Leishmania braziliensis enhances monocyte responses to promote anti-tumor activity.

Innate immune cells can undergo long-term functional reprogramming after certain infections, a process called trained immunity (TI). Here, we focus on antigens of Leishmania braziliensis, which induced anti-tumor effects via trained immunity in human monocytes. We reveal that monocytes exposed to promastigote antigens of L. braziliensis develop an enhanced response to subsequent exposure to Toll-like receptor (TLR)2 or TLR4 ligands. Mechanistically, the induction of TI in monocytes by L. braziliensis is mediated by multiple pattern recognition receptors, changes in metabolism, and increased deposition of H3K4me3 at the promoter regions of immune genes. The administration of L. braziliensis exerts potent anti-tumor capabilities by delaying tumor growth and prolonging survival of mice with non-Hodgkin lymphoma. Our work reveals mechanisms of TI induced by L. braziliensis in vitro and identifies its potential for cancer immunotherapy.

γH2AX in mouse embryonic stem cells: Distribution during differentiation and following γ-irradiation.

Phosphorylated histone H2AX (γH2AX) represents a sensitive molecular marker of DNA double-strand breaks (DSBs) and is implicated in stem cell biology. We established a model of mouse embryonic stem cell (mESC) differentiation and examined the dynamics of γH2AX foci during the process. Our results revealed high numbers of γH2AX foci in undifferentiated mESCs, decreasing as the cells differentiated towards the endothelial cell lineage. Notably, we observed two distinct patterns of γH2AX foci: the typical discrete γH2AX foci, which colocalize with the transcriptionally permissive chromatin mark H3K4me3, and the less well-characterized clustered γH2AX regions, which were only observed in intermediate progenitor cells. Next, we explored responses of mESCs to γ-radiation (137Cs). Following exposure to γ-radiation, mESCs showed a reduction in cell viability and increased γH2AX foci, indicative of radiosensitivity. Despite irradiation, surviving mESCs retained their differentiation potential. To further exemplify our findings, we investigated neural stem progenitor cells (NSPCs). Similar to mESCs, NSPCs displayed clustered γH2AX foci associated with progenitor cells and discrete γH2AX foci indicative of embryonic stem cells or differentiated cells. In conclusion, our findings demonstrate that γH2AX serves as a versatile marker of DSBs and may have a role as a biomarker in stem cell differentiation. The distinct patterns of γH2AX foci in differentiating mESCs and NSPCs provide valuable insights into DNA repair dynamics during differentiation, shedding light on the intricate balance between genomic integrity and cellular plasticity in stem cells. Finally, the clustered γH2AX foci observed in intermediate progenitor cells is an intriguing feature, requiring further exploration.

Metaboloepigenetics in cancer, immunity, and cardiovascular disease.

The influence of cellular metabolism on epigenetic pathways is well documented but misunderstood. Scientists have long known of the metabolic impact on epigenetic determinants. More often than not, that title role for DNA methylation was portrayed by the metabolite S-adenosylmethionine. Technically speaking, there are many other metabolites that drive epigenetic processes that instruct seemingly distant-yet highly connect pathways-and none more so than our understanding of the cancer epigenome. Recent studies have shown that available energy links the extracellular environment to influence cellular responses. This focused review examines the recent interest in epigenomics and casts cancer, metabolism, and immunity in unfamiliar roles-cooperating. There are not only language lessons from cancer research, we have come round to appreciate that reaching into areas previously thought of as too distinct are also object lessons in understanding health and disease. The Warburg effect is one such signature of how glycolysis influences metabolic shift during oncogenesis. That shift in metabolism-now recognized as central to proliferation in cancer biology-influences core enzymes that not only control gene expression but are also central to replication, condensation, and the repair of nucleic acid. These nuclear processes rely on metabolism, and with glucose at centre stage, the role of respiration and oxidative metabolism is now synonymous with the mitochondria as the powerhouses of metaboloepigenetics. The emerging evidence for metaboloepigenetics in trained innate immunity has revealed recognizable signalling pathways with antecedent extracellular stimulation. With due consideration to immunometabolism, we discuss the striking signalling similarities influencing these core pathways. The immunometabolic-epigenetic axis in cardiovascular disease has deeply etched connections with inflammation, and we examine the chromatin template as a carrier of epigenetic indices that determine the expression of genes influencing atherosclerosis and vascular complications of diabetes.

A unifying model for extrachromosomal circular DNA load in eukaryotic cells.

Extrachromosomal circular DNA (eccDNA) with exons and whole genes are common features of eukaryotic cells. Work from especially tumours and the yeast Saccharomyces cerevisiae has revealed that eccDNA can provide large selective advantages and disadvantages. Besides the phenotypic effect due to expression of an eccDNA fragment, eccDNA is different from other mutations in that it is released from 1:1 segregation during cell division. This means that eccDNA can quickly change copy number, pickup secondary mutations and reintegrate into a chromosome to establish substantial genetic variation that could not have evolved via canonical mechanisms. We propose a unifying 5-factor model for conceptualizing the eccDNA load of a eukaryotic cell, emphasizing formation, replication, segregation, selection and elimination. We suggest that the magnitude of these sequential events and their interactions determine the copy number of eccDNA in mitotically dividing cells. We believe that our model will provide a coherent framework for eccDNA research, to understand its biology and the factors that can be manipulated to modulate eccDNA load in eukaryotic cells.

Immune modulatory effects of progesterone on oxLDL-induced trained immunity in monocytes.

Atherosclerotic cardiovascular diseases (CVD) are among the leading causes of death in the world. Monocyte-derived macrophages are key players in the pathophysiology of atherosclerosis. Innate immune memory following exposure of monocytes to atherogenic compounds, such as oxidized low-density lipoproteins (oxLDL), termed trained immunity, can contribute to atherogenesis. The current study aimed to elucidate intracellular mechanisms of oxLDL-induced trained immunity. Using untargeted intracellular metabolomics in isolated human primary monocytes, we show that oxLDL-induced trained immunity results in alterations in the balance of intracellular steroid hormones in monocytes. This was reflected by a decrease in extracellular progesterone concentrations following LPS stimulation. To understand the potential effects of steroid hormones on trained immunity, monocytes were costimulated with oxLDL and the steroid hormones progesterone, hydrocortisone, dexamethasone, ß-estradiol, and dihydrotestosterone. Progesterone showed a unique ability to attenuate the enhanced TNFα and IL-6 production following oxLDL-induced trained immunity. Single nucleotide polymorphisms in the nuclear glucocorticoid, progesterone, and mineralocorticoid receptor were shown to correlate with ex vivo oxLDL-induced trained immunity in 243 healthy volunteers. Pharmacologic inhibition experiments revealed that progesterone exerts the suppression of TNFα in trained immunity via the nuclear glucocorticoid and mineralocorticoid receptors. Our data show that progesterone has a unique ability to suppress oxLDL-induced trained immunity. We hypothesize that this effect might contribute to the lower incidence of CVD in premenopausal women.

oxLDL-Induced Trained Immunity Is Dependent on Mitochondrial Metabolic Reprogramming.

Following brief exposure to endogenous atherogenic particles, such as oxidized low-density lipoprotein (oxLDL), monocytes/macrophages can adopt a long-term pro-inflammatory phenotype, which is called trained immunity. This mechanism might contribute to the chronic low-grade inflammation that characterizes atherosclerosis. In this study, we aim to elucidate immunometabolic pathways that drive oxLDL-induced trained immunity. Primary isolated human monocytes were exposed to oxLDL for 24 h, and after five days stimulated with LPS to measure the cytokine production capacity. RNA-sequencing revealed broad increases in genes enriched in mitochondrial pathways after 24 h of oxLDL exposure. Further omics profiling of oxLDL-trained macrophages via intracellular metabolomics showed an enrichment for tricarboxylic acid (TCA) cycle metabolites. Single cell analysis revealed that oxLDL-trained macrophages contain larger mitochondria, potentially likely linked to increased oxidative phosphorylation (OXPHOS) activity. Co-incubation with pharmacological blockers of OXPHOS inhibited oxLDL-induced trained immunity. The relevance of OXPHOS was confirmed in a cohort of 243 healthy subjects showing that genetic variation in genes coding for enzymes relevant to OXPHOS correlated with the capacity of monocytes to be trained with oxLDL. Interestingly, OXPHOS appears to play an important role in the increased cytokine hyperresponsiveness by oxLDL-trained macrophages. The TCA-cycle can also be fuelled by glutamine and free fatty acids, and pharmacological blockade of these pathways could prevent oxLDL-induced trained immunity. This study demonstrates that the mitochondria of oxLDL-trained macrophages undergo changes to their function and form with OXPHOS being an important mechanism for trained immunity, which could unveil novel pharmacological targets to prevent atherogenesis.

The role of sirtuin 1 on the induction of trained immunity.

Sirtuin 1 (SIRT1) has been described to modify immune responses by modulation of gene transcription. As transcriptional reprogramming is the molecular substrate of trained immunity, a de facto innate immune memory, we investigated the role of SIRT1 in the induction of trained immunity. We identified various SIRT1 genetic single nucleotide polymorphisms affecting innate and adaptive cytokine production of human peripheral blood mononuclear cells (PBMCs) in response to various stimuli on the one hand, and in vitro induction of trained immunity on the other hand. Furthermore, inhibition of SIRT1 upregulated pro-inflammatory innate cytokine production upon stimulation of PBMCs. However, inhibition of SIRT1 in vitro had no effect on cytokine responses upon induction of trained immunity, while activation of SIRT1 mildly modified trained immunity responses. In conclusion, SIRT1 modifies innate cytokine production by PBMCs in response to various microbes, but has only a secondary role for BCG and ß-glucan-induced trained immunity responses.

Hyperglycemic Memory of Innate Immune Cells Promotes In Vitro Proinflammatory Responses of Human Monocytes and Murine Macrophages.

It has been well established that the presence of diabetes is accompanied by a chronic inflammatory state promoting various diabetes-associated complications. One potential driver of this enhanced inflammatory state in patients with diabetes is hyperglycemia. Even after blood glucose control is achieved, diabetes-associated complications persist, suggesting the presence of a "hyperglycemic memory." Innate immune cells, critically involved in various complications associated with diabetes, can build nonspecific, immunological memory (trained immunity) via epigenetic regulation. We examine the potential involvement of hyperglycemia-induced trained immunity in promoting inflammation. Our results show that hyperglycemia induces a trained phenotype in vivo in mice and in vitro in human monocytes, representative by an increased TNF-α secretion after ex vivo stimulation with LPS. These effects were largely mediated by epigenetic changes controlled by the mixed lineage leukemia (MLL) family because treatment with the MLL inhibitor menin-MLL during the process of trained immunity acquisition repressed the proinflammatory phenotype. Collectively, our results identify a novel link between hyperglycemia and inflammation in innate immune cells that might explain the increased proinflammatory state during diabetes potentially contributing to the development of various diabetes-associated complications.

Trained immunity as a molecular mechanism for BCG immunotherapy in bladder cancer.

Intravesical BCG instillation is the gold-standard adjuvant immunotherapy for patients with high-risk non-muscle-invasive bladder cancer. However, the precise mechanism of action by which BCG asserts its beneficial effects is still unclear. BCG has been shown to induce a non-specific enhancement of the biological function in cells of the innate immune system, creating a de facto heterologous immunological memory that has been termed trained immunity. Trained immunity or innate immune memory enables innate immune cells to mount a more robust response to secondary non-related stimuli after being initially primed (or trained) by a challenge such as BCG. BCG-induced trained immunity is characterized by the metabolic rewiring of monocyte intracellular metabolism and epigenetic modifications, which subsequently lead to functional reprogramming effects, such as an increased production of cytokines, on restimulation. Results from BCG vaccination studies in humans show that trained immunity might at least partly account for the heterologous beneficial effects of BCG vaccination. Additionally, immunity might have a role in the effect of BCG immunotherapy for bladder cancer. Based on these indications, we propose that trained immunity could be one of the important mechanisms mediating BCG immunotherapy and could provide a basis for further improvements towards a personalized approach to BCG therapy in non-muscle-invasive bladder cancer.

Correction to: Rewiring of glucose metabolism defines trained immunity induced by oxidized low-density lipoprotein.

The correct name of the 17th Author is presented in this paper.

Rewiring of glucose metabolism defines trained immunity induced by oxidized low-density lipoprotein.

Stimulation of monocytes with microbial and non-microbial products, including oxidized low-density lipoprotein (oxLDL), induces a protracted pro-inflammatory, atherogenic phenotype sustained by metabolic and epigenetic reprogramming via a process called trained immunity. We investigated the intracellular metabolic mechanisms driving oxLDL-induced trained immunity in human primary monocytes and observed concomitant upregulation of glycolytic activity and oxygen consumption. In two separate cohorts of healthy volunteers, we assessed the impact of genetic variation in glycolytic genes on the training capacity of monocytes and found that variants mapped to glycolytic enzymes PFKFB3 and PFKP influenced trained immunity by oxLDL. Subsequent functional validation with inhibitors of glycolytic metabolism revealed dose-dependent inhibition of trained immunity in vitro. Furthermore, in vivo administration of the glucose metabolism modulator metformin abrogated the ability for human monocytes to mount a trained response to oxLDL. These findings underscore the importance of cellular metabolism for oxLDL-induced trained immunity and highlight potential immunomodulatory strategies for clinical management of atherosclerosis. KEY MESSAGES: Brief stimulation of monocytes to oxLDL induces a prolonged inflammatory phenotype. This is due to upregulation of glycolytic metabolism. Genetic variation in glycolytic genes modulates oxLDL-induced trained immunity. Pharmacological inhibition of glycolysis prevents trained immunity.

The Set7 Lysine Methyltransferase Regulates Plasticity in Oxidative Phosphorylation Necessary for Trained Immunity Induced by ß-Glucan.

Trained immunity confers a sustained augmented response of innate immune cells to a secondary challenge, via a process dependent on metabolic and transcriptional reprogramming. Because of its previous associations with metabolic and transcriptional memory, as well as the importance of H3 histone lysine 4 monomethylation (H3K4me1) to innate immune memory, we hypothesize that the Set7 methyltransferase has an important role in trained immunity induced by ß-glucan. Using pharmacological studies of human primary monocytes, we identify trained immunity-specific immunometabolic pathways regulated by Set7, including a previously unreported H3K4me1-dependent plasticity in the induction of oxidative phosphorylation. Recapitulation of ß-glucan training in vivo additionally identifies Set7-dependent changes in gene expression previously associated with the modulation of myelopoiesis progenitors in trained immunity. By revealing Set7 as a key regulator of trained immunity, these findings provide mechanistic insight into sustained metabolic changes and underscore the importance of characterizing regulatory circuits of innate immune memory.

Catecholamines Induce Trained Immunity in Monocytes In Vitro and In Vivo.

RATIONALE: Exposure to high catecholamine levels is associated with inflammatory changes of myeloid cells and atherosclerosis, but the underlying mechanisms are only partly understood. OBJECTIVE: To investigate whether the proinflammatory effects of noradrenaline and adrenaline can, in part, be explained by the induction of an immunologic memory in innate immune cells, termed trained immunity. METHODS AND RESULTS: In vitro, we exposed human primary monocytes to (nor)adrenaline for 24 hours, after which cells were rested and differentiated to macrophages over 5 days. After restimulation with lipopolysaccharide on day 6, (nor)adrenaline-exposed cells showed increased TNF-α (tumor necrosis factor-α) production. This coincided with an increase in glycolysis and oxidative phosphorylation measured with Seahorse technology on day 6 before restimulation. Inhibition of the ß-adrenoreceptor-cAMP signaling pathway prevented the induction of training. In vivo, we studied the functional, transcriptional, and epigenetic impact of peak-wise exposure to high catecholamine levels on monocytes isolated from pheochromocytoma/paraganglioma (PHEO) patients. In PHEO patients (n=10), the peripheral blood cell composition showed a myeloid bias and an increase of the inflammatory CD14++CD16+ (cluster of differentiation) intermediate monocyte subset compared with controls with essential hypertension (n=14). Ex vivo production of proinflammatory cytokines was higher in PHEO patients. These inflammatory changes persisted for 4 weeks after surgical removal of PHEO. Transcriptome analysis of circulating monocytes at baseline showed various differentially expressed genes in inflammatory pathways in PHEO patients; epigenetic profiling of the promoters of these genes suggests enrichment of the transcriptionally permissive chromatin mark H3K4me3 (trimethylation of lysine 4 on histone H3), indicative of in vivo training. CONCLUSIONS: Catecholamines induce long-lasting proinflammatory changes in monocytes in vitro and in vivo, indicating trained immunity. Our data contribute to the understanding of pathways driving inflammatory changes in conditions characterized by high catecholamine levels and propose that trained immunity underlies the increased cardiovascular event rate in PHEO patients.

Genetic variation in Interleukin-32 influence the immune response against New World Leishmania species and susceptibility to American Tegumentary Leishmaniasis.

Interleukin-32 is a novel inflammatory mediator that has been described to be important in the immunopathogenesis and control of infections caused by Leishmania parasites. By performing experiments with primary human cells in vitro, we demonstrate that the expression of IL-32 isoforms is dependent on the time exposed to L. amazonensis and L. braziliensis antigens. Moreover, for the first time we show the functional consequences of three different genetic variations in the IL32 (rs4786370, rs4349147, rs1555001) modulating IL-32γ expression, influencing innate and adaptive cytokine production after Leishmania exposure. Using a Brazilian cohort of 107 American Tegumentary Leishmaniasis patients and a control cohort of 245 healthy individuals, the IL32 rs4786370 genetic variant was associated with protection against ATL, whereas the IL32 rs4349147 was associated with susceptibility to the development of localized cutaneous and mucosal leishmaniasis. These novel insights may help improve therapeutic strategies and lead to benefits for patients suffering from Leishmania infections.

Aldosterone induces trained immunity: the role of fatty acid synthesis.

AIMS: Supranormal levels of aldosterone are associated with an increased cardiovascular risk in humans, and with accelerated atherosclerosis in animal models. Atherosclerosis is a low-grade inflammatory disorder, with monocyte-derived macrophages as major drivers of plaque formation. Monocytes can adopt a long-term pro-inflammatory phenotype after brief stimulation with microbial pathogens or endogenous atherogenic lipoproteins via a process termed trained immunity. In this study, we aimed to investigate whether aldosterone can induce trained immunity in primary human monocytes in vitro and explored the underlying mechanism. METHODS AND RESULTS: We exposed human monocytes to aldosterone for 24 h, after which they were rested to differentiate into monocyte-derived macrophages for 5 days, and re-stimulated with toll-like receptor 2 and 4 ligands on day 6. We demonstrated that aldosterone augments pro-inflammatory cytokine production and reactive oxygen species production in monocyte-derived macrophages after re-stimulation, via the mineralocorticoid receptor. Fatty acid synthesis was identified as a crucial pathway necessary for this induction of trained immunity and pharmacological inhibition of this pathway blunted aldosterone-induced trained immunity. At the level of gene regulation, aldosterone promoted enrichment of the transcriptionally permissive H3K4me3 modification at promoters of genes central to the fatty acid synthesis pathway. CONCLUSION: Aldosterone induces trained immunity in vitro, which is dependent on epigenetically mediated up-regulation of fatty acid synthesis. These data provide mechanistic insight into the contribution of aldosterone to inflammation, atherosclerosis, and cardiovascular disease.

ß-Glucan-Induced Trained Immunity Protects against Leishmania braziliensis Infection: a Crucial Role for IL-32.

American tegumentary leishmaniasis is a vector-borne parasitic disease caused by Leishmania protozoans. Innate immune cells undergo long-term functional reprogramming in response to infection or Bacillus Calmette-Guérin (BCG) vaccination via a process called trained immunity, conferring non-specific protection from secondary infections. Here, we demonstrate that monocytes trained with the fungal cell wall component ß-glucan confer enhanced protection against infections caused by Leishmania braziliensis through the enhanced production of proinflammatory cytokines. Mechanistically, this augmented immunological response is dependent on increased expression of interleukin 32 (IL-32). Studies performed using a humanized IL-32 transgenic mouse highlight the clinical implications of these findings in vivo. This study represents a definitive characterization of the role of IL-32γ in the trained phenotype induced by ß-glucan or BCG, the results of which improve our understanding of the molecular mechanisms governing trained immunity and Leishmania infection control.

Trained immunity and diabetic vascular disease.

Trained immunity is a recently described phenomenon whereby innate immune cells undergo functional reprogramming in response to microbial products, vaccines, or other stimuli, leading them to mount a sensitized nonspecific response to subsequent stimulation. While it is essential for the host response to pathogens, many diseases are the product of excessive or chronic inflammation. Atherosclerosis is a disease characterized by chronic low-grade inflammation of the arterial wall leading to plaque formation, where macrophages are the most abundant cell regulating plaque progression and stability. Recent studies have revealed a role for endogenous compounds related to atherosclerosis in the induction of trained immunity, which can enhance the expression of genes implicated in atherosclerosis and associated cardiovascular disease. Accelerated atherosclerosis remains the principal cause of morbidity and premature mortality in patients with diabetes, and the burden of vascular complications is greatly enhanced by prior periods of inadequate control of blood glucose. Recent findings suggest that long-term changes in bone marrow myeloid progenitors, similar to those induced by microbial products or high cholesterol diets in mice, may help to explain the chronic inflammatory state driving atherosclerosis and cardiovascular risk that exists for patients with diabetes despite improved metabolic control. From an immunometabolic perspective, we speculate that changes supporting the trained macrophage phenotype, such as up-regulation of glycolysis, indicate that a high glucose environment could enhance the pro-inflammatory consequences of trained immunity thereby contributing to the accelerated progression of atherosclerosis in patients with diabetes.

Epigenetics and Trained Immunity.

SIGNIFICANCE: A growing body of clinical and experimental evidence has challenged the traditional understanding that only the adaptive immune system can mount immunological memory. Recent findings describe the adaptive characteristics of the innate immune system, underscored by its ability to remember antecedent foreign encounters and respond in a nonspecific sensitized manner to reinfection. This has been termed trained innate immunity. Although beneficial in the context of recurrent infections, this might actually contribute to chronic immune-mediated diseases, such as atherosclerosis. Recent Advances: In line with its proposed role in sustaining cellular memories, epigenetic reprogramming has emerged as a critical determinant of trained immunity. Recent technological and computational advances that improve unbiased acquisition of epigenomic profiles have significantly enhanced our appreciation for the complexities of chromatin architecture in the contexts of diverse immunological challenges. CRITICAL ISSUES: Key to resolving the distinct chromatin signatures of innate immune memory is a comprehensive understanding of the precise physiological targets of regulatory proteins that recognize, deposit, and remove chemical modifications from chromatin as well as other gene-regulating factors. Drawing from a rapidly expanding compendium of experimental and clinical studies, this review details a current perspective of the epigenetic pathways that support the adapted phenotypes of monocytes and macrophages. FUTURE DIRECTIONS: We explore future strategies that are aimed at exploiting the mechanism of trained immunity to improve the prevention and treatment of infections and immune-mediated chronic disorders.

Monocyte and macrophage immunometabolism in atherosclerosis.

Atherosclerosis is characterized by chronic low grade inflammation of arteries that results in the development of lipid dense plaques. Chronic inflammation induced by Western-type diet is associated with the risk of developing atherosclerosis, and new insights shed light on the importance of metabolic and functional reprogramming in monocytes and macrophages for progression of atherosclerosis. This review aims to provide an overview of our current understanding into how the metabolic reprogramming of glucose, cholesterol, fatty acid, and amino acid metabolism in macrophages contributes to inflammation during atherosclerosis. Recent insights suggest that transcriptional and epigenetic adaptation within innate immune cells (termed trained immunity) play an important role in the pathogenesis of atherosclerosis. We propose that metabolic changes induced by pro-atherogenic lipoproteins partly mediate these changes in trained macrophages. Finally, we discuss the possibility of manipulating cellular metabolism of immune cells for targeted therapeutic intervention against atherosclerosis.