Heme Drives Susceptibility of Glomerular Endothelium to Complement Overactivation Due to Inefficient Upregulation of Heme Oxygenase-1

Atypical hemolytic uremic syndrome (aHUS) is a severe disease characterized by microvascular endothelial cell (EC) lesions leading to thrombi formation, mechanical hemolysis and organ failure, predominantly renal. Complement system overactivation is a hallmark of aHUS. To investigate this selective susceptibility of the microvascular renal endothelium to complement attack and thrombotic microangiopathic lesions, we compared complement and cyto-protection markers on EC, from different vascular beds, in in vitro and in vivo models as well as in patients. No difference was observed for complement deposits or expression of complement and coagulation regulators between macrovascular and microvascular EC, either at resting state or after inflammatory challenge. After prolonged exposure to hemolysis-derived heme, higher C3 deposits were found on glomerular EC, in vitro and in vivo, compared with other EC in culture and in mice organs (liver, skin, brain, lungs and heart). This could be explained by a reduced complement regulation capacity due to weaker binding of Factor H and inefficient upregulation of thrombomodulin (TM). Microvascular EC also failed to upregulate the cytoprotective heme-degrading enzyme heme-oxygenase 1 (HO-1), normally induced by hemolysis products. Only HUVEC (Human Umbilical Vein EC) developed adaptation to heme, which was lost after inhibition of HO-1 activity. Interestingly, the expression of KLF2 and KLF4—known transcription factors of TM, also described as possible transcription modulators of HO-1- was weaker in micro than macrovascular EC under hemolytic conditions. Our results show that the microvascular EC, and especially glomerular EC, fail to adapt to the stress imposed by hemolysis and acquire a pro-coagulant and complement-activating phenotype. Together, these findings indicate that the vulnerability of glomerular EC to hemolysis is a key factor in aHUS, amplifying complement overactivation and thrombotic microangiopathic lesions

An intercomparison exercise of good laboratory practices for nano-aerosols sizemeasurements by mobility spectrometers

International audienceAn intercomparison campaign on nanoparticle size measurement was organized in the frame of the French nanoMetrology club. The aim of this study is to make an inventory of the metrological capabilities of all measurement techniques in France involved in the “nano” size range, including the SMPS (Scanning Mobility Particle Sizer) concerning aerosol metrology. For this study, four samples have been proposed, namely (1) - a SiO2 colloidal suspension (FD304) consisting of a monomodal population, (2) - two samples consisting of two nanoparticle populations of SiO2 having proportions to be determined and (3) - a TiO2 colloidal suspension. Ten SMPS associated to five participants around a common experimental setup were performed in link with a control SMPS to have simultaneous measurements with a same instrument in each laboratory in parallel with the SMPS used by each partner. This article presents SMPS results of this study associated with the description of the experimental set-up and the sample preparation protocol with an identified schedule and comparison with SEM measurements. The present paper does not focus on the actual capability of the tested mobility spectrometers, but aims to highlights the good laboratory practices using their own but common resources in terms of aerosol generation and measurement set-ups

Lipid cell biology. Polyunsaturated phospholipids facilitate membrane deformation and fission by endocytic proteins.

PublicationPhospholipids (PLs) with polyunsaturated acyl chains are extremely abundant in a few specialized cellular organelles such as synaptic vesicles and photoreceptor discs, but their effect on membrane properties is poorly understood. Here, we found that polyunsaturated PLs increased the ability of dynamin and endophilin to deform and vesiculate synthetic membranes. When cells incorporated polyunsaturated fatty acids into PLs, the plasma membrane became more amenable to deformation by a pulling force and the rate of endocytosis was accelerated, in particular, under conditions in which cholesterol was limiting. Molecular dynamics simulations and biochemical measurements indicated that polyunsaturated PLs adapted their conformation to membrane curvature. Thus, by reducing the energetic cost of membrane bending and fission, polyunsaturated PLs may help to support rapid endocytosis

Modulation of cellular membrane properties as a potential therapeutic strategy to counter lipointoxication in obstructive pulmonary diseases

International audienceMaintaining the equilibrium between saturated and unsaturated fatty acids within membrane phospholipids (PLs) is crucial to sustain the optimal membrane biophysical properties, compatible with selective organellebased processes. Lipointoxication is a pathological condition under which saturated PLs tend to accumulate within the cell at the expense of unsaturated species, with major impacts on organelle function. Here, we show that human bronchial epithelial cells extracted from lungs of patients with Obstructive Pulmonary Diseases (OPDs), i. e. Cystic Fibrosis (CF) individuals and Smokers, display a characteristic lipointoxication signature, with excessive amounts of saturated PLs. Reconstitution of this signature in cellulo and in silico revealed that such an imbalance results in altered membrane properties and in a dramatic disorganization of the intracellular network of bronchial epithelial cells, in a process which can account for several OPD traits. Such features include Endoplasmic Reticulum-stress, constitutive IL8 secretion, bronchoconstriction and, ultimately, epithelial cell death by apoptosis. We also demonstrate that a recently-identified lipid-like molecule, which has been shown to behave as a "membrane-reshaper", counters all the lipointoxication hallmarks tested. Altogether, these insights highlight the modulation of membrane properties as a potential new strategy to heal and prevent highly detrimental symptoms associated with OPDs

Fit αβ T-Cell Receptor suppresses leukemogenesis of Pten-deficient thymocytes.

International audienceSignaling through the αβT cell receptor (TCR) is a crucial determinant of T-cell fate and can induce two opposite outcomes during thymocyte development: cell death or survival and differentiation. To date, the role played by T cell receptor in the oncogenic transformation of developing T-cells remains unclear. Here we show that human primary T-cell acute lymphoblastic leukemias expressing a αβT cell receptor are frequently deficient for phosphatase and tensin homolog protein (PTEN), and fail to strongly respond to T cell receptor activation. Using Pten-deficient T-cell acute lymphoblastic leukemia mouse models, we confirm that T cell receptor signaling is involved in leukemogenesis. We show that abrogation of T cell receptor expression accelerated tumor onset, while enforced expression of a fit transgenic T cell receptor led to the development of T cell receptor-negative lymphoma and delayed tumorigenesis. We further demonstrate that pre-tumoral Pten-deficient thymocytes harboring fit T cell receptors undergo early clonal deletion, thus preventing their malignant transformation; while cells with unfit T cell receptors that should normally be deleted during positive selection, pass selection and develop T-cell acute lymphoblastic leukemias. Altogether, our data show that fit T cell receptor signaling suppresses tumor development mediated by Pten loss-of-function and pinpoint to a role of Pten in positive selection

Heme Drives Susceptibility of Glomerular Endothelium to Complement Overactivation Due to Inefficient Upregulation of Heme Oxygenase-1

International audienceAtypical hemolytic uremic syndrome (aHUS) is a severe disease characterized by microvascular endothelial cell (EC) lesions leading to thrombi formation, mechanical hemolysis and organ failure, predominantly renal. Complement system overactivation is a hallmark of aHUS. To investigate this selective susceptibility of the microvascular renal endothelium to complement attack and thrombotic microangiopathic lesions, we compared complement and cyto-protection markers on EC, from different vascular beds, in in vitro and in vivo models as well as in patients. No difference was observed for complement deposits or expression of complement and coagulation regulators between macrovascular and microvascular EC, either at resting state or after inflammatory challenge. After prolonged exposure to hemolysis-derived heme, higher C3 deposits were found on glomerular EC, in vitro and in vivo, compared with other EC in culture and in mice organs (liver, skin, brain, lungs and heart). This could be explained by a reduced complement regulation capacity due to weaker binding of Factor H and inefficient upregulation of thrombomodulin (TM). Microvascular EC also failed to upregulate the cytoprotective heme-degrading enzyme heme-oxygenase 1 (HO-1), normally induced by hemolysis products. Only HUVEC (Human Umbilical Vein EC) developed adaptation to heme, which was lost after inhibition of HO-1 activity. Interestingly, the expression of KLF2 and KLF4-known transcription factors of TM, also described as possible transcription modulators of HO-1- was weaker in micro than macrovascular EC under hemolytic conditions. Our results show that the microvascular EC, and especially glomerular EC, fail to adapt to the stress imposed by hemolysis and acquire a pro-coagulant and complement-activating phenotype. Together, these findings indicate that the vulnerability of glomerular EC to hemolysis is a key factor in aHUS, amplifying complement overactivation and thrombotic microangiopathic lesions

Site- and allele-specific polycomb dysregulation in T-cell leukaemia

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Assessment of preoperative noninvasive ventilation before lung cancer surgery: The preOVNI randomized controlled study

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