Inhibition of Gsk3β in cartilage induces osteoarthritic features through activation of the canonical Wnt signaling pathway

Inhibitory Effect of a Tankyrase Inhibitor on Mechanical Stress-Induced Protease Expression in Human Articular Chondrocytes

We investigated the effects of a Tankyrase (TNKS-1/2) inhibitor on mechanical stress-induced gene expression in human chondrocytes and examined TNKS-1/2 expression in human osteoarthritis (OA) cartilage. Cells were seeded onto stretch chambers and incubated with or without a TNKS-1/2 inhibitor (XAV939) for 12 h. Uni-axial cyclic tensile strain (CTS) (0.5 Hz, 8% elongation, 30 min) was applied and the gene expression of type II collagen a1 chain (COL2A1), aggrecan (ACAN), SRY-box9 (SOX9), TNKS-1/2, a disintegrin and metalloproteinase with thrombospondin motifs-5 (ADAMTS-5), and matrix metalloproteinase-13 (MMP-13) were examined by real-time PCR. The expression of ADAMTS-5, MMP-13, nuclear translocation of nuclear factor-κB (NF-κB), and β-catenin were examined by immunocytochemistry and Western blotting. The concentration of IL-1β in the supernatant was examined by enzyme-linked immunosorbent assay (ELISA). TNKS-1/2 expression was assessed by immunohistochemistry in human OA cartilage obtained at the total knee arthroplasty. TNKS-1/2 expression was increased after CTS. The expression of anabolic factors were decreased by CTS, however, these declines were abrogated by XAV939. XAV939 suppressed the CTS-induced expression of catabolic factors, the release of IL-1β, as well as the nuclear translocation of NF-κB and β-catenin. TNKS-1/2 expression increased in mild and moderate OA cartilage. Our results demonstrated that XAV939 suppressed mechanical stress-induced expression of catabolic proteases by the inhibition of NF-κB and activation of β-catenin, indicating that TNKS-1/2 expression might be associated with OA pathogenesis.

Role of Wnt signaling pathway in joint development and cartilage degeneration

Osteoarthritis (OA) is a prevalent musculoskeletal disease that affects approximately 500 million people worldwide. Unfortunately, there is currently no effective treatment available to stop or delay the degenerative progression of joint disease. Wnt signaling pathways play fundamental roles in the regulation of growth, development, and homeostasis of articular cartilage. This review aims to summarize the role of Wnt pathways in joint development during embryonic stages and in cartilage maintenance throughout adult life. Specifically, we focus on aberrant mechanical loading and inflammation as major players in OA progression. Excessive mechanical load activates Wnt pathway in chondrocytes, resulting in chondrocyte apoptosis, matrix destruction and other osteoarthritis-related changes. Additionally, we discuss emerging Wnt-related modulators and present an overview of emerging treatments of OA targeting Wnt signaling. Ultimately, this review provides valuable insights towards discovering new drugs or gene therapies targeting Wnt signaling pathway for diagnosing and treating osteoarthritis and other degenerative joint diseases.

Glycogen Synthase Kinase 3β inhibits BMSCs Chondrogenesis in Inflammation via the Cross-Reaction between NF-κB and β-Catenin in the Nucleus

Inflammation can influence the pluripotency and self-renewal of mesenchymal stem cells (MSCs), thereby altering their cartilage regeneration ability. Sprague-Dawley (SD) rat bone marrow mesenchymal stem cells (BMSCs) were isolated and found to be defective in differentiation potential in the interleukin-1β- (IL-1β-) induced inflammatory microenvironment. Glycogen synthase kinase-3β (GSK-3β) is an evolutionarily conserved serine/threonine kinase that plays a role in numerous cellular processes. The role of GSK-3β in inflammation may be related to the nuclear factor-κB (NF-κB) signaling pathway and the Wnt/β-catenin signaling pathway, whose mechanism remains unclear. In this study, we found that GSK-3β can inhibit chondrogenesis of IL-1β-impaired BMSCs by disrupting metabolic balance and promoting cell apoptosis. By using the inhibitors LiCl and SN50, we demonstrated that GSK-3β regulates the chondrogenesis via the NF-κB and Wnt/β-catenin signaling pathways and possibly mediates the cross-reaction between NF-κB and β-catenin in the nucleus. Given the molecular mechanisms of GSK-3β in chondrogenic differentiation in inflammation, GSK-3β is a crucial target for the treatment of inflammation-induced cartilage disease.

GSK3B Overexpression Alleviates Posttraumatic Osteoarthritis in Mice by Promoting DNMT1-Mediated Hypermethylation of NR4A3 Promoter

Background

Glycogen synthase kinase 3β (GSK3B) is reported to be a protective factor for the degradation of chondrocytes by extracellular mechanisms. Nuclear receptor subfamily 4 group A member 3 (NR4A3) is a proinflammatory factor in osteoarthritis. Their regulation mechanism in posttraumatic osteoarthritis (PTOA) is not fully understood.

Methods

GSK3B expression in the cartilage tissue of PTOA patients was analyzed by western blotting. IL-1β-induced chondrocytes were transfected with pcDNA-GSK3B, and then, the cell viability, apoptosis, expression of the chondrocyte extracellular matrix degradation-related genes MMP13, aggrecan, and type II collagen, and secretion of inflammatory factors TNF-α and IL-6 were detected. Co-IP was used to analyze the interaction between GSK3B and DNMT1. Ch-IP and methylation-specific PCR assays were used for methylation. Also, cells were transfected with pcDNA-GSK3B or together with pcDNA-NR4A3, as well as transfected with si-NR4A3, and then, cell functions were tested. Then, the mice subjected to destabilization of medial meniscus (DMM) surgery were intra-articular injected with 100 μL of the following adeno-related virus vectors (empty vector, Ad-GSK3B, scrambled shRNA, and sh-NR4A3), respectively, and the virus titer was 2 × 10⁸ TU/mL. Cartilage integrity was evaluated by safranin O/fast green staining, HE staining, and Osteoarthritis Research Society International (OARSI) score.

Results

The expression of GSK3B protein was downregulated in PTOA patients. GSK3B overexpression alleviated IL-1β-induced chondrocyte apoptosis and extracellular matrix degradation, as well as cartilage mineralization in PTOA model mice. NR4A3 overexpression reversed the effect of GSK3B on IL-1β-induced chondrocyte functions. GSK3B could recruit DNMT1 to the NR4A3 promoter region to promote the methylation of NR4A3 and inhibit the expression of NR4A3 protein. Similarly, NR4A3 interference alleviated cartilage degradation under stimulating conditions by inhibiting the activation of the JAK2/STAT3 signaling pathway.

Conclusion

GSK3B recruits DNMT1 to the NR4A3 promoter region and inhibits the activation of the NR4A3-mediated JAK2/STAT3 signaling pathway, thereby alleviating PTOA.

A dysfunctional TRPV4-GSK3β pathway prevents osteoarthritic chondrocytes from sensing changes in extracellular matrix viscoelasticity

Changes in the composition and viscoelasticity of the extracellular matrix in load-bearing cartilage influence the proliferation and phenotypes of chondrocytes, and are associated with osteoarthritis. However, the underlying molecular mechanism is unknown. Here we show that the viscoelasticity of alginate hydrogels regulates cellular volume in healthy human chondrocytes (with faster stress relaxation allowing cell expansion and slower stress relaxation restricting it) but not in osteoarthritic chondrocytes. Cellular volume regulation in healthy chondrocytes was associated with changes in anabolic gene expression, in the secretion of multiple pro-inflammatory cytokines, and in the modulation of intracellular calcium regulated by the ion-channel protein transient receptor potential cation channel subfamily V member 4 (TRPV4), which controls the phosphorylation of glycogen synthase kinase 3β (GSK3β), an enzyme with pleiotropic effects in osteoarthritis. A dysfunctional TRPV4-GSK3β pathway in osteoarthritic chondrocytes rendered the cells unable to respond to environmental changes in viscoelasticity. Our findings suggest strategies for restoring chondrocyte homeostasis in osteoarthritis.

Single-cell RNA-sequencing Reveals Thoracolumbar Vertebra Heterogeneity and Rib-genesis in Pigs

Thoracolumbar vertebra (TLV) and rib primordium (RP) development is a common evolutionary feature across vertebrates, although whole-organism analysis of TLV and RP gene expression dynamics has been lacking. Here we investigated the single-cell transcriptomic landscape of thoracic vertebra (TV), lumbar vertebra (LV), and RP cells from a pig embryo at 27 days post-fertilization (dpf) and identified six cell types with distinct gene-expression signatures. In-depth dissection of the gene-expression dynamics and RNA velocity revealed a coupled process of osteogenesis and angiogenesis during TLV and rib development. Further analysis of cell-type-specific and strand-specific expression uncovered the extremely high levels of Hoxa10 3'-untranslated region (UTR) sequence specific to osteoblast of LV cells, which may function as anti-Hoxa10-antisense by counteracting the Hoxa10-antisense effect to determine TLV transition. Thus, this work provides a valuable resource for understanding embryonic osteogenesis and angiogenesis underlying vertebrate TLV and RP development at the cell-type-specific resolution, which serves as a comprehensive view on the transcriptional profile of animal embryo development.

Excessive mechanical stretch‑mediated osteoblasts promote the catabolism and apoptosis of chondrocytes via the Wnt/β‑catenin signaling pathway

Excessive biomechanical loading is considered an important cause of osteoarthritis. Although the mechanical responses of chondrocytes and osteoblasts have been investigated, their communication during mechanical loading and the underlying molecular mechanisms are not yet fully known. The present study investigated the effects of excessive mechanically stretched osteoblasts on the metabolism and apoptosis of chondrocytes, and also assessed the involvement of the Wnt/β‑catenin signaling pathway. In the present study, rat chondrocytes and osteoblasts were subjected to mechanical tensile strain, and an indirect chondrocyte‑osteoblast co‑culture model was established. Reverse transcription‑quantitative PCR and western blotting were performed to determine the expression levels of genes and proteins of interest. An ELISA was performed to investigate the levels of cytokines, including matrix metalloproteinase (MMP) 13, MMP 3, interleukin‑6 (IL‑6) and prostaglandin E2 (PG E2), released from osteoblasts. Flow cytometry was performed to detect the apoptosis of chondrocytes exposed to stretched osteoblast conditioned culture medium. The levels of MMP 13, IL‑6 and PG E2 increased significantly in the supernatants of stretched osteoblasts compared with the un‑stretched group. By contrast, the mRNA expression levels of Collagen 1a and alkaline phosphatase were significantly decreased in osteoblasts subjected to mechanical stretch compared with the un‑stretched group. The mRNA expression level of Collagen 2a was significantly decreased, whereas the expression levels of MMP 13 and a disintegrin and metalloproteinase with thrombospondin‑like motifs 5 were significantly increased in chondrocytes subjected to mechanical stretch compared with the un‑stretched group. In the co‑culture model, the results indicated that excessive mechanically stretched osteoblasts induced the catabolism and apoptosis of chondrocytes, which was partly inhibited by Wnt inhibitor XAV‑939. The results of the present study demonstrated that excessive mechanical stretch led to chondrocyte degradation and inhibited osteoblast osteogenic differentiation; furthermore, excessive mechanically stretched osteoblasts induced the catabolism and apoptosis of chondrocytes via the Wnt/β‑catenin signaling pathway.

Curcumin ameliorates IL-1β-induced apoptosis by activating autophagy and inhibiting the NF-κB signaling pathway in rat primary articular chondrocytes

Articular cartilage damage and chondrocyte apoptosis are common features of rheumatoid arthritis and osteoarthritis. Recently, curcumin has been reported to exhibit protective effects on degeneration in articular cartilage diseases. However, the effects and mechanisms of curcumin on articular chondrocyte injury remain to be elucidated. The aim of the present study is to investigate the chondroprotective mechanisms of curcumin on interleukin-1β (IL-1β)-induced chondrocyte apoptosis in vitro. The results revealed that IL-1β decreased cell viability and induced apoptosis in primary articular chondrocytes. Curcumin pretreatment reduced IL-1β-induced articular chondrocyte apoptosis. In addition, treatment with curcumin increased autophagy in articular chondrocytes and protected against IL-1β-induced apoptosis. The curcumin-mediated protection against IL-1β induced apoptosis was abolished when cells were treated with the autophagy inhibitor 3-methyladenine or transfected with Beclin-1 small interfering RNA. Furthermore, IL-1β stimulation significantly increased the phosphorylation levels of nuclear factor (NF)-κB p65 and glycogen synthase kinase-3β, and decreased the phosphorylation levels of β-catenin in articular chondrocytes, and these alterations to the phosphorylation levels were partly reversed by treatment with curcumin. Dual-luciferase and electrophoretic mobility shift assays demonstrated that IL-1β increased NF-κB p65 promoter activity in chondrocytes, and this was also reversed by curcumin. Pretreatment with the NF-κB inhibitor pyrrolidine dithiocarbamate enhanced the protective effects of curcumin on chondrocyte apoptosis, but Wnt/β-catenin inhibitor, XAV-939, did not exhibit this effect. Molecular docking and dynamic simulation studies results showed that curcumin could bound to RelA (p65) protein. These results indicate that curcumin may suppress IL-1β-induced chondrocyte apoptosis through activating autophagy and restraining NF-κB signaling pathway.

WNT Signalling in Osteoarthritis and Its Pharmacological Targeting

Osteoarthritis (OA) is a highly disabling musculoskeletal condition affecting millions of people worldwide. OA is characterised by progressive destruction and irreversible morphological changes of joint tissues and architecture. At molecular level, de-regulation of several pathways contributes to the disruption of tissue homeostasis in the joint. Overactivation of the WNT/β-catenin signalling pathway has been associated with degenerative processes in OA. However, the multiple layers of complexity in the modulation of the signalling and the still insufficient knowledge of the specific molecular drivers of pathogenetic mechanisms have made difficult the pharmacological targeting of this pathway for therapeutic purposes. This review aims to provide an overview of the WNT/β-catenin signalling in OA with a particular focus on its role in the articular cartilage. Pathway components whose targeting showed therapeutic potential will be highlighted and described. A specific section will be dedicated to Lorecivivint, the first inhibitor of the β-catenin-dependent pathway currently in phase III clinical trial as OA-modifying agent.

Tetrahedral Framework Nucleic Acid Inhibits Chondrocyte Apoptosis and Oxidative Stress through Activation of Autophagy

Osteoarthritis (OA) is a degenerative articular cartilage pathogenic process that is accompanied by excessive chondrocyte apoptosis. The occurrence of chondrocyte death and OA is related to decreased autophagy. Tetrahedral framework nucleic acid (TFNA), a potent bioactive DNA nanomaterial, exerts antiapoptotic and antioxidative effects in various diseases, resulting in autophagy promotion and inhibition of the Wnt/β-catenin-signaling pathway. Here, we aimed to elucidate the therapeutic effects of TFNA on OA and its potential molecular mechanism of action. TFNA was synthesized and characterized by established methods. An interleukin (IL)-1β stimulated OA cell model was established and treated with TFNA. Cellular uptake of TFNA and intracellular reactive oxygen species levels were examined via immunofluorescence and flow cytometry. Apoptotic cell death was documented by the Cell Counting Kit-8 (CCK8) assay and flow cytometry. Transmission electron microscopy was applied to view the autophagosomes. The expression of BCL2, BAX, caspase-3, Nrf2, HO-1, LC3-II, Beclin1, Atg7, β-catenin, Lef-1, and CyclinD1 was detected by immunofluorescence and western blotting. TFNA was successfully synthesized and effectively entered chondrocytes in the absence or presence of IL-1β without the help of transfection agents. TFNA treatment in IL-1β-induced chondrocytes reduced apoptosis by activating the BCL2/BAX/caspase-3 pathway, inhibited oxidative stress by regulating the Nrf2/HO-1-signaling pathway, and enhanced autophagy through upregulated LC3-II, Beclin1, and Atg7. Moreover, TFNA showed chondroprotective effects by regulating the Wnt/β-catenin-signaling pathway. Overall, TFNA may have utility as a therapeutic nanomedicine for OA.

Molecular Signaling Interactions and Transport at the Osteochondral Interface: A Review

Articular joints are comprised of different tissues, including cartilage and bone, with distinctive structural and mechanical properties. Joint homeostasis depends on mechanical and biological integrity of these components and signaling exchanges between them. Chondrocytes and osteocytes actively sense, integrate, and convert mechanical forces into biochemical signals in cartilage and bone, respectively. The osteochondral interface between the bone and cartilage allows these tissues to communicate with each other and exchange signaling and nutritional molecules, and by that ensure an integrated response to mechanical stimuli. It is currently not well known how molecules are transported between these tissues. Measuring molecular transport in vivo is highly desirable for tracking cartilage degeneration and osteoarthritis progression. Since transport of contrast agents, which are used for joint imaging, also depend on diffusion through the cartilage extracellular matrix, contrast agent enhanced imaging may provide a high resolution, non-invasive method for investigating molecular transport in the osteochondral unit. Only a few techniques have been developed to track molecular transport at the osteochondral interface, and there appear opportunities for development in this field. This review will describe current knowledge of the molecular interactions and transport in the osteochondral interface and discuss the potential of using contrast agents for investigating molecular transport and structural changes of the joint.

The combination of microfracture with induction of Wnt / β- Catenin pathway, leads to enhanced cartilage regeneration

INTRODUCTION

Microfracture does not lead to complete healing of full-thickness cartilage defects. The aim of this study was to evaluate the effect of modifying Wnt/β-catenin signaling following microfracture, on the restoration of a full-thickness cartilage defect in a rabbit model. The modification of the canonical Wnt pathway was achieved through per os administration of lithium carbonate, which is an intracellular inhibitor of glycogen synthase kinase 3-β (Gsk3-β) and therefore induces Wnt/β-catenin signaling.

MATERIALS AND METHODS

Full-thickness cartilage defects of 4 mm in diameter were created in the patellar groove of the right femurs of 18 male New Zealand white rabbits. The rabbits were divided into three groups of six (n = 6) based on post-surgery treatment differences, as follows: microfracture only (group 1), microfracture plus lithium carbonate 7 mM in the drinking water for 1 week (group 2), microfracture plus lithium carbonate 7 mM in the drinking water for 4 weeks (group 3). All animals were sacrificed 9 weeks after surgery. The outcome was assessed histologically, by using the International Cartilage Repair Society (ICRS) visual histological scale. Immunohistochemistry for type II collagen was also conducted.

RESULTS

Statistical analysis of the histological ICRS scores showed that group 3 was significantly superior to group 1 in four out of six ICRS categories, while group 2 was superior to 1 in only two out of six.

CONCLUSION

The combination of microfracture and systematic administration of lithium carbonate 7 mM for 4 weeks shows statistically significant superiority in four out of six ICRS categories compared with microfracture only for the treatment of full-thickness cartilage defects in a rabbit experimental model.

Neural EGFL like 1 as a potential pro-chondrogenic, anti-inflammatory dual-functional disease-modifying osteoarthritis drug

Arthritis, an inflammatory condition that causes pain and cartilage destruction in joints, affects over 54.4 million people in the US alone. Here, for the first time, we demonstrated the emerging role of neural EGFL like 1 (NELL-1) in arthritis pathogenesis by showing that Nell-1-haploinsufficient (Nell-1^+/6R) mice had accelerated and aggravated osteoarthritis (OA) progression with elevated inflammatory markers in both spontaneous primary OA and chemical-induced secondary OA models. In the chemical-induced OA model, intra-articular injection of interleukin (IL)1β induced more severe inflammation and cartilage degradation in the knee joints of Nell-1^+/6R mice than in wildtype animals. Mechanistically, in addition to its pro-chondrogenic potency, NELL-1 also effectively suppressed the expression of inflammatory cytokines and their downstream cartilage catabolic enzymes by upregulating runt-related transcription factor (RUNX)1 in mouse and human articular cartilage chondrocytes. Notably, NELL-1 significantly reduced IL1β-stimulated inflammation and damage to articular cartilage in vivo. In particular, NELL-1 administration markedly reduced the symptoms of antalgic gait observed in IL1β-challenged Nell-1^+/6R mice. Therefore, NELL-1 is a promising pro-chondrogenic, anti-inflammatory dual-functional disease-modifying osteoarthritis drug (DMOAD) candidate for preventing and suppressing arthritis-related cartilage damage.

Basic Calcium Phosphate Crystals Induce Osteoarthritis-Associated Changes in Phenotype Markers in Primary Human Chondrocytes by a Calcium/Calmodulin Kinase 2-Dependent Mechanism

Chondrocytes in osteoarthritis undergo a phenotype shift leading to increased production of cartilage-degrading enzymes. There are similarities between the phenotype of osteoarthritic chondrocytes and those of growth plate chondrocytes. Hydroxyapatite can promote chondrocyte differentiation in the growth plate. Basic calcium phosphate (BCP) crystals (which consist of hydroxyapatite, octacalcium apatite and tricalcium phosphate) are frequently found in osteoarthritic joints. The objective of this study was to determine whether BCP crystals induce disease-associated changes in phenotypic marker expression in chondrocytes. Primary human chondrocytes isolated from macroscopically normal cartilage were treated with BCP for up to 48 h. Expression of indian hedgehog (IHH), matrix metalloproteinase 13 (MMP13), interleukin-6 (IL-6) and type X collagen (COLX) were higher, and expression of sry-box 9 (SOX9) lower, in BCP-treated chondrocytes (50 µg/mL) compared to untreated controls. COLX protein was also present in BCP-treated chondrocytes. Intracellular calcium and levels of phosphorylated and total calcium/calmodulin kinase 2 (CaMK2) were elevated following BCP treatment due to BCP-induced release of calcium from intracellular stores. CaMK2 inhibition or knockdown ameliorated the BCP-induced changes in SOX9, IHH, COLX, IL-6 and MMP13 expression. BCP crystals induce osteoarthritis-associated changes in phenotypic marker expression in chondrocytes by calcium-mediated activation of CaMK2. The presence of BCP crystals in osteoarthritic joints may contribute to disease progression.

Chrysin protects human osteoarthritis chondrocytes by inhibiting inflammatory mediator expression via HMGB1 suppression

High‑mobility group box chromosomal protein (HMGB‑1) contributes to osteoarthritis (OA) by modulating various oxidative, inflammatory and apoptotic signaling pathways. The effect of chrysin (CH), a natural plant flavonoid, and its functional interaction with HMGB‑1, was investigated in a chondrocyte model of OA. Human chondrocytes were pre‑treated with CH, and then subsequently treated with IL‑1β to induce the formation of chondrocytes similar to those found in OA joints. Next, the expression level of HMGB‑1 was determined by immunofluorescence and western blot analysis. Additionally, inflammatory factor expression was measured by ELISA, and cell apoptosis was analyzed with flow cytometry. To further explore the effects of CH, HMGB‑1 expression was silenced following CH treatment with small interfering (si)RNA. The results demonstrated that CH inhibited cell apoptosis, dose‑dependently reduced matrix metalloproteinase (MMP) 13, collagenase and IL‑6 expression, and increased collagen α‑1 (II) chain (COL2A1) expression in human osteoarthritis chondrocytes. These effects of CH were accompanied by decreased HMGB‑1 expression. Additionally, the expression of MMP13, collagenase, IL‑6 and COL2A1, as well as apoptosis, was significantly reduced by HMGB‑1 siRNA. These results demonstrated that HMGB‑1 is critical for the protective effect of CH on human osteoarthritis chondrocytes, including cell apoptosis and inflammatory factor inhibition, which suggests that CH may have potential therapeutic effect in treating OA by protecting human osteoarthritis chondrocytes via HMGB1 suppression.

Growth factor signalling in osteoarthritis

Osteoarthritis (OA) is one of the most common diseases, affecting more than 10% of populations and thus creating immense socioeconomic burden. The pathological changes of OA involve the entire joint, which is composed of multiple types of tissues and cells, exemplified by cartilage degradation, subchondral bone thickening, osteophyte formation, synovium inflammation and hypertrophy, and ligament degeneration. As joint homeostasis requires a complex network of growth factors to regulate anabolic and catabolic events, the dysregulation of growth factor signalling would have negative impacts on structure and function of multiple joint tissues and eventually lead to the onset and progression of OA. In this review, we will discuss TGF-β, NGF, Hedgehog and Wnt, the four growth factors which have received extensive attention in the field of OA and clinical/translational interrogation about their application in OA therapies.

Role of Forkhead Box O Transcription Factors in Oxidative Stress-Induced Chondrocyte Dysfunction: Possible Therapeutic Target for Osteoarthritis?

Chondrocyte dysfunction occurs during the development of osteoarthritis (OA), typically resulting from a deleterious increase in oxidative stress. Accordingly, strategies for arresting oxidative stress-induced chondrocyte dysfunction may lead to new potential therapeutic targets for OA treatment. Forkhead box O (FoxO) transcription factors have recently been shown to play a protective role in chondrocyte dysfunction through the regulation of inflammation, autophagy, aging, and oxidative stress. They also regulate growth, maturation, and matrix synthesis in chondrocytes. In this review, we discuss the recent progress made in the field of oxidative stress-induced chondrocyte dysfunction. We also discuss the protective role of FoxO transcription factors as potential molecular targets for the treatment of OA. Understanding the function of FoxO transcription factors in the OA pathology may provide new insights that will facilitate the development of next-generation therapies to prevent OA development and to slow OA progression.

Role of Forkhead Box O Transcription Factors in Oxidative Stress-Induced Chondrocyte Dysfunction: Possible Therapeutic Target for Osteoarthritis?

Chondrocyte dysfunction occurs during the development of osteoarthritis (OA), typically resulting from a deleterious increase in oxidative stress. Accordingly, strategies for arresting oxidative stress-induced chondrocyte dysfunction may lead to new potential therapeutic targets for OA treatment. Forkhead box O (FoxO) transcription factors have recently been shown to play a protective role in chondrocyte dysfunction through the regulation of inflammation, autophagy, aging, and oxidative stress. They also regulate growth, maturation, and matrix synthesis in chondrocytes. In this review, we discuss the recent progress made in the field of oxidative stress-induced chondrocyte dysfunction. We also discuss the protective role of FoxO transcription factors as potential molecular targets for the treatment of OA. Understanding the function of FoxO transcription factors in the OA pathology may provide new insights that will facilitate the development of next-generation therapies to prevent OA development and to slow OA progression.

Aberrantly expressed messenger RNAs and long noncoding RNAs in degenerative nucleus pulposus cells co-cultured with adipose-derived mesenchymal stem cells

Background

Stem cell therapy is considered as a promising alternative to treat intervertebral disc degeneration (IDD). Extensive work had been done on identifying and comparing different types of candidate stem cells, both in vivo and in vitro. However, few studies have shed light on degenerative nucleus pulposus cells (NPCs), especially their biological behavior under the influence of exogenous stem cells, specifically the gene expression and regulation pattern. In the present study, we aimed to determine messenger RNAs (mRNAs) and long non-coding RNAs (lncRNAs), which are differentially expressed during the co-culturing process with adipose-derived mesenchymal stem cells (ASCs) and to explore the involved signaling pathways and the regulatory networks.

Methods

We compared degenerative NPCs co-cultured with ASCs with those cultured solely using lncRNA-mRNA microarray analysis. Based on these data, we investigated the significantly regulated signaling pathways based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway database. Moreover, 23 micro RNAs (miRNAs), which were demonstrated to be involved in IDD were chosen; we investigated their theoretic regulatory importance associated with our microarray data.

Results

We found 632 lncRNAs and 1682 mRNAs were differentially expressed out of a total of 40,716 probes. We then confirmed the microarray data by real-time PCR. Furthermore, we demonstrated 197 upregulated, and 373 downregulated Gene Ontology terms and 176 significantly enriched pathways, such as the mitogen-activated protein kinase (MAPK) pathway. Also, a signal-net was constructed to reveal the interplay among differentially expressed genes. Meanwhile, a mRNA-lncRNA co-expression network was constructed for the significantly changed mRNAs and lncRNAs. Also, the competing endogenous RNA (ceRNA) network was built.

Conclusion

Our results present the first comprehensive identification of differentially expressed lncRNAs and mRNAs of degenerative NPCs, altered by co-culturing with ASCs, and outline the gene expression regulation pattern. These may provide valuable information for better understanding of stem cell therapy and potential candidate biomarkers for IDD treatment.

Electronic supplementary material

The online version of this article (10.1186/s13075-018-1677-x) contains supplementary material, which is available to authorized users.

BIO alleviated compressive mechanical force-mediated mandibular cartilage pathological changes through Wnt/β-catenin signaling activation

Osteoarthritis induced by compressive mechanical force is characterized by decreased chondrocyte proliferation and degradation of the ECM. To examine underlying mechanisms of the pathological changes of mandibular cartilage induced by compressive mechanical force, an established animal model was used to examine Wnt signaling activation by glycogen synthase kinase-3 beta (GSK3β) inhibitor 6-Bromoindirubin-3'-oxime (BIO) injection in vivo. Histological changes in mandibular cartilage were assessed via hematoxylin & eosin (HE), masson, and alcian blue staining. Immunohistochemistry and real-time PCR were performed to evaluate activation of the Wnt signaling pathway and chondrocytes proliferation markers. Chondrocytes apoptosis was examined by TUNEL staining. During the compressive mechanical force loading-mediated process, Wnt signaling was largely inhibited, which showed the inhibited expression of β-catenin and the increased expression of GSK-3β. The expression of chondrocytes proliferation markers Ki67, and proliferating cell nuclear antigen (PCNA) also decreased. With BIO injection, the Wnt signaling was restored and the proliferation of mandibular chondrocytes was also increased in the late stage (7 days) of compressive mechanical force loading. Finally, the decreasing mandibular cartilage thickness, the degradation of extracellular matrix, and the erosion of bone trabecula were subsequently restored. Also, the changes of extracellular matrix markers such as collagen II and collagen X, matrix metalloproteases, and inflammatory cytokines were reversed followed by the injection of BIO. In summary, compressive mechanical force decreased endogenously Wnt signaling, leading to impaired proliferation in chondrocytes and degradation in cartilage matrix. Restoration of Wnt signaling largely recovered the proliferation defects and alleviated the pathological changes of mandibular cartilage. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1228-1237, 2018.

Tyrosine kinase Fyn promotes osteoarthritis by activating the β-catenin pathway

OBJECTIVES

To investigate the role of tyrosine kinase Fyn in the development of osteoarthritis (OA) and the underlying mechanisms, and to define whether targeting Fyn could prevent OA in mice.

METHODS

Cartilage samples from normal and aged mice were analysed with proteome-wide screening. Fyn expression was examined with immunofluorescence in human and age-dependent or experimental mouse OA cartilage samples. Experimental OA in Fyn-knockout mice was induced by destabilisation of the medial meniscus. Primary cultured mouse chondrocytes were treated with proinflammatory cytokine interleukin-1β. The inhibitor of Src kinase family, AZD0530 (saracatinib), and inhibitor of Fyn, PP1, were used to treat experimental OA in mice.

RESULTS

Fyn expression was markedly upregulated in human OA cartilage and in cartilage from aged mice and those with post-traumatic OA. Fyn accumulates in articular chondrocytes and interacts directly with and phosphorylates β-catenin at Tyr142, which stabilises β-catenin and promotes its nuclear translocation. The deletion of Fyn effectively delayed the development of post-traumatic and age-dependent OA in mice. Fyn inhibitors AZD0530 and PP1 significantly attenuated OA progression by blocking the β-catenin pathway and reducing the levels of extracellular matrix catabolic enzymes in the articular cartilage.

CONCLUSIONS

Fyn accumulates and activates β-catenin signalling in chondrocytes, accelerating the degradation of the articular cartilage and OA development. Targeting Fyn is a novel and potentially therapeutic approach to the treatment of OA.

Glycogen Synthase Kinase-3β Inhibition Links Mitochondrial Dysfunction, Extracellular Matrix Remodelling and Terminal Differentiation in Chondrocytes

Following inflammatory stimuli, GSK3 inhibition functions as a hub with pleiotropic effects leading to cartilage degradation. However, little is known about the effects triggered by its direct inhibition as well as the effects on mitochondrial pathology, that contributes to osteoarthritis pathogenesis. To this aim we assessed the molecular mechanisms triggered by GSK3β inactivating stimuli on 3-D (micromass) cultures of human articular chondrocytes. Stimuli were delivered either at micromass seeding (long term) or after maturation (short term) to explore “late” effects on terminal differentiation or “early” mitochondrial effects, respectively. GSK3β inhibition significantly enhanced mitochondrial oxidative stress and damage and endochondral ossification based on increased nuclear translocation of Runx-2 and β-catenin, calcium deposition, cell death and enhanced remodelling of the extracellular matrix as demonstrated by the increased collagenolytic activity of supernatants, despite unmodified (MMP-1) or even reduced (MMP-13) collagenase gene/protein expression. Molecular dissection of the underlying mechanisms showed that GSK3β inhibition achieved with pharmacological/silencing strategies impacted on the control of collagenolytic activity, via both decreased inhibition (reduced TIMP-3) and increased activation (increased MMP-10 and MMP-14). To conclude, the inhibition of GSK3β enhances terminal differentiation via concerted effects on ECM and therefore its activity represents a tool to keep articular cartilage homeostasis.

A Qualitative Model of the Differentiation Network in Chondrocyte Maturation: A Holistic View of Chondrocyte Hypertrophy

Differentiation of chondrocytes towards hypertrophy is a natural process whose control is essential in endochondral bone formation. It is additionally thought to play a role in several pathophysiological processes, with osteoarthritis being a prominent example. We perform a dynamic analysis of a qualitative mathematical model of the regulatory network that directs this phenotypic switch to investigate the influence of the individual factors holistically. To estimate the stability of a SOX9 positive state (associated with resting/proliferation chondrocytes) versus a RUNX2 positive one (associated with hypertrophy) we employ two measures. The robustness of the state in canalisation (size of the attractor basin) is assessed by a Monte Carlo analysis and the sensitivity to perturbations is assessed by a perturbational analysis of the attractor. Through qualitative predictions, these measures allow for an in silico screening of the effect of the modelled factors on chondrocyte maintenance and hypertrophy. We show how discrepancies between experimental data and the model’s results can be resolved by evaluating the dynamic plausibility of alternative network topologies. The findings are further supported by a literature study of proposed therapeutic targets in the case of osteoarthritis.

Attenuation of the progression of articular cartilage degeneration by inhibition of TGF-β1 signaling in a mouse model of osteoarthritis

Transforming growth factor beta 1 (TGF-β1) is implicated in osteoarthritis. We therefore studied the role of TGF-β1 signaling in the development of osteoarthritis in a developmental stage-dependent manner. Three different mouse models were investigated. First, the Tgf-β receptor II (Tgfbr2) was specifically removed from the mature cartilage of joints. Tgfbr2-deficient mice were grown to 12 months of age and were then euthanized for collection of knee and temporomandibular joints. Second, Tgfbr2-deficient mice were subjected to destabilization of the medial meniscus (DMM) surgery. Knee joints were then collected from the mice at 8 and 16 weeks after the surgery. Third, wild-type mice were subjected to DMM at the age of 8 weeks. Immediately after the surgery, these mice were treated with the Tgfbr2 inhibitor losartan for 8 weeks and then euthanized for collection of knee joints. All joints were characterized for evidences of articular cartilage degeneration. Initiation or acceleration of articular cartilage degeneration was not observed by the genetic inactivation of Tgfbr2 in the joints at the age of 12 months. In fact, the removal of Tgfbr2 and treatment with losartan both delayed the progression of articular cartilage degeneration induced by DMM compared with control littermates. Therefore, we conclude that inhibition of Tgf-β1 signaling protects adult knee joints in mice against the development of osteoarthritis.

Glycogen synthase kinase-3β inhibition depletes the population of prostate cancer stem/progenitor-like cells and attenuates metastatic growth

Cancer cells with stem or progenitor properties play a pivotal role in the initiation, recurrence and metastatic potential of solid tumors, including those of the human prostate. Cancer stem cells are generally more resistant to conventional therapies thus requiring the characterization of key pathways involved in the formation and/or maintenance of this malignant cellular subpopulation.

To this end, we identified Glycogen Synthase Kinase-3β (GSK-3β) as a crucial kinase for the maintenance of prostate cancer stem/progenitor-like cells and pharmacologic inhibition of GSK-3β dramatically decreased the size of this cellular subpopulation. This was paralleled by impaired clonogenicity, decreased migratory potential and dramatic morphological changes. In line with our in vitro observations, treatment with a GSK-3β inhibitor leads to a complete loss of tumorigenicity and a decrease in metastatic potential in preclinical in vivo models. These observed anti-tumor effects appear to be largely Wnt-independent as simultaneous Wnt inhibition does not reverse the observed antitumor effects of GSK-3β blockage. We found that GSK-3β activity is linked to cytoskeletal protein F-actin and inhibition of GSK-3β leads to disturbance of F-actin polymerization. This may underlie the dramatic effects of GSK-3β inhibition on prostate cancer migration. Furthermore, GSK-3β inhibition led to strongly decreased expression of several integrin types including the cancer stem cell-associated α2β1 integrin. Taken together, our mechanistic observations highlight the importance of GSK-3β activity in prostate cancer stemness and may facilitate the development of novel therapy for advanced prostate cancer.

Physicochemical and biomechanical stimuli in cell-based articular cartilage repair

Articular cartilage is a unique load-bearing connective tissue with a low intrinsic capacity for repair and regeneration. Its avascularity makes it relatively hypoxic and its unique extracellular matrix is enriched with cations, which increases the interstitial fluid osmolarity. Several physicochemical and biomechanical stimuli are reported to influence chondrocyte metabolism and may be utilized for regenerative medical approaches. In this review article, we summarize the most relevant stimuli and describe how ion channels may contribute to cartilage homeostasis, with special emphasis on intracellular signaling pathways. We specifically focus on the role of calcium signaling as an essential mechanotransduction component and highlight the role of phosphatase signaling in this context.

O-Phenanthroline as modulator of the hypoxic and catabolic response in cartilage tissue-engineering models

Hypoxia has been shown to be important for maintaining cartilage homeostasis as well as for inducing chondrogenic differentiation. Ensuring low oxygen levels during in vitro culture is difficult, therefore we assessed the chondro-inductive capabilities of the hypoxia-mimicking agent O-phenanthroline, which is also known as a non-specific matrix metalloproteinase (MMP) inhibitor. We found that O-phenanthroline reduced the expression of MMP3 and MMP13 mRNA levels during chondrogenic differentiation of human chondrocytes (hChs), as well as after TNFα/IL-1β exposure in an explant model. Interestingly, O-phenanthroline significantly inhibited matrix degradation in a TNFα/IL-1β-dependent model of cartilage degeneration when compared to control and natural hypoxia (2.5% O₂ ). O-Phenanthroline had limited ability to improve the chondrogenic differentiation or matrix deposition in the chondrogenic pellet model. Additionally, O-phenanthroline alleviated MMP-induced cartilage degradation without affecting chondrogenesis in the explant culture. The data presented in this study indicate that the inhibitory effect of O-phenanthroline on MMP expression is dominant over the hypoxia-mimicking effect. Copyright © 2014 John Wiley & Sons, Ltd.

Glycogen synthase kinase 3 inhibition stimulates human cartilage destruction and exacerbates murine osteoarthritis

OBJECTIVE

To assess the role of glycogen synthase kinase 3 (GSK-3) as a regulator of cartilage destruction in human tissue and a murine model of osteoarthritis (OA).

METHODS

Surgical destabilization of the medial meniscus (DMM) was performed to induce experimental murine OA, and joint damage was assessed histologically. Bovine nasal and human OA cartilage samples were incubated with interleukin-1 (IL-1) plus oncostatin M (OSM) and GSK-3 inhibitor. Collagen and proteoglycan release was assessed by hydroxyproline measurement and dye binding assay, collagenase activity was assessed by bioassay, and gene expression was analyzed by real-time polymerase chain reaction. Human articular chondrocytes were isolated by enzymatic digestion and cultured prior to gene silencing and immunoblotting of cell lysates and nuclear fractions.

RESULTS

Mice treated with GSK-3 inhibitor exhibited significantly greater cartilage damage compared with sham-operated control mice. GSK-3 inhibition in bovine cartilage dramatically accelerated IL-1 plus OSM-stimulated degradation, concomitant with a profound increase in collagenase activity. GSK-3 inhibitor induced collagen release from human OA cartilage in the presence of IL-1 plus OSM and increased proteoglycan loss. Gene expression profiling of resorbing OA cartilage revealed a marked procatabolic switch in gene expression upon GSK-3 inhibition. This was mirrored in human articular chondrocytes following GSK3 silencing, particularly with the GSK-3β isoform. GSK-3 inhibition or silencing led to enhanced IL-1 plus OSM-stimulated abundance and activity of Jun, and silencing of c-jun ameliorated GSK-3 inhibitor-mediated procatabolic gene expression.

CONCLUSION

GSK-3 is an important regulator of matrix metalloproteinase (MMP)-mediated joint destruction, the inhibition of which by proinflammatory stimuli de-represses catabolic gene expression. Therapeutic strategies that maintain cartilage GSK-3 activity may therefore help curtail aberrant MMP activity during pathologic joint destruction.

Gene expression profiling of peri-implant healing of PLGA-Li+ implants suggests an activated Wnt signaling pathway in vivo

Bone development and regeneration is associated with the Wnt signaling pathway that, according to literature, can be modulated by lithium ions (Li+). The aim of this study was to evaluate the gene expression profile during peri-implant healing of poly(lactic-co-glycolic acid) (PLGA) implants with incorporated Li+, while PLGA without Li+ was used as control, and a special attention was then paid to the Wnt signaling pathway. The implants were inserted in rat tibia for 7 or 28 days and the gene expression profile was investigated using a genome-wide microarray analysis. The results were verified by qPCR and immunohistochemistry. Histomorphometry was used to evaluate the possible effect of Li+ on bone regeneration. The microarray analysis revealed a large number of significantly differentially regulated genes over time within the two implant groups. The Wnt signaling pathway was significantly affected by Li+, with approximately 34% of all Wnt-related markers regulated over time, compared to 22% for non-Li+ containing (control; Ctrl) implants. Functional cluster analysis indicated skeletal system morphogenesis, cartilage development and condensation as related to Li+. The downstream Wnt target gene, FOSL1, and the extracellular protein-encoding gene, ASPN, were significantly upregulated by Li+ compared with Ctrl. The presence of β-catenin, FOSL1 and ASPN positive cells was confirmed around implants of both groups. Interestingly, a significantly reduced bone area was observed over time around both implant groups. The presence of periostin and calcitonin receptor-positive cells was observed at both time points. This study is to the best of the authors' knowledge the first report evaluating the effect of a local release of Li+ from PLGA at the fracture site. The present study shows that during the current time frame and with the present dose of Li+ in PLGA implants, Li+ is not an enhancer of early bone growth, although it affects the Wnt signaling pathway.

Signaling pathways in cartilage repair

In adult healthy cartilage, chondrocytes are in a quiescent phase characterized by a fine balance between anabolic and catabolic activities. In ageing, degenerative joint diseases and traumatic injuries of cartilage, a loss of homeostatic conditions and an up-regulation of catabolic pathways occur. Since cartilage differentiation and maintenance of homeostasis are finely tuned by a complex network of signaling molecules and biophysical factors, shedding light on these mechanisms appears to be extremely relevant for both the identification of pathogenic key factors, as specific therapeutic targets, and the development of biological approaches for cartilage regeneration. This review will focus on the main signaling pathways that can activate cellular and molecular processes, regulating the functional behavior of cartilage in both physiological and pathological conditions. These networks may be relevant in the crosstalk among joint compartments and increased knowledge in this field may lead to the development of more effective strategies for inducing cartilage repair.

GDF5 reduces MMP13 expression in human chondrocytes via DKK1 mediated canonical Wnt signaling inhibition

OBJECTIVE

Growth differentiation factor 5 (GDF5) is important for joint formation and associated with osteoarthritis (OA). Its role for the homeostasis of cartilage extracellular matrix (ECM) is, however, unknown. The canonical Wnt signaling pathway is also implemented in OA and activation of the pathway has detrimental effects on the cartilage ECM. The objective of this study was to investigate the effect of GDF5 stimulation on the Wnt signaling pathway and on the expression of known modulators of cartilage ECM.

DESIGN

Human chondrocytes were cultured in the pellet mass system and stimulated with increasing concentrations of GDF5. Expression of matrix modulating enzymes and canonical Wnt inhibitors dickkopf 1 (DKK1) and frizzled related protein (FRZB) were measured with quantitative PCR (qPCR). Protein levels of matrix metalloprotease 13 (MMP13), DKK1 and β-catenin were measured with enzyme-linked immunosorbent assay (ELISA). Canonical Wnt signaling was stimulated with Wnt3a and small molecule CHIR-99021 and DKK1 was blocked with small molecule WAY-262611.

RESULTS

In this study, we show that GDF5 stimulation of human chondrocytes inhibits expression of the cartilage ECM degrading enzymes MMP13 and ADAMTS4 and stimulates the expression of cartilage anabolic genes ACAN and SOX9. We further show that the stimulation inhibits the canonical Wnt signaling pathway through expression of the canonical Wnt inhibitors DKK1 and FRZB. Finally we show that inhibition of MMP13 expression through GDF5 stimulation is mediated by DKK1.

CONCLUSION

Herein, we provide evidence of a previously unknown link between GDF5 signaling and canonical Wnt signaling that may contribute to the understanding of the molecular mechanisms of OA.

Chondroprotective Activity of Murraya exotica through Inhibiting β -Catenin Signaling Pathway

Osteoarthritis (OA) is a degenerative joint disease that affects millions of people. Currently, there is no effective drug treatment for it. The purpose of this study is to investigate the chondroprotective effects of Murraya exotica (L.) on OA. The rat OA models were duplicated to prepare for separating OA chondrocytes, synovial fluid (SF), and serum containing M. exotica (50 mg/kg, 100 mg/kg, and 200 mg/kg), M. exotica showed the activity of decreasing the contents of TNF-α and IL-1β in SF and the chondrocyte apoptosis in a dose-dependent manner. To investigate the probable mechanism, quantitative real-time polymerase chain reaction (qRT-PCR) and western blotting were used to determine gene expression and protein profiles, respectively. The results reveal that M. exotica can downregulate mRNA and protein expressions of β-catenin and COX-2 and reporter activity significantly. Conclusively, M. exotica exhibits antiapoptotic chondroprotective activity probably through inhibiting β-catenin signaling.

Quantitative proteomics reveals regulatory differences in the chondrocyte secretome from human medial and lateral femoral condyles in osteoarthritic patients

Background

Osteoarthritis (OA) is a destructive joint disease and there are no known biomarkers available for an early diagnosis. To identify potential disease biomarkers and gain further insight into the disease mechanisms of OA we applied quantitative proteomics with SILAC technology on the secretomes from chondrocytes of OA knees, designated as high Mankin (HM) scored secretome. A quantitative comparison was made between the secretomes of the medial and lateral femur condyle chondrocytes in the same knee since the medial femur condyle is usually more affected in OA than the lateral condyle, which was confirmed by Mankin scoring. The medial/lateral comparison was also made on the secretomes from chondrocytes taken from one individual with no clinically apparent joint-disease, designated as low Mankin (LM) scored secretome.

Results

We identified 825 proteins in the HM secretome and 69 of these showed differential expression when comparing the medial and lateral femoral compartment. The LM scored femoral condyle showed early signs of OA in the medial compartment as assessed by Mankin score. We here report the identification and relative quantification of several proteins of interest for the OA disease mechanism e.g. CYTL1, DMD and STAB1 together with putative early disease markers e.g. TIMP1, PPP2CA and B2M.

Conclusions

The present study reveals differences in protein abundance between medial/lateral femur condyles in OA patients. These regulatory differences expand the knowledge regarding OA disease markers and mechanisms.

Cartilage to bone transitions in health and disease

Aberrant redeployment of the 'transient' events responsible for bone development and postnatal longitudinal growth has been reported in some diseases in what is otherwise inherently 'stable' cartilage. Lessons may be learnt from the molecular mechanisms underpinning transient chondrocyte differentiation and function, and their application may better identify disease aetiology. Here, we review the current evidence supporting this possibility. We firstly outline endochondral ossification and the cellular and physiological mechanisms by which it is controlled in the postnatal growth plate. We then compare the biology of these transient cartilaginous structures to the inherently stable articular cartilage. Finally, we highlight specific scenarios in which the redeployment of these embryonic processes may contribute to disease development, with the foresight that deciphering those mechanisms regulating pathological changes and loss of cartilage stability will aid future research into effective disease-modifying therapies.

Small molecule inhibitors of WNT/β-catenin signaling block IL-1β- and TNFα-induced cartilage degradation

Introduction

In this study, we tested the ability of small molecule inhibitors of WNT/β-catenin signaling to block interleukin 1β (IL-1β)- and tumor necrosis factor α (TNFα)-induced cartilage degradation. Proinflammatory cytokines such as IL-1β and TNFα are potent inducers of cartilage degradation by upregulating matrix metalloproteinase (MMP) expression and activity. Because WNT/β-catenin signaling was found to be involved in IL-1β- and TNFα-induced upregulation of MMP activity, we hypothesized that inhibition of WNT/β-catenin signaling might block IL-1β- and TNFα-induced cartilage degradation. We tested the effect of small molecules that block the interaction between β-catenin and TCF/Lef transcription factors on IL-1β- and TNFα-induced cartilage degradation in mouse fetal metatarsals.

Methods

We used mouse fetal metatarsals treated with IL-1β and TNFα as an ex vivo model for cytokine-induced cartilage degradation. Metatarsals were treated with IL-1β and TNFα in combination with the small molecules PKF115-584, PKF118-310 and CGP049090 at different concentrations and then harvested them for histological and gene expression analysis.

Results

We found that IL-1β- and TNFα-induced cartilage degradation in mouse fetal metatarsals was blocked by inhibiting WNT/β-catenin signaling using small molecule PKF115-584 and partially using CGP049090 dose-dependently. In addition, we found that PKF115-584 blocked IL-1β- and TNFα-induced MMP mRNA expression, but did not reverse the inhibitory effect of IL-1β on the expression of cartilage anabolic genes.

Conclusion

In this study, we show that inhibition of WNT/β-catenin signaling by small molecules can effectively prevent IL-1β- and TNFα-induced cartilage degradation by blocking MMP expression and activity. Furthermore, we elucidate the involvement of WNT/β-catenin signaling in IL-1β- and TNFα-induced cartilage degradation.

Rats treated with AZD2858, a GSK3 inhibitor, heal fractures rapidly without endochondral bone formation

Fracture healing is a complex interplay between endochondral and intramembranous bone formation processes. The canonical Wnt/β-catenin pathway enhances new bone formation and may play a role in fracture healing. Glycogen synthase kinase 3β (GSK3β) is a key regulator of β-catenin degradation. In this study, we investigate the effects of AZD2858, an orally bioactive GSK3 inhibitor, on fracture healing. Femoral fractures were produced in rats after the insertion of a femoral nail. The rats were treated with oral administration of AZD2858 at a dose of 30 μmol/kg (20mg/kg) daily for up to 3 weeks, while control animals were administered vehicle. At 4days, and at 1, 2 and 3 weeks, histological analysis was performed, and at the 2 and 3 week time points, we performed peripheral quantitative computed tomography (pQCT), X-rays, and four-point bending tests. Peripheral QCT showed an increase in both mineral density (of 28% at 2 weeks and 38% at 3weeks) and mineral content (of 81% at 2 weeks and 93% at 3 weeks) in the calluses from AZD2858 treated animals as compared to vehicle treated animals. Histological analysis demonstrated that rats treated with GSK3 inhibitor healed their fractures rapidly, but without the pre-formation of cartilage tissue. Furthermore, four-point bending tests of fractured femora from animals treated for 2 and 3 weeks showed an increase in strength in treated animals compared to their vehicle-treated controls. In conclusion, AZD2858, a potent GSK3 inhibitor, has a substantial impact on fracture healing. The fractures healed with a bony callus without an obvious endochondral component, suggesting that AZD2858 drives mesenchymal cells into the osteoblastic pathway. This leads to direct bone repair in an unstable fracture milieu.

Wnt signaling in bone formation and its therapeutic potential for bone diseases

The Wnt signaling pathway plays an important role not only in embryonic development but also in the maintenance and differentiation of the stem cells in adulthood. In particular, Wnt signaling has been shown as an important regulatory pathway in the osteogenic differentiation of mesenchymal stem cells. Induction of the Wnt signaling pathway promotes bone formation while inactivation of the pathway leads to osteopenic states. Our current understanding of Wnt signaling in osteogenesis elucidates the molecular mechanisms of classic osteogenic pathologies. Activating and inactivating aberrations of the canonical Wnt signaling pathway in osteogenesis results in sclerosteosis and osteoporosis respectively. Recent studies have sought to target the Wnt signaling pathway to treat osteogenic disorders. Potential therapeutic approaches attempt to stimulate the Wnt signaling pathway by upregulating the intracellular mediators of the Wnt signaling cascade and inhibiting the endogenous antagonists of the pathway. Antibodies against endogenous antagonists, such as sclerostin and dickkopf-1, have demonstrated promising results in promoting bone formation and fracture healing. Lithium, an inhibitor of glycogen synthase kinase 3β, has also been reported to stimulate osteogenesis by stabilizing β catenin. Although manipulating the Wnt signaling pathway has abundant therapeutic potential, it requires cautious approach due to risks of tumorigenesis. The present review discusses the role of the Wnt signaling pathway in osteogenesis and examines its targeted therapeutic potential.

To Wnt or not to Wnt: the bone and joint health dilemma

The Wnt signalling cascades have essential roles in development, growth and homeostasis of joints and the skeleton. Progress in basic research, particularly relating to our understanding of intracellular signalling cascades and fine regulation of receptor activation in the extracellular space, has provided novel insights into the roles of Wnt signalling in chronic arthritis. Cartilage and bone homeostasis require finely tuned Wnt signalling; both activation and suppression of the Wnt-β-catenin cascade can lead to osteoarthritis in rodent models. Genetic associations with the Wnt antagonist encoded by FRZB and the transcriptional regulator encoded by Dot1l with osteoarthritis further corroborate the essential part played by Wnts in the joint. In rheumatoid arthritis, inhibition of Wnt signalling has a role in the persistence of bone erosions, whereas Wnts have been associated with the ankylosing phenotype in spondyloarthritis. Together, these observations identify the Wnt pathway as an attractive target for therapeutic intervention; however, the complexity of the Wnt signalling cascades and the potential secondary effects of drug interventions targeting them highlight the need for further research and suggest that our understanding of this exciting pathway is still in its infancy.

New findings in osteoarthritis pathogenesis: therapeutic implications

This review focuses on the new perspectives which can provide insight into the crucial pathways that drive cartilage-bone physiopathology. In particular, we discuss the critical signaling and effector molecules that can activate cellular and molecular processes in both cartilage and bone cells and which may be relevant in cross talk among joint compartments: growth factors (bone morphogenetic proteins and transforming growth factor), hypoxia-related factors, cell-matrix interactions [discoidin domain receptor 2 (DDR2) and syndecan 4], signaling molecules [WNT, Hedgehog (Hh)]. With the continuous progression of our knowledge on the molecular pathways involved in cartilage and bone changes in osteoarthritis (OA), an increasing number of potentially effective candidates for OA therapy are already under scrutiny in clinical trials to ascertain their possible safe use in an attempt to identify molecules active in slowing or halting OA progression and reducing joint pain. We then review the principal molecules currently under clinical investigation.

Osteoarthritis year 2012 in review: biology

This review focuses on recent findings in pathobiology of osteoarthritis (OA). The progress in this field will be illustrated based on three questions; 1. What factors maintain or alter the articular chondrocyte phenotype? 2. What is the role of inflammation in OA? 3. Is there a role for aging-related genes in OA? Recent findings make it more and more obvious that OA is not a single tissue disease, but that development and progression of OA is the resulted of an integrated complex of local and systemic factors that contribute to the pathobiology of this widespread disease.