Itaconate Inhibits TET DNA Dioxygenases to Dampen Inflammatory Responses

Abstract The immune-response gene 1 (IRG1) plays a key role in anti-pathogen defense, as deletion of Irg1 in mice causes severe defects in response to bacterial and viral infection, and decreased survival 1, 2 . IRG1 transcription is rapidly induced by pathogen infection and inflammatory conditions primarily in cells of myeloid lineage 3 . IRG1 encodes a mitochondrial metabolic enzyme, aconitate decarboxylase 1 (ACOD1), that catalyzes the decarboxylation of cis-aconitate to produce the anti-inflammatory metabolite itaconic acid (ITA) 4 . Several molecular processes are affected by ITA, including succinate dehydrogenase (SDH) inhibition 5 , resulting in succinate accumulation and metabolic reprogramming 6, 7 , and alkylation of protein cysteine residues, inducing the electrophilic stress response mediated by NRF2 and IκBζ 8, 9 and impairing aerobic glycolysis 10 . However, the mechanisms by which ITA exerts its profound anti-inflammatory effect still remains to be fully elucidated. Here, we show that ITA is a potent inhibitor of the TET family DNA dioxygenases, which catalyze the conversion of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC) during the process of active DNA demethylation. ITA binds to the same site of α-ketoglutarate (α-KG) in TET2, inhibiting its catalytic activity. Lipopolysaccharides (LPS) treatment, which induces Irg1 expression and ITA accumulation, inhibits Tet activity in macrophages. Transcriptome analysis reveals TET2 is a major target of ITA in suppressing LPS-induced genes, including those regulated by NF-κB and STAT signaling pathways. In vivo, ITA decreases 5hmC, reduces LPS-induced acute pulmonary edema and lung and liver injury, and protects mice against lethal endotoxaemia in a manner that is dependent on the catalytic activity of Tet2. Our study thus identifies ITA as an immune modulatory metabolite that selectively inhibits TET enzymes to dampen the inflammatory response.