Cited by 526Immune cells in cancerImmune responses and vaccinationsMicrobial metabolism and enzyme function

The DOI matches its Crossref record; 52 of the 52 references it cites were found in a registry or an index; none of the 41 sources its claims cite is checked for support yet.

Immunoresponsive Gene 1 and Itaconate Inhibit Succinate Dehydrogenase to Modulate Intracellular Succinate Levels

Open access

Abstract

Metabolic reprogramming is emerging as a hallmark of the innate immune response, and the dynamic control of metabolites such as succinate serves to facilitate the execution of inflammatory responses in macrophages and other immune cells. Immunoresponsive gene 1 (Irg1) expression is induced by inflammatory stimuli, and its enzyme product cis-aconitate decarboxylase catalyzes the production of itaconate from the tricarboxylic acid cycle. Here we identify an immunometabolic regulatory pathway that links Irg1 and itaconate production to the succinate accumulation that occurs in the context of innate immune responses. Itaconate levels and Irg1 expression correlate strongly with succinate during LPS exposure in macrophages and non-immune cells. We demonstrate that itaconate acts as an endogenous succinate dehydrogenase inhibitor to cause succinate accumulation. Loss of itaconate production in activated macrophages from Irg1(-/-) mice decreases the accumulation of succinate in response to LPS exposure. This metabolic network links the innate immune response and tricarboxylic acid metabolism to function of the electron transport chain.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

This paper identifies an immunometabolic pathway in which Irg1/CAD-derived itaconate inhibits succinate dehydrogenase (SDH), causing succinate accumulation during LPS exposure. Loss of Irg1 in macrophages reduces itaconate and succinate, linking innate immune metabolism to TCA cycle and electron transport chain function.

Key findings

  • In LPS-activated RAW 264.7 macrophages, itaconate and succinate levels showed similar trends over 6 h, unlike citrate, α-ketoglutarate, fumarate, and malate; basal oxygen consumption rate remained unchanged.
  • Exogenous itaconate (0–25 mM, 6 h) increased intracellular itaconate dose-dependently and correlated strongly with succinate in resting and LPS-activated RAW 264.7 macrophages (r = 0.99) and in A549 cells (r = 0.99), while other TCA intermediates correlated poorly or negatively.
  • Itaconate was not metabolized to succinate: [1-13C]glutamine labeling produced ~65% M1 itaconate but no succinate labeling, and prelabeling with [U-13C6]glucose/[U-13C5]glutamine left succinate labeling ~90% after unlabeled itaconate.
  • Itaconate inhibited SDH/complex II: dose-dependent OCR inhibition in permeabilized RAW 264.7 macrophages and BMDMs with succinate, >75% reduction with 10 mM itaconate plus succinate/rotenone, and no effect on complex I or IV substrates; Irg1 KO BMDMs failed to produce itaconate and had significantly lower succinate than WT after LPS, while Irg1 overexpression in A549 cells increased succinate.

Methods

  • Cell models and treatments: RAW 264.7 macrophages, A549 lung adenocarcinoma cells, and primary BMDMs from C57BL/6J and Irg1 KO mice; LPS at 10 ng/ml; itaconate at 5, 10, and 25 mM for 6 h; A549 cells transfected with pCMV6-Irg1 or empty vector.
  • Metabolite and isotope analysis: GC-MS quantification of itaconate and TCA intermediates using external standard curves; isotopic labeling with [1-13C]glutamine, [U-13C6]glucose, and [U-13C5]glutamine; mass isotopomer distributions corrected for natural abundance.
  • Respiration and statistics: Seahorse XF96 oxygen consumption measurements in intact and permeabilized cells (perfringolysin O) with succinate/rotenone, glutamate/malate, pyruvate/malate, or ascorbate/TMPD/antimycin A; Pearson correlation and two-tailed Student’s t tests.

Limitations

  • Stated: The authors note variability in succinate accumulation between RAW 264.7 macrophages and BMDMs, likely due to cell, medium, and LPS variability; they also state that the physiological role of itaconate and Irg1 requires further investigation, particularly in macrophage development and differentiation.
  • Stated: It is not known whether downstream inflammatory responses are mediated directly by succinate or itaconate or through other mechanisms; no mammalian mitochondrial or plasma membrane itaconate transporters have been described, and other succinate-producing pathways (GABA shunt, glutaminolysis) could compensate.
  • Evident from the text: Most mechanistic experiments use cultured cells and exogenous itaconate up to 25 mM, whereas endogenous macrophage itaconate is cited as up to 8 mM; no in vivo inflammation or disease model is presented.

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Integrity signals

Registry

Crossref · 10.1074/jbc.m115.685792

Cites

52 of 52 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Verification

Claims the paper makes

0 of 41 cited sources checked · 0 supported · 0 flagged

Show all 57 claims

  • It may state two separate claims as one. 10
  • Probably not a substantial claim. 13
19 of 19
  • The paper relies on this without support.

    The specific driver(s) of succinate accumulation in inflammatory macrophages have not yet been identified.

    “However, the specific driver(s) of this phenomenon has/have not yet been identified.”
  • The paper relies on this without support.

    A potential role of endogenously produced itaconate in succinate accumulation under inflammatory conditions has not yet been addressed and is unknown.

    “a potential role of endogenously produced itaconate in succinate accumulation under inflammatory conditions has not yet been addressed and is unknown.”
  • The paper relies on this without support.

    The Irg1 KO mouse model specifically abolishes itaconate production without other metabolic adaptations that affect succinate levels.

    “Notably, succinate concentrations in stimulated BMDMs from Irg1 KO mice were significantly lower than those quantified in BMDMs from WT mice, suggesting that CAD-derived itaconate influences succinate accumulation in LPS-induced macrophages (Fig. 6c).”
  • The paper relies on this without support.

    The effects of exogenous itaconate on succinate accumulation reflect the physiological role of endogenous itaconate.

    “In the cells studied, exogenous and endogenous, CAD-produced itaconate strongly correlated with succinate accumulation.”
  • The paper relies on this without support.

    The cell models used are representative of macrophages in vivo for conclusions about immune cell metabolism.

    “However, we consistently observed increased succinate downstream of itaconate production or administration in a variety of cell types.”
5 of 5

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Inconsistent itaconate concentrations for respiration assays

    Minor

    The methods list four itaconate concentrations for the permeabilized-cell respiration assay, but the Figure 5 caption lists five, including 2.5 mM.

  • Opposite claims about succinate's effect on HIF-1α signaling

    Minor

    The discussion says succinate inhibits HIF-1α signaling, whereas the earlier account says succinate stabilizes HIF-1α and enhances its downstream effect.

2 of 2

Citations

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Metadata

Authors
Cordes, T., Wallace, M., Michelucci, A., Divakaruni, A. S., Sapcariu, S. C., Sousa, C., Koseki, H., Cabrales, P., Murphy, A. N., Hiller, K., & Metallo, C. M.
Affiliations
  • University of California San Diego (US)
  • University of Luxembourg (LU)
  • RIKEN Center for Integrative Medical Sciences (JP)
Corresponding author
Metallo, Christian M.
Venue
Journal of Biological Chemistry
Publisher
Elsevier BV
Published
2016-07
Volume
291
Issue
27
Pages
14274-14284
ISSN
0021-9258 (ISSN-L)
OpenAlex
W2361586644
Cited by
526
References
52
Citations by year
2026: 55 · 2025: 60 · 2024: 68 · 2023: 55 · 2022: 58 · 2021: 69 · 2020: 64 · 2019: 42 · 2018: 27 · 2017: 23 · 2016: 5
FWCI
19.57
Type
journal article
Language
en
Open access
Locations
  • Journal of Biological Chemistry (publishedVersion, cc-by)
  • PubMed Central (publishedVersion)
  • PubMed (publishedVersion)
  • eScholarship (California Digital Library) (submittedVersion)
  • Open Repository and Bibliography (University of Luxembourg) (submittedVersion, cc-by-nc-sa)
Funders
  • National Institutes of Health (R01CA188652, P01DK054441)
  • National Institute of Allergy and Infectious Diseases (R01AI082610)
  • National Heart, Lung, and Blood Institute (R53HL123015, P01HL110900, R01HL052684)
Topics
  • Life Sciences › Immunology and Microbiology › Immunology › Immune cells in cancer
  • Life Sciences › Immunology and Microbiology › Immunology › Immune responses and vaccinations
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Microbial metabolism and enzyme function
Keywords
IRG1, itaconate, succinate accumulation, succinate dehydrogenase inhibition, cis-aconitate decarboxylase, TCA cycle, metabolic reprogramming, innate immunity, macrophages, lipopolysaccharide, electron transport chain, immunometabolism
MeSH terms
Animals, Cell Line, Hydro-Lyases, Lipopolysaccharides, Macrophages, Succinate Dehydrogenase, Succinates, Succinic Acid, Mice

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