The relationship between fibrogenic TGFβ1 signaling in the joint and cartilage degradation in post-injury osteoarthritis

Andrographolide suppresses fibrogenic phenotype of chondrocytes and ameliorates osteoarthritis by regulating miR-137/BMP7 axis

Background

Pathogenic degeneration of cartilage and the generation of fibrotic cartilage are crucial characteristics linked to the progression of osteoarthritis (OA). The current research aims to explore the potential function of the miR-137/BMP7 pathway in regulating the fibrogenic transition of chondrocytes associated with OA, as well as assess the therapeutic potential of andrographolide.

Methods

Samples of cartilage from the knees of patients with OA and individuals without OA were gathered to investigate the expression patterns of miR-137, BMP7, and markers associated with fibrosis. A cell model using primary chondrocytes stimulated with interleukin (IL)-1β was developed to study the involvement of the miR-137/BMP7 axis during the fibrogenic transition of these cells. Additionally, we utilized an animal model of OA in order to assess the beneficial effects of the anti-inflammatory natural compound andrographolide on the fibrogenesis induced by OA in vivo.

Results

Elevated levels of fibrogenic and inflammatory factors were linked to decreased miR-137 expression in OA samples. In IL-1β-treated chondrocytes, there was an upregulation of fibrogenic markers alongside a reduction in miR-137 levels. The overexpression of miR-137 inhibited fibrogenesis through the negative regulation of BMP7. Additionally, treatment with andrographolide was effective in attenuating the fibrogenic phenotype in chondrocytes and mitigating OA pathogenesis via modulating the miR-137/BMP7 pathway.

Conclusion

miR-137 downregulation and BMP7 overexpression might contribute to the fibrogenic features in OA-related chondrocytes. Andrographolide attenuates fibrogenic phenotype in chondrocytes and alleviates the severity of OA by modulating the miR-137/BMP7 axis.

Local delivery of TGF-β1-mRNA decreases fibrosis in osteochondral defects

Osteoarthritis (OA) is a condition that affects the quality of life of millions of patients worldwide. Current clinical treatments, in most cases, lead to cartilage repair with deposition of fibrocartilage tissue, which is mechanically inferior and not as durable as hyaline cartilage tissue. We designed an mRNA delivery strategy to enhance the natural healing potential of autologous bone marrow aspirate concentrate (BMAC) for articular cartilage repair. We used mineral-coated microparticles to deliver TGF-β1 mRNA to autologous BMAC. mRNA-activated BMAC was suspended in peripheral blood to generate therapeutic BMAC clots, which were then implanted in rabbit osteochondral defects. Tracking studies revealed that the clots were reliably maintained in the defects for at least 2 weeks. TGF-β1 mRNA delivery significantly increased TGF-β1 production in BMAC clots and increased early expression of articular chondrocyte markers within osteochondral defects. At 9 weeks post-surgery, the mRNA-treated defects had a superior macroscopic cartilage appearance, decreased type I collagen deposition, increased stain intensity for type II collagen and increased glycosaminoglycan deposition area when compared to the controls. Despite the transient expression of therapeutic mRNA we have detected lasting effects, such as a decrease in fibrocartilage formation demonstrated by the decrease in type I collagen deposition and the improvement in macroscopic appearance in the treatment group.

The study on bone marrow mesenchymal stem cell-derived extracellular matrix promoting the repair of damaged chondrocytes by regulating the Notch1/RBPJ pathway

Cartilage and joint damage can lead to cartilage degeneration. Bone marrow mesenchymal stem cells (BMSCs) have the potential to address cartilage damage. Hence, this study probed the mechanism of BMSC-extracellular matrix (BMSC-ECM) in promoting damaged chondrocyte repair by regulating the Notch1/RBPJ pathway. Human immortalized chondrocytes were cultured in vitro and treated with Notch1 small interfering (si)RNA, pCDNA3.1-Notch1, RBPJ siRNA and their negative controls (NCs). Damaged chondrocytes were constructed. Damaged chondrocyte-BMSC co-culture system was established and treated with lentiviral vector carrying short hairpin-Notch1 and its NC. Cell viability and apoptosis were assessed by CCK-8 and flow cytometry assays. Levels of glycosaminoglycan (GAG), Notch1 and RBPJ mRNA, and Notch1, RBPJ, Col2α1, mmp3, Hes1 and Hey1 were determined by a kit, RT-qPCR and Western blot. NICD nuclear translocation was detected by immunofluorescence. Damaged chondrocytes exhibited down-regulated Notch1 expression, reduced cell viability, and enhanced apoptosis. Further Notch1 knockdown aggravated chondrocyte damage, whereas its overexpression enhanced chondrocyte viability and decreased apoptosis. NICD translocated into the nucleus and bound to RBPJ to activate the Notch1 pathway. RBPJ silencing partly annulled Notch1-regulated damaged chondrocyte apoptosis. BMSC-damaged chondrocyte co-culture up-regulated Notch1, RBPJ, Col2α1, mmp3, Hes1, Hey1 and GAG levels, enhanced cell viability, and reduced apoptosis in chondrocytes, which were partly negated by Notch1 suppression, indicating that BMSC-ECM facilitated damaged chondrocyte repair by activating the Notch1/RBPJ pathway. BMSC-ECM promoted the repair of damaged chondrocytes by promoting NICD translocation into the nucleus and binding to RBPJ to activate the Notch1 pathway.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10616-024-00702-6.

β1-Integrin-Mediated Uptake of Chondrocyte Extracellular Vesicles Regulates Chondrocyte Homeostasis

Osteoarthritis (OA) is the most prevalent age-related degenerative disorder, which severely reduces the quality of life of those affected. Whilst management strategies exist, no cures are currently available. Virtually all joint resident cells generate extracellular vesicles (EVs), and alterations in chondrocyte EVs during OA have previously been reported. Herein, we investigated factors influencing chondrocyte EV release and the functional role that these EVs exhibit. Both 2D and 3D models of culturing C28I/2 chondrocytes were used for generating chondrocyte EVs. We assessed the effect of these EVs on chondrogenic gene expression as well as their uptake by chondrocytes. Collectively, the data demonstrated that chondrocyte EVs are sequestered within the cartilage ECM and that a bi-directional relationship exists between chondrocyte EV release and changes in chondrogenic differentiation. Finally, we demonstrated that the uptake of chondrocyte EVs is at least partially dependent on β1-integrin. These results indicate that chondrocyte EVs have an autocrine homeostatic role that maintains chondrocyte phenotype. How this role is perturbed under OA conditions remains the subject of future work.

Inhibiting Lysyl Oxidases prevents pathologic cartilage calcification

Lysyl oxidases (LOX(L)) are enzymes that catalyze the formation of cross-links in collagen and elastin fibers during physiologic calcification of bone. However, it remains unknown whether they may promote pathologic calcification of articular cartilage, an important hallmark of debilitating arthropathies. Here, we have studied the possible roles of LOX(L) in cartilage calcification, related and not related to their cross-linking activity. We first demonstrated that inhibition of LOX(L) by β-aminoproprionitrile (BAPN) significantly reduced calcification in murine and human chondrocytes, and in joint of meniscectomized mice. These BAPN's effects on calcification were accounted for by different LOX(L) roles. Firstly, reduced LOX(L)-mediated extracellular matrix cross-links downregulated Anx5, Pit1 and Pit2 calcification genes. Secondly, BAPN reduced collagen fibrotic markers Col1 and Col3. Additionally, LOX(L) inhibition blocked chondrocytes hypertrophic differentiation (Runx2 and COL10), pro-inflammatory IL-6 release and reactive oxygen species (ROS) production, all triggers of chondrocyte calcification. Through unbiased transcriptomic analysis we confirmed a positive correlation between LOX(L) genes and genes for calcification, hypertrophy and extracellular matrix catabolism. This association was conserved throughout species (mouse, human) and tissues that can undergo pathologic calcification (kidney, arteries, skin). Overall, LOX(L) play a critical role in the process of chondrocyte calcification and may be therapeutic targets to treat cartilage calcification in arthropathies.

Rotator cuff muscle degeneration in a mouse model of glenohumeral osteoarthritis induced by monoiodoacetic acid

BACKGROUND

Osteoarthritis (OA) is a disease of joint degeneration and impaired function. Muscle atrophy, fatty infiltration, and fibrosis are degenerative features of muscle injury and predict poor outcomes in some degenerative and exercise-related injuries. Patients with glenohumeral joint OA usually have rotator cuff muscle degeneration, even though the rotator cuff is intact. However, the mechanism and correlation between OA and degeneration of muscles around joints are still unknown.

METHODS

Forty-five 12-month-old C57BL/6J mice received a single injection of monoiodoacetic acid into the right glenohumeral joint. The sham group was injected with saline on the same day in the right glenohumeral joint. Three and 6 weeks after the operation, gait analysis was conducted to evaluate the function of the forelimb. Then, the shoulder joint and supraspinatus muscle were collected for histologic staining, reverse transcription quantitative polymerase chain reaction, and biomechanics test. Correlations between fat area fraction in muscle, percentage wet muscle weight change or Osteoarthritis Research Society International score, and gait analysis/muscle mechanics tests were assessed using Pearson's correlation coefficient or Spearman's correlation coefficient.

RESULTS

Compared with the sham group, the monoiodoacetic acid group developed significant glenohumeral joint OA and the supraspinatus muscle developed significant fatty infiltration and muscle atrophy. Shoulder function correlated with glenohumeral joint OA/rotator cuff muscle severity, weight loss, and fatty infiltration.

CONCLUSION

In mice, glenohumeral joint OA can lead to rotator cuff degeneration and inferior limb function. The small animal model could be a powerful tool to further study the potential mechanisms between glenohumeral OA and rotator cuff muscle degeneration.

Connexin43 in Musculoskeletal System: New Targets for Development and Disease Progression

Connexin43, which is the most highly expressed connexin subtype in the musculoskeletal system, exists in a variety of bone cells, synovial tissue, and cartilage tissue. Connexin43 has been suggested to be a key regulator of bone homeostasis. Studies have shown aberrant Connexin43 expression in musculoskeletal disorders, such as osteoporosis, osteoarthritis, and rheumatoid arthritis. During cellular activities, Connexin43 can participate in the formation of functionally specific gap junctions and hemichannels and can exert independent cellular regulatory and signaling functions through special C-termini. The critical role of Connexin43 in physiological development and disease progression has been gradually revealed. In this article, the function of Connexin43 in musculoskeletal tissues is summarized, revealing the potential role of Connexin43 as a key target in the treatment of related bone and muscle disorders and the need for further discovery.

Platelet rich plasma versus Carboxytherapy in the treatment of Periorbital dark circles: A split-face study

BACKGROUND

Periorbital hyperpigmentation is a recurrent problem in dermatologic clinics that affect the patients' quality of life and their psychological status. Platelet-rich plasma (PRP) may serve as a source of different growth factors which may reduce the pigmentation in this problem. Carboxytherapy is carbon dioxide infusion into human tissue for therapeutic purposes.

OBJECTIVE

to evaluate and compare the clinical efficacy of PRP and carboxytherapy in the treatment of periorbital dark circles (PODC). Histopathological evaluation was also done.

PATIENTS AND METHODS

Split-face study of 23 patients with PODC treated with PRP at the right side and carboxytherapy at the left side. Patients received four sessions; one session/week. Final follow-up evaluation was done 3 months after the last session by clinical and histopathological assessment.

RESULTS

PRP showed significant better response (p=0.002), shorter downtime and tolerable side effects than caboxytherapy. Reduction in area percent of melanin after PRP injections showed 46.6% improvement, while after carboxytherapy, it showed only 14.3% improvement.

CONCLUSION

The present study had showed that PRP is more effective and tolerable than caboxytherapy in the treatment of PODC.

Platelet-Rich Plasma Does Not Inhibit Inflammation or Promote Regeneration in Human Osteoarthritic Chondrocytes In Vitro Despite Increased Proliferation

OBJECTIVE

The aims of the study were to assess the anti-inflammatory properties of platelet-rich plasma (PRP) and investigate its regenerative potential in osteoarthritic (OA) human chondrocytes. We hypothesized that PRP can modulate the inflammatory response and stimulate cartilage regeneration.

DESIGN

Primary human chondrocytes from OA knees were treated with manually prepared PRP, after which cell migration and proliferation were assessed. Next, tumor necrosis factor-α-stimulated chondrocytes were treated with a range of concentrations of PRP. Expression of genes involved in inflammation and chondrogenesis was determined by real-time polymerase chain reaction. In addition, chondrocytes were cultured in PRP gels and fibrin gels consisting of increasing concentrations of PRP. The production of cartilage extracellular matrix (ECM) was assessed. Deposition and release of glycosaminoglycans (GAG) and collagen was quantitatively determined and visualized by (immuno)histochemistry. Proliferation was assessed by quantitative measurement of DNA.

RESULTS

Both migration and the inflammatory response were altered by PRP, while proliferation was stimulated. Expression of chondrogenic markers COL2A1 and ACAN was downregulated by PRP, independent of PRP concentration. Chondrocytes cultured in PRP gel for 28 days proliferated significantly more when compared with chondrocytes cultured in fibrin gels. This effect was dose dependent. Significantly less GAGs and collagen were produced by chondrocytes cultured in PRP gels when compared with fibrin gels. This was qualitatively confirmed by histology.

CONCLUSIONS

PRP stimulated chondrocyte proliferation, but not migration. Also, production of cartilage ECM was strongly downregulated by PRP. Furthermore, PRP did not act anti-inflammatory on chondrocytes in an in vitro inflammation model.

BMP-4, TGF-β e Smad3 como moduladores da viabilidade das células do líquido sinovial

Objective  Our goal was to evaluate the modulation of the synovial fluid cells (SFC) from patients with and without osteoarthritis (OA) by bone morphogenetic protein 4 (BMP-4), Smad-3 and transforming growth factor beta (TGF-β).

Methods  Synovial fluid was collected from patients submitted to knee arthroscopy or replacement and were centrifuged to isolate cells from the fluid. Cells were cultured for 21 days and characterized as mesenchymal stem cells (MSCs) according to the criteria of the International Society of Cell Therapy. Then, we performed an [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay (MTT) assay after exposing cells with and without OA to TGF-β, Smad3 and BMP-4 pathway inhibitors and to different concentrations of BMP4.

Results  Exposure to the TGF-β, Smad3 and BMP-4 inhibitors modifies the mitochondrial activity of the SFCs. The activity of the SFCs is modified by influences of increasing concentrations of BMP4, but there is no difference in cellular activity between patients with and without OA.

Conclusion  TGF-β, Smad3 and BMP-4 modulate the activity of SFCs from patients with and without knee OA.

Articular Chondrocyte Phenotype Regulation through the Cytoskeleton and the Signaling Processes That Originate from or Converge on the Cytoskeleton: Towards a Novel Understanding of the Intersection between Actin Dynamics and Chondrogenic Function

Numerous studies have assembled a complex picture, in which extracellular stimuli and intracellular signaling pathways modulate the chondrocyte phenotype. Because many diseases are mechanobiology-related, this review asked to what extent phenotype regulators control chondrocyte function through the cytoskeleton and cytoskeleton-regulating signaling processes. Such information would generate leverage for advanced articular cartilage repair. Serial passaging, pro-inflammatory cytokine signaling (TNF-α, IL-1α, IL-1β, IL-6, and IL-8), growth factors (TGF-α), and osteoarthritis not only induce dedifferentiation but also converge on RhoA/ROCK/Rac1/mDia1/mDia2/Cdc42 to promote actin polymerization/crosslinking for stress fiber (SF) formation. SF formation takes center stage in phenotype control, as both SF formation and SOX9 phosphorylation for COL2 expression are ROCK activity-dependent. Explaining how it is molecularly possible that dedifferentiation induces low COL2 expression but high SF formation, this review theorized that, in chondrocyte SOX9, phosphorylation by ROCK might effectively be sidelined in favor of other SF-promoting ROCK substrates, based on a differential ROCK affinity. In turn, actin depolymerization for redifferentiation would “free-up” ROCK to increase COL2 expression. Moreover, the actin cytoskeleton regulates COL1 expression, modulates COL2/aggrecan fragment generation, and mediates a fibrogenic/catabolic expression profile, highlighting that actin dynamics-regulating processes decisively control the chondrocyte phenotype. This suggests modulating the balance between actin polymerization/depolymerization for therapeutically controlling the chondrocyte phenotype.

A SMOC2 variant inhibits BMP signaling by competitively binding to BMPR1B and causes growth plate defects

Endochondral ossification is the major process of long bone formation, and chondrogenesis is the final step of this process. Several studies have indicated that bone morphogenetic proteins (BMPs) are required for chondrogenesis and regulate multiple growth plate features. Abnormal BMP pathways lead to growth plate defects, resulting in osteochondrodysplasia. The SPARC-related modular calcium binding 2 (SMOC2) gene encodes an extracellular protein that is considered to be an antagonist of BMP signaling. In this study, we generated a mouse model by knocking-in the SMOC2 mutation (c.1076 T > G), which showed short-limbed dwarfism, reduced, disorganized, and hypocellular proliferative zones and expanded hypertrophic zones in tibial growth plates. To determine the underlying pathophysiological mechanism of SMOC2 mutation, we used knock-in mice to investigate the interaction between SMOC2 and the BMP-SMAD1/5/9 signaling pathway in vivo and in vitro. Eventually, we found that mutant SMOC2 could not bind to COL9A1 and HSPG. Furthermore, mutant SMOC2 inhibited BMP signaling by competitively binding to BMPR1B, which lead to defects in growth plates and short-limbed dwarfism in knock-in mice.

Mechanotransduction and Stiffness-Sensing: Mechanisms and Opportunities to Control Multiple Molecular Aspects of Cell Phenotype as a Design Cornerstone of Cell-Instructive Biomaterials for Articular Cartilage Repair

Since material stiffness controls many cell functions, we reviewed the currently available knowledge on stiffness sensing and elucidated what is known in the context of clinical and experimental articular cartilage (AC) repair. Remarkably, no stiffness information on the various biomaterials for clinical AC repair was accessible. Using mRNA expression profiles and morphology as surrogate markers of stiffness-related effects, we deduced that the various clinically available biomaterials control chondrocyte (CH) phenotype well, but not to equal extents, and only in non-degenerative settings. Ample evidence demonstrates that multiple molecular aspects of CH and mesenchymal stromal cell (MSC) phenotype are susceptible to material stiffness, because proliferation, migration, lineage determination, shape, cytoskeletal properties, expression profiles, cell surface receptor composition, integrin subunit expression, and nuclear shape and composition of CHs and/or MSCs are stiffness-regulated. Moreover, material stiffness modulates MSC immuno-modulatory and angiogenic properties, transforming growth factor beta 1 (TGF-β1)-induced lineage determination, and CH re-differentiation/de-differentiation, collagen type II fragment production, and TGF-β1- and interleukin 1 beta (IL-1β)-induced changes in cell stiffness and traction force. We then integrated the available molecular signaling data into a stiffness-regulated CH phenotype model. Overall, we recommend using material stiffness for controlling cell phenotype, as this would be a promising design cornerstone for novel future-oriented, cell-instructive biomaterials for clinical high-quality AC repair tissue.

Notch Signaling in Skeletal Development, Homeostasis and Pathogenesis

Skeletal development is a complex process which requires the tight regulation of gene activation and suppression in response to local signaling pathways. Among these pathways, Notch signaling is implicated in governing cell fate determination, proliferation, differentiation and apoptosis of skeletal cells-osteoblasts, osteoclasts, osteocytes and chondrocytes. Moreover, human genetic mutations in Notch components emphasize the critical roles of Notch signaling in skeletal development and homeostasis. In this review, we focus on the physiological roles of Notch signaling in skeletogenesis, postnatal bone and cartilage homeostasis and fracture repair. We also discuss the pathological gain- and loss-of-function of Notch signaling in bone and cartilage, resulting in osteosarcoma and age-related degenerative diseases, such as osteoporosis and osteoarthritis. Understanding the physiological and pathological function of Notch signaling in skeletal tissues using animal models and human genetics will provide new insights into disease pathogenesis and offer novel approaches for the treatment of bone/cartilage diseases.

Two-photon fluorescence and second harmonic generation characterization of extracellular matrix remodeling in post-injury murine temporomandibular joint osteoarthritis

End stage temporomandibular joint osteoarthritis (TMJ-OA) is characterized by fibrillations, fissures, clefts, and erosion of the mandibular condylar cartilage. The goal of this study was to define changes in pericellular and interterritorial delineations of the extracellular matrix (ECM) that occur preceding and concurrent with the development of this end stage degeneration in a murine surgical instability model. Two-photon fluorescence (TPF) and second harmonic generation (SHG) microscopy was used to evaluate TMJ-OA mediated changes in the ECM. We illustrate that TPF/SHG microscopy reconstructs the three-dimensional network of key fibrillar and micro-fibrillar collagens altered during the progression of TMJ-OA. This method not only generates spatially distinct pericellular and interterritorial delineations of the ECM but distinguishes early and end stage TMJ-OA by signal organization, orientation, and composition. Early stage TMJ-OA at 4- and 8-weeks post-injury is characterized by two structurally distinct regions containing dense, large fiber collagens and superficial, small fiber collagens rich in types I, III, and VI collagen oriented along the mesiodistal axis of the condyle. At 8-weeks post-injury, type VI collagen is locally diminished on the central and medial condyle, but the type I/III rich superficial layer is still present. Twelve- and 16-weeks post-injury mandibular cartilage is characteristic of end-stage disease, with hypocellularity and fibrillations, fissures, and clefts in the articular layer that propagate along the mediolateral axis of the MCC. We hypothesize that the localized depletion of interterritorial and pericellular type VI collagen may signify an early marker for the transition from early to end stage TMJ-OA, influence the injury response of the tissue, and underlie patterns of degeneration that follow attritional modes of failure.

Osteoarthritic Synovial Fluid Modulates Cell Phenotype and Metabolic Behavior In Vitro

Synovial fluid holds a population of mesenchymal stem cells (MSC) that could be used for clinical treatment. Our goal was to characterize the inflammatory and metabolomic profile of the synovial fluid from osteoarthritic patients and to identify its modulatory effect on synovial fluid cells. Synovial fluid was collected from non-OA and OA patients, which was centrifuged to isolate cells. Cells were cultured for 21 days, characterized with specific markers for MSC, and exposed to a specific cocktail to induce chondrogenic, osteogenic, and adipogenic differentiation. Then, we performed a MTT assay exposing SF cells from non-OA and OA patients to a medium containing non-OA and OA synovial fluid. Synovial fluid from non-OA and OA patients was submitted to ELISA to evaluate BMP-2, BMP-4, IL-6, IL-10, TNF-α, and TGF-β1 concentrations and to a metabolomic evaluation using 1H-NMR. Synovial fluid cells presented spindle-shaped morphology in vitro. Samples from OA patients formed a higher number of colonies than the ones from non-OA patients. After 21 days, the colony-forming cells from OA patients differentiated into the three mesenchymal cell lineages, under the appropriated induction protocols. Synovial fluid cells increased its metabolic activity after being exposed to the OA synovial fluid. ELISA assay showed that OA synovial fluid samples presented higher concentration of IL-10 and TGF-β1 than the non-OA, while the NMR showed that OA synovial fluid presents higher concentrations of glucose and glycerol. In conclusion, SFC activity is modulated by OA synovial fluid, which presents higher concentration of IL-10, TGF-β, glycerol, and glucose.

Cartilage regeneration and ageing: Targeting cellular plasticity in osteoarthritis

Ageing processes play a major contributing role for the development of Osteoarthritis (OA). This prototypic degenerative condition of ageing is the most common form of arthritis and is accompanied by a general decline, chronic pain and mobility deficits. The disease is primarily characterized by articular cartilage degradation, followed by subchondral bone thickening, osteophyte formation, synovial inflammation and joint degeneration. In the early stages, osteoarthritic chondrocytes undergo phenotypic changes that increase cell proliferation and cluster formation and enhance the production of matrix-remodelling enzymes. In fact, chondrocytes exhibit differentiation plasticity and undergo phenotypic changes during the healing process. Current studies are focusing on unravelling whether OA is a consequence of an abnormal wound healing response. Recent investigations suggest that alterations in different proteins, such as TGF-ß/BMPs, NF-Kß, Wnt, and Cx43, or SASP factors involved in signalling pathways in wound healing response, could be directly implicated in the initiation of OA. Several findings suggest that osteoarthritic chondrocytes remain in an immature state expressing stemness-associated cell surface markers. In fact, the efficacy of new disease-modifying OA drugs that promote chondrogenic differentiation in animal models indicates that this may be a drug-sensible state. In this review, we highlight the current knowledge regarding cellular plasticity in chondrocytes and OA. A better comprehension of the mechanisms involved in these processes may enable us to understand the molecular pathways that promote abnormal repair and cartilage degradation in OA. This understanding would be advantageous in identifying novel targets and designing therapies to promote effective cartilage repair and successful joint ageing by preventing functional limitations and disability.

The clustering and morphology of chondrocytes in normal and mildly degenerate human femoral head cartilage studied by confocal laser scanning microscopy

Chondrocytes are the major cell type present in hyaline cartilage and they play a crucial role in maintaining the mechanical resilience of the tissue through a balance of the synthesis and breakdown of extracellular matrix macromolecules. Histological assessment of cartilage suggests that articular chondrocytes in situ typically occur singly and demonstrate a rounded/elliptical morphology. However, there are suggestions that their grouping and fine shape is more complex and that these change with cartilage degeneration as occurs in osteoarthritis. In the present study we have used confocal laser scanning microscopy and fluorescently labelled in situ human chondrocytes and advanced imaging software to visualise chondrocyte clustering and detailed morphology within grade-0 (non-degenerate) and grade-1 (mildly degenerate) cartilage from human femoral heads. Graded human cartilage explants were incubated with 5-chloromethylfluorescein diacetate and propidium iodide to identify the morphology and viability, respectively, of in situ chondrocytes within superficial, mid- and deep zones. In grade-0 cartilage, the analysis of confocal microscope images showed that although the majority of chondrocytes were single and morphologically normal, clusters (i.e. three or more chondrocytes within the enclosed lacunar space) were occasionally observed in the superficial zone, and 15-25% of the cell population exhibited at least one cytoplasmic process of ~ 5 μm in length. With degeneration, cluster number increased (~ 50%) but not significantly; however, the number of cells/cluster (P < 0.001) and the percentage of cells forming clusters increased (P = 0.0013). In the superficial zone but not the mid- or deep zones, the volume of clusters and average volume of chondrocytes in clusters increased (P < 0.001 and P < 0.05, respectively). The percentage of chondrocytes with processes, the number of processes/cell and the length of processes/cell increased in the superficial zone of grade-1 cartilage (P = 0.0098, P = 0.02 and P < 0.001, respectively). Processes were categorised based on length (L0 - no cytoplasmic processes; L1 < 5 μm; 5 < L2 ≤ 10 μm; 10 < L3 ≤ 15 μm; L4 > 15 μm). With cartilage degeneration, for chondrocytes in all zones, there was a significant decrease (P = 0.015) in the percentage of chondrocytes with 'normal' morphology (i.e. L0), with no change in the percentage of cells with L1 processes; however, there were significant increases in the other categories. In grade-0 cartilage, chondrocyte clustering and morphological abnormalities occurred and with degeneration these were exacerbated, particularly in the superficial zone. Chondrocyte clustering and abnormal morphology are associated with aberrant matrix metabolism, suggesting that these early changes to chondrocyte properties may be associated with cartilage degeneration.

TGF‑β1 expression in adults with non‑traumatic osteonecrosis of the femoral head

Non-traumatic osteonecrosis of the femoral head (NONFH) is a common clinical osteoarthropathy. The present study aimed to investigate the association between transforming growth factor β1 (TGF‑β1) and NONFH. Femoral head specimens were collected from patients with NONFH. Patients with traumatic osteonecrosis served as the control. Hematoxylin and eosin (H&E) staining was used to visualize the bone tissue architecture. Immunohistochemistry and densitometry were performed to quantify TGF‑β1 expression in tissues. Flow cytometry was used to detect cluster of differentiation (CD)3+, CD4+ and CD8+ cells, and the ratio of CD4+ to CD8+ T cells in the peripheral blood. H&E staining revealed osteonecrosis, disintegration of osteocytes with karyopyknosis and karyorrhexis, loss of osteocyte lacunae, aberrantly arranged circumferential lamellae, as well as dissolution of the lamellae and subtle osteogenesis in the experimental group, as opposed to the control group. Immunohistochemistry revealed that the expression of TGF‑β1 was significantly reduced in the experimental group (P<0.01). Further, the NONFH group had a decrease in the CD3+ and CD4+ cell populations (P<0.05 and P<0.01, respectively), an increase in the CD8+ cell population (P<0.05), as well as a reduction in the ratio of CD4+ to CD8+ cells (P<0.01). The present study indicated that TGF‑β1 expression was reduced in NONFH. This was associated with impaired repairing capacity of the femoral head and dysregulated subsets of T‑lymphocytes and possible immune functions.

Trauma and Stem Cells: Biology and Potential Therapeutic Implications

Trauma may cause irreversible tissue damage and loss of function despite current best practice. Healing is dependent both on the nature of the injury and the intrinsic biological capacity of those tissues for healing. Preclinical research has highlighted stem cell therapy as a potential avenue for improving outcomes for injuries with poor healing capacity. Additionally, trauma activates the immune system and alters stem cell behaviour. This paper reviews the current literature on stem cells and its relevance to trauma care. Emphasis is placed on understanding how stem cells respond to trauma and pertinent mechanisms that can be utilised to promote tissue healing. Research involving notable difficulties in trauma care such as fracture non-union, cartilage damage and trauma induced inflammation is discussed further.

Effect of adenovirus-mediated TGF-β1 gene transfer on the function of rabbit articular chondrocytes

BACKGROUND

Articular chondrocytes are important in maintaining normal cartilage tissue and preventing articular degeneration. Exogenous genes have previously been transduced into articular cells using adenoviral vectors to contribute to the maintenance of cell function. This study aimed to transfer the transforming growth factor-β1 gene (TGF-β1) into rabbit articular chondrocytes by adenovirus infection to elucidate its effects on cell function.

METHODS

Rabbit chondrocytes were isolated and cultured both as monolayers and three-dimensional culture systems. To achieve overexpression, TGF-β1 was transfected by adenovirus infection, using the LacZ gene as a control. TGF-β1 protein expression was analyzed by western blotting. Quantitative DNA fluorometric analysis evaluated cell proliferation, and quantitative reverse transcriptase PCR determined the mRNA expression of related chondrocyte marker genes. Western blotting and glycosaminoglycan quantitative testing were used to examine changes in extracellular matrix components.

RESULTS

TGF-β1 protein expression was found to increase in Adv-TGF-β1-transduced cells, reaching a maximum after chondrocytes had been cultured for 4 weeks. Adv-hTGF-β1 transduction altered chondrocyte morphology from fibrocyte-like long spindle-shaped to round or oval. TGF-β1-transduced cells showed an increase in DNA synthesis, glycosaminoglycan content, and increased aggrecan and collagen II protein expression, while collagen I was significantly decreased. Moreover, TGF-β1 overexpression significantly promoted the mRNA expression of the chondrogenic gene SOX9, and inhibited that of the hypertrophic marker COL10A1 and the mineralization marker MMP-13.

CONCLUSIONS

TGF-β1 overexpression positively improved the phenotype, function, and proliferation of chondrocytes, even after several generations.

Mesenchymal Stem Cells and Their Clinical Applications in Osteoarthritis

Osteoarthritis is a chronic degenerative joint disorder characterized by articular cartilage destruction and osteophyte formation. Chondrocytes in the matrix have a relatively slow turnover rate, and the tissue itself lacks a blood supply to support repair and remodeling. Researchers have evaluated the effectiveness of stem cell therapy and tissue engineering for treating osteoarthritis. All sources of stem cells, including embryonic, induced pluripotent, fetal, and adult stem cells, have potential use in stem cell therapy, which provides a permanent biological solution. Mesenchymal stem cells (MSCs) isolated from bone marrow, adipose tissue, and umbilical cord show considerable promise for use in cartilage repair. MSCs can be sourced from any or all joint tissues and can modulate the immune response. Additionally, MSCs can directly differentiate into chondrocytes under appropriate signal transduction. They also have immunosuppressive and anti-inflammatory paracrine effects. This article reviews the current clinical applications of MSCs and future directions of research in osteoarthritis.

Human genome-wide expression analysis reorients the study of inflammatory mediators and biomechanics in osteoarthritis

A major objective of this article is to examine the research implications of recently available genome-wide expression profiles of cartilage from human osteoarthritis (OA) joints. We propose that, when viewed in the light of extensive earlier work, this novel data provides a unique opportunity to reorient the design of experimental systems toward clinical relevance. Specifically, in the area of cartilage explant biology, this will require a fresh evaluation of existing paradigms, so as to optimize the choices of tissue source, cytokine/growth factor/nutrient addition, and biomechanical environment for discovery. Within this context, we firstly discuss the literature on the nature and role of potential catabolic mediators in OA pathology, including data from human OA cartilage, animal models of OA, and ex vivo studies. Secondly, due to the number and breadth of studies on IL-1β in this area, a major focus of the article is a critical analysis of the design and interpretation of cartilage studies where IL-1β has been used as a model cytokine. Thirdly, the article provides a data-driven perspective (including genome-wide analysis of clinical samples, studies on mutant mice, and clinical trials), which concludes that IL-1β should be replaced by soluble mediators such as IL-17 or TGF-β1, which are much more likely to mimic the disease in OA model systems. We also discuss the evidence that changes in early OA can be attributed to the activity of such soluble mediators, whereas late-stage disease results more from a chronic biomechanical effect on the matrix and cells of the remaining cartilage and on other local mediator-secreting cells. Lastly, an updated protocol for in vitro studies with cartilage explants and chondrocytes (including the use of specific gene expression arrays) is provided to motivate more disease-relevant studies on the interplay of cytokines, growth factors, and biomechanics on cellular behavior.

Intraarticular Matrix Metalloproteinases and Aggrecan Degradation Are Elevated After Articular Fracture

BACKGROUND

Posttraumatic osteoarthritis (OA) is a variant of OA that can develop after articular injury. Although the mechanism(s) of posttraumatic OA are uncertain, the presence and impact of postinjury proteolytic enzymes on articular cartilage remain unknown. To our knowledge, there are no studies that evaluate the presence of matrix metalloproteinases (MMPs) or aggrecan degradation after articular fracture.

QUESTIONS/PURPOSES

(1) Are MMP concentrations and aggrecan degradation elevated after intraarticular fracture? (2) Are MMP concentrations and aggrecan degradation greater in high-energy injuries compared with low-energy injuries? (3) Do the concentrations of these biomarkers remain elevated at a secondary aspiration?

METHODS

Between December 2011 and June 2013, we prospectively enrolled patients older than 18 years of age with acute tibial plateau fracture. Exclusion criteria included age older than 60 years, preexisting knee OA, injury greater than 24 hours before evaluation, contralateral knee injury, history of autoimmune disease, open fracture, and non-English-speaking patients. During the enrollment period, we enrolled 45 of the 91 (49%) tibial plateau fractures treated at our facility. Knee synovial fluid aspirations were obtained from both the injured and uninjured knees; two patients received aspirations in the emergency department and the remaining patients received aspirations in the operating room. Twenty patients who underwent spanning external fixator followed by definitive fixation were aspirated during both surgical procedures. MMP-1, -2, -3, -7, -9, -10, -12, and -13 concentrations were quantified using multiplex assays. Aggrecan degradation was quantified using sandwich enzyme-linked immunosorbent assay.

RESULTS

There were higher concentrations of MMP-1 (3.89 ng/mL [95% confidence interval {CI}, 2.37-6.37] versus 0.37 ng/mL [95% CI, 0.23-0.61], p < 0.001), MMP-3 (457.35 ng/mL [95% CI, 274.5-762.01] versus 129.17 ng/mL [95% CI, 77.01-216.66], p < 0.001), MMP-9 (6.52 ng/mL [95% CI, 3.86-11.03] versus 0.96 ng/mL [95% CI, 0.56-1.64], p < 0.001), MMP-10 (0.52 ng/mL [95% CI, 0.40-0.69] versus 0.23 ng/mL [95% CI, 0.17-0.30], p < 0.001), and MMP-12 (0.18 ng/mL [95% CI, 0.14-0.23] versus 0.10 ng/mL [95% CI, 0.0.081-0.14], p = 0.005) in injured knees compared with uninjured knees. There was not a detectable difference in MMP concentrations or aggrecan degradation between high- and low-energy injuries. MMP-1 (53.25 versus 3.89 ng/mL, p < 0.001), MMP-2 (76.04 versus 0.37 ng/mL, p < 0.001), MMP-3 (1250.62 versus 457.35 ng/mL, p = 0.002), MMP-12 (1.37 versus 0.18, p < 0.001), MMP-13 (0.98 versus 0.032 ng/mL, p < 0.001), and aggrecan degradation (0.58 versus 0.053, p < 0.001) were increased at the second procedure (mean, 9.5 days; range, 3-21 days) as compared with the initial procedure.

CONCLUSIONS

Because MMPs and aggrecan degradation are elevated after articular fracture, future studies are necessary to evaluate the impact of elevated MMPs and aggrecan degradation on human articular cartilage.

CLINICAL RELEVANCE

If further clinical followup can demonstrate a relationship between posttraumatic OA and elevated MMPs and aggrecan degradation, they may provide potential for therapeutic targets to prevent or delay the destruction of the joint. Additionally, these markers may offer prognostic information for patients.

CCN1 (Cyr61) Is Overexpressed in Human Osteoarthritic Cartilage and Inhibits ADAMTS-4 (Aggrecanase 1) Activity

OBJECTIVE

ADAMTS-4, also called aggrecanase 1, is considered to play a key role in aggrecan degradation in human osteoarthritic (OA) cartilage, but information about regulators of ADAMTS-4 aggrecanase activity remains limited. We undertook this study to search for molecules that modulate ADAMTS-4 activity.

METHODS

Molecules copurified with ADAMTS-4 from ADAMTS-4-transfected chondrocytic cells were sequenced by nanoscale liquid chromatography tandem mass spectrometry. Binding activity was determined by immunoprecipitation and solid-phase binding assay. Effects on ADAMTS-4 activity were examined by aggrecan digestion assay. Expression of the binding molecule in OA cartilage and chondrocytes was examined by immunohistochemistry and reverse transcription-polymerase chain reaction.

RESULTS

We identified CCN1 (Cyr61) as an ADAMTS-4-binding protein and showed specific binding to the ADAMTS-4 cysteine-rich domain. Aggrecanase activity of ADAMTS-4 was inhibited by interaction with CCN1. Expression of messenger RNA for CCN1 was significantly higher in human OA cartilage than in normal cartilage. CCN1 was immunolocalized to chondrocytes in OA cartilage, showing direct correlations of immunoreactivity with the Mankin score of cartilage lesions and chondrocyte cloning. CCN1 and ADAMTS-4 were commonly coexpressed in clustered chondrocytes. CCN1 expression in OA chondrocytes was down-regulated by interleukin-1α (IL-1α) and up-regulated by transforming growth factor β (TGFβ). ADAMTS-4 expression was induced by treatment with IL-1α or TGFβ, but aggrecanase activity was detected only under stimulation with IL-1α. TGFβ-treated chondrocytes exhibited aggrecanase activity when CCN1 expression was knocked down.

CONCLUSION

Our findings provide the first evidence that CCN1 suppresses ADAMTS-4 activity and that CCN1 overexpression is directly correlated with chondrocyte cloning in OA cartilage. Our results suggest that the TGFβ/CCN1 axis plays a role in chondrocyte cluster formation through inhibition of ADAMTS-4.

Unravelling osteoarthritis-related synovial fibrosis: a step closer to solving joint stiffness

Synovial fibrosis is often found in OA, contributing heavily to joint pain and joint stiffness, the main symptoms of OA. At this moment the underlying mechanism of OA-related synovial fibrosis is not known and there is no cure available. In this review we discuss factors that have been reported to be involved in synovial fibrosis. The aim of the study was to gain insight into how these factors contribute to the fibrotic process and to determine the best targets for therapy in synovial fibrosis. In this regard, the following factors are discussed: TGF-β, connective tissue growth factor, procollagen-lysine, 2-oxoglutarate 5-dioxygenase 2, tissue inhibitor of metalloproteinase 1, A disintegrin and metalloproteinase domain 12, urotensin-II, prostaglandin F2α and hyaluronan.

TGFβ signaling in cartilage development and maintenance

Members of the transforming growth factor beta (TGFβ) superfamily of secreted factors play essential roles in nearly every aspect of cartilage formation and maintenance. However, the mechanisms by which TGFβs transduce their effects in cartilage in vivo remain poorly understood. Mutations in several TGFβ family members, their receptors, extracellular modulators, and intracellular transducers have been described, and these usually impact the development of the cartilaginous skeleton. Furthermore, genome-wide association studies have linked components of the (TGFβ) superfamily to susceptibility to osteoarthritis. This review focuses on recent discoveries from genetic studies in the mouse regarding the regulation of TGFβ signaling in developing growth plate and articular cartilage, as well as the different modes of crosstalk between canonical and noncanonical TGFβ signaling. These new insights into TGFβ signaling in cartilage may open new prospects for therapies that maintain healthy articular cartilage.

Therapeutic effects of intra-articular ultra-purified low endotoxin alginate administration on an experimental canine osteoarthritis model

OBJECTIVE

This study aimed to elucidate the therapeutic effects of intra-articular administration of ultra-purified low endotoxin alginate (UPLE-alginate) on osteoarthritis (OA) using a canine anterior cruciate ligament transection (ACLT) model.

DESIGN

We used 20 beagle dogs. ACLT was performed on the left knee of each dog and a sham operation was performed on the right knee as a control. All animals were randomly divided into the control (saline) and therapeutic (UPLE-alginate) groups. Animals in the control and therapeutic groups received weekly injections with 0.7 mL normal saline or 0.7 mL 0.5% UPLE-alginate, respectively, from 0 to 3 weeks after ACLT or sham operation. At 9 weeks after ACLT, the knee joints of all animals were observed using arthroscopy. All animals were euthanized at 14 weeks after ACLT and evaluated using morphologic assessment, histologic assessment, and biomechanical testing.

RESULTS

Arthroscopic findings showed intact cartilage surface in both groups. Morphologic findings in the therapeutic group showed milder degeneration compared with those of the control group, but there were no significant differences between groups. Histologic scores of the medial femoral condyle (MFC) and lateral femoral condyle (LFC) were better in the therapeutic group than the control group (MFC: p = 0.009, LFC: p = 0.009). Joint lubrication did not differ significantly between groups.

CONCLUSION

Intra-articular administration of UPLE-alginate in the early stage of OA slowed disease progression in canines. UPLE-alginate may have potential as a therapeutic agent for OA patients and reduce the number of patients who need to undergo total joint arthroplasty.

The potential utility of high-intensity ultrasound to treat osteoarthritis

Osteoarthritis (OA) is a widespread musculoskeletal disease that reduces quality of life and for which there is no cure. The treatment of OA is challenging since cartilage impedes the local and systemic delivery of therapeutic compounds (TCs). This review identifies high-intensity ultrasound (HIU) as a non-contact technique to modify articular cartilage and subchondral bone. HIU enables new approaches to overcome challenges associated with drug delivery to cartilage and new non-invasive approaches for the treatment of joint disease. Specifically, HIU has the potential to facilitate targeted drug delivery and release deep within cartilage, to repair soft tissue damage, and to physically alter tissue structures including cartilage and bone. The localized, non-invasive ultrasonic delivery of TCs to articular cartilage and subchondral bone appears to be a promising technique in the immediate future.

Signaling pathways in cartilage repair

In adult healthy cartilage, chondrocytes are in a quiescent phase characterized by a fine balance between anabolic and catabolic activities. In ageing, degenerative joint diseases and traumatic injuries of cartilage, a loss of homeostatic conditions and an up-regulation of catabolic pathways occur. Since cartilage differentiation and maintenance of homeostasis are finely tuned by a complex network of signaling molecules and biophysical factors, shedding light on these mechanisms appears to be extremely relevant for both the identification of pathogenic key factors, as specific therapeutic targets, and the development of biological approaches for cartilage regeneration. This review will focus on the main signaling pathways that can activate cellular and molecular processes, regulating the functional behavior of cartilage in both physiological and pathological conditions. These networks may be relevant in the crosstalk among joint compartments and increased knowledge in this field may lead to the development of more effective strategies for inducing cartilage repair.

Notch signaling in skeletal stem cells

The skeleton originates from stem cells residing in the sclerotome and neural crest that undergo proliferation, migration, and commitment. The development of the skeletal stem cells is influenced by many signaling pathways that govern cell fate determination, proliferation, differentiation, and apoptosis. This review will focus on Notch signaling functions in regulating the different cell types that form the skeletal system as well as the interplay between them to maintain homeostasis. Osteochondroprogenitors require Notch signaling to maintain multipotency and to prevent premature differentiation into osteoblasts. Subsequently, overactivation of Notch signaling suppresses osteoblast maturation. Moreover, Notch signaling in osteochondroprogenitors is required for chondrocyte proliferation and hypertrophy and suppresses terminal differentiation. Translational studies demonstrated a crucial role of Notch signaling in osteosarcoma and osteoarthritis, where concepts derived from developmental pathways are often recapitulated. This brings hope of taking advantage of the molecular mechanisms learned from development to approach the pathological processes underlying abnormal bone/cartilage metabolism or tumorigenesis. Pharmacological agents that target Notch receptors or ligands in a tissue-specific fashion would offer new opportunities for treating bone/cartilage diseases caused by dysregulation of Notch signaling.

ADAMTS5 is required for biomechanically-stimulated healing of murine tendinopathy

A recently developed murine model of tendinopathy, induced by TGF-β1 injection, has been used to examine the reparative capacity of tendinopathic Achilles in Adamts5(-/-) mice. After TGF-β1 injection and 2 weeks of treadmill exercise, the Achilles from Adamts5(-/-) mice exhibited a reduction in maximum tensile stress of approximately 60%. However, in contrast to wild type mice previously characterized by this model, Adamts5(-/-) mice subjected to further treadmill exercise were unable to reverse this biomechanical deficit. This nonreparative phenotype was accompanied by a major deficiency, relative to wild-type, in expression of Col1a1 and Col3a1 and an abnormally elevated expression of a wide range of integrins. In addition, the tendinopathic Adamts5(-/-) mice showed a persistent accumulation of chondrogenic cells in the tendon body and an aggrecan-rich fibrocartilaginous matrix within disorganized collagen fiber bundles. Moreover, consistent with the compromised biomechanical properties of the Achilles in the Adamts5(-/-) mice, in vivo gait analysis revealed a strong trend (p = 0.07) towards increased swing time of the injected limb in Adamts5(-/-) relative to wild-type mice. These findings demonstrate that a deficiency in ADAMTS5 promotes a chondrogenic response to TGF-β1 injection that is not reversed by treadmill exercise. Hence, repair of biomechanically compromised tendons exhibiting midsubstance chondroid accumulation requires ADAMTS5.

Mesenchymal stem cells in joint disease and repair

Osteoarthritis (OA), a prevalent chronic condition with a striking impact on quality of life, represents an enormous societal burden that increases greatly as populations age. Yet no approved pharmacological intervention, biologic therapy or procedure prevents the progressive destruction of the OA joint. Mesenchymal stem cells (MSCs)-multipotent precursors of connective tissue cells that can be isolated from many adult tissues, including those of the diarthrodial joint-have emerged as a potential therapy. Endogenous MSCs contribute to maintenance of healthy tissues by acting as reservoirs of repair cells or as immunomodulatory sentinels to reduce inflammation. The onset of degenerative changes in the joint is associated with aberrant activity or depletion of these cell reservoirs, leading to loss of chondrogenic potential and preponderance of a fibrogenic phenotype. Local delivery of ex vivo cultures of MSCs has produced promising outcomes in preclinical models of joint disease. Mechanistically, paracrine signalling by MSCs might be more important than differentiation in stimulating repair responses; thus, paracrine factors must be assessed as measures of MSC therapeutic potency, to replace traditional assays based on cell-surface markers and differentiation. Several early-stage clinical trials, initiated or underway in 2013, are testing the delivery of MSCs as an intra-articular injection into the knee, but optimal dose and vehicle are yet to be established.

Adult cartilage-specific peroxisome proliferator-activated receptor gamma knockout mice exhibit the spontaneous osteoarthritis phenotype

Osteoarthritis (OA) is an age-related progressive degenerative joint disease. Peroxisome proliferator-activated receptor gamma (PPARγ), a transcription factor, is suggested as an attractive therapeutic target to counteract degradative mechanisms associated with OA. Studies suggest that activation of PPARγ by its agonists can reduce the synthesis of OA catabolic and inflammatory factors and the development of cartilage lesions in OA animal models. Because these agonists impart several PPARγ-independent effects, the specific in vivo function of PPARγ in cartilage homeostasis and OA remains largely unknown. Herein, we describe the in vivo role of PPARγ in OA using cartilage-specific PPARγ knockout (KO) mice generated using the Cre-lox system. Adult PPARγ KO mice exhibited a spontaneous OA phenotype associated with enhanced cartilage degradation, hypocellularity, synovial and cartilage fibrosis, synovial inflammation, mononuclear cell influx in the synovium, and increased expression of catabolic factors, including matrix metalloproteinase-13, accompanied by an increase in staining for matrix metalloproteinase-generated aggrecan and type II collagen neoepitopes (VDIPEN and C1-2C). We demonstrate that PPARγ-deficient articular cartilage exhibits elevated expression of the additional catabolic factors hypoxia-inducible factor-2α, syndecan-4, and a disintegrin and metalloproteinase with thrombospondin motifs 5 and of the inflammatory factors cyclooxygenase-2 and inducible nitric oxide synthase. In conclusion, PPARγ is a critical regulator of cartilage health, the lack of which leads to an accelerated spontaneous OA phenotype.

New findings in osteoarthritis pathogenesis: therapeutic implications

This review focuses on the new perspectives which can provide insight into the crucial pathways that drive cartilage-bone physiopathology. In particular, we discuss the critical signaling and effector molecules that can activate cellular and molecular processes in both cartilage and bone cells and which may be relevant in cross talk among joint compartments: growth factors (bone morphogenetic proteins and transforming growth factor), hypoxia-related factors, cell-matrix interactions [discoidin domain receptor 2 (DDR2) and syndecan 4], signaling molecules [WNT, Hedgehog (Hh)]. With the continuous progression of our knowledge on the molecular pathways involved in cartilage and bone changes in osteoarthritis (OA), an increasing number of potentially effective candidates for OA therapy are already under scrutiny in clinical trials to ascertain their possible safe use in an attempt to identify molecules active in slowing or halting OA progression and reducing joint pain. We then review the principal molecules currently under clinical investigation.

Lead induces an osteoarthritis-like phenotype in articular chondrocytes through disruption of TGF-β signaling

Lead remains a significant environmental toxin, and we believe we may have identified a novel target of lead toxicity in articular chondrocytes. These cells are responsible for the maintenance of joint matrix, and do so under the regulation of TGF-β signaling. As lead is concentrated in articular cartilage, we hypothesize that it can disrupt normal chondrocyte phenotype through suppression of TGF-β signaling. These experiments examine the effects of lead exposure in vivo and in vitro at biologically relevant levels, from 1 nM to 10 µM on viability, collagen levels, matrix degrading enzyme activity, TGF-β signaling, and articular surface morphology. Our results indicate that viability was unchanged at levels ≤100 µM Pb, but low and high level lead in vivo exposure resulted in fibrillation and degeneration of the articular surface. Lead treatment also decreased levels of type II collagen and increased type X collagen, in vivo and in vitro. Additionally, MMP13 activity increased in a dose-dependent manner. Active caspase 3 and 8 were dose-dependently elevated, and treatment with 10 µM Pb resulted in increases of 30% and 500%, respectively. Increasing lead treatment resulted in a corresponding reduction in TGF-β reporter activity, with a 95% reduction at 10µM. Levels of phosphoSmad2 and 3 were suppressed in vitro and in vivo and lead dose-dependently increased Smurf2. These changes closely parallel those seen in osteoarthritis. Over time this phenotypic shift could compromise maintenance of the joint matrix.

Hyaluronan injection in murine osteoarthritis prevents TGFbeta 1-induced synovial neovascularization and fibrosis and maintains articular cartilage integrity by a CD44-dependent mechanism

Introduction

The mechanism by which intra-articular injection of hyaluronan (HA) ameliorates joint pathology is unknown. Animal studies have shown that HA can reduce synovial activation, periarticular fibrosis and cartilage erosion; however, its specific effects on the different cell types involved remain unclear. We have used the TTR (TGFbeta1 injection and Treadmill Running) model of murine osteoarthritis (OA), which exhibits many OA-like changes, including synovial activation, to examine in vivo tissue-specific effects of intra-articular HA.

Methods

The kinetics of clearance of fluorotagged HA from joints was examined with whole-body imaging. Naïve and treated knee joints were examined macroscopically for cartilage erosion, meniscal damage and fibrosis. Quantitative histopathology was done with Safranin O for cartilage and with Hematoxylin & Eosin for synovium. Gene expression in joint tissues for Acan, Col1a1, Col2a1, Col3a1, Col5a1, Col10a1, Adamts5 and Mmp13 was done by quantitative PCR. The abundance and distribution of aggrecan, collagen types I, II, III, V and X, ADAMTS5 and MMP13 were examined by immunohistochemistry.

Results

Injected HA showed a half-life of less than 2 h in the murine knee joint. At the tissue level, HA protected against neovascularization and fibrosis of the meniscus/synovium and maintained articular cartilage integrity in wild-type but not in Cd44 knockout mice. HA injection enhanced the expression of chondrogenic genes and proteins and blocked that of fibrogenic/degradative genes and proteins in cartilage/subchondral bone, whereas it blocked activation of both groups in meniscus/synovium. In all locations it reduced the expression/protein for Mmp13 and blocked Adamts5 expression but not its protein abundance in the synovial lining.

Conclusions

The injection of HA, 24 h after TGFbeta1 injection, inhibited the cascade of OA-like joint changes seen after treadmill use in the TTR model of OA. In terms of mechanism, tissue protection by HA injection was abrogated by Cd44 ablation, suggesting that interaction of the injected HA with CD44 is central to its protective effects on joint tissue remodeling and degeneration in OA progression.

Cam morphology in the human hip

A growing interest exists in the diagnosis and treatment of femoroacetabular impingement. Although cam morphology of the proximal femur may conceptually appear to be a relatively simple topographical aberrancy, it is actually positioned amid a complex developmental, kinematic, and biomechanical region of the human body. The authors introduce a new classification scheme and review the historical and anthropological considerations, biomechanics, and genetic factors involved in cam morphology.

Coexistence of fibrotic and chondrogenic process in the capsule of idiopathic frozen shoulders

OBJECTIVE

To analyze changes in the capsule from idiopathic frozen shoulders and clarify their etiology.

MATERIALS AND METHODS

Samples (the rotator interval capsule, middle glenohumeral ligament (MGHL), and inferior glenohumeral ligament (IGHL)) were collected from 12 idiopathic frozen shoulders with severe stiffness and 18 shoulders with rotator cuff tears as a control. The number of cells was counted and the tissue elasticity of the samples was calculated by scanning acoustic microscopy (SAM). The amount of glycosaminoglycan content was assessed by alcian blue staining. Gene and protein expressions related to fibrosis, inflammation, and chondrogenesis were analyzed by quantitative polymerase chain reaction (qPCR) and immunohistochemistry (IHC). Furthermore, the total genes of the two groups were compared by DNA microarray analysis.

RESULTS

The number of cells was significantly higher and the capsular tissue was significantly stiffer in idiopathic frozen shoulders compared with shoulders with rotator cuff tears. Staining intensity of alcian blue was significantly stronger in idiopathic frozen shoulders. Gene expressions related to fibrosis, inflammation, and chondrogenesis were significantly higher in idiopathic frozen shoulders compared with shoulders with rotator cuff tears assessed by both qPCR and DNA microarray analysis.

CONCLUSION

In addition to fibrosis and inflammation, which used to be considered the main pathology of frozen shoulders, chondrogenesis is likely to have a critical role in pathogenesis of idiopathic frozen shoulders.

Recent progress in understanding molecular mechanisms of cartilage degeneration during osteoarthritis

Osteoarthritis (OA) is a highly prevalent disease affecting more than 20% of American adults. Predispositions include joint injury, heredity, obesity, and aging. Biomechanical alterations are commonly involved. However, the molecular mechanisms of this disease are complex, and there is currently no effective disease-modifying treatment. The initiation and progression of OA subtypes is a complex process that at the molecular level probably involves many cell types, signaling pathways, and changes in extracellular matrix. Ex vivo studies with tissue derived from OA patients and in vivo studies with mutant mice have suggested that pathways involving receptor ligands such as TGF-β1, WNT3a, and Indian hedgehog; signaling molecules such as Smads, β-catenin, and HIF-2a; and peptidases such as MMP13 and ADAMTS4/5 are probably involved to some degree. This review focuses on molecular mechanisms of OA development related to recent findings.