Immune-Responsive Gene 1 (Irg1) is a mitochondrial enzyme that produces itaconate under inflammatory conditions, principally in cells of myeloid lineage. Cell culture studies suggest that itaconate ...regulates inflammation through its inhibitory effects on cytokine and reactive oxygen species production. To evaluate the functions of Irg1 in vivo, we challenged wild-type (WT) and
mice with
(
) and monitored disease progression.
, but not WT, mice succumbed rapidly to
, and mortality was associated with increased infection, inflammation, and pathology. Infection of
-Cre
,
-Cre
, and
-Cre
conditional knockout mice along with neutrophil depletion experiments revealed a role for Irg1 in
myeloid cells in preventing neutrophil-mediated immunopathology and disease. RNA sequencing analyses suggest that Irg1 and its production of itaconate temper
-induced inflammatory responses in myeloid cells at the transcriptional level. Thus, an Irg1 regulatory axis modulates inflammation to curtail
-induced lung disease.
Elevated risk of developing Alzheimer’s disease (AD) is associated with hypomorphic variants of TREM2, a surface receptor required for microglial responses to neurodegeneration, including ...proliferation, survival, clustering, and phagocytosis. How TREM2 promotes such diverse responses is unknown. Here, we find that microglia in AD patients carrying TREM2 risk variants and TREM2-deficient mice with AD-like pathology have abundant autophagic vesicles, as do TREM2-deficient macrophages under growth-factor limitation or endoplasmic reticulum (ER) stress. Combined metabolomics and RNA sequencing (RNA-seq) linked this anomalous autophagy to defective mammalian target of rapamycin (mTOR) signaling, which affects ATP levels and biosynthetic pathways. Metabolic derailment and autophagy were offset in vitro through Dectin-1, a receptor that elicits TREM2-like intracellular signals, and cyclocreatine, a creatine analog that can supply ATP. Dietary cyclocreatine tempered autophagy, restored microglial clustering around plaques, and decreased plaque-adjacent neuronal dystrophy in TREM2-deficient mice with amyloid-β pathology. Thus, TREM2 enables microglial responses during AD by sustaining cellular energetic and biosynthetic metabolism.
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•TREM2-deficient microglia undergo increased autophagy in an AD mouse model•Microglia in humans with AD-risk-associated TREM2 alleles display marked autophagy•TREM2 deficiency impairs microglial mTOR activation and metabolism•Cyclocreatine improves microglia metabolism and pathology in TREM2-deficient AD mice
The Alzheimer’s disease risk factor TREM2 regulates microglial function through modulation of cellular biosynthetic metabolism.
Macrophages undergo programmatic changes with age, leading to altered cytokine polarization and immune dysfunction, shifting these critical immune cells from protective sentinels to disease ...promoters. The molecular mechanisms underlying macrophage inflammaging are poorly understood. Using an unbiased RNA sequencing (RNA-seq) approach, we identified Mir146b as a microRNA whose expression progressively and unidirectionally declined with age in thioglycollate-elicited murine macrophages. Mir146b deficiency led to altered macrophage cytokine expression and reduced mitochondrial metabolic activity, two hallmarks of cellular aging. Single-cell RNA-seq identified patterns of altered inflammation and interferon gamma signaling in Mir146b-deficient macrophages. Identification of Mir146b as a potential regulator of macrophage aging provides novel insights into immune dysfunction associated with aging.
A central hallmark of cancer cells is the reprogramming of cellular metabolism to meet the bioenergetic and biosynthetic demands of malignant growth. Here, we report that the miR-17∼92 microRNA ...(miRNA) cluster is an oncogenic driver of tumor metabolic reprogramming. Loss of miR-17∼92 in Myc+ tumor cells leads to a global decrease in tumor cell metabolism, affecting both glycolytic and mitochondrial metabolism, whereas increased miR-17∼92 expression is sufficient to drive increased nutrient usage by tumor cells. We mapped the metabolic control element of miR-17∼92 to the miR-17 seed family, which influences cellular metabolism and mammalian target of rapamycin complex 1 (mTORC1) signaling through negative regulation of the LKB1 tumor suppressor. miR-17-dependent tuning of LKB1 levels regulates both the metabolic potential of Myc+ lymphomas and tumor growth in vivo. Our results establish metabolic reprogramming as a central function of the oncogenic miR-17∼92 miRNA cluster that drives the progression of MYC-dependent tumors.
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•miR-17∼92 is required for metabolic reprogramming of Myc+ tumor cells•miR-17/20 is the primary metabolic regulatory element of miR-17∼92•miR-17 negatively regulates the tumor suppressor LKB1•miR-17-dependent silencing of LKB1 dictates metabolic and tumorigenic potential
Cancer cells re-wire cellular metabolic pathways to help fuel the increased bioenergetic and biosynthetic demands of malignant growth. Work by Izreig et al. demonstrate that this process is controlled in lymphoma cells by the miR-17∼92 microRNA cluster, which coordinates tumor metabolism by silencing the LKB1 tumor suppressor pathway.
Pseudomonas syringae utilizes a type III secretion system (T3SS) encoded by the hrp/hrc genes to translocate virulence proteins called effectors into plant cells. To ensure that the T3SS functions at ...appropriate times during infection, hrp/hrc and effector gene expression is modulated by environmental conditions and a complex network of transcription factors. The sigma factor HrpL activates hrp/hrc and effector genes, while σ54 and enhancer binding proteins HrpR and HrpS regulate hrpL. To better understand how environmental conditions control the T3SS regulatory cascade in P. syringae pathovar tomato strain DC3000, we tested the effects of various growth media and carbon sources on expression of the hrpRS operon, hrpL, and the effector avrPto. Fructose optimally induced hrpRS expression, while most other carbon sources had only mild stimulatory effects. In contrast, hrpL and avrPto were highly induced by several sugars and organic acids, yet expression decreased as cultures reached higher cell densities. This cell density-dependent regulation was not due to alteration of the pH of the medium, although involvement of a quorum sensing signal was also not apparent. Our findings may explain conflicting results from previous studies and additionally indicate that culture conditions should be considered carefully when examining T3SS gene expression.
The impact of healthy aging on molecular programming of immune cells is poorly understood. Here, we report comprehensive characterization of healthy aging in human classical monocytes, with a focus ...on epigenomic, transcriptomic, and proteomic alterations, as well as the corresponding proteomic and metabolomic data for plasma, using healthy cohorts of 20 young and 20 older males (~27 and ~64 years old on average). For each individual, we performed eRRBS-based DNA methylation profiling, which allowed us to identify a set of age-associated differentially methylated regions (DMRs) - a novel, cell-type specific signature of aging in DNA methylome. Hypermethylation events were associated with H3K27me3 in the CpG islands near promoters of lowly-expressed genes, while hypomethylated DMRs were enriched in H3K4me1 marked regions and associated with age-related increase of expression of the corresponding genes, providing a link between DNA methylation and age-associated transcriptional changes in primary human cells.
Metabolic regulation has been recognized as a powerful principle guiding immune responses. Inflammatory macrophages undergo extensive metabolic rewiring
marked by the production of substantial ...amounts of itaconate, which has recently been described as an immunoregulatory metabolite
. Itaconate and its membrane-permeable derivative dimethyl itaconate (DI) selectively inhibit a subset of cytokines
, including IL-6 and IL-12 but not TNF. The major effects of itaconate on cellular metabolism during macrophage activation have been attributed to the inhibition of succinate dehydrogenase
, yet this inhibition alone is not sufficient to account for the pronounced immunoregulatory effects observed in the case of DI. Furthermore, the regulatory pathway responsible for such selective effects of itaconate and DI on the inflammatory program has not been defined. Here we show that itaconate and DI induce electrophilic stress, react with glutathione and subsequently induce both Nrf2 (also known as NFE2L2)-dependent and -independent responses. We find that electrophilic stress can selectively regulate secondary, but not primary, transcriptional responses to toll-like receptor stimulation via inhibition of IκBζ protein induction. The regulation of IκBζ is independent of Nrf2, and we identify ATF3 as its key mediator. The inhibitory effect is conserved across species and cell types, and the in vivo administration of DI can ameliorate IL-17-IκBζ-driven skin pathology in a mouse model of psoriasis, highlighting the therapeutic potential of this regulatory pathway. Our results demonstrate that targeting the DI-IκBζ regulatory axis could be an important new strategy for the treatment of IL-17-IκBζ-mediated autoimmune diseases.
Remodeling of the tricarboxylic acid (TCA) cycle is a metabolic adaptation accompanying inflammatory macrophage activation. During this process, endogenous metabolites can adopt regulatory roles that ...govern specific aspects of inflammatory response, as recently shown for succinate, which regulates the pro-inflammatory IL-1β-HIF-1α axis. Itaconate is one of the most highly induced metabolites in activated macrophages, yet its functional significance remains unknown. Here, we show that itaconate modulates macrophage metabolism and effector functions by inhibiting succinate dehydrogenase-mediated oxidation of succinate. Through this action, itaconate exerts anti-inflammatory effects when administered in vitro and in vivo during macrophage activation and ischemia-reperfusion injury. Using newly generated Irg1−/− mice, which lack the ability to produce itaconate, we show that endogenous itaconate regulates succinate levels and function, mitochondrial respiration, and inflammatory cytokine production during macrophage activation. These studies highlight itaconate as a major physiological regulator of the global metabolic rewiring and effector functions of inflammatory macrophages.
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•Exogenous itaconate exerts anti-inflammatory effects in vitro and in vivo•Itaconate inhibits Sdh and regulates succinate levels in LPS-activated macrophages•Itaconate controls mitochondrial respiration changes in inflammatory macrophages•Itaconate limits IL-1β, IL-18, IL-6, IL-12, NO, and HIF-1α, but not TNF-α, production
Macrophage activation is accompanied by TCA cycle remodeling, resulting in endogenous metabolites moonlighting as regulatory mediators of the inflammatory response. Lampropoulou et al. investigate the role of itaconate, one of the most highly induced metabolites in activated macrophages, and show that itaconate regulates succinate levels, mitochondrial respiration, and cytokine production.
Macrophage polarization involves a coordinated metabolic and transcriptional rewiring that is only partially understood. By using an integrated high-throughput transcriptional-metabolic profiling and ...analysis pipeline, we characterized systemic changes during murine macrophage M1 and M2 polarization. M2 polarization was found to activate glutamine catabolism and UDP-GlcNAc-associated modules. Correspondingly, glutamine deprivation or inhibition of N-glycosylation decreased M2 polarization and production of chemokine CCL22. In M1 macrophages, we identified a metabolic break at Idh, the enzyme that converts isocitrate to alpha-ketoglutarate, providing mechanistic explanation for TCA cycle fragmentation. 13C-tracer studies suggested the presence of an active variant of the aspartate-arginosuccinate shunt that compensated for this break. Consistently, inhibition of aspartate-aminotransferase, a key enzyme of the shunt, inhibited nitric oxide and interleukin-6 production in M1 macrophages, while promoting mitochondrial respiration. This systems approach provides a highly integrated picture of the physiological modules supporting macrophage polarization, identifying potential pharmacologic control points for both macrophage phenotypes.
•Glutamine deprivation affects M2 polarization but not M1 polarization•UDP-GlcNAc biosynthesis and N-glycosylation are important for M2 polarization•There is no reverse or direct flow through Idh or malic enzyme in M1 macrophages•Aspartate-arginosuccinate shunt connects the NO and TCA cycles in M1 polarization
Polarization of macrophages involves a metabolic and transcriptional rewiring that is only partially understood. Artyomov and colleagues used an integrated high-throughput transcriptional-metabolic profiling and analysis pipeline to identify metabolic modules that support macrophage polarization and function.
Cancer cells adapt metabolically to proliferate under nutrient limitation. Here we used combined transcriptional-metabolomic network analysis to identify metabolic pathways that support ...glucose-independent tumor cell proliferation. We found that glucose deprivation stimulated re-wiring of the tricarboxylic acid (TCA) cycle and early steps of gluconeogenesis to promote glucose-independent cell proliferation. Glucose limitation promoted the production of phosphoenolpyruvate (PEP) from glutamine via the activity of mitochondrial PEP-carboxykinase (PCK2). Under these conditions, glutamine-derived PEP was used to fuel biosynthetic pathways normally sustained by glucose, including serine and purine biosynthesis. PCK2 expression was required to maintain tumor cell proliferation under limited-glucose conditions in vitro and tumor growth in vivo. Elevated PCK2 expression is observed in several human tumor types and enriched in tumor tissue from non-small-cell lung cancer (NSCLC) patients. Our results define a role for PCK2 in cancer cell metabolic reprogramming that promotes glucose-independent cell growth and metabolic stress resistance in human tumors.
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•Tumor cell metabolic flexibility enables glucose-independent cell proliferation•PCK2 helps generate glycolytic intermediates under low-glucose conditions•PCK2 expression is regulated by glucose and required for in vivo tumor growth•PCK2 expression is elevated in non-small-cell lung carcinoma (NSCLC)
Cancer cells adapt metabolically to maintain proliferation under nutrient limitation. Vincent et al. demonstrate that cancer cells can engage the early steps of gluconeogenesis—a process regulated by mitochondrial PEPCK (PCK2)—to generate biosynthetic intermediates required for tumor cell proliferation.
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