Increased expression of the novel proinflammatory cytokine high mobility group box chromosomal protein 1 in skin lesions of patients with lupus erythematosus

High Mobility Group Box 1 (HMGB1): Molecular Signaling and Potential Therapeutic Strategies

High Mobility Group Box 1 (HMGB1) is a highly conserved non-histone chromatin-associated protein across species, primarily recognized for its regulatory impact on vital cellular processes, like autophagy, cell survival, and apoptosis. HMGB1 exhibits dual functionality based on its localization: both as a non-histone protein in the nucleus and as an inducer of inflammatory cytokines upon extracellular release. Pathophysiological insights reveal that HMGB1 plays a significant role in the onset and progression of a vast array of diseases, viz., atherosclerosis, kidney damage, cancer, and neurodegeneration. However, a clear mechanistic understanding of HMGB1 release, translocation, and associated signaling cascades in mediating such physiological dysfunctions remains obscure. This review presents a detailed outline of HMGB1 structure-function relationship and its regulatory role in disease onset and progression from a signaling perspective. This review also presents an insight into the status of HMGB1 druggability, potential limitations in understanding HMGB1 pathophysiology, and future perspective of studies that can be undertaken to address the existing scientific gap. Based on existing paradigm of various studies, HMGB1 is a critical regulator of inflammatory cascades and drives the onset and progression of a broad spectrum of dysfunctions. Studies focusing on HMGB1 druggability have enabled the development of biologics with potential clinical benefits. However, deeper understanding of post-translational modifications, redox states, translocation mechanisms, and mitochondrial interactions can potentially enable the development of better courses of therapy against HMGB1-mediated physiological dysfunctions.

IL-1β and IL-17 in cutaneous lupus erythematous skin biopsies: could immunohistochemicals indicate a tendency towards systemic involvement?

BACKGROUND

Only a fraction of patients with cutaneous lupus erythematosus (CLE) will eventually progress toward systemic disease (SLE).

OBJECTIVE

To find inflammatory biomarkers which could predict the progression of cutaneous lupus erythematosus (CLE) into systemic lupus erythematosus (SLE) using immunohistochemical (IHC) assays.

METHODS

Immunohistochemical markers for cytotoxic, inflammatory, and anti-inflammatory responses and morphometric methods were applied to routine paraffin sections of skin biopsies, taken from lesions of 59 patients with discoid lupus, subacute lupus, and lupus tumidus. For the diagnosis of SLE, patients were classified by both the American College of Rheumatology (ACR-82) and the Systemic Lupus International Collaborating Clinics (SLICC-12) systems.

RESULTS

Skin samples from CLE/SLE+patients presented higher expression of IL-1β (ARC-82: p=0.024; SLICC-12: p=0.0143) and a significantly higher number of cells marked with granzyme B and perforin (ARC: p=0.0097; SLICC-12: p=0.0148). Biopsies from CLE/SLE- individuals had higher expression of IL-17 (ARC-82: p=0.0003; SLICC-12: p=0.0351) and presented a positive correlation between the density of granzyme A+and FoxP3+ cells (ARC-82: p=0.0257; SLICC-12: p=0.0285) and CD8+ cells (ARC-82: p=0.0075; SLICC-12: p=0.0102), as well as between granulysin-positive and CD8+ cells (ARC-82: p=0.0024; SLICC-12: p=0.0116).

STUDY LIMITATIONS

Patients were evaluated at a specific point in their evolution and according to the presence or not of systemic disease. The authors cannot predict how many more, from each group, would have evolved towards SLE in the following years.

CONCLUSIONS

In this cohort, immunohistochemical findings suggested that patients with a tendency to systemic disease will show strong reactivity for IL-1β, while those with purely cutaneous involvement will tend to express IL-17 more intensely.

HMGB1 and Toll-like receptors: potential therapeutic targets in autoimmune diseases

HMGB1, a nucleoprotein, is expressed in almost all eukaryotic cells. During cell activation and cell death, HMGB1 can function as an alarm protein (alarmin) or damage-associated molecular pattern (DAMP) and mediate early inflammatory and immune response when it is translocated to the extracellular space. The binding of extracellular HMGB1 to Toll-like receptors (TLRs), such as TLR2 and TLR4 transforms HMGB1 into a pro-inflammatory cytokine, contributing to the occurrence and development of autoimmune diseases. TLRs, which are members of a family of pattern recognition receptors, can bind to endogenous DAMPs and activate the innate immune response. Additionally, TLRs are key signaling molecules mediating the immune response and play a critical role in the host defense against pathogens and the maintenance of immune balance. HMGB1 and TLRs are reported to be upregulated in several autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus, type 1 diabetes mellitus, and autoimmune thyroid disease. The expression levels of HMGB1 and some TLRs are upregulated in tissues of patients with autoimmune diseases and animal models of autoimmune diseases. The suppression of HMGB1 and TLRs inhibits the progression of inflammation in animal models. Thus, HMGB1 and TLRs are indispensable biomarkers and important therapeutic targets for autoimmune diseases. This review provides comprehensive strategies for treating or preventing autoimmune diseases discovered in recent years.

Autophagy and Breast Cancer: Connected in Growth, Progression, and Therapy

Despite an increase in the incidence of breast cancer worldwide, overall prognosis has been consistently improving owing to the development of multiple targeted therapies and novel combination regimens including endocrine therapies, aromatase inhibitors, Her2-targeted therapies, and cdk4/6 inhibitors. Immunotherapy is also being actively examined for some breast cancer subtypes. This overall positive outlook is marred by the development of resistance or reduced efficacy of the drug combinations, but the underlying mechanisms are somewhat unclear. It is interesting to note that cancer cells quickly adapt and evade most therapies by activating autophagy, a catabolic process designed to recycle damaged cellular components and provide energy. In this review, we discuss the role of autophagy and autophagy-associated proteins in breast cancer growth, drug sensitivity, tumor dormancy, stemness, and recurrence. We further explore how autophagy intersects and reduces the efficacy of endocrine therapies, targeted therapies, radiotherapy, chemotherapies as well as immunotherapy via modulating various intermediate proteins, miRs, and lncRNAs. Lastly, the potential application of autophagy inhibitors and bioactive molecules to improve the anticancer effects of drugs by circumventing the cytoprotective autophagy is discussed.

Recent advances in cutaneous lupus

Cutaneous lupus erythematosus (CLE) is an inflammatory and autoimmune skin condition that affects patients with systemic lupus erythematosus (SLE) and exists as an isolated entity without associated SLE. Flares of CLE, often triggered by exposure to ultraviolet (UV) light result in lost productivity and poor quality of life for patients and can be associated with trigger of systemic inflammation. In the past 10 years, the knowledge of CLE etiopathogenesis has grown, leading to promising targets for better therapies. Development of lesions likely begins in a pro-inflammatory epidermis, conditioned by excess type I interferon (IFN) production to undergo increased cell death and inflammatory cytokine production after UV light exposure. The reasons for this inflammatory predisposition are not well-understood, but may be an early event, as ANA + patients without criteria for autoimmune disease exhibit similar (although less robust) findings. Non-lesional skin of SLE patients also exhibits increased innate immune cell infiltration, conditioned by excess IFNs to release pro-inflammatory cytokines, and potentially increase activation of the adaptive immune system. Plasmacytoid dendritic cells are also found in non-lesional skin and may contribute to type I IFN production, although this finding is now being questioned by new data. Once the inflammatory cycle begins, lesional infiltration by numerous other cell populations ensues, including IFN-educated T cells. The heterogeneity amongst lesional CLE subtypes isn't fully understood, but B cells appear to discriminate discoid lupus erythematosus from other subtypes. Continued discovery will provide novel targets for additional therapeutic pursuits. This review will comprehensively discuss the contributions of tissue-specific and immune cell populations to the initiation and propagation of disease.

Pentoxifylline/Valsartan co-delivery in liposomal gel alters the inflammatory HMGB-1/ TLR pathway and promotes faster healing in burn wounds: A promising repurposed approach

Burn wounds are one of the most severe complex forms of trauma. Hence, new treatment strategies that facilitate the healing process; reduce the severity and the healing time is the main concern of the health care systems. In this work, pentoxifylline-valsartan, (PTX- VAL), loaded liposomes integrated into gel were designed for the first time as a novel co-delivery carrier for the treatment of burn wounds. The objective of this work was to investigate the ability of the nano-based liposomal system to co-entrap two repurposed drugs; hydrophilic pentoxifylline and lipophilic valsartan for topical treatment of burn wounds. The impact of increasing the phospholipid amount to enhance the co-entrapment of PTX and VAL was investigated and in-vitro evaluation of the prepared formulations was conducted to choose the optimum composition with the highest entrapment of both drugs adopting a simple, reliable derivative spectrophotometric method. Structure elucidation was also performed using a transmission electron microscope. In addition, A simple selected derivative spectrophotometric method was developed for the assay of PTX-VAL novel combination. The proven selectivity, precision and accuracy assured the reliability of this analytical method. Being economic and fast makes routine application of the developed analytical method is recommended in pharmaceutical industry. The selected liposomal formulation integrated into gel matrix (PTX-VAL-LG) showed; nanometric size, acceptable entrapment efficiency of both PTX and VAL as well as sustained release profiles and thus, enhanced action.

Gut Barrier Damage and Gut Translocation of Pathogen Molecules in Lupus, an Impact of Innate Immunity (Macrophages and Neutrophils) in Autoimmune Disease

The gut barrier is a single cell layer that separates gut micro-organisms from the host, and gut permeability defects result in the translocation of microbial molecules from the gut into the blood. Despite the silent clinical manifestation, gut translocation of microbial molecules can induce systemic inflammation that might be an endogenous exacerbating factor of systemic lupus erythematosus. In contrast, circulatory immune-complex deposition and the effect of medications on the gut, an organ with an extremely large surface area, of patients with active lupus might cause gut translocation of microbial molecules, which worsens lupus severity. Likewise, the imbalance of gut microbiota may initiate lupus and/or interfere with gut integrity which results in microbial translocation and lupus exacerbation. Moreover, immune hyper-responsiveness of innate immune cells (macrophages and neutrophils) is demonstrated in a lupus model from the loss of inhibitory Fc gamma receptor IIb (FcgRIIb), which induces prominent responses through the cross-link between activating-FcgRs and innate immune receptors. The immune hyper-responsiveness can cause cell death, especially apoptosis and neutrophil extracellular traps (NETosis), which possibly exacerbates lupus, partly through the enhanced exposure of the self-antigens. Leaky gut monitoring and treatments (such as probiotics) might be beneficial in lupus. Here, we discuss the current information on leaky gut in lupus.

An insight in Salmonella typhi associated autoimmunity candidates' prediction by molecular mimicry

Autoimmune diseases develop when the immune system targets healthy cells and tissues of an individual. In developing countries, S. typhi (a gram-negative pathogenic bacteria) remains a major public health issue. This study aimed to employ bioinformatics analyses to determine the 3D structural-based molecular mimicry and sequence of S. typhi and human host proteins. In addition, to classify possible antigenic microbial peptides homologous to human peptides and comprehend the molecular basis of S. typhi-related autoimmune disorders. Protein sequences were obtained from the NCBI database, and redundancy was removed using the CD-HIT tool. The BLASTp comparative sequence analysis was followed for molecular mimicry identification of human and S. typhi protein sequences. The PathDIP database was utilized to simulate essential physical relationships between proteins and curated pathways for metabolic processes. Subsequently, the IEDB database was used to find cross-reactive MHC class-II binding epitopes that could trigger an autoimmune reaction. SPARKS-X computational biology resource was also used to determine the structural homology between human and S. typhi peptides. The BLASTp study showed that S. typhi and the human host have several proteins holding considerable sequence similarities based on a set threshold of e ≤ 10-6 and bit score ≥100. The PathDIP putatively identified that these proteins enriched in a total of 68 metabolic pathways by a significant P-value (P < 0.005). The PSORTb analysis predicted that 26 out of these proteins are cytosolic, 1 predicted to be periplasmic protein, and 1 predicted to be localized in the cytoplasmic membrane. IEDB data analysis predicted many S.typhi and human homologs epitopes as a good binder of human HLA, i.e. DRB1*01:01, DPA1*03:01/DPB1*04:02, and DQA1*01:02/DQB1*06:02 with IC₅₀ < 50 nM. Finally, the docking data demonstrated that homolog lead epitopes promisingly interact with HLA and immune TLR4 receptors by exhibiting the best docking scores and molecular interactions. The analyses ultimately identified several potential candidate proteins and peptides that could cause S.typhi infection-mediated autoimmune diseases in humans.

Current Concepts on Pathogenic Mechanisms and Histopathology in Cutaneous Lupus Erythematosus

Cutaneous lupus erythematosus (CLE) is an interferon (IFN)-driven autoimmune disease that may be limited to the skin or can be associated with systemic lupus erythematosus (SLE). CLE occurs in several morphologic subtypes ranging from isolated, disc-shaped plaques to disseminated skin lesions. The typical histopathologic pattern of skin lesions is named interface dermatitis and characterized by a lymphocytic infiltrate and necroptotic keratinocytes at the dermo-epidermal junction. Other histopathologic patterns primarily involve the dermis or subcutis, depending on the subtype. One critical mechanism in CLE is the chronic reactivation of innate and adaptive immune pathways. An important step in this process is the recognition of endogenous nucleic acids released from dying cells by various pattern recognition receptors (PRRs), including Toll-like receptors (TLRs) and other cytosolic receptors. Crucial cells in CLE pathogenesis comprise plasmacytoid dendritic cells (pDCs) as major producers of type I IFN, T cells exerting cytotoxic effects, and B cells, previously believed to contribute via secretion of autoantibodies. However, B cells are increasingly considered to have additional functions, supported by studies finding them to occur in highest numbers in chronic discoid lupus erythematosus (CDLE), a subtype in which autoantibodies are often absent. More precise knowledge of how CLE subtypes differ pathophysiologically may allow a tailored pharmacotherapy in the future, taking into account the specific molecular signature in relation to the morphologic subtype.

The Genetic Landscape of Cutaneous Lupus Erythematosus

Cutaneous lupus erythematosus (CLE) is an autoimmune connective tissue disease that can exist as a disease entity or within the context of systemic lupus erythematosus (SLE). Over the years, efforts to elucidate the genetic underpinnings of CLE and SLE have yielded a wealth of information. This review examines prior studies investigating the genetics of CLE at the DNA and RNA level and identifies future research areas. In this literature review, we examined the English language literature captured within the MEDLINE and Embase databases using pre-defined search terms. First, we surveyed studies investigating various DNA studies of CLE. We identified three predominant areas of focus in HLA profiling, complement deficiencies, and genetic polymorphisms. An increased frequency of HLA-B8 has been strongly linked to CLE. In addition, multiple genes responsible for mediating innate immune response, cell growth, apoptosis, and interferon response confer a higher risk of developing CLE, specifically TREX1 and SAMHD1. There was a strong association between C2 complement deficiency and CLE. Second, we reviewed literature studying aberrations in the transcriptomes of patients with CLE. We reviewed genetic aberrations initiated by environmental insults, and we examined the interplay of dysregulated inflammatory, apoptotic, and fibrotic pathways in the context of the pathomechanism of CLE. These current learnings will serve as the foundation for further advances in integrating personalized medicine into the care of patients with CLE.

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.

Extracellular HMGB1 blockade inhibits tumor growth through profoundly remodeling immune microenvironment and enhances checkpoint inhibitor-based immunotherapy

BACKGROUND

High-mobility group box 1 (HMGB1) is a multifunctional redox-sensitive protein involved in various intracellular (eg, chromatin remodeling, transcription, autophagy) and extracellular (inflammation, autoimmunity) processes. Regarding its role in cancer development/progression, paradoxical results exist in the literature and it is still unclear whether HMGB1 mainly acts as an oncogene or a tumor suppressor.

METHODS

HMGB1 expression was first assessed in tissue specimens (n=359) of invasive breast, lung and cervical cancer and the two distinct staining patterns detected (nuclear vs cytoplasmic) were correlated to the secretion profile of malignant cells, patient outcomes and the presence of infiltrating immune cells within tumor microenvironment. Using several orthotopic, syngeneic mouse models of basal-like breast (4T1, 67NR and EpRas) or non-small cell lung (TC-1) cancer, the efficacy of several HMGB1 inhibitors alone and in combination with immune checkpoint blockade antibodies (anti-PD-1/PD-L1) was then investigated. Isolated from retrieved tumors, 14 immune cell (sub)populations as well as the activation status of antigen-presenting cells were extensively analyzed in each condition. Finally, the redox state of HMGB1 in tumor-extruded fluids and the influence of different forms (oxidized, reduced or disulfide) on both dendritic cell (DC) and plasmacytoid DC (pDC) activation were determined.

RESULTS

Associated with an unfavorable prognosis in human patients, we clearly demonstrated that targeting extracellular HMGB1 elicits a profound remodeling of tumor immune microenvironment for efficient cancer therapy. Indeed, without affecting the global number of (CD45+) immune cells, drastic reductions of monocytic/granulocytic myeloid-derived suppressor cells (MDSC) and regulatory T lymphocytes, a higher M1/M2 ratio of macrophages as well as an increased activation of both DC and pDC were continually observed following HMGB1 inhibition. Moreover, blocking HMGB1 improved the efficacy of anti-PD-1 cancer monoimmunotherapy. We also reported that a significant fraction of HMGB1 encountered within cancer microenvironment (interstitial fluids) is oxidized and, in opposite to its reduced isoform, oxidized HMGB1 acts as a tolerogenic signal in a receptor for advanced glycation endproducts-dependent manner.

CONCLUSION

Collectively, we present evidence that extracellular HMGB1 blockade may complement first-generation cancer immunotherapies by remobilizing antitumor immune response.

Lupus Erythematosus Tumidus with Pseudolymphomatous Infiltrates: A Case Report

A 39-year-old Japanese woman presented with a pruritic infiltrated erythematous plaque on the right cheek. Histopathologic analysis of the erythema showed dermal edema, separation of collagen bundles, and nodular perivascular and periadnexal infiltration of lymphocytes in the whole dermis, without epidermal changes. Alcian blue staining intensity was elevated between the collagen bundles, indicating dermal mucinosis. The nodular infiltrates consisted of CD3+ T cell clusters and CD20+ B cell clusters (ratio, approximately 3:1) and included numerous CD123+ cells, indicative of plasmacytoid dendritic cells. Blood analysis revealed serum antinuclear antibody at a titer of 1:160 (homogeneous, speckled pattern). Lupus erythematosus tumidus with pseudolymphomatous infiltrates was diagnosed. Hydroxychloroquine treatment partially improved symptoms; however, the addition of prednisolone was required for complete resolution. Lupus erythematosus tumidus is sometimes accompanied by pseudolymphomatous infiltrates. Dermal mucinosis and the presence of numerous plasmacytoid dendritic cells are useful in differentiating lupus erythematosus tumidus from pseudolymphoma.

Decreased Expression of the High Mobility Group Box 1 (HMGB1) Gene in Peripheral Blood in Patients with Mild or Moderate Clostridioides difficile Infection

Cytokines are mediators of inflammation induced in the course of Clostridioides difficile infection (CDI). High Mobility Group Box 1 (HMGB1) is a cytokine playing an important role in the pathogenesis of numerous inflammatory and autoimmune diseases. The aim of the study was to assess the HMGB1 gene expression in the course of CDI. We have performed a prospective case-control study- including 55 adult patients, among them 27 with CDI, who were hospitalized from October 2018 to February 2020 and 28 healthy volunteers. We assessed: a complete blood count with differential leukocyte count, blood creatinine, albumin, and C-reactive protein (CRP) levels. Then, the expression of the HMGB1 gene was evaluated using quantitative Real-Time PCR. Patients with CDI were found to have a significant increase in white blood cells (WBC), neutrophil count, and CRP levels, they also exhibited decreased levels of albumin compared with controls. The HMGB1 gene expression was significantly lower among patients with CDI compared with the control group and significantly, inversely correlated with CRP level in blood. In conclusion, we have observed a decreased expression of the HMGB1 gene in peripheral blood of patients with mild or moderate CDI, which hypothetically could reflect their diminished capability to fight the pathogen.

Cutaneous lupus erythematosus and cardiovascular disease: current knowledge and insights into pathogenesis

Multiple autoinflammatory diseases, including psoriasis, psoriatic arthritis, and systemic lupus erythematosus, have been linked to increased risk of cardiovascular disease. Inflammation is known to play a key role in the pathogenesis of atherosclerosis, thus the contribution of systemic immune dysregulation, which characterizes such inflammatory conditions, towards the development of cardiovascular disease has garnered considerable interest. Cutaneous lupus erythematosus (CLE) is a chronic inflammatory skin disease, but risk of cardiovascular disease amongst patients with cutaneous lupus is less well known. Observational studies, including those of large nationwide cohorts, have been conducted to examine cardiovascular disease risk in CLE, with varying findings. As with other inflammatory diseases, immunologic mechanisms may provide plausible causal links between CLE and cardiovascular risk. On a macrolevel, several disease-related characteristics may also contribute to cardiovascular risk amongst CLE patients. This represents an area of research that should be prioritized, as understanding cardiovascular disease risk has important clinical implications for CLE patients.

Current Insights in Cutaneous Lupus Erythematosus Immunopathogenesis

Cutaneous Lupus Erythematosus (CLE) is a clinically diverse group of autoimmune skin diseases with shared histological features of interface dermatitis and autoantibodies deposited at the dermal-epidermal junction. Various genetic and environmental triggers of CLE promote infiltration of T cells, B cells, neutrophils, antigen presenting cells, and NK cells into lesional skin. In this mini-review, we will discuss the clinical features of CLE, insights into CLE immunopathogenesis, and novel treatment approaches.

Triggers of Autoimmunity: The Role of Bacterial Infections in the Extracellular Exposure of Lupus Nuclear Autoantigens

Infections are considered important environmental triggers of autoimmunity and can contribute to autoimmune disease onset and severity. Nucleic acids and the complexes that they form with proteins—including chromatin and ribonucleoproteins—are the main autoantigens in the autoimmune disease systemic lupus erythematosus (SLE). How these nuclear molecules become available to the immune system for recognition, presentation, and targeting is an area of research where complexities remain to be disentangled. In this review, we discuss how bacterial infections participate in the exposure of nuclear autoantigens to the immune system in SLE. Infections can instigate pro-inflammatory cell death programs including pyroptosis and NETosis, induce extracellular release of host nuclear autoantigens, and promote their recognition in an immunogenic context by activating the innate and adaptive immune systems. Moreover, bacterial infections can release bacterial DNA associated with other bacterial molecules, complexes that can elicit autoimmunity by acting as innate stimuli of pattern recognition receptors and activating autoreactive B cells through molecular mimicry. Recent studies have highlighted SLE disease activity-associated alterations of the gut commensals and the expansion of pathobionts that can contribute to chronic exposure to extracellular nuclear autoantigens. A novel field in the study of autoimmunity is the contribution of bacterial biofilms to the pathogenesis of autoimmunity. Biofilms are multicellular communities of bacteria that promote colonization during chronic infections. We review the very recent literature highlighting a role for bacterial biofilms, and their major components, amyloid/DNA complexes, in the generation of anti-nuclear autoantibodies and their ability to stimulate the autoreactive immune response. The best studied bacterial amyloid is curli, produced by enteric bacteria that commonly cause infections in SLE patients, including Escherichia coli and Salmonella spps. Evidence suggests that curli/DNA complexes can trigger autoimmunity by acting as danger signals, molecular mimickers, and microbial chaperones of nucleic acids.

Enhanced myelopoiesis and aggravated arthritis in S100a8-deficient mice

Expressed strongly by myeloid cells, damage-associated molecular pattern (DAMP) proteins S100A8 and S100A9 are found in the serum of patients with infectious and autoimmune diseases. Compared to S100A9, the role of S100A8 is controversial. We investigated its biological activity in collagen-induced arthritis using the first known viable and fertile S100a8-deficient (S100a8^-/-) mouse. Although comparable to the wild type (WT) in terms of lymphocyte distribution in blood and in the primary and secondary lymphoid organs, S100a8^-/- mice had increased numbers of neutrophils, monocytes and dendritic cells in the blood and bone marrow, and these all expressed myeloid markers such as CD11b, Ly6G and CD86 more strongly. Granulocyte-macrophage common precursors were increased in S100a8^-/- bone marrow and yielded greater numbers of macrophages and dendritic cells in culture. The animals also developed more severe arthritic disease leading to aggravated osteoclast activity and bone destruction. These findings were correlated with increased inflammatory cell infiltration and cytokine secretion in the paws. This study suggests that S100A8 is an anti-inflammatory DAMP that regulates myeloid cell differentiation, thereby mitigating the development of experimental arthritis.

High-Mobility Group Box 1 Is Associated with the Inflammatory Pathogenesis of Graves' Orbitopathy

Background: High-mobility group box 1 (HMGB1) has been implicated in the pathogenesis of inflammatory autoimmune diseases. This study investigated the influence and mechanisms of HMGB1 in Graves' orbitopathy (GO). Methods: HMGB1 and its receptors (receptor for advanced glycation end products [RAGE], Toll-like receptor [TLR] 2, and TLR4) mRNA levels were evaluated by real-time polymerase chain reaction (RT-PCR) in GO and non-GO orbital tissues. The mRNA expressions of HMGB1 and its receptors were evaluated in primary cultured orbital fibroblasts from six GO patients and five healthy control subjects under interleukin (IL)-1β or tumor necrosis factor (TNF)-α stimulation using RT-PCR. HMGB1 secretions under IL-1β or TNF-α stimulation were evaluated by enzyme-linked immunosorbent assay (ELISA). The effects of an anti-HMGB1 antibody, RAGE antagonist (FPS-ZM1), and anti-TLR2 antibody on the expressions of IL-1β or TNF-α induced pro-inflammatory cytokines and phosphorylated nuclear factor kappa-light-chain-enhancer of activated B cells were evaluated using ELISA and Western blot analysis, respectively. The plasma levels of HMGB1 were compared among patients with active GO (n = 51), inactive GO (n = 48), Graves' disease without GO (n = 30), and healthy control subjects (n = 46) by ELISA. Results: The genes encoding HMGB1 and its receptors, as well as HMGB1 protein expression, were increased in GO orbital tissues compared to non-GO tissues. IL-1β and TNF-α stimulation increased the mRNA levels of HMGB1, RAGE, and TLR2 and the secretion of HMGB1 protein further in GO cells. Anti-HMGB1 antibody, FPS-ZM1, and anti-TLR2 antibody reduced IL-1β- or TNF-α-induced production of pro-inflammatory cytokines and phosphorylated nuclear factor kappa-light-chain-enhancer of activated B cells. The plasma levels of HMGB1 were highly increased in patients with active GO, and were significantly correlated with the clinical activity score (r = 0.566, p = 0.002) and levels of thyrotropin binding inhibitory immunoglobulin (r = 0.506, p < 0.001). Conclusions: This study demonstrates an association of HMGB1 and its receptors in the inflammatory mechanisms of GO. HMGB1, RAGE, and TLR2 blockers reduced the production of pro-inflammatory molecules, providing a rationale for blocking the HMGB1 pathway to treat patients with GO. HMGB1 proteins were secreted further in the plasma of patients with active GO, suggesting that HMGB1 can be used as a biomarker of GO activity.

Diagnostic value of serum high-mobility group box-1 in pediatric systemic lupus erythematosus

BACKGROUND

High-mobility group box-1 (HMGB1) acts as a damage-associated molecular pattern or as an alarmin and it stimulates inflammatory and immunological activities.

AIM

We sought to investigate serum HMGB1 protein expression in patients with pediatric systemic lupus erythematosus (pSLE) in relation to the disease characteristics and activity.

PATIENTS AND METHODS

This is a controlled cross-sectional study which comprised 50 children and adolescents with Systemic lupus erythematosus (SLE) and 50 age- and sex-matched healthy subjects who served as a control group. Study measurements included clinical assessment, laboratory workup for SLE (complete blood count, erythrocyte sedimentation rate, serum creatinine, creatinine clearance and 24-hour urinary protein, C3 and anti-double-stranded DNA, lupus anticoagulant and anticardiolipin antibodies) and measurement of serum HMGB1 by enzyme-linked immunosorbent assay in patients and controls.

RESULTS

Serum HMGB1 expression was significantly higher in the pSLE patients than the control group (P < 0.001). Patients with lupus nephritis (LN) had significantly higher serum HMGB1 as compared to those with normal kidneys (P < 0.04). Serum HMGB1 in LN patients correlated positively to the SLE Disease Activity Index (P < 0.0001), and 24 hours urinary proteins and negatively to creatinine clearance (P < 0.001). At a cut-off point of ≥40 µg/L, serum HMGB1 showed good diagnostic value for pSLE with sensitivity and specificity of 98% and 95%, respectively.

CONCLUSION

Serum HMGB1 seems to be a reliable biomarker for diagnosis of pSLE and monitoring disease status, especially in LN. HMBG1 might prove to be a potential therapeutic target in LN.

Increased dermal expression of chromatin-associated protein HMGB1 and concomitant T-cell expression of the DNA RAGE in patients with psoriasis vulgaris

PURPOSE

Psoriasis vulgaris (PV) is an autoimmune-related chronic inflammatory disease of the skin, with both vascular and metabolic effects. Aggravating factors have been identified that initiate and maintain inflammation, including expression of Th1-, Th17-, and Th22-cell derived cytokines. Recently, we showed that the evolutionarily ancient and highly conserved damage-associated molecular pattern molecule "high mobility group box 1 (HMGB1)" is significantly increased in the serum of PV patients with disease progression and is decreased under standard therapies.

MATERIALS AND METHODS

To better understand the role of HMGB1 in the pathogenesis of PV, we recruited 22 untreated psoriatic patients with either mild or severe disease, defined by the Psoriasis Area Severity Index. We assessed HMGB1 and receptor for advanced glycation end products (RAGE) expression in the skin by immunohistochemistry and analyzed the immune-phenotype of Treg and Th17 cells by flow cytometry.

RESULTS

We found increased staining for HMGB1 in the dermis of psoriatic plaques in comparison to uninvolved skin of patients with PV. In addition, the major histocompatibility complex class III-encoded DNA and HMGB1 RAGE, induced by HMGB1, were highly expressed on psoriatic CD8+ T cells and CD4+ Treg. High expression of HMGB1 in the lesional skin was associated with even higher expression of its receptor, RAGE, on the cell surface of keratino-cytes in patients with severe PV.

CONCLUSION

The presence of HMGB1 and RAGE signaling may impact orchestration of chronic inflammation in PV which might have implications for Treg and Th17 cells.

HMGB1+ microparticles present in urine are hallmarks of nephritis in patients with systemic lupus erythematosus

Non-classical monocytes infiltrate the kidney parenchyma and participate in tissue damage in patients with lupus nephritis (LN). Circulating microparticles (MPs) seem to play critical roles in the activation of monocytes in systemic lupus erythematosus (SLE) patients. This study aims to characterize the phenotypes of MPs and monocyte subsets in LN patients and to determine their potential to discriminate between SLE patients with and without LN. Blood and urine samples from SLE patients were collected. In monocyte subsets from whole blood samples several phenotypic markers were evaluated. MPs were isolated from platelet-poor plasma and urine by centrifugation. This phenotypic marker characterization was performed using multiparametric flow cytometry. We observed that patients with active LN have lower counts of non-classical monocytes than do those without renal involvement. All monocyte subsets exhibited lower expression of CX3CR1 and ICAM-1 in LN than in patients without LN. High frequencies of MP-HMGB1⁺ and MP-HLA-DR⁺ were detected in circulation and urine of LN patients. Although MP-HMGB1⁺ , MP-HLA-DR⁺ , and MP-CX3CR1⁺ from urine were able to discriminate between patients with and without LN, only urinary MP-HMGB1⁺ were different between patients with active and inactive LN. Therefore, these vesicles may be useful as biomarkers of LN.

Alarmins of the extracellular space

The ability of the immune system to discriminate between healthy-self, abnormal-self, and non-self has been attributed mainly to alarmins signaling as "danger signals". It is now evident, however, that alarmins are much more complex and can perform specialized functions that can regulate a wide spectrum of processes ranging from propagation of disease to tissue homeostasis. As such, alarmins and their signaling mechanisms are now actively pursued as therapeutic targets. The clinical utility of alarmins requires an understanding of their specific localization. Specifically, many alarmins can function paradoxically depending upon their localization, intra or extracellular. The present review focuses upon alarmin presence and differential expression in the extracellular space versus within the cell and how variation of the localization of alarmins can reveal important mechanistic insights into alarmin functions and their efficacy as biomarkers of disease and therapeutic targets.

Up-regulation of HMGB1 and TLR4 in skin lesions of lichen planus

Lichen planus (LP) is a chronic, mucocutaneous inflammatory disease of an unknown aetiology. The disease has been associated with certain viruses, and the factors such as DAMPs (damage-associated molecular patterns) and PAMPs (pathogen-associated molecular patterns) may also contribute to the inflammatory response in LP. HMGB1 (high mobility group box 1 protein) is one of the major DAMPs that induces inflammation and could trigger LP disease. The present study was aimed to examine TLR4, RAGE and HMGB1 production in epidermis or dermis by immunohistochemistry and the respective expression of these targets in the skin lesions of patients with LP. Moreover, we measured HMGB1 serum levels by ELISA. The results showed similar profile of expression by HMGB1 and TLR4, which are decreased at epidermis and up-regulated at dermis of skin lesions of LP patients that was sustained by intense cellular infiltration. RAGE expression was also increased in dermis of LP. Although there is increased RAGE protein levels, a decreased RAGE transcript levels was detected. Similar HMGB1 serum levels were detected in the LP and control groups. This study demonstrates that HMGB1 and TLR4 could contribute to the inflammatory LP process in skin.

Reduced-HMGB1 suppresses poly(I:C)-induced inflammation in keratinocytes

BACKGROUND

High mobility group box 1 (HMGB1) is a nuclear protein that stabilizes DNA and facilitates gene transcription. Additionally, cell stress or death induces the release of HMGB1 outside the cell membrane, where HMGB1 functions as an alarmin, causing an inflammatory response in combination with other cytokines, damage-associated molecular patterns (DAMPs), and pathogen-associated molecular patterns (PAMPs).

OBJECTIVE

To evaluate the effect of reduced-HMGB1 (previously termed chemoattractive-HMGB1) on polyinosine-polycytidylic acid [poly(I:C)]-induced inflammation in normal human keratinocytes (NHKs).

METHODS

We focused on downstream components of the poly(I:C)-Toll-like receptor 3 (TLR3), retinoic acid-inducible gene-I (RIG-I), and melanoma differentiation-associated protein 5 (MDA5) pathways, including IκBα, nuclear factor (NF)-κB p65, mitogen-activated protein kinase (MAPK), and interferon regulatory factor 3 (IRF3), and assessed whether these pathways are involved in the suppression of poly(I:C)-induced inflammation in NHKs by HMGB1. An immunoprecipitation was performed to know whether HMGB1 could bind to poly(I:C), and immunofluorescence staining and flow cytometric analysis were performed to check whether reduced-HMGB interferes with cellular uptake of poly(I:C) translocation (possibly by endocytosis).

RESULTS

Application of exogenous HMGB1 before, but not after, exerted a suppressive effect on poly(I:C)-induced inflammation in NHKs. In addition, reduced-HMGB1, but not disulfide-HMGB1, exerted a suppressive effect on poly(I:C)-induced inflammation in NHKs, suggesting the importance of the redox status of exogenous HMGB1. Pre-treatment with reduced-HMGB1 inhibited the phosphorylation of IκBα, NF-κB p65, and IRF3 induced by poly(I:C) stimulation in NHKs; however, phosphorylation of p38, extracellular signal-regulated kinase (ERK), and c-Jun N-terminal kinase (JNK) was unaffected. Disulfide-HMGB1 formed a complex with poly(I:C), as did reduced- and oxidized-HMGB1, albeit to a lesser extent. Immunofluorescence staining and flow cytometric analysis indicated that reduced-HMGB interferes with cellular uptake of poly(I:C) translocation (possibly by endocytosis).

CONCLUSION

These findings suggest that pre-treatment with reduced-HMGB1 ameliorates poly(I:C)-mediated inflammation in NHKs.

HMGB1, an innate alarmin, plays a critical role in chronic inflammation of adipose tissue in obesity

Obesity has emerged as an imminent global public health concern over the past several decades. It has now become evident that obesity is characterized by the persistent and low-grade inflammation in the adipose tissue, and serves as an independent risk factor for many metabolic disorders such as diabetes and cardiovascular disease. Particularly, adipocytes originated from obese mice and humans likely predominate necrosis upon stressful insults, leading to passive release of cellular contents including the high mobility group box 1 (HMGB1) into the extracellular milieu. Extracellular HMGB1 acts as an innate alarmin to stimulate the activation of resident immune cells in the adipose tissue. Upon activation, those resident immune cells actively secrete additional HMGB1, which in turn activates/recruits additional immune cells, and induces adipocyte death. This review summarizes those novel discoveries in terms of HMGB1 in the initiation and maintenance of chronic inflammatory state in adipose tissue in obesity, and discusses its potential application in clinical settings.

The phenolic fraction of extra virgin olive oil modulates the activation and the inflammatory response of T cells from patients with systemic lupus erythematosus and healthy donors

SCOPE

Systemic lupus erythematosus (SLE) is a chronic multiorgan autoimmune disease characterized by immune deregulation, which involves altered T-cell response and imbalance of cytokine production. The phenolic fraction (PE) of extra virgin olive oil (EVOO) possesses anti-inflammatory and immunomodulatory properties and exerts preventive effects in murine models of immune-inflammatory diseases, such as SLE. The present study was designed to determine the in vitro effects of the PE from EVOO on peripheral blood mononuclear cells (PBMC) from inactive patients with SLE and healthy donors.

METHODS AND RESULTS

T-cell phenotype was investigated by flow cytometry, cytokine levels were determined by ELISA, and protein expression was detected by Western blot. The PE of EVOO decreased the frequency of CD69⁺ cells and the secretion of IFN-γ, TNF-α, IL-6, IL-1β, and IL-10. Moreover, PE increased the expression of I-kappa-B-α and decreased extracellular signal regulated kinase phosphorylation on PBMC from patients with SLE and healthy donors.

CONCLUSION

PE modulates cytokine production and attenuates induced T-cell activation, probably through NF-κB signaling pathway, providing the first evidence that PE from EVOO has an anti-inflammatory and immunomodulatory role in SLE patients and it might therefore be considered as a dietary complement in SLE management.

HMGB1-TLR4 signaling contributes to the secretion of interleukin 6 and interleukin 8 by nasal epithelial cells

BACKGROUND

Alarmins play important roles in the pathogenesis of inflammatory and autoimmune diseases. However, the role of the alarmin protein high-mobility group box 1 (HMGB1) in upper airway inflammation is unclear.

OBJECTIVE

To determine if HMGB1 is present in the nasal mucosa and, if so, to elucidate its role in upper airway inflammation.

METHODS

Nasal secretions were collected from a total of 32 patients with chronic rhinosinusitis with nasal polyp, allergic rhinitis, and control subjects. The concentration of HMGB1 in nasal secretions and its tissue and cellular localization were examined by enzyme immunoassays and immunofluorescent staining of nasal polyps and cultured nasal epithelial cells. We then examined whether nasal epithelial cells secrete HMGB1 after inflammatory stimulation by tumor necrosis factor (TNF) α. The effects of HMGB1 on the production and secretion of interleukin (IL) 6 and IL-8 were also examined in cultured nasal epithelial cells.

RESULTS

Significantly higher concentrations of HMGB1 were found in nasal secretions from patients with chronic rhinosinusitis with nasal polyp or allergic rhinitis compared with the control subjects. HMGB1 expression was localized in the nuclei of epithelial cells and other constitutive cells in nasal polyps and in the nuclei of cultured nasal epithelial cells. TNF-α stimulated the production and secretion of HMGB1 by cultured nasal epithelial cells. HMGB1 stimulated the production and secretion of IL-6 and IL-8 by cultured nasal epithelial cells, and anti-toll-like receptor 4 blocking antibody significantly inhibited HMGB1-induced secretion of IL-6 and IL-8.

CONCLUSIONS

Nasal secretions contain substantial amounts of HMGB1. TNF-α stimulates the production of HMGB1, which, in turn, upregulates the production and secretion of IL-6 and IL-8 by nasal epithelial cells via toll-like receptor 4, which indicated that HMGB1 plays an important role in the pathogenesis of upper airway inflammation.

HMGB1 in the Pathogenesis of Nasal Inflammatory Diseases and its Inhibition as New Therapeutic Approach: A Review from the Literature

Introduction  This study is a systematic review on recent developments about the importance of HMGB1 protein in the pathogenesis of rhino-sinusal inflammatory diseases. We also report data on the use of 18-β-glycyrrhetic acid (GA), which has been shown able to inhibit the pro-inflammatory activities of HMGB1, in young patients affected by allergic rhinitis and complaining of nasal obstruction as main symptom.

Objectives  The objective of this study was to review the literature to demonstrate the importance of HMGB1 in the pathogenesis of nasal inflammatory disorders and understand whether the inhibition of this protein may be an efficacious and innovative therapeutic strategy for patients with rhino-sinusal inflammation.

Data Synthesis  Authors searched for pertinent articles indexed in PubMed, Scopus, and other health journals between 2004 and 2015.

In total, the authors gathered 258 articles: 219 articles through Pubmed and 39 articles from other search engines. The search terms used were as follows: HMGB1 AND “respiratory epithelium,” “airway inflammation,” “rhinitis,” “allergic rhinitis,” “rhinosinusitis,” “nasal polyposis,” “glycyrrhetic acid,” “children.”

Conclusions  Patients with severe symptoms have the highest serum levels and the highest extracellular expression of HMGB1. GA inhibits HMGB1 chemotactic and mitogenic function by a scavenger mechanism on extracellular HMGB1 accumulation stimulated by lipopolysaccharides in vitro. Treatment of allergic rhinitis with GA is not associated with local or systemic side effects in children and adults.

High mobility group box 1 skews macrophage polarization and negatively influences phagocytosis of apoptotic cells

OBJECTIVES

Decreased phagocytosis of apoptotic cells plays an important role in the pathogenesis of SLE. This can lead to secondary necrosis and release of nuclear proteins, such as high mobility group box 1 (HMGB1). We hypothesized that increased HMGB1 levels, as present in SLE, skew macrophage differentiation towards M1-like phenotypes and thereby diminish uptake of apoptotic cells. The aim of this study was to investigate the effect of HMGB1 on macrophage polarization and on phagocytic capacity of differentiated macrophages.

METHODS

SLE patients with quiescent disease (SLEDAI ⩽4) and healthy controls (HCs) were included. Monocytes and differentiated M1 and M2 macrophages were assessed for expression of M1 and M2 markers and for phagocytic capacity. HMGB1 was added during differentiation and during phagocytosis.

RESULTS

Expression of CD86 (M1) was not different, whereas CD163 (M2) was significantly lower on SLE monocytes. After differentiation, no differences regarding surface receptor expression and phagocytic capacity were observed between M1 and M2 macrophages from SLE patients and HCs. Addition of HMGB1 during M2 differentiation resulted in high IL-6 and TNF-α mRNA expression and reduced phagocytic capacity of apoptotic cells. Furthermore, adding HMGB1 to apoptotic Jurkat cells diminished phagocytosis of these cells.

CONCLUSION

Circulating monocytes from SLE patients display an M1-like phenotype compared with HCs, but in vitro differentiation abolishes this difference. HMGB1 skews differentiation of M2-like macrophages towards an M1-like phenotype and, subsequently, reduces phagocytosis of apoptotic cells. These data imply that the phenotype of monocytes or macrophages is determined by their environment, such as the presence of cytokines and HMGB1.

HMGB1, IL-1α, IL-33 and S100 proteins: dual-function alarmins

Our immune system is based on the close collaboration of the innate and adaptive immune systems for the rapid detection of any threats to the host. Recognition of pathogen-derived molecules is entrusted to specific germline-encoded signaling receptors. The same receptors have now also emerged as efficient detectors of misplaced or altered self-molecules that signal tissue damage and cell death following, for example, disruption of the blood supply and subsequent hypoxia. Many types of endogenous molecules have been shown to provoke such sterile inflammatory states when released from dying cells. However, a group of proteins referred to as alarmins have both intracellular and extracellular functions which have been the subject of intense research. Indeed, alarmins can either exert beneficial cell housekeeping functions, leading to tissue repair, or provoke deleterious uncontrolled inflammation. This group of proteins includes the high-mobility group box 1 protein (HMGB1), interleukin (IL)-1α, IL-33 and the Ca²⁺-binding S100 proteins. These dual-function proteins share conserved regulatory mechanisms, such as secretory routes, post-translational modifications and enzymatic processing, that govern their extracellular functions in time and space. Release of alarmins from mesenchymal cells is a highly relevant mechanism by which immune cells can be alerted of tissue damage, and alarmins play a key role in the development of acute or chronic inflammatory diseases and in cancer development.

Translocation of the novel cytokine HMGB1 to the cytoplasm and extracellular space coincides with the peak of clinical activity in experimentally UV-induced lesions of cutaneous lupus erythematosus

HMGB1 is a pro-inflammatory cytokine that together with TNF-α and IL-1β is involved in the pathogenesis of spontaneously occurring skin lesions in lupus erythematosus. The purpose of the present study was to explore the sequence of events in HMGB1, TNF-α and IL-1β expression under development and resolution of experimentally induced CLE lesions. The study involved investigation of 38 serial skin biopsies acquired from photoprovoked skin lesions of nine CLE patients, using immunohistochemical staining of tissue sections. In biopsies from the clinically most active phase of skin involvement extracellular, secreted HMGB1 and increased cytoplasmic HMGB1 were found, as compared with the late and fading lesions or non-lesional skin. Besides HMGB1, increased expression of TNF-α and IL-1β was observed in dermal infiltrates of the induced CLE lesions. These cytokines were however not upregulated in all lesions, and increased expression of IL-1β was seen predominantly in late biopsies.

In conclusion, extracellular and cytoplasmic HMGB1 coincides with the clinically most active phase of photoinduced lesions of cutaneous lupus, and suggests that HMGB1 is an important factor in the inflammatory autoimmune process of CLE. HMGB1 can induce expression of TNF-α and IL-1β, and formation of a pro-inflammatory loop between HMGB1, TNF-α, and IL-1β may be responsible for the prolonged and sustained inflammation in CLE. Lupus (2007) 16, 794—802.

HMGB1 as biomarker and drug target

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

High mobility group box 1 is increased in the sera of psoriatic patients with disease progression

BACKGROUND

Psoriasis vulgaris (PV) is an autoimmune-related chronic inflammatory disease, which appears mostly in skin, but also affects the vascular and metabolic system. The incidence of PV is 2-3% in the general population and there is still no possibility to cure. Trigger factors have been identified to initiate and maintain inflammation in the skin, which is characterized by Th1-, Th17- and Th22- cells.

OBJECTIVE

We hypothesize that the damage-associated molecular pattern (DAMP) molecule high mobility group box 1 (HMGB1) plays a role in the pathogenesis of PV. HMGB1 is a DNA-binding protein located in the nucleus, which acquires cytokine-like properties once released from the cell upon necrotic cell death or actively secreted by immune cells in inflammation and cancer.

METHODS

We recruited 90 psoriatic patients under and without therapy with mild, intermediate and severe progression of disease, defined by the Psoriasis Area Severity Index. Serum levels of HMGB1 in patients with PV were detected by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Our results show an increased level of HMGB1 in the sera of patients with PV in comparison to healthy donors. Furthermore, our analyses reveal that HMGB1 levels are significantly increased with disease progression and are downregulated after standard therapies for PV have been conducted.

CONCLUSION

Our data provide insights into a possible role of HMGB1 for inflammation in PV.

Lupus erythematosus revisited

Lupus erythematosus (LE) is a multifactorial autoimmune disease with clinical manifestations of differing severity. The exact pathomechanisms and interactions resulting in the inflammatory and immunological processes of this heterogeneous disease remain elusive. Approaches in the understanding of the pathomechanisms revealed that the clinical expression of LE is predisposed by susceptibility genes and that various environmental factors are responsible for an abnormal immune response. Several studies demonstrated that ultraviolet (UV) light is one of the major factors in the pathogenesis of the disease. Standardized photoprovocation in patients with LE has been shown to be a safe and efficient model for evaluating the underlying pathomechanisms which lead to the production of autoantibodies and immune complexes. In particular, interferons were defined as important players in the early activation of the immune system and were observed to play a specific role in the immunological interface between the innate and the adaptive immune system. Abnormalities or disturbances in the different processes of cell death, such as apoptosis or necrosis, have also been recognized as crucial in the pathogenesis of LE. Although each process is different and characterized by unique features, the processes are interrelated and result in a complex disease.

HMGB1 in the pathogenesis of ultraviolet-induced ocular surface inflammation

High-mobility group box 1 (HMGB1) functions as a transcription-enhancing nuclear protein as well as a crucial cytokine that regulates inflammation. This study demonstrated that secretion of HMGB1 due to ultraviolet (UV) radiation inducing ocular surface inflammation-mediated reactive oxygen species (ROS) production. After treating conjunctival epithelial cells with UV radiation, HMGB1 was translocated from the nucleus to the cytoplasm and then eventually to the extracellular space. HMGB1 played a crucial role in UV-induced conjunctival neutrophil infiltration, which subsided when mice were pretreated with the HMGB1 inhibitors soluble receptor for advanced glycation endproducts (sRAGEs) and HMGB1 A box protein. In case of using ROS quencher, there was decrease in UV-induced HMGB1 secretion in conjunctival epithelial cells and mice. Considering that UV-induced chronic inflammation causes ocular surface change as pterygium, we have confirmed high HMGB1 translocation and ROS expression in human pterygium. Our findings therefore revealed a previously unknown mechanism of UV-induced ocular inflammation related to ROS and HMGB1 suggesting a new medical therapeutic target.

Emerging roles for HMGB1 protein in immunity, inflammation, and cancer

High-mobility group box 1 (HMGB1) protein is a member of the highly conserved non-histone DNA binding protein family. First identified in 1973, as one of a group of chromatin-associated proteins with high acidic and basic amino acid content, it was so named for its characteristic rapid mobility in polyacrylamide gel electrophoresis. HMGB1 was later discovered to have another function. It is released from a variety of cells into the extracellular milieu to act on specific cell-surface receptors. In this latter role, HMGB1 is a proinflammatory cytokine that may contribute to many inflammatory diseases, including sepsis. Therefore, HMGB1 regulates intracellular cascades influencing immune cell functions, including chemotaxis and immune modulation. The bioactivity of the HMGB1 is determined by specific posttranslational modifications that regulate its role in inflammation and immunity. During tumor development, HMGB1 has been reported to play paradoxical roles in promoting both cell survival and death by regulating multiple signaling pathways. In this review, we focus on the role of HMGB1 in physiological and pathological responses, as well as the mechanisms by which it contributes to immunity, inflammation, and cancer progression.

Various forms of tissue damage and danger signals following hematopoietic stem-cell transplantation

Hematopoietic stem-cell transplantation (HSCT) is the most potent curative therapy for many malignant and non-malignant disorders. Unfortunately, a major complication of HSCT is graft-versus-host disease (GVHD), which is mediated by tissue damage resulting from the conditioning regimens before the transplantation and the alloreaction of dual immune components (activated donor T-cells and recipient’s antigen-presenting cells). This tissue damage leads to the release of alarmins and the triggering of pathogen-recognition receptors that activate the innate immune system and subsequently the adaptive immune system. Alarmins, which are of endogenous origin, together with the exogenous pathogen-associated molecular patterns (PAMPs) elicit similar responses of danger signals and represent the group of damage-associated molecular patterns (DAMPs). Effector cells of innate and adaptive immunity that are activated by PAMPs or alarmins can secrete other alarmins and amplify the immune responses. These complex interactions and loops between alarmins and PAMPs are particularly potent at inducing and then aggravating the GVHD reaction. In this review, we highlight the role of these tissue damaging molecules and their signaling pathways. Interestingly, some DAMPs and PAMPs are organ specific and GVHD-induced and have been shown to be interesting biomarkers. Some of these molecules may represent potential targets for novel therapeutic approaches.

The presence of high mobility group box-1 and soluble receptor for advanced glycation end-products in juvenile idiopathic arthritis and juvenile systemic lupus erythematosus

BACKGROUND

The involvement of high mobility group box-1 (HMGB1) in various inflammatory and autoimmune diseases has been documented but clinical trials on the contribution of this pro-inflammatory alarmin in children with juvenile idiopathic arthritis (JIA) and systemic lupus erythematosus (SLE) are basically absent. To address the presence of HMGB1 and a soluble receptor for advanced glycation end products (sRAGE) in different subtypes of JIA and additionally in children with SLE, we enrolled a consecutive sample of children harvested peripheral blood as well as synovial fluids (SF) at diagnosis and correlated it with ordinary acute-phase reactants and clinical markers.

METHODS

Serum and synovial fluids levels of HMGB1 and sRAGE in total of 144 children (97 with JIA, 19 with SLE and 27 healthy controls) were determined by ELISA.

RESULTS

The children with JIA and those with SLE were characterised by significantly higher serum levels of HMGB1 and significantly lower sRAGE levels compared to the healthy controls. A positive correlation between serum HMGB1 and ESR, CRP, α2 globulin was found while serum sRAGE levels were inversely correlated with the same inflammatory markers in children with JIA. Additionally, high level of serum HMGB1 was related to hepatosplenomegaly or serositis in systemic onset JIA.

CONCLUSION

The inverse relationship of the HMGB1 and its soluble receptor RAGE in the blood and SF indicates that inflammation triggered by alarmins may play a role in pathogenesis of JIA as well as SLE. HMGB1 may serve as an inflammatory marker and a potential target of biological therapy in these patients. Further studies need to show whether the determination of HMGB1 levels in patients with JIA can be a useful guideline for detecting disease activity.

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.

The role of high mobility group box 1 in innate immunity

With growing accounts of inflammatory diseases such as sepsis, greater understanding the immune system and the mechanisms of cellular immunity have become primary objectives in immunology studies. High mobility group box 1 (HMGB1) is a ubiquitous nuclear protein that is implicated in various aspects of the innate immune system as a damage-associated molecular pattern molecule and a late mediator of inflammation, as well as in principal cellular processes, such as autophagy and apoptosis. HMGB1 functions in the nucleus as a DNA chaperone; however, it exhibits cytokine-like activity when secreted by injurious or infectious stimuli. Extracellular HMGB1 acts through specific receptors to promote activation of the NF-κB signaling pathway, leading to production of cytokines and chemokines. These findings further implicate HMGB1 in lethal inflammatory diseases as a crucial regulator of inflammatory, injurious, and infectious responses. In this paper, we summarize the role of HMGB1 in inflammatory and non-inflammatory states and assess potential therapeutic approaches targeting HMGB1 in inflammatory diseases.

Chance, genetics, and the heterogeneity of disease and pathogenesis in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a remarkably complex and heterogeneous systemic autoimmune disease. Disease complexity within individuals and heterogeneity among individuals, even genetically identical individuals, is driven by stochastic execution of a complex inherited program. Genome-wide association studies (GWAS) have progressively improved understanding of which genes are most critical to the potential for SLE and provided illuminating insight about the immune mechanisms that are engaged in SLE. What initiates expression of the genetic program to cause SLE within an individual and how that program is initiated remains poorly understood. If we extrapolate from all of the different experimental mouse models for SLE, we can begin to appreciate why SLE is so heterogeneous and consequently why prediction of disease outcome is so difficult. In this review, we critically evaluate extrinsic versus intrinsic cellular functions in the clearance and elimination of cellular debris and how dysfunction in that system may promote autoimmunity to nuclear antigens. We also examine several mouse models genetically prone to SLE either because of natural inheritance or inheritance of induced mutations to illustrate how different immune mechanisms may initiate autoimmunity and affect disease pathogenesis. Finally, we describe the heterogeneity of disease manifestations in SLE and discuss the mechanisms of disease pathogenesis with emphasis on glomerulonephritis. Particular attention is given to discussion of how anti-DNA autoantibody initiates experimental lupus nephritis (LN) in mice.

Rad50-CARD9 interactions link cytosolic DNA sensing to IL-1β production

Double-stranded DNA (dsDNA) in the cytoplasm triggers the production of interleukin 1β (IL-1β) as an antiviral host response, and deregulation of the pathways involved can promote inflammatory disease. Here we report a direct cytosolic interaction between the DNA-damage sensor Rad50 and the innate immune system adaptor CARD9. Transfection of dendritic cells with dsDNA or infection of dendritic cells with a DNA virus induced the formation of dsDNA-Rad50-CARD9 signaling complexes for activation of the transcription factor NF-κB and the generation of pro-IL-1β. Primary cells conditionally deficient in Rad50 or lacking CARD9 consequently exhibited defective DNA-induced production of IL-1β, and Card9(-/-) mice had impaired inflammatory responses after infection with a DNA virus in vivo. Our results define a cytosolic DNA-recognition pathway for inflammation and a physical and functional connection between a conserved DNA-damage sensor and the innate immune response to pathogens.

Molecular mechanism and therapeutic modulation of high mobility group box 1 release and action: an updated review

High mobility group box 1 (HMGB1) is an evolutionarily conserved protein, and is constitutively expressed in virtually all types of cells. Infection and injury converge on common inflammatory responses that are mediated by HMGB1 secreted from immunologically activated immune cells or passively released from pathologically damaged cells. Herein we review the emerging molecular mechanisms underlying the regulation of pathogen-associated molecular patterns (PAMPs)-induced HMGB1 secretion, and summarize many HMGB1-targeting therapeutic strategies for the treatment of infection- and injury-elicited inflammatory diseases. It may well be possible to develop strategies that specifically attenuate damage-associated molecular patterns (DAMPs)-mediated inflammatory responses without compromising the PAMPs-mediated innate immunity for the clinical management of infection- and injury-elicited inflammatory diseases.

The alarmin functions of high-mobility group box-1 and IL-33 in the pathogenesis of systemic lupus erythematosus

'Alarmins' are a group of endogenous proteins or molecules that are released from cells during cellular demise to alert the host innate immune system. Two of them, high-mobility group box-1 (HMGB1) and IL-33 shared many similarities of cellular localization, functions and involvement in various inflammatory diseases including systemic lupus erythematosus (SLE). The expressions of HMGB1 and IL-33, and their corresponding receptors RAGE (receptor for advanced glycation end products) and ST2, respectively, are substantially upregulated in patients with lupus nephritis (LN). This review highlights the emerging roles of alarmin proteins in various pathologies of LN, by focusing on classical HMGB1 and a newly discovered alarmin IL-33.

The role of HMGB1 in the pathogenesis of inflammatory and autoimmune diseases

High-mobility group box 1 (HMGB1) protein is a highly abundant protein that can promote the pathogenesis of inflammatory and autoimmune diseases once it is in an extracellular location. This translocation can occur with immune cell activation as well as cell death, with the conditions for release associated with the expression of different isoforms. These isoforms result from post-translational modifications, with the redox states of three cysteines at positions 23, 45 and 106 critical for activity. Depending on the redox states of these residues, HMGB1 can induce cytokine production via toll-like receptor 4 (TLR4) or promote chemotaxis by binding the chemokine CXCL12 for stimulation via CXCR4. Fully oxidized HMGB1 is inactive. During the course of inflammatory disease, HMGB1 can therefore play a dynamic role depending on its redox state. As a mechanism to generate alarmins, cell death is an important source of HMGB1, although each major cell death form (necrosis, apoptosis, pyroptosis and NETosis) can lead to different isoforms of HMGB1 and variable levels of association of HMGB1 with nucleosomes. The association of HMGB1 with nucleosomes may contribute to the pathogenesis of systemic lupus erythematosus by producing nuclear material whose immunological properties are enhanced by the presence of an alarmin. Since HMGB1 levels in blood or tissue are elevated in many inflammatory and autoimmune diseases, this molecule can serve as a unique biomarker as well as represent a target of novel therapies to block its various activities.

Recent developments in the role of high-mobility group box 1 in systemic lupus erythematosus

High-mobility group box 1 (HMGB1) is an important molecule for several nuclear processes. Recently, HMGB1 has gained much attention as a damage-associated molecular pattern (DAMP) and has been implicated in the pathogenesis of several (auto)-immune diseases, in particular, systemic lupus erythematosus (SLE). A main pathogenic feature in SLE is the accumulation of apoptotic cells. Since HMGB1 is released from apoptotic cells it has been hypothesized that HMGB1 might fuel the inflammatory processes, as seen in this disease, and play a fundamental role in the pathogenesis. In this review, we discuss evidence in support of the theory that HMGB1 is an important mediator in SLE and may be considered a new autoantigen.