Glutamine is required for M1-like polarization in response to Mycobacterium tuberculosis infection

In response to Mycobacterium tuberculosis infection, macrophages mount early proinflammatory and antimicrobial responses similar to those observed in M1 macrophages classically activated by LPS and IFN-γ. A metabolic reprogramming to HIF-1-mediated uptake of glucose and its metabolism by glycolysis is required for M1-like polarization, but little is known about other metabolic programs driving M1-like polarization during M. tuberculosis infection. Identification and quantification of labeling patterns of U 13 C glutamine and U 13 C glucose-derived metabolites demonstrated that glutamine, rather than glucose, is catabolized in both the oxidative and reductive TCA cycle of M1-like macrophages, thereby generating signaling molecules that include succinate, biosynthetic precursors such as aspartate, and the antimicrobial metabolite itaconate. This conclusion is corroborated by diminished M1 polarization via chemical inhibition of glutaminase (GLS), the key enzyme of the glutaminolysis pathway, and by genetic deletion of GLS in infected macrophages. Furthermore, characterization of the labeling distribution pattern of U 15 N glutamine in M1-like macrophages indicates that glutamine serves as a nitrogen source for the synthesis of intermediates of purine and pyrimidine metabolism plus amino acids including aspartate. Thus, the catabolism of glutamine, as an integral component of metabolic reprogramming in activating macrophages, fulfills the cellular demand for bioenergetic and biosynthetic precursors of M1-like macrophages. Knowledge of these new immunometabolic features of M1-like macrophages is expected to advance the development of host-directed therapies that will enhance bacterial clearance and prevent immunopathology during tuberculosis.