Changes in type of collagen synthesized as clones of chick chondrocytes grow and eventually lose division capacity

Anaphylatoxins and their corresponding receptors as potential drivers in cartilage calcification during osteoarthritis progression

OBJECTIVE

The complement cascade as major fluid phase innate immune system is activated during progression of osteoarthritis (OA). Generated anaphylatoxins and the corresponding receptors C3aR and C5aR1 are associated with the calcification of blood vessels and involved in osteogenic differentiation. This study aims on elucidating whether complement activation products contribute to cartilage calcification of OA cartilage.

METHOD

Human articular chondrocytes were osteogenically differentiated in vitro in the presence or absence of C3a, C5a, and bone morphogenetic protein (BMP) 2. Furthermore, macroscopically intact (OARSI grade ≤ 1) and highly degenerated human cartilage (OARSI grade ≥ 3) was used for C3aR and C5aR1 histochemistry. Calcification of the cartilage was assessed by Alizarin Red S and von Kossa staining.

RESULTS

C3a and C5a amplified matrix mineralization during in vitro osteogenesis, while inhibition of the corresponding receptors impaired calcium deposition. Moreover, C3aR and C5aR1 expression was upregulated during osteogenic differentiation and also in degenerated cartilage. Additionally, anaphylatoxin receptor expression was positively associated with calcification of native cartilage tissue and calcium deposition during osteogenic differentiation. Finally, the pro-hypertrophic growth factor BMP2 induced the expression of C5aR1.

CONCLUSIONS

Our findings indicate that anaphylatoxins and their receptors play a decisive role in cartilage calcification processes during OA progression.

A New Method for the Production of High-Concentration Collagen Bioinks with Semiautonomic Preparation

It is believed that 3D bioprinting will greatly help the field of tissue engineering and regenerative medicine, as live patient cells are incorporated into the material, which directly creates a 3D structure. Thus, this method has potential in many types of human body tissues. Collagen provides an advantage, as it is the most common extracellular matrix present in all kinds of tissues and is, therefore, very natural for cells and the organism. Hydrogels with highly concentrated collagen make it possible to create 3D structures without additional additives to crosslink the polymer, which could negatively affect cell proliferation and viability. This study established a new method for preparing highly concentrated collagen bioinks, which does not negatively affect cell proliferation and viability. The method is based on two successive neutralizations of the prepared hydrogel using the bicarbonate buffering mechanisms of the 2× enhanced culture medium and pH adjustment by adding NaOH. Collagen hydrogel was used in concentrations of 20 and 30 mg/mL dissolved in acetic acid with a concentration of 0.05 and 0.1 wt.%. The bioink preparation process is automated, including colorimetric pH detection and adjustment. The new method was validated using bioprinting and subsequent cultivation of collagen hydrogels with incorporated stromal cells. After 96 h of cultivation, cell proliferation and viability were not statistically significantly reduced.

Pericellular Matrix Formation and Atomic Force Microscopy of Single Primary Human Chondrocytes Cultured in Alginate Microgels

One of the main components of articular cartilage is the chondrocyte's pericellular matrix (PCM), which is critical for regulating mechanotransduction, biochemical cues, and healthy cartilage development. Here, individual primary human chondrocytes (PHC) are encapsulated and cultured in 50 µm diameter alginate microgels using drop-based microfluidics. This unique culturing method enables PCM formation and manipulation of individual cells. Over ten days, matrix formation is observed using autofluorescence imaging, and the elastic moduli of isolated cells are measured using AFM. Matrix production and elastic modulus increase are observed for the chondrons cultured in microgels. Furthermore, the elastic modulus of cells grown in microgels increases ≈ten-fold over ten days, nearly reaching the elastic modulus of in vivo PCM. The AFM data is further analyzed using a Gaussian mixture model and shows that the population of PHCs grown in microgels exhibit two distinct populations with elastic moduli averaging 9.0 and 38.0 kPa. Overall, this work shows that microgels provide an excellent culture platform for the growth and isolation of PHCs, enabling PCM formation that is mechanically similar to native PCM. The microgel culture platform presented here has the potential to revolutionize cartilage regeneration procedures through the inclusion of in vitro developed PCM.

Chondrocyte De-Differentiation: Biophysical Cues to Nuclear Alterations

Autologous chondrocyte implantation (ACI) is a cell therapy to repair cartilage defects. In ACI a biopsy is taken from a non-load bearing area of the knee and expanded in-vitro. The expansion process provides the benefit of generating a large number of cells required for implantation; however, during the expansion these cells de-differentiate and lose their chondrocyte phenotype. In this review we focus on examining the de-differentiation phenotype from a mechanobiology and biophysical perspective, highlighting some of the nuclear mechanics and chromatin changes in chondrocytes seen during the expansion process and how this relates to the gene expression profile. We propose that manipulating chondrocyte nuclear architecture and chromatin organization will highlight mechanisms that will help to preserve the chondrocyte phenotype.

Cartilage regeneration using improved surface electrospun bilayer polycaprolactone scaffolds loaded with transforming growth factor-beta 3 and rabbit muscle-derived stem cells

Polycaprolactone (PCL) has recently received significant attention due to its mechanical strength, low immunogenicity, elasticity, and biodegradability. Therefore, it is perfectly suitable for cartilage tissue engineering. PCL is relatively hydrophobic in nature, so its hydrophilicity needs to be enhanced before its use in scaffolding. In our study, first, we aimed to improve the hydrophilicity properties after the network of the bilayer scaffold was formed by electrospinning. Electrospun bilayer PCL scaffolds were treated with ozone and further loaded with transforming growth factor-beta 3 (TGFβ3). In vitro studies were performed to determine the rabbit muscle-derived stem cells’ (rMDSCs) potential to differentiate into chondrocytes after the cells were seeded onto the scaffolds. Statistically significant results indicated that ozonated (O) scaffolds create a better environment for rMDSCs because collagen-II (Coll2) concentrations at day 21 were higher than non-ozonated (NO) scaffolds. In in vivo studies, we aimed to determine the cartilage regeneration outcomes by macroscopical and microscopical/histological evaluations at 3- and 6-month time-points. The Oswestry Arthroscopy Score (OAS) was the highest at both mentioned time-points using the scaffold loaded with TGFβ3 and rMDSCs. Evaluation of cartilage electromechanical quantitative parameters (QPs) showed significantly better results in cell-treated scaffolds at both 3 and 6 months. Safranin O staining indicated similar results as in macroscopical evaluations—cell-treated scaffolds revealed greater staining with safranin, although an empty defect also showed better results than non-cell-treated scaffolds. The scaffold with chondrocytes represented the best score when the scaffolds were evaluated with the Mankin histological grading scale. However, as in previous in vivo evaluations, cell-treated scaffolds showed better results than non-cell-treated scaffolds. In conclusion, we have investigated that an ozone-treated scaffold containing TGFβ3 with rMDSC is a proper combination and could be a promising scaffold for cartilage regeneration.

Highly Organized Porous Gelatin-Based Scaffold by Microfluidic 3D-Foaming Technology and Dynamic Culture for Cartilage Tissue Engineering

A gelatin-based hydrogel scaffold with highly uniform pore size and biocompatibility was fabricated for cartilage tissue engineering using microfluidic 3D-foaming technology. Mainly, bubbles with different diameters, such as 100 μm and 160 μm, were produced by introducing an optimized nitrogen gas and gelatin solution at an optimized flow rate, and N₂/gelatin bubbles were formed. Furthermore, a cross-linking agent (1-ethyl-3-(3-dimethyl aminopropyl)-carbodiimide, EDC) was employed for the cross-linking reaction of the gelatin-based hydrogel scaffold with uniform bubbles, and then the interface between the close cells were broken by degassing. The pore uniformity of the gelatin-based hydrogel scaffolds was confirmed by use of a bright field microscope, conjugate focus microscope and scanning electron microscope. The in vitro degradation rate, mechanical properties, and swelling rate of gelatin-based hydrogel scaffolds with highly uniform pore size were studied. Rabbit knee cartilage was cultured, and its extracellular matrix content was analyzed. Histological analysis and immunofluorescence staining were employed to confirm the activity of the rabbit knee chondrocytes. The chondrocytes were seeded into the resulting 3D porous gelatin-based hydrogel scaffolds. The growth conditions of the chondrocyte culture on the resulting 3D porous gelatin-based hydrogel scaffolds were evaluated by MTT analysis, live/dead cell activity analysis, and extracellular matrix content analysis. Additionally, a dynamic culture of cartilage tissue was performed, and the expression of cartilage-specific proteins within the culture time was studied by immunofluorescence staining analysis. The gelatin-based hydrogel scaffold encouraged chondrocyte proliferation, promoting the expression of collagen type II, aggrecan, and sox9 while retaining the structural stability and durability of the cartilage after dynamic compression and promoting cartilage repair.

The clinical potential of articular cartilage-derived progenitor cells: a systematic review

Over the past two decades, evidence has emerged for the existence of a distinct population of endogenous progenitor cells in adult articular cartilage, predominantly referred to as articular cartilage-derived progenitor cells (ACPCs). This progenitor population can be isolated from articular cartilage of a broad range of species, including human, equine, and bovine cartilage. In vitro, ACPCs possess mesenchymal stromal cell (MSC)-like characteristics, such as colony forming potential, extensive proliferation, and multilineage potential. Contrary to bone marrow-derived MSCs, ACPCs exhibit no signs of hypertrophic differentiation and therefore hold potential for cartilage repair. As no unique cell marker or marker set has been established to specifically identify ACPCs, isolation and characterization protocols vary greatly. This systematic review summarizes the state-of-the-art research on this promising cell type for use in cartilage repair therapies. It provides an overview of the available literature on endogenous progenitor cells in adult articular cartilage and specifically compares identification of these cell populations in healthy and osteoarthritic (OA) cartilage, isolation procedures, in vitro characterization, and advantages over other cell types used for cartilage repair. The methods for the systematic review were prospectively registered in PROSPERO (CRD42020184775).

pH Modification of High-Concentrated Collagen Bioinks as a Factor Affecting Cell Viability, Mechanical Properties, and Printability

The 3D bioprinting of cell-incorporated gels is a promising direction in tissue engineering applications. Collagen-based hydrogels, due to their similarity to extracellular matrix tissue, can be a good candidate for bioink and 3D bioprinting applications. However, low hydrogel concentrations of hydrogel (<10 mg/mL) provide insufficient structural support and, in highly concentrated gels, cell proliferation is reduced. In this study, we showed that it is possible to print highly concentrated collagen hydrogels with incorporated cells, where the viability of the cells in the gel remains very good. This can be achieved simply by optimizing the properties of the bioink, particularly the gel composition and pH modification, as well as by optimizing the printing parameters. The bioink composed of porcine collagen hydrogel with a collagen concentration of 20 mg/mL was tested, while the final bioink collagen concentration was 10 mg/mL. This bioink was modified with 0, 5, 9, 13, 17 and 20 μL/mL of 1M NaOH solution, which affected the resulting pH and gelling time. Cylindrical samples based on the given bioink, with the incorporation of porcine adipose-derived stromal cells, were printed with a custom 3D bioprinter. These constructs were cultivated in static conditions for 6 h, and 3 and 5 days. Cell viability and morphology were evaluated. Mechanical properties were evaluated by means of a compression test. Our results showed that optimal composition and the addition of 13 μL NaOH per mL of bioink adjusted the pH of the bioink enough to allow cells to grow and divide. This modification also contributed to a higher elastic modulus, making it possible to print structures up to several millimeters with sufficient mechanical resistance. We optimized the bioprinter parameters for printing low-viscosity bioinks. With this experiment, we showed that a high concentration of collagen gels may not be a limiting factor for cell proliferation.

De novo neo-hyaline-cartilage from bovine organoids in viscoelastic hydrogels

Regenerative therapies for articular cartilage are currently clinically available. However, they are associated with several drawbacks that require resolution. Optimizing chondrocyte expansion and their assembly, can reduce the time and costs of these therapies and more importantly increase their clinical success. In this study, cartilage organoids were quickly mass produced from bovine chondrocytes with a new suspension expansion protocol. This new approach led to massive cell proliferation, high viability and the self-assembly of organoids. These organoids were composed of collagen type II, type VI, glycosaminoglycans, with Sox9 positive cells, embedded in a pericellular and interterritorial matrix similarly to hyaline cartilage. With the goal of producing large scale tissues, we then encapsulated these organoids into alginate hydrogels with different viscoelastic properties. Elastic hydrogels constrained the growth and fusion of the organoids inhibiting the formation of a tissue. In contrast, viscoelastic hydrogels allowed the growth and fusion of the organoids into a homogenous tissue that was rich in collagen type II and glycosaminoglycans. The encapsulation of organoids to produce in vitro neocartilage also proved to be superior to the conventional method of encapsulating 2D expanded chondrocytes. This study describes a multimodal approach that involves chondrocyte expansion, organoid formation and their assembly into neohyaline-cartilage which proved to be superior to the current standard approaches used in cartilage tissue engineering. STATEMENT OF SIGNIFICANCE: In this manuscript, we describe a new and simple methodology to quickly mass produce self-assembling cartilage organoids. Due to their matrix content and structure similarities with native cartilage, these organoids on their own have the potential to revolutionize cartilage research and the manner in which we study signaling pathways, disease progression, tissue engineering, drug development, etc. Furthermore, these organoids and their fast mass production were combined with a key relatively ignored hydrogel characteristic, viscoelasticity, to demonstrate their fusion into a neo-tissue. This has the potential to open the door for large scale cartilage regeneration such as for entire joint surfaces.

Three-dimensional (3D) hydrogel serves as a platform to identify potential markers of chondrocyte dedifferentiation by combining RNA sequencing

Dedifferentiation of chondrocyte greatly restricts its function and application, however, it is poorly understood except a small number of canonical markers. The non-cell-adhesive property endows polysaccharide hydrogel with the ability to maintain chondrocyte phenotype, which can serve as a platform to identify new molecular markers and therapeutic targets of chondrocyte dedifferentiation. In this study, the high-throughput RNA sequencing (RNA-seq) was first performed on articular chondrocytes at primary (P0) and passage 1 (P1) stages to explore the global alteration of gene expression along with chondrocyte dedifferentiation. Significantly, several potential marker genes, such as PFKFB3, KDM6B, had been identified via comparatively analyzing their expression in P0 and P1 chondrocytes as well as in 3D constructs (i.e. chondrocyte-laden alginate hydrogel and HA-MA hydrogel) at both mRNA and protein level. Besides, the changes in cellular morphology and enriched pathway of differentially expressed genes during chondrocyte dedifferentiation was studied in detail. This study developed the use of hydrogel as a platform to investigate chondrocyte dedifferentiation; the results provided new molecular markers and potential therapeutic targets of chondrocyte dedifferentiation.

Adult ovine chondrocytes in expansion culture adopt progenitor cell properties that are favorable for cartilage tissue engineering

Human chondrocytes in expansion culture can become progenitor-like in their ability to proliferate extensively and secrete neocartilage in chondrogenic culture. Sheep are used as a large animal model for cartilage tissue engineering, although for testing progenitor-like chondrocytes it is important that ovine chondrocytes resemble human in the ability to adopt progenitor properties. Here, we investigate whether ovine chondrocytes can adopt progenitor properties as indicated by rapid proliferation in a colony-forming fashion, and high levels of neocartilage secretion in chondrogenic culture. In conditions known to promote expansion of mesenchymal stromal cells, ovine chondrocytes proliferated through approximately 12 population doublings in 10 days. Time-lapse imaging indicated rapid proliferation in a colony-forming pattern. Expanded ovine chondrocytes that were seeded into agarose and cultured in chondrogenic medium accumulated neocartilage over 2 weeks, to a greater extent than primary chondrocytes. These data confirm that ovine chondrocytes resemble human chondrocytes in their ability to acquire progenitor properties that are important for cartilage tissue engineering. Given the broad interest in using progenitor cells to heal connective tissues, next we compared proliferation and trilineage differentiation of ovine chondrocytes, meniscus cells, and tenocytes. Meniscus cells and tenocytes experienced more than 13 population doublings in 10 days. In chondrogenic culture, cartilage matrix accumulation, and gene expression were largely similar among the cell types. All cell types resisted osteogenesis, while expanded tenocytes and meniscal cells were capable of adipogenesis. While ovine connective tissue cells demonstrated limited lineage plasticity, these data support the potential to promote certain progenitor properties with expansion.

Micropatterned Biphasic Nanocomposite Platform for Maintaining Chondrocyte Morphology

One major limitation hindering the translation of in vitro osteoarthritis research into clinical disease-modifying therapies is that chondrocytes rapidly spread and dedifferentiate under standard monolayer conditions. Current strategies to maintain rounded morphologies of chondrocytes in culture either unnaturally restrict adhesion and place chondrocytes in an excessively stiff mechanical environment or are impractical for use in many applications. To address the limitations of current techniques, we have developed a unique composite thin-film cell culture platform, the CellWell, to model articular cartilage that utilizes micropatterned hemispheroidal wells, precisely sized to fit individual cells (12-18 μm diameters), to promote physiologically spheroidal chondrocyte morphologies while maintaining compatibility with standard cell culture and analytical techniques. CellWells were constructed of 15-μm-thick 5% agarose films embedded with electrospun poly(vinyl alcohol) (PVA) nanofibers. Transmission electron microscope (TEM) images of PVA nanofibers revealed a mean diameter of 60.9 ± 24 nm, closely matching the observed 53.8 ± 29 nm mean diameter of human ankle collagen II fibers. Using AFM nanoindentation, CellWells were found to have compressive moduli of 158 ± 0.60 kPa at 15 μm/s indentation, closely matching published stiffness values of the native pericellular matrix. Primary human articular chondrocytes taken from ankle cartilage were seeded in CellWells and assessed at 24 h. Chondrocytes maintained their rounded morphology in CellWells (mean aspect ratio of 0.87 ± 0.1 vs three-dimensional (3D) control [0.86 ± 0.1]) more effectively than those seeded under standard conditions (0.65 ± 0.3), with average viability of >85%. The CellWell's design, with open, hemispheroidal wells in a thin film substrate of physiological stiffness, combines the practical advantages of two-dimensional (2D) culture systems with the physiological advantages of 3D systems. Through its ease of use and ability to maintain the physiological morphology of chondrocytes, we expect that the CellWell will enhance the clinical translatability of future studies conducted using this culture platform.

Gene expression markers in horse articular chondrocytes: Chondrogenic differentiaton IN VITRO depends on the proliferative potential and ageing. Implication for tissue engineering of cartilage

Chondrocyte dedifferentiation is a key limitation in therapies based on autologous chondrocyte implantation for cartilage repair. Articular chondrocytes, obtained from (metacarpophalangeal and metatarsophalangeal) joints of different aged horses, were cultured in monolayer for several passages (P0 to P8). Cumulative Populations Doublings Levels (PDL) and gene expression of relevant chondrocyte phenotypic markers were analysed during culturing. Overall data confirmed that, during proliferation in vitro, horse chondrocytes undergo marked morphological and phenotypic alterations of their differentiation status. Particularly, the dedifferentiation started early in culture (P0-P1) and was very marked at P3 subculture (PDL 4-6): proliferative phase after P3 could be critical for maintenance/loss of differentiation potential. In elderly animals, chondrocytes showed aspects of dedifferentiation shortly after their isolation, associated with reduced proliferative capacity. Regarding the gene expression of major cartilage markers (Col2, Aggrecan, SOX9) there was a very early reduction (P1) in proliferating chondrocytes independent of age. The chondrocytes from adult donors showed a more stable expression (up to P3) of some (Col6, Fibromodulin, SOX6, TGβ1) markers of mature cartilage; these markers could be tested as parameter to determine the dedifferentiation level. This study can provide parameters to identify up to which "culture step" chondrocytes for implantation with a conserved phenotypic potential can be obtained, and to test the efficiency of biomaterial scaffold or chondroinductive media/signals to maintain/recover the chondrocyte phenotype. Moreover, the determination of levels and time related expression of these markers can be useful during the chondroinduction of mesenchymal stem cells.

Inhibition of CD44 intracellular domain production suppresses bovine articular chondrocyte de-differentiation induced by excessive mechanical stress loading

CD44 fragmentation is enhanced in chondrocytes of osteoarthritis (OA) patients. We hypothesized that mechanical stress-induced enhancement of CD44-intracellular domain (CD44-ICD) production plays an important role in the de-differentiation of chondrocytes and OA. This study aimed to assess the relationship between CD44-ICD and chondrocyte gene expression. Monolayer cultured primary bovine articular chondrocytes (BACs) were subjected to cyclic tensile strain (CTS) loading. ADAM10 inhibitor (GI254023X) and γ-secretase inhibitor (DAPT) were used to inhibit CD44 cleavage. In overexpression experiments, BACs were electroporated with a plasmid encoding CD44-ICD. CTS loading increased the expression of ADAM10 and subsequent CD44 cleavage, while decreasing the expression of SOX9, aggrecan, and type 2 collagen (COL2). Overexpression of CD44-ICD also resulted in decreased expression of these chondrocyte genes. Both GI254023X and DAPT reduced the production of CD44-ICD upon CTS loading, and significantly rescued the reduction of SOX9 expression by CTS loading. Chemical inhibition of CD44-ICD production also rescued aggrecan and COL2 expression following CTS loading. Our findings suggest that CD44-ICD is closely associated with the de-differentiation of chondrocytes. Excessive mechanical stress loading promoted the de-differentiation of BACs by enhancing CD44 cleavage and CD44-ICD production. Suppression of CD44 cleavage has potential as a novel treatment strategy for OA.

The Effects of ROCK Inhibition on Mesenchymal Stem Cell Chondrogenesis Are Culture Model Dependent

Rho-associated protein kinase (ROCK) signaling correlates with cell shape, with decreased cell spreading accompanied by decreased ROCK activity. However, how cell shape and ROCK activity impact the chondrogenesis of mesenchymal stem cells (MSCs) remains inconclusive. Here we examine the effects of ROCK inhibition on human MSC chondrogenesis in four different culture models, including three-dimensional (3D) microribbon (μRB) scaffolds, two-dimensional hydrogel (2D-HG) substrates, 3D hydrogels (3D-HGs), and pellet. For each culture model involving biomaterials, four polymers were compared, including gelatin, chondroitin sulfate, hyaluronic acid, and polyethylene glycol. ROCK inhibition decreased MSC chondrogenesis in μRB model, enhanced chondrogenesis in pellet, and had minimal effect in 2D-HG or 3D-HG models. Furthermore, we demonstrate that MSC chondrogenesis cannot be predicted using ROCK signaling alone. While varying biomaterial compositions can impact the amount or phenotype of resulting cartilage, varying biomaterials did not change the chondrogenic response to ROCK inhibition within each culture model. Regardless of culture model or ROCK expression, increased cartilage formation was always accompanied by enhanced N-cadherin expression and production, suggesting that N-cadherin is a robust marker to select culture conditions that promote chondrogenesis. Together, the results from this study may be used to enhance MSC-based cartilage regeneration in different culture models. Impact Statement Here we assessed the effects of Rho-associated protein kinase (ROCK) inhibition on mesenchymal stem cell (MSC) chondrogenesis in different culture models, including three-dimensional (3D) microribbon scaffolds, two-dimensional hydrogel substrates, 3D hydrogels, and pellet culture. Our results demonstrate that effects of ROCK inhibition on MSC chondrogenesis differ substantially depending on culture models. Furthermore, MSC chondrogenesis cannot be predicted using ROCK signaling alone. The results from this study fill in a gap of knowledge in the correlation between ROCK signaling and MSC chondrogenesis, which may be used to enhance MSC-based cartilage regeneration in different culture models.

Programmed conversion of hypertrophic chondrocytes into osteoblasts and marrow adipocytes within zebrafish bones

Much of the vertebrate skeleton develops from cartilage templates that are progressively remodeled into bone. Lineage tracing studies in mouse suggest that chondrocytes within these templates persist and become osteoblasts, yet the underlying mechanisms of this process and whether chondrocytes can generate other derivatives remain unclear. We find that zebrafish cartilages undergo extensive remodeling and vascularization during juvenile stages to generate fat-filled bones. Growth plate chondrocytes marked by sox10 and col2a1a contribute to osteoblasts, marrow adipocytes, and mesenchymal cells within adult bones. At the edge of the hypertrophic zone, chondrocytes re-enter the cell cycle and express leptin receptor (lepr), suggesting conversion into progenitors. Further, mutation of matrix metalloproteinase 9 (mmp9) results in delayed growth plate remodeling and fewer marrow adipocytes. Our data support Mmp9-dependent growth plate remodeling and conversion of chondrocytes into osteoblasts and marrow adipocytes as conserved features of bony vertebrates.

The MEK-ERK1/2 signaling pathway regulates hyaline cartilage formation and the redifferentiation of dedifferentiated chondrocytes in vitro

The aim of this study was to investigate the role of the mitogen-activated protein kinase kinase-extracellular signal-regulated kinases 1/2 (MEK-ERK1/2) signaling pathway in chondrocyte differentiation and cartilage tissue construction in vitro. Chondrocytes were stimulated with rat serum (RS) and fetal bovine serum (FBS), and chondrocyte phenotypes were investigated microscopically. Chondrocyte proliferation was analyzed using fluorescence activated cell sorting (FACS) and the CCK8 method. Protein and mRNA expressions were assessed by western blot and RT-qPCR. Constructed cartilage tissues were examined by Safranin O-Fast Green FCF staining and immunofluorescence. In contrast to FBS, RS induced rapid dedifferentiation of chondrocytes and decreased type II collagen expression and proteoglycan synthesis. ERK1/2 and type I collagen expression increased during dedifferentiation and decreased during redifferentiation. Increased MEK-ERK1/2 pathway activity resulted in chondrocyte dedifferentiation, and inhibition of ERK1/2 by the inhibitor PD0325901 reversed dedifferentiation and led to redifferentiation. These data suggest strongly that inhibition of MEK-ERK1/2 activation prevents chondrocyte dedifferentiation and fibrocartilage formation.

In search of chondrocyte-specific antigen

The purpose of this work was to establish, whether rat chondrocyte associated antigen, transmembrane Tmp21 protein belonging to the p24 protein family may immunize rats and thus be included into the panel of immunogens potentially involved in cartilage pathology. For immunization of rats extract from cultured chondrocytes containing surface chondrocyte proteins suspended in incomplete Freund's adjuvant was used. Control animals were injected with incomplete Freund's adjuvant without chondrocyte extract. Morphological observations indicated that both in control and experimental animals occurred subperiosteal resorption of bone, suggesting that it arised as the response to adjuvant. In trachea, however, resorption of cartilage and inflammatory changes in the respiratory epithelium and lamina propria were present only in animals exposed to antigen. Unexpectedly, sera from immunized rats strongly reacted with other antigen, which we were able to identify by Western blot and protein sequencing as cartilage oligomeric matrix protein (COMP). COMP is attached to chondrocyte membrane by integrins and its presence in chondrocyte extract is not surprising. Antibody response to COMP raises a question whether the observed changes in tracheal cartilage and epithelium represent anti-COMP reaction or were caused by some other, no specified factors. COMP is used as the marker of osteoarthritis progression, but its role in polychondritis, cartilage pathology involving i.a. tracheal cartilage resorption remains unknown. Thus, our observations may serve as the starting point for future studies in this direction.

Maintenance of chondrocyte phenotype during expansion on PLLA microtopographies

Articular chondrocytes are difficult to grow, as they lose their characteristic phenotype following expansion on standard tissue culture plates. Here, we show that culturing them on surfaces of poly(L-lactic acid) of well-defined microtopography allows expansion and maintenance of characteristic chondrogenic markers. We investigated the dynamics of human chondrocyte dedifferentiation on the different poly(L-lactic acid) microtopographies by the expression of collagen type I, collagen type II and aggrecan at different culture times. When seeded on poly(L-lactic acid), chondrocytes maintained their characteristic hyaline phenotype up to 7 days, which allowed to expand the initial cell population approximately six times without cell dedifferentiation. Maintenance of cell phenotype was afterwards correlated to cell adhesion on the different substrates. Chondrocytes adhesion occurs via the α₅β₁ integrin on poly(L-lactic acid), suggesting cell–fibronectin interactions. However, α₂β₁ integrin is mainly expressed on the control substrate after 1 day of culture, and the characteristic chondrocytic markers are lost (collagen type II expression is overcome by the synthesis of collagen type I). Expanding chondrocytes on poly(L-lactic acid) might be an effective solution to prevent dedifferentiation and improving the number of cells needed for autologous chondrocyte transplantation.

Antigenic and immunogenic properties of chondrocytes. Implications for chondrocyte therapeutic transplantation and pathogenesis of inflammatory and degenerative joint diseases

In physiological conditions chondrocytes are protected from contact with immunocompetent cells by the extracellular matrix, and transplanted fragments of allogeneic cartilage are not rejected. Cartilage produced by allogeneic chondrocytes, however, evokes the immune response of the recipient and is gradually destroyed. Immunisation by allogeneic chondrocytes is induced by the contact of their surface molecules with cells of the immune system. Chondrocytes constitutively express class I and, in some species, class II major histocompatibility complex (MHC) molecules. Expression of MHC class II molecules is induced in vitro by pro-inflammatory cytokines and in vivo in the course of the rejection of transplanted allogeneic cartilage. Low level of MHC class II molecules is found on the surface of human articular chondrocytes in patients with rheumatoid arthritis and osteoarthritis. Cartilage produced by transplanted allogeneic chondrocytes is destroyed by monocytes/macrophages and cytotoxic T and natural killer (NK) cells. NK cells show spontaneous cytotoxic reactivity against isolated chondrocytes and participate in the rejection of transplanted isolated chondrocytes. Chondrocytes express molecules that can serve as potential antigens in inflammatory joint diseases. Chondrocytes express cartilage-specific membrane antigen (CH65), human cartilage glycoprotein-39 (HC gp-39), hyaluronan binding adhesion molecule CD44, thymocyte antigen-1 (Thy-1) – CD90, signal transducer – CD24, lymphocyte function-associated antigen-3 (LFA-3) – CD58, and type I transmembrane protein Tmp21. On the other hand, although chondrocytes express major histocompatibility complex (MHC) class I and class II molecules, they can also exert immunosuppressive and immunomodulatory effects on immunocompetent cells. Isolated chondrocytes do not trigger an efficient allogeneic immune response in vitro and suppress, in a contact-dependent manner, proliferation of activated T cells. This suppression is associated with the expression by chondrocytes of multiple negative regulators of immune response. Chondrocytes express programmed death-ligand (PD-L), chondromodulin-I and indoleamine 2,3-dioxygenase (IDO), molecules that promote self-tolerance and suppress the immune system.

Use of mesenchymal stem cells seeded on the scaffold in articular cartilage repair

Articular cartilage has poor capacity for repair. Once damaged, they degenerate, causing functional impairment of joints. Allogeneic cartilage transplantation has been performed for functional recovery of articular cartilage. However, there is only a limited amount of articular cartilage available for transplantation. Mesenchymal stem cells (MSCs) could be potentially suitable for local implantation. MSCs can differentiate into chondrocytes. Several studies have demonstrated the therapeutic potential of MSCs in the repair of articular cartilage in animal models of articular cartilage damage and in patients with damaged articular cartilage. To boost post-implantation MSC differentiation into chondrocytes, the alternative delivery methods by scaffolds, using hyaluronic acid (HA) or poly-lactic-co-glycolic-acid (PLGA), have developed. In this review, we report recent data on the repair of articular cartilage and discuss future developments.

Effects of Type I Collagen Concentration in Hydrogel on the Growth and Phenotypic Expression of Rat Chondrocytes

It is controversial whether type I collagen itself can maintain and improve chondrogenic phenotype of chondrocytes in a three-dimensional (3D) environment. In this study, we examined the effect of type I collagen concentration in hydrogel (0.5, 1, and 2 mg/ml) on the growth and phenotype expression of rat chondrocytes in vitro. All collagen hydrogels showed substantial contractions during culture, in a concentration-dependent manner, which was due to the cell proliferation. The cell viability was shown to be the highest in 2 mg/ml collagen gel. The mRNA expression of chondrogenic phenotypes, including SOX9, type II collagen, and aggrecan, was significantly up-regulated, particularly in 1 mg/ml collagen gel. Furthermore, the production of type II collagen and glycosaminoglycan (GAG) content was also enhanced. The results suggest that type I collagen hydrogel is not detrimental to, but may be useful for, the chondrocyte culture for cartilage tissue engineering.

Physiological concentrations of soluble uric acid are chondroprotective and anti-inflammatory

High uric acid levels are a risk factor for cardiovascular disorders and gout; however, the role of physiological concentrations of soluble uric acid (sUA) is poorly understood. This study aimed to clarify the effects of sUA in joint inflammation. Both cell cultures of primary porcine chondrocytes and mice with collagen-induced arthritis (CIA) were examined. We showed that sUA inhibited TNF-α- and interleukin (IL)-1β–induced inducible nitric oxide synthase, cyclooxygenase-2 and matrix metalloproteinase (MMP)-13 expression. Examination of the mRNA expression of several MMPs and aggrecanases confirmed that sUA exerts chondroprotective effects by inhibiting the activity of many chondro-destructive enzymes. These effects attenuated collagen II loss in chondrocytes and reduced proteoglycan degradation in cartilage explants. These results were reproduced in chondrocytes cultured in three-dimensional (3-D) alginate beads. Molecular studies revealed that sUA inhibited the ERK/AP-1 signalling pathway, but not the IκBα-NF-κB signalling pathway. Increases in plasma uric acid levels facilitated by the provision of oxonic acid, a uricase inhibitor, to CIA mice exerted both anti-inflammatory and arthroprotective effects in these animals, as demonstrated by their arthritis severity scores and immunohistochemical analysis results. Our study demonstrated that physiological concentrations of sUA displayed anti-inflammatory and chondroprotective effects both in vitro and in vivo.

Building and maintaining joints by exquisite local control of cell fate

We owe the flexibility of our bodies to sophisticated articulations between bones. Establishment of these joints requires the integration of multiple tissue types: permanent cartilage that cushions the articulating bones, synovial membranes that enclose a lubricating fluid-filled cavity, and a fibrous capsule and ligaments that provide structural support. Positioning the prospective joint region involves establishment of an "interzone" region of joint progenitor cells within a nascent cartilage condensation, which is achieved through the interplay of activators and inhibitors of multiple developmental signaling pathways. Within the interzone, tight regulation of BMP and TGFβ signaling prevents the hypertrophic maturation of joint chondrocytes, in part through downstream transcriptional repressors and epigenetic modulators. Synovial cells then acquire further specializations through expression of genes that promote lubrication, as well as the formation of complex structures such as cavities and entheses. Whereas genetic investigations in mice and humans have uncovered a number of regulators of joint development and homeostasis, recent work in zebrafish offers a complementary reductionist approach toward understanding joint positioning and the regulation of chondrocyte fate at joints. The complexity of building and maintaining joints may help explain why there are still few treatments for osteoarthritis, one of the most common diseases in the human population. A major challenge will be to understand how developmental abnormalities in joint structure, as well as postnatal roles for developmental genes in joint homeostasis, contribute to birth defects and degenerative diseases of joints. WIREs Dev Biol 2017, 6:e245. doi: 10.1002/wdev.245 For further resources related to this article, please visit the WIREs website.

Efficiency of Human Epiphyseal Chondrocytes with Differential Replication Numbers for Cellular Therapy Products

The cell-based therapy for cartilage or bone requires a large number of cells; serial passages of chondrocytes are, therefore, needed. However, fates of expanded chondrocytes from extra fingers remain unclarified. The chondrocytes from human epiphyses morphologically changed from small polygonal cells to bipolar elongated spindle cells and to large polygonal cells with degeneration at early passages. Gene of type II collagen was expressed in the cells only at a primary culture (Passage 0) and Passage 1 (P1) cells. The nodules by implantation of P0 to P8 cells were composed of cartilage and perichondrium. The cartilage consisted of chondrocytes with round nuclei and type II collagen-positive matrix, and the perichondrium consisted of spindle cells with type I collage-positive matrix. The cartilage and perichondrium developed to bone with marrow cavity through enchondral ossification. Chondrogenesis and osteogenesis by epiphyseal chondrocytes depended on replication number in culture. It is noteworthy to take population doubling level in correlation with pharmaceutical efficacy into consideration when we use chondrocytes for cell-based therapies.

Lessons on skeletal cell plasticity from studying jawbone regeneration in zebrafish

Three major mesenchymal cell types have important roles in determining the shapes of vertebrate animals: bone-producing osteoblasts, cartilage-producing chondrocytes, and fat-producing adipocytes. Although often considered discrete cell types, accumulating evidence is revealing mesenchymal cells of intermediate identities and interconversion of cell types. Such plasticity is particularly evident during adult skeletal repair. In this Review, we highlight recent work in zebrafish showing a role for hybrid cartilage-bone cells in large-scale regeneration of the adult jawbone, as well as their origins in the periosteum. An emerging theme is that the unique mechanical and signaling environment of the adult wound causes skeletal cell differentiation to diverge from the discrete lineages seen during development, which may aid in rapid and extensive regeneration of bone.

Ihha induces hybrid cartilage-bone cells during zebrafish jawbone regeneration

The healing of bone often involves a cartilage intermediate, yet how such cartilage is induced and utilized during repair is not fully understood. By studying a model of large-scale bone regeneration in the lower jaw of adult zebrafish, we show that chondrocytes are crucial for generating thick bone during repair. During jawbone regeneration, we find that chondrocytes co-express genes associated with osteoblast differentiation and produce extensive mineralization, which is in marked contrast to the behavior of chondrocytes during facial skeletal development. We also identify the likely source of repair chondrocytes as a population of Runx2(+)/Sp7(-) cells that emanate from the periosteum, a tissue that normally contributes only osteoblasts during homeostasis. Analysis of Indian hedgehog homolog a (ihha) mutants shows that the ability of periosteal cells to generate cartilage in response to injury depends on a repair-specific role of Ihha in the induction as opposed to the proliferation of chondrocytes. The large-scale regeneration of the zebrafish jawbone thus employs a cartilage differentiation program distinct from that seen during development, with the bone-forming potential of repair chondrocytes potentially due to their derivation from osteogenic cells in the periosteum.

AIMP1 downregulation restores chondrogenic characteristics of dedifferentiated/degenerated chondrocytes by enhancing TGF-β signal

Dedifferentiation and degeneration of chondrocytes critically influences the efficiency of cartilage repair. One of the causes is the defect of transforming growth factor (TGF)-β signaling that promotes chondrogenic differentiation and degeneration. In the present study, we found that aminoacyl-tRNA synthetase-interacting multifunctional protein 1 (AIMP1) negatively regulates TGF-β signaling via interactions with Smad2 and Smad3 in immunoprecipitation assay and luciferase assay. In addition, we observed that the AIMP1 expression level was significantly increased in osteoarthritis (OA) patient-derived degenerated chondrocytes compared with healthy control. So, we hypothesized that downregulation of AIMP1 using small-interfering RNA (siRNA) technology in dedifferentiated (collected at passage #6) and degenerated (obtained from OA-affected areas) chondrocytes could lead to recover TGF-β signaling in both chondrocytes. Indeed, AIMP1 downregulation restored TGF-β signaling by promoting phosphorylation of Smad2 and Smad3, which shows redifferentiated characteristics in both dedifferentiated and degenerated chondrocytes. Additionally, implantation analyses using in vivo mouse model clearly showed that AIMP1 downregulation resulted in the increased chondrogenic potential as well as the enhanced cartilage tissue formation in both dedifferentiated and degenerated chondrocytes. Histological analyses clarified that AIMP1 downregulation increased expression levels of collagen type II (Col II) and aggrecan, but not Col I expression. Taken together, these data indicate that AIMP1 downregulation using siRNA is a novel tool to restore TGF-β signaling and thereby increases the chondrogenic potential of dedifferentiated/degenerated chondrocytes, which could be further developed as a therapeutic siRNA to treat OA.

Collagen Type II enhances chondrogenic differentiation in agarose-based modular microtissues

BACKGROUND AIMS

Cell-based therapies have made an impact on the treatment of osteoarthritis; however, the repair and regeneration of thick cartilage defects is an important and growing clinical problem. Next-generation therapies that combine cells with biomaterials may provide improved outcomes. We have developed modular microenvironments that mimic the composition of articular cartilage as a delivery system for consistently differentiated cells.

METHODS

Human bone marrow-derived mesenchymal stem cells (MSC) were embedded in modular microbeads consisting of agarose (AG) supplemented with 0%, 10% and 20% collagen Type II (COL-II) using a water-in-oil emulsion technique. AG and AG/COL-II microbeads were characterized in terms of their structural integrity, size distribution and protein content. The viability of embedded MSC and their ability to differentiate into osteogenic, adipogenic and chondrogenic lineages over 3 weeks in culture were also assessed.

RESULTS

Microbeads made with <20% COL-II were robust, generally spheroidal in shape and 80 ± 10 µm in diameter. MSC viability in microbeads was consistently high over a week in culture, whereas viability in corresponding bulk hydrogels decreased with increasing COL-II content. Osteogenic differentiation of MSC was modestly supported in both AG and AG/COL-II microbeads, whereas adipogenic differentiation was strongly inhibited in COL-II containing microbeads. Chondrogenic differentiation of MSC was clearly promoted in microbeads containing COL-II, compared with pure AG matrices.

CONCLUSIONS

Inclusion of collagen Type II in agarose matrices in microbead format can potentiate chondrogenic differentiation of human MSC. Such compositionally tailored microtissues may find utility for cell delivery in next-generation cartilage repair therapies.

Analyzing Biological Performance of 3D-Printed, Cell-Impregnated Hybrid Constructs for Cartilage Tissue Engineering

Three-dimensional (3D) bioprinting of hybrid constructs is a promising biofabrication method for cartilage tissue engineering because a synthetic polymer framework and cell-impregnated hydrogel provide structural and biological features of cartilage, respectively. During bioprinting, impregnated cells may be subjected to high temperatures (caused by the adjacent melted polymer) and process-induced mechanical forces, potentially compromising cell function. This study addresses these biofabrication issues, evaluating the heat distribution of printed polycaprolactone (PCL) strands and the rheological property and structural stability of alginate hydrogels at various temperatures and concentrations. The biocompatibility of parameters from these studies was tested by culturing 3D hybrid constructs bioprinted with primary cells from embryonic chick cartilage. During initial two-dimensional culture expansion of these primary cells, two morphologically and molecularly distinct cell populations ("rounded" and "fibroblastic") were isolated. The biological performance of each population was evaluated in 3D hybrid constructs separately. The cell viability, proliferation, and cartilage differentiation were observed at high levels in hybrid constructs of both cell populations, confirming the validity of these 3D bioprinting parameters for effective cartilage tissue engineering. Statistically significant performance variations were observed, however, between the rounded and fibroblastic cell populations. Molecular and morphological data support the notion that such performance differences may be attributed to the relative differentiation state of rounded versus fibroblastic cells (i.e., differentiated chondrocytes vs. chondroprogenitors, respectively), which is a relevant issue for cell-based tissue engineering strategies. Taken together, our study demonstrates that bioprinting 3D hybrid constructs of PCL and cell-impregnated alginate hydrogel is a promising approach for cartilage tissue engineering.

Effects of Nanoscale Spatial Arrangement of Arginine-Glycine-Aspartate Peptides on Dedifferentiation of Chondrocytes

Cell dedifferentiation is of much importance in many cases such as the classic problem of dedifferentiation of chondrocytes during in vitro culture in cartilage tissue engineering. While cell differentiation has been much investigated, studies of cell dedifferentiation are limited, and the nanocues of cell dedifferentiation have little been reported. Herein, we prepared nanopatterns and micro/nanopatterns of cell-adhesive arginine-glycine-aspartate (RGD) peptides on nonfouling poly(ethylene glycol) (PEG) hydrogels to examine the effects of RGD nanospacing on adhesion and dedifferentiation of chondrocytes. The relatively larger RGD nanospacing above 70 nm was found to enhance the maintainence of the chondrocyte phenotype in two-dimensional culture, albeit not beneficial for adhesion of chondrocytes. A unique micro/nanopattern was employed to decouple cell spreading, cell shape, and cell-cell contact from RGD nanospacing. Under given spreading size and shape of single cells, the large RGD nanospacing was still in favor of preserving the normal phenotype of chondrocytes. Hence, the nanoscale spatial arrangement of cell-adhesive ligands affords a new independent regulator of cell dedifferentiation, which should be taken into consideration in biomaterial design for regenerative medicine.

Modulation of the Effect of Transforming Growth Factor-β3 by Low-Intensity Pulsed Ultrasound on Scaffold-Free Dedifferentiated Articular Bovine Chondrocyte Tissues

The aim of this study was to evaluate how low-intensity pulsed ultrasound (LIPUS) modulates the effect of transforming growth factor-β3 (TGF-β3) on the differentiation of scaffold-free dedifferentiated bovine articular chondrocyte tissues toward a cartilage-like phenotype. Specifically, the effect of these stimuli on the expression of hypertrophic markers collagen type I, collagen type X, and cartilage-degrading collagenase gene expression for a scaffold-free model was analyzed. A bioreactor that applied LIPUS directly from the transducer through a silicone gel to a six-well plate containing the tissues allowed simple, sterile, and large-scale experiments. Tissues were subjected to LIPUS of 55 mW/cm(2) in a 200 μs burst sine wave of 1 MHz over a 10-day period with or without TGF-β3 (10 ng/mL). Tissues exposed to TGF-β3 had significantly increased glycosaminoglycan and total collagen protein production along with upregulated cartilage-specific gene expression, resulting in tissues with a higher Young's Modulus. However, these tissues had also upregulated gene expression for hypertrophic markers collagen type I, collagen type X, MMP-1, MMP-13, MMP-2, and also an increase in the phosphorylation of p38. The expression of these matrix-degrading enzymes was remediated by hypertrophic development and differentiate dedifferentiated bovine articular chondrocytes towards a chondrogenic lineage allowing it to be a valuable tool in cartilage tissue engineering.

Tissue engineering strategies to study cartilage development, degeneration and regeneration

Cartilage tissue engineering has primarily focused on the generation of grafts to repair cartilage defects due to traumatic injury and disease. However engineered cartilage tissues have also a strong scientific value as advanced 3D culture models. Here we first describe key aspects of embryonic chondrogenesis and possible cell sources/culture systems for in vitro cartilage generation. We then review how a tissue engineering approach has been and could be further exploited to investigate different aspects of cartilage development and degeneration. The generated knowledge is expected to inform new cartilage regeneration strategies, beyond a classical tissue engineering paradigm.

Long-term expansion, enhanced chondrogenic potential, and suppression of endochondral ossification of adult human MSCs via WNT signaling modulation

Mesenchymal stem cells (MSCs) are a potential source of chondrogenic cells for the treatment of cartilage disorders, but loss of chondrogenic potential during in vitro expansion and the propensity of cartilage to undergo hypertrophic maturation impede their therapeutic application. Here we report that the signaling protein WNT3A, in combination with FGF2, supports long-term expansion of human bone marrow-derived MSCs. The cells retained their chondrogenic potential and other phenotypic and functional properties of multipotent MSCs, which were gradually lost in the absence of WNT3A. Moreover, we discovered that endogenous WNT signals are the main drivers of the hypertrophic maturation that follows chondrogenic differentiation. Inhibition of WNT signals during differentiation prevented calcification and maintained cartilage properties following implantation in a mouse model. By maintaining potency during expansion and preventing hypertrophic maturation following differentiation, the modulation of WNT signaling removes two major obstacles that impede the clinical application of MSCs in cartilage repair.

•

WNT3A and FGF2 synergistically promote MSC proliferation

•

WNT3A and FGF2 synergistically enhance MSC chondrogenic potential during expansion

•

WNT3A and FGF2 maintain MSC characteristics over multiple passages

•

In vitro WNT signaling modulation leads to stable cartilage formation in vivo

Chondroitin sulfate microparticles modulate transforming growth factor-β1-induced chondrogenesis of human mesenchymal stem cell spheroids

Mesenchymal stem cells (MSCs) have been previously explored as a part of cell-based therapies for the repair of damaged cartilage. Current MSC chondrogenic differentiation strategies employ large pellets; however, we have developed a technique to form small MSC aggregates (500-1,000 cells) that can reduce transport barriers while maintaining a multicellular structure analogous to cartilaginous condensations. The objective of this study was to examine the effects of incorporating chondroitin sulfate methacrylate (CSMA) microparticles (MPs) within small MSC spheroids cultured in the presence of transforming growth factor (TGF)-β1 on chondrogenesis. Spheroids with MPs induced earlier increases in collagen II and aggrecan gene expression (chondrogenic markers) than spheroids without MPs, although no large differences in immunostaining for these matrix molecules were observed by day 21 between these groups. Collagen I and X were also detected in the extracellular matrix (ECM) of all spheroids by immunostaining. Interestingly, histology revealed that CSMA MPs clustered together near the center of the MSC spheroids and induced circumferential alignment of cells and ECM around the material core. This study demonstrates the use of CSMA materials to further examine the effects of matrix molecules on MSC phenotype as well as potentially direct differentiation in a more spatially controlled manner that better mimics the architecture of specific musculoskeletal tissues.

Cannabinoid WIN-55,212-2 mesylate inhibits interleukin-1β induced matrix metalloproteinase and tissue inhibitor of matrix metalloproteinase expression in human chondrocytes

OBJECTIVE

Interleukin-1β (IL-1β) is involved in the up-regulation of matrix metalloproteinases (MMPs) leading to cartilage degradation. Cannabinoids are anti-inflammatory and reduce joint damage in animal models of arthritis. This study aimed to determine a mechanism whereby the synthetic cannabinoid WIN-55,212-2 mesylate (WIN-55) may inhibit cartilage degradation.

METHODS

Effects of WIN-55 were studied on IL-1β stimulated production of MMP-3 and -13 and their inhibitors TIMP-1 and -2 in human chondrocytes. Chondrocytes were obtained from articular cartilage of patients undergoing total knee replacement. Chondrocytes were grown in monolayer and 3D alginate bead cultures. Real-time polymerase chain reaction (PCR) was used to determine the gene expression of MMP-3, -13, TIMP-1 and -2 and Enzyme Linked Immunosorbent Assay (ELISA) to measure the amount of MMP-3 and MMP-13 protein released into media. Immunocytochemistry was used to investigate the expression of cannabinoid receptors in chondrocyte cultures.

RESULTS

Treatment with WIN-55 alone or in combination with IL-1β, decreased or abolished MMP-3, -13, TIMP-1 and -2 gene expression in human chondrocyte monolayer and alginate bead cultures in both a concentration and time dependent manner. WIN-55 treatment alone, and in combination with IL-1β, reduced MMP-3 and -13 protein production by chondrocytes cultured in alginate beads. Immunocytochemistry demonstrated the expression of cannabinoid receptors in chondrocyte cultures.

CONCLUSION

Cannabinoid WIN-55 can reduce both basal and IL-1β stimulated gene and protein expression of MMP-3 and -13. However WIN-55 also decreased basal levels of TIMP-1 and -2 mRNA. These actions of WIN-55 suggest a mechanism by which cannabinoids may act to prevent cartilage breakdown in arthritis.

Mesenchymal stem cells in the treatment of traumatic articular cartilage defects: a comprehensive review

Articular cartilage has a limited capacity to repair following injury. Early intervention is required to prevent progression of focal traumatic chondral and osteochondral defects to advanced cartilage degeneration and osteoarthritis. Novel cell-based tissue engineering techniques have been proposed with the goal of resurfacing defects with bioengineered tissue that recapitulates the properties of hyaline cartilage and integrates into native tissue. Transplantation of mesenchymal stem cells (MSCs) is a promising strategy given the high proliferative capacity of MSCs and their potential to differentiate into cartilage-producing cells - chondrocytes. MSCs are historically harvested through bone marrow aspiration, which does not require invasive surgical intervention or cartilage extraction from other sites as required by other cell-based strategies. Biomaterial matrices are commonly used in conjunction with MSCs to aid cell delivery and support chondrogenic differentiation, functional extracellular matrix formation and three-dimensional tissue development. A number of specific transplantation protocols have successfully resurfaced articular cartilage in animals and humans to date. In the clinical literature, MSC-seeded scaffolds have filled a majority of defects with integrated hyaline-like cartilage repair tissue based on arthroscopic, histologic and imaging assessment. Positive functional outcomes have been reported at 12 to 48 months post-implantation, but future work is required to assess long-term outcomes with respect to other treatment modalities. Despite relatively positive outcomes, further investigation is required to establish a consensus on techniques for treatment of chondral and osteochondral defects with respect to cell source, isolation and expansion, implantation density, in vitro precultivation, and scaffold composition. This will allow for further optimization of MSC proliferation, chondrogenic differentiation, bioengineered cartilage integration, and clinical outcome.

Interference with the contractile machinery of the fibroblastic chondrocyte cytoskeleton induces re-expression of the cartilage phenotype through involvement of PI3K, PKC and MAPKs

Chondrocytes rapidly lose their phenotypic expression of collagen II and aggrecan when grown on 2D substrates. It has generally been observed that a fibroblastic morphology with strong actin-myosin contractility inhibits chondrogenesis, whereas chondrogenesis may be promoted by depolymerization of the stress fibers and/or disruption of the physical link between the actin stress fibers and the ECM, as is the case in 3D hydrogels. Here we studied the relationship between the actin-myosin cytoskeleton and expression of chondrogenic markers by culturing fibroblastic chondrocytes in the presence of cytochalasin D and staurosporine. Both drugs induced collagen II re-expression; however, renewed glycosaminoglycan synthesis could only be observed upon treatment with staurosporine. The chondrogenic effect of staurosporine was augmented when blebbistatin, an inhibitor of myosin/actin contractility, was added to the staurosporine-stimulated cultures. Furthermore, in 3D alginate cultures, the amount of staurosporine required to induce chondrogenesis was much lower compared to 2D cultures (0.625 nM vs. 2.5 nM). Using a selection of specific signaling pathway inhibitors, it was found that PI3K-, PKC- and p38-MAPK pathways positively regulated chondrogenesis while the ERK-pathway was found to be a negative regulator in staurosporine-induced re-differentiation, whereas down-regulation of ILK by siRNA indicated that ILK is not determining for chondrocyte re-differentiation. Furthermore, staurosporine analog midostaurin displayed only a limited chondrogenic effect, suggesting that activation/deactivation of a specific set of key signaling molecules can control the expression of the chondrogenic phenotype. This study demonstrates the critical importance of mechanobiological factors in chondrogenesis suggesting that the architecture of the actin cytoskeleton and its contractility control key signaling molecules that determine whether the chondrocyte phenotype will be directed along a fibroblastic or chondrogenic path.

A unique tool to selectively detect the chondrogenic IIB form of human type II procollagen protein

Type II collagen, the major fibrillar collagen of cartilage, is synthesized as precursor forms (procollagens) containing N- and C-terminal propeptides. Three splice variants are thought to be translated to produce procollagen II isoforms (IIA/D and IIB) which differ in their amino propeptide parts. The IIA and IID are transient embryonic isoforms that include an additional cysteine-rich domain encoded by exon 2. The IIA and IID transcripts are co-expressed during chondrogenesis then decline and the IIB isoform is the only one expressed and synthesized in fully differentiated chondrocytes. Additionally, procollagens IIA/D can be re-expressed by dedifferentiating chondrocytes and in osteoarthritic cartilage. Therefore, it is an important point to determine which isoform(s) is (are) synthesized in vivo in normal and pathological situations and in vitro, to fully assess the phenotype of cells producing type II collagen protein. Antibodies directed against the cysteine-rich extra domain found in procollagens IIA and IID are already available but antibodies detecting only the chondrogenic IIB form of type II procollagen were missing so far. A synthetic peptide encompassing the junction between exon 1 and exon 3 of the human sequence was used as immunogen to produce rabbit polyclonal antibodies to procollagen IIB. After affinity purification on immobilized peptide their absence of crossreaction with procollagens IIA/D and with the fibrillar procollagens I, III and V was demonstrated by Western blotting. These antibodies were used to reveal at the protein level that the treatment of dedifferentiated human chondrocytes by bone morphogenic protein (BMP)-2 induces the synthesis of the IIB (chondrocytic) isoform of procollagen II. In addition, immunohistochemical staining of bovine cartilage demonstrates the potential of these antibodies in the analysis of the differential spatiotemporal distribution of N-propeptides of procollagens IIA/D and IIB during normal development and in pathological situations.

Culture of human bone marrow-derived mesenchymal stem cells on of poly(L-lactic acid) scaffolds: potential application for the tissue engineering of cartilage

PURPOSE

Due to the attractive properties of poly(L-lactic acid) (PLLA) for tissue engineering, the aim was to determine the growth and differentiation capacity of mesenchymal stromal cells (MSCs) in PLLA scaffolds and their potential use in the treatment of cartilage diseases.

METHODS

MSCs were cultured in PLLA films and thin porous membranes to study adherence and proliferation. Permeability and porosity were determined for the different scaffolds employed. The optimal conditions for cell seeding were first determined, as well as cell density and distribution inside the PLLA. Scaffolds were then maintained in expansion or chondrogenic differentiation media for 21 days. Apoptosis, proliferation and chondrogenic differentiation was assessed after 21 days in culture by immunohistochemistry. Mechanical characteristics of scaffolds were determined before and after cell seeding.

RESULTS

MSCs uniformly adhered to PLLA films as well as to porous membranes. Proliferation was detected only in monolayers of pure PLLA, but was no longer detected after 10 days. Mechanical characterization of PLLA scaffolds showed differences in the apparent compression elastic modulus for the two sizes used. After determining high efficiencies of seeding, the production of extracellular matrix (ECM) was determined and contained aggrecan and collagens type I and X. ECM produced by the cells induced a twofold increase in the apparent elastic modulus of the composite.

CONCLUSIONS

Biocompatible PLLA scaffolds have been developed that can be efficiently loaded with MSCs. The scaffold supports chondrogenic differentiation and ECM deposition that improves the mechanics of the scaffold. Although this improvement does not met the expectations of a hyaline-like cartilage ECM, in part due to the lack of a mechanical stimulation, their potential use in the treatment of cartilage pathologies encourages to improve the mechanical component.

FGF, TGFβ and Wnt crosstalk: embryonic to in vitro cartilage development from mesenchymal stem cells

Articular cartilage is easily damaged, yet difficult to repair. Cartilage tissue engineering seems a promising therapeutic solution to restore articular cartilage structure and function, with mesenchymal stem cells (MSCs) receiving increasing attention for their promise to promote cartilage repair. It is known from embryology that members of the fibroblast growth factor (FGF), transforming growth factor-β (TGFβ) and wingless-type (Wnt) protein families are involved in controlling different differentiation stages during chondrogenesis. Individually, these pathways have been extensively studied but so far attempts to recapitulate embryonic development in in vitro MSC chondrogenesis have failed to produce stable and functioning articular cartilage; instead, transient hypertrophic cartilage is obtained. We believe a better understanding of the simultaneous integration of these factors will improve how we relate embryonic chondrogenesis to in vitro MSC chondrogenesis. This narrative review attempts to define current knowledge on the crosstalk between the FGF, TGFβ and Wnt signalling pathways during different stages of mesenchymal chondrogenesis. Connecting embryogenesis and in vitro differentiation of human MSCs might provide insights into how to improve and progress cartilage tissue engineering for the future.

Maintenance of "stem cell" features of cartilage cell sub-populations during in vitro propagation

Background

The discovery of mesenchymal stem cells (MSCs) or MSC-like cells in cartilage tissue does not tie in well with the established view that MSCs derive from a perivascular niche. The presence of MSCs may raise concerns about specificity and application safety, particularly in terms of the regulatory site. The aim of the present study was to investigate the benefits or possible risks of the MSC-like properties of cells isolated from cartilage in the context of autologous chondrocyte implantation.

Methods

Chondrocytic cells were isolated from cartilage or intervertebral disc tissue. Flow cytometry was used to analyze the expression of cell surface antigens. MSC-like cells were either enriched or depleted by means of magnetic cell sorting (MACS) involving the monoclonal antibodies W5C5/SUSD2 and W8B2/MSCA-1. We addressed the issues of prolonged expansion of such cells as well as the influence of culture medium as a trigger for selecting a single cell type. Established protocols were used to study in vitro differentiation. In addition to histological and biochemical assessment, the acquired phenotypes were also evaluated on the mRNA transcript level.

Results

In the studied cells, we found strongly analogous expression of antigens typically expressed on MSCs, including CD49e, CD73, CD90, CD105, CD140b and CD166. The expression of W5C5 and W8B2 antigens in cartilage cell sub-populations did not correlate with multi-potency. We demonstrated that a chondroid precursor, but not a bona fide multipotent mesenchymal, cell type can be obtained under established in vitro culture conditions. The culture media used for expansion influenced the cell phenotype.

Conclusions

The risk of adverse adipose or osseous differentiation is not posed by expanded chondrocyte cultures, even after enrichment of putative MSC-like cell populations by MACS. It is possible that this limited “stemness” in chondrocytes, expanded for use in ACI, may instead be beneficial as it allows re-differentiation under appropriate conditions despite prolonged times in culture.

Equine articular chondrocytes on MACT scaffolds for cartilage defect treatment

Treatment of cartilage defects poses challenging problems in human and veterinary medicine, especially in horses. This study examines the suitability of applying scaffold materials similar to those used for human cartilage regeneration on equine chondrocytes. Chondrocytes gained from biopsies of the talocrural joint of three horses were propagated in 2D culture and grown on two different scaffold materials, hyaluronan (HYAFF®) and collagen (BioGide®), and evaluated by light and electron microscopy. The equine chondrocytes developed well in both types of materials. They were vital and physiologically highly active. On the surface of the scaffolds, they formed cell multilayers. Inside the hyaluronan web, the chondrocytes were regularly distributed and spanned the large scaffold fibre distances by producing their own matrix sheath. Half-circle-like depressions occasionally found in the cell membrane were probably related to movement on the flexible matrix sheath. Inside the dense collagen scaffold, only single cells were found. They passed through the scaffold strands by cell shape adaptation. This study showed that the examined scaffold materials can be used for equine chondrocyte cultivation. Chondrocytes tend to form multilayers on the surface of both, very dense and very porous scaffolds, and have strategies to span between and move in large gaps.

Redifferentiation of dedifferentiated human articular chondrocytes: comparison of 2D and 3D cultures

OBJECTIVE

Three-dimensional (3D) cultures are widely used to redifferentiate chondrocytes. However, the rationale behind the choice for 3D above two-dimensional (2D) cultures is poorly systematically investigated and mainly based on mRNA expression and glycosaminoglycan (GAG) content. The objective was to determine the differential redifferentiation characteristics of human articular chondrocytes (HACs) in monolayer, alginate beads and pellet culture by investigating mRNA expression, protein expression, GAG content and cell proliferation.

DESIGN

Dedifferentiated HACs from six individuals were redifferentiated in identical medium conditions for 7 days in monolayer, alginate beads or pellet culture. Read-out parameters were expression of chondrogenic and hypertrophic mRNAs and proteins, GAG content and cell proliferation.

RESULTS

3D cultures specifically expressed chondrogenic mRNAs [collagen type II (COL2A1), SRY (sex determining region Y)-box 9 (SOX9), aggrecan (ACAN)), whereas 2D cultures did not. Hypertrophic mRNAs (collagen type X (COL10A1), runt-related transcription factor 2 (RUNX2), matrix metalloproteinase 13 (MMP13), vascular endothelial growth factor A (VEGFA), osteopontin (OPN), alkaline phosphatase (ALP)) were highly increased in 2D cultures and lower in 3D cultures. Collagen type I (COL1A1) mRNA expression was highest in 3D cultures. Protein expression supports most of the mRNA data, although an important discrepancy was found between mRNA and protein expression of COL2A1 and SOX9 in monolayer culture, stressing on the importance of protein expression analysis. GAG content was highest in 3D cultures, whereas chondrocyte proliferation was almost specific for 2D cultures.

CONCLUSIONS

For redifferentiation of dedifferentiated HACs, 3D cultures exhibit the most potent chondrogenic potential, whereas a hypertrophic phenotype is best achieved in 2D cultures. This is the first human study that systematically evaluates the differences between proliferation, GAG content, protein expression and mRNA expression of commonly used 2D and 3D chondrocyte culture techniques.

Thermally reversible colloidal gels for three-dimensional chondrocyte culture

Healthy cells are required in large numbers to form a tissue-engineered construct and primary cells must therefore be increased in number in a process termed 'expansion'. There are significant problems with existing procedures, including cell injury and an associated loss of phenotype, but three-dimensional culture has been reported to offer a solution. Reversible gels, which allow for the recovery of cells after expansion would therefore have great value in the expansion of chondrocytes for tissue engineering applications, but they have received relatively little attention to date. In this study, we examined the synthesis and use of thermoresponsive polymers that form reversible three-dimensional gels for chondrocyte cell culture. A series of polymers comprising N-isopropylacrylamide (NIPAM) and styrene was synthesized before studying their thermoresponsive solution behaviour and gelation. A poly(NIPAM-co-styrene-graft-N-vinylpyrrolidone) variant was also synthesized in order to provide increased water content. Both random- and graft-copolymers formed particulate gels above the lower critical solution temperature and, on cooling, re-dissolved to allow enzyme-free cell recovery. Chondrocytes remained viable in all of these materials for 24 days, increased in number and produced collagen type II and glycosaminoglycans.

Engineered cartilage maturation regulates cytokine production and interleukin-1β response

BACKGROUND

Because the injured joint has an actively inflammatory environment, the survival and repair potential of cartilage grafts may be influenced by inflammatory processes. Understanding the interactions of those processes with the graft may lead to concepts for pharmacologic or surgical solutions allowing improved cartilage repair.

QUESTIONS/PURPOSES

We asked whether the maturation level of cartilaginous tissues generated in vitro by expanded human articular chondrocytes (HACs) modulate (1) the spontaneous production of cytokines and (2) the response to interleukin (IL)-1β.

METHODS

Twelve pellets/donor prepared with monolayer-expanded HACs (n = 6 donors) were evaluated at six different culture times for mRNA expression (n = 72) and spontaneous baseline release of monocyte chemoattractant protein (MCP)-1, IL-8, and transforming growth factor (TGF)-β1 (n = 72). We cultured 24 pellets/donor from each of four donors for 1 or 14 days (defined as immature and mature, respectively) and exposed the pellets to IL-1β for 3 days. MCP-1, IL-8, TGF-β1, and metalloprotease (MMP)-1 and MMP-13 were quantified in pellets and culture supernatants.

RESULTS

By increasing culture time, the spontaneous release of IL-8 and MCP-1 decreased (12.0- and 5.5-fold, respectively), whereas that of TGF-β1 increased (5.4-fold). As compared with immature pellets, mature pellets responded to IL-1β by releasing lower amounts of MMP-1 (2.9-fold) and MMP-13 (1.7-fold) and increased levels of IL-8, MCP-1, and TGF-β1 (1.5-, 5.0-, and 7.5-fold, respectively). IL-8 and MCP-1 promptly returned to baseline on withdrawal of IL-1β.

CONCLUSIONS

Our observations suggest more mature cartilaginous tissues are more resistant to IL-1β exposure and can activate chemokines required to initiate tissue repair processes.

CLINICAL RELEVANCE

The implantation of more mature cartilaginous tissues might provide superior graft survival and improve/accelerate cartilage repair.

Chondrogenic potential of electrospun nanofibres for cartilage tissue engineering

Articular cartilage has a heterogeneous structure, comprising elongated cells at the articulating surface and rounded cells elsewhere. This feature poses a complex challenge when fabricating 3D tissue engineering scaffolds able to mimic the native extracellular matrix (ECM) of cartilage for tissue repair and regeneration. Nanofibre scaffolds can provide an ECM-like structure, but are mechanically weak and typically have subcellular pore geometries. In this study, the use of poly(L,D-lactide) (PLDLA) nanofibre coatings on PLDLA microfibres or films (nanofibre composites) to influence bovine chondrocyte behaviour was investigated. It was demonstrated that electrospun nanofibres facilitated the adhesion of chondrocytes and helped to maintain smaller projected cell areas and a rounded cell phenotype, when compared to PLDLA films or microfibres. Random nanofibre composites were associated with the smallest and most rounded cells and aligned nanofibre composites also demonstrated a similar tendency. Quantitative PCR revealed that nanofibres promoted the expression of chondrogenic markers, such as collagen type IIaI and aggrecan, while maintaining low levels of collagen IaI. It was also found, by water contact angle measurement, that nanofibres were significantly more hydrophobic than cast films. The lower wettability of polymeric nanofibres favoured the maintenance of rounded chondrocyte morphology. To our knowledge this is the first study to confirm the positive influence on preserving chondrogenic phenotype and gene expression at the interface of true nano-microfibrous composites by using individual microfibres coated with aligned nanofibres. Such composites can potentially be fabricated into mechanically durable 3D scaffolds with better cell infiltration throughout the scaffolds.