Synovial fluid from patients with early osteoarthritis modulates fibroblast-like synoviocyte responses to toll-like receptor 4 and toll-like receptor 2 ligands via soluble CD14

Senile Osteoarthritis Regulated by the Gut Microbiota: From Mechanisms to Treatments

Osteoarthritis (OA) is a chronic, progressive degenerative joint disease that affects the entire synovial joint, leading to the progressive degeneration of articular cartilage. It seriously affects the quality of life and global disability of patients. OA is affected by a variety of factors; the most significant risk factor for OA is age. As individuals age, the risk and severity of OA increase due to the exacerbation of cartilage degeneration and wear and tear. In recent years, research has indicated that the gut microbiota may play a significant role in the aging and OA processes. It is anticipated that regulating the gut microbiota may offer novel approaches to the treatment of OA. The objective of this paper is to examine the relationship between the gut microbiota and senile OA, to investigate the potential mechanisms involved. This review also summarizes the therapeutic strategies related to gut flora in OA management, such as prebiotics and probiotics, diet, exercise, traditional Chinese medicine (TCM) modification, and fecal microbiota transplantation (FMT), highlighting the potential clinical value of gut flora and elucidating the current challenges. The foundation for future research directions is established through the summarization of current research progress.

Exploring the Link Between Infections and Primary Osteoarthritis: A Next-Generation Metagenomic Sequencing Approach

This prospective pilot study examined the association between microorganisms and knee osteoarthritis by identifying pathogens in the synovial membrane, synovial fluid, and blood samples from two patients with primary bilateral knee osteoarthritis, using metagenomic next-generation sequencing (mNGS). Intraoperatively, during routine knee arthroplasty procedures, we collected the following 12 samples from each patient: two synovial membrane samples, two synovial fluid samples, and two venous blood samples. After DNA isolation and library construction, each sample was subjected to deep whole-genome sequencing using the DNBSEQT17 platform with the read length PE150 as the default. Metagenomic sequencing data were mapped to the NCBI NT database to determine species abundance. The predominant species in all samples tested were classified under the Enterobacterales order, the most abundant being Yersinia enterocolitica. The second and third most common microorganisms detected were Escherichia coli and autotrophic, Gram-negative bacteria Synechococcus sp., which is a bioaerosol component, indicating a risk of inhalation of the toxic metabolites of this latter microorganism. This article provides an initial exploration of mNGS use to study the etiopathogenetic mechanisms of knee osteoarthritis (OA). While our analysis identified bacterial DNA, particularly from Yersinia, further cross-sectional studies in larger populations with and without OA are needed to determine the role of these agents in OA pathogenesis.

TAK-242 (Resatorvid) inhibits proinflammatory cytokine production through the inhibition of NF-κB signaling pathway in fibroblast-like synoviocytes in osteoarthritis patients

BACKGROUND

Fibroblast-like synoviocytes (FLSs) are involved in osteoarthritis (OA) pathogenesis through pro-inflammatory cytokine production. TAK-242, a TLR4 blocker, has been found to have a significant impact on the gene expression profile of pro-inflammatory cytokines such as IL1-β, IL-6, TNF-α, and TLR4, as well as the phosphorylation of Ikβα, a regulator of the NF-κB signaling pathway, in OA-FLSs. This study aims to investigate this effect because TLR4 plays a crucial role in inflammatory responses.

MATERIALS AND METHODS

Ten OA patients' synovial tissues were acquired, and isolated FLSs were cultured in DMEM in order to assess the effectiveness of TAK-242. The treated FLSs with TAK-242 and Lipopolysaccharides (LPS) were analyzed for the mRNA expression level of IL1-β, IL-6, TNF-α, and TLR4 levels by Real-Time PCR. Besides, we used western blot to assess the protein levels of Ikβα and pIkβα.

RESULTS

The results represented that TAK-242 effectively suppressed the gene expression of inflammatory cytokines IL1-β, IL-6, TNF-α, and TLR4 which were overexpressed upon LPS treatment. Additionally, TAK-242 inhibited the phosphorylation of Ikβα which was increased by LPS treatment.

CONCLUSION

According to our results, TAK-242 shows promising inhibitory effects on TLR4-mediated inflammatory responses in OA-FLSs by targeting the NF-κB pathway. TLR4 inhibitors, such as TAK-242, may be useful therapeutic agents to reduce inflammation and its associated complications in OA patients, since traditional and biological treatments may not be adequate for all of them.

Therapeutic mechanisms of modified Jiawei Juanbi decoction in early knee osteoarthritis: A multimodal analysis

Modified Jiawei Juanbi decoction (MJD) is used for the treatment of early-stage knee osteoarthritis (KOA). Here, modified Jiawei Juanbi decoction (MJD) was employed for the treatment of early-stage knee osteoarthritis (KOA) and its mechanisms were assessed via metabonomics and network pharmacology. A total of 24 male Sprague-Dawley rats were randomly allocated into a normal control group, a model group, and an MJD group (n = 8 rats per group). Each rat group was further equally divided into two subgroups for investigation for either 14 or 28 days. A rat model of early-stage KOA was constructed and rats were treated with MJD. Effects were evaluated based on changes in knee circumference, mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL). We also analyzed histopathological changes in articular cartilage. High-resolution mass spectrometry was used to analyze the chemical profile of MJD, identifying 228 components. Using an LC-Q-TOF-MS metabonomics approach, 33 differential metabolites were identified. The relevant pathways significantly associated with MJD include arginine and proline metabolism, vitamin B6 metabolism, as well as the biosynthesis of phenylalanine, tyrosine and tryptophan. The system pharmacology paradigm revealed that MJD contains 1027 components and associates with 1637 genes, of which 862 disease genes are related to osteoarthritis. The construction of the MJD composition-target-KOA network revealed a total of 140 intersection genes. A total of 39 hub genes were identified via integration of betweenness centrality values greater than 100 using CytoHubba. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed several significantly affected signaling pathways including the HIF-1, AGE-RAGE (in diabetic complications), IL-17, rheumatoid arthritis and TNF pathways. Integrated-omics and network pharmacology approaches revealed a necessity for further detailed investigation focusing on two major targets, namely NOS2 and NOS3, along with their essential metabolite (arginine) and associated pathways (HIF-1 signaling and arginine and proline metabolism). Real-time PCR validated significantly greater downregulation of NOS2 and HIF-1ɑ in the MJD as compared to the model group. Molecular docking analysis further confirmed the binding of active MJD with key active components. Our findings elucidate the impact of MJD on relevant pathophysiological and metabolic networks relevant to KOA and assess the drug efficacy of MJD and its underlying mechanisms of action.

Inhibition of TLR4 signalling to dampen joint inflammation in osteoarthritis

Local and systemic low-grade inflammation, mainly involving the innate immune system, plays an important role in the development of OA. A receptor playing a key role in initiation of this inflammation is the pattern-recognition receptor Toll-like receptor 4 (TLR4). In the joint, various ligands for TLR4, many of which are damage-associated molecular patterns (DAMPs), are present that can activate TLR4 signalling. This leads to the production of pro-inflammatory and catabolic mediators that cause joint damage. In this narrative review, we will first discuss the involvement of TLR4 ligands and signalling in OA. Furthermore, we will provide an overview of methods for inhibit, TLR4 signalling by RNA interference, neutralizing anti-TLR4 antibodies, small molecules and inhibitors targeting the TLR4 co-receptor MD2. Finally, we will focus on possible applications and challenges of these strategies in the dampening of inflammation in OA.

TLR4 antagonism provides short-term but not long-term clinical benefit in a full-depth cartilage defect mouse model

PURPOSE/AIM

Cartilage injury and subsequent osteoarthritis (OA) are debilitating conditions affecting millions worldwide. As there are no cures for these ailments, novel therapies are needed to suppress disease pathogenesis. Given that joint injuries are known to produce damage-associated molecular patterns (DAMPs), our central premise is that the Toll-like receptor 4 (TLR4) pathway is a principal driver in the early response to cartilage damage and subsequent pathology. We postulate that TLR4 activation is initiated/perpetuated by DAMPs released following joint damage. Thus, antagonism of the TLR4 pathway immediately after injury may suppress the development of joint surface defects.

MATERIALS AND METHODS

Two groups were utilized: (1) 8-week-old, male C57BL6 mice treated systemically with a known TLR4 antagonist and (2) mice injected with vehicle control. A full-depth cartilage lesion on the midline of the patellofemoral groove was created in the right knee of each mouse. The left knee was used as a sham surgery control. Gait changes were evaluated over 4 weeks using a quantitative gait analysis system. At harvest, knee joints were processed for pathologic assessment, Nanostring® transcript expression, and immunohistochemistry (IHC).

RESULTS

Short-term treatment with a TLR4 antagonist at 14-days significantly improved relevant gait parameters; improved cartilage metrics and modified Mankin scores were also seen. Additionally, mRNA expression and IHC showed reduced expression of inflammatory mediators in animals treated with the TLR4 antagonist.

CONCLUSIONS

Collectively, this work demonstrates that systemic treatment with a TLR4 antagonist is protective to further cartilage damage 14-days post-injury in a murine model of induced disease.

Imaging mass cytometry reveals tissue-specific cellular immune phenotypes in the mouse knee following ACL injury

Objective

To develop an imaging mass cytometry method for identifying complex cell phenotypes, inter-cellular interactions, and population changes in the synovium and infrapatellar fat pad (IFP) of the mouse knee following a non-invasive compression injury.

Design

Fifteen male C57BL/6 mice were fed a high-fat diet for 8 weeks prior to random assignment to sham, 0.88 ​mm, or 1.7 ​mm knee compression displacement at 24 weeks of age. 2-weeks after loading, limbs were prepared for histologic and imaging mass cytometry analysis, focusing on myeloid immune cell populations in the synovium and IFP.

Results

1.7 ​mm compression caused anterior cruciate ligament (ACL) rupture, development of post-traumatic osteoarthritis, and a 2- to 3-fold increase in cellularity of synovium and IFP tissues compared to sham or 0.88 ​mm compression. Imaging mass cytometry identified 11 myeloid cell subpopulations in synovium and 7 in IFP, of which approximately half were elevated 2 weeks after ACL injury in association with the vasculature. Notably, two monocyte/macrophage subpopulations and an MHC IIhi population were elevated 2-weeks post-injury in the synovium but not IFP. Vascular and immune cell interactions were particularly diverse in the synovium, incorporating 8 unique combinations of 5 myeloid cell populations, including a monocyte/macrophage population, an MHC IIhi population, and 3 different undefined F4/80+ myeloid populations.

Conclusions

Developing an imaging mass cytometry method for the mouse enabled us to identify a diverse array of synovial and IFP vascular-associated myeloid cell subpopulations. These subpopulations were differentially elevated in synovial and IFP tissues 2-weeks post injury, providing new details on tissue-specific immune regulation.

The novel hyaluronic acid granular hydrogel attenuates osteoarthritis progression by inhibiting the TLR-2/NF-κB signaling pathway through suppressing cellular senescence

In patients with mild osteoarthritis (OA), two to four monthly injections are required for 6 months due to the degradation of hyaluronic acid (HA) by peroxidative cleavage and hyaluronidase. However, frequent injections may lead to local infection and also cause inconvenience to patients during the COVID-19 pandemic. Herein, we developed a novel HA granular hydrogel (n-HA) with improved degradation resistance. The chemical structure, injectable capability, morphology, rheological properties, biodegradability, and cytocompatibility of the n-HA were investigated. In addition, the effects of the n-HA on the senescence-associated inflammatory responses were studied via flow cytometry, cytochemical staining, Real time quantitative polymerase chain reaction (RT-qPCR), and western blot analysis. Importantly, the treatment outcome of the n-HA with one single injection relative to the commercial HA product with four consecutive injections within one treatment course in an OA mouse model underwent anterior cruciate ligament transection (ACLT) was systematically evaluated. Our developed n-HA exhibited a perfect unification of high crosslink density, good injectability, excellent resistance to enzymatic hydrolysis, satisfactory biocompatibility, and anti-inflammatory responses through a series of in vitro studies. Compared to the commercial HA product with four consecutive injections, a single injection of n-HA contributed to equivalent treatment outcomes in an OA mouse model in terms of histological analysis, radiographic, immunohistological, and molecular analysis results. Furthermore, the amelioration effect of the n-HA on OA development was partially ascribed to the attenuation of chondrocyte senescence, thereby leading to inhibition of TLR-2 expression and then blockade of NF-κB activation. Collectively, the n-HA may be a promising therapeutic alternative to current commercial HA products for OA treatment.

"Cross-talk" between gut microbiome dysbiosis and osteoarthritis progression: a systematic review

Objectives

The aim of this systematic review was to summarize the available literature on gut microbiome (GMB) and osteoarthritis (OA), analyze the correlation between GMB and OA, and explore potential underlying mechanisms.

Methods

A systematic search of the PubMed, Embase, Cochrane, and Web of Science with the keywords "Gut Microbiome" and "Osteoarthritis" was conducted to identify the human and animal studies exploring the association between GMB and OA. The retrieval time range was from the database inception to July 31, 2022. Studies reported the other arthritic diseases without OA, reviews, and studies focused on the microbiome in other parts of the body with OA, such as oral or skin, were excluded. The included studies were mainly reviewed for GMB composition, OA severity, inflammatory factors, and intestinal permeability.

Results

There were 31 studies published met the inclusion criteria and were analyzed, including 10 human studies and 21 animal studies. Human and animal studies have reached a consistent conclusion that GMB dysbiosis could aggravate OA. In addition, several studies have found that alterations of GMB composition can increase intestinal permeability and serum levels of inflammatory factors, while regulating GMB can alleviate the changes. Owing to the susceptibility of GMB to internal and external environments, genetics, and geography, the included studies were not consistent in GMB composition analysis.

Conclusion

There is a lack of high-quality studies evaluating the effects of GMB on OA. Available evidence indicated that GMB dysbiosis aggravated OA through activating the immune response and subsequent induction of inflammation. Future studies should focus on more prospective, cohort studies combined with multi-omics to further clarify the correlation.

S100A8 alarmin supports IL-6 and metalloproteinase-9 production by fibroblasts in the synovial microenvironment of peripheral spondyloarthritis

Introduction

Spondyloarthritis (SpA) is a common autoinflammatory disease. S100A8/ S100A9 alarmin is strongly expressed in the synovial sublining layers of psoriatic arthritis. S100A8/ S100A9 is the most abundant protein in rheumatoid arthritis synovial fluid (SF) and has a key role in promoting IL-6 expression in fibroblast-like synoviocytes (FLS). The molecular mechanisms and the role of S100-alarmins in the synovial microenvironment of SpA have never been demonstrated.

Methods and Results

Here, we confirm the effect of the synovial microenvironment of peripheral SpA on interleukin-6 (IL-6) and metalloproteinase (MMP)-9 production by FLS. MMP-9 expression and activity were detected, which were reduced in the presence of anti-IL-6R. Analyzing cell signaling mechanisms, we found that stimulation with IL-6 co-triggered MMP-9 and IL-10 secretion. MMP-9 secretion depended on JNK and p38 MAPKs, whereas IL-10 secretion was dependent on the JAK pathway as a potential feedback mechanism controlling IL-6-induced MMP-9 expression. Using a proteomic approach, we identified S100A8 in the peripheral SpA SF. This presence was confirmed by immunoblotting. S100A8 increased the IL-6 secretion via ERK and p38 MAPK pathways. Furthermore, anti-S100A8/A9 reduced both IL-6 and MMP-9 production induced by SpA SF in FLS.

Discussion

Our data reveal a marked relationship between S100A8 alarmin with IL-6 and MMP-9 secretion by FLS in the real synovial microenvironment of peripheral SpA. These results identify a mechanism linking S100A8 to the pathogenesis of peripheral SpA.

Breakthrough of extracellular vesicles in pathogenesis, diagnosis and treatment of osteoarthritis

Osteoarthritis (OA) is a highly prevalent whole-joint disease that causes disability and pain and affects a patient's quality of life. However, currently, there is a lack of effective early diagnosis and treatment. Although stem cells can promote cartilage repair and treat OA, problems such as immune rejection and tumorigenicity persist. Extracellular vesicles (EVs) can transmit genetic information from donor cells and mediate intercellular communication, which is considered a functional paracrine factor of stem cells. Increasing evidences suggest that EVs may play an essential and complex role in the pathogenesis, diagnosis, and treatment of OA. Here, we introduced the role of EVs in OA progression by influencing inflammation, metabolism, and aging. Next, we discussed EVs from the blood, synovial fluid, and joint-related cells for diagnosis. Moreover, we outlined the potential of modified and unmodified EVs and their combination with biomaterials for OA therapy. Finally, we discuss the deficiencies and put forward the prospects and challenges related to the application of EVs in the field of OA.

Assessment of disease activity in patients with rheumatoid arthritis using plasma tumour M2-pyruvate kinase test

Background

Pyruvate kinase M2 (PKM2) is an enzyme that regulates the final process of glycolysis and exists in tetrameric and dimeric forms. The dimeric form of PKM2, also known as tumour M2-PK, increases when aerobic glycolysis is augmented, a feature observed in rheumatoid arthritis (RA). We investigated whether plasma tumour M2-PK is elevated in patients with RA and whether its levels correlate with disease activity.

Methods

Plasma levels of tumour M2-PK were measured for patients with RA (n=151), those with osteoarthritis (OA) (n=37), and controls (n=37). We evaluated the association between plasma tumour M2-PK and continuous variables using Pearson’s correlation analysis, and multivariate logistic regression analysis to determine the association between plasma tumour M2-PK and disease activity status. Knee synovial tissue blocks from patients with RA and OA were subjected to real-time quantitative PCR (qPCR) using two different primers for PKM2 and tumour M2-PK immunohistochemical (IHC) staining.

Results

The tumour M2-PK level significantly correlated with the disease activity score in 28 joints (DAS28)-erythrocyte sedimentation rate (ESR) (r=0.546, p<0.001) and DAS28-C-reactive protein (CRP) (r=0.589, p<0.001). Moreover, repeat testing of tumour M2-PK levels in 20 patients revealed a significant decline in tumour M2-PK levels after reduction in inflammation (p<0.001). Area under the receiver operating characteristic curve (AUROC) analysis demonstrated that upon incorporation of tumour M2-PK, ESR, and CRP, the area under the curve was 0.962 for distinguishing moderate/high from remission/low disease activity. Adjusted logistic regression also revealed that a tumour M2-PK >43.9 U/mL (OR 3.672, p=0.042) independently predicted moderate/high disease activity status. Furthermore, tumour M2-PK levels in patients with RA were significantly higher than in those with OA and controls (all p<0.001). However, no differences were found in PKM2 expression in RA and OA synovial tissues as assessed by qPCR, and IHC analysis revealed negligible tumour M2-PK expression in the synovial tissues.

Conclusion

Circulating plasma tumour M2-PK levels may be a clinically useful indicator for evaluating disease activity and RA diagnosis.

Celastrol ameliorates osteoarthritis via regulating TLR2/NF-κB signaling pathway

Objectives: Osteoarthritis (OA) is a joint disease characterized by degeneration of joint cartilage and is a significant cause of severe joint pain, physical disability, and impaired quality of life in the aging population. Celastrol, a Chinese herbal medicine, has attracted wide interests because of its anti-inflammatory effects on a variety of diseases. This study aimed to investigate the effect of celastrol on OA as well as the mechanisms in vivo and in vitro.

Methods: A rat knee OA model was established using “medial collateral ligament transection (MCLT) + partial meniscectomy (pMMT)”. Eight weeks after surgery, the OA rats started to receive intra-articular injection of celastrol (1 mg/kg) once a week. Safranin O-fast green (S&F) and hematoxylin and eosin (H&E) staining were used to estimate histopathological changes. Micro-CT was used to evaluate bone volume of the subchondral bone of the knee joint. Chondrocytes were isolated from the knee cartilage of rats and OA patients. Enzyme linked immunosorbent assay (ELISA), Western Blot (WB), Polymerase Chain Reaction (PCR), and Immunohistochemistry (IHC) were used to detect the expression of inflammatory factors and stromal proteins, respectively.

Results: We found that celastrol treatment significantly delayed the progression of cartilage damage with a significant reduction in osteophyte formation and bone resorption in OA rat model. In IL-1β-stimulated rat chondrocytes, celastrol significantly suppressed the production of inflammatory factors such as cyclooxygenase-2 (COX2), interleukin-6 (IL-6), and prostaglandin E2 (PEG2), and reduced IL-1β-induced matrix degradation by down-regulating the expression of matrix metalloproteinase 13 (MMP13). In addition, we found that toll-like receptor 2 (TLR2) was up-regulated in OA patients and rat knee OA models, while celastrol inhibited TLR2 signal and its downstream nuclear factor-kappa B (NF-κB) phosphorylation.

Conclusion: In summary, celastrol may improve OA by inhibiting the TLR2/NF-κB signaling pathway, which provides innovative strategies for the treatment of OA.

Association Between Gut Microbiota and Osteoarthritis: A Review of Evidence for Potential Mechanisms and Therapeutics

Osteoarthritis (OA) is a multifactorial joint disease characterized by degeneration of articular cartilage, which leads to joints pain, disability and reduced quality of life in patients with OA. Interpreting the potential mechanisms underlying OA pathogenesis is crucial to the development of new disease modifying treatments. Although multiple factors contribute to the initiation and progression of OA, gut microbiota has gradually been regarded as an important pathogenic factor in the development of OA. Gut microbiota can be regarded as a multifunctional “organ”, closely related to a series of immune, metabolic and neurological functions. This review summarized research evidences supporting the correlation between gut microbiota and OA, and interpreted the potential mechanisms underlying the correlation from four aspects: immune system, metabolism, gut-brain axis and gut microbiota modulation. Future research should focus on whether there are specific gut microbiota composition or even specific pathogens and the corresponding signaling pathways that contribute to the initiation and progression of OA, and validate the potential of targeting gut microbiota for the treatment of patients with OA.

CD14+ monocytes and soluble CD14 of synovial fluid are associated with osteoarthritis progression

Objectives

This study aims to investigate the role of cluster of differentiation 14 (CD14) expressed monocytes and soluble CD14-mediated pathway in the synovial inflammation of knee osteoarthritis (OA).

Patients and methods

Between May 2012 and July 2013, a total of 35 patients with knee OA (9 males, 26 females; mean age: 66.3±8.8 years; range, 52 to 79 years) were included in this cross-sectional study. Synovial fluid was obtained from knee joints of 35 OA patients. The CD14⁺ monocytes from synovial fluid mononuclear cells (SFMCs) were isolated using the MACS. The fibroblast-like synoviocytes (FLSs) isolated from knee joint tissue were incubated with recombinant CD14 and lipopolysaccharide (LPS) for 24 h. Cytokine profiling was performed with the Luminex® Performance Assay or magnetic bead panel kit. The expression of CD14 and CD16 was analyzed by immunohistochemistry and flow cytometry.

Results

The concentration of sCD14 in synovial fluid was correlated with the interleukin-6 (IL-6) level (n=35) (ρ=0.654, p<0.001). The culture supernatants of CD14⁺ monocytes isolated from SFMC (n=15) showed a correlation between sCD14 and IL-6 (ρ=0.784, p=0.001), along with complement component 3 (ρ=0.756, p=0.010), IL-1b (ρ=0.652, p=0.012), and tumor necrosis factor-alpha (ρ=0.806, p=0.001). Following recombinant CD14 and LPS treatment, OA FLS synergistically enhanced the secretion of IL-6, IL-8, and matrix metalloproteinase 3 (n=3, p<0.05). In five paired-samples from identical patients, the proportions of CD14⁺ monocytes were significantly elevated in recurred synovial fluid compared to those in initial synovial fluid (p=0.043). When monocyte subsets were analyzed in SFMC (n=26), CD14⁺CD16⁺monocytes were abundant (p=0.019) and had higher toll-like receptor 4 expression than CD14⁺CD16^- (p<0.001).

Conclusion

Our study results suggest that CD14⁺ monocytes and the sCD14-mediated pathway play an important role in OA aggravation through inflammatory cytokine secretion.

CircRNA-miRNA networks in regulating bone disease

Circular RNA (circRNA) is a class of endogenous noncoding RNA (ncRNA), presenting as a special covalent closed loop without a 5' cap or 3' tail, maintaining resistance to RNA exonuclease and keeping high stability. Although lowly expressed in most situations, circRNA makes an active difference in regulating physiological or pathological processes by modulating gene expression by regulation of transcription, protein, and miRNA functions through various mechanisms in particular tissues. Recent studies have demonstrated the roles of the miRNA-circRNA network in the development of several bone diseases such as osteoporosis, a multiple-mechanism disease resulting from defective bone quality and low bone mass, osteoarthritis, whose main pathomechanism is inflammation and articular cartilage degradation, as well as osteosarcoma, known as one of the most common bone cancers. However, the specific mechanism of how circRNA along with miRNA influences those diseases is not well documented, showing potential for the development of new therapies for those bone diseases.

Osteoarthritis in year 2021: biochemical markers

OBJECTIVE

To summarize recent scientific advances in protein-derived soluble biomarkers of osteoarthritis.

DESIGN

A systematic search on the PubMed electronic database of clinical studies on protein-derived soluble biochemical markers of osteoarthritis in humans that were published between January 1st 2020 and March 31th 2021. The studies were selected on the basis of objective criteria and summarized in a table. Then they were described in a narrative review.

RESULTS

Out of 1971 publications, 48 fulfilled all selection criteria and 16 were selected by the author for the narrative review. The papers were classified according their clinical significance as defined in the BIPEDS classification. Two papers investigated the "burden of disease", two were dedicated to "investigative biomarkers", four papers question the "prognosis", three the "efficacy of treatment" and five the "diagnosis and phenotyping" value of protein-derived biomarkers.

CONCLUSIONS

Currently, biomarkers research is focused on their use as tools to identify molecular endotypes and clinical phenotypes and to facilitate patient screening and monitoring in clinical trials. This approach should allow a more targeted management of patients suffering from osteoarthritis.

TNF-α impairs EP4 signaling through the association of TRAF2-GRK2 in primary fibroblast-like synoviocytes

Our previous study showed that chronic treatment with tumor necrosis factor-α (TNF-α) decreased cAMP concentration in fibroblast-like synoviocytes (FLSs) of collagen-induced arthritis (CIA) rats. In this study we investigated how TNF-α impairs cAMP homeostasis, particularly clarifying the potential downstream molecules of TNF-α and prostaglandin receptor 4 (EP4) signaling that would interact with each other. Using a cAMP FRET biosensor PM-ICUE3, we demonstrated that TNF-α (20 ng/mL) blocked ONO-4819-triggered EP4 signaling, but not Butaprost-triggered EP2 signaling in normal rat FLSs. We showed that TNF-α (0.02-20 ng/mL) dose-dependently reduced EP4 membrane distribution in normal rat FLS. TNF-α significantly increased TNF receptor 2 (TNFR2) expression and stimulated proliferation in human FLS (hFLS) via ecruiting TNF receptor-associated factor 2 (TRAF2) to cell membrane. More interestingly, we revealed that TRAF2 interacted with G protein-coupled receptor kinase (GRK2) in the cytoplasm of primary hFLS and helped to bring GRK2 to cell membrane in response of TNF-α stimulation, the complex of TRAF2 and GRK2 then separated on the membrane, and translocated GRK2 induced the desensitization and internalization of EP4, leading to reduced production of intracellular cAMP. Silencing of TRAF2 by siRNA substantially diminished TRAF2-GRK2 interaction, blocked the translocation of GRK2, and resulted in upregulated expression of membrane EP4 and intracellular cAMP. In CIA rats, administration of paroxetine to inhibit GRK2 effectively improved the symptoms and clinic parameters with significantly reduced joint synovium inflammation and bone destruction. These results elucidate a novel form of cross-talk between TNFR (a cytokine receptor) and EP4 (a typical G protein-coupled receptor) signaling pathways. The interaction between TRAF2 and GRK2 may become a potential new drug target for the treatment of inflammatory diseases.

Effects of adenovirus-mediated knockdown of IRAK4 on synovitis in the osteoarthritis rabbit model

BACKGROUND

The use of interleukin-1 receptor-associated kinase 4 (IRAK4) inhibitor as a treatment for the inflammatory joint disease is a promising method. However, its underlying mechanism in osteoarthritis (OA) remains unclear. The purpose of this study is to look into the effects of adenovirus-mediated knockdown of IRAK4 on synovitis in the OA rabbit model.

METHODS

Ad-shIRAK4 was injected two weeks after anterior cruciate ligament resection. Six weeks later, the rabbits were killed. The expression of IRAK4, TNFR-associated factor 6(TRAF6), TGF-activated kinase 1(TAK1), p-IKB kinase (p-IKK), p-nuclear factor kappa-B (p-NFκB), p38, and p-p38 in the synovial membrane was detected by western blot, qRT-PCR, and immunohistochemistry analysis. Immunohistochemistry was to detect the expression of IRAK4 proteins in articular cartilage. H&E staining was to assess the pathological changes of synovium and cartilage. The levels of interleukin (IL)-1β, tumor necrosis factor-α(TNF-α), and MMP-13 in the synovial fluid were measured by ELISA. X-ray and micro-computerized tomography (μCT) scans were used to assess knee joint conditions and microstructure of subchondral bone.

RESULTS

IRAK4 expression levels in synovial tissues of the OA model group exhibited a significant upward trend. Ad-shIRAK4 significantly reduced IRAK4 mRNA expression in synovium tissues. Notably, Ad-shIRAK4 suppressed the Toll-like receptor/interleukin-1 receptor (TLR/IL-1R) signaling. In addition, in the Ad-shIRAK4 treatment group, we can see less inflammatory cell infiltration and reduced hyperplasia and angiogenesis. The levels of IL-1β, TNF-α, and MMP-13 in the synovial fluid in the OA model group were significantly higher than that in the control group, which were reduced by Ad-shIRAK4 treatment. Finally, Results of HE stains, immunohistochemistry, and μCT showed that Ad-shIRAK4 treatment has a protective effect on cartilage damage.

CONCLUSIONS

IRAK4 is significantly upregulated in the synovium from the osteoarthritis rabbit model. In addition, Ad-shIRAK4 reduced the expression of IRAK4 and suppressed TLR/IL-1R signaling in the synovium from the osteoarthritis rabbit model. Ad-shIRAK4 could alleviate synovitis and cartilage degradation in the osteoarthritis rabbit model, and thus alleviate the symptoms of OA and prevent the progression of OA.

A Roadmap of In Vitro Models in Osteoarthritis: A Focus on Their Biological Relevance in Regenerative Medicine

Osteoarthritis (OA) is a multifaceted musculoskeletal disorder, with a high prevalence worldwide. Articular cartilage and synovial membrane are among the main biological targets in the OA microenvironment. Gaining more knowledge on the accuracy of preclinical in vitro OA models could open innovative avenues in regenerative medicine to bridge major gaps, especially in translation from animals to humans. Our methodological approach entailed searches on Scopus, the Web of Science Core Collection, and EMBASE databases to select the most relevant preclinical in vitro models for studying OA. Predicting the biological response of regenerative strategies requires developing relevant preclinical models able to mimic the OA milieu influencing tissue responses and organ complexity. In this light, standard 2D culture models lack critical properties beyond cell biology, while animal models suffer from several limitations due to species differences. In the literature, most of the in vitro models only recapitulate a tissue compartment, by providing fragmented results. Biotechnological advances may enable scientists to generate new in vitro models that combine easy manipulation and organ complexity. Here, we review the state-of-the-art of preclinical in vitro models in OA and outline how the different preclinical systems (inflammatory/biomechanical/microfluidic models) may be valid tools in regenerative medicine, describing their pros and cons. We then discuss the prospects of specific and combinatorial models to predict biological responses following regenerative approaches focusing on mesenchymal stromal cells (MSCs)-based therapies to reduce animal testing.

Mechanism of Modified Danggui Sini Decoction for Knee Osteoarthritis Based on Network Pharmacology and Molecular Docking

Objective

This study aimed to explore the mechanism of Modified Danggui Sini Decoction in the treatment of knee osteoarthritis via a combination of network pharmacology and molecular docking.

Methods

The main chemical components and corresponding targets of Modified Danggui Sini Decoction were searched and screened in TCMSP database. The disease targets of knee osteoarthritis were summarized in GeneCards, OMIM, PharmGkb, TTD, and DrugBank databases. The visual interactive network of “drugs-active components-disease targets” was drawn by Cytoscape 3.8.1 software. The protein-protein interaction network was constructed by STRING database. Then, GO function and KEGG pathway enrichment were analyzed by Bioconductor/R, and the pathway of the highest degree of correlation with knee osteoarthritis was selected for specific analysis. Finally, molecular docking was used to screen and verify core genes by AutoDockTools software.

Results

Seventy-one main components of Modified Danggui Sini Decoction and 116 potential therapeutic targets of knee osteoarthritis were selected. The KEGG pathway and the GO function enrichment analysis showed that the targets of Modified Danggui Sini Decoction in the treatment of knee osteoarthritis were mainly concentrated on PI3K-Akt signaling pathway, TNF signaling pathway, IL-17 signaling pathway, apoptosis signaling pathway, Toll-like receptor signaling pathway, Th17 cell differentiation signaling pathway, HIF-1 signaling pathway, and NF-κB signaling pathway. It mainly involved inflammatory reaction, regulation of apoptotic signaling pathway, cellular response to regulation of inflammatory response, cellular response to oxidative stress, and other biological processes. The molecular docking results showed that ESR1-wogonin, MAPK1-quercetin, RELA-wogonin, RELA-baicalein, TP53-baicalein, TP53-quercetin, and RELA-quercetin have strong docking activities.

Conclusion

Modified Danggui Sini Decoction has the hierarchical network characteristics of “multicomponent, multitarget, multifunction, and multipathway” in the treatment of knee osteoarthritis. It mainly regulates the proliferation and apoptosis of chondrocytes by regulating the PI3K-Akt signaling pathway and establishes cross-talk with many downstream inflammatory-related pathways to reduce the overall inflammatory response. Meanwhile, HIF-1 expression was used to ensure the normal function and metabolism of knee joint under hypoxia condition, and the above processes play a key role in the treatment of knee osteoarthritis.

Recombinant Adiponectin Induces the Production of Pro-Inflammatory Chemokines and Cytokines in Circulating Mononuclear Cells and Fibroblast-Like Synoviocytes From Non-Inflamed Subjects

Adiponectin is an adipokine with a modulatory role in metabolism and exerting both anti- and pro-inflammatory effects. Levels of adiponectin are increased in serum and synovial fluid from patients with rheumatoid arthritis (RA). Adiponectin is able to stimulate the production of different pro-inflammatory factors from peripheral blood mononuclear cells (PBMCs) and fibroblast-like synoviocytes (FLS) from subjects with established RA. As increased circulating adiponectin levels are a risk factor for future development of RA in subjects with obesity, we hypothesize that adiponectin is implicated in the development of RA at an early stage by initiating the pro-inflammatory processes associated with the disease pathogenesis. Therefore, we aimed to determine if adiponectin is able to induce pro-inflammatory responses in cells involved in the pathogenesis of RA, but collected from subjects without any known inflammatory disease. PBMCs and FLS were obtained from non-inflamed subjects and stimulated with 5 μg/ml human recombinant adiponectin. Supernatants collected after 48 h were analyzed for the production of 13 chemokines and 12 cytokines using multiplex assay and ELISA. Adiponectin significantly stimulated the production of CXCL1, CXCL5, and interleukin (IL)-6 in both PBMCs and FLS, whereas it induced CCL20, CCL4, CCL3, CCL17, tumor necrosis factor (TNF), granulocyte-macrophage colony-stimulating factor and IL-10 only in PBMCs, and CXCL8, CXCL10, CCL5, CCL11, and CCL2 only in FLS. Pre-stimulation with TNF of FLS from non-inflamed subjects did not significantly enhance the release of most pro-inflammatory factors compared to adiponectin alone. Our findings indicate that PBMCs and FLS from non-inflamed subjects react to adiponectin stimulation with the secretion of several pro-inflammatory chemokines and cytokines. These results suggest that adiponectin is able to initiate pro-inflammatory responses in cells from non-inflamed subjects and support the hypothesis that adiponectin is implicated in the early phases of RA pathogenesis.

Current Models for Development of Disease-Modifying Osteoarthritis Drugs

Osteoarthritis (OA) is a painful and disabling disease that affects millions of people worldwide. Symptom-alleviating treatments exist, although none with long-term efficacy. Furthermore, there are currently no disease-modifying OA drugs (DMOADs) with demonstrated efficacy in OA patients, which is, in part, attributed to a lack of full understanding of the pathogenesis of OA. The inability to translate findings from basic research to clinical applications also highlights the deficiencies in the available OA models at simulating the clinically relevant pathologies and responses to treatments in humans. In this review, the current status in the development of DMOADs will be first presented, with special attention to those in Phase II-IV clinical trials. Next, current in vitro, ex vivo, and in vivo OA models are summarized and the respective advantages and disadvantages of each are highlighted. Of note, the development and application of microphysiological or tissue-on-a-chip systems for modeling OA in humans are presented and the issues that need to be addressed in the future are discussed. Microphysiological systems should be given serious consideration for their inclusion in the DMOAD development pipeline, both for their ability to predict drug safety and efficacy in human clinical trials at present, as well as for their potential to serve as a test platform for personalized medicine. Impact statement At present, no disease-modifying osteoarthritis (OA) drugs (DMOADs) have been approved for widespread clinical use by regulatory bodies. The failure of developing effective DMOADs is likely owing to multiple factors, not the least of which are the intrinsic differences between the intact human knee joint and the preclinical models. This work summarizes the current OA models for the development of DMOADs, discusses the advantages/disadvantages of each, and then proposes future model development to aid in the discovery of effective and personalized DMOADs. The review also highlights the microphysiological systems, which are emerging as a new platform for drug development.

Differential synovial tissue expression of TLRs in seropositive and seronegative rheumatoid arthritis: A preliminary report

Toll-like receptors (TLRs) are known to have an important role in triggering the innate immune response and in priming antigen-specific adaptive immunity and inflammation. The differences in synovial tissue expression of the TLRs between seronegative and seropositive rheumatoid arthritis (RA) were examined from 9 seropositive RA, 5 seronegative RA and 4 osteoarthritis (OA) patients. Synovitis status was assessed using Krenn's scoring and TLR 1-9 expression by immunohistochemistry. Tissue citrulline content was analysed by HPLC method. In RA TLR expression was generally higher than in OA. TLR2 expression was higher in both seronegative and seropositive RA compared to OA. TLR 1, 4 and 8 expressions were higher in seropositive RA than in seronegative RA or in OA. For TLRs 3, 5, 6, 7 and 9 local differences of expression were found between groups. TLR 1-9 expression correlated with the synovitis grade. No statistical difference was found in synovial tissue citrulline content between the groups. In seropositive RA, the TLR repertoire in the synovial tissue differs from seronegative RA and could explain differences in disease outcomes. The high expression of protein sensing (TLR1, TLR2 and TLR4) and nucleic acid sensing TLRs (TLR7, TLR8 and TLR9) in the seropositive RA could make the synovium primed for reacting to citrullinated proteins and nucleic acids that could be released to extracellular space in formation of neutrophil extracellular traps. This reactivity could be augmented by Fc receptor activation by anti-citrullinated protein antibody immunocomplexes associated with seropositive RA.

Exploring the Association of Innate Immunity Biomarkers With MRI Features in Both Early and Late Stages Osteoarthritis

Objective: To evaluate the association between biomarkers of innate immunity and the magnetic resonance imaging (MRI) features of earlier and later stages of knee osteoarthritis (KOA). Methods: From 139 and 20 participants with earlier and later stages of KOA, respectively, we analyzed knee MRIs scored using the Boston Leeds Osteoarthritis Knee Score (BLOKS) at recruitment with biomarkers. In paired serum (s) and synovial fluid (sf), we quantified three biomarkers related to innate immunity: lipopolysaccharide binding protein (LBP), CD14 and Toll-like receptor 4 (TLR4), and three proinflammatory biomarkers [interleukin-6 (IL6), IL8, and tumor necrosis factor alpha (TNFα)]. Results: In participants with earlier KOA, (s) LBP was statistically significantly associated with meniscal extrusion, and (sf) CD14 was associated with effusion after adjustment with age, sex, and body mass index. In participants with later stage of KOA, (sf) LBP was associated with effusion. (sf) CD14 was associated with cartilage loss and BML. In earlier stage of KOA, the proinflammatory biomarkers IL6, IL8, and TNFα were associated with most MRI features. Conclusion: Innate immunity biomarkers (s) LBP was associated with MRI meniscal extrusion; (sf) CD14 was associated with MRI synovial inflammation in earlier stage and BMLs in later stage of KOA. Associations between proinflammatory biomarkers and various MRI features in earlier stage of KOA were observed.

Cross-Talk between Diet-Associated Dysbiosis and Hand Osteoarthritis

Hand osteoarthritis (OA) is a degenerative joint disease which leads to pain and disability. Recent studies focus on the role of obesity and metabolic syndrome in inducing or worsening joint damage in hand OA patients, suggesting that chronic low-grade systemic inflammation may represent a possible linking factor. The gut microbiome has a crucial metabolic role which is fundamental for immune system development, among other important functions. Intestinal microbiota dysbiosis may favour metabolic syndrome and low-grade inflammation-two important components of hand OA onset and evolution. The aim of this narrative is to review the recent literature concerning the possible contribution of dysbiosis to hand OA onset and progression, and to discuss the importance of gut dysbiosis on general health and disease.

TLR-4, TLR-5 and IRF4 are diagnostic markers of knee osteoarthritis in the middle-aged and elderly patients and related to disease activity and inflammatory factors

Expression and diagnostic value of serum toll-like receptor-4 (TLR-4), Toll-like receptor-5 (TLR-5) and interferon regulatory factor 4 (IRF4) in middle-aged and elderly patients with knee osteoarthritis (KOA) and their correlation with Interleukin 1β (IL-1β), interleukin-6 (IL-6), matrix metalloproteinase-1 and tumor necrosis factor-α (TNF-α) were investigated. Sixty-eight middle-aged and elderly patients with KOA in Puyang Hospital of Traditional Chinese Medicine were selected as the study group and 49 healthy people receiving physical examination were the control group. Levels of serum TLR-4, TLR-5, IRF4, IL-1β, IL-6, MMP-1 and TNF-α were measured by enzyme linked immunosorbent assay (ELISA). Correlation between the expression levels of serum TLR-4, TLR-5, IRF4 and K-L grades was determined by Spearman correlation analysis. The diagnostic efficacy of serum TLR-4, TLR-5 and IRF4 for KOA was analyzed by the receiver operator characteristics analysis (ROC). Expression of serum TLR-4, TLR-5 and IRF4 in the study group was significantly higher than those in the control group. The sensitivity and specificity of TLR-4 in the diagnosis of KOA were, respectively, 76.47 and 93.88%, those of TLR-5 were 73.29 and 87.76%, those of IRF4 were 72.06 and 95.92%, and those of TLR-4, TLR-5 and IRF4 were 94.12 and 97.96%. Expression of serum TLR-4, TLR-5 and IRF4 was significantly higher in the severe group than in the moderate group, and significantly higher in the moderate group than those the in mild group, and significantly higher in the mild group than those in the suspected mild group. Expression of TLR-4, TLR-5 and IRF4 in serum was positively correlated with the concentration of IL-1β, IL-6, MMP-1 and TNF-α, respectively (P<0.001). The combined detection of TLR-4, TLR-5 and IRF4 can be used for early diagnosis of KOA, and they are positively correlated with IL-1β and IL-6, MMP-1 and TNF-α.

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.

Pathogenesis of Osteoarthritis: Risk Factors, Regulatory Pathways in Chondrocytes, and Experimental Models

As the most common chronic degenerative joint disease, osteoarthritis (OA) is the leading cause of pain and physical disability, affecting millions of people worldwide. Mainly characterized by articular cartilage degradation, osteophyte formation, subchondral bone remodeling, and synovial inflammation, OA is a heterogeneous disease that impacts all component tissues of the articular joint organ. Pathological changes, and thus symptoms, vary from person to person, underscoring the critical need of personalized therapies. However, there has only been limited progress towards the prevention and treatment of OA, and there are no approved effective disease-modifying osteoarthritis drugs (DMOADs). Conventional treatments, including non-steroidal anti-inflammatory drugs (NSAIDs) and physical therapy, are still the major remedies to manage the symptoms until the need for total joint replacement. In this review, we provide an update of the known OA risk factors and relevant mechanisms of action. In addition, given that the lack of biologically relevant models to recapitulate human OA pathogenesis represents one of the major roadblocks in developing DMOADs, we discuss current in vivo and in vitro experimental OA models, with special emphasis on recent development and application potential of human cell-derived microphysiological tissue chip platforms.

Infrapatellar Fat Pad/Synovium Complex in Early-Stage Knee Osteoarthritis: Potential New Target and Source of Therapeutic Mesenchymal Stem/Stromal Cells

The infrapatellar fat pad (IFP) has until recently been viewed as a densely vascular and innervated intracapsular/extrasynovial tissue with biomechanical roles in the anterior compartment of the knee. Over the last decade, secondary to the proposition that the IFP and synovium function as a single unit, its recognized tight molecular crosstalk with emerging roles in the pathophysiology of joint disease, and the characterization of immune-related resident cells with varying phenotypes (e.g., pro and anti-inflammatory macrophages), this structural complex has gained increasing attention as a potential therapeutic target in patients with various knee pathologies including osteoarthritis (KOA). Furthermore, the description of the presence of mesenchymal stem/stromal cells (MSC) as perivascular cells within the IFP (IFP-MSC), exhibiting immunomodulatory, anti-fibrotic and neutralizing activities over key local mediators, has promoted the IFP as an alternative source of MSC for cell-based therapy protocols. These complementary concepts have supported the growing notion of immune and inflammatory events participating in the pathogenesis of KOA, with the IFP/synovium complex engaging not only in amplifying local pathological responses, but also as a reservoir of potential therapeutic cell-based products. Consequently, the aim of this review is to outline the latest discoveries related with the IFP/synovium complex as both an active participant during KOA initiation and progression thus emerging as a potential target, and a source of therapeutic IFP-MSCs. Finally, we discuss how these notions may help the design of novel treatments for KOA through modulation of local cellular and molecular cascades that ultimately lead to joint destruction.

Soluble CD14 Induces Pro-inflammatory Cytokines in Rheumatoid Arthritis Fibroblast-Like Synovial Cells via Toll-Like Receptor 4

OBJECTIVES

Synovial fluids of rheumatoid arthritis (RA) patients commonly contain high concentrations of soluble CD14 (sCD14). To investigate its potential role in RA pathogenesis, we tested whether sCD14 binding transmits a signal to fibroblast-like synoviocytes from RA patients (RA-FLS).

METHODS

The induction of pro-inflammatory cytokines, chemokines, and mediators by sCD14 stimulation of RA-FLS was quantified by real-time PCR and ELISA. Cell proliferation was assessed by the BrdU assay. LPS-RS, a Toll-like receptor 4 (TLR-4) antagonist, was used to block TLR-4 signaling.

RESULTS

Soluble CD14 induced the expression of IL-6 mRNA and secretion of the protein. The expression of other pro-inflammatory cytokines and mediators, such as TNF-α, IL-8, intercellular adhesion molecule-1 (ICAM-1), MMP-3, and RANK ligand (RANKL), was also induced by sCD14. In addition, sCD14 stimulation promoted RA-FLS proliferation. LPS-RS abolished IL-6, IL-8, and ICAM-1 mRNA induction by sCD14 in RA-FLS. On the other hand, TNF-α and IL-17A increased TLR-4 expression by RA-FLS and amplified their sCD14-induced IL-6 expression.

CONCLUSIONS

Soluble CD14 transmits inflammatory signals to RA-FLS via TLR-4. The effects of sCD14 may be augmented in inflammatory milieu. Our results suggest that sCD14 is involved in the pathogenesis of RA and may be a novel therapeutic target.

Pathophysiological landscape of osteoarthritis

A sharp rise in osteoarthritis (OA) incidence is expected as over 25% of world population ages in the coming decade. Although OA is considered a degenerative disease, mounting evidence suggests a strong connection with chronic metabolic conditions and low-grade inflammation. OA pathology is increasingly understood as a complex interplay of multiple pathological events including oxidative stress, synovitis and immune responses revealing its intricate nature. Cellular, biochemical and molecular aspects of these pathological events along with major outcomes of the relevant research studies in this area are discussed in the present review. With reference to their published and unpublished work, the authors strongly propose synovitis as a central OA pathology and the key OA pathological events are described in connection with it. Recent research outcomes also have succeeded to establish a linkage between metabolic syndrome and OA, which has been precisely included in the present review. Impact of aging process cannot be neglected in OA. Cell senescence is an important mechanism of aging through which it facilitates development of OA like other degenerative disorders, also discussed within a frame of OA. Conclusively, the reviewers urge low-grade inflammation linked to aging and derailed immune function as a pathological platform for OA development and progression. Thus, interventions targeted to prevent inflammaging hold a promising potential in effective OA management and efforts should be invested in this direction.

On the Mechanisms of Action of the Low Molecular Weight Fraction of Commercial Human Serum Albumin in Osteoarthritis

The low molecular weight fraction of commercial human serum albumin (LMWF5A) has been shown to successfully relieve pain and inflammation in severe osteoarthritis of the knee (OAK). LMWF5A contains at least three active components that could account for these antiinflammatory and analgesic effects. We summarize in vitro experiments in bone marrow-derived mesenchymal stem cells, monocytic cell lines, chondrocytes, peripheral blood mononuclear cells, fibroblast-like synoviocytes, and endothelial cells on the biochemistry of anti-inflammatory changes induced by LMWF5A. We then look at four of the major pathways that cut across cell-type considerations to examine which biochemical reactions are affected by mTOR, COX-2, CD36, and AhR pathways. All three components show anti-inflammatory activities in at least some of the cell types. The in vitro experiments show that the effects of LMWF5A in chondrocytes and bone marrow- derived stem cells in particular, coupled with recent data from previous clinical trials of single and multiple injections of LMWF5A into OAK patients demonstrated improvements in pain, function, and Patient Global Assessment (PGA), as well as high responder rates that could be attributed to the multiple mechanism of action (MOA) pathways are summarized here. In vitro and in vivo data are highly suggestive of LMWF5A being a disease-modifying drug for OAK.

Chondroprotective and anti-inflammatory effects of amurensin H by regulating TLR4/Syk/NF-κB signals

The low-grade, chronic inflammation initiated by TLR4-triggered innate immune responses has a central role on early osteoarthritis. Amurensin H is a resveratrol dimer with anti-inflammatory and anti-apoptotic effects, while its effects on TLR-4 signals to inhibit osteoarthritis are still unclear. In the present study, treatment with amurensin H for 2 weeks in monosodium iodoacetate-induced mice significantly slows down cartilage degeneration and inflammation using macroscopic evaluation, haematoxylin and eosin (HE) staining and micro-magnetic resonance imaging. In IL-1β-stimulated rat chondrocytes, amurensin H suppresses the production of inflammatory mediators including nitric oxide, IL-6, IL-17, PGE2 and TNF-α using Greiss and ELISA assay. Amurensin H inhibits matrix degradation via decreasing levels of MMP-9 and MMP-13 using Western blot assay, promotes synthesis of type II collagen and glycosaminoglycan using immunostaining and safranin O staining, respectively. Amurensin H inhibits intracellular and mitochondrial reactive oxygen species (ROS) generation, and mitochondrial membrane depolarization using DCFH-DA, MitoSOX Red and JC-1 assay as well. IL-1β stimulates TLR4 activation and Syk phosphorylation in chondrocytes, while amurensin H inhibits TLR4/Syk signals and downstream p65 phosphorylation and translocation in a time and dose-dependent manner. Together, these results suggest that amurensin H exerts chondroprotective effects by attenuating oxidative stress, inflammation and matrix degradation via the TLR4/Syk/NF-κB pathway.

An emerging role for Toll-like receptors at the neuroimmune interface in osteoarthritis

Osteoarthritis (OA) is a chronic progressive, painful disease of synovial joints, characterized by cartilage degradation, subchondral bone remodeling, osteophyte formation, and synovitis. It is now widely appreciated that the innate immune system, and in particular Toll-like receptors (TLRs), contributes to pathological changes in OA joint tissues. Furthermore, it is now also increasingly recognized that TLR signaling plays a key role in initiating and maintaining pain. Here, we reviewed the literature of the past 5 years with a focus on how TLRs may contribute to joint damage and pain in OA. We discuss biological effects of specific damage-associated molecular patterns (DAMPs) which act as TLR ligands in vitro, including direct effects on pain-sensing neurons. We then discuss the phenotype of transgenic mice that target TLR pathways, and provide evidence for a complex balance between pro- and anti-inflammatory signaling pathways activated by OA DAMPs. Finally, we summarize clinical evidence implicating TLRs in OA pathogenesis, including polymorphisms and surrogate markers of disease activity. Our review of the literature led us to propose a model where multi-directional crosstalk between connective tissue cells (chondrocytes, fibroblasts), innate immune cells, and sensory neurons in the affected joint may promote OA pathology and pain.

Upregulation of stanniocalcin-1 inhibits the development of osteoarthritis by inhibiting survival and inflammation of fibroblast-like synovial cells

OBJECTIVE

Osteoarthritis (OA) is a progressive and disabling disorder, characterized by synovial inflammation and joint effusion. This study aimed to explore the role of stanniocalcin-1 (STC1) in the development of OA by regulating the survival and inflammation of fibroblast-like synovial (FLS) cells.

METHODS

Microarray analyses were adopted to screen differentially expressed genes (DEGs) related to OA, and regulatory microRNA (miR) was also identified. Synovial tissue samples from patients with OA and healthy individuals were obtained to determine the expression levels of miR-454, STC1, IL-6, IL-8, and MMP3/13. The targeted relationship between miR-454 and STC1 was verified by dual-luciferase reporter gene assay. With the treatment of miR-454 mimic and STC1 overexpression vector, the effect of miR-454 and STC1 on FLS cell viability and apoptosis as well as production of inflammatory cytokines were tested.

RESULTS

STC1 with aberrant low expression was screened from GSE1919 profile in OA. STC1 was found to be downregulated in OA-FLS tissues and cells. STC1 overexpression inhibited OA-FLS cell viability but induced apoptosis of OA-FLS cells. Moreover, STC1 overexpression decreased levels of IL-6, IL-8, and MMP3/13, suggesting that STC1 overexpression suppressed inflammatory reactions. In addition, miR-454 blocked the inhibitory effects of STC1 overexpression on OA-FLS cell viability and inflammatory reaction and exerted a promotion effect of STC1 overexpression on apoptosis of OA-FLS cells.

CONCLUSIONS

Taken together, the results revealed that upregulation of STC1 could repress proliferation of OA-FLS cells and inflammatory reaction, and enhance apoptosis of OA-FLS cells, which was negatively regulated by miR-454.

Deficiency of the pattern-recognition receptor CD14 protects against joint pathology and functional decline in a murine model of osteoarthritis

Objective

CD14 is a monocyte/macrophage pattern-recognition receptor that modulates innate inflammatory signaling. Soluble CD14 levels in knee OA synovial fluids are associated with symptoms and progression of disease. Here we investigate the role of this receptor in development of OA using a murine joint injury model of disease.

Methods

10-week-old Male C57BL/6 (WT) and CD14-deficient (CD14^-/-) mice underwent destabilization of the medial meniscus (DMM) surgery to induce OA. Joint histopathology was used to examine cartilage damage, and microCT to evaluate subchondral bone (SCB) remodeling at 6 and 19 weeks after surgery. Synovial and fat pad expression of macrophage markers (F4/80, CD11c, CD68, iNOS, CCR7, CD163 and CD206) was assessed by flow cytometry and droplet digital (dd)PCR. Changes in locomotive activity indicative of joint pain were evaluated longitudinally up to 16 weeks by automated behavioral analysis.

Results

Early cartilage damage scores 6 weeks post-DMM were similar in both strains (Mean score ±SEM WT: 4.667±1.38, CD14^-/-: 4.6±0.6), but at 19 weeks were less severe in CD14^-/- (6.0±0.46) than in WT mice (13.44±2.5, p = 0.0002). CD14^-/- mice were protected from both age-related and post-surgical changes in SCB mineral density and trabecular thickness. In addition, CD14^-/- mice were protected from decreases in climbing activity (p = 0.015 vs. WT, 8 weeks) observed after DMM. Changes in synovial/fat pad expression of CCR7, a marker of M1 macrophages, were slightly reduced post-DMM in the absence of CD14, while expression of CD68 (pan-macrophage marker) and CD163 (M2 marker) were unchanged.

Conclusion

CD14 plays an important role in progression of structural and functional features of OA in the DMM model, and may provide a new target for therapeutic development.

Bioinformatics analysis to identify key genes and pathways influencing synovial inflammation in osteoarthritis

Osteoarthritis (OA) is a chronic arthropathy that occurs in the middle-aged and elderly population. The present study aimed to identify gene signature differences between synovial cells from OA synovial membrane with and without inflammation, and to explain the potential mechanisms involved. The differentially expressed genes (DEGs) between 12 synovial membrane with inflammation and 12 synovial membrane without inflammation from the dataset GSE46750 were identified using the Gene Expression Omnibus 2R. The DEGs were subjected to enrichment analysis, protein-protein interaction (PPI) analysis and module analysis. The analysis results were compared with text-mining results. A total of 174 DEGs were identified. Gene Ontology enrichment results demonstrated that functional molecules encoded by the DEGs primarily had extracellular location, molecular functions predominantly involving ‘chemokine activity’ and ‘cytokine activity’, and were associated with biological processes, including ‘inflammatory response’ and ‘immune response’. The Kyoto Encyclopedia of Genes and Genomes results demonstrated that DEGS may function through pathways associated with ‘rheumatoid arthritis’, ‘chemokine signaling pathway’, ‘complement and coagulation cascades’, ‘TNF signaling pathway’, ‘intestinal immune networks for IgA production’, ‘cytokine-cytokine receptor interaction’, ‘allograft rejection’, ‘Toll-like receptor signaling pathway’ and ‘antigen processing and presentation’. The top 10 hub genes [interleukin (IL)6, IL8, matrix metallopeptidase (MMP)9, colony stimulating factor 1 receptor, FOS proto-oncogene, AP1 transcription factor subunit, insulin-like growth factor 1, TYRO protein tyrosine kinase binding protein, MMP3, cluster of differentiation (CD)14 and CD163] and four gene modules were identified from the PPI network using Cytoscape. In addition, text-mining was used to identify the commonly used drugs and their targets for the treatment of OA. It was initially verified whether the results of the present study were useful for the study of OA treatment targets and pathways. The present study provided insight for the molecular mechanisms of OA synovitis. The hub genes and associated pathways derived from analysis may be targets for OA treatment. IL8 and MMP9, which were validated by text-mining, may be used as molecular targets for the OA treatment, while other hub genes require further validation.

Transient Receptor Potential Ankyrin 1 (TRPA1) Mediates Lipopolysaccharide (LPS)-Induced Inflammatory Responses in Primary Human Osteoarthritic Fibroblast-Like Synoviocytes

Transient receptor potential ankyrin 1 (TRPA1) is a membrane-associated cation channel, widely expressed in neuronal and non-neuronal cells. Recently, emerging evidences suggested the crucial role of TRPA1 in the disease progression of osteoarthritis (OA). Therefore, we aimed to investigate whether TRPA1 mediate lipopolysaccharide (LPS)-induced inflammatory responses in primary human OA fibroblast-like synoviocytes (OA-FLS). The expression of TRPA1 in LPS-treated OA-FLS was assessed by polymerase chain reaction (PCR) and western blot (WB), and the functionality of TRPA1 channel by Ca²⁺ influx measurements. Meanwhile, production of interleukin (IL)-1β, tumor necrosis factor (TNF)-α, IL-6, matrix metalloproteinase (MMP)-1, and MMP-3 in LPS-treated cells was measured by immunoassay. Histological observation after inhibition of TRPA1 was also performed in rats with LPS-induced inflammatory arthritis. After being induced by LPS, the gene and protein expression of TRPA1 was increased in the time-dependent or dose-dependent manner. Meanwhile, Ca²⁺ influx mediated by TRPA1 in human OA-FLS was also enhanced. In addition, pharmacological inhibition and gene silencing of TRPA1 downregulated the production of IL-1β, TNF-α, IL-6, MMP-1, and MMP-3 in LPS-treated FLS. Finally, synovial inflammation and cartilage degeneration were also reduced by the TRPA1 antagonist. We found the LPS caused the increased functional expression of TRPA1, the activation of which involved in LPS-reduced inflammatory responses in primary human OA-FLS, and the inhibition of TRPA1 produces protective effect in LPS-induced arthritis.

Carnosine Prevents Type 2 Diabetes-Induced Osteoarthritis Through the ROS/NF-κB Pathway

Background: The anti-inflammatory and antioxidant capacity of carnosine (CAR) has been investigated in autoimmune diseases. The aim of this study was to evaluate the potential protective effects of oral CAR supplements to ameliorate type 2 diabetes mellitus (T2DM)-induced osteoarthritis (OA) in rats and its mechanism.

Methods: Seventy male Sprague–Dawley rats were randomly divided into the control group (CG, n = 10) and the T2DM group (n = 60). A rat model of T2DM was established using a high fat diet and streptozotocin (30 mg/kg, i.p.). The 41 rats that developed T2DM were chosen and randomly divided into four groups: T2DM-induced OA group (OAG, n = 11), and the T2DM-induced OA with low, moderate, and high-doses of CAR for 8 weeks group (CAR-L, CAR-M, and CAR-H, n = 10). After 13 weeks, all rats were evaluated by enzyme-linked immunosorbent assay (ELISA), histology, immunohistochemistry, and western blotting. Fibroblast-like synoviocytes (FLSs) were obtained from the knee joints of all rats. The effects of CAR on the inflammatory response in interleukin (IL)-1β-stimulated FLSs under a high glucose environment were evaluated by real-time quantitative polymerase chain reaction, western blotting, flow cytometry, and immunofluorescence.

Results: The results of ELISA (IL-1β and tumor necrosis factor-α), the histological evaluation (Mankin and OARSI score), western blotting [COL2A1, matrix metalloproteinase (MMP)-3, MMP-13, IL-1β, and nuclear factor-kappaB (NF-κB) p65], and immunohistochemistry (COL2A1, MMP-3, and MMP-13) indicated that oral CAR attenuated the development of T2DM-induced OA and suppressed the inflammatory response. Moreover, CAR alleviated MMP-3 and MMP-13 expression levels by decreasing reactive oxygen species content and suppressing nuclear translocation of NF-κB p65 on IL-1β-induced FLSs in a high glucose environment.

Conclusion: These findings indicate that oral CAR had chondroprotective effects on T2DM-induced OA through the reactive oxygen species (ROS)/NF-κB pathway.

Vasoactive intestinal peptide alleviates osteoarthritis effectively via inhibiting NF-κB signaling pathway

BACKGROUND

To investigate the treatment effect of vasoactive intestinal peptide (VIP) on osteoarthritis (OA) and the relative mechanism.

METHOD

The OA model on the SD rat knee was established using the modified Hulth method, and the recombinant pcDNA3.1+/VIP plasmid was constructed. One month after the plasmids VIP were injected intra-articularly into the right knee joint of OA and sham-operated rats, the pathological changes of the OA knee joint were observed by Hematoxylin-eosin (HE) and Safranin O/fast green staining. The levels of VIP and serum inflammatory cytokines (TNF-α, IL-2 and IL-4) were measured by ELISA kits. Meanwhile, synoviocytes isolated from OA rat and sham-operated rat were cultured in vitro, and transfected with the VIP plasmid. The proliferation of synoviocytes was determined using BrdU kits. The protein expressions of TNF-α, IL-2, CollagenII, osteoprotegerin (OPG), matrix-degrading enzymes (MMP-13, ADAMTS-5), and the related protein of NF-κB signaling pathway (phosphorylated p65, phosphorylated IκBα) were evaluated by western blot.

RESULTS

The VIP plasmid could effectively improve the pathological state of the OA rats knee joint, significantly decrease the levels of serum TNF-α and IL-2, and clearly increase the levels of VIP and serum IL-4. At the same time, after the OA synoviocytes were treated with the VIP plasmid, the proliferation ability of OA synoviocytes was reduced, the protein expressions of Collagen II and OPG were remarkably up-regulated, and the protein expressions of TNF-α, IL-2, MMP-13 and ADAMTS-5 were significantly down-regulated. In addition, the p-p65 expression decreased and p-IκBα expression increased.

CONCLUSION

Osteoarthritis was effectively treated by VIP via inhibiting the NF-κB signaling pathway.

Identification of MAVS as a Novel Risk Factor for the Development of Osteoarthritis

Evidence indicated that inflammatory response and some pattern-recognition receptors play important roles in the occurrence and progression of osteoarthritis. This study is conducted to evaluate the role of RIG-I and its adaptor protein MAVS in the pathogenesis of osteoarthritis. Four SNPs in RIG-I gene and four in MAVS gene were genotyped in 1056 Chinese Han population. We also overexpressed MAVS in murine chondrogenic ATDC5 cells and analyzed the cell viability and apoptosis. Rs11795343 (P_-allele: 0.063394) in RIG-I, rs17857295 (P_-allele: 0.073518) and rs7262903 (P_-allele: 0.054052, P_-genotype: 0.067930) in MAVS were marginally associated with OA. Rs7269320 (P_-allele: 0.014783, P_-genotype: 0.03272) in MAVS was significant associated with OA. Further analyses in different genders indicated that rs7262903 (P_-allele: 0.017256, P_-genotype: 0.045683) and rs7269320 (P_-allele: 0.013073, P_-genotype: 0.038881) are significantly associated with OA in female group. Haplotype analyses indicated G-C-G (χ²: 4.328, P_-value: 0.037503) in rs10813821-rs11795343-rs659527 block of RIG-I, G-C-A-T (χ²: 4.056, P_-value: 0.044028) and G-C-C-C (χ²: 14.295, P_-value: 0.000158) in rs17857295-rs2326369-rs7262903-rs7269320 block of MAVS were significantly associated with OA. Furthermore, forced expression of MAVS could suppress the viability and promote the apoptosis of ATDC5 chondrogenic cells. In conclusion, this study indicated that RIG-I and MAVS are probably associated with OA in the females of Chinese Han population. And MAVS might be a novel risk factor for OA which may involve in growth of chondrocytes and cartilage homeostasis.

Icariin Regulates Cellular Functions and Gene Expression of Osteoarthritis Patient-Derived Human Fibroblast-Like Synoviocytes

Synovial inflammation plays an important role in the pathogenesis and progress of osteoarthritis (OA). There is an urgent need to find safe and effective drugs that can reduce the inflammation and regulate the pathogenesis of cytokines of the OA disease. Here, we investigated the effect of icariin, the major pharmacological active component of herb Epimedium on human osteoarthritis fibroblast-like synoviocytes (OA–FLSs). The OA–FLSs were isolated from patients with osteoarthritis and cultured in vitro with different concentrations of icariin. Then, cell viability, proliferation, and migration were investigated; MMP14, GRP78, and IL-1β gene expression levels were detected via qRT-PCR. Icariin showed low cytotoxicity to OA–FLSs at a concentration of under 10 μM and decreased the proliferation of the cells at concentrations of 1 and 10 μM. Icariin inhibited cell migration with concentrations ranging from 0.1 to 1 μM. Also, the expression of three cytokines for the pathogenesis of OA which include IL-1β, MMP14 and GRP78 was decreased by the various concentrations of icariin. These preliminary results imply that icariin might be an effective compound for the treatment of OA disease.

Role of CD44 in Regulating TLR2 Activation of Human Macrophages and Downstream Expression of Proinflammatory Cytokines

Osteoarthritis (OA) is a low-grade chronic inflammatory joint disease. Innate immunity contributes to OA progression, mediated by TLR2 and TLR4. We evaluated the role of cluster determinant 44 (CD44), a transmembrane glycoprotein, in regulating TLR2-linked macrophage activation and resultant proinflammatory responses. TLR2 stimulation was performed on differentiated THP-1 macrophages in the presence or absence of a CD44-specific Ab or hyaluronan (HA). NF-κB nuclear translocation, IL-1 β and TNF-α gene expression, and protein concentrations were determined. Anti-CD44 Ab and HA treatments reduced NF-κB translocation, IL-1β and TNF-α expression, and production (p < 0.001). Inhibition of proinflammatory response in macrophages by HA was mediated by CD44. Protein phosphatase 2A mediated the reduction in NF-κB translocation by HA. CD44 knockdown reduced NF-κB nuclear translocation and downstream IL-1β and TNF-α protein production following TLR2 receptor stimulation (p < 0.001). CD44^+/+ murine bone marrow-derived macrophages produced higher TNF-α compared with CD44^-/- macrophages following TLR2 stimulation (p < 0.01). HA dose-dependently inhibited TLR2-induced TNF-α production by murine bone marrow-derived macrophages (p < 0.001). OA synovial fluids (SF) stimulated TLR2 and TLR4 receptors and induced NF-κB translocation in THP-1 macrophages. Anti-CD44 Ab treatment significantly reduced macrophage activation by OA SF (p < 0.01). CD44 regulated TLR2 responses in human macrophages, whereby a reduction in CD44 levels or engagement of CD44 by its ligand (HA) or a CD44-specific Ab reduced NF-κB translocation and downstream proinflammatory cytokine production. A CD44-specific Ab reduced macrophage activation by OA SF, and CD44 is a potentially novel target in OA treatment.

The Absence of Detectable ADAMTS-4 (Aggrecanase-1) Activity in Synovial Fluid Is a Predictive Indicator of Autologous Chondrocyte Implantation Success

BACKGROUND

Autologous chondrocyte implantation (ACI) is used worldwide in the treatment of cartilage defects in the knee. Several demographic and injury-specific risk factors have been identified that can affect the success of ACI treatment. However, the discovery of predictive biomarkers in this field has thus far been overlooked.

PURPOSE

To identify potential biomarkers in synovial fluid and plasma that can be used in the preoperative setting to help optimize patient selection for cell-based cartilage repair strategies.

STUDY DESIGN

Controlled laboratory study.

METHODS

Fifty-four ACI-treated patients were included. Cartilage oligomeric matrix protein (COMP), hyaluronan, soluble CD14 levels, and aggrecanase-1 (ADAMTS-4) activity in synovial fluid and COMP and hyaluronan in plasma were measured. Baseline and postoperative functional outcomes were determined using the patient-reported Lysholm score. To find predictors of postoperative function, linear and logistic regression analyses were performed. The dependent variables were the baseline and postoperative Lysholm score; the independent variables were patient age and body mass index, defect location, defect area, having a bone-on-bone defect, type of defect patch (periosteum or collagen), requirement of an extra procedure, and baseline biomarker levels.

RESULTS

The mean baseline Lysholm score was 47.4 ± 17.0, which improved to 64.6 ± 21.7 postoperatively. The activity of ADAMTS-4 in synovial fluid was identified as an independent predictor of the postoperative Lysholm score. Indeed, simply the presence or absence of ADAMTS-4 activity in synovial fluid appeared to be the most important predictive factor. As determined by contingency analysis, when ADAMTS-4 activity was detectable, the odds of being a responder were 3 times smaller than when ADAMTS-4 activity was not detectable. Other predictive factors were the baseline Lysholm score, age at ACI, and defect patch type used.

CONCLUSION

The absence of ADAMTS-4 activity in the synovial fluid of joints with cartilage defects may be used in conjunction with known demographic risk factors in the development of an ACI treatment algorithm to help inform the preclinical decision.

Toll-like receptors and their soluble forms differ in the knee and thumb basal osteoarthritic joints

Background and purpose - Although the pathogenesis of osteoarthritis (OA) is not well understood, chondrocyte-mediated inflammatory responses (triggered by the activation of innate immune receptors by damage-associated molecules) are thought to be involved. We examined the relationship between Toll-like receptors (TLRs) and OA in cartilage from 2 joints differing in size and mechanical loading: the first carpometacarpal (CMC-I) and the knee. Patients and methods - Samples of human cartilage obtained from OA CMC-I and knee joints were immunostained for TLRs (1-9) and analyzed using histomorphometry and principal component analysis (PCA). mRNA expression levels were analyzed with RT-PCR. Collected synovial fluid (SF) samples were screened for the presence of soluble forms of TLR2 and TLR4 by enzyme-linked immunosorbent assay (ELISA). Results - In contrast to knee OA, TLR expression in CMC-I OA did not show grade-dependent overall profile changes, but PCA revealed that TLR expression profiles clustered according to their cellular compartment organization. Protein levels of TLR4 were substantially higher in knee OA than in CMC-I OA, while the opposite was the case at the mRNA level. ELISA assays confirmed the presence of soluble forms of TLR2 and TLR4 in SF, with sTLR4 being considerably higher in CMC-I OA than in knee OA. Interpretation - We observed that TLRs are differentially expressed in OA cartilage, depending on the joint. Soluble forms of TLR2 and TLR4 were detected for the first time in SF of osteoarthritic joints, with soluble TLR4 being differentially expressed. Together, our results suggest that negative regulatory mechanisms of innate immunity may be involved in the pathomolecular mechanisms of osteoarthritis.

NEAT1/miR-181c Regulates Osteopontin (OPN)-Mediated Synoviocyte Proliferation in Osteoarthritis

Osteoarthritis (OA) is characterized by progressive destruction of articular cartilage, resulting in significant disability. Inflammatory cytokines commonly initiate the extreme changes in the synovium and cartilage microenvironment of the OA patients, subsequently resulting in cell dysfunctions, especially synoviocyte dysfunction. We revealed that the expression of osteopontin (OPN), which has been reported to regulate expression of various inflammatory factors associating with the pathogenesis of OA including matrix metalloprotease 13 (MMP13), interlukine-6 and 8 (IL-6 and IL-8), is significantly upregulated in OA tissues. In the present study, online tools were used to screen out the candidate miRNAs of OPN. Among the candidate miRNAs, miR-181c inhibited OPN mRNA expression the most strongly. Ectopic expression of miR-181c significantly repressed synoviocyte proliferation, as well as the levels of OPN, MMP13, IL-6, and IL-8. Further, the candidate lncRNAs of miR-181c were screened out by using DianaTools; among which NEAT1 showed to inversely regulate miR-181c. By performing Luciferase assays, we revealed that NEAT1 competed with OPN for miR-181c binding. After NEAT1 knockdown, MMP13, IL-6, and IL-8 expression was reduced; the synoviocyte proliferation was repressed, as well as OPN protein levels; the suppressive effect of NETA1 knockdown on synoviocyte proliferation and the indicated factors were partially reversed by miR-181c inhibition. In OA tissues, OPN mRNA, and NEAT1 expression was upregulated, whereas miR-181c expression was downregulated, indicating that targeting NEAT1 to rescue miR-181c expression so as to inhibit OPN expression and synoviocyte proliferation might be an efficient strategy for OA treatment. J. Cell. Biochem. 118: 3775-3784, 2017. © 2017 Wiley Periodicals, Inc.

Gender-specific differential expression of exosomal miRNA in synovial fluid of patients with osteoarthritis

The pathogenesis of osteoarthritis (OA) is poorly understood, and therapeutic approaches are limited to preventing progression of the disease. Recent studies have shown that exosomes play a vital role in cell-to-cell communication, and pathogenesis of many age-related diseases. Molecular profiling of synovial fluid derived exosomal miRNAs may increase our understanding of OA progression and may lead to the discovery of novel biomarkers and therapeutic targets. In this article we report the first characterization of exosomes miRNAs from human synovial fluid. The synovial fluid exosomes share similar characteristics (size, surface marker, miRNA content) with previously described exosomes in other body fluids. MiRNA microarray analysis showed OA specific exosomal miRNA of male and female OA. Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis identified gender-specific target genes/signaling pathways. These pathway analyses showed that female OA specific miRNAs are estrogen responsive and target TLR (toll-like receptor) signaling pathways. Furthermore, articular chondrocytes treated with OA derived extracellular vesicles had decreased expression of anabolic genes and elevated expression of catabolic and inflammatory genes. In conclusion, synovial fluid exosomal miRNA content is altered in patients with OA and these changes are gender specific.

Temporal Role for MyD88 in a Model of Brucella-Induced Arthritis and Musculoskeletal Inflammation

Brucella spp. are facultative intracellular Gram-negative bacteria that cause the zoonotic disease brucellosis, one of the most common global zoonoses. Osteomyelitis, arthritis, and musculoskeletal inflammation are common focal complications of brucellosis in humans; however, wild-type (WT) mice infected systemically with conventional doses of Brucella do not develop these complications. Here we report C57BL/6 WT mice infected via the footpad with 10³ to 10⁶ CFU of Brucella spp. display neutrophil and monocyte infiltration of the joint space and surrounding musculoskeletal tissue. Joint inflammation is detectable as early as 1 day postinfection and peaks 1 to 2 weeks later, after which WT mice are able to slowly resolve inflammation. B and T cells were dispensable for the onset of swelling but required for resolution of joint inflammation and infection. At early time points, MyD88^-/- mice display decreased joint inflammation, swelling, and proinflammatory cytokine levels relative to WT mice. Subsequently, swelling of MyD88^-/- joints surpassed WT joint swelling, and resolution of joint inflammation was prolonged. Joint bacterial loads in MyD88^-/- mice were significantly greater than those in WT mice by day 3 postinfection and at all time points thereafter. In addition, MyD88^-/- joint inflammatory cytokine levels on day 3 and beyond were similar to WT levels. Collectively these data demonstrate MyD88 signaling mediates early inflammatory responses in the joint but also contributes to subsequent clearance of Brucella and resolution of inflammation. This work also establishes a mouse model for studying Brucella-induced arthritis, musculoskeletal complications, and systemic responses, which will lead to a better understanding of focal complications of brucellosis.