Inhibition of beta-catenin signaling in articular chondrocytes results in articular cartilage destruction

Parathyroid hormone (1-34) retards the lumbar facet joint degeneration and activates Wnt/β-catenin signaling pathway in ovariectomized rats

PURPOSE

Facet joint degeneration (FJD) is a major cause of low back pain. Parathyroid hormone (PTH) (1-34) is commonly used to treat osteoporosis. However, little is known about its effects on FJD induced by estrogen deficiency. This study aims to investigate the effects of PTH (1-34) on FJD induced by estrogen deficiency and the underlying pathogenesis of the disease.

METHODS

Forty 3-month-old female Sprague-Dawley rats were randomly divided into four groups: 30 received bilateral ovariectomy (OVX) followed by 12 weeks of treatment with normal saline, PTH (1-34) or 17β-estradiol (E2), and 10 received sham surgery followed by administration of normal saline. Status and Wnt/β-catenin signaling activity in the cartilage and subchondral bone of the L4-L5 FJs and serum biomarkers were analyzed.

RESULTS

Administration of PTH (1-34) and E2 ameliorated cartilage lesions, and significantly decreased MMP-13 and caspase-3 levels and chondrocyte apoptosis. PTH (1-34) but not E2 significantly increased cartilage thickness, number of chondrocytes, and the expression of aggrecan. PTH (1-34) significantly improved microarchitecture parameters of subchondral bone, increased the expression of collagen I and osteocalcin, and decreased RANKL/OPG ratio. E2 treatment significantly increased the OPG level and decreased the RANKL/OPG ratio in the subchondral bone of ovariectomized rats, but it did not significantly improve the microarchitecture parameters of subchondral bone. Wnt3a and β-catenin expression was significantly reduced in the articular cartilage and subchondral bone in OVX rats, but PTH (1-34) could increase the expression of these proteins. E2 significantly increased the activity of Wnt/β-catenin pathway only in cartilage, but not in subchondral bone. The restoration of Wnt/β-catenin signaling had an obvious correlation with the improvement of some parameters associated with the FJs status.

CONCLUSION

Wnt/β-catenin signaling may be a potential therapeutic target for FJD induced by estrogen deficiency. PTH (1-34) is effective in treating this disease with better efficacy than 17β-estradiol, and the efficacy may be attributed to its restoration of Wnt/β-catenin signaling.

Signalling interaction between β-catenin and other signalling molecules during osteoarthritis development

Osteoarthritis (OA) is the most prevalent disorder of synovial joint affecting multiple joints. In the past decade, we have witnessed conceptual switch of OA pathogenesis from a 'wear and tear' disease to a disease affecting entire joint. Extensive studies have been conducted to understand the underlying mechanisms of OA using genetic mouse models and ex vivo joint tissues derived from individuals with OA. These studies revealed that multiple signalling pathways are involved in OA development, including the canonical Wnt/β-catenin signalling and its interaction with other signalling pathways, such as transforming growth factor β (TGF-β), bone morphogenic protein (BMP), Indian Hedgehog (Ihh), nuclear factor κB (NF-κB), fibroblast growth factor (FGF), and Notch. The identification of signalling interaction and underlying mechanisms are currently underway and the specific molecule(s) and key signalling pathway(s) playing a decisive role in OA development need to be evaluated. This review will focus on recent progresses in understanding of the critical role of Wnt/β-catenin signalling in OA pathogenesis and interaction of β-catenin with other pathways, such as TGF-β, BMP, Notch, Ihh, NF-κB, and FGF. Understanding of these novel insights into the interaction of β-catenin with other pathways and its integration into a complex gene regulatory network during OA development will help us identify the key signalling pathway of OA pathogenesis leading to the discovery of novel therapeutic strategies for OA intervention.

Cbfβ regulates Wnt/β-catenin, Hippo/Yap, and Tgfβ signaling pathways in articular cartilage homeostasis and protects from ACLT surgery-induced osteoarthritis

As the most common degenerative joint disease, osteoarthritis (OA) contributes significantly to pain and disability during aging. Several genes of interest involved in articular cartilage damage in OA have been identified. However, the direct causes of OA are poorly understood. Evaluating the public human RNA-seq dataset showed that CBFB (subunit of a heterodimeric Cbfβ/Runx1, Runx2, or Runx3 complex) expression is decreased in the cartilage of patients with OA. Here, we found that the chondrocyte-specific deletion of Cbfb in tamoxifen-induced Cbfbf/f;Col2a1-CreERT mice caused a spontaneous OA phenotype, worn articular cartilage, increased inflammation, and osteophytes. RNA-sequencing analysis showed that Cbfβ deficiency in articular cartilage resulted in reduced cartilage regeneration, increased canonical Wnt signaling and inflammatory response, and decreased Hippo/Yap signaling and Tgfβ signaling. Immunostaining and western blot validated these RNA-seq analysis results. ACLT surgery-induced OA decreased Cbfβ and Yap expression and increased active β-catenin expression in articular cartilage, while local AAV-mediated Cbfb overexpression promoted Yap expression and diminished active β-catenin expression in OA lesions. Remarkably, AAV-mediated Cbfb overexpression in knee joints of mice with OA showed the significant protective effect of Cbfβ on articular cartilage in the ACLT OA mouse model. Overall, this study, using loss-of-function and gain-of-function approaches, uncovered that low expression of Cbfβ may be the cause of OA. Moreover, Local admission of Cbfb may rescue and protect OA through decreasing Wnt/β-catenin signaling, and increasing Hippo/Yap signaling and Tgfβ/Smad2/3 signaling in OA articular cartilage, indicating that local Cbfb overexpression could be an effective strategy for treatment of OA.

Osteoarthritis versus psoriasis arthritis: Physiopathology, cellular signaling, and therapeutic strategies

Osteoarthritis and psoriasis arthritis are two degenerative forms of arthritis that share similar yet also different manifestations at the histological, cellular, and clinical levels. Rheumatologists have marked them as two entirely distinct arthropathies. Given recent discoveries in disease initiation and progression, potential mechanisms, cellular signaling pathways, and ongoing clinical therapeutics, there are now more opportunities for discovering osteoarthritis drugs. This review summarized the osteoarthritis and psoriasis arthritis signaling pathways, crosstalk between BMP, WNT, TGF-β, VEGF, TLR, and FGF signaling pathways, biomarkers, and anatomical pathologies. Through bench research, we demonstrated that regenerative medicine is a promising alternative for treating osteoarthritis by highlighting significant scientific discoveries on entheses, multiple signaling blockers, and novel molecules such as immunoglobulin new antigen receptors targeted for potential drug evaluation. Furthermore, we offered valuable therapeutic approaches with a multidisciplinary strategy to treat patients with osteoarthritis or psoriasis arthritis in the coming future in the clinic.

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.

WNT5A regulates the proliferation, apoptosis and stemness of human stem Leydig cells via the β-catenin signaling pathway

Stem Leydig cells (SLCs) are essential for maintaining normal spermatogenesis as the significant component of testis microenvironment and gonadal aging. Although progress has been achieved in the regulation of male germ cells in mammals and humans, it remains unknown about the genes and signaling pathways of human SLCs. Here we have demonstrated, for the first time, that WNT5A (Wnt family member 5a) mediates the proliferation, apoptosis, and stemness of human SLCs, namely NGFR+ Leydig cells. We revealed that NGFR+ Leydig cells expressed NGFR, PDGFRA, NES, NR2F2, and THY1, hallmarks for SLCs. RNA-sequencing showed that WNT5A was expressed at a higher level in human SLCs than non-SLCs, while immunohistochemistry and Western blots further illustrated that WNT5A was predominantly expressed in human SLCs. Notably, CCK-8, EdU and Western blots displayed that WNT5A enhanced the proliferation and DNA synthesis and retained stemness of human SLCs, whereas flow cytometry and TUNEL analyses demonstrated that WNT5A inhibited the apoptosis of these cells. WNT5A knockdown caused an increase in LC lineage differentiation of human SLCs and reversed the effect of WNT5A overexpression on fate decisions of human SLCs. In addition, WNT5A silencing  resulted in the decreases in nuclear translocation of β-catenin and expression levels of c-Myc, CD44, and Cyclin D1. Collectively, these results implicate that WNT5A regulates the proliferation, apoptosis and stemness of human SLCs through the activation of the β-catenin signaling pathway. This study thus provides a novel molecular mechanism underlying the fate determinations of human SLCs, and it offers a new insight into the niche regulation of human testis.

WTAP-mediated m6A modification of FRZB triggers the inflammatory response via the Wnt signaling pathway in osteoarthritis

Osteoarthritis (OA) is the most common form of arthritis. However, the exact pathogenesis remains unclear. Emerging evidence shows that N6-methyladenosine (m6A) modification may have an important role in OA pathogenesis. This study aimed to investigate the role of m6A writers and the underlying mechanisms in osteoarthritic cartilage. Among m6A methyltransferases, Wilms tumor 1-associated protein (WTAP) expression most significantly differed in clinical osteoarthritic cartilage. WTAP regulated extracellular matrix (ECM) degradation, inflammation and antioxidation in human chondrocytes. Mechanistically, the m6A modification and relative downstream targets in osteoarthritic cartilage were assessed by methylated RNA immunoprecipitation sequencing (MeRIP-seq) and RNA sequencing, which indicated that the expression of frizzled-related protein (FRZB), a secreted Wnt antagonist, was abnormally decreased and accompanied by high m6A modification in osteoarthritic cartilage. In vitro dysregulated WTAP had positive effects on β-catenin expression by targeting FRZB, which finally contributed to the cartilage injury phenotype in chondrocytes. Intra-articular injection of adeno-associated virus-WTAP alleviated OA progression in a mouse model, while this protective effect could be reversed by the application of a Wnt/β-catenin activator. In summary, this study revealed that WTAP-dependent RNA m6A modification contributed to Wnt/β-catenin pathway activation and OA progression through post-transcriptional regulation of FRZB mRNA, thus providing a potentially effective therapeutic strategy for OA treatment.

Cbfβ regulates Wnt/β-catenin, Hippo/Yap, and TGFβ signaling pathways in articular cartilage homeostasis and protects from ACLT surgery-induced osteoarthritis

As the most common degenerative joint disease, osteoarthritis (OA) contributes significantly to pain and disability during aging. Several genes of interest involved in articular cartilage damage in OA have been identified. However, the direct causes of OA are poorly understood. Evaluating the public human RNA-seq dataset showed that Cbfβ, (subunit of a heterodimeric Cbfβ/Runx1,Runx2, or Runx3 complex) expression is decreased in the cartilage of patients with OA. Here, we found that the chondrocyte-specific deletion of Cbfβ in tamoxifen-induced Cbfβf/fCol2α1-CreERT mice caused a spontaneous OA phenotype, worn articular cartilage, increased inflammation, and osteophytes. RNA-sequencing analysis showed that Cbfβ deficiency in articular cartilage resulted in reduced cartilage regeneration, increased canonical Wnt signaling and inflammatory response, and decreased Hippo/YAP signaling and TGF-β signaling. Immunostaining and western blot validated these RNA-seq analysis results. ACLT surgery-induced OA decreased Cbfβ and Yap expression and increased active β-catenin expression in articular cartilage, while local AAV-mediated Cbfβ overexpression promoted Yap expression and diminished active β-catenin expression in OA lesions. Remarkably, AAV-mediated Cbfβ overexpression in knee joints of mice with OA showed the significant protective effect of Cbfβ on articular cartilage in the ACLT OA mouse model. Overall, this study, using loss-of-function and gain-of-function approaches, uncovered that low expression of Cbfβ may be the cause of OA. Moreover, Local admission of Cbfβ may rescue and protect OA through decreasing Wnt/β-catenin signaling, and increasing Hippo/Yap signaling and TGFβ/Smad2/3 signaling in OA articular cartilage, indicating that local Cbfβ overexpression could be an effective strategy for treatment of OA.

Exploring Omega-3's Impact on the Expression of Bone-Related Genes in Meagre (Argyrosomus regius)

Dietary supplementation with Omega-3 fatty acids seems to promote skeletal health. Therefore, their consumption at imbalanced or excessive levels has offered less beneficial or even prejudicial effects. Fish produced in aquaculture regimes are prone to develop abnormal skeletons. Although larval cultures are usually fed with diets supplemented with Omega-3 Long Chain Polyunsaturated fatty acids (LC-PUFAs), the lack of knowledge about the optimal requirements for fatty acids or about their impact on mechanisms that regulate skeletal development has impeded the design of diets that could improve bone formation during larval stages when the majority of skeletal anomalies appear. In this study, Argyrosomus regius larvae were fed different levels of Omega-3s (2.6% and 3.6% DW on diet) compared to a commercial diet. At 28 days after hatching (DAH), their transcriptomes were analyzed to study the modulation exerted in gene expression dynamics during larval development and identify impacted genes that can contribute to skeletal formation. Mainly, both levels of supplementation modulated bone-cell proliferation, the synthesis of bone components such as the extracellular matrix, and molecules involved in the interaction and signaling between bone components or in important cellular processes. The 2.6% level impacted several genes related to cartilage development, denoting a special impact on endochondral ossification, delaying this process. However, the 3.6% level seemed to accelerate this process by enhancing skeletal development. These results offered important insights into the impact of dietary Omega-3 LC-PUFAs on genes involved in the main molecular mechanism and cellular processes involved in skeletal development.

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.

Bulk RNA-seq analyses of mandibular condylar cartilage in a post-traumatic TMJ osteoarthritis rabbit model

OBJECTIVE

The temporomandibular joint (TMJ) is anatomically comprised of the mandibular condylar cartilage (CC) lined with fibrocartilaginous superficial zone and is crucial for eating and dental occlusion. TMJ osteoarthritis (OA) leads to pain, joint dysfunction and permanent loss of cartilage tissue. However, there are no drugs clinically available that ameliorate OA and little is known about global profiles of genes that contribute to TMJ OA. Furthermore, animal models that recapitulate the complexity of signalling pathways contributing to OA pathogenesis are crucial for designing novel biologics that thwart OA progression. We have previously developed a New Zealand white rabbit TMJ injury model that demonstrates CC degeneration. Here, we performed genome-wide profiling to identify new signalling pathways critical for cellular functions during OA pathology.

MATERIALS AND METHODS

Temporomandibular joint OA was surgically induced in New Zealand white rabbits. Three months following injury, we performed global gene expression profiling of the TMJ condyle. RNA samples from TMJ condyles were subjected to sequencing. After raw RNA-seq data were mapped to relevant genomes, differential expression was analysed with DESeq2. Gene ontology enrichment analysis and Kyoto Encyclopedia of Genes and Genomes pathway analysis were conducted.

RESULTS/CONCLUSIONS

Our study revealed multiple pathways altered during TMJ OA induction including the Wnt, Notch and PI3K-Akt signalling pathways. We demonstrate an animal model that recapitulates the complexity of the cues and signals underlying TMJ OA pathogenesis, which is essential for developing and testing novel pharmacologic agents to treat OA.

Identification of genetic variants associated with anterior cruciate ligament rupture and AKC standard coat color in the Labrador Retriever

Canine anterior cruciate ligament (ACL) rupture is a common complex disease. Prevalence of ACL rupture is breed dependent. In an epidemiological study, yellow coat color was associated with increased risk of ACL rupture in the Labrador Retriever. ACL rupture risk variants may be linked to coat color through genetic selection or through linkage with coat color genes. To investigate these associations, Labrador Retrievers were phenotyped as ACL rupture case or controls and for coat color and were single nucleotide polymorphism (SNP) genotyped. After filtering, ~ 697 K SNPs were analyzed using GEMMA and mvBIMBAM for multivariate association. Functional annotation clustering analysis with DAVID was performed on candidate genes. A large 8 Mb region on chromosome 5 that included ACSF3, as well as 32 additional SNPs, met genome-wide significance at P < 6.07E-7 or Log10(BF) = 3.0 for GEMMA and mvBIMBAM, respectively. On chromosome 23, SNPs were located within or near PCCB and MSL2. On chromosome 30, a SNP was located within IGDCC3. SNPs associated with coat color were also located within ADAM9, FAM109B, SULT1C4, RTDR1, BCR, and RGS7. DZIP1L was associated with ACL rupture. Several significant SNPs on chromosomes 2, 3, 7, 24, and 26 were located within uncharacterized regions or long non-coding RNA sequences. This study validates associations with the previous ACL rupture candidate genes ACSF3 and DZIP1L and identifies novel candidate genes. These variants could act as targets for treatment or as factors in disease prediction modeling. The study highlighted the importance of regulatory SNPs in the disease, as several significant SNPs were located within non-coding regions.

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.

Responding to ACL Injury and its Treatments: Comparative Gene Expression between Articular Cartilage and Synovium

The relationship between cartilage and synovium is a rapidly growing area of osteoarthritis research. However, to the best of our knowledge, the relationships in gene expression between these two tissues have not been explored in mid-stage disease development. The current study compared the transcriptomes of these two tissues in a large animal model one year following posttraumatic osteoarthritis induction and multiple surgical treatment modalities. Thirty-six Yucatan minipigs underwent transection of the anterior cruciate ligament. Subjects were randomized to no further intervention, ligament reconstruction, or ligament repair augmented with an extracellular matrix (ECM) scaffold, followed by RNA sequencing of the articular cartilage and synovium at 52 weeks after harvest. Twelve intact contralateral knees served as controls. Across all treatment modalities, the primary difference in the transcriptomes was that the articular cartilage had greater upregulation of genes related to immune activation compared to the synovium-once baseline differences between cartilage and synovium were adjusted for. Oppositely, synovium featured greater upregulation of genes related to Wnt signaling compared to articular cartilage. After adjusting for expression differences between cartilage and synovium seen following ligament reconstruction, ligament repair with an ECM scaffold upregulated pathways related to ion homeostasis, tissue remodeling, and collagen catabolism in cartilage relative to synovium. These findings implicate inflammatory pathways within cartilage in the mid-stage development of posttraumatic osteoarthritis, independent of surgical treatment. Moreover, use of an ECM scaffold may exert a chondroprotective effect over gold-standard reconstruction through preferentially activating ion homeostatic and tissue remodeling pathways within cartilage.

Upregulation of β-catenin signaling represents a single common pathway leading to the various phenotypes of spinal degeneration and pain

Spine degeneration is an aging-related disease, but its molecular mechanisms remain unknown, although elevated β-catenin signaling has been reported to be involved in intervertebral disc degeneration. Here, we determined the role of β-catenin signaling in spinal degeneration and in the homeostasis of the functional spinal unit (FSU), which includes the intervertebral disc, vertebra and facet joint and is the smallest physiological motion unit of the spine. We showed that pain sensitivity in patients with spinal degeneration is highly correlated with β-catenin protein levels. We then generated a mouse model of spinal degeneration by transgenic expression of constitutively active β-catenin in Col2⁺ cells. We found that β-catenin-TCF7 activated the transcription of CCL2, a known critical factor in osteoarthritic pain. Using a lumbar spine instability model, we showed that a β-catenin inhibitor relieved low back pain. Our study indicates that β-catenin plays a critical role in maintaining spine tissue homeostasis, its abnormal upregulation leads to severe spinal degeneration, and its targeting could be an avenue to treat this condition.

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.

Evaluation of the anti-RANKL monoclonal antibody in rheumatoid arthritis rats

Objectives: In this study, we aimed to investigate the therapeutic effect of anti-receptor activator of nuclear factor kappa-κB ligand (RANKL) monoclonal antibodies R748-1-1-1, R748-1-1-2 and R748-1-1-3 on rheumatoid arthritis (RA) in a rat model.

Materials and methods: Gene cloning, hybridoma technology, affinity purification, enzyme-linked immunosorbent assay, general observation, hematoxylin-eosin staining, X-ray, and many other experimental techniques were used in this study.

Results: Improved collagen-induced arthritis (CIA) modeling was successfully constructed. The RANKL gene was cloned and the anti-RANKL monoclonal antibody was prepared. Following treatment with the anti-RANKL monoclonal antibody, the soft tissue swelling of the hind paws, the joint thickening, the narrowed joint gap, and the blurred edge of the bone joint were improved. The pathological changes such as synovial hyperplasia of fibrous tissue, cartilage and bone destruction were significantly decreased in the anti-RANKL monoclonal antibody-treated CIA group. Compared to the normal control group and phosphate buffer saline (PBS)-treated CIA group, the expression of tumor necrosis factor-alpha (TNF-α) and interleukin-1 (IL-1) in antibody-treated CIA group, positive drug-treated CIA group, and IgG-treated CIA group were decreased (p<0.05).

Conclusion: The anti-RANKL monoclonal antibody can promote the therapeutic effect of RA rats, indicating that the anti-RANKL monoclonal antibody has a certain potential value and may be beneficial to the further study of the mechanism of RA treatment.

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.

Synovial fibroblasts assume distinct functional identities and secrete R-spondin 2 in osteoarthritis

OBJECTIVES

Synovium is acutely affected following joint trauma and contributes to post-traumatic osteoarthritis (PTOA) progression. Little is known about discrete cell types and molecular mechanisms in PTOA synovium. We aimed to describe synovial cell populations and their dynamics in PTOA, with a focus on fibroblasts. We also sought to define mechanisms of synovial Wnt/β-catenin signalling, given its emerging importance in arthritis.

METHODS

We subjected mice to non-invasive anterior cruciate ligament rupture as a model of human joint injury. We performed single-cell RNA-sequencing to assess synovial cell populations, subjected Wnt-GFP reporter mice to joint injury to study Wnt-active cells, and performed intra-articular injections of the Wnt agonist R-spondin 2 (Rspo2) to assess whether gain of function induced pathologies characteristic of PTOA. Lastly, we used cultured fibroblasts, macrophages and chondrocytes to study how Rspo2 orchestrates crosstalk between joint cell types.

RESULTS

We uncovered seven distinct functional subsets of synovial fibroblasts in healthy and injured synovium, and defined their temporal dynamics in early and established PTOA. Wnt/β-catenin signalling was overactive in PTOA synovium, and Rspo2 was strongly induced after injury and secreted exclusively by Prg4^hi lining fibroblasts. Trajectory analyses predicted that Prg4^hi lining fibroblasts arise from a pool of Dpp4+ mesenchymal progenitors in synovium, with SOX5 identified as a potential regulator of this emergence. We also showed that Rspo2 orchestrated pathological crosstalk between synovial fibroblasts, macrophages and chondrocytes.

CONCLUSIONS

Synovial fibroblasts assume distinct functional identities during PTOA in mice, and Prg4^hi lining fibroblasts secrete Rspo2 that may drive pathological joint crosstalk after injury.

CRISPR interference for sequence-specific regulation of fibroblast growth factor receptor A in Schistosoma mansoni

Employing the flatworm parasite Schistosoma mansoni as a model, we report the first application of CRISPR interference (CRISPRi) in parasitic helminths for loss-of-function studies targeting the SmfgfrA gene which encodes the stem cell marker, fibroblast growth factor receptor A (FGFRA). SmFGFRA is essential for maintaining schistosome stem cells and critical in the schistosome-host interplay. The SmfgfrA gene was targeted in S. mansoni adult worms, eggs and schistosomula using a catalytically dead Cas9 (dCas9) fused to a transcriptional repressor KRAB. We showed that SmfgfrA repression resulted in considerable phenotypic differences in the modulated parasites compared with controls, including reduced levels of SmfgfrA transcription and decreased protein expression of SmFGFRA, a decline in EdU (thymidine analog 5-ethynyl-2'-deoxyuridine, which specifically stains schistosome stem cells) signal, and an increase in cell apoptosis. Notably, reduced SmfgfrA transcription was evident in miracidia hatched from SmfgfrA-repressed eggs, and resulted in a significant change in miracidial behavior, indicative of a durable repression effect caused by CRISPRi. Intravenous injection of mice with SmfgfrA-repressed eggs resulted in granulomas that were markedly reduced in size and a decline in the level of serum IgE, emphasizing the importance of SmFGFRA in regulating the host immune response induced during schistosome infection. Our findings show the feasibility of applying CRISPRi for effective, targeted transcriptional repression in schistosomes, and provide the basis for employing CRISPRi to selectively perturb gene expression in parasitic helminths on a genome-wide scale.

Induced inactivation of Wnt16 in young adult mice has no impact on osteoarthritis development

Osteoarthritis (OA) is a common disorder and a major cause of disability in the elderly population. WNT16 has been suggested to play important roles in joint formation, bone homeostasis and OA development, but the mechanism of action is not clear. Transgenic mice lacking Wnt16 expression (Wnt16-/-) have a more severe experimental OA than control mice. In addition, Wnt16-/- mice have a reduced cortical thickness and develop spontaneous fractures. Herein, we have used Cre-Wnt16flox/flox mice in which Wnt16 can be conditionally ablated at any age through tamoxifen-inducible Cre-mediated recombination. Wnt16 deletion was induced in 7-week-old mice to study if the Cre-Wnt16flox/flox mice have a more severe OA phenotype after destabilizing the medial meniscus (DMM surgery) than littermate controls with normal Wnt16 expression (Wnt16flox/flox). WNT16 deletion was confirmed in articular cartilage and cortical bone in Cre-Wnt16flox/flox mice, shown by immunohistochemistry and reduced cortical bone area compared to Wnt16flox/flox mice. After DMM surgery, there was no difference in OA severity in the articular cartilage in the knee joint between the Cre-Wnt16flox/flox and Wnt16flox/flox mice in neither female nor male mice. In addition, there was no difference in osteophyte size in the DMM-operated tibia between the genotypes. In conclusion, inactivation of Wnt16 in adult mice do not result in a more severe OA phenotype after DMM surgery. Thus, presence of WNT16 in adult mice does not have an impact on experimental OA development. Taken together, our results from Cre-Wnt16flox/flox mice and previous results from Wnt16-/- mice suggest that WNT16 is crucial during synovial joint establishment leading to limited joint degradation also later in life, after onset of OA. This may be important when developing new therapeutics for OA treatment.

Wnt/β-catenin signaling pathway is activated in the progress of mandibular condylar cartilage degeneration and subchondral bone loss induced by overloaded functional orthopedic force (OFOF)

Objective

To explore the role of Wnt/β-catenin signaling pathway in the pathogenesis and progression of temporomandibular joint osteoarthritis (TMJ OA) caused by overloaded force.

Materials and methods

We generated a rat model of forward mandibular extension device to induce TMJ OA by overloaded force. Condylar cartilage samples were collected at 2wk, 4wk, and 8wk after appliances were installed. Changes of the condylar cartilage and subchondral bone were evaluated by hematoxylin and eosin (HE), Safranin O and Fast Green staining (SO&FG), micro-CT, tartrate resistant acid phosphatase (TRAP) staining. The expression levels of β-catenin, COL-2, MMP3 and sclerostin (SOST) were detected by immunohistochemistry (IHC) and PCR.

Results

HE, SO&FG, micro-CT, OARSI and Mankin scores showed that the condyle cartilage layer was significantly thinner and proteoglycan loss in the overloded group. TRAP staining exhibited that the number of positive osteoclasts increased and OPG level decreased in the overload group. IHC, PCR showed that the expression of COL2 and SOST decreased, while MMP3 and β-catenin increased in the overload group.

Conclusion

Wnt/β-catenin signaling pathway is activated in the progress of mandibular condylar cartilage degeneration and subchondral bone loss induced by overloaded functional orthopedic force (OFOF)

Primary Cilia: A Cellular Regulator of Articular Cartilage Degeneration

Osteoarthritis (OA) is the most common joint disease that can cause pain and disability in adults. The main pathological characteristic of OA is cartilage degeneration, which is caused by chondrocyte apoptosis, cartilage matrix degradation, and inflammatory factor destruction. The current treatment for patients with OA focuses on delaying its progression, such as oral anti-inflammatory analgesics or injection of sodium gluconate into the joint cavity. Primary cilia are an important structure involved in cellular signal transduction. Thus, they are very sensitive to mechanical and physicochemical stimuli. It is reported that the primary cilia may play an important role in the development of OA. Here, we review the correlation between the morphology (location, length, incidence, and orientation) of chondrocyte primary cilia and OA and summarize the relevant signaling pathways in chondrocytes that could regulate the OA process through primary cilia, including Hedgehog, Wnt, and inflammation-related signaling pathways. These data provide new ideas for OA treatment.

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.

Small molecules of herbal origin for osteoarthritis treatment: in vitro and in vivo evidence

Osteoarthritis (OA) is one of the most common musculoskeletal degenerative diseases and contributes to heavy socioeconomic burden. Current pharmacological and conventional non-pharmacological therapies aim at relieving the symptoms like pain and disability rather than modifying the underlying disease. Surgical treatment and ultimately joint replacement arthroplasty are indicated in advanced stages of OA. Since the underlying mechanisms of OA onset and progression have not been fully elucidated yet, the development of novel therapeutics to prevent, halt, or reverse the disease is laborious. Recently, small molecules of herbal origin have been reported to show potent anti-inflammatory, anti-catabolic, and anabolic effects, implying their potential for treatment of OA. Herein, the molecular mechanisms of these small molecules, their effect on physiological or pathological signaling pathways, the advancement of the extraction methods, and their potential clinical translation based on in vitro and in vivo evidence are comprehensively reviewed.

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.

Regulatory Mechanisms of Prg4 and Gdf5 Expression in Articular Cartilage and Functions in Osteoarthritis

Owing to the rapid aging of society, the numbers of patients with joint disease continue to increase. Accordingly, a large number of patients require appropriate treatment for osteoarthritis (OA), the most frequent bone and joint disease. Thought to be caused by the degeneration and destruction of articular cartilage following persistent and excessive mechanical stimulation of the joints, OA can significantly impair patient quality of life with symptoms such as knee pain, lower limb muscle weakness, or difficulty walking. Because articular cartilage has a low self-repair ability and an extremely low proliferative capacity, healing of damaged articular cartilage has not been achieved to date. The current pharmaceutical treatment of OA is limited to the slight alleviation of symptoms (e.g., local injection of hyaluronic acid or non-steroidal anti-inflammatory drugs); hence, the development of effective drugs and regenerative therapies for OA is highly desirable. This review article summarizes findings indicating that proteoglycan 4 (Prg4)/lubricin, which is specifically expressed in the superficial zone of articular cartilage and synovium, functions in a protective manner against OA, and covers the transcriptional regulation of Prg4 in articular chondrocytes. We also focused on growth differentiation factor 5 (Gdf5), which is specifically expressed on the surface layer of articular cartilage, particularly in the developmental stage, describing its regulatory mechanisms and functions in joint formation and OA pathogenesis. Because several genetic studies in humans and mice indicate the involvement of these genes in the maintenance of articular cartilage homeostasis and the presentation of OA, molecular targeting of Prg4 and Gdf5 is expected to provide new insights into the aetiology, pathogenesis, and potential treatment of OA.

Multiscale Strain Transfer in Cartilage

The transfer of stress and strain signals between the extracellular matrix (ECM) and cells is crucial for biochemical and biomechanical cues that are required for tissue morphogenesis, differentiation, growth, and homeostasis. In cartilage tissue, the heterogeneity in spatial variation of ECM molecules leads to a depth-dependent non-uniform strain transfer and alters the magnitude of forces sensed by cells in articular and fibrocartilage, influencing chondrocyte metabolism and biochemical response. It is not fully established how these nonuniform forces ultimately influence cartilage health, maintenance, and integrity. To comprehend tissue remodelling in health and disease, it is fundamental to investigate how these forces, the ECM, and cells interrelate. However, not much is known about the relationship between applied mechanical stimulus and resulting spatial variations in magnitude and sense of mechanical stimuli within the chondrocyte’s microenvironment. Investigating multiscale strain transfer and hierarchical structure-function relationships in cartilage is key to unravelling how cells receive signals and how they are transformed into biosynthetic responses. Therefore, this article first reviews different cartilage types and chondrocyte mechanosensing. Following this, multiscale strain transfer through cartilage tissue and the involvement of individual ECM components are discussed. Finally, insights to further understand multiscale strain transfer in cartilage are outlined.

Role of WNT Agonists, BMP and VEGF Antagonists in Rescuing Osteoarthritic Knee Cartilage in a Rat Model

INTRODUCTION

The superficial zone of articular cartilage (AC) is vital for its function and biomechanics. The damaged AC gets vascularized and undergoes hypertrophy and ossification. Studies have highlighted these two as the major causative factors in osteoarthritis (OA). We aimed at preventing the OA progression in a rat knee instability model by inhibiting the vascular ingrowth and ossification using VEGF and BMP antagonist. A WNT agonist was also used to promote AC regeneration because of its protective effect on the superficial layer.

METHODS

Rat knee OA was created by surgical excision of the medial meniscus and medial collateral ligament. Forty rats were divided into two groups of twenty each for surgical control and tests (surgery + intra-articular injection of drugs every two weeks). Ten animals from each group were sacrificed at four and eight weeks. Histology was mainly used to evaluate the outcome.

RESULTS

A surgical OA model was successfully created with higher histological scores for operated knees, both in short- (P = 0.0001) and long-term (P = 0.001). Modified Mankin score was lesser in the test animals as compared to control (P = 0.17) in the short-term, but the trend was reversed in the long-term (P = 0.13). Subgroup analysis revealed that repeated injections in the anterolateral compartment contributed to higher scores in the lateral (P = 0.03) and anterior (P = 0.03) compartment of the knee in the long-term.

CONCLUSION

The combinatorial approach was effective in controlling the OA in short-term. Further studies are needed to test the sustained drug delivery system to improve the outcome.

Low-Intensity Pulsed Ultrasound Alleviates Osteoarthritis Condition Through Focal Adhesion Kinase-Mediated Chondrocyte Proliferation and Differentiation

OBJECTIVE

Osteoarthritis (OA) is a prevalent chronic multifactorial degenerative disease characterized by joint tissue inflammation, osteophyte formation, subchondral bone sclerosis, and articular cartilage degradation. Low-intensity pulsed ultrasound (LIPUS), a noninvasive ultrasound technique, is widely used to attenuate diseases. The aim of this study was to investigate whether LIPUS can ameliorate OA, and to explore its underlying molecular mechanism.

DESIGN

The OA model was established in a C57BL/6 mouse by the anterior cruciate ligament transaction method. OA was assessed using arthritis scoring and weightbearing parameters. Chondrocyte proliferation was detected by a CCK-8 assay. The levels of interleukin-6 (IL-6), IL-8 and tumor necrosis factor-α (TNF-α) in synovial fluid of the mice were measured by enzyme-linked immunosorbent assay.

RESULTS

In OA mice, the arthritis score and weightbearing abilities were dramatically improved by LIPUS treatment. LIPUS also remarkably declined the levels of inflammatory cytokines IL-6, IL-8, and TNF-α in synovial fluid of OA mice. Moreover, LIPUS promoted chondrocyte proliferation and differentiation by activating focal adhesion kinase (FAK) signaling. Inhibition of FAK significantly blocked LIPUS-mediated cell proliferation and differentiation in vitro, as well as inflammation condition in OA mice.

CONCLUSION

LIPUS alleviates OA through promoting chondrocytes proliferation and differentiation by activating FAK, which could act as an intervening target for OA treatment.

Thrombospondin 2 Promotes IL-6 Production in Osteoarthritis Synovial Fibroblasts via the PI3K/AKT/NF-κB Pathway

Background

It is known that osteoarthritis (OA) pathogenesis involves inflammation that drives pathologic changes and that the matricellular protein, thrombospondin-2 (TSP2), is involved in angiogenesis, carcinogenesis, and inflammation. However, how TSP2 contributes to OA inflammatory processes is unclear.

Objective

The aim of current study was to elucidate whether TSP2 could promote interleukin-6 (IL-6), a pro-inflammatory cytokine, expression in osteoarthritis synovial fibroblasts (OASFs).

Methods

The synovial fibroblasts isolated from osteoarthritis and healthy donors were incubated with recombinant TSP2 to evaluate its effect in OA pathogenesis. The SFs were incubated with recombinant TSP2, followed by determining the IL-6 expression by qPCR and Western blot. After SFs were incubated with TSP2 for different time interval, the Western blot was performed to investigate the activation of signal pathway. The different strategies including neutralizing antibodies, siRNAs, and chemical inhibitors were used to discover the signal transduction in response to TSP2 incubation in OASFs. To evaluate the therapeutic potential of TSP2 in osteoarthritis, the anterior cruciate ligament transection (ACLT) in SD rats was performed in the presence or absence of TSP neutralizing antibody treatment.

Results

Our investigations have revealed that TSP2 promoted IL-6 expression in OASFs in a dose-dependent manner, especially in 30 and 100 ng/mL concentration (p < 0.05). Using different strategies including neutralizing antibodies, siRNAs, and chemical inhibitors, all of which attenuated signal pathway components in OASFs, we found evidence for the involvement of integrin α_vβ₃, PI3K, Akt, and NF-κB in TSP2-mediated upregulation of IL-6 (p < 0.05). Finally, in the result of rat ACLT surgical model, we found that TSP2 neutralizing antibody had protective effects in cartilage destruction during OA progression.

Conclusion

Thrombospondin-2 palys an important role in osteoarthritis pathogenesis and provides an opportunity to deal with osteoarthritis.

Human pluripotent stem cell-derived cartilaginous organoids promote scaffold-free healing of critical size long bone defects

Background

Bones have a remarkable capacity to heal upon fracture. Yet, in large defects or compromised conditions healing processes become impaired, resulting in delayed or non-union. Current therapeutic approaches often utilize autologous or allogeneic bone grafts for bone augmentation. However, limited availability of these tissues and lack of predictive biological response result in limitations for clinical demands. Tissue engineering using viable cell-based implants is a strategic approach to address these unmet medical needs.

Methods

Herein, the in vitro and in vivo cartilage and bone tissue formation potencies of human pluripotent stem cells were investigated. The induced pluripotent stem cells were specified towards the mesodermal lineage and differentiated towards chondrocytes, which subsequently self-assembled into cartilaginous organoids. The tissue formation capacity of these organoids was then challenged in an ectopic and orthotopic bone formation model.

Results

The derived chondrocytes expressed similar levels of collagen type II as primary human articular chondrocytes and produced stable cartilage when implanted ectopically in vivo. Upon targeted promotion towards hypertrophy and priming with a proinflammatory mediator, the organoids mediated successful bridging of critical size long bone defects in immunocompromised mice.

Conclusions

These results highlight the promise of induced pluripotent stem cell technology for the creation of functional cartilage tissue intermediates that can be explored for novel bone healing strategies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02580-7.

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.

Ultrasonographic assessment of femoral cartilage thickness in patients with Helicobacter pylori infection

OBJECTIVES

Helicobacter pylori is a major cause of gastritis and a potential trigger of inflammatory disease. The effect of H pylori infection on distal femoral cartilage has yet to be evaluated. The aim of this study was to evaluate femoral cartilage thickness in patients with H pylori infection and to find whether this infection affects femoral cartilage thickness.

METHODS

This cross-sectional study included 199 patients. To measure the thickness of femoral articular cartilage, 99 patients with H pylori infections and 100 with H pylori-negative controls were enrolled into two groups. The measurements were made using linear probe ultrasonography with the patients in supine positions and their knees in maximum flexion. Demographic, clinical, endoscopic and laboratory data were collected for all patients.

RESULTS

Both the right and left femoral condyles had thinner cartilage thickness in the H pylori-positive group than in the H pylori-negative group (P = .016, P = .036). For the intercondylar area and lateral femoral condyles, although the H pylori-positive patients had thinner femoral cartilage thickness than the H pylori-negative individuals for both extremities, this finding was not statistically significant (P > .05).

CONCLUSION

Femoral cartilage was thinner in patients with H pylori than patients without H pylori for right and left medial femoral condyles. This study suggests that H pylori infections may affect femoral cartilage thickness and potentially increase the risk of cartilage degeneration.

The intervention of intestinal Wnt/β-catenin pathway alters inflammation and disease severity of CIA

Autoreactive T cell is one of the leading causes of immunological tolerance defects in the chronic inflammatory lesions of rheumatoid arthritis (RA). There have been several extracellular signals and intracellular pathways reported in regulating this process but largely remain unknown yet. In this study, we explored the roles of intestinal Wnt/β-catenin on disease severity during collagen-induced arthritis model (CIA), an animal model of RA. We first testified the activity pattern Wnt/β-catenin shifted by intragastric administration of LiCl and DKK-1 in the intestine by real-time PCR and WB analysis. The arthritis scores showing the disease severity in the DKK-1 group was significantly ameliorated compared with the control group at the late stage of the disease, while in the LiCl group, the scores were significantly elevated which was consistent with pathology score analysis of H&E staining. Next, ELISA was performed and showed that TNF-α and IL-17 in the LiCl group were significantly higher than that of the control group. IL-10 in the DKK-1 group was significantly higher than that in the LiCl-1 group and control group, P < 0.05. Flow cytometry of spleen T cells differentiation ratio showed that: Th1 from the DKK-1 and LiCl groups and Th17 from the LiCl group was significantly different from that of the blank model group, P < 0.05. Finally, we explored the effects of intestinal Wnt/β-catenin on T cell differentiation regulator ROR-γt and TCF1 and found that both transcription factors were up-regulated in the LiCl group. Together, these data suggested the pro-information role of Wnt/β-catenin pathway from the intestine in the CIA mouse, implying its use as a potential therapeutic target for the treatment of inflammatory diseases such as RA.

A Molecular Cascade Underlying Articular Cartilage Degeneration

Preserving of articular cartilage is an effective way to protect synovial joints from becoming osteoarthritic (OA) joints. Understanding of the molecular basis of articular cartilage degeneration will provide valuable information in the effort to develop cartilage preserving drugs. There are currently no disease-modifying OA drugs (DMOADs) available to prevent articular cartilage destruction during the development of OA. Current drug treatments for OA focus on the reduction of joint pain, swelling, and inflammation at advanced stages of the disease. However, based on discoveries from several independent research laboratories and our laboratory in the past 15 to 20 years, we believe that we have a functional molecular understanding of articular cartilage degeneration. In this review article, we present and discuss experimental evidence to demonstrate a sequential chain of the molecular events underlying articular cartilage degeneration, which consists of transforming growth factor beta 1, high-temperature requirement A1 (a serine protease), discoidin domain receptor 2 (a cell surface receptor tyrosine kinase for native fibrillar collagens), and matrix metalloproteinase 13 (an extracellularmatrix degrading enzyme). If, as we strongly suspect, this molecular pathway is responsible for the initiation and acceleration of articular cartilage degeneration, which eventually leads to progressive joint failure, then these molecules may be ideal therapeutic targets for the development of DMOADs.

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.

Src Homology 2 Domain-Containing Protein Tyrosine Phosphatase Promotes Inflammation and Accelerates Osteoarthritis by Activating β-Catenin

Osteoarthritis (OA) is a chronic articular disease characterized by cartilage degradation, subchondral bone remodeling and osteophyte formation. Src homology 2 domain-containing protein tyrosine phosphatase (SHP2) has not been fully investigated in the pathogenesis of OA. In this study, we found that SHP2 expression was significantly increased after interleukin-1β (IL-1β) treatment in primary mouse chondrocytes. Inhibition of SHP2 using siRNA reduced MMP3, MMP13 levels, but increased AGGRECAN, COL2A1, SOX9 expression in vitro. On the contrary, overexpression of SHP2 exerted the opposite results and promoted cartilage degradation. Mechanistically, SHP2 activated Wnt/β-catenin signaling possibly through directly binding to β-catenin. SHP2 also induced inflammation through activating Mitogen-activated protein kinase (MAPK) and nuclear factor κB (NF-κB) pathways. Our in vivo studies showed that SHP2 knockdown effectively delayed cartilage destruction and reduced osteophyte formation in the mouse model of OA induced by destabilization of the medial meniscus (DMM). Altogether, our study identifies that SHP2 is a novel and potential therapeutic target of OA.

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 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.

WNT Signalling in Osteoarthritis and Its Pharmacological Targeting

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

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

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

Emerging pharmaceutical therapies for osteoarthritis

The prevalence of osteoarthritis (OA) and the burden associated with the disease are steadily increasing worldwide, representing a major public health challenge for the coming decades. The lack of specific treatments for OA has led to it being recognized as a serious disease that has an unmet medical need. Advances in the understanding of OA pathophysiology have enabled the identification of a variety of potential therapeutic targets involved in the structural progression of OA, some of which are promising and under clinical investigation in randomized controlled trials. Emerging therapies include those targeting matrix-degrading proteases or senescent chondrocytes, promoting cartilage repair or limiting bone remodelling, local low-grade inflammation or Wnt signalling. In addition to these potentially disease-modifying OA drugs (DMOADs), several targets are being explored for the treatment of OA-related pain, such as nerve growth factor inhibitors. The results of these studies are expected to considerably reshape the landscape of OA management over the next few years. This Review describes the pathophysiological processes targeted by emerging therapies for OA, along with relevant clinical data and discussion of the main challenges for the further development of these therapies, to provide context for the latest advances in the field of pharmaceutical therapies for OA.

Lorecivivint, a Novel Intraarticular CDC-like Kinase 2 and Dual-Specificity Tyrosine Phosphorylation-Regulated Kinase 1A Inhibitor and Wnt Pathway Modulator for the Treatment of Knee Osteoarthritis: A Phase II Randomized Trial

OBJECTIVE

To assess the safety and efficacy of a novel Wnt pathway modulator, lorecivivint (SM04690), for treating pain and inhibiting structural progression in moderately to severely symptomatic knee osteoarthritis (OA).

METHODS

Subjects in this 52-week, phase IIa, multicenter, randomized, double-blind, placebo-controlled, dose-ranging trial received a single 2-ml intraarticular injection of lorecivivint (dose of 0.03 mg, 0.07 mg, or 0.23 mg) or placebo. Efficacy was assessed based on change from baseline on the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score subscales for pain and function (scale 0-100 for each) and change from baseline in the radiographic medial joint space width (JSW). Baseline-adjusted analysis of covariance with multiple imputation was performed separately to evaluate efficacy. This proof-of-concept study evaluated the intent-to-treat population as well as a prespecified group of subjects with unilateral symptoms of knee OA (designated UNI) and an additional post hoc subgroup of subjects with unilateral symptoms but without widespread pain (designated UNI WP-).

RESULTS

In this trial, 455 subjects were randomized to a treatment group. The primary end point, significant improvement in the WOMAC pain score compared with placebo at week 13, was not met by any lorecivivint dose group (mean ± SD change from baseline, -23.3 ± 2.2 in the 0.03 mg group, -23.5 ± 2.1 in the 0.07 mg group, -21.3 ± 2.2 in the 0.23 mg group, and -22.1 ± 2.1 in the placebo group; each P > 0.05 versus placebo). All groups (including placebo) demonstrated clinically meaningful (≥20-point) improvements from baseline in the WOMAC pain score. The durability of response was evaluated through week 52. In the prespecified UNI group and post hoc UNI WP- group at week 52, treatment with 0.07 mg lorecivivint significantly improved the WOMAC pain score (between-group difference versus placebo, -8.73, 95% confidence interval [95% CI] -17.44, -0.03 [P = 0.049] and -11.21, 95% CI -20.99, -1.43 [P = 0.025], respectively) and WOMAC function score (between-group difference versus placebo, -10.26, 95% CI -19.82, -0.69 [P = 0.036] and -13.38, 95% CI -24.33, -2.43 [P = 0.017], respectively). Relative to baseline, the mean change in the medial JSW at week 52 was -0.04 mm in the 0.03 mg cohort, -0.09 mm in the 0.07 mg cohort, -0.16 mm in the 0.23 mg cohort, and -0.14 mm in the placebo cohort; no treatment group achieved a significant change in medial JSW compared with placebo at week 52. In both unilateral symptom subgroups, the 0.07 mg lorecivivint dose significantly increased medial JSW compared with placebo at week 52 (medial JSW 0.39 mm, 95% CI 0.06, 0.72 in the UNI group [P = 0.021] and 0.42 mm, 95% CI 0.04, 0.80 in the UNI WP- group [P = 0.032]). Changes observed in the 0.03 mg and 0.23 mg dose groups were not significantly different from those in the placebo group for any of these measures. Lorecivivint appeared safe and well tolerated.

CONCLUSION

This phase IIa, proof-of-concept trial in patients with symptomatic knee OA did not meet its primary end point. Nevertheless, the study identified a target population in whom to evaluate the potential efficacy of lorecivivint for the treatment of knee OA.

Lessons from joint development for cartilage repair in the clinic

More than 250 years ago, William Hunter stated that when cartilage is destroyed it never recovers. In the last 20 years, the understanding of the mechanisms that lead to joint formation and the knowledge that some of these mechanisms are reactivated in the homeostatic responses of cartilage to injury has offered an unprecedented therapeutic opportunity to achieve cartilage regeneration. Very large investments in ambitious clinical trials are finally revealing that, although we do not have perfect medicines yet, disease modification is a feasible possibility for human osteoarthritis.

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

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

Transglutaminase-2 regulates Wnt and FoxO3a signaling to determine the severity of osteoarthritis

Transglutaminase 2 (TG2), also known as tissue transglutaminase, is a calcium-dependent enzyme that has a variety of intracellular and extracellular substrates. TG2 not only increases in osteoarthritis (OA) tissue but also affects the progression of OA. However, it is still unclear how TG2 affects cartilage degradation in OA at the molecular level. Surgically induced OA lead to an increase of TG2 in the articular cartilage and growth plate, and it was dependent on TGFβ1 in primary chondrocytes. The inhibition of TG2 enzymatic activity with intra-articular injection of ZDON, the peptide-based specific TG2 inhibitor, ameliorated the severity of surgically induced OA as well as the expression of MMP-3 and MMP-13. ZDON attenuated MMP-3 and MMP-13 expression in TGFβ- and calcium ionophore-treated chondrocytes in a Runx2-independent manner. TG2 inhibition with ZDON suppressed canonical Wnt signaling through a reduction of β-catenin, which was mediated by ubiquitination-dependent proteasomal degradation. In addition, TG2 activation by a calcium ionophore enhanced the phosphorylation of AMPK and FoxO3a and the nuclear translocation of FoxO3a, which was responsible for the increase in MMP-13. In conclusion, TG2 plays an important role in the pathogenesis of OA as a major catabolic mediator that affects the stability of β-catenin and FoxO3a-mediated MMP-13 production.

Pathogenesis of Osteoarthritis: Risk Factors, Regulatory Pathways in Chondrocytes, and Experimental Models

As the most common chronic degenerative joint disease, osteoarthritis (OA) is the leading cause of pain and physical disability, affecting millions of people worldwide. Mainly characterized by articular cartilage degradation, osteophyte formation, subchondral bone remodeling, and synovial inflammation, OA is a heterogeneous disease that impacts all component tissues of the articular joint organ. Pathological changes, and thus symptoms, vary from person to person, underscoring the critical need of personalized therapies. However, there has only been limited progress towards the prevention and treatment of OA, and there are no approved effective disease-modifying osteoarthritis drugs (DMOADs). Conventional treatments, including non-steroidal anti-inflammatory drugs (NSAIDs) and physical therapy, are still the major remedies to manage the symptoms until the need for total joint replacement. In this review, we provide an update of the known OA risk factors and relevant mechanisms of action. In addition, given that the lack of biologically relevant models to recapitulate human OA pathogenesis represents one of the major roadblocks in developing DMOADs, we discuss current in vivo and in vitro experimental OA models, with special emphasis on recent development and application potential of human cell-derived microphysiological tissue chip platforms.