Enhanced chondrocyte proliferation and mesenchymal stromal cells chondrogenesis in coculture pellets mediate improved cartilage formation

In this study, we aimed at investigating the interactions between primary chondrocytes and mesenchymal stem/stromal cells (MSC) accounting for improved chondrogenesis in coculture systems. Expanded MSC from human bone marrow (BM-MSC) or adipose tissue (AT-MSC) were cultured in pellets alone (monoculture) or with primary human chondrocytes from articular (AC) or nasal (NC) cartilage (coculture). In order to determine the reached cell number and phenotype, selected pellets were generated by combining: (i) human BM-MSC with bovine AC, (ii) BM-MSC from HLA-A2+ with AC from HLA-A2- donors, or (iii) human green fluorescent protein transduced BM-MSC with AC. Human BM-MSC and AC were also cultured separately in transwells. Resulting tissues and/or isolated cells were assessed immunohistologically, biochemically, cytofluorimetrically, and by RT-PCR. Coculture of NC or AC (25%) with BM-MSC or AT-MSC (75%) in pellets resulted in up to 1.6-fold higher glycosaminoglycan content than what would be expected based on the relative percentages of the different cell types. This effect was not observed in the transwell model. BM-MSC decreased in number (about fivefold) over time and, if cocultured with chondrocytes, increased type II collagen and decreased type X collagen expression. Instead, AC increased in number (4.2-fold) if cocultured with BM-MSC and maintained a differentiated phenotype. Chondro-induction in MSC-chondrocyte coculture is a robust process mediated by two concomitant effects: MSC-induced chondrocyte proliferation and chondrocyte-enhanced MSC chondrogenesis. The identified interactions between progenitor and mature cell populations may lead to the efficient use of freshly harvested chondrocytes for ex vivo cartilage engineering or in situ cartilage repair.     

Calcification or dedifferentiation: Requirement to lock mesenchymal stem cells in a desired differentiation stage

A current challenge in mesenchymal stem cell (MSC)‐based cartilage repair is to solve donor and tissue‐dependent variability of MSC cultures and to prevent chondrogenic cells from terminal differentiation like in the growth plate. The aim of this study was to select the best source for MSC which could promise stable cartilage formation in the absence of hypertrophy and ectopic in vivo mineralization. We hypothesized that MSC from synovium are superior to bone marrow‐ and adipose tissue‐derived MSC since they are derived from a joint tissue. MSC were characterized by flow cytometry. MSC pellets were cultured under chondrogenic conditions and differentiation was evaluated by histology, gene expression analysis, and determination of alkaline phosphatase activity (ALP). After chondrogenic induction, pellets were transplanted subcutaneously into SCID mice. MSC from bone marrow, adipose tissue, and synovium revealed similar COL2A1/COL10A1 mRNA levels after chondrogenic induction and were positive for collagen‐type‐X. Bone marrow‐derived and adipose tissue‐derived MSC showed significantly higher ALP activity than MSC from synovium. Low ALP‐activity before transplantation of pellets correlated with marginal calcification of explants. Surprisingly, non‐mineralizing transplants specifically lost their collagen‐type II, but not collagen‐type I deposition in vivo, or were fully degraded. In conclusion, the lower donor‐dependent ALP activation and reduced mineralization of synovium‐derived heterotopic transplants did not lead to stable ectopic cartilage as known from articular chondrocytes, but correlated with fibrous dedifferentation or complete degeneration of MSC pellets. This emphasizes that beside appropriate induction of differentiation, locking of MSC in the desired differentiation state is a major challenge for MSC‐based repair strategies. J. Cell. Physiol. 219: 219–226, 2009. © 2008 Wiley‐Liss, Inc.     

Biodegradable zinc oxide composite scaffolds promote osteochondral differentiation of mesenchymal stem cells

Osteoarthritis (OA) involves the degeneration of articular cartilage and subchondral bone. The capacity of articular cartilage to repair and regenerate is limited. A biodegradable, fibrous scaffold containing zinc oxide (ZnO) was fabricated and evaluated for osteochondral tissue engineering applications. ZnO has shown promise for a variety of biomedical applications but has had limited use in tissue engineering. Composite scaffolds consisted of ZnO nanoparticles embedded in slow degrading, polycaprolactone to allow for dissolution of zinc ions over time. Zinc has well-known insulin-mimetic properties and can be beneficial for cartilage and bone regeneration. Fibrous ZnO composite scaffolds, having varying concentrations of 1–10 wt.% ZnO, were fabricated using the electrospinning technique and evaluated for human mesenchymal stem cell (MSC) differentiation along chondrocyte and osteoblast lineages. Slow release of the zinc was observed for all ZnO composite scaffolds. MSC chondrogenic differentiation was promoted on low percentage ZnO composite scaffolds as indicated by the highest collagen type II production and expression of cartilage-specific genes, while osteogenic differentiation was promoted on high percentage ZnO composite scaffolds as indicated by the highest alkaline phosphatase activity, collagen production, and expression of bone-specific genes. This study demonstrates the feasibility of ZnO-containing composites as a potential scaffold for osteochondral tissue engineering.     

Chondrogenic differentiation of bovine bone marrow mesenchymal stem cells (MSCs) in different hydrogels: influence of collagen type II extracellular matrix on MSC chondrogenesis

Bone marrow mesenchymal stem cells (MSCs) are candidate cells for cartilage tissue engineering. This is due to their ability to undergo chondrogenic differentiation after extensive expansion in vitro and stimulation with various biomaterials in three-dimensional (3-D) systems. Collagen type II is one of the major components of the hyaline cartilage and plays a key role in maintaining chondrocyte function. This study aimed at analyzing the MSC chondrogenic response during culture in different types of extracellular matrix (ECM) with a focus on the influence of collagen type II on MSC chondrogenesis. Bovine MSCs were cultured in monolayer as well as in alginate and collagen type I and II hydrogels, in both serum free medium and medium supplemented with transforming growth factor (TGF) beta1. Chondrogenic differentiation was detected after 3 days of culture in 3-D hydrogels, by examining the presence of glycosaminoglycan and newly synthesized collagen type II in the ECM. Differentiation was most prominent in cells cultured in collagen type II hydrogel, and it increased in a time-dependent manner. The expression levels of the of chondrocyte specific genes: sox9, collagen type II, aggrecan, and COMP were measured by quantitative "Real Time" RT-PCR, and genes distribution in the hydrogel beads were localized by in situ hybridization. All genes were upregulated by the presence of collagen, particularly type II, in the ECM. Additionally, the chondrogenic influence of TGF beta1 on MSCs cultured in collagen-incorporated ECM was analyzed. TGF beta1 and dexamethasone treatment in the presence of collagen type II provided more favorable conditions for expression of the chondrogenic phenotype. In this study, we demonstrated that collagen type II alone has the potential to induce and maintain MSC chondrogenesis, and prior interaction with TGF beta1 to enhance the differentiation.     

Retention of the native chondrocyte pericellular matrix results in significantly improved matrix production.

The interaction of the cell with its surrounding extracellular matrix (ECM) has a major effect on cell metabolism. We have previously shown that chondrons, chondrocytes with their in vivo-formed pericellular matrix, can be enzymatically isolated from articular cartilage. To study the effect of the native chondrocyte pericellular matrix on ECM production and assembly, chondrons were compared with chondrocytes isolated without any pericellular matrix. Immediately after isolation from human cartilage, chondrons and chondrocytes were centrifuged into pellets and cultured. Chondron pellets had a greater increase in weight over 8 weeks, were more hyaline appearing, and had more type II collagen deposition and assembly than chondrocyte pellets. Minimal type I procollagen immunofluorescence was detected for both chondron and chondrocyte pellets. Chondron pellets had a 10-fold increase in proteoglycan content compared with a six-fold increase for chondrocyte pellets over 8 weeks (P<0.0001). There was no significant cell division for either chondron or chondrocyte pellets. The majority of cells within both chondron and chondrocyte pellets maintained their polygonal or rounded shape except for a thin, superficial edging of flattened cells. This edging was similar to a perichondrium with abundant type I collagen and fibronectin, and decreased type II collagen and proteoglycan content compared with the remainder of the pellet. This study demonstrates that the native pericellular matrix promotes matrix production and assembly in vitro. Further, the continued matrix production and assembly throughout the 8-week culture period make chondron pellet cultures valuable as a hyaline-like cartilage model in vitro.     

Caprine articular,meniscus and intervertebral disc cartilage: An integral analysis of collagen network and chondrocytes

Cartilage is a tissue with only limited reparative capacities. A small part of its volume is composed of cells, the remaining part being the hydrated extracellular matrix (ECM) with collagens and proteoglycans as its main constituents. The functioning of cartilage depends heavily on its ECM. Although it is known that the various (fibro)cartilaginous tissues (articular cartilage, annulus fibrosus, nucleus pulposus, and meniscus) differ from one each other with respect to their molecular make-up, remarkable little quantitative information is available with respect to its biochemical constituents, such as collagen content, or the various posttranslational modifications of collagen. Furthermore, we have noticed that tissue-engineering strategies to replace cartilaginous tissues pay in general little attention to the biochemical differences of the tissues or the phenotypical differences of the (fibro)chondrocytes under consideration. The goal of this paper is therefore to provide quantitative biochemical data from these tissues as a reference for further studies. We have chosen the goat as the source of these tissues, as this animal is widely accepted as an animal model in orthopaedic studies, e.g. in the field of cartilage degeneration and tissue engineering. Furthermore, we provide data on mRNA levels (from genes encoding proteins/enzymes involved in the synthesis and degradation of the ECM) from (fibro)chondrocytes that are freshly isolated from these tissues and from the same (fibro)chondrocytes that are cultured for 18 days in alginate beads. Expression levels of genes involved in the cross-linking of collagen were different between cells isolated from various cartilaginous tissues. This opens the possibility to include more markers than the commonly used chondrogenic markers type II collagen and aggrecan for cartilage tissue-engineering applications.     

Dehydration rates of meniscus and articular cartilage in vitro using a fast and accurate laser-based coordinate digitizing system

When used in in vitro studies, soft tissues such as the meniscus and articular cartilage are susceptible to dehydration and its effects, such as changes in size and shape as well as changes in structural and material properties. To quantify the effect of dehydration on the meniscus and articular cartilage, the first two objectives of this study were to (1) determine the percent change in meniscal dimensions over time due to dehydration, and (2) determine the percent change in articular cartilage thickness due to dehydration. To satisfy these two objectives, the third objective was to develop a new laser-based three-dimensional coordinate digitizing system (3-DCDS II) that can scan either the meniscus or articular cartilage surface within a time such that there is less than a 5% change in measurements due to dehydration. The new instrument was used to measure changes in meniscal and articular cartilage dimensions of six cadaveric specimens, which were exposed to air for 120 and 130 min, respectively. While there was no change in meniscal width, meniscal height decreased linearly by 4.5% per hour. Articular cartilage thickness decreased nonlinearly at a rate of 6% per hour after 10 min, and at a rate of 16% per hour after 130 min. The system bias and precision of the new instrument at 0 degrees slope of the surface being scanned were 0.0 and 2.6 microm, respectively, while at 45 degrees slope the bias and precision were 31.1 and 22.6 microm, respectively. The resolution ranged between 200 and 500 microm. Scanning an area of 60 x 80 mm (approximately the depth and width of a human tibial plateau) took 8 min and a complete scan of all five sides of a meniscus took 24 min. Thus, the 3-DCDS II can scan an entire meniscus with less than 2% change in dimensions due to dehydration and articular cartilage with less than 0.4% change. This study provides new information on the amount of time that meniscal tissue and articular cartilage can be exposed to air before marked changes in size and shape, and possibly biomechanical, structural and material properties, occur. The new 3-DCDS II designed for this study provides fast and accurate dimensional measurements of both soft and hard tissues.     

Fragmentation of decorin, biglycan, lumican and keratocan is elevated in degenerate human meniscus, knee and hip articular cartilages compared with age-matched macroscopically normal and control tissues

Introduction

The small leucine-rich proteoglycans (SLRPs) modulate tissue organization, cellular proliferation, matrix adhesion, growth factor and cytokine responses, and sterically protect the surface of collagen type I and II fibrils from proteolysis. Catabolism of SLRPs has important consequences for the integrity of articular cartilage and meniscus by interfering with their tissue homeostatic functions.

Methods

SLRPs were dissociatively extracted from articular cartilage from total knee and hip replacements, menisci from total knee replacements, macroscopically normal and fibrillated knee articular cartilage from mature age-matched donors, and normal young articular cartilage. The tissue extracts were digested with chondroitinase ABC and keratanase-I before identification of SLRP core protein species by Western blotting using antibodies to the carboxyl-termini of the SLRPs.

Results

Multiple core-protein species were detected for all of the SLRPs (except fibromodulin) in the degenerate osteoarthritic articular cartilage and menisci. Fibromodulin had markedly less fragments detected with the carboxyl-terminal antibody compared with other SLRPs. There were fewer SLRP catabolites in osteoarthritic hip than in knee articular cartilage. Fragmentation of all SLRPs in normal age-matched, nonfibrillated knee articular cartilage was less than in fibrillated articular cartilage from the same knee joint or total knee replacement articular cartilage specimens of similar age. There was little fragmentation of SLRPs in normal control knee articular cartilage. Only decorin exhibited a consistent increase in fragmentation in menisci in association with osteoarthritis. There were no fragments of decorin, biglycan, lumican, or keratocan that were unique to any tissue. A single fibromodulin fragment was detected in osteoarthritic articular cartilage but not meniscus. All SLRPs showed a modest age-related increase in fragmentation in knee articular and meniscal cartilage but not in other tissues.

Conclusion

Enhanced fragmentation of SLRPs is evident in degenerate articular cartilage and meniscus. Specific decorin and fibromodulin core protein fragments in degenerate meniscus and/or human articular cartilage may be of value as biomarkers of disease. Once the enzymes responsible for their generation have been identified, further research may identify them as therapeutic targets.     

Three-dimensional culture of human meniscal cells: Extracellular matrix and proteoglycan production

Background  

The meniscus is a complex tissue whose cell biology has only recently begun to be explored. Published models rely upon initial culture in the presence of added growth factors. The aim of this study was to test a three-dimensional (3D) collagen sponge microenvironment (without added growth factors) for its ability to provide a microenvironment supportive for meniscal cell extracellular matrix (ECM) production, and to test the responsiveness of cells cultured in this manner to transforming growth factor-β (TGF-β).     

Type III collagen is a key regulator of the collagen fibrillar structure and biomechanics of articular cartilage and meniscus

Despite the fact that type III collagen is the second most abundant collagen type in the body, its contribution to the physiologic maintenance and repair of skeletal tissues remains poorly understood. This study queried the role of type III collagen in the structure and biomechanical functions of two structurally distinctive tissues in the knee joint, type II collagen-rich articular cartilage and type I collagen-dominated meniscus. Integrating outcomes from atomic force microscopy-based nanomechanical tests, collagen fibril nanostructural analysis, collagen cross-link analysis and histology, we elucidated the impact of type III collagen haplodeficiency on the morphology, nanostructure and biomechanical properties of articular cartilage and meniscus in Col3a1^+/− mice. Reduction of type III collagen leads to increased heterogeneity and mean thickness of collagen fibril diameter, as well as reduced modulus in both tissues, and these effects became more pronounced with skeletal maturation. These data suggest a crucial role of type III collagen in mediating fibril assembly and biomechanical functions of both articular cartilage and meniscus during post-natal growth. In articular cartilage, type III collagen has a marked contribution to the micromechanics of the pericellular matrix, indicating a potential role in mediating the early stage of type II collagen fibrillogenesis and chondrocyte mechanotransduction. In both tissues, reduction of type III collagen leads to decrease in tissue modulus despite the increase in collagen cross-linking. This suggests that the disruption of matrix structure due to type III collagen deficiency outweighs the stiffening of collagen fibrils by increased cross-linking, leading to a net negative impact on tissue modulus. Collectively, this study is the first to highlight the crucial structural role of type III collagen in both articular cartilage and meniscus extracellular matrices. We expect these results to expand our understanding of type III collagen across various tissue types, and to uncover critical molecular components of the microniche for regenerative strategies targeting articular cartilage and meniscus repair.     

Effects of co‐cultures of meniscus cells and articular chondrocytes on PLLA scaffolds

The knee meniscus, a fibrocartilaginous tissue located in the knee joint, is characterized by heterogeneity in extracellular matrix and biomechanical properties. To recreate these properties using a tissue engineering approach, co‐cultures of meniscus cells (MCs) and articular chondrocytes (ACs) were seeded in varying ratios (100:0, 75:25, 50:50, 25:75, and 0:100) on poly‐L ‐lactic acid (PLLA) scaffolds and cultured in serum‐free medium for 4 weeks. Histological, biochemical, and biomechanical tests were used to assess constructs at the end time point. Strong staining for collagen and glycosaminoglycan (GAG) was observed in all groups. Constructs with 100% MCs were positive for collagen I and constructs cultured with 100% ACs were positive for collagen II, while a mixture of collagen I and II was observed in other co‐culture groups. Total collagen and GAG per construct increased as the percentage of ACs increased (27 ± 8 µg, 0% AC to 45 ± 8 µg, 100% ACs for collagen and 12 ± 4 µg, 0% ACs to 40 ± 5 µg, 100% ACs for GAG). Compressive modulus (instantaneous and relaxation modulus) of the constructs was significantly higher in the 100% ACs group (63 ± 12 and 22 ± 9 kPa, respectively) when compared to groups with higher percentage of MCs. No differences in tensile properties were noted among groups. Specific co‐culture ratios were identified mimicking the GAG/DW of the inner (0:100, 25:75, and 50:50) and outer regions (100:0) of the meniscus. Overall, it was demonstrated that co‐culturing MCs and ACs on PLLA scaffolds results in functional tissue engineered meniscus constructs with a spectrum of biochemical and biomechanical properties. Biotechnol. Bioeng. 2009;103: 808–816. © 2009 Wiley Periodicals, Inc.     

Transplantation of autologous rabbit BM-derived mesenchymal stromal cells embedded in hyaluronic acid gel sponge into osteochondral defects of the knee

BACKGROUND: Mesenchymal stromal cells (MSC) have the potential to differentiate into distinct mesenchymal tissues including cartilage, suggesting that these cells are an attractive cell source for cartilage tissue engineering approaches. Various methods, such as using hyaluronan-based materials, have been employed to improve transplantation for repair. Our objective was to study the effects of autologous transplantation of rabbit MSC with hyaluronic acid gel sponges into full-thickness osteochondral defects of the knee. METHODS: Rabbit BM-derived MSC were cultured and expanded with fibroblast growth factor (FGF). Specimens were harvested at 4 and 12 weeks after implantation, examined histologically for morphologic features, and stained immunohistochemically for type II collagen and CD44. RESULTS: The regenerated area after autologous transplantation of hyaluronic acid gel sponge loaded with MSC into the osteochondral defect at 12 weeks after surgery showed well-repaired cartilage tissue, resembling the articular cartilage of the surrounding structure, of which the histologic score was significantly better than that of the untreated osteochondral defect. In the regenerated cartilage, type II collagen was found in the pericellular matrix of regenerative chondrocytes, while CD44 expression in the regenerative tissue could not be revealed. DISCUSSION: These data suggest that the autologous transplantation of MSC embedded in hyaluronan-based material may support chondrogenic differentiation and be useful for osteochondral defect repair.     

Immunochemical and mechanical characterization of cartilage subtypes in rabbit.

Cartilage is categorized into three general subgroups, hyaline, elastic, and fibrocartilage, based primarily on morphologic criteria and secondarily on collagen (Types I and II) and elastin content. To more precisely define the different cartilage subtypes, rabbit cartilage isolated from joint, nose, auricle, epiglottis, and meniscus was characterized by immunohistochemical (IHC) localization of elastin and of collagen Types I, II, V, VI, and X, by biochemical analysis of total glycosaminoglycan (GAG) content, and by biomechanical indentation assay. Toluidine blue staining and safranin-O staining were used for morphological assessment of the cartilage subtypes. IHC staining of the cartilage samples showed a characteristic pattern of staining for the collagen antibodies that varied in both location and intensity. Auricular cartilage is discriminated from other subtypes by interterritorial elastin staining and no staining for Type VI collagen. Epiglottal cartilage is characterized by positive elastin staining and intense staining for Type VI collagen. The unique pattern for nasal cartilage is intense staining for Type V collagen and collagen X, whereas articular cartilage is negative for elastin (interterritorially) and only weakly positive for collagen Types V and VI. Meniscal cartilage shows the greatest intensity of staining for Type I collagen, weak staining for collagens V and VI, and no staining with antibody to collagen Type X. Matching cartilage samples were categorized by total GAG content, which showed increasing total GAG content from elastic cartilage (auricle, epiglottis) to fibrocartilage (meniscus) to hyaline cartilage (nose, knee joint). Analysis of aggregate modulus showed nasal and auricular cartilage to have the greatest stiffness, epiglottal and meniscal tissue the lowest, and articular cartilage intermediate. This study illustrates the differences and identifies unique characteristics of the different cartilage subtypes in rabbits. The results provide a baseline of data for generating and evaluating engineered repair cartilage tissue synthesized in vitro or for post-implantation analysis.     

Compound screening platform using human induced pluripotent stem cells to identify small molecules that promote chondrogenesis

Articular cartilage, which is mainly composed of collagen II, enables smooth skeletal movement. Degeneration of collagen II can be caused by various events, such as injury, but degeneration especially increases over the course of normal aging. Unfortunately, the body does not fully repair itself from this type of degeneration, resulting in impaired movement. Microfracture, an articular cartilage repair surgical technique, has been commonly used in the clinic to induce the repair of tissue at damage sites. Mesenchymal stem cells (MSC) have also been used as cell therapy to repair degenerated cartilage. However, the therapeutic outcomes of all these techniques vary in different patients depending on their age, health, lesion size and the extent of damage to the cartilage. The repairing tissues either form fibrocartilage or go into a hypertrophic stage, both of which do not reproduce the equivalent functionality of endogenous hyaline cartilage. One of the reasons for this is inefficient chondrogenesis by endogenous and exogenous MSC. Drugs that promote chondrogenesis could be used to induce self-repair of damaged cartilage as a non-invasive approach alone, or combined with other techniques to greatly assist the therapeutic outcomes. The recent development of human induced pluripotent stem cell (iPSCs), which are able to self-renew and differentiate into multiple cell types, provides a potentially valuable cell resource for drug screening in a “more relevant” cell type. Here we report a screening platform using human iPSCs in a multi-well plate format to identify compounds that could promote chondrogenesis.     

Mechanical injury of explants from the articulating surface of the inner meniscus

Knee osteoarthritis is accelerated by damage to the meniscus, a fibrocartilage tissue that assists in load transmission. However, little is known about the mechanical or cellular response of the meniscus to injurious overloading. Here, in vitro studies explored injury to meniscal explants using a compressive overloading protocol that has been well characterized for articular cartilage. Cartilage samples were processed in parallel as a reference to the extensive literature on cartilage injury. Injured meniscal explants showed extensive cell death at the articulating surface but no gross tissue damage, while similar conditions of peak stress and strain resulted in cartilage surface fissures and cell death consistent with moderate overloading. Post-injury gene expression in meniscal explants indicated a decrease in seven of the nine catabolic and pro-inflammatory molecules surveyed, while cartilage experienced a downregulation in ADAMTS-5 and TNF-α only. These data demonstrated a resiliency of the meniscus to injury, and that an acute increase in catabolic activities is not necessarily a consequence of mechanical overloading.     

Differentiation of transplanted mesenchymal stem cells in a large osteochondral defect in rabbit

BACKGROUND: Although accumulating evidence shows that mesenchymal stem cells (MSC) are a promising cell source for articular cartilage repair, the fate of transplanted MSC has not been extensively studied. METHODS: To monitor their persistence and differentiation, we labeled uninduced MSC with a fluorescent dye, PKH26, and transplanted them, in a poly-glycolic-acid scaffold, to full-thickness defects made in the weight-bearing area of rabbit femoral trochleae with hyaluronate sheets. The fate of the labeled cells was monitored for up to 8 weeks. RESULTS: Two weeks after transplantation, immature cartilage containing collagen type II had formed. By 8 weeks, this cartilage had thinned and immunolabeling for collagen type II gradually disappeared from the basal region, which became positive for collagen type I. Most chondrocytes within the regenerated cartilage were PKH26-positive and, therefore, derived from transplanted MSC, whereas osteoblasts within the regenerated bone were a mixture of donor- and host-derived cells. The thickness of the cartilage became thinner up to 8 weeks and then remained stable up to 42 weeks after surgery. DISCUSSION: These results showed that uninduced MSC were able to survive osteochondral defects and differentiated according to the environment, making a major contribution to initial cartilage formation and a partial contribution to bone regeneration.     

Efficient differentiation of human iPSC‐derived mesenchymal stem cells to chondroprogenitor cells

Induced pluripotent stem cells (iPSC) hold tremendous potential for personalized cell‐based repair strategies to treat musculoskeletal disorders. To establish human iPSCs as a potential source of viable chondroprogenitors for articular cartilage repair, we assessed the in vitro chondrogenic potential of the pluripotent population versus an iPSC‐derived mesenchymal‐like progenitor population. We found the direct plating of undifferentiated iPSCs into high‐density micromass cultures in the presence of BMP‐2 promoted chondrogenic differentiation, however these conditions resulted in a mixed population of cells resembling the phenotype of articular cartilage, transient cartilage, and fibrocartilage. The progenitor cells derived from human iPSCs exhibited immunophenotypic features of mesenchymal stem cells (MSCs) and developed along multiple mesenchymal lineages, including osteoblasts, adipocytes, and chondrocytes in vitro. The data indicate the derivation of a mesenchymal stem cell population from human iPSCs is necessary to limit culture heterogeneity as well as chondrocyte maturation in the differentiated progeny. Moreover, as compared to pellet culture differentiation, BMP‐2 treatment of iPSC‐derived MSC‐like (iPSC–MSC) micromass cultures resulted in a phenotype more typical of articular chondrocytes, characterized by the enrichment of cartilage‐specific type II collagen (Col2a1), decreased expression of type I collagen (Col1a1) as well as lack of chondrocyte hypertrophy. These studies represent a first step toward identifying the most suitable iPSC progeny for developing cell‐based approaches to repair joint cartilage damage. J. Cell. Biochem. 114: 480–490, 2013. © 2012 Wiley Periodicals, Inc.