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Zuozhen Tian,1 Frances S Shofer,1,2 Alec Z Sandroni,1 Lan Zhao,3 Carla R Scanzello,4,5 Yejia Zhang1,6 1Department of Physical Medicine & Rehabilitation, Hospital of the University of Pennsylvania, Philadelphia, PA, USA; 2Department of Emergency Medicine, University of Pennsylvania, Philadelphia, PA, USA; 3Department of Orthopedic Surgery, Rush University Medical Center, Chicago, IL, USA; 4Division of Rheumatology, Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA; 5Section of Rheumatology, Corporal Michael J. Crescenz Veterans Affairs Medical Center, Philadelphia, PA, USA; 6Section of Rehabilitation Medicine, Corporal Michael J. Crescenz Veterans Affairs Medical Center, Philadelphia, PA, USACorrespondence: Yejia Zhang, Department of Physical Medicine & Rehabilitation, Hospital of the University of Pennsylvania, Philadelphia, PA, USA, Email yejia.zhang@pennmedicine.upenn.edu; yejia.zhang@va.govObjective: To examine the effects of human interleukin (IL) 8 expression on mouse behavior.Methods: A mouse line expressing human IL8 in the intervertebral discs (IVD) and cartilaginous tissues (hIL8+) was generated. Mouse spontaneous behaviors, including locomotion, climbing, rearing, grooming, eating, drinking, and immobility were recorded with a fully automatic, non-invasive platform.Results: Distance traveled by the hIL8+ mice declined with age compared with control littermates, and male hIL8+ mice traveled a shorter distance than male controls and females of either genotype (p < 0.05). The hIL8+ mice also spent less time in locomotion than control mice (p < 0.01), and male hIL8+ mice spent the least amount of time and had lowest count in locomotion compared with the other 3 groups at 12 weeks of age or greater (p < 0.05). The hIL8+ mice spent less time climbing than controls, and male mice spent less time climbing than female mice of the same genotype (p < 0.01). The hIL8+ mice spent more time eating and less time drinking than controls, and all mice spent less time eating and more time drinking with increasing age. Finally, hIL8+ mice spent more time immobile than controls, and male hIL8+ mice spent more time immobile than any other group (p < 0.05).Conclusion: The hIL8+ mice, especially hIL8+ males, showed reduced ambulation and climbing. Mice showed age-related decrease in eating and increase in drinking and grooming time that was also influenced by expression of hIL8. These changes in natural behaviors in control mice are consistent with functional decline with age. Effects of hIL8 superimposed on the natural aging process could involve systemic (e.g., on the brain) and local (e.g., in the spine and joint tissues) mechanisms. Future exploration of these mechanisms might be productive.Keywords: interleukin (IL) 8, mouse, behavior, age, decline

ObjectiveOsteoarthritis (OA) is a leading cause of chronic pain, yet OA pain management remains poor. Age is the strongest predictor of OA development, and mechanisms driving OA pain are unclear. While injury-induced OA models are useful, only a subset of OA is linked to traumatic injury. Here, we aimed to characterize age-associated joint damage, mechanical sensitization, and dorsal root ganglia (DRG) immune phenotypes in mice of both sexes.MethodsMale or female mice aged 6- or 20-months old were evaluated for histopathologic knee OA, pain-related behaviors, and L3-L5 dorsal root ganglia (DRG) immune characterization via flow cytometry. DRG gene expression in aged mice and humans was also examined.ResultsTwenty-month old male mice had worse cartilage degeneration than 6-month old mice. Older female knees showed increased cartilage degeneration, but to a lesser degree than males. Older mice of both sexes had worse mechanical allodynia, knee hyperalgesia, and grip strength compared to younger mice. For both sexes, DRGs from older mice showed decreased CD45+ cells, and a significant increase in F4/80+ macrophages and CD11c+ dendritic cells. Older male DRGs showed increased expression of Ccl2 and Ccl5 and older female DRGs showed increased Cxcr4 and Ccl3 compared to 6-month DRGs, among other differentially expresssed genes. Human DRG analysis from six individuals >80 years old revealed elevated CCL2 in male DRGs compared to females, whereas CCL3 was higher in female DRGs.ConclusionsHere we show that aging in male and female mice is accompanied by mild knee OA, mechanical sensitization, and changes to immune cell populations in the DRG, suggesting novel avenues for development of analgesic therapies.

We showed previously that inflammatory mediators, including IL8, in intervertebral disc tissues from patients with discogenic back pain may play a key role in back pain. To investigate the molecular mechanism of IL8 signaling in back pain, we generated a mouse model that conditionally expresses human (h) IL8. We hypothesized that hIL8 levels affect mouse activity and function. Briefly, hIL8 cDNA was inserted into the pCALL2 plasmid, linearized, and injected into mouse embryos. Resulting pCALL2–hIL8 mice were then bred with GDF5–Cre mice to express the transgene in cartilage and intervertebral disc (IVD) tissues. Functional capacities including nest-making and other natural behaviors were measured. Both male and female mice expressing hIL8 showed lower nesting scores than did littermates that did not express hIL8 (n = 14 to 16 per group). At 28 wk of age, mice expressing hIL8 (n = 35) spent more time immobile and eating during each night than littermate controls (n = 33). Furthermore, hIL8-expressing mice traveled shorter distances and at a lower average speed than littermate controls. Thus, in an initial effort to investigate the relationship between this chemokine and mouse behavior, we have documented changes in normal activities in mice conditionally expressing hIL8.

Osteoarthritis (OA) most commonly affects knee joints, and the next most commonly affected sites are the hands and hips. Three distinct hand OA phenotypes have been described: erosive hand OA (EHOA), nodal hand OA - also known as non-erosive hand OA (non-EHOA) - and first carpometacarpal joint OA. EHOA predominantly affects women and is the most aggressive form of hand OA, characterized by a severe clinical onset and progression, leading to joint damage, disability and reduction of quality of life. Clinical signs of inflammation associated with EHOA include the acute onset of pain, swelling and redness. Moreover, EHOA is characterized by radiographic features such as central erosion, saw-tooth and gull-wing lesions and, rarely, ankylosis. The aim of this Review is to report the latest findings on epidemiology, clinical features, pathology and aetiopathogenesis, biomarkers, imaging modalities and treatments for EHOA. The ongoing development of new hand OA classification criteria should facilitate standardization between studies.

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

Objective: Interleukin-15 (IL-15) is a pro-inflammatory cytokine that is increased in joint fluids of early-stage osteoarthritis (OA) patients, and has been associated with expression of proteases that can damage cartilage, and the development of neuropathic pain-like symptoms (NP) after nerve injury. The objective of this study was to further explore the role of IL-15 in the pathogenesis of OA cartilage degeneration and test genetic variation in the IL-15 receptor α gene (IL15RA) for an association with OA with radiographic severity and symptoms.Methods: Cartilage samples from donors (n = 10) were analyzed for expression of the IL15 receptor α-chain using immunohistochemistry, and for responses to IL-15 in vitro using explant cultures. Data from two independent Nottinghamshire-based studies (n = 795 and n = 613) were used to test genetic variants in the IL15RA gene (rs2228059 and rs7097780) for an association with radiographic severity, symptomatic vs. asymptomatic OA and NP.Results: IL-15Rα was expressed in chondrocytes from cartilage obtained from normal and degenerative knees. IL-15 significantly increased the release of matrix metalloproteinase-1 and -3 (MMP-1 and -3), but did not affect loss of proteoglycan from the articular matrix. Genetic variants in the IL15RA gene are associated with risk of symptomatic vs. asymptomatic OA (rs7097780 OR = 1.48 95% 1.10–1.98 p < 0.01) and with the risk of NP post-total joint replacement (rs2228059 OR = 0.76 95% 0.63–0.92 p < 0.01) but not with radiographic severity.Conclusions: In two different cohorts of patients, we show an association between genetic variation at the IL15 receptor and pain. Although ex vivo cartilage explants could respond to IL-15 with increased protease production, we found no effect of IL-15 on cartilage matrix loss and no association between IL15RA variants and radiographic severity. Together, these results suggest that IL-15 signaling may be a target for pain, but may not impact structural progression, in OA.

Background: The corrective procedures for meniscal injury are dependent on tear type, severity, and location. Vertical longitudinal tears are common in young and active individuals, but their natural progression and impact on osteoarthritis (OA) development are not known. Root tears are challenging and they often indicate poor outcomes, although the timing and mechanisms of initiation of joint dysfunction are poorly understood, particularly in large-animal and human models. Purpose/Hypothesis: In this study, vertical longitudinal and root tears were made in a large-animal model to determine the progression of joint-wide dysfunction. We hypothesized that OA onset and progression would depend on the extent of injury-based load disruption in the tissue, such that root tears would cause earlier and more severe changes to the joint. Study Design: Controlled laboratory study. Methods: Sham surgeries and procedures to create either vertical longitudinal or root tears were performed in juvenile Yucatan mini pigs through randomized and bilateral arthroscopic procedures. Animals were sacrificed at 1, 3, or 6 months after injury and assessed at the joint and tissue level for evidence of OA. Functional measures of joint load transfer, cartilage indentation mechanics, and meniscal tensile properties were performed, as well as histological evaluation of the cartilage, meniscus, and synovium. Results: Outcomes suggested a progressive and sustained degeneration of the knee joint and meniscus after root tear, as evidenced by histological analysis of the cartilage and meniscus. This occurred in spite of spontaneous reattachment of the root, suggesting that this reattachment did not fully restore the function of the native attachment. In contrast, the vertical longitudinal tear did not cause significant changes to the joint, with only mild differences compared with sham surgery at the 6-month time point. Conclusion: Given that the root tear, which severs circumferential connectivity and load transfer, caused more intense OA compared with the circumferentially stable vertical longitudinal tear, our findings suggest that without timely and mechanically competent fixation, root tears may cause irreversible joint damage. Clinical Relevance: More generally, this new model can serve as a test bed for experimental surgical, scaffold-based, and small molecule–driven interventions after injury to prevent OA progression.

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.

Inflammatory changes in joint tissues can be detected by modern imaging techniques in osteoarthritis patients, but may be clinically subtle compared with many other types of arthritis. These changes associate with disease progression and clinical severity, and many inflammatory mediators may have biomarker utility. Moreover, a number of inflammatory mechanisms play a role in animal models of disease, but it is still not clear which mechanisms predominate and might be therapeutically manipulated most effectively. This review highlights specific examples of recent advances published in the past 18 months that have advanced this field.Clinical investigators now show that synovial inflammation is associated with pain sensitization, and similar to knee osteoarthritis, is a common and important feature of hand osteoarthritis. In addition, recent advances in basic studies demonstrate inflammatory markers and mechanisms related to leukocyte activity, innate immune mechanisms, and the chondrocyte-intrinsic inflammatory response that might provide better opportunities for early detection, prognosis, or therapeutic intervention.Inflammation plays a central role in osteoarthritis pathogenesis, but additional translational work in this field is necessary, as are more clinical trials of anti-inflammatory approaches.

ObjectivesIdentification of osteoarthritis(OA)-specific synovial inflammatory pathways, and when in the clinical course they are active, is critical for their utility as therapeutic targets. We directly compared the mononuclear inflammatory/immune-cell responses following joint injury that does and does-not lead to OA, to define bona-fide OA-associated cellular events.MethodsWe undertook detailed temporal flow-cytometric and mRNA expression analysis in mice after sham or medial-meniscal-destiblization (DMM) surgery. We compared this with patients with meniscal injury and OA, and evaluated the role of synovial monocytes/macrophages versus lymphocytes in catabolic metalloproteinase secrection in vitro. We determined the effect of transient acute or delayed systemic T-cell depletion on DMM-induced OA pathology.ResultsOA-inducing/DMM and non-OA-inducing/Sham surgery had identical synovial monocyte/macrophage number, activation and polarization. The number and activation of synovial (not splenic or peripheral-blood) CD4 and CD8 lymphocytes was increased from 1-day after DMM versus Sham, and showed a persistent cyclical elevation throughout OA onset and progression. There was a temporal imbalance in synovial Th17/Treg and Th1/Th2 lymphocytes during DMM-induced OA initiation and progression. We confirmed early post-injury and late-OA CD3/CD8 T-cell responses in synovial tissues from patients, identified an association between CD8 and early post-injury symptoms, and defined a significant role for CD3+T-cells in synovial metalloproteinase secretion. Anti-CD3 cell-depletion studies in mice confirmed a key role for the earliest post-injury T-cell response in long-term OA pathology.ConclusionsWe identify a hitherto unappreciated pathophysiological role of acute T-cell activation after joint injury in long-term post-traumatic OA risk, providing a novel diagnostic and therapeutic target.Key MessagesWhat is already known about this subject?The presence of synovitis/joint-inflammation increases the risk not only of osteoarthritis (OA) progression but incident disease. While numerous inflammatory effectors including macrophages and lymphocytes have been identified in OA, their disease-specificity, temporal regulation, and association with risk of pathology onset and progression is lacking.How does this study add?By directly comparing the mononuclear inflammatory/immune-cell responses following significant joint injury that does (medial-meniscal-destabilization; DMM) and does-not (Sham-surgery) lead to OA in mice, we have defined bona-fide OA-associated cellular events. There was no difference in synovial or systemic monocyte/macrophage cell number, activation or polarization between DMM and Sham, both showing a successful wound-healing response. In contrast, increases in number and activation of synovial Th1- and Th17-CD4, and CD8 T-cells in DMM compared with Sham occurred within the first 3 days, and while recurring cyclically through subsequent disease onset, depletion studies indicated this initial influx was key to long-term ptOA risk.How might this impact on clinical practice of future developments?Acute increases in synovial T-cells following jont injury may be both a novel marker of OA risk, and a target to reduce long term structural damage.

Although osteoarthritis (OA) was historically referred to as the non-inflammatory arthritis, it is now considered a condition involving persistent low-grade inflammation and activation of innate inflammatory pathways. Synovitis increases the risk of OA onset and progression and involves the recruitment of monocytes, lymphocytes, and other leukocytes. In particular, macrophages are important mediators of synovial inflammatory activity and pathologic cartilage and bone responses that are characteristic of OA. Advances in understanding how damage-associated molecular patterns (DAMPs) trigger monocyte/macrophage recruitment and activation in joints provide opportunities for disease-modifying therapies. However, the complexity and plasticity of macrophage phenotypes that exist in vivo have thus far prevented the successful development of macrophage-targeted treatments. Current studies show that synovial macrophages are derived from distinct cellular lineages, which correspond to unique functional roles for maintaining joint homeostasis. An improved understanding of the aetiology of synovial inflammation in specific OA-subtypes, such as with obesity or genetic risk, is a potential strategy for developing patient selection criteria for future precision therapies.

Objective To develop an evidence-based guideline for the comprehensive management of osteoarthritis (OA) as a collaboration between the American College of Rheumatology (ACR) and the Arthritis Foundation, updating the 2012 ACR recommendations for the management of hand, hip, and knee OA. Methods We identified clinically relevant population, intervention, comparator, outcomes questions and critical outcomes in OA. A Literature Review Team performed a systematic literature review to summarize evidence supporting the benefits and harms of available educational, behavioral, psychosocial, physical, mind-body, and pharmacologic therapies for OA. Grading of Recommendations Assessment, Development and Evaluation methodology was used to rate the quality of the evidence. A Voting Panel, including rheumatologists, an internist, physical and occupational therapists, and patients, achieved consensus on the recommendations. Results Based on the available evidence, either strong or conditional recommendations were made for or against the approaches evaluated. Strong recommendations were made for exercise, weight loss in patients with knee and/or hip OA who are overweight or obese, self-efficacy and self-management programs, tai chi, cane use, hand orthoses for first carpometacarpal (CMC) joint OA, tibiofemoral bracing for tibiofemoral knee OA, topical nonsteroidal antiinflammatory drugs (NSAIDs) for knee OA, oral NSAIDs, and intraarticular glucocorticoid injections for knee OA. Conditional recommendations were made for balance exercises, yoga, cognitive behavioral therapy, kinesiotaping for first CMC OA, orthoses for hand joints other than the first CMC joint, patellofemoral bracing for patellofemoral knee OA, acupuncture, thermal modalities, radiofrequency ablation for knee OA, topical NSAIDs, intraarticular steroid injections and chondroitin sulfate for hand OA, topical capsaicin for knee OA, acetaminophen, duloxetine, and tramadol. Conclusion This guideline provides direction for clinicians and patients making treatment decisions for the management of OA. Clinicians and patients should engage in shared decision-making that accounts for patients' values, preferences, and comorbidities. These recommendations should not be used to limit or deny access to therapies.

ObjectiveCD14 is a monocyte/macrophage pattern-recognition receptor that modulates innate inflammatory signaling. Soluble CD14 levels in knee OA synovial fluids are associated with symptoms and progression of disease. Here we investigate the role of this receptor in development of OA using a murine joint injury model of disease.Methods10-week-old Male C57BL/6 (WT) and CD14-deficient (CD14-/-) mice underwent destabilization of the medial meniscus (DMM) surgery to induce OA. Joint histopathology was used to examine cartilage damage, and microCT to evaluate subchondral bone (SCB) remodeling at 6 and 19 weeks after surgery. Synovial and fat pad expression of macrophage markers (F4/80, CD11c, CD68, iNOS, CCR7, CD163 and CD206) was assessed by flow cytometry and droplet digital (dd)PCR. Changes in locomotive activity indicative of joint pain were evaluated longitudinally up to 16 weeks by automated behavioral analysis.ResultsEarly cartilage damage scores 6 weeks post-DMM were similar in both strains (Mean score ±SEM WT: 4.667±1.38, CD14-/-: 4.6±0.6), but at 19 weeks were less severe in CD14-/- (6.0±0.46) than in WT mice (13.44±2.5, p = 0.0002). CD14-/- mice were protected from both age-related and post-surgical changes in SCB mineral density and trabecular thickness. In addition, CD14-/- mice were protected from decreases in climbing activity (p = 0.015 vs. WT, 8 weeks) observed after DMM. Changes in synovial/fat pad expression of CCR7, a marker of M1 macrophages, were slightly reduced post-DMM in the absence of CD14, while expression of CD68 (pan-macrophage marker) and CD163 (M2 marker) were unchanged.ConclusionCD14 plays an important role in progression of structural and functional features of OA in the DMM model, and may provide a new target for therapeutic development.

SummaryInflammation is a variable feature of osteoarthritis (OA), associated with joint symptoms and progression of disease. Signs of inflammation can be observed in joint fluids and tissues from patients with joint injuries at risk for development of post-traumatic osteoarthritis (PTOA). Furthermore, inflammatory mechanisms are hypothesized to contribute to the risk of OA development and progression after injury. Animal models of PTOA have been instrumental in understanding factors and mechanisms involved in chronic progressive cartilage degradation observed after a predisposing injury. Specific aspects of inflammation observed in humans, including cytokine and chemokine production, synovial reaction, cellular infiltration and inflammatory pathway activation, are also observed in models of PTOA. Many of these models are now being utilized to understand the impact of post-injury inflammatory response on PTOA development and progression, including risk of progressive cartilage degeneration and development of chronic symptoms post-injury. As evidenced from these models, a vigorous inflammatory response occurs very early after joint injury but is then sustained at a lower level at the later phases. This early inflammatory response contributes to the development of PTOA features including cartilage erosion and is potentially modifiable, but specific mediators may also play a role in tissue repair. Although the optimal approach and timing of anti-inflammatory interventions after joint injury are yet to be determined, this body of work should provide hope for the future of disease modification tin PTOA.

Summary Objective In patients with knee OA, synovitis is associated with knee pain and symptoms. We previously identified synovial mRNA expression of a set of chemokines (CCL19, IL-8, CCL5, XCL-1, CCR7) associated with synovitis in patients with meniscal tears but without radiographic OA. CCL19 and CCR7 were also associated with knee symptoms. This study sought to validate expression of these chemokines and association with knee symptoms in more typical patients presenting for meniscal arthroscopy, many who have pre-existing OA. Design Synovial fluid (SF) and biopsies were collected from patients undergoing meniscal arthroscopy. Synovial mRNA expression was measured using quantitative RT-PCR. The Knee Injury and Osteoarthritis Outcome Score (KOOS) was administered preoperatively. Regression analyses determined if associations between chemokine mRNA levels and KOOS scores were independent of other factors including radiographic OA. CCL19 in SF was measured by ELISA, and compared to patients with advanced knee OA and asymptomatic organ donors. Results 90% of patients had intra-operative evidence of early cartilage degeneration. CCL19, IL-8, CCL5, XCL1, CCR7 transcripts were detected in all patients. Synovial CCL19 mRNA levels independently correlated with KOOS Activities of Daily Living (ADL) scores (95% CI [−8.071, −0.331], P = 0.036), indicating higher expression was associated with more knee-related dysfunction. SF CCL19 was detected in 7 of 10 patients, compared to 4 of 10 asymptomatic donors. Conclusion In typical patients presenting for meniscal arthroscopy, synovial CCL19 mRNA expression was associated with knee-related difficulty with ADL, independent of other factors including presence of radiographic knee OA.

Fibronectin (FN) is a widely expressed molecule that can participate in development of osteoarthritis (OA) affecting cartilage, meniscus, and synovial membrane (SM). The alternatively spliced isoforms of FN in joint tissues other than cartilage have not been extensively studied previously. The present study compares FN splice variation in patients with varying degrees of osteoarthritic change. Joint tissues were collected from asymptomatic donors and patients undergoing arthroscopic procedures. Total RNA was amplified by PCR using primers flanking alternatively spliced Extra Domain A (EDA), Extra Domain B (EDB) and Variable (V) regions. EDB+, EDB− and EDA− and V+ variants were present in all joint tissues, while the EDA+ variant was rarely detected. Expression levels of EDB+ and EDV+ variants were similar in cartilage, synovium, and meniscal tissues. Synovial expression of V+ FN in arthroscopy patients varied with degree of cartilage degeneration. Two V− isoforms, previously identified in cartilage, were also present in SM and meniscus. Fibronectin splicing in meniscus and SM bears striking resemblance to that of cartilage. Expression levels of synovial V+ FN varied with degree of cartilage degeneration. V+ FN should be investigated as a potential biomarker of disease stage or progression in larger populations. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:556–562, 2015.

Elevated chemokine receptor Ccr7 is observed in knee osteoarthritis (OA) and associated with severity of symptoms. In this study, we confirmed that CCR7 protein expression is elevated in synovial tissue from OA patients by immunohistochemical staining. We then investigated whether Ccr7 deficiency impacted structural and functional joint degeneration utilizing a murine model of OA. OA-like disease was induced in male C57BL/6 and Ccr7-deficient (Ccr7-/-) mice by destabilization of the medial meniscus (DMM). Functional deficits were measured by computer integrated monitoring of spontaneous activity every 4 weeks after DMM surgery up 16 weeks. Joint degeneration was evaluated at 6 and 19 weeks post-surgery by histopathology, and subchondral bone changes analyzed by microCT. Results showed reduction in locomotor activities in DMM-operated C57BL/6 mice by 8 weeks, while activity decreases in Ccr7-/- mice were delayed until 16 weeks. Histopathologic evaluation showed minimal protection from early cartilage degeneration (p = 0.06) and osteophytosis (p = 0.04) in Ccr7-/- mice 6 weeks post-DMM compared to C57BL/6 controls, but not at 19 weeks. However, subchondral bone mineral density (p = 0.03) and histologic sclerosis (p = 0.02) increased in response to surgery in C57BL/6 mice at 6 weeks, while Ccr7-/- mice were protected from these changes. Our results are the first to demonstrate a role for Ccr7 in early development of functional deficits and subchondral bone changes in the DMM model. Understanding the mechanism of Ccr7 receptor signaling in the initiation of joint pathology and disability will inform the development of innovative therapies to slow symptomatic OA development after injury. This article is protected by copyright. All rights reserved

Fibronectin (FN), a molecule with diverse biologic functions, can exist in multiple variants that arise from alternative splicing of a single pre-mRNA.3, 4 In most human tissues, the FN exists in up to 20 variants due to inclusion or exclusion of the EDA or EDB domains, and the variable (V) domain can be spliced five different ways by partial inclusion of this region. The diversity of FN forms is further increased in cartilage tissues: there is a variant with 15th type III domain and 10th type I domain together with the entire V region excluded, the [V+III15+I10]− described in canine cartilage,5 and [V+I10]−, or [V+III15]− variants, described in bovine articular cartilage. Finally, the [V+I10]− variant has been identified in the human IVD tissues and articular cartilage and meniscus (Anderson et al.6 and Zhang lab unpublished data). Thus, in the IVD tissues, there are as many as 32 splice forms. Although the functions of these diverse forms have not been thoroughly elucidated yet,7-9 their potential roles in IVD development early in life and repair in adults should not be overlooked. The total amount of FN-fs increases with disc degeneration.10 However, neither the pathophysiological concentrations of the individual fragments nor the mechanism of FN fragmentation in the IVD were characterized previously. The N-terminal region of FN is thought to initiate matrix assembly by assisting in the formation of a fibrillar meshwork.9, 11 Free N-terminal fragments may interfere with matrix assembly in certain embryonic systems.11 In extracellular matrix networks of adult tissues, FN-fs can cause further tissue degradation as seen in osteoarthritis. The N-terminal FN-fs present in the arthritic knee 12 induce nitric oxide (NO) production by activating focal adhesion kinase (FAK) and mitogen-activated protein kinases (MAPKs) without activating α5β1 integrin.13 In the IVD tissue, data supporting a pathophysiological role of FN-fs are emerging: the 29 kDa N-terminal FN-f is capable of causing disc degeneration in the rabbit.14, 15 To assess the relevance of previous studies in human IVD disease, in the present work we aimed to determine the content of FN N-terminal fragments in human IVDs that showed different grades of degeneration. Furthermore, both enzymatic cleavage and repetitive mechanical loading could potentially result in FN fragmentation. We hypothesize that proteolytic enzymes within the IVD tissue are responsible, at least in part, for FN-fragmentation. ADAM-8 appears to be responsible for FN degradation in knee articular cartilage, resulting in the VRAA271 and 272VYQP neoepitopes.16, 17 However, the presence and activity of ADAM-8 in IVD tissues have not been previously shown. Thus, in this study, we aimed to investigate the possible presence of ADAM-8 as a FN-degrading enzyme in human disc tissue.

Objective Interleukin-6 (IL-6), interleukin-10 (IL-10), interferon-alpha (IFN-α), and free light chains (FLCs: lambda, kappa) have all been noted to be of importance in systemic lupus erythematosus (SLE). Herein, we quantified and explored the relationship between these inflammatory mediators and disease activity in SLE; and stratified by their current anti-dsDNA antibody status. Methods Seventy-seven SLE patients underwent assessment of disease activity using the SLE disease activity index (SLEDAI). Serum FLC (lambda, kappa, and total), IL-6, IL-10, and IFN-α were quantified. Demographics of disease characteristics were determined by chart reviews. Statistical analyses included Mann–Whitney test, chi square, and linear regression analyses. Results Mean (SD) age of the patients was 44.9 ± 12.7 years; SLEDAI (mean ± SD) was 3.4 ± 4.0. Serum lambda FLC levels had a moderate correlation ( r = 0.46 with physician global assessment, 0.44 with SLEDAI) and the strongest correlation with disease activity as compared with other inflammatory mediators including current dsDNA antibody status. After adjusting for prednisone use, the correlation of lambda FLC with PGA ( r = 0.48) and SLEDAI ( r = 0.52) was better than of current dsDNA antibody status with PGA ( r = 0.33) and adjusted SLEDAI ( r = 0.24), respectively. IL-10 and IFN-α activity did not correlate with disease activity. Serum FLC and IL-6 levels could differentiate between active and inactive SLE patients. Serum lambda FLC and IL-6 levels differed significantly among patients with and without current dsDNA antibodies. Serum lambda FLC levels accounted for 31% of variance in SLEDAI scores. Conclusion Serum FLC and IL-6 are potentially useful biomarkers of disease activity in SLE. Further studies, with larger study sample and longitudinal design, are indicated.

SummaryObjectiveSynovitis is associated with pain and other symptoms in patients with knee osteoarthritis (OA), and in patients with meniscal tears even in the absence of radiographic OA. Patients undergoing arthroscopic partial meniscectomy were followed for 2 years to determine whether synovitis predicts post-operative symptoms.DesignThirty-three patients scheduled for arthroscopy were recruited for this pilot study. Symptoms were assessed using a knee pain scale, the Lysholm score, and the short form-12 (SF-12®) pre-operatively and at 16 weeks, 1 year and 2 years post-operatively. Synovial inflammation and hyperplasia were graded on surgical biopsies. Linear mixed effects models were tested to determine whether inflammation or hyperplasia is associated with outcome scores over time.ResultsLysholm scores and SF-12® physical component sub-scores were worse pre-operatively in patients with inflammation (Lysholm: 52.42 [95% confidence interval (CI) 42.37, 62.47] vs 72.38 [66.03, 78.72], P

Objective The pathophysiology of the most common joint disease, osteoarthritis (OA), remains poorly understood. Since synovial fluid (SF) bathes joint cartilage and synovium, we reasoned that a comparative analysis of its protein constituents in health and OA could identify pathways involved in joint damage. We undertook this study to perform a proteomic analysis of knee SF from OA patients and control subjects and to compare the results to microarray expression data from cartilage and synovium. Methods Age-matched knee SF samples from 10 control subjects, 10 patients with early-stage OA, and 10 patients with late-stage OA were compared using 2-dimensional difference-in-gel electrophoresis and mass spectrometry (MS). MS with a multiplexed peptide selected reaction monitoring assay was used to confirm differential expression of a subset of proteins in an independent OA patient cohort. Proteomic results were analyzed by Ingenuity Pathways Analysis and compared to published synovial tissue and cartilage messenger RNA profiles. Results Sixty-six proteins were differentially present in healthy and OA SF. Three major pathways were identified among these proteins: the acute-phase response signaling pathway, the complement pathway, and the coagulation pathway. Differential expression of 5 proteins was confirmed by selected reaction monitoring assay. A focused analysis of transcripts corresponding to the differentially present proteins indicated that both synovial and cartilage tissues may contribute to the OA SF proteome. Conclusion Proteins involved in the acute-phase response signaling pathway, the complement pathway, and the coagulation pathway are differentially regulated in SF from OA patients, suggesting that they contribute to joint damage. Validation of these pathways and their utility as biomarkers or therapeutic targets in OA is warranted.

Elevated chemokine receptor Ccr7 is observed in knee osteoarthritis (OA) and associated with severity of symptoms. In this study, we confirmed that CCR7 protein expression is elevated in synovial tissue from OA patients by immunohistochemical staining. We then investigated whether Ccr7 deficiency impacted structural and functional joint degeneration utilizing a murine model of OA. OA-like disease was induced in male C57BL/6 and Ccr7-deficient (Ccr7(−/−)) mice by destabilization of the medial meniscus (DMM). Functional deficits were measured by computer integrated monitoring of spontaneous activity every 4 weeks after DMM surgery up 16 weeks. Joint degeneration was evaluated at 6 and 19 weeks post-surgery by histopathology, and subchondral bone changes analyzed by microCT. Results showed reduction in locomotor activities in DMM-operated C57BL/6 mice by 8 weeks, while activity decreases in Ccr7(−/−) mice were delayed until 16 weeks. Histopathologic evaluation showed minimal protection from early cartilage degeneration (p = 0.06) and osteophytosis (p = 0.04) in Ccr7(−/−) mice 6 weeks post-DMM compared to C57BL/6 controls, but not at 19 weeks. However, subchondral bone mineral density (p = 0.03) and histologic sclerosis (p = 0.02) increased in response to surgery in C57BL/6 mice at 6 weeks, while Ccr7(−/−) mice were protected from these changes. Our results are the first to demonstrate a role for Ccr7 in early development of functional deficits and subchondral bone changes in the DMM model. Understanding the mechanism of Ccr7 receptor signaling in the initiation of joint pathology and disability will inform the development of innovative therapies to slow symptomatic OA development after injury. Published 2017. This article is a U.S. Government work and is in the public domain in the USA.

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.

Synovial inflammation, a feature of both osteoarthritis (OA) and meniscal injury, is hypothesized to be triggered in part via stimulation of Toll-like receptors (TLRs). We undertook this study to test whether a TLR-2- or TLR-4-stimulating factor in synovial fluid (SF) from patients with early knee OA with meniscal injury could lead to inflammatory activation of synoviocytes.SF was obtained from patients with early OA cartilage damage undergoing arthroscopic meniscal procedures. SF was used to stimulate primary cultures of fibroblast-like synoviocytes (FLS) and cell lines transfected with TLR-2 or TLR-4. SF was used either alone or in combination with a TLR-2 stimulus (palmitoyl-3-cysteine-serine-lysine-4 [Pam3CSK4]) or a TLR-4 stimulus (lipopolysaccharide [LPS]). In blocking experiments, SF was preincubated with anti-CD14 antibody.SF from these patients did not stimulate interleukin-8 (IL-8) release from TLR transfectants. Compared with SF on its own, SF (at concentrations of 0.09-25%) in combination with TLR-2 or TLR-4 ligands resulted in significant augmentation of IL-8 release from both transfectants and primary FLS. Soluble CD14 (sCD14), a coreceptor for TLRs, was measured in SF from patients with early OA at levels comparable to those in patients with advanced OA and patients with rheumatoid arthritis. Blockade with anti-CD14 antibody abolished the ability of SF to augment IL-8 production in response to LPS, and diminished Pam3CSK4 responses.SF augments FLS responses to TLR-2 and TLR-4 ligands. This effect was largely due to sCD14. Our results demonstrate that sCD14 in the setting of OA and meniscal injury sensitizes FLS to respond to inflammatory stimuli such as TLR ligands.

Osteoarthritis, characterized by the breakdown of articular cartilage in synovial joints, has long been viewed as the result of 'wear and tear'. Although low-grade inflammation is detected in osteoarthritis, its role is unclear. Here we identify a central role for the inflammatory complement system in the pathogenesis of osteoarthritis. Through proteomic and transcriptomic analyses of synovial fluids and membranes from individuals with osteoarthritis, we find that expression and activation of complement is abnormally high in human osteoarthritic joints. Using mice genetically deficient in complement component 5 (C5), C6 or the complement regulatory protein CD59a, we show that complement, specifically, the membrane attack complex (MAC)-mediated arm of complement, is crucial to the development of arthritis in three different mouse models of osteoarthritis. Pharmacological modulation of complement in wild-type mice confirmed the results obtained with genetically deficient mice. Expression of inflammatory and degradative molecules was lower in chondrocytes from destabilized joints from C5-deficient mice than C5-sufficient mice, and MAC induced production of these molecules in cultured chondrocytes. Further, MAC colocalized with matrix metalloprotease 13 (MMP13) and with activated extracellular signal-regulated kinase (ERK) around chondrocytes in human osteoarthritic cartilage. Our findings indicate that dysregulation of complement in synovial joints has a key role in the pathogenesis of osteoarthritis.

Objective Traumatic and degenerative meniscal tears have different anatomic features and different proposed etiologies, yet both are associated with the development or progression of osteoarthritis (OA). In established OA, synovitis is associated with pain and progression, but a relationship between synovitis and symptoms in isolated meniscal disease has not been reported. Accordingly, we sought to characterize synovial pathology in patients with traumatic meniscal injuries and determine the relationships between inflammation, meniscal and cartilage pathology, and symptoms. Methods Thirty-three patients without evidence of OA who were undergoing arthroscopic meniscectomy for meniscal injuries were recruited. Pain and function were assessed preoperatively; meniscal and cartilage abnormalities were documented at the time of surgery. Inflammation in synovial biopsy specimens was scored, and associations between inflammation and clinical outcomes were determined. Microarray analysis of synovial tissue was performed, and gene expression patterns in patients with and those without inflammation were compared. Results Synovial inflammation was present in 43% of the patients and was associated with worse preoperative pain and function scores, independent of age, sex, or cartilage pathology. Microarray analysis and real-time polymerase chain reaction revealed a chemokine signature in synovial biopsy specimens with increased inflammation scores. Conclusion Our findings indicate that in patients with traumatic meniscal injury undergoing arthroscopic meniscectomy without radiographic evidence of OA, synovial inflammation occurs frequently and is associated with increased pain and dysfunction. Synovia with increased inflammation scores exhibit a unique chemokine signature. Chemokines may contribute to the development of synovial inflammation in patients with meniscal pathology; they also represent potential therapeutic targets for reducing inflammatory symptoms.

Objective: Much of what is known about the inflammatory response in the synovial membrane (SM) of patients with osteoarthritis (OA) comes from studies of synovial tissues from end-stage disease. In this study, we sought to better characterize the inflammatory infiltrate in symptomatic patients with early signs of knee CA, and to determine how inflammatory cell populations relate to the pattern of cytokine and degradative enzyme production. Methods: Study populations comprised patients with degenerative meniscal tears and early cartilage thinning undergoing arthroscopic procedures (early CA) and patients undergoing total knee replacement for end-stage OA. Quantitative real-time polymerase chain reaction (PCR) was used to measure expression of SM cytolkines and enzymes implicated in the pathogenesis of inflammatory arthritis and CA, as well as cell lineage-specific markers. We quantified synovial fluid (SF) cytokines and enzymes by enzyme-linked immunosorbent assay (ELISA) and SM cell populations by immunohistochemistry. Results: We found increased levels of SF interleukin-15 (IL-15) protein in the early knee OA patients when compared to end-stage OA. Both SF IL-15 protein and numbers of CD8 cells within SM correlated with matrix metalloproteinase-1 (MMP-1) and three levels. TNF-alpha, IL-6 and IL-21 were also detectable in the SF of the majority of patients, and IL-15 levels were associated with IL-6 levels. Conclusion: IL-15 is elevated in early knee CA, suggesting activation of an innate immune response in the SM. The association of IL-15 expression with CD8 transcripts and MMPs implicates this cytokine in OA pathogenesis and as a candidate therapeutic target. (C) 2009 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.

Synovial inflammation is increasingly recognized as an important pathophysiologic process in osteoarthritis, but the stimuli and downstream pathways activated are not well defined. Innate immune system activation, best documented in responses to pathogens, likely plays a role in induction of inflammatory mediators and the specific cellular infiltrate seen in osteoarthritis. Thus, the Toll-like receptors (TLRs) and their signaling pathways are of particular interest. These innate pattern-recognition receptors are activated not only by pathogens but by endogenous 'danger signals'. In this report, we review evidence that certain extracellular matrix components of joint tissues (hyaluronan and fibronectin) may act as TLR stimuli, and summarize recent literature implicating TLR activation in osteoarthritis.Convincing evidence exists that hyaluronan/TLR interactions drive responses to tissue injury. Evidence of a similar role for fibronectin is growing. TLRs are expressed and functional in the joint, and many proteases and cytokines that promote cartilage catabolism are dependent on nuclear factor-kappaB, a TLR-activated transcription factor.Activation of TLR pathways seems likely in osteoarthritis and may play a central role in disease development and progression. A model of osteoarthritis as a chronic wound, in which the innate immune response is triggered by molecular signals of tissue damage, is presented as a framework for future study of inflammation in this prevalent joint disease.

To quantify inflammatory changes in synovial membranes from orthopaedic "non-inflammatory" arthropathies (Orth. A).Synovial membranes from patients with femur fracture, avascular necrosis of the femur, plica syndrome, and meniscus and/or ligament injury (n = 23); rheumatoid arthritis (n = 28); osteoarthritis (OA; n = 25); and from normal controls (n = 10) were assessed by light microscopy, a histological synovitis score, immunostaining for CD3, CD20, CD38, CD68, Ki-67 and von Willebrand factor, and with an immunohistochemical inflammation score.Orth. A histology varied between normal and markedly inflamed. Predominant abnormalities were mild lining hyperplasia, scattered inflammatory cells and small perivascular infiltrates. The synovitis score classified Orth. A as "mild synovitis". Inflammatory cells occurred frequently: CD68+ cells in 100% of Orth. A specimens; CD3+, 91%; CD38+, 70%; and CD20+, 39%. Orth. A had 36% greater lining thickness (p = 0.04), 40% higher vascular density (p = 0.009) and 51.3-fold higher CD38+ cell density (p = 0.02) than normal controls; and 60% fewer subintimal Ki-67+ cells (p = 0.003), 42% fewer CD68+ lining cells (p0.01) and 40% fewer subintimal CD68+ cells (p0.01) than OA. The immunohistochemical inflammation score was 2.2-fold higher in Orth. A than in controls (p = 0.048) and similar to OA, with three Orth. A specimens showing marked inflammation.Synovial membranes from "non-inflammatory" arthropathies featured neovascularisation and inflammation intermediate between normal and OA synovium. These results expand previous findings that mechanical joint injury may lead to a mild-to-moderate synovitis.

s / Osteoarthritis and Cartilage 23 (2015) A82eA416 A259 0.06 log eu/mL, p1⁄40.04). LPS concentration was associated with body fat (r1⁄40.62, p1⁄40.003), Lactobacillus spp. 16s rRNA gene copy number (r1⁄4-0.60, p1⁄40.009), and six serum inflammatory markers: GCSF (r1⁄40.49, p1⁄40.03), serum IL-1a (r1⁄4 -0.48, p1⁄40.048), IL-4 (r1⁄4-0.52, p1⁄40.02), IL-6 (r1⁄4-0.49, p1⁄40.03), IL-13 (r1⁄4-0.59, p1⁄40.007), IFNg (r1⁄4-0.49, p1⁄40.03). Together, Methanobrevibacter spp. and Lactobacillus spp. levels had a strong relationship predictive withModifiedMankin Scores when evaluated using linear regression modelling (r21⁄40.50, p

Fibronectin (FN) is a widely expressed molecule that can participate in development of osteoarthritis (OA) affecting cartilage, meniscus, and synovial membrane (SM). The alternatively spliced isoforms of FN in joint tissues other than cartilage have not been extensively studied previously. The present study compares FN splice variation in patients with varying degrees of osteoarthritic change. Joint tissues were collected from asymptomatic donors and patients undergoing arthroscopic procedures. Total RNA was amplified by PCR using primers flanking alternatively spliced Extra Domain A (EDA), Extra Domain B (EDB) and Variable (V) regions. EDB(+) , EDB(-) and EDA(-) and V(+) variants were present in all joint tissues, while the EDA(+) variant was rarely detected. Expression levels of EDB(+) and EDV(+) variants were similar in cartilage, synovium, and meniscal tissues. Synovial expression of V(+) FN in arthroscopy patients varied with degree of cartilage degeneration. Two V(-) isoforms, previously identified in cartilage, were also present in SM and meniscus. Fibronectin splicing in meniscus and SM bears striking resemblance to that of cartilage. Expression levels of synovial V(+) FN varied with degree of cartilage degeneration. V(+) FN should be investigated as a potential biomarker of disease stage or progression in larger populations.

TH1 cytokines have recently been detected in rheumatoid arthritis (RA) and osteoarthritis (OA). For this reason we studied the TH-1-promoting cytokine IL-12 in synovial membranes from patients with RA and OA. IL-12 transcripts and protein were analyzed by reverse transcriptase-polymerase chain reaction (PCR) and immunohistochemistry, respectively. In addition, IL-12 transcripts were quantitated by competitive PCR. IL-12 transcripts (p40) were detected in 8 of 13 patients with RA and in 10 of 18 patients with OA. Their levels did not differ significantly between RA and OA. IL-12 heterodimer protein was detected by immunostaining using an anti-IL-12p70 mAb. Double labeling with anti-IL-12p70 and anti-CD68 mAbs showed that synovial lining cells and monocytes/macrophages expressed IL-12 p70 protein. The presence of IL-12 p70 protein in the synovial membranes of patients with RA and OA suggests that IL-12 may play an important immunoregulatory role in these diseases by perpetuating inflammation.

The synovial membrane in osteoarthritis (OA) often exhibits inflammatory infiltrates, but the role of T cells in these infiltrates is not known. T-cell activation antigens were analyzed by immunohistochemistry, and T-cell cytokine transcripts were measured by competitive PCR in synovial membranes from patients with OA and rheumatoid arthritis (RA). Lymphoid cell aggregates, containing primarily CD3 1 T lymphocytes, were found in 65% of patients with OA. Mononuclear cells expressing the activation antigens CD69, CD25, CD38, CD43, CD45RO, and HLA class II were present in both patient groups, although in higher numbers in patients with RA. Interleukin 2 (IL-2) transcripts were found in 10 of 18 patients with OA versus 12 of 13 patients with RA (P 5 0.03). Gamma interferon (IFN-g) transcripts were detected in 9 of 18 patients with OA versus 10 of 13 patients with RA (not significant), whereas IL-10 transcripts were found in nearly all patients. IL-4 and IL-5 were not detected in any patients. The levels of IFN-g and IL-2 transcripts, normalized for T-cell number equivalents, were not statistically different between OA and RA, but the levels of IFN-g, normalized for total cell number equivalents, were lower in OA than in RA (P 5 0.01). Synovial membranes that expressed IL-2 and IFN-g transcripts were more likely to have heavier infiltrations of T cells and cells bearing activation markers than synovial membranes that did not express these cytokines. The presence of activated T cells and TH1 cytokine transcripts in chronic joint lesions of patients with OA suggests that T cells contribute to chronic inflammation in a large proportion of these patients. Osteoarthritis (OA), although a heterogeneous disease, is generally believed by rheumatologists to be primarily a disease of biomechanical alteration (18). However, apart from the relatively rare type of erosive inflammatory OA which clearly shows a strong inflammatory component, certain patients with OA exhibit inflammatory infiltrates in the synovial membrane (SM) (15, 17, 23, 28). These mononuclear infiltrates have not been fully characterized, and their possible role in the pathogenesis of the disease is not clearly understood. In certain patients with OA, mononuclear cell infiltrates in SM may resemble those found in rheumatoid arthritis (RA). In RA, significant evidence demonstrating that T cells play a significant role in the pathogenesis of the disease has accumulated (reviewed in reference 46). This evidence includes the amelioration of the disease by treatments directed against T cells, the association of the disease with certain HLA-DR4 alleles, and the presence in the SM of patients with RA of infiltrating T cells which express activation antigens, produce cytokines, and contain oligoclonal populations of T cells (reviewed in reference 46). T-cell-derived cytokines are major determinants of the outcome of immune responses. TH1 cytokines (interleukin 2 [IL-2] and gamma interferon [IFN-g]) are associated with macrophae activation, enhancement of cell-mediated cytotoxicity, delayed-type hypersensitivity responses, and effective responses to intracellular pathogens (38, 48, 62). TH2 cytokines (IL-4 and IL-5) are associated with allergic diseases, helminthic infections, and progressive infections by intracellular bacteria (38). A biased cytokine pattern is also found in animal models of autoimmune disease. For example, in experimental allergic encephalomyelitis, IL-2 and IFN-g, but not IL-4, are expressed in the brain of rats at the peak of disease, whereas during recovery, the expression of IL-2 and IFN-g decrease with the concomitant appearance of IL-4 (24). Also, in nonobese diabetic mice, IL-4 production is compromised, while administration of IL-4 to prediabetic mice prevents the development of diabetes (44). Although several studies have examined the TH1/TH2 cytokine pattern in SM of patients with RA and have reported the prevalence of a TH1 pattern (9, 25, 33, 42, 47, 51, 58), the role of T cells and the pattern of TH1/TH2 cytokines in patients with OA are largely unknown. In this study, we employed (i) immunohistochemistry with a panel of monoclonal antibodies (MAbs) to antigens expressed on activated T cells to characterize the mononuclear cell infiltrates, and (ii) reverse transcriptase (RT) PCR and competitive PCR to detect and quantitate T-cell cytokine transcripts in SM from patients with OA.

The pathophysiology of the most common joint disease, osteoarthritis (OA), remains poorly understood. Since synovial fluid (SF) bathes joint cartilage and synovium, we reasoned that a comparative analysis of its protein constituents in health and OA could identify pathways involved in joint damage. We undertook this study to perform a proteomic analysis of knee SF from OA patients and control subjects and to compare the results to microarray expression data from cartilage and synovium.Age-matched knee SF samples from 10 control subjects, 10 patients with early-stage OA, and 10 patients with late-stage OA were compared using 2-dimensional difference-in-gel electrophoresis and mass spectrometry (MS). MS with a multiplexed peptide selected reaction monitoring assay was used to confirm differential expression of a subset of proteins in an independent OA patient cohort. Proteomic results were analyzed by Ingenuity Pathways Analysis and compared to published synovial tissue and cartilage messenger RNA profiles.Sixty-six proteins were differentially present in healthy and OA SF. Three major pathways were identified among these proteins: the acute-phase response signaling pathway, the complement pathway, and the coagulation pathway. Differential expression of 5 proteins was confirmed by selected reaction monitoring assay. A focused analysis of transcripts corresponding to the differentially present proteins indicated that both synovial and cartilage tissues may contribute to the OA SF proteome.Proteins involved in the acute-phase response signaling pathway, the complement pathway, and the coagulation pathway are differentially regulated in SF from OA patients, suggesting that they contribute to joint damage. Validation of these pathways and their utility as biomarkers or therapeutic targets in OA is warranted.

Osteoarthritis (OA) is the most common form of arthritis and a major cause of pain and disability in older adults (1). Often OA is referred to as degenerative joint disease “(DJD)”. This is a misnomer because OA is not simply a process of wear and tear but rather abnormal remodeling of joint tissues driven by a host of inflammatory mediators within the affected joint. The most common risk factors for OA include age, gender, prior joint injury, obesity, genetic predisposition, and mechanical factors, including malalignment and abnormal joint shape (2, 3). Despite the multifactorial nature of OA, the pathological changes seen in osteoarthritic joints have common features that affect the entire joint structure resulting in pain, deformity and loss of function. The pathologic changes seen in OA joints (Figures 1 and ​and2)2) include degradation of the articular cartilage, thickening of the subchondral bone, osteophyte formation, variable degrees of synovial inflammation, degeneration of ligaments and, in the knee, the menisci, and hypertrophy of the joint capsule. There can also be changes in periarticular muscles, nerves, bursa, and local fat pads that may contribute to OA or the symptoms of OA. The findings of pathological changes in all of the joint tissues are the impetus for considering OA as a disease of the joint as an organ resulting in “joint failure”. In this review, we will summarize the key features of OA in the various joint tissues affected and provide an overview of the basic mechanisms currently thought to contribute to the pathological changes seen in these tissues. Open in a separate window Figure 1 Sagittal inversion recovery (A–C) and coronal fast spin echo (D–F) images illustrating the magnetic resonance imaging findings of osteoarthritis. (A) reactive synovitis (thick white arrow), (B) subchondral cyst formation (white arrow), (C) bone marrow edema (thin white arrows), (D) partial thickness cartilage wear (thick black arrow), (E–F) full thickness cartilage wear (thin black arrows), subchondral sclerosis (arrowhead) and marginal osteophyte formation (double arrow). Image courtesy of Drs. Hollis Potter and Catherine Hayter, Hospital for Special Surgery, New York, NY

Our current understanding of the role of synovitis in osteoarthritis has evolved substantially over the past decade. We understand that inflammation is present even early in the course of the disease and is associated with symptoms, function, and progression of cartilage damage (Fig. 1). Whether synovitis is a predictive marker in posttraumatic osteoarthritis remains to be established. Data from a recently published rodent model suggested that synovitis may be a good therapeutic target in posttraumatic osteoarthritis [1]. Elucidating how synovial inflammation is triggered and sustained in the joint is likely to guide the design of future treatment regimens targeting synovitis in osteoarthritis. Fig. 1 Relationship between synovitis and outcomes in osteoarthritis and important remaining questions. Synovitis has been associated with pain, joint dysfunction, and rate of structural progression in osteoarthritis. Important questions remaining are how variable ... Acknowledgement Carla R. Scanzello is supported by 1K08AR057859 award from the National Institute of Arthritis, Musculoskeletal and Skin Diseases. Rush University Medical Center and the Hospital for Special Surgery have filed a patent application on behalf of the author on inflammatory biomarkers in osteoarthritis.