Chondrocyte ferroptosis contribute to the progression of osteoarthritis

Research progress on the mechanism of interleukin-1β on epiphyseal plate chondrocytes

Epiphyseal plate injury, a common problem in pediatric orthopedics, may result in poor bone repair or growth defects. Epiphyseal plate, also known as growth plate is a layer of hyaline cartilage tissue between the epiphysis and metaphyseal and has the ability to grow longitudinally. Under normal physiological conditions, the epiphyseal plate has a certain axial resistance to stress, but it is fragile in growth phase and can be damaged by excessive stress, leading to detachment or avulsion of the epiphysis, resulting in life-long devastating consequences for patients. There is an obvious inflammatory response in the phase of growth plate injury, the limited physiological inflammatory response locally favors tissue repair and the organism, but uncontrolled chronic inflammation always leads to tissue destruction and disease progression. Interleukin-1β (IL-1β), as representative inflammatory factors, not only affect the inflammatory phase response to bone and soft tissue injury, but have a potentially important role in the later repair phase, though the exact mechanism is not fully understood. At present, epiphyseal plate injuries are mainly treated by corrective and reconstructive surgery, which is highly invasive with limited effectiveness, thus new therapeutic approaches are urgently needed, so a deeper understanding and exploration of the pathological mechanisms of epiphyseal plate injuries at the cellular molecular level is an entry point. In this review, we fully introduced the key role of IL-1 in the progression of epiphyseal plate injury and repair, deeply explored the mechanism of IL-1 on the molecular transcript level and endocrine metabolism of chondrocytes from multiple aspects, and summarized other possible mechanisms to provide theoretical basis for the clinical treatment and in-depth study of epiphyseal plate injury in children.

Molecular mechanisms of ferroptosis and relevance to inflammation

INTRODUCTION

Inflammation is a defensive response of the organism to irritation which is manifested by redness, swelling, heat, pain and dysfunction. The inflammatory response underlies the role of various diseases. Ferroptosis, a unique modality of cell death, driven by iron-dependent lipid peroxidation, is regulated by multifarious cellular metabolic pathways, including redox homeostasis, iron processing and metabolism of lipids, as well as various signaling pathways associated with diseases. A growing body of evidence suggests that ferroptosis is involved in inflammatory response, and targeting ferroptosis has great prospects in preventing and treating inflammatory diseases.

MATERIALS AND METHODS

Relevant literatures on ferroptosis, inflammation, inflammatory factors and inflammatory diseases published from January 1, 2010 to now were searched in PubMed database.

CONCLUSION

In this review, we summarize the regulatory mechanisms associated with ferroptosis, discuss the interaction between ferroptosis and inflammation, the role of mitochondria in inflammatory ferroptosis, and the role of targeting ferroptosis in inflammatory diseases. As more and more studies have confirmed the relationship between ferroptosis and inflammation in a wide range of organ damage and degeneration, drug induction and inhibition of ferroptosis has great potential in the treatment of immune and inflammatory diseases.

Differential expression of cyclins CCNB1 and CCNG1 is involved in the chondrocyte damage of kashin-beck disease

The purpose of this study was clarify the relationship between the differential expression of cyclins CCNB1 and CCNG1 and chondrocyte damage in Kashin-Beck disease. Systematic review and high-throughput sequencing of chondrocytes derived from Kashin-Beck disease patients were combined to identify the differentially expressed cyclins and cyclin-dependent kinase genes. In parallel, weaned SD rats were treated with low selenium for 4 weeks and then T-2 toxin for 4 weeks. Knee cartilage was collected to harvest chondrocytes for gene expression profiling. Finally, the protein expression levels of CCNB1 and CCNG1 were verified in knee cartilage tissue of Kashin-Beck disease patients and normal controls by immunohistochemical staining. The systematic review found 52 cartilage disease-related cyclins and cyclin-dependent kinase genes, 23 of which were coexpressed in Kashin-Beck disease, including 15 upregulated and 8 downregulated genes. Under the intervention of a low selenium diet and T-2 toxin exposure, CCNB1 (FC = 0.36) and CCNG1 (FC = 0.73) showed a downward expression trend in rat articular cartilage. Furthermore, compared to normal controls, CCNB1 protein in Kashin-Beck disease articular cartilage was 71.98% and 66.27% downregulated in the superficial and middle zones, respectively, and 12.06% upregulated in the deep zone. CCNG1 protein was 45.66% downregulated in the superficial zone and 12.19% and 9.13% upregulated in the middle and deep zones, respectively. The differential expression of cyclins CCNB1 and CCNG1 may be related to articular cartilage damage in Kashin-Beck disease.

Focusing on the hypoxia-inducible factor pathway: role, regulation, and therapy for osteoarthritis

Osteoarthritis (OA) is a common chronic disabling disease that affects hundreds of millions of people around the world. The most important pathological feature is the rupture and loss of articular cartilage, and the characteristics of avascular joint tissues lead to limited repair ability. Currently, there is no effective treatment to prevent cartilage degeneration. Studies on the mechanism of cartilage metabolism revealed that hypoxia-inducible factors (HIFs) are key regulatory genes that maintain the balance of cartilage catabolism-matrix anabolism and are considered to be the major OA regulator and promising OA treatment target. Although the exact mechanism of HIFs in OA needs to be further clarified, many drugs that directly or indirectly act on HIF signaling pathways have been confirmed by animal experiments and regarded as promising treatments for OA. Targeting HIFs will provide a promising strategy for the development of new OA drugs. This article reviews the regulation of HIFs on intra-articular cartilage homeostasis and its influence on the progression of osteoarthritis and summarizes the recent advances in OA therapies targeting the HIF system.

Teriparatide ameliorates articular cartilage degradation and aberrant subchondral bone remodeling in DMM mice

Objective

Knee osteoarthritis (KOA) is a highly prevalent musculoskeletal disorder characterized by degeneration of cartilage and abnormal remodeling of subchondral bone (SCB). Teriparatide (PTH (1-34)) is an effective anabolic drug for osteoporosis (OP) and regulates osteoprotegerin (OPG)/receptor activator of nuclear factor ligand (RANKL)/RANK signaling, which also has a therapeutic effect on KOA by ameliorating cartilage degradation and inhibiting aberrant remodeling of SCB. However, the mechanisms of PTH (1-34) in treating KOA are still uncertain and remain to be explored. Therefore, we compared the effect of PTH (1-34) on the post-traumatic KOA mouse model to explore the potential therapeutic effect and mechanisms.

Methods

In vivo study, eight-week-old male mice including wild-type (WT) (n ​= ​54) and OPG^-/- (n ​= ​54) were investigated and compared. Post-traumatic KOA model was created by destabilization of medial meniscus (DMM). WT mice were randomly assigned into three groups: the sham group (WT-sham; n ​= ​18), the DMM group (WT-DMM; n ​= ​18), and the PTH (1-34)-treated group (WT-DMM ​+ ​PTH (1-34); n ​= ​18). Similarly, the OPG^-/- mice were randomly allocated into three groups as well. The designed mice were executed at the 4th, 8th, and 12th weeks to evaluate KOA progression. To further explore the chondro-protective of PTH (1-34), the ATDC5 chondrocytes were stimulated with different concentrations of PTH (1-34) in vitro.

Results

Compared with the WT-sham mice, significant wear of cartilage in terms of reduced cartilage thickness and glycosaminoglycan (GAG) loss was detected in the WT-DMM mice. PTH (1-34) exhibited cartilage-protective by alleviating wear, retaining the thickness and GAG contents. Moreover, the deterioration of the SCB was alleviated and the expression of PTH1R/OPG/RANKL/RANK were found to increase after PTH (1-34) treatment. Among the OPG^-/- mice, the cartilage of the DMM mice displayed typical KOA change with higher OARSI score and thinner cartilage. The damage of the cartilage was alleviated but the abnormal remodeling of SCB didn't show any response to the PTH (1-34) treatment. Compared with the WT-DMM mice, the OPG^-/--DMM mice caught more aggressive KOA with thinner cartilage, sever cartilage damage, and more abnormal remodeling of SCB. Moreover, both the damaged cartilage from the WT-DMM mice and the OPG^-/--DMM mice were alleviated but only the deterioration of SCB in WT-DMM mice was alleviated after the administration of PTH (1-34). In vitro study, PTH (1-34) could promote the viability of chondrocytes, enhance the synthesis of extracellular matrix (ECM) (AGC, COLII, and SOX9) at the mRNA and protein level, but inhibit the secretion of inflammatory cytokines (TNF-α and IL-6).

Conclusion

Both wear of the cartilage was alleviated and aberrant remodeling of the SCB was inhibited in the WT mice, but only the cartilage-protective effect was observed in the OPG^-/- mice. PTH (1-34) exhibited chondro-protective effect by decelerating cartilage degeneration in vivo as well as by promoting the proliferation and enhancing ECM synthesis of chondrocytes in vitro. The current investigation implied that the rescue of the disturbed SCB is dependent on the regulation of OPG while the chondro-protective effect is independent of modulation of OPG, which provides proof for the treatment of KOA.

The translational potential of this article

Systemic administration of PTH (1-34) could exert a therapeutic effect on both cartilage and SCB in different mechanisms to alleviate KOA progression, which might be a novel therapy for KOA.

Theaflavin-3,3'-Digallate Inhibits Erastin-Induced Chondrocytes Ferroptosis via the Nrf2/GPX4 Signaling Pathway in Osteoarthritis

There is evidence that osteoarthritis (OA) is associated with ferroptosis which is a kind of lipid peroxidation-related cell death. Theaflavin-3,3'-digallate(TF3), a polyphenol compound extracted from black tea, possesses antioxidative and anti-inflammatory properties, but its effects on chondrocyte ferroptosis in osteoarthritis (OA) remain unclear. Our present study aims at exploring the protective role and underlying mechanisms of TF3 against erastin-induced chondrocyte ferroptosis in OA. In human primary chondrocytes treated with erastin alone or combined with different doses of TF3, cell viability was assessed by MTS. Ferroptosis-related proteins, including Gpx4, HO-1, and FTH1, were detected by western blot. The levels of lipid peroxidation and Fe2⁺ were determined by fluorescence staining. Meanwhile, the change of related proteins in the Nrf2/Gpx4 signaling pathway was determined by western blot. siRNA-mediated Nrf2 knockdown and the Gpx4 inhibitor RSL3 were used to explore molecular mechanisms for TF3-induced ferroptosis in OA chondrocyte. The magnetic resonance imaging (MRI), HE staining, Masson's staining, and immunohistochemistry were used to evaluate articular cartilage damages in the rat OA model. The results showed that Gpx4 expression was markedly downregulated in the chondrocytes of OA patients. TF3 reversed erastin-induced ferroptosis of human cultured chondrocytes, lipid ROS, and Fe2⁺ production in mitochondria. Moreover, the expression of Gpx4, HO-1, FTH1, and Nrf2 was markedly induced by TF3 in the erastin-treated chondrocytes. The antiferroptotic effect of TF3 was related to enhance Nrf2/Gpx4 signaling pathway. Finally, TF3 inhibited OA progression by alleviating in vivo cartilage damage related to chondrocyte ferroptosis. Thus, TF3 significantly inhibits chondrocyte ferroptosis by activating the Nrf2/Gpx4 signaling pathway, suggesting that TF3 serves as a potential therapeutic supplement for OA treatment.

Identification of SLC3A2 as a Potential Therapeutic Target of Osteoarthritis Involved in Ferroptosis by Integrating Bioinformatics, Clinical Factors and Experiments

Osteoarthritis (OA) is a type of arthritis that causes joint pain and limited mobility. In recent years, some studies have shown that the pathological process of OA chondrocytes is related to ferroptosis. Our study aims to identify and validate differentially expressed ferroptosis-related genes (DEFRGs) in OA chondrocytes and to investigate the potential molecular mechanisms. RNA-sequencing and microarray datasets were downloaded from Gene Expression Omnibus (GEO) data repository. Differentially expressed genes (DEGs) were screened by four methods: limma-voom, edgeR, DESeq2, and Wilcoxon rank-sum test. Weighted correlation network analysis (WGCNA), protein-protein interactions (PPI), and cytoHubba of Cytoscape were applied to identify hub genes. Clinical OA cartilage specimens were collected for quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis, western blotting (WB), histological staining, transmission electron microscopy (TEM), and transfection. Sankey diagram was used to visualize the relationships between the expression level of SLC3A2 in the damaged area and clinical factors. Based on bioinformatics analysis, clinical factors, and experiment validation, SLC3A2 was identified as a hub gene. It was down-regulated in OA cartilage compared to normal cartilage (p < 0.05). Functional enrichment analysis revealed that SLC3A2 was associated with ferroptosis-related functions. Spearman correlation analysis showed that the expression level of SLC3A2 in the OA cartilage-damaged area was closely related to BMI, obesity grade, and Kellgren-Lawrence grade. Furthermore, in vitro experiments validated that SLC3A2 inhibited ferroptosis and suppressed cartilage degeneration in OA. In summary, we demonstrated that SLC3A2 inhibited ferroptosis and suppressed cartilage degeneration in OA. These findings provide a new idea for the study of the pathogenesis of OA, thus providing new means for the clinical diagnosis and targeted therapy of OA.

Ferroptosis and musculoskeletal diseases: “Iron Maiden” cell death may be a promising therapeutic target

Ferroptosis is a novel form of cell death precisely regulated by iron metabolism, antioxidant processes, and lipid metabolism that plays an irreplaceable role in the development of many diseases. Musculoskeletal disorders (MSKs), including osteoporosis, osteoarthritis, rheumatoid arthritis, intervertebral disc degeneration, sarcopenia, and rhabdomyolysis, have become one of the most common causes of disability and a major burden on public health and social care systems. The mechanism of ferroptosis in MSKs has recently been elucidated. In this review, we briefly introduce the ferroptosis mechanism and illustrate the pathological roles of ferroptosis in MSKs with a focus on how ferroptosis can be exploited as a promising treatment strategy. Notably, because the toxicity of compounds that inhibit or induce ferroptosis in other organs is largely unknown, ferroptosis appears to be a double-edged sword. We point out that more research is needed in the future to verify the therapeutic effects based on ferroptosis in MSKs.

The Influence of Diet and Physical Activity on Oxidative Stress in Romanian Females with Osteoarthritis

Osteoarthritis (OA) is the most prevalent chronic joint disease, increases in prevalence with age, and affects most individuals over 65. The present study aimed to assess the oxidative status in relation to diet and physical activity in patients with OA. We used a cross-sectional study applied to 98 females with OA. Blood samples were collected to determine oxidative stress markers: malonyl dialdehyde (MDA), reduced glutathione (GSH), oxidized glutathione (GSSG), and GSH/GSSG. Diet was estimated with a standardized food frequency questionnaire. We used the International Physical Activity Questionnaire (IPAQ) to assess the females’ physical activity. Multiple regression analyses were executed to determine the association between the oxidative markers and the intake of vegetables and fruit. The study showed that most patients were overweight or obese (88.8%). The level of physical activity was above the recommended level for adults, mainly based on household activities. The intake of vegetables and fruit was low. The MDA marker was inversely, statistically significantly associated with the consumption of vegetables (p < 0.05). Public health policies must address modifiable risk factors to reduce energy intake and obesity and increase the intake of vegetables and fruit. Higher consumption of vegetables and fruit may provide natural antioxidants that can balance oxidative compounds.

Naringenin protects against iron overload-induced osteoarthritis by suppressing oxidative stress

BACKGROUND

The traditional Chinese medicine Gusuibu, the rhizome of Rhizoma Drynariae, is used to treat rheumatism and fractures. Naringenin (NAR) is an active ingredient in Gusuibu and has significant anti-inflammatory and antioxidant effects. However, the role of naringenin in iron overload-induced osteoarthritis (IOOA) is unknown.

HYPOTHESIS

NAR reduces cartilage damage in IOOA.

METHODS

The effects of NAR on the viability of IOOA chondrocytes and the synthesis ability of type II collagen were evaluated using cell counting kit (CCK8) and toluidine blue assays. To determine the mechanism of action and characteristics of NAR, the intracellular iron ion content, apoptosis rate, and mitochondrial membrane potential (MMP) change, and malondialdehyde (MDA) levels, as well as the degree of reactive oxygen species (ROS) and lipid hydroperoxide (LPO) accumulation in the cells were detected in vitro and verified using western blotting and quantitative real-time PCR (qRT-PCR). To verify the role of NAR in vivo, IOOA mice were established using iron dextran and surgery-induced destabilised medial meniscus. Changes in the articular cartilage and subchondral bone were examined using Safranin O-fast Green staining (S-O), haematoxylin-eosin staining (H&E), and microcomputed tomography (μCT).

RESULTS

In vitro, NAR attenuated the impairment of cell viability, apoptosis, and MMP caused by ferric ammonium citrate and interleukin-1β co-culture, increased the levels of MDA, reduced the expression of matrix metallopeptidase (MMP)3, MMP13, and Bax, and restored the expression of type II collagen (Col II). NAR showed a slight iron accumulation-reducing effect. NAR alleviated the accumulation of ROS and LPO in IOOA chondrocytes and upregulated antioxidant genes nuclear factor E2-related factor 2 (NRF2) and haem oxygenase 1 (HO-1). When ML385, a specific NRF-2 inhibitor, was added, the protective effect of NAR was significantly inhibited. In vivo, NAR reduced synovitis and attenuated cartilage damage and subchondral bone proliferation in IOOA mice.

CONCLUSIONS

NAR can reduce oxidative stress through the NRF2-HO-1 pathway, alleviate cartilage damage under iron overload, and has the potential to treat IOOA.

Astaxanthin attenuates osteoarthritis progression via inhibiting ferroptosis and regulating mitochondrial function in chondrocytes

Ferroptosis is a novel form of regulated cell death that has a close association with mitochondrial dysfunction and is characterized by iron overload, the accumulation of reactive oxygen species (ROS), and lipid ROS. Chondrocytes ferroptosis accelerates the progression of osteoarthritis (OA). Astaxanthin (ATX) is a xanthophyll carotenoid that possesses anti-inflammatory and antioxidant properties and has been explored in research studies for the treatment of diabetes and cardiovascular disease. However, the role it plays in OA, particularly in chondrocyte ferroptosis, has not yet been reported. In this study, ferroptosis-related events were analyzed in rat chondrocytes in vitro. A surgical destabilized medial meniscus was performed for the establishment of in vivo OA model. The results showed that interleukin-1β (IL-1β) induced inflammatory injury in chondrocytes through the promotion of the expressions of inflammatory factors including inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX2). IL-1β triggered chondrocyte ferroptosis by increasing the levels of intracellular ROS, lipid ROS, iron, and mitochondrial iron and inhibiting the expressions of SLC7A11/glutathione peroxidase 4 (GPX4) and Ferritin. The above indices were ameliorated by ferrostatin-1 (Fer-1, a classic ferroptosis inhibitor) and ATX. Furthermore, Fer-1 and ATX rescued the IL-1β-induced down-regulating collagen type II (collagen Ⅱ) and up-regulating matrix metalloproteinase 13 (MMP13). Following treatment with IL-1β, mitochondrial membrane potential decreased and the mitochondrial membrane was broken. At the same time, the mitochondrion shrank, becoming deformed as the mitochondrial cristae reduced and became disrupted. These changes were entirely consistent with ferroptosis features. All the aforementioned phenomena were reversed by Fer-1 and ATX. In addition, intra-articular injection of Fer-1 and ATX delayed articular cartilage degradation and OA progression. This study demonstrated that IL-1β can induce inflammatory damage and ferroptosis in chondrocytes. Both Fer-1 and ATX have the ability to mitigate chondrocyte injury and osteoarthritis progression by inhibiting ferroptosis and the regulation of mitochondrial function. Targeting ferroptosis has the potential to be a promising future treatment method for OA.

Molecular Mechanism of Ferroptosis in Orthopedic Diseases

Ferroptosis is a new iron-dependent programmed cell death process that is directly mediated by the accumulation of lipid peroxides and reactive oxygen species. Numerous studies have shown that ferroptosis is important in regulating the occurrence and development of bone-related diseases, but the underlying mechanisms are not completely clear. Herein, we review the progress of the mechanism of ferroptosis in bone marrow injury, osteoporosis, osteoarthritis, and osteosarcoma and attempt to deeply understand the regulatory targets of ferroptosis, which will open up a new way for the prevention and treatment of orthopedic diseases.

Current understanding of osteoarthritis pathogenesis and relevant new approaches

Osteoarthritis (OA) is the most common degenerative joint disease that causes painful swelling and permanent damage to the joints in the body. The molecular mechanisms of OA are currently unknown. OA is a heterogeneous disease that affects the entire joint, and multiple tissues are altered during OA development. To better understand the pathological mechanisms of OA, new approaches, methods, and techniques need to be used to understand OA pathogenesis. In this review, we first focus on the epigenetic regulation of OA, with a particular focus on DNA methylation, histone modification, and microRNA regulation, followed by a summary of several key mediators in OA-associated pain. We then introduce several innovative techniques that have been and will continue to be used in the fields of OA and OA-associated pain, such as CRISPR, scRNA sequencing, and lineage tracing. Next, we discuss the timely updates concerning cell death regulation in OA pathology, including pyroptosis, ferroptosis, and autophagy, as well as their individual roles in OA and potential molecular targets in treating OA. Finally, our review highlights new directions on the role of the synovial lymphatic system in OA. An improved understanding of OA pathogenesis will aid in the development of more specific and effective therapeutic interventions for OA.

Magnetic resonance imaging R2* sequences can better detect microstructural cartilage changes than T2 mapping in cynomolgus monkeys with limited knee kinematics: preliminary imaging findings

BACKGROUND

The difference between MRI (Magnetic resonance imaging)-R2* and T2 mapping sequences regarding their superiority in the detection of microstructural cartilage changes in knees with limited ROM (range of motion) was unknown.

METHODS

Twenty male cynomolgus monkeys (mean age: 10.65 ± 0.97 years) underwent knee ROM evaluations and were divided into three groups: Group A (n = 10), with similar left and right knee ROM; Group B (n = 5), with left knee ROM superior to right; and Group C (n = 5), with left knee ROM inferior to right. Twenty-eight ROIs (regions of interest) in the cartilage of the lateral (L) and medial (M) femoral trochlea (FT), anterior (A)/central (C)/posterior (P) femoral condyle (FC) and tibial plateau (TP) of both knees were identified in each monkey. The corresponding ROI values in R2* and T2 mapping sequences were recorded for analysis. One-way ANOVA, Chi-square tests and Pearson's correlation analysis were used for statistical analyses.

RESULTS

Among the total 1120 ROIs, significant differences in R2* values among the three groups existed in two ROIs: cartilage of the right MPTP (F = 5.216, P = 0.017) and left MAFC (F = 4.919, P = 0.021). However, the T2 mapping values of all ROIs were similar among the three groups. Microstructural cartilage changes occurred more frequently in the medial (40 ROIs) than in the lateral (0 ROIs) knee compartment (χ² = 43.077, P < 0.001). The Group B cartilage R2* value of the right MPTP increased with the difference in bilateral knee ROM (r = 0.913, P = 0.030).

CONCLUSIONS

In knees with limited ROM, MRI-R2* sequence is superior to T2 mapping in the detection of microstructural cartilage changes, which the medial knee compartment was more susceptible to. Cartilage R2* values tend to increase with the amount of knee ROM loss.

Icariin protects vertebral endplate chondrocytes against apoptosis and degeneration via activating Nrf-2/HO-1 pathway

Cartilage endplate (CEP) plays important roles in the onset and progression of intervertebral disc degeneration (IVDD). Icariin (ICA) is the major active ingredient of Herba Epimedii and has various biological activities such as anti-inflammatory and antioxidant, which is used to treat many degenerative diseases. However, the effects and mechanism of ICA on endplate chondrocytes are still unclear. Herein, we studied the effects of ICA on CEP degeneration and elucidated the underlying mechanisms. Endplate chondrocytes were isolated, and TNF-α and TBHP were applied to mimic an IVDD pathological environment. Also, an IVDD mice model was established by transection of bilateral facet joints to investigate the protective effect of ICA in vivo. We found that ICA treatment inhibited the chondrocytes apoptosis and the decrease of extracellular matrix production in a dose-dependent manner. Our in vivo experiments demonstrated that ICA could ameliorate IVDD development and CEP calcification. We also found that the ICA-activated Nrf-2/HO-1 pathway thus promoted the Parkin-mediated mitophagy process and inhibited chondrocytes ferroptosis, thus alleviated redox imbalance and mitochondrial dysfunction and eventually improved cell survival. Knockdown of Nrf-2 using siRNA reversed the protective effect of ICA on endplate chondrocytes apoptosis and degeneration. In conclusion, our study demonstrated that ICA could protect against CEP degeneration and calcification under IVDD pathological conditions, the associated mechanism may be related to Nrf-2/HO-1-mediated mitophagy activation and ferroptosis inhibition. Our results suggest that ICA may be a potential effective medicine for IVDD prevention and treatment.

TRPM7 channel inhibition attenuates rheumatoid arthritis articular chondrocyte ferroptosis by suppression of the PKCα-NOX4 axis

A role for ferroptosis in articular cartilage destruction associated with rheumatoid arthritis (RA) has not been identified. We previously reported transient receptor potential melastatin 7 (TRPM7) expression was correlated with RA cartilage destruction. Herein, we further characterized a role for TRPM7 in chondrocyte ferroptosis. The expression of TRPM7 was found to be elevated in articular chondrocytes derived from adjuvant arthritis (AA) rats, human RA patients, and cultured chondrocytes treated with the ferroptosis inducer, erastin. TRPM7 knockdown or pharmacological inhibition protected primary rat articular chondrocytes and human chondrocytes (C28/I2 cells) from ferroptosis. Moreover, TRPM7 channel activity was demonstrated to contribute to chondrocyte ferroptosis by elevation of intracellular Ca2+. Mechanistically, the PKCα-NOX4 axis was found to respond to stimulation with erastin, which resulted in TRPM7-mediated chondrocyte ferroptosis. Meanwhile, PKCα was shown to directly bind to NOX4, which could be reduced by TRPM7 channel inhibition. Adeno-associated virus 9-mediated TRPM7 silencing or TRPM7 blockade with 2-APB alleviated articular cartilage destruction in AA rats and inhibited chondrocyte ferroptosis. Collectively, both genetic and pharmacological inhibitions of TRPM7 attenuated articular cartilage damage and chondrocyte ferroptosis via the PKCα-NOX4 axis, suggesting that TRPM7-mediated chondrocyte ferroptosis is a promising target for the prevention and treatment of RA.

Recharge of chondrocyte mitochondria by sustained release of melatonin protects cartilage matrix homeostasis in osteoarthritis

Recent evidence indicates that the mitochondrial functions of chondrocytes are impaired in the pathogenesis of osteoarthritis (OA). Melatonin can attenuate cartilage degradation through its antioxidant functions. This study aims to investigate whether melatonin could rescue the impaired mitochondrial functions of OA chondrocytes and protect cartilage metabolism. OA chondrocytes showed a compromised matrix synthesis capacity associated with mitochondrial dysfunction and aberrant oxidative stress. In vitro treatments with melatonin promoted the expression of cartilage extracellular matrix (ECM) components, improved adenosine triphosphate production, and attenuated mitochondrial oxidative stress. Mechanistically, either silencing of SOD2 or inhibition of SIRT1 abolished the protective effects of melatonin on mitochondrial functions and ECM synthesis. To achieve a sustained release effect, a melatonin-laden drug delivery system (DDS) was developed and intra-articular injection with DDS successfully improved cartilage matrix degeneration in a posttraumatic rat OA model. These findings demonstrate that melatonin-mediated recharge of mitochondria to rescue the mitochondrial functions of chondrocytes represents a promising therapeutic strategy to protect cartilage from OA.

Iron overload promotes intervertebral disc degeneration via inducing oxidative stress and ferroptosis in endplate chondrocytes

Iron overload is a common phenomenon in the elderly population. Many clinical studies have indicated an association between iron overload and the incidence and pathological progression of intervertebral disc degeneration (IVDD). However, the role and underlying mechanism by which iron participates in the progression of IVDD has not yet been reported. In the present study, we aimed to elucidate the connection between iron overload and IVDD, and explore the underlying mechanisms of disease. Firstly, a clinical epidemiology study was conducted and revealed that iron overload is an independent risk factor for human IVDD. To elucidate the role of iron overload in IVDD, an iron overload mouse model was established, and we observed that iron overload promoted IVDD and cartilage endplate degeneration in a dose dependent manner. Endplate chondrocytes were further isolated and treated with FAC to mimic iron overload in vitro. Excess iron significantly promoted mineralization of endplate chondrocytes in addition to their degeneration via oxidative stress. Moreover, a high dose of excess iron promoted chondrocytes ferroptosis. An iron chelator (DFO), an antioxidant (NAC) and a ferroptosis inhibitor (Fer-1) demonstrated effective inhibition of endplate chondrocyte degeneration induced by iron overload, and our in vivo studies further demonstrated that DFO, NAC and Fer-1 could rescue high dose iron-induced IVDD and cartilage endplate calcification. In conclusion, our results indicate that iron overload is strongly associated with the onset and development of IVDD via oxidative stress and ferroptosis. Inhibiting oxidative stress or ferroptosis could therefore be promising therapeutic strategies for IVDD induced by iron overload.

Identification and verification of ferroptosis-related genes in the synovial tissue of osteoarthritis using bioinformatics analysis

Background: Osteoarthritis (OA) is a major factor causing pain and disability. Studies performed to date have suggested that synovitis is possibly a critical OA-related pathological change. Ferroptosis represents a novel type of lipid peroxidation-induced iron-dependent cell death. However, its effect on OA remains largely unclear.

Objective: This work focused on identifying and validating the possible ferroptosis-related genes (FRGs) involved in synovitis of OA through bioinformatics analysis.

Materials and Methods: The microarray dataset GSE55235 was downloaded in the database Gene Expression Omnibus (GEO). By the Venn diagram and GEO2R, differentially expressed genes (DEGs) and ferroptosis DEGs (FDEGs) were detected. DEGs were screened by GO and KEGG enrichment analysis, as well as protein-protein interaction (PPI) analysis. Besides, the software Cytoscape and database STRING were utilized to construct hub gene networks. Moreover, this study used the database NetworkAnalyst to predict the target miRNAs of the hub genes. Finally, the hub genes were confirmed by analysis of the receiver operating characteristic (ROC) curve on the GSE12021 and GSE1919 databases. Considering the relationship between ferroptosis and immunity, this study applied CIBERSORTx to analyze the immune infiltration in OA in addition.

Results: This work discovered seven genes, including ATF3, IL6, CDKN1A, IL1B, EGR1, JUN, and CD44, as the hub FDEGs. The ROC analysis demonstrated that almost all hub genes had good diagnostic properties in GSE12021 and GSE 1919.

Conclusion: This study discovered seven FDEGs to be the possible diagnostic biomarkers and therapeutic targets of synovitis during OA, which sheds more light on the pathogenesis of OA at the transcriptome level.

The Role Played by Ferroptosis in Osteoarthritis: Evidence Based on Iron Dyshomeostasis and Lipid Peroxidation

Ferroptosis, a recently discovered regulated cell death modality, is characterised by iron-dependent accumulation of lipid hydroperoxides, which can reach lethal levels but can be specifically reversed by ferroptosis inhibitors. Osteoarthritis (OA), the most common degenerative joint disease, is characterised by a complex pathogenesis involving mechanical overload, increased inflammatory mediator levels, metabolic alterations, and cell senescence and death. Since iron accumulation and oxidative stress are the universal pathological features of OA, the role played by ferroptosis in OA has been extensively explored. Increasing evidence has shown that iron dyshomeostasis and lipid peroxidation are closely associated with OA pathogenesis. Therefore, in this review, we summarize recent evidence by focusing on ferroptotic mechanisms and the role played by ferroptosis in OA pathogenesis from the perspectives of clinical findings, animal models, and cell research. By summarizing recent research advances that characterize the relationship between ferroptosis and OA, we highlight avenues for further research and potential therapeutic targets.

New Insights into the Regulatory Role of Ferroptosis in Ankylosing Spondylitis via Consensus Clustering of Ferroptosis-Related Genes and Weighted Gene Co-Expression Network Analysis

Background: The pathogenesis of ankylosing spondylitis (AS) remains undetermined. Ferroptosis is a newly discovered form of regulated cell death involved in multiple autoimmune diseases. Currently, there are no reports on the connection between ferroptosis and AS. Methods: AS samples from the Gene Expression Omnibus were divided into two subgroups using consensus clustering of ferroptosis-related genes (FRGs). Weighted gene co-expression network analysis (WGCNA) of the intergroup differentially expressed genes (DEGs) and protein–protein interaction (PPI) analysis of the key module were used to screen out hub genes. A multifactor regulatory network was then constructed based on hub genes. Results: The 52 AS patients in dataset GSE73754 were divided into cluster 1 (n = 24) and cluster 2 (n = 28). DEGs were mainly enriched in pathways related to mitochondria, ubiquitin, and neurodegeneration. Candidate hub genes, screened by PPI and WGCNA, were intersected. Subsequently, 12 overlapping genes were identified as definitive hub genes. A multifactor interaction network with 45 nodes and 150 edges was generated, comprising the 12 hub genes and 32 non-coding RNAs. Conclusions: AS can be divided into two subtypes according to FRG expression. Ferroptosis might play a regulatory role in AS. Tailoring treatment according to the ferroptosis status of AS patients can be a promising direction.

Emerging Potential Therapeutic Targets of Ferroptosis in Skeletal Diseases

Ferroptosis is a new programmed cell death characterized by the accumulation of lipid peroxidation mediated by iron and inflammation. Since the transcentury realization of ferroptosis as an iron-dependent modality of nonapoptotic cell death in 2012, there has been growing interest in the function of ferroptosis and its relationship to clinical diseases. Recent studies have shown that ferroptosis is associated with multiple diseases, including degenerative diseases, ischemia reperfusion injury, cardiovascular disease, and cancer. Cell death induced by ferroptosis has also been related to several skeletal diseases, such as inflammatory arthritis, osteoporosis, and osteoarthritis. Research on ferroptosis can clarify the pathogenesis of skeletal diseases and provide a novel therapeutic target for its treatment. In this review, we summarize current information about the molecular mechanism of ferroptosis and describe its emerging role and therapeutic potential in skeletal diseases.

Ferroptosis in inflammatory arthritis: A promising future

Ferroptosis is a kind of regulatory cell death (RCD) caused by iron accumulation and lipid peroxidation, which is characterized by mitochondrial morphological changes and has a complex regulatory network. Ferroptosis has been gradually emphasized in the pathogenesis of inflammatory arthritis. In this review, we summarized the relevant research on ferroptosis in various inflammatory arthritis including rheumatoid arthritis (RA), osteoarthritis, gout arthritis, and ankylosing spondylitis, and focused on the relationship between RA and ferroptosis. In patients with RA and animal models of RA, there was evidence of iron overload and lipid peroxidation, as well as mitochondrial dysfunction that may be associated with ferroptosis. Ferroptosis inducers have shown good application prospects in tumor therapy, and some anti-rheumatic drugs such as methotrexate and sulfasalazine have been shown to have ferroptosis modulating effects. These phenomena suggest that the role of ferroptosis in the pathogenesis of inflammatory arthritis will be worth further study. The development of therapeutic strategies targeting ferroptosis for patients with inflammatory arthritis may be a promising future.

The Regulatory Role of Ferroptosis in Bone Homeostasis

Ferroptosis is an iron-dependent form of programmed cell death and an important type of biological catabolism. Through the action of divalent iron or ester oxygenase, ferroptosis can induce lipid peroxidation and cell death, regulating a variety of physiological processes. The role of ferroptosis in the modulation of bone homeostasis is a significant topic of interest. Herein, we review and discuss recent studies exploring the mechanisms and functions of ferroptosis in different bone-related cells, including mesenchymal stem cells, osteoblasts, osteoclasts, and osteocytes. The association between ferroptosis and disorders of bone homeostasis is also explored in this review. Overall, we aim to provide a detailed overview of ferroptosis, summarizing recent understanding on its role in regulation of bone physiology and bone disease pathogenesis.

FGF23 and SOX9 expression in hemophilic cartilage: In vitro studies of the effects of iron

INTRODUCTION

Clarifying the links between iron and FGF23, SOX9 expression in chondrocytes would be helpful for comprehending articular cartilage degradation pathogenesis in blood-induced arthritis and exploring new protective methods.

AIM

The purpose of this study was to determine iron regulation of fibroblast growth factor 23 (FGF23) and SRY-box 9 (SOX9) in human chondrocytes, an area which is unexplored in blood-induced arthritis cartilage degradation pathogenesis.

METHODS

Expression of FGF23, SOX9, MMP13 and collagen Ⅱ in articular cartilage of patients with osteoarthritis (OA) or haemophilic arthritis (HA) was determined by western blot (WB). Iron induced FGF23 and SOX9 mRNA and protein expression in primary human normal chondrocyte cells (HUM-iCell-s018) was quantifified by qRT-PCR and WB, respectively.

RESULTS

We found that compared with OA patients, the expression of FGF23, MMP13 in articular cartilage of patients with HA was up-regulated, while the expression of SOX9, collagen Ⅱ was down-regulated. Iron induced FGF23 and suppressed SOX9 expression in chondrocytes in a dose-dependent manner.

CONCLUSIONS

These findings demonstrated that iron were involved in hemophilic cartilage lesion directly via changing cartilage phenotype through regulation of FGF23 and SOX9 expression in chondrocytes.

Research Progress of Ferroptosis Regulatory Network and Bone Remodeling in Osteoporosis

Ferroptosis was induced the programmed cell death with iron overload Fenton reaction. Currently, ferroptosis has not been studied thoroughly. Existing studies have confirmed that ferroptosis involves the metabolisms of the Fe, lipids, amino acid, each mechanism is mutually independent but interrelated, and they are formed a complex regulatory network. Other evidence supports that ferroptosis is participated osteoporotic bone remodeling, predominantly affecting the interaction between bone formation and bone resorption, explicitly bone resorption exceeded bone formation. Based on previous studies, this review will summarize the regulatory network mechanism of ferroptosis on bone remodeling and reveal the role of ferroptosis in osteoporosis (OP).

Targeting Ferroptosis Attenuates Inflammation, Fibrosis, and Mast Cell Activation in Chronic Prostatitis

Purpose

Chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) is a common urological disorder. Although ferroptosis is closely associated with inflammation, oxidative stress, and neuropathic pain, its role in CP/CPPS has not yet been elucidated. Therefore, we sought to explore the role and mechanism of ferroptosis in the prostatitis development.

Methods

The experimental autoimmune prostatitis (EAP) was established through intradermal immunization of prostate extract. Iron chelator deferoxamine (DFO) and free radical scavenger edaravone (EDA) were applied to evaluate the effects of ferroptosis inhibition on oxidative stress, ferroptosis, inflammation, fibrosis, and mast cell activation in the context of CP/CPPS.

Results

Increased generation of lipid peroxidation products (ROS and MDA) and decreased activities of antioxidant enzymes (SOD and CAT) suggested an aberrant oxidative stress status in EAP model. Elevated iron concentration was observed in the EAP model. Meanwhile, we discovered significant biological performances associated with ferroptosis in CP/CPPS, including the downregulation of the system Xc^-/GPX4 axis and the upregulation of the ACSL4/LPCAT3 axis. EAP rats performed serious leukocyte infiltration, advanced inflammatory grade, and abnormal expression of inflammatory mediators. Abundant collagen deposition, enhanced RhoA, ROCK1, and α-SMA protein levels indicated that EAP rats were prone to suffer from stromal fibrosis compared with control group. An elevated number of degranulated mast cells and corresponding marker TPSB2 represented that mast cell-sensitized pain was amplified in the EAP model. Furthermore, reduction of NRF2/HO-1 indicated a vulnerability of EAP towards ferroptosis response. However, application of DFO and EDA had partially reversed the adverse influences mentioned above.

Conclusion

We first demonstrated that ferroptosis might be a crucial factor of chronic prostatitis progression. Inhibition of ferroptosis using DFO and EDA represented a promising approach for treating prostatitis by ameliorating inflammation, fibrosis, and mast cell activation.

Antisense Oligonucleotide-Based Therapy on miR-181a-5p Alleviates Cartilage Degradation of Temporomandibular Joint Osteoarthritis via Promoting SIRT1

Temporomandibular joint osteoarthritis (TMJOA) condylar cartilage degeneration and abnormal subchondral bone pathological remodeling induce pain and joint dysfunction, and cartilage degeneration is considered irreversible. Very few therapeutic approaches are administrated in practice. Nucleotides have demonstrated considerable potential as a next-generation medication, and they have been applied in several models of osteoarthritis. There is a need to establish an effective protocol for TMJOA gene therapy. In the current study unilateral anterior crossbite (UAC) surgery was used to simulate mechanical stress-induced TMJOA in mice. Degeneration of condylar cartilage and destruction of subchondral bone were observed in damaged joints, and miR-181a-5p was elevated in chondrocytes. Intra-articular injection of miR-181a-5p antisense oligonucleotide (ASO) could reduce the cartilage damage and alleviate UAC-induced TMJOA progression, but it did not restore injured subchondral bone. Mechanically, miR-181a-5p evidently targeted the 3’ untranslated region of Sirt1 directly, resulting in inhibition of silent information regulator 1 expression and promoting apoptosis by elevating p53-dependent signaling, indicating that miR181a-5p ASO promoted chondrocyte survival. The present study suggests that ASO-based gene therapy may be an effective TMJOA treatment.

Osteoarthritis Pain

Joint pain is the hallmark symptom of osteoarthritis (OA) and the main reason for patients to seek medical assistance. OA pain greatly contributes to functional limitations of joints and reduced quality of life. Although several pain-relieving medications are available for OA treatment, the current intervention strategy for OA pain cannot provide satisfactory pain relief, and the chronic use of the drugs for pain management is often associated with significant side effects and toxicities. These observations suggest that the mechanisms of OA-related pain remain undefined. The current review mainly focuses on the characteristics and mechanisms of OA pain. We evaluate pathways associated with OA pain, such as nerve growth factor (NGF)/tropomyosin receptor kinase A (TrkA), calcitonin gene-related peptide (CGRP), C–C motif chemokine ligands 2 (CCL2)/chemokine receptor 2 (CCR2) and tumor necrosis factor alpha (TNF-α), interleukin-1beta (IL-1β), the NOD-like receptor (NLR) family, pyrin domain-containing protein 3 (NLRP3) inflammasome, and the Wnt/β-catenin signaling pathway. In addition, animal models currently used for OA pain studies and emerging preclinical studies are discussed. Understanding the multifactorial components contributing to OA pain could provide novel insights into the development of more specific and effective drugs for OA pain management.

Deferoxamine Alleviates Osteoarthritis by Inhibiting Chondrocyte Ferroptosis and Activating the Nrf2 Pathway

Objective: Osteoarthritis (OA) is a common disease with a complex pathology including mechanical load, inflammation, and metabolic factors. Chondrocyte ferroptosis contributes to OA progression. Because iron deposition is a major pathological event in ferroptosis, deferoxamine (DFO), an effective iron chelator, has been used to inhibit ferroptosis in various degenerative disease models. Nevertheless, its OA treatment efficacy remains unknown. We aimed to determine whether DFO alleviates chondrocyte ferroptosis and its effect on OA and to explore its possible mechanism. Methods: Interleukin-1β (IL-1β) was used to simulate inflammation, and chondrocyte ferroptosis was induced by erastin, a classic ferroptosis inducer. A surgical destabilized medial meniscus mouse model was also applied to simulate OA in vivo, and erastin was injected into the articular cavity to induce mouse knee chondrocyte ferroptosis. We determined the effects of DFO on ferroptosis and injury-related events: chondrocyte inflammation, extracellular matrix degradation, oxidative stress, and articular cartilage degradation. Results: IL-1β increased the levels of ROS, lipid ROS, and the lipid peroxidation end product malondialdehyde (MDA) and altered ferroptosis-related protein expression in chondrocytes. Moreover, ferrostatin-1 (Fer-1), a classic ferroptosis inhibitor, rescued the IL-1β-induced decrease in collagen type II (collagen II) expression and increase in matrix metalloproteinase 13 (MMP13) expression. Erastin promoted MMP13 expression in chondrocytes but inhibited collagen II expression. DFO alleviated IL-1β- and erastin-induced cytotoxicity in chondrocytes, abrogated ROS and lipid ROS accumulation and the increase in MDA, improved OA-like changes in chondrocytes, and promoted nuclear factor E2-related factor 2 (Nrf2) antioxidant system activation. Finally, intra-articular injection of DFO enhanced collagen II expression in OA model mice, inhibited erastin-induced articular chondrocyte death, and delayed articular cartilage degradation and OA progression. Conclusion: Our research confirms that ferroptosis occurs in chondrocytes under inflammatory conditions, and inhibition of chondrocyte ferroptosis can alleviate chondrocyte destruction. Erastin-induced chondrocyte ferroptosis can stimulate increased MMP13 expression and decreased collagen II expression in chondrocytes. DFO can suppress chondrocyte ferroptosis and promote activation of the Nrf2 antioxidant system, which is essential for protecting chondrocytes. In addition, ferroptosis inhibition by DFO injection into the articular cavity may be a new OA treatment.

Fuzi decoction ameliorates pain and cartilage degeneration of osteoarthritic rats through PI3K-Akt signaling pathway and its clinical retrospective evidence

BACKGROUND

Osteoarthritis (OA) is a difficult disease but the clinic lacks effective therapy. As a classic formula of traditional Chinese medicine (TCM), Fuzi decoction (FZD) has been clinically applied for treating OA-related syndromes, but its anti-OA efficacy and mechanism remain unclear.

PURPOSE

To experimentally and clinically determine the anti-OA efficacy of FZD and clarify the underlying mechanism.

METHODS

UPLC/MS/MS was applied to identify the main components of FZD. A monoiodoacetate (MIA)-induced OA rat model was employed to evaluate the in vivo efficacy of FZD against OA, by using pain behavior assessment, histopathological observation, and immunohistochemical analysis. Primary rat chondrocytes were isolated to determine the in vitro effects of FZD by using cell viability assay, wound healing assay, and real-time PCR (qPCR) analysis on anabolic/catabolic mRNA expressions. RNA sequencing (RNA-seq) and network pharmacology analysis were conducted and the overlapping data were used to predict the mechanism of FZD, followed by verification with qPCR and Western blot assays. Finally, a retrospective analysis was performed to confirm FZD's efficacy and safety in OA patients.

RESULTS

The UPLC/MS/MS result showed that FZD contained atractylenolide I, benzoylhypaconitine, benzoylmesaconitine, benzoylaconitine, hypaconitine, mesaconitine, aconitine, lobetyolin, paeoniflorin, and pachymic acid. The in vivo data showed that FZD restored the cartilage degeneration in MIA-induced OA rats by ameliorating pain behavior parameters, recovering histopathological alterations, benefitting cartilage anabolism (up-regulating Col2 expression), and suppressing catabolism (down-regulating MMP13 and Col10 expressions). The in vitro data showed that FZD increased cell viability and wound healing capacity of chondrocytes, and restored the altered expressions of anabolic and catabolic genes of chondrocytes. The overlapping results of RNA-seq and network pharmacology analysis suggested that PI3K/Akt signaling mediated the anti-OA mechanism of FZD, which was verified by qPCR and Western blot experiments. Clinically, the anti-OA efficacy and safety of FZD were confirmed by the retrospective analysis on OA patients.

CONCLUSION

The scientific innovation of this study was the determination of anti-OA efficacy of FZD by experimental and clinical evidence and the discovery of its mechanism by integrated RNA-seq, network pharmacology, and molecular experiments, which suggests FZD as a promising TCM agency for OA treatment.

Targeting ferroptosis suppresses osteocyte glucolipotoxicity and alleviates diabetic osteoporosis

Diabetic osteoporosis (DOP) is the leading complication continuously threatening the bone health of patients with diabetes. A key pathogenic factor in DOP is loss of osteocyte viability. However, the mechanism of osteocyte death remains unclear. Here, we identified ferroptosis, which is iron-dependent programmed cell death, as a critical mechanism of osteocyte death in murine models of DOP. The diabetic microenvironment significantly enhanced osteocyte ferroptosis in vitro, as shown by the substantial lipid peroxidation, iron overload, and aberrant activation of the ferroptosis pathway. RNA sequencing showed that heme oxygenase-1 (HO-1) expression was notably upregulated in ferroptotic osteocytes. Further findings revealed that HO-1 was essential for osteocyte ferroptosis in DOP and that its promoter activity was controlled by the interaction between the upstream NRF2 and c-JUN transcription factors. Targeting ferroptosis or HO-1 efficiently rescued osteocyte death in DOP by disrupting the vicious cycle between lipid peroxidation and HO-1 activation, eventually ameliorating trabecular deterioration. Our study provides insight into DOP pathogenesis, and our results provide a mechanism-based strategy for clinical DOP treatment.

Whole Transcriptome Mapping Identifies an Immune- and Metabolism-Related Non-coding RNA Landscape Remodeled by Mechanical Stress in IL-1β-Induced Rat OA-like Chondrocytes

Background: Osteoarthritis (OA) is a common degenerative joint disease. The aims of this study are to explore the effects of mechanical stress on whole transcriptome landscape and to identify a non-coding transcriptome signature of mechanical stress.

Methods: Next-generation RNA sequencing (RNA-seq) was performed on IL-1β-induced OA-like chondrocytes stimulated by mechanical stress. Integrated bioinformatics analysis was performed and further verified by experimental validations.

Results: A total of 5,022 differentially expressed mRNAs (DEMs), 88 differentially expressed miRNAs (DEMIs), 1,259 differentially expressed lncRNAs (DELs), and 393 differentially expressed circRNAs (DECs) were identified as the transcriptome response to mechanical stress. The functional annotation of the DEMs revealed the effects of mechanical stress on chondrocyte biology, ranging from cell fate, metabolism, and motility to endocrine, immune response, and signaling transduction. Among the DELs, ∼92.6% were identified as the novel lncRNAs. According to the co-expressing DEMs potentially regulated by the responsive DELs, we found that these DELs were involved in the modification of immune and metabolism. Moreover, immune- and metabolism-relevant DELs exhibited a notable involvement in the competing endogenous RNA (ceRNA) regulation networks. Silencing lncRNA TCONS_00029778 attenuated cellular senescence induced by mechanical stress. Moreover, the expression of Cd80 was elevated by mechanical stress, which was rescued by silencing TCONS_00029778.

Conclusion: The transcriptome landscape of IL-1β-induced OA-like chondrocytes was remarkably remodeled by mechanical stress. This study identified an immune- and metabolism-related ncRNA transcriptome signature responsive to mechanical stress and provides an insight of ncRNAs into chondrocyte biology and OA.

Ferroptosis in Rheumatoid Arthritis: A Potential Therapeutic Strategy

Ferroptosis is one of the newly discovered forms of cell-regulated death characterized by iron-dependent lipid peroxidation. Extensive research has focused on the roles of ferroptosis in tumors, blood diseases, and neurological diseases. Some recent findings have indicated that ferroptosis may also be related to the occurrence and development of inflammatory arthritis. Ferroptosis may be a potential therapeutic target, and few studies in vitro and animal models have shown implications in the pathogenesis of inflammatory arthritis. This mini review discussed the common features between ferroptosis and the pathogenesis of rheumatoid arthritis (RA), and evaluated therapeutic applications of ferroptosis regulators in preclinical and clinical research. Some critical issues worth paying attention to were also raised to guide future research efforts.

Iron Overload Induces Oxidative Stress, Cell Cycle Arrest and Apoptosis in Chondrocytes

Clinical and experimental evidence point to the presence of considerable links between arthropathy, osteoarthritis (OA) in particular, and iron overload possibly due to oxidative stress and tissue damage. However, the specific cellular targets of iron overload-related oxidative stress in OA remain ambiguous. We examined the effects of iron overload on chondrocyte health using the C-20/A4 chondrocyte cell line. Cells were treated with increasing concentrations of ferric ammonium citrate (FAC) to mimic iron overload in vitro. Treated cells were assessed for cell viability, cycling, apoptosis, collagen II synthesis, and oxidative stress along with cellular iron content and the expression of key iron regulatory genes. FAC treatment resulted in an increase in ferritin expression and a significant decrease in the expression of hepcidin, ferroportin, transferrin receptors 1 (TfR1) and TfR2. Increased labile iron content was also evident, especially in cells treated with high FAC at 24 h. High doses of FAC treatment also induced higher levels of reactive oxygen species, reduced collagen II production, disrupted cell cycle and higher cell death as compared with untreated controls. In conclusion, findings presented here demonstrate that iron overload disrupts cellular iron homeostasis, which compromises the functional integrity of chondrocytes and leads to oxidative stress and apoptosis.

Interplay Between Iron Overload and Osteoarthritis: Clinical Significance and Cellular Mechanisms

There are multiple diseases or conditions such as hereditary hemochromatosis, hemophilia, thalassemia, sickle cell disease, aging, and estrogen deficiency that can cause iron overload in the human body. These diseases or conditions are frequently associated with osteoarthritic phenotypes, such as progressive cartilage degradation, alterations in the microarchitecture and biomechanics of the subchondral bone, persistent joint inflammation, proliferative synovitis, and synovial pannus. Growing evidences suggest that the conditions of pathological iron overload are associated with these osteoarthritic phenotypes. Osteoarthritis (OA) is an important complication in patients suffering from iron overload-related diseases and conditions. This review aims to summarize the findings and observations made in the field of iron overload-related OA while conducting clinical and basic research works. OA is a whole-joint disease that affects the articular cartilage lining surfaces of bones, subchondral bones, and synovial tissues in the joint cavity. Chondrocytes, osteoclasts, osteoblasts, and synovial-derived cells are involved in the disease. In this review, we will elucidate the cellular and molecular mechanisms associated with iron overload and the negative influence that iron overload has on joint homeostasis. The promising value of interrupting the pathologic effects of iron overload is also well discussed for the development of improved therapeutics that can be used in the field of OA.

Contribution of ferroptosis and GPX4's dual functions to osteoarthritis progression

Background

Osteoarthritis (OA) is the most common joint disease and is the leading cause of chronic disability among older people. Chondrocyte death and extracellular matrix (ECM) degradation was involved in OA pathogenesis. Ferroptosis was an iron-dependent cell death associated with peroxidation of lipids. Here, we proved that ferroptosis exists in OA and identified glutathione peroxidase 4 (GPX4) as an important regulator of OA.

Methods

Ferroptosis-related alterations were analyzed in human OA and undamaged cartilage. Expression of GPX4 was examined in 55 paired human OA samples. Ferrostatin-1 (Fer-1) and Deferoxamine (DFO) were used to treat OA, in vitro and in vivo. Alterations of GPX4-mediated signaling pathway were identified by RNA-seq analysis. AAV-Gpx4-shRNA were used to downregulate GPX4 expression in vivo.

Findings

Transcriptomic, biochemical, and microscopical analyses indicated that ferroptosis was closely associated with OA. Expression of GPX4 in the OA cartilage from 55 OA patients were significantly lower than undamaged cartilage. Fer-1 and DFO could protect OA in a necroptosis-independent manner, suggesting that ferroptosis exists in OA prog. Importantly, GPX4 downregulation could increase the sensitivity of chondrocytes to oxidative stress and aggravate ECM degradation through the MAPK/NFκB pathway. Furthermore, downregulation of GPX4 expression by AAV-Gpx4 shRNA aggravated OA in vivo.

Interpretation

Ferroptosis contributes to OA pathogenesis and GPX4 was the intersection of two mechanisms in regulating OA progression: ferroptosis and ECM degradation.

Targeting Cell Death: Pyroptosis, Ferroptosis, Apoptosis and Necroptosis in Osteoarthritis

New research has shown that the development of osteoarthritis (OA) is regulated by different mechanisms of cell death and types of cytokines. Therefore, elucidating the mechanism of action among various cytokines, cell death processes and OA is important towards better understanding the pathogenesis and progression of the disease. This paper reviews the pathogenesis of OA in relation to different types of cytokine-triggered cell death. We describe the cell morphological features and molecular mechanisms of pyroptosis, apoptosis, necroptosis, and ferroptosis, and summarize the current research findings defining the molecular mechanisms of action between different cell death types and OA.

Ferroptosis: A potential target for the intervention of intervertebral disc degeneration

Ferroptosis, an iron-dependent form of programmed cell death marked by phospholipid peroxidation, is regulated by complex cellular metabolic pathways including lipid metabolism, iron balance, redox homeostasis, and mitochondrial activity. Initial research regarding the mechanism of ferroptosis mainly focused on the solute carrier family 7 member 11/glutathione/glutathione peroxidase 4 (GPX4) signal pathway. Recently, novel mechanisms of ferroptosis, independent of GPX4, have been discovered. Numerous pathologies associated with extensive lipid peroxidation, such as drug-resistant cancers, ischemic organ injuries, and neurodegenerative diseases, are driven by ferroptosis. Ferroptosis is a new therapeutic target for the intervention of IVDD. The role of ferroptosis in the modulation of intervertebral disc degeneration (IVDD) is a significant topic of interest. This is a novel research topic, and research on the mechanisms of IVDD and ferroptosis is ongoing. Herein, we aim to review and discuss the literature to explore the mechanisms of ferroptosis, the relationship between IVDD and ferroptosis, and the regulatory networks in the cells of the nucleus pulposus, annulus fibrosus, and cartilage endplate to provide references for future basic research and clinical translation for IVDD treatment.

Stigmasterol alleviates interleukin-1beta-induced chondrocyte injury by down-regulatingsterol regulatory element binding transcription factor 2 to regulateferroptosis

Stigmasterol (STM), one of the main active components of Achyranthes bidentata, has been shown to effectively inhibit proinflammatory factors and matrix degradation in chondrocytes. However, the effect of STM on interleukin (IL)-1β-induced chondrocytes and its specific mechanism remain unclear. The purpose of the present study was to explore the effect and mechanism of sterol regulatory element binding transcription factor 2 (SREBF2) on IL-1β induced chondrocytes in the presence of STM. CCK-8 was used to detect the effect of STM on the cell viability of mouse chondrogenic cells (ATDC5). After ATDC5 cells were induced by IL-1β, the expression of SREBF2 in osteoarthritis cells was detected by RT-qPCR. The content of iron ion in the cells was detected by using an iron colorimetric assay kit. After further transfection of a SREBF2 overexpressing vector (Oe-SREBF2) or addition of a ferroptosis inhibitor, the expression levels of inflammation and matrix degradation-related proteins were detected via Western blotting. The levels of oxidative stress in cells were determined by using an ELISA kit. The results revealed that STM had no significant effect on the viability of ATDC5 cells. STM reduced IL-1β-induced ATDC5 cell damage and ferroptosis through SREBF2 and enhanced the inhibitory effect of ferroptosis inhibitors on IL-1β-induced ATDC5 cell injury. The present data suggest that STM attenuated chondrocyte injury induced by IL-1β by regulating ferroptosis via down-regulation of SREBF2, and may have potential as a novel therapeutic method for knee osteoarthritis.

MCC950, the NLRP3 Inhibitor, Protects against Cartilage Degradation in a Mouse Model of Osteoarthritis

Osteoarthritis (OA), characterized by chronic systemic low-level inflammation and cartilage degeneration, is a type of arthritis closely associated with aging. Inflammation and aging play a pivotal role in the occurrence and progression of OA. NLRP3 inflammasome is involved in many inflammatory and aging diseases, and NLRP3 inhibitor MCC950 has anti-inflammatory and antisenescence effects on some diseases such as Alzheimer's disease. In the present study, we found that NLRP3 protein was upregulated in human and mouse OA cartilage. Moreover, NLRP3 and Caspase1 expression induced by IL-1β in chondrocytes was blocked by MCC950. In addition, MCC950 inhibited the expression of inflammatory mediators, matrix-degrading enzymes, senescence marker protein P16 (INK4A), and β-galactosidase, as well as excessive production of ROS. Meanwhile, MCC950 promoted autophagy-related protein expression and autophagy flux under the inflammatory condition. However, autophagy inhibitor 3-MA reversed anti-inflammatory and anticatabolic effects of MCC950. In in vivo experiments, intra-articular administration of MCC950 further showed its protective effect on cartilage degeneration. Bioinformatic analysis and in vitro experimental results revealed that MCC950 might play a protective role in cartilage by regulating Nrf2/HO-1/NQO1, PI3k/Akt/mTOR, P38/MAPK, and JNK/MAPK pathways. In conclusion, our work demonstrated that NLRP3 inhibitor MCC950 might serve as a promising strategy for OA treatment.

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.

Ferroptosis-related gene SOCS1, a marker for tuberculosis diagnosis and treatment, involves in macrophage polarization and facilitates bone destruction in tuberculosis

This study was aimed to reveal the role of ferroptosis in tuberculosis infection. To elucidate the ferroptosis-related DEGs, GEO datasets associated with tuberculosis infection were downloaded. The two external validation GEO datasets were exploited for subsequent verification of the ferroptosis-related DEGs. We further evaluated the correlation among the ferroptosis-related DEGs, therapeutic effects, and drug resistance. Finally, we tried to reveal the engagement of the ferroptosis-related DEGs in bone destruction during TB infection. The present study identified SOCS1 as the only ferroptosis-related DEGs. Compared to the non-TB patients, up-regulation of SOCS1 was evident in the TB patients. After receiving standard anti-TB treatment, significant down-regulation of SOCS1 confirmed its acceptance as the marker for therapeutic efficacy. The involvement of SOCS1 has also been suggested in the regulation of the micro immune environment in TB. Furthermore, SOCS1 might play an important role in causing bone destruction during TB infection. FRGs-SOCS1 may be the key gene involved in the pathogenesis and progression of TB infection.

Iron Overload-Induced Ferroptosis Impairs Porcine Oocyte Maturation and Subsequent Embryonic Developmental Competence in vitro

Accumulating evidence indicates that ferroptosis is an iron-dependent form of regulated cell death. This type of iron-dependent programmed cell death is different from traditional forms of regulated cell death, such as apoptosis and autophagy. However, the role of ferroptosis in porcine oocyte maturation and the associated mechanism remain unclear. In the present research, we investigated the effects of ferric ammonium citrate (FAC), a specific ferroptosis inducer, on porcine oocyte meiotic maturation and quality and subsequent embryonic developmental competence. FAC treatment caused obvious accumulation of intracellular ferrous ions in porcine oocytes. At the end of the in vitro maturation (IVM) period, there was a significant decrease in the polar body (PB) extrusion rate and an increase in the percentage of abnormal oocytes in the FAC treatment groups, indicating that iron overload-induced ferroptosis may suppress the meiotic process during porcine oocyte maturation. We also found that after FAC treatment, the subsequent two-cell rate, four-cell rate and blastocyst formation rate were significantly decreased in porcine parthenogenetic activation (PA) embryos, indicating that iron overload-induced ferroptosis decreased porcine oocyte quality. Further analysis revealed that FAC treatment not only enhanced intracellular reactive oxygen species (ROS) generation, decreased intracellular free thiol levels and induced mitochondrial dysfunction but also triggered autophagy in porcine oocytes. Taken together, these findings suggest that iron overload-induced ferroptosis impairs porcine oocyte meiosis and decreases porcine oocyte quality, possibly by increasing oxidative stress, inducing mitochondrial dysfunction and triggering autophagy.

Comparison of the major cell populations among osteoarthritis, Kashin-Beck disease and healthy chondrocytes by single-cell RNA-seq analysis

Chondrocytes are the key target cells of the cartilage degeneration that occurs in Kashin–Beck disease (KBD) and osteoarthritis (OA). However, the heterogeneity of articular cartilage cell types present in KBD and OA patients and healthy controls is still unknown, which has prevented the study of the pathophysiology of the mechanisms underlying the roles of different populations of chondrocytes in the processes leading to KBD and OA. Here, we aimed to identify the transcriptional programmes and all major cell populations in patients with KBD, patients with OA and healthy controls to identify the markers that discriminate among chondrocytes in these three groups. Single-cell RNA sequencing was performed to identify chondrocyte populations and their gene signatures in KBD, OA and healthy cells to investigate their differences as related to the pathogenetic mechanisms of these two osteochondral diseases. We performed immunohistochemistry and quantitative reverse-transcription PCR (qRT-PCR) assays to validate the markers for chondrocyte population. Ten clusters were labelled by cell type according to the expression of previously described markers, and one novel population was identified according to the expression of a new set of markers. The homeostatic and mitochondrial chondrocyte populations, which were identified by the expression of the unknown markers MT1X and MT2A and MT-ND1 and MT-ATP6, were markedly expanded in KBD. The regulatory chondrocyte population, identified by the expression of CHI3L1, was markedly expanded in OA. Our study allows us to better understand the heterogeneity of chondrocytes in KBD and OA and provides new evidence of differences in the pathogenetic mechanisms between these two diseases.

Musculoskeletal complications associated with pathological iron toxicity and its molecular mechanisms

Iron is fundamental for several biological functions, but when in excess can lead to the development of toxic events. Some tissues and cells are more susceptible than others, but systemic iron levels can be controlled by treating patients with iron-chelating molecules and phlebotomy. An early diagnostic can be decisive to limit the progression of musculoskeletal complications like osteoarthritis and osteoporosis because of iron toxicity. In iron-related osteoarthritis, aggravation can be associated to a few events that can contribute to joints articular cartilage exposure to high iron concentrations, which can promote articular degeneration with very little chance of tissue regeneration. In contrast, bone metabolism is much more dynamic than cartilage, but progressive iron accumulation and ageing can be decisive factors for bone health. The iron overload associated with hereditary diseases like hemochromatosis, hemophilias, thalassemias and other hereditary anaemias increase the negative impact of iron toxicity in joints and bone, as well as in life quality, even when iron levels can be controlled. The molecular mechanisms by which iron can compromise cartilage and bone have been illusive and only in the last 20 years studies have started to shed some light into the molecular mechanisms associated with iron toxicity. Ferroptosis and the regulation of intracellular iron levels is instrumental in the balance between detoxification and induced cell death. In addition, these complications are accompanied with multiple susceptibility factors that can aggravate iron toxicity and should be identified. Therefore, understanding tissues microenvironment and cell communication is fundamental to contextualize iron toxicity.