Core immunometabolic reprogramming of Mycobacterium tuberculosis-infected mouse lungs and stage-specific effects by glutamine supplementation
An emerging field of immunometabolism in tuberculosis (TB), an infectious disease caused by Mycobacterium tuberculosis, offers an opportunity for the development of urgently needed host-directed therapies (HDTs). Combining hypothesis-generating widely targeted metabolomics screening with transcriptome profiling in a mouse model of TB, we identify core metabolic programs and induction of signaling pathway mediated by mTORC1, the central regulator for cell metabolism, during immune cell activation. In addition to expected enhanced glycolysis and arginine biosynthesis and catabolism, induction of glutaminolysis-associated pathways, as well as serine synthesis and its catabolism by mitochondrial branch of folate cycle underscores the pivotal role of amino acids and mitochondria metabolism in orchestrating host immunity against M. tuberculosis. A further test of the hypothesis reveals that glutamine supplementation of M. tuberculosis-infected mice not only reduces lung bacillary load, but also ameliorates progression of lung pathology. Pathway analysis of transcriptomic data further unveils infection stage-specific effects of glutamine on the immunometabolic response of immune cells. Glutamine bolsters host protective immunity during the chronic phase of infection by promoting core metabolic pathways, including glycolysis, while attenuating the overall host immune response during the acute phase. Collectively, the data emphasize the central role of amino acid and mitochondrial metabolism, in concert with other signaling and metabolic pathways, including glycolysis, in meeting the demand of activating immune cells for energy, signaling molecules, and anabolic precursors. These novel observations will provide therapeutic strategies for the development of novel HDTs for TB treatment by targeting specific metabolic pathways. Overall design: To investigate the effects of glutamine supplmention on the immunometabolic response in lungs of Mtb-infected mice at different stages of the infection. C57BL/6 mice were subjected to infection with approximately 100 Colony Forming Units (CFU) of Mycobacterium tuberculosis strain H37Rv in a low-dose aerosol model of Tuberculosis. Following infection, the mice were arbitrarily assigned to one of two groups: (1) phosphate-buffered saline (PBS) or (2) glutamine supplementation. Glutamine was administered orally via gavage at a dosage of 500 mg/kg/day throughout the duration of the experiments. On days 12, 25, and 55 post-infection, both infected mice and uninfected control mice were humanely sacrificed, and their lung tissues were collected and rapidly frozen in liquid nitrogen for subsequent RNA extraction and RNA-seq analysis. Frozen lung samples were disrupted in RNAzol in a beadbeater and RNA was extracted using RNAzol® RT Column Kit (Molecular research Center, Cincinnati, OH) The library construction was performed using NEBNext® Ultra™ II Directional RNA Library Prep Kit for Illumina® (New England BioLabs Inc., Massachusetts, USA) and RNA sequencing by a NovaSeq S4 V1.5 (Illumina, California, USA).