B cell metabolism in autoimmunity

Abstract

Metabolic reprogramming has been recognised as a major hallmark of immune cell activation. While researchers have gained detailed insight about this process in many different immune cells like T cells and macrophages, the B cell lineage lacks this level of understanding. In this thesis, I aimed at elucidating the metabolic profile of B cells and plasma cells to modulate their function by pharmaceutical inhibition of their respective metabolic profile. Using flow cytometry, plasma cells and B cells were analysed with regard to the basic metabolic parameters glucose uptake and mitochondrial mass, as well as antibody synthesis and the activity of the unfolded protein response (UPR) on the single cell level. These parameters were analysed after treatment with glycolysis inhibitor 2-deoxyglucose (2-DG) in vitro in either isolated B cells activated with lipopolysaccharides (LPS) or whole spleen cells without stimulant. In addition, B6.NZM-Sle1NZM2410/Aeg Sle2NZM2410/Aeg Sle3NZM2410/Aeg/Lmoj (BcN) mice, a mouse strain developing lupus-like symptoms due to the deletion of three lupus susceptibility loci, were injected with 2-DG to analyse its effect on B lineage cells in spleen and bone marrow in vivo. Plasma cells from spleen showed high glucose uptake, but low mitochondrial mass. Furthermore, 2-DG treatment lead to a distinct decrease in splenic plasma cell numbers both in vitro and in vivo, indicating a preference for aerobic glycolysis. However, the number of bone marrow plasma cells was not affected by 2-DG treatment. In addition, 2-DG treatment in vitro resulted in a decrease in the concentration of IgM, IgG and IgA antibodies in cell culture supernatant, while only the number of IgM+ plasma cells was decreased. Instead of a decrease in numbers, IgG+ and IgA+ plasma cells showed an increase in the amount of intracellular antibodies and UPR activity, indicating defective protein synthesis or secretion due to 2-DG. Some (but not all) of the effects of 2-DG could be prevented by adding mannose to the cell culture, an effect that could not be found when replacing 2-DG with the structurally similar glycolysis inhibitor 2-fluorodeoxyglucose (2-FDG). In conclusion, these data show that plasma cells adopt aerobic glycolysis after differentiation, a metabolic profile similar to other mTOR-dependent immune cells like Type 1 or Type 17 T helper cells (Th1, Th17) or M1 macrophages. The dependence on aerobic glycolysis makes plasma cells susceptible to treatment with glycolysis inhibitors. While the impact of 2-DG on plasma cells is in part due to its function as a glycolysis inhibitor, it also inhibits mannose metabolism, leading to defective protein folding, flawed lysosome assembly thereby eventually inducing UPR activity. Due to its specificity towards plasma cells, 2-DG has potential to become a novel therapy approach in autoimmune diseases, reducing autoantibody production by plasma cells while simultaneously increasing the expression of the anti-inflammatory cytokine interleukin 10 (IL-10) in B cells.