WNT16 antagonises excessive canonical WNT activation and protects cartilage in osteoarthritis

Prg4-Expressing Chondroprogenitor Cells in the Superficial Zone of Articular Cartilage

Joint-resident chondrogenic precursor cells have become a significant therapeutic option due to the lack of regenerative capacity in articular cartilage. Progenitor cells are located in the superficial zone of the articular cartilage, producing lubricin/Prg4 to decrease friction of cartilage surfaces during joint movement. Prg4-positive progenitors are crucial in maintaining the joint's structure and functionality. The disappearance of progenitor cells leads to changes in articular hyaline cartilage over time, subchondral bone abnormalities, and the formation of ectopic ossification. Genetic labeling cell technology has been the main tool used to characterize Prg4-expressing progenitor cells of articular cartilage in vivo through drug injection at different time points. This technology allows for the determination of the origin of progenitor cells and the tracking of their progeny during joint development and cartilage damage. We endeavored to highlight the currently known information about the Prg4-producing cell population in the joint to underline the significance of the role of these cells in the development of articular cartilage and its homeostasis. This review focuses on superficial progenitors in the joint, how they contribute to postnatal articular cartilage formation, their capacity for regeneration, and the consequences of Prg4 deficiency in these cells. We have accumulated information about the Prg4+ cell population of articular cartilage obtained through various elegantly designed experiments using transgenic technologies to identify potential opportunities for further research.

Identification and verification of a novel signature that combines cuproptosis-related genes with ferroptosis-related genes in osteoarthritis using bioinformatics analysis and experimental validation

BACKGROUND

Exploring the pathogenesis of osteoarthritis (OA) is important for its prevention, diagnosis, and treatment. Therefore, we aimed to construct novel signature genes (c-FRGs) combining cuproptosis-related genes (CRGs) with ferroptosis-related genes (FRGs) to explore the pathogenesis of OA and aid in its treatment.

MATERIALS AND METHODS

Differentially expressed c-FRGs (c-FDEGs) were obtained using R software. Enrichment analysis was performed and a protein-protein interaction (PPI) network was constructed based on these c-FDEGs. Then, seven hub genes were screened. Three machine learning methods and verification experiments were used to identify four signature biomarkers from c-FDEGs, after which gene set enrichment analysis, gene set variation analysis, single-sample gene set enrichment analysis, immune function analysis, drug prediction, and ceRNA network analysis were performed based on these signature biomarkers. Subsequently, a disease model of OA was constructed using these biomarkers and validated on the GSE82107 dataset. Finally, we analyzed the distribution of the expression of these c-FDEGs in various cell populations.

RESULTS

A total of 63 FRGs were found to be closely associated with 11 CRGs, and 40 c-FDEGs were identified. Bioenrichment analysis showed that they were mainly associated with inflammation, external cellular stimulation, and autophagy. CDKN1A, FZD7, GABARAPL2, and SLC39A14 were identified as OA signature biomarkers, and their corresponding miRNAs and lncRNAs were predicted. Finally, scRNA-seq data analysis showed that the differentially expressed c-FRGs had significantly different expression distributions across the cell populations.

CONCLUSION

Four genes, namely CDKN1A, FZD7, GABARAPL2, and SLC39A14, are excellent biomarkers and prospective therapeutic targets for OA.

Identification of novel potential drugs for the treatment and prevention of osteoarthritis

Objectives

Osteoarthritis (OA) is characterized by a high prevalence, poor prognosis, and a propensity to lead to disability. Despite the availability of standard therapies, they are associated with potential side effects and don't provide a complete cure for patients. Consequently, there is an urgent demand for the development of novel drugs.

Method

The gene expression profiles (GSE64394, GSE178557 and GSE215039) of normal and OA chondrocytes samples were downloaded from the Gene Expression Omnibus (GEO) database. Differentially expressed genes (DEGs) were identified by the "LIMMA" R package. Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment were conducted using the R package clusterProfiler. A protein-protein (PPI) interaction network was performed to identify hub genes by using the Search Tool for the Retrieval of Interacting Genes (STRING) and Cytoscape. Small molecule compounds linked to OA were predicted through the NetworkAnalyst platform. Finally, molecular docking was conducted using AutoDock and Pymol software.

Results

We identified 98 DEGs primarily implicated in endochondral ossification, extracellular matrix degradation, and Wnt signaling pathways. 23 DEGs were closely associated with OA, and 10 hub genes were found to be potential drug targets for OA. Two new targeted compounds, tetrachlorodibenzodioxin (TCDD) and valproic acid (VPA), were screened. And they both exhibited strong binding affinity to their respective targets.

Conclusions

Reducing exposure to TCDD could be a crucial strategy in preventing OA, and VPA has gained recognition as a novel drug candidate for OA treatment.

TNFRSF19 within the 13q12.12 Risk Locus Functions as a Lung Cancer Suppressor by Binding Wnt3a to Inhibit Wnt/β-Catenin Signaling

Cancer risk loci provide special clues for uncovering pathogenesis of cancers. The TNFRSF19 gene located within the 13q12.12 lung cancer risk locus encodes TNF receptor superfamily member 19 (TNFRSF19) protein and has been proved to be a key target gene of a lung tissue-specific tumor suppressive enhancer, but its functional role in lung cancer pathogenesis remains to be elucidated. Here we showed that the TNFRSF19 gene could protect human bronchial epithelial Beas-2B cells from pulmonary carcinogen nicotine-derived nitrosamine ketone (NNK)-induced malignant transformation. Knockout of the TNFRSF19 significantly increased NNK-induced colony formation rate on soft agar. Moreover, TNFRSF19 expression was significantly reduced in lung cancer tissues and cell lines. Restoration of TNFRSF19 expression in A549 lung cancer cell line dramatically suppressed the tumor formation in xenograft mouse model. Interestingly, the TNFRSF19 protein that is an orphan membrane receptor could compete with LRP6 to bind Wnt3a, thereby inhibiting the Wnt/β-catenin signaling pathway that is required for NNK-induced malignant transformation as indicated by protein pulldown, site mutation, and fluorescence energy resonance transfer experiments. Knockout of the TNFRSF19 enhanced LRP6-Wnt3a interaction, promoting β-catenin nucleus translocation and the downstream target gene expression, and thus sensitized the cells to NNK carcinogen. In conclusion, our study demonstrated that the TNFRSF19 inhibited lung cancer carcinogenesis by competing with LRP6 to combine with Wnt3a to inhibit the Wnt/β-catenin signaling pathway.

IMPLICATIONS

These findings revealed a novel anti-lung cancer mechanism, highlighting the special significance of TNFRSF19 gene within the 13q12.12 risk locus in lung cancer pathogenesis.

The interplay between biochemical mediators and mechanotransduction in chondrocytes: Unravelling the differential responses in primary knee osteoarthritis

In primary or idiopathic osteoarthritis (OA), it is unclear which factors trigger the shift of articular chondrocyte activity from pro-anabolic to pro-catabolic. In fact, there is a controversy about the aetiology of primary OA, either mechanical or inflammatory. Chondrocytes are mechanosensitive cells, that integrate mechanical stimuli into cellular responses in a process known as mechanotransduction. Mechanotransduction occurs thanks to the activation of mechanosensors, a set of specialized proteins that convert physical cues into intracellular signalling cascades. Moderate levels of mechanical loads maintain normal tissue function and have anti-inflammatory effects. In contrast, mechanical over- or under-loading might lead to cartilage destruction and increased expression of pro-inflammatory cytokines. Simultaneously, mechanotransduction processes can regulate and be regulated by pro- and anti-inflammatory soluble mediators, both local (cells of the same joint, i.e., the chondrocytes themselves, infiltrating macrophages, fibroblasts or osteoclasts) and systemic (from other tissues, e.g., adipokines). Thus, the complex process of mechanotransduction might be altered in OA, so that cartilage-preserving chondrocytes adopt a different sensitivity to mechanical signals, and mechanic stimuli positively transduced in the healthy cartilage may become deleterious under OA conditions. This review aims to provide an overview of how the biochemical exposome of chondrocytes can alter important mechanotransduction processes in these cells. Four principal mechanosensors, i.e., integrins, Ca2+ channels, primary cilium and Wnt signalling (canonical and non-canonical) were targeted. For each of these mechanosensors, a brief summary of the response to mechanical loads under healthy or OA conditions is followed by a concise overview of published works that focus on the further regulation of the mechanotransduction pathways by biochemical factors. In conclusion, this paper discusses and explores how biological mediators influence the differential behaviour of chondrocytes under mechanical loads in healthy and primary OA.

Mechanical stress and inflammation have opposite effects on Wnt signaling in human chondrocytes

Dysregulation of Wingless and Int-1 (Wnt) signaling has been strongly associated with development and progression of osteoarthritis (OA). Here, we set out to investigate the independent effects of either mechanical stress (MS) or inflammation on Wnt signaling in human neocartilage pellets, and to relate this Wnt signaling to OA pathophysiology. OA synovium-conditioned media (OAS-CM) was collected after incubating synovium from human end-stage OA joints for 24 h in medium. Cytokine levels in the OAS-CM were determined with a multiplex immunoassay (Luminex). Human neocartilage pellets were exposed to 20% MS, 2% OAS-CM or 1 ng/mL Interleukin-1β (IL-1β). Effects on expression levels of Wnt signaling members were determined by reverse transcription-quantitative polymerase chain reaction. Additionally, the expression of these members in articular cartilage from human OA joints was analyzed in association with joint space narrowing (JSN) and osteophyte scores. Protein levels of IL-1β, IL-6, IL-8, IL-10, tumor necrosis factor α, and granulocyte-macrophage colony-stimulating factor positively correlated with each other. MS increased noncanonical WNT5A and FOS expression. In contrast, these genes were downregulated upon stimulation with OAS-CM or IL-1β. Furthermore, Wnt inhibitors DKK1 and FRZB decreased in response to OAS-CM or IL-1β exposure. Finally, expression of WNT5A in OA articular cartilage was associated with increased JSN scores, but not osteophyte scores. Our results demonstrate that MS and inflammatory stimuli have opposite effects on canonical and noncanonical Wnt signaling in human neocartilage. Considering the extent to which MS and inflammation contribute to OA in individual patients, we hypothesize that targeting specific Wnt pathways offers a more effective, individualized approach.

IĸB Protein BCL3 as a Controller of Osteogenesis and Bone Health

OBJECTIVE

IĸB protein B cell lymphoma 3-encoded protein (BCL3) is a regulator of the NF-κB family of transcription factors. NF-κB signaling fundamentally influences the fate of bone-forming osteoblasts and bone-resorbing osteoclasts, but the role of BCL3 in bone biology has not been investigated. The objective of this study was to evaluate BCL3 in skeletal development, maintenance, and osteoarthritic pathology.

METHODS

To assess the contribution of BCL3 to skeletal homeostasis, neonatal mice (n = 6-14) lacking BCL3 (Bcl3-/- ) and wild-type (WT) controls were characterized for bone phenotype and density. To reveal the contribution to bone phenotype by the osteoblast compartment in Bcl3-/- mice, transcriptomic analysis of early osteogenic differentiation and cellular function (n = 3-7) were assessed. Osteoclast differentiation and function in Bcl3-/- mice (n = 3-5) was assessed. Adult 20-week Bcl3-/- and WT mice bone phenotype, strength, and turnover were assessed. A destabilization of the medial meniscus model of osteoarthritic osteophytogenesis was used to understand adult bone formation in Bcl3-/- mice (n = 11-13).

RESULTS

Evaluation of Bcl3-/- mice revealed congenitally increased bone density, long bone dwarfism, increased bone biomechanical strength, and altered bone turnover. Molecular and cellular characterization of mesenchymal precursors showed that Bcl3-/- cells displayed an accelerated osteogenic transcriptional profile that led to enhanced differentiation into osteoblasts with increased functional activity, which could be reversed with a mimetic peptide. In a model of osteoarthritis-induced osteophytogenesis, Bcl3-/- mice exhibited decreased pathological osteophyte formation (P < 0.05).

CONCLUSION

Cumulatively, these findings demonstrate that BCL3 controls developmental mineralization to enable appropriate bone formation, whereas in a pathological setting, it contributes to skeletal pathology.

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.

Wnt pathway in bone: knowledge structure and hot spots from 1993 to 2022

Background: The role of the Wnt pathway in bone and its targets in skeletal disease has garnered interest, but the field lacks a systematic analysis of research. This paper presents a bibliometric study of publications related to the Wnt signaling pathway in bone to describe the current state of study and predict future outlooks. Methods: All relevant articles and reviews from 1993 to 2022 were collected from the Web of Science Core Collection (WoSCC). Bibliometric analysis and visualization were performed using CiteSpace 6.1 R3, VOSviewer 1.6.15, and the Online Analysis Platform of Literature Metrology (http://bibliometric.com/). Results: A total of 7,184 papers were retrieved, authored by 28,443 researchers from 89 countries/regions and published in 261 academic journals. The annual publication numbers peaked in 2021. China and United States are the leading countries, with the University of California and Harvard University as the most active institutions. Wang, Yang is the most prolific author. Bone has the most published research, while Proceedings of the National Academy of Sciences of the United States is the most cited journal on average. The main keywords include expression, Wnt, osteoporosis, bone, and osteogenic differentiation. Current and developing research hotspots focus on bone mass, sclerostin antibody, multiple myeloma, and cartilage development. Conclusion: This paper provides new insights for researchers to delve into the mechanisms of Wnt and bone related diseases and translate into clinical studies. It reveals the development and future research trends in Wnt and skeletal-related studies.

The role of apoptosis in the pathogenesis of osteoarthritis

PURPOSE

Apoptosis is an important physiological process, making a great difference to development and tissue homeostasis. Osteoarthritis (OA) is a chronic joint disease characterized by degeneration and destruction of articular cartilage and bone hyperplasia. This purpose of this study is to provide an updated review of the role of apoptosis in the pathogenesis of osteoarthritis.

METHODS

A comprehensive review of the literature on osteoarthritis and apoptosis was performed, which mainly focused on the regulatory factors and signaling pathways associated with chondrocyte apoptosis in osteoarthritis and other pathogenic mechanisms involved in chondrocyte apoptosis.

RESULTS

Inflammatory mediators such as reactive oxygen species (ROS), nitric oxide (NO), IL-1β, tumor necrosis factor-α (TNF-α), and Fas are closely related to chondrocyte apoptosis. NF-κB signaling pathway, Wnt signaling pathway, and Notch signaling pathway activate proteins and gene targets that promote or inhibit the progression of osteoarthritis disease, including chondrocyte apoptosis and ECM degradation. Long non-coding RNAs (LncRNAs) and microRNAs (microRNAs) have gradually replaced single and localized research methods and become the main research approaches. In addition, the relationship between cellular senescence, autophagy, and apoptosis was also briefly explained.

CONCLUSION

This review offers a better molecular delineation of apoptotic processes that may help in designing new therapeutic options for OA treatment.

The role of WNT and IL-1 signaling in osteoarthritis: therapeutic implications for platelet-rich plasma therapy

Different from inflammatory arthritis, where biologicals and targeted synthetic molecules have revolutionized the disease course, no drug has demonstrated a disease modifying activity in osteoarthritis, which remains one of the most common causes of disability and chronic pain worldwide. The pharmacological therapy of osteoarthritis is mainly directed towards symptom and pain relief, and joint replacement is still the only curative strategy. Elucidating the disease pathophysiology is essential to understand which mechanisms can be targeted by innovative therapies. It has extensively been demonstrated that aberrant WNT and IL-1 signaling pathways are responsible for cartilage degeneration, impaired chondrocyte metabolism and differentiation, increased extracellular matrix degradation, and altered subchondral bone homeostasis. Platelet-rich plasma is an autologous blood derivative containing a concentration of platelets that is much higher than the whole blood counterpart and has shown promising results in the treatment of early knee osteoarthritis. Among the proposed mechanisms, the modulation of WNT and IL-1 pathways is of paramount importance and is herein reviewed in light of the proposed regenerative approaches.

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.

Targeting strategies for bone diseases: signaling pathways and clinical studies

Since the proposal of Paul Ehrlich's magic bullet concept over 100 years ago, tremendous advances have occurred in targeted therapy. From the initial selective antibody, antitoxin to targeted drug delivery that emerged in the past decades, more precise therapeutic efficacy is realized in specific pathological sites of clinical diseases. As a highly pyknotic mineralized tissue with lessened blood flow, bone is characterized by a complex remodeling and homeostatic regulation mechanism, which makes drug therapy for skeletal diseases more challenging than other tissues. Bone-targeted therapy has been considered a promising therapeutic approach for handling such drawbacks. With the deepening understanding of bone biology, improvements in some established bone-targeted drugs and novel therapeutic targets for drugs and deliveries have emerged on the horizon. In this review, we provide a panoramic summary of recent advances in therapeutic strategies based on bone targeting. We highlight targeting strategies based on bone structure and remodeling biology. For bone-targeted therapeutic agents, in addition to improvements of the classic denosumab, romosozumab, and PTH1R ligands, potential regulation of the remodeling process targeting other key membrane expressions, cellular crosstalk, and gene expression, of all bone cells has been exploited. For bone-targeted drug delivery, different delivery strategies targeting bone matrix, bone marrow, and specific bone cells are summarized with a comparison between different targeting ligands. Ultimately, this review will summarize recent advances in the clinical translation of bone-targeted therapies and provide a perspective on the challenges for the application of bone-targeted therapy in the clinic and future trends in this area.

Re-thinking osteoarthritis pathogenesis: what can we learn (and what do we need to unlearn) from mouse models about the mechanisms involved in disease development

Efforts to develop effective disease-modifying drugs to treat osteoarthritis have so far proved unsuccessful with a number of promising drug candidates from pre-clinical studies failing to show efficacy in clinical trials. It is therefore timely to re-evaluate our current understanding of osteoarthritis pathogenesis and the similarities and differences in disease development between commonly used pre-clinical mouse models and human patients. There is substantial heterogeneity between patients presenting with osteoarthritis and mounting evidence that the pathways involved in osteoarthritis (e.g. Wnt signalling) differ between patient sub-groups. There is also emerging evidence that the pathways involved in osteoarthritis differ between the STR/ort mouse model (the most extensively studied mouse model of spontaneously occurring osteoarthritis) and injury-induced osteoarthritis mouse models. For instance, while canonical Wnt signalling is upregulated in the synovium and cartilage at an early stage of disease in injury-induced osteoarthritis mouse models, this does not appear to be the case in the STR/ort mouse. Such findings may prove insightful for understanding the heterogeneity in mechanisms involved in osteoarthritis pathogenesis in human disease. However, it is important to recognise that there are differences between mice and humans in osteoarthritis pathogenesis. A much more extensive array of pathological changes are evident in osteoarthritic joints in individual mice with osteoarthritis compared to individual patients. There are also specified differences in the pathways involved in disease development. For instance, although increased TGF-β signalling is implicated in osteoarthritis development in both mouse models of osteoarthritis and human disease, in mice, this is mainly mediated through TGF-β3 whereas in humans, it is through TGF-β1. Studies in other tissues have shown TGF-β1 is more potent than TGF-β3 in inducing the switch to SMAD1/5 signalling that occurs in osteoarthritic cartilage and that TGF-β1 and TGF-β3 have opposing effects on fibrosis. It is therefore possible that the relative contribution of TGF-β signalling to joint pathology in osteoarthritis differs between murine models and humans. Understanding the similarities and differences in osteoarthritis pathogenesis between mouse models and humans is critical for understanding the translational potential of findings from pre-clinical studies.

Wnt signalling in the articular cartilage: A matter of balance

Degradation of the articular cartilage is a hallmark of osteoarthritis, a progressive and chronic musculoskeletal condition, affecting millions of people worldwide. The activation of several signalling cascades is altered during disease development: among them, the Wnt signalling plays a pivotal role in the maintenance of tissue homeostasis. Increasing evidence is showing that its activation needs to be maintained within a certain range to avoid the triggering of degenerative mechanisms. In this review, we summarise our current knowledge about how a balanced activation of the Wnt signalling is maintained in the articular cartilage, with a particular focus on receptor-mediated mechanisms.

WNT16 Regulation of the Articular Chondrocyte Phenotype in Mice

The anabolic effects of WNT16 on osteoblasts are well established, however, little is known regarding the role of WNT16 in chondrocytes. In this study, we evaluated Wnt16 expression and its biological effects on mouse articular chondrocytes (ACs), since these cells are key to the development of osteoarthritis. While ACs derived from the long bone epiphysis of 7-day old C57BL/6J mice express multiple Wnts, Wnt5b and Wnt16 represent the two most highly expressed Wnts (expressed at several-fold higher levels than other Wnts). Treatment of serum-free AC cultures, with 100 ng/mL of recombinant human (rh) WNT16 for 24 h (hrs), increased proliferation (20%, p < 0.05) and expression levels of makers (Sox9 and Col2) of immature chondrocytes at both 24 h and 72 h, while Acan increased at 72 h. Expression of Mmp9, a marker of mature chondrocytes was decreased at 24 h. Additionally, WNT16 treatment regulated expression levels of Wnt ligands in a biphasic manner, inhibiting its expression at 24 h, while stimulating expression at 72 h. To determine whether WNT16 exerted anabolic effects on the AC phenotype, ex vivo cultures of tibial epiphyses were treated with rhWNT16 or vehicle for 9 days, and the articular cartilage phenotype was evaluated by safranin O cartilage staining and expression of articular cartilage marker genes. Both articular cartilage area and expression levels of AC markers were increased after rhWNT16 treatment. Our data suggest that Wnt16 expressed in ACs may play a role in regulating joint cartilage homeostasis via its direct effect, as well as through modulating the expression of other Wnt ligands.

Osteoarthritis: pathogenic signaling pathways and therapeutic targets

Osteoarthritis (OA) is a chronic degenerative joint disorder that leads to disability and affects more than 500 million population worldwide. OA was believed to be caused by the wearing and tearing of articular cartilage, but it is now more commonly referred to as a chronic whole-joint disorder that is initiated with biochemical and cellular alterations in the synovial joint tissues, which leads to the histological and structural changes of the joint and ends up with the whole tissue dysfunction. Currently, there is no cure for OA, partly due to a lack of comprehensive understanding of the pathological mechanism of the initiation and progression of the disease. Therefore, a better understanding of pathological signaling pathways and key molecules involved in OA pathogenesis is crucial for therapeutic target design and drug development. In this review, we first summarize the epidemiology of OA, including its prevalence, incidence and burdens, and OA risk factors. We then focus on the roles and regulation of the pathological signaling pathways, such as Wnt/β-catenin, NF-κB, focal adhesion, HIFs, TGFβ/ΒΜP and FGF signaling pathways, and key regulators AMPK, mTOR, and RUNX2 in the onset and development of OA. In addition, the roles of factors associated with OA, including MMPs, ADAMTS/ADAMs, and PRG4, are discussed in detail. Finally, we provide updates on the current clinical therapies and clinical trials of biological treatments and drugs for OA. Research advances in basic knowledge of articular cartilage biology and OA pathogenesis will have a significant impact and translational value in developing OA therapeutic strategies.

Microarray analysis identifies coding and non-coding RNA markers of liver injury in whole body irradiated mice

Radiation injury from medical, accidental, or intentional sources can induce acute and long-term hepatic dysregulation, fibrosis, and cancer. This long-term hepatic dysregulation decreases quality of life and may lead to death. Our goal in this study is to determine acute changes in biological pathways and discover potential RNA biomarkers predictive of radiation injury. We performed whole transcriptome microarray analysis of mouse liver tissue (C57BL/6 J) 48 h after whole-body irradiation with 1, 2, 4, 8, and 12 Gray to identify significant expression changes in mRNAs, lncRNAs, and miRNAs, We also validated changes in specific RNAs through qRT-PCR. We used Ingenuity Pathway Analysis (IPA) to identify pathways associated with gene expression changes. We observed significant dysregulation of multiple mRNAs across all doses. In contrast, miRNA dysregulation was observed upwards of 2 Gray. The most significantly upregulated mRNAs function as tumor suppressors: Cdkn1a, Phlda3, and Eda2r. The most significantly downregulated mRNAs were involved in hemoglobin synthesis, inflammation, and mitochondrial function including multiple members of Hbb and Hba. The most significantly upregulated miRNA included: miR-34a-5p, miR-3102-5p, and miR-3960, while miR-342-3p, miR-142a-3p, and miR-223-3p were most significantly downregulated. IPA predicted activation of cell cycle checkpoint control pathways and inhibition of pathways relevant to inflammation and erythropoietin. Clarifying expression of mRNA, miRNA and lncRNA at a short time point (48 h) offers insight into potential biomarkers, including radiation markers shared across organs and animal models. This information, once validated in human models, can aid in development of bio-dosimetry biomarkers, and furthers our understanding of acute pathway dysregulation.

Disease modification and symptom relief in osteoarthritis using a mutated GCP-2/CXCL6 chemokine

We showed that the chemokine receptor C-X-C Motif Chemokine Receptor 2 (CXCR2) is essential for cartilage homeostasis. Here, we reveal that the CXCR2 ligand granulocyte chemotactic protein 2 (GCP-2) was expressed, during embryonic development, within the prospective permanent articular cartilage, but not in the epiphyseal cartilage destined to be replaced by bone. GCP-2 expression was retained in adult articular cartilage. GCP-2 loss-of-function inhibited extracellular matrix production. GCP-2 treatment promoted chondrogenesis in vitro and in human cartilage organoids implanted in nude mice in vivo. To exploit the chondrogenic activity of GCP-2, we disrupted its chemotactic activity, by mutagenizing a glycosaminoglycan binding sequence, which we hypothesized to be required for the formation of a GCP-2 haptotactic gradient on endothelia. This mutated version (GCP-2-T) had reduced capacity to induce transendothelial migration in vitro and in vivo, without affecting downstream receptor signaling through AKT, and chondrogenic activity. Intra-articular adenoviral overexpression of GCP-2-T, but not wild-type GCP-2, reduced pain and cartilage loss in instability-induced osteoarthritis in mice. We suggest that GCP-2-T may be used for disease modification in osteoarthritis.

Whole-genome RNA sequencing identifies distinct transcriptomic profiles in impingement cartilage between patients with femoroacetabular impingement and hip osteoarthritis

Femoroacetabular impingement (FAI) has a strong clinical association with the development of hip osteoarthritis (OA); however, the pathobiological mechanisms underlying the transition from focal impingement to global joint degeneration remain poorly understood. The purpose of this study is to use whole-genome RNA sequencing to identify and subsequently validate differentially expressed genes (DEGs) in femoral head articular cartilage samples from patients with FAI and hip OA secondary to FAI. Thirty-seven patients were included in the study with whole-genome RNA sequencing performed on 10 gender-matched patients in the FAI and OA cohorts and the remaining specimens were used for validation analyses. We identified a total of 3531 DEGs between the FAI and OA cohorts with multiple targets for genes implicated in canonical OA pathways. Quantitative reverse transcription-polymerase chain reaction validation confirmed increased expression of FGF18 and WNT16 in the FAI samples, while there was increased expression of MMP13 and ADAMTS4 in the OA samples. Expression levels of FGF18 and WNT16 were also higher in FAI samples with mild cartilage damage compared to FAI samples with severe cartilage damage or OA cartilage. Our study further expands the knowledge regarding distinct genetic reprogramming in the cartilage between FAI and hip OA patients. We independently validated the results of the sequencing analysis and found increased expression of anabolic markers in patients with FAI and minimal histologic cartilage damage, suggesting that anabolic signaling may be increased in early FAI with a transition to catabolic and inflammatory gene expression as FAI progresses towards more severe hip OA. Clinical significance:Cam-type FAI has a strong clinical association with hip OA; however, the cellular pathophysiology of disease progression remains poorly understood. Several previous studies have demonstrated increased expression of inflammatory markers in FAI cartilage samples, suggesting the involvement of these inflammatory pathways in the disease progression. Our study further expands the knowledge regarding distinct genetic reprogramming in the cartilage between FAI and hip OA patients. In addition to differences in inflammatory gene expression, we also identified differential expression in multiple pathways involved in hip OA progression.

Induction of iPSC-derived Prg4-positive cells with characteristics of superficial zone chondrocytes and fibroblast-like synovial cells

Background

Lubricin, a proteoglycan encoded by the PRG4 gene, is synthesised by superficial zone (SFZ) chondrocytes and synovial cells. It reduces friction between joints and allows smooth sliding of tendons. Although lubricin has been shown to be effective against osteoarthritis and synovitis in animals, its clinical application remains untested. In this study, we aimed to induce lubricin-expressing cells from pluripotent stem cells (iPSCs) and applied them locally via cell transplantation.

Methods

To generate iPSCs, OCT3/4, SOX2, KLF4, and L-MYC were transduced into fibroblasts derived from Prg4-mRFP1 transgenic mice. We established a protocol for the differentiation of iPSC-derived Prg4-mRFP1-positive cells and characterised their mRNA expression profile. Finally, we injected Prg4-mRFP1-positive cells into the paratenon, surrounding the Achilles tendons and knee joints of severe combined immunodeficient mice and assessed lubricin expression.

Result

Wnt3a, activin A, TGF-β1, and bFGF were applied to induce the differentiation of iPSC-derived Prg4-mRFP1-positive cells. Markers related to SFZ chondrocytes and fibroblast-like synovial cells (FLSs) were expressed during differentiation. RNA-sequencing indicated that iPSC-derived Prg4-mRFP1-positive cells manifested expression profiles typical of SFZ chondrocytes and FLSs. Transplanted iPSC-derived Prg4-mRFP1-positive cells survived around the Achilles tendons and in knee joints.

Conclusions

The present study describes a protocol for the differentiation of iPSC-derived Prg4-positive cells with characteristics of SFZ chondrocytes and FLSs. Transplantation of lubricin-expressing cells offers promise as a therapy against arthritis and synovitis.

"Genetic scissors" CRISPR/Cas9 genome editing cutting-edge biocarrier technology for bone and cartilage repair

CRISPR/Cas9 is a revolutionary genome editing technology with the tremendous advantages such as precisely targeting/shearing ability, low cost and convenient operation, becoming an efficient and indispensable tool in biological research. As a disruptive technique, CRISPR/Cas9 genome editing has a great potential to realize a future breakthrough in the clinical bone and cartilage repairing as well. This review highlights the research status of CRISPR/Cas9 system in bone and cartilage repair, illustrates its mechanism for promoting osteogenesis and chondrogenesis, and explores the development tendency of CRISPR/Cas9 in bone and cartilage repair to overcome the current limitations.

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.

Mice Lacking Wnt9a or Wnt4 Are Prone to Develop Spontaneous Osteoarthritis With Age and Display Alteration in Either the Trabecular or Cortical Bone Compartment

Osteoarthritis (OA) is a common degenerative disease of the joint, with a complex multifactorial not yet fully understood etiology. Over the past years, the Wnt signaling pathway has been implicated in osteoarthritis. In a recent genomewide association study (GWAS), the chromosomal location on chromosome 1, linked to the Wnt3a-Wnt9a gene locus, was identified as the most significant locus associated with a thumb osteoarthritis endophenotype. Previously, it was shown that WNT9a is involved in maintaining synovial cell identity in the elbow joint during embryogenesis. Here, we report that the conditional loss of Wnt9a in the Prx1-Cre expressing limb mesenchyme or Prg4-CreER expressing cells predispositions the mice to develop spontaneous OA-like changes with age. In addition, the trabecular bone volume is altered in these mice. Similarly, mice with a conditional loss of Wnt4 in the limb mesenchyme are also more prone to develop spontaneously OA-like joint alterations with age. These mice display additional alterations in their cortical bone. The combined loss of Wnt9a and Wnt4 increased the likelihood of the mice developing osteoarthritis-like changes and enhanced disease severity in the affected mice. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

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.

The superficial zone of articular cartilage

The superficial zone of articular cartilage contributes to smooth joint motion through the production of proteoglycan 4 (PRG4), also known as lubricin. Recent studies indicate novel effects of PRG4 as a signaling molecule, other than a simple extracellular matrix protein. Additionally, the accumulating evidence displays that various molecules and signaling pathways are involved in regulating the superficial zone and PRG4 expression. In addition, Prg4-expressing cells include a progenitor population of articular chondrocytes. Several non-clinical and clinical studies have shown that PRG4 and related molecules are promising candidates for disease-modifying drugs for treating osteoarthritis. Since PRG4 is also expressed in the synovium, tendons, and ligaments, further studies of PRG4-related pathways and PRG4-positive cells may elucidate the mechanisms underlying joint homeostasis.

ANP32A represses Wnt signaling across tissues thereby protecting against osteoarthritis and heart disease

OBJECTIVES

To investigate how ANP32A, previously linked to the antioxidant response, regulates Wnt signaling as unraveled by transcriptome analysis of Anp32a-deficient mouse articular cartilage, and its implications for osteoarthritis (OA) and diseases beyond the joint.

METHODS

Anp32a knockdown chondrogenic ATDC5 cells were cultured in micromasses. Wnt target genes, differentiation markers and matrix deposition were quantified. Wnt target genes were determined in articular cartilage from Anp32a-deficient mice and primary human articular chondrocytes upon ANP32A silencing, using qPCR, luciferase assays and immunohistochemistry. Co-immunoprecipitation, immunofluorescence and chromatin-immunoprecipitation quantitative PCR probed the molecular mechanism via which ANP32A regulates Wnt signaling. Anp32a-deficient mice were subjected to the destabilization of the medial meniscus (DMM) OA model and treated with a Wnt inhibitor and an antioxidant. Severity of OA was assessed by cartilage damage and osteophyte formation. Human Protein Atlas data analysis identified additional organs where ANP32A may regulate Wnt signaling. Wnt target genes were determined in heart and hippocampus from Anp32a-deficient mice, and cardiac hypertrophy and fibrosis quantified.

RESULTS

Anp32a loss triggered Wnt signaling hyper-activation in articular cartilage. Mechanistically, ANP32A inhibited target gene expression via histone acetylation masking. Wnt antagonist treatment reduced OA severity in Anp32a-deficient mice by preventing osteophyte formation but not cartilage degradation, contrasting with antioxidant treatment. Dual therapy ameliorated more OA features than individual treatments. Anp32a-deficient mice also showed Wnt hyper-activation in the heart, potentially explaining the cardiac hypertrophy phenotype found.

CONCLUSIONS

ANP32A is a novel translationally relevant repressor of Wnt signaling impacting osteoarthritis and cardiac disease.

Intra-articular injection of a novel Wnt pathway inhibitor, SM04690, upregulates Wnt16 expression and reduces disease progression in temporomandibular joint osteoarthritis

Abnormal Wnt signaling has been shown to be involved in the pathogenesis of temporomandibular joint osteoarthritis (TMJOA). Recent studies demonstrates that SM04690, a small-molecule inhibitor of the Wnt signaling pathway, is able to promote cartilage regeneration in a rat model of knee joint osteoarthritis. However, whether SM04690 has any effect on TMJOA is unknown. Here we first performed partial TMJ discectomy to induce TMJOA in rabbit and rat. Histology, TRAP staining, immunohistochemistry and μCT analysis showed intra-articular injection of SM04690 protected condylar cartilage from degeneration and attenuated abnormal subchondral bone remodeling of TMJ condylar in both rabbit and rat model TMJOA. We isolated and cultured primary condylar chondrocytes for in vitro studies to investigate molecular mechanisms and downstream effects of SM04690. We found that SM04690 inhibited the canonical Wnt pathway, upregulated the expression of Wnt16 and cartilage anabolic factors including COL2A1, SOX9 and aggrecan, suppressed the expression of cartilage catabolic factor MMP13 and protected chondrocytes from TNF-α-induced inflammatory response. Previous studies have identified fibrocartilage stem cells (FCSCs) localized within the TMJ condyle superficial zone niche that regenerate cartilage and repair joint injury. Here we showed that intra-articular injection of SM04690 increased the number of the TMJ condyle superficial zone (SZ) cells in vivo. Further in vitro studies revealed that SM04690 enhanced FCSCs chondrogenesis and formation of cartilaginous-like tissue in pellet cultures. Taken together, our work demonstrates that SM04690 treatment might be able to promote FCSCs chondrogenesis and repair TMJ cartilage, highlighting the therapeutic potential of intra-articular injection of SM04690 in TMJOA.

Modular Bioreactor Design for Directed Tendon/Ligament Tissue Engineering

Functional tissue-engineered tendons and ligaments remain to be prepared in a reproducible and scalable manner. This study evaluates an acellular 3D extracellular matrix (ECM) scaffold for tendon/ligament tissue engineering and their ability to support strain-induced gene regulation associated with the tenogenesis of cultured mesenchymal stromal cells. Preliminary data demonstrate unique gene regulation patterns compared to other scaffold forms, in particular in Wnt signaling. However, the need for a robust bioreactor system that minimizes process variation was also evident. A design control process was used to design and verify the functionality of a novel bioreactor. The system accommodates 3D scaffolds with clinically-relevant sizes, is capable of long-term culture with customizable mechanical strain regimens, incorporates in-line load measurement for continuous monitoring and feedback control, and allows a variety of scaffold configurations through a unique modular grip system. All critical functional specifications were met, including verification of physiological strain levels from 1–10%, frequency levels from 0.2–0.5 Hz, and accurate load measurement up to 50 N, which can be expanded on the basis of load cell capability. The design process serves as a model for establishing statistical functionality and reliability of investigative systems. This work sets the stage for detailed analyses of ECM scaffolds to identify critical differentiation signaling responses and essential matrix composition and cell–matrix interactions.

KIF26B Silencing Prevents Osseous Transdifferentiation of Progenitor/Stem Cells and Attenuates Ectopic Calcification in a Murine Model

Ectopic calcification is an osteogenic process that leads to the formation of inappropriate bone within intra-articular soft tissues, often in response to injury or surgery. The molecular mechanisms governing this phenotype have yet to be determined. Using a population genetics approach, we identified an association of the kinesin superfamily member 26b (Kif26b) with injury-induced ectopic calcification through quantitative trait locus analysis of recombinant inbred mouse strains, consistent with a genomewide association study that identified KIF26B as a severity locus for ectopic calcification in patients with hip osteoarthritis. Despite these associations of KIF26B with ectopic calcification, its mechanistic role and functional implications have not yet been fully elucidated. Here, we aim to decipher the functional role of KIF26B in osseous and chondrogenic transdifferentiation of human and murine progenitor/stem cells and in a murine model of non-invasive injury-induced intra-articular ectopic calcification. We found that KIF26B ablation via lentivirus-mediated shRNA significantly arrested osteogenesis of progenitor/stem cells and suppressed the expression of typical osteogenic marker genes. Conversely, KIF26B loss-of-function increased chondrogenesis as demonstrated by enhanced Safranin-O staining and by the elevated expression of chondrogenic marker genes. Furthermore, cell function analysis revealed that KIF26B knockdown significantly decreased cell viability and proliferation and induced cellular apoptosis. Mechanistically, loss of osteogenesis was reverted by the addition of a Wnt agonist, SKL2001, demonstrating a role of KIF26B in canonical Wnt/β-catenin signaling. Finally, intra-articular delivery of Kif26b shRNA in B6-129SF2/J mice significantly hampered the development of intra-articular ectopic calcification at 8 weeks after injury compared with mice treated with non-target scrambled shRNA. In summary, these observations highlight that KIF26B plays a crucial role in ectopic bone formation by repressing osteogenesis, but not chondrogenesis, potentially via modulating Wnt/β-catenin signaling. These findings establish KIF26B as a critical determinant of the osteogenic process in pathologic endochondral bone formation and an actionable target for pharmacotherapy to mitigate ectopic calcification (and heterotopic ossification). © 2021 American Society for Bone and Mineral Research (ASBMR).

Wnt Pathway Extracellular Components and Their Essential Roles in Bone Homeostasis

The Wnt pathway is involved in several processes essential for bone development and homeostasis. For proper functioning, the Wnt pathway is tightly regulated by numerous extracellular elements that act by both activating and inhibiting the pathway at different moments. This review aims to describe, summarize and update the findings regarding the extracellular modulators of the Wnt pathway, including co-receptors, ligands and inhibitors, in relation to bone homeostasis, with an emphasis on the animal models generated, the diseases associated with each gene and the bone processes in which each member is involved. The precise knowledge of all these elements will help us to identify possible targets that can be used as a therapeutic target for the treatment of bone diseases such as osteoporosis.

Wnt16 signaling in bone homeostasis and osteoarthristis

Wnts are secreted cysteine-rich glycoproteins involved in joint development and skeletal homeostasis and have been implicated in the occurrence of osteoarthritis. Over the past decade, Wnt16, a member of the Wnt family, has received widespread attention for its strong association with bone mineral density, cortical bone thickness, bone strength, and osteoporotic fracture risk. In recent years, further studies have shed light on the role of Wnt16 a positive regulator of bone mass and protective regulator of osteoarthritis progression. Transduction mechanisms and crosstalk involving Wnt16 signaling have also been illustrated. More importantly, local Wnt16 treatment has been shown to ease osteoarthritis, inhibit bone resorption, and promote new bone formation in bone defect models. Thus, Wnt16 is now a potential therapeutic target for skeletal diseases and osteoarthritis. This paper reviews our current understanding of the mechanisms by which Wnt16 signaling regulates bone homeostasis and osteoarthritis.

Mechanosignalling in cartilage: an emerging target for the treatment of osteoarthritis

Mechanical stimuli have fundamental roles in articular cartilage during health and disease. Chondrocytes respond to the physical properties of the cartilage extracellular matrix (ECM) and the mechanical forces exerted on them during joint loading. In osteoarthritis (OA), catabolic processes degrade the functional ECM and the composition and viscoelastic properties of the ECM produced by chondrocytes are altered. The abnormal loading environment created by these alterations propagates cell dysfunction and inflammation. Chondrocytes sense their physical environment via an array of mechanosensitive receptors and channels that activate a complex network of downstream signalling pathways to regulate several cell processes central to OA pathology. Advances in understanding the complex roles of specific mechanosignalling mechanisms in healthy and OA cartilage have highlighted molecular processes that can be therapeutically targeted to interrupt pathological feedback loops. The potential for combining these mechanosignalling targets with the rapidly expanding field of smart mechanoresponsive biomaterials and delivery systems is an emerging paradigm in OA treatment. The continued advances in this field have the potential to enable restoration of healthy mechanical microenvironments and signalling through the development of precision therapeutics, mechanoregulated biomaterials and drug systems in the near future.

SETD2-mediated epigenetic regulation of noncanonical Wnt5A during osteoclastogenesis

To define the role of SETD2 in the WNT5a signaling in the context of osteoclastogenesis, we exploited two different models: in vitro osteoclast differentiation, and K/BxN serum-induced arthritis model. We found that SETD2 and WNT5a were upregulated during osteoclast differentiation and after induction of arthritis. Using gain- and loss-of-function approaches in the myeloid cell, we confirmed that SETD2 regulated the osteoclast markers, and WNT5a via modulating active histone marks by enriching H3K36me3, and by reducing repressive H3K27me3 mark. Additionally, during osteoclastic differentiation, the transcription of Wnt5a was also associated with the active histone H3K9 and H4K8 acetylations. Mechanistically, SETD2 directed induction of NF-κβ expression facilitated the recruitment of H3K9Ac and H4K8Ac around the TSS region of the Wnt5a gene, thereby, assisting osteoclast differentiation. Together these findings for the first time revealed that SETD2 mediated epigenetic regulation of Wnt5a plays a critical role in osteoclastogenesis and induced arthritis. Model for the Role of SETD2 dependent regulation of osteoclastic differentiation. A In monocyte cells SETD2-dependent H3K36 trimethylation help to create open chromatin region along with active enhancer mark, H3K27Ac. This chromatin state facilitated the loss of a suppressive H3K27me3 mark. B Additionally, SETD2 mediated induction of NF-κβ expression leads to the recruitment of histone acetyl transferases, P300/PCAF, to the Wnt5a gene and establish H3K9Ac and H4K8Ac marks. Along with other activation marks, these acetylation marks help in Wnt5a transcription which leads to osteoclastogenesis.

WNT16 is Robustly Increased by Oncostatin M in Mouse Calvarial Osteoblasts and Acts as a Negative Feedback Regulator of Osteoclast Formation Induced by Oncostatin M

Background

Bone loss is often observed adjacent to inflammatory processes. The WNT signaling pathways have been implicated as novel regulators of both immune responses and bone metabolism. WNT16 is important for cortical bone mass by inhibiting osteoclast differentiation, and we have here investigated the regulation of WNT16 by several members of the pro-inflammatory gp130 cytokine family.

Methods

The expression and regulation of Wnt16 in primary murine cells were studied by qPCR, scRNAseq and in situ hybridization. Signaling pathways were studied by siRNA silencing. The importance of oncostatin M (OSM)-induced WNT16 expression for osteoclastogenesis was studied in cells from Wnt16-deficient and wild-type mice.

Results

We found that IL-6/sIL-6R and OSM induce the expression of Wnt16 in primary mouse calvarial osteoblasts, with OSM being the most robust stimulator. The induction of Wnt16 by OSM was dependent on gp130 and OSM receptor (OSMR), and downstream signaling by the SHC1/STAT3 pathway, but independent of ERK. Stimulation of the calvarial cells with OSM resulted in enhanced numbers of mature, oversized osteoclasts when cells were isolated from Wnt16 deficient mice compared to cells from wild-type mice. OSM did not affect Wnt16 mRNA expression in bone marrow cell cultures, explained by the finding that Wnt16 and Osmr are expressed in distinctly different cells in bone marrow, nor was osteoclast differentiation different in OSM-stimulated bone marrow cell cultures isolated from Wnt16^−/- or wild-type mice. Furthermore, we found that Wnt16 expression is substantially lower in cells from bone marrow compared to calvarial osteoblasts.

Conclusion

These findings demonstrate that OSM is a robust stimulator of Wnt16 mRNA in calvarial osteoblasts and that WNT16 acts as a negative feedback regulator of OSM-induced osteoclast formation in the calvarial bone cells, but not in the bone marrow.

Wnt16 protects chondrocytes from lumbar facet joint osteoarthritis through the Wnt/β-catenin pathway in low back pain patients

PURPOSE

Low back pain (LBP) is a long-lasting and chronic symptom without any exact cause. This study attempts to propose a new staging system based on the original grading system combined with pathological results and clinical symptoms to better clarify the dynamic evolution of LBP related to cartilage degeneration during facet joint osteoarthritis (FJOA). To explore a potential target for diagnosis, treatment, and drug intervention of facet joint osteoarthritis related LBP via protecting chondrocytes.

MATERIALS AND METHODS

All the facet joints were divided into 4 groups according to our new degenerative staging system based on Weishaupt grade, CT and MRI. Collect the facet joint samples from patients whom suffered lumbar fusion surgery for lumbar disc herniation. Molecular biology experiments were used to explore the effect of Wnt16 on the degeneration of facet joints. Micro-CT examination and pain stimulation test checked the biological function of Wnt16 in rats.

RESULTS

Wnt16 was significantly increased and more aggregated in the facet joint chondrocytes in the Phase III and Phase IV, which is consistent with the pathological findings of cartilage degeneration (OARSI). We found that Wnt16 participated in the regulation of FJOA via Wnt/β-catenin pathway in vitro, which was inhibited by specific inhibitor DKK1. The rats, rich expressed Wnt16, showed higher paw withdrawal thresholds and prolonged paw withdrawal latency to FJOA related LBP. Micro-CT examination for the lumbar spine of rats showed Wnt16 protected the chondrocytes from FJOA.

CONCLUSIONS

This study defined a new staging system for LBP related cartilage degeneration of facet joint based on the original grading system combined with pathological results and clinical symptoms. Wnt16 is expected to be a potential target for treatment of FJOA via protecting chondrocytes.

The Interaction between microRNAs and the Wnt/β-Catenin Signaling Pathway in Osteoarthritis

Osteoarthritis (OA) is a chronic disease affecting the whole joint, which still lacks a disease-modifying treatment. This suggests an incomplete understanding of underlying molecular mechanisms. The Wnt/β-catenin pathway is involved in different pathophysiological processes of OA. Interestingly, both excessive stimulation and suppression of this pathway can contribute to the pathogenesis of OA. microRNAs have been shown to regulate different cellular processes in different diseases, including the metabolic activity of chondrocytes and osteocytes. To bridge these findings, here we attempt to give a conclusive overview of microRNA regulation of the Wnt/β-catenin pathway in bone and cartilage, which may provide insights to advance the development of miRNA-based therapeutics for OA treatment.

ROR2 blockade as a therapy for osteoarthritis

Osteoarthritis is characterized by the loss of the articular cartilage, bone remodeling, pain, and disability. No pharmacological intervention can currently halt progression of osteoarthritis. Here, we show that blocking receptor tyrosine kinase-like orphan receptor 2 (ROR2) improves cartilage integrity and pain in osteoarthritis models by inhibiting yes-associated protein (YAP) signaling. ROR2 was up-regulated in the cartilage in response to inflammatory cytokines and mechanical stress. The main ligand for ROR2, WNT5A, and the targets YAP and connective tissue growth factor were up-regulated in osteoarthritis in humans. In vitro, ROR2 overexpression inhibited chondrocytic differentiation. Conversely, ROR2 blockade triggered chondrogenic differentiation of C3H10T¹/₂ cells and suppressed the expression of the cartilage-degrading enzymes a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-4 and ADAMTS-5. The chondrogenic effect of ROR2 blockade in the cartilage was independent of WNT signaling and was mediated by down-regulation of YAP signaling. ROR2 signaling induced G protein and Rho-dependent nuclear accumulation of YAP, and YAP inhibition was required but not sufficient for ROR2 blockade-induced chondrogenesis. ROR2 silencing protected mice from instability-induced osteoarthritis with improved structural outcomes, sustained pain relief, and without apparent side effects or organ toxicity. Last, ROR2 silencing in human articular chondrocytes transplanted in nude mice led to the formation of cartilage organoids with more and better differentiated extracellular matrix, suggesting that the anabolic effect of ROR2 blockade is conserved in humans. Thus, ROR2 blockade is efficacious and well tolerated in preclinical animal models of osteoarthritis.

The ciliary protein IFT88 controls post-natal cartilage thickness and influences development of osteoarthritis

OBJECTIVE

Mechanical and biological cues drive cellular signalling in cartilage development, health, and disease. Proteins of the primary cilium, implicated in transduction of biophysiochemical signals, control cartilage formation during skeletal development, but their influence in post-natal cartilage remains unknown.

METHODS

Ift88^fl/fl  and AggrecanCreER^T2  mice were crossed to create a cartilage-specific, inducible knockout mouse AggrecanCreER^T2 ;Ift88^fl/fl . Tibial articular cartilage (AC) thickness was assessed, through adolescence and adulthood, by histomorphometry and integrity by OARSI score. In situ mechanisms were investigated by immunohistochemistry (IHC), RNA scope and qPCR of micro-dissected cartilage. OA was induced by surgical destabilisation (DMM). Mice voluntarily exercised using wheels.

RESULTS

Deletion of IFT88 resulted in progressive reductions in medial AC thickness during adolescence, and marked atrophy in adulthood. At 34 weeks of age, medial thickness was reduced from 104.00μm, [100.30-110.50, 95% CI] in Ift88^fl/fl to 89.42μm [84.00-93.49, 95% CI] in AggrecanCreER^T2 ;Ift88^fl/fl (p<0.0001), associated with reductions in calcified cartilage. Occasionally, atrophy was associated with complete, spontaneous, medial cartilage degradation. Following DMM, AggrecanCreER^T2 ;Ift88^fl/fl mice had increased OA scores. Atrophy in mature AC was not associated with obvious increases in aggrecanase-mediated destruction or chondrocyte hypertrophy. Of 44 candidate genes analysed, only Tcf7l2 correlated with Ift88 expression in micro-dissected cartilage. However, RNA scope revealed increased hedgehog (Hh) signalling (Gli1), associated with reductions in Ift88, in AggrecanCreER^T2 ;Ift88^fl/fl cartilage. Wheel exercise restored both AC thickness and levels of Hh signalling in AggrecanCreER^T2 ;Ift88^fl/fl .

CONCLUSION

Our results demonstrate that IFT88 is chondroprotective, regulating AC thickness, potentially by thresholding a Hh response to physiological loading that controls cartilage calcification.

WNT3A-loaded exosomes enable cartilage repair

Cartilage defects repair poorly. Recent genetic studies suggest that WNT3a may contribute to cartilage regeneration, however the dense, avascular cartilage extracellular matrix limits its penetration and signalling to chondrocytes. Extracellular vesicles actively penetrate intact cartilage. This study investigates the effect of delivering WNT3a into large cartilage defects in vivo using exosomes as a delivery vehicle. Exosomes were purified by ultracentrifugation from conditioned medium of either L-cells overexpressing WNT3a or control un-transduced L-cells, and characterized by electron microscopy, nanoparticle tracking analysis and marker profiling. WNT3a loaded on exosomes was quantified by western blotting and functionally characterized in vitro using the SUPER8TOPFlash reporter assay and other established readouts including proliferation and proteoglycan content. In vivo pathway activation was assessed using TCF/Lef:H2B-GFP reporter mice. Wnt3a loaded exosomes were injected into the knees of mice, in which large osteochondral defects were surgically generated. The degree of repair was histologically scored after 8 weeks. WNT3a was successfully loaded on exosomes and resulted in activation of WNT signalling in vitro. In vivo, recombinant WNT3a failed to activate WNT signalling in cartilage, whereas a single administration of WNT3a loaded exosomes activated canonical WNT signalling for at least one week, and eight weeks later, improved the repair of osteochondral defects. WNT3a assembled on exosomes, is efficiently delivered into cartilage and contributes to the healing of osteochondral defects.

Experimental observation of the sequence of tibial plateau chondrocyte and matrix degeneration in spontaneous osteoarthritis in Guinea pigs

Background

To observe the sequence of chondrocyte degeneration and matrix degradation in the superficial surface cartilage of the tibial plateau in guinea pigs with spontaneous knee osteoarthritis (OA).

Methods

Sixty guinea pigs were euthanized at the ages of 8 months (n = 20),10 months (n = 20) and 12 months (n = 20) respectively. The degree of degeneration of the tibial plateau cartilage was evaluated by Osteoarthritis Research Society International (OARSI) score. The levels of Aggrecan,CollagenX,MMP-13 and Caspase-3 in the chondrocytes were detected by immunohistochemistry (IHC). The serum concentration of CTX-II was measured and compared. Western blot analysis was used to detect the levels of Aggrecan,CollagenX,MMP-13 and Caspase-3 in the cartilage tissue.

Results

The OARSI scores both in 8-month-old group and 10-month-old group were lower than that in the 12-month-old group. The levels of Aggrecan in articular chondrocyte were higher both in 8-month-old group and 10-month-old group than that in 12-month-old group. The level of Collagen X increased with the age of guinea pigs. And the levels of MMP-13 and caspase-3 both in 10-month-old group and 12-month-old group were higher than those in 8-month-old group. The concentration of CTX-II in serum increased significantly in 12 months old group.

Conclusion

The superficial chondrocytes of the tibial plateau first appeared to be hypertrophic and then apoptotic, and the matrix was further degraded when spontaneous knee osteoarthritis occurred in guinea pigs. Changes in the physiological state of chondrocytes are the initiating factors in the pathogenesis of knee OA.

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.

Osteoarthritis: Insights Offered by the Study of Bone Mass Genetics

PURPOSE OF REVIEW

This paper reviews how bone genetics has contributed to our understanding of the pathogenesis of osteoarthritis. As well as identifying specific genetic mechanisms involved in osteoporosis which also contribute to osteoarthritis, we review whether bone mineral density (BMD) plays a causal role in OA development.

RECENT FINDINGS

We examined whether those genetically predisposed to elevated BMD are at increased risk of developing OA, using our high bone mass (HBM) cohort. HBM individuals were found to have a greater prevalence of OA compared with family controls and greater development of radiographic features of OA over 8 years, with predominantly osteophytic OA. Initial Mendelian randomisation analysis provided additional support for a causal effect of increased BMD on increased OA risk. In contrast, more recent investigation estimates this relationship to be bi-directional. However, both these findings could be explained instead by shared biological pathways. Pathways which contribute to BMD appear to play an important role in OA development, likely reflecting shared common mechanisms as opposed to a causal effect of raised BMD on OA. Studies in HBM individuals suggest this reflects an important role of mechanisms involved in bone formation in OA development; however further work is required to establish whether the same applies to more common forms of OA within the general population.

Calcium calmodulin kinase II activity is required for cartilage homeostasis in osteoarthritis

WNT ligands can activate several signalling cascades of pivotal importance during development and regenerative processes. Their de-regulation has been associated with the onset of different diseases. Here we investigated the role of the WNT/Calcium Calmodulin Kinase II (CaMKII) pathway in osteoarthritis. We identified Heme Oxygenase I (HMOX1) and Sox-9 as specific markers of the WNT/CaMKII signalling in articular chondrocytes through a microarray analysis. We showed that the expression of the activated form of CaMKII, phospho-CaMKII, was increased in human and murine osteoarthritis and the expression of HMOX1 was accordingly reduced, demonstrating the activation of the pathway during disease progression. To elucidate its function, we administered the CaMKII inhibitor KN93 to mice in which osteoarthritis was induced by resection of the anterior horn of the medial meniscus and of the medial collateral ligament in the knee joint. Pharmacological blockade of CaMKII exacerbated cartilage damage and bone remodelling. Finally, we showed that CaMKII inhibition in articular chondrocytes upregulated the expression of matrix remodelling enzymes alone and in combination with Interleukin 1. These results suggest an important homeostatic role of the WNT/CaMKII signalling in osteoarthritis which could be exploited in the future for therapeutic purposes.

Wnt16 Elicits a Protective Effect Against Fractures and Supports Bone Repair in Zebrafish

Bone homeostasis is a dynamic, multicellular process that is required throughout life to maintain bone integrity, prevent fracture, and respond to skeletal damage. WNT16 has been linked to bone fragility and osteoporosis in human genome wide‐association studies, as well as the functional hematopoiesis of leukocytes in vivo. However, the mechanisms by which WNT16 promotes bone health and repair are not fully understood. In this study, CRISPR‐Cas9 was used to generate mutant zebrafish lacking Wnt16 (wnt16^−/−) to study its effect on bone dynamically. The wnt16 mutants displayed variable tissue mineral density (TMD) and were susceptible to spontaneous fractures and the accumulation of bone calluses at an early age. Fractures were induced in the lepidotrichia of the caudal fins of wnt16^−/− and WT zebrafish; this model was used to probe the mechanisms by which Wnt16 regulates skeletal and immune cell dynamics in vivo. In WT fins, wnt16 expression increased significantly during the early stages for bone repair. Mineralization of bone during fracture repair was significantly delayed in wnt16 mutants compared with WT zebrafish. Surprisingly, there was no evidence that the recruitment of innate immune cells to fractures or soft callus formation was altered in wnt16 mutants. However, osteoblast recruitment was significantly delayed in wnt16 mutants postfracture, coinciding with precocious activation of the canonical Wnt signaling pathway. In situ hybridization suggests that canonical Wnt‐responsive cells within fractures are osteoblast progenitors, and that osteoblast differentiation during bone repair is coordinated by the dynamic expression of runx2a and wnt16. This study highlights zebrafish as an emerging model for functionally validating osteoporosis–associated genes and investigating fracture repair dynamically in vivo. Using this model, it was found that Wnt16 protects against fracture and supports bone repair, likely by modulating canonical Wnt activity via runx2a to facilitate osteoblast differentiation and bone matrix deposition. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

WNT16 is upregulated early in mouse TMJ osteoarthritis and protects fibrochondrocytes against IL-1β induced inflammatory response by regulation of RUNX2/MMP13 cascade

WNT16 has been shown to play important roles in joint formation, bone homeostasis and knee joint osteoarthritis. However, whether WNT16 has any effect during temporomandibular joint osteoarthritis (TMJOA) is still unknown. Here, we first established a surgically induced TMJOA model by performing partial discectomy in discs of TMJ in mice. Further, we investigated the role of WNT16 during the initiation and progression of TMJOA. Our results showed that WNT16 expression is upregulated early at 4 weeks after initiation of osteoarthritis by partial discectomy in mouse TMJ cartilage, but decreased after 12 weeks post-surgery. Further cellular and molecular analyses revealed that WNT16 signals via both the canonical WNT/β-catenin and non-canonical WNT/JNK-cJUN pathways, upregulates the expression of Lubricin and SOX9, and protects against IL-1β induced inflammatory response by regulation of RUNX2/MMP13 cascade in fibrochondrocytes. In conclusion, WNT16 may play an important role in the early stage of TMJOA by regulating cartilage anabolic and catabolic factors, and may serve as novel therapeutic targets for TMJOA.

Molecular mechanisms of mechanical load-induced osteoarthritis

INTRODUCTION

Mechanical loading enhances the progression of osteoarthritis. However, its molecular mechanisms have not been established.

OBJECTIVE

The aim of this review was to summarize the probable mechanisms of mechanical load-induced osteoarthritis.

METHODS

A comprehensive search strategy was used to search PubMed and EMBASE databases (from the 15th of January 2015 to the 20th of October 2020). Search terms included "osteoarthritis", "mechanical load", and "mechanism".

RESULTS

Abnormal mechanical loading activates the interleukin-1β, tumour necrosis factor-α, nuclear factor kappa-B, Wnt, transforming growth factor-β, microRNAs pathways, and the oxidative stress pathway. These pathways induce the pathological progression of osteoarthritis. Mechanical stress signal receptors such as integrin, ion channel receptors, hydrogen peroxide-inducible clone-5, Gremlin-1, and transient receptor potential channel 4 are present in the articular cartilages.

CONCLUSION

This review highlights the molecular mechanisms of mechanical loading in inducing chondrocyte apoptosis and extracellular matrix degradation. These mechanisms provide potential targets for osteoarthritis prevention and treatment.

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.

Wnt signaling in breast cancer: biological mechanisms, challenges and opportunities

Wnt signaling is a highly conserved signaling pathway that plays a critical role in controlling embryonic and organ development, as well as cancer progression. Genome-wide sequencing and gene expression profile analyses have demonstrated that Wnt signaling is involved mainly in the processes of breast cancer proliferation and metastasis. The most recent studies have indicated that Wnt signaling is also crucial in breast cancer immune microenvironment regulation, stemness maintenance, therapeutic resistance, phenotype shaping, etc. Wnt/β-Catenin, Wnt-planar cell polarity (PCP), and Wnt-Ca2+ signaling are three well-established Wnt signaling pathways that share overlapping components and play different roles in breast cancer progression. In this review, we summarize the main findings concerning the relationship between Wnt signaling and breast cancer and provide an overview of existing mechanisms, challenges, and potential opportunities for advancing the therapy and diagnosis of breast cancer.

Mechanism of Action of Acupotomy in Inhibiting Chondrocyte Apoptosis in Rabbits with KOA through the PI3K/Akt Signaling Pathway

Objective

We examined the effects of acupotomy on the PI3K/Akt signaling pathway to elucidate the mechanism of action of acupotomy on articular chondrocyte apoptosis among rabbits with knee osteoarthritis (KOA).

Methods

New Zealand rabbits were randomly assigned to a healthy control group, placebo group, acupotomy group, and drug group, with 10 rabbits in each group. Changes in chondrocytes were examined by hematoxylin and eosin staining, and articular chondrocyte apoptosis was measured by electron microscopy and immunofluorescence. The mRNA and protein expression levels of PI3K and Akt were measured by real-time quantitative PCR and Western blot.

Results

In contrast, less chromatin margination and clear and smooth nuclear envelope boundary were visible in the acupotomy group and drug group. The number of apoptotic chondrocytes in the knee joint of rabbits was significantly higher in the placebo group than that in the acupotomy group and drug group (P < 0.05). The acupotomy group had a nonsignificantly lower number of apoptotic chondrocytes than the drug group (P > 0.05). Furthermore, the mRNA and protein expression levels of PI3K and Akt were significantly higher in the acupotomy group and drug group than those in the placebo group (P < 0.05) and were closer to normal levels in the acupotomy group than those in the drug group (P < 0.05). PI3K and Akt expression levels were negatively correlated with chondrocyte apoptosis in the knee joint of rabbits in all groups.

Conclusion

Inhibiting chondrocyte apoptosis in the knee joint of KOA rabbits by upregulating the PI3K/Akt signaling pathway may be a possible mechanism of acupotomy in treating KOA.