NLRP3 as a potentially novel biomarker for the management of osteoarthritis

Evaluation of the protective effects of chondroitin sulfate oligosaccharide against osteoarthritis via inactivation of NLRP3 inflammasome by in vivo and in vitro studies

Osteoarthritis (OA) is the most prevalent degenerative arthritis disease linked to aging, obesity, diet, and accumulation of octacalcium phosphate (OCP) crystals in joints. Current research has focused on inflammation and chondrocytes apoptosis as underlying OA mechanisms. Inflammatory cytokines like IL-1β activate matrix metalloproteinase-13 (MMP-13) and aggrecanase (the member of A Disintegrin and Metalloproteinase with Thrombospondin motifs family, ADAMTS), leading to cartilage matrix degradation. The NLRP3 inflammasome also contributes to OA pathogenesis by maturing IL-1β. Natural products like chondroitin sulfate oligosaccharides (oligo-CS) show promise in OA treatment by inhibiting inflammation. Our study evaluates the protective effects of oligo-CS against OA by targeting NLRP3 inflammation. Stimulating human SW1353 chondrocytes and human mononuclear macrophage THP-1 cells with OCP showed increased NLRP3 inflammation initiation, NF-κB pathway activation, and the production of inflammatory cytokines (IL-1β, IL-6) and the metabolic index (MMP-13, ADAMTS-5), leading to cartilage matrix degradation. However, oligo-CS treatment significantly reduced inflammation. In a 28-day in vivo study with C57BL/6 female mice, OCP was injected into their right knee and oligo-CS was orally administered. The OCP group exhibited significant joint space narrowing and chondrocyte loss, while the oligo-CS group maintained cartilage integrity. Oligo-CS groups also regulated gut microbiota composition to a healthier state. Taken together, our findings suggest that oligo-CS can be considered as a protective compound against OA.

Pectolinarigenin targeting FGFR3 alleviates osteoarthritis progression by regulating the NF-κB/NLRP3 inflammasome pyroptotic pathway

OBJECTIVE

Osteoarthritis (OA) is a chronic degenerative disease characterized by cartilage degeneration, involving inflammation, pyroptosis, and degeneration of the extracellular matrix (ECM). Pectolinarigenin (PEC) is a natural flavonoid with antioxidant, anti-inflammatory and anti-tumor properties. This study aims to explore the potential of PEC in ameliorating OA progression and its underlying mechanisms.

METHODS

Chondrocytes were exposed to 10 ng/mL IL-1β to simulate OA-like changes. The effect of PEC on IL-1β-treated chondrocytes was assessed using ELISA, western blot, and immunofluorescence. The mRNA sequencing (mRNA-seq) was employed to explore the possible targets of PEC in delaying OA progression. The OA mouse model was induced through anterior cruciate ligament transection (ACLT) and divided into sham, ACLT, ACLT+5 mg/kg PEC, and ACLT+10 mg/kg PEC groups. Micro-computed tomography and histological analysis were conducted to confirm the beneficial effects of PEC on OA in vivo.

RESULTS

PEC mitigated chondrocyte pyroptosis, as evidenced by reduced levels of pyroptosis-related proteins. Additionally, PEC attenuated IL-1β-mediated chondrocyte ECM degradation and inflammation. Mechanistically, mRNA-seq showed that FGFR3 was a downstream target of PEC. FGFR3 silencing reversed the beneficial effects of PEC on IL-1β-exposed chondrocytes. PEC exerted anti-pyroptotic, anti-ECM degradative, and anti-inflammatory effects through upregulating FGFR3 to inhibit the NF-κB/NLRP3 pyroptosis-related pathway. Consistently, in vivo experiments demonstrated the chondroprotective effects of PEC in OA mice.

CONCLUSION

PEC alleviate OA progression by FGFR3/NF-κB/NLRP3 pathway mediated chondrocyte pyroptosis, ECM degradation and inflammation, suggesting the potential of PEC as a therapeutic agent for OA.

Trehalose Rescues Postmenopausal Osteoporosis Induced by Ovariectomy through Alleviating Osteoblast Pyroptosis via Promoting Autophagy

BACKGROUND

Osteoporosis, a prevalent bone metabolic disease, often requires long-term drug treatments that may lead to serious side effects. Trehalose, a natural disaccharide found in various organisms, has been shown to have a promoting effect on autophagy. However, whether trehalose can improve bone mass recovery in ovariectomized rats and its underlying mechanisms remains unclear. In this study, trehalose was administered to ovariectomized rats to evaluate its therapeutic potential for osteoporosis following ovariectomy.

METHODS

Micro-computed tomography (Micro-CT), hematoxylin and eosin (HE) and immunohistochemical staining techniques were utilized to evaluate the impact of trehalose on osteoporosis induced by ovariectomy (OVX) in mice, both in imaging and histological dimensions. Furthermore, the influence of trehalose on osteoblastogenesis and functional activity was quantified through Alizarin Red S (ARS) staining and immunoblotting assays.

RESULTS

Trehalose effectively mitigated bone loss, elevated autophagy and suppressed pyroptosis in ovariectomized rats. Furthermore, 3-methyladenine diminished the protective effects of trehalose, particularly in promoting autophagy and inhibiting pyroptosis.

CONCLUSIONS

Trehalose demonstrates significant potential in treating osteoporosis by suppressing NLRP3 inflammasome-driven pyroptosis, primarily through autophagy promotion. This suggests that trehalose could be a promising, safer alternative treatment for osteoporosis.

Predicting the potential mechanism of radix chimonanthi pracecocis in treating osteoarthritis by network pharmacology analysis combined with experimental validation

ETHNOPHARMACOLOGICAL RELEVANCE

Radix Chimonanthi Pracecocis (RCP), also known as Tiekuaizi, widely used by the Miao community in Guizhou, exhibits diverse biological activities and holds promise for the treatment of osteoarthritis (OA). However, there is a lack of contemporary pharmacological research in this area.

AIMS OF THE STUDY

This study aims to explore the potential of targets and mechanisms of RCP in the treatment of OA.

MATERIALS AND METHODS

The chemical components of RCP were identified using UPLC-MS/MS, and active components were determined based on the Lipinski rule. RCP and OA-related targets were retrieved from public databases such as TCMSP and GeneCards. Network pharmacology approaches were employed to identify key genes. The limma package (version 3.40.2) in R 4.3.2 was used to screen for differentially expressed genes (DEGs) between OA and healthy individuals in GSE82107. DEGs were analyzed using an independent sample t-test and receiver operating characteristic analysis in GraphPad Prism 9.5.1. Additionally, molecular docking (SYBYL2.1.1) was used to analyze the binding interactions between the active components and target proteins. Finally, we established a papain-induced osteoarthritis (OA) rat model and treated it with RCP aqueous extract by gavage. We validated relevant indicators using real-time fluorescence quantitative polymerase chain reaction, Western blot, immunohistochemistry, and enzyme-linked immunosorbent assays.

RESULTS

Seven active components and 53 targets were identified. The results of GO and KEGG enrichment analyses confirmed the significant role of RCP in the regulation of pyroptosis. Hypoxia-inducible factor-1α (HIF-1α) was identified as a key gene involved in the main biological functions. Molecular docking analysis revealed that Praecoxin, Isofraxidin, Esculin, and Naringenin can bind to the nucleotide-binding domain, leucine-rich repeat, and pyrin domain-containing protein 3 (NLRP3) (T-Score >5). Additionally, Praecoxin can bind to HIF-1α (T-Score >5). In vivo experiments demonstrated that RCP significantly affects the NLRP3 inflammasome, which is regulated by the HIF-1α pathway. RCP inhibited pyroptosis and reduced synovial inflammation.

CONCLUSIONS

This study confirmed the efficacy of RCP aqueous extract in the treatment of OA and identified seven active components (esculin, dihydrokaempferol, naringenin, praecoxin, carnosol, hydroxyvalerenic acid, isofraxidin) that may play an anti-pyroptosis role in the treatment of OA by downregulating the expression of HIF-1α and NLRP3 inflammasome.

GDF11 protects against mitochondrial-dysfunction-dependent NLRP3 inflammasome activation to attenuate osteoarthritis

INTRODUCTION

Osteoarthritis (OA) is a highly prevalent degenerative disease worldwide, and tumor necrosis factor (TNF-α) is closely associated with its development. Growth differentiation factor 11 (GDF11) has demonstrated anti-injury and anti-aging abilities in certain tissues; however, its regulatory role in OA remains unclear and requires further investigation.

OBJECTIVES

To identify whether GDF11 can attenuate osteoarthritis. To exploring the the potential mechanism of GDF11 in alleviating osteoarthritis.

METHODS

In this study, we cultured and stimulated mouse primary chondrocytes with or without TNF-α, analyzing the resulting damage phenotype through microarray analysis. Additionally, we employed GDF11 conditional knockout mice OA model to examine the relationship between GDF11 and OA. To investigate the target of GDF11's function, we utilized NLRP3 knockout mice and its inhibitor to verify the potential involvement of the NLRP3 inflammasome.

RESULTS

Our in vitro experiments demonstrated that endogenous overexpression of GDF11 significantly inhibited TNF-α-induced cartilage matrix degradation and inflammatory expression in chondrocytes. Furthermore, loss of GDF11 led to NLRP3 inflammasome activation, inflammation, and metabolic dysfunction. In an in vivo surgically induced mouse model, intraarticular administration of recombinant human GDF11 alleviated OA pathogenesis, whereas GDF11 conditional knockout reversed this effect. Additionally, findings from the NLRP3-knockout DMM mouse model revealed that GDF11 exerted its protective effect by inhibiting NLRP3.

CONCLUSION

These findings demonstrate the ability of GDF11 to suppress TNF-α-induced inflammation and cartilage degeneration by preventing mitochondrial dysfunction and inhibiting NLRP3 inflammasome activation, suggesting its potential as a promising therapeutic drug for osteoarthritis.

DDIT3 aggravates TMJOA cartilage degradation via Nrf2/HO-1/NLRP3-mediated autophagy

OBJECTIVE

DNA damage-inducible transcript 3 (DDIT3), as a downstream transcription factor of endoplasmic reticulum stress, is reported to regulate chondrogenic differentiation under physiological and pathological state. However, the specific involvement of DDIT3 in the degradation of condylar cartilage of temporomandibular joint osteoarthritis (TMJOA) is unclarified.

DESIGN

The expression patterns of DDIT3 in condylar cartilage from monosodium iodoacetate-induced TMJOA mice were examined to uncover the potential role of DDIT3 in TMJOA. The Ddit3 knockout (Ddit3-/-) mice and their wildtype littermates (Ddit3+/+) were used to clarify the effect of DDIT3 on cartilage degradation. Primary condylar chondrocytes and ATDC5 cells were applied to explore the mechanisms of DDIT3 on autophagy and extracellular matrix (ECM) degradation in chondrocytes. The autophagy inhibitor chloroquine (CQ) was used to determine the effect of DDIT3-inhibited autophagy in vivo.

RESULTS

DDIT3 were highly expressed in condylar cartilage from TMJOA mice. Ddit3 knockout alleviated condylar cartilage degradation and subchondral bone loss, compared with their wildtype littermates. In vitro study demonstrated that DDIT3 exacerbated ECM degradation in chondrocytes induced by TNF-α through inhibiting autophagy. The intraperitoneal injection of CQ further confirmed that Ddit3 knockout alleviated cartilage degradation in TMJOA through activating autophagy in vivo.

CONCLUSIONS

Our findings identified the crucial role of DDIT3-inhibited autophagy in condylar cartilage degradation during the development of TMJOA.

NLRP3 Expression and Its Predictive Role in Heart Failure with Preserved Ejection Fraction among Non-Valvular Atrial Fibrillation Patients

INTRODUCTION

The aim of this study was to investigate the expression and predictive value of NOD-like receptor thermal protein domain-related protein 3 (NLRP3) in patients with non-valvular atrial fibrillation (NVAF) with heart failure with preserved ejection fraction (HFpEF).

METHODS

This was a retrospective analysis of 121 patients diagnosed with NVAF. According to the occurrence of HFpEF, 81 patients were assigned to the NVAF group and 40 patients to the NVAF/HFpEF group. The levels of NLRP3, B natriuretic peptide (BNP), and interleukin-1β (IL-1β) were determined using ELISA. Independent predictors for HFpEF in NVAF were determined using logistic regression. The receiver operating characteristic (ROC) curve was used to evaluate the predictive value of each factor.

RESULTS

Expression levels of NLRP3, BNP, and IL-1β in the NVAF/HFpEF group, as well as the H2FPEF score were significantly higher than those in the NVAF group. Pearson analysis showed that NLRP3, BNP, and IL-1β expression levels in NVAF patients and the H2FPEF score was positively correlated (r = 0.409, r = 0.244, r = 0.299, p < 0.001). Multivariate logistic regression analysis showed that the NLRP3, BNP, or H2FPEF score can be used as independent factor for predicting the occurrence of HFpEF in NVAF. ROC curves showed that the areas under the curve of NLRP3, BNP, and H2FPEF scores for predicting the occurrence of HFpEF in NVAF patients were 0.856, 0.831, and 0.811, respectively.

CONCLUSION

The NLRP3 level is elevated in the peripheral blood of NVAF patients with HFpEF and is positively correlated with the H2FPEF score. NLRP3 may serve as a potential predictor of HFpEF in patients with NVAF.

TBK1 pharmacological inhibition mitigates osteoarthritis through attenuating inflammation and cellular senescence in chondrocytes

Objectives

TANK-binding kinase 1 (TBK1) is pivotal in autoimmune and inflammatory diseases, yet its role in osteoarthritis (OA) remains elusive. This study sought to elucidate the effect of the TBK1 inhibitor BX795 on OA and to delineate the underlying mechanism by which it mitigates OA.

Methods

Interleukin-1 Beta (IL-1β) was utilized to simulate inflammatory responses and extracellular matrix degradation in vitro. In vivo, OA was induced in 8-week-old mice through destabilization of the medial meniscus surgery. The impact of BX795 on OA was evaluated using histological analysis, X-ray, micro-CT, and the von Frey test. Additionally, Western blot, RT-qPCR, and immunofluorescence assays were conducted to investigate the underlying mechanisms of BX795.

Results

Phosphorylated TBK1 (P-TBK1) levels were found to be elevated in OA knee cartilage of both human and mice. Furthermore, intra-articular injection of BX795 ameliorated cartilage degeneration and alleviated OA-associated pain. BX795 also counteracted the suppression of anabolic processes and the augmentation of catabolic activity, inflammation, and senescence observed in the OA mice. In vitro studies revealed that BX795 reduced P-TBK1 levels and reversed the effects of anabolism inhibition, catabolism promotion, and senescence induction triggered by IL-1β. Mechanistically, BX795 inhibited the IL-1β-induced activation of the cGAS-STING and TLR3-TRIF signaling pathways in chondrocytes.

Conclusions

Pharmacological inhibition of TBK1 with BX795 protects articular cartilage by inhibiting the activation of the cGAS-STING and TLR3-TRIF signaling pathways. This action attenuates inflammatory responses and cellular senescence, positioning BX795 as a promising therapeutic candidate for OA treatment.

The translational potential of this article

This study furnishes experimental evidence and offers a potential mechanistic explanation supporting the efficacy of BX795 as a promising candidate for OA treatment.

Synovial fluid monocyte-to-lymphocyte ratio in knee osteoarthritis patients predicts patient response to conservative treatment: a retrospective cohort study

BACKGROUND

Biomarkers that predict the treatment response in patients with knee osteoarthritis are scarce. This study aimed to investigate the potential role of synovial fluid cell counts and their ratios as biomarkers of primary knee osteoarthritis.

METHODS

This retrospective study investigated 96 consecutive knee osteoarthritis patients with knee effusion who underwent joint fluid aspiration analysis and received concomitant intra-articular corticosteroid injections and blood tests. The monocyte-to-lymphocyte ratio (MLR) and neutrophil-to-lymphocyte ratio (NLR) were calculated. After 6 months of treatment, patients were divided into two groups: the responder group showing symptom resolution, defined by a visual analog scale (VAS) score of ≤ 3, without additional treatment, and the non-responder group showing residual symptoms, defined by a VAS score of > 3 and requiring further intervention, such as additional medication, repeated injections, or surgical treatment. Unpaired t-tests and univariate and multivariate logistic regression analyses were conducted between the two groups to predict treatment response after conservative treatment. The predictive value was calculated using the area under the receiver operating characteristic curve, and the optimal cutoff value was determined.

RESULTS

Synovial fluid MLR was significantly higher in the non-responder group compared to the responder group (1.86 ± 1.64 vs. 1.11 ± 1.37, respectively; p = 0.02). After accounting for confounding variables, odds ratio of non-responder due to increased MLR were 1.63 (95% confidence interval: 1.11-2.39). The optimal MLR cutoff value for predicting patient response to conservative treatment was 0.941.

CONCLUSIONS

MLR may be a potential biomarker for predicting the response to conservative treatment in patients with primary knee osteoarthritis.

Ginkgolide C inhibits ROS-mediated activation of NLRP3 inflammasome in chondrocytes to ameliorate osteoarthritis

ETHNOPHARMACOLOGICAL RELEVANCE

Ginkgo biloba, as the most widely available medicinal plant worldwide, has been frequently utilized for treat cardiovascular, cerebrovascular, diabetic and other diseases. Due to its distinct pharmacological effects, it has been broadly applications in pharmaceuticals, health products, dietary supplements, and so on. Ginkgolide C (GC), a prominent extract of Ginkgo biloba, possesses potential in anti-inflammatory and anti-oxidant efficacy.

AIMS OF THE STUDY

To determine whether GC mitigated the progressive degeneration of articular cartilage in a Monosodium Iodoacetate (MIA)-induced osteoarthritis (OA) rat model by inhibiting the activation of the NLRP3 inflammasome, and the specific underlying mechanisms.

MATERIALS AND METHODS

In vivo, an OA rat model was established by intra-articular injection of MIA. The protective effect of GC (10 mg/kg) on articular cartilage was evaluated. Application of ATDC5 cells to elucidate the mechanism of the protective effect of GC on articular cartilage. Specifically, the expression levels of molecules associated with cartilage ECM degrading enzymes, OS, ERS, and NLRP3 inflammasome activation were analyzed.

RESULTS

In vivo, GC ameliorated MIA-induced OA rat joint pain, and exhibited remarkable anti-inflammatory and anti- ECM degradation effects via inhibition of the activation of NLRP3 inflammasome, the release of inflammatory factors, and the expression of matrix-degrading enzymes in cartilage. Mechanically, GC inhibited the activation of NLRP3 inflammasome by restraining ROS-mediated p-IRE1α and activating Nrf2/NQO1 signal path, thereby alleviating OA. The ROS scavenger NAC was as effective as GC in reducing ROS production and inhibiting the activation of NLRP3 inflammasome.

CONCLUSIONS

GC have exerted chondroprotective effects by inhibiting the activation of NLRP3 inflammasome.

Association between hyperuricemia and the risk of mortality in patients with osteoarthritis: A study based on the National Health and Nutrition Examination Survey database

BACKGROUND

The purpose of this study was to evaluate the relationship between hyperuricemia and the risks of all-cause mortality and cardiovascular disease (CVD) mortality in patients with osteoarthritis (OA).

METHODS

A retrospective cohort study was performed on 3,971 patients using data from the National Health and Nutrition Examination Survey database between 1999 and 2018. OA was diagnosed through specific questions and responses. The weighted COX regression models were used to explore the factors associated with all-cause mortality/CVD mortality in OA patients. Subgroup analyses were conducted based on age, gender, hypertension, dyslipidemia, CVD, and chronic kidney disease (CKD). Hazard ratio (HR) and 95% confidence interval (95% CI) were measured as the evaluation indexes.

RESULTS

During the duration of follow-up time (116.38 ± 2.19 months), 33.69% (1,338 patients) experienced all-cause mortality, and 11.36% (451 patients) died from CVD. Hyperuricemia was associated with higher risks of all-cause mortality (HR: 1.22, 95% CI: 1.06-1.41, P = 0.008) and CVD mortality (HR: 1.32, 95% CI: 1.02-1.72, P = 0.036) in OA patients. Subgroup analyses showed that hyperuricemia was related to the risk of all-cause mortality in OA patients aged >65 years (HR: 1.17, 95% CI: 1.01-1.36, P = 0.042), in all male patients (HR: 1.41, 95% CI: 1.10-1.80, P = 0.006), those diagnosed with hypertension (HR: 1.17, 95% CI: 1.01-1.37, P = 0.049), dyslipidemia (HR: 1.18, 95% CI: 1.01-1.39, P = 0.041), CVD (HR: 1.30, 95% CI: 1.09-1.55, P = 0.004), and CKD (HR: 1.31, 95% CI: 1.01-1.70, P = 0.046). The association between hyperuricemia and a higher risk of CVD mortality was found in OA patients aged ≤ 65 years (HR: 1.90, 95% CI: 1.06-3.41, P = 0.032), who did not suffer from diabetes (HR: 1.36, 95% CI: 1.01-1.86, P = 0.048), who did not suffer from hypertension (HR: 2.56, 95% CI: 1.12-5.86, P = 0.026), and who did not suffer from dyslipidemia (HR: 2.39, 95% CI: 1.15-4.97, P = 0.020).

CONCLUSION

These findings emphasize the importance of monitoring serum uric acid levels in OA patients for potentially reducing mortality associated with the disease.

Extremely low frequency-electromagnetic fields promote chondrogenic differentiation of adipose-derived mesenchymal stem cells through a conventional genetic program

Progressive cartilage deterioration leads to chronic inflammation and loss of joint function, causing osteoarthritis (OA) and joint disease. Although symptoms vary among individuals, the disease can cause severe pain and permanent disability, and effective therapies are urgently needed. Human Adipose-Derived Stem Cells (ADSCs) may differentiate into chondrocytes and are promising for treating OA. Moreover, recent studies indicate that electromagnetic fields (EMFs) could positively affect the chondrogenic differentiation potential of ADSCs. In this work, we investigated the impact of EMFs with frequencies of 35 Hertz and 58 Hertz, referred to as extremely low frequency-EMFs (ELF-EMFs), on the chondrogenesis of ADSCs, cultured in both monolayer and 3D cell micromasses. ADSC cultures were daily stimulated for 36 min with ELF-EMFs or left unstimulated, and the progression of the differentiation process was evaluated by morphological analysis, extracellular matrix deposition, and gene expression profiling of chondrogenic markers. In both culturing conditions, stimulation with ELF-EMFs did not compromise cell viability but accelerated chondrogenesis by enhancing the secretion and deposition of extracellular matrix components at earlier time points in comparison to unstimulated cells. This study showed that, in an appropriate chondrogenic microenvironment, ELF-EMFs enhance chondrogenic differentiation and may be an important tool for supporting and accelerating the treatment of OA through autologous adipose stem cell therapy.

Sipeimine ameliorates osteoarthritis progression by suppression of NLRP3 inflammasome-mediated pyroptosis through inhibition of PI3K/AKT/NF-κB pathway: An in vitro and in vivo study

Background

Osteoarthritis (OA) is a chronic and degenerative condition that persists and progresses over time. Sipeimine (Sip), a steroidal alkaloid derived from Fritillariae Cirrhosae Bulbus, has attracted considerable attention due to its exceptional anti-inflammatory, analgesic, antioxidant, and anti-cancer characteristics. However, Sip's effects on OA and its mechanism still need further research.

Methods

This study utilized network pharmacology to identify initial targets for Sip. Functional associations of Sip in OA were clarified through Gene Ontology (GO) enrichment analysis, bioinformatically analyzing a list of targets. Subsequently, Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis assessed pathways linked to Sip's therapeutic efficacy in OA. Molecular docking techniques explored Sip's binding affinity with key targets. In vitro experiments assessed Sip's impact on lipopolysaccharide (LPS)-induced pro-inflammatory factors and its protective effects on collagen-II and aggrecan degradation within the extracellular matrix (ECM). Western blotting and fluorescence analyses were conducted to determine Sip-mediated signaling pathways. Moreover, in vivo experiments using a mouse OA model validated Sip's therapeutic efficacy.

Results

The results from network pharmacology revealed a total of 57 candidate targets for Sip in OA treatment. GO enrichment analysis demonstrated a robust correlation between Sip and inflammatory response, response to LPS and NF-κB-inducing kinase activity in OA. KEGG enrichment analysis highlighted the significance of NF-κB and PI3K-AKT pathways in Sip's therapeutic potential for OA. Furthermore, molecular docking results demonstrated Sip's robust binding affinity with p65 and PI3K. In vitro experiments demonstrated Sip's effectively suppressed the expression of pro-inflammatory factors induced by LPS, such as COX-2, iNOS, IL-1β, and IL-18. Besides, Sip counteracted the degradation of collagen-II and aggrecan within the ECM and the expression of MMP-13 and ADAMTS-5 mediated by LPS. The safeguarding effects of Sip were ascribed to its inhibition of PI3K/AKT/NF-κB pathway and NLRP3 inflammasome mediated pyroptosis. Additionally, in vivo experiments revealed that Sip could alleviate the subchondral remodeling, cartilage degeneration, synovitis as well as ECM degradation a mouse model of OA.

Conclusion

Sip exhibited potential in attenuating OA progression by suppressing the PI3K/AKT/NF-κB pathway, consequently inhibiting the activation of NLRP3 inflammasome and pyroptosis.

The translational potential statement

The translational potential of this articleThis study provides a biological rationale for the use of Sip as a potential candidate for OA treatment, provide a new concept for the cartilage targeted application of natural compounds.

Pterostilbene Protects against Osteoarthritis through NLRP3 Inflammasome Inactivation and Improves Gut Microbiota as Evidenced by In Vivo and In Vitro Studies

Osteoarthritis (OA) is a persistent inflammatory disease, and long-term clinical treatment often leads to side effects. In this study, we evaluated pterostilbene (PT), a natural anti-inflammatory substance, for its protective effects and safety during prolonged use on OA. Results showed that PT alleviated the loss of chondrocytes and widened the narrow joint space in an octacalcium phosphate (OCP)-induced OA mouse model (n = 3). In vitro experiments demonstrate that PT reduced NLRP3 inflammation activation (relative protein expression: C: 1 ± 0.09, lipopolysaccharide (LPS): 1.14 ± 0.07, PT: 0.91 ± 0.07, LPS + PT: 0.68 ± 0.04) and the release of inflammatory cytokines through NF-κB signaling inactivation (relative protein expression: C: 1 ± 0.03, LPS: 3.49 ± 0.02, PT: 0.66 ± 0.08, LPS + PT: 2.78 ± 0.05), ultimately preventing cartilage catabolism. Interestingly, PT also altered gut microbiota by reducing inflammation-associated flora and increasing the abundance of healthy bacteria in OA groups. Collectively, these results suggest that the PT can be considered as a protective strategy for OA.

Lysosomal destabilization: A missing link between pathological calcification and osteoarthritis

Calcification of cartilage by hydroxyapatite is a hallmark of osteoarthritis and its deposition strongly correlates with the severity of osteoarthritis. However, no effective strategies are available to date on the prevention of hydroxyapatite deposition within the osteoarthritic cartilage and its role in the pathogenesis of this degenerative condition is still controversial. Therefore, the present work aims at uncovering the pathogenic mechanism of intra-cartilaginous hydroxyapatite in osteoarthritis and developing feasible strategies to counter its detrimental effects. With the use of in vitro and in vivo models of osteoarthritis, hydroxyapatite crystallites deposited in the cartilage are found to be phagocytized by resident chondrocytes and processed by the lysosomes of those cells. This results in lysosomal membrane permeabilization (LMP) and release of cathepsin B (CTSB) into the cytosol. The cytosolic CTSB, in turn, activates NOD-like receptor protein-3 (NLRP3) inflammasomes and subsequently instigates chondrocyte pyroptosis. Inhibition of LMP and CTSB in vivo are effective in managing the progression of osteoarthritis. The present work provides a conceptual therapeutic solution for the prevention of osteoarthritis via alleviation of lysosomal destabilization.

FOXQ1 inhibits the progression of osteoarthritis by regulating pyroptosis

BACKGROUND

Osteoarthritis (OA) is the most common age-related joint disease, and the NLRP3-induced pyroptosis has been demonstrated in its progression. The upstream molecules or specific mechanisms controlling NLRP3 and pyroptosis in OA remain unclear.

METHODS

Transcriptome sequencing was performed in the OA mice model, and the expression levels of differentially expressed genes were assessed by qRT-PCR. The cell model was constructed by IL-1β-induced ATDC5 cells. The cell proliferation was examined using CCK-8 assay, and apoptosis was tested using flow cytometry. Western blot was used in protein inspection, and ELISA was used in inflammatory response evaluation.

RESULTS

Compared with the control group, there were 229 up-regulated and 32 down-regulated genes in model group. We detected that FOXQ1 was down-regulated in the OA mice model, improved proliferation, and restrained apoptosis of chondrocytes. Over-expression of FOXQ1 could inhibit pyroptosis-related proteins and inflammatory cytokines, containing NLRP3, Caspase-1, GSDMD, IL-6, IL-18, and TNF-α, and in contrast, FOXQ1 silencing exerted the opposite trend.

CONCLUSIONS

FOXQ1 may inhibit OA progression via down-regulating NLRP3-induced pyroptosis in the present study.

Emerging Roles of Macrophage Polarization in Osteoarthritis: Mechanisms and Therapeutic Strategies

Osteoarthritis (OA) is the most common chronic degenerative joint disease in middle-aged and elderly people, characterized by joint pain and dysfunction. Macrophages are key players in OA pathology, and their activation state has been studied extensively. Various studies have suggested that macrophages might respond to stimuli in their microenvironment by changing their phenotypes to pro-inflammatory or anti-inflammatory phenotypes, which is called macrophage polarization. Macrophages accumulate and become polarized (M1 or M2) in many tissues, such as synovium, adipose tissue, bone marrow, and bone mesenchymal tissues in joints, while resident macrophages as well as other stromal cells, including fibroblasts, chondrocytes, and osteoblasts, form the joint and function as an integrated unit. In this study, we focus exclusively on synovial macrophages, adipose tissue macrophages, and osteoclasts, to investigate their roles in the development of OA. We review recent key findings related to macrophage polarization and OA, including pathogenesis, molecular pathways, and therapeutics. We summarize several signaling pathways in macrophage reprogramming related to OA, including NF-κB, MAPK, TGF-β, JAK/STAT, PI3K/Akt/mTOR, and NLRP3. Of note, despite the increasing availability of treatments for osteoarthritis, like intra-articular injections, surgery, and cellular therapy, the demand for more effective clinical therapies has remained steady. Therefore, we also describe the current prospective therapeutic methods that deem macrophage polarization to be a therapeutic target, including physical stimulus, chemical compounds, and biological molecules, to enhance cartilage repair and alleviate the progression of OA.

Bioactives and their roles in bone metabolism of osteoarthritis: evidence and mechanisms on gut-bone axis

Bioactives significantly modify and maintain human health. Available data suggest that Bioactives might play a beneficial role in chronic inflammatory diseases. Although promised, defining their mechanisms and opting to weigh their benefits and limitations is imperative. Detailed mechanisms by which critical Bioactives, including probiotics and prebiotics such as dietary lipids (DHA, EPA, alpha LA), vitamin D, polysaccharides (fructooligosaccharide), polyphenols (curcumin, resveratrol, and capsaicin) potentially modulate inflammation and bone metabolism is limited. Certain dietary bioactive significantly impact the gut microbiota, immune system, and pain response via the gut-immune-bone axis. This narrative review highlights a recent update on mechanistic evidence that bioactive is demonstrated demonstrated to reduce osteoarthritis pathophysiology.

Promoting the proliferation of osteoarthritis chondrocytes by resolvin D1 regulating the NLRP3/caspase-1 signaling pathway

Osteoarthritis (OA) is a degenerative joint disease commonly found in middle-aged and older people. Chondrocytes are the only cells in joint cartilage that are difficult to heal after pyroptosis, and they will aggravate the wear and tear of joint cartilage and affect the progression of OA. Pyroptosis is a novel form of programmed cell death, and the classical pyroptosis pathway is a programmed cell death pattern mediated by inflammatory cysteine protease-1. Activation of NLRP3 leads to activation and cleavage of caspase-1 precursors, which in turn leads to activation and cleavage of GSDMD proteins and the release of proinflammatory factors. Resolvin D1 (RvD1) is a specialized pro-resolving mediator (SPM) derived from omega-3 unsaturated fatty acids that reduces inflammation and catabolic responses in OA chondrocytes. However, it is unclear whether RvD1 promotes OA chondrocyte proliferation and thus joint cartilage repair. Our results show that RvD1 regulates the NLRP3/caspase-1 signaling pathway by inhibiting the expression of caspase-1, promoting the proliferation of OA chondrocytes, promoting the repair of articular cartilage in rats and delaying the progression of osteoarthritis.

The role of vitamin D3 in modulating the interplay between NLRP3 inflammasome and autophagy in NASH

Damage-associated molecular patterns released upon hepatocyte injury ensuing non-alcoholic steatohepatitis (NASH) can stimulate innate immunity by activating NOD-like receptor family pyrin domain-containing protein 3 (NLRP3) inflammasome, thereby triggering pro-inflammatory cascades in the liver. Aberrant NLRP3 activation allied to compromised autophagic clearance of its components contributes to the progression of multiple inflammatory diseases. Such intricate interplay, however, was not fully deciphered in NASH. Prior studies have illuminated the ability of vitamin D3 to temper inflammasome activation in several contexts, prompting us to probe the impact of vitamin D3, particularly its active form, calcitriol (CAL), on NLRP3 overactivation in a high-fat diet (HFD)-based NASH model and its potential dependence on autophagy. Hydroxychloroquine (HCQ), an autophagy inhibitor, was co-administered with CAL to examine the likely modulation of the NLRP3/autophagy crosstalk. Our results showed that treatment with CAL countervailed the histopathological derangement reported in the livers of HFD-fed mice that paralleled a restoration of vitamin D receptor gene expression and reduction in sterol regulatory element binding protein 1c levels. Moreover, p62 was curtailed with CAL treatment indicating autophagy induction. CAL also prompted a reduction in NLRP3, caspase-1, gasdermin D, and IL-18 protein levels along with the apoptosis-associated speck-like protein (ASC) gene expression. Treatment with CAL also reduced IL-1β and caspase-3 immunoreactivities compared to control. Intriguingly, CAL modulatory effects on inflammasome activation were curbed in the group that received HCQ, suggesting a potential autophagy dependency. Accordingly, the current study suggests that CAL was capable of ameliorating NASH via inhibiting NLRP3 inflammasome activation in an autophagy-dependent manner.

MiR-203a-3p attenuates apoptosis and pyroptosis of chondrocytes by regulating the MYD88/NF-κB pathway to alleviate osteoarthritis progression

BACKGROUND

Osteoarthritis (OA) is a degenerative joint disease that imposes a significant socioeconomic burden worldwide. Our previous studies revealed a down-regulation of miR-203a-3p in the knee tissues of OA patients. However, the underlying mechanism through which miR-203a-3p mediates the pathological process of OA remains unknown. Thus, we aimed to determine the effects of miR-203a-3p in the progression of OA.

METHODS

Rat primary chondrocytes were stimulated with 10 μg/mL lipopolysaccharide (LPS) for 24 hours, followed by transfection with 50 nM miR-203a-3p mimic, inhibitor, and siRNA for MYD88 or consistent negative controls for 48 hours. To evaluate the effects of miR-203a-3p on cartilage matrix degradation, oxidative stress, apoptosis, and pyroptosis in chondrocytes, various techniques such as immunofluorescence staining, biochemical analysis, Western blotting, and the TUNEL staining were utilized. In the rat OA model, all rats were randomly divided into four groups: Sham, OA, OA+Agomir negative control (NC), and OA+Agomir. They received intra-articular injections of 25 nmol miR-203a-3p agomir, agomir NC, or normal saline twice a week for the duration of 8 weeks after OA induction. Immunofluorescence staining was performed to evaluate the effects of miR-203a-3p on cartilage matrix degradation in rats.

RESULTS

MiR-203a-3p was down-regulated in LPS-treated rat chondrocytes and OA cartilage, and directly targeted MYD88. Moreover, miR-203a-3p significantly inhibited LPS-induced cartilage matrix degradation, oxidative stress, apoptosis, and pyroptosis of chondrocytes via targeting MYD88. Mechanistically, miR-203a-3p exerted protective effects via the inhibition of the MYD88/NF-κB pathway. In the rat OA model, intra-articular injections of miR-203a-3p agomir also significantly inhibited cartilage matrix degradation, thereby alleviating OA progression. Furthermore, the miR-203a-3p agomir-treated arthritic rat dramatically exhibited better articular tissue morphology and lower OARSI scores.

CONCLUSIONS

MiR-203a-3p plays a role in alleviating the progression of OA by regulating the MYD88/NF-κB pathway, thereby inhibiting cartilage matrix degradation, oxidative stress, apoptosis, and pyroptosis of chondrocytes. It highlights the potential significance of miR-203a-3p as an important regulator of OA.

Dual-engineered cartilage-targeting extracellular vesicles derived from mesenchymal stem cells enhance osteoarthritis treatment via miR-223/NLRP3/pyroptosis axis: Toward a precision therapy

Osteoarthritis (OA) is the most common disabling joint disease with no effective disease modifying drugs. Extracellular vesicles released by several types of mesenchymal stem cells could promote cartilage repair and ameliorate OA pathology in animal models, representing a novel therapeutic strategy. In this study, we demonstrated that extracellular vesicles derived from human umbilical cord mesenchymal stem cells (hUC-EVs) could maintain chondrocyte homeostasis and alleviate OA, and further revealed a novel molecular mechanism of this therapeutic effect. miR-223, which could directly bind with the 3'UTR of NLRP3 mRNA, was found to be a key miRNA for hUC-EVs to exert beneficial effects on inflammation inhibiting and cartilage protecting. For enhancing the effect on mitigating osteoarthritis, exogenous miR-223 was loaded into hUC-EVs by electroporation, and a collagen II-targeting peptide (WYRGRL) was modified onto the surface of hUC-EVs by genetic engineering to achieve a more targeted and efficient RNA delivery to the cartilage. The dual-engineered EVs showed a maximal effect on inhibiting the NLRP3 inflammasome activation and chondrocyte pyroptosis, and offered excellent results for the treatment of OA. This study provides a novel theoretical basis and a promising therapeutic strategy for the application of engineered extracellular vesicles in OA treatment.

Pyroptosis of chondrocytes activated by synovial inflammation accelerates TMJ osteoarthritis cartilage degeneration via ROS/NLRP3 signaling

OBJECTIVES

Synovial inflammation and chondrocyte death have been widely acknowledged as key contributors to the pathological progression of temporomandibular joint osteoarthritis (TMJ-OA), a degenerative joint disease currently lacking definitive treatments. This study aims to understand the regulatory role of chondrocyte pyroptosis in condylar cartilage degradation during TMJ-OA.

METHODS

The levels of cytokines, cartilage degeneration markers, and pyroptotic biomarkers in the synovium and synovial fluid of temporomandibular disorders (TMD) patients were examined. The synovitis, cartilage degradation, and chondrocyte pyroptosis in wild-type and alpha-kinase 1 (ALPK1)-deficient TMJ-OA mice were then compared following monosodium iodoacetate (MIA) induction. Subsequently, we investigated the downstream mechanisms of cytokines- or macrophage supernatants-induced metabolic disorders and pyroptosis in chondrocytes using primary TMJ chondrocytes and ATDC5 chondrocyte cultures.

RESULTS

We found a positive correlation between pyroptotic biomarkers and cartilage degradation mediators and cytokines in the synovial fluid of TMD patients. MIA-induced TMJ-OA mice demonstrated significant synovitis, cartilage degradation, and chondrocyte pyroptosis, which were mitigated in ALPK1-deficient TMJ-OA mice, inflammation-restrained mice. Ex-vivo study revealed the contribution of reactive oxygen species (ROS) to inflammation-irritated macrophage supernatants-induced pyroptosis and metabolic disorders in chondrocytes. Targeting NOD-like receptor protein 3 (NLRP3) alleviated cytokines- or ROS-induced pyroptosis and metabolic disorders in chondrocytes by inhibiting caspase-1 activation and interleukin-1β (IL-1β) secretion.

CONCLUSION

Our findings offer novel insight into the role of synovial inflammation-induced chondrocyte pyroptosis in promoting cartilage degradation during TMJ-OA via the ROS and NLRP3 signaling pathway.

Orientin inhibits inflammation in chondrocytes and attenuates osteoarthritis through Nrf2/NF-κB and SIRT6/NF-κB pathway

Effects of Orientin on murine chondrocytes treated with interleukin-1β (IL-1β) were evaluated using qPCR, western blot analysis, ELISA, and immunofluorescent staining in vitro. In vivo, We established a standard OA model by performing the destabilized medial meniscus (DMM) surgery on C57BL/6 mice, and assessed healing effect of Orientin by X-ray imaging, histopathological analysis, immunohistochemical staining. Osteoarthritis (OA) is the most common form of degenerative joint disease in clinic and the chondrocyte inflammation plays the most important role in OA development. The natural flavonoid compound (Orientin) has anti-inflammatory bioactive properties in the treatment of various diseases. But studies have not explored whether Orientin modulates OA progression. In this study, a significant suppression in IL-1β-mediated pro-inflammatory mediators and the degradation of cartilage extracellular matrix (ECM) was observed in vitro through qPCR, western blot analysis, ELISA, and immunofluorescent staining after the treatment with Orientin. In addition, Orientin abrogated DMM surgery induced cartilage degradation in mice, which was assessed by X-ray imaging, histopathological analysis, immunohistochemical staining. Mechanistic studies showed that Orientin suppressed OA development by downregulating activation of NF-κB by activating Nrf2/HO-1 axis and SIRT6 signaling pathway. These results provide evidence that Orientin serves as a potentially viable compound for the treatment of OA.

Xanthohumol alleviates palmitate-induced inflammation and prevents osteoarthritis progression by attenuating mitochondria dysfunction/NLRP3 inflammasome axis

Osteoarthritis (OA) is a prevalent chronic degenerative joint disease worldwide. Obesity has been linked to OA, and increased free fatty acid levels (e.g., palmitate) contribute to inflammatory responses and cartilage degradation. Xanthohumol (Xn), a bioactive prenylated chalcone, was shown to exhibit antioxidative, anti-inflammatory, and anti-obesity capacities in multiple diseases. However, a clear description of the preventive effects of Xn on obesity-associated OA is unavailable. This study aimed to assess the chondroprotective function of Xn on obesity-related OA. The in vitro levels of inflammatory and ECM matrix markers in human chondrocytes were assessed after the chondrocytes were treated with PA and Xn. Additionally, in vivo cartilage degeneration was assessed following oral administration of HFD and Xn. This study found that Xn treatment completely reduces the inflammation and extracellular matrix degradation caused by PA. The proposed mechanism involves AMPK signaling pathway activation by Xn, which increases mitochondrial biogenesis, attenuates mitochondrial dysfunction, and inhibits NLRP3 inflammasome and the NF-κB signaling pathway induced by PA. In summary, this study highlights that Xn could decrease inflammation reactions and the degradation of the cartilage matrix induced by PA by inhibiting the NLRP3 inflammasome and attenuating mitochondria dysfunction in human chondrocytes.

TRPV4-mediated mitochondrial dysfunction induces pyroptosis and cartilage degradation in osteoarthritis via the Drp1-HK2 axis

Osteoarthritis (OA) is an age-related chronic degenerative disease with complex pathophysiological mechanisms. Accumulating evidence indicates that nod-like receptor pyrin domain 3 (NLRP3) inflammasome-mediated pyroptosis of chondrocytes plays a crucial role in the OA progression. Transient Receptor Potential Vanilloid 4 (TRPV4), described as a calcium-permeable cation channel, isassociated with proinflammatory factors and pyroptosis. In this study, we studied the potential functions of TRPV4 in chondrocyte pyroptosis and cartilage degradation. We found that lipopolysaccharides(LPS)-induced mitochondrial reactive oxygen species (mtROS) accumulation aggravated chondrocyte pyroptosis and cartilage degeneration. TRPV4 induces dynamin-related protein 1 (Drp1) mitochondrial translocation through the Ca2+-calmodulin-dependent protein kinase II (CaMKII) signaling pathway, which subsequently caused the mitochondrial dysfunction (e.g., mPTP over opening; Δψm depolarization; ATP production decreased; mtROS accumulation), pyroptosis and extracellular matrix (ECM) degradation through hexokinase 2 (HK2) dissociation from mitochondrial membrane. Moreover, TRPV4 inhibition reversed Drp1-involved chondrocyte pyroptosis and cartilage degeneration in the anterior cruciate ligament transection (ACLT) mouse model. Our findings revealed the internal mechanisms underlying TRPV4 regulation in chondrocytes and its intrinsic therapeutic efficacy for OA.

Fundamentals of osteoarthritis: Inflammatory mediators in osteoarthritis

OBJECTIVES

As more has become known of the pathophysiology of osteoarthritis (OA), evidence that inflammation plays a critical role in its development and progression has accumulated. Here, we aim to review current knowledge of the complex inflammatory network in the OA joint.

DESIGN

This narrative review is presented in three main sections: local inflammation, systemic inflammation, and therapeutic implications. We focused on inflammatory mediators and their link to OA structural changes in the joint.

RESULTS

OA is characterized by chronic and low-grade inflammation mediated mostly by the innate immune system, which results in cartilage degradation, bone remodeling and synovial changes. Synovitis is regarded as an OA characteristic and associated with increased severity of symptoms and joint dysfunction. However, the articular cartilage and the subchondral bone also produce several pro-inflammatory mediators thus establishing a complex interplay between the different tissues of the joint. In addition, systemic low-grade inflammation induced by aging, obesity and metabolic syndrome can contribute to OA development and progression. The main inflammatory mediators associated with OA include cytokines, chemokines, growth factors, adipokines, and neuropeptides.

CONCLUSIONS

Future research is needed to deeper understand the molecular pathways mediating the inflammation in OA to provide new therapeutics that target these pathways, or to repurpose existing drugs.

Betulinic Acid Attenuates Osteoarthritis via Limiting NLRP3 Inflammasome Activation to Decrease Interleukin-1β Maturation and Secretion

Introduction

Osteoarthritis (OA) is the most common degenerative joint disorder. Prior studies revealed that activation of NLRP3 inflammasome could promote the activation and secretion of interleukin-1β (IL-1β), which has an adverse effect on the progression of OA. Betulinic acid (BA) is a compound extract of birch, whether it can protect against OA and the mechanisms involved are still unknown.

Materials and Methods

In vivo experiments, using gait analysis, ELISA, micro-CT, and scanning electron microscopy (SEM), histological staining, immunohistological (IHC) and immunofluorescence (IF) staining, and atomic force microscopy (AFM) to assess OA progression after intraperitoneal injection of 5 and 15 mg/kg BA in an OA mouse model. In vitro experiments, caspase-1, IL-1β, and the N-terminal fragment of gasdermin D (GSDMD-NT) were measured in bone marrow-derived macrophages (BMDMs) by using ELISA, western blot, and immunofluorescence staining.

Results

We demonstrated that OA progression can be postponed with intraperitoneal injection of 5 and 15 mg/kg BA in an OA mouse model. Specifically, BA postponed DMM-induced cartilage deterioration, alleviated subchondral bone sclerosis, and relieved synovial inflammation. In vitro studies, the activated NLRP3 inflammasome produces mature IL-1β by facilitating the cleavage of pro-IL-1β, and BA could inhibit the activation of NLRP3 inflammasome in BMDMs.

Conclusions

Taken together, our analyses revealed that BA attenuates OA via limiting NLRP3 inflammasome activation to decrease the IL-1β maturation and secretion.

Study on the mechanism of NLRP3 effect on the skeleton of de-ovalized mice

Postmenopausal osteoporosis caused by estrogen deficiency affects millions of women worldwide. By influencing both osteoblast and osteoclast development, NOD-like receptor thermoprotein structural domain-associated protein 3 (NLRP3) is a key player in the etiology of osteoporosis (OP). The purpose of this research was to look into the mechanism of action of NLRP3 in osteoporosis caused by a lack of estrogen, highlighting that NLRP3 induces osteoblast pyroptosis and thus inflammatory responses in de-ovulated mice, thereby inhibiting osteogenic differentiation and participating in the development of osteoporosis. In de-ovulated mice, we found an enhanced inflammatory response and suppression of osteogenic activity. In vitro experiments, we found a significant increase in markers of cell pyroptosis and inflammatory responses and a significant decrease in markers of osteogenic differentiation in osteoblasts from de-ovulated mice. However, knockdown of the NLRP3 gene inhibited this cell pyroptosis and improved osteogenic differentiation of osteoblasts. Our findings indicate a potential therapeutic potential for the treatment of estrogen deficiency-induced osteoporosis by demonstrating the critical role that NLRP3 inflammatory vesicles and their downstream-mediated cellular pyroptosis play in bone differentiation.

Cardamonin protects against iron overload induced arthritis by attenuating ROS production and NLRP3 inflammasome activation via the SIRT1/p38MAPK signaling pathway

Iron homeostasis plays an essential role in joint health, while iron overload can cause damage and death of cartilage cells. Cardamonin (CAR) is a substance found in the fruit of the chasteberry plant and has anti-inflammatory and anti-tumor activities. We first administered iron dextran (500 mg/kg) intraperitoneally to establish an iron overload mouse model and surgically induced osteoarthritis. The extent of OA and iron deposition were assessed using Micro-ct, Safranin-O/fast green staining, H&E staining, and Prussian Blue 10 weeks later. We administered primary chondrocytes with Ferric Ammonium Citrate (FAC) to evaluate the chondrocyte changes. Chondrocytes were identified in vitro by toluidine blue staining, and chondrocyte viability was evaluated by CCK-8. The rate of apoptosis was determined by Annexin V-FITC/PI assay. The mechanism of action of CAR was verified by adding the SIRT1 inhibitor EX527, and the expression of SIRT1 and MAPK signaling pathways was detected by Western blot. Iron overload also promoted chondrocyte apoptosis, a process that was reversed by CAR. In addition, CAR reduced NLRP3 inflammasome production via the SIRT1-MAPK pathway, and the SIRT1 inhibitor EX527 inhibited the treatment of OA by CAR.CAR inhibited cartilage degeneration induced by iron overload both in vivo and in vitro. Besides, our study showed that iron overload not only inhibited type II collagen expression but also induced MMP expression by catalyzing the generation of NLRP3 inflammasome. Our results suggest that CAR can treat KOA by promoting SIRT1 expression and inhibiting p38MAPK pathway expression to reduce the production of NLRP3 inflammasome vesicles.

DEAD-box helicase 54 regulates microglial inflammatory response in rats with chronic constriction injuries through NF-κB/NLRP3 signaling axis

Neuropathic pain (NP) is caused by damage to or disease of the somatosensory nervous system, but its mechanism is still not fully understood. In this study, DEAD-box helicase 54 (DDX54) was targeted, and its regulatory role was explored in a chronic constriction injury (CCI) rat model. Microglia and HMC3 cells were stimulated with LPS. The interaction between DDX54 and myeloid differentiation factor-88 adapter protein (MYD88) was verified. A CCI of sciatic nerve model in rats was established. Behavioral testing was performed before and after the CCI. The expressions of IL-1β, TNF-α, and IL-6 were upregulated, and those of DDX54, MYD88, NF-κB, and NOD-like receptor 3 (NLRP3) were upregulated in microglia and HMC3 cells after LPS induction. DDX54 knockdown in microglia and HMC3 cells inhibited IL-1β, TNF-α, and IL-6 expressions and downregulated the protein levels of MYD88, p-NF-κB p65 (p-p65), and NLRP3. DDX54 overexpression promoted the stability of MYD88 mRNA. DDX54 binds to the MYD88-3'-untranslated region (UTR). DDX54 interference in rats could alleviate the decrease of paw withdrawal mechanical threshold (PWMT) and paw withdrawal thermal latency (PWTL) induced by CCI, inhibit Iba1 expression, and reduce inflammatory factors as well as MYD88 and NF-κB expressions. DDX54 promotes the activation of NF-κB/NLRP3 signaling by regulating MYD88 mRNA stability, thereby affecting inflammatory response and NP progression in CCI rats.NEW & NOTEWORTHY The role of DDX54 protein in LPS-induced microglia and a chronic constriction injury (CCI) rat model was investigated for the first time. DDX54 interference can inhibit microglial activation and reduce the secretion of inflammatory factors. The interaction between DDX54 protein and MYD88 mRNA was explored for the first time. DDX54 promotes NF-κB/NLRP3 signaling activation by regulating MYD88 transcription in a CCI rat model.

Roles of pyroptosis in intervertebral disc degeneration

Intervertebral disc degeneration (IDD), the key pathological process in low back pain, is characterized by chronic inflammation and progressive cell death. Pyroptosis is a type of pro-inflammatory programmed necrosis mediated by inflammasomes that is dependent on the gasdermin family of proteins. An in-depth study of the pathological mechanisms of IDD has revealed that pyroptosis plays an important role in its occurrence and development. The molecular characteristics and activation signaling mechanisms of pyroptosis are reviewed in this paper. Moreover, the specific roles of pyroptosis in IDD pathology are outlined and various targeted drugs for its treatment are highlighted.

Targeting macrophagic PIM-1 alleviates osteoarthritis by inhibiting NLRP3 inflammasome activation via suppressing mitochondrial ROS/Cl- efflux signaling pathway

BACKGROUND

Osteoarthritis (OA), in which macrophage-driven synovitis is considered closely related to cartilage destruction and could occur at any stage, is an inflammatory arthritis. However, there are no effective targets to cure the progression of OA. The NOD-, LRR-,and pyrin domain-containing protein 3 (NLRP3) inflammasome in synovial macrophages participates in the pathological inflammatory process and treatment strategies targeting it are considered to be an effective approach for OA. PIM-1 kinase, as a downstream effector of many cytokine signaling pathways, plays a pro-inflammatory role in inflammatory disease.

METHODS

In this study, we evaluated the expression of the PIM-1 and the infiltration of synovial macrophages in the human OA synovium. The effects and mechanism of PIM-1 were investigated in mice and human macrophages stimulated by lipopolysaccharide (LPS) and different agonists such as nigericin, ATP, Monosodium urate (MSU), and Aluminum salt (Alum). The protective effects on chondrocytes were assessed by a modified co-culture system induced by macrophage condition medium (CM). The therapeutic effect in vivo was confirmed by the medial meniscus (DMM)-induced OA in mice.

RESULTS

The expression of PIM-1 was increased in the human OA synovium which was accompanied by the infiltration of synovial macrophages. In vitro experiments, suppression of PIM-1 by SMI-4a, a specific inhibitor, rapidly inhibited the NLRP3 inflammasome activation in mice and human macrophages and gasdermin-D (GSDME)-mediated pyroptosis. Furthermore, PIM-1 inhibition specifically blocked the apoptosis-associated speck-like protein containing a CARD (ASC) oligomerization in the assembly stage. Mechanistically, PIM-1 inhibition alleviated the mitochondrial reactive oxygen species (ROS)/chloride intracellular channel proteins (CLICs)-dependent Cl- efflux signaling pathway, which eventually resulted in the blockade of the ASC oligomerization and NLRP3 inflammasome activation. Furthermore, PIM-1 suppression showed chondroprotective effects in the modified co-culture system. Finally, SMI-4a significantly suppressed the expression of PIM-1 in the synovium and reduced the synovitis scores and the Osteoarthritis Research Society International (OARSI) score in the DMM-induced OA model.

CONCLUSIONS

Therefore, PIM-1 represented a new class of promising targets as a treatment of OA to target these mechanisms in macrophages and widened the road to therapeutic strategies for OA.

Du Huo Ji Sheng Tang inhibits Notch1 signaling and subsequent NLRP3 activation to alleviate cartilage degradation in KOA mice

BACKGROUND

Knee osteoarthritis (KOA) has a complex pathological mechanism and is difficult to cure. The traditional medicine Du Huo Ji Sheng Tang (DHJST) has been used for the treatment of KOA for more than one thousand years, but its mechanism for treating KOA has not been revealed. In our previous study, we confirmed that DHJST inhibited the activation of NLRP3 signaling in rats and humans. In the current study, we aimed to determine how DHJST inhibits NLRP3 to alleviate knee cartilage damage.

METHODS

Mice were injected with NLRP3 shRNA or Notch1-overexpressing adenovirus into the tail vein to construct systemic NLRP3 low-expressing or Notch1 high-expressing mice. Mice were injected with papain into the knee joint to replicate the KOA model. DHJST was used to treat KOA model mice with different backgrounds. The thickness of the right paw was measured to evaluate toe swelling. The pathohistological changes and the levels of IL-1β, MMP2, NLRP3, Notch1, collagen 2, collagen 4, HES1, HEY1, and Caspase3 were detected by HE staining, ELISA, immunohistochemical staining, western blotting, or real-time qPCR.

RESULTS

DHJST reduced tissue swelling and serum and knee cartilage IL-1β levels, inhibited cartilage MMP2 expression, increased collagen 2 and collagen 4 levels, decreased Notch1 and NLRP3 positive expression rates in cartilage, and decreased HES1 and HEY1 mRNA levels in KOA model mice. In addition, NLRP3 interference decreased cartilage MMP2 expression and increased collagen 2 and collagen 4 levels without affecting the expression levels of notch1, HES1 and HEY1 mRNA levels in the synovium of KOA mice. In KOA mice with NLRP interference, DHJST further reduced tissue swelling and knee cartilage damage in mice. Finally, Notch1-overexpressing mice not only showed more severe tissue swelling and knee cartilage degradation but also abolished the therapeutic effect of DHJST on KOA mice. Importantly, the inhibitory effects of DHJST on the mRNA expression of NLRP3, Caspase3 and IL-1β in the knee joint of KOA mice were completely limited after Notch1 overexpression.

CONCLUSION

DHJST significantly reduced inflammation and cartilage degradation in KOA mice by inhibiting Ntoch1 signaling and its subsequent NLRP3 activation in the knee joint.

Holomycin, a novel NLRP3 inhibitor, attenuates cartilage degeneration and inflammation in osteoarthritis

The contribution of the NLRP3 inflammasome in osteoarthritis (OA) pathogenesis has been uncovered in recent years. Holomycin (HL) has recently been identified as a novel NLRP3 inflammasome inhibitor. Herein, we aimed to explore the benefits of HL for OA. A chondrocyte-macrophage co-culture system and the destabilization of the medial meniscus (DMM) mouse model were established to study the effect of HL on OA in vitro and in vivo. ECM degradation-related proteins (MMP-13, aggrecan, and Collagen II) were detected by Western blot (WB) and immunohistochemistry (IHC). The chondrocyte senescence was determined by cell cycle, p16 and p21 expressions, and SA-β-Gal staining. The cartilage degeneration was evaluated by OARSI score and Safranin O and H&E staining. Inflammation and NLRP3 inflammasome activation were investigated via RT-PCR, ELISA, WB, and IHC. In vitro studies showed that IL-1β stimulation caused a significant increase of MMP13, p16, p21, and β-galactosidase expressions, a G1-phase arrest, and a down-regulation of aggrecan and Collagen II in chondrocytes, and the increased expressions of IL-6, CXCL-1, IL-1β, NLRP3, and Caspase 1 p20 in both chondrocyte and macrophage. Meanwhile, HL administration could partly reverse these effects induced by IL-1β. In DMM mouse models, intra-articular administration of HL alleviated cartilage degeneration and inflammation, as evidenced by the decrease of OARSI score and MMP13, p16, p21, Collagen II, IL-6, and CXCL-1 expressions and the restoration of chondrocyte number, proteoglycan, and MMP13 expression in cartilage tissues. This study identified HL as a promising agent for OA.

Monotropein attenuates apoptosis and pyroptosis in chondrocytes and alleviates osteoarthritis progression in mice

BACKGROUND

Osteoarthritis (OA) is a chronic degenerative joint disease characterized by loss of joint function, which seriously reduces the quality of life of the elderly and imposes a heavy socioeconomic burden worldwide. Monotropein (MON), the main active ingredient of Morinda officinalis F.C. How, has exhibited therapeutic effects in different disease models. However, its potential effects on chondrocytes in an arthritic model remain unclear. This study aimed to evaluate the effects of MON in chondrocytes and a mouse model of OA, and explore the potential mechanisms.

MATERIALS AND METHODS

Murine primary chondrocytes were pretreated with 10 ng/ml interleukin (IL)-1β for 24 h to establish an in vitro model of OA, and then treated with different concentrations of MON (0, 25, 50 and 100 μM) for 24 h. The proliferation of the chondrocytes was assayed using ethynyl-deoxyuridine (EdU) staining. Immunofluorescence staining, western blotting and TUNEL staining were performed to assess the effects of MON on cartilage matrix degradation, apoptosis and pyroptosis. The mouse model of OA was constructed by surgical destabilization of the medial meniscus (DMM), and the animals were randomly divided into the sham-operated, OA and OA + MON groups. Following OA induction, the mice were given intraarticular injection of 100 μM MON or equal volume of normal saline twice a week for 8 weeks. The effects of MON on cartilage matrix degradation, apoptosis and pyroptosis were assessed as indicated.

RESULTS

MON significantly accelerated the proliferation of chondrocytes, and inhibited cartilage matrix degradation, apoptosis and pyroptosis in the IL-1β-stimulated cells by blocking the nuclear factor-kappa B (NF-κB) signaling pathway. In the mouse model as well, MON treatment alleviated OA progression and promoted cartilage repair by inhibiting cartilage matrix degradation, and chondrocyte apoptosis and pyroptosis through the inactivation of the NF-κB signaling pathway. Furthermore, the MON-treated arthritic mice exhibited better articular tissue morphology and lower OARSI scores.

CONCLUSIONS

MON alleviated OA progression by inhibiting cartilage matrix degradation, and the apoptosis and pyroptosis of chondrocytes via NF-κB pathway inactivation, and is a promising alternative for the treatment of OA.

PPAR-γ Activation Alleviates Osteoarthritis through Both the Nrf2/NLRP3 and PGC-1α/Δψm Pathways by Inhibiting Pyroptosis

Osteoarthritis (OA) is a common degenerative joint disease with a gradually increasing morbidity in the aging and obese population. Emerging evidence has implicated pyroptosis in the etiology of OA and it may be recognized as a therapeutic target in OA. We have previously reported regarding another disease that peroxisome proliferator-activated receptor gamma (PPAR-γ) activation exerts an anti-inflammatory effect by suppressing the nucleotide-binding and oligomerization domain-like receptor containing protein (NLRP) 3 inflammasome. However, the relationship between PPAR-γ and NLRP3-mediated pyroptosis in OA cartilage and its underlying mechanisms is fully unclear. In this study, we found that the level of NLRP3-mediated pyroptosis in severe lateral femoral condyle cartilage wear in the knee of an OA patient was significantly higher than that in the mild lateral femoral condyle cartilage wear areas. Moreover, in lipopolysaccharide (LPS)/adenosine triphosphate (ATP)-induced primary chondrocytes and knee OA rat models, we demonstrated that activation of PPAR-γ by pioglitazone (Piog) attenuated LPS/ATP-induced chondrocyte pyroptosis and arthritis. These effects were partially counteracted by either blocking the nuclear factor erythroid-2-related factor (Nrf2)/NLRP3 or PGC1-α/Δψm signaling pathway. Simultaneous depression of these two signaling pathways can completely abrogate the protective effects of Piog on OA and chondrocytes. Taken together, Piog protects OA cartilage against pyroptosis-induced damage by simultaneously activating both the Nrf2/NLRP3 and PGC-1α/Δψm pathways, which enhances antioxidative and anti-inflammatory responses as well as mitochondrial biogenesis. Therefore, Piog may be a promising agent for human OA cartilage damage in future clinical treatments.

Achyranthoside D attenuates chondrocyte loss and inflammation in osteoarthritis via targeted regulation of Wnt3a

BACKGROUND

Achyranthes bidentata Blume (A. bidentata) is a common Chinese herb used to treat osteoarthritis (OA). Achyranthoside D (Ach-D) is a glucuronide saponin isolated from A. bidentata.

PURPOSE

To assess the mechanisms of action of Ach-D and its effects on OA.

METHODS

The effects of Ach-D were evaluated in rats underwent anterior cruciate ligament transection (ACLT) with medial meniscectomy (MMx) and in interleukin (IL)-1β-induced chondrocytes. Histological changes in rat cartilage tissues were detected using Safranin O-Fast green and haematoxylin-eosin staining. Immunohistochemical staining, qRT-PCR, ELISA, immunoblotting, and immunofluorescence were conducted to examine cartilage degeneration-related and inflammation-related factor expression. CCK-8, LDH assay, and EdU staining were performed to detect chondrocyte death.

RESULTS

Ach-D dose-dependently reduced the Osteoarthritis Research Society International (OARSI) scores, alleviated cartilage injury, and decreased the serum concentrations of CTX-II and COMP in ACLT-MMx models. Ach-D increased the expression levels of collagen II and aggrecan and decreased the levels of cartilage degeneration-related proteins, ADAMTS-5, MMP13, and MMP3, in rat cartilage tissues. Additionally, nod-like receptor protein 3 (NLRP3)-related inflammation was reduced by Ach-D, as shown by the significantly inhibited expression levels of NLRP3, ASC, GSDMD, IL-6, TNF-α, IL-1β, and IL-18 in rat cartilage tissues. In primary rat chondrocytes, Ach-D protected against IL-1β-induced viability loss and LDH release. Wnt3a is the target protein of Ach-D. Mechanistically, Ach-D alleviated OA by inhibiting Wnt signalling.

CONCLUSION

ACH-D may reduce inflammation and cartilage degeneration by inhibiting the Wnt signalling pathway, thereby reducing OA.

Emerging role of mesenchymal stem/stromal cells (MSCs) and MSCs-derived exosomes in bone- and joint-associated musculoskeletal disorders: a new frontier

Exosomes are membranous vesicles with a 30 to 150 nm diameter secreted by mesenchymal stem/stromal cells (MSCs) and other cells, such as immune cells and cancer cells. Exosomes convey proteins, bioactive lipids, and genetic components to recipient cells, such as microRNAs (miRNAs). Consequently, they have been implicated in regulating intercellular communication mediators under physiological and pathological circumstances. Exosomes therapy as a cell-free approach bypasses many concerns regarding the therapeutic application of stem/stromal cells, including undesirable proliferation, heterogeneity, and immunogenic effects. Indeed, exosomes have become a promising strategy to treat human diseases, particularly bone- and joint-associated musculoskeletal disorders, because of their characteristics, such as potentiated stability in circulation, biocompatibility, low immunogenicity, and toxicity. In this light, a diversity of studies have indicated that inhibiting inflammation, inducing angiogenesis, provoking osteoblast and chondrocyte proliferation and migration, and negative regulation of matrix-degrading enzymes result in bone and cartilage recovery upon administration of MSCs-derived exosomes. Notwithstanding, insufficient quantity of isolated exosomes, lack of reliable potency test, and exosomes heterogeneity hurdle their application in clinics. Herein, we will deliver an outline respecting the advantages of MSCs-derived exosomes-based therapy in common bone- and joint-associated musculoskeletal disorders. Moreover, we will have a glimpse the underlying mechanism behind the MSCs-elicited therapeutic merits in these conditions.

A novel sorbicillinoid compound as a potent anti-inflammation agent through inducing NLRP3 protein degradation

BACKGROUND AND PURPOSE

Chronic inflammation is pathogenic and contributes to human diseases, causing a significant threat to public health. The NLR family pyrin domain-containing protein 3 (NLRP3) is the best-characterized factor regulating inflammation. Therefore, targeting NLRP3 has the potential to treat inflammatory diseases and improve human health.

EXPERIMENTAL APPROACH

Lipopolysaccharide was used to induce inflammation in cell cultures. Lipopolysaccharide/d-galactosamine and dextran sulfate sodium salt were used to induce acute liver inflammation and ulcerative colitis respectively in C57BL/6J mice. Western blotting, immunofluorescence, immunoprecipitation, quantitative PCR and enzyme-linked immunosorbent assay (ELISA) were used to evaluate the activation of the inflammatory response in cell cultures and in mice.

KEY RESULTS

JNUTS013, a novel sorbicillinoid compound recently synthesized by us, significantly inhibited inflammation both in cell cultures and in mouse models. Mechanistically, JNUTS013 induced proteasome-dependent degradation of NLRP3. Hence, it suppressed the formation of the NLRP3 inflammasome and the production of downstream inflammatory cytokines and chemokines. The inhibitory effect of JNUTS013 on NLRP3 protein expression was confirmed in mice. Importantly, JNUTS013 failed to ameliorate bowel inflammation in Nlrp3^-/- knockout mice, supporting NLRP3 as the biological target by which JNUTS013 inhibits inflammation. Further studies revealed critical chemical moieties of JNUTS013 required for inducing NLRP3 degradation.

CONCLUSION AND IMPLICATIONS

This study identifies a novel compound JNUTS013 that inhibits inflammation through inducing NLRP3 protein degradation in vitro and in vivo, which not only supports the development of JNUTS013 as an anti-inflammation agent but also creates a new way for the treatment of inflammation by chemically inducing NLRP3 degradation.

Pyroptosis and degenerative diseases of the elderly

Pyroptosis is a recently described mechanism of programmed cell death mediated by proteins of the gasdermin family. Widely recognized signaling cascades include the classical, non-classical, caspase-3-dependent gasdermin E and caspase-8-dependent gasdermin D pathways. Additional pyroptotic pathways have been subsequently reported. With the rising prevalence of advanced age, the role of pyroptosis in the degenerative diseases of the elderly has attracted increased research attention. This article reviews the primary mechanisms of pyroptosis and summarizes progress in the research of degenerative diseases of the elderly such as presbycusis, age-related macular degeneration, Alzheimer's disease, intervertebral disc degeneration, and osteoarthritis.

Deficiency of immune-responsive gene 1 exacerbates interleukin-1beta-elicited the inflammatory response of chondrocytes via enhancing the activation of NLRP3 inflammasome

Immune-responsive gene 1 (IRG1) is a multifunctional protein that mediates inflammatory responses in numerous pathological conditions. However, whether IRG1 has a relevance with osteoarthritis remains unaddressed. The inflammatory response of chondrocytes contributes to the progression of osteoarthritis. This study focused on assessing the functional link between IRG1 and interleukin-1beta (IL-1β)-elicited the inflammatory response of chondrocytes. The expression levels of IRG1 increased markedly in osteoarthritis cartilage compared to normal healthy cartilage. IRG1 level also increased after IL-1β stimulation in chondrocytes. The knockdown of IRG1 exacerbated IL-1β-elicited apoptosis and degradation of the extracellular matrix in chondrocytes. The nucleotide-binding oligomerization domain-like receptor 3 (NLRP3) inflammasome activation evoked by IL-1β stimulation was enhanced in IRG1-deficient chondrocytes. Importantly, restraint of the NLRP3 inflammasome was able to diminish IRG1-deficiency-amplified effects on IL-1β-stimulated chondrocytes. Additionally, the supplement of itaconate could ameliorate IL-1β-induced the inflammatory response of chondrocytes and reverse any IRG1-deficiency-induced effects. Altogether, our findings document a vital role for IRG1/itaconate in settling the inflammatory response of chondrocytes via effects on the NLRP3 inflammasome.

Exosomal miR-93-5p regulated the progression of osteoarthritis by targeting ADAMTS9

Osteoarthritis (OA) is a type of common degenerative joint disorder, in which adipose mesenchymal stem cells (ADSCs) and the secreted exosomes play an important role. The purpose of this study was to investigate the role and mechanism of exosomes derived from ADSCs (ADSC-exos) in OA. The gradient of IL-1β concentration was designed to construct the articular chondrocyte model of arthritic mice. The expression of miR-93-5p and ADAMTS9 in articular chondrocytes was detected by reverse transcription quantitative polymerase chain reaction. Dual luciferase reporter gene assay was performed to verify the interaction between them. Monodansylcadaverine staining was used to visualize the autophagosome formation and cell apoptosis was analyzed by flow cytometry. ADSC-exos were authenticated by transmission electron microscope and western blot assay. miR-93-5p was found to be downregulated in IL-1β-treated articular chondrocytes compared with OA cartilage while ADAMTS9 was upregulated, which was identified as a direct target gene of miR-93-5p. Silencing of ADAMTS9 attenuated the effects of miR-93-5p. Exosomal miR-93-5p can reduce the release of inflammatory factors in mouse arthritis cell models. This study first described the mechanism under that ADSC-exos inhibited inflammation and alleviated OA through the innovative targets miR-93-5p/ADAMTS9 signal axis. This provided a new method for the treatment of OA.

Attenuation of experimental osteoarthritis with human adipose-derived mesenchymal stem cell therapy: inhibition of the pyroptosis in chondrocytes

AIM

To explore the role and mechanism of human adipose-derived mesenchymal stem cells (hAD-MSCs) in the treatment of osteoarthritis (OA).

METHODS

OA hulth model of Sprague Dawley (SD) rats and 20 ng/ml TNF-α treated chondrocytes were used as models of OA in vivo and in vitro, respectively. hAD-MSCs were administrated in the articular cavity by injection in vivo and co-cultured with chondrocytes using transwell in vitro. Haematoxylin and eosin staining and Safranin-O/Fast green staining were performed to detect tissue destruction and histopathology. Scanning electron microscopy and transmission electron microscopy were used to observe the ultrastructure of chondrocytes. The pyroptosis signaling pathway-related proteins were detected by immunohistochemistry, immunofluorescence, qRT-PCR and Western blot. And small interference technology was used to study the mechanism in depth.

RESULTS

hAD-MSCs could delay the development of rat OA, improve the pathological changes of joints, inhibit the expression of NLRP3, Caspase1, GSDMD and TNFR1. In vitro, the expression of pyroptosis signal proteins in chondrocytes was significantly elevated when stimulated with TNF-α, the level of inflammatory factors such as IL-1β, IL-18 was increased, and the cell morphology was significantly destroyed. While co-cultured with hAD-MSCs, these syndromes were reversed. Knockout of TNFR1 also returned the upregulation of pyroptosis signals which caused by TNF-α.

CONCLUSION

These results demonstrated that hAD-MSCs could inhibit pyroptosis signaling pathway of chondrocytes induced by TNF-α, which have raised our understanding of the role of hAD-MSCs as promising therapy for the management of OA.

Targeting inflammasome-dependent mechanisms as an emerging pharmacological approach for osteoarthritis therapy

Arthritic diseases have attracted enormous scientific interest because of increased worldwide prevalence and represent a significant socioeconomic burden. Osteoarthritis (OA) is the most prevalent form of arthritis. It is a disorder of the diarthrodial joints, characterized by degeneration and loss of articular cartilage associated with adjacent subchondral bone changes. Chronic and unresolving inflammation has been identified as a critical factor driving joint degeneration and pain in OA. Despite numerous attempts at therapeutic intervention, no effective disease-modifying agents targeting OA inflammation are available to the patients. Inflammasomes are protein complexes known to play a critical role in the inflammatory pathology of several diseases, and their roles in OA pathogenesis have become evident over the last decade. In this sense, it is relevant to evaluate the vital role of inflammasomes as potential modulators of pathogenic features in OA. This review will provide an overview and perspectives on why understanding inflammasome activation is critical for identifying effective OA therapies. We elaborate on the contribution of extracellular mediators from the circulatory system and synovial fluid as well as intracellular activators within the synovial fibroblasts and articular chondrocytes toward invoking the inflammasome in OA. We further discuss the merits of emerging inflammasome targeting therapies and speculate on the potential strategies for inflammasome blockade for OA therapy.

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.

Leptin-depended NLRP3 inflammasome activation in osteoarthritic chondrocytes is mediated by ROS

Leptin and ROS are implicated in the regulation of inflammatory pathways including NLRP3-inflammasome. We investigated the functional link between leptin, ROS and NLRP3-inflammasome formation/activation in osteoarthritis (OA), an age-related disease. We found that inflammasome components' (NLRP3, ASC, Caspase-1 and cleaved Caspase-1) protein expression were increased in OA cartilage biopsies and chondrocytes compared to healthy cartilage and chondrocytes. Immunofluorescence showed increased co-localization of NLRP3/ASC and NLRP3/Caspase-1, ASC-specks formation and ROS levels in OA compared to normal chondrocytes. NOX4 mRNA expression and IL-1β/IL-18 secretion levels were also elevated in OA chondrocytes. Furthermore, NLRP3-siRNA in OA chondrocytes revealed significant MMP-9/MMP-13 downregulation. To elucidate leptin/ROS/NLRP3-inflammasome interactions, OA chondrocytes were treated with ROS-inhibitor NAC, NOXs-inhibitor DPI, NOX4-inhibitor GLX351322 and leptin-siRNA, while normal chondrocytes were incubated with leptin with or without DPI or GLX351322. We observed attenuated ROS levels and NLRP3-inflammasome formation/activation in NAC-, DPI- or GLX351322-treated OA chondrocytes, while the same effect was shown after transfection with leptin-siRNA. Furthermore, incubation of normal chondrocytes with leptin enhanced ROS production and inflammasome formation/activation, while pretreatment with DPI or GLX351322 abolished leptin's stimulatory effects confirming leptin-NOX4-ROS-inflammasome regulatory axis. Overall, our findings provide novel evidence indicating that leptin-induced NLRP3-inflammasome formation/activation in OA chondrocytes is mediated by NOX4-dependent ROS production.

Senkyunolide A inhibits the progression of osteoarthritis by inhibiting the NLRP3 signalling pathway

CONTEXT

Osteoarthritis (OA) is a degenerative disease. Senkyunolide A (SenA) is an important phthalide from Ligusticum chuanxiong Hort (Umbelliferae) with anti-spasmodic and neuroprotective effects.

OBJECTIVE

We explored the effect of SenA on IL-1β-stimulated chondrocytes and OA mice.

MATERIALS AND METHODS

Chondrocytes were stimulated by IL-1β (10 ng/mL) to establish an OA model in vitro. Cells were treated with SenA (20, 40, 80 and 160 μg/mL) for 48 h. The in vivo OA model was established by cutting off the medial meniscus tibial ligament (MMTL) at right knee incision of male C57BL/6 mice. One week after surgery, mice were injected with SenA (intraperitoneally one week) and divided into four groups (n = 6 per group): Sham, OA, OA + SenA 20 mg/kg and OA + SenA 40 mg/kg. The OA progression was examined by haematoxylin and eosin (H&E) staining.

RESULTS

SenA treatment increased cell viability (33%), proliferation (71%), inhibited apoptosis (21%), decreased levels of catabolic marker proteins (MMP13, 23%; ADAMTS4, 31%; ADAMTS5, 19%), increased levels of anabolic marker proteins (IGF-1, 57%; aggrecan, 75%; Col2a1, 48%), reduced levels of inflammation cytokines (TNF-α, 31%; IL-6, 19%; IL-18, 20%) and decreased levels of NLRP3 (21%), ASC (20%) and caspase-1 (29%) of chondrocytes. However, NLRP3 agonist nigericin increased levels of MMP13 (55%), ADAMTS4 (70%), ADAMTS5 (53%), decreased levels of IGF-1 (36%), aggrecan (26%), Col2a1 (25%), inhibited proliferation (61%) and promoted apoptosis (76%).

DISCUSSION AND CONCLUSIONS

SenA alleviates OA progression by inhibiting NLRP3 signalling pathways. These findings provide an experimental basis for the clinical application of drugs in the treatment of OA.

Targeting NLRP3 Inflammasome Alleviates Synovitis by Reducing Pyroptosis in Rats with Experimental Temporomandibular Joint Osteoarthritis

The mechanism of temporomandibular joint osteoarthritis (TMJOA), which leads to the final erosion of cartilage and subchondral bone, has been widely demonstrated, but still not clearly elucidated. Many studies have pointed that NLRP3-mediated inflammation played a vital role in degenerative diseases. However, its interaction with synovitis of TMJOA has remained poorly investigated. In our study, we explored the role of NLRP3 inflammasome in TMJOA synovitis and the therapeutic potential of caspase-1 and NLRP3 inhibitors. By establishing a rat TMJOA model, we found that NLRP3 was upregulated in synovial tissue of TMJOA. It was involved in the progress of a programmed cell death called pyroptosis, which was caspase-1 dependent and ultimately triggered inflammatory mediator interleukin IL-1β release. Treatment with Ac-YVAD-cmk and MCC950, inhibitors targeting caspase-1 and NLRP3, respectively, significantly suppressed pyroptosis in TMJOA synovial tissue. Then, a macrophage- and fibroblast-like synoviocyte (FLS) cocultured model further verified the above results. Macrophage somehow promoted FLS pyroptosis in this study. Our results suggested that the NLRP3 inflammasome-mediated pyroptosis participated in synovial inflammation of TMJOA. Interfering with the progress could be a potential option for controlling TMJOA development.

α-Chaconine Facilitates Chondrocyte Pyroptosis and Nerve Ingrowth to Aggravate Osteoarthritis Progression by Activating NF-κB Signaling

BACKGROUND

With the rapid growth of the elderly population, the incidence of osteoarthritis (OA) increases annually, which has attracted extensive attention in public health. The roles of dietary intake in controlling joint disorders are perhaps one of the most frequently posed questions by OA patients, while the information about the interaction between dietary intake and OA based on scientific research is limited. α-Chaconine is the richest glycoalkaloid in eggplants such as potatoes. Previous evidence suggests that α-Chaconine is a toxic compound to nervous and digestive systems with potentially severe and fatal consequences for humans and farm animals, but its effect on OA development remains obscure.

OBJECTIVE

To determine whether α-Chaconine deteriorates OA progression through sensory innervation and chondrocyte pyroptosis via regulating nuclear factor-κB (NF-κB) signaling, providing evidence for a possible linkage between α-Chaconine and OA progression.

METHODS

We established a mouse OA model by destabilization of medial meniscus (DMM) surgery and then intra-articular injection of 20 or 100 μM α-Chaconine into the OA mice for 8 and 12 weeks. The severity of OA progression was evaluated by histological staining and radiographic analyses. The expressions of matrix metabolic indicators, Col2, Mmp3, and Mmp13, as well as pyroptosis-related proteins, Nlrp3, Caspase-1, Gsdmd, IL-1β, IL-18, were determined by immunohistochemistry. And the changes in sensory nerve ingrowth and activity of NF-κB signaling were determined by immunofluorescence.

RESULTS

We found that α-Chaconine could exacerbate mouse OA progression, resulting in subchondral sclerosis, osteophyte formation, and higher OARSI scores. Specifically, α-Chaconine could augment cartilage matrix degradation and induce chondrocyte pyroptosis and nerve ingrowth. Mechanistical analysis revealed that α-Chaconine stimulated NF-κB signaling by promoting I-κB α phosphorylation and p65 nuclear translocation.

CONCLUSION

Collectively, our findings raise the possibility that α-Chaconine intake can boost chondrocyte pyroptosis and nerve ingrowth to potentiate OA progression by activating NF-κB signaling.