SNAT2-mediated amino acid import maintains osmotic balance to restrain macrophage metabolic reprogramming and inflammasome activation

Macrophages undergo metabolic reprogramming during inflammatory responses to microbial infection, in part because of activation of the transcription factor HIF-1α (hypoxia-inducible factor 1α). Here, we identified regulators of HIF-1α–dependent gene expression during immune activation induced by lipopolysaccharide (LPS) and during the hypoxic response using genome-wide CRISPR screens in cultured mouse macrophages. The small neutral amino acid transporter SNAT2 (encoded by Slc38a2 ) was a key inhibitor of HIF-1α activation and metabolic reprogramming in cultured and bone marrow–derived mouse macrophages in response to LPS but not to hypoxia. Inflammatory stimulation increased SNAT2 protein abundance and dynamically expanded intracellular amino acid pools in a largely SNAT2-dependent manner. Consistent with the role of intracellular amino acids as osmolytes, SNAT2 deficiency resulted in osmotic imbalance and aberrant activation of NFAT5, a central transcriptional regulator of osmotic stress responses. In turn, NFAT5 promoted nitric oxide– and HIF-1α–dependent metabolic reprogramming and augmented NLRP3 inflammasome activation under hyperosmotic conditions. Supplementation with organic osmolytes mitigated both the excessive metabolic reprogramming and hyperosmotic inflammasome activation in SNAT2-deficient macrophages. Consistent with the heightened inflammatory phenotype in vitro, myeloid-specific deletion of SNAT2 reduced bacterial burden in mice infected with Listeria monocytogenes . Together, these findings identify SNAT2 as a negative feedback regulator that restrains macrophage metabolic reprogramming and inflammatory activation by maintaining amino acid availability that supports osmotic homeostasis.