Chondrocyte Hypertrophy in Osteoarthritis: Mechanistic Studies and Models for the Identification of New Therapeutic Strategies

Association between ethylene oxide exposure and osteoarthritis risk mediated by oxidative stress: evidence from NHANES 2013-2020

Ethylene oxide is extensively used for sterilizing medical equipment, and its carcinogenicity has been well documented. Furthermore, the onset of multiple diseases, including diabetes and hypertension, has been demonstrated to be associated with exposure to this compound. However, its association with osteoarthritis risk remains elusive. The study analyzed data from the National Health and Nutrition Examination Survey from 2013-2020, which included 6088 American adults, among whom 763 (12.5%) were diagnosed with osteoarthritis. We utilized a weighted generalized linear model to assess the correlation between ethylene oxide exposure levels and osteoarthritis risk. This study used mediation analysis to assess the functions of indicators of oxidative stress (γ-glutamyl transferase) and inflammation (alkaline phosphatase, white blood cell count, neutrophil count, and lymphocyte count) as mediators of how ethylene oxide affects osteoarthritis. The analysis revealed that elevated levels of ethylene oxide were correlated with a higher risk of osteoarthritis, even when controlling for other variables. The odds of developing osteoarthritis were 1.86 times higher in the fourth quartile than in the first quartile (95% confidence interval: 1.20-2.88, P = 0.0097, P for trend = 0.0087). Subgroup analyses indicated consistency across different cohorts. Mediation analysis revealed that oxidative stress (γ-glutamyl transferase), not inflammation, was the mediator linking ethylene oxide levels to the risk of osteoarthritis. This finding in a sample of American adults revealed a direct relationship between exposure to ethylene oxide and increased osteoarthritis risk. Oxidative stress has been suggested as a possible biological explanation for osteoarthritis caused by ethylene oxide.

SEMA6D modulates extracellular matrix metabolism in osteoarthritis by inhibiting the AGT/AGTR1a/IL-1β axis

The tissue-localized renin-angiotensin system (tRAS) plays a pivotal role in the crosstalk between cardiovascular factors and osteoarthritis (OA). Semaphorin 6D (SEMA6D), a cardiovascular neuroeffector, may contribute to chondrocyte homeostasis; however, its cartilage-specific functions remain unclear. Chondrocytes with altered SEMA6D expression were established via gene transfection. RNA sequencing was performed to identify SEMA6D-related genes and pathways, with preliminary validation in human OA samples. Furthermore, biochemical methods were employed to investigate the role of the AGT/AGTR1a/IL-1β axis in mediating SEMA6D-associated extracellular matrix metabolism (ECM). An AAV5-based lentiviral vector was used to generate OA rat models overexpressing SEMA6D, followed by radiological and histological analyses. SEMA6D overexpression significantly enhanced ECM homeostasis, marked by increased Aggrecan, COL2A1 and decreased COL10A1, MMP13, and Runx2 expression. These SEMA6D-induced genes were enriched in the tRAS pathway, with AGT, AGTR1a, and IL-1β identified as critical targets. Furthermore, the AGT/AGTR1a/IL-1β axis activated ECM degradation in chondrocytes, while SEMA6D overexpression effectively suppressed this signaling. In the OA rat model, elevated SEMA6D expression significantly reduced cartilage degradation. SEMA6D confers chondroprotective effects in OA by modulating the tRAS pathway, likely through inhibition of the AGT/AGTR1a/IL-1β axis, thereby regulating ECM metabolism and chondrocyte hypertrophy. These findings enhance our understanding of cardiovascular influences on cartilage health and reveal tissue-specific regulatory mechanisms in OA.

Metformin as a disease-modifying therapy in osteoarthritis: bridging metabolism and joint health

Background

Osteoarthritis (OA) and impaired glucose tolerance (IGT) frequently coexist, leading to compounded clinical and metabolic challenges. This study investigates the effects of metformin in improving both clinical outcomes (pain, stiffness, physical function) and metabolic parameters (inflammatory markers, lipid profile, BMI) in patients with knee OA and IGT.

Methods

The study included 60 patients diagnosed with knee OA and IGT. Participants were divided into two groups: 26 patients received standard OA treatment without metformin (Without Metf), while 34 received metformin (500 mg twice daily) for 3 months, in addition to standard treatment (With Metf). Clinical assessments (WOMAC, Lequesne Algofunctional Index, KOOS, VAS) and metabolic markers (CRP, NLR, SOD, lipid profile, BMI) were measured before treatment, after 1 month, and after 3 months.

Results

The With Metf group showed significantly greater improvements in pain, stiffness, physical function, and quality of life compared to the Without Metf group. Metformin also led to significant reductions in inflammatory markers and improvements in lipid profiles and metabolic health indicators. The With Metf group demonstrated enhanced BMI, waist-to-hip ratio, and waist-to-height ratio. Furthermore, the need for increased NSAID doses was predicted by factors such as pain severity and inflammatory markers.

Conclusion

Metformin effectively alleviates osteoarthritis symptoms and improves metabolic health in patients with both OA and IGT. Further research is needed to explore its long-term effects on joint health, inflammatory markers, and its potential role in OA management in patients without IGT.

Zonal Characteristics of Collagen Ultrastructure and Responses to Mechanical Loading in Articular Cartilage

The biomechanical properties of articular cartilage arise from a complex bioenvironment comprising hierarchically organised collagen networks within the extracellular matrix (ECM) that interact with the proteoglycan-rich interstitial fluid. This network features a depth-dependent fibril organisation across different zones. Understanding how collagen fibrils respond to external loading is key to elucidating the mechanisms behind lesion formation and managing degenerative conditions like osteoarthritis. This study employs polarisation-resolved second harmonic generation (pSHG) microscopy to quantify the ultrastructural organisation of collagen fibrils and their spatial gradient along the depth of bone-cartilage explants under a close-to-in vivo condition. By combining with in-situ loading, we examined the responses of collagen fibrils by quantifying changes in their principal orientation and degree of alignment. The spatial gradient and heterogeneity of collagen organisation were captured at high resolution (1 μm) along the longitudinal plane of explants (0.5 mm by 2 mm). Zone-specific ultrastructural characteristics were quantified to aid in defining zonal borders, revealing consistent zonal proportions with varying overall thicknesses. Under compression, the transitional zone exhibited the most significant re-organisation of collagen fibrils. It initially allowed large deformation through the re-orientation of fibrils, which then tightened fibril alignment to prevent excessive deformation, indicating a dynamic adaptation mechanism in response to increasing strain levels. Our results provide comprehensive, zone-specific baselines of cartilage ultrastructure and micromechanics, crucial for investigating the onset and progression of degenerative conditions, setting therapeutic intervention targets, and guiding cartilage repair and regeneration efforts. STATEMENT OF SIGNIFICANCE: Achieved unprecedented quantification of the spatial gradient and heterogeneity of collagen ultrastructural organisation at a high resolution (1 μm) along the full depth of the longitudinal plane of osteochondral explants (0.5 mm by 2 mm) under close-to-in vivo condition. Suggested new anatomical landmarks based on ultrastructural features for determining zonal borders and found consistent zonal proportions in explants with different overall thicknesses. Demonstrated that collagen fibrils initially respond by reorienting themselves at low strain levels, playing a significant role in cartilage deformation, particularly within the transitional zone. At higher strain levels, more collagen fibrils re-aligned, indicating a dynamic shift in the response mechanism at varying strain levels.

The Effect of Nerve Growth Factor on Cartilage Fibrosis and Hypertrophy during In Vitro Chondrogenesis Using Induced Pluripotent Stem Cells

Nerve growth factor (NGF) is a neurotrophic factor usually involved in the survival, differentiation, and growth of sensory neurons and nociceptive function. Yet, it has been suggested to play a role in the pathogenesis of osteoarthritis (OA). Previous studies suggested a possible relationship between NGF and OA; however, the underlying mechanisms remain unknown. Therefore, we investigated the impact of NGF in chondrogenesis using human induced pluripotent stem cells (hiPSCs)-derived chondrogenic pellets. To investigate how NGF affects the cartilage tissue, hiPSC-derived chondrogenic pellets were treated with NGF on day 3 of differentiation, expression of chondrogenic, hypertrophic, and fibrotic markers was confirmed. Also, inflammatory cytokine arrays were performed using the culture medium of the NGF treated chondrogenic pellets. As a result, NGF treatment decreased the expression of pro-chondrogenic markers by approximately 2~4 times, and hypertrophic (pro-osteogenic) markers and fibrotic markers were increased by approximately 3-fold or more in the NGF-treated cartilaginous pellets. In addition, angiogenesis was upregulated by approximately 4-fold or more, bone formation by more than 2-fold, and matrix metalloproteinase induction by more than 2-fold. These inflammatory cytokine array were using the NGF-treated chondrogenic pellet cultured medium. Furthermore, it was confirmed by Western blot to be related to the induction of the glycogen synthase kinase-3 beta (GSK3β) pathway by NGF. In Conclusions, these findings provide valuable insights into the multifaceted role of NGF in cartilage hypertrophy and fibrosis, which might play a critical role in OA progression.

Targeting Chondrocyte Hypertrophy as Strategies for the Treatment of Osteoarthritis

Osteoarthritis (OA) is a common joint disease characterized by pain and functional impairment, which severely impacts the quality of life of middle-aged and elderly individuals. During normal bone development, chondrocyte hypertrophy is a natural physiological process. However, in the progression of OA, chondrocyte hypertrophy becomes one of its key pathological features. Although there is no definitive evidence to date confirming that chondrocyte hypertrophy is the direct cause of OA, substantial experimental data indicate that it plays an important role in the disease's pathogenesis. In this review, we first explore the mechanisms underlying chondrocyte hypertrophy in OA and offer new insights. We then propose strategies for inhibiting chondrocyte hypertrophy from the perspectives of targeting signaling pathways and tissue engineering, ultimately envisioning the future prospects of OA treatment.

Impact of eggshell membrane on metabolism and cell adhesion in oxidatively stressed canine chondrocytes

Eggshell membrane (ESM) is a rich source of bioactive compounds, including proteins, peptides, and antioxidants, contributing to its potential therapeutic benefits. These natural antioxidants might help neutralize reactive oxygen species (ROS) and modulate inflammatory responses, which are often linked with chondrocyte damage in osteoarthritis. In this study, we investigated the functional effects of ESM proteins on H2O2-induced oxidative stress in a neonatal canine chondrocytes. The isolated neonatal chondrocytes demonstrated a high proliferation rate and increased glycosaminoglycan (GAG) production during cultivation. In addition, the expression of key cartilage markers, including collagen types II and IX, and aggrecan, confirmed the retention of the chondrocyte phenotype. Under in vitro conditions, post-treatment with ESM improved chondrocyte viability, indicating that ESM may have a reparative role in mitigating oxidative damage. This significant therapeutic potential was validated through XTT assays, which measured cell metabolic activity at 24 h, and Real-time Cell Analysis (RTCA), providing continuous monitoring over 98 h. In contrast, the preventive effects of ESM against stress were observed exclusively in the XTT analysis. By investigating these aspects, we provide insight into the potential of ESM proteins to protect chondrocytes from oxidative damage, particularly in cartilage repair and joint health. This study is one of the first to create a vital platform based on canine neonatal chondrocytes for monitoring dietary supplements designed to prevent or repair dog cartilage damage. Thus, the study offers a valuable contribution to understanding how ESM bioactive compounds can be used therapeutically, bridging the gap between in vitro findings and practical applications in veterinary medicine.

Wharton's Jelly Mesenchymal Stem Cells: Shaping the Future of Osteoarthritis Therapy with Advancements in Chitosan-Hyaluronic Acid Scaffolds

This review explores the potential of Wharton's jelly-derived mesenchymal stem cells (WJ-MSCs) in cartilage regeneration and osteoarthritis treatment. It covers key factors influencing chondrogenesis, including growth factors, cytokines, and hypoxia, focusing on precise timing. The effectiveness of three-dimensional cultures and scaffold-based strategies in chondrogenic differentiation is discussed. Specific biomaterials such as chitosan and hyaluronic acid are highlighted for tissue engineering. The document reviews clinical applications, incorporating evidence from animal research and early trials and molecular and histological assessments of chondrogenic differentiation processes. It addresses challenges and strategies for optimizing MSC-derived chondrocyte therapy, emphasizing the immunomodulatory properties of these cells. The review concludes as a comprehensive road map for future research and clinical applications in regenerative medicine.

In Vitro Induction of Hypertrophic Chondrocyte Differentiation of Naïve MSCs by Strain

In the context of bone fractures, the influence of the mechanical environment on the healing outcome is widely accepted, while its influence at the cellular level is still poorly understood. This study explores the influence of mechanical load on naïve mesenchymal stem cell (MSC) differentiation, focusing on hypertrophic chondrocyte differentiation. Unlike primary bone healing, which involves the direct differentiation of MSCs into bone-forming cells, endochondral ossification uses an intermediate cartilage template that remodels into bone. A high-throughput uniaxial bioreactor system (StrainBot) was used to apply varying percentages of strain on naïve MSCs encapsulated in GelMa hydrogels. This research shows that cyclic uniaxial compression alone directs naïve MSCs towards a hypertrophic chondrocyte phenotype. This was demonstrated by increased cell volumes and reduced glycosaminoglycan (GAG) production, along with an elevated expression of hypertrophic markers such as MMP13 and Type X collagen. In contrast, Type II collagen, typically associated with resting chondrocytes, was poorly detected under mechanical loading alone conditions. The addition of chondrogenic factor TGFβ1 in the culture medium altered these outcomes. TGFβ1 induced chondrogenic differentiation, as indicated by higher GAG/DNA production and Type II collagen expression, overshadowing the effect of mechanical loading. This suggests that, under mechanical strain, hypertrophic differentiation is hindered by TGFβ1, while chondrogenesis is promoted. Biochemical analyses further confirmed these findings. Mechanical deformation alone led to a larger cell size and a more rounded cell morphology characteristic of hypertrophic chondrocytes, while lower GAG and proteoglycan production was observed. Immunohistology staining corroborated the gene expression data, showing increased Type X collagen with mechanical strain. Overall, this study indicates that mechanical loading alone drives naïve MSCs towards a hypertrophic chondrocyte differentiation path. These insights underscore the critical role of mechanical forces in MSC differentiation and have significant implications for bone healing, regenerative medicine strategies and rehabilitation protocols.

An Advanced Mechanically Active Osteoarthritis-on-Chip Model to Test Injectable Therapeutic Formulations: The SYN321 Case Study

Current treatments for osteoarthritis (OA) often fail to address the underlying pathophysiology and may have systemic side effects, particularly associated with long-term use of non-steroidal anti-inflammatory drugs (NSAIDs). Thus, researchers are currently directing their efforts toward innovative polymer-drug combinations, such as mixtures of hyaluronic acid viscoelastic hydrogels and NSAIDs like diclofenac, to ensure sustained release of the NSAID within the joint following intra-articular injection. However, the progress of novel injectable therapies for OA is hindered by the absence of preclinical models that accurately represent the pathology of the disease. The uBeat® MultiCompress platform is here presented as a novel approach for studying anti-OA injectable therapeutics on human mechanically-damaged OA cartilage microtissues, in a physiologically relevant environment. This platform can accommodate injectable therapeutic formulations and is successfully tested with SYN321, a novel diclofenac-sodium hyaluronate conjugate under development as a treatment for knee OA. Results indicate the platform's effectiveness in evaluating therapeutic potential, showing downregulation of inflammatory markers and reduction in matrix degradation in OA cartilage micro-tissues treated with SYN321. The uBeat® MultiCompress platform thus represents a valuable tool for OA research, offering a bridge between traditional in vitro studies and potential clinical applications, with implications for future drug discovery.

New role of calcium-binding fluorescent dye alizarin complexone in detecting permeability from articular cartilage to subchondral bone

Osteoarthritis (OA) is a chronic degenerative joint disorder characterized by the progressive deterioration of articular cartilage and concomitant alterations in subchondral bone architecture. However, the precise mechanisms underlying the initiation and progression of OA remains poorly understood. In the present study, we explored whether the calcification in the articular cartilage occurred in the early stage of mouse OA model, generated by the surgery destabilization of the medial meniscus (DMM), via the intra-articular injection of alizarin complexone due to its anionic nature for binding calcium-containing crystals. Although we did not observe the calcification in the articular cartilage of early stage of DMM mice, we unexpectedly identified alizarin complexone had the diffusion capacity for detecting the permeability from the articular cartilage to subchondral bone. Our data showed that the diffusion of alizarin complexone from the articular cartilage to calcified cartilage was greater in the early stage of DMM mice than that in sham controls. Additionally, we observed enhanced penetration of alizarin complexone through the periosteum in DMM mice compared to sham mice. In summary, we developed a novel imaging method that offers a valuable tool for further exploration of biochemical communication underlying OA development. Our findings provided new evidence that increased molecular interactions between the articular cartilage and subchondral bone is involved in the pathogenesis of OA progression.

IHH-GLI-1-HIF-2α signalling influences hypertrophic chondrocytes to exacerbate osteoarthritis progression

Background

Chondrocyte hypertrophy is a potential target for osteoarthritis (OA) treatment, with Indian hedgehog (IHH), glioma-associated oncogene homolog (GLI), and hypoxia-inducible factor-2α (HIF-2α) being closely associated with chondrocyte hypertrophy during OA progression. Whereas IHH can modulate chondrocyte hypertrophy, interference with IHH signalling has not achieved the anticipated therapeutic effects and poses safety concerns, necessitating further clarification of the specific mechanisms by which IHH affects articular cartilage degeneration. Inhibition of the HIF-2α overexpression in cartilage slows the progression of early OA, but the mechanisms underlying HIF-2α accumulation in OA cartilage remain unclear. The aim of this study was to determine the function of Ihh, as well as its downstream factors, in chondrocytes, based on an early osteoarthritis (OA) mouse model and in vitro chondrocyte model.

Methods

Investigated the expression levels and locations of IHH-GLI-1 pathway in normal and early degenerated human cartilage, comparing them with HIF-2α and its downstream factors. RT-qPCR, Western blotting, Crystal violet staining, and EdU assays were used to evaluate the pecific regulatory mechanisms of the IHH-GLI-1-HIF-2α signalling axis in normal chondrocytes and in chondrocytes under inflammatory conditions. Validated the impact of IHH on early cartilage degeneration and the relationship between the IHH-GLI-1 pathway and the expression levels and expression locations of HIF-2α and its downstream factors in Col2a1-CreERT2;Ihhfl/fl mice.

Results

In early-stage degenerative joint cartilage, the GLI-1 pathway in hypertrophic chondrocytes exhibited similar changes in location and levels to HIF-2α and its downstream factor vascular endothelial growth factor (VEGF). In vitro, IHH-GLI-1-HIF-2α signalling activation in chondrocytes under physiological hypoxic conditions inhibited chondrocyte proliferation. In chondrocytes stimulated by inflammatory environments, IHH inhibited the degradation of HIF-2α via the GLI-1 pathway, thereby promoting HIF-2α protein expression. Elevated HIF-2α expression further enhanced intracellular IHH-GLI-1 levels, generating a positive feedback loop to collectively regulate the expression of downstream hypertrophic factors and matrix-degradation factors. In vivo, conditional Ihh knockout in mouse chondrocytes downregulated Hif-2α protein expression in early degenerative cartilage tissue and affected the expression of downstream Vegf and hypertrophic factors.

Conclusions

During OA progression, the IHH-GLI-1-HIF-2α axis mainly operates within hypertrophic chondrocytes, exacerbating cartilage degeneration by regulating hypertrophic chondrocyte functions, cartilage matrix degradation, and microvascular invasion.

The translational potential of this article

This study identifies the IHH-GLI-1-HIF-2α signalling axis and reveals its potential as a therapeutic target for OA.

Catabolic mediators from TLR2-mediated proteoglycan aggrecan peptide-stimulated chondrocytes are reduced by Lactobacillus-conditioned media

In osteoarthritis (OA), extracellular matrix (ECM) digestion by cartilage-degrading enzymes drives cartilage destruction and generates ECM fragments, such as proteoglycan aggrecan (PG) peptides. PG peptides have been shown to induce immunological functions of chondrocytes. However, the role of PG peptides in stimulating catabolic mediators from chondrocytes has not been investigated. Therefore, we aim to determine the effects and its mechanism by which PG peptides induce chondrocytes to produce catabolic mediators in OA. Human chondrocytes were stimulated with IFNγ and various PG peptides either (i) with or (ii) without TLR2 blockade or (iii) with Lactobacillus species-conditioned medium (LCM), a genus of bacteria with anti-inflammatory properties. Transcriptomic analysis, cartilage-degrading enzyme production and TLR2-intracellular signaling activation were investigated. Chondrocytes treated with PG peptides p16-31 and p263-280 increased expression levels of genes associated with chondrocyte hypertrophy, cartilage degradation and proteolytic enzyme production. TLR2 downstream signaling proteins (STAT3, IkBα and MAPK9) were significantly phosphorylated in p263-280 peptide-stimulated chondrocytes. MMP-1 and ADAMTS-4 were significantly reduced in p263-280 peptides-treated condition with TLR2 blockade or LCM treatment. Phosphorylation levels of IkBa, ERK1/2 and MAPK9 were significantly decreased with TLR2 blockade, but only phosphorylation levels of MAPK9 was significantly decreased with LCM treatment. Our study showed that PG peptide stimulation via TLR2 induced cartilage-degrading enzyme production via activation of MAPK, NFκB and STAT3 pathways.

Critical signaling molecules in the temporomandibular joint osteoarthritis under different magnitudes of mechanical stimulation

The mechanical stress environment in the temporomandibular joint (TMJ) is constantly changing due to daily mandibular movements. Therefore, TMJ tissues, such as condylar cartilage, the synovial membrane and discs, are influenced by different magnitudes of mechanical stimulation. Moderate mechanical stimulation is beneficial for maintaining homeostasis, whereas abnormal mechanical stimulation leads to degeneration and ultimately contributes to the development of temporomandibular joint osteoarthritis (TMJOA), which involves changes in critical signaling molecules. Under abnormal mechanical stimulation, compensatory molecules may prevent degenerative changes while decompensatory molecules aggravate. In this review, we summarize the critical signaling molecules that are stimulated by moderate or abnormal mechanical loading in TMJ tissues, mainly in condylar cartilage. Furthermore, we classify abnormal mechanical stimulation-induced molecules into compensatory or decompensatory molecules. Our aim is to understand the pathophysiological mechanism of TMJ dysfunction more deeply in the ever-changing mechanical environment, and then provide new ideas for discovering effective diagnostic and therapeutic targets in TMJOA.

Engineered human osteoarthritic cartilage organoids

The availability of human cell-based models capturing molecular processes of cartilage degeneration can facilitate development of disease-modifying therapies for osteoarthritis [1], a currently unmet clinical need. Here, by imposing specific inflammatory challenges upon mesenchymal stromal cells at a defined stage of chondrogenesis, we engineered a human organotypic model which recapitulates main OA pathological traits such as chondrocyte hypertrophy, cartilage matrix mineralization, enhanced catabolism and mechanical stiffening. To exemplify the utility of the model, we exposed the engineered OA cartilage organoids to factors known to attenuate pathological features, including IL-1Ra, and carried out mass spectrometry-based proteomics. We identified that IL-1Ra strongly reduced production of the transcription factor CCAAT/enhancer-binding protein beta [2] and demonstrated that inhibition of the C/EBPβ-activating kinases could revert the degradative processes. Human OA cartilage organoids thus represent a relevant tool towards the discovery of new molecular drivers of cartilage degeneration and the assessment of therapeutics targeting associated pathways.

TMF suppresses chondrocyte hypertrophy in osteoarthritic cartilage by mediating the FOXO3a/BMPER pathway

Osteoarthritis (OA) is a disease of the joints, characterized by chronic inflammation, cartilage destruction and extracellular matrix (ECM) remodeling. Aberrant chondrocyte hypertrophy promotes cartilage destruction and OA development. Collagen X, the biomarker of chondrocyte hypertrophy, is upregulated by runt-related transcription factor 2 (Runx2), which is mediated by the bone morphogenetic protein 4 (BMP4)/Smad1 signaling pathway. BMP binding endothelial regulator (BMPER), a secreted glycoprotein, acts as an agonist of BMP4. 5,7,3',4'-tetramethoxyflavone (TMF) is a natural flavonoid derived from Murraya exotica L. Results of our previous study demonstrated that TMF exhibits chondroprotective effects against OA development through the activation of Forkhead box protein O3a (FOXO3a) expression. However, whether TMF suppresses chondrocyte hypertrophy through activation of FOXO3a expression and inhibition of BMPER/BMP4/Smad1 signaling remains unknown. Results of the present study revealed that TMF inhibited collagen X and Runx2 expression, inhibited BMPER/BMP4/Smad1 signaling, and activated FOXO3a expression; thus, protecting against chondrocyte hypertrophy and OA development. However, BMPER overexpression and FOXO3a knockdown impacted the protective effects of TMF. Thus, TMF inhibited chondrocyte hypertrophy in OA cartilage through mediating the FOXO3a/BMPER signaling pathway.

Significance of radiographic temporomandibular degenerative joint disease findings

The field of orthodontics has seen a recent increase in the number of patients over the age of 50 seeking treatment and also an increase in the use of cone beam technology. Similar to other joints in the body, the temporomandibular joint (TMJ) is associated with age-related degeneration. However, unlike other joints, degeneration of the TMJ is rarely symptomatic and when there is pain, it is usually self-limiting. In this article, we will review: a) the incidence and prevalence of TMJ degenerative diseases, b) similarities and differences of TMJ vs knee degenerative diseases, and c) current treatment recommendations for TMJ degenerative diseases. In the vast majority of people, radiographic evidence of TMJ degeneration is an incidental finding. Future longitudinal research is needed to follow the natural course of TMJ degenerative patients.

The role of YAP/TAZ on joint and arthritis

Osteoarthritis (OA) and rheumatoid arthritis (RA) are two common forms of arthritis with undefined etiology and pathogenesis. Yes-associated protein (YAP) and its homolog transcriptional coactivator with PDZ-binding motif (TAZ), which act as sensors for cellular mechanical and inflammatory cues, have been identified as crucial players in the regulation of joint homeostasis. Current studies also reveal a significant association between YAP/TAZ and the pathogenesis of OA and RA. The objective of this review is to elucidate the impact of YAP/TAZ on different joint tissues and to provide inspiration for further studying the potential therapeutic implications of YAP/TAZ on arthritis. Databases, such as PubMed, Cochran Library, and Embase, were searched for all available studies during the past two decades, with keywords "YAP," "TAZ," "OA," and "RA."

An Advanced Bioconjugation Strategy for Covalent Tethering of TGFβ3 with Silk Fibroin Matrices and its Implications in the Chondrogenesis Profile of Human BMSCs and Human Chondrocytes: A Paradigm Shift in Cartilage Tissue Engineering

The transforming growth factor-β class of cytokines plays a significant role in articular cartilage formation from mesenchymal condensation to chondrogenic differentiation. However, their exogenous addition to the chondrogenic media makes the protocol expensive. It reduces the bioavailability of the cytokine to the cells owing to their burst release. The present study demonstrates an advanced bioconjugation strategy to conjugate transforming growth factor-β3 (TGFβ3) with silk fibroin matrix covalently via a cyanuric chloride coupling reaction. The tethering and change in secondary conformation are confirmed using various spectroscopic analyses. To assess the functionality of the chemically modified silk matrix, human bone marrow-derived mesenchymal stem cells (hBMSCs) and chondrocytes are cultured for 28 days in a chondrogenic differentiation medium. Gene expression and histological analysis reveal enhanced expression of chondrogenic markers with intense Safranin-O and Alcian Blue staining in TGFβ3 conjugated silk matrices than where TGFβ3 is exogenously added to the media for both hBMSCs and chondrocytes. Therefore, this study successfully recapitulates the native niche of TGFβ3 and the role of the silk as a growth factor stabilizer. When cultured over TGFβ3 conjugated silk matrices, hBMSCs display increased proteoglycan secretion and maximum chondrogenic trait with attenuation of chondrocyte hypertrophy over human chondrocytes.

Covalent Conjugation of Small Molecule Inhibitors and Growth Factors to a Silk Fibroin-Derived Bioink to Develop Phenotypically Stable 3D Bioprinted Cartilage

Implantation of a phenotypically stable cartilage graft could represent a viable approach for repairing osteoarthritic (OA) cartilage lesions. In the present study, we investigated the effects of modulating the bone morphogenetic protein (BMP), transforming growth factor beta (TGFβ), and interleukin-1 (IL-1) signaling cascades in human bone marrow stromal cell (hBMSC)-encapsulated silk fibroin gelatin (SF-G) bioink. The selected small molecules LDN193189, TGFβ3, and IL1 receptor antagonist (IL1Ra) are covalently conjugated to SF-G biomaterial to ensure sustained release, increased bioavailability, and printability, confirmed by ATR-FTIR, release kinetics, and rheological analyses. The 3D bioprinted constructs with chondrogenically differentiated hBMSCs were incubated in an OA-inducing medium for 14 days and assessed through a detailed qPCR, immunofluorescence, and biochemical analyses. Despite substantial heterogeneity in the observations among the donors, the IL1Ra molecule illustrated the maximum efficiency in enhancing the expression of articular cartilage components, reducing the expression of hypertrophic markers (re-validated by the GeneMANIA tool), as well as reducing the production of inflammatory molecules by the hBMSCs. Therefore, this study demonstrated a novel strategy to develop a chemically decorated, printable and biomimetic SF-G bioink to produce hyaline cartilage grafts resistant to acquiring OA traits that can be used for the treatment of degenerated cartilage lesions.

Assessing the advantages of 3D bioprinting and 3D spheroids in deciphering the osteoarthritis healing mechanism using human chondrocytes and polarized macrophages

The molecular niche of an osteoarthritic microenvironment comprises the native chondrocytes, the circulatory immune cells, and their respective inflammatory mediators. Although M2 macrophages infiltrate the joint tissue during osteoarthritis (OA) to initiate cartilage repair, the mechanistic crosstalk that dwells underneath is still unknown. Our study established a co-culture system of human OA chondrocytes and M2 macrophages in 3D spheroids and 3D bioprinted silk-gelatin constructs. It is already well established that Silk fibroin-gelatin bioink supports chondrogenic differentiation due to upregulation of the Wnt/β-catenin pathway. Additionally, the presence of anti-inflammatory M2 macrophages significantly upregulated the expression of chondrogenic biomarkers (COL-II, ACAN) with an attenuated expression of the chondrocyte hypertrophy (COL-X), chondrocyte dedifferentiation (COL-I) and matrix catabolism (MMP-1 and MMP-13) genes even in the absence of the interleukins. Furthermore, the 3D bioprinted co-culture model displayed an upper hand in stimulating cartilage regeneration and OA inhibition than the spheroid model, underlining the role of silk fibroin-gelatin in encouraging chondrogenesis. Additionally, the 3D bioprinted silk-gelatin constructs further supported the maintenance of stable anti-inflammatory phenotype of M2 macrophage. Thus, the direct interaction between the primary OAC and M2 macrophages in the 3D context, along with the release of the soluble anti-inflammatory factors by the M2 cells, significantly contributed to a better understanding of the molecular mechanisms responsible for immune cell-mediated OA healing.

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.

Inflammatory and Metabolic Signaling Interfaces of the Hypertrophic and Senescent Chondrocyte Phenotypes Associated with Osteoarthritis

Osteoarthritis (OA) is a complex disease of whole joints with progressive cartilage matrix degradation and chondrocyte transformation. The inflammatory features of OA are reflected in increased synovial levels of IL-1β, IL-6 and VEGF, higher levels of TLR-4 binding plasma proteins and increased expression of IL-15, IL-18, IL-10 and Cox2, in cartilage. Chondrocytes in OA undergo hypertrophic and senescent transition; in these states, the expression of Sox-9, Acan and Col2a1 is suppressed, whereas the expression of RunX2, HIF-2α and MMP-13 is significantly increased. NF-kB, which triggers many pro-inflammatory cytokines, works with BMP, Wnt and HIF-2α to link hypertrophy and inflammation. Altered carbohydrate metabolism and the upregulation of GLUT-1 contribute to the formation of end-glycation products that trigger inflammation via the RAGE pathway. In addition, a glycolytic shift, increased rates of oxidative phosphorylation and mitochondrial dysfunction generate reactive oxygen species with deleterious effects. An important surveyor mechanism, the YAP/TAZ signaling system, controls chondrocyte differentiation, inhibits ageing by protecting the nuclear envelope and suppressing NF-kB, MMP-13 and aggrecanases. The inflammatory microenvironment and synthesis of key matrix components are also controlled by SIRT1 and mTORc. Senescent chondrocytes represent the functional end stage of hypertrophic differentiation and characteristically upregulate p16 and p21, but also a variety of inflammatory cytokines, chemokines and metalloproteinases, developing the senescence-associated secretory phenotype. Senolysis with dendrobin, miR29b-5p and other agents has been shown to be efficient under experimental conditions, and appears to be a promising tool for the treatment of OA, as it restores COL2A1 and aggrecan synthesis, suppressing NF-kB and destructive metalloproteinases.

Controlled-Release Hydrogel Microspheres to Deliver Multipotent Stem Cells for Treatment of Knee Osteoarthritis

Osteoarthritis (OA) is the most common form of joint disease affecting articular cartilage and peri-articular tissues. Traditional treatments are insufficient, as they are aimed at mitigating symptoms. Multipotent Stromal Cell (MSC) therapy has been proposed as a treatment capable of both preventing cartilage destruction and treating symptoms. While many studies have investigated MSCs for treating OA, therapeutic success is often inconsistent due to low MSC viability and retention in the joint. To address this, biomaterial-assisted delivery is of interest, particularly hydrogel microspheres, which can be easily injected into the joint. Microspheres composed of hyaluronic acid (HA) were created as MSC delivery vehicles. Microrheology measurements indicated that the microspheres had structural integrity alongside sufficient permeability. Additionally, encapsulated MSC viability was found to be above 70% over one week in culture. Gene expression analysis of MSC-identifying markers showed no change in CD29 levels, increased expression of CD44, and decreased expression of CD90 after one week of encapsulation. Analysis of chondrogenic markers showed increased expressions of aggrecan (ACAN) and SRY-box transcription factor 9 (SOX9), and decreased expression of osteogenic markers, runt-related transcription factor 2 (RUNX2), and alkaline phosphatase (ALPL). In vivo analysis revealed that HA microspheres remained in the joint for up to 6 weeks. Rats that had undergone destabilization of the medial meniscus and had overt OA were treated with empty HA microspheres, MSC-laden microspheres, MSCs alone, or a control vehicle. Pain measurements taken before and after the treatment illustrated temporarily decreased pain in groups treated with encapsulated cells. Finally, the histopathological scoring of each group illustrated significantly less OA damage in those treated with encapsulated cells compared to controls. Overall, these studies demonstrate the potential of using HA-based hydrogel microspheres to enhance the therapeutic efficacy of MSCs in treating OA.

Oxidative stress as a key modulator of cell fate decision in osteoarthritis and osteoporosis: a narrative review

During aging and after traumatic injuries, cartilage and bone cells are exposed to various pathophysiologic mediators, including reactive oxygen species (ROS), damage-associated molecular patterns, and proinflammatory cytokines. This detrimental environment triggers cellular stress and subsequent dysfunction, which not only contributes to the development of associated diseases, that is, osteoporosis and osteoarthritis, but also impairs regenerative processes. To counter ROS-mediated stress and reduce the overall tissue damage, cells possess diverse defense mechanisms. However, cellular antioxidative capacities are limited and thus ROS accumulation can lead to aberrant cell fate decisions, which have adverse effects on cartilage and bone homeostasis. In this narrative review, we address oxidative stress as a major driver of pathophysiologic processes in cartilage and bone, including senescence, misdirected differentiation, cell death, mitochondrial dysfunction, and impaired mitophagy by illustrating the consequences on tissue homeostasis and regeneration. Moreover, we elaborate cellular defense mechanisms, with a particular focus on oxidative stress response and mitophagy, and briefly discuss respective therapeutic strategies to improve cell and tissue protection.

Biomimetic Hydrogel Applications and Challenges in Bone, Cartilage, and Nerve Repair

Tissue engineering and regenerative medicine is a highly sought-after field for researchers aiming to compensate and repair defective tissues. However, the design and development of suitable scaffold materials with bioactivity for application in tissue repair and regeneration has been a great challenge. In recent years, biomimetic hydrogels have shown great possibilities for use in tissue engineering, where they can tune mechanical properties and biological properties through functional chemical modifications. Also, biomimetic hydrogels provide three-dimensional (3D) network spatial structures that can imitate normal tissue microenvironments and integrate cells, scaffolds, and bioactive substances for tissue repair and regeneration. Despite the growing interest in various hydrogels for biomedical use in previous decades, there are still many aspects of biomimetic hydrogels that need to be understood for biomedical and clinical trial applications. This review systematically describes the preparation of biomimetic hydrogels and their characteristics, and it details the use of biomimetic hydrogels in bone, cartilage, and nerve tissue repair. In addition, this review outlines the application of biomimetic hydrogels in bone, cartilage, and neural tissues regarding drug delivery. In particular, the advantages and shortcomings of biomimetic hydrogels in biomaterial tissue engineering are highlighted, and future research directions are proposed.

Current and Novel Therapeutics for Articular Cartilage Repair and Regeneration

Articular cartilage repair is a sophisticated process that has is being recently investigated. There are several different approaches that are currently reported to promote cartilage repair, like cell-based therapies, biologics, and physical therapy. Cell-based therapies involve the using stem cells or chondrocytes, which make up cartilage, to promote the growth of new cartilage. Biologics, like growth factors, are also being applied to enhance cartilage repair. Physical therapy, like exercise and weight-bearing activities, can also be used to promote cartilage repair by inducing new cartilage growth and improving joint function. Additionally, surgical options like osteochondral autograft, autologous chondrocyte implantation, microfracture, and others are also reported for cartilage regeneration. In the current literature review, we aim to provide an up-to-date discussion about these approaches and discuss the current research status.

Effects of Modified Glucosamine on the Chondrogenic Potential of Circulating Stem Cells under Experimental Inflammation

Glucosamine (GlcN) is a glycosaminoglycan (GAGs) constituent in connective tissues. It is naturally produced by our body or consumed from diets. In the last decade, in vitro and in vivo trials have demonstrated that the administration of GlcN or its derivates has a protective effect on cartilage when the balance between catabolic and anabolic processes is disrupted and cells are no longer able to fully compensate for the loss of collagen and proteoglycans. To date, these benefits are still controversial because the mechanism of action of GlcN is not yet well clarified. In this study, we have characterized the biological activities of an amino acid (AA) derivate of GlcN, called DCF001, in the growth and chondrogenic induction of circulating multipotent stem cells (CMCs) after priming with tumor necrosis factor-alpha (TNFα), a pleiotropic cytokine commonly expressed in chronic inflammatory joint diseases. In the present work, stem cells were isolated from the human peripheral blood of healthy donors. After priming with TNFα (10 ng/mL) for 3 h, cultures were treated for 24 h with DCF001 (1 μg/mL) dissolved in a proliferative (PM) or chondrogenic (CM) medium. Cell proliferation was analyzed using a Corning^® Cell Counter and trypan blue exclusion technique. To evaluate the potentialities of DCF001 in counteracting the inflammatory response to TNFα, we measured the amount of extracellular ATP (eATP) and the expression of adenosine-generating enzymes CD39/CD73, TNFα receptors, and NF-κB inhibitor IκBα using flow cytometry. Finally, total RNA was extracted to perform a gene expression study of some chondrogenic differentiation markers (COL2A1, RUNX2, and MMP13). Our analysis has shed light on the ability of DCF001 to (a) regulate the expression of CD39, CD73, and TNF receptors; (b) modulate eATP under differentiative induction; (c) enhance the inhibitory activity of IκBα, reducing its phosphorylation after TNFα stimulation; and (d) preserve the chondrogenic potentialities of stem cells. Although preliminary, these results suggest that DCF001 could be a valuable supplement for ameliorating the outcome of cartilage repair interventions, enhancing the efficacy of endogenous stem cells under inflammatory stimuli.