Chondrocyte Dysfunction Research Articles

Aberrant energy metabolism causes chondrocyte dysfunction in osteoarthritis

Purpose: Metabolic pathways are a series of chemical reactions by which cells break-down nutrients to acquire the energy and processes building blocks that they need to maintain critical cellular processes. The details of chondrocyte metabolism and how it rewires in osteoarthritis (OA) disease progression is not well characterised. Central carbon metabolism (CCM) is an interconnected metabolic system that transforms carbon through glycolysis, gluconeogenesis, the pentose phosphate pathway, and the tricarboxylic acid (TCA) cycle pathway into energy that is essential for the physiology of chondrocytes. The aim of this research is to identify how changes in the energy metabolic state, in particular the central carbon metabolism, contributes to OA. Methods: OA and non-OA cartilage specimens were harvested from patients who required total knee arthroplasty (n=8 patient samples). In order to investigate the metabolism differences an integrated isotype assisted U-13C metabolic flux labelling approach was utilized on chondrocytes growing in limited glucose conditions. Isotopologue profiles of key metabolites were obtained by liquid chromatography/mass spectrometry (LC/MS). Expression profiles of genes regulating energy metabolism of OA cartilage of human and OA rat models were determined using RNA-Seq analysis. We further used extracellular flux assays, which allow for direct evaluation of cellular bioenergetic profiles ex vivo by measuring oxygen consumption rate (OCR, measure of oxidative phosphorylation) and extracellular acidification rate (ECAR, measure of aerobic glycolysis), to test the bio-energetic profile of OA chondrocytes. Results: Firstly, U-13C-labeling identified significant metabolic differences between OA chondrocytes vs. non-OA chondrocytes. In particular, OA chondrocytes displayed remarkably diverse rate of glucose utilization. Higher levels of glucose 6-phosphate (G6P), fructose 1,6-disphosphate (F16DP), glyceraldehyde 3-phosphate (GA3P) and lactate (LAC) were detected in OA chondrocytes. Furthermore, there was also a marked increase in 13C labelled enrichment of oxaloacetic acid (OAA) in TCA cycle of OA chondrocytes, while decrease in the rest substrates such as alpha-Ketoglutarate (aKG) and succinate (SUC). Together, these results demonstrated altered metabolism in OA chondrocytes (Figure 1). Secondly, analysis of the metabolic pathway differentially expressed genes revealed that genes involved in central carbon metabolism were altered in OA chondrocytes compared to non-OA cells. Thirdly, mitochondria and glycolysis stress tests utilizing seahorse technology revealed that basal glycolysis was increased in OA chondrocytes (Non-OA: 46.72±11.03; OA: 81.45±24.91 mpH/min, p<0.05) while basal mitochondrial oxidative phosphorylation was decreased (Non-OA: 24.26±10.35; OA: 6.94±3.06 pmol/min, p<0.05). Stress tests also showed that maximum glycolysis capacity was higher in OA chondrocytes (Non-OA: 47.86±15.01; OA: 91.67±36.31 mpH/min, p<0.05) while maximum oxidative phosphorylation capacity increased in non-OA chondrocytes (Non-OA: 121.22±54.70; OA: 40.25±9.83 pmol/min, p<0.01). These results demonstrated that OA chondrocytes switch to conditions of higher glycolysis and lower mitochondrial oxidative during OA progression. Conclusions: Altogether, this study, which is the first comprehensive comparative analysis of metabolism in chondrocytes, provides a foundation for targeting metabolism for therapeutic benefit in OA.

Characterization of spontaneous facet joint osteoarthritis

Purpose: Although rodent models of traumatically or chemically induced spinal facet joint osteoarthritis (FJOA) were previously described, animal models of typical spontaneous FJOA haven’t been documented. This study aimed to identify the characteristics of murine spontaneous FJOA and its molecular mechanisms. Methods: The lumbar facet joints of mice bearing mutant NFAT1 alleles and of wild-type (WT, control) mice were examined by histopathology, quantitative gene expression, immunohistochemistry, and histomorphometry using a novel FJOA scoring system at 2, 6, 12, and 18 months of age. The reproducibility of the FJOA scoring system was confirmed by inter-observer and intra-observer variability tests. Tissue-specific histomorphometric and gene expression changes were statistically analyzed. Results: NFAT1-mutant facet joints displayed dysfunction of articular chondrocytes and synovial cells with aberrant gene and protein expression in cartilage and synovium as early as 2 months. osteoarthritic structural changes such as articular surface destruction and chondro-osteophyte formation became evident in NFAT1-mutant facet joints at 6 months. Severe FJOA changes including deeper cartilage loss, synovial thickening, separation of cartilage from thickened subchondral bone, as well as tissue-specific molecular and cellular alterations were evident in NFAT1-mutant mice at 12 and 18 months. OA-like structural changes were not detected in WT facet joints at any ages, though aging-related cartilage degeneration was observed at 18 months. Conclusions: This study characterized a novel murine model of spontaneous FJOA and developed the first FJOA scoring system. The age- and tissue-specific molecular and cellular characteristics in the NFAT1-mutant facet joints have provided new insights into the pathogenetic mechanisms for initiation and progression of spontaneous FJOA.

Mitoprotective therapy reduces inflammation and prevents cartilage turnover in an in vivo model of posttraumatic osteoarthritis

Mitoprotective therapy reduces inflammation and prevents cartilage turnover in an in vivo model of posttraumatic osteoarthritis

LncRNA KCNQ1OT1 attenuates osteoarthritic chondrocyte dysfunction via the miR-218-5p/PIK3C2A axis.

The occurrence of osteoarthritis is closely related to chondrocyte dysfunction caused by cellular inflammatory response and matrix degradation, which seriously affect the quality of life of patients. Therefore, this study aimed to investigate the role of potassium voltage-gated channel subfamily Q member 1 overlapping transcript 1 (KCNQ1OT1), a member of the lncRNA voltage-gated channel subfamily Q, in the development of osteoarthritis. In this study, RT-qPCR results showed that KCNQ1OT1 expression was downregulated in osteoarthritic chondrocytes compared with normal chondrocytes. In addition, upregulation of KCNQ1OT1 significantly enhanced the viability of osteoarthritic chondrocytes, inhibited cell apoptosis, and reduced the release of inflammatory cytokines and metal matrix enzymes. Next, bioinformatics analysis and luciferase reporter gene analysis predicted and validated the targeting relationship between KCNQ1OT1 and miR-218-5p. We found that the expression of miR-218-5p was significantly upregulated in osteoarthritic chondrocytes, and knockdown of miR-218-5p significantly enhanced the viability of osteoarthritic chondrocytes, inhibited apoptosis, and decreased the abundance of inflammatory cytokines and metal matrix enzymes. Furthermore, the targeting relationship between miR-218-5p and recombinant phosphoinositide-3-kinase class-2-alpha polypeptide (PIK3C2A) was identified, and overexpression of PIK3C2A enhanced cell viability, and reduced apoptosis and secretion of inflammatory factors. Finally, we found that miR-218-5p overexpression reversed the protective effect of overexpression of KCNQ1OT1 or PIK3C2A on osteoarthritic chondrocytes. In conclusion, our results demonstrated that KCNQ1OT1 upregulated PIK3C2A and activated the PI3K/AKT/mTOR pathway to reduce chondrocyte dysfunction by targeting miR-218-5p, providing new insights into the pathogenesis of osteoarthritis.

MiR-214-3p, a novel possible therapeutic target for the pathogenesis of osteoarthritis

MiR-214-3p, a novel possible therapeutic target for the pathogenesis of osteoarthritis

Inhibition of Inducible Nitric Oxide Synthase Prevents IL-1β-Induced Mitochondrial Dysfunction in Human Chondrocytes.

Interleukin (IL)-1β is an important pro-inflammatory cytokine in the progression of osteoarthritis (OA), which impairs mitochondrial function and induces the production of nitric oxide (NO) in chondrocytes. The aim was to investigate if blockade of NO production prevents IL-1β-induced mitochondrial dysfunction in chondrocytes and whether cAMP and AMP-activated protein kinase (AMPK) affects NO production and mitochondrial function. Isolated human OA chondrocytes were stimulated with IL-1β in combination with/without forskolin, L-NIL, AMPK activator or inhibitor. The release of NO, IL-6, PGE2, MMP3, and the expression of iNOS were measured by ELISA or Western blot. Parameters of mitochondrial respiration were measured using a seahorse analyzer. IL-1β significantly induced NO release and mitochondrial dysfunction. Inhibition of iNOS by L-NIL prevented IL-1β-induced NO release and mitochondrial dysfunction but not IL-1β-induced release of IL-6, PGE2, and MMP3. Enhancement of cAMP by forskolin reduced IL-1β-induced NO release and prevented IL-1β-induced mitochondrial impairment. Activation of AMPK increased IL-1β-induced NO production and the negative impact of IL-1β on mitochondrial respiration, whereas inhibition of AMPK had the opposite effects. NO is critically involved in the IL-1β-induced impairment of mitochondrial respiration in human OA chondrocytes. Increased intracellular cAMP or inhibition of AMPK prevented both IL-1β-induced NO release and mitochondrial dysfunction.

Circ_0045714 alleviates TNF-α-induced chondrocyte injury and extracellular matrix degradation through miR-218-5p/HRAS axis.

Emerging evidence suggests that dysregulated circular RNAs (circRNAs) play a pivotal role in osteoarthritis (OA). Circ_0045714 is a functional circRNAs, and has been revealed to involve in the process of OA. However, the molecular mechanisms by which circ_0045714 regulates OA progression are not thoroughly elucidated. Circ_0045714 expression was decreased in OA and TNF-α-induced chondrocytes, ectopic overexpression of circ_0045714 abolished TNF-α-induced cell apoptosis, inflammation, extracellular matrix (ECM) degradation promotion and proliferation inhibition. In a mechanical study, circ_0045714 targeted miR-218-5p, and miR-218-5p overexpression reversed the effects of circ_0045714 on TNF-α-induced chondrocytes. Besides that, HRAS was a target of miR-218-5p, and HRAS knockdown attenuated the protective effects of miR-218-5p inhibition on TNF-α-induced chondrocyte dysfunction. Additionally, circ_0045714 could regulate HRAS expression via miR-218-5p in chondrocytes. Up-regulation of circ_0045714 suppressed TNF-α-induced chondrocyte growth inhibition, inflammation, and ECM degradation via miR-218-5p/HRAS axis, suggesting a novel insight into the pathogenesis of OA and the potential protective role of circ_0045714 in the occurrence and development of OA.

The Role of Autophagy in Osteoarthritis.

Chondrocytes are the only cell type in normal cartilage. The pathological changes of osteoarthritis (OA) mostly revolve around the apoptosis and dysfunction of chondrocytes. Autophagy, as an intracellular degradation system that maintains the steady state of energy metabolism in cells, has been shown to restore the function of damaged chondrocytes, alleviating the occurrence and progression of OA. In this review, we explored the relationship between autophagy and OA and the key molecules of autophagy pathway that regulate the progression of OA, providing new ideas for OA treatment by targeting autophagy.

Mitochondrial dysfunction triggers a catabolic response in chondrocytes via ROS-mediated activation of the JNK/AP1 pathway.

Mitochondrial function is impaired in osteoarthritis (OA) but its impact on cartilage catabolism is not fully understood. Here, we investigated the molecular mechanism of mitochondrial dysfunction-induced activation of the catabolic response in chondrocytes. Using cartilage slices from normal and OA cartilage, we showed that mitochondrial membrane potential was lower in OA cartilage, and that this was associated with increased production of mitochondrial superoxide and catabolic genes [interleukin 6 (IL-6), COX-2 (also known as PTGS2), MMP-3, -9, -13 and ADAMTS5]. Pharmacological induction of mitochondrial dysfunction in chondrocytes and cartilage explants using carbonyl cyanide 3-chlorophenylhydrazone increased mitochondrial superoxide production and the expression of IL-6, COX-2, MMP-3, -9, -13 and ADAMTS5, and cartilage matrix degradation. Mitochondrial dysfunction-induced expression of catabolic genes was dependent on the JNK (herein referring to the JNK family)/activator protein 1 (AP1) pathway but not the NFκB pathway. Scavenging of mitochondrial superoxide with MitoTEMPO, or pharmacological inhibition of JNK or cFos and cJun, blocked the mitochondrial dysfunction-induced expression of the catabolic genes in chondrocytes. We demonstrate here that mitochondrial dysfunction contributes to OA pathogenesis via JNK/AP1-mediated expression of catabolic genes. Our data shows that AP1 could be used as a therapeutic target for OA management.This article has an associated First Person interview with the first author of the paper.

Homocysteine induces oxidative stress and ferroptosis of nucleus pulposus via enhancing methylation of GPX4

Homocysteine (Hcy) is an amino acid involved in gene methylation. Plasma concentration of Hcy is elevated in the pathological condition hyperhomocysteinemia (HHcy), which increases the risk of disorders of the vascular, nervous and musculoskeletal systems, including chondrocyte dysfunction. The present study aimed to explore the role of Hcy in intervertebral disc degeneration (IVDD), using a range of techniques. A clinical epidemiological study showed that HHcy is an independent risk factor for human IVDD. Cell culture using rat nucleus pulposus cells showed that Hcy promotes a degenerative cell phenotype (involving increased oxidative stress and cell death by ferroptosis) which is mediated by upregulated methylation of GPX4. An in-vivo mouse ‘puncture’ model of IVDD showed that folic acid (which is used to treat HHcy in humans) reduced the ability of diet-induced HHcy to promote IVDD. We conclude that Hcy upregulates oxidative stress and ferroptosis in the nucleus pulposus via enhancing GPX4 methylation, and is a new contributing factor in IVDD.

Irisin Mitigates Oxidative Stress, Chondrocyte Dysfunction and Osteoarthritis Development through Regulating Mitochondrial Integrity and Autophagy.

Compromised autophagy and mitochondrial dysfunction downregulate chondrocytic activity, accelerating the development of osteoarthritis (OA). Irisin, a cleaved form of fibronectin type III domain containing 5 (FNDC5), regulates bone turnover and muscle homeostasis. Little is known about the effect of Irisin on chondrocytes and the development of osteoarthritis. This study revealed that human osteoarthritic articular chondrocytes express decreased level of FNDC5 and autophagosome marker LC3-II but upregulated levels of oxidative DNA damage marker 8-hydroxydeoxyguanosine (8-OHdG) and apoptosis. Intra-articular administration of Irisin further alleviated symptoms of medial meniscus destabilization, like cartilage erosion and synovitis, while improved the gait profiles of the injured legs. Irisin treatment upregulated autophagy, 8-OHdG and apoptosis in chondrocytes of the injured cartilage. In vitro, Irisin improved IL-1β-mediated growth inhibition, loss of specific cartilage markers and glycosaminoglycan production by chondrocytes. Irisin also reversed Sirt3 and UCP-1 pathways, thereby improving mitochondrial membrane potential, ATP production, and catalase to attenuated IL-1β-mediated reactive oxygen radical production, mitochondrial fusion, mitophagy, and autophagosome formation. Taken together, FNDC5 loss in chondrocytes is correlated with human knee OA. Irisin repressed inflammation-mediated oxidative stress and extracellular matrix underproduction through retaining mitochondrial biogenesis, dynamics and autophagic program. Our analyses shed new light on the chondroprotective actions of this myokine, and highlight the remedial effects of Irisin on OA development.

Mitochondrial transfer from bone-marrow-derived mesenchymal stromal cells to chondrocytes protects against cartilage degenerative mitochondrial dysfunction in rats chondrocytes.

BackgroundPrevious studies have reported that mitochondrial dysfunction participates in the pathological process of osteoarthritis (OA). However, studies that improve mitochondrial function are rare in OA. Mitochondrial transfer from mesenchymal stem cells (MSCs) to OA chondrocytes might be a cell-based therapy for the improvement of mitochondrial function to prevent cartilage degeneration. This study aimed to determine whether MSCs can donate mitochondria and protect the mitochondrial function and therefore reduce cartilage degeneration.MethodsBone-marrow-derived mesenchymal stromal cells (BM-MSCs) were harvested from the marrow cavities of femurs and tibia in young rats. OA chondrocytes were gathered from the femoral and tibial plateau in old OA model rats. BM-MSCs and OA chondrocytes were co-cultured and mitochondrial transfer from BM-MSCs to chondrocytes was identified. Chondrocytes with mitochondria transferred from BM-MSCs were selected by fluorescence-activated cell sorting. Mitochondrial function of these cells, including mitochondrial membrane potential (Δψm), the activity of mitochondrial respiratory chain (MRC) enzymes, and adenosine triphosphate (ATP) content were quantified and compared to OA chondrocytes without mitochondrial transfer. Chondrocytes proliferation, apoptosis, and secretion ability were also analyzed between the two groups.ResultsMitochondrial transfer was found from BM-MSCs to OA chondrocytes. Chondrocytes with mitochondrial from MSCs (MSCs + OA group) showed increased mitochondrial membrane potential compared with OA chondrocytes without mitochondria transfer (OA group) (1.79 ± 0.19 vs. 0.71 ± 0.12, t = 10.42, P < 0.0001). The activity of MRC enzymes, including MRC complex I, II, III, and citrate synthase was also improved (P < 0.05). The content of ATP in MSCs + OA group was significantly higher than that in OA group (161.90 ± 13.49 vs. 87.62 ± 11.07 nmol/mg, t = 8.515, P < 0.0001). Meanwhile, we observed decreased cell apoptosis (7.09% ± 0.68% vs.15.89% ± 1.30%, t = 13.39, P < 0.0001) and increased relative secretion of type II collagen (2.01 ± 0.14 vs.1.06 ± 0.11, t = 9.141, P = 0.0008) and proteoglycan protein (2.08 ± 0.20 vs. 0.97 ± 0.12, t = 8.227, P = 0.0012) in MSCs + OA group, contrasted with OA group.ConclusionsMitochondrial transfer from BM-MSCs provided protection for OA chondrocytes against mitochondrial dysfunction and degeneration through improving mitochondrial function, cell proliferation, and inhibiting apoptosis in chondrocytes. This finding may offer a new therapeutic direction for OA.

Metformin Mitigates Cartilage Degradation by Activating AMPK/SIRT1-Mediated Autophagy in a Mouse Osteoarthritis Model.

Chondrocyte dysfunction is a key mechanism underlying osteoarthritis. Metformin has shown protective effects in many diseases. The present study aimed to investigate the effects of metformin on autophagy and apoptosis in the process of osteoarthritis. A mouse osteoarthritis model was set up by surgically destabilizing medial meniscus in the knee. Intraarticular injection of metformin or vehicle was applied in the right knee for eight weeks. Mouse articular chondrocytes were isolated and passaged for in vitro experiments. Small interfering RNA (siRNA) transfection was used to silence target genes. Western blotting, immunohistochemistry, transmission electron microscopy were used. After eight weeks, metformin restored surgery-induced upregulation of MMP13 and downregulation of type II collagen in the joint cartilage. In cultured primary murine chondrocytes, IL-1β aggravated apoptosis and catabolic response in a dose-dependent manner. In the presence of IL-1β, metformin increased phosphorylated levels of AMPKα and upregulated SIRT1 protein expression, leading to an increase in autophagy as well as a decrease in catabolism and apoptosis. Inactivating AMPKα or inhibiting SIRT1 prevented the augmented autophagy in the presence of metformin. Silencing AMPKα2, but not AMPKα1, reduced SIRT1 expression and downregulated autophagy in cultured chondrocytes. Metformin protects against IL-1β-induced extracellular matrix (ECM) degradation in cultured chondrocytes and in mouse osteoarthritis model through activating AMPKα/SIRT1 signaling. Metformin shed light on the treatment of osteoarthritis.

The role of SIRT3-mediated mitochondrial homeostasis in osteoarthritis.

Osteoarthritis is the most common degenerative joint disease and causes major pain and disability in adults. It has been reported that mitochondrial dysfunction in chondrocytes is associated with osteoarthritis. Sirtuins are a family of nicotinamide adenine dinucleotide-dependent histone deacetylases that have the ability to deacetylate protein targets and play an important role in the regulation of cell physiological and pathological processes. Among sirtuin family members, sirtuin 3, which is mainly located in mitochondria, can exert its deacetylation activity to regulate mitochondrial function, regeneration, and dynamics; these processes are presently recognized to maintain redox homeostasis to prevent oxidative stress in cell metabolism. In this review, we provide present opinions on the effect of mitochondrial dysfunction in osteoarthritis. Furthermore, the potential protective mechanism of SIRT3-mediated mitochondrial homeostasis in the progression of osteoarthritis is discussed.

MicroRNA-128A interrupting circadian rhythmicity signaling to accelerate progress of osteoarthritis

Purpose: Osteoarthritis (OA) is a common disease that exhibits various clinical symptoms, like joint disorder, cartilage erosion, synovial inflammation, and pain. Proceed degradation of articular cartilage cause remodeling of cartilage integrity, chondrocyte dysfunction, and molecular mechanisms alteration. However, microRNAs exhibited epigenetically regulation of multiple complex mechanisms still not yet univocally clarified in the pathogenesis of OA development. This study aims to represent miR-128a as being detrimental to articular cartilage integrity.

Transcription factor NFAT1 deficiency causes lumbar facet joint osteoarthritis in mice

Purpose: Facet joint osteoarthritis (FJOA) is widely prevalent in middle-aged and older populations and is thought to be a common cause of back pain. The etiopathogenesis of FJ OA remains unclear. NFAT1 (NFATc2) is a member of the family of nuclear factor of activated T cells (NFAT/Nfat) transcription factors. Previous studies revealed that mice with a global deletion of the Nfat1 gene displayed osteoarthritic changes in appendicular synovial joints. However, whether NFAT1 deficiency affects synovial joints of the spine remains unknown. This study aimed to test our hypothesis that NFAT1 deficiency causes FJOA in mice because NFAT1 is essential for maintaining homeostasis of articular cartilage and synovium of the facet joints. Methods: Lumbar spine tissue samples were harvested from Nfat1 knockout (Nfat1-/-) mice and wild-type (WT) mice as negative controls at the age of 2, 6, and 12 months for histopathological and molecular biological analyses. L3-S1 lumbar spine samples were fixed in 2% paraformaldehyde. Tissue sections prepared with decalcification and embedded in paraffin were used for safranin-O and fast green staining to identify cartilage cells and matrices. Hematoxylin and Eosin (H&E) staining was performed for structural/cellular analysis of bone and soft tissues. Total RNA isolated from articular cartilage and synovium (with a thin layer of fibrous capsular tissue) of L3-S1 facet joints were reverse-transcribed for gene expression analysis using quantitative real-time RT-PCR (qPCR). All animal procedures were approved by the Institutional Animal Care and Use Committee. Statistical analyses were performed with the Student t-test and ANOVA. Results: At 2 months of age, the intensity of safranin-O staining (for proteoglycans) in articular cartilage of the lumbar facet joints was substantially reduced in Nfat1-/- mice, compared to that of the WT mice. OA-like structural changes (e.g. articular surface fibrillations/clefts and osteophyte formation) were not evident. At 6 months, mild to moderate OA structural changes occurred in the lumbar facet joints of Nfat1-/- mice, but not in WT mice. At 12 months, severe OA structural changes were observed in the lumbar facet joints of Nfat1-/- mice, but not in WT mice. Subchondral bone changes were not remarkable in the Nfat1-/- facet joints at any time points. qPCR gene expression analysis demonstrated significantly decreased expression of mRNA for aggrecan (Acan) with significantly increased expression of mRNA for interleukin-1β (Il1b) in the Nfat1-/- facet joint cartilage at 2 months. Significantly decreased expression of mRNA for collagen-II (Col2a1) and significantly increased expression of mRNAs for collagen-10, matrix metalloproteinase-3 (Mmp3), a disintegrin and metalloproteinase with thrombospondin motifs-5 (Adamts5), Il1b, and β-catenin (Ctnnb1) was detected in the Nfat1-/- facet joint cartilage at 6 and 12 months. Gene expression analysis of the synovial-capsular tissues revealed significantly increased Tnfa mRNA at 2 months and significantly increased Mmp3 and Adamts5 at 6 and 12 months. No sex differences were identified in the histological or gene expression analyses. Conclusions: The present study demonstrated for the first time that NFAT1 deficiency causes severe FJOA in mice. FJOA in the Nfat1-deficient mouse model initiates with increased expression of proinflammatory cytokines in articular cartilage and synovium, suggesting that inflammation may play an important role in the initiation stage of NFAT1 deficiency-induced FJOA in mice. These results support our hypothesis that NFAT1 deficiency causes FJOA through dysfunction of both articular chondrocytes and synovial cells.

Mitophagy loss along with mitochondrial dysfunction accelerates losing of chondrocyte activity in osteoarthritis

Purpose: Mitochondrial machinery loss provokes chondrocyte dysfunction, which speeds up cartilage degeneration and osteoarthritis (OA). Mitophagy is an organelle autophagy related to disposal of dysfunctional mitochondria, indispensably maintaining intracellular homeostasis and cell fate. Little is characterized mitophagic reactions within articular chondrocytes in OA joints. This study is undertaken to the biological function of mitophagy to chondrocyte fate in OA cartilage.

Myokine irisin curtails chondrocyte dysfunction and osteoarthritis through repressing WNT3A signaling

Purpose: Loss of chondrocytic activity, like repressed survival and extracellular matrix (ECM) underproduction, escalating articular cartilage damage in the development of osteoarthritis (OA). Moderate physical exercise is known to reduce the risk of OA of the knee. Myokine Irisin, a soluble and cleaved form of fibronectin type III domain containing 5 (FNDC5), is increased upon regular exercise regular and physical workout, regulating muscle strength, energy metabolism, skeletal homeostasis, and inflammation. Little is understood about whether this myokine changed ECM metabolism or cartilage integrity in OA joints remains uncertain. This study is aimed to investigate the Irisin action to chondrocyte survival and OA development. Methods: Articular cartilage specimens were harvested from patients with end-stage knee OA who required total knee arthroplasty and patients with femoral neck fracture who required total hip replacement. Knee joints in mice overexpressing FNDC5 were subjected to destabilized medial meniscus (DMM)-induced OA. Injured knees were intra-articularly injected with Irisin recombinant proteins. Articular cartilage integrity was quantified using OARSI scoring system. Osteophyte formation was probed using μCT scanning. Irisin, matrix metalloproteinases (MMPs), inflammatory cytokine and Wnt3a expression were probed with RT-quantitative PCR and immunohistochemistry. Results: Chondrocyte in human end-stage knee OA cartilage displayed weak FNDC5 immunostaining along with strong cell apoptosis marker TUNEL staining as compared to the non-OA group. Mice overexpressing FNDC5 showed mild OA signs, like cartilage degradation, adipose oveproduction, synovial hypercellularity, swelling and osteophyte formation in experimental OA models, along with improved gait profile of the injured legs. Likewise, intra-articular injection of Irisin recombinant protein downregulated chondrocyte apoptosis and cartilage matrix loss, as well as improved articular integrity and walking patterns of injured knees. In vitro, Irisin recombinant proteins attenuated MMP3, MMP9, IL-6 expression and apoptosis, whereas autophagy program and ECM proteoglycan production were preserved in inflamed chondrocytes. The IL-1β-augmented Wnt3a signaling was downregulated upon Irisin treatment. Conclusions: FNDC5 and Irisin losses are correlated with the development of human end-stage knee OA. The myokine maintains chondrocyte survival and ECM synthesis through repressing chondrocyte inhibitory factor Wnt3a to control autophagic and apoptotic programs. This study sheds new light onto the protective action of Irisin to chondrocyte function and articular integrity in the development of OA. Profound analysis also provides the prospective of therapeutic potential of Irisin recombinant protein for slowing down knee OA development.

KLF10 is upregulated in osteoarthritis and inhibits chondrocyte proliferation and migration by upregulating Acvr1 and suppressing inhbb expression

BackgroudOsteoarthritis (OA) is a common disease caused by chondrocyte dysfunction. KLF10 is a member of the Sp1-like transcription factor family that is involved in regulating osteoblasts, but its expression and regulatory mechanism(s) in chondrocytes are unclear. In the present study, we aimed to investigate the regulatory role of KLF10 on the pathological process of OA. MethodsKLF10 expression in the cartilaginous tissue of patients with osteoarthritis (OA) was evaluated by immunohistochemistry (IHC). Next, we generated an OA mouse model, and the histological changes in cartilage tissue were verified using H&E staining, Safranin O-Fast Green staining, and IHC assays. KLF10 expression in the articular chondrocytes of OA mice was determined by qRT-PCR and Western blotting. To investigate the role of KLF10 in regulating cell proliferation and migration, a KLF10 overexpression plasmid was constructed and transfected into primary mouse chondrocytes. Subsequently, we used RNA sequencing (RNA-seq) to screen differentially expressed genes in chondrocytes with or without KLF10 overexpression. qRT-PCR was used for verification purposes. ResultsWe found that KLF10 was upregulated in the cartilaginous tissue of patients with OA as well as in cartilaginous tissue of the OA mouse model. KLF10 overexpression inhibited the proliferation and migration of chondrocytes. Furthermore, RNA sequencing results identified increased expression of Acvr1 and decreased expression of Inhbb in cells overexpressing KLF10. Changes in mRNA expression of Acvr1 and Inhbb were confirmed by qRT-PCR. ConclusionsKLF10 inhibits chondrocyte proliferation and migration by regulating the expression of Acvr1 and Inhbb in both human and mouse OA. These data suggest that KLF10 may be a potential therapeutic target for the treatment of OA.

Theobromine mitigates IL-1β-induced oxidative stress, inflammatory response, and degradation of type II collagen in human chondrocytes

Osteoarthritis is one of the major causes of disability in elderly adults. Chondrocytes are responsible for the formation and remodeling of articular cartilage in joint tissue. The dysfunction of chondrocytes is a significant factor in the development of osteoarthritis. In the current study, we found that theobromine, a constituent of the cacao plant, possesses a preventive effect against interleukin (IL)-1β-induced chondrocyte dysfunction. Theobromine ameliorates IL-1β-induced production of cellular reactive oxygen species (ROS) and inflammatory mediators including cyclooxygenase-2 (COX-2) and prostaglandin E2 (PGE2). The presence of theobromine suppresses IL-1β-induced inducible nitro oxide synthase (iNOS) expression and cellular nitro oxide (NO) production. Theobromine also suppresses IL-1β-induced production of the pro-inflammatory cytokines tumor necrosis factor-α (TNF-α) and monocyte chemoattractant protein-1 (MCP-1), as well as matrix metalloproteinases (MMP)-3 and MMP-13. Additionally, theobromine mitigates IL-1β-induced type II collagen degradation. Mechanistically, we show that theobromine inhibits IL-1β-induced IκBα activation, nuclear factor-κB (NF-κB) protein p65 accumulation, and transfected NF-κB promoter activity, indicating that theobromine suppresses the NF-κB pathway in chondrocytes. Collectively, our study demonstrates that the natural molecule theobromine has a protective effect to counter cytokine-induced chondrocyte dysfunction, implying its beneficial effect in the prevention of osteoarthritis.