Glutamine alleviates immunosuppression in polymicrobial sepsis by augmenting bacterial phagocytosis through sustaining the GFAT-DRP1 dependent mitochondrial calcium dynamics

Sepsis triggers impaired macrophage bacterial phagocytosis, rendering the host more vulnerable to secondary infections, a manifestation termed sepsis-associated immunosuppression. Glutamine is a vital nutrient in critical illness that not only supports energy production and biomass synthesis but also potentially exerts immunomodulatory effects. The aim of this study was to investigate whether supplementation of glutamine modulates macrophage phagocytosis and mitigates sepsis-induced immunosuppression. Using a murine model of polymicrobial sepsis, we evaluated the effects of glutamine supplementation on bacterial load, cytokine production, and survival. In multiple in vitro assays, we employed molecular and pharmacological approaches to dissect glutamine-dependent signaling pathways in recovering the immunosuppressive macrophages. We found that glutamine deficiency impaired macrophage phagocytosis and exacerbated sepsis-induced immunosuppression. In contrast, exogenous glutamine supplementation restored macrophage function and improved survival in septic mice—effects that were abolished upon macrophage depletion. Mechanistically, glutamine promoted glutamine-fructose-6-phosphate transaminase (GFAT)-dependent protein O-GlcNAcylation, leading to dynamin-related protein 1 (DRP1) oligomerization. Concurrently, glutamine activated a GFAT-mediated, CDK1-dependent pathway that induced DRP1 phosphorylation at Ser616 irrelevant of O-GlcNAcylation. These effects enhanced DRP1-mediated mitochondrial fission, increased mitochondrial calcium efflux, and sustained cytosolic calcium levels essential for phagocytosis. In conclusion, our study demonstrates that glutamine strengthens macrophage phagocytosis and alleviates immunosuppression in sepsis through a dual GFAT-DRP1 mechanism coordinating mitochondrial dynamics and calcium signaling, highlighting the GFAT–DRP1–calcium axis as a potential therapeutic target for treating sepsis-induced immunosuppression.