l'influence d'une leishmaniose viscérale sur la polarisation des macrophages. De façon originale, nous avons montré l'induction d'un phénotype M2b-like des macrophages en présence de Leishmania infantum, associé à une surexpression de trois récepteurs lectine de type C (Dectine-1, MR et SIGNR3/DC-SIGN). Nous avons également démontré que ces récepteurs influençaient le devenir de l'infection à L. infantum. Ainsi, les récepteurs Dectine-1 et MR interviennent dans l'entrée de Leishmania dans les macrophages et la production d'intermédiaires réactifs de l'oxygène et de médiateurs inflammatoires lipidiques et cytokiniques, tels que le leucotriène B4 (LTB4) et l'interleukine 1beta, qui permettent l'élimination du parasite. Inversement, SIGNR3/DC-SIGN participe à la phagocytose de Leishmania et favorise la prolifération du parasite en inhibant l'activité microbicide des macrophages. Ce travail réalisé sur des souris invalidées pour ces récepteurs lectine a été confirmé dans des macrophages humains et mettent en évidence le rôle divergent de ces lectines de type C et des voies de signalisation qui leur sont associées dans la pathogenèse de la leishmaniose viscérale. Ce travail démontre l'importance de l'axe lectines/LTB4/LXA4 dans le contrôle de la production de médiateurs inflammatoires responsables de l'élimination des parasites, axe qui constitue donc une cible de premier ordre pour le traitement et la prévention de la leishmaniose viscérale. Ainsi, la modulation de ces facteurs cellulaires et moléculaires pourrait permettre d'orienter l'interaction Leishmania-macrophage pour le bénéfice du patient. Ce travail est publié dans Immunity, 2013, May 23;38(5):1038-49. doi: 10.1016/j.immuni.2013.04.010.Macrophages are key cells of the innate immune response and have phenotypic and functional plasticity which allows them to adapt to their microenvironment. Among these signals, the inflammatory and metabolic states, as well as the pathogenic agents, will influence the macrophage polarization. In this work, we focused on two environmental factors (i) the type 2 diabetes, characterized by a low grade inflammation and an increased susceptibility to fungal infections (ii) a parasitic infection, the visceral leishmaniasis. We have shown that a high fat diet induced-insulin resistance promoted an inflammatory M2b polarization of macrophages associated with an increased susceptibility to gastrointestinal candidiasis. We then demonstrated that ligands of the nuclear receptor PPARgamma shift the M2b polarization toward M2a phenotype, effective to eliminate Candida albicans. This macrophage polarization is characterized by the overexpression of Dectin-1 and Mannose (MR), two membrane macrophage C-type lectin receptors involved in the yeast internalization and in the production of reactive oxygen intermediates (ROS). This work is published in PLoS One, 2010, September 20, 5 (9): e12828. doi: 10.1371/journal.pone.0012828. Thus, the study of the signaling pathways leading to PPAR? activation could be of therapeutic interest during fungal infections. Therefore, we focused on the LRH-1 nuclear receptor, known to regulate the expression of enzymes involved in the synthesis of potential PPARgamma ligands. Here, we demonstrated for the first time the involvement of LRH-1 in the M2 macrophage polarization. Indeed, LRH-1 is implicated in the production of PPARgamma endogenous ligands and hence in its activation. We also showed that mice deficient for LRH-1 specifically in macrophages exhibit increased susceptibility to Candida albicans infection, associated with altered M2 polarization related-candidacidal functions. These results suggest that LRH-1 could be a novel therapeutic target in the treatment of fungal infections, promoting M2 polarization favorable for the host. This work is currently under submission. In the second part of this work, we studied the influence of visceral leishmaniasis on the macrophage polarization. Interestingly, we report that the macrophage response in vivo against Leishmania infantum is characterized by a M2b-like phenotype displaying a C-type lectin receptors signature composed of Dectin-1, MR and the DC-SIGN homologue SIGNR3. We also demonstrated that these receptors influenced the outcome of L. infantum infection. Indeed, Dectin-1 and MR are involved in the L. infantum internalization by macrophages and in the production of ROS, inflammatory bioactive lipids, and cytokines such as leukotriene B4 (LTB4) and interleukin 1beta, which enable parasite elimination. By contrast, SIGNR3/DC-SIGN favors parasite resilience through inhibition of the microbicidal functions of macrophages. Confirmation of these results in primary human macrophages highlights the divergent role for these C-type lectin receptors to the pathogenesis of Leishmania infantum. This work demonstrates the importance of lectins/LTB4/LXA4 axis in the control of the inflammatory mediator's production responsible for parasite elimination. Our findings suggest that effective modulation of these cellular and molecular factors might shift the Leishmania-macrophage interaction for the benefit of the patient. This work is published in Immunity, 2013, May 23;38(5):1038-49. doi: 10.1016/j.immuni.2013.04.010

Double-walled carbon nanotubes trigger IL-1β release in human monocytes through Nlrp3 inflammasome activation

Because of their outstanding physical properties, carbon nanotubes (CNTs) are promising new materials in the field of nanotechnology. It is therefore imperative to assess their adverse effects on human health. Monocytes/macrophages that recognize and eliminate the inert particles constitute the main target of CNTs. In this article, we report our finding that double-walled CNTs (DWCNTs) synergize with Tolllike receptor agonists to enhance IL-1β release in human monocytes. We show that DWCNTs–induced IL-1β secretion is exclusively linked to caspase-1 and to Nlrp3 inflammasome activation in human monocytes. We also establish that this activation requires DWCNTs phagocytosis and potassium efflux, but not reactive oxygen specied (ROS) generation. Moreover, inhibition of lysosomal acidification or cathepsin-B activation reduces DWCNT-induced IL-1β secretion, suggesting that Nlrp3 inflammasome activation occurs via lysosomal destabilization. Thus, DWCNTs present a health hazard due to their capacity to activate Nlrp3 inflammasome, recalling the inflammation caused by asbestos and hence demonstrating that they should be used with caution. From the Clinical Editor: This is a very important biosafety/toxicity study regarding double walled carbon nanotubes. The investigators demonstrate that such nanotubes do represent a health hazard due to their capacity to activate Nlrp3 inflammasome, resembling the inflammation caused by asbestos. While further study of this phenomenon is definitely needed, the above findings clearly suggest that special precautions need to be taken when applying these nanoparticles in human disease research

PPARγ ligands switched high fat diet-induced macrophage M2b polarization toward M2a thereby improving intestinal Candida elimination.

International audienceObesity is associated with a chronic low-grade inflammation that predisposes to insulin resistance and the development of type 2 diabetes. In this metabolic context, gastrointestinal (GI) candidiasis is common. We recently demonstrated that the PPARγ ligand rosiglitazone promotes the clearance of Candida albicans through the activation of alternative M2 macrophage polarization. Here, we evaluated the impact of high fat diet (HFD)-induced obesity and the effect of rosiglitazone (PPARγ ligand) or WY14643 (PPARα ligand) both on the phenotypic M1/M2 polarization of peritoneal and cecal tissue macrophages and on the outcome of GI candidiasis. We demonstrated that the peritoneal macrophages and the cell types present in the cecal tissue from HF fed mice present a M2b polarization (TNF-α(high), IL-10(high), MR, Dectin-1). Interestingly, rosiglitazone induces a phenotypic M2b-to-M2a (TNF-α(low), IL-10(low), MR(high), Dectin-1(high)) switch of peritoneal macrophages and of the cells present in the cecal tissue. The incapacity of WY14643 to switch this polarization toward M2a state, strongly suggests the specific involvement of PPARγ in this mechanism. We showed that in insulin resistant mice, M2b polarization of macrophages present on the site of infection is associated with an increased susceptibility to GI candidiasis, whereas M2a polarization after rosiglitazone treatment favours the GI fungal elimination independently of reduced blood glucose. In conclusion, our data demonstrate a dual benefit of PPARγ ligands because they promote mucosal defence mechanisms against GI candidiasis through M2a macrophage polarization while regulating blood glucose level

Predicting Pneumonia and Influenza Mortality from Morbidity Data

BACKGROUND: Few European countries conduct reactive surveillance of influenza mortality, whereas most monitor morbidity. METHODOLOGY/PRINCIPAL FINDINGS: We developed a simple model based on Poisson seasonal regression to predict excess cases of pneumonia and influenza mortality during influenza epidemics, based on influenza morbidity data and the dominant types/subtypes of circulating viruses. Epidemics were classified in three levels of mortality burden (“high”, “moderate” and “low”). The model was fitted on 14 influenza seasons and was validated on six subsequent influenza seasons. Five out of the six seasons in the validation set were correctly classified. The average absolute difference between observed and predicted mortality was 2.8 per 100,000 (18% of the average excess mortality) and Spearman's rank correlation coefficient was 0.89 (P = 0.05). CONCLUSIONS/SIGNIFICANCE: The method described here can be used to estimate the influenza mortality burden in countries where specific pneumonia and influenza mortality surveillance data are not available

A Triple Amino Acid Substitution at Position 88/94/95 in Glycoprotein GP2a of Type 1 Porcine Reproductive and Respiratory Syndrome Virus (PRRSV1) Is Responsible for Adaptation to MARC-145 Cells

The Meat Animal Research Center-145 (MARC-145) cell line has been proven to be valuable for viral attenuation regarding vaccine development and production. Cell-adaptation is necessary for the efficient replication of porcine reproductive and respiratory syndrome virus (PRRSV) in these cells. Multiple sequence analysis revealed consistent amino acid substitutions in GP2a (V88F, M94I, F95L) of MARC-145 cell-adapted strains. To investigate the putative effect of these substitutions, mutations at either position 88, 94, 95, and their combinations were introduced into two PRRSV1 (13V091 and IVI-1173) infectious clones followed by the recovery of viable recombinants. When comparing the replication kinetics in MARC-145 cells, a strongly positive effect on the growth characteristics of the 13V091 strain (+2.1 log10) and the IVI-1173 strain (+1.7 log10) compared to wild-type (WT) virus was only observed upon triple amino acid substitution at positions 88 (V88F), 94 (M94I), and 95 (F95L) of GP2a, suggesting that the triple mutation is a determining factor in PRRSV1 adaptation to MARC-145 cells

Nrf2, a PPARγ Alternative Pathway to Promote CD36 Expression on Inflammatory Macrophages: Implication for Malaria

CD36 is the major receptor mediating nonopsonic phagocytosis of Plasmodium falciparum-parasitized erythrocytes by macrophages. Its expression on macrophages is mainly controlled by the nuclear receptor PPARγ. Here, we demonstrate that inflammatory processes negatively regulate CD36 expression on human and murine macrophages, and hence decrease Plasmodium clearance directly favoring the worsening of malaria infection. This CD36 downregulation in inflammatory conditions is associated with a failure in the expression and activation of PPARγ. Interestingly, using siRNA mediating knock down of Nrf2 in macrophages or Nrf2- and PPARγ-deficient macrophages, we establish that in inflammatory conditions, the Nrf2 transcription factor controls CD36 expression independently of PPARγ. In these conditions, Nrf2 activators, but not PPARγ ligands, enhance CD36 expression and CD36-mediated Plasmodium phagocytosis. These results were confirmed in human macrophages and in vivo where only Nrf2 activators improve the outcome of severe malaria. Collectively, this report highlights that the Nrf2 transcription factor could be an alternative target to PPARγ in the control of severe malaria through parasite clearance

Evidence of the Superparamagnetic State in the Zero-Field Microwave Susceptibility Spectra of Ferrimagnetic Nanoparticles

International audienceStatic and dynamic magnetic properties of Zn0.4Fe2.6O4 nanoparticles synthesized by thermal decomposition have been investigated. Two ranges of diameter have been used: small particles (diameter about 6.2 nm) and larger ones (diameter about 22.4 nm). The nanoparticle microstructure has been characterized by transmission electron microscopy. The temperature dependence of the zero-field dynamic permeability for both nanoparticle sizes has been studied, revealing a superparamagnetic state for the small ones. Effects of the nanoparticle size on the dynamic permeability have been studied, and linked to the superparamagnetic state. A dynamic susceptibility model has been found to reproduce the experimental behavior as well as its temperature dependence

Aspirin topic treatment improves cutaneous wound healing in diabetic mice through lipoxygenase‐dependent production of pro‐resolving lipid mediator

International audienceIntroduction: Healing disorders are one of the leading causes of morbidity and mortality of diabetic patients. The understanding of the deregulation of cellular and molecular mechanisms of the wound healing process is a key issue for the development of new therapeutic strategies. Delayed healing in diabetic patients is due to dysregulations of the inflammatory process. The arrest of inflammatory phase, which involves the recruitment of polarized M2 macrophages, is a key step in the resolution of inflammation and tissue repair. Our hypothesis was that deregulation of diabetic wound healing was the result of an impairment in the polarization of macrophages.Methods: We developed a new full‐thickness wound model in type 2 diabetic mice (in high fat diet or db/db mice) associated with the development of an innovative device to treat the wound, follow its evolution and characterized phenotypically and functionally cells within the exsudates.Results: We demonstrated that the severe impairment of healing in diabetic mice is correlated to a strong neutrophil and inflammatory macrophage M1 infiltration, a lack of influx of anti‐inflammatory macrophages M2, leading to a failure in the inflammatory cells apoptosis and efferocytosis. We established a decrease of lipoxin A4 (LXA4), a bioactive lipid from arachidonic acid (AA) metabolism involved in the resolution of inflammation, and an increase of potent chemotactic lipid leukotriene B4 (LTB4). We demonstrated that topical daily application of acetylsalicylic acid on the wound, 3 days after the skin lesion, orients the AA metabolism towards the synthesis of LXA4 at the expense of LTB4, triggers the recruitment of M2‐polarized macrophages, and promotes apoptosis of neutrophils and their efferocytosis.Conclusions: The resolution of inflammation by an original mechanism toward the 12/15‐LOX induction regardless of the COX‐2 expression allows us to envisage the development of a new therapeutic strategy to promote diabetic wound healing