Mouse models of osteoarthritis: surgical model of posttraumatic osteoarthritis induced by destabilization of the medial meniscus

Chondrocyte fatty acid oxidation drives osteoarthritis via SOX9 degradation and epigenetic regulation

Osteoarthritis is the most prevalent age-related degenerative joint disease and is closely linked to obesity. However, the underlying mechanisms remain unclear. Here we show that altered lipid metabolism in chondrocytes, particularly enhanced fatty acid oxidation (FAO), contributes to osteoarthritis progression. Excessive FAO causes acetyl-CoA accumulation, thereby altering protein-acetylation profiles, where the core FAO enzyme HADHA is hyperacetylated and activated, reciprocally boosting FAO activity and exacerbating OA progression. Mechanistically, elevated FAO reduces AMPK activity, impairs SOX9 phosphorylation, and ultimately promotes its ubiquitination-mediated degradation. Additionally, acetyl-CoA orchestrates epigenetic modulation, affecting multiple cellular processes critical for osteoarthritis pathogenesis, including the transcriptional activation of MMP13 and ADAMTS7. Cartilage-targeted delivery of trimetazidine, an FAO inhibitor and AMPK activator, demonstrates superior efficacy in a mouse model of metabolism-associated post-traumatic osteoarthritis. These findings suggest that targeting chondrocyte-lipid metabolism may offer new therapeutic strategies for osteoarthritis.

Chondroprotective Effect of Campylaephora hypnaeoides Extract in Primary Chondrocytes and Rat OA Model

Campylaephora hypnaeoides (C. hypnaeoides) was extracted using fermented ethanol. The effect of fermented ethanol extract of C. hypnaeoides (FeCH) on chondrocyte viability was analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-iphenyltetrazolium bromide assay, which showed no cytotoxicity at 2 mg/mL. FeCH pretreatment in IL-1β-stimulated chondrocytes significantly inhibited the accumulation of nitric oxide and prostaglandin E2, which was analyzed using the ELISA assay. In addition, protein expression levels of inflammatory-related factors, such as inducible nitric oxide synthase, cyclooxygenase-2, interleukin-6, tumor necrosis factor-alpha, and cartilage-degrading-related enzymes, such as matrix metalloproteinases-1, -3, and -13, and a disintegrin and metalloproteinase with thrombospondin motifs-4 and -5 were significantly decreased in IL-1β-stimulated chondrocytes pretreated with FeCH, which were analyzed using western blot analysis. In addition, as a result of analyzing the content of collagen type II (Col II) and proteoglycan through western blot analysis and alcian blue staining, FeCH pretreatment prevented the degradation of Col II and proteoglycan. It was analyzed through western blot analysis that the chondroprotective effect of FeCH may be mediated through MAPKs and NF-κB-signaling mechanisms. In an in vivo study, an osteoarthritis experimental animal model with damaged medial meniscus (DMM) was utilized and orally administered daily for 8 weeks after surgery. At the study end point, knee joints were harvested and subjected to histological analysis with safranin O staining. As a result, articular cartilage was significantly protected in the FeCH group compared to the DMM group. These results suggest FeCH as a candidate material for the development of pharmaceutical materials for the treatment or prevention of degenerative arthritis.

New role of calcium-binding fluorescent dye alizarin complexone in detecting permeability from articular cartilage to subchondral bone

Osteoarthritis (OA) is a chronic degenerative joint disorder characterized by the progressive deterioration of articular cartilage and concomitant alterations in subchondral bone architecture. However, the precise mechanisms underlying the initiation and progression of OA remains poorly understood. In the present study, we explored whether the calcification in the articular cartilage occurred in the early stage of mouse OA model, generated by the surgery destabilization of the medial meniscus (DMM), via the intra-articular injection of alizarin complexone due to its anionic nature for binding calcium-containing crystals. Although we did not observe the calcification in the articular cartilage of early stage of DMM mice, we unexpectedly identified alizarin complexone had the diffusion capacity for detecting the permeability from the articular cartilage to subchondral bone. Our data showed that the diffusion of alizarin complexone from the articular cartilage to calcified cartilage was greater in the early stage of DMM mice than that in sham controls. Additionally, we observed enhanced penetration of alizarin complexone through the periosteum in DMM mice compared to sham mice. In summary, we developed a novel imaging method that offers a valuable tool for further exploration of biochemical communication underlying OA development. Our findings provided new evidence that increased molecular interactions between the articular cartilage and subchondral bone is involved in the pathogenesis of OA progression.

Disuse atrophy of articular cartilage can be restored by mechanical reloading in mice

BACKGROUND

Moderate mechanical stress generated by normal joint loading and movements helps maintain the health of articular cartilage. Despite growing interest in the pathogenesis of cartilage degeneration caused by reduced mechanical stress, its reversibility by mechanical reloading is less understood. This study aimed to investigate the response of articular cartilage exposed to mechanical reloading after unloading in vivo and in vitro.

METHODS AND RESULTS

Disuse atrophy was induced in the knee joint cartilage of adult mice through hindlimb unloading by tail suspension. For in vivo experiments, mice were subjected to reloading with or without daily exercise intervention or surgical destabilization of the knee joint. Microcomputed tomography and histomorphometric analyses were performed on the harvested knee joints. Matrix loss and thinning of articular cartilage due to unloading were fully or partially restored by reloading, and exercise intervention enhanced the restoration. Subchondral bone density decreased by unloading and increased to above-normal levels by reloading. The severity of cartilage damage caused by joint instability was not different even with prior non-weight bearing. For in vitro experiments, articular chondrocytes isolated from the healthy or unloaded joints of the mice were embedded in agarose gel. After dynamic compression loading, the expression levels of anabolic (Sox9, Col2a1, and Acan) and catabolic (Mmp13 and Adamts5) factors of cartilage were analyzed. In chondrocytes isolated from the unloaded joints, similar to those from healthy joints, dynamic compression increased the expression of anabolic factors but suppressed the expression of catabolic factors.

CONCLUSION

The results of this study indicate that the morphological changes in articular cartilage exposed to mechanical unloading may be restored in response to mechanical reloading by shifting extracellular matrix metabolism in chondrocytes to anabolism.

A synoptic literature review of animal models for investigating the biomechanics of knee osteoarthritis

Osteoarthritis (OA) is a common chronic disease largely driven by mechanical factors, causing significant health and economic burdens worldwide. Early detection is challenging, making animal models a key tool for studying its onset and mechanically-relevant pathogenesis. This review evaluate current use of preclinical in vivo models and progressive measurement techniques for analysing biomechanical factors in the specific context of the clinical OA phenotypes. It categorizes preclinical in vivo models into naturally occurring, genetically modified, chemically-induced, surgically-induced, and non-invasive types, linking each to clinical phenotypes like chronic pain, inflammation, and mechanical overload. Specifically, we discriminate between mechanical and biological factors, give a new explanation of the mechanical overload OA phenotype and propose that it should be further subcategorized into two subtypes, post-traumatic and chronic overloading OA. This review then summarises the representative models and tools in biomechanical studies of OA. We highlight and identify how to develop a mechanical model without inflammatory sequelae and how to induce OA without significant experimental trauma and so enable the detection of changes indicative of early-stage OA in the absence of such sequelae. We propose that the most popular post-traumatic OA biomechanical models are not representative of all types of mechanical overloading OA and, in particular, identify a deficiency of current rodent models to represent the chronic overloading OA phenotype without requiring intraarticular surgery. We therefore pinpoint well standardized and reproducible chronic overloading models that are being developed to enable the study of early OA changes in non-trauma related, slowly-progressive OA. In particular, non-invasive models (repetitive small compression loading model and exercise model) and an extra-articular surgical model (osteotomy) are attractive ways to present the chronic natural course of primary OA. Use of these models and quantitative mechanical behaviour tools such as gait analysis and non-invasive imaging techniques show great promise in understanding the mechanical aspects of the onset and progression of OA in the context of chronic knee joint overloading. Further development of these models and the advanced characterisation tools will enable better replication of the human chronic overloading OA phenotype and thus facilitate mechanically-driven clinical questions to be answered.

Osteoarthritis as a Systemic Disease Promoted Prostate Cancer In Vivo and In Vitro

Osteoarthritis (OA) is increasing worldwide, and previous work found that OA increases systemic cartilage oligomeric matrix protein (COMP), which has also been implicated in prostate cancer (PCa). As such, we sought to investigate whether OA augments PCa progression. Cellular proliferation and migration of RM1 murine PCa cells treated with interleukin (IL)-1α, COMP, IL-1α + COMP, or conditioned media from cartilage explants treated with IL-1α (representing OA media) and with inhibitors of COMP were assessed. A validated murine model was used for tumor growth and marker expression analysis. Both proliferation and migration were greater in PCa cells treated with OA media compared to controls (p < 0.001), which was not seen with direct application of the stimulants. Migration and proliferation were not negatively affected when OA media was mixed with downstream and COMP inhibitors compared to controls (p > 0.05 for all). Mice with OA developed tumors 100% of the time, whereas mice without OA only 83.4% (p = 0.478). Tumor weight correlated with OA severity (Pearson correlation = 0.813, p = 0.002). Moreover, tumors from mice with OA demonstrated increased Ki-67 expression compared to controls (mean 24.56% vs. 6.91%, p = 0.004) but no difference in CD31, PSMA, or COMP expression (p > 0.05). OA appears to promote prostate cancer in vitro and in vivo.

Exploring the pharmacological mechanism of Glycyrrhiza uralensis against KOA through integrating network pharmacology and experimental assessment

Knee osteoarthritis (KOA), a major health and economic problem facing older adults worldwide, is a degenerative joint disease. Glycyrrhiza uralensis Fisch. (GC) plays an integral role in many classic Chinese medicine prescriptions for treating knee osteoarthritis. Still, the role of GC in treating KOA is unclear. To explore the pharmacological mechanism of GC against KOA, UPLC-Q-TOF/MS was conducted to detect the main compounds in GC. The therapeutic effect of GC on DMM-induced osteoarthritic mice was assessed by histomorphology, μCT, behavioural tests, and immunohistochemical staining. Network pharmacology and molecular docking were used to predict the potential targets of GC against KOA. The predicted results were verified by immunohistochemical staining Animal experiments showed that GC had a protective effect on DMM-induced KOA, mainly in the improvement of movement disorders, subchondral bone sclerosis and cartilage damage. A variety of flavonoids and triterpenoids were detected in GC via UPLC-Q-TOF/MS, such as Naringenin. Seven core targets (JUN, MAPK3, MAPK1, AKT1, TP53, RELA and STAT3) and three main pathways (IL-17, NF-κB and TNF signalling pathways) were discovered through network pharmacology analysis that closely related to inflammatory response. Interestingly, molecular docking results showed that the active ingredient Naringenin had a good binding effect on anti-inflammatory-related proteins. In the verification experiment, after the intervention of GC, the expression levels of pp65 and F4/80 inflammatory indicators in the knee joint of KOA model mice were significantly downregulated. GC could improve the inflammatory environment in DMM-induced osteoarthritic mice thus alleviating the physiological structure and dysfunction of the knee joint. GC might play an important role in the treatment of knee osteoarthritis.

Protecting the regenerative environment: selecting the optimal delivery vehicle for cartilage repair-a narrative review

Focal cartilage defects are common in youth and older adults, cause significant morbidity and constitute a major risk factor for developing osteoarthritis (OA). OA is the most common musculoskeletal (MSK) disease worldwide, resulting in pain, stiffness, loss of function, and is currently irreversible. Research into the optimal regenerative approach and methods in the setting of either focal cartilage defects and/or OA holds to the ideal of resolving both diseases. The two fundamentals required for cartilage regenerative treatment are 1) the biological element contributing to the regeneration (e.g., direct application of stem cells, or of an exogenous secretome), and 2) the vehicle by which the biological element is suspended and delivered. The vehicle provides support to the regenerative process by providing a protective environment, a structure that allows cell adherence and migration, and a source of growth and regenerative factors that can activate and sustain regeneration. Models of cartilage diseases include osteochondral defect (OCD) (which usually involve one focal lesion), or OA (which involves a more diffuse articular cartilage loss). Given the differing nature of these models, the optimal regenerative strategy to treat different cartilage diseases may not be universal. This could potentially impact the translatability of a successful approach in one condition to that of the other. An analogy would be the repair of a pothole (OCD) versus repaving the entire road (OA). In this narrative review, we explore the existing literature evaluating cartilage regeneration approaches for OCD and OA in animal then in human studies and the vehicles used for each of these two conditions. We then highlight strengths and challenges faced by the different approaches presented and discuss what might constitute the optimal cartilage regenerative delivery vehicle for clinical cartilage regeneration.

Therapeutic Effects of Non-Euphorigenic Cannabis Extracts in Osteoarthritis

Introduction: Osteoarthritis (OA) is disabling and degenerative disease of the joints that is clinically characterized by pain and loss of function. With no disease-modifying treatment available, current therapies aim at pain management but are of limited efficacy. Cannabis products, specifically cannabinoids, are widely used to control pain and inflammation in many diseases with no scientific evidence demonstrating their efficacy in OA. Objective: We investigated the effects of non-euphorigenic cannabis extracts, CBD oil and cannabigerol oil (CBG oil), on pain and disease progression in OA mice. Methods and Results: Twelve-week-old male C57BL/6J mice received either sham or destabilization of the medial meniscus (DMM) surgery. DMM mice were treated with vehicle, CBD oil, or CBG oil. The gait of DMM mice was impaired as early as 2 weeks following surgery and continued deteriorating until week 8, which was restored by CBD oil and CBG oil treatments throughout the disease course. Mechanical allodynia developed in DMM mice, however, was not ameliorated by any of the treatments. On the other hand, both CBD oil and CBG oil ameliorated cold allodynia. In open field test, both oil treatments normalized changes in the locomotor activity of DMM mice. CBD oil and CBG oil treatments significantly reduced synovitis in DMM mice. Only CBG oil reduced cartilage degeneration, chondrocyte loss, and matrix metalloproteinase 13 expression, with a significant increase in the number of anabolic chondrocytes. Subchondral bone remodeling found in vehicle-treated DMM mice was not ameliorated by either CBD or CBG oil. Conclusions: Our results show evidence for the therapeutic efficacy of CBD oil and CBG oil, where both oils ameliorate pain and inflammation, and improve gait and locomotor activity in OA mice, representing clinical pain and function. Importantly, only CBG oil is chondroprotective, which may provide superior efficacy in future studies in OA patients.

Development of Anti-OSCAR Antibodies for the Treatment of Osteoarthritis

Osteoarthritis (OA) is the most common joint disease that causes local inflammation and pain, significantly reducing the quality of life and normal social activities of patients. Currently, there are no disease-modifying OA drugs (DMOADs) available, and treatment relies on pain relief agents or arthroplasty. To address this significant unmet medical need, we aimed to develop monoclonal antibodies that can block the osteoclast-associated receptor (OSCAR). Our recent study has revealed the importance of OSCAR in OA pathogenesis as a novel catabolic regulator that induces chondrocyte apoptosis and accelerates articular cartilage destruction. It was also shown that blocking OSCAR with a soluble OSCAR decoy receptor ameliorated OA in animal models. In this study, OSCAR-neutralizing monoclonal antibodies were isolated and optimized by phage display. These antibodies bind to and directly neutralize OSCAR, unlike the decoy receptor, which binds to the ubiquitously expressed collagen and may result in reduced efficacy or deleterious off-target effects. The DMOAD potential of the anti-OSCAR antibodies was assessed with in vitro cell-based assays and an in vivo OA model. The results demonstrated that the anti-OSCAR antibodies significantly reduced cartilage destruction and other OA signs, such as subchondral bone plate sclerosis and loss of hyaline cartilage. Hence, blocking OSCAR with a monoclonal antibody could be a promising treatment strategy for OA.

FGF1 reduces cartilage injury in osteoarthritis via regulating AMPK/Nrf2 pathway

Osteoarthritis (OA) is a systemic joint degenerative disease involving a variety of cytokines and growth factors. In this study, we investigated the protective effect of fibroblast growth factor 1 (FGF1) knockdown on OA and its underlying mechanisms in vitro. In addition, we evaluated the effect of FGF1 knockout on the destabilization of the medial meniscus (DMM) and examined the anterior and posterior cruciate ligament model in vivo. FGF1 affects OA cartilage destruction by increasing the protein expression of Nuclear factor E2-related factor 2 (Nrf2) and heme oxygenase 1 (HO-1), which is associated with the phosphorylation of AMPK and its substrates. Our study showed that FGF1 knockdown could reverse the oxidative damage associated with osteoarthritis. Nrf2 knockdown eliminated the antioxidant effect of FGF1 knockdown on chondrocytes. Furthermore, AMPK knockdown could stop the impact of FGF1 knockdown on osteoarthritis. These findings suggested that FGF1 knockdown could effectively prevent and reverse osteoarthritis by activating AMPK and Nrf2 in articular chondrocytes.

Low-frequency whole-body vibration can enhance cartilage degradation with slight changes in subchondral bone in mice with knee osteoarthritis and does not have any morphologic effect on normal joints

PURPOSES

To evaluate the effects of low frequency whole-body vibration (WBV) on degeneration of articular cartilage and subchondral bone in mice with destabilization of the medial meniscus (DMM)induced osteoarthritis(OA) and mice with normal knee.

METHODS

Ten-week-old C57BL/6J male mice received DMM on right knees, while the left knees performed sham operation. There were six groups: DMM, SHAM DMM, DMM+WBV,SHAM DMM+WBV, DMM+ NON-WBV and SHAM DMM+NON-WBV. After four weeks, the knees were harvested from the DMM and SHAM DMM group. The remaining groups were treated with WBV (10 Hz) or NON-WBV. Four weeks later, the knees were harvested. Genes, containing Aggrecan(Acan) and CollagenⅡ(Col2a1), Matrix Metalloproteinases 3 and 13(MMP3,13), TNFα and IL6, were measured and staining was also performed. OA was graded with OARSI scores, and tibial plateaubone volume to tissue volume ratio(BV/TV), bone surface area to bone volume ratio (BS/BV), trabecular number(Tb.N) and trabecular thickness separation(TS) between groups were analyzed.

RESULTS

Increased OARSI scores and cartilage degradation were observed after WBV. BV/TV, Tb.N and TS were not significant between the groups. Significant reductions were observed in MMP3, MMP13, Col2a1, Acan, TNFα and IL6 in the DMM+WBV compared to SHAM DMM+WBV group. BV/TV, BS/BV, Tb.N, TS and OARSI scores were not significantly changed in the left knees. IL6 expression in the SHAM DMM+WBV group was significantly increased compared with the SHAM DMM+ NON-WBV group, while Col2a1, Acan and MMP13 expression decreased.

CONCLUSION

WBV accelerated cartilage degeneration and caused slight changes in subchondral bone in a DMM-induced OA model. WBV had no morphologic effect on normal joints.

Inhibition of a signaling modality within the gp130 receptor enhances tissue regeneration and mitigates osteoarthritis

Adult mammals are incapable of multitissue regeneration, and augmentation of this potential may shift current therapeutic paradigms. We found that a common co-receptor of interleukin 6 (IL-6) cytokines, glycoprotein 130 (gp130), serves as a major nexus integrating various context-specific signaling inputs to either promote regenerative outcomes or aggravate disease progression. Via genetic and pharmacological experiments in vitro and in vivo, we demonstrated that a signaling tyrosine 814 (Y814) within gp130 serves as a major cellular stress sensor. Mice with constitutively inactivated Y814 (F814) were resistant to surgically induced osteoarthritis as reflected by reduced loss of proteoglycans, reduced synovitis, and synovial fibrosis. The F814 mice also exhibited enhanced regenerative, not reparative, responses after wounding in the skin. In addition, pharmacological modulation of gp130 Y814 upstream of the SRC and MAPK circuit by a small molecule, R805, elicited a protective effect on tissues after injury. Topical administration of R805 on mouse skin wounds resulted in enhanced hair follicle neogenesis and dermal regeneration. Intra-articular administration of R805 to rats after medial meniscal tear and to canines after arthroscopic meniscal release markedly mitigated the appearance of osteoarthritis. Single-cell sequencing data demonstrated that genetic and pharmacological modulation of Y814 resulted in attenuation of inflammatory gene signature as visualized by the anti-inflammatory macrophage and nonpathological fibroblast subpopulations in the skin and joint tissue after injury. Together, our study characterized a molecular mechanism that, if manipulated, enhances the intrinsic regenerative capacity of tissues through suppression of a proinflammatory milieu and prevents pathological outcomes in injury and disease.

Contribution of joint tissue properties to load-induced osteoarthritis

Objective

Clinical evidence suggests that abnormal mechanical forces play a major role in the initiation and progression of osteoarthritis (OA). However, few studies have examined the mechanical environment that leads to disease. Thus, using a mouse tibial loading model, we quantified the cartilage contact stresses and examined the effects of altering tissue material properties on joint stresses during loading.

Design

Using a discrete element model (DEA) in conjunction with joint kinematics data from a murine knee joint compression model, the magnitude and distribution of contact stresses in the tibial cartilage during joint loading were quantified at levels ranging from 0 to 9 N in 1 N increments. In addition, a simplified finite element (FEA) contact model was developed to simulate the knee joint, and parametric analyses were conducted to investigate the effects of altering bone and cartilage material properties on joint stresses during compressive loading.

Results

As loading increased, the peak contact pressures were sufficient to induce fibrillations on the cartilage surfaces. The computed areas of peak contact pressures correlated with experimentally defined areas of highest cartilage damage. Only alterations in cartilage properties and geometry caused large changes in cartilage contact pressures. However, changes in both bone and cartilage material properties resulted in significant changes in stresses induced in the bone during compressive loading.

Conclusions

The level of mechanical stress induced by compressive tibial loading directly correlated with areas of biological change observed in the mouse knee joint. These results, taken together with the parametric analyses, are the first to demonstrate both experimentally and computationally that the tibial loading model is a useful preclinical platform with which to predict and study the effects of modulating bone and/or cartilage properties on attenuating OA progression. Given the direct correlation between computational modeling and experimental results, the effects of tissue-modifying treatments may be predicted prior to in vivo experimentation, allowing for novel therapeutics to be developed.

Transient neonatal shoulder paralysis causes early osteoarthritis in a mouse model

Neonatal brachial plexus palsy (NBPP) occurs in approximately 1.5 of every 1,000 live births. The majority of children with NBPP recover function of the shoulder. However, the long-term risk of osteoarthritis (OA) in this population is unknown. The purpose of this study was to investigate the development of OA in a mouse model of transient neonatal shoulder paralysis. Neonatal mice were injected twice per week for 4 weeks with saline in the right supraspinatus muscle (Saline, control) and botulinum toxin A (BtxA, transient paralysis) in the left supraspinatus muscle, and then allowed to recover for 20 or 36 weeks. Control mice received no injections, and all mice were sacrificed at 24 or 40 weeks. BtxA mice exhibited abnormalities in gait compared to controls through 10 weeks of age, but these differences did not persist into adulthood. BtxA shoulders had decreased bone volume (-9%) and abnormal trabecular microstructure compared to controls. Histomorphometry analysis demonstrated that BtxA shoulders had higher murine shoulder arthritis scale scores (+30%), and therefore more shoulder OA compared to controls. Articular cartilage of BtxA shoulders demonstrated stiffening of the tissue. Compared with controls, articular cartilage from BtxA shoulders had 2-fold and 10-fold decreases in Dkk1 and BMP2 expression, respectively, and 3-fold and 14-fold increases in Col10A1 and BGLAP expression, respectively, consistent with established models of OA. In summary, a brief period of paralysis of the neonatal mouse shoulder was sufficient to generate early signs of OA in adult cartilage and bone.

Modelling osteoarthritis in mice via surgical destabilization of the medial meniscus with or without a stereomicroscope

Aims

To evaluate inducing osteoarthritis (OA) by surgical destabilization of the medial meniscus (DMM) in mice with and without a stereomicroscope.

Methods

Based on sample size calculation, 70 male C57BL/6 mice were randomly assigned to three surgery groups: DMM aided by a stereomicroscope; DMM by naked eye; or sham surgery. The group information was blinded to researchers. Mice underwent static weightbearing, von Frey test, and gait analysis at two-week intervals from eight to 16 weeks after surgery. Histological grade of OA was determined with the Osteoarthritis Research Society International (OARSI) scoring system.

Results

Surgical DMM with or without stereomicroscope led to decrease in the mean of weightbearing percentages (-20.64% vs -21.44%, p = 0.792) and paw withdrawal response thresholds (-21.35% vs -24.65%, p = 0.327) of the hind limbs. However, the coefficient of variation (CV) of weight-bearing percentages and paw withdrawal response thresholds in naked-eye group were significantly greater than that in the microscope group (19.82% vs 6.94%, p < 0.001; 21.85% vs 9.86%, p < 0.001). The gait analysis showed a similar pattern. Cartilage degeneration was observed in both DMM-surgery groups, evidenced by increased OARSI scores (summed score: 11.23 vs 11.43, p = 0.842), but the microscope group showed less variation in OARSI score than the naked-eye group (CV: 21.03% vs 32.44%; p = 0.032).

Conclusion

Although surgical DMM aided by stereomicroscope is technically difficult, it produces a relatively more homogeneous OA model in terms of the discrete degree of pain behaviours and histopathological grading when compared with surgical DMM without stereomicroscope. Cite this article: Bone Joint Res 2022;11(8):518–527.

Interleukin-6 signaling mediates cartilage degradation and pain in posttraumatic osteoarthritis in a sex-specific manner

Osteoarthritis (OA) and posttraumatic OA (PTOA) are caused by an imbalance in catabolic and anabolic processes in articular cartilage and proinflammatory changes throughout the joint, leading to joint degeneration and pain. We examined whether interleukin-6 (IL-6) signaling contributed to cartilage degradation and pain in PTOA. Genetic ablation of Il6 in male mice decreased PTOA-associated cartilage catabolism, innervation of the knee joint, and nociceptive signaling without improving PTOA-associated subchondral bone sclerosis or chondrocyte apoptosis. These effects were not observed in female Il6^-/- mice. Compared with wild-type mice, the activation of the IL-6 downstream mediators STAT3 and ERK was reduced in the knees and dorsal root ganglia (DRG) of male Il6^-/- mice after knee injury. Janus kinases (JAKs) were critical for STAT and ERK signaling in cartilage catabolism and DRG pain signaling in tissue explants. Whereas STAT3 signaling was important for cartilage catabolism, ERK signaling mediated neurite outgrowth and the activation of nociceptive neurons. These data demonstrate that IL-6 mediates both cartilage degradation and pain associated with PTOA in a sex-specific manner and identify tissue-specific contributions of downstream effectors of IL-6 signaling, which are potential therapeutic targets for disease-modifying OA drugs.

Early Gβγ-GRK2 Inhibition Ameliorates Osteoarthritis Development by Simultaneous Anti-Inflammatory and Chondroprotective Effects

The G-protein-coupled receptor kinase 2 (GRK2) is an important regulator of inflammation and pathological macrophage phenotype in a variety of diseases. We hypothesize that Gβγ-GRK2 signaling promotes the early inflammatory response and chondrocyte loss in osteoarthritis (OA). Using the destabilization of the medial meniscus (DMM) model in 12-week-old male C57BL/6 mice, we determined the role of Gβγ-GRK2 signaling in synovitis, macrophage activation, and OA development. We achieved Gβγ-GRK2 inhibition at the time of DMM by administering the Gβγ inhibitor “gallein” and the GRK2 inhibitor “paroxetine” daily, starting from 2 days before DMM surgery, for a duration of 1 or 12 weeks. Synovial and cartilage structural changes were evaluated by histomorphometry, and molecular events and macrophage activation were examined. We studied the direct role of Gβγ-GRK2 in synovitis and macrophage activation in vitro using SW982 and THP1 cells. Continuous Gβγ-GRK2 inhibition initiated at the time of DMM attenuated OA development and decreased chondrocyte loss more effectively than delayed treatment. GRK2 expression and the M1 macrophage phenotype were elevated in the inflamed synovium, while early gallein and paroxetine treatment for 1 and 12 weeks following DMM resulted in their reduction and an upregulated M2 macrophage phenotype. In vitro experiments showed that Gβγ-GRK2 inhibition attenuated synoviocyte inflammation and the M1 phenotype. We show that early Gβγ-GRK2 inhibition is of higher therapeutic efficacy in OA than delayed inhibition, as it prevents OA development by inhibiting the early inflammatory response.

Development and characterization of a humanized mouse model of osteoarthritis

OBJECTIVE

In light of the role of immune cells in OA pathogenesis, the development of sophisticated animal models closely mimicking the immune dysregulation during the disease development and progression could be instrumental for the preclinical evaluation of novel treatments. Among these models, immunologically humanized mice may represent a relevant system, particularly for testing immune-interacting DMOADs or cell therapies before their transfer to the clinic. Our objective, therefore, was to develop an experimental model of OA by destabilization of the medial meniscus (DMM) in humanized mice.

METHOD

Irradiated 5-week-old NOD/LtSz-scid IL2Rγ^null (NSG) mice were humanized by intravenous injection of CD34⁺ human hematopoietic stem cells. The engraftment efficiency was evaluated by flow cytometry 17 weeks after the humanization procedure. Humanized and non-humanized NSG mice underwent DMM or sham surgery and OA development was assessed 1, 6, and 12 weeks after the surgery.

RESULTS

120 days after the humanization, human T and B lymphocytes, macrophages and NK cells, were present in the blood and spleen of the humanized NSG mice. The DMM surgery induced articular cartilage and meniscal alterations associated with an increase in OA and the meniscal score. Moreover, the surgery triggered an inflammatory response that was sustained at a low grade in the DMM group.

CONCLUSIONS

Our study shows for the first time the feasibility of inducing OA by DMM in humanized mice. This novel OA model could constitute a useful tool to bridge the gap between the preclinical and clinical evaluation of immune interacting DMOADs and cell-based therapies.

Imaging articular cartilage in osteoarthritis using targeted peptide radiocontrast agents

Background

Established MRI and emerging X-ray contrast agents for non-invasive imaging of articular cartilage rely on non-selective electrostatic interactions with negatively charged proteoglycans. These contrast agents have limited prognostic utility in diseases such as osteoarthritis (OA) due to the characteristic high turnover of proteoglycans. To overcome this limitation, we developed a radiocontrast agent that targets the type II collagen macromolecule in cartilage and used it to monitor disease progression in a murine model of OA.

Methods

To confer radiopacity to cartilage contrast agents, the naturally occurring tyrosine derivative 3,5-diiodo-L-tyrosine (DIT) was introduced into a selective peptide for type II collagen. Synthetic DIT peptide derivatives were synthesised by Fmoc-based solid-phase peptide synthesis and binding to ex vivo mouse tibial cartilage evaluated by high-resolution micro-CT. Di-Iodotyrosinated Peptide Imaging of Cartilage (DIPIC) was performed ex vivo and in vivo 4, 8 and 12 weeks in mice after induction of OA by destabilisation of the medial meniscus (DMM). Finally, human osteochondral plugs were imaged ex vivo using DIPIC.

Results

Fifteen DIT peptides were synthesised and tested, yielding seven leads with varying cartilage binding strengths. DIPIC visualised ex vivo murine articular cartilage comparably to the ex vivo contrast agent phosphotungstic acid. Intra-articular injection of contrast agent followed by in vivo DIPIC enabled delineation of damaged murine articular cartilage. Finally, the translational potential of the contrast agent was confirmed by visualisation of ex vivo human cartilage explants.

Conclusion

DIPIC has reduction and refinement implications in OA animal research and potential clinical translation to imaging human disease.

Epigenetic Regulation of Chondrocytes and Subchondral Bone in Osteoarthritis

The aim of this review is to provide an updated review of the epigenetic factors involved in the onset and development of osteoarthritis (OA). OA is a prevalent degenerative joint disease characterized by chronic inflammation, ectopic bone formation within the joint, and physical and proteolytic cartilage degradation which result in chronic pain and loss of mobility. At present, no disease-modifying therapeutics exist for the prevention or treatment of the disease. Research has identified several OA risk factors including mechanical stressors, physical activity, obesity, traumatic joint injury, genetic predisposition, and age. Recently, there has been increased interest in identifying epigenetic factors involved in the pathogenesis of OA. In this review, we detail several of these epigenetic modifications with known functions in the onset and progression of the disease. We also review current therapeutics targeting aberrant epigenetic regulation as potential options for preventive or therapeutic treatment.

Pleiotropic Roles of NOTCH1 Signaling in the Loss of Maturational Arrest of Human Osteoarthritic Chondrocytes

Notch signaling has been identified as a critical regulator of cartilage development and homeostasis. Its pivotal role was established by both several joint specific Notch signaling loss of function mouse models and transient or sustained overexpression. NOTCH1 is the most abundantly expressed NOTCH receptors in normal cartilage and its expression increases in osteoarthritis (OA), when chondrocytes exit from their healthy “maturation arrested state” and resume their natural route of proliferation, hypertrophy, and terminal differentiation. The latter are hallmarks of OA that are easily evaluated in vitro in 2-D or 3-D culture models. The aim of our study was to investigate the effect of NOTCH1 knockdown on proliferation (cell count and Picogreen mediated DNA quantification), cell cycle (flow cytometry), hypertrophy (gene and protein expression of key markers such as RUNX2 and MMP-13), and terminal differentiation (viability measured in 3-D cultures by luminescence assay) of human OA chondrocytes. NOTCH1 silencing of OA chondrocytes yielded a healthier phenotype in both 2-D (reduced proliferation) and 3-D with evidence of decreased hypertrophy (reduced expression of RUNX2 and MMP-13) and terminal differentiation (increased viability). This demonstrates that NOTCH1 is a convenient therapeutic target to attenuate OA progression.

BNIP3-Dependent Mitophagy via PGC1α Promotes Cartilage Degradation

Since mitochondria are suggested to be important regulators in maintaining cartilage homeostasis, turnover of mitochondria through mitochondrial biogenesis and mitochondrial degradation may play an important role in the pathogenesis of osteoarthritis (OA). Here, we found that mitochondrial dysfunction is closely associated with OA pathogenesis and identified the peroxisome proliferator-activated receptor-gamma co-activator 1-alpha (PGC1α) as a potent regulator. The expression level of PGC1α was significantly decreased under OA conditions, and knockdown of PGC1α dramatically elevated the cartilage degradation by upregulating cartilage degrading enzymes and apoptotic cell death. Interestingly, the knockdown of PGC1α activated the parkin RBR E3 ubiquitin protein ligase (PRKN)-independent selective mitochondria autophagy (mitophagy) pathway through the upregulation of BCL2 and adenovirus E1B 19-kDa-interacting protein 3 (BNIP3). The overexpression of BNIP3 stimulated mitophagy and cartilage degradation by upregulating cartilage-degrading enzymes and chondrocyte death. We identified microRNA (miR)-126-5p as an upstream regulator for PGC1α and confirmed the direct binding between miR-126-5p and 3′ untranslated region (UTR) of PGC1α. An in vivo OA mouse model induced by the destabilization of medial meniscus (DMM) surgery, and the delivery of antago-miR-126 via intra-articular injection significantly decreased cartilage degradation. In sum, the loss of PGC1α in chondrocytes due to upregulation of miR-126-5p during OA pathogenesis resulted in the activation of PRKN-independent mitophagy through the upregulation of BNIP3 and stimulated cartilage degradation and apoptotic death of chondrocytes. Therefore, the regulation of PGC1α:BNIP3 mitophagy axis could be of therapeutic benefit to cartilage-degrading diseases.

Osteoking Decelerates Cartilage Degeneration in DMM-Induced Osteoarthritic Mice Model Through TGF-β/smad-dependent Manner

Osteoarthritis (OA) is a common disease characterized by cartilage degeneration. In recent years much attention has been paid to Traditional Chinese Medicine (TCM) since its treatments have shown efficacy for ameliorating cartilage degradation with mild side effects. Osteoking is a TCM prescription that has long been used in OA treatment. However, the exact mechanism of Osteoking are not fully elucidated. In the current study, destabilization of the medial meniscus (DMM)-induced OA mice was introduced as a wild type animal model. After 8 weeks of administration of Osteoking, histomorphometry, OARSI scoring, gait analysis, micro-CT, and immunohistochemical staining for Col2, MMP-13, TGFβRII and pSmad-2 were conducted to evaluate the chondroprotective effects of Osteoking in vivo. Further in vitro experiments were then performed to detect the effect of Osteoking on chondrocytes. TGFβRII^Col2ER transgenic mice were constructed and introduced in the current study to validate whether Osteoking exerts its anti-OA effects via the TGF-β signaling pathway. Results demonstrated that in wild type DMM mice, Osteoking ameliorated OA-phenotype including cartilage degradation, subchondral bone sclerosis, and gait abnormality. Col2, TGFβRII, and pSmad-2 expressions were also found to be up-regulated after Osteoking treatment, while MMP-13 was down-regulated. In vitro, the mRNA expression of MMP-13 and ADAMTS5 decreased and the mRNA expression of Aggrecan, COL2, and TGFβRII were up-regulated after the treatment of Osteoking in IL-1β treated chondrocytes. The additional treatment of SB505124 counteracted the positive impact of Osteoking on primary chondrocytes. In TGFβRII^Col2ER mice, spontaneous OA-liked phenotype was observed and treatment of Osteoking failed to reverse the OA spontaneous progression. In conclusion, Osteoking ameliorates OA progression by decelerating cartilage degradation and alleviating subchondral bone sclerosis partly via the TGF-β signaling pathway.

Update on pain in arthritis

PURPOSE OF REVIEW

Osteoarthritis is a degenerative joint disease that features pain as a hallmark symptom. This review summarises progress and obstacles in our understanding of pain mechanisms in arthritis.

RECENT FINDINGS

Pain phenotypes in osteoarthritis are poorly characterized in clinical studies and animal studies are largely carti-centric. Different animal models incur variable disease progression patterns and activation of distinct pain pathways, but studies reporting both structural and pain outcomes permit better translational insights. In patients, classification of osteoarthritis disease severity is only based on structural integrity of the joint, but pain outcomes do not consistently correlate with joint damage. The complexity of this relationship underlines the need for pain detection in criteria for osteoarthritis classification and patient-reported outcome measures.

SUMMARY

Variable inflammatory and neuropathic components and spatiotemporal evolution underlie the heterogeneity of osteoarthritis pain phenotypes, which must be considered to adequately stratify patients. Revised classification of osteoarthritis at different stages encompassing both structural and pain outcomes would significantly improve detection and diagnosis at both early and late stages of disease. These are necessary advancements in the field that would also improve trial design and provide better understanding of basic mechanisms of disease progression and pain in osteoarthritis.

BMP5 silencing inhibits chondrocyte senescence and apoptosis as well as osteoarthritis progression in mice

In this study, we using the in vivo destabilization of the medial meniscus (DMM) mouse model to investigate the role of bone morphogenetic protein 5 (BMP5) in osteoarthritis (OA) progression mediated via chondrocyte senescence and apoptosis. BMP5 expression was significantly higher in knee articular cartilage tissues of OA patients and DMM model mice than the corresponding controls. The Osteoarthritis Research Society International scores based on histological staining of knee articular cartilage sections were lower in DMM mice where BMP5 was knocked down in chondrocytes than the corresponding controls 4 weeks after DMM surgery. DMM mice with BMP5-deficient chondrocytes showed reduced levels of matrix-degrading enzymes such as MMP13 and ADAMTS5 as well as reduced cartilage destruction. BMP5 knockdown also decreased chondrocyte apoptosis and senescence by suppressing the activation of p38 and ERK MAP kinases. These findings demonstrate that BMP5 silencing inhibits chondrocyte senescence and apoptosis as well as OA progression by downregulating activity in the p38/ERK signaling pathway.

Antiosteoarthritic Effect of Morroniside in Chondrocyte Inflammation and Destabilization of Medial Meniscus-Induced Mouse Model

Osteoarthritis (OA) is a common degenerative disease that results in joint inflammation as well as pain and stiffness. A previous study has reported that Cornus officinalis (CO) extract inhibits oxidant activities and oxidative stress in RAW 264.7 cells. In the present study, we isolated bioactive compound(s) by fractionating the CO extract to elucidate its antiosteoarthritic effects. A single bioactive component, morroniside, was identified as a potential candidate. The CO extract and morroniside exhibited antiosteoarthritic effects by downregulating factors associated with cartilage degradation, including cyclooxygenase-2 (Cox-2), matrix metalloproteinase 3 (Mmp-3), and matrix metalloproteinase 13 (Mmp-13), in interleukin-1 beta (IL-1β)-induced chondrocytes. Furthermore, morroniside prevented prostaglandin E2 (PGE2) and collagenase secretion in IL-1β-induced chondrocytes. In the destabilization of the medial meniscus (DMM)-induced mouse osteoarthritic model, morroniside administration attenuated cartilage destruction by decreasing expression of inflammatory mediators, such as Cox-2, Mmp3, and Mmp13, in the articular cartilage. Transverse microcomputed tomography analysis revealed that morroniside reduced DMM-induced sclerosis in the subchondral bone plate. These findings suggest that morroniside may be a potential protective bioactive compound against OA pathogenesis.

Paroxetine-mediated GRK2 inhibition is a disease-modifying treatment for osteoarthritis

Osteoarthritis (OA) is a debilitating joint disease characterized by progressive cartilage degeneration, with no available disease-modifying therapy. OA is driven by pathological chondrocyte hypertrophy (CH), the cellular regulators of which are unknown. We have recently reported the therapeutic efficacy of G protein-coupled receptor kinase 2 (GRK2) inhibition in other diseases by recovering protective G protein-coupled receptor (GPCR) signaling. However, the role of GPCR-GRK2 pathway in OA is unknown. Thus, in a surgical OA mouse model, we performed genetic GRK2 deletion in chondrocytes or pharmacological inhibition with the repurposed U.S. Food and Drug Administration (FDA)-approved antidepressant paroxetine. Both GRK2 deletion and inhibition prevented CH, abated OA progression, and promoted cartilage regeneration. Supporting experiments with cultured human OA cartilage confirmed the ability of paroxetine to mitigate CH and cartilage degradation. Our findings present elevated GRK2 signaling in chondrocytes as a driver of CH in OA and identify paroxetine as a disease-modifying drug for OA treatment.

Development of Subject Specific Finite Element Models of the Mouse Knee Joint for Preclinical Applications

Osteoarthritis is the most common musculoskeletal disabling disease worldwide. Preclinical studies on mice are commonly performed to test new interventions. Finite element (FE) models can be used to study joint mechanics, but usually simplified geometries are used. The aim of this project was to create a realistic subject specific FE model of the mouse knee joint for the assessment of joint mechanical properties. Four different FE models of a C57Bl/6 female mouse knee joint were created based on micro-computed tomography images of specimens stained with phosphotungstic acid in order to include different features: individual cartilage layers with meniscus, individual cartilage layers without meniscus, homogeneous cartilage layers with two different thickness values, and homogeneous cartilage with same thickness for both condyles. They were all analyzed under compressive displacement and the cartilage contact pressure was compared at 0.3 N reaction force. Peak contact pressure in the femur cartilage was 25% lower in the model with subject specific cartilage compared to the simpler model with homogeneous cartilage. A much more homogeneous pressure distribution across the joint was observed in the model with meniscus, with cartilage peak pressure 5–34% lower in the two condyles compared to that with individual cartilage layers. In conclusion, modeling the meniscus and individual cartilage was found to affect the pressure distribution in the mouse knee joint under compressive load and should be included in realistic models for assessing the effect of interventions preclinically.

Nociceptive mechanisms driving pain in a post-traumatic osteoarthritis mouse model

In osteoarthritis (OA), pain is the dominant clinical symptom, yet the therapeutic approaches remain inadequate. The knowledge of the nociceptive mechanisms in OA, which will allow to develop effective therapies for OA pain, is of utmost need. In this study, we investigated the nociceptive mechanisms involved in post-traumatic OA pain, using the destabilization of the medial meniscus (DMM) mouse model. Our results revealed the development of peripheral pain sensitization, reflected by augmented mechanical allodynia. Along with the development of pain behaviour, we observed an increase in the expression of calcitonin gene-related peptide (CGRP) in both the sensory nerve fibers of the periosteum and the dorsal root ganglia. Interestingly, we also observed that other nociceptive mechanisms commonly described in non-traumatic OA phenotypes, such as infiltration of the synovium by immune cells, neuropathic mechanisms and also central sensitization were not present. Overall, our results suggest that CGRP in the sensory nervous system is underlying the peripheral sensitization observed after traumatic knee injury in the DMM model, highlighting the CGRP as a putative therapeutic target to treat pain in post-traumatic OA. Moreover, our findings suggest that the nociceptive mechanisms involved in driving pain in post-traumatic OA are considerably different from those in non-traumatic OA.

Osteoclast-associated receptor blockade prevents articular cartilage destruction via chondrocyte apoptosis regulation

Osteoarthritis (OA), primarily characterized by articular cartilage destruction, is the most common form of age-related degenerative whole-joint disease. No disease-modifying treatments for OA are currently available. Although OA is primarily characterized by cartilage destruction, our understanding of the processes controlling OA progression is poor. Here, we report the association of OA with increased levels of osteoclast-associated receptor (OSCAR), an immunoglobulin-like collagen-recognition receptor. In mice, OSCAR deletion abrogates OA manifestations, such as articular cartilage destruction, subchondral bone sclerosis, and hyaline cartilage loss. These effects are a result of decreased chondrocyte apoptosis, which is caused by the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in induced OA. Treatments with human OSCAR-Fc fusion protein attenuates OA pathogenesis caused by experimental OA. Thus, this work highlights the function of OSCAR as a catabolic regulator of OA pathogenesis, indicating that OSCAR blockade is a potential therapy for OA.

Osteoarthritis (OA) is associated with cartilage disruption, but the underlying mechanisms remain unclear. Here, the authors show that expression of osteoclast-associated receptor (OSCAR) is associated with OA, that its genetic ablation or targeting with OSCAR-Fc fusion protein ameliorates OA in mice by decreasing chondrocyte apoptosis.

Impaired chondrocyte U3 snoRNA expression in osteoarthritis impacts the chondrocyte protein translation apparatus

Although pathways controlling ribosome activity have been described to regulate chondrocyte homeostasis in osteoarthritis, ribosome biogenesis in osteoarthritis is unexplored. We hypothesized that U3 snoRNA, a non-coding RNA involved in ribosomal RNA maturation, is critical for chondrocyte protein translation capacity in osteoarthritis. U3 snoRNA was one of a number of snoRNAs with decreased expression in osteoarthritic cartilage and osteoarthritic chondrocytes. OA synovial fluid impacted U3 snoRNA expression by affecting U3 snoRNA gene promoter activity, while BMP7 was able to increase its expression. Altering U3 snoRNA expression resulted in changes in chondrocyte phenotype. Interference with U3 snoRNA expression led to reduction of rRNA levels and translational capacity, whilst induced expression of U3 snoRNA was accompanied by increased 18S and 28S rRNA levels and elevated protein translation. Whole proteome analysis revealed a global impact of reduced U3 snoRNA expression on protein translational processes and inflammatory pathways. For the first time we demonstrate implications of a snoRNA in osteoarthritis chondrocyte biology and investigated its role in the chondrocyte differentiation status, rRNA levels and protein translational capacity.

Standardized Histomorphometric Evaluation of Osteoarthritis in a Surgical Mouse Model

One of the most prevalent joint disorders in the United States, osteoarthritis (OA) is characterized by progressive degeneration of articular cartilage, primarily in the hip and knee joints, which results in significant impacts on patient mobility and quality of life. To date, there are no existing curative therapies for OA able to slow down or inhibit cartilage degeneration. Presently, there is an extensive body of ongoing research to understand OA pathology and discover novel therapeutic approaches or agents that can efficiently slow down, stop, or even reverse OA. Thus, it is crucial to have a quantitative and reproducible approach to accurately evaluate OA-associated pathological changes in the joint cartilage, synovium, and subchondral bone. Currently, OA severity and progression are primarily assessed using the Osteoarthritis Research Society International (OARSI) or Mankin scoring systems. In spite of the importance of these scoring systems, they are semiquantitative and can be influenced by user subjectivity. More importantly, they fail to accurately evaluate subtle, yet important, changes in the cartilage during the early disease states or early treatment phases. The protocol we describe here uses a computerized and semiautomated histomorphometric software system to establish a standardized, rigorous, and reproducible quantitative methodology for the evaluation of joint changes in OA. This protocol presents a powerful addition to the existing systems and allows for more efficient detection of pathological changes in the joint.

Suppression of murine osteoarthritis by 4-methylumbelliferone

Using in vitro models, we previously reported that 4-methylumbelliferone (4-MU) blocked many of the pro-catabolic features of activated chondrocytes. 4-MU also blocked safranin O loss from human cartilage explants exposed to interleukin 1β (IL1β) in vitro. However, the mechanism for this chondroprotective effect was independent of the action of 4-MU as a hyaluronan (HA) inhibitor. Interestingly, overexpression of HA synthase 2 (HAS2) also blocked the same pro-catabolic features of activated chondrocytes as 4-MU via a mechanism independent of extracellular HA accumulation. Data suggest that altering UDP-sugars may be behind these changes in chondrocyte metabolism. However, all of our previous experiments with 4-MU or HAS2 overexpression were performed in vitro. The purpose of this study was to confirm whether 4-MU was effective at limiting the effects of osteoarthritis (OA) on articular cartilage in vivo. The progression of OA was evaluated after destabilization of the medial meniscus (DMM) surgery on C57BL/6 mice in the presence or absence of 4-MU-containing chow. Mice fed 4-MU after DMM surgery exhibited significant suppression of OA starting from an early stage in vivo. Mice fed 4-MU exhibited lower OARSI scores after DMM; reduced osteophyte formation and reduced MMP3 and MMP13 immunostaining. 4-MU also exerted pronounced chondroprotective effects on murine joint cartilage exposed to IL1β in vitro and, blocked IL1β-enhanced lactate production in cartilage explants. Therefore, 4-MU is effective at significantly reducing the loss of proteoglycan and reducing MMP production both in vitro and in vivo as well as cartilage damage and osteophyte formation in vivo after DMM. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res. 38:1122-1131, 2020.

High-fat feeding primes the mouse knee joint to develop osteoarthritis and pathologic infrapatellar fat pad changes after surgically induced injury

OBJECTIVE

Obesity is one of the greatest risk factors for osteoarthritis (OA) and evidence is accumulating that inflammatory mediators and innate immunity play an important role. The infrapatellar fat pad (IPFP) could be a potential local source of inflammatory mediators in the knee. Here, we combine surgical joint damage with high-fat feeding in mice to investigate inflammatory responses in the IPFP during OA development.

DESIGN

Mice (n = 30) received either a low-fat diet (LFD), high-fat diet (HFD) for 18 weeks or switched diets (LFD > HFD) after 10 weeks. OA was induced by surgical destabilization of the medial meniscus (DMM), contralateral knees served as sham controls. An additional HFD-only group (n = 15) received no DMM.

RESULTS

The most pronounced inflammation, characterized by macrophage crown-like structures (CLS), was found in HFD + DMM mice, CLS increased compared to HFD only (mean difference = 7.26, 95%CI [1.52-13.0]) and LFD + DMM (mean difference = 6.35, 95%CI [0.53-12.18). The M1 macrophage marker iNOS increased by DMM (ratio = 2.48, 95%CI [1.37-4.50]), while no change in M2 macrophage marker CD206 was observed. Fibrosis was minimal by HFD alone, but in combination with DMM it increased with 23.45% (95%CI [13.67-33.24]).

CONCLUSIONS

These findings indicate that a high-fat diet alone does not trigger inflammation or fibrosis in the infrapatellar fat pad, but in combination with an extra damage trigger, like DMM, induces inflammation and fibrosis in the infrapatellar fat pad. These data suggest that HFD provides a priming effect on the infrapatellar fat pad and that combined actions bring the joint in a metabolic state of progressive OA.

Mechanobiological Mechanisms of Load-Induced Osteoarthritis in the Mouse Knee

Osteoarthritis (OA) is a degenerative joint disease that affects millions of people worldwide, yet its disease mechanism is not clearly understood. Animal models have been established to study disease progression by initiating OA through modified joint mechanics or altered biological activity within the joint. However, animal models often do not have the capability to directly relate the mechanical environment to joint damage. This review focuses on a novel in vivo approach based on controlled, cyclic tibial compression to induce OA in the mouse knee. First, we discuss the development of the load-induced OA model, its different loading configurations, and other techniques used by research laboratories around the world. Next, we review the lessons learned regarding the mechanobiological mechanisms of load-induced OA and relate these findings to the current understanding of the disease. Then, we discuss the role of specific genetic and cellular pathways involved in load-induced OA progression and the contribution of altered tissue properties to the joint response to mechanical loading. Finally, we propose using this approach to test the therapeutic efficacy of novel treatment strategies for OA. Ultimately, elucidating the mechanobiological mechanisms of load-induced OA will aid in developing targeted treatments for this disabling disease.

Inhibition of TET1 prevents the development of osteoarthritis and reveals the 5hmC landscape that orchestrates pathogenesis

Osteoarthritis (OA) is a degenerative disease of the joint, which results in pain, loss of mobility, and, eventually, joint replacement. Currently, no disease-modifying drugs exist, partly because of the multiple levels at which cartilage homeostasis is disrupted. Recent studies have highlighted the importance of epigenetic dysregulation in OA, sparking interest in the epigenetic modulation for this disease. In our previous work, we characterized a fivefold increase in cytosine hydroxymethylation (5hmC), an oxidized derivative of cytosine methylation (5mC) associated with gene activation, accumulating at OA-associated genes. To test the role of 5hmC in OA, here, we used a mouse model of surgically induced OA and found that OA onset was accompanied by a gain of ~40,000 differentially hydroxymethylated sites before the notable histological appearance of disease. We demonstrated that ten-eleven-translocation enzyme 1 (TET1) mediates the 5hmC deposition because 98% of sites enriched for 5hmC in OA were lost in Tet1−/− mice. Loss of TET1-mediated 5hmC protected the Tet1−/− mice from OA development, including degeneration of the cartilage surface and osteophyte formation, by directly preventing the activation of multiple OA pathways. Loss of TET1 in human OA chondrocytes reduced the expression of the matrix metalloproteinases MMP3 and MMP13 and multiple inflammatory cytokines. Intra-articular injections of a dioxygenases inhibitor, 2-hydroxyglutarate, on mice after surgical induction of OA stalled disease progression. Treatment of human OA chondrocytes with the same inhibitor also phenocopied TET1 loss. Collectively, these data demonstrate that TET1-mediated 5hmC deposition regulates multiple OA pathways and can be modulated for therapeutic intervention.

Low-level cyclic tibial compression attenuates early osteoarthritis progression after joint injury in mice

OBJECTIVE

Mechanical loading and joint health have a unique relationship in osteoarthritis (OA) onset and progression. Although high load levels adversely affect cartilage health, exercise that involves low to moderate load levels can alleviate OA symptoms. We sought to isolate the beneficial effects of mechanical loading using controlled in vivo cyclic tibial compression. We hypothesized that low-level cyclic compression would attenuate post-traumatic OA symptoms induced by destabilization of the medial meniscus (DMM).

METHODS

10-week-old C57Bl/6J male mice underwent DMM surgery (n = 51). After a 5-day post-operative recovery period, we applied daily cyclic tibial compression to the operated limbs at low (1.0N or 2.0N) or moderate (4.5N) magnitudes for 2 or 6 weeks. At the completion of loading, we compared cartilage and peri-articular bone features of mice that underwent DMM and loading to mice that only underwent DMM.

RESULTS

Compared to DMM alone, low-level cyclic compression for 6 weeks attenuated DMM-induced cartilage degradation (OARSI score, P = 0.008, 95% confidence interval (CI): 0.093 to 0.949). Low-level loading attenuated DMM-induced osteophyte formation after 2 weeks (osteophyte size, P = 0.033, 95% CI: 3.27-114.45 μm), and moderate loading attenuated subchondral bone sclerosis after 6 weeks (tissue mineral density (TMD), P = 0.011, 95% CI: 6.32-70.60 mg HA/ccm) compared to limbs that only underwent DMM. Finally, loading had subtle beneficial effects on cartilage cellularity and aggrecanase activity after DMM.

CONCLUSION

Low-level cyclic compression is beneficial to joint health after an injury. Therefore, the progression of early OA may be attenuated by applying well controlled, low-level loading shortly following joint trauma.

Inducible knockout of CHUK/IKKα in adult chondrocytes reduces progression of cartilage degradation in a surgical model of osteoarthritis

CHUK/IKKα contributes to collagenase-driven extracellular matrix remodeling and chondrocyte hypertrophic differentiation in vitro, in a kinase-independent manner. These processes contribute to osteoarthritis (OA), where chondrocytes experience a phenotypic shift towards hypertrophy concomitant with abnormal matrix remodeling. Here we investigated the contribution of IKKα to OA in vivo. To this end, we induced specific IKKα knockout in adult chondrocytes in AcanCreER^T2/+; IKKα^f/f mice treated with tamoxifen (cKO). Vehicle-treated littermates were used as wild type controls (WT). At 12 weeks of age, WT and cKO mice were subjected to the destabilization of medial meniscus (DMM) model of post-traumatic OA. The cKO mice showed reduced cartilage degradation and collagenase activity and fewer hypertrophy-like features at 12 weeks after DMM. Interestingly, in spite of the protection from structural articular cartilage damage, the postnatal growth plates of IKKα cKO mice after DMM displayed abnormal architecture and composition associated with increased chondrocyte apoptosis, which were not as evident in the articular chondrocytes of the same animals. Together, our results provide evidence of a novel in vivo functional role for IKKα in cartilage degradation in post-traumatic OA, and also suggest intrinsic, cell-autonomous effects of IKKα in chondrocytes that control chondrocyte phenotype and impact on cell survival, matrix homeostasis, and remodeling.

The commercial pig as a model of spontaneously-occurring osteoarthritis

BACKGROUND

Preclinical osteoarthritis models where damage occurs spontaneously may better reflect the initiation and development of human osteoarthritis. The aim was to assess the commercial pig as a model of spontaneous osteoarthritis development by examining pain-associated behaviour, joint cartilage integrity, as well as the use of porcine cartilage explants and isolated chondrocytes and osteoblasts for ex vivo and in vitro studies.

METHODS

Female pigs (Large white x Landrace x Duroc) were examined at different ages from 6 weeks to 3-4 years old. Lameness was assessed as a marker of pain-associated behaviour. Femorotibial joint cartilage integrity was determined by chondropathy scoring and histological staining of proteoglycan. IL-6 production and proteoglycan degradation was assessed in cartilage explants and primary porcine chondrocytes by ELISA and DMMB assay. Primary porcine osteoblasts from damaged and non-damaged joints, as determined by chondropathy scoring, were assessed for mineralisation, proliferative and mitochondrial function as a marker of metabolic capacity.

RESULTS

Pigs aged 80 weeks and older exhibited lameness. Osteoarthritic lesions in femoral condyle and tibial plateau cartilage were apparent from 40 weeks and increased in severity with age up to 3-4 years old. Cartilage from damaged joints exhibited proteoglycan loss, which positively correlated with chondropathy score. Stimulation of porcine cartilage explants and primary chondrocytes with either IL-1β or visfatin induced IL-6 production and proteoglycan degradation. Primary porcine osteoblasts from damaged joints exhibited reduced proliferative, mineralisation, and metabolic capacity.

CONCLUSION

In conclusion, the commercial pig represents an alternative model of spontaneous osteoarthritis and an excellent source of tissue for in vitro and ex vivo studies.

Pros and cons of mouse models for studying osteoarthritis

Osteoarthritis (OA) is one of the most common chronic conditions in the world today. It results in breakdown of cartilage in joints and causes the patient to experience intense pain and even disability. The pathophysiology of OA is not fully understood; therefore, there is currently no cure for OA. Many researchers are investigating the pathophysiology of the disease and attempting to develop methods to alleviate the symptoms or cure the OA entirely using animal models. Most studies on OA use animal models; this is necessary as the disease develops very slowly in humans and presents differently in each patient. This makes it difficult to effectively study the progression of osteoarthritis. Animal models can be spontaneous, in which OA naturally occurs in the animal. Genetic modifications can be used to make the mice more susceptible to developing OA. Osteoarthritis can also be induced via surgery, chemical injections, or non-invasive trauma. This review aims to describe animal models of inducing osteoarthritis with a focus on the models used on mice and their advantages and disadvantages that each model presents.

Curcumin improves age-related and surgically induced osteoarthritis by promoting autophagy in mice

Reduced autophagy has been implied in chondrocyte death and osteoarthritis. Curcumin (Cur) owns therapeutic effect against osteoarthritis (OA) and enhances autophagy in various tumor cells. Whether the cartilage protection of curcumin is associated with autophagy promotion and the potential signaling pathway involved remains unclear. The present study aimed to investigate the role of autophagy in the anti-OA activity of curcumin using spontaneous and surgically induced OA mice model. Spontaneous and surgically induced OA mice model was established and treated with Cur. Articular cartilage destruction and proteoglycan loss were scored through Safranin O/Fast green staining. Apoptotic cell death was detected with TUNEL (terminal deoxynucleotidyl transferase-mediated dTUP-biotin nick end labeling assay) staining and Western blot for caspase-3, Bcl-2 associated X protein (Bax), and Bcl-2 (B-cell lymphoma-2). Light chain 3 (LC3) immunohistochemistry was used to evaluate autophagy. In vitro, primary chondrocytes were treated with interleukin 1 beta (IL-1β) and Cur. Autophagy was inhibited using 3-methyladenine. Apoptosis and autophagy were detected using flow cytometry and Western blotting assay. Curcumin treatment enhanced autophagy, reduced apoptosis, and cartilage loss in both OA models. In vitro, curcumin treatment improved IL-1β induced autophagy inhibition, cell viability decrease, and apoptosis. Mechanistically, in vivo studies suggested curcumin promoted autophagy through regulating Akt/mTOR pathway. In conclusion, our results demonstrate that curcumin-induced autophagy via Akt/mTOR signaling pathway contributes to the anti-OA effect of curcumin.

An Alternative Method to Characterize the Quasi-Static, Nonlinear Material Properties of Murine Articular Cartilage

With the onset and progression of osteoarthritis (OA), articular cartilage (AC) mechanical properties are altered. These alterations can serve as an objective measure of tissue degradation. Although the mouse is a common and useful animal model for studying OA, it is extremely challenging to measure the mechanical properties of murine AC due to its small size (thickness < 50 μm). In this study, we developed novel and direct approach to independently quantify two quasi-static mechanical properties of mouse AC: the load-dependent (nonlinear) solid matrix Young's modulus (E) and drained Poisson's ratio (ν). The technique involves confocal microscope-based multiaxial strain mapping of compressed, intact murine AC followed by inverse finite element analysis (iFEA) to determine E and ν. Importantly, this approach yields estimates of E and ν that are independent of the initial guesses used for iterative optimization. As a proof of concept, mechanical properties of AC on the medial femoral condyles of wild-type mice were obtained for both trypsin-treated and control specimens. After proteolytic tissue degradation induced through trypsin treatment, a dramatic decrease in E was observed (compared to controls) at each of the three tested loading conditions. A significant decrease in ν due to trypsin digestion was also detected. These data indicate that the method developed in this study may serve as a valuable tool for comparative studies evaluating factors involved in OA pathogenesis using experimentally induced mouse OA models.

Elf3 Contributes to Cartilage Degradation in vivo in a Surgical Model of Post-Traumatic Osteoarthritis

The E-74 like factor 3 (ELF3) is a transcription factor induced by inflammatory factors in various cell types, including chondrocytes. ELF3 levels are elevated in human cartilage from patients with osteoarthritis (OA), and ELF3 contributes to the IL-1β-induced expression of genes encoding Mmp13, Nos2, and Ptgs2/Cox2 in chondrocytes in vitro. Here, we investigated the contribution of ELF3 to cartilage degradation in vivo, using a mouse model of OA. To this end, we generated mouse strains with cartilage-specific Elf3 knockout (Col2Cre:Elf3^f/f) and Comp-driven Tet-off-inducible Elf3 overexpression (TRE-Elf3:Comp-tTA). To evaluate the contribution of ELF3 to OA, we induced OA in 12-week-old Col2Cre:Elf3^f/f and 6-month-old TRE-Elf3:Comp-tTA male mice using the destabilization of the medial meniscus (DMM) model. The chondrocyte-specific deletion of Elf3 led to decreased levels of IL-1β- and DMM-induced Mmp13 and Nos2 mRNA in vitro and in vivo, respectively. Histological grading showed attenuation of cartilage loss in Elf3 knockout mice compared to wild type (WT) littermates at 8 and 12 weeks following DMM surgery that correlated with reduced collagenase activity. Accordingly, Elf3 overexpression led to increased cartilage degradation post-surgery compared to WT counterparts. Our results provide evidence that ELF3 is a central contributing factor for cartilage degradation in post-traumatic OA in vivo.

Bushenhuoxue formula attenuates cartilage degeneration in an osteoarthritic mouse model through TGF-β/MMP13 signaling

BACKGROUND

Articular cartilage degeneration plays a key role in the pathogenesis of osteoarthritis (OA). Bushenhuoxue formula (BSHXF) has been widely used in the treatment of OA in clinics. However, the molecular mechanisms responsible for the chondroprotective effect of BSHXF remain to be elucidated. The purpose of this study was to explore the effects of BSHXF on OA mice model.

METHODS

In this study, we investigated the effects of BSHXF on destabilization of the medial meniscus (DMM)-induced chondrocyte degradation in OA mice model. At 12 weeks post-surgery, the joints were harvested for tissue analyses, including histology, histomorphometry, TUNEL, OARSI scoring, micro-CT and immunohistochemistry for COL2, TGFBR2, pSMAD2 and MMP13. Additionally, we also evaluated the effects of BSHXF on Mmp13 mRNA and protein expression in chondrogenic ATDC5 cells through real-time PCR and Western blot respectively. Moreover, we investigated the chondroprotective effect of BSHXF on mice with Tgfbr2 conditional knockout (Tgfbr2 ^Col2ER mice) in chondrocyte, including the relative experiments mentioned above. We transfected Tgfbr2 siRNA in ATDC5 to further evaluate the changes of Mmp13 mRNA and protein expression followed by BSHXF treatment.

RESULTS

Amelioration of cartilage degradation and chondrocyte apoptosis were observed in DMM-induced mice, with increases in cartilage area and thickness, proteoglycan matrix, COL2 content and decreases in OARSI score at 12 weeks post surgery. Moreover, the elevated TGFBR2 and pSMAD2, and reduced MMP13 positive cells were also revealed in DMM-induced mice treated with BSHXF. Besides, decreased Mmp13 mRNA and protein expression were observed inchondrogenic ATDC5 cells culture in serum containing BSHXF. As expected, Tgfbr2 ^Col2ER mice exhibited significant OA-like phenotype. Interestingly, obvious improvement in articular cartilage structure was still observed in Tgfbr2 ^Col2ER mice after BSHXF treatment via up-regulated pSMAD2 and down-regulated MMP13 expressional levels in articular cartilage.

CONCLUSIONS

BSHXF could inhibit cartilage degradation through TGF-β/MMP13 signaling, and be considered a good option for the treatment of OA.

Role of subchondral bone properties and changes in development of load-induced osteoarthritis in mice

OBJECTIVE

Animal models recapitulating post-traumatic osteoarthritis (OA) suggest that subchondral bone (SCB) properties and remodeling may play major roles in disease initiation and progression. Thus, we investigated the role of SCB properties and its effects on load-induced OA progression by applying a tibial loading model on two distinct mouse strains treated with alendronate (ALN).

DESIGN

Cyclic compression was applied to the left tibia of 26-week-old male C57Bl/6 (B6, low bone mass) and FVB (high bone mass) mice. Mice were treated with ALN (26 μg/kg/day) or vehicle (VEH) for loading durations of 1, 2, or 6 weeks. Changes in articular cartilage and subchondral and epiphyseal cancellous bone were analyzed using histology and microcomputed tomography.

RESULTS

FVB mice exhibited thicker cartilage, a thicker SCB plate, and higher epiphyseal cancellous bone mass and tissue mineral density than B6 mice. Loading induced cartilage pathology, osteophyte formation, and SCB changes; however, lower initial SCB mass and stiffness in B6 mice did not attenuate load-induced OA severity compared to FVB mice. By contrast, FVB mice exhibited less cartilage damage, and slower-growing and less mature osteophytes. In B6 mice, inhibiting bone remodeling via ALN treatment exacerbated cartilage pathology after 6 weeks of loading, while in FVB mice, inhibiting bone remodeling protected limbs from load-induced cartilage loss.

CONCLUSIONS

Intrinsically lower SCB properties were not associated with attenuated load-induced cartilage loss. However, inhibiting bone remodeling produced differential patterns of OA pathology in animals with low compared to high SCB properties, indicating that these factors do influence load-induced OA progression.

Yougui Pills Attenuate Cartilage Degeneration via Activation of TGF-β/Smad Signaling in Chondrocyte of Osteoarthritic Mouse Model

Yougui pills (YGPs) have been used for centuries in the treatment of Chinese patients with Kidney-Yang Deficiency Syndrome. Despite the fact that the efficiency of YGPs on treating osteoarthritis has been verified in clinic, the underlying mechanisms are not totally understood. The present study observes the therapeutic role of YGPs and mechanisms underlying its chondroprotective action in osteoarthritic cartilage. To evaluate the chondroprotective effects of YGPs, we examined the impact of orally administered YGPs in a model of destabilization of the medial meniscus (DMM). Male C57BL/6J mice were provided a daily treatment of YGPs and a DMM surgery was performed on the right knee. At 12 weeks post-surgery, the joints were harvested for tissue analyses, including histomorphometry, OARSI scoring, micro-CT and immunohistochemistry for COL-2, MMP-13 and pSMAD-2. We also performed the relative experiments mentioned above in mice with Tgfbr2 conditional knockout (TGF-βRII^Col2ER mice) in articular cartilage. To evaluate the safety of YGPs, hematology was determined in each group. Amelioration of cartilage degradation was observed in the YGPs group, with increases in cartilage area and thickness, proteoglycan matrix, and decreases in OARSI score at 12 weeks post surgery. In addition, reduced BV/TV and Tb. Th, and elevated Tb. Sp were observed in DMM-induced mice followed by YGPs treatment. Moreover, the preservation of cartilage correlated with reduced MMP-13, and elevated COL-2 and pSMAD-2 protein expressional levels were also revealed in DMM-induced mice treated with YGPs. Similarly, TGF-βRII^Col2ER mice exhibited significant OA-like phenotype. However, no significant difference in cartilage structure was observed in TGF-βRII^Col2ER mice after YGPs treatment. Interestingly, no obvious adverse effects were observed in mice from each group based on the hematologic analyses. These findings suggested that YGPs could inhibit cartilage degradation through enhancing TGF-β/Smad signaling activation, and be considered a good option for the treatment of osteoarthritis.