Dissection génétique et études fonctionnelles du locus de contrôle de l'atopie Aiid3 et du locus de contrôle de la toxoplasmose Toxo1 dans le modèle des rats BN et LEW

Chez l'homme, le développement des maladies multifactorielles résulte d'interactions complexes entre des événements environnementaux et des facteurs de prédisposition génétiques. L'hétérogénéité de ces paramètres complique l'identification des gènes et des mécanismes physiopathologiques impliqués mais l'utilisation de modèles animaux expérimentaux permet de contourner ces difficultés. Nous avons utilisé les souches de rats BN et LEW qui différent largement dans leurs réponses immunitaires normales et pathologiques pour étudier le déterminisme génétique des susceptibilités à l'infection toxoplasmique et aux désordres immunologiques induits par les sels de métaux lourd. Notre travail a permis l'identification d'un locus majeur baptisé Toxo1 sur le chromosome 10 (c10) déterminant l'issu de l'infection chez le rat de façon indépendante du fond génétique. Par ailleurs, nos études fonctionnelles associent la résistance in vivo dépendante du locus Toxo1 à l'incapacité du parasite à proliférer et survivre in vitro dans les macrophages et les monocytes. La même stratégie génétique a été mise en œuvre pour l'étude de la susceptibilité aux désordres immunopathologiques induits par les sels de métaux lourds et a conduit à identifier une zone de 117Kb comprenant 4 gènes dont 2 sont polymorphes et impliqués dans le fonctionnement du système immunitaire. Ce travail fournit des informations précieuses pour des études génétiques ciblées dans des cohortes de patients et pour la compréhension des mécanismes physiopathologiques impliqués.Most human immune diseases are multifactorial, resulting from interactions between genetic and environmental factors. Their studies are hampered by genetic heterogeneity of human populations and by the variability of environment. In experimental conditions, using rodent models, environmental and genetic factors are under control. BN and LEW rats represent a powerful model to study immune-mediated diseases since they show strong differences in normal and pathological immune response. We used these strains to study genetic control of toxoplasmosis issue and mercury susceptibility. Linkage analyses in F2 (LEWxBN) rats followed by genetic dissection using reciprocal congenic and sub-congenic lines lead us to identified identified a major locus on chromosome 10 (c10) called Toxo1 in a 1.09Mb region that direct toxoplasmosis outcome independently of the genetic background. Two major candidate genes have been identified and their implications in congenital toxoplasmosis outcome in human cohorts are under investigation. By a similar strategy, genetic control of heavy metal-mediated immune disorder has been investigated. In the BN rats, mercury salt induced IgE production, auto-antibodies-mediated nephritic syndrome and ANCA-associated vasculatis while the LEW rats are completely resistant to the disease induction. In this work, we show that the Aiid3 locus previously identified by our group control the set of the mercury-induced symptoms. Genetic dissection of the locus leads us to localize the gene(s) of control within a critical 117Kb region. 4 genes are present within this region and 2 are both polymorph and implicated in immune system homeostasis and function and appear as major candidate genes for the Aiid3-mediated biological effect

Novel PLCG2 Mutation in a Patient With APLAID and Cutis Laxa.

Background: The auto-inflammation and phospholipase Cγ2 (PLCγ2)-associated antibody deficiency and immune dysregulation (APLAID) syndrome is a rare primary immunodeficiency caused by a gain-of-function mutation S707Y in the PLCG2 gene previously described in two patients from one family. The APLAID patients presented with early-onset blistering skin lesions, posterior uveitis, inflammatory bowel disease (IBD) and recurrent sinopulmonary infections caused by a humoral defect, but lacked circulating autoantibodies and had no cold-induced urticaria, contrary to the patients with the related PLAID syndrome. Case: We describe a new APLAID patient who presented with vesiculopustular rash in the 1st weeks of life, followed by IBD, posterior uveitis, recurrent chest infections, interstitial pneumonitis, and also had sensorineural deafness and cutis laxa. Her disease has been refractory to most treatments, including IL1 blockers and a trial with ruxolitinib has been attempted. Results: In this patient, we found a unique de novo heterozygous missense L848P mutation in the PLCG2 gene, predicted to affect the PLCγ2 structure. Similarly to S707Y, the L848P mutation led to the increased basal and EGF-stimulated PLCγ2 activity in vitro. Whole blood assays showed reduced production of IFN-γ and IL-17 in response to polyclonal T-cell stimulation and reduced production of IL-10 and IL-1β after LPS stimulation. Reduced IL-1β levels and the lack of clinical response to treatment with IL-1 blockers argue against NLRP3 inflammasome hyperactivation being the main mechanism mediating the APLAID pathogenesis. Conclusion: Our findings indicate that L848P is novel a gain-of-function mutation that leads to PLCγ2 activation and suggest cutis laxa as a possible clinical manifestations of the APLAID syndrome

Biallelic RIPK1 mutations in humans cause severe immunodeficiency, arthritis, and intestinal inflammation.

RIPK1 (receptor-interacting serine/threonine kinase 1) is a master regulator of signaling pathways leading to inflammation and cell death and is of medical interest as a drug target. We report four patients from three unrelated families with complete RIPK1 deficiency caused by rare homozygous mutations. The patients suffered from recurrent infections, early-onset inflammatory bowel disease, and progressive polyarthritis. They had immunodeficiency with lymphopenia and altered production of various cytokines revealed by whole-blood assays. In vitro, RIPK1-deficient cells showed impaired mitogen-activated protein kinase activation and cytokine secretion and were prone to necroptosis. Hematopoietic stem cell transplantation reversed cytokine production defects and resolved clinical symptoms in one patient. Thus, RIPK1 plays a critical role in the human immune system

Dissection génétique et études fonctionnelles du locus de contrôle de l'atopie Aiid3 et du locus contrôle de la toxoplasmose Toxo1, dans le modèle des rats BN et LEW

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Topoisomerase 2β and DNA topology during B cell development

Topoisomerase 2β (TOP2B) introduces transient double strand breaks in the DNA helix to remove supercoiling structures and unwind entangled DNA strains. Advances in genomic technologies have enabled the discovery of novel functions for TOP2B in processes such as releasing of the paused RNA polymerase II and maintaining the genome organization through DNA loop domains. Thus, TOP2B can regulate transcription directly by acting on transcription elongation and indirectly by controlling interactions between enhancer and promoter regions through genome folding. The identification of TOP2B mutations in humans unexpectedly revealed a unique role of TOP2B in B-cell progenitors. Here we discuss the functions of TOP2B and the mechanisms leading to the B-cell development defect in patients with TOP2B deficiency

Genetic control of HgCl2-induced IgE and autoimmunity by a 117-kb interval on rat chromosome 9 through CD4 CD45RC(high) T cells

International audienceGold or mercury salts trigger a dramatic IgE response and a CD4 T-cell-dependent nephropathy in Brown-Norway (BN), but not in Lewis (LEW) rats. We previously identified the 1.1-Mb Iresp3 (immunoglobin response QTL3) locus on chromosome 9 that controls these gold salt-triggered immune disorders. In the present work, we investigated the genetic control of HgCl2-induced immunological disorders and assessed the relative contribution of the CD45RC(high) and CD45RC(low) CD4 T-cell subpopulations in this control. By using interval-specific congenic lines, we narrowed down Iresp3 locus to 117-kb and showed that BN rats congenic for the LEW 117-kb were protected from HgCl2-triggered IgE response and nephropathy. This 117-kb interval also controls CD45RC expression by CD4 T cells and the ability of CD45RC(high) CD4 T cells to trigger the autoimmune disorders resulting from HgCl2 administration. This 117-kb region contains four genes, including Vav1, a strong candidate gene according to its cellular function and exclusive expression in hematopoietic cells. Thus, this study highlights the role of the CD45RC(high) CD4 T-cell subpopulation in the opposite susceptibility of BN and LEW rats to HgCl2-triggered immune disorders and identifies a 117-kb interval on chromosome 9 that has a key role in their functions

A highly conserved toxo1 haplotype directs resistance to toxoplasmosis and its associated caspase-1 dependent killing of parasite and host macrophage.

International audienceNatural immunity or resistance to pathogens most often relies on the genetic make-up of the host. In a LEW rat model of refractoriness to toxoplasmosis, we previously identified on chromosome 10 the Toxo1 locus that directs toxoplasmosis outcome and controls parasite spreading by a macrophage-dependent mechanism. Now, we narrowed down Toxo1 to a 891 kb interval containing 29 genes syntenic to human 17p13 region. Strikingly, Toxo1 is included in a haplotype block strictly conserved among all refractory rat strains. The sequencing of Toxo1 in nine rat strains (5 refractory and 4 susceptible) revealed resistant-restricted conserved polymorphisms displaying a distribution gradient that peaks at the bottom border of Toxo1, and highlighting the NOD-like receptor, Nlrp1a, as a major candidate. The Nlrp1 inflammasome is known to trigger, upon pathogen intracellular sensing, pyroptosis programmed-cell death involving caspase-1 activation and cleavage of IL-1β. Functional studies demonstrated that the Toxo1-dependent refractoriness in vivo correlated with both the ability of macrophages to restrict T. gondii growth and a T. gondii-induced death of intracellular parasites and its host macrophages. The parasite-induced cell death of infected macrophages bearing the LEW-Toxo1 alleles was found to exhibit pyroptosis-like features with ROS production, the activation of caspase-1 and IL1-β secretion. The pharmacological inactivation of caspase-1 using YVAD and Z-VAD inhibitors prevented the death of both intravacuolar parasites and host non-permissive macrophages but failed to restore parasite proliferation. These findings demonstrated that the Toxo1-dependent response of rat macrophages to T. gondii infection may trigger two pathways leading to the control of parasite proliferation and the death of parasites and host macrophages. The NOD-like receptor NLRP1a/Caspase-1 pathway is the best candidate to mediate the parasite-induced cell death. These data represent new insights towards the identification of a major pathway of innate resistance to toxoplasmosis and the prediction of individual resistance