Trained immunity in chronic inflammatory diseases and cancer

A decade after the term 'trained immunity' (TRIM) was coined to reflect the long-lasting hyper-responsiveness of innate immune cells with an epigenetically imprinted 'memory' of earlier stimuli, our understanding has broadened to include the potential implications of TRIM in health and disease. Here, after summarizing the well-documented beneficial effects of TRIM against infections, we discuss emerging evidence that TRIM is also a major underlying mechanism in chronic inflammation-related disorders such as periodontitis, rheumatoid arthritis and cardiovascular disease. Furthermore, mounting evidence indicates that the induction of TRIM by certain agonists confers protective antitumour responses. Although the mechanisms underlying TRIM require further study, the current knowledge enables the experimental development of innovative therapeutic approaches to stimulate or inhibit TRIM in a context-appropriate manner, such as the stimulation of TRIM in cancer or its inhibition in inflammatory disorders.

Mechanistic target of rapamycin in regulating macrophage function in inflammatory cardiovascular diseases

The mechanistic target of rapamycin (mTOR) is evolutionarily conserved from yeast to humans and is one of the most fundamental pathways of living organisms. Since its discovery three decades ago, mTOR has been recognized as the center of nutrient sensing and growth, homeostasis, metabolism, life span, and aging. The role of dysregulated mTOR in common diseases, especially cancer, has been extensively studied and reported. Emerging evidence supports that mTOR critically regulates innate immune responses that govern the pathogenesis of various cardiovascular diseases. This review discusses the regulatory role of mTOR in macrophage functions in acute inflammation triggered by ischemia and in atherosclerotic cardiovascular disease (ASCVD) and heart failure with preserved ejection fraction (HFpEF), in which chronic inflammation plays critical roles. Specifically, we discuss the role of mTOR in trained immunity, immune senescence, and clonal hematopoiesis. In addition, this review includes a discussion on the architecture of mTOR, the function of its regulatory complexes, and the dual-arm signals required for mTOR activation to reflect the current knowledge state. We emphasize future research directions necessary to understand better the powerful pathway to take advantage of the mTOR inhibitors for innovative applications in patients with cardiovascular diseases associated with aging and inflammation.

Trained immunity in atherosclerotic cardiovascular disease

Trained immunity, also known as innate immune memory, is a persistent hyper-responsive functional state of innate immune cells. Accumulating evidence implicates trained immunity as an underlying mechanism of chronic inflammation in atherosclerotic cardiovascular disease. In this context, trained immunity is induced by endogenous atherosclerosis-promoting factors, such as modified lipoproteins or hyperglycaemia, causing broad metabolic and epigenetic reprogramming of the myeloid cell compartment. In addition to traditional cardiovascular risk factors, lifestyle factors, including unhealthy diets, sedentary lifestyle, sleep deprivation and psychosocial stress, as well as inflammatory comorbidities, have been shown to activate trained immunity-like mechanisms in bone marrow haematopoietic stem cells. In this Review, we discuss the molecular and cellular mechanisms of trained immunity, its systemic regulation through haematopoietic progenitor cells in the bone marrow, and the activation of these mechanisms by cardiovascular disease risk factors. We also highlight other trained immunity features that are relevant for atherosclerotic cardiovascular disease, including the diverse cell types that show memory characteristics and transgenerational inheritance of trained immunity traits. Finally, we propose potential strategies for the therapeutic modulation of trained immunity to manage atherosclerotic cardiovascular disease.

Trained immunity in diabetes and hyperlipidemia: Emerging opportunities to target cardiovascular complications and design new therapies

Some metabolic diseases, such as diabetes and hyperlipidemia, are associated with a state of inflammation, which adversely affects cardiovascular health. Emerging evidence suggests that long-term hyperactivation of innate immune cells and their bone marrow progenitors, termed trained immunity, functions to accelerate atherosclerosis and its complications in cardiometabolic diseases. This review will focus on how trained immunity is established, particularly through metabolic and epigenetic reprogramming, to cause persistent and deleterious changes in immune cell function, even after the original stimulus has been corrected or removed. Understanding the mechanisms driving maladaptive trained immunity and its fundamental contribution to cardiovascular disease might enable the development of novel disease-modifying therapeutics for the reduction in cardiovascular risk in diabetes, hyperlipidemia, and related cardiometabolic states.

Extrinsic and intrinsic modulators of inflammation-resolution signaling in heart failure

Chronic and uncleared inflammation is the root cause of various cardiovascular diseases. Fundamentally, acute inflammation is supportive when overlapping with safe clearance of inflammation termed resolution; however, if the lifestyle-directed extrinsic factors such as diet, sleep, exercise, or physical activity are misaligned, that results in unresolved inflammation. Although genetics play a critical role in cardiovascular health, four extrinsic risk factors-unhealthy processed diet, sleep disruption or fragmentation, sedentary lifestyle, thereby, subsequent stress-have been identified as heterogeneous and polygenic triggers of heart failure (HF), which can result in several complications with indications of chronic inflammation. Extrinsic risk factors directly impact endogenous intrinsic factors, such as using fatty acids by immune-responsive enzymes [lipoxygenases (LOXs)/cyclooxygenases (COXs)/cytochromes-P450 (CYP450)] to form resolution mediators that activate specific resolution receptors. Thus, the balance of extrinsic factors such as diet, sleep, and physical activity feed-forward the coordination of intrinsic factors such as fatty acids-enzymes-bioactive lipid receptors that modulates the immune defense, metabolic health, inflammation-resolution signaling, and cardiac health. Future research on lifestyle- and aging-associated molecular patterns is warranted in the context of intrinsic and extrinsic factors, immune fitness, inflammation-resolution signaling, and cardiac health.

Hematopoietic Stem Cells in Wound Healing Response

Significance: Emerging evidence has shown a link between the status of hematopoietic stem cells (HSCs) and wound healing responses. Thus, better understanding HSCs will contribute to further advances in wound healing research. Recent Advances: Myeloid cells such as neutrophils and monocyte-derived macrophages are critical players in the process of wound healing. HSCs actively respond to wound injury and other tissue insults, including infection and produce the effector myeloid cells, and a failing of the HSC response can result in impaired wound healing. Technological advances such as transcriptome at single-cell resolution, epigenetics, three-dimensional imaging, transgenic animals, and animal models, have provided novel concepts of myeloid generation (myelopoiesis) from HSCs, and have revealed cell-intrinsic and -extrinsic mechanisms that can impact HSC functions in the context of health conditions. Critical Issues: The newer concepts include-the programmed cellular fate at a differentiation stage that is used to be considered as the multilineage, the signaling pathways that can activate HSCs directly and indirectly, the mechanisms that can deteriorate HSCs, the roles and remodeling of the surrounding environment for HSCs and their progenitors (the niche). Future Directions: The researches on HSCs, which produce blood cells, should contribute to the development of blood biomarkers predicting a risk of chronic wounds, which may transform clinical practice of wound care with precision medicine for patients at high risk of poor healing.

The future clinical implications of trained immunity

INTRODUCTION

Trained Immunity (TI) refers to the long-term modulation of the innate immune response, based on previous interactions with microbes, microbial ligands or endogenous substances. Through metabolic and epigenetic reprogramming, monocytes, macrophages and neutrophils develop an enhanced capacity to mount innate immune responses to subsequent stimuli and this is persistent due to alterations at the myeloid progenitor compartment.

AREAS COVERED

The purpose of this article is to review the current understanding of the TI process and discuss about its potential clinical implications in the near future. We address the evidence of TI involvement in various diseases, the currently developed new therapy, and discuss how TI may lead to new clinical tools to improve existing standards of care.

EXPERT OPINION

The state of art in this domain has made considerable progress, linking TI-related mechanisms in multiple immune-mediated pathologies, starting with infections to autoimmune disorders and cancers. As a relatively new area of immunology, it has seen fast progress with many of its applications ready to be investigated in clinical settings.

Apolipoprotein A1 deficiency in mice primes bone marrow stem cells for T cell lymphopoiesis

The bone marrow has emerged as a potentially important target in cardiovascular disease as it generates all leukocytes involved in atherogenesis. In the current study, we evaluated whether a change in bone marrow functionality underlies the increased atherosclerosis susceptibility associated with high-density lipoprotein (HDL) deficiency. We found that HDL deficiency in mice due to the genetic lack of hepatocyte-derived apolipoprotein A1 (APOA1) was associated with an increase in the Lin⁻Sca-1⁺Kit⁺ (LSK) bone marrow stem cell population and lymphoid-primed multipotent progenitor numbers, which translated into a higher production and systemic flux of T cell subsets. In accordance with APOA1 deficiency-associated priming of stem cells to increase T lymphocyte production, atherogenic diet-fed low-density lipoprotein receptor knockout mice transplanted with bone marrow from APOA1-knockout mice displayed marked lymphocytosis as compared to wild-type bone marrow recipients. However, atherosclerotic lesion sizes and collagen contents were similar in the two groups of bone marrow recipients. In conclusion, systemic lack of APOA1 primes bone marrow stem cells for T cell lymphopoiesis. Our data provide novel evidence for a regulatory role of HDL in bone marrow functioning in normolipidemic mice.

Summary: Changes in cholesterol metabolism, that is, in high-density lipoprotein levels, can significantly impact leukocyte numbers via modulating bone marrow functionality.

Innate immune cells in the pathophysiology of calcific aortic valve disease: lessons to be learned from atherosclerotic cardiovascular disease?

Calcific aortic valve disease (CAVD) is the most common valvular disease in the developed world with currently no effective pharmacological treatment available. CAVD results from a complex, multifactorial process, in which valvular inflammation and fibro-calcific remodelling lead to valve thickening and cardiac outflow obstruction. The exact underlying pathophysiology of CAVD is still not fully understood, yet the development of CAVD shows many similarities with the pathophysiology of atherosclerotic cardiovascular disease (ASCVD), such as coronary artery disease. Innate immune cells play a crucial role in ASCVD and might also play a pivotal role in the development of CAVD. This review summarizes the current knowledge on the role of innate immune cells, both in the circulation and in the aortic valve, in the development of CAVD and the similarities and differences with ASCVD. Trained immunity and clonal haematopoiesis of indeterminate potential are proposed as novel immunological mechanisms that possibly contribute to the pathophysiology of CAVD and new possible treatment targets are discussed.

Nucleus-mitochondria positive feedback loop formed by ERK5 S496 phosphorylation-mediated poly (ADP-ribose) polymerase activation provokes persistent pro-inflammatory senescent phenotype and accelerates coronary atherosclerosis after chemo-radiation

The incidence of cardiovascular disease (CVD) is higher in cancer survivors than in the general population. Several cancer treatments are recognized as risk factors for CVD, but specific therapies are unavailable. Many cancer treatments activate shared signaling events, which reprogram myeloid cells (MCs) towards persistent senescence-associated secretory phenotype (SASP) and consequently CVD, but the exact mechanisms remain unclear. This study aimed to provide mechanistic insights and potential treatments by investigating how chemo-radiation can induce persistent SASP. We generated ERK5 S496A knock-in mice and determined SASP in myeloid cells (MCs) by evaluating their efferocytotic ability, antioxidation-related molecule expression, telomere length, and inflammatory gene expression. Candidate SASP inducers were identified by high-throughput screening, using the ERK5 transcriptional activity reporter cell system. Various chemotherapy agents and ionizing radiation (IR) up-regulated p90RSK-mediated ERK5 S496 phosphorylation. Doxorubicin and IR caused metabolic changes with nicotinamide adenine dinucleotide depletion and ensuing mitochondrial stunning (reversible mitochondria dysfunction without showing any cell death under ATP depletion) via p90RSK-ERK5 modulation and poly (ADP-ribose) polymerase (PARP) activation, which formed a nucleus-mitochondria positive feedback loop. This feedback loop reprogramed MCs to induce a sustained SASP state, and ultimately primed MCs to be more sensitive to reactive oxygen species. This priming was also detected in circulating monocytes from cancer patients after IR. When PARP activity was transiently inhibited at the time of IR, mitochondrial stunning, priming, macrophage infiltration, and coronary atherosclerosis were all eradicated. The p90RSK-ERK5 module plays a crucial role in SASP-mediated mitochondrial stunning via regulating PARP activation. Our data show for the first time that the nucleus-mitochondria positive feedback loop formed by p90RSK-ERK5 S496 phosphorylation-mediated PARP activation plays a crucial role of persistent SASP state, and also provide preclinical evidence supporting that transient inhibition of PARP activation only at the time of radiation therapy can prevent future CVD in cancer survivors.

Nutrigenomics and Nutrigenetics in Metabolic- (Dysfunction) Associated Fatty Liver Disease: Novel Insights and Future Perspectives

Metabolic- (dysfunction) associated fatty liver disease (MAFLD) represents the predominant hepatopathy and one of the most important systemic, metabolic-related disorders all over the world associated with severe medical and socio-economic repercussions due to its growing prevalence, clinical course (steatohepatitis and/or hepatocellular-carcinoma), and related extra-hepatic comorbidities. To date, no specific medications for the treatment of this condition exist, and the most valid recommendation for patients remains lifestyle change. MAFLD has been associated with metabolic syndrome; its development and progression are widely influenced by the interplay between genetic, environmental, and nutritional factors. Nutrigenetics and nutrigenomics findings suggest nutrition's capability, by acting on the individual genetic background and modifying the specific epigenetic expression as well, to influence patients' clinical outcome. Besides, immunity response is emerging as pivotal in this multifactorial scenario, suggesting the interaction between diet, genetics, and immunity as another tangled network that needs to be explored. The present review describes the genetic background contribution to MAFLD onset and worsening, its possibility to be influenced by nutritional habits, and the interplay between nutrients and immunity as one of the most promising research fields of the future in this context.

Trained Immunity and Reactivity of Macrophages and Endothelial Cells

Innate immune cells can develop exacerbated immunologic response and long-term inflammatory phenotype following brief exposure to endogenous or exogenous insults, which leads to an altered response towards a second challenge after the return to a nonactivated state. This phenomenon is known as trained immunity (TI). TI is not only important for host defense and vaccine response but also for chronic inflammations such as cardiovascular and metabolic diseases such as atherosclerosis. TI can occur in innate immune cells such as monocytes/macrophages, natural killer cells, endothelial cells (ECs), and nonimmune cells, such as fibroblast. In this brief review, we analyze the significance of TI in ECs, which are also considered as innate immune cells in addition to macrophages. TI can be induced by a variety of stimuli, including lipopolysaccharides, BCG (bacillus Calmette-Guerin), and oxLDL (oxidized low-density lipoprotein), which are defined as risk factors for cardiovascular and metabolic diseases. Furthermore, TI in ECs is functional for inflammation effectiveness and transition to chronic inflammation. Rewiring of cellular metabolism of the trained cells takes place during induction of TI, including increased glycolysis, glutaminolysis, increased accumulation of tricarboxylic acid cycle metabolites and acetyl-coenzyme A production, as well as increased mevalonate synthesis. Subsequently, this leads to epigenetic remodeling, resulting in important changes in chromatin architecture that enables increased gene transcription and enhanced proinflammatory immune response. However, TI pathways and inflammatory pathways are separated to ensure memory stays when inflammation undergoes resolution. Additionally, reactive oxygen species play context-dependent roles in TI. Therefore, TI plays significant roles in EC and macrophage pathology and chronic inflammation. However, further characterization of TI in ECs and macrophages would provide novel insights into cardiovascular disease pathogenesis and new therapeutic targets. Graphic Abstract: A graphic abstract is available for this article.

Impact of bone marrow ATP-binding cassette transporter A1 deficiency on atherogenesis is independent of the presence of the low-density lipoprotein receptor

BACKGROUND AND AIMS

There is extensive evidence from bone marrow transplantation studies that hematopoietic ATP binding cassette A1 (Abca1) is atheroprotective in low-density lipoprotein receptor (Ldlr) deficient mice. In contrast, studies using lysosyme M promoter-driven deletion of Abca1 in Ldlr deficient mice failed to show similar effects. It was hypothesized that the discrepancy between these studies might be due to the presence of Ldlr in bone marrow-derived cells in the transplantation model. In this study, we aim to determine the contribution of Ldlr to the atheroprotective effect of hematopoietic Abca1 in the murine bone marrow transplantation model.

METHODS

Wild-type, Ldlr^-/-, Abca1^-/-, and Abca1^-/-Ldlr^-/- bone marrow was transplanted into hypercholesterolemic Ldlr^-/- mice.

RESULTS

Bone marrow Lldr deficiency did not influence the effects of Abca1 on macrophage cholesterol efflux, foam cell formation, monocytosis or plasma cholesterol. Ldlr deficiency did reduce circulating and peritoneal lymphocyte counts, albeit only in animals lacking Abca1 in bone marrow-derived cells. Importantly, the effects of Abca1 deficiency on atherosclerosis susceptibility were unaltered by the presence or absence of Ldlr. Bone marrow Ldlr deficiency did lead to marginally but consistently decreased atherosclerosis, regardless of Abca1 deficiency. Thus, Ldlr expression on bone marrow-derived cells does, to a minimal extent, influence atherosclerotic lesion development, albeit independent of Abca1.

CONCLUSIONS

This study provides novel insight into the relative impact of Ldlr and Abca1 in bone marrow-derived cells on macrophage foam cell formation and atherosclerosis development in vivo. We have shown that Ldlr and Abca1 differentially and independently influence atherosclerosis development in a murine bone marrow transplantation model of atherosclerosis.

Targeting inflammation in atherosclerosis - from experimental insights to the clinic

Atherosclerosis, a dominant and growing cause of death and disability worldwide, involves inflammation from its inception to the emergence of complications. Targeting inflammatory pathways could therefore provide a promising new avenue to prevent and treat atherosclerosis. Indeed, clinical studies have now demonstrated unequivocally that modulation of inflammation can forestall the clinical complications of atherosclerosis. This progress pinpoints the need for preclinical investigations to refine strategies for combatting inflammation in the human disease. In this Review, we consider a gamut of attractive possibilities for modifying inflammation in atherosclerosis, including targeting pivotal inflammatory pathways such as the inflammasomes, inhibiting cytokines, manipulating adaptive immunity and promoting pro-resolution mechanisms. Along with lifestyle measures, pharmacological interventions to mute inflammation could complement traditional targets, such as lipids and hypertension, to make new inroads into the management of atherosclerotic risk.

The Anti-atherogenic Role of Exercise Is Associated With the Attenuation of Bone Marrow-Derived Macrophage Activation and Migration in Hypercholesterolemic Mice

An early event in atherogenesis is the recruitment and infiltration of circulating monocytes and macrophage activation in the subendothelial space. Atherosclerosis subsequently progresses as a unresolved inflammatory disease, particularly in hypercholesterolemic conditions. Although physical exercise training has been a widely accepted strategy to inhibit atherosclerosis, its impact on arterial wall inflammation and macrophage phenotype and function has not yet been directly evaluated. Thus, the aim of this study was to investigate the effects of aerobic exercise training on the inflammatory state of atherosclerotic lesions with a focus on macrophages. Hypercholesterolemic LDL-receptor-deficient male mice were subjected to treadmill training for 8 weeks and fed a high-fat diet. Analyses included plasma lipoprotein and cytokine levels; aortic root staining for lipids (oil red O); macrophages (CD68, MCP1 and IL1β); oxidative (nitrotyrosine and, DHE) and endoplasmic reticulum (GADD) stress markers. Primary bone marrow-derived macrophages (BMDM) were assayed for migration activity, motility phenotype (Rac1 and F-actin) and inflammation-related gene expression. Plasma levels of HDL cholesterol were increased, while levels of proinflammatory cytokines (TNFa, IL1b, and IL6) were markedly reduced in the exercised mice. The exercised mice developed lower levels of lipid content and inflammation in atherosclerotic plaques. Additionally, lesions in the exercised mice had lower levels of oxidative and ER stress markers. BMDM isolated from the exercised mice showed a marked reduction in proinflammatory cytokine gene expression and migratory activity and a disrupted motility phenotype. More importantly, bone marrow from exercised mice transplanted into sedentary mice led to reduced atherosclerosis in the recipient sedentary mice, thus suggesting that epigenetic mechanisms are associated with exercise. Collectively, the presented data indicate that exercise training prevents atherosclerosis by inhibiting bone marrow-derived macrophage recruitment and activation.

Immuno-Modulation of Hematopoietic Stem and Progenitor Cells in Inflammation

Lifelong blood production is maintained by bone marrow (BM)-residing hematopoietic stem cells (HSCs) that are defined by two special properties: multipotency and self-renewal. Since dysregulation of either may lead to a differentiation block or extensive proliferation causing dysplasia or neoplasia, the genomic integrity and cellular function of HSCs must be tightly controlled and preserved by cell-intrinsic programs and cell-extrinsic environmental factors of the BM. The BM had been long regarded an immune-privileged organ shielded from immune insults and inflammation, and was thereby assumed to provide HSCs and immune cells with a protective environment to ensure blood and immune homeostasis. Recently, accumulating evidence suggests that hemato-immune challenges such as autoimmunity, inflammation or infection elicit a broad spectrum of immunological reactions in the BM, and in turn, influence the function of HSCs and BM environmental cells. Moreover, in analogy with the emerging concept of “trained immunity”, certain infection-associated stimuli are able to train HSCs and progenitors to produce mature immune cells with enhanced responsiveness to subsequent challenges, and in some cases, form an inflammatory or infectious memory in HSCs themselves. In this review, we will introduce recent findings on HSC and hematopoietic regulation upon exposure to various hemato-immune stimuli and discuss how these challenges can elicit either beneficial or detrimental outcomes on HSCs and the hemato-immune system, as well as their relevance to aging and hematologic malignancies.

Exposome and Immunity Training: How Pathogen Exposure Order Influences Innate Immune Cell Lineage Commitment and Function

Immune memory is a defining characteristic of adaptive immunity, but recent work has shown that the activation of innate immunity can also improve responsiveness in subsequent exposures. This has been coined “trained immunity” and diverges with the perception that the innate immune system is primitive, non-specific, and reacts to novel and recurrent antigen exposures similarly. The “exposome” is the cumulative exposures (diet, exercise, environmental exposure, vaccination, genetics, etc.) an individual has experienced and provides a mechanism for the establishment of immune training or immunotolerance. It is becoming increasingly clear that trained immunity constitutes a delicate balance between the dose, duration, and order of exposures. Upon innate stimuli, trained immunity or tolerance is shaped by epigenetic and metabolic changes that alter hematopoietic stem cell lineage commitment and responses to infection. Due to the immunomodulatory role of the exposome, understanding innate immune training is critical for understanding why some individuals exhibit protective phenotypes while closely related individuals may experience immunotolerant effects (e.g., the order of exposure can result in completely divergent immune responses). Research on the exposome and trained immunity may be leveraged to identify key factors for improving vaccination development, altering inflammatory disease development, and introducing potential new prophylactic treatments, especially for diseases such as COVID-19, which is currently a major health issue for the world. Furthermore, continued exposome research may prevent many deleterious effects caused by immunotolerance that frequently result in host morbidity or mortality.

Trained Immunity: An Underlying Driver of Inflammatory Atherosclerosis

Atherosclerosis, a chronic inflammatory disease of the arterial wall, is among the leading causes of morbidity and mortality worldwide. The persistence of low-grade vascular inflammation has been considered to fuel the development of atherosclerosis. However, fundamental mechanistic understanding of the establishment of non-resolving low-grade inflammation is lacking, and a large number of atherosclerosis-related cardiovascular complications cannot be prevented by current therapeutic regimens. Trained immunity is an emerging new concept describing a prolonged hyperactivation of the innate immune system after exposure to certain stimuli, leading to an augmented immune response to a secondary stimulus. While it exerts beneficial effects for host defense against invading pathogens, uncontrolled persistent innate immune activation causes chronic inflammatory diseases. In light of the above, the long-term over-activation of the innate immune system conferred by trained immunity has been recently hypothesized to serve as a link between non-resolving vascular inflammation and atherosclerosis. Here, we provide an overview of current knowledge on trained immunity triggered by various exogenous and endogenous inducers, with particular emphasis on its pro-atherogenic effects and the underlying intracellular mechanisms that act at both the cellular level and systems level. We also discuss how trained immunity could be mechanistically linked to atherosclerosis from both preclinical and clinical perspectives. This review details the mechanisms underlying the induction of trained immunity by different stimuli, and highlights that the intracellular training programs can be different, though partly overlapping, depending on the stimulus and the biological system. Thus, clinical investigation of risk factor specific innate immune memory is necessary for future use of trained immunity-based therapy in atherosclerosis.

Western Diet and the Immune System: An Inflammatory Connection

The consumption of Western-type calorically rich diets combined with chronic overnutrition and a sedentary lifestyle in Western societies evokes a state of chronic metabolic inflammation, termed metaflammation. Metaflammation contributes to the development of many prevalent non-communicable diseases (NCDs), and these lifestyle-associated pathologies represent a rising public health problem with global epidemic dimensions. A better understanding of how modern lifestyle and Western diet (WD) activate immune cells is essential for the development of efficient preventive and therapeutic strategies for common NCDs. Here, we review the current mechanistic understanding of how the Western lifestyle can induce metaflammation, and we discuss how this knowledge can be translated to protect the public from the health burden associated with their selected lifestyle.

IL-27 receptor-regulated stress myelopoiesis drives abdominal aortic aneurysm development

Abdominal aortic aneurysm (AAA) is a prevalent life-threatening disease, where aortic wall degradation is mediated by accumulated immune cells. Although cytokines regulate inflammation within the aorta, their contribution to AAA via distant alterations, particularly in the control of hematopoietic stem cell (HSC) differentiation, remains poorly defined. Here we report a pathogenic role for the interleukin-27 receptor (IL-27R) in AAA, as genetic ablation of IL-27R protects mice from the disease development. Mitigation of AAA is associated with a blunted accumulation of myeloid cells in the aorta due to the attenuation of Angiotensin II (Ang II)-induced HSC expansion. IL-27R signaling is required to induce transcriptional programming to overcome HSC quiescence and increase differentiation and output of mature myeloid cells in response to stress stimuli to promote their accumulation in the diseased aorta. Overall, our studies illuminate how a prominent vascular disease can be distantly driven by a cytokine-dependent regulation of bone marrow precursors.

Western Diet Triggers NLRP3-Dependent Innate Immune Reprogramming

Long-term epigenetic reprogramming of innate immune cells in response to microbes, also termed "trained immunity," causes prolonged altered cellular functionality to protect from secondary infections. Here, we investigated whether sterile triggers of inflammation induce trained immunity and thereby influence innate immune responses. Western diet (WD) feeding of Ldlr^-/- mice induced systemic inflammation, which was undetectable in serum soon after mice were shifted back to a chow diet (CD). In contrast, myeloid cell responses toward innate stimuli remained broadly augmented. WD-induced transcriptomic and epigenomic reprogramming of myeloid progenitor cells led to increased proliferation and enhanced innate immune responses. Quantitative trait locus (QTL) analysis in human monocytes trained with oxidized low-density lipoprotein (oxLDL) and stimulated with lipopolysaccharide (LPS) suggested inflammasome-mediated trained immunity. Consistently, Nlrp3^-/-/Ldlr^-/- mice lacked WD-induced systemic inflammation, myeloid progenitor proliferation, and reprogramming. Hence, NLRP3 mediates trained immunity following WD and could thereby mediate the potentially deleterious effects of trained immunity in inflammatory diseases.

Nutritional Modulation of Innate Immunity: The Fat-Bile-Gut Connection

Altered nutritional behavior in Western societies has unleashed numerous metabolic disorders, intimately linked to profound disruptions of the immune system. Here we summarize how nutrition modulates innate immunity. We outline recent findings regarding nutrient signaling and we particularly focus on the collateral impact of nutrition on the microbiome and on the bile acid (BA) pool. We discuss how the integration of postprandial signals by the gut microbiota, along with the absorption routes of metabolites, differentially affects immune niches to orchestrate immune responses. Finally, we discuss the potential consequences of these signals in the light of trained immunity. A better understanding of nutrition signaling will permit the optimization of therapeutic and dietary strategies against the arising immune disorders.

The role of monocytosis and neutrophilia in atherosclerosis

Monocytosis and neutrophilia are frequent events in atherosclerosis. These phenomena arise from the increased proliferation of hematopoietic stem and multipotential progenitor cells (HSPCs) and HSPC mobilization from the bone marrow to other immune organs and circulation. High cholesterol and inflammatory signals promote HSPC proliferation and preferential differentiation to the myeloid precursors (i.e., myelopoiesis) that than give rise to pro-inflammatory immune cells. These cells accumulate in the plaques thereby enhancing vascular inflammation and contributing to further lesion progression. Studies in animal models of atherosclerosis showed that manipulation with HSPC proliferation and differentiation through the activation of LXR-dependent mechanisms and restoration of cholesterol efflux may have a significant therapeutic potential.

Genomic 5-mC contents in peripheral blood leukocytes were independent protective factors for coronary artery disease with a specific profile in different leukocyte subtypes

Background

Alterations in DNA methylation are demonstrated in atherosclerosis pathogenesis. However, changing rules of global DNA methylation and hydroxymethylation in peripheral blood leukocytes (PBLs) and different blood cell subtypes of coronary artery disease (CAD) patients are still inconclusive, and much less is known about mechanisms underlying.

Results

We recruited 265 CAD patients and 270 healthy controls with genomic DNA from PBLs, of which 50 patients and 50 controls were randomly chosen with DNA from isolated neutrophils, lymphocytes and monocytes, and RNA from PBLs. Genomic 5-methylcytosine (5-mC) and 5-hydroxymethylcytosine (5-hmC) contents were quantified by liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) assay. Genomic 5-mC contents were negatively associated with the serum total cholesterol (TC) level (P = 0.010), age (P = 0.016), and PBL classifications (P = 0.023), explaining 6.8% individual variation in controls. Furthermore, genomic 5-mC contents were inversely associated with an increased risk of CAD (odds ratio (OR) = 0.325, 95% confidence interval (CI) = 0.237~0.445, P = 2.62 × 10^− 12), independent of PBL counts and classifications, age, sex, histories of hyperlipidemia, hypertension, and diabetes. Within-individual analysis showed a general 5-mC decrease in PBL subtypes, but significant difference was found in monocytes only (P = 0.001), accompanied by increased 5-hmC (P = 3.212 × 10^− 4). In addition, coincident to the reduced DNMT1 expression in patients’ PBLs, the expression level of DNMT1 was significantly lower (P = 0.022) in oxidized low-density lipoprotein (ox-LDL) stimulated THP-1-derived foam cells compared to THP-1 monocytes, with decreased genomic 5-mdC content (P = 0.038).

Conclusions

Global hypomethylation of blood cells defined dominantly by the monocyte DNA hypomethylation is independently associated with the risk of CAD in Chinese Han population. The importance of monocytes in atherosclerosis pathophysiology may demonstrate via an epigenetic pathway, but prospective studies are still needed to test the causality.

Electronic supplementary material

The online version of this article (10.1186/s13148-018-0443-x) contains supplementary material, which is available to authorized users.

Epigenetic mechanisms in coronary artery disease: The current state and prospects

Coronary artery disease (CAD) is the leading cause of morbidity and mortality. CAD has both genetic and environmental causes. In the past two decades, the understanding of epigenetics has advanced swiftly and vigorously. It has been demonstrated that epigenetic modifications are associated with the onset and progression of CAD. This review aims to improve the understanding of the epigenetic mechanisms closely related to CAD and to provide a novel perspective on the onset and development of CAD. Epigenetic changes include DNA methylation, histone modification, microRNA and lncRNA, which are interrelated with critical genes and influence the expression of those genes. In addition, miRNA plays a diverse role in the pathological process of CAD. Numerous studies have found that some cardiac-specific miRNAs have potential as certain diagnostic biomarkers and treatment targets for CAD. In this review, the aberrant epigenetic mechanisms that contribute to CAD will be discussed. We will also provide novel insight into the epigenetic mechanisms that target CAD.

Innate immune memory: Implications for host responses to damage-associated molecular patterns

Cells of the innate immune system build immunological memory via epigenetic reprogramming after stimulations with microbial ligands. This functional readjustment allows for enhanced nonspecific inflammatory responses upon secondary challenges, a process termed "trained immunity." The epigenomic blueprint of trained monocytes has been recently reported, which revealed several important immunologic and metabolic mechanisms that underlie these changes. Interestingly, similar long-term reprogramming of cytokine production has also been described to be induced by endogenous damage-associated molecular patterns (DAMPs). Here, we present an overview of the novel data showing that endogenous alarm signals associated with tissue damage and sterile inflammation can induce trained immunity through epigenetic regulation of transcriptional programs. We describe new and old evidence of persistent effects of DAMPs in driving inflammation and enforce the concept that the influence of tissue-derived signals is critical in adjusting the magnitude and type of immune response built by the host. The better characterization of trained immunity for the persistence of inflammation induced by DAMPs would provide new possibilities for intervention in aging and autoinflammatory disorders.

Long-term activation of the innate immune system in atherosclerosis

Efforts to reverse the pathologic consequences of vulnerable plaques are often stymied by the complex treatment resistant pro-inflammatory environment within the plaque. This suggests that pro-atherogenic stimuli, such as LDL cholesterol and high fat diets may impart longer lived signals on (innate) immune cells that persist even after reversing the pro-atherogenic stimuli. Recently, a series of studies challenged the traditional immunological paradigm that innate immune cells cannot display memory characteristics. Epigenetic reprogramming in these myeloid cell subsets, after exposure to certain stimuli, has been shown to alter the expression of genes upon re-exposure. This phenomenon has been termed trained innate immunity or innate immune memory. The changed responses of 'trained' innate immune cells can confer nonspecific protection against secondary infections, suggesting that innate immune memory has likely evolved as an ancient mechanism to protect against pathogens. However, dysregulated processes of immunological imprinting mediated by trained innate immunity may also be detrimental under certain conditions as the resulting exaggerated immune responses could contribute to autoimmune and inflammatory diseases, such as atherosclerosis. Pro-atherogenic stimuli most likely cause epigenetic modifications that persist for prolonged time periods even after the initial stimulus has been removed. In this review we discuss the concept of trained innate immunity in the context of a hyperlipidemic environment and atherosclerosis. According to this idea the epigenome of myeloid (progenitor) cells is presumably modified for prolonged periods of time, which, in turn, could evoke a condition of continuous immune cell over-activation.

Parainflammation, chronic inflammation, and age-related macular degeneration

Inflammation is an adaptive response of the immune system to noxious insults to maintain homeostasis and restore functionality. The retina is considered an immune-privileged tissue as a result of its unique anatomic and physiologic properties. During aging, the retina suffers from a low-grade chronic oxidative insult, which sustains for decades and increases in level with advancing age. As a result, the retinal innate-immune system, particularly microglia and the complement system, undergoes low levels of activation (parainflammation). In many cases, this parainflammatory response can maintain homeostasis in the healthy aging eye. However, in patients with age-related macular degeneration, this parainflammatory response becomes dysregulated and contributes to macular damage. Factors contributing to the dysregulation of age-related retinal parainflammation include genetic predisposition, environmental risk factors, and old age. Dysregulated parainflammation (chronic inflammation) in age-related macular degeneration damages the blood retina barrier, resulting in the breach of retinal-immune privilege, leading to the development of retinal lesions. This review discusses the basic principles of retinal innate-immune responses to endogenous chronic insults in normal aging and in age-related macular degeneration and explores the difference between beneficial parainflammation and the detrimental chronic inflammation in the context of age-related macular degeneration.

From inflammaging to healthy aging by dietary lifestyle choices: is epigenetics the key to personalized nutrition?

The progressively older population in developed countries is reflected in an increase in the number of people suffering from age-related chronic inflammatory diseases such as metabolic syndrome, diabetes, heart and lung diseases, cancer, osteoporosis, arthritis, and dementia. The heterogeneity in biological aging, chronological age, and aging-associated disorders in humans have been ascribed to different genetic and environmental factors (i.e., diet, pollution, stress) that are closely linked to socioeconomic factors. The common denominator of these factors is the inflammatory response. Chronic low-grade systemic inflammation during physiological aging and immunosenescence are intertwined in the pathogenesis of premature aging also defined as ‘inflammaging.’ The latter has been associated with frailty, morbidity, and mortality in elderly subjects. However, it is unknown to what extent inflammaging or longevity is controlled by epigenetic events in early life. Today, human diet is believed to have a major influence on both the development and prevention of age-related diseases. Most plant-derived dietary phytochemicals and macro- and micronutrients modulate oxidative stress and inflammatory signaling and regulate metabolic pathways and bioenergetics that can be translated into stable epigenetic patterns of gene expression. Therefore, diet interventions designed for healthy aging have become a hot topic in nutritional epigenomic research. Increasing evidence has revealed that complex interactions between food components and histone modifications, DNA methylation, non-coding RNA expression, and chromatin remodeling factors influence the inflammaging phenotype and as such may protect or predispose an individual to many age-related diseases. Remarkably, humans present a broad range of responses to similar dietary challenges due to both genetic and epigenetic modulations of the expression of target proteins and key genes involved in the metabolism and distribution of the dietary constituents. Here, we will summarize the epigenetic actions of dietary components, including phytochemicals, and macro- and micronutrients as well as metabolites, that can attenuate inflammaging. We will discuss the challenges facing personalized nutrition to translate highly variable interindividual epigenetic diet responses to potential individual health benefits/risks related to aging disease.

Maternal High-Fat Diet Exaggerates Atherosclerosis in Adult Offspring by Augmenting Periaortic Adipose Tissue-Specific Proinflammatory Response

Objective—

Maternal obesity elicits offspring’s metabolic disorders via developmental modifications of visceral adipose tissue; however, its effect on atherogenesis remains undefined. Perivascular adipose tissue has recently been implicated in vascular remodeling and vasoreactivity. We hypothesize that developmental modifications of perivascular adipose tissue by maternal high-fat diet (HFD) exposure promotes atherosclerosis in adult offspring.

Approach and Results—

Eight-week-old female apolipoprotein E-deficient mice were fed an HFD or normal diet (ND) during gestation and lactation. Offspring were fed a high-cholesterol diet from 8 weeks of age. Twenty-week-old male offspring of HFD-fed dams (O-HFD) showed a 2.1-fold increase in atherosclerotic lesion of the entire aorta compared with those of ND-fed dams (O-ND). Although mRNA expressions of interleukin-6, tumor necrosis factor, and monocyte chemotactic protein-1 and accumulation of macrophages in epididymal white adipose tissue were less in O-HFD than in O-ND, thoracic periaortic adipose tissue (tPAT) showed an exaggerated inflammatory response in O-HFD. Intra-abdominal transplantation of tPAT from 8-week-old O-HFD alongside the distal abdominal aorta exaggerated atherosclerosis development of the infrarenal aorta in recipient apolipoprotein E-deficient mice compared with tPAT from O-ND (210%, P <0.01). Although macrophage accumulation was rarely detected in tPAT of 8-week-old offspring, mRNA expression and protein levels of macrophage colony–stimulating factor were markedly elevated in O-HFD (2.3-fold, 3.3-fold, respectively, P <0.05), suggesting that increased macrophage colony–stimulating factor expression contributes to the augmented accumulation of macrophages, followed by the enhanced proinflammatory response.

Conclusions—

Our findings demonstrate that maternal HFD exaggerates atherosclerosis development in offspring by augmenting tPAT-specific inflammatory response proceeded by an increased expression of macrophage colony–stimulating factor.

The epigenetic memory of monocytes and macrophages as a novel drug target in atherosclerosis

PURPOSE

Atherosclerosis is characterized by a persistent inflammation of the arterial wall. Monocyte-derived macrophages are the most abundant immune cells in atherosclerotic plaques. After stimulation, monocytes can adopt a long-term proinflammatory phenotype. This nonspecific memory of innate immune cells is mediated by epigenetic reprogramming and has recently been termed "trained innate immunity." The goal of this study was to describe the potential role of trained immunity in the development of atherosclerosis and to discuss the potential clinical implications of this concept.

METHODS

We performed a comprehensive literature search (PubMed) on the role of epigenetic programming of histones, and of trained immunity in particular, in atherogenesis.

FINDINGS

In vitro studies demonstrate that modified LDL particles can induce a long-term proinflammatory phenotype in monocytes/macrophages by epigenetic reprogramming at the level of histone methylation. This scenario is associated with increased production of proatherogenic cytokines and chemokines and increased formation of foam cells.

IMPLICATIONS

Preclinical evidence suggests that trained innate immunity may contribute to vascular wall inflammation in patients with risk factors for atherosclerosis. Epigenetic reprogramming is regulated by enzymes that are amenable to pharmacologic modulation. Therefore, this mechanism could be used to develop novel pharmacologic targets for the prevention or treatment of atherosclerotic vascular disease.

Cholesterol, inflammation and innate immunity

Hypercholesterolaemia leads to cholesterol accumulation in macrophages and other immune cells, which promotes inflammatory responses, including augmentation of Toll-like receptor (TLR) signalling, inflammasome activation, and the production of monocytes and neutrophils in the bone marrow and spleen. On a cellular level, activation of TLR signalling leads to decreased cholesterol efflux, which results in further cholesterol accumulation and the amplification of inflammatory responses. Although cholesterol accumulation through the promotion of inflammatory responses probably has beneficial effects in the response to infections, it worsens diseases that are associated with chronic metabolic inflammation, including atherosclerosis and obesity. Therapeutic interventions such as increased production or infusion of high-density lipoproteins may sever the links between cholesterol accumulation and inflammation, and have beneficial effects in patients with metabolic diseases.

Epigenetic modulation in the treatment of atherosclerotic disease

Cardiovascular disease is the single largest cause of death in the western world and its incidence is on the rise globally. Atherosclerosis, characterized by the development of atheromatus plaque, can trigger luminal narrowing and upon rupture result in myocardial infarction or ischemic stroke. Epigenetic phenomena are a focus of considerable research interest due to the role they play in gene regulation. Epigenetic mechanisms such as DNA methylation and histone acetylation have been identified as potential drug targets in the treatment of cardiovascular disease. miRNAs are known to play a role in gene silencing, which has been widely investigated in cancer. In comparison, the role they play in cardiovascular disease and plaque rupture is not well understood. Nutritional epigenetic modifiers from dietary components, for instance sulforaphane found in broccoli, have been shown to suppress the pro-inflammatory response through transcription factor activation. This review will discuss current and potential epigenetic therapeutics for the treatment of cardiovascular disease, focusing on the use of miRNAs and dietary supplements such as sulforaphane and protocatechuic aldehyde.

Cholesterol efflux pathways regulate myelopoiesis: a potential link to altered macrophage function in atherosclerosis

Atherosclerotic cardiovascular disease is a chronic inflammatory disease of the blood vessels that can lead to myocardial infarction or stroke. The major cell in the atherosclerotic lesion, the macrophage, is thought to be an important contributor to the production of inflammatory mediators that exacerbate this disease. Macrophages are generally derived from circulating monocytes, which are in turn produced by hematopoietic stem and multipotential progenitor cells (HSPCs) in the bone marrow and other medullary organs. Recent studies suggest that disruption in cholesterol homeostasis or prolonged exposure to a hypercholesterolemic environment can influence HSPCs to over-produce monocytes, resulting in monocytosis. These monocytes may carry a pre-programed ability to become M1-like macrophages once they enter the atherosclerotic lesion. Future studies may help to differentiate the role of such pre-programing versus responses to local environmental cues in determining M1, M2, or other macrophage phenotypes in atherosclerotic lesions.