Critical role of RAGE and HMGB1 in inflammatory heart disease

Oxidative Stress-Induced HMGB1 Release from Melanocytes: A Paracrine Mechanism Underlying the Cutaneous Inflammation in Vitiligo

Vitiligo is a cutaneous depigmentation disorder caused by the destruction of epidermal melanocytes. The generation and the skin infiltration of autoreactive CD8⁺ cytotoxic T cells triggered by oxidative stress play a critical role in vitiligo. High-mobility group protein B1 (HMGB1) is a classic damage-associated molecular pattern molecule with strong proinflammatory effects in inflammatory reactions. A previous study reported an enhanced expression of HMGB1 in vitiligo lesions, but the role of HMGB1 in cutaneous inflammation of vitiligo is still unknown. In the present study, we initially found that HMGB1 was released from the nucleus of melanocytes in vitiligo perilesional skin. Furthermore, cultured normal human melanocytes could release HMGB1 under treatment with hydrogen peroxide. Moreover, HMGB1 facilitated the secretion of CXCL16 and IL-8 from keratinocytes by binding to the receptor for advanced glycation end products and activating NF-κB and extracellular signal-regulated kinase signaling pathways. Subsequently, HMGB1 led to the formation of chemotaxis for the migration of CD8⁺ T cells from patients with vitiligo by increasing the release of CXCL16 from keratinocytes. Additionally, HMGB1 promoted the maturation of dendritic cells from patients with vitiligo. Altogether, our study demonstrates that HMGB1 released from melanocytes contributes to the formation of oxidative stress-induced autoimmunity in vitiligo.

The RAGE signaling pathway is involved in intestinal inflammation and represents a promising therapeutic target for Inflammatory Bowel Diseases

Inflammatory Bowel Diseases (IBD) are chronic inflammatory conditions of the intestinal tract. IBD are believed to result from an inappropriate immune response against the intestinal flora in genetically predisposed patients. The precise etiology of these diseases is not fully understood, therefore treatments rely on the dampening of symptoms, essentially inflammation, rather than on the cure of the disease. Despite the availability of biologics, such as anti-TNF antibodies, some patients remain in therapeutic failure and new treatments are thus needed. The multiligand receptor for advanced glycation end-products (RAGE) is a pattern recognition receptor implicated in inflammatory reactions and immune system activation. Here, we investigated the role of RAGE in intestinal inflammation and its potential as a therapeutic target in IBD. We showed that RAGE was upregulated in inflamed tissues from IBD patients compared to controls. Rage^-/- mice were less susceptible to intestinal and colonic inflammation development than WT mice. WT mice treated with the RAGE-specific inhibitor FPS-ZM1 experienced less severe enteritis and colitis. We demonstrated that RAGE could induce intestinal inflammation by promoting oxidative stress and endothelial activation which were diminished by FPS-ZM1 treatment. Our results revealed the RAGE signaling pathway as a promising therapeutic target for IBD patients.

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.

High mobility group box-1 induces pro-inflammatory signaling in human nucleus pulposus cells via toll-like receptor 4-dependent pathway

Intervertebral disc (IVD) degeneration (DD) is associated with low back pain, the leading cause of disability worldwide. Damage-associated molecular patterns (DAMPs) that contribute to inflammation and trigger DD have not been well characterized. Extracellular high mobility group box-1 (HMGB1) protein has been implicated as a potent DAMP and pro-inflammatory stimulus in the immune system. In this study, we show that HMGB1 and IL-6 levels increase in patients with advanced DD in comparison to early DD. This study further tested the hypothesis that HMGB1 promotes inflammatory signaling driving DD in human nucleus pulposus (NP) cells and tissue. Immunofluorescence and western blot analysis confirmed the expression of HMGB1 and its extracellular release by NP cells under cell stress. Gene expression and protein quantification indicate that HMGB1 stimulates the expression IL-6 and MMP-1 in a dose-dependent manner. The contributions of toll-like receptor (TLR) -2, -4 and receptor for advanced glycation end products (RAGE) as receptors mediating HMGB1 signaling was examined using small molecule inhibitors. Inhibition of TLR-4 signaling, with TAK-242, completely abrogated HMGB1 induced IL-6 and MMP-1 expression, whereas inhibition of TLR-2, with O-vanillin, or RAGE, with FPS-ZM1, had mild inhibitory effects. HMGB1 stimulation activated NF-ĸB signaling while TAK-242 co-treatment abrogated it. Lastly, effects of HMGB1 on matrix deposition was evaluated in a 3D culture system of human NP cells. These results implicate HMGB1 as a potent DAMP that promotes inflammation in NP cells and degradation of NP tissues. TLR4-HMGB1 axis is a potential major pathway to alleviate disc inflammation and mitigate DD. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Novel dihydroartemisinin derivative DHA-37 induces autophagic cell death through upregulation of HMGB1 in A549 cells

Dihydroartemisinin (DHA) and its analogs are reported to possess selective anticancer activity. Here, we reported a novel DHA derivative DHA-37 that exhibited more potent anticancer activity on the cells tested. Distinct from DHA-induced apoptosis, DHA-37 triggered excessive autophagic cell death, and became the main contributor to DHA-37-induced A549 cell death. Incubation of the cells with DHA-37 but not DHA produced increased dots distribution of GFP-LC3 and expression ratio of LC3-II/LC3-I, and enhanced the formation of autophagic vacuoles as revealed by TEM. Treatment with the autophagy inhibitor 3-MA, LY294002, or chloroquine could reverse DHA-37-induced cell death. In addition, DHA-37-induced cell death was associated significantly with the increased expression of HMGB1, and knockdown of HMGB1 could reverse DHA-37-induced cell death. More importantly, the elevated HMGB1 expression induced autophagy through the activation of the MAPK signal but not PI3K-AKT–mTOR pathway. In addition, DHA-37 also showed a wonderful performance in A549 xenograft mice model. These findings suggest that HMGB1 as a target candidate for apoptosis-resistant cancer treatment and artemisinin-based drugs could be used in inducing autophagic cell death.

Inhibiting Receptor of Advanced Glycation End Products Attenuates Pressure Overload-Induced Cardiac Dysfunction by Preventing Excessive Autophagy

The receptor for advanced glycation end products (RAGE) is involved in heart failure (HF) by mediating diverse pathologic processes, including the promotion of inflammation and autophagy. However, the role of RAGE in pressure overload-induced HF is not well understood. We found that stimulation of RAGE triggered the death of neonatal rat ventricular myocytes (NRVMs), while cell death was alleviated by ATG5 knockdown. Using transverse aortic constriction (TAC) in mice as a model of pressure overload-induced HF, we demonstrated that RAGE knockout or RAGE blockade attenuated cardiac hypertrophy and fibrosis as well as cardiac dysfunction at 8 weeks after TAC. Importantly, RAGE knockout reversed upregulation of autophagy related proteins (LC3BII/I and Beclin 1) and reduced cardiomyocyte death, indicating that excessive autophagy after TAC was inhibited. Moreover, RAGE knockout or blockade reduced the upregulation of pp65-NFκB and BNIP3, which mediate autophagy. Taken together, these results suggest that RAGE plays an important role in the progression of HF by regulating autophagy. Therefore, inhibition of the RAGE-autophagy axis could be a promising new strategy for treatment of heart failure.

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.

RAGE and TLRs as Key Targets for Antiatherosclerotic Therapy

Receptor for advanced glycation end-products (RAGE) and toll-like receptors (TLRs) are the key factors indicating a danger to the organism. They recognize the microbial origin pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patterns (DAMPs). The primary response induced by PAMPs or DAMPs is inflammation. Excessive stimulation of the innate immune system occurs in arterial wall with the participation of effector cells. Persistent adaptive responses can also cause tissue damage and disease. However, inflammation mediated by the molecules innate responses is an important way in which the adaptive immune system protects us from infection. The specific detection of PAMPs and DAMPs by host receptors drives a cascade of signaling that converges at nuclear factor-κB (NF-κB) and interferon regulatory factors (IRFs) and induces the secretion of proinflammatory cytokines, type I interferon (IFN), and chemokines, which promote direct killing of the pathogen. Therefore, signaling of these receptors' pathways also appear to present new avenue for the modulation of inflammatory responses and to serve as potential novel therapeutic targets for antiatherosclerotic therapy.

Degradation of histone deacetylase 4 via the TLR4/JAK/STAT1 signaling pathway promotes the acetylation of high mobility group box 1 (HMGB1) in lipopolysaccharide-activated macrophages

High mobility group box 1 (HMGB1) has been proposed as crucial in the pathogenesis of many diseases including sepsis. Acetylation of HMGB1 prevents its entry into the nucleus and leads to its secretion from the cell where it can trigger inflammation. We hypothesized that histone deacetylase 4 (HDAC4) controls the acetylation of HMGB1 in lipopolysaccharide (LPS)‐stimulated RAW264.7 cells via the janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway. The results showed that LPS treatment promoted the degradation of HDAC4 in a proteasome‐dependent manner, which led to HMGB1 acetylation. In LPS‐activated RAW264.7 cells, treatment with TAK‐242 (a toll like receptor 4 inhibitor) and pyridone 6 (a JAK inhibitor) significantly inhibited HDAC4 degradation and acetylation of HMGB1, and thus prevented secretion of HMGB1. Decreased phosphorylation of STAT1 was also observed. Interestingly, HDAC4 overexpression significantly prevented the acetylation and secretion of HMGB1 in both RAW264.7 cells and isolated murine peritoneal macrophages. We conclude that HDAC4 might be a useful target for the treatment of sepsis.

Hyperglycemia drives intestinal barrier dysfunction and risk for enteric infection

Obesity, diabetes, and related manifestations are associated with an enhanced, but poorly understood, risk for mucosal infection and systemic inflammation. Here, we show in mouse models of obesity and diabetes that hyperglycemia drives intestinal barrier permeability, through GLUT2-dependent transcriptional reprogramming of intestinal epithelial cells and alteration of tight and adherence junction integrity. Consequently, hyperglycemia-mediated barrier disruption leads to systemic influx of microbial products and enhanced dissemination of enteric infection. Treatment of hyperglycemia, intestinal epithelial-specific GLUT2 deletion, or inhibition of glucose metabolism restores barrier function and bacterial containment. In humans, systemic influx of intestinal microbiome products correlates with individualized glycemic control, indicated by glycated hemoglobin levels. Together, our results mechanistically link hyperglycemia and intestinal barrier function with systemic infectious and inflammatory consequences of obesity and diabetes.

RAGE-mediated extracellular matrix proteins accumulation exacerbates HySu-induced pulmonary hypertension

Aims

Extracellular matrix (ECM) proteins accumulation contributes to the progression of pulmonary arterial hypertension (PAH), a rare and fatal cardiovascular condition defined by high pulmonary arterial pressure, whether primary, idiopathic, or secondary to other causes. The receptor for advanced glycation end products (RAGE) is constitutively expressed in the lungs and plays an important role in ECM deposition. Nonetheless, the mechanisms by which RAGE mediates ECM deposition/formation in pulmonary arteries and its roles in PAH progression remain unclear.

Methods and results

Expression of RAGE and its activating ligands, S100/calgranulins and high mobility group box 1 (HMGB1), were increased in both human and mouse pulmonary arterial smooth muscle cells (PASMCs) under hypoxic conditions and were also strikingly upregulated in pulmonary arteries in hypoxia plus SU5416 (HySu)-induced PAH in mice. RAGE deletion alleviated pulmonary arterial pressure and restrained extracellular matrix accumulation in pulmonary arteries in HySu-induced PAH murine model. Moreover, blocking RAGE activity with a neutralizing antibody in human PASMCs, or RAGE deficiency in mouse PASMCs exposed to hypoxia, suppressed the expression of fibrotic proteins by reducing TGF-β1 expression. RAGE reconstitution in deficient mouse PASMCs restored hypoxia-stimulated TGF-β1 production via ERK1/2 and p38 MAPK pathway activation and subsequently increased ECM protein expression. Interestingly, HMGB1 acting on RAGE, not toll-like receptor 4 (TLR4), induced ECM deposition in PASMCs. Finally, in both idiopathic PAH patients and HySu-induced PAH mice, soluble RAGE (sRAGE) levels in serum were significantly elevated compared to those in controls.

Conclusions

Activation of RAGE facilitates the development of hypoxia-induced pulmonary hypertension by increase of ECM deposition in pulmonary arteries. Our results indicate that sRAGE may be a potential biomarker for PAH diagnosis and disease severity, and that RAGE may be a promising target for PAH treatment.

Dengue fatal cases present virus-specific HMGB1 response in peripheral organs

Dengue is an important infectious disease that presents high incidence and yields a relevant number of fatal cases (about 20,000) every year worldwide. Despite its epidemiological relevance, there are many knowledge gaps concerning dengue pathogenesis, especially with regards to the circumstances that drive a mild clinical course to a severe disease. In this work, we investigated the participation of high mobility group box 1 (HMGB1), an important modulator of inflammation, in dengue fatal cases. Histopathological and ultrastructural analyses revealed that liver, lung and heart post-mortem samples were marked by tissue abnormalities, such as necrosis and apoptotic cell death. These observations go in line with an HMGB1-mediated response and raised concerns regarding the participation of this cytokine in promoting/perpetuating inflammation in severe dengue. Further experiments of immunohistochemistry (IHC) showed increased expression of cytoplasmic HMGB1 in dengue-extracted tissues when compared to non-dengue controls. Co-staining of DENV RNA and HMGB1 in the host cell cytoplasm, as found by in situ hybridization and IHC, confirmed the virus specific induction of the HMGB1-mediated response in these peripheral tissues. This report brings the first in-situ evidence of the participation of HMGB1 in severe dengue and highlights novel considerations in the development of dengue immunopathogenesis.

Genetic predisposition to ischaemic stroke by RAGE and HMGB1 gene variants in Chinese Han population

Emerging evidence suggests that the multiligand receptor for advanced glycation end products (RAGE) and its ligand high mobility group box 1 protein (HMGB1) contribute to the pathophysiology of ischaemic stroke (IS). The present study aimed to investigate the association of RAGE and HMGB1 variants with the risk of IS. A total of 1,034 patients and 1,015 age- and sex-matched healthy controls were genotyped to detect five genetic variants of the RAGE gene and four genetic variants of the HMGB1 gene using the Multiplex SNaPshot assay. We found that the rs2070600 variant of RAGE was associated with an increased risk of IS (OR = 1.19, 95% CI: 1.02-1.38, P = 0.043), whereas the rs2249825 variant of HMGB1 was associated with a decreased risk of IS (OR = 0.83, 95% CI: 0.71-0.98, P = 0.041). Further stratification by IS subtypes revealed that the presence of the TT genotype of the RAGE rs2070600 variant confers a higher risk of the large artery atherosclerosis subtype of IS (P = 0.036). Moreover, patients with the variant T allele of the RAGE rs2070600 variant presented with reduced serum soluble RAGE production. Patients carrying the variant G allele of the HMGB1 rs2249825 variant exhibited significantly lower infarct volumes than those with the major CC genotype. These clues may help in the development of optimal personalized therapeutic approaches for IS patients.

A Consensus Definitive Classification of Scavenger Receptors and Their Roles in Health and Disease

Scavenger receptors constitute a large family of proteins that are structurally diverse and participate in a wide range of biological functions. These receptors are expressed predominantly by myeloid cells and recognize a diverse variety of ligands including endogenous and modified host-derived molecules and microbial pathogens. There are currently eight classes of scavenger receptors, many of which have multiple names, leading to inconsistencies and confusion in the literature. To address this problem, a workshop was organized by the United States National Institute of Allergy and Infectious Diseases, National Institutes of Health, to help develop a clear definition of scavenger receptors and a standardized nomenclature based on that definition. Fifteen experts in the scavenger receptor field attended the workshop and, after extensive discussion, reached a consensus regarding the definition of scavenger receptors and a proposed scavenger receptor nomenclature. Scavenger receptors were defined as cell surface receptors that typically bind multiple ligands and promote the removal of nonself or altered-self targets. They often function by mechanisms that include endocytosis, phagocytosis, adhesion, and signaling that ultimately lead to the elimination of degraded or harmful substances. Based on this definition, nomenclature and classification of these receptors into 10 classes were proposed. This classification was discussed at three national meetings and input from participants at these meetings was requested. The following manuscript is a consensus statement that combines the recommendations of the initial workshop and incorporates the input received from the participants at the three national meetings.

The role of damage- and pathogen-associated molecular patterns in inflammation-mediated vulnerability of atherosclerotic plaques

Atherosclerosis is a chronic inflammatory disease resulting in the formation of the atherosclerotic plaque. Plaque formation starts with the inflammation in fatty streaks and progresses through atheroma, atheromatous plaque, and fibroatheroma leading to development of stable plaque. Hypercholesterolemia, dyslipidemia, and hyperglycemia are the risk factors for atherosclerosis. Inflammation, infection with viruses and bacteria, and dysregulation in the endothelial and vascular smooth muscle cells leads to advanced plaque formation. Death of the cells in the intima due to inflammation results in secretion of damage-associated molecular patterns (DAMPs) such as high mobility group box 1 (HMGB1), receptor for advanced glycation end products (RAGE), alarmins (S100A8, S100A9, S100A12, and oxidized low-density lipoproteins), and infection with pathogens leads to secretion of pathogen-associated molecular patterns (PAMPs) such as lipopolysaccharides, lipoteichoic acids, and peptidoglycans. DAMPs and PAMPs further activate the inflammatory surface receptors such as TREM-1 and toll-like receptors and downstream signaling kinases and transcription factors leading to increased secretion of pro-inflammatory cytokines such as tumor necrosis factor α, interleukin (IL)-1β, IL-6, and interferon-γ and matrix metalloproteinases (MMPs). These mediators and cytokines along with MMPs render the plaque vulnerable for rupture leading to ischemic events. In this review, we have discussed the role of DAMPs and PAMPs in association with inflammation-mediated plaque vulnerability.

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.

Anti-high Mobility Group Box 1 Antibody Ameliorates Albuminuria in MRL/lpr Lupus-Prone Mice

We evaluated the efficacy of a neutralizing anti-high mobility group box 1 (HMGB1) monoclonal antibody in MRL/lpr lupus-prone mice. The anti-HMGB1 monoclonal antibody (5 mg/kg weight) or class-matched control immunoglobulin G2a (IgG2a) was administered intravenously twice a week for 4-15 weeks. Urine albumin was monitored, and histological evaluation of the kidneys was conducted at 16 weeks. Lymphadenopathies were evaluated by 1-(2'-deoxy-2'-[¹⁸F]fluoro-β-D-arabinofuranosyl)cytosine ([¹⁸F]FAC) positron emission tomography/computed tomography (PET/CT) at 12 weeks. Following 4-week treatment, [¹⁸F]FAC-PET/CT showed similar accumulation in cervical and axillary lymph nodes at 12 weeks of age. However, anti-HMGB1 monoclonal antibody sufficiently inhibited the increase in albuminuria compared to an isotype control following 15-week treatment. Complement deposition was also improved; however, there were no significant differences in IgG deposition and renal pathological scores between the two groups. Anti-double-stranded DNA (dsDNA) antibody titers and cytokine and chemokine levels were also unaltered. Although there were no significant differences in glomerular macrophage infiltration, neutrophil infiltration was significantly decreased by the anti-HMGB1 monoclonal antibody. Antagonizing HMGB1 treatment suppressed HMGB1 translocation from nuclei in the kidney and suppressed neutrophil extracellular traps. The anti-HMGB1 monoclonal antibody demonstrated therapeutic potential against albuminuria in lupus nephritis by inhibiting neutrophil recruitment and neutrophil extracellular traps.

Alteration of serum high-mobility group protein 1 (HMGB1) levels in children with enterovirus 71-induced hand, foot, and mouth disease

Hand, foot, and mouth disease (HFMD) is a common pediatric disease caused by enterovirus infection. It typically presents as a fever along with flat, discolored spots and bumps on the hands, feet, and mouth. Compared with other viruses, enterovirus 71 (EV71)-induced HFMD is more prone to cause severe complications in children, such as brainstem encephalitis, cardiopulmonary disorders, and even death. More in-depth studies are still necessary to understand the characteristics of EV71-induced HFMD, although some related research has been reported so far. High-mobility group box 1 (HMGB1) is an inflammatory cytokine that can upregulate other inflammatory factors through its receptors, such as Toll-like receptors and the receptor for advanced glycation endproducts.We prospectively investigated the alteration of serum HMGB1, interleukin (IL)-6, and tumor necrosis factor (TNF)-α levels before and after treatment in 82 children with HFMD.We found that the serum HMGB1, IL-6, and TNF-α levels were significantly increased in EV71-induced HFMD, and that these changes were more serious in the severe and critical HMFD groups; however, there was no significant difference in the HMGB1 level between the normal control and mild HMFD groups. Moreover, the serum HMGB1 level was positively correlated with the alteration of serum IL-6 and TNF-α concentrations.These results suggest that HMGB1 is involved in the inflammatory pathogenesis of EV71-induced HFMD and that the serum level of HMGB1 could be applied as a clinical indicator for the severity of HFMD, and also a sign for the recovery prognosis of HFMD.

Clinical use of high mobility group box 1 and the receptor for advanced glycation end products in the prognosis and risk stratification of heart failure: a literature review

Heart failure (HF) is a clinical syndrome that represents the end stage of heart disease and remains the leading cause of morbidity and mortality worldwide. As heart failure mortality rates remain elevated, additional biomarkers that facilitate early detection or risk stratification in HF is of particularly great interest. High mobility group box 1 (HMGB1) and receptor for advanced glycation end products (RAGE) cause the activation of intracellular signaling, gene expression, and production of inflammatory cytokines and have been linked to many inflammatory disease states such as diabetes mellitus and atherosclerosis. Few studies have investigated their role in the pathophysiology of HF and any significant correlation remains uncertain. Review of the available literature discussing HMGB1 and RAGE clinical values as independent prognostic variables in HF resulted in the inclusion of 11 studies, which enrolled a total of 2025 heart failure patients. Overall, the data suggests a statistically significant positive correlation between RAGE and HF, with increasing RAGE levels associated with increasing New York Heart Association (NYHA) functional class of heart failure. HMGB1 correlations were not as extensively studied, but there is evidence that both HMGB1 and RAGE have a definite potential as biomarkers for the prognosis and risk stratification of HF patients.

Key Events Participating in the Pathogenesis of Alcoholic Liver Disease

Alcoholic liver disease (ALD) is a leading cause of morbidity and mortality worldwide. It ranges from fatty liver to steatohepatitis, fibrosis, cirrhosis and hepatocellular carcinoma. The most prevalent forms of ALD are alcoholic fatty liver, alcoholic hepatitis (AH) and alcoholic cirrhosis, which frequently progress as people continue drinking. ALD refers to a number of symptoms/deficits that contribute to liver injury. These include steatosis, inflammation, fibrosis and cirrhosis, which, when taken together, sequentially or simultaneously lead to significant disease progression. The pathogenesis of ALD, influenced by host and environmental factors, is currently only partially understood. To date, lipopolysaccharide (LPS) translocation from the gut to the portal blood, aging, gender, increased infiltration and activation of neutrophils and bone marrow-derived macrophages along with alcohol plus iron metabolism, with its associated increase in reactive oxygen species (ROS), are all key events contributing to the pathogenesis of ALD. This review aims to introduce the reader to the concept of alcohol-mediated liver damage and the mechanisms driving injury.

Cardiac Autoimmunity: Myocarditis

Myocarditis is the inflammation of the muscle tissues of the heart (myocardium). After a pathologic cardiac-specific inflammatory process, it may progress to chronic damage and dilated cardiomyopathy. The latter is characterized by systolic dysfunction, whose clinical correlate is heart failure. Nevertheless, other acute complications may arise as consequence of tissue damage and electrophysiologic disturbances. Different etiologies are involved in triggering myocarditis. In some cases, such as giant cell myocarditis or eosinophilic necrotizing myocarditis, it is an autoimmune process. Several factors predispose the development of autoimmune myocarditis such as systemic/local primary autoimmunity, viral infection, HLA and gender bias, exposure of cryptic antigens, mimicry, and deficient thymic training/Treg induction. Once the anti-myocardium autoimmune process is triggered, several components of the immune response orchestrate a sustained attack toward myocardial tissues with particular timing and immunopathogenic features. Innate response mediated by monocytes/macrophages, neutrophils, and eosinophils parallels the adaptive response, playing a final effector role and not only a priming function. Stromal cells like fibroblast are also involved in the process through specific cytokines. Furthermore, adaptive T cell responses have anti-paradigmatic features, as Th17 response is dispensable for acute myocarditis but is the main driver of the process leading to dilated cardiomyopathy. Humoral response, thought to be a bystander, is important in the appearance of late-stage hemodynamic complications. The complexity of that process, as well as the unspecific and variable clinical presentation, had generated difficulties for diagnosis and treatment, which remain suboptimal. In this chapter, we will discuss the most relevant immunopathogenic findings from a basic science and clinical perspective.

HMGB1 Protein: A Therapeutic Target Inside and Outside the Cell

High-mobility group box 1 protein (HMGB1) is a nonhistone chromosomal protein discovered more than 30 years ago. It is an abundant nuclear protein that has a dual function-in the nucleus, it binds DNA and participates in practically all DNA-dependent processes serving as an architectural factor. Outside the cell, HMGB1 plays a different role-it acts as an alarmine that activates a large number of HMGB1-"competent" cells and mediates a broad range of physiological and pathological responses. This universality makes it an attractive target for innovative therapeutic strategies in the treatment of various diseases. Here we present an overview of the major nuclear and extracellular properties of HMGB1 and describe its interaction with different molecular partners as specific receptors or inhibitors, which are important for its role as a target in multiple diseases. We highlight its pivotal role as a target for cancer treatment at two aspects: first in terms of its substantial impact on the repair capacity of cancer cells, thus affecting the effectiveness of chemotherapy with the antitumor drug cis-platinum and, second, the possibility to be targeted by microRNAs influencing different pathways of human diseases, thus making it a promising candidate for a new strategy for therapeutic interventions against various pathological conditions but mainly cancer.

Role of HMGB1 translocation to neuronal nucleus in rat model with septic brain injury

High-mobility Group Box-1 (HMGB1) is a central late proinflammatory cytokine that triggers the inflammatory response during sepsis. However, whether HMGB1 is involved in the pathogenesis of septic brain damage is unknown. In this study, we investigated the role of HMGB1 in regulating brain injury in a rat model of sepsis. Wistar rats were subjected to cecal ligation and puncture (CLP) to induce septic brain injury. Hematoxylin and eosin staining was used to detect pathological changes in the cortex. The cellular localization of HMGB1 was determined using immunostaining. Cortical levels of HMGB1, its receptor for advanced glycation end-products (RAGE), and downstream effecter, nuclear factor kappa-B (NF-κB) subunit p65, were detected via western blot.HMGB1was increased in the cytoplasm via translocation from the nucleus predominantly in neurons. Moreover, RAGE and NF-κB p65 were upregulated after septic brain injury. Ethyl pyruvate, an inhibitor of HMGB1, down-regulated the expression of RAGE and NF-κB p65via inhibiting HMGB1 expression in the cytoplasm. Collectively, our findings suggest that HMGB1 and its signaling transduction have critical roles in the pathogenesis of septic brain injury. HMGB1 inhibition might be a potential new therapeutic target for septic brain injury.

Relationship between Advanced Glycation End Products and Steroidogenesis in PCOS

BACKGROUND

Women with PCOS have elevated levels of the harmful Advanced Glycation End Products (AGEs), which are highly reactive molecules formed after glycation of lipids and proteins. Additionally, AGEs accumulate in the ovaries of women with PCOS potentially contributing to the well-documented abnormal steroidogenesis and folliculogenesis.

MAIN BODY

A systematic review of articles and abstracts available in PubMed was conducted and presented in a systemic manner. This article reports changes in steroidogenic enzyme activity in granulosa and theca cells in PCOS and PCOS-models. It also described the changes in AGEs and their receptors in the ovaries of women with PCOS and presents the underlying mechanism(s) whereby AGEs could be responsible for the PCOS-related changes in granulosa and theca cell function thus adversely impacting steroidogenesis and follicular development. AGEs are associated with hyperandrogenism in PCOS possibly by altering the activity of various enzymes such as cholesterol side-chain cleavage enzyme cytochrome P450, steroidogenic acute regulatory protein, 17α-hydroxylase, and 3β-hydroxysteroid dehydrogenase. AGEs also affect luteinizing hormone receptor and anti-Mullerian hormone receptor expression as well as their signaling pathways in granulosa cells.

CONCLUSIONS

A better understanding of how AGEs alter granulosa and theca cell function is likely to contribute meaningfully to a conceptual framework whereby new interventions to prevent and/or treat ovarian dysfunction in PCOS can ultimately be developed.

DNA sensor cGAS-mediated immune recognition

The host takes use of pattern recognition receptors (PRRs) to defend against pathogen invasion or cellular damage. Among microorganism-associated molecular patterns detected by host PRRs, nucleic acids derived from bacteria or viruses are tightly supervised, providing a fundamental mechanism of host defense. Pathogenic DNAs are supposed to be detected by DNA sensors that induce the activation of NFκB or TBK1-IRF3 pathway. DNA sensor cGAS is widely expressed in innate immune cells and is a key sensor of invading DNAs in several cell types. cGAS binds to DNA, followed by a conformational change that allows the synthesis of cyclic guanosine monophosphate–adenosine monophosphate (cGAMP) from adenosine triphosphate and guanosine triphosphate. cGAMP is a strong activator of STING that can activate IRF3 and subsequent type I interferon production. Here we describe recent progresses in DNA sensors especially cGAS in the innate immune responses against pathogenic DNAs.

Cardiac troponin I exacerbates myocardial ischaemia/reperfusion injury by inducing the adhesion of monocytes to vascular endothelial cells via a TLR4/NF-κB-dependent pathway

Cardiac troponin I (cTnI), a biomarker for myocardial damage and risk stratification, may be involved in the pathogenesis of cardiovascular diseases, which was ascribed to the effect of cTnI auto-antibodies. Whether or not cTnI itself has a direct impact on acute myocardial injury is unknown. To exclude the influence of cTnI antibody on the cardiac infarct size, we studied the effect of cTnI shortly after myocardial ischaemia-reperfusion (I/R) injury when cTnI antibodies were not elevated. Pretreatment with cTnI augmented the myocardial infarct size caused by I/R, accompanied by an increase in inflammatory markers in the blood and myocardium. Additional experiments using human umbilical vein endothelial cells (HUVECs) showed that the detrimental effect of cTnI was related to cTnI-induced increase in vascular cell adhesion molecule-1 (VCAM-1) expression and VCAM-1 mediated adhesion of human monocytes (THP-1) to HUVECs, which could be neutralized by VCAM-1 antibody. Both toll-like receptor 4 (TLR4) and nuclear factor-κB (NF-κB) were involved in the signalling pathway, because blockade of either TLR4 or NF-κB inhibited the cTnI's effect on VCAM-1 expression and adhesion of monocytes to endothelial cells. Moreover, TLR4 inhibition reduced cTnI-augmented cardiac injury in rats with I/R injury. We conclude that cTnI exacerbates myocardial I/R injury by inducing the adhesion of monocytes to vascular endothelial cells via activation of the TLR4/NF-κB pathway. Inhibition of TLR4 may be an alternative strategy to reduce cTnI-induced myocardial I/R injury.

Diagnostic Potential of Evaluation of SDF-1α and sRAGE Levels in Threatened Premature Labor

Preterm birth remains the most prevalent cause of neonatal morbidity. This study aimed to evaluate the diagnostic value of SDF-1α, resistin, secretory RAGE (sRAGE), and endogenous secretory RAGE (esRAGE) in preterm labor. A total of 211 pregnant women participated in the study. Group A contained 72 women between 22 and 36 weeks of gestation, with premature labor, who finally had preterm birth. Group B contained 66 women in labor between 37 and 41 weeks of gestation. Women in group A had lower SDF-1α and sRAGE levels than those in group B. Moreover, in group A, SDF-1α and sRAGE levels were correlated with the latency period from the occurrence of premature labor symptoms until delivery. Sensitivity and specificity of studied parameters for prediction of preterm birth were 95% and 40% for SDF-1α and 51.3% and 93.5% for sRAGE, respectively. The prognostic value of plasma SDF-1α and sRAGE levels was comparable with that of cervical length ultrasound measurement and serum C-reactive protein levels. We conclude that SDF-1α and sRAGE appear to play a major role in the diagnosis of preterm birth and its evaluation could be convenient and useful for predicting preterm birth.

HMGB1 as biomarker and drug target

High Mobility Group Box 1 protein was discovered as a nuclear protein, but it has a "second life" outside the cell where it acts as a damage-associated molecular pattern. HMGB1 is passively released or actively secreted in a number of diseases, including trauma, chronic inflammatory disorders, autoimmune diseases and cancer. Extracellular HMGB1 triggers and sustains the inflammatory response by inducing cytokine release and by recruiting leucocytes. These characteristics make extracellular HMGB1 a key molecular target in multiple diseases. A number of strategies have been used to prevent HMGB1 release or to inhibit its activities. Current pharmacological strategies include antibodies, peptides, decoy receptors and small molecules. Noteworthy, salicylic acid, a metabolite of aspirin, has been recently found to inhibit HMGB1. HMGB1 undergoes extensive post-translational modifications, in particular acetylation and oxidation, which modulate its functions. Notably, high levels of serum HMGB1, in particular of the hyper-acetylated and disulfide isoforms, are sensitive disease biomarkers and are associated with different disease stages. In the future, the development of isoform-specific HMGB1 inhibitors may potentiate and fine-tune the pharmacological control of inflammation. We review here the current therapeutic strategies targeting HMGB1, in particular the emerging and relatively unexplored small molecules-based approach.

HMGB1-RAGE Axis Makes No Contribution to Cardiac Remodeling Induced by Pressure-Overload

High-mobility group box1 (HMGB1) exerts effects on inflammation by binding to receptor for advanced glycation end products (RAGE) or Toll-like receptor 4. Considering that inflammation is involved in pressure overload-induced cardiac hypertrophy, we herein attempted to investigate whether HMGB1 plays a role in myocardial hypertrophy in RAGE knockout mice as well as in the growth and apoptosis of cardiomyocytes. The myocardial expression of RAGE was not significantly changed while TLR4 mRNA was upregulated in response to transverse aortic constriction (TAC) for 1 week. The myocardial expression of HMGB1 protein was markedly increased in TAC group when compared to the sham group. Heart weight to body weight ratio (HW/BW) and lung weight to body weight ratio (LW/BW) were evaluated in RAGE knockout (KO) and wild-type (WT) mice 1 week after TAC. Significant larger HW/BW and LW/BW ratios were found in TAC groups than the corresponding sham groups, but no significant difference was found between KO and WT TAC mice. Similar results were also found when TAC duration was extended to 4 weeks. Cultured neonatal rat cardiomyocytes were treated with different concentrations of recombinant HMGB1, then cell viability was determined using MTT and CCK8 assays and cell apoptosis was determined by Hoechst staining and TUNEL assay. The results came out that HMGB1 exerted no influence on viability or apoptosis of cardiomyocytes. Besides, the protein expression levels of Bax and Bcl2 in response to different concentrations of HMGB1 were similar. These findings indicate that HMGB1 neither exerts influence on cardiac remodeling by binding to RAGE nor induces apoptosis of cardiomyocytes under physiological condition.

Chronic Heart Failure and Inflammation

As a greater proportion of patients survive their initial cardiac insult, medical systems worldwide are being faced with an ever-growing need to understand the mechanisms behind the pathogenesis of chronic heart failure (HF). There is a wealth of information about the role of inflammatory cells and pathways during acute injury and the reparative processes that are subsequently activated. We discuss the different causes that lead to chronic HF development and how the sum of initial inflammatory and reparative responses only sets the trajectory for disease progression. Unfortunately, comparatively little is known about the contribution of the immune system once the trajectory has been set, and chronic HF has been established—which clinically represents the majority of patients. It is known that chronic HF is associated with circulating inflammatory cytokines that can predict clinical outcomes, yet the causative role inflammation plays in disease progression is not well defined, and the majority of clinical trials that target aspects of inflammation in patients with chronic HF have largely been negative. This review will present what is currently known about inflammation in chronic HF in both humans and animal models as a means to highlight the gap in our knowledge base that requires further examination.

Effect of hemoadsorption during cardiopulmonary bypass surgery - a blinded, randomized, controlled pilot study using a novel adsorbent

Background

Cardiopulmonary bypass (CPB) surgery initiates a systemic inflammatory response, which is associated with postoperative morbidity and mortality. Hemoadsorption (HA) of cytokines may suppress inflammatory responses and improve outcomes. We tested a new sorbent used for HA (CytoSorb™; CytoSorbents Europe GmbH, Berlin, Germany) installed in the CPB circuit on changes of pro- and anti-inflammatory cytokines levels, inflammation markers, and differences in patients’ perioperative course.

Methods

In this first pilot trial, 37 blinded patients were undergoing elective CPB surgery at the Medical University of Vienna and were randomly assigned to HA (n = 19) or control group (n = 18). The primary outcome was differences of cytokine levels (IL-1β, IL-6, IL-18, TNF-α, and IL-10) within the first five postoperative days. We also analyzed whether we can observe any differences in ex vivo lipopolysaccharide (LPS)-induced TNF-α production, a reduction of high-mobility box group 1 (HMGB1), or other inflammatory markers. Additionally, measurements for fluid components, blood products, catecholamine treatment, bioelectrical impedance analysis (BIA), and 30-day mortality were analyzed.

Results

We did not find differences in our primary outcome immediately following the HA treatment, although we observed differences for IL-10 24 hours after CPB (HA: median 0.3, interquartile range (IQR) 0–4.5; control: not traceable, P = 0.0347) and 48 hours after CPB (median 0, IQR 0–1.2 versus not traceable, P = 0.0185). We did not find any differences for IL-6 between both groups, and other cytokines were rarely expressed. We found differences in pretreatment levels of HMGB1 (HA: median 0, IQR 0–28.1; control: median 48.6, IQR 12.7–597.3, P = 0.02083) but no significant changes to post-treatment levels. No differences in inflammatory markers, fluid administration, blood substitution, catecholamines, BIA, or 30-day mortality were found.

Conclusions

We did not find any reduction of the pro-inflammatory response in our patients and therefore no changes in their perioperative course. However, IL-10 showed a longer-lasting anti-inflammatory effect. The clinical impact of prolonged IL-10 needs further evaluation. We also observed strong inter-individual differences in cytokine levels; therefore, patients with an exaggerated inflammatory response to CPB need to be identified. The implementation of HA during CPB was feasible.

Trial registration

ClinicalTrials.gov: NCT01879176, registration date: June 7, 2013.

Small Molecule Inhibition of Ligand-Stimulated RAGE-DIAPH1 Signal Transduction

The receptor for advanced glycation endproducts (RAGE) binds diverse ligands linked to chronic inflammation and disease. NMR spectroscopy and x-ray crystallization studies of the extracellular domains of RAGE indicate that RAGE ligands bind by distinct charge- and hydrophobicity-dependent mechanisms. The cytoplasmic tail (ct) of RAGE is essential for RAGE ligand-mediated signal transduction and consequent modulation of gene expression and cellular properties. RAGE signaling requires interaction of ctRAGE with the intracellular effector, mammalian diaphanous 1 or DIAPH1. We screened a library of 58,000 small molecules and identified 13 small molecule competitive inhibitors of ctRAGE interaction with DIAPH1. These compounds, which exhibit in vitro and in vivo inhibition of RAGE-dependent molecular processes, present attractive molecular scaffolds for the development of therapeutics against RAGE-mediated diseases, such as those linked to diabetic complications, Alzheimer’s disease, and chronic inflammation, and provide support for the feasibility of inhibition of protein-protein interaction (PPI).