Downregulation of protein kinase CK2 activity facilitates tumor necrosis factor-α-mediated chondrocyte death through apoptosis and autophagy

Oxymatrine protects articular chondrocytes from IL-1β-induced damage through autophagy activation via AKT/mTOR signaling pathway inhibition

BACKGROUND

Osteoarthritis (OA) is a common degenerative joint disease characterized by persistent articular cartilage degeneration and synovitis. Oxymatrine (OMT) is a quinzolazine alkaloid extracted from the traditional Chinese medicine, matrine, and possesses anti-inflammatory properties that may help regulate the pathogenesis of OA; however, its mechanism has not been elucidated. This study aimed to investigate the effects of OMT on interleukin-1β (IL-1β)-induced damage and the potential mechanisms of action.

METHODS

Chondrocytes were isolated from Sprague-Dawley rats. Toluidine blue and Collagen II immunofluorescence staining were used to determine the purity of the chondrocytes. Thereafter, the chondrocytes were subjected to IL-1β stimulation, both in the presence and absence of OMT, or the autophagy inhibitor 3-methyladenine (3-MA). Cell viability was assessed using the MTT assay and SYTOX Green staining. Additionally, flow cytometry was used to determine cell apoptosis rate and reactive oxygen species (ROS) levels. The protein levels of AKT, mTOR, LC3, P62, matrix metalloproteinase-13, and collagen II were quantitatively analyzed using western blotting. Immunofluorescence was used to assess LC3 expression.

RESULTS

OMT alleviated IL-1β-induced damage in chondrocytes, by increasing the survival rate, reducing the apoptosis rates of chondrocytes, and preventing the degradation of the cartilage matrix. In addition, OMT decreased the ROS levels and inhibited the AKT/mTOR signaling pathway while promoting autophagy in IL-1β treated chondrocytes. However, the effectiveness of OMT in improving chondrocyte viability under IL-1β treatment was limited when autophagy was inhibited by 3-MA.

CONCLUSIONS

OMT decreases oxidative stress and inhibits the AKT/mTOR signaling pathway to enhance autophagy, thus inhibiting IL-1β-induced damage. Therefore, OMT may be a novel and effective therapeutic agent for the clinical treatment of OA.

Curcumin in Cancer and Inflammation: An In-Depth Exploration of Molecular Interactions, Therapeutic Potentials, and the Role in Disease Management

This paper delves into the diverse and significant roles of curcumin, a polyphenolic compound from the Curcuma longa plant, in the context of cancer and inflammatory diseases. Distinguished by its unique molecular structure, curcumin exhibits potent biological activities including anti-inflammatory, antioxidant, and potential anticancer effects. The research comprehensively investigates curcumin's molecular interactions with key proteins involved in cancer progression and the inflammatory response, primarily through molecular docking studies. In cancer, curcumin's effectiveness is determined by examining its interaction with pivotal proteins like CDK2, CK2α, GSK3β, DYRK2, and EGFR, among others. These interactions suggest curcumin's potential role in impeding cancer cell proliferation and survival. Additionally, the paper highlights curcumin's impact on inflammation by examining its influence on proteins such as COX-2, CRP, PDE4, and MD-2, which are central to the inflammatory pathway. In vitro and clinical studies are extensively reviewed, shedding light on curcumin's binding mechanisms, pharmacological impacts, and therapeutic application in various cancers and inflammatory conditions. These studies are pivotal in understanding curcumin's functionality and its potential as a therapeutic agent. Conclusively, this review emphasizes the therapeutic promise of curcumin in treating a wide range of health issues, attributed to its complex chemistry and broad pharmacological properties. The research points towards curcumin's growing importance as a multi-faceted natural compound in the medical and scientific community.

Advances in understanding effects of miRNAs on apoptosis, autophagy, and pyroptosis in knee osteoarthritis

MicroRNAs (miRNAs) are a class of endogenous small non-coding RNAs. MicroRNAs-mediated signaling pathways play a critical regulatory role in inducing apoptosis, autophagy, and pyroptosis in developing knee osteoarthritis (KOA). Given this, we searched databases, such as PubMed, using keywords including "miRNA," "knee osteoarthritis," "apoptosis," "autophagy," "pyroptosis", and their combinations. Through an extensive literature review, we conclude that miRNAs can be modulated through various signaling pathways, such as Wnt/β-catenin, TGF-β, PI3K/AKT/mTOR, and NLRP3/Caspase-1, to regulate apoptosis, autophagy, and pyroptosis in KOA. Furthermore, we note that P2X7R and HMGB1 may be crucial regulatory molecules involved in the interconnected regulation of apoptosis, autophagy, and pyroptosis in KOA. Additionally, we describe that miR-140-5p and miR-107 can modulate the advancement of KOA chondrocytes by targeting distinct molecules involved in apoptosis, autophagy, and pyroptosis, respectively. Therefore, we conclude that miRNAs may be potential biomarkers and therapeutic targets for the early prediction, diagnosis, and effective therapeutic approaches of KOA.

Anti-Osteoarthritic Effects of Cartilage-Derived Extracellular Matrix in a Rat Osteoarthritis Model

BACKGROUND

The extracellular matrix (ECM) has many functions, such as segregating tissues, providing support, and regulating intercellular communication. Cartilage-derived ECM (CECM) can be prepared via consecutive processes of chemical decellularization and enzyme treatment. The purpose of this study was to improve and treat osteoarthritis (OA) using porcine knee articular CECM.

METHODS

We assessed the rheological characteristics and pH of CECM solutions. Furthermore, we determined the effects of CECM on cell proliferation and cytotoxicity in the chondrocytes of New Zealand rabbits. The inhibitory effect of CECM on tumor necrosis factor (TNF)-α-induced cellular apoptosis was assessed using New Zealand rabbit chondrocytes and human synoviocytes. Finally, we examined the in vivo effects of CECM on inflammation control and cartilage degradation in an experimental OA-induced rat model. The rat model of OA was established by injecting monosodium iodoacetate into the intra-articular knee joint. The rats were then injected with CECM solution. Inflammation control and cartilage degradation were assessed by measuring the serum levels of proinflammatory cytokines and C-telopeptide of type II collagen and performing a histomorphological analysis.

RESULTS

CECM was found to be biocompatible and non-immunogenic, and could improve cell proliferation without inducing a toxic reaction. CECM significantly reduced cellular apoptosis due to TNF-α, significantly improved the survival of cells in inflammatory environments, and exerted anti-inflammatory effects.

CONCLUSION

Our findings suggest that CECM is an appropriate injectable material that mediates OA-induced inflammation.

CK2 and the Hallmarks of Cancer

Cancer is a leading cause of death worldwide. Casein kinase 2 (CK2) is commonly dysregulated in cancer, impacting diverse molecular pathways. CK2 is a highly conserved serine/threonine kinase, constitutively active and ubiquitously expressed in eukaryotes. With over 500 known substrates and being estimated to be responsible for up to 10% of the human phosphoproteome, it is of significant importance. A broad spectrum of diverse types of cancer cells has been already shown to rely on disturbed CK2 levels for their survival. The hallmarks of cancer provide a rationale for understanding cancer's common traits. They constitute the maintenance of proliferative signaling, evasion of growth suppressors, resisting cell death, enabling of replicative immortality, induction of angiogenesis, the activation of invasion and metastasis, as well as avoidance of immune destruction and dysregulation of cellular energetics. In this work, we have compiled evidence from the literature suggesting that CK2 modulates all hallmarks of cancer, thereby promoting oncogenesis and operating as a cancer driver by creating a cellular environment favorable to neoplasia.

Plin5, a New Target in Diabetic Cardiomyopathy

Abnormal lipid accumulation is commonly observed in diabetic cardiomyopathy (DC), which can create a lipotoxic microenvironment and damage cardiomyocytes. Lipid toxicity is an important pathogenic factor due to abnormal lipid accumulation in DC. As a lipid droplet (LD) decomposition barrier, Plin5 can protect LDs from lipase decomposition and regulate lipid metabolism, which is involved in the occurrence and development of cardiovascular diseases. In recent years, studies have shown that Plin5 expression is involved in the pathogenesis of DC lipid toxicity, such as oxidative stress, mitochondrial dysfunction, endoplasmic reticulum (ER) stress, and insulin resistance (IR) and has become a key target of DC research. Therefore, understanding the relationship between Plin5 and DC progression as well as the mechanism of this process is crucial for developing new therapeutic approaches and exploring new therapeutic targets. This review is aimed at exploring the latest findings and roles of Plin5 in lipid metabolism and DC-related pathogenesis, to explore possible clinical intervention approaches.

How can a traffic light properly work if it is always green? The paradox of CK2 signaling

CK2 is a constitutively active protein kinase that assuring a constant level of phosphorylation to its numerous substrates supports many of the most important biological functions. Nevertheless, its activity has to be controlled and adjusted in order to cope with the varying needs of a cell, and several examples of a fine-tune regulation of its activity have been described. More importantly, aberrant regulation of this enzyme may have pathological consequences, e.g. in cancer, chronic inflammation, neurodegeneration, and viral infection. Our review aims at summarizing our current knowledge about CK2 regulation. In the first part, we have considered the most important stimuli shown to affect protein kinase CK2 activity/expression. In the second part, we focus on the molecular mechanisms by which CK2 can be regulated, discussing controversial aspects and future perspectives.

Canonical, Non-Canonical and Atypical Pathways of Nuclear Factor кb Activation in Preeclampsia

Although higher nuclear factor κB (NFκB) expression and activity is observed in preeclamptic placentas, its mechanism of activation is unknown. This is the first study to investigate whether the canonical, non-canonical, or atypical NFκB activation pathways may be responsible for the higher activation of NFκB observed in preeclamptic placentas. The study included 268 cases (130 preeclamptic women and 138 controls). We studied the expression of the genes coding for NFκB activators (NIK, IKKα, IKKβ, and CK2α) and inhibitors (IκBα and IκBβ) using RT-PCR in real time. The RT-PCR results were verified on the protein level using ELISA and Western blot. To determine the efficiency of the pathways, the ratios of activator(s) to one of the inhibitors (IκBα or IκBβ) were calculated for each studied pathway. The preeclamptic placentas demonstrated significantly lower IKKα and CK2α but higher IκBα and IκBβ protein levels. In addition, the calculated activator(s) to inhibitor (IκBα or IκBβ) ratios suggested that all studied pathways might be downregulated in preeclamptic placentas. Our results indicate that preeclamptic placentas may demonstrate mechanisms of NFκB activation other than the canonical, non-canonical, and atypical forms. In these mechanisms, inhibitors of NFκB may play a key role. These observations broaden the existing knowledge regarding the molecular background of preeclampsia development.

Protein Kinase CK2 in Cancer Energetics

Protein kinase CK2 (formerly known as casein kinase 2) is abnormally elevated in many cancers. This may increase tumor aggressiveness through CK2-dependent phosphorylation of key proteins in several signaling pathways. In this work, we have compiled evidence from the literature to suggest that CK2 also modulates a metabolic switch characteristic of cancer cells that enhances resistance to death, due to either drugs or to a microenvironment deficient in oxygen or nutrients. Concurrently, CK2 may help to preserve mitochondrial activity in a PTEN-dependent manner. PTEN, widely recognized as a tumor suppressor, is another CK2 substrate in the PI3K/Akt signaling pathway that promotes cancer viability and aerobic glycolysis. Given that CK2 can regulate Akt as well as two of its main effectors, namely mTORC1 and β-catenin, we comprehensively describe how CK2 may modulate cancer energetics by regulating expression of key targets and downstream processes, such as HIF-1 and autophagy, respectively. Thus, the specific inhibition of CK2 may lead to a catastrophic death of cancer cells, which could become a feasible therapeutic strategy to beat this devastating disease. In fact, ATP-competitive inhibitors, synthetic peptides and antisense oligonucleotides have been designed as CK2 inhibitors, some of them used in preclinical models of cancer, of which TBB and silmitasertib are widely known. We will finish by discussing a hypothetical scenario in which cancer cells are "addicted" to CK2; i.e., in which many proteins that regulate signaling pathways and metabolism-linked processes are highly dependent on this kinase.

Autophagy compensates for defects in mitochondrial dynamics

Compromising mitochondrial fusion or fission disrupts cellular homeostasis; however, the underlying mechanism(s) are not fully understood. The loss of C. elegans fzo-1MFN results in mitochondrial fragmentation, decreased mitochondrial membrane potential and the induction of the mitochondrial unfolded protein response (UPRmt). We performed a genome-wide RNAi screen for genes that when knocked-down suppress fzo-1MFN(lf)-induced UPRmt. Of the 299 genes identified, 143 encode negative regulators of autophagy, many of which have previously not been implicated in this cellular quality control mechanism. We present evidence that increased autophagic flux suppresses fzo-1MFN(lf)-induced UPRmt by increasing mitochondrial membrane potential rather than restoring mitochondrial morphology. Furthermore, we demonstrate that increased autophagic flux also suppresses UPRmt induction in response to a block in mitochondrial fission, but not in response to the loss of spg-7AFG3L2, which encodes a mitochondrial metalloprotease. Finally, we found that blocking mitochondrial fusion or fission leads to increased levels of certain types of triacylglycerols and that this is at least partially reverted by the induction of autophagy. We propose that the breakdown of these triacylglycerols through autophagy leads to elevated metabolic activity, thereby increasing mitochondrial membrane potential and restoring mitochondrial and cellular homeostasis.

Inhibition of protein kinase CK2 facilitates cellular senescence by inhibiting the expression of HO-1 in articular chondrocytes

Protein kinase casein kinase 2 (CK2) is important in the regulation of cell proliferation and death, even under pathological conditions. Previously, we reported that CK2 regulates the expression of heme oxygenase‑1 (HO‑1) in stress‑induced chondrocytes. In the present study, it was shown that CK2 is involved in the dedifferentiation and cellular senescence of chondrocytes. Treatment of primary articular chondrocytes with CK2 inhibitors, 4,5,6,7‑terabromo‑2‑azabenzimidazole (TBB) or 5,6‑dichlorobenzimidazole 1‑β‑D‑ribofuranoside (DRB), induced an increase in senescence‑associated β‑galactosidase (SA‑β‑gal) staining. In addition, TBB reduced the expression of type II collagen and stimulated the accumulation of β‑catenin, phenotypic markers of chondrocyte differentiation and dedifferentiation, respectively. It was also observed that the abrogation of CK2 activity by CK2 small interfering RNA induced phenotypes of chondrocyte senescence. The association between HO‑1 and cellular senescence was also examined in CK2 inhibitor‑treated chondrocytes. Pretreatment with 3‑morpholinosydnonimine hydrochloride, an inducer of the HO‑1 expression, or overexpression of the HO‑1 gene significantly delayed chondrocyte senescence. These results show that CK2 is associated with chondrocyte differentiation and cellular senescence and that this is due to regulation of the expression of HO‑1. Furthermore, the findings suggest that CK2 is crucial as an anti‑aging factor during chondrocyte senescence.

Dietary fat-associated osteoarthritic chondrocytes gain resistance to lipotoxicity through PKCK2/STAMP2/FSP27

Free fatty acids (FFAs), which are elevated with metabolic syndrome, are considered the principal offender exerting lipotoxicity. Few previous studies have reported a causal relationship between FFAs and osteoarthritis pathogenesis. However, the molecular mechanism by which FFAs exert lipotoxicity and induce osteoarthritis remains largely unknown. We here observed that oleate at the usual clinical range does not exert lipotoxicity while oleate at high pathological ranges exerted lipotoxicity through apoptosis in articular chondrocytes. By investigating the differential effect of oleate at toxic and nontoxic concentrations, we revealed that lipid droplet (LD) accumulation confers articular chondrocytes, the resistance to lipotoxicity. Using high fat diet-induced osteoarthritis models and articular chondrocytes treated with oleate alone or oleate plus palmitate, we demonstrated that articular chondrocytes gain resistance to lipotoxicity through protein kinase casein kinase 2 (PKCK2)—six-transmembrane protein of prostate 2 (STAMP2)—and fat-specific protein 27 (FSP27)-mediated LD accumulation. We further observed that the exertion of FFAs-induced lipotoxicity was correlated with the increased concentration of cellular FFAs freed from LDs, whether FFAs are saturated or not. In conclusion, PKCK2/STAMP2/FSP27-mediated sequestration of FFAs in LD rescues osteoarthritic chondrocytes. PKCK2/STAMP2/FSP27 should be considered for interventions against metabolic OA.

Cartilage tissue deals with the stress of exposure to free fatty acids by sequestering the toxic molecules into sub-cellular oil droplets. Young Hyun Yoo from Dong-A University College of Medicine in Busan, South Korea, and coworkers exposed rat cartilage cells to increasing levels of a fatty acid called oleate, a by-product of fat metabolism, and observed that the accumulation of oil droplets conferred resistance to oleate-induced toxicity. In these rat cells and in experiments involving mouse models of osteoarthritis fed a high-fat diet, the researchers then identified three of the protective proteins needed for cartilage tissue to properly quarantine fatty acids into oil droplets. Those proteins — and their connected regulatory networks — could now serve as drug targets for treating metabolic syndrome-associated osteoarthritis.

Use of integrative epigenetic and mRNA expression analyses to identify significantly changed genes and functional pathways in osteoarthritic cartilage

Aim

Osteoarthritis (OA) is caused by complex interactions between genetic and environmental factors. Epigenetic mechanisms control the expression of genes and are likely to regulate the OA transcriptome. We performed integrative genomic analyses to define methylation-gene expression relationships in osteoarthritic cartilage.

Patients and Methods

Genome-wide DNA methylation profiling of articular cartilage from five patients with OA of the knee and five healthy controls was conducted using the Illumina Infinium HumanMethylation450 BeadChip (Illumina, San Diego, California). Other independent genome-wide mRNA expression profiles of articular cartilage from three patients with OA and three healthy controls were obtained from the Gene Expression Omnibus (GEO) database. Integrative pathway enrichment analysis of DNA methylation and mRNA expression profiles was performed using integrated analysis of cross-platform microarray and pathway software. Gene ontology (GO) analysis was conducted using the Database for Annotation, Visualization and Integrated Discovery (DAVID).

Results

We identified 1265 differentially methylated genes, of which 145 are associated with significant changes in gene expression, such as DLX5, NCOR2 and AXIN2 (all p-values of both DNA methylation and mRNA expression < 0.05). Pathway enrichment analysis identified 26 OA-associated pathways, such as mitogen-activated protein kinase (MAPK) signalling pathway (p = 6.25 × 10-4), phosphatidylinositol (PI) signalling system (p = 4.38 × 10-3), hypoxia-inducible factor 1 (HIF-1) signalling pathway (p = 8.63 × 10-3 pantothenate and coenzyme A (CoA) biosynthesis (p = 0.017), ErbB signalling pathway (p = 0.024), inositol phosphate (IP) metabolism (p = 0.025), and calcium signalling pathway (p = 0.032).

Conclusion

We identified a group of genes and biological pathwayswhich were significantly different in both DNA methylation and mRNA expression profiles between patients with OA and controls. These results may provide new clues for clarifying the mechanisms involved in the development of OA.

Cite this article: A. He, Y. Ning, Y. Wen, Y. Cai, K. Xu, Y. Cai, J. Han, L. Liu, Y. Du, X. Liang, P. Li, Q. Fan, J. Hao, X. Wang, X. Guo, T. Ma, F. Zhang. Use of integrative epigenetic and mRNA expression analyses to identify significantly changed genes and functional pathways in osteoarthritic cartilage. Bone Joint Res 2018;7:343–350. DOI: 10.1302/2046-3758.75.BJR-2017-0284.R1.

Association between tumor necrosis factor alpha rs1800629 polymorphism and risk of osteoarthritis in a Chinese population

Osteoarthritis (OA) is the most common degenerative disease affecting articular cartilage. Some studies indicate that tumor necrosis factor alpha (TNF-α) gene rs1800629 polymorphism was associated with OA risk among Caucasian populations. To examine the role of this candidate gene in Asian populations, we conducted a hospital-based case-control study involving 257 knee OA patients and 305 controls in a Chinese population. Genotyping was performed using a custom-by-design 48-Plex single nucleotide polymorphism (SNP) Scan^™ kit. Our study indicated that the AA genotype of TNF-α rs1800629 polymorphism was associated with increased risk of OA. Subsequently, we conducted a meta-analysis and found that rs1800629 polymorphism increased the risk of OA in the recessive and homozygous models. Stratification analysis of ethnicity also obtained a significant association among Asian populations. In conclusion, TNF-α rs1800629 polymorphism confers susceptibility to OA, especially among Asians. Larger studies with more diverse ethnic populations are needed to confirm these results.

Inflammatory Biomarker Profiling in Total Joint Arthroplasty and Its Relevance to Circulating Levels of Lubricin, a Novel Proteoglycan

Lubricin, also known as proteoglycan 4, acts as an antiadhesive and boundary lubricant to prevent cartilage damage in healthy joints. Following injury, a decrease in synovial fluid (SF) lubricin may lead to secondary osteoarthritis (OA). Inflammatory biomarkers, such as IL-1β and TNF-α, are also implicated in the pathophysiology of OA. Interestingly, they have been shown to suppress the expression and secretion of lubricin in SF. This study aims to compare circulating levels of inflammatory biomarkers and lubricin between total joint arthroplasty (TJA) patients and healthy individuals. Doing so may better elucidate their roles in OA and extend the understanding of inflammation as a regulator of lubricin. Deidentified plasma samples were obtained 1 day preoperatively and 1 day postoperatively from patients undergoing TJA. Utilizing biochip array technology, they were profiled for IL-2, IL-4, IL-6, IL-8, IL-10, VEGF, IFN-γ, IL-1α, IL-1β, MCP-1, EGF, and TNF-α. Circulating lubricin levels were also measured using enzyme-linked immunosorbent assay. Compared to healthy controls, IL-6, IL-8, VEGF, IL-1β, MCP-1, EGF, and TNF-α were significantly increased pre- and postoperatively. Lubricin was significantly decreased. This may indicate that elevations in inflammatory cytokines initiate a cascade of events, leading to decreased lubricin, which places the joint at increased risk of developing OA.

Downregulation of protein kinase CK2 activity induces age-related biomarkers in C. elegans

Studies show that a decrease in protein kinase CK2 (CK2) activity is associated with cellular senescence. However, the role of CK2 in organism aging is still poorly understood. Here, we investigated whether protein kinase CK2 (CK2) modulated longevity in Caenorhabditis elegans. CK2 activity decreased with advancing age in the worms. Knockdown of kin-10 (the ortholog of CK2β) led to a short lifespan phenotype and induced age-related biomarkers, including retardation of locomotion, decreased pharyngeal pumping rate, increased lipofuscin accumulation, and reduced resistance to heat and oxidative stress. The long lifespan of age-1 and akt-1 mutants was significantly suppressed by kin-10 RNAi, suggesting that CK2 acts downstream of AGE-1 and AKT-1. Kin-10 knockdown did not further shorten the short lifespan of daf-16 mutant worms but either decreased or increased the transcriptional activity of DAF-16 depending on the promoters of the target genes, indicating that CK2 is an upstream regulator of DAF-16 in C. elegans. Kin-10 knockdown increased production of reactive oxygen species (ROS) in the worms. Finally, the ROS scavenger N-acetyl-L-cysteine significantly counteracts the lifespan shortening and lipofuscin accumulation induced by kin-10 knockdown. Therefore, the present results suggest that age-dependent CK2 downregulation reduces longevity by associating with both ROS generation and the AGE-1-AKT-1-DAF-16 pathway in C. elegans.

Zhuangguguanjie formulation protects articular cartilage from degeneration in joint instability-induced murine knee osteoarthritis

Zhuangguguanjie formulation (ZG) can provide noticeable relief from joint pain in patients suffering from knee osteoarthritis (OA). However, the underlying mechanism has not been fully described. Male C57BL/6 mice were administered either ZG or normal saline (NS) following surgical destabilization of the medial meniscus (DMM). At weeks 4, 6 and 8 (post-surgery), knee joints were harvested and assessed with Safranin-O staining. Blood serum was collected and tested. In vitro analysis was carried out to evaluate the effects of ZG on the expression of the OA-related genes. DMM mice indicated reduced cartilage destruction and lower blood serum biomarkers of OA (COMP1 and CTX-1) following ZG treatment. Moreover, the femoral condyle and tibial plateau histological scores were significantly reduced following ZG treatment of the DMM mice. ZG could markedly downregulate the expression of OA-related genes namely, ADAMTS5, MMP3 and MMP13, while it simultaneously upregulated collagen II as demonstrated by in vitro assays. Moreover, chondrocyte apoptosis was significantly decreased following ZG treatment. These results may be caused by the up-regulation of p-AKT expression levels, since the anti-apoptotic effects of ZG can be blocked by treatment with an AKT inhibitor. ZG is capable of preventing and/or reducing the progression of OA by inhibiting chondrocyte apoptosis via the p-AKT/Caspase 3 pathway.

miR-4262 regulates chondrocyte viability, apoptosis, autophagy by targeting SIRT1 and activating PI3K/AKT/mTOR signaling pathway in rats with osteoarthritis

The present study aimed to investigate the effect and underlying mechanism of microRNA (miR)-4262 in the development of osteoarthritis (OA) in rats. Primary chondrocytes were separated from Sprague-Dawley rats and then treated with tumor necrosis factor-α (TNF-α). The level of miR-4262 was detected in TNF-α-treated chondrocytes, and then the miR-4262 or its target gene sirtuin type 1 (SIRT1) level was overexpressed, or knocked down. Furthermore, cell viability, cell apoptosis, cell autophagy and matrix synthesis, as well as the expressions of proteins associated with the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signaling pathway were detected. miR-4262 was significantly overexpressed in TNF-α-treated chondrocytes compared with untreated cells (P<0.05). TNF-α treatment or miR-4262 overexpression significantly decreased cell viability, autophagy-related proteins levels and matrix synthesis-related proteins levels, as well as increased the apoptotic rate in chondrocytes (P<0.05). Overexpression of SIRT1 significantly increased cell viability, autophagy-related proteins levels and matrix synthesis-related proteins levels, as well as decreased the apoptotic rate in TNF-α-treated chondrocytes (P<0.05). In addition, the effects of miR-4262 on cell viability, cell apoptosis, cell autophagy and matrix synthesis were inhibited by SIRT1 (P<0.05). Furthermore, upregulated miR-4262 remarkably increased the expressions of phosphorylated (p)-PI3K, p-AKT and p-mTOR (P<0.05) in TNF-α treated chondrocytes. The present study revealed that the upregulation of miR-4262 may promote the occurrence and development of OA in rats by regulating cell viability, cell apoptosis, cell autophagy, and matrix synthesis. Furthermore, these roles of miR-4262 may be associated with PI3K/AKT/mTOR signaling pathway.

Oxidized low density lipoprotein facilitates tumor necrosis factor‑α mediated chondrocyte death via autophagy pathway

We aimed to investigate the role of oxidized low density lipoprotein (ox-LDL) in tumor necrosis factor-α (TNF-α) mediated chondrocyte death and explore the mechanisms. Ten osteoarthritis (OA) and normal control cartilage tissue and synovial fluid (SF) samples were collected, and the expression of lectin-like ox-LDL receptor-1 (LOX-1) and ox-LDL level was examined by real time quantitative PCR and enzyme-linked immunosorbent assay (ELISA). An in vitro chondrocyte model was established by the introduction of TNF-α and ox-LDL, cell death was analyzed by trypan blue assay and the mechanisms were explored based on the apoptosis related pathway and autophagy pathway. Significantly increased ox-LDL level (70.30±17.83 vs. 37.22±19.97, P<0.05) in SF sample and LOX-1 expression level (0.51±0.10 vs. 0.32±0.04, P<0.05) in cartilage tissue was found in OA patients compared to those corresponding samples from control subjects. Ox-LDL could facilitate TNF-α mediated chondrocyte death and this effect could be blocked by LOX-1 antibody neutralization. Autophagy inhibition by 3-MA and Atg-5 siRNA could reverse the cell death effect mediated by TNF-α and ox-LDL co-treatment on chondrocytes. Oxidized low density lipoprotein facilitates tumor necrosis factor-α mediated chondrocyte death via its interaction with LOX-1, and autophagy is involved in the mechanisms.

Excessive Autophagy Activation and Increased Apoptosis Are Associated with Palmitic Acid-Induced Cardiomyocyte Insulin Resistance

Diabetic cardiomyopathy (DCM) remains the major cause of death associated with diabetes. Researchers have demonstrated the importance of impaired cardiac insulin signaling in this process. Insulin resistance (IR) is an important predictor of DCM. Previous studies examining the dynamic changes in autophagy during IR have yielded inconsistent results. This study aimed to investigate the dynamic changes in autophagy and apoptosis in the rat H9c2 cardiomyocyte IR model. H9c2 cells were treated with 500 μM palmitic acid (PA) for 24 hours, resulting in the induction of IR. To examine autophagy, monodansylcadaverine staining, GFP-LC3 puncta confocal observation, and Western blot analysis of LC3I-to-LC3II conversion were used. Results of these studies showed that autophagic acid vesicles increased in numbers during the first 24 hours and then decreased by 36 hours after PA treatment. Western blot analysis showed that treatment of H9c2 cells with 500 μM PA for 24 hours decreased the expression of Atg12-Atg5, Atg16L1, Atg3, and PI3Kp85. Annexin V/PI flow cytometry revealed that PA exposure for 24 hours increased the rate of apoptosis. Together, this study demonstrates that PA induces IR in H9c2 cells and that this process is accompanied by excessive activation of autophagy and increases in apoptosis.

Insights on Molecular Mechanisms of Chondrocytes Death in Osteoarthritis

Osteoarthritis (OA) is a joint pathology characterized by progressive cartilage degradation. Medical care is mainly based on alleviating pain symptoms. Compelling studies report the presence of empty lacunae and hypocellularity in cartilage with aging and OA progression, suggesting that chondrocyte cell death occurs and participates to OA development. However, the relative contribution of apoptosis per se in OA pathogenesis appears complex to evaluate. Indeed, depending on technical approaches, OA stages, cartilage layers, animal models, as well as in vivo or in vitro experiments, the percentage of apoptosis and cell death types can vary. Apoptosis, chondroptosis, necrosis, and autophagic cell death are described in this review. The question of cell death causality in OA progression is also addressed, as well as the molecular pathways leading to cell death in response to the following inducers: Fas, Interleukin-1β (IL-1β), Tumor Necrosis factor-α (TNF-α), leptin, nitric oxide (NO) donors, and mechanical stresses. Furthermore, the protective role of autophagy in chondrocytes is highlighted, as well as its decline during OA progression, enhancing chondrocyte cell death; the transition being mainly controlled by HIF-1α/HIF-2α imbalance. Finally, we have considered whether interfering in chondrocyte apoptosis or promoting autophagy could constitute therapeutic strategies to impede OA progression.

Alpha B-Crystallin Protects Rat Articular Chondrocytes against Casein Kinase II Inhibition-Induced Apoptosis

Although alpha (α)B-crystallin is expressed in articular chondrocytes, little is known about its role in these cells. Protein kinase casein kinase 2 (CK2) inhibition induces articular chondrocyte death. The present study examines whether αB-crystallin exerts anti-apoptotic activity in articular chondrocytes. Primary rat articular chondrocytes were isolated from knee joint slices. Cells were treated with CK2 inhibitors with or without αB-crystallin siRNA. To examine whether the silencing of αB-crystallin sensitizes rat articular chondrocytes to CK2 inhibition-induced apoptosis, we assessed apoptosis by performing viability assays, mitochondrial membrane potential measurements, flow cytometry, nuclear morphology observations, and western blot analysis. To investigate the mechanism by which αB-crystallin modulates the extent of CK2 inhibition-mediated chondrocyte death, we utilized confocal microscopy to observe the subcellular location of αB-crystallin and its phosphorylated forms and performed a co-immunoprecipitation assay to observe the interaction between αB-crystallin and CK2. Immunochemistry was employed to examine αB-crystallin expression in cartilage obtained from rats with experimentally induced osteoarthritis (OA). Our results demonstrated that silencing of αB-crystallin sensitized rat articular chondrocytes to CK2 inhibitor-induced apoptosis. Furthermore, CK2 inhibition modulated the expression and subcellular localization of αB-crystallin and its phosphorylated forms and dissociated αB-crystallin from CK2. The population of rat articular chondrocytes expressing αB-crystallin and its phosphorylated forms was reduced in an experimentally induced rat model of OA. In summary, αB-crystallin protects rat articular chondrocytes against CK2 inhibition-induced apoptosis. αB-crystallin may represent a suitable target for pharmacological interventions to prevent OA.

Leptin protects rat articular chondrocytes from cytotoxicity induced by TNF-α in the presence of cyclohexamide

OBJECTIVE

Although leptin appears to be an important local and systemic factor influencing cartilage homeostasis, the role of leptin in chondrocyte death is largely unknown. Tumor necrosis factor α (TNF-α) is a pro-inflammatory cytokine that plays a central role in the pathogenesis of articular diseases. This study examines whether leptin modulates TNF-α-induced articular chondrocyte death.

METHODS

Primary rat articular chondrocytes were isolated from knee joint cartilage slices. To induce cell death, the chondrocytes were treated with TNF-α. To examine whether leptin modulates the extent of TNF-α-mediated chondrocyte death, the cells were pretreated with leptin for 3 h before TNF-α treatment followed by viability analysis. To examine the mechanism by which leptin modulates the extent of TNF-α-mediated chondrocyte death, we utilized mitochondrial membrane potential (MMP) measurements, flow cytometry, nuclear morphology observation, co-immunoprecipitation, western blot analysis and confocal microscopy.

RESULTS

We demonstrated that leptin suppresses TNF-α induced chondrocyte death. We further found that apoptosis partially contributes to TNF-α induced chondrocyte death while necroptosis primarily contributes to TNF-α induced chondrocyte death. In addition, we observed that leptin exerts anti-TNF-α toxicity via c-jun N-terminal kinase (JNK) in rat articular chondrocytes.

CONCLUSION

Based on our findings, we suggest that the leptin present in the articular joint fluid protects articular chondrocytes against cumulative mechanical load and detrimental stresses throughout a lifetime, delaying the onset of degenerative changes in chondrocytes. We can further hypothesize that leptin protects articular chondrocytes against destructive stimuli even in the joints of osteoarthritis (OA) patients.

TNF Accelerates Death of Mandibular Condyle Chondrocytes in Rats with Biomechanical Stimulation-Induced Temporomandibular Joint Disease

Objective

To determine if temporomandibular joint chondrocyte apoptosis is induced in rats with dental biomechanical stimulation and what a role TNF takes.

Methods

Thirty-two rats were divided into 4 groups (n = 8/group) and exposed to incisor mal-occlusion induced by unilateral anterior crossbite biomechanical stimulation. Two groups were sampled at 2 or 4 weeks. The other two groups were treated with local injections of a TNF inhibitor or PBS into the temporomandibular joints area at 2 weeks and then sampled at 4 weeks. Twenty-four rats either served as unilateral anterior crossbite mock operation controls (n = 8/group) with sampling at 2 or 4 weeks or received a local injection of the TNF inhibitor at 2 weeks with sampling at 4 weeks. Chondrocytes were isolated from the temporomandibular joints of 6 additional rats and treated with TNF in vitro. Joint samples were assessed using Hematoxylin&eosin, Safranin O, TUNEL and immunohistochemistry staining, real-time PCR, fluorogenic activity assays and Western blot analyses. The isolated chondrocytes were also analyzed by flow cytometry.

Results

Unilateral anterior crossbite stimulation led to temporomandibular joint cartilage degradation, associated with an increase in TUNEL-positive chondrocytes number, caspase-9 expression levels, and the release of cytochrome c from mitochondria at 2 weeks without changes in TNF and caspase-8 levels until after 4 weeks. TNF stimulated apoptosis of the isolated chondrocytes and up-regulated caspase-8 expression, but did not change caspase-9 expression levels. Local injection of TNF inhibitor down-regulated caspase-8 expression and reduced TUNEL-positive cell number, but did not reverse cartilage thickness reduction, caspase-9 up-regulation or cytochrome c release.

Conclusions

Unilateral anterior crossbite stimulation induces mitochondrion-mediated apoptosis of articular chondrocytes. TNF accelerated the unilateral anterior crossbite induced chondrocytes apoptosis via death-receptor pathway. However, anti-TNF therapy does not prevent cartilage loss in this model of temporomandibular joint.

The paracrine effect of adipose-derived stem cells inhibits osteoarthritis progression

Background

This study aimed to determine whether intra-articularly injected adipose-derived stem cells (ADSCs) inhibited articular cartilage degeneration during osteoarthritis (OA) development in a rabbit anterior cruciate ligament transection (ACLT) model. The paracrine effects of ADSCs on chondrocytes were investigated using a co-culture system.

Methods

ACLT was performed on both knee joints of 12 rabbits. ADSCs were isolated from the subcutaneous adipose tissue. ADSCs with hyaluronic acid were intra-articularly injected into the left knee, and hyaluronic acid was injected into the right knee. The knees were compared macroscopically, histologically, and immunohistochemically at 8 and 12 weeks. In addition, cell viability was determined using co-culture system of ADSCs and chondrocytes.

Results

Macroscopically, osteoarthritis progression was milder in the ADSC-treated knees than in the control knees 8 weeks after ACLT. Histologically, control knees showed obvious erosions in both the medial and lateral condyles at 8 weeks, while cartilage was predominantly retained in the ADSC-treated knees. At 12 weeks, the ADSC-treated knees showed a slight suppression of cartilage degeneration, unlike the control knees.

Immunohistochemically, MMP-13 expression was less in the ADSC-treated cartilage than in the control knees. The cell viability of chondrocytes co-cultured with ADSCs was higher than that of chondrocytes cultured alone. TNF-alpha-induced apoptotic stimulation was similar between the two groups.

Conclusions

Intra-articularly injected ADSCs inhibited cartilage degeneration progression by homing to the synovium and secreting a liquid factor having chondro-protective effects such as chondrocyte proliferation and cartilage matrix protection.

Autophagy modulates articular cartilage vesicle formation in primary articular chondrocytes

Chondrocyte-derived extracellular organelles known as articular cartilage vesicles (ACVs) participate in non-classical protein secretion, intercellular communication, and pathologic calcification. Factors affecting ACV formation and release remain poorly characterized; although in some cell types, the generation of extracellular vesicles is associated with up-regulation of autophagy. We sought to determine the role of autophagy in ACV production by primary articular chondrocytes. Using an innovative dynamic model with a light scatter nanoparticle counting apparatus, we determined the effects of autophagy modulators on ACV number and content in conditioned medium from normal adult porcine and human osteoarthritic chondrocytes. Healthy articular chondrocytes release ACVs into conditioned medium and show significant levels of ongoing autophagy. Rapamycin, which promotes autophagy, increased ACV numbers in a dose- and time-dependent manner associated with increased levels of autophagy markers and autophagosome formation. These effects were suppressed by pharmacologic autophagy inhibitors and short interfering RNA for ATG5. Caspase-3 inhibition and a Rho/ROCK inhibitor prevented rapamycin-induced increases in ACV number. Osteoarthritic chondrocytes, which are deficient in autophagy, did not increase ACV number in response to rapamycin. SMER28, which induces autophagy via an mTOR-independent mechanism, also increased ACV number. ACVs induced under all conditions had similar ecto-enzyme specific activities and types of RNA, and all ACVs contained LC3, an autophagosome-resident protein. These findings identify autophagy as a critical participant in ACV formation, and augment our understanding of ACVs in cartilage disease and repair.

Articular cartilage changes in maturing athletes: new targets for joint rejuvenation

Context:

Articular cartilage has a unique functional architecture capable of providing a lifetime of pain-free joint motion. This tissue, however, undergoes substantial age-related physiologic, mechanical, biochemical, and functional changes that reduce its ability to overcome the effects of mechanical stress and injury. Many factors affect joint function in the maturing athlete—from chondrocyte survival and metabolism to structural composition and genetic/epigenetic factors governing cartilage and synovium. An evaluation of age-related changes for joint homeostasis and risk for osteoarthritis is important to the development of new strategies to rejuvenate aging joints.

Objective:

This review summarizes the current literature on the biochemical, cellular, and physiologic changes occurring in aging articular cartilage.

Data Sources:

PubMed (1969-2013) and published books in sports health, cartilage biology, and aging.

Study Selection:

Keywords included aging, athlete, articular cartilage, epigenetics, and functional performance with age.

Study Design:

Systematic review.

Level of Evidence:

Level 3.

Data Extraction:

To be included, research questions addressed the effect of age-related changes on performance, articular cartilage biology, molecular mechanism, and morphology.

Results:

The mature athlete faces challenges in maintaining cartilage health and joint function due to age-related changes to articular cartilage biology, morphology, and physiology. These changes include chondrocyte loss and a decline in metabolic response, alterations to matrix and synovial tissue composition, and dysregulation of reparative responses.

Conclusion:

Although physical decline has been regarded as a normal part of aging, many individuals maintain overall fitness and enjoy targeted improvement to their athletic capacity throughout life. Healthy articular cartilage and joints are needed to maintain athletic performance and general activities. Genetic and potentially reversible epigenetic factors influence cartilage physiology and its response to mechanical and injurious stimuli. Improved understandings of the physical and molecular changes to articular cartilage with aging are important to develop successful strategies for joint rejuvenation.

Tumor necrosis factor-α induces ADAMTS-4 expression in human osteoarthritis chondrocytes

Tumor necrosis factor (TNF)-α and a disintegrin and metalloproteinase with thrombospondin motifs 4 (ADAMTS-4) are important in osteoarthritis (OA) cartilage degradation. In the present study, we explored the interaction between the two proteins by examining the effect of TNF-α on ADAMTS-4 expression and activity in osteoarthritic chondrocytes. Human osteoarthritic chondrocytes were treated with TNF-α in different concentrations (5, 15, 30, 45 and 60 ng/ml) for different lengths of time (1, 6, 12, 18 and 24 h) with or without the TNF receptor 1 (TNFR1) inhibitor SPD304 or different kinase inhibitors. TNF-α increased the ADAMTS-4 mRNA level in a statistically significant dose- and time-dependent manner within 18 h, which was reflected in the dose-dependent induction of the ADAMTS-4 promoter activity, ADAMTS-4 protein expression and ADAMTS-4 activity. SPD304 (50 µM) and p38 mitogen-activated protein kinase (MAPK) siRNA and inhibitor PD169316 (25 µM) completely eradicated the promoting effect of TNF-α on ADAMTS-4 expression and activity. TNF-α induces ADAMTS-4 expression and activity in human osteoarthritic chondrocytes at the transcriptional level via TNFR1 by a p38 MAPK-dependent mechanism. To the best of our knowledge, this is the first evidence of crosstalk between TNF-α and ADAMTS-4 in relation to OA cartilage degradation, which adds novel insight into the pathophysiology of OA and cartilage degradation.

Cisplatin-induced downregulation of SOX1 increases drug resistance by activating autophagy in non-small cell lung cancer cell

SOX1 was aberrant methylated in hepatocellular cancer and non-small cell lung cancer (NSCLC). Long-term cisplatin exposure promotes methylation of SOX1 in ovarian cancer cell, suggesting that SOX1 may be involved in cisplatin resistance. Our aim was to test the hypothesis that cisplatin resistance is associated with alteration of SOX1 expression in NSCLC. Expression of levels of SOX1 was examined using RT-PCR in cisplatin resistance cells and parental cells. The level of SOX1 mRNA in cisplatin resistance cells was markedly reduced when compared to parental cells. Promoter methylation of SOX1 was induced in cisplatin resistance cells. We also found that SOX1 silencing enhanced the cisplatin-mediated autophagy in NSCLC. This study shows that inactivation of SOX1 by promoter hypermethylation, at least in part, is responsible for cisplatin resistance in human NSCLC.

Chondroprotective and anti-inflammatory role of melanocortin peptides in TNF-α activated human C-20/A4 chondrocytes

BACKGROUND AND PURPOSE

Melanocortin MC(1) and MC(3 ) receptors, mediate the anti-inflammatory effects of melanocortin peptides. Targeting these receptors could therefore lead to development of novel anti-inflammatory therapeutic agents. We investigated the expression of MC(1) and MC(3) receptors on chondrocytes and the role of α-melanocyte-stimulating hormone (α-MSH) and the selective MC(3) receptor agonist, [DTRP(8) ]-γ-MSH, in modulating production of inflammatory cytokines, tissue-destructive proteins and induction of apoptotic pathway(s) in the human chondrocytic C-20/A4 cells.

EXPERIMENTAL APPROACH

Effects of α-MSH, [DTRP(8) ]-γ-MSH alone or in the presence of the MC(3/4) receptor antagonist, SHU9119, on TNF-α induced release of pro-inflammatory cytokines, MMPs, apoptotic pathway(s) and cell death in C-20/A4 chondrocytes were investigated, along with their effect on the release of the anti-inflammatory cytokine IL-10.

KEY RESULTS

C-20/A4 chondrocytes expressed functionally active MC(1,3) receptors. α-MSH and [DTRP(8) ]-γ-MSH treatment, for 30 min before TNF-α stimulation, provided a time-and-bell-shaped concentration-dependent decrease in pro-inflammatory cytokines (IL-1β, IL-6 and IL-8) release and increased release of the chondroprotective and anti-inflammatory cytokine, IL-10, whilst decreasing expression of MMP1, MMP3, MMP13 genes.α-MSH and [DTRP(8) ]-γ-MSH treatment also inhibited TNF-α-induced caspase-3/7 activation and chondrocyte death. The effects of [DTRP(8) ]-γ-MSH, but not α-MSH, were abolished by the MC(3/4) receptor antagonist, SHU9119.

CONCLUSION AND IMPLICATIONS

Activation of MC(1) /MC(3) receptors in C-20/A4 chondrocytes down-regulated production of pro-inflammatory cytokines and cartilage-destroying proteinases, inhibited initiation of apoptotic pathways and promoted release of chondroprotective and anti-inflammatory cytokines. Developing small molecule agonists to MC(1) /MC(3) receptors could be a viable approach for developing chondroprotective and anti-inflammatory therapies in rheumatoid and osteoarthritis.

MiR-186, miR-216b, miR-337-3p, and miR-760 cooperatively induce cellular senescence by targeting α subunit of protein kinase CKII in human colorectal cancer cells

We previously demonstrated that downregulation of protein kinase CKII induces cellular senescence in human colon cancer HCT116 cells. To investigate the role of microRNAs (miRNAs) in CKII downregulation during senescence, we employed computational algorithms. Four miRNAs (miR-186, miR-216b, miR-337-3p, and miR-760) were predicted to be miRNAs against CKIIα mRNA. Mimics of all four miRNAs jointly downregulated CKIIα expression in HCT116 cells. Reporter analysis and RT-PCR have suggested that these four miRNAs may stimulate degradation of CKIIα mRNA by targeting its 3' untranslated regions (UTRs). The four miRNA mimics increased senescent-associated β-galactosidase (SA-β-gal) staining, p53 and p21(Cip1/WAF1) expression, and reactive oxygen species (ROS) production. In contrast, concomitant knockdown of the four miRNAs by antisense inhibitors increased the CKIIα protein level and suppressed CKII inhibition-mediated senescence. Finally, CKIIα overexpression antagonized senescence induced by the four miRNA mimics. Therefore, the present results show that miR-186, miR-216b, miR-337-3p, and miR-760 cooperatively promote cellular senescence through the p53-p21(Cip1/WAF1) pathway by CKII downregulation-mediated ROS production in HCT116 cells.

Increased macroautophagy in the pathological process of intervertebral disc degeneration in rats

OBJECTIVE

Macroautophagy increases with age in rat intervertebral discs; however, the effect of macroautophagy on the process of intervertebral disc degeneration (IVDD) is still unclear. The aim of this study was to examine the presence of autophagosome, as well as the levels of Beclin-1 and LC3 proteins, in vivo. Additionally, in vitro evidence of macroautophagy and GRP78 and GADD153 protein levels were investigated to explore the mechanism of macroautophagy in the process of IVDD.

METHODS

Male Sprague-Dawley rats, aged 2 months, were randomly divided into six groups (three control and three model groups, n = 8 per group). At the 6-, 12-, and 18-week time points, autophagosomes in nucleus pulposus cells were detected with transmission electron microscope (TEM). Expression of Beclin-1 and LC3 protein levels within intervertebral disc was detected using Western blotting analysis. Then, the rat annulus fibrosus cells were isolated and cultured with Earle's balanced salt solution. At 1, 2, and 3 hr of culture, autophagosomes were detected using monodansylcadaverine assay, and LC3, Beclin-1, GRP78, and GADD153 protein levels were detected using Western blotting analysis.

RESULTS

Transmission electron microscopy revealed autophagosomes within nucleus pulposus cells in both the control and model groups. At 6-, 12-, and 18-week posttreatments, the levels of Beclin-1 and the LC3-II/LC3-I protein ratio in the model groups were higher than those in the control groups (p < 0.05). Compared with the control rats, amino acid starvation increased the number of monodansylcadaverine-positive cells and the LC3-II/LC3-I protein ratio in the model rats. Moreover, the in vitro levels of Beclin-1, GRP78, and GADD153 proteins were increased with the prolongation of amino acid starvation (p < 0.05).

CONCLUSIONS

Macroautophagy was present and was associated with increased pathological process of IVDD in rats. Macroautophagy of intervertebral disc cells is possibly secondary to endoplasmic reticulum stress.

Chondrocyte hypertrophy and osteoarthritis: role in initiation and progression of cartilage degeneration?

OBJECTIVE

To review the literature on the role and regulation of chondrocyte terminal differentiation (hypertrophy-like changes) in osteoarthritis (OA) and to integrate this in a conceptual model of primary OA development.

METHODS

Papers investigating chondrocyte terminal differentiation in human OA cartilage and experimental models of OA were recapitulated and discussed. Focus has been on the occurrence of hypertrophy-like changes in chondrocytes and the factors described to play a role in regulation of chondrocyte hypertrophy-like changes in OA.

RESULTS

Chondrocyte hypertrophy-like changes are reported in both human OA and experimental OA models by most investigators. These changes play a crucial part in the OA disease process by protease-mediated cartilage degradation. We propose that altered chondrocyte behavior and concomitant cartilage degradation result in a disease-amplifying loop, leading to a mixture of disease stages and cellular responses within an OA joint.

CONCLUSION

Chondrocyte hypertrophy-like changes play a role in early and late stage OA. Since not all cells in an OA joint are synchronized, inhibition of hypertrophy-like changes might be a therapeutic target to slow down further OA progression.

Events in articular chondrocytes with aging

It is well accepted that aging is one of the most prominent risk factors for the initiation and progression of osteoarthritis. One of the most pronounced age-related changes in chondrocytes is the exhibition of a senescent phenotype, which is the result of several factors including the accumulation of reactive oxygen species and advanced glycation end products. Compared with a normal chondrocyte, senescent chondrocytes exhibit an impaired ability to respond to many mechanical and inflammatory insults to the articular cartilage. Furthermore, protein secretion is altered in aging chondrocytes, demonstrated by a decrease in anabolic activity and increased production of proinflammatory cytokines and matrix-degrading enzymes. Together, these events may make the articular cartilage matrix more susceptible to damage and lead to the onset of osteoarthritis. A better understanding of the mechanisms underlying age-related chondrocyte pathophysiology may be critical for the development of novel therapeutic interventions for progressive joint diseases.