Chondrogenic differentiation of cultured human mesenchymal stem cells from marrow

Bioengineering of articular cartilage: past, present and future

The treatment of cartilage defects poses a clinical challenge owing to the lack of intrinsic regenerative capacity of cartilage. The use of tissue engineering techniques to bioengineer articular cartilage is promising and may hold the key to the successful regeneration of cartilage tissue. Natural and synthetic biomaterials have been used to recreate the microarchitecture of articular cartilage through multilayered biomimetic scaffolds. Acellular scaffolds preserve the microarchitecture of articular cartilage through a process of decellularization of biological tissue. Although promising, this technique often results in poor biomechanical strength of the graft. However, biomechanical strength could be improved if biomaterials could be incorporated back into the decellularized tissue to overcome this limitation.

Myocilin stimulates osteogenic differentiation of mesenchymal stem cells through mitogen-activated protein kinase signaling

Myocilin is a secreted glycoprotein that is expressed in ocular and non-ocular tissues. Mutations in the MYOCILIN gene may lead to juvenile- and adult-onset primary open-angle glaucoma. Here we report that myocilin is expressed in bone marrow-derived mesenchymal stem cells (MSCs) and plays a role in their differentiation into osteoblasts in vitro and in osteogenesis in vivo. Expression of myocilin was detected in MSCs derived from mouse, rat, and human bone marrow, with human MSCs exhibiting the highest level of myocilin expression. Expression of myocilin rose during the course of human MSC differentiation into osteoblasts but not into adipocytes, and treatment with exogenous myocilin further enhanced osteogenesis. MSCs derived from Myoc-null mice had a reduced ability to differentiate into the osteoblastic lineage, which was partially rescued by exogenous extracellular myocilin treatment. Myocilin also stimulated osteogenic differentiation of wild-type MSCs, which was associated with activation of the p38, Erk1/2, and JNK MAP kinase signaling pathways as well as up-regulated expression of the osteogenic transcription factors Runx2 and Dlx5. Finally, cortical bone thickness and trabecular volume, as well as the expression level of osteopontin, a known factor of bone remodeling and osteoblast differentiation, were reduced dramatically in the femurs of Myoc-null mice compared with wild-type mice. These data suggest that myocilin should be considered as a target for improving the bone regenerative potential of MSCs and may identify a new role for myocilin in bone formation and/or maintenance in vivo.

Agonism of Wnt-β-catenin signalling promotes mesenchymal stem cell (MSC) expansion

Promoting mesenchymal stem cell (MSC) proliferation has numerous applications in stem cell therapies, particularly in the area of regenerative medicine. In order for cell-based regenerative approaches to be realized, MSC proliferation must be achieved in a controlled manner without compromising stem cell differentiation capacities. Here we demonstrate that 6-bromoindirubin-3'-oxime (BIO) increases MSC β-catenin activity 106-fold and stem cell-associated gene expression ~33-fold, respectively, over untreated controls. Subsequently, BIO treatment increases MSC populations 1.8-fold in typical 2D culture conditions, as well as 1.3-fold when encapsulated within hydrogels compared to untreated cells. Furthermore, we demonstrate that BIO treatment does not reduce MSC multipotency where MSCs maintain their ability to differentiate into osteoblasts, chondrocytes and adipocytes using standard conditions. Taken together, our results demonstrate BIO's potential utility as a proliferative agent for cell transplantation and tissue regeneration.

Induction of mesenchymal stem cell chondrogenesis by polyacrylate substrates

Mesenchymal stem cells (MSCs) can generate chondrocytes in vitro, but typically need to be cultured as aggregates in the presence of transforming growth factor beta (TGF-β), which makes scale-up difficult. Here we investigated if polyacrylate substrates modelled on the functional group composition and distribution of the Arg-Gly-Asp (RGD) integrin-binding site could induce MSCs to undergo chondrogenesis in the absence of exogenous TGF-β. Within a few days of culture on the biomimetic polyacrylates, both mouse and human MSCs, and a mesenchymal-like mouse-kidney-derived stem cell line, began to form multi-layered aggregates and started to express the chondrocyte-specific markers, Sox9, collagen II and aggrecan. Moreover, collagen II tended to be expressed in the centre of the aggregates, similarly to developing limb buds in vivo. Surface analysis of the substrates indicated that those with the highest surface amine content were most effective at promoting MSC chondrogenesis. These results highlight the importance of surface group functionality and the distribution of those groups in the design of substrates to induce MSC chondrogenesis.

Anisotropic rigidity sensing on grating topography directs human mesenchymal stem cell elongation

Through mechanotransduction, cells can sense physical cues from the extracellular environment and convert them into internal signals that affect various cellular functions. For example, human mesenchymal stem cells (hMSCs) cultured on topographical gratings have been shown to elongate and differentiate to different extents depending on grating width. Using a combination of experiments and mathematical modeling, the physical parameters of substrate topography that direct cell elongation were determined. On a variety of topographical gratings with different grating widths, heights and rigidity, elongation of hMSCs was measured and a monotonic increase was observed for grating aspect ratio (crosssectional height to line-width ratio) between 0.035 and 2. The elongation was also dependent on the grating substrate rigidity over a range of 0.18-1.43 MPa. A mathematical model was developed to explain our observations by relating cell elongation to the anisotropic deformation of the gratings and how this anisotropy depends on the aspect ratio and rigidity of the gratings. Our model was in good agreement with the experimental data for the range of grating aspect ratio and substrate rigidity studied. In addition, we also showed that the percentage of aligned cells, which had a strong linear correlation with elongation for slightly elongated cells, saturated toward 100 % at higher level of cell elongation. Our results may be useful in designing gratings to elicit specific cellular responses that may depend on the extent of cell elongation.

Synthesis of photodegradable macromers for conjugation and release of bioactive molecules

Hydrogel scaffolds are used in biomedicine to study cell differentiation and tissue evolution, where it is critical to control the delivery of chemical cues both spatially and temporally. While large molecules can be physically entrapped in a hydrogel, moderate molecular weight therapeutics must be tethered to the hydrogel network through a labile linkage to allow controlled release. We synthesized and characterized a library of polymerizable ortho-nitrobenzyl (o-NB) macromers with different functionalities at the benzylic position (alcohol, amine, BOC-amine, halide, acrylate, carboxylic acid, activated disulfide, N-hydroxysuccinyl ester, biotin). This library of polymerizable macromers containing o-NB groups should allow direct conjugation of nearly any type of therapeutic agent and its subsequent controlled photorelease from a hydrogel network. As proof-of-concept, we incorporated the N-hydroxysuccinyl ester macromer into hydrogels and then reacted phenylalanine with the NHS ester. Upon exposure to light (λ = 365 nm; 10 mW/cm(2), 10 min), 81.3% of the phenylalanine was released from the gel. Utilizing the photodegradable macromer incorporating an activated disulfide, we conjugated a cell-adhesive peptide (GCGYGRGDSPG), a protein that exhibits enzymatic activity (bovine serum albumin (BSA)), and a growth factor (transforming growth factor-β1 (TGF-β1)) into hydrogels, controlled their release with light (λ = 365 nm; 10 mW/cm(2), 0-20 min), and verified the bioactivity of the photoreleased molecules. The photoreleasable peptide allows real-time control over cell adhesion. BSA maintains full enzymatic activity upon sequestration and release from the hydrogel. Photoreleased TGF-β1 is able to induce chondrogenic differentiation of human mesenchymal stem cells comparable to native TGF-β1. Through this approach, we have demonstrated that photodegradable tethers can be used to sequester peptides and proteins into hydrogel depots and release them in an externally controlled, predictable manner without compromising biological function.

In vitro generation of whole osteochondral constructs using rabbit bone marrow stromal cells, employing a two-chambered co-culture well design

The regeneration of whole osteochondral constructs with a physiological structure has been a significant issue, both clinically and academically. In this study, we present a method using rabbit bone marrow stromal cells (BMSCs) cultured on a silk-RADA peptide scaffold in a specially designed two-chambered co-culture well for the generation of multilayered osteochondral constructs in vitro. This specially designed two-chambered well can simultaneously provide osteogenic and chondrogenic stimulation to cells located in different regions of the scaffold. We demonstrated that this co-culture approach could successfully provide specific chemical stimulation to BMSCs located on different layers within a single scaffold, resulting in the formation of multilayered osteochondral constructs containing cartilage-like and subchondral bone-like tissue, as well as the intermediate osteochondral interface. The cells in the intermediate region were found to be hypertrophic chondrocytes, embedded in a calcified extracellular matrix containing glycosaminoglycans and collagen types I, II and X. In conclusion, this study provides a single-step approach that highlights the feasibility of rabbit BMSCs as a single-cell source for multilayered osteochondral construct generation in vitro.

Growth differentiation factor-5 enhances in vitro mesenchymal stromal cell chondrogenesis and hypertrophy

The regenerative potential for adult bone marrow-derived mesenchymal stromal cells (MSCs) has been extensively investigated in the setting of arthritic disease and focal cartilage defects. In vitro chondrogenic differentiation of MSCs is regularly accomplished by the widely used pellet culture system where MSCs are maintained in high-density pellets to mimic mesenchymal condensation during development. Supplementation of chondrogenic MSC pellet cultures with growth differentiation factor-5 (GDF-5), a highly regulated gene in the chondrogenic phase of endochondral ossification (EO), was investigated here under the hypothesis that GDF-5 will enhance the chondrogenic differentiation of MSCs, thereby supporting their entry into ossification. The supplementation of chondrogenic MSC pellets with the recombinant human GDF-5 protein significantly enhanced MSC chondrogenic differentiation, as demonstrated by enhanced collagen type II and sulfated glycosaminoglycan (GAG) incorporation into the extracellular matrix. Increased P-SMADs 1-5-8 were observed in pellets treated with GDF-5 and transforming growth factor (TGF)-β 3 when compared to the pellets treated with TGF-β 3 alone, demonstrated by immunostaining and western blot analysis of the chondrogenic pellet extract. A concurrent increase in alkaline phosphatase, collagen types I and X, and osteopontin secretion indicated a transition of these cultures to hypertrophy. Together, these data support the application of GDF-5 to enhance MSC chondrogenic differentiation and hypertrophy as a precursor to EO.

Informing future cartilage repair strategies: a comparative study of three different human cell types for cartilage tissue engineering

A major clinical need exists for cartilage repair and regeneration. Despite many different strategies having been pursued, the identification of an optimised cell type and of pre-treatment conditions remains a challenge. This study compares the cartilage-like tissue generated by human bone marrow stromal cells (HBMSCs) and human neonatal and adult chondrocytes cultured on three-dimensional (3D) scaffolds under various conditions in vitro and in vivo with the aim of informing future cartilage repair strategies based upon tissue-engineering approaches. After 3 weeks in vitro culture, all three cell types showed cartilage-like tissue formation on 3D poly (lactide-co-glycolide) acid scaffolds only when cultured in chondrogenic medium. After 6 weeks of chondro-induction, neonatal chondrocyte constructs revealed the most cartilage-like tissue formation with a prominent superficial zone-like layer, a middle zone-like structure and the thinnest fibrous capsule. HBMSC constructs had the thickest fibrous capsule formation. Under basal culture conditions, neonatal articular chondrocytes failed to form any tissue, whereas HBMSCs and adult chondrocytes showed thick fibrous capsule formation at 6 weeks. After in vivo implantation, all groups generated more compact tissues compared with in vitro constructs. Pre-culturing in chondrogenic media for 1 week before implantation reduced fibrous tissue formation in all cell constructs at week 3. After 6 weeks, only the adult chondrocyte group pre-cultured in chondrogenic media was able to maintain a more chondrogenic/less fibrocartilaginous phenotype. Thus, pre-culture under chondrogenic conditions is required to maintain a long-term chondrogenic phenotype, with adult chondrocytes being a more promising cell source than HBMSCs for articular cartilage tissue engineering.

Adipose-derived mesenchymal stem cells and regenerative medicine

Adipose tissue-derived mesenchymal stem cells (ADSCs) are multipotent and can differentiate into various cell types, including osteocytes, adipocytes, neural cells, vascular endothelial cells, cardiomyocytes, pancreatic β-cells, and hepatocytes. Compared with the extraction of other stem cells such as bone marrow-derived mesenchymal stem cells (BMSCs), that of ADSCs requires minimally invasive techniques. In the field of regenerative medicine, the use of autologous cells is preferable to embryonic stem cells or induced pluripotent stem cells. Therefore, ADSCs are a useful resource for drug screening and regenerative medicine. Here we present the methods and mechanisms underlying the induction of multilineage cells from ADSCs.

In vitro hypertrophy and calcification of human fracture haematoma-derived cells in chondrogenic differentiation

PURPOSE

The haematoma at a fracture site plays an important role in fracture healing. Previously, we demonstrated that a fracture haematoma contains multilineage mesenchymal progenitor cells. We postulated that the haematoma provided a source of chondrogenic cells for endochondral ossification during fracture healing and preservation of the cells contributed to biological fracture healing. In this study, we investigated whether haematoma-derived cells (HCs) could differentiate into hypertrophic chondrocytes and finally induce calcification of the extracellular matrix in vitro.

METHODS

Fracture haematomas were obtained from four patients. HCs were cultured for five weeks under conditions that induce chondrogenic differentiation, followed by two weeks of hypertrophic induction using a pellet culture system. The pellets were analysed histologically and immunohistochemically. The gene expression levels of chondrogenic, hypertrophic, osteogenic, and angiogenic markers were measured by real-time PCR.

RESULTS

The histological and immunohistochemical analyses revealed that HCs differentiated into chondrocytes and hypertrophic chondrocytes, followed by calcification of the extracellular matrix. This sequential differentiation was also reflected in the gene expression profiles. After chondrogenic induction, expression of osteogenic and angiogenic markers was not significantly upregulated. However, the expression of these markers was significantly upregulated following hypertrophic induction. These in vitro observations mimicked the process of endochondral ossification during fracture healing.

CONCLUSIONS

Our results suggest that the fracture haematoma may offer a source of cells with chondrogenic potential that play key roles in endochondral ossification during fracture healing. These findings support the opinion that the haematoma should be preserved for biological fracture healing.

Salient features of mesenchymal stem cells-implications for Ewing sarcoma modeling

Despite a heightened appreciation of the many defining molecular aberrations in Ewing sarcoma, the cooperative genetic environment and permissive cell of origin essential for EWS/ETS-mediated oncogenesis remain elusive. Consequently, inducible animal and in vitro models of Ewing sarcoma from a native cellular context are unable to fully recapitulate malignant transformation. Despite these shortcomings, human, and murine mesenchymal stem cells (MSCs) are the closest working in vitro systems available. MSCs are tolerant of ectopic EWS/FLI expression, which is accompanied by a molecular signature most similar to Ewing sarcoma. Whether MSCs are the elusive cell of origin or simply a tolerant platform of the EWS/FLI transcriptome, these cells have become an excellent molecular tool to investigate and manipulate oncogenesis in Ewing sarcoma. Our understanding of the biological complexity and heterogeneity of human MSCs (hMSCs) has increased substantially over time and as such, appreciation and utilization of these salient complexities may greatly enhance the efficient use of these cells as surrogate models for Ewing sarcoma tumorigenesis.

Reproductive stem cell differentiation: extracellular matrix, tissue microenvironment, and growth factors direct the mesenchymal stem cell lineage commitment

The mesenchymal stem cells (MSCs) have awakened interest in regenerative medicine due to its high capability to proliferate and differentiate in multiple specialized lineages under defined conditions. The reproductive system is considered a valuable source of MSCs, which needs further investigations. Many factors have been reported as critical for these cell lineage specification and determination. In this review, we discuss the main effects of extracellular matrix or tissue environment and growth factors in the cell lineage commitment, including the reproductive stem cells. The MSCs responses to culture medium stimuli or to soluble factors probably occur through several intracellular activation pathways. However, the molecular mechanisms in which the cells respond to these mechanical or chemical perturbations remain elusive. Recent findings suggest a synergic effect of microenvironment and soluble cell culture factors affecting cell differentiation. For future applications in cell therapy, protocols of reproductive MSCs differentiation must be established.

In vitro generation of a multilayered osteochondral construct with an osteochondral interface using rabbit bone marrow stromal cells and a silk peptide-based scaffold

Tissue engineering of a biological osteochondral multilayered construct with a cartilage-interface subchondral bone layer is a key challenge. This study presented a rabbit bone marrow stromal cell (BMSC)/silk fibroin scaffold-based co-culture approach to generate tissue-engineered osteochondral grafts with an interface. BMSC-seeded scaffolds were first cultured separately in osteogenic and chondrogenic stimulation media. The two differentiated pieces were then combined using an RADA self-assembling peptide and subsequently co-cultured. Gene expression, histological and biochemical analyses were used to evaluate the multilayered structure of the osteochondral graft. A complete osteochondral construct with a cartilage-subchondral bone interface was regenerated and BMSCs were used as the only cell source for the osteochondral construct and interface regeneration. Furthermore, in the intermediate region of co-cultured samples, hypertrophic chondrogenic gene markers type X collagen and MMP-13 were found on both chondrogenic and osteogenic section edges after co-culture. However, significant differences gene expression profile were found in distinct zones of the construct during co-culture and the section in the intermediate region had significantly higher hypertrophic chondrocyte gene expression. Biochemical analyses and histology results further supported this observation. This study showed that specific stimulation from osteogenic and chondrogenic BMSCs affected each other in this co-culture system and induced the formation of an osteochondral interface. Moreover, this system provided a possible approach for generating multilayered osteochondral constructs.

Comparison of autogenic and allogenic bone marrow derived mesenchymal stem cells for repair of segmental bone defects in rabbits

Autogenic and allogenic bone marrow derived mesenchymal stem cells (BM-MSCs) were compared for repair of bone gap defect in rabbits. BM-MSCs were isolated from bone marrow aspirates and cultured in vitro for allogenic and autogenic transplantation. A 5mm segmental defect was created in mid-diaphysis of the radius bone. The defect was filled with hydroxyapatite alone, hydroxyapatite with autogeneic BM-MSCs and hydroxyapatite with allogenic BM-MSCs in groups A, B and C, respectively. On an average 3.45×10(6) cells were implanted at each defect site. Complete bridging of bone gap with newly formed bone was faster in both treatment groups as compared to control group. Histologically, increased osteogenesis, early and better reorganization of cancellous bone and more bone marrow formation were discernible in treatment groups as compared to control group. It was concluded that in vitro culture expanded allogenic and autogenic BM-MSCs induce similar, but faster and better healing as compared to control.

Activin/BMP2 chimeric ligands direct adipose-derived stem cells to chondrogenic differentiation

Human adipose derived stem cells (hASCs) can be easily isolated and their plasticity has been well characterized. Several TGF-β superfamily ligands can direct hASCs towards chondrocytes. However, these ligands are difficult to purify and expensive. We have developed a library of Activin/BMP2 chimeric ligands (AB2 ligands) by systematically mixing their sequence segments and have tested their chondrogenic potential in hASCs. Cells cultured in monolayer or in a pellet culture system were incubated with a chemically defined medium supplemented with the chimeric ligands for 4 or 6 weeks and showed higher expression levels of type II collagen, aggrecan, and Sox9 mRNAs when compared with control and non-treated cells. Moreover, toluidine blue, alcian blue, and Masson's trichrome staining was markedly increased in treated cells, both in cell pellet and monolayer assays. In addition, immunohistochemical staining for detection of type I collagen, type II collagen, and Sox 9 demonstrated the acquisition of a chondrogenic phenotype in both culture systems. We present here an inexpensive and robust protocol for differentiation of hASCs towards chondrocytes in a reproducible and highly efficient manner. The AB2 ligands employed are easily produced and have properties that may become useful in cell therapy.

Effect of parathyroid hormone-related protein in an in vitro hypertrophy model for mesenchymal stem cell chondrogenesis

PURPOSE

Mesenchymal stem cells (MSCs) express markers of hypertrophic chondrocytes during chondrogenic differentiation. We tested the suitability of parathyroid hormone-related protein (PTHrP), a regulator of chondrocyte hypertrophy in embryonic cartilage development, for the suppression of hypertrophy in an in vitro hypertrophy model of chondrifying MSCs.

METHODS

Chondrogenesis was induced in human MSCs in pellet culture for two weeks and for an additional two weeks cultures were either maintained in standard chondrogenic medium or transferred to a hypertrophy-enhancing medium. PTHrP(1-40) was added to the medium throughout the culture period at concentrations from 1 to 1,000 pM. Pellets were harvested on days one, 14 and 28 for biochemical and histological analysis.

RESULTS

Hypertrophic medium clearly enhanced the hypertrophic phenotype, with increased cell size, and strong alkaline phosphatase (ALP) and type X collagen staining. In chondrogenic medium, 1-100 pM PTHrP(1-40) did not inhibit chondrogenic differentiation, whereas 1,000 pM PTHrP(1-40) significantly reduced chondrogenesis. ALP activity was dose-dependently reduced by PTHrP(1-40) at 10-1,000 pM in chondrogenic conditions. Under hypertrophy-enhancing conditions, PTHrP(1-40) did not inhibit the induction of the hypertrophy. At the highest concentration (1,000 pM) in the hypertrophic group, aggregates were partially dedifferentiated and differentiated areas of these aggregates maintained their hypertrophic appearance.

CONCLUSIONS

PTHrP(1-40) treatment dose-dependently reduced ALP expression in MSC pellets cultured under standard chondrogenic conditions and is thus beneficial for the maintenance of the chondrogenic phenotype in this medium condition. When cultured under hypertrophy-enhancing conditions, PTHrP(1-40) could not diminish the induced enhancement of hypertrophy in the MSC pellets.

Mesenchymal stem cells and their use in therapy: what has been achieved?

The considerable therapeutic potential of human multipotent mesenchymal stromal cells or mesenchymal stem cells (MSCs) has generated increasing interest in a wide variety of biomedical disciplines. Nevertheless, researchers report studies on MSCs using different methods of isolation and expansion, as well as different approaches to characterize them; therefore, it is increasingly difficult to compare and contrast study outcomes. To begin to address this issue, the Mesenchymal and Tissue Stem Cell Committee of the International Society for Cellular Therapy proposed minimal criteria to define human MSCs. First, MSCs must be plastic-adherent when maintained in standard culture conditions (α minimal essential medium plus 20% fetal bovine serum). Second, MSCs must express CD105, CD73 and CD90, and MSCs must lack expression of CD45, CD34, CD14 or CD11b, CD79α or CD19 and HLA-DR surface molecules. Third, MSCs must differentiate into osteoblasts, adipocytes and chondroblasts in vitro. MSCs are isolated from many adult tissues, in particular from bone marrow and adipose tissue. Along with their capacity to differentiate and transdifferentiate into cells of different lineages, these cells have also generated great interest for their ability to display immunomodulatory capacities. Indeed, a major breakthrough was the finding that MSCs are able to induce peripheral tolerance, suggesting that they may be used as therapeutic tools in immune-mediated disorders. Although no significant adverse events have been reported in clinical trials to date, all interventional therapies have some inherent risks. Potential risks for undesirable events, such as tumor development, that might occur while using these stem cells for therapy must be taken into account and contrasted against the potential benefits to patients.

Chondrogenic potentials of human synovium-derived cells sorted by specific surface markers

OBJECTIVE

We aimed to evaluate expression levels of nine candidate surface markers for chondrogenic potential in human synovial cells and to determine whether cell pellets positively sorted by each specific marker would have valuable chondrogenic potential.

METHODS

The expression levels of the selected nine leading surface markers in synovial cells from knee joints in 15 patients with primary knee osteoarthritis were evaluated at the stage of isolation and after cultivation using flow cytometry. We obtained positive and negative cells for each surface marker using a magnetically activated cell sorting method and compared chondrogenic potentials between the positive and the negative cell pellets.

RESULTS

CD29, CD44, CD73, and CD90 were expressed on the most synovial cells at the isolation stage and on almost all cells at stage of P0 and P1. CD133 was rarely expressed at any stages of the evaluated cells. CD166 was expressed in 7.1% of cells at the isolation stage on average, but this expression increased after cell passages. The expressions of CD10 and CD105 also increased after cell passages while the expression of CD49a made no significant difference at progressive stages of isolation and passage. Comparison of chondrogenic potentials between positive and negative cell pellets for each marker revealed that only CD105- and CD166-positive cell pellets showed better chondrogenic potentials (type II collagen gene expression, cartilage matrix formation, and GAG expression) than the corresponding negative cell pellets.

CONCLUSION

Our study suggests that CD105 and CD166 would be valuable surface markers associated with chondrogenic potential; thus, CD105- and CD166-enriched cells derived from human synovium would be practical and valuable sources for cartilage regeneration.

Isolation, enumeration, and expansion of human mesenchymal stem cells in culture

Human bone marrow (BM) contains a population of non-hematopoietic stem cells also termed stromal cells, mesenchymal cells or multipotent mesenchymal stromal cells (MSCs). These cells have unique stem cell-like properties including their ability to self-renew, differentiate into multiple tissue types, and modulate immune cell responses through paracrine effects. These properties have positioned mesenchymal cells as biological agents in clinical trials for various diseases since the 1990s. Mesenchymal cells have been isolated from various tissues and cultured using various media and methods resulting in a lack of standardization in culture methods for these cells. Consequently, cells cultured in different laboratories exhibit different characteristics of MSC-like cells. This chapter outlines protocols for optimal isolation, enumeration, and expansion of human MSCs from BM in fetal bovine serum (FBS)-containing medium, as well as in xeno-free medium.

High-density cell systems incorporating polymer microspheres as microenvironmental regulators in engineered cartilage tissues

To address the significant clinical need for tissue-engineered therapies for the repair and regeneration of articular cartilage, many systems have recently been developed using bioactive polymer microspheres as regulators of the chondrogenic microenvironment within high-density cell cultures. In this review, we highlight various densely cellular systems utilizing polymer microspheres as three-dimensional (3D) structural elements within developing engineered cartilage tissue, carriers for cell expansion and delivery, vehicles for spatiotemporally controlled growth factor delivery, and directors of cell behavior via regulation of cell-biomaterial interactions. The diverse systems described herein represent a shift from the more traditional tissue engineering approach of combining cells and growth factors within a biomaterial scaffold, to the design of modular systems that rely on the assembly of cells and bioactive polymer microspheres as building blocks to guide the creation of articular cartilage. Cell-based assembly of 3D microsphere-incorporated structures represents a promising avenue for the future of tissue engineering.

Nanotechnology and mesenchymal stem cells with chondrocytes in prevention of partial growth plate arrest in pigs

INTRODUCTION

This study describes the results achieved using a combination of allogeneic mesenchymal stem cells (MSCs) with chondrocytes (CHC) and a new scaffold consisting of type-I collagen and chitosan nanofibers in the prevention of partial growth plate arrest after iatrogenic injury in pigs.

MATERIAL AND METHODS

The miniature pig was selected as an experimental model to compare the results in the left femoral bones (MSCs and CHC in scaffold transplantation into the iatrogenic partial distal growth plate defect) and right femoral bones (scaffold alone transplantation). The experimental group consisted of 10 animals. Bone marrow from os ilium as the source of MSCs was used. A porous cylinder consisting of 0.5% by weight type-I collagen and 30% by weight chitosan, was the optimal choice. The length of the bone and angular deformity of distal femur after the healing period was measured and the quality and structure of the newly formed cartilage was histologically examined.

RESULTS

Transplantation of the composite scaffold in combination with MSCs and chondrocytes led to the prevention of growth disorder and angular deformity in the distal epiphysis of the left femur. Compared to the right (control) femur, tissue similar to hyaline cartilage with signs of columnar organization typical of the growth plate occurred in most cases.

CONCLUSIONS

The promising results of this study reveal the new and effective means for the prevention of bone bridge formation after growth plate injury.

Effective, safe nonviral gene transfer to preserve the chondrogenic differentiation potential of human mesenchymal stem cells

BACKGROUND

Genetic modification of mesenchymal stem cells (MSCs) comprises a promising tool to generate cell- and gene-based platforms for regenerative approaches of articular cartilage repair. In the present study, we systematically screened a panel of 15 nonviral compounds for their ability to promote safe, efficient and durable gene expression in human bone marrow-derived MSCs (hMSCS) without impeding their commitment towards chondrogenic differentiation.

METHODS

Primary hMSCs were transfected with plasmid vectors carrying sequences for the Photinus pyralis luciferase Escherichia coli β-galactosidase, or human insulin-like growth factor I via 15 nonviral formulations. Transgene expression and transfection efficiencies were monitored for each component in parallel with the effects on cell viability and cytotoxicity. Upon optimization, the most promising reagent was then evaluated for a possible influence on the chondrogenic potential of hMSCs.

RESULTS

Among all formulations tested, GeneJammer® gave the best results for transgene expression and transfection efficacy (25-14% from days 2-21 in monolayer cultures and 35% in 21-day aggregate cultures), allowing for high levels of viability (92-94%) and modest cytotoxicity (< 12%). Most notably, the application of this reagent did not affect the potential of the cells for chondrogenic differentiation when maintained in long-term (21 days) three-dimensional (aggregate) cultures.

CONCLUSIONS

The data indicate that safe, efficient transgene expression can be achieved in hMSCs over time using the nonviral GeneJammer® compound, showing promise for future therapeutic settings aiming to treat human articular cartilage disorders.

Transient serum exposure regimes to support dual differentiation of human mesenchymal stem cells

Human mesenchymal stem cells (MSCs), which can generate both osteoblasts and chondrocytes, represent an ideal resource for orthopaedic repair using tissue-engineering approaches. One major difficulty for the development of osteochondral constructs using undifferentiated MSCs is that serum is typically used in culture protocols to promote differentiation of the osteogenic component, whereas existing chondrogenic differentiation protocols rely on the use of serum-free conditions. In order to define conditions which could be compatible with both chondrogenic and osteogenic differentiation in a single bioreactor, we have analysed the efficiency of new biphasic differentiation regimes based on transient serum exposure followed by serum-free treatment. MSC differentiation was assessed either in serum-free medium or with a range of transient exposure to serum, and compared to continuous serum-containing treatment. Although osteogenic differentation was not supported in the complete absence of serum, marker expression and extensive mineralization analyses established that 5 days of transient exposure triggered a level of differentiation comparable to that observed when serum was present throughout. This initial phase of serum exposure was further shown to support the successful chondrogenic differentiation of MSCs, comparable to controls maintained in serum-free conditions throughout. This study indicates that a culture based on temporal serum exposure followed by serum-free treatment is compatible with both osteogenic and chondrogenic differentiation of MSCs. These results will allow the development of novel strategies for osteochondral tissue engineering approaches using MSCs for regenerative medicine.

Human stem cells and articular cartilage regeneration

The regeneration of articular cartilage damaged due to trauma and posttraumatic osteoarthritis is an unmet medical need. Current approaches to regeneration and tissue engineering of articular cartilage include the use of chondrocytes, stem cells, scaffolds and signals, including morphogens and growth factors. Stem cells, as a source of cells for articular cartilage regeneration, are a critical factor for articular cartilage regeneration. This is because articular cartilage tissue has a low cell turnover and does not heal spontaneously. Adult stem cells have been isolated from various tissues, such as bone marrow, adipose, synovial tissue, muscle and periosteum. Signals of the transforming growth factor beta superfamily play critical roles in chondrogenesis. However, adult stem cells derived from various tissues tend to differ in their chondrogenic potential. Pluripotent stem cells have unlimited proliferative capacity compared to adult stem cells. Chondrogenesis from embryonic stem (ES) cells has been studied for more than a decade. However, establishment of ES cells requires embryos and leads to ethical issues for clinical applications. Induced pluripotent stem (iPS) cells are generated by cellular reprogramming of adult cells by transcription factors. Although iPS cells have chondrogenic potential, optimization, generation and differentiation toward articular chondrocytes are currently under intense investigation.

Sequential differentiation of mesenchymal stem cells in an agarose scaffold promotes a physis-like zonal alignment of chondrocytes

Chondrocytes of the epiphyseal growth plate (physis) differentiate and mature in defined linear zones. The current study examines the differentiation of human bone marrow derived mesenchymal stem cells (hBMSCs) into zonal physeal cartilage. hBMSCs were embedded in an agarose scaffold with only the surface of the scaffold in direct contact with the culture medium. The cells were differentiated using a two-step system involving the sequential addition of TGFβ followed by BMP2. The resultant samples displayed a heterogenic population of physis-like collagen type 2 positive cells including proliferating chondrocytes and mature chondrocytes showing hypertrophy, expression of early bone markers and matrix mineralization. Histological analysis revealed a physis-like linear zonal alignment of chondrocytes in varying stages of differentiation. The less mature chondrocytes were seen at the base of the construct while hypertrophic chondrocytes and matrix mineralization was observed closer to the surface of the construct. The described differentiation protocol using hBMSCs in an agarose scaffold can be used to study the factors and conditions that influence the differentiation, proliferation, maturation, and zonal alignment of physeal chondrocytes.

Cell sources for the regeneration of articular cartilage: the past, the horizon and the future

Avascular, aneural articular cartilage has a low capacity for self-repair and as a consequence is highly susceptible to degradative diseases such as osteoarthritis. Thus the development of cell-based therapies that repair focal defects in otherwise healthy articular cartilage is an important research target, aiming both to delay the onset of degradative diseases and to decrease the need for joint replacement surgery. This review will discuss the cell sources which are currently being investigated for the generation of chondrogenic cells. Autologous chondrocyte implantation using chondrocytes expanded ex vivo was the first chondrogenic cellular therapy to be used clinically. However, limitations in expansion potential have led to the investigation of adult mesenchymal stem cells as an alternative cell source and these therapies are beginning to enter clinical trials. The chondrogenic potential of human embryonic stem cells will also be discussed as a developmentally relevant cell source, which has the potential to generate chondrocytes with phenotype closer to that of articular cartilage. The clinical application of these chondrogenic cells is much further away as protocols and tissue engineering strategies require additional optimization. The efficacy of these cell types in the regeneration of articular cartilage tissue that is capable of withstanding biomechanical loading will be evaluated according to the developing regulatory framework to determine the most appropriate cellular therapy for adoption across an expanding patient population.

Controlling mesenchymal stem cell gene expression using polymer-mediated delivery of siRNA

siRNA treatment has great promise to specifically control gene expression and select cell behaviors but has delivery challenges limiting its use. Particularly for applications in regenerative medicine, uniform and consistent delivery of siRNA to control gene expression and subsequent stem cell functions, such as differentiation, is paramount. Therefore, a diblock copolymer was examined for its ability to effectively deliver siRNA to mesenchymal stem cells (MSCs). The diblock copolymers, which are composed of cationic blocks for siRNA complexation, protection, and uptake and pH-responsive blocks for endosomal escape, were shown to facilitate nearly 100% MSC uptake of siRNA. This is vastly superior to a commercially available control, DharmaFECT, which resulted in only ~60% siRNA positive MSCs. Moreover, the diblock copolymer, at conditions that result in excellent knockdown (down to ~10% of control gene expression), was cytocompatible, causing no negative effects on MSC survivability. In contrast, DharmaFECT/siRNA treatment resulted in only ~60% survivability of MSCs. Longitudinal knockdown after siRNA treatment was examined and protein knockdown persists for ~6 days regardless of delivery system (diblock copolymer or DharmaFECT). Finally, MSC phenotype and differentiation capacity was examined after treatment with control siRNA. There was no statistically significant differences on cell surface markers of diblock copolymer/siRNA or DharmaFECT/siRNA-treated or cells measured 2 weeks after siRNA delivery compared to untreated cells. Upon differentiation with typical media/culture conditions to adipogenic, chondrogenic, and osteogenic lineages and examination of histological staining markers, there was no discernible differences between treated and untreated cells, regardless of delivery mechanism. Thus, diblock copolymers examined herein facilitated uniform siRNA treatment of MSCs, inducing siRNA-specific gene and protein knockdown without adversely affecting MSC survival or differentiation capacity and therefore show great promise for use within regenerative medicine applications.

Covalently tethered transforming growth factor beta in PEG hydrogels promotes chondrogenic differentiation of encapsulated human mesenchymal stem cells

Methods to precisely control growth factor presentation in a local and sustained fashion are of increasing interest for a number of complex tissue engineering applications. The cytokine transforming growth factor beta (TGFβ) plays a key role in promoting the chondrogenic differentiation of human mesenchymal stem cells (hMSCs). Traditional chondrogenic approaches utilize soluble delivery, an approach with limited application for clinical translation. In this work, we introduce a reactive thiol onto TGFβ and covalently tether the growth factor into poly(ethylene glycol) (PEG) hydrogels using a photoinitiated thiol-acrylate polymerization mechanism. We demonstrate the bioactivity of thiolated TGFβ, before and after polymerization, using a SMAD2 reporter cell line. hMSCs were encapsulated in PEG hydrogels with and without tethered TGFβ, and subsequently assayed for glycosaminoglycan and collagen II production as indicators of chondrogenesis. Over a 21-day time course, tethered TGFβ promoted chondrogenesis at levels similar to a positive control using solubly dosed growth factor. These results provide evidence that tethered TGFβ materials can be successfully used to promote chondrogenic differentiation of MSCs.

Multilayer thin film coatings capable of extended programmable drug release: application to human mesenchymal stem cell differentiation

The promise of cellular therapy lies in healing damaged tissues and organs in vivo as well as generating tissue constructs in vitro for subsequent transplantation. Adult stem cells are ideally suited for cellular therapies due to their pulripotency and the ease with which they can be cultured on novel functionalized substrates. Creating environments to control and successively driving their differentiation toward a lineage of choice is one of the most important challenges of current cell-based engineering strategies. In recent years, a variety of biomedical platforms have been prepared for stem cell cultures, primarily to provide efficient delivery of growth or survival factors to cells and a conducive microenvironment for their growth. Here, we demonstrate that repeating tetralayer structures composed of biocompatible poly(methacrylic acid) (PMAA)/poly(acryl amide) (PAAm)/poly(methacrylic acid) (PMAA)/poly(ethylene oxide)-block-poly(ε-caprolactone) (PEO-b-PCL) micelles arrayed in layer-by-layer (LbL) films can serve as a payload region for dexamethasone (dex) delivery to human mesenchymal stem cells (MSCs). This architecture can induce MSC differentiation into osteoblasts in a dose-dependent manner. The amount of dex loaded in the films is controlled by varying the deposition conditions and the film thickness. Furthermore, release of dex is also controlled by changing the amount of covalent crosslinking of multilayers via thermal treatments. The multilayer architecture including payload and cell-adhesion region introduced here are well suited for extended cell culture thus affording the important and protective effect of both dex release and immobilization. These films may find applications in the local delivery of immobilized therapeutics for biomedical applications, as they can be deposited on a wide range of substrates with different shapes, sizes, and composition.

The effects of cyclic hydrostatic pressure on chondrogenesis and viability of human adipose- and bone marrow-derived mesenchymal stem cells in three-dimensional agarose constructs

This study investigates the effects of cyclic hydrostatic pressure (CHP) on chondrogenic differentiation of human adipose-derived stem cells (hASCs) in three-dimensional (3-D) agarose constructs maintained in a complete growth medium without soluble chondrogenic inducing factors. hASCs were seeded in 2% agarose hydrogels and exposed to 7.5 MPa CHP for 4 h per day at a frequency of 1 Hz for up to 21 days. On days 0, 7, 14, and 21, the expression levels of collagen II, Sox9, aggrecan, and cartilage oligomeric matrix protein (COMP) were examined by real-time reverse transcriptase-polymerase chain reaction analysis. Gene expression analysis found collagen II mRNA expression in only the CHP-loaded construct at day 14 and at no other time during the study. CHP-loaded hASCs exhibited upregulated mRNA expression of Sox9, aggrecan, and COMP at day 7 relative to unloaded controls, suggesting that CHP initiated chondrogenic differentiation of hASCs in a manner similar to human bone marrow-derived mesenchymal stem cells (hMSC). By day 14, however, loaded hASC constructs exhibited significantly lower mRNA expression of the chondrogenic markers than unloaded controls. Additionally, by day 21, the samples exhibited little measurable mRNA expression at all, suggesting a decreased viability. Histological analysis validated the lack of mRNA expression at day 21 for both the loaded and unloaded control samples with a visible decrease in the cell number and change in morphology. A comparative study with hASCs and hMSCs further examined long-term cell viability in 3-D agarose constructs of both cell types. Decreased cell metabolic activity was observed throughout the 21-day experimental period in both the CHP-loaded and control constructs of both hMSCs and hASCs, suggesting a decrease in cell metabolic activity, alluding to a decrease in cell viability. This suggests that a 2% agarose hydrogel may not optimally support hASC or hMSC viability in a complete growth medium in the absence of soluble chondrogenic inducing factors over long culture durations. This is the first study to examine the ability of mechanical stimuli alone, in the absence of chondrogenic factors transforming growth factor beta (TGF-β)3, TGF-β1 and/or bone morphogenetic protein 6 (BMP6) to induce hASC chondrogenic differentiation. The findings of this study suggest that CHP initiates hASC chondrogenic differentiation, even in the absence of soluble chondrogenic inductive factors, confirming the importance of considering both mechanical stimuli and appropriate 3-D culture for cartilage tissue engineering using hASCs.

Synovial fluid progenitors expressing CD90+ from normal but not osteoarthritic joints undergo chondrogenic differentiation without micro-mass culture

OBJECTIVE

Mesenchymal progenitor cells (MPCs) can differentiate into osteoblasts, adipocytes, and chondrocytes, and are in part responsible for maintaining tissue integrity. Recently, a progenitor cell population has been found within the synovial fluid that shares many similarities with bone marrow MPCs. These synovial fluid MPCs (sfMPCs) share the ability to differentiate into bone and fat, with a bias for cartilage differentiation. In this study, sfMPCs were isolated from human and canine synovial fluid collected from normal individuals and those with osteoarthritis (human: clinician-diagnosed, canine: experimental) to compare the differentiation potential of CD90+ vs. CD90- sfMPCs, and to determine if CD90 (Thy-1) is a predictive marker of synovial fluid progenitors with chondrogenic capacity in vitro.

METHODS

sfMPCs were derived from synovial fluid from normal and OA knee joints. These cells were induced to differentiate into chondrocytes and analyzed using quantitative PCR, immunofluorescence, and electron microscopy.

RESULTS

The CD90+ subpopulation of sfMPCs had increased chondrogenic potential compared to the CD90- population. Furthermore, sfMPCs derived from healthy joints did not require a micro-mass step for efficient chondrogenesis. Whereas sfMPCs from OA synovial fluid retain the ability to undergo chondrogenic differentiation, they require micro-mass culture conditions.

CONCLUSIONS

Overall, this study has demonstrated an increased chondrogenic potential within the CD90+ fraction of human and canine sfMPCs and that this population of cells derived from healthy normal joints do not require a micro-mass step for efficient chondrogenesis, while sfMPCs obtained from OA knee joints do not differentiate efficiently into chondrocytes without the micro-mass procedure. These results reveal a fundamental shift in the chondrogenic ability of cells isolated from arthritic joint fluids, and we speculate that the mechanism behind this change of cell behavior is exposure to the altered milieu of the OA joint fluid, which will be examined in further studies.

In vitro chondrogenesis transformation study of mouse dental pulp stem cells

A major challenge in the application of mesenchymal stem cells in cartilage reconstruction is that whether the cells are able to differentiate into fully mature chondrocytes before grafting. The aim of this study was to isolate mouse dental pulp stem cells (DPSC) and differentiate them into chondrocytes. For this investigation, morphological, molecular, and biochemical analyses for differentiated cells were used. To induce the chondrocyte differentiation, DPSC were cultured in chondrogenic medium (Zen-Bio, Inc.). Based on morphological analyses using toluidine blue staining, proteoglycan products appear in DPSC after 21 days of chondrocyte induction. Biochemical analyses in differentiated group showed that alkaline phosphatase activity was significantly increased at day 14 as compared to control (P < 0.05). Cell viability analyses during the differentiation to chondrocytes also showed that these cells were viable during differentiation. However, after the 14th day of differentiation, there was a significant decrease (P < 0.05) in the viability proportion among differentiated cells as compared to the control cells. In RT-PCR molecular analyses, mouse DPSC expressed Cd146 and Cd166 which indicated that these cells belong to mesenchymal stem cells. Coll I and Coll II markers showed high expression after 14 and 21 days, respectively. In conclusion, this study showed that DPSC successfully differentiated into chondrocytes.

Evaluation of the use of induced pluripotent stem cells (iPSCs) for the regeneration of tracheal cartilage

The treatment of laryngotracheal stenosis remains a challenge as treatment often requires multistaged procedures, and successful decannulation sometimes fails after a series of operations. Induced pluripotent stem cells (iPSCs) were generated in 2006. These cells are capable of unlimited symmetrical self-renewal, thus providing an unlimited cell source for tissue-engineering applications. We have previously reported tracheal wall regeneration using a three-dimensional (3D) scaffold containing iPSCs. However, the efficiency of differentiation into cartilage was low. In addition, it could not be proven that the cartilage tissues were in fact derived from the implanted iPSCs. The purpose of this study was to evaluate and improve the use of iPSCs for the regeneration of tracheal cartilage. iPSCs were cultured in vitro in a 3D scaffold in chondrocyte differentiation medium. After cultivation, differentiation into chondrocytes was examined. The ratio of undifferentiated cells was analyzed by flow cytometry. The 3D scaffolds were implanted into tracheal defects, as an injury site, in 24 nude rats. Differentiation into chondrocytes in vitro was confirmed histologically, phenotypically, and genetically. Flow cytometric analysis demonstrated that the population of undifferentiated cells was decreased. Cartilage tissue was observed in the regenerated tracheal wall in 6 of 11 rats implanted with induced iPSCs, but in none of 13 rats implanted with the control and noninduced iPSCs. The expression of cartilage-specific protein was also demonstrated in vivo in 3D scaffolds containing iPSCs. The presence of the GFP gene derived from iPSCs was confirmed in samples of cartilage tissue by the combination of laser microdissection (LMD) and polymerase chain reaction (PCR) techniques. Our study demonstrated that iPSCs have the potential to differentiate into chondrogenic cells in vitro. Cartilage tissue was regenerated in vivo. Our results suggest that iPSCs could be a new cell source for the regeneration of tracheal cartilage.

Therapeutic potential of mesenchymal stem cells overexpressing human forkhead box A2 gene in the regeneration of damaged liver tissues

BACKGROUND AND AIM

Although a liver transplantation is considered to be the only effective long-term treatment in many cases of liver diseases, it is limited by a lack of donor organs and immune rejection. As an autologous stem cell approach, this study was conducted to assess whether forkhead box A2 (Foxa2) gene overexpression in bone marrow-derived mesenchymal stem cells (MSC) could protect the liver from hepatic diseases by stimulating tissue regeneration after cell transplantation.

METHODS

Rat MSC (rMSC) were isolated, characterized, and induced to hepatocytes that expressed liver-specific markers. Four different treatments (control [phosphate-buffered saline], rMSC alone, rMSC/pIRES-enhanced green fluorescent protein (EGFP) vector, and rMSC/pIRES-EGFP/human Foxa2) were injected into the spleen of carbon tetrachloride-injured rats. Biochemical and histological analyses on days 30, 60, and 90 post-transplantation were performed to evaluate the therapeutic capacities of MSC overexpressing hFoxa2.

RESULTS

rMSC transfected with hFoxa2 were induced into hepatogenic linage and expressed several liver-specific genes, such as, Foxa2, α-fetoprotein, cytokeratin-18, hepatocyte nuclear factor-1α, and hepatocyte growth factor. A group of animals treated with MSC/hFoxa2 showed significant recovery of liver-specific enzyme expressions to normal levels at the end of the study (90 days). Furthermore, when compared to the fibrotic areas of the samples treated with MSC alone or MSC/vector, the fibrotic area of the samples treated with rMSC/hFoxa2 for 90 days significantly decreased, until they were completely gone.

CONCLUSIONS

Human Foxa2 efficiently promoted the incorporation of MSC into liver grafts, suggesting that hFoxa2 genes could be used for the structural or functional recovery of damaged liver cells.

Polyvalent display of RGD motifs on turnip yellow mosaic virus for enhanced stem cell adhesion and spreading

Turnip yellow mosaic virus (TYMV) is a stable 28 nm icosahedral plant virus that can be isolated in gram quantities. In order to study the polyvalent effect of Arg-Gly-Asp (RGD) clustering on the response of bone marrow stem cells (BMSCs), an RGD motif was genetically displayed on the coat protein of the TYMV capsid. Composite films composed of either wild-type TYMV or TYMV-RGD44, in combination with poly(allylamine hydrochloride) (PAH), were fabricated by a layer-by-layer adsorption of virus and PAH. The deposition process was studied by quartz crystal microbalance, UV-visible spectroscopy and atomic force microscopy. BMSC adhesion assays showed enhanced cell adhesion and spreading on TYMV-RGD44 coated substrates compared to native TYMV. These results demonstrate the potential of TYMV as a viable scaffold for bioactive peptide display and cell culturing studies.

Spatiotemporal regulation of chondrogenic differentiation with controlled delivery of transforming growth factor-β1 from gelatin microspheres in mesenchymal stem cell aggregates

The precise spatial and temporal presentation of growth factors is critical for cartilage development, during which tightly controlled patterns of signals direct cell behavior and differentiation. Recently, chondrogenic culture of human mesenchymal stem cells (hMSCs) has been improved through the addition of polymer microspheres capable of releasing growth factors directly to cells within cellular aggregates, eliminating the need for culture in transforming growth factor-β1 (TGF-β1)-containing medium. However, the influence of specific patterns of spatiotemporal growth factor presentation on chondrogenesis within microsphere-incorporated cell systems is unclear. In this study, we examined the effects of altering the chondrogenic microenvironment within hMSC aggregates through varying microsphere amount, growth factor concentration per microsphere, and polymer degradation time. Cartilage formation was evaluated in terms of DNA, glycosaminoglycan, and type II collagen in hMSCs from three donors. Chondrogenesis equivalent to or greater than that of aggregates cultured in medium containing TGF-β1 was achieved in some conditions, with varied differentiation based on the specific conditions of microsphere incorporation. A more spatially distributed delivery of TGF-β1 from a larger mass of fast-degrading microspheres improved differentiation by comparison with delivery from a smaller mass of microspheres with a higher TGF-β1 concentration per microsphere, although the total amount of growth factor per aggregate was the same. Results also indicated that the rate and degree of chondrogenesis varied on a donor-to-donor basis. Overall, this study elucidates the effects of varied conditions of TGF-β1-loaded microsphere incorporation on hMSC chondrogenesis, demonstrating that both spatiotemporal growth factor presentation and donor variability influence chondrogenic differentiation within microsphere-incorporated cellular constructs.

A comparative study of aggrecan synthesis between natural articular chondrocytes and differentiated chondrocytes from adipose derived stem cells in 3D culture

Introduction:

The main obstacle for tissue engineering is to find the most appropriate cell which is able to produce extracellular matrix (ECM) similar or better than natural chondrocytes in vitro. This study compared aggrecan synthesis's potential between differentiated chondrocytes (DCs) from adipose-derived stem cells (ADSCs) and natural articular chondrocytes (NCs) in 3D culture in vitro.

Materials and Methods:

Human ADSCs were isolated from sub-cutaneous adipose tissue and then the surface markers including CD 14, 45 CD105, CD90, CD44 were analyzed by flow cytometry. Also human articular chondrocytes were yielded of non-weight bearing area of Knee cartilage. Both types of the cells were encapsulated in alginate scaffolds and cultured in chondrogenic medium with and without TGFβ3 for 3 weeks. Then the extent of aggercan (AGC) production was evaluated by ELISA on days 14 and 21.

Results:

Our findings indicated that differentiated chondrocytes (DCs) with and without TGFβ3 synthesized more AGC than natural chondrocytes (NCs) on day 14. But DCs without TGFβ3 had higher production than other groups on day 21. Application of TGFβ3 resulted in an increase of amount of AGC in DCs on day 14 but a decrease on day 21 than same group.

Conclusion:

Since, aggrecan is an important chondrogenic marker, it was concluded that ADSCs can be possible reliable alternative cell source for cartilage tissue engineering in future.

Tailoring of mesenchymal stem cells behavior on plasma-modified polytetrafluoroethylene

By altering the surface properties of polytetrafluoroethylene (PTFE) substrates using a special PIII technique, mesenchymal stem cells (MSCs) proliferation and osteogenesis can be promoted in culture without osteogenic supplements. The structures are created intrinsically in the PTFE for no risk of materials delamination. Large-scale features and locally different functions can also be readily produced on the same substrate by this technique.

Chromosomal variability of human mesenchymal stem cells cultured under hypoxic conditions

Bone marrow derived human mesenchymal stem cells (hMSCs) have attracted great interest from both bench and clinical researchers because of their pluripotency and ease of expansion ex vivo. However, these cells do finally reach a senescent stage and lose their multipotent potential. Proliferation of these cells is limited up to the time of their senescence, which limits their supply, and they may accumulate chromosomal changes through ex vivo culturing. The safe, rapid expansion of hMSCs is critical for their clinical application. Chromosomal aberration is known as one of the hallmarks of human cancer, and therefore it is important to understand the chromosomal stability and variability of ex vivo expanded hMSCs before they are used widely in clinical applications. In this study, we examined the effects of culturing under ambient (20%) or physiologic (5%) O₂ concentrations on the rate of cell proliferation and on the spontaneous transformation of hMSCs in primary culture and after expansion, because it has been reported that culturing under hypoxic conditions accelerates the propagation of hMSCs. Bone marrow samples were collected from 40 patients involved in clinical research. We found that hypoxic conditions promote cell proliferation more favourably than normoxic conditions. Chromosomal aberrations, including structural instability or aneuploidy, were detected in significantly earlier passages under hypoxic conditions than under normoxic culture conditions, suggesting that amplification of hMSCs in a low-oxygen environment facilitated chromosomal instability. Furthermore, smoothed hazard-function modelling of chromosomal aberrations showed increased hazard after the fourth passage under both sets of culture conditions, and showed a tendency to increase the detection rate of primary karyotypic abnormalities among donors aged 60 years and over. In conclusion, we propose that the continuous monitoring of hMSCs will be required before they are used in therapeutic applications in the clinic, especially when cells are cultured under hypoxic conditions.