Targeting the ACOD1-itaconate axis stabilizes atherosclerotic plaques.

Inflammatory macrophages are key drivers of atherosclerosis that can induce rupture-prone vulnerable plaques. Skewing the plaque macrophage population towards a more protective phenotype and reducing the occurrence of clinical events is thought to be a promising method of treating atherosclerotic patients. In the current study, we investigate the immunomodulatory properties of itaconate, an immunometabolite derived from the TCA cycle intermediate cis-aconitate and synthesised by the enzyme Aconitate Decarboxylase 1 (ACOD1, also known as IRG1), in the context of atherosclerosis. Ldlr-/- atherogenic mice transplanted with Acod1-/- bone marrow displayed a more stable plaque phenotype with smaller necrotic cores and showed increased recruitment of monocytes to the vessel intima. Macrophages from Acod1-/- mice contained more lipids whilst also displaying reduced induction of apoptosis. Using multi-omics approaches, we identify a metabolic shift towards purine metabolism, in addition to an altered glycolytic flux towards production of glycerol for triglyceride synthesis. Overall, our data highlight the potential of therapeutically blocking ACOD1 with the aim of stabilizing atherosclerotic plaques.

Adenine is an anti-inflammatory metabolite found to be more abundant in M-CSF over GM-CSF-differentiated human macrophages.

Immunometabolism has been unveiled in the last decade to play a major role in controlling macrophage metabolism and inflammation. There has been a constant effort to understand the immunomodulating properties of regulated metabolites during inflammation with the aim of controlling and re-wiring aberrant macrophages in inflammatory diseases. M-CSF and GM-CSF-differentiated macrophages play a key role in mounting successful innate immune responses. When a resolution phase is not achieved however, GM-CSF macrophages contribute substantially more towards an adverse inflammatory milieu than M-CSF macrophages, consequently driving disease progression. Whether there are specific immunometabolites that determine the homoeostatic or inflammatory nature of M-CSF and GM-CSF-differentiated macrophages is still unknown. As such, we performed metabolomics analysis on LPS and IL-4-stimulated M-CSF and GM-CSF-differentiated human macrophages to identify differentially accumulating metabolites. Adenine was distinguished as a metabolite significantly higher in M-CSF-differentiated macrophages after both LPS or IL-4 stimulation. Human macrophages treated with adenine before LPS stimulation showed a reduction in inflammatory gene expression, cytokine secretion and surface marker expression. Adenine caused macrophages to become more quiescent by lowering glycolysis and OXPHOS which resulted in reduced ATP production. Moreover, typical metabolite changes seen during LPS-induced macrophage metabolic reprogramming were absent in the presence of adenine. Phosphorylation of metabolic signalling proteins AMPK, p38 MAPK and AKT were not responsible for the suppressed metabolic activity of adenine-treated macrophages. Altogether, in this study we highlight the immunomodulating capacity of adenine in human macrophages and its function in driving cellular quiescence.

d-2-Hydroxyglutarate is an anti-inflammatory immunometabolite that accumulates in macrophages after TLR4 activation.

Macrophages undergo extensive metabolic rewiring upon activation which assist the cell in roles beyond energy production and synthesis of anabolic building blocks. So-called immunometabolites that accumulate upon immune activation can serve as co-factors for enzymes and can act as signaling molecules to modulate cellular processes. As such, the Krebs-cycle-associated metabolites succinate, itaconate and alpha-ketoglutarate (αKG) have emerged as key regulators of macrophage function. Here, we describe that 2-hydroxyglutarate (2HG), which is structurally similar to αKG and exists as two enantiomers, accumulates during later stages of LPS-induced inflammatory responses in mouse and human macrophages. D-2HG was the most abundant enantiomer in macrophages and its LPS-induced accumulation followed the induction of Hydroxyacid-Oxoacid Transhydrogenase (HOT). HOT interconverts αKG and gamma-hydroxybutyrate into D-2HG and succinic semialdehyde, and we here identified this enzyme as being immune-responsive and regulated during the course of macrophage activation. The buildup of D-2HG may be further explained by reduced expression of D-2HG Dehydrogenase (D2HGDH), which converts D-2HG back into αKG, and showed inverse kinetics with HOT and D-2HG levels. We tested the immunomodulatory effects of D-2HG during LPS-induced inflammatory responses by transcriptomic analyses and functional profiling of D-2HG-pre-treated macrophages in vitro and mice in vivo. Together, these data suggest a role for D-2HG in the negative feedback regulation of inflammatory signaling during late-stage LPS-responses in vitro and as a regulator of local and systemic inflammatory responses in vivo. Finally, we show that D-2HG likely exerts distinct anti-inflammatory effects, which are in part independent of αKG-dependent dioxygenase inhibition. Together, this study reveals an immunometabolic circuit resulting in the accumulation of the immunomodulatory metabolite D-2HG that can inhibit inflammatory macrophage responses.

An HLA-A*11:01-Binding Neoantigen from Mutated NPM1 as Target for TCR Gene Therapy in AML.

Acute myeloid leukemia (AML) is a hematological malignancy caused by clonal expansion of myeloid progenitor cells. Most patients with AML respond to chemotherapy, but relapses often occur and infer a very poor prognosis. Thirty to thirty-five percent of AMLs carry a four base pair insertion in the nucleophosmin 1 gene (NPM1) with a C-terminal alternative reading frame of 11 amino acids. We previously identified various neopeptides from the alternative reading frame of mutant NPM1 (dNPM1) on primary AML and isolated an HLA-A*02:01-restricted T-cell receptor (TCR) that enables human T-cells to kill AML cells upon retroviral gene transfer. Here, we isolated T-cells recognizing the dNPM1 peptide AVEEVSLRK presented in HLA-A*11:01. The TCR cloned from a T-cell clone recognizing HLA-A*11:01+ primary AML cells conferred in vitro recognition and lysis of AML upon transfer to CD8 cells, but failed to induce an anti-tumor effect in immunodeficient NSG mice engrafted with dNPM1 OCI-AML3 cells. In conclusion, our data show that AVEEVSLRK is a dNPM1 neoantigen on HLA-A*11:01+ primary AMLs. CD8 cells transduced with an HLA-A*11:01-restricted TCR for dNPM1 were reactive against AML in vitro. The absence of reactivity in a preclinical mouse model requires further preclinical testing to predict the potential efficacy of this TCR in clinical development.

Myeloid-Specific Acly Deletion Alters Macrophage Phenotype In Vitro and In Vivo without Affecting Tumor Growth.

Cancer cells rely on ATP-citrate lyase (Acly)-derived acetyl-CoA for lipid biogenesis and proliferation, marking Acly as a promising therapeutic target. However, inhibitors may have side effects on tumor-associated macrophages (TAMs). TAMs are innate immune cells abundant in the tumor microenvironment (TME) and play central roles in tumorigenesis, progression and therapy response. Since macrophage Acly deletion was previously shown to elicit macrophages with increased pro- and decreased anti-inflammatory responses in vitro, we hypothesized that Acly targeting may elicit anti-tumor responses in macrophages, whilst inhibiting cancer cell proliferation. Here, we used a myeloid-specific knockout model to validate that absence of Acly decreases IL-4-induced macrophage activation. Using two distinct tumor models, we demonstrate that Acly deletion slightly alters tumor immune composition and TAM phenotype in a tumor type-dependent manner without affecting tumor growth. Together, our results indicate that targeting Acly in macrophages does not have detrimental effects on myeloid cells.

Myeloid ATP Citrate Lyase Regulates Macrophage Inflammatory Responses In Vitro Without Altering Inflammatory Disease Outcomes.

Macrophages are highly plastic, key regulators of inflammation. Deregulation of macrophage activation can lead to excessive inflammation as seen in inflammatory disorders like atherosclerosis, obesity, multiple sclerosis and sepsis. Targeting intracellular metabolism is considered as an approach to reshape deranged macrophage activation and to dampen the progression of inflammatory disorders. ATP citrate lyase (Acly) is a key metabolic enzyme and an important regulator of macrophage activation. Using a macrophage-specific Acly-deficient mouse model, we investigated the role of Acly in macrophages during acute and chronic inflammatory disorders. First, we performed RNA sequencing to demonstrate that Acly-deficient macrophages showed hyperinflammatory gene signatures in response to acute LPS stimulation in vitro. Next, we assessed endotoxin-induced peritonitis in myeloid-specific Acly-deficient mice and show that, apart from increased splenic Il6 expression, systemic and local inflammation were not affected by Acly deficiency. Also during obesity, both chronic low-grade inflammation and whole-body metabolic homeostasis remained largely unaltered in mice with Acly-deficient myeloid cells. Lastly, we show that macrophage-specific Acly deletion did not affect the severity of experimental autoimmune encephalomyelitis (EAE), an experimental model of multiple sclerosis. These results indicate that, despite increasing inflammatory responses in vitro, macrophage Acly deficiency does not worsen acute and chronic inflammatory responses in vivo. Collectively, our results indicate that caution is warranted in prospective long-term treatments of inflammatory disorders with macrophage-specific Acly inhibitors. Together with our earlier observation that myeloid Acly deletion stabilizes atherosclerotic lesions, our findings highlight that therapeutic targeting of macrophage Acly can be beneficial in some, but not all, inflammatory disorders.

Succinate Is an Inflammation-Induced Immunoregulatory Metabolite in Macrophages.

Immunometabolism revealed the crucial role of cellular metabolism in controlling immune cell phenotype and functions. Macrophages, key immune cells that support progression of numerous inflammatory diseases, have been well described as undergoing vast metabolic rewiring upon activation. The immunometabolite succinate particularly gained a lot of attention and emerged as a crucial regulator of macrophage responses and inflammation. Succinate was originally described as a metabolite that supports inflammation via distinct routes. Recently, studies have indicated that succinate and its receptor SUCNR1 can suppress immune responses as well. These apparent contradictory effects might be due to specific experimental settings and particularly the use of distinct succinate forms. We therefore compared the phenotypic and functional effects of distinct succinate forms and receptor mouse models that were previously used for studying succinate immunomodulation. Here, we show that succinate can suppress secretion of inflammatory mediators IL-6, tumor necrosis factor (TNF) and nitric oxide (NO), as well as inhibit Il1b mRNA expression of inflammatory macrophages in a SUCNR1-independent manner. We also observed that macrophage SUCNR1 deficiency led to an enhanced inflammatory response without addition of exogenous succinate. While our study does not reveal new mechanistic insights into how succinate elicits different inflammatory responses, it does indicate that the inflammatory effects of succinate and its receptor SUCNR1 in macrophages are clearly context dependent.

Let's Enter the Wonderful World of Immunometabolites.

Over the past decade, cancer metabolism research taught us that metabolites are much more than intermediate or end products of metabolism. As such, the name 'oncometabolite' emerged. Immunometabolism research has developed tremendously over the past few years and, in analogy to the cancer metabolism field, the term 'immunometabolite' has been used for different metabolites and purposes. Here, we propose a definition for the term 'immunometabolite' and provide some historical background and future perspectives on this matter. By doing so, we aim to increase interest in this fast-expanding field and to encourage further research.