Sepsis promotes splenic production of a protective platelet pool with high CD40 ligand expression.

Platelets have a wide range of functions including critical roles in hemostasis, thrombosis, and immunity. We hypothesized that during acute inflammation, such as in life-threatening sepsis, there are fundamental changes in the sites of platelet production and phenotypes of resultant platelets. Here, we showed during sepsis that the spleen was a major site of megakaryopoiesis and platelet production. Sepsis provoked an adrenergic-dependent mobilization of megakaryocyte-erythrocyte progenitors (MEPs) from the bone marrow to the spleen, where IL-3 induced their differentiation into megakaryocytes (MKs). In the spleen, immune-skewed MKs produced a CD40 ligandhi platelet population with potent immunomodulatory functions. Transfusions of post-sepsis platelets enriched from splenic production enhanced immune responses and reduced overall mortality in sepsis-challenged animals. These findings identify a spleen-derived protective platelet population that may be broadly immunomodulatory in acute inflammatory states such as sepsis.NHS Blood and Transplant European Union's Horizon 2020 (ERC-2014-CoG-648765) MRC-AMED (MR/V005421/1

Liver X receptors are required for thymic resilience and T cell output

The thymus is a primary lymphoid organ necessary for optimal T cell development. Here, we show that liver X receptors (LXRs)-a class of nuclear receptors and transcription factors with diverse functions in metabolism and immunity-critically contribute to thymic integrity and function. LXRαβ-deficient mice develop a fatty, rapidly involuting thymus and acquire a shrunken and prematurely immunoinhibitory peripheral T cell repertoire. LXRαβ's functions are cell specific, and the resulting phenotypes are mutually independent. Although thymic macrophages require LXRαβ for cholesterol efflux, thymic epithelial cells (TECs) use LXRαβ for self-renewal and thymocytes for negative selection. Consequently, TEC-derived LXRαβ protects against homeostatic premature involution and orchestrates thymic regeneration following stress, while thymocyte-derived LXRαβ limits cell disposal during negative selection and confers heightened sensitivity to experimental autoimmune encephalomyelitis. These results identify three distinct but complementary mechanisms by which LXRαβ governs T lymphocyte education and illuminate LXRαβ's indispensable roles in adaptive immunity

ADAM8 signaling drives neutrophil migration and ARDS severity

Acute respiratory distress syndrome (ARDS) results in catastrophic lung failure and has an urgent, unmet need for improved early recognition and therapeutic development. Neutrophil influx is a hallmark of ARDS and is associated with the release of tissue-destructive immune effectors, such as matrix metalloproteinases (MMPs) and membrane-anchored metalloproteinase disintegrins (ADAMs). Here, we observed using intravital microscopy that Adam8–/– mice had impaired neutrophil transmigration. In mouse pneumonia models, both genetic deletion and pharmacologic inhibition of ADAM8 attenuated neutrophil infiltration and lung injury while improving bacterial containment. Unexpectedly, the alterations of neutrophil function were not attributable to impaired proteolysis but resulted from reduced intracellular interactions of ADAM8 with the actin-based motor molecule Myosin1f that suppressed neutrophil motility. In 2 ARDS cohorts, we analyzed lung fluid proteolytic signatures and identified that ADAM8 activity was positively correlated with disease severity. We propose that in acute inflammatory lung diseases such as pneumonia and ARDS, ADAM8 inhibition might allow fine-tuning of neutrophil responses for therapeutic gain

Rôles de la PI3 kinase de classe II alpha et de la PI3K de classe III, vps34, dans la production et les fonctions plaquettaires

Les mégacaryocytes sont des cellules de la moelle osseuse qui par un processus complexe et encore mal caractérisé, mégacaryopoïèse/thrombopoïèse, donnent naissance, in fine, aux plaquettes sanguines. La différenciation mégacaryocytaire nécessite un intense remodelage nucléaire et cytoplasmique, guidé à la fois par des facteurs intrinsèques mais aussi par des facteurs extrinsèques tel que le microenvironnement médullaire. Les plaquettes sanguines sont des acteurs essentiels du maintien de l'intégrité vasculaire. Elles sont les premiers éléments cellulaires à intervenir dans l'arrêt du saignement lors d'une blessure vasculaire par la formation d'un thrombus via des mécanismes d'adhésion, de sécrétion et d'agrégation, trois étapes majeures de l'hémostase physiologique. Dans un premier temps, mes travaux de thèse visent à déterminer le rôle inconnu de l'isoforme alpha des PI3Ks de classe II (PI3KC2a), de la PI3K de classe III (Vps34) et de leur produit, le phosphatidylinositol 3 monophosphate (PI3P), dans la production et les fonctions plaquettaires. Grâce à un modèle murin présentant une inactivation partielle de la PI3KC2a, j'ai mis en évidence son rôle clé dans la génération d'un pool basal de PI3P dans les plaquettes. L'inactivation de la PI3KC2a affecte la composition du cortex sous-membranaire plaquettaire induisant une morphologie plaquettaire anormale, une accumulation de plaquettes à deux corps appelées " barbell-shaped proplatelets ", un défaut de formation du thrombus ex vivo et un retard d'occlusion de la carotide après lésion in vivo. Ainsi, la PI3KC2a joue un rôle majeur dans le maintien de l'intégrité du squelette membranaire contrôlant la structure et la dynamique membranaire, processus critique à la production de plaquettes fonctionnelles. D'autre part, la délétion de Vps34 spécifiquement dans la lignée mégacaryocyte/plaquette se traduit par une microthrombopénie modérée associée à une migration anormale des mégacaryocytes liées à un défaut de trafic vésiculaire et une diminution du taux de PI3P. De façon intéressante, Vps34 joue aussi un rôle dans l'activation plaquettaire en régulant la production de PI3P sous stimulation, la croissance du thrombus ex vivo et les capacités thrombotiques in vivo. Le rôle de Vps34 dans la plaquette indépendamment de son rôle dans le mégacaryocyte a été confirmé via l'utilisation de nouveaux inhibiteurs spécifiques de Vps34, SAR405 et INH1, ex vivo. Vps34 est donc critique dans la régulation de la production plaquettaire par les mégacaryocytes ainsi que dans l'activation plaquettaire. Dans un deuxième temps, je me suis intéressé à l'impact du microenvironnement médullaire sur la mégacaryopoïèse, et plus spécifiquement sur la communication entre adipocytes médullaires et progéniteurs hématopoïétiques lors de leur différenciation en mégacaryocytes. Grace à un système de coculture in vitro, j'ai montré que les adipocytes améliorent la différenciation mégacaryocytaire via un transfert direct de lipides, dans un but non-énergétique. Dans un contexte d'obésité, nous observons, in vivo, associée à une adiposité médullaire augmentée une maturation mégacaryocytaire exacerbée, une production et une demi-vie plaquettaire défectueuses ayant pour conséquence une macrothrombopénie. Ainsi, le microenvironnement médullaire et plus particulièrement l'adipocyte impacte directement sur la mégacaryopoïèse et la production plaquettaire. En conclusion, ces travaux de thèse contribuent à caractériser les mécanismes de production et de fonction plaquettaire régulés par des facteurs intrinsèques tels que le PI3KC2a et Vps34, ainsi que par des facteurs extrinsèques tels que l'adipocyte médullaire.Megakaryopoiesis is a highly specialised and complex process occurring in the bone marrow, by which megakaryocytes give rise to de novo circulating blood platelets. Megakaryocyte differentiation implies cytoplasmic and nuclear rearrangements regulated by intrinsic as well as extrinsic factors such as bone marrow microenvironment. Platelets play a critical role in preventing blood loss after vascular injury by orchestrating clot formation through mechanisms of adhesion, secretion and aggregation. These mechanisms are the three major steps of physiological haemostasis leading to the maintenance of vascular integrity. Firstly, my thesis work focused on characterizing the role of class II PI3K alpha isoform (PI3KC2a), class III PI3K (Vps34) and their common product the phosphatidylinositol 3 monophosphate (PI3P) in platelet production and function. Using a unique mouse model partially inactivated for PI3KC2a, I highlighted its key role in the production of a basal PI3P housekeeping pool in platelets. PI3KC2a partial inactivation affects platelet membrane skeleton composition leading to an abnormal platelet morphology, an enrichment of platelet with two cell bodies recently called "barbell-shaped proplatelets", an ex vivo defective thrombus formation and an in vivo delayed carotid occlusion following injury. Thus, PI3KC2a plays a major role in membrane structure and dynamics by maintaining membrane skeleton integrity, which is crucial for functional platelet production. On the other hand, Vps34 specific deletion in megakaryocyte/platelet lineage induced mild microthombopenia correlated to an abnormal megakaryocyte migration linked to an affected PI3P production as well as vesicular trafficking in megakaryocytes. In platelets, Vps34 plays a role in their activation by regulating PI3P production under stimulation, ex vivo thrombus growth and in vivo thrombotic capacity. Vps34 role in platelet independently from its role in megakaryocyte was confirmed using two recently developed inhibitors, SAR405 and INH1, which reproduced ex vivo thrombus growth defects. Therefore, Vps34 is critical for platelet production by megakaryocyte as well as platelet activation. Secondly, I studied the impact of bone marrow microenvironment on megakaryopoiesis and more specifically the crosstalk between medullar adipocytes and hematopoietic progenitors differentiating towards the megakaryocyte lineage. Using an in vitro coculture assay, I demonstrated that adipocytes enhanced megakaryocyte differentiation through a direct lipid transfer, in a non-energetic aim. In the context of obesity, increased marrow adipocity is associated to enhanced megakaryocyte differentiation and defective platelet production and lifespan leading to macrothrombopenia. Thus, bone marrow microenvironment through adipocytes impact directly on megakaryopoiesis and platelet production. Altogether my thesis work contributes to better understand platelet production and function, mechanisms regulated by intrinsic factors such as PI3KC2a and Vps34 as well as extrinsic factors like medullar adipocytes

Roles of class II alpha PI3 kinases and class III (Vps34) in platelet production and function

Les mégacaryocytes sont des cellules de la moelle osseuse qui par un processus complexe et encore mal caractérisé, mégacaryopoïèse/thrombopoïèse, donnent naissance, in fine, aux plaquettes sanguines. La différenciation mégacaryocytaire nécessite un intense remodelage nucléaire et cytoplasmique, guidé à la fois par des facteurs intrinsèques mais aussi par des facteurs extrinsèques tel que le microenvironnement médullaire. Les plaquettes sanguines sont des acteurs essentiels du maintien de l'intégrité vasculaire. Elles sont les premiers éléments cellulaires à intervenir dans l'arrêt du saignement lors d'une blessure vasculaire par la formation d'un thrombus via des mécanismes d'adhésion, de sécrétion et d'agrégation, trois étapes majeures de l'hémostase physiologique. Dans un premier temps, mes travaux de thèse visent à déterminer le rôle inconnu de l'isoforme alpha des PI3Ks de classe II (PI3KC2a), de la PI3K de classe III (Vps34) et de leur produit, le phosphatidylinositol 3 monophosphate (PI3P), dans la production et les fonctions plaquettaires. Grâce à un modèle murin présentant une inactivation partielle de la PI3KC2a, j'ai mis en évidence son rôle clé dans la génération d'un pool basal de PI3P dans les plaquettes. L'inactivation de la PI3KC2a affecte la composition du cortex sous-membranaire plaquettaire induisant une morphologie plaquettaire anormale, une accumulation de plaquettes à deux corps appelées " barbell-shaped proplatelets ", un défaut de formation du thrombus ex vivo et un retard d'occlusion de la carotide après lésion in vivo. Ainsi, la PI3KC2a joue un rôle majeur dans le maintien de l'intégrité du squelette membranaire contrôlant la structure et la dynamique membranaire, processus critique à la production de plaquettes fonctionnelles. D'autre part, la délétion de Vps34 spécifiquement dans la lignée mégacaryocyte/plaquette se traduit par une microthrombopénie modérée associée à une migration anormale des mégacaryocytes liées à un défaut de trafic vésiculaire et une diminution du taux de PI3P. De façon intéressante, Vps34 joue aussi un rôle dans l'activation plaquettaire en régulant la production de PI3P sous stimulation, la croissance du thrombus ex vivo et les capacités thrombotiques in vivo. Le rôle de Vps34 dans la plaquette indépendamment de son rôle dans le mégacaryocyte a été confirmé via l'utilisation de nouveaux inhibiteurs spécifiques de Vps34, SAR405 et INH1, ex vivo. Vps34 est donc critique dans la régulation de la production plaquettaire par les mégacaryocytes ainsi que dans l'activation plaquettaire. Dans un deuxième temps, je me suis intéressé à l'impact du microenvironnement médullaire sur la mégacaryopoïèse, et plus spécifiquement sur la communication entre adipocytes médullaires et progéniteurs hématopoïétiques lors de leur différenciation en mégacaryocytes. Grace à un système de coculture in vitro, j'ai montré que les adipocytes améliorent la différenciation mégacaryocytaire via un transfert direct de lipides, dans un but non-énergétique. Dans un contexte d'obésité, nous observons, in vivo, associée à une adiposité médullaire augmentée une maturation mégacaryocytaire exacerbée, une production et une demi-vie plaquettaire défectueuses ayant pour conséquence une macrothrombopénie. Ainsi, le microenvironnement médullaire et plus particulièrement l'adipocyte impacte directement sur la mégacaryopoïèse et la production plaquettaire. En conclusion, ces travaux de thèse contribuent à caractériser les mécanismes de production et de fonction plaquettaire régulés par des facteurs intrinsèques tels que le PI3KC2a et Vps34, ainsi que par des facteurs extrinsèques tels que l'adipocyte médullaire.Megakaryopoiesis is a highly specialised and complex process occurring in the bone marrow, by which megakaryocytes give rise to de novo circulating blood platelets. Megakaryocyte differentiation implies cytoplasmic and nuclear rearrangements regulated by intrinsic as well as extrinsic factors such as bone marrow microenvironment. Platelets play a critical role in preventing blood loss after vascular injury by orchestrating clot formation through mechanisms of adhesion, secretion and aggregation. These mechanisms are the three major steps of physiological haemostasis leading to the maintenance of vascular integrity. Firstly, my thesis work focused on characterizing the role of class II PI3K alpha isoform (PI3KC2a), class III PI3K (Vps34) and their common product the phosphatidylinositol 3 monophosphate (PI3P) in platelet production and function. Using a unique mouse model partially inactivated for PI3KC2a, I highlighted its key role in the production of a basal PI3P housekeeping pool in platelets. PI3KC2a partial inactivation affects platelet membrane skeleton composition leading to an abnormal platelet morphology, an enrichment of platelet with two cell bodies recently called "barbell-shaped proplatelets", an ex vivo defective thrombus formation and an in vivo delayed carotid occlusion following injury. Thus, PI3KC2a plays a major role in membrane structure and dynamics by maintaining membrane skeleton integrity, which is crucial for functional platelet production. On the other hand, Vps34 specific deletion in megakaryocyte/platelet lineage induced mild microthombopenia correlated to an abnormal megakaryocyte migration linked to an affected PI3P production as well as vesicular trafficking in megakaryocytes. In platelets, Vps34 plays a role in their activation by regulating PI3P production under stimulation, ex vivo thrombus growth and in vivo thrombotic capacity. Vps34 role in platelet independently from its role in megakaryocyte was confirmed using two recently developed inhibitors, SAR405 and INH1, which reproduced ex vivo thrombus growth defects. Therefore, Vps34 is critical for platelet production by megakaryocyte as well as platelet activation. Secondly, I studied the impact of bone marrow microenvironment on megakaryopoiesis and more specifically the crosstalk between medullar adipocytes and hematopoietic progenitors differentiating towards the megakaryocyte lineage. Using an in vitro coculture assay, I demonstrated that adipocytes enhanced megakaryocyte differentiation through a direct lipid transfer, in a non-energetic aim. In the context of obesity, increased marrow adipocity is associated to enhanced megakaryocyte differentiation and defective platelet production and lifespan leading to macrothrombopenia. Thus, bone marrow microenvironment through adipocytes impact directly on megakaryopoiesis and platelet production. Altogether my thesis work contributes to better understand platelet production and function, mechanisms regulated by intrinsic factors such as PI3KC2a and Vps34 as well as extrinsic factors like medullar adipocytes

Multi-tracer study of continental erosion and sediment transport to the Red Sea and the Gulf of Aden during the last 20 ka

International audienceMineralogical compositions and grain-size distributions combined with 87Sr/86Sr and εNd values of the detrital fraction were studied on cores recovered from the Gulf of Aden (MD92-1002) and the Red Sea (MD92-1008) basins in order to document past changes in Indian monsoon and northwesterly winds during the last glacial-interglacial transition (the last 20 ka), encompassing the African Humid Period (AHP). The εNd vs. 87Sr/86Sr plot indicates that sediments result from the mixing of two main sedimentary sources corresponding to the Afar volcanic rocks in Ethiopia and to the Arabian-Nubian Shield. Variations of sediment isotopic and mineralogical composition point to a diminution of the volcanic source contribution during the last deglaciation. Changes of mineral-accumulation rates and grain-size distributions denote a decline in the aridity of the source regions during the Holocene, particularly of the Afar volcanic region. In this area, the reduction of detrital supply, from 15 cal ka BP, can be explained by an increase of precipitations during the AHP, which resulted in an expansion of the vegetation cover and lake extensions in East Africa. In the Arabian Peninsula, precipitations were confined to the south, allowing sediments to be transported even during the Holocene. Our data suggest that the southwest monsoon was not the main carrier of aeolian sediments to the Red Sea and Gulf of Aden basins, but the Northwesterlies. In the Red Sea, the isotopic and mineralogical tracers reveal a contribution from Saharan dust between 16 and 12 cal ka BP, transported from the Nile catchment after aridification during Heinrich event 1

GPR35 promotes neutrophil recruitment in response to serotonin metabolite 5-HIAA

Rapid neutrophil recruitment to sites of inflammation is crucial for innate immune responses. Here, we reveal that the G-protein-coupled receptor GPR35 is upregulated in activated neutrophils, and it promotes their migration. GPR35-deficient neutrophils are less recruited from blood vessels into inflamed tissue, and the mice are less efficient in clearing peritoneal bacteria. Using a bioassay, we find that serum and activated platelet supernatant stimulate GPR35, and we identify the platelet-derived serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) as a GPR35 ligand. GPR35 function in neutrophil recruitment is strongly dependent on platelets, with the receptor promoting transmigration across platelet-coated endothelium. Mast cells also attract GPR35+ cells via 5-HIAA. Mice deficient in 5-HIAA show a loss of GPR35-mediated neutrophil recruitment to inflamed tissue. These findings identify 5-HIAA as a GPR35 ligand and neutrophil chemoattractant and establish a role for platelet- and mast cell-produced 5-HIAA in cell recruitment to the sites of inflammation and bacterial clearance

Profiling grape gene expression during leaf development and senescence by cDNA arrays

International audienc