Mechanisms of disease: role of chondrocytes in the pathogenesis of osteoarthritis--structure, chaos and senescence

Predisposal of Interferon Regulatory Factor 1 Deficiency to Accumulate DNA Damage and Promote Osteoarthritis Development in Cartilage

OBJECTIVE

Interferon regulatory factor 1 (IRF1) is a transcriptional regulator conventionally associated with immunomodulation. Recent molecular analyses mapping DNA binding sites of IRF1 have suggested its potential function in DNA repair. However, the physiologic significance of this noncanonical function remains unexplored. Here, we investigated the role of IRF1 in osteoarthritis (OA), a condition marked by senescence and chronic joint inflammation.

METHODS

OA progression was examined in wild-type and Irf1-/- mice using histologic assessments and microcomputed tomography analysis of whole-joint OA manifestations and behavioral assessments of joint pain. An integrated analysis of assay for transposase-accessible chromatin with sequencing and whole transcriptome data was conducted for the functional assessment of IRF1 in chondrocytes. The role of IRF1 in DNA repair and senescence was investigated by assaying γ-H2AX foci and senescence-associated beta-galactosidase activity.

RESULTS

Our genome-wide investigation of IRF1 footprinting in chondrocytes revealed its primary occupancies in the promoters of DNA repair genes without noticeable footprint patterns in those of interferon-responsive genes. Chondrocytes lacking IRF1 accumulated irreversible DNA damage under oxidative stress, facilitating their entry into cellular senescence. IRF1 was down-regulated in the cartilage of human and mouse OA. Although IRF1 overexpression did not elicit an inflammatory response in joints or affect OA development, genetic deletion of Irf1 caused enhanced chondrocyte senescence and exacerbated post-traumatic OA in mice.

CONCLUSION

IRF1 offers DNA damage surveillance in chondrocytes, protecting them from oxidative stress associated with OA risk factors. Our study provides a crucial and cautionary perspective that compromising IRF1 activity renders chondrocytes vulnerable to cellular senescence and promotes OA development.

Characterization of clinical data for patient stratification in moderate osteoarthritis with support vector machines, regulatory network models, and verification against osteoarthritis Initiative data

Knee osteoarthritis (OA) diagnosis is based on symptoms, assessed through questionnaires such as the WOMAC. However, the inconsistency of pain recording and the discrepancy between joint phenotype and symptoms highlight the need for objective biomarkers in knee OA diagnosis. To this end, we study relationships among clinical and molecular data in a cohort of women (n = 51) with Kellgren-Lawrence grade 2-3 knee OA through a Support Vector Machine (SVM) and a regulation network model. Clinical descriptors (i.e., pain catastrophism, depression, functionality, joint pain, rigidity, sensitization and synovitis) are used to classify patients. A Youden's test is performed for each classifier to determine optimal binarization thresholds for the descriptors. Thresholds are tested against patient stratification according to baseline WOMAC data from the Osteoarthritis Initiative, and the mean accuracy is 0.97. For our cohort, the data used as SVM inputs are knee OA descriptors, synovial fluid proteomic measurements (n = 25), and transcription factor activation obtained from regulatory network model stimulated with the synovial fluid measurements. The relative weights after classification reflect input importance. The performance of each classifier is evaluated through ROC-AUC analysis. The best classifier with clinical data is pain catastrophism (AUC = 0.9), highly influenced by funcionality and pain sensetization, suggesting that kinesophobia is involved in pain perception. With synovial fluid proteins used as input, leptin strongly influences every classifier, suggesting the importance of low-grade inflammation. When transcription factors are used, the mean AUC is limited to 0.608, which can be related to the pleomorphic behaviour of osteoarthritic chondrocytes. Nevertheless, funcionality has an AUC of 0.7 with a decisive importance of FOXO downregulation. Though larger and longitudinal cohorts are needed, this unique combination of SVM and regulatory network model shall help to stratify knee OA patients more objectively.

Osteoarthritis, adipokines and the translational research potential in small animal patients

Osteoartritis (OA) is a debilitating disease affecting both humans and animals. In the early stages, OA is characterized by damage to the extracellular matrix (ECM) and apoptosis and depletion of chondrocytes. OA progression is characterized by hyaline cartilage loss, chondrophyte and osteophyte formation, thickening of the joint capsule and function loss in the later stages. As the regenerative potential of cartilage is very limited and osteoarthritic changes are irreversible, prevention of OA, modulation of existing osteoarthritic joint inflammation, reducing joint pain and supporting joint function are the only options. Progression of OA and pain may necessitate surgical intervention with joint replacement or arthrodesis as end-stage procedures. In human medicine, the role of adipokines in the development and progression of OA has received increasing interest. At present, the known adipokines include leptin, adiponectin, visfatin, resistin, progranulin, chemerin, lipocalin-2, vaspin, omentin-1 and nesfatin. Adipokines have been demonstrated to play a pivotal role in joint homeostasis by modulating anabolic and catabolic balance, autophagy, apoptosis and inflammatory responses. In small animals, in terms of dogs and cats, naturally occurring OA has been clearly demonstrated as a clinical problem. Similar to humans, the etiology of OA is multifactorial and has not been fully elucidated. Humans, dogs and cats share many joint related degenerative diseases leading to OA. In this review, joint homeostasis, OA, adipokines and the most common joint diseases in small animals leading to naturally occurring OA and their relation with adipokines are discussed. The purpose of this review is highlighting the translational potential of OA and adipokines research in small animal patients.

SKP2-mediated ubiquitination and degradation of KLF11 promotes osteoarthritis via modulation of JMJD3/NOTCH1 pathway

Osteoarthritis (OA) is the main cause of cartilage damage and disability. This study explored the biological function of S-phase kinase-associated protein 2 (SKP2) and Kruppel-like factor 11 (KLF11) in OA progression and its underlying mechanisms. C28/I2 chondrocytes were stimulated with IL-1β to mimic OA in vitro. We found that SKP2, Jumonji domain-containing protein D3 (JMJD3), and Notch receptor 1 (NOTCH1) were upregulated, while KLF11 was downregulated in IL-1β-stimulated chondrocytes. SKP2/JMJD3 silencing or KLF11 overexpression repressed apoptosis and extracellular matrix (ECM) degradation in chondrocytes. Mechanistically, SKP2 triggered the ubiquitination and degradation of KLF11 to transcriptionally activate JMJD3, which resulted in activation of NOTCH1 through inhibiting H3K27me3. What's more, the in vivo study found that KLF11 overexpression delayed OA development in rats via restraining apoptosis and maintaining the balance of ECM metabolism. Taken together, ubiquitination and degradation of KLF11 regulated by SKP2 contributed to OA progression by activation of JMJD3/NOTCH1 pathway. Our findings provide promising therapeutic targets for OA.

The role of autophagy in mitigating osteoarthritis progression via regulation of chondrocyte apoptosis: A review

Osteoarthritis (OA) is the most prevalent chronic joint disease with an immense socioeconomic burden; however, no treatment has achieved complete success in effectively halting or reversing cartilage degradation, which is the central pathophysiological feature of OA. Chondrocytes loss or dysfunction is a significant contributing factor to the progressive cartilage deterioration as these sole resident cells have a crucial role to produce extracellular matrix proteins, thus maintaining cartilage structure and homeostasis. It has been previously suggested that death of chondrocytes occurring through apoptosis substantially contributes to cartilage degeneration. Although the occurrence of apoptosis in osteoarthritic cartilage and its correlation with cartilage degradation is evident, the causes of chondrocyte apoptosis leading to matrix loss are still not well-understood. Autophagy, an intracellular degradative mechanism that eliminates dysfunctional cytoplasmic components to aid cell survival in unfavourable conditions, is a potential therapeutic target to inhibit chondrocyte apoptosis and reduce OA severity. Despite accumulating evidence indicating significant cytoprotective effects of autophagy against chondrocyte apoptosis, the mechanistic link between autophagy and apoptosis in chondrocytes remains to be further explored. In this review, we summarize the relevant mechanistic events that perpetuate chondrocyte apoptosis and highlight the prominent role of autophagy in modulating these events to mitigate OA progression.

MiR-98-5p plays suppressive effects on IL-1β-induced chondrocyte injury associated with osteoarthritis by targeting CASP3

BACKGROUND

This study aims to explore how miR-98-5p affects osteoarthritis, focusing on its role in chondrocyte inflammation, apoptosis, and extracellular matrix (ECM) degradation.

METHODS

Quantitative real-time PCR was used to measure miR-98-5p and CASP3 mRNA levels in OA cartilage tissues and IL-1β-treated CHON-001 cells. We predicted miR-98-5p and CASP3 binding sites using TargetScan and confirmed them via luciferase reporter assays. Chondrocyte viability was analyzed using CCK-8 assays, while pro-inflammatory cytokines (IL-1β, IL-6, TNF-α) were quantified via ELISA. Caspase-3 activity was examined to assess apoptosis, and Western blotting was conducted for protein marker quantification.

RESULTS

Our results showed lower miR-98-5p levels in both OA cartilage and IL-1β-stimulated cells. Increasing miR-98-5p resulted in reduced pro-inflammatory cytokines, decreased caspase-3 activity, and improved cell viability. Furthermore, miR-98-5p overexpression hindered IL-1β-induced ECM degradation, evident from the decline in MMP-13 and β-catenin levels, and an increase in COL2A1 expression. MiR-98-5p's impact on CASP3 mRNA directly influenced its expression. Mimicking miR-98-5p's effects, CASP3 knockdown also inhibited IL-1β-induced inflammation, apoptosis, and ECM degradation. In contrast, CASP3 overexpression negated the suppressive effects of miR-98-5p.

CONCLUSIONS

In conclusion, our data collectively suggest that miR-98-5p plays a protective role against IL-1β-induced damage in chondrocytes by targeting CASP3, highlighting its potential as a therapeutic target for OA.

5-aminosalicylic acid suppresses osteoarthritis through the OSCAR-PPARγ axis

Osteoarthritis (OA) is a progressive and irreversible degenerative joint disease that is characterized by cartilage destruction, osteophyte formation, subchondral bone remodeling, and synovitis. Despite affecting millions of patients, effective and safe disease-modifying osteoarthritis drugs are lacking. Here we reveal an unexpected role for the small molecule 5-aminosalicylic acid (5-ASA), which is used as an anti-inflammatory drug in ulcerative colitis. We show that 5-ASA competes with extracellular-matrix collagen-II to bind to osteoclast-associated receptor (OSCAR) on chondrocytes. Intra-articular 5-ASA injections ameliorate OA generated by surgery-induced medial-meniscus destabilization in male mice. Significantly, this effect is also observed when 5-ASA was administered well after OA onset. Moreover, mice with DMM-induced OA that are treated with 5-ASA at weeks 8-11 and sacrificed at week 12 have thicker cartilage than untreated mice that were sacrificed at week 8. Mechanistically, 5-ASA reverses OSCAR-mediated transcriptional repression of PPARγ in articular chondrocytes, thereby suppressing COX-2-related inflammation. It also improves chondrogenesis, strongly downregulates ECM catabolism, and promotes ECM anabolism. Our results suggest that 5-ASA could serve as a DMOAD.

Effect of vitamin D supplementation on circulating level of autophagosome protein LC3A, inflammation, and physical performance in knee osteoarthritis

Aberrant autophagic activity is observed in osteoarthritic joints. Vitamin D was shown to alleviate not only osteoarthritis severity, but also autophagy process. However, the influence of vitamin D on autophagy in knee osteoarthritis (KOA) remains ambiguous. This study aimed to determine the effect of vitamin D2 on serum levels of autophagosome protein LC3A in patients with KOA and whether LC3A levels were correlated with serum 25-hydroxyvitamin D (25(OH)D) and clinical outcomes of patients with KOA. A total of 165 patients with KOA and 25 healthy controls were recruited. Vitamin D2 (ergocalciferol) was administered to patients with KOA at a weekly dosage of 40,000 IU. Serum LC3A, knee pain and functional scores, muscle strength, physical performance, and biochemical parameters were examined before and after 6 months of vitamin D2 supplementation. Serum LC3A levels were significantly higher in patients with KOA than healthy controls. In patients with KOA, vitamin D2 supplementation significantly decreased serum LC3A levels. Furthermore, baseline levels of serum LC3A were significantly associated with radiographic severity, pain and functional scores, total cholesterol, hs-CRP, IL-6, protein carbonyl, and serum 25(OH)D. After adjusting for established confounders, independent relationships among serum LC3A and radiographic severity, pain and functional scores, total cholesterol, hs-CRP, IL-6, protein carbonyl, and serum 25(OH)D were also observed. Vitamin D2 supplementation was shown to not only decrease serum levels of LC3A, inflammatory markers, as well as oxidative stress, but also improve muscle strength and physical performance in patients with KOA.

A Review of the Role of Bioreactors for iPSCs-Based Tissue-Engineered Articular Cartilage

BACKGROUND

Osteoarthritis (OA) is the most common degenerative joint disease without an ultimate treatment. In a search for novel approaches, tissue engineering (TE) has shown great potential to be an effective way for hyaline cartilage regeneration and repair in advanced stages of OA. Recently, induced pluripotent stem cells (iPSCs) have been appointed to be essential stem cells for degenerative disease treatment because they allow a personalized medicine approach. For clinical translation, bioreactors in combination with iPSCs-engineerd cartilage could match patients needs, serve as platform for large-scale patient specific cartilage production, and be a tool for patient OA modelling and drug screening. Furthermore, to minimize in vivo experiments and improve cell differentiation and cartilage extracellular matrix (ECM) deposition, TE combines existing approaches with bioreactors.

METHODS

This review summarizes the current understanding of bioreactors and the necessary parameters when they are intended for cartilage TE, focusing on the potential use of iPSCs.

RESULTS

Bioreactors intended for cartilage TE must resemble the joint cavity niche. However, recreating human synovial joints is not trivial because the interactions between various stimuli are not entirely understood.

CONCLUSION

The use of mechanical and electrical stimulation to differentiate iPSCs, and maintain and test chondrocytes are key stimuli influencing hyaline cartilage homeostasis. Incorporating these stimuli to bioreactors can positively impact cartilage TE approaches and their possibility for posterior translation into the clinics.

Bulk RNA-seq analyses of mandibular condylar cartilage in a post-traumatic TMJ osteoarthritis rabbit model

OBJECTIVE

The temporomandibular joint (TMJ) is anatomically comprised of the mandibular condylar cartilage (CC) lined with fibrocartilaginous superficial zone and is crucial for eating and dental occlusion. TMJ osteoarthritis (OA) leads to pain, joint dysfunction and permanent loss of cartilage tissue. However, there are no drugs clinically available that ameliorate OA and little is known about global profiles of genes that contribute to TMJ OA. Furthermore, animal models that recapitulate the complexity of signalling pathways contributing to OA pathogenesis are crucial for designing novel biologics that thwart OA progression. We have previously developed a New Zealand white rabbit TMJ injury model that demonstrates CC degeneration. Here, we performed genome-wide profiling to identify new signalling pathways critical for cellular functions during OA pathology.

MATERIALS AND METHODS

Temporomandibular joint OA was surgically induced in New Zealand white rabbits. Three months following injury, we performed global gene expression profiling of the TMJ condyle. RNA samples from TMJ condyles were subjected to sequencing. After raw RNA-seq data were mapped to relevant genomes, differential expression was analysed with DESeq2. Gene ontology enrichment analysis and Kyoto Encyclopedia of Genes and Genomes pathway analysis were conducted.

RESULTS/CONCLUSIONS

Our study revealed multiple pathways altered during TMJ OA induction including the Wnt, Notch and PI3K-Akt signalling pathways. We demonstrate an animal model that recapitulates the complexity of the cues and signals underlying TMJ OA pathogenesis, which is essential for developing and testing novel pharmacologic agents to treat OA.

Inflammatory and Metabolic Signaling Interfaces of the Hypertrophic and Senescent Chondrocyte Phenotypes Associated with Osteoarthritis

Osteoarthritis (OA) is a complex disease of whole joints with progressive cartilage matrix degradation and chondrocyte transformation. The inflammatory features of OA are reflected in increased synovial levels of IL-1β, IL-6 and VEGF, higher levels of TLR-4 binding plasma proteins and increased expression of IL-15, IL-18, IL-10 and Cox2, in cartilage. Chondrocytes in OA undergo hypertrophic and senescent transition; in these states, the expression of Sox-9, Acan and Col2a1 is suppressed, whereas the expression of RunX2, HIF-2α and MMP-13 is significantly increased. NF-kB, which triggers many pro-inflammatory cytokines, works with BMP, Wnt and HIF-2α to link hypertrophy and inflammation. Altered carbohydrate metabolism and the upregulation of GLUT-1 contribute to the formation of end-glycation products that trigger inflammation via the RAGE pathway. In addition, a glycolytic shift, increased rates of oxidative phosphorylation and mitochondrial dysfunction generate reactive oxygen species with deleterious effects. An important surveyor mechanism, the YAP/TAZ signaling system, controls chondrocyte differentiation, inhibits ageing by protecting the nuclear envelope and suppressing NF-kB, MMP-13 and aggrecanases. The inflammatory microenvironment and synthesis of key matrix components are also controlled by SIRT1 and mTORc. Senescent chondrocytes represent the functional end stage of hypertrophic differentiation and characteristically upregulate p16 and p21, but also a variety of inflammatory cytokines, chemokines and metalloproteinases, developing the senescence-associated secretory phenotype. Senolysis with dendrobin, miR29b-5p and other agents has been shown to be efficient under experimental conditions, and appears to be a promising tool for the treatment of OA, as it restores COL2A1 and aggrecan synthesis, suppressing NF-kB and destructive metalloproteinases.

Lgr5-expressing secretory cells form a Wnt inhibitory niche in cartilage critical for chondrocyte identity

Osteoarthritis is a degenerative joint disease that causes pain, degradation, and dysfunction. Excessive canonical Wnt signaling in osteoarthritis contributes to chondrocyte phenotypic instability and loss of cartilage homeostasis; however, the regulatory niche is unknown. Using the temporomandibular joint as a model in multiple species, we identify Lgr5-expressing secretory cells as forming a Wnt inhibitory niche that instruct Wnt-inactive chondroprogenitors to form the nascent synovial joint and regulate chondrocyte lineage and identity. Lgr5 ablation or suppression during joint development, aging, or osteoarthritis results in depletion of Wnt-inactive chondroprogenitors and a surge of Wnt-activated, phenotypically unstable chondrocytes with osteoblast-like properties. We recapitulate the cartilage niche and create StemJEL, an injectable hydrogel therapy combining hyaluronic acid and sclerostin. Local delivery of StemJEL to post-traumatic osteoarthritic jaw and knee joints in rabbit, rat, and mini-pig models restores cartilage homeostasis, chondrocyte identity, and joint function. We provide proof of principal that StemJEL preserves the chondrocyte niche and alleviates osteoarthritis.

miR-5581 Contributes to Osteoarthritis by Targeting NRF1 to Disturb the Proliferation and Functions of Chondrocytes

Chondrocyte survival is critical for the preservation of a healthy cartilage matrix. Limited chondrocyte function and survival can result in articular cartilage failure, thereby contributing to osteoarthritis (OA). In this study, miR-5581 was significantly up-regulated in OA samples, and miR-5581-associated genes were enriched in Kras signaling. miR-5581 up-regulation was observed in clinical OA samples and IL-1β-stimulated chondrocytes. miR-5581 inhibition attenuated IL-1β-induced chondrocyte proliferation suppression, extracellular matrix (ECM) synthesis suppression and degradation, and IL-1β-suppressed Kras signaling activation. miR-5581 was targeted to inhibit NRF1. In IL-1β-treated chondrocytes, NRF1 overexpression attenuated IL-1β-induced cellular damage and partially abolished the effects of miR-5581 overexpression on IL-1β-stimulated chondrocytes. NRF1 was down-regulated in knee joint cartilage of OA mice. In conclusion, miR-5581, which was up-regulated in OA samples and IL-1β-stimulated chondrocytes, inhibited chondrocyte proliferation and ECM synthesis, and promoted ECM degradation through targeting NRF1, whereby Kras signaling might be involved.

Apoptosis Regulation in Osteoarthritis and the Influence of Lipid Interactions

Osteoarthritis (OA) is one of the most common chronic diseases in human and animal joints. The joints undergo several morphological and histological changes during the development of radiographically visible osteoarthritis. The most discussed changes include synovial inflammation, the massive destruction of articular cartilage and ongoing joint destruction accompanied by massive joint pain in the later stadium. Either the increased apoptosis of chondrocytes or the insufficient apoptosis of inflammatory macrophages and synovial fibroblasts are likely to underly this process. In this review, we discuss the current state of research on the pathogenesis of OA with special regard to the involvement of apoptosis.

Reduction of systemic exposure and side effects by intra-articular injection of anti-inflammatory agents for osteoarthritis: what is the safer strategy?

Osteoarthritis (OA) is a chronic degenerative joint disease associated with pain, inflammation, and cartilage degradation. However, no current treatment can effectively halt the progression of the disease. Therefore, the use of NSAIDs and intra-articular corticosteroids is usually recommended as the primary treatment for OA-associated pain and inflammation. However, there is accumulating evidence that the long-term use of oral NSAIDs and intra-articular corticosteroids can lead to a myriad of negative side effects. Although numerous efforts have been made to develop intra-articular formulations for NSAIDs, the systemic exposure of intra-articular injection of NSAIDs and its potential side effects have not been explicitly investigated. To ascertain the evident and potential side effects of intra-articular injection of anti-inflammatory agents, we have summarised in this review the systemic exposure, local side effects, and systemic side effects of intra-articular injections of anti-inflammatory agents, including NSAIDs and corticosteroids. For developing a safer treatment to fulfil the unmet long-term use needs of patients, a new therapy, which combines the locally active drug and a sustained-release formulation, has been proposed in this review.

The role of apoptosis in the pathogenesis of osteoarthritis

PURPOSE

Apoptosis is an important physiological process, making a great difference to development and tissue homeostasis. Osteoarthritis (OA) is a chronic joint disease characterized by degeneration and destruction of articular cartilage and bone hyperplasia. This purpose of this study is to provide an updated review of the role of apoptosis in the pathogenesis of osteoarthritis.

METHODS

A comprehensive review of the literature on osteoarthritis and apoptosis was performed, which mainly focused on the regulatory factors and signaling pathways associated with chondrocyte apoptosis in osteoarthritis and other pathogenic mechanisms involved in chondrocyte apoptosis.

RESULTS

Inflammatory mediators such as reactive oxygen species (ROS), nitric oxide (NO), IL-1β, tumor necrosis factor-α (TNF-α), and Fas are closely related to chondrocyte apoptosis. NF-κB signaling pathway, Wnt signaling pathway, and Notch signaling pathway activate proteins and gene targets that promote or inhibit the progression of osteoarthritis disease, including chondrocyte apoptosis and ECM degradation. Long non-coding RNAs (LncRNAs) and microRNAs (microRNAs) have gradually replaced single and localized research methods and become the main research approaches. In addition, the relationship between cellular senescence, autophagy, and apoptosis was also briefly explained.

CONCLUSION

This review offers a better molecular delineation of apoptotic processes that may help in designing new therapeutic options for OA treatment.

Chondrocyte Thrombomodulin Protects against Osteoarthritis

Osteoarthritis (OA) is a prevalent form of arthritis that affects over 32.5 million adults worldwide, causing significant cartilage damage and disability. Unfortunately, there are currently no effective treatments for OA, highlighting the need for novel therapeutic approaches. Thrombomodulin (TM), a glycoprotein expressed by chondrocytes and other cell types, has an unknown role in OA. Here, we investigated the function of TM in chondrocytes and OA using various methods, including recombinant TM (rTM), transgenic mice lacking the TM lectin-like domain (TM^LeD/LeD), and a microRNA (miRNA) antagomir that increased TM expression. Results showed that chondrocyte-expressed TM and soluble TM [sTM, like recombinant TM domain 1 to 3 (rTMD123)] enhanced cell growth and migration, blocked interleukin-1β (IL-1β)-mediated signaling and protected against knee function and bone integrity loss in an anterior cruciate ligament transection (ACLT)-induced mouse model of OA. Conversely, TM^LeD/LeD mice exhibited accelerated knee function loss, while treatment with rTMD123 protected against cartilage loss even one-week post-surgery. The administration of an miRNA antagomir (miR-up-TM) also increased TM expression and protected against cartilage damage in the OA model. These findings suggested that chondrocyte TM plays a crucial role in counteracting OA, and miR-up-TM may represent a promising therapeutic approach to protect against cartilage-related disorders.

LncRNA ZFAS1 protects chondrocytes from IL-1β-induced apoptosis and extracellular matrix degradation via regulating miR-7-5p/FLRT2 axis

BACKGROUND

Increasing evidence suggested that long non-coding RNAs (lncRNAs) played vital roles in osteoarthritis (OA) progression. In this study, we aimed to reveal the protective roles of lncRNA ZFAS1 in osteoarthritis (OA) and further investigated its underlying mechanism.

METHODS

The chondrocytes were stimulated by IL-1β to establish an in vitro OA model. Then, the expression of ZFAS1, miR-7-5p, and FLRT2 in chondrocytes was determined by qRT-PCR. Gain- and loss-of-function assays of ZFAS1, miR-7-5p and FLRT2 were conducted. CCK-8 assay and flow cytometry analysis were performed to detect cell viability and apoptosis rate. The expression levels of cartilage-related proteins, including MMP13, ADAMTS5, Collagen II, and Aggrecan, were measured by western blot analysis. The interaction between ZFAS1 and miR-7-5p, as well as miR-7-5p and FLRT2, was confirmed by dual-luciferase reporter assay and RNA immunoprecipitation assay.

RESULTS

The expression of ZFAS1 and FLRT2 was down-regulated, while the expression of miR-7-5p was up-regulated in chondrocytes exposed to IL-1β. ZFAS1 overexpression promoted cell viability and suppressed apoptosis in IL-1β-treated chondrocytes. Besides, ZFAS1 overexpression suppressed the expression of MMP13 and ADAMTS5, but promoted the expression of Collagen II and Aggrecan to suppress ECM degradation. The mechanistic study showed that ZFAS1 sponged miR-7-5p to regulate FLRT2 expression. Furthermore, the overexpression of miR-7-5p could neutralize the effect of ZFAS1 in IL-1β-treated chondrocytes, and suppression of FLRT2 counteracted the miR-7-5p down-regulation role in IL-1β-treated chondrocytes.

CONCLUSIONS

ZFAS1 could promote cell viability of IL-1β-treated chondrocytes via regulating miR-7-5p/FLRT2 axis. Trial registration Not applicable.

A chemo-mechano-biological modeling framework for cartilage evolving in health, disease, injury, and treatment

BACKGROUND AND OBJECTIVE

Osteoarthritis (OA) is a pervasive and debilitating disease, wherein degeneration of cartilage features prominently. Despite extensive research, we do not yet understand the cause or progression of OA. Studies show biochemical, mechanical, and biological factors affect cartilage health. Mechanical loads influence synthesis of biochemical constituents which build and/or break down cartilage, and which in turn affect mechanical loads. OA-associated biochemical profiles activate cellular activity that disrupts homeostasis. To understand the complex interplay among mechanical stimuli, biochemical signaling, and cartilage function requires integrating vast research on experimental mechanics and mechanobiology-a task approachable only with computational models. At present, mechanical models of cartilage generally lack chemo-biological effects, and biochemical models lack coupled mechanics, let alone interactions over time.

METHODS

We establish a first-of-its kind virtual cartilage: a modeling framework that considers time-dependent, chemo-mechano-biologically induced turnover of key constituents resulting from biochemical, mechanical, and/or biological activity. We include the "minimally essential" yet complex chemical and mechanobiological mechanisms. Our 3-D framework integrates a constitutive model for the mechanics of cartilage with a novel model of homeostatic adaptation by chondrocytes to pathological mechanical stimuli, and a new application of anisotropic growth (loss) to simulate degradation clinically observed as cartilage thinning.

RESULTS

Using a single set of representative parameters, our simulations of immobilizing and overloading successfully captured loss of cartilage quantified experimentally. Simulations of immobilizing, overloading, and injuring cartilage predicted dose-dependent recovery of cartilage when treated with suramin, a proposed therapeutic for OA. The modeling framework prompted us to add growth factors to the suramin treatment, which predicted even better recovery.

CONCLUSIONS

Our flexible framework is a first step toward computational investigations of how cartilage and chondrocytes mechanically and biochemically evolve in degeneration of OA and respond to pharmacological therapies. Our framework will enable future studies to link physical activity and resulting mechanical stimuli to progression of OA and loss of cartilage function, facilitating new fundamental understanding of the complex progression of OA and elucidating new perspectives on causes, treatments, and possible preventions.

SPTLC2 ameliorates chondrocyte dysfunction and extracellular matrix metabolism disturbance in vitro and in vivo in osteoarthritis

Disturbances in chondrocyte extracellular matrix (ECM) metabolism in osteoarthritis (OA) are a major cause of OA and potentially lead to personal disability, placing a huge burden on society. Chondrocyte apoptosis and ECM catabolism have a major role in the OA process. Firstly, bioinformatics analysis was performed to screen differentially expressed genes (DEGs) in OA, and serine palmitoyltransferase subunit 2 (SPTLC2) was chosen, which had high-level expression in the OA cartilage tissues and OA chondrocytes. Overexpression and knockdown of SPTLC2 were achieved in OA chondrocytes and normal chondrocytes respectively to study the effect of SPTLC2 upon ECM metabolism of chondrocytes. Cell viability and apoptosis were measured using MTT and flow cytometry analyses; SPTLC2 overexpression enhanced the OA chondrocyte viability and decreased apoptotic rate. In addition, Western blot detection of ECM-related factors (Collagen I, Collage II, MMP-1, MMP-3, and MMP-13) revealed that SPTLC2 overexpression promoted the expression of collagens (Collagen I and Collage II) and suppressed matrix metalloproteinase (MMP-1, MMP-3, and MMP-13) level. In contrast, SPTLC2 knockdown in normal chondrocytes showed opposite effects on cell viability, apoptosis, and ECM degeneration. The articular cartilage of OA rats was transfected with lentivirus overexpressing SPTLC2; HE and Safranin-O fast green demonstrated that SPTLC2 overexpression could alleviate chondrocyte injuries and slow down the development of OA. In conclusion, SPTLC2 plays a role in OA and may be a potential target gene for the treatment of OA.

HECTD1-Mediated Ubiquitination and Degradation of Rubicon Regulates Autophagy and Osteoarthritis Pathogenesis

OBJECTIVE

Osteoarthritis (OA) is one of the most common degenerative joint diseases and is associated with autophagy suppression. However, the molecular mechanism of autophagy regulation in the context of OA is not fully understood. In this study, we sought to determine the role that HECTD1 plays in the pathogenesis of OA.

METHODS

We used RNA sequencing analysis to explore the differential expression of E3 ubiquitin ligase genes in healthy human cartilage and human cartilage affected by OA. Using surgery- and aging-induced OA mouse models, we comprehensively analyzed the function of the screened gene Hectd1 in the development of OA; furthermore, we dissected the mechanism by which HECTD1 regulates autophagy and OA progression using a combination of molecular biologic, cell biologic, and biochemical approaches.

RESULTS

HECTD1 was significantly down-regulated in human OA cartilage samples compared to healthy cartilage samples. Overexpression of HECTD1 in mouse joints alleviated OA pathogenesis, whereas conditional depletion of Hectd1 in cartilage samples aggravated surgery- and aging-induced OA pathogenesis. Mechanistically, HECTD1 bound to Rubicon and ubiquitinated Rubicon at lysine residue 534, which targets Rubicon for proteasomal degradation. More importantly, HECTD1-mediated Rubicon degradation regulated chondrocyte autophagy, leading to mitigation of stress-induced chondrocyte death and the subsequent progression of OA.

CONCLUSION

HECTD1 plays a crucial role in the pathogenesis of OA, in that HECTD1 regulates chondrocyte autophagy by ubiquitinating and targeting Rubicon for proteasomal degradation.

HU308 Mitigates Osteoarthritis by Stimulating Sox9-Related Networks of Carbohydrate Metabolism

Osteoarthritis (OA) is characterized by progressive, irreversible erosion of articular cartilage accompanied by severe pain and immobility. This study aimed to assess the effect and mechanism of action of HU308, a selective cannabinoid receptor type 2 (CB2) agonist, in preventing OA-related joint damage. To test the assumption that HU308 could prevent OA-related joint damage, Cnr2 null mice and wild type (WT) mice were aged to reach 20 months and analyzed for joint structural features. OA was induced in WT mice via a post-traumatic procedure or aging, followed by HU308 local (intra-articular) or systemic (intraperitoneal) administration, respectively. Additional analyses of time and dose courses for HU308 were carried out in human primary chondrocytes, analyzed by RNA sequencing, RT-PCR, chromatin immunoprecipitation, and immunoblotting. Our results showed that Cnr2 null mice exhibited enhanced age-related OA severity and synovitis compared to age-matched WT mice. Systemic administration of HU308 to 16-month-old mice improved pain sensitivity and maintained joint integrity, which was consistent with the intra-articular administration of HU308 in post-traumatic OA mice. When assessing human chondrocytes treated with HU308, we uncovered a dose- and time-related increase in ACAN and COL2A1 expression, which was preceded by increased SOX9 expression due to pCREB transcriptional activity. Finally, transcriptomic analysis of patient-derived human chondrocytes identified patient subpopulations exhibiting HU308-responsive trends as judged by enhanced SOX9 expression, accompanied by enriched gene networks related to carbohydrate metabolism. Collectively, the results showed that HU308 reduced trauma and age-induced OA via CB2-pCREB dependent activation of SOX9, contributing to augmented gene networks related to carbohydrate metabolism. © 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).

Intra-Articular Mesenchymal Stem Cell Injection for Knee Osteoarthritis: Mechanisms and Clinical Evidence

Knee osteoarthritis presents higher incidences than other joints, with increased prevalence during aging. It is a progressive process and may eventually lead to disability. Mesenchymal stem cells (MSCs) are expected to repair damaged issues due to trilineage potential, trophic effects, and immunomodulatory properties of MSCs. Intra-articular MSC injection was reported to treat knee osteoarthritis in many studies. This review focuses on several issues of intra-articular MSC injection for knee osteoarthritis, including doses of MSCs applied for injection and the possibility of cartilage regeneration following MSC injection. Intra-articular MSC injection induced hyaline-like cartilage regeneration, which could be seen by arthroscopy in several studies. Additionally, anatomical, biomechanical, and biochemical changes during aging and other causes participate in the development of knee osteoarthritis. Conversely, appropriate intervention based on these anatomical, biomechanical, biochemical, and functional properties and their interactions may postpone the progress of knee OA and facilitate cartilage repair induced by MSC injection. Hence, post-injection rehabilitation programs and related mechanisms are discussed.

Lactobacillus (LA-1) and butyrate inhibit osteoarthritis by controlling autophagy and inflammatory cell death of chondrocytes

Osteoarthritis (OA) reduces the quality of life as a result of the pain caused by continuous joint destruction. Inactivated Lactobacillus (LA-1) ameliorated osteoarthritis and protected cartilage by modulating inflammation. In this study, we evaluated the mechanism by which live LA-1 ameliorated OA. To investigate the effect of live LA-1 on OA progression, we administered LA-1 into monosodium iodoacetate (MIA)-induced OA animals. The pain threshold, cartilage damage, and inflammation of the joint synovial membrane were improved by live LA-1. Furthermore, the analysis of intestinal tissues and feces in the disease model has been shown to affect the systems of the intestinal system and improve the microbiome environment. Interestingly, inflammation of the intestinal tissue was reduced, and the intestinal microbiome was altered by live LA-1. Live LA-1 administration led to an increase in the level of Faecalibacterium which is a short-chain fatty acid (SCFA) butyrate-producing bacteria. The daily supply of butyrate, a bacterial SCFA, showed a tendency to decrease necroptosis, a type of abnormal cell death, by inducing autophagy and reversing impaired autophagy by the inflammatory environment. These results suggest that OA is modulated by changes in the gut microbiome, suggesting that activation of autophagy can reduce aberrant cell death. In summary, live LA-1 or butyrate ameliorates OA progression by modulating the gut environment and autophagic flux. Our findings suggest the regulation of the gut microenvironment as a therapeutic target for OA.

Lipid Metabolism in Cartilage Development, Degeneration, and Regeneration

Lipids affect cartilage growth, injury, and regeneration in diverse ways. Diet and metabolism have become increasingly important as the prevalence of obesity has risen. Proper lipid supplementation in the diet contributes to the preservation of cartilage function, whereas excessive lipid buildup is detrimental to cartilage. Lipid metabolic pathways can generate proinflammatory substances that are crucial to the development and management of osteoarthritis (OA). Lipid metabolism is a complicated metabolic process involving several regulatory systems, and lipid metabolites influence different features of cartilage. In this review, we examine the current knowledge about cartilage growth, degeneration, and regeneration processes, as well as the most recent research on the significance of lipids and their metabolism in cartilage, including the extracellular matrix and chondrocytes. An in-depth examination of the involvement of lipid metabolism in cartilage metabolism will provide insight into cartilage metabolism and lead to the development of new treatment techniques for metabolic cartilage damage.

The Role of Mitochondrial Metabolism, AMPK-SIRT Mediated Pathway, LncRNA and MicroRNA in Osteoarthritis

Osteoarthritis (OA) is the most common joint disease characterized by degeneration of articular cartilage and causes severe joint pain, physical disability, and impaired quality of life. Recently, it was found that mitochondria not only act as a powerhouse of cells that provide energy for cellular metabolism, but are also involved in crucial pathways responsible for maintaining chondrocyte physiology. Therefore, a growing amount of evidence emphasizes that impairment of mitochondrial function is associated with OA pathogenesis; however, the exact mechanism is not well known. Moreover, the AMP-activated protein kinase (AMPK)–Sirtuin (SIRT) signaling pathway, long non-coding RNA (lncRNA), and microRNA (miRNA) are important for regulating the physiological and pathological processes of chondrocytes, indicating that these may be targets for OA treatment. In this review, we first focus on the importance of mitochondria metabolic dysregulation related to OA. Then, we show recent evidence on the AMPK-SIRT mediated pathway associated with OA pathogenesis and potential treatment options. Finally, we discuss current research into the effects of lncRNA and miRNA on OA progression or inhibition.

Melatonin: A novel candidate for the treatment of osteoarthritis

Osteoarthritis (OA), characterized by cartilage erosion, synovium inflammation, and subchondral bone remodeling, is a common joint degenerative disease worldwide. OA pathogenesis is regulated by multiple predisposing factors, including imbalanced matrix metabolism, aberrant inflammatory response, and excessive oxidative stress. Moreover, melatonin has been implicated in development of several degenerative disorders owing to its potent biological functions. With regards to OA, melatonin reportedly promotes synthesis of cartilage matrix, inhibition of chondrocyte apoptosis, attenuation of inflammatory response, and suppression of matrix degradation by regulating the TGF-β, MAPK, or NF-κB signaling pathways. Notably, melatonin has been associated with amelioration of oxidative damage by restoring the OA-impaired intracellular antioxidant defense system in articular cartilage. Findings from preliminary application of melatonin or melatonin-loaded biomaterials in animal models have affirmed its potential anti-arthritic effects. Herein, we summarize the anti-arthritic effects of melatonin on OA cartilage and demonstrate that melatonin has potential therapeutic efficacy in treating OA.

Serum netrin-1 and netrin receptor levels in fibromyalgia and osteoarthritis

Objectives: This study aims to define serum levels of netrin-1 and netrin receptors in patients with fibromyalgia (FM) and osteoarthritis (OA).

Patients and methods: This cross-sectional study was conducted with a total of 150 female participants (mean age: 47.2±16.1 years; range, 18 to 89 years) at Fırat University between June 2016 and December 2016. The participants were evaluated in three groups: the FM group with 50 patients, the OA group with 50 patients, and the control group, which included 50 healthy volunteers. Netrin-1, netrin receptors (DCC, UNC5B, and UNC5D), interleukin (IL)-6, IL-10, and IL-17 levels were analyzed by the enzyme-linked immunosorbent assay from the serum samples of the participants.

Results: The level of serum netrin-1 was significantly lower in the FM group than in the control and OA groups (p<0.01 and p<0.001, respectively). However, the difference between patients with OA and healthy controls in terms of netrin-1 was not statistically significant (p>0.05). In addition, serum levels of netrin receptors and cytokines in the FM group were similar to the control group (p>0.05). However, serum DCC, UNC5D, IL-6, and IL-10 levels were higher in the OA group compared to the control group (p<0.001, p<0.05, p<0.01, and p<0.001, respectively).

Conclusion: Serum netrin-1 level is suppressed in FM, which suggests that netrin-1 is influential in FM pathogenesis.

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.

Anti-Dlx5 Retards the Progression of Osteoarthritis through Inhibiting Chondrocyte Hypertrophy and Apoptosis

Osteoarthritis is a common degenerative joint disease that can cause pain and disability in patients. There is still a lack of effective treatments to improve pathological changes of osteoarthritis cartilages and reverse the progression of osteoarthritis. Our study aimed to investigate the role of Dlx5 in papain-induced osteoarthritis. Osteoarthritis was induced through intraarticular injection of papain. The pathological damage of cartilage tissues was analyzed by H&E staining. The apoptosis of cartilage tissues was detected by TUNEL assay. Immunohistochemical staining was performed to detect DLX5 and BMP-2. Western blot was performed to detect the expressions of SP7, caspase-3, and MYC. The results showed that administration of anti-Dlx5 improved pathological changes of osteoarthritis cartilages, characterized by decreased chondrocyte proliferation, chondrocyte hypertrophy, and matrix damage. Anti-Dlx5 treatment decreased the expressions of BMP-2 and SP7, which are positive regulators of chondrocyte hypertrophy. Moreover, MYC and caspase-3, the critical mediators for chondrocyte apoptosis, were both decreased after anti-Dlx5 treatment. In conclusion, anti-Dlx5 retarded the progression of osteoarthritis by downregulating chondrocyte hypertrophy and chondrocyte apoptosis-related genes. Our findings suggests that Dlx5 is a promising target for osteoarthritis treatment.

Maclurin Promotes the Chondrogenic Differentiation of Bone Marrow Mesenchymal Stem Cells by Regulating miR-203a-3p/Smad1

Bone marrow mesenchymal stem cells (BMSCs) differentiate into chondrocytes under appropriate conditions, providing a method for the treatment of bone- and joint-related diseases. Previously, we found that mulberry (Morus nigra) promoted the chondrogenic differentiation of BMSCs. Although the mechanism of action and active ingredients remain unknown, several studies describe the involvement of micro-RNAs. We obtained BMSCs from the bone marrow of Sprague Dawley rats. Cell Counting Kit-8 assays showed that maclurin (25 μg/mL) treatment was not toxic to BMSCs, and compared with untreated controls, maclurin upregulated Sox9 and Col2a expression. Quantitative-PCR revealed that miR-203a-3p levels decreased significantly during chondrogenic differentiation of BMSCs promoted by maclurin. Compared with treatment with an miR-203a-3p inhibitor, miR-203a-3p mimic inhibited expression of Sox9 and Col2a as evidenced by immunofluorescence staining and Western blotting. Smad1 was identified as a key target gene of miR-203a-3p according to biological-prediction software, and miR-203a-3p negatively regulated its transcription and translation in the dual-luciferase reporter gene assay and Western blotting. Sox9 and Col2a expression was downregulated following transfection of short interfering Smad1 (siSmad1) plasmids into BMSCs. We elucidated how maclurin promotes the chondrogenic differentiation of BMSCs by regulating miR-203a-3p/Smad1, which provides a strategy for future exploration of osteoarthritis therapy through cell transplantation.

Butorphanol tartrate mitigates cellular senescence against tumor necrosis factor –α (TNF-α) in human HC-A chondrocytes

Aging is an important risk factor for osteoarthritis (OA). Butorphanol is a preoperative sedative and analgesic that possesses anti-inflammatory activity. However, the effect of butorphanol on OA has not been reported. Here we aimed to explore the effect of butorphanol tartrate on the cellular senescence of human chondrocyte-articular (HC-A) cells in response to tumor necrosis factor-α (TNF-α) stimulation. Butorphanol tartrate attenuated the TNF-α-caused cellular senescence of HC-A cells, with decreased positive senescence-associated-β-galactosidase (SA-β-gal) staining and elevated telomerase activity. Butorphanol tartrate prevented TNF-α-caused cell cycle arrest in the G0/G1 phase in HC-A cells and decreased p21 expression. The TNF-α-induced production of interleukin (IL)-6 and IL-8 in HC-A cells were mitigated by butorphanol tartrate. In addition, butorphanol tartrate reduced p-NF-κB p65/total p65 and p-STAT3/STAT3 ratios in HC-A cells cultured with TNF-α. Taken together, butorphanol tartrate protected HC-A cells from TNF-α-caused cellular senescence through inactivation of NF-κB and STAT3. These results imply that butorphanol tartrate might be used as a potential agent for the treatment of aging-related OA.

CircSCAPER contributes to IL-1β-induced osteoarthritis in vitro via miR-140-3p/EZH2 axis

Aims

Circular RNA (circRNA) S-phase cyclin A-associated protein in the endoplasmic reticulum (ER) (circSCAPER, ID: hsa_circ_0104595) has been found to be highly expressed in osteoarthritis (OA) patients and has been associated with the severity of OA. Hence, the role and mechanisms underlying circSCAPER in OA were investigated in this study.

Methods

In vitro cultured human normal chondrocyte C28/I2 was exposed to interleukin (IL)-1β to mimic the microenvironment of OA. The expression of circSCAPER, microRNA (miR)-140-3p, and enhancer of zeste homolog 2 (EZH2) was detected using quantitative real-time polymerase chain reaction and Western blot assays. The extracellular matrix (ECM) degradation, proliferation, and apoptosis of chondrocytes were determined using Western blot, cell counting kit-8, and flow cytometry assays. Targeted relationships were predicted by bioinformatic analysis and verified using dual-luciferase reporter and RNA immunoprecipitation (RIP) assays. The levels of phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) pathway-related protein were detected using Western blot assays.

Results

CircSCAPER was highly expressed in OA cartilage tissues and IL-1β-induced chondrocytes. Knockdown of circSCAPER reduced IL-1β-evoked ECM degradation, proliferation arrest, and apoptosis enhancement in chondrocytes. Mechanistically, circSCAPER directly bound to miR-140-3p, and miR-140-3p inhibition reversed the effects of circSCAPER knockdown on IL-1β-induced chondrocytes. miR-140-3p was verified to target EZH2, and overexpression of miR-140-3p protected chondrocytes against IL-1β-induced dysfunction via targeting EZH2. Additionally, we confirmed that circSCAPER could regulate EZH2 through sponging miR-140-3p, and the circSCAPER/miR-140-3p/EZH2 axis could activate the PI3K/AKT pathway.

Conclusion

CircSCAPER promoted IL-1β-evoked ECM degradation, proliferation arrest, and apoptosis enhancement in chondrocytes via regulating miR-140-3p/EZH2 axis, which gained a new insight into the pathogenesis of OA.

Cite this article: Bone Joint Res 2022;11(2):61–72.

Metallothionein 1: A New Spotlight on Inflammatory Diseases

MT1 has been demonstrated to be an essential stress protein in maintaining physiological balance and regulating immune homeostasis. While the immunological involvement of MT1 in central nervous system disorders and cancer has been extensively investigated, mounting evidence suggests that MT1 has a broader role in inflammatory diseases and can shape innate and adaptive immunity. In this review, we will first summarize the biological features of MT1 and the regulators that influence MT1 expression, emphasizing metal, inflammation, and immunosuppressive factors. We will then focus on the immunoregulatory function of MT1 on diverse immune cells and the signaling pathways regulated by MT1. Finally, we will discuss recent advances in our knowledge of the biological role of MT1 in several inflammatory diseases to develop novel therapeutic strategies.

miR-7/EGFR/MEGF9 axis regulates cartilage degradation in osteoarthritis via PI3K/AKT/mTOR signaling pathway

Osteoarthritis (OA) is a common degenerative disease in middle-aged and elderly people. Our previous study has proved that microRNA-7 (miR-7) exacerbated the OA process. This study was aimed to explore the downstream genes and mechanism regulated by miR-7 to affect OA. Multiple EGF-like-domains 9 (MEGF9) was the predicted target of miR-7 by databases. Luciferase report experiment results confirmed that MEGF9 could bind to miR-7. Among the 10 collected pairs of OA and healthy samples, the expression levels of miR-7 and MEGF9 were both up-regulated when compared with healthy subjects by qRT-PCR and immunohistochemistry (IHC). The increased MEGF9 levels were due to the interaction with epidermal growth factor receptor (EGFR) by co-immunoprecipitation. Evaluations found that upregulation of miR-7 or MEGF9 can increase the expression of EGFR, matrix metalloproteinase-13 (MMP-13) and a disintegrin like and metallopeptidase with thrombospondin type 1 motif 5 (ADAMTS-5), so as to aggravate cartilage degradation. In addition, this effect induced by miR-7/EGFR/MEGF9 axis was by activation of PI3K/AKT signaling. The IHC and western blot assay results on OA model mice also demonstrated that miR-7/EGFR/MEGF9 axis regulated cartilage degradation in vivo. In summary, miR-7/EGFR/MEGF9 axis may perform a crucial function in the regulation of OA, providing potential for OA treatment.

Circ_0128846/miR-140-3p/JAK2 Network in Osteoarthritis Development

Circular RNAs (circRNAs) titrate the function of microRNAs (miRNAs), regulate transcription, and interfere with splicing. This study attempted to confirm the role of a novel circRNA circ_0128846 during osteoarthritis (OA) progression. Tissues and chondrocytes were isolated from OA patients. Overexpression and knockdown of target genes were generated using cell transfection and siRNA interference. Expression levels of genes were measured by qRT-PCR, Western blot, and immunohistochemistry, respectively. The interactions among circ_0128846, miR-140-3p, and JAK2 were verified by bioinformatics prediction, a dual-luciferase reporter assay, and RNA immunoprecipitation assay. The role of circ_0128846 in vivo was confirmed by the construction of experimental OA rats. Pathological changes were evaluated by hematoxylin and eosin and Safranin O staining. In OA patients, the level of circ_0128846 and JAK2 were up-regulated with down-regulated level of miR-140-3p. Circ_0128846 was principally located in the cytoplasm. Circ_0128846 silence enhanced cells viability, but reduced apoptosis rate and inflammatory response, which was obviously reversed by miR-140-3p knockdown. The overexpression of JAK2 reversed the effects of miR-140-3p on cell phenotypes. Circ_0128846 silence suppressed the level of MMP-13 and promoted the expression of collagen II by up-regulating miR-140-3p and down-regulating JAK2 in OA cells. Results of animal experiments demonstrated that circ_0128846 silence promoted collagen II expression and attenuated the OA progression by regulating the miR-140-3p/JAK2 axis. Circ_0128846 contributes to OA development through acting as a sponge RNA for miR-140-3p and thereby increasing JAK2 expression. Results indicated that targeting circ_0128846 may have the potential to alleviate OA progression.Abbreviations:circRNAs: Circular RNAs; miRNAs: microRNAs; OA: osteoarthritis; RIP: RNA immunoprecipitation; H&E: hematoxylin and eosin; ncRNAs: noncoding RNAs; ceRNA: competitive endogenous RNA; DMEM: Dulbecco's modified Eagle's medium; PBS: phosphate buffered saline; OE-circ_0128846: overexpression vector for circ_0128846; pcDNA3.1-JAK2: pcDNA3.1 overexpression vector for Janus kinase 2; NC: negative control; CCK-8: Cell Counting Kit-8; PI: propidium iodide; WT: Wild-type; mutants (MUT); SD rats: Sprague Dawley rats; DMM: destabilization of medial meniscus; IHC: immunohistochemistry; DAB: diaminobenzene; pre-Mrna: precursor mRNA.

C1q/TNF-related protein-9 suppresses inflammation in synovial cells from patients with osteoarthritis

Objective: Synovial inflammation contributes to cartilage degeneration and osteoarthritis (OA) development. Targeting the inflammation process may provide a promising strategy for OA treatment. It has been demonstrated that C1q/tumour necrosis factor-related protein-9 (CTRP9) has immunosuppression capabilities. Thus, we conducted this study to investigate the role of CTRP9 in OA and its therapeutic potential.Method: The expression level of CTRP9 was quantified in peripheral blood mononuclear cells (PBMCs), serum, and synovial cells (SCs) isolated from OA patients by quantitative polymerase chain reaction and enzyme-linked immunosorbent assay. The relationship between the expression level of CTRP9 and the disease activity of OA was determined. The inflammation-suppressing effects of CTRP9 were assessed in vitro.Results: The expression level of CTRP9 was increased in the PBMCs and serum of OA compared to healthy controls. The serum level of CTRP9 was found to be positively correlated with erythrocyte sedimentation rate, C-reactive protein, and visual analogue scale score. In addition, CTRP9 protein suppressed the expression of pro-inflammatory cytokines, including tumour necrosis factor-α, interleukin-6, and interleukin-1β, in PBMCs and SCs in vitro. CTRP9 was increased in OA patients and positively correlated with the disease activity. The recombinant CTRP9 had inflammation-suppressing activities in vitro.Conclusion: CTRP9 may have therapeutic potential for treating OA.Osteoarthritis (OA) is characterized as cartilage destruction resulting from synovial inflammation (1-6). According to the clinical symptoms and levels of inflammation, OA has been divided into primary generalized osteoarthritis (PGOA) and erosive inflammatory osteoarthritis (EIOA) (7). The only available treatment for OA is joint replacement. Thus, it is necessary to develop novel and effective therapeutic strategies to treat OA.Because synovial inflammation contributes to OA development, targeting the inflammation process may provide a promising strategy for OA treatment. Previous investigations showed that pro-inflammatory factors promoted OA development (8-10), while anti-inflammatory factors suppressed it (11-14). Thus, we conducted the present study to investigate the role of C1q/tumour necrosis factor-related protein-9 (CTRP9), an anti-inflammatory factor (15), in OA, and its therapeutic potential.

Knockdown of long noncoding RNA HOTAIR inhibits osteoarthritis chondrocyte injury by miR-107/CXCL12 axis

BACKGROUND

Osteoarthritis (OA) is a joint disease characterized via destruction of cartilage. Chondrocyte damage is associated with cartilage destruction during OA. Long noncoding RNAs (lncRNAs) are implicated in the regulation of chondrocyte damage in OA progression. This study aims to investigate the role and underlying mechanism of lncRNA homeobox antisense intergenic RNA (HOTAIR) in OA chondrocyte injury.

METHODS

Twenty-three OA patients and healthy controls without OA were recruited. Chondrocytes were isolated from OA cartilage tissues. HOTAIR, microRNA-107 (miR-107) and C-X-C motif chemokine ligand 12 (CXCL12) levels were measured by quantitative real-time polymerase chain reaction and western blot. Cell proliferation, apoptosis and extracellular matrix (ECM) degradation were measured using cell counting kit-8, flow cytometry and western blot. The target interaction was explored by bioinformatics, luciferase reporter and RNA immunoprecipitation assays.

RESULTS

HOTAIR expression was enhanced, and miR-107 level was reduced in OA cartilage samples. HOTAIR overexpression inhibited cell proliferation, but induced cell apoptosis and ECM degradation in chondrocytes. HOTAIR knockdown caused an opposite effect. MiR-107 was sponged and inhibited via HOTAIR, and knockdown of miR-107 mitigated the effect of HOTAIR silence on chondrocyte injury. CXCL12 was targeted by miR-107. CXCL12 overexpression attenuated the roles of miR-107 overexpression or HOTAIR knockdown in the proliferation, apoptosis and ECM degradation. CXCL12 expression was decreased by HOTAIR silence, and restored by knockdown of miR-107.

CONCLUSION

HOTAIR knockdown promoted chondrocyte proliferation, but inhibited cell apoptosis and ECM degradation in OA chondrocytes by regulating the miR-107/CXCL12 axis.

Roles of long non‑coding RNA in osteoarthritis (Review)

Osteoarthritis (OA) is a chronic bone and joint disease characterized by articular cartilage degeneration and joint inflammation and is the most common form of arthritis. The clinical manifestations of OA are chronic pain and joint activity disorder, which severely affect the patient quality of life. Long non-coding RNA (lncRNA) is a class of RNA molecules >200 nucleotides long that are expressed in animals, plants, yeast, prokaryotes and viruses. lncRNA molecules lack an open reading frame and are not translated into protein. The present review collated the results of recent studies on the role of lncRNA in the pathogenesis of OA to provide information for the prevention, diagnosis and treatment of OA.

Effects of miR-146a-5p on chondrocyte interleukin-1-induced inflammation and apoptosis involving thioredoxin interacting protein regulation

Objective

Osteoarthritis (OA) is a chronic degenerative arthropathy characterized by articular cartilage degeneration, subchondral osteosclerosis, and hyperosteogeny. MicroRNAs (miRNAs) play an important regulatory role in its pathological development, so this study explored the effect and potential mechanism of miR-146a-5p in interleukin (IL)-1β-induced OA cartilage injury.

Methods

The human chondrosarcoma cell line SW1353 and normal human chondrocytes C28/I2 were stimulated by IL-1β to construct the OA chondrocyte model. miR-146a-5p and thioredoxin interacting protein (TXNIP) expression levels were detected by quantitative real-time (qRT)-PCR and western blot. Their expression was modified by transfecting an miR-146a-5p inhibitor, mimic, and pcDNA-TXNIP. The relationship between miR-146a-5p and TXNIP was analyzed by the dual-luciferase assay, while cell viability, apoptosis, and inflammatory expression were determined by cell counting, TUNEL staining, and ELISA, respectively.

Results

miR-146a-5p expression was upregulated in SW1353 and C28/I2 cells stimulated by IL-1β. miR-146a-5p knockdown significantly enhanced cell activity, inhibited inflammatory factor expression, and reduced cell apoptosis. The dual-luciferase assay revealed TXNIP as a target gene of miR-146a-5p and suggested that miR-146a-5p promotion of OA damage could be reversed by upregulating TXNIP.

Conclusion

These results suggest that miR-146a-5p inhibits cell proliferation and promotes apoptosis and the inflammatory response in OA cartilage injury by modulating TXNIP.

Recent Progress in Cartilage Lubrication

Healthy articular cartilage, covering the ends of bones in major joints such as hips and knees, presents the most efficiently-lubricated surface known in nature, with friction coefficients as low as 0.001 up to physiologically high pressures. Such low friction is indeed essential for its well-being. It minimizes wear-and-tear and hence the cartilage degradation associated with osteoarthritis, the most common joint disease, and, by reducing shear stress on the mechanotransductive, cartilage-embedded chondrocytes (the only cell type in the cartilage), it regulates their function to maintain homeostasis. Understanding the origins of such low friction of the articular cartilage, therefore, is of major importance in order to alleviate disease symptoms, and slow or even reverse its breakdown. This progress report considers the relation between frictional behavior and the cellular mechanical environment in the cartilage, then reviews the mechanism of lubrication in the joints, in particular focusing on boundary lubrication. Following recent advances based on hydration lubrication, a proposed synergy between different molecular components of the synovial joints, acting together in enabling the low friction, has been proposed. Additionally, recent development of natural and bio-inspired lubricants is reviewed.

Two reactive behaviors of chondrocytes in an IL-1β-induced inflammatory environment revealed by the single-cell RNA sequencing

Objective: To investigate the heterogeneous responses of in vitro expanded chondrocytes, which were cultured in an interleukin (IL)-1β -induced inflammatory environment.

Method: Human articular chondrocytes were expanded, in vitro, for 13 days and treated with IL-1β for 0, 24, and 48 h. Cells were collected and subjected to single-cell RNA sequencing. Multiple bioinformatics tools were used to determine the signatures that define chondrocyte physiology.

Results: Two major cell clusters with distinct expression patterns were identified at the initial phase and were with heterogeneous variation that coincides with inflammation progress. They transformed into two terminal cell clusters one of which exhibited OA-phenotype and proinflammatory characteristics through two paths, “response-to-inflammation” and “atypical response-to-inflammation”, respectively. The involved cell clusters exhibited intrinsic relationship with cell types within native cartilage from OA patients. Genes controlling cell transformation to OA-phenotype were relating to the tumor necrosis factor (TNF) signaling pathway via NFKB, up-regulated KRAS signaling and the IL2/STAT5 signaling pathway and pathways relating to apoptosis and reactive oxygen species.

Conclusion: The in vitro expanded chondrocytes under IL-1β-induced inflammatory progression behave heterogeneously. One of the initial cell clusters could transform into a proinflammatory subpopulation through a termed response-to-inflammation path, which may serve as the core target to alleviate OA progression.

Nuts and bolts of the salt-inducible kinases (SIKs)

The salt-inducible kinases, SIK1, SIK2 and SIK3, most closely resemble the AMP-activated protein kinase (AMPK) and other AMPK-related kinases, and like these family members they require phosphorylation by LKB1 to be catalytically active. However, unlike other AMPK-related kinases they are phosphorylated by cyclic AMP-dependent protein kinase (PKA), which promotes their binding to 14-3-3 proteins and inactivation. The most well-established substrates of the SIKs are the CREB-regulated transcriptional co-activators (CRTCs), and the Class 2a histone deacetylases (HDAC4/5/7/9). Phosphorylation by SIKs promotes the translocation of CRTCs and Class 2a HDACs to the cytoplasm and their binding to 14-3-3s, preventing them from regulating their nuclear binding partners, the transcription factors CREB and MEF2. This process is reversed by PKA-dependent inactivation of the SIKs leading to dephosphorylation of CRTCs and Class 2a HDACs and their re-entry into the nucleus. Through the reversible regulation of these substrates and others that have not yet been identified, the SIKs regulate many physiological processes ranging from innate immunity, circadian rhythms and bone formation, to skin pigmentation and metabolism. This review summarises current knowledge of the SIKs and the evidence underpinning these findings, and discusses the therapeutic potential of SIK inhibitors for the treatment of disease.

Activation of autophagy contributes to the protective effects of lycopene against oxidative stress-induced apoptosis in rat chondrocytes

Oxidative stress is commonly associated with osteoarthritis (OA). Lycopene (LYC), a natural carotenoid compound, is an effective antioxidant with potential cartilage-protecting actions. However, how it affects hydrogen peroxide (H₂ O₂ )-induced damage to the cartilage is unclear. In this study, an in vitro oxidative stress model was developed via treating primary chondrocytes with H₂ O₂ . Western blot, immunohistochemistry, and quantitative RT-PCR (qRT-PCR) were used to assess the levels of related factors. Reactive oxygen species (ROS) and apoptosis levels were analyzed by the use of appropriate probes and flow cytometry. The expression and activity of stress-specific enzymes (malondialdehyde, superoxide dismutase, and catalase) were also assessed. The role of autophagy was explored by using the inhibitor, 3-methyladenine (3-MA), as well as monodansylcadaverine staining, western blotting, and red fluorescent protein-green fluorescent protein-light chain 3 lentivirus infection. The result showed LYC exerted significant chondrocyte-protective effects, including reduced inflammation and chondrocyte degradation, increased chondrocyte proliferation, apoptosis inhibition, and reduced ROS production. LYC could effectively induce autophagy in the H₂ O₂ treatment group, and this effect could be attenuated by 3-MA. In terms of mechanism, LYC played a role in inhibiting MAPK and PI3K/Akt/NF-κB axis, which down-regulates levels of mTOR and had a potential therapeutic significance for cartilage degeneration.

A Randomized Controlled Trial to Compare Analgesia and Functional Improvement After Continuous Neuroablative and Pulsed Neuromodulative Radiofrequency Treatment of the Genicular Nerves in Patients with Knee Osteoarthritis up to One Year After the Intervention

OBJECTIVES

To compare the analgesic and functional outcomes of continuous neuroablative radiofrequency (CNARF) and pulsed neuromodulative radiofrequency (PNMRF) treatment of genicular nerves up to 1 year after the intervention and to identify predictors associated with a successful outcome (defined as an at least 50% reduction in the pre-interventional visual analog scale [VAS] rating) after genicular radiofrequency treatment.

DESIGN

A prospective randomized controlled trial.

SETTING

The Pain Department of the Jerez de la Frontera University Hospital, Cadíz, Spain, from January 2018 until May 2019.

SUBJECTS

Patients with grade 3-4 gonarthritis suffering from knee pain, with a VAS score ≥5 for >6 months.

METHODS

Eligible participants were randomly assigned to receive either CNARF or PNMRF of the superior medial, superior lateral, and inferior medial genicular nerves. The VAS and Western Ontario and McMaster Universities Osteoarthritis (WOMAC) scores were assessed before and at 1, 6, and 12 months after treatment. Medication use was quantified before and at 6 months after the intervention. Potential characteristics associated with the efficacy of radiofrequency intervention were explored by using multivariable statistical models.

RESULTS

A total of 188 participants were included. The magnitude and duration of beneficial effect and reduction in analgesic use were significantly greater in the CNARF group. Success at 6 months after radiofrequency treatment decreased with grade 4 gonarthritis; higher pre-interventional VAS score; and concomitant depression, anxiety disorder, and diabetes mellitus.

CONCLUSIONS

Therapeutic efficacy and reduction in analgesic consumption were superior after CNARF. Treatment success at 6 months after radiofrequency intervention decreased with more severe gonarthritis; higher pre-interventional pain intensity; and concomitant depression, anxiety disorder, and diabetes mellitus.

The role of stromal cell-derived factor 1 on cartilage development and disease

Stromal cell-derived factor 1 (SDF-1), also known as CXC motif chemokine ligand 12 (CXCL12), is recognized as a homeostatic cytokine with strong chemotactic potency. It plays an important role in physiological and pathological processes, such as the development of multiple tissues and organs, the regulation of cell distribution, and tumour metastasis. SDF-1 has two receptors, CXC chemokine receptor type 4 (CXCR4) and CXC chemokine receptor type 7 (CXCR7). SDF-1 affects the proliferation, survival, differentiation and maturation of chondrocytes by binding to CXCR4 on chondrocytes. Therefore, SDF-1 has been used as an exogenous regulatory target in many studies to explore the mechanism of cartilage development. SDF-1 is also a potential therapeutic target for osteoarthritis (OA) and rheumatoid arthritis (RA), because of its role in pathological initiation and regulation. In addition, SDF-1 shows potent capacity in the repair of cartilage defects by recruiting endogenous stem cells in a cartilage tissue engineering context. To summarize the specific role of SDF-1 on cartilage development and disease, all articles had been screened out in PubMed by May 30, 2020. The search was limited to studies published in English. Search terms included SDF-1; CXCL12; CXCR4; chondrocyte; cartilage; OA; RA, and forty-seven papers were studied. Besides, we reviewed references in the articles we searched to get additional relevant backgrounds. The review aims to conclude the current knowledge regarding the physiological and pathological role of SDF-1 on the cartilage and chondrocyte. More investigations are required to determine methods targeted SDF-1 to cartilage development and interventions to cartilage diseases.

Knee Cartilage Thickness Differs Alongside Ages: A 3-T Magnetic Resonance Research Upon 2,481 Subjects via Deep Learning

Background: It was difficult to distinguish the cartilage thinning of an entire knee joint and to track the evolution of cartilage morphology alongside ages in the general population, which was of great significance for studying osteoarthritis until big imaging data and artificial intelligence are fused. The purposes of our study are (1) to explore the cartilage thickness in anatomical regions of the knee joint among a large collection of healthy knees, and (2) to investigate the relationship between the thinning pattern of the cartilages and the increasing ages. Methods: In this retrospective study, 2,481 healthy knees (subjects ranging from 15 to 64 years old, mean age: 35 ± 10 years) were recruited. With magnetic resonance images of knees acquired on a 3-T superconducting scanner, we automatically and precisely segmented the cartilage via deep learning and calculated the cartilage thickness in 14 anatomical regions. The thickness readings were compared using ANOVA by considering the factors of age, sex, and side. We further tracked the relationship between the thinning pattern of the cartilage thickness and the increasing ages by regression analysis. Results: The cartilage thickness was always thicker in the femur than corresponding regions in the tibia (p < 0.05). Regression analysis suggested cartilage thinning alongside ages in all regions (p < 0.05) except for medial and lateral anterior tibia in both females and males (p > 0.05). The thinning speed of men was faster than women in medial anterior and lateral anterior femur, yet slower in the medial patella (p < 0.05). Conclusion: We established the calculation method of cartilage thickness using big data and deep learning. We demonstrated that cartilage thickness differed across individual regions in the knee joint. Cartilage thinning alongside ages was identified, and the thinning pattern was consistent in the tibia while inconsistent in patellar and femoral between sexes. These findings provide a potential reference to detect cartilage anomaly.

Regenerative Medicine for Equine Musculoskeletal Diseases

Simple Summary

Lameness due to musculoskeletal disease is the most common diagnosis in equine veterinary practice. Many of these orthopaedic disorders are chronic problems, for which no clinically satisfactory treatment exists. Thus, high hopes are pinned on regenerative medicine, which aims to replace or regenerate cells, tissues, or organs to restore or establish normal function. Some regenerative medicine therapies have already made their way into equine clinical practice mainly to treat tendon injures, tendinopathies, cartilage injuries and degenerative joint disorders with promising but diverse results. This review summarises the current knowledge of commonly used regenerative medicine treatments and critically discusses their use.

Abstract

Musculoskeletal injuries and chronic degenerative diseases commonly affect both athletic and sedentary horses and can entail the end of their athletic careers. The ensuing repair processes frequently do not yield fully functional regeneration of the injured tissues but biomechanically inferior scar or replacement tissue, causing high reinjury rates, degenerative disease progression and chronic morbidity. Regenerative medicine is an emerging, rapidly evolving branch of translational medicine that aims to replace or regenerate cells, tissues, or organs to restore or establish normal function. It includes tissue engineering but also cell-based and cell-free stimulation of endogenous self-repair mechanisms. Some regenerative medicine therapies have made their way into equine clinical practice mainly to treat tendon injures, tendinopathies, cartilage injuries and degenerative joint disorders with promising results. However, the qualitative and quantitative spatiotemporal requirements for specific bioactive factors to trigger tissue regeneration in the injury response are still unknown, and consequently, therapeutic approaches and treatment results are diverse. To exploit the full potential of this burgeoning field of medicine, further research will be required and is ongoing. This review summarises the current knowledge of commonly used regenerative medicine treatments in equine patients and critically discusses their use.