Human chondrocytes express functional chemokine receptors and release matrix-degrading enzymes in response to C-X-C and C-C chemokines

The infrapatellar fat pad in inflammaging, knee joint health, and osteoarthritis

Osteoarthritis (OA) is the most common form of arthritis and accounts for nearly $140 billion in annual healthcare expenditures only in the United States. Obesity, aging, and joint injury are major risk factors for OA development and progression, but the mechanisms contributing to pathology remain unclear. Emerging evidence suggests that cellular dysregulation and inflammation in joint tissues, including intra-articular adipose tissue depots, may contribute to disease severity. In particular, the infrapatellar fat pad (IFP), located in the knee joint, which provides a protective cushion for joint loading, also secretes multiple endocrine factors and inflammatory cytokines (inflammaging) that can regulate joint physiology and disease. Correlates of cartilage degeneration and OA-associated disease severity include inflammation and fibrosis of IFP in model organisms and human studies. In this article, we discuss recent progress in understanding the roles and regulation of intra-articular fat tissue in regulating joint biology and OA.

The Impact of 45S5-Bioactive Glass on Synovial Cells in Knee Osteoarthritis-An In Vitro Study

Synovial inflammation in osteoarthritis (OA) is characterized by the release of cartilage-degrading enzymes and inflammatory cytokines. 45S5-bioactive glass (45S5-BG) can modulate inflammation processes; however, its influence on OA-associated inflammation has hardly been investigated. In this study, the effects of 45S5-BG on the release of cartilage-degrading metalloproteinases and cytokines from synovial membrane cells (SM) isolated from patients with knee OA was assessed in vitro. SM were cultivated as SM monocultures in the presence or absence of 45S5-BG. On day 1 (d1) and d7 (d7), the concentrations of Matrix Metalloproteinases (MMPs) and cytokines were assessed. In 45S5-BG-treated SM cultures, MMP9 concentration was significantly reduced at d1 and d7, whilst MMP13 was significantly increased at d7. Concentrations of interleukin (IL)-1B and C-C motif chemokine ligand 2 (CCL2) in 45S5-BG-treated SM cultures were significantly increased at both time points, as were interferon gamma (IFNG) and IL-6 at d7. Our data show an effect of 45S5-BG on SM activity, which was not clearly protective, anti-inflammatory, or pro-inflammatory. The influence of 45S5-BG on MMP release was more suggestive of a cartilage protective effect, but 45S5-BG also increased the release of pro-inflammatory cytokines. Further studies are needed to analyze the effect of BGs on OA inflammation, including the anti-inflammatory modification of BG compositions.

CC chemokines and receptors in osteoarthritis: new insights and potential targets

Osteoarthritis (OA) is a prevalent degenerative disease accompanied by the activation of innate and adaptive immune systems-associated inflammatory responses. Due to the local inflammation, the expression of various cytokines was altered in affected joints, including CC motif chemokine ligands (CCLs) and their receptors (CCRs). As essential members of chemokines, CCLs and CCRs played an important role in the pathogenesis and treatment of OA. The bindings between CCLs and CCRs on the chondrocyte membrane promoted chondrocyte apoptosis and the release of multiple matrix-degrading enzymes, which resulted in cartilage degradation. In addition, CCLs and CCRs had chemoattractant functions to attract various immune cells to osteoarthritic joints, further leading to the aggravation of local inflammation. Furthermore, in the nerve endings of joints, CCLs and CCRs, along with several cellular factors, contributed to pain hypersensitivity by releasing neurotransmitters in the spinal cord. Given this family's diverse and complex functions, targeting the functional network of CCLs and CCRs is a promising strategy for the prognosis and treatment of OA in the future.

Randomized, double-blind, four-arm pilot study on the effects of chicken essence and type II collagen hydrolysate on joint, bone, and muscle functions

BACKGROUND

Knee osteoarthritis (OA) is a leading cause of disability among older adults. Medical and surgical treatments are costly and associated with side effects. A natural nutraceutical, collagen hydrolysate, has received considerable attention due to its relieving effects on OA-associated symptoms. This study investigated the effects of hydrolyzed collagen type II (HC-II) and essence of chicken (BRAND'S Essence of Chicken) with added HC-II (EC-HC-II) on joint, muscle, and bone functions among older adults with OA.

METHODS

Patients (n = 160) with grade 1-3 knee OA according to the Kellgren-Lawrence classification system, joint pain for ≥ 3 months, and a Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score of > 6 were randomly assigned with equal probability to consume EC-HC-II, HC-II, glucosamine HCl, or a placebo for 24 weeks in combination with resistance training. Outcome measurements were WOMAC score, visual analogue scale (VAS) pain score, grip strength, fat-free mass (FFM), and bone mass.

RESULTS

All groups exhibited similar levels of improvement in WOMAC index scores after 24 weeks. HC-II significantly reduced VAS pain score by 0.9 ± 1.89 (p = 0.034) after 14 days. A repeated-measures analysis of variance showed that HC-II reduced pain levels more than the placebo did (mean ± standard error: - 1.3 ± 0.45, p = 0.021) after 14 days; the EC-HC-II group also had significantly higher FFM than the glucosamine HCl (p = 0.02) and placebo (p = 0.017) groups and significantly higher grip strength than the glucosamine HCl group (p = 0.002) at 24 weeks.

CONCLUSION

HC-II reduces pain, and EC-HC-II may improve FFM and muscle strength. This suggests that EC-HC-II may be a novel holistic solution for mobility by improving joint, muscle, and bone health among older adults. Large-scale studies should be conducted to validate these findings.

TRIAL REGISTRATION

This trial was retrospectively registered at ClinicalTrials.gov (NCT04483024).

Genetically predicted circulating levels of cytokines and the risk of osteoarthritis: A mendelian randomization study

Background: The association between inflammatory cytokines and osteoarthritis (OA) has been reported in several observational studies, but the causal relationship between these two remains unknown. Hence, we performed this two-sample Mendelian randomization (MR) to confirm the causal relationship between circulating levels of inflammatory factors and osteoarthritis risk.

Method: We used genetic variants associated with cytokine circulation levels from a meta-analysis of genome-wide association studies (GWASs) in 8,293 Finns as instrumental variables and obtained OA data from the United Kingdom Biobank, including a total of 345,169 subjects of European ancestry (66,031 diagnosed OA cases and 279,138 controls). Inverse variance weighting (IVW), MR-Egger, Wald Ratio, weighted median, and MR multiplicity residual sums with outliers (MR-PRESSO) were used.

Result: We found a causal relationship between circulating levels of macrophage inflammatory protein-1beta (MIP-1β) and risk of OA (OR = 0.998, 95% CI = 0.996–0.999p = 9.61 × 10−5); tumour necrosis factor beta (TNF-β) was also causally associated with risk of OA (OR = 0.996,95%CI = 0.994–0.999, p = 0.002); finally we found a suggestive association between C-C motif chemokine ligand 5(CCL5, also called Rantes) and OA risk (OR = 1.013, 95%CI = 1.002–1.024,p = 0.016).

Conclusion: Our findings offer promising leads for the development of new therapeutic targets in the treatment of osteoarthritis. By identifying the role of inflammatory cytokines in this debilitating condition through a genetic epidemiological approach, our study contributes to a better understanding of the underlying disease mechanisms. These insights may ultimately pave the way for more effective treatments that improve patient outcomes.

Soluble and EV-Associated Diagnostic and Prognostic Biomarkers in Knee Osteoarthritis Pathology and Detection

Osteoarthritis (OA) is the most common degenerative disease of the connective tissue of the human musculoskeletal system. Despite its widespread prevalence, there are many limitations in its diagnosis and treatment. OA diagnosis currently relies on the presence of clinical symptoms, sometimes accompanied by changes in joint X-rays or MRIs. Biomarkers help not only to diagnose early disease progression but also to understand the process of OA in many ways. In this article, we briefly summarize information on articular joints and joint tissues, the pathogenesis of OA and review the literature about biomarkers in the field of OA, specifically inflammatory cytokines/chemokines, proteins, miRNA, and metabolic biomarkers found in the blood, synovial fluid and in extracellular vesicles.

Senescence in osteoarthritis: from mechanism to potential treatment

Osteoarthritis (OA) is an age-related cartilage degenerative disease, and chondrocyte senescence has been extensively studied in recent years. Increased numbers of senescent chondrocytes are found in OA cartilage. Selective clearance of senescent chondrocytes in a post-traumatic osteoarthritis (PTOA) mouse model ameliorated OA development, while intraarticular injection of senescent cells induced mouse OA. However, the means and extent to which senescence affects OA remain unclear. Here, we review the latent mechanism of senescence in OA and propose potential therapeutic methods to target OA-related senescence, with an emphasis on immunotherapies. Natural killer (NK) cells participate in the elimination of senescent cells in multiple organs. A relatively comprehensive discussion is presented in that section. Risk factors for OA are ageing, obesity, metabolic disorders and mechanical overload. Determining the relationship between known risk factors and senescence will help elucidate OA pathogenesis and identify optimal treatments.

Identification of thrombin as a key regulator of chondrocyte catabolic activity through RNA-Seq and experimental verification

The present study was designed to explore the relationship between thrombin and catabolic activity in chondrocytes. Primary rat chondrocytes were cultured for 24 h with rat serum (RS), rat plasma (RP), or rat plasma supplemented with thrombin (RPT). RNA-sequencing was then performed. Cell proliferation was analyzed by EdU uptake, CCK-8 assays and protein-protein interaction (PPI) network of proliferation-related genes. Heatmaps were used to visualize differences in gene expression. Gene Ontology (GO) enrichment analyses of up- and down-regulated differentially expressed genes were conducted. Molecular probes were used to label the endoplasmic reticulum in chondrocytes from three treatment groups. Immunofluorescence and Safranin O staining were used to assess type II collagen (Col2a1) expression and proteoglycan synthesis, whereas Lox expression was assessed by immunocytochemistry. The expression of enzymes involved in the synthesis and maturation of extracellular matrix (ECM) components and chemokines were measured by qPCR while matrix metalloproteinases (MMPs) levels were evaluated by Western blotting. Relevant nodules were selected through further PPI network analyses. A total of 727 and 1162 genes were up- and down-regulated based on the Venn diagrams comparison among groups. Thrombin was thus able to promote chondrocyte proliferation and a shift towards fibrotic morphology, while upregulating MMPs and chemokines linked to ECM degradation. In addition, thrombin decreased the enzyme expression involved in the synthesis and maturation of ECM.

Dynamics of local gene regulations in synovial fluid leukocytes from horses with lipopolysaccharide-induced arthritis

The role of resident cells such a synoviocytes and chondrocytes in intra-articular inflammation is well-characterized, however the in vivo gene expression patterns of cells (predominantly leukocytes) in the synovial fluid (SF) of an inflamed joint have never previously been investigated. The aim of this study was to investigate gene expression in SF leukocytes from the inflamed joint cavity after intra-articular lipopolysaccharide (LPS) injection in horses to improve our understanding of the temporal regulation of the intra-articular inflammatory response. Gene expression was investigated in SF samples available from six horses 2, 4, 8 16 and 24 h after experimental induction of inflammation in the radiocarpal joint by lipopolysaccharide (LPS) injection. Leukocytic expression of 43 inflammation-related genes was studied using microfluidic high throughput qPCR (Fluidigm®). Expression of 26 genes changed significantly over the 24 h study period, including pro- and anti-inflammatory genes such as interleukin (IL)1, IL6, tumor necrosis factor (TNF), cyclooxygenase 2 (COX2), IL1 receptor antagonist (IL1RN), IL10, and superoxide dismutase 2 (SOD2), chemokine genes, apoptosis-related genes, and genes related to cartilage turnover (matrix metalloproteinase 8 and tissue inhibitor of metalloproteinase 1). The inflammatory responses appeared to be regulated, as an early increase (at 2 h) in expression of the pro-inflammatory genes IL1, IL6, TNF and COX2 was rapidly followed by increased expression (at 4 h) of several anti-inflammatory genes (IL10, IL1RN and SOD2). Similarly, both pro- and anti-apoptotic gene expression as well as expression of chondrodegenerative and chondroprotective genes were activated in SF leukocytes. Thus, the inflammatory response in leukocytes infiltrating the joint in the acute stage of arthritis was well orchestrated in this single-hit LPS-induced arthritis model. This study is the first to describe gene expression patterns in SF-derived leukocytes in vivo during severe joint inflammation, and the results thus expand our knowledge of basic inflammatory mechanisms in the early local response in an inflamed joint.

Senescent Tissue-Resident Mesenchymal Stromal Cells Are an Internal Source of Inflammation in Human Osteoarthritic Cartilage

Human osteoarthritic cartilage contains not only chondrocytes (OACs), but also mesenchymal stromal cells (OA-MSCs), whose abundance increases during osteoarthritis (OA). However, it is not clear how OA-MSC contributes to OA pathogenesis. Here, we show that aging OA-MSC plays an important role in cell senescence, fibrosis, and inflammation in cartilage. Protein array analysis indicates that OA-MSC expresses pro-inflammatory senescence associated secretory phenotype (SASP) including IL-1β, IL-6, IL-8, and CXCL1, 5, and 6, which play key roles in OA pathogenesis. OAC is a main recipient of the inflammatory signals by expressing receptors of cytokines. RNAseq analysis indicates that the transition from normal cartilage stromal cells (NCSCs) to OA-MSC during aging results in activation of SASP gene expression. This cell transition process can be recapitulated by a serial passage of primary OAC in cell culture comprising (1) OAC dedifferentiation into NCSC-like cells, and (2) its subsequent senescence into pro-inflammatory OA-MSC. While OAC dedifferentiation is mediated by transcriptional repression of chondrogenic gene expression, OA-MSC senescence is mediated by transcriptional activation of SASP gene expression. We postulate that, through replication-driven OAC dedifferentiation and mesenchymal stromal cell (MSC) senescence, OA-MSC becomes an internal source of sterile inflammation in human cartilage joint.

Cytokines and Chemokines Involved in Osteoarthritis Pathogenesis

Osteoarthritis is a common cause of disability worldwide. Although commonly referred to as a disease of the joint cartilage, osteoarthritis affects all joint tissues equally. The pathogenesis of this degenerative process is not completely understood; however, a low-grade inflammation leading to an imbalance between anabolic and katabolic processes is a well-established factor. The complex network of cytokines regulating these processes and cell communication has a central role in the development and progression of osteoarthritis. Concentrations of both proinflammatory and anti-inflammatory cytokines were found to be altered depending on the osteoarthritis stage and activity. In this review, we analyzed individual cytokines involved in the immune processes with an emphasis on their function in osteoarthritis.

Low-dose radiation therapy for osteoarthritis and enthesopathies: a review of current data

BACKGROUND

Osteoarthritis (OA), the most common degenerative joint disease, is associated with severe functional limitation and impairment of quality of life. Numerous reports have documented the clinical efficacy of low-dose radiotherapy (LD-RT) in the management of various inflammatory disorders, including OA. In this paper, we assessed the clinical literature involving the use of LD-RT in the treatment of OA, its dose-response features, possible underlying mechanistic features, and optimal therapeutic dose range.

METHODS

We carried out a systematic review based on the guidelines of the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) statements and evaluated articles meeting the inclusion criteria for this review.

RESULTS

A total of 361 articles were identified from databases, such as Scopus, PubMed, Embase, and Science Direct out of which 224 articles were duplicates and were discarded. Of the remaining 137 articles, 74 articles were un-related, 27 articles were review articles, eight were conference abstracts, three were letters, two were editorials, two were notes, and one was a book chapter. Finally, 20 articles met all the inclusion criteria and were included in this systematic review.

DISCUSSION

Several single-arm retrospective/prospective studies showed advantages for LD-RT in the management of OA in terms of pain relief, improvement of mobility and function, and showed minimal side effects. Mechanistic considerations involve positive subcellular effects mediated by the activation of a nuclear factor erythroid 2-related transcription factor (Nrf2) mediated antioxidant response. Further research on both the short- and long-term effects of LD-RT on OA and other inflammatory disorders is recommended.

Chemokine-like factor-like MARVEL transmembrane domain-containing family in autoimmune diseases

The chemokine-like factor (CKLF)-like MARVEL transmembrane domain-containing family (CMTM) is widely expressed in the immune system. Abnormal expression of CMTM is associated with the development of various diseases. This article summarizes the relevant research on the role of the CMTM family in immune disorders. This information will increase our understanding of pathogenesis and identify promising targets for the diagnosis and treatment of autoimmune diseases. The CMTM family is highly expressed in peripheral blood mononuclear cells. CKLF1 may be involved in the development of arthritis through its interaction with C-C chemokine receptor 4. CKLF1 is associated with the pathogenesis of lupus nephritis and psoriasis. Both CMTM4 and CMTM5 are associated with the pathogenesis of systemic lupus erythematosus. CMTM1, CMTM2, CMTM3, and CMTM6 play a role in rheumatoid arthritis, systemic sclerosis, Sjögren syndrome, and anti-phospholipid syndrome, respectively. The CMTM family has been implicated in various autoimmune diseases. Further research on the mechanism of the action of CMTM family members may lead to the development of new treatment strategies for autoimmune diseases.

Correlation between osteoarthritis and monocyte chemotactic protein-1 expression: a meta-analysis

Objective

We evaluated the association between monocyte chemotactic protein-1 (MCP-1) and osteoarthritis.

Methods

We searched PubMed, Cochrane Library, Embase, Web of Science, China National Knowledge Infrastructure (CNKI), VIP (Chinese database), and Wan Fang (Chinese database) (before May 10, 2020), with no language limitations. STATA version 12.0 and Revman version 5.3 were used for data analysis. The standard mean difference (SMD) and corresponding 95% confidence intervals (95% CIs) were calculated. Nine clinical studies, including 376 patients with osteoarthritis and 306 healthy controls, were evaluated.

Results

The combined SMDs of MCP-1 expression levels suggested that MCP-1 expression was significantly higher in patients with osteoarthritis than healthy controls (SMD = 1.97, 95% CI = 0.66–3.28, p = 0.003). Moreover, subgroup analysis implied that osteoarthritis patients from both Asians and mixed populations had higher MCP-1 expression levels than controls, whereas Caucasians did not (p > 0.05). Serum MCP-1 levels (SMD = 2.83, 95% CI = 1.07–4.6, p < 0.00001) were significantly higher in patients with osteoarthritis than in controls; however, this difference was not significant in synovial fluid and cartilage tissue. Subgroup analysis for ethnicity showed that MCP-1 levels were significantly higher in Chinese, Dutch, and Brazilian patients with osteoarthritis than in control groups, although significant differences were not observed for American and Italian subgroups.

Conclusions

Our meta-analysis demonstrated that MCP-1 expression levels were higher in patients with osteoarthritis than in healthy controls and that MCP-1 may play important roles in the progression of osteoarthritis. Serum MCP-1 levels may serve as a potential biomarker for the diagnosis of osteoarthritis.

Clinical Application of the Basic Science of Articular Cartilage Pathology and Treatment

The joint is an organ with each tissue playing critical roles in health and disease. Intact articular cartilage is an exquisite tissue that withstands incredible biologic and biomechanical demands in allowing movement and function, which is why hyaline cartilage must be maintained within a very narrow range of biochemical composition and morphologic architecture to meet demands while maintaining health and integrity. Unfortunately, insult, injury, and/or aging can initiate a cascade of events that result in erosion, degradation, and loss of articular cartilage such that joint pain and dysfunction ensue. Importantly, articular cartilage pathology affects the health of the entire joint and therefore should not be considered or addressed in isolation. Treating articular cartilage lesions is challenging because left alone, the tissue is incapable of regeneration or highly functional and durable repair. Nonoperative treatments can alleviate symptoms associated with cartilage pathology but are not curative or lasting. Current surgical treatments range from stimulation of intrinsic repair to whole-surface and whole-joint restoration. Unfortunately, there is a relative paucity of prospective, randomized controlled, or well-designed cohort-based clinical trials with respect to cartilage repair and restoration surgeries, such that there is a gap in knowledge that must be addressed to determine optimal treatment strategies for this ubiquitous problem in orthopedic health care. This review article discusses the basic science rationale and principles that influence pathology, symptoms, treatment algorithms, and outcomes associated with articular cartilage defects in the knee.

Anti-Inflammatory Effect of Carprofen Is Enhanced by Avocado/Soybean Unsaponifiables, Glucosamine and Chondroitin Sulfate Combination in Chondrocyte Microcarrier Spinner Culture

OBJECTIVE

Osteoarthritis is a painful, chronic joint disease affecting man and animals with no known curative therapies. Palliative nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly used but they cause adverse side effects prompting the search for safer alternatives. To address this need, we evaluated the anti-inflammatory activity of avocado/soybean unsaponifiables (ASU), glucosamine (GLU), and chondroitin sulfate (CS) with or without the NSAID carprofen.

DESIGN

Canine chondrocytes were propagated in microcarrier spinner culture and incubated with (1) control medium, (2) ASU (8.3 µg/mL) + GLU (11 µg/mL) + CS (20 µg/mL) combination for 24 hours; and/or carprofen (40 ng/mL). Cultures were next incubated with control medium alone or IL-1β (10 ng/mL) for another 24 hours. Production of PGE2, IL-6, IL-8, and MCP-1 (also known as CCL-2) were measured by ELISA.

RESULTS

Chondrocytes proliferated in microcarrier spinner culture and produced type II collagen and aggrecan. Stimulation with IL-1β induced significant increases in PGE2, IL-6, IL-8, and MCP-1 production. The increases in production were suppressed by carprofen as well as [ASU+GLU+CS]. The combination of carprofen and [ASU+GLU+CS] reduced PGE2 production significantly more than either preparation alone. The inhibitory effect of carprofen on IL-6, IL-8, and MCP-1 production was significantly less than that of [ASU+GLU+CS], whereas the combination did not reduce the production of these molecules significantly more than [ASU+GLU+CS] alone.

CONCLUSIONS

The potentiating effect of [ASU+GLU+CS] on low-dose carprofen was identified in chondrocyte microcarrier spinner cultures. Our results suggest that the combination of low-dose NSAIDs like carprofen with [ASU+GLU+CS] could offer a safe, effective management for joint pain.

Articular cartilage regeneration: The role of endogenous mesenchymal stem/progenitor cell recruitment and migration

BACKGROUND

Trauma- or osteoarthritis-related cartilage damage resulted in functional decline of joints and heavy burden of public health. Recently, the reparative role of mesenchymal stem/progenitor cells (MSCs) in articular cartilage (AC) reconstruction is drawing more and more attention.

OBJECTIVE

To provide a review on (1) the locations and categories of joint-resident MSCs, (2) the regulation of chondrogenic capacities of MSCs, (3) the migratory approaches of MSCs to diseased AC and regulatory mechanisms.

METHODS

PubMed and Web of Science were searched for English-language articles related to MSC recruitment and migration for AC repair until June 2019. The presence of various MSCs in or around joints, the potential approaches to diseased AC` and the regenerative capacities of MSCs were reviewed.

RESULTS

Various intra- and peri-articular MSCs, with inherent migratory potentials, are present in multiple stem cell niches in or around joints. The recruitment and migration of joint-resident MSCs play crucial roles in endogenous AC repair. Multiple recruiting signals, such as chemokines, growth factors, etc., emerge during the development of AC diseases and participate in the regulation of MSC mobilization. Motivated MSCs could migrate into cartilage lesions and then exert multiple reparative potentials, including extracellular matrix (ECM) reconstruction and microenvironment modulation.

CONCLUSION

In general, AC repair based on endogenous MSC recruitment and migration is a feasible strategy, and a promising research field. Furthermore, endogenous AC repair mediated by native MSCs would provide new opportunities to efficient preventative or therapeutic options for AC diseases.

Polyamine supplementation reduces DNA damage in adipose stem cells cultured in 3-D

According to previous research, natural polyamines exert a role in regulating cell committment and differentiation from stemness during skeletal development. In order to assess whether distinct polyamine patterns are associated with different skeletal cell types, primary cultures of stem cells, chondrocytes or osteoblasts were dedicated for HPLC analysis of intracellular polyamines. Spermine (SPM) and Spermidine (SPD) levels were higher in adipose derived stem cells (ASC) compared to mature skeletal cells, i.e. chondrocytes and osteoblasts, confirming the connection of polyamine content with stemness. To establish whether polyamines can protect ASC against oxidative DNA damage in a 3-D differentiation model, the level of γH2AX was measured by western blot, and found to correlate with age and BMI of patients. Addition of either polyamine to ASC was able to hinder DNA damage in the low micromolecular range, with marked reduction of γH2AX level at 10 µM SPM and 5 µM SPD. Molecular analysis of the mechanisms that might underlie the protective effect of polyamine supplementation evidences a possible involvement of autophagy. Altogether, these results support the idea that polyamines are able to manage both stem cell differentiation and cell oxidative damage, and therefore represent appealing tools for regenerative and cell based applications.

Long Non-coding RNA HOTTIP Promotes CCL3 Expression and Induces Cartilage Degradation by Sponging miR-455-3p

Long non-coding RNAs (lncRNAs) play pivotal roles in diseases such as osteoarthritis (OA). However, knowledge of the biological roles of lncRNAs is limited in OA. We aimed to explore the biological function and molecular mechanism of HOTTIP in chondrogenesis and cartilage degradation. We used the human mesenchymal stem cell (hMSC) model of chondrogenesis, in parallel with, tissue biopsies from normal and OA cartilage to detect HOTTIP, CCL3, and miR-455-3p expression in vitro. Biological interactions between HOTTIP and miR-455-3p were determined by RNA silencing and overexpression in vitro. We evaluated the effect of HOTTIP on chondrogenesis and degeneration, and its regulation of miR-455-3p via competing endogenous RNA (ceRNA). Our in vitro ceRNA findings were further confirmed within animal models in vivo. Mechanisms of ceRNAs were determined by bioinformatic analysis, a luciferase reporter system, RNA pull-down, and RNA immunoprecipitation (RIP) assays. We found reduced miR-455-3p expression and significantly upregulated lncRNA HOTTIP and CCL3 expression in OA cartilage tissues and chondrocytes. The expression of HOTTIP and CCL3 was increased in chondrocytes treated with interleukin-1β (IL-1β) in vitro. Knockdown of HOTTIP promoted cartilage-specific gene expression and suppressed CCL3. Conversely, HOTTIP overexpression reduced cartilage-specific genes and increased CCL3. Notably, HOTTIP negatively regulated miR-455-3p and increased CCL3 levels in human primary chondrocytes. Mechanistic investigations indicated that HOTTIP functioned as ceRNA for miR-455-3p enhanced CCL3 expression. Taken together, the ceRNA regulatory network of HOTTIP/miR-455-3p/CCL3 plays a critical role in OA pathogenesis and suggests HOTTIP is a potential target in OA therapy.

Calorie restriction with regular chow, but not a high-fat diet, delays onset of spontaneous osteoarthritis in the Hartley guinea pig model

BACKGROUND

Obesity is a leading risk factor for osteoarthritis (OA). In contrast, calorie restriction (CR) may lessen OA due to improved systemic inflammatory status and reduced weight-bearing. The aim of this study was to determine how CR with regular chow versus a high-fat diet (HFD) alters OA progression using the Hartley guinea pig model of disease.

METHODS

Twenty-four male guinea pigs were allocated to four groups at 2 months of age: (1) ad libitum regular chow (obese), (2) CR regular chow (lean), (3) ad libitum HFD, and (4) CR HFD. Animals in both HFD groups ate identical amounts and were combined into one HFD group for analyses. At 5 months, hind limbs were harvested for microcomputed tomography (microCT) and histopathologic evaluation of knee OA. Total body, gonad fat, and infrapatellar fat pad (IFP) masses were recorded. IFPs were collected for gene expression analysis. Immunohistochemistry for monocyte chemoattractant protein-1 (MCP-1) was performed on intact joints. Serum was utilized for protein C3 measurement. All data were compared using ordinary one-way ANOVA analyses with Tukey's post-hoc tests.

RESULTS

Body mass in the lean and HFD groups were similar and lower than the obese group. Despite this, gonad fat pads in the HFD group were comparable to the obese group. MicroCT and histologic OA scores were similar in obese and HFD groups; both scores were significantly lower in the lean group. Obese and HFD groups displayed increased gene expression of pro-inflammatory and catabolic mediators in IFPs relative to lean animals. Consistent with this, immunohistochemistry for MCP-1 in knee joints demonstrated strong positive staining in obese and HFD groups but was minimally detected in lean animals. Serum protein C3 levels were also statistically higher.

CONCLUSIONS

This study demonstrated that CR with a regular chow diet lessened knee OA in the Hartley guinea pig and was associated with decreased local and systemic inflammation compared to obese animals. HFD animals, although under CR conditions, had OA scores and inflammatory markers similar to obese animals. Thus, diet composition, and not solely body weight, may be a key factor in development of OA.

Time-dependent changes in gene expression induced in vitro by interleukin-1β in equine articular cartilage

Osteoarthritis is an inflammatory and degenerative joint disease commonly affecting horses. To identify genes of relevance for cartilage pathology in osteoarthritis we studied the time-course effects of interleukin (IL)-1β on equine articular cartilage. Articular cartilage explants from the distal third metacarpal bone were collected postmortem from three horses without evidence of joint disease. The explants were stimulated with IL-1β for 27 days and global gene expression was measured by microarray. Gene expression was compared to that of unstimulated explants at days 3, 9, 15, 21 and 27. Release of inflammatory proteins was measured using Proximity Extension Assay. Stimulation with IL-1β led to time-dependent changes in gene expression related to inflammation, the extracellular matrix (ECM), and phenotypic alterations. Gene expression and protein release of cytokines, chemokines, and matrix-degrading enzymes increased in the stimulated explants. Collagen type II was downregulated from day 15, whereas other ECM molecules were downregulated earlier. In contrast molecules involved in ECM signaling (perlecan, chondroitin sulfate proteoglycan 4, and syndecan 4) were upregulated. At the late time points, genes related to a chondrogenic phenotype were downregulated, and genes related to a hypertrophic phenotype were upregulated, suggesting a transition towards hypertrophy later in the culturing period. The data suggest that this in vitro model mimics time course events of in vivo inflammation in OA and it may be valuable as an in vitro tool to test treatments and to study disease mechanisms.

CXCL10 is upregulated in synovium and cartilage following articular fracture

The objective of this study was to investigate the expression of the chemokine CXCL10 and its role in joint tissues following articular fracture. We hypothesized that CXCL10 is upregulated following articular fracture and contributes to cartilage degradation associated with post-traumatic arthritis (PTA). To evaluate CXCL10 expression following articular fracture, gene expression was quantified in synovial tissue from knee joints of C57BL/6 mice that develop PTA following articular fracture, and MRL/MpJ mice that are protected from PTA. CXCL10 protein expression was assessed in human cartilage in normal, osteoarthritic (OA), and post-traumatic tissue using immunohistochemistry. The effects of exogenous CXCL10, alone and in combination with IL-1, on porcine cartilage explants were assessed by quantifying the release of catabolic mediators. Synovial tissue gene expression of CXCL10 was upregulated by joint trauma, peaking one day in C57BL/6 mice (25-fold) versus 3 days post-fracture in MRL/MpJ mice (15-fold). CXCL10 protein in articular cartilage was most highly expressed following trauma compared with normal and OA tissue. In a dose dependent manner, exogenous CXCL10 significantly reduced total matrix metalloproteinase (MMP) and aggrecanase activity of culture media from cartilage explants. CXCL10 also trended toward a reduction in IL-1α-stimulated total MMP activity (p = 0.09) and S-GAG (p = 0.09), but not NO release. In conclusion, CXCL10 was upregulated in synovium and chondrocytes following trauma. However, exogenous CXCL10 did not induce a catabolic response in cartilage. CXCL10 may play a role in modulating the chondrocyte response to inflammatory stimuli associated with joint injury and the progression of PTA. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1220-1227, 2018.

Emerging Players at the Intersection of Chondrocyte Loss of Maturational Arrest, Oxidative Stress, Senescence and Low-Grade Inflammation in Osteoarthritis

The prevalence of Osteoarthritis (OA) is increasing because of the progressive aging and unhealthy lifestyle. These risk factors trigger OA by removing constraints that keep the tightly regulated low turnover of the extracellular matrix (ECM) of articular cartilage, the correct chondrocyte phenotype, and the functionality of major homeostatic mechanisms, such as mitophagy, that allows for the clearance of dysfunctional mitochondria, preventing increased production of reactive oxygen species, oxidative stress, and senescence. After OA onset, the presence of ECM degradation products is perceived as a “danger” signal by the chondrocytes and the synovial macrophages that release alarmins with autocrine/paracrine effects on the same cells. Alarmins trigger innate immunity in the joint, with important systemic crosstalks that explain the beneficial effects of dietary interventions and improved lifestyle. Alarmins also boost low-grade inflammation: the release of inflammatory molecules and chemokines sustained by continuous triggering of NF-κB within an altered cellular setting that allows its higher transcriptional activity. Chemokines exert pleiotropic functions in OA, including the recruitment of inflammatory cells and the induction of ECM remodeling. Some chemokines have been successfully targeted to attenuate structural damage or pain in OA animal models. This represents a promising strategy for the future management of human OA.

The Multifunctional Role of the Chemokine System in Arthritogenic Processes

PURPOSE OF REVIEW

The involvement of chemokines and their receptors in the genesis and perpetuation of rheumatoid arthritis, spondyloarthritis, and osteoarthritis has been clearly recognized for a long time. Nevertheless, the complexity of their contribution to these diseases is now becoming evident and this review focuses on published evidence on their mechanism of action.

RECENT FINDINGS

Studies performed on patients and in vivo models have identified a number of chemokine-mediated pathways involved in various aspects of arthritogenic processes. Chemokines promote leukocyte infiltration and activation, angiogenesis, osteoclast differentiation, and synoviocyte proliferation and activation and participate to the generation of pain by regulating the release of neurotransmitters. A number of chemokines are expressed in a timely controlled fashion in the joint during arthropathies, regulating all the aspects of inflammation as well as the equilibrium between damage and repair and between relief and pain. Thus, the targeting of specific chemokine/chemokine receptor interactions is considered a promising tool for therapeutic intervention.

Chemokines and inflammation in osteoarthritis: Insights from patients and animal models

Evidence has been building that the pathologic drive for development of osteoarthritis (OA) involves more than simple mechanical "wear and tear." Inflammatory mechanisms play an important role in the tissue response to joint injury, and are involved in development of post-traumatic OA. Inflammation also appears integral to the progression of OA, whether post-traumatic or spontaneous, contributing to the evolution of joint tissue degradation and remodeling as well as joint pain. Both patient-based studies and in vivo models of disease have shed light on a number of inflammatory pathways and mediators that impact various aspects of this disease, both structurally and symptomatically. Recent work in this field has implicated inflammatory chemokines in osteoarthritis pathogenesis. Expression of multiple chemokines and their receptors is modulated during disease in both patients and animal models. Although best known for their effects on leukocyte migration and trafficking within the immune system, chemokines can have a wide variety of effects on both motile and non-motile cell types, impacting proliferation, differentiation, and activation of cellular responses. Their role in OA models has also demonstrated diverse effects on disease that exemplify their wide-ranging effects. Understanding how these important mediators of inflammation impact joint disease, and whether they can be targeted therapeutically, is actively being investigated by many groups in this field. This narrative review focuses on evidence published within the last 5 years highlighting chemokine-mediated pathways with mechanistic involvement in osteoarthritis and joint tissue repair. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:735-739, 2017.

Blood chemokine profile in untreated early rheumatoid arthritis: CXCL10 as a disease activity marker

Background

We have recently analyzed the profile of T-cell subtypes based on chemokine receptor expression in blood from untreated early rheumatoid arthritis (ueRA) patients compared to healthy controls (HC). Here, we compared the levels of the respective chemokines in blood plasma of ueRA patients with those of HC. We also studied the association of chemokine levels with the proportions of circulating T-cell subsets and the clinical disease activity.

Methods

Peripheral blood was obtained from 43 patients with ueRA satisfying the ACR 2010 criteria and who had not received any disease-modifying anti-rheumatic drugs (DMARD) or prednisolone, and from 14 sex- and age-matched HC. Proportions of T helper cells in blood, including Th0, Th1, Th2, Th17, Th1Th17, TFh, and regulatory T cells, were defined by flow cytometry. Fifteen chemokines, including several CXCL and CCL chemokines related to the T-cell subtypes as well as to other major immune cells, were measured in blood plasma using flow cytometry bead-based immunoassay or ELISA. Clinical disease activity in patients was evaluated by assessing the following parameters: Disease Activity Score in 28 joints (DAS28), Clinical Disease Activity Index (CDAI), swollen joint counts (SJC), tender joint counts (TJC), C-reactive protein (CRP), and erythrocyte sedimentation rate (ESR). The data were analyzed using multivariate factor analyses followed by univariate analyses.

Results

Multivariate discriminant analysis showed that patients with ueRA were separated from HC based on the blood plasma chemokine profile. The best discriminators were CXCL9, CXCL10, CXCL13, CCL4, and CCL22, which were significantly higher in ueRA compared to HC in univariate analyses. Among the chemokines analyzed, only CXCL10 correlated with multiple disease activity measures, including DAS28-CRP, DAS28-ESR, CDAI, SJC in 66 joints, CRP, and ESR.

Conclusions

High circulating levels of CXCL10 in the plasma of ueRA patients and the association with the clinical disease activity suggests that CXCL10 may serve as a disease activity marker in early rheumatoid arthritis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-017-1224-1) contains supplementary material, which is available to authorized users.

Low-grade inflammation as a key mediator of the pathogenesis of osteoarthritis

Osteoarthritis (OA) has long been viewed as a degenerative disease of cartilage, but accumulating evidence indicates that inflammation has a critical role in its pathogenesis. Furthermore, we now appreciate that OA pathogenesis involves not only breakdown of cartilage, but also remodelling of the underlying bone, formation of ectopic bone, hypertrophy of the joint capsule, and inflammation of the synovial lining. That is, OA is a disorder of the joint as a whole, with inflammation driving many pathologic changes. The inflammation in OA is distinct from that in rheumatoid arthritis and other autoimmune diseases: it is chronic, comparatively low-grade, and mediated primarily by the innate immune system. Current treatments for OA only control the symptoms, and none has been FDA-approved for the prevention or slowing of disease progression. However, increasing insight into the inflammatory underpinnings of OA holds promise for the development of new, disease-modifying therapies. Indeed, several anti-inflammatory therapies have shown promise in animal models of OA. Further work is needed to identify effective inhibitors of the low-grade inflammation in OA, and to determine whether therapies that target this inflammation can prevent or slow the development and progression of the disease.

A homeostatic function of CXCR2 signalling in articular cartilage

OBJECTIVE

ELR+ CXC chemokines are heparin-binding cytokines signalling through the CXCR1 and CXCR2 receptors. ELR+ CXC chemokines have been associated with inflammatory arthritis due to their capacity to attract inflammatory cells. Here, we describe an unsuspected physiological function of these molecules in articular cartilage homeostasis.

METHODS

Chemokine receptors and ligands were detected by immunohistochemistry, western blotting and RT-PCR. Osteoarthritis was induced in wild-type and CXCR2(-/-) mice by destabilisation of the medial meniscus (DMM). CXCR1/2 signalling was inhibited in vitro using blocking antibodies or siRNA. Chondrocyte phenotype was analysed using Alcian blue staining, RT-PCR and western blotting. AKT phosphorylation and SOX9 expression were upregulated using constitutively active AKT or SOX9 plasmids. Apoptosis was detected by terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) assay.

RESULTS

CXCL6 was expressed in healthy cartilage and was retained through binding to heparan sulfate proteoglycans. CXCR2(-/-) mice developed more severe osteoarthritis than wild types following DMM, with increased chondrocyte apoptosis. Disruption of CXCR1/2 in human and CXCR2 signalling in mouse chondrocytes led to a decrease in extracellular matrix production, reduced expression of chondrocyte differentiation markers and increased chondrocyte apoptosis. CXCR2-dependent chondrocyte homeostasis was mediated by AKT signalling since forced expression of constitutively active AKT rescued the expression of phenotypic markers and the apoptosis induced by CXCR2 blockade.

CONCLUSIONS

Our study demonstrates an important physiological role for CXCR1/2 signalling in maintaining cartilage homeostasis and suggests that the loss of ELR+ CXC chemokines during cartilage breakdown in osteoarthritis contributes to the characteristic loss of chondrocyte phenotypic stability.

IL-36α: a novel cytokine involved in the catabolic and inflammatory response in chondrocytes

Recent studies confer to IL-36α pro-inflammatory properties. However, little is known about the expression and function of IL-36α in cartilage. This study sought to analyze the expression of IL-36α in healthy and OA cartilage. Next, we determined the effects of recombinant IL-36α on catabolism and inflammation in chondrocytes. For completeness, part of the signaling pathway elicited by IL-36α was also explored. IL-36α expression was evaluated by immunohistochemistry and RT-qPCR. Expression of MMP-13, NOS2 and COX-2 was also determined in OA articular chondrocytes treated with recombinant IL-36α. IκB-α and P-p38 was explored by western blot. We observed a low constitutive expression of IL-36α in healthy human chondrocytes. However, OA chondrocytes likely expressed more IL-36α than healthy chondrocytes. In addition, immune cells infiltrated into the joint and PBMCs express higher levels of IL-36α in comparison to chondrocytes. OA chondrocytes, treated with IL-36α, showed significant increase in the expression of MMP-13, NOS2 and COX-2. Finally, IL-36α stimulated cells showed NFκB and p38 MAPK activated pathways. IL-36α acts as a pro-inflammatory cytokine at cartilage level, by increasing the expression of markers of inflammation and cartilage catabolism. Like other members of IL-1 family, IL-36α acts through the activation of NFκB and p38 MAPK pathway.

Aging-related inflammation in osteoarthritis

It is well accepted that aging is an important contributing factor to the development of osteoarthritis (OA). The mechanisms responsible appear to be multifactorial and may include an age-related pro-inflammatory state that has been termed "inflamm-aging." Age-related inflammation can be both systemic and local. Systemic inflammation can be promoted by aging changes in adipose tissue that result in increased production of cytokines such as interleukin (IL)-6 and tumor necrosis factor-α (TNFα). Numerous studies have shown an age-related increase in blood levels of IL-6 that has been associated with decreased physical function and frailty. Importantly, higher levels of IL-6 have been associated with an increased risk of knee OA progression. However, knockout of IL-6 in male mice resulted in worse age-related OA rather than less OA. Joint tissue cells, including chondrocytes and meniscal cells, as well as the neighboring infrapatellar fat in the knee joint, can be a local source of inflammatory mediators that increase with age and contribute to OA. An increased production of pro-inflammatory mediators that include cytokines and chemokines, as well as matrix-degrading enzymes important in joint tissue destruction, can be the result of cell senescence and the development of the senescence-associated secretory phenotype (SASP). Further studies are needed to better understand the basis for inflamm-aging and its role in OA with the hope that this work will lead to new interventions targeting inflammation to reduce not only joint tissue destruction but also pain and disability in older adults with OA.

HIF-2α-induced chemokines stimulate motility of fibroblast-like synoviocytes and chondrocytes into the cartilage-pannus interface in experimental rheumatoid arthritis mouse models

Introduction

Pannus formation and resulting cartilage destruction during rheumatoid arthritis (RA) depends on the migration of synoviocytes to cartilage tissue. Here, we focused on the role of hypoxia-inducible factor (HIF)-2α-induced chemokines by chondrocytes in the regulation of fibroblast-like synoviocyte (FLS) migration into the cartilage-pannus interface and cartilage erosion.

Methods

Collagen-induced arthritis (CIA), K/BxN serum transfer, and tumor necrosis factor-α transgenic mice were used as experimental RA models. Expression patterns of HIF-2α and chemokines were determined via immunostaining, Western blotting and RT-PCR. FLS motility was evaluated using transwell migration and invasion assays. The specific role of HIF-2α was determined via local deletion of HIF-2α in joint tissues or using conditional knockout (KO) mice. Cartilage destruction, synovitis and pannus formation were assessed via histological analysis.

Results

HIF-2α and various chemokines were markedly upregulated in degenerating cartilage and pannus of RA joints. HIF-2α induced chemokine expression by chondrocytes in both primary culture and cartilage tissue. HIF-2α -induced chemokines by chondrocytes regulated the migration and invasion of FLS. Local deletion of HIF-2α in joint tissues inhibited pannus formation adjacent to cartilage tissue and cartilage destruction caused by K/BxN serum transfer. Furthermore, conditional knockout of HIF-2α in cartilage blocked pannus formation in adjacent cartilage but not bone tissue, along with inhibition of cartilage erosion caused by K/BxN serum transfer.

Conclusion

Our findings suggest that chemokines induced by IL-1β or HIF-2α in chondrocytes regulate pannus expansion by stimulating FLS migration and invasion, leading to cartilage erosion during RA pathogenesis.

T Cell Migration in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammation in joints, associated with synovial hyperplasia and with bone and cartilage destruction. Although the primacy of T cell-related events early in the disease continues to be debated, there is strong evidence that autoantigen recognition by specific T cells is crucial to the pathophysiology of rheumatoid synovitis. In addition, T cells are key components of the immune cell infiltrate detected in the joints of RA patients. Initial analysis of the cytokines released into the synovial membrane showed an imbalance, with a predominance of proinflammatory mediators, indicating a deleterious effect of Th1 T cells. There is nonetheless evidence that Th17 cells also play an important role in RA. T cells migrate from the bloodstream to the synovial tissue via their interactions with the endothelial cells that line synovial postcapillary venules. At this stage, selectins, integrins, and chemokines have a central role in blood cell invasion of synovial tissue, and therefore in the intensity of the inflammatory response. In this review, we will focus on the mechanisms involved in T cell attraction to the joint, the proteins involved in their extravasation from blood vessels, and the signaling pathways activated. Knowledge of these processes will lead to a better understanding of the mechanism by which the systemic immune response causes local joint disorders and will help to provide a molecular basis for therapeutic strategies.

The chemokine CCL20 induces proinflammatory and matrix degradative responses in cartilage

INTRODUCTION

Local inflammation plays a role in the pathophysiology of osteoarthritis (OA) and chemokines exert catabolic effects on articular cartilage either through paracrine and/or autocrine mechanisms. We sought to compare the expression levels of the chemokine (C-C motif) ligand 20 (CCL20) and its chemokine receptor 6 (CCR6) in donor and osteoarthritic (OA) cartilage and to investigate the role of CCL20 in the pathogenesis of OA and chondrocyte phenotype.

METHODS

Cartilage/chondrocytes from donor and OA knee joints was analyzed for CCL20 and CCR6 expression by RT-PCR and immunohistochemistry. Effects of CCL20 on cytokines and mediators of cartilage degradation were examined by RT-PCR for mRNA expression levels, enzyme-linked immunosorbent assays, and proteoglycan (GAG) assays.

RESULTS

CCL20 and CCR6 proteins were abundantly expressed in OA cartilage sections compared to donor sections as judged by immunohistochemistry. RT-PCR of cartilage extracts confirmed the predominance of CCL20/CCR6 mRNA expression in OA cartilage. CCL20 mRNA expression was low in donor chondrocytes but increased after stimulation with proinflammatory cytokines. mRNA expression levels of IL-6, cyclooxygenase-2, and iNOS were elevated in donor chondrocyte cultures treated with rhCCL20. The release of MMP1/13, PGE2, proteoglycan GAG fragments, and IL-6 from cartilage explant cultures was markedly augmented in the presence of CCL-20. CCL-20 stimulated MMP-13, ADAMTS-5, and col type X mRNA but inhibited col type II mRNA expression in freshly explanted and cultured cartilage specimens.

CONCLUSIONS

CCL20/CCR6 may play an important role in the pathogenesis of OA by inducing changes in phenotype and catabolic gene expression in chondrocytes.

Potential roles of cytokines and chemokines in human intervertebral disc degeneration: interleukin-1 is a master regulator of catabolic processes

OBJECTIVE

These studies investigated cytokine and chemokine receptor profiles in nucleus pulposus (NP) cells, and the effects of receptor stimulation on mRNA levels of extracellular matrix (ECM) components, degrading enzymes and cytokine and chemokine expression.

METHOD

Immunohistochemistry (IHC) was performed to localise expression of CD4, CCR1, CXCR1 and CXCR2 in human NP tissue samples. Effects of cytokine and chemokine stimulation was performed to investigate effects related to ECM remodelling and modulation of cytokine and chemokine mRNA expression.

RESULTS

IHC identified CD4, CCR1, CXCR1 and CXCR2 expression by NP cells. Differential expression profiles were observed for CD4 and CXCR2 in tissue samples from degenerate and infiltrated IVDs. In vitro stimulations of primary human NP cultures with IL-16, CCL2, CCL3, CCL7 or CXCL8 did not identify any modulatory effects on parameters associated with ECM remodelling or expression of other cytokines and chemokines. Conversely, IL-1 was seen to modulate ECM remodelling and expression of all other cytokines and chemokines investigated.

CONCLUSION

This study demonstrates for the first time that NP cells express a number of cytokine and chemokine receptors and thus could respond in an autocrine or paracrine manner to cytokines and chemokines produced by NP cells, particularly during tissue degeneration. However, this study failed to demonstrate regulatory effects on ECM genes and degradative enzymes or other cytokines and chemokines for any target investigated, with the exception of IL-1. This suggests that IL-1 is a master regulator within the IVD and may exert regulatory potential over a plethora of other cytokines and chemokines.

The chemokine receptor CCR5 plays a role in post-traumatic cartilage loss in mice, but does not affect synovium and bone

OBJECTIVE

C-C chemokine receptor type 5 (CCR5) has been implicated in rheumatoid arthritis and several inflammatory diseases, where its blockade resulted in reduced joint destruction. However, its role in modulating cartilage and bone changes in post-traumatic osteoarthritis (OA) has not yet been investigated. In this study, we investigated changes in articular cartilage, synovium and bone in a post-traumatic OA model using CCR5-deficient (CCR5(-/-)) mice.

METHOD

Destabilization of the medial meniscus (DMM) was performed on the right knee of 10-week old CCR5(-/-) and C57BL/6J wild-type (WT) mice to induce post-traumatic OA. The contralateral left knee served as sham-operated control. Knee joints were analyzed at 4-, 8- and 12-weeks after surgery to evaluate cartilage degeneration and synovitis by histology, and bone changes via micro-CT.

RESULTS

Our findings showed that CCR5(-/-) mice exhibited significantly less cartilage degeneration than WT mice at 8- and 12-weeks post-surgery. CCR5(-/-) mice showed some altered bone parameters 18- and 22-weeks of age, but body size and weight were not affected. The effect of CCR5-ablation was insignificant at all time points post-surgery for synovitis and for bone parameters such as bone volume/total volume, connectivity density index (CDI), structure model index (SMI), subchondral bone plate thickness, and trabecular bone number, thickness and spacing.

CONCLUSION

These findings suggest that CCR5(-/-) mice developed less cartilage degeneration, which may indicate a potential protective role of CCR5-ablation in cartilage homeostasis. There were no differences in bone or synovial response to surgery suggesting that CCR5 functions primarily in cartilage during the development of post-traumatic OA.

Role of G-proteins in the differentiation of epiphyseal chondrocytes

Herein, we review the regulation of differentiation of the growth plate chondrocytes by G-proteins. In connection with this, we summarize the current knowledge regarding each family of G-protein α subunit, specifically, Gα(s), Gα(q/11), Gα(12/13), and Gα(i/o). We discuss different mechanisms involved in chondrocyte differentiation downstream of G-proteins and different G-protein-coupled receptors (GPCRs) activating G-proteins in the epiphyseal chondrocytes. We conclude that among all G-proteins and GPCRs expressed by chondrocytes, Gα(s) has the most important role and prevents premature chondrocyte differentiation. Receptor for parathyroid hormone (PTHR1) appears to be the major activator of Gα(s) in chondrocytes and ablation of either one leads to accelerated chondrocyte differentiation, premature fusion of the postnatal growth plate, and ultimately short stature.

Chopping off the chondrocyte proteome

The progressive nature of osteoarthritis is manifested by the dynamic increase of degenerated articular cartilage, which is one of the major characteristics of this debilitating disease. As articular chondrocytes become exposed to inflammatory stress they enter a pro-catabolic state, which leads to the secretion and activation of a plethora of proteases. In aim to detect the disease before massive areas of cartilage are destroyed, various protein and non-protein biomarkers have been examined in bodily fluids and correlated with disease severity. This review will discuss the widely research extracellular degraded products as well as products generated by affected cellular pathways upon increased protease activity. While extracellular components could be more abundant, cleaved cellular proteins are less abundant and are suggested to possess a significant effect on cell metabolism and cartilage secretome. Subtle changes in cell secretome could potentially act as indicators of the chondrocyte metabolic and biological state. Therefore, it is envisioned that combined biomarkers composed of both cell and extracellular-degraded secretome could provide a valuable platform for testing drug efficacy to halt disease progression at its early stages.

Monocyte chemotactic protein-1 inhibits chondrogenesis of synovial mesenchymal progenitor cells: an in vitro study

Osteoarthritis (OA) is a multifactorial, often progressive, painful disease. OA often progresses with an apparent irreversible loss of articular cartilage, exposing underlying bone, resulting in pain and loss of mobility. This cartilage loss is thought to be permanent due to ineffective repair and apparent lack of stem/progenitor cells in that tissue. However, the adjacent synovial lining and synovial fluid are abundant with mesenchymal progenitor/stem cells (synovial mesenchymal progenitor cells [sMPCs]) capable of differentiating into cartilage both in vitro and in vivo. Previous studies have demonstrated that MPCs can home to factors such as monocyte chemotactic protein 1 (MCP-1/CCL2) expressed after injury. While MCP-1 (and its corresponding receptors) appears to play a role in recruiting stem cells to the site of injury, in this study, we have demonstrated that MCP-1 is upregulated in OA synovial fluid and that exposure to MCP-1 activates sMPCs, while concurrently inhibiting these cells from undergoing chondrogenesis in vitro. Furthermore, exposure to physiological (OA knee joint synovial fluid) levels of MCP-1 triggers changes in the transcriptome of sMPCs and prolonged exposure to the chemokine induces the expression of MCP-1 in sMPCs, resulting in a positive feedback loop from which sMPCs cannot apparently escape. Therefore, we propose a model where MCP-1 (normally expressed after joint injury) recruits sMPCs to the area of injury, but concurrently triggers changes in sMPC transcriptional regulation, leading to a blockage in the chondrogenic program. These results may open up new avenues of research into the lack of endogenous repair observed after articular cartilage injury and/or arthritis.

Chondrocyte-specific pathology during skeletal growth and therapeutics in a murine model of pseudoachondroplasia

Mutations in the gene encoding cartilage oligomeric matrix protein (COMP) cause pseudoachondroplasia (PSACH), a severe dwarfing condition. Pain, a significant complication, has generally been attributed to joint abnormalities and erosion and early onset osteoarthritis. Previously, we found that the inflammatory-related transcripts were elevated in growth plate and articular cartilages, indicating that inflammation plays an important role in the chondrocyte disease pathology and may contribute to the overall pain sequelae. Here, we describe the effects of D469-delCOMP expression on the skeleton and growth plate chondrocytes with the aim to define a treatment window and thereby reduce pain. Consistent with the human PSACH phenotype, skeletal development of D469del-COMP mice was normal and similar to controls at birth. By postnatal day 7 (P7), the D469del-COMP skeleton, limbs, skull and snout were reduced and this reduction was progressive during postnatal growth, resulting in a short-limbed dwarfed mouse. Modulation of prenatal and postnatal expression of D469del-COMP showed minimal retention/cell death at P7 with some retention/cell death by P14, suggesting that earlier treatment intervention at the time of PSACH diagnosis may produce optimal results. Important and novel findings were an increase in inflammatory proteins generally starting at P21 and that exercise exacerbates inflammation. These observations suggest that pain in PSACH may be related to an intrinsic inflammatory process that can be treated symptomatically and is not related to early joint erosion. We also show that genetic ablation of CHOP dampens the inflammatory response observed in mice expressing D469del-COMP. Toward identifying potential treatments, drugs known to decrease cellular stress (lithium, phenylbutyric acid, and valproate) were assessed. Interestingly, all diminished the chondrocyte pathology but had untoward outcomes on mouse growth, development, and longevity. Collectively, these results define an early treatment window in which chondrocytes can be salvaged, thereby potentially increasing skeletal growth and decreasing pain.

Ginkgo biloba extract individually inhibits JNK activation and induces c-Jun degradation in human chondrocytes: potential therapeutics for osteoarthritis

Osteoarthritis (OA) is a common joint disorder with varying degrees of inflammation. The ideal anti-OA drug should have immunomodulatory effects while at the same time having limited or no toxicity. We examined the anti-inflammatory effects of Ginkgo biloba extract (EGb) in interleukin-1 (IL-1)-stimulated human chondrocytes. Chondrocytes were prepared from cartilage specimens taken from patients with osteoarthritis who had received total hip or total knee replacement. The concentrations of chemokines and the degree of cell migration were determined by ELISA and chemotaxis assays, respectively. The activation of inducible nitric oxide synthase (iNOS), mitogen-activated protein kinases (MAPKs), activator protein-1 (AP-1), and nuclear factor-kappaB (NF-κB) was determined by immunoblotting, immunohistochemistry, and electrophoretic mobility shift assay. We found that EGb inhibited IL-1-induced production of chemokines, which in turn resulted in attenuation of THP-1 cell migration toward EGb-treated cell culture medium. EGb also suppressed IL-1-stimulated iNOS expression and release of nitric oxide (NO). The EGb-mediated suppression of the iNOS-NO pathway correlated with the attenuation of activator protein-1 (AP-1) but not nuclear factor-kappaB (NF-κB) DNA-binding activity. Of the mitogen-activated protein kinases (MAPKs), EGb inhibited only c-Jun N-terminal kinase (JNK). Unexpectedly, EGb selectively caused degradation of c-Jun protein. Further investigation revealed that EGb-mediated c-Jun degradation was preceded by ubiquitination of c-Jun and could be prevented by the proteosome inhibitor MG-132. The results imply that EGb protects against chondrocyte degeneration by inhibiting JNK activation and inducing ubiquitination-dependent c-Jun degradation. Although additional research is needed, our results suggest that EGb is a potential therapeutic agent for the treatment of OA.

Conditioned media from adipose-tissue-derived mesenchymal stem cells downregulate degradative mediators induced by interleukin-1β in osteoarthritic chondrocytes

Osteoarthritis (OA) is the most frequent joint disorder and an important cause of disability. Recent studies have shown the potential of adipose-tissue-derived mesenchymal stem cells (AD-MSC) for cartilage repair. We have investigated whether conditioned medium from AD-MSC (CM) may regulate in OA chondrocytes a number of key mediators involved in cartilage degeneration. CM enhanced type II collagen expression in OA chondrocytes while decreasing matrix metalloproteinase (MMP) activity in cell supernatants as well as the levels of MMP-3 and MMP-13 proteins and mRNA in OA chondrocytes stimulated with interleukin- (IL-) 1β. In addition, CM increased IL-10 levels and counteracted the stimulating effects of IL-1β on the production of tumor necrosis factor-α, IL-6, prostaglandin E₂, and NO measured as nitrite and the mRNA expression of these cytokines, CCL-2, CCL-3, CCL-4, CCL-5, CCL-8, CCL-19, CCL-20, CXCL-1, CXCL-2, CXCL-3, CXCL-5, CXCL-8, cyclooxygenase-2, microsomal prostaglandin E synthase-1, and inducible NO synthase. These effects may be dependent on the inhibition of nuclear factor-κB activation by CM. Our data demonstrate the chondroprotective actions of CM and provide support for further studies of this approach in joint disease.

Duffy antigen receptor for chemokines regulates post-fracture inflammation

There is now considerable experimental data to suggest that inflammatory cells collaborate in the healing of skeletal fractures. In terms of mechanisms that contribute to the recruitment of inflammatory cells to the fracture site, chemokines and their receptors have received considerable attention. Our previous findings have shown that Duffy antigen receptor for chemokines (Darc), the non-classical chemokine receptor that does not signal, but rather acts as a scavenger of chemokines that regulate cell migration, is a negative regulator of peak bone density in mice. Furthermore, because Darc is expressed by inflammatory and endothelial cells, we hypothesized that disruption of Darc action will affect post-fracture inflammation and consequently will affect fracture healing. To test this hypothesis, we evaluated fracture healing in mice with targeted disruption of Darc and corresponding wild type (WT) control mice. We found that fracture callus cartilage formation was significantly greater (33%) at 7 days post-surgery in Darc-KO compared to WT mice. The increased cartilage was associated with greater Collagen (Col) II expression at 3 days post-fracture and Col-X at 7 days post-fracture compared to WT mice, suggesting that Darc deficiency led to early fracture cartilage formation and differentiation. We then compared the expression of cytokine and chemokine genes known to be induced during inflammation. Interleukin (Il)-1β, Il-6, and monocyte chemotactic protein 1 were all down regulated in the fractures derived from Darc-KO mice at one day post-fracture, consistent with an altered inflammatory response. Furthermore, the number of macrophages was significantly reduced around the fractures in Darc-KO compared to WT mice. Based on these data, we concluded that Darc plays a role in modulating the early inflammatory response to bone fracture and subsequent cartilage formation. However, the early cartilage formation was not translated with an early bone formation at the fracture site in Darc-KO compared to WT mice.

Correlation of fractalkine concentrations in serum and synovial fluid with the radiographic severity of knee osteoarthritis

BACKGROUND

Fractalkine has been detected in synovial fluid (SF) from osteoarthritis (OA) patients. This study aims to examine the relation of fractalkine concentrations in serum and SF with the radiographic severity of OA.

METHODS

Fractalkine concentrations of serum and SF were measured using an enzyme-linked immunosorbent assay method in 223 patients with knee OA and 165 healthy controls. The progression of OA was classified according to the Kellgren-Lawrence grading system.

RESULTS

Elevated concentrations of fractalkine in serum were found in knee OA patients compared with healthy controls [all results median (interquartile range) 226.25 (183.19-259.91) vs. 127.42 (99.54-154.98) pg/mL, P < 0.001]. The case group included 71 knee OA patients with grade 2, 98 with grade 3, and 54 with grade 4. Knee OA patients with KL grade 4 had significantly higher fractalkine concentrations in serum and SF compared with those with KL grade 2 and 3 [serum: 247.68 (215.05-278.64) vs. 212.45 (169.19-247.96) pg/mL, P < 0.001, and 247.68 (215.05-278.64) vs. 222.00 (179.80-254.98) pg/mL, P = 0.005, respectively; SF: 94.95 (76.46-106.68) vs. 74.31 (63.64-84.79) pg/mL, P < 0.001, and 94.95 (76.46-106.68) vs. 80.34 (68.84-96.39) pg/mL, P = 0.001, respectively]. Knee OA patients with KL grade 3 showed significantly elevated concentrations of fractalkine in SF compared with those with KL grade 2 [80.34 (68.84-96.39) vs. 74.31 (63.64-84.79) pg/mL, P = 0.004]. Fractalkine concentrations in serum and SF of knee OA patients were both significantly associated with the disease severity evaluated by KL grading criteria (r = 0.261, P < 0.001 and r = 0.366, P < 0.001, respectively).

CONCLUSION

The fractalkine concentrations in serum and SF may serve as an effective biomarker for the severity of OA.

Adipose-derived mesenchymal stem cells exert antiinflammatory effects on chondrocytes and synoviocytes from osteoarthritis patients through prostaglandin E2

OBJECTIVE

To examine the effect of different sources of good manufacturing practice clinical grade adipose-derived mesenchymal stem cells (AD-MSCs) on inflammatory factors in osteoarthritic (OA) chondrocytes and synoviocytes.

METHODS

AD-MSCs from infrapatellar Hoffa fat, subcutaneous (SC) hip fat, and SC abdominal fat were cocultured in Transwells with chondrocytes or synoviocytes. Inflammatory factors (interleukin-1β [IL-1β], tumor necrosis factor α, IL-6, CXCL1/growth-related oncogene α, CXCL8/IL-8, CCL2/monocyte chemotactic protein 1, CCL3/macrophage inflammatory protein 1α, and CCL5/RANTES) were evaluated by quantitative reverse transcription-polymerase chain reaction or multiplex bead-based immunoassay. The role of different immunomodulators was analyzed.

RESULTS

All the inflammatory factors analyzed were down-modulated at the messenger RNA or protein level independently by all 3 AD-MSC sources or by allogeneic AD-MSCs used in coculture with chondrocytes or synoviocytes. Inflammatory factor down-modulation was observed only when AD-MSCs were cocultured with chondrocytes or synoviocytes that produced high levels of inflammatory factors, but no effect was observed in cells that produced low levels of those factors, thus highlighting a dependence of the AD-MSC effect on existing inflammation. The immunomodulators IL-10, IL-1 receptor antagonist, fibroblast growth factor 2, indoleamine 2,3-dioxygenase 1, and galectin 1 were not involved in AD-MSC effects, whereas the cyclooxygenase 2 (COX-2)/prostaglandin E2 (PGE2 ) pathway exerted a role in the mechanism of antiinflammatory AD-MSC action.

CONCLUSION

The antiinflammatory effects of AD-MSCs are probably not dependent on AD-MSC adipose tissue sources and donors but rather on the inflammatory status of OA chondrocytes and synoviocytes. AD-MSCs seem to be able to sense and respond to the local environment. Even though a combination of different molecules may be involved in AD-MSC effects, the COX-2/PGE2 pathway may play a role, suggesting that AD-MSCs may be useful for therapies in osteoarticular diseases.

Immunopathogenesis of osteoarthritis

Even though osteoarthritis (OA) is mainly considered as a degradative condition of the articular cartilage, there is increasing body of data demonstrating the involvement of all branches of the immune system. Genetic, metabolic or mechanical factors cause an initial injury to the cartilage resulting in release of several cartilage specific auto-antigens, which trigger the activation of immune response. Immune cells including T cells, B cells and macrophages infiltrate the joint tissues, cytokines and chemokines are released from different kinds of cells present in the joint, complement system is activated, and cartilage degrading factors such as matrix metalloproteinases (MMPs) and prostaglandin E2 (PGE2) are released, resulting in further damage to the articular cartilage. There is considerable success in the treatment of rheumatoid arthritis using anti-cytokine therapies. In OA, however, these therapies did not show much effect, highlighting more complex nature of pathogenesis of OA. This needs the development of more novel approaches to treat OA, which may include therapies that act on multiple targets. Plant natural products have this kind of property and may be considered for future drug development efforts. Here we reviewed the studies implicating different components of the immune system in the pathogenesis of OA.

TGF-β type II receptor/MCP-5 axis: at the crossroad between joint and growth plate development

Despite its clinical significance, the mechanisms of joint morphogenesis are elusive. By combining laser-capture microdissection for RNA sampling with microarrays, we show that the setting in which joint-forming interzone cells develop is distinct from adjacent growth plate chondrocytes and is characterized by downregulation of chemokines, such as monocyte-chemoattractant protein-5 (MCP-5). Using in vivo, ex vivo, and in vitro approaches, we show that low levels of interzone-MCP-5 are essential for joint formation and contribute to proper growth plate organization. Mice lacking the TGF-β-type-II-receptor (TβRII) in their limbs (Tgfbr2(Prx1KO)), which lack joint development and fail chondrocyte hypertrophy, show upregulation of interzone-MCP-5. In vivo and ex vivo blockade of the sole MCP-5 receptor, CCR2, led to the rescue of joint formation and growth plate maturation in Tgfbr2(Prx1KO) but an acceleration of growth plate mineralization in control mice. Our study characterized the TβRII/MCP-5 axis as an essential crossroad for joint development and endochondral growth.