Insights on Molecular Mechanisms of Chondrocytes Death in Osteoarthritis

The essential anti-angiogenic strategies in cartilage engineering and osteoarthritic cartilage repair

In the cartilage matrix, complex interactions occur between angiogenic and anti-angiogenic components, growth factors, and environmental stressors to maintain a proper cartilage phenotype that allows for effective load bearing and force distribution. However, as seen in both degenerative disease and tissue engineering, cartilage can lose its vascular resistance. This vascularization then leads to matrix breakdown, chondrocyte apoptosis, and ossification. Research has shown that articular cartilage inflammation leads to compromised joint function and decreased clinical potential for regeneration. Unfortunately, few articles comprehensively summarize what we have learned from previous investigations. In this review, we summarize our current understanding of the factors that stabilize chondrocytes to prevent terminal differentiation and applications of these factors to rescue the cartilage phenotype during cartilage engineering and osteoarthritis treatment. Inhibiting vascularization will allow for enhanced phenotypic stability so that we are able to develop more stable implants for cartilage repair and regeneration.

Circ_0020093 Overexpression Alleviates Interleukin-1 Beta-induced Inflammation, Apoptosis and Extracellular Matrix Degradation in Human Chondrocytes by Targeting the miR-181a-5p/ERG Pathway

Osteoarthritis (OA) is a well-known chronic degenerative joint disease, with multiple changes in the phenotype of chondrocytes. Circular RNAs (circRNAs) have been shown to be involved in various human diseases, including OA. The purpose of this study was to determine the role of circ_0020093 in OA pathological changes in vitro. C28/I2 cells were treated with interleukin-1 beta (IL-1β) to mimic OA pathological conditions. The expression levels of circ_0020093, miR-181a-5p and ETS-related gene (ERG) mRNA were measured by quantitative real-time PCR (qRT-PCR). For functional analyses, cell proliferative capacity was detected using EdU assay and CCK-8 assay. Inflammatory response was assessed by determining the release of pro-inflammatory factors using ELISA kits. Cell apoptosis was examined by flow cytometry assay. The levels of apoptosis-related proteins and extracellular matrix (ECM)-associated proteins were assessed by Western blot. The binding relationship between miR-181a-5p and circ_0020093 or ERG was confirmed by RNA pull-down assay, dual-luciferase reporter assay or RIP assay. The expression level of circ_0020093 was decreased in IL-1β-treated C28/I2 cells. Circ_0020093 overexpression relieved inflammatory responses, cell apoptosis and ECM degradation in IL-1β-induced C28/I2 cells. Circ_0020093 directly targeted miR-181a-5p, and miR-181a-5p bound to the 3' -untranslated region (3'UTR) of ERG to regulate ERG expression. Circ_0020093 overexpression promoted the expression of ERG by sponging miR-181a-5p. Rescue experiments showed that miR-181a-5p overexpression or ERG knockdown could reverse the inhibitory effects of circ_0020093 overexpression on the pathological changes in IL-1β-induced C28/I2 cells. Circ_0020093 overexpression alleviated IL-1β-induced human chondrocyte inflammatory injury, apoptosis and ECM degradation by targeting miR-181a-5p/ERG pathway.

LIM mineralization protein-1 inhibits IL-1β-induced human chondrocytes injury by altering the NF-κB and MAPK/JNK pathways

Osteoarthritis (OA) is a common degenerative disease that is associated with the degradation of articular cartilage. Accumulating evidence has confirmed that LIM mineralization protein-1 (LMP-1) is an important agent of bone formation and has been shown to be osteoinductive in various types of disease. However, the underlying mechanisms of LMP-1 in the pathogenesis of OA remain unknown. The present study aimed to evaluate the role and potential mechanism of LMP-1 in IL-1β-stimulated OA chondrocytes. CHON-001 cells were transfected with pcDNA3.1-LMP-1, pcDNA3.1, negative control-small interfering (si)RNA or LMP-1 siRNA for 24 h and then induced by IL-1β for 12 h to establish an OA model in vitro. Cell viability, apoptosis and inflammatory cytokine (IL-6, IL-8 and TNF-α) release were assessed using MTT assay, flow cytometry and ELISA, respectively. The expression levels of LMP-1, cleaved-caspase 3, phosphorylated (p)-p65, p65, p-JNK and JNK were analyzed using reverse transcription-quantitative PCR and western blotting. Overexpression of LMP-1 notably alleviated the IL-1β-induced inflammatory response in CHON-001 cells, as shown by increased cell viability, decreased apoptosis, suppressed expression of cleaved-caspase 3 and a decreased cleaved-caspase 3/caspase 3 ratio. Moreover, IL-1β-induced secretion of IL-6, IL-8 and TNF-α in CHON-001 cells; this was reversed by pcDNA3.1-LMP-1. However, knocking down LMP-1 expression exert opposite effects on the IL-1β-induced inflammatory response in CHON-001 cells, as evidenced by the decreased cell viability, increased apoptosis, enhanced expression of cleaved-caspase 3 and cleaved-caspase 3/caspase 3 ratio and enhanced secretion of IL-6, IL-8 and TNF-α observed. The present data demonstrated that LMP-1 siRNA notably inhibited LMP-1 expression, suppressed cell viability, promoted apoptosis and enhanced cleaved-caspase 3 expression and cleaved-caspase 3/caspase 3 ratio. In addition, LMP-1 siRNA promoted the release of inflammatory factors in CHON-001 cells. It was also found that pcDNA3.1-LMP-1 inhibited p-p65 and p-JNK expression, as well as decreasing the p-p65/p65 and p-JNK/JNK ratio. Nevertheless, there was no significant difference in the mRNA expression levels of p65 and JNK between the groups. Taken together, these findings indicated that overexpression of LMP-1 alleviated IL-1β-induced chondrocytes injury by regulating the NF-κB and MAPK/JNK pathways, suggesting that LMP-1 may be a valuable therapeutic agent for OA treatment.

Identification of the Resveratrol Potential Targets in the Treatment of Osteoarthritis

Objectives

Osteoarthritis (OA) is a chronic joint degenerative disease and has become an important health problem for the elderly. However, there is still a lack of effective drugs for the treatment of OA. Our research combines bioinformatics and experimental strategies to determine the target of resveratrol for OA treatment.

Methods

First, the differentially expressed genes (DEGs) of OA joint tissues were obtained from the related microarray gene expression data. Second, resveratrol, a natural polyphenol compound, was used to screen the drug treatment target genes. Third, the drug-disease network was established, and the resveratrol target genes for OA treatment were obtained and verified through experimental verification.

Results

A total of 300 differentially expressed genes with 246 upregulated and 54 downregulated were found in OA joint tissues, and 310 resveratrol potential target genes were obtained. Finally, six genes, namely, CXCL1, HIF1A, IL-6, MMP3, NOX4, and PTGS2, were selected to validate the treatment effects of the resveratrol. The results showed that all six genes in human OA chondrocytes were significantly increased. In addition, in these chondrocytes, CXCL1, HIF1A, IL-6, MMP3, NOX4, and PTGS2 were reduced considerably, but HIF1A was significantly increased after resveratrol treatment.

Conclusions

Our data indicates that CXCL1, HIF1A, IL-6, MMP3, NOX4, and PTGS2 are all targets of resveratrol therapy. Our findings may provide valuable information for the mechanism and therapeutic of OA.

Intra-Articular Drug Delivery for Osteoarthritis Treatment

Osteoarthritis (OA) is the most prevalent degenerative joint disease affecting millions of people worldwide. Currently, clinical nonsurgical treatments of OA are only limited to pain relief, anti-inflammation, and viscosupplementation. Developing disease-modifying OA drugs (DMOADs) is highly demanded for the efficient treatment of OA. As OA is a local disease, intra-articular (IA) injection directly delivers drugs to synovial joints, resulting in high-concentration drugs in the joint and reduced side effects, accompanied with traditional oral or topical administrations. However, the injected drugs are rapidly cleaved. By properly designing the drug delivery systems, prolonged retention time and targeting could be obtained. In this review, we summarize the drugs investigated for OA treatment and recent advances in the IA drug delivery systems, including micro- and nano-particles, liposomes, and hydrogels, hoping to provide some information for designing the IA injected formulations.

Preparation of EGCG decorated, injectable extracellular vesicles for cartilage repair in rat arthritis

Arthritis is a kind of chronic inflammatory autoimmune disease, which can destroy joint cartilage and bone, leading to joint pain, joint swelling, and limited mobility. Traditional therapies have many side effects or focus too much on anti-inflammation while neglecting joint repair. In this experiment, we combined Epigallocatechin gallate (EGCG) with extracellular vesicles derived from macrophages to treat rheumatoid arthritis. Sustained-release resulted in a significant decrease in chondrocyte expression of hypoxia-inducible factor 1-alpha, a decrease in apoptosis-related proteins Cytochrome C, Caspase-3, Caspase-9, and Bax. Molecular biological analysis showed that extracellular vesicles-encapsulated EGCG (EVs-EGCG) more significantly upregulated type II collagen expression by about 1.8-fold than EGCG alone, which was more beneficial for arthritis repair. Animal experiments revealed that these EGCG-coated extracellular vesicles significantly reduced swelling, decreased synovial hyperplasia, repaired cartilage, and attenuated arthritis-related pathology scores in arthritic rats. Measurement data showed that EVs-EGCG treatment reduced joint swelling by approximately 39.5% in rheumatoid rats. In vitro studies have shown that this EVs-EGCG can increase the expression of cartilage type II collagen and reduce apoptosis of chondrocytes. Moreover, it was demonstrated in vivo experiments to reduce cartilage destruction in rheumatoid arthritis rats, providing a solution for the treatment of rheumatoid arthritis.

Hypoxia Inducible Factor-1α Is a Regulator of Autophagy in Osteoarthritic Chondrocytes

OBJECTIVE

To investigate the relationship between hypoxia inducible factor-1α (HIF-1α) and the autophagic response in osteoarthritic chondrocytes (OA), under inflammatory insult as represented by in vitro OA model.

METHODS

Human chondrocyte cell line C28/I2 was cultured in both normoxic and hypoxic conditions and treated with interleukin-1β (IL1β) to emulate OA inflammatory insult in vitro. Cellular HIF-1α expression was silenced using siRNA transfection and cellular autophagic (P62/LC3II) response and OA chondrocyte damage (COL2A1/MMP13) related proteins were examined using western blotting. Cellular mitophagic (BNIP3/PINK1/Parkin) and apoptotic (Caspase/Cleaved Caspase 3) were also evaluated to assess mitophagy-mediated cell death due to HIF-1α silencing.

RESULTS

Chondrocyte basal autophagy levels were higher in a HIF-1α elevated environment and was more resistant to IL1β-induced inflammatory insult. Increase in autophagic proteins showed better chondrocyte repair, which resulted a lower level of reactive oxygen species production, and lesser damage to chondrocyte integrity. Silencing HIF-1α activates cellular PINK1/Parkin and BNIP3 mitophagic proteins, which leads to the activation of Caspase/Cleaved Caspase 3 apoptotic cascade.

CONCLUSION

Our results show that chondrocyte autophagy is dependent on HIF-1α expression, showing the importance of HIF-1α in hypoxic chondrocyte function in OA. Dysregulation of HIF-1α expression results in the activation of mitophagy-mediated apoptosis.

An Insight into the Role of Apoptosis and Autophagy in Nitric Oxide-Induced Articular Chondrocyte Cell Death

OBJECTIVE

To investigate the role and characterize the molecular mechanisms regulating apoptosis and autophagy in nitric oxide (NO)-induced chondrocyte cell death.

DESIGN

Cell apoptosis and autophagy were evaluated in chondrocytes treated with sodium nitroprusside (SNP) combined with the presence or absence of interleukin-1 beta (IL-1β) and nutrient-deprived conditions. The concentration of nitrite was determined by Griess reaction. Activation of apoptosis and autophagy were determined by immunocytochemistry, Western blot, and quantitative real-time polymerase chain reaction (qPCR) analysis. Flow cytometry and MTT assay were used to assess cell viability.

RESULTS

Cotreatment of chondrocytes with SNP and IL-1β under nutrient-deprived condition potentially enhanced the effect of NO-induced cell death. Immunocytochemistry, Western blot, and qPCR analysis indicated that treatment of chondrocytes with SNP significantly reduced autophagic activity, autophagic flux, and multiple autophagy-related (Atg) genes expression. These findings were associated with an increase in ERK, Akt, and mTOR phosphorylation, whereas autophagy induction through mTOR/p70S6K inhibition by rapamycin significantly suppressed NO-induced cell apoptosis. Furthermore, the cleavage of poly(ADP-ribose) polymerase (PARP) and caspase-3 activation in response to apoptosis was weakly detected. These results corresponded with a significant increase in apoptosis-inducing factor (AIF) expression, suggesting the involvement of the caspase-independent pathway.

CONCLUSIONS

These results demonstrate that in chondrocyte cultures with cells induced into an osteoarthritis state, NO inhibits autophagy and induces chondrocyte apoptosis mainly, but not completely through the caspase-independent pathway. Our data suggest that autophagy is a protective mechanism in the pathogenesis of osteoarthritis and could be proposed as a therapeutic target for degenerative joint diseases.

A review on the molecular basis underlying the protective effects of Andrographis paniculata and andrographolide against myocardial injury

Andrographolide is the major compound found in the medicinal plant, Andrographis paniculata (Burm.f.) Nees, which accounts for its medicinal properties. Both the plant extract and compound have been reported to exhibit potential cardiovascular activities. This review summarises related studies describing the biological activities and target mechanisms of A. paniculata and andrographolide in vivo and in vitro. The current evidence unambiguously indicated the protective effects provided by A. paniculata and andrographolide administration against myocardial injury. The intervention ameliorates the symptoms of myocardial injury by interfering with the inductive phase of a) inflammatory response mediated by nuclear factor-kappa B (NF-κB), phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt), mitogen-activated protein kinase (MAPK) and signal transducer and activator of transcription 3 (STAT3) signalling molecules; b) oxidative stress via activation of nuclear factor erythroid 2-related factor (Nrf-2) and reduction of enzymes responsible for generating reactive oxygen and nitrogen species; c) intrinsic and extrinsic mechanisms in apoptosis regulated by upstream insulin-like growth factor-1 receptor (IGF-1R) and peroxisome proliferator-activated receptor-alpha (PPAR-α); d) profibrotic growth factors thus reducing cardiac fibrosis, improving endothelial function and fibrinolytic function. In conclusion, A. paniculata and andrographolide possess therapeutic potential in the management of myocardial injury, which requires further validation in human clinical trials.

D-mannose alleviates osteoarthritis progression by inhibiting chondrocyte ferroptosis in a HIF-2α-dependent manner

OBJECTIVES

Chondrocyte ferroptosis contributes to osteoarthritis (OA) progression, and D-mannose shows therapeutic value in many inflammatory conditions. Here, we investigated whether D-mannose interferes in chondrocyte ferroptotic cell death during osteoarthritic cartilage degeneration.

MATERIALS AND METHODS

In vivo anterior cruciate ligament transection (ACLT)-induced OA mouse model and an in vitro study of chondrocytes in an OA microenvironment induced by interleukin-1β (IL-1β) exposure were employed. Combined with Epas1 gene gain- and loss-of-function, histology, immunofluorescence, quantitative RT-PCR, Western blot, cell viability and flow cytometry experiments were performed to evaluate the chondroprotective effects of D-mannose in OA progression and the role of hypoxia-inducible factor 2 alpha (HIF-2 α) in D-mannose-induced ferroptosis resistance of chondrocytes.

RESULTS

D-mannose exerted a chondroprotective effect by attenuating the sensitivity of chondrocytes to ferroptosis and alleviated OA progression. HIF-2α was identified as a central mediator in D-mannose-induced ferroptosis resistance of chondrocytes. Furthermore, overexpression of HIF-2α in chondrocytes by Ad-Epas1 intra-articular injection abolished the chondroprotective effect of D-mannose during OA progression and eliminated the role of D-mannose as a ferroptosis suppressor.

CONCLUSIONS

D-mannose alleviates osteoarthritis progression by suppressing HIF-2α-mediated chondrocyte sensitivity to ferroptosis, indicating D-mannose to be a potential therapeutic strategy for ferroptosis-related diseases.

Mesenchymal Stem Cell-Derived Extracellular Vesicles for Osteoarthritis Treatment: Extracellular Matrix Protection, Chondrocyte and Osteocyte Physiology, Pain and Inflammation Management

Osteoarthritis (OA) is a common degenerative disease that can lead to persistent pain and motion restriction. In the last decade, stem cells, particularly mesenchymal stem cells (MSCs), have been explored as a potential alternative OA therapy due to their regenerative capacity. Furthermore, it has been shown that trophic factors enveloped in extracellular vesicles (EVs), including exosomes, are a crucial aspect of MSC-based treatment for OA. Evidently, EVs derived from different MSC sources might rescue the OA phenotype by targeting many biological processes associated with cartilage extracellular matrix (ECM) degradation and exerting protective effects on different joint cell types. Despite this advancement, different studies employing EV treatment for OA have revealed reverse outcomes depending on the EV cargo, cell source, and pathological condition. Hence, in this review, we aim to summarize and discuss the possible effects of MSC-derived EVs based on recent findings at different stages of OA development, including effects on cartilage ECM, chondrocyte biology, osteocytes and bone homeostasis, inflammation, and pain management. Additionally, we discuss further strategies and technical advances for manipulating EVs to specifically target OA to bring the therapy closer to clinical use.

Roles of mechanosensitive channel Piezo1/2 proteins in skeleton and other tissues

Mechanotransduction is a fundamental ability that allows living organisms to receive and respond to physical signals from both the external and internal environments. The mechanotransduction process requires a range of special proteins termed mechanotransducers to convert mechanical forces into biochemical signals in cells. The Piezo proteins are mechanically activated nonselective cation channels and the largest plasma membrane ion channels reported thus far. The regulation of two family members, Piezo1 and Piezo2, has been reported to have essential functions in mechanosensation and transduction in different organs and tissues. Recently, the predominant contributions of the Piezo family were reported to occur in the skeletal system, especially in bone development and mechano-stimulated bone homeostasis. Here we review current studies focused on the tissue-specific functions of Piezo1 and Piezo2 in various backgrounds with special highlights on their importance in regulating skeletal cell mechanotransduction. In this review, we emphasize the diverse functions of Piezo1 and Piezo2 and related signaling pathways in osteoblast lineage cells and chondrocytes. We also summarize our current understanding of Piezo channel structures and the key findings about PIEZO gene mutations in human diseases.

Beneficial effects of secretome derived from mesenchymal stem cells with stigmasterol to negate IL-1β-induced inflammation in-vitro using rat chondrocytes-OA management

Osteoarthritis (OA) is the most prevalent joint disease predominantly characterized by inflammation which drives cartilage destruction. Mesenchymal stem cells-condition medium (MSC-CM) or the secretome is enriched with bioactive factors and possesses anti-inflammatory and regenerative effects. The present study aimed at evaluating the effects of combining MSC-conditioned medium with stigmasterol compared with the individual treatments in alleviating interleukin-1 beta (IL-1β)-induced inflammation in rat chondrocytes. Stigmasterol is a phytosterol exhibiting anti-inflammatory effects. IL-1β (10 ng/ml) was used to induce inflammation and mimic OA in-vitro in primary rat articular chondrocytes. The IL-1β-stimulated chondrocytes were treated with MSC-CM, stigmasterol, and a combination of MSC-CM and stigmasterol for 24 h. Cell viability was measured using MTT assay. Protein expression of inducible nitric oxide synthase (iNOS), interleukin-6 (IL-6), collagen II (COL2A1) and matrix metalloproteinase (MMP)-13 were evaluated by immunofluorescence. Gene expression levels of MMP-3, MMP-13 and A Disintegrin-like and Metalloproteinases with Thrombospondin Motifs (ADAMTS)-5 were measured using qRT-PCR. NF-κB signaling pathway was studied using western blotting. A significant reduction in the expression of iNOS, IL-6, MMP-3, MMP-13 and ADAMTS-5, and a significant increase in COL2A1 expression was observed in the rat chondrocytes across all the treatment groups. However, the combination treatment of MSC-CM and stigmasterol remarkably reversed the IL-1β-induced pro-inflammatory/pro-catabolic responses to near normal levels comparable to the control group. The combination treatment (MSC-CM + stigmasterol) elicited a superior anti-inflammatory/anti-catabolic effect by inhibiting the IL-1β-induced NF-κB activation evidenced by the negligible phosphorylation of p65 and IκBα subunits, thereby emphasizing the benefit of the combination therapy over the individual treatments.

Key miRNAs in Modulating Aging and Longevity: A Focus on Signaling Pathways and Cellular Targets

Aging is a multifactorial procedure accompanied by gradual deterioration of most biological procedures of cells. MicroRNAs (miRNAs) are a class of short non-coding RNAs that post-transcriptionally regulate the expression of mRNAs through sequence-specific binding, and contributing to many crucial aspects of cell biology. Several miRNAs are expressed differently in various organisms through aging. The function of miRNAs in modulating aging procedures has been disclosed recently with the detection of miRNAs that modulate longevity in the invertebrate model organisms, through the IIS pathway. In these model organisms, several miRNAs have been detected to both negatively and positively regulate lifespan via commonly aging pathways. miRNAs modulate age-related procedures and disorders in different mammalian tissues by measuring their tissue-specific expression in older and younger counterparts, including heart, skin, bone, brain, and muscle tissues. Moreover, several miRNAs have been contributed to modulating senescence in different human cells, and the roles of these miRNAs in modulating cellular senescence have allowed illustrating some mechanisms of aging. The review discusses the available data on miRNAs through the aging process and we highlight the roles of miRNAs as aging biomarkers and regulators of longevity in cellular senescence, tissue aging, and organism lifespan.

LncRNAs as a new regulator of chronic musculoskeletal disorder

Objectives

In recent years, long non‐coding RNAs (lncRNAs) have been found to play a role in the occurrence, progression and prognosis of chronic musculoskeletal disorders.

Design and methods

Literature exploring on PubMed was conducted using the combination of keywords 'LncRNA' and each of the following: 'osteoarthritis', 'rheumatoid arthritis', 'osteoporosis', 'osteogenesis', 'osteoclastogenesis', 'gout arthritis', 'Kashin‐Beck disease', 'ankylosing spondylitis', 'cervical spondylotic myelopathy', 'intervertebral disc degeneration', 'human muscle disease' and 'muscle hypertrophy and atrophy'. For each disorder, we focused on the publications in the last five years (5/1/2016‐2021/5/1, except for Kashin‐Beck disease). Finally, we excluded publications that had been reported in reviews of various musculoskeletal disorders during the last three years. Here, we summarized the progress of research on the role of lncRNA in multiple pathological processes during musculoskeletal disorders.

Results

LncRNAs play a crucial role in regulating downstream gene expression and maintaining function and homeostasis of cells, especially in chondrocytes, synovial cells, osteoblasts, osteoclasts and skeletal muscle cells.

Conclusions

Understanding the mechanisms of lncRNAs in musculoskeletal disorders may provide promising strategies for clinical practice.

Bardoxolone-Methyl Prevents Oxidative Stress-Mediated Apoptosis and Extracellular Matrix Degradation in vitro and Alleviates Osteoarthritis in vivo

PURPOSE

Oxidative stress-induced chondrocyte apoptosis and extracellular matrix (ECM) degradation plays an important role in the progression of osteoarthritis (OA). Bardoxolone methyl (BM), a semisynthetic triterpenoid, exerts strong effect against oxidative stress. The purpose of the present study was to determine the effectiveness of bardoxolone-methyl (BM) in preventing oxidative stress-induced chondrocyte apoptosis and extracellular ECM degradation in vitro and the role of alleviating OA progression in vivo.

METHODS

Oxidative damage was induced by 25 mM tert-butyl hydroperoxide (TBHP) for 24 h in rat chondrocytes. 0.025 and 0.05 µM bardoxolone-methyl (BM) were used in vitro treatment. Ex-vivo cartilage explant model was established to evaluate the effect of BM on oxidative stress-induced ECM degradation. The mouse OA model was induced by surgical destabilization of the medial meniscus.

RESULTS

In vitro, 0.025 and 0.05 µM BM reduced TBHP-induced excessive ROS generation, improved cell viability, increased malondialdehyde level and decreased superoxide dismutase level. 0.025 and 0.05 µM BM prevented TBHP-induced mitochondrial damage and apoptosis in chondrocytes BM activated heme oxygenase-1 (HO-1)/NADPH quinone oxidoreductase 1 (NOQ1) signaling pathway through targeting nuclear factor erythroid derived-2-related factor 2 (Nrf2). Additionally, BM treatment enhanced the expression levels of aggrecan and collagen II and inhibited the expression levels of matrix metalloproteinase 9 (MMP 9), MMP 13, Bax and cleaved-caspase-3. BM increased proteoglycan staining area and IOD value in ex vivo cultured experiment cartilage explants and improved the OARSI score, stands, max contact mean intensity, print area and duty cycle in mouse OA model.

CONCLUSION

BM prevented oxidative stress-induced chondrocyte apoptosis and ECM degradation in vitro and alleviated OA in vivo, suggesting that BM serves as an effective drug for treatment with OA.

Osteoarthritis is not a disease, but rather an accumulation of predisposing factors. A systematic review

Introduction: Although they do not endanger the life of the individual, the major symptoms of osteoarthritis (OA), such as pain, inflammation and dysfunction, it will slowly decrease quality of life and performance, leading finally to disabilities. Due to the fact that this disease has no cure, strategies are still being sought to slow its evolution. The lack of understanding of the predisposing and triggering factors of OA, has led to different approaches to this pathology so discussed, but with modest results. This systematic review aims to debate the main phenomena underlying joint destruction in OA, and etiopathogenic theories. Materials and Methods: In this study were included 58 bibliographic sources, of which title 39 refers to OA, 6 with inflammation, 28 with cartilage, 3 with chondrocytes, and 5 with synovitis. In this study were discussed the etiopathogenic theories of OA which include: age, alteration of the cartilaginous matrix, alteration of chondrocyte metabolism, microtrauma and major trauma, inflammation of the joints - synovitis and obesity. Results: Increasing the level of understanding of predisposing factors, the occurrence of acute inflammatory phenomenon and the perpetuation of mechanisms that latently maintain chronic inflammation that over time develops a destructive effect on articular cartilage, would limit the negative effects of OA, delay the evolution and optimally combat that maintain the vicious circle: inflammation → production of enzymes → chondrolysis → inflammation. Conclusions: These studies contribute significantly to the understanding of destructive phenomena in OA. More studies are needed on the risk factors of OA and its production mechanisms, to find increasingly effective therapies that limiting its progression. Keywords: Osteoarthritis, etiopathogenic theories, chronic inflammation, age, obesity, cartilaginous matrixm, chondrocyte metabolism

Mineral deposition intervention through reduction of phosphorus intake suppresses osteoarthritic lesions in temporomandibular joint

OBJECTIVE

To explore the suppressing impact of low phosphorus intake on osteoarthritic temporomandibular joint and the possible mechanisms of nuclear acid injury in the insulted chondrocytes.

DESIGN

Chondrocytes were loaded with fluid flow shear stress (FFSS) with or without low phosphorus medium. Seventy-two mice (sampled at 3-, 7- and 11-wk, n = 6) and forty-eight rats (sampled at 12-wks for different testing purpose, n = 6) were applied with unilateral anterior crossbite (UAC) with or without low phosphorus diet. In the FFSS model, the Ca and P content, molecules related to nucleic acid degradation and the mineral-producing responses in chondrocytes were detected. The effect of culture dish stiffness on chondrocytes osteogenic differentiation was measured. In the UAC model, the content of Ca and P in serum were tested. The condylar cartilage ossification and stiffness were detected using micro-CT, scanning electron microscope and atomic force microscope.

RESULTS

FFSS induced nucleic acid degradation, Pi accumulation and mineral-producing responses in the cultured chondrocytes, all were alleviated by low P medium. Stiffer dish bottoms promoted the osteogenic differentiation of the cultured chondrocytes. UAC stimulated cartilage degeneration and chondrocytes nucleic acid damage, increased PARP 1 and serum P content, and enhanced ossification and stiffening of the cartilage, all were suppressed by low phosphorus diet (all, P < 0.05).

CONCLUSION

Nucleic acid damage takes a role in phosphorus production in osteoarthritic cartilage, contributing to the enhanced mineralization and stiffness of the cartilage that in turn promotes cartilage degradation, which can be alleviated by low phosphorus intake.

Peripheral shift in the viable chondrocyte population of the medial femoral condyle after anterior cruciate ligament injury in the porcine knee

Anterior cruciate ligament injuries result in posttraumatic osteoarthritis in the medial compartment of the knee, even after surgical treatment. How the chondrocyte distribution within the articular cartilage changes early in this process is currently unknown. The study objective was to investigate the chondrocyte distribution within the medial femoral condyle after an anterior cruciate ligament transection in a preclinical model. Forty-two adolescent Yucatan minipigs were allocated to receive unilateral anterior cruciate ligament surgery (n = 36) or no surgery (n = 6). Central coronal sections of the medial femoral condyle were obtained at 1- and 4 weeks after surgery, and the chondrocyte distribution was measured via whole slide imaging and a cell counting batch processing tool utilized in ImageJ. Ki-67 immunohistochemistry was performed to identify proliferating cells. Empty lacunae, karyolysis, karyorrhexis, and pyknosis were used to identify areas of irreversible cell injury. The mean area of irreversible cell injury was 0% in the intact controls, 13.4% (95% confidence interval: 6.4, 20.3) at 1-week post-injury and 19.3% (9.7, 28.9) at 4 weeks post-injury (p < .015). These areas occurred closest to the femoral intra-articular notch. The remaining areas containing viable chondrocytes had Ki-67-positive cells (p < .02) and increased cell density in the middle (p < .03) and deep zones (p = .001). For the entire section, the total chondrocyte number did not change significantly post-operatively; however, the density of cells in the peripheral regions of the medial femoral condyle increased significantly at 1- and 4 weeks post-injury relative to the intact control groups (p = .032 and .004, respectively). These data demonstrate a peripheral shift in the viable chondrocyte population of the medial femoral condyle after anterior cruciate ligament injury and further suggest that chondrocytes with the capacity to proliferate are not confined to one particular cartilage layer.

Targeting Soluble Epoxide Hydrolase and Cyclooxygenases Enhance Joint Pain Control, Stimulate Collagen Synthesis, and Protect Chondrocytes From Cytokine-Induced Apoptosis

Objective: To determine the symptomatic and disease-modifying capabilities of sEH and COX inhibitors during joint inflammation. Methods: Using a blinded, randomized, crossover experimental design, 6 adult healthy horses were injected with lipopolysaccharide (LPS; 3 μg) from E. coli in a radiocarpal joint and concurrently received the non-selective cyclooxygenase (COX) inhibitor phenylbutazone (2 mg/kg), the sEH inhibitor t-TUCB (1 mg/kg) or both (2 mg/kg phenylbutazone and 0.1, 0.3, and 1 mg/kg t-TUCB) intravenously. There were at least 30 days washout between treatments. Joint pain (assessed via inertial sensors and peak vertical forces), synovial fluid concentrations of prostanoids (PGE₂, TxB₂), cytokines (IL-1β, IL-6, TNF-α) and biomarkers of collagen synthesis (CPII) and degradation (C2C) were measured at pre-determined intervals over a 48-h period. The anti-apoptotic effect of COX and sEH inhibitors was determined via ELISA technique in primary equine chondrocytes incubated with TNF-α (10 ng/ml) for 24 h. Apoptosis was also determined in chondrocytes incubated with sEH-generated metabolites. Results: Combined COX and sEH inhibition produced significantly better control of joint pain, prostanoid responses, and collagen synthesis-degradation balance compared to each compound separately. When administered separately, pain control was superior with COX vs. sEH inhibition. Cytokine responses were not different during COX and/or sEH inhibition. In cultured chondrocytes, sEH inhibition alone or combined with COX inhibition, but not COX inhibition alone had significant anti-apoptotic effects. However, sEH-generated metabolites caused concentration-dependent apoptosis. Conclusions: Combined COX and sEH inhibition optimize pain control, attenuate loss of articular cartilage matrix during joint inflammation and cytokine-induced chondrocyte apoptosis.

Conditioned Medium of Adipose-Derived Mesenchymal Stem Cells as a Promising Candidate to Protect High Glucose-Induced Injury in Cultured C28I2 Chondrocytes

Purpose: The aim of this study was to evaluate the protective effect of conditioned medium derived from human adipose mesenchymal stem cells (CM-hADSCs) on C28I2 chondrocytes against oxidative stress and mitochondrial apoptosis induced by high glucose (HG).

Methods: C28I2 cells were pre-treated with CM-hADSCs for 24 hours followed by HG exposure (75 mM) for 48 hours. MTT assay was used to assess the cell viability. Reactive oxygen species (ROS) and lipid peroxidation were determined by 2,7-dichlorofluorescein diacetate (DCFHDA) and thiobarbituric acid reactive substances (TBARS) assays, respectively. Expressions of glutathione peroxidase 3 (GPX 3), heme oxygenase-1 (HO-1), and NAD(P)H quinone dehydrogenase 1 (NQO1) were analyzed by RT-PCR. Finally, western blot analysis was used to measure Bax, Bcl-2, cleaved caspase-3, and Nrf-2 expression at protein levels.

Results: CM-hADSCs pretreatment mitigated the cytotoxic effect of HG on C28I2 viability. Treatment also markedly reduced the levels of ROS, lipid peroxidation, and augmented the expression of HO-1, NQO1, and GPx3 genes in HG-exposed group. CM-ADSCs enhanced Nrf-2 protein expression and reduced mitochondrial apoptosis through reducing Bax/Bcl-2 ratio and Caspase-3 activation.

Conclusion: MSCs, probably through its paracrine effects, declined the deleterious effect of HG on chondrocytes. Hence, therapies based on MSCs secretomes appear to be a promising therapeutic approaches to prevent joint complications in diabetic patients.

Diagnostic and Therapeutic Role of Extracellular Vesicles in Articular Cartilage Lesions and Degenerative Joint Diseases

Two leading contributors to the global disability are cartilage lesions and degenerative joint diseases, which are characterized by the progressive cartilage destruction. Current clinical treatments often fail due to variable outcomes and an unsatisfactory long-term repair. Cell-based therapies were once considered as an effective solution because of their anti-inflammatory and immunosuppression characteristics as well as their differentiation capacity to regenerate the damaged tissue. However, stem cell-based therapies have inherent limitations, such as a high tumorigenicity risk, a low retention, and an engraftment rate, as well as strict regulatory requirements, which result in an underwhelming therapeutic effect. Therefore, the non-stem cell-based therapy has gained its popularity in recent years. Extracellular vesicles (EVs), in particular, like the paracrine factors secreted by stem cells, have been proven to play a role in mediating the biological functions of target cells, and can achieve the therapeutic effect similar to stem cells in cartilage tissue engineering. Therefore, a comprehensive review of the therapeutic role of EVs in cartilage lesions and degenerative joint diseases can be discussed both in terms of time and favorability. In this review, we summarized the physiological environment of a joint and its pathological alteration after trauma and consequent changes in EVs, which are lacking in the current literature studies. In addition, we covered the potential working mechanism of EVs in the repair of the cartilage and the joint and also discussed the potential therapeutic applications of EVs in future clinical use.

Role of lincRNA-Cox2 targeting miR-150 in regulating the viability of chondrocytes in osteoarthritis

Osteoarthritis (OA) is a joint disease characterised by progressive cartilage degradation and inflammation, but the detailed pathogenesis of OA remains unclear. The present study aimed to investigate the role of long intergenic non-coding RNA (lincRNA)-Cox2 in OA progression and the potential mechanism. An OA mouse model was used for in vivo experiments, and IL-1β-induced injury of mouse chondrocytes was conducted for in vitro experiments. Small interfering (si)-Cox2 was transfected into chondrocytes to elucidate the effect of lincRNA-Cox2 on OA. Quantitative reverse transcription PCR assays were conducted to detect the expression of lincRNA-Cox2 and microRNA (miR)-150. Cell proliferation and apoptosis were analysed based on an MTT assay and annexin V/propidium iodide staining, respectively. Western blotting was performed to evaluate the protein expression levels of Ki-67, PCNA, Bax, cleaved (c)-Caspase-3, c-Caspase-9 and Wnt/β-catenin pathway-associated proteins in chondrocytes. High levels of lincRNA-Cox2 were observed in cartilage tissues of the OA mouse model in vivo. In the in vitro experiments, the expression of lincRNA-Cox2 was increased in IL-1β-treated chondrocytes. Knockdown of lincRNA-Cox2 promoted the proliferation and inhibited the apoptosis of chondrocytes. Mechanistically, lincRNA-Cox2 was found to directly target miR-150, acting as a competing endogenous RNA, and the effect of si-Cox2 on the proliferation and apoptosis of chondrocytes was reversed by miR-150 inhibitors. Moreover, lincRNA-Cox2 activated the Wnt/β-catenin pathway to regulate chondrocyte proliferation and apoptosis. The present study demonstrated that silencing lincRNA-Cox2 expression plays a protective role in OA by enhancing the proliferation and suppressing the apoptosis of chondrocytes, which is related to increased miR-150 expression and activation of the Wnt/β-catenin pathway.

SETD7 mediates the vascular invasion in articular cartilage and chondrocytes apoptosis in osteoarthriis

The pathological characteristics of osteoarthritis are cartilage matrix degradation, chondrocytes apoptosis, and low-grade inflammation of the joint. Recent studies have shown that blood vessels grow from the subchondral bone to the articular cartilage. However, the relationship among inflammation, angiogenesis, and chondrocyte apoptosis is still unclear. We found that chondrocytes could secrete chemokines and VEGF to promote the migration of vascular endothelial cells in response to TNF-α stimulation. The invasion of blood vessels leads to increased oxygen tension in the local environment, which increased the expression of SETD7 in chondrocytes by activating the JAK-STAT5 pathway. The bond of phosphorylated STAT5 and the specific locus in the promoter of SETD7 directly increased the transcription of SETD7. On the one hand, SETD7-regulated chemokine expression by forming a positive loop; on the other hand, SETD7-mediated chondrocyte apoptosis by inhibiting the nuclear localization of HIF-1α. In this study, we discovered a novel function of chondrocytes as mediators of inflammation and angiogenesis. Our study demonstrates that SETD7 is a potential molecular target to prevent OA development and progression.

Effects of Androgen Receptor Overexpression on Chondrogenic Ability of Rabbit Articular Chondrocytes

BACKGROUND

The role of sex hormones and their receptors has drawn much attention in the process of cartilage regeneration. This study aimed to investigate the effect of androgen receptor (AR) on the chondrogenic ability of articular chondrocytes and the related mechanism.

METHODS

Articular chondrocytes were isolated, cultured, identified by toluidine blue staining and then transduced with lentivirus carrying the AR gene. The cell viability was determined using Cell Counting Kit-8, and cell apoptosis was assessed by flow cytometry analysis. The effects of AR overexpression on the expression of cartilage-specific proteins and some signalling molecules were evaluated by real-time PCR and Western blotting. Using 24 New Zealand rabbits, the regeneration of rabbit articular cartilage defects was further investigated in vivo and evaluated histologically.

RESULTS

The overexpression of AR significantly reduced the apoptosis rate of chondrocytes but did not affect their proliferation. The overexpression of AR also promoted the expression of Sry-related HMG box 9, collagen II and aggrecan, decreased the expression of matrix metalloproteinase-13, and downregulated p-S6 and RICTOR. The experimental group with AR-overexpressing chondrocytes exhibited superior regeneration of cartilage defects.

CONCLUSION

AR overexpression can maintain the phenotype of chondrocytes and promote chondrogenesis in vitro and in vivo. mTOR-related signalling was inhibited.

Sinensetin Reduces Osteoarthritis Pathology in the Tert-Butyl Hydroperoxide-Treated Chondrocytes and the Destabilization of the Medial Meniscus Model Mice via the AMPK/mTOR Signaling Pathway

As a common degenerative disease, osteoarthritis (OA) usually causes disability in the elderly and socioeconomic burden. Previous studies have shown that proper autophagy has a protective effect on OA. Sinensetin (Sin) is a methylated flavonoid derived from citrus fruits. Studies have shown that Sin is a good autophagy inducer and has shown excellent therapeutic effects in a variety of diseases; however, its role in the treatment of OA is not fully understood. This study proved the protective effect of Sin on OA through a series of in vivo and in vitro experiments. In vitro experiments have shown that Sin may inhibit chondrocyte apoptosis induced by tert-butyl hydroperoxide (TBHP); at the same time, it might also inhibit the production of MMP13 and promote the production of aggrecan and collagen II. Mechanism studies have shown that Sin promotes chondrocyte autophagy by activating AMPK/mTOR signaling pathway. On the contrary, inhibition of autophagy can partially abolish the protective effect of Sin on TBHP-treated chondrocytes. In vivo experiments show that Sin may protect against DMM-induced OA pathogenesis. These results provide evidence that Sin serves as a potential candidate for the treatment of OA.

Leptin attenuates hypoxia-induced apoptosis in human periodontal ligament cells via the reactive oxygen species-hypoxia-inducible factor-1α pathway

NEW FINDINGS

What is the central question of this study? Does leptin have an effect on hypoxia-induced apoptosis in human periodontal ligament cells (hPDLCs), and what is the potential underlying mechanism? What is the main finding and its importance? Hypoxia induces cell apoptosis and leptin expression in hPDLCs through the induction of hypoxia-inducible factor-1α and accumulation of reactive oxygen species (ROS). Leptin shows feedback inhibition on hypoxia-induced ROS-mediated apoptosis in hPDLCs, suggesting a new application of leptin for hypoxic damage in periodontal diseases.

ABSTRACT

Hypoxia-induced apoptosis of human periodontal ligament cells (hPDLCs) is an important contributor to the progression of various periodontal diseases. Although leptin has been shown to protect connective tissue cells against hypoxia-induced injury, whether it might do so by attenuating hypoxia-induced apoptosis in hPDLCs remains unclear. Here, using CoCl₂ treatment, we simulated hypoxic conditions in hPDLCs and explored whether apoptosis and reactive oxygen species (ROS) levels were related to hypoxia. After small interfering RNA (siRNA) inhibition of leptin and hypoxia-inducible factor-1α (HIF-1α), the levels of apoptosis, ROS and leptin expression were measured. We showed that in CoCl₂ -treated hPDLCs, significantly higher cell apoptosis rates and ROS accumulation were observed. Cobalt chloride also increased leptin and HIF-1α expression in hPDLCs. Further investigation of the pathway demonstrated that inhibition of ROS attenuated hypoxia-induced cell apoptosis and leptin expression, whereas siRNA inhibition of leptin aggravated hypoxia-induced cell apoptosis and ROS accumulation. Hypoxia induces cell apoptosis and leptin expression in hPDLCs through the induction of ROS and HIF-1α pathways, and leptin shows feedback inhibition on ROS-mediated apoptosis in hPDLCs. These findings suggest a new application of leptin for hypoxic damage in periodontal diseases.

PR11-364P22.2/ATF3 protein interaction mediates IL-1β-induced catabolic effects in cartilage tissue and chondrocytes

Osteoarthritis (OA) is a degenerative joint disease which lacks effective medical treatment due to ill-defined molecular mechanisms underlying the pathology. Inflammation is a key factor that induces and aggravates OA. Therefore, the current study aims to explore roles of the dysregulated long non-coding RNAs in the pro-inflammatory cytokine IL-1β-mediated catabolic effects in cartilage tissue and chondrocytes. We identified RP11-364P22.2 as dysregulated in OA patient-derived cartilage tissues and highly responsive to IL-1β stimulus. RNA pull-down coupled with mass spectrometry demonstrated that RP11-364P22.2 physically binds to activating transcription factor 3 (ATF3) and thus increases the protein stability and facilitates its nuclear translocation. Loss- and gain-of-function assays indicated that the interaction between RP11-364P22.2 and ATF3 is indispensable for the detrimental effects of IL-1β including growth inhibition, apoptosis induction as well as degradation of the key chondrocyte structural proteins of type II collage and Aggrecan and synthesis of the extracellular matrix-degrading enzyme MMP13 in chondrocytes. In vivo, depletion of the RP11-364P22.2 effector ATF3 drastically prevented OA development in the rats with surgical destabilization of the medial meniscus (DMM). These results highlight the important roles of lncRNAs in the pathogenesis of OA and indicate the RP11-364P22.2/ATF3 regulatory axis as a potential therapeutic target of inflammation-induced OA.

S-Equol Protects Chondrocytes against Sodium Nitroprusside-Caused Matrix Loss and Apoptosis through Activating PI3K/Akt Pathway

Osteoarthritis (OA) is a common chronic disease with increasing prevalence in societies with more aging populations, therefore, it is causing more concern. S-Equol, a kind of isoflavones, was reported to be bioavailable and beneficial to humans in many aspects, such as improving menopausal symptoms, osteoporosis and prevention of cardiovascular disease. This study investigated the effects of S-Equol on OA progress in which rat primary chondrocytes were treated with sodium nitroprusside (SNP) to mimic OA progress with or without the co-addition of S-Equol for the evaluation of S-Equol's efficacy on OA. Results showed treatment of 0.8 mM SNP caused cell death, and increased oxidative stress (NO and H₂O₂), apoptosis, and proteoglycan loss. Furthermore, the expressions of MMPs of MMP-2, MMP-3, MMP-9, and MMP-13 and p53 were increased. The addition of 30 μM S-Equol could lessen those caused by SNP. Moreover, S-Equol activates the PI₃K/Akt pathway, which is an upstream regulation of p53 and NO production and is associated with apoptosis and matrix degradation. As a pretreatment of phosphoinositide ₃-kinases (PI₃K) inhibitor, all S-Equol protective functions against SNP decrease or disappear. In conclusion, through PI₃K/Akt activation, S-Equol can protect chondrocytes against SNP-induced matrix degradation and apoptosis, which are commonly found in OA, suggesting S-Equol is a potential for OA prevention.

LncRNA CASC19 accelerates chondrocytes apoptosis and proinflammatory cytokine production to exacerbate osteoarthritis development through regulating the miR-152-3p/DDX6 axis

Background

Osteoarthritis (OA) is one kind of degenerative joint disease that happens in articular cartilage and other joint tissues. Long non-coding RNAs (lncRNAs) have been reported to serve as pivotal regulators in many diseases, including OA. However, the role and relevant regulatory mechanisms of CASC19 in OA remain unknown.

Methods

The expression levels of CASC19, miR-152-3p, and DDX6 were identified by reverse-transcription polymerase chain reaction (RT-qPCR). Cell viability and apoptosis were determined by Cell Counting Kit-8 (CCK-8) and flow cytometry assays, respectively. The relationship between miR-152-3p and CASC19 or DDX6 was predicted by bioinformatics tools and verified by the dual-luciferase reporter assay.

Results

CASC19 was verified to exhibit higher expression in OA tissues and cells. Moreover, inhibition of CASC19 weakened proinflammatory cytokine (IL-6, IL-8, and TNF-α) production and cell apoptosis but facilitated cell viability. Experiments of the ceRNA mechanism elucidated that miR-152-3p was a sponge for CASC19, and miR-152-3p targeted DDX6, suggesting that CASC19 sponged miR-152-3p to release DDX6. Finally, results from rescue assays proved that the impacts of CASC19 silencing on chondrocytes apoptosis and proinflammatory cytokine production could be reversed by DDX6 overexpression.

Conclusions

It was concluded that lncRNA CASC19 accelerated chondrocytes apoptosis and proinflammatory cytokine production to exacerbate osteoarthritis development through regulating the miR-152-3p/DDX6 axis. These findings may offer an effective biological target for OA treatment.

Hydrogen sulfide protects against IL-1β-induced inflammation and mitochondrial dysfunction-related apoptosis in chondrocytes and ameliorates osteoarthritis

The inflammatory environment and excessive chondrocyte apoptosis have been demonstrated to play crucial roles in the onset of osteoarthritis (OA). Hydrogen sulfide (H2 S), a gaseous signalling molecule, exerts an inhibitory effect on inflammation and apoptosis in several degenerative diseases. However, the protective effect of H2 S against OA has not been fully clarified, and its underlying mechanism should be examined further. In the current study, the role of endogenous H2 S in the pathogenesis of OA and its protective effects on interleukin (IL)-1β-induced chondrocytes were identified. Our data revealed decreased H2 S expression in both human degenerative OA cartilage tissue and IL-1β-induced chondrocytes. Pretreatment with the H2 S donor sodium hydrosulfide (NaHS) dramatically attenuated IL-1β-induced overproduction of inflammatory cytokines and improved the balance between anabolic and catabolic chondrocyte capacities, and these effects were dependent on PI3K/AKT pathway-mediated inhibition of nuclear factor kappa B (NF-κB). Moreover, mitochondrial dysfunction-related apoptosis was significantly reversed by NaHS in IL-1β-stimulated chondrocytes. Mechanistically, NaHS partially suppressed IL-1β-induced phosphorylation of the mitogen-activated protein kinase (MAPK) cascades. Furthermore, in the destabilization of the medial meniscus mouse model, OA progression was ameliorated by NaHS administration. Taken together, these results suggest that H2 S may antagonize IL-1β-induced inflammation and mitochondrial dysfunction-related apoptosis via selective suppression of the PI3K/Akt/NF-κB and MAPK signalling pathways, respectively, in chondrocytes and may be a potential therapeutic agent for the treatment of OA.

Small Noncoding RNAs in Knee Osteoarthritis: The Role of MicroRNAs and tRNA-Derived Fragments

Knee osteoarthritis (OA) is a degenerative knee joint disease that results from the breakdown of joint cartilage and underlying bone, affecting about 3.3% of the world's population. As OA is a multifactorial disease, the underlying pathological process is closely associated with genetic changes in articular cartilage and bone. Many studies have focused on the role of small noncoding RNAs in OA and identified numbers of microRNAs that play important roles in regulating bone and cartilage homeostasis. The connection between other types of small noncoding RNAs, especially tRNA-derived fragments and knee osteoarthritis is still elusive. The observation that there is limited information about small RNAs different than miRNAs in knee OA was very surprising to us, especially given the fact that tRNA fragments are known to participate in a plethora of human diseases and a portion of them are even more abundant than miRNAs. Inspired by these findings, in this review we have summarized the possible involvement of microRNAs and tRNA-derived fragments in the pathology of knee osteoarthritis.

Circ_0020093 ameliorates IL-1β-induced apoptosis and extracellular matrix degradation of human chondrocytes by upregulating SPRY1 via targeting miR-23b

Osteoarthritis (OA) is a chronic disease characterized by articular cartilage degeneration and uncontrolled chondrocyte apoptosis. At present, accumulating evidence introduces that circular RNA (circRNA) is involved in the development of OA. The aim of our study was to explore the role and the functional mechanism of circ_0020093 in OA cell model. Human chondrocytes were treated with interleukin-1 beta (IL-1β) to construct OA model. The expression of circ_0020093, miR-23b, and Sprouty 1 (SPRY1) mRNA was measured by quantitative real-time polymerase chain reaction (qRT-PCR). Cell apoptosis was assessed by flow cytometry assay. The expression of extracellular matrix (ECM)-associated markers and SPRY1 protein level was detected by qRT-PCR and Western blot. Bioinformatics analysis-predicted relationship between miR-23b and circ_0020093 or SPRY1 was further verified by dual-luciferase reporter assay and RNA pull-down assay. In this study, we found that the expression of circ_0020093 and SPRY1 was declined, while miR-23b expression was elevated in IL-1β-treated chondrocytes. IL-1β induced chondrocyte apoptosis and ECM degradation, while these negative effects were alleviated by circ_0020093 overexpression or miR-23b inhibition. MiR-23b was a target of circ_0020093, and SPRY1 was a downstream target of miR-23b. Rescue experiments showed that miR-23b enrichment reversed the role of circ_0020093 overexpression, and SPRY1 knockdown also reversed the effects of miR-23b inhibition. Importantly, circ_0020093 positively regulated SPRY1 expression by targeting miR-23b. In conclusion, circ_0020093 ameliorates IL-1β-induced apoptosis and ECM degradation of human chondrocytes by regulating the miR-23b/SPRY1 axis.

Pathological mechanism of chondrocytes and the surrounding environment during osteoarthritis of temporomandibular joint

Temporomandibular joint (TMJ) osteoarthritis is a common chronic degenerative disease of the TMJ. In order to explore its aetiology and pathological mechanism, many animal models and cell models have been constructed to simulate the pathological process of TMJ osteoarthritis. The main pathological features of TMJ osteoarthritis include chondrocyte death, extracellular matrix (ECM) degradation and subchondral bone remodelling. Chondrocyte apoptosis accelerates the destruction of cartilage. However, autophagy has a protective effect on condylar chondrocytes. Degradation of ECM not only changes the properties of cartilage but also affects the phenotype of chondrocytes. The loss of subchondral bone in the early stages of TMJ osteoarthritis plays an aetiological role in the onset of osteoarthritis. In recent years, increasing evidence has suggested that chondrocyte hypertrophy and endochondral angiogenesis promote TMJ osteoarthritis. Hypertrophic chondrocytes secrete many factors that promote cartilage degeneration. These chondrocytes can further differentiate into osteoblasts and osteocytes and accelerate cartilage ossification. Intrachondral angiogenesis and neoneurogenesis are considered to be important triggers of arthralgia in TMJ osteoarthritis. Many molecular signalling pathways in endochondral osteogenesis are responsible for TMJ osteoarthritis. These latest discoveries in TMJ osteoarthritis have further enhanced the understanding of this disease and contributed to the development of molecular therapies. This paper summarizes recent cognition on the pathogenesis of TMJ osteoarthritis, focusing on the role of chondrocyte hypertrophy degeneration and cartilage angiogenesis.

Click chemistry-based pre-targeting cell delivery for cartilage regeneration

A fraction of the OA patient population is affected by post-traumatic osteoarthritis (PTOA) following acute joint injuries. Stopping or reversing the progression of PTOA following joint injury could improve long-term functional outcomes, reduced disability, and medical costs. To more effectively treat articular cartilage injury, we have developed a novel cell-based therapy that involves the pre-targeting of apoptotic chondrocytes and the delivery of healthy, metabolically active chondrocytes using click chemistry. Specifically, a pre-targeting agent was prepared via conjugating apoptotic binding peptide (ApoPep-1) and trans-cyclooctene (TCO) onto polyethylene glycol (PEG) polymer carrier. The pre-targeting agent would be introduced to injured areas of articular cartilage, leading to the accumulation of TCO groups on the injured areas from actively binding to apoptotic chondrocytes. Subsequently, methyltetrazine (Tz)-bearing chondrocytes would be immobilized on the surface of TCO-coated injured cartilage via Tz-TCO click chemistry reaction. Using an ex vivo human cartilage explant PTOA model, the effectiveness of this new approach was evaluated. Our studies show that this novel approach (Tz-TCO click chemistry) significantly enhanced the immobilization of healthy and metabolically active chondrocytes to the areas of apoptotic chondrocytes. Histological analyses demonstrated that this treatment regimen would significantly reduce the area of cartilage degeneration and enhance ECM regeneration. The results support that Tz-TCO click chemistry-mediated cell delivery approach has great potential in clinical applications for targeting and treatment of cartilage injury.

S-Allylcysteine Inhibits Chondrocyte Inflammation to Reduce Human Osteoarthritis via Targeting RAGE, TLR4, JNK and Nrf2 Signaling: Comparison with Colchicine

Discovery of new pharmacological agents is needed to control the progression of osteoarthritis (OA) characterized by progressive joint cartilage damage. Human OA chondrocyte cultures (OAC) were either applied to S-Allyl cysteine (SAC), a sulfur-containing amino acid derivative, or colchicine, an ancient anti-inflammatory therapeutic, for 24 hours. SAC or colchicine did not change viability at 1 nM-10 µM but inhibited p-JNK/pan-JNK. While SAC seems to be more effective, both agents inhibited reactive oxygen species (ROS), 3-nitrotyrosine (3-NT), lipid-hydroperoxides (LPO), advanced lipoxidation end-products (ALEs as 4-hydroxy-2-nonenal, HNE) and advanced glycation end-products (AGEs), and increased glutathione-peroxidase (GPx) and type-II-collagen (COL2). IL-1β, IL-6 and osteopontin (OPN) were more strongly inhibited by SAC than in colchicine. In contrast, TNF-α was inhibited only by SAC, and COX2 only by colchicine. Casp-1/ICE, GM-CSF, receptor for advanced glycation end-products (RAGE) and toll-like receptors (TLR4) were inhibited by both agents, but bone morphogenetic protein 7 (BMP7) was partially inhibited by SAC while induced by colchicine. The nuclear factor erythroid 2-related factor 2 (Nrf2) was induced by SAC; in contrast it was inhibited by colchicine. Although exerting opposite effects on TNF-α, COX2, BMP7 and Nrf2, SAC and colchicine exhibit anti-osteoarthritic properties in OAC by modulating redox sensitive inflammatory signaling.

Cryptotanshinone interferes with chondrocyte apoptosis in osteoarthritis by inhibiting the expression of miR‑574‑5p

Chondrocyte apoptosis is an important factor in the development and progression of osteoarthritis (OA). Cryptotanshinone (CTS) can inhibit chondrocyte apoptosis, but the specific mechanism remains unknown. The aim of the present study was to explore how CTS may affect chondrocyte apoptosis. Reverse transcription-quantitative PCR and western blotting were used to validate microRNA (miR)-574-5p, YY1-associated factor 2 (YAF2), Bcl-2 and Bax expression levels. H&E, Safranin O and TUNEL staining assays were used to evaluate the apoptosis of arthritic chondrocytes in vivo. A Cell Counting Kit-8 assay and flow cytometry were performed to detect cell proliferation and apoptosis of chondrocytes in vitro. The methylation level of the miR-574-5p promoter was measured via methylation specific PCR. The degree of chondrocyte apoptosis and the expression levels of YAF2 and Bcl-2 were decreased in the mice with OA, and were increased in the OA + CTS mice, while the expression levels of miR-574-5p and Bax showed opposite changes. Furthermore, the degree of chondrocyte apoptosis and the expression levels of the aforementioned key factors in chondrocytes were consistent with those observed in vivo. The methylation degree of the miR-574-5p promoter was increased by the addition of CTS, and was reduced after the addition of a methylation inhibitor, 5-aza-CdR, indicating that CTS could regulate the methylation of miR-574-5p promoter. The present study suggested that CTS could downregulate the expression of miR-574-5p by regulating its methylation, and thus, could improve YAF2 expression and affect chondrocyte apoptosis.

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.

Neutrophil Elastase Induces Chondrocyte Apoptosis and Facilitates the Occurrence of Osteoarthritis via Caspase Signaling Pathway

Osteoarthritis (OA) is the most common and prevalent chronic joint disorders in the elderly population across the globe, resulting in severe disability and impairment of quality of life. Existing treatment can only alleviate the symptoms and delay the progression of OA. Therefore, novel and effective therapeutics strategies for OA need to be developed. Our present study first found that neutrophil elastase (NE) was significantly increased in OA patients’ synovial fluid. Next, we examined the effect of neutrophil elastase (NE) on chondrocytes in vitro and in vivo. The results showed that NE suppressed cell proliferation, induced apoptosis and prevented cell migration in chondrocytes in vitro, accompanied by the elevation of intracellular ROS and calcium level. Moreover, NE enhanced the cleaved caspase-3 levels and disrupted the mitochondrial transmembrane potential balance. Meanwhile, chondrocytes apoptosis induced by NE can be alleviated by caspase inhibitor, zVAD-FMK and antioxidants, GSH. Besides, treatment of sivelestat, the inhibitor of NE, significantly reduced the pathological processes in OA model rats in vivo. The results of our study suggested that NE is an important factor in OA, which induces chondrocyte apoptosis and facilitates the occurrence of OA via caspase signaling pathway, and targeting the crucial signal centering around NE may be the potential therapies for OA.

CircSERPINE2 weakens IL-1β-caused apoptosis and extracellular matrix degradation of chondrocytes by regulating miR-495/TGFBR2 axis

The dysregulated circular RNAs (circRNAs) are relevant to the development of osteoarthritis (OA). The circRNA serpin family E member 2 (circSERPINE2) is dysregulated in OA, while the role and mechanism of circSERPINE2 in OA are largely unknown. The aim of our research is to explore how and whether circSERPINE2 regulates interleukin-1β (IL-1β)-caused chondrocyte damage in OA. In the present study, the chondrocytes (CHON-001 cells) were exposed to IL-1β to mimic the injury in OA. CircSERPINE2, microRNA-495 (miR-495) and transforming growth factor-β receptor 2 (TGFBR2) abundances were detected via quantitative reverse-transcription polymerase chain reaction (qRT-PCR) or Western blot. Cell apoptosis was assessed via viability, apoptotic rate and caspase-3 activity. Extracellular matrix was investigated by levels of Sry-type high-mobility-group box 9 (SOX9), collagen type II α 1 (COL2A1) and Aggrecan using Western blot. The interaction among circSERPINE2, miR-495 and TGFBR2 was assessed via dual-luciferase reporter analysis and RNA immunoprecipitation (RIP). The results showed that circSERPINE2 expression was reduced in OA patients and IL-1β-treated chondrocytes. CircSERPINE2 overexpression mitigated IL-1β-caused apoptosis and extracellular matrix degradation. miR-495 was targeted by circSERPINE2 and up-regulated in OA patients and IL-1β-treated chondrocytes. miR-495 up-regulation reversed overexpression of circSERPINE2-mediated inhibition of apoptosis and extracellular matrix degradation. TGFBR2 was targeted by miR-495 and lowly expressed in OA patients and IL-1β-treated chondrocytes. CircSERPINE2 could mediate TGFBR2 expression by binding with miR-495. As a conclusion, circSERPINE2 attenuated IL-1β-caused apoptosis and extracellular matrix degradation of chondrocytes by regulating miR-495/TGFBR2 axis, indicating a new target for OA treatment.

An Update on Mesenchymal Stem Cell-Centered Therapies in Temporomandibular Joint Osteoarthritis

Temporomandibular joint osteoarthritis (TMJOA) is a degenerative disease characterized by cartilage degeneration, disrupted subchondral bone remodeling, and synovitis, seriously affecting the quality of life of patients with chronic pain and functional disabilities. Current treatments for TMJOA are mainly symptomatic therapies without reliable long-term efficacy, due to the limited self-renewal capability of the condyle and the poorly elucidated pathogenesis of TMJOA. Recently, there has been increased interest in cellular therapies for osteoarthritis and TMJ regeneration. Mesenchymal stem cells (MSCs), self-renewing and multipotent progenitor cells, play a promising role in TMJOA treatment. Derived from a variety of tissues, MSCs exert therapeutic effects through diverse mechanisms, including chondrogenic differentiation; fibrocartilage regeneration; and trophic, immunomodulatory, and anti-inflammatory effects. Here, we provide an overview of the therapeutic roles of various tissue-specific MSCs in osteoarthritic TMJ or TMJ regenerative tissue engineering, with an additional focus on joint-resident stem cells and other cellular therapies, such as exosomes and adipose-derived stromal vascular fraction (SVF). Additionally, we summarized the updated pathogenesis of TMJOA to provide a better understanding of the pathological mechanisms of cellular therapies. Although limitations exist, MSC-centered therapies still provide novel, innovative approaches for TMJOA treatment.

LncRNA MEG3 Protects Chondrocytes From IL-1β-Induced Inflammation via Regulating miR-9-5p/KLF4 Axis

Background

Osteoarthritis (OA) is a chronic degenerative disease of the joints characterized by articular cartilage damage, subchondral bone remodeling, osteophyte formation, and inflammatory changes. This work aims to investigate the protective role of long non-coding RNA (lncRNA) maternally expressed 3 (MEG3) against the apoptosis of chondrocytes.

Methods

Chondrocyte cell lines, CHON-001, and ATDC5 were treated with different doses of interleukin-1β (IL-1β) to mimic the inflammatory response during OA pathogenesis. Quantitative real-time polymerase chain reaction was performed to measure MEG3, miR-9-5p, and Krüppel-like factor 4 (KLF4) mRNA expression levels. MEG3 and KLF4 overexpression plasmids, MEG3 shRNA, miR-9-5p mimics, and miR-9-5p inhibitors were transfected into the cells. Cell counting kit-8, wound healing assay, and flow cytometry were conducted to determine cell viability, migration, and apoptotic rate. Dual-luciferase reporter assay was adopted to verify the targeting relationships among MEG3, miR-9-5p, and KLF4. Western blot was used to detect KLF4 protein expression. Enzyme-linked immunosorbent assay was employed to measure the levels of inflammatory factors.

Results

MEG3 expression in chondrocytes was down-regulated by the stimulation of IL-1β, and MEG3 negatively regulated miR-9-5p expression but positively regulated KLF4 expression. MEG3 overexpression strengthened the viability and migration of CHON-001 and ATDC5 cells but restrained the apoptosis and inflammatory response, while MEG3 knockdown had opposite effects. miR-9-5p inhibition or KLF4 overexpression could counteract the effects of MEG3 knockdown on chondrocytes. Besides that, MEG3 was proved to be a molecular sponge for miR-9-5p, and KLF4 was verified as the target of miR-9-5p.

Conclusion

MEG3 can promote chondrocyte proliferation and migration and inhibit apoptosis and inflammation by sponging miR-9-5p to induce KLF4 expression, which provides a promising therapy target for OA treatment.

Immunomodulatory biomaterials and their application in therapies for chronic inflammation-related diseases

The degree of tissue injuries such as the level of scarring or organ dysfunction, and the immune response against them primarily determine the outcome and speed of healing process. The successful regeneration of functional tissues requires proper modulation of inflammation-producing immune cells and bioactive factors existing in the damaged microenvironment. In the tissue repair and regeneration processes, different types of biomaterials are implanted either alone or by combined with other bioactive factors, which will interact with the immune systems including immune cells, cytokines and chemokines etc. to achieve different results highly depending on this interplay. In this review article, the influences of different types of biomaterials such as nanoparticles, hydrogels and scaffolds on the immune cells and the modification of immune-responsive factors such as reactive oxygen species (ROS), cytokines, chemokines, enzymes, and metalloproteinases in tissue microenvironment are summarized. In addition, the recent advances of immune-responsive biomaterials in therapy of inflammation-associated diseases such as myocardial infarction, spinal cord injury, osteoarthritis, inflammatory bowel disease and diabetic ulcer are discussed.

Kaempferia parviflora Extract Alleviated Rat Arthritis, Exerted Chondroprotective Properties In Vitro, and Reduced Expression of Genes Associated with Inflammatory Arthritis

Kaempferia parviflora Wall. ex Baker (KP) has been reported to attenuate cartilage destruction in rat model of osteoarthritis. Previously, we demonstrated that KP rhizome extract and its active components effectively suppressed mechanisms associated with RA in SW982 cells. Here, we further evaluated the anti-arthritis potential of KP extract by using multi-level models, including a complete Freund’s adjuvant-induced arthritis and a cartilage explant culture model, and to investigate the effects of KP extract and its major components on related gene expressions and underlying mechanisms within cells. In arthritis rats, the KP extract reduced arthritis indexes, with no significant changes in biological parameters. In the cartilage explant model, the KP extract exerted chondroprotective potential by suppressing sulfated glycosaminoglycans release while preserving high accumulation of proteoglycans. In human chondrocyte cell line, a mixture of the major components equal to their amounts in KP extract showed strong suppression the expression of genes-associated inflammatory joint disease similar to that of the extract. Additionally, KP extract significantly suppressed NF-κB and MAPK signaling pathways. The suppressing expression of necroptosis genes and promoted anti-apoptosis were also found. Collectively, these results provided supportive evidence of the anti-arthritis properties of KP extract, which are associated with its three major components.

Circ_0134111 knockdown relieves IL-1β-induced apoptosis, inflammation and extracellular matrix degradation in human chondrocytes through the circ_0134111-miR-515-5p-SOCS1 network

BACKGROUND

Osteoarthritis (OA) is characterized by chondrocyte injury and dysfunction, such as excessive apoptosis, inflammatory response and extracellular matrix (ECM) degradation. Circular RNA (circRNA) deregulation is reported to be involved in OA. Our study aimed to explore the role of circ_0134111 in OA.

METHODS

Human chondrocytes were treated with interleukin-1β (IL-1β) to mimic OA cell model. The expression of circ_0134111, miR-515-5p and suppressor of cytokine signaling 1 (SOCS1) mRNA was measured by real-time quantitative polymerase chain reaction (RT-qPCR), and the protein levels of SOCS1 and apoptosis-/inflammation-/ECM-related markers were determined by western blot. Cell proliferation and cell apoptosis were assessed using cell counting kit-8 (CCK-8) and flow cytometry assay, respectively. For mechanism analysis, the predicted interaction between miR-515-5p and circ_0134111 or SOCS1 was verified by dual-luciferase reporter assay, pull-down assay and RNA immunoprecipitation (RIP) assay. Rescue experiments were performed to explore the interplay between miR-515-5p and circ_0134111 or SOCS1.

RESULTS

Circ_0134111 was overexpressed in OA cartilage tissues and IL-1β-induced chondrocytes. IL-1β-induced chondrocyte apoptosis, inflammatory responses and ECM degradation were alleviated by circ_0134111 knockdown or miR-515-5p restoration. Circ_0134111 acted as miR-515-5p sponge to regulate miR-515-5p expression, and miR-515-5p deficiency reversed the effects of circ_0134111 knockdown in IL-1β-induced chondrocytes. MiR-515-5p directly bound to SOCS1, and circ_0134111 decoyed miR-515-5p to increase SOCS1 level. MiR-515-5p restoration alleviated IL-1β-induced chondrocyte apoptosis, inflammatory responses and ECM degradation, While SOCS1 overexpression partly abolished these effects.

CONCLUSION

Circ_0134111 knockdown alleviated apoptosis, inflammatory responses and ECM degradation in OA cell model by mediating the miR-515-5p-SOCS1 network, hinting that circ_0134111 was involved in OA progression.

High expression of NDRG3 in osteoarthritis patients

BACKGROUND

Osteoarthritis (OA), as a common disease, seriously affects the quality of life of the victims, but its pathogenesis remains unclear. It has been confirmed that hypoxia-induced factor (HIF)-mediated hypoxia response plays an important role in the development and progression of OA. As a member of the N-myc downstream regulatory gene families, NDRG3 has been reported to independently regulate the hypoxic response of tumour cells, but the relationship between NDRG3 and OA development has not been reported so far.

METHODS

In this study, seven OA patients were admitted to Guizhou Provincial People's Hospital from January 2017 to December 2018. The OA group included 5 patients clinically diagnosed with hip/knee OA, which required arthroplasty. The normal group included 2 patients with no previous history of OA and rheumatoid arthritis, which required amputation due to trauma or tumour. The articular cartilage samples were collected to detect the expression of HIF-1α, HIF-2α and NDRG3 using immunohistochemical (IHC), haematoxylin and eosin (HE) and toluidine blue (TB) staining.

RESULTS

HE and TB staining indicated that the cartilage surface of the normal group was smooth and intact, with a columnar arrangement of hyaline chondrocytes, while the cartilage surface of the OA group was discontinuous, with cartilage missing and fibrous soft tissue growing into the defect site. HIF-1α staining was positive in both groups. Moreover, HIF-2α and NDRG3 staining was weakly positive in the normal group, but were uniformly and strongly positive in the OA group. The positively stained areas and integral optical density for NDRG3 were significantly greater in OA group than in the normal group (p < 0.05).

CONCLUSIONS

NDRG3 might be closely related to the development and progression of OA. However, the relationship between NDRG3 and OA, which is independent of the HIF pathway, warrants further research.

CCL2 induces articular chondrocyte MMP expression through ERK and p38 signaling pathways

Objective

In previous studies, we determined an association between increased serum and articular cartilage levels of CCL2 with osteoarthritis (OA) progression, cartilage damage and increased MMP13 in cartilage. Here we analyzed CCL2 downstream signaling mediators that lead to gene expression of cartilage catabolic markers, in healthy and OA human articular chondrocytes.

Design

Human articular chondrocytes obtained from healthy or OA subjects were treated with or without recombinant human CCL2; cell lysates or mRNA were collected for immunoblotting or qRT-PCR. For pathway analysis, chondrocytes were pre-incubated with an inhibitor of CCR2 (the unique CCL2 receptor), ERK inhibitor or p38 inhibitor prior to CCL2 treatment.

Results

CCL2 treatment of both healthy and OA chondrocytes activated ERK and p38 via CCR2. In healthy chondrocytes, short (6h) and prolonged (24-72h) CCL2 treatments led to Ccr2, Mmp-1, Mmp-3, Mmp-13 and Timp1 upregulation. In OA chondrocytes, CCL2 induced expression of Ccr2, Mmp-1 and Mmp-3, but not Mmp1 and Timp1, and only following longer treatments (72h). In both healthy and OA chondrocytes, the CCL2-mediated upregulation of Ccr2 and cartilage catabolic markers was mediated by ERK and p38 signaling.

Conclusions

The triggering of the CCL2/CCR2 axis in articular chondrocytes activates specific MAPK pathways leading to gene expression of cartilage degrading enzymes. However, some differences in the response to CCL2 stimulation are detected in healthy vs OA chondrocytes with respect to the number of activated genes and to the time of exposure to CCL2, suggesting that CCL2 action in articular cartilage may be dependent on OA stage and severity.

Circular RNA CSNK1G1 promotes the progression of osteoarthritis by targeting the miR‑4428/FUT2 axis

Osteoarthritis (OA) is a chronic disease that results in chronic arthralgia and functional disability of the affected joint. To date, there is no effective treatment available for this disease. Circular RNAs (circRNAs) are a type of intracellular stable RNA that can regulate the development and progression of OA. However, the function of circCSNK1G1 in OA has not yet been investigated. In the present study, it was found that circCSNK1G1 was upregulated in OA cartilage tissues. The upregulation of circCSNK1G1 was associated with extracellular matrix (ECM) degradation and chondrocyte apoptosis. Moreover, the expression of miR‑4428 was downregulated and that of fucosyltransferase 2 (FUT2) was upregulated in OA‑affected cartilage tissues. Dual‑luciferase reporter assay and RNA immunoprecipitation confirmed that miR‑4428 targeted FUT2 mRNA to inhibit FUT2 expression. circCSNK1G1 and FUT2 induced ECM degradation and chondrocyte apoptosis. The negative effects of circCSNK1G1 and FUT2 were reversed by miR‑4428. On the whole, the present study demonstrates that circCSNK1G1 promotes the development of OA by targeting the miR‑4428/FUT2 axis. Thus, the circCSNK1G1/miR‑4428/FUT2 axis may present a novel target for the treatment of OA in the clinical setting.