The enhancement of in vitro survival and chondrogenesis of limb bud cells by cartilage conditioned medium

In vitro chondrogenic commitment of human Wharton's jelly stem cells by co-culture with human articular chondrocytes

Wharton's jelly stem cells (WJSCs) are a potential source of transplantable stem cells in cartilage-regenerative strategies, due to their highly proliferative and multilineage differentiation capacity. We hypothesized that a non-direct co-culture system with human articular chondrocytes (hACs) could enhance the potential chondrogenic phenotype of hWJSCs during the expansion phase compared to those expanded in monoculture conditions. Primary hWJSCs were cultured in the bottom of a multiwell plate separated by a porous transwell membrane insert seeded with hACs. No statistically significant differences in hWJSCs duplication number were observed under either of the culture conditions during the expansion phase. hWJSCs under co-culture conditions show upregulations of collagen type I and II, COMP, TGFβ1 and aggrecan, as well as of the main cartilage transcription factor, SOX9, when compared to those cultured in the absence of chondrocytes. Chondrogenic differentiation of hWJSCs, previously expanded in co-culture and monoculture conditions, was evaluated for each cellular passage using the micromass culture model. Cells expanded in co-culture showed higher accumulation of glycosaminoglycans (GAGs) compared to cells in monoculture, and immunohistochemistry for localization of collagen type I revealed a strong detection signal when hWJSCs were expanded under monoculture conditions. In contrast, type II collagen was detected when cells were expanded under co-culture conditions, where numerous round-shaped cell clusters were observed. Using a micromass differentiation model, hWJSCs, previously exposed to soluble factors secreted by hACs, were able to express higher levels of chondrogenic genes with deposition of cartilage extracellular matrix components, suggesting their use as an alternative cell source for treating degenerated cartilage. Copyright © 2015 John Wiley & Sons, Ltd.

Mesenchymal stem cell differentiation and roles in regenerative medicine

Adult stem cells with multi or unipotent differentiation potential are present in almost all tissues of adult organisms. The main function of these stem cells is to support normal repair and rejuvenation of diseased and aging tissues. Mesenchymal stem cells (MSCs) isolated from the bone marrow have the potential to differentiate into multiple connective tissues. Advancements in understanding tissue specific differentiation of MSCs in conjunction with global genomic and proteomic profiling of MSCs have not only provided insights into their biology but also made MSC based clinical trials a reality for treating various debilitating diseases and genetic disorders. The emerging evidence that MSCs are immunosuppressive makes them an even more attractive candidate for regenerative medicine as rejections of transplants by the recipient could be a limiting step for moving the stem cells based therapies from "bedside to bed side." To a large extent the therapeutic potential of MSCs is attributed to their differentiation ability. The fate and commitment of MSCs are regulated by various instructive signals from their immediate vicinity or microenvironment, which comprises many biological molecules (soluble and insoluble) and biomechanical forces. These biochemical and biophysical factors play a pivotal role in determining the efficacy of MSC differentiation and their contribution to the repair process. In this review, we discuss the characteristics of MSCs, their differentiation potential toward different skeletal tissues (cartilage and bone), and their emerging role in regenerative medicine.

Chondrogenesis of synovium-derived mesenchymal stem cells in gene-transferred co-culture system

A co-culture strategy has been developed in this study wherein rabbit synovial mesenchymal stem cells (SMSCs) are co-cultured with growth factor (GF) transfected articular chondrocytes. Toward this end, both SMSCs and early passage rabbit articular chondrocytes that had been adenovirally transduced with transforming growth factor-beta 3 (TGF-beta3) gene were separately encapsulated in alginate beads and co-cultured in the same pool of chondrogenic medium. The chondrocytes act as transfected companion cells (TCCs) providing GF supply to induce chondrogenic differentiation of SMSCs that play the role of therapeutic progenitor cells (TPCs). Against the same TCC based TGF-beta3 release profile, the co-culture was started at different time points (Day 0, Day 10 and Day 20) but made to last for identical periods of exposure (30 days) so that the exposure conditions could be optimized in terms of initiation and duration. Transfection of TCCs prevents the stem cell based TPCs from undergoing the invasive procedure. It also prevents unpredictable complications in the TPCs caused by long-term constitutive over-expression of a GF. The adenovirally transfected TCCs exhibit a transient GF expression which results in a timely termination of GF supply to the TPCs. The TCC-sourced transgenic TGF-beta3 successfully induced chondrogenesis in the TPCs. Real-time PCR results show enhanced expression of cartilage markers and immuno/histochemical staining for Glycosaminoglycans (GAG) and Collagen II also shows abundant extracellular matrix (ECM) production and chondrogenic morphogenesis in the co-cultured TPCs. These results confirm the efficacy of directing stem cell differentiation towards chondrogenesis and cartilage tissue formation by co-culturing them with GF transfected chondrocytes.

Derivation of chondrogenically-committed cells from human embryonic cells for cartilage tissue regeneration

Background

Heterogeneous and uncontrolled differentiation of human embryonic stem cells (hESCs) in embryoid bodies (EBs) limits the potential use of hESCs for cell-based therapies. More efficient strategies are needed for the commitment and differentiation of hESCs to produce a homogeneous population of specific cell types for tissue regeneration applications.

Methodology/Principal Findings

We report here that significant chondrocytic commitment of feeder-free cultured human embryonic stem cells (FF-hESCs), as determined by gene expression and immunostaining analysis, was induced by co-culture with primary chondrocytes. Furthermore, a dynamic expression profile of chondrocyte-specific genes was observed during monolayer expansion of the chondrogenically-committed cells. Chondrogenically-committed cells synergistically responded to transforming growth factor-β1 (TGF-β1) and β1-integrin activating antibody by increasing tissue mass in pellet culture. In addition, when encapsulated in hydrogels, these cells formed cartilage tissue both in vitro and in vivo. In contrast, the absence of chondrocyte co-culture did not result in an expandable cell population from FF-hESCs.

Conclusions/Significance

The direct chondrocytic commitment of FF-hESCs can be induced by morphogenetic factors from chondrocytes without EB formation and homogenous cartilage tissue can be formed in vitro and in vivo.

Controlled differentiation of stem cells

The extracellular microenvironment plays a significant role in controlling cellular behavior. Identification of appropriate biomaterials that support cellular attachment, proliferation and, most importantly in the case of human embryonic stem cells, lineage-specific differentiation is critical for tissue engineering and cellular therapy. In addition to growth factors and morphogenetic factors known to induce lineage commitment of stem cells, a number of scaffolding materials, including synthetic and naturally-derived biomaterials, have been utilized in tissue engineering approaches to direct differentiation. This review focuses on recent emerging findings and well-characterized differentiation models of human embryonic stem cells. Additionally, we also discuss about various strategies that have been used in stem cell expansion.

Differentiation of adipose stem cells by nucleus pulposus cells: configuration effect

Degenerative disc disease (DDD) is a major cause of chronic low back pain. For mild/intermediate DDD, regeneration by injecting adipose stem cells (ASCs) into the nucleus pulposus (NP) may be considered. The goal of this study is to investigate whether NP cells can direct ASCs towards the NP phenotype. Interactions between NP cells and ASCs were studied in transwell co-cultures, employing both monolayer and micromass configurations. Micromass culturing significantly up-regulated aggrecan and collagen type II gene expression in NP cells. In ASCs, expression of these genes and of osteopontin, collagen type I and PPAR-gamma were not significantly affected. Strikingly, only when both cell types were micromass-cultured, ASCs could be chondrogenically differentiated, as shown by induction of collagen type II and aggrecan, and concomitant down-regulation of osteopontin, collagen type I and PPAR-gamma. We conclude that ASCs can be directed towards the NP cell-like phenotype by soluble factor(s) secreted by NP cells.

Morphogenetic signals from chondrocytes promote chondrogenic and osteogenic differentiation of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are potentially useful cells for musculoskeletal tissue engineering. However, controlling MSC differentiation and tissue formation in vivo remains a challenge. There is a significant need for well-defined and efficient protocols for directing MSC behaviors in vivo. We hypothesize that morphogenetic signals from chondrocytes may regulate MSC differentiation. In micromass culture of MSCs, incubation with chondrocyte-conditioned medium (CCM) significantly enhanced the production of cartilage specific matrix including type II collagen. In addition, incubation of MSCs with conditioned medium supplemented with osteogenic factors induced more osteogenesis and accumulation of calcium and increased ALP activity. These findings reveal that chondrocyte-secreted factors promote chondrogenesis as well as osteogenesis of MSCs during in vitro micromass culture. Moreover, when MSCs expanded with chondrocyte-conditioned medium were encapsulated in hydrogels and subsequently implanted into athymic mice, basophilic extracellular matrix deposition characteristic of neocartilage was evident. These results indicate that articular chondrocytes produce suitable morphogenetic factors that induce the differentiation program of MSCs in vitro and in vivo.

Directing stem cell differentiation into the chondrogenic lineage in vitro

A major area in regenerative medicine is the application of stem cells in cartilage tissue engineering and reconstructive surgery. This requires well-defined and efficient protocols for directing the differentiation of stem cells into the chondrogenic lineage, followed by their selective purification and proliferation in vitro. The development of such protocols would reduce the likelihood of spontaneous differentiation of stem cells into divergent lineages upon transplantation, as well as reduce the risk of teratoma formation in the case of embryonic stem cells. Additionally, such protocols could provide useful in vitro models for studying chondrogenesis and cartilaginous tissue biology. The development of pharmacokinetic and cytotoxicity/genotoxicity screening tests for cartilage-related biomaterials and drugs could also utilize protocols developed for the chondrogenic differentiation of stem cells. Hence, this review critically examines the various strategies that could be used to direct the differentiation of stem cells into the chondrogenic lineage in vitro.

In vitro development of hypertrophic chondrocytes starting from selected clones of dedifferentiated cells

Single cells from enzymatically dissociated chick embryo tibiae have been cloned and expanded in fresh or conditioned culture media. A cloning efficiency of approximately 13% was obtained using medium conditioned by dedifferentiated chondrocytes. A cloning efficiency of only 1.4% was obtained when conditioned medium from hypertrophic chondrocytes was used, and efficiencies of essentially 0 were found with fresh medium or medium conditioned by J2-3T3 mouse fibroblasts. Cell clones were selected by morphological criteria and clones showing a dedifferentiated phenotype (fibroblast-like) were further characterized. Out of 38 clones analyzed, 17 were able to differentiate to the hypertrophic chondrocyte stage and reconstitute hypertrophic cartilage when placed in the appropriate culture conditions. Cells from these clones expressed the typical markers of chondrocyte differentiation, i.e., type II and type X collagens. Clones not undergoing differentiation continued to express only type I collagen. Hypertrophic chondrocytes from differentiating clones were analyzed at the single cell level by immunofluorescence; all the cells were positive for type X collagen, while approximately 50% of them showed positivity for type II collagen.

Induction and prevention of chondrocyte hypertrophy in culture

Primary chondrocytes from whole chick embryo sterna can be maintained in suspension culture stabilized with agarose for extended periods of time. In the absence of FBS, the cells remain viable only when seeded at high densities. They do not proliferate at a high rate but they deposit extracellular matrix with fibrils resembling those of authentic embryonic cartilage in their appearance and collagen composition. The cells exhibit many morphological and biochemical characteristics of resting chondrocytes and they do not produce collagen X, a marker for hypertrophic cartilage undergoing endochondral ossification. At low density, cells survive in culture without FBS when the media are conditioned by chondrocytes grown at high density. Thus, resting cartilage cells in agarose cultures can produce factors required for their own viability. Addition of FBS to the culture media leads to profound changes in the phenotype of chondrocytes seeded at low density. Cells form colonies at a high rate and assume properties of hypertrophic cells, including the synthesis of collagen X. They extensively deposit extracellular matrix resembling more closely that of adult rather than embryonic cartilage.

Separation of precursor myogenic and chondrogenic cells in early limb bud mesenchyme by a monoclonal antibody

We have addressed the problem of the segregation of cell lineages during the development of cartilage and muscle in the chick limb bud. The following experiments demonstrate that early limb buds consist of at least two independent subpopulations of committed precursor cells--those in (a) the myogenic and (b) the chondrogenic lineage--which can be physically separated. Cells obtained from stage 20, 21, and 22 limb buds were cultured for 5 h in the presence of a monoclonal antibody that was originally isolated for its ability to detach preferentially myogenic cells from extracellular matrices. The detached limb bud cells were collected and replated in normal medium. Within 2 d nearly all of the replated cells had differentiated into myoblasts and myotubes; no chondroblasts differentiated in these cultures. In contrast, the original adherent population that remained after the antibody-induced detachment of the myogenic cells differentiated largely into cartilage and was devoid of muscle. Rearing the antibody-detached cells (i.e., replicating myogenic precursors and postmitotic myoblasts) in medium known to promote chondrogenesis did not induce these cells to chondrify. Conversely, rearing the attached precursor cells (i.e., chondrogenic precursors) in medium known to promote myogenesis did not induce these cells to undergo myogenesis. The definitive mononucleated myoblasts and multinucleated myotubes were identified by muscle-specific antibodies against light meromyosin or desmin, whereas the definitive chondroblasts were identified by a monoclonal antibody against the keratan sulfate chains of the cartilage-specific sulfated proteoglycan. These findings are interpreted as supporting the lineage hypothesis in which the differentiation program of a cell is determined by means of transit through compartments of a lineage.

Selective emergence of differentiated chondrocytes during serum-free culture of cells derived from fetal rat calvaria

Cells dispersed from the chondrocranial portions of fetal rat calvaria proliferated and performed specialized functions during primary culture in a chemically defined medium. Mature cultures were typified by multilayered clusters of redifferentiating cartilage cells. Flattened cells that lacked distinguishing features occupied areas between the clusters. Alkaline phosphate-enriched, ultrastructurally typical chondrocytes within the clusters were encased in a dense extracellular matrix that stained prominently for chondroitin sulfate proteoglycans. This matrix contained fibrils measuring 19 nm in diameter, which were associated with proteoglycan granules that preferentially bound ruthenium red. A progressive increase in the number of cells indicated the proliferation of certain elements in the primary culture. The cells in primary culture were biochemically as well as morphologically heterogeneous since they were found to synthesize type I and type II collagens. Homogeneous populations of redifferentiated chondrocytes were recovered as floating cells and were shown to express the chondrocyte phenotype in secondary culture. Subcultured cells synthesized type II collagen and its precursors almost exclusively and incorporated 35SO4 into proteoglycan monomer and aggregates to a greater degree than the cells in primary culture. The pattern of proteoglycan monomer and aggregate labeling resembled that of intact cartilage segments and bovine articular chondrocytes. Skin fibroblasts harvested from the same rat fetuses failed to proliferate when maintained under identical conditions. Hence, exogenous hormones, growth factors, and protein are not required for chondrocyte growth and maturation.