Céline Colacios

A Role for VAV1 in Experimental Autoimmune Encephalomyelitis and Multiple Sclerosis

VAV1 plays a role in regulating proinflammatory cytokines, which underlie the susceptibility for developing experimental autoimmune encephalomyelitis and multiple sclerosis. Rat Genetics Moving Up Multiple sclerosis (MS) is a common autoimmune disease with a complex etiology that attacks the brain and spinal cord and emerges as a result from both genetic and environmental factors. At present, there is no predictive biomarker for MS and no cure for adults who present with the disease, and only a few genes have been unambiguously linked to its development. The hunt has been to address these challenges, but also to uncover new targets that are associated with a high susceptibility for MS to augment disease-modifying treatments that are in clinical use. Using experimental autoimmune encephalomyelitis, an animal model of MS, Jagodic et al. have focused on a region of the rat genome on chromosome 9 that encodes the gene Vav1. Although this gene was initially identified as an oncogene, it later was found to be an important signal transducer with a pivotal role in immune cells, the very first hint being its specific activation after T cell receptor stimulation. The authors show that a specific mutation identified in rat Vav1 altered Vav1 protein abundances, immune cell activation, and neuroinflammation induction. Taking this observation a step further, among 12,735 individuals of European descent, Jagodic et al. reveal an association between a set of common variants within the first intron of VAV1 and susceptibility for MS. Like what they observed in the rat, common VAV1 variants altered VAV1 expression and immune activation in the peripheral blood and in the cerebrospinal fluid cells of MS patients. This study displays the power of using rat genetics to encourage the discovery of human genetic targets in common diseases such as MS. Multiple sclerosis, the most common cause of progressive neurological disability in young adults, is a chronic inflammatory disease. There is solid evidence for a genetic influence in multiple sclerosis, and deciphering the causative genes could reveal key pathways influencing the disease. A genome region on rat chromosome 9 regulates experimental autoimmune encephalomyelitis, a model for multiple sclerosis. Using interval-specific congenic rat lines and association of single-nucleotide polymorphisms with inflammatory phenotypes, we localized the gene of influence to Vav1, which codes for a signal-transducing protein in leukocytes. Analysis of seven human cohorts (12,735 individuals) demonstrated an association of rs2546133-rs2617822 haplotypes in the first VAV1 intron with multiple sclerosis (CA: odds ratio, 1.18; CG: odds ratio, 0.86; TG: odds ratio, 0.90). The risk CA haplotype also predisposed for higher VAV1 messenger RNA expression. VAV1 expression was increased in individuals with multiple sclerosis and correlated with tumor necrosis factor and interferon-γ expression in peripheral blood and cerebrospinal fluid cells. We conclude that VAV1 plays a central role in controlling central nervous system immune-mediated disease and proinflammatory cytokine production critical for disease pathogenesis.

Functional and Genetic Analysis of Two CD8 T Cell Subsets Defined by the Level of CD45RC Expression in the Rat

Differential cytokine production by T cells plays an important role in the outcome of the immune response. We show that the level of CD45RC expression differentiates rat CD8 T cells in two subpopulations, CD45RChigh and CD45RClow, that have different cytokine profiles and functions. Upon in vitro stimulation, in an Ag-presenting cell-independent system, CD45RChigh CD8 T cells produce IL-2 and IFN-γ while CD45RClow CD8 T cells produce IL-4, IL-10, and IL-13. In vitro, these subsets also exhibit different cytotoxic and suppressive functions. The CD45RChigh/CD45RClow CD8 T cell ratio was determined in Lewis (LEW) and Brown-Norway (BN) rats. These two rat strains differ with respect to the Th1/Th2 polarization of their immune responses and to their susceptibility to develop distinct immune diseases. The CD45RChigh/CD45RClow CD8 T cell ratio is higher in LEW than in BN rats, and this difference is dependent on hemopoietic cells. Linkage analysis in a F2(LEW × BN) intercross identified two quantitative trait loci on chromosomes 9 and 20 controlling the CD45RChigh/CD45RClow CD8 T cell ratio. This genetic control was confirmed in congenic rats. The region on chromosome 9 was narrowed down to a 1.2-cM interval that was found to also control the IgE response in a model of Th2-mediated disorder. Identification of genes that control the CD45RChigh/CD45RClow CD8 T cell subsets in these regions could be of great interest for the understanding of the pathophysiology of immune-mediated diseases.

Studies of Congenic Lines in the Brown Norway Rat Model of Th2-Mediated Immunopathological Disorders Show That the Aurothiopropanol Sulfonate-Induced Immunological Disorder (Aiid3) Locus on Chromosome 9 Plays a Major Role Compared to Aiid2 on Chromosome 10

Brown Norway (BN) rats treated with aurothiopropanol-sulfonate (Atps) constitute a model of Th2-mediated immunological disorders associated with elevated IgE responses and renal IgG deposits. Using F2 offspring between Atps-susceptible BN and Atps-resistant Lewis rats, we had previously mapped three quantitative trait loci on chromosomes 9, 10, and 20 for which BN alleles increased susceptibility to Atps-induced immunological disorders (Aiid). In this study we have used congenic lines for the latter two quantitative trait loci, formerly called Atps2 and Atps3 and now named Aiid2 (chromosome 10) and Aiid3 (chromosome 9), for fine mapping and characterization of their impact on Atps-triggered reactions. In Aiid2 congenic lines, the gene(s) controlling part of the IgE response to Atps was mapped to an ∼7-cM region, which includes the IL-4 cytokine gene cluster. Two congenic lines in which the introgressed segments shared only a portion of this 7-cM region, showed an intermediate IgE response, indicating the involvement of several genes within this region. Results from BN rats congenic for the Lewis Aiid3 locus, which we mapped to a 1.2-cM interval, showed a stronger effect of this region. In this congenic line, the Atps-triggered IgE response was 10-fold lower than in the BN parental strain, and glomerular IgG deposits were either absent or dramatically reduced. Further genetic and functional dissections of these loci should provide insights into pathways that lead to Th2-adverse reactions.

The p.Arg63Trp polymorphism controls Vav1 functions and Foxp3 regulatory T cell development

A single nucleotide polymorphism causing constitutive activation of Vav1 results in increased natural Treg generation and is responsible for the imbalance between Vav1 GEF and adaptor functions.

A Natural Variant of the Signaling Molecule Vav1 Enhances Susceptibility to Myasthenia Gravis and Influences the T Cell Receptor Repertoire

The guanine nucleotide exchange factor Vav1 is essential for transducing T cell receptor (TCR) signals and plays an important role in T cell development and activation. Previous genetic studies identified a natural variant of Vav1 characterized by the substitution of an arginine (R) residue by a tryptophane (W) at position 63 (Vav1R63W). This variant impacts Vav1 adaptor functions and controls susceptibility to T cell-mediated neuroinflammation. To assess the implication of this Vav1 variant on the susceptibility to antibody-mediated diseases, we used the animal model of myasthenia gravis, experimental autoimmune myasthenia gravis (EAMG). To this end, we generated a knock-in (KI) mouse model bearing a R to W substitution in the Vav1 gene (Vav1R63W) and immunized it with either torpedo acetylcholine receptor (tAChR) or the α146-162 immunodominant peptide. We observed that the Vav1R63W conferred increased susceptibility to EAMG, revealed by a higher AChR loss together with an increased production of effector cytokines (IFN-γ, IL-17A, GM-CSF) by antigen-specific CD4+ T cells, as well as an increased frequency of antigen-specific CD4+ T cells. This correlated with the emergence of a dominant antigen-specific T cell clone in KI mice that was not present in wild-type mice, suggesting an impact on thymic selection and/or a different clonal selection threshold following antigen encounter. Our results highlight the key role of Vav1 in the pathophysiology of EAMG and this was associated with an impact on the TCR repertoire of AChR reactive T lymphocytes.