Risk factor prediction and immune correlation analysis of cuproptosis-related gene in osteoarthritis.

Osteoarthritis (OA) is a widespread inflammatory joint disease with significant global disability burden. Cuproptosis, a newly identified mode of cell death, has emerged as a crucial factor in various pathological conditions, including OA. In this context, our study aims to investigate the intrinsic relationship between cuproptosis-related genes (CRGs) and OA, and assess their potential as biomarkers for OA diagnosis and treatment. Datasets from the GEO databases were analysed the differential expression of CRGs, leading to the identification of 10 key CRGs (CDKN2A, DLD, FDX1, GLS, LIAS, LIPT1, MTF1, PDHA1, DLAT and PDHB). A logistic regression analysis and calibration curves were used to show excellent diagnostic accuracy. Consensus clustering revealed two CRG patterns, with Cluster 1 indicating a closer association with OA progression. RT-PCR confirmed a significant increase in the expression levels of these nine key genes in IL-1ß-induced C28/i2 cells, and the expression of CDKN2A and FDX1 were also elevated in conditioned monocytes, while the expression of GLS and MTF1 were significantly decreased. In vitro experiments demonstrated that the expression levels of these 7/10 CRGs were significantly increased in chondrocytes induced by IL-1ß, and upon stimulation with cuproptosis inducers, chondrocyte apoptosis was exacerbated, accompanied by an increase in the expression of cuproptosis-related proteins. These further substantiated our research findings and indicated that the nine selected cuproptosis genes have high potential for application in the diagnosis of OA.

MiR-539-3p Alleviates Apoptosis and Extracellular Matrix Degradation in Chondrocytes of Childhood-Onset Osteoarthritis by Targeting RUNX2.

Recent research has identified that miR-539-3p impedes chondrogenic differentiation, yet its specific role and underlying mechanisms in childhood-onset osteoarthritis (OA) remain unclear. This study found that miR-539-3p levels were considerably lower in cartilage samples derived from childhood-onset OA patients compared to the control group. Enhancing miR-539-3p expression or suppressing RUNX2 expression notably reduced apoptosis, inflammation, and extracellular matrix (ECM) degradation in OA chondrocytes. In contrast, reducing miR-539-3p or increasing RUNX2 had the opposite effects. RUNX2 was confirmed as a direct target of miR-539-3p. Further experiments demonstrated that miR-539-3p targeting RUNX2 effectively lessened apoptosis, inflammation, and ECM degradation in OA chondrocytes, accompanied by changes in key molecular markers like reduced caspase-3 and matrix etallopeptidase 13 (MMP-13) levels, and increased B-cell lymphoma 2 (Bcl-2) and collagen type X alpha 1 chain (COL2A1). This study underscores the pivotal role of miR-539-3p in alleviating inflammation and ECM degradation in childhood-onset OA through targeting RUNX2, offering new insights for potential therapeutic strategies against this disease.

Circadian rhythm disruption upregulating Per1 in mandibular condylar chondrocytes mediating temporomandibular joint osteoarthritis via GSK3ß/ß-CATENIN pathway.

BACKGROUND: Temporomandibular joint osteoarthritis (TMJOA) has a high incidence rate, but its pathogenesis remains unclear. Circadian rhythm is an important oscillation in the human body and influences various biological activities. However, it is still unclear whether circadian rhythm affects the onset and development of TMJOA. METHODS: We disrupted the normal rhythm of rats and examined the expression of core clock genes in the mandibular condylar cartilage of the jaw and histological changes in condyles. After isolating rat mandibular condylar chondrocytes, we upregulated or downregulated the clock gene Per1, examined the expression of cartilage matrix-degrading enzymes, tested the activation of the GSK3ß/ß-CATENIN pathway and verified it using agonists and inhibitors. Finally, after downregulating the expression of Per1 in the mandibular condylar cartilage of rats with jet lag, we examined the expression of cartilage matrix-degrading enzymes and histological changes in condyles. RESULTS: Jet lag led to TMJOA-like lesions in the rat mandibular condyles, and the expression of the clock gene Per1 and cartilage matrix-degrading enzymes increased in the condylar cartilage of rats. When Per1 was downregulated or upregulated in mandibular condylar chondrocytes, the GSK3ß/ß-CATENIN pathway was inhibited or activated, and the expression of cartilage matrix-degrading enzymes decreased or increased, which can be rescued by activator and inhibitor of the GSK3ß/ß-CATENIN pathway. Moreover, after down-regulation of Per1 in mandibular condylar cartilage in vivo, significant alleviation of cartilage degradation, cartilage loss, subchondral bone loss induced by jet lag, and inhibition of the GSK3ß/ß-CATENIN signaling pathway were observed. Circadian rhythm disruption can lead to TMJOA. The clock gene Per1 can promote the occurrence of TMJOA by activating the GSK3ß/ß-CATENIN pathway and promoting the expression of cartilage matrix-degrading enzymes. The clock gene Per1 is a target for the prevention and treatment of TMJOA.

Non-coding RNAs as regulators of autophagy in chondrocytes: Mechanisms and implications for osteoarthritis.

Osteoarthritis (OA) is a chronic degenerative joint disease with multiple causative factors such as aging, mechanical injury, and obesity. Autophagy is a complex dynamic process that is involved in the degradation and modification of intracellular proteins and organelles under different pathophysiological conditions. Autophagy, as a cell survival mechanism under various stress conditions, plays a key role in regulating chondrocyte life cycle metabolism and cellular homeostasis. Non-coding RNAs (ncRNAs) are heterogeneous transcripts that do not possess protein-coding functions, but they can act as effective post-transcriptional and epigenetic regulators of gene and protein expression, thus participating in numerous fundamental biological processes. Increasing evidence suggests that ncRNAs, autophagy, and their crosstalk play crucial roles in OA pathogenesis. Therefore, we summarized the complex role of autophagy in OA chondrocytes and focused on the regulatory role of ncRNAs in OA-associated autophagy to elucidate the complex pathological mechanisms of the ncRNA-autophagy network in the development of OA, thus providing new research targets for the clinical diagnosis and treatment of OA.

Protective effect of clusterin against interleukin-1ß-induced apoptosis and inflammation in human knee osteoarthritis chondrocytes.

Chondrocyte apoptosis is recognized as one of the pathological features involved in cartilage degeneration driving the onset and progression of knee osteoarthritis (OA). This study aimed to determine the molecular mechanism underlying the effect of clusterin (CLU), anti-apoptotic molecule, in human knee OA chondrocytes. Primary knee OA chondrocytes were isolated from the cartilage of knee OA patients and divided into five groups: (1) the cells treated with interleukin (IL)-1ß, (2) CLU alone, (3) a combination of IL-1ß and CLU, (4) LY294002 (PI3K inhibitor) along with IL-1ß and CLU, and (5) the untreated cells. Production of apoptotic, inflammatory, anabolic, and catabolic mediators in knee OA chondrocytes was determined after treatment for 24 h. Our in vitro study uncovered that CLU significantly suppressed the production of inflammatory mediators [nitric oxide (NO), IL6, and tumor necrosis factor (TNF)-α] and apoptotic molecule (caspase-3, CASP3). CLU significantly upregulated messenger ribonucleic acid (mRNA) expressions of anabolic factors [SRY-box transcription factor-9 (SOX9) and aggrecan (ACAN)], but significantly downregulated mRNA expressions of IL6, nuclear factor kappa-B (NF-κB), CASP3, and matrix metalloproteinase-13 (MMP13). Anti-apoptotic and anti-inflammatory effects of CLU were mediated through activating PI3K/Akt signaling pathway. The findings suggest that CLU might have beneficial effects on knee OA chondrocytes by exerting anti-apoptotic and anti-inflammatory functions via PI3K/Akt pathway, making CLU a promising target for potential therapeutic interventions in knee OA.

IRF1 regulation of ZBP1 links mitochondrial DNA and chondrocyte damage in osteoarthritis.

BACKGROUND: Z-DNA binding protein 1 (ZBP1) is a nucleic acid sensor that is involved in multiple inflammatory diseases, but whether and how it contributes to osteoarthritis (OA) are unclear. METHODS: Cartilage tissues were harvested from patients with OA and a murine model of OA to evaluate ZBP1 expression. Subsequently, the functional role and mechanism of ZBP1 were examined in primary chondrocytes, and the role of ZBP1 in OA was explored in mouse models. RESULTS: We showed the upregulation of ZBP1 in articular cartilage originating from OA patients and mice with OA after destabilization of the medial meniscus (DMM) surgery. Specifically, knockdown of ZBP1 alleviated chondrocyte damage and protected mice from DMM-induced OA. Mechanistically, tumor necrosis factor alpha induced ZBP1 overexpression in an interferon regulatory factor 1 (IRF1)-dependent manner and elicited the activation of ZBP1 via mitochondrial DNA (mtDNA) release and ZBP1 binding. The upregulated and activated ZBP1 could interact with receptor-interacting protein kinase 1 and activate the transforming growth factor-beta-activated kinase 1-NF-κB signaling pathway, which led to chondrocyte inflammation and extracellular matrix degradation. Moreover, inhibition of the mtDNA-IRF1-ZBP1 axis with Cyclosporine A, a blocker of mtDNA release, could delay the progression of DMM-induced OA. CONCLUSIONS: Our data revealed the pathological role of the mtDNA-IRF1-ZBP1 axis in OA chondrocytes, suggesting that inhibition of this axis could be a viable therapeutic approach for OA.

Silencing of CircTRIM25/miR-138-5p/CREB1 axis promotes chondrogenesis in osteoarthritis.

BACKGROUND: Dysregulated circular RNAs (circRNAs) are involved in osteoarthritis (OA) progression. OBJECTIVE: We aimed to explore the effect of hsa_circ_0044719 (circTRIM25) on the ferroptosis of chondrocytes. METHODS: Chondrocytes were treated with interleukin (IL)-1ß to generate cell model. Cellular behaviours were measured using cell counting kit-8, enzyme-linked immunosorbent assay, relevant kits, propidium iodide staining, and immunofluorescence assay. Quantitative real-time polymerase chain reaction was performed to examine the expression of circTRIM25, miR-138-5p, and cAMP responsive element binding protein 1 (CREB1), and their interactions were assessed using luciferase reporter analysis and RNA pull-down assay. RESULTS: CircTRIM25 was upregulated in OA tissues and IL-1ß-stimulated chondrocytes. Knockdown of circTRIM25 facilitated the viability and suppressed ferroptosis and inflammation of IL-1ß-induced cells. CircTRIM25 served as a sponge of miR-138-5p, which directly targets CREB1. Downregulation of miR-138-5p abrogated the effect induced by knockdown of circTRIM25. Furthermore, enforced CREB1 reversed the miR-138-5p induced effect. Moreover, knockdown of circTRIM25 attenuated cartilage injury in vivo. CONCLUSION: Silencing of circTRIM25 inhibited ferroptosis of chondrocytes via the miR-138-5p/CREB axis and thus attenuated OA progression.

PDZK1 protects against mechanical overload-induced chondrocyte senescence and osteoarthritis by targeting mitochondrial function.

Mechanical overloading and aging are two essential factors for osteoarthritis (OA) development. Mitochondria have been identified as a mechano-transducer situated between extracellular mechanical signals and chondrocyte biology, but their roles and the associated mechanisms in mechanical stress-associated chondrocyte senescence and OA have not been elucidated. Herein, we found that PDZ domain containing 1 (PDZK1), one of the PDZ proteins, which belongs to the Na+/H+ Exchanger (NHE) regulatory factor family, is a key factor in biomechanically induced mitochondrial dysfunction and chondrocyte senescence during OA progression. PDZK1 is reduced by mechanical overload, and is diminished in the articular cartilage of OA patients, aged mice and OA mice. Pdzk1 knockout in chondrocytes exacerbates mechanical overload-induced cartilage degeneration, whereas intraarticular injection of adeno-associated virus-expressing PDZK1 had a therapeutic effect. Moreover, PDZK1 loss impaired chondrocyte mitochondrial function with accumulated damaged mitochondria, decreased mitochondrion DNA (mtDNA) content and increased reactive oxygen species (ROS) production. PDZK1 supplementation or mitoubiquinone (MitoQ) application alleviated chondrocyte senescence and cartilage degeneration and significantly protected chondrocyte mitochondrial functions. MRNA sequencing in articular cartilage from Pdzk1 knockout mice and controls showed that PDZK1 deficiency in chondrocytes interfered with mitochondrial function through inhibiting Hmgcs2 by increasing its ubiquitination. Our results suggested that PDZK1 deficiency plays a crucial role in mediating excessive mechanical load-induced chondrocyte senescence and is associated with mitochondrial dysfunction. PDZK1 overexpression or preservation of mitochondrial functions by MitoQ might present a new therapeutic approach for mechanical overload-induced OA.

Biallelic variants in SLC26A2 cause multiple epiphyseal dysplasia-4 by disturbing chondrocyte homeostasis.

BACKGROUND: Multiple epiphyseal dysplasia-4 (MED-4, MIM 226900) is a rare autosomal recessive disease characterized by disproportionate height and early onset osteoarthritis of the lower limbs. MED-4 is caused by homozygous or compound heterozygous pathogenic variants in the SLC26A2 gene. However, the underlying pathogenic mechanisms in chondrocytes remains unknown. This study aimed to identify the pathogenic variants within a MED-4 family and explore the molecular etiology of this condition in human primary chondrocyte cells. METHODS: Clinical data were recorded and peripheral blood samples were collected for analysis. Whole exome sequencing (WES) and bioinformatic analyses were performed to determine causative variants. Wild-type SLC26A2 and corresponding mutant expression plasmids were constructed and transfected into human primary chondrocytes. The expression and subcellular distribution of SLC26A2 protein in chondrocytes were detected by immunoblotting and immunofluorescence. Effects of these variants on chondrocytes viability and apoptosis were measured by Cell Counting Kit-8 (CCK-8) assay. Expression of genes related to cartilage homeostasis was subsequently analyzed by quantitative real-time polymerase chain reaction (qRT-PCR). RESULTS: We identified two compound heterozygous variants c.1020_1022delTGT(p.Val341del) and c.1262 T > C(p.Ile421Thr) in the SLC26A2 gene in the patients. Mutant SLC26A2Val341del and SLC26A2Ile421Thr proteins were distributed in relatively few cells and were observed only within the nucleus. The viability of chondrocytes with the SLC26A2 variant group was similar to the wild-type (WT) group. However, the protein expressions of SLC26A2Val341del and SLC26A2Ile421Thr were decreased compared with SLC26A2WT. Expression levels of matrix metallopeptidase 13 (MMP13), α-1 chain of type X collagen (COL10A1), and Runt-related transcription factor 2 (RUNX2) were significantly decreased in the variant group. However, aggrecan (ACAN) expression was higher in the variant group than the WT group. CONCLUSIONS: Overall, our data demonstrate that the variants p.Val341del and p.Ile421Thr in SLC26A2 cause MED-4 and that these two variants promote chondrocyte proliferation while inhibiting chondrocyte differentiation.

Analysis of the Actions of RARγ Agonists on Growing Osteochondromas in a Mouse Model.

The actions of the retinoic acid nuclear receptor gamma (RARγ) agonist, palovarotene, on pre-existing osteochondromas were investigated using a mouse multiple osteochondroma model. This approach was based on the knowledge that patients often present to the clinic after realizing the existence of osteochondroma masses, and the findings from preclinical investigations are the effects of drugs on the initial formation of osteochondromas. Systemic administration of palovarotene, with increased doses (from 1.76 to 4.0 mg/kg) over time, fully inhibited tumor growth, keeping the tumor size (0.31 ± 0.049 mm3) similar to the initial size (0.27 ± 0.031 mm3, p = 0.66) while the control group tumor grew (1.03 ± 0.23 mm3, p = 0.023 to the drug-treated group). Nanoparticle (NP)-based local delivery of the RARγ agonist also inhibited the growth of osteochondromas at an early stage (Control: 0.52 ± 0.11 mm3; NP: 0.26 ± 0.10, p = 0.008). Transcriptome analysis revealed that the osteoarthritis pathway was activated in cultured chondrocytes treated with palovarotene (Z-score = 2.29), with the upregulation of matrix catabolic genes and the downregulation of matrix anabolic genes, consistent with the histology of palovarotene-treated osteochondromas. A reporter assay performed in cultured chondrocytes demonstrated that the Stat3 pathway, but not the Stat1/2 pathway, was stimulated by RARγ agonists. The activation of Stat3 by palovarotene was confirmed using immunoblotting and immunohistochemistry. These findings suggest that palovarotene treatment is effective against pre-existing osteochondromas and that the Stat3 pathway is involved in the antitumor actions of palovarotene.

circSLTM knockdown attenuates chondrocyte inflammation, apoptosis and ECM degradation in osteoarthritis by regulating the miR-515-5p/VAPB axis.

Osteoarthritis (OA) is a prevalent joint disorder characterized by cartilage degeneration. Circular RNAs (circRNAs) have emerged as pivotal players in OA progression, orchestrating various biological processes such as proliferation, apoptosis, inflammation, and extracellular matrix (ECM) reorganization. Among these circRNAs, circSLTM exhibits aberrant expression in OA, yet its precise regulatory mechanism remains elusive. This study aimed to elucidate the regulatory mechanisms of circSLTM in OA pathogenesis, with a focus on its role as a competing endogenous RNA (ceRNA). Human cartilage tissues were procured from both OA patients and non-OA individuals, while human chondrocyte cells were subjected to lipopolysaccharide (LPS) treatment to mimic OA-like conditions. Our findings revealed upregulation of circSLTM in OA patients and LPS-treated chondrocytes. Loss-of-function assays were conducted, demonstrating that silencing circSLTM via shRNAs mitigated LPS-induced effects on chondrocytes, as evidenced by enhanced proliferation, reduced apoptosis, and inflammatory factors, and altered expression of extracellular matrix proteins. Further exploration into the regulatory mechanism of circSLTM unveiled its interaction with microRNA-515-5p (miR-515-5p) to modulate vesicle-associated membrane protein (VAPB) expression in chondrocytes. VAPB, also upregulated in OA, was positively regulated by circSLTM. Rescue assays corroborated that VAPB overexpression reinstated the protective effects of circSLTM knockdown on LPS-treated chondrocytes. Moreover, concurrent knockdown of both circSLTM and VAPB demonstrated synergistic protection against LPS-induced chondrocyte injury. Additionally, we delineated that LPS triggered the activation of the NF-κB pathway in chondrocytes, which was counteracted by circSLTM silencing. To assess the effects of circSLTM on OA in vivo, anterior cruciate ligament transection (ACLT) mouse models were established, revealing that circSLTM deficiency ameliorated cartilage defects in vivo. In conclusion, circSLTM exacerbates osteoarthritis progression by orchestrating the miR-515-5p/VAPB axis and activating the NF-κB pathway, providing novel insights for targeted therapy in OA management.

Liraglutide, a glucagon-like peptide-1 receptor agonist, ameliorates inflammation and apoptosis via inhibition of receptor for advanced glycation end products signaling in AGEs induced chondrocytes.

BACKGROUND: This study aimed to investigate functions of GLP-1R agonist by liraglutide (LIRA) and revealing the mechanism related to AGEs/RAGE in chondrocytes. METHODS: To illustrate potential effect of GLP-1R agonist on AGEs induced chondrocytes, chondrocytes were administrated by AGEs with LIRA and GLP-1R inhibitor exendin. Inflammatory factors were assessed using ELISA. Real-time PCR was used to evaluate the catabolic activity MMPs and ADAMTS mRNA level, as well as anabolic activity (aggrecan and collagen II). RAGE expression was investigated by Western blotting. TUNEL, caspase3 activity and immunofluorescence were performed to test the apoptotic activity. RESULTS: Our results showed that treatment with LIRA at > 100 nM attenuated the AGE-induced chondrocyte viability. Western bolt demonstrated that GLP-1R activation by LIRA treatment reduced RAGE protein expression compared with the AGEs groups. ELISA showed that LIRA hindered the AGEs-induced production of inflammatory cytokines (IL-6, IL-12 and TNF-α) in primary chondrocytes. AGEs induced catabolism levels (MMP-1, -3, -13 and ADAMTS-4, 5) are also attenuated by LIRA, causing the retention of more extracellular matrix (Aggrecan and Collagen II). TUNEL, caspase3 activity and immunofluorescence results indicated that LIRA inhibited the AGEs-induced production of inflammatory cytokines in primary chondrocytes and attenuated the caspase 3 level, leading to the reduced apoptotic activity. All the protective effects are reversed by exendin (GLP-1R blockers). CONCLUSIONS: The present study demonstrates for the first time that LIRA, an agonist for GLP-1R which is commonly used in type 2 diabetes reverses AGEs induced chondrocyte inflammation and apoptosis through suppressing RAGE signaling, contributing to reduced catabolism and retention of more extracellular matrix. The above results indicate the possible effect of GLP-1R agonist on treating OA.

IL-40 is up-regulated in the synovial fluid and cartilage of osteoarthritis patients and contributes to the alteration of chondrocytes phenotype in vitro.

INTRODUCTION: IL-40 is a novel cytokine associated with autoimmune connective tissue disorders such as rheumatoid arthritis (RA) or Sjögren syndrome. We have previously shown an accumulation of IL-40 in the RA joint and its expression by immune cells and fibroblasts. Therefore, we aimed to assess the role of IL-40 in association with hyaline cartilage and chondrocyte activity. METHODS: Immunohistochemistry was employed to detect IL-40 in paired samples of loaded and unloaded regions of osteoarthritis (OA) cartilage (n=5). Synovial fluid IL-40 was analysed by ELISA in OA (n=31) and control individuals after knee injury (n=34). The impact of IL-40 on chondrocytes was tested in vitro. RESULTS: IL-40 was found in chondrocytes of the superficial zone of the OA cartilage, both in loaded and unloaded explants. Additionally, only biopsies from loaded explants showed significant IL-40 positivity in transitional zone chondrocytes. Levels of IL-40 were significantly elevated in the synovial fluid from OA patients compared to controls (p<0.0009) and correlated with synovial fluid leukocyte counts in OA (r=0.444, p=0.014). Chondrocytes exposed to IL-40 dose dependently increased in the secretion of pro-inflammatory cytokines IL-6 (p<0.0001) and IL-8 (p=0.004). Moreover, a dose dependent up-regulation of matrix degrading metalloproteinases MMP-1 (p=0.004), MMP-3 (p=0.031) and MMP-13 (p=0.0002) upon IL-40 treatment was observed in contrast to untreated chondrocytes. CONCLUSION: This study is the first to demonstrate the accumulation of IL-40 in OA cartilage and its up-regulation in the synovial fluid of OA patients compared to controls. In addition, extracellular IL-40 appears to play a role in promoting inflammation and cartilage destruction by driving chondrocyte behaviour towards a more aggressive phenotype.

Mitochondrial Role on Cellular Apoptosis, Autophagy, and Senescence during Osteoarthritis Pathogenesis.

Authors have demonstrated that apoptosis activation is a pathway related to cartilage degradation characteristics of the OA process. Autophagy is an adaptive response to protect cells from various environmental changes, and defects in autophagy are linked to cell death. In this sense, decreased autophagy of chondrocytes has been observed in OA articular cartilage. The aim of this work was to study the role of OA mitochondria in apoptosis, autophagy, and senescence, using OA and Normal (N) transmitochondrial cybrids. Results: OA cybrids incubated with menadione showed a higher percentage of late apoptosis and necrosis than N cybrids. Stimulation of cybrids with staurosporine and IL-1ß showed that OA cybrids were more susceptible to undergoing apoptosis than N cybrids. An analysis of the antioxidant response using menadione on gene expression revealed a lower expression of nuclear factor erythroid 2-like 2 and superoxide dismutase 2 in OA than N cybrids. Activation of microtubule-associated protein 1A/1B-light chain 3 was reduced in OA compared to N cybrids. However, the percentage of senescent cells was higher in OA than N cybrids. Conclusion: This work suggests that mitochondria from OA patients could be involved in the apoptosis, autophagy, and senescence of chondrocytes described in OA cartilage.

The metabolic characteristics and changes of chondrocytes in vivo and in vitro in osteoarthritis.

Osteoarthritis (OA) is an intricate pathological condition that primarily affects the entire synovial joint, especially the hip, hand, and knee joints. This results in inflammation in the synovium and osteochondral injuries, ultimately causing functional limitations and joint dysfunction. The key mechanism responsible for maintaining articular cartilage function is chondrocyte metabolism, which involves energy generation through glycolysis, oxidative phosphorylation, and other metabolic pathways. Some studies have shown that chondrocytes in OA exhibit increased glycolytic activity, leading to elevated lactate production and decreased cartilage matrix synthesis. In OA cartilage, chondrocytes display alterations in mitochondrial activity, such as decreased ATP generation and increased oxidative stress, which can contribute to cartilage deterioration. Chondrocyte metabolism also involves anabolic processes for extracellular matrix substrate production and energy generation. During OA, chondrocytes undergo considerable metabolic changes in different aspects, leading to articular cartilage homeostasis deterioration. Numerous studies have been carried out to provide tangible therapies for OA by using various models in vivo and in vitro targeting chondrocyte metabolism, although there are still certain limitations. With growing evidence indicating the essential role of chondrocyte metabolism in disease etiology, this literature review explores the metabolic characteristics and changes of chondrocytes in the presence of OA, both in vivo and in vitro. To provide insight into the complex metabolic reprogramming crucial in chondrocytes during OA progression, we investigate the dynamic interaction between metabolic pathways, such as glycolysis, lipid metabolism, and mitochondrial function. In addition, this review highlights prospective future research directions for novel approaches to diagnosis and treatment. Adopting a multifaceted strategy, our review aims to offer a comprehensive understanding of the metabolic intricacies within chondrocytes in OA, with the ultimate goal of identifying therapeutic targets capable of modulating chondrocyte metabolism for the treatment of OA.

Activation of kappa opioid receptor suppresses post-traumatic osteoarthritis via sequestering STAT3 on the plasma membrane.

OBJECTIVE: Kappa opioid receptor (KOR) signaling is involved in joint development and inflammation in Osteoarthritis (OA), while the biochemical mechanism remains unclarified. This study aims to investigate downstream molecular events of KOR activation, to provide novel perspectives in OA pathology. METHODS: U50,488H, a selective KOR agonist, was intra-articularly injected in mice upon destabilization of the medial meniscus (DMM) as OA models, with PBS injection as control. The behavioral and histological evaluation was assessed by hot plate test and red solid green staining, respectively. Alterations in mRNA and protein expression were assessed by RNA-seq, RT-qPCR, immunohistochemistry and western blotting (WB) in chondrocytes treated with TNF-α or TNF-α + U50,488H. Proteins interacted with KOR were explored using proximity labeling followed by mass spectrometry and then testified by co-immunoprecipitation (Co-IP) assay and immunofluorescence (IF). RESULTS: OA-induced pain was reduced and cartilage degeneration was alleviated upon KOR activation in DMM mice. In chondrocytes, activation of KOR reversed the upregulation of MMPs, IL-6, IL-1ß and phosphorylated(p-) STAT3, stimulated by TNF-α, while the expression of NF-κB, MAPKs and AKT signaling weren't reversed. RNA-seq and IF results presented that KOR activation evidently reduced STAT3 nuclear translocation in chondrocytes upon TNF-α stimuli. The reduction may be resulted from the binding of KOR and STAT3 in the plasma membrane, revealed by proximity labeling and Co-IP results. CONCLUSIONS: KOR activation protects cartilage from OA, and this protective effect is mainly exerted via sequestering STAT3 on the plasma membrane, resulting in inactivation of STAT3-dependent immune responses which otherwise contributes to OA.

The Role of MicroRNAs in the Pathophysiology of Osteoarthritis.

Worldwide, osteoarthritis (OA) is the most common cause of joint pain in older people. Many factors contribute to osteoarthritis' development and progression, including secondary osteoarthritis' underlying causes. It is important to note that osteoarthritis affects all four tissues: cartilage, bone, joint capsule, and articular apparatus. An increasingly prominent area of research in osteoarthritis regulation is microRNAs (miRNAs), a small, single-stranded RNA molecule that controls gene expression in eukaryotes. We aimed to assess and summarize current knowledge about the mechanisms of the action of miRNAs and their clinical significance. Osteoarthritis (OA) is affected by the interaction between miRNAs and inflammatory processes, as well as cartilage metabolism. MiRNAs also influence cartilage cell apoptosis, contributing to the degradation of the cartilage in OA. Studies have shown that miRNAs may have both an inhibitory and promoting effect on osteoporosis progression through their influence on molecular mechanisms. By identifying these regulators, targeted treatments for osteoarthritis may be developed. In addition, microRNA may also serve as a biomarker for osteoarthritis. By using these biomarkers, the disease could be detected faster, and early intervention can be instituted to prevent mobility loss and slow deterioration.

Excessive load promotes temporomandibular joint chondrocyte apoptosis via Piezo1/endoplasmic reticulum stress pathway.

Excessive load on the temporomandibular joint (TMJ) is a significant factor in the development of TMJ osteoarthritis, contributing to cartilage degeneration. The specific mechanism through which excessive load induces TMJ osteoarthritis is not fully understood; however, mechanically-activated (MA) ion channels play a crucial role. Among these channels, Piezo1 has been identified as a mediator of chondrocyte catabolic responses and is markedly increased in osteoarthritis. Our observations indicate that, under excessive load conditions, endoplasmic reticulum stress in chondrocytes results in apoptosis of the TMJ chondrocytes. Importantly, using the Piezo1 inhibitor GsMTx4 demonstrates its potential to alleviate this condition. Furthermore, Piezo1 mediates endoplasmic reticulum stress in chondrocytes by inducing calcium ion influx. Our research substantiates the role of Piezo1 as a pivotal ion channel in mediating chondrocyte overload. It elucidates the link between excessive load, cell apoptosis, and calcium ion influx through Piezo1. The findings underscore Piezo1 as a key player in the pathogenesis of TMJ osteoarthritis, shedding light on potential therapeutic interventions for this condition.

Loss of ß-arrestin2 aggravated condylar cartilage degeneration at the early stage of temporomandibular joint osteoarthritis.

OBJECTIVE: Temporomandibular joint osteoarthritis (TMJOA) is a chronic degenerative joint disorder characterized by extracellular matrix degeneration and inflammatory response of condylar cartilage. ß-arrestin2 is an important regulator of inflammation response, while its role in TMJOA remains unknown. The objective of this study was to investigate the role of ß-arrestin2 in the development of TMJOA at the early stage and the underlying mechanism. METHODS: A unilateral anterior crossbite (UAC) model was established on eight-week-old wild-type (WT) and ß-arrestin2 deficiency mice to simulate the progression of TMJOA. Hematoxylin-eosin (HE) staining and microcomputed tomography (micro-CT) analysis were used for histological and radiographic assessment. Immunohistochemistry was performed to detect the expression of inflammatory and degradative cytokines, as well as autophagy related factors. Terminal-deoxynucleotidyl transferase mediated nick end labeling (TUNEL) assay was carried out to assess chondrocyte apoptosis. RESULTS: The loss of ß-arrestin2 aggravated cartilage degeneration and subchondral bone destruction in the model of TMJOA at the early stage. Furthermore, in UAC groups, the expressions of degradative (Col-X) and inflammatory (TNF-α and IL-1ß) factors in condylar cartilage were increased in ß-arrestin2 null mice compared with WT mice. Moreover, the loss of ß-arrestin2 promoted apoptosis and autophagic process of chondrocytes at the early stage of TMJOA. CONCLUSION: In conclusion, we demonstrated for the first time that ß-arrestin2 plays a protective role in the development of TMJOA at the early stage, probably by inhibiting apoptosis and autophagic process of chondrocytes. Therefore, ß-arrestin2 might be a potential therapeutic target for TMJOA, providing a new insight for the treatment of TMJOA at the early stage.

Vitamin B6 alleviates osteoarthritis by suppressing inflammation and apoptosis.

BACKGROUND: Although various anti-inflammatory medicines are widely recommended for osteoarthritis (OA) treatment, no significantly clinical effect has been observed. This study aims to examine the effects of vitamin B6, a component that has been reported to be capable of alleviating inflammation and cell death in various diseases, on cartilage degeneration in OA. METHODS: Collagen-induced arthritis (CIA) mice model were established and the severity of OA in cartilage was determined using the Osteoarthritis Research Society International (OARSI) scoring system. The mRNA and protein levels of indicators associated with extracellular matrix (ECM) metabolism, apoptosis and inflammation were detected. The effect of vitamin B6 (VB6) on the mice were assessed using HE staining and masson staining. The apoptosis rate of cells was assessed using TdT-mediated dUTP nick end labeling. RESULTS: Our results showed a trend of improved OARSI score in mice treated with VB6, which remarkably inhibited the hyaline cartilage thickness, chondrocyte disordering, and knees hypertrophy. Moreover, the VB6 supplementation reduced the protein expression of pro-apoptosis indicators, including Bax and cleaved caspase-3 and raised the expression level of anti-apoptosis marker Bcl-2. Importantly, VB6 improved ECM metabolism in both in vivo and in vitro experiments. CONCLUSIONS: This study demonstrated that VB6 alleviates OA through regulating ECM metabolism, inflammation and apoptosis in chondrocytes and CIA mice. The findings in this study provide a theoretical basis for targeted therapy of OA, and further lay the theoretical foundation for studies of mechanisms of VB6 in treating OA.