Glucocorticoids and their effects on immunometabolism in type 2 inflammation during asthma

Glucocorticoids (GCs) are indispensable to clinical practice, serving as a cornerstone in the treatment of inflammatory and autoimmune diseases. In asthma, a disease characterized by type 2 inflammation driven by exacerbated activation of infiltrating eosinophils and resident macrophages, GCs remain the first-line therapy to control airway inflammation. Emerging evidence highlights that rewiring of immune cell function via metabolic reprogramming is central for the GC effects. Such immunometabolic modulation by GCs has been partially described in the context of type 1 inflammation. However, and despite their widespread use, limited knowledge exists on how GCs modulate immune cell metabolism during type 2 inflammation, particularly in eosinophils. This thesis examines how the metabolism of immune cells involved in type 2 inflammation contributes to the efficacy of GC treatment during asthma. Using an ovalbumin-induced asthma mouse model, we analyzed immune cell populations in the lung, their cytokine expression, and metabolic alterations in oxidative phosphorylation (OXPHOS) and glycolysis invivo. The cell-specific GC effects on eosinophil metabolism in vitro were examined in murine bone-marrow-derived eosinophils via flux analysis, metabolic inhibitors, gene, cytokine and protein expression analyses. Our findings demonstrate that GCs partially restore OXPHOS in lung cells during type2inflammation. In eosinophils, GCs reprogram metabolism by significantly counteracting IL-33-induced glycolysis while moderately reducing elevated OXPHOS, promoting a quiescent metabolic state. Notably, GC-mediated suppression of IL-4 production partially depends on glycolytic modulation, as shown by inhibition with 2- deoxy-D-glucose (2-DG). Furthermore, we provide evidence that GCs promote a selective alternative phenotype in eosinophils beyond classical immunosuppression. We further identify functional itaconate metabolism as critical for cytokine suppression and eosinophil infiltration into the lung in vivo. However, in Acod1-deficient eosinophils in vitro, cytokine suppression by GCs remains intact, suggesting an itaconate- independent regulatory pathway of GC action in eosinophils. Partial results of the present work have been published in Auger et al. Metabolic rewiring promotes anti-inflammatory effects of glucocorticoids. Nature, 2024. This is noted in the figure descriptions of the results section for the corresponding data. In summary, this thesis advances our understanding of GC-mediated immunometabolic reprogramming in eosinophils during type 2 inflammation in asthma. Our findings indicate that the anti-inflammatory effects of GCs extend beyond broad immunosuppression but involve cell type-specific metabolic reprogramming. In eosinophils, modulation of glycolysis appears crucial for GC-mediated IL-4 suppression, whereas functional itaconate metabolism in vitro is dispensable for GC action, unlike in vivo. The identification of an eosinophil-intrinsic itaconate-independent pathway underlying these observations opens new avenues for further research. These findings may support the development of strategies that selectively target metabolic pathways to improve therapeutic efficacy while minimizing GC-associated side effects. In the long term, this could provide a foundation for novel therapeutic approaches for the treatment of refractory or GC-resistant asthma.