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The endogenous metabolite itaconate has recently emerged as a regulator of macrophage function, but its precise mechanism of action remains poorly understood1-3. Here we show that itaconate is required for the activation of the anti-inflammatory transcription factor Nrf2 (also known as NFE2L2) by lipopolysaccharide in mouse and human macrophages. We find that itaconate directly modifies proteins via alkylation of cysteine residues. Itaconate alkylates cysteine residues 151, 257, 288, 273 and 297 on the protein KEAP1, enabling Nrf2 to increase the expression of downstream genes with anti-oxidant and anti-inflammatory capacities. The activation of Nrf2 is required for the anti-inflammatory action of itaconate. We describe the use of a new cell-permeable itaconate derivative, 4-octyl itaconate, which is protective against lipopolysaccharide-induced lethality in vivo and decreases cytokine production. We show that type I interferons boost the expression of Irgi (also known as Acodl) and itaconate production. Furthermore, we find that itaconate production limits the type I interferon response, indicating a negative feedback loop that involves interferons and itaconate. Our findings demonstrate that itaconate is a crucial anti-inflammatory metabolite that acts via Nrf2 to limit inflammation and modulate type I interferons.
Macrophages have a key role in innate immunity. They respond rapidly to pathogens and subsequently promote an anti-inflammatory phenotype to limit damage and promote tissue repair. The factors driving these changes are incompletely understood. Itaconate, a metabolite synthesized by the enzyme encoded by Irgi1, is increased in lipopolysaccharide (LPS)-activated macrophages2 and has been suggested to limit inflammation by inhibiting succinate dehydrogenase (SDH), a crucial pro-inflammatory regulator4; however, the details remain unclear.
Itaconate was the most abundant metabolite in LPS-treated human macrophages (Fig. 1a) and reached 5 mM in mouse bone marrowderived macrophages (BMDMs) after LPS stimulation (Fig. 1b, c). Itaconate can disrupt SDH activity, but is less potent than the classic SDH inhibitor malonate (Extended Data Fig. 1), suggesting that it may exert its anti-inflammatory effects via additional mechanisms.
Itaconate contains an electrophilic a,ß-unsaturated carboxylic acid that could potentially alkylate protein cysteine residues by a Michael addition to form a 2,3-dicarboxypropyl adduct. An attractive candidate protein that undergoes cysteine alkylation is KEAP1, a central player in the anti-oxidant response (Fig. 1d). KEAP1 normally associates with and promotes the degradation of Nrf2, but alkylation of crucial KEAP1 cysteine...