Opposing roles of WNT-5A and WNT-11 in interleukin-1beta regulation of type II collagen expression in articular chondrocytes

Control of articular degeneration by extracellular vesicles from stem/stromal cells as a potential strategy for the treatment of osteoarthritis

Osteoarthritis (OA) is a degenerative joint condition that contributes to years lived with disability. Current therapeutic approaches are limited as there are no disease-modifying interventions able to delay or inhibit the progression of disease. In recent years there has been an increasing interest in the immunomodulatory and regenerative properties of mesenchymal stem/stromal cells (MSCs) to develop new OA therapies. Extracellular vesicles (EVs) mediate many of the biological effects of these cells and may represent an alternative avoiding the limitations of cell-based therapy. There is also a growing interest in EV modifications to enhance their efficacy and applications. Recent preclinical studies have provided strong evidence supporting the potential of MSC EVs for the development of OA treatments. Thus, MSC EVs may regulate chondrocyte functions to avoid cartilage destruction, inhibit abnormal subchondral bone metabolism and synovial tissue alterations, and control pain behavior. EV actions may be mediated by the transfer of their cargo to target cells, with an important role for proteins and non-coding RNAs modulating signaling pathways relevant for OA progression. Nevertheless, additional investigations are needed concerning EV optimization, and standardization of preparation procedures. More research is also required for a better knowledge of possible effects on different OA phenotypes, pharmacokinetics, mechanism of action, long-term effects and safety profile. Furthermore, MSC EVs have a high potential as vehicles for drug delivery or as adjuvant therapy to potentiate or complement the effects of other approaches.

Targeting WNT signalling pathways as new therapeutic strategies for osteoarthritis

Osteoarthritis (OA) is a highly prevalent chronic joint disease and the leading cause of disability. Currently, no drugs are available to control joint damage or ease the associated pain. The wingless-type (WNT) signalling pathway is vital in OA progression. Excessive activation of the WNT signalling pathway is pertinent to OA progression and severity. Therefore, agonists and antagonists of the WNT pathway are considered potential drug candidates for OA treatment. For example, SM04690, a novel small molecule inhibitor of WNT signalling, has demonstrated its potential in a recent phase III clinical trial as a disease-modifying osteoarthritis drug (DMOAD). Therefore, targeting the WNT signalling pathway may be a distinctive approach to developing particular agents helpful in treating OA. This review aims to update the most recent progress in OA drug development by targeting the WNT pathway. In this, we introduce WNT pathways and their crosstalk with other signalling pathways in OA development and highlight the role of the WNT signalling pathway as a key regulator in OA development. Several articles have reviewed the Wnt pathway from different aspects. This candid review provides an introduction to WNT pathways and their crosstalk with other signalling pathways in OA development, highlighting the role of the WNT signalling pathway as a key regulator in OA development with the latest research. Particularly, we emphasise the state-of-the-art in targeting the WNT pathway as a promising therapeutic approach for OA and challenges in their development and the nanocarrier-based delivery of WNT modulators for treating OA.

Characterization and potential of periosteum-derived cells: an overview

As a thin fibrous layer covering the bone surface, the periosteum plays a significant role in bone physiology during growth, development and remodeling. Over the past several decades, the periosteum has received considerable scientific attention as a source of mesenchymal stem cells (MSCs). Periosteum-derived cells (PDCs) have emerged as a promising strategy for tissue engineering due to their chondrogenic, osteogenic and adipogenic differentiation capacities. Starting from the history of PDCs, the present review provides an overview of their characterization and the procedures used for their isolation. This study also summarizes the chondrogenic, osteogenic, and adipogenic abilities of PDCs, serving as a reference about their potential therapeutic applications in various clinical scenarios, with particular emphasis on the comparison with other common sources of MSCs. As techniques continue to develop, a comprehensive analysis of the characterization and regulation of PDCs can be conducted, further demonstrating their role in tissue engineering. PDCs present promising potentials in terms of their osteogenic, chondrogenic, and adipogenic capacities. Further studies should focus on exploring their utility under multiple clinical scenarios to confirm their comparative benefit over other commonly used sources of MSCs.

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.

The Wnt signaling cascade in the pathogenesis of osteoarthritis and related promising treatment strategies

Osteoarthritis (OA) is the most prevalent joint disease, characterized by the degradation of articular cartilage, synovial inflammation, and changes in periarticular and subchondral bone. Recent studies have reported that Wnt signaling cascades play an important role in the development, growth, and homeostasis of joints. The Wnt signaling cascade should be tightly regulated to maintain the homeostasis of cartilage in either the over-activation or the suppression of Wnt/β-catenin, as this could lead to OA. This review summarizes the role and mechanism of canonical Wnt cascade and noncanonical Wnt cascade experiments in vivo and in vitro. The Wnt cascade is controlled by several agonists and antagonists in the extracellular medium and the cytoplasm. These antagonists and agonists serve as key molecules in drug intervention into the Wnt pathway and may provide potential approaches for the treatment of OA. However, the complexity of the Wnt signaling cascade and the pharmaceutical effects on its mechanism are still not fully understood, which forces us to conduct further research and develop efficient therapeutic approaches to treat OA.

Nanosilicate-Reinforced Silk Fibroin Hydrogel for Endogenous Regeneration of Both Cartilage and Subchondral Bone

Osteochondral defects are characterized by injuries to both cartilage and subchondral bone, which is a result of trauma, inflammation, or inappropriate loading. Due to the unique biological properties of subchondral bone and cartilage, developing a tissue engineering scaffold that can promote dual-lineage regeneration of cartilage and bone simultaneously remains a great challenge. In this study, a microporous nanosilicate-reinforced enzymatically crosslinked silk fibroin (SF) hydrogel is fabricated by introducing montmorillonite (MMT) nanoparticles via intercalation chemistry. In vitro studies show that SF-MMT nanocomposite hydrogel has improved mechanical properties and hydrophilicity, as well as the bioactivities to promote the osteogenic differentiation of bone marrow mesenchymal stem cells and maintain chondrocyte phenotype compared with SF hydrogel. Global proteomic analysis verifies the dual-lineage bioactivities of SF-MMT nanocomposite hydrogel, which are probably regulated by multiple signaling pathways. Furthermore, it is observed that the biophysical interaction of cells and SF-MMT nanocomposite hydrogel is partially mediated by clathrin-mediated endocytosis and its downstream processes. In vivo, the SF-MMT nanocomposite hydrogel effectively promotes osteochondral regeneration as evidenced by macroscopic, micro-CT, and histological evaluation. In conclusion, a functionalized SF-MMT nanocomposite hydrogel is developed with dual-lineage bioactivity for osteochondral regeneration, indicating its potential in osteochondral tissue engineering.

Reversing the miRNA -5p/-3p stoichiometry reveals physiological roles and targets of miR-140 miRNAs

The chondrocyte-specific miR-140 miRNAs are necessary for normal endochondral bone growth in mice. miR-140 deficiency causes dwarfism and craniofacial deformity. However, the physiologically important targets of miR-140 miRNAs are still unclear. The miR-140 gene (Mir140) encodes three chondrocyte-specific microRNAs, miR-140-5p, derived from the 5' strand of primary miR-140, and miR140-3p.1 and -3p.2, derived from the 3' strand of primary miR-140. miR-140-3p miRNAs are 10 times more abundant than miR-140-5p likely due to the nonpreferential loading of miR-140-5p to Argonaute proteins. To differentiate the role of miR-140-5p and -3p miRNAs in endochondral bone development, two distinct mouse models, miR140-C > T, in which the first nucleotide of miR-140-5p was altered from cytosine to uridine, and miR140-CG, where the first two nucleotides of miR-140-3p were changed to cytosine and guanine, were created. These changes are expected to alter Argonaute protein loading preference of -5p and -3p to increase -5p loading and decrease -3p loading without changing the function of miR140-5p. These models presented a mild delay in epiphyseal development with delayed chondrocyte maturation. Using RNA-sequencing analysis of the two models, direct targets of miR140-5p, including Wnt11, were identified. Disruption of the predicted miR140-5p binding site in the 3' untranslated region of Wnt11 was shown to increase Wnt11 mRNA expression and caused a modest acceleration of epiphyseal development. These results show that the relative abundance of miRNA-5p and -3p can be altered by changing the first nucleotide of miRNAs in vivo, and this method can be useful to identify physiologically important miRNA targets.

Lef1 ablation alleviates cartilage mineralization following posttraumatic osteoarthritis induction

Cartilage mineralization is imperative in various processes such as skeletal growth and fracture repair. However, this process may also be pathological, as in the case of the degenerative joint disease, osteoarthritis (OA). Using a posttraumatic OA model (PTOA), we find that cartilage-specific Sirt1 genetic nulls caused severe synovitis and mineralization of the lateral joint compartment, due to augmented Lef1 gene expression. Conversely, cartilage-specific Lef1 nulls exhibited impaired synovitis and mineralization of the lateral joint, accompanied by a reduction of local pain. Consistently, transcriptomic profiles of Lef1-ablated chondrocytes exhibited enhanced anabolism, yet impaired pathways related to calcification and inflammation. Accordingly, cartilage mineralization of the lateral joint compartment relies on amplified inflammatory pathways, contributing to articular damage following PTOA.

Cartilage mineralization is a tightly controlled process, imperative for skeletal growth and fracture repair. However, in osteoarthritis (OA), cartilage mineralization may impact the joint range of motion, inflict pain, and increase chances for joint effusion. Here we attempt to understand the link between inflammation and cartilage mineralization by targeting Sirtuin 1 (SIRT1) and lymphoid enhancer binding factor 1 (LEF1), both reported to have contrasting effects on cartilage. We find that inflammatory-dependent cleavage of SIRT1 or its cartilage-specific genetic ablation, directly enhanced LEF1 expression accompanied by a catabolic response. Applying a posttraumatic OA (PTOA) model to cartilage-specific Sirt1 nulls displayed severe OA, which was accompanied by synovitis, meniscal mineralization, and osteophyte formation of the lateral joint compartment. Alternatively, cartilage-specific Lef1 nulls presented reduced lateral mineralization, OA severity, and local pain. Differential gene expression analysis revealed that Lef1 ablation reduced nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and Toll-like receptor (Tlr) pathways, while enhancing SRY-Box transcription factor 9 (Sox9) and cartilaginous extracellular matrix genes. The results support a link between inflammation and Lef1-dependent cartilage mineralization, mediated by the inactivation of Sirt1. By ablating Lef1 in a PTOA model, the structural and pain-related phenotypes of OA were reduced, in part, by preventing cartilage mineralization of the lateral joint compartment, partially manifested by meniscal tissue mineralization. Overall, these data provide a molecular axis to link between inflammation and cartilage in a PTOA model.

Osteogenic and Chondrogenic Potential of Periosteum-Derived Mesenchymal Stromal Cells: Do They Hold the Key to the Future?

The periosteum, with its outer fibrous and inner cambium layer, lies in a dynamic environment with a niche of pluripotent stem cells for their reparative needs. The inner cambium layer is rich in mesenchymal progenitors, osteogenic progenitors, osteoblasts, and fibroblasts in a scant collagen matrix environment. Their role in union and remodeling of fracture is well known. However, the periosteum as a source of mesenchymal stem cells has not been explored in detail. Moreover, with the continuous expansion of techniques, newer insights have been acquired into the roles and regulation of these periosteal cells. From a therapeutic standpoint, the periosteum as a source of tissue engineering has gained much attraction. Apart from its role in bone repair, analysis of the bone-forming potential of periosteum-derived stem cells is lacking. Hence, this article elucidates the role of the periosteum as a potential source of mesenchymal stem cells along with their capacity for osteogenic and chondrogenic differentiation for therapeutic application in the future.

The Effect of Wnt Family Member 5a Gene Silencing on the Proliferation of Achondroplasia Using a DNAzymes-CoOOH Nanocomposite

Achondroplasia is a kind of congenital dysplasia due to the defect of endochondral ossification. Achondroplasia is considered to be a protein folding disease leading to endoplasmic reticulum stress. Endoplasmic reticulum stress may lead to disease by affecting the function and survival state of chondrocytes, but the specific mechanism requires further study. In this study, bioinformatics methods, online database mining, screening of differentially expressed genes for pathway enrichment, and interaction analysis were conducted to detect the Wnt family member 5a (Wnt5a) gene. Additionally, we designed a novel DNAzymes-based nanocomposite that can simultaneously silence Wnt5a genes in chondrocytes. The nanocomposite was composed of amino-functionalized cobalt oxyhydroxide nanoflakes modified by DNAzymes that target the Wnt5a gene. Further, we conducted in vitro experiments to verify that Wnt5a can mediate the mitogen-activated protein kinase signaling pathway through the endoplasmic reticulum stress pathway to affect the proliferation of chondrocytes.

Molecular Mechanisms of Chondrocyte Proliferation and Differentiation

Cartilage is a kind of connective tissue that buffers pressure and is essential to protect joint movement. It is difficult to self-recover once cartilage is damaged due to the lack of blood vessels, lymph, and nerve tissues. Repair of cartilage injury is mainly achieved by stimulating chondrocyte proliferation and extracellular matrix (ECM) synthesis. Cartilage homeostasis involves the regulation of multiple growth factors and the transduction of cellular signals. It is a very complicated process that has not been elucidated in detail. In this review, we summarized a variety of signaling molecules related to chondrocytes function. Especially, we described the correlation between chondrocyte-specific regulatory factors and cell signaling molecules. It has potential significance for guiding the treatment of cartilage injury.

Promising targets for therapy of osteoarthritis: a review on the Wnt and TGF-β signalling pathways

Osteoarthritis (OA) is the most common chronic joint disorder worldwide, with a high personal burden for the patients and an important socio-economic impact. Current therapies are largely limited to pain management and rehabilitation and exercise strategies. For advanced cases, joint replacement surgery may be the only option. Hence, there is an enormous need for the development of effective and safe disease-modifying anti-OA drugs. A strong focus in OA research has been on the identification and role of molecular signalling pathways that contribute to the balance between anabolism and catabolism in the articular cartilage. In this context, most insights have been gained in understanding the roles of the transforming growth factor-beta (TGF-β) and the Wingless-type (Wnt) signalling cascades. The emerging picture demonstrates a high degree of complexity with context-dependent events. TGF-β appears to protect cartilage under healthy conditions, but shifts in its receptor use and subsequent downstream signalling may be deleterious in aged individuals or in damaged cartilage. Likewise, low levels of Wnt activity appear important to sustain chondrocyte viability but excessive activation is associated with progressive joint damage. Emerging clinical data suggest some potential for the use of sprifermin, a recombinant forms of fibroblast growth factor 18, a distant TGF-β superfamily member, and for lorecivivint, a Wnt pathway modulator.

Casein kinase 1 epsilon facilitates cartilage destruction in osteoarthritis through JNK pathway

Osteoarthritis (OA) is a high-morbidity skeletal disease worldwide and the exact mechanisms underlying OA pathogenesis are not fully understood. Casein kinase 1 epsilon (CK1ε) is a serine/threonine protein kinase, but its relationship with OA is still unknown. We demonstrated that CK1ε was upregulated in articular cartilage of human patients with OA and mice with experimentally induced OA. Activity of CK1ε, demonstrated by analysis of phosphorylated substrates, was significantly elevated in interleukin (IL)-1β-induced OA-mimicking chondrocytes. CK1ε inhibitor or CK1ε short hairpin RNA (shRNA) partially blocked matrix metalloproteinase (MMP) expression by primary chondrocytes induced by IL-1β, and also inhibited cartilage destruction in knee joints of experimental OA model mice. Conversely, overexpression of CK1ε promoted chondrocyte catabolism. Previous studies indicated that CK1ε was involved in canonical Wnt/β-catenin signaling and noncanonical Wnt/c-Jun N-terminal kinase (JNK) signaling pathway. Interestingly, the activity of JNK but not β-catenin decreased after CK1ε knockdown in IL-1β-treated chondrocytes in vitro, and JNK inhibition reduced MMP expression in chondrocytes overexpressing CK1ε, which illustrated that CK1ε-mediated OA was based on JNK pathway. In conclusion, our results demonstrate that CK1ε promotes OA development, and inhibition of CK1ε could be a potential strategy for OA treatment in the future.

Genome-wide analysis of DNA methylation profile identifies differentially methylated loci associated with human intervertebral disc degeneration

BACKGROUND

Environmental and endogenous factors under genetic predisposition are considered to initiate the human intervertebral disc (IVD) degeneration. DNA methylation is an essential mechanism to ensure cell-specific gene expression for normal development and tissue stability. Aberrant epigenetic alterations play a pivotal role in several diseases, including osteoarthritis. However, epigenetic alternations, including DNA methylation, in IVD degeneration have not been evaluated. The purpose of this study was to comprehensively compare the genome-wide DNA methylation profiles of human IVD tissues, specifically nucleus pulpous (NP) tissues, with early and advanced stages of disc degeneration.

METHODS

Human NP tissues were used in this study. The samples were divided into two groups: early stage degeneration (n = 8, Pfirrmann's MRI grade: I-III) and advanced stage degeneration (n = 8, grade: IV). Genomic DNA was processed for genome-wide DNA methylation profiling using the Infinium MethylationEPIC BeadChip array. Extraction of raw methylation data, clustering and scatter plot of each group values of each sample were performed using a methylation module in GenomeStudio software. The identification of differentially methylated loci (DMLs) and the Gene Ontology (GO) analysis were performed using R software with the ChAMP package.

RESULTS

Unsupervised hierarchical clustering revealed that early and advanced stage degenerated IVD samples segregated into two main clusters by their DNA methylome. A total of 220 DMLs were identified between early and advanced disc degeneration stages. Among these, four loci were hypomethylated and 216 loci were hypermethylated in the advanced disc degeneration stage. The GO enrichment analysis of genes containing DMLs identified two significant GO terms for biological processes, hemophilic cell adhesion and cell-cell adhesion.

CONCLUSIONS

We conducted a genome-wide DNA methylation profile comparative study and observed significant differences in DNA methylation profiles between early and advanced stages of human IVD degeneration. These results implicate DNA methylation in the process of human IVD degeneration.

Wnt signaling: a promising target for osteoarthritis therapy

Osteoarthritis (OA) is the most common joint disease worldwide and a leading cause of disability. Characterized by degradation of articular cartilage, synovial inflammation, and changes in periarticular and subchondral bone, OA can negatively impact an individual's physical and mental well-being. Recent studies have reported several critical signaling pathways as key regulators and activators of cellular and molecular processes during OA development. Wnt signaling is one such pathway whose signaling molecules and regulators were shown to be abnormally activated or suppressed. As such, agonists and antagonists of those molecules are potential candidates for OA treatment. Notably, a recent phase I clinical trial (NCT02095548) demonstrated the potential of SM04690, a small-molecule inhibitor of the Wnt signaling pathway, as a disease-modifying oseoarthritis drug (DMOAD). This review summarizes the role and mechanism of Wnt signaling and related molecules in regulating OA progression, with a view to accelerating the translation of such evidence into the development of strategies for OA treatment, particularly with respect to potential applications of molecules targeting the Wnt signaling pathway.

Interleukin-1β signaling in osteoarthritis - chondrocytes in focus

Osteoarthritis (OA) can be regarded as a chronic, painful and degenerative disease that affects all tissues of a joint and one of the major endpoints being loss of articular cartilage. In most cases, OA is associated with a variable degree of synovial inflammation. A variety of different cell types including chondrocytes, synovial fibroblasts, adipocytes, osteoblasts and osteoclasts as well as stem and immune cells are involved in catabolic and inflammatory processes but also in attempts to counteract the cartilage loss. At the molecular level, these changes are regulated by a complex network of proteolytic enzymes, chemokines and cytokines (for review: [1]). Here, interleukin-1 signaling (IL-1) plays a central role and its effects on the different cell types involved in OA are discussed in this review with a special focus on the chondrocyte.

Exosomes derived from miR-92a-3p-overexpressing human mesenchymal stem cells enhance chondrogenesis and suppress cartilage degradation via targeting WNT5A

Background

WNT5A is known to be involved in the pathogenesis of osteoarthritis. This study investigated the molecular mechanism of exosomal miR-92a-3p and WNT5A in chondrogenesis and cartilage degeneration.

Methods

Exosomal miR-92a-3p expression was assessed in vitro in a human mesenchymal stem cell (MSC) model of chondrogenesis and in normal and OA primary human chondrocytes (PHCs). MSCs and PHCs were treated with exosomes derived from MSC-miR-92a-3p (MSC-miR-92a-3p-Exos) or its antisense inhibitor (MSC-anti-miR-92a-3p-Exos), respectively. Small interfering RNAs (siRNAs) and luciferase reporter assay were used to reveal the molecular role of exosomal miR-92a-3p and WNT5A in chondrogenesis. The protective effect of exosomes in vivo was measured using Safranin-O and Fast Green staining and immunohistochemical staining.

Results

Exosomal miR-92a-3p expression was elevated in the MSC chondrogenic exosome, while it was significantly reduced in the OA chondrocyte-secreted exosome compared with normal cartilage. Treatment with MSC-miR-92a-3p-Exos promoted cartilage proliferation and matrix genes expression in MSCs and PHCs, respectively. In contrast, treatment with MSC-anti-miR-92a-3p-Exos repressed chondrogenic differentiation and reduced cartilage matrix synthesis by enhancing the expression of WNT5A. Luciferase reporter assay demonstrated that miR-92a-3p suppressed the activity of a reporter construct containing the 3’-UTR and inhibited WNT5A expression in both MSCs and PHCs. MSC-miR-92a-3p-Exos inhibit cartilage degradation in the OA mice model.

Conclusions

Our results suggest that exosomal miR-92a-3p regulates cartilage development and homeostasis by directly targeting WNT5A. This indicates that exosomal miR-92a-3p may act as a Wnt inhibitor and exhibits potential as a disease-modifying osteoarthritis drug.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-1004-0) contains supplementary material, which is available to authorized users.

Transcriptome analyses reveal molecular mechanisms that regulate endochondral ossification in amphibian Bufo gargarizans during metamorphosis

BACKGROUND

A developmental transition from aquatic to terrestrial existence is one of the most important events in the evolution of terrestrial vertebrates. Amphibian metamorphosis is a classic model to study this transition. The development of the vertebrate skeleton can reflect its evolutionary history. Endochondral ossification serves a vital role in skeletal development. Thus, we sought to unravel molecular mechanisms that regulate endochondral ossification during Bufo gargarizans metamorphosis.

METHODS

The alizarin red-alcian blue double staining method was used to visualize the skeletal development of B. gargarizans during metamorphosis. RNA sequencing (RNA-seq) was used to explore the transcriptome of B. gargarizans in four key developmental stages during metamorphosis. Real-time quantitative PCR (RT-qPCR) was used to validate the expression patterns of endochondral ossification related genes.

RESULTS

Endochondral ossification increased gradually in skeletal system of B. gargarizans during metamorphosis. A total of 137,264 unigenes were assembled and 44,035 unigenes were annotated. 10,352 differentially expressed genes (DEGs) were further extracted among four key developmental stages. In addition, 28 endochondral ossification related genes were found by searching for DEG libraries in B. gargarizans. Of the 28 genes, 10 genes were validated using RT-qPCR.

CONCLUSIONS

The exquisite coordination of the 28 genes is essential for regulation of endochondral ossification during B. gargarizans metamorphosis.

GENERAL SIGNIFICANCE

The present study will not only provide an invaluable genomic resource and background for further research of endochondral ossification in amphibians but will also aid in enhancing our understanding of the evolution of terrestrial vertebrates.

Interleukin-1 beta promotes neuronal differentiation through the Wnt5a/RhoA/JNK pathway in cortical neural precursor cells

Pro-inflammatory cytokine interleukin-1 beta (IL-1β) is a key mediator of inflammation and stress in the central nervous system (CNS), and is highly expressed in the developing brain. In this study, we investigated the possible role of IL-1β in neuronal differentiation of cortical neural precursor cells (NPCs). We showed that stimulation with IL-1β increased expression levels of neurotrophin-3 (NT3) and neurogenin 1 (Ngn1) and promoted neurite outgrowth. We also found that IL-1β increased mRNA and protein levels of Wnt5a. Knockdown of Wnt5a by transfection with Wnt5a siRNA inhibited IL-1β-induced neuronal differentiation. Moreover, IL-1β-induced Wnt5a expression was regulated by nuclear factor kappa B (NF-κB) activation, which is involved in IL-1β-mediated neuronal differentiation. To examine the role of Wnt5a in neuronal differentiation of NPCs, we exogenously added Wnt5a. We found that exogenous Wnt5a promotes neuronal differentiation, and activates the RhoA/Rho-associated kinase (ROCK)/c-jun N-terminal kinase (JNK) pathway. In addition, Wnt5a-induced neuronal differentiation was blocked by RhoA siRNA, as well as by a specific Rho-kinase inhibitor (Y27632) or a SAPK/JNK inhibitor (SP600125). Furthermore, treatment with RhoA siRNA, Y27632, or SP600125 suppressed the IL-1β-induced neuronal differentiation. Therefore, these results suggest that the sequential Wnt5a/RhoA/ROCK/JNK pathway is involved in IL-1β-induced neuronal differentiation of NPCs.

Wnt5a suppresses inflammation-driven intervertebral disc degeneration via a TNF-α/NF-κB-Wnt5a negative-feedback loop

OBJECTIVE

This study was to investigate the molecular role of Wnt5a on inflammation-driven intervertebral disc degeneration (IVDD).

METHODS

The expression of Wnt5a was analyzed in human nucleus pulposus (NP) tissues with immunohistochemical staining. The effects of Wnt5a on matrix production were assessed by RT-qPCR and western blotting. Small interfering RNAs (siRNAs), promoter deletion assay, and promoter binding site mutant were used to reveal the molecular role of Wnt5a in TNF-α-induced matrix metalloproteinase (MMP) expression. The regulatory effects of TNF-α on Wnt5a were investigated with pharmachemical inhibitors and siRNA experiment.

RESULTS

The expression of Wnt5a was elevated in moderately degenerated human NP tissue with similar expression pattern of TNF-α. In NP cells, Wnt5a significantly increased aggrecan and collagen II expression. Inhibition of JNK or interfering Sox9 gene expression significantly suppressed Wnt5a-induced matrix production. AP-1(JunB) binding sites were located in Sox9 promoter and mutation of these sites sabotaged Wnt5a-induced Sox9 up-regulation and subsequent matrix genes expression. Notably, Wnt5a, which was induced by TNF-α, on the other way round suppressed TNF-α-NF-κB (p65) signaling and subsequent MMPs expression. In vivo studies with MR imaging confirmed the protective role of Wnt5a in IVDD.

CONCLUSIONS

Wnt5a, which can be induced by TNF-α, increased matrix production in a Sox9-dependent manner through the activation of JNK-AP1 (JunB) signaling, and antagonized TNF-α-induced up-regulation of MMPs through the inhibition of NF-κB signaling. It indicates that Wnt5a suppresses IVDD through a TNF-α/NF-κB-Wnt5a negative-feedback loop.

Non-canonical Wnt induces chondrocyte de-differentiation through Frizzled 6 and DVL-2/B-raf/CaMKIIα/syndecan 4 axis

Dysregulation of Wnt signaling has been implicated in developmental defects and in the pathogenesis of many diseases such as osteoarthritis; however, the underlying mechanisms are poorly understood. Here, we report that non-canonical Wnt signaling induced loss of chondrocyte phenotype through activation of Fz-6/DVL-2/SYND4/CaMKIIα/B-raf/ERK1/2 cascade. We show that in response to Wnt-3a, Frizzled 6 (Fz-6) triggers the docking of CaMKIIα to syndecan 4 (SYND4) and that of B-raf to DVL-2, leading to the phosphorylation of B-raf by CaMKIIα and activation of extracellular signal-regulated kinase 1 and 2 (ERK1/2) signaling, which leads to chondrocyte de-differentiation. We demonstrate that CaMKIIα associates and phosphorylates B-raf in vitro and in vivo. Our study reveals the mechanism by which non-canonical Wnt activates ERK1/2 signaling that induces loss of chondrocyte phenotype, and demonstrates a direct functional relationship between CaMKIIα and B-raf during chondrocyte de-differentiation. The identification of Fz-6, SYND4, and B-raf as novel physiological regulators of chondrocyte phenotype may provide new potential anti-osteoarthritic targets.

Fibroblast Growth Factor Ligand Dependent Proliferation and Chondrogenic Differentiation of Synovium-Derived Stem Cells and Concomitant Adaptation of Wnt/Mitogen-Activated Protein Kinase Signals

Cell expansion techniques commonly utilize exogenous factors to increase cell proliferation and create a larger cell population for use in cell-based therapies. One strategy for cartilage regenerative therapies is autologous stem cell expansion and fibroblast growth factor (FGF) supplementation during cell expansion, particularly FGF-2. However, it is unknown whether FGF-10, another FGF implicated in limb and skeletal development, can elicit the same rejuvenation responses in terms of proliferation and differentiation of human synovium-derived stem cells (SDSCs). In this study, we expanded SDSCs in either FGF-2 or FGF-10 for 7 days; a control group had no treatment. FGF-2 and FGF-10 supplementation was also exclusively tested during the differentiation phase. Expanded SDSCs were evaluated for their ability to successfully engage in chondrogenic and osteogenic differentiation. We found that FGF-2 supplementation during proliferation, but not differentiation, was able to increase glycosaminoglycan deposition, pellet size, and chondrogenic gene expression following chondrogenic induction, as well as increased calcium deposition, alkaline phosphatase activity, and expression of vital osteogenic differentiation genes following osteogenic induction. FGF-10 did not elicit a similar preconditioning effect. We also observed changes of both Wnt signals and mitogen-activated protein kinase expression during SDSC chondrogenesis, which occurred in a manner dependent upon the supplementation phase of FGF-2 administration. These results indicated that FGF-2, but not FGF-10, may be supplemented during stem cell expansion to prime cells for successful chondrogenesis and osteogenesis.

Emerging potential of gene silencing approaches targeting anti-chondrogenic factors for cell-based cartilage repair

The field of cartilage repair has exponentially been growing over the past decade. Here, we discuss the possibility to achieve satisfactory regeneration of articular cartilage by means of human mesenchymal stem cells (hMSCs) depleted of anti-chondrogenic factors and implanted in the site of injury. Different types of molecules including transcription factors, transcriptional co-regulators, secreted proteins, and microRNAs have recently been identified as negative modulators of chondroprogenitor differentiation and chondrocyte function. We review the current knowledge about these molecules as potential targets for gene knockdown strategies using RNA interference (RNAi) tools that allow the specific suppression of gene function. The critical issues regarding the optimization of the gene silencing approach as well as the delivery strategies are discussed. We anticipate that further development of these techniques will lead to the generation of implantable hMSCs with enhanced potential to regenerate articular cartilage damaged by injury, disease, or aging.

Wnt5a induces catabolic signaling and matrix metalloproteinase production in human articular chondrocytes

OBJECTIVE

Aberrant Wnt signaling may contribute to osteoarthritis (OA) but the Wnt family members involved have not been fully identified. The purpose of this study was to investigate the role of Wnt5a as a potential mediator of cartilage destruction in OA.

DESIGN

Immunohistochemistry to detect Wnt5a was performed using normal and OA human articular cartilage. Cultured normal human chondrocytes were treated with fibronectin fragments (FN-f) as a catabolic stimulus or recombinant Wnt5a protein with or without pretreatment using a panel of signaling inhibitors. Expression of Wnt5a, anabolic genes and catabolic genes were determined by quantitative real-time PCR. Production of Wnt5a protein and matrix metalloproteinases (MMPs) as well as activation of signaling proteins were analyzed by immunoblotting.

RESULTS

Wnt5a was present in human articular cartilage with OA changes and its expression and secretion were increased in FN-f stimulated chondrocytes. FN-f stimulated Wnt5a production through the c-Jun N-terminal kinase (JNK) and extracellular signal-related kinase (ERK) pathways. Wnt5a reduced aggrecan gene expression after 48 h of treatment. Wnt5a seemed to promote MMP1, -3, and -13 expression as well as MMP1 and MMP13 protein production in normal human chondrocytes. Wnt5a inhibitor peptides did not affect FN-f induced MMP production. Wnt5a activated β-catenin independent signaling including calmodulin-dependent protein kinase II (CaMKII), JNK, p38, ERK1/2, p65 and Akt. Inhibition of JNK, p38, ERK, PI-3 kinase and CaMKII by specific signaling inhibitors suppressed Wnt5a mediated MMP1 and MMP13 production.

CONCLUSIONS

Wnt5a is present in human OA cartilage and can promote chondrocyte catabolic activity through non-canonical Wnt signaling, which suggests a potential role in OA.

The secreted protein WNT5A regulates condylar chondrocyte proliferation, hypertrophy and migration

OBJECTIVE

Our previous study showed that WNT5A, a member of the noncanonical WNT pathway, is involved in interleukin-1beta induced matrix metalloproteinase expression in temporomandibular joint (TMJ) condylar chondrocytes. The purpose of this study is to further explore the roles of WNT5A in cartilage biology of the TMJ.

METHODS

An early TMJ osteoarthritis-like rat model was constructed by a mechanical method (steady mouth-opening). The gene and protein levels of WNT5A during the condylar cartilage changes were measured. Effects of WNT5A on chondrocyte proliferation, hypertrophy and migration were analyzed after WNT5A gain or loss of function in vitro. A c-Jun N-terminal kinase (JNK) inhibitor SP600125 was used to evaluate the involvement of JNK pathway in these effects of WNT5A. The expression and transcription activity of cell cycle regulators c-MYC and Cyclin D1 were examined to determine the mechanism behind WNT5A regulation of chondrocyte proliferation.

RESULTS

WNT5A was significantly upregulated in the condylar cartilage of rats in the early TMJ osteoarthritis-like model. Activating WNT5A facilitated condylar chondrocyte proliferation, hypertrophy and migration. Conversely, inhibiting WNT5A activity in chondrocytes decreased their proliferation, hypertrophy and migration. Blockage of the JNK pathway by its inhibitor, SP600125, impaired these effects of WNT5A on chondrocytes. WNT5A regulated both the expression and transcriptional activity of c-MYC and Cyclin D1 in chondrocytes, both of which were upregulated in condylar cartilage of the rat early TMJ osteoarthritis.

CONCLUSION

WNT5A regulates condylar chondrocyte proliferation, hypertrophy and migration. These findings provide new insights into the role of WNT5A signaling in TMJ cartilage biology and its potential in future therapy for TMJ degenerative diseases.

The Signaling Pathways Involved in Chondrocyte Differentiation and Hypertrophic Differentiation

Chondrocytes communicate with each other mainly via diffusible signals rather than direct cell-to-cell contact. The chondrogenic differentiation of mesenchymal stem cells (MSCs) is well regulated by the interactions of varieties of growth factors, cytokines, and signaling molecules. A number of critical signaling molecules have been identified to regulate the differentiation of chondrocyte from mesenchymal progenitor cells to their terminal maturation of hypertrophic chondrocytes, including bone morphogenetic proteins (BMPs), SRY-related high-mobility group-box gene 9 (Sox9), parathyroid hormone-related peptide (PTHrP), Indian hedgehog (Ihh), fibroblast growth factor receptor 3 (FGFR3), and β-catenin. Except for these molecules, other factors such as adenosine, O₂ tension, and reactive oxygen species (ROS) also have a vital role in cartilage formation and chondrocyte maturation. Here, we outlined the complex transcriptional network and the function of key factors in this network that determine and regulate the genetic program of chondrogenesis and chondrocyte differentiation.

Environmental preconditioning rejuvenates adult stem cells' proliferation and chondrogenic potential

Adult stem cells are a promising cell source for cartilage regeneration. Unfortunately, due to donor age and ex vivo expansion, stem cell senescence becomes a huge hurdle for these cells to be used clinically. Increasing evidence indicates that environmental preconditioning is a powerful approach in promoting stem cells' ability to resist a harsh environment post-engraftment, such as hypoxia and inflammation. However, few reports organize and evaluate the literature regarding the rejuvenation effect of environmental preconditioning on stem cell proliferation and chondrogenic differentiation capacity, which are important variables for stem cell based tissue regeneration. This report aims to identify several critical environmental factors such as oxygen concentration, growth factors, and extracellular matrix and to discuss their preconditioning influence on stem cells' rejuvenation including proliferation and chondrogenic potential as well as underlying molecular mechanisms. We believe that environmental preconditioning based rejuvenation is a simpler and safer strategy to program pre-engraftment stem cells for better survival and enhanced proliferation and differentiation capacity without the undesired effects of some treatments, such as genetic manipulation.

Silencing of Wnt5a prevents interleukin-1β-induced collagen type II degradation in rat chondrocytes

Osteoarthritis (OA) is a joint disease, and few treatments to date have been able to delay OA progression. The degradation of collagen type II (COL2) in the cartilage matrix is an important initiating factor for OA progression; the upregulation of Wnt5a protein activates COL2 degradation. In the present study, small interfering RNA of Wnt-5a was delivered by a lentiviral vector (LV-Wnt5a-RNAi) to silence Wnt-5a mRNA and prevent COL2 degradation. To determine the function of LV-Wnt5a-RNAi, the OA chondrocyte model (OA-like chondrocytes) were constructed using interleukin (IL)-1β. Detected using reverse transcription-quantitative polymerase chain reaction (RT-qPCR), Wnt-5a mRNA in the OA-like chondrocytes were upregulated in a time-dependent manner, indicating that OA-like chondrocytes were successfully constructed. The bioactivity of OA-like chondrocytes was determined using Live-Dead staining, and the result illustrated that the OA-like chondrocytes stimulated with IL-1β for 6 h remained viable, and these were used in Wnt5a silencing. The OA-like chondrocytes were divided into three groups: Group I, cultivated with common medium; group II, cultivated with common medium supplemented with empty lentiviral vector; group III, cultivated with common medium supplemented with LV-Wnt5a-RNAi. The efficiency of LV-Wnt5a-RNAi transfection was determined using fluorescence microscopy, the result of which indicated that LV-Wnt5a-RNAi could efficiently be transfected into the OA-like chondrocytes. The LV-Wnt5a-RNAi efficiency for the Wnt5a mRNA silencing was determined using RT-qPCR. The result illustrated that the mRNA of Wnt5a in group III was significantly lower in group I compared with that in group II (P<0.05), indicating that the LV-Wnt5a-RNAi could successfully silence Wnt5a mRNA. To further verify whether the silencing of Wnt5a mRNA could prevent COL2 degradation, western blotting and immunohistochemical analyses were performed. The results demonstrated that COL2 in group III was significantly higher compared with that in groups I and II (P<0.05), which illustrated that the silencing of Wnt5a mRNA could prevent COL2 degradation. In conclusion, LV-Wnt5a-RNAi was formed successfully and could efficiently silence Wnt5a mRNA expressed by OA-like chondrocytes. In addition, the silencing of Wnt5a mRNA could prevent the degradation of COL2 in OA-like chondrocytes, confirming that LV-Wnt5a-RNAi may be used as a novel tool for OA treatment.

The Expression of Osteopontin and Wnt5a in Articular Cartilage of Patients with Knee Osteoarthritis and Its Correlation with Disease Severity

Objectives. This study is undertaken to investigate the relation between osteopontin (OPN) and Wnt5a expression in the progression and pathogenesis of osteoarthritis (OA). Methods. 50 cartilage tissues from knee OA patients and normal controls were divided into four groups of severe, moderate, minor, and normal lesions based on the modified grading system of Mankin. Immunohistochemistry and real-time PCR were utilized to analyze the OPN and Wnt5a expression in articular cartilage. Besides, the relations between OPN and Wnt5a expression and the severity of OA were explored. Results. OPN and Wnt5a could be identified in four groups' tissues. Amongst the groups, the intercomparisons of OPN expression levels showed statistical differences (P < 0.01). Besides, the intercomparisons of Wnt5a expression degrees showed statistical differences (P < 0.05), except that between the minor and normal groups (P > 0.05). The scores of Mankin were demonstrated to relate to OPN expression (r = -0.847, P < 0.01) and Wnt5a expression in every group (r = -0.843, P < 0.01). Also, a positive correlation can be observed between the OPN and Wnt5a expression (r = 0.769, P < 0.01). Conclusion. In articular cartilage, the expressions of OPN and Wnt5a are positively related to progressive damage of knee OA joint. The correlation between Wnt5a and OPN might be important to the progression and pathogenesis of knee OA.

Recent advances in the understanding of molecular mechanisms of cartilage degeneration, synovitis and subchondral bone changes in osteoarthritis

Osteoarthritis (OA), the most common form of degenerative joint disease, is linked to high morbidity. It is predicted to be the single greatest cause of disability in the general population by 2030. The development of disease-modifying therapy for OA currently face great obstacle mainly because the onset and development of the disease involve complex molecular mechanisms. In this review, we will comprehensively summarize biological and pathological mechanisms of three key aspects: degeneration of articular cartilage, synovial immunopathogenesis, and changes in subchondral bone. For each tissue, we will focus on the molecular receptors, cytokines, peptidases, related cell, and signal pathways. Agents that specifically block mechanisms involved in synovial inflammation, degeneration of articular cartilage, and subchondral bone remodeling can potentially be exploited to produce targeted therapy for OA. Such new comprehensive agents will benefit affected patients and bring exciting new hope for the treatment of OA.

Wnt16 Signaling Is Required for IL-1β-Induced Matrix Metalloproteinase-13-Regulated Proliferation of Human Stem Cell-Derived Osteoblastic Cells

We established a differentiation method for homogeneous α7 integrin-positive human skeletal muscle stem cell (α7⁺hSMSC)-derived osteoblast-like (α7⁺hSMSC-OB) cells, and found that interleukin (IL)-1β induces matrix metalloproteinase (MMP)-13-regulated proliferation of these cells. These data suggest that MMP-13 plays a potentially unique physiological role in the regeneration of osteoblast-like cells. Here, we examined whether up-regulation of MMP-13 activity by IL-1β was mediated by Wingless/int1 (Wnt) signaling and increased the proliferation of osteoblast-like cells. IL-1β increased the mRNA and protein levels of Wnt16 and the Wnt receptor Lrp5/Fzd2. Exogenous Wnt16 was found to increase MMP-13 mRNA, protein and activity, and interestingly, the proliferation rate of these cells. Treatment with small interfering RNAs against Wnt16 and Lrp5 suppressed the IL-1β-induced increase in cell proliferation. We revealed that a unique signaling cascade IL-1β→Wnt16→Lrp5→MMP-13, was intimately involved in the proliferation of osteoblast-like cells, and suggest that IL-1β-induced MMP-13 expression and changes in cell proliferation are regulated by Wnt16.

Delineation of in vitro chondrogenesis of human synovial stem cells following preconditioning using decellularized matrix

As a tissue-specific stem cell for chondrogenesis, synovium-derived stem cells (SDSCs) are a promising cell source for cartilage repair. However, a small biopsy can only provide a limited number of cells. Cell senescence from both in vitro expansion and donor age presents a big challenge for stem cell based cartilage regeneration. Here we found that expansion on decellularized extracellular matrix (dECM) full of three-dimensional nanostructured fibers provided SDSCs with unique surface profiles, low elasticity but large volume as well as a fibroblast-like shape. dECM expanded SDSCs yielded larger pellets with intensive staining of type II collagen and sulfated glycosaminoglycans compared to those grown on plastic flasks while SDSCs grown in ECM yielded 28-day pellets with minimal matrix as evidenced by pellet size and chondrogenic marker staining, which was confirmed by both biochemical data and real-time PCR data. Our results also found lower levels of inflammatory genes in dECM expanded SDSCs that might be responsible for enhanced chondrogenic differentiation. Despite an increase in type X collagen in chondrogenically induced cells, dECM expanded cells had significantly lower potential for endochondral bone formation. Wnt and MAPK signals were actively involved in both expansion and chondrogenic induction of dECM expanded cells. Since young and healthy people can be potential donors for this matrix expansion system and decellularization can minimize immune concerns, human SDSCs expanded on this future commercially available dECM could be a potential cell source for autologous cartilage repair.

Dkk-1-mediated inhibition of Wnt signaling in bone ameliorates osteoarthritis in mice

OBJECTIVE

Wnt signaling is a master regulator of joint homeostasis, but its role in osteoarthritis (OA) remains unclear. This study was undertaken to characterize the activation of Wnt/β-catenin in knee joints of mice with OA and to assess how inhibiting this pathway in bone could affect cartilage.

METHODS

OA was induced by partial meniscectomy in Topgal mice and in transgenic mice overexpressing Dkk-1 under the control of the 2.3-kb Col1a1 promoter (Col1a1-Dkk-1-Tg mice). Wnt/β-catenin activation was assessed by X-Gal staining at baseline and at weeks 4, 6, and 9. Cartilage and bone damage was analyzed in Col1a1-Dkk-1-Tg mice with OA at week 6. Primary chondrocytes and cartilage explants were used to assess the effect of Dkk-1 on cartilage catabolism.

RESULTS

In meniscectomized Topgal mice, Wnt was mainly activated in osteocytes from the subchondral bone at week 6 after OA induction, as well as in osteophytes and synovium at week 4. Chondrocytes from damaged zones expressed X-Gal from week 4. Dkk-1 expression was high in chondrocytes in control mouse knees (mean ± SEM 84.2 ± 3.1%) but decreased greatly in knees of meniscectomized mice from week 4 (mean ± SEM 14.4 ± 3.8%). The OA score was lower in meniscectomized Col1a1-Dkk-1-Tg mice at week 6 compared with wild-type mice (5.1 ± 0.6 versus 8.4 ± 0.6; P = 0.002). Subchondral bone fraction and osteophyte volume were decreased. However, cartilage explants from Col1a1-Dkk-1-Tg mice showed proteoglycan loss and increased NITEGE expression. Expression of vascular endothelial growth factor (VEGF) was reduced in osteoblasts from Col1a1-Dkk-1-Tg mice, thereby decreasing expression of messenger RNA for matrix metalloproteinases in chondrocytes.

CONCLUSION

Wnt activation in OA affects the whole joint, particularly bone. Selective inhibition of this pathway in bone by Dkk-1 decreased OA severity through VEGF inhibition.

Loss of sclerostin promotes osteoarthritis in mice via β-catenin-dependent and -independent Wnt pathways

Introduction

Sclerostin is a Wnt inhibitor produced by osteocytes that regulates bone formation. Because bone tissue contributes to the development of osteoarthritis (OA), we investigated the role of sclerostin in bone and cartilage in a joint instability model in mice.

Methods

Ten-week-old SOST-knockout (SOST-KO) and wild-type (WT) mice underwent destabilization of the medial meniscus (DMM). We measured bone volume at the medial femoral condyle and osteophyte volume and determined the OA score and expression of matrix proteins. Primary murine chondrocytes were cultured with Wnt3a and sclerostin to assess the expression of matrix proteins, proteoglycan release and glycosaminoglycan accumulation.

Results

Sclerostin was expressed in calcified cartilage of WT mice with OA. In SOST-KO mice, cartilage was preserved despite high bone volume. However, SOST-KO mice with DMM had a high OA score, with increased expression of aggrecanases and type X collagen. Moreover, SOST-KO mice with OA showed disrupted anabolic–catabolic balance and cartilage damage. In primary chondrocytes, sclerostin addition abolished Wnt3a-increased expression of a disintegrin and metalloproteinase with thrombospondin motifs, matrix metalloproteinases and type X collagen by inhibiting the canonical Wnt pathway. Moreover, sclerostin inhibited Wnt-phosphorylated c-Jun N-terminal kinase (JNK) and rescued the expression of anabolic genes. Furthermore, sclerostin treatment inhibited both Wnt canonical and non-canonical JNK pathways in chondrocytes, thus preserving metabolism.

Conclusion

Sclerostin may play an important role in maintaining cartilage integrity in OA.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0540-6) contains supplementary material, which is available to authorized users.

A review of crosstalk between MAPK and Wnt signals and its impact on cartilage regeneration

Chondrogenesis is a developmental process that is controlled and coordinated by many growth and differentiation factors, in addition to environmental factors that initiate or suppress cellular signaling pathways and the transcription of specific genes in a temporal-spatial manner. As key signaling molecules in regulating cell proliferation, homeostasis and development, both mitogen-activated protein kinases (MAPK) and the Wnt family participate in morphogenesis and tissue patterning, playing important roles in skeletal development, especially chondrogenesis. Recent findings suggest that both signals are also actively involved in arthritis and related diseases. Despite the implication that crosstalk between MAPK and Wnt signaling has a significant function in cancer, few studies have summarized this interaction and its regulation of chondrogenesis. In this review, we focus on MAPK and Wnt signaling, referencing their relationships in various types of cells and particularly to their influence on chondrogenesis and cartilage development. We also discuss the interactions between MAPK and Wnt signaling with respect to cartilage-related diseases such as osteoarthritis and explore potential therapeutic targets for disease treatments.

Subchondral bone influences chondrogenic differentiation and collagen production of human bone marrow-derived mesenchymal stem cells and articular chondrocytes

Introduction

Osteoarthritis (OA) is characterized by an imbalance in cartilage and underlying subchondral bone homeostasis. We hypothesized that signals from the subchondral bone may modulate production of matrix components, alter chondrogenic differentiation potential of cocultured bone marrow-derived mesenchymal stem cells (BMSC) and induce a phenotypic shift in differentiated OA chondrocytes.

Methods

We established a novel coculture model between BMSC, mixed cultures (BMSC and chondrocytes) and chondrocytes embedded in fibrin gel with OA and normal subchondral bone explants (OAB and NB). Tissues and cells were either derived from OA or trauma patients. In addition, we used adipose-derived stem cells (ASC) from liposuction. With gene expression analysis, biochemical assays, immunofluorescence and biomechanical tests we characterized the properties of newly generated extracellular matrix (ECM) from chondrocytes and chondrogenically differentiating BMSC cocultured with OAB or NB in comparison with monocultures (cultures without bone explants).

Results

Overall, gene expression of collagens of OAB and NB cocultured cells was reduced compared to monocultures. Concomitantly, we observed significantly lower collagen I, II and III and glycosaminoglycan (GAG) production in OAB cocultured cell lysates. In parallel, we detected increased concentrations of soluble GAGs and basic fibroblast growth factor (bFGF), interleukin (IL)-6 and IL-8 in supernatants of OAB and NB cocultures mainly at early time points. IL-1ß concentration was increased in supernatants of OAB cocultures, but not in NB cocultures. Cell-free NB or OAB explants released different amounts of IL-1ß, bFGF and soluble GAG into cell culture supernatants. In comparison to cocultures, monocultures exhibited higher Young’s modulus and equilibrium modulus. Stimulation of monocultures with IL-1ß led to a downregulation of aggrecan (ACAN) gene expression and in general to induced matrix metalloprotease (MMP)2, MMP3 and MMP-13 gene expression while IL-6 and IL-8 stimulation partly reduced ACAN, MMP3 and MMP-13 gene expression.

Conclusions

Our results suggest an alteration of molecular composition and mechanical properties of the newly formed ECM in subchondral bone cocultures. We suggest that soluble factors, that is interleukins and bFGF, released in cocultures exert inhibitory effects on collagen and temporary effects on proteoglycan production, which finally results in a reduction of mechanical strength of newly formed fibrillar networks.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-014-0453-9) contains supplementary material, which is available to authorized users.

Expansion on a matrix deposited by nonchondrogenic urine stem cells strengthens the chondrogenic capacity of repeated-passage bone marrow stromal cells

Human urine-derived stem cells (hUSCs) are a newly found type of stem cell with a potential for therapeutic application in urology. The aim of this study is to investigate whether hUSCs contribute to cartilage regeneration. Despite their characterization with multi-lineage differentiation capacities, in terms of osteogenesis, adipogenesis and myogenesis, hUSCs do not show the ability to differentiate into chondrocytes. Human bone marrow stromal cells (hBMSCs) are a tissue-specific stem cell for endochondral bone formation; however, repeated-passage hBMSCs have a lower capacity for chondrogenic differentiation. We found that the extracellular matrix (ECM) deposited by hUSCs (UECM) can greatly recharge repeated-passage hBMSCs toward chondrogenic differentiation, a result that might be explained by trophic factors released from hUSCs being immobilized in UECM. We also found that ECM from repeated-passage hBMSCs (BECM) have a limited rejuvenation effect. The Wnt11-mediated noncanonical signaling pathway might be responsible for UECM-mediated hBMSC rejuvenation and subsequent chondrogenic differentiation. Our data indicate that commercially available UECM from young healthy donors might represent a simple and promising approach for autologous hBMSC rejuvenation. This study also provides an excellent model for investigating the effect of trophic factors released by stem cells on tissue regeneration without interference by stem cell differentiation.

Low-density lipoprotein receptor-related protein 5 governs Wnt-mediated osteoarthritic cartilage destruction

Introduction

Wnt ligands bind to low-density lipoprotein receptor–related protein (LRP) 5 or 6, triggering a cascade of downstream events that include β-catenin signaling. Here we explored the roles of LRP5 in interleukin 1β (IL-1β)- or Wnt-mediated osteoarthritic (OA) cartilage destruction in mice.

Methods

The expression levels of LRP5, type II collagen, and catabolic factors were determined in mouse articular chondrocytes, human OA cartilage, and mouse experimental OA cartilage. Experimental OA in wild-type, Lrp5 total knockout (Lrp5^-/-) and chondrocyte-specific knockout (Lrp5^fl/fl;Col2a1-cre) mice was caused by aging, destabilization of the medial meniscus (DMM), or intra-articular injection of collagenase. The role of LRP5 was confirmed in vitro by small interfering RNA–mediated knockdown of Lrp5 or in Lrp5^-/- cells treated with IL-1β or Wnt proteins.

Results

IL-1β treatment increased the expression of LRP5 (but not LRP6) via JNK and NF-κB signaling. LRP5 was upregulated in human and mouse OA cartilage, and Lrp5 deficiency in mice inhibited cartilage destruction. Treatment with IL-1β or Wnt decreased the level of Col2a1 and increased those of Mmp3 or Mmp13, whereas Lrp5 knockdown ameliorated these effects. In addition, we found that the functions of LRP5 in arthritic cartilage were subject to transcriptional activation by β-catenin. Moreover, Lrp5^-/- and Lrp5^fl/fl;Col2a1-cre mice exhibited decreased cartilage destruction (and related changes in gene expression) in response to experimental OA.

Conclusions

Our findings indicate that LRP5 (but not LRP6) plays an essential role in Wnt/β-catenin-signaling-mediated OA cartilage destruction in part by regulating the expression levels of type II collagen, MMP3, and MMP13.

Overexpression of Wnt11 promotes chondrogenic differentiation of bone marrow-derived mesenchymal stem cells in synergism with TGF-β

Bone marrow-derived mesenchymal stem cells (MSCs), the most widely used cell source for cartilage tissue engineering, are multipotent cells which have been shown to differentiate into various mesenchyme-lineage cell types including chondrocytes. However, the molecular mechanisms controlling the chondrogenic differentiation of MSCs remain to be fully elucidated. It has been demonstrated that Wnt signaling involves regulating chondrogenesis and MSC differentiation. The aim of the present study was to investigate the role of Wnt11, a member of noncanonical Wnts, in MSCs during chondrogenic differentiation. We observed that overexpression of Wnt11 inhibited proliferation of MSCs and caused a G0/G1 cell cycle arrest. The expression level of chondrogenic markers, aggrecan and Collagen II, was significantly increased in MSCs transduced with Wnt11 as compared with non-transduced cells or MSCs transduced with the empty lentiviral vector. Furthermore, ectopic expression of Wnt11 stimulated gene expression of chondrogenic regulators, SRY-related gene 9, Runt-related transcription factor 2, and Indian hedgehog. Finally, Wnt11 overexpression promoted chondrogenic differentiation of MSCs in synergism with TGF-β. Collectively, these results indicate that Wnt11 plays a crucial role in regulating MSC chondrogenic differentiation.

WNT signaling and chondrocytes: from cell fate determination to osteoarthritis physiopathology

CONTEXT

Osteoarthritis (OA) is an articular disorder leading to the degradation of articular cartilage phenotypical chondrocytes modifications, including the acquisition of a fibroblast-like morphology, decreased expression of collagen type II, and increased expression of fetal collagen type I, metalloproteinase 13 and nitric oxide synthase. This promotes matrix degradation and unsuccessful cartilage repair. WNT signaling constitutes one of the most critical biological processes during cell fate assignment and homeostasis.

OBJECTIVES

This review aims to give an insight on results from the studies that were interested in the involvement of WNT in OA.

METHODS

Studies were selected through a pubmed search.

RESULTS

Recent genetic data showed that aberration in WNT signaling may be involved in OA. WNT signals are transduced through at least three cascades: the canonical WNT/β-catenin pathway, the WNT/Ca(2+) pathway and the WNT/planar cell polarity pathway. Most of the studies used in-vitro models to elucidate the involvement of WNT in the physiopathology of OA. These studies analyzed the expression pattern of WNT pathway components during OA such as WNT5, WNT7, co-receptor LRP, β-catenin, WNT target genes (c-jun, cyclins) and/or the interaction of these components with the secretion of OA most important markers such as IL-1, collagens, MMPs. Results from these studies are in favor of a deep involvement of the WNT signaling in the physiopathology of OA either by having a protective or a destructive role.

CONCLUSION

Deeper researches may eventually allow scientists to target WNT pathway in order to help develop efficient therapeutic approaches to treat OA.

Wnt inhibitory factor 1 deficiency uncouples cartilage and bone destruction in tumor necrosis factor α-mediated experimental arthritis

OBJECTIVE

Wnt signaling plays a pivotal role in skeletal development and in the control of cartilage and bone turnover. We have recently shown that the secreted Wnt antagonist Wnt inhibitory factor 1 (WIF-1) is mainly expressed in the upper layers of epiphyseal and articular cartilage and, to a lesser extent, in bone. Nevertheless, WIF-1(-/-) mice develop normally. In light of these findings, we undertook this study to analyze the role of WIF-1 in arthritis.

METHODS

Expression analyses for WIF-1 were performed by real-time reverse transcription-polymerase chain reaction (RT-PCR). WIF-1(-/-) and tumor necrosis factor (TNF)-transgenic mice were crossbred, and the progression of arthritis in TNF-transgenic WIF-1(-/-) mice and littermate controls was evaluated. Structural joint damage was analyzed by histologic staining, histomorphometry, and micro-computed tomography. Wnt/β-catenin signaling was investigated by real-time RT-PCR and immunofluorescence on primary chondrocytes.

RESULTS

WIF-1 expression was repressed by TNFα in chondrocytes and osteoblasts and down-regulated in experimental arthritis and in articular cartilage from patients with rheumatoid arthritis. WIF-1 deficiency partially protected TNF-transgenic mice against bone erosion and loss of trabecular bone, probably as a result of less osteoclast activity. In contrast, arthritis-related cartilage damage was aggravated by WIF-1 deficiency, while overexpression of WIF-1 attenuated cartilage degradation in TNF-transgenic mice. In chondrocytes, TNFα stimulated canonical Wnt signaling, which could be blocked by WIF-1, indicating a direct effect of TNFα and WIF-1 on Wnt signaling in this system.

CONCLUSION

These data suggest that WIF-1 may take part in the fine-tuning of cartilage and bone turnover, promoting the balance of cartilage versus bone anabolism.

Rejuvenation of chondrogenic potential in a young stem cell microenvironment

Autologous cells suffer from limited cell number and senescence during ex vivo expansion for cartilage repair. Here we found that expansion on extracellular matrix (ECM) deposited by fetal synovium-derived stem cells (SDSCs) (FE) was superior to ECM deposited by adult SDSCs (AE) in promoting cell proliferation and chondrogenic potential. Unique proteins in FE might be responsible for the rejuvenation effect of FE while advantageous proteins in AE might contribute to differentiation more than to proliferation. Compared to AE, the lower elasticity of FE yielded expanded adult SDSCs with lower elasticity which could be responsible for the enhancement of chondrogenic and adipogenic differentiation. MAPK and noncanonical Wnt signals were actively involved in ECM-mediated adult SDSC rejuvenation.

Interplay between cartilage and subchondral bone contributing to pathogenesis of osteoarthritis

Osteoarthritis (OA) is a common debilitating joint disorder, affecting large sections of the population with significant disability and impaired quality of life. During OA, functional units of joints comprising cartilage and subchondral bone undergo uncontrolled catabolic and anabolic remodeling processes to adapt to local biochemical and biological signals. Changes in cartilage and subchondral bone are not merely secondary manifestations of OA but are active components of the disease, contributing to its severity. Increased vascularization and formation of microcracks in joints during OA have suggested the facilitation of molecules from cartilage to bone and vice versa. Observations from recent studies support the view that both cartilage and subchondral bone can communicate with each other through regulation of signaling pathways for joint homeostasis under pathological conditions. In this review we have tried to summarize the current knowledge on the major signaling pathways that could control the cartilage-bone biochemical unit in joints and participate in intercellular communication between cartilage and subchondral bone during the process of OA. An understanding of molecular communication that regulates the functional behavior of chondrocytes and osteoblasts in both physiological and pathological conditions may lead to development of more effective strategies for treating OA patients.

WNT/β-catenin signaling induces IL-1β expression by alveolar epithelial cells in pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a lethal lung disease of unknown etiology. It is characterized by alterations of the alveolar epithelium, myofibroblast activation, and increased extracellular matrix deposition. Recently, reactivation of the developmental WNT/β-catenin pathway has been linked with pulmonary fibrosis. The cell-specific mechanisms and mediators of WNT/β-catenin signaling in the lung, however, remain elusive. Here, we applied an unbiased gene expression screen to identify epithelial cell-specific mediators of WNT/β-catenin signaling. We found the proinflammatory cytokine IL-1β to be one of the most up-regulated genes in primary murine alveolar epithelial Type II (ATII) cells after WNT3a treatment. Increased transcript and protein expression of IL-1β upon WNT3a treatment was further detected in primary ATII cells by quantitative RT-PCR (log fold change, 2.0 ± 0.5) and ELISA (1.8-fold increase). We observed significant up-regulation of IL-1β and IL-6 in bronchoalveolar lavage fluid (BALF) in bleomycin-induced lung fibrosis in vivo. Importantly, primary fibrotic ATII cells isolated from lungs subjected to bleomycin secreted enhanced IL-1β and IL-6 in vitro. Furthermore, the orotracheal application of recombinant WNT protein in the Tcf optimal promoter (TOP)-β-galactosidase reporter animals led to WNT/β-catenin activation in epithelial cells, along with significant increases in IL-1β and IL-6 in vivo (2.7-fold and 6.0-fold increases, respectively). Finally, we found increased WNT3a protein in fibrotic alveolar epithelia, accompanied by enhanced IL-1β and IL-6 concentrations in BALF from patients with IPF. Taken together, our findings reveal that the alveolar epithelium is a relevant source of proinflammatory cytokines induced by active WNT/β-catenin in pulmonary fibrosis. Thus, WNT/interleukin signaling represents a novel link between developmental pathway reactivation and inflammation in the development of pulmonary fibrosis.

Regulation of lubricin/superficial zone protein by Wnt signalling in bovine synoviocytes

Lubricin, homologous to superficial zone protein (SZP), functions as a boundary lubricant in articular cartilage and plays an essential role in the maintenance of joint function and homeostasis. Wnt signalling plays a key role in joint development, including synovial joint formation, and several Wnt proteins are expressed in the synovium and articular cartilage in arthritis. The aim of this study was to determine the role of Wnt signalling on SZP accumulation in synoviocytes. Isolated synoviocytes from bovine knee joints were cultured with Wnt proteins (Wnt-3a and Wnt-5a) and antagonists or agonists of the Wnt-β-catenin pathway or Wnt-Ca(2+) pathway in serum-free chemically defined medium. SZP accumulation in the culture medium was determined by enzyme-linked immunosorbent assay. Wnt-3a suppressed SZP accumulation via a Wnt-β-catenin-dependent pathway. In contrast, Wnt-5a stimulated SZP accumulation via a β-catenin independent pathway. The present investigation provides novel insights into the role of the Wnt signalling pathways in SZP accumulation in synoviocytes and their roles in the homeostasis of normal joints.