The role of itaconate in host defense and inflammation

Bacterial metabolism in the host and its association with virulence

The host restricted pathogens are competently dependent on their respective host for nutritional requirements. The bacterial metabolic pathways are surprisingly varied and remarkably flexible that in turn help them to successfully overcome competition and colonise their host. The metabolic adaptation plays pivotal role in bacterial pathogenesis. The understanding of host-pathogen metabolic crosstalk needs to be prioritized to decipher host-pathogen interactions. The review focuses on various aspects of host pathogen interactions that majorly involves adaptation of bacterial metabolism to counteract immune mechanisms by rectifying metabolic cues that provides pathogen the idea of different anatomical sites and the local physiology of the host. The key set of metabolites that are recognized as centre of competition between host and its pathogens are also briefly discussed. The factors that control the timely expression of virulence of bacterial pathogens is poorly understood. The perspective presented herein will facilitate us with a broader view of molecular mechanisms that modulates the expression of virulence factors in bacterial pathogens. The knowledge of crosslinked metabolic pathways of bacteria and their host will serve to develop novel potential therapeutics.

Single-cell analysis of diquat-induced oxidative stress and its impact on organ-specific toxicity

Diquat (DQ) is a commonly used herbicide, and its improper use can lead to multi-organ damage. The characteristics of multi-organ damage induced by DQ are not yet well understood. In this study, we conducted single-cell/single-nucleus RNA sequencing (scRNA-seq/snRNA-seq) on the lungs, liver, and kidneys of mice at consecutive time points (10 hours, 20 hours, and 36 hours) after DQ poisoning, as well as in a control group. In a multi-organ single-cell atlas comprising over 270,000 cells from mice, we found that DQ induces an oxidative stress microenvironment in endothelial and parenchymal cells, primarily characterized by activation of the oxidative phosphorylation pathway and an enhanced inflammatory response. This oxidative stress microenvironment prompted regulatory cell death in parenchymal and immune cells, releasing inflammatory factors and further exacerbating the oxidative environment. Additionally, metabolic reprogramming occurred in both parenchymal and immune cells under oxidative stress, leading to alterations in energy metabolism, reduced hepatic detoxification capabilities, and changes in the activation modes of immune cells, thereby intensifying tissue damage. Notably, no significant fibrosis was observed in the tissue damage caused by DQ, underscoring the importance of early intervention. Overall, using a mouse model, this study revealed the central role of the DQ-induced oxidative stress microenvironment in multi-organ damage and enhanced our understanding of the pathophysiology and complex molecular mechanisms underlying DQ-induced multi-organ injury.

4-octyl itaconate reduces human NLRP3 inflammasome constitutive activation with the cryopyrin-associated periodic syndrome p.R262W, p.D305N and p.T350M variants

Cryopyrin-associated periodic syndrome (CAPS) is a condition characterized by dominant genetic variants in the NLRP3 gene, which lead to the formation of constitutively active inflammasomes. These inflammasomes play a crucial role in CAPS patients' inflammatory episodes, these being primarily driven by the production of interleukin (IL)-1b. Although treatment with IL-1 blockers is effective for CAPS, some patients develop refractory responses and adverse reactions to these therapies. Consequently, there is a need for novel treatments for CAPS patients. Promising candidates are the derivatives of itaconate, which have been shown to impair NLRP3 inflammasome activation and IL-1β release in blood mononuclear cells from CAPS patients. In this study, we provide insight into the inhibitory mechanisms by which the itaconate derivative 4-octyl itaconate (4-OI) acts on NLRP3 that has different gain-of-function mutations (p.R262W, p.D305N and p.T350M) associated with CAPS. Notably, 4-OI effectively blocks the basal auto-activation of the inflammasome formed by NLRP3 p.R262W, p.D305N and p.T350M variants, which in turn reduces caspase-1 activation, gasdermin D processing, and IL-18 release. Furthermore, after lipopolysaccharide priming of macrophages, 4-OI also decreases IL-1β gene expression and release. Overall, 4-OI impairs CAPS-associated inflammasome function at multiple levels, meaning that therapeutic agents based on itaconate could be a promising therapeutic approach to managing inflammatory episodes in CAPS patients carrying p.R262W, p.D305N or p.T350M variants.

Immunometabolism shapes chronic Staphylococcus aureus infection: insights from biofilm infection models

Staphylococcus aureus is both a commensal bacterium and versatile pathogen, capable of transitioning from a benign colonizer to cause invasive disease. Its ability to form biofilm - a resilient, highly structured bacterial community - plays a key role in chronic infections, including those associated with medical implants and native tissues. The unique microenvironments of these biofilm niches create challenges for the host immune system, complicating pathogen clearance. Immunometabolism, the interplay between immune function and metabolic programming, plays a crucial role in dictating how the host combats S. aureus biofilms. Leukocytes undergo profound metabolic changes in response to biofilm, which can lead to dysregulated immune responses and persistent infection. This review explores recent insights defining the metabolic landscape of immune responses to S. aureus biofilm with a focus on two clinically relevant models, namely, craniotomy and prosthetic joint infection.

Macrophage-Derived Itaconate Suppresses Dendritic Cell Function to Promote Acquired Resistance to Anti-PD-1 Immunotherapy

Adaptive resistance to immunotherapy remains a significant challenge in cancer treatment. The reshaping of the tumor immune microenvironment in response to therapeutic pressures is a crucial factor contributing to this resistance. In this study, by comprehensive metabolic profiling of tumor tissues, we identified elevated itaconate in response to anti-PD-1 therapy as an adaptive resistance mechanism that promoted immune escape and tumor progression. CD8+ T-cell-derived IFNγ induced a significant upregulation of cis-aconitate decarboxylase 1 (ACOD1) in macrophages via the JAK-STAT1 pathway, thereby rewiring the Krebs cycle toward itaconate production. In murine models, macrophage-specific deletion of Acod1 increased the antitumor efficacy of anti-PD-1 therapy and improved survival. Additionally, itaconate and its derivative, 4-octyl itaconate, suppressed the tumor antigen presentation and cross-priming ability of dendritic cells, resulting in the impairment of antigen-specific T-cell antitumor responses. In summary, these findings identify an IFNγ-dependent immunometabolic mechanism of anti-PD-1 resistance, providing a promising strategy for combination therapy. Significance: Elevated itaconate production by macrophages induced by IFNγ is a critical negative feedback immunoregulatory metabolic response to anti-PD-1 immunotherapy that inhibits the cross-priming function of dendritic cells and confers immunotherapy resistance.

Nontargeted metabolomics uncovering metabolite signatures in glioblastoma: a preliminary study on candidate biomarker discovery for IDH subtyping and survival prediction

Background

Currently, there are no established tumor-derived metabolic biomarkers in clinical practice that can simultaneously differentiate among nontumorous brain tissues, isocitrate dehydrogenase (IDH) wild-type glioblastomas (GBMs), and IDH mutant GBMs, or accurately predict patient survival. The aim of this study was to identify GBM biomarkers for molecular classification and survival prediction via nontargeted metabolomics.

Methods

Brain tissue samples from nontumors, IDH-mutant GBMs, and IDH-wild-type GBMs were analyzed via liquid chromatography-mass spectrometry (LC-MS). Metabolites for molecular classification and survival prediction were identified via sparse partial least-squares discriminant analysis (sPLS-DA) and extreme gradient boosting (XGBoost) models, respectively. Both sets of metabolites were then validated via bootstrap resampling. The biomarkers for survival prediction were further validated using an independent metabolomics dataset.

Results

In total, 185 human-derived metabolites were identified with high confidence levels. Two non-overlapping sets of 11 candidate biomarkers for molecular subtyping and survival prediction were screened out. In the validation models for molecular subtyping, the random forest model achieved the highest accuracy (0.787, 95% CI: 0.780-0.795) and a Kappa value of 0.681. The Cox proportional hazards regression model established based on cholic acid and citrulline had an AUC of 0.942 (95% CI: 0.920-0.956) at 84 days and an AUC of 0.812 (95% CI: 0.746-0.826) at 297 days.

Conclusion

This exploratory study identified potential metabolic biomarkers for GBM subtyping and prognosis prediction. However, further validation in large-scale clinical studies and mechanistic investigations are needed to confirm their applicability and reliability.

Reprogramming mitochondrial metabolism to enhance macrophages polarization by ROS-responsive nanoparticles for osteoarthritis

Osteoarthritis (OA) is a chronic low-grade inflammatory joint disease closely related to the inflammatory pathological microenvironment caused by synovial M1 macrophages. In contrast to the proinflammatory role of M1 macrophages, M2 macrophages contribute to anti-inflammatory responses and tissue repair. Therefore, shifting the M2/M1 phenotype ratio in favor of M2 macrophages has become a promising therapeutic strategy for OA. However, current therapeutics cannot penetrate the synovium and only show limited drug retention time. Herein, we developed an OA microenvironment-responsive nanocarrier with thioketal bonds in the main chain and β-1,3-d-glucan and triphenylphosphine units in the side chain, which can respond to reactive oxygen species (ROS) and target macrophages and mitochondrial aggregation. For OA treatment, 4-octyl itaconate and dexamethasone were encapsulated within the nanocarrier, forming HBPTG@OD that effectively eliminated mitochondrial ROS and inducible nitric oxide synthase in M1 macrophages. HBPTG@OD significantly suppressed the release of inflammatory factors by macrophages and thereby reducing chondrocyte death. In vivo studies in a destabilized medial meniscus (DMM)-induced OA model showed that HBPTG@OD effectively converted M1 synovial macrophages to M2 macrophages, consequently delaying chondrogenic apoptosis. This study presents a nanocarrier-based strategy that effectively repolarizes M1 macrophages, demonstrating great promise for the treatment of OA.

Metabolic adaptations driving innate immune memory: mechanisms and therapeutic implications

Immune memory is a hallmark of the adaptive immune system. However, recent research reveals that innate immune cells also retain memory of prior pathogen exposure that prompts enhanced responses to subsequent infections. This phenomenon is termed "innate immune memory" or "trained immunity." Notably, remodeling of cellular metabolism, which closely links to epigenetic reprograming, is a prominent feature of innate immune memory. Adaptations in glycolysis, the tricarboxylic acid cycle, oxidative phosphorylation, glutaminolysis, and lipid synthesis pathways are critical for establishing innate immune memory. This review provides an overview of the current understanding of how metabolic adaptations drive innate immune memory. This understanding is fundamental to understanding innate immune system functions and advancing therapies against infectious diseases.

Gang of 3: How the Krebs cycle-linked metabolites itaconate, succinate, and fumarate regulate macrophages and inflammation

The reprogramming of metabolic pathways and processes in immune cells has emerged as an important aspect of the immune response. Metabolic intermediates accumulate as a result of metabolic adaptations and mediate functions outside of metabolism in the regulation of immunity and inflammation. In macrophages, there has been a major focus on 3 metabolites linked to the Krebs cycle, itaconate, succinate, and fumarate, which have been shown to regulate multiple processes. Here, we discuss recent progress on these 3 metabolites with regard to their effect on macrophages in host defense and inflammatory diseases. We also consider the therapeutic opportunities presented from the mimicry of these metabolites or by targeting the enzymes that make or metabolize them in order to leverage the body's own anti-inflammatory response.

Itaconate potentiates hepatic gluconeogenesis through NRF2 induction

The interplay between systemic metabolism and immune responses is increasingly recognized as a significant factor in the dysregulation of glucose homeostasis associated with diabetes and obesity. Immune metabolites play crucial roles in mediating this crosstalk, with itaconate emerging as an important immune metabolite involved in the inflammatory response of macrophages. Recent studies have highlighted the role of itaconate as a regulator of glucose metabolism, particularly in the context of obesity, although the underlying mechanisms remain poorly understood. In this study, we identified itaconate as one of the metabolites that significantly increase in the liver during fasting compared to fed conditions. Mechanistically, we found that itaconate enhances glucagon-induced liver gluconeogenesis independently of insulin signaling. Notably, itaconate upregulates the expression of gluconeogenic genes both under basal conditions and in the presence of palmitic acid. Furthermore, our data indicate that the effects of itaconate occur independently of CREB activation. Instead, we demonstrate that these potentiating effects are mediated through the induction of nuclear factor erythroid 2-related factor 2 (NRF2). Our findings demonstrate that itaconate has a glucagon-potentiating effects in the liver, suggesting that itaconate may play a significant role in the pathogenesis of metabolic-associated liver diseases.

Development of Itaconate Polymers Microparticles for Intracellular Regulation of Pro-Inflammatory Macrophage Activation

Itaconate (IA) is an endogenous metabolite and a potent regulator of the innate immune system. It's use in immunomodulatory therapies has faced limitations due to challenges in controlled delivery and requirements of high extracellular concentrations for internalization of the highly polar small molecule to achieve its intracellular therapeutic activity. Microparticle (MP)-based delivery strategies are a promising approach for intracellular delivery of small molecule metabolites through macrophage phagocytosis and subsequent intracellular polymer degradation-based delivery. Toward the goal of intracellular delivery of IA, degradable polyester polymer- (poly(dodecyl itaconate)) based IA polymer microparticles (IA-MPs) are generated using an emulsion method, forming micron-scale (≈1.5 µm) degradable microspheres. IA-MPs are characterized with respect to their material properties and IA release kinetics to inform particle fabrication. Treatment of murine bone marrow-derived macrophages with an optimized particle concentration of 0.1 mg million-1 cells enables phagocytosis-mediated internalization and low levels of cytotoxicity. Flow cytometry demonstrates IA-MP-specific regulation of IA-sensitive inflammatory targets. Metabolic analyses demonstrate that IA-MP internalization inhibits oxidative metabolism and induced glycolytic reliance, consistent with the established mechanism of IA-associated inhibition of succinate dehydrogenase. This development of IA-based polymer microparticles provides a basis for additional innovative metabolite-based microparticle drug delivery systems for the treatment of inflammatory disease.

Itaconate Has Limited Protective Effects in Experimental Malaria Models

In severe malaria, dysregulated metabolism and excessive inflammatory responses contribute to fatal outcomes. Therapeutic strategies that address both metabolic and inflammatory balances are thus required. Itaconate, a metabolite produced by aconitate decarboxylase 1 (ACOD1), is a potent inhibitor of both inflammation and glycolysis with protective effects in various inflammatory diseases. Although elevated itaconate levels have been observed in Plasmodium-infected individuals, its role in malaria is still poorly understood, making further investigation essential for assessing its therapeutic potential. We investigated the role of itaconate in both severe and mild malaria using Plasmodium berghei NK65 (PbNK65) and Plasmodium chabaudi AS (PcAS) models, respectively. Using 13C-tracer metabolomics, we detected increased itaconate levels in various organs during infection and identified inflammatory monocytes as the source of this production. Nevertheless, ACOD1 knockout mice displayed no significant changes in phenotype after PbNK65 infection, and treatment of PbNK65-infected mice with 4-octyl itaconate did not affect disease severity either. However, in the PcAS model, ACOD1 deficiency worsened the disease, as indicated by increased weight loss, higher clinical scores, and elevated parasitemia. Therefore, in contrast to the findings in recent literature, our study shows that itaconate does not contribute to susceptibility, but rather provides limited protection to malaria.

Dexmedetomidine modulates peritoneal macrophage to attenuate lipopolysaccharide-induced inflammation

PURPOSE

To investigate how Dexmedetomidine (Dex) modulates the function of peritoneal macrophages (PMs) to reduce lipopolysaccharide (LPS)-induced inflammation.

METHODS

The anti-inflammatory effect of Dex on LPS-stimulated PMs was assessed by examining its impact on their proliferation, phagocytosis, and polarization. Proliferation and phagocytic activity were measured using CCK-8 and Neutral Red staining assays, respectively. The levels of inflammatory mediators were quantified using ELISA. Additionally, macrophage polarization was evaluated via ELISA, flow cytometry, and Western blot analysis to identify shifts in macrophage phenotypes.

RESULTS

Dex increased the proliferation and phagocytic capabilities of PMs, thereby mitigating LPS-induced inflammation. It suppressed pro-inflammatory mediators, including tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and high mobility group box 1 (HMGB1), while increasing levels of the anti-inflammatory cytokine interleukin-10 (IL-10). Furthermore, Dex promoted M2-type macrophage polarization, characterized by increased expression of IL-10, CD206, Arg-1, and CD11c. This effect was mediated through the JAK1/STAT6 signaling pathway, promoting M2 polarization, which was attenuated when JAK1 and STAT6 expression were downregulated.

CONCLUSION

Dex reduces LPS-induced inflammation in part by enhancing the proliferation, phagocytosis, and M2 polarization of PMs, with a key role for the JAK1/STAT6 pathway in promoting anti-inflammatory responses during sepsis.

4-Octyl Itaconate Modulates Dendritic Cells Function and Tumor Immunity via NRF2 Activation

Objective

Dendritic cells (DCs) play a pivotal role in orchestrating anti-tumor immune responses. However, various factors can suppress DCs function and compromise anti-tumor immunity. Itaconate, a metabolite activated during inflammation and infection, has been identified to possess immunomodulatory properties, but its role on DCs remains largely unexplored. In this study, we aimed to investigate the role of itaconate in regulating the maturation and function of DCs and its underlying molecular mechanism.

Methods

Bone marrow-derived dendritic cells (BMDCs) were treated with 4-octyl itaconate (4OI). The expression levels of CD40, CD80, CD86, and MHC-II on BMDCs were analyzed by flow cytometry. The mRNA expression of cytokines was assessed using RT-qPCR. BMDCs with different treatment were adoptively transferred to B16-OVA tumor-bearing mice. The production of IFN-γ, IL-2, and TNF-α in CD4+ T and CD8+ T cells were analyzed by flow cytometry. The protein level of NRF2 in BMDCs was analyzed by Western blot.

Results

Treatment with 4OI represses DC maturation and function. Specifically, 4OI-treated DCs exhibited impaired phenotypic and functional maturation, characterized by decreased expression of co-stimulatory molecules CD40, CD80, and CD86, as well as lower levels of pro-inflammatory cytokines IL-12, IL-6, TNF-α and IL-1β. Furthermore, these DCs demonstrated a diminished capacity to stimulate T cell responses both in vitro and in vivo. Mechanistically, 4OI inhibits DCs maturation and function through enhancing and activating KEAP1/NRF2 pathway.

Conclusion

This study reveals that 4OI inhibits DC function through NRF2 activation, elucidating the immunomodulatory mechanisms of itaconate and emphasizing its pivotal role in developing targeted DC-based tumor immunotherapy strategies.

Glutamine limits NLRP3 inflammasome activation and pyroptosis in macrophages by sustaining the IRG1/itaconate axis

Aberrant activation of NACHT, LRR, and PYD domains-containing protein 3 (NLRP3) inflammasome increases the release of mature pro-inflammatory cytokines interleukin (IL)-1β and IL-18, and enhances pyroptosis; thereby necessitating tight regulation of the NLRP3 inflammasome. Dysfunctional glutamine metabolism contributes to the pathogenesis of multiple inflammatory disorders, and the precise mechanism remains to be elucidated. Here, we provide evidence that glutamine deprivation enhances NLRP3 inflammasome activation in macrophages. Indeed, the absence of exogenous glutamine specifically enhanced NLRP3 inflammasome assembly, thereby accelerating pyroptosis and promoting the maturation of IL-1β and IL-18. Inhibition of glutaminolysis exhibited a similar effect to glutamine deprivation, whereas this effect was reversed by α-ketoglutarate (α-KG), a tricarboxylic acid (TCA)-cycle intermediate that can be replenished by glutamine supply. We further observed reduced generation of endogenous itaconate by glutamine deprivation and verified that both exogenous supplementation of itaconate derivative and increased endogenous itaconate production by overexpressing immune-responsive gene 1 [IRG1; also known as aconitate decarboxylase 1 (ACOD1)] could replace glutamine to inhibit the NLRP3 inflammasome. Mechanistically, glutamine deprivation decreased the source of substrate and inhibited transcription factor EB (TFEB)-dependent transcriptional upregulation of IRG1, thereby impairing the IRG1/itaconate axis that suppresses the NLRP3 inflammasome. Furthermore, glutamine deficiency was detected in a murine sepsis model, whereas extrinsic glutamine supplementation conferred protection against intestinal inflammation and tissue damage in septic mice. Taken together, our findings provide a novel insight into the link between glutamine metabolism and NLRP3 inflammasome activation, highlighting the target of glutamine metabolism, which holds as a potential therapeutic strategy for inflammatory diseases.

Reprogramming Glucose Metabolism of Macrophage for Acute Liver Failure Therapy with Itaconate Lipo-Nanodrug

Acute liver failure (ALF) is a life-threatening disease featuring comprehensive inflammatory response and metabolic disorders in which macrophages exert central roles. A glucose metabolism mediator of macrophages, itaconate, has demonstrated potent anti-inflammatory efficacy in various diseases, implying that itaconate could work in treating ALF. However, systemic administration of itaconate may lead to immune disorder, making targeting the delivery of itaconate to the liver lesion area highly important. Herein, a liposomal nanodrug incorporating itaconate is developed, and its potential in treating acute liver failure in an ALF murine model established by LPS/D-GalN administration is tested. The nanodrug shows preferential liver accumulation to effectively alleviate LPS/D-GalN-induced hepatic histopathological injury by decreasing oxidative stress. Moreover, it reprograms the glucose metabolism of macrophages, resulting in macrophage repolarization toward the anti-inflammatory phenotype. Furthermore, western-blot and immunohistochemical assays verifies that the nanodrug may inhibit aerobic glycolysis of macrophages in an NRF2 and STING-dependent manner. These results underline the promise of the nanodrug for ALF treatment by reprogramming glucose metabolism.

Unveiling the crossroads of STING signaling pathway and metabolic reprogramming: the multifaceted role of the STING in the TME and new prospects in cancer therapies

The cGAS-STING signaling pathway serves as a critical link between DNA sensing and innate immunity, and has tremendous potential to improve anti-tumor immunity by generating type I interferons. However, STING agonists have shown decreasing biotherapeutic efficacy in clinical trials. Tumor metabolism, characterized by aberrant nutrient utilization and energy production, is a fundamental hallmark of tumorigenesis. And modulating metabolic pathways in tumor cells has been discovered as a therapeutic strategy for tumors. As research concerning STING progressed, emerging evidence highlights its role in metabolic reprogramming, independent its immune function, indicating metabolic targets as a strategy for STING activation in cancers. In this review, we delve into the interplay between STING and multiple metabolic pathways. We also synthesize current knowledge on the antitumor functions of STING, and the metabolic targets within the tumor microenvironment (TME) that could be exploited for STING activation. This review highlights the necessity for future research to dissect the complex metabolic interactions with STING in various cancer types, emphasizing the potential for personalized therapeutic strategies based on metabolic profiling.

Elevated GFI1 in Alveolar Macrophages Suppresses ACOD1 Expression and Exacerbates Lipopolysaccharide-Induced Lung Injury in Obesity

To investigate the mechanisms behind the worsening of acute lung injury (ALI) in obesity, transcriptomic sequencing is performed, and significantly reduced mRNA levels of Aconitate Decarboxylase 1 (ACOD1) in the lung tissue of high-fat diet (HFD) mice are found. Clinical samples are collected, an ALI model is established in HFD mice, and both human and mouse samples are analyzed, revealing a significant decrease in ACOD1 expression in lung tissue and alveolar macrophages in obesity. Further in vivo and in vitro experiments show that ACOD1 knockdown worsens lung injury, inflammation, and oxidative stress, while ACOD1 overexpression alleviates these effects. Moreover, nuclear factor erythroid 2-related factor 2 (Nrf2) inhibition diminishes the protective effects of ACOD1 overexpression in ALI exacerbated by obesity. Additionally, in the context of obesity, growth factor independent 1 (GFI1) protein levels are elevated in alveolar macrophages, and its knockdown leads to upregulated ACOD1 expression. Therefore, this study suggests that ACOD1 downregulation in alveolar macrophages is a key factor in worsening ALI in obesity, likely driven by GFI1 upregulation.

The landscape of ATF3 in tumors: Metabolism, expression regulation, therapy approach, and open concerns

Cellular stress response is a pivotal process in tumor development and therapy. Activating transcription factor 3 (ATF3), a representative stress-responsive protein, plays pleiotropic roles in various biological processes. Over the past decade, studies have described not only the general role of ATF3 in tumor metabolism but also the complexity of ATF3 expression regulation and its associated modifications, including phosphorylation, ubiquitination, SUMOylation, and NEDDylation. Interestingly, beyond being a transcription factor, ATF3 can act as a modifier to control the ubiquitination of target molecules, such as p53, to exert its function in tumors. These advances in uncovering ATF3 biological function have yielded new insights into the cellular stress response during tumor development and will be instrumental in developing novel interventions. In this review, we update the role of ATF3 as a nexus in amino acid metabolism, lipid metabolism, glycometabolism, and other metabolic pathways in tumors; delineate the underlying mechanisms involving DNA level regulation, epigenetic regulation, and post-translational modifications of ATF3; and summarize the progression of tumor mono/combination therapies related to ATF3. In particular, we discuss the challenges that need to be addressed to provide a new conceptual framework for further understanding the potential therapeutic value of ATF3 in ongoing clinical trials.

Entamoeba histolytica extracellular vesicles drive pro-inflammatory monocyte signaling

The parasitic protozoan Entamoeba histolytica secretes extracellular vesicles (EVs), but so far little is known about their function in the interaction with the host immune system. Infection with E. histolytica trophozoites can lead to formation of amebic liver abscesses (ALAs), in which pro-inflammatory immune responses of Ly6Chi monocytes contribute to liver damage. Men exhibit a more severe pathology as the result of higher monocyte recruitment and a stronger immune response. To investigate the role of EVs and pathogenicity in the host immune response, we studied the effect of EVs secreted by low pathogenic EhA1 and highly pathogenic EhB2 amebae on monocytes. Size and quantity of isolated EVs from both clones were similar. However, they differed in their proteome and miRNA cargo, providing insight into factors potentially involved in amebic pathogenicity. In addition, EVs were enriched in proteins with signaling peptides compared with the total protein content of trophozoites. Exposure to EVs from both clones induced monocyte activation and a pro-inflammatory immune response as evidenced by increased surface presentation of the activation marker CD38 and upregulated gene expression of key signaling pathways (including NF-κB, IL-17 and TNF signaling). The release of pro-inflammatory cytokines was increased in EV-stimulated monocytes and more so in male- than in female-derived cells. While EhA1 EV stimulation caused elevated myeloperoxidase (MPO) release by both monocytes and neutrophils, EhB2 EV stimulation did not, indicating the protective role of MPO during amebiasis. Collectively, our results suggest that parasite-released EVs contribute to the male-biased immunopathology mediated by pro-inflammatory monocytes during ALA formation.

Metabolic reprogramming shapes post-translational modification in macrophages

Polarized macrophages undergo metabolic reprogramming, as well as extensive epigenetic and post-translational modifications (PTMs) switch. Metabolic remodeling and dynamic changes of PTMs lead to timely macrophage response to infection or antigenic stimulation, as well as its transition from a pro-inflammatory to a reparative phenotype. The transformation of metabolites in the microenvironment also determines the PTMs of macrophages. Here we reviewed the current understanding of the altered metabolites of glucose, lipids and amino acids in macrophages shape signaling and metabolism pathway during macrophage polarization via PTMs, and how these metabolites in some macrophage-associated diseases affect disease progression by shaping macrophage PTMs.

Identification of the Pseudomonas aeruginosa AgtR-CspC-RsaL pathway that controls Las quorum sensing in response to metabolic perturbation and Staphylococcus aureus

Environmental metabolites and metabolic pathways significantly influence bacterial pathogenesis and interspecies competition. We previously discovered that a mutation in the triosephosphate isomerase gene, tpiA, in Pseudomonas aeruginosa led to defective type III secretion and increased susceptibility to aminoglycoside antibiotics. In this study, we found that the tpiA mutation enhances the Las quorum sensing system due to reduced translation of the negative regulator RsaL. Further investigations demonstrated an upregulation of CspC, a CspA family protein that represses rsaL translation. DNA pull-down assay, along with genetic studies, revealed the role of AgtR in regulating cspC transcription. AgtR is known to regulate pyocyanin production in response to N-acetylglucosamine (GlcNAc), contributing to competition against Staphylococcus aureus. We demonstrated that CspC activates the Las quorum sensing system and subsequent pyocyanin production in response to GlcNAc and S. aureus. Overall, our results elucidate the AgtR-CspC-RsaL-LasI pathway that regulates bacterial virulence factors and its role in competition against S. aureus.

ACOD1-mediated lysosomal membrane permeabilization contributes to Mycobacterium tuberculosis-induced macrophage death

Mycobacterium tuberculosis (Mtb) primarily infects macrophages. In vitro without antibiotics, wild-type Mtb hastens death of the macrophages, but the processes leading to rapid cell death are not well understood. Our earlier work indicated that the death of Mtb-infected mouse macrophages in vitro is markedly exacerbated by induction of interferon-β (IFN-β) [L. Zhang et al., J. Exp. Med. 18, e20200887 (2021)]. Here, we identified a key downstream response to IFN-β in the context of Mtb infection as the massive induction of cis-aconitate decarboxylase (ACOD1), not only in its canonical subcellular localization in mitochondria but also in the cytosol, where it bound to the lysosome-stabilizing protein HSP70. ACOD1's product, itaconate, protected Mtb-infected macrophages. However, the contrasting and predominant effect of high-level ACOD1 expression was to act in a noncatalytic manner to promote HSP70's degradation, leading to lysosomal membrane permeabilization (LMP). Mtb-induced macrophage death was markedly diminished by inhibitors of cysteine proteases, consistent with lysosome-mediated cell death. Neither ACOD1 inhibitors nor cysteine protease inhibitors are suitable for potential host-directed therapy (HDT) of tuberculosis. Instead, this work directs attention to how ACOD1 acts nonenzymatically to promote the degradation of HSP70.

Dynamic optimization elucidates higher-level pathogenicity strategies of Pseudomonas aeruginosa

Multiple dangerous pathogens from the World Health Organization's priority list possess a plethora of virulence components, including the ability to survive inside macrophages. Often, the pathogens rely on a multi-layered defence strategy in order to defend themselves against the immune system. Here, a minimal model is proposed to study such a strategy. By way of example, we consider the interaction between Pseudomonas aeruginosa and the human host, in which the host and the pathogen counter each other in a back-and-forth interaction. In particular, the pathogen attacks the host, macrophages of the host engulf the pathogen and reduce its access to glucose, the pathogen activates the glyoxylate shunt, which is started by the enzyme isocitrate lyase (Icl), the host inhibits it by itaconic acid, and the pathogen metabolizes itaconic acid using the enzyme succinyl-CoA:itaconate CoA transferase (Ict). The flux through the glyoxylate shunt allows the pathogen to avoid carbon loss and oxidative stress. These functions are of utmost importance inside a phagolysosome. Therefore, the pathogen needs to allocate its limited protein resource between the enzymes Icl and Ict in order to maximize the time integral of a flux through the enzyme Icl. We use both random search and dynamic optimization to identify the enzyme Ict as a cost-effective means of counter-counter-counter-defence and as a possible drug target during the early phase of infection.

FGF21 ameliorates septic liver injury by restraining proinflammatory macrophages activation through the autophagy/HIF-1α axis

INTRODUCTION

Sepsis, a systemic immune syndrome caused by severe trauma or infection, poses a substantial threat to the health of patients worldwide. The progression of sepsis is heavily influenced by septic liver injury, which is triggered by infection and cytokine storms, and has a significant impact on the tolerance and prognosis of septic patients. The objective of our study is to elucidate the biological role and molecular mechanism of fibroblast growth factor 21 (FGF21) in the process of sepsis.

OBJECTIVES

This study was undertaken in an attempt to elucidate the function and molecular mechanism of FGF21 in therapy of sepsis.

METHODS

Serum concentrations of FGF21 were measured in sepsis patients and septic mice. Liver injury was compared between mice FGF21 knockout (KO) mice and wildtype (WT) mice. To assess the therapeutic potential, recombinant human FGF21 was administered to septic mice. Furthermore, the molecular mechanism of FGF21 was investigated in mice with myeloid-cell specific HIF-1α overexpression mice (LyzM-CreDIO-HIF-1α) and myeloid-cell specific Atg7 knockout mice (Atg7△mye).

RESULTS

Serum level of FGF21 was significantly increased in sepsis patients and septic mice. Through the use of recombinant human FGF21 (rhFGF21) and FGF21 KO mice, we found that FGF21 mitigated septic liver injury by inhibiting the initiation and propagation of inflammation. Treatment with rhFGF21 effectively suppressed the activation of proinflammatory macrophages by promoting macroautophagy/autophagy degradation of hypoxia-inducible factor-1α (HIF-1α). Importantly, the therapeutic effect of rhFGF21 against septic liver injury was nullified in LyzM-CreDIO-HIF-1α mice and Atg7△mye mice.

CONCLUSIONS

Our findings demonstrate that FGF21 considerably suppresses inflammation upon septic liver injury through the autophagy/ HIF-1α axis.

Effects of natural products on macrophage immunometabolism: A new frontier in the treatment of metabolic diseases

Immunometabolic variations in macrophages critically influence their differentiation into pro-inflammatory or anti-inflammatory phenotypes, thereby contributing to immune homeostasis, defense against infection, and tissue repair. Dysregulation of macrophage immunometabolism has been closely implicated in several metabolic diseases, including obesity, type 2 diabetes mellitus (T2DM), non-alcoholic fatty liver disease (NAFLD), hypertension, atherosclerosis, and gout, which positions macrophages as potential therapeutic targets. Recently, several natural products that target macrophage metabolic pathways have shown significant efficacy in managing metabolic diseases; however, a systematic review of these findings has yet to be conducted. This study consolidates natural products with immunoregulatory properties, including flavonoids, phenols, terpenoids, and naphthoquinones, which can alleviate chronic inflammation associated with metabolic disorders by modulating macrophage metabolic pathways, such as aerobic glycolysis, oxidative phosphorylation (OXPHOS), and fatty acid oxidation (FAO). This review aims to elucidate the metabolic regulation of the immune system, analyze metabolic alterations in macrophage associated with metabolic diseases, and summarize the beneficial roles of natural products in immunometabolism, providing novel insights for the prevention and therapeutic management of metabolic diseases.

In-depth proteomic profiling identifies potentiation of the LPS response by 7-ketocholesterol

In patients with stable coronary artery disease, plasma levels of 7-ketocholesterol (7-KC), found at high levels in atherosclerotic lesions, predict risk of incident heart failure dose dependently, potentially contributing to disease aetiology. Previous studies demonstrated that 7-KC can elicit effects on macrophage function; however, effects of 7-KC on the macrophage proteome have not been studied systematically. Here we used quantitative mass spectrometry to establish the effect of 7-KC on the mouse macrophage proteome. 7-KC independently mediated dynamic changes, including on atherogenic/M1 markers, cholesterol metabolism, biosynthesis and transport, as well as nutrient transport more broadly. These changes were however insufficient alone to drive changes in cytokine and chemokine secretion. Rather, they prime the macrophage, potentiating LPS-stimulated TNF alpha secretion and key pro-inflammatory enzymes. Our results indicate that 7-KC has independent metabolic effects on the macrophage; however, effects on the immune system are primarily due to the changes in metabolism priming the response to an inflammatory stimulus. Earlier findings from CANTOS and the recent FDA approval of colchicine highlight that inflammation is a viable target for cardiovascular disease; however, it is currrently unclear which will be the best anti-inflammatory targets to pursue in the future. In this context, our findings suggest that drugs targeting atherogenic markers induced by 7-KC might be well tolerated, as they will not necessarily be expected to be immunosuppressive.

Mitochondrial genetics, signalling and stress responses

Mitochondria are multifaceted organelles with crucial roles in energy generation, cellular signalling and a range of synthesis pathways. The study of mitochondrial biology is complicated by its own small genome, which is matrilineally inherited and not subject to recombination, and present in multiple, possibly different, copies. Recent methodological developments have enabled the analysis of mitochondrial DNA (mtDNA) in large-scale cohorts and highlight the far-reaching impact of mitochondrial genetic variation. Genome-editing techniques have been adapted to target mtDNA, further propelling the functional analysis of mitochondrial genes. Mitochondria are finely tuned signalling hubs, a concept that has been expanded by advances in methodologies for studying the function of mitochondrial proteins and protein complexes. Mitochondrial respiratory complexes are of dual genetic origin, requiring close coordination between mitochondrial and nuclear gene-expression systems (transcription and translation) for proper assembly and function, and recent findings highlight the importance of the mitochondria in this bidirectional signalling.

OLFML3 Promotes IRG1 Mitochondrial Localization and Modulates Mitochondrial Function in Macrophages

Olfactomedin-like protein 3 (OLFML3), belonging to olfactomedin (OLF) protein family, has poorly defined functions. Recent studies have reported the functions of OLFML3 in anti-viral immunity and tumorigenesis. In this study, we investigated the roles of OLFML3 in macrophages. In LPS- or Pseudomonas aeruginosa-induced acute lung injury (ALI) mouse model, OLFML3 depletion exacerbated inflammatory response, leading to reduced survival. OLFML3 achieved the in vivo activity by regulating macrophage phagocytosis and migration. Mass spectrometry analysis revealed immunoresponsive gene 1 (IRG1) as an OLFML3-interacting protein. IRG1 is a mitochondrial decarboxylase that catalyzes the conversion of cis-aconitate to itaconate, a myeloid-borne mitochondrial metabolite with immunomodulatory activities. Further investigation showed that OLFML3 could prevent LPS-induced mitochondrial dysfunction in macrophages by maintaining the homeostasis of mitochondrial membrane potential (MMP), mitochondrial reactive oxygen species (mtROS) and itaconate-related metabolites. In-depth protein-protein interaction studies showed that OLFML3 could promote IRG1 mitochondrial localization via a mitochondrial transport protein, apoptosis inducing factor mitochondria associated 1 (AIFM1). In summary, our study showed that OLFML3 could facilitate IRG1 mitochondrial localization and prevent LPS-induced mitochondrial dysfunction in macrophages.

4-Octyl Itaconate Attenuates Postmenopausal Osteoporosis by Inhibiting Ferroptosis and Enhancing Osteogenesis via the Nrf2 Pathway

Bone marrow mesenchymal stem cells (BMSCs) play an important role in bone metabolism and tissue repair, and their ability to differentiate into osteoblasts is crucial in the treatment of bone diseases such as postmenopausal osteoporosis (PMOP). However, the function of BMSCs may be affected by ferroptosis. Ferroptosis is a cell death mode characterized by excess Fe2+ and lipid peroxidation, which significantly affects the survival rate and differentiation ability of BMSCs. This study investigated the effect of exogenous itaconate derivative 4-octyl itaconate (4-OI) on Erastin-induced BMSCs ferroptosis. The results showed that 4-OI significantly inhibited Erastin-induced BMSCs ferroptosis by activating the nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway, reduced reactive oxygen species levels and oxidative damage, and restored antioxidant capacity. At the same time, 4-OI promoted the osteogenic differentiation of BMSCs. Further experiments showed that Nrf2-IN-1, an inhibitor of the Nrf2 pathway, could reverse the protective effect of 4-OI. In vivo, 4-OI was shown to reduce bone loss in ovariectomized (OVX) mice, as assessed by Micro-CT analysis. Immunofluorescence staining further revealed increased GPX4 and Nrf2 expression in vertebral tissues following 4-OI treatment. These results indicate that 4-OI improves ferroptosis of BMSCs and enhances osteogenic differentiation ability by activating the Nrf2 pathway, providing new research ideas and potential targets for the treatment of PMOP.

Anti-Inflammatory Effects of SGLT2 Inhibitors: Focus on Macrophages

A growing body of evidence indicates that nonglycemic effects of sodium-glucose cotransporter 2 (SGLT2) inhibitors play an important role in the protective effects of these drugs in diabetes, chronic kidney disease, and heart failure. In recent years, the anti-inflammatory potential of SGLT2 inhibitors has been actively studied. This review summarizes results of clinical and experimental studies on the anti-inflammatory activity of SGLT2 inhibitors, with a special focus on their effects on macrophages, key drivers of metabolic inflammation. In patients with type 2 diabetes, therapy with SGLT2 inhibitors reduces levels of inflammatory mediators. In diabetic and non-diabetic animal models, SGLT2 inhibitors control low-grade inflammation by suppressing inflammatory activation of tissue macrophages, recruitment of monocytes from the bloodstream, and macrophage polarization towards the M1 phenotype. The molecular mechanisms of the effects of SGLT2 inhibitors on macrophages include an attenuation of inflammasome activity and inhibition of the TLR4/NF-κB pathway, as well as modulation of other signaling pathways (AMPK, PI3K/Akt, ERK 1/2-MAPK, and JAKs/STAT). The review discusses the state-of-the-art concepts and prospects of further investigations that are needed to obtain a deeper insight into the mechanisms underlying the effects of SGLT2 inhibitors on the molecular, cellular, and physiological levels.

4-octyl Itaconate Attenuates Acute Pancreatitis and Associated Lung Injury by Suppressing Ferroptosis in Mice

Acute pancreatitis (AP) is a common gastrointestinal emergency requiring hospitalization. In recent years, several studies have demonstrated a role for 4-octyl itaconate (4-OI) in anti-inflammatory and oxidative stress injury. However, the potential effects of 4-OI in AP have not been investigated. Caerulein and LPS were used to induce experimental AP models in mice and AR42J cells and then studied by histopathology, biochemical, and molecular analysis. Ferroptosis inhibitor ferrostatin-1 effectively improves pancreatic injury and reduces lipid peroxidation products in experimental AP mice. 4-OI treatment significantly alleviated pancreatic and AP-associated lung injury and inflammation in experimental AP mice by inhibiting ferroptosis. The ferroptosis activator Erastin blocked the protective effect of 4-OI against pancreatic injury in AP, validating that 4-OI alleviates pancreatitis injury through ferroptosis. In vitro experiments further confirmed that 4-OI treatment ameliorated AP-induced pancreatic injury by inhibiting ferroptosis. Our study, for the first time, found that 4-OI ameliorates AP and AP-related lung injury by inhibiting ferroptosis in experimental AP mice, providing a new therapeutic target for alleviating AP.

Itaconate and its derivatives as anti-pathogenic agents

Pathogenic microorganisms and viruses cause outbreaks and pandemics that affect millions of people worldwide. Despite recent advances in pharmacology and medicine, the ability of infectious diseases to spread in the modern era is accelerating due to various factors contributing to increased human-to-human and human-animal contacts. With the global rise of drug resistance among pathogens and frequently occurring viral outbreaks, alternative drugs and therapies that specifically inhibit microbial virulence or regulate immune responses are attracting growing interest. The present review focuses on itaconate and its derivatives as potential anti-pathogenic agents. It summarizes the current state of research on itaconate metabolism in bacteria, fungi and mammals. This is followed by a comprehensive review of recent advances studying itaconate and its derivatives as anti-inflammatory, immunoregulatory, antimicrobial and antiviral compounds, along with their mechanisms of action. Finally, the review emphasises the existing challenges and future research directions for the application of itaconate and its derivatives as anti-pathogenic agents.

Development of itaconate polymer microparticles for intracellular regulation of pro-inflammatory macrophage activation

Itaconate (IA) is an endogenous metabolite and a potent regulator of the innate immune system. Its use in immunomodulatory therapies has faced limitations due to inherent challenges in achieving controlled delivery and requirements for high extracellular concentrations to achieve internalization of the highly polar small molecule to achieve its intracellular therapeutic activity. Microparticle (MP)-based delivery strategies are a promising approach for intracellular delivery of small molecule metabolites through macrophage phagocytosis and subsequent intracellular polymer degradation-based delivery. Toward the goal of intracellular delivery of IA, degradable polyester polymer-(poly(itaconate-co-dodecanediol)) based IA polymer microparticles (IA-MPs) were generated using an emulsion method, forming micron-scale (∼ 1.5 µm) degradable microspheres. IA-MPs were characterized with respect to their material properties and IA release kinetics to inform particle fabrication. Treatment of murine bone marrow-derived macrophages with an optimized particle concentration of 0.1 mg/million cells enabled phagocytosis-mediated internalization and low levels of cytotoxicity. Flow cytometry demonstrated IA-MP-specific regulation of IA-sensitive inflammatory targets. Metabolic analyses demonstrated that IA-MP internalization inhibited oxidative metabolism and induced glycolytic reliance, consistent with the established mechanism of IA-associated inhibition of succinate dehydrogenase. This development of IA-based polymer microparticles provides a basis for additional innovative metabolite-based microparticle drug delivery systems for the treatment of inflammatory disease.

IRG1/itaconate enhances efferocytosis by activating Nrf2-TIM4 signaling pathway to alleviate con A induced autoimmune liver injury

Immune response gene 1 (IRG1) is highly expressed in mitochondria of macrophages in a pro-inflammatory state. IRG1 and its metabolites play important roles in infection, immune-related diseases and tumor progression by exerting resistance of pathogens, attenuating inflammation and producing antioxidant substances through various pathways and mechanisms. IRG1 deficiency aggravates liver injury. Efferocytosis is a vital mechanism for preventing the progression of inflammatory tissue damage. However, the mechanism by how IRG1/itaconate regulates efferocytosis in autoimmune hepatitis has yet to be fully understood. Therefore, we explored the influence of IRG1-/- on efferocytosis and its effects on regulating the nuclear factor erythroid 2-associated factor 2 (Nrf2)-T-cell immunoglobulin domain and mucin domain 4 (TIM4) pathway and autoimmune liver injury. An autoimmune hepatitis model was established by injecting Con A into wild-type and IRG1-/- mice via the tail vein. Liver injury and inflammatory response were assessed. The efferocytosis role of IRG1-/- macrophages and its potential regulatory mechanisms were also analysed. Exogenous 4-octyl itaconate (OI) supplementation promoted the expression of Nrf2 and TIM4 and restored IRG1-/- bone marrow-derived macrophage (BMDM) efferocytosis, whereas inhibition of Nrf2 mediated by ML385 led to impaired efferocytosis of BMDMs, decreased expression of TIM4, and aggravated liver inflammation injury. Additionally, after supplementing Nrf2-/- BMDMs with exogenous OI, we evaluated the changes in its efferocytosis effect, efferocytosis did not change, and the protective effect of OI disappeared. However, when TIM4 was blocked, the efferocytotic effect of BMDMs was attenuated, inflammatory liver injury and oxidative stress were aggravated. OI promoted the transformation of macrophages into M2 macrophages, and this was inhibited when TIM4 was blocked. To our best understanding, this is the initial exploration to show that TIM4, a downstream molecule of the IRG1/itaconate-Nrf2 pathway, regulates macrophage efferocytosis. These findings suggest a new mechanism and potential treatment for promoting the resolution of inflammation and efferocytosis in autoimmune hepatitis.

Itaconate transporter SLC13A3 confers immunotherapy resistance via alkylation-mediated stabilization of PD-L1

Itaconate is a metabolite catalyzed by cis-aconitate decarboxylase (ACOD1), which is mainly produced by activated macrophages and secreted into the extracellular environment to exert complex bioactivity. In the tumor microenvironment, itaconate is concentrated and induces an immunosuppressive response. However, whether itaconate can be taken up by tumor cells and its mechanism of action remain largely unclear. Here, we identified solute carrier family 13 member 3 (SLC13A3) as a key protein transporting extracellular itaconate into cells, where it elevates programmed cell death ligand 1 (PD-L1) protein levels and decreases the expression of immunostimulatory molecules, thereby promoting tumor immune evasion. Mechanistically, itaconate alkylates the cysteine 272 residue on PD-L1, antagonizing PD-L1 ubiquitination and degradation. Consequently, SLC13A3 inhibition enhances the efficacy of anti-CTLA-4 (cytotoxic T lymphocyte-associated antigen-4) immunotherapy and improves the overall survival rate in syngeneic mouse tumor models. Collectively, our findings identified SLC13A3 as a key transporter of itaconate and revealed its immunomodulatory role, providing combinatorial strategies to overcome immunotherapy resistance in tumors.

The Effects of Fisetin on Gene Expression Profile and Cellular Metabolism in IFN-γ-Stimulated Macrophage Inflammation

Although interferon-gamma (IFN-γ) is known as a critical factor in polarizing macrophages into the pro-inflammatory state for immune response, how dietary flavonoids regulate IFN-γ response for anti-inflammation is incompletely elucidated. This study aims to investigate the effect of fisetin, a typical flavonol, on the inhibition of IFN-γ-induced inflammation by RNA sequencing (RNA-Seq) and cellular metabolism analysis. RAW264 macrophages pretreated with fisetin following IFN-γ stimulation were subjected to RNA-Seq to analyze alterations in gene expression. Cellular signaling and transcription were investigated using enrichment analysis, motif analysis, and transcription factor prediction. Cellular metabolic state was assessed by measuring the oxygen consumption rate (OCR) and lactate level to reflect mitochondrial respiration and glycolysis. Alterations in signaling proteins were confirmed by Western blot. The results revealed that fisetin downregulated the IFN-γ-induced expression of pro-inflammatory genes and M1 marker genes such as Cxcl9, Il6, Cd80, Cd86, and Nos2. In cellular metabolism, fisetin upregulated the oxidative phosphorylation (OXPHOS) pathway, restored impaired OCR, and reduced lactate production induced by IFN-γ. Motif analysis suggested that fisetin suppressed the activation of IFN-regulatory factor 1 (IRF1). Western blot data further confirmed that fisetin inhibited the phosphorylation of Jak1, Jak2, and STAT1, and decreased the nuclear accumulation of phosphorylated STAT1 and IRF1 induced by IFN-γ. Taken together, our data revealed that fisetin is a potent flavonoid that attenuates IFN-γ-stimulated murine macrophage inflammation and ameliorates disrupted cellular metabolism with a possible Jak1/2-STAT1-IRF1 pathway.

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.

4-Octyl Itaconate Attenuates Neuroinflammation in Experimental Autoimmune Encephalomyelitis Via Regulating Microglia

Abnormal activation of microglia, the resident macrophages in the central nervous system, plays an important role in the pathogenesis of multiple sclerosis (MS). The immune responsive gene 1(IRG1)/itaconate axis is involved in regulating microglia-mediated neuroinflammation. 4-Octyl itaconate (4-OI), a derivative of itaconate, plays a crucial immunomodulatory role in macrophages. This study investigated the effects and mechanisms of action of 4-OI on experimental autoimmune encephalomyelitis (EAE) and inflammatory BV2 microglia. In an EAE mouse model, clinical evaluation was conducted during the disease course. Hematoxylin and eosin staining was performed to assess inflammatory infiltration and Luxol Fast Blue was used to visualize pathological damage. Quantitative real-time polymerase chain reaction, western blotting and immunofluorescence were used to evaluate inflammatory response and microglial function status in EAE mice. BV2 microglia were used to further investigate the effects and mechanisms of action of 4-OI in vitro. 4-OI significantly alleviated the clinical symptoms of EAE, the inflammatory infiltration, and demyelination; reduced the levels of inflammatory factors; and inhibited the classical activation of microglia in the spinal cord. 4-OI successfully suppressed the classical activation of BV2 microglia and decreased the levels of inflammatory factors by activating the Nrf2/HO-1 signaling pathway. Furthermore, 4-OI downregulated IRG1 expression in both EAE mice and inflammatory BV2 microglia. 4-OI attenuates the microglia-mediated neuroinflammation and has promising therapeutic effects in MS.

New anti-inflammatory mechanism of glucocorticoids uncovered

Glucocorticoids (GCs) are potent anti-inflammatory drugs. A new study by Auger et al. found that GCs increase itaconate, an anti-inflammatory tricarboxylic acid (TCA) cycle intermediate, by promoting movement of cytosolic pyruvate dehydrogenase (PDH) to mitochondria. Itaconate was sufficient for mediating the anti-inflammatory effects of GCs in mice, overriding the notion that nuclear glucocorticoid receptor (GR) is necessary for inflammation inhibition.

IĸBζ as a Central Modulator of Inflammatory Arthritis Pathogenesis

OBJECTIVE

Current therapies targeting individual factors in inflammatory arthritis show variable efficacy, often requiring treatment with combinations of drugs, and are associated with undesirable side effects. NF-ĸB is critical for the production and function of most inflammatory cytokines. However, given its essential role in physiologic processes, targeting NF-ĸB is precarious. Hence, identifying pathways downstream of NF-ĸB that selectively govern the expression of inflammatory cytokines in inflammatory arthritis would be advantageous. We have previously identified IĸBζ as a unique inflammatory signature of NF-ĸB that controls the transcription of inflammatory cytokines only under pathologic conditions while sparing physiologic NF-ĸB signals.

METHODS

We generated mice harboring myeloid, lymphoid, and global deletion of Nfkbiz (the gene encoding IĸBζ). These models were subjected to serum transfer-induced arthritis. Additionally, pharmacologic inhibitors of IĸBζ were injected intraperitonially. Joint swelling, microcomputed tomography, immunohistochemistry, flow cytometry, and cytokine measurements were conducted using synovial tissue samples.

RESULTS

Global deletion of Nfkbiz or depletion of neutrophils (vastly IĸBζ+ cells) reduced inflammatory synovial cells and increased anti-inflammatory and regenerative synovial cells, plummeted expression of inflammatory factors and ameliorated experimental mouse inflammatory arthritis. Further, expression of immune responsive gene-1, the enzyme responsible for itaconate production, was increased in synovial cells. Accordingly, the itaconate derivative dimethyl itaconate (DI) inhibited IĸBζ-mediated inflammatory factors. Further, in silico screen identified 8-hydroxyquinoline (HQ) as a putative inhibitor of IĸBζ not affecting physiologic NF-ĸB activity. Congruently, systemic administration of either DI or HQ inhibited joint swelling and damage.

CONCLUSION

Our study positions IĸBζ as an inflammation-specific target for therapeutic consideration in rheumatoid arthritis because its inhibition spares the beneficial functions of NF-ĸB.

Recent advances in surface functionalization of cardiovascular stents

Cardiovascular diseases (CVD) are the leading global threat to human health. The clinical application of vascular stents improved the survival rates and quality of life for patients with cardiovascular diseases. However, despite the benefits stents bring to patients, there are still notable complications such as thrombosis and in-stent restenosis (ISR). Surface modification techniques represent an effective strategy to enhance the clinical efficacy of vascular stents and reduce complications. This paper reviews the development strategies of vascular stents based on surface functional coating technologies aimed at addressing the limitations in clinical application, including the inhibition of intimal hyperplasia, promotion of re-endothelialization. These strategies have improved endothelial repair and inhibited vascular remodeling, thereby promoting vascular healing post-stent implantation. However, the pathological microenvironment of target vessels and the lipid plaques are key pathological factors in the development of atherosclerosis (AS) and impaired vascular repair after percutaneous coronary intervention (PCI). Therefore, restoring normal physiological environment and removing the plaques are also treatment focuses after PCI for promoting vascular repair. Unfortunately, research in this area is limited. This paper reviews the advancements in vascular stents based on surface engineering technologies over the past decade, providing guidance for the development of stents.

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.

Positive feedback loop involving AMPK and CLYBL acetylation links metabolic rewiring and inflammatory responses

Metabolic rewiring underlies effective macrophages defense to respond disease microenvironment. However, the underlying mechanisms driving metabolic rewiring to enhance macrophage effector functions remain unclear. Here, we demonstrated that the metabolic reprogramming in inflammatory macrophages depended on the acetylation of CLYBL, a citramalyl-CoA lyase, at lysine 154 (K154), and blocking CLYBL-K154 acetylation restricted the release of pro-inflammatory factors. Mechanistically, we found a crucial AMPK-CLYBL acetylation positive feedback loop, triggered by toll-like receptors (TLRs), involving AMPK hypophosphorylation and CLYBL hyperacetylation. The deacetylase enzyme SIRT2 acted as the bridge between AMPK phosphorylation and CLYBL acetylation, thereby regulating macrophage polarization and the release of pro-inflammatory cytokines. Furthermore, CLYBL hypoacetylation decreased monocyte infiltration, thereby alleviating cardiac remodeling. These findings suggest that the AMPK-CLYBL acetylation positive feedback loop serves as a metabolic switch driving inflammatory response and inhibiting CLYBL-K154 acetylation may offer a promising therapeutic strategy for inflammatory response-related disorders.

Mitochondrial fatty acid oxidation regulates monocytic type I interferon signaling via histone acetylation

Although lipid-derived acetyl-coenzyme A (CoA) is a major carbon source for histone acetylation, the contribution of fatty acid β-oxidation (FAO) to this process remains poorly characterized. To investigate this, we generated mitochondrial acetyl-CoA acetyltransferase 1 (ACAT1, distal FAO enzyme) knockout macrophages. 13C-carbon tracing confirmed reduced FA-derived carbon incorporation into histone H3, and RNA sequencing identified diminished interferon-stimulated gene expression in the absence of ACAT1. Chromatin accessibility at the Stat1 locus was diminished in ACAT1-/- cells. Chromatin immunoprecipitation analysis demonstrated reduced acetyl-H3 binding to Stat1 promoter/enhancer regions, and increasing histone acetylation rescued Stat1 expression. Interferon-β release was blunted in ACAT1-/- and recovered by ACAT1 reconstitution. Furthermore, ACAT1-dependent histone acetylation required an intact acetylcarnitine shuttle. Last, obese subjects' monocytes exhibited increased ACAT1 and histone acetylation levels. Thus, our study identifies an intriguing link between FAO-mediated epigenetic control of type I interferon signaling and uncovers a potential mechanistic nexus between obesity and type I interferon signaling.

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.

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.

Inhibition of Mitochondrial Succinate Dehydrogenase with Dimethyl Malonate Promotes M2 Macrophage Polarization by Enhancing STAT6 Activation

Macrophages exhibit diverse phenotypes depending on environment status, which contribute to physiological and pathological processes of immunological diseases, including sepsis, asthma, multiple sclerosis and colitis. The alternative activation of macrophages is tightly regulated to avoid excessive activation and damage of tissues and organs. Certain works characterized that succinate dehydrogenase (SDH) altered function of macrophages and promoted inflammatory response in M1 macrophages via mitochondrial reactive oxygen species (ROS). However, the effect of succinate dehydrogenase on M2 macrophage polarization remains incompletely understood. We employed dimethyl malonate (DMM) to inhibit succinate dehydrogenase activity and took use of RNA-seq to analyze the changes of inflammatory response of LPS-activated M1 macrophages or IL 4-activated M2 macrophages. Our data revealed that inhibition of SDH with DMM increased expression of M2 macrophages-associated signature genes, including Arg1, Ym1 and Mrc1. Consistent with previous work, we also observed that inhibition of SDH decreased the expression of IL-1β and enhanced the levels of IL-10 in M1 macrophages. Additionally, inhibition of SDH with DMM inhibited the production of chemokines, such as Cxcl3, Cxcl12, Ccl20 and Ccl9. DMM also amplified the M2 macrophages-related signature genes in IL-13-activated M2 macrophages. Mechanistic studies revealed that DMM promoted M2 macrophages polarization through mitochondrial ROS dependent STAT6 activation. Blocking ROS with mitoTEMPO or inhibiting STAT6 activation with ruxolitinib abrogated the promotion effect of DMM on M2 macrophages. Finally, dimethyl malonate treatment promoted peritoneal M2 macrophages differentiation and exacerbated OVA-induced allergy asthma in vivo. Collectively, we identified SDH as a braker to suppress M2 macrophage polarization via mitochondrial ROS, suggesting a novel strategy to treatment of M2 macrophages-mediated inflammatory diseases.