Cardiac autoimmunity as a novel biomarker, mediator, and therapeutic target of heart disease in type 1 diabetes

T-Cell Receptor Sequences Identify Combined Coxsackievirus-Streptococci Infections as Triggers for Autoimmune Myocarditis and Coxsackievirus-Clostridia Infections for Type 1 Diabetes

Recent research suggests that T-cell receptor (TCR) sequences expanded during human immunodeficiency virus and SARS-CoV-2 infections unexpectedly mimic these viruses. The hypothesis tested here is that TCR sequences expanded in patients with type 1 diabetes mellitus (T1DM) and autoimmune myocarditis (AM) mimic the infectious triggers of these diseases. Indeed, TCR sequences mimicking coxsackieviruses, which are implicated as triggers of both diseases, are statistically significantly increased in both T1DM and AM patients. However, TCRs mimicking Clostridia antigens are significantly expanded in T1DM, whereas TCRs mimicking Streptococcal antigens are expanded in AM. Notably, Clostridia antigens mimic T1DM autoantigens, such as insulin and glutamic acid decarboxylase, whereas Streptococcal antigens mimic cardiac autoantigens, such as myosin and laminins. Thus, T1DM may be triggered by combined infections of coxsackieviruses with Clostridia bacteria, while AM may be triggered by coxsackieviruses with Streptococci. These TCR results are consistent with both epidemiological and clinical data and recent experimental studies of cross-reactivities of coxsackievirus, Clostridial, and Streptococcal antibodies with T1DM and AM antigens. These data provide the basis for developing novel animal models of AM and T1DM and may provide a generalizable method for revealing the etiologies of other autoimmune diseases. Theories to explain these results are explored.

Advances in research on molecular markers in immune checkpoint inhibitor-associated myocarditis

Immune checkpoint inhibitors (ICIs) play a crucial role in the immunotherapy of malignant tumors, preventing immune evasion by tumor cells and activating autoimmune cells to eliminate the tumor. Despite their proven effectiveness in antitumor therapy, potential immune-related adverse effects must be recognized, particularly ICI-associated myocarditis (ICIAM). ICIAM is the most lethal form of organ immunotoxicity, with a significant impact on short-term mortality. However, ICIAM is predominantly asymptomatic or mildly nonspecific. It is difficult to diagnose, especially due to the lack of unique molecular markers. This article aims to provide a comprehensive overview of the progress made in identifying molecular markers for ICIAM.

Coronary Microvascular Dysfunction in Diabetes Mellitus: Pathogenetic Mechanisms and Potential Therapeutic Options

Diabetic patients are frequently affected by coronary microvascular dysfunction (CMD), a condition consisting of a combination of altered vasomotion and long-term structural change to coronary arterioles leading to impaired regulation of blood flow in response to changing cardiomyocyte oxygen requirements. The pathogenesis of this microvascular complication is complex and not completely known, involving several alterations among which hyperglycemia and insulin resistance play particularly central roles leading to oxidative stress, inflammatory activation and altered barrier function of endothelium. CMD significantly contributes to cardiac events such as angina or infarction without obstructive coronary artery disease, as well as heart failure, especially the phenotype associated with preserved ejection fraction, which greatly impact cardiovascular (CV) prognosis. To date, no treatments specifically target this vascular damage, but recent experimental studies and some clinical investigations have produced data in favor of potential beneficial effects on coronary micro vessels caused by two classes of glucose-lowering drugs: glucagon-like peptide 1 (GLP-1)-based therapy and inhibitors of sodium-glucose cotransporter-2 (SGLT2). The purpose of this review is to describe pathophysiological mechanisms, clinical manifestations of CMD with particular reference to diabetes, and to summarize the protective effects of antidiabetic drugs on the myocardial microvascular compartment.

Antiplatelet and Antithrombotic Therapy in Type I Diabetes Mellitus: Update on Current Data

Diabetes mellitus type 1 (T1DM) is an autoimmune disease characterized by a markedly elevated cardiovascular (CV) risk due to premature atherosclerosis. Previous studies have shown that intense glycemic control reduces the incidence of CV disease. Antiplatelet therapy is considered to be a very important therapy for secondary prevention of recurrent atherothrombotic events in patients with DM, while it may be considered for primary prevention in individuals with T1DM with additional CV risk factors. The aim of the present review is to summarize existing literature data regarding the thrombotic risk in T1DM patients and discuss current treatment strategies.

Long-term population-based trends in the incidence of cardiovascular disease in individuals with type 1 diabetes from Finland: a retrospective, nationwide, cohort study

BACKGROUND

Cardiovascular disease is the main determinant of premature mortality in patients with type 1 diabetes. However, time trends regarding different types of cardiovascular disease in childhood-onset type 1 diabetes with a long timespan from the diagnosis of diabetes are not well established. This study aimed to investigate the cumulative incidence of cardiovascular disease in individuals with type 1 diabetes in a population-based cohort in Finland, the country with the world's highest incidence of type 1 diabetes.

METHODS

In this retrospective, nationwide registry-based, cohort study, all patients who were diagnosed between Jan 1, 1965, and Dec 31, 1999 with type 1 diabetes when they were younger than 15 years old in Finland were followed up and monitored for the occurrence of cardiovascular disease (including coronary artery disease, stroke, peripheral artery disease, and heart failure) until the end of 2016 and for cardiovascular disease mortality until 2017. Cumulative incidences of cardiovascular disease were calculated by the Fine and Gray method according to the year of diabetes diagnosis using six diagnosis cohorts: 1965-69, 1970-74, 1975-1979, 1980-84, 1985-89, 1990-94, and 1990-95. Trends in cardiovascular disease event rates were analysed by Fine and Gray competing risks regression models using year of diabetes diagnosis as continuous variable. In addition, non-linearity in trends was assessed with restricted cubic splines. The excess risk of coronary artery disease and stroke was estimated by comparison with the risk in the Finnish general population by calculating standardised incidence ratios (SIRs) and their time trends. The data for Finnish general population were drawn from the Cardiovascular Disease Register of the National Institute of Health and Welfare. The SIRs were calculated as ratios of observed and expected number of events in individuals with type 1 diabetes during 1991-2014.

FINDINGS

11 766 individuals were included in this study. During 361 033 person-years of follow-up and a median of 29·6 years (IQR 22·3-37·9) follow-up, a total of 1761 individuals had single or multiple types of cardiovascular disease events. 2686 events (864 [32·2%] coronary artery disease events, of which 663 were acute myocardial infarctions; 497 [18·5%] strokes; 854 [31·8%] peripheral artery diseases, of which 498 were lower extremity amputations; and 471 [17·5%] heart failure events) were reported until Dec 31, 2016, and 1467 deaths until Dec 31, 2017. Cardiovascular disease risk decreased linearly by 3·8% (hazard ratio [HR] 0·96 [95% CI 0·96-0·97]; p<0·0001) by later calendar year of diabetes diagnosis (p<0·0001). There was a decrease in the SIRs for both coronary artery disease and stroke within all 10-year age groups under 65 years, except for stroke in the oldest age group. However, the SIR was still 8·9 (95% CI 3·9-17·5) for coronary artery disease and 2·9 (1·3-5·7) for stroke in those diagnosed with type 1 diabetes in the 1990s. Finally, the cardiovascular disease death rate decreased constantly by diagnosis year.

INTERPRETATION

The risk of cardiovascular disease has decreased over time in Finland in individuals with childhood-onset type 1 diabetes. However, there is still considerable excess cardiovascular disease risk in individuals with type 1 diabetes compared with the general population. These results highlight the need for studies on the mechanisms of atherosclerosis from the time of diagnosis of type 1 diabetes to facilitate early and effective prevention of cardiovascular disease in these individuals.

FUNDING

Folkhälsan Research Foundation, Academy of Finland, Wilhelm and Else Stockmann Foundation, Liv och Hälsa Society, Novo Nordisk Foundation, Finnish Foundation for Cardiovascular Research, Finnish Diabetes Research Foundation, Diabetes Research Foundation, Medical Society of Finland, Sigrid Jusélius Foundation, and Helsinki University Hospital Research Funds.

T cell checkpoint regulators in the heart

T lymphocyte-mediated immune responses in the heart are potentially dangerous because they can interfere with the electromechanical function. Furthermore, the myocardium has limited regenerative capacity to repair damage caused by effector T cells. Myocardial T cell responses are normally suppressed by multiple mechanisms of central and peripheral tolerance. T cell inhibitory molecules, so called immune checkpoints, limit the activation and effector function of heart antigen-reactive T cells that escape deletion during development in the thymus. Programmed cell protein death-1 (PD-1) and cytotoxic T-lymphocyte-associated protein-4 (CTLA-4) are checkpoint molecules homologous to the costimulatory receptor CD28, and they work to block activating signals from the T cell antigen receptor and CD28. Nonetheless, PD-1 and CTLA-4 function in different ways and at different steps in a T cell response to antigen. Studies in mice have established that genetic deficiencies of checkpoint molecules, including PD-1, PD-L1, CTLA-4, and lymphocyte activation gene-3, result in enhanced risk of autoimmune T cell-mediated myocarditis and increased pathogenicity of heart antigen-specific effector T cells. The PD-1/PD-L1 pathway appears to be particularly important in cardiac protection from T cells. PD-L1 is markedly up-regulated on myocardial cells by interferon-gamma secreted by T cells and PD-1 or PD-L1 deficiency synergizes with other defects in immune regulation in promoting myocarditis. Consistent with these studies, myocarditis has emerged as a serious adverse reaction of cancer therapies that target checkpoint molecules to enhance anti-tumour T cell responses. Histopathology and immunohistochemical analyses of myocardial tissue from immune checkpoint blockade (ICB)-treated patients echoes findings in checkpoint-deficient mice. Many questions about myocarditis in the setting of cancer immunotherapy still need to be answered, including the nature of the target antigens, genetic risk factors, and variations in the disease with combined therapies. Addressing these questions will require further immunological analyses of blood and heart tissue from patients treated with ICB.

Genome-wide association study on coronary artery disease in type 1 diabetes suggests beta-defensin 127 as a risk locus

AIMS

Diabetes is a known risk factor for coronary artery disease (CAD). There is accumulating evidence that CAD pathogenesis differs for individuals with type 1 diabetes (T1D). However, the genetic background has not been extensively studied. We aimed to discover genetic loci increasing CAD susceptibility, especially in T1D, to examine the function of these discoveries and to study the role of the known risk loci in T1D.

METHODS AND RESULTS

We performed the largest genome-wide association study to date for CAD in T1D, comprising 4869 individuals with T1D (cases/controls: 941/3928). Two loci reached genome-wide significance, rs1970112 in CDKN2B-AS1 [odds ratio (OR) = 1.32, P = 1.50 × 10-8], and rs6055069 on DEFB127 promoter (OR = 4.17, P = 2.35 × 10-9), with consistent results in survival analysis. The CDKN2B-AS1 variant replicated (P = 0.04) when adjusted for diabetic kidney disease in three additional T1D cohorts (cases/controls: 434/3123). Furthermore, we explored the function of the lead discoveries with a cardio-phenome-wide analysis. Among the eight suggestive loci (P < 1 × 10-6), rs70962766 near B3GNT2 associated with central blood pressure, rs1344228 near CNTNAP5 with intima media thickness, and rs2112481 on GRAMD2B promoter with serum leucocyte concentration. Finally, we calculated genetic risk scores for individuals with T1D with the known susceptibility loci. General population risk variants were modestly but significantly associated with CAD also in T1D (P = 4.21 × 10-7).

CONCLUSION

While general population CAD risk loci had limited effect on the risk in T1D, for the first time, variants at the CDKN2B-AS1 locus were robustly associated with CAD in individuals with T1D. The novel finding on β-defensin DEFB127 promoter provides a link between diabetes, infection susceptibility, and CAD, although pending on future confirmation.

Cardiovascular disease in type 1 diabetes

Cardiovascular disease (CVD) is a well-recognized complication of diabetes. Although the association of type 2 diabetes with CVD has been well described, the mechanisms, risk stratification and screening strategies of CVD in type 1 diabetes (T1D) are less understood. This review aims to evaluate recent literature and guidelines regarding CVD in T1D. At the cellular level, the early stage of CVD is characterized by endothelial dysfunction. Recent studies have shown that endothelial function is unaffected in younger T1D patients but there is a significant degree of endothelial dysfunction in the older T1D population compared with healthy age-matched controls, highlighting the importance of the endothelial dysfunction in T1D as a major age-dependent cardiovascular risk factor. T1D risk assessment tools have been developed similar to those seen in type 2 diabetes. Foremost among these are the Danish Steno Type 1 risk engine, the Swedish T1D risk score, the Scottish T1D risk score and the QRISK risk calculator. The latter risk prediction tool is used for all patients but contains T1D as an independent risk variable and has the advantage of being derived from, and validated in, a large and diverse population. The latest version (QRISK3) is likely to be recommended for routine use in T1D patients in upcoming guidelines by the National Institute of Clinical Excellence. Mortality in adults with T1D is increasingly due to CVD. This is driven by hyperglycaemia-mediated oxidative stress and vascular inflammation, resulting in atherosclerosis and cardiac autonomic neuropathy. Coronary artery disease is the most significant contributor to CVD and in T1D, has a propensity towards a more silent and severe form. Routine screening of coronary artery disease does not alter outcomes and is therefore not recommended; however, risk prediction tools are being developed to aid identification of high-risk individuals for aggressive risk factor modification strategies.

Heart macrophages and dendritic cells in sickness and in health: A tale of a complicated marriage

Heart disease is the major cause of death and it is broadly recognized that the immune system plays a central role in healthy and injured heart. Here, we focus on the contribution of various subsets of mononuclear phagocytes in the cardiac system. Macrophages and dendritic cells reside in the healthy myocardium to fulfill homeostatic functions and rapidly increase in numbers in diseases like myocardial ischemia and myocarditis to contribute to disease or resolve it. Recent experiments have revealed the extraordinary heterogeneity of cardiac mononuclear phagocytes that differ in origin, lifespan, phenotype and function. Although many studies described cardiac phagocytes in the mouse, subsets of cardiac mononuclear phagocytes can also be broadly found in the human heart, opening up the potential of selective targeting of these cells in a therapeutic setting. Before this goal can be achieved we need better understanding not only of the detrimental but also beneficial functions of these highly diverse cells in the heart.

CCAAT/enhancer binding protein homologous protein knockdown alleviates hypoxia-induced myocardial injury in rat cardiomyocytes exposed to high glucose

Diabetic patients are more sensitive to ischemic injury than non-diabetics. Endoplasmic reticulum (ER) stress has been reported to be closely associated with the pathophysiology of ischemic injury in diabetes. The aim of the present study was to investigate the mechanisms involved in the progression of diabetes complicated by myocardial infarction (MI) and further verify the role of CCAAT/enhancer binding protein (C/EBP)-homologous protein (CHOP) using an in vitro model of diabetes/MI. The rats were exposed to 65 mg/kg streptozotocin (STZ) and left anterior descending (LAD) coronary artery ligation. ST-segment elevation, heart rate, left ventricular systolic pressure (LVSP) and LV end-diastolic pressure (LVEDP) were measured. Serum creatinine kinase-MB (CK-MB) and cardiac troponin T (cTnT) levels were examined by ELISA. Infarct size and apoptosis were measured by triphenyltetrazolium chloride staining and terminal deoxynucleotidyl-transferase-mediated dUTP nick end labeling assay. Pathological changes were evaluated by hematoxylin and eosin staining. H9c2 cells were used to establish an in vitro model of diabetes complicated by MI. Following CHOP knockdown, cell viability, cell cycle distribution and apoptosis were examined by Cell Counting Kit-8 assay, flow cytometry and Hoechst staining. Glucose-regulated protein 78 (GRP78), CHOP, B-cell lymphoma 2 (Bcl-2), Bcl-2-associated X protein (Bax), endoplasmic reticulum oxidoreductase 1 (Ero1)-α, Ero1β and protein disulfide isomerase (PDI) levels in both myocardial tissues and H9c2 cells were determined by western blotting. In the present study, diabetes complicated by MI promoted ST-segment elevation and myocardial apoptosis, increased infarct size, induced pathological changes and elevated LVEDP, CK-MB, cTnT, GRP78, CHOP, Bax, Ero1α, Ero1β and PDI; however, it decreased heart rate, LVSP and Bcl-2. Additionally, high glucose combined with hypoxic treatment reduced cell viability, induced cell cycle arrest at G1 phase, promoted cell apoptosis, and activated the GRP78/CHOP and Ero1/PDI signaling pathways, which were reversed by CHOP knockdown. Thus, CHOP may be an effective therapeutic target for the treatment of diabetes complicated by MI.

Understanding the role of the gut ecosystem in diabetes mellitus

Diabetes mellitus is a type of metabolic disorder whereby patients are unable to regulate glycemia. It is currently a worldwide public health issue, and is a burden to society because of its disabling and common complications. Diabetes is multifactorial, and also induces the onset of other diseases. In the present report, we review the labyrinth encompassing the gut microbiota and gut microbiota-derived metabolites in type 1 diabetes and type 2 diabetes pathogenesis. There have been exceptional improvements in deoxyribonucleic acid sequencing and mass spectrometry technologies throughout these past years, and these have allowed the comprehensive collection of information on our unique gut ecosystem. We would like to advocate incorporating metagenome and metabolome information for a comprehensive perspective of the complex interrelationships between the gut environment, host metabolism and diabetes pathogenesis. We hope that with this improved understanding we would be able to provide exciting novel therapeutic approaches to engineer an ideal gut ecosystem for optimal health.

Myocardial Infarction Primes Autoreactive T Cells through Activation of Dendritic Cells

Peripheral tolerance is crucial for avoiding activation of self-reactive T cells to tissue-restricted antigens. Sterile tissue injury can break peripheral tolerance, but it is unclear how autoreactive T cells get activated in response to self. An example of a sterile injury is myocardial infarction (MI). We hypothesized that tissue necrosis is an activator of dendritic cells (DCs), which control tolerance to self-antigens. DC subsets of a murine healthy heart consisted of IRF8-dependent conventional (c)DC1, IRF4-dependent cDC2, and monocyte-derived DCs. In steady state, cardiac self-antigen α-myosin was presented in the heart-draining mediastinal lymph node (mLN) by cDC1s, driving the proliferation of antigen-specific CD4⁺ TCR-M T cells and their differentiation into regulatory cells (Tregs). Following MI, all DC subsets infiltrated the heart, whereas only cDCs migrated to the mLN. Here, cDC2s induced TCR-M proliferation and differentiation into interleukin-(IL)-17/interferon-(IFN)γ-producing effector cells. Thus, cardiac-specific autoreactive T cells get activated by mature DCs following myocardial infarction.

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IRF8⁺ cDC1, IRF4⁺ cDC2, moDCs, and macrophages are the APCs of the murine heart

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Self-antigen presentation in the steady state drives Treg development via cDC1s

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Myocardial infarction promotes infiltration, activation, and maturation of all DCs

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Myocardial infarction promotes priming of Th1/Th17 autoreactive T cells via cDC2s

Coronary microvascular disease as an early culprit in the pathophysiology of diabetes and metabolic syndrome

Metabolic syndrome (MetS) is a group of cardio-metabolic risk factors that includes obesity, insulin resistance, hypertension, and dyslipidemia; these are also a combination of independent coronary artery disease (CAD) risk factors. Alarmingly, the prevalence of MetS risk factors are increasing and a leading cause for mortality. In the vasculature, complications from MetS and type 2 diabetes (T2D) can be divided into microvascular (retinopathy and nephropathy) and macrovascular (cardiovascular diseases and erectile dysfunction). In addition to vascular and endothelial dysfunction, vascular remodeling and stiffness are also hallmarks of cardiovascular disease (CVD), and well-characterized vascular changes that are observed in the early stages of hypertension, T2D, and obesity [1-3]. In the heart, the link between obstructive atherosclerosis of coronary macrovessels and myocardial ischemia (MI) is well established. However, recent studies show that abnormalities in the coronary microcirculation are associated with functional and structural changes in coronary microvessels (classically defined as being ≤150-200μm internal diameter), which may cause or contribute to MI even in the absence of obstractive CAD. This suggests a prognostic value of an abnormal coronary microcirculation as an early sub-clinical culprit in the pathogenesis and progression of heart disease in T2D and MetS. The aim of this review is to summarize recent studies investigating the coronary microvascular remodeling in an early pre-atherosclerotic phase of MetS and T2D, and to explore potential mechanisms associated with the timing of coronary microvascular remodeling relative to that of the macrovasculature.

Cardiac antibody production to self-antigens in children and adolescents during and following the correction of severe diabetic ketoacidosis

Diabetic cardiomyopathy (DC) is an independent phenotype of diabetic cardiovascular disease. The understanding of the pathogenesis of DC in young patients with type 1 diabetes (T1D) is limited. The cardiac insults of diabetic ketoacidosis (DKA) and progression of DC could include development of antibodies (Abs) to cardiac self-antigens (SAgs) such as: myosin (M), vimentin (V) and k-alpha 1 tubulin (Kα1T). The goal of this study is to determine if the insults of severe DKA and its inflammatory cascade are associated with immune responses to SAgs. Development of Abs to the SAgs were determined by an ELISA using sera collected at three time points in relation to severe DKA (pH < 7.2). Results demonstrate significant differences between the development of Abs to VIM and a previously reported diastolic abnormality (DA) during DKA and its treatment and a NDA group at 2-3 months post DKA (p = 0.0452). A significant association is present between T1D duration (<3 years) and Abs to Kα1T (p = 0.0134). Further, Abs to MYO and VIM are associated with inflammatory cytokines. We propose that severe DKA initiates the synthesis of Abs to cardiac SAgs that are involved in the early immunopathogenesis of DC in young patients with T1D.

Enhanced A2A adenosine receptor-mediated increase in coronary flow in type I diabetic mice

Adenosine A2A receptor (A2AAR) activation plays a major role in the regulation of coronary flow (CF). Recent studies from our laboratory and others have suggested that A2AAR expression and/or signaling is altered in disease conditions. However, the coronary response to AR activation, in particular A2AAR, in diabetes is not fully understood. In this study, we use an STZ mouse model of type 1 diabetes (T1D) to look at CF responses to the nonspecific AR agonist NECA and the A2AAR specific agonist CGS 21680 in-vivo and ex-vivo. Using immunofluorescence, we also explored the effect of diabetes on A2AAR expression in coronary arteries. NECA mediated increase in CF was significantly increased in hearts isolated from STZ-induced diabetic mice. In addition, both in in-vivo and ex-vivo responses to A2AAR activation using CGS 21680 were significantly higher in diabetic mice when compared to their controls. Immunohistochemistry showed an upregulation of A2AAR in both coronary smooth muscle and endothelial cells (~160% and ~140%, respectively). Our data suggest that diabetes resulted in an increased A2AAR expression in coronary arteries which resulted in enhanced A2AAR-mediated increase in CF observed in diabetic hearts. This is the first report implying that A2AAR has a role in the regulation of CF in diabetes, supporting recent studies suggesting that the use of adenosine and its A2A selective agonist (regadenoson, Lexiscan®) may not be appropriate for the detection of coronary artery diseases in T1D and the estimation of coronary reserve.