Molecular pathogenesis of OA pain: Past, present, and future.

OBJECTIVE: To provide a historical perspective and narrative review on research into the molecular pathogenesis of osteoarthritis pain. DESIGN: PubMed databases were searched for combinations of "osteoarthritis", "pain" and "animal models" for papers that represented key phases in the history of osteoarthritis pain discovery research including epidemiology, pathology, imaging, preclinical modeling and clinical trials. RESULTS: The possible anatomical sources of osteoarthritis pain were identified over 50 years ago, but relatively slow progress has been made in understanding the apparent disconnect between structural changes captured by radiography and symptom severity. Translationally relevant animal models of osteoarthritis have aided in our understanding of the structural and molecular drivers of osteoarthritis pain, including molecules such as nerve growth factor and C-C motif chemokine ligand 2. Events leading to persistent osteoarthritis pain appear to involve a two-step process involving changes in joint innervation, including neo-innervation of the articular cartilage, as well as sensitization at the level of the joint, dorsal root ganglion and central nervous system. CONCLUSIONS: There remains a great need for the development of treatments to reduce osteoarthritis pain in patients. Harnessing all that we have learned over the past several decades is helping us to appreciate the important interaction between structural disease and pain, and this is likely to facilitate development of new disease modifying therapies in the future.

Artificial intelligence in osteoarthritis: repair by knee joint distraction shows association of pain, radiographic and immunological outcomes.

OBJECTIVES: Knee joint distraction (KJD) has been associated with clinical and structural improvement and SF marker changes. The current objective was to analyse radiographic changes after KJD using an automatic artificial intelligence-based measurement method and relate these to clinical outcome and SF markers. METHODS: Twenty knee osteoarthritis patients were treated with KJD in regular care. Radiographs and WOMAC were collected before and ∼1 year post-treatment. SF was aspirated before, during and after treatment; biomarker levels were assessed by immunoassay. Radiographs were analysed to obtain compartmental minimum and standardized joint space width (JSW), Kellgren-Lawrence (KL) grades, compartmental joint space narrowing (JSN) scores, and osteophytosis and sclerosis scores. Results were analysed for the most affected compartment (MAC) and least affected compartment. Radiographic changes were analysed using the Wilcoxon signed rank test for categorical and paired t-test for continuous variables. Linear regression was used to calculate associations between changes in JSW, WOMAC pain and SF markers. RESULTS: Sixteen patients could be evaluated. JSW, KL and JSN improved in around half of the patients, significant only for MAC JSW (P < 0.05). MAC JSW change was positively associated with WOMAC pain change (P < 0.04). Greater monocyte chemoattractant protein 1 (MCP-1) and lower TGFß-1 increases were significantly associated with changes in MAC JSW (P < 0.05). MCP-1 changes were positively associated with WOMAC pain changes (P < 0.05). CONCLUSION: Automatic radiographic measurements show improved joint structure in most patients after KJD in regular care. MAC JSW increased significantly and was associated with SF biomarker level changes and even with improvements in pain as experienced by these patients.

Ciliary proteins specify the cell inflammatory response by tuning NFκB signalling, independently of primary cilia.

Complex inflammatory signalling cascades define the response to tissue injury but also control development and homeostasis, limiting the potential for these pathways to be targeted therapeutically. Primary cilia are subcellular regulators of cellular signalling, controlling how signalling is organized, encoded and, in some instances, driving or influencing pathogenesis. Our previous research revealed that disruption of ciliary intraflagellar transport (IFT), altered the cell response to IL-1ß, supporting a putative link emerging between cilia and inflammation. Here, we show that IFT88 depletion affects specific cytokine-regulated behaviours, changing cytosolic NFκB translocation dynamics but leaving MAPK signalling unaffected. RNA-seq analysis indicates that IFT88 regulates one third of the genome-wide targets, including the pro-inflammatory genes Nos2, Il6 and Tnf Through microscopy, we find altered NFκB dynamics are independent of assembly of a ciliary axoneme. Indeed, depletion of IFT88 inhibits inflammatory responses in the non-ciliated macrophage. We propose that ciliary proteins, including IFT88, KIF3A, TTBK2 and NPHP4, act outside of the ciliary axoneme to tune cytoplasmic NFκB signalling and specify the downstream cell response. This is thus a non-canonical function for ciliary proteins in shaping cellular inflammation.This article has an associated First Person interview with the first author of the paper.

The Extracellular Matrix of Articular Cartilage Controls the Bioavailability of Pericellular Matrix-Bound Growth Factors to Drive Tissue Homeostasis and Repair.

The extracellular matrix (ECM) has long been regarded as a packing material; supporting cells within the tissue and providing tensile strength and protection from mechanical stress. There is little surprise when one considers the dynamic nature of many of the individual proteins that contribute to the ECM, that we are beginning to appreciate a more nuanced role for the ECM in tissue homeostasis and disease. Articular cartilage is adapted to be able to perceive and respond to mechanical load. Indeed, physiological loads are essential to maintain cartilage thickness in a healthy joint and excessive mechanical stress is associated with the breakdown of the matrix that is seen in osteoarthritis (OA). Although the trigger by which increased mechanical stress drives catabolic pathways remains unknown, one mechanism by which cartilage responds to increased compressive load is by the release of growth factors that are sequestered in the pericellular matrix. These are heparan sulfate-bound growth factors that appear to be largely chondroprotective and displaced by an aggrecan-dependent sodium flux. Emerging evidence suggests that the released growth factors act in a coordinated fashion to drive cartilage repair. Thus, we are beginning to appreciate that the ECM is the key mechano-sensor and mechano-effector in cartilage, responsible for directing subsequent cellular events of relevance to joint health and disease.

The Musculoskeletal Manifestations of Marfan Syndrome: Diagnosis, Impact, and Management.

PURPOSE OF REVIEW: Marfan syndrome (MFS) is an autosomal dominant heritable disorder of fibrillin-1 (FBN1) with predominantly ocular, cardiovascular, and musculoskeletal manifestations that has a population prevalence of approximately 1 in 5-10,000 (Chiu et al. Mayo Clin Proc. 89(1):34-42, 146, Dietz 3, Loeys et al. J Med Genet. 47(7):476-85, 4). RECENT FINDINGS: The vascular complications of MFS still pose the greatest threat, but effective management options, such as regular cardiac monitoring and elective surgical intervention, have reduced the risk of life-threatening cardiovascular events, such as aortic dissection. Although cardiovascular morbidity and mortality remains high, these improvements in cardiovascular management have extended the life expectancy of those with MFS by perhaps 30-50 years from an estimated mean of 32 years in 1972 (Dietz 3, Gott et al. Eur J Cardio-thoracic Surg. 10(3):149-58, 147, Murdoch et al. N Engl J Med. 286(15):804-8, 148). The musculoskeletal manifestations of MFS, which to date have received less attention, can also have a significant impact on the quality of life and are likely to become more important as the age of the Marfan syndrome population increases (Hasan et al. Int J Clin Pract. 61(8):1308-1320, 127). In addition, musculoskeletal manifestations are often critically important in the diagnosis of MFS. Here, we review the main clinically relevant and diagnostically useful musculoskeletal features of MFS, which together contribute to the "systemic features score" (referred to hereafter as systemic score), part of the revised Ghent nosology for MFS. We discuss current treatment strategies and highlight the need for a multidisciplinary approach to diagnosis and management. Finally, we review new pharmacological approaches that may be disease modifying and could help to improve the outcome for individuals with this syndrome.

Heparan Sulfate Proteoglycan Synthesis Is Dysregulated in Human Osteoarthritic Cartilage.

Osteoarthritis (OA) is a common degenerative joint disease, characterized by cartilage loss and subchondral bone remodeling in response to abnormal mechanical load. Heparan sulfate (HS) proteoglycans bind to many proteins that regulate cartilage homeostasis, including growth factors, morphogens, proteases, and their inhibitors, and modulate their localization, retention, and biological activity. Changes in HS expression and structure may thus have important consequences for joint health. We analyzed normal and osteoarthritic human knee cartilage, and found HS biosynthesis was markedly disrupted in OA, with 45% of the 38 genes analyzed differentially regulated in diseased cartilage. The expression of several HS core proteins, biosynthesis, and modification enzymes was increased in OA cartilage, whereas the expression of the HS proteoglycans syndecan 4 and betaglycan was reduced. The structure of HS was also altered, with increased levels of 6-O-sulfation in osteoarthritic samples, which correlated with increased expression of HS6ST1, a 6-O-sulfotransferase, and GLCE, an epimerase that promotes 6-O-sulfation. siRNA silencing of HS6ST1 expression in primary OA chondrocytes inhibited extracellular signal-regulated kinase phosphorylation in response to fibroblast growth factor 2, showing that changes in 6-O-sulfation impact a key cartilage signaling pathway. Given the broad range of homeostatic and repair pathways that HS regulates, these changes in proteoglycan expression and HS structure are likely to have significant effects on joint health and progression of OA.

Design and Evaluation of Magnetic Hall Effect Tactile Sensors for Use in Sensorized Splints.

Splinting techniques are widely used in medicine to inhibit the movement of arthritic joints. Studies into the effectiveness of splinting as a method of pain reduction have generally yielded positive results, however, no significant difference has been found in clinical outcomes between splinting types. Tactile sensing has shown great promise for the integration into splinting devices and may offer further information into applied forces to find the most effective methods of splinting. Hall effect-based tactile sensors are of particular interest in this application owing to their low-cost, small size, and high robustness. One complexity of the sensors is the relationship between the elastomer geometry and the measurement range. This paper investigates the design parameters of Hall effect tactile sensors for use in hand splinting. Finite element simulations are used to locate the areas in which sensitivity is high in order to optimise the deflection range of the sensor. Further simulations then investigate the mechanical response and force ranges of the elastomer layer under loading which are validated with experimental data. A 4 mm radius, 3 mm-thick sensor is identified as meeting defined sensing requirements for range and sensitivity. A prototype sensor is produced which exhibits a pressure range of 45 kPa normal and 6 kPa shear. A proof of principle prototype demonstrates how this can be integrated to form an instrumented splint with multi-axis sensing capability and has the potential to inform clinical practice for improved splinting.

Mechanoadaptation: articular cartilage through thick and thin.

The articular cartilage is exquisitely sensitive to mechanical load. Its structure is largely defined by the mechanical environment and destruction in osteoarthritis is the pathophysiological consequence of abnormal mechanics. It is often overlooked that disuse of joints causes profound loss of volume in the articular cartilage, a clinical observation first described in polio patients and stroke victims. Through the 1980s, the results of studies exploiting experimental joint immobilisation supported this. Importantly, this substantial body of work was also the first to describe metabolic changes that resulted in decreased synthesis of matrix molecules, especially sulfated proteoglycans. The molecular mechanisms that underlie disuse atrophy are poorly understood despite the identification of multiple mechanosensing mechanisms in cartilage. Moreover, there has been a tendency to equate cartilage loss with osteoarthritic degeneration. Here, we review the historic literature and clarify the structural, metabolic and clinical features that clearly distinguish cartilage loss due to disuse atrophy and those due to osteoarthritis. We speculate on the molecular sensing pathways in cartilage that may be responsible for cartilage mechanoadaptation.

Active immunisation targeting nerve growth factor attenuates chronic pain behaviour in murine osteoarthritis.

OBJECTIVES: Nerve growth factor (NGF) has emerged as a key driver of pain in osteoarthritis (OA) and antibodies to NGF are potent analgesics in human disease. Here, we validate a novel vaccine strategy to generate anti-NGF antibodies for reversal of pain behaviour in a surgical model of OA. METHODS: Virus-like particles were derived from the cucumber mosaic virus (CuMV) and coupled to expressed recombinant NGF to create the vaccine. 10-week-old male mice underwent partial meniscectomy to induce OA or sham-surgery. Spontaneous pain behaviour was measured by Linton incapacitance and OA severity was quantified using OARSI histological scoring. Mice (experimental and a sentinel cohort) were inoculated with CuMVttNGF (Vax) or CuMVttctrl (Mock) either before surgery or once pain was established. Efficacy of anti-NGF from the plasma of sentinel vaccinated mice was measured in vitro using a neurite outgrowth assay in PC12 cells. RESULTS: Anti-NGF titres were readily detectable in the vaccinated but not mock vaccinated mice. Regular boosting with fresh vaccine was required to maintain anti-NGF titres as measured in the sentinel cohort. Both prophylactic and therapeutic vaccination demonstrated a reversal of pain behaviour by incapacitance testing, and a meta-analysis of the two studies showing analgesia at peak anti-NGF titres was highly statistically significant. Serum anti-NGF was able to inhibit neurite outgrowth equivalent to around 150 ug/mL of recombinant monoclonal antibody. CONCLUSIONS: This study demonstrates therapeutic efficacy of a novel NGF vaccine strategy that reversibly alleviates spontaneous pain behaviour in surgically induced murine OA.

FGF-2 promotes osteocyte differentiation through increased E11/podoplanin expression.

E11/podoplanin is critical in the early stages of osteoblast-to-osteocyte transitions (osteocytogenesis), however, the upstream events which regulate E11 expression are unknown. The aim of this study was to examine the effects of FGF-2 on E11-mediated osteocytogenesis and to reveal the nature of the underlying signaling pathways regulating this process. Exposure of MC3T3 osteoblast-like cells and murine primary osteoblasts to FGF-2 (10 ng/ml) increased E11 mRNA and protein expression (p < 0.05) after 4, 6, and 24 hr. FGF-2 induced changes in E11 expression were also accompanied by significant (p < 0.01) increases in Phex and Dmp1 (osteocyte markers) expression and decreases in Col1a1, Postn, Bglap, and Alpl (osteoblast markers) expression. Immunofluorescent microscopy revealed that FGF-2 stimulated E11 expression, facilitated the translocation of E11 toward the cell membrane, and subsequently promoted the formation of osteocyte-like dendrites in MC3T3 and primary osteoblasts. siRNA knock down of E11 expression achieved >70% reduction of basal E11 mRNA expression (p < 0.05) and effectively abrogated FGF-2-related changes in E11 expression and dendrite formation. FGF-2 strongly activated the ERK signaling pathway in osteoblast-like cells but inhibition of this pathway did not block the ability of FGF-2 to enhance E11 expression or to promote acquisition of the osteocyte phenotype. The results of this study highlight a novel mechanism by which FGF-2 can regulate osteoblast differentiation and osteocyte formation. Specifically, the data suggests that FGF-2 promotes osteocytogenesis through increased E11 expression and further studies will identify if this regulatory pathway is essential for bone development and maintenance in health and disease.

Connective tissue growth factor contributes to joint homeostasis and osteoarthritis severity by controlling the matrix sequestration and activation of latent TGFß.

OBJECTIVES: One mechanism by which cartilage responds to mechanical load is by releasing heparin-bound growth factors from the pericellular matrix (PCM). By proteomic analysis of the PCM, we identified connective tissue growth factor (CTGF) and here investigate its function and mechanism of action. METHODS: Recombinant CTGF (rCTGF) was used to stimulate human chondrocytes for microarray analysis. Endogenous CTGF was investigated by in vitro binding assays and confocal microscopy. Its release from cut cartilage (injury CM) was analysed by Western blot under reducing and non-reducing conditions. A postnatal, conditional CtgfcKO mouse was generated for cartilage injury experiments and to explore the course of osteoarthritis (OA) by destabilisation of the medial meniscus. siRNA knockdown was performed on isolated human chondrocytes. RESULTS: The biological responses of rCTGF were TGFß dependent. CTGF displaced latent TGFß from cartilage and both were released on cartilage injury. CTGF and latent TGFß migrated as a single high molecular weight band under non-reducing conditions, suggesting that they were in a covalent (disulfide) complex. This was confirmed by immunoprecipitation. Using CtgfcKO mice, CTGF was required for sequestration of latent TGFß in the matrix and activation of the latent complex at the cell surface through TGFßR3. In vivo deletion of CTGF increased the thickness of the articular cartilage and protected mice from OA. CONCLUSIONS: CTGF is a latent TGFß binding protein that controls the matrix sequestration and activation of TGFß in cartilage. Deletion of CTGF in vivo caused a paradoxical increase in Smad2 phosphorylation resulting in thicker cartilage that was protected from OA.

Night-time immobilization of the distal interphalangeal joint reduces pain and extension deformity in hand osteoarthritis.

OBJECTIVE: DIP joint OA is common but has few cost-effective, evidence-based interventions. Pain and deformity [radial or ulnar deviation of the joint or loss of full extension (extension lag)] frequently lead to functional and cosmetic issues. We investigated whether splinting the DIP joint would improve pain, function and deformity. METHODS: A prospective, radiologist-blinded, non-randomized, internally controlled trial of custom splinting of the DIP joint was carried out. Twenty-six subjects with painful, deforming DIP joint hand OA gave written, informed consent. One intervention joint and one control joint were nominated. A custom gutter splint was worn nightly for 3 months on the intervention joint, with clinical and radiological assessment at baseline, 3 and 6 months. Differences in the change were compared by the Wilcoxon signed rank test. RESULTS: The median average pain at baseline was similar in the intervention (6/10) and control joints (5/10). Average pain (primary outcome measure) and worst pain in the intervention joint were significantly lower at 3 months compared with baseline (P = 0.002, P = 0.02). Differences between intervention and control joint average pain reached significance at 6 months (P = 0.049). Extension lag deformity was significantly improved in intervention joints at 3 months and in splinted joints compared with matched contralateral joints (P = 0.016). CONCLUSION: Short-term night-time DIP joint splinting is a safe, simple treatment modality that reduces DIP joint pain and improves extension of the digit, and does not appear to give rise to non-compliance, increased stiffness or joint restriction. TRIAL REGISTRATION: clinical trials.gov, http://clinicaltrials.gov, NCT01249391.

Src and fibroblast growth factor 2 independently regulate signaling and gene expression induced by experimental injury to intact articular cartilage.

OBJECTIVE: To investigate whether cartilage injury activates protein tyrosine kinases distinct from fibroblast growth factor (FGF)-related signaling, and whether they contribute to injury-induced gene responses. METHODS: Phosphokinases and protein tyrosine phosphorylation were assayed by Western blotting of cartilage lysates. Immunoprecipitation and Western blotting with 4G10 antibody and immunoprecipitation kinase assay were carried out. Tyrosine-phosphorylated proteins on silver-stained gels of injured cartilage lysates were identified by mass spectrometry. Messenger RNA induction in cartilage explants was assessed by quantitative reverse transcriptase-polymerase chain reaction. RESULTS: Protein tyrosine phosphorylation occurred within seconds of injury to the surface of intact articular cartilage, as did activation of MAPKs and IKK. Activation did not reoccur upon reinjury of cultured explants. The prominent tyrosine-phosphorylated proteins focal adhesion kinase, paxillin, and cortactin were identified as substrates of Src family kinases. The Src family kinase inhibitor PP2 blocked injury-induced tyrosine phosphorylation. It did not prevent activation of the MAPKs and IKK but differentially inhibited 8 of 10 inflammatory response genes that were induced by injury. In contrast, FGF signaling blockade with PD173074 reduced all MAPK and IKK activation by ∼50% and inhibited a different subset of genes but had no effect on Src-like signaling. CONCLUSION: Injury to the surface of intact articular cartilage activates Src-like kinases as well as MAPKs and IKK (implying NF-κB activation). FGF-2 contributes to MAPK/IKK activation but not to Src-like signaling, suggesting that the latter is a parallel pathway that also regulates the injury-induced inflammatory gene response.

Fibroblast growth factor 2 drives changes in gene expression following injury to murine cartilage in vitro and in vivo.

OBJECTIVE: The articular cartilage is known to be highly mechanosensitive, and a number of mechanosensing mechanisms have been proposed as mediators of the cellular responses to altered mechanical load. These pathways are likely to be important in tissue homeostasis as well as in the pathogenesis of osteoarthritis. One important injury-activated pathway involves the release of pericellular fibroblast growth factor 2 (FGF-2) from the articular cartilage. Using a novel model of murine cartilage injury and surgically destabilized joints in mice, we examined the extent to which FGF-2 contributes to the cellular gene response to injury. METHODS: Femoral epiphyses from 5-week-old wild-type mice were avulsed and cultured in serum-free medium. Explant lysates were Western blotted for phospho-JNK, phospho-p38, and phospho-ERK or were fixed for immunohistochemical analysis of the nuclear translocation of p65 (indicative of NF-κB activation). RNA was extracted from injured explants, rested explants that had been stimulated with recombinant FGF-2 or FGF-18, or whole joints from either wild-type mice or FGF-2(-/-) mice. Reverse transcription-polymerase chain reaction was performed to examine a number of inflammatory response genes that had previously been identified in a microarray analysis. RESULTS: Murine cartilage avulsion injury resulted in rapid activation of the 3 MAP kinase pathways as well as NF-κB. Almost all genes identified in murine joints following surgical destabilization were also regulated in cartilage explants upon injury. Many of these genes, including those for activin A (Inhba), tumor necrosis factor-stimulated gene 6 (Tnfaip6), matrix metalloproteinase 19 (Mmp19), tissue inhibitor of metalloproteinases 1 (Timp1), and podoplanin (Pdpn), were significantly FGF-2 dependent following injury to cartilage in vitro and to joint tissues in vivo. CONCLUSION: FGF-2-dependent gene expression occurs in vitro and in vivo in response to cartilage/joint injury in mice.

Sulforaphane represses matrix-degrading proteases and protects cartilage from destruction in vitro and in vivo.

OBJECTIVE: Sulforaphane (SFN) has been reported to regulate signaling pathways relevant to chronic diseases. The aim of this study was to investigate the impact of SFN treatment on signaling pathways in chondrocytes and to determine whether sulforaphane could block cartilage destruction in osteoarthritis. METHODS: Gene expression, histone acetylation, and signaling of the transcription factors NF-E2-related factor 2 (Nrf2) and NF-κB were examined in vitro. The bovine nasal cartilage explant model and the destabilization of the medial meniscus (DMM) model of osteoarthritis in the mouse were used to assess chondroprotection at the tissue and whole-animal levels. RESULTS: SFN inhibited cytokine-induced metalloproteinase expression in primary human articular chondrocytes and in fibroblast-like synovial cells. SFN acted independently of Nrf2 and histone deacetylase activity to regulate metalloproteinase expression in human articular chondrocytes but did mediate prolonged activation of JNK and p38 MAPK. SFN attenuated NF-κB signaling at least through inhibition of DNA binding in human articular chondrocytes, with decreased expression of several NF-κB-dependent genes. Compared with cytokines alone, SFN (10 µM) abrogated cytokine-induced destruction of bovine nasal cartilage at both the proteoglycan and collagen breakdown levels. An SFN-rich diet (3 µmoles/day SFN versus control chow) decreased the arthritis score in the DMM model of osteoarthritis in the mouse, with a concurrent block of early DMM-induced gene expression changes. CONCLUSION: SFN inhibits the expression of key metalloproteinases implicated in osteoarthritis, independently of Nrf2, and blocks inflammation at the level of NF-κB to protect against cartilage destruction in vitro and in vivo.

Could sex-specific subtypes of hand osteoarthritis exist? A retrospective study in women presenting to secondary care.

Introduction: Hand osteoarthritis is more common in women, and its risk increases around the time of the menopause. We set out to describe the timing between menopause and the onset of symptomatic hand osteoarthritis (OA), and associations with the use of hormone replacement therapy (HRT) or its discontinuation, describing any identifiable subgroups of women. Methods: Retrospective healthcare-records study of sequential women referred to a specialist hand OA clinic, 2007-2015. Confirmation of hand OA diagnosis was by clinican, by accepted criteria. Demographics and clinical variables were from healthcare-records, recorded by standardised proforma. Outcomes of interest were reported age of onset of hand symptoms, reported age at final menstrual period (FMP), time from FMP to reported onset of hand symptoms and time from cessation of HRT to reported onset of hand symptoms. Exposure categories for systemic HRT use were never users, current users, previous users. Analysis of Variance compared groups; linear regression analysed associations of exposure with outcome. Results: 82/92(89%) of eligible women were post-menopausal, mean age at FMP 49.9 years (SD5.4). In these post-menopausal women, median time from FMP to hand symptom onset was 3 years. 48/82 (59%) developed hand symptoms within the defined peri-menopausal period (FMP ± 4 years), whilst some women developed their symptoms before or after (range -25, 30 years). In women who discontinued HRT prior to symptom onset, the median time from HRT cessation to onset of hand symptoms was 6 months. Past HRT users were older at hand symptom onset than women who had not taken HRT [coeff.4.7 years (0.92, 8.39); P = 0.015]. Conclusions: This study adds to evidence associating the menopause/sex hormone deficiency with hand OA symptom onset in a sizeable subgroup of women (but not all). HRT use/cessation appears to influence the timing of onset of hand OA symptoms. It is not possible to interpret from this type of study whether sex hormone deficiency is causative of disease or modulates its symptoms. It is also not possible to judge whether painful hand osteoarthritis in post-menopausal women is a subtype of disease. Further investigation is indicated of sex-specific subtypes and potential for personalised medicine for post-menopausal women with hand osteoarthritis, as a clearly definable high-risk subgroup.

The Effect of Acute Knee Injuries and Related Knee Surgery on Serum Levels of Pro- and Anti-inflammatory Lipid Mediators and Their Associations With Knee Symptoms.

BACKGROUND: Despite an acute knee injury being a major risk factor for osteoarthritis, the factors that initiate and maintain this risk of longer-term knee symptoms are poorly understood. Bioactive lipids derived from omega-3 and -6 polyunsaturated fatty acids have key roles in the regulation of the inflammatory response and have been linked to joint damage and osteoarthritis pain in translational models. HYPOTHESIS: There would be associations between systemic levels of bioactive lipids and knee symptoms longitudinally after an acute knee injury and related knee surgery. STUDY DESIGN: Controlled laboratory study. METHODS: This study analyzed a subset of young, active adults who had sustained an acute knee injury (recruited via a surgical care pathway) and healthy age- and sex-matched controls. Surgery, if performed, was conducted after the baseline serum sample was taken and before the 3-month and 2-year visits. Liquid chromatography-tandem mass spectrometry of 41 bioactive lipids was carried out in sera of (1) 47 injured participants (median age, 28 years) collected at baseline (median, 24 days after injury), 3 months, and 2 years, along with the Knee injury and Osteoarthritis Outcome Score, and (2) age- and sex-matched controls. RESULTS: Levels of the omega-3 polyunsaturated fatty acids eicosapentaenoic acid (P≤ .0001) and docosahexaenoic acid (P≤ .0001) and the pro-resolving lipid mediators 17- and 14-hydroxydocosahexaenoic acid, and 18-hydroxyeicosapentaenoic acid were all significantly greater at baseline in injured participants compared with the later time points and also higher than in healthy controls (P = .0019 and P≤ .0001, respectively). Levels of pro-inflammatory prostaglandins E2 and D2, leukotriene B4, and thromboxane B2 were significantly lower at baseline compared with the later time points. Higher levels of 8,9-, 11,12-, and 14,15-dihydroxyeicosatrienoic acid (DHET) were cross-sectionally associated with more severe knee pain/symptoms according to the Knee injury and Osteoarthritis Outcome Score at 2 years (P = .0004, R2 = 0.251; P = .0002, R2 = 0.278; and P = .0012, R2 = 0.214, respectively). CONCLUSION: The profile of pro-resolving versus pro-inflammatory lipids at baseline suggests an initial activation of pro-resolution pathways, followed by the later activation of pro-inflammatory pathways. CLINICAL RELEVANCE: In this largely surgically managed cohort, the association of soluble epoxide hydrolase metabolites, the DHETs, with more severe knee symptoms at 2 years provides a rationale for further investigation into the role of this pathway in persisting knee symptoms in this population, including potential therapeutic strategies.

Joint immobilization prevents murine osteoarthritis and reveals the highly mechanosensitive nature of protease expression in vivo.

OBJECTIVE: Mechanical joint loading is critical for the development of osteoarthritis (OA). Although once regarded as a disease of cartilage attrition, OA is now known to be controlled by the expression and activity of key proteases, such as ADAMTS-5, that drive matrix degradation. This study was undertaken to investigate the link between protease expression and mechanical joint loading in vivo. METHODS: We performed a microarray analysis of genes expressed in the whole joint following surgical induction of murine OA (by cutting the medial meniscotibial ligament). Gene expression changes were validated by reverse transcriptase-polymerase chain reaction in whole joints and microdissected tissues of the joint, including the articular cartilage, meniscus, and epiphysis. Following surgery, mouse joints were immobilized, either by prolonged anesthesia or by sciatic neurectomy. RESULTS: Many genes were regulated in the whole joint within 6 hours of surgical induction of OA in the mouse. These included Arg1, Ccl2, Il6, Tsg6, Mmp3, Il1b, Adamts5, Adamts4, and Adamts1. All of these were significantly regulated in the articular cartilage. When joints were immobilized by prolonged anesthesia, regulation of the vast majority of genes was abrogated. When joints were immobilized by sciatic neurectomy, regulation of selected genes was abrogated, and OA was prevented up to 12 weeks postsurgery. CONCLUSION: These findings indicate that gene expression in the mouse joint following the induction of OA is rapid and highly mechanosensitive. Regulated genes include the known pathogenic protease ADAMTS-5. Targeting the mechanosensing mechanisms of joint tissue may offer new strategies for disease modification.

Genome-Wide Association Studies to Drug: Identifying Retinoic Acid Metabolism Blocking Agents to Suppress Mechanoflammation in Osteoarthritis.

Osteoarthritis (OA) is a highly prevalent debilitating joint disease for which there are currently no licensed disease-modifying treatments. The pathogenesis of OA is complex, involving genetic, mechanical, biochemical, and environmental factors. Cartilage injury, arguably the most important driving factor in OA development, is able to activate both protective and inflammatory pathways within the tissue. Recently, >100 genetic risk variants for OA have been identified through Genome Wide Association Studies, which provide a powerful tool to validate existing putative disease pathways and discover new ones. Using such an approach, hypomorphic variants within the aldehyde dehydrogenase 1 family member A2 (ALDH1A2) gene were shown to be associated with increased risk of severe hand OA. ALDH1A2 encodes the enzyme that synthesizes all-trans retinoic acid (atRA), an intracellular signaling molecule. This review summarizes the influence of the genetic variants on expression and function of ALDH1A2 in OA cartilage, its role in the mechanical injury response of cartilage, and its potent anti-inflammatory effect after cartilage injury. In doing so it identifies atRA metabolism-blocking agents as potential treatments for suppressing mechanoflammation in OA.