Crosstalk between FLS and chondrocytes is regulated by HIF-2α-mediated cytokines in arthritis

Nanodrug delivery systems targeting ferroptosis as an innovative therapeutic approach for Rheumatoid Arthritis

Rheumatoid Arthritis (RA) is a chronic inflammatory disease characterized by joint inflammation, progressive cartilage degradation, and bone erosion. Recent research has implicated ferroptosis not only in autoimmune hepatitis but also in the pathogenesis and progression of autoimmune disorders like RA. Consequently, numerous therapeutic strategies have begun to target the ferroptosis pathway, particularly in the design and development of nanodrug delivery systems (NDDSs). While previous reviews have comprehensively discussed the mechanisms of ferroptosis, related signaling pathways, and NDDS materials, recent studies have further elucidated the interplay between ferroptosis and various metabolic pathways, providing a robust theoretical basis for the design of NDDS-based ferroptosis strategies. This review focuses on investigating the role of ferroptosis in the development of RA, aiming to elucidate how targeting ferroptosis can offer novel therapeutic concepts and potential treatments for RA patients. Specifically, it summarizes the design strategies of ferroptosis-based NDDSs via different pathways and highlights the feasibility of RA treatment regimens based on the ferroptosis mechanism. Furthermore, the review critically discusses the current limitations of NDDSs and offers perspectives on future research directions in this field.

Transcriptomic integration and ligand-receptor crosstalk reveal the underlying molecular mechanisms between hip cartilage and subchondral bone in osteonecrosis of femoral head

Osteonecrosis of femoral head (ONFH) is characterized not only by ischemic bone tissue necrosis but also by cartilage degeneration, which plays an essential role in the pathogenesis of ONFH. The molecular communication between tissues contributes to disease progression, however the communication between cartilage and subchondral bone in the progression of ONFH remains unclear. In this study, we integrated transcriptomic data from ONFH cartilage and subchondral bone, exploring common differentially expressed genes (DEGs), pathway and function enrichment analyses, the protein-protein interaction (PPI) network, and hub genes to comprehensively study molecular integration. Additionally, we explored the molecular crosstalk between and within cartilage and subchondral bone using ligand-receptor pairs and ONFH cartilage proteomic data. Finally, key genes and ligand-receptor pairs were validated by quantitative real-time PCR (qRT-PCR). There were 27 common DEGs and five hub genes in cartilage and subchondral bone. The defined hub genes included COL1A1, COLIA2, CTSK, SPARC, and MXRA5. Notably, pathways related to ossification, extracellular matrix, and collagen formation were significantly altered in ONFH. Ligand-receptor data combined with DEGs revealed 60 differentially expressed ligands and 51 differentially expressed receptors in cartilage and four ligands and three receptors in subchondral bone. In inter-tissue comparisons, ligands from chondrocytes predominantly paired with receptors on osteoblasts in the subchondral bone, such as FN1, MMP2, and FGF1. Conversely, ligands from osteoblasts and osteocytes in the subchondral bone frequently paired with chondrocyte receptors, including FN1, COL1A1, and SEMA7A. At the protein level, we identified thirteen ligands and one receptor, with COL3A1 being the most highly expressed ligand and CD82 the only differentially expressed receptor in ONFH. This study highlights common molecular mechanisms and ligand-receptor crosstalk between and within cartilage and subchondral bone in ONFH, offering new insights into the disease's pathophysiology and potential molecular targets for therapeutic intervention.

Exploring the therapeutic potential of "Tianyu" medicine pair in rheumatoid arthritis: an integrated study combining LC-MS/MS, bioinformatics, network pharmacology, and experimental validation

Background

Rheumatoid arthritis (RA) is a widespread chronic autoimmune disease that primarily causes joint inflammation and damage. In advanced stages, RA can result in joint deformities and loss of function, severely impacting patients' quality of life. The "Tianyu" pair (TYP) is a traditional Chinese medicine formulation developed from clinical experience and has shown some effectiveness in treating RA. However, its role in the complex biological mechanisms underlying RA remains unclear and warrants further investigation.

Methods

We obtained gene sequencing data of synovial tissues from both RA patients and healthy individuals using two gene microarrays, GSE77298 and GSE55235, from the GEO database. Through an integrated approach involving bioinformatics, machine learning, and network pharmacology, we identified the core molecular targets of the "Tianyu" medicine pair (TYP) for RA treatment. Liquid chromatography-mass spectrometry was then employed to analyze the chemical components of TYP. To validate our findings, we conducted animal experiments with Wistar rats, comparing histopathological and key gene expression changes before and after TYP treatment.

Results

Our data analysis suggests that the onset of RA may be associated with inflammation-related immune cells involved in both adaptive and innate immune responses. Potential key targets for TYP treatment in RA include AKR1B10, MMP13, FABP4, NCF1, SPP1, COL1A1, and RASGRP1. Among the components of TYP, Kaempferol, Quercetin, and Salidroside were identified as key, with MMP13 and NCF1 showing the strongest binding affinity to these compounds. Animal experiments confirmed the findings from bioinformatics and network pharmacology, validating the key targets and therapeutic effects of TYP in treating RA.

Conclusion

Our study reveals that TYP has potential clinical value in the treatment of rheumatoid arthritis. This research enhances our understanding of RA's pathogenesis and provides insight into potential therapeutic mechanisms.

Synovial microenvironment in temporomandibular joint osteoarthritis: crosstalk with chondrocytes and potential therapeutic targets

Temporomandibular joint osteoarthritis (TMJOA) is considered to be a low-grade inflammatory disease involving multiple joint tissues. The crosstalk between synovium and cartilage plays an important role in TMJOA. Synovial cells are a group of heterogeneous cells and synovial microenvironment is mainly composed of synovial fibroblasts (SF) and synovial macrophages. In TMJOA, SF and synovial macrophages release a large number of inflammatory cytokines and extracellular vesicles and promote cartilage destruction. Cartilage wear particles stimulate SF proliferation and macrophages activation and exacerbate synovitis. In TMJOA, chondrocytes and synovial cells exhibit increased glycolytic activity and lactate secretion, leading to impaired chondrocyte matrix synthesis. Additionally, the synovium contains mesenchymal stem cells, which are the seed cells for cartilage repair in TMJOA. Co-culture of chondrocytes and synovial mesenchymal stem cells enhances the chondrogenic differentiation of stem cells. This review discusses the pathological changes of synovium in TMJOA, the means of crosstalk between synovium and cartilage, and their influence on each other. Based on the crosstalk between synovium and cartilage in TMJOA, we illustrate the treatment strategies for improving synovial microenvironment, including reducing cell adhesion, utilizing extracellular vesicles to deliver biomolecules, regulating cellular metabolism and targeting inflammatory cytokines.

A personalized osteoarthritic joint-on-a-chip as a screening platform for biological treatments

Osteoarthritis (OA) is a highly disabling pathology, characterized by synovial inflammation and cartilage degeneration. Orthobiologics have shown promising results in OA treatment thanks to their ability to influence articular cells and modulate the inflammatory OA environment. Considering their complex mechanism of action, the development of reliable and relevant joint models appears as crucial to select the best orthobiologics for each patient. The aim of this study was to establish a microfluidic OA model to test therapies in a personalized human setting. The joint-on-a-chip model included cartilage and synovial compartments, containing hydrogel-embedded chondrocytes and synovial fibroblasts, separated by a channel for synovial fluid. For the cartilage compartment, a Hyaluronic Acid-based matrix was selected to preserve chondrocyte phenotype. Adding OA synovial fluid induced the production of inflammatory cytokines and degradative enzymes, generating an OA microenvironment. Personalized models were generated using patient-matched cells and synovial fluid to test the efficacy of mesenchymal stem cells on OA signatures. The patient-specific models allowed monitoring changes induced by cell injection, highlighting different individual responses to the treatment. Altogether, these results support the use of this joint-on-a-chip model as a prognostic tool to screen the patient-specific efficacy of orthobiologics.

Role of crosstalk between synovial cells and chondrocytes in osteoarthritis (Review)

Osteoarthritis (OA) is a low-grade, nonspecific inflammatory disease that affects the entire joint. This condition is characterized by synovitis, cartilage erosion, subchondral bone defects, and subpatellar fat pad damage. There is mounting evidence demonstrating the significance of crosstalk between synovitis and cartilage destruction in the development of OA. To comprehensively explore the phenotypic alterations of synovitis and cartilage destruction, it is important to elucidate the crosstalk mechanisms between chondrocytes and synovial cells. Furthermore, the updated iteration of single-cell sequencing technology reveals the interaction between chondrocyte and synovial cells. In the present review, the histological and pathological alterations between cartilage and synovium during OA progression are described, and the mode of interaction and molecular mechanisms between synovial cells and chondrocytes in OA, both of which affect the OA process mainly by altering the inflammatory environment and cellular state, are elucidated. Finally, the current OA therapeutic approaches are summarized and emerging therapeutic targets are reviewed in an attempt to provide potential insights into OA treatment.

Low-dose radiotherapy of osteoarthritis: from biological findings to clinical effects-challenges for future studies

Osteoarthritis (OA) is one of the most common and socioeconomically relevant diseases, with rising incidence and prevalence especially with regard to an ageing population in the Western world. Over the decades, the scientific perception of OA has shifted from a simple degeneration of cartilage and bone to a multifactorial disease involving various cell types and immunomodulatory factors. Despite a wide range of conventional treatment modalities available, a significant proportion of patients remain treatment refractory. Low-dose radiotherapy (LDRT) has been used for decades in the treatment of patients with inflammatory and/or degenerative diseases and has proven a viable option even in cohorts of patients with a rather poor prognosis. While its justification mainly derives from a vast body of empirical evidence, prospective randomized trials have until now failed to prove the effectiveness of LDRT. Nevertheless, over the decades, adaptions of LDRT treatment modalities have evolved using lower dosages with establishment of different treatment schedules for which definitive clinical proof is still pending. Preclinical research has revealed that the immune system is modulated by LDRT and very recently osteoimmunological mechanisms have been described. Future studies and investigations further elucidating the underlying mechanisms are an essential key to clarify the optimal patient stratification and treatment procedure, considering the patients' inflammatory status, age, and sex. The present review aims not only to present clinical and preclinical knowledge about the mechanistic and beneficial effects of LDRT, but also to emphasize topics that will need to be addressed in future studies. Further, a concise overview of the current status of the underlying radiobiological knowledge of LDRT for clinicians is given, while seeking to stimulate further translational research.

Deletion of the chondrocyte glucocorticoid receptor attenuates cartilage degradation through suppression of early synovial activation in murine posttraumatic osteoarthritis

OBJECTIVE

Disruption of endogenous glucocorticoid signalling in bone cells attenuates osteoarthritis (OA) in aged mice, however, the role of endogenous glucocorticoids in chondrocytes is unknown. Here, we investigated whether deletion of the glucocorticoid receptor, specifically in chondrocytes, also alters OA progression.

DESIGN

Knee OA was induced by surgical destabilisation of the medial meniscus (DMM) in male 22-week-old tamoxifen-inducible glucocorticoid receptor knockout (chGRKO) mice and their wild-type (WT) littermates (n = 7-9/group). Mice were harvested 2, 4, 8 and 16 weeks after surgery to examine the spatiotemporal changes in molecular, cellular, and histological characteristics.

RESULTS

At all time points following DMM, cartilage damage was significantly attenuated in chGRKO compared to WT mice. Two weeks after DMM, WT mice exhibited increased chondrocyte and synoviocyte hypoxia inducible factor (HIF)-2α expression resulting in extensive synovial activation characterised by synovial thickening and increased interleukin-1 beta expression. At 2 and 4 weeks after DMM, WT mice displayed pronounced chondrocyte senescence and elevated catabolic signalling (reduced Yes-associated protein 1 (YAP1) and increased matrix metalloprotease [MMP]-13 expression). Contrastingly, at 2 weeks after DMM, HIF-2α expression and synovial activation were much less pronounced in chGRKO than in WT mice. Furthermore, chondrocyte YAP1 and MMP-13 expression, as well as chondrocyte senescence were similar in chGRKO-DMM mice and sham-operated controls.

CONCLUSION

Endogenous glucocorticoid signalling in chondrocytes promotes synovial activation, chondrocyte senescence and cartilage degradation by upregulation of catabolic signalling through HIF-2α in murine posttraumatic OA. These findings indicate that inhibition of glucocorticoid signalling early after injury may present a promising way to slow osteoarthritic cartilage degeneration.

Role of reactive oxygen species and mitochondrial damage in rheumatoid arthritis and targeted drugs

Rheumatoid arthritis (RA) is an autoimmune disease characterized by synovial inflammation, pannus formation, and bone and cartilage damage. It has a high disability rate. The hypoxic microenvironment of RA joints can cause reactive oxygen species (ROS) accumulation and mitochondrial damage, which not only affect the metabolic processes of immune cells and pathological changes in fibroblastic synovial cells but also upregulate the expression of several inflammatory pathways, ultimately promoting inflammation. Additionally, ROS and mitochondrial damage are involved in angiogenesis and bone destruction, thereby accelerating RA progression. In this review, we highlighted the effects of ROS accumulation and mitochondrial damage on inflammatory response, angiogenesis, bone and cartilage damage in RA. Additionally, we summarized therapies that target ROS or mitochondria to relieve RA symptoms and discuss the gaps in research and existing controversies, hoping to provide new ideas for research in this area and insights for targeted drug development in RA.

The Association of uPA, uPAR, and suPAR System with Inflammation and Joint Damage in Rheumatoid Arthritis: suPAR as a Biomarker in the Light of a Personalized Medicine Perspective

BACKGROUND

In recent years, the involvement of the soluble urokinase Plasminogen Activator Receptor (suPAR) in the pathophysiological modulation of Rheumatoid Arthritis (RA) has been documented, resulting in the activation of several intracellular inflammatory pathways.

METHODS

We investigated the correlation of urokinase Plasminogen Activator (uPA)/urokinase Plasminogen Activator Receptor (uPAR) expression and suPAR with inflammation and joint damage in RA, evaluating their potential role in a precision medicine context.

RESULTS

Currently, suPAR has been shown to be a potential biomarker for the monitoring of Systemic Chronic Inflammation (SCI) and COVID-19. However, the effects due to suPAR interaction in immune cells are also involved in both RA onset and progression. To date, the literature data on suPAR in RA endorse its potential application as a biomarker of inflammation and subsequent joint damage.

CONCLUSION

Available evidence about suPAR utility in the RA field is promising, and future research should further investigate its use in clinical practice, resulting in a big step forward for precision medicine. As it is elevated in different types of inflammation, suPAR could potentially work as an adjunctive tool for the screening of RA patients. In addition, a suPAR system has been shown to be involved in RA pathogenesis, so new data about the therapeutic response to Jak inhibitors can represent a possible way to develop further studies.

LncRNAs as a new regulator of chronic musculoskeletal disorder

OBJECTIVES

In recent years, long non-coding RNAs (lncRNAs) have been found to play a role in the occurrence, progression and prognosis of chronic musculoskeletal disorders.

DESIGN AND METHODS

Literature exploring on PubMed was conducted using the combination of keywords 'LncRNA' and each of the following: 'osteoarthritis', 'rheumatoid arthritis', 'osteoporosis', 'osteogenesis', 'osteoclastogenesis', 'gout arthritis', 'Kashin-Beck disease', 'ankylosing spondylitis', 'cervical spondylotic myelopathy', 'intervertebral disc degeneration', 'human muscle disease' and 'muscle hypertrophy and atrophy'. For each disorder, we focused on the publications in the last five years (5/1/2016-2021/5/1, except for Kashin-Beck disease). Finally, we excluded publications that had been reported in reviews of various musculoskeletal disorders during the last three years. Here, we summarized the progress of research on the role of lncRNA in multiple pathological processes during musculoskeletal disorders.

RESULTS

LncRNAs play a crucial role in regulating downstream gene expression and maintaining function and homeostasis of cells, especially in chondrocytes, synovial cells, osteoblasts, osteoclasts and skeletal muscle cells.

CONCLUSIONS

Understanding the mechanisms of lncRNAs in musculoskeletal disorders may provide promising strategies for clinical practice.

The role of hypoxia-inducible factors in the development of chronic pathology

This review highlights the current understanding of hypoxia-inducible factors (HIFs) role as regulators of oxygen-dependent reactions and inducers of genes expression in human organism. The focus is on the most significant relationships between the activation or inhibition of the HIFs intracellular system and development of the inflammatory process in various organs, chronic diseases of gastrointestinal tract, osteoarticular system, kidneys as well as hematological, endocrine and metabolic disorders.

Marker Genes Change of Synovial Fibroblasts in Rheumatoid Arthritis Patients

Background

Rheumatoid arthritis (RA) is a chronic condition that manifests as inflammation of synovial joints, leading to joint destruction and deformity.

Methods

We identified single-cell RNA-seq data of synovial fibroblasts from RA and osteoarthritis (OA) patients in GSE109449 dataset. RA- and OA-specific cellular subpopulations were identified, and enrichment analysis was performed. Further, key genes for RA and OA were obtained by combined analysis with differentially expressed genes (DEGs) between RA and OA in GSE56409 dataset. The diagnostic role of key genes for RA was predicted using receiver operating characteristic (ROC) curve. Finally, we identified differences in immune cell infiltration between RA and OA patients, and utilized flow cytometry, qRT-PCR, and Western blot were used to examine the immune cell and key genes in RA patients.

Results

The cluster 0 matched OA and cluster 3 matched RA and significantly enriched for neutrophil-mediated immunity and ECM receptor interaction, respectively. We identified 478 DEGs. In the top 20 degrees of connection in the PPI network, the key genes for RA were obtained by comparing with the gene markers of cluster 0 and cluster 3, respectively. ROC curve showed that CCL2 and MMP13 might be diagnostic markers for RA. We found aberrant levels of CD8+T, neutrophil, and B cells in RA fibroblasts, which were validated in clinical samples. Importantly, we also validated the differential expression of key genes between RA and OA.

Conclusion

High expression of CCL2 and MMP13 in RA may be a diagnostic and therapeutic target.

The role of metabolism in chondrocyte dysfunction and the progression of osteoarthritis

Osteoarthritis (OA) is a degenerative joint disease characterized by low-grade inflammation and high levels of clinical heterogeneity. Aberrant chondrocyte metabolism is a response to changes in the inflammatory microenvironment and may play a key role in cartilage degeneration and OA progression. Under conditions of environmental stress, chondrocytes tend to adapt their metabolism to microenvironmental changes by shifting from one metabolic pathway to another, for example from oxidative phosphorylation to glycolysis. Similar changes occur in other joint cells, including synoviocytes. Switching between these pathways is implicated in metabolic alterations that involve mitochondrial dysfunction, enhanced anaerobic glycolysis, and altered lipid and amino acid metabolism. The shift between oxidative phosphorylation and glycolysis is mainly regulated by the AMP-activated protein kinase (AMPK) and mechanistic target of rapamycin (mTOR) pathways. Chondrocyte metabolic changes are likely to be a feature of different OA phenotypes. Determining the role of chondrocyte metabolism in OA has revealed key features of disease pathogenesis. Future research should place greater emphasis on immunometabolism and altered metabolic pathways as a means to understand the pathophysiology of age-related OA. This knowledge will advance the development of new drugs against therapeutic targets of metabolic significance.

CCL22 induces pro-inflammatory changes in fibroblast-like synoviocytes

Synovitis is common in patients with osteoarthritis (OA) and is associated with pain and disease progression. We have previously demonstrated that the chemokine C-C motif chemokine 22 (CCL22) induces chondrocyte apoptosis in vitro; however, the effects of CCL22 on the synovium remain unknown. Therefore, our goal was to investigate the effect of CCL22 on fibroblast-like synoviocytes (FLS). CCL22 treatment suppressed expression of IL-4 and IL-10 and promoted expression of S100A12 in FLS. The response of FLS to CCL22 was not dependent on the disease state of the joint (e.g., normal versus OA), but was instead correlated with the individuals' synovial fluid level of CCL22. CCL22 induction of S100A12 in FLS was attenuated after knockdown of CCR3, yet ligands of CCR3 (CCL7, CCL11) did not induce S100A12 expression. In the presence of CCL22, CCR3-positive FLS upregulate CCL22 and S100A12 driving a potential feedforward pro-inflammatory mechanism distinct from canonical CCL22 and CCR3 pathways.

Hypoxia-inducible factor 2-alpha-dependent induction of IL-6 protects the heart from ischemia/reperfusion injury

Myocardial ischemia-reperfusion injury (MIRI) results in increased myocardial infarct size and leads to poor clinical outcomes. Hypoxia-inducible factor 2-alpha (HIF2α) exerts myocardial protective effects during MIRI through as yet unclear mechanisms. Here, we show that knockdown of HIF2α with cardiotropic recombinant adeno-associated virus serotype 9 (rAAV9) in mouse hearts significantly increased the infarct sizes during myocardial ischemia/reperfusion (MI/R). In addition, HIF2α transcriptionally regulated the expression of interleukin 6 (IL-6) in cardiomyocytes to elicit cardioprotection. Likewise, IL-6 deficiency aggravated MIRI, while treatment with recombinant IL-6 had cardioprotective effects and rescued the mice with HIF2α knockdown. Furthermore, IL-6 treatment significantly activated the PI3K/Akt and STAT3 signaling pathways in the myocardium during MI/R, and the specific inhibitors wortmannin (specific phosphoinositide 3-kinase inhibitor) and Stattic (specific STAT3 inhibitor) substantially abolished HIF2α/IL-6-induced cardioprotection. These studies suggest that HIF2α transcription regulates the expression of IL-6 in cardiomyocytes and plays a protective role during MI/R.

CypB-CD147 Signaling Is Involved in Crosstalk between Cartilage and FLS in Collagen-Induced Arthritis

To investigate the crosstalk between cartilage and fibroblast-like synoviocytes (FLS) in rheumatoid arthritis (RA), we adopted an in vitro coculture system model of collagen-induced arthritis (CIA) cartilage and CIA FLS monolayer. CIA rat samples of the synovium and femur head were collected for isolation of FLS and coculture system. Cartilages were treated with vehicle (Ctrl group), 10 ng/mL interleukin- (IL-) 1α (IL-1α group), and 10 ng/mL IL-1α plus 10 μM dexamethasone (Dex group) for 3 days before coculture with FLS for further 2 days. After the coculture, FLS were collected to determine the influences of articular cartilage on synoviocytes. Whether the CypB-CD147 signaling pathway is involved in the interactions between cartilage and FLS is assayed. Results showed that IL-1α-stimulated CIA cartilage promoted the proliferation and reduced the apoptosis of FLS. Increased inflammatory cytokines and decreased p57 expression were found in cocultured FLS stimulated by IL-1α-challenged CIA cartilage. Upregulation of NF-κB and I-κB kinase β (IKK-β) and downregulation of the inhibitor of NF-κBα (I-κBα) protein were observed in cocultured FLS. After coculture, significant increases in the expression of cyclophilin B (CypB) and CD147 were observed in CIA cartilage and FLS, respectively. Furthermore, results of immunofluorescence staining showed that the anti-CD147 antibody significantly suppressed p65 nuclear translocation in cocultured FLS stimulated by IL-1α-challenged CIA cartilage. In conclusion, inflammatory effects in the cartilage-FLS coculture system are associated with the CypB-CD147 mediating NF-κB pathway which may further enhance the inflammation in RA.

Cross-talk between synovial fibroblasts and chondrocytes in condylar hyperplasia: an in vitro pilot study

OBJECTIVE

Increasing evidence indicates an interaction between the synovium and the cartilage in the temporomandibular joint (TMJ) and other joints. We recently demonstrated that the expression of proangiogenic factors was enhanced and that of factors promoting matrix degradation was decreased in synovial fibroblasts in condylar hyperplasia (CH). The aim of this study was to explore whether CH chondrocytes can affect the expression of these factors of synovial fibroblasts in a co-culture system.

STUDY DESIGN

The expressions of vascular endothelial growth factor (VEGF), cluster of differentiation 34 (CD34), fibroblast growth factor 2 (FGF-2), and tissue inhibitor of metalloproteinase 1 (TIMP1) from CH condylar tissues were observed by using immunohistochemical methods. Synovial fibroblasts of control tissues were co-cultured with the chondrocytes of CH, and protein expressions of VEGF, FGF-2, thrombospondin 1 (TSP1), matrix metalloproteinase 3 (MMP3), and TIMP1 were examined by using Western blotting.

RESULTS

Positive staining for VEGF, CD34, FGF-2, and TIMP1 was found in the hypertrophic cartilage layer of CH condylar tissues. Protein expressions of VEGF, FGF-2, and TIMP1 were significantly increased in co-cultured synovial fibroblasts, but TSP1 and MMP3 expressions were decreased.

CONCLUSIONS

The angiogenic factors and matrix degradation-related factors in synovial fibroblasts co-cultured with CH chondrocytes showed the same trends as those in synovial fibroblasts from CH tissue, suggesting potential cross-talk between synovial fibroblasts and chondrocytes during CH progression.

An Update on the Emerging Role of Visfatin in the Pathogenesis of Osteoarthritis and Pharmacological Intervention

Osteoarthritis (OA) is one of the most common degenerative joint diseases that affects millions of people worldwide, mainly the aging population. Despite numerous published reports, little is known about the pathology of this disease, and no feasible treatment plan exists to stop OA progression. Recently, extensive basic and clinical studies have shown that adipokines play a key role in OA development. Moreover, some drugs associated with adipokines have shown chondroprotective and anti-inflammatory effects on OA. Visfatin has been shown to play a detrimental role in the progression of OA. It increases the production of matrix metalloproteinases and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS), induces the production of interleukin (IL)-1β, IL-6, and tumor necrosis factor-α, affects the differentiation of mesenchymal stem cells to adipocytes, and induces osteophyte formation by inhibiting osteoclastogenesis. Although some side effects of chemical visfatin inhibitors have been reported, they were shown to be successful in the treatment of diabetes, cancer, and other diseases that can utilize Chinese herbs, further suggesting that similar therapeutic strategies could be used in OA prevention and treatment. Here, we describe the pathophysiological mechanism of visfatin in OA and discuss some potential pharmacological interventions using Chinese herbs.

The Fibroblast-Like Synoviocyte Derived Exosomal Long Non-coding RNA H19 Alleviates Osteoarthritis Progression Through the miR-106b-5p/TIMP2 Axis

Osteoarthritis (OA) is a common degenerative joint disease that affects people worldwide. The interaction between fibroblast-like synoviocytes (FLSs) and chondrocytes may play a vital role in OA disease pathology. However, the underlying mechanisms by which FLSs exert regulatory effects on chondrocytes still need to be elucidated. Exosomes, small membrane vesicles secreted from living cells, are known to play a variety of roles in mediating cell-to-cell communication through the transferring of biological components such as non-coding RNAs and proteins. Here, we investigate the cellular processes of chondrocytes regulated by FLS-derived exosomes and the mechanisms of action underlying the functions of exosomes in OA pathogenesis. We observed that exosome-mediated cartilage repair was characterized by increased cell viability and migration as well as alleviated matrix degradation. Using chondrocyte cultures, the enhanced cellular proliferation and migration during exosome-mediated cartilage repair was linked to the exosomal lncRNA H19-mediated regulation of the miR-106b-5p/TIMP2 axis. Transfection of miR-106-5p mimics in chondrocytes significantly decreased cell proliferation and migration, promoted matrix degradation characterized by elevated MMP13 and ADAMTS5 expression, and reduced the expression of COL2A1 and ACAN in chondrocytes. Furthermore, we found that TIMP2 was directly regulated by miR-106-5p. Co-transfections of miR-106-5p mimics and TIMP2 resulted in higher levels of COL2A1 and ACAN, but lower levels of MMP13 and ADAMTS5. Together, these observations demonstrated that the lncRNA H19 may promote chondrocyte proliferation and migration and inhibit matrix degradation in OA possibly by targeting the miR-106b-5p/TIMP2 axis. In the future, H19 may serve as a potential therapeutic target for the treatment of OA.

The role of indoleamine 2,3 dioxygenase 1 in the osteoarthritis

Osteoarthritis (OA) is a chronic degenerative joint disease and a leading cause of disability. It involves articular cartilage destruction and a whole joint inflammation. In spite of OA pathogenesis is still unclear, new studies on the OA pathophysiological aetiology and immunomodulation therapy continuously achieve significant advances with new concepts. Here, we focus on the indoleamine-2,3-dioxygenase1 (IDO1) activity in the osteoarthritis (OA), which is one of the noticeable enzymes in the synovial fluid of arthritis patients. It was recognized as an essential mediator of autoreactive B and T cell responses in rheumatoid arthritis (RA) and an interesting therapeutic target against RA. However, the role IDO1 plays in the OA pathogenesis hasn't been discussed. The new OA experimental analysis evidenced IDO1 overexpression in the synovial fluid of OA patients, and recent studies reported that IDO1 metabolites were found higher in the OA synovial fluid than RA and spondyloarthropathies (SpA) patients. Moreover, the positive relation of IDO1 metabolites with OA pain and joint stiffness has been confirmed. Thus, the IDO1 plays a pivotal role in the pathogenesis of OA. In this review, the role IDO1 plays in the OA pathogenesis has been deeply discussed. It could be a promising target in the immunotherapy of OA disease.

DPSCs Attenuate Experimental Progressive TMJ Arthritis by Inhibiting the STAT1 Pathway

Severe inflammation, progressive cartilage, and bone destruction are typical pathologic changes in temporomandibular joint (TMJ) arthritis and lead to great difficulty for treatment. However, current therapy is inefficient to improve degenerative changes in progressive TMJ arthritis. This study investigated the therapeutic effects of human dental pulp stem cells (DPSCs) on severe inflammatory TMJ diseases. Progressive TMJ arthritis in rats was induced by intra-articular injection of complete Freund's adjuvant and monosodium iodoacetate. DPSCs were injected into the articular cavity to treat rat TMJ arthritis, with normal saline injection as control. Measurement of head withdrawal threshold, micro-computed tomography scanning, and histologic staining were applied to evaluate the severity of TMJ arthritis. Results showed that local injection of DPSCs in rats with TMJ arthritis relieved hyperalgesia and synovial inflammation, attenuated cartilage matrix degradation, and induced bone regeneration. Inflammatory factors TNF-α and IFN-γ were elevated in progressive TMJ arthritis and partially decreased by local injection of DPSCs. MMP3 and MMP13 were elevated in the arthritis + normal saline group and decreased in the arthritis + DPSCs group, which indicated amelioration of matrix degradation. The isolated primary synoviocytes were cocultured with DPSCs after inflammatory factors stimulated to explore the possible biological mechanisms. The expression of MMP3 and MMP13 in synoviocytes was elevated after TNF-α and IFN-γ stimulation and partially reversed by DPSC treatment in the in vitro study. The signal transducer and activator of transcription 1 (STAT1) was activated by inflammatory stimulation and suppressed by DPSC coculture. The upregulation of MMP3 and MMP13 triggered by inflammation was blocked by STAT1-specific inhibitor, suggesting that STAT1 regulated the expression of MMP3 and MMP13. In conclusion, this study demonstrated the possible therapeutic effects of local injection of DPSCs on progressive TMJ arthritis by inhibiting the expression of MMP3 and MMP13 through the STAT1 pathway.

Dual Role of Chondrocytes in Rheumatoid Arthritis: The Chicken and the Egg

Rheumatoid arthritis (RA) is one of the inflammatory joint diseases that display features of articular cartilage destruction. The underlying disturbance results from immune dysregulation that directly and indirectly influence chondrocyte physiology. In the last years, significant evidence inferred from studies in vitro and in the animal model offered a more holistic vision of chondrocytes in RA. Chondrocytes, despite being one of injured cells in RA, also undergo molecular alterations to actively participate in inflammation and matrix destruction in the human rheumatoid joint. This review covers current knowledge about the specific cellular and biochemical mechanisms that account for the chondrocyte signatures of RA and its potential applications for diagnosis and prognosis in RA.

The importance of ultrasound in identifying and differentiating patients with early inflammatory arthritis: a narrative review

Early differentiation between different types of inflammatory arthritis and subsequent initiation of modern treatments can improve patient outcomes by reducing disease activity and preventing joint damage. Routine clinical evaluation, laboratory testing, and radiographs are typically sufficient for differentiating between inflammatory and predominantly degenerative arthritis (e.g., osteoarthritis). However, in some patients with inflammatory arthritis, these techniques fail to accurately identify the type of early-stage disease. Further evaluation by ultrasound imaging can delineate the inflammatory arthritis phenotype present. Ultrasound is a noninvasive, cost-effective method that enables the evaluation of several joints at the same time, including functional assessments. Further, ultrasound can visualize pathophysiological changes such as synovitis, tenosynovitis, enthesitis, bone erosions, and crystal deposits at a subclinical level, which makes it an effective technique to identify and differentiate most common types of inflammatory arthritis. Limitations associated with ultrasound imaging should be considered for its use in the differentiation and diagnosis of inflammatory arthritides.

Systematic Analysis of Differential Expression Profile in Rheumatoid Arthritis Chondrocytes Using Next-Generation Sequencing and Bioinformatics Approaches

Cartilage destruction in rheumatoid arthritis (RA) occurs primarily in the pannus-cartilage interface. The close contact of the synovium-cartilage interface implicates crosstalk between synovial fibroblasts and chondrocytes. The aim of this study is to explore the differentially expressed genes and novel microRNA regulations potentially implicated in the dysregulated cartilage homeostasis in joint destruction of RA. Total RNAs were extracted from human primary cultured normal and RA chondrocytes for RNA and small RNA expression profiling using next-generation sequencing. Using systematic bioinformatics analyses, we identified 463 differentially expressed genes in RA chondrocytes were enriched in biological functions related to altered cell cycle process, inflammatory response and hypoxic stimulation. Moreover, fibroblast growth factor 9 (FGF9), kynureninase (KYNU), and regulator of cell cycle (RGCC) were among the top dysregulated genes identified to be potentially affected in the RA joint microenvironment, having similar expression patterns observed in arrays of clinical RA synovial tissues from the Gene Expression Omnibus database. Additionally, among the 31 differentially expressed microRNAs and 10 candidate genes with potential microRNA-mRNA interactions in RA chondrocytes, the novel miR-140-3p-FGF9 interaction was validated in different microRNA prediction databases, and proposed to participate in the pathogenesis of joint destruction through dysregulated cell growth in RA. The findings provide new perspectives for target genes in the management of cartilage destruction in RA.

uPA/uPAR signaling in rheumatoid arthritis: Shedding light on its mechanism of action

Rheumatoid arthritis (RA) is a systemic and chronic autoimmune inflammatory disorder affecting multiple joints. Various cytokines, chemokines and growth factors synergistically modulate the joint physiology leading to bone erosion and cartilage degradation. Other than these conventional mediators that are well established in the past, the newly identified plasminogen activator (PA) family of proteins have been witnessed to possess a multifactorial approach in mediating RA pathogenesis. One such family of proteins comprises of the urokinase-type plasminogen activator (uPA) and its receptor (uPAR)/soluble-type plasminogen activator receptor (suPAR). PA family of proteins are classified into two types namely: uPA and tissue type plasminogen activator (tPA). Both these subtypes have been implicated to play a key role in RA disease progression. However during RA pathogenesis, uPA secreted by neutrophils, chondrocytes, and monocytes are designated to interact with uPAR expressed on macrophages, fibroblast-like synoviocytes (FLS), chondrocytes and endothelial cells. Interaction of uPA/uPAR promotes the disease progression of RA through secretion of several cytokines, chemokines, growth factors and matrix metalloproteinases (MMPs). Moreover, uPA/uPAR initiates inflammatory responses in macrophages and FLS through activation of PI3K/Akt signaling pathways. Furthermore, uPAR plays a dual role in osteoclastogenesis under the presence/absence of growth factors like monocyte-colony stimulating factor (M-CSF). Overall, this review emphasizes the role of uPA/uPAR on various immune cells, signaling pathways and osteoclastogenesis involved in RA pathogenesis.

The Tumor-Like Phenotype of Rheumatoid Synovium: Molecular Profiling and Prospects for Precision Medicine

Rheumatoid arthritis (RA) is a systemic autoimmune disease characterized by destructive hyperplasia of the synovium. Fibroblast-like synoviocytes (FLS) are a major component of synovial pannus and actively participate in the pathologic progression of RA. How rheumatoid FLS acquire and sustain such a uniquely aggressive phenotype remains poorly understood. We describe the current state of knowledge of the molecular alterations in rheumatoid FLS at the genomic, epigenomic, transcriptomic, proteomic, and metabolomic levels, which offers a means to reconstruct the pathways leading to rheumatoid pannus. Such data provide new pathologic insight and suggest means to more sensitively assess disease activity and response to therapy, as well as support new avenues for therapeutic development.

Anti-Inflammatory Effects of p-Coumaric Acid, a Natural Compound of Oldenlandia diffusa, on Arthritis Model Rats

Objectives

In China, Oldenlandia diffusa (OD) is a natural herb that is widely used and has been proven to be effective in the treatment of rheumatoid arthritis (RA). This study aimed to preliminarily reveal the mechanism by which OD exerts its beneficial effect.

Methods

Ultra-performance liquid chromatography photodiode array was applied to identify the absorbable compounds in the plasma of collagen-induced arthritis (CIA) model rats. After 2 weeks, an OD decoction or the identified absorbable compound was administered to CIA rats. Morphology, X-ray images of the joints, pathological images, arthritis index, and cytokine (TNF-α and IL-6) levels were evaluated.

Results

p-Coumaric acid (p-CA) was identified as the absorbed compound in plasma. After administration of p-CA solution or the OD decoction, symptoms in the treated rats were alleviated as compared to the untreated model rats, and inflammatory cell infiltration was suppressed. The arthritis index and serum levels of TNF-α and IL-6 were decreased as compared to the control group.

Conclusions

OD may exert its anti-inflammatory effect on RA via its active ingredient, p-CA. This information sheds light on the mechanism by which OD exerts its anti-inflammatory effort in RA and forms the basis for further development of therapeutic agents for RA.

Hypothermia Promotes Cell-Protective and Chondroprotective Effects After Blunt Cartilage Trauma

BACKGROUND

Cryotherapy is routinely administered after sports injuries of synovial joints. Although positive clinical effects on periarticular swelling and pain have been described, the effects on the cell biological activities of cartilage and synovial cells remain largely unknown so far.

HYPOTHESIS

Local hypothermia alleviates synovial reactions and prevents chondrocyte death as well as cartilage destructive processes after blunt cartilage trauma.

STUDY DESIGN

Controlled laboratory study.

METHODS

Human cartilage explants were impacted by a drop-tower apparatus (0.59 J) and cultured at 24 hours or 7 days in different temperature conditions (2 hours [short term], 16 hours [medium term], or throughout [long term] at 27°C; afterwards or throughout at 37°C). Besides, isolated human fibroblast-like synoviocytes (FLS) were stimulated with traumatized cartilage conditioned medium and cultured as mentioned above up to 4 days. The effects of hypothermia were evaluated by cell viability, gene expression, type II collagen synthesis and cleavage, as well as the release of matrix metalloproteinase (MMP)-2, MMP-13, and interleukin 6 (IL-6).

RESULTS

Seven days after trauma, hypothermic treatment throughout improved cell viability (short term: 10.1% [ P = .016]; medium term: 6% [ P = .0362]; long term: 12.5% [ P = .0039]). Short-term hypothermia attenuated the expression of catabolic MMP-13 (mRNA: -2.2-fold [ P = .0119]; protein: -2-fold [ P = .0238]). Whereas type II collagen synthesis (1.7-fold [ P = .0227]) was increased after medium-term hypothermia, MMP-13 expression (mRNA: -30.8-fold [ P = .0025]; protein: -10.3-fold [ P < .0001]) and subsequent cleavage of type II collagen (-1.1-fold [ P = .0489]) were inhibited. Long-term hypothermia further suppressed MMP release (pro-MMP-2: -3-fold [ P = .0222]; active MMP-2: -5.2-fold [ P = .0183]; MMP-13: -56-fold [ P < .0001]) and type II collagen breakdown (-1.6-fold [ P = .0036]). Four days after FLS stimulation, hypothermia significantly suppressed the gene expression of matrix-destructive enzymes after medium-term (MMP-3: -4.1-fold [ P = .0211]) and long-term exposure (a disintegrin and metalloproteinase with thrombospondin motifs 4 [ADAMTS4]: -4.3-fold [ P = .0045]; MMP-3: -25.8-fold [ P = .014]; MMP-13: -122-fold [ P = .0444]) and attenuated IL-6 expression by trend.

CONCLUSION

After blunt cartilage trauma, initial hypothermia for only 2 hours and/or 16 hours induced significant cell-protective and chondroprotective effects and promoted the anabolic activity of chondrocytes, while the expression of matrix-destructive enzymes by stimulated FLS was attenuated by prolonged hypothermia.

CLINICAL RELEVANCE

The findings of this preliminary ex vivo investigation indicate that optimized cryotherapy management after cartilage trauma might prevent matrix-degenerative processes associated with the pathogenesis of posttraumatic osteoarthritis.

Regenerative approaches for cartilage repair in the treatment of osteoarthritis

Osteoarthritis (OA) as a debilitating affliction of joints currently affects millions of people and remains an unsolved problem. The disease involves multiple cellular and molecular pathways that converge on the progressive destruction of cartilage. Activation of cartilage regenerative potential and specific targeting pathogenic mediators have been the major focus of research efforts aimed at slowing the progression of cartilage degeneration and preserve joint function. This review will summarize recent key discoveries toward better understanding of the complex mechanisms behind OA development and highlight the latest advances in basic and clinical research in the approach for cartilage regeneration. Prospectively, more potent therapeutic strategies against progressive cartilage deterioration may use a combination of cytotherapy, pharmacotherapy, and bioscaffoldings for improved chondrogenic differentiation and stem/progenitor cell homing as well as the concomitant reduced enzymatic matrix degradation and inflammation. Further, treatments need to be provided with increased preciseness of targeted therapy. One might expect that the regenerative therapies could potentially control or even possibly cure OA if performed at early stages of the disease.

Endogenous glucocorticoid signaling in chondrocytes attenuates joint inflammation and damage

Previous studies demonstrated that endogenous glucocorticoid signaling in osteoblasts promotes inflammation in murine immune arthritis. The current study determined whether disruption of endogenous glucocorticoid signaling in chondrocytes also modulates the course and severity of arthritis. Tamoxifen-inducible chondrocyte-targeted glucocorticoid receptor-knockout (chGRKO) mice were generated by breeding GR^flox/flox mice with tamoxifen-inducible collagen 2a1 Cre (Col2a1-CreER^T2) mice. Antigen-induced arthritis (AIA) and K/BxN serum transfer-induced arthritis (STIA) were induced in both chGRKO mice and their Cre-negative GR^flox/flox littermates [wild type (WT)]. Arthritis was assessed by measurement of joint swelling and histology of joints collected at d 14. Neutrophil activity and gene expression patterns associated with cartilage damage were also evaluated. In both arthritis models clinical (joint swelling) and histologic indices of inflammatory activity were significantly greater in chGRKO than in WT mice. The STIA model was characterized by early up-regulation of CXCR2/CXCR2 ligand gene expression in ankle tissues, and significant and selective expansion of splenic CXCR2⁺ neutrophils in chGRKO arthritic compared to WT arthritic mice. At later stages, gene expression of enzymes involved in cartilage degradation was up-regulated in chGRKO but not WT arthritic mice. Therefore, we summarize that chondrocytes actively mitigate local joint inflammation, cartilage degradation and systemic neutrophil activity via a glucocorticoid-dependent pathway.-Tu, J., Stoner, S., Fromm, P. D., Wang, T., Chen, D., Tuckermann, J., Cooper, M. S., Seibel, M. J., Zhou, H. Endogenous glucocorticoid signaling in chondrocytes attenuates joint inflammation and damage.

Time-dependent proteomic and genomic alterations in Toll-like receptor-4-activated human chondrocytes: increased expression of lamin A/C and annexins

Activation of Toll-like receptor-4 (TLR-4) in articular chondrocytes increases the catabolic compartment and leads to matrix degradation during the development of osteoarthritis. In this study, we determined the proteomic and genomic alterations in human chondrocytes during lipopolysaccharide (LPS)-induced inflammation to elucidate the underlying mechanisms and consequences of TLR-4 activation. Human chondrocytes were cultured with LPS for 12, 24, and 36 h to induce TLR-4 activation. The TLR-4-induced inflammatory response was confirmed by real-time PCR analysis of increased interleukin-1 beta (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor alpha (TNF-α) expression levels. In TLR-4-activated chondrocytes, proteomic changes were determined by two-dimensional electrophoresis and matrix-assisted laser desorption/ionization-mass spectroscopy analysis, and genomic changes were determined by microarray and gene ontology analyses. Proteomics analysis identified 26 proteins with significantly altered expression levels; these proteins were related to the cytoskeleton and oxidative stress responses. Gene ontology analysis indicated that LPS treatment altered specific functional pathways including ‘chemotaxis’, ‘hematopoietic organ development’, ‘positive regulation of cell proliferation’, and ‘regulation of cytokine biosynthetic process’. Nine of the 26 identified proteins displayed the same increased expression patterns in both proteomics and genomics analyses. Western blot analysis confirmed the LPS-induced increases in expression levels of lamin A/C and annexins 4/5/6. In conclusion, this study identified the time-dependent genomic, proteomic, and functional pathway alterations that occur in chondrocytes during LPS-induced TLR-4 activation. These results provide valuable new insights into the underlying mechanisms that control the development and progression of osteoarthritis.

IL-6 secretion in osteoarthritis patients is mediated by chondrocyte-synovial fibroblast cross-talk and is enhanced by obesity

Increasing evidence suggests that inflammation plays a central role in driving joint pathology in certain patients with osteoarthritis (OA). Since many patients with OA are obese and increased adiposity is associated with chronic inflammation, we investigated whether obese patients with hip OA exhibited differential pro-inflammatory cytokine signalling and peripheral and local lymphocyte populations, compared to normal weight hip OA patients. No differences in either peripheral blood or local lymphocyte populations were found between obese and normal-weight hip OA patients. However, synovial fibroblasts from obese OA patients were found to secrete greater amounts of the pro-inflammatory cytokine IL-6, compared to those from normal-weight patients (p < 0.05), which reflected the greater levels of IL-6 detected in the synovial fluid of the obese OA patients. Investigation into the inflammatory mechanism demonstrated that IL-6 secretion from synovial fibroblasts was induced by chondrocyte-derived IL-6. Furthermore, this IL-6 inflammatory response, mediated by chondrocyte-synovial fibroblast cross-talk, was enhanced by the obesity-related adipokine leptin. This study suggests that obesity enhances the cross-talk between chondrocytes and synovial fibroblasts via raised levels of the pro-inflammatory adipokine leptin, leading to greater production of IL-6 in OA patients.