The role of TGF-β2 in cartilage development and diseases

New insights into Smad3 in cardiac fibrosis

Damage to myocardial tissues, leading to myocardial fibrosis, is a significant pathological hallmark across various heart diseases. SMAD3, a central transcriptional regulator within the transforming growth factor-beta (TGF-β) signaling pathway, plays a pivotal role in the pathological progression of myocardial fibrosis and cardiac remodeling. It intricately regulates physiological and pathological processes encompassing cell proliferation, differentiation, tissue repair, and fibrosis. Notably, SMAD3 exerts crucial influences in myocardial fibrosis subsequent to myocardial infarction, pressure overload-induced myocardial fibrosis, diabetic cardiomyopathy (DCM), aging-associated cardiac fibrosis and myocarditis-related myocardial fibrosis. The targeted modulation of genes or the utilization of compounds, including traditional Chinese medicine (paeoniflorin, baicalin, and genistein et al.) and other pharmaceutical agents that modulate SMAD3, may offer avenues for restraining the pathological cascade of myocardial fibrosis. Consequently, targeted regulation of SMAD3 associated with myocardial fibrosis may herald novel therapeutic paradigms for ameliorating myocardial diseases.

Advances in Regenerative Medicine for Orthopedic Injuries: A Comprehensive Review

Orthopedics is one field that greatly benefits from the new ideas provided by regenerative medicine. This review pulls together the most recent publications involving stem cell therapy, platelet-rich plasma, growth factor, gene therapy, tissue engineering, stem cell-derived extracellular vesicles, and other regenerative technologies in the context of bone, cartilage, tendon, and ligament healing. Recent studies show that these new therapies can alter cell development, division, and production of fiber and ground substance to remodel tissues. Nevertheless, the clinical application has several issues such as the standardization of cell procurement and preparation, the control of cytokine/gene delivery, the revascularization of tissues, and the requirements of large samples, positively controlled clinical trials. More research must be conducted to overcome such barriers and make practicing more applicable in real life.

TGF-β2 enhances nanoscale cortex stiffness via condensation of cytoskeleton-focal adhesion plaque

Physical spatiotemporal characteristics of cellular cortex dominate cell functions and even determine cell fate. The cellular cortex is able to reorganize to a dynamic steady status with changed stiffnesses once stimulated, and thus alter the physiological and pathological activities of almost all types of cells. TGF-β2, a potent pleiotropic growth factor, plays important roles in cartilage development, endochondral ossification, and cartilage diseases. However, it is not yet known whether TGF-β2 would alter the physical spatiotemporal characteristics of the cell cortex such as cortex stiffness, thereby affecting the function of chondrocytes. In this study, we investigated the influence of TGF-β2 on cellular cortex stiffness of chondrocytes and the underlying mechanism. We firstly detected TGF-β2-induced changes in cytoskeleton and focal adhesion plaque, which were closely related to cellular cortex stiffness. We then characterized the landscape of nanoscale cortex stiffness in individual chondrocytes induced by TGF-β2 via atomic force microscopy. By using inhibitors, latrunculin A and blebbistatin, we verified the importance of cytoskeleton-focal adhesion plaque axis on cellular cortex stiffness of chondrocytes induced by TGF-β2. We finally elucidated that TGF-β2 enhanced the phosphorylation of Smad3 and facilitated the nuclear accumulation of p-Smad3. The p-Smad3 aggregated in the nuclei enhanced the cytoskeleton and focal adhesion plaque at transcriptional level, thereby mediating changes in cell cortex stiffness. Taken together, these results provide an understanding about the role of TGF-β2 on physical spatiotemporal properties of cell cortex in chondrocytes, and might provide cues for interpretation of cartilage development and interventions to cartilage diseases.

Cyclic loading failed to promote growth in a pig model of midfacial hypoplasia

Yucatan miniature pigs, often used as large animal models in clinical research, are distinguished by a breed-specific midfacial hypoplasia with anterior crossbite. Although this deformity can be corrected by distraction osteogenesis, a less invasive method is desirable. We chose a mechanical cyclic stimulation protocol that has been successful in enhancing sutural growth in small animals and in a pilot study on standard pigs. Yucatan minipigs (n = 14) were obtained in pairs, with one of each pair randomly assigned to sham or loaded groups. All animals had loading implants installed on the right nasal and frontal bones and received labels for cell proliferation and mineral apposition. After a week of healing and under anesthesia, experimental animals received cyclic tensile loads (2.5 Hz, 30 min) delivered to the right nasofrontal suture daily for 5 days. Sutural strains were recorded at the final session for experimental animals. Sham animals received the same treatment except without loading or strain gauge placement. In contrast to pilot results on standard pigs, the treatment did not produce the expected sutural widening and increased growth. Although sutures were not fused and strains were in the normal range, the targeted right nasofrontal suture was narrowed rather than widened, with no statistically significant changes in sutural cell proliferation, mineral apposition, or vascularity. In general, Yucatan minipig sutures were more vascular than those of standard pigs and also tended to have more proliferating cells. In conclusion, either because the sutures themselves are abnormal or because of growth restrictions elsewhere in the skull, this cyclic loading protocol was unable to produce the desired response of sutural widening and growth. This treatment, effective in normal animals, did not improve naturally occurring midfacial hypoplasia in Yucatan minipigs.

Comparative Analysis of Osteoarthritis Therapeutics: A Justification for Harnessing Retrospective Strategies via an Inverted Pyramid Model Approach

In this review, we seek to explore two distinct approaches to the clinical management of OA: a prospective approach, addressing primarily one's genetic predisposition to OA and generating early intervention options, and the retrospective approach, aimed at halting or reversing OA progression post-symptom onset. The clinical management of OA remains challenging, largely due to the limited availability of preventative treatments and failure of existing therapies to modify or reverse the underlying pathophysiology. The prospective approach involves the identification of genetic markers associated with OA and utilizes in vitro and in vivo models to characterize the underlying disease mechanism. Further, this approach focuses on identifying genetic predispositions and unique molecular subtypes of OA to develop individualized treatment plans based on patient genotypes. While the current literature investigating this strategy has been notable, this approach faces substantial challenges, such as extensive time burdens and utilization of extensive genetic testing that may not be economically feasible. Additionally, there is questionable justification for such extensive investigations, given OA's relatively low mortality rates and burden when contrasted with diseases like specific forms of cancer, which rely heavily on the prospective approach. Alternatively, the retrospective approach primarily focuses on intervention following symptom onset and aims to utilize novel therapeutics to slow or reverse the inflammatory cascade typically seen in disease progression. These treatments, like Hippo pathway inhibitors, have shown initial promise in halting OA progression and alleviating OA symptomology by modulating cellular processes to preserve articular cartilage. In comparison to the prospective approach, the retrospective strategy is likely more cost-effective, more widely applicable, and does not necessitate thorough and invasive genetic screening. However, this approach must still be weighed against the typical natural history of disease progression, which frequently results in total knee arthroplasty and unacceptable outcomes for 15-20% of patients. From a comparative analysis of these two approaches, this review argues that the retrospective strategy, with ideally lower time and economic burden and greater accessibility, offers a more reasonable and effective solution in the context of OA management. Using a similar approach to other management of chronic diseases, we suggest an "Inverted Pyramid" model algorithm, a structured research and development regimen that prioritizes generating widely effective therapies first, with subsequent refinement of treatments based on the development of patient resistance to these therapies. We argue that this strategy may reduce the need for total knee arthroplasty while improving patient outcomes and accessibility.

TGF-β2 enhances glycolysis in chondrocytes via TβRI/p-Smad3 signaling pathway

Chondrocytes rely heavily on glycolysis to maintain the metabolic homeostasis and cartilage matrix turnover. Glycolysis in chondrocytes is remodeled by diverse biochemical and biomechanical factors due to the sporty joint microenvironment. Transforming growth factor-β2 (TGF-β2), one of the most abundant TGF-β superfamily members in chondrocytes, has increasingly attracted attention in cartilage physiology and pathology. Although previous studies have emphasized the importance of TGF-β superfamily members on cell metabolism, whether and how TGF-β2 modulates glycolysis in chondrocytes remains elusive. In the current study, we investigated the effects of TGF-β2 on glycolysis in chondrocytes and explored the underlying biomechanisms. The results showed that TGF-β2 could enhance glycolysis in chondrocytes by increasing glucose consumption, up-regulating liver-type ATP-dependent 6-phosphofructokinase (Pfkl) expression, and boosting lactate production. The TGF-β2 signal entered chondrocytes via TGF-β receptor type I (TβRI), and activated p-Smad3 signaling to regulate the glycolytic pathway. Subsequent experiments employing specific inhibitors of TβRI and p-Smad3 further substantiated the role of TGF-β2 in enhancement of glycolysis via TβRI/p-Smad3 axis in chondrocytes. The results provide new understanding of the metabolic homeostasis in chondrocytes induced by TGF-β superfamily and might shed light on the prevention and treatment of related osteoarticular diseases.

Growth factor-functionalized titanium implants for enhanced bone regeneration: A review

Titanium and titanium alloys are widely favored materials for orthopedic implants due to their exceptional mechanical properties and biological inertness. The additional benefit of sustained local release of bioactive substances further promotes bone tissue formation, thereby augmenting the osseointegration capacity of titanium implants and attracting increasing attention in bone tissue engineering. Among these bioactive substances, growth factors have shown remarkable osteogenic and angiogenic induction capabilities. Consequently, researchers have developed various physical, chemical, and biological loading techniques to incorporate growth factors into titanium implants, ensuring controlled release kinetics. In contrast to conventional treatment modalities, the localized release of growth factors from functionalized titanium implants not only enhances osseointegration but also reduces the risk of complications. This review provides a comprehensive examination of the types and mechanisms of growth factors, along with a detailed exploration of the methodologies used to load growth factors onto the surface of titanium implants. Moreover, it highlights recent advancements in the application of growth factors to the surface of titanium implants (Scheme 1). Finally, the review discusses current limitations and future prospects for growth factor-functionalized titanium implants. In summary, this paper presents cutting-edge design strategies aimed at enhancing the bone regenerative capacity of growth factor-functionalized titanium implants-a significant advancement in the field of enhanced bone regeneration.

Regulation of bone homeostasis: signaling pathways and therapeutic targets

As a highly dynamic tissue, bone is continuously rebuilt throughout life. Both bone formation by osteoblasts and bone resorption by osteoclasts constitute bone reconstruction homeostasis. The equilibrium of bone homeostasis is governed by many complicated signaling pathways that weave together to form an intricate network. These pathways coordinate the meticulous processes of bone formation and resorption, ensuring the structural integrity and dynamic vitality of the skeletal system. Dysregulation of the bone homeostatic regulatory signaling network contributes to the development and progression of many skeletal diseases. Significantly, imbalanced bone homeostasis further disrupts the signaling network and triggers a cascade reaction that exacerbates disease progression and engenders a deleterious cycle. Here, we summarize the influence of signaling pathways on bone homeostasis, elucidating the interplay and crosstalk among them. Additionally, we review the mechanisms underpinning bone homeostatic imbalances across diverse disease landscapes, highlighting current and prospective therapeutic targets and clinical drugs. We hope that this review will contribute to a holistic understanding of the signaling pathways and molecular mechanisms sustaining bone homeostasis, which are promising to contribute to further research on bone homeostasis and shed light on the development of targeted drugs.

Osteoarthritis in the Elderly Population: Preclinical Evidence of Nutrigenomic Activities of Flavonoids

Osteoarthritis (OA) is a degenerative joint disease that is age-related and progressive. It causes the destruction of articular cartilage and underlying bone, often aggravated by inflammatory processes and oxidative stresses. This pathology impairs the quality of life of the elderly, causing pain, reduced mobility, and functional disabilities, especially in obese patients. Phytochemicals with anti-inflammatory and antioxidant activities may be used for long-term treatment of OA, either in combination with current anti-inflammatories and painkillers, or as an alternative to other products such as glucosamine and chondroitin, which improve cartilage structure and elasticity. The current systematic review provides a comprehensive understanding of the use of flavonoids. It highlights chondrocyte, cartilage, and subchondral bone activities, with a particular focus on their nutrigenomic effects. The molecular mechanisms of these molecules demonstrate how they can be used for the prevention and treatment of OA in the elderly population. However, clinical trials are still needed for effective use in clinical practice.

The role of EDIL3 in maintaining cartilage extracellular matrix and inhibiting osteoarthritis development

Aims

Therapeutic agents that prevent chondrocyte loss, extracellular matrix (ECM) degradation, and osteoarthritis (OA) progression are required. The expression level of epidermal growth factor (EGF)-like repeats and discoidin I-like domains-containing protein 3 (EDIL3) in damaged human cartilage is significantly higher than in undamaged cartilage. However, the effect of EDIL3 on cartilage is still unknown.

Methods

We used human cartilage plugs (ex vivo) and mice with spontaneous OA (in vivo) to explore whether EDIL3 has a chondroprotective effect by altering OA-related indicators.

Results

EDIL3 protein prevented chondrocyte clustering and maintained chondrocyte number and SOX9 expression in the human cartilage plug. Administration of EDIL3 protein prevented OA progression in STR/ort mice by maintaining the number of chondrocytes in the hyaline cartilage and the number of matrix-producing chondrocytes (MPCs). It reduced the degradation of aggrecan, the expression of matrix metalloproteinase (MMP)-13, the Osteoarthritis Research Society International (OARSI) score, and bone remodelling. It increased the porosity of the subchondral bone plate. Administration of an EDIL3 antibody increased the number of matrix-non-producing chondrocytes (MNCs) in cartilage and exacerbated the serum concentrations of OA-related pro-inflammatory cytokines, including monocyte chemotactic protein-3 (MCP-3), RANTES, interleukin (IL)-17A, IL-22, and GROα. Administration of β1 and β3 integrin agonists (CD98 protein) increased the expression of SOX9 in OA mice. Hence, EDIL3 might activate β1 and β3 integrins for chondroprotection. EDIL3 may also protect cartilage by attenuating the expression of IL-1β-enhanced phosphokinase proteins in chondrocytes, especially glycogen synthase kinase 3 alpha/beta (GSK-3α/β) and phospholipase C gamma 1 (PLC-γ1).

Conclusion

EDIL3 has a role in maintaining the cartilage ECM and inhibiting the development of OA, making it a potential therapeutic drug for OA.

Human Chondrocytes, Metabolism of Articular Cartilage, and Strategies for Application to Tissue Engineering

Hyaline cartilage, which is characterized by the absence of vascularization and innervation, has minimal self-repair potential in case of damage and defect formation in the chondral layer. Chondrocytes are specialized cells that ensure the synthesis of extracellular matrix components, namely type II collagen and aggregen. On their surface, they express integrins CD44, α1β1, α3β1, α5β1, α10β1, αVβ1, αVβ3, and αVβ5, which are also collagen-binding components of the extracellular matrix. This article aims to contribute to solving the problem of the possible repair of chondral defects through unique methods of tissue engineering, as well as the process of pathological events in articular cartilage. In vitro cell culture models used for hyaline cartilage repair could bring about advanced possibilities. Currently, there are several variants of the combination of natural and synthetic polymers and chondrocytes. In a three-dimensional environment, chondrocytes retain their production capacity. In the case of mesenchymal stromal cells, their favorable ability is to differentiate into a chondrogenic lineage in a three-dimensional culture.

Biomimetic Fibers Based on Equidistant Micropillar Arrays Determines Chondrocyte Fate via Mechanoadaptability

It is recognized that the changes in the physical properties of extracellular matrix (ECM) result in fine-tuned cell responses including cell morphology, proliferation and differentiation. In this study, a novel patterned equidistant micropillar substrate based on polydimethylsiloxane (PDMS) is designed to mimic the collagen fiber-like network of the cartilage matrix. By changing the component of the curing agent to an oligomeric base, micropillar substrates with the same topology but different stiffnesses are obtained and it is found that chondrocytes seeded onto the soft micropillar substrate maintain their phenotype by gathering type II collagen and aggrecan more effectively than those seeded onto the stiff micropillar substrate. Moreover, chondrocytes sense and respond to micropillar substrates with different stiffnesses by altering the ECM-cytoskeleton-focal adhesion axis. Further, it is found that the soft substrate-preserved chondrocyte phenotype is dependent on the activation of Wnt/β-catenin signaling. Finally, it is indicated that the changes in osteoid-like region formation and cartilage phenotype loss in the stiffened sclerotic area of osteoarthritis cartilage to validate the changes triggered by micropillar substrates with different stiffnesses. This study provides the cell behavior changes that are more similar to those of real chondrocytes at tissue level during the transition from a normal state to a state of osteoarthritis.

In Vitro Chondrogenesis Induction by Short Peptides of the Carboxy-Terminal Domain of Transforming Growth Factor β1

Τransforming growth factor β1 (TGF-β1) comprises a key regulator protein in many cellular processes, including in vivo chondrogenesis. The treatment of human dental pulp stem cells, separately, with Leu83-Ser112 (C-terminal domain of TGF-β1), as well as two very short peptides, namely, 90-YYVGRKPK-97 (peptide 8) and 91-YVGRKP-96 (peptide 6) remarkably enhanced the chondrogenic differentiation capacity in comparison to their full-length mature TGF-β1 counterpart either in monolayer cultures or 3D scaffolds. In 3D scaffolds, the reduction of the elastic modulus and viscous modulus verified the production of different amounts and types of ECM components. Molecular dynamics simulations suggested a mode of the peptides' binding to the receptor complex TβRII-ALK5 and provided a possible structural explanation for their role in inducing chondrogenesis, along with endogenous TGF-β1. Further experiments clearly verified the aforementioned hypothesis, indicating the signal transduction pathway and the involvement of TβRII-ALK5 receptor complex. Real-time PCR experiments and Western blot analysis showed that peptides favor the ERK1/2 and Smad2 pathways, leading to an articular, extracellular matrix formation, while TGF-β1 also favors the Smad1/5/8 pathway which leads to the expression of the metalloproteinases ADAMTS-5 and MMP13 and, therefore, to a hypertrophic chondrocyte phenotype. Taken together, the two short peptides, and, mainly, peptide 8, could be delivered with a scaffold to induce in vivo chondrogenesis in damaged articular cartilage, constituting, thus, an alternative therapeutic approach for osteoarthritis.

Altered Sox9 and FGF signaling gene expression in Aga2 OI mice negatively affects linear growth

Osteogenesis imperfecta (OI), or brittle bone disease, is a disorder characterized by bone fragility and increased fracture incidence. All forms of OI also feature short stature, implying an effect on endochondral ossification. Using the Aga2+/- mouse, which has a mutation in type I collagen, we show an affected growth plate primarily due to a shortened proliferative zone. We used single-cell RNA-Seq analysis of tibial and femoral growth plate tissues to understand transcriptional consequences on growth plate cell types. We show that perichondrial cells, which express abundant type I procollagen, and growth plate chondrocytes, which were found to express low amounts of type I procollagen, had ER stress and dysregulation of the same unfolded protein response pathway as previously demonstrated in osteoblasts. Aga2+/- proliferating chondrocytes showed increased FGF and MAPK signaling, findings consistent with accelerated differentiation. There was also increased Sox9 expression throughout the growth plate, which is expected to accelerate early chondrocyte differentiation but reduce late hypertrophic differentiation. These data reveal that mutant type I collagen expression in OI has an impact on the cartilage growth plate. These effects on endochondral ossification indicate that OI is a biologically complex phenotype going beyond its known impacts on bone to negatively affect linear growth.

Appraising causal risk and protective factors for rheumatoid arthritis

Aims

Mendelian randomization (MR) is considered to overcome the bias of observational studies, but there is no current meta-analysis of MR studies on rheumatoid arthritis (RA). The purpose of this study was to summarize the relationship between potential pathogenic factors and RA risk based on existing MR studies.

Methods

PubMed, Web of Science, and Embase were searched for MR studies on influencing factors in relation to RA up to October 2022. Meta-analyses of MR studies assessing correlations between various potential pathogenic factors and RA were conducted. Random-effect and fixed-effect models were used to synthesize the odds ratios of various pathogenic factors and RA. The quality of the study was assessed using the Strengthening the Reporting of Observational Studies in Epidemiology using Mendelian Randomization (STROBE-MR) guidelines.

Results

A total of 517 potentially relevant articles were screened, 35 studies were included in the systematic review, and 19 studies were eligible to be included in the meta-analysis. Pooled estimates of 19 included studies (causality between 15 different risk factors and RA) revealed that obesity, smoking, coffee intake, lower education attainment, and Graves' disease (GD) were related to the increased risk of RA. In contrast, the causality contribution from serum mineral levels (calcium, iron, copper, zinc, magnesium, selenium), alcohol intake, and chronic periodontitis to RA is not significant.

Conclusion

Obesity, smoking, education attainment, and GD have real causal effects on the occurrence and development of RA. These results may provide insights into the genetic susceptibility and potential biological pathways of RA.

Effect of surface matching mismatch of focal knee articular prosthetic on tibiofemoral contact stress using finite element analysis

Aims

Focal knee arthroplasty is an attractive alternative to knee arthroplasty for young patients because it allows preservation of a large amount of bone for potential revisions. However, the mechanical behaviour of cartilage has not yet been investigated because it is challenging to evaluate in vivo contact areas, pressure, and deformations from metal implants. Therefore, this study aimed to determine the contact pressure in the tibiofemoral joint with a focal knee arthroplasty using a finite element model.

Methods

The mechanical behaviour of the cartilage surrounding a metal implant was evaluated using finite element analysis. We modelled focal knee arthroplasty with placement flush, 0.5 mm deep, or protruding 0.5 mm with regard to the level of the surrounding cartilage. We compared contact stress and pressure for bone, implant, and cartilage under static loading conditions.

Results

Contact stress on medial and lateral femoral and tibial cartilages increased and decreased, respectively, the most and the least in the protruding model compared to the intact model. The deep model exhibited the closest tibiofemoral contact stress to the intact model. In addition, the deep model demonstrated load sharing between the bone and the implant, while the protruding and flush model showed stress shielding. The data revealed that resurfacing with a focal knee arthroplasty does not cause increased contact pressure with deep implantation. However, protruding implantation leads to increased contact pressure, decreased bone stress, and biomechanical disadvantage in an in vivo application.

Conclusion

These results show that it is preferable to leave an edge slightly deep rather than flush and protruding.

Platelet-derived growth factor PDGF-AA upregulates connexin 43 expression and promotes gap junction formations in osteoblast cells through p-Akt signaling

Gap junctions, which are mainly composed of connexin units, play an indispensable role in cell morphogenesis, proliferation, migration, adhesion and differentiation of osteoblast lineage cells, and thus mediate bone development, homeostasis and disease occurrence. Platelet-derived growth factor-AA (PDGF-AA) is proved to have a great influence on osteoblast cell lines and is widely applied in the field of bone defect and wound healing. However, the role of PDGF-AA on gap junction formation in the osteoblast lineage remains elusive. In the current study, we aimed to investigate the impact of PDGF-AA on gap junction formation and cell-to-cell communication in the osteoblast lineage and explore its underlying biomechanism. We first found that PDGF-AA promoted cell proliferation and thus increased gap junction formations in living primary osteoblasts and MC3T3-E1 cells through scrape loading and dye transfer (SL/DT) assay. We then confirmed that PDGF-AA enhanced gap junction formations through up-regulation of connexin 43 (Cx43). We next detected the activation of p-Akt signaling in primary osteoblasts and MC3T3-E1 cells that were induced by PDGF-AA. Through inhibitory experiments, we further confirmed that PDGF-AA-mediated gap junction formation occurred via the activation of PI3K/Akt signaling. Taking together, our results provided evidences that PDGF-AA promoted gap junction formation in the osteoblast lineage through p-Akt signaling, which helped to understand the role of PDGF-AA in bone regeneration and diseases.

Stiffened fibre-like microenvironment based on patterned equidistant micropillars directs chondrocyte hypertrophy

Articular cartilage, composed of collagen type II as a major extracellular matrix and chondrocyte as a unique cell type, is a specialized connective tissue without blood vessels, lymphatic vessels and nerves. This distinctive characteristic of articular cartilage determines its very limited ability to repair when damaged. It is well known that physical microenvironmental signals regulate many cell behaviors such as cell morphology, adhesion, proliferation and cell communication even determine chondrocyte fate. Interestingly, with increasing age or progression of joint diseases such as osteoarthritis (OA), the major collagen fibrils in the extracellular matrix of articular cartilage become larger in diameter, leading to stiffening of articular tissue and reducing its resistance to external tension, which in turn aggravates joint damage or progression of joint diseases. Therefore, designing a physical microenvironment closer to the real tissue and thus obtaining data closer to the real cellular behaviour, and then revealing the biological mechanisms of chondrocytes in pathological states is of crucial importance for the treatment of OA disease. Here we fabricated micropillar substrates with the same topology but different stiffnesses to mimic the matrix stiffening that occurs in the transition from normal to diseased cartilage. It was first found that chondrocytes responded to stiffened micropillar substrates by showing a larger cell spreading area, a stronger enhancement of cytoskeleton rearrangement and more stability of focal adhesion plaques. The activation of Erk/MAPK signalling in chondrocytes was detected in response to the stiffened micropillar substrate. Interestingly, a larger nuclear spreading area of chondrocytes at the interface layer between the cells and top surfaces of micropillars was observed in response to the stiffened micropillar substrate. Finally, it was found that the stiffened micropillar substrate promoted chondrocyte hypertrophy. Taken together, these results revealed the cell responses of chondrocytes in terms of cell morphology, cytoskeleton, focal adhesion, nuclei and cell hypertrophy, and may be beneficial for understanding the cellular functional changes affected by the matrix stiffening that occurs during the transition from a normal state to a state of osteoarthritis.

A Network Pharmacology and Multi-Omics Combination Approach to Reveal the Effect of Strontium on Ca2+ Metabolism in Bovine Rumen Epithelial Cells

Strontium (Sr) belongs to the same group in the periodic table as calcium (Ca). Sr level can serve as an index of rumen Ca absorption capacity; however, the effects of Sr on Ca²⁺ metabolism are unclear. This study aims to investigate the effect of Sr on Ca²⁺ metabolism in bovine rumen epithelial cells. The bovine rumen epithelial cells were isolated from the rumen of newborn Holstein male calves (n = 3, 1 day old, 38.0 ± 2.8 kg, fasting). The half maximal inhibitory concentration (IC50) of Sr-treated bovine rumen epithelial cells and cell cycle were used to establish the Sr treatment model. Transcriptomics, proteomics, and network pharmacology were conducted to investigate the core targets of Sr-mediated regulation of Ca²⁺ metabolism in bovine rumen epithelial cells. The data of transcriptomics and proteomics were analyzed using bioinformatic analysis (Gene Ontology and Kyoto Encyclopedia of genes/protein). Quantitative data were analyzed using one-way ANOVA in GraphPad Prism 8.4.3 and the Shapiro-Wilk test was used for the normality test. Results presented that the IC50 of Sr treatment bovine rumen epithelial cells for 24 h was 43.21 mmol/L, and Sr increased intracellular Ca²⁺ levels. Multi-omics results demonstrated the differential expression of 770 mRNAs and 2436 proteins after Sr treatment; network pharmacology and reverse transcriptase polymerase chain reaction (RT-PCR) revealed Adenosylhomocysteine hydrolase-like protein 2 (AHCYL2), Semaphoring 3A (SEMA3A), Parathyroid hormone-related protein (PTHLH), Transforming growth factor β2 (TGF-β2), and Cholesterol side-chain cleavage enzyme (CYP11A1) as potential targets for Sr-mediated Ca²⁺ metabolism regulation. Together these results will improve the current comprehension of the regulatory effect of Sr on Ca²⁺ metabolism and pave a theoretical basis for Sr application in bovine hypocalcemia.

The role of fibroblast growth factor 7 in cartilage development and diseases

Fibroblast growth factor 7 (FGF7), also known as keratinocyte growth factor (KGF), shows a crucial biological significance in tissue development, wound repair, tumorigenesis, and immune reconstruction. In the skeletal system, FGF7 directs the cellular synaptic extension of individual cells and facilities functional gap junction intercellular communication of a collective of cells. Moreover, it promotes the osteogenic differentiation of stem cells via a cytoplasmic signaling network. For cartilage, reports have indicated the potential role of FGF7 on the regulation of key molecules Cx43 in cartilage and Runx2 in hypertrophic cartilage. However, the molecular mechanism of FGF7 in chondrocyte behaviors and cartilage pathological process remains largely unknown. In this review, we systematically summarize the recent biological function of FGF7 and its regulatory role on chondrocytes and cartilage diseases, especially through the hot focus of two key molecules, Runx2 and Cx43. The current knowledge of FGF7 on the physiological and pathological processes of chondrocytes and cartilage provides us new cues for wound repair of cartilage defect and therapy of cartilage diseases.

The role of mechano growth factor in chondrocytes and cartilage defects: a concise review

Mechano growth factor (MGF), an isoform of insulin-like growth factor 1 (IGF-1), is recognized as a typical mechanically sensitive growth factor and has been shown to play an indispensable role in the skeletal system. In the joint cavity, MGF is highly expressed in chondrocytes, especially in the damaged cartilage tissue caused by trauma or degenerative diseases such as osteoarthritis (OA). Cartilage is an extremely important component of joints because it functions as a shock absorber and load distributer at the weight-bearing interfaces in the joint cavity, but it can hardly be repaired once injured due to its lack of blood vessels, lymphatic vessels, and nerves. MGF has been proven to play an important role in chondrocyte behaviors, including cell proliferation, migration, differentiation, inflammatory reactions and apoptosis, in and around the injury site. Moreover, under the normalized mechanical microenvironment in the joint cavity, MGF can sense and respond to mechanical stimuli, regulate chondrocyte activity, and maintain the homeostasis of cartilage tissue. Recent reports continue to explain its effects on various cell types and sport-related tissues, but its role in cartilage development, homeostasis and disease occurrence is still controversial, and its internal biological mechanism is still elusive. In this review, we summarize recent discoveries on the role of MGF in chondrocytes and cartilage defects, including tissue repair at the macroscopic level and chondrocyte activities at the microcosmic level, and discuss the current state of research and potential gaps in knowledge.

A chemo-mechano-biological modeling framework for cartilage evolving in health, disease, injury, and treatment

BACKGROUND AND OBJECTIVE

Osteoarthritis (OA) is a pervasive and debilitating disease, wherein degeneration of cartilage features prominently. Despite extensive research, we do not yet understand the cause or progression of OA. Studies show biochemical, mechanical, and biological factors affect cartilage health. Mechanical loads influence synthesis of biochemical constituents which build and/or break down cartilage, and which in turn affect mechanical loads. OA-associated biochemical profiles activate cellular activity that disrupts homeostasis. To understand the complex interplay among mechanical stimuli, biochemical signaling, and cartilage function requires integrating vast research on experimental mechanics and mechanobiology-a task approachable only with computational models. At present, mechanical models of cartilage generally lack chemo-biological effects, and biochemical models lack coupled mechanics, let alone interactions over time.

METHODS

We establish a first-of-its kind virtual cartilage: a modeling framework that considers time-dependent, chemo-mechano-biologically induced turnover of key constituents resulting from biochemical, mechanical, and/or biological activity. We include the "minimally essential" yet complex chemical and mechanobiological mechanisms. Our 3-D framework integrates a constitutive model for the mechanics of cartilage with a novel model of homeostatic adaptation by chondrocytes to pathological mechanical stimuli, and a new application of anisotropic growth (loss) to simulate degradation clinically observed as cartilage thinning.

RESULTS

Using a single set of representative parameters, our simulations of immobilizing and overloading successfully captured loss of cartilage quantified experimentally. Simulations of immobilizing, overloading, and injuring cartilage predicted dose-dependent recovery of cartilage when treated with suramin, a proposed therapeutic for OA. The modeling framework prompted us to add growth factors to the suramin treatment, which predicted even better recovery.

CONCLUSIONS

Our flexible framework is a first step toward computational investigations of how cartilage and chondrocytes mechanically and biochemically evolve in degeneration of OA and respond to pharmacological therapies. Our framework will enable future studies to link physical activity and resulting mechanical stimuli to progression of OA and loss of cartilage function, facilitating new fundamental understanding of the complex progression of OA and elucidating new perspectives on causes, treatments, and possible preventions.

The nasal septum and midfacial growth

The nasal septum is the only element of the chondrocranium which never completely ossifies. The persistence of this nonarticular cartilage has given rise to a variety of theories concerning cranial mechanics and growth of the midface. Previously, using pigs, we demonstrated that the septum is not a strut supporting the snout and that septal growth seems capable of stretching the overlying nasofrontal suture, a major contributor to snout elongation. Here we investigate whether abnormalities of the septum are implicated in cases of midfacial hypoplasia, in which growth of the midface is inadequate. Mild midfacial hypoplasia is common in domestic pig breeds and often severe in the Yucatan minipig, a popular laboratory breed. Normal-snouted and midfacial hypoplastic heads of standard (farm mixed breed) and minipigs ranging in age from perinatal to 12 months were dissected, imaged by CT, and/or prepared for histology. Even at birth, Yucatan minipigs with midfacial hypoplasia exhibited greater caudal ossification than normal; the ventral cartilaginous sphenoidal "tail" was diminished or missing. In addition, cells that morphologically appeared to have divided recently were less numerous than in newborn standard pigs. Juvenile Yucatan minipigs lacked caudal cartilaginous growth zones almost completely. In standard newborns, the ventral caudal septum was more replicative than the dorsal, but this trend was not seen in Yucatan newborns. In conclusion, accelerated maturation of the caudal septum was associated with midfacial hypoplasia, a further indication that the septum, particularly its ventral portion, is important for midfacial elongation.

SDF-1α Promotes Chondrocyte Autophagy through CXCR4/mTOR Signaling Axis

SDF-1α, the most common isoform of stromal cell-derived factor 1, has shown vital effects in regulating chondrocyte proliferation, maturation, and chondrogenesis. Autophagy is a highly conserved biological process to help chondrocytes survive in harsh environments. However, the effect of SDF-1α on chondrocyte autophagy is still unknown. This study aims to investigate the effect of SDF-1α on chondrocyte autophagy and the underlying biomechanism. Transmission electron microscope assays and mRFP-GFP-LC3 adenovirus double label transfection assays were performed to detect the autophagic flux of chondrocytes. Western blots and immunofluorescence staining assays were used to detect the expression of autophagy-related proteins in chondrocytes. RNA sequencing and qPCR were conducted to assess changes in autophagy-related mRNA expression. SDF-1α upregulated the number of autophagosomes and autolysosomes in chondrocytes. It also increased the expression of autophagy-related proteins including ULK-1, Beclin-1 and LC3B, and decreased the expression of p62, an autophagy substrate protein. SDF-1α-mediated autophagy of chondrocytes required the participation of receptor CXCR4. Moreover, SDF-1α-enhanced autophagy of chondrocytes was through the inhibition of phosphorylation of mTOR signaling on the upstream of autophagy. Knockdown by siRNA and inhibition by signaling inhibitor further confirmed the importance of the CXCR4/mTOR signaling axis in SDF-1α-induced autophagy of chondrocytes. For the first time, this study elucidated that SDF-1α promotes chondrocyte autophagy through the CXCR4/mTOR signaling axis.

The role of TGF-beta3 in cartilage development and osteoarthritis

Articular cartilage serves as a low-friction, load-bearing tissue without the support with blood vessels, lymphatics and nerves, making its repair a big challenge. Transforming growth factor-beta 3 (TGF-β3), a vital member of the highly conserved TGF-β superfamily, plays a versatile role in cartilage physiology and pathology. TGF-β3 influences the whole life cycle of chondrocytes and mediates a series of cellular responses, including cell survival, proliferation, migration, and differentiation. Since TGF-β3 is involved in maintaining the balance between chondrogenic differentiation and chondrocyte hypertrophy, its regulatory role is especially important to cartilage development. Increased TGF-β3 plays a dual role: in healthy tissues, it can facilitate chondrocyte viability, but in osteoarthritic chondrocytes, it can accelerate the progression of disease. Recently, TGF-β3 has been recognized as a potential therapeutic target for osteoarthritis (OA) owing to its protective effect, which it confers by enhancing the recruitment of autologous mesenchymal stem cells (MSCs) to damaged cartilage. However, the biological mechanism of TGF-β3 action in cartilage development and OA is not well understood. In this review, we systematically summarize recent progress in the research on TGF-β3 in cartilage physiology and pathology, providing up-to-date strategies for cartilage repair and preventive treatment.

The roles of Runx1 in skeletal development and osteoarthritis: A concise review

Runt-related transcription factor-1 (Runx1) is well known for its functions in hematopoiesis and leukemia but recent research has focused on its role in skeletal development and osteoarthritis (OA). Deficiency of the Runx1 gene is fatal in early embryonic development, and specific knockout of Runx1 in cell lineages of cartilage and bone leads to delayed cartilage formation and impaired bone calcification. Runx1 can regulate genes including collagen type II (Col2a1) and X (Col10a1), SRY-box transcription factor 9 (Sox9), aggrecan (Acan) and matrix metalloproteinase 13 (MMP-13), and the up-regulation of Runx1 improves the homeostasis of the whole joint, even in the pathological state. Moreover, Runx1 is activated as a response to mechanical compression, but impaired in the joint with the pathological progress associated with osteoarthritis. Therefore, interpretation about the role of Runx1 could enlarge our understanding of key marker genes in the skeletal development and an increased understanding of Runx1 could be helpful to identify treatments for osteoarthritis. This review provides the most up-to-date advances in the roles and bio-mechanisms of Runx1 in healthy joints and osteoarthritis from all currently published articles and gives novel insights in therapeutic approaches to OA based on Runx1.

Bisphosphonate use is associated with a decreased joint narrowing rate in the non-arthritic hip

Aims

The preventive effects of bisphosphonates on articular cartilage in non-arthritic joints are unclear. This study aimed to investigate the effects of oral bisphosphonates on the rate of joint space narrowing in the non-arthritic hip.

Methods

We retrospectively reviewed standing whole-leg radiographs from patients who underwent knee arthroplasties from 2012 to 2020 at our institute. Patients with previous hip surgery, Kellgren–Lawrence grade ≥ II hip osteoarthritis, hip dysplasia, or rheumatoid arthritis were excluded. The rate of hip joint space narrowing was measured in 398 patients (796 hips), and the effects of the use of bisphosphonates were examined using the multivariate regression model and the propensity score matching (1:2) model.

Results

A total of 45 of 398 (11.3%) eligible patients were taking an oral bisphosphonate at the time of knee surgery, with a mean age of 75.8 years (SD 6.2) in bisphosphonate users and 75.7 years (SD 6.8) in non-users. The mean joint space narrowing rate was 0.04 mm/year (SD 0.11) in bisphosphonate users and 0.12 mm/year (SD 0.25) in non-users (p < 0.001). In the multivariate model, age (standardized coefficient = 0.0867, p = 0.016) and the use of a bisphosphonate (standardized coefficient = −0.182, p < 0.001) were associated with the joint space narrowing rate. After successfully matching 43 bisphosphonate users and 86 non-users, the joint narrowing rate was smaller in bisphosphonate users (p < 0.001).

Conclusion

The use of bisphosphonates is associated with decreased joint degeneration in non-arthritic hips after knee arthroplasty. Bisphosphonates slow joint degeneration, thus maintaining the thickness of joint cartilage in the normal joint or during the early phase of osteoarthritis. Cite this article: Bone Joint Res 2022;11(11):826–834.

ATF3 as a potential diagnostic marker of early-stage osteoarthritis and its correlation with immune infiltration through bioinformatics analysis

AIMS

This study aimed, through bioinformatics analysis, to identify the potential diagnostic markers of osteoarthritis, and analyze the role of immune infiltration in synovial tissue.

METHODS

The gene expression profiles were downloaded from the Gene Expression Omnibus (GEO) database. The differentially expressed genes (DEGs) were identified by R software. Functional enrichment analyses were performed and protein-protein interaction networks (PPI) were constructed. Then the hub genes were screened. Biomarkers with high value for the diagnosis of early osteoarthritis (OA) were validated by GEO datasets. Finally, the CIBERSORT algorithm was used to evaluate the immune infiltration between early-stage OA and end-stage OA, and the correlation between the diagnostic marker and infiltrating immune cells was analyzed.

RESULTS

A total of 88 DEGs were identified. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses indicated that DEGs were significantly enriched in leucocyte migration and interleukin (IL)-17 signalling pathways. Disease ontology (DO) indicated that DEGs were mostly enriched in rheumatoid arthritis. Six hub genes including FosB proto-oncogene, AP-1 transcription factor subunit (FOSB); C-X-C motif chemokine ligand 2 (CXCL2); CXCL8; IL-6; Jun proto-oncogene, AP-1 transcription factor subunit (JUN); and Activating transcription factor 3 (ATF3) were identified and verified by GEO datasets. ATF3 (area under the curve = 0.975) turned out to be a potential biomarker for the diagnosis of early OA. Several infiltrating immune cells varied significantly between early-stage OA and end-stage OA, such as resting NK cells (p = 0.016), resting dendritic cells (p = 0.043), and plasma cells (p = 0.043). Additionally, ATF3 was significantly correlated with resting NK cells (p = 0.034), resting dendritic cells (p = 0.026), and regulatory T cells (Tregs, p = 0.018).

CONCLUSION

ATF3 may be a potential diagnostic marker for early diagnosis and treatment of OA, and immune cell infiltration provides new perspectives for understanding the mechanism during OA progression.Cite this article: Bone Joint Res 2022;11(9):679-689.

BMP2 as a promising anticancer approach: functions and molecular mechanisms

Bone morphogenetic protein 2 (BMP2), a pluripotent factor, is a member of the transforming growth factor-beta (TGF-β) superfamily and is implicated in embryonic development and postnatal homeostasis in tissues and organs. Experimental research in the contexts of physiology and pathology has indicated that BMP2 can induce macrophages to differentiate into osteoclasts and accelerate the osteolytic mechanism, aggravating cancer cell bone metastasis. Emerging studies have stressed the potent regulatory effect of BMP2 in cancer cell differentiation, proliferation, survival, and apoptosis. Complicated signaling networks involving multiple regulatory proteins imply the significant biological functions of BMP2 in cancer. In this review, we comprehensively summarized and discussed the current evidence related to the modulation of BMP2 in tumorigenesis and development, including evidence related to the roles and molecular mechanisms of BMP2 in regulating cancer stem cells (CSCs), epithelial-mesenchymal transition (EMT), cancer angiogenesis and the tumor microenvironment (TME). All these findings suggest that BMP2 may be an effective therapeutic target for cancer and a new marker for assessing treatment efficacy.

Immunomodulatory role of T helper cells in rheumatoid arthritis : a comprehensive research review

Rheumatoid arthritis (RA) is an autoimmune disease that involves T and B cells and their reciprocal immune interactions with proinflammatory cytokines. T cells, an essential part of the immune system, play an important role in RA. T helper 1 (Th1) cells induce interferon-γ (IFN-γ), tumour necrosis factor-α (TNF-α), and interleukin (IL)-2, which are proinflammatory cytokines, leading to cartilage destruction and bone erosion. Th2 cells primarily secrete IL-4, IL-5, and IL-13, which exert anti-inflammatory and anti-osteoclastogenic effects in inflammatory arthritis models. IL-22 secreted by Th17 cells promotes the proliferation of synovial fibroblasts through induction of the chemokine C-C chemokine ligand 2 (CCL2). T follicular helper (Tfh) cells produce IL-21, which is key for B cell stimulation by the C-X-C chemokine receptor 5 (CXCR5) and coexpression with programmed cell death-1 (PD-1) and/or inducible T cell costimulator (ICOS). PD-1 inhibits T cell proliferation and cytokine production. In addition, there are many immunomodulatory agents that promote or inhibit the immunomodulatory role of T helper cells in RA to alleviate disease progression. These findings help to elucidate the aetiology and treatment of RA and point us toward the next steps.

Cite this article: Bone Joint Res 2022;11(7):426–438.

Identification of mechanics-responsive osteocyte signature in osteoarthritis subchondral bone

Aims

Osteoarthritis (OA) is a common degenerative joint disease. The osteocyte transcriptome is highly relevant to osteocyte biology. This study aimed to explore the osteocyte transcriptome in subchondral bone affected by OA.

Methods

Gene expression profiles of OA subchondral bone were used to identify disease-relevant genes and signalling pathways. RNA-sequencing data of a bone loading model were used to identify the loading-responsive gene set. Weighted gene co-expression network analysis (WGCNA) was employed to develop the osteocyte mechanics-responsive gene signature.

Results

A group of 77 persistent genes that are highly relevant to extracellular matrix (ECM) biology and bone remodelling signalling were identified in OA subchondral lesions. A loading responsive gene set, including 446 principal genes, was highly enriched in OA medial tibial plateaus compared to lateral tibial plateaus. Of this gene set, a total of 223 genes were identified as the main contributors that were strongly associated with osteocyte functions and signalling pathways, such as ECM modelling, axon guidance, Hippo, Wnt, and transforming growth factor beta (TGF-β) signalling pathways. We limited the loading-responsive genes obtained via the osteocyte transcriptome signature to identify a subgroup of genes that are highly relevant to osteocytes, as the mechanics-responsive osteocyte signature in OA. Based on WGCNA, we found that this signature was highly co-expressed and identified three clusters, including early, late, and persistently responsive genes.

Conclusion

In this study, we identified the mechanics-responsive osteocyte signature in OA-lesioned subchondral bone.

Cite this article: Bone Joint Res 2022;11(6):362–370.

Human acellular amniotic membrane scaffolds encapsulating juvenile cartilage fragments accelerate the repair of rabbit osteochondral defects

Aims

The purpose of this study was to explore a simple and effective method of preparing human acellular amniotic membrane (HAAM) scaffolds, and explore the effect of HAAM scaffolds with juvenile cartilage fragments (JCFs) on osteochondral defects.

Methods

HAAM scaffolds were constructed via trypsinization from fresh human amniotic membrane (HAM). The characteristics of the HAAM scaffolds were evaluated by haematoxylin and eosin (H&E) staining, picrosirius red staining, type II collagen immunostaining, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Human amniotic mesenchymal stem cells (hAMSCs) were isolated, and stemness was verified by multilineage differentiation. Then, third-generation (P3) hAMSCs were seeded on the HAAM scaffolds, and phalloidin staining and SEM were used to detect the growth of hAMSCs on the HAAM scaffolds. Osteochondral defects (diameter: 3.5 mm; depth: 3 mm) were created in the right patellar grooves of 20 New Zealand White rabbits. The rabbits were randomly divided into four groups: the control group (n = 5), the HAAM scaffolds group (n = 5), the JCFs group (n = 5), and the HAAM + JCFs group (n = 5). Macroscopic and histological assessments of the regenerated tissue were evaluated to validate the treatment results at 12 weeks.

Results

In vitro, the HAAM scaffolds had a network structure and possessed abundant collagen. The HAAM scaffolds had good cytocompatibility, and hAMSCs grew well on the HAAM scaffolds. In vivo, the macroscopic scores of the HAAM + JCFs group were significantly higher than those of the other groups. In addition, histological assessments demonstrated that large amounts of hyaline-like cartilage formed in the osteochondral defects in the HAAM + JCFs group. Integration with surrounding normal cartilage and regeneration of subchondral bone in the HAAM + JCFs group were better than those in the other groups.

Conclusion

HAAM scaffolds combined with JCFs promote the regenerative repair of osteochondral defects.

Cite this article: Bone Joint Res 2022;11(6):349–361.

Osteoblasts induce glucose-derived ATP perturbations in chondrocytes through noncontact communication

Cartilage and subchondral bone communicate with each other through material and signal exchanges. However, direct evidence provided by experimental studies on their interactions is insufficient. In the present study, we establish a noncontact co-culture model with a transwell chamber to explore the energetic perturbations in chondrocytes influenced by osteoblasts. Our results indicate that osteoblasts induce more ATP generation in chondrocytes through an energetic shift characterized by enhanced glycolysis and impaired mitochondrial tricarboxylic acid cycle. Enhanced glycolysis is shown by an increase of secreted lactate and the upregulation of glycolytic enzymes, including glucose-6-phosphate isomerase (Gpi), liver type ATP-dependent 6-phosphofructokinase (Pfkl), fructose-bisphosphate aldolase C (Aldoc), glyceraldehyde-3-phosphate dehydrogenase (Gapdh), triosephosphate isomerase (Tpi1), and phosphoglycerate kinase 1 (Pgk1). Impaired mitochondrial tricarboxylic acid cycle is characterized by the downregulation of cytoplasmic aspartate aminotransferase (Got1) and mitochondrial citrate synthase (Cs). Osteoblasts induce the activation of Akt and P38 signaling to mediate ATP perturbations in chondrocytes. This study may deepen our understanding of the maintenance of metabolic homeostasis in the bone-cartilage unit.

The role of AGEs in pathogenesis of cartilage destruction in osteoarthritis

Osteoarthritis (OA) is a degenerative disease resulting from progressive joint destruction caused by many factors. Its pathogenesis is complex and has not been elucidated to date. Advanced glycation end products (AGEs) are a series of irreversible and stable macromolecular complexes formed by reducing sugar with protein, lipid, and nucleic acid through a non-enzymatic glycosylation reaction (Maillard reaction). They are an important indicator of the degree of ageing. Currently, it is considered that AGEs accumulation in vivo is a molecular basis of age-induced OA, and AGEs production and accumulation in vivo is one of the important reasons for the induction and acceleration of the pathological changes of OA. In recent years, it has been found that AGEs are involved in a variety of pathological processes of OA, including extracellular matrix degradation, chondrocyte apoptosis, and autophagy. Clearly, AGEs play an important role in regulating the expression of OA-related genes and maintaining the chondrocyte phenotype and the stability of the intra-articular environment. This article reviews the latest research results of AGEs in a variety of pathological processes of OA, to provide a new direction for the study of OA pathogenesis and a new target for prevention and treatment.

Cite this article: Bone Joint Res 2022;11(5):292–300.

TGF-β2 increases cell-cell communication in chondrocytes via p-Smad3 signalling

Connexin 43 (Cx43)-mediated gap junction intercellular communication (GJIC) plays a crucial role in the pathology and physiology of joint tissues. Transforming growth factor-β2 (TGF-β2), one of the potent regulatory factors in chondrocytes, plays a key role in the regulation of cell cycle and development of joint diseases. However, it is still unknown how TGF-β2 mediates GJIC in chondrocytes. The aim of this study was to explore the potential mechanism by which TGF-β2 regulates GJIC in chondrocytes. CCK-8 assays and scratch assays were performed to define the role of TGF-β2 on cell proliferation and migration. The scrape loading/dye transfer assay and scanning electron microscopy (SEM) were used to verify the effect of TGF-β2 on GJIC between chondrocytes. qPCR was performed to analyse the expression of genes in the gap junction protein family in chondrocytes. The expression of the Cx43 protein and phosphorylated Smad3 (p-Smad3) was evaluated by western blot assay. Immunofluorescence staining was used to explore p-Smad3 signalling pathway activation and Cx43 distribution. From these experiments, we found that the Cx43 protein was the most highly expressed member of the gap junction protein family in chondrocytes. We also found that TGF-β2 facilitated cell-to-cell communication in chondrocytes by upregulating Cx43 expression in chondrocytes. Finally, we found that TGF-β2 activated Smad3 signalling and promoted the nuclear aggregation of p-Smad3. Inhibition experiments by SIS3 also confirmed that TGF-β2-mediated GJIC through p-Smad3 signalling. For the first time, this study confirmed that TGF-β2 could regulate the formation of Cx43-mediated GJIC in chondrocytes via the canonical p-Smad3 signalling pathway.

The role of fibroblast growth factor 8 in cartilage development and disease

Fibroblast growth factor 8 (FGF‐8), also known as androgen‐induced growth factor (AIGF), is presumed to be a potent mitogenic cytokine that plays important roles in early embryonic development, brain formation and limb development. In the bone environment, FGF‐8 produced or received by chondrocyte precursor cells binds to fibroblast growth factor receptor (FGFR), causing different levels of activation of downstream signalling pathways, such as phospholipase C gamma (PLCγ)/Ca²⁺, RAS/mitogen‐activated protein kinase‐extracellular regulated protein kinases (RAS/MAPK‐MEK‐ERK), and Wnt‐β‐catenin‐Axin2 signalling, and ultimately controlling chondrocyte proliferation, differentiation, cell survival and migration. However, the molecular mechanism of FGF‐8 in normal or pathological cartilage remains unclear, and thus, FGF‐8 represents a novel exploratory target for studies of chondrocyte development and cartilage disease progression. In this review, studies assessing the relationship between FGF‐8 and chondrocytes that have been published in the past 5 years are systematically summarized to determine the probable mechanism and physiological effect of FGF‐8 on chondrocytes. Based on the existing research results, a therapeutic regimen targeting FGF‐8 is proposed to explore the possibility of treating chondrocyte‐related diseases.