Immune-responsive gene 1 protein links metabolism to immunity by catalyzing itaconic acid production

Metabolic Regulation of Inflammation: Exploring the Potential Benefits of Itaconate in Autoimmune Disorders

Itaconic acid and its metabolites have demonstrated significant therapeutic potential in various immune diseases. Originating from the tricarboxylic acid cycle in immune cells, itaconic acid can modulate immune responses, diminish inflammation, and combat oxidative stress. Recent research has uncovered multiple mechanisms through which itaconic acid exerts its effects, including the inhibition of inflammatory cytokine production, activation of anti-inflammatory pathways, and modulation of immune cell function by regulating cellular metabolism. Cellular actions are influenced by the modulation of metabolic pathways, such as inhibiting succinate dehydrogenase (SDH) activity or glycolysis, activation of nuclear-factor-E2-related factor 2 (Nrf2), boosting cellular defences against oxidative stress, and suppression of immune cell inflammation through the NF-κB pathway. This comprehensive review discusses the initiation, progression, and mechanisms of action of itaconic acid and its metabolites, highlighting their modulatory effects on various immune cell types. Additionally, it examines their involvement in immune disease like rheumatoid arthritis, multiple sclerosis, type 1 diabetes mellitus, and autoimmune hepatitis, offering greater understanding for creating new therapies for these ailments.

The cell autonomous and non-autonomous roles of itaconate in immune response

Itaconate which is discovered as a mammalian metabolite possessing antimicrobial and immunoregulatory activity has attracted much attention in the field of immunometabolism. Itaconate is synthesized by myeloid cells under conditions of pathogen infection and sterile inflammation. In addition to regulating immune response of myeloid cells, itaconate secreted from myeloid cells can also be taken up by non-myeloid cells to exert immunoregulatory effects in a cell non-autonomous manner. In this review, we recap the discovery of itaconate as a distinct immunologic regulator and effector, describe the development of itaconate biosensor, and detail the recent findings that decipher the mechanism underlying intercellular transport of itaconate. Based on these knowledges, we propose itaconate is a messenger transmitting immunologic signals from myeloid cells to other types of cells during host inflammation and immune defense.

Nonenzymatic lysine D-lactylation induced by glyoxalase II substrate SLG dampens inflammatory immune responses

Immunometabolism is critical in the regulation of immunity and inflammation; however, the mechanism of preventing aberrant activation-induced immunopathology remains largely unclear. Here, we report that glyoxalase II (GLO2) in the glycolysis branching pathway is specifically downregulated by NF-κB signaling during innate immune activation via tristetraprolin (TTP)-mediated mRNA decay. As a result, its substrate S-D-lactoylglutathione (SLG) accumulates in the cytosol and directly induces D-lactyllysine modification of proteins. This nonenzymatic lactylation by SLG is greatly facilitated by a nearby cysteine residue, as it initially reacts with SLG to form a reversible S-lactylated thiol intermediate, followed by SN-transfer of the lactyl moiety to a proximal lysine. Lactylome profiling identifies 2255 lactylation sites mostly in cytosolic proteins of activated macrophages, and global protein structure analysis suggests that proximity to a cysteine residue determines the susceptibility of lysine to SLG-mediated D-lactylation. Furthermore, lactylation is preferentially enriched in proteins involved in immune activation and inflammatory pathways, and D-lactylation at lysine 310 (K310) of RelA attenuates inflammatory signaling and NF-κB transcriptional activity to restore immune homeostasis. Accordingly, TTP-binding site mutation or overexpression of GLO2 in vivo blocks this feedback lactylation in innate immune cells and promotes inflammation, whereas genetic deficiency or pharmacological inhibition of GLO2 restricts immune activation and attenuates inflammatory immunopathology both in vitro and in vivo. Importantly, dysregulation of the GLO2/SLG/D-lactylation regulatory axis is closely associated with human inflammatory phenotypes. Overall, our findings uncover an immunometabolic feedback loop of SLG-induced nonenzymatic D-lactylation and implicate GLO2 as a promising target for combating clinical inflammatory disorders.

Jingfang Granule promotes the tricarboxylic acid cycle to improve chronic fatigue syndrome by increasing the expression of Idh1 and Idh2

ETHNOPHARMACOLOGICAL RELEVANCE

Chronic fatigue syndrome (CFS), as a complex, multisystemic, and multisystemic disorder affecting multiple organs and systems, often accompanies by symptoms such as post-exercise discomfort, sleep disorders, cognitive difficulties, and orthostatic intolerance. Jingfang Granule (JFG) is a traditional Chinese medicine that have significant protective effects on CFS, but the mechanism is still vague.

AIM OF STUDY

This study was designed to evaluate the protective mechanism of JFG on mice with CFS.

MATERIALS AND METHODS

The combined stimuli method was used to establish the mice CFS model, and JFG was orally administered. The body weight, exhaustion swimming training and tail suspension test were assayed every 7 days to evaluate the improvement of JFG on CFS. Lactic acid, adenosine triphosphate (ATP), malondialdehyde (MDA), superoxide dismutase (SOD), reactive oxygen species (ROS), IL-1β, TNF-α, IL-6 in serum and liver glycogen, muscle glycogen in muscle were analyzed. Transmission electron microscopy was used to detect mitochondrial morphology. The regulatory networks were investigated by proteomics and central carbon metabolomics, which were verified by Western blot.

RESULTS

JFG reversed the loss of weight and reduce of exhaust swimming time (P < 0.05) induced by CFS in mice, and increased the tail suspension time (P < 0.05), indicating that JFG has an improving effect on CFS. Meanwhile, JFG increased the spleen index (P < 0.05), decreased the thymus index (P < 0.05) and cardiac index (P < 0.05), inhibited the secretion of Lactic acid (P < 0.05), and increased the content of liver glycogen (P < 0.05), muscle glycogen (P < 0.05), and ATP (P < 0.05), and improved mitochondrial morphology in mice with CFS. JFG also inhibited the release of TNF-α (P < 0.05), IL-1β (P < 0.05) and IL-6 (P < 0.05) in serum by inhibiting TLR4/NF-κB signaling pathway and NLRP3 inflammasome signaling pathway, and inhibited oxidative stress by activating Nrf2/HO-1/NQO1 axis. Integrated central carbon metabolomics, proteomics and Western blot showed that JFG intervened in CFS by increasing the expression of Idh1 (P < 0.05) and Idh2 (P < 0.01) to promote tricarboxylic acid (TCA) cycle.

CONCLUSIONS

This study confirmed that JFG promoted the TCA cycle by increasing the expression of Idh1 and Idh2, and then inhibited inflammation and oxidative stress to prevent CFS injury, which provided a potential drug candidate for CFS treatment.

Itaconate mechanism of action and dissimilation in Mycobacterium tuberculosis

Itaconate, an abundant metabolite produced by macrophages upon interferon-γ stimulation, possesses both antibacterial and immunomodulatory properties. Despite its crucial role in immunity and antimicrobial control, its mechanism of action and dissimilation are poorly understood. Here, we demonstrate that infection of mice with Mycobacterium tuberculosis increases itaconate levels in lung tissues. We also show that exposure to itaconate inhibits M. tuberculosis growth in vitro, in macrophages, and mice. We report that exposure to sodium itaconate (ITA) interferes with the central carbon metabolism of M. tuberculosis. In addition to the inhibition of isocitrate lyase (ICL), we demonstrate that itaconate inhibits aldolase and inosine monophosphate (IMP) dehydrogenase in a concentration-dependent manner. Previous studies have shown that Rv2498c from M. tuberculosis is the bona fide (S)-citramalyl-CoA lyase, but the remaining components of the pathway remain elusive. Here, we report that Rv2503c and Rv3272 possess itaconate:succinyl-CoA transferase activity, and Rv2499c and Rv3389c possess itaconyl-CoA hydratase activity. Relative to the parental and complemented strains, the ΔRv3389c strain of M. tuberculosis was attenuated for growth in itaconate-containing medium, in macrophages, mice, and guinea pigs. The attenuated phenotype of ΔRv3389c strain of M. tuberculosis is associated with a defect in the itaconate dissimilation and propionyl-CoA detoxification pathway. This study thus reveals that multiple metabolic enzymes are targeted by itaconate in M. tuberculosis. Furthermore, we have assigned the two remaining enzymes responsible for the degradation of itaconic acid into pyruvate and acetyl-CoA. Finally, we also demonstrate the importance of enzymes involved in the itaconate dissimilation pathway for M. tuberculosis pathogenesis.

IRG1/Itaconate inhibits hepatic stellate cells ferroptosis and attenuates TAA-induced liver fibrosis by regulating SLC39A14 expression

This study aimed to elucidate the protective roles of Immune Response Gene-1 (IRG1) and exogenous itaconate in murine models of hepatic fibrosis and to delineate the underlying mechanistic pathways using both wild-type and IRG1-deficient (IRG1-/-) mice. Primary murine stellate cells (mHSC) and bone marrow-derived macrophages (BMDM) were isolated and cocultured. Hepatocellular fibrosis was induced in vitro using Transforming Growth Factor-beta (TGF-β) to evaluate the protective efficacy of IRG1/itaconate. Histopathological damage in the hepatic tissues was assessed using Hematoxylin and Eosin (H&E), Masson's trichrome, and Sirius red staining, followed by hepatic fibrosis scoring. The levels of released inflammatory cytokines were quantified using enzyme-linked immunosorbent assay (ELISA) kits. Immunohistochemistry was used to detect 4-Hydroxynonenal (4-HNE) levels and Perls staining was used to assess ferroptosis. RNA sequencing and gene enrichment analyses were performed to identify implicated molecular entities and signaling pathways. IRG1 and SLC39A14 knockdown and overexpression cell lines were generated. Quantitative real-time PCR (qRT-PCR) and western blotting (WB) were used to measure the mRNA and protein expression levels in hepatic tissues and cells. Kits were used to assess reactive oxygen species (ROS) and malondialdehyde (MDA) levels, and the concentrations of liver enzymes, iron, GSH, and GSSG within hepatic tissues and cells.4-octyl itaconate (4-OI) significantly attenuated the histopathological damage in hepatic tissues, preserved the normal hepatic function, effectively reduced the release of inflammatory cytokines, and mitigated oxidative stress markers such as ROS and MDA in Thioacetamide (TAA)-induced fibrotic mice. Notably, this study is the first to reveal the pivotal role of SLC39A14 in the pathogenesis of hepatic fibrosis in murine models and elucidate how IRG1/itaconate mediates downstream ferroptosis-related signaling pathways by targeting SLC39A14, thereby inhibiting ferroptosis-induced hepatic fibrosis. IRG1/itaconate can alleviate the TAA-induced hepatic fibrosis in mice by regulating the expression of SLC39A14, consequently suppressing hepatic stellate cell ferroptosis.

The absence of IRG1 exacerbates bone loss in a mouse model of ovariectomy-induced osteoporosis by increasing osteoclastogenesis through the potentiation of NLRP3 inflammasome activation

The immune-responsive gene 1 (IRG1) protein plays a role in various pathological processes by connecting cellular metabolism to a range of cellular activities through the production of itaconate. Recent studies have highlighted the significance of IRG1 and itaconate in bone metabolism and homeostasis. However, the precise role of IRG1 in osteoporosis remains inadequately documented. This study aimed to determine the role of IRG1 in osteoporosis through the utilization of IRG1 knockout (KO) mice and a model of ovariectomy (OVX)-induced osteoporosis. The expression of IRG1 was found to be higher in the bone tissues of postmenopausal osteoporotic mice induced by OVX in comparison to sham control mice. When compared to wild type (WT) mice, OVX-induced bone loss was significantly worse in IRG1 KO mice, and this was accompanied by an increase in osteoclastogenesis and bone resorption. However, the loss of bone and the process of osteoclastogenesis and bone resorption were effectively reversed when the IRG1 KO mice were replenished with itaconate. The osteoclastogenesis induced by receptor activator of nuclear factor kappa-Β ligand (RANKL) in bone marrow-derived macrophages (BMMs) was found to be enhanced by IRG1 deficiency, which could be reversed through the replenishment of itaconate. Further investigation revealed that IRG1 deficiency potentiated the activation of NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome. The inhibition of NLRP3 inflammasome using a targeted inhibitor significantly ameliorated RANKL-induced osteoclastogenesis in IRG1 KO BMMs. Overall, this study highlights the significance of IRG1 in regulating osteoclastogenesis and proposes it as a potential target for osteoporosis treatment.

Dihydrotanshinone I Attenuates Diet-Induced Nonalcoholic Fatty Liver Disease via Up-Regulation of IRG1

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease, but effective therapeutic drugs are still lacking. Dihydrotanshinone I (DHTS), a natural product isolated from Salvia miltiorrhiza, has been shown to have ameliorative effects on NAFLD. The aim of this study was to investigate the hepatoprotective effect of DHTS on NAFLD and its mechanism. A model of NAFLD and DHTS treatment was established using a Western diet to observe the effect of DHTS on NAFLD, which were detected by immunohistochemical, immunofluorescence, and other experiments. The mechanism was further explored by constructing immune responsive gene 1 (IRG1) knockout mice, RNA sequence, and molecular docking. The results revealed that DHTS significantly improved diet-induced metabolic disorders in mice, notably alleviating liver inflammation, oxidative stress, and fibrosis. Further analysis revealed that the intervention of DHTS was associated with the activation of IRG1. Subsequent experiments confirmed that IRG1 gene deletion reversed the above protective effects of DHTS in NAFLD. Mechanistically, DHTS enhanced the antioxidant nuclear factor-erythroid 2-related factor 2 (Nrf2) pathway through IRG1/itaconate and blocked the oxidative stress response in the liver. In addition, DHTS also inhibited the activation of NACHT-, leucine-rich repeat (LRR)-, and pyrin domain (PYD)-containing protein 3 (NLRP3) inflammasome via IRG1/itaconate, blocking the inflammatory amplification effect in the liver. The study suggests that DHTS may be a potential drug for the treatment of NAFLD, which exerts protective regulatory effects mainly through the IRG1/itaconate molecular pathway.

4-Octyl Itaconate Alleviates Myocardial Ischemia-Reperfusion Injury Through Promoting Angiogenesis via ERK Signaling Activation

Myocardial ischemia-reperfusion (IR) injury is a critical complication following revascularization therapy for ischemic heart disease. Itaconate, a macrophage-derived metabolite, has been implicated in inflammation and metabolic regulation. This study investigates the protective role of itaconate derivatives against IR injury. Using a mice model of IR injury, the impact of 7-day 4-Octyl itaconate (4-OI) administration on cardiac function is assessed. Exogenous administration of 4-OI significantly reduces myocardial damage, enhances angiogenesis, and alleviates myocardial hypoxia injury during reperfusion. RNA sequencing and molecular docking techniques are used to find the target of itaconate, and changes in cardiac function are observed in Immune-Responsive Gene1 (IRG1) global knockout mice. In cell culture studies, 4-OI promotes endothelial cell proliferation and migration, mediated by Mitogen-Activated Protein Kinases (MAPK) signaling pathway activation, particularly through Extracellular Signal-Regulated Kinase (ERK) signaling. Inhibition of ERK blocks these beneficial effects on endothelial cells. Furthermore, itaconate synthesis inhibition worsens myocardial damage, which is mitigated by 4-OI supplementation. The results indicate that 4-OI promotes angiogenesis by activating MAPK signaling via FMS-like tyrosine kinase 1 (Flt1), highlighting its potential as a therapeutic strategy for myocardial IR injury.

Dissecting S-itaconation at host-pathogen interactions with chemical proteomics tools

The molecular essence of the battle between host and pathogens lies in the protein-protein or protein-metabolite interactions. Itaconate is one of the most upregulated immunometabolites, regulating immune responses through either noncovalent binding or covalent modification in the host. We herein briefly review recent progresses in the discoveries of physiological and pathological roles of itaconate and applications of chemical proteomic technologies in exploring itaconate modifications on cysteines (S-itaconation) at the interface of host-pathogen interactions. Key challenges are also proposed as future outlook.

High-fat diet and neuroinflammation: The role of mitochondria

In recent years, increasing evidence has supported that high-fat diet (HFD) can induce the chronic, low-grade neuroinflammation in the brain, which is closely associated with the impairment of cognitive function. As the key organelles responsible for energy metabolism in the cell, mitochondria are believed to involved in the pathogenesis of a variety of neurological disorders. This review summarizes the current progress in the field of the relationship between HFD exposure and neurodegenerative diseases, and outline the major routines of HFD induced neuroinflammation and its pathological significance in the pathogenesis of neurodegenerative diseases. Furthermore, the article highlights the pivotal role of mitochondrial dysfunction in driving the neuroinflammation in the setting of HFD. Danger-associated molecular patterns (DAMPs) from damaged mitochondria can activate innate immune signaling pathways, while mitochondrial dysfunction itself can lead to metabolic remodeling of inflammatory cells, thus inducing neuroinflammation. More importantly, mitochondrial damage, neuroinflammation, and insulin resistance caused by HFD form a mutually reinforcing vicious cycle, ultimately leading to the death of neurons and promoting the progression of neurodegenerative diseases. Thus, in-depth elucidation of the role and underlying mechanisms of mitochondrial dysfunction in HFD-induced metabolic disorders may not only expand our understanding of the mechanistic linkages between HFD and etiology of neurodegenerative diseases, but also help develop the specific strategies for the prevention and treatment of neurodegenerative diseases.

Genomic basis of schistosome resistance in a molluscan vector of human schistosomiasis

Freshwater snails are obligate intermediate hosts for the transmission of schistosomiasis, one of the world's most devastating parasitic diseases. To decipher the mechanisms underlying snail resistance to schistosomes, recombinant inbred lines (RILs) were developed from two well-defined homozygous lines (iM line and iBS90) of the snail Biomphalaria glabrata. Whole-genome sequencing (WGS) was used to scan the genomes of 46 individual RIL snails, representing 46 RILs, half of which were resistant or susceptible to Schistosoma mansoni. Genome-wide association study (GWAS) and bin marker-assisted quantitative trait loci (QTLs) analysis, aided by our chromosome-level assembled genome, were conducted. A small genomic region (∼3 Mb) on chromosome 5 was identified as being associated with schistosome resistance, designated the B. glabrata schistosome resistance region 1 (BgSRR1). This study, built on our recently developed genetic and genomic resources, provides valuable insights into anti-schistosome mechanisms and the future development of snail-targeted biocontrol programs for schistosomiasis.

Freshwater browning as a hidden threat - Transcriptomic responses in fish gills exposed to fulvic acid

Human activities and climate change have significantly increased humic substances in freshwater ecosystems over the last few decades. This increase is particularly concerning during seasonal changes or after heavy rainfall, when concentrations can easily increase up to tenfold. This phenomenon, known as "browning," has unknown consequences for aquatic organisms. This study is the first to determine the effects of increasing humic substance concentrations on the transcriptomic and structural responses in the gills of rainbow trout (Oncorhynchus mykiss). Overall, 27 genes mainly involved in xenobiotic metabolism (cyp1a3, cyp1b1, pik3r6), immune response (rgs2, dll1, ccl19, acod1), and mucosal glycoprotein expression (muc2, prg4) were upregulated. No significant alterations were noted in gill morphology, although the molecular data strongly indicated a proinflammatory response. Our results highlight the risks posed by increasing humic substance concentrations for fish and aquatic ecosystems and emphasize the urgent need to implement effective monitoring and resource management strategies to address browning waters.

Early and delayed STAT1-dependent responses drive local trained immunity of macrophages in the spleen

Trained immunity (TI) is the process wherein innate immune cells gain functional memory upon exposure to specific ligands or pathogens, leading to augmented inflammatory responses and pathogen clearance upon secondary exposure. While the differentiation of hematopoietic stem cells (HSCs) and reprogramming of bone marrow (BM) progenitors are well-established mechanisms underpinning durable TI protection, remodeling of the cellular architecture within the tissue during TI remains underexplored. Here, we study the effects of peritoneal Bacillus Calmette-Guérin (BCG) administration to find TI-mediated protection in the spleen against a subsequent heterologous infection by the Gram-negative pathogen Salmonella Typhimurium (S.Tm). Utilizing single cell RNA-sequencing and flow cytometry, we discerned STAT1-regulated genes in TI-associated resident and recruited splenic myeloid populations. The temporal dynamics of TI were further elucidated, revealing both early and delayed myeloid subsets with time-dependent, cell-type-specific STAT1 signatures. Using lineage tracing, we find that tissue-resident red pulp macrophages (RPM), initially depleted by BCG exposure, are restored from both tissue-trained, self-renewing macrophages and from bone marrow-derived progenitors, fostering long lasting local defense. Early inhibition of STAT1 activation, using specific JAK-STAT inhibitors, reduces both RPM loss and recruitment of trained monocytes. Our study suggests a temporal window soon after BCG vaccination, in which STAT1-dependent activation of long-lived resident cells in the tissue mediates localized protection.

The Development and Characterization of Two Monoclonal Antibodies Against the Conjugates and Derivatives of the Immunometabolite Itaconate

We have developed two monoclonal antibodies, CPTC-2MeSC-1 and CPTC-2MeSC-2, against itaconate and its conjugates with sulfhydryl-containing biomolecules such as cysteines. Itaconate is a dicarboxylic acid metabolite that has recently gained much interest for its anti-inflammatory properties in many biological models. We have synthesized an itaconate-cysteine conjugate ITA-Cys designed to mimic in vivo Michael adducts of itaconate. Two monoclonal antibodies against ITA-Cys, CPTC-2MeSC-1 and CPTC-2MeSC, were developed and shown to have high immunoreactivity to unconjugated itaconate, itaconate-BSA conjugates, and Michael adducts of dimethyl itaconate. We found that CPTC-2MeSC-1 and CPTC-2MeSC-2 are specific and do not bind to other structurally similar cysteine Michael adducts, including those obtained from "sister" metabolites (fumarate, cis-aconitate), itaconate isomers (citraconate), and some itaconate esters. CPTC-2MeSC-2 is a useful tool in both studying biological actions of itaconate and developing therapeutic applications of itaconate and its derivatives.

How macrophage heterogeneity affects tuberculosis disease and therapy

Macrophages are the primary host cell type for infection by Mycobacterium tuberculosis in vivo. Macrophages are also key immune effector cells that mediate the control of bacterial growth. However, the specific macrophage phenotypes that are required for optimal immune control of M. tuberculosis infection in vivo remain poorly defined. There are two distinct macrophage lineages in the lung, comprising embryonically derived, tissue-resident alveolar macrophages and recruited, blood monocyte-derived interstitial macrophages. Recent studies have shown that these lineages respond divergently to similar immune environments within the tuberculosis granuloma. Here, we discuss how the differing responses of macrophage lineages might affect the control or progression of tuberculosis disease. We suggest that the ability to reprogramme macrophage responses appropriately, through immunological or chemotherapeutic routes, could help to optimize vaccines and drug regimens for tuberculosis.

Integration of metabolomics methodologies for the development of predictive models for mortality risk in elderly patients with severe COVID-19

BACKGROUND

The rapid evolution of the COVID-19 pandemic and subsequent global immunization efforts have rendered early metabolomics studies potentially outdated, as they primarily involved non-exposed, non-vaccinated populations. This paper presents a predictive model developed from up-to-date metabolomics data integrated with clinical data to estimate early mortality risk in critically ill COVID-19 patients. Our study addresses the critical gap in current research by utilizing current patient samples, providing fresh insights into the pathophysiology of the disease in a partially immunized global population.

METHODS

One hundred elderly patients with severe COVID-19 infection, including 46 survivors and 54 non-survivors, were recruited in January-February 2023 at the Second Hospital affiliated with Harbin Medical University. A predictive model within 24 h of admission was developed using blood metabolomics and clinical data. Differential metabolite analysis and other techniques were used to identify relevant characteristics. Model performance was assessed by comparing the area under the receiver operating characteristic curve (AUROC). The final prediction model was externally validated in a cohort of 50 COVID-19 elderly critically ill patients at the First Hospital affiliated with Harbin Medical University during the same period.

RESULTS

Significant disparities in blood metabolomics and laboratory parameters were noted between individuals who survived and those who did not. One metabolite indicator, Itaconic acid, and four laboratory tests (LYM, IL-6, PCT, and CRP), were identified as the five variables in all four models. The external validation set demonstrated that the KNN model exhibited the highest AUC of 0.952 among the four models. When considering a 50% risk of mortality threshold, the validation set displayed a sensitivity of 0.963 and a specificity of 0.957.

CONCLUSIONS

The prognostic outcome of COVID-19 elderly patients is significantly influenced by the levels of Itaconic acid, LYM, IL-6, PCT, and CRP upon admission. These five indicators can be utilized to assess the mortality risk in affected individuals.

Innate immune response to bone fracture healing

The field of osteoimmunology has primarily focused on fracture healing in isolated musculoskeletal injuries. The innate immune system is the initial response to fracture, with inflammatory macrophages, cytokines, and neutrophils arriving first at the fracture hematoma, followed by an anti-inflammatory phase to begin the process of new bone formation. This review aims to first discuss the current literature and knowledge gaps on the immune responses governing single fracture healing by encompassing the individual role of macrophages, neutrophils, cytokines, mesenchymal stem cells, bone cells, and other immune cells. This paper discusses the interactive effects of these cellular responses underscoring the field of osteoimmunology. The critical role of the metabolic environment in guiding the immune system properties will be highlighted along with some effective therapeutics for fracture healing in the context of osteoimmunology. However, compared to isolated fractures, which frequently heal well, long bone fractures in over 30 % of polytrauma patients exhibit impaired healing. Clinical evidence suggests there may be distinct physiologic and inflammatory pathways altered in polytrauma resulting in nonunion. Nonunion is associated with worse patient outcomes and increased societal healthcare costs. The dysregulated immunomodulatory/inflammatory response seen in polytrauma may lead to this increased nonunion rate. This paper will investigate the differences in immune response between isolated and polytrauma fractures. Finally, future directions for fracture studies are explored with consideration of the emerging roles of newly discovered immune cell functions in fracture healing, the existing challenges and conflicting results in the field, the translational potential of these studies in clinic, and the more complex nature of polytrauma fractures that can alter cell functions in different tissues.

Itaconic acid ameliorates necrotizing enterocolitis through the TFEB-mediated autophagy-lysosomal pathway

Excessive autophagy has been implicated in the pathogenesis of necrotizing enterocolitis (NEC), yet the molecular underpinnings of the autophagy-lysosomal pathway (ALP) in NEC are not well characterized. This study aimed to elucidate alterations within the ALP in NEC by employing RNA sequencing on intestinal tissues obtained from affected infants. Concurrently, we established animal and cellular models of NEC to assess the therapeutic efficacy of itaconic acid (ITA). Our results indicate that the ALP is significantly disrupted in NEC. Notably, ITA was found to modulate the ALP, enhancing autophagic flux and lysosomal function, which consequently alleviated NEC symptoms. Further analysis revealed that ITA's beneficial effects are mediated through the promotion of TFEB nuclear translocation, thereby augmenting the ALP. These findings suggest that targeting the ALP with ITA to modulate TFEB activity may represent a viable therapeutic approach for NEC.

Itaconate facilitates viral infection via alkylating GDI2 and retaining Rab GTPase on the membrane

Metabolic reprogramming of host cells plays critical roles during viral infection. Itaconate, a metabolite produced from cis-aconitate in the tricarboxylic acid cycle (TCA) by immune responsive gene 1 (IRG1), is involved in regulating innate immune response and pathogen infection. However, its involvement in viral infection and underlying mechanisms remain incompletely understood. Here, we demonstrate that the IRG1-itaconate axis facilitates the infections of VSV and IAV in macrophages and epithelial cells via Rab GTPases redistribution. Mechanistically, itaconate promotes the retention of Rab GTPases on the membrane via directly alkylating Rab GDP dissociation inhibitor beta (GDI2), the latter of which extracts Rab GTPases from the membrane to the cytoplasm. Multiple alkylated residues by itaconate, including cysteines 203, 335, and 414 on GDI2, were found to be important during viral infection. Additionally, this effect of itaconate needs an adequate distribution of Rab GTPases on the membrane, which relies on Rab geranylgeranyl transferase (GGTase-II)-mediated geranylgeranylation of Rab GTPases. The single-cell RNA sequencing data revealed high expression of IRG1 primarily in neutrophils during viral infection. Co-cultured and in vivo animal experiments demonstrated that itaconate produced by neutrophils plays a dominant role in promoting viral infection. Overall, our study reveals that neutrophils-derived itaconate facilitates viral infection via redistribution of Rab GTPases, suggesting potential targets for antiviral therapy.

Immunometabolic reprogramming in macrophages infected with active and dormant Cryptococcus neoformans: differential modulation of respiration, glycolysis, and fatty acid utilization

Dormancy is an adaptation in which cells reduce their metabolism, transcription, and translation to stay alive under stressful conditions, preserving the capacity to reactivate once the environment reverts to favorable conditions. Dormancy and reactivation of Cryptococcus neoformans (Cn) are closely linked to intracellular residency within macrophages. Our previous work showed that in vitro murine macrophages rely on the viable but not cultivable (VBNC-a dormancy phenotype) fungus from active Cn, with striking differences in immunometabolic gene expression. Here, we analyzed the influence of VBNC and active Cn on the immunometabolism of infected macrophages, combining metabolic gene expression, mitochondrial membrane potential (ΔΨm), oxygen consumption analysis, and uptake of glucose and fatty acids. The active fungus induced mitochondrial depolarization, and increased glycolysis and mitochondrial oxygen consumption. VBNC infection in bone marrow-derived macrophage (BMDM) caused an attenuated modification in mitochondrial metabolism. However, we found differences in BMDM infected with VBNC vs those infected with active fungus, where VBNC induced an increment in fatty acid uptake in M0 and M1 BMDM, measured by incorporation of BODIPY-palmitate, accompanied by an increase in expression of fatty acid transporters Fabp1 and Fabp4. Overall, distinct fatty acid-related responses induced by VBNC and active Cn suggest different immunomodulatory reactions, depending on the microbial growth stage. We posit that, for VBNC, some of these macrophage metabolic responses reflect the establishment of prolonged microbial intracellular residency and possibly initial stages of granuloma formation.

Salmonella multimutants enable efficient identification of SPI-2 effector protein function in gut inflammation and systemic colonization

Salmonella enterica spp. rely on translocation of effector proteins through the SPI-2 encoded type III secretion system (T3SS) to achieve pathogenesis. More than 30 effectors contribute to manipulation of host cells through diverse mechanisms, but interdependency or redundancy between effectors complicates the discovery of effector phenotypes using single mutant strains. Here, we engineer six mutant strains to be deficient in cohorts of SPI-2 effector proteins, as defined by their reported function. Using various animal models of infection, we show that three principle phenotypes define the functional contribution of the SPI-2 T3SS to infection. Multimutant strains deficient for intracellular replication, for manipulation of host cell defences, or for expression of virulence plasmid effectors all showed strong attenuation in vivo, while mutants representing approximately half of the known effector complement showed phenotypes similar to the wild-type parent strain. By additionally removing the SPI-1 T3SS, we find cohorts of effector proteins that contribute to SPI-2 T3SS-driven enhancement of gut inflammation. Further, we provide an example of how iterative mutation can be used to find a minimal number of effector deletions required for attenuation, and thus establish that the SPI-2 effectors SopD2 and GtgE are critical for the promotion of gut inflammation and mucosal pathology. This strategy provides a powerful toolset for simultaneous parallel screening of all known SPI-2 effectors in a single experimental context, and further facilitates the identification of the responsible effectors, and thereby provides an efficient approach to study how individual effectors contribute to disease.

Itaconate transporter SLC13A3 impairs tumor immunity via endowing ferroptosis resistance

Immune checkpoint blockade (ICB) triggers tumor ferroptosis. However, most patients are unresponsive to ICB. Tumors might evade ferroptosis in the tumor microenvironment (TME). Here, we discover SLC13A3 is an itaconate transporter in tumor cells and endows tumor ferroptosis resistance, diminishing tumor immunity and ICB efficacy. Mechanistically, tumor cells uptake itaconate via SLC13A3 from tumor-associated macrophages (TAMs), thereby activating the NRF2-SLC7A11 pathway and escaping from immune-mediated ferroptosis. Structural modeling and molecular docking analysis identify a functional inhibitor for SLC13A3 (SLC13A3i). Deletion of ACOD1 (an essential enzyme for itaconate synthesis) in macrophages, genetic ablation of SLC13A3 in tumors, or treatment with SLC13A3i sensitize tumors to ferroptosis, curb tumor progression, and bolster ICB effectiveness. Thus, we identify the interplay between tumors and TAMs via the SLC13A3-itaconate-NRF2-SLC7A11 axis as a previously unknown immune ferroptosis resistant mechanism in the TME and SLC13A3 as a promising immunometabolic target for treating SLC13A3+ cancer.

Itaconate Ameliorates Experimental Autoimmune Uveitis by Modulating Teff/Treg Cell Imbalance Via the DNAJA1/CDC45 Axis

Purpose

The aim of this study was to elucidate the effect of itaconate (ITA) on experimental autoimmune uveitis (EAU), to explore its potential mechanism, and to identify potential therapeutic targets.

Methods

We established an animal model of EAU by constructing an immune map of mice treated with ITA and exploring the therapeutic mechanism of ITA by single-cell RNA sequencing and flow cytometry.

Results

ITA mitigated ocular inflammation associated with EAU and reversed the pathogenic differentiation linked to Th17 induction by EAU, along with the reactive oxygen species (ROS) and oxidative stress pathways. Subsequent to ITA intervention, the downregulated differentially expressed genes in the T-cell subset primarily centered around the heat shock protein (HSP) family. Activation of HSPs reversed the anti-inflammatory effects of ITA in EAU mice. ITA decreased ROS levels and HSP expression in CD4+ T cells, with DnaJ heat shock protein family (HSP40) member A1 (DNAJA1) exhibiting the most notable alterations among the HSPs. ITA suppressed the expression of DNAJA1/cell division cycle protein 45 (CDC45), thereby disrupting the pathogenic division cycle of CD4+ T cells and reducing their proliferation. Inhibiting DNAJA1 also held promise for modulating the Th17/Treg imbalance. Notably, ITA curtailed the expansion of CD4+ T cells in uveitis patients.

Conclusions

Our research delved into the potential therapeutic mechanisms underlying ITA therapy in EAU, offering fresh perspectives on its utility in the treatment of autoimmune conditions. DNAJA1 emerges as a promising candidate for targeted therapeutic interventions in uveitis.

The role of the interplay between macrophage glycolytic reprogramming and NLRP3 inflammasome activation in acute lung injury/acute respiratory distress syndrome

Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is a severe respiratory condition associated with elevated morbidity and mortality. Understanding their complex pathophysiological mechanisms is crucial for developing new preventive and therapeutic strategies. Recent studies highlight the significant role of inflammation involved in ALI/ARDS, particularly the hyperactivation of the NOD-like receptor thermal protein domain-associated protein 3 (NLRP3) inflammasome in macrophages. This activation drives pulmonary inflammation by releasing inflammatory signalling molecules and is linked to metabolic reprogramming, marked by increased glycolysis and reduced oxidative phosphorylation. However, the relationship between NLRP3 inflammasome activation and macrophage glycolytic reprogramming in ALI/ARDS, as well as the molecular mechanisms regulating these processes, remain elusive. This review provides a detailed description of the interactions and potential mechanisms linking NLRP3 inflammasome activation with macrophage glycolytic reprogramming, proposing that glycolytic reprogramming may represent a promising therapeutic target for mitigating inflammatory responses in ALI/ARDS. KEY POINTS: NLRP3 inflammasome activation is pivotal in mediating the excessive inflammatory response in ALI/ARDS. Glycolytic reprogramming regulates NLRP3 inflammasome activation. Therapeutic potential of targeting glycolytic reprogramming to inhibit NLRP3 inflammasome activation in ALI/ARDS.

Engineering thioesterase as a driving force for novel itaconate production via its degradation scheme

Incorporation of irreversible steps in pathway design enhances the overall thermodynamic favorability and often leads to better bioconversion yield given functional enzymes. Using this concept, here we constructed the first non-natural itaconate biosynthesis pathway driven by thioester hydrolysis. Itaconate is a commercially valuable platform chemical with wide applications in the synthetic polymer industry. Production of itaconate has long relied on the decarboxylation of TCA cycle intermediate cis-aconitate as the only biosynthetic route. Inspired by nature's design of itaconate detoxification, here we engineered a novel itaconate producing pathway orthogonal to native metabolism with no requirement of auxotrophic knock-out. The reversed degradation pathway initiates with pyruvate and acetyl-CoA condensation forming (S)-citramalyl-CoA, followed by its dehydration and isomerization into itaconyl-CoA then hydrolysis into itaconate. Phenylacetyl-CoA thioesterase (PaaI) from Escherichia coli was identified via screening to deliver the highest itaconate formation efficiency when coupled to the reversible activity of citramalate lyase and itaconyl-CoA hydratase. The preference of PaaI towards itaconyl-CoA hydrolysis over acetyl-CoA and (S)-citramalyl-CoA also minimized the inevitable precursor loss due to enzyme promiscuity. With acetate recycling, acetyl-CoA conservation, and condition optimization, we achieved a final itaconate titer of 1 g/L using the thioesterase driven pathway, which is a significant improvement compared to the original degradation pathway based on CoA transferase. This study illustrates the significance of thermodynamic favorability as a design principle in pathway engineering.

Dimethyl itaconate modulates neuroprotective effect on primary rat astrocytes under inflammatory condition by regulating the expression of neurotrophic factors and TrkA/B-P75 receptors

INTRODUCTION

Astrocytes, specialized glial cells, are essential for maintaining the central nervous system homeostasis. Inflammatory conditions can disrupt neurotrophic factors and receptor expression in astrocytes, leading to potential central nervous system damage. Itaconate, recently identified for its anti-inflammatory properties, was investigated in this study for its effects on neurotrophic factors in LPS-stimulated primary rat astrocytes.

METHODS

Primary rat astrocyte cells were isolated from one-day-old Wistar rats and exposed to 1 µg/ml lipopolysaccharide (LPS) for 6 h to stimulate inflammation. The effect of DMI (62.5, 125, and 250 µM for 18 h) on the cell viability of astrocyte cells exposed to LPS was evaluated by the MTT assay. The effects of DMI on the mRNA and protein levels of NGF, BDNF, and GDNF were evaluated using ELISA and qRT-PCR assays. Protein and mRNA levels of neurotrophic factor receptors (TrkA, TrkB, and P75) were evaluated using qRT-PCR and Western blot analyses.

RESULTS

The results showed that DMI suppressed astrocytes cell death induced by LPS in a dose-dependent manner. DMI dose-dependently restored the reduced mRNA and protein levels of NGF, BDNF, GDNF, and TrkA and TrkB receptors in LPS-treated astrocytes, but it significantly decreased the p75 expression in the same condition.

CONCLUSION

In conclusion, DMI may be able to support astrocyte survival and functions based on the restoration of neurotrophic factors and their receptors expression in LPS-stimulated astrocyte cells. This suggests that DMI could be a promising therapeutic option for neurodegenerative diseases characterized by inflammation-induced astrocyte dysfunction.

4-Octyl itaconate attenuates renal tubular injury in db/db mice by activating Nrf2 and promoting PGC-1α-mediated mitochondrial biogenesis

Objectives: The aim of this study was to investigate the mechanism of itaconate's potential effect in diabetic kidney disease.

Methods: Renal immune responsive gene 1 (IRG1) levels were measured in db/db mice and streptozotocin (STZ) + high-fat diet (HFD)-induced diabetic mice. Irg1 knockout mice were generated. db/db mice were treated with 4-octyl itaconate (4-OI, 50 mg/kg), a derivative of itaconate, for 4 weeks. Renal function and morphological changes were investigated. Ultrastructural alterations were determined by transmission electron microscopy.

Results: Renal IRG1 levels were reduced in two diabetic models. STZ+HFD-treated Irg1 knockout mice exhibited aggravated renal tubular injury and worsened renal function. Treatment with 4-OI lowered urinary albumin-to-creatinine ratio and blood urea nitrogen levels, and restored renal histological changes in db/db mice. It improved mitochondrial damage, increased expressions of peroxisome-proliferator-activated receptor γ coactivator-1α (PGC-1α) and mitochondrial transcription factor A (TFAM) in the renal cortex of db/db mice. These were confirmed in vitro; 4-OI improved high glucose-induced abnormal mitochondrial morphology and TFAM expression in HK-2 cells, effects that were inhibited by PGC-1α silencing. Moreover, 4-OI reduced the number of apoptotic cells in the renal cortex of db/db mice. Further study showed that 4-OI increased renal Nrf2 expression and decreased oxidative stress levels in db/db mice. In HK-2 cells, 4-OI decreased high glucose-induced mitochondrial ROS production, which was reversed by Nrf2 silencing. Nrf2 depletion also inhibited 4-OI-mediated regulation of PGC-1α, TFAM, and mitochondrial apoptotic protein expressions.

Conclusions: 4-OI attenuates renal tubular injury in db/db mice by activating Nrf2 and promoting PGC-1α-mediated mitochondrial biogenesis.

Itaconate suppresses house dust mite-induced allergic airways disease and Th2 cell differentiation

Itaconate was initially identified as an antimicrobial compound produced by myeloid cells. Beyond its antimicrobial role, itaconate may also serve as a crucial metabolic and immune modulator. We therefore examined the roles of aconitate decarboxylase 1 (Acod1) and itaconate in house dust mite (HDM)-sensitized and -challenged mice, a model of T helper 2 (Th2)-driven allergic airways disease. HDM treatment induced lung Acod1 mRNA expression and bronchoalveolar lavage (BAL) itaconate levels in wild-type C57BL/6 mice. Acod1 knockout mice (Acod1-KO) with negligible BAL itaconate showed heightened HDM-induced type 2 cytokine expression, increased serum IgE, and enhanced recruitment of Th2 cells in the lung, indicating a shift towards a more pronounced Th2 immune response. Acod1-KO mice also showed increased eosinophilic airway inflammation and hyperresponsiveness. Experiments in chimeric mice demonstrated that bone marrow from Acod1-KO mice is sufficient to increase type 2 cytokine expression in wild-type mice, and that restitution of bone marrow from wild type mice attenuates mRNA expression of Th2 cytokines in Acod1-KO mice. Specific deletion of Acod1 in lysozyme-secreting macrophages (LysM-cre+Acod1flox/flox) recapitulated the exaggerated phenotype observed in whole-body Acod1-KO mice. Adoptive transfer of Acod1-KO bone marrow-derived macrophages also increased lung mRNA expression of Th2 cytokines. In addition, treatment of Th2-polarized CD4 cells with itaconate impeded Th2 cell differentiation, as shown by reduced expression of Gata3 and decreased release of IL-5 and IL-13. Finally, public datasets of human samples show lower Acod1 expression in subjects with allergic asthma, consistent with a protective role of itaconate in asthma pathogenesis. Together, these data suggest that itaconate plays a protective, immunomodulatory role in limiting airway type 2 inflammation after allergen challenge by attenuating T cell responses.

Selective production of the itaconic acid-derived compounds 2-hydroxyparaconic and itatartaric acid

There is a strong interest in itaconic acid in the medical and pharmaceutical sectors, both as an anti-bacterial compound and as an immunoregulator in mammalian macrophages. Fungal hosts also produce itaconic acid, and in addition they can produce two derivatives 2-hydroxyparaconic and itatartaric acid. Not much is known about these two derivatives, while their structural analogy to itaconate could open up several applications. In this study, we report the production of these two itaconate-derived compounds. By overexpressing the itaconate P450 monooxygenase Cyp3 in a previously engineered itaconate-overproducing Ustilago cynodontis strain, itaconate was converted to its lactone 2-hydroxyparaconate. The second product itatartarate is most likely the result of the subsequent lactone hydrolysis. A major challenge in the production of 2-hydroxyparaconate and itatartarate is their co-production with itaconate, leading to difficulties in their purification. Achieving high derivatives specificity was therefore the paramount objective. Different strategies were evaluated including process parameters such as substrate and pH, as well as strain engineering focusing on Cyp3 expression and product export. 2-hydroxyparaconate and itatartarate were successfully produced from glucose and glycerol, with the latter resulting in a higher derivatives specificity due to an overall slower metabolism on this non-preferred carbon source. The derivatives specificity could be further increased by metabolic engineering approaches including the exchange of the native itaconate transporter Itp1 with the Aspergillus terreus itaconate transporter MfsA. Both 2-hydroxyparaconate and itatartarate were recovered from fermentation supernatants following a pre-existing protocol. 2-hydroxyparaconate was recovered first through a process of evaporation, lactonization, and extraction with ethyl acetate. Subsequently, itatartarate could be obtained in the form of its sodium salt by saponification of the purified 2-hydroxyparaconate. Finally, several analytical methods were used to characterize the resulting products and their structures were confirmed by nuclear magnetic resonance spectroscopy. This work provides a promising foundation for obtaining 2-hydroxyparaconate and itatartarate in high purity and quantity. This will allow to unravel the full spectrum of potential applications of these novel compounds.

Enteric bacterial infection stimulates remodelling of bile metabolites to promote intestinal homeostasis

The liver makes bile, an aqueous solution critical for fat absorption, which is secreted into the duodenum. Despite extensive studies on bile salts, other components of bile are less well characterized. Here we used global metabolomic analysis on bile from specific-pathogen-free, germ-free, Citrobacter rodentium-infected or Listeria monocytogenes-infected mice and identified a metabolome of 812 metabolites that were altered by both microbiota and enteric infection. Hepatic transcriptomics identified enteric-infection-triggered pathways that probably underlie bile remodelling. Enteric infection increased levels of four dicarboxylates in bile, including itaconate. Analysis of Acod1-/- mice indicated that increased itaconate also increased tuft cell abundance, altered microbiota composition and function as detected by metagenomic analysis, and modulated host defence, leading to reduced Vibrio cholerae colonization. Our data suggest that enteric-infection-associated signals are relayed between the intestine and liver and induce transcriptional programmes that shape the bile metabolome, modifying the immunomodulatory and host defence functions of bile.

Nanoparticle-based itaconate treatment recapitulates low-cholesterol/low-fat diet-induced atherosclerotic plaque resolution

Current pharmacologic treatments for atherosclerosis do not completely protect patients; additional protection can be achieved by dietary modifications, such as a low-cholesterol/low-fat diet (LCLFD), that mediate plaque stabilization and inflammation reduction. However, this lifestyle modification can be challenging for patients. Unfortunately, incomplete understanding of the underlying mechanisms has thwarted efforts to mimic the protective effects of a LCLFD. Here, we report that the tricarboxylic acid cycle intermediate itaconate (ITA), produced by plaque macrophages, is key to diet-induced plaque resolution. ITA is produced by immunoresponsive gene 1 (IRG1), which we observe is highly elevated in myeloid cells of vulnerable plaques and absent from early or stable plaques in mice and humans. We additionally report development of an ITA-conjugated lipid nanoparticle that accumulates in plaque and bone marrow myeloid cells, epigenetically reduces inflammation via H3K27ac deacetylation, and reproduces the therapeutic effects of LCLFD-induced plaque resolution in multiple atherosclerosis models.

Differential Effects of Itaconate and its Esters on the Glutathione and Glucose Metabolism of Cultured Primary Rat Astrocytes

Itaconate is produced as endogenous metabolite by decarboxylation of the citric acid cycle intermediate cis-aconitate. As itaconate has anti-microbial and anti-inflammatory properties, this substance is considered as potential therapeutic drug for the treatment of inflammation in various diseases including traumatic brain injury and stroke. To test for potential adverse effects of itaconate on the viability and metabolism of brain cells, we investigated whether itaconate or its membrane permeable derivatives dimethyl itaconate (DI) and 4-octyl itaconate (OI) may affect the basal glucose and glutathione (GSH) metabolism of cultured primary astrocytes. Acute exposure of astrocytes to itaconate, DI or OI in concentrations of up to 300 µM for up to 6 h did not compromise cell viability. Of the tested substances, only OI stimulated aerobic glycolysis as shown by a time- and concentration-dependent increase in glucose-consumption and lactate release. None of the tested itaconates affected the pentose-phosphate pathway-dependent reduction of the water-soluble tetrazolium salt 1 (WST1). In contrast, both DI and OI, but not itaconate, depleted cellular GSH in a time- and concentration-dependent manner. For OI this depletion was accompanied by a matching increase in the extracellular GSH content that was completely prevented in the presence of the multidrug resistance protein 1 (Mrp1)-inhibitor MK571, while in DI-treated cultures GSH was depleted both in cells and medium. These data suggest that OI stimulates Mrp1-mediated astrocytic GSH export, while DI reacts with GSH to a conjugate that is not detectable by the GSH assay applied. The data presented demonstrate that itaconate, DI and OI differ strongly in their effects on the GSH and glucose metabolism of cultured astrocytes. Such results should be considered in the context of the discussed potential use of such compounds as therapeutic agents.

Acod1-mediated inhibition of aerobic glycolysis suppresses osteoclast differentiation and attenuates bone erosion in arthritis

OBJECTIVES

Metabolic changes are crucially involved in osteoclast development and may contribute to bone degradation in rheumatoid arthritis (RA). The enzyme aconitate decarboxylase 1 (Acod1) is known to link the cellular function of monocyte-derived macrophages to their metabolic status. As osteoclasts derive from the monocyte lineage, we hypothesised a role for Acod1 and its metabolite itaconate in osteoclast differentiation and arthritis-associated bone loss.

METHODS

Itaconate levels were measured in human peripheral blood mononuclear cells (PBMCs) of patients with RA and healthy controls by mass spectrometry. Human and murine osteoclasts were treated with the itaconate derivative 4-octyl-itaconate (4-OI) in vitro. We examined the impact of Acod1-deficiency and 4-OI treatment on bone erosion in mice using K/BxN serum-induced arthritis and human TNF transgenic (hTNFtg) mice. SCENITH and extracellular flux analyses were used to evaluate the metabolic activity of osteoclasts and osteoclast progenitors. Acod1-dependent and itaconate-dependent changes in the osteoclast transcriptome were identified by RNA sequencing. CRISPR/Cas9 gene editing was used to investigate the role of hypoxia-inducible factor (Hif)-1α in Acod1-mediated regulation of osteoclast development.

RESULTS

Itaconate levels in PBMCs from patients with RA were inversely correlated with disease activity. Acod1-deficient mice exhibited increased osteoclast numbers and bone erosion in experimental arthritis while 4-OI treatment alleviated inflammatory bone loss in vivo and inhibited human and murine osteoclast differentiation in vitro. Mechanistically, Acod1 suppressed osteoclast differentiation by inhibiting succinate dehydrogenase-dependent production of reactive oxygen species and Hif1α-mediated induction of aerobic glycolysis.

CONCLUSION

Acod1 and itaconate are crucial regulators of osteoclast differentiation and bone loss in inflammatory arthritis.

SYNLAC prime probiotics enhances growth performance, and resistance of white shrimp, Penaeus vannamei to Enterocytozoon hepatopenaei and Vibrio alginollyticus: Insights into immune and metabolic pathway modulations

This study explores the impact of SYNLAC Prime probiotics on the growth performance, health status, and metabolic profile of white shrimp, Penaeus vannamei. Shrimp fed with the experimental diets, including the control diet without probiotic supplementation, and the diets supplemented with SYNLAC Prime probiotics at concentrations of 105 CFU (g diet)-1 (P5) and 106 CFU (g diet)-1 (P6) for 56 days. Results indicated a significant enhancement in growth performance in probiotic-treated shrimp relative to the control group, attributed to structural improvements in the digestive tract, particularly the increased abundances of B cells in the hepatopancreas. The administration of dietary probiotics markedly reduced the severity of Enterocytozoon hepatopenaei (EHP) infection and decreased cumulative mortalities following Vibrio alginolyticus challenge. Shrimp in the P6 group exhibited significant elevations in phenoloxidase activity, respiratory burst, lysozyme activity and phagocytic activity compared to control group. Furthermore, there was an upregulation of several immune-related genes in hepatopancreas, including serine protease (SP), prophenoloxidase (proPO) I, proPO II, and penaeidin 3a. Additionally, the expression of β-1, 3-glucan binding protein and SP mRNA was significantly increased in hemocytes. Untargeted metabolomics analysis using LC-MS/MS revealed significant changes in the hepatopancreas metabolic profile, highlighting alterations in energy metabolisms pathways, such as citrate cycle and nicotinate and nicotinamide metabolism, as well as amino acid metabolisms pathways including arginine and proline metabolism, taurine and hypotaurine metabolism, and histidine metabolism. These findings underscore the potential of SYNLAC Prime probiotics in enhancing shrimp growth, immune function, and metabolic pathways, offering valuable insights for advancing health management strategies in shrimp aquaculture.

Protective role of aconitate decarboxylase 1 in neuroinflammation-induced dysfunctions of the paraventricular thalamus and sleepiness

Sleepiness is commonly associated with neuroinflammation; however, the underlying neuroregulatory mechanisms remain unclear. Previous research suggests that the paraventricular thalamus (PVT) plays a crucial role in regulating sleep-wake dynamics; thus, neurological abnormalities in the PVT may contribute to neuroinflammation-induced sleepiness. To test this hypothesis, we performed electroencephalography recordings in mice treated with lipopolysaccharide (LPS) and found that the mice exhibited temporary sleepiness lasting for 7 days. Using the Fos-TRAP method, fiber photometry recordings, and immunofluorescence staining, we detected temporary PVT neuron hypoactivation and microglia activation from day 1 to day 7 post-LPS treatment. Combining the results of bulk and single-cell RNA sequencing, we found upregulation of aconitate decarboxylase 1 (Acod1) in PVT microglia post-LPS treatment. To investigate the role of Acod1, we manipulated Acod1 gene expression in PVT microglia via stereotactic injection of short hairpin RNA adenovirus. Knockdown of Acod1 exacerbated inflammation, neuronal hypoactivation, and sleepiness. Itaconate is a metabolite synthesized by the enzyme encoded by Acod1. Finally, we confirmed that exogenous administration of an itaconate derivative, 4-octyl itaconate, could inhibit microglia activation, alleviate neuronal dysfunction, and relieve sleepiness. Our findings highlight PVT's role in inflammation-induced sleepiness and suggest Acod1 as a potential therapeutic target for neuroinflammation.

Emerging insights into epigenetics and hematopoietic stem cell trafficking in age-related hematological malignancies

BACKGROUND

Hematopoiesis within the bone marrow (BM) is a complex and tightly regulated process predominantly influenced by immune factors. Aging, diabetes, and obesity are significant contributors to BM niche damage, which can alter hematopoiesis and lead to the development of clonal hematopoiesis of intermediate potential (CHIP). Genetic/epigenetic alterations during aging could influence BM niche reorganization for hematopoiesis or clonal hematopoiesis. CHIP is driven by mutations in genes such as Tet2, Dnmt3a, Asxl1, and Jak2, which are associated with age-related hematological malignancies.

OBJECTIVE

This literature review aims to provide an updated exploration of the functional aspects of BM niche cells within the hematopoietic microenvironment in the context of age-related hematological malignancies. The review specifically focuses on how immunological stressors modulate different signaling pathways that impact hematopoiesis.

METHODS

An extensive review of recent studies was conducted, examining the roles of various BM niche cells in hematopoietic stem cell (HSC) trafficking and the development of age-related hematological malignancies. Emphasis was placed on understanding the influence of immunological stressors on these processes.

RESULTS

Recent findings reveal a significant microheterogeneity and temporal stochasticity of niche cells across the BM during hematopoiesis. These studies demonstrate that niche cells, including mesenchymal stem cells, osteoblasts, and endothelial cells, exhibit dynamic interactions with HSCs, significantly influenced by the BM microenvironment as the age increases. Immunosurveillance plays a crucial role in maintaining hematopoietic homeostasis, with alterations in immune signaling pathways contributing to the onset of hematological malignancies. Novel insights into the interaction between niche cells and HSCs under stress/aging conditions highlight the importance of niche plasticity and adaptability.

CONCLUSION

The involvement of age-induced genetic/epigenetic alterations in BM niche cells and immunological stressors in hematopoiesis is crucial for understanding the development of age-related hematological malignancies. This comprehensive review provides new insights into the complex interplay between niche cells and HSCs, emphasizing the potential for novel therapeutic approaches that target niche cell functionality and resilience to improve hematopoietic outcomes in the context of aging and metabolic disorders.

NOVELTY STATEMENT

This review introduces novel concepts regarding the plasticity and adaptability of BM niche cells in response to immunological stressors and epigenetics. It proposes that targeted therapeutic strategies aimed at enhancing niche cell resilience could mitigate the adverse effects of aging, diabetes, and obesity on hematopoiesis and clonal hematopoiesis. Additionally, the review suggests that understanding the precise temporal and spatial dynamics of niche-HSC interactions and epigenetics influence may lead to innovative treatments for age-related hematological malignancies.

Itaconate uptake via SLC13A3 improves hepatic antibacterial innate immunity

Itaconate is an immunoregulatory metabolite produced by the mitochondrial enzyme immune-responsive gene 1 (IRG1) in inflammatory macrophages. We recently identified an important mechanism by which itaconate is released from inflammatory macrophages. However, it remains unknown whether extracellular itaconate is taken up by non-myeloid cells to exert immunoregulatory functions. Here, we used a custom-designed CRISPR screen to identify the dicarboxylate transporter solute carrier family 13 member 3 (SLC13A3) as an itaconate importer and to characterize the role of SLC13A3 in itaconate-improved hepatic antibacterial innate immunity. Functionally, liver-specific deletion of Slc13a3 impairs hepatic antibacterial innate immunity in vivo and in vitro. Mechanistically, itaconate uptake via SLC13A3 induces transcription factor EB (TFEB)-dependent lysosomal biogenesis and subsequently improves antibacterial innate immunity in mouse hepatocytes. These findings identify SLC13A3 as a key itaconate importer in mouse hepatocytes and will aid in the development of potent itaconate-based antibacterial therapeutics.

Itaconate drives mtRNA-mediated type I interferon production through inhibition of succinate dehydrogenase

Itaconate is one of the most highly upregulated metabolites in inflammatory macrophages and has been shown to have immunomodulatory properties. Here, we show that itaconate promotes type I interferon production through inhibition of succinate dehydrogenase (SDH). Using pharmacological and genetic approaches, we show that SDH inhibition by endogenous or exogenous itaconate leads to double-stranded mitochondrial RNA (mtRNA) release, which is dependent on the mitochondrial pore formed by VDAC1. In addition, the double-stranded RNA sensors MDA5 and RIG-I are required for IFNβ production in response to SDH inhibition by itaconate. Collectively, our data indicate that inhibition of SDH by itaconate links TCA cycle modulation to type I interferon production through mtRNA release.

Cancer cell-intrinsic biosynthesis of itaconate promotes tumor immunogenicity

The Krebs cycle byproduct itaconate has recently emerged as an important metabolite regulating macrophage immune functions, but its role in tumor cells remains unknown. Here, we show that increased tumor-intrinsic cis-aconitate decarboxylase (ACOD1 or CAD, encoded by immune-responsive gene 1, Irg1) expression and itaconate production promote tumor immunogenicity and anti-tumor immune responses. Furthermore, we identify thimerosal, a vaccine preservative, as a specific inducer of IRG1 expression in tumor cells but not in macrophages, thereby enhancing tumor immunogenicity. Mechanistically, thimerosal induces itaconate production through a ROS-RIPK3-IRF1 signaling axis in tumor cells. Further, increased IRG1/itaconate upregulates antigen presentation-related gene expression via promoting TFEB nuclear translocation. Intratumoral injection of thimerosal induced itaconate production, activated the tumor immune microenvironment, and inhibited tumor growth in a T cell-dependent manner. Importantly, IRG1 deficiency markedly impaired tumor response to thimerosal treatment. Furthermore, itaconate induction by thimerosal potentiates the anti-tumor efficacy of adoptive T-cell therapy and anti-PD1 therapy in a mouse lymphoma model. Hence, our findings identify a new role for tumor intrinsic IRG1/itaconate in promoting tumor immunogenicity and provide a translational means to increase immunotherapy efficacy.

Immunometabolism: signaling pathways, homeostasis, and therapeutic targets

Immunometabolism plays a central role in sustaining immune system functionality and preserving physiological homeostasis within the organism. During the differentiation and activation, immune cells undergo metabolic reprogramming mediated by complex signaling pathways. Immune cells maintain homeostasis and are influenced by metabolic microenvironmental cues. A series of immunometabolic enzymes modulate immune cell function by metabolizing nutrients and accumulating metabolic products. These enzymes reverse immune cells' differentiation, disrupt intracellular signaling pathways, and regulate immune responses, thereby influencing disease progression. The huge population of immune metabolic enzymes, the ubiquity, and the complexity of metabolic regulation have kept the immune metabolic mechanisms related to many diseases from being discovered, and what has been revealed so far is only the tip of the iceberg. This review comprehensively summarized the immune metabolic enzymes' role in multiple immune cells such as T cells, macrophages, natural killer cells, and dendritic cells. By classifying and dissecting the immunometabolism mechanisms and the implications in diseases, summarizing and analyzing advancements in research and clinical applications of the inhibitors targeting these enzymes, this review is intended to provide a new perspective concerning immune metabolic enzymes for understanding the immune system, and offer novel insight into future therapeutic interventions.

Macrophage polarization and metabolic reprogramming in abdominal aortic aneurysm

BACKGROUND

Abdominal aortic aneurysm (AAA) is a macrovascular disease with high morbidity and mortality in the elderly. The limitation of the current management is that most patients can only be followed up until the AAA diameter increases to a threshold, and surgical intervention is recommended. The development of preventive and curative drugs for AAA is urgently needed. Macrophage-mediated immune inflammation is one of the key pathological links in the occurrence and development of AAA.

AIMS

This review article aims to evaluate the impact of immunometabolism on macrophage biology and its role in AAA.

METHODS

We analyze publications focusing on the polarization and metabolic reprogramming in macrophages as well as their potential impact on AAA, and summarize the potential interventions that are currently available to regulate these processes.

RESULTS

The phenotypic and functional changes in macrophages are accompanied by significant alterations in metabolic pathways. The interaction between macrophage polarization and metabolic pathways significantly influences the progression of AAA.

CONCLUSION

Macrophage polarization is a manifestation of the gross dichotomy of macrophage function into pro-inflammatory killing and tissue repair, that is, classically activated M1 macrophages and alternatively activated M2 macrophages. Macrophage functions are closely linked to metabolic changes, and the emerging field of immunometabolism is providing unique insights into the role of macrophages in AAA. It is essential to further investigate the precise metabolic changes and their functional consequences in AAA-associated macrophages.

Suppressing neutrophil itaconate production attenuates Mycoplasma pneumoniae pneumonia

Mycoplasma pneumoniae is a common cause of community-acquired pneumonia in which neutrophils play a critical role. Immune-responsive gene 1 (IRG1), responsible for itaconate production, has emerged as an important regulator of inflammation and infection, but its role during M. pneumoniae infection remains unknown. Here, we reveal that itaconate is an endogenous pro-inflammatory metabolite during M. pneumoniae infection. Irg1 knockout (KO) mice had lower levels of bacterial burden, lactate dehydrogenase (LDH), and pro-inflammatory cytokines compared with wild-type (WT) controls after M. pneumoniae infection. Neutrophils were the major cells producing itaconate during M. pneumoniae infection in mice. Neutrophil counts were positively correlated with itaconate concentrations in bronchoalveolar lavage fluid (BALF) of patients with severe M. pneumoniae pneumonia. Adoptive transfer of Irg1 KO neutrophils, or administration of β-glucan (an inhibitor of Irg1 expression), significantly attenuated M. pneumoniae pneumonia in mice. Mechanistically, itaconate impaired neutrophil bacterial killing and suppressed neutrophil apoptosis via inhibiting mitochondrial ROS. Moreover, M. pneumoniae induced Irg1 expression by activating NF-κB and STAT1 pathways involving TLR2. Our data thus identify Irg1/itaconate pathway as a potential therapeutic target for the treatment of M. pneumoniae pneumonia.

Microbial dysbiosis in the gut–mammary axis as a mechanism for mastitis in dairy cows

Mastitis is a significant and costly disease in dairy cows, reducing milk production and affecting herd health. Recent research highlights the role of gastrointestinal microbial dysbiosis in the development of mastitis. This review focuses on how microbial imbalances in the rumen and intestines can compromise the integrity of the gastrointestinal barriers, allowing harmful bacteria and endotoxins, such as lipopolysaccharide, to enter the bloodstream and reach the mammary gland, triggering inflammation. This process links gastrointestinal health to mammary gland inflammation through the gut–mammary axis. Furthermore, disruptions in glucose metabolism and immune responses are implicated in the progression of mastitis. This review underscores the potential for non‐antibiotic interventions aimed at restoring microbial balance to reduce mastitis incidence, providing new insights into improving dairy cow health and farm productivity. Our findings emphasise the critical need to explore preventive measures targeting the rumen and intestinal microbiota for effective mastitis control.

ACOD1 mediates Staphylococcus aureus-induced inflammatory response via the TLR4/NF-κB signaling pathway

Staphylococcus aureus (SA) is a common Gram-positive bacterium that activates inflammatory cells, expressing various cytokines and inducing an inflammatory response. Recent research revealed aconitate decarboxylase 1 (ACOD1) as a regulator of the immune response through various metabolic pathways, playing a dual role in the inflammatory response. However, the mechanism by which ACOD1 participates in the regulation of SA-induced inflammatory responses in macrophages remains unknown. Therefore, this study aims to investigate the function and underlying regulatory mechanisms of ACOD1 in SA-induced inflammatory response. This study reveals that SA induced a macrophage inflammatory response and upregulated ACOD1 expression. ACOD1 knockdown significantly inhibited SA-induced macrophage inflammatory response, attenuated SA-induced nuclear envelope wrinkling, and plasma membrane rupture, and suppressed the TLR4/NF-κB signaling pathway. Furthermore, ACOD1 knockdown reduced the inflammatory response and alleviated lung tissue injury and cellular damage, leading to decreased bacterial loads in the lungs of SA-infected mice. Collectively, these findings demonstrate that SA induces an inflammatory response in macrophages and increases ACOD1 expression. ACOD1 enhances SA-induced inflammatory responses via the TLR4/NF-κB signaling pathway. Our findings highlight the significant role of ACOD1 in mediating the inflammatory response in SA-infected macrophages and elucidate its molecular mechanism in regulating the SA-induced inflammatory response.

Metabolite regulation of epigenetics in cancer

The catalytic activity of most epigenetic enzymes requires a metabolite produced by central carbon metabolism as a cofactor or (co-)substrate. The concentrations of these metabolites undergo dynamic changes in response to nutrient levels and environmental conditions, reprogramming metabolic processes and epigenetic landscapes. Abnormal accumulations of epigenetic modulatory metabolites resulting from mutations in metabolic enzymes contribute to tumorigenesis. In this review, we first present the concept that metabolite regulation of gene expression represents an evolutionarily conserved mechanism from prokaryotes to eukaryotes. We then review how individual metabolites affect epigenetic enzymes and cancer development. Lastly, we discuss the advancement of and opportunity for therapeutic targeting of metabolite-epigenetic regulation in cancer therapy.

Multifaceted roles of mitochondria in asthma

Mitochondria are essential organelles within cells, playing various roles in numerous cellular processes, including differentiation, growth, apoptosis, energy conversion, metabolism, and cellular immunity. The phenotypic variation of mitochondria is specific to different tissues and cell types, resulting in significant differences in their function, morphology, and molecular characteristics. Asthma is a chronic, complex, and heterogeneous airway disease influenced by external factors such as environmental pollutants and allergen exposure, as well as internal factors at the tissue, cellular, and genetic levels, including lung and airway structural cells, immune cells, granulocytes, and mast cells. Therefore, a comprehensive understanding of the specific responses of mitochondria to various external environmental stimuli and internal changes are crucial for elucidating the pathogenesis of asthma. Previous research on mitochondrial-targeted therapy for asthma has primarily focused on antioxidants. Consequently, it is necessary to summarize the multifaceted roles of mitochondria in the pathogenesis of asthma to discover additional strategies targeting mitochondria in this context. In this review, our goal is to describe the changes in mitochondrial function in response to various exposure factors across different cell types and other relevant factors in the context of asthma, utilizing a new mitochondrial terminology framework that encompasses cell-dependent mitochondrial characteristics, molecular features, mitochondrial activity, function, and behavior.

Macrophage variants in laboratory research: most are well done, but some are RAW

Macrophages play a pivotal role in the innate immune response. While their most characteristic function is phagocytosis, it is important not to solely characterize macrophages by this activity. Their crucial roles in body development, homeostasis, repair, and immune responses against pathogens necessitate a broader understanding. Macrophages exhibit remarkable plasticity, allowing them to modify their functional characteristics in response to the tissue microenvironment (tissue type, presence of pathogens or inflammation, and specific signals from neighboring cells) swiftly. While there is no single defined "macrophage" entity, there is a diverse array of macrophage types because macrophage ontogeny involves the differentiation of progenitor cells into tissue-resident macrophages, as well as the recruitment and differentiation of circulating monocytes in response to tissue-specific cues. In addition, macrophages continuously sense and respond to environmental cues and tissue conditions, adjusting their functional and metabolic states accordingly. Consequently, it is of paramount importance to comprehend the heterogeneous origins and functions of macrophages employed in in vitro studies, as each available in vitro macrophage model is associated with specific sets of strengths and limitations. This review centers its attention on a comprehensive comparison between immortalized mouse macrophage cell lines and primary mouse macrophages. It provides a detailed analysis of the strengths and weaknesses inherent in these in vitro models. Finally, it explores the subtle distinctions between diverse macrophage cell lines, offering insights into numerous factors beyond the model type that can profoundly influence macrophage function.