RAGE-independent autoreactive B cell activation in response to chromatin and HMGB1/DNA immune complexes

Leveraging diverse cell-death patterns to predict the prognosis, immunotherapy and drug sensitivity of clear cell renal cell carcinoma

Clear cell renal cell carcinoma (ccRCC) poses clinical challenges due to its varied prognosis, tumor microenvironment attributes, and responses to immunotherapy. We established a novel Programmed Cell Death-related Signature (PRS) for ccRCC assessment, derived through the Least Absolute Shrinkage and Selection Operator (LASSO) regression method. We validated PRS using the E-MTAB-1980 dataset and created PCD-related clusters via non-negative matrix factorization (NMF). Our investigation included an in-depth analysis of immune infiltration scores using various algorithms. Additionally, we integrated data from the Cancer Immunome Atlas (TCIA) for ccRCC immunotherapy insights and leveraged the Genomics of Drug Sensitivity in Cancer (GDSC) database to assess drug sensitivity models. We complemented our findings with single-cell sequencing data and employed the Clinical Proteomic Tumor Analysis Consortium (CPTAC) and qRT-PCR to compare gene expression profiles between cancerous and paracancerous tissues. PRS serves as a valuable tool for prognostication, immune characterization, tumor mutation burden estimation, immunotherapy response prediction, and drug sensitivity assessment in ccRCC. We identify five genes with significant roles in cancer promotion and three genes with cancer-suppressive properties, further validated by qRT-PCR and CPTAC analyses, showcasing gene expression differences in ccRCC tissues. Our study introduces an innovative PCD model that amalgamates diverse cell death patterns to provide accurate predictions for clinical outcomes, mutational profiles, and immune characteristics in ccRCC. Our findings hold promise for advancing personalized treatment strategies in ccRCC patients.

Targeting HMGB1: A Potential Therapeutic Strategy for Chronic Kidney Disease

High-mobility group protein box 1 (HMGB1) is a member of a highly conserved high-mobility group protein present in all cell types. HMGB1 plays multiple roles both inside and outside the cell, depending on its subcellular localization, context, and post-translational modifications. HMGB1 is also associated with the progression of various diseases. Particularly, HMGB1 plays a critical role in CKD progression and prognosis. HMGB1 participates in multiple key events in CKD progression by activating downstream signals, including renal inflammation, the onset of persistent fibrosis, renal aging, AKI-to-CKD transition, and important cardiovascular complications. More importantly, HMGB1 plays a distinct role in the chronic pathophysiology of kidney disease, which differs from that in acute lesions. This review describes the regulatory role of HMGB1 in renal homeostasis and summarizes how HMGB1 affects CKD progression and prognosis. Finally, some promising therapeutic strategies for the targeted inhibition of HMGB1 in improving CKD are summarized. Although the application of HMGB1 as a therapeutic target in CKD faces some challenges, a more in-depth understanding of the intracellular and extracellular regulatory mechanisms of HMGB1 that underly the occurrence and progression of CKD might render HMGB1 an attractive therapeutic target for CKD.

Regulation of beta-amyloid for the treatment of Alzheimer's disease: Research progress of therapeutic strategies and bioactive compounds

Alzheimer's disease (AD) is a progressive neurodegenerative disease that is difficult to treat. Extracellular amyloid is the principal pathological criterion for the diagnosis of AD. Amyloid β (Aβ) interacts with various receptor molecules on the plasma membrane and mediates a series of signaling pathways that play a vital role in the occurrence and development of AD. Research on receptors that interact with Aβ is currently ongoing. Overall, there are no effective medications to treat AD. In this review, we first discuss the importance of Aβ in the pathogenesis of AD, then summarize the latest progress of Aβ-related targets and compounds. Finally, we put forward the challenges and opportunities in the development of effective AD therapies.

Programmed Cell Death Tunes Tumor Immunity

The demise of cells in various ways enables the body to clear unwanted cells. Studies over the years revealed distinctive molecular mechanisms and functional consequences of several key cell death pathways. Currently, the most intensively investigated programmed cell death (PCD) includes apoptosis, necroptosis, pyroptosis, ferroptosis, PANoptosis, and autophagy, which has been discovered to play crucial roles in modulating the immunosuppressive tumor microenvironment (TME) and determining clinical outcomes of the cancer therapeutic approaches. PCD can play dual roles, either pro-tumor or anti-tumor, partly depending on the intracellular contents released during the process. PCD also regulates the enrichment of effector or regulatory immune cells, thus participating in fine-tuning the anti-tumor immunity in the TME. In this review, we focused primarily on apoptosis, necroptosis, pyroptosis, ferroptosis, PANoptosis, and autophagy, discussed the released molecular messengers participating in regulating their intricate crosstalk with the immune response in the TME, and explored the immunological consequence of PCD and its implications in future cancer therapy developments.

HMGB1-Mediated Activation of the Inflammatory-Reparative Response Following Myocardial Infarction

Different cell types belonging to the innate and adaptive immune system play mutually non-exclusive roles during the different phases of the inflammatory-reparative response that occurs following myocardial infarction. A timely and finely regulation of their action is fundamental for the process to properly proceed. The high-mobility group box 1 (HMGB1), a highly conserved nuclear protein that in the extracellular space can act as a damage-associated molecular pattern (DAMP) involved in a large variety of different processes, such as inflammation, migration, invasion, proliferation, differentiation, and tissue regeneration, has recently emerged as a possible regulator of the activity of different immune cell types in the distinct phases of the inflammatory reparative process. Moreover, by activating endogenous stem cells, inducing endothelial cells, and by modulating cardiac fibroblast activity, HMGB1 could represent a master regulator of the inflammatory and reparative responses following MI. In this review, we will provide an overview of cellular effectors involved in these processes and how HMGB1 intervenes in regulating each of them. Moreover, we will summarize HMGB1 roles in regulating other cell types that are involved in the different phases of the inflammatory-reparative response, discussing how its redox status could affect its activity.

Peritumoral B cells drive proangiogenic responses in HMGB1-enriched esophageal squamous cell carcinoma

Several B-cell subsets with distinct functions and polarized cytokine profiles that extend beyond antibody production have been reported in different cancers. Here we have demonstrated that proliferating B cells were predominantly found in the peritumoral region of esophageal squamous cell carcinoma (ESCC). These B cells were enriched in tumor nests with high expression of high-mobility group box 1 (HMGB1). High densities of peritumoral proliferating B cells and concomitantly high intratumoral HMGB1 expression showed improved prognostic significance, surpassing prognostic stratification of ESCC patients based on HMGB1 positivity alone. This striking association led us to set up models to test whether cancer-derived HMGB1 could shape tumor microenvironment via modulation on B cells. Overexpression of HMGB1 in ESCC cell lines (KYSE510 and EC18) enhanced proliferation and migration of B cells. Transcriptomic analysis showed that migratory B cells exhibited high enrichment of proangiogenic genes. VEGF expression in proliferating B cells was induced upon co-culture of HMGB1-overexpressing tumor cells and B cells. Secretome array profiling of conditioned media (CM) from the co-culture revealed rich expression of proangiogenic proteins. Consequently, incubation of human umbilical vein endothelial cells with CM promoted angiogenesis in tube formation and migration assays. HMGB1 inhibitor, glycyrrhizin, abolishes all the observed proangiogenic phenotypes. Finally, co-injection of B cells and CM with HMGB1-overexpressing tumor cells, but not with glycyrrhizin, significantly enhanced tumor growth associated with increased microvascular density in ESCC xenograft mice model. Our results indicate that cancer-derived HMGB1 elevates angiogenesis in ESCC by shifting the balance toward proangiogenic signals in proliferating B cells.

Elucidating the Motif for CpG Oligonucleotide Binding to the Dendritic Cell Receptor DEC-205 Leads to Improved Adjuvants for Liver-Resident Memory

DEC-205 is a cell-surface receptor that transports bound ligands into the endocytic pathway for degradation or release within lysosomal endosomes. This receptor has been reported to bind a number of ligands, including keratin, and some classes of CpG oligodeoxynucleotides (ODN). In this study, we explore in detail the requirements for binding ODNs, revealing that DEC-205 efficiently binds single-stranded, phosphorothioated ODN of ≥14 bases, with preference for the DNA base thymidine, but with no requirement for a CpG motif. DEC-205 fails to bind double-stranded phosphodiester ODN, and thus does not bind the natural type of DNA found in mammals. The ODN binding preferences of DEC-205 result in strong binding of B class ODN, moderate binding to C class ODN, minimal binding to P class ODN, and no binding to A class ODN. Consistent with DEC-205 binding capacity, induction of serum IL-12p70 or activation of B cells by each class of ODN correlated with DEC-205 dependence in mice. Thus, the greater the DEC-205 binding capacity, the greater the dependence on DEC-205 for optimal responses. Finally, by covalently linking a B class ODN that efficiently binds DEC-205, to a P class ODN that shows poor binding, we improved DEC-205 binding and increased adjuvancy of the hybrid ODN. The hybrid ODN efficiently enhanced induction of effector CD8 T cells in a DEC-205-dependent manner. Furthermore, the hybrid ODN induced robust memory responses, and was particularly effective at promoting the development of liver tissue-resident memory T cells.

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.

Dysbiosis-Related Advanced Glycation Endproducts and Trimethylamine N-Oxide in Chronic Kidney Disease

Chronic kidney disease (CKD) is a public health concern that affects approximately 10% of the global population. CKD is associated with poor outcomes due to high frequencies of comorbidities such as heart failure and cardiovascular disease. Uremic toxins are compounds that are usually filtered and excreted by the kidneys. With the decline of renal function, uremic toxins are accumulated in the systemic circulation and tissues, which hastens the progression of CKD and concomitant comorbidities. Gut microbial dysbiosis, defined as an imbalance of the gut microbial community, is one of the comorbidities of CKD. Meanwhile, gut dysbiosis plays a pathological role in accelerating CKD progression through the production of further uremic toxins in the gastrointestinal tracts. Therefore, the gut-kidney axis has been attracting attention in recent years as a potential therapeutic target for stopping CKD. Trimethylamine N-oxide (TMAO) generated by gut microbiota is linked to the progression of cardiovascular disease and CKD. Also, advanced glycation endproducts (AGEs) not only promote CKD but also cause gut dysbiosis with disruption of the intestinal barrier. This review summarizes the underlying mechanism for how gut microbial dysbiosis promotes kidney injury and highlights the wide-ranging interventions to counter dysbiosis for CKD patients from the view of uremic toxins such as TMAO and AGEs.

Nuclear Alarmin Cytokines in Inflammation

Pathogen-associated molecular patterns (PAMPs) are some nonspecific and highly conserved molecular structures of exogenous specific microbial pathogens, whose products can be recognized by pattern recognition receptor (PRR) on innate immune cells and induce an inflammatory response. Under physiological stress, activated or damaged cells might release some endogenous proteins that can also bind to PRR and cause a harmful aseptic inflammatory response. These endogenous proteins were named damage-associated molecular patterns (DAMPs) or alarmins. Indeed, alarmins can also play a beneficial role in the tissue repair in certain environments. Besides, some alarmin cytokines have been reported to have both nuclear and extracellular effects. This group of proteins includes high-mobility group box-1 protein (HMGB1), interleukin (IL)-33, IL-1α, IL-1F7b, and IL-16. In this article, we review the involvement of nuclear alarmins such as HMGB1, IL-33, and IL-1α under physiological state or stress state and suggest a novel activity of these molecules as central initiators in the development of sterile inflammation.

High Mobility Group Box 1 in Human Cancer

High mobility group box 1 (HMGB1) is an extremely versatile protein that is located predominantly in the nucleus of quiescent eukaryotic cells, where it is critically involved in maintaining genomic structure and function. During cellular stress, however, this multifaceted, cytokine-like protein undergoes posttranslational modifications that promote its translocation to the cytosol, from where it is released extracellularly, either actively or passively, according to cell type and stressor. In the extracellular milieu, HMGB1 triggers innate inflammatory responses that may be beneficial or harmful, depending on the magnitude and duration of release of this pro-inflammatory protein at sites of tissue injury. Heightened awareness of the potentially harmful activities of HMGB1, together with a considerable body of innovative, recent research, have revealed that excessive production of HMGB1, resulting from misdirected, chronic inflammatory responses, appears to contribute to all the stages of tumorigenesis. In the setting of established cancers, the production of HMGB1 by tumor cells per se may also exacerbate inflammation-related immunosuppression. These pro-inflammatory mechanisms of HMGB1-orchestrated tumorigenesis, as well as the prognostic potential of detection of elevated expression of this protein in the tumor microenvironment, represent the major thrusts of this review.

Impact of HMGB1, RAGE, and TLR4 in Alzheimer's Disease (AD): From Risk Factors to Therapeutic Targeting

Alzheimer’s disease (AD) is a devastating neurodegenerative disorder and a leading cause of dementia, with accumulation of amyloid-beta (Aβ) and neurofibrillary tangles (NFTs) as defining pathological features. AD presents a serious global health concern with no cure to date, reflecting the complexity of its pathogenesis. Recent evidence indicates that neuroinflammation serves as the link between amyloid deposition, Tau pathology, and neurodegeneration. The high mobility group box 1 (HMGB1) protein, an initiator and activator of neuroinflammatory responses, has been involved in the pathogenesis of neurodegenerative diseases, including AD. HMGB1 is a typical damage-associated molecular pattern (DAMP) protein that exerts its biological activity mainly through binding to the receptor for advanced glycation end products (RAGE) and toll-like receptor 4 (TLR4). RAGE and TLR4 are key components of the innate immune system that both bind to HMGB1. Targeting of HMGB1, RAGE, and TLR4 in experimental AD models has demonstrated beneficial effects in halting AD progression by suppressing neuroinflammation, reducing Aβ load and production, improving spatial learning, and inhibiting microglial stimulation. Herein, we discuss the contribution of HMGB1 and its receptor signaling in neuroinflammation and AD pathogenesis, providing evidence of its beneficial effects upon therapeutic targeting.

Effect of high mobility group box 1 on Toll-like receptor 9 in B cells in myeloperoxidase-ANCA-associated vasculitis

High mobility group box 1 (HMGB1) played pathogenic role in antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). Recent findings demonstrated that Toll-like receptor 9 (TLR9) was involved in B cell tolerance breaking of autoimmune disease, including AAV. Here, we investigated the effect of HMGB1 on TLR9 in B cells of AAV. In the present work, patients with myeloperoxidase (MPO)-AAV in active stage were recruited. Intracellular TLR9 expression in various B cell subpopulations of the whole blood was detected by flow cytometry and the correlation with clinical data was analysed. Our results showed that intracellular TLR9 expression in B cells, memory B cells and plasmablasts correlated with erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP). In particular, TLR9 expression in plasma cells correlated with ESR, CRP, serum creatinine, eGFR, and Birmingham Vasculitis Activity Score. To further explore the effect of HMGB1 on B cell, peripheral blood mononuclear cells (PBMCs) from AAV patients were isolated. After stimulated with HMGB1, TLR9 expression in various B cell subpopulations and proliferation ratio of live B cells were analysed by flow cytometry. We found that TLR9 expression in plasma cells and the proliferation ratio of live B cells by HMGB1 stimulation were significantly upregulated compared with the control group. Therefore, TLR9 expression in plasma cells was associated with disease activity of MPO-AAV. HMGB1 could enhance TLR9 expression in plasma cells and B cell proliferation. These indicated a role of HMGB1 on TLR9 in B cells in MPO-AAV, which would provide potential clues for intervention strategies.

Emergence of antibodies endowed with proteolytic activity against High-mobility group box 1 protein (HMGB1) in patients surviving septic shock

High-mobility group box 1 (HMGB1) concentration in serum or plasma has been proposed as an important biological marker in various inflammation-related pathologies. We previously showed that low titer autoantibodies against HMGB1 could emerge during the course of sepsis. Importantly their presence was positively related with patients' survival. In this study, we focused on plasma samples from 2 patients who survived sepsis and exhibited high titer antibodies to HMGB1. These antibodies were proved to be specific for HMGB1 since they did not bind to HMGB2 or to human serum albumin. Following IgG purification, it has shown that both patients secreted HMGB1-hydrolyzing autoantibodies in vitro. These findings suggested that proteolytic antibodies directed against HMGB1 can be produced in patients surviving septic shock.

The Receptor for Advanced Glycation End Products (RAGE) and DIAPH1: Implications for vascular and neuroinflammatory dysfunction in disorders of the central nervous system

The Receptor for Advanced Glycation End Products (RAGE) is expressed by multiple cell types in the brain and spinal cord that are linked to the pathogenesis of neurovascular and neurodegenerative disorders, including neurons, glia (microglia and astrocytes) and vascular cells (endothelial cells, smooth muscle cells and pericytes). Mounting structural and functional evidence implicates the interaction of the RAGE cytoplasmic domain with the formin, Diaphanous1 (DIAPH1), as the key cytoplasmic hub for RAGE ligand-mediated activation of cellular signaling. In aging and diabetes, the ligands of the receptor abound, both in the central nervous system (CNS) and in the periphery. Such accumulation of RAGE ligands triggers multiple downstream events, including upregulation of RAGE itself. Once set in motion, cell intrinsic and cell-cell communication mechanisms, at least in part via RAGE, trigger dysfunction in the CNS. A key outcome of endothelial dysfunction is reduction in cerebral blood flow and increased permeability of the blood brain barrier, conditions that facilitate entry of activated leukocytes into the CNS, thereby amplifying primary nodes of CNS cellular stress. This contribution details a review of the ligands of RAGE, the mechanisms and consequences of RAGE signal transduction, and cites multiple examples of published work in which RAGE contributes to the pathogenesis of neurovascular perturbation. Insights into potential therapeutic modalities targeting the RAGE signal transduction axis for disorders of CNS vascular dysfunction and neurodegeneration are also discussed.

Clinical Implications of Excessive Neutrophil Extracellular Trap Formation in Renal Autoimmune Diseases

Neutrophil extracellular traps (NETs) are extracellular DNA structures covered with antimicrobial peptides, danger molecules, and autoantigens that can be released by neutrophils. NETs are an important first-line defense mechanism against bacterial, viral, fungal, and parasitic infections, but they can also play a role in autoimmune diseases. NETs are immunogenic and toxic structures that are recognized by the autoantibodies of patients with antineutrophil cytoplasmic antibodies−associated vasculitis (AAV) (i.e., against myeloperoxidase or proteinase-3) and systemic lupus erythematosus (SLE) (i.e., against double-stranded DNA, histones, or nucleosomes). There is cumulating preclinical and clinical evidence that both excessive formation and impaired degradation of NETs are involved in the pathophysiology of AAV and SLE. These autoimmune diseases give rise to 2 clinically and pathologically distinct forms of glomerulonephritis (GN), respectively, crescentic pauci-immune GN and immune complex−mediated GN. Therefore, it is relevant to understand the different roles NET formation can play in the pathophysiology of these most prevalent renal autoimmune diseases. This review summarizes the current concepts on the role of NET formation in the pathophysiology of AAV and SLE, and provides a translational perspective on the clinical implications of NETs, such as potential therapeutic approaches that target NET formation in these renal autoimmune diseases.

Inflammation and autoimmunity in pulmonary hypertension: is there a role for endothelial adhesion molecules? (2017 Grover Conference Series)

While pulmonary hypertension (PH) has traditionally not been considered as a disease that is directly linked to or, potentially, even caused by inflammation, a rapidly growing body of evidence has demonstrated the accumulation of a variety of inflammatory and immune cells in PH lungs, in and around the wall of remodeled pulmonary resistance vessels and in the vicinity of plexiform lesions, respectively. Concomitantly, abundant production and release of various inflammatory mediators has been documented in both PH patients and experimental models of PH. While these findings unequivocally demonstrate an inflammatory component in PH, they have fueled an intense and presently ongoing debate as to the nature of this inflammatory aspect: is it a mere bystander of or response to the actual disease process, or is it a pathomechanistic contributor or potentially even a trigger of endothelial injury, smooth muscle hypertrophy and hyperplasia, and the resulting lung vascular remodeling? In this review, we will discuss the present evidence for an inflammatory component in PH disease with a specific focus on the potential role of the endothelium in this scenario and highlight future avenues of experimental investigation which may lead to novel therapeutic interventions.

Effects of subconjunctival administration of anti-high mobility group box 1 on dry eye in a mouse model of Sjӧgren's syndrome

Purpose

Extracellular high mobility group box 1 (HMGB1) acts as a damage associated molecular pattern molecule through the Toll-like receptor to promote autoreactive B cell activation, which may be involved in the pathogenesis of Sjӧgren’s syndrome. The aim of this study was to investigate the effect of subconjunctival administration of anti-HMGB1 on dry eye in a mouse model of Sjӧgren’s syndrome.

Methods

Ten weeks-old NOD.B10.H2^b mice were subconjunctivally injected with 0.02 to 2 μg of anti-HMGB1 antibodies or PBS twice a week for two consecutive weeks. Tear volume and corneal staining scores were measured and compared between before- and after-treatment. Goblet cell density was counted in PAS stained forniceal conjunctiva and inflammatory foci score (>50 cells/focus) was measured in extraorbital glands. Flow cytometry was performed to evaluate the changes in BrdU⁺ cells, IL-17-, IL-10-, or IFNγ-secreting cells, functional B cells, and IL-22 secreting innate lymphoid cells (ILC3s) in cervical lymph nodes. The level of IL-22 in intraorbital glands was measured by ELISA.

Results

Injection of 2 μg or 0.02 μg anti-HMGB1 attenuated corneal epithelial erosions and increased tear secretion (p<0.05). Goblet cell density was increased in 0.2 μg and 2 μg anti-HMGB1-treated-mice with marginal significance. The inflammatory foci score, and the number of BrdU⁺ cells, IL-17-, IL-10-, IFNγ-secreting cells, and functional B cells did not significantly change following anti-HMGB1 treatment. Surprisingly, the percentage of ILC3s was significantly increased in the draining lymph nodes (p<0.05), and the expression of IL-22 was significantly increased in the intraorbital glands (p<0.05) after administration of 2 μg anti-HMGB1.

Conclusion

This study shows that subconjunctival administration of anti-HMGB1 attenuates clinical manifestations of dry eye. The improvement of dry eye may involve an increase of ILC3s, rather than modulation of B or plasma cells, as shown using a mouse model of Sjӧgren’s syndrome.

High mobility group box 1 protein attenuates myocardial ischemia reperfusion injury via inhibition of the p38 mitogen-activated protein kinase signaling pathway

The present study aimed to determine the effects of high mobility group box 1 protein (HMGB1) on myocardial ischemia reperfusion (I/R) injury in rats following acute myocardial ischemia and investigate the underlying molecular mechanisms of these effects. Male Wistar rats were randomly divided into the following groups (n=10/group): Sham operation; I/R; HMGB50 (50 ng/kg HMGB1 before I/R); HMGB100 (100 ng/kg HMGB1 before I/R); and HMGB200 (200 ng/kg HMGB1 before I/R). Serum cardiac troponin I (cTnI), interleukin (IL)-6 and tumor necrosis factor (TNF)-α levels were subsequently measured. Myocardial levels of malondialdehyde (MDA) and superoxide dismutase (SOD) were also determined. Myocardial infarction size (IS) was determined by 2,3,5-triphenyltetrazolium chloride staining. Myocardial expression of hypoxia inducible factor (HIF)-1α and phosphorylated p38 mitogen-activated protein kinase (P-p38 MAPK) protein was measured using western blotting. The results demonstrated that HMGB1 significantly decreased serum levels of cTnI, IL-6 and TNF-α and myocardial IS in I/R rats compared with the sham group (all P<0.05). HMGB1 also significantly decreased and increased myocardial levels of MDA and SOD, respectively (both P<0.05). HMGB1 significantly increased myocardial expression of HIF-1α and decreased expression of P-p38 MAPK following I/R (both P<0.05). These effects of HMGB1 occurred in a dose-dependent manner. The results of the current study indicate that the cardioprotective effects of intravenous HMGB1 are associated with increased myocardial expression of HIF-1α via inhibition of P-p38 MAPK expression, leading to inhibition of the P-p38 MAPK signaling pathway.

Heterogeneity of B Cell Functions in Stroke-Related Risk, Prevention, Injury, and Repair

It is well established that post-stroke inflammation contributes to neurovascular injury, blood-brain barrier disruption, and poor functional recovery in both animal and clinical studies. However, recent studies also suggest that several leukocyte subsets, activated during the post-stroke immune response, can exhibit both pro-injury and pro-recovery phenotypes. In accordance with these findings, B lymphocytes, or B cells, play a heterogeneous role in the adaptive immune response to stroke. This review highlights what is currently understood about the various roles of B cells, with an emphasis on stroke risk factors, as well as post-stroke injury and repair. This includes an overview of B cell functions, such as antibody production, cytokine secretion, and contribution to the immune response as antigen presenting cells. Next, evidence for B cell-mediated mechanisms in stroke-related risk factors, including hypertension, diabetes, and atherosclerosis, is outlined, followed by studies that focus on B cells during endogenous protection from stroke. Subsequently, animal studies that investigate the role of B cells in post-stroke injury and repair are summarized, and the final section describes current B cell-related clinical trials for stroke, as well as other central nervous system diseases. This review reveals the complex role of B cells in stroke, with a focus on areas for potential clinical intervention for a disease that affects millions of people globally each year.

Apoptotic cell responses in the splenic marginal zone: a paradigm for immunologic reactions to apoptotic antigens with implications for autoimmunity

Apoptotic cells drive innate regulatory responses that result in tolerogenic immunity. This is a critical aspect of cell physiology as apoptotic cells expose potentially dangerous nuclear antigens on the surface in apoptotic blebs, and failure in their recognition, phagocytosis, or destruction can cause dramatic autoimmunity in experimental models and is linked to development and progression of systemic pathology in human. The marginal zone is a specialized splenic environment that serves as a transitional site from circulation to peripheral lymphoid structures. The marginal zone serves a key role in trapping of particulates and initiation of innate responses against systemic microbial pathogens. However in recent years, it has become clear the marginal zone is also important for initiation of immune tolerance to apoptotic cells, driving a coordinated response involving multiple phagocyte and lymphocyte subsets. Recent reports linking defects in splenic macrophage function to systemic lupus erythematosus in a manner analogous to marginal zone macrophages in lupus-prone mice provide an impetus to better understand the mechanistic basis of the apoptotic cell response in the marginal zone and its general applicability to apoptotic cell-driven tolerance at other tissue sites. In this review, we discuss immune responses to apoptotic cells in the spleen in general and the marginal zone in particular, the relationship of these responses to autoimmune disease, and comparisons to apoptotic cell immunity in humans.

Intravenous high mobility group box 1 upregulates the expression of HIF-1α in the myocardium via a protein kinase B-dependent pathway in rats following acute myocardial ischemia

The effects of intravenous high mobility group box 1 (HMGB1) on myocardial ischemia/reperfusion (I/R) injury remains to be elucidated. The purpose of the present study was to investigate the effects of intravenous HMGB1 on the expression of hypoxia inducible factor-1α (HIF-1α) in the myocardium of rats following acute myocardial ischemia, and to examine the effects of intravenous HMGB1 on myocardial I/R injury. Male Wistar rats were divided into the following groups: Sham operation group (n=10), a group exposed to ischemia for 30 min and reperfusion for 4 h (I/R group) as a control (n=10), an HMGB group, in which 100 ng/kg HMGB was administered intravenously 30 min prior to ischemia (n=10), an LY group, in whic LY294002, an inhibitor of phosphoinositide 3-kinase (PI3K), was administered intravenously (0.3 mg/kg) 40 min prior to ischemia (n=10), and the HMGB1+LY group, in which HMGB1 (100 ng/kg) and LY294002 (0.3 mg/kg) were administered intravenously 30 min and 40 min prior to ischemia, respectively (n=10). The serum levels of cardiac troponin I (cTnI) and tumor necrosis factor-α (TNF-α), and myocardial infarct size were measured. The expression levels of phosphorylated Akt and HIF-1α were investigated using western blot analyses. The results showed that pre-treatment with HMGB1 significantly decreased serum levels of cTnI, and TNF-α, and reduced myocardial infarct size following 4 h reperfusion (all P<0.05). HMGB1 also increased the expression levels of HIF-1α and p-Akt induced by I/R (P<0.05). LY294002 was found to eliminate the effects of intravenous HMGB1 on myocardial I/R injury (P<0.05). These results suggest that intravenous pre-treatment with HMGB1 may exert its cardioprotective effects via the upregulation of the myocardial expression of HIF-1α, which may be regulated by the PI3K/Akt signaling pathway, in rats following acute myocardial I/R.

Hematopoietic stem and multipotent progenitor cells produce IL-17, IL-21 and other cytokines in response to TLR signals associated with late apoptotic products and augment memory Th17 and Tc17 cells in the bone marrow of normal and lupus mice

We studied effects of early and late apoptotic (necroptotic) cell products, related damage associated alarmins and TLR agonists, on hematopoietic stem and progenitor cells (HSPC). Surprisingly, normal HSPC themselves produced IL-17 and IL-21 after 1½days of stimulation, and the best stimulators were TLR 7/8 agonist; HMGB1-DNA; TLR 9 agonist, and necroptotic B cells. The stimulated HSPC expressed additional cytokines/mediators, directly causing rapid expansion of IL-17(+) memory CD4 T (Th17), and CD8 T (Tc17) cells, and antigen-experienced IL-17(+) T cells with "naïve" phenotype. In lupus marrow, HSPC were spontaneously pre-stimulated by endogenous signals to produce IL-17 and IL-21. In contrast to HSPC, megakaryocyte progenitors (MKP) did not produce IL-17, and unlike HSPC, they could process and present particulate apoptotic autoantigens to augment autoimmune memory Th17 response. Thus abnormally stimulated primitive hematopoietic progenitors augment expansion of IL-17 producing immune and autoimmune memory T cells in the bone marrow, which may affect central tolerance.

Microparticles That Form Immune Complexes as Modulatory Structures in Autoimmune Responses

Microparticles (MPs) are induced during apoptosis, cell activation, and even “spontaneous” release. Initially MPs were considered to be inert cellular products with no biological function. However, an extensive research and functional characterization have shown that the molecular composition and the effects of MPs depend upon the cellular background and the mechanism inducing them. They possess a wide spectrum of biological effects on intercellular communication by transferring different molecules able to modulate other cells. MPs interact with their target cells through different mechanisms: membrane fusion, macropinocytosis, and receptor-mediated endocytosis. However, when MPs remain in the extracellular milieu, they undergo modifications such as citrullination, glycosylation, and partial proteolysis, among others, becoming a source of neoantigens. In rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE), reports indicated elevated levels of MPs with different composition, content, and effects compared with those isolated from healthy individuals. MPs can also form immune complexes amplifying the proinflammatory response and tissue damage. Their early detection and characterization could facilitate an appropriate diagnosis optimizing the pharmacological strategies, in different diseases including cancer, infection, and autoimmunity. This review focuses on the current knowledge about MPs and their involvement in the immunopathogenesis of SLE and RA.

HMGB1 in health and disease

Complex genetic and physiological variations as well as environmental factors that drive emergence of chromosomal instability, development of unscheduled cell death, skewed differentiation, and altered metabolism are central to the pathogenesis of human diseases and disorders. Understanding the molecular bases for these processes is important for the development of new diagnostic biomarkers, and for identifying new therapeutic targets. In 1973, a group of non-histone nuclear proteins with high electrophoretic mobility was discovered and termed high-mobility group (HMG) proteins. The HMG proteins include three superfamilies termed HMGB, HMGN, and HMGA. High-mobility group box 1 (HMGB1), the most abundant and well-studied HMG protein, senses and coordinates the cellular stress response and plays a critical role not only inside of the cell as a DNA chaperone, chromosome guardian, autophagy sustainer, and protector from apoptotic cell death, but also outside the cell as the prototypic damage associated molecular pattern molecule (DAMP). This DAMP, in conjunction with other factors, thus has cytokine, chemokine, and growth factor activity, orchestrating the inflammatory and immune response. All of these characteristics make HMGB1 a critical molecular target in multiple human diseases including infectious diseases, ischemia, immune disorders, neurodegenerative diseases, metabolic disorders, and cancer. Indeed, a number of emergent strategies have been used to inhibit HMGB1 expression, release, and activity in vitro and in vivo. These include antibodies, peptide inhibitors, RNAi, anti-coagulants, endogenous hormones, various chemical compounds, HMGB1-receptor and signaling pathway inhibition, artificial DNAs, physical strategies including vagus nerve stimulation and other surgical approaches. Future work further investigating the details of HMGB1 localization, structure, post-translational modification, and identification of additional partners will undoubtedly uncover additional secrets regarding HMGB1's multiple functions.

High-mobility group box 1 (HMGB1) in childhood: from bench to bedside

High-mobility group box protein 1 (HMGB1) is a nonhistone nuclear protein that has a dual function. Inside the cell, HMGB1 binds DNA, regulating transcription and determining chromosomal architecture. Outside the cell, HMGB1 activates the innate system and mediates a wide range of physiological and pathological responses. HMGB1 exerts these actions through differential engagement of multiple surface receptors, including Toll-like receptor (TLR)2, TLR4, and receptor for advanced glycation end products (RAGE). HMGB1 is implicated as a late mediator of sepsis and is also involved in inflammatory and autoimmune diseases, such as rheumatoid arthritis and systemic lupus erythematosus. Interestingly, HMGB1 was associated with tumor progression, becoming a potential therapeutic target, due to its involvement in the resistance to chemotherapy. Its implication on the pathogenesis of systemic vasculitis and inflammatory bowel diseases has also been evaluated. Moreover, it regulates neuroinflammation after traumatic brain injuries or cerebral infectious diseases. The aim of this review is to analyze these different roles of HMGB1, both in physiological and pathological conditions, discussing clinical and scientific implications in the field of pediatrics.

CONCLUSION

HMGB1 plays a key role in several pediatric diseases, opening new scenarios for diagnostic biomarkers and therapeutic strategies development.

High-mobility group box 1 inhibition alleviates lupus-like disease in BXSB mice

High-mobility group box 1 protein (HMGB1), a ubiquitous nuclear DNA-binding protein, functions as a potent proinflammatory factor. In this study, we evaluated the effects of HMGB1 inhibition on murine lupus using the lupus-prone model. We treated male BXSB mice with neutralizing anti-HMGB1 monoclonal antibody (HMGB1 mAb) from age 16 weeks to 26 weeks. The control group received the same amount of control IgG. Lupus-prone male BXSB mice treated with HMGB1mAb showed attenuated proteinuria, glomerulonephritis, circulating anti-dsDNA and immune complex deposition. Levels of serum IL-1β, IL-6, IL-17 and IL-18 were also significantly decreased by administration of HMGB1mAb in lupus-prone BXSB mice. HMGB1mAb treatment also decreased the caspase-1 activity in the kidneys of BXSB mice and reduced the mouse mortality. Our study supports that HMGB1 inhibition alleviates lupus-like disease in BXSB mice and might be a potential treatment option for human SLE.

TLR9 expressed on plasma membrane acts as a negative regulator of human B cell response

Toll-like receptors (TLRs) are positioned at the interface between innate and adaptive immunity. Unlike others, those such as TLR9, that recognize nucleic acids, are confined to the endosomal compartment and are scarce on the cell surface. Here, we present evidence for TLR9 expression on the plasma membrane of B cells. In contrast to endosomal TLR9, cell surface TLR9 does not bind CpG-B oligodeoxynucleotides. After B cell-receptor (BCR) stimulation, TLR9 was translocated into lipid rafts with the BCR, suggesting that it could serve as a co-receptor for BCR. Nevertheless, stimulation of B cells with anti-TLR9 antibodies did not modify the BCR-induced responses despite up-regulation of tyrosine phosphorylation of proteins. However, CpG-B activation of B cells, acting synergistically with BCR signals, was inhibited by anti-TLR9 stimulation. Induction of CD25 expression and proliferation of B cells were thus down-regulated by the engagement of cell surface TLR9. Overall, our results indicate that TLR9 expressed on the plasma membrane of B cells might be a negative regulator of endosomal TLR9, and could provide a novel control by which activation of autoreactive B cells is restrained.

A novel antagonist of Toll-like receptors 7, 8 and 9 suppresses lupus disease-associated parameters in NZBW/F1 mice

Systemic Lupus Erythematosus is an autoimmune disease characterized by production of autoantibodies against nucleic acid-associated antigens. Endogenous DNA and RNA associated with these antigens stimulate inflammatory responses through Toll-like receptors (TLRs) and exacerbate lupus disease pathology. We have evaluated an antagonist of TLR7, 8 and 9 as a therapeutic agent in lupus-prone NZBW/F1 mice. NZBW/F1 mice treated with the antagonist had lower serum levels of autoantibodies targeting DNA, RNP, Smith antigen, SSA and SSB than did untreated mice. Reduction in blood urea nitrogen and proteinuria and improvements in kidney histopathology were observed in antagonist-treated mice. The antagonist treatment also reduced serum IL-12 and IL-1β and increased IL-10 levels. Levels of mRNA for IL-6, iNOS and IL-1β were lower in the kidneys and spleen of antagonist-treated mice than in those of untreated mice. Levels of mRNA for IP-10, TNFRSF9 and FASL were lower and IL-4 mRNA were higher in spleens of antagonist-treated mice than in spleens of untreated mice. mRNA for the inflammasome component NLRP3 was lower and mRNA for the antioxidant enzymes, catalase and glutathione peroxidase 1 was higher in the kidneys of antagonist-treated mice than in those of untreated mice. These results show that the antagonist of TLR7, 8 and 9 effectively inhibits inflammatory pathways involved in the development of lupus in NZBW/F1 mice and constitutes a potential therapeutic approach for the treatment of lupus and other autoimmune diseases.

Anti-high mobility group box 1 monoclonal antibody ameliorates experimental autoimmune encephalomyelitis

High mobility group box 1 (HMGB1) is an established inflammatory mediator when released from cells. Recent studies have implicated extracellular HMGB1 in the pathogenesis of various autoimmune diseases. The objective of this study was to determine whether HMGB1 could be a therapeutic target for experimental autoimmune encephalomyelitis (EAE). In this study, an anti-HMGB1 monoclonal antibody was injected intraperitoneally into a mouse model of EAE. We also measured serum cytokines levels in EAE and anti-HMGB1 monoclonal antibody-treated EAE. As a result, intraperitoneal injection of an anti-HMGB1 monoclonal antibody ameliorated the clinical and pathological severity of EAE and attenuated interleukin-17 up-regulation in serum. In conclusion, HMGB1 is involved in EAE pathogenesis and could trigger inflammation in the central nervous system. The novel aspect of this study is the demonstration that anti-HMGB1 ameliorates EAE. HMGB1 may be a novel therapeutic strategy for multiple sclerosis.

HMGB1: The Central Cytokine for All Lymphoid Cells

High-mobility group box 1 (HMGB1) is a leaderless cytokine, like the IL-1 and FGF family members, that has primary roles within the nucleus and the cytosol. Within the nucleus, it serves as another guardian of the genome, protecting it from oxidant injury and promoting access to transcriptional complexes such as nuclear hormone/nuclear hormone receptors and p53/p73 complexes. Within the cytosol it promotes autophagy and recruitment of the myddosome to Toll-like receptor (TLR) 9 vesicular compartments. Outside of the cell, it can either bind to specific receptors itself, or with high affinity to DNA, nucleosomes, IL-1β, lipopolysaccharide, and lipoteichoic acid to mediate responses in specific physiological or pathological conditions. Currently identified receptors include TLR2, TLR4, the receptor for advanced glycation end products, CD24-Siglec G/10, chemokine CXC receptor 4, and TIM-3. In terms of its effects or functions within lymphoid cells, HMGB1 is principally secreted from mature dendritic cells (DCs) to promote T-cell and B-cell reactivity and expansion and from activated natural killer cells to promote DC maturation during the afferent immune response. Some studies suggest that its primary role in the setting of chronic inflammation is to promote immunosuppression. As such, HMGB1 is a central cytokine for all lymphoid cells playing a role complementary to its better studied role in myeloid cells.

Accessory molecules for Toll-like receptors and their function

Toll-like receptors (TLRs) are essential components of the innate immune system. Accessory proteins are required for the biosynthesis and activation of TLRs. Here, we summarize recent findings on TLR accessory proteins that are required for cell-surface and endosomal TLR function, and we classify these proteins based on their function as ligand-recognition and delivery cofactors, chaperones and trafficking proteins. Because of their essential roles in TLR function, targeting of such accessory proteins may benefit strategies aimed at manipulating TLR activation for therapeutic applications.

Involvement of damage-associated molecular patterns in tumor response to photodynamic therapy: surface expression of calreticulin and high-mobility group box-1 release

Damage-associated molecular patterns (DAMPs), danger signal molecules expressed after injury or infection, have become recognized as prerequisite for orchestrating effective anti-tumor host response. The expression of two prototypical DAMPs, calreticulin and high-mobility group box-1 (HMGB1) protein, was examined following Photofrin-photodynamic therapy (PDT) of Lewis lung carcinoma (LLC) cells in vitro and LLC tumors growing in syngeneic mice. Cell surface expression of calreticulin was found to be highly increased at 1 h after PDT treatment both in vitro and in vivo. Increased exposure of calreticulin was also detected on the surface of macrophages from PDT-treated LLC tumors. At the same time interval, a rise in serum HMGB1 was detected in host mice. Intracellular staining of macrophages co-incubated for 16 h with PDT-treated LLC cells revealed elevated levels of HMGB1 in these cells. The knowledge of the involvement of these DAMPs uncovers important mechanistic insights into the development of host response induced by PDT.

Nucleic acid sensing Toll-like receptors in autoimmunity

Trafficking and activation of the nucleic acid sensing TLRs is subject to unique regulatory requirements imposed by the risk of self-recognition. Like all TLRs these receptors traffick through the Golgi, however, access to the secretory pathway is controlled by a binding partner present in the ER. Receptor activation in the endolysosome is regulated through a proteolytic mechanism that requires activity of compartment-resident proteases, thereby preventing activation in other regions of the cell. Advances in our understanding of the cell biology of these receptors have been paralleled by efforts to understand their precise roles in autoimmunity. Mouse models have revealed that TLR7 and TLR9 make unique contributions to the types of self-molecules recognized in disease and possibly disease severity. Currently, methods of inhibiting TLR7 and TLR9 are being tested in clinical trials for systemic lupus erythamatosus.

Role for toll-like receptors in autoimmune disease: the example of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a multisystem disease characterized by an autoimmune response to nuclear antigens. Although the pathophysiology of SLE remains incompletely understood, many recent studies indicate a major role for innate immunity. The toll-like receptors (TLRs), which play a key role in innate responses to infections, are also involved in acute and chronic inflammatory processes induced by endogenous ligands. Numerous in vitro studies have established that TLR7 and TLR9 are involved in immune complex recognition. Activation of these receptors leads to activation of immune cells, most notably B cells and dendritic cells, and to the inappropriate production of many cytokines known to be directly involved in the pathogenesis of SLE. These data prompted studies in several murine models of SLE to assess the impact of inactivation or overexpression of genes encoding TLRs or molecules involved in TLR signaling pathways. The results confirmed the major role for TLR7 and suggested involvement of TLR4 in the induction of an aggressive autoimmune response. However, in vivo data suggest a protective effect of TLR9, thus contradicting the in vitro results. In humans, genetic studies have identified polymorphisms associated with increased susceptibility to SLE.

HMGB1 in systemic lupus Erythematosus: Its role in cutaneous lesions development

The chromatin non-histone DNA binding protein high mobility group box one (HMGB1) has recently been extensively studied in autoimmune diseases. In addition to its nuclear functions, HMGB1 has been identified as alarmin that can 'alarm' both innate and adaptive immunity. HMGB1 can amplify inflammation and enhance immune responses by interacting with the receptor for Advanced Glycation End Products (RAGE) and Toll-like receptors 2,4 and 9 (TLRs) . Release of HMGB1 occurs during cell activation as well as cell death. Cells die by apoptosis and eventually necrosis which both are thought to lead to release of HMGB1 into the microenvironment. In the past years disturbed apoptosis or clearance of apoptotic cells has been put forward as a major pathophysiological feature in autoimmune diseases such as Systemic Lupus Erythematosus (SLE), which is a prototypic autoimmune disease that affects many organs. Accumulation of apoptotic cells has been found in SLE. Also, elevated levels of HMGB1 have been detected in the serum of SLE patients and increased expression of HMGB1 was demonstrated in skin lesions of lupus patients. In this review the general characteristics and activities of HMGB1 are highlighted and its role in SLE will be discussed with special attention to its involvement in the pathogenesis of skin lesions.

Nucleic acid sensing receptors in systemic lupus erythematosus: development of novel DNA- and/or RNA-like analogues for treating lupus

Double-stranded (ds) DNA, DNA- or RNA-associated nucleoproteins are the primary autoimmune targets in SLE, yet their relative inability to trigger similar autoimmune responses in experimental animals has fascinated scientists for decades. While many cellular proteins bind non-specifically negatively charged nucleic acids, it was discovered only recently that several intracellular proteins are involved directly in innate recognition of exogenous DNA or RNA, or cytosol-residing DNA or RNA viruses. Thus, endosomal Toll-like receptors (TLR) mediate responses to double-stranded RNA (TLR-3), single-stranded RNA (TLR-7/8) or unmethylated bacterial cytosine (phosphodiester) guanine (CpG)-DNA (TLR-9), while DNA-dependent activator of IRFs/Z-DNA binding protein 1 (DAI/ZBP1), haematopoietic IFN-inducible nuclear protein-200 (p202), absent in melanoma 2 (AIM2), RNA polymerase III, retinoic acid-inducible gene-I (RIG-I) and melanoma differentiation-associated gene 5 (MDA5) mediate responses to cytosolic dsDNA or dsRNA, respectively. TLR-induced responses are more robust than those induced by cytosolic DNA- or RNA- sensors, the later usually being limited to interferon regulatory factor 3 (IRF3)-dependent type I interferon (IFN) induction and nuclear factor (NF)-kappaB activation. Interestingly, AIM2 is not capable of inducing type I IFN, but rather plays a role in caspase I activation. DNA- or RNA-like synthetic inhibitory oligonucleotides (INH-ODN) have been developed that antagonize TLR-7- and/or TLR-9-induced activation in autoimmune B cells and in type I IFN-producing dendritic cells at low nanomolar concentrations. It is not known whether these INH-ODNs have any agonistic or antagonistic effects on cytosolic DNA or RNA sensors. While this remains to be determined in the future, in vivo studies have already shown their potential for preventing spontaneous lupus in various animal models of lupus. Several groups are exploring the possibility of translating these INH-ODNs into human therapeutics for treating SLE and bacterial DNA-induced sepsis.

Pathogenic mechanisms in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic inflammatory disease characterized by the dysfunction of T cells, B cells, and dendritic cells and by the production of antinuclear autoantibodies. This editorial provides a synopsis of newly discovered genetic factors and signaling pathways in lupus pathogenesis that are documented in 11 state-of-the-art reviews and original articles. Mitochondrial hyperpolarization underlies mitochondrial dysfunction, depletion of ATP, oxidative stress, abnormal activation, and death signal processing in lupus T cells. The mammalian target of rapamycin, which is a sensor of the mitochondrial transmembrane potential, has been successfully targeted for treatment of SLE with rapamycin or sirolimus in both patients and animal models. Inhibition of oxidative stress, nitric oxide production, expression of endogenous retroviral and repetitive elements such as HRES-1, the long interspersed nuclear elements 1, Trex1, interferon alpha (IFN-alpha), toll-like receptors 7 and 9 (TLR-7/9), high-mobility group B1 protein, extracellular signal-regulated kinase, DNA methyl transferase 1, histone deacetylase, spleen tyrosine kinase, proteasome function, lysosome function, endosome recycling, actin cytoskeleton formation, the nuclear factor kappa B pathway, and activation of cytotoxic T cells showed efficacy in animal models of lupus. Although B cell depletion and blockade of anti-DNA antibodies and T-B cell interaction have shown success in animal models, human studies are currently ongoing to establish the value of several target molecules for treatment of patients with lupus. Ongoing oxidative stress and inflammation lead to accelerated atherosclerosis that emerged as a significant cause of mortality in SLE.