HMGB1: A pleiotropic activity

The mechanism of high mobility group box-1 protein and its bidirectional regulation in tumors

High-mobility group box-1 protein (HMGB1) is a nonhistone chromatin-related protein widely found in eukaryotic cells. It is involved in the transcription, replication, and repair of DNA to maintain nuclear homeostasis. It participates in cell growth, differentiation, and signal transduction. Recent studies showed that HMGB1 has a bidirectional regulatory effect on tumors by regulating TLR4/MYD88/NF-κB and RAGE/AMPK/mTOR signaling pathways. On the one hand, it is highly expressed in a variety of tumors, promoting tumor proliferation and invasion, while on the other hand, it induces autophagy and apoptosis of tumor cells and stimulates tumor-infiltrating lymphocytes to produce an anti-tumor immune response. At present, HMGB1 could be used as a target to regulate the drug resistance and prognostication in cancer. Clinical applications of HMGB1 in cancer need further in-depth studies.

A Review of Proposed Mechanisms in Rheumatoid Arthritis and Therapeutic Strategies for the Disease

Rheumatoid arthritis (RA) is characterized by synovial edema, inflammation, bone and cartilage loss, and joint degradation. Patients experience swelling, stiffness, pain, limited joint movement, and decreased mobility as the condition worsens. RA treatment regimens often come with various side effects, including an increased risk of developing cancer and organ failure, potentially leading to mortality. However, researchers have proposed mechanistic hypotheses to explain the underlying causes of synovitis and joint damage in RA patients. This review article focuses on the role of synoviocytes and synoviocytes resembling fibroblasts in the RA synovium. Additionally, it explores the involvement of epigenetic regulatory systems, such as microRNA pathways, silent information regulator 1 (SIRT1), Peroxisome proliferatoractivated receptor-gamma coactivator (PGC1-α), and protein phosphatase 1A (PPM1A)/high mobility group box 1 (HMGB1) regulators. These mechanisms are believed to modulate the function of receptors, cytokines, and growth factors associated with RA. The review article includes data from preclinical and clinical trials that provide insights into potential treatment options for RA.

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

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

Developmental expression of high-mobility group box 1 (HMGB1) in the mouse cochlea

The expression changes of high-mobility group box 1 (HMGB1) in the mouse cochlea have recently been implicated in noise-induced hearing loss, suggesting that HMGB1 participates in regulating cochlear function. However, the precise role of HMGB1 in the auditory system remains largely unclear. This study aimed to investigate its function in the developing mouse cochlea by examining the expression pattern of HMGB1 in the mouse cochlea from embryonic day (E) 18.5 to postnatal day (P) 28 using double immunofluorescence on frozen sections. Our findings revealed that HMGB1 was extensively expressed in the cell nucleus across various regions of the mouse cochlea, including the organ of Corti. Furthermore, its expression underwent developmental regulation during mouse cochlear development. Specifically, HMGB1 was found to be localized in the tympanic border cells at each developmental stage, coinciding with the gradual anatomical in this region during development. In addition, HMGB1 was expressed in the greater epithelial ridge (GER) and supporting cells of the organ of Corti, as validated by the supporting cell marker Sox2 at P1 and P8. However, at P14, the expression of HMGB1 disappeared from the GER, coinciding with the degeneration of the GER into the inner sulcus cells. Moreover, we observed that HMGB1 co-localized with Ki-67-positive proliferating cells in several cochlear regions during late embryonic and early postnatal stages, including the GER, the tympanic border cells, cochlear lateral wall, and cochlear nerves. Furthermore, by dual-staining Ki-67 with neuronal marker TUJ1 and glial marker Sox10, we determined the expression of Ki-67 in the neonatal glial cells. Our spatial-temporal analysis demonstrated that HMGB1 exhibited distinct expression patterns during mouse cochlear development. The co-localization of HMGB1 with Ki-67-positive proliferating cells suggested that HMGB1 may play a role in cochlear development.

The role of HMGB1 in COVID-19-induced cytokine storm and its potential therapeutic targets: A review

Hyperinflammation characterized by elevated proinflammatory cytokines known as 'cytokine storms' is the major cause of high severity and mortality seen in COVID-19 patients. The pathology behind the cytokine storms is currently unknown. Increased HMGB1 levels in serum/plasma of COVID-19 patients were reported by many studies, which positively correlated with the level of proinflammatory cytokines. Dead cells following SARS-CoV-2 infection might release a large amount of HMGB1 and RNA of SARS-CoV-2 into extracellular space. HMGB1 is a well-known inflammatory mediator. Additionally, extracellular HMGB1 might interact with SARS-CoV-2 RNA because of its high capability to bind with a wide variety of molecules including nucleic acids and could trigger massive proinflammatory immune responses. This review aimed to critically explore the many possible pathways by which HMGB1-SARS-CoV-2 RNA complexes mediate proinflammatory responses in COVID-19. The contribution of these pathways to impair host immune responses against SARS-CoV-2 infection leading to a cytokine storm was also evaluated. Moreover, since blocking the HMGB1-SARS-CoV-2 RNA interaction might have therapeutic value, some of the HMGB1 antagonists have been reviewed. The HMGB1- SARS-CoV-2 RNA complexes might trigger endocytosis via RAGE which is linked to lysosomal rupture, PRRs activation, and pyroptotic death. High levels of the proinflammatory cytokines produced might suppress many immune cells leading to uncontrolled viral infection and cell damage with more HMGB1 released. Altogether these mechanisms might initiate a proinflammatory cycle leading to a cytokine storm. HMGB1 antagonists could be considered to give benefit in alleviating cytokine storms and serve as a potential candidate for COVID-19 therapy.

Changes in inflammatory biomarkers in the nasal mucosal secretion after septoplasty

Deviated nasal septum (DNS) is suggested to be associated with nonspecific inflammation of the nasal mucosa. The authors hypothesized septoplasty may reduce nasal mucosal inflammation, therefore the authors aimed to measure various inflammatory biomarkers in the nasal secretion following septoplasty. Prospectively, 17 patients undergoing elective septoplasty were included. Symptomatic changes after septoplasty were evaluated with Sino-nasal Outcome Test (SNOT-22) and Nasal obstruction symptom evaluation (NOSE) scores. Using acoustic rhinometry, changes of the nasal airway volume were measured. Nasal secretion was collected within 2 weeks and 3 months before and after septoplasty, respectively. The inflammatory biomarker high-mobility group box 1 (HMGB1) and vasoactive intestinal peptide (VIP), and inflammatory cytokines including tumor necrosis factor α (TNF α), interferon γ (IFN-γ), interleukin-4 (IL-4), eotaxin-1, and regulated upon activation, normal T cell expressed and presumably secreted (RANTES) were quantified in the nasal secretion by enzyme-linked immunosorbent assays or multiplex bead array assays. The patients' mean age was 30.5 ± 6.8 (ranging from 19 to 43), consisting of 15 male and 2 female patients. The median SNOT-22 and NOSE scores changed from 54 to 14 and 78 to 15, respectively, both showing a significant decrease. In acoustic rhinometry, nasal cavity volume of convex side significantly increased after septoplasty, whereas significant discrepancy of nasal airway volume between concave and convex sides became insignificant. No significant difference was noted both before and after septoplasty between the concave and convex sides in all seven biomarkers. The HMGB1, RANTES, IL-4, and TNF-α concentrations following septoplasty showed significant decrease in 34 nasal cavities of 17 patients (all p < 0.05). However, when the 17 concave and 17 convex sides were analyzed separately, the significant reduction in four biomarkers were only significant in the concave sides (all p < 0.05), but not significantly reduced in convex sides. Septoplasty may have benefited not only in normalizing the nasal airflow and symptom improvement, but also in nonspecific inflammation attenuation in the nasal airway.

The Prothrombotic State Associated with SARS-CoV-2 Infection: Pathophysiological Aspects

Severe coronavirus disease-2019 (COVID-19) is frequently associated with microvascular thrombosis, especially in the lung, or macrovascular thrombosis, mainly venous thromboembolism, which significantly contributes to the disease mortality burden. COVID-19 patients also exhibit distinctive laboratory abnormalities that are compatible with a prothrombotic state. The key event underlying COVID-19-associated thrombotic complications is an excessive host inflammatory response to severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) infection generating multiple inflammatory mediators, mainly cytokines and complement activation products. The latter, along with the virus itself, the increased levels of angiotensin II and hypoxia, drive the major cellular changes promoting thrombosis, which include: (1) aberrant expression of tissue factor by activated alveolar epithelial cells, monocytes-macrophages and neutrophils, and production of other prothrombotic factors by activated endothelial cells (ECs) and platelets; (2) reduced expression of physiological anticoagulants by dysfunctional ECs, and (3) suppression of fibrinolysis by the endothelial overproduction of plasminogen activator inhibitor-1 and, likely, by heightened thrombin-mediated activation of thrombin-activatable fibrinolysis inhibitor. Moreover, upon activation or death, neutrophils and other cells release nuclear materials that are endowed with potent prothrombotic properties. The ensuing thrombosis significantly contributes to lung injury and, in most severe COVID-19 patients, to multiple organ dysfunction. Insights into the pathogenesis of COVID-19-associated thrombosis may have implications for the development of new diagnostic and therapeutic tools.

HMGB1: A pleiotropic activity

High-mobility group box 1 (HMGB1) is a nuclear protein involved in DNA replication, transcription, recombination, and repair. In the extracellular space, the HMGB1 plays an essential role in the onset and perpetuation of inflammation, belonging to the group of damage-associated molecular pattern (DAMP) molecules, also called alarmins. For this, HMGB1 has been studied in several acute and chronic inflammatory diseases as an early biomarker of inflammation. An increased concentration of HMGB1 has been detected in serum, as the expression of systemic inflammation, and in specific samples (such as stool, synovial fluid, nasal lavage fluid, sputum, and cerebrospinal fluid), as the expression of local production, in several infectious and/or inflammatory diseases. These data are particularly important because they open new futuristic possibilities for target therapies, potentially also for the COVID-19 treatment.