Enhancement of tracheal cartilage regeneration by local controlled release of stromal cell-derived factor 1α with gelatin hydrogels and systemic administration of high-mobility group box 1 peptide

Introduction

This present study evaluated the effect of combination therapy with stromal cell-derived factor 1α (SDF-1α) and high-mobility group box 1 (HMGB1) peptide on the regeneration of tracheal injury in a rat model.

Methods

To improve this effect, SDF-1α was incorporated into a gelatin hydrogel, which was then applied to the damaged tracheal cartilage of rats for local release. Furthermore, HMGB1 peptide was repeatedly administered intravenously. Regeneration of damaged tracheal cartilage was evaluated in terms of cell recruitment.

Results

Mesenchymal stem cells (MSC) with C-X-C motif chemokine receptor 4 (CXCR4) were mobilized more into the injured area, and consequently the fastest tracheal cartilage regeneration was observed in the combination therapy group eight weeks after injury.

Conclusions

The present study demonstrated that combination therapy with gelatin hydrogel incorporating SDF-1α and HMGB1 peptide injected intravenously can enhance the recruitment of CXCR4-positive MSC, promoting the regeneration of damaged tracheal cartilage.

Chemokine Binding to Tenascin-C Influences Chemokine-Induced Immune Cell Migration

Tenascin-C (TNC) is a complex glycoprotein of the extracellular matrix (ECM) involved in a plethora of (patho-)physiological processes, such as oncogenesis and inflammation. Since chemokines play an essential role in both disease processes, we have investigated here the binding of TNC to some of the key chemokines, namely CCL2, CCL26, CXCL8, CXCL10, and CXCL12. Thereby, a differential chemokine-TNC binding pattern was observed, with CCL26 exhibiting the highest and CCL2 the lowest affinity for TNC. Heparan sulfate (HS), another member of the ECM, proved to be a similarly high-affinity ligand of TNC, with a Kd value of 730 nM. Chemokines use glycosa-minoglycans such as HS as co-receptors to induce immune cell migration. Therefore, we assumed an influence of TNC on immune cell chemotaxis due to co-localization within the ECM. CCL26- and CCL2-induced mobilization experiments of eosinophils and monocytes, respectively, were thus performed in the presence and the absence of TNC. Pre-incubation of the immune cells with TNC resulted in a 3.5-fold increase of CCL26-induced eosinophil chemotaxis, whereas a 1.3-fold de-crease in chemotaxis was observed when monocytes were pre-incubated with CCL2. As both chemokines have similar HS binding but different TNC binding affinities, we speculate that TNC acts as an attenuator in monocyte and as an amplifier in eosinophil mobilization by impeding CCL2 from binding to HS on the one hand, and by reinforcing CCL26 to bind to HS on the other hand.

Sterile inflammation in liver transplantation

Sterile inflammation is the immune response to damage-associated molecular patterns (DAMPs) released during cell death in the absence of foreign pathogens. In the setting of solid organ transplantation, ischemia-reperfusion injury results in mitochondria-mediated production of reactive oxygen and nitrogen species that are a major cause of uncontrolled cell death and release of various DAMPs from the graft tissue. When properly regulated, the immune response initiated by DAMP-sensing serves as means of damage control and is necessary for initiation of recovery pathways and re-establishment of homeostasis. In contrast, a dysregulated or overt sterile inflammatory response can inadvertently lead to further injury through recruitment of immune cells, innate immune cell activation, and sensitization of the adaptive immune system. In liver transplantation, sterile inflammation may manifest as early graft dysfunction, acute graft failure, or increased risk of immunosuppression-resistant rejection. Understanding the mechanisms of the development of sterile inflammation in the setting of liver transplantation is crucial for finding reliable biomarkers that predict graft function, and for development of therapeutic approaches to improve long-term transplant outcomes. Here, we discuss the recent advances that have been made to elucidate the early signs of sterile inflammation and extent of damage from it. We also discuss new therapeutics that may be effective in quelling the detrimental effects of sterile inflammation.

HMGB1, angel or devil, in ischemic stroke

INTRODUCTION

High-mobility group box 1 protein (HMGB1) is extensively involved in causing ischemic stroke, pathological damage of ischemic brain injury, and neural tissue repair after ischemic brain injury. However, the precise role of HMGB1 in ischemic stroke remains to be elucidated.

METHODS

Comprehensive literature search and narrative review to summarize the current field of HMGB1 in cerebral ischemic based on the basic structure, structural modification, and functional roles of HMGB1 described in the literature.

RESULTS

Studies have exhibited the crucial roles of HMGB1 in cell death, immunity and inflammation, thrombosis, and remodeling and repair. HMGB1 released after cerebral infarction is extensively involved in the pathological injury process in the early stage of cerebral infarction, whereas it is involved in the promotion of brain tissue repair and remodeling in the late stage of cerebral infarction. HMGB1 plays a neurotrophic role in acute white matter stroke, whereas it causes sustained activation of inflammation and plays a damaging role in chronic white matter ischemia.

CONCLUSIONS

HMGB1 plays a complex role in cerebral infarction, which is related to not only the modification of HMGB1 and bound receptors but also different stages and subtypes of cerebral infarction. future studies on HMGB1 should investigate the spatial and temporal dynamics of HMGB1 after cerebral infarction. Moreover, future studies on HMGB1 should attempt to integrate different stages and infarct subtypes of cerebral infarction.

CXCL12/CXCR4 Axis is Involved in the Recruitment of NK Cells by HMGB1 Contributing to Persistent Airway Inflammation and AHR During the Late Stage of RSV Infection

We previously showed that both high-mobility group box-1 (HMGB1) and natural killer (NK) cells contribute to respiratory syncytial virus (RSV)-induced persistent airway inflammation and airway hyperresponsiveness (AHR). Meanwhile, Chemokine (C-X-C motif) ligand 12 (CXCL12) and its specific receptor (chemokine receptor 4, CXCR4) play important roles in recruitment of immune cells. CXCL12 has been reported to form a complex with HMGB1 that binds to CXCR4 and increases inflammatory cell migration. The relationship between HMGB1, NK cells and chemokines in RSV-infected model remains unclear. An anti-HMGB1 neutralizing antibody and inhibitor of CXCR4 (AMD3100) was administered to observe changes of NK cells and airway disorders in nude mice and BALB/c mice. Results showed that the mRNA expression and protein levels of HMGB1 were elevated in late stage of RSV infection and persistent airway inflammation and AHR were diminished after administration of anti-HMGB1 antibodies, with an associated significant decrease in CXCR4⁺ NK cells. In addition, CXCL12 and CXCR4 were reduced after HMGB1 blockade. Treatment with AMD3100 significantly suppressed the recruitment of NK cells and alleviated the airway disorders. Thus, CXCL12/CXCR4 axis is involved in the recruitment of NK cells by HMGB1, contributing to persistent airway inflammation and AHR during the late stage of RSV infection.

HMGB1 is a Potential and Challenging Therapeutic Target for Parkinson's Disease

Parkinson's disease (PD) is one of the most common degenerative diseases of the human nervous system and has a wide range of serious impacts on human health and quality of life. Recently, research targeting high mobility group box 1 (HMGB1) in PD has emerged, and a variety of laboratory methods for inhibiting HMGB1 have achieved good results to a certain extent. However, given that HMGB1 undergoes a variety of intracellular modifications and three different forms of extracellular redox, the possible roles of these forms in PD are likely to be different. General inhibition of all forms of HMGB1 is obviously not ideal and has become one of the biggest obstacles in the clinical application of targeting HMGB1. In this review, pure mechanistic research of HMGB1 and in vivo research targeting HMGB1 were combined, the effects of HMGB1 on neurons and immune cell responses in PD are discussed in detail, and the problems that need to be focused on in the future are addressed.

The Role of HMGB1 in Rheumatic Diseases

HMGB1, a highly conserved non-histone nuclear protein, is widely expressed in mammalian cells. HMGB1 in the nucleus binds to the deoxyribonucleic acid (DNA) to regulate the structure of chromosomes and maintain the transcription, replication, DNA repair, and nucleosome assembly. HMGB1 is actively or passively released into the extracellular region during cells activation or necrosis. Extracellular HMGB1 as an alarmin can initiate immune response alone or combined with other substances such as nucleic acid to participate in multiple biological processes. It has been reported that HMGB1 is involved in various inflammatory responses and autoimmunity. This review article summarizes the physiological function of HMGB1, the post-translational modification of HMGB1, its interaction with different receptors, and its recent advances in rheumatic diseases and strategies for targeted therapy.

Sensory Neuron TLR4 mediates the development of nerve-injury induced mechanical hypersensitivity in female mice

Recent studies have brought to light the necessity to discern sex-specific differences in various pain states and different cell-types that mediate these differences. These studies have uncovered the role of neuroimmune interactions to mediate pain states in a sex-specific fashion. While investigating immune function in pain development, we discovered that females utilize immune components of sensory neurons to mediate neuropathic pain development. We utilized two novel transgenic mouse models that eitherrestore expression of toll-like receptor (TLR) 4 inNa_v1.8 nociceptors on a TLR4-null background (TLR4^LoxTB) or remove TLR4 specifically from Na_v1.8 nociceptors (TLR4^fl/fl). After spared nerve injury (SNI), a model of neuropathic injury, we observed a robust female-specific onset of mechanical hypersensitivity in our transgenic animals. Female Na_v1.8-TLR4^fl/fl knockout animals were less mechanically sensitive than cre-negative TLR4^fl/fl littermates. Conversely, female Na_v1.8-TLR4^LoxTB reactivated animals were as mechanically sensitive as their wild-type counterparts. These sex and cell-specific effects were not recapitulated in male animals of either strain. Additionally, we find the danger associated molecular pattern, high mobility group box-1 (HGMB1), a potent TLR4 agonist, localization and ATF3 expression in females is dependent on TLR4 expression in dorsal root ganglia (DRG) populations following SNI. These experiments provide novel evidence toward sensory neuron specific modulation of pain in a sex-dependent manner.

Liver regeneration and inflammation: from fundamental science to clinical applications

Liver regeneration is a complex process involving the crosstalk of multiple cell types, including hepatocytes, hepatic stellate cells, endothelial cells and inflammatory cells. The healthy liver is mitotically quiescent, but following toxic damage or resection the cells can rapidly enter the cell cycle to restore liver mass and function. During this process of regeneration, epithelial and non-parenchymal cells respond in a tightly coordinated fashion. Recent studies have described the interaction between inflammatory cells and a number of other cell types in the liver. In particular, macrophages can support biliary regeneration, contribute to fibrosis remodelling by repressing hepatic stellate cell activation and improve liver regeneration by scavenging dead or dying cells in situ. In this Review, we describe the mechanisms of tissue repair following damage, highlighting the close relationship between inflammation and liver regeneration, and discuss how recent findings can help design novel therapeutic approaches.

HMGB1 promotes CXCL12-dependent egress of murine B cells from Peyer's patches in homeostasis

High mobility group box-1 protein (HMGB1) is an alarmin that, once released, promotes inflammatory responses, alone and as a complex with the chemokine CXCL12. Here, we report that the HMGB1-CXCL12 complex plays an essential role also in homeostasis by controlling the migration of B lymphocytes. We show that extracellular HMGB1 is critical for the CXCL12-dependent egress of B cells from the Peyer's patches (PP). This promigratory function of the complex was restricted to the PPs, since HMGB1 was not required for B-cell migratory processes in other locations. Accordingly, we detected higher constitutive levels of the HMGB1-CXCL12 complex in PPs than in other lymphoid organs. HMGB1-CXCL12 in vivo inhibition was associated with a reduced basal IgA production in the gut. Collectively, our results demonstrate a role for the HMGB1-CXCL12 complex in orchestrating B-cell trafficking in homeostasis, and provide a novel target to control lymphocyte migration in mucosal immunity.

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.

Sterile inflammation in thoracic transplantation

The life-saving benefits of organ transplantation can be thwarted by allograft dysfunction due to both infectious and sterile inflammation post-surgery. Sterile inflammation can occur after necrotic cell death due to the release of endogenous ligands [such as damage-associated molecular patterns (DAMPs) and alarmins], which perpetuate inflammation and ongoing cellular injury via various signaling cascades. Ischemia-reperfusion injury (IRI) is a significant contributor to sterile inflammation after organ transplantation and is associated with detrimental short- and long-term outcomes. While the vicious cycle of sterile inflammation and cellular injury is remarkably consistent amongst different organs and even species, we have begun understanding its mechanistic basis only over the last few decades. This understanding has resulted in the developments of novel, yet non-specific therapies for mitigating IRI-induced graft damage, albeit with moderate results. Thus, further understanding of the mechanisms underlying sterile inflammation after transplantation is critical for identifying personalized therapies to prevent or interrupt this vicious cycle and mitigating allograft dysfunction. In this review, we identify common and distinct pathways of post-transplant sterile inflammation across both heart and lung transplantation that can potentially be targeted.

Non-Thermal Plasma Application in Tumor-Bearing Mice Induces Increase of Serum HMGB1

The application of cold atmospheric plasma (CAP) in cancer therapy could be one of the new anticancer strategies. In the current work, we used cold atmospheric plasma jet for the treatment of cultured cells and mice. We showed that CAP induced the death of MX-7 mouse rhabdomyosarcoma cells with the hallmarks of immunogenic cell death (ICD): calreticulin and heat shock protein 70 (HSP70) externalization and high-mobility group box 1 protein (HMGB1) release. The intensity of HMGB1 release after the CAP treatment correlated directly with the basal extracellular HMGB1 level. Releasing from dying cells, HMGB1 can act as a proinflammatory cytokine. Our in vivo study demonstrated that cold atmospheric plasma induces a short-term two-times increase in serum HMGB1 level only in tumor-bearing mice with no effect in healthy mice. These findings support our hypothesis that CAP-dependent HMGB1 release from dying cancer cells can change the serum HMGB1 level. At the same time, we showed a weak cytokine response to CAP irradiation in healthy mice that can characterize CAP as an immune-safety physical antitumor approach.

Regulation of Neurogenesis in Mouse Brain by HMGB1

The High Mobility Group Box 1 (HMGB1) is the most abundant nuclear nonhistone protein that is involved in transcription regulation. In addition, HMGB1 has previously been found as an extracellularly acting protein enhancing neurite outgrowth in cultured neurons. Although HMGB1 is widely expressed in the developing central nervous system of vertebrates and invertebrates, its function in the developing mouse brain is poorly understood. Here, we have analyzed developmental defects of the HMGB1 null mouse forebrain, and further examined our findings in ex vivo brain cell cultures. We find that HMGB1 is required for the proliferation and differentiation of neuronal stem cells/progenitor cells. Enhanced apoptosis is also found in the neuronal cells lacking HMGB1. Moreover, HMGB1 depletion disrupts Wnt/β-catenin signaling and the expression of transcription factors in the developing cortex, including Foxg1, Tbr2, Emx2, and Lhx6. Finally, HMGB1 null mice display aberrant expression of CXCL12/CXCR4 and reduced RAGE signaling. In conclusion, HMGB1 plays a critical role in mammalian neurogenesis and brain development.

High-mobility group box 1 protein antagonizes the immunosuppressive capacity and therapeutic effect of mesenchymal stem cells in acute kidney injury

Background

Kidney ischemia reperfusion injury (IRI) is a common cause of acute kidney injury and an unavoidable consequence of kidney transplantation and still lacks specific therapeutics. Recently, mesenchymal stem cell (MSC) has been emerging as a promising cell-based therapy for IRI in the context of transplantation. MSC negatively regulates the secretion of pro-inflammatory as well as the activation of immune cells during IRI through its unique immunosuppressive property.

Methods

We employed mice kidney IRI model and MSC cell line to monitor the IRI related checkpoints. siRNAs were utilized to knock down the potential key factors for mechanistic analysis. Statistical analysis was performed by using one-way ANOVA with Tukey’s post hoc procedure by SPSS.

Results

The expression of high-mobility group box 1 protein (HMGB1) is increased in the acute phase as well as the recovery stage of IRI. Importantly, the HMGB1 upregulation is correlated with the injury severity. HMGB1 diminishes the MSC induced immunosuppressive capacity in the presence of pro-inflammatory cytokines in vitro. Toll like receptor 4 (TLR4)-mediated inducible nitric oxide synthase (iNOS) inhibition contributes to the negative effect of HMGB1 on MSCs. HMGB1-TLR4 signaling inhibition augments the therapeutic efficacy of MSCs in mice renal IRI model.

Conclusions

These findings demonstrate that HMGB1 plays a crucial role in shaping the immunoregulatory property of MSCs within the microenvironments, providing novel insights into the crosstalk between MSCs and microenvironment components, suggesting HMGB1 signals as a promising target to improve MSC-based therapy.

HIMF (Hypoxia-Induced Mitogenic Factor) Signaling Mediates the HMGB1 (High Mobility Group Box 1)-Dependent Endothelial and Smooth Muscle Cell Crosstalk in Pulmonary Hypertension

OBJECTIVE

HIMF (hypoxia-induced mitogenic factor; also known as FIZZ1 [found in inflammatory zone-1] or RELM [resistin-like molecule-α]) is an etiological factor of pulmonary hypertension (PH) in rodents, but its underlying mechanism is unclear. We investigated the immunomodulatory properties of HIMF signaling in PH pathogenesis. Approach and Results: Gene-modified mice that lacked HIMF (KO [knockout]) or overexpressed HIMF human homolog resistin (hResistin) were used for in vivo experiments. The pro-PH role of HIMF was verified in HIMF-KO mice exposed to chronic hypoxia or sugen/hypoxia. Mechanistically, HIMF/hResistin activation triggered the HMGB1 (high mobility group box 1) pathway and RAGE (receptor for advanced glycation end products) in pulmonary endothelial cells (ECs) of hypoxic mouse lungs in vivo and in human pulmonary microvascular ECs in vitro. Treatment with conditioned medium from hResistin-stimulated human pulmonary microvascular ECs induced an autophagic response, BMPR2 (bone morphogenetic protein receptor 2) defects, and subsequent apoptosis-resistant proliferation in human pulmonary artery (vascular) smooth muscle cells in an HMGB1-dependent manner. These effects were confirmed in ECs and smooth muscle cells isolated from pulmonary arteries of patients with idiopathic PH. HIMF/HMGB1/RAGE-mediated autophagy and BMPR2 impairment were also observed in pulmonary artery (vascular) smooth muscle cells of hypoxic mice, effects perhaps related to FoxO1 (forkhead box O1) dampening by HIMF. Experiments in EC-specific hResistin-overexpressing transgenic mice confirmed that EC-derived HMGB1 mediated the hResistin-driven pulmonary vascular remodeling and PH.

CONCLUSIONS

In HIMF-induced PH, HMGB1-RAGE signaling is pivotal for mediating EC-smooth muscle cell crosstalk. The humanized mouse data further support clinical implications for the HIMF/HMGB1 signaling axis and indicate that hResistin and its downstream pathway may constitute targets for the development of novel anti-PH therapeutics in humans.

Chemokines in COPD: From Implication to Therapeutic Use

: Chronic Obstructive Pulmonary Disease (COPD) represents the 3rd leading cause of death in the world. The underlying pathophysiological mechanisms have been the focus of extensive research in the past. The lung has a complex architecture, where structural cells interact continuously with immune cells that infiltrate into the pulmonary tissue. Both types of cells express chemokines and chemokine receptors, making them sensitive to modifications of concentration gradients. Cigarette smoke exposure and recurrent exacerbations, directly and indirectly, impact the expression of chemokines and chemokine receptors. Here, we provide an overview of the evidence regarding chemokines involvement in COPD, and we hypothesize that a dysregulation of this tightly regulated system is critical in COPD evolution, both at a stable state and during exacerbations. Targeting chemokines and chemokine receptors could be highly attractive as a mean to control both chronic inflammation and bronchial remodeling. We present a special focus on the CXCL8-CXCR1/2, CXCL9/10/11-CXCR3, CCL2-CCR2, and CXCL12-CXCR4 axes that seem particularly involved in the disease pathophysiology.

Cancer-cell-secreted CXCL11 promoted CD8+ T cells infiltration through docetaxel-induced-release of HMGB1 in NSCLC

BACKGROUND

Chemotherapy combined with immunotherapy becomes the main trend in lung cancer intervention; however, how chemotherapy promotes the immune function remains elusive. Therefore, we sought to determine how chemotherapy promotes the immune function.

METHODS

We determined in 100 NSCLC patients the expression of CD8, functional markers (IFN-γ, Granzyme B, and Perforin) and specific chemokines by quantitative real-time reverse transcriptase-PCR. Functional experiments were carried out to check whether docetaxel (DOC), a chemotherapeutic agent, modifies the expression of HMGB1 and CXCL11, and influences the infiltration properties of CD8⁺ T cells to the tumor microenvironment. The mechanism of the release of HMGB1 and CXCL11 was determined by flow cytometry, immunofluorescence and western blotting. In in vivo experiment, we confirmed how DOC enhanced the recruitment of HER2-CAR T cells to tumor sites.

RESULTS

We found that DOC upregulated the expression of chemokine receptor ligand CXCL11 in tumor microenvironment and subsequently enhanced CD8⁺ T cell recruitment. DOC treatment significantly increased HMGB1 release in an ROS-dependent manner. Recombinant protein HMGB1 stimulated the secretion of CXCL11 via NF-κB activation in vitro. Tumors from DOC-treated mice exhibited higher expression of HMGB1 and CXCL11, more HER2-CAR T cell infiltration, and reduced progression, relative to control. Increased HMGB1 and CXCL11 expressions were positively correlated with prolonged overall survival of lung cancer patients.

CONCLUSIONS

Our results demonstrate that DOC induces CD8⁺ T cell recruitment to the tumor microenvironment by enhancing the secretion of HMGB1 and CXCL11, thus improving the anti-tumor efficacy, indicating that modulating the HMGB1-CXCL11 axis might be helpful for NSCLC treatment.

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.

Redox-Mediated Mechanisms Fuel Monocyte Responses to CXCL12/HMGB1 in Active Rheumatoid Arthritis

Chemokine synergy-inducing molecules are emerging as regulating factors in cell migration. The alarmin HMGB1, in its reduced form, can complex with CXCL12 enhancing its activity on monocytes via the chemokine receptor CXCR4, while the form containing a disulfide bond, by binding to TLR2 or TLR4, initiates a cascade of events leading to production of cytokines and chemokines. So far, the possibility that the CXCL12/HMGB1 heterocomplex could be maintained in chronic inflammation was debated, due to the release of reactive oxygen species. Therefore, we have assessed if the heterocomplex could remain active in Rheumatoid Arthritis (RA) and its relevance in the disease assessment. Monocytes from RA patients with active disease require a low concentration of HMGB1 to enhance CXCL12-induced migration, in comparison to monocytes from patients in clinical remission or healthy donors. The activity of the heterocomplex depends on disease activity, on the COX2 and JAK/STAT pathways, and is determined by the redox potential of the microenvironment. In RA, the presence of an active thioredoxin system correlates with the enhanced cell migration, and with the presence of the heterocomplex in the synovial fluid. The present study highlights how, in an unbalanced microenvironment, the activity of the thioredoxin system plays a crucial role in sustaining inflammation. Prostaglandin E2 stimulation of monocytes from healthy donors is sufficient to recapitulate the response observed in patients with active RA. The activation of mechanisms counteracting the oxidative stress in the extracellular compartment preserves HMGB1 in its reduced form, and contributes to fuel the influx of inflammatory cells. Targeting the heterocomplex formation and its activity could thus be an additional tool for dampening the inflammation sustained by cell recruitment, for those patients with chronic inflammatory conditions who poorly respond to current therapies.

Asthma Endotyping and Biomarkers in Childhood Asthma

Childhood asthma represents a heterogeneous challenging disease, in particular in its severe forms. The identification of different asthma phenotypes has stimulated research in underlying molecular mechanisms, such as the endotypes, and paved the way to the search for related specific biomarkers, which may guide diagnosis, management, and predict response to treatment. A limited number of biomarkers are currently available in clinical practice in the pediatric population, mostly reflecting type 2-high airway inflammation. The identification of biomarkers of childhood asthma is an active area of research that holds a potential great clinical utility and may represent a step forward toward tailored management and therapy: the so-called Precision Medicine. The aim of the present review is to provide an updated overview of asthma endotyping, mostly focusing on novel noninvasive biomarkers in childhood asthma.

Induction of high-mobility group Box-1 in vitro and in vivo by respiratory syncytial virus

BackgroundDespite decades that have passed since its discovery, accurate biomarkers of respiratory syncytial virus (RSV) disease activity and effective therapeutic strategies are still lacking. The high-mobility group box type 1 (HMGB1) protein has been proposed as a possible link between RSV and immune system, but only limited information is currently available to support this hypothesis.MethodsExpression of HMGB1 gene and protein was analyzed by quantitative PCR, enzyme-linked immunosorbent assay (ELISA), western blot, immunocytochemistry, and confocal microscopy in immortalized and primary human bronchial epithelial cells, as well as in rat pup lungs. The role of HMGB1 in RSV infection was explored using glycyrrhizin, a selective HMGB1 inhibitor.ResultsRSV infection strongly induced HMGB1 expression both in vitro and in vivo. Glycyrrhizin dose-dependently inhibited HMGB1 upregulation in both RSV-infected immortalized and primary human bronchial epithelial cells, and this effect was associated with significant reduction of viral replication.ConclusionOur data suggest that HMGB1 expression increases during RSV replication. This seems to have a critical pathogenic role as its selective inhibition virtually modified the infection. These observations provide further insight into the pathophysiology of RSV infection and uncover a potential biomarker and therapeutic target for the most common respiratory infection of infancy.

Insight on the regulation of chemokine activities

The activity of chemokines is regulated by several mechanisms that control the final cellular response. The present review discusses the complexity of the regulation of the chemokine system, and the novel findings describing how in persistent infections, the expression of chemokine receptors on the surface of T cells does not correlate with their homing potential. Thanks to the latest advances in our comprehension of the chemokine system, novel approaches targeting chemokines, chemokine receptors, or protein of their signaling pathway should be considered in order to achieve a personalized therapy.

The differentiation of mesenchymal stem cells to vascular cells regulated by the HMGB1/RAGE axis: its application in cell therapy for transplant arteriosclerosis

BACKGROUND

Mesenchymal stem cell (MSC) transplantation shows promise for treating transplant arteriosclerosis, at least partly via promoting endothelial regeneration. However, the efficacy and safety are still under investigation especially regarding recent findings that neointimal smooth muscle cells are derived from MSC-like cells. The high mobility group box 1 (HMGB1)/receptor for advanced glycation end-product (RAGE) axis is involved in regulating proliferation, migration, and differentiation of MSCs, and therefore it can be presumably applied to improve the outcome of cell therapy. The aim of the current study was to investigate this hypothesis.

METHODS

Rat MSCs were treated with HMGB1 or modified with HMGB1 vectors to activate the HMGB1/RAGE axis. RAGE was targeted and inhibited by specific short hairpin RNA vectors. We assessed the capacity for cell proliferation, migration, and differentiation after vector transfection in vitro and in a rat model of transplant arteriosclerosis. The expression of CD31 and α-smooth muscle actin (αSMA) was determined to evaluate the differentiation of MSCs to endothelial cells and smooth muscle cells.

RESULTS

Exogenous HMGB1 treatment and transfection with HMGB1 vectors promoted MSC migration and vascular endothelial growth factor (VEGF)-induced differentiation to CD31+ cells while inhibiting their proliferation and platelet-derived growth factor (PDGF)-induced differentiation to αSMA+ cells. Such an effect was blocked by RAGE knockdown. HMGB1-modified cells preferably migrated to graft neointima and differentiated to CD31+ cells along with significant relief of transplant arteriosclerosis and inhibition of HMGB1 and RAGE expression in graft vessels. RAGE knockdown inhibited cell migration to graft vessels.

CONCLUSIONS

HMGB1 stimulated MSCs to migrate and differentiate to endothelial cells via RAGE signaling, which we translated to successful application in cell therapy for transplant arteriosclerosis.

Alarmins in Frozen Shoulder: A Molecular Association Between Inflammation and Pain

BACKGROUND

The pathophysiological mechanisms behind proliferation of fibroblasts and deposition of dense collagen matrix in idiopathic frozen shoulder remain unclear. Alarmins (also known as danger signals) are endogenous molecules that are released into the extracellular milieu after infection or tissue injury and that signal cell and tissue damage.

PURPOSE

To investigate whether the presence of alarmins is higher in patients with idiopathic frozen shoulder than in control subjects.

STUDY DESIGN

Controlled laboratory study.

METHODS

Shoulder capsule samples were collected from 10 patients with idiopathic frozen shoulder and 10 patients with unstable shoulders (control). The samples were stained with hematoxylin and eosin (H&E) and analyzed by immunohistochemistry using antibodies against alarmin molecules including high-mobility group protein B1 (HMGB1), interleukin 33, S100A8, S100A9, and the peripheral nerve marker PGP9.5. Immunoreactivities were rated in a blinded fashion from "none" to "strong." Immunohistochemical distribution within the capsule was noted. Before surgery, patient-ranked pain frequency, severity, stiffness, and the range of passive shoulder motion were recorded and statistically analyzed.

RESULTS

Compared with control patients, patients with frozen shoulder had greater frequency and severity of self-reported pain ( P = .02) and more restricted range of motion in all planes ( P < .05). H&E-stained capsular tissue from frozen shoulder showed fibroblastic hypercellularity and increased subsynovial vascularity. Immunoreactivity of alarmins was significantly stronger in frozen shoulder capsules compared with control capsules ( P < .05). Furthermore, the expression of the alarmin molecule HMGB1 significantly correlated ( r > 0.9, P < .05) with the severity of patient-reported pain.

CONCLUSION

This study demonstrates a potential role for key molecular danger signals in frozen shoulder and suggests an association between the expression of danger molecules and the pain experienced by patients.

Innate Immune Cells: Gatekeepers of Endometriotic Lesions Growth and Vascularization

Infiltration by inflammatory leukocytes is a hallmark of all forms of endometriosis. Conversely, the innate immune system plays a key role in regulating events such as cell adhesion, migration, survival and neoangiogenesis of transformed or ectopic tissue. All these features are involved, and possibly required, in the development of endometriotic lesions. Recent data suggest that infiltrating leukocytes are not a mere epiphenomenon but represent an actual requirement for the development of the disease. In this scenario, the functional plasticity of infiltrating macrophages is a key event in the origin and maintenance of endometriotic lesions: the erroneous polarization of macrophages towards cells sustaining angiogenesis and tissue remodeling represents a potential target for novel molecular therapies.

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.

HMGB1 as a new biomarker of celiac disease in children: A multicenter study

OBJECTIVE

Despite the availability of specific sierology and point-of-care tests, the phenotypic heterogeneity and the symptoms fluctuation as well as the "open-window" existing among the late and silent forms cause often a delayed celiac disease (CD) diagnosis. Recently, it has been reported that high mobility group box 1 (HMGB1) mediates inflammation and gastrointestinal barrier failure. The aim of this study was to detect serum HMGB1 levels at CD diagnosis and to evaluate the relationship between serum HMGB1 levels and clinical and histologic phenotypes.

METHODS

49 CD children and 44 healthy children were enrolled. Specific antitissue transglutaminase type 2, antideaminated form of gliadin antibodies, serum HMGB1 levels, and typical histopathological changes in duodenal mucosa were performed in all patients. Mucosal lesions were classified according to Marsh classification. In relation to clinical presentation, we classified patients into: typical, atypical and silent forms.

RESULTS

Serum HMGB1 levels were significantly higher in those with CD than those in the healthy control group (P < 0.001). Significant differences in serum HMGB1 levels were detected in children with typical CD form compared to both children with atypical CD form (P < 0.001) and children with silent CD form (P < 0.001). By using the Marsh classification, significant differences were found between subjects with grade 3 B-B1 and 3 C-B2 and villous atrophy, respectively (P < 0.05). On the contrary, no significant differences in serum HMGB1 levels in subgroups of children with grade 3 A compared to grade 3 B-B1 were detected.

CONCLUSIONS

HMGB1 is upregulated at diagnosis in all CD children, especially in typical form, and reflecting the histologic severity of disease.

RAGE Enhances TLR Responses through Binding and Internalization of RNA

Nucleic acid recognition is an important mechanism that enables the innate immune system to detect microbial infection and tissue damage. To minimize the recognition of self-derived nucleic acids, all nucleic acid-sensing signaling receptors are sequestered away from the cell surface and are activated in the cytoplasm or in endosomes. Nucleic acid sensing in endosomes relies on members of the TLR family. The receptor for advanced glycation end-products (RAGE) was recently shown to bind DNA at the cell surface, facilitating DNA internalization and subsequent recognition by TLR9. In this article, we show that RAGE binds RNA molecules in a sequence-independent manner and enhances cellular RNA uptake into endosomes. Gain- and loss-of-function studies demonstrate that RAGE increases the sensitivity of all ssRNA-sensing TLRs (TLR7, TLR8, TLR13), suggesting that RAGE is an integral part of the endosomal nucleic acid-sensing system.

High mobility group box 1 (HMGB1): dual functions in the cochlear auditory neurons in response to stress?

High mobility group box 1 (HMGB1) is a DNA-binding protein that facilitates gene transcription and may act extracellularly as a late mediator of inflammation. The roles of HMGB1 in the pathogenesis of the spiral ganglion neurons (SGNs) of the cochlea are currently unknown. In the present study, we tested the hypothesis that early phenotypical changes in the SGNs of the amikacin-poisoned rat cochlea are mediated by HMGB1. Our results showed that a marked downregulation of HMGB1 had occurred by completion of amikacin treatment, coinciding with acute damage at the dendrite extremities of the SGNs. A few days later, during the recovery of the SGN dendrites, the protein was re-expressed and transiently accumulated within the nuclei of the SGNs. The phosphorylated form of the transcription factor c-Jun (p-c-Jun) was concomitantly detected in the nuclei of the SGNs where it often co-localized with HMGB1, while the anti-apoptotic protein BCL2 was over-expressed in the cytoplasm. In animals co-treated with amikacin and the histone deacetylase inhibitor trichostatin A, both HMGB1 and p-c-Jun were exclusively found within the cytoplasm. The initial disappearance of HMGB1 from the affected SGNs may be due to its release into the external medium, where it may have a cytokine-like function. Once re-expressed and translocated into the nucleus, HMGB1 may facilitate the transcriptional activity of p-c-Jun, which in turn may promote repair mechanisms. Our study therefore suggests that HMGB1 can positively influence the survival of SGNs following ototoxic exposure via both its extracellular and intranuclear functions.

Modulation of Chemokine Responses: Synergy and Cooperativity

Chemokine biology is mediated by more complex interactions than simple monomolecular ligand–receptor interactions, as chemokines can form higher order quaternary structures, which can also be formed after binding to glycosaminoglycans (GAGs) on endothelial cells, and their receptors are found as dimers and/or oligomers at the cell surface. Due to the complexity of the chemokine binding and signaling system, several mechanisms have been proposed to provide an explanation for the synergy observed between chemokines in leukocyte migration. Pioneering studies on interactions between different chemokines have revealed that they can act as antagonists, or synergize with other chemokines. The synergism can occur at different levels, involving either two chemokine receptors triggered simultaneously or sequentially exposed to their agonists, or the activation of one type of chemokine receptor triggered by chemokine heterocomplexes. In addition to the several chemokines that, by forming a heterocomplex with chemokine receptor agonists, act as enhancers of molecules of the same family, we have recently identified HMGB1, an endogenous damage-associated molecular patterns (DAMPs) molecule, as an enhancer of the activity of CXCL12. It is now evident that synergism between chemokines is crucial at the very early stage of inflammation. In addition, the low-affinity interaction with GAGs has recently been shown to induce cooperativity allowing synergy or inhibition of activity by displacement of other ligands.

Disruption of a Regulatory Network Consisting of Neutrophils and Platelets Fosters Persisting Inflammation in Rheumatic Diseases

A network of cellular interactions that involve blood leukocytes and platelets maintains vessel homeostasis. It plays a critical role in the response to invading microbes by recruiting intravascular immunity and through the generation of neutrophil extracellular traps (NETs) and immunothrombosis. Moreover, it enables immune cells to respond to remote chemoattractants by crossing the endothelial barrier and reaching sites of infection. Once the network operating under physiological conditions is disrupted, the reciprocal activation of cells in the blood and the vessel walls determines the vascular remodeling via inflammatory signals delivered to stem/progenitor cells. A deregulated leukocyte/mural cell interaction is an early critical event in the natural history of systemic inflammation. Despite intense efforts, the signals that initiate and sustain the immune-mediated vessel injury, or those that enforce the often-prolonged phases of clinical quiescence in patients with vasculitis, have only been partially elucidated. Here, we discuss recent evidence that implicates the prototypic damage-associated molecular pattern/alarmin, the high mobility group box 1 (HMGB1) protein in systemic vasculitis and in the vascular inflammation associated with systemic sclerosis. HMGB1 could represent a player in the pathogenesis of rheumatic diseases and an attractive target for molecular interventions.

The Emerging Role of HMGB1 in Neuropathic Pain: A Potential Therapeutic Target for Neuroinflammation

Neuropathic pain (NPP) is intolerable, persistent, and specific type of long-term pain. It is considered to be a direct consequence of pathological changes affecting the somatosensory system and can be debilitating for affected patients. Despite recent progress and growing interest in understanding the pathogenesis of the disease, NPP still presents a major diagnostic and therapeutic challenge. High mobility group box 1 (HMGB1) mediates inflammatory and immune reactions in nervous system and emerging evidence reveals that HMGB1 plays an essential role in neuroinflammation through receptors such as Toll-like receptors (TLR), receptor for advanced glycation end products (RAGE), C-X-X motif chemokines receptor 4 (CXCR4), and N-methyl-D-aspartate (NMDA) receptor. In this review, we present evidence from studies that address the role of HMGB1 in NPP. First, we review studies aimed at determining the role of HMGB1 in NPP and discuss the possible mechanisms underlying HMGB1-mediated NPP progression where receptors for HMGB1 are involved. Then we review studies that address HMGB1 as a potential therapeutic target for NPP.

The role of high mobility group box 1 (HMGB1) in the pathogenesis of kidney diseases

High mobility group box 1 (HMGB1) is a nuclear protein that can bind to DNA and act as a co-factor for gene transcription. When released into extracellular fluid, it plays a proinflammatory role by acting as a damage-associated molecular pattern molecule (DAMP) (also known as an alarmin) to initiate innate immune responses by activating multiple cell surface receptors such as the receptor for advanced glycation end-products (RAGE) and toll-like receptors (TLRs), TLR2, TLR4 or TLR9. This proinflammatory role is now considered to be important in the pathogenesis of a wide range of kidney diseases whether they result from hemodynamic changes, renal tubular epithelial cell apoptosis, kidney tissue fibrosis or inflammation. This review summarizes our current understanding of the role of HMGB1 in kidney diseases and how the HMGB1-mediated signaling pathway may constitute a new strategy for the treatment of kidney diseases.

Vascular Remodelling and Mesenchymal Transition in Systemic Sclerosis

Fibrosis of the skin and of internal organs, autoimmunity, and vascular inflammation are hallmarks of Systemic Sclerosis (SSc). The injury and activation of endothelial cells, with hyperplasia of the intima and eventual obliteration of the vascular lumen, are early features of SSc. Reduced capillary blood flow coupled with deficient angiogenesis leads to chronic hypoxia and tissue ischemia, enforcing a positive feed-forward loop sustaining vascular remodelling, further exacerbated by extracellular matrix accumulation due to fibrosis. Despite numerous developments and a growing number of controlled clinical trials no treatment has been shown so far to alter SSc natural history, outlining the need of further investigation in the molecular pathways involved in the pathogenesis of the disease. We review some processes potentially involved in SSc vasculopathy, with attention to the possible effect of sustained vascular inflammation on the plasticity of vascular cells. Specifically we focus on mesenchymal transition, a key phenomenon in the cardiac and vascular development as well as in the remodelling of injured vessels. Recent work supports the role of transforming growth factor-beta, Wnt, and Notch signaling in these processes. Importantly, endothelial-mesenchymal transition may be reversible, possibly offering novel cues for treatment.

Emphysema requires the receptor for advanced glycation end-products triggering on structural cells

Pulmonary emphysema is characterized by persistent inflammation and progressive alveolar destruction. The receptor for advanced glycation end-products (RAGE) is a multiligand cell surface receptor reported to be involved in the process of acute alveolar epithelial cell injury. However, studies that address the role of RAGE in pulmonary emphysema are inconclusive. We investigated the role of RAGE in the development of elastase-induced pulmonary inflammation and emphysema in mice. RAGE-sufficient (RAGE(+/+)) mice and RAGE-deficient (RAGE(-/-)) mice were treated with intratracheal elastase on Day 0. Airway inflammation, static lung compliance, lung histology, and the levels of neutrophil-related chemokine and proinflammatory cytokines in bronchoalveolar lavage fluid were determined on Days 4 and 21. Neutrophilia in bronchoalveolar lavage fluid, seen in elastase-treated RAGE(+/+) mice, was reduced in elastase-treated RAGE(-/-) mice on Day 4, and was associated with decreased levels of keratinocyte chemoattractant, macrophage inflammatory protein-2, and IL-1β. Static lung compliance values and emphysematous changes in the lung tissue were decreased in RAGE(-/-) mice compared with RAGE(+/+) mice on Day 21 after elastase treatment. Experiments using irradiated, bone marrow-chimeric mice showed that the mice expressing RAGE on radioresistant structural cells, but not hematopoietic cells, developed elastase-induced neutrophilia and emphysematous change in the lung. In contrast, mice expressing RAGE on hematopoietic cells, but not radioresistant structural cells, showed reduced neutrophilia and emphysematous change in the lung. These data identify the importance of RAGE expressed on lung structural cells in the development of elastase-induced pulmonary inflammation and emphysema. Thus, RAGE represents a novel therapeutic target for preventing pulmonary emphysema.

The role of danger signals and ectonucleotidases in acute graft-versus-host disease

Allogeneic hematopoietic cell transplantation (allo-HCT) represents the only curative treatment approach for many patients with benign or malignant diseases of the hematopoietic system. However, post-transplant morbidity and mortality are significantly increased by the development of acute graft-versus-host disease (GvHD). While alloreactive T cells act as the main cellular mediator of the GvH reaction, recent evidence suggests a critical role of the innate immune system in the early stages of GvHD initiation. Danger-associated molecular patterns released from the intracellular space as well as from the extracellular matrix activate antigen-presenting cells and set pro-inflammatory pathways in motion. This review gives an overview about danger signals representing therapeutic targets with a clinical perspective with a particular focus on extracellular nucleotides and ectonucleotidases.

Cell death, clearance and immunity in the skeletal muscle

The skeletal muscle is an immunologically unique tissue. Leukocytes, virtually absent in physiological conditions, are quickly recruited into the tissue upon injury and persist during regeneration. Apoptosis, necrosis and autophagy coexist in the injured/regenerating muscles, including those of patients with neuromuscular disorders, such as inflammatory myopathies, dystrophies, metabolic and mitochondrial myopathies and drug-induced myopathies. Macrophages are able to alter their function in response to microenvironment conditions and as a consequence coordinate changes within the tissue from the early injury throughout regeneration and eventual healing, and regulate the activation and the function of stem cells. Early after injury, classically activated macrophages ('M1') dominate the picture. Alternatively activated M2 macrophages predominate during resolution phases and regulate the termination of the inflammatory responses. The dynamic M1/M2 transition is increasingly felt to be the key to the homeostasis of the muscle. Recognition and clearance of debris originating from damaged myofibers and from dying stem/progenitor cells, stromal cells and leukocytes are fundamental actions of macrophages. Clearance of apoptotic cells and M1/M2 transition are causally connected and represent limiting steps for muscle healing. The accumulation of apoptotic cells, which reflects their defective clearance, has been demonstrated in various tissues to prompt autoimmunity against intracellular autoantigens. In the muscle, in the presence of type I interferon, apoptotic myoblasts indeed cause the production of autoantibodies, lymphocyte infiltration and continuous cycles of muscle injury and regeneration, mimicking human inflammatory myopathies. The clearance of apoptotic cells thus modulates the homeostatic response of the skeletal muscle to injury. Conversely, defects in the process may have deleterious local effects, guiding maladaptive tissue remodeling with collagen and fat accumulation and promoting autoimmunity itself. There is strong promise for novel treatments based on new knowledge of cell death, clearance and immunity in the muscle.

Leukocytes recruited by tumor-derived HMGB1 sustain peritoneal carcinomatosis

The factors that determine whether disseminated transformed cells in vivo yield neoplastic lesions have only been partially identified. We established an ad hoc model of peritoneal carcinomatosis by injecting colon carcinoma cells in mice. Tumor cells recruit inflammatory leukocytes, mostly macrophages, and generate neoplastic peritoneal lesions. Phagocyte depletion via clodronate treatment reduces neoplastic growth. Colon carcinoma cells release a prototypic damage-associated molecular pattern (DAMP)/alarmin, High Mobility Group Box1 (HMGB1), which attracts leukocytes. Exogenous HMGB1 accelerates leukocyte recruitment, macrophage infiltration, tumor growth and vascularization. Lentiviral-based HMGB1 knockdown or pharmacological interference with its extracellular impair macrophage recruitment and tumor growth. Our findings provide a preclinical proof of principle that strategies based on preventing HMGB1-driven recruitment of leukocytes could be used for treating peritoneal carcinomatosis.

High mobility group box 1-immobilized nanofibrous scaffold enhances vascularization, osteogenesis and stem cell recruitment

An engineered, multi-functional HMGB1-immobilized scaffold is developed. HMGB1 is immobilized on the surface of electrospinning poly-l-lactide (PLLA)/polycaprolactone (PCL) nanofibers via heparin, which is used as a “trigger” signal to make the bone scaffold capable of enhancing vascularization, inducing osteogenesis and recruiting stem cells.

Chemokine interaction with synergy-inducing molecules: fine tuning modulation of cell trafficking

Review on synergistic activities induced by heterocomplexes formed with chemokines.

Directed migration and arrest of leukocytes during homeostasis, inflammation, and tumor development is mediated by the chemokine system, which governs leukocyte migration and activities. Although we understand well the effects of different chemokines one by one, much less was known about the potential consequences of the concomitant expression of multiple chemokines or of their interaction with inflammatory molecules on leukocyte migration and functions. In the past 10 yr, several studies revealed the existence of additional features of chemokines: they can antagonize chemokine receptors or synergize with other chemokines, also by forming heterocomplexes. Moreover, recent data show that not only chemokines but also the alarmin high-mobility group box 1 can for a complex with CXCL12, enhancing its potency on CXCR4. The molecular mechanism underlying the effect of the heterocomplex has been partially elucidated, whereas its structure is a matter of current investigations. The present review discusses the current knowledge and relevance of the functions of heterocomplexes formed between chemokines or between the chemokine CXCL12 and the alarmin high-mobility group box 1. These studies highlight the importance of taking into account, when approaching innovative therapies targeting the chemokine system, also the fact that some chemokines and molecules released in inflammation, can considerably affect the activity of chemokine receptor agonists.

The HMGB1-RAGE Inflammatory Pathway: Implications for Brain Injury-Induced Pulmonary Dysfunction

SIGNIFICANCE

Deceased patients who have suffered severe traumatic brain injury (TBI) are the largest source of organs for lung transplantation. However, due to severely compromised pulmonary lung function, only one-third of these patients are eligible organ donors, with far fewer capable of donating lungs (∼ 20%). As a result of this organ scarcity, understanding and controlling the pulmonary pathophysiology of potential donors are key to improving the health and long-term success of transplanted lungs.

RECENT ADVANCES

Although the exact mechanism by which TBI produces pulmonary pathophysiology remains unclear, it may be related to the release of damage-associated molecular patterns (DAMPs) from the injured tissue. These heterogeneous, endogenous host molecules can be rapidly released from damaged or dying cells and mediate sterile inflammation following trauma. In this review, we highlight the interaction of the DAMP, high-mobility group box protein 1 (HMGB1) with the receptor for advanced glycation end-products (RAGE), and toll-like receptor 4 (TLR4).

CRITICAL ISSUES

Recently published studies are reviewed, implicating the release of HMGB1 as producing marked changes in pulmonary inflammation and physiology following trauma, followed by an overview of the experimental evidence demonstrating the benefits of blocking the HMGB1-RAGE axis.

FUTURE DIRECTIONS

Targeting the HMGB1 signaling axis may increase the number of lungs available for transplantation and improve long-term benefits for organ recipient patient outcomes.

Innate Immunity and Biomaterials at the Nexus: Friends or Foes

Biomaterial implants are an established part of medical practice, encompassing a broad range of devices that widely differ in function and structural composition. However, one common property amongst biomaterials is the induction of the foreign body response: an acute sterile inflammatory reaction which overlaps with tissue vascularisation and remodelling and ultimately fibrotic encapsulation of the biomaterial to prevent further interaction with host tissue. Severity and clinical manifestation of the biomaterial-induced foreign body response are different for each biomaterial, with cases of incompatibility often associated with loss of function. However, unravelling the mechanisms that progress to the formation of the fibrotic capsule highlights the tightly intertwined nature of immunological responses to a seemingly noncanonical “antigen.” In this review, we detail the pathways associated with the foreign body response and describe possible mechanisms of immune involvement that can be targeted. We also discuss methods of modulating the immune response by altering the physiochemical surface properties of the biomaterial prior to implantation. Developments in these areas are reliant on reproducible and effective animal models and may allow a “combined” immunomodulatory approach of adapting surface properties of biomaterials, as well as treating key immune pathways to ultimately reduce the negative consequences of biomaterial implantation.

Extracellular high-mobility group box 1 protein (HMGB1) as a mediator of persistent pain

Although originally described as a highly conserved nuclear protein, high-mobility group box 1 protein (HMGB1) has emerged as a danger-associated molecular pattern molecule protein (DAMP) and is a mediator of innate and specific immune responses. HMGB1 is passively or actively released in response to infection, injury and cellular stress, providing chemotactic and cytokine-like functions in the extracellular environment, where it interacts with receptors such as receptor for advanced glycation end products (RAGE) and several Toll-like receptors (TLRs). Although HMGB1 was first revealed as a key mediator of sepsis, it also contributes to a number of other conditions and disease processes. Chronic pain arises as a direct consequence of injury, inflammation or diseases affecting the somatosensory system and can be devastating for the affected patients. Emerging data indicate that HMGB1 is also involved in the pathology of persistent pain. Here, we give an overview of HMGB1 as a proinflammatory mediator, focusing particularly on the role of HMGB1 in the induction and maintenance of hypersensitivity in experimental models of pain and discuss the therapeutic potential of targeting HMGB1 in conditions of chronic pain.

Necrotic cell-derived high mobility group box 1 attracts antigen-presenting cells but inhibits hepatocyte growth factor-mediated tropism of mesenchymal stem cells for apoptotic cell death

Tissue damage due to apoptotic or necrotic cell death typically initiates distinct cellular responses, leading either directly to tissue repair and regeneration or to immunological processes first, to clear the site, for example, of potentially damage-inducing agents. Mesenchymal stem cells (MSC) as well as immature dendritic cells (iDC) and monocytes migrate to injured tissues. MSC have regenerative capacity, whereas monocytes and iDC have a critical role in inflammation and induction of immune responses, including autoimmunity after tissue damage. Here, we investigated the influence of apoptotic and necrotic cell death on recruitment of MSC, monocytes and iDC, and identified hepatocyte growth factor (HGF) and the alarmin high mobility group box 1 (HMGB1) as key factors differentially regulating these migratory responses. MSC, but not monocytes or iDC, were attracted by apoptotic cardiomyocytic and neuronal cells, whereas necrosis induced migration of monocytes and iDC, but not of MSC. Only apoptotic cell death resulted in HGF production and HGF-mediated migration of MSC towards the apoptotic targets. In contrast, HMGB1 was predominantly released by the necrotic cells and mediated recruitment of monocytes and iDC via the receptor of advanced glycation end products. Moreover, necrotic cardiomyocytic and neuronal cells caused an HMGB1/toll-like receptor-4-dependent inhibition of MSC migration towards apoptosis or HGF, while recruitment of monocytes and iDC by necrosis or HMGB1 was not affected by apoptotic cells or HGF. Thus, the type of cell death differentially regulates recruitment of either MSC or monocytes and iDC through HGF and HMGB1, respectively, with a dominant, HMGB1-mediated role of necrosis in determining tropism after tissue injury.