Alterations in periarticular bone and cross talk between subchondral bone and articular cartilage in osteoarthritis

Exosomes of stem cells: a potential frontier in the treatment of osteoarthritis

The aging population has led to a global issue of osteoarthritis (OA), which not only impacts the quality of life for patients but also poses a significant economic burden on society. While biotherapy offers hope for OA treatment, currently available treatments are unable to delay or prevent the onset or progression of OA. Recent studies have shown that as nanoscale bioactive substances that mediate cell communication, exosomes from stem cell sources have led to some breakthroughs in the treatment of OA and have important clinical significance. This paper summarizes the mechanism and function of stem cell exosomes in delaying OA and looks forward to the development prospects and challenges of exosomes.

Unbalanced occlusal loading elicited remodeling responses in growing rat temporomandibular joints and Notch1/Hes1 signaling pathway expression

OBJECTIVE

We aimed to assess the impact of unbalanced occlusal loading on the TMJ and the expression of the Notch1/Hes1 signaling pathway using a unilateral occlusal loss rat model.

METHODS

We established a unilateral occlusal defect animal model. At three different times, all female Wistar rats were randomized into three groups (4 weeks, 6 weeks, and 10 weeks): (1) unilateral occlusal loss experiment group (extraction of the left mandibular molars and trimming of the left mandibular incisors every other day), (2) restoring incisal occlusion experiment group (extraction of the left mandibular molars and trimming of the left mandibular incisors every other day for 4 weeks, and then the incisor trimming was stopped until 10 weeks), (3) control group (normal loading). Micro-CT, histological staining, immunofluorescence, immunohistochemistry, and real-time quantitative polymerase chain reaction were used to identify changes in condylar cartilage, subchondral bone, and articular discs.

RESULTS

Temporomandibular joint condylar cartilage degradation was induced by unbalanced occlusal loading, especially on the extraction side. The dropped cartilage thickness, Cyclin D1 positive chondrocytes, TB staining and collagen II positive areas, the decreased expression levels of Notch1, Jagged1, and Hes1 in condylar cartilage, the loss of TMJ subchondral bone were all reversed in the restoring incisal occlusion experiment group at 6 weeks. The experiment group exhibited catabolic degradative alterations at the molecular level in TMJ discs, showing a notable decrease in the mRNA expression levels of Col I, Col II, and ALP.

CONCLUSIONS

The growing rat TMJ condyle exhibits a significant remodeling capacity in altered occlusal loading, which can be degenerative and recuperative, respectively, in reaction to decreased occlusal loading and restored occlusal loading. Appropriate occlusal loading is essential for transducing the Notch1/Hes1 signaling pathway and normal metabolism of the TMJ disc.

Mechanosensitive lncRNA H19 promotes chondrocyte autophagy, but not pyroptosis, by targeting miR-148a in post-traumatic osteoarthritis

OBJECTIVE

Investigating whether mechanosensitive lncRNA H19 can directly target miR-148a to alleviate cartilage damage in post-traumatic osteoarthritis (PTOA).

METHODS

Thirty-two female rats were randomly divided into four groups: Sham-operated group (Sham group, n = 8), treadmill running group (R group, n = 8), anterior cruciate ligament transection (ACLT) group (ACLT group, n = 8), and ACLT + treadmill running group (ACLT + R group, n = 8). Histological evaluation was performed to observe the pathological changes in the cartilage of the rat knee. Micro-CT was performed to detect the bone morphological changes in the subchondral bone. RT-qPCR and Western-Blot were performed to detect changes in mRNA and protein levels of metabolic and inflammatory factors as well as changes in the expression of lncRNA H19 and miR-148a in cartilage. The Flexcell 5000™ Tension System was used to further validate that lncRNA H19 has mechanosensitivity in vitro. Finally, cell transfection techniques were used to knock down the expression of lncRNA H19 in chondrocytes to validate the regulatory role of lncRNA H19/miR-148a in cartilage metabolism.

RESULTS

ACLT combined with treadmill running aggravated the abnormal hyperplasia of subchondral bone in the lateral tibial plateau of the rat knee joint, disturbed the balance of cartilage metabolism, induced cartilage inflammatory response and chondrocyte pyroptosis, which eventually led to cartilage damage and PTOA. Importantly, we found that the expression of lncRNA H19 was significantly downregulated in the cartilage of the ACLT + R group. Bioinformatics analysis revealed that miR-148a may be a direct target of lncRNA H19. Subsequently, we focused on the mechanosensitive of lncRNA H19. Subsequently, moderate-intensity mechanical tension stress reversed the expression of lncRNA H19 and autophagy-related factors in inflammatory chondrocytes, while miR-148a showed an opposite expression trend, demonstrating that mechanosensitive lncRNA H19 may be involved in regulating the chondrocyte inflammatory response by targeting miR-148a and activating autophagy. Cell transfection experiments revealed that lncRNA H19 knockdown upregulated miR-148a expression and significantly inhibited the autophagy level of chondrocytes without significant alteration of chondrocyte pyroptosis, which in turn exacerbated the inflammatory response of chondrocytes.

CONCLUSIONS

Mechanosensitive lncRNA H19 can promote chondrocyte autophagy rather than pyroptosis by targeting miR-148a, thus alleviating cartilage damage in PTOA. LncRNA H19 may be a potential therapeutic target for PTOA.

Forkhead box C1 promotes the pathology of osteoarthritis in subchondral bone osteoblasts via the Piezo1/YAP axis

Subchondral bone sclerosis is a key characteristic of osteoarthritis (OA). Prior research has shown that Forkhead box C1 (FoxC1) plays a role in the synovial inflammation of OA, but its specific role in the subchondral bone of OA has not been explored. Our research revealed elevated expression levels of FoxC1 and Piezo1 in OA subchondral bone tissues. Further experiments on OA subchondral bone osteoblasts with FoxC1 or Piezo1 overexpression showed increased cell proliferation activity, expression of Yes-associated Protein 1 (YAP) and osteogenic markers, and secretion of proinflammatory factors. Mechanistically, the overexpression of FoxC1 through Piezo1 activation, in combination with downstream YAP signaling, led to increased levels of alkaline phosphatase (ALP), collagen type 1 (COL1) A1, RUNX2, Osteocalcin, matrix metalloproteinase (MMP) 3, and MMP9 expression. Notably, inhibition of Piezo1 reversed the regulatory function of FoxC1. The binding of FoxC1 to the targeted area (ATATTTATTTA, residues +612 to +622) and the activation of Piezo1 transcription were verified by the dual luciferase assays. Additionally, Reduced subchondral osteosclerosis and microangiogenesis were observed in knee joints from FoxC1-conditional knockout (CKO) and Piezo1-CKO mice, indicating reduced lesions. Collectively, our study reveals the significant involvement of FoxC1 in the pathologic process of OA subchondral bone via the Piezo1/YAP signaling pathway, potentially establishing a novel therapeutic target.

Obesity-induced fibrosis in osteoarthritis: Pathogenesis, consequences and novel therapeutic opportunities

Osteoarthritis (OA) is a significant global burden, affecting more than half a billion people across the world. It is characterized by degeneration and loss of articular cartilage, synovial inflammation, and subchondral bone sclerosis, leading to pain and functional impairment. After age, obesity is a major modifiable risk factor for OA, and it has recently been identified as a chronic disease by the World Health Organization (WHO). Obesity is associated with high morbidity and mortality, imposing a significant cost on individuals and society. Obesity increases the risk of knee OA through increased joint loading, altered body composition, and elevated pro-inflammatory adipokines in the systemic circulation. Moreover, obesity triggers fibrotic processes in different organs and tissues, including those involved in OA. Fibrosis in OA refers to the abnormal accumulation of fibrous tissue within and around the joints. It can be driven by increased adiposity, low-grade inflammation, oxidative stress, and metabolic alterations. However, the clinical outcomes of fibrosis in OA are unclear. This review focuses on the link between obesity and OA, explores the mechanism of obesity-driven fibrosis, and examines potential therapeutic opportunities for targeting fibrotic processes in OA.

Quantitative ultrashort echo time MR imaging of knee osteochondral junction: An ex vivo feasibility study

Compositional changes can occur in the osteochondral junction (OCJ) during the early stages and progressive disease evolution of knee osteoarthritis (OA). However, conventional magnetic resonance imaging (MRI) sequences are not able to image these regions efficiently because of the OCJ region's rapid signal decay. The development of new sequences able to image and quantify OCJ region is therefore highly desirable. We developed a comprehensive ultrashort echo time (UTE) MRI protocol for quantitative assessment of OCJ region in the knee joint, including UTE variable flip angle technique for T1 mapping, UTE magnetization transfer (UTE-MT) modeling for macromolecular proton fraction (MMF) mapping, UTE adiabatic T1ρ (UTE-AdiabT1ρ) sequence for T1ρ mapping, and multi-echo UTE sequence for T2* mapping. B1 mapping based on the UTE actual flip angle technique was utilized for B1 correction in T1, MMF, and T1ρ measurements. Ten normal and one abnormal cadaveric human knee joints were scanned on a 3T clinical MRI scanner to investigate the feasibility of OCJ imaging using the proposed protocol. Volumetric T1, MMF, T1ρ, and T2* maps of the OCJ, as well as the superficial and full-thickness cartilage regions, were successfully produced using the quantitative UTE imaging protocol. Significantly lower T1, T1ρ, and T2* relaxation times were observed in the OCJ region compared with those observed in both the superficial and full-thickness cartilage regions, whereas MMF showed significantly higher values in the OCJ region. In addition, all four UTE biomarkers showed substantial differences in the OCJ region between normal and abnormal knees. These results indicate that the newly developed 3D quantitative UTE imaging techniques are feasible for T1, MMF, T1ρ, and T2* mapping of knee OCJ, representative of a promising approach for the evaluation of compositional changes in early knee OA.

Soybean Isoflavones Alleviate Osteoarthritis Through Modulation of the TSC1/mTORC1 Signaling Pathway to Reduce Intrachondral Angiogenesis

BACKGROUND

The incidence of osteoarthritis (OA) is increasing, yet its pathogenesis remains largely unknown. Recent studies suggest that abnormal subchondral bone remodeling plays a crucial role in OA development, highlighting a gap in clinical treatments targeting this aspect. Soybean Isoflavone (SI) has shown potential in treating OA, although its mechanisms are not fully understood.

METHODS

This research investigated the effects of SI on subchondral bone remodeling in an OA rat model, assessing joint damage, OARSI scores, and type H vessel formation (CD31hiEmcnhi expression). Additionally, the expression of ALP, OCN, BMP, and TSC1 was evaluated to determine involvement of the mTORC1 pathway. In vitro studies on IL-1β-induced osteoblasts further examined the impact of SI on TSC1/mTORC1 signaling and related markers.

RESULTS

SI treatment reduced joint damage and OARSI scores in the rat OA model, significantly decreasing CD31hiEmcnhi expression, indicating a reduction in type H vessel formation. SI also downregulated ALP, OCN, and BMP expression while upregulating TSC1, suggesting inhibition of the mTORC1 signaling pathway and VEGF release. In vitro, SI increased TSC1 expression and decreased mTORC1 signaling, VEGF, ALP, OCN, and BMP levels in IL-1β-induced osteoblasts.

CONCLUSION

SI targets the TSC1/mTORC1 signaling pathway to suppress osteoblast activation and VEGF release, inhibiting type H vessel formation and slowing abnormal subchondral bone remodeling. These findings provide a novel therapeutic approach for OA by focusing on subchondral bone remodeling mechanisms.

Assessment of post-trauma microstructural alterations in the rabbit knee cartilage and subchondral bone

Early diagnosis of post-traumatic osteoarthritis (PTOA) is critical for designing better treatments before the degradation becomes irreversible. We utilized multimodal high-resolution imaging to investigate early-stage deterioration in articular cartilage and the subchondral bone plate from a sub-critical impact to the knee joint, which initiates PTOA. The knee joints of 12 adult rabbits were mechanically impacted once on the femoral articular surface to initiate deterioration. At 2- and 14-week post-impact surgery, cartilage-bone blocks were harvested from the impact region in the animals (N = 6 each). These blocks were assessed for deterioration using polarized light microscopy (PLM), microcomputed tomography (μCT), and biochemical analysis. Statistically significant changes were noted in the impact tissues across the calcified zone (CZ) at 14 weeks post-impact: the optical retardation values in the CZ of impact cartilage had a drop of 29.0% at 14 weeks, while the calcium concentration in the CZ of impact cartilage also had a significant drop at 14 weeks. A significant reduction of 6.3% in bone mineral density (BMD) was noted in the subchondral bone plate of the impact samples at 14 weeks. At 2 weeks post-impact, only minor, non-significant changes were measured. Furthermore, the impact knees after 14 weeks had greater structural changes compared with the 2-week impact knees, indicating progressive degradation over time. The findings of this study facilitated a connection between mineralization alterations and the early deterioration of knee cartilage after a mechanical injury. In a broader context, these findings can be beneficial in improving clinical strategies to manage joint injuries.

The Correlation between the Elastic Modulus of the Achilles Tendon Enthesis and Bone Microstructure in the Calcaneal Crescent

BACKGROUND

The calcaneal enthesis, an osseous footprint where the Achilles tendon seamlessly integrates with the bone, represents a complex interface crucial for effective force transmission. Bone adapts to mechanical stress and remodels based on the applied internal and external forces. This study explores the relationship between the elasticity of the Achilles tendon enthesis and the bone microstructure in the calcaneal crescent.

METHODS

In total, 19 calcaneal-enthesis sections, harvested from 10 fresh-frozen human cadaveric foot-ankle specimens (73.8 ± 6.0 years old, seven female), were used in this study. Indentation tests were performed at the enthesis region, and Hayes' elastic modulus was calculated for each specimen. Micro-CT scanning was performed at 50-micron voxel size to assess trabecular bone microstructure within six regions of interest (ROIs) and the cortical bone thickness along the calcaneal crescent.

RESULTS

Significant Spearman correlations were observed between the enthesis elastic modulus and trabecular bone thickness in the distal entheseal (ROI 3) and proximal plantar (ROI 4) regions (R = 0.786 and 0.518, respectively).

CONCLUSION

This study highlights the potential impacts of Achilles tendon enthesis on calcaneal bone microstructure, which was pronounced in the distal calcaneal enthesis, suggesting regional differences in load transfer mechanism that require further investigation.

Research progress of ultrasound in accurate evaluation of cartilage injury in osteoarthritis

Osteoarthritis (OA) is a prevalent cause of joint algesia, loss of function, and disability in adults, with cartilage injury being its core pathological manifestation. Since cartilage damage is non-renewable, the treatment outcome in the middle and late stages of OA is unsatisfactory, which can be minimized by changing lifestyle and other treatment modalities if diagnosed and managed in the early stages, indicating the importance of early diagnosis and monitoring of cartilage injury. Ultrasound technology has been used for timely diagnosis and even cartilage injury treatment, which is convenient and safe for the patient owing to no radiation exposure. Studies have demonstrated the effectiveness of ultrasound and its various quantitative ultrasound parameters, like ultrasound roughness index (URI), reflection coefficient (R), apparent integrated backscatter (AIB), thickness, and ultrasound elastography, in the early and accurate assessment of OA cartilage pathological changes, including surface and internal tissue, hardness, and thickness. Although many challenges are faced in the clinical application of this technology in diagnosis, ultrasound and ultrasound-assisted techniques offer a lot of promise for detecting early cartilage damage in OA. In this review, we have discussed the evaluation of ultrasonic cartilage quantitative parameters for early pathological cartilage changes.

siRNA therapy in osteoarthritis: targeting cellular pathways for advanced treatment approaches

Osteoarthritis (OA) is a common joint disorder characterized by the degeneration of cartilage and inflammation, affecting millions worldwide. The disease's complex pathogenesis involves various cell types, such as chondrocytes, synovial cells, osteoblasts, and immune cells, contributing to the intricate interplay of factors leading to tissue degradation and pain. RNA interference (RNAi) therapy, particularly through the use of small interfering RNA (siRNA), emerges as a promising avenue for OA treatment due to its capacity for specific gene silencing. siRNA molecules can modulate post-transcriptional gene expression, targeting key pathways involved in cellular proliferation, apoptosis, senescence, autophagy, biomolecule secretion, inflammation, and bone remodeling. This review delves into the mechanisms by which siRNA targets various cell populations within the OA milieu, offering a comprehensive overview of the potential therapeutic benefits and challenges in clinical application. By summarizing the current advancements in siRNA delivery systems and therapeutic targets, we provide a solid theoretical foundation for the future development of novel siRNA-based strategies for OA diagnosis and treatment, paving the way for innovative and more effective approaches to managing this debilitating disease.

Signalling interaction between β-catenin and other signalling molecules during osteoarthritis development

Osteoarthritis (OA) is the most prevalent disorder of synovial joint affecting multiple joints. In the past decade, we have witnessed conceptual switch of OA pathogenesis from a 'wear and tear' disease to a disease affecting entire joint. Extensive studies have been conducted to understand the underlying mechanisms of OA using genetic mouse models and ex vivo joint tissues derived from individuals with OA. These studies revealed that multiple signalling pathways are involved in OA development, including the canonical Wnt/β-catenin signalling and its interaction with other signalling pathways, such as transforming growth factor β (TGF-β), bone morphogenic protein (BMP), Indian Hedgehog (Ihh), nuclear factor κB (NF-κB), fibroblast growth factor (FGF), and Notch. The identification of signalling interaction and underlying mechanisms are currently underway and the specific molecule(s) and key signalling pathway(s) playing a decisive role in OA development need to be evaluated. This review will focus on recent progresses in understanding of the critical role of Wnt/β-catenin signalling in OA pathogenesis and interaction of β-catenin with other pathways, such as TGF-β, BMP, Notch, Ihh, NF-κB, and FGF. Understanding of these novel insights into the interaction of β-catenin with other pathways and its integration into a complex gene regulatory network during OA development will help us identify the key signalling pathway of OA pathogenesis leading to the discovery of novel therapeutic strategies for OA intervention.

Subchondral bone expansion in advanced knee osteoarthritis: Relation with radiographic severity and role in surgical decision-making

Background

Joint space width (JSW) is a traditional imaging marker for knee osteoarthritis (OA) severity, but it lacks sensitivity in advanced cases. We propose tibial subchondral bone area (TSBA), a new CT imaging marker to explore its relationship with OA radiographic severity, and to test its performance for classifying surgical decisions between unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) compared to JSW.

Methods

We collected clinical, radiograph, and CT data from 182 patients who underwent primary knee arthroplasty (73 UKA, 109 TKA). The radiographic severity was scored using Kellgren-Lawrence (KL) grading system. TSBA and JSW were extracted from 3D CT-reconstruction model. We used independent t-test to investigate the relationship between TSBA and KL grade, and binary logistic regression to identify factors associated with TKA risk. The accuracy of TSBA, JSW and established classification model in differentiating between UKA and TKA was assessed using AUC.

Results

All parameters exhibited inter- and intra-class coefficients greater than 0.966. Patients with KL grade 4 had significantly larger TSBA than those with KL grade 3. TSBA (0.708 of AUC) was superior to minimal/average JSW (0.547/0.554 of AUC) associated with the risk of receiving TKA. Medial TSBA, together with gender and Knee Society Knee Score, emerged as independent classification factors in multivariate analysis. The overall AUC of composite model for surgical decision-making was 0.822.

Conclusion

Tibial subchondral bone area is an independent imaging marker for radiographic severity, and is superior to JSW for surgical decision-making between UKA and TKA in advanced OA patients.

Consistent and informed choice of drug and route of administration is key to increasing adherence to osteoarthritis treatment

The need to follow an integrated approach when prescribing treatment for patients suffering from osteoarthritis (OA) is beyond doubt. It is clear that success depends on the implementation of recommendations for both lifestyle modification and the introduction of pharmacological agents with different compositions and mechanisms of action aimed at reducing pain, stiffness, inflammation, normalizing joint function, and preventing cartilage destruction. The arsenal of such drugs is increasing, and the evidence base of effectiveness and safety is being enriched. Considering the heterogeneity of OA patients seeking help in terms of gender, age, body mass index, financial wealth, comorbidity, clinical manifestations of the disease, radiological stage of the disease and its duration, experience of previous treatment, a reasonable and agreed upon choice with the patient not only of the drug is relevant, but also the method of administration. The article provides a clinical example of a justified and coordinated choice of treatment for a patient with a generalized form of OA, synovitis of the knee joint, suffering from obesity, depression, low adherence to treatment using the example of prescribing a chondroprotector, the active component of which is a bioactive extract from small sea fish. The treatment effect was confirmed by clinical and instrumental assessment methods over time.

PTH treatment before cyclic joint loading improves cartilage health and attenuates load-induced osteoarthritis development in mice

Osteoarthritis (OA) treatment is limited by the lack of effective nonsurgical interventions to slow disease progression. Here, we examined the contributions of the subchondral bone properties to OA development. We used parathyroid hormone (PTH) to modulate bone mass before OA initiation and alendronate (ALN) to inhibit bone remodeling during OA progression. We examined the spatiotemporal progression of joint damage by combining histopathological and transcriptomic analyses across joint tissues. The additive effect of PTH pretreatment before OA initiation and ALN treatment during OA progression most effectively attenuated load-induced OA pathology. Individually, PTH directly improved cartilage health and slowed the development of cartilage damage, whereas ALN primarily attenuated subchondral bone changes associated with OA progression. Joint damage reflected early transcriptomic changes. With both treatments, the structural changes were associated with early modulation of immunoregulation and immunoresponse pathways that may contribute to disease mechanisms. Overall, our results demonstrate the potential of subchondral bone-modifying therapies to slow the progression of OA.

SIRT3 alleviates high glucose-induced chondrocyte injury through the promotion of autophagy and suppression of apoptosis in osteoarthritis progression

A growing amount of epidemiological evidence proposes diabetes mellitus (DM) to be an independent risk factor for osteoarthritis (OA). Sirtuin 3 (SIRT3), which is mainly located in mitochondria, belongs to the family of nicotinamide adenine dinucleotide (NAD+)-dependent protein deacetylases and is involved in the physiological and pathological processes of cell regulation. The aim of this study was to investigate the effects of SIRT3 on diabetic OA and underlying mechanisms in the prevention of type 2 DM (T2DM)-induced articular cartilage damage. High-fat and high-sugar diets combined with streptozotocin (STZ) injection were used for establishing an experimental T2DM rat model. The destabilization of medial meniscus (DMM) surgery was applied to induce the rat OA model. Primary rat chondrocytes were cultivated with a concentration of gradient glucose. Treatment with intra-articular injection of SIRT3 overexpression lentivirus was achieved in vivo, and intervention with SIRT3 knockdown was performed using siRNA transfection in vitro. High glucose content was found to activate inflammatory response, facilitate apoptosis, downregulate autophagy, and exacerbate mitochondrial dysfunction in a dose-dependent manner in rat chondrocytes, which can be deteriorated by SIRT3 knockdown. In addition, articular cartilage damage was found to be more severe in T2DM-OA rats than in DMM-induced OA rats, which can be mitigated by the intra-articular injection of SIRT3 overexpression lentivirus. Targeting SIRT3 is a potential therapeutic strategy for the alleviation of diabetic OA.

Microarchitecture Alternations of Osteochondral Junction in Patients with Osteonecrosis of the Femoral Head

The study was aimed to investigate microarchitecture of osteochondral junction in patients with osteonecrosis of the femoral head (ONFH). We hypothesis that there were microarchitecture alternations in osteochondral junction and regional differences between the necrotic region (NR) and adjacent non-necrotic region(ANR) in patients with ONFH. Femoral heads with ONFH or femoral neck fracture were included in ONFH group (n = 11) and control group (n = 11). Cylindrical specimens were drilled on the NR/ANR of femoral heads in ONFH group and matched positions in control group (CO.NR/ CO.ANR). Histology, micro-CT, and scanning electron microscope were used to investigate microarchitecture of osteochondral junction. Layered analysis of subchondral bone plate was underwent. Mankin scores on NR were higher than that on ANR or CO.NR, respectively (P < 0.001, P < 0.001). Calcified cartilage zone on the NR and ANR was thinner than that on the CO.NR and CO.ANR, respectively (P = 0.002, P = 0.002). Tidemark roughness on the NR was larger than that on the ANR (P = 0.002). Subchondral bone plate of NR and ANR was thicker than that on the CON.NR and CON.ANR, respectively (P = 0.002, P = 0.009). Bone volume fraction of subchondral bone plate on the NR was significantly decreasing compared to ANR and CON.NR, respectively (P = 0.015, P = 0.002). Subchondral bone plate on the NR had larger area percentages and more numbers of micropores than ANR and CON.NR (P = 0.002/0.002, P = 0.002/0.002). Layered analysis showed that bone mass loss and hypomineralization were mainly on the cartilage side of subchondral bone plate in ONFH. There were microarchitecture alternations of osteochondral junction in ONFH, including thinned calcified cartilage zone, thickened subchondral bone plate, decreased bone mass, altered micropores, and hypomineralization of subchondral bone plate. Regional differences in microarchitecture of osteochondral junction were found between necrotic regions and adjacent non-necrotic regions. Subchondral bone plate in ONFH had uneven distribution of bone volume fraction and bone mineral density, which might aggravate cartilage degeneration by affecting the transmission of mechanical stresses.

Effect of Traditional Chinese Non-Pharmacological Therapies on Knee Osteoarthritis: A Narrative Review of Clinical Application and Mechanism

Knee osteoarthritis (KOA) stands as a degenerative ailment with a substantial and escalating prevalence. The practice of traditional Chinese non-pharmacological therapy has become a prevalent complementary and adjunctive approach. A mounting body of evidence suggests its efficacy in addressing KOA. Recent investigations have delved into its underlying mechanism, yielding some headway. Consequently, this comprehensive analysis seeks to encapsulate the clinical application and molecular mechanism of traditional Chinese non-pharmacological therapy in KOA treatment. The review reveals that various therapies, such as acupuncture, electroacupuncture, warm needle acupuncture, tuina, and acupotomy, primarily target localized knee components like cartilage, subchondral bone, and synovium. Moreover, their impact extends to the central nervous system and intestinal flora. More perfect experimental design and more comprehensive research remain a promising avenue in the future.

Systematic review of computed tomography parameters used for the assessment of subchondral bone in osteoarthritis

OBJECTIVE

To systematically review the published parameters for the assessment of subchondral bone in human osteoarthritis (OA) using computed tomography (CT) and gain an overview of current practices and standards.

DESIGN

A literature search of Medline, Embase and Cochrane Library databases was performed with search strategies tailored to each database (search from 2010 to January 2023). The search results were screened independently by two reviewers against pre-determined inclusion and exclusion criteria. Studies were deemed eligible if conducted in vivo/ex vivo in human adults (>18 years) using any type of CT to assess subchondral bone in OA. Extracted data from eligible studies were compiled in a qualitative summary and formal narrative synthesis.

RESULTS

This analysis included 202 studies. Four groups of CT modalities were identified to have been used for subchondral bone assessment in OA across nine anatomical locations. Subchondral bone parameters measuring similar features of OA were combined in six categories: (i) microstructure, (ii) bone adaptation, (iii) gross morphology (iv) mineralisation, (v) joint space, and (vi) mechanical properties.

CONCLUSIONS

Clinically meaningful parameter categories were identified as well as categories with the potential to become relevant in the clinical field. Furthermore, we stress the importance of quantification of parameters to improve their sensitivity and reliability for the evaluation of OA disease progression and the need for standardised measurement methods to improve their clinical value.

High biocompatible polyacrylamide hydrogels fabricated by surface mineralization for subchondral bone tissue engineering

The subchondral bone is an important part of cartilage which contains a large amount of hydroxyapatite. The mineral components of subchondral bone is the key factor which determines the biomechanical strength, and then affects the biological function of articular cartilage. Here, a mineralized polyacrylamide (PAM-Mineralized) hydrogel with good ALP activity, cell adhesion and biocompatibility was fabricated for subchondral bone tissue engineering. The micromorphology, composition and mechanical properties of PAM and PAM-Mineralized hydrogels were studied. The PAM hydrogels showed a porous structure, while the PAM-Mineralized hydrogels had well-distributed layers of hydroxyapatite mineralization on the surface. The XRD results show that the characteristic peak of hydroxyapatite (HA) was measured in PAM-Mineralized, indicating that the main component of the mineralized structure formed on the surface of the hydrogel after mineralization is HA. The formation of HA ectively decreased the rate of equilibrium swelling of the PAM hydrogel, with PAM-M reaching swelling equilibrium at 6 h. Meanwhile, compressive strength of PAM-Mineralized hydrogel (moisture state) reached 290 ± 30 kPa, compressive modulus reached 130 ± 4 kPa. PAM-Mineralized hydrogels did not affect the growth and proliferation of MC3T3-E1 cells. Surface mineralization of PAM hydrogel could significantly improve osteogenic differentiation of MC3T3-E1 cells. These results showed that PAM-Mineralized hydrogel could possess potential application in the field of subchondral bone tissue engineering.

COL3A1, COL5A1 and COL6A2 serve as potential molecular biomarkers for osteoarthritis based on weighted gene co‑expression network analysis bioinformatics analysis

Osteoarthritis (OA) is a non-inflammatory degenerative joint disease, characterized by joint pain and stiffness. The prevalence of OA increases with age. However, the relationship between biomarkers [collagen type III α1 (COL3A1), COL5A1, COL6A2, COL12A1] and OA remains unclear. The OA subchondral bone dataset GSE51588 was downloaded from the GEO database, and the differentially expressed genes (DEGs) were screened. Weighted gene co-expression network analysis was performed, and a protein-protein interaction network was constructed and further analyzed using Cytoscape and STRING. Functional enrichment analysis was performed using Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, and then Gene Set Enrichment Analysis (GSEA) was used to formulate the molecular functions and pathways based on the results of GO and KEGG analyses. Comparative Toxicogenomics Database and TargetScan were used to identify the hub-gene-related diseases and the microRNAs that regulated the central hub genes. Immunohistochemical staining was performed to confirm the expression of related proteins in OA and non-OA tissue samples. A total of 1,679 DEGs were identified. GO analysis showed that the DEGs were primarily enriched in the process of 'immune system', 'extracellular region', 'secretory granule', 'collagen-containing extracellular matrix', 'ECM-receptor, glycosaminoglycan binding' and 'systemic lupus erythematosus'. The results of GSEA were similar to those of GO and KEGG enrichment terms for DEGs. A total of 25 important modules were generated, and two core gene clusters and seven core genes were obtained (COL6A2, COL5A2, COL12A1, COL5A1, COL6A1, LUM and COL3A1). Core genes were expressed differentially between OA subchondral bone and normal tissue samples. The expression levels of COL3A1, COL5A1 and COL6A2 in OA subchondral bone tissue were higher compared with those in normal tissues, but COL12A1 expression was not significantly increased; all stained markers were highly expressed in surrounding tissues of immunohistochemical staining. In conclusion, COL3A1, COL5A1 and COL6A2 may be potential molecular biomarkers for OA.

The role of cells and signal pathways in subchondral bone in osteoarthritis

Osteoarthritis (OA) is mainly caused by ageing, strain, trauma, and congenital joint abnormalities, resulting in articular cartilage degeneration. During the pathogenesis of OA, the changes in subchondral bone (SB) are not only secondary manifestations of OA, but also an active part of the disease, and are closely associated with the severity of OA. In different stages of OA, there were microstructural changes in SB. Osteocytes, osteoblasts, and osteoclasts in SB are important in the pathogenesis of OA. The signal transduction mechanism in SB is necessary to maintain the balance of a stable phenotype, extracellular matrix (ECM) synthesis, and bone remodelling between articular cartilage and SB. An imbalance in signal transduction can lead to reduced cartilage quality and SB thickening, which leads to the progression of OA. By understanding changes in SB in OA, researchers are exploring drugs that can regulate these changes, which will help to provide new ideas for the treatment of OA.

Disruption of Col9a2 expression leads to defects in osteochondral homeostasis and osteoarthritis-like phenotype in mice

Background/Objective

As one of the branched chains of Type IX collagen (Col9), Collagen IX alpha2 (Col9a2) has been reported to be associated with several orthopedic conditions. However, the relationship between Col9a2 and knee osteoarthritis (KOA) remains to be elucidated.

Methods

To probe the relationship between Col9a2 and KOA, we performed a systematic analysis of Col9a2-deficient (Col9a2-/-) mice using whole-mount skeletal staining, Micro-CT (μCT), biomechanics, histomorphometry, immunohistochemistry (IHC), immunofluorescence (IF) and Elisa.

Results

We found that the subchondral bone (SCB) in the knee joint of Col9a2-/- mice became sparse and deformed in the early stage, with altered bone morphometric parameters, reduced load-bearing capacity, dysfunctional bone homeostasis (decreased osteogenesis capacity and elevated bone resorption capacity), diminished cartilage proteoglycans and disrupted cartilage extracellular matrix (ECM) anabolism and catabolism compared with the Col9a2+/+ mice. In the late stage, the cartilage degeneration in Col9a2-/- mice were particularly pronounced compared to Col9a2+/+ mice, as evidenced by severe cartilage destruction and a marked reduction in cartilage thickness and area.

Conclusion

Overall, Col9a2 is essential for maintaining osteochondral homeostasis in the knee joint of mice, and the absence of this gene is accompanied by distinct sclerosis of the SCB and a reduction in load-bearing capacity; in the late stage, in the lack of SCB stress inhibition, excessive load is consistently exerted on the cartilage, ultimately leading to osteoarthritic-like articular cartilage damage.

Computed tomography Osteoabsorptiometry: Review of bone density, mechanical strength of material and clinical application

Computed Tomography (CT) imaging is an effective non-invasive examination. It is widely used in the diagnosis of fractures, arthritis, tumor, and some anatomical characteristics of patients. The density value (Hounsfield unit, HU) of a material in computed tomography can be the same for materials with varying elemental compositions. This value depends on the mass density of the material and the degree of X-ray attenuation. Computed Tomography Osteoabsorptiometry (CTOAM) imaging technology is developed on the basis of CT imaging technology. By applying pseudo-color image processing to the articular surface, it is used to analyze the distribution of bone mineralization under the articular cartilage, evaluate the position of prosthesis implantation, track the progression of osteoarthritis, and determine the joint injury prognosis. Furthermore, this technique was combined with indentation testing to discuss the relationship between the high bone density area of the articular surface, the mechanical strength of the bone, and the anchorage stability of the implant, in addition to the study of the relationship between mechanical strength and bone density. This narrative study discusses the pre- and postoperative evaluation of medical device implantation position, orthopedic surgery, and the clinical treatment of bone injury and degeneration. It also discusses the research status of CTOAM technology in image post-processing engineering and the relationship between bone material and mechanical strength.

Three-Dimensional Analysis of the Trapezium Subchondral Bone and its Association with Trapeziometacarpal Joint Osteoarthritis

Subchondral bone properties are associated with the pathogenesis of osteoarthritis (OA), but this relationship has not been confirmed in the trapeziometacarpal joint (TMCJ). We aimed to evaluate the thickness (SBT) and density (SBD) of three-dimensional (3D) trapezium subchondral bone models derived from computed tomography (CT) images, and their relationships with early-stage TMCJ OA. We reviewed patients with a distal radius fracture who underwent conventional CT scans and such osteoporosis evaluations as bone mineral density (BMD) and bone turnover markers (BTMs). From 3D trapezium subchondral bone models, we measured SBT and SBD according to the OA stage and performed multivariate analyses to evaluate their associations with age, sex, body mass index, BMD, and BTMs. As results, a total of 156 patients (78 men and 78 age-matched women; mean age, 67 ± 10 years) were analyzed. There were 30 (19%) with grade 0, 71 (45%) with grade 1, 13 (8%) with grade 2, and 42 (27%) with grade 3 TMCJ OA. SBT was significantly lower in patients with grade 1 OA than those with grade 0 or grade 3 OA, but SBD generally increased according to the OA severity. Low SBT was associated with low BMD, and low SBD with low BMD, high osteocalcin levels, and severe OA grades. In conclusion, patients with early-stage radiographic TMCJ OA have a lower SBT at the trapezium, which may support the potential role of subchondral bone in OA pathogenesis. This study also shows that subchondral bone properties are associated with BMD and osteocalcin levels.

The effects of dietary patterns and food groups on symptomatic osteoarthritis: A systematic review

AIM

To systematically review current literature to determine the association between symptomatic osteoarthritis and dietary patterns, diet quality and food groups in adults aged ≥45 years.

METHODS

The review was registered on PROSPERO (CRD42021270891). Cochrane Central Library, Cumulative Index of Nursing and Allied Health Literature, Embase, Medline and Web of Science databases were searched. A total of 3816 records were identified. Eligible articles involved populations aged ≥45 years with symptomatic osteoarthritis, assessing dietary patterns, diet quality or food groups, with pain in joints as outcomes. The Joanna Briggs Institute Critical Appraisal Checklists were used for quality assessment. Grading of Recommendations, Assessment, Development and Evaluation was used to assess the certainty of evidence.

RESULTS

Six cohort studies were included. The Prudent dietary pattern and the Mediterranean dietary pattern reduced the progression of osteoarthritis symptoms. The Western dietary pattern increased symptomatic osteoarthritis progression. Increased total fibre consumption reduced symptomatic osteoarthritis progression and pain worsening, but the effects of fibre from each food group were inconclusive. Diet with high inflammatory potential increased risk of new onset symptomatic osteoarthritis, but the effects of overall diet quality were inconclusive.

CONCLUSIONS

The Prudent dietary pattern showed the highest protection on symptomatic osteoarthritis in adults aged 45 years and over. The body of evidence is limited, suggesting that further research is needed to corroborate the estimated effect at a high certainty of evidence, and to incorporate previously unstudied dietary patterns and food groups. Identifying the most beneficial dietary pattern may inform future guidelines for reducing symptomatic osteoarthritis in middle aged and older adults.

Contrast-enhanced micro-computed tomography of compartment and time-dependent changes in femoral cartilage and subchondral plate in a murine model of osteoarthritis

A lack of understanding of the mechanisms underlying osteoarthritis (OA) progression limits the development of effective long-term treatments. Quantitatively tracking spatiotemporal patterns of cartilage and bone degeneration is critical for assessment of more appropriately targeted OA therapies. In this study, we use contrast-enhanced micro-computed tomography (μCT) to establish a timeline of subchondral plate (SCP) and cartilage changes in the murine femur after destabilization of the medial meniscus (DMM). We performed DMM or sham surgery in 10-12-week-old male C57Bl/6J mice. Femora were imaged using μCT after 0, 2, 4, or 8 weeks. Cartilage-optimized scans were performed after immersion in contrast agent CA4+. Bone mineral density distribution (BMDD), cartilage attenuation, SCP, and cartilage thickness and volume were measured, including lateral and medial femoral condyle and patellar groove compartments. As early as 2 weeks post-DMM, cartilage thickness significantly increased and cartilage attenuation, SCP volume, and BMDD mean significantly decreased. Trends in cartilage and SCP metrics within each joint compartment reflected those seen in global measurements, and both BMDD and SCP thickness were consistently greater in the lateral and medial condyles than the patellar groove. Sham surgery also resulted in significant changes to SCP and cartilage metrics, highlighting a potential limitation of using surgical models to study tissue morphology or composition changes during OA progression. Contrast-enhanced μCT analysis is an effective tool to monitor changes in morphology and composition of cartilage, and when combined with bone-optimized μCT, can be used to assess the progression of degenerative changes after joint injury.

Extracellular vesicles in osteoarthritis of peripheral joint and temporomandibular joint

Osteoarthritis (OA) is a disabling disease with significant morbidity worldwide. OA attacks the large synovial joint, including the peripheral joints and temporomandibular joint (TMJ). As a representative of peripheral joint OA, knee OA shares similar symptoms with TMJ OA. However, these two joints also display differences based on their distinct development, anatomy, and physiology. Extracellular vesicles (EVs) are phospholipid bilayer nanoparticles, including exosomes, microvesicles, and apoptotic bodies. EVs contain proteins, lipids, DNA, micro-RNA, and mRNA that regulate tissue homeostasis and cell-to-cell communication, which play an essential role in the progression and treatment of OA. They are likely to partake in mechanical response, extracellular matrix degradation, and inflammatory regulation during OA. More evidence has shown that synovial fluid and synovium-derived EVs may serve as OA biomarkers. More importantly, mesenchymal stem cell-derived EV shows a therapeutic effect on OA. However, the different function of EVs in these two joints is largely unknown based on their distinct biological characteristic. Here, we reviewed the effects of EVs in OA progression and compared the difference between the knee joint and TMJ, and summarized their potential therapeutic role in the treatment of OA.

Mineral Crystal Thickness in Calcified Cartilage and Subchondral Bone in Healthy and Osteoarthritic Human Knees

Osteoarthritis (OA) is the most common joint disease, where articular cartilage degradation is often accompanied with sclerosis of the subchondral bone. However, the association between OA and tissue mineralization at the nanostructural level is currently not understood. In particular, it is technically challenging to study calcified cartilage, where relevant but poorly understood pathological processes such as tidemark multiplication and advancement occur. Here, we used state-of-the-art microfocus small-angle X-ray scattering with a 5-μm spatial resolution to determine the size and organization of the mineral crystals at the nanostructural level in human subchondral bone and calcified cartilage. Specimens with a wide spectrum of OA severities were acquired from both medial and lateral compartments of medial compartment knee OA patients (n = 15) and cadaver knees (n = 10). Opposing the common notion, we found that calcified cartilage has thicker and more mutually aligned mineral crystals than adjoining bone. In addition, we, for the first time, identified a well-defined layer of calcified cartilage associated with pathological tidemark multiplication, containing 0.32 nm thicker crystals compared to the rest of calcified cartilage. Finally, we found 0.2 nm thicker mineral crystals in both tissues of the lateral compartment in OA compared with healthy knees, indicating a loading-related disease process because the lateral compartment is typically less loaded in medial compartment knee OA. In summary, we report novel changes in mineral crystal thickness during OA. Our data suggest that unloading in the knee might be involved with the growth of mineral crystals, which is especially evident in the calcified cartilage. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Roles of the calcified cartilage layer and its tissue engineering reconstruction in osteoarthritis treatment

Sandwiched between articular cartilage and subchondral bone, the calcified cartilage layer (CCL) takes on both biomechanical and biochemical functions in joint development and ordinary activities. The formation of CCL is not only unique in articular cartilage but can also be found in the chondro-osseous junction adjacent to the growth plate during adolescence. The formation of CCL is an active process under both cellular regulation and intercellular communication. Abnormal alterations of CCL can be indications of degenerative diseases including osteoarthritis. Owing to the limited self-repair capability of articular cartilage and core status of CCL in microenvironment maintenance, tissue engineering reconstruction of CCL in damaged cartilage can be of great significance. This review focuses on possible tissue engineering reconstruction methods targeting CCL for further OA treatment.

Meniscus surface texture is associated with degenerative changes in biological and biomechanical properties

Meniscal degeneration is defined by semi-quantitative assessment of multiple histological findings and has been implicated in biomechanical dysfunction, yet little is known about its relationship with biological properties. This paper aimed to quantitatively evaluate degenerative findings in human meniscus to examine their relationship with gene expression and biomechanical properties, and to extract histological findings that reflect biological properties like gene expression and cytokine secretion. This study included lateral menisci of 29 patients who underwent total knee arthroplasty. The menisci were divided into six samples. For each sample, Pauli's histological evaluation and corresponding quantitative assessment (surface roughness, DNA content, collagen orientation, and GAG content) were performed, with surface roughness showing the highest correlation with the histological evaluation in a single correlation analysis (r = 0.66, p < 0.0001) and multivariate analysis (p < 0.0001). Furthermore, surface roughness was associated with gene expression related to meniscal degeneration and with tangent modulus which decreases with increasing degeneration (r = - 0.49, p = 0.0002). When meniscal tissue was classified by surface integrity, inflammatory cytokine secretion tended to be higher in severe degenerated menisci. These results suggest that the evaluation of meniscal surface texture could predict the degree of degeneration and inflammatory cytokine secretion.

Neratinib Exerts Dual Effects on Cartilage Degradation and Osteoclast Production in Osteoarthritis by Inhibiting the Activation of the MAPK/NF-κB Signaling Pathways

Osteoarthritis (OA) is a degenerative disease caused by the progressive destruction of cartilage and subchondral bone. [1] Studies have shown that by inhibiting the degradation of cartilage cells and the loss of subchondral bone, OA can be prevented and treated. Neratinib, as a small molecule compound with anti-inflammatory and anti-tumor properties, is a very effective inhibitor of IL-1β-induced chondrocyte inflammation and anabolic metabolism. By investigating the effect of neratinib in ATDC5 chondrocytes, the study finds that neratinib reduces inflammation by inhibiting the MAPK and NF-κB signaling pathways, and at the same time reduces pyrolysis (indicated by the results of reverse transcription quantitative PCR and western blotting). For anabolic metabolism, after high-density cell culture, IL-1β-induced catalytic changes and degradation of the extracellular matrix were evaluated by toluidine blue staining. Since osteoclasts are key participants in the process of subchondral bone remodeling in OA, we also studied the effect of neratinib on the maturation of osteoclasts. The results showed that neratinib also acts as an anti-osteoclast agent in vitro. By inhibiting the NF-κB and MAPK pathways, it reduces the expression of osteoclast-related genes, thereby inhibiting RANKL-induced osteoclastogenesis. The results of in vivo animal experiments supported the conclusions from the experiments in vitro. Neratinib inhibited both the destruction of medial meniscus induced cartilage degradation and osteoclast formation, which proves that neratinib has a dual effect, protecting cartilage and inhibiting osteoclast formation. These results indicate that neratinib can be a brand-new latent strategy for the treatment of OA.

Metformin alleviates osteoarthritis in mice by inhibiting chondrocyte ferroptosis and improving subchondral osteosclerosis and angiogenesis

BACKGROUND

Osteoarthritis (OA) is the most common musculoskeletal disease, and it has a complex pathology and unknown pathogenesis. Chondrocyte ferroptosis is closely associated with the development of OA. As a common drug administered for the treatment of type 2 diabetes, metformin (Met) is known to inhibit the development of ferroptosis. However, its therapeutic effect in OA remains unknown. The present study aimed to explore the effects of Met on cartilage and subchondral bone in a mouse OA model and to explore the potential underlying mechanisms.

METHODS

A mouse OA model was induced using destabilization of the medial meniscus (DMM) surgery, chondrocyte ferroptosis was induced using an intra-articular injection of Erastin, and Met (200 mg/kg/day) was intragastrically administered for 8 weeks after surgery. H&E and Safranin O‑fast green staining were used to evaluate cartilage degeneration, and μ‑computed tomography was used to evaluate changes in subchondral bone microarchitecture. Moreover, immunohistochemical staining was performed to detect mechanistic metalloproteinases 13, type II collagen, glutathione peroxidase 4, acyl-CoA synthetase long-chain family member 4, solute carrier family 7 member 11 and p53. Runt-associated transcription factor 2 and CD31 were detected using immunofluorescent staining.

RESULTS

Met protected articular cartilage and reversed the abnormal expression of ferroptosis-related proteins in the chondrocytes of DMM mice. Moreover, intra-articular injection of Erastin induced ferroptosis in mouse chondrocytes, and Met eliminated the ferroptosis effects induced by Erastin and protected articular cartilage. In addition, the results of the present study demonstrated that Met alleviated the microstructural changes of subchondral osteosclerosis and reduced heterotypic angiogenesis in DMM mice.

CONCLUSION

Met alleviates the pathological changes of OA by inhibiting ferroptosis in OA chondrocytes, alleviating subchondral sclerosis and reducing abnormal angiogenesis in subchondral bone in advanced OA.

Feasibility of ultrashort echo time (UTE) T2* cartilage mapping in the hip: a pilot study

BACKGROUND

Ultrashort echo time (UTE) T2* is sensitive to molecular changes within the deep calcified layer of cartilage. Feasibility of its use in the hip needs to be established to determine suitability for clinical use.

PURPOSE

To establish feasibility of UTE T2* cartilage mapping in the hip and determine if differences in regional values exist.

MATERIAL AND METHODS

MRI scans with UTE T2* cartilage maps were prospectively acquired on eight hips. Hip cartilage was segmented into whole and deep layers in anterosuperior, superior, and posterosuperior regions. Quantitative UTE T2* maps were analyzed (independent one-way ANOVA) and reliability was calculated (ICC).

RESULTS

UTE T2* mean values (anterosuperior, superior, posterosuperior): full femoral layer (19.55, 18.43, 16.84 ms) (P=0.004), full acetabular layer (19.37, 17.50, 16.73 ms) (P=0.013), deep femoral layer (18.68, 17.90, 15.74 ms) (P=0.010), and deep acetabular layer (17.81, 16.18, 15.31 ms) (P=0.007). Values were higher in anterosuperior compared to posterosuperior regions (mean difference; 95% confidence interval [CI]): full femur layer (2.71 ms; 95% CI 0.91-4.51: P=0.003), deep femur layer (2.94 ms; 95% CI 0.69-5.19; P=0.009), full acetabular layer (2.63 ms 95% CI 0.55-4.72; P=0.012), and deep acetabular layer (2.50 ms; 95% CI 0.69-4.30; P=0.006). Intra-reader (ICC 0.89-0.99) and inter-reader reliability (ICC 0.63-0.96) were good to excellent for the majority of cartilage layers.

CONCLUSION

UTE T2* cartilage mapping was feasible in the hip with mean values in the range of 16.84-19.55 ms in the femur and 16.73-19.37 ms in the acetabulum. Significantly higher values were present in the anterosuperior region compared to the posterosuperior region.

Characterization of Changes in Subchondral Bone Tissue Density of the Ankle Joint in Taekwondo Players

Background: It has been found that ankle joint impingement can cause articular cartilage injury, and the change of subchondral bone density and distribution under long-term stress loading can reflect the stress interaction of the articular surface and the difference in bone remodeling degree and predict the location of cartilage injury.

Objective: To investigate the bone density distribution pattern of ankle joint subchondral bone under mechanical stress loading of Taekwondo, the volume proportion of bone tissue with different bone densities, and the distribution characteristics of bone remodeling position.

Study design: A controlled laboratory study.

Methods: Computed tomography data were collected from the feet of 10 normal subjects (control group) and 10 high-level Taekwondo athletes. First, the distribution pattern of the high-density area of the articular surface was determined by computed tomography osteoabsorptiometry and the nine-grid anatomical region localization method. Second, the percentage of bone volume (%BTV) and the distribution trend of bone tissue were measured.

Result: In the present study, it was found that there were high-density areas in the 1st, 2nd, 3rd, 4th, 6th, 7th, and 9th regions of the distal tibia of Taekwondo athletes, and the distribution track was consistent with the high-density areas of the talar dome surface (1st, 2nd, 3rd, 4th, 6th, 7th, and 9th regions). In Taekwondo athletes, the percentage of bone tissue volume in the distal tibia and talus with high and moderate bone density was significantly higher than that in the control group (p < 0.05).

Conclusion: The impact stress, ground reaction force, intra-articular stress, lower limb movement technology, lower limb muscle, and tendon stress caused by Taekwondo lead to special pressure distribution patterns and bone tissue remodeling in the ankle.

Diterbutyl phthalate attenuates osteoarthritis in ACLT mice via suppressing ERK/c-fos/NFATc1 pathway, and subsequently inhibiting subchondral osteoclast fusion

Osteoarthritis (OA) is the most common arthritis with a rapidly increasing prevalence. Disease progression is irreversible, and there is no curative therapy available. During OA onset, abnormal mechanical loading leads to excessive osteoclastogenesis and bone resorption in subchondral bone, causing a rapid subchondral bone turnover, cyst formation, sclerosis, and finally, articular cartilage degeneration. Moreover, osteoclast-mediated angiogenesis and sensory innervation in subchondral bone result in abnormal vascularization and OA pain. The traditional Chinese medicine Panax notoginseng (PN; Sanqi) has long been used in treatment of bone diseases including osteoporosis, bone fracture, and OA. In this study we established two-dimensional/bone marrow mononuclear cell/cell membrane chromatography/time of flight mass spectrometry (2D/BMMC/CMC/TOFMS) technique and discovered that diterbutyl phthalate (DP) was the active constituent in PN inhibiting osteoclastogenesis. Then we explored the therapeutic effect of DP in an OA mouse model with anterior cruciate ligament transaction (ACLT). After ACLT was conducted, the mice received DP (5 mg·kg^-1·d^-1, ip) for 8 weeks. Whole knee joint tissues of the right limb were harvested at weeks 2, 4, and 8 for analysis. We showed that DP administration impeded overactivated osteoclastogenesis in subchondral bone and ameliorated articular cartilage deterioration. DP administration blunted aberrant H-type vessel formation in subchondral bone marrow and alleviated OA pain assessed in Von Frey test and thermal plantar test. In RANKL-induced RAW264.7 cells in vitro, DP (20 μM) retarded osteoclastogenesis by suppressing osteoclast fusion through inhibition of the ERK/c-fos/NFATc1 pathway. DP treatment also downregulated the expression of dendritic cell-specific transmembrane protein (DC-STAMP) and d2 isoform of the vacuolar (H+) ATPase V0 domain (Atp6v0d2) in the cells. In conclusion, we demonstrate that DP prevents OA progression by inhibiting abnormal osteoclastogenesis and associated angiogenesis and neurogenesis in subchondral bone.

Nangibotide attenuates osteoarthritis by inhibiting osteoblast apoptosis and TGF-β activity in subchondral bone

Osteoarthritis (OA) is a chronic joint disorder that causes cartilage degradation and subchondral bone abnormalities. Nangibotide, also known as LR12, is a dodecapeptide with considerable anti-inflammatory properties, but its significance in OA is uncertain. The aim of the study was to determine whether nangibotide could attenuate the progression of OA, and elucidate the underlying mechanism. In vitro experiments showed that nangibotide strongly inhibited TNF-α-induced osteogenic reduction, significantly enhanced osteoblast proliferation and prevented apoptosis in MC3T3-E1 cells. Male C57BL/6 J mice aged 2 months were randomly allocated to three groups: sham, ACLT, and ACLT with nangibotide therapy. Nangibotide suppressed ACLT-induced cartilage degradation and MMP-13 expression. MicroCT analysis revealed that nangibotide attenuated in vivo subchondral bone loss induced by ACLT. Histomorphometry results showed that nangibotide attenuated ACLT-induced osteoblast inhibition; TUNEL assays and immunohistochemical staining of cleaved-caspase3 further confirmed the in vivo anti-apoptotic effect of nangibotide on osteoblasts. Furthermore, we found that nangibotide exerted protective effects by suppressing TGF-β signaling mediated by Smad2/3 to restore coupled bone remodeling in the subchondral bone. In conclusion, the findings suggest that nangibotide might exert a protective effect on the bone-cartilage unit and maybe an alternative treatment option for OA.

Alterations of the Subchondral Bone in Osteoarthritis: Complying with Wolff's law

Osteoarthritis (OA) is a whole joint disease that is significantly related to abnormal mechanical loads. Subchondral bone alterations, during the evolution course of OA, are considered as a reflection of adaptation of the bone tissue to mechanical loads. However, some of these alterations are taken as detriment and paradoxical. What are these structure, composition, and mechanical property alterations or mechanical functions for are not quite clear. In this review, we evaluate the possibility that these alterations are used for maintaining joint function. With taking excessive load as a risk factor and under conditions of articular cartilage gradually loss its thickness and its function of evenly distributing load on subchondral bone plate, and applying poroelasticity. Moreover, Boussinesq's pressure bulb theory and bone optimal design principles are utilized for bone mechanics. We found that each subchondral bone alteration has its unique mechanical function in resisting loads and maintaining joint function, and these alterations comply with both bone optimal design principles and Wolff's law within a proper range.

PGE2 activates EP4 in subchondral bone osteoclasts to regulate osteoarthritis

Prostaglandin E2 (PGE2), a major cyclooxygenase-2 (COX-2) product, is highly secreted by the osteoblast lineage in the subchondral bone tissue of osteoarthritis (OA) patients. However, NSAIDs, including COX-2 inhibitors, have severe side effects during OA treatment. Therefore, the identification of novel drug targets of PGE2 signaling in OA progression is urgently needed. Osteoclasts play a critical role in subchondral bone homeostasis and OA-related pain. However, the mechanisms by which PGE2 regulates osteoclast function and subsequently subchondral bone homeostasis are largely unknown. Here, we show that PGE2 acts via EP4 receptors on osteoclasts during the progression of OA and OA-related pain. Our data show that while PGE2 mediates migration and osteoclastogenesis via its EP2 and EP4 receptors, tissue-specific knockout of only the EP4 receptor in osteoclasts (EP4^LysM) reduced disease progression and osteophyte formation in a murine model of OA. Furthermore, OA-related pain was alleviated in the EP4^LysM mice, with reduced Netrin-1 secretion and CGRP-positive sensory innervation of the subchondral bone. The expression of platelet-derived growth factor-BB (PDGF-BB) was also lower in the EP4^LysM mice, which resulted in reduced type H blood vessel formation in subchondral bone. Importantly, we identified a novel potent EP4 antagonist, HL-43, which showed in vitro and in vivo effects consistent with those observed in the EP4^LysM mice. Finally, we showed that the Gαs/PI3K/AKT/MAPK signaling pathway is downstream of EP4 activation via PGE2 in osteoclasts. Together, our data demonstrate that PGE2/EP4 signaling in osteoclasts mediates angiogenesis and sensory neuron innervation in subchondral bone, promoting OA progression and pain, and that inhibition of EP4 with HL-43 has therapeutic potential in OA.

Associations between serum biomarkers of cartilage metabolism and serum hyaluronic acid, with risk factors, pain categories, and disease severity in knee osteoarthritis: a pilot study

BACKGROUND

Specific serum biomarkers of cartilage metabolism such as cartilage oligomeric matrix protein (sCOMP) and procollagen type II C-terminal propeptide (sPIICP) as well as hyaluronan (sHA), a biomarker of synovitis, have been implicated in the pathophysiology of knee osteoarthritis (OA). However, the associations of these biomarkers with the severity of the disease and OA risk factors, including age and obesity remain inconclusive. This analysis examines the associations between these serum biomarkers and the radiographic severity of OA and knee pain, as wells as obesity, the age and gender of the participants, and other OA risk factors.

METHODS

From 44 patients with early knee OA and 130 patients with late knee OA we analyzed the radiographic severity of the disease using the Kellgren and Lawrence (KL) grading system. Moreover, 38 overweight healthy individuals were used as a control group. Specific information was collected from all participants during their recruitment. The levels of the three serum biomarkers were quantified using commercially available ELISA kits. Serum biomarkers were analyzed for associations with the average KL scores and pain in both knees, as well as with specific OA risk factors.

RESULTS

The levels of sCOMP were elevated in patients with severe late OA and knee pain and correlated weakly with OA severity. A weakly correlation of sHA levels and OA severity OA was observed. We demonstrated that only sPIICP levels were markedly decreased in patients with late knee OA suggesting the alterations of cartilage metabolism in this arthritic disease. Moreover, we found that sPIICP has the strongest correlation with obesity and the severity of OA, as well as with the knee pain at rest and during walking regardless of the severity of the disease. ROC analysis showed that the area under the ROC curve (AUC) was 0.980 (95% CI: 0.945-0.995; p < 0.0001), suggesting high diagnostic accuracy of sPIICP. Interestingly, gender and age had also an effect on the levels of sPIICP.

CONCLUSION

This study revealed the potential of serum PIICP to be used as a biomarker to monitor the progression of knee OA, however, further studies are warranted to elucidate its clinical implication.

Subchondral bone plate thickness is associated with micromechanical and microstructural changes in the bovine patella osteochondral junction with different levels of cartilage degeneration

The influence of joint degeneration on the biomechanical properties of calcified cartilage and subchondral bone plate at the osteochondral junction is relatively unknown. Common experimental difficulties include accessibility to and visualization of the osteochondral junction, application of mechanical testing at the appropriate length scale, and availability of tissue that provides a consistent range of degenerative changes. This study addresses these challenges. A well-established bovine patella model of early joint degeneration was employed, in which micromechanical testing of fully hydrated osteochondral sections was carried out in conjunction with high-resolution imaging using differential interference contrast (DIC) optical light microscopy. A total of forty-two bovine patellae with different grades of tissue health ranging from healthy to mild, moderate, and severe cartilage degeneration, were selected. From the distal-lateral region of each patella, two adjacent osteochondral sections were obtained for the mechanical testing and the DIC imaging, respectively. Mechanical testing was carried out using a robotic micro-force acquisition system, applying compression tests over an array (area: 200 μm × 1000 μm, step size: 50 μm) across the osteochondral junction to obtain a stiffness map. Morphometric analysis was performed for the DIC images of fully hydrated cryo-sections. The levels of cartilage degeneration, DIC images, and the stiffness maps were used to associate the mechanical properties onto the specific tissue regions of cartilage, calcified cartilage, and subchondral bone plate. The results showed that there were up to 20% and 24% decreases (p < 0.05) in the stiffness of calcified cartilage and subchondral bone plate, respectively, in the severely degenerated group compared to the healthy group. Furthermore, there were increases (p < 0.05) in the number of tidemarks, bone spicules at the cement line, and the mean thickness of the subchondral bone plate with increasing levels of degeneration. The decreasing stiffness in the subchondral bone plate coupled with the presence of bone spicules may be indicative of a subchondral remodeling process involving new bone formation. Moreover, the mean thickness of the subchondral bone plate was found to be the strongest indicator of mechanical and associated structural changes in the osteochondral joint tissues.

Farnesoid X receptor agonist attenuates subchondral bone osteoclast fusion and osteochondral pathologies of osteoarthritis via suppressing JNK1/2/NFATc1 pathway

Osteoarthritis (OA) is a prevalent degenerative disease of the joint, featured by articular cartilage destruction and subchondral bone marrow lesions. Articular cartilage and subchondral bone constitute an osteochondral unit that guarantees joint homeostasis. During OA initiation, activated osteoclasts in subchondral bone ultimately result in impaired capacities of the subchondral bone in response to mechanical stress, followed by the degradation of overlying articular cartilage. Thus, targeting osteoclasts could be a potential therapeutic option for treating OA. Here, we observed that farnesoid X receptor (FXR) expression and osteoclast fusion and activity in subchondral bone were concomitantly changed during early-stage OA in the OA mouse model established by anterior cruciate ligament transection (ACLT). Then, we explored the therapeutic effects of FXR agonist GW4064 on the osteochondral pathologies in ACLT mice. We showed that GW4064 obviously ameliorated subchondral bone deterioration, associated with reduction in tartrate-resistant acid phosphatase (TRAP) positive multinuclear osteoclast number, as well as articular cartilage degradation, which were blocked by the treatment with FXR antagonist Guggulsterone. Mechanistically, GW4064 impeded osteoclastogenesis through inhibiting subchondral bone osteoclast fusion via suppressing c-Jun N-terminal kinase (JNK) 1/2/nuclear factor of activated T-cells 1 (NFATc1) pathway. Taken together, our results present evidence for the protective effects of GW4064 against OA by blunting osteoclast-mediated aberrant subchondral bone loss and subsequent cartilage deterioration. Therefore, GW4064 demonstrates the potential as an alternative therapeutic option against OA for further drug development.

Senescent skeletal cells cross-talk with synovial cells plays a key role in the pathogenesis of osteoarthritis

Osteoarthritis (OA) has been recognized as an age-related degenerative disease commonly seen in the elderly that affects the whole “organ” including cartilage, subchondral bone, synovium, and muscles. An increasing number of studies have suggested that the accumulation of senescent cells triggering by various stresses in the local joint contributes to the pathogenesis of age-related diseases including OA. In this review, we mainly focus on the role of the senescent skeletal cells (chondrocytes, osteoblasts, osteoclasts, osteocyte, and muscle cells) in initiating the development and progression of OA alone or through cross-talk with the macrophages/synovial cells. Accordingly, we summarize the current OA-targeted therapies based on the abovementioned theory, e.g., by eliminating senescent skeletal cells and/or inhibiting the senescence-associated secretory phenotype (SASP) that drives senescence. Furthermore, the existing animal models for the study of OA from the perspective of senescence are highlighted to fill the gap between basic research and clinical applications. Overall, in this review, we systematically assess the current understanding of cellular senescence in OA, which in turn might shed light on the stratified OA treatments.

Antinociceptive and chondroprotective effects of prolonged β-caryophyllene treatment in the animal model of osteoarthritis: Focus on tolerance development

Osteoarthritis (OA) is a chronic joint disease in which cartilage degeneration leads to chronic pain. The endocannabinoid system has attracted attention as an emerging drug target for OA. However, the therapeutic potential of cannabinoids is limited by psychoactive side-effects related to CB1 activation and tolerance development for analgesic effects. β-Caryophyllene (BCP) is a low-efficacy natural agonist of CB2 and a common constituent of human diet with well-established anti-inflammatory properties. The results presented herein show the anti-nociceptive and chondroprotective potential of BCP in an animal model of OA induced by intra-articular injection of monoiodoacetate (MIA). Behavioural assessment included pressure application measurement and kinetic weight bearing tests. Histological assessment of cartilage degeneration was quantified using OARSI scoring. Experiments established the dose-response effects of BCP and pharmacological mechanisms of the antinociceptive action dependent on CB2 and opioid receptors. Chronic BCP treatment was able to hamper cartilage degeneration without producing tolerance for the analgesic effects. The data presented herein show that BCP is able to produce both acute and prolonged antinociceptive and chondroprotective effects. Together with the safety profile and legal status of BCP, these results indicate a novel and promising disease-modifying strategy for treating OA.

Exploring the translational potential of clusterin as a biomarker of early osteoarthritis

BACKGROUND

Clusterin (CLU; also known as apolipoprotein J) is an ATP-independent holdase chaperone that prevents proteotoxicity as a consequence of protein aggregation. It is a ∼60 kDa disulfide-linked heterodimeric protein involved in the clearance of cellular debris and the regulation of apoptosis. CLU has been proposed to protect cells from cytolysis by complement components and has been implicated in Alzheimer's disease due to its ability to bind amyloid-β peptides and prevent aggregate formation in the brain. Recent studies suggest that CLU performs moonlighting functions. CLU exists in two major forms: an intracellular form and a secreted extracellular form. The intracellular form of CLU may suppress stress-induced apoptosis by forming complexes with misfolded proteins and facilitates their degradation. The secreted form of CLU functions as an extracellular chaperone that prevents protein aggregation.

METHODS

In this review, we discuss the published literature on the biology of CLU in cartilage, chondrocytes, and other synovial joint tissues. We also review clinical studies that have examined the potential for using this protein as a biomarker in synovial and systemic fluids of patients with rheumatoid arthritis (RA) or osteoarthritis (OA).

RESULTS

Since CLU functions as an extracellular chaperone, we propose that it may be involved in cytoprotective functions in osteoarticular tissues. The secreted form of CLU can be measured in synovial and systemic fluids and may have translational potential as a biomarker of early repair responses in OA.

CONCLUSION

There is significant potential for investigating synovial and systemic CLU as biomarkers of OA. Future translational and clinical orthopaedic studies should carefully consider the diverse roles of this protein and its involvement in other comorbidities. Therefore, future biomarker studies should not correlate circulating CLU levels exclusively to the process of OA pathogenesis and progression. Special attention should be paid to CLU levels in synovial fluid.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE

There is significant potential for investigating synovial and systemic CLU as a predictive biomarker of osteoarthritis (OA) progression and response to novel treatments and interventions. Given that CLU plays diverse roles in other comorbidities such as rheumatoid arthritis (RA) and obesity, future translational and clinical orthopaedic biomarker studies should not directly correlate circulating CLU levels to the process of OA pathogenesis and progression. However, special attention should be paid to CLU levels in synovial fluid. The cytoprotective properties of CLU may support the implementation of regenerative strategies and new approaches for developing targeted therapeutics for OA.

Effect of Suppression of Rotational Joint Instability on Cartilage and Meniscus Degeneration in Mouse Osteoarthritis Model

OBJECTIVE

Joint instability and meniscal dysfunction contribute to the onset and progression of knee osteoarthritis (OA). In the destabilization of the medial meniscus (DMM) model, secondary OA occurs due to the rotational instability and increases compressive stress resulting from the meniscal dysfunction. We created a new controlled abnormal tibial rotation (CATR) model that reduces the rotational instability that occurs in the DMM model. So, we aimed to investigate whether rotational instability affects articular cartilage degeneration using the DMM and CATR models, as confirmed using histology and immunohistochemistry.

DESIGN

Twelve-week-old male mice were randomized into 3 groups: DMM group, CATR group, and INTACT group (right knee of the DMM group). After 8 and 12 weeks, we performed the tibial rotational test, safranin-O/fast green staining, and immunohistochemical staining for tumor necrosis factor (TNF)-α and metalloproteinase (MMP)-13.

RESULTS

The rotational instability in the DMM group was significantly higher than that of the other groups. And articular cartilage degeneration was higher in the DMM group than in the other groups. However, meniscal degeneration was observed in both DMM and CATR groups. The TNF-α and MMP-13 positive cell rates in the articular cartilage of the CATR group were lower than those in the DMM group.

CONCLUSIONS

We found that the articular cartilage degeneration was delayed by controlling the rotational instability caused by meniscal dysfunction. These findings suggest that suppression of rotational instability in the knee joint may be an effective therapeutic measure for preventing OA progression.