Early stage blockade of the alarmin HMGB1 reduces cartilage destruction in experimental OA

Osteoimmunology in Osteoarthritis: Unraveling the Interplay of Immunity, Inflammation, and Joint Degeneration

Osteoarthritis (OA) is a degenerative joint disease influenced by multiple factors, with its etiology arising from intricate interactions among mechanical stress, inflammatory processes, and disruptions in bone metabolism. Recent research in bone immunology indicates that immune-mediated mechanisms significantly contribute to the progression of OA, highlighting the interactions among immune cells, cytokine networks, and bone components. Immune cells interact with osteoclasts, osteoblasts, and chondrocytes in a variety of ways. These interactions foster a pro-inflammatory microenvironment, contributing to cartilage breakdown, synovial inflammation, and the sclerosis of subchondral bone. In this article, we present a comprehensive review of bone immunology in OA, focusing on the critical role of immune cells and their cytokine-mediated feedback loops in the pathophysiology of OA. In addition, we are exploring novel therapeutic strategies targeting bone immune pathways, including macrophage polarization, T-cell differentiation, and stem cell therapy to restore the metabolic balance between immunity and bone. By integrating cutting-edge research in bone immunology, this review integrates the latest advancements in bone immunology to construct a comprehensive framework for unraveling the pathogenesis of OA, laying a theoretical foundation for the development of innovative precision therapies.

EZH2/miR-142-3p/HMGB1 axis mediates chondrocyte pyroptosis by regulating endoplasmic reticulum stress in knee osteoarthritis

BACKGROUND

Knee osteoarthritis (OA) is still challenging to prevent or treat. Enhanced endoplasmic reticulum (ER) stress and increased pyroptosis in chondrocytes may be responsible for cartilage degeneration. This study aims to investigate the effect of ER stress on chondrocyte pyroptosis and the upstream regulatory mechanisms, which have rarely been reported.

METHODS

The expression of the histone methyltransferase enhancer of zeste homolog 2 (EZH2), microRNA-142-3p (miR-142-3p), and high mobility group box 1 (HMGB1) and the levels of ER stress, pyroptosis, and metabolic markers in normal and OA chondrocytes were investigated by western blotting, quantitative polymerase chain reaction, immunohistochemistry, fluorescence in situ hybridization, fluorescein amidite-tyrosine-valine-alanine-aspartic acid-fluoromethyl ketone (FAM-YVAD-FMK)/Hoechst 33342/propidium iodide (PI) staining, lactate dehydrogenase (LDH) release assays, and cell viability assessments. The effects of EZH2, miR-142-3p, and HMGB1 on ER stress and pyroptosis and the hierarchical regulatory relationship between them were analyzed by chromatin immunoprecipitation, luciferase reporters, gain/loss-of-function assays, and rescue assays in interleukin (IL)-1β-induced OA chondrocytes. The mechanistic contribution of EZH2, miR-142-3p, and HMGB1 to chondrocyte ER stress and pyroptosis and therapeutic prospects were validated radiologically, histologically, and immunohistochemically in surgically induced OA rats.

RESULTS

Increased EZH2 and HMGB1, decreased miR-142-3p, enhanced ER stress, and activated pyroptosis in chondrocytes were associated with OA occurrence and progression. EZH2 and HMGB1 exacerbated and miR-142-3p alleviated ER stress and pyroptosis in OA chondrocytes. EZH2 transcriptionally silenced miR-142-3p via H3K27 trimethylation, and miR-142-3p posttranscriptionally silenced HMGB1 by targeting the 3'-UTR of the HMGB1 gene. Moreover, ER stress mediated the effects of EZH2, miR-142-3p, and HMGB1 on chondrocyte pyroptosis. In vivo experiments mechanistically validated the hierarchical regulatory relationship between EZH2, miR-142-3p, and HMGB1 and their effects on chondrocyte ER stress and pyroptosis.

CONCLUSIONS

A novel EZH2/miR-142-3p/HMGB1 axis mediates chondrocyte pyroptosis and cartilage degeneration by regulating ER stress in OA, contributing novel mechanistic insights into OA pathogenesis and providing potential targets for future therapeutic research.

Cartilage protective and anti-edema effects of JTF in osteoarthritis via inhibiting NCOA4-HMGB1-driven ferroptosis and aquaporin dysregulation

BACKGROUND

Preventing joint edema is crucial in halting osteoarthritis (OA) progression. Growing clinical evidence indicate that Jianpi-Tongluo Formula (JTF) may have a promising anti-edema effect. However, the therapeutic properties of JTF and the underlying mechanisms remains unclear.

MATERIALS AND METHODS

An OA rat model was established and employed to evaluate pharmacological effects of JTF in vivo based on dynamic histopathologic assessments and micro-CT observations. Then, OA-related genes and potential targets of JTF were identified through clinical transcriptomic data analysis and "disease gene-drug target" network analysis, which were verified by a series of in vivo experiments.

RESULTS

JTF administration effectively reduced pain and joint edema, inhibited matrix degradation, chondrocyte apoptosis, and aquaporin expression in OA rats. Notably, JTF dose-dependently reversed damage-associated molecular patterns and inflammatory factor upregulation. Mechanically, our "disease gene-drug target" network analysis indicated that the NCOA4-HMGB1-GSK3B-AQPs axis, implicated in ferroptosis and aquaporin dysregulation, may be potentially served as a target of JTF against OA. Accordingly, JTF mitigated NCOA4, HMGB1, and GSK3B expression, oxidative stress, and iron metabolism aberrations in OA rats. Furthermore, JTF treatment significantly attenuated the aberrant upregulation of AQP1, AQP3, and AQP4 proteins observed in cartilage tissues of OA rats.

CONCLUSION

Our data reveal for the first time that JTF may exert cartilage protective and anti-edema effects in osteoarthritis therapy by inhibiting NCOA4-HMGB1-driven ferroptosis and aquaporin dysregulation.

The Role of Alarmins in the Pathogenesis of Rheumatoid Arthritis, Osteoarthritis, and Psoriasis

Alarmins are immune-activating factors released after cellular injury or death. By secreting alarmins, cells can interact with immune cells and induce a variety of inflammatory responses. The broad family of alarmins involves several members, such as high-mobility group box 1, S100 proteins, interleukin-33, and heat shock proteins, among others. Studies have found that the concentrations and expression profiles of alarmins are altered in immune-mediated diseases. Furthermore, they are involved in the pathogenesis of inflammatory conditions. The aim of this narrative review is to present the current evidence on the role of alarmins in rheumatoid arthritis, osteoarthritis, and psoriasis. We discuss their potential involvement in mechanisms underlying the progression of these diseases and whether they could become therapeutic targets. Moreover, we summarize the impact of pharmacological agents used in the treatment of these diseases on the expression of alarmins.

High mobility group box-1: A therapeutic target for analgesia and associated symptoms in chronic pain

The number of patients with chronic pain continues to increase against the background of an ageing society and a high incidence of various epidemics and disasters. One factor contributing to this situation is the absence of truly effective analgesics. Chronic pain is a persistent stress for the organism and can trigger a variety of neuropsychiatric symptoms. Hence, the search for useful analgesic targets is currently being intensified worldwide, and it is anticipated that the key to success may be molecules involved in emotional as well as sensory systems. High mobility group box-1 (HMGB1) has attracted attention as a therapeutic target for a variety of diseases. It is a very unique molecule having a dual role as a nuclear protein while also functioning as an inflammatory agent outside the cell. In recent years, numerous studies have shown that HMGB1 acts as a pain inducer in primary sensory nerves and the spinal dorsal horn. In addition, HMGB1 can function in the brain, and is involved in the symptoms of depression, anxiety and cognitive dysfunction that accompany chronic pain. In this review, we will summarize recent research and discuss the potential of HMGB1 as a useful drug target for chronic pain.

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.

Forsythoside B alleviates osteoarthritis through the HMGB1/TLR4/NF-κB and Keap1/Nrf2/HO-1 pathways

Osteoarthritis (OA) is a joint pain and dysfunction syndrome resulting from severe joint degeneration. Inflammation and degeneration of the articular cartilage are two main features of OA and have tight interactions during OA progression. Conventional treatment with nonsteroidal anti-inflammatory drugs has been widely utilized clinically, whereas the side effects have restricted their application. Forsythoside B has been found with anti-inflammatory effects and antiapoptosis in inflammatory diseases, whereas in OA it remains poorly understood. Interleukin (IL)-1β (10 ng/mL) was taken to induce an OA cell model on HC-A chondrocytes and an OA rat model was constructed for in vivo experiments. Forsythoside B was adopted to treat HC-A chondrocytes and OA rats. As shown by the data, Forsythoside B hampered IL-1β-elicited rat chondrocyte apoptosis, oxidative stress, and facilitated proliferation. The profiles of inflammatory factors, NOD-like receptor family pyrin domain containing 3 inflammasomes, Kelch-like epichlorohydrin-associated protein-1 (Keap1), and nuclear factor-κB (NF-κB) phosphorylation were suppressed by Forsythoside B, whereas the nuclear factor E2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) levels were promoted. Further, Forsythoside B mitigated cartilage damage and degeneration. Moreover, the oxidative stress and inflammation mediators in the cartilage tissue of OA rats were remarkably abated. Collectively, Forsythoside B hinders the NF-κB and Keap1/Nrf2/HO-1 pathways to curb IL-1β-elicited OA rat oxidative stress and inflammation both in vivo and ex vivo, ameliorating OA development. All over, this study provides an underlying strategy for treating OA, which might help the clinical treatment of OA patients.

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.

Piperlongumine mediates amelioration of osteoarthritis via inhibition of chondrocyte senescence and inflammation in a goat ex vivo model

In osteoarthritis (OA), chondrocytes manifest senescence, which results in a vicious signaling loop that aids the progression of the disease. More specifically, inflammation-associated senescence is one of the major regulators of the initiation and progression of OA. Therefore, we targeted senescence through inflammation with a pharmacological approach for OA amelioration. In this study, we first confirmed the suitability of the IL1β-induced goat ex vivo OA model (emphasizing 3R's principle) for the screening of senotherapeutics, namely, ABT-263, ABT-737, and Piperlongumine (PL), wherein PL showed a positive outcome in the preliminary studies. Thereafter, we determined the cytocompatible concentrations of PL using live/dead staining. Further, treatment of ex vivo OA cartilage with PL exhibited a concentration-dependent increase in the retention of key cartilage matrix components. We then examined the effect of PL on chondrocyte senescence and observed a decreased expression of major senescence markers in the PL-treated groups. Interestingly, PL treatment reduced the expression of major downstream effectors of the chondrocyte senescence pathway in a concentration-dependent manner at both gene and protein levels. Moreover, IL1β-induced elevated levels of oxidative stress and DNA damage in cartilage explants were rescued by all the tested concentrations of PL. In addition, PL also reduced the expression of major inflammatory markers of OA in the goat ex vivo OA model. Finally, we proposed a model for the mechanism of action of PL in the treatment of OA. Overall, PL showed a promising outcome as a senotherapeutic for the amelioration of OA in the goat ex vivo OA model.

The multifunctional protein HMGB1: 50 years of discovery

Fifty years since the initial discovery of HMGB1 in 1973 as a structural protein of chromatin, HMGB1 is now known to regulate diverse biological processes depending on its subcellular or extracellular localization. These functions include promoting DNA damage repair in the nucleus, sensing nucleic acids and inducing innate immune responses and autophagy in the cytosol and binding protein partners in the extracellular environment and stimulating immunoreceptors. In addition, HMGB1 is a broad sensor of cellular stress that balances cell death and survival responses essential for cellular homeostasis and tissue maintenance. HMGB1 is also an important mediator secreted by immune cells that is involved in a range of pathological conditions, including infectious diseases, ischaemia-reperfusion injury, autoimmunity, cardiovascular and neurodegenerative diseases, metabolic disorders and cancer. In this Review, we discuss the signalling mechanisms, cellular functions and clinical relevance of HMGB1 and describe strategies to modify its release and biological activities in the setting of various diseases.

Identification and validation of FPR1, FPR2, IL17RA and TLR7 as immunogenic cell death related genes in osteoarthritis

Immunogenic cell death (ICDs) has gained increasing attention for its significant clinical efficacy in various diseases. Similarly, more and more attention has been paid in the role of immune factors in the pathological process of osteoarthritis (OA). The objective of this study is to reveal the relationship between ICD-related genes and the process of OA at the gene level through bioinformatics analysis. In this study, Limma R package was applied to identify differentially expressed genes (DEG), and OA related module genes were determined by weighted gene co-expression network analysis. The ICD-related genes were extracted from a previous study. The module genes related to DEGs and ICD were overlapped. Then, hub genes were identified by a series of analyses using the Least absolute shrinkage and selection operator and random forest algorithm, the expression level and diagnostic value of hub genes were evaluated by Logistic regression. In addition, we used Spearman rank correlation analysis to clarify the relationship between hub genes and infiltrating immune cells and immune pathways. The expression levels of FPR1, FPR2, IL17RA, and TLR7 was verified in SD rat knee joint model of OA by immunohistochemistry. The expression levels of FPR1, FPR2, IL17RA, and TLR7 mRNA were detected in the IL-1β induced rat chondrocytes in qPCR experiment in vitro. Four hub genes (FPR1, FPR2, IL17RA, and TLR7) were ultimately identified as OA biomarkers associated with ICD. And knockdown of TLR7 reversed collagen II and ADAMTS-5 degradation in IL-1β-stimulated chondrocytes. This research may provide new immune related biomarkers for the diagnosis of OA and serve as a reference for disease treatment monitoring.

Hsa_circ_0007292 promotes chondrocyte injury in osteoarthritis via targeting the miR-1179/HMGB1 axis

BACKGROUND

Circular RNAs (circRNAs) have been demonstrated to participate in the progression of osteoarthritis (OA). This study aimed to investigate the role and molecular mechanism of hsa_circ_0007292 in OA.

METHODS

Hsa_circ_0007292 was identified by analyzing a circRNA microarray from the Gene Expression Omnibus (GEO) database, and its expression was detected by real-time PCR in OA cartilage tissues and interleukin (IL)-1β-induced two human chondrocytes (CHON-001 and C28/I2), the OA cell models. The effects of hsa_circ_0007292 knockdown and miR-1179 overexpression on IL-1β-induced chondrocyte injury were examined by CCK-8, BrdU, flow cytometry, ELISA, and western blot. RNA pull-down assay and dual-luciferase reporter gene assay were used to analyze the interaction between hsa_circ_0007292 and miR-1179. Rescue experiments were carried out to determine the correlations among hsa_circ_0007292, miR-1179 and high mobility group box-1 (HMGB1).

RESULTS

Hsa_circ_0007292 expression was upregulated in OA tissues and IL-1β-induced chondrocytes. Both downregulation of hsa_circ_0007292 and miR-1179 overexpression increased the proliferation and Aggrecan expression, suppressed apoptosis, matrix catabolic enzyme MMP13 expression and inflammatory factor (TNF-α, IL-6, and IL-8) levels. There was a negative correlation between hsa_circ_0007292 and miR-1179, and a positive correlation between hsa_circ_0007292 and HMGB1 in OA tissues. The mechanistic study showed that hsa_circ_0007292 prevented HMGB1 downregulation by sponging miR-1179. Upregulation of HMGB1 could reverse the influence of hsa_circ_0007292 downregulation on IL-1β-induced chondrocyte injury.

CONCLUSIONS

Downregulation of hsa_circ_0007292 relieved apoptosis, extracellular matrix degradation and inflammatory response in OA via the miR-1179/HMGB1 axis, suggesting that hsa_circ_0007292 might be a potential therapeutic target for OA treatment.

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.

Bone marrow lesions in osteoarthritis: From basic science to clinical implications

Osteoarthritis (OA) is the most prevalent musculoskeletal disease characterized by multiple joint structure damages, including articular cartilage, subchondral bone and synovium, resulting in disability and economic burden. Bone marrow lesions (BMLs) are common and important magnetic resonance imaging (MRI) features in OA patients. Basic and clinical research on subchondral BMLs in the pathogenesis of OA has been a hotspot. New evidence shows that subchondral bone degeneration, including BML and angiogenesis, occurs not only at or after cartilage degeneration, but even earlier than cartilage degeneration. Although BMLs are recognized as important biomarkers for OA, their exact roles in the pathogenesis of OA are still unclear, and disputes about the clinical impact and treatment of BMLs remain. This review summarizes the current basic and clinical research progress of BMLs. We particularly focus on molecular pathways, cellular abnormalities and microenvironmental changes of subchondral bone that contributed to the formation of BMLs, and emphasize the crosstalk between subchondral bone and cartilage in OA development. Finally, potential therapeutic strategies targeting BMLs in OA are discussed, which provides novel strategies for OA treatment.

Targeting strategies for bone diseases: signaling pathways and clinical studies

Since the proposal of Paul Ehrlich's magic bullet concept over 100 years ago, tremendous advances have occurred in targeted therapy. From the initial selective antibody, antitoxin to targeted drug delivery that emerged in the past decades, more precise therapeutic efficacy is realized in specific pathological sites of clinical diseases. As a highly pyknotic mineralized tissue with lessened blood flow, bone is characterized by a complex remodeling and homeostatic regulation mechanism, which makes drug therapy for skeletal diseases more challenging than other tissues. Bone-targeted therapy has been considered a promising therapeutic approach for handling such drawbacks. With the deepening understanding of bone biology, improvements in some established bone-targeted drugs and novel therapeutic targets for drugs and deliveries have emerged on the horizon. In this review, we provide a panoramic summary of recent advances in therapeutic strategies based on bone targeting. We highlight targeting strategies based on bone structure and remodeling biology. For bone-targeted therapeutic agents, in addition to improvements of the classic denosumab, romosozumab, and PTH1R ligands, potential regulation of the remodeling process targeting other key membrane expressions, cellular crosstalk, and gene expression, of all bone cells has been exploited. For bone-targeted drug delivery, different delivery strategies targeting bone matrix, bone marrow, and specific bone cells are summarized with a comparison between different targeting ligands. Ultimately, this review will summarize recent advances in the clinical translation of bone-targeted therapies and provide a perspective on the challenges for the application of bone-targeted therapy in the clinic and future trends in this area.

Inflammaging and Osteoarthritis

Osteoarthritis is a highly prevalent disease particularly in subjects over 65 years of age worldwide. While in the past it was considered a mere consequence of cartilage degradation leading to anatomical and functional joint impairment, in recent decades, there has been a more dynamic view with the synovium, the cartilage, and the subchondral bone producing inflammatory mediators which ultimately lead to cartilage damage. Inflammaging is defined as a chronic, sterile, low-grade inflammation state driven by endogenous signals in the absence of infections, occurring with aging. This chronic status is linked to the production of reactive oxygen species and molecules involved in the development of age-related disease such as cancer, diabetes, and cardiovascular and neurodegenerative diseases. Inflammaging contributes to osteoarthritis development where both the innate and the adaptive immune response are involved. Elevated systemic and local inflammatory cytokines and senescent molecules promote cartilage degradation, and antigens derived from damaged joints further trigger inflammation through inflammasome activation. B and T lymphocyte populations also change with inflammaging and OA, with reduced regulatory functions, thus implicating self-reactivity as an additional mechanism of joint damage. The discovery of the underlying pathogenic pathways may help to identify potential therapeutic targets for the management or the prevention of osteoarthritis. We will provide a comprehensive evaluation of the current literature on the role of inflammaging in osteoarthritis and discuss the emerging therapeutic strategies.

Association of HMGB1 levels in synovial fluid with the severity of temporomandibular joint osteoarthritis

BACKGROUND

HMGB1 usually serves as a damage-associated molecular pattern (DAMP) molecule (also known as alarmin) that regulates the inflammatory and immune responses via different receptors or direct uptake. Numerous studies have reported the association between HMGB1 and inflammatory diseases; however, its role in temporomandibular joint (TMJ) osteoarthritis (OA) has not been elucidated. In this retrospective study, we aimed to investigate HMGB1 levels in the synovial fluid (SF) in patients with TMJOA and TMID, their correlation with TMJOA and TMID severity, and the therapeutic effect of sodium hyaluronate (hyaluronic acid, HA) on TMJOA.

METHODS

SF samples were analyzed for 30 patients with TMJ internal derangement (TMJID) and TMJOA, along with visual analog scale (VAS) scores, radiographic stages, and mandibular functional limitations. The SF levels of HMGB1, IL-1β, IL-18, PGE2, RAGE, TLR4, and iNOS were determined via an enzyme-linked immunosorbent assay. To evaluate the therapeutic effects of HA, pre-treatment and post-treatment clinical symptoms were also compared in patients of the TMJOA group who had received an intra-articular injection of HA.

RESULTS

VAS and Jaw Functional Limitation Scale (JFLS) scores were significantly higher in the TMJOA group than in the TMNID group, as were SF levels of HMGB1, TLR4, IL-1β, IL-18, PGE2, and iNOS. The synovial HMGB1 level was positively correlated with the VAS score (r = 0.5512, p = 0.0016) and mandibular functional limitations (r = 0.4684, p = 0.0054). The cut-off value for the HMGB1 level as a diagnostic biomarker was 986.8 pg/ml. The SF level of HMGB1 yielded an area under the curve value (AUC) of 0.8344 for predicting TMJOA. HA alleviated TMJ disorders by significantly reducing the VAS score and improving the maximum extent of mouth opening in both the TMJID and TMJOA groups (p < 0.05). Moreover, patients in both the TMJID and TMJOA groups exhibited significant improvement in the JFLS score following HA treatment.

CONCLUSIONS

Our results indicate that HMGB1 is a potential marker for predicting the severity of TMJOA. Intra-articular HA injection exerts a positive therapeutic effect on TMJOA; however, further investigations are warranted to validate its therapeutic effect in the late phase of visco-supplementation treatment.

The alarmins high mobility group box protein 1 and S100A8/A9 display different inflammatory profiles after acute knee injury

OBJECTIVE

To compare the concentrations of high mobility group box 1 protein (HMGB1) and S100A8/A9 in synovial fluid between patients with knee injuries and osteoarthritis (OA), and knee healthy subjects. To investigate associations of alarmin levels with different joint injuries and with biomarkers of inflammation, Wnt signaling, complement system, bone and cartilage degradation.

METHODS

HMGB1 and S100A8/A9 were measured in synovial fluid by immunoassays in patients with knee injuries, with OA and from knee healthy subjects, and were related to time from injury and with biomarkers obtained from previous studies. Hierarchical cluster and enrichment analyses of biomarkers associated to HMGB1 and S100A8/A9 were performed.

RESULTS

The synovial fluid HMGB1 and S100A8/A9 concentrations were increased early after knee injury; S100A8/A9 levels were negatively associated to time after injury and was lower in the old compared to recent injury group, while HMGB1 was not associated to time after injury. The S100A8/A9 levels were also increased in OA. The initial inflammatory response was similar between the alarmins, and HMGB1 and S100A8/A9 shared 9 out of 20 enriched pathways. The alarmins displayed distinct response profiles, HMGB1 being associated to cartilage biomarkers while S100A8/A9 was associated to proinflammatory cytokines.

CONCLUSIONS

HMGB1 and S100A8/A9 are increased as an immediate response to knee trauma. While they share many features in inflammatory and immunoregulatory mechanisms, S100A8/A9 and HMGB1 are associated to different downstream responses, which may have impact on the OA progression after acute knee injuries.

Inhibition of HMGB1 suppresses inflammation and catabolism in temporomandibular joint osteoarthritis <em>via</em> NF-κB signaling pathway

HMGB1 is a highly conserved nuclear protein that is rapidly released into the extracellular environment during infection or tissue damage. In osteoarthritis, HMGB1 acts as a pro-inflammatory cytokine inducing a positive feedback loop for synovial inflammation and cartilage degradation. The aim of this study was to explore the role of HMGB1 in inflammation and catabolism of temporomandibular joint osteoarthritis (TMJOA) and whether inhibition of HMGB1 affects TMJOA. Human synovial fibroblasts were incubated with HMGB1, the expression of pro-inflammatory cytokines and catabolic mediators were measured by Western blot and ELISA. NF-κB signaling pathway involvement was studied by the NF-κB inhibitor and detected by Western blotting and immunofluorescence staining. TMJOA was induced by an injection of complete Freund’s adjuvant (CFA) into anterosuperior compartment of rat’s joint. An anti-HMGB1 antibody was used to assess the effect to HMGB1 in the synovium and cartilage of the CFA-induced TMJOA rats by hematoxylin and eosin, Safranin O, Masson trichrome staining, immunohistochemistry and immunofluorescence. HMGB1 markedly increased the production of MMP13, ADAMTS5, IL-1β and IL-6 through activating NF-κB signaling pathway in human synovial fibroblasts. In vivo, application of the HMGB1 neutralizing antibody effectively ameliorated the detrimental extent of TMJOA. Furthermore, the HMGB1 neutralizing antibody reduced the expression of NF-κB, pro-inflammatory cytokines and catabolic mediators in the synovium and cartilage of CFA-induced TMJOA rats. HMGB1 inhibition alleviates TMJOA by reducing synovial inflammation and cartilage catabolism possibly through suppressing the NF-κB signaling pathway and may become a therapeutic method against TMJOA.

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.

Necroptotic TNFα-Syndecan 4-TNFα Vicious Cycle as a Therapeutic Target for Preventing Temporomandibular Joint Osteoarthritis

Temporomandibular joint osteoarthritis (TMJOA) is a chronic degenerative disease for which the underlying mechanism still remains unclear. Compared with apoptosis and autophagy, necroptosis causes greater harm to tissue homeostasis by releasing damage-associated molecular patterns (DAMPs). However, the role of necroptosis and downstream key DAMPs in TMJOA is unknown. Here, rodent models of TMJOA were established by the unilateral anterior crossbite (UAC). Transmission electron microscopy (TEM) and immunohistochemistry of receptor interacting protein kinase 3 (RIPK3)/phosphorylation of mixed lineage kinase domain-like protein (pMLKL) were conducted to evaluate the occurrence of necroptosis in vivo. The therapeutic effects of blocking necroptosis were achieved by intra-articularly injecting RIPK3 or MLKL inhibitors and using RIPK3 or MLKL knockout mice. In vitro necroptosis of condylar chondrocyte was induced by combination of tumor necrosis factor alpha (TNFα), second mitochondria-derived activator of caspases (SMAC) mimetics and carbobenzoxy-valyl-alanyl-aspartyl-[O-methyl]- fluoromethylketone (z-VAD-fmk). The possible DAMPs released by necroptotic chondrocytes were screened by quantitative proteomics and blocked by specific antibody. Translucent cytosol, swollen organelles, and ruptured cell membranes, features of necroptosis, were frequently manifested in chondrocytes at the early stage of condylar cartilage degeneration in TMJOA, which was accompanied by upregulation of RIPK3/pMLKL. Inhibiting or knocking out RIPK3/MLKL significantly prevented cartilage degeneration. DAMPs released by necroptotic condylar chondrocytes, such as syndecan 4 (SDC4) and heat shock protein 90 (HSP90), were verified. Furthermore, blocking the function of SDC4 significantly attenuated the expression of TNFα in cartilage and synovium, and accordingly increased cartilage thickness and reduced synovial inflammation. Thus, the necroptotic vicious cycle of TNFα-SDC4-TNFα contributes to cartilage degeneration and synovitis, and can serve as a potential therapeutic target for treating TMJOA. © 2022 American Society for Bone and Mineral Research (ASBMR).

Synovial inflammation in osteoarthritis progression

Osteoarthritis (OA) is a progressive degenerative disease resulting in joint deterioration. Synovial inflammation is present in the OA joint and has been associated with radiographic and pain progression. Several OA risk factors, including ageing, obesity, trauma and mechanical loading, play a role in OA pathogenesis, likely by modifying synovial biology. In addition, other factors, such as mitochondrial dysfunction, damage-associated molecular patterns, cytokines, metabolites and crystals in the synovium, activate synovial cells and mediate synovial inflammation. An understanding of the activated pathways that are involved in OA-related synovial inflammation could form the basis for the stratification of patients and the development of novel therapeutics. This Review focuses on the biology of the OA synovium, how the cells residing in or recruited to the synovium interact with each other, how they become activated, how they contribute to OA progression and their interplay with other joint structures.

High Mobility Group Box 1: Biological Functions and Relevance in Oxidative Stress Related Chronic Diseases

In the early 1970s, a group of non-histone nuclear proteins with high electrophoretic mobility was discovered and named high-mobility group (HMG) proteins. High-mobility group box 1 (HMGB1) is the most studied HMG protein that detects and coordinates cellular stress response. The biological function of HMGB1 depends on its subcellular localization and expression. It plays a critical role in the nucleus and cytoplasm as DNA chaperone, chromosome gatekeeper, autophagy maintainer, and protector from apoptotic cell death. HMGB1 also functions as an extracellular alarmin acting as a damage-associated molecular pattern molecule (DAMP). Recent findings describe HMGB1 as a sophisticated signal of danger, with a pleiotropic function, which is useful as a clinical biomarker for several disorders. HMGB1 has emerged as a mediator in acute and chronic inflammation. Furthermore, HMGB1 targeting can induce beneficial effects on oxidative stress related diseases. This review focus on HMGB1 redox status, localization, mechanisms of release, binding with receptors, and its activities in different oxidative stress-related chronic diseases. Since a growing number of reports show the key role of HMGB1 in socially relevant pathological conditions, to our knowledge, for the first time, here we analyze the scientific literature, evaluating the number of publications focusing on HMGB1 in humans and animal models, per year, from 2006 to 2021 and the number of records published, yearly, per disease and category (studies on humans and animal models).

Unraveling the Signaling Secretome of Platelet-Rich Plasma: Towards a Better Understanding of Its Therapeutic Potential in Knee Osteoarthritis

Platelets and their secretory products play an important role in determining the balance between tissue repair and tissue damage. To obtain novel insights into the molecular composition of platelet-rich plasma (PRP) and contextualize them in knee osteoarthritis (OA), two different plasma formulations, namely PRP and platelet-poor plasma (PPP), were prepared from six healthy donors following a biobank-automated protocol. Inter-donor differences were analyzed, and pools were created before performing multiplexing protein arrays. In addition, PRP and PPP were prepared from six patients following our in-house protocols. Supernatants from PRP and PPP were harvested one hour after calcium chloride activation. Multiplexing protein arrays were performed in parallel for all plasma formulations. Results were normalized to fold change in relation to PPP and examined using Ingenuity Pathway Analysis Software. Bioinformatic predictions showed that PRPs constitute a signaling system with interrelated networks of inflammatory and angiogenic proteins, including but not limited to interleukin-6 and -8 (IL-6, IL-8), insulin like growth factor 1 (IGF-1), transforming growth factor beta, (TGF-b), and vascular endothelial growth factor (VEGF) signaling, underlying biological actions. Predictions of canonical systems activated with PRP molecules include various inflammatory pathways, including high-mobility group box protein (HMGB1) and interleukin 17 (IL-17) signaling, neuroinflammation, and nuclear factor-kappa b (NF-κB) pathways. Eventually, according to these predictions and OA evolving knowledge, selected PRP formulations should be tailored to modulate different inflammatory phenotypes, i.e., meta-inflammation, inflame-aging or posttraumatic inflammatory osteoarthritis. However, further research to discriminate the peculiarities of autologous versus allogeneic formulations and their effects on the various OA inflammatory phenotypes is needed to foster PRPs.

Differential regulation of the water channel protein aquaporins in chondrocytes of human knee articular cartilage by aging

Knee cartilage is in an aqueous environment filled with synovial fluid consisting of water, various nutrients, and ions to maintain chondrocyte homeostasis. Aquaporins (AQPs) are water channel proteins that play an important role in water exchange in cells, and AQP1, -3, and -4 are known to be expressed predominantly in cartilage. We evaluated the changes in AQP expression in chondrocytes from human knee articular cartilage in patients of different ages and identified the key factor(s) that mediate age-induced alteration in AQP expression. The mRNA and protein expression of AQP1, -3 and -4 were significantly decreased in fibrocartilage compared to hyaline cartilage and in articular cartilage from older osteoarthritis patients compared to that from young patients. Gene and protein expression of AQP1, -3 and -4 were altered during the chondrogenic differentiation of C3H10T1/2 cells. The causative factors for age-associated decrease in AQP included H₂O₂, TNFα, and HMGB1 for AQP1, -3, and -4, respectively. In particular, the protective effect of AQP4 reduction following HMGB1 neutralization was noteworthy. The identification of other potent molecules that regulate AQP expression represents a promising therapeutic approach to suppress cartilage degeneration during aging.

Cell Interplay in Osteoarthritis

Osteoarthritis (OA) is a common chronic disease and a significant health concern that needs to be urgently solved. OA affects the cartilage and entire joint tissues, including the subchondral bone, synovium, and infrapatellar fat pads. The physiological and pathological changes in these tissues affect the occurrence and development of OA. Understanding complex crosstalk among different joint tissues and their roles in OA initiation and progression is critical in elucidating the pathogenic mechanism of OA. In this review, we begin with an overview of the role of chondrocytes, synovial cells (synovial fibroblasts and macrophages), mast cells, osteoblasts, osteoclasts, various stem cells, and engineered cells (induced pluripotent stem cells) in OA pathogenesis. Then, we discuss the various mechanisms by which these cells communicate, including paracrine signaling, local microenvironment, co-culture, extracellular vesicles (exosomes), and cell tissue engineering. We particularly focus on the therapeutic potential and clinical applications of stem cell-derived extracellular vesicles, which serve as modulators of cell-to-cell communication, in the field of regenerative medicine, such as cartilage repair. Finally, the challenges and limitations related to exosome-based treatment for OA are discussed. This article provides a comprehensive summary of key cells that might be targets of future therapies for OA.

Microenvironment in subchondral bone: predominant regulator for the treatment of osteoarthritis

Osteoarthritis (OA) is a degenerative joint disease in the elderly. Although OA has been considered as primarily a disease of the articular cartilage, the participation of subchondral bone in the pathogenesis of OA has attracted increasing attention. This review summarises the microstructural and histopathological changes in subchondral bone during OA progression that are due, at the cellular level, to changes in the interactions among osteocytes, osteoblasts, osteoclasts (OCs), endothelial cells and sensory neurons. Therefore, we focus on how pathological cellular interactions in the subchondral bone microenvironment promote subchondral bone destruction at different stages of OA progression. In addition, the limited amount of research on the communication between OCs in subchondral bone and chondrocytes (CCs) in articular cartilage during OA progression is reviewed. We propose the concept of 'OC-CC crosstalk' and describe the various pathways by which the two cell types might interact. Based on the 'OC-CC crosstalk', we elaborate potential therapeutic strategies for the treatment of OA, including restoring abnormal subchondral bone remodelling and blocking the bridge-subchondral type H vessels. Finally, the review summarises the current understanding of how the subchondral bone microenvironment is related to OA pain and describes potential interventions to reduce OA pain by targeting the subchondral bone microenvironment.

An Evidence-Based Systematic Review of Human Knee Post-Traumatic Osteoarthritis (PTOA): Timeline of Clinical Presentation and Disease Markers, Comparison of Knee Joint PTOA Models and Early Disease Implications

Understanding the causality of the post-traumatic osteoarthritis (PTOA) disease process of the knee joint is important for diagnosing early disease and developing new and effective preventions or treatments. The aim of this review was to provide detailed clinical data on inflammatory and other biomarkers obtained from patients after acute knee trauma in order to (i) present a timeline of events that occur in the acute, subacute, and chronic post-traumatic phases and in PTOA, and (ii) to identify key factors present in the synovial fluid, serum/plasma and urine, leading to PTOA of the knee in 23-50% of individuals who had acute knee trauma. In this context, we additionally discuss methods of simulating knee trauma and inflammation in in vivo, ex vivo articular cartilage explant and in vitro chondrocyte models, and answer whether these models are representative of the clinical inflammatory stages following knee trauma. Moreover, we compare the pro-inflammatory cytokine concentrations used in such models and demonstrate that, compared to concentrations in the synovial fluid after knee trauma, they are exceedingly high. We then used the Bradford Hill Framework to present evidence that TNF-α and IL-6 cytokines are causal factors, while IL-1β and IL-17 are credible factors in inducing knee PTOA disease progresssion. Lastly, we discuss beneficial infrastructure for future studies to dissect the role of local vs. systemic inflammation in PTOA progression with an emphasis on early disease.

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.

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.