AHR activation and mechanisms of cell alteration in myasthenia gravis model – ATM

Numerous groups have demonstrated that environmental factors (endocrine disruptors) through their nuclear receptor, the Aryl hydrocarbon receptor (AhR), activate transduction pathways that regulate the immune system and contribute to autoimmunity. Research groups evidence that prenatal or early-life exposures to pollutants can influence later in life, immune system function and autoimmune incidence. The effects of AhR activation, by endocrine disruptor, are well known on T-cell subsets, but over-looked for the cells sustaining T-cell development and differentiation, the thymic epithelial cells (TECs, the key cells for immune central tolerance). Of note, autoimmunity is a combined consequence of central immune tolerance breakdown to self-components occurring in the thymus and T-cell imbalance in periphery. Recently, Partner 1 has demonstrated that estrogen modulate the immune central tolerance and contribute to higher female susceptibility to autoimmunity.
Autoimmune myasthenia gravis (MG) is a prototype of autoimmune disease characterized by muscle weaknesses due to autoantibodies targeting components of the neuromuscular junction, mainly the acetylcholine receptor (AChR). In this disease, the thymus is the site of T-cell disequilibrium, immune tolerance breakdown and the production of AChR autoantibodies. The autoantibody impairs nerve-muscle transmission with subsequent consequences on muscle regeneration and muscle stem cell function.
Preliminary data suggest that in MG patients, AhR is activated in the two tissues involved in the physiopathology events occurring in the disease.
Of note, AhR modulates sets of genes involved in muscular adaptation to physical training and in muscle regeneration (muscle stem cells (MuSC)).
In the ATM project, we hypothesize that AhR
1- induces breakdown or disruption in thymic tolerance mechanisms that contributes to the development of this autoimmune disease,
2- induces, in the muscle tissue, an exacerbation in disease course by altering muscle stem cell function and muscle physiology

In the WP1, we will investigate the impact of AhR activation,in vitro on 1) TEC physiology (proliferation, viability and apoptosis of primary cultured human TECs) and 2) on TEC function in central tolerance (gene expressions of Aire, Prdm, Fezf2 and tissue specific antigens). In vitro data will be validated by evaluation in mice (Wildtype and AhR-/-), the impact of AhR ligands combined with estrogen on 1) the TEC homeostasis (identification and analysis of TEC subsets by Cytof analysis), 2) the thymus capacity to generate T-cells (TREC analysis), and 3) consequently, the susceptibility to autoimmune disease (experimental autoimmune myasthenia gravis (EAMG) and experimental thyroiditis (disease incidence and scores, clinical evaluation, antibody content)).
In the WP2, we will investigate, in vitro, the impact of AhR activation on muscle stem cells (MusC) and myoblast physiology (cell proliferation, differentiation by immunohistochemistry analysis and exposure molecular signature by RNA seq analysis). To validate the specific candidate transduction pathways and the specific cellular cross-talks identified in vitro, we will establish two cell-specific AhR defective mouse models and challenge them with EAMG. In this model, we will assess the muscle function (force), the MuSC quiescence, proliferation and differentiation potential, the muscle regeneration after physical injury and the molecular signature by transcriptomic investigation of Facs sorted MuSC cells.
Our ATM project will improve the knowledge on cellular, molecular and physiological mechanisms controlled by environmental factors (PAH, smoking, medecine) that lead to disruption of central thymic tolerance and muscle impairments.
This work will shed light on the contribution of environmental components in the increase of autoimmune pathologies and muscle disorders that represents one of the main causes of disability in the world.