Inhibition of SAT1 alleviates chondrocyte inflammation and ferroptosis by repressing ALOX15 expression and activating the Nrf2 pathway.

Aims: Osteoarthritis (OA) is the most common chronic pathema of human joints. The pathogenesis is complex, involving physiological and mechanical factors. In previous studies, we found that ferroptosis is intimately related to OA, while the role of Sat1 in chondrocyte ferroptosis and OA, as well as the underlying mechanism, remains unclear. Methods: In this study, interleukin-1ß (IL-1ß) was used to simulate inflammation and Erastin was used to simulate ferroptosis in vitro. We used small interfering RNA (siRNA) to knock down the spermidine/spermine N1-acetyltransferase 1 (Sat1) and arachidonate 15-lipoxygenase (Alox15), and examined damage-associated events including inflammation, ferroptosis, and oxidative stress of chondrocytes. In addition, a destabilization of the medial meniscus (DMM) mouse model of OA induced by surgery was established to investigate the role of Sat1 inhibition in OA progression. Results: The results showed that inhibition of Sat1 expression can reduce inflammation, ferroptosis changes, reactive oxygen species (ROS) level, and lipid-ROS accumulation induced by IL-1ß and Erastin. Knockdown of Sat1 promotes nuclear factor-E2-related factor 2 (Nrf2) signalling. Additionally, knockdown Alox15 can alleviate the inflammation-related protein expression induced by IL-1ß and ferroptosis-related protein expression induced by Erastin. Furthermore, knockdown Nrf2 can reverse these protein expression alterations. Finally, intra-articular injection of diminazene aceturate (DA), an inhibitor of Sat1, enhanced type II collagen (collagen II) and increased Sat1 and Alox15 expression. Conclusion: Our results demonstrate that inhibition of Sat1 could alleviate chondrocyte ferroptosis and inflammation by downregulating Alox15 activating the Nrf2 system, and delaying the progression of OA. These findings suggest that Sat1 provides a new approach for studying and treating OA.

DMT1-mediated iron overload accelerates cartilage degeneration in Hemophilic Arthropathy through the mtDNA-cGAS-STING axis.

INTRODUCTION: Excess iron contributes to Hemophilic Arthropathy (HA) development. Divalent metal transporter 1 (DMT1) delivers iron into the cytoplasm, thus regulating iron homeostasis. OBJECTIVES: We aimed to investigate whether DMT1-mediated iron homeostasis is involved in bleeding-induced cartilage degeneration and the molecular mechanisms underlying iron overload-induced chondrocyte damage. METHODS: This study established an in vivo HA model by puncturing knee joints of coagulation factor VIII gene knockout mice with a needle, and mimicked iron overload conditions in vitro by treatment of Ferric ammonium citrate (FAC). RESULTS: We demonstrated that blood exposure caused iron overload and cartilage degeneration, as well as elevated expression of DMT1. Furthermore, DMT1 silencing alleviated blood-induced iron overload and cartilage degeneration. In hemophilic mice, articular cartilage degeneration was also suppressed by intro-articularly injection of DMT1 adeno-associated virus 9 (AAV9). Mechanistically, RNA-sequencing analysis indicated the association between iron overload and cGAS-STING pathway. Further, iron overload triggered mtDNA-cGAS-STING pathway activation, which could be effectively mitigated by DMT1 silencing. Additionally, we discovered that RU.521, a potent Cyclic GMP-AMP Synthase (cGAS) inhibitor, successfully suppressed the downward cascades of cGAS-STING, thereby protecting against chondrocyte damage. CONCLUSION: Taken together, DMT1-mediated iron overload promotes chondrocyte damage and murine HA development, and targeted DMT1 may provide therapeutic and preventive approaches in HA.

Erratum: Mitoquinone alleviates osteoarthritis progress by activating the NRF2-Parkin axis.

[This corrects the article DOI: 10.1016/j.isci.2023.107647.].

P21 resists ferroptosis in osteoarthritic chondrocytes by regulating GPX4 protein stability.

Ferroptosis is involved in the pathogenesis of osteoarthritis (OA) while suppression of chondrocyte ferroptosis has a beneficial effect on OA. However, the molecular mechanism of ferroptosis in OA remains to be elucidated. P21, an indicator of aging, has been reported to inhibit ferroptosis, but the relationship between P21 and ferroptosis in OA remains unclear. Here, we aimed to investigate the expression and function of P21 in OA chondrocytes, and the involvement of P21 in the regulation of ferroptosis in chondrocytes. First, we demonstrated that high P21 expression was observed in the cartilage from OA patients and destabilized medial meniscus (DMM) mice, and in osteoarthritic chondrocytes induced by IL-1ß, FAC and erastin. P21 knockdown exacerbated the reduction of Col2a1 and promoted the upregulation of MMP13 in osteoarthritic chondrocytes. Meanwhile, P21 knockdown exacerbated cartilage degradation in DMM-induced OA mouse models and decreased GPX4 expression in vivo. Furthermore, P21 knockdown sensitized chondrocytes to ferroptosis induced by erastin, which was closely associated with the accumulation of lipid peroxides. In mechanism, we demonstrated that P21 regulated the stability of GPX4 protein, and the regulation was independent of NRF2. Meanwhile, we found that P21 significantly affected the recruitment of GPX4 to linear ubiquitin chain assembly complex (LUBAC) and regulated the level of M1-linked ubiquitination of GPX4. Overall, our results suggest that P21 plays an essential anti-ferroptosis role in OA by regulating the stability of GPX4.

Mitoquinone alleviates osteoarthritis progress by activating the NRF2-Parkin axis.

Osteoarthritis (OA) is a prevalent degenerative disease of the elderly. The NRF2 antioxidant system plays a critical role in maintaining redox balance. Mitoquinone (MitoQ) is a mitochondria-targeted antioxidant. This research aimed to determine whether MitoQ alleviated OA and the role of the NRF2/Parkin axis in MitoQ-mediated protective effects. In interleukin (IL)-1ß-induced OA chondrocytes, MitoQ activated the NRF2 pathway, reducing extracellular matrix (ECM) degradation and inflammation. MitoQ also increased glutathione peroxidase 4 (GPX4) expression, leading to decreased levels of reactive oxygen species (ROS) and lipid ROS. Silencing NRF2 weakened MitoQ's protective effects, while knockdown of Parkin upregulated the NRF2 pathway, inhibiting OA progression. Intra-articular injection of MitoQ mitigated cartilage destruction in destabilized medial meniscus (DMM)-induced OA mice. Our study demonstrates that MitoQ maintains cartilage homeostasis in vivo and in vitro through the NRF2/Parkin axis. We supplemented the negative feedback regulation mechanism between NRF2 and Parkin. These findings highlight the therapeutic potential of MitoQ for OA treatment.

Lipid peroxidation in osteoarthritis: focusing on 4-hydroxynonenal, malondialdehyde, and ferroptosis.

Osteoarthritis (OA) is a multifactorial and increasingly prevalent degenerative disease that affects the whole joint. The pathogenesis of OA is poorly understood and there is a lack of therapeutic interventions to reverse the pathological process of this disease. Accumulating studies have shown that the overproduction of reactive oxygen species (ROS) and ROS-induced lipid peroxidation are involved in the pathogenesis of OA. 4-Hydroxy-2-nonenal (4-HNE) and malondialdehyde (MDA) have received considerable attention for their role in cartilage degeneration and subchondral bone remodeling during OA development. Ferroptosis is a form of cell death characterized by a lack of control of membrane lipid peroxidation and recent studies have suggested that chondrocyte ferroptosis contributes to OA progression. In this review, we aim to discuss lipid peroxidation-derived 4-HNE and MDA in the progression of OA. In addition, the therapeutic potential for OA by controlling the accumulation of lipid peroxidation and inhibiting chondrocyte ferroptosis are discussed.

The roles of the Hippo-YAP signalling pathway in Cartilage and Osteoarthritis.

Osteoarthritis (OA) is an age-related disease, characterized by cartilage degeneration. The pathogenesis of OA is complicated and the current therapeutic approaches for OA are limited. Cartilage, an integral part of the skeletal system composed of chondrocytes, is essential for skeletal development, tissue patterning, and maintaining the normal activity of joints. The development, homeostasis and degeneration of cartilage are tightly associated with OA. Over the past decade, accumulating evidence indicates that Hippo/YAP is a vital biochemical signalling pathway that strictly governs tissue development and homeostasis. The joint tissues, especially for cartilage, are sensitive to changes of Hippo/YAP signalling. In this review, we summarize the role of Hippo/YAP signalling in cartilage and discuss its involvement in OA progression from points of cartilage degradation, subchondral bone remodeling, and synovial alteration. We also highlight the potential therapeutic implications of Hippo/YAP signalling and further discuss current limitations and controversy on Hippo/YAP-based application for OA treatment.

Corrigendum: Deferoxamine alleviates osteoarthritis by inhibiting chondrocyte ferroptosis and activating the Nrf2 pathway.

[This corrects the article DOI: 10.3389/fphar.2022.791376.].

Inhibition of TRADD ameliorates chondrocyte necroptosis and osteoarthritis by blocking RIPK1-TAK1 pathway and restoring autophagy.

Osteoarthritis (OA) is an age-related disease characterized by cartilage degeneration. TNFR1-associated death domain protein (TRADD) is a key upstream molecule of TNF-α signals but its role in OA pathogenesis is unknown. This study aimed to verify that whether inhibition of TRADD could protect against chondrocyte necroptosis and OA, and further elucidate the underlying mechanism. We demonstrated that TNF-α-related OA-like phenotypes including inflammation response, extracellular matrix degradation, apoptosis, and necroptosis in chondrocytes were inhibited by TRADD deficiency. Furthermore, TRADD interacted with TRAF2 and knockdown of TRADD suppressed the activation of RIPK1-TAK1-NF-κB signals and restored impaired autophagy. ICCB-19, the selective inhibitor of TRADD, also attenuated necroptosis in chondrocytes. Mechanismly, ICCB-19 blocked the phosphorylation of TAK1-NF-κB signals and restored impaired autophagy, whereas inhibiting autophagic process with 3-Methyladenine compromised these effects of ICCB-19. The in vivo study showed that the intra-articular injection of ICCB-19 rescued the expression of collagen alpha-1(II) chain and LC3, and mitigated the cartilage degeneration of OA mice. This study demonstrates that TRADD mediates TNF-α-induced necroptosis and OA-like phenotypes of chondrocytes and suggests that ICCB-19 suppresses chondrocyte damage and cartilage degeneration by inhibiting TNF-α-TRADD-mediated signals and dysregulation of autophagy in chondrocytes. ICCB-19 may serve as an important option for OA therapy.

JNK-JUN-NCOA4 axis contributes to chondrocyte ferroptosis and aggravates osteoarthritis via ferritinophagy.

Interruption of iron homeostasis is correlated with cell ferroptosis and degenerative diseases. Nuclear receptor coactivator 4 (NCOA4)-mediated ferritinophagy has been reported as a vital mechanism to control cellular iron levels, but its impact on osteoarthritis (OA) pathology and the underline mechanism are unknown. Herein we aimed to investigate the role and regulatory mechanism of NCOA4 in chondrocyte ferroptosis and OA pathogenesis. We demonstrated that NCOA4 was highly expressed in cartilage of patients with OA, aged mice, post-traumatic OA mice, and inflammatory chondrocytes. Importantly, Ncoa4 knockdown inhibited IL-1ß-induced chondrocyte ferroptosis and extracellular matrix degradation. Contrarily, overexpression of NCOA4 promoted chondrocyte ferroptosis and the delivery of Ncoa4 adeno-associated virus 9 into knee joint of mice aggravated post-traumatic OA. Mechanistic study revealed that NCOA4 was upregulated in a JNK-JUN signaling-dependent manner in which JUN could directly bind to the promoter of Ncoa4 and initial the transcription of Ncoa4. NCOA4 could interact with ferritin and increase autophagic degradation of ferritin and iron levels, which caused chondrocyte ferroptosis and extracellular matrix degradation. In addition, inhibition of JNK-JUN-NCOA4 axis by SP600125, a specific inhibitor of JNK, attenuated development of post-traumatic OA. This work highlights the role of JNK-JUN-NCOA4 axis and ferritinophagy in chondrocyte ferroptosis and OA pathogenesis, suggesting this axis as a potential target for OA treatment.

Desferoxamine protects against hemophilic arthropathy through the upregulation of HIF-1α-BNIP3 mediated mitophagy.

AIMS: Hemophilic arthropathy (HA) is a typically iron overload induced joint disease secondary to continuous joint bleeding, however, the exact role of iron chelators in HA has not been fully elucidated. In the present study, we investigated whether desferoxamine (DFO), an iron chelator, could limit the development of HA and the underlying mechanisms. MATERIALS AND METHODS: A HA mice model was established by needle puncture in the left knees of FVIII-deficient hemophilic mice. HA progression was evaluated at 8 weeks after DFO administration. Moreover, chondrocytes were treated with ferric ammonium citrate (FAC) to mimic iron overload in vitro. Modulating effect of DFO on iron overload induced oxidative stress, chondrocytes apoptosis and extracellular matrix (ECM) degradation and the role of HIF-1α-BNIP3 mediated mitophagy were examined. KEY FINDINGS: We found that DFO limited the development of HA and protected iron overload induced ECM degradation, chondrocytes apoptosis and oxidative stress. Besides chelating Fe2+, we found that HIF-1α-BNIP3 mediated mitophagy played important roles in the protective effect of DFO. HIF-1α inhibition suppressed chondrocytes mitophagy process and partly diminished the protective effect of DFO on chondrocytes iron overload. SIGNIFICANCE: In conclusion, DFO could protect against HA development via HIF-1α-BNIP3 mediated mitophagy, suggesting DFO might be a potential therapeutic supplement for HA treatment.

Indirubin protects chondrocytes and alleviates OA by inhibiting the MAPK and NF-κB pathways.

PHARMACOLOGICAL RELEVANCE: Indirubin (IR) is a key active ingredient in the traditional Chinese medication QingDai, also called indigo naturalis, which are extensively used in China to treat chronic diseases, such as inflammation and cancer. However, the function of IR in reducing chondrocyte inflammation in osteoarthritis (OA) is still unclear. AIM OF THE STUDY: The aim of this research was to examine how IR inhibits arthritis and to highlight some of its cellular-level processes. MATERIALS AND METHODS: Chondrocytes from the knee joint of C57 mice were gathered and grown for in vitro tests and used to determine the toxicity of IR toward chondrocytes using a CCK8 kit. Chondrocytes were treated with IL-1ß and IR or with IL-1ß alone, and western blotting was used to determine the expression levels of inflammatory mediators. Meanwhile, through the identification and examination of pertinent markers via quantitative PCR. By using PCR assays, western blotting, toluidine blue staining and safranin O staining, the expression of proteoglycan (AGG) and type II collagen (collagen II) was investigated. Furthermore, western blotting was used to detect activation of the NF-κB and MAPK signaling pathways, and immunofluorescence was used to detect p65 nuclear translocation. In an in vivo experiment, C57BL/6 mice were subjected to destabilization of the medial meniscus (DMM) surgery to produce an OA model, and IR was injected into the articular cavity for 8 weeks. Eventually, the mice were killed, and samples of the knee joints were obtained for histological examination and analysis. RESULTS: IR significantly reduced the expression of inflammatory regulators in chondrocytes treated with IL-1ß, including iNOS and COX-2. Inhibition of IL-1ß induced production of the key catabolic enzymes MMP3, MMP13 and A5. Additionally, an improvement in the downregulation of collagen II and AGG expression was observed. Moreover, IR prevented the aberrant IL-1ß-induced activation of the NF-κB and MAPK signaling pathways, which resulted in downregulation of p65 and p38 expression. Compared to the DMM group, the severity of cartilage injury in animals was dramatically lessened and OARSI scores were lower in the treated groups. CONCLUSION: According to the above findings, IR is quite effective in preventing arthritis both in vivo and in vitro, suggesting that IR may be employed as a possible anti-arthritis drug.

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-1ß (IL-1ß) 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-1ß 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-1ß-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-1ß- 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.

Iron homeostasis in arthropathies: From pathogenesis to therapeutic potential.

Iron is an essential element for proper functioning of cells within mammalian organ systems; in particular, iron homeostasis is critical for joint health. Excess iron can induce oxidative stress damage, associated with the pathogenesis of iron-storage and ageing-related diseases. Therefore, iron levels in body tissues and cells must be tightly regulated. In the past decades, excess iron content within joints has been found in some patients with joint diseases including hemophilic arthropathy, hemochromatosis arthropathy, and osteoarthritis (OA). Currently, increased evidence has shown that iron accumulation is closely associated with multiple pathological changes of these arthropathies. This review summarizes system-level and intracellular regulation of iron homeostasis, and emphasizes the role of iron in synovial alterations, cartilage degeneration, and subchondral bone of several arthropathies. Of note, we discuss the potential link between iron homeostasis and OA pathogenesis. Finally, we discuss the therapeutic potential of maintaining iron homeostasis in these arthropathies.