Methionine metabolism shapes immune response against Mycobacterium tuberculosis

Limited reports have elucidated the role of one-carbon metabolism and its impact on the production of pro-inflammatory cytokines in tuberculosis (TB). In this study, analysis of the earlier reported scRNAseq data of alveolar macrophages (AMs) from the Mycobacterium tuberculosis (Mtb) H37Rv-infected C57BL/6 mice showed downregulation of phosphoglycerate dehydrogenase (PHGDH) and neutral amino acid transporter, i.e. Slc7a5. PHGDH is involved in the serine biosynthesis from the glycolytic node, and its downregulation in the AMs indicates that extracellular methionine mainly contributes carbon units for one-carbon metabolism. But lower expression of Slc7a5 reflects lower methionine uptake in macrophages in the Mtb-infected group. Global metabolome analysis of the Mtb-infected bone marrow-derived macrophages (BMDMs) showed a major biochemical shift at 24 hours post-infection (hpi) with perturbation of various nodes connected to the one-carbon metabolism, including serine-methionine metabolism and polyamine synthesis. A significantly low intracellular serine, methionine and polyamine levels with a high adenine, hypoxanthine, guanine and reduced-glutathione (GSH) levels indicated that the flux from one-carbon metabolism is diverted towards nucleotide salvage and glutathione production at 24 hpi in the Mtb-infected BMDMs. Proteome profiling of these Mtb-infected BMDMs indicated increased nucleotide salvage, glutathione production and a suppressed IL-1 response. This rewiring of the metabolic pathways suppressed the immune response and dampened the mycobacterial clearance. Further, methionine (1 mM) supplemented BMDMs upon Mtb infection showed improved cell viability with accelerated mycobacterial clearance by producing significantly higher IL-1β levels. Methionine supplementation, to C57BL/6 mice, in drinking water for two weeks, helped in enhancing mycobacterial clearance in lungs, spleen and BMDMs by increasing pro-inflammatory response, especially by increasing IL-1β and IFN-γ production. Supplementation of methionine also increased Mtb-specific TNF-α-producing activated CD4+ cells in the spleen. So, methionine supplementation in macrophages and mice helped in mounting a better acute pro-inflammatory response, which could be used as a dietary supplementation strategy to improve clinical outcomes in TB.