ApoE regulates hematopoietic stem cell proliferation, monocytosis, and monocyte accumulation in atherosclerotic lesions in mice

Effects of phytochemicals on macrophage cholesterol efflux capacity: Impact on atherosclerosis

High-density lipoprotein cholesterol (HDL) is the major promoter of reverse cholesterol transport and efflux of excess cellular cholesterol. The functions of HDL, such as cholesterol efflux, are associated with cardiovascular disease rather than HDL levels. We have reviewed the evidence base on the major classes of phytochemicals, including polyphenols, alkaloids, carotenoids, phytosterols, and fatty acids, and their effects on macrophage cholesterol efflux and its major pathways. Phytochemicals show the potential to improve the efficiency of each of these pathways. The findings are mainly in preclinical studies, and more clinical research is warranted in this area to develop novel clinical applications.

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.

Apoptotic Ablation of Platelets Reduces Atherosclerosis in Mice With Diabetes

OBJECTIVE

People with diabetes are at a significantly higher risk of cardiovascular disease, in part, due to accelerated atherosclerosis. Diabetic subjects have increased number of platelets that are activated, more reactive, and respond suboptimally to antiplatelet therapies. We hypothesized that reducing platelet numbers by inducing their premature apoptotic death would decrease atherosclerosis. Approach and Results: This was achieved by targeting the antiapoptotic protein Bcl-x_L (B-cell lymphoma-extra large; which is essential for platelet viability) via distinct genetic and pharmacological approaches. In the former, we transplanted bone marrow from mice carrying the Tyr15 to Cys loss of function allele of Bcl-x (known as Bcl-x^Plt20) or wild-type littermate controls into atherosclerotic-prone Ldlr^+/- mice made diabetic with streptozotocin and fed a Western diet. Reduced Bcl-x_L function in hematopoietic cells significantly decreased platelet numbers, exclusive of other hematologic changes. This led to a significant reduction in atherosclerotic lesion formation in Bcl-x^Plt20 bone marrow transplanted Ldlr^+/- mice. To assess the potential therapeutic relevance of reducing platelets in atherosclerosis, we next targeted Bcl-x_L with a pharmacological strategy. This was achieved by low-dose administration of the BH3 (B-cell lymphoma-2 homology domain 3) mimetic, ABT-737 triweekly, in diabetic Apoe^-/- mice for the final 6 weeks of a 12-week study. ABT-737 normalized platelet numbers along with platelet and leukocyte activation to that of nondiabetic controls, significantly reducing atherosclerosis while promoting a more stable plaque phenotype.

CONCLUSIONS

These studies suggest that selectively reducing circulating platelets, by targeting Bcl-x_L to promote platelet apoptosis, can reduce atherosclerosis and lower cardiovascular disease risk in diabetes. Graphic Abstract: A graphic abstract is available for this article.

Preclinical techniques to investigate exercise training in vascular pathophysiology

Atherosclerosis is a dynamic process starting with endothelial dysfunction and inflammation and eventually leading to life-threatening arterial plaques. Exercise generally improves endothelial function in a dose-dependent manner by altering hemodynamics, specifically by increased arterial pressure, pulsatility, and shear stress. However, athletes who regularly participate in high-intensity training can develop arterial plaques, suggesting alternative mechanisms through which excessive exercise promotes vascular disease. Understanding the mechanisms that drive atherosclerosis in sedentary versus exercise states may lead to novel rehabilitative methods aimed at improving exercise compliance and physical activity. Preclinical tools, including in vitro cell assays, in vivo animal models, and in silico computational methods, broaden our capabilities to study the mechanisms through which exercise impacts atherogenesis, from molecular maladaptation to vascular remodeling. Here, we describe how preclinical research tools have and can be used to study exercise effects on atherosclerosis. We then propose how advanced bioengineering techniques can be used to address gaps in our current understanding of vascular pathophysiology, including integrating in vitro, in vivo, and in silico studies across multiple tissue systems and size scales. Improving our understanding of the antiatherogenic exercise effects will enable engaging, targeted, and individualized exercise recommendations to promote cardiovascular health rather than treating cardiovascular disease that results from a sedentary lifestyle.

CNS and peripheral immunity in cerebral ischemia: partition and interaction

Stroke elicits excessive immune activation in the injured brain tissue. This well-recognized neural inflammation in the brain is not just an intrinsic organ response but also a result of additional intricate interactions between infiltrating peripheral immune cells and the resident immune cells in the affected areas. Given that there is a finite number of immune cells in the organism at the time of stroke, the partitioned immune systems of the central nervous system (CNS) and periphery must appropriately distribute the limited pool of immune cells between the two domains, mounting a necessary post-stroke inflammatory response by supplying a sufficient number of immune cells into the brain while maintaining peripheral immunity. Stroke pathophysiology has mainly been neurocentric in focus, but understanding the distinct roles of the CNS and peripheral immunity in their concerted action against ischemic insults is crucial. This review will discuss stroke-induced influences of the peripheral immune system on CNS injury/repair and of neural inflammation on peripheral immunity, and how comorbidity influences each.

The association of serum lipid and lipoprotein levels with total and differential leukocyte counts: Results of a cross-sectional and longitudinal analysis of the UK Biobank

BACKGROUND AND AIMS

There is some evidence of a cross-sectional, and possibly causal, relationship of lipid levels with leukocyte counts in mice and humans. This study investigates the cross-sectional and longitudinal relationship of blood lipid and lipoprotein levels with leukocyte counts in the UK Biobank cohort.

METHODS

The primary cross-sectional analysis included 417,132 participants with valid data on lipid measures and leukocyte counts. A subgroup analysis was performed in 333,668 participants with valid data on lipoprotein(a). The longitudinal analysis included 9058 participants with valid baseline and follow-up data on lipid and lipoprotein levels and leukocyte counts. The association of lipid and lipoprotein levels with leukocyte counts was analysed by multivariable linear regression.

RESULTS

Several relationships were significant in both cross-sectional and longitudinal analysis. After adjustment for demographic, socioeconomic and other confounding factors, a higher eosinophil count was associated with lower HDL cholesterol and apolipoprotein A-I concentration (p < 0.001). Higher triglycerides levels were associated with higher total leukocyte, basophil, eosinophil, monocyte and neutrophil counts (all p < 0.01). A higher lymphocyte count was associated with a higher apolipoprotein B level (p < 0.001). In the longitudinal analysis, lipoprotein(a) was inversely associated with basophil count in men but not women (p < 0.001).

CONCLUSIONS

Triglyceride levels demonstrate a robust positive association with total and differential leukocyte counts suggesting they may be directly involved in leukogenesis. However, unlike in murine models, the remainder of these relationships is modest, which suggests that cholesterol and lipoproteins are minimally involved in leukogenesis in humans.

Low High-Density Lipoprotein Cholesterol and High White Blood Cell Counts: A Mendelian Randomization Study

OBJECTIVE

Animal studies suggest that HDL (high-density lipoprotein) regulates proliferation and differentiation of hematopoietic stem cells. Using a Mendelian randomization approach, we tested the hypothesis that low HDL cholesterol is associated with high white blood cell counts. Approach and Results: We included 107 952 individuals aged 20 to 100 years from the Copenhagen General Population Study with information on HDL cholesterol, white blood cell counts, and 9 genetic variants associated with HDL cholesterol. In multivariable-adjusted observational analyses, HDL cholesterol was inversely associated with white blood cell counts. On a continuous scale, a 1-mmol/L (39 mg/dL) lower HDL cholesterol was associated with 5.1% (95% CI, 4.7%-5.4%) higher leukocytes, 4.5% (95% CI, 4.0%-4.9%) higher neutrophils, 5.7% (95% CI, 5.3%-6.1%) higher lymphocytes, 5.7% (95% CI, 5.3%-6.2%) higher monocytes, 14.8% (95% CI, 13.9%-15.8%) higher eosinophils, and 3.9% (95% CI, 3.1%-4.7%) higher basophils. In age- and sex-adjusted genetic analyses using the inverse-variance weighted analysis, a 1-mmol/L (39 mg/dL) genetically determined lower HDL cholesterol was associated with 2.2% (95% CI, 0.3%-4.1%) higher leukocytes, 4.3% (95% CI, 1.6%-7.1%) higher lymphocytes, 4.3% (95% CI, 2.6%-6.1%) higher monocytes, and 4.8% (95% CI, 1.2%-8.5%) higher eosinophils. Overall, the genetic associations were robust across sensitivity analyses and replicated using summary statistics from the UK Biobank with up to 350 470 individuals.

CONCLUSIONS

Genetic and hence lifelong low HDL cholesterol was associated with high peripheral blood leukocytes, including high lymphocytes, monocytes, and eosinophils. The concordance between observational and genetic estimates and independent replication suggest a potential causal relationship.

Inhibition of macrophage proliferation dominates plaque regression in response to cholesterol lowering

Statins induce plaque regression characterized by reduced macrophage content in humans, but the underlying mechanisms remain speculative. Studying the translational APOE*3-Leiden.CETP mouse model with a humanized lipoprotein metabolism, we find that systemic cholesterol lowering by oral atorvastatin or dietary restriction inhibits monocyte infiltration, and reverses macrophage accumulation in atherosclerotic plaques. Contrary to current believes, none of (1) reduced monocyte influx (studied by cell fate mapping in thorax-shielded irradiation bone marrow chimeras), (2) enhanced macrophage egress (studied by fluorescent bead labeling and transfer), or (3) atorvastatin accumulation in murine or human plaque (assessed by mass spectrometry) could adequately account for the observed loss in macrophage content in plaques that undergo phenotypic regression. Instead, suppression of local proliferation of macrophages dominates phenotypic plaque regression in response to cholesterol lowering: the lower the levels of serum LDL-cholesterol and lipid contents in murine aortic and human carotid artery plaques, the lower the rates of in situ macrophage proliferation. Our study identifies macrophage proliferation as the predominant turnover determinant and an attractive target for inducing plaque regression.

Transplacental Innate Immune Training via Maternal Microbial Exposure: Role of XBP1-ERN1 Axis in Dendritic Cell Precursor Programming

We recently reported that offspring of mice treated during pregnancy with the microbial-derived immunomodulator OM-85 manifest striking resistance to allergic airways inflammation, and localized the potential treatment target to fetal conventional dendritic cell (cDC) progenitors. Here, we profile maternal OM-85 treatment-associated transcriptomic signatures in fetal bone marrow, and identify a series of immunometabolic pathways which provide essential metabolites for accelerated myelopoiesis. Additionally, the cDC progenitor compartment displayed treatment-associated activation of the XBP1-ERN1 signalling axis which has been shown to be crucial for tissue survival of cDC, particularly within the lungs. Our forerunner studies indicate uniquely rapid turnover of airway mucosal cDCs at baseline, with further large-scale upregulation of population dynamics during aeroallergen and/or pathogen challenge. We suggest that enhanced capacity for XBP1-ERN1-dependent cDC survival within the airway mucosal tissue microenvironment may be a crucial element of OM-85-mediated transplacental innate immune training which results in postnatal resistance to airway inflammatory disease.

Trained Immunity and Cardiometabolic Disease: The Role of Bone Marrow

Until recently, immunologic memory was considered an exclusive characteristic of adaptive immunity. However, recent advances suggest that the innate arm of the immune system can also mount a type of nonspecific memory responses. Innate immune cells can elicit a robust response to subsequent inflammatory challenges after initial activation by certain stimuli, such as fungal-derived agents or vaccines. This type of memory, termed trained innate immunity (also named innate immune memory), is associated with epigenetic and metabolic alterations. Hematopoietic progenitor cells, which are the cells responsible for the generation of mature myeloid cells at steady-state and during inflammation, have a critical contribution to the induction of innate immune memory. Inflammation-triggered alterations in cellular metabolism, the epigenome and transcriptome of hematopoietic progenitor cells in the bone marrow promote long-lasting functional changes, resulting in increased myelopoiesis and consequent generation of trained innate immune cells. In the present brief review, we focus on the involvement of hematopoietic progenitors in the process of trained innate immunity and its possible role in cardiometabolic disease.

Genetically determined hypercholesterolaemia results into premature leucocyte telomere length shortening and reduced haematopoietic precursors

AIMS

Leucocyte telomere length (LTL) shortening is a marker of cellular senescence and associates with increased risk of cardiovascular disease (CVD). A number of cardiovascular risk factors affect LTL, but the correlation between elevated LDL cholesterol (LDL-C) and shorter LTL is debated: in small cohorts including subjects with a clinical diagnosis of familial hypercholesterolaemia (FH). We assessed the relationship between LDL-C and LTL in subjects with genetic familial hypercholesterolaemia (HeFH) compared to those with clinically diagnosed, but not genetically confirmed FH (CD-FH), and normocholesterolaemic subjects.

METHODS AND RESULTS

LTL was measured in mononuclear cells-derived genomic DNA from 206 hypercholesterolaemic subjects (135 HeFH and 71 CD-FH) and 272 controls. HeFH presented shorter LTL vs. controls (1.27 ± 0.07 vs. 1.59 ± 0.04, P = 0.045). In particular, we found shorter LTL in young HeFH as compared to young controls (<35 y) (1.34 ± 0.08 vs. 1.64 ± 0.08, P = 0.019); moreover, LTL was shorter in statin-naïve HeFH subjects as compared to controls (1.23 ± 0.08 vs. 1.58 ± 0.04, P = 0.001). HeFH subjects presented shorter LTL compared to LDL-C matched CD-FH (1.33 ± 0.05 vs. 1.55 ± 0.08, P = 0.029). Shorter LTL was confirmed in leucocytes of LDLR-KO vs. wild-type mice and associated with lower abundance of long-term haematopoietic stem and progenitor cells (LT-HSPCs) in the bone marrow. Accordingly, HeFH subjects presented lower circulating haematopoietic precursors (CD34 + CD45dim cells) vs. CD-FH and controls.

CONCLUSIONS

We found (i) shorter LTL in genetically determined hypercholesterolaemia, (ii) lower circulating haematopoietic precursors in HeFH subjects, and reduced bone marrow resident LT-HSPCs in LDLR-KO mice. We support early cellular senescence and haematopoietic alterations in subjects with FH.

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.

Inhibition of interleukin-1β signalling promotes atherosclerotic lesion remodelling in mice with inflammatory arthritis

OBJECTIVES

Rheumatoid arthritis (RA), an inflammatory joint disorder, independently increases the risk of cardiovascular disease (CVD). IL-1β contributes to both RA and CVD. We hypothesised that inhibiting IL-1 signalling with the IL-1R antagonist, anakinra, would dampen inflammation and promote resolution of atherosclerosis in arthritic mice.

METHODS

Low-density lipoprotein receptor (Ldlr)-deficient mice were fed a Western-type diet for 14 weeks to develop atherosclerotic plaques. Mice were then switched to a chow diet, promoting lesion regression, and randomised to a control group or into groups where arthritis was induced by passive transfer of K/BxN arthritogenic serum. The arthritic mice were further randomised to vehicle or anakinra.

RESULTS

Arthritis impaired atherosclerotic lesion regression when cholesterol was lowered. This was associated with a higher burden of plaque macrophages, likely due to monocytosis, driven by myelopoiesis in the bone marrow and spleen. Interestingly, delayed intervention with anakinra had no effect on arthritis in these mice. However, a significant improvement in atherosclerotic plaque remodelling to a more stable phenotype was observed. This was associated with fewer circulating monocytes, caused by a reduction in splenic extramedullary myelopoiesis.

CONCLUSION

We show that inhibiting IL-1 signalling in arthritic mice with pre-existing atherosclerosis promotes lesion remodelling to a more stable phenotype, that is less likely to rupture and cause ischemic events such as myocardial infarction. This suggests that IL-1R antagonism may suppress CVD complications in patients with RA. Furthermore, inhibiting IL-1β signalling in other patients with inflammatory diseases that also predispose to CVD may also benefit from anti-IL-1 therapy.

Immunometabolic control of hematopoiesis

Hematopoietic stem cells (HSC) lie at the center of the hematopoiesis process, as they bear capacity to self-renew and generate all hematopoietic lineages, hence, all mature blood cells. The ability of HSCs to recognize systemic infection or inflammation or other forms of peripheral stress, such as blood loss, is essential for demand-adapted hematopoiesis. Also of critical importance for HSC function, specific metabolic cues (e.g., associated with changes in energy or O₂ levels) can regulate HSC function and fate decisions. In this regard, the metabolic adaptation of HSCs facilitates their switching between different states, namely quiescence, self-renewal, proliferation and differentiation. Specific metabolic alterations in hematopoietic stem and progenitor cells (HSPCs) have been linked with the induction of trained myelopoiesis in the bone marrow as well as with HSPC dysfunction in aging and clonal hematopoiesis of indeterminate potential (CHIP). Thus, HSPC function is regulated by both immunologic/inflammatory and metabolic cues. The immunometabolic control of HSPCs and of hematopoiesis is discussed in this review along with the translational implications thereof, that is, how metabolic pathways can be therapeutically manipulated to prevent or reverse HSPC dysfunction or to enhance or attenuate trained myelopoiesis according to the needs of the host.

Liver X Receptors: Regulators of Cholesterol Metabolism, Inflammation, Autoimmunity, and Cancer

The interplay between cellular stress and immune response can be variable and sometimes contradictory. The mechanisms by which stress-activated pathways regulate the inflammatory response to a pathogen, in autoimmunity or during cancer progression remain unclear in many aspects, despite our recent knowledge of the signalling and transcriptional pathways involved in these diseases. In this context, over the last decade many studies demonstrated that cholesterol metabolism is an important checkpoint for immune homeostasis and cancer progression. Indeed, cholesterol is actively metabolized and can regulate, through its mobilization and/or production of active derivatives, many aspects of immunity and inflammation. Moreover, accumulation of cholesterol has been described in cancer cells, indicating metabolic addiction. The nuclear receptors liver-X-receptors (LXRs) are important regulators of intracellular cholesterol and lipids homeostasis. They have also key regulatory roles in immune response, as they can regulate inflammation, innate and adaptive immunity. Moreover, activation of LXRs has been reported to affect the proliferation and survival of different cancer cell types that show altered metabolic pathways and accumulation of cholesterol. In this minireview we will give an overview of the recent understandings about the mechanisms through which LXRs regulate inflammation, autoimmunity, and cancer, and the therapeutic potential for future treatment of these diseases through modulation of cholesterol metabolism.

Stress erythropoiesis in atherogenic mice

Bone marrow erythropoiesis is mainly homeostatic and a demand of oxygen in tissues activates stress erythropoiesis in the spleen. Here, we show an increase in the number of circulating erythrocytes in apolipoprotein E-/- mice fed a Western high-fat diet, with similar number of circulating leukocytes and CD41+ events (platelets). Atherogenic conditions increase spleen erythropoiesis with no variations of this cell lineage in the bone marrow. Spleens from atherogenic mice show augmented number of late-stage erythroblasts and biased differentiation of progenitor cells towards the erythroid cell lineage, with an increase of CD71+CD41CD34-CD117+Sca1-Lin- cells (erythroid-primed megakaryocyte-erythroid progenitors), which is consistent with the way in which atherogenesis modifies the expression of pro-erythroid and pro-megakaryocytic genes in megakaryocyte-erythroid progenitors. These data explain the transiently improved response to an acute severe hemolytic anemia insult found in atherogenic mice in comparison to control mice, as well as the higher burst-forming unit-erythroid and colony forming unit-erythroid capacity of splenocytes from atherogenic mice. In conclusion, our work demonstrates that, along with the well stablished enhancement of monocytosis during atherogenesis, stress erythropoiesis in apolipoprotein E-/- mice fed a Western high fat diet results in increased numbers of circulating red blood cells.

Contribution of Extramedullary Hematopoiesis to Atherosclerosis. The Spleen as a Neglected Hub of Inflammatory Cells

Cardiovascular diseases (CVDs) incidence is becoming higher. This fact is promoted by metabolic disorders such as obesity, and aging. Atherosclerosis is the underlying cause of most of these pathologies. It is a chronic inflammatory disease that begins with the progressive accumulation of lipids and fibrotic materials in the blood-vessel wall, which leads to massive leukocyte recruitment. Rupture of the fibrous cap of the atherogenic cusps is responsible for tissue ischemic events, among them myocardial infarction. Extramedullary hematopoiesis (EMH), or blood cell production outside the bone marrow (BM), occurs when the normal production of these cells is impaired (chronic hematological and genetic disorders, leukemia, etc.) or is altered by metabolic disorders, such as hypercholesterolemia, or after myocardial infarction. Recent studies indicate that the main EMH tissues (spleen, liver, adipose and lymph nodes) complement the hematopoietic function of the BM, producing circulating inflammatory cells that infiltrate into the atheroma. Indeed, the spleen, which is a secondary lymphopoietic organ with high metabolic activity, contains a reservoir of myeloid progenitors and monocytes, constituting an important source of inflammatory cells to the atherosclerotic lesion. Furthermore, the spleen also plays an important role in lipid homeostasis and immune-cell selection. Interestingly, clinical evidence from splenectomized subjects shows that they are more susceptible to developing pathologies, such as dyslipidemia and atherosclerosis due to the loss of immune selection. Although CVDs represent the leading cause of death worldwide, the mechanisms involving the spleen-atherosclerosis-heart axis cross-talk remain poorly characterized.

Implications of metabolism-driven myeloid dysfunctions in cancer therapy

Immune homeostasis is maintained by an adequate balance of myeloid and lymphoid responses. In chronic inflammatory states, including cancer, this balance is lost due to dramatic expansion of myeloid progenitors that fail to mature to functional inflammatory neutrophils, macrophages, and dendritic cells (DCs), thus giving rise to a decline in the antitumor effector lymphoid response. Cancer-related inflammation orchestrates the production of hematopoietic growth factors and cytokines that perpetuate recruitment and activation of myeloid precursors, resulting in unresolved and chronic inflammation. This pathologic inflammation creates profound alterations in the intrinsic cellular metabolism of the myeloid progenitor pool, which is amplified by competition for essential nutrients and by hypoxia-induced metabolic rewiring at the tumor site. Therefore, persistent myelopoiesis and metabolic dysfunctions contribute to the development of cancer, as well as to the severity of a broad range of diseases, including metabolic syndrome and autoimmune and infectious diseases. The aims of this review are to (1) define the metabolic networks implicated in aberrant myelopoiesis observed in cancer patients, (2) discuss the mechanisms underlying these clinical manifestations and the impact of metabolic perturbations on clinical outcomes, and (3) explore new biomarkers and therapeutic strategies to restore immunometabolism and differentiation of myeloid cells towards an effector phenotype to increase host antitumor immunity. We propose that the profound metabolic alterations and associated transcriptional changes triggered by chronic and overactivated immune responses in myeloid cells represent critical factors influencing the balance between therapeutic efficacy and immune-related adverse effects (irAEs) for current therapeutic strategies, including immune checkpoint inhibitor (ICI) therapy.

Aryl hydrocarbon receptor connects dysregulated immune cells to atherosclerosis

As a chronic inflammatory disease with autoimmune components, atherosclerosis is the major cause of cardiovascular morbidity and mortality. Recent studies have revealed that the development of atherosclerosis is strongly linked to the functional activities of aryl hydrocarbon receptor (AHR), a chemical sensor that is also important for the development, maintenance, and function of a variety of immune cells. In this review, we focus on the impact of AHR signaling on the different cell types that are closely related to the atherogenesis, including T cells, B cells, dendritic cells, macrophages, foam cells, and hematopoietic stem cells in the arterial walls, and summarize the latest development on the interplay between this environmental sensor and immune cells in the context of atherosclerosis. Hopefully, elucidation of the role of AHR in atherosclerosis will facilitate the understanding of case variation in disease prevalence and may aid in the development of novel therapies.

Targeted deletion of PD-1 in myeloid cells induces antitumor immunity

PD-1, a T cell checkpoint receptor and target of cancer immunotherapy, is also expressed on myeloid cells. The role of myeloid-specific versus T cell-specific PD-1 ablation on antitumor immunity has remained unclear because most studies have used either PD-1-blocking antibodies or complete PD-1 KO mice. We generated a conditional allele, which allowed myeloid-specific (PD-1^f/fLysMcre) or T cell-specific (PD-1^f/fCD4cre) targeting of Pdcd1 gene. Compared with T cell-specific PD-1 ablation, myeloid cell-specific PD-1 ablation more effectively decreased tumor growth. We found that granulocyte/macrophage progenitors (GMPs), which accumulate during cancer-driven emergency myelopoiesis and give rise to myeloid-derived suppressor cells (MDSCs), express PD-1. In tumor-bearing PD-1^f/fLysMcre but not PD-1^f/fCD4cre mice, accumulation of GMP and MDSC was prevented, whereas systemic output of effector myeloid cells was increased. Myeloid cell-specific PD-1 ablation induced an increase of T effector memory cells with improved functionality and mediated antitumor protection despite preserved PD-1 expression in T cells. In PD-1-deficient myeloid progenitors, growth factors driving emergency myelopoiesis induced increased metabolic intermediates of glycolysis, pentose phosphate pathway, and TCA cycle but, most prominently, elevated cholesterol. Because cholesterol is required for differentiation of inflammatory macrophages and DC and promotes antigen-presenting function, our findings indicate that metabolic reprogramming of emergency myelopoiesis and differentiation of effector myeloid cells might be a key mechanism of antitumor immunity mediated by PD-1 blockade.

Tau at the interface between neurodegeneration and neuroinflammation

Tau is an evolutionary conserved protein that promotes the assembly and stabilization of microtubules in neuronal axons. Complex patterns of posttranslational modifications (PTMs) dynamically regulate tau biochemical properties and consequently its functions. An imbalance in tau PTMs has been connected with a broad spectrum of neurodegenerative conditions which are collectively known as tauopathies and include Alzheimer's disease (AD), progressive supranuclear palsy (PSP), and corticobasal degeneration (CBD) among others. The hallmark of these neurological disorders is the presence in the brain of fibrillary tangles constituted of misfolded species of hyper-phosphorylated tau. The pathological events leading to tau aggregation are still largely unknown but increasing evidence suggests that neuroinflammation plays a critical role in tangle formation. Moreover, tau aggregation itself could enhance inflammation through feed-forward mechanisms, amplifying the initial neurotoxic insults. Protective effects of tau against neuroinflammation have been also documented, adding another layer of complexity to this phenomenon. Here, we will review the current knowledge on tau regulation and function in health and disease. In particular, we will address its emerging role in connecting neurodegenerative and neuroinflammatory processes.

Myocardial Infarction Does Not Accelerate Atherosclerosis in a Mouse Model of Type 1 Diabetes

In addition to increasing the risk of an initial myocardial infarction (MI), diabetes increases the risk of a recurrent MI. Previous work suggests that an experimental MI can accelerate atherosclerosis via monocytosis. To test whether diabetes and experimental MI synergize to accelerate atherosclerosis, we performed ligation of the left anterior descending coronary artery to induce experimental MI or sham surgery in nondiabetic and diabetic mice with preexisting atherosclerosis. All mice subjected to experimental MI had significantly reduced left ventricular function. In our model, in comparisons with nondiabetic sham mice, neither diabetes nor MI resulted in monocytosis. Neither diabetes nor MI led to increased atherosclerotic lesion size, but diabetes accelerated lesion progression, exemplified by necrotic core expansion. The necrotic core expansion was dependent on monocyte recruitment, as mice with myeloid cells deficient in the adhesion molecule integrin α4 were protected from necrotic core expansion. In summary, diabetes, but not MI, accelerates lesion progression, suggesting that the increased risk of recurrent MI in diabetes is due to a higher lesional burden and/or elevated risk factors rather than the acceleration of the underlying pathology from a previous MI.

Non-hematopoietic erythropoietin-derived peptides for atheroprotection and treatment of cardiovascular diseases

Relevance: Cardiovascular diseases continue to be the leading cause of premature adult death.

Lipid profile and atherogenesis: Dislipidaemia leads to subsequent lipid accumulation and migration of immunocompetent cells into the vessel intima. Macrophages accumulate cholesterol forming foam cells – the morphological substrate of atherosclerosis in its initial stage.

Inflammation and atherogenesis: Pro-inflammatory factors provoke oxidative stress, vascular wall damage and foam cells formation.

Endothelial and mitochondrial dysfunction in the development of atherosclerosis: Endothelial mitochondria are some of the organelles most sensitive to oxidative stress. Damaged mitochondria produce excess superoxide and H2O2, which are the main factors of intracellular damage, further increasing endothelial dysfunction.

Short non-hematopoietic erythropoietin-based peptides as innovative atheroprotectors: Research in recent decades has shown that erythropoietin has a high cytoprotective activity, which is mainly associated with exposure to the mitochondrial link and has been confirmed in various experimental models. There is also a short-chain derivative, the 11-amino acid pyroglutamate helix B surface peptide (PHBSP), which selectively binds to the erythropoietin heterodymic receptor and reproduces its cytoprotective properties. This indicates the promising use of short-chain derivatives of erythropoietin for the treatment and prevention of atherosclerotic vascular injury. In the future, it is planned to study the PHBSP derivatives, the modification of which consists in adding RGD and PGP tripeptides with antiaggregant properties to the original 11-member peptide.

Apo AI Nanoparticles Delivered Post Myocardial Infarction Moderate Inflammation

RATIONALE

Decades of research have examined immune-modulatory strategies to protect the heart after an acute myocardial infarction and prevent progression to heart failure but have failed to translate to clinical benefit.

OBJECTIVE

To determine anti-inflammatory actions of n-apo AI (Apo AI nanoparticles) that contribute to cardiac tissue recovery after myocardial infarction.

METHODS AND RESULTS

Using a preclinical mouse model of myocardial infarction, we demonstrate that a single intravenous bolus of n-apo AI (CSL111, 80 mg/kg) delivered immediately after reperfusion reduced the systemic and cardiac inflammatory response. N-apo AI treatment lowered the number of circulating leukocytes by 30±7% and their recruitment into the ischemic heart by 25±10% (all P<5.0×10^-2). This was associated with a reduction in plasma levels of the clinical biomarker of cardiac injury, cardiac troponin-I, by 52±17% (P=1.01×10^-2). N-apo AI reduced the cardiac expression of chemokines that attract neutrophils and monocytes by 60% to 80% and lowered surface expression of integrin CD11b on monocytes by 20±5% (all P<5.0×10^-2). Fluorescently labeled n-apo AI entered the infarct and peri-infarct regions and colocalized with cardiomyocytes undergoing apoptosis and with leukocytes. We further demonstrate that n-apo AI binds to neutrophils and monocytes, with preferential binding to the proinflammatory monocyte subtype and partially via SR-BI (scavenger receptor BI). In patients with type 2 diabetes, we also observed that intravenous infusion of the same n-apo AI (CSL111, 80 mg/kg) similarly reduced the level of circulating leukocytes by 12±5% (all P<5.0×10^-2).

CONCLUSIONS

A single intravenous bolus of n-apo AI delivered immediately post-myocardial infarction reduced the systemic and cardiac inflammatory response through direct actions on both the ischemic myocardium and leukocytes. These data highlight the anti-inflammatory effects of n-apo AI and provide preclinical support for investigation of its use for management of acute coronary syndromes in the setting of primary percutaneous coronary interventions.

Inhibition of JAK2 Suppresses Myelopoiesis and Atherosclerosis in Apoe-/- Mice

OBJECTIVE

Increased myelopoiesis has been linked to risk of atherosclerotic cardiovascular disease (ACD). Excessive myelopoiesis can be driven by dyslipidemia and cholesterol accumulation in hematopoietic stem and progenitor cells (HSPC) and may involve increased signaling via Janus kinase 2 (JAK2). Constitutively activating JAK2 mutants drive biased myelopoiesis and promote development of myeloproliferative neoplasms (MPN) or clonal hematopoiesis, conditions associated with increased risk of ACD. JAK2 inhibitors have been developed as a therapy for MPNs. The potential for JAK2 inhibitors to protect against atherosclerosis has not been tested. We therefore assessed the impact of JAK2 inhibition on atherogenesis.

METHODS

A selective JAK2 inhibitor TG101348 (fedratinib) or vehicle was given to high-fat high-cholesterol Western diet (WD)-fed wild-type (WT) or Apoe^-/- mice. Hematopoietic cell profiles, cell proliferation, and atherosclerosis in WT or Apoe^-/- mice were assessed.

RESULTS

TG101348 selectively reversed neutrophilia, monocytosis, HSPC, and granulocyte-macrophage progenitor (GMP) expansion in Apoe^-/- mice with decreased cellular phosphorylated STAT5 and ERK1/2 and reduced cell cycling and BrdU incorporation in HSPCs, indicating inhibition of JAK/STAT signaling and cell proliferation. Ten-week WD feeding allowed the development of marked aortic atherosclerosis in Apoe^-/- mice which was substantially reduced by TG101348.

CONCLUSIONS

Selective JAK2 inhibition reduces atherogenesis by suppressing excessive myelopoiesis in hypercholesterolemic Apoe^-/- mice. These findings suggest selective JAK2 inhibition as a potential therapeutic approach to decrease ACD risk in patients with increased myelopoiesis and leukocytosis.

Renal denervation mitigates atherosclerosis in ApoE-/- mice via the suppression of inflammation

Atherosclerosis is a chronic pathological process characterized by the accumulation of inflammation. Overactivation of the sympathetic nervous system accelerates the progression of atherosclerosis. Renal denervation (RDN) reduces the activity of the sympathetic nerve system (SNS) by disrupting sympathetic nerves surrounding renal arteries. We sought to determine whether RDN could mitigate atherosclerosis through the suppression of inflammation. First, we investigated the correlation between plasma norepinephrine concentrations and circulatory inflammation in the progression of atherosclerosis. Then, forty ApoE-/- mice underwent renal denervation or a sham operation after 6 weeks or 12 weeks of feeding with a high-fat diet. The effects of RDN on atherosclerosis in mice were explored. In the development of atherosclerosis, positive correlations were found between SNS activation and the accumulation of circulatory myeloid cells and inflammatory cytokines. In the second part of the study, inhibition of the increase in plaque size was found in both RDN groups compared with that in the sham operation (SO) groups (P<0.05), and RDN also ameliorated inflammation in plaques. Furthermore, RDN attenuated the accumulation of circulating neutrophils and monocytes (P<0.05), which is associated with a significant reduction in levels of several circulating inflammatory cytokines related to hemopoiesis (P<0.05). Flow cytometry analysis revealed comparable levels of neutrophils and monocytes in the bone marrow between all four groups. However, RDN decreased the production and proportions of neutrophils and monocytes in the spleen and reduced splenic sympathetic activity (P<0.05). In summary, our study reveals a novel link between SNS activity and inflammation in atherosclerosis and identifies RDN as a potential anti-inflammatory therapeutic strategy for the treatment of atherosclerosis by restricting the production of splenic immune cells.

Epithelial membrane protein 2 governs transepithelial migration of neutrophils into the airspace

Whether respiratory epithelial cells regulate the final transit of extravasated neutrophils into the inflamed airspace or are a passive barrier is poorly understood. Alveolar epithelial type 1 (AT1) cells, best known for solute transport and gas exchange, have few established immune roles. Epithelial membrane protein 2 (EMP2), a tetraspan protein that promotes recruitment of integrins to lipid rafts, is highly expressed in AT1 cells but has no known function in lung biology. Here, we show that Emp2-/- mice exhibit reduced neutrophil influx into the airspace after a wide range of inhaled exposures. During bacterial pneumonia, Emp2-/- mice had attenuated neutrophilic lung injury and improved survival. Bone marrow chimeras, intravital neutrophil labeling, and in vitro assays suggested that defective transepithelial migration of neutrophils into the alveolar lumen occurs in Emp2-/- lungs. Emp2-/- AT1 cells had dysregulated surface display of multiple adhesion molecules, associated with reduced raft abundance. Epithelial raft abundance was dependent upon putative cholesterol-binding motifs in EMP2, whereas EMP2 supported adhesion molecule display and neutrophil transmigration through suppression of caveolins. Taken together, we propose that EMP2-dependent membrane organization ensures proper display on AT1 cells of a suite of proteins required to instruct paracellular neutrophil traffic into the alveolus.

c-Myb Exacerbates Atherosclerosis through Regulation of Protective IgM-Producing Antibody-Secreting Cells

Mechanisms that govern transcriptional regulation of inflammation in atherosclerosis remain largely unknown. Here, we identify the nuclear transcription factor c-Myb as an important mediator of atherosclerotic disease in mice. Atherosclerosis-prone animals fed a diet high in cholesterol exhibit increased levels of c-Myb in the bone marrow. Use of mice that either harbor a c-Myb hypomorphic allele or where c-Myb has been preferentially deleted in B cell lineages revealed that c-Myb potentiates atherosclerosis directly through its effects on B lymphocytes. Reduced c-Myb activity prevents the expansion of atherogenic B2 cells yet associates with increased numbers of IgM-producing antibody-secreting cells (IgM-ASCs) and elevated levels of atheroprotective oxidized low-density lipoprotein (OxLDL)-specific IgM antibodies. Transcriptional profiling revealed that c-Myb has a limited effect on B cell function but is integral in maintaining B cell progenitor populations in the bone marrow. Thus, targeted disruption of c-Myb beneficially modulates the complex biology of B cells in cardiovascular disease.

Impact of Cholesterol Metabolism in Immune Cell Function and Atherosclerosis

Cholesterol, the most important sterol in mammals, helps maintain plasma membrane fluidity and is a precursor of bile acids, oxysterols, and steroid hormones. Cholesterol in the body is obtained from the diet or can be de novo synthetized. Cholesterol homeostasis is mainly regulated by the liver, where cholesterol is packed in lipoproteins for transport through a tightly regulated process. Changes in circulating lipoprotein cholesterol levels lead to atherosclerosis development, which is initiated by an accumulation of modified lipoproteins in the subendothelial space; this induces significant changes in immune cell differentiation and function. Beyond lesions, cholesterol levels also play important roles in immune cells such as monocyte priming, neutrophil activation, hematopoietic stem cell mobilization, and enhanced T cell production. In addition, changes in cholesterol intracellular metabolic enzymes or transporters in immune cells affect their signaling and phenotype differentiation, which can impact on atherosclerosis development. In this review, we describe the main regulatory pathways and mechanisms of cholesterol metabolism and how these affect immune cell generation, proliferation, activation, and signaling in the context of atherosclerosis.

LXRα Phosphorylation in Cardiometabolic Disease: Insight From Mouse Models

Posttranslational modifications, such as phosphorylation, are a powerful means by which the activity and function of nuclear receptors such as LXRα can be altered. However, despite the established importance of nuclear receptors in maintaining metabolic homeostasis, our understanding of how phosphorylation affects metabolic diseases is limited. The physiological consequences of LXRα phosphorylation have, until recently, been studied only in vitro or nonspecifically in animal models by pharmacologically or genetically altering the enzymes enhancing or inhibiting these modifications. Here we review recent reports on the physiological consequences of modifying LXRα phosphorylation at serine 196 (S196) in cardiometabolic disease, including nonalcoholic fatty liver disease, atherosclerosis, and obesity. A unifying theme from these studies is that LXRα S196 phosphorylation rewires the LXR-modulated transcriptome, which in turn alters physiological response to environmental signals, and that this is largely distinct from the LXR-ligand-dependent action.

Train to Lose: Innate Immune Memory in Metaflammation

Westernized diets and lifestyle are linked to the development of metabolic syndrome, characterized by obesity, type 2 diabetes, and increased cardiovascular disease risk. Systemic low-grade inflammation is a common feature of chronic metabolic disorders and is believed to promote disease progression. Therefore, modulating inflammation is a commonly explored strategy to prevent obesity-associated co-morbidities. In this review, how current knowledge on the recently described concept of innate immune memory could underline metaflammation in the context of metabolic syndrome is explored. It is hoped that these insights provide a new perspective to address the question of innate immune activation during disease progression.

Transient Intermittent Hyperglycemia Accelerates Atherosclerosis by Promoting Myelopoiesis

RATIONALE

Treatment efficacy for diabetes mellitus is largely determined by assessment of HbA1c (glycated hemoglobin A1c) levels, which poorly reflects direct glucose variation. People with prediabetes and diabetes mellitus spend >50% of their time outside the optimal glucose range. These glucose variations, termed transient intermittent hyperglycemia (TIH), appear to be an independent risk factor for cardiovascular disease, but the pathological basis for this association is unclear.

OBJECTIVE

To determine whether TIH per se promotes myelopoiesis to produce more monocytes and consequently adversely affects atherosclerosis.

METHODS AND RESULTS

To create a mouse model of TIH, we administered 4 bolus doses of glucose at 2-hour intervals intraperitoneally once to WT (wild type) or once weekly to atherosclerotic prone mice. TIH accelerated atherogenesis without an increase in plasma cholesterol, seen in traditional models of diabetes mellitus. TIH promoted myelopoiesis in the bone marrow, resulting in increased circulating monocytes, particularly the inflammatory Ly6-C^hi subset, and neutrophils. Hematopoietic-restricted deletion of S100a9, S100a8, or its cognate receptor Rage prevented monocytosis. Mechanistically, glucose uptake via GLUT (glucose transporter)-1 and enhanced glycolysis in neutrophils promoted the production of S100A8/A9. Myeloid-restricted deletion of Slc2a1 (GLUT-1) or pharmacological inhibition of S100A8/A9 reduced TIH-induced myelopoiesis and atherosclerosis.

CONCLUSIONS

Together, these data provide a mechanism as to how TIH, prevalent in people with impaired glucose metabolism, contributes to cardiovascular disease. These findings provide a rationale for continual glucose control in these patients and may also suggest that strategies aimed at targeting the S100A8/A9-RAGE (receptor for advanced glycation end products) axis could represent a viable approach to protect the vulnerable blood vessels in diabetes mellitus. Graphic Abstract: A graphic abstract is available for this article.

Small rodent models of atherosclerosis

The ease of breeding, low cost of maintenance, and relatively short period for developing atherosclerosis make rodents ideal for atherosclerosis research. However, none of the current models accurately model human lipoprotein profile or atherosclerosis progression since each has its advantages and disadvantages. The advent of transgenic technologies much supports animal models' establishment. Notably, two classic transgenic mouse models, apoE-/- and Ldlr-/-, constitute the primary platforms for studying underlying mechanisms and development of pharmaceutical approaches. However, there exist crucial differences between mice and humans, such as the unhumanized lipoprotein profile, and the different plaque progression and characteristics. Among rodents, hamsters and guinea pigs might be the more realistic models in atherosclerosis research based on the similarities in lipoprotein metabolism to humans. Studies involving rat models, a rodent with natural resistance to atherosclerosis, have revealed evidence of atherosclerotic plaques under dietary induction and genetic manipulation by novel technologies, notably CRISPR-Cas9. Ldlr-/- hamster models were established in recent years with severe hyperlipidemia and atherosclerotic lesion formation, which could offer an alternative to classic transgenic mouse models. In this review, we provide an overview of classic and innovative small rodent models in atherosclerosis researches, including mice, rats, hamsters, and guinea pigs, focusing on their lipoprotein metabolism and histopathological changes.

Immunometabolism orchestrates training of innate immunity in atherosclerosis

Atherosclerosis is characterized by a persistent, low-grade inflammation of the arterial wall. Monocytes and monocyte-derived macrophages play a pivotal role in the various stages of atherosclerosis. In the past few years, metabolic reprogramming has been identified as an important controller of myeloid cell activation status. In addition, metabolic and epigenetic reprogramming are key regulatory mechanisms of trained immunity, which denotes the non-specific innate immune memory that can develop after brief stimulation of monocytes with microbial or non-microbial stimuli. In this review, we build the case that metabolic reprogramming of monocytes and macrophages, and trained immunity in particular, contribute to the pathophysiology of atherosclerosis. We discuss the specific metabolic adaptations, including changes in glycolysis, oxidative phosphorylation, and cholesterol metabolism, that have been reported in atherogenic milieus in vitro and in vivo. In addition, we will focus on the role of these metabolic pathways in the development of trained immunity.

Generation of Myeloid Cells in Cancer: The Spleen Matters

Myeloid cells are key components of the tumor microenvironment and critical regulators of disease progression. These innate immune cells are usually short-lived and require constant replenishment. Emerging evidence indicates that tumors alter the host hematopoietic system and induce the biased differentiation of myeloid cells to tip the balance of the systemic immune activities toward tumor-promoting functions. Altered myelopoiesis is not restricted to the bone marrow and also occurs in extramedullary organs. In this review, we outline the recent advances in the field of cancer-associated myelopoiesis, with a focus on the spleen, the major site of extramedullary hematopoiesis in the cancer setting. We discuss the functional specialization, distinct mechanisms, and clinical relevance of cancer-associated myeloid cell generation from early progenitors in the spleen and its potential as a novel therapeutic target.

Hematopoiesis is regulated by cholesterol efflux pathways and lipid rafts: connections with cardiovascular diseases

Lipid rafts are highly ordered regions of the plasma membrane that are enriched in cholesterol and sphingolipids and play important roles in many cells. In hematopoietic stem and progenitor cells (HSPCs), lipid rafts house receptors critical for normal hematopoiesis. Lipid rafts also can bind and sequester kinases that induce negative feedback pathways to limit proliferative cytokine receptor cycling back to the cell membrane. Modulation of lipid rafts occurs through an array of mechanisms, with optimal cholesterol efflux one of the major regulators. As such, cholesterol homeostasis also regulates hematopoiesis. Increased lipid raft content, which occurs in response to changes in cholesterol efflux in the membrane, can result in prolonged receptor occupancy in the cell membrane and enhanced signaling. In addition, certain diseases, like diabetes, may contribute to lipid raft formation and affect cholesterol retention in rafts. In this review, we explore the role of lipid raft-related mechanisms in hematopoiesis and CVD (specifically, atherosclerosis) and discuss how defective cholesterol efflux pathways in HSPCs contribute to expansion of lipid rafts, thereby promoting myelopoiesis and thrombopoiesis. We also discuss the utility of cholesterol acceptors in contributing to lipid raft regulation and disruption, and highlight the potential to manipulate these pathways for therapeutic gain in CVD as well as other disorders with aberrant hematopoiesis.jlr;61/5/667/F1F1f1.

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.

High-density lipoprotein cholesterol concentration and acute kidney injury after noncardiac surgery

Background

Abnormal High-density Lipoprotein Cholesterol Concentration is closely related to postoperative acute kidney injury (AKI) after cardiac surgeries. The purpose of this study was to analyze the relationship between High-density Lipoprotein Cholesterol Concentration and acute kidney injury after non-cardiac surgeries.

Method

This was a single-center cohort study for elective non-cardiac non-kidney surgery from January 1, 2012, to December 31, 2017. The endpoint was the occurrence of acute kidney injury (AKI) 7 days postoperatively in the hospital. Preoperative serum High-density Lipoprotein Cholesterol Concentration was examined by multivariate logistic regression models before and after propensity score weighting analysis.

Results

Of the 74,284 surgeries, 4.4% (3159 cases) suffered acute kidney injury. The odds ratio for HDL (0.96–1.14 as reference, < 0.96, 1.14–1.35, > 1.35) was 1.28 (1.14–1.41), P < 0.001; 0.91 (0.80–1.03), P = 0.150; 0.75 (0.64–0.85), P < 0.001, respectively. Using a dichotomized cutoff point for propensity analysis, Preoperative serum HDL <  1.03 mmol/L (> 1.03 as reference) was associated with increased risk of postoperative AKI, with odds ratio 1.40 (1.27 ~ 1.52), P < 0.001 before propensity score weighting, and 1.32 (1.21–1.46), P < 0.001 after propensity score weighting. Sensitivity analysis with other cut values of HDL showed similar results.

Conclusions

Using multivariate regression analyses before and after propensity score weighting, in addition to multiple sensitivity analysis methods, this study found that following non-cardiac surgery, low HDL cholesterol levels were independent risk factors for AKI.

Hematopoiesis and Cardiovascular Disease

A central feature of atherosclerosis, the most prevalent chronic vascular disease and root cause of myocardial infarction and stroke, is leukocyte accumulation in the arterial wall. These crucial immune cells are produced in specialized niches in the bone marrow, where a complex cell network orchestrates their production and release. A growing body of clinical studies has documented a correlation between leukocyte numbers and cardiovascular disease risk. Understanding how leukocytes are produced and how they contribute to atherosclerosis and its complications is, therefore, critical to understanding and treating the disease. In this review, we focus on the key cells and products that regulate hematopoiesis under homeostatic conditions, during atherosclerosis and after myocardial infarction.

Altered Tregs Differentiation and Impaired Autophagy Correlate to Atherosclerotic Disease

Atherosclerosis is a progressive vascular disease representing the primary cause of morbidity and mortality in developed countries. Formerly, atherosclerosis was considered as a mere passive accumulation of lipids in blood vessels. However, it is now clear that atherosclerosis is a complex and multifactorial disease, in which the involvement of immune cells and inflammation play a key role. A variety of studies have shown that autophagy-a cellular catalytic mechanism able to remove injured cytoplasmic components in response to cellular stress-may be proatherogenic. So far, in this context, its role has been investigated in smooth muscle cells, macrophages, and endothelial cells, while the function of this catabolic protective process in lymphocyte functionality has been overlooked. The few studies carried out so far, however, suggested that autophagy modulation in lymphocyte subsets may be functionally related to plaque formation and development. Therefore, in this research, we aimed at better clarifying the role of lymphocyte subsets, mainly regulatory T cells (Tregs), in human atherosclerotic plaques and in animal models of atherosclerosis investigating the contribution of autophagy on immune cell homeostasis. Here, we investigate basal autophagy in a mouse model of atherosclerosis, apolipoprotein E (ApoE)-knockout (KO) mice, and we analyze the role of autophagy in driving Tregs polarization. We observed defective maturation of Tregs from ApoE-KO mice in response to tumor growth factor-β (TGFβ). TGFβ is a well-known autophagy inducer, and Tregs maturation defects in ApoE-KO mice seem to be related to autophagy impairment. In this work, we propose that autophagy underlies Tregs maturation, advocating that the study of this process in atherosclerosis may open new therapeutic strategies.

The haematopoietic stem cell niche: a new player in cardiovascular disease?

Haematopoiesis, the process of blood production, can be altered during the initiation or progression of many diseases. Cardiovascular disease (CVD) has been shown to be heavily influenced by changes to the haematopoietic system, including the types and abundance of immune cells produced. It is now well established that innate immune cells are increased in people with CVD, and the mechanisms contributing to this can be vastly different depending on the risk factors or comorbidities present. Many of these changes begin at the level of the haematopoietic stem and progenitor cells (HSPCs) that reside in the bone marrow (BM). In general, the HSPCs and downstream myeloid progenitors are expanded via increased proliferation in the setting of atherosclerotic CVD. However, HSPCs can also be encouraged to leave the BM and colonise extramedullary sites (i.e. the spleen). Within the BM, HSPCs reside in specialized microenvironments, often referred to as a niche. To date in depth studies assessing the damage or dysregulation that occurs in the BM niche in varying CVDs are scarce. In this review, we provide a general overview of the complex components and interactions within the BM niche and how they influence the function of HSPCs. Additionally, we discuss the main findings regarding changes in the HSPC niche that influence the progression of CVD. We hypothesize that understanding the influence of the BM niche in CVD will aid in delineating new pathways for therapeutic interventions.

Defining trained immunity and its role in health and disease

Immune memory is a defining feature of the acquired immune system, but activation of the innate immune system can also result in enhanced responsiveness to subsequent triggers. This process has been termed ‘trained immunity’, a de facto innate immune memory. Research in the past decade has pointed to the broad benefits of trained immunity for host defence but has also suggested potentially detrimental outcomes in immune-mediated and chronic inflammatory diseases. Here we define ‘trained immunity’ as a biological process and discuss the innate stimuli and the epigenetic and metabolic reprogramming events that shape the induction of trained immunity.

Here a group of leaders in the field define our current understanding of ‘trained immunity’, which refers to the memory-type responses that occur in the innate immune system. The authors discuss our current understanding of the key epigenetic and metabolic processes involved in trained immunity and consider its relevance in immune-mediated diseases and cancer.

Combination of MEK1/2 inhibitor and LXR ligand synergistically inhibit atherosclerosis in LDLR deficient mice

Combined LXR ligand (T0901317) and MEK1/2 inhibitor (U0126) not only reduces atherosclerosis in apoE deficient mice, but also blocks LXR ligand-induced fatty liver and hypertriglyceridemia. However, the atheroprotective function of combined T0901317 and U0126 should be further investigated in LDLR deficient (LDLR^-/-) mice since deficiency of LDLR not apoE can occur to humans with a high frequency. Herein, we validated the effectiveness of this combinational therapy on the development of atherosclerosis in LDLR^-/- mice to demonstrate its potential application in clinic. We found although T0901317 or U0126 alone reduced atherosclerotic plaques in en face and aortic root areas in HFD-fed LDLR^-/- mice, their combination inhibited lesions in a synergistic manner. Combined U0126 and T0901317 had no effect on serum total cholesterol levels. T0901317 deceased HDL-cholesterol levels, which was restored by combined U0126. Meanwhile, U0126 alleviated T0901317-induced triglyceride accumulation, the major adverse effect of T0901317 which limits its clinical utility. Mechanistically, U0126 reduced fatty acid de novo synthesis by inhibiting hepatic fatty acid synthase (FASN) expression, thereby correcting T0901317-induced triglyceride overproduction. In conclusion, our study demonstrates that combination of MEK1/2 inhibitor and LXR ligand can synergistically reduce atherosclerosis in LDLR deficient mice without lipogenic side effects.

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.

GM-CSF drives dysregulated hematopoietic stem cell activity and pathogenic extramedullary myelopoiesis in experimental spondyloarthritis

Dysregulated hematopoiesis occurs in several chronic inflammatory diseases, but it remains unclear how hematopoietic stem cells (HSCs) in the bone marrow (BM) sense peripheral inflammation and contribute to tissue damage in arthritis. Here, we show the HSC gene expression program is biased toward myelopoiesis and differentiation skewed toward granulocyte-monocyte progenitors (GMP) during joint and intestinal inflammation in experimental spondyloarthritis (SpA). GM-CSF-receptor is increased on HSCs and multipotent progenitors, favoring a striking increase in myelopoiesis at the earliest hematopoietic stages. GMP accumulate in the BM in SpA and, unexpectedly, at extramedullary sites: in the inflamed joints and spleen. Furthermore, we show that GM-CSF promotes extramedullary myelopoiesis, tissue-toxic neutrophil accumulation in target organs, and GM-CSF prophylactic or therapeutic blockade substantially decreases SpA severity. Surprisingly, besides CD4+ T cells and innate lymphoid cells, mast cells are a source of GM-CSF in this model, and its pathogenic production is promoted by the alarmin IL-33.

Comorbidities of HIV infection: role of Nef-induced impairment of cholesterol metabolism and lipid raft functionality

Combination antiretroviral therapy has dramatically changed the outcome of HIV infection, turning it from a death sentence to a manageable chronic disease. However, comorbidities accompanying HIV infection, such as metabolic and cardio-vascular diseases, as well as cognitive impairment, persist despite successful virus control by combination antiretroviral therapy and pose considerable challenges to clinical management of people living with HIV. These comorbidities involve a number of pathological processes affecting a variety of different tissues and cells, making it challenging to identify a common cause(s) that would link these different diseases to HIV infection. In this article, we will present evidence that impairment of cellular cholesterol metabolism may be a common factor driving pathogenesis of HIV-associated comorbidities. Potential implications for therapeutic approaches are discussed.

Lower HDL-C levels are associated with higher expressions of CD16 on monocyte subsets in coronary atherosclerosis

Background: Increased expressions of CD16 on classical monocytes precede their transition to intermediate monocytes. Thus far, the influence of lipids on the expression of CD14 and CD16 on monocyte subsets in coronary atherosclerosis (CA) remains unclear. The aim of this study was to investigate the underlying association between blood lipids and the expression of CD14 and CD16 on monocyte subsets. Methods: This study enrolled 112 healthy controls and 110 CA patients. Monocyte subsets [CD14⁺⁺CD16^- (classical), CD14⁺⁺CD16⁺ (intermediate) and CD14⁺CD16⁺⁺ (non-classical)] were analyzed by flow cytometry. Median fluorescent intensity (MFI) was used to evaluate the expression levels of CD14 and CD16 on monocyte subsets. Results: Compared with the control group, the expression of CD16 was significantly increased on all three monocyte subsets in the patient group. Correlation analysis revealed that serum HDL-C was inversely associated with the expression of CD16 on intermediate monocytes after Bonferroni correction in the control group. In addition, a significant decrease in classical monocytes and an increase in intermediate monocytes were detected in patients. In linear regression analysis, intermediate monocytes showed an inverse association with serum HDL-C in the control group. Although CD14 was correlated with serum TC and HDL-C, there was no statistical difference in CD14 expression between the two groups. Conclusion: Low serum HDL-C may induce upregulation of CD16 on classical monocytes, which may in turn lead to the increase of intermediate monocytes in coronary atherosclerosis patients.

Roles of Achieved Levels of Low-Density Lipoprotein Cholesterol and High-Sensitivity C-Reactive Protein on Cardiovascular Outcome in Statin Therapy

In statin therapy, the prognostic role of achieved low-density lipoprotein cholesterol (LDL-C) and high-sensitivity C-reactive protein (hsCRP) in cardiovascular outcomes has not been fully elucidated. A total of 4,803 percutaneous coronary intervention (PCI)-naïve patients who prescribed moderate intensity of statin therapy were followed up. Total and each component of major adverse cardiovascular events (MACE) according to LDL-C and hsCRP quartiles were compared. The incidence of 5-year total MACEs in the highest quartile group according to the followed-up hsCRP was higher than that in the lowest quartile (hazard ratio (HR) = 2.16, p < 0.001). However, there was no difference between the highest and lowest quartiles of the achieved LDL-C (HR = 0.95, p = 0.743). After adjustment of potential confounders, the incidence of total death, de novo PCI, atrial fibrillation, and heart failure in the highest quartile of followed-up hsCRP, was higher than that in the lowest quartile (all p < 0.05). However, other components except for de novo PCI in the highest quartile by achieved LDL-C was not different to that in the lowest quartile. These results suggest that followed-up hsCRP can be more useful for predicting future cardiovascular outcome than achieved LDL-C in PCI-naïve patients with statin therapy.