Diabetes-mediated myelopoiesis and the relationship to cardiovascular risk

Changes in Haematological Parameters and Lipid Profiles in Diabetes Mellitus: A Literature Review

Diabetes mellitus is a metabolic disorder characterized by elevated blood glucose that has sequelae on cellular, haematological, and metabolic parameters, including lipid profile disturbed homeostasis, which manifest in alterations in haematological parameters and lipid profiles. These changes in haematological parameters and lipid profiles have been reported by previous research; however, the pattern of these changes and their correlation have not been elucidated. This review aims to assess these changes and investigate the degree of correlation between haematological parameters and lipid profiles in patients with type 2 diabetes mellitus (T2DM). The method adopted was a traditional review approach that included a narrative of concepts and a critical assessment of a few selected articles. Findings highlight that haematological parameters and lipid profiles show varied alterations and correlations in T2DM. For instance, statistical significances at p < 0.05 are reported for WBC count (r = -0.75) showing negative correlations (p < 0.001), where RBC count (r = 0.56) showed correlation with high-density lipoprotein cholesterol (HDLC), whereas anaemia (packed cell volume: r = -0.51) and RBC indices (mean corpuscular volume: r = -0.75; mean corpuscular haemoglobin: r = -089) show negative correlations with total cholesterol (TC). The specific haematological parameters, namely, RBC and WBC with differential and platelet counts, as well as indices, showed varied changes and correlation with lipid profiles, namely, HDLC, low-density lipoprotein cholesterol, TC, and triglyceride, in the six reviewed articles. Diabetes is characterized by changes in haematological parameters and lipid profiles. A better understanding of the negative and positive correlating changes could be utilized in routine evaluation of subjects with prediabetes as well as managing complications in diabetes. Correlation between haematological parameters and lipid profiles over the course of diabetes progression using HbA1c as an index of glucose control is necessary for additional empirical data and updates.

An Investigation of the Inflammatory Landscape in the Brain and Bone Marrow of the APP/PS1 Mouse

Background

The APP/PS1 mouse model recapitulates pathology of human Alzheimer's disease (AD). While amyloid-β peptide deposition and neurodegeneration are features of AD, the pathology may involve inflammation and impaired vascular regeneration.

Objective

This study evaluated inflammatory environments in the brain and bone marrow (BM), and the impact on brain microvascular density.

Methods

BM and frontal cortex from male nine-month-old APP/PS1 or the control C57Bl6/j mice were studied. Vascular density and inflammatory cells were evaluated in the sections of frontal cortex by immunohistochemistry. Different subsets of hematopoietic stem/progenitor cells (BM) and monocyte-macrophages were characterized by flow cytometry and by clonogenic assays. Myelopoietic or inflammatory factors were evaluated by real-time RT-PCR or by western blotting.

Results

CD34+ or CD31+ vascular structures were lower (p < 0.01, n = 6) in the frontal cortex that was associated with decreased number of Lin-Sca-1+cKit+ vasculogenic progenitor cells in the BM and circulation (p < 0.02, n = 6) compared to the control. Multipotent progenitor cells MPP4, common lymphoid, common myeloid and myeloid progenitor cells were higher in the APP/PS1-BM compared to the control, which agreed with increased numbers of monocytes and pro-inflammatory macrophages. The expression of pro-myelopoietic factors and alarmins was higher in the APP/PS1 BM-HSPCs or in the BM-supernatants compared to the control. Frontal cortices of APP/PS1 mice showed higher number of pro-inflammatory macrophages (CD11b+F4/80+ or CD80+) and microglia (OX42+Iba1+).

Conclusions

These findings show that AD pathology in APP/PS1 mice is associated with upregulated myelopoiesis, which contributes to the brain inflammation and decreased vascularity.

Defective interferon signaling in the circulating monocytes of type 2 diabetic mice

Type 2 diabetes mellitus (T2DM) is associated with poor outcome after stroke. Peripheral monocytes play a critical role in the secondary injury and recovery of damaged brain tissue after stroke, but the underlying mechanisms are largely unclear. To investigate transcriptome changes and molecular networks across monocyte subsets in response to T2DM and stroke, we performed single-cell RNA-sequencing (scRNAseq) from peripheral blood mononuclear cells and bulk RNA-sequencing from blood monocytes from four groups of adult mice, consisting of T2DM model db/db and normoglycemic control db/+ mice with or without ischemic stroke. Via scRNAseq we found that T2DM expands the monocyte population at the expense of lymphocytes, which was validated by flow cytometry. Among the monocytes, T2DM also disproportionally increased the inflammatory subsets with Ly6C+ and negative MHC class II expression (MO.6C+II-). Conversely, monocytes from control mice without stroke are enriched with steady-state classical monocyte subset of MO.6C+II+ but with the least percentage of MO.6C+II- subtype. Apart from enhancing inflammation and coagulation, enrichment analysis from both scRNAseq and bulk RNAseq revealed that T2DM specifically suppressed type-1 and type-2 interferon signaling pathways crucial for antigen presentation and the induction of ischemia tolerance. Preconditioning by lipopolysaccharide conferred neuroprotection against ischemic brain injury in db/+ but not in db/db mice and coincided with a lesser induction of brain Interferon-regulatory-factor-3 in the brains of the latter mice. Our results suggest that the increased diversity and altered transcriptome in the monocytes of T2DM mice underlie the worse stroke outcome by exacerbating secondary injury and potentiating stroke-induced immunosuppression.

Significance Statement

The mechanisms involved in the detrimental diabetic effect on stroke are largely unclear. We show here, for the first time, that peripheral monocytes have disproportionally altered the subsets and changed transcriptome under diabetes and/or stroke conditions. Moreover, genes in the IFN-related signaling pathways are suppressed in the diabetic monocytes, which underscores the immunosuppression and impaired ischemic tolerance under the T2DM condition. Our data raise a possibility that malfunctioned monocytes may systemically and focally affect the host, leading to the poor outcome of diabetes in the setting of stroke. The results yield important clues to molecular mechanisms involved in the detrimental diabetic effect on stroke outcome.

Persistent epigenetic signals propel a senescence-associated secretory phenotype and trained innate immunity in CD34+ hematopoietic stem cells from diabetic patients

BACKGROUND

Diabetes-induced trained immunity contributes to the development of atherosclerosis and its complications. This study aimed to investigate in humans whether epigenetic signals involved in immune cell activation and inflammation are initiated in hematopoietic stem/progenitor cells (HSPCs) and transferred to differentiated progeny.

METHODS AND RESULTS

High glucose (HG)-exposure of cord blood (CB)-derived HSPCs induced a senescent-associated secretory phenotype (SASP) characterized by cell proliferation lowering, ROS production, telomere shortening, up-regulation of p21 and p27genes, upregulation of NFkB-p65 transcription factor and increased secretion of the inflammatory cytokines TNFα and IL6. Chromatin immunoprecipitation assay (ChIP) of p65 promoter revealed that H3K4me1 histone mark accumulation and methyltransferase SetD7 recruitment, along with the reduction of repressive H3K9me3 histone modification, were involved in NFkB-p65 upregulation of HG-HSPCs, as confirmed by increased RNA polymerase II engagement at gene level. The differentiation of HG-HSPCs into myeloid cells generated highly responsive monocytes, mainly composed of intermediate subsets (CD14hiCD16+), that like the cells from which they derive, were characterized by SASP features and similar epigenetic patterns at the p65 promoter. The clinical relevance of our findings was confirmed in sternal BM-derived HSPCs of T2DM patients. In line with our in vitro model, T2DM HSPCs were characterized by SASP profile and SETD7 upregulation. Additionally, they generated, after myeloid differentiation, senescent monocytes mainly composed of proinflammatory intermediates (CD14hiCD16+) characterized by H3K4me1 accumulation at NFkB-p65 promoter.

CONCLUSIONS

Hyperglycemia induces marked chromatin modifications in HSPCs, which, once transmitted to the cell progeny, contributes to persistent and pathogenic changes in immune cell function and composition.

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

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

Cardiovascular characterisation of a novel mouse model that combines hypertension and diabetes co-morbidities

Epidemiologic data suggest that the prevalence of hypertension in patients with diabetes mellitus is ∼1.5-2.0 times greater than in matched non-diabetic patients. This co-existent disease burden exacerbates cardiac and vascular injury, leading to structural and functional changes to the myocardium, impaired cardiac function and heart failure. Oxidative stress and persistent low-grade inflammation underlie both conditions, and are identified as major contributors to pathological cardiac remodelling. There is an urgent need for effective therapies that specifically target oxidative stress and inflammation to protect against cardiac remodelling. Animal models are a valuable tool for testing emerging therapeutics, however, there is a notable lack of appropriate animal models of co-morbid diabetes and hypertension. In this study, we describe a novel preclinical mouse model combining diabetes and hypertension to investigate cardiac and vascular pathology of co-morbid disease. Type 1 diabetes was induced in spontaneously hypertensive, 8-week old, male Schlager (BPH/2) mice via 5 consecutive, daily injections of streptozotocin (55 mg/kg in citrate buffer; i.p.). Non-diabetic mice received citrate buffer only. After 10 weeks of diabetes induction, cardiac function was assessed by echocardiography prior to post-mortem evaluation of cardiomyocyte hypertrophy, interstitial fibrosis and inflammation by histology, RT-PCR and flow cytometry. We focussed on the oxidative and inflammatory stress pathways that contribute to cardiovascular remodelling. In particular, we demonstrate that markers of inflammation (monocyte chemoattractant protein; MCP-1), oxidative stress (urinary 8-isoprostanes) and fibrosis (connective tissue growth factor; CTGF) are significantly increased, whilst diastolic dysfunction, as indicated by prolonged isovolumic relaxation time (IVRT), is elevated in this diabetic and hypertensive mouse model. In summary, this pre-clinical mouse model provides researchers with a tool to test therapeutic strategies unique to co-morbid diabetes and hypertension, thereby facilitating the emergence of novel therapeutics to combat the cardiovascular consequences of these debilitating co-morbidities.

Dysregulated transforming growth factor-beta mediates early bone marrow dysfunction in diabetes

Diabetes affects select organs such as the eyes, kidney, heart, and brain. Our recent studies show that diabetes also enhances adipogenesis in the bone marrow and reduces the number of marrow-resident vascular regenerative stem cells. In the current study, we have performed a detailed spatio-temporal examination to identify the early changes that are induced by diabetes in the bone marrow. Here we show that short-term diabetes causes structural and molecular changes in the marrow, including enhanced adipogenesis in tibiae of mice, prior to stem cell depletion. This enhanced adipogenesis was associated with suppressed transforming growth factor-beta (TGFB) signaling. Using human bone marrow-derived mesenchymal progenitor cells, we show that TGFB pathway suppresses adipogenic differentiation through TGFB-activated kinase 1 (TAK1). These findings may inform the development of novel therapeutic targets for patients with diabetes to restore regenerative stem cell function.

How dysregulation of the immune system promotes diabetes mellitus and cardiovascular risk complications

Diabetes mellitus (DM) is a chronic metabolic disorder characterized by persistent hyperglycemia due to insulin resistance or failure to produce insulin. Patients with DM develop microvascular complications that include chronic kidney disease and retinopathy, and macrovascular complications that mainly consist in an accelerated and more severe atherosclerosis compared to the general population, increasing the risk of cardiovascular (CV) events, such as stroke or myocardial infarction by 2- to 4-fold. DM is commonly associated with a low-grade chronic inflammation that is a known causal factor in its development and its complications. Moreover, it is now well-established that inflammation and immune cells play a major role in both atherosclerosis genesis and progression, as well as in CV event occurrence. In this review, after a brief presentation of DM physiopathology and its macrovascular complications, we will describe the immune system dysregulation present in patients with type 1 or type 2 diabetes and discuss its role in DM cardiovascular complications development. More specifically, we will review the metabolic changes and aberrant activation that occur in the immune cells driving the chronic inflammation through cytokine and chemokine secretion, thus promoting atherosclerosis onset and progression in a DM context. Finally, we will discuss how genetics and recent systemic approaches bring new insights into the mechanisms behind these inflammatory dysregulations and pave the way toward precision medicine.

Loss of PRMT2 in myeloid cells in normoglycemic mice phenocopies impaired regression of atherosclerosis in diabetic mice

The regression, or resolution, of inflammation in atherosclerotic plaques is impaired in diabetes. However, the factors mediating this effect remain incomplete. We identified protein arginine methyltransferase 2 (PRMT2) as a protein whose expression in macrophages is reduced in hyperglycemia and diabetes. PRMT2 catalyzes arginine methylation to target proteins to modulate gene expression. Because PRMT2 expression is reduced in cells in hyperglycemia, we wanted to determine whether PRMT2 plays a causal role in the impairment of atherosclerosis regression in diabetes. We, therefore, examined the consequence of deleting PRMT2 in myeloid cells during the regression of atherosclerosis in normal and diabetic mice. Remarkably, we found significant impairment of atherosclerosis regression under normoglycemic conditions in mice lacking PRMT2 (Prmt2^-/-) in myeloid cells that mimic the decrease in regression of atherosclerosis in WT mice under diabetic conditions. This was associated with increased plaque macrophage retention, as well as increased apoptosis and necrosis. PRMT2-deficient plaque CD68+ cells under normoglycemic conditions showed increased expression of genes involved in cytokine signaling and inflammation compared to WT cells. Consistently, Prmt2^-/- bone marrow-derived macrophages (BMDMs) showed an increased response of proinflammatory genes to LPS and a decreased response of inflammation resolving genes to IL-4. This increased response to LPS in Prmt2^-/- BMDMs occurs via enhanced NF-kappa B activity. Thus, the loss of PRMT2 is causally linked to impaired atherosclerosis regression via a heightened inflammatory response in macrophages. That PRMT2 expression was lower in myeloid cells in plaques from human subjects with diabetes supports the relevance of our findings to human atherosclerosis.

Maladaptive trained immunity and clonal hematopoiesis as potential mechanistic links between periodontitis and inflammatory comorbidities

Periodontitis is bidirectionally associated with systemic inflammatory disorders. The prevalence and severity of this oral disease and linked comorbidities increases with aging. Here, we review two newly emerged concepts, trained innate immunity (TII) and clonal hematopoiesis of indeterminate potential (CHIP), which together support a potential hypothesis on how periodontitis affects and is affected by comorbidities and why the susceptibility to periodontitis and comorbidities increases with aging. Given that chronic diseases are largely triggered by the action of inflammatory immune cells, modulation of their bone marrow precursors, the hematopoietic stem and progenitor cells (HSPCs), may affect multiple disorders that emerge as comorbidities. Such alterations in HSPCs can be mediated by TII and/or CHIP, two non-mutually exclusive processes sharing a bias for enhanced myelopoiesis and production of innate immune cells with heightened proinflammatory potential. TII is a state of elevated immune responsiveness based on innate immune (epigenetic) memory. Systemic inflammation can initiate TII in the bone marrow via sustained rewiring of HSPCs, which thereby display a skewing toward the myeloid lineage, resulting in generation of hyper-reactive or "trained" myeloid cells. CHIP arises from aging-related somatic mutations in HSPCs, which confer a survival and proliferation advantage to the mutant HSPCs and give rise to an outsized fraction of hyper-inflammatory mutant myeloid cells in the circulation and tissues. This review discusses emerging evidence that supports the notion that TII and CHIP may underlie a causal and age-related association between periodontitis and comorbidities. A holistic mechanistic understanding of the periodontitis-systemic disease connection may offer novel diagnostic and therapeutic targets for treating inflammatory comorbidities.

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.

When a Friend Becomes Your Enemy: Natural Killer Cells in Atherosclerosis and Atherosclerosis-Associated Risk Factors

Atherosclerosis (ATS), the change in structure and function of arteries with associated lesion formation and altered blood flow, is the leading cause of cardiovascular disease, the number one killer worldwide. Beyond dyslipidemia, chronic inflammation, together with aberrant phenotype and function of cells of both the innate and adaptive immune system, are now recognized as relevant contributors to atherosclerosis onset and progression. While the role of macrophages and T cells in atherosclerosis has been addressed in several studies, Natural Killer cells (NKs) represent a poorly explored immune cell type, that deserves attention, due to NKs’ emerging contribution to vascular homeostasis. Furthermore, the possibility to re-polarize the immune system has emerged as a relevant tool to design new therapies, with some succesfull exmples in the field of cancer immunotherapy. Thus, a deeper knowledge of NK cell pathophysiology in the context of atherosclerosis and atherosclerosis-associated risk factors could help developing new preventive and treatment strategies, and decipher the complex scenario/history from “the risk factors for atherosclerosis” Here, we review the current knowledge about NK cell phenotype and activities in atherosclerosis and selected atherosclerosis risk factors, namely type-2 diabetes and obesity, and discuss the related NK-cell oriented environmental signals.

Pathogenesis and Clinical Significance of In-Stent Restenosis in Patients with Diabetes

Diabetes mellitus (DM) is a strong risk factor for the development of cardiovascular diseases such as coronary heart disease, cerebrovascular disease, and peripheral arterial disease (PAD). In the population of people living with DM, PAD is characterised by multi-level atherosclerotic lesions as well as greater involvement of the arteries below the knee. DM is also a factor that significantly increases the risk of lower limb amputation. Percutaneous balloon angioplasty with or without stent implantation is an important method of the treatment for atherosclerotic cardiovascular diseases, but restenosis is a factor limiting its long-term effectiveness. The pathogenesis of atherosclerosis in the course of DM differs slightly from that in the general population. In the population of people living with DM, more attention is drawn to such factors as inflammation, endothelial dysfunction, platelet dysfunction, blood rheological properties, hypercoagulability, and additional factors stimulating vascular smooth muscle cell proliferation. DM is a risk factor for restenosis. The purpose of this paper is to provide a review of the literature and to present the most important information on the current state of knowledge on mechanisms and the clinical significance of restenosis and in-stent restenosis in patients with DM, especially in association with the endovascular treatment of PAD. The role of such processes as inflammation, neointimal hyperplasia and neoatherosclerosis, allergy, resistance to antimitotic drugs used for coating stents and balloons, genetic factors, and technical and mechanical factors are discussed. The information on restenosis collected in this publication may be helpful in planning further research in this field, which may contribute to the formulation of more and more precise recommendations for the clinical practice.

Inflammatory Modulation of Hematopoiesis: Linking Trained Immunity and Clonal Hematopoiesis with Chronic Disorders

Inflammation-adapted hematopoietic stem and progenitor cells (HSPCs) have long been appreciated as key drivers of emergency myelopoiesis, thereby enabling the bone marrow to meet the elevated demand for myeloid cell generation under various stress conditions, such as systemic infection, inflammation, or myelosuppressive insults. In recent years, HSPC adaptations were associated with potential involvement in the induction of long-lived trained immunity and the emergence of clonal hematopoiesis of indeterminate potential (CHIP). Whereas trained immunity has context-dependent effects, protective in infections and tumors but potentially detrimental in chronic inflammatory diseases, CHIP increases the risk for hematological neoplastic disorders and cardiometabolic pathologies. This review focuses on the inflammatory regulation of HSPCs in the aforementioned processes and discusses how modulation of HSPC function could lead to novel therapeutic interventions. Expected final online publication date for the Annual Review of Physiology, Volume 84 is February 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Exercise and Adipose Tissue Immunity: Outrunning Inflammation

Chronic inflammation is considered a precipitating factor and possibly an underlying cause of many noncommunicable diseases, including cardiovascular disease, metabolic diseases, and some cancers. Obesity, which manifests in more than 650 million people worldwide, is the most common chronic inflammatory condition, with visceral adiposity thought to be the major inflammatory hub that links obesity and chronic disease. Adipose tissue (AT) inflammation is triggered or heightened in large part by (1) accelerated immune cell recruitment, (2) reshaping of the AT stromal-immuno landscape (e.g., immune cells, endothelial cells, fibroblasts, adipocyte progenitors), and (3) perturbed AT immune cell function. Exercise, along with diet management, is a cornerstone in promoting weight loss and preventing weight regain. This review focuses on evidence that increased physical activity reduces AT inflammation caused by hypercaloric diets or genetic obesity. The precise cell types and mechanisms responsible for the therapeutic effects of exercise on AT inflammation remain poorly understood. This review summarizes what is known about obesity-induced AT inflammation and immunomodulation and highlights mechanisms by which aerobic exercise combats inflammation by remodeling the AT immune landscape. Furthermore, key areas are highlighted that require future exploration and novel discoveries into the burgeoning field of how the biology of exercise affects AT immunity.

Diabetes and Metabolic Drivers of Trained Immunity

Accumulating evidence shows how diverse physiological functions, such as metabolism, immunity, tissue homeostasis, and hematopoiesis, are intricately and profoundly intertwined at multiple levels. This brief review will present evidence from a rapidly expanding field of immunometabolism, highlighting how cells that are relevant to processes at play in determining vascular health and disease can be programmed by changes in their metabolic environment. It will focus on how such changes can be imprinted or trained, particularly through epigenetic modifications, such that adaptations driven by metabolic signals can cause persistent changes in cell function, even after the original stimulus has been corrected or removed. Recognition of these processes and elucidation of the mechanisms underlying them stand to have far-reaching implications for the diagnosis and treatment of diabetes and related metabolic states.

ACE2 gene transfer ameliorates vasoreparative dysfunction in CD34+ cells derived from diabetic older adults

Diabetes increases the risk for ischemic vascular diseases, which is further elevated in older adults. Bone marrow-derived hematopoietic CD34+ stem/progenitor cells have the potential of revascularization; however, diabetes attenuates vasoreparative functions. Angiotensin-converting enzyme 2 (ACE2) is the vasoprotective enzyme of renin-angiotensin system in contrast with the canonical angiotensin-converting enzyme (ACE). The present study tested the hypothesis that diabetic dysfunction is associated with ACE2/ACE imbalance in hematopoietic stem/progenitor cells (HSPCs) and that increasing ACE2 expression would restore reparative functions. Blood samples from male and female diabetic (n=71) or nondiabetic (n=62) individuals were obtained and CD34+ cells were enumerated by flow cytometry. ACE and ACE2 enzyme activities were determined in cell lysates. Lentiviral (LV) approach was used to increase the expression of soluble ACE2 protein. Cells from diabetic older adults (DB) or nondiabetic individuals (Control) were evaluated for their ability to stimulate revascularization in a mouse model of hindlimb ischemia (HLI). DB cells attenuated the recovery of blood flow to ischemic areas in nondiabetic mice compared with that observed with Control cells. Administration of DB cells modified with LV-ACE2 resulted in complete restoration of blood flow. HLI in diabetic mice resulted in poor recovery with amputations, which was not reversed by either Control or DB cells. LV-ACE2 modification of Control or DB cells resulted in blood flow recovery in diabetic mice. In vitro treatment with Ang-(1-7) modified paracrine profile in diabetic CD34+ cells. The present study suggests that vasoreparative dysfunction in CD34+ cells from diabetic older adults is associated with ACE2/ACE imbalance and that increased ACE2 expression enhances the revascularization potential.

Local and systemic mechanisms linking periodontal disease and inflammatory comorbidities

Periodontitis, a major inflammatory disease of the oral mucosa, is epidemiologically associated with other chronic inflammation-driven disorders, including cardio-metabolic, neurodegenerative and autoimmune diseases and cancer. Emerging evidence from interventional studies indicates that local treatment of periodontitis ameliorates surrogate markers of comorbid conditions. The potential causal link between periodontitis and its comorbidities is further strengthened by recent experimental animal studies establishing biologically plausible and clinically consistent mechanisms whereby periodontitis could initiate or aggravate a comorbid condition. This multi-faceted ‘mechanistic causality’ aspect of the link between periodontitis and comorbidities is the focus of this Review. Understanding how certain extra-oral pathologies are affected by disseminated periodontal pathogens and periodontitis-associated systemic inflammation, including adaptation of bone marrow haematopoietic progenitors, may provide new therapeutic options to reduce the risk of periodontitis-associated comorbidities.

Periodontitis has been causally linked to the development of other chronic inflammatory diseases outside the oral mucosa. In this Review, George Hajishengallis and Triantafyllos Chavakis consider the molecular basis of these links.

The Role of Inflammation in Diabetic Retinopathy

Inflammation is central to pathogenic processes in diabetes mellitus and the metabolic syndrome and particularly implicates innate immunity in the development of complications. Inflammation is a primary event in Type 1 diabetes where infectious (viral) and/or autoimmune processes initiate disease; in contrast, chronic inflammation is typical in Type 2 diabetes and is considered a sequel to increasing insulin resistance and disturbed glucose metabolism. Diabetic retinopathy (DR) is perceived as a vascular and neurodegenerative disease which occurs after some years of poorly controlled diabetes. However, many of the clinical features of DR are late events and reflect the nature of the retinal architecture and its cellular composition. Retinal microvascular disease is, in fact, an early event pathogenetically, induced by low grade, persistent leukocyte activation which causes repeated episodes of capillary occlusion and, progressive, attritional retinal ischemia. The later, overt clinical signs of DR are a consequence of the retinal ischemia. Metabolic dysregulation involving both lipid and glucose metabolism may lead to leukocyte activation. On a molecular level, we have shown that macrophage-restricted protein tyrosine phosphatase 1B (PTP1B) is a key regulator of inflammation in the metabolic syndrome involving insulin resistance and it is possible that PTP1B dysregulation may underlie retinal microvascular disease. We have also shown that adherent CCR5⁺CD11b⁺ monocyte macrophages appear to be selectively involved in retinal microvascular occlusion. In this review, we discuss the relationship between early leukocyte activation and the later features of DR, common pathogenetic processes between diabetic microvascular disease and other vascular retinopathies, the mechanisms whereby leukocyte activation is induced in hyperglycemia and dyslipidemia, the signaling mechanisms involved in diabetic microvascular disease, and possible interventions which may prevent these retinopathies. We also address a possible role for adaptive immunity in DR. Although significant improvements in treatment of DR have been made with intravitreal anti-VEGF therapy, a sizeable proportion of patients, particularly with sight-threatening macular edema, fail to respond. Alternative therapies targeting inflammatory processes may offer an advantage.

Bone marrow fat: friend or foe in people with diabetes mellitus?

Global trends in the prevalence of overweight and obesity put the adipocyte in the focus of huge medical interest. This review highlights a new topic in adipose tissue biology, namely the emerging pathogenic role of fat accumulation in bone marrow (BM). Specifically, we summarize current knowledge about the origin and function of BM adipose tissue (BMAT), provide evidence for the association of excess BMAT with diabetes and related cardiovascular complications, and discuss potential therapeutic approaches to correct BMAT dysfunction. There is still a significant uncertainty about the origins and function of BMAT, although several subpopulations of stromal cells have been suggested to have an adipogenic propensity. BM adipocytes are higly plastic and have a distinctive capacity to secrete adipokines that exert local and endocrine functions. BM adiposity is abundant in elderly people and has therefore been interpreted as a component of the whole-body ageing process. BM senescence and BMAT accumulation has been also reported in patients and animal models with Type 2 diabetes, being more pronounced in those with ischaemic complications. Understanding the mechanisms responsible for excess and altered function of BMAT could lead to new treatments able to preserve whole-body homeostasis.

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.

Neutrophil extracellular traps promote macrophage inflammation and impair atherosclerosis resolution in diabetic mice

Neutrophil extracellular traps (NETs) promote inflammation and atherosclerosis progression. NETs are increased in diabetes and impair the resolution of inflammation during wound healing. Atherosclerosis resolution, a process resembling wound healing, is also impaired in diabetes. Thus, we hypothesized that NETs impede atherosclerosis resolution in diabetes by increasing plaque inflammation. Indeed, transcriptomic profiling of plaque macrophages from NET+ and NET- areas in low-density lipoprotein receptor-deficient (Ldlr-/-) mice revealed inflammasome and glycolysis pathway upregulation, indicating a heightened inflammatory phenotype. We found that NETs declined during atherosclerosis resolution, which was induced by reducing hyperlipidemia in nondiabetic mice, but they persisted in diabetes, exacerbating macrophage inflammation and impairing resolution. In diabetic mice, deoxyribonuclease 1 treatment reduced plaque NET content and macrophage inflammation, promoting atherosclerosis resolution after lipid lowering. Given that humans with diabetes also exhibit impaired atherosclerosis resolution with lipid lowering, these data suggest that NETs contribute to the increased cardiovascular disease risk in this population and are a potential therapeutic target.

Dendritic Cell-Restricted Progenitors Contribute to Obesity-Associated Airway Inflammation via Adam17-p38 MAPK-Dependent Pathway

Proliferation of dendritic cell (DC)—restricted progenitor cells in bone marrow compartment is tightly regulated at steady state and responds to multiple tissue-specific triggers during disturbed homeostasis such as obesity. DCs in the lung stem from a rapidly dividing DC-restricted progenitor cells and are effective at generating adaptive immune responses in allergic airway inflammation. Precisely, how DC-restricted progenitor expansion and differentiation are influenced by airway inflammation to maintain constant supply of myeloid DCs is poorly understood. Here we show that a high fat diet (HFD) induces oxidative stress and accelerates the expansion of DC- restricted progenitor cells in bone marrow and correlates with persistent induction of p38 mitogen activated protein kinase (MAPK), which is blocked with a selective p38α/β MAPK inhibitor. Mice fed a HFD and sensitized to inhaled allergen house dust mite (HDM) led to alterations of DC- restricted progenitor cells that were characterized by increased expansion and seeding of lung DCs in airway inflammation. Mechanistically, we establish that the expansion induced by HFD dysregulates the expression of a disintegrin and metallopeptidase domain 17 (Adam17) and is required for p38 MAPK activation in DC-restricted progenitors. These results demonstrates that obesity produces persistent changes in DC precursors and that elevation of Adam17 expression is tightly coupled to p38 MAPK and is a key driver of proliferation. Altogether, these data provide phenotypic and mechanistic insight into dendritic cell supply chain in obesity-associated airway inflammation.

HDL and Reverse Cholesterol Transport

Cardiovascular disease, with atherosclerosis as the major underlying factor, remains the leading cause of death worldwide. It is well established that cholesterol ester-enriched foam cells are the hallmark of atherosclerotic plaques. Multiple lines of evidence support that enhancing foam cell cholesterol efflux by HDL (high-density lipoprotein) particles, the first step of reverse cholesterol transport (RCT), is a promising antiatherogenic strategy. Yet, excitement towards the therapeutic potential of manipulating RCT for the treatment of cardiovascular disease has faded because of the lack of the association between cardiovascular disease risk and what was typically measured in intervention trials, namely HDL cholesterol, which has an inconsistent relationship to HDL function and RCT. In this review, we will summarize some of the potential reasons for this inconsistency, update the mechanisms of RCT, and highlight conditions in which impaired HDL function or RCT contributes to vascular disease. On balance, the evidence still argues for further research to better understand how HDL functionality contributes to RCT to develop prevention and treatment strategies to reduce the risk of cardiovascular disease.

Diabetic pre-programming of myelopoiesis impairs tissue repair

Bone marrow-derived monocyte-macrophages promote healing of injured tissue cooperatively with vasculogenic hematopoietic stem/progenitor cells. However, diabetes dysregulates hematopoiesis and attenuates bone marrow-derived tissue-reparative responses. In a recent issue of The Journal of Pathology, Barman et al extensively characterized myelopoietic responses in bone marrow following skin wounding in a type 2 model of diabetes. The study demonstrated that accumulation of monocyte-macrophages in the peripheral tissues is increased due to diabetic myelopoiesis that would oppose the reparative process following tissue injury. Interestingly, in this model, pathological myelopoiesis is independent of IL-1β. The potential prophylactic and therapeutic implications of these data are discussed in terms of paracrine signaling, macrophage polarization, and hematopoietic stem cell mobilization/retention. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Monocytes and macrophages in atherogenesis

PURPOSE OF REVIEW

Monocytes and macrophages are key players in the pathogenesis of atherosclerosis and dictate atherogenesis growth and stability. The heterogeneous nature of myeloid cells concerning their metabolic and phenotypic function is increasingly appreciated. This review summarizes the recent monocyte and macrophage literature and highlights how differing subsets contribute to atherogenesis.

RECENT FINDINGS

Monocytes are short-lived cells generated in the bone marrow and released to circulation where they can produce inflammatory cytokines and, importantly, differentiate into long-lived macrophages. In the context of cardiovascular disease, a myriad of subtypes, exist with each differentially contributing to plaque development. Herein we describe recent novel characterizations of monocyte and macrophage subtypes and summarize the recent literature on mediators of myelopoiesis.

SUMMARY

An increased understanding of monocyte and macrophage phenotype and their molecular regulators is likely to translate to the development of new therapeutic targets to either stem the growth of existing plaques or promote plaque stabilization.

Hematopoietic progenitor cells as integrative hubs for adaptation to and fine-tuning of inflammation

Recent advances have highlighted the ability of hematopoietic stem and progenitor cells in the bone marrow to sense peripheral inflammation or infection and adapt through increased proliferation and skewing toward the myeloid lineage. Such adaptations can meet the increased demand for innate immune cells and can be beneficial in response to infection or myeloablation. However, the inflammation-induced adaptation of hematopoietic and myeloid progenitor cells toward enhanced myelopoiesis might also perpetuate inflammation in chronic inflammatory or cardio-metabolic diseases by generating a feed-forward loop between inflammation-adapted hematopoietic progenitor cells and the inflammatory disorder. Sustained adaptive responses of progenitor cells in the bone marrow can also contribute to trained immunity, a non-specific memory of earlier encounters that in turn facilitates the heightened response of these cells, as well as that of their progeny, to future challenges. Here we discuss the mechanisms that govern the adaptation of hematopoietic progenitor cells to inflammation and its sequelae in the pathogenesis of human disease.

TNF, but not hyperinsulinemia or hyperglycemia, is a key driver of obesity-induced monocytosis revealing that inflammatory monocytes correlate with insulin in obese male mice

Inflammation contributes to obesity-related hyperinsulinemia and insulin resistance, which often precede type 2 diabetes. Inflammation is one way that obesity can promote insulin resistance. It is not clear if the extent of obesity, hyperinsulinemia, or hyperglycemia, underpins changes in cellular immunity during diet-induced obesity. In particular, the requirement for obesity or directionality in the relationship between insulin resistance and monocyte characteristics is poorly defined. Inflammatory cytokines such as tumor necrosis factor (TNF) can contribute to insulin resistance. It is unclear if TNF alters monocytosis or specific markers of cellular immunity in the context of obesity. We measured bone marrow and blood monocyte characteristics in WT and TNF-/- mice that were fed obesogenic, high fat (HF) diets. We also used hyperglycemic Akita mice and mice implanted with insulin pellets in order to determine if glucose or insulin were sufficient to alter monocyte characteristics. We found that diet-induced obesity in male mice increased the total number of monocytes in blood, but not in bone marrow. Immature, inflammatory (Ly6Chigh ) monocytes decreased within the bone marrow and increased within peripheral blood of HF-fed mice. We found that neither hyperinsulinemia nor hyperglycemia was sufficient to induce the observed changes in circulating monocytes in the absence of diet-induced obesity. In obese HF-fed mice, antibiotic treatment lowered insulin and insulin resistance, but did not alter circulating monocyte characteristics. Fewer Ly6Chigh monocytes were present within the blood of HF-fed TNF-/- mice in comparison to HF-fed wild-type (WT) mice. The prevalence of immature Ly6Chigh monocytes in the blood correlated with serum insulin and insulin resistance irrespective of the magnitude of adipocyte or adipose tissue hypertrophy in obese mice. These data suggest that diet-induced obesity instigates a TNF-dependent increase in circulating inflammatory monocytes, which predicts increased blood insulin and insulin resistance independently from markers of adiposity or adipose tissue expansion.

Glucose metabolism controls disease-specific signatures of macrophage effector functions

BACKGROUND

In inflammatory blood vessel diseases, macrophages represent a key component of the vascular infiltrates and are responsible for tissue injury and wall remodeling.

METHODS

To examine whether inflammatory macrophages in the vessel wall display a single distinctive effector program, we compared functional profiles in patients with either coronary artery disease (CAD) or giant cell arteritis (GCA).

RESULTS

Unexpectedly, monocyte-derived macrophages from the 2 patient cohorts displayed disease-specific signatures and differed fundamentally in metabolic fitness. Macrophages from CAD patients were high producers for T cell chemoattractants (CXCL9, CXCL10), the cytokines IL-1β and IL-6, and the immunoinhibitory ligand PD-L1. In contrast, macrophages from GCA patients upregulated production of T cell chemoattractants (CXCL9, CXCL10) but not IL-1β and IL-6, and were distinctly low for PD-L1 expression. Notably, disease-specific effector profiles were already identifiable in circulating monocytes. The chemokinehicytokinehiPD-L1hi signature in CAD macrophages was sustained by excess uptake and breakdown of glucose, placing metabolic control upstream of inflammatory function.

CONCLUSIONS

We conclude that monocytes and macrophages contribute to vascular inflammation in a disease-specific and discernible pattern, have choices to commit to different functional trajectories, are dependent on glucose availability in their immediate microenvironment, and possess memory in their lineage commitment.

FUNDING

Supported by the NIH (R01 AR042527, R01 HL117913, R01 AI108906, P01 HL129941, R01 AI108891, R01 AG045779 U19 AI057266, R01 AI129191), I01 BX001669, and the Cahill Discovery Fund.

Loss of Angiotensin-Converting Enzyme 2 Exacerbates Diabetic Retinopathy by Promoting Bone Marrow Dysfunction

Angiotensin-converting enzyme 2 (ACE2) is the primary enzyme of the vasoprotective axis of the renin angiotensin system (RAS). We tested the hypothesis that loss of ACE2 would exacerbate diabetic retinopathy by promoting bone marrow dysfunction. ACE2^-/y were crossed with Akita mice, a model of type 1 diabetes. When comparing the bone marrow of the ACE2^-/y -Akita mice to that of Akita mice, we observed a reduction of both short-term and long-term repopulating hematopoietic stem cells, a shift of hematopoiesis toward myelopoiesis, and an impairment of lineage^- c-kit⁺ hematopoietic stem/progenitor cell (HS/PC) migration and proliferation. Migratory and proliferative dysfunction of these cells was corrected by exposure to angiotensin-1-7 (Ang-1-7), the protective peptide generated by ACE2. Over the duration of diabetes examined, ACE2 deficiency led to progressive reduction in electrical responses assessed by electroretinography and to increases in neural infarcts observed by fundus photography. Compared with Akita mice, ACE2^-/y -Akita at 9-months of diabetes showed an increased number of acellular capillaries indicative of more severe diabetic retinopathy. In diabetic and control human subjects, CD34⁺ cells, a key bone marrow HS/PC population, were assessed for changes in mRNA levels for MAS, the receptor for Ang-1-7. Levels were highest in CD34⁺ cells from diabetics without retinopathy. Higher serum Ang-1-7 levels predicted protection from development of retinopathy in diabetics. Treatment with Ang-1-7 or alamandine restored the impaired migration function of CD34⁺ cells from subjects with retinopathy. These data support that activation of the protective RAS within HS/PCs may represents a therapeutic strategy for prevention of diabetic retinopathy. Stem Cells 2018;36:1430-1440.

Poststatin era in atherosclerosis management: lessons from epidemiologic and genetic studies

PURPOSE OF REVIEW

Cardiovascular diseases (CVD) are the leading cause of death worldwide with over 17 million deaths every year and represent a major public health challenge. The last decade has seen the emergence of novel antiatherogenic therapies.

RECENT FINDINGS

Despite intensive lipid and blood pressure interventions, the burden of CVD is expected to markedly progress because of the global aging of the population and increasing exposure to detrimental lifestyle-related risk. Epidemiologic and genetic studies helped to better apprehend the biology of atherosclerosis and allowed pharmaceutical innovation and recent translational successes. This includes the development of novel lipid and glucose-lowering therapies and the leverage of anti-inflammatory therapies.

SUMMARY

Here, we discuss promises and expectations of emerging scientific and pharmaceutical innovations and translational successes to meet the global therapeutic demand.

12/15 lipoxygenase: A crucial enzyme in diverse types of cell death

The 12/15-lipoxygenase (12/15-LOX) enzymes react with polyunsaturated fatty acids producing active lipid metabolites that are involved in plethora of human diseases including neurological disorders. A great many of elegant studies over the last decades have contributed to unraveling the mechanism how 12/15-lipoxygenase play a role in these diseases. And the way it works is mainly through apoptosis. However, recent years have found that the way 12/15-lipoxygenase works is also related to autophagy and ferroptosis, a newly defined type of cell death by Stockwell's lab in 2012. Figuring out how 12/15-lipoxygenase participate in these modes of cell death is of vital importance to understand its role in disease. The review aims to give a sight on our current knowledge on the role of this enzyme in apoptosis, autophagy and ferroptosis. And the relevant diseases that 12/15-lipoxygenase may be involved.

Regression of atherosclerosis: lessons learned from genetically modified mouse models

PURPOSE OF REVIEW

Regression, or reversal, of atherosclerosis has become an important clinical objective. The development of consistent models of murine atherosclerosis regression has accelerated this field of research. The purpose of this review is to highlight recent mouse studies that reveal molecular mechanisms as well as therapeutics targeted for regression.

RECENT FINDINGS

Atherosclerosis regression does not involve the same mechanisms as progression in reverse order. Distinct molecular processes within the plaque characterize regression. These processes remained elusive until the advent of murine regression models including aortic transplant, the Reversa mouse, gene complementation and dietary intervention. Studies revealed that depletion of plaque macrophages is a quintessential characteristic of regression, driven by reduced monocyte recruitment into plaques, increased egress of macrophages from plaques and reduced macrophage proliferation. In addition, regression results in polarization of remaining plaque macrophages towards an anti-inflammatory phenotype, smaller necrotic cores and promotion of an organized fibrous cap. Furthermore, type 1 diabetes hinders plaque regression, and several therapeutic interventions show promise in slowing plaque progression or inducing regression.

SUMMARY

Mouse models of atherosclerosis regression have accelerated our understanding of the molecular mechanisms governing lesion resolution. These insights will be valuable in identifying therapeutic targets aimed at atherosclerosis regression.