Oxidative metabolism and PGC-1beta attenuate macrophage-mediated inflammation

Immunometabolism in the tumor microenvironment and its related research progress

The tumor immune microenvironment has been a research hot spot in recent years. The cytokines and metabolites in the microenvironment can promote the occurrence and development of tumor in various ways and help tumor cells get rid of the surveillance of the immune system and complete immune escape. Many studies have shown that the existence of tumor microenvironment is an important reason for the failure of immunotherapy. The impact of the tumor microenvironment on tumor is a systematic study. The current research on this aspect may be only the tip of the iceberg, and a relative lack of integrity, may be related to the heterogeneity of tumor. This review mainly discusses the current status of glucose metabolism and lipid metabolism in the tumor microenvironment, including the phenotype of glucose metabolism and lipid metabolism in the microenvironment; the effects of these metabolic methods and their metabolites on three important immune cells Impact: regulatory T cells (Tregs), tumor-associated macrophages (TAM), natural killer cells (NK cells); and the impact of metabolism in the targeted microenvironment on immunotherapy. At the end of this article,the potential relationship between Ferroptosis and the tumor microenvironment in recent years is also briefly described.

Intramyocardial hemorrhage drives fatty degeneration of infarcted myocardium

Sudden blockage of arteries supplying the heart muscle contributes to millions of heart attacks (myocardial infarction, MI) around the world. Although re-opening these arteries (reperfusion) saves MI patients from immediate death, approximately 50% of these patients go on to develop chronic heart failure (CHF) and die within a 5-year period; however, why some patients accelerate towards CHF while others do not remains unclear. Here we show, using large animal models of reperfused MI, that intramyocardial hemorrhage - the most damaging form of reperfusion injury (evident in nearly 40% of reperfused ST-elevation MI patients) - drives delayed infarct healing and is centrally responsible for continuous fatty degeneration of the infarcted myocardium contributing to adverse remodeling of the heart. Specifically, we show that the fatty degeneration of the hemorrhagic MI zone stems from iron-induced macrophage activation, lipid peroxidation, foam cell formation, ceroid production, foam cell apoptosis and iron recycling. We also demonstrate that timely reduction of iron within the hemorrhagic MI zone reduces fatty infiltration and directs the heart towards favorable remodeling. Collectively, our findings elucidate why some, but not all, MIs are destined to CHF and help define a potential therapeutic strategy to mitigate post-MI CHF independent of MI size.

Self-Renewal of Macrophages: Tumor-Released Factors and Signaling Pathways

Macrophages are the most abundant immune cells of the tumor microenvironment (TME) and have multiple important functions in cancer. During tumor growth, both tissue-resident macrophages and newly recruited monocyte-derived macrophages can give rise to tumor-associated macrophages (TAMs), which have been associated with poor prognosis in most cancers. Compelling evidence indicate that the high degree of plasticity of macrophages and their ability to self-renew majorly impact tumor progression and resistance to therapy. In addition, the microenvironmental factors largely affect the metabolism of macrophages and may have a major influence on TAMs proliferation and subsets functions. Thus, understanding the signaling pathways regulating TAMs self-renewal capacity may help to identify promising targets for the development of novel anticancer agents. In this review, we focus on the environmental factors that promote the capacity of macrophages to self-renew and the molecular mechanisms that govern TAMs proliferation. We also highlight the impact of tumor-derived factors on macrophages metabolism and how distinct metabolic pathways affect macrophage self-renewal.

PGC-1β maintains mitochondrial metabolism and restrains inflammatory gene expression

Metabolic programming of the innate immune cells known as dendritic cells (DCs) changes in response to different stimuli, influencing their function. While the mechanisms behind increased glycolytic metabolism in response to inflammatory stimuli are well-studied, less is known about the programming of mitochondrial metabolism in DCs. We used lipopolysaccharide (LPS) and interferon-β (IFN-β), which differentially stimulate the use of glycolysis and oxidative phosphorylation (OXPHOS), respectively, to identify factors important for mitochondrial metabolism. We found that the expression of peroxisome proliferator-activated receptor gamma co-activator 1β (PGC-1β), a transcriptional co-activator and known regulator of mitochondrial metabolism, decreases when DCs are activated with LPS, when OXPHOS is diminished, but not with IFN-β, when OXPHOS is maintained. We examined the role of PGC-1β in bioenergetic metabolism of DCs and found that PGC-1β deficiency indeed impairs their mitochondrial respiration. PGC-1β-deficient DCs are more glycolytic compared to controls, likely to compensate for reduced OXPHOS. PGC-1β deficiency also causes decreased capacity for ATP production at steady state and in response to IFN-β treatment. Loss of PGC-1β in DCs leads to increased expression of genes in inflammatory pathways, and reduced expression of genes encoding proteins important for mitochondrial metabolism and function. Collectively, these results demonstrate that PGC-1β is a key regulator of mitochondrial metabolism and negative regulator of inflammatory gene expression in DCs.

Sevoflurane exposure induces neurotoxicity by regulating mitochondrial function of microglia due to NAD insufficiency

Developmental neurons received with sevoflurane, the commonly used inhalational anesthetic agent in clinical surgery, several times tend to be destroyed. Microglia, the resident immune cells of the central nervous system (CNS), are activated after sevoflurane exposure, accompanied by releasing proinflammatory cytokines that damage developing neurons. The sevoflurane-induced neurotoxicity could be attributed to activated microglia presenting proinflammatory and anti-inflammatory functions. Proinflammatory microglia release cytokines to impair the CNS, while anti-inflammatory microglia engulf damaged neurons to maintain CNS homeostasis. Sevoflurane exposure promotes the secretion of proinflammatory cytokines by microglia, inhibiting the microglial phagocytic function. Microglia with poor phagocytic function cannot engulf damaged neurons, leading to the accumulation of damaged neurons. The mechanism underlying poor phagocytic function may be attributed to mitochondrial dysfunction of microglia induced by sevoflurane exposure, in which affected mitochondria cannot generate adequate ATP and NAD to satisfy the energy demand. We discovered that sevoflurane treatment impaired the mitochondrial metabolism of microglia, which resulted in NAD deficiency and couldn’t produce sufficient energy to clear damaged neurons to maintain CNS development. Our findings provide an explanation of a new mechanism underlying sevoflurane-induced neurotoxicity.

An anti-inflammatory activation sequence governs macrophage transcriptional dynamics during tissue injury in zebrafish

Macrophages are essential for tissue repair and regeneration. Yet, the molecular programs, as well as the timing of their activation during and after tissue injury are poorly defined. Using a high spatio-temporal resolution single cell analysis of macrophages coupled with live imaging after sensory hair cell death in zebrafish, we find that the same population of macrophages transitions through a sequence of three major anti-inflammatory activation states. Macrophages first show a signature of glucocorticoid activation, then IL-10 signaling and finally the induction of oxidative phosphorylation by IL-4/Polyamine signaling. Importantly, loss-of-function of glucocorticoid and IL-10 signaling shows that each step of the sequence is independently activated. Lastly, we show that IL-10 and IL-4 signaling act synergistically to promote synaptogenesis between hair cells and efferent neurons during regeneration. Our results show that macrophages, in addition to a switch from M1 to M2, sequentially and independently transition though three anti-inflammatory pathways in vivo during tissue injury in a regenerating organ.

Effects of acute intravenous lipopolysaccharide administration on the plasma lipidome and metabolome in lactating Holstein cows experiencing hyperlipidemia

INTRODUCTION

The effects of lipopolysaccharides (i.e., endotoxin; LPS) on metabolism are poorly defined in lactating dairy cattle experiencing hyperlipidemia.

OBJECTIVES

Our objective was to explore the effects of acute intravenous LPS administration on metabolism in late-lactation Holstein cows experiencing hyperlipidemia induced by intravenous triglyceride infusion and feed restriction.

METHODS

Ten non-pregnant lactating Holstein cows (273 ± 35 d in milk) were administered a single bolus of saline (3 mL of saline; n [Formula: see text] 5) or LPS (0.375 [Formula: see text]g of LPS/kg of body weight; n [Formula: see text] 5). Simultaneously, cows were intravenously infused a triglyceride emulsion and feed restricted for 16 h to induce hyperlipidemia in an attempt to model the periparturient period. Blood was sampled at routine intervals. Changes in circulating total fatty acid concentrations and inflammatory parameters were measured. Plasma samples were analyzed using untargeted lipidomics and metabolomics.

RESULTS

Endotoxin increased circulating serum amyloid A, LPS-binding protein, and cortisol concentrations. Endotoxin administration decreased plasma lysophosphatidylcholine (LPC) concentrations and increased select plasma ceramide concentrations. These outcomes suggest modulation of the immune response and insulin action. Lipopolysaccharide decreased the ratio of phosphatidylcholine to phosphatidylethanomanine, which potentially indicate a decrease in the hepatic activation of phosphatidylethanolamine N-methyltransferase and triglyceride export. Endotoxin administration also increased plasma concentrations of pyruvic and lactic acids, and decreased plasma citric acid concentrations, which implicate the upregulation of glycolysis and downregulation of the citric acid cycle (i.e., the Warburg effect), potentially in leukocytes.

CONCLUSION

Acute intravenous LPS administration decreased circulating LPC concentrations, modified ceramide and glycerophospholipid concentrations, and influenced intermediary metabolism in dairy cows experiencing hyperlipidemia.

The matricellular protein SPARC induces inflammatory interferon-response in macrophages during aging

The risk of chronic diseases caused by aging is reduced by caloric restriction (CR)-induced immunometabolic adaptation. Here, we found that the matricellular protein, secreted protein acidic and rich in cysteine (SPARC), was inhibited by 2 years of 14% sustained CR in humans and elevated by obesity. SPARC converted anti-inflammatory macrophages into a pro-inflammatory phenotype with induction of interferon-stimulated gene (ISG) expression via the transcription factors IRF3/7. Mechanistically, SPARC-induced ISGs were dependent on toll-like receptor-4 (TLR4)-mediated TBK1, IRF3, IFN-β, and STAT1 signaling without engaging the Myd88 pathway. Metabolically, SPARC dampened mitochondrial respiration, and inhibition of glycolysis abrogated ISG induction by SPARC in macrophages. Furthermore, the N-terminal acidic domain of SPARC was required for ISG induction, while adipocyte-specific deletion of SPARC reduced inflammation and extended health span during aging. Collectively, SPARC, a CR-mimetic adipokine, is an immunometabolic checkpoint of inflammation and interferon response that may be targeted to delay age-related metabolic and functional decline.

BAFF antagonism via the BAFF receptor 3 binding site attenuates BAFF 60-mer-induced classical NF-κB signaling and metabolic reprogramming of B cells

Human recombinant B cell activating factor (BAFF) is secreted as 3-mers, which can associate to form 60-mers in culture supernatants. However, the presence of BAFF multimers in humans is still debated and it is incompletely understood how BAFF multimers activate the B cells. Here, we demonstrate that BAFF can exist as 60-mers or higher order multimers in human plasma. In vitro, BAFF 60-mer strongly induced the transcriptome of B cells which was partly attenuated by antagonism using a soluble fragment of BAFF receptor 3. Furthermore, compared to BAFF 3-mer, BAFF 60-mer strongly induced a transient classical and prolonged alternate NF-κB signaling, glucose oxidation by both aerobic glycolysis and oxidative phosphorylation, and succinate utilization by mitochondria. BAFF antagonism selectively attenuated classical NF-κB signaling and glucose oxidation. Altogether, our results suggest critical roles of BAFF 60-mer and its BAFF receptor 3 binding site in hyperactivation of B cells.

Immunometabolism of macrophages regulates skeletal muscle regeneration

Sarcopenia is an age-related progressive loss of skeletal muscle mass, quality, and strength disease. In addition, sarcopenia is tightly correlated with age-associated pathologies, such as sarcopenic obesity and osteoporosis. Further understanding of disease mechanisms and the therapeutic strategies in muscle regeneration requires a deeper knowledge of the interaction of skeletal muscle and other cells in the muscle tissue. Skeletal muscle regeneration is a complex process that requires a series of highly coordinated events involving communication between muscle stem cells and niche cells, such as muscle fibro/adipogenic progenitors and macrophages. Macrophages play a critical role in tissue regeneration and the maintenance of muscle homeostasis by producing growth factors and cytokines that regulate muscle stem cells and myofibroblast activation. Furthermore, the aging-related immune dysregulation associated with the release of trophic factors and the polarization in macrophages transiently affect the inflammatory phase and impair muscle regeneration. In this review, we focus on the role and regulation of macrophages in skeletal muscle regeneration and homeostasis. The aim of this review is to highlight the important roles of macrophages as a therapeutic target in age-related sarcopenia and the increasing understanding of how macrophages are regulated will help to advance skeletal muscle regeneration.

The emerging role of microbiota-derived short-chain fatty acids in immunometabolism

The accumulating evidence revealed that microbiota plays a significant function in training, function, and the induction of host immunity. Once this interaction (immune system-microbiota) works correctly, it enables the production of protective responses against pathogens and keeps the regulatory pathways essential for maintaining tolerance to innocent antigens. This concept of immunity and metabolic activity redefines the realm of immunometabolism, paving the way for innovative therapeutic interventions to modulate immune cells through immune metabolic alterations. A body of evidence suggests that microbiota-derived metabolites, including short-chain fatty acids (SCFAs) such as butyrate, acetate, and propionate, play a key role in immune balance. SCFAs act on many cell types to regulate various vital biological processes, including host metabolism, intestinal function, and the immune system. Such SCFAs generated by gut bacteria also impact immunity, cellular function, and immune cell fate. This is a new concept of immune metabolism, and better knowledge about how lifestyle affects intestinal immunometabolism is crucial for preventing and treating disease. In this review article, we explicitly focus on the function of SCFAs in the metabolism of immune cells, especially macrophages, neutrophils, dendritic cells (DCs), B cells, T (Th) helper cells, and cytotoxic T cells (CTLs).

Novel insights into the regulation of cellular catabolic metabolism in macrophages through nuclear receptors

Regulation of cellular catabolic metabolism in immune cells has recently become a major concept for resolution of inflammation. Nuclear receptors (NRs), including peroxisome proliferator activator receptors (PPARs), 1,25-dihydroxyvitamin D(3) receptor (VDR), liver X receptors (LXRs), glucocorticoid receptors (GRs), estrogen-related receptor α (ERRα) and Nur77, have been identified as major modulators of inflammation, affecting innate immune cells, such as macrophages. Evidence emerges on how NRs regulate cellular metabolism in macrophages during inflammatory processes and contribute to the resolution of inflammation. This could have new implications for our understanding of how NRs shape immune responses and inform anti-inflammatory drug design. This review will highlight the recent developments about NRs and their role in cellular metabolism in macrophages.

Escherichia coli O88 induces intestinal damage and inflammatory response through the oxidative phosphorylation and ribosome pathway in Pekin ducks

Colibacillosis is one of the major health threats in the poultry industry worldwide. Understanding the pathogenic mechanisms involved in Escherichia coli-induced inflammatory response may lead to the development of new therapies to combat the disease. To address this, a total of 96 1-day-old male lean Pekin ducklings were employed and randomly allocated to two treatments, each with six replicates of eight ducks. Ducks in the experiment group (EG) and the control group (CG) were separately orally administered with 0.2 ml of pathogenic E. coli O88 (3 × 109 CFU/ml) or equivalent volumes of 0.9% sterile saline solution on day 7, two times with an 8-h interval. Serum and intestinal samples were collected on days 9, 14, and 28. Results showed that ducks challenged with E. coli had lower average daily gain and higher feed intake/weight gain during days 9–14 and overall (P < 0.05). Histopathological examination showed that E. coli decreased the villus height and the ratio of villus height/crypt depth in the jejunum (P < 0.05) on days 9 and 14. The intestinal barrier was disrupted, presenting in E. coli ducks having higher serum DAO and D-LA on days 9 and 14 (P < 0.05) and greater content of serum LPS on day 9 (P < 0.05). Escherichia coli infection also triggered a systemic inflammatory response including the decrease of the serum IgA, IgM, and jejunal sIgA on day 14 (P < 0.05). In addition to these, 1,062 differentially expressed genes were detected in the jejunum tissues of ducks by RNA-seq, consisting of 491 upregulated and 571 downregulated genes. Based on the KEGG database, oxidative phosphorylation and the ribosome pathway were the most enriched. These findings reveal the candidate pathways and genes that may be involved in E. coli infection, allow a better understanding of the molecular mechanisms of inflammation progression and may facilitate the genetic improvement of ducks, and provide further insights to tackle the drug sensitivity and animal welfare issues.

Macrophage Polarization Mediated by Mitochondrial Dysfunction Induces Adipose Tissue Inflammation in Obesity

Obesity is one of the prominent global health issues, contributing to the growing prevalence of insulin resistance and type 2 diabetes. Chronic inflammation in adipose tissue is considered as a key risk factor for the development of insulin resistance and type 2 diabetes in obese individuals. Macrophages are the most abundant immune cells in adipose tissue and play an important role in adipose tissue inflammation. Mitochondria are critical for regulating macrophage polarization, differentiation, and survival. Changes to mitochondrial metabolism and physiology induced by extracellular signals may underlie the corresponding state of macrophage activation. Macrophage mitochondrial dysfunction is a key mediator of obesity-induced macrophage inflammatory response and subsequent systemic insulin resistance. Mitochondrial dysfunction drives the activation of the NLRP3 inflammasome, which induces the release of IL-1β. IL-1β leads to decreased insulin sensitivity of insulin target cells via paracrine signaling or infiltration into the systemic circulation. In this review, we discuss the new findings on how obesity induces macrophage mitochondrial dysfunction and how mitochondrial dysfunction induces NLRP3 inflammasome activation. We also summarize therapeutic approaches targeting mitochondria for the treatment of diabetes.

Microenvironment in Oral Potentially Malignant Disorders: Multi-Dimensional Characteristics and Mechanisms of Carcinogenesis

Oral potentially malignant disorders (OPMDs) are a group of diseases involving the oral mucosa and that have a risk of carcinogenesis. The microenvironment is closely related to carcinogenesis and cancer progression by regulating the immune response, cell metabolic activities, and mechanical characteristics. Meanwhile, there are extensive interactions between the microenvironments that remodel and provide favorable conditions for cancer initiation. However, the changes, exact roles, and interactions of microenvironments during the carcinogenesis of OPMDs have not been fully elucidated. Here, we present an updated landscape of the microenvironments in OPMDs, emphasizing the changes in the immune microenvironment, metabolic microenvironment, mechanical microenvironment, and neural microenvironment during carcinogenesis and their carcinogenic mechanisms. We then propose an immuno–metabolic–mechanical–neural interaction network to describe their close relationships. Lastly, we summarize the therapeutic strategies for targeting microenvironments, and provide an outlook on future research directions and clinical applications. This review depicts a vivid microenvironment landscape and sheds light on new strategies to prevent the carcinogenesis of OPMDs.

Elp3-mediated codon-dependent translation promotes mTORC2 activation and regulates macrophage polarization

Macrophage polarization is a process whereby macrophages acquire distinct effector states (M1 or M2) to carry out multiple and sometimes opposite functions. We show here that translational reprogramming occurs during macrophage polarization and that this relies on the Elongator complex subunit Elp3, an enzyme that modifies the wobble uridine base U34 in cytosolic tRNAs. Elp3 expression is downregulated by classical M1‐activating signals in myeloid cells, where it limits the production of pro‐inflammatory cytokines via FoxO1 phosphorylation, and attenuates experimental colitis in mice. In contrast, alternative M2‐activating signals upregulate Elp3 expression through a PI3K‐ and STAT6‐dependent signaling pathway. The metabolic reprogramming linked to M2 macrophage polarization relies on Elp3 and the translation of multiple candidates, including the mitochondrial ribosome large subunit proteins Mrpl3, Mrpl13, and Mrpl47. By promoting translation of its activator Ric8b in a codon‐dependent manner, Elp3 also regulates mTORC2 activation. Elp3 expression in myeloid cells further promotes Wnt‐driven tumor initiation in the intestine by maintaining a pool of tumor‐associated macrophages exhibiting M2 features. Collectively, our data establish a functional link between tRNA modifications, mTORC2 activation, and macrophage polarization.

Metabolic reprogramming consequences of sepsis: adaptations and contradictions

During sepsis, the importance of alterations in cell metabolism is underappreciated. The cellular metabolism, which has a variable metabolic profile in different cells and disease stages, is largely responsible for the immune imbalance and organ failure associated with sepsis. Metabolic reprogramming, in which glycolysis replaces OXPHOS as the main energy-producing pathway, is both a requirement for immune cell activation and a cause of immunosuppression. Meanwhile, the metabolites produced by OXPHOS and glycolysis can act as signaling molecules to control the immune response during sepsis. Sepsis-induced "energy shortage" leads to stagnated cell function and even organ dysfunction. Metabolic reprogramming can alleviate the energy crisis to some extent, enhance host tolerance to maintain cell survival functions, and ultimately increase the adaptation of cells during sepsis. However, a switch from glycolysis to OXPHOS is essential for restoring cell function. This review summarized the crosstalk between metabolic reprogramming and immune cell activity as well as organ function during sepsis, discussed the benefits and drawbacks of metabolic reprogramming to show the contradictions of metabolic reprogramming during sepsis, and assessed the feasibility of treating sepsis through targeted metabolism. Using metabolic reprogramming to achieve metabolic homeostasis could be a viable therapy option for sepsis.

Regulation of metabolic and transcriptional responses by the thyroid hormone in cellular models of murine macrophages

Oncogene-immortalized bone marrow-derived macrophages are considered to be a good model for the study of immune cell functions, but the factors required for their survival and proliferation are still unknown. Although the effect of the thyroid hormones on global metabolic and transcriptional responses in macrophages has not yet been examined, there is increasing evidence that they could modulate macrophage functions. We show here that the thyroid hormone T3 is an absolute requirement for the growth of immortal macrophages. The hormone regulates the activity of the main signaling pathways required for proliferation and anabolic processes, including the phosphorylation of ERK and p38 MAPKs, AKT, ribosomal S6 protein, AMPK and Sirtuin-1. T3 also alters the levels of metabolites controlling transcriptional and post-transcriptional actions in macrophages, and causes widespread transcriptomic changes, up-regulating genes needed for protein synthesis and cell proliferation, while down-regulating genes involved in immune responses and endocytosis, among others. This is not observed in primary bone marrow-derived macrophages, where only p38 and AMPK activation is regulated by T3 and in which the metabolic and transcriptomic effects of the hormone are much weaker. However, the response to IFN-γ is reduced by T3 similarly in immortalized macrophages and in the primary cells, confirming previous results showing that the thyroid hormones can antagonize JAK/STAT-mediated signaling. These results provide new perspectives on the relevant pathways involved in proliferation and survival of macrophage cell culture models and on the crosstalk between the thyroid hormones and the immune system.

Macrophage Polarization, Metabolic Reprogramming, and Inflammatory Effects in Ischemic Heart Disease

Macrophages are highly plastic cells, and the polarization-activating actions that represent their functional focus are closely related to metabolic reprogramming. The metabolic reprogramming of macrophages manifests itself as a bias toward energy utilization, transforming their inflammatory phenotype by changing how they use energy. Metabolic reprogramming effects crosstalk with the biological processes of inflammatory action and are key to the inflammatory function of macrophages. In ischemic heart disease, phenotypic polarization and metabolic shifts in circulating recruitment and tissue-resident macrophages can influence the balance of inflammatory effects in the heart and determine disease regression and prognosis. In this review, we present the intrinsic link between macrophage polarization and metabolic reprogramming, discussing the factors that regulate macrophages in the inflammatory effects of ischemic heart disease. Our aim is to estabilsh reliable regulatory pathways that will allow us to better target the macrophage metabolic reprogramming process and improve the symptoms of ischemic heart disease.

TNFα-induced metabolic reprogramming drives an intrinsic anti-viral state

Cytokines induce an anti-viral state, yet many of the functional determinants responsible for limiting viral infection are poorly understood. Here, we find that TNFα induces significant metabolic remodeling that is critical for its anti-viral activity. Our data demonstrate that TNFα activates glycolysis through the induction of hexokinase 2 (HK2), the isoform predominantly expressed in muscle. Further, we show that glycolysis is broadly important for TNFα-mediated anti-viral defense, as its inhibition attenuates TNFα’s ability to limit the replication of evolutionarily divergent viruses. TNFα was also found to modulate the metabolism of UDP-sugars, which are essential precursor substrates for glycosylation. Our data indicate that TNFα increases the concentration of UDP-glucose, as well as the glucose-derived labeling of UDP-glucose and UDP-N-acetyl-glucosamine in a glycolytically-dependent manner. Glycolysis was also necessary for the TNFα-mediated accumulation of several glycosylated anti-viral proteins. Consistent with the importance of glucose-driven glycosylation, glycosyl-transferase inhibition attenuated TNFα’s ability to promote the anti-viral cell state. Collectively, our data indicate that cytokine-mediated metabolic remodeling is an essential component of the anti-viral response.

Viral infection often activates a host cell’s intrinsic immune response resulting in the cellular secretion of cytokines, important host-defense molecules. These cytokines act on neighboring cells to make them less permissive to viral infection. Many of the mechanisms through which cytokines promote a less permissive cell state remain unclear. Our data indicate that treatment with the anti-viral cytokine TNFα induces substantial changes to cellular metabolic activity, including activating glucose metabolism. We find that these TNFα-induced metabolic changes are critical for TNFα to limit the replication of diverse viruses including Human Cytomegalovirus and two Coronaviruses, OC43 and SARS-CoV-2. Inhibition of glucose metabolism during TNFα treatment prevented the expression of a variety of known cellular anti-viral proteins. Collectively, our data indicate that cytokine-induced metabolic remodeling is an important component of TNFα’s ability to promote a less permissive cell state and raises further questions about the mechanisms through which specific cytokine-induced metabolic activities contribute to various aspects of anti-viral defense.

Metabolic Reprogramming Induces Macrophage Polarization in the Tumor Microenvironment

Macrophages are one of the most important cells in the innate immune system, they are converted into two distinct subtypes with completely different molecular phenotypes and functional features under different stimuli of the microenvironment: M1 macrophages induced by IFN-γ/lipopolysaccharides(LPS) and M2 macrophages induced by IL-4/IL-10/IL-13. Tumor-associated macrophages (TAMs) differentiate from macrophages through various factors in the tumor microenvironment (TME). TAMs have the phenotype and function of M2 macrophages and are capable of secreting multiple cytokines to promote tumor progression. Both tumor cells and macrophages can meet the energy needs for rapid cell growth and proliferation through metabolic reprogramming, so a comprehensive understanding of pro-tumor and antitumor metabolic switches in TAM is essential to understanding immune escape mechanisms. This paper focuses on the functions of relevant signaling pathways and cytokines during macrophage polarization and metabolic reprogramming, and briefly discusses the effects of different microenvironments and macrophage pathogenicity, in addition to describing the research progress of inhibitory drugs for certain metabolic and polarized signaling pathways.

Acylcarnitines: Nomenclature, Biomarkers, Therapeutic Potential, Drug Targets, and Clinical Trials

Acylcarnitines are fatty acid metabolites that play important roles in many cellular energy metabolism pathways. They have historically been used as important diagnostic markers for inborn errors of fatty acid oxidation and are being intensively studied as markers of energy metabolism, deficits in mitochondrial and peroxisomal β -oxidation activity, insulin resistance, and physical activity. Acylcarnitines are increasingly being identified as important indicators in metabolic studies of many diseases, including metabolic disorders, cardiovascular diseases, diabetes, depression, neurologic disorders, and certain cancers. The US Food and Drug Administration-approved drug L-carnitine, along with short-chain acylcarnitines (acetylcarnitine and propionylcarnitine), is now widely used as a dietary supplement. In light of their growing importance, we have undertaken an extensive review of acylcarnitines and provided a detailed description of their identity, nomenclature, classification, biochemistry, pathophysiology, supplementary use, potential drug targets, and clinical trials. We also summarize these updates in the Human Metabolome Database, which now includes information on the structures, chemical formulae, chemical/spectral properties, descriptions, and pathways for 1240 acylcarnitines. This work lays a solid foundation for identifying, characterizing, and understanding acylcarnitines in human biosamples. We also discuss the emerging opportunities for using acylcarnitines as biomarkers and as dietary interventions or supplements for many wide-ranging indications. The opportunity to identify new drug targets involved in controlling acylcarnitine levels is also discussed. SIGNIFICANCE STATEMENT: This review provides a comprehensive overview of acylcarnitines, including their nomenclature, structure and biochemistry, and use as disease biomarkers and pharmaceutical agents. We present updated information contained in the Human Metabolome Database website as well as substantial mapping of the known biochemical pathways associated with acylcarnitines, thereby providing a strong foundation for further clarification of their physiological roles.

Glycolysis in Innate Immune Cells Contributes to Autoimmunity

Autoimmune diseases (AIDs) refer to connective tissue inflammation caused by aberrant autoantibodies resulting from dysfunctional immune surveillance. Most of the current treatments for AIDs use non-selective immunosuppressive agents. Although these therapies successfully control the disease process, patients experience significant side effects, particularly an increased risk of infection. There is a great need to study the pathogenesis of AIDs to facilitate the development of selective inhibitors for inflammatory signaling to overcome the limitations of traditional therapies. Immune cells alter their predominant metabolic profile from mitochondrial respiration to glycolysis in AIDs. This metabolic reprogramming, known to occur in adaptive immune cells, i.e., B and T lymphocytes, is critical to the pathogenesis of connective tissue inflammation. At the cellular level, this metabolic switch involves multiple signaling molecules, including serine–threonine protein kinase, mammalian target of rapamycin, and phosphoinositide 3-kinase. Although glycolysis is less efficient than mitochondrial respiration in terms of ATP production, immune cells can promote disease progression by enhancing glycolysis to satisfy cellular functions. Recent studies have shown that active glycolytic metabolism may also account for the cellular physiology of innate immune cells in AIDs. However, the mechanism by which glycolysis affects innate immunity and participates in the pathogenesis of AIDs remains to be elucidated. Therefore, we reviewed the molecular mechanisms, including key enzymes, signaling pathways, and inflammatory factors, that could explain the relationship between glycolysis and the pro-inflammatory phenotype of innate immune cells such as neutrophils, macrophages, and dendritic cells. Additionally, we summarize the impact of glycolysis on the pathophysiological processes of AIDs, including systemic lupus erythematosus, rheumatoid arthritis, vasculitis, and ankylosing spondylitis, and discuss potential therapeutic targets. The discovery that immune cell metabolism characterized by glycolysis may regulate inflammation broadens the avenues for treating AIDs by modulating immune cell metabolism.

The mitochondrial pyruvate carrier at the crossroads of intermediary metabolism

Pyruvate metabolism, a central nexus of carbon homeostasis, is an evolutionarily conserved process and aberrant pyruvate metabolism is associated with and contributes to numerous human metabolic disorders including diabetes, cancer, and heart disease. As a product of glycolysis, pyruvate is primarily generated in the cytosol before being transported into the mitochondrion for further metabolism. Pyruvate entry into the mitochondrial matrix is a critical step for efficient generation of reducing equivalents and ATP and for the biosynthesis of glucose, fatty acids, and amino acids from pyruvate. However, for many years, the identity of the carrier protein(s) that transported pyruvate into the mitochondrial matrix remained a mystery. In 2012, the molecular-genetic identification of the mitochondrial pyruvate carrier (MPC), a heterodimeric complex composed of protein subunits MPC1 and MPC2, enabled studies that shed light on the many metabolic and physiological processes regulated by pyruvate metabolism. A better understanding of the mechanisms regulating pyruvate transport and the processes affected by pyruvate metabolism may enable novel therapeutics to modulate mitochondrial pyruvate flux to treat a variety of disorders. Herein, we review our current knowledge of the MPC, discuss recent advances in the understanding of mitochondrial pyruvate metabolism in various tissue and cell types, and address some of the outstanding questions relevant to this field.

Cyclosporine A regulates PMN-MDSCs viability and function through MPTP in acute GVHD: Old medication, new target

Myeloid-derived suppressor cells (MDSCs), a population of myeloid lineage cells with immunosuppressive capacity, can mitigate acute graft-versus-host disease (aGVHD) after allogeneic hematopoietic stem cell transplantation (allo-HSCT). We previously found that the immunosuppressive function of polymorphonuclear population (PMN-MDSCs) was impaired in aGVHD milieu. The aim of this study was to explore the intrinsic mechanism regulating the fate and function of donor-derived PMN-MDSCs during allo-HSCT. We firstly found that mitochondrial permeability transition pore (MPTP) opened in the PMN-MDSCs in response to the intense inflammatory environment of aGVHD, which induced mitochondrial damage, oxidative stress, and apoptosis of PMN-MDSCs. Inhibiting MPTP opening by a traditional immunosuppressant, cyclosporine A (CsA), could restore the immunosuppressive function and viability of PMN-MDSCs in vitro and in vivo, which reveals a new mechanism of CsA application.

Integrative understanding of immune-metabolic interaction

Recent studies have revealed that the immune system plays a critical role in various physiological processes beyond its classical pathogen control activity. Even under a sterile condition, various cells and tissues can utilize the immune system to meet a specific demand for proper physiological functions. Particularly, a strong link between immunity and metabolism has been identified. Studies have identified the reciprocal regulation between these two systems. For example, immune signals can regulate metabolism, and metabolism (cellular or systemic) can regulate immunity. In this review, we will summarize recent findings on this reciprocal regulation between immunity and metabolism, and discuss potential biological rules behind this interaction with integrative perspectives.

Fungal Patterns Induce Cytokine Expression through Fluxes of Metabolic Intermediates That Support Glycolysis and Oxidative Phosphorylation

Cytokine expression is fine-tuned by metabolic intermediates, which makes research on immunometabolism suitable to yield drugs with a wider prospect of application than the biological therapies that block proinflammatory cytokines. Switch from oxidative phosphorylation (OXPHOS) to glycolysis has been considered a characteristic feature of activated immune cells. However, some stimuli might enhance both routes concomitantly. The connection between the tricarboxylic acid cycle and cytokine expression was scrutinized in human monocyte-derived dendritic cells stimulated with the fungal surrogate zymosan. Results showed that nucleocytosolic citrate and ATP-citrate lyase activity drove IL1B, IL10, and IL23A expression by yielding acetyl-CoA and oxaloacetate, with the latter one supporting glycolysis and OXPHOS by maintaining cytosolic NAD⁺ and mitochondrial NADH levels through mitochondrial shuttles. Succinate dehydrogenase showed a subunit-specific ability to modulate IL23A and IL10 expression. Succinate dehydrogenase A subunit activity supported cytokine expression through the control of the 2-oxoglutarate/succinate ratio, whereas C and D subunits underpinned cytokine expression by conveying electron flux from complex II to complex III of the electron transport chain. Fatty acids may also fuel the tricarboxylic acid cycle and influence cytokine expression. Overall, these results show that fungal patterns support cytokine expression through a strong boost of glycolysis and OXPHOS supported by the use of pyruvate, citrate, and succinate, along with the compartmentalized NAD(H) redox state maintained by mitochondrial shuttles.

Neutrophil phenotypes and functions in cancer: A consensus statement

Neutrophils are the first responders to infection and inflammation and are thus a critical component of innate immune defense. Understanding the behavior of neutrophils as they act within various inflammatory contexts has provided insights into their role in sterile and infectious diseases; however, the field of neutrophils in cancer is comparatively young. Here, we summarize key concepts and current knowledge gaps related to the diverse roles of neutrophils throughout cancer progression. We discuss sources of neutrophil heterogeneity in cancer and provide recommendations on nomenclature for neutrophil states that are distinct in maturation and activation. We address discrepancies in the literature that highlight a need for technical standards that ought to be considered between laboratories. Finally, we review emerging questions in neutrophil biology and innate immunity in cancer. Overall, we emphasize that neutrophils are a more diverse population than previously appreciated and that their role in cancer may present novel unexplored opportunities to treat cancer.

CD36, a signaling receptor and fatty acid transporter that regulates immune cell metabolism and fate

CD36 is a type 2 cell surface scavenger receptor widely expressed in many immune and non-immune cells. It functions as both a signaling receptor responding to DAMPs and PAMPs, as well as a long chain free fatty acid transporter. Recent studies have indicated that CD36 can integrate cell signaling and metabolic pathways through its dual functions and thereby influence immune cell differentiation and activation, and ultimately help determine cell fate. Its expression along with its dual functions in both innate and adaptive immune cells contribute to pathogenesis of common diseases, including atherosclerosis and tumor progression, which makes CD36 and its downstream effectors potential therapeutic targets. This review comprehensively examines the dual functions of CD36 in a variety of immune cells, especially macrophages and T cells. We also briefly discuss CD36 function in non-immune cells, such as adipocytes and platelets, which impact the immune system via intercellular communication. Finally, outstanding questions in this field are provided for potential directions of future studies.

Donor Heterogeneity in the Human Macrophage Response to a Biomaterial under Hyperglycemia in vitro

Macrophages have a commanding role in scaffold-driven in situ tissue regeneration. Depending on their polarization state, macrophages mediate the formation and remodeling of new tissue by secreting growth factors and cytokines. Therefore, successful outcomes of material-driven in situ tissue vascular tissue engineering depends largely on the immuno-regenerative potential of the recipient. A large cohort of patients requiring vascular replacements suffers from systemic multifactorial diseases, like diabetes, which gives rise to a hyperglycemic and aggressive oxidative inflammatory environment that is hypothesized to hamper a well-balanced regenerative process. Here, we aimed to fundamentally explore the effects of hyperglycemia, as one of the hallmarks of diabetes, on the macrophage response to 3D electrospun synthetic biomaterials for in situ tissue engineering, in terms of inflammatory profile and tissue regenerative capacity. To simulate the early phases of the in situ regenerative cascade, we used a bottom-up in vitro approach. Primary human macrophages (n=8 donors) and (myo)fibroblasts in mono- or co-culture were seeded in 2D, as well as in a 3D electrospun resorbable polycaprolactone bisurea (PCL-BU) scaffold and exposed to normoglycemic (5.5 mM glucose), hyperglycemic (25 mM glucose) and osmotic control conditions (5.5 mM glucose, 19.5 mM mannitol). The results showed that macrophage polarization by biochemical stimuli was effective under all glycemic conditions and that the polarization states dictated expression of the receptors SCL2A1 (glucose transporter 1) and CD36 (fatty acid transporter). In 3D, the macrophage response to hyperglycemic conditions was strongly donor-dependent in terms of phenotype, cytokine secretion profile, and metabolic receptor expression. When co-cultured with (myo)fibroblasts, hyperglycemic conditions led to an increased expression of fibrogenic markers (ACTA2, COL1, COL3, IL-1β). Together, these findings show that the hyperglycemic and hyperosmotic conditions may indeed influence the process of macrophage-driven in situ tissue engineering, and that the extent of this is likely to be patient-specific.

Divergence of acetate uptake in proinflammatory and inflammation-resolving macrophages: implications for imaging atherosclerosis

BACKGROUND

Metabolic divergence of macrophages polarized into different phenotypes represents a mechanistically relevant target for non-invasive characterization of atherosclerotic plaques using positron emission tomography (PET). Carbon-11 (11C)-labeled acetate is a clinically available tracer which accumulates in atherosclerotic plaques, but its biological and clinical correlates in atherosclerosis are undefined.

METHODS AND RESULTS

Histological correlates of 14C-acetate uptake were determined in brachiocephalic arteries of western diet-fed apoE-/- mice. The effect of polarizing stimuli on 14C-acetate uptake was determined by proinflammatory (interferon-γ + lipopolysaccharide) vs inflammation-resolving (interleukin-4) stimulation of murine macrophages and human carotid endarterectomy specimens over 2 days. 14C-acetate accumulated in atherosclerotic regions of arteries. CD68-positive monocytes/macrophages vs smooth muscle actin-positive smooth muscle cells were the dominant cells in regions with high vs low 14C-acetate uptake. 14C-acetate uptake progressively decreased in proinflammatory macrophages to 25.9 ± 4.5% of baseline (P < .001). A delayed increase in 14C-acetate uptake was induced in inflammation-resolving macrophages, reaching to 164.1 ± 21.4% (P < .01) of baseline. Consistently, stimulation of endarterectomy specimens with interferon-γ + lipopolysaccharide decreased 14C-acetate uptake to 66.5 ± 14.5%, while interleukin-4 increased 14C-acetate uptake to 151.5 ± 25.8% compared to non-stimulated plaques (P < .05).

CONCLUSIONS

Acetate uptake by macrophages diverges upon proinflammatory and inflammation-resolving stimulation, which may be exploited for immunometabolic characterization of atherosclerosis.

Macrophage polarization in hypoxia and ischemia/reperfusion: Insights into the role of energetic metabolism

Macrophages, the key cells of innate immunity, possess wide phenotypical and functional heterogeneity. In vitro studies showed that microenvironment signals could induce the so-called polarization of macrophages into two phenotypes: classically activated macrophages (M1) or alternatively activated macrophages (M2). Functionally, they are considered as proinflammatory and anti-inflammatory/pro-regenerative, respectively. However, in vivo studies into macrophage states revealed a continuum of phenotypes from M1 to M2 state instead of the clearly distinguished extreme phenotypes. An important role in determining the type of polarization of macrophages is played by energy metabolism, including the activity of oxidative phosphorylation. In this regard, hypoxia and ischemia that affect cellular energetics can modulate macrophage polarization. Here, we overview the data on macrophage polarization during metabolic shift-associated pathologies including ischemia and ischemia/reperfusion in various organs and discuss the role of energy metabolism potentially triggering the macrophage polarization.

Low expression of PGC-1β and other mitochondrial biogenesis modulators in melanoma is associated with growth arrest and the induction of an immunosuppressive gene expression program dependent on MEK and IRF-1

Mitochondria are specialized metabolic and immune organelles that have important roles in tumor progression, metastasis, and response to chemotherapy and immunotherapy. Mitochondrial biogenesis and function are under the control of the peroxisome-proliferator activated receptor-gamma (PGC-1) transcriptional coactivators. Recent research unveiled the role of PGC-1α in bolstering mitochondrial oxidative functions and in the suppression of metastasis in melanoma, but the role of PGC-1s in tumor immunology remains elusive. Herein, we show that low PGC-1s expression in human melanoma tumors is associated with increased expression of a repertoire of immunosuppressive (CD73, PD-L2, Galectin-9) and pro-inflammatory (IL-8, TNF, IL-1β) transcripts, and that experimental depletion of PGC-1β recapitulates this signature in human melanoma cell lines. The depletion of PGC-1β reduces the expression of HSPA9, impairs mitochondrial activity, and leads to cell cycle arrest. Using pharmacological and gene silencing approaches, we further show that MEK1/2 and IRF-1 mediate the observed immune transcriptional response. Overall, this research suggests that mitochondrial biogenesis modulators can modulate tumor progression, immune evasion, and response to therapeutics through transcriptional control of immune pathways.

Expression of PINK1 and Parkin in human apical periodontitis

AIM

PTEN-induced putative kinase 1 (PINK1) and Parkin E3 ubiquitin-protein ligase (Parkin) are critical for immune and inflammatory regulation in health and disease. PINK1 and Parkin have been confirmed to be involved in the progression of apical periodontitis by affecting mitophagy-related osteoblast apoptosis; however, the expression of PINK1 and Parkin in macrophages, one of the most important cells in apical periodontitis, remains unknown. This study aimed to investigate the expression of PINK1 and Parkin in human apical periodontitis lesions, as well as their possible localization in macrophages.

METHODOLOGY

Thirty-seven human periapical tissues, including periapical granulomas (PGs, n=12), radicular cysts (RCs, n=11), and healthy gingival tissues (n=14) were examined. The inflammatory infiltrates of lesions were evaluated by haemotoxylin staining, and the expression of PINK1 and Parkin was detected by immunohistochemistry. Double immunofluorescence was used to explore the colocalization of microtubule-associated protein 1 light chain 3 (LC3) and TOMM20, as well as the localization of PINK1 and Parkin, in macrophages of human apical periodontitis lesions. The ultrastructural morphology of mitochondria in human apical periodontitis lesions was visualized by transmission electron microscopy (TEM). Data were analyzed by one-way ANOVA with Student-Newman-Keul's test and Mann-Whitney test. P < 0.05 was considered statistically significant.

RESULTS

Immunohistochemistry demonstrated a significantly higher expression of PINK1 and Parkin proteins in human apical periodontitis lesions than in healthy gingival tissues (P < 0.0001), but no significant difference was demonstrated between PGs and RCs (P > 0.05). The higher expression of LC3 and the presence of more LC3-TOMM20 double-positive cells were also observed in human apical periodontitis. Double-labeling analysis of PINK1, Parkin, and LC3 with CD68 indicated that macrophage mitophagy might be present in the progression of human apical periodontitis. Finally, the results of TEM morphological analysis revealed the appearance of double-membraned mitophagosomes and vacuolated mitochondria in macrophage-like cells of apical periodontitis lesions.

CONCLUSIONS

Our findings indicated that PINK1 and Parkin proteins were highly expressed in clinical apical periodontitis lesions.

Amelioration of Endotoxemia by a Synthetic Analog of Omega-3 Epoxyeicosanoids

Sepsis, a systemic inflammatory response to pathogenic factors, is a difficult to treat life-threatening condition associated with cytokine and eicosanoid storms and multi-organ damage. Omega-3 polyunsaturated fatty acids, such as eicosapentaenoic (EPA) and docosahexaenoic acid, are the precursors of potent anti-inflammatory lipid mediators, including 17,18-epoxyeicosatetraenoic acid (17,18-EEQ), the main metabolite of EPA generated by cytochrome P450 epoxygenases. Searching for novel therapeutic or preventative agents in sepsis, we tested a metabolically robust synthetic analog of 17,18-EEQ (EEQ-A) for its ability to reduce mortality, organ damage, and pro-inflammatory cytokine transcript level in a mouse model of lipopolysaccharide (LPS)-induced endotoxemia, which is closely related to sepsis. Overall survival significantly improved following preventative EEQ-A administration along with decreased transcript level of pro-inflammatory cytokines. On the other hand, the therapeutic protocol was effective in improving survival at 48 hours but insignificant at 72 hours. Histopathological analyses showed significant reductions in hemorrhagic and necrotic damage and infiltration in the liver. In vitro studies with THP-1 and U937 cells showed EEQ-A mediated repression of LPS-induced M1 polarization and enhancement of IL-4-induced M2 polarization of macrophages. Moreover, EEQ-A attenuated the LPS-induced decline of mitochondrial function in THP-1 cells, as indicated by increased basal respiration and ATP production as well as reduction of the metabolic shift to glycolysis. Taken together, these data demonstrate that EEQ-A has potent anti-inflammatory and immunomodulatory properties that may support therapeutic strategies for ameliorating the endotoxemia.

Nitric oxide favours tumour-promoting inflammation through mitochondria-dependent and -independent actions on macrophages

Production of nitric oxide (NO) has been demonstrated in several malignancies, however its role remains not fully understood, specifically in relation to the metabolic and functional implications that it may have on immune cells participating in tumorigenesis. Here, we show that inducible NO synthase (iNOS) is expressed in cancers of the colon and the prostate, mainly by tumour cells, and NO generation is evidenced by widespread nitrotyrosine (NT) staining in tumour tissue. Furthermore, presence of NT is observed in the majority of tumour-associated macrophages (TAMs), despite low iNOS expression by these cells, suggesting that NO from the tumour microenvironment affects TAMs. Indeed, using a co-culture model, we demonstrate that NO produced by colon and prostate cancer cells is sufficient to induce NT formation in neighbouring macrophages. Moreover, exposure to exogenous NO promotes mitochondria-dependent and -independent changes in macrophages, which orientate their polarity towards an enhanced pro-inflammatory phenotype, whilst decreasing antigen-presenting function and wound healing capacity. Abrogating endogenous NO generation in murine macrophages, on the other hand, decreases their pro-inflammatory phenotype. These results suggest that the presence of NO in cancer may regulate TAM metabolism and function, favouring the persistence of inflammation, impairing healing and subverting adaptive immunity responses.

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Nitric oxide (NO) from the cancer microenvironment acts on tumour-associated macrophages (TAMs).

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NO induces a phenotypic shift in macrophages through mitochondria-dependent and -independent pathways.

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NO favours pro-inflammatory cytokine production whilst decreasing macrophage function as antigen presenting cell.

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NO impairs repair function of macrophages.

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Presence of NO in cancer may regulate TAM metabolism and function, favouring tumour-promoting inflammation.

An integrated toolbox to profile macrophage immunometabolism

Macrophages are dynamic immune cells that can adopt several activation states. Fundamental to these functional activation states is the regulation of cellular metabolic processes. Especially in mice, metabolic alterations underlying pro-inflammatory or homeostatic phenotypes have been assessed using various techniques. However, researchers new to the field may encounter ambiguity in choosing which combination of techniques is best suited to profile immunometabolism. To address this need, we have developed a toolbox to assess cellular metabolism in a semi-high-throughput 96-well-plate-based format. Application of the toolbox to activated mouse and human macrophages enables fast metabolic pre-screening and robust measurement of extracellular fluxes, mitochondrial mass and membrane potential, and glucose and lipid uptake. Moreover, we propose an application of SCENITH technology for ex vivo metabolic profiling. We validate established activation-induced metabolic rewiring in mouse macrophages and report new insights into human macrophage metabolism. By thoroughly discussing each technique, we hope to guide readers with practical workflows for investigating immunometabolism.

Impacts and mechanisms of metabolic reprogramming of tumor microenvironment for immunotherapy in gastric cancer

Metabolic disorders and abnormal immune function changes occur in tumor tissues and cells to varying degrees. There is increasing evidence that reprogrammed energy metabolism contributes to the development of tumor suppressive immune microenvironment and influences the course of gastric cancer (GC). Current studies have found that tumor microenvironment (TME) also has important clinicopathological significance in predicting prognosis and therapeutic efficacy. Novel approaches targeting TME therapy, such as immune checkpoint blockade (ICB), metabolic inhibitors and key enzymes of immune metabolism, have been involved in the treatment of GC. However, the interaction between GC cells metabolism and immune metabolism and how to make better use of these immunotherapy methods in the complex TME in GC are still being explored. Here, we discuss how metabolic reprogramming of GC cells and immune cells involved in GC immune responses modulate anti-tumor immune responses, as well as the effects of gastrointestinal flora in TME and GC. It is also proposed how to enhance anti-tumor immune response by understanding the targeted metabolism of these metabolic reprogramming to provide direction for the treatment and prognosis of GC.

Macrophage Dysfunction in Autoimmune Rheumatic Diseases and Atherosclerosis

One of the problems of modern medical science is cardiovascular pathology caused by atherosclerotic vascular lesions in patients with autoimmune rheumatic diseases (ARDs). The similarity between the mechanisms of the immunopathogenesis of ARD and chronic low-grade inflammation in atherosclerosis draws attention. According to modern concepts, chronic inflammation associated with uncontrolled activation of both innate and acquired immunity plays a fundamental role in all stages of ARDs and atherosclerotic processes. Macrophage monocytes play an important role among the numerous immune cells and mediators involved in the immunopathogenesis of both ARDs and atherosclerosis. An imbalance between M1-like and M2-like macrophages is considered one of the causes of ARDs. The study of a key pathogenetic factor in the development of autoimmune and atherosclerotic inflammation-activated monocyte/macrophages will deepen the knowledge of chronic inflammation pathogenesis.

Characterization of vaginal immune response to a polypropylene mesh: Diabetic vs. normoglycemic conditions

OBJECTIVE

Urogynecology meshes, typically manufactured from polypropylene, are widely used in the surgical treatment of stress urinary incontinence and pelvic organ prolapse. However, mesh-associated complications such as mesh exposure can develop in women undergoing mesh implantation, for which diabetes is an independent risk factor. We aimed to define the impact of diabetes on the vaginal immune response to mesh by comparing diabetic vs. normoglycemic conditions longitudinally in a rat sacrocolpopexy model.

METHODS

Diabetes (blood glucose ≥ 300 mg/dL) was induced in middle-aged female Wistar rats with streptozotocin (STZ). A polypropylene mesh was implanted on the vagina via modified sacrocolpopexy following bilateral ovariectomy and supracervical hysterectomy for 3-, 7-, and 42-days. Sham-operated controls underwent the same procedures without mesh. Mesh-associated inflammation, immune cell populations and cytokine/chemokine profiles were examined in the excised vaginal tissues.

RESULTS

Diabetes was reliably induced starting on the 3rd day following STZ injection. Under both normoglycemic and diabetic conditions, mesh caused a prolonged inflammatory response in the vagina with increased proinflammatory chemokines MCP-1 and MIP-1α as compared to Sham. Major differences between the two conditions were found at the later stage (42 days post-surgery), including an increased inflammation with larger foreign body granuloma and more giant cells at the mesh-tissue interface, increased fraction of macrophages in the immune cell population, and higher proinflammatory chemokine IP-10 in the diabetic group.

CONCLUSION

Polypropylene mesh implanted on the vagina induces prolonged inflammation at the mesh-tissue interface. Diabetes increases the mesh-associated inflammation in the long term, which is related to a dysregulated macrophage response.

STATEMENT OF SIGNIFICANCE

This study investigated the mechanism underlying the increased risk in women with diabetes for developing mesh complications such as mesh exposure. The significance includes: (1) it is the first study investigating vaginal host response to a prosthesis under the influence of diabetes; (2) the longitudinal study design elucidated the dynamic changes of vaginal immune response to mesh from very early to late stages; (3) our findings may inform future mechanistic studies and studies investigating preventive/therapeutic strategies to improve the outcomes of women with diabetes receiving vaginal implants.

Mitochondrial function in spinal cord injury and regeneration

Many people around the world suffer from some form of paralysis caused by spinal cord injury (SCI), which has an impact on quality and life expectancy. The spinal cord is part of the central nervous system (CNS), which in mammals is unable to regenerate, and to date, there is a lack of full functional recovery therapies for SCI. These injuries start with a rapid and mechanical insult, followed by a secondary phase leading progressively to greater damage. This secondary phase can be potentially modifiable through targeted therapies. The growing literature, derived from mammalian and regenerative model studies, supports a leading role for mitochondria in every cellular response after SCI: mitochondrial dysfunction is the common event of different triggers leading to cell death, cellular metabolism regulates the immune response, mitochondrial number and localization correlate with axon regenerative capacity, while mitochondrial abundance and substrate utilization regulate neural stem progenitor cells self-renewal and differentiation. Herein, we present a comprehensive review of the cellular responses during the secondary phase of SCI, the mitochondrial contribution to each of them, as well as evidence of mitochondrial involvement in spinal cord regeneration, suggesting that a more in-depth study of mitochondrial function and regulation is needed to identify potential targets for SCI therapeutic intervention.

SENP1-Sirt3 signaling promotes α-ketoglutarate production during M2 macrophage polarization

The metabolic program is altered during macrophage activation and influences macrophage polarization. Glutaminolysis promotes accumulation of α-ketoglutarate (αKG), leading to Jumonji domain-containing protein D3 (Jmjd3)-dependent demethylation at H3K27me3 during M2 polarization of macrophages. However, it remains unclear how αKG accumulation is regulated during M2 polarization of macrophages. This study shows that SENP1-Sirt3 signaling controls glutaminolysis, leading to αKG accumulation during IL-4-stimulated M2 polarization. Activation of the SENP1-Sirt3 axis augments M2 macrophage polarization through the accumulation of αKG via glutaminolysis. We also identify glutamate dehydrogenase 1 (GLUD1) as an acetylated protein in mitochondria. The SENP1-Sirt3 axis deacetylates GLUD1 and increases its activity in glutaminolysis to promote αKG production, leading to M2 polarization of macrophages. Therefore, SENP1-Sirt3 signaling plays a critical role in αKG accumulation via glutaminolysis to promote M2 polarization.

MEF2C promotes M1 macrophage polarization and Th1 responses

The polarization of macrophages to the M1 or M2 phenotype has a pivotal role in inflammation and host defense; however, the underlying molecular mechanism remains unclear. Here, we show that myocyte enhancer factor 2 C (MEF2C) is essential for regulating M1 macrophage polarization in response to infection and inflammation. Global gene expression analysis demonstrated that MEF2C deficiency in macrophages downregulated the expression of M1 phenotypic markers and upregulated the expression of M2 phenotypic markers. MEF2C significantly promoted the expression of interleukin-12 p35 subunit (Il12a) and interleukin-12 p40 subunit (Il12b). Myeloid-specific Mef2c-knockout mice showed reduced IL-12 production and impaired Th1 responses, which led to susceptibility to Listeria monocytogenes infection and protected against DSS-induced IBD in vivo. Mechanistically, we showed that MEF2C directly activated the transcription of Il12a and Il12b. These findings reveal a new function of MEF2C in macrophage polarization and Th1 responses and identify MEF2C as a potential target for therapeutic intervention in inflammatory and autoimmune diseases.

CARD19 Interacts with Mitochondrial Contact Site and Cristae Organizing System Constituent Proteins and Regulates Cristae Morphology

CARD19 is a mitochondrial protein of unknown function. While CARD19 was originally reported to regulate TCR-dependent NF-κB activation via interaction with BCL10, this function is not recapitulated ex vivo in primary murine CD8+ T cells. Here, we employ a combination of SIM, TEM, and confocal microscopy, along with proteinase K protection assays and proteomics approaches, to identify interacting partners of CARD19 in macrophages. Our data show that CARD19 is specifically localized to the outer mitochondrial membrane. Through deletion of functional domains, we demonstrate that both the distal C-terminus and transmembrane domain are required for mitochondrial targeting, whereas the CARD is not. Importantly, mass spectrometry analysis of 3×Myc-CARD19 immunoprecipitates reveals that CARD19 interacts with the components of the mitochondrial intermembrane bridge (MIB), consisting of mitochondrial contact site and cristae organizing system (MICOS) components MIC19, MIC25, and MIC60, and MICOS-interacting proteins SAMM50 and MTX2. These CARD19 interactions are in part dependent on a properly folded CARD. Consistent with previously reported phenotypes upon siRNA silencing of MICOS subunits, absence of CARD19 correlates with irregular cristae morphology. Based on these data, we propose that CARD19 is a previously unknown interacting partner of the MIB and the MIC19–MIC25–MIC60 MICOS subcomplex that regulates cristae morphology.

Metabolism in atherosclerotic plaques: immunoregulatory mechanisms in the arterial wall

Over the last decade, there has been a growing interest to understand the link between metabolism and the immune response in the context of metabolic diseases but also beyond, giving then birth to a new field of research. Termed 'immunometabolism', this interdisciplinary field explores paradigms of both immunology and metabolism to provided unique insights into different disease pathogenic processes, and the identification of new potential therapeutic targets. Similar to other inflammatory conditions, the atherosclerotic inflammatory process in the artery has been associated with a local dysregulated metabolic response. Thus, recent studies show that metabolites are more than just fuels in their metabolic pathways, and they can act as modulators of vascular inflammation and atherosclerosis. In this review article, we describe the most common immunometabolic pathways characterised in innate and adaptive immune cells, and discuss how macrophages' and T cells' metabolism may influence phenotypic changes in the plaque. Moreover, we discuss the potential of targeting immunometabolism to prevent and treat cardiovascular diseases (CVDs).

Macrophage mitochondrial bioenergetics and tissue invasion are boosted by an Atossa-Porthos axis in Drosophila

Cellular metabolism must adapt to changing demands to enable homeostasis. During immune responses or cancer metastasis, cells leading migration into challenging environments require an energy boost, but what controls this capacity is unclear. Here, we study a previously uncharacterized nuclear protein, Atossa (encoded by CG9005), which supports macrophage invasion into the germband of Drosophila by controlling cellular metabolism. First, nuclear Atossa increases mRNA levels of Porthos, a DEAD‐box protein, and of two metabolic enzymes, lysine‐α‐ketoglutarate reductase (LKR/SDH) and NADPH glyoxylate reductase (GR/HPR), thus enhancing mitochondrial bioenergetics. Then Porthos supports ribosome assembly and thereby raises the translational efficiency of a subset of mRNAs, including those affecting mitochondrial functions, the electron transport chain, and metabolism. Mitochondrial respiration measurements, metabolomics, and live imaging indicate that Atossa and Porthos power up OxPhos and energy production to promote the forging of a path into tissues by leading macrophages. Since many crucial physiological responses require increases in mitochondrial energy output, this previously undescribed genetic program may modulate a wide range of cellular behaviors.

Triglyceride breakdown from lipid droplets regulates the inflammatory response in macrophages

Lipid droplets (LDs) are ubiquitous organelles that play important roles in cellular energy homeostasis, tightly regulating the accumulation and release of lipids. In macrophages, lipids accumulate in LDs during inflammation. However, it is unclear how inflammatory activation promotes the accumulation of lipids in LDs, and how the dynamic between lipid accumulation and breakdown could drive or inhibit inflammation. Elucidating the role of lipid accumulation during inflammation may provide important knowledge to influence inflammatory processes during health and disease. We identify the importance of the hypoxia-inducible lipid droplet–associated protein and the intracellular adipose triglyceride lipase in the regulation of lipid accumulation and breakdown in inflammatory macrophages. Furthermore, we determine the regulatory effect of lipid breakdown from LDs in supporting inflammation.

In response to inflammatory activation by pathogens, macrophages accumulate triglycerides in intracellular lipid droplets. The mechanisms underlying triglyceride accumulation and its exact role in the inflammatory response of macrophages are not fully understood. Here, we aim to further elucidate the mechanism and function of triglyceride accumulation in the inflammatory response of activated macrophages. Lipopolysaccharide (LPS)-mediated activation markedly increased triglyceride accumulation in macrophages. This increase could be attributed to up-regulation of the hypoxia-inducible lipid droplet–associated (HILPDA) protein, which down-regulated adipose triglyceride lipase (ATGL) protein levels, in turn leading to decreased ATGL-mediated triglyceride hydrolysis. The reduction in ATGL-mediated lipolysis attenuated the inflammatory response in macrophages after ex vivo and in vitro activation, and was accompanied by decreased production of prostaglandin-E2 (PGE2) and interleukin-6 (IL-6). Overall, we provide evidence that LPS-mediated activation of macrophages suppresses lipolysis via induction of HILPDA, thereby reducing the availability of proinflammatory lipid precursors and suppressing the production of PGE2 and IL-6.

Fatty acid oxidation fuels glioblastoma radioresistance with CD47-mediated immune evasion

Glioblastoma multiforme (GBM) remains the top challenge to radiotherapy with only 25% one-year survival after diagnosis. Here, we reveal that co-enhancement of mitochondrial fatty acid oxidation (FAO) enzymes (CPT1A, CPT2 and ACAD9) and immune checkpoint CD47 is dominant in recurrent GBM patients with poor prognosis. A glycolysis-to-FAO metabolic rewiring is associated with CD47 anti-phagocytosis in radioresistant GBM cells and regrown GBM after radiation in syngeneic mice. Inhibition of FAO by CPT1 inhibitor etomoxir or CRISPR-generated CPT1A^-/-, CPT2^-/-, ACAD9^-/- cells demonstrate that FAO-derived acetyl-CoA upregulates CD47 transcription via NF-κB/RelA acetylation. Blocking FAO impairs tumor growth and reduces CD47 anti-phagocytosis. Etomoxir combined with anti-CD47 antibody synergizes radiation control of regrown tumors with boosted macrophage phagocytosis. These results demonstrate that enhanced fat acid metabolism promotes aggressive growth of GBM with CD47-mediated immune evasion. The FAO-CD47 axis may be targeted to improve GBM control by eliminating the radioresistant phagocytosis-proofing tumor cells in GBM radioimmunotherapy.

Inclisiran inhibits oxidized low-density lipoprotein-induced foam cell formation in Raw264.7 macrophages via activating the PPARγ pathway

Proprotein convertase subtilisin kexin type 9 (PCSK9) is a well-known proprotein convertase that influences foam cell formation and modulates atherosclerosis. Inclisiran is a novel chemosynthetic small interfering RNA that inhibits PCSK9 synthesis. This study aimed to explore the effect of inclisiran on oxidized low-density lipoprotein (ox-LDL)-induced foam cell formation in Raw264.7 macrophages and to investigate the underlying mechanisms. Raw264.7 cells were treated with ox-LDL to induce the formation of macrophage-derived foam cells. Oil Red O staining and high-performance liquid chromatography were performed to detect lipid accumulation and cholesterol levels. Dil-ox-LDL uptake assay, CCK-8, RT-qPCR, and Western blotting analysis were performed to examine ox-LDL uptake, cell viability, and expression of scavenger receptor-related factors. Inclisiran reduced lipid accumulation in ox-LDL-treated macrophages in a dose-dependent manner. Inclisiran significantly inhibited the levels of total cholesterol, free cholesterol, and cholesterol ester in the supernatant of Raw264.7 cells. Inclisiran reduced ox-LDL uptake and increased Raw264.7 cell viability. Meanwhile, inclisiran downregulated the expression of SR-A, LOX-1, and CD36 and upregulated SR-BI, ApoE, and ABCA1. Furthermore, inclisiran increased PPARγ activity and decreased NF-κB activity. An inhibitor of PPARγ (T0070907) reversed the beneficial effects of inclisiran on ox-LDL uptake, NF-κB inactivation, and cytokine expression. In conclusion, these data suggested that inclisiran inhibited the formation of macrophage-derived foam cells by activating the PPARγ pathway.HighlightsInclisiran reduces lipid accumulation in Raw264.7 cells;Inclisiran reduces ox-LDL uptake and increases Raw264.7 cell viability;Inclisiran inhibits foam cell formation by activating the PPARγ pathway.