Aldosterone induces trained immunity: the role of fatty acid synthesis

Role of Immune Cells in Perivascular Adipose Tissue in Vascular Injury in Hypertension

Hypertension is associated with vascular injury characterized by vascular dysfunction, remodeling, and stiffening, which contributes to end-organ damage leading to cardiovascular events and potentially death. Innate (macrophages and dendritic cells), innate-like (γδ T cells) and adaptive immune cells (T and B cells) play a role in hypertension and vascular injury. Perivascular adipose tissue that is the fourth layer of the blood vessel wall is an important homeostatic regulator of vascular tone. Increased infiltration of immune cells in perivascular adipose tissue in hypertension results in generation of oxidative stress and production of cytokines that may cause vascular injury. This review presents an overview of the role of the different immune cells that infiltrate the perivascular adipose tissue and are involved in the pathophysiology of hypertension.

Integrating angio-IMR and CMR-assessed microvascular obstruction for improved risk stratification of STEMI patients

Early detection of coronary microvascular dysfunction (CMD) in ST-segment elevation myocardial infarction (STEMI) patients undergoing percutaneous coronary intervention (PCI), is challenging. The index of microcirculatory resistance (caIMR), derived from computational pressure-fluid dynamics (CPFD), allows practical assessment of CMD using only routine coronary angiography. However, the prognostic implications of combining caIMR with microvascular obstruction (MVO) identified through cardiac magnetic resonance (CMR) imaging are unclear. This retrospective study investigates the utility of CPFD-caIMR and CMR-derived MVO in predicting major adverse cardiovascular events (MACEs) in 292 STEMI patients who underwent primary PCI, followed by caIMR and CMR evaluations. Patients were stratified into four groups based on caIMR thresholds (≤ 40 U or > 40 U) and the presence/absence of MVO. The primary endpoint was MACEs, defined as cardiac death, recurrent myocardial infarction, target vessel revascularization, or heart failure readmission. Overall, 101/292 patient exhibited discordant caIMR and MVO results. Specifically, 103 patients had caIMR ≤ 40 U without MVO, while 88 patients showed caIMR > 40 U with MVO. Multivariate analysis identified both caIMR > 40 U and MVO as independent predictors of MACEs, with an HR of 3.572 for each unit increase in CPFD-caIMR > 40 U. Combination of CPFD-caIMR and MVO significantly enhanced predictive accuracy. CPFD-caIMR is a reliable, minimally invasive tool for identifying microvascular dysfunction. Combination with CMR-derived MVO improves risk stratification in STEMI patients following PCI, holding promise for the early identification of high-risk patients, enabling targeted and personalized management.

The Role of Innate Priming in Modifying Tumor-associated Macrophage Phenotype

Tumor-associated macrophages (TAMs) are innate immune cells that exert far reaching influence over the tumor microenvironment (TME). Depending on cues within the local environment, TAMs may promote tumor angiogenesis, cancer cell invasion and immunosuppression, or, alternatively, inhibit tumor progression via neoantigen presentation, tumoricidal reactive oxygen species generation and pro-inflammatory cytokine secretion. Therefore, TAMs have a pivotal role in determining tumor progression and response to therapy. TAM phenotypes are driven by cytokines and physical cues produced by tumor cells, adipocytes, fibroblasts, pericytes, immune cells, and other cells within the TME. Research has shown that TAMs can be primed by environmental stimuli, adding another layer of complexity to the environmental context that determines TAM phenotype. Innate priming is a functional consequence of metabolic and epigenetic reprogramming of innate cells by a primary stimulant, resulting in altered cellular response to future secondary stimulation. Innate priming offers a novel target for development of cancer immunotherapy and improved prognosis of disease, but also raises the risk of exacerbating existing inflammatory pathologies. This review will discuss the mechanisms underlying innate priming including metabolic and epigenetic modification, its relevance to TAMs and tumor progression, and possible clinical implications for cancer treatment.

Trained innate immunity as a potential link between preeclampsia and future cardiovascular disease

Preeclampsia (PE) is a complex pregnancy syndrome characterized by hypertension with or without proteinuria, affecting 2-6% of pregnancies globally. PE is characterized by excessive release of damage-associated molecular patterns (DAMPs) into the maternal circulation. This DAMP-rich milieu acts on innate immune cells, inducing a proinflammatory state characterized by elevated cytokines such as IL-1β and IL-18. This proinflammatory state in the mother and placenta results in the endothelial dysfunction strongly associated with cardiovascular disorders. While the immediate maternal and fetal risks of PE are well-documented, accumulating evidence indicates that PE also confers long-term cardiovascular risks to the mother, including hypertension, coronary heart disease, stroke, and heart failure. The underlying mechanisms connecting PE to these chronic cardiovascular conditions remain unclear. This article explores the potential role of trained innate immunity (TRIM) as a mechanistic link between PE and increased long-term cardiovascular risk. We propose that the persistent exposure to DAMPs during PE may epigenetically reprogram maternal innate immune cells and their progenitors, leading to TRIM. This reprogramming enhances the inflammatory response to subsequent stimuli, potentially contributing to endothelial dysfunction and chronic inflammation that predispose women to cardiovascular diseases later in life. Understanding the role of TRIM in PE could provide novel insights into the pathophysiology of PE-related cardiovascular complications and identify potential targets for therapeutic intervention. Further research is warranted to investigate the epigenetic and metabolic alterations in innate immune cells induced by PE and to determine how these changes may influence long-term maternal cardiovascular health.

Trained immunity: A link between risk factors and cardiovascular disease

Cardiovascular diseases are significant contributors to human mortality, closely associated with inflammation. With the changing living conditions and the extension of human lifespan, greater attention has been directed towards understanding the impact of early, long-term events on the development of cardiovascular events. Lifestyle factors such as stress, unhealthy diet and physical inactivity can increase the risk of cardiovascular diseases. Interestingly, even if the risk factors are addressed later, their influence may persist. Recently, the concept of trained innate immunity (TRIM), defined as sustained alterations in the function of innate immunocyte that promote a more robust response to downstream stimuli, has been proposed to be involved in cardiovascular diseases. It is hypothesized that TRIM may serve as a mediator bridging the impacts of aforementioned risk factors. This review aims to elucidate the role of TRIM in cardiovascular diseases and highlight its significance in uncovering new mechanisms and therapeutic targets.

Advances in Metabolic Regulation of Macrophage Polarization State

Macrophages are significant immune-related cells that are essential for tissue growth, homeostasis maintenance, pathogen resistance, and damage healing. The studies on the metabolic control of macrophage polarization state in recent years and the influence of polarization status on the development and incidence of associated disorders are expounded upon in this article. Firstly, we reviewed the origin and classification of macrophages, with particular attention paid to how the tricarboxylic acid cycle and the three primary metabolites affect macrophage polarization. The primary metabolic hub that controls macrophage polarization is the tricarboxylic acid cycle. Finally, we reviewed the polarization state of macrophages influences the onset and progression of cancers, inflammatory disorders, and other illnesses.

Aldosterone, Methylglyoxal, and Glycated Albumin Interaction with Macrophage Cells Affects Their Viability, Activation, and Differentiation

BACKGROUND

The inflammatory response in diabetes is strongly correlated with increasing amounts of advanced glycation end products (AGEs), methylglyoxal (MGO), aldosterone (Aldo), and activation of macrophages. Aldo is known to be associated with increased pro-inflammatory responses in general, but its significance in inflammatory responses under glycated circumstances has yet to be understood. In the current work, the aim of our study was to study the macrophage immune response in the presence of AGEs, MGO, and Aldo to comprehend their combined impact on diabetes-associated complications.

METHODS AND RESULTS

The viability of macrophages upon treatment with glycated HSA (Gly-HSA) promoted cell growth as the concentration increased from 100 to 500 μg/mL, whereas MGO at a high concentration (≥300 μM) significantly hampered cell growth. At lower concentrations (0.5-5 nM), Aldo strongly promoted cell growth, whereas at higher concentrations (50 nM), it was seen to inhibit growth when used for cell treatment for 24 h. Aldo had no effect on MGO-induced cell growth inhibition after 24 h of treatment. However, compared to MGO or Aldo treatment alone, an additional decrease in viability could be seen after 48 h of treatment with a combination of MGO and Aldo. Treatment with Aldo and MGO induced expression of TNF-α independently and when combined. However, when combined, Aldo and MGO significantly suppressed the expression of TGF-β. Aldo, Gly-HSA, and MGO strongly induced the transcription of NF-κB and RAGE mRNA and, as expected, also promoted the formation of reactive oxygen species. Also, by inducing iNOS and MHC-II and suppressing CD206 transcript expression, Gly-HSA strongly favored the differentiation of macrophages into M1 type (pro-inflammatory). On the other hand, the combination of Aldo and MGO strongly induced the expression of MHC-II, CD206, and ARG1 (M2 macrophage marker). These findings suggest that Gly-HSA, MGO, and Aldo differently influence macrophage survival, activation, and differentiation.

CONCLUSIONS

Overall, this study gives an insight into the effects of glycated protein and MGO in the presence of Aldo on macrophage survival, activation, differentiation, and inflammatory response.

Trained immunity - basic concepts and contributions to immunopathology

Trained immunity is a functional state of the innate immune response and is characterized by long-term epigenetic reprogramming of innate immune cells. This concept originated in the field of infectious diseases - training of innate immune cells, such as monocytes, macrophages and/or natural killer cells, by infection or vaccination enhances immune responses against microbial pathogens after restimulation. Although initially reported in circulating monocytes and tissue macrophages (termed peripheral trained immunity), subsequent findings indicate that immune progenitor cells in the bone marrow can also be trained (that is, central trained immunity), which explains the long-term innate immunity-mediated protective effects of vaccination against heterologous infections. Although trained immunity is beneficial against infections, its inappropriate induction by endogenous stimuli can also lead to aberrant inflammation. For example, in systemic lupus erythematosus and systemic sclerosis, trained immunity might contribute to inflammatory activity, which promotes disease progression. In organ transplantation, trained immunity has been associated with acute rejection and suppression of trained immunity prolonged allograft survival. This novel concept provides a better understanding of the involvement of the innate immune response in different pathological conditions, and provides a new framework for the development of therapies and treatment strategies that target epigenetic and metabolic pathways of the innate immune system.

Trained immunity in monocyte/macrophage: Novel mechanism of phytochemicals in the treatment of atherosclerotic cardiovascular disease

Atherosclerosis (AS) is the pathology of atherosclerotic cardiovascular diseases (ASCVD), characterized by persistent chronic inflammation in the vessel wall, in which monocytes/macrophages play a key role. It has been reported that innate immune system cells can assume a persistent proinflammatory state after short stimulation with endogenous atherogenic stimuli. The pathogenesis of AS can be influenced by this persistent hyperactivation of the innate immune system, which is termed trained immunity. Trained immunity has also been implicated as a key pathological mechanism, leading to persistent chronic inflammation in AS. Trained immunity is mediated via epigenetic and metabolic reprogramming and occurs in mature innate immune cells and their bone marrow progenitors. Natural products are promising candidates for novel pharmacological agents that can be used to prevent or treat cardiovascular diseases (CVD). A variety of natural products and agents exhibiting antiatherosclerotic abilities have been reported to potentially interfere with the pharmacological targets of trained immunity. This review describes in as much detail as possible the mechanisms involved in trained immunity and how phytochemicals of this process inhibit AS by affecting trained monocytes/macrophages.

Prophylactic and therapeutic insights into trained immunity: A renewed concept of innate immune memory

Trained immunity is a renewed concept of innate immune memory that facilitates the innate immune system to have the capacity to remember and train cells via metabolic and transcriptional events to enable them to provide nonspecific defense against the subsequent encounters with a range of pathogens and acquire a quicker and more robust immune response, but different from the adaptive immune memory. Reversing the epigenetic changes or targeting the immunological pathways may be considered potential therapeutic approaches to counteract the hyper-responsive or hypo-responsive state of trained immunity. The efficient regulation of immune homeostasis and promotion or inhibition of immune responses is required for a balanced response. Trained immunity-based vaccines can serve as potent immune stimuli and help in the clearance of pathogens in the body through multiple or heterologous effects and confer protection against nonspecific and specific pathogens. This review highlights various features of trained immunity and its applications in developing novel therapeutics and vaccines, along with certain detrimental effects, challenges as well as future perspectives.

Innate Immune Memory in Monocytes and Macrophages: The Potential Therapeutic Strategies for Atherosclerosis

Atherosclerosis is a complex metabolic disease characterized by the dysfunction of lipid metabolism and chronic inflammation in the intimal space of the vessel. As the most abundant innate immune cells, monocyte-derived macrophages play a pivotal role in the inflammatory response, cholesterol metabolism, and foam cell formation. In recent decades, it has been demonstrated that monocytes and macrophages can establish innate immune memory (also termed trained immunity) via endogenous and exogenous atherogenic stimuli and exhibit a long-lasting proinflammatory phenotype. The important cellular metabolism processes, including glycolysis, oxidative phosphorylation (OXPHOS), the tricarboxylic acid (TCA) cycle, fatty acid synthesis, and cholesterol synthesis, are reprogrammed. Trained monocytes/macrophages with innate immune memory can be persistently hyperactivated and can undergo extensive epigenetic rewiring, which contributes to the pathophysiological development of atherosclerosis via increased proinflammatory cytokine production and lipid accumulation. Here, we provide an overview of the regulation of cellular metabolic processes and epigenetic modifications of innate immune memory in monocytes/macrophages as well as the potential endogenous and exogenous stimulations involved in the progression of atherosclerosis that have been reported recently. These elucidations might be beneficial for further understanding innate immune memory and the development of therapeutic strategies for inflammatory diseases and atherosclerosis.

Innate Immune Training of Human Macrophages by Cathelicidin Analogs

Trained innate immunity can be induced in human macrophages by microbial ligands, but it is unknown if exposure to endogenous alarmins such as cathelicidins can have similar effects. Previously, we demonstrated sustained protection against infection by the chicken cathelicidin-2 analog DCATH-2. Thus, we assessed the capacity of cathelicidins to induce trained immunity. PMA-differentiated THP-1 (dTHP1) cells were trained with cathelicidin analogs for 24 hours and restimulated after a 3-day rest period. DCATH-2 training of dTHP-1 cells amplified their proinflammatory cytokine response when restimulated with TLR2/4 agonists. Trained cells displayed a biased cellular metabolism towards mTOR-dependent aerobic glycolysis and long-chain fatty acid accumulation and augmented microbicidal activity. DCATH-2-induced trained immunity was inhibited by histone acetylase inhibitors, suggesting epigenetic regulation, and depended on caveolae/lipid raft-mediated uptake, MAPK p38 and purinergic signaling. To our knowledge, this is the first report of trained immunity by host defense peptides.

Mechanisms of Post-critical Illness Cardiovascular Disease

Prolonged critical care stays commonly follow trauma, severe burn injury, sepsis, ARDS, and complications of major surgery. Although patients leave critical care following homeostatic recovery, significant additional diseases affect these patients during and beyond the convalescent phase. New cardiovascular and renal disease is commonly seen and roughly one third of all deaths in the year following discharge from critical care may come from this cluster of diseases. During prolonged critical care stays, the immunometabolic, inflammatory and neurohumoral response to severe illness in conjunction with resuscitative treatments primes the immune system and parenchymal tissues to develop a long-lived pro-inflammatory and immunosenescent state. This state is perpetuated by persistent Toll-like receptor signaling, free radical mediated isolevuglandin protein adduct formation and presentation by antigen presenting cells, abnormal circulating HDL and LDL isoforms, redox and metabolite mediated epigenetic reprogramming of the innate immune arm (trained immunity), and the development of immunosenescence through T-cell exhaustion/anergy through epigenetic modification of the T-cell genome. Under this state, tissue remodeling in the vascular, cardiac, and renal parenchymal beds occurs through the activation of pro-fibrotic cellular signaling pathways, causing vascular dysfunction and atherosclerosis, adverse cardiac remodeling and dysfunction, and proteinuria and accelerated chronic kidney disease.

Trained Immunity and HIV Infection

Findings that certain infections induce immunity not only against the causing agent, but also against an unrelated pathogen have intrigued investigators for many years. Recently, underlying mechanisms of this phenomenon have started to come to light. It was found that the key cells responsible for heterologous protection are innate immune cells such as natural killer cells (NKs), dendritic cells, and monocytes/macrophages. These cells are 'primed' by initial infection, allowing them to provide enhanced response to subsequent infection by the same or unrelated agent. This phenomenon of innate immune memory was termed 'trained immunity'. The proposed mechanism for trained immunity involves activation by the first stimulus of metabolic pathways that lead to epigenetic changes, which maintain the cell in a "trained" state, allowing enhanced responses to a subsequent stimulus. Innate immune memory can lead either to enhanced responses or to suppression of subsequent responses ('tolerance'), depending on the strength and length of the initial stimulation of the immune cells. In the context of HIV infection, innate memory induced by infection is not well understood. In this Hypothesis and Theory article, we discuss evidence for HIV-induced trained immunity in human monocytes, its possible mechanisms, and implications for HIV-associated co-morbidities.

Trained Immunity in Primary Sjögren's Syndrome: Linking Type I Interferons to a Pro-Atherogenic Phenotype

Background

Trained immunity - or innate immune memory - can be described as the long-term reprogramming of innate immune cells towards a hyperresponsive state which involves intracellular metabolic changes. Trained immunity has been linked to atherosclerosis. A subgroup of patients with primary Sjögren's syndrome (pSS) exhibits systemic type I interferon (IFN) pathway activation, indicating innate immune hyperactivation. Here, we studied the link between type I IFNs and trained immunity in an in vitro monocytic cell model and peripheral blood mononuclear cells (PBMCs) from pSS patients.

Methods

The training stimuli heat killed Candida albicans, muramyl dipeptide, IFNβ, and patient serum were added to THP-1 cells for 24 hours, after which the cells were washed, rested for 48 hours and subsequently re-stimulated with LPS, Pam3Cys, poly I:C, IFNβ or oxLDL for 4-24 hours. PBMCs from pSS patients and healthy controls were stimulated with LPS, Pam3Cys, poly I:C or IFNβ for 0.5-24 hours.

Results

Training with IFNβ induced elevated production of pro-atherogenic cytokines IL-6, TNFα and CCL2, differential cholesterol- and glycolysis-related gene expression, and increased glucose consumption and oxLDL uptake upon re-stimulation. Type I IFN production was increased in Candida albicans- and IFNβ-trained cells after LPS re-stimulation, but was reduced after poly I:C re-stimulation. Training with muramyl dipeptide and IFNβ, but not Candida albicans, affected the IFN-stimulated gene expression response to IFNβ re-stimulation. PBMCs from pSS patients consumed more glucose compared with healthy control PBMCs and tended to produce more TNFα and type I IFNs upon LPS stimulation, but less type I IFNs upon poly I:C stimulation.

Conclusions

Type I IFN is a trainer inducing a trained immunity phenotype with pro-atherogenic properties in monocytes. Conversely, trained immunity also affects the production of type I IFNs and transcriptional response to type I IFN receptor re-stimulation. The phenotype of pSS PBMCs is consistent with trained immunity. This connection between type I IFN, trained immunity and cholesterol metabolism may have important implications for pSS and the pathogenesis of (subclinical) atherosclerosis in these patients.

Role of the hematopoietic stem cells in immunological memory

Purpose of review

Immunological memory is an important evolutionary adaptation of the immune system. Previously restricted to the adaptive immune system, the concept of memory has recently been broadened to the innate immune system. This review summarizes recent studies that highlight the contribution of the hematopoietic stem cells (HSCs) in supporting immunological memory.

Recent findings

Short-lived innate immune cells can build a long-lasting memory of infection to improve their response to secondary challenges. Studies show that these unexpected properties of the innate immune system are sustained by epigenetic and metabolic changes in the HSC compartment.

Summary

HSCs are durably altered in response to pathogens and serve as long-term support for innate immune memory. Many questions remain regarding the mechanisms contributing to the induction and the maintenance of this immune memory in HSCs. Answering these questions will open new perspectives to understand how environmental factors shape the HSC activity over time.

Trained Immunity: An Overview and the Impact on COVID-19

Effectively treating infectious diseases often requires a multi-step approach to target different components involved in disease pathogenesis. Similarly, the COVID-19 pandemic has become a global health crisis that requires a comprehensive understanding of Severe Acute Respiratory Syndrome Corona Virus 2 (SARS-CoV-2) infection to develop effective therapeutics. One potential strategy to instill greater immune protection against COVID-19 is boosting the innate immune system. This boosting, termed trained immunity, employs immune system modulators to train innate immune cells to produce an enhanced, non-specific immune response upon reactivation following exposure to pathogens, a process that has been studied in the context of in vitro and in vivo clinical studies prior to the COVID-19 pandemic. Evaluation of the underlying pathways that are essential to inducing protective trained immunity will provide insight into identifying potential therapeutic targets that may alleviate the COVID-19 crisis. Here we review multiple immune training agents, including Bacillus Calmette-Guérin (BCG), β-glucan, and lipopolysaccharide (LPS), and the two most popular cell types involved in trained immunity, monocytes and natural killer (NK) cells, and compare the signaling pathways involved in innate immunity. Additionally, we discuss COVID-19 trained immunity clinical trials, emphasizing the potential of trained immunity to fight SARS-CoV-2 infection. Understanding the mechanisms by which training agents activate innate immune cells to reprogram immune responses may prove beneficial in developing preventive and therapeutic targets against COVID-19.

Hematopoietic Progenitors and the Bone Marrow Niche Shape the Inflammatory Response and Contribute to Chronic Disease

It is now well understood that the bone marrow (BM) compartment can sense systemic inflammatory signals and adapt through increased proliferation and lineage skewing. These coordinated and dynamic alterations in responding hematopoietic stem and progenitor cells (HSPCs), as well as in cells of the bone marrow niche, are increasingly viewed as key contributors to the inflammatory response. Growth factors, cytokines, metabolites, microbial products, and other signals can cause dysregulation across the entire hematopoietic hierarchy, leading to lineage-skewing and even long-term functional adaptations in bone marrow progenitor cells. These alterations may play a central role in the chronicity of disease as well as the links between many common chronic disorders. The possible existence of a form of “memory” in bone marrow progenitor cells is thought to contribute to innate immune responses via the generation of trained immunity (also called innate immune memory). These findings highlight how hematopoietic progenitors dynamically adapt to meet the demand for innate immune cells and how this adaptive response may be beneficial or detrimental depending on the context. In this review, we will discuss the role of bone marrow progenitor cells and their microenvironment in shaping the scope and scale of the immune response in health and disease.

Innate Immune Memory and the Host Response to Infection

Unlike the adaptive immune system, the innate immune system has classically been characterized as being devoid of memory functions. However, recent research shows that innate myeloid and lymphoid cells have the ability to retain memory of prior pathogen exposure and become primed to elicit a robust, broad-spectrum response to subsequent infection. This phenomenon has been termed innate immune memory or trained immunity. Innate immune memory is induced via activation of pattern recognition receptors and the actions of cytokines on hematopoietic progenitors and stem cells in bone marrow and innate leukocytes in the periphery. The trained phenotype is induced and sustained via epigenetic modifications that reprogram transcriptional patterns and metabolism. These modifications augment antimicrobial functions, such as leukocyte expansion, chemotaxis, phagocytosis, and microbial killing, to facilitate an augmented host response to infection. Alternatively, innate immune memory may contribute to the pathogenesis of chronic diseases, such as atherosclerosis and Alzheimer's disease.

Weight cycling induces innate immune memory in adipose tissue macrophages

Introduction

Weight loss improves obesity-associated diabetes risk. However, most individuals regain weight, which worsens the risk of developing diabetes and cardiovascular disease. We previously reported that male mice retain obesity-associated immunological changes even after weight loss, suggesting that immune cells may remember the state of obesity. Therefore, we hypothesized that cycles of weight gain and loss, otherwise known as weight cycling, can induce innate memory in adipose macrophages.

Methods

Bone marrow derived macrophages were primed with palmitic acid or adipose tissue conditioned media in a culture model of innate immune memory. Mice also put on low fat or high fat diets over 14-27 weeks to induce weight gain, weight loss, and weight cycling.

Results

Priming cells with palmitic acid or adipose tissue conditioned media from obese mice increased maximal glycolysis and oxidative phosphorylation and increased LPS-induced TNFα and IL-6 production. Palmitic acid effects were dependent on TLR4 and impaired by methyltransferase inhibition and AMPK activation. While weight loss improved glucose tolerance in mice, adipose macrophages were primed for greater activation to subsequent stimulation by LPS ex vivo as measured by cytokine production. In the model of weight cycling, adipose macrophages had elevated metabolism and secreted higher levels of basal TNFα, suggesting that weight loss can also prime macrophages for heighted activation to weight regain.

Discussion

Together, these data suggest that weight loss following obesity can prime adipose macrophages for enhanced inflammation upon weight regain. This innate immune memory response may contribute to worsened glucose tolerance following weight cycling.

The role of the mineralocorticoid receptor in immune cells in in cardiovascular disease

Chronic low-grade inflammation and immune cell activation are important mechanisms in the pathophysiology of cardiovascular disease (CVD). Therefore, targeted immunosuppression is a promising novel therapy to lower cardiovascular risk. In this review, we identify the mineralocorticoid receptor (MR) on immune cells as a potential target to modulate inflammation. The MR is present in almost all cells of the cardiovascular system, including immune cells. Activation of the MR in innate and adaptive immune cells induces inflammation which can contribute to CVD, by inducing endothelial dysfunction and hypertension. Moreover, it accelerates atherosclerotic plaque formation and destabilization and impairs tissue regeneration after ischemic events. Identifying the molecular targets for these non-renal actions of the MR provide promising novel cardiovascular drug targets for mineralocorticoid receptor antagonists (MRAs), which are currently mainly applied in hypertension and heart failure.

Immune Memory in Aging: a Wide Perspective Covering Microbiota, Brain, Metabolism, and Epigenetics

Non-specific innate and antigen-specific adaptive immunological memories are vital evolutionary adaptations that confer long-lasting protection against a wide range of pathogens. Adaptive memory is established by memory T and B lymphocytes following the recognition of an antigen. On the other hand, innate immune memory, also called trained immunity, is imprinted in innate cells such as macrophages and natural killer cells through epigenetic and metabolic reprogramming. However, these mechanisms of memory generation and maintenance are compromised as organisms age. Almost all immune cell types, both mature cells and their progenitors, go through age-related changes concerning numbers and functions. The aging immune system renders the elderly highly susceptible to infections and incapable of mounting a proper immune response upon vaccinations. Besides the increased infectious burden, older individuals also have heightened risks of metabolic and neurodegenerative diseases, which have an immunological component. This review discusses how immune function, particularly the establishment and maintenance of innate and adaptive immunological memory, regulates and is regulated by epigenetics, metabolic processes, gut microbiota, and the central nervous system throughout life, with a focus on old age. We explain in-depth how epigenetics and cellular metabolism impact immune cell function and contribute or resist the aging process. Microbiota is intimately linked with the immune system of the human host, and therefore, plays an important role in immunological memory during both homeostasis and aging. The brain, which is not an immune-isolated organ despite former opinion, interacts with the peripheral immune cells, and the aging of both systems influences the health of each other. With all these in mind, we aimed to present a comprehensive view of the aging immune system and its consequences, especially in terms of immunological memory. The review also details the mechanisms of promising anti-aging interventions and highlights a few, namely, caloric restriction, physical exercise, metformin, and resveratrol, that impact multiple facets of the aging process, including the regulation of innate and adaptive immune memory. We propose that understanding aging as a complex phenomenon, with the immune system at the center role interacting with all the other tissues and systems, would allow for more effective anti-aging strategies.

DAMPs and Innate Immune Training

The ability to remember a previous encounter with pathogens was long thought to be a key feature of the adaptive immune system enabling the host to mount a faster, more specific and more effective immune response upon the reencounter, reducing the severity of infectious diseases. Over the last 15 years, an increasing amount of evidence has accumulated showing that the innate immune system also has features of a memory. In contrast to the memory of adaptive immunity, innate immune memory is mediated by restructuration of the active chromatin landscape and imprinted by persisting adaptations of myelopoiesis. While originally described to occur in response to pathogen-associated molecular patterns, recent data indicate that host-derived damage-associated molecular patterns, i.e. alarmins, can also induce an innate immune memory. Potentially this is mediated by the same pattern recognition receptors and downstream signaling transduction pathways responsible for pathogen-associated innate immune training. Here, we summarize the available experimental data underlying innate immune memory in response to damage-associated molecular patterns. Further, we expound that trained immunity is a general component of innate immunity and outline several open questions for the rising field of pathogen-independent trained immunity.

Postnatal inflammation in ApoE-/- mice is associated with immune training and atherosclerosis

BACKGROUND AND AIMS

Preterm birth is associated with increased risk of cardiovascular disease (CVD). This may reflect a legacy of inflammatory exposures such as chorioamnionitis which complicate pregnancies delivering preterm, or recurrent early-life infections, which are common in preterm infants. We previously reported that experimental chorioamnionitis followed by postnatal inflammation has additive and deleterious effects on atherosclerosis in ApoE-/- mice. Here, we aimed to investigate whether innate immune training is a contributory inflammatory mechanism in this murine model of atherosclerosis.

METHODS

Bone marrow-derived macrophages and peritoneal macrophages were isolated from 13-week-old ApoE-/- mice, previously exposed to prenatal intra-amniotic (experimental choriomanionitis) and/or repeated postnatal (peritoneal) lipopolysaccharide (LPS). Innate immune responses were assessed by cytokine responses following ex vivo stimulation with toll-like receptor (TLR) agonists (LPS, Pam3Cys) and RPMI for 24-h. Bone marrow progenitor populations were studied using flow cytometric analysis.

RESULTS

Following postnatal LPS exposure, bone marrow-derived macrophages and peritoneal macrophages produced more pro-inflammatory cytokines following TLR stimulation than those from saline-treated controls, characteristic of a trained phenotype. Cytokine production ex vivo correlated with atherosclerosis severity in vivo. Prenatal LPS did not affect cytokine production capacity. Combined prenatal and postnatal LPS exposure was associated with a reduction in populations of myeloid progenitor cells in the bone marrow.

CONCLUSIONS

Postnatal inflammation results in a trained phenotype in atherosclerosis-prone mice that is not enhanced by prenatal inflammation. If analogous mechanisms occur in humans, then there may be novel early life opportunities to reduce CVD risk in infants with early life infections.

Glutathione Metabolism Contributes to the Induction of Trained Immunity

The innate immune system displays heterologous memory characteristics, which are characterized by stronger responses to a secondary challenge. This phenomenon termed trained immunity relies on epigenetic and metabolic rewiring of innate immune cells. As reactive oxygen species (ROS) production has been associated with the trained immunity phenotype, we hypothesized that the increased ROS levels and the main intracellular redox molecule glutathione play a role in the induction of trained immunity. Here we show that pharmacological inhibition of ROS in an in vitro model of trained immunity did not influence cell responsiveness; the modulation of glutathione levels reduced pro-inflammatory cytokine production in human monocytes. Single nucleotide polymorphisms (SNPs) in genes involved in glutathione metabolism were found to be associated with changes in pro-inflammatory cytokine production capacity upon trained immunity. Also, plasma glutathione concentrations were positively associated with ex vivo IL-1β production, a biomarker of trained immunity, produced by monocytes of BCG-vaccinated individuals. In conclusion, glutathione metabolism is involved in the induction of trained immunity, and future studies are warranted to explore its functional consequences in human diseases.

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.

The Role of Cell Metabolism in Innate Immune Memory

Immunological memory is classically attributed to adaptive immune responses, but recent studies have shown that challenged innate immune cells can display long-term functional changes that increase nonspecific responsiveness to subsequent infections. This phenomenon, coined trained immunity or innate immune memory, is based on the epigenetic reprogramming and the rewiring of intracellular metabolic pathways. Here, we review the different metabolic pathways that are modulated in trained immunity. Glycolysis, oxidative phosphorylation, the tricarboxylic acid cycle, amino acid, and lipid metabolism are interplaying pathways that are crucial for the establishment of innate immune memory. Unraveling this metabolic wiring allows for a better understanding of innate immune contribution to health and disease. These insights may open avenues for the development of future therapies that aim to harness or dampen the power of the innate immune response.

Immunometabolic control of trained immunity

Innate immune cells can adopt long-term inflammatory phenotypes following brief encounters with exogenous (microbial) or endogenous stimuli. This phenomenon is named trained immunity and can improve host defense against (recurrent) infections. In contrast, trained immunity can also be maladaptive in the context of chronic inflammatory disorders, such as atherosclerosis. Key to future therapeutic exploitation of this mechanism is thorough knowledge of the mechanisms driving trained immunity, which can be used as pharmacological targets. These mechanisms include profound changes in intracellular metabolism, which are closely intertwined with epigenetic reprogramming at the level of histone modifications. Glycolysis, glutamine replenishment of the tricarboxylic acid cycle with accumulation of fumarate, and the mevalonate pathway have all been identified as critical pathways for trained immunity in monocytes and macrophages. In this review, we provide a state-of-the-art overview of how these metabolic pathways interact with epigenetic programs to develop trained immunity.

Vasculometabolic and Inflammatory Effects of Aldosterone in Obesity

CONTEXT

Not all obese individuals develop cardiovascular disease (CVD). Hyperaldosteronism is suggested to cause inflammation and metabolic dysregulation, and might contribute to CVD development in obese individuals.

OBJECTIVE

We aimed to investigate the association of aldosterone concentrations with inflammation, metabolic disturbances, and atherosclerosis in overweight and obese individuals. Additionally, we measured renin concentrations to investigate whether the observed effects reflected general activation of the renin-angiotensin-aldosterone system (RAAS).

DESIGN

A cross-sectional cohort study (300-OB study) was conducted. Various inflammatory parameters, traits of the metabolic syndrome, lipidome and metabolome parameters, fat distribution, and carotid atherosclerosis were associated with plasma aldosterone and renin levels.

SETTING

The setting of this study was the Radboudumc (i.o. Radboudumc), the Netherlands.

PATIENTS

A total of 302 individuals with a body mass index greater than or equal to 27 kg/m2 participated.

MAIN OUTCOME MEASURES AND RESULTS

Aldosterone was associated with various markers of inflammation and metabolic dysregulation, which partly differed from the associations observed for renin. Although both were associated with inflammatory cell numbers, only renin was associated with classical markers of systemic inflammation. Both were associated with the metabolic syndrome and hepatic steatosis. Of the traits that constitute metabolic syndrome, aldosterone, but not renin, was associated with triglyceride concentrations. Accordingly, aldosterone was associated with large very low-density lipoprotein particles; metabolomics studies further associated aldosterone with urate concentrations and derivatives of the linoleic acid metabolism pathway. Neither aldosterone nor renin was associated with atherosclerotic plaque thickness.

CONCLUSIONS

Aldosterone is not an important driver of systemic inflammation in the obese, whereas aldosterone concentrations and metabolic dysregulation are strongly intertwined in these individuals. Although prospective studies are necessary to validate these results, the independent effects of aldosterone on carotid atherosclerosis appear modest.

Trained Immunity: Linking Obesity and Cardiovascular Disease across the Life-Course?

Obesity, a chronic inflammatory disease, is the most prevalent modifiable risk factor for cardiovascular disease. The mechanisms underlying inflammation in obesity are incompletely understood. Recent developments have challenged the dogma of immunological memory occurring exclusively in the adaptive immune system and show that the innate immune system has potential to be reprogrammed. This innate immune memory (trained immunity) is characterized by epigenetic and metabolic reprogramming of myeloid cells following endogenous or exogenous stimulation, resulting in enhanced inflammation to subsequent stimuli. Trained immunity phenotypes have now been reported for other immune and non-immune cells. Here, we provide a novel perspective on the putative role of trained immunity in mediating the adverse cardiovascular effects of obesity and highlight potential translational pathways.

Arterial Wall Inflammation and Increased Hematopoietic Activity in Patients With Primary Aldosteronism

CONTEXT

Primary aldosteronism (PA) confers an increased risk of cardiovascular disease (CVD), independent of blood pressure. Animal models have shown that aldosterone accelerates atherosclerosis through proinflammatory changes in innate immune cells; human data are scarce.

OBJECTIVE

The objective of this article is to explore whether patients with PA have increased arterial wall inflammation, systemic inflammation, and reprogramming of monocytes.

DESIGN

A cross-sectional cohort study compared vascular inflammation on 2'-deoxy-2'-(18F)fluoro-D-glucose; (18F-FDG) positron emission tomography-computed tomography, systemic inflammation, and monocyte phenotypes and transcriptome between PA patients and controls.

SETTING

This study took place at Radboudumc and Rijnstate Hospital, the Netherlands.

PATIENTS

Fifteen patients with PA and 15 age-, sex-, and blood pressure-matched controls with essential hypertension (EHT) participated.

MAIN OUTCOME MEASURES AND RESULTS

PA patients displayed a higher arterial 18F-FDG uptake in the descending and abdominal aorta (P < .01, P < .05) and carotid and iliac arteries (both P < .01). In addition, bone marrow uptake was higher in PA patients (P < .05). Although PA patients had a higher monocyte-to-lymphocyte ratio (P < .05), systemic inflammatory markers, cytokine production capacity, and transcriptome of circulating monocytes did not differ. Monocyte-derived macrophages from PA patients expressed more TNFA; monocyte-derived macrophages of healthy donors cultured in PA serum displayed increased interleukin-6 and tumor necrosis factor-α production.

CONCLUSIONS

Because increased arterial wall inflammation is associated with accelerated atherogenesis and unstable plaques, this might importantly contribute to the increased CVD risk in PA patients. We did not observe inflammatory reprogramming of circulating monocytes. However, subtle inflammatory changes are present in the peripheral blood cell composition and monocyte transcriptome of PA patients, and in their monocyte-derived macrophages. Most likely, arterial inflammation in PA requires interaction between various cell types.

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

Abstract

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.

Electronic supplementary material

The online version of this article (10.1007/s00109-020-01915-w) contains supplementary material, which is available to authorized users.

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.

Common innate pathways to autoimmune disease

Until recently, autoimmune disease research has primarily been focused on elucidating the role of the adaptive immune system. In the past decade or so, the role of the innate immune system in the pathogenesis of autoimmunity has increasingly been realized. Recent findings have elucidated paradigm-shifting concepts, for example, the implications of "trained immunity" and a dysbiotic microbiome in the susceptibility of predisposed individuals to clinical autoimmunity. In addition, the application of modern technologies such as the quantum dot (Qdot) system and 'Omics' (e.g., genomics, proteomics, and metabolomics) data-processing tools has proven fruitful in revisiting mechanisms underlying autoimmune pathogenesis and in identifying novel therapeutic targets. This review highlights recent findings discussed at the American Autoimmune Related Disease Association (AARDA) 2019 colloquium. The findings covering autoimmune diseases and autoinflammatory diseases illustrate how new developments in common innate immune pathways can contribute to the better understanding and management of these immune-mediated disorders.