BACKGROUND: Knee osteoarthritis (OA) is still challenging to prevent or treat. Enhanced endoplasmic reticulum (ER) stress and increased pyroptosis in chondrocytes may be responsible for cartilage degeneration. This study aims to investigate the effect of ER stress on chondrocyte pyroptosis and the upstream regulatory mechanisms, which have rarely been reported. METHODS: The expression of the histone methyltransferase enhancer of zeste homolog 2 (EZH2), microRNA-142-3p (miR-142-3p), and high mobility group box 1 (HMGB1) and the levels of ER stress, pyroptosis, and metabolic markers in normal and OA chondrocytes were investigated by western blotting, quantitative polymerase chain reaction, immunohistochemistry, fluorescence in situ hybridization, fluorescein amidite-tyrosine-valine-alanine-aspartic acid-fluoromethyl ketone (FAM-YVAD-FMK)/Hoechst 33342/propidium iodide (PI) staining, lactate dehydrogenase (LDH) release assays, and cell viability assessments. The effects of EZH2, miR-142-3p, and HMGB1 on ER stress and pyroptosis and the hierarchical regulatory relationship between them were analyzed by chromatin immunoprecipitation, luciferase reporters, gain/loss-of-function assays, and rescue assays in interleukin (IL)-1β-induced OA chondrocytes. The mechanistic contribution of EZH2, miR-142-3p, and HMGB1 to chondrocyte ER stress and pyroptosis and therapeutic prospects were validated radiologically, histologically, and immunohistochemically in surgically induced OA rats. RESULTS: Increased EZH2 and HMGB1, decreased miR-142-3p, enhanced ER stress, and activated pyroptosis in chondrocytes were associated with OA occurrence and progression. EZH2 and HMGB1 exacerbated and miR-142-3p alleviated ER stress and pyroptosis in OA chondrocytes. EZH2 transcriptionally silenced miR-142-3p via H3K27 trimethylation, and miR-142-3p posttranscriptionally silenced HMGB1 by targeting the 3'-UTR of the HMGB1 gene. Moreover, ER stress mediated the effects of EZH2, miR-142-3p, and HMGB1 on chondrocyte pyroptosis. In vivo experiments mechanistically validated the hierarchical regulatory relationship between EZH2, miR-142-3p, and HMGB1 and their effects on chondrocyte ER stress and pyroptosis. CONCLUSIONS A novel EZH2/miR-142-3p/HMGB1 axis mediates chondrocyte pyroptosis and cartilage degeneration by regulating ER stress in OA, contributing novel mechanistic insights into OA pathogenesis and providing potential targets for future therapeutic research.
Enhancer of Zeste Homolog 2 Protein/genetics* ; Osteoarthritis, Knee/pathology* ; Chondrocytes/metabolism* ; Pyroptosis/physiology* ; HMGB1 Protein/genetics* ; MicroRNAs/metabolism* ; Endoplasmic Reticulum Stress/genetics* ; Humans ; Animals ; Rats ; Male ; Rats, Sprague-Dawley ; Middle Aged

Osteoarthritis (OA) is the most common degenerative joint disease. Its pathological process is related to inflammatory response, chondrocyte apoptosis, and cartilage degeneration. Hippo-yes-associate protein(YAP) signaling pathway plays an important role in mediating organ size and tissue homeostasis. In recent years, the key effector protein YAP in the Hippo-YAP pathway has become a research hotspot in osteoarthritis. This article introduces the activation process of Hippo-YAP signaling pathway and the biological role of YAP. It reviews the progress of YAP in regulating osteoarthritis by influencing the proliferation and differentiation of mesenchymal stem cells and the proliferation, differentiation, and apoptosis of articular chondrocytes. It analyzed the problems encountered in YAP research in OA, introduces the research potential of YAP in other orthopedic diseases, and provides new ideas for subsequent research in Osteoarthritis.
Osteoarthritis/metabolism* ; Humans ; Signal Transduction ; Protein Serine-Threonine Kinases/physiology* ; Hippo Signaling Pathway ; YAP-Signaling Proteins ; Adaptor Proteins, Signal Transducing/physiology* ; Animals ; Transcription Factors ; Chondrocytes/cytology* ; Cell Cycle Proteins

OBJECTIVES: Osteoarthritis (OA) is one of the most common chronic degenerative diseases, with chondrocyte apoptosis and extracellular matrix (ECM) degradation as the major pathological changes. The mechanical stimulation can attenuate chondrocyte apoptosis and promote ECM synthesis, but the underlying molecular mechanisms remain unclear. This study aims to investigate the role of primary cilia (PC) in mediating the effects of mechanical stimulation on OA progression. METHODS: In vivo, conditional knockout mice lacking intraflagellar transport 88 (IFT88^flox/flox IFT88 knockout; i.e., primary cilia-deficient mice) were generated, with wild-type mice as controls. OA models were established via anterior cruciate ligament transection combined with destabilization of the medial meniscus, followed by treadmill exercise intervention. OA progression was evaluated by hematoxylin-eosin staining, safranin O-fast green staining, and immunohistochemistry; apoptosis was assessed by TUNEL staining; and limb function by rotarod testing. In vitro, primary articular chondrocytes were isolated from mice and transfected with lentiviral vectors to suppress IFT88 expression, thereby constructing a primary cilia-deficient cell model. Interleukin-1β (IL-1β) was used to induce an inflammatory environment, while cyclic tensile strain (CTS) was applied via a cell stretcher to mimic mechanical loading on chondrocytes. Immunofluorescence and Western blotting were used to detect the protein expression levels of type II collagen α1 chain (COL2A1), primary cilia, IFT88, and caspase-12; reverse transcription polymerase chain reaction was performed to assess COL2A1 mRNA levels; and flow cytometry was used to evaluate apoptosis. RESULTS: In vivo, treadmill exercise significantly reduced Osteoarthritis Research Society International (OARSI) scores and apoptotic cell rates, and improved balance ability in wild-type OA mice, whereas IFT88-deficient OA mice showed no significant improvement. In vitro, CTS inhibited IL-1β-induced ECM degradation and apoptosis in primary chondrocytes; however, this protective effect was abolished in cells with suppressed primary cilia expression. CONCLUSIONS Mechanical stimulation delays OA progression by mediating signal transduction through primary cilia, thereby inhibiting cartilage degeneration and chondrocyte apoptosis.
Animals ; Chondrocytes/cytology* ; Apoptosis/physiology* ; Mice ; Cilia/metabolism* ; Osteoarthritis/pathology* ; Extracellular Matrix/metabolism* ; Mice, Knockout ; Disease Progression ; Interleukin-1beta ; Male ; Cells, Cultured

Meniscus injuries are widespread and the available treatments do not offer enough healing potential. Here, we provide critical support for using pigs as a biological model for meniscal degeneration and the development of cutting-edge therapies in orthopedics. We present a single-cell transcriptome atlas of the meniscus, consisting of cell clusters corresponding to four major cell types: chondrocytes, endothelial cells, smooth muscle cells, and immune cells. Five distinct chondrocyte subclusters (CH0‒CH4) were annotated, of which only one was widespread in both the red and white zones, indicating a major difference in the cellular makeup of the zones. Subclusters distinct to the white zone appear responsible for cartilage-specific matrix deposition and protection against adverse microenvironmental factors, while those in the red zone exhibit characteristics of mesenchymal stem cells and are more likely to proliferate and migrate. Additionally, they induce remodeling actions in other chondrocyte subclusters and promote the proliferation and maturation of endothelial cells, inducing healing and vascularization processes. Considering that they have substantial remodeling capabilities, these subclusters should be of great interest for tissue engineering studies. We also show that the cellular makeup of the pig meniscus is comparable to that of humans, which supports the use of pigs as a model in orthopedic therapy development.
Animals ; Swine ; Chondrocytes/physiology* ; Single-Cell Analysis ; Meniscus/blood supply* ; Endothelial Cells/cytology* ; Transcriptome ; Mesenchymal Stem Cells/cytology* ; Neovascularization, Physiologic ; Cell Proliferation

OBJECTIVES: This study aims to investigate the effects and mechanisms of chondroitin sulfate (CS), dermatan sulfate (DS), and heparin (HEP) on chondrogenesis of murine chondrogenic cell line (ATDC5) cells and the maintenance of murine articular cartilage in vitro. METHODS: ATDC5 and articular cartilage tissue explant were cultured in the medium containing different sulfated glycosaminoglycans. Cell proliferation, differentiation, cartilage formation, and mechanism were observed using cell proliferation assay, Alcian blue staining, real-time quantitative polymerase chain reaction (RT-qPCR), and Western blot, respectively. RESULTS: Results showed that HEP and DS primarily activated the bone morphogenetic protein (BMP) signal pathway, while CS primarily activated the protein kinase B (AKT) signal pathway, further promoted ATDC5 cell proliferation and matrix production, and increased Sox9, Col2a1, and Aggrecan expression. CONCLUSIONS This study investigated the differences and mechanisms of different sulfated glycosaminoglycans in chondrogenesis and cartilage homeostasis maintenance. HEP promotes cartilage formation and maintains the normal state of cartilage tissue in vitro, while CS plays a more effective role in the regeneration of damaged cartilage tissue.
Animals ; Mice ; Cartilage/metabolism* ; Cell Differentiation ; Cells, Cultured ; Chondrocytes/metabolism* ; Chondrogenesis/physiology* ; Glycosaminoglycans/pharmacology*

The study aims to explore the effect of mesenchymal stem cells-derived exosomes (MSCs-Exo) on staurosporine (STS)-induced chondrocyte apoptosis before and after exposure to pulsed electromagnetic field (PEMF) at different frequencies. The AMSCs were extracted from the epididymal fat of healthy rats before and after exposure to the PEMF at 1 mT amplitude and a frequency of 15, 45, and 75 Hz, respectively, in an incubator. MSCs-Exo was extracted and identified. Exosomes were labeled with DiO fluorescent dye, and then co-cultured with STS-induced chondrocytes for 24 h. Cellular uptake of MSC-Exo, apoptosis, and the protein and mRNA expression of aggrecan, caspase-3 and collagenⅡA in chondrocytes were observed. The study demonstrated that the exposure of 75 Hz PEMF was superior to 15 and 45 Hz PEMF in enhancing the effect of exosomes in alleviating chondrocyte apoptosis and promoting cell matrix synthesis. This study lays a foundation for the regulatory mechanism of PEMF stimulation on MSCs-Exo in inhibiting chondrocyte apoptosis, and opens up a new direction for the prevention and treatment of osteoarthritis.
Animals ; Rats ; Apoptosis ; Chondrocytes ; Electromagnetic Fields ; Exosomes/physiology* ; Mesenchymal Stem Cells/metabolism*

After the articular cartilage injury, the metabolic level is increased during the progressive degeneration, the chondrocytes secrete a variety of inflammatory factors, and the original cell phenotype is gradually changed. For a long time, a large number of researchers have done a lot of researches to promote anabolism of chondrocytes and to maintain the stability of chondrocyte phenotype. There are many molecular signaling pathways involved in the process of promoting cartilage repair. This review focuses on the key signaling molecules in articular cartilage repair, such as transforming growth factor-beta and bone morphogenetic protein, and reveals their roles in the process of cartilage injury and repair, so that researchers in related fields can understand the molecular mechanism of cartilage injury and repair widely and deeply. Based on this, they may find promising targets and biological methods for the treatment of cartilage injury.
Bone Morphogenetic Proteins ; physiology ; Cartilage, Articular ; growth & development ; injuries ; Chondrocytes ; physiology ; Humans ; Regeneration ; Signal Transduction ; Transforming Growth Factor beta ; physiology

This study determined the effects of selenium on the growth of Fusarium strains and the effects of products extracted from the fungal cultures on relevant indicators of chondrocytes injury. The results showed that selenium supplementation resulted in differential effects on the mycelial growth of the strains. Levels of the chondrocyte injury indicators, including cell viability, proteoglycan and type II collagen contents and their mRNA expressions, were all reduced to varying degrees when the chondrocytes were incubated with fermentation extracts, the inhibitory effect varied depending on selenium content supplemented to fungal culture media. The results indicated that certain chain relations existed between the content of selenium in the environment, the production of some metabolites by fungi, and the occurrence of chondrocyte damage. The extent of this relationship and the role it plays in Kaschin-Beck disease pathogenesis merit further study.
Animals ; Cell Survival ; Cells, Cultured ; Chondrocytes ; pathology ; Fermentation ; Fusarium ; drug effects ; physiology ; Rabbits ; Selenium ; pharmacology

OBJECTIVETo investigate chondrocyte apoptosis and the expression of biochemical markers associated with apoptosis in Kashin-Beck disease (KBD) and in an established T-2 toxin- and selenium (Se) deficiency-induced rat model.

METHODSCartilages were collected from the hand phalanges of five patients with KBD and five healthy children. Sprague-Dawley rats were administered a selenium-deficient diet for 4 weeks prior to T-2 toxin exposure. The apoptotic chondrocytes were observed by terminal deoxynucleotidyl transferase dUTP nick end labeling staining. Caspase-3, p53, Bcl-2, and Bax proteins in the cartilages were visualized by immunohistochemistry, their protein levels were determined by Western blotting, and mRNA levels were determined by real-time reverse transcription polymerase chain reaction.

RESULTSIncreased chondrocyte apoptosis was observed in the cartilages of children with KBD. Increased apoptotic and caspase-3-stained cells were observed in the cartilages of rats fed with normal and Se-deficient diets plus T-2 toxin exposure compared to those in rats fed with normal and Se-deficient diets. Caspase-3, p53, and Bax proteins and mRNA levels were higher, whereas Bcl-2 levels were lower in rats fed with normal or Se-deficiency diets supplemented with T-2 toxin than the corresponding levels in rats fed with normal diet.

CONCLUSIONT-2 toxin under a selenium-deficient nutritional status induces chondrocyte death, which emphasizes the role of chondrocyte apoptosis in cartilage damage and progression of KBD.

Adolescent ; Animals ; Apoptosis ; drug effects ; Biomarkers ; Cartilage, Articular ; physiopathology ; Child ; Chondrocytes ; physiology ; Female ; Humans ; Kashin-Beck Disease ; etiology ; physiopathology ; Male ; Matrilin Proteins ; genetics ; metabolism ; Models, Animal ; Random Allocation ; Rats ; Rats, Sprague-Dawley ; Selenium ; deficiency ; T-2 Toxin ; pharmacology

BACKGROUNDSeveral studies have revealed that adipose-derived mesenchymal stem cells (ADSCs) can be used as seed cells for the treatment of spinal cord injury (SCI). Chondroitinase ABC (ChABC) decomposes chondroitin sulfate proteoglycans in the glial scar that forms following SCI, allowing stem cells to penetrate through the scar and promote recovery of nerve function. This study aimed to establish ADSCs that stably express ChABC (ChABC-ADSCs) and evaluate the migratory capability of ChABC-ADSCs in vitro.

METHODSADSCs were obtained from Sprague-Dawley rats using secondary collagenase digestion. Their phenotypes were characterized using flow cytometry detection of cell surface antigens and their stem cell properties were confirmed by induction of differentiation. After successful culture, ADSCs were transfected with lentiviral vectors and ChABC-ADSCs were obtained. Proliferation curves of ChABC-ADSCs were determined using the Cell Counting Kit-8 method, ChABC expression was verified using Western blotting, and the migration of ChABC-ADSCs was analyzed using the transwell assay.

RESULTSSecondary collagenase digestion increased the isolation efficiency of primary ADSCs. Following transfection using lentiviral vectors, the proliferation of ChABC-ADSCs was reduced in comparison with control ADSCs at 48 h (P < 0.05). And the level of ChABC expression in the ChABC-ADSC group was significantly higher than that of the ADSC group (P < 0.05). Moreover, ChABC-ADSC migration in matrigel was significantly enhanced in comparison with the control (P < 0.05).

CONCLUSIONSSecondary collagenase digestion can be used to effectively isolate ADSCs. ChABC-ADSCs constructed using lentiviral vector transfection stably express ChABC, and ChABC expression significantly enhances the migratory capacity of ADSCs.

Adipocytes ; cytology ; metabolism ; Adipose Tissue ; cytology ; Animals ; Cell Differentiation ; physiology ; Cell Movement ; physiology ; Cell Proliferation ; physiology ; Cells, Cultured ; Chondrocytes ; cytology ; metabolism ; Chondroitin ABC Lyase ; metabolism ; Flow Cytometry ; Male ; Mesenchymal Stromal Cells ; cytology ; metabolism ; Osteoblasts ; cytology ; metabolism ; Rats ; Rats, Sprague-Dawley