High mobility group box 1 potentiates the pro-inflammatory effects of interleukin-1β in osteoarthritic synoviocytes

The role of high mobility group proteins in cellular senescence mechanisms

Aging is a universal physiological phenomenon, and chronic age-related diseases have become one of the leading causes of human mortality, accounting for nearly half of all deaths. Studies have shown that reducing the incidence of these diseases can not only extend lifespan but also promote healthy aging. In recent years, the potential role of non-histone high-mobility group proteins (HMGs) in the regulation of aging and lifespan has attracted widespread attention. HMGs play critical roles in cellular senescence and associated diseases through various pathways, encompassing multi-layered mechanisms involving protein interactions, molecular regulation, and chromatin dynamics. This review provides a comprehensive analysis of the interactions between HMG family proteins and senescence-associated secretory phenotype (SASP), chromatin structure, and histone modifications, offering a deeper exploration of the pivotal functions and impacts of HMGs in the aging process. Furthermore, we summarize recent findings on the contributions of HMG proteins to aging and age-related diseases. HMG proteins not only regulate senescence-associated inflammation through modulating the SASP but also influence genomic stability and cell fate decisions via interactions with chromatin and histones. Targeting HMG proteins holds great potential in delaying the progression of aging and its associated diseases. This review aims to provide a systematic overview of HMG proteins' roles in aging and to lay a solid foundation for future anti-aging drug development and therapeutic strategies. With the advancing understanding of the mechanisms by which HMGs regulate aging, developing therapeutic interventions targeting HMGs may emerge as a promising approach to extending lifespan and enhancing healthspan.

Pyroptosis-related crosstalk in osteoarthritis: Macrophages, fibroblast-like synoviocytes and chondrocytes

The pathogenesis of osteoarthritis (OA) involves a multifaceted interplay of inflammatory processes. The initiation of pyroptosis involves the secretion of pro-inflammatory cytokines and has been identified as a critical factor in regulating the development of OA. Upon initiation of pyroptosis, a multitude of inflammatory mediators are released and can be disseminated throughout the synovial fluid within the joint cavity, thereby facilitating intercellular communication across the entire joint. The main cellular components of joints include chondrocytes (CC), fibroblast-like synoviocytes (FLS) and macrophages (MC). Investigating their interplay can enhance our understanding of OA pathogenesis. Therefore, we comprehensively examine the mechanisms underlying pyroptosis and specifically investigate the intercellular interactions associated with pyroptosis among these three cell types, thereby elucidating their collective contribution to the progression of OA. We propose the concept of ' CC-FLS-MC pyroptosis-related crosstalk', describe the various pathways of pyroptotic interactions among these three cell types, and focus on recent advances in intervening pyroptosis in these three cell types for treating OA. We hope this will provide a possible direction for diversification of treatment for OA. The Translational potential of this article. The present study introduces the concept of 'MC-FLS-CC pyroptosis-related crosstalk' and provides an overview of the mechanisms underlying pyroptosis, as well as the pathways through which it affects MC, FLS, and CC. In addition, the role of regulation of these three types of cellular pyroptosis in OA has also been concerned. This review offers novel insights into the interplay between these cell types, with the aim of providing a promising avenue for diversified management of OA.

n-3 polyunsaturated fatty acids alleviate the progression of obesity-related osteoarthritis and protect cartilage through inhibiting the HMGB1-RAGE/TLR4 signaling pathway

Osteoarthritis (OA) is a common joint degenerative disease. There is currently no cure for OA. Dietary fatty acids have potential value in the prevention and treatment of OA. n-3 polyunsaturated fatty acids (PUFAs) have anti-inflammatory effects, but their anti-OA mechanism remains unclear. High-mobility group box 1 (HMGB1) promotes inflammation and participates the pathogenesis of OA. The purpose of this study was to investigate the protective effect of n-3 PUFAs on cartilage and whether n-3 PUFAs could exert an anti-OA effect through inhibiting HMGB1-RAGE/TLR4 signaling pathway. We established an obesity-related post-traumatic OA mice model and an in vitro study was conducted to explore the regulatory mechanism of n-3 PUFAs on HMGB1 and its signal pathway against OA. We found that diet rich in n-3 PUFAs alleviated OA-like lesions of articular cartilage with the decrease of HMGB1-RAGE/TLR4 signaling protein in mice. In SW1353 cells, DHA significantly reduced the expression of HMGB1-RAGE/TLR4 signaling protein which was up-regulated by IL-1β stimulation. HMGB1 overexpression reversed the inhibitory effect of DHA on HMGB1-RAGE/TLR4 signaling pathway. The activation of SIRT1 may participate the inhibitory effect of DHA on HMGB1-RAGE/TLR4 signaling pathway. In conclusion, n-3 PUFAs could attenuate the progression of obesity-related OA and exert protective effect on cartilage by inhibiting HMGB1-RAGE/TLR4 signaling pathway, which may be associated with the activation of SIRT1. Dietary n-3 PUFAs supplements can be considered as a potential therapeutic substance for OA.

The Role of Alarmins in Osteoarthritis Pathogenesis: HMGB1, S100B and IL-33

Osteoarthritis (OA) is a multifactorial disease in which genetics, aging, obesity, and trauma are well-known risk factors. It is the most prevalent joint disease and the largest disability problem worldwide. Recent findings have described the role of damage-associated molecular patterns (DAMPs) in the course of the disease. In particular, alarmins such as HMGB1, IL-33, and S100B, appear implicated in enhancing articular inflammation and favouring a catabolic switch in OA chondrocytes. The aims of this review are to clarify the molecular signalling of these three molecules in OA pathogenesis, to identify their possible use as staging biomarkers, and, most importantly, to find out whether they could be possible therapeutic targets. Osteoarthritic cartilage expresses increased levels of all three alarmins. HMGB1, in particular, is the most studied alarmin with increased levels in cartilage, synovium, and synovial fluid of OA patients. High levels of HMGB1 in synovial fluid of OA joints are positively correlated with radiological and clinical severity. Counteracting HMGB1 strategies have revealed improving results in articular cells from OA patients and in OA animal models. Therefore, drugs against this alarmin, such as anti-HMGB1 antibodies, could be new treatment possibilities that can modify the disease course since available medications only alleviate symptoms.

The Role of Genetics and Epigenetic Regulation in the Pathogenesis of Osteoarthritis

Osteoarthritis (OA) is progressive disease characterised by cartilage degradation, subchondral bone remodelling and inflammation of the synovium. The disease is associated with obesity, mechanical load and age. However, multiple pro-inflammatory immune mediators regulate the expression of metalloproteinases, which take part in cartilage degradation. Furthermore, genetic factors also contribute to OA susceptibility. Recent studies have highlighted that epigenetic mechanisms may regulate the expression of OA-associated genes. This review aims to present the mechanisms of OA pathogenesis and summarise current evidence regarding the role of genetics and epigenetics in this process.

The Nrf2/HMGB1/NF-κB axis modulates chondrocyte apoptosis and extracellular matrix degradation in osteoarthritis

Osteoarthritis (OA) is a degenerative or posttraumatic condition of the joints. In OA chondrocytes, Nrf2 functions as a stress response regulator with antioxidant and anti-inflammatory effects. This study aims to investigate the role of Nrf2 and its downstream pathway in the development of osteoarthritis. IL-1β treatment suppresses Nrf2, aggrecan, and COL2A1 levels and cell viability but promotes apoptosis in chondrocytes. IL-1β stimulation induces cell apoptosis, upregulates the mRNA expression of inflammatory factors, decreases aggrecan, COL2A1, and Bcl-2 levels but increases ADAMTS-5, ADAMTS-4, MMP13, cleaved caspase 3, and BAX levels, and promotes p65 phosphorylation. Nrf2 overexpression exerts opposite effects on IL-1β-treated chondrocytes, as demonstrated by the significant attenuation of IL-1β-induced changes in chondrocytes. By binding to the HMGB1 promoter region, Nrf2 suppresses HMGB1 expression. Similar to Nrf2 overexpression, HMGB1 knockdown also attenuates IL-1β-induced changes in chondrocytes. Notably, under IL-1β stimulation, the effects of Nrf2 overexpression or tert-butylhydroquinone (TBHQ, an activator of Nrf2) on apoptosis, inflammatory factor expression, ECM and apoptosis, and NF-κB pathway activity in chondrocytes are remarkably reversed by HMGB1 overexpression or recombinant HMGB1 (rHMGB1). Similarly, rHMGB1 could partially counteract the curative effect of TBHQ on OA damage in mice. In OA cartilage tissue samples, the level of Nrf2 is lower, while the levels of HMGB1, apoptotic, and inflammatory factors are increased compared to normal cartilage tissue samples. In conclusion, for the first time, the Nrf2/HMGB1 axis was found to modulate apoptosis, ECM degradation, inflammation and activation of NF-κB signaling in chondrocytes and OA mice.

High mobility group box 1, ATP, lipid mediators, and tissue factor are elevated in COVID-19 patients: HMGB1 as a biomarker of worst prognosis

The severe acute respiratory syndrome coronavirus 2, the agent of the ongoing coronavirus disease 2019 (COVID-19) pandemic, has spread worldwide since it was first identified in November 2019 in Wuhan, China. Since then, progress in pathogenesis linked severity of this systemic disease to the hyperactivation of network of cytokine-driven pro-inflammatory cascades. Here, we aimed to identify molecular biomarkers of disease severity by measuring the serum levels of inflammatory mediators in a Brazilian cohort of patients with COVID-19 and healthy controls (HCs). Critically ill patients in the intensive care unit were defined as such by dependence on oxygen supplementation (93% intubated and 7% face mask), and computed tomography profiles showing ground-glass opacity pneumonia associated to and high levels of D-dimer. Our panel of mediators included HMGB1, ATP, tissue factor, PGE₂ , LTB₄ , and cys-LTs. Follow-up studies showed increased serum levels of every inflammatory mediator in patients with COVID-19 as compared to HCs. Originally acting as a transcription factor, HMGB1 acquires pro-inflammatory functions following secretion by activated leukocytes or necrotic tissues. Serum levels of HMGB1 were positively correlated with cys-LTs, D-dimer, aspartate aminotransferase, and alanine aminotransferase. Notably, the levels of the classical alarmin HMGB1 were higher in deceased patients, allowing their discrimination from patients that had been discharged at the early pulmonary and hyperinflammatory phase of COVID-19. In particular, we verified that HMGB1 levels above 125.4 ng/ml is the cutoff that distinguishes patients that are at higher risk of death. In conclusion, we propose the use of serum levels of HMGB1 as a biomarker of severe prognosis of COVID-19.

Pyroptosis: A Novel Intervention Target in the Progression of Osteoarthritis

Osteoarthritis (OA) is one of the most common chronic joint diseases and is gradually becoming the main cause of disability and joint pain in the elderly worldwide. Pyroptosis is a regulated programmed cell death triggered by inflammasomes. It leads to cell swelling, lysis, and bioactive molecule secretion. Studies found that the damaged chondrocytes in OA joints had morphological characteristics of pyroptosis, and the cytokines associated with pyroptosis in synovial fluid increased, indicating that pyroptosis may have certain impacts on the pathological progression of OA. This review briefly summarizes the molecular mechanisms of pyroptosis and the epidemiology and pathogenesis of OA. Furthermore, we discussed the role of pyroptosis in articular cartilage and synovium during OA and reviewed the progress of pyroptosis-related molecules in the targeted therapy of OA joints, hoping to provide feasible directions for the diversified treatment of OA.

Low-Grade Inflammation in the Pathogenesis of Osteoarthritis: Cellular and Molecular Mechanisms and Strategies for Future Therapeutic Intervention

Osteoarthritis (OA) is a musculoskeletal disease characterized by cartilage degeneration and stiffness, with chronic pain in the affected joint. It has been proposed that OA progression is associated with the development of low-grade inflammation (LGI) in the joint. In support of this principle, LGI is now recognized as the major contributor to the pathogenesis of obesity, aging, and metabolic syndromes, which have been documented as among the most significant risk factors for developing OA. These discoveries have led to a new definition of the disease, and OA has recently been recognized as a low-grade inflammatory disease of the joint. Damage-associated molecular patterns (DAMPs)/alarmin molecules, the major cellular components that facilitate the interplay between cells in the cartilage and synovium, activate various molecular pathways involved in the initiation and maintenance of LGI in the joint, which, in turn, drives OA progression. A better understanding of the pathological mechanisms initiated by LGI in the joint represents a decisive step toward discovering therapeutic strategies for the treatment of OA. Recent findings and discoveries regarding the involvement of LGI mediated by DAMPs in OA pathogenesis are discussed. Modulating communication between cells in the joint to decrease inflammation represents an attractive approach for the treatment of OA.

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.

Troxerutin-Mediated Complement Pathway Inhibition is a Disease-Modifying Treatment for Inflammatory Arthritis

Troxerutin (TXR) is a phytochemical reported to possess anti-inflammatory and hepatoprotective effects. In this study, we aimed to exploit the antiarthritic properties of TXR using an adjuvant-induced arthritic (AIA) rat model. AIA-induced rats showed the highest arthritis score at the disease onset and by oral administration of TXR (50, 100, and 200 mg/kg body weight), reduced to basal level in a dose-dependent manner. Isobaric tags for relative and absolute quantitative (iTRAQ) proteomics tool were employed to identify deregulated joint homogenate proteins in AIA and TXR-treated rats to decipher the probable mechanism of TXR action in arthritis. iTRAQ analysis identified a set of 434 proteins with 65 deregulated proteins (log₂ case/control≥1.5) in AIA. Expressions of a set of important proteins (AAT, T-kininogen, vimentin, desmin, and nucleophosmin) that could classify AIA from the healthy ones were validated using Western blot analysis. The Western blot data corroborated proteomics findings. In silico protein–protein interaction study of tissue-proteome revealed that complement component 9 (C9), the major building blocks of the membrane attack complex (MAC) responsible for sterile inflammation, get perturbed in AIA. Our dosimetry study suggests that a TXR dose of 200 mg/kg body weight for 15 days is sufficient to bring the arthritis score to basal levels in AIA rats. We have shown the importance of TXR as an antiarthritic agent in the AIA model and after additional investigation, its arthritic ameliorating properties could be exploited for clinical usability.

Glycyrrhizin, an HMGB1 inhibitor, Suppresses Interleukin-1β-Induced Inflammatory Responses in Chondrocytes from Patients with Osteoarthritis

BACKGROUND

High mobility group box 1 (HMGB1) is increased in osteoarthritis (OA) tissue and chondrocytes stimulated with interleukin-1β (IL-1β). Suppression of HMGB1 expression is correlated with reduced inflammatory responses induced by IL-1β. This study aimed to investigate how inhibition of HMGB1 by glycyrrhizin might affect inflammatory responses and viability of OA patient-derived chondrocytes treated with IL-1β.

DESIGN

The amounts of HMGB1 in the cartilage tissue and synovial fluid in patients with OA were assessed by Western blot and enzyme-linked immunosorbent assay (ELISA). Chondrocytes were extracted from OA patients and maintained in culture. The impact of glycyrrhizin on IL-1β-induced cell toxicity and inflammatory mediators and cytokines, including prostaglandin E2 (PGE₂), nitric oxide (NO), proinflammatory cytokines, and metalloproteases (MMPs), were assessed by ELISA, Western blot, quantitative real-time polymerase chain reaction, and the Griess reagent assay.

RESULTS

We confirmed that HMGB1 was significantly upregulated in specimens acquired from patients with OA. HMGB1 inhibition by glycyrrhizin improved cell viability of chondrocytes treated with IL-1β. Glycyrrhizin suppressed IL-1β-induced upregulation of HMGB1 and inflammatory mediators and cytokines, including PGE₂, NO, proinflammatory cytokines, and MMPs.

CONCLUSION

Our results indicate that glycyrrhizin may be a potential therapy for OA patients and these promising findings warrant further study for clinical application.

The potential remedy of melatonin on osteoarthritis

Osteoarthritis (OA), the most common arthritis worldwide, is a degenerative joint disease characterized by progressive cartilage breakdown, subchondral remodeling, and synovial inflammation. Although conventional pharmaceutical therapies aimed to prevent further cartilage loss and joint dysfunction, there are no ideal strategies that target the pathogenesis of OA. Melatonin exhibits a variety of regulatory properties by binding to specific receptors and downstream molecules and exerts a myriad of receptor-independent actions via intracellular targets as a chondrocyte protector, an anti-inflammation modulator, and a free radical scavenger. Melatonin also modulates cartilage regeneration and degradation by directly/indirectly regulating the expression of main circadian clock genes, such as transcriptional activators [brain and muscle aryl hydrocarbon receptor nuclear translocator-like protein (Bmal) and circadian locomotor output cycles kaput (Clock)], transcriptional repressors [period circadian regulator (Per)1/2, cryptochrome (Cry)1/2, and Dec2], and nuclear hormone receptors [Rev-Erbs and retinoid acid-related orphan receptors (Rors)]. Owing to its effects on cartilage homeostasis, we propose a potential role for melatonin in the prevention and therapy of OA via the modulation of circadian clock genes, mitigation of chondrocyte apoptosis, anti-inflammatory activity, and scavenging of free radicals.

Efficacy and Mechanism of Electroacupuncture Treatment of Rabbits With Different Degrees of Knee Osteoarthritis: A Study Based on Synovial Innate Immune Response

Knee osteoarthritis (KOA) is a chronic degenerative bone and joint disease, which is often clinically manifested as pain, joint swelling, and deformity. Its pathological manifestations are mainly synovial inflammation and cartilage degeneration. This study aims to investigate the efficacy of electro-acupuncture (EA) on model rabbits with varying degrees of KOA and to study the mechanism of EA on KOA based on the innate immune response. Mild and moderate rabbit KOA models were established using a modified Hluth method, and EA was given to both the mild and moderate model groups. The Lequesne-MG index was used to evaluate the behavioral changes in the rabbits before and after EA treatment. Morphological changes in the synovial membrane and cartilage of each group were observed by H&E staining. The Mankin scoring standard and the Krenn scoring standard were used to score the pathology of the cartilage tissue and synovial tissue, respectively. The inflammatory factors and metalloproteinases were detected in the serum of each group by ELISA. The protein and messenger RNA (mRNA) expressions of important elements related to Toll-like receptors (TLRs)-mediated innate immune response in the synovial tissue were detected by Western blot and quantitative PCR (qPCR). The Lequesne-MG index score of the rabbits gradually increased with the modeling prolonged but decreased significantly after EA treatment, indicating that EA has a better effect on alleviating the pain and improving the dysfunction. The morphological analysis showed that the inflammation of and the damage to the synovial membrane and the cartilage tissue gradually deteriorated with the modeling prolonged. However, the synovial membrane inflammation was significantly relieved after EA treatment, and the cartilage injury showed signs of repair. The ELISA analysis showed that, with the modeling prolonged, the serum-related inflammatory factors and mechanism of metalloproteinases gradually increased but decreased after EA treatment. The tumor necrosis factor alpha (TNF-α), interleukin 6 (IL-6), and matrix metalloproteinase3 (MMP3) of EA1 group were significantly lower than those of EA2 group. Both Western blot and qPCR results showed that the protein and mRNA expressions of the elements related to the innate immune response in the synovial membrane increased gradually with the modeling prolonged, but decreased significantly after EA treatment. Additionally, the expression of some components in EA1 group was significantly lower than that in EA2 group. These results confirm that synovial inflammation gradually aggravated with time from the early to mid-stage of KOA. EA alleviated the inflammation and histological changes in KOA rabbits by inhibiting the TLRs-mediated innate synovial immune response. This suggests that using EA in the early stage of KOA may achieve a desirable efficacy.

[Mechanism of high expression of high mobility group protein 1 in a rat model of knee osteoarthritis]

OBJECTIVE

To investigate the molecular mechanism triggering pyroptosis of synovial fibroblast-like synoviocytes(FLSs)and the release of high mobility group protein 1(HMGB1)in a rat model of knee osteoarthritis(KOA).

METHODS

Twelve SD rats were randomized equally into blank control group without any treatment and KOA group with anterior cruciate ligament amputation (ACLT) to induce KOA.HE staining and Mankin score were used to evaluate the damage of knee cartilage.Western blotting was used to detect the expression of pyroptosis-related proteins and HMGB1 in the synovial tissue.In the cell experiment, rat FLSs were treated with PBS (control group), LPS+ATP (to induce cell pyroptosis), or LPS+ATP+siRNAs (to inhibit pyroptosis of the FLSs), and the cellular expressions of apoptosis-related proteins and HMGB1 were detected using Western blotting; the level of HMGB1 in the culture supernatant was detected with ELISA.

RESULTS

In the rat models of KOA, the expressions of pyroptosis-related proteins and HMGB1 in the synovial tissue and Mankin score were significantly increased as compared with those in the control group(P < 0.05).In cultured rat FLSs, the expressions of apoptosis related proteins and HMGB1 were significantly higher in the pyroptosis group than in the control group and in cells transfected with the siRNAs targeting NLRP1, NLRP3, ASC and caspase-1(P < 0.05).The protein level of HMGB1 in the culture supernatant was significantly higher in pyroptosis group than in the control and siRNA groups (P < 0.05).

CONCLUSION

In the pathological process of KOA, NLRPs inflammasome-mediated FLS pyroptosis causes massive release of HMGB1, which is associated with the activation of the downstream molecule caspase-1.

Tuning Monocytes and Macrophages for Personalized Therapy and Diagnostic Challenge in Rheumatoid Arthritis

Monocytes/macrophages play a central role in chronic inflammatory disorders, including rheumatoid arthritis (RA). Activation of these cells results in the production of various mediators responsible for inflammation and RA pathogenesis. On the other hand, the depletion of macrophages using specific antibodies or chemical agents can prevent their synovial tissue infiltration and subsequently attenuates inflammation. Their plasticity is a major feature that helps the switch from a pro-inflammatory phenotype (M1) to an anti-inflammatory state (M2). Therefore, understanding the precise strategy targeting pro-inflammatory monocytes/macrophages should be a powerful way of inhibiting chronic inflammation and bone erosion. In this review, we demonstrate potential consequences of different epigenetic regulations on inflammatory cytokines production by monocytes. In addition, we present unique profiles of monocytes/macrophages contributing to identification of new biomarkers of disease activity or predicting treatment response in RA. We also outline novel approaches of tuning monocytes/macrophages by biologic drugs, small molecules or by other therapeutic modalities to reduce arthritis. Finally, the importance of cellular heterogeneity of monocytes/macrophages is highlighted by single-cell technologies, which leads to the design of cell-specific therapeutic protocols for personalized medicine in RA in the future.

Meta-Analysis of Methamphetamine Modulation on Amyloid Precursor Protein through HMGB1 in Alzheimer's Disease

The deposition of amyloid-beta (Aβ) through the cleavage of amyloid-beta precursor protein (APP) is a biomarker of Alzheimer’s disease (AD). This study used QIAGEN Ingenuity Pathway Analysis (IPA) to conduct meta-analysis on the molecular mechanisms by which methamphetamine (METH) impacts AD through modulating the expression of APP. All the molecules affected by METH and APP were collected from the QIAGEN Knowledge Base (QKB); 78 overlapping molecules were identified. Upon simulation of METH exposure using the “Molecule Activity Predictor” feature, eight molecules were found to be affected by METH and exhibited activation relationships on APP expression at a confidence of p = 0.000453 (Z-score = 3.51, two-tailed). Core Analysis of these eight molecules identified High Mobility Group Box protein 1 (HMGB1) signaling pathway among the top 5 canonical pathways with most overlap with the 8-molecule dataset. Simulated METH exposure increased APP expression through HMGB1 at a confidence of p < 0.00001 (Z-score = 7.64, two-tailed). HMGB1 is a pathogenic hallmark in AD progression. It not only increases the production of inflammatory mediators, but also mediates the disruption of the blood-brain barrier. Our analyses suggest the involvement of HMGB1 signaling pathway in METH-induced modulation of APP as a potential casual factor of AD.

The P2X7 Receptor in Osteoarthritis

Osteoarthritis (OA) is the most common joint disease. With the increasing aging population, the associated socio-economic costs are also increasing. Analgesia and surgery are the primary treatment options in late-stage OA, with drug treatment only possible in early prevention to improve patients' quality of life. The most important structural component of the joint is cartilage, consisting solely of chondrocytes. Instability in chondrocyte balance results in phenotypic changes and cell death. Therefore, cartilage degradation is a direct consequence of chondrocyte imbalance, resulting in the degradation of the extracellular matrix and the release of pro-inflammatory factors. These factors affect the occurrence and development of OA. The P2X7 receptor (P2X7R) belongs to the purinergic receptor family and is a non-selective cation channel gated by adenosine triphosphate. It mediates Na⁺, Ca²⁺ influx, and K⁺ efflux, participates in several inflammatory reactions, and plays an important role in the different mechanisms of cell death. However, the relationship between P2X7R-mediated cell death and the progression of OA requires investigation. In this review, we correlate potential links between P2X7R, cartilage degradation, and inflammatory factor release in OA. We specifically focus on inflammation, apoptosis, pyroptosis, and autophagy. Lastly, we discuss the therapeutic potential of P2X7R as a potential drug target for OA.

Elevation of Proinflammatory Cytokine HMGB1 in the Synovial Fluid of Patients With Legg-Calvé-Perthes Disease and Correlation With IL-6

Legg-Calvé-Perthes disease (LCPD) is a childhood ischemic osteonecrosis (ON) of the femoral head associated with the elevation of proinflammatory cytokine interleukin-6 (IL-6) in the synovial fluid. Currently, there is no effective medical therapy for patients with LCPD. In animal models of ischemic ON, articular chondrocytes produce IL-6 in response to ischemic ON induction and IL-6 receptor blockade improves bone healing. High-mobility group box 1 (HMGB1) is a damage-associated molecular pattern released from dying cells. In addition, extracellular HMGB1 protein is a well-known proinflammatory cytokine elevated in the synovial fluid of patients with rheumatoid arthritis and osteoarthritis. The purpose of this study was to investigate IL-6-related proinflammatory cytokines, including HMGB1, in the synovial fluid of patients with LCPD. Our working hypothesis was that HMGB1, produced by articular chondrocytes following ischemic ON, plays an important role in IL-6 upregulation. Here, HMGB1 protein levels were significantly higher in the synovial fluid of patients with LCPD by threefold compared with controls (p < 0.05), and were highly correlated with IL-6 levels (Pearson correlation coefficient 0.94, p < 0.001, R 2 = 0.87). In the mouse model of ischemic ON, both HMGB1 gene expression and protein levels were elevated in the articular cartilage. In vitro studies revealed a significant elevation of HMGB1 and IL-6 proteins in the supernatants of human chondrocytes exposed to hypoxic and oxidative stresses. Overexpressed HMGB1 protein in the supernatants of chondrocytes synergistically increased IL-6 protein. Silencing HMGB1 RNA in human chondrocytes significantly repressed inteleukin-1β (IL-1β) gene expression, but not IL-6. Further, both IL-1β and tumor necrosis factor-α (TNF-α) protein levels in the synovial fluid of patients with LCPD were significantly correlated with IL-6 protein levels. Taken together, these results suggest that proinflammatory cytokines, HMGB1, tumor necrosis factor-α (TNF-α), and IL-1β, are significantly involved with IL-6 in the pathogenesis of LCPD. This study is clinically relevant because the availability of multiple therapeutic targets may improve the development of therapeutic strategy for LCPD. © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

The Damage-Associated Molecular Patterns (DAMPs) as Potential Targets to Treat Osteoarthritis: Perspectives From a Review of the Literature

During the osteoarthritis (OA) process, activation of immune systems, whether innate or adaptive, is strongly associated with low-grade systemic inflammation. This process is initiated and driven in the synovial membrane, especially by synovium cells, themselves previously activated by damage-associated molecular patterns (DAMPs) released during cartilage degradation. These fragments exert their biological activities through pattern recognition receptors (PRRs) that, as a consequence, induce the activation of signaling pathways and beyond the release of inflammatory mediators, the latter contributing to the vicious cycle between cartilage and synovial membrane. The primary endpoint of this review is to provide the reader with an overview of these many molecules categorized as DAMPs and the contribution of the latter to the pathophysiology of OA. We will also discuss the different strategies to control their effects. We are convinced that a better understanding of DAMPs, their receptors, and associated pathological mechanisms represents a decisive issue for degenerative joint diseases such as OA.

Common risk factors and therapeutic targets in obstructive sleep apnea and osteoarthritis: An unexpectable link?

Osteoarthritis (OA) and Obstructive Sleep Apnea (OSA) are two highly prevalent chronic diseases for which effective therapies are urgently needed. Recent epidemiologic studies, although scarce, suggest that the concomitant occurrence of OA and OSA is associated with more severe manifestations of both diseases. Moreover, OA and OSA share risk factors, such as aging and metabolic disturbances, and co-morbidities, including cardiovascular and metabolic diseases, sleep deprivation and depression. Whether this coincidental occurrence is fortuitous or involves cause-effect relationships is unknown. This review aims at collating and integrating present knowledge on both diseases by providing a brief overview of their epidemiology and pathophysiology, analyzing current evidences relating OA and OSA and discussing potential common mechanisms by which they can aggravate each other. Such mechanisms constitute potential therapeutic targets whose pharmacological modulation may provide more efficient ways of reducing the consequences of OA and OSA and, thus, lessen the huge individual and social burden that they impose.

Relationship between the pyroptosis of fibroblast‑like synoviocytes and HMGB1 secretion in knee osteoarthritis

High mobility group box 1 (HMGB1) is an important downstream product of pyroptosis in macrophages, and it serves a vital role in numerous inflammatory diseases. Previous studies have reported that HMGB1 is released by fibroblast-like synoviocytes (FLSs) that are activated by inflammatory cytokines in knee osteoarthritis (KOA); however, the mechanism via which FLS promotes HMGB1 secretion in KOA remains unknown. According to our previous study, pyroptosis occurs in FLSs of patients with KOA and is mediated by Nod-like receptor protein (NLRP)1 or NLRP3 inflammasomes. However, the specific relationship between HMGB1 secretion and FLS pyroptosis requires further investigation. In the present study, the association between HMGB1 secretion and FLS pyroptosis was investigated in vitro and in vivo. In this study, western blotting, ELISA and reverse transcription-quantitative PCR were used to measure expression levels of proteins and mRNA. Caspase-1 activity assay and Hoechst 33342/PI double staining were used to observe the pyroptosis of FLSs. Hematoxylin and eosin staining was used to observe the destruction of cartilage in KOA. Increased expression levels of pyroptosis-related proteins and HMGB1 in the synovium of rat anterior cruciate ligament transection-induced KOA models were identified, and these changes were significantly mitigated via the intra-articular injection of a caspase-1 inhibitor. In vitro, FLSs were treated with lipopolysaccharide (LPS) + ATP to induce pyroptosis, and HMGB1 secretion was subsequently measured. LPS + ATP significantly increased the expression levels of pyroptosis-related proteins and HMGB1 in FLSs, and these effects were significantly mitigated by small interfering RNAs targeting NLRP1, NLRP3, apoptosis-associated speck-like protein with a caspase-recruitment domain or caspase-1. Therefore, the present results indicated that NLRP1/NLRP3 inflammasome-mediated and caspase-1-dependent FLS pyroptosis increased HMGB1 secretion in KOA. These findings may provide a therapeutic strategy to decrease synovial inflammatory responses during KOA progression.

Beneficial Effects of Glycyrrhizin in Chronic Periodontitis Through the Inhibition of Inflammatory Response

Elevated inflammatory cytokines and high mobility group box 1 (HMGB1) production are associated with chronic periodontitis (CP). Glycyrrhizin is the major constituent of Glycyrrhiza glabra. L. (Fabaceae) root with anti-inflammation activities. This study evaluated the effects of glycyrrhizin on CP. TNF-α-treated human periodontal ligament stem cell (hPDLSC) model was established, and was administrated with 1, 2 or 5 mM glycyrrhizin for 24 h. After treatment, the expression of HMGB1and inflammatory cytokines was monitored. Significantly increased HMGB1 (median: 5646.4, range: 1918.2-8233.7 vs median: 204.5, range: 98.7-283.6, pg/mL), TNF-α (median: 345.5, range: 161.0-567.9 vs median: 93.5, range: 58.1-159.3, pg/mL), IL-1β (median: 2014.6, range: 209.5-4308.1 vs median: 224.5, range: 48.8-335.8, pg/mL) and IL-6 (median: 1223.6, range: 398.2-2183.8 vs median: 240.4, range: 105.2-400.5, pg/mL) were detected in gingival crevicular fluid from CP patients. Glycyrrhizin significantly prevented TNF-α-induced expression of HMGB1 (691.5 ± 136.4 vs 142.8 ± 57.3 pg/mL), IL-6 (388.1 ± 85.2 vs 189.4 ± 61.2 pg/mL) and IL-1β (176.3 ± 47.2 vs 53.9 ± 25.7 pg/mL) in hPDLSC. In CP rats, glycyrrhizin significantly decreased HMGB1 (5795.6 ± 1121.5 vs 586.4 ± 436.8 pg/mL), TNF-α (421.8 ± 93.7 vs 87.9 ± 21.6 pg/mL), IL-6 (1423.8 ± 235.2 vs 622.6 ± 176.1 pg/mL) and IL-1β (1562.8 ± 334.3 vs 733.5 ± 265.1 pg/mL) in gingival crevicular fluid. Glycyrrhizin suppresses inflammatory activities in CP rats and represents a promising molecule for controlling CP.

Human Chondrocyte Activation by Toxins From Premolis semirufa, an Amazon Rainforest Moth Caterpillar: Identifying an Osteoarthritis Signature

Pararamosis is a disease that occurs due to contact with the hairs of the larval stage of the Brazilian moth Premolis semirufa. Envenomation induces osteoarticular alterations with cartilage impairment that resembles joint synovitis. Thus, the toxic venom present in the caterpillar hairs interferes with the phenotype of the cells present in the joints, resulting in inflammation and promoting tissue injury. Therefore, to address the inflammatory mechanisms triggered by envenomation, we studied the effects of P. semirufa hair extract on human chondrocytes. We have selected for the investigation, cytokines, chemokines, matrix metalloproteinases (MMPs), complement components, eicosanoids, and extracellular matrix (ECM) components related to OA and RA. In addition, for measuring protein-coding mRNAs of some molecules associated with osteoarthritis (OA) and rheumatoid arthritis (RA), reverse transcription (RT) was performed followed by quantitative real-time PCR (RT-qPCR) and we performed the RNA-sequencing (RNA-seq) analysis of the chondrocytes transcriptome. In the supernatant of cell cultures treated with the extract, we observed increased IL-6, IL-8, MCP-1, prostaglandin E2, metalloproteinases (MMP-1, MMP-2, MMP-3 and MMP-13), and complement system components (C3, C4, and C5). We noticed a significant decrease in both aggrecan and type II collagen and an increase in HMGB1 protein in chondrocytes after extract treatment. RNA-seq analysis of the chondrocyte transcriptome allowed us to identify important pathways related to the inflammatory process of the disease, such as the inflammatory response, chemotaxis of immune cells and extracellular matrix (ECM) remodeling. Thus, these results suggest that components of Premolis semirufa hair have strong inflammatory potential and are able to induce cartilage degradation and ECM remodeling, promoting a disease with an osteoarthritis signature. Modulation of the signaling pathways that were identified as being involved in this pathology may be a promising approach to develop new therapeutic strategies for the control of pararamosis and other inflammatory joint diseases.

Exploring the therapeutic promise of targeting HMGB1 in rheumatoid arthritis

High mobility group box-1 (HMGB1) protein is a diverse, single polypeptide moiety, present in mammalian eukaryotic cells. In response to stimuli, this nuclear protein is actively secreted in to the extracellular compartment or passively released by the necrotic cells, in order to mediate inflammatory responses, by forming complexes with IL-1α, IL-1β, LPS and other moieties, and binding to RAGE, TLR and other receptor ligands, initiating downstream, signaling processes. This molecule acts as a proinflammatory cytokine and contributes to the progression of diseases like, acute lung injury, autoimmune liver damage, graft rejection immune response and arthritis. Small concentrations of HMGB1 are released during apoptosis, which facilitates oxidative regulation on Cys106, and propagates immune inactivating tolerogenic signals in the body. The review portrays the role of HMGB1 in rheumatoid arthritis, evidently supported by pre-clinical and clinical investigations, demonstrating extensive HMGB1 expression in synovial tissue and fluid as well as serum, excessive expression of transduction receptor signaling molecules, bone remodeling and uncontrolled expression of bone destroying osteoclastogenesis, resulting in destruction of articular cartilage, bone deformation and synovial proliferation, alleviating the pathogenesis in RA disease. Moreover, the review highlights the therapeutic regime targeting HMGB1, facilitating inhibition of its actions and release into the extracellular compartment, to ameliorate the destructive events that prevail in rheumatoid arthritis.

MicroRNA-410-3p modulates chondrocyte apoptosis and inflammation by targeting high mobility group box 1 (HMGB1) in an osteoarthritis mouse model

Background

Osteoarthritis (OA) is the most prevalent type of arthritis, which commonly involves inflammation in the articular cartilage in OA pathogenesis. MicroRNAs (miRNAs) play essential roles in the regulation and pathophysiology of various diseases including OA. MiR-410-3p has been demonstrated to mediate inflammatory pathways, however, the regulatory functions of miR-410-3p in OA remain largely unknown.

Methods

The regulations of miR-410-3p were investigated in OA. Mouse primary chondrocytes and mouse in vivo models were used. The expression levels of miR-410-3p and HMGB1 were measured by qPCR. The transcription activity of NF-κB was assessed by luciferase reporter assay. MTT assay was performed to assess cellular proliferation. Cell apoptosis was evaluated with the Fluorescein Isothiocyanate (FITC) Annexin V assay. Expression levels of proteins were determined by Western blot.

Results

The results demonstrated that miR-410-3p was markedly downregulated in articular cartilage tissues as well as in lipopolysaccharide (LPS)-treated chondrocytes in OA mice. In addition, upregulation of miR-410-3p markedly inhibited LPS-induced apoptosis of chondrocytes. The results also demonstrated that the high mobility group box 1 (HMGB1) was a target of miR-410-3p. LPS-induced upregulated expression of HMGB1 significantly suppressed expression of miR-410-3p. Furthermore, upregulation of miR-410-3p markedly inhibited HMGB1 expression, the nuclear factor (NF)-kB activity and pro-inflammatory cytokines production. Taken together, the results suggested that miR-410-3p targeted HMGB1 and modulated chondrocytes apoptosis and inflammation through the NF-κB signaling pathway.

Conclusions

These findings provide insights into the potential of miR-410-3p/ HMGB1 as therapeutic targets for OA treatment.

The emerging role of fibroblast-like synoviocytes-mediated synovitis in osteoarthritis: An update

Osteoarthritis (OA), the most ubiquitous degenerative disease affecting the entire joint, is characterized by cartilage degradation and synovial inflammation. Although the pathogenesis of OA remains poorly understood, synovial inflammation is known to play an important role in OA development. However, studies on OA pathophysiology have focused more on cartilage degeneration and osteophytes, rather than on the inflamed and thickened synovium. Fibroblast-like synoviocytes (FLS) produce a series of pro-inflammatory regulators, such as inflammatory cytokines, nitric oxide (NO) and prostaglandin E₂ (PGE₂ ). These regulators are positively associated with the clinical symptoms of OA, such as inflammatory pain, joint swelling and disease development. A better understanding of the inflammatory immune response in OA-FLS could provide a novel approach to comprehensive treatment strategies for OA. Here, we have summarized recently published literatures referring to epigenetic modifications, activated signalling pathways and inflammation-associated factors that are involved in OA-FLS-mediated inflammation. In addition, the current related clinical trials and future perspectives were also summarized.

Anti-Inflammatory and Chondroprotective Effects of Vanillic Acid and Epimedin C in Human Osteoarthritic Chondrocytes

In osteoarthritis (OA), inhibition of excessively expressed pro-inflammatory cytokines in the OA joint and increasing the anabolism for cartilage regeneration are necessary. In this ex-vivo study, we used an inflammatory model of human OA chondrocytes microtissues, consisting of treatment with cytokines (interleukin 1β (IL-1β)/tumor necrosis factor α (TNF-α)) with or without supplementation of six herbal compounds with previously identified chondroprotective effect. The compounds were assessed for their capacity to modulate the key catabolic and anabolic factors using several molecular analyses. We selectively investigated the mechanism of action of the two most potent compounds Vanillic acid (VA) and Epimedin C (Epi C). After identification of the anti-inflammatory and anabolic properties of VA and Epi C, the Ingenuity Pathway Analysis showed that in both treatment groups, osteoarthritic signaling pathways were inhibited. In the treatment group with VA, nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling was inhibited by attenuation of the nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor alpha (IκBα) phosphorylation. Epi C showed a significant anabolic effect by increasing the expression of collagenous and non-collagenous matrix proteins. In conclusion, VA, through inhibition of phosphorylation in NF-κB signaling pathway and Epi C, by increasing the expression of extracellular matrix components, showed significant anti-inflammatory and anabolic properties and might be potentially used in combination to treat or prevent joint OA.

The GSK‑3β/β‑catenin signaling pathway is involved in HMGB1‑induced chondrocyte apoptosis and cartilage matrix degradation

Knee osteoarthritis (KOA) is a common joint disease with a high incidence rate among middle‑aged and elderly individuals. However, the precise underlying pathological mechanisms and effective treatment of this disease remain to be determined. To explore the effect of high mobility group box 1 (HMGB1) on chondrocyte apoptosis and catabolism, the ATDC5 cell line was cultured as an in vitro model for cartilage research. Cultured cells were treated with recombinant HMGB1 at different concentrations. Hoechst staining and flow cytometry demonstrated that HMGB1 administration significantly induced apoptosis of ATDC5 cells, which was the same as the effect of interleukin‑1β treatment. HMGB1 also induced cartilage matrix degradation, as shown by Alcian blue staining. Moreover, HMGB1 markedly upregulated the expression levels of matrix metallopeptidases (MMPs) and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS), while genetic silencing of HMGB1 significantly suppressed their expressions. The glycogen synthase kinase (GSK)‑3β/β‑catenin pathway was activated upon HMGB1 treatment. Pharmacological inhibitors or HMGB1 knockdown inactivated the GSK‑3β/β‑catenin pathway, inhibited the expression levels of downstream genes, including MMPs and ADAMTS, and attenuated the apoptosis of ATDC5 cells. Furthermore, the data demonstrated that HMGB1 promoted chondrocyte dysfunction via the regulation of estrogen sulfotransferase and Runt‑related transcription factor 2. Thus, the findings of the present study demonstrated that HMGB1 induces chondrocyte cell apoptosis via activation of GSK‑3β/β‑catenin and the subsequent expression of multiple targeted genes.

MIR-140-5p affects chondrocyte proliferation, apoptosis, and inflammation by targeting HMGB1 in osteoarthritis

OBJECTIVE

This study aimed to test the expression and biological function of miR-140-5p in osteoarthritis (OA), and identify its target gene and explore its mechanism in OA.

METHODS

Differential genes were screened and analyzed by gene microarray and WGCNA analysis. The normal human chondrocytes C28/I2 were induced by IL-1β to construct the OA cell model. The expression of miR-140-5p and high mobility group box 1 (HMGB1) was quantified by quantitative real-time PCR (qRT-PCR) in OA tissues and IL-1β-induced chondrocytes. Western blotting was performed to evaluate the expression of HMGB1 and PI3K/AKT pathway activation. The concentrations of tumor necrosis factor (TNF)-α, interleukin (IL)-6, MMP-1 and MMP-3 were determined by ELISA. CCK-8 and flow cytometry were conducted to determine the cellular capabilities of proliferation and cell apoptosis.

RESULTS

Bioinformatics analysis demonstrated that HMGB1 was highly expressed in OA and activated PI3K/AKT pathway. Also, HMGB1 was predicted as a target of miR-140-5p. The levels of miR-140-5p were negatively correlated with HMGB1 in OA tissues and IL-1β-induced chondrocytes. The overexpression of miR-140-5p reduced the expression of HMGB1 protein, p-AKT (Ser473) and p-PI3K in IL-1β-induced chondrocytes. Besides, the expression of p-AKT (Ser473) and p-PI3K was significantly upregulated by employing miR-140-5p inhibitor, but retrieved after treating with LY294002. Furthermore, miR-140-5p inhibited inflammation, matrix metalloprotease expression and apoptosis in IL-1β-induced chondrocytes through regulating HMGB1.

CONCLUSION

MiR-140-5p was down-regulated while HMGB1 was upregulated in OA. MiR-140-5p could inhibit the PI3K/AKT signaling pathway and suppress the progression of OA through targeting HMGB1.

NOV/CCN3 induces cartilage protection by inhibiting PI3K/AKT/mTOR pathway

Osteoarthritis (OA), an age‐related degenerative joint disease, is pathologically characterized by articular cartilage degeneration and synovial inflammation. Nephroblastoma overexpressed (NOV or CCN3), a matricellular protein, is a primary member of the CCN family (Cyr61, Ctgf, NOV) of proteins and is involved in various inflammatory disorders. Previous studies reported that CCN3 might play a therapeutic role in OA. However, the underlying mechanism remains unclear. In this study, we confirmed the expression of CCN3 was decreased in human and rat OA articular cartilage. Recombinant CCN3 ameliorated the IL‐1β‐induced matrix catabolism, as demonstrated by MMP1, MMP3, MMP13, ADAMTS5 and iNOS expression, in vitro. In addition, the degradation of cartilage matrix such as collagen 2 and aggrecan could be reversed by CCN3. Furthermore, we found CCN3 promoted autophagy as Atg5, Beclin1 and LC3‐II expression were increased. High‐mobility group box 1 was negatively correlated with CCN3 in IL‐1β‐induced osteoarthritis responses, and HMGB1 is involved in the protective effect of CCN3 in OA. Moreover, CCN3 overexpression decreased the expression of HMGB1 and reversed the IL‐1β induced MMPs production. Additionally, recombinant CCN3 or CCN3 overexpression attenuated the activation of PI3K/AKT/mTOR pathway induced by IL‐1β. Our study presents new mechanisms of CCN3 in osteoarthritis and indicates that CCN3 can serve as a novel potential therapeutic target for osteoarthritis.

Dual regulatory roles of HMGB1 in inflammatory reaction of chondrocyte cells and mice

Osteoarthritis (OA) is one of the most common bone diseasesas it is reported that the impact of knee osteoarthritis symptomatic form is estimated at 240/100,000 people per year. The inflammation of articular cartilageis thought to be the pathologic drive for development of this disease. HMGB1(high mobility group box-1), a regulatory factor for gene transcription, could stimulate inflammation response. However, theexact regulatory role of HMGB1 in the inflammation of articular cartilage still need to be elucidated. In the current study, we used Quantitative Real-Time PCR(Q-PCR) to detect them RNA levels of Collagen Type II Alpha 1(Col2a1), Aggrecan, MMP3(Matrix Metallopeptidase 3), MMP13, ADAMTs4 and ADAMTs5; Enzyme-Linked Immunosorbent Assay(ELISA) was used to detect the content of IL-1β and calpain protein; Cell apoptosis was evaluated by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling(TUNEL) assay and flow cytometryanalysis; Western blot and immunofluorescence assays were applied to assess the expression of HMGB1; Lastly autophagic activity was mainly verified by monodansylcadaverine (MDC) staining. Our data revealed that in the early stage of chondrocyte inflammation(3 and 6 h of LPS stimulation), cytosolic HMGB1 attenuated inflammation response by facilitating cell autophagy and preventing cell apoptosis. While in the late stage (24 and 48 h of LPS stimulation), the extracellular HMGB1 stimulated inflammation reaction and contributed to the cartilage destruction in OA.

NF-κB Signaling Pathways in Osteoarthritic Cartilage Destruction

Osteoarthritis (OA) is a type of joint disease associated with wear and tear, inflammation, and aging. Mechanical stress along with synovial inflammation promotes the degradation of the extracellular matrix in the cartilage, leading to the breakdown of joint cartilage. The nuclear factor-kappaB (NF-κB) transcription factor has long been recognized as a disease-contributing factor and, thus, has become a therapeutic target for OA. Because NF-κB is a versatile and multi-functional transcription factor involved in various biological processes, a comprehensive understanding of the functions or regulation of NF-κB in the OA pathology will aid in the development of targeted therapeutic strategies to protect the cartilage from OA damage and reduce the risk of potential side-effects. In this review, we discuss the roles of NF-κB in OA chondrocytes and related signaling pathways, including recent findings, to better understand pathological cartilage remodeling and provide potential therapeutic targets that can interfere with NF-κB signaling for OA treatment.

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

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

Inflammation in osteoarthritis: is it time to dampen the alarm(in) in this debilitating disease?

Osteoarthritis (OA) is the most common joint disease that strongly reduces the quality of life in patients; However, no disease-modifying therapy is available. For a long time, OA was considered a non-inflammatory disease that was the result of 'wear-and-tear' and abnormal mechanics, and therefore many considered the term 'osteoarthritis' a misnomer. However, during the last decades the notion arose that inflammation is not only present in the majority of OA patients but, rather, actively involved in the progression of the disease. Influx of immune cells is observed in the synovium and a plethora of inflammatory mediators is present in tissues and fluids from OA patients. These mediators cause the production of degrading enzymes that break down the cartilage matrix, which is the main hallmark of OA. Alarmins, which belong to the group of danger signals, have been implicated in many inflammatory diseases. They are among the first factors to be released upon cell stress due to, for example, infection, damage and inflammation. They attract and activate cells of the immune system and therefore lie at the base of the inflammatory reaction. In this narrative review, an overview of the history of OA, the evolving concept of inflammation as important factor in the OA pathogenesis, and particularly the central role that alarmins play in the initiation and maintenance of the low-grade inflammatory response in OA, is provided. Moreover, the targeting of alarmins as a promising approach to dampen the inflammation in OA is highlighted.

High Mobility Group Box 1 Influences HSV1716 Spread and Acts as an Adjuvant to Chemotherapy

High Mobility Group Box 1 (HMGB1) is a multifunctional protein that plays various roles in the processes of inflammation, cancer, and other diseases. Many reports document abundant HMGB1 release following infection with oncolytic viruses (OVs). Further, other groups including previous reports from our laboratory highlight the synergistic effects of OVs with chemotherapy drugs. Here, we show that virus-free supernatants have varying cytotoxic potential, and HMGB1 is actively secreted by two established fibroblast cell lines (NIH 3T3 and 3T6-Swiss albino) following HSV1716 infection in vitro. Further, pharmacologic inhibition or genetic knock-down of HMGB1 reveals a role for HMGB1 in viral restriction, the ability to modulate bystander cell proliferation, and drug sensitivity in 3T6 cells. These data further support the multifactorial role of HMGB1, and suggest it could be a target for modulating the efficacy of oncolytic virus therapies alone or in combination with other frontline cancer treatments.

Anti-epileptic effect of ifenprodil on neocortical pyramidal neurons in patients with malformations of cortical development

Ifenprodil has been demonstrated to reduce spontaneous action potentials observed by local field potential in animal models. To investigate whether ifenprodil exerts an anti-epileptic effect on neuronal levels in humans, whole-cell patch clamp recordings were used to study the electrophysiological membrane properties of neocortical pyramidal neurons in human brain tissues. Electrophysiological membrane properties and spontaneous spikes of neocortical pyramidal neurons were investigated by using whole-cell patch clamp recordings, prior to and following the application of ifenprodil. In the present study, ifenprodil significantly decreased the membrane input resistance (P<0.01), membrane time constant (P<0.01), action potential amplitude (P<0.01), action potential rising rate (P<0.05) and falling rate (P<0.05) on neocortical pyramidal neurons in patients with epilepsy caused by malformations of cortical development (MCD). These results suggested that ifenprodil decreased neuronal excitability of neocortical pyramidal neurons in patients with epilepsy and MCD and demonstrated that ifenprodil may be a potentially specific treatment for refractory epilepsy caused by MCD.

High Mobility Group Box 1 Protein Level as a Novel Biomarker for the Development of Peri-Implant Disease

Peri-implant disease is a chronic inflammation of the soft and hard tissues around a dental implant, resulting from bacterial infection. Recent evidence indicates that some pro-inflammatory cytokines and chemokines released by immunocytes are substantially responsible for the progress and consequence of inflammation. High mobility group box 1 (HMGB1) is released into the extracellular matrix and acts as a key pro-inflammatory factor during injury, necrosis and inflammation. A higher concentration of HMGB1 has been found in gingival crevicular fluid from inflammatory gingival tissue than from healthy sites. HMGB1 mRNA and protein are overexpressed in murine periodontal ligament fibroblasts stimulated with lipopolysaccharide (LPS) and IL-1β. Thus, this study sought to assess HMGB1 expression in peri-implant crevicular fluid (PICF) at each stage of peri-implant disease and to investigate the correlation between HMGB1 and peri-implant disease progress. The results demonstrated that the HMGB1 expression level in PICF is indicative of the progress of peri-implant disease and hence may be a useful diagnostic and prognostic biomarker for peri-implant tissue.

DAMPs Synergize with Cytokines or Fibronectin Fragment on Inducing Chondrolysis but Lose Effect When Acting Alone

OBJECTIVE AND DESIGN

To investigate whether endogenous damage-associated molecular patterns (DAMPs) or alarmins originated from mitochondria or nucleus stimulates inflammatory response in articular chondrocytes to cause chondrolysis which leads to cartilage degradation featured in posttraumatic osteoarthritis (PTOA).

MATERIALS

Primary cultures of bovine or human chondrocytes isolated from cartilage of weight-bearing joints.

TREATMENT

Chondrocytes were subjected to mitochondrial DAMPs (MTDs) or HMGB1, a nuclear DAMP (NuD), with or without the presence of an N-terminal 29 kDa fibronectin fragment (Fn-f) or proinflammatory cytokines (IL-1β and TNF-α). Injured cartilage-conditioned culturing medium containing a mixture of DAMPs was employed as a control. After 24 hrs, the protein expression of cartilage degrading metalloproteinases and iNOS in culture medium or cell lysates was examined with Western blotting, respectively.

RESULTS

HMGB1 was synergized with IL-1β in upregulating expression of MMP-3, MMP-13, ADAMTS-5, ADAM-8, and iNOS. Moreover, a moderate synergistic effect was detected between HMGB1 and Fn-f or between MTDs and TNF-α on MMP-3 expression. However, when acting alone, MTDs or HMGB1 did not upregulate cartilage degrading enzymes or iNOS.

CONCLUSION

MTDs or HMGB1 could only stimulate inflammatory response in chondrocytes with the presence of cytokines or Fn-f.

Increased expression of damage-associated molecular patterns (DAMPs) in osteoarthritis of human knee joint compared to hip joint

Osteoarthritis (OA) is a degenerative disease characterized by the destruction of cartilage. The greatest risk factors for the development of OA include age and obesity. Recent studies suggest the role of inflammation in the pathogenesis of OA. The two most common locations for OA to occur are in the knee and hip joints. The knee joint experiences more mechanical stress, cartilage degeneration, and inflammation than the hip joint. This could contribute to the increased incidence of OA in the knee joint. Damage-associated molecular patterns (DAMPs), including high-mobility group box-1, receptor for advanced glycation end products, and alarmins (S100A8 and S100A9), are released in the joint in response to stress-mediated chondrocyte and cartilage damage. This facilitates increased cartilage degradation and inflammation in the joint. Studies have documented the role of DAMPs in the pathogenesis of OA; however, the comparison of DAMPs and its influence on OA has not been discussed. In this study, we compared the DAMPs between OA knee and hip joints and found a significant difference in the levels of DAMPs expressed in the knee joint compared to the hip joint. The increased levels of DAMPs suggest a difference in the underlying pathogenesis of OA in the knee and the hip and highlights DAMPs as potential therapeutic targets for OA in the future.

Macrophage-derived IL-1α promotes sterile inflammation in a mouse model of acetaminophen hepatotoxicity

The metabolic intermediate of acetaminophen (APAP) can cause severe hepatocyte necrosis, which triggers aberrant immune activation of liver non-parenchymal cells (NPC). Overzealous hepatic inflammation determines the morbidity and mortality of APAP-induced liver injury (AILI). Interleukin-1 receptor (IL-1R) signaling has been shown to play a critical role in various inflammatory conditions, but its precise role and underlying mechanism in AILI remain debatable. Herein, we show that NLRP3 inflammasome activation of IL-1β is dispensable to AILI, whereas IL-1α, the other ligand of IL-1R1, accounts for hepatic injury by a lethal dose of APAP. Furthermore, Kupffer cells function as a major source of activated IL-1α in the liver, which is activated by damaged hepatocytes through TLR4/MyD88 signaling. Finally, IL-1α is able to chemoattract and activate CD11b⁺Gr-1⁺ myeloid cells, mostly neutrophils and inflammatory monocytes, to amplify deteriorated inflammation in the lesion. Therefore, this work identifies that MyD88-dependent activation of IL-1α in Kupffer cells plays a central role in the immunopathogenesis of AILI and implicates that IL-1α is a promising therapeutic target for AILI treatment.

Inflammation in epileptogenesis after traumatic brain injury

Background

Epilepsy is a common and debilitating consequence of traumatic brain injury (TBI). Seizures contribute to progressive neurodegeneration and poor functional and psychosocial outcomes for TBI survivors, and epilepsy after TBI is often resistant to existing anti-epileptic drugs. The development of post-traumatic epilepsy (PTE) occurs in a complex neurobiological environment characterized by ongoing TBI-induced secondary injury processes. Neuroinflammation is an important secondary injury process, though how it contributes to epileptogenesis, and the development of chronic, spontaneous seizure activity, remains poorly understood. A mechanistic understanding of how inflammation contributes to the development of epilepsy (epileptogenesis) after TBI is important to facilitate the identification of novel therapeutic strategies to reduce or prevent seizures.

Body

We reviewed previous clinical and pre-clinical data to evaluate the hypothesis that inflammation contributes to seizures and epilepsy after TBI. Increasing evidence indicates that neuroinflammation is a common consequence of epileptic seizure activity, and also contributes to epileptogenesis as well as seizure initiation (ictogenesis) and perpetuation. Three key signaling factors implicated in both seizure activity and TBI-induced secondary pathogenesis are highlighted in this review: high-mobility group box protein-1 interacting with toll-like receptors, interleukin-1β interacting with its receptors, and transforming growth factor-β signaling from extravascular albumin. Lastly, we consider age-dependent differences in seizure susceptibility and neuroinflammation as mechanisms which may contribute to a heightened vulnerability to epileptogenesis in young brain-injured patients.

Conclusion

Several inflammatory mediators exhibit epileptogenic and ictogenic properties, acting on glia and neurons both directly and indirectly influence neuronal excitability. Further research is required to establish causality between inflammatory signaling cascades and the development of epilepsy post-TBI, and to evaluate the therapeutic potential of pharmaceuticals targeting inflammatory pathways to prevent or mitigate the development of PTE.

Expression and Significance of High-Mobility Group Protein B1 (HMGB1) and the Receptor for Advanced Glycation End-Product (RAGE) in Knee Osteoarthritis

Background

This study was performed with the aim to explore the expression of high-mobility group protein B1 (HMGB1) and the receptor for advanced glycation end-product (RAGE) in knee osteoarthritis (KOA) and its clinical significance.

Material/Methods

A total of 108 synovial tissues selected from KOA patients were included in the experimental group. Seventy-five synovial tissues of knee joints, selected from patients who were clinically and pathologically confirmed without joint lesion, were included in the control group. The mRNA and protein expressions of HMGB1 and RAGE were determined by using RT-PCR and immunohistochemistry, respectively. Western blotting was used for measuring relative protein expression. An ROC curve was drawn to evaluate the diagnostic value of HMGB1 and RAGE for KOA.

Results

The positive cell number and positive expression intensity of HMGB1 and RAGE in synovial tissue was higher in the experimental group than in the control group. PI for HMGB1 and RAGE expression in KOA patients was positively correlated with clinical classification of X-ray films (P<0.05). HMGB1 and RAGE mRNA expressions, as well as relative protein expression of HMGB1 and RAGE in synovial tissue, were higher in the experimental group than in the control group (all P<0.05). The sensitivity of HMGB1 protein, RAGE protein, HMGB1 mRNA, and RAGE mRNA were 76.9%, 64.8%, 86.1%, and 64.8%, respectively; and the specificity was 100%, 96%, 74.7%, and 80%, respectively.

Conclusions

The protein and mRNA expressions of HMGB1 and RAGE are both increased in KOA patients, suggesting that they are involved in KOA.

Characterization of the Inflammatory Properties of Actively Released HMGB1 in Juvenile Idiopathic Arthritis

AIMS

Pathogenic effects of the endogenous inflammatory mediator high mobility group box protein 1 (HMGB1) have been described in several inflammatory diseases. Recent reports have underlined the importance of post-translational modifications (PTMs) in determination of HMGB1 function and release mechanisms. We investigated the occurrence of PTMs of HMGB1 obtained from synovial fluid (SF) of juvenile idiopathic arthritis (JIA) patients.

RESULTS

Analyses of 17 JIA patients confirmed high HMGB1 levels in SF. Liquid chromatography tandem mass-spectrometry (LC-MS/MS) analyses of PTMs revealed that total HMGB1 levels were not associated with increased lactate dehydrogenase activity but strongly correlated with nuclear location sequence 2 (NLS2) hyperacetylation, indicating active release of HMGB1. The correlation between total HMGB1 levels and NLS2 hypoacetylation suggests additional, acetylation-independent release mechanisms. Monomethylation of lysine 43 (K43), a proposed neutrophil-specific PTM, was strongly associated with high HMGB1 levels, implying that neutrophils are a source of released HMGB1. Analysis of cysteine redox isoforms, fully reduced HMGB1, disulfide HMGB1, and oxidized HMGB1, revealed that HMGB1 acts as both a chemotactic and a cytokine-inducing mediator. These properties were associated with actively released HMGB1.

INNOVATION

This is the first report that characterizes HMGB1-specific PTMs during a chronic inflammatory condition.

CONCLUSION

HMGB1 in SF from JIA patients is actively released through both acetylation-dependent and -nondependent manners. The presence of various functional HMGB1 redox isoforms confirms the complexity of their pathogenic role during chronic inflammation. Defining HMGB1 release pathways and redox isoforms is critical for the understanding of the contribution of HMGB1 during inflammatory processes.

A Network Pharmacology Approach to Uncover the Pharmacological Mechanism of XuanHuSuo Powder on Osteoarthritis

As the most familiar type of arthritis and a chronic illness of the joints, Osteoarthritis (OA) affects a great number of people on the global scale. XuanHuSuo powder (XHSP), a conventional herbal formula from China, has been extensively applied in OA treatment. Nonetheless, its pharmacological mechanism has not been completely expounded. In this research, a network pharmacology approach has been chosen to study the pharmacological mechanism of XHSP on OA, and the pharmacology networks were established based on the relationship between four herbs found in XHSP, compound targets, and OA targets. The pathway enrichment analysis revealed that the significant bioprocess networks of XHSP on OA were regulation of inflammation, interleukin-1β (IL-1β) production and nitric oxide (NO) biosynthetic process, response to cytokine or estrogen stimuli, and antiapoptosis. These effects have not been reported previously. The comprehensive network pharmacology approach developed by our research has revealed, for the first time, a connection between four herbs found in XHSP, corresponding compound targets, and OA pathway systems that are conducive to expanding the clinical application of XHSP. The proposed network pharmacology approach could be a promising complementary method by which researchers might better evaluate multitarget or multicomponent drugs on a systematic level.