Phenotypic characterization of human chondrocyte cell line C-20/A4: a comparison between monolayer and alginate suspension culture

Chondrocyte Invasion May Be a Mechanism for Persistent Staphylococcus Aureus Infection In Vitro

BACKGROUND

Recurrent bone and joint infection with Staphylococcus aureus is common. S. aureus can invade and persist in osteoblasts and fibroblasts, but little is known about this mechanism in chondrocytes. If S. aureus were able to invade and persist within chondrocytes, this could be a difficult compartment to treat.

QUESTION/PURPOSE

Can S. aureus infiltrate and persist intracellularly within chondrocytes in vitro?

METHODS

Cell lines were cultured in vitro and infected with S. aureus. Human chondrocytes (C20A4) were compared with positive controls of human osteoblasts (MG63) and mouse fibroblasts (NIH3T3), which have previously demonstrated S. aureus invasion and persistence (human fibroblasts were not available to us). Six replicates per cell type were followed for 6 days after infection. Cells were treated daily with antibiotic media for extracellular killing. To determine whether S. aureus can infiltrate chondrocytes, fluorescence microscopy was performed to qualitatively assess the presence of intracellular bacteria, and intracellular colony-forming units (CFU) were enumerated 2 hours after infection. To determine whether S. aureus can persist within chondrocytes, intracellular CFUs were enumerated from infected host cells each day postinfection.

RESULTS

S. aureus invaded human chondrocytes (C20A4) at a level (2.8 x 10 5 ± 5.5 x 10 4 CFUs/mL) greater than positive controls of human osteoblasts (MG63) (9.5 x 10 2 ± 2.5 x 10 2 CFUs/mL; p = 0.01) and mouse fibroblasts (NIH3T3) (9.1 x 10 4 ± 2.5 x 10 4 CFUs/mL; p = 0.02). S. aureus also persisted within human chondrocytes (C20A4) for 6 days at a level (1.4 x 10 3 ± 5.3 x 10 2 CFUs/mL) greater than that of human osteoblasts (MG63) (4.3 x 10 2 ± 3.5 x 10 1 CFUs/mL; p = 0.02) and mouse fibroblasts (NIH3T3) (0 CFUs/mL; p < 0.01). S. aureus was undetectable within mouse fibroblasts (NIH3T3) after 4 days. There were 0 CFUs yielded from cell media, confirming extracellular antibiotic treatment was effective.

CONCLUSION

S. aureus readily invaded human chondrocytes (C20A4) in vitro and persisted viably for 6 days after infection, evading extracellular antibiotics. Chondrocytes demonstrated a greater level of intracellular invasion and persistence by S. aureus than positive control human osteoblast (MG63) and mouse fibroblast (NIH3T3) cell lines.

CLINICAL RELEVANCE

Chondrocyte invasion and persistence may contribute to recurrent bone and joint infections. Additional research should assess longer periods of persistence and whether this mechanism is present in vivo.

Isolation, Identification, and Characterization of Bioactive Peptides in Human Bone Cells from Tortoiseshell and Deer Antler Gelatin

Tortoiseshell and deer antler gelatin has been used to treat bone diseases in Chinese society. A pepsin-digested gelatin peptide with osteoblast-proliferation-stimulating properties was identified via LC-MS/MS. The resulting pentapeptide, TSKYR, was presumably subjected to further degradation into TSKY, TSK, and YR fragments in the small intestine. The above four peptides were chemically synthesized. Treatment of tripeptide TSK can lead to a significant 30- and 50-fold increase in the mineralized nodule area and density in osteoblast cells and a 47.5% increase in the number of chondrocyte cells. The calcium content in tortoiseshell was relatively higher than in human soft tissue. The synergistic effects of calcium ions and the peptides were observed for changes in osteoblast proliferation and differentiation. Moreover, these peptides can enhance the expression of RUNX2, OCN, FGFR2, and FRFR3 genes in osteoblasts, and aggrecan and collagen type II in chondrocyte (patent pending).

Combining Innovative Bioink and Low Cell Density for the Production of 3D-Bioprinted Cartilage Substitutes: A Pilot Study

3D bioprinting offers interesting opportunities for 3D tissue printing by providing living cells with appropriate scaffolds with a dedicated structure. Biological advances in bioinks are currently promising for cell encapsulation, particularly that of mesenchymal stem cells (MSCs). We present herein the development of cartilage implants by 3D bioprinting that deliver MSCs encapsulated in an original bioink at low concentration. 3D-bioprinted constructs (10 × 10 × 4 mm) were printed using alginate/gelatin/fibrinogen bioink mixed with human bone marrow MSCs. The influence of the bioprinting process and chondrogenic differentiation on MSC metabolism, gene profiles, and extracellular matrix (ECM) production at two different MSC concentrations (1 million or 2 million cells/mL) was assessed on day 28 (D28) by using MTT tests, real-time RT-PCR, and histology and immunohistochemistry, respectively. Then, the effect of the environment (growth factors such as TGF-β1/3 and/or BMP2 and oxygen tension) on chondrogenicity was evaluated at a 1 M cell/mL concentration on D28 and D56 by measuring mitochondrial activity, chondrogenic gene expression, and the quality of cartilaginous matrix synthesis. We confirmed the safety of bioextrusion and gelation at concentrations of 1 million and 2 million MSC/mL in terms of cellular metabolism. The chondrogenic effect of TGF-β1 was verified within the substitute on D28 by measuring chondrogenic gene expression and ECM synthesis (glycosaminoglycans and type II collagen) on D28. The 1 M concentration represented the best compromise. We then evaluated the influence of various environmental factors on the substitutes on D28 (differentiation) and D56 (synthesis). Chondrogenic gene expression was maximal on D28 under the influence of TGF-β1 or TGF-β3 either alone or in combination with BMP-2. Hypoxia suppressed the expression of hypertrophic and osteogenic genes. ECM synthesis was maximal on D56 for both glycosaminoglycans and type II collagen, particularly in the presence of a combination of TGF-β1 and BMP-2. Continuous hypoxia did not influence matrix synthesis but significantly reduced the appearance of microcalcifications within the extracellular matrix. The described strategy is very promising for 3D bioprinting by the bioextrusion of an original bioink containing a low concentration of MSCs followed by the culture of the substitutes in hypoxic conditions under the combined influence of TGF-β1 and BMP-2.

Chondroprotection by urocortin involves blockade of the mechanosensitive ion channel Piezo1

Osteoarthritis (OA) is characterised by progressive destruction of articular cartilage and chondrocyte cell death. Here, we show the expression of the endogenous peptide urocortin1 (Ucn1) and two receptor subtypes, CRF-R1 and CRF-R2, in primary human articular chondrocytes (AC) and demonstrate its role as an autocrine/paracrine pro-survival factor. This effect could only be removed using the CRF-R1 selective antagonist CP-154526, suggesting Ucn1 acts through CRF-R1 when promoting chondrocyte survival. This cell death was characterised by an increase in p53 expression, and cleavage of caspase 9 and 3. Antagonism of CRF-R1 with CP-154526 caused an accumulation of intracellular calcium (Ca2+) over time and cell death. These effects could be prevented with the non-selective cation channel blocker Gadolinium (Gd3+). Therefore, opening of a non-selective cation channel causes cell death and Ucn1 maintains this channel in a closed conformation. This channel was identified to be the mechanosensitive channel Piezo1. We go on to determine that this channel inhibition by Ucn1 is mediated initially by an increase in cyclic adenosine monophosphate (cAMP) and a subsequent inactivation of phospholipase A2 (PLA2), whose metabolites are known to modulate ion channels. Knowledge of these novel pathways may present opportunities for interventions that could abrogate the progression of OA.

Targets, models and challenges in osteoarthritis research

Osteoarthritis is a chronic degenerative disorder of the joint and represents one of the most common diseases worldwide. Its prevalence and severity are increasing owing to aging of the population, but treatment options remain largely limited to painkillers and anti-inflammatory drugs, which only provide symptomatic relief. In the late stages of the disease, surgical interventions are often necessary to partially restore joint function. Although the focus of osteoarthritis research has been originally on the articular cartilage, novel findings are now pointing to osteoarthritis as a disease of the whole joint, in which failure of different joint components can occur. In this Review, we summarize recent progress in the field, including data from novel ‘omics’ technologies and from a number of preclinical and clinical trials. We describe different in vitro and in vivo systems that can be used to study molecules, pathways and cells that are involved in osteoarthritis. We illustrate that a comprehensive and multisystem approach is necessary to understand the complexity and heterogeneity of the disease and to better guide the development of novel therapeutic strategies for osteoarthritis.

FOXO3A regulation by miRNA-29a Controls chondrogenic differentiation of mesenchymal stem cells and cartilage formation

Skeletal development and cartilage formation require stringent regulation of gene expression for mesenchymal stem cells (MSCs) to progress through stages of differentiation. Since microRNAs (miRNAs) regulate biological processes, the objective of the present study was to identify novel miRNAs involved in the modulation of chondrogenesis. We performed miRNA profiling and identify miR-29a as being one of the most down-regulated miRNAs during the chondrogenesis. Using chromatin immunoprecipitation, we showed that SOX9 down-regulates its transcription. Moreover, the over-expression of miR-29a strongly inhibited the expression of chondrocyte-specific markers during in vitro chondrogenic differentiation of MSCs. We identified FOXO3A as a direct target of miR-29a and showed a down- and up-regulation of FOXO3a protein levels after transfection of, respectively, premiR- and antagomiR-29a oligonucleotides. Finally, we showed that using the siRNA or premiR approach, chondrogenic differentiation was inhibited to a similar extent. Together, we demonstrate that the down-regulation of miR-29a, concomitantly with FOXO3A up-regulation, is essential for the differentiation of MSCs into chondrocytes and in vivo cartilage/bone formation. The delivery of miRNAs that modulate MSC chondrogenesis may be applicable for cartilage regeneration and deserves further investigation.

Chondroprotective and anti-inflammatory role of melanocortin peptides in TNF-α activated human C-20/A4 chondrocytes

BACKGROUND AND PURPOSE

Melanocortin MC(1) and MC(3 ) receptors, mediate the anti-inflammatory effects of melanocortin peptides. Targeting these receptors could therefore lead to development of novel anti-inflammatory therapeutic agents. We investigated the expression of MC(1) and MC(3) receptors on chondrocytes and the role of α-melanocyte-stimulating hormone (α-MSH) and the selective MC(3) receptor agonist, [DTRP(8) ]-γ-MSH, in modulating production of inflammatory cytokines, tissue-destructive proteins and induction of apoptotic pathway(s) in the human chondrocytic C-20/A4 cells.

EXPERIMENTAL APPROACH

Effects of α-MSH, [DTRP(8) ]-γ-MSH alone or in the presence of the MC(3/4) receptor antagonist, SHU9119, on TNF-α induced release of pro-inflammatory cytokines, MMPs, apoptotic pathway(s) and cell death in C-20/A4 chondrocytes were investigated, along with their effect on the release of the anti-inflammatory cytokine IL-10.

KEY RESULTS

C-20/A4 chondrocytes expressed functionally active MC(1,3) receptors. α-MSH and [DTRP(8) ]-γ-MSH treatment, for 30 min before TNF-α stimulation, provided a time-and-bell-shaped concentration-dependent decrease in pro-inflammatory cytokines (IL-1β, IL-6 and IL-8) release and increased release of the chondroprotective and anti-inflammatory cytokine, IL-10, whilst decreasing expression of MMP1, MMP3, MMP13 genes.α-MSH and [DTRP(8) ]-γ-MSH treatment also inhibited TNF-α-induced caspase-3/7 activation and chondrocyte death. The effects of [DTRP(8) ]-γ-MSH, but not α-MSH, were abolished by the MC(3/4) receptor antagonist, SHU9119.

CONCLUSION AND IMPLICATIONS

Activation of MC(1) /MC(3) receptors in C-20/A4 chondrocytes down-regulated production of pro-inflammatory cytokines and cartilage-destroying proteinases, inhibited initiation of apoptotic pathways and promoted release of chondroprotective and anti-inflammatory cytokines. Developing small molecule agonists to MC(1) /MC(3) receptors could be a viable approach for developing chondroprotective and anti-inflammatory therapies in rheumatoid and osteoarthritis.

The phenotypic characterization of A13/BACii, a novel bovine chondrocytic cell line with differentiation potential

In cartilage research bovine articular cartilage is used as an alternative to human tissue. However, animal material is subject to availability and primary cultures undergo senescence, limiting their use. Here we report the immortalization of primary bovine chondrocytes, which could be used as a surrogate for freshly isolated chondrocytes. Chondrocytes were isolated from cartilage explants and immortalized using 1.0 µg/ml benzo[alpha]pyrene. For 3-dimensional culture, chondrocytes were resuspended in 0.5% low-melt agarose at high density (HD) and cultured for 24 h prior to determining changes in expression profile and morphology. A13/BACii chondrocytes acquired a 'flat' irregular morphology and a foetal-like cell volume (1,509.59 ± 182.04 µm(3)). The human cell line C-20/A4 showed a statistically similar volume and length to A13/BACii. Two-dimensional-cultured A13/BACii expressed elevated levels of type I collagen (col1), reduced levels of type II collagen (col2) compared to freshly isolated chondrocytes and an overall col2 to col1 expression ratio (col2:col1) of 0.11 ± 0.01. Upon 3-dimensional encapsulation, there was a significant rise in col2 expression in both A13/BACii and C-20/A4, suggesting a capacity for redifferentiation in both cell lines with a return of col2:col1 values of A13/BACii to values previously observed in primary chondrocytes. A13/BACii chondrocytes expressed aggrecan, matrix metalloproteinase (MMP)-3, MMP-9 and MMP-13, further supporting indications of the differentiated phenotype. Here we report the creation of a novel chondrocytic cell line and demonstrate its strong potential for redifferentiation upon HD 3-dimensional encapsulation, providing an alternative to conventional dedifferentiated cell lines and primary culture.

Vimentin contributes to changes in chondrocyte stiffness in osteoarthritis

Actin and tubulin cytoskeletal components are studied extensively in chondrocytes, but less is known about vimentin intermediate filaments. In other cell types, vimentin is a determinant of cell stiffness and disruption of vimentin networks weakens the mechanical integrity of cells. Changes in vimentin organization correlate with osteoarthritis progression, but the functional consequences of these changes remain undetermined in chondrocytes. The objective of this study was to compare the contribution of vimentin to the mechanical stiffness of primary human chondrocytes isolated from normal versus osteoarthritic cartilage. Chondrocytes were embedded in alginate and vimentin networks disrupted with acrylamide. Constructs were imaged while subjected to 20% nominal strain on a confocal microscope stage, and the aspect ratios of approximately 1,900 cells were measured. Cytosolic stiffness was estimated with a finite element model, and live-cell imaging of GFP-vimentin was used to further analyze the nature of vimentin disruption. Vimentin in normal chondrocytes formed an inner cage-like network that was substantially stiffer than the rest of the cytosol and contributed significantly to overall cellular stiffness. Disruption of vimentin reduced stiffness approximately 2.8-fold in normal chondrocytes. In contrast, osteoarthritic chondrocytes were less stiff and less affected by vimentin disruption. This 3D experimental system revealed contributions of vimentin to chondrocyte stiffness previously not apparent, and correlated changes in vimentin-based chondrocyte stiffness with osteoarthritis.

Development and characterization of a human articular cartilage-derived chondrocyte cell line that retains chondrocyte phenotype

Chondrocytes, the only cell type present in articular cartilage, regulate tissue homeostasis by a fine balance of metabolism that includes both anabolic and catabolic activities. Therefore, the biology of chondrocytes is critical for understanding cartilage metabolism. One major limitation when studying primary chondrocytes in culture is their loss of phenotype. To overcome this hurdle, limited attempts have been made to develop human chondrocyte cell lines that retain the phenotype for use as a good surrogate model. In this study, we report a novel approach to the establishment and characterization of human articular cartilage-derived chondrocyte cell lines. Adenoviral infection followed by culture of chondrocytes in 3-dimensional matrix within 48 h post-infection maintained the phenotype prior to clonal selection. Cells were then placed in culture either as monolayer, or in 3-dimensional matrix of alginate or agarose. The clones were characterized by their basal gene expression profile of chondrocyte markers. Based on type II collagen expression, 21 clones were analyzed for gene expression following treatment with IL-1 or BMP-7 and compared to similarly stimulated primary chondrocytes. This resulted in selection of two clones that retained the chondrocyte phenotype as evidenced by expression of type II collagen and other extra-cellular matrix molecules. In addition, one clone (AL-4-17) showed similar responses as primary chondrocytes when treated with IL-1 or BMP-7. In summary, this report provides a novel procedure to develop human articular cartilage-derived chondrocyte cell lines, which preserve important characteristics of articular chondrocytes and represent a useful model to study chondrocyte biology.

Phenotyping of chondrocytes in vivo and in vitro using cDNA array technology

The cDNA array technology is a powerful tool to analyze a high number of genes in parallel. We investigated whether large-scale gene expression analysis allows clustering and identification of cellular phenotypes of chondrocytes in different in vivo and in vitro conditions. In 100% of cases, clustering analysis distinguished between in vivo and in vitro samples, suggesting fundamental differences in chondrocytes in situ and in vitro regardless of the culture conditions or disease status. It also allowed us to differentiate between healthy and osteoarthritic cartilage. The clustering also revealed the relative importance of the investigated culturing conditions (stimulation agent, stimulation time, bead/monolayer). We augmented the cluster analysis with a statistical search for genes showing differential expression. The identified genes provided hints to the molecular basis of the differences between the sample classes. Our approach shows the power of modern bioinformatic algorithms for understanding and classifying chondrocytic phenotypes in vivo and in vitro. Although it does not generate new experimental data per se, it provides valuable information regarding the biology of chondrocytes and may provide tools for diagnosing and staging the osteoarthritic disease process.

Human immortalized chondrocytes carrying heterozygous FGFR3 mutations: an in vitro model to study chondrodysplasias

Achondroplasia and thanatophoric dysplasia are human chondrodysplasias caused by mutations in the fibroblast growth factor receptor 3 (FGFR3) gene. We have developed an immortalized human chondrocyte culture model to study the regulation of chondrocyte functions. One control and eight mutant chondrocytic lines expressing different FGFR3 heterozygous mutations were obtained. FGFR3 signaling pathways were modified in the mutant lines as revealed by the constitutive activation of the STAT pathway and an increased level of P21(WAF1/CIP1) protein. This model will be useful for the study of FGFR3 function in cartilage studies and future therapeutic approaches in chondrodysplasias.

Engineering of human tracheal tissue with collagen-enforced poly-lactic-glycolic acid non-woven mesh: a preliminary study in nude mice

The purpose of the current study is to fabricate tissue engineered trachea with poly-lactic-glycolic acid (PLGA) non-woven mesh enforced by collagen type I. PLGA fibres coated with collagen solution were put together and fabricated into the shape of a human trachea, after drying and cross-linking treatment, a non-woven mesh with "C" shape formed. Chondrocytes from sheep nasal septum cartilage were expanded in vitro and seeded into PLGA/collagen non-woven mesh in the density of 5.0 x 10(7)mL(-1). After 5 days of in vitro incubation, six Cell-PLGA/collagen composites were implanted subcutaneously into the back of 6 nude mice to prefabricate a tissue engineering trachea. Eight weeks later, the cartilage formation was observed by gross inspection and histological examination. Cartilage-like tissue in the shape of the initial PLGA/collagen scaffold had been regenerated successfully without obvious inflammatory response. The tissue engineered trachea cartilage consisted of evenly spaced lacunae embedded in matrix stained red with safranin-O staining. The amount of GAGs in tissue engineered trachea cartilage reached 71.42% of normal value in native cartilage. This study demonstrated that collagen-enforced PLGA non-woven mesh facilitated the adhesion and proliferation of chondrocytes, it also owned adequate mechanical strength to serve as an ideal scaffold for trachea tissue engineering without internal support.

NAD(P)H oxidase activity of Nox4 in chondrocytes is both inducible and involved in collagenase expression

Reactive oxygen species (ROS) are regulators of redox-sensitive cell signaling pathways. In osteoarthritis, human interleukin-1beta is implicated in cartilage destruction through an ROS-dependent matrix metalloproteinase production. To determine the molecular source of ROS production in the human IL-1beta (hIL-1beta)-sensitive chondrocyte immortalized cell line C-20/A4, transfected cells were constructed that overexpress NAD(P)H oxidases. First, RT-PCR analysis showed that the C-20/A4 cell line expressed Nox2, Nox4, p22( phox ), and p67( phox ), but not p47( phox ). It was found that ROS production by C-20/A4 chondrocytes does not depend on PMA and ionomycin activation. This indicates that Nox2 was not involved in the production of ROS. In C- 20/A4 cells that overexpress Nox4, hIL-1beta stimulated ROS production three times more than the normal production of C-20/A4 cells. Moreover, there was a fourfold increase in the production of collagenase (MMP-1) by chondrocytes that overexpress Nox4. Interestingly, MMP-1 production in cells that overexpress Nox2 was not sensitive to hIL-1beta. These data suggest that under hIL-1beta stimulation, C-20/A4 chondrocytes produce MMP-1 through a Nox4-mediated, ROS-dependent pathway.

Cartilage tissue engineering: its potential and uses

PURPOSE OF REVIEW

The prevalent nature of osteoarthritis, a cartilage degenerative disease that results in the erosion of joint surfaces and loss of mobility, underscores the importance of developing functional articular cartilage replacement. Recent research efforts have focused on tissue engineering as a promising approach for cartilage regeneration and repair. Tissue engineering is a multidisciplinary research area that incorporates both biological and engineering principles for the purpose of generating new, living tissues to replace the diseased/damaged tissue and restore tissue/organ function. This review surveys and highlights the current concepts and recent progress in cartilage tissue engineering, and discusses the challenges and potential of this rapidly advancing field of biomedical research.

RECENT FINDINGS

Cartilage tissue engineering is critically dependent on selection of appropriate cells (differentiated or progenitor cells); fabrication and utilization of biocompatible and mechanically suitable scaffolds for cell delivery; stimulation with chondrogenically bioactive molecules introduced in the form of recombinant proteins or via gene transfer; and application of dynamic, mechanical loading regimens for conditioning of the engineered tissue constructs, including the design of specialized biomechanically active bioreactors.

SUMMARY

Cell selection, scaffold design and biological stimulation remain the challenges of function tissue engineering. Successful regeneration or replacement of damaged or diseased cartilage will depend on future advances in our understanding of the biology of cartilage and stem cells and technological development in engineering.