Targeting T cell glutamine metabolism in severe asthma

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SUMMARY Asthma is a debilitating disease of airway inflammation with increasing worldwide occurrence. With higher incidence in females, asthma is exacerbated by obesity and metabolic disease. Underlying asthma is activation of innate immune and T cells that drive inflammation. Airway inflammation in severe asthma is caused in part by an imbalance between effector CD4 T cells (including Th2 and Th17) and suppressive regulatory (Treg) T cells. This imbalance is particularly heightened in obese females and leads to increased eosinophils and/or neutrophils in the airway, increased airway hyperresponsiveness, and increased mucus production. It is now clear that T cell metabolism plays a critical role to regulate immune function and the distinct metabolic programs of each T cell subset can influence inflammation and play roles in asthma. In addition to a requirement of T cells for glycolysis, our data show that glutamine metabolism plays a key role to support inflammatory T cells in asthma. Metabolomics data from bronchoalveolar fluid and mass cytometry of T cells from donors with severe asthma showed markers of elevated glutaminolysis. While IL17 producing cells both in vitro and from lungs had the highest expression of metabolic markers, both Th17 and Th2 cells relied on glutamine for differentiation and cytokine production. Glutamine metabolism is regulated through uptake by the transporter ASCT2 and Glutaminase (GLS)-dependent conversion to glutamate and α-ketoglutarate that supports mitochondrial electron transport and regulates epigenetic marks that control chromatin and gene expression. We have now shown through inhibition, gene targeting, and in vivo primary T cell CRISPR screening in lung inflammation that ASCT2 and GLS are essential for Th17 and Th2 cells. These genes are dispensable for Treg and blocking glutamine uptake can instead enhance Treg differentiation. Importantly, we also show in an animal model that high fat diet fed female mice have selectively increased frequencies of Th17 cells. This effect is sex-specific, as high fat diet fed female, but not male, mice developed increased IL17 production and we show that the Estrogen Receptor (ERα) plays a key role in females to elevate CD4 T cell glycolysis and mitochondrial metabolism. We hypothesize that airway allergen exposure and inflammatory cytokines induce T cell glutamine metabolism, driving Th2 and Th17 cells that contribute to asthma incidence and severity in obese females. To test this hypothesis, we will: (1) Determine the role and mechanism of GLS and ASCT2-dependent glutamine metabolism to regulate the balance of Th2, Th17 and Treg cells in a mixed model of allergic airway inflammation and (2) Test if obesity- induced exacerbation of asthma severity in females is dependent on enhanced T cell glutamine metabolism in animal models and from peripheral blood and excised lungs of healthy and severe asthma normal weight or obese donors. These studies will establish metabolic mechanisms and if inhibiting glutamine uptake or metabolism through ASCT2 or GLS can shift the balance of Th17 and Th2 cells to instead favor Treg and protect against asthma to help alleviate this health disparity observed in females with metabolic disease.