A role for chemokines in the induction of chondrocyte phenotype modulation

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.

CXCR4/CXCL12 axis: "old" pathway as "novel" target for anti-inflammatory drug discovery

Inflammation is the body's defense response to exogenous or endogenous stimuli, involving complex regulatory mechanisms. Discovering anti-inflammatory drugs with both effectiveness and long-term use safety is still the direction of researchers' efforts. The inflammatory pathway was initially identified to be involved in tumor metastasis and HIV infection. However, research in recent years has proved that the CXC chemokine receptor type 4 (CXCR4)/CXC motif chemokine ligand 12 (CXCL12) axis plays a critical role in the upstream of the inflammatory pathway due to its chemotaxis to inflammatory cells. Blocking the chemotaxis of inflammatory cells by CXCL12 at the inflammatory site may block and alleviate the inflammatory response. Therefore, developing CXCR4 antagonists has become a novel strategy for anti-inflammatory therapy. This review aimed to systematically summarize and analyze the mechanisms of action of the CXCR4/CXCL12 axis in more than 20 inflammatory diseases, highlighting its crucial role in inflammation. Additionally, the anti-inflammatory activities of CXCR4 antagonists were discussed. The findings might help generate new perspectives for developing anti-inflammatory drugs targeting the CXCR4/CXCL12 axis.

Rongjin Niantong Fang ameliorates cartilage degeneration by regulating the SDF-1/CXCR4-p38MAPK signalling pathway

CONTEXT

Rongjin Niantong Fang (RJNTF) is a Traditional Chinese Medicine formulation with a good therapeutic effect on osteoarthritis (OA). However, the underlying mechanisms remain unclear.

OBJECTIVE

This study investigates whether RJNTF could delay OA cartilage degeneration by regulating the SDF-1/CXCR4-p38MAPK signalling pathway.

MATERIALS AND METHODS

The Sprague-Dawley (SD) rats were used to establish the OA model by a modified Hulth's method. SD rats were divided into three groups (n = 10): blank group, model group (0.9% saline, 10 mL/kg/day), and treatment group (RJNTF, 4.5 g/kg/day). After 12 weeks of treatment, each group was analysed by H&E, Safranine-O solid green, ELISA, Immunohistochemistry, and Western blot. An in vitro model was induced with 100 ng/mL SDF-1 by ELISA, the blank group, model group, RJNTF group, and inhibitor group with intervention for 12 h, each group was analysed by Immunofluorescence staining and Western blot.

RESULTS

SDF-1 content in the synovium was reduced in RJNTF treatment group compared to non-treatment model group (788.10 vs. 867.32 pg/mL) and down-regulation of CXCR4, MMP-3, MMP-9, MMP-13 protein expression, along with p38 protein phosphorylated were observed in RJNTF treatment group. In vitro results showed that RJNTF (IC₅₀ = 8.925 mg/mL) intervention could down-regulate SDF-1 induced CXCR4 and p38 protein phosphorylated and reduce the synthesis of MMP-3, MMP-9, and MMP-13 proteins of chondrocytes from SD rat cartilage tissues.

DISCUSSION AND CONCLUSION

RJNTF alleviates OA cartilage damage by SDF-1/CXCR4-p38MAPK signalling pathway inhibition. Our ongoing research focuses on Whether RJNTF treats OA through alternative pathways.

Long noncoding and micro-RNA expression in a model of articular chondrocyte degeneration induced by stromal cell-derived factor-1

Background

Gene regulatory network analysis has found that long noncoding ribonucleic acids (lncRNAs) are strongly associated with the pathogenesis of osteoarthritis.

Objectives

To determine the differential expression of lncRNAs and microRNAs (miRNAs) in normal chondrocytes and those from a model of articular chondrocyte degeneration.

Methods

Chondrocytes were cultured from cartilage obtained from patients diagnosed with osteoarthritis of the knee. Stromal cell-derived factor-1 (SDF-1) was used to induce their degeneration. Total RNA was extracted, analyzed, amplified, labeled, and hybridized on a chip to determine expression. The set of enriched differentially expressed miRNAs was analyzed by gene ontology and the Kyoto Encyclopedia of Genes and Genomes to describe the functional properties of the key biological processes and pathways. We conducted a bioinformatics analysis using Cytoscape to elucidate the interactions between miRNAs and proteins.

Results

We found that the expression of 186 lncRNAs was significantly different in the model of chondrocyte degeneration, in which 88 lncRNAs were upregulated, and 98 were downregulated. Expression of 684 miRNAs was significantly different. Analysis of the protein-protein interaction (PPI) network indicated that the genes for CXCL10, ISG15, MYC, MX1, OASL, IFIT1, RSAD2, MX2, IFI44L, and BST2 are the top 10 core genes, identifying the most important functional modules to elucidate the differential expression of miRNAs.

Conclusions

These data may provide new insights into the molecular mechanisms of chondrocyte degeneration in osteoarthritis, and the identification of lncRNAs and miRNAs may provide potential targets for the differential diagnosis and therapy of osteoarthritis.

Chondrocyte death involvement in osteoarthritis

Chondrocyte apoptosis is known to contribute to articular cartilage damage in osteoarthritis and is correlated to a number of cartilage disorders. Micromass cultures represent a convenient means for studying chondrocyte biology, and, in particular, their death. In this review, we focused the different kinds of chondrocyte death through a comparison between data reported in the literature. Chondrocytes show necrotic features and, occasionally, also apoptotic features, but usually undergo a new form of cell death called Chondroptosis, which occurs in a non-classical manner. Chondroptosis has some features in common with classical apoptosis, such as cell shrinkage, chromatin condensation, and involvement, not always, of caspases. The most crucial peculiarity of chondroptosis relates to the ultimate elimination of cellular remnants. Independent of phagocytosis, chondroptosis may serve to eliminate cells without inflammation in situations in which phagocytosis would be difficult. This particular death mechanism is probably due to the unusual condition chondrocytes both in vivo and in micromass culture. This review highlights on the morpho-fuctional alterations of articular cartilage and focus attention on various types of chondrocyte death involved in this degeneration. The death features have been detailed and discussed through in vitro studies based on tridimensional chondrocyte culture (micromasses culture). The study of this particular mechanism of cartilage death and the characterization of different biological and biochemical underlying mechanisms can lead to the identification of new potentially therapeutic targets in various joint diseases.

The role of stromal cell-derived factor 1 on cartilage development and disease

Stromal cell-derived factor 1 (SDF-1), also known as CXC motif chemokine ligand 12 (CXCL12), is recognized as a homeostatic cytokine with strong chemotactic potency. It plays an important role in physiological and pathological processes, such as the development of multiple tissues and organs, the regulation of cell distribution, and tumour metastasis. SDF-1 has two receptors, CXC chemokine receptor type 4 (CXCR4) and CXC chemokine receptor type 7 (CXCR7). SDF-1 affects the proliferation, survival, differentiation and maturation of chondrocytes by binding to CXCR4 on chondrocytes. Therefore, SDF-1 has been used as an exogenous regulatory target in many studies to explore the mechanism of cartilage development. SDF-1 is also a potential therapeutic target for osteoarthritis (OA) and rheumatoid arthritis (RA), because of its role in pathological initiation and regulation. In addition, SDF-1 shows potent capacity in the repair of cartilage defects by recruiting endogenous stem cells in a cartilage tissue engineering context. To summarize the specific role of SDF-1 on cartilage development and disease, all articles had been screened out in PubMed by May 30, 2020. The search was limited to studies published in English. Search terms included SDF-1; CXCL12; CXCR4; chondrocyte; cartilage; OA; RA, and forty-seven papers were studied. Besides, we reviewed references in the articles we searched to get additional relevant backgrounds. The review aims to conclude the current knowledge regarding the physiological and pathological role of SDF-1 on the cartilage and chondrocyte. More investigations are required to determine methods targeted SDF-1 to cartilage development and interventions to cartilage diseases.

A Novel Strategy to Enhance Microfracture Treatment With Stromal Cell-Derived Factor-1 in a Rat Model

Background

Microfracture is one of the most widely used techniques for the repair of articular cartilage. However, microfracture often results in filling of the chondral defect with fibrocartilage, which exhibits poor durability and sub-optimal mechanical properties. Stromal cell-derived factor-1 (SDF-1) is a potent chemoattractant for mesenchymal stem cells (MSCs) and is expressed at high levels in bone marrow adjacent to developing cartilage during endochondral bone formation. Integrating SDF-1 into an implantable collagen scaffold may provide a chondro-conductive and chondro-inductive milieu via chemotaxis of MSCs and promotion of chondrogenic differentiation, facilitating more robust hyaline cartilage formation following microfracture.

Objective

This work aimed to confirm the chemoattractive properties of SDF-1 in vitro and develop a one-step method for incorporating SDF-1 in vivo to enhance cartilage repair using a rat osteochondral defect model.

Methods

Bone marrow-derived MSCs (BMSCs) were harvested from the femurs of Sprague–Dawley rats and cultured in low-glucose Dulbecco’s modified Eagle’s medium containing 10% fetal bovine serum, with the medium changed every 3 days. Passage 1 MSCs were analyzed by flow cytometry with an S3 Cell Sorter (Bio-Rad). In vitro cell migration assays were performed on MSCs by labeling cells with carboxyfluorescein diacetate, succinimidyl ester (CFDA-SE; Bio-Rad). For the microfracture model, a 1.6-mm-diameter osteochondral defect was created in the femoral trochleae of 20 Sprague–Dawley rats bilaterally until bone marrow spillage was seen under saline irrigation. One knee was chosen at random to receive implantation of the scaffold, and the contralateral knee was left unfilled as an empty control. Type I collagen scaffolds (Kensey Nash) were coated with either gelatin only or gelatin and SDF-1 using a dip coating process. The rats received implantation of either a gelatin-only scaffold (N = 10) or gelatin-and-SDF-1 scaffold (N = 10) at the site of the microfracture. Femurs were collected for histological analyses at 4- and 8-week time points post-operatively, and sections were stained with Safranin O/Fast Green. The samples were graded blindly by two observers using the Modified O’Driscoll score, a validated scoring system for chondral repair. A minimum of 10 separate grading scores were made per sample and averaged. Quantitative comparisons of cell migration in vitro were performed with one-way ANOVA. Cartilage repair in vivo was also compared among groups with one-way ANOVA, and the results were presented as mean ± standard deviation, with P-values < 0.05 considered as statistically significant.

Results

MSC migration showed a dose–response relationship with SDF-1, with an optimal dosage for chemotaxis between 10 and 100 ng/ml. After scaffold implantation, the SDF-1-treated group demonstrated complete filling of the cartilage defect with mature cartilage tissue, exhibiting strong proteoglycan content, smooth borders, and good incorporation into marginal cartilage. Modified O’Driscoll scores after 8 weeks showed a significant improvement of cartilage repair in the SDF-1 group relative to the empty control group (P < 0.01), with a trend toward improvement when compared with the gelatin-only-scaffold group (P < 0.1). No significant differences in scores were found between the empty defect group and gelatin-only group.

Conclusion

In this study, we demonstrated a simple method for improving the quality of cartilage defect repair in a rat model of microfracture. We confirmed the chemotactic properties of SDF-1 on rat MSCs and found an optimized dosage range for chemotaxis between 10 and 100 ng/ml. Furthermore, we demonstrated a strategy to incorporate SDF-1 into gelatin–collagen I scaffolds in vivo at the site of an osteochondral defect. SDF-1-treated defects displayed robust hyaline cartilage resurfacing of the defect with minimal fibrous tissue, in contrast to the empty control group. The results of the in vitro and in vivo studies together suggest that SDF-1-mediated signaling may significantly improve the quality of cartilage regeneration in an osteochondral defect.

Proinflammatory T cell polarization is already present in patients with early knee osteoarthritis

Background

Investigating the pathophysiological mechanisms of early osteoarthritis (OA) is of utmost interest since this stage holds the strongest promise for therapeutic interventions. The aims of this study were to analyze if synovial inflammation is already present in early OA and to characterize the involved cell populations, by investigating synovial fluid (SF) and synovial membrane (SM) of early OA patients for the presence and polarization status of CD4 T cells.

Methods

A quantitative analysis of CD4⁺ T cell infiltration in SF and SM compared to peripheral blood (PB) was performed in patients with early stages of OA. We further investigated intracellular staining (ICS), surface marker, and chemokine receptor expression profiles of CD4⁺ T cells in SF, SM, and PB, as well as cytokine expression in native SF and PB. Matched samples of SF, SM, and PB were harvested from 40 patients with early OA at the time of surgery. Early OA was confirmed by independent surgeons intraoperatively. Samples were analyzed by flow cytometry for surface markers and cytokines, which are preferentially expressed by distinct T cell subsets (Th1, Th2, Th17, regulatory T cells). Furthermore, we analyzed native SF and PB supernatants using MACSPlex for multiple cytokine expression profiles.

Results

SF and SM showed a distinct infiltration of CD4⁺ T lymphocytes, with significantly increased expression of chemokine receptors CXCR3/CCR5, cytokine IFN-γ (preferentially expressed by Th1 cells), and CD161 (preferentially expressed by IL-17 producing Th17 cells) compared to PB. Furthermore, the percentage of CD4⁺ T cells polarized to Treg was significantly increased in SM compared to SF and PB. No significant differences were observed for CCR3 and CCR4 (preferentially expressed by Th2 cells), although IL-4 values were significantly higher in SM and SF compared to PB. Cytokine analysis showed comparable results between PB and SF, with only IL-6 being significantly increased in SF.

Conclusions

Early OA joints show already significant inflammation through CD4⁺ T cell infiltration, with predominant Th1 cell polarization. Inflammation seems to be driven by direct proinflammatory cell interaction. Cytokine signaling seems to be negligible at the site of inflammation in early OA, with only IL-6 being significantly increased in SF compared to PB.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-020-02410-w.

Association of serum CXCL12 levels with arthropathy in patients with systemic sclerosis

AIM

Systemic sclerosis (SSc) is an autoimmune connective tissue disease, in which extensive fibrotic change and vasculopathy affect the skin and various internal organs. It also involves the joints, causing stiffness, arthralgia, and arthritis. Although arthropathy is commonly observed in SSc, its underlying mechanism remains unknown. CXCL12, also known as stromal cell derived factor 1, is associated with inflammation, mesenchymal cell recruitment, angiogenesis, and collagen production, and is implicated in the development of various joint diseases. To assess the potential contribution of CXCL12 to SSc development, we investigated the clinical association of serum CXCL12 levels in patients with SSc.

METHOD

We conducted a cross-sectional analysis of 68 patients with SSc and 20 healthy controls recruited in a single center over 9 years. Serum CXCL12 levels were measured by enzyme-linked immunosorbent assay.

RESULTS

Serum CXCL12 levels were significantly higher in patients with SSc than in healthy controls (median 1554.0 pg/mL, 25th-75th centiles 1313.0-1914.0 pg/mL vs 967.4 pg/mL, 608.8-1271.0 pg/mL, P < 0.001). Patients with SSc with elevated CXCL12 levels had significantly more cases of arthropathy than those with normal CXCL12 levels (85.7% vs 25.0%, P = 0.01). Furthermore, patients with SSc with elevated CXCL12 levels showed an increased trend in the prevalence of limited range of motion of the finger joints compared with those with normal CXCL12 levels (60.0% vs 18.6%, P =0 .07). Moreover, serum CXCL12 levels were significantly correlated with the titers of rheumatoid factor in patients with SSc (r = .41, P = 0.001).

CONCLUSION

Elevated serum CXCL12 levels may be related to the development of SSc arthropathy.

Osteoarthritis: Prognosis and emerging therapeutic approach for disease management

Osteoarthritis (OA), a disorder of joints, is prevalent in older age. The contemporary cure for OA is aimed to confer symptomatic relief, consisting of temporary pain and swelling relief. In this paper, we discuss various modalities responsible for the onset of OA and associated with its severity. Inhibition of chondrocytes receptors such as DDR2, SDF-1, Asporin, and CXCR4 by specific pharmacological inhibitors attenuates OA, a critical step for finding potential disease modifying drugs. We critically analyzed recent OA studies with an emphasis on intermediate target molecules for OA intervention. We also explored some novel and safe treatments for OA by considering disease prognosis crosstalk with cellular signaling pathways.

Role of the SDF-1/CXCR4 signaling pathway in cartilage and subchondral bone in temporomandibular joint osteoarthritis induced by overloaded functional orthopedics in rats

OBJECTIVES

To (i) use a mandibular advancement appliance in rats to investigate the role of the stromal cell-derived factor/CXC receptor 4 (SDF-1/CXCR4) signaling pathway in temporomandibular joint osteoarthritis (TMJ OA) induced by overloaded functional orthopedics (OFO) and (ii) provide a cellular and molecular basis for efficacious treatment of skeletal class-II malocclusion and avoidance of TMJ OA.

METHOD

Male Sprague-Dawley rats (6 weeks) were divided randomly into control + normal saline (NS), EXP + ADM3100 (SDF-1 antagonist), EXP + NS, and control + ADM3100 groups. Changes in articular cartilage and subchondral bone after TMJ OA in these four groups were observed by hematoxylin and eosin (H&E), immunofluorescence double staining (IDS), Safranin-O staining, immunohistochemical (IHC) staining, real-time polymerase chain reaction, and micro-computed tomography at 2, 4, and 8 weeks.

RESULTS

OFO led to increased expression of SDF-1, CXCR4, and matrix metalloproteinase (MMP) 13 and decreased expression of collagen II. The thickness of the hypertrophic cartilage layer was reduced at 4 weeks in the EXP + NS group, and damage to subchondral bone was observed at 2 weeks. Using ADM3100 to inhibit SDF-1 signaling could attenuate expression of MMP13, cartilage damage, and osteoblast differentiation. IDS showed that the areas of expression of SDF-1 and OSX in subchondral bone overlapped.

CONCLUSIONS

Overloaded functional orthopedics (OFO) induced TMJ OA. The destruction of subchondral bone in TMJ OA caused by OFO occurred before damage to cartilage. SDF-1/CXCR4 may induce the osteogenic differentiation and cause cartilage degradation in TMJ OA caused by OFO.

Progenitor Cells Activated by Platelet Lysate in Human Articular Cartilage as a Tool for Future Cartilage Engineering and Reparative Strategies

Regenerative strategies for human articular cartilage are still challenging despite the presence of resident progenitor cell population. Today, many efforts in the field of regenerative medicine focus on the use of platelet derivatives due to their ability to reactivate endogenous mechanisms supporting tissue repair. While their use in orthopedics continues, mechanisms of action and efficacy need further characterization. We describe that the platelet lysate (PL) is able to activate chondro-progenitor cells in a terminally differentiated cartilage tissue. Primary cultures of human articular chondrocytes (ACs) and cartilage explants were set up from donor hip joint biopsies and were treated in vitro with PL. PL recruited a chondro-progenitors (CPCs)-enriched population from ex vivo cartilage culture, that showed high proliferation rate, clonogenicity and nestin expression. CPCs were positive for in vitro tri-lineage differentiation and formed hyaline cartilage-like tissue in vivo without hypertrophic fate. Moreover, the secretory profile of CPCs was analyzed, together with their migratory capabilities. Some CPC-features were also induced in PL-treated ACs compared to fetal bovine serum (FBS)-control ACs. PL treatment of human articular cartilage activates a stem cell niche responsive to injury. These facts can improve the PL therapeutic efficacy in cartilage applications.

Regulatory Effects and Interactions of the Wnt and OPG-RANKL-RANK Signaling at the Bone-Cartilage Interface in Osteoarthritis

Cartilage and the bordering subchondral bone form a functionally active regulatory interface with a prominent role in osteoarthritis pathways. The Wnt and the OPG-RANKL-RANK signaling systems, as key mediators, interact in subchondral bone remodeling. Osteoarthritic osteoblasts polarize into two distinct phenotypes: a low secretory and an activated, pro-inflammatory and anti-resorptive subclass producing high quantities of IL-6, PGE2, and osteoprotegerin, but low levels of RANKL, thus acting as putative effectors of subchondral bone sclerosis. Wnt agonists, Wnt5a, Wisp-1 initiate excessive bone remodeling, while Wnt3a and 5a simultaneously cause loss of proteoglycans and phenotype shift in chondrocytes, with decreased expression of COL2A, aggrecan, and Sox-9. Sclerostin, a Wnt antagonist possesses a protective effect for the cartilage, while DKK-1 inhibits VEGF, suspending neoangiogenesis in the subchondral bone. Experimental conditions mimicking abnormal mechanical load, the pro-inflammatory milieu, but also a decreased OPG/RANKL ratio in the cartilage, trigger chondrocyte apoptosis and loss of the matrix via degradative matrix metalloproteinases, like MMP-13 or MMP-9. Hypoxia, an important cofactor exerts a dual role, promoting matrix synthesis via HIF-1α, a Wnt silencer, but turning on HIF-2α that enhances VEGF and MMP-13, along with aberrant collagen expression and extracellular matrix deterioration in the presence of pro-inflammatory cytokines.

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.

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.

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.

Biochemical and biophysical characterization of cytokine-like protein 1 (CYTL1)

Cytokine-like protein 1 (CYTL1) is a small widely expressed secreted protein lacking significant primary sequence homology to any other known protein. CYTL1 expression appears to be highest in the hematopoietic system and in chondrocytes; however, maintenance of cartilage in mouse models of arthritis is its only reported function in vivo. Despite lacking sequence homology to chemokines, CYTL1 is predicted by computational methods to fold like a chemokine, and has been reported to function as a chemotactic agonist at the chemokine receptor CCR2 in mouse monocyte/macrophages. Nevertheless, since chemokines are defined by structure and chemokine receptors are able to bind many non-chemokine ligands, direct determination of the CYTL1 tertiary structure will ultimately be required to know whether it actually folds as a chemokine and therefore is a chemokine. Towards this goal, we have developed a method for producing functional recombinant human CYTL1 in bacteria, and we provide new evidence about the biophysical and biochemical properties of recombinant CYTL1. Circular dichroism analysis showed that, like chemokines, CYTL1has a higher content of beta-sheet than alpha-helix secondary structure. Furthermore, recombinant CYTL1 promoted calcium flux in chondrocytes. Nevertheless, unlike chemokines, CYTL1 had limited affinity to proteoglycans. Together, these properties further support cytokine-like properties for CYTL1 with some overlap with the chemokines.

Chondrogenic progenitor cells promote vascular endothelial growth factor expression through stromal-derived factor-1

OBJECTIVE

Vascular endothelial growth factor (VEGF) is elevated in joint fluids from patients diagnosed with osteoarthritis (OA). VEGF is known to contribute to vascular tidemark invasion and osteophyte formation, which are classic features of advanced OA. Among the factors that may drive VEGF accumulation in diseased joints, stromal cell-derived factor-1α (SDF-1α) is a likely culprit, as it is enriched in synovial fluids from osteoarthritic joints and is a potent inducer of VEGF expression. Chondrogenic progenitor cells (CPCs) that overexpress SDF-1α are abundant in osteoarthritic cartilage, implicating them in elevating synovial SDF-1α levels. Here we conducted a series of experiments to determine the potential for CPCs to stimulate VEGF expression via autocrine and paracrine mechanisms.

DESIGN

Immunohistochemistry, immunoblotting, and PCR were used to evaluate the effects of SDF-1α on VEGF expression in CPCs and chondrocytes, and the effects of CPC-conditioned medium on chondrocytes. An SDF-1α receptor antagonist and inhibitors of mitogen-activated protein kinases (MAPKs) were used to probe the pathway linking SDF-1 with VEGF expression in CPCs.

RESULTS

SDF-1α and CPC-conditioned medium stimulated VEGF expression in chondrocytes. In both chondrocytes and CPCs, SDF-1α stimulated increased VEGF expression via C-X-C chemokine receptor type 4 (CXCR4), a cell-surface SDF-1α receptor. This response in CPCs is dependent on p38 MAPK activation, but not on ERK or c-Jun N-terminal kinase (JNK) activation.

CONCLUSIONS

By secreting SDF-1α, CPCs stimulate VEGF expression in nearby cells. The co-expression of SDF-1 and its receptor by CPCs indicates they are capable of self-sustained VEGF expression via an autocrine mechanism.

Effects of mechanical stress on chondrocyte phenotype and chondrocyte extracellular matrix expression

Mechanical factors play a key role in regulating the development of cartilage degradation in osteoarthritis. This study aimed to identify the influence of mechanical stress in cartilage and chondrocytes. To explore the effects of mechanical stress on cartilage morphology, we observed cartilages in different regions by histological and microscopic examination. Nanoindentation was performed to assess cartilage biomechanics. To investigate the effects of mechanical stress on chondrocytes, cyclic tensile strain (CTS, 0.5 Hz, 10%) was applied to monolayer cultures of human articular chondrocytes by using Flexcell-5000. We quantified the mechanical properties of chondrocytes by atomic force microscopy. Chondrocytes were stained with Toluidine blue and Alcian blue after exposure to CTS. The expression of extracellular matrix (ECM) molecules was detected by qPCR and immunofluorescence analyses in chondrocytes after CTS. Our results demonstrated distinct morphologies and mechanical properties in different cartilage regions. In conclusion, mechanical stress can affect the chondrocyte phenotype, thereby altering the expression of chondrocyte ECM.

Histone deacetylase 3 supports endochondral bone formation by controlling cytokine signaling and matrix remodeling

Histone deacetylase (HDAC) inhibitors are efficacious epigenetic-based therapies for some cancers and neurological disorders; however, each of these drugs inhibits multiple HDACs and has detrimental effects on the skeleton. To better understand how HDAC inhibitors affect endochondral bone formation, we conditionally deleted one of their targets, Hdac3, pre- and postnatally in type II collagen α1 (Col2α1)-expressing chondrocytes. Embryonic deletion was lethal, but postnatal deletion of Hdac3 delayed secondary ossification center formation, altered maturation of growth plate chondrocytes, and increased osteoclast activity in the primary spongiosa. HDAC3-deficient chondrocytes exhibited increased expression of cytokine and matrix-degrading genes (Il-6, Mmp3, Mmp13, and Saa3) and a reduced abundance of genes related to extracellular matrix production, bone development, and ossification (Acan, Col2a1, Ihh, and Col10a1). Histone acetylation increased at and near genes that had increased expression. The acetylation and activation of nuclear factor κB (NF-κB) were also increased in HDAC3-deficient chondrocytes. Increased cytokine signaling promoted autocrine activation of Janus kinase (JAK)-signal transducer and activator of transcription (STAT) and NF-κB pathways to suppress chondrocyte maturation, as well as paracrine activation of osteoclasts and bone resorption. Blockade of interleukin-6 (IL-6)-JAK-STAT signaling, NF-κB signaling, and bromodomain extraterminal proteins, which recognize acetylated lysines and promote transcriptional elongation, significantly reduced Il-6 and Mmp13 expression in HDAC3-deficient chondrocytes and secondary activation in osteoclasts. The JAK inhibitor ruxolitinib also reduced osteoclast activity in Hdac3 conditional knockout mice. Thus, HDAC3 controls the temporal and spatial expression of tissue-remodeling genes and inflammatory responses in chondrocytes to ensure proper endochondral ossification during development.

Inhibition of SDF-1α/CXCR4 Signalling in Subchondral Bone Attenuates Post-Traumatic Osteoarthritis

Previous studies showed that SDF-1α is a catabolic factor that can infiltrate cartilage, decrease proteoglycan content, and increase MMP-13 activity. Inhibiting the SDF-1α/CXCR4 signalling pathway can attenuate the pathogenesis of osteoarthritis (OA). Recent studies have also shown that SDF-1α enhances chondrocyte proliferation and maturation. These results appear to be contradictory. In the current study, we used a destabilisation OA animal model to investigate the effects of SDF-1α/CXCR4 signalling in the tibial subchondral bone and the OA pathological process. Post-traumatic osteoarthritis (PTOA) mice models were prepared by transecting the anterior cruciate ligament (ACLT), or a sham surgery was performed, in a total of 30 mice. Mice were treated with phosphate buffer saline (PBS) or AMD3100 (an inhibitor of CXCR4) and sacrificed at 30 days post ACLT or sham surgery. Tibial subchondral bone status was quantified by micro-computed tomography (μCT). Knee-joint histology was analysed to examine the articular cartilage and joint degeneration. The levels of SDF-1α and collagen type I c-telopeptidefragments (CTX-I) were quantified by ELISA. Bone marrow mononuclear cells (BMMCs) were used to clarify the effects of SDF-1α on osteoclast formation and activity in vivo. μCT analysis revealed significant loss of trabecular bone from tibial subchondral bone post-ACLT, which was effectively prevented by AMD3100. AMD3100 could partially prevent bone loss and articular cartilage degeneration. Serum biomarkers revealed an increase in SDF-1α and bone resorption, which were also reduced by AMD3100. SDF-1α can promote osteoclast formation and the expression oftartrate resistant acid phosphatase (TRAP), cathepsin K (CK), and matrix metalloproteinase (MMP)-9 in osteoclasts by activating the MAPK pathway, including ERK and p38, but not JNK. In conclusion, inhibition of SDF-1α/CXCR4signalling was able to prevent trabecular bone loss and attenuated cartilage degeneration in PTOA mice.

Cells and secretome--towards endogenous cell re-activation for cartilage repair

Regenerative medicine approaches to cartilage tissue repair have mainly been concerned with the implantation of a scaffold material containing monolayer expanded cells into the defect, with the aim to differentiate the cells into chondrocytes. While this may be a valid approach, the secretome of the implanted cells and its effects on the endogenous resident cells, is gaining in interest. This review aims to summarize the knowledge on the secretome of mesenchymal stem cells, including knowledge from other tissues, in order to indicate how these mechanisms may be of value in repairing articular cartilage defects. Potential therapies and their effects on the repair of articular cartilage defects will be discussed, with a focus on the transition from classical cell therapy to the implantation of cell free matrices releasing specific cytokines.

Concentrations of stromal cell-derived factor-1 in serum, plasma, and synovial fluid of horses with osteochondral injury

OBJECTIVE

To determine whether stromal cell-derived factor-1 (SDF-1) concentrations in serum, plasma, and synovial fluid differed among untrained, race-trained, and osteochondral-injured Thoroughbred racehorses.

ANIMALS

22 racehorses without osteochondral injury and 37 racehorses with osteochondral injury.

PROCEDURES

Horses without osteochondral injury were examined before and after 5 to 6 months of race training. Horses with osteochondral injury were undergoing arthroscopic surgery for removal of osteochondral fragments from carpal or metacarpophalangeal or metatarsophalangeal joints (fetlock joints). Serum, plasma, and fetlock or carpal synovial fluid samples were obtained and analyzed for SDF-1 concentration by use of an ELISA.

RESULTS

In horses with fetlock or carpal joint injury, mean synovial fluid SDF-1 concentrations were significantly higher, serum SDF-1 concentrations were significantly lower, and synovial fluid-to-serum SDF-1 ratios were significantly higher than in untrained and trained horses. Synovial fluid SDF-1 concentrations were not significantly different between trained and untrained horses. Plasma SDF-1 concentrations were not different among the 3 groups. Results obtained with serum, compared with synovial fluid and plasma, had better sensitivity for differentiating between osteochondral-injured horses and uninjured horses. In horses with fetlock joint osteochondral injury, serum SDF-1 concentrations were correlated with radiographic and arthroscopic inflammation scores, but not arthroscopic cartilage scores.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that serum SDF-1 concentrations were more sensitive than plasma and synovial fluid concentrations for detection of osteochondral injury in the fetlock or carpal joint of racehorses. Analysis of serum and synovial SDF-1 concentrations in horses with experimentally induced joint injury may help define the onset and progression of post-traumatic osteoarthritis and aid in the evaluation of anti-inflammatory treatments.

Homeostatic mechanisms in articular cartilage and role of inflammation in osteoarthritis

Osteoarthritis (OA) is a whole joint disease, in which thinning and disappearance of cartilage is a critical determinant in OA progression. The rupture of cartilage homeostasis whatever its cause (aging, genetic predisposition, trauma or metabolic disorder) induces profound phenotypic modifications of chondrocytes, which then promote the synthesis of a subset of factors that induce cartilage damage and target other joint tissues. Interestingly, among these factors are numerous components of the inflammatory pathways. Chondrocytes produce cytokines, chemokines, alarmins, prostanoids, and adipokines and express numerous cell surface receptors for cytokines and chemokines, as well as Toll-like receptors. These receptors activate intracellular signaling pathways involved in inflammatory and stress responses of chondrocytes in OA joints. This review focuses on mechanisms responsible for the maintenance of cartilage homeostasis and highlights the role of inflammatory processes in OA progression.

Combined degenerative and regenerative remodeling responses of the mandibular condyle to experimentally induced disordered occlusion

INTRODUCTION

The purposes of this research were to investigate the long-term responses of mandibular condylar cartilage to experimentally induced disordered occlusion and to evaluate changes in the expression of the SDF-1/CXCR4 axis.

METHODS

Experimentally induced disordered occlusions were created in 8-week-old female Sprague-Dawley rats by orthodontic methods. After 24 weeks, remodeling of the mandibular condylar cartilage was assessed by hematoxylin and eosin staining. Protein and mRNA expression of SDF-1, CXCR4, MMP9, IL6, OPG, and RANKL were investigated by means of immunohistochemical staining and real-time polymerase chain reaction.

RESULTS

Obvious cartilage degenerative remodeling responses were observed; they appeared as uneven distributions of cellular disposition, loss of cartilage surface integrity, and cell-free areas. Regenerative responses presenting as thickening of the whole and the calcified cartilage layers in the experimental group were also observed. Compared with the age-matched controls, the protein and mRNA levels of SDF-1, CXCR4, MMP9, IL6, and OPG, but not RANKL, were increased in the experimental group (all, P <0.05). In addition, the mRNA level of RANKL/OPG showed a decreasing trend in the experimental group compared with the age-matched controls (P = 0.052).

CONCLUSIONS

This study demonstrated that long-term experimentally induced disordered occlusion leads to a combined response in degeneration and regeneration of mandibular cartilage, accompanied by active interaction of the SDF-1/CXCR4 axis and local upregulation of MMP9, IL6, and OPG.

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.

The cytokine and chemokine expression profile of nucleus pulposus cells: implications for degeneration and regeneration of the intervertebral disc

INTRODUCTION

The aims of these studies were to identify the cytokine and chemokine expression profile of nucleus pulposus (NP) cells and to determine the relationships between NP cell cytokine and chemokine production and the characteristic tissue changes seen during intervertebral disc (IVD) degeneration.

METHODS

Real-time q-PCR cDNA Low Density Array (LDA) was used to investigate the expression of 91 cytokine and chemokine associated genes in NP cells from degenerate human IVDs. Further real-time q-PCR was used to investigate 30 selected cytokine and chemokine associated genes in NP cells from non-degenerate and degenerate IVDs and those from IVDs with immune cell infiltrates (‘infiltrated’). Immunohistochemistry (IHC) was performed for four selected cytokines and chemokines to confirm and localize protein expression in human NP tissue samples.

RESULTS

LDA identified the expression of numerous cytokine and chemokine associated genes including 15 novel cytokines and chemokines. Further q-PCR gene expression studies identified differential expression patterns in NP cells derived from non-degenerate, degenerate and infiltrated IVDs. IHC confirmed NP cells as a source of IL-16, CCL2, CCL7 and CXCL8 and that protein expression of CCL2, CCL7 and CXCL8 increases concordant with histological degenerative tissue changes.

CONCLUSIONS

Our data indicates that NP cells are a source of cytokines and chemokines within the IVD and that these expression patterns are altered in IVD pathology. These findings may be important for the correct assessment of the ‘degenerate niche’ prior to autologous or allogeneic cell transplantation for biological therapy of the degenerate IVD.

Chondrogenesis, chondrocyte differentiation, and articular cartilage metabolism in health and osteoarthritis

Chondrogenesis occurs as a result of mesenchymal cell condensation and chondroprogenitor cell differentiation. Following chondrogenesis, the chondrocytes remain as resting cells to form the articular cartilage or undergo proliferation, terminal differentiation to chondrocyte hypertrophy, and apoptosis in a process termed endochondral ossification, whereby the hypertrophic cartilage is replaced by bone. Human adult articular cartilage is a complex tissue of matrix proteins that varies from superficial to deep layers and from loaded to unloaded zones. A major challenge to efforts to repair cartilage by stem cell-based and other tissue-engineering strategies is the inability of the resident chondrocytes to lay down a new matrix with the same properties as it had when it was formed during development. Thus, understanding and comparing the mechanisms of cartilage remodeling during development, osteoarthritis (OA), and aging may lead to more effective strategies for preventing cartilage damage and promoting repair. The pivotal proteinase that marks OA progression is matrix metalloproteinase 13 (MMP-13), the major type II collagen-degrading collagenase, which is regulated by both stress and inflammatory signals. We and other investigators have found that there are common mediators of these processes in human OA cartilage. We also observe temporal and spatial expression of these mediators in early through late stages of OA in mouse models and are analyzing the consequences of knockout or transgenic overexpression of critical genes. Since the chondrocytes in adult human cartilage are normally quiescent and maintain the matrix in a low turnover state, understanding how they undergo phenotypic modulation and promote matrix destruction and abnormal repair in OA may to lead to identification of critical targets for therapy to block cartilage damage and promote effective cartilage repair.

Attenuation of osteoarthritis via blockade of the SDF-1/CXCR4 signaling pathway

Introduction

This study was performed to evaluate the attenuation of osteoarthritic (OA) pathogenesis via disruption of the stromal cell-derived factor-1 (SDF-1)/C-X-C chemokine receptor type 4 (CXCR4) signaling with AMD3100 in a guinea pig OA model.

Methods

OA chondrocytes and cartilage explants were incubated with SDF-1, siRNA CXCR4, or anti-CXCR4 antibody before treatment with SDF-1. Matrix metalloproteases (MMPs) mRNA and protein levels were measured with real-time polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA), respectively. The 35 9-month-old male Hartley guinea pigs (0.88 kg ± 0.21 kg) were divided into three groups: AMD-treated group (n = 13); OA group (n = 11); and sham group (n = 11). At 3 months after treatment, knee joints, synovial fluid, and serum were collected for histologic and biochemical analysis. The severity of cartilage damage was assessed by using the modified Mankin score. The levels of SDF-1, glycosaminoglycans (GAGs), MMP-1, MMP-13, and interleukin-1 (IL-1β) were quantified with ELISA.

Results

SDF-1 infiltrated cartilage and decreased proteoglycan staining. Increased glycosaminoglycans and MMP-13 activity were found in the culture media in response to SDF-1 treatment. Disrupting the interaction between SDF-1 and CXCR4 with siRNA CXCR4 or CXCR4 antibody attenuated the effect of SDF-1. Safranin-O staining revealed less cartilage damage in the AMD3100-treated animals with the lowest Mankin score compared with the control animals. The levels of SDF-1, GAG, MMP1, MMP-13, and IL-1β were much lower in the synovial fluid of the AMD3100 group than in that of control group.

Conclusions

The binding of SDF-1 to CXCR4 induces OA cartilage degeneration. The catabolic processes can be disrupted by pharmacologic blockade of SDF-1/CXCR4 signaling. Together, these findings raise the possibility that disruption of the SDF-1/CXCR4 signaling can be used as a therapeutic approach to attenuate cartilage degeneration.

Engineered cartilage maturation regulates cytokine production and interleukin-1β response

BACKGROUND

Because the injured joint has an actively inflammatory environment, the survival and repair potential of cartilage grafts may be influenced by inflammatory processes. Understanding the interactions of those processes with the graft may lead to concepts for pharmacologic or surgical solutions allowing improved cartilage repair.

QUESTIONS/PURPOSES

We asked whether the maturation level of cartilaginous tissues generated in vitro by expanded human articular chondrocytes (HACs) modulate (1) the spontaneous production of cytokines and (2) the response to interleukin (IL)-1β.

METHODS

Twelve pellets/donor prepared with monolayer-expanded HACs (n = 6 donors) were evaluated at six different culture times for mRNA expression (n = 72) and spontaneous baseline release of monocyte chemoattractant protein (MCP)-1, IL-8, and transforming growth factor (TGF)-β1 (n = 72). We cultured 24 pellets/donor from each of four donors for 1 or 14 days (defined as immature and mature, respectively) and exposed the pellets to IL-1β for 3 days. MCP-1, IL-8, TGF-β1, and metalloprotease (MMP)-1 and MMP-13 were quantified in pellets and culture supernatants.

RESULTS

By increasing culture time, the spontaneous release of IL-8 and MCP-1 decreased (12.0- and 5.5-fold, respectively), whereas that of TGF-β1 increased (5.4-fold). As compared with immature pellets, mature pellets responded to IL-1β by releasing lower amounts of MMP-1 (2.9-fold) and MMP-13 (1.7-fold) and increased levels of IL-8, MCP-1, and TGF-β1 (1.5-, 5.0-, and 7.5-fold, respectively). IL-8 and MCP-1 promptly returned to baseline on withdrawal of IL-1β.

CONCLUSIONS

Our observations suggest more mature cartilaginous tissues are more resistant to IL-1β exposure and can activate chemokines required to initiate tissue repair processes.

CLINICAL RELEVANCE

The implantation of more mature cartilaginous tissues might provide superior graft survival and improve/accelerate cartilage repair.

Chondrogenesis by chemotactic homing of synovium, bone marrow, and adipose stem cells in vitro

Cell transplantation has been well explored for cartilage regeneration. We recently showed that the entire articular surface of a synovial joint can regenerate by endogenous cell homing and without cell transplantation. However, the sources of endogenous cells that regenerate articular cartilage remain elusive. Here, we studied whether cytokines not only chemotactically recruit adipose stem cells (ASCs), mesenchymal stem cells (MSCs), and synovium stem cells (SSCs) but also induce chondrogenesis of the recruited cells. Recombinant human transforming growth factor-β3 (TGF-β3; 100 ng) and/or recombinant human stromal derived factor-1β (SDF-1β; 100 ng) was control released into an acellular collagen sponge cube with underlying ASCs, MSCs, or SSCs in monolayer culture. Although all cell types randomly migrated into the acellular collagen sponge cube, TGF-β3 and/or SDF-1β recruited significantly more cells than the cytokine-free control group. In 6 wk, TGF-β3 alone recruited substantial numbers of ASCs (558±65) and MSCs (302±52), whereas codelivery of TGF-β3 and SDF-1β was particularly chemotactic to SSCs (400±120). Proliferation of the recruited cells accounted for some, but far from all, of the observed cellularity. TGF-β3 and SDF-1β codelivery induced significantly higher aggrecan gene expression than the cytokine-free group for ASCs, MSCs, and SSCs. Type II collagen gene expression was also significantly higher for ASCs and SSCs by SDF-1 and TGF-β3 codelivery. Remarkably, the expression of aggrecan and type II collagen was detected among all cell types. Thus, homing of multiple stem/progenitor cell populations may potentially serve as an alternative or adjunctive approach to cell transplantation for cartilage regeneration.

Trends in cardiovascular mortality in patients with rheumatoid arthritis over 50 years: a systematic review and meta-analysis of cohort studies

OBJECTIVES

RA is known to be associated with a high cardiovascular (CV) risk. Longitudinal data suggest that RA disease course may have become milder over the past decades. Thus, we set out to estimate the magnitude of the overall increase in CV mortality associated with RA and to determine whether it has decreased over the past 50 years.

METHODS

We performed a systematic review and a meta-analysis of literature in MEDLINE and EMBASE databases from January 1960 to November 2008. All cohort studies reporting CV mortality risk were included. We then calculated pooled standardized mortality ratios (SMRs) of CV mortality, and determined their evolution with time using meta-regression analysis.

RESULTS

Seventeen studies were analysed, corresponding to a total of 91 916 patients. The overall pooled SMR was 1.6 (95% CI 1.5, 1.8; I(2) = 93%; P(het) < 0.0001). Mid-cohort year ranged from 1945 to 1995 (<1980, seven studies; 1980-90, five studies; >1990, five studies). Meta-regression analyses revealed neither any trend in SMR over time (P = 0.784) nor any relation with disease duration at the time of inclusion (P = 0.513).

CONCLUSIONS

Our results show that RA is associated with a 60% increase in risk of CV death compared with general population. Despite changes in RA course over the past decades, SMR for CV death has not changed. This suggests that targeting a reduction in CV mortality should still be considered as a major issue in RA.

The role of chemokines in rheumatoid arthritis and osteoarthritis

The directed movement of immune cells is highly dependent on the chemokine network. Chemokines are key molecules early in the embryogenesis of lymph nodes and throughout adult life, where they regulate immune responses against pathogens. Although immune cells are best known for expressing chemokine receptors, through which they can respond to matching chemokines, endothelial cells also express chemokine receptors. The directed movement of endothelial cells facilitates angiogenesis. In chronic inflammatory conditions, such as rheumatoid arthritis (RA), chemokines are abundantly present at the site of inflammation and form a group of potential therapeutic targets. Some agents that block chemokine-chemokine receptor interaction are already under clinical investigation. The expression of chemokine receptors has also been found in cell types other than immune cells and endothelial cells. Chondrocytes, for instance, express several chemokine receptors. Elucidating their function may provide new insights into joint degradation in RA as well as in other conditions, including osteoarthritis (OA).

Differential requirements for IKKalpha and IKKbeta in the differentiation of primary human osteoarthritic chondrocytes

OBJECTIVE

Osteoarthritic (OA) chondrocytes behave in an intrinsically deregulated manner, characterized by chronic loss of healthy cartilage and inappropriate differentiation to a hypertrophic-like state. IKKalpha and IKKbeta are essential kinases that activate NF-kappaB transcription factors, which in turn regulate cell differentiation and inflammation. This study was undertaken to investigate the differential roles of each IKK in chondrocyte differentiation and hypertrophy.

METHODS

Expression of IKKalpha or IKKbeta was ablated in primary human chondrocytes by retro-transduction of specific short-hairpin RNAs. Micromass cultures designed to reproduce chondrogenesis with progression to the terminal hypertrophic stage were established, and anabolism and remodeling of the extracellular matrix (ECM) were investigated in the micromasses using biochemical, immunohistochemical, and ultrastructural techniques. Cellular parameters of hypertrophy (i.e., proliferation, viability, and size) were also analyzed.

RESULTS

The processes of ECM remodeling and mineralization, both characteristic of terminally differentiated hypertrophic cells, were defective following the loss of IKKalpha or IKKbeta. Silencing of IKKbeta markedly enhanced accumulation of glycosaminoglycan in conjunction with increased SOX9 expression. Ablation of IKKalpha dramatically enhanced type II collagen deposition independent of SOX9 protein levels but in association with suppressed levels of runt-related transcription factor 2. Moreover, IKKalpha-deficient cells retained the phenotype of cells in a pre-hypertrophic-like state, as evidenced by the smaller size and faster proliferation of these cells prior to micromass seeding, along with the enhanced viability of their differentiated micromasses.

CONCLUSION

IKKalpha and IKKbeta exert differential roles in ECM remodeling and endochondral ossification, which are events characteristic of hypertrophic chondrocytes and also complicating factors often found in OA. Because the effects of IKKalpha were more profound and pleotrophic in nature, our observations suggest that exacerbated IKKalpha activity may be responsible, at least in part, for the characteristic abnormal phenotypes of OA chondrocytes.

Key regulatory molecules of cartilage destruction in rheumatoid arthritis: an in vitro study

Background

Rheumatoid arthritis (RA) is a chronic, inflammatory and systemic autoimmune disease that leads to progressive cartilage destruction. Advances in the treatment of RA-related destruction of cartilage require profound insights into the molecular mechanisms involved in cartilage degradation. Until now, comprehensive data about the molecular RA-related dysfunction of chondrocytes have been limited. Hence, the objective of this study was to establish a standardized in vitro model to profile the key regulatory molecules of RA-related destruction of cartilage that are expressed by human chondrocytes.

Methods

Human chondrocytes were cultured three-dimensionally for 14 days in alginate beads and subsequently stimulated for 48 hours with supernatants from SV40 T-antigen immortalized human synovial fibroblasts (SF) derived from a normal donor (NDSF) and from a patient with RA (RASF), respectively. To identify RA-related factors released from SF, supernatants of RASF and NDSF were analyzed with antibody-based protein membrane arrays. Stimulated cartilage-like cultures were used for subsequent gene expression profiling with oligonucleotide microarrays. Affymetrix GeneChip Operating Software and Robust Multi-array Analysis (RMA) were used to identify differentially expressed genes. Expression of selected genes was verified by real-time RT-PCR.

Results

Antibody-based protein membrane arrays of synovial fibroblast supernatants identified RA-related soluble mediators (IL-6, CCL2, CXCL1–3, CXCL8) released from RASF. Genome-wide microarray analysis of RASF-stimulated chondrocytes disclosed a distinct expression profile related to cartilage destruction involving marker genes of inflammation (adenosine A2A receptor, cyclooxygenase-2), the NF-κB signaling pathway (toll-like receptor 2, spermine synthase, receptor-interacting serine-threonine kinase 2), cytokines/chemokines and receptors (CXCL1–3, CXCL8, CCL20, CXCR4, IL-1β, IL-6), cartilage degradation (matrix metalloproteinase (MMP)-10, MMP-12) and suppressed matrix synthesis (cartilage oligomeric matrix protein, chondroitin sulfate proteoglycan 2).

Conclusion

Differential transcriptome profiling of stimulated human chondrocytes revealed a disturbed catabolic–anabolic homeostasis of chondrocyte function and disclosed relevant pharmacological target genes of cartilage destruction. This study provides comprehensive insight into molecular regulatory processes induced in human chondrocytes during RA-related destruction of cartilage. The established model may serve as a human in vitro disease model of RA-related destruction of cartilage and may help to elucidate the molecular effects of anti-rheumatic drugs on human chondrocyte gene expression.

Biomechanical signals inhibit IKK activity to attenuate NF-kappaB transcription activity in inflamed chondrocytes

OBJECTIVE

While the effects of biomechanical signals in the form of joint movement and exercise are known to be beneficial to inflamed joints, limited information is available regarding the intracellular mechanisms of their actions. This study was undertaken to examine the intracellular mechanisms by which biomechanical signals suppress proinflammatory gene induction by the interleukin-1-beta (IL-1beta)-induced NF-kappaB signaling cascade in articular chondrocytes.

METHODS

Primary rat articular chondrocytes were exposed to biomechanical signals in the form of cyclic tensile strain, and the effects on the NF-kappaB signaling cascade were examined by Western blot analysis, real-time polymerase chain reaction, and immunofluorescence.

RESULTS

Cyclic tensile strain rapidly inhibited the IL-1beta-induced nuclear translocation of NF-kappaB, but not its IL-1beta-induced phosphorylation at serine 276 and serine 536, which are necessary for its transactivation and transcriptional efficacy, respectively. Examination of upstream events revealed that cyclic tensile strain also inhibited the cytoplasmic protein degradation of IkappaBbeta and IkappaBalpha, as well as repressed their gene transcription. Additionally, cyclic tensile strain induced a rapid nuclear translocation of IkappaBalpha to potentially prevent NF-kappaB binding to DNA. Furthermore, the inhibition of IL-1beta-induced degradation of IkappaB by cyclic tensile strain was mediated by down-regulation of IkappaB kinase activity.

CONCLUSION

These results indicate that the signals generated by cyclic tensile strain act at multiple sites within the NF-kappaB signaling cascade to inhibit IL-1beta-induced proinflammatory gene induction. Taken together, these findings provide insight into how biomechanical signals regulate and reduce inflammation, and underscore their potential in enhancing the ability of chondrocytes to curb inflammation in diseased joints.

Microenvironmental changes during differentiation of mesenchymal stem cells towards chondrocytes

Chondrogenesis is a process involving stem-cell differentiation through the coordinated effects of growth/differentiation factors and extracellular matrix (ECM) components. Recently, mesenchymal stem cells (MSCs) were found within the cartilage, which constitutes a specific niche composed of ECM proteins with unique features. Therefore, we hypothesized that the induction of MSC differentiation towards chondrocytes might be induced and/or influenced by molecules from the microenvironment. Using microarray analysis, we previously identified genes that are regulated during MSC differentiation towards chondrocytes. In this study, we wanted to precisely assess the differential expression of genes associated with the microenvironment using a large-scale real-time PCR assay, according to the simultaneous detection of up to 384 mRNAs in one sample. Chondrogenesis of bone-marrow-derived human MSCs was induced by culture in micropellet for various periods of time. Total RNA was extracted and submitted to quantitative RT-PCR. We identified molecules already known to be involved in attachment and cell migration, including syndecans, glypicans, gelsolin, decorin, fibronectin, and type II, IX and XI collagens. Importantly, we detected the expression of molecules that were not previously associated with MSCs or chondrocytes, namely metalloproteases (MMP-7 and MMP-28), molecules of the connective tissue growth factor (CTGF); cef10/cyr61 and nov (CCN) family (CCN3 and CCN4), chemokines and their receptors chemokine CXC motif ligand (CXCL1), Fms-related tyrosine kinase 3 ligand (FlT3L), chemokine CC motif receptor (CCR3 and CCR4), molecules with A Disintegrin And Metalloproteinase domain (ADAM8, ADAM9, ADAM19, ADAM23, A Disintegrin And Metalloproteinase with thrombospondin type 1 motif ADAMTS-4 and ADAMTS-5), cadherins (4 and 13) and integrins (alpha4, alpha7 and beta5). Our data suggest that crosstalk between ECM components of the microenvironment and MSCs within the cartilage is responsible for the differentiation of MSCs into chondrocytes.

Global analyses of gene expression in early experimental osteoarthritis

OBJECTIVE

To analyze genome-wide changes in chondrocyte gene expression in a surgically induced model of early osteoarthritis (OA) in rats, to assess the similarity of this model to human OA, and to identify genes and mechanisms leading to OA pathogenesis.

METHODS

OA was surgically induced in 5 rats by anterior cruciate ligament transection and partial medial meniscectomy. Sham surgery was performed in 5 additional animals, which were used as controls. Both groups underwent 4 weeks of forced mobilization, 3 times per week. RNA was extracted directly from articular chondrocytes in the OA (operated), contralateral, and sham-operated knees. Affymetrix GeneChip expression arrays were used to assess genome-wide changes in gene expression. Expression patterns of selected dysregulated genes, including Col2a1, Mmp13, Adamts5, Ctsc, Ptges, and Cxcr4, were validated by real-time polymerase chain reaction, immunofluorescence, or immunohistochemistry 2, 4, and 8 weeks after surgery.

RESULTS

After normalization, comparison of OA and sham-operated samples showed 1,619 differentially expressed probe sets with changes in their levels of expression > or = 1.5-fold, 722 with changes > or = 2-fold, 135 with changes > or = 4-fold, and 20 with changes of 8-fold. Dysregulated genes known to be involved in human OA included Mmp13, Adamts5, and Ptgs2, among others. Several dysregulated genes (e.g., Reln, Phex, and Ltbp2) had been identified in our earlier microarray study of hypertrophic chondrocyte differentiation. Other genes involved in cytokine and chemokine signaling, including Cxcr4 and Ccl2, were identified. Changes in gene expression were also observed in the contralateral knee, validating the sham operation as the appropriate control.

CONCLUSION

Our results demonstrate that the animal model mimics gene expression changes seen in human OA, supporting the relevance of newly identified genes and pathways to early human OA. We propose new avenues for OA pathogenesis research and potential targets for novel OA treatments, including cathepsins and cytokine, chemokine, and growth factor signaling pathways, in addition to factors controlling the progression of chondrocyte differentiation.

Odontoblast marker gene expression is enhanced by a CC-chemokine family protein MIP-3alpha in human mesenchymal stem cells

OBJECTIVE

Macrophage inflammatory protein-3 alpha (MIP-3alpha) is a major CC-chemokine family protein, which serves as a differentiation factor for mesenchymal cells, including osteoblasts and dental pulp cells. The purpose of this study was to investigate the influence of MIP-3alpha on human mesenchymal stem cell differentiation in vitro.

DESIGN

Human mesenchymal stem cells were maintained in Dulbecco's modified Eagle's medium in the presence or absence of MIP-3alpha and the presence or absence of osteogenic factors (dexamethasone, beta-glycerophoshate and ascorbic acid). Alkaline phosphatase (ALP) activity was measured, and expression of odontoblast and osteoblast markers were examined by RT-PCR and Western blotting.

RESULTS

MIP-3alpha alone did not increase ALP activity, as compared to controls. The combination of MIP-3alpha and osteogenic factors increased ALP activity beyond increases observed with osteogenic factors alone. mRNA expression of the odontoblast marker dspp was only detectable when MIP-3alpha was added together with osteogenic factors at day 7 in three out of four samples. DSP protein level was increased only in the samples treated with both MIP-3alpha and osteogenic factors until day 5. In contrast, MIP-3alpha did not influence levels of the osteoblast markers CBFA1 or BSP.

CONCLUSIONS

The present study demonstrated that MIP-3alpha enhanced gene expression and protein levels of odontoblast-related genes, without affecting levels of the osteogenic proteins CBFA1 or BSP.

Chondrocyte hypertrophy and apoptosis induced by GROalpha require three-dimensional interaction with the extracellular matrix and a co-receptor role of chondroitin sulfate and are associated with the mitochondrial splicing variant of cathepsin B

CXCR2 ligands contribute to chondrocyte hypertrophy and apoptosis, important determinants in cartilage pathophysiology. We unraveled the kinetics of signaling, biochemical, transcriptional, and morphological events triggered by GROalpha in human osteoarthritic chondrocytes kept in three-dimensional culture. p38 MAPK activation was assessed with a highly sensitive ELISA. Effector caspase activation was evaluated by cleavage of a fluorogenic substrate. Gene expression of key markers of hypertrophy (MMP-13, Runx-2) and matrix synthesis (aggrecan), and of cathepsin B isoform CB(-2,3) was evaluated by real time PCR. Occurrence of the morphological markers of apoptosis was investigated by transmission electron microscopy (TEM). GROalpha led to p38 MAPK activation in passaged chondrocytes cultured in micromass but not as a high-density monolayer. This caused the downstream triggering of chondrocyte hypertrophy (MMP-13 and Runx-2 upregulation, and calcium deposition) and apoptosis/anoikis following concurrence of matrix degrading activity, and inhibition of matrix synthesis which also involved the induction of CB(-2,3). These phenomena proved to be dependent on the co-receptor role of sulfated glycosaminoglycans (sGAG) and the activation of p38 MAPK, since they were abrogated either by preincubation with soluble chondroitin-4 sulfate or p38 MAPK inhibitors. The co-receptor role of sGAG was further demonstrated by colocalization experiments of these molecules with GROalpha in the stimulated micromasses. These findings suggest that extracellular matrix exerts a regulatory role in chondrocytes differentiation, and that meaningful investigation of the effects of chemokines on chondrocyte biology requires culture conditions respectful of both the differentiated status of the chondrocytes and of their three-dimensional interaction with the extracellular matrix.

Biomechanical signals exert sustained attenuation of proinflammatory gene induction in articular chondrocytes

OBJECTIVES

Physical therapies are commonly used for limiting joint inflammation. To gain insight into their mechanisms of actions for optimal usage, we examined persistence of mechanical signals generated by cyclic tensile strain (CTS) in chondrocytes, in vitro. We hypothesized that mechanical signals induce anti-inflammatory and anabolic responses that are sustained over extended periods.

METHODS

Articular chondrocytes obtained from rats were subjected to CTS for various time intervals followed by a period of rest, in the presence of interleukin-1beta (IL-1beta). The induction for cyclooxygenase (COX-2), inducible nitric oxide synthase (iNOS), matrix metalloproteinase (MMP)-9, MMP-13 and aggrecan was analyzed by real-time polymerase chain reaction (PCR), Western blot analysis and immunofluorescence.

RESULTS

Exposure of chondrocytes to constant CTS (3% CTS at 0.25 Hz) for 4-24 h blocked more than 90% (P<0.05) of the IL-1beta-induced transcriptional activation of proinflammatory genes, like iNOS, COX-2, MMP-9 and MMP-13, and abrogated inhibition of aggrecan synthesis. CTS exposure for 4, 8, 12, 16, or 20 h followed by a rest for 20, 16, 12, 8 or 4h, respectively, revealed that 8h of CTS optimally blocked (P<0.05) IL-1beta-induced proinflammatory gene induction for ensuing 16 h. However, CTS for 8h was not sufficient to inhibit iNOS expression for ensuing 28 or 40 h.

CONCLUSIONS

Data suggest that constant application of CTS blocks IL-1beta-induced proinflammatory genes at transcriptional level. The signals generated by CTS are sustained after its removal, and their persistence depends upon the length of CTS exposure. Furthermore, the sustained effects of mechanical signals are also reflected in their ability to induce aggrecan synthesis. These findings, once extrapolated to human chondrocytes, may provide insight in obtaining optimal sustained effects of physical therapies in the management of arthritic joints.

Technology Insight: gene transfer and the design of novel treatments for rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by systemic inflammation and joint destruction. Novel therapies have emerged during the past decade, marking a new era in the treatment of RA. Meanwhile, in vivo and in vitro gene-transfer studies have provided valuable insights into mechanisms of disease pathogenesis. Advanced gene-delivery techniques and animal models promise further progress in RA research and the development of novel therapeutic strategies for this disease. In this article we provide an overview of the wide spectrum of potential targets that have been identified so far, discuss currently available gene-transfer methods, and outline the barriers that need to be overcome for these approaches to be successfully applied in daily practice.

Cell and matrix morpho-functional analysis in chondrocyte micromasses

Micromass cultures represent a convenient means of studying chondrocyte physiology in the context of a tridimensional culture model. In this study, we present the first ultrastructural analysis of the distribution and organization of the extracellular components in micromasses in comparison with their cartilaginous counterparts. Primary chondrocytes obtained from osteoarthritis patients were pelleted in micromasses. Transmission electron microscopy and immunofluorescence were used to evaluate the distribution of major extracellular matrix proteins, i.e., aggrecan, chondroitin-4-sulfate, chondroitin-6-sulfate, and collagen I and II. Both approaches revealed a number of morphological features shared by micromass and cartilage chondrocytes. In particular, in micromasses, chondrocytes are in close contact with an organized extracellular matrix that adequately mimics that of cartilage. Cells were observed to establish specialized junctions for cell-extracellular matrix crosstalk. Noteworthy, cells seem endowed in a chondroitin sulfate-rich microenvironment, and thus possibly ensuring the immobilization of chemokines, a family of molecules emerging in osteoarthritis pathogenesis, in a haptotactic-like gradient to the chondrocytes, which facilitates the binding to their receptors. To determine the suitability of this model to investigate osteoarthritis pathogenesis, a potential apoptotic stimulus (endothelial IL-8) was used, and ultrastructural analysis assessed apoptosis induction. Micromass cultures were proved to be an experimental technique providing a large number of properly differentiated chondrocytes, and thus allowing reliable biochemical and morphological studies. They represent, therefore, a novel approach to osteoarthritis investigation that promises more thorough understanding of chondrocyte physiology in osteoarthritis.