A standardized approach to evaluation and reporting of synovial histopathology in two surgically induced murine models of osteoarthritis.

OBJECTIVE: Synovial pathology has been linked to osteoarthritis (OA) pain in patients. Microscopic grading systems for synovial changes in human OA have been described, but a standardized approach for murine models of OA is needed. We sought to develop a reproducible approach and set of minimum recommendations for reporting of synovial histopathology in mouse models of OA. METHODS: Coronal and sagittal sections from male mouse knee joints subjected to destabilization of medial meniscus (DMM) or partial meniscectomy (PMX) were collected as part of other studies. Stains included Hematoxylin and Eosin (H&E), Toluidine Blue (T-Blue), and Safranin O/Fast Green (Saf-O). Four blinded readers graded pathological features (hyperplasia, cellularity, and fibrosis) at specific anatomic locations. Inter-reader agreement of each feature score was determined. RESULTS: There was acceptable to very good agreement when using 3-4 individual readers. After DMM and PMX, expected medial predominant changes in hyperplasia and cellularity were observed, with fibrosis noted at 12 weeks post-PMX. Synovial changes were consistent from section to section in the mid-joint area. When comparing stains, H&E and T-blue resulted in better agreement compared to Saf-O stain. CONCLUSIONS: To account for the pathologic and anatomic variability in synovial pathology and allow for a more standardized evaluation that can be compared across studies, we recommend evaluating a minimum set of 3 pathological features at standardized anatomic areas. Further, we suggest reporting individual feature scores separately before relying on a single summed "synovitis" score. H&E or T-blue are preferred, inter-reader agreement for each feature should be considered.

Erosive Hand Osteoarthritis: Recent Advances and Future Treatments.

PURPOSE OF THE REVIEW: Erosive hand osteoarthritis (EHOA) is an aggressive form of hand osteoarthritis that leads to significant disability, and recent data suggests that it is increasing in prevalence. This review provides an update of our current understanding of epidemiology, genetic associations, biomarkers, pathogenesis, and treatment of EHOA, with particular focus on studies published within the last 5 years. RECENT FINDINGS: New studies of EHOA have identified new genetic loci associated with disease, including variants in genes involved in inflammation and bone remodeling. Preclinical studies implicate pathways of innate immunity, including some that may be causal in the condition. Recent novel studies showed that inflammatory features identified by ultrasound and MRI are associated with development of erosive lesions over time on conventional radiography. In the future, these imaging modalities may be useful in identifying patients at risk of adverse outcomes. Promising new findings in genetics, biomarkers, and treatment targets will hopefully allow for future therapeutic options for this debilitating condition.

Modulating mechanobiology as a therapeutic target for synovial fibrosis to restore joint lubrication.

OBJECTIVES: Fibroses are disorders linked to persistence of myofibroblasts due to biochemical (e.g., Transforming growth factor-ß) and biophysical cues (e.g., a stiff microenvironment). In the context of osteoarthritis, fibrotic changes in the joint-lining synovium have been linked with disease progression. The objective of this study was to probe synovial fibroblast mechanobiology and how essential functions (i.e., lubrication) are altered in fibrotic environments. DESIGN: Both ex vivo and in vitro synovium models were assessed for fibrotic and lubrication biomarkers to better understand the role of mechanobiology and lubrication. Additionally, in vitro, work on small molecules targeting mechanobiology was assessed. RESULTS: Our results indicated that modulating mechanobiology could rescue the fibrotic phenotype instigated by stiffening microenvironment that resulted in altered lubricant expression. A small molecule therapeutic, fasudil, blocked ROCK-mediated contractility and this inhibition of the fibrotic mechano-response of synovial fibroblasts restored proper lubrication function, providing insight into mechanisms of disease progression as well as a new avenue for therapeutic development. CONCLUSION: This study identifies synovial fibrosis as a condition that potentially has joint-wide deficits through inhibiting lubrication. Additionally, modulating mechanobiology (i.e., ROCK-mediated contractility) may pose a potential target for small molecule therapies that can be delivered to the joint space. CLASSIFICATION: Applied Biological Sciences.

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

Objective: To develop an imaging mass cytometry method for identifying complex cell phenotypes, inter-cellular interactions, and population changes in the synovium and infrapatellar fat pad (IFP) of the mouse knee following a non-invasive compression injury. Design: Fifteen male C57BL/6 mice were fed a high-fat diet for 8 weeks prior to random assignment to sham, 0.88 â€‹mm, or 1.7 â€‹mm knee compression displacement at 24 weeks of age. 2-weeks after loading, limbs were prepared for histologic and imaging mass cytometry analysis, focusing on myeloid immune cell populations in the synovium and IFP. Results: 1.7 â€‹mm compression caused anterior cruciate ligament (ACL) rupture, development of post-traumatic osteoarthritis, and a 2- to 3-fold increase in cellularity of synovium and IFP tissues compared to sham or 0.88 â€‹mm compression. Imaging mass cytometry identified 11 myeloid cell subpopulations in synovium and 7 in IFP, of which approximately half were elevated 2 weeks after ACL injury in association with the vasculature. Notably, two monocyte/macrophage subpopulations and an MHC IIhi population were elevated 2-weeks post-injury in the synovium but not IFP. Vascular and immune cell interactions were particularly diverse in the synovium, incorporating 8 unique combinations of 5 myeloid cell populations, including a monocyte/macrophage population, an MHC IIhi population, and 3 different undefined F4/80+ myeloid populations. Conclusions: Developing an imaging mass cytometry method for the mouse enabled us to identify a diverse array of synovial and IFP vascular-associated myeloid cell subpopulations. These subpopulations were differentially elevated in synovial and IFP tissues 2-weeks post injury, providing new details on tissue-specific immune regulation.

Recommendations For a Standardized Approach to Histopathologic Evaluation of Synovial Membrane in Murine Models of Experimental Osteoarthritis.

Background: Synovial pathology has been linked to osteoarthritis (OA) pain in patients. Microscopic grading systems for synovial changes in human OA have been described, but a standardized approach for murine models of OA is needed. We sought to develop a reproducible approach and set of minimum recommendations for synovial histopathology in mouse models of OA. Methods: Coronal and sagittal sections from male mouse knee joints subjected to destabilization of medial meniscus (DMM) or partial meniscectomy (PMX) were collected as part of other studies. Stains included Hematoxylin and Eosin (H&E), Toluidine Blue (T-Blue) and Safranin O/Fast Green (Saf-O). Four blinded readers graded pathological features (hyperplasia, cellularity, and fibrosis) at specific anatomic locations in the medial and lateral compartments. Inter-reader reliability of each feature was determined. Results: There was acceptable to very good agreement between raters. After DMM, increased hyperplasia and cellularity and a trend towards increased fibrosis were observed 6 weeks after DMM in the medial locations, and persisted up to 16 weeks. In the PMX model, cellularity and hyperplasia were evident in both medial and lateral compartments while fibrotic changes were largely seen on the medial side. Synovial changes were consistent from section to section in the mid-joint area mice. H&E, T-blue, and Saf-O stains resulted in comparable reliability. Conclusions: To allow for a standard evaluation that can be implemented and compared across labs and studies, we recommend using 3 readers to evaluate a minimum set of 3 pathological features at standardized anatomic areas. Pre-defining areas to be scored, and reliability for each pathologic feature should be considered.

Corticosteroid Injections for Symptomatic Treatment of Osteoarthritis of the Knee: A Pilot Blinded Randomized Trial.

OBJECTIVE: To quantify the effect of corticosteroids compared to lidocaine-only injections over 12 weeks among patients with knee osteoarthritis (KOA). METHODS: Participants with KOA were randomized to receive a knee injection of methylprednisolone acetate 1 mL (40 mg) plus 2 mL lidocaine (1%) or 1 mL saline and 2 mL lidocaine. Participants and providers were blinded to treatment allocation using an opacified syringe. The outcome was the average change from baseline of the total Knee Injury and Osteoarthritis Outcome Score (KOOS) (range 0-100) assessed at 2-week intervals over 12 weeks. Participants received KOOS questionnaires on their smartphones through a web-based platform. We used linear mixed-effects regressions with robust variance estimators to evaluate the association between the intervention and change in KOOS total and subscales (ClinicalTrials.gov identifier NCT03835910; registered 2019-02-11). RESULTS: Of the 33 randomized participants, 31 were included in the final analysis. The predicted mean (SE) change in total KOOS over the 12-week follow-up was 9.4 (3.2) in the corticosteroids arm versus -1.3 (1.4) in the control arm (P = 0.003). Of participants, 47% achieved change as large as the minimal clinically important difference (16 units) in the intervention arm compared to 6% of participants in the lidocaine arm. Further, there were greater improvements in the intervention arm for KOOS subscales and for Patient Reported Outcomes Measurement Information System (PROMIS) assessments of pain intensity, behavior, and interference. CONCLUSION: Corticosteroid injections demonstrated clinically meaningful improvements in KOA symptoms over 12 weeks of follow-up. These data support larger studies to better quantify short-term benefits.

Age-Associated Changes in Knee Osteoarthritis, Pain-Related Behaviors, and Dorsal Root Ganglia Immunophenotyping of Male and Female Mice.

OBJECTIVE: Osteoarthritis (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. We undertook this study to characterize age-associated changes in knee OA, pain-related behaviors, and dorsal root ganglion (DRG) molecular phenotypes in mice of both sexes. METHODS: Male or female C57BL/6 mice 6 or 20 months of age were evaluated for histopathologic knee OA, pain-related behaviors, and L3-L5 DRG immune characterization via flow cytometry. DRG gene expression in older mice and humans was also examined. RESULTS: Male mice at 20 months of age had worse cartilage degeneration than 6-month-old mice. Older female mouse knees showed increased cartilage degeneration but to a lesser degree than those of male mice. 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 mouse DRGs showed increased expression of Ccl2 and Ccl5, and older female mouse DRGs showed increased Cxcr4 and Ccl3 expression compared to 6-month-old mouse DRGs, among other differentially expressed genes. Human DRG analysis from 6 individuals >80 years of age revealed elevated CCL2 in men compared to women, whereas CCL3 was higher in DRGs from women. CONCLUSION: We found 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 OA therapies.

Proteomics identifies novel biomarkers of synovial joint disease in a canine model of mucopolysaccharidosis I.

Mucopolysaccharidosis I is a lysosomal storage disorder characterized by deficient alpha-L-iduronidase activity, leading to abnormal accumulation of glycosaminoglycans in cells and tissues. Synovial joint disease is prevalent and significantly reduces patient quality of life. There is a critical need for improved understanding of joint disease pathophysiology in MPS I, including specific biomarkers to predict and monitor joint disease progression, and response to treatment. The objective of this study was to leverage the naturally-occurring MPS I canine model and undertake an unbiased proteomic screen to identify systemic biomarkers predictive of local joint disease in MPS I. Synovial fluid and serum samples were collected from MPS I and healthy dogs at 12 months-of-age, and protein abundance characterized using liquid chromatography tandem mass spectrometry. Stifle joints were evaluated postmortem using magnetic resonance imaging (MRI) and histology. Proteomics identified 40 proteins for which abundance was significantly correlated between serum and synovial fluid, including markers of inflammatory joint disease and lysosomal dysfunction. Elevated expression of three biomarker candidates, matrix metalloproteinase 19, inter-alpha-trypsin inhibitor heavy-chain 3 and alpha-1-microglobulin, was confirmed in MPS I cartilage, and serum abundance of these molecules was found to correlate with MRI and histological degenerative grades. The candidate biomarkers identified have the potential to improve patient care by facilitating minimally-invasive, specific assessment of joint disease progression and response to therapeutic intervention.

Dose-dependent effects of enzyme replacement therapy on skeletal disease progression in mucopolysaccharidosis VII dogs.

Mucopolysaccharidosis (MPS) VII is an inherited lysosomal storage disorder characterized by deficient activity of the enzyme ß-glucuronidase. Skeletal abnormalities are common in patients and result in diminished quality of life. Enzyme replacement therapy (ERT) for MPS VII using recombinant human ß-glucuronidase (vestronidase alfa) was recently approved for use in patients; however, to date there have been no studies evaluating therapeutic efficacy in a large animal model of MPS VII. The objective of this study was to establish the effects of intravenous ERT, administered at either the standard clinical dose (4 mg/kg) or a high dose (20 mg/kg), on skeletal disease progression in MPS VII using the naturally occurring canine model. Untreated MPS VII animals exhibited progressive synovial joint and vertebral bone disease and were no longer ambulatory by age 6 months. Standard-dose ERT-treated animals exhibited modest attenuation of joint disease, but by age 6 months were no longer ambulatory. High-dose ERT-treated animals exhibited marked attenuation of joint disease, and all were still ambulatory by age 6 months. Vertebral bone disease was recalcitrant to ERT irrespective of dose. Overall, our findings indicate that ERT administered at higher doses results in significantly improved skeletal disease outcomes in MPS VII dogs.

Protocol for a multi-center randomized controlled trial to evaluate the benefits of exercise incentives and corticosteroid injections in osteoarthritis of the knee (MOVE-OK).

BACKGROUND: Knee osteoarthritis (KOA) is a high-priority problem among the aging population. While exercise has been shown to be beneficial in management of the disease, scalable and low-cost interventions to improve exercise in this population are lacking. Recent controversy over the value of corticosteroid injections for palliation has also arisen. Therefore, we designed a randomized, double-blind, placebo-controlled clinical trial with a 2-period crossover design to study (1) behavioral incentives to promote exercise and (2) corticosteroid injections to reduce pain and improve function in patients with KOA when compared to lidocaine only. METHODS: The study design is a pragmatic factorial and crossover randomized clinical trial. Patients with KOA who are deemed eligible by their provider to receive knee injections and are able to walk without assistive devices will be recruited from clinical practices at four sites within the Veterans Affairs (VA) Health System in the USA. In total, 220 participants will be randomized to receive social incentives with gamification (i.e., incorporation of game elements) to promote exercise and compared to controls that receive a Fitbit but no incentive. Each patient will also be assigned to receive a blinded corticosteroid injection and a lidocaine-only injection in random order. The primary outcomes are the change in average daily step counts from baseline and the change in Knee Osteoarthritis Outcome Score (KOOS) from baseline. The study team will continuously collect step count, heart rate, and sleep data using activity monitors and patient-reported outcomes using the Way to Health (WTH) platform at two four-week intervals over eight months of follow-up. Mixed effects regression incorporating all available data points will be used for analysis. DISCUSSION: The "Marching on for Veterans with Osteoarthritis of the Knee" (MOVE-OK) trial will take a pragmatic approach to evaluate (1) whether incentives based on behaviorally enhanced gamification can improve physical activity in this patient population and (2) whether corticosteroids injections reduce pain and disability in patients with KOA. Results of this trial will help to direct clinical practice and inform management guidelines. TRIAL REGISTRATION: ClinicalTrials.gov NCT05035810 . Registered on 5 September 2021.

Expression of Human Interleukin 8 in Mice Alters Their Natural Behaviors.

Objective: 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.

Erosive hand osteoarthritis: latest findings and outlook.

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.

Six-Month Outcomes of Clinically Relevant Meniscal Injury in a Large-Animal Model.

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.

IL-15 and IL15RA in Osteoarthritis: Association With Symptoms and Protease Production, but Not Structural Severity.

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.

Functional Deficits in Mice Expressing Human Interleukin 8.

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.

Innate inflammation and synovial macrophages in osteoarthritis pathophysiology.

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.

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

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

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

OBJECTIVE: CD14 is a monocyte/macrophage pattern-recognition receptor that modulates innate inflammatory signaling. Soluble CD14 levels in knee OA synovial fluids are associated with symptoms and progression of disease. Here we investigate the role of this receptor in development of OA using a murine joint injury model of disease. METHODS: 10-week-old Male C57BL/6 (WT) and CD14-deficient (CD14-/-) mice underwent destabilization of the medial meniscus (DMM) surgery to induce OA. Joint histopathology was used to examine cartilage damage, and microCT to evaluate subchondral bone (SCB) remodeling at 6 and 19 weeks after surgery. Synovial and fat pad expression of macrophage markers (F4/80, CD11c, CD68, iNOS, CCR7, CD163 and CD206) was assessed by flow cytometry and droplet digital (dd)PCR. Changes in locomotive activity indicative of joint pain were evaluated longitudinally up to 16 weeks by automated behavioral analysis. RESULTS: Early cartilage damage scores 6 weeks post-DMM were similar in both strains (Mean score ±SEM WT: 4.667±1.38, CD14-/-: 4.6±0.6), but at 19 weeks were less severe in CD14-/- (6.0±0.46) than in WT mice (13.44±2.5, p = 0.0002). CD14-/- mice were protected from both age-related and post-surgical changes in SCB mineral density and trabecular thickness. In addition, CD14-/- mice were protected from decreases in climbing activity (p = 0.015 vs. WT, 8 weeks) observed after DMM. Changes in synovial/fat pad expression of CCR7, a marker of M1 macrophages, were slightly reduced post-DMM in the absence of CD14, while expression of CD68 (pan-macrophage marker) and CD163 (M2 marker) were unchanged. CONCLUSION: CD14 plays an important role in progression of structural and functional features of OA in the DMM model, and may provide a new target for therapeutic development.

Chemokine receptor-7 (CCR7) deficiency leads to delayed development of joint damage and functional deficits in a murine model of osteoarthritis.

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. J Orthop Res 36:864-875, 2018.