Role of high-mobility group box 1 protein in post-infarction healing process and left ventricular remodelling

Targeting high-mobility-group-box-1-mediated inflammation: a promising therapeutic approach for myocardial infarction

Myocardial ischemia, resulting from coronary artery blockage, precipitates cardiac arrhythmias, myocardial structural changes, and heart failure. The pathophysiology of MI is mainly based on inflammation and cell death, which are essential in aggravating myocardial ischemia and reperfusion injury. Emerging research highlights the functionality of high mobility group box-1, a non-histone nucleoprotein functioning as a chromosomal stabilizer and inflammatory mediator. HMGB1's release into the extracellular compartment during ischemia acts as damage-associated molecular pattern, triggering immune reaction by pattern recognition receptors and exacerbating tissue inflammation. Its involvement in signaling pathways like PI3K/Akt, TLR4/NF-κB, and RAGE/HMGB1 underscores its significance in promoting angiogenesis, apoptosis, and reducing inflammation, which is crucial for MI treatment strategies. This review highlights the complex function of HMGB1 in the pathogenesis of myocardial infarction by summarizing novel findings on the protein in ischemic situations. Understanding the mechanisms underlying HMGB1 could widen the way to specific treatments that minimize the severity of MI and enhance patient outcomes.

High Mobility Group Box 1 and Cardiovascular Diseases: Study of Act and Connect

Cardiovascular disease is the deadly disease that can result in sudden death, and inflammation plays an important role in its onset and progression. High mobility group box 1 (HMGB1) is a nuclear protein that regulates transcription, DNA replication, repair, and nucleosome assembly. HMGB1 is released passively by necrotic tissues and actively secreted by stressed cells. Extracellular HMGB1 functions as a damage associated molecular patterns molecule, producing numerous redox forms that induce a range of cellular responses by binding to distinct receptors and interactors, including tissue inflammation and regeneration. Extracellular HMGB1 inhibition reduces inflammation and is protective in experimental models of myocardial ischemia/reperfusion damage, myocarditis, cardiomyopathies caused by mechanical stress, diabetes, bacterial infection, or chemotherapeutic drugs. HMGB1 administration following a myocardial infarction followed by permanent coronary artery ligation improves cardiac function by stimulating tissue regeneration. HMGB1 inhibits contractility and produces hypertrophy and death in cardiomyocytes, while also stimulating cardiac fibroblast activity and promoting cardiac stem cell proliferation and differentiation. Maintaining normal nuclear HMGB1 levels, interestingly, protects cardiomyocytes from apoptosis by limiting DNA oxidative stress, and mice with HMGB1cardiomyocyte-specific overexpression are partially protected from cardiac injury. Finally, elevated levels of circulating HMGB1 have been linked to human heart disease. As a result, following cardiac damage, HMGB1 elicits both detrimental and helpful responses, which may be due to the formation and stability of the various redox forms, the particular activities of which in this context are mostly unknown. This review covers recent findings in HMGB1 biology and cardiac dysfunction.

HMGB1, an evolving pleiotropic protein critical for cellular and tissue homeostasis: Role in aging and age-related diseases

Aging is a universal biological process characterized by a progressive, cumulative decline in homeostatic capabilities and physiological functions, which inevitably increases vulnerability to diseases. A number of molecular pathomechanisms and hallmarks of aging have been recognized, yet we miss a thorough understanding of their complex interconnectedness. This review explores the molecular and cellular mechanisms underlying human aging, with a focus on the multiple roles of high mobility group Box 1 protein (HMGB1), the archetypal damage-associated molecular pattern (DAMP) molecule. In the nucleus, this non-histone chromatin-associated protein functions as a DNA chaperone and regulator of gene transcription, influencing DNA structure and gene expression. Moreover, this versatile protein can translocate to the cytoplasm to orchestrate other processes, such as autophagy, or be unconventionally secreted into the extracellular environment, where it acts as a DAMP, combining inflammatory and regenerative properties. Notably, lower expression of HMGB1 within the cell and its heightened extracellular release have been associated with diverse age-associated traits, making it a suitable candidate as a universal biomarker of aging. In this review, we outline the evidence implicating HMGB1 in aging, also in light of an evolutionary perspective on its functional pleiotropy, and propose critical issues that need to be addressed to gauge the value of HMGB1 as a potential biomarker across age-related diseases and therapeutic target to promote healthy longevity.

Expression of HMGB1, TGF-β1, BIRC3, ADAM17, CDKN1A, and FTO in Relation to Left Ventricular Remodeling in Patients Six Months after the First Myocardial Infarction: A Prospective Study

Background: After myocardial infarction (MI), adverse left ventricular (LV) remodeling may occur. This is followed by LV hypertrophy and eventually heart failure. The remodeling process is complex and goes through multiple phases. The aim of this study was to investigate the expression of HMGB1, TGF-β1, BIRC3, ADAM17, CDKN1A, and FTO, each involved in a specific step of LV remodeling, in association with the change in the echocardiographic parameters of LV structure and function used to assess the LV remodeling process in the peripheral blood mononuclear cells (PBMCs) of patients six months after the first MI. The expression of selected genes was also determined in PBMCs of controls. Methods: The study group consisted of 99 MI patients, who were prospectively followed-up for 6 months, and 25 controls. Cardiac parameters, measured via conventional 2D echocardiography, were evaluated at two time points: 3-5 days and 6 months after MI. The mRNA expression six-months-post-MI was detected using TaqMan® technology (Applied Biosystems, Thermo Fisher Scientific, Waltham, MA, USA). Results:HMGB1 mRNA was significantly higher in patients with adverse LV remodeling six-months-post-MI than in patients without adverse LV remodeling (p = 0.04). HMGB1 mRNA was significantly upregulated in patients with dilated LV end-diastolic diameter (LVEDD) (p = 0.03); dilated LV end-diastolic volume index (LVEDVi) (p = 0.03); severely dilated LV end-systolic volume index (LVESVi) (p = 0.006); impaired LV ejection fraction (LVEF) (p = 0.01); and LV enlargement (p = 0.03). It was also significantly upregulated in PBMCs from patients compared to controls (p = 0.005). TGF-β1 and BIRC3 mRNA were significantly lower in patients compared to controls (p = 0.02 and p = 0.05, respectively). Conclusions: Our results suggest that HMGB1 is involved in adverse LV remodeling six-months-post-MI, even on the mRNA level. Further research and validation are needed.

The Role of Alarmins in the Pathogenesis of Atherosclerosis and Myocardial Infarction

Atherosclerosis is a condition that is associated with lipid accumulation in the arterial intima. Consequently, the enlarging lesion, which is also known as an atherosclerotic plaque, may close the blood vessel lumen, thus leading to organ ischaemia. Furthermore, the plaque may rupture and initiate the formation of a thrombus, which can cause acute ischaemia. Atherosclerosis is a background pathological condition that can eventually lead to major cardiovascular diseases such as acute coronary syndrome or ischaemic stroke. The disorder is associated with an altered profile of alarmins, stress response molecules that are secreted due to cell injury or death and that induce inflammatory responses. High-mobility group box 1 (HMGB1), S100 proteins, interleukin-33, and heat shock proteins (HSPs) also affect the behaviour of endothelial cells and vascular smooth muscle cells (VSMCs). Thus, alarmins control the inflammatory responses of endothelial cells and proliferation of VSMCs, two important processes implicated in the pathogenesis of atherosclerosis. In this review, we will discuss the role of alarmins in the pathophysiology of atherosclerosis and myocardial infarction.

Repair of the Infarcted Heart: Cellular Effectors, Molecular Mechanisms and Therapeutic Opportunities

The adult mammalian heart has limited endogenous regenerative capacity and heals through the activation of inflammatory and fibrogenic cascades that ultimately result in the formation of a scar. After infarction, massive cardiomyocyte death releases a broad range of damage-associated molecular patterns that initiate both myocardial and systemic inflammatory responses. TLRs (toll-like receptors) and NLRs (NOD-like receptors) recognize damage-associated molecular patterns (DAMPs) and transduce downstream proinflammatory signals, leading to upregulation of cytokines (such as interleukin-1, TNF-α [tumor necrosis factor-α], and interleukin-6) and chemokines (such as CCL2 [CC chemokine ligand 2]) and recruitment of neutrophils, monocytes, and lymphocytes. Expansion and diversification of cardiac macrophages in the infarcted heart play a major role in the clearance of the infarct from dead cells and the subsequent stimulation of reparative pathways. Efferocytosis triggers the induction and release of anti-inflammatory mediators that restrain the inflammatory reaction and set the stage for the activation of reparative fibroblasts and vascular cells. Growth factor-mediated pathways, neurohumoral cascades, and matricellular proteins deposited in the provisional matrix stimulate fibroblast activation and proliferation and myofibroblast conversion. Deposition of a well-organized collagen-based extracellular matrix network protects the heart from catastrophic rupture and attenuates ventricular dilation. Scar maturation requires stimulation of endogenous signals that inhibit fibroblast activity and prevent excessive fibrosis. Moreover, in the mature scar, infarct neovessels acquire a mural cell coat that contributes to the stabilization of the microvascular network. Excessive, prolonged, or dysregulated inflammatory or fibrogenic cascades accentuate adverse remodeling and dysfunction. Moreover, inflammatory leukocytes and fibroblasts can contribute to arrhythmogenesis. Inflammatory and fibrogenic pathways may be promising therapeutic targets to attenuate heart failure progression and inhibit arrhythmia generation in patients surviving myocardial infarction.

Serum HMGB1 is a biomarker for acute myocardial infarction with or without heart failure

This study measured serum high mobility group box 1 (HMGB1) levels in patients with acute myocardial infarction (AMI) and/or heart failure (HF) and evaluated their relationship with peripheral inflammatory biomarkers and cardiac biomarkers, which have not been reported before. Of the patients, 55 had AMI without HF (AMI-HF ), 42 had AMI with HF (AMI+HF ), and 60 had HF without AMI (HF-AMI ) compared with 50 healthy controls. Blood samples were collected to assess serum HMGB1 levels and blood test-related inflammatory biomarkers (e.g., erythrocyte sedimentation rate [ESR], hs-CRP, uric acid, and white blood cell count) and cardiac biomarkers (e.g., MYO, cTnI, CKMB, CK, NT-proBNP, LDH, aspartate aminotransferase [AST], and alanine aminotransferase [ALT]). Compared to healthy controls, three groups of patients, especially those with AMI+HF , had significantly higher levels of serum HMGB1. All tested inflammatory biomarkers (except uric acid) were significantly positively correlated with HMGB1 in patients with AMI patients but not in patients with non-AMI. In addition, all tested cardiac biomarkers (except NT-proBNP in AMI-HF ) were significantly higher in patients with AMI than in control individuals. The levels of MYO, cTnI, CKMB, CK, AST, and ALT were not significantly changed in patients with HF-AMI compared to control individuals, but were still much lower than those in patients with AMI (except ALT). In all patients, the levels of NT-proBNP, and cTnI were significantly correlated with HMGB1 levels. Except for MYO, LDH, AST, and ALT, all cardiac biomarkers in AMI-HF and AMI+HF showed a significant correlation with HMGB1. Among risk factors, hypertension, diabetes, previous heart disease, and reduced left ventricular ejection fraction showed a significant correlation with HMGB1 in all disease groups.

Involvement of HIF1α/Reg protein in the regulation of HMGB3 in myocardial infarction

AIMS

Myocardial ischemia and infarction are the number one cause of cardiovascular disease associated mortality. Cardiomyocyte death during ischemia leads to the loss of cardiac tissue and initiates a signaling cascade between the infarct zone and the area at risk of the myocardium. Here, we sought to determine the involvement of one of the damage-associated molecular patterns HMGB3 in myocardial ischemia and infarction.

METHODS AND RESULTS

We used the left anterior descending coronary artery ligation model to study the involvement of HMGB3 in myocardial ischemia and infarction. Our results indicated the presence of HMGB3 at a low level under normal conditions, while myocardial injury caused a robust increase in HMGB3 levels in the heart. Further, intra-cardiac injection of mabHMGB3 had improved cardiac function at day 3 by downregulating HMGB3 levels. In contrast, injection of recombinant rat HMGB3 for 7 days during the adaptation phase of myocardial ischemia improved cardiac functional parameters by increasing regenerative protein family expression. Further, to mimic the disease condition, neonatal rat ventricle cardiomyocytes and fibroblasts were exposed to hypoxia; we observed a significant upregulation in the HMGB3, HIF1α, and Reg1α levels. Endothelial cells exposed to recombinant HMGB3 increased the tubule length. Further, the mitochondrial oxygen consumption rate was reduced with the acute induction of recombinant HMGB3 on cardiomyocytes and fibroblasts.

CONCLUSION

HMGB3 plays a dual role during the progression of myocardial ischemia and infarction. Clinically, post-myocardial infarction HMGB3-induced sterile inflammation needs to be tightly controlled, as it plays both a pro-inflammatory role and improves cardiac function during the cardiac remodeling phase.

HMGB family proteins: Potential biomarkers and mechanistic factors in cardiovascular diseases

Cardiovascular disease (CVD) is the most fatal disease that causes sudden death, and inflammation contributes substantially to its occurrence and progression. The prevalence of CVD increases as the population ages, and the pathophysiology is complex. Anti-inflammatory and immunological modulation are the potential methods for CVD prevention and treatment. High-Mobility Group (HMG) chromosomal proteins are one of the most abundant nuclear nonhistone proteins which act as inflammatory mediators in DNA replication, transcription, and repair by producing cytokines and serving as damage-associated molecular patterns in inflammatory responses. The most common and well-studied HMG proteins are those with an HMGB domain, which participate in a variety of biological processes. HMGB1 and HMGB2 were the first members of the HMGB family to be identified and are present in all investigated eukaryotes. Our review is primarily concerned with the involvement of HMGB1 and HMGB2 in CVD. The purpose of this review is to provide a theoretical framework for diagnosing and treating CVD by discussing the structure and function of HMGB1 and HMGB2.

Circulatory HMGB1 is an early predictive and prognostic biomarker of ARDS and mortality in a swine model of polytrauma

Acute respiratory distress syndrome (ARDS) is a leading cause of morbidity and mortality in polytrauma patients. Pharmacological treatments of ARDS are lacking, and ARDS patients rely on supportive care. Accurate diagnosis of ARDS is vital for early intervention and improved outcomes but is presently delayed up to days. The use of biomarkers for early identification of ARDS development is a potential solution. Inflammatory mediators high-mobility group box 1 (HMGB1), syndecan-1 (SDC-1), and C3a have been previously proposed as potential biomarkers. For this study, we analyzed these biomarkers in animals undergoing smoke inhalation and 40% total body surface area burns, followed by intensive care for 72 h post-injury (PI) to determine their association with ARDS and mortality. We found that the levels of inflammatory mediators in serum were affected, as well as the degree of HMGB1 and Toll-like receptor 4 (TLR4) signal activation in the lung. The results showed significantly increased HMGB1 expression levels in animals that developed ARDS compared with those that did not. Receiver operating characteristic (ROC) analysis showed that HMGB1 levels at 6 h PI were significantly associated with ARDS development (AUROC=0.77) and mortality (AUROC=0.82). Logistic regression analysis revealed that levels of HMGB1 ≥24.10 ng/ml are associated with a 13-fold higher incidence of ARDS [OR:13.57 (2.76-104.3)], whereas the levels of HMGB1 ≥31.39 ng/ml are associated with a 12-fold increase in mortality [OR: 12.00 (2.36-93.47)]. In addition, we found that mesenchymal stem cell (MSC) therapeutic treatment led to a significant decrease in systemic HMGB1 elevation but failed to block SDC-1 and C3a increases. Immunohistochemistry analyses showed that smoke inhalation and burn injury induced the expression of HMGB1 and TLR4 and stimulated co-localization of HMGB1 and TLR4 in the lung. Interestingly, MSC treatment reduced the presence of HMGB1, TLR4, and the HMGB1-TLR4 co-localization. These results show that serum HMGB1 is a prognostic biomarker for predicting the incidence of ARDS and mortality in swine with smoke inhalation and burn injury. Therapeutically blocking HMGB1 signal activation might be an effective approach for attenuating ARDS development in combat casualties or civilian patients.

HMGB1 Is a Prognostic Factor for Mortality in Acute Kidney Injury Requiring Renal Replacement Therapy

INSTRUCTION

High mobility group box 1 (HMGB1) is a pro-inflammatory cytokine that reportedly causes kidney injury and other organ damage in rodent acute kidney injury (AKI) models. However, it remains unclear whether HMGB1 is associated with clinical AKI and related outcomes. This study aimed to evaluate the association with HMGB1 and prognosis of AKI requiring continuous renal replacement therapy (CRRT).

METHODS

AKI patients treated with CRRT in our intensive care unit were enrolled consecutively during 2013-2016. Plasma HMGB1 was measured on initiation. Classic initiation was defined as presenting at least one of the following conventional indications: hyperkalemia (K ≥6.5 mEq/L), severe acidosis (pH <7.15), uremia (UN >100 mg/dL), and diuretics-resistant pulmonary edema. Early initiation was defined as presenting no conventional indications. The primary outcome was defined as 90-day mortality.

RESULTS

A total of 177 AKI patients were enrolled in this study. HMGB1 was significantly associated with the primary outcome (hazard ratio, 1.06; 95% CI, 1.04-1.08). When the patients were divided into two-by-two groups by the timing of CRRT initiation and the HMBG1 cutoff value obtained by receiver operating curve (ROC) analysis, the high HMGB1 group (>10 ng/mL) with classic initiation was significantly associated with the primary outcome compared with the others, even after adjusting for other factors including the nonrenal serial organ failure assessment (SOFA) score.

CONCLUSION

HMGB1 was associated with 90-day mortality in AKI patients requiring CRRT. Notably, the highest mortality was observed in the high HMGB1 group with classic initiation. These findings suggest that CRRT should be considered for AKI patients with high HMGB1, regardless of the conventional indications.

High-mobility group box 1 protein, receptor for advanced glycation end products and nucleosomes increases after marathon

Background: Prolonged and strenuous exercise has been linked to potential exercise-induced myocardial damages. One potential key to unmask the discussed underlying mechanisms of this subclinical cardiac damage could be markers of immunogenic cell damage (ICD). We investigated the kinetics of high-mobility group box 1 protein (HMGB1), soluble receptor for advanced glycation end products (sRAGE), nucleosomes, high sensitive troponin T (hs-TnT) and high sensitive C-reactive protein (hs-CRP) before and up to 12 weeks post-race and described associations with routine laboratory markers and physiological covariates. Methods: In our prospective longitudinal study, 51 adults (82% males; 43 ± 9 years) were included. All participants underwent a cardiopulmonary evaluation 10-12 weeks pre-race. HMGB1, sRAGE, nucleosomes, hs-TnT and, hs-CRP were analysed 10-12 weeks prior, 1-2 weeks before, immediately, 24 h, 72 h, and 12 weeks post-race. Results: HMGB1, sRAGE, nucleosomes and hs-TnT increased significantly from pre- to immediately post-race (0.82-2.79 ng/mL; 1132-1388 pg/mL; 9.24-56.65 ng/mL; 6-27 ng/L; p < 0.001) and returned to baseline within 24-72 h. Hs-CRP increased significantly 24 h post-race (0.88-11.5 mg/L; p < 0.001). Change in sRAGE was positively associated with change in hs-TnT (rs = 0.352, p = 0.011). Longer marathon finishing time was significantly associated with decreased levels of sRAGE [-9.2 pg/mL (β = -9.2, SE = 2.2, p < 0.001)]. Conclusion: Prolonged and strenuous exercise increases markers of ICD immediately post-race, followed by a decrease within 72 h. An acute marathon event results in transient alterations of ICD, we assume that this is not solely driven by myocyte damages.

High mobility group box 1 derived mainly from platelet microparticles exacerbates microvascular obstruction in no reflow

INTRODUCTION

No reflow manifests coronary microvascular injury caused by continuous severe myocardial ischemia and reperfusion. Microvascular obstruction (MVO) has emerged as one fundamental mechanism of no reflow. However, the underlying pathophysiology remains incompletely defined. Herein, we explore the contribution of high mobility group box 1 (HMGB1), derived mainly from platelet microparticles exacerbating MVO in no reflow.

MATERIALS AND METHODS

44 STEMI patients undergoing successful primary percutaneous coronary intervention (PCI) were included in our study. Plasma HMGB1 levels in both the peripheral artery (PA) and infarct-related coronary artery (IRA) were measured by ELISA. Flow cytometry and confocal microscopy assessed the level of HMGB1⁺ platelet derived microparticles (PMPs) and platelet activation. Flow cytometry and western blot evaluated the procoagulant activity (PCA) and the release of inflammatory factors of human microvascular endothelial cells (HCEMCs).

RESULTS

HMGB1 levels were significantly higher in the IRA in no-reflow patients. The levels of HMGB1⁺ PMPs were considerably higher in the IRA of patients with no reflow and were strongly associated with platelet activation. Moreover, our results show that HMGB1 interacts with human microvascular endothelial cells primarily through TLR4, inducing HCMEC proinflammatory, procoagulant phenotype, and monocyte recruitment, accelerating microvascular obstruction and facilitating the development of no reflow.

CONCLUSION

Our results illustrate a novel mechanism by which HMGB1, derived mainly from PMPs, plays a crucial role in the pathogenesis of no-reflow, revealing a novel therapeutic target.

Quo Vadis? Immunodynamics of Myeloid Cells after Myocardial Infarction

Myocardial infarction (MI), a major contributor to worldwide morbidity and mortality, is caused by a lack of blood flow to the heart. Affected heart tissue becomes ischemic due to deficiency of blood perfusion and oxygen delivery. In case sufficient blood flow cannot be timely restored, cardiac injury with necrosis occurs. The ischemic/necrotic area induces a systemic inflammatory response and hundreds of thousands of leukocytes are recruited from the blood to the injured heart. The blood pool of leukocytes is rapidly depleted and urgent re-supply of these cells is needed. Myeloid cells are generated in the bone marrow (BM) and spleen, released into the blood, travel to sites of need, extravasate and accumulate inside tissues to accomplish various functions. In this review we focus on the "leukocyte supply chain" and will separately evaluate different myeloid cell compartments (BM, spleen, blood, heart) in steady state and after MI. Moreover, we highlight the local and systemic kinetics of extracellular factors, chemokines and danger signals involved in the regulation of production/generation, release, transportation, uptake, and activation of myeloid cells during the inflammatory phase of MI.

Non-invasive tragus stimulation improves cardiac post-ischemic remodeling by regulating cardiac parasympathetic activity

AIMS

Our previous study proved that low-level tragus nerve stimulation (LL-TS) could improve left ventricular remodelling by cardiac down-stream mechanisms. However, the cardiac up-stream mechanisms remain unknown.

METHODS AND RESULTS

Twenty-eight adult beagle dogs were randomly divided into an MI group (myocardial infarction was induced by permanent ligation of the left coronary artery, n = 10), an LL-TS group (MI plus intermittent LL-TS treatment, n = 10), and a control group (sham ligation with the same stimulation as the LL-TS group, n = 8). Auricular tragus nerve was bilaterally delivered to the tragus via ear-clips connected to a custom-made stimulator. The voltage slowing sinus rate was used as the threshold to set the LL-TS 80% below this level. At the end of 4 weeks post-MI, LL-TS could significantly increase atrial ganglion plex (GP) activity, decreased left stellate ganglion (LSG) activity, reduced LV dilation, and improved ventricular functions. Chronic intermittent LL-TS treatment significantly attenuated left ventricular remodelling via the up-regulation of α7nAChR expression and the down-regulation of MMP-9 level in post-MI LV tissue. The elevated protein and mRNA of MMP-9 levels in remote areas were significantly ameliorated by LL-TS treatment.

CONCLUSIONS

Chronic LL-TS increased GP neural activity and improved ventricular remodelling possibly via α7nAChR/MMP-9 axis.

Concomitant elevated serum levels of tenascin, MMP-9 and YKL-40, suggest ongoing remodeling of the heart up to 3 months after cardiac surgery after normalization of the revascularization markers

BACKGROUND

The recovery from cardiac surgery involves resolving inflammation and remodeling with significant connective tissue turnover. Dynamics of smoldering inflammation and injury (white blood cells, platelets, CRP, IL-8, IL-6), vascular inflammation (IL-15, VEGF, RANTES), connective tissue remodeling (tenascin, MMP-9), cardiac injury and remodeling (YKL-40), and vascular remodeling (epiregulin, MCP-1, VEGF) were assessed up to 3 months after cardiac surgery. We hypothesize that at 3 months, studied markers will return to pre-surgical levels.

METHODS

Patients (n = 139) scheduled for non-emergent heart surgery were included, except for patients with pre-existing immunological aberrancies. Blood was collected before surgery(t_baseline), 24 h later(t_24h) after the first sample, 7 days(t_7d), and 3 months(t_3m) after t_baseline. Serum markers were measured via multiplex or ELISA. Electronic medical records (EMR) were used to extract demographical, pre-existing conditions and clinical data. Disposition (discharge home, discharge to facility, death, re-admission) was determined at 28 days and 3 months from admission.

RESULTS

Not all inflammatory markers returned to baseline (CRP↑↑, leukocytosis, thrombocytosis, IL-8↓, IL-6↓). Tenascin and YKL-40 levels remained elevated even at t_3m. YKL-40 serum levels were significantly elevated at t_24h and t_7d while normalized at t_3m. VEGF returned to the baseline, yet MCP-1 remained elevated at 3 months. CCL28 increased at 3 months, while RANTES and IL-15 declined at the same time. Disposition at discharge was determined by serum MMP-9, while YKL-40 correlated with duration of surgery and APACHE II_24h.

CONCLUSIONS

The data demonstrated an ongoing extracellular matrix turnover at 3 months, while acute inflammation and vascular remodeling resolved only partially.

Serum high mobility group box-1 levels associated with cardiovascular events after lower extremity revascularization: a prospective study of a diabetic population

Background

Peripheral arterial disease (PAD) is one of the most disabling cardiovascular complications of type 2 diabetes mellitus and is indeed associated with a high risk of cardiovascular and limb adverse events. High mobility group box-1 (HMGB-1) is a nuclear protein involved in the inflammatory response that acts as a pro-inflammatory cytokine when released into the extracellular space. HMBG-1 is associated with PAD in diabetic patients.

The aim of this study was to evaluate the association between serum HMGB-1 levels and major adverse cardiovascular events (MACE) and major adverse limb events (MALE) after lower-extremity endovascular revascularization (LER) in a group of diabetic patients with chronic limb-threatening ischemia (CLTI).

Methods

We conducted a prospective observational study of 201 diabetic patients with PAD and CLTI requiring LER. Baseline serum HMGB-1 levels were determined before endovascular procedure. Data on cardiovascular and limb outcomes were collected in a 12-month follow-up.

Results

During the follow-up period, 81 cases of MACE and 93 cases of MALE occurred. Patients who subsequently developed MACE and MALE had higher serum HMGB-1 levels. Specifically, 7.5 ng/mL vs 4.9 ng/mL (p < 0.01) for MACE and 7.2 ng/mL vs 4.8 ng/mL (p < 0.01) for MALE. After adjusting for traditional cardiovascular risk factors, the association between serum HMGB-1 levels and cardiovascular outcomes remained significant in multivariable analysis. In our receiver operating characteristic (ROC) curve analysis, serum HMGB-1 levels were a good predictor of MACE incidence (area under the curve [AUC] = 0.78) and MALE incidence (AUC = 0.75).

Conclusions

This study demonstrates that serum HMGB-1 levels are associated with the incidence of MACE and MALE after LER in diabetic populations with PAD and CLTI.

Role of High Mobility Group Box 1 in Cardiovascular Diseases

High Mobility Group Box 1 (HMGB1) is a ubiquitous, highly conserved nuclear and cytosolic protein that has diverse biological roles depending on its cellular location and posttranslational modifications. The HMGB1 is localized in the nucleus but can be translocated to the cytoplasm to modulate the intracellular signaling and eventually secreted outside the cells. It is widely established that HMGB1 plays a key role in inflammation; however, the role of HMGB1 in the cardiovascular diseases is not well understood. In this review, we will discuss the latest reports on the pathophysiological link between HMGB1 and cardiovascular complications, with special emphasis on the inflammation. Thus, the understanding of the role of HMGB1 may provide new insights into developing new HMGB1-based therapies.

CCCTC-binding factor-mediated microRNA-340-5p suppression aggravates myocardial injury in rats with severe acute pancreatitis through activation of the HMGB1/TLR4 axis

BACKGROUND

Severe acute pancreatitis (SAP) is a life-threatening disorder associated with multisystem organ failure. This study aimed to investigate the function of high mobility group box 1 (HMGB1) in SAP-induced myocardial injury.

METHODS

A rat model with SAP was induced. The pathological changes in rat pancreatic and cardiac tissues were examined by HE staining. Cardiomyocyte apoptosis in rat cardiac tissues, and the serum levels of myocardial injury markers and pro-inflammatory cytokines were examined. Rat primary cardiomyocytes were treated with H₂O₂ for in vitro experiments. The regulatory molecules of HMGB1 were predicted by bioinformatics analysis. Altered expression of HMGB1, microRNA (miR)-340-5p and CCCTC-binding factor (CTCF) was introduced in rats or cells to investigate their roles in myocardial injury.

RESULTS

CTCF and HMGB1 were highly expressed but miR-340-5p was poorly expressed in cardiac tissues of rats with SAP. HMGB1 silencing reduced toll-like receptor 4 (TLR4) expression to promote proliferation and reduce apoptosis of H₂O₂-treated cardiomyocytes. miR-340-5p targeted HMGB1 mRNA, while CTCF suppressed miR-340-5p transcription. CTCF upregulation or miR-340-5p downregulation blocked the effects of HMGB1 silencing on cardiomyocytes. In vivo, CTCF silencing alleviated injury in rat pancreatic and cardiac tissues and reduced the expression of creatine kinase-MB (CK-MB), lactic dehydrogenase, interleukin (IL)-1β, IL-6 and tumor necrosis factor-α (TNF-α) in rat serum. But further overexpression of HMGB1 or inhibition of miR-340-5p aggravated the symptoms in rats.

CONCLUSION

This study demonstrated that CTCF reduces transcription of miR-340-5p to promote HMGB1 expression, which activates TLR4 expression and promotes myocardial injury in rats with SAP.

Exercise Training: The Holistic Approach in Cardiovascular Prevention

Nowadays, there are robust clinical and pathophysiological evidence supporting the beneficial effects of physical activity on cardiovascular (CV) system. Thus, the physical activity is considered a key strategy for CV prevention. In fact, exercise training exerts favourable effects on all risk factors for CV diseases (i.e. essential hypertension, type 2 diabetes mellitus, hypercholesterolemia, obesity, metabolic syndrome, etc…). In addition, all training modalities such as the aerobic (continuous walking, jogging, cycling, etc.) or resistance exercise (weights), as well as the leisure-time physical activity (recreational walking, gardening, etc) prevent the development of the major CV risk factors, or delay the progression of target organ damage improving cardio-metabolic risk. Exercise training is also the core component of all cardiac rehabilitation programs that have demonstrated to improve the quality of life and to reduce morbidity in patients with CV diseases, mostly in patients with coronary artery diseases. Finally, it is still debated whether or not exercise training can influence the occurrence of atrial and ventricular arrhythmias. In this regard, there is some evidence that exercise training is protective predominantly for atrial arrhythmias, reducing the incidence of atrial fibrillation. In conclusion, the salutary effects evoked by physical acitvity are useful in primary and secondary CV prevention.

Apoptosis of hematopoietic progenitor-derived adipose tissue-resident macrophages contributes to insulin resistance after myocardial infarction

Patients with insulin resistance have high risk of cardiovascular disease such as myocardial infarction (MI). However, it is not known whether MI can initiate or aggravate insulin resistance. We observed that patients with ST-elevation MI and mice with MI had de novo hyperglycemia and features of insulin resistance, respectively. In mouse models of both myocardial and skeletal muscle injury, we observed that the number of visceral adipose tissue (VAT)-resident macrophages decreased because of apoptosis after these distant organ injuries. Patients displayed a similar decrease in VAT-resident macrophage numbers and developed systemic insulin resistance after ST-elevation MI. Loss of VAT-resident macrophages after MI injury led to systemic insulin resistance in non-diabetic mice. Danger signaling-associated protein high mobility group box 1 was released by the dead myocardium after MI in rodents and triggered macrophage apoptosis via Toll-like receptor 4. The VAT-resident macrophage population in the steady state in mice was transcriptomically distinct from macrophages in the brain, skin, kidney, bone marrow, lungs, and liver and was derived from hematopoietic progenitor cells just after birth. Mechanistically, VAT-resident macrophage apoptosis and de novo insulin resistance in mouse models of MI were linked to diminished concentrations of macrophage colony-stimulating factor and adiponectin. Collectively, these findings demonstrate a previously unappreciated role of adipose tissue-resident macrophages in sensing remote organ injury and promoting MI pathogenesis.

Prednisolone Suppresses the Extracellular Release of HMGB-1 and Associated Inflammatory Pathways in Kawasaki Disease

Innate immune activity plays an essential role in the development of Kawasaki disease (KD) vasculitis. Extracellular release of high mobility group box-1 (HMGB-1), an endogenous damage-associated molecular pattern protein that can activate the innate immune system and drive host inflammatory responses, may contribute to the development of coronary artery abnormalities in KD. Prednisolone (PSL) added to intravenous immunoglobulin treatment for acute KD may reduce such abnormalities. Here, we evaluate the dynamics of HMGB-1 and therapeutic effects of PSL on HMGB-1-mediated inflammatory pathways on KD vasculitis in vitro. Serum samples were collected prior to initial treatment from patients with KD, systemic juvenile idiopathic arthritis (sJIA), and from healthy controls (VH), then incubated with human coronary artery endothelial cells (HCAECs). Following treatment of KD serum-activated HCAECs with PSL or PBS as a control, effects on the HMGB-1 signaling pathway were evaluated. Compared to that from VH and sJIA, KD serum activation induced HCAEC cytotoxicity and triggered extracellular release of HMGB-1. KD serum-activated HCAECs up-regulated extracellular signal-regulated kinase (ERK)1/2, c-Jun N-terminal kinase (JNK) and, p38 phosphorylation in the cytoplasm and nuclear factor kappa B (NF-κB) phosphorylation in the nucleus and increased interleukin (IL)-1β and tumor necrosis factor (TNF)-α production. PSL treatment of KD serum-activated HCAECs inhibited extracellular release of HMGB-1, down-regulated ERK1/2, JNK, p38, and NF-κB signaling pathways, and decreased IL-1β and TNF-α production. Our findings suggest that extracellular HMGB-1 plays an important role in mediating KD pathogenesis and that PSL treatment during the acute phase of KD may ameliorate HMGB-1-mediated inflammatory responses in KD vasculitis.

Can the calcium-regulating hormones counteract the detrimental impact of pro-inflammatory damage-associated molecular patterns in the development of heart failure?

Growing evidence suggests an important role of the inflammatory component in heart failure (HF). Recent developments in this field indicate an ambiguous role that innate immunity plays in immune-driven HF. Damaged or stressed cells, cardiomyocytes, in particular, emit damage-associated molecular patterns (DAMPs) including HMGB1, S100 A8/A9, HSP70, and other molecules, unfolding paracrine mechanisms that induce an innate immune response. Designed as an adaptive, regenerative reaction, innate immunity may nevertheless become overactivated and thus contribute to the development of HF by altering the pacemaker rhythm, contraction, and electromechanical coupling, presumably by impairing the calcium homeostasis. The current review will explore a hypothesis of the involvement of the calcium-regulating hormones such as parathyroid hormone and parathyroid hormone–related protein in counteracting the detrimental impact of the excess of DAMPs and therefore improving the functional cardiac characteristics especially in the acute phase of the disease.

The Effect and Regulatory Mechanism of High Mobility Group Box-1 Protein on Immune Cells in Inflammatory Diseases

High mobility group box-1 protein (HMGB1), a member of the high mobility group protein superfamily, is an abundant and ubiquitously expressed nuclear protein. Intracellular HMGB1 is released by immune and necrotic cells and secreted HMGB1 activates a range of immune cells, contributing to the excessive release of inflammatory cytokines and promoting processes such as cell migration and adhesion. Moreover, HMGB1 is a typical damage-associated molecular pattern molecule that participates in various inflammatory and immune responses. In these ways, it plays a critical role in the pathophysiology of inflammatory diseases. Herein, we review the effects of HMGB1 on various immune cell types and describe the molecular mechanisms by which it contributes to the development of inflammatory disorders. Finally, we address the therapeutic potential of targeting HMGB1.

High-mobility group box 1 serves as an inflammation driver of cardiovascular disease

Cardiovascular disease (CVD) is the most deadly disease, which can cause sudden death, in which inflammation is a key factor in its occurrence and development. High-mobility group box 1 (HMGB1) is a novel nuclear DNA-binding protein that activates innate immunity to induce inflammation in CVD. HMGB1 exists in the cytoplasm and nucleus of different cell types, including those in the heart. By binding to its receptors, HMGB1 triggers a variety of signaling cascades, leading to inflammation and CVD. To help develop HMGB1-targeted therapies, here we discuss HMGB1 and its biological functions, receptors, signaling pathways, and pathophysiology related to inflammation and CVD, including cardiac remodeling, cardiac hypertrophy, myocardial infarction, heart failure, pulmonary hypertension, atherosclerosis, and cardiomyopathy.

Damage-Associated Molecular Patterns in Myocardial Infarction and Heart Transplantation: The Road to Translational Success

In the setting of myocardial infarction (MI), ischemia reperfusion injury (IRI) occurs due to occlusion (ischemia) and subsequent re-establishment of blood flow (reperfusion) of a coronary artery. A similar phenomenon is observed in heart transplantation (HTx) when, after cold storage, the donor heart is connected to the recipient's circulation. Although reperfusion is essential for the survival of cardiomyocytes, it paradoxically leads to additional myocardial damage in experimental MI and HTx models. Damage (or danger)-associated molecular patterns (DAMPs) are endogenous molecules released after cellular damage or stress such as myocardial IRI. DAMPs activate pattern recognition receptors (PRRs), and set in motion a complex signaling cascade resulting in the release of cytokines and a profound inflammatory reaction. This inflammatory response is thought to function as a double-edged sword. Although it enables removal of cell debris and promotes wound healing, DAMP mediated signalling can also exacerbate the inflammatory state in a disproportional matter, thereby leading to additional tissue damage. Upon MI, this leads to expansion of the infarcted area and deterioration of cardiac function in preclinical models. Eventually this culminates in adverse myocardial remodeling; a process that leads to increased myocardial fibrosis, gradual further loss of cardiomyocytes, left ventricular dilation and heart failure. Upon HTx, DAMPs aggravate ischemic damage, which results in more pronounced reperfusion injury that impacts cardiac function and increases the occurrence of primary graft dysfunction and graft rejection via cytokine release, cardiac edema, enhanced myocardial/endothelial damage and allograft fibrosis. Therapies targeting DAMPs or PRRs have predominantly been investigated in experimental models and are potentially cardioprotective. To date, however, none of these interventions have reached the clinical arena. In this review we summarize the current evidence of involvement of DAMPs and PRRs in the inflammatory response after MI and HTx. Furthermore, we will discuss various current therapeutic approaches targeting this complex interplay and provide possible reasons why clinical translation still fails.

MAIR-II deficiency ameliorates cardiac remodelling post-myocardial infarction by suppressing TLR9-mediated macrophage activation

Macrophages are fundamental components of inflammation in post‐myocardial infarction (MI) and contribute to adverse cardiac remodelling and heart failure. However, the regulatory mechanisms in macrophage activation have not been fully elucidated. Previous studies showed that myeloid‐associated immunoglobulin–like receptor II (MAIR‐II) is involved in inflammatory responses in macrophages. However, its role in MI is unknown. Thus, this study aimed to determine a novel role and mechanism of MAIR‐II in MI. We first identified that MAIR‐II–positive myeloid cells were abundant from post‐MI days 3 to 5 in infarcted hearts of C57BL/6J (WT) mice induced by permanent left coronary artery ligation. Compared to WT, MAIR‐II–deficient (Cd300c2^−/−) mice had longer survival, ameliorated cardiac remodelling, improved cardiac function and smaller infarct sizes. Moreover, we detected lower pro‐inflammatory cytokine and fibrotic gene expressions in Cd300c2^−/−‐infarcted hearts. These mice also had less infiltrating pro‐inflammatory macrophages following MI. To elucidate a novel molecular mechanism of MAIR‐II, we considered macrophage activation by Toll‐like receptor (TLR) 9–mediated inflammation. In vitro, we observed that Cd300c2^−/− bone marrow–derived macrophages stimulated by a TLR9 agonist expressed less pro‐inflammatory cytokines compared to WT. In conclusion, MAIR‐II may enhance inflammation via TLR9‐mediated macrophage activation in MI, leading to adverse cardiac remodelling and poor prognosis.

Role of the CXCR4-SDF1-HMGB1 pathway in the directional migration of cells and regeneration of affected organs

In recent years, several studies have reported positive outcomes of cell-based therapies despite insufficient engraftment of transplanted cells. These findings have created a huge interest in the regenerative potential of paracrine factors released from transplanted stem or progenitor cells. Interestingly, this notion has also led scientists to question the role of proteins in the secretome produced by cells, tissues or organisms under certain conditions or at a particular time of regenerative therapy. Further studies have revealed that the secretomes derived from different cell types contain paracrine factors that could help to prevent apoptosis and induce proliferation of cells residing within the tissues of affected organs. This could also facilitate the migration of immune, progenitor and stem cells within the body to the site of inflammation. Of these different paracrine factors present within the secretome, researchers have given proper consideration to stromal cell-derived factor-1 (SDF1) that plays a vital role in tissue-specific migration of the cells needed for regeneration. Recently researchers recognized that SDF1 could facilitate site-specific migration of cells by regulating SDF1-CXCR4 and/or HMGB1-SDF1-CXCR4 pathways which is vital for tissue regeneration. Hence in this study, we have attempted to describe the role of different types of cells within the body in facilitating regeneration while emphasizing the HMGB1-SDF1-CXCR4 pathway that orchestrates the migration of cells to the site where regeneration is needed.

High Mobility Group Box-1 (HMGB1): A Potential Target in Therapeutics

High mobility group box-1 (HMGB1) mainly belongs to the non-histone DNA-binding protein. It has been studied as a nuclear protein that is present in eukaryotic cells. From the HMG family, HMGB1 protein has been focused particularly for its pivotal role in several pathologies. HMGB-1 is considered as an essential facilitator in diseases such as sepsis, collagen disease, atherosclerosis, cancers, arthritis, acute lung injury, epilepsy, myocardial infarction, and local and systemic inflammation. Modulation of HMGB1 levels in the human body provides a way in the management of these diseases. Various strategies, such as HMGB1-receptor antagonists, inhibitors of its signalling pathway, antibodies, RNA inhibitors, vagus nerve stimulation etc. have been used to inhibit expression, release or activity of HMGB1. This review encompasses the role of HMGB1 in various pathologies and discusses its therapeutic potential in these pathologies.

Prognostic role of serum high mobility group box 1 concentration in cardiac surgery

Outcomes of cardiac surgery are influenced by systemic inflammation. High mobility group box 1 (HMGB1), a pivotal inflammatory mediator, plays a potential role as a prognostic biomarker in cardiovascular disease. The aim of this prospective, observational study was to investigate the relationship between serum HMGB1 concentrations and composite of morbidity endpoints in cardiac surgery. Arterial blood samples for HMGB1 measurement were collected from 250 patients after anaesthetic induction (baseline) and 1 h after weaning from cardiopulmonary bypass (post-CPB). The incidence of composite of morbidity endpoints (death, myocardial infarction, stroke, renal failure and prolonged ventilator care) was compared in relation to the tertile distribution of serum HMGB1 concentrations. The incidence of composite of morbidity endpoints was significantly different with respect to the tertile distribution of post-CPB HMGB1 concentrations (p = 0.005) only, and not to the baseline. Multivariable analysis revealed post-CPB HMGB1 concentration (OR, 1.072; p = 0.044), pre-operative creatinine and duration of CPB as independent risk factors of adverse outcome. Accounting for its prominent role in mediating sterile inflammation and its relation to detrimental outcome, HMGB1 measured 1 h after weaning from CPB would serve as a useful biomarker for accurate risk stratification in cardiac surgical patients and may guide tailored anti-inflammatory therapy.

High Mobility Group Box-1 and Diabetes Mellitus Complications: State of the Art and Future Perspectives

Diabetes mellitus (DM) is an endemic disease, with growing health and social costs. The complications of diabetes can affect potentially all parts of the human body, from the heart to the kidneys, peripheral and central nervous system, and the vascular bed. Although many mechanisms have been studied, not all players responsible for these complications have been defined yet. High Mobility Group Box-1 (HMGB1) is a non-histone nuclear protein that has been implicated in many pathological processes, from sepsis to ischemia. The purpose of this review is to take stock of all the most recent data available on the role of HMGB1 in the complications of DM.

CD8+ T-cells negatively regulate inflammation post-myocardial infarction

The adaptive immune response is key for cardiac wound healing post-myocardial infarction (MI) despite low T-cell numbers. We hypothesized that CD8⁺ T-cells regulate the inflammatory response, leading to decreased survival and cardiac function post-MI. We performed permanent occlusion of the left anterior descending coronary artery on C57BL/6J and CD8a^tm1mak mice (deficient in functional CD8⁺ T-cells). CD8a^tm1mak mice had increased survival at 7 days post-MI compared with that of the wild-type (WT) and improved cardiac physiology at day 7 post-MI. Despite having less mortality, 100% of the CD8a^tm1mak group died because of cardiac rupture compared with only 33% of the WT. Picrosirius red staining and collagen immunoblotting indicated an acceleration of fibrosis in the infarct area as well as remote area in the CD8a^tm1mak mice; however, this increase was due to elevated soluble collagen implicating poor scar formation. Plasma and tissue inflammation were exacerbated as indicated by higher levels of Cxcl1, Ccl11, matrix metalloproteinase (MMP)-2, and MMP-9. Immunohistochemistry and flow cytometry indicated that the CD8a^tm1mak group had augmented numbers of neutrophils and macrophages at post-MI day 3 and increased mast cell markers at post-MI day 7. Cleavage of tyrosine-protein kinase MER was increased in the CD8a^tm1mak mice, resulting in delayed removal of necrotic tissue. In conclusion, despite having improved cardiac physiology and overall survival, CD8a^tm1mak mice had increased innate inflammation and poor scar formation, leading to higher incidence of cardiac rupture. Our data suggest that the role of CD8⁺ T-cells in post-MI recovery may be both beneficial and detrimental to cardiac remodeling and is mediated via a cell-specific mechanism.NEW & NOTEWORTHY We identified new mechanisms implicating CD8⁺ T-cells as regulators of the post-myocardial infarction (MI) wound healing process. Mice without functional CD8⁺ T-cells had improved cardiac physiology and less mortality 7 days post MI compared with wild-type animals. Despite having better overall survival, animals lacking functional CD8⁺ T-cells had delayed removal of necrotic tissue, leading to poor scar formation and increased cardiac rupture, suggesting that CD8⁺ T-cells play a dual role in the cardiac remodeling process.

PARP1 interacts with HMGB1 and promotes its nuclear export in pathological myocardial hypertrophy

High-mobility group box 1 (HMGB1) exhibits various functions according to its subcellular location, which is finely conditioned by diverse post-translational modifications, such as acetylation. The nuclear HMGB1 may prevent from cardiac hypertrophy, whereas its exogenous protein is proven to induce hypertrophic response. This present study sought to investigate the regulatory relationships between poly(ADP-ribose) polymerase 1 (PARP1) and HMGB1 in the process of pathological myocardial hypertrophy. Primary-cultured neonatal rat cardiomyocytes (NRCMs) were respectively incubated with three cardiac hypertrophic stimulants, including angiotensin II (Ang II), phenylephrine (PE), and isoproterenol (ISO), and cell surface area and the mRNA expression of hypertrophic biomarkers were measured. the catalytic activity of PARP1 was remarkably enhanced, meanwhile HMGB1 excluded from the nucleus. PARP1 overexpression by infecting with adenovirus PARP1 (Ad-PARP1) promoted the nuclear export of HMGB1, facilitated its secretion outside the cell, aggravated cardiomyocyte hypertrophy, which could be alleviated by HMGB1 overexpression. PE treatment led to the similar results, while that effect was widely depressed by PARP1 silencing or its specific inhibitor AG14361. Moreover, SD rats were intraperitoneally injected with 3-aminobenzamide (3AB, 20 mg/kg every day, a well-established PARP1 inhibitor) 7 days after abdominal aortic constriction (AAC) surgery for 6 weeks, echocardiography and morphometry of the hearts were measured. Pre-treatment of 3AB relieved AAC-caused the translocation of nuclear HMGB1 protein, cardiac hypertrophy, and heart dysfunction. Our research offers a novel evidence that PARP1 combines with HMGB1 and accelerates its translocation from nucleus to cytoplasm, and the course finally causes cardiac hypertrophy.

Association of high mobility group box 1 protein with coronary artery disease

BACKGROUND

Recently, the role of inflammation in coronary artery disease and the association of inflammatory biomarkers with adverse outcomes have been investigated in many studies. We investigated the relationship between high serum mobility group box 1 protein levels and established risk factors for coronary artery disease.

METHODS

Fifty-five patients who presented to our Cardiovascular Surgery Clinic and subsequently underwent coronary artery bypass surgery for coronary artery disease and 50 healthy subjects presenting to the cardiology outpatient clinic without any cardiovascular problem were included in the study. The mean age was 61.47 ± 9.38 years for patients and 58.20 ± 10.15 years for controls.

RESULTS

There was no statistically significant difference between groups with respect to age or sex. Family history of coronary artery disease, aspirin use, hypertension, and type 2 diabetes were significantly more prevalent in the patient group versus the control group. A significant difference was found between patients and healthy controls with respect to high mobility group box 1 protein levels ( p = 0.001).

CONCLUSIONS

Serum high mobility group box 1 protein was significantly increased in patients with coronary artery disease in comparison to healthy subjects. No associations were found between high mobility group box 1 protein level and certain risk factors for coronary artery disease.

The Janus face of HMGB1 in heart disease: a necessary update

High mobility group box 1 (HMGB1) is a ubiquitous nuclear protein involved in transcription regulation, DNA replication and repair and nucleosome assembly. HMGB1 is passively released by necrotic tissues or actively secreted by stressed cells. Extracellular HMGB1 acts as a damage-associated molecular pattern (DAMPs) molecule and gives rise to several redox forms that by binding to different receptors and interactors promote a variety of cellular responses, including tissue inflammation or regeneration. Inhibition of extracellular HMGB1 in experimental models of myocardial ischemia/reperfusion injury, myocarditis, cardiomyopathies induced by mechanical stress, diabetes, bacterial infection or chemotherapeutic drugs reduces inflammation and is protective. In contrast, administration of HMGB1 after myocardial infarction induced by permanent coronary artery ligation ameliorates cardiac performance by promoting tissue regeneration. HMGB1 decreases contractility and induces hypertrophy and apoptosis in cardiomyocytes, stimulates cardiac fibroblast activities, and promotes cardiac stem cell proliferation and differentiation. Interestingly, maintenance of appropriate nuclear HMGB1 levels protects cardiomyocytes from apoptosis by preventing DNA oxidative stress, and mice with HMGB1cardiomyocyte-specific overexpression are partially protected from cardiac damage. Finally, higher levels of circulating HMGB1 are associated to human heart diseases. Hence, during cardiac injury, HMGB1 elicits both harmful and beneficial responses that may in part depend on the generation and stability of the diverse redox forms, whose specific functions in this context remain mostly unexplored. This review summarizes recent findings on HMGB1 biology and heart dysfunctions and discusses the therapeutic potential of modulating its expression, localization, and oxidative-dependent activities.

HMGB1 and repair: focus on the heart

High-mobility group box 1 (HMGB1) is one of the most abundant proteins in eukaryotes and the best characterized damage-associated molecular pattern (DAMP). The biological activities of HMGB1 depend on its subcellular location, context and post-translational modifications. Inside the nucleus, HMGB1 is engaged in many DNA events such as DNA repair, transcription regulation and genome stability; in the cytoplasm, its main function is to regulate the autophagic flux while in the extracellular environment, it possesses more complicated functions and it is involved in a large variety of different processes such as inflammation, migration, invasion, proliferation, differentiation and tissue regeneration. Due to this pleiotropy, the role of HMGB1 has been vastly investigated in various pathological diseases and a large number of studies have explored its function in cardiovascular pathologies. However, in this contest, the precise mechanism of action of HMGB1 and its therapeutic potential are still very controversial since is debated whether HMGB1 is involved in tissue damage or plays a role in tissue repair and regeneration. The main focus of this review is to provide an overview of the effects of HMGB1 in different ischemic heart diseases and to discuss its functions in these pathological conditions.

Acetylation of HMGB1 by JNK1 Signaling Promotes LPS-Induced Peritoneal Mesothelial Cells Apoptosis

Increased high mobility group box 1 (HMGB1) in dialysis effluence is associated with the presence of peritoneal dialysis-related peritonitis in patients and peritoneal dysfunction in acute peritonitis mice model, but it remains unclear whether HMGB1 is involved in peritoneal mesothelial cell injury and functions via molecular posttranslational modifications by acetylation in this process. Here we first showed correlation between HMGB1 acetylation level in dialysis effluence of patients and occurrence of Gram-negative peritonitis. The increased level of acetylated HMGB1 was similarly observed under the lipopolysaccharides (LPS) treatment in both human peritoneal mesothelial cell line (HMrSV5) and mice visceral peritoneum tissue. Overexpression of wild-type, but not hypoacetylation mutant of HMGB1, enhanced LPS-induced apoptosis in HMrSV5 cells, which was accompanied by elevated protein levels of BAX and cleaved-caspase 3 compared to the control. Pretreatment of HMrSV5 cell with JNK inhibitor attenuated LPS-induced HMGB1 acetylation. Consistently, primary peritoneal mesothelial cells from Jnk1^-/- mice showed a lower protein contents of acetylated HMGB1, fewer apoptosis, and decreased protein expression of BAX and cleaved-caspase3 after LPS exposure, as compared to those from wild-type mice. In conclusion, our data demonstrated HMGB1 promotes LPS-induced peritoneal mesothelial cells apoptosis, which is associated with JNK1-mediated upregulation of HMGB1 acetylation.

Long noncoding RNA MALAT1 downregulates cardiac transient outward potassium current by regulating miR-200c/HMGB1 pathway

The dysregulation of long noncoding RNAs (lncRNAs) and microRNAs (miRNAs) participates in the remodeling of electrophysiological/ion channel in cardiomyocytes during arrhythmia. The lncRNA metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) is reported to be highly expressed in myocardial ischemia-reperfusion injury and offsets cardioprotective effects of fentanyl. However, the roles of MALAT1 and its related miRNAs during arrhythmia are poorly understood. In this study, the overexpression of MALAT1 was firstly indicated in cardiomyocytes from arrhythmic model rats. After downregulation of MALAT1 by RNA interference, transient outward potassium current (Ito), peak current density, and the levels of Kv4.2 and Kv4.3 channel proteins were increased in rat cardiomyocytes. Then, miR-200c was predicted and convinced to be a direct target of MALAT1, and high-mobility group box 1 (HMGB1) was verified to be a target of miR-200c during arrhythmia. HMGB1 expression reduced by the knockdown of MALAT1 was further decreased by miR-200c overexpression. In addition, cardiac Ito, peak current density, and the levels of Kv4.2 and Kv4.3 in arrhythmic model rats were detected to be negatively correlated with the expression of HMGB1, and to be positively with miR-200c expression. Taken together, these results suggested that MALAT1 may act as a competing endogenous RNA for miR-200c to upregulate the expression of HMGB1 and downregulate cardiac Ito.

Immune cells in repair of the infarcted myocardium

The immune system plays a critical role in both repair and remodeling of the infarcted myocardium. Danger signals released by dying cardiomyocytes mobilize, recruit, and activate immune cells, triggering an inflammatory reaction. CXC chemokines containing the ELR motif attract neutrophils, while CC chemokines mediate recruitment of mononuclear cell subpopulations, contributing to clearance of the infarct from dead cells and matrix debris. Immune cell subsets also participate in suppression and containment of the postinfarction inflammatory response by secreting anti-inflammatory mediators, such as IL-10 and TGF-β. As proinflammatory signaling is suppressed, macrophage subpopulations, mast cells and lymphocytes, activate fibrogenic and angiogenic responses, contributing to scar formation. In the viable remodeling myocardium, chronic activation of immune cells may promote fibrosis and hypertrophy. This review discusses the role of immune cells in repair and remodeling of the infarcted myocardium. Understanding the role of immune cells in myocardial infarction is critical for the development of therapeutic strategies aimed at protecting the infarcted heart from adverse remodeling. Moreover, modulation of immune cell phenotype may be required in order to achieve the visionary goal of myocardial regeneration.

Inflammatory Mechanisms of Cardiovascular Remodeling

Inflammation and fibrosis play an important role in the development and progression of cardiovascular diseases. Acute coronary syndrome (ACS) is caused by rupture of inflamed atherosclerotic plaque and subsequent atherothrombosis. Recent studies have shown that inflammatory markers such as C-reactive protein (CRP) can predict ACS development and have demonstrated the effectiveness of new therapeutic approaches targeting inflammation. Studies have also shown that an enhanced inflammatory response after myocardial infarction (MI) is associated with cardiac rupture, ventricular aneurysm formation, and exacerbation of left ventricular (LV) remodeling. Inflammation is a physiological reaction in which fibrosis is induced to facilitate the healing of tissue damage. However, when an excessive inflammatory response consisting mainly of monocytes/macrophages is induced by various factors, impaired reparative fibrosis and resulting pathological remodeling processes may occur. A similar phenomenon is observed in abdominal aortic aneurysm (AAA) expansion. In contrast, myocardial diseases such as inflammatory dilated cardiomyopathy (DCMI) and valvular diseases such as aortic valve stenosis (AS) are characterized by chronic inflammation mediated mainly by T lymphocytes and the associated enhancement of reactive fibrosis. Thus, inflammation can take 2 paths (the inhibition or promotion of fibrosis), depending on the phase of inflammation, inducing pathological cardiovascular remodeling. Elucidation of the regulatory mechanisms of inflammation and fibrosis will contribute to the development of new therapeutic approaches for cardiovascular diseases.

High-Mobility Group Box 1 Mediates Fibroblast Activity via RAGE-MAPK and NF-κB Signaling in Keloid Scar Formation

Emerging studies have revealed the involvement of high-mobility group box 1 (HMGB1) in systemic fibrotic diseases, yet its role in the cutaneous scarring process has not yet been investigated. We hypothesized that HMGB1 may promote fibroblast activity to cause abnormal cutaneous scarring. In vitro wound healing assay with normal and keloid fibroblasts demonstrated that HMGB1 administration promoted the migration of both fibroblasts with increased speed and a greater traveling distance. Treatment of the HMGB1 inhibitor glycyrrhizic acid (GA) showed an opposing effect on both activities. To analyze the downstream mechanism, the protein levels of extracellular signal-regulated kinase (ERK) 1/2, protein kinase B (AKT), and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) were measured by western blot analysis. HMGB1 increased the expression levels of ERK1/2, AKT, and NF-κB compared to the control, which was suppressed by GA. HMGB1 promoted both normal and keloid fibroblasts migration to a degree equivalent to that achieved with TGF-β. We concluded that HMGB1 activates fibroblasts via the receptor for advanced glycation end product (RAGE)—mitogen-activated protein kinases (MAPK) and NF-κB interaction signaling pathways. Further knowledge of the relationship of HMGB1 with skin fibrosis may lead to a promising clinical approach to manage abnormal scarring.

Porphyromonas Gingivalis Elevated High-Mobility Group Box 1 Levels After Myocardial Infarction in Mice

High mobility group box 1 (HMGB1) is a nuclear protein released from necrotic cells, inducing inflammatory responses. Epidemiological studies suggested a possible association between periodontitis and cardiovascular diseases (CVDs). Due to tissue damage and necrosis of cardiac cells following myocardial infarction (MI), HMGB1 is released, activating an inflammatory reaction. However, it remains unclear whether periodontitis is also involved in myocardial damage. The purpose of this study was to determine the effect of the periodontal pathogen Porphyromonas gingivalis (P.g.) after MI in mice.C57BL/6J wild type mice in post-MI were inoculated with P.g. in the infected group (P.g.-inoculated MI group) and with phosphate buffer saline (PBS) in the control group (PBS-injected MI group). Plasma samples and twelve tissue samples from mice hearts after MI were obtained. We determined the expression of HMGB1 by ELISA and immunohistochemistry.The level of HMGB1 protein in the P.g.-inoculated MI group was significantly higher than in the PBS-injected MI group on day 5, but not on day 14. Immunohistochemistry analysis revealed that HMGB1 was mainly expressed in cardiomyocytes, immune cells, and vascular endothelial cells in the PBS-injected MI group, while HMGB1 was seen broadly in degenerated cardiomyocytes, extracellular fields, immune cells, and vascular endothelial cells in the P.g.-inoculated MI group. A significant increase in the number of HMGB1 positive cells was observed in the P.g.-inoculated MI group compared to the PBS-injected MI group.Infection with P.g. after MI enhanced myocardial HMGB1 expression. There is a possible relationship between periodontitis and post-infarction myocardial inflammation through HMGB-1.

DPP4 Inhibition Ameliorates Cardiac Function by Blocking the Cleavage of HMGB1 in Diabetic Mice After Myocardial Infarction

High mobility group box 1 (HMGB1), a ubiquitous DNA-binding protein, promotes angiogenesis and tissue repair, resulting in restored cardiac function after myocardial infarction (MI). Although dipeptidyl peptidase 4 (DPP4) degrades certain peptides, it remains unclear as to whether HMGB1 is a substrate of DPP4 and whether DPP4 inhibition prevents the cleavage of HMGB1.In transgenic mice with cardiac-specific overexpression of HMGB1 (TG) and wild-type mice (WT), a diabetic state was induced by streptozotocin, and MI was created by ligation of the left anterior descending coronary artery. To inhibit DPP4 activity, a DPP4 inhibitor anagliptin was used. The plasma levels of HMGB1, infarct size, echocardiographic data, angiogenesis, and vascular endothelial growth factor (VEGF) expression in the peri-infarct area were compared among non-diabetic MI WT/TG, diabetic MI WT/TG, and anagliptin-treated diabetic MI WT/TG mice.DPP4 activity was increased in the diabetic state and blocked by anagliptin administration. The HMGB1 plasma levels were reduced in the diabetic TG compared with the non-diabetic TG mice, but DPP4 inhibition with anagliptin increased HMGB1 plasma levels in the diabetic TG mice. The infarct area was significantly larger in the diabetic TG than in the non-diabetic TG mice, and it was reduced by DPP4 inhibition. Cardiac function, angiogenesis, and VEGF expression were impaired in the diabetic TG mice, but they were ameliorated by the DPP4 inhibition to levels similar to those found in the non-diabetic TG mice.The DPP4 inhibitor ameliorated cardiac function by inhibiting the inactivation of HMGB1 in diabetic mice after MI.

Diabetes increases the susceptibility to acute kidney injury after myocardial infarction through augmented activation of renal Toll-like receptors in rats

Acute kidney injury (AKI) after acute myocardial infarction (MI) worsens the prognosis of MI patients. Although type 2 diabetes mellitus (DM) is a major risk factor of AKI after MI, the underlying mechanism remains unclear. Here, we examined the roles of renal Toll-like receptors (TLRs) in the impact of DM on AKI after MI. MI was induced by coronary artery ligation in Otsuka-Long-Evans-Tokushima fatty (OLETF) rats, a rat DM model, and Long-Evans-Tokushima-Otsuka (LETO) rats, nondiabetic controls. Sham-operated rats served as no-MI controls. Renal mRNA levels of TLR2 and myeloid differentiation factor 88 (MyD88) were significantly higher in sham-operated OLETF rats than in sham-operated LETO rats, although levels of TLR1, TLR3, and TLR4 were similar. At 12 h after MI, protein levels of kidney injury molecule-1 (KIM-1) and neutrophil gelatinase-associated lipocalin (NGAL) in the kidney were elevated by 5.3- and 4.0-fold, respectively, and their mRNA levels were increased in OLETF but not LETO rats. The increased KIM-1 and NGAL expression levels after MI in the OLETF kidney were associated with upregulated expression of TLR1, TLR2, TLR4, MyD88, IL-6, TNF-α, chemokine (C-C motif) ligand 2, and transforming growth factor-β₁ and also with activation of p38 MAPK, JNK, and NF-κB. Cu-CPT22, a TLR1/TLR2 antagonist, administered before MI significantly suppressed MI-induced upregulation of KIM-1, TLR2, TLR4, MyD88, and chemokine (C-C motif) ligand 2 levels and activation of NF-κB, whereas NGAL levels and IL-6 and TNF-α expression levels were unchanged. The results suggest that DM increases the susceptibility to AKI after acute MI by augmented activation of renal TLRs and that TLR1/TLR2-mediated signaling mediates KIM-1 upregulation after MI.NEW & NOTEWORTHY This is the first report to demonstrate the involvement of Toll-like recpetors (TLRs) in diabetes-induced susceptibility to acute kidney injury after acute myocardial infarction. We propose that the TLR1/TLR2 heterodimer may be a new therapeutic target for the prevention of acute kidney injury in diabetic patients.

Non-oxidizable HMGB1 induces cardiac fibroblasts migration via CXCR4 in a CXCL12-independent manner and worsens tissue remodeling after myocardial infarction

Myocardial infarction (MI) is a major health burden worldwide. Extracellular High mobility group box 1 (HMGB1) regulates tissue healing after injuries. The reduced form of HMGB1 (fr-HMGB1) exerts chemotactic activity by binding CXCL12 through CXCR4, while the disulfide form, (ds-HMGB1), induces cytokines expression by TLR4. Here, we assessed the role of HMGB1 redox forms and the non-oxidizable mutant (3S) on human cardiac fibroblast (hcFbs) functions and cardiac remodeling after infarction. Among HMGB1 receptors, hcFbs express CXCR4. Fr-HMGB1 and 3S, but not ds-HMGB1, promote hcFbs migration through Src activation, while none of HMGB1 redox forms induces proliferation or inflammatory mediators. 3S is more effective than fr-HMGB1 in stimulating hcFbs migration and Src phosphorylation being active at lower concentrations and in oxidizing conditions. Notably, chemotaxis toward both proteins is CXCR4-dependent but, in contrast to fr-HMGB1, 3S does not require CXCL12 since hcFbs migration persists in the presence of the CXCL12/CXCR4 inhibitor AMD3100 or an anti-CXCL12 antibody. Interestingly, 3S interacts with CXCR4 and induces a different receptor conformation than CXCL12. Mice undergoing MI and receiving 3S exhibit adverse LV remodeling owing to an excessive collagen deposition promoted by a higher number of myofibroblasts. On the contrary, fr-HMGB1 ameliorates cardiac performance enhancing neoangiogenesis and reducing the infarcted area and fibrosis. Altogether, our results demonstrate that non-oxidizable HMGB1 induce a sustained cardiac fibroblasts migration despite the redox state of the environment and by altering CXCL12/CXCR4 axis. This affects proper cardiac remodeling after an infarction.