title: GCN2-dependent metabolic stress is essential for endotoxemic cytokine induction and pathology.
abstract: Activated inflammatory macrophages can express indoleamine 2,3-dioxygenase (IDO) and thus actively deplete their own tryptophan supply; however, it is not clear how amino acid depletion influences macrophage behavior in inflammatory environments. In this report, we demonstrate that the stress response kinase GCN2 promotes macrophage inflammation and mortality in a mouse model of septicemia. In vitro, enzymatic amino acid consumption enhanced sensitivity of macrophages to the Toll-like receptor 4 (TLR4) ligand lipopolysaccharide (LPS) with significantly increased interleukin 6 (IL-6) production. Tryptophan withdrawal induced the stress response proteins ATF4 and CHOP/GADD153; however, LPS stimulation rapidly enhanced expression of both proteins. Moreover, LPS-driven cytokine production under amino acid-deficient conditions was dependent on GCN2, as GCN2 knockout (GCN2KO) macrophages had a significant reduction of cytokine gene expression after LPS stimulation. To test the in vivo relevance of these findings, monocytic-lineage-specific GCN2KO mice were challenged with a lethal dose of LPS intraperitoneally (i.p.). The GCN2KO mice showed reduced inflammatory responses, with decreased IL-6 and IL-12 expression correlating with significant reduction in animal mortality. Thus, the data show that amino acid depletion stress signals (via GCN2) synergize with proinflammatory signals to potently increase innate immune responsiveness.
authors.affiliation: Cancer Immunology, Inflammation, and Tolerance Program, GRU Cancer Center, Medical College of Georgia, Georgia Regents University, Augusta, Georgia, USA.
authors.forename: Haiyun
authors.initials: H
authors.lastname: Liu
authors.forename: Lei
authors.initials: L
authors.lastname: Huang
authors.forename: Jillian
authors.initials: J
authors.lastname: Bradley
authors.forename: Kebin
authors.initials: K
authors.lastname: Liu
authors.forename: Kankana
authors.initials: K
authors.lastname: Bardhan
authors.forename: David
authors.initials: D
authors.lastname: Ron
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Mellor
authors.forename: David H
authors.initials: DH
authors.lastname: Munn
authors.forename: Tracy L
authors.initials: TL
authors.lastname: McGaha
mesh_terms: D051701:Activating Transcription Factor 4 / Q000235:genetics / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D016207:Cytokines / Q000235:genetics / Q000378:metabolism*; D019446:Endotoxemia / Q000235:genetics / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase / Q000235:genetics / Q000378:metabolism; D018836:Inflammation Mediators / Q000378:metabolism; D018664:Interleukin-12 / Q000378:metabolism; D015850:Interleukin-6 / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics; D013312:Stress, Physiological; D016019:Survival Analysis; D051197:Toll-Like Receptor 4 / Q000819:agonists / Q000378:metabolism; D051742:Transcription Factor CHOP / Q000235:genetics / Q000378:metabolism; D014364:Tryptophan / Q000378:metabolism
chemical_list: C081452:Atf4 protein, mouse; D016207:Cytokines; C497250:Ddit3 protein, mouse; C583637:IDO1 protein, mouse; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase; D018836:Inflammation Mediators; D015850:Interleukin-6; D008070:Lipopolysaccharides; D051197:Toll-Like Receptor 4; D051701:Activating Transcription Factor 4; D051742:Transcription Factor CHOP; D018664:Interleukin-12; D014364:Tryptophan; C070634:Eif2ak4 protein, mouse; D017346:Protein Serine-Threonine Kinases