Fibroblast growth factor-2 induced chondrocyte cluster formation in experimentally wounded articular cartilage is blocked by soluble Jagged-1

The iPSC secretome is beneficial for in vitro propagation of primary osteoarthritic chondrocytes cell lines

BACKGROUND

One of the obstacles to autologous chondrocyte implantation (ACI) is obtaining a large quantity of chondrocytes without depletion of their properties. The conditioned medium (CM) from different subpopulations of stem cells (mesenchymal stromal cells (MSC) or induced pluripotent stem cells (iPSC)) could be a gamechanger. MSCs' potential is related to the donor's health and age, which could be omitted when, as a source, iPSCs are used. There is a lack of data regarding their use in the chondrocyte culture expansion. Thus, we wanted to verify whether iPSC-CM could be beneficial for the cell culture of primary chondrocyte cells.

METHODS

We added the iPSC-CMs from GPCCi001-A and ND 41658*H cells to the culture of primary chondrocyte cell lines isolated from OA patients (n = 6) for other two passages. The composition of the CM was evaluated using Luminex technology. Then, we analysed the senescence, proliferation rate and using flow cytometry: viability, distribution of cell cycle phases, production of reactive oxygen species (ROS) and double-strand breaks. The cartilage-related markers were evaluated using Western blot and immunofluorescence. Additionally, a three-dimensional cell culture was used to determine the potential to form cartilage particles.

RESULTS

iPSC-CM increased proliferation and diminished cell ROS production and senescence. CM influenced the cartilage-related protein expression and promoted the growth of cartilage particles. The cell exposed to CM did not lose the ECM proteins, suggesting the chondroprotective effect for prolonged culture time.

CONCLUSION

Our preliminary results suggest a beneficial effect on maintaining chondrocyte biology during in vitro expansion.

Histological analysis of nucleus pulposus tissue from patients with lumbar disc herniation after condoliase administration

Background

Condoliase is an enzyme used as a treatment for lumbar disc herniation (LDH). This enzyme degrades chondroitin sulfate (CS) in the nucleus pulposus of the intervertebral disc (IVD). However, there are cases in which symptoms do not improve, despite condoliase administration. This study reports histological analysis of lumbar disc tissue of LDH patients who underwent surgery because condoliase had no therapeutic effect.

Methods

Between March 2019 and August 2019, 12 LDH patients who underwent full endoscopic spine surgery (FESS) discectomy at the Dezawa Akira PED Clinic were the subjects of the study. There are two study groups: six cases underwent FESS after condoliase administration, while six underwent FESS without condoliase administration. The average duration from drug administration to surgery was 152 days. Herniated disc removed at surgery was evaluated by histological staining including immunohistochemistry by anti-CS antibodies.

Results

Multiple large clusters (40-120 μm in diameter) were observed in the nucleus pulposus of those who received condoliase, but no clusters were observed in those who did not. The lumbar disc tissues, including the nucleus pulposus of recipients, were stained with anti-CS antibodies that recognize the CS unsaturated disaccharide, but non-administration tissue was not stained. These findings suggest that the enzyme acted on the nucleus pulposus, even in cases where symptoms were not improved by condoliase administration. Furthermore, there was no histological difference between stained images of the extracellular matrix in those who did or did not receive condoliase, suggesting that condoliase acted specifically on CS in the nucleus pulposus.

Conclusions

We demonstrated that CS in the nucleus pulposus was degraded in patients in whom condoliase did not have a therapeutic effect. Moreover, condoliase acts in human IVD without causing necrosis of chondrocytes and surrounding tissues.

Insights into the Notch signaling pathway in degenerative musculoskeletal disorders: Mechanisms and perspectives

Degenerative musculoskeletal disorders are a group of age-related diseases of the locomotive system that severely affects the patient's ability to work and cause adverse sequalae such as fractures and even death. The incidence and prevalence of degenerative musculoskeletal disorders is rising owing to the aging of the world's population. The Notch signaling pathway, which is expressed in almost all organ systems, extensively regulates cell proliferation and differentiation as well as cellular fate. Notch signaling shows increased activity in degenerative musculoskeletal disorders and retards the progression of degeneration to some extent. The review focuses on four major degenerative musculoskeletal disorders (osteoarthritis, intervertebral disc degeneration, osteoporosis, and sarcopenia) and summarizes the pathophysiological functions of Notch signaling in these disorders, especially its role in stem/progenitor cells in each disorder. Finally, a conclusion will be presented to explore the research and application of the perspectives on Notch signaling in degenerative musculoskeletal disorders.

Characterization of human placenta-derived exosome (pExo) as a potential osteoarthritis disease modifying therapeutic

OBJECTIVE

Human placenta-derived exosomes (pExo) were generated, characterized, and evaluated as a therapeutic candidate for the treatment of osteoarthritis (OA).

METHODS

pExo was generated from full-term human placenta tissues by sequential centrifugation, purification, and sterile filtration. Upon analysis of particle size, cytokine composition, and exosome marker expression, pExo was further tested in cell-based assays to examine its effects on human chondrocytes. In vivo therapeutic efficacies were evaluated in a medial meniscal tear/medial collateral ligament tear (MCLT + MMT) rat model, in which animals received pExo injections intraarticularly and weight bearing tests during in-life stage while histopathology and immunohistochemistry were performed as terminal endpoints.

RESULTS

pExo displayed typical particle size, expressed maker proteins of exosome, and contained proteins with pro-proliferative, pro-anabolic, anti-catabolic, or anti-inflammatory activities. In vitro, pExo promoted chondrocyte migration and proliferation dose-dependently, which may involve its activation of cell growth-related signaling pathways. Expression of inflammatory and catabolic genes induced in a cellular OA model was significantly suppressed by pExo. In the rat OA model, pExo alleviated pain burden, restored cartilage degeneration, and downregulated expressions of pro-inflammatory, catabolic, or apoptotic proteins in a dose-dependent manner.

CONCLUSIONS

Our study demonstrates that pExo has multiple potential therapeutic effects including symptom control and disease modifying characteristics. This may make it an attractive candidate for further development as an anti-OA therapeutic.

The catabolic-to-anabolic shift seen in the canine osteoarthritic cartilage treated with knee joint distraction occurs after the distraction period

Background

Methods

Results

Conclusion

The Translational Potential of this Article

Pleiotropic Roles of NOTCH1 Signaling in the Loss of Maturational Arrest of Human Osteoarthritic Chondrocytes

Notch signaling has been identified as a critical regulator of cartilage development and homeostasis. Its pivotal role was established by both several joint specific Notch signaling loss of function mouse models and transient or sustained overexpression. NOTCH1 is the most abundantly expressed NOTCH receptors in normal cartilage and its expression increases in osteoarthritis (OA), when chondrocytes exit from their healthy “maturation arrested state” and resume their natural route of proliferation, hypertrophy, and terminal differentiation. The latter are hallmarks of OA that are easily evaluated in vitro in 2-D or 3-D culture models. The aim of our study was to investigate the effect of NOTCH1 knockdown on proliferation (cell count and Picogreen mediated DNA quantification), cell cycle (flow cytometry), hypertrophy (gene and protein expression of key markers such as RUNX2 and MMP-13), and terminal differentiation (viability measured in 3-D cultures by luminescence assay) of human OA chondrocytes. NOTCH1 silencing of OA chondrocytes yielded a healthier phenotype in both 2-D (reduced proliferation) and 3-D with evidence of decreased hypertrophy (reduced expression of RUNX2 and MMP-13) and terminal differentiation (increased viability). This demonstrates that NOTCH1 is a convenient therapeutic target to attenuate OA progression.

Hybrid fluorescence-AFM explores articular surface degeneration in early osteoarthritis across length scales

Atomic force microscopy (AFM) has become a powerful tool for the characterization of materials at the nanoscale. Nevertheless, its application to hierarchical biological tissue like cartilage is still limited. One reason is that such samples are usually millimeters in size, while the AFM delivers much more localized information. Here a combination of AFM and fluorescence microscopy is presented where features on a millimeter sized tissue sample are selected by fluorescence microscopy on the micrometer scale and then mapped down to nanometer precision by AFM under native conditions. This served us to show that local changes in the organization of fluorescent stained cells, a marker for early osteoarthritis, correlate with a significant local reduction of the elastic modulus, local thinning of the collagen fibers, and a roughening of the articular surface. This approach is not only relevant for cartilage, but in general for the characterization of native biological tissue from the macro- to the nanoscale. STATEMENT OF SIGNIFICANCE: Different length scales have to be studied to understand the function and dysfunction of hierarchically organized biomaterials or tissues. Here we combine a highly stable AFM with fluorescence microscopy and precisely motorized movement to correlate micro- and nanoscopic properties of articular cartilage on a millimeter sized sample under native conditions. This is necessary for unraveling the relationship between microscale organization of chondrocytes, micrometer scale changes in articular cartilage properties and nanoscale organization of collagen (including D-banding). We anticipate that such studies pave the way for a guided design of hierarchical biomaterials.

Perspectives on long pentraxin 3 and rheumatoid arthritis: several potential breakthrough points relying on study foundation of the past

Rheumatoid arthritis (RA) is a systemic chronic autoimmune inflammatory disease which is mainly characterized by synovitis and results in a severe burden for both the individual and society. To date, the underlying mechanisms of RA are still poorly understood. Pentraxin 3 (PTX3) is a typical long pentraxin protein which has been highly conserved during evolution. Meanwhile, functions as well as properties of PTX3 have been extensively studied. Several studies identified that PTX3 plays a predominate role in infection, inflammation, immunity and tumor. Interestingly, PTX3 has also been verified to be closely associated with development of RA. We therefore accomplished an elaboration of the relationships between PTX3 and RA. Herein, we mainly focus on the associated cell types and cognate cytokines involved in RA, in combination with PTX3. This review infers the insight into the interaction of PTX3 in RA and aims to provide novel clues for potential therapeutic target of RA in clinic.

p66shc siRNA Nanoparticles Ameliorate Chondrocytic Mitochondrial Dysfunction in Osteoarthritis

Background

Osteoarthritis (OA) is the most common type of joint disease associated with cartilage breakdown. However, the role played by mitochondrial dysfunction in OA remains inadequately understood. Therefore, we investigated the role played by p66shc during oxidative damage and mitochondrial dysfunction in OA and the effects of p66shc downregulation on OA progression.

Methods

Monosodium iodoacetate (MIA), which is commonly used to generate OA animal models, inhibits glycolysis and biosynthetic processes in chondrocytes, eventually causing cell death. To observe the effects of MIA and poly(lactic-co-glycolic acid) (PLGA)-based nanoparticles, histological analysis, immunohistochemistry, micro-CT, mechanical paw withdrawal thresholds, quantitative PCR, and measurement of oxygen consumption rate and extracellular acidification rate were conducted.

Results

p-p66shc was highly expressed in cartilage from OA patients and rats with MIA-induced OA. MIA caused mitochondrial dysfunction and reactive oxygen species (ROS) production, and the inhibition of p66shc phosphorylation attenuated MIA-induced ROS production in human chondrocytes. Inhibition of p66shc by PLGA-based nanoparticles-delivered siRNA ameliorated pain behavior, cartilage damage, and inflammatory cytokine production in the knee joints of MIA-induced OA rats.

Conclusion

p66shc is involved in cartilage degeneration in OA. By delivering p66shc-siRNA-loaded nanoparticles into the knee joints with OA, mitochondrial dysfunction-induced cartilage damage can be significantly decreased. Thus, p66shc siRNA PLGA nanoparticles may be a promising option for the treatment of OA.

p47phox siRNA-Loaded PLGA Nanoparticles Suppress ROS/Oxidative Stress-Induced Chondrocyte Damage in Osteoarthritis

Osteoarthritis (OA) is the most common joint disorder that has had an increasing prevalence due to the aging of the population. Recent studies have concluded that OA progression is related to oxidative stress and reactive oxygen species (ROS). ROS are produced at low levels in articular chondrocytes, mainly by the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, and ROS production and oxidative stress have been found to be elevated in patients with OA. The cartilage of OA-affected rat exhibits a significant induction of p47phox, a cytosolic subunit of the NADPH oxidase, similarly to human osteoarthritis cartilage. Therefore, this study tested whether siRNA p47phox that is introduced with poly (D,L-lactic-co-glycolic acid) (PLGA) nanoparticles (p47phox si_NPs) can alleviate chondrocyte cell death by reducing ROS production. Here, we confirm that p47phox si_NPs significantly attenuated oxidative stress and decreased cartilage damage in mono-iodoacetate (MIA)-induced OA. In conclusion, these data suggest that p47phox si_NPs may be of therapeutic value in the treatment of osteoarthritis.

The Secretome Derived From 3D-Cultured Umbilical Cord Tissue MSCs Counteracts Manifestations Typifying Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an autoimmune disorder whose treatment is mostly restricted to pain and symptom management and to the delay of joint destruction. Mesenchymal stem/stromal cells from the umbilical cord tissue (UC-MSCs) have previously been proven to be immunomodulatory and more efficient than bone marrow-derived MSCs in causing remission of local and systemic arthritic manifestations in vivo. Given the paracrine nature of UC-MSC activity, their application as active substances can be replaced by their secretome, thus avoiding allogeneic rejection and safety issues related to unwanted grafting. In this work, we aimed at demonstrating the viability of applying the 3D-primed UC-MSC secretome for the amelioration of arthritic signs. A proteomic analysis was performed to both, media conditioned by UC-MSC monolayer (CM2D) and 3D cultures (CM3D). The analysis of relevant trophic factors confirmed secretome profiles with very significant differences in terms of therapeutic potential. Whereas, CM3D was characterised by a prevailing expression of anti-inflammatory cytokines such as IL-10 and LIF, along with trophic factors involved in different mechanisms leading to tissue regeneration, such as PDGF-BB, FGF-2, I-309, SCF, and GM-CSF; CM2D presented relatively higher levels of IL-6, MCP-1, and IL-21, with recognised pro-inflammatory roles in joint disease and pleiotropic effects in the progression of rheumatoid arthritis (RA). Accordingly, different motogenic effects over mouse chondrocytes and distinct capacities of inducing glycosaminoglycan synthesis in vitro were observed between CM3D and CM2D. Finally, the evaluation of arthritic manifestations in vivo, using an adjuvant-induced model for arthritis (AIA), suggested a significantly higher therapeutic potential of CM3D over CM2D and even UC-MSCs. Histological analysis confirmed a faster remission of local and systemic arthritic manifestations of CM3D-treated animals. Overall, the results show that the use of UC-MSC CM3D is a viable and better strategy than direct UC-MSC administration for counteracting AIA-related signs. This strategy represents a novel MSC-based but nonetheless cell-free treatment for arthritic conditions such as those characterising RA.

Inhibition of Notch1 induces population and suppressive activity of regulatory T cell in inflammatory arthritis

Inhibition of Notch signalling has shown anti-inflammatory properties in vivo and in vitro models of rheumatoid arthritis (RA). The objective of this study was to determine whether Notch1 might play a role in regulating T-regulatory cells (Tregs) in animal models of RA.

Methods: Collagen-induced arthritis (CIA) and collagen antibody-induced arthritis (CAIA) were induced in C57BL/6, Notch1 antisense transgenic (NAS) or DBA1/J mice. We examined whether pharmacological inhibitors of γ-secretase (an enzyme required for Notch1 activation) and antisense-mediated knockdown of Notch1 could attenuate the severity of inflammatory arthritis in CIA and CAIA mice. Proportions of CD4⁺CD25⁺Foxp3⁺ Treg cells were measured by flow cytometry. To assess the suppressive capacity of Treg toward responder cells, CFSE-based suppression assay of Treg was performed.

Results: γ-secretase inhibitors and antisense-mediated knockdown of Notch1 reduced the severity of inflammatory arthritis in both CIA and CAIA mice. Pharmacological and genetic inhibition of Notch1 signalling induced significant elevation of Treg cell population in CIA and CAIA mice. We also demonstrated that inhibition of Notch signalling suppressed the progression of inflammatory arthritis through modulating the expansion and suppressive function of regulatory T (Treg) cells.

Conclusion: Pharmacological and genetic inhibition of Notch1 signalling suppresses the progression of inflammatory arthritis through modulating the population and suppressive function of Treg cells in animal models of RA.

Platelet-rich plasma induces post-natal maturation of immature articular cartilage and correlates with LOXL1 activation

Platelet-rich plasma (PRP) is used to stimulate the repair of acute and chronic cartilage damage even though there is no definitive evidence of how this is achieved. Chondrocytes in injured and diseased situations frequently re-express phenotypic biomarkers of immature cartilage so tissue maturation is a potential pathway for restoration of normal structure and function. We used an in vitro model of growth factor-induced maturation to perform a comparative study in order to determine whether PRP can also induce this specific form of remodeling that is characterised by increased cellular proliferation and tissue stiffness. Gene expression patterns specific for maturation were mimicked in PRP treated cartilage, with chondromodulin, collagen types II/X downregulated, deiodinase II and netrin-1 upregulated. PRP increased cartilage surface cell density 1.5-fold (P < 0.05), confirmed by bromodeoxyuridine incorporation and proportionate increases in proliferating cell nuclear antigen gene expression. Atomic force microscopy analysis of PRP and growth factor treated cartilage gave a 5-fold increase in stiffness correlating with a 10-fold upregulation of lysyl oxidase like-1 gene expression (P < 0.001). These data show PRP induces key aspects of post-natal maturation in immature cartilage and provides the basis to evaluate a new biological rationale for its activity when used clinically to initiate joint repair.

Chondrocyte clusters adjacent to sites of cartilage degeneration have characteristics of progenitor cells

The purpose of this study was to investigate the site-specific characteristics and roles of chondrocyte clusters in human knee osteoarthritis. Cartilage explants were obtained from 45 knees undergoing total knee replacement surgery. The explants were taken from 4 locations in the knee: the medial femoral condyle, the medial posterior femoral condyle (MPC), the lateral femoral condyle, and the lateral posterior femoral condyle (LPC). Cartilage degeneration, cell density, and cell arrangement were compared histologically. A live/dead cell viability assay and immunohistochemical analyses using antibodies against STRO-1, FGF2, and Ki-67 were performed. Cell proliferation and cartilaginous nodule production in MPC and LPC explants in monolayer culture were compared. Finally, MPC cartilage explants were cultured to observe histological changes. The cell density of the MPC explants was higher than that of the LPC because of clustering. MPC explants contained more live cells than the LPC did, and the expression of IHC markers in MPC explants was higher than that in LPC. Chondrocytes from MPC proliferated faster and produced more nodules in monolayer culture than those from the LPC and MPC explants were repaired during organ culture. In conclusion, chondrocyte clusters adjacent to severe cartilage degeneration have specific characteristics, with progenitor and proliferative potential.

Strategies for controlled delivery of biologics for cartilage repair

The delivery of biologics is an important component in the treatment of osteoarthritis and the functional restoration of articular cartilage. Numerous factors have been implicated in the cartilage repair process, but the uncontrolled delivery of these factors may not only reduce their full reparative potential but can also cause unwanted morphological effects. It is therefore imperative to consider the type of biologic to be delivered, the method of delivery, and the temporal as well as spatial presentation of the biologic to achieve the desired effect in cartilage repair. Additionally, the delivery of a single factor may not be sufficient in guiding neo-tissue formation, motivating recent research toward the delivery of multiple factors. This review will discuss the roles of various biologics involved in cartilage repair and the different methods of delivery for appropriate healing responses. A number of spatiotemporal strategies will then be emphasized for the controlled delivery of single and multiple bioactive factors in both in vitro and in vivo cartilage tissue engineering applications.

Viability, growth kinetics and stem cell markers of single and clustered cells in human intervertebral discs: implications for regenerative therapies

PURPOSE

There is much interest in the development of a cellular therapy for the repair or regeneration of degenerate intervertebral discs (IVDs) utilising autologous cells, with some trials already underway. Clusters of cells are commonly found in degenerate IVDs and are formed via cell proliferation, possibly as a repair response. We investigated whether these clusters may be more suitable as a source of cells for biological repair than the single cells in the IVD.

METHODS

Discs were obtained at surgery from 95 patients and used to assess the cell viability, growth kinetics and stem or progenitor cell markers in both the single and clustered cell populations.

RESULTS

Sixty-nine percent (±15) of cells in disc tissue were viable. The clustered cell population consistently proliferated more slowly in monolayer than single cells, although this difference was only significant at P0-1 and P3-4. Both populations exhibited progenitor or notochordal cell markers [chondroitin sulphate epitopes (3B3(-), 7D4, 4C3 and 6C3), Notch-1, cytokeratin 8 and 19] via immunohistochemical examination; stem cell markers assessed with flow cytometry (CD73, 90 and 105 positivity) were similar to those seen on bone marrow-derived mesenchymal stem cells.

CONCLUSIONS

These results confirm those of previous studies indicating that progenitor or stem cells reside in adult human intervertebral discs. However, although the cell clusters have arisen via proliferation, there appear to be no greater incidence of these progenitor cells within clusters compared to single cells. Rather, since they proliferate more slowly in vitro than the single cell population, it may be beneficial to avoid the use of clustered cells when sourcing autologous cells for regenerative therapies.

Osteochondral repair using a scaffold-free tissue-engineered construct derived from synovial mesenchymal stem cells and a hydroxyapatite-based artificial bone

For an ideal osteochondral repair, it is important to facilitate zonal restoration of the subchondral bone and the cartilage, layer by layer. Specifically, restoration of the osteochondral junction and secure integration with adjacent cartilage could be considered key factors. The purpose of the present study was to investigate the feasibility of a combined material comprising a scaffold-free tissue-engineered construct (TEC) derived from synovial mesenchymal stem cells (MSCs) and a hydroxyapatite (HA) artificial bone using a rabbit osteochondral defect model. Osteochondral defects were created on the femoral groove of skeletally mature rabbits. The TEC and HA artificial bone were hybridized to develop a combined implant just before use, which was then implanted into defects (N=23). In the control group, HA alone was implanted (N=18). Histological evaluation and micro-indentation testing was performed for the evaluation of repair tissue. Normal knees were used as an additional control group for biomechanical testing (N=5). At hybridization, the TEC rapidly attached onto the surface of HA artificial bone block, which was implantable to osteochondral defects. Osteochondral defects treated with the combined implants exhibited more rapid subchondral bone repair coupled with the development of cartilaginous tissue with good tissue integration to the adjacent host cartilage when assessed at 6 months post implantation. Conversely, the control group exhibited delayed subchondral bone repair. In addition, the repair cartilaginous tissue in this group had poor integration to adjacent cartilage and contained clustered chondrocytes, suggesting an early osteoarthritis (OA)-like degenerative change at 6 months post implantation. Biomechanically, the osteochondral repair tissue treated with the combined implants at 6 months restored tissue stiffness, similar to normal osteochondral tissue. The combined implants significantly accelerated and improved osteochondral repair. Specifically, earlier restoration of subchondral bone, as well as good tissue integration of repair cartilage to adjacent host tissue could be clinically relevant in terms of the acceleration of postoperative rehabilitation and longer-term durability of repaired articular surface in patients with osteochondral lesions, including those with OA. In addition, the combined implant could be considered a promising MSC-based bio-implant with regard to safety and cost-effectiveness, considering that the TEC is a scaffold-free implant and HA artificial bone has been widely used in clinical practice.

Fibroblast growth factor 2 involved in the pathogenesis of synovial chondromatosis of temporomandibular joint

BACKGROUND

Synovial chondromatosis (SC) of temporomandibular joint (TMJ) is a rare proliferative disorder characterized by the formation of cartilaginous or osteocartilaginous nodules in synovium and joint space. Fibroblast growth factor 2 (FGF-2) is frequently applied in chondrogenic differentiation assays. Therefore, we hypothesized that FGF-2 might involved in the pathogenesis of SC.

METHODS

SC synovium and loose bodies (LBs) specimens were observed by histological and immunohistochemical methods. Real-time PCR was conducted for comparing genes expressions in SC and normal synovium. SC synoviocytes were stimulated by FGF-2 in the presence or absence of its antagonist long pentraxin-3 (PTX3) for 6 days. Real-time PCR and alkaline phosphatase (ALP) activity were performed to examine the effects exerted by FGF-2 and PTX3.

RESULTS

SC synovium, no matter facing the articular cavity or covering LB, was characterized by increased quantity of synoviocytes and blood vessels. FGF-2 was expressed in chondrocytes and fibroblast-like cells of LBs, and the wall of blood vessels. Expressions of chondrogenic genes (Sox9 and Wnt-4), osteogenic genes (Foxc2), FGF-2, and VEGF-A mRNA were significantly higher in SC synovium than that of the control group. The stimulation of FGF-2 on SC synoviocytes increased ALP activity and expressions of chondrogenic genes (Sox9, Col2α1, and Aggrecan), osteogenic genes (Foxc2, osteocalcin, and Col1α1), and VEGF-A, but PTX3 inhibited these effects.

CONCLUSION

FGF-2 was responsible for the formation of cartilaginous loose bodies and involved in the pathogenesis of SC.

Inhibition of notch signalling ameliorates experimental inflammatory arthritis

OBJECTIVE

To test the hypothesis that Notch signalling plays a role in the pathogenesis of rheumatoid arthritis (RA) and to determine whether pharmacological inhibition of Notch signalling with γ-secretase inhibitors can ameliorate the RA disease process in an animal model.

METHODS

Collagen-induced arthritis was induced in C57BL/6 or Notch antisense transgenic mice by immunisation with chicken type II collagen (CII). C57BL/6 mice were administered with different doses of inhibitors of γ-secretase, an enzyme required for Notch activation, at disease onset or after onset of symptoms. Severity of arthritis was monitored by clinical and histological scores, and in vivo non-invasive near-infrared fluorescence (NIRF) images. Micro-CT was used to confirm joint destruction. The levels of CII antibodies and cytokines in serum were determined by ELISA and bead-based cytokine assay. The expression levels of cytokines were studied by quantitative PCR in rheumatoid synovial fibroblasts.

RESULTS

The data show that Notch signalling stimulates synoviocytes and accelerates their production of proinflammatory cytokines and immune responses involving the upregulation of IgG1 and IgG2a. Pharmacological inhibition of γ-secretase and antisense-mediated knockdown of Notch attenuates the severity of inflammatory arthritis, including arthritis indices, paw thickness, tissue damage and neutrophil infiltration, and reduces the levels of active NF-κB, ICAM-1, proinflammatory cytokines and matrix metalloproteinase-3 activity in the mouse model of RA.

CONCLUSIONS

These results suggest that Notch is involved in the pathogenesis of RA and that inhibition of Notch signalling is a novel approach for treating RA.

Fibroblast growth factor-1 is a mesenchymal stromal cell-secreted factor stimulating proliferation of osteoarthritic chondrocytes in co-culture

Previously, we showed that mesenchymal stromal cells (MSCs) in co-culture with primary chondrocytes secrete soluble factors that increase chondrocyte proliferation. The objective of this study is to identify these factors. Human primary chondrocytes (hPCs) isolated from late-stage osteoarthritis patients were co-cultured with human bone marrow-derived MSCs (hMSCs) in pellets. Genome-wide mRNA expression analysis and quantitative polymerase chain reactions (qPCR) were used to identify soluble factors that were specifically induced in co-cultures. Immunofluorescent staining combined with cell tracking and enzyme-linked immunosorbent assay (ELISA) were performed to validate up-regulation at the protein level and to identify the cellular origin of the increased proteins. Chemical blockers and neutralizing antibodies were used to elucidate the role of the identified candidate genes in co-cultures. A number of candidate factors were differentially regulated in co-cultures at the mRNA level. Of these, fibroblast growth factor-1 (FGF-1) mRNA and protein expression were markedly increased in co-cultures predominantly due to up-regulated expression in MSCs. Blocking of FGF signaling in co-culture pellets by specific FGF receptor inhibitors or FGF-1 neutralizing antibodies completely blocked hPCs proliferation. We demonstrate that MSCs increase FGF-1 secretion on co-culture with hPCs, which, in turn, is responsible for increased hPCs proliferation in pellet co-cultures.

Lentiviral-mediated RNAi knockdown of Cbfa1 gene inhibits endochondral ossification of antler stem cells in micromass culture

Articular cartilage (AC) lacks ability to repair defects due to its avascular nature as healing process relies on cells being brought in by blood vessels. Multiple approaches have been taken to facilitate cartilage repair in clinics, to date there is no effective treatment available that can restores the AC lesion to a normally functioning level over extended periods. In this regard, antler cartilage is unique in being richly vascularised and hence can effectively repair and regenerate. Interestingly, antler stem cells, from which the vascularised cartilage is derived, can form avascular cartilage when taken away from their original niche, suggesting that the vascular or avascular state of antler cartilage is controlled by extrinsic factors. Understanding the mechanisms underlying this phenotype switch may help us to devise a way to trigger the effective intrinsic repair of AC. However, adoption of antler cartilage model for AC repair requires the demonstration that the cartilage specific signalling pathways also prevail in antler chondrogenesis. To achieve this, in the present study we silenced expression of Cbfa1, a key factor regulatingendochondral ossification, using RNAi, and showed that expression of the downstream genes type I collagen and osteocalcin were suppressed which, in turn, inhibited endochondral ossification process taking place in the antler stem cell-formed nodules. Therefore, we provided further evidence at molecular level that antler could be developed as novel model for the study of AC repair. The eventual identification of the extrinsic factors dictating the phenotype switch between the vascular and avascular state of antler cartilage will open up a new avenue for the cure of osteoarthritis.

Expression patterns of Notch receptors and their ligands in human osteoarthritic and healthy articular cartilage

Notch pathway plays a pivotal role in cell fate determination. There is much interest surrounding its therapeutic potential, in osteoarthritis, but the expression profile of Notch-related molecules, as well as their relation with cartilage pathological parameters, remains unclear. The purpose of our study is to analyze the expression pattern of Notch family members, type II and type I collagen, in normal (healthy) and osteoarthritic human knee cartilage. Osteoarthritic cartilages were obtained from 3 patients undergoing a total knee replacement. Macroscopically normal cartilage was dissected from 3 human knees at the time of autopsy or surgery. Immunohistochemical staining was performed using Notch1,2,3 and 4, Delta, Jagged, type II collagen and type I collagen antibodies. In healthy cartilage, type II collagen was abundantly expressed while type I was absent. This latter increased proportionally to the osteoarthritic grade. Type II collagen expression remained intense in osteoarthritic cartilage. In healthy cartilage as well as in cartilage with minor lesions, Notch family member's proteins were not or just weakly expressed at the surface and in the cells. However, Notch molecules were over-expressed in osteoarthritic cartilage compared to healthy one. This expression pattern was different according to the cartilage zone and the severity of OA. Our data suggest that Notch signaling is activated in osteoarthritic cartilage, compared to healthy cartilage, with a much more abundant expression in the most damaged areas.

Notch signaling and the developing skeleton

Notch signaling is an important regulator of skeletogenesis at multiple developmental stages. The Notch signaling pathway is involved in the promotion of somite segmentation, patterning and differentiation into sclerotome pre-chondrogenic cells to allow for appropriate axial skeleton development. In addition, studies performed in vitro and in vivo demonstrate that Notch signaling suppresses chondrogenic and osteoblastic differentiation and negatively regulates osteoclast formation and proliferation. Through the use of in vitro and in vivo approaches, Notch signaling has been shown to regulate somitogenesis, chondrogenesis, osteoblastogenesis and osteoclastogenesis that ultimately affect skeletogenesis. Dysregulation of Notch signaling results in congenital skeletal malformations that could reveal therapeutic potential.

Correlation between plasma and synovial fluid basic fibroblast growth factor with radiographic severity in primary knee osteoarthritis

PURPOSE

The aim of this study was to investigate plasma and synovial fluid basic fibroblast growth factor (bFGF) levels in patients with primary knee osteoarthritis (OA) and to evaluate the correlation between bFGF levels and disease severity.

METHODS

Thirty-five patients with knee OA and 15 healthy individuals were recruited into this study. Knee OA grading was performed according to the Kellgren-Lawrence classification. bFGF concentrations in both plasma and synovial fluid were determined using enzyme-linked immunosorbent assay.

RESULTS

Plasma and synovial fluid bFGF levels in knee OA patients were significantly higher than in controls (P < 0.001). Moreover, plasma and synovial fluid bFGF concentrations were positively correlated with radiographic severity (r = 0.535, P < 0.001 and r = 0.570, P < 0.001, respectively). Further analysis revealed that there was a positive correlation between plasma and synovial fluid bFGF levels (r = 0.674, P < 0.001).

CONCLUSIONS

Plasma and synovial fluid bFGF levels were significantly increased in OA patients, and these elevated levels were positively correlated with radiographic severity. These findings indicate that bFGF levels may be a monitor of disease severity and could play an essential part in the pathophysiology of degenerative process in OA.

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

OBJECTIVE

To review the literature on modulation of chondrocyte activities in the osteoarthritic joint, and to discuss these changes in relation to established hard and soft tissue repair paradigms, with an emphasis on transforming growth factor beta (TGFβ1)-mediated signaling which can promote either a chondrogenic or fibrogenic phenotype.

METHODS

Papers addressing the close relationship between repair in general, and the specific post-injury response of joint tissues are summarized. Different interpretations of the role of TGFβ1 in the emergence of an "osteoarthritic" chondrocyte are compared and the phenotypic plasticity of "reparative" progenitor cells is examined. Lastly, emerging data on a central role for A-Disintegrin-And-Metalloproteinase-with-Thrombospondin-like-Sequences-5 (ADAMTS5) activity in modulating TGFβ1 signaling through activin receptor-like kinase 1 (ALK1) and activin receptor-like kinase 5 (ALK5) pathways is discussed.

RESULTS

The review illustrates how a transition from ALK5-mediated fibrogenic signaling to ALK1-mediated chondrogenic signaling in joint cells represents the critical transition from a non-reparative to a reparative cell phenotype. Data from cell and in vivo studies illustrates the mechanism by which ablation of ADAMTS5 activity allows the transition to reparative chondrogenesis. Multiple large gene expression studies of normal and osteoarthritis (OA) human cartilages (CAs) also support an important role for TGFβ1-mediated pro-fibrogenic activities during disease progression.

CONCLUSIONS

We conclude that progressive articular CA damage in post-injury OA results primarily from biomechanical, cell biologic and mediator changes that promote a fibroblastic phenotype in joint cells. Since ADAMTS5 and TGFβ1 appear to control this process, agents which interfere with their activities may not only enhance endogenous CA repair in vivo, but also improve the properties of tissue-engineered CA for implantation.