Plasticity of clonal populations of dedifferentiated adult human articular chondrocytes

Multipotential nestin and Isl-1 positive mesenchymal stem cells isolated from human pancreatic islets

Mesenchymal cells in the developing pancreas express the neural stem cell marker nestin and the transcription factor islet-1 (Isl-1). Using defined culture conditions we isolated on a single cell basis nestin producing cells from human pancreatic islets. These cells were immortalized with lentiviral vectors coding for telomerase and mBmi. They are positive for Isl-1 and nestin and have the potential to adopt a pancreatic endocrine phenotype with expression of critical transcription factors including Ipf-1, Isl-1, Ngn-3, Pax4, Pax6, Nkx2.2, and Nkx6.1 as well as the islet hormones insulin, glucagon, and somatostatin. In addition, they can be differentiated into human albumin producing cells in vivo when grafted into a SCID mouse liver. In accordance with a mesenchymal phenotype, the cells were also able to adopt adipocytic or osteocytic phenotypes in vitro. In conclusion, cultured pancreatic islets contain nestin and Isl-1 positive mesenchymal stem cells with multipotential developmental capacity.

Cartilage tissue engineering by expanded goat articular chondrocytes

In this study we investigated whether expanded goat chondrocytes have the capacity to generate cartilaginous tissues with biochemical and biomechanical properties improving with time in culture. Goat chondrocytes were expanded in monolayer with or without combinations of FGF-2, TGF-beta1, and PDGFbb, and the postexpansion chondrogenic capacity assessed in pellet cultures. Expanded chondrocytes were also cultured for up to 6 weeks in HYAFF-M nonwoven meshes or Polyactive foams, and the resulting cartilaginous tissues were assessed histologically, biochemically, and biomechanically. Supplementation of the expansion medium with FGF-2 increased the proliferation rate of goat chondrocytes and enhanced their postexpansion chondrogenic capacity. FGF-2-expanded chondrocytes seeded in HYAFF-M or Polyactive scaffolds formed cartilaginous tissues with wet weight, glycosaminoglycan, and collagen content, increasing from 2 days to 6 weeks culture (up to respectively 2-, 8-, and 41-fold). Equilibrium and dynamic stiffness measured in HYAFF M-based constructs also increased with time, up to, respectively, 1.3- and 16-fold. This study demonstrates the feasibility to engineer goat cartilaginous tissues at different stages of development by varying culture time, and thus opens the possibility to test the effect of maturation stage of engineered cartilage on the outcome of cartilage repair in orthotopic goat models.

Cartilage-Derived Stromal Cells: Is It a Novel Cell Resource for Cell Therapy to Regenerate Infarcted Myocardium?

Human cartilage is reported to contain multipotent stromal cells. We evaluated the effect of human cartilage-derived stromal cells (CDSCs) on heart function when transplanted into the infarcted myocardium of rats. CDSCs were isolated and cultured from human articular cartilage and subjected to fluorescence-activated cell sorting (FACS) analysis. The CDSCs were consistently negative for CD14, CD34, CD38, CD45, CD49f, CD104, CD105, CD106, CD117, HLA-DR, and ABCG-2, and positive for CD10, CD44, CD71, CD73, CD90, CD147, and HLA-A, -B, and -C by FACS analysis. Myocardial infarction (MI) was created in rats by ligation of the left anterior descending artery. Three weeks after MI, the CDSCs labeled with Hoechst stain were injected into the infarct and border zone. Echocardiography, histological examination, and reverse transcription-polymerase chain reaction (RT-PCR) were performed 4 weeks after cell transplantation. Echocardiography indicated that CDSC transplantation could improve heart function. The number of capillaries increased in the injection regions in the transplantation group. Histological examination showed that Hoechst-labeled CDSCs in islands within the infarcted region were stained positively for desmin and smooth muscle actin but negatively for alpha-sarcomeric actin and troponin-I. RT-PCR results indicated the expression level of collagen I, collagen III, tissue inhibitor of metalloproteinase-1, transforming growth factor-beta1, and vascular endothelia growth factor were much higher in the scar tissue in the transplantation group than in the medium and control groups. Our findings suggested that CDSCs might promote angiogenesis, prevent left ventricular remodeling, and improve the heart function when transplanted into injured heart in the rat model of myocardial infarction.

Clonal populations of chondrocytes with progenitor properties identified within human articular cartilage

The aim of the present study was to identify and characterize progenitor properties of human articular chondrocytes selected by using agarose suspension culture. In this chondrogenic selective culture condition, about 3.6% of seeded surplus chondrocytes from patients undergoing articular chondrocyte transplantation proliferated and formed cell clusters after 6 weeks. Phase-contrast microscopy and transmission electron microscopy revealed four different types of cell clusters differing in cellular content and matrix production. Based on their morphological features, they were named the homogenous (H), the homogenous matrix (HM), the differentiated matrix (DM) and the differentiated (D) cell clusters. All cell clusters showed positive safranin O staining, and matrix was positive for antibodies detecting type II collagen and aggrecan. The clusters were further demonstrated to express the genes for fibroblast growth factor receptor 3, type IIA collagen and type IIB collagen, while type X collagen was not expressed. After subcloning, the H and HM clusters demonstrated the best proliferative capacity. Chondrocytes from these two cell clusters also showed phenotypic plasticity in chondrogenic, adipogenic as well as osteogenic assays. This study demonstrates that existing subpopulations of cells with chondroprogenitor properties can be isolated from human adult articular cartilage using agarose suspension cultures.

Expansion on specific substrates regulates the phenotype and differentiation capacity of human articular chondrocytes

In this study, we investigated if monolayer expansion of adult human articular chondrocytes (AHAC) on specific substrates regulates cell phenotype and post-expansion multilineage differentiation ability. AHAC isolated from cartilage biopsies of five donors were expanded on plastic dishes (PL), on dishes coated with collagen type II (COL), or on slides coated with a ceramic material (Osteologic, OS). The phenotype of expanded chondrocytes was assessed by flow cytometry and real-time RT-PCR. Cells were then cultured in previously established conditions promoting differentiation toward the chondrogenic or osteogenic lineage. AHAC differentiation was assessed histologically, biochemically, and by real-time RT-PCR. As compared to PL-expanded AHAC, those expanded on COL did not exhibit major phenotypic changes, whereas OS-expanded cells expressed (i) higher bone sialoprotein (BSP) (22.6-fold) and lower collagen type II (9.3-fold) mRNA levels, and (ii) lower CD26, CD90 and CD140 surface protein levels (1.4-11.1-fold). Following chondrogenic differentiation, COL-expanded AHAC expressed higher mRNA levels of collagen type II (2.3-fold) and formed tissues with higher glycosaminoglycan (GAG) contents (1.7-fold), whereas OS-expanded cells expressed 16.5-fold lower collagen type II and generated pellets with 2.0-fold lower GAG contents. Following osteogenic differentiation, OS-expanded cells expressed higher levels of BSP (3.9-fold) and collagen type I (2.8-fold) mRNA. In summary, AHAC expansion on COL or OS modulated the de-differentiated cell phenotype and improved the cell differentiation capacity respectively toward the chondrogenic or osteogenic lineage. Phenotypic changes induced by AHAC expansion on specific substrates may mimic pathophysiological events occurring at different stages of osteoarthritis and may be relevant for the engineering of osteochondral tissues.

Reparative medicine: from tissue engineering to joint surface regeneration

Biological regeneration is proving to be an increasingly attractive alternative/complement to prosthetic replacement of tissues and organs. In cell-based therapeutic approaches, cells are manipulated in vitro and administered to patients as living and dynamic biological agents. In this review, we have focused on the regeneration of the injured joint surface to discuss novel issues that these new therapeutic agents raise and are difficult to address within the paradigms of traditional pharmacology. They include: determination of the mechanism of action and dose, evaluation of potency, safety and toxicity, as well as upscale, delivery and identification of proper indications. Finally, novel potential approaches are proposed in which resident progenitor cells are targeted to regenerate the damaged tissue.

Human articular chondrocytes suppress in vitro proliferation of anti-CD3 activated peripheral blood mononuclear cells

OBJECTIVE

To investigate whether mature human articular chondrocytes (AC) exhibit an antiproliferative effect on activated peripheral blood mononuclear cells (PBMC) and to compare this effect with other cells of mesenchymal origin.

METHODS

AC from healthy cadaveric cartilage were grown for different passages, in the absence (control) or presence of factors enhancing cell de-differentiation (transforming growth factor (TGF)beta1, fibroblast growth factor (FGF)-2, and platelet derived growth factor (PDGF)bb-TFP medium). Cell ability to suppress PBMC proliferation driven by anti-CD3 antibody was measured by tritiated thymidine uptake following incubation for 48 h at different PBMC:AC ratios and expressed as percent of residual proliferation (RP). AC antiproliferative effect was compared to that of control dermal fibroblasts (DF) and bone marrow stromal cells (BMSC).

RESULTS

AC exhibited a cell number-dependent antiproliferative effect. The strongest effect (up to 2% RP) was measured using the least expanded AC cultures. The use of TFP medium for AC expansion resulted in a significantly lower antiproliferative effect, in the range of that induced by BMSC (up to 18% RP). Also DF induced a marked antiproliferative effect (up to 11% RP).

CONCLUSION

We report for the first time that human AC have a marked antiproliferative effect on anti-CD3 stimulated PBMC, which is reduced upon culture in medium-inducing extensive cell de-differentiation. These results reflect the immunosuppressive properties observed for other different mesenchymal cell types and raise the question of a potential common physiological role in local tissue protection.

Activation of WNT and BMP signaling in adult human articular cartilage following mechanical injury

Acute full thickness joint surface defects can undergo repair, which involves tissue patterning and endochondral bone formation. Molecular signals regulating this process may contribute to the repair outcome, chronic evolution and, eventually, the onset of osteoarthritis. We tested the hypothesis that mechanical injury modulates morphogenetic pathways in adult human articular cartilage explants. Adjacent articular cartilage explants were obtained from preserved areas of the femoral condyles of patients undergoing arthroplasty for osteoarthritis, or from a normal joint of a patient undergoing lower limb amputation. Paired explants were individually maintained in explant culture. From each pair, one explant was mechanically injured and the other left uninjured as a control. Cultures were terminated at different time points for histochemistry, immunohistochemistry and gene expression analysis by reverse transcription real time PCR. Bone morphogenetic protein 2 (BMP-2) mRNA was upregulated in the injured explants. We detected phosphorylation of SMAD-1 and SMAD-5, consistent with activation of the bone morphogenetic protein (BMP) pathway. FRZB-1 mRNA was downregulated in the injured explants, suggesting de-repression of WNT signaling. Accordingly, expression of the canonical WNT target genes Axin-2 and c-JUN was upregulated in the injured explants. Activation of the canonical WNT signaling pathway by LiCl treatment induced upregulation of COL2A1 and Aggrecan mRNA, suggesting an anabolic effect. Phosphorylation of SMAD-1/-5 and downregulation of FRZB were confirmed in vivo in a mouse model of joint surface injury. Taken together, these data show modulation of the BMP and WNT pathways following mechanical injury in vitro and in vivo, which may play a role in the reparative response of the joint surface. These pathways may, therefore, represent potential targets in protocols of biological joint surface defect repair.

Cell and matrix morpho-functional analysis in chondrocyte micromasses

Micromass cultures represent a convenient means of studying chondrocyte physiology in the context of a tridimensional culture model. In this study, we present the first ultrastructural analysis of the distribution and organization of the extracellular components in micromasses in comparison with their cartilaginous counterparts. Primary chondrocytes obtained from osteoarthritis patients were pelleted in micromasses. Transmission electron microscopy and immunofluorescence were used to evaluate the distribution of major extracellular matrix proteins, i.e., aggrecan, chondroitin-4-sulfate, chondroitin-6-sulfate, and collagen I and II. Both approaches revealed a number of morphological features shared by micromass and cartilage chondrocytes. In particular, in micromasses, chondrocytes are in close contact with an organized extracellular matrix that adequately mimics that of cartilage. Cells were observed to establish specialized junctions for cell-extracellular matrix crosstalk. Noteworthy, cells seem endowed in a chondroitin sulfate-rich microenvironment, and thus possibly ensuring the immobilization of chemokines, a family of molecules emerging in osteoarthritis pathogenesis, in a haptotactic-like gradient to the chondrocytes, which facilitates the binding to their receptors. To determine the suitability of this model to investigate osteoarthritis pathogenesis, a potential apoptotic stimulus (endothelial IL-8) was used, and ultrastructural analysis assessed apoptosis induction. Micromass cultures were proved to be an experimental technique providing a large number of properly differentiated chondrocytes, and thus allowing reliable biochemical and morphological studies. They represent, therefore, a novel approach to osteoarthritis investigation that promises more thorough understanding of chondrocyte physiology in osteoarthritis.

Mesenchymal stem cell therapy to rebuild cartilage

Disorders affecting cartilage touch almost the whole population and are one of the leading causes of invalidity in adults. To repair cartilage, therapeutic approaches initially focused on the implantation of autologous chondrocytes, but this technique proved unsatisfactory because of the limited number of chondrocytes obtained at harvest. The discovery that several adult human tissues contain mesenchymal stem cells (MSCs) capable of differentiating into chondrocytes raised the possibility of injecting MSCs to repair cartilages. The important data published recently on the factors controlling chondrocyte commitment must be thoroughly considered to make further progress towards this therapeutic approach. The potential application of MSC therapy provides new hope for the development of innovative treatments for the repair of cartilage disorders.

Regeneration of articular cartilage--evaluation of osteochondral defect repair in the rabbit using multiphasic implants

OBJECTIVE

To investigate whether two different multiphasic implants could initiate and sustain repair of osteochondral defects in rabbits. The implants address the malleable properties of cartilage while also addressing the rigid characteristics of subchondral bone.

DESIGN

The bone region of both devices consisted of D, D-L, L-polylactic acid invested with hyaluronan (HY). The cartilage region of the first device was a polyelectrolytic complex (PEC) hydrogel of HY and chitosan. In the second device the cartilage region consisted of type I collagen scaffold. Eighteen rabbits were implanted bilaterally with a device, or underwent defect creation with no implant. At 24 weeks, regenerated tissues were evaluated grossly, histologically and via immunostaining for type II collagen.

RESULTS

PEC devices induced a significantly better repair than untreated shams. Collagen devices resulted in a quality of repair close to that of the PEC group, although its mean repair score (19.0+/-4.2) did not differ significantly from that of the PEC group (20.4+/-3.7) or the shams (16.5+/-6.3). The percentage of hyaline-appearing cartilage in the repair was highest with collagen implants, while the degree of bonding of repair to the host, structural integrity of the neocartilage, and reconstitution of the subchondral bone was greatest with PEC devices. Cartilage in both device-treated sites stained positive for type II collagen and GAG.

CONCLUSIONS

Both implants are capable of maintaining hyaline-appearing tissue at 24 weeks. The physicochemical region between the cartilage and bone compartments makes these devices well suited for delivery of different growth factors or drugs in each compartment, or different doses of the same factor. It also renders these devices excellent vehicles for chondrocyte or stem cell transplantation.

The regulation of expanded human nasal chondrocyte re-differentiation capacity by substrate composition and gas plasma surface modification

Optimizing re-differentiation of clinically relevant cell sources on biomaterial substrates in serum containing (S+) and serum-free (SF) media is a key consideration in scaffold-based articular cartilage repair strategies. We investigated whether the adhesion and post-expansion re-differentiation of human chondrocytes could be regulated by controlled changes in substrate surface chemistry and composition in S+ and SF media following gas plasma (GP) treatment. Expanded human nasal chondrocytes were plated on gas plasma treated (GP+) or untreated (GP-) poly(ethylene glycol)-terephthalate-poly(butylene terephthalate) (PEGT/PBT) block co-polymer films with two compositions (low or high PEG content). Total cellularity, cell morphology and immunofluorescent staining of vitronectin (VN) and fibronectin (FN) integrin receptors were evaluated, while post-expansion chondrogenic phenotype was assessed by collagen types I and II mRNA expression. We observed a direct relationship between cellularity, cell morphology and re-differentiation potential. Substrates supporting high cell adhesion and a spread morphology (i.e. GP+ and low PEG content films), resulted in a significantly greater number of cells expressing alpha5beta1 FN to alpha(V)beta3 VN integrin receptors, concomitant with reduced collagen type II/ImRNA gene expression. Substrates supporting low cell adhesion and a spherical morphology (GP- and high PEG content films) promoted chondrocyte re-differentiation indicated by high collagen type II/I gene expression and a low percentage of alpha5beta1 FN integrin expressing cells. This study demonstrates that cell-substrate interactions via alpha5beta1 FN integrin mediated receptors negatively impacts expanded human nasal chondrocyte re-differentiation capacity. GP treatment promotes cell adhesion in S+ media but reverses the ability of low PEG content PEGT/PBT substrates to maintain chondrocyte phenotype. We suggest alternative cell immobilization techniques to GP are necessary for clinical application in articular cartilage repair.

Cryopreservation and in vitro expansion of chondroprogenitor cells isolated from the superficial zone of articular cartilage

Understanding the proliferation mechanisms of chondroprogenitor cells and their influence on cell differentiation is crucial in order to develop large-scale expansion processes for tissue engineering applications. Proliferation control mechanisms were mainly attributed to substrate limitation and cell-cell contact inhibition. The limiting substrates were found to be components of the FCS, with an optimal proliferation rate achieved in the presence of 40% FCS. In addition, the medium supply rate was found to be essential in reducing substrate limitation. In terms of FCS, 10 microL FCS cm(-2) h(-1) was the threshold feed rate required to prevent substrate limitation. Above this rate, maximum cell densities of 5.3 x 10(5) cells/cm2 were achieved, representing a 53-fold expansion. To reduce the need for high supply rates, the effect of specific growth factors was also investigated. Cell densities of 3.3 x 10(5) cells/cm2 were achieved in batch cultures using 40% FCS and 1 ng/mL TGF-beta1. Chondroprogenitor cells were expanded in this medium up to three passages without compromising their ability to differentiate and produce cartilage-like matrix in pellet cultures. In addition to substrate limitation, cell-cell contact, even at very sparse subconfluent densities, appeared capable of exerting some degree of growth inhibition. The cells exhibited deceleratory growth kinetics, characterized by a decrease of specific growth rates over time.

Effects of scaffold composition and architecture on human nasal chondrocyte redifferentiation and cartilaginous matrix deposition

We investigated whether the post-expansion redifferentiation and cartilage tissue formation capacity of adult human nasal chondrocytes can be regulated by controlled modifications of scaffold composition and architecture. As a model system, we used poly(ethylene glycol)-terephthalate-poly(butylene)-terephthalate block copolymer scaffolds from two compositions (low or high PEG content, resulting in different wettability) and two architectures (generated by compression molding or three-dimensional (3D) fiber deposition) with similar porosity and mechanical properties, but different interconnecting pore architectures. Scaffolds were seeded with expanded human chondrocytes and the resulting constructs assessed immunohistochemically, biochemically and at the mRNA expression level following up to 4 weeks of static culture. For a given 3D architecture, the more hydrophilic scaffold enhanced cell redifferentiation and cartilaginous tissue formation after 4 weeks culture, as assessed by higher mRNA expression of collagen type II, increased deposition of glycosaminoglycan (GAG) and predominance of type II over type I collagen immunostain. The fiber-deposited scaffolds, with a more accessible pore volume and larger interconnecting pores, supported increased GAG deposition, but only if a more hydrophilic composition was used. By applying controlled and selective modifications of chemico-physical scaffold parameters, we demonstrate that both scaffold composition and architecture are instructive for expanded human chondrocytes in the generation of 3D cartilaginous tissues. The observed effects of composition and architecture were likely to have been mediated, respectively, by differential serum protein adsorption and efficiency of nutrient/waste exchange.

Promotion of the intrinsic damage-repair response in articular cartilage by fibroblastic growth factor-2

OBJECTIVE

To identify the effect of fibroblastic growth factor-2 (FGF-2) on the intrinsic damage-repair response in articular cartilage in vitro.

METHODS

Articular equine cartilage explants, without subchondral bone, had a single impact load of 500 g applied from a height of 2.5 cm. Explants were then cultured in 0, 12, 25, 50 or 100 ng/ml FGF-2 for up to 28 days. Unimpacted discs served as controls for each time-point. Histological and immunohistochemical techniques were used to quantify and characterise the response of putative chondrocyte progenitor cells (CPC) to damage and FGF-2 treatment.

RESULTS

FGF-2 significantly accelerated the appearance and increased the numbers of de novo repair cells identified histologically at the cartilage surface. The response was affected by the dose of FGF-2. The repair cells were shown to be chondrocytes by their expression of collagen types II, IX/XI, but not of type I collagen. In addition, these cells, and those underlying the articular surface, were shown to be immunopositive for Notch-1 and PCNA, markers for proliferating cartilage progenitor cells.

CONCLUSIONS

The results of this study indicate that, following single impact load, CPC can be stimulated in mature articular cartilage in vitro. These CPC and the cells arising from them appear to represent the cartilage's response to damage. The timing of the appearance of CPC and their overall numbers can be significantly increased by FGF-2, providing further evidence for an important role for FGF-2 in modulating cartilage repair. These results indicate that further study into the mechanisms of repair in mature cartilage using this in vitro model are vital in understanding the repair capacity of mature cartilage.

Molecular and functional characterization of ovine cardiac valve-derived interstitial cells in primary isolates and cultures

At present the involvement of cardiac valve interstitial cells (VICs) in growth, repair, and tissue engineering is understudied. Therefore, this study aims at characterizing ovine VICs in order to provide a solid base for tissue engineering of heart valves. Ovine ICs of the four heart valves were isolated by the explant outgrowth method and expanded in vitro up to passage 5. Vimentin and collagen I gene expression from freshly isolated or cultured ICs was measured by reverse transcriptase-polymerase chain reaction. Immunocytochemical stainings of vimentin, alpha-smooth muscle actin (ASMA), smooth muscle myosin, and procollagen I were performed on aortic VICs. In addition, migration and extracellular matrix deposition were studied in vitro in aortic VICs. ICs show stable vimentin and collagen I expression in culture. Expression is approximately doubled in cultured ICs compared with fresh isolates. More than 95% of ICs in each passage stain for vimentin and procollagen I. Freshly isolated ICs are ASMA and myosin negative, but ICs in culture partially stain for these contractile markers. ICs have stable matrix production for up to five passages, associated with stable migration of the cells. We conclude that ovine valve interstitial cells undergo phenotypic modulation to activated myofibroblasts under culture conditions but retain stable matrix production.

A kinetic modeling of chondrocyte culture for manufacture of tissue-engineered cartilage

For repairing articular cartilage defects, innovative techniques based on tissue engineering have been developed and are now entering into the practical stage of clinical application by means of grafting in vitro cultured products. A variety of natural and artificial materials available for scaffolds, which permit chondrocyte cells to aggregate, have been designed for their ability to promote cell growth and differentiation. From the viewpoint of the manufacturing process for tissue-engineered cartilage, the diverse nature of raw materials (seeding cells) and end products (cultured cartilage) oblige us to design a tailor-made process with less reproducibility, which is an obstacle to establishing a production doctrine based on bioengineering knowledge concerning growth kinetics and modeling as well as designs of bioreactors and culture operations for certification of high product quality. In this article, we review the recent advances in the manufacturing of tissue-engineered cartilage. After outlining the manufacturing processes for tissue-engineered cartilage in the first section, the second and third sections, respectively, describe the three-dimensional culture of chondrocytes with Aterocollagen gel and kinetic model consideration as a tool for evaluating this culture process. In the final section, culture strategy is discussed in terms of the combined processes of monolayer growth (ex vivo chondrocyte cell expansion) and three-dimensional growth (construction of cultured cartilage in the gel).

Experimental and mathematical study of the influence of growth factors on the growth kinetics of adult human articular chondrocytes

This study aimed at determining how kinetic parameters of adult human articular chondrocytes (AHAC) growth are modulated by the growth factor combination TGFbeta1, FGF-2, and PDGF BB (TFP), recently shown to stimulate AHAC proliferation. AHAC, isolated from cartilage biopsies of three individuals, were cultured in medium without (CTR) or with TFP. For growth curves, AHAC were seeded at 1,000 cells/cm(2) and cultured for 12 days, with cell numbers measured fluorimetrically in the same wells every 12 h. For microcolony tests, AHAC were seeded at 2.5 cells/cm(2) and cultured for 6 days, with cell numbers determined for each microcolony by phase contrast microscopy every 8 h. A mathematical model combining delay and logistic equations was developed to capture the growth kinetic parameters and to enable the description of the complete growth process of the cell culture. As compared to CTR medium, the presence of TFP increased the number of cells/well starting from the fifth day of culture, and a four-fold larger cell number was reached at confluency. For single microcolonies, TFP reduced the time for the first cell division by 26.6%, the time for subsequent cell divisions (generation time) by 16.8%, and the percentage of quiescent cells (Q(c)) by 42.5%. The mathematical model fitted well the experimental data of the growth kinetic. Finally, using both microcolony tests and the mathematical model, we determined that prolonged cell expansion induces an enrichment of AHAC with shorter first division time, but not of those with shorter generation time.

Retroviral transduction with SOX9 enhances re-expression of the chondrocyte phenotype in passaged osteoarthritic human articular chondrocytes

OBJECTIVES

Articular chondrocytes proliferate in monolayer culture, but the expression of the transcription factor SOX9 falls and the ability of the cells to reform cartilage tissue declines. We have investigated whether retroviral SOX9 expression in extensively passaged human articular chondrocytes from osteoarthritic (OA) joints enables the cells to regain a cartilage matrix forming phenotype in pellet culture.

DESIGN

Chondrocytes from normal and OA joints were retrovirally transduced with SOX9 and grown to passages 7-10 before being cultured as pellets of 500,000 cells for 14 days. Pellets were analysed by real time polymerase chain reaction, histology, immunohistochemistry and 1,9-dimethylmethylene blue assay.

RESULTS

Chondrocytes from OA joints displayed higher expression of COL2A1 gene when transduced with SOX9 and cultured as pellets with 10% serum, but glycosaminoglycan (GAG) synthesis was low. Addition of transforming growth factor beta-3 and insulin like growth factor-1 increased collagen II expression and GAG synthesis in these SOX9 transduced cell pellets. The cells adopted a rounded morphology and there was increased deposition of collagen II protein compared to control green fluorescent protein transduced cell pellets. Similar results were seen with transduced chondrocytes from OA or healthy cartilage. SOX9 transduced human dermal fibroblasts did not show any chondrogenic response.

DISCUSSION

Transduction with SOX9 primed the passaged articular chondrocytes to regain a chondrocytic phenotype in pellet culture and to form a cartilaginous matrix, which was enhanced by growth factors. Following transduction, chondrocytes from OA joints showed a similar capacity for chondrogenic recovery as those from healthy joints, which suggested that OA does not permanently compromise the chondrocyte phenotype.

Mesenchymal stem cells in osteoarthritis

PURPOSE OF REVIEW

Accumulating evidence indicates that every tissue contains stem cells. Our understanding of the biology of stem cells reveals that these cell populations have a critical role in the homeostasis and repair of tissues. Besides the local stem cell niches, additional compartments in the body such as the bone marrow may serve as reservoirs for stem cell populations. On more extensive tissue damage, and guided by local repair responses, "reparative" cell populations are mobilized from more distant stem cell reservoirs and migrate to the site of injury, thereby contributing in many aspects of local tissue repair.

RECENT FINDINGS

Osteoarthritis has long been regarded as an imbalance between destructive and reparative processes. The lack of repair of the weight-bearing articular cartilage and the associated subchondral bone changes are considered of critical importance in the progression of the disease. Recent findings indicate a depletion and/or functional alteration of mesenchymal stem cell populations in osteoarthritis. These preliminary data suggest that in joint diseases such as osteoarthritis, it is of importance to investigate further the involvement of the stem cell pool in the mechanisms contributing to joint homeostasis and driving disease progression.

SUMMARY

In view of the emerging body of evidence pointing to a potential therapeutic utility of stem cell technology, it is not surprising that local delivery of mesenchymal stem cells has been explored as a therapeutic approach in animal models of osteoarthritis.

Cultivation of human tenocytes in high-density culture

Limited supplies of tendon tissue for use in reconstructive surgery require development of phenotypically stable tenocytes cultivated in vitro. Tenocytes in monolayer culture display an unstable phenotype and tend to dedifferentiate, but those in three-dimensional culture may remain phenotypically and functionally differentiated. In this study we established a three-dimensional high-density culture system for cultivation of human tenocytes for tissue engineering. Human tenocytes were expanded in monolayer culture before transfer to high-density culture. The synthesis of major extracellular matrix proteins and the ultrastructural morphology of the three-dimensional cultures were investigated for up to 2 weeks by electron microscopy, immunohistochemistry, immunoblotting and quantitative, real-time PCR. Differentiated tenocytes were able to survive over a period of 14 days in high-density culture. During the culture period tenocytes exhibited a typical tenocyte morphology embedded in an extensive extracellular matrix containing cross-striated collagen type I fibrils and proteoglycans. Moreover, expression of the tendon-specific marker scleraxis underlined the tenocytic identity of these cells. Taken together, we conclude that the three-dimensional high-density cultures may be useful as a new approach for obtaining differentiated tenocytes for autologous tenocyte transplantation to support tendon and ligament healing and to investigate the effect of tendon-affecting agents on tendon in vitro.

Identification of subpopulations with characteristics of mesenchymal progenitor cells from human osteoarthritic cartilage using triple staining for cell surface markers

We first identified and isolated cellular subpopulations with characteristics of mesenchymal progenitor cells (MPCs) in osteoarthritic cartilage using fluorescence-activated cell sorting (FACS). Cells from osteoarthritic cartilage were enzymatically isolated and analyzed directly or after culture expansion over several passages by FACS using various combinations of surface markers that have been identified on human MPCs (CD9, CD44, CD54, CD90, CD166). Culture expanded cells combined and the subpopulation derived from initially sorted CD9⁺, CD90⁺, CD166⁺ cells were tested for their osteogenic, adipogenic and chondrogenic potential using established differentiation protocols. The differentiation was analyzed by immunohistochemistry and by RT-PCR for the expression of lineage related marker genes. Using FACS analysis we found that various triple combinations of CD9, CD44, CD54, CD90 and CD166 positive cells within osteoarthritic cartilage account for 2–12% of the total population. After adhesion and cultivation their relative amount was markedly higher, with levels between 24% and 48%. Culture expanded cells combined and the initially sorted CD9/CD90/CD166 triple positive subpopulation had multipotency for chondrogenic, osteogenic and adipogenic differentiation. In conclusion, human osteoarthritic cartilage contains cells with characteristics of MPCs. Their relative enrichment during in vitro cultivation and the ability of cell sorting to obtain more homogeneous populations offer interesting perspectives for future studies on the activation of regenerative processes within osteoarthritic joints.

Gene expression during redifferentiation of human articular chondrocytes

OBJECTIVE

The aim of the present study was to investigate gene expression during the in vitro redifferentiation process of human articular chondrocytes isolated from clinical samples from patient undergoing an autologous chondrocyte transplantation therapy (ACT).

METHOD

Monolayer (ML) expanded human articular chondrocytes from four donors were cultured in a 3D pellet model and the redifferentiation was investigated by biochemistry, histology, immunohistochemistry and microarray analysis.

RESULTS

The culture expanded chondrocytes redifferentiated in the pellet model as seen by an increase in collagen type II immunoreactivity between day 7 and 14. The gene expression from ML to pellet at day 7 included an increase in cartilage matrix proteins like collagen type XI, tenascin C, dermatopontin, COMP and fibronectin. The late phase consisted of a strong downregulation of extracellular signal-regulated protein kinase (ERK-1) and an upregulation of p38 kinase and SOX-9, suggesting that the late phase mimicked parts of the signaling processes involved in the early chondrogenesis in limb bud cells. Other genes, which indicated a transition from proliferation to tissue formation, were the downregulated cell cycle genes GSPT1 and the upregulated growth-arrest-specific protein (gas). The maturation of the pellets included no signs of hypertrophy or apoptosis as seen by downregulation of collagen type X, Matrix Gla protein and increased expression of caspase 3.

CONCLUSION

Our data show that human articular chondrocytes taken from surplus cells of patient undergoing ACT treatment and expanded in ML, redifferentiate and form cartilage like matrix in vitro and that this dynamic process involves genes known to be expressed in early chondrogenesis.

Dedifferentiated adult articular chondrocytes: a population of human multipotent primitive cells

OBJECTIVE

To test the hypothesis that dedifferentiated adult human cartilage chondrocytes (HAC) are a true multipotent primitive population.

METHODS

Studies to characterize dedifferentiated HAC included cell cycle and quiescence analysis, cell fusion, flow-FISH telomere length assays, and ABC transporter analysis. Dedifferentiated HAC were characterized by flow cytometry, in parallel with bone marrow mesenchymal stem cells (MSC) and processed lipoaspirate (PLA) cells. The in vitro differentiation potential of dedifferentiated HAC was studied by cell culture under several inducing conditions, in multiclonal and clonal cell populations.

RESULTS

Long-term HAC cultures were chromosomically stable and maintained cell cycle dynamics while showing telomere shortening. The phenotype of dedifferentiated HAC was quite similar to that of human bone marrow MSC. In addition, this population expressed human embryonic stem cell markers. Multiclonal populations of dedifferentiated HAC differentiated to chondrogenic, osteogenic, adipogenic, myogenic, and neurogenic lineages. Following VEGF induction, dedifferentiated HAC expressed characteristics of endothelial cells, including AcLDL uptake. A total of 53 clonal populations of dedifferentiated HAC were efficiently expanded; 17 were able to differentiate to chondrogenic, osteogenic, and adipogenic lineages. No correlation was observed between telomere length or quiescent population and differentiation potential in the clones assayed.

CONCLUSION

Dedifferentiated HAC should be considered a human multipotent primitive population.

ACTH enhances chondrogenesis in multipotential progenitor cells and matrix production in chondrocytes

The association of melanocortin peptide overproduction with enhanced linear growth prompted the current investigation of adrenocorticotropin hormone (ACTH) effects on multipotential chondroprogenitor populations and committed chondrocytes in culture. Two multipotential progenitor populations, rat bone marrow stromal cells (BMSC) and the clonal multipotential cell line RCJ3.1, and two committed chondrocyte populations, resting chondrocytes (RC) isolated from the rib of young rats and the chondrocyte restricted cell line RCJ3.1C5.18 (C5.18), were cultured in differentiation medium plus or minus ACTH. Alcian blue stain was used to quantitate proteoglycan matrix production in all populations treated with a range of ACTH concentrations. Changes in proliferation due to ACTH treatment of all cell types were measured using 3H-thymidine incorporation. Differences in matrix production of ACTH-treated and -untreated RC and C5.18 cells were determined using 3H-proline incorporation. Relative transcript expression of the chondrocyte matrix proteins collagen type II (COLL II) and aggrecan (AGR) in treated and untreated cells was analyzed by Northern blot. Collagen type X (COLL X), a marker of hypertrophic differentiation, was measured in committed chondrocytic populations. Western analysis was used to detect the melanocortin-3 receptor (MC3-R), which was a suspected mediator of the ACTH signal. Matrix deposition was dose-dependently increased by ACTH in all cell populations as measured by alcian blue stain. ACTH treatment increased proliferation in multipotential progenitor populations (BMSC and RCJ3.1) while proliferation was decreased in committed chondrocyte populations (RC and C5.18). Total protein and total cell-associated collagen production were significantly increased by ACTH treatment in committed populations. Relative COLL II and AGR transcript expressions were significantly increased in both the RC- and C5.18-committed population and very significantly increased in the progenitor populations. Additionally, collagen type X expression was detected earlier and in greater abundance in ACTH-treated committed chondrocyte populations. Finally, the melanocortin-3 receptor was detected in all examined cell types by Western blot. These data show that ACTH promotes the development of the chondrocyte phenotype from multipotential mesenchymal progenitor populations and increases matrix production and differentiation of committed chondrocytes. These findings, together with the detection of the MC3-R in all of these cell types, indicate a role for the melanocortin system in chondrogenesis.

Age related changes in human articular chondrocyte yield, proliferation and post-expansion chondrogenic capacity

OBJECTIVE

We investigated how aging effects human chondrocyte yield, proliferation, post-expansion chondrogenic capacity, and response to specific growth factors supplemented during expansion.

METHODS

Fifty-two samples of human articular cartilage were harvested from cadavers 20 to 91 years old and grouped into age decades. Cell yields were normalised to tissue wet weight. Cell proliferation rates were calculated during expansion in medium without (CTR) or with TGF beta 1, FGF-2 and PDGF-BB (TFP). Chondrogenic capacity of CTR- and TFP-expanded cells was assessed by cultivation as 3D pellets in a defined serum-free medium, followed by histological, immunohistochemical, biochemical and real-time RT-PCR analyses.

RESULTS

Cell yields were similar in donors up to 40 years of age and significantly lower (1.8-fold) in older donors. Cell proliferation rates in CTR medium significantly decreased after 30 years of age and remained similar in older donors. In the presence of TFP, proliferation rates were higher (up to 3.7-fold) in all age groups and decreased only slightly with age. The glycosaminoglycan (GAG) content of pellets obtained from CTR-expanded cells was not correlated with age. Pellets from TFP-expanded cells reproducibly contained more GAG (up to 3.2-fold) than those from CTR-expanded cells only if donors were younger than 40. Safranin O staining intensity and collagen type II expression and accumulation were consistent with GAG contents.

CONCLUSION

Medium supplementation with the growth factor combination TFP during chondrocyte expansion supports higher proliferation rates at any age and higher post-expansion chondrogenic capacity in donors up to 40 years. These findings may be relevant for chondrocyte-based cartilage repair procedures.

Cell Yield, Proliferation, and Postexpansion Differentiation Capacity of Human Ear, Nasal, and Rib Chondrocytes

Human ear, nasal, and rib chondrocytes were compared with respect to their suitability to generate autologous cartilage grafts for nonarticular reconstructive surgery. Cells were expanded for two passages in medium containing 10% fetal bovine serum without (control) or with transforming growth factor beta(1) (TGF-beta(1)), fibroblast growth factor 2 (FGF-2), and platelet-derived growth factor bb (PDGF-bb) (TFP). Expanded cells were cultured as three-dimensional pellets in chondrogenic serum-free medium containing insulin, dexamethasone, and TGF-beta(1). Chondrocytes from all three sources were successfully isolated, increased their proliferation rate in response to TFP, and dedifferentiated during passaging. Redifferentiation by ear and nasal, but not rib, chondrocytes was enhanced after TFP expansion, as assessed by the significant increase in glycosaminoglycan (GAG)/DNA content and collagen type II mRNA expression in the resulting pellets. TFP-expanded ear and nasal chondrocytes generated pellets of better quality than rib chondrocytes, as assessed by the significantly higher GAG/DNA content and collagen type II mRNA expression, and by the relative stain intensities for GAG and collagen types I and II. In conclusion, postexpansion cell yields suggest that all three sources investigated could be used to generate autologous grafts of clinically relevant size. However, ear and nasal chondrocytes, if expanded with TFP, display superior postexpansion chondrogenic potential and may be a preferred cell source for cartilage tissue engineering.

Chondrogenesis of expanded adult human articular chondrocytes is enhanced by specific prostaglandins

OBJECTIVE

To investigate the effects of the cyclooxygenase-2 (cox-2)-dependent prostaglandins D(2) (PGD(2)), E(2) (PGE(2)) and F(2)alpha (PGF(2)alpha) on the redifferentiation and cartilage matrix production of dedifferentiated articular chondrocytes.

METHODS

Human articular chondrocytes from three adult donors were dedifferentiated by monolayer expansion and induced to redifferentiate by culture as 3D pellets in a defined serum-free medium containing TGF-beta(1) and dexamethasone, without or with further supplementation with PGD(2), PGE(2) or PGF(2)alpha. After 2 weeks, pellets were assessed histologically, immunohistochemically, biochemically and by real-time quantitative reverse transcriptase-polymerase chain reaction.

RESULTS

All three PGs, but predominantly PGE(2), reduced the staining intensity of pellets for collagen type I, whereas PGD(2) and PGF(2)alpha increased the staining intensity of pellets for collagen type II and glycosaminoglycans (GAG). The GAG/DNA content of pellets was not affected by PGE(2) but was increased 1.5- and 2.1-fold by PGD(2) and PGF(2)alpha respectively. PGE(2) reduced the expression of collagen type I mRNA (9.0-fold), whereas PGD(2) and PGF(2)alpha increased the mRNA expression of collagen type II (6.2- and 4.1-fold respectively) and aggrecan (29.8- and 10.7-fold respectively).

CONCLUSION

In contrast to PGE(2), PGD(2) and PGF(2)alpha enhanced chondrogenic differentiation and hyaline cartilage matrix deposition by expanded human articular chondrocytes, and could thus be used to improve in vitro or in vivo cartilage regeneration approaches based on these cells.

Enumeration and phenotypic characterization of synovial fluid multipotential mesenchymal progenitor cells in inflammatory and degenerative arthritis

OBJECTIVE

To evaluate synovial fluid (SF) for the presence of mesenchymal progenitor cells (MPCs), to compare SF MPCs with bone marrow (BM) MPCs, and to enumerate these cells in both inflammatory arthritis and osteoarthritis (OA).

METHODS

SF from 100 patients with arthritis (53 rheumatoid arthritis [RA], 20 OA, and 27 other arthropathies) was evaluated. To establish multipotentiality, polyclonal and single cell-derived cultures of SF fibroblasts were examined by standard and quantitative differentiation assays. Their phenotype before and after expansion was determined by multiparameter flow cytometry. A colony-forming unit-fibroblast assay was used for SF MPC enumeration.

RESULTS

Regardless of the nature of the arthritis, both polyclonal and single cell-derived cultures of SF fibroblasts possessed trilineage mesenchymal differentiation potentials. The number of MPCs in a milliliter of SF was higher in OA (median 37) than in RA (median 2) (P < 0.00001). No significant differences in MPC numbers were found between early and established RA (median 3 and 2 cells/ml, respectively). Culture-expanded SF and BM MPCs had the same phenotype (negative for CD45 and positive for D7-FIB, CD13, CD105, CD55, and CD10). Rare, uncultured SF fibroblasts were CD45(low) and expressed low-affinity nerve growth factor receptor, similar to in vivo BM MPCs.

CONCLUSION

Our findings prove the presence of rare tripotential MPCs, at the single-cell level, in the SF of patients with arthritis. SF MPCs are clonogenic and multipotential fibroblasts that, despite the pathologic environment within a diseased joint, have a phenotype similar to that of uncultured BM MPCs. The higher prevalence of MPCs in OA SF suggests their likely origin from disrupted joint structures. These findings could determine the role of MPCs in the pathogenesis of inflammatory arthritis, together with their role in attempted joint regeneration in degenerative arthritis, which has yet to be established.

Transduction of Passaged Human Articular Chondrocytes with Adenoviral, Retroviral, and Lentiviral Vectors and the Effects of Enhanced Expression of SOX9

Chondrocytes form and maintain the extracellular matrix of cartilage. The cells can be isolated from cartilage for applications such as tissue engineering, but their expansion in monolayer culture causes a progressive loss of chondrogenic phenotype. In this work, we have investigated the isolation of human articular chondrocytes from osteoarthritic (OA) cartilage at joint replacement, their expansion in monolayer culture, and their transduction with adenoviral, retroviral, and lentiviral vectors, using the gene encoding green fluorescent protein as a marker gene. The addition of growth factors (transforming growth factor beta(1), fibroblast growth factor 2, and platelet-derived growth factor BB) during cell culture was found to greatly increase cell proliferation and thereby to selectively enhance the efficiency of transduction with retrovirus. With adenoviral and lentiviral vectors the transduction efficiency achieved was 95 and 85%, respectively. Using growth factor-supplemented medium with a retroviral vector, efficiency in excess of 80% was achieved. The expression was stable for several months with both retrovirus and lentivirus when analyzed by fluorescence-activated cell-sorting flow analysis and immunoblotting. Transduction with SOX9 was investigated as a method to reinitiate cartilage matrix gene expression in passaged human OA chondrocytes. Endogenous collagen II expression (both mRNA and protein) was increased in monolayer culture using both adenoviral and retroviral vectors. Furthermore, collagen II gene expression in chondrocytes retrovirally transduced with SOX9 was stimulated by alginate bead culture, whereas in control chondrocytes it was not. These results demonstrated methods for rapid expansion and highly efficient transduction of human OA chondrocytes and the potential for the recovery of key features of chondrocyte phenotype by transduction with SOX9.

Immunophenotypic analysis of human articular chondrocytes: Changes in surface markers associated with cell expansion in monolayer culture

Cartilage tissue engineering relies on in vitro expansion of primary chondrocytes. Monolayer is the chosen culture model for chondrocyte expansion because in this system the proliferative capacity of chondrocytes is substantially higher compared to non-adherent systems. However, human articular chondrocytes (HACs) cultured as monolayers undergo changes in phenotype and gene expression known as "dedifferentiation." To gain a better understanding of the cellular mechanisms involved in the dedifferentiation process, our research focused on the characterization of the surface molecule phenotype of HACs in monolayer culture. Adult HACs were isolated by enzymatic digestion of cartilage samples obtained post-mortem. HACs cultured in monolayer for different time periods were analyzed by flow cytometry for the expression of cell surface markers with a panel of 52 antibodies. Our results show that HACs express surface molecules belonging to different categories: integrins and other adhesion molecules (CD49a, CD49b, CD49c, CD49e, CD49f, CD51/61, CD54, CD106, CD166, CD58, CD44), tetraspanins (CD9, CD63, CD81, CD82, CD151), receptors (CD105, CD119, CD130, CD140a, CD221, CD95, CD120a, CD71, CD14), ectoenzymes (CD10, CD26), and other surface molecules (CD90, CD99). Moreover, differential expression of certain markers in monolayer culture was identified. Up-regulation of markers on HACs regarded as distinctive for mesenchymal stem cells (CD10, CD90, CD105, CD166) during monolayer culture suggested that dedifferentiation leads to reversion to a primitive phenotype. This study contributes to the definition of HAC phenotype, and provides new potential markers to characterize chondrocyte differentiation stage in the context of tissue engineering applications.

Telomere length and telomerase activity during expansion and differentiation of human mesenchymal stem cells and chondrocytes

Chondrocyte ex vivo expansion currently performed to replace damaged articular surfaces is associated with a loss of telomeric repeats similar to decades of aging in vivo. This might affect the incidence or time of onset of age-related disorders within transplanted cells or tissues. This study examined whether more immature progenitor cells, such as mesenchymal stem cells (MSC), which can be expanded and subsequently differentiated into chondrocytes is advantageous regarding telomere-length related limitations of expansion protocols. Primary chondrocytes and bone-marrow-derived MSC were isolated from 12 donors, expanded separately to 4 x 10(6) cells, and (re-)differentiated as three-dimensional chondrogenic spheroids. Cells were collected during expansion, after three-dimensional culturing and chondrogenic differentiation, and sequential analyses of telomere length and telomerase activity were performed. Surprisingly, telomeres of expanded MSC were significantly shorter than those from expanded chondrocytes from the same donor (11.4+/-2.5 vs. 13.4+/-2.2 kb) and tended to remain shorter after differentiation in chondrogenic spheroids (11.9+/-1.8 vs. 13.0+/- kb). While telomere lengths in native chondrocytes and MSC were not related to the age of the donor, significant negative correlations with age were observed in expanded (136 bp/year), three-dimensionally reconstituted (188 bp/year), and redifferentiated (229 bp/year) chondrocytes. Low levels of telomerase activity were found in MSC and chondrocytes during expansion and after (re-)differentiation to chondrogenic spheroids. In terms of replicative potential, as determined by telomere length, ex vivo expansion followed by chondrogenic differentiation of MSC did not provide a benefit compared to the expansion of adult chondrocytes. However, accelerated telomere shortening with age during expansion and redifferentiation argues for an "age phenotype" in chondrocytes as opposed to MSC and suggests an advantage for the use of MSC especially in older individuals and protocols requiring extensive expansion

Dynamic compression of cartilage constructs engineered from expanded human articular chondrocytes

Recent works have shown that mechanical loading can alter the metabolic activity of chondrocytes cultured in 3D scaffolds. In this study we determined whether the stage of development of engineered cartilaginous constructs (expanded adult human articular chondrocytes/Polyactive foams) regulates the effect of dynamic compression on glycosaminoglycan (GAG) metabolism. Construct maturation depended on the culture time (3-14 days) and the donor (4 individuals). When dynamic compression was subsequently applied for 3 days, changes in GAG synthesized, accumulated, and released were significantly positively correlated to the GAG content of the constructs prior to loading, and resulted in stimulation of GAG formation only in the most developed tissues. Conversely, none of these changes were correlated with the expression of collagen type II mRNA, indicating that the response of chondrocytes to dynamic compression does not depend directly upon the stage of cell differentiation, but rather on the extracellular matrix surrounding the cells.