Effects of transforming growth factor beta1 and dexamethasone on the growth and chondrogenic differentiation of adipose-derived stromal cells

The effects of BMP6 overexpression on adipose stem cell chondrogenesis: Interactions with dexamethasone and exogenous growth factors

Adipose-derived stem cells (ASCs) are multipotent progenitors that can be chondrogenically induced by growth factors such as bone morphogenetic protein 6 (BMP-6). We hypothesized that nonviral transfection of a BMP-6 construct (pcDNA3-BMP6) would induce chondrogenic differentiation of ASCs encapsulated in alginate beads and that differentiation would be enhanced by the presence of the synthetic glucocorticoid dexamethasone (DEX) or the combination of epidermal growth factor (EGF), fibroblast growth factor-2 (FGF-2), and transforming growth factor beta-1 (TGF-beta1), collectively termed expansion factors (EFs). Chondrogenesis was assessed using quantitative real-time polymerase chain reaction for types I, II, and X collagen, aggrecan, and BMP6. Immunohistochemistry was performed with antibodies for types I, II, and X collagen and chondroitin-4-sulfate. BMP6 overexpression alone induced a moderate chondrogenic response. The inclusion of EFs promoted robust type II collagen expression but also increased type I and X collagen deposition, consistent with a hypertrophic chondrocyte phenotype. Early gene expression data indicated that DEX was synergistic with BMP-6 for chondrogenesis, but immunohistochemistry at 28 days showed that DEX reduced glycosaminoglycan accumulation. These results suggest that chondrogenic differentiation of ASCs depends on complex interactions among various growth factors and media supplements, as well as the concentration and duration of growth factor exposure.

Isolation of adipose-derived stem cells and their induction to a chondrogenic phenotype

The ability to isolate, expand and differentiate adult stem cells into a chondrogenic lineage is an important step in the development of tissue engineering approaches for cartilage repair or regeneration for the treatment of joint injury or osteoarthritis, as well as for their application in plastic or reconstructive surgery. Adipose-derived stem cells (ASCs) provide an abundant and easily accessible source of adult stem cells for use in such regenerative approaches. This protocol first describes the isolation of ASCs from liposuction aspirate. The cell culture conditions provided for ASC expansion provide a large number of multipotent stem cells. Instructions for growth factor-based induction of ASCs into chondrocyte-like cells using either cell pellet or alginate bead systems are detailed. These methods are similar to those published for chondrogenesis of bone marrow-derived mesenchymal stem cells but distinct because of the unique nature of ASCs. Investigators can expect consistent differentiation of ASCs, allowing for slight variation as a result of donor and serum lot effects. Approximately 10-12 weeks are needed for the entire process of ASC isolation, including the characterization of chondrocyte-like cells, which is also described.

Differential expression of Shh and BMP signaling in the potential conversion of human adipose tissue stem cells into neuron-like cells in vitro

The nervous system (NS) has a limited self-repair capability and adult neurogenesis is limited to certain regions of the brain. This generates a great interest in using stem cells to repair the NS. Previous reports have shown the differentiation of adipose tissue-derived mesenchymal stem cells (ASCs) in neuron-like cells when cultures are enriched with growth factors participating in embryonic and adult neurogenesis. Therefore, it could be thought that there exists a functional parallelism between neurogenesis and neuronal differentiation of ASCs. For this reason, the goal of this work was to study the differential gene expression of Shh and BMP genetic pathways involved in cell fate determination and proliferation. In this study we demonstrated that hASCs are endowed with active Hedgehog and BMP signaling pathways through the expression of genes of both cascades and that their expressions are downregulated after neuronal induction. This idea is in accordance with the facts that Shh and BMP signaling is involved in the maintenance of cells with stem cells properties and that proliferation decreases during the process of differentiation. Furthermore, Noggin expression was detected in induced hASCs whereas there was no expression in noninduced cells, which indicates that these cells are probably adopting a neuronal fate because noggin diverts neural stem cells from glial to neuronal fate. We also detected FM1-43 and synaptophisin staining, which is evidence of the presence of putative functional presynaptic terminals, a neuron-specific property. These results could partially contribute to the elucidation of the molecular mechanisms involved in neuronal differentiation of adult human nonneural tissues.

Distribution of adipose-derived stem cells in adipose tissues from human cadavers

BACKGROUND

Adipose-derived stem cells (ASCs) possess multipotency in vivo and in vitro, and thus are thought to be very promising precursors for use in regenerative medicine. ASCs can be concentrated from adipose tissue by enzymatic digestion and transplanted to increase angiogenesis or for cosmesis. ASC transplants are now being performed in a clinical setting. Although data on ASCs are extensive, the distribution of ASCs in human fat tissue has not been fully clarified. Thus, it is important to identify the distribution of ASCs to obtain cell populations rich in ASCs for clinical use.

METHODS

ASCs express CD34, a cell surface marker. As CD34 is also expressed by endothelial cells, we immunohistochemically stained 2-μm-thick serial paraffin sections of fat tissue obtained from various parts of formalin-fixed cadavers with anti-CD31 and anti-CD34 antibodies to distinguish ASCs from endothelial cells.

RESULTS

CD34(+)/CD31(-) cells were mainly found in connective tissue tracts and perivascularly. Among fat tissues obtained from various sites, fat tissues in the thoracic back and lower abdomen were richest in CD34(+)/CD31(-) cells.

CONCLUSION

The concentrations of CD34(+)/CD31(-) cells in adipose tissues differ between sites. The sites most highly enriched for ASCs were identified, and it is now possible to select the best sites for collection of ASCs for transplantation.

Chondrogenic differentiation of adipose-derived adult stem cells by a porous scaffold derived from native articular cartilage extracellular matrix

Adipose-derived adult stem cells (ASCs) have the ability to differentiate into a chondrogenic phenotype in response to specific environmental signals such as growth factors or artificial biomaterial scaffolds. In this study, we examined the hypothesis that a porous scaffold derived exclusively from articular cartilage can induce chondrogenesis of ASCs. Human ASCs were seeded on porous scaffolds derived from adult porcine articular cartilage and cultured in standard medium without exogenous growth factors. Chondrogenesis of ASCs seeded within the scaffold was evident by quantitative RT-PCR analysis for cartilage-specific extracellular matrix (ECM) genes. Histological and immunohistochemical examination showed abundant production of cartilage-specific ECM components-particularly, type II collagen-after 4 or 6 weeks of culture. After 6 weeks of culture, the cellular morphology in the ASC-seeded constructs resembled those in native articular cartilage tissue, with rounded cells residing in the glycosaminoglycan-rich regions of the scaffolds. Biphasic mechanical testing showed that the aggregate modulus of the ASC-seeded constructs increased over time, reaching 150 kPa by day 42, more than threefold higher than that of the unseeded controls. These results suggest that a porous scaffold derived from articular cartilage has the ability to induce chondrogenic differentiation of ASCs without exogenous growth factors, with significant synthesis and accumulation of ECM macromolecules, and the development of mechanical properties approaching those of native cartilage. These findings support the potential for a processed cartilage ECM as a biomaterial scaffold for cartilage tissue engineering. Additional in vivo evaluation is necessary to fully recognize the clinical implication of these observations.

Mechanics and mechanobiology of mesenchymal stem cell-based engineered cartilage

In this review, we outline seminal and recent work highlighting the potential of mesenchymal stem cells (MSCs) in producing cartilage-like tissue equivalents. Specific focus is placed on the mechanical properties of engineered MSC-based cartilage and how these properties relate to that of engineered cartilage based on primary chondrocytes and to native tissue properties. We discuss current limitations and/or concerns that must be addressed for the clinical realization of MSC-based cartilage therapeutics, and provide some insight into potential underpinnings for the observed deviations from chondrocyte-based engineered constructs. We posit that these differences reveal specific deficits in terms of our description of chondrogenesis, and suggest that new benchmarks must be developed towards this end. Further, we describe the growing body of literature on the mechanobiology of MSC-based cartilage, highlighting positive findings with regards to the furtherance of the chondrogenic phenotype. We likewise discuss the failure of early molecular changes to translate directly into engineered constructs with improved mechanical properties. Finally, we highlight recent work from our group and others that may point to new strategies for enhancing the formation of engineered cartilage based on MSCs.

Use of adipose stem cells and polylactide discs for tissue engineering of the temporomandibular joint disc

There is currently no suitable replacement for damaged temporomandibular joint (TMJ) discs after discectomy. In the present study, we fabricated bilayer biodegradable polylactide (PLA) discs comprising a non-woven mat of poly(L/D)lactide (P(L/D)LA) 96/4 and a P(L/DL)LA 70/30 membrane plate. The PLA disc was examined in combination with adipose stem cells (ASCs) for tissue engineering of the fibrocartilaginous TMJ disc in vitro. ASCs were cultured in parallel in control and chondrogenic medium for a maximum of six weeks. Relative expression of the genes, aggrecan, type I collagen and type II collagen present in the TMJ disc extracellular matrix increased in the ASC-seeded PLA discs in the chondrogenic medium. The hypertrophic marker, type X collagen, was moderately induced. Alcian blue staining showed accumulation of sulphated glycosaminoglycans. ASC differentiation in the PLA discs was close to that observed in pellet cultures. Comparison of the mRNA levels revealed that the degree of ASC differentiation was lower than that in TMJ disc-derived cells and tissue. The pellet format supported the phenotype of the TMJ disc-derived cells under chondrogenic conditions and also enhanced their hyalinization potential, which is considered part of the TMJ disc degeneration process. Accordingly, the combination of ASCs and PLA discs has potential for the development of a tissue-engineered TMJ disc replacement.

Repair of articular cartilage defects: review and perspectives

Articular cartilage defects heal poorly and lead to catastrophic degenerative arthritis. Clinical experience has indicated that no existing medication substantially promotes the healing process and the cartilage defect requires surgical replacement, preferably with an autograft. However, there is a shortage of articular cartilage that can be donated for autografting. A review of previous unsuccessful experiences reveals the reason for the current strategy to graft cartilage defects with regenerated cartilage. Autologous cartilage regeneration is a cell-based therapy in which autogenous chondrocytes or other chondrogenic cells are cultured to constitute cartilaginous tissue according to the principles of tissue engineering. Current studies are concentrating on improving such techniques from the three elements of tissue engineering, namely the cells, biomaterial scaffolds, and culture conditions. Some models of articular cartilage regeneration have yielded good repair of cartilage defects, in animal models and clinical settings, but the overall results suggest that there is room for improvement of this technique before its routine clinical application. Autologous cartilage regeneration remains the mainstay for repairing articular cartilage defects but more studies are required to optimize the efficacy of regeneration. A more abundant supply of more stable cells, i.e. capable of maintaining the phenotype of chondrogenesis, has to be identified. Porous scaffolds of biocompatible, biodegradable materials that maintain and support the presentation of the chondrogenic cells need to be fabricated. If the cells are not implanted early to allow their in vivo constitution of cartilage, a suitable in vitro cultivation method has to be devised for a consistent yield of regenerative cartilage.

Tissue engineering in plastic surgery: an up-to-date review of the current literature

Tissue engineering is an interdisciplinary field that applies the principles of engineering and life sciences toward the development of biological substitutes that restore, maintain, or improve tissue function. This field has enjoyed tremendous growth in the past 10 years fuelled by its potential role in regenerating new tissues and naturally healing injured or diseased organs. Stem cells due to their pluripotentiality and unlimited capacity for self-renewal, may allow significant advances for distinct reconstructive and cosmetic procedures. This review aims at outlining the principles of tissue engineering, focusing on the use of adult-derived stem cells as applied to the research and practice of plastic surgery. Review categories have been divided into tissue engineering of the skin and connective tissue, bone marrow, cartilage, adipose tissue, and breast tissue. An analytical review of the current literature on stem cell technology on the above mentioned areas is presented. There have been reports of side effects and unsuccessful treatments. The key to the progress of tissue engineering is an understanding between basic scientists, biochemical engineers, clinicians, and industry. Although there has been an ongoing research pointing to the enormous potential of using stem cells in cosmetic and reconstructive surgery, at this stage, stem cell therapy is still a hope that has not been fully studied and approved. More long-term studies are needed and many questions remain to be answered.

Chondrogenic differentiation of adipose tissue-derived mesenchymal stem cells: greater doses of growth factor are necessary

There have been controversies regarding the chondrogenic potential of adipose tissue-derived mesenchymal stem cells (ATMSCs) compared with bone marrow-derived mesenchymal stem cells (BMMSCs). The purpose of this study was to confirm the hypothesis that chondrogenesis can be achieved from ATMSCs comparable to that from BMMSCs by using greater dose of currently known chondrogenic growth factors. Chondrogenesis was induced from ATMSCs by culturing them in pellets under the following conditions: #1 without growth factors (negative control); #2 5 ng/mL of TGF-beta2; #3 5 ng/mL of TGF-beta2 and 100 ng/mL of IGF-I; #4 15 ng/mL of TGF-beta2; #5 15 ng/mL of TGF-beta2 and 300 ng/mL of IGF-I; #6 25 ng/mL of TGF-beta2; #7 25 ng/mL of TGF-beta2 and 500 ng/mL of IGF-I. After 4 weeks of in vitro culture, the pellets were harvested for DNA quantification, analysis of the glycosaminoglycan content, reverse transcription, and real-time PCR for collagen type I (COL1A1), collagen type II (COL2A1), and Sox-9. Safranin-O and immunohistochemical staining for type II collagen also were carried out, and histological grading was performed based on the findings. A combination of 25 ng/mL TGF-beta2 and 500 ng/mL IGF-I produced results comparable to the positive control (BMMSCs treated with 5 ng/mL TGF-beta2) as demonstrated by DNA amount, GAG analysis, real-time PCR, and histological findings. Although ATMSCs have lower chondrogenic potentials than BMMSCs, chondrogenesis comparable to BMMSCs can be induced from ATMSCs using a greater dose combination of growth factors. These results lend a further support to the application of ATMSCs for cartilage tissue engineering.

Comparison of chondrogenic potential in equine mesenchymal stromal cells derived from adipose tissue and bone marrow

OBJECTIVE

To compare the chondrogenic potential of adult equine mesenchymal stem cells derived from bone marrow (MSCs) or adipose tissue (ASCs).

STUDY DESIGN

In vitro experimental study.

ANIMALS

Adult Thoroughbred horses (n=11).

METHODS

BM (5 horses; mean [+/-SD] age, 4+/-1.4 years) or adipose tissue (6 horses; mean age, 3.5+/-1.1 years) samples were obtained. Cryopreserved MSCs and ASCs were used for pellet cultures in stromal medium (C) or induced into chondrogenesis+/-transforming growth factor-3 (TGFbeta(3)) and bone morphogenic factor-6 (BMP-6). Pellets harvested after 3, 7, 14, and 21 days were examined for cross-sectional size and tissue composition (hematoxylin and eosin), glycosaminoglycan (GAG) staining (Alcian blue), collagen type II immunohistochemistry, and by transmission electron microscopy. Pellet GAG and total DNA content were measured using dimethylmethylene blue and Hoechst DNA assays.

RESULTS

Collagen type II synthesis was predominantly observed in MSC pellets from Day 7 onward. Unlike ASC cultures, MSC pellets had hyaline-like matrix by Day 14. GAG deposition occurred earlier in MSC cultures compared with ASC cultures and growth factors enhanced both MSC GAG concentrations (P<.0001) and MSC pellet size (P<.004) after 2 weeks in culture.

CONCLUSION

Equine MSCs have superior chondrogenic potential compared with ASCs and the equine ASC growth factor response suggests possible differences compared with other species.

CLINICAL RELEVANCE

Elucidation of equine ASC and MSC receptor profiles will enhance the use of these cells in regenerative cartilage repair.

Osteogenic effects of rest inserted and continuous cyclic tensile strain on hASC lines with disparate osteodifferentiation capabilities

We investigated the effects of two types of cyclic tensile strain, continuous and rest inserted, on osteogenic differentiation of human adipose-derived adult stem cells (hASCs). The influence of these mechanical strains was tested on two hASC lines having different mineral deposition potential, with one cell line depositing approximately nine times as much calcium as the other hASC line after 14 days of culture in osteogenic medium on tissue culture plastic. Results showed that both continuous (10% strain, 1 Hz) and rest inserted cyclic tensile strain (10% strain, 1 Hz, 10 s rest after each cycle) regimens increased the amount and rate of calcium deposition for both high and low calcium depositing hASC lines as compared to unstrained controls. The response was similar for both types of tensile strain for a given cell line, however, cyclic tensile strain had a much stronger osteogenic effect on the high calcium depositing hASC line, suggesting that mechanical loading has a greater effect on cell lines that already have an innate ability to produce bone as compared to cell lines that do not. This is the first study to investigate the osteodifferentiation effects of cyclic tensile strain on hASCs and the first to show that both continuous (10%, 1 Hz) and rest inserted (10%, 1 Hz, 10 s rest) cyclic tensile strain accelerate hASC osteodifferentiation and increase calcium accretion.

Differentiation of adipose stem cells

The broad definition of a stem cell is a cell that has the ability to self-renew and differentiate into one or more specialized terminally differentiated cell types. It has become evident that stem cells persist in, and can be isolated from, many adult tissues. Adipose tissue has been shown to contain a population of cells that retain a high proliferation capacity in vitro and the ability to undergo extensive differentiation into multiple cell lineages. These cells are referred to as adipose stem cells and are biologically similar, although not identical, to mesenchymal stem cells derived from the bone marrow. Differentiation causes stem cells to adopt the phenotypic, biochemical, and functional properties of more terminally differentiated cells. This chapter will provide investigators with some background on stem cells derived from adipose tissue and then provide details on adipose stem cell multilineage differentiation along osteogenic, adipogenic, chondrogenic, and neurogenic lineages.

Upregulation of Runx2 and Osterix during in vitro chondrogenesis of human adipose-derived stromal cells

The aim of this study was to create a gene expression profile to better define the phenotype of human adipose-derived stromal cells (HADSCs) during in vitro chondrogenesis, osteogenesis and adipogenesis. A novel aspect of this work was the analysis of the same subset of genes during HADSC differentiation into all three lineages. Chondrogenic induction resulted in increased mRNA expression of Sox transcription factors, COL2A1,COL10A1, Runx2, and Osterix. This is the first report demonstrating significant upregulation in expression of osteogenesis-related transcription factors Runx2 and Osterix by TGF-beta3 induction of HADSCs during in vitro chondrogenesis. These findings suggest that the commonly-used chondrogenic induction reagents promote differentiation suggestive of hypertrophic chondrocytes and osteoblasts. We conclude that alternative strategies are required to induce efficient articular chondrocyte differentiation in order for HADSCs to be of clinical use in cartilage tissue engineering.

Role of gender and anatomical region on induction of osteogenic differentiation of human adipose-derived stem cells

Adipose-derived stem cells (ASCs) display multilineage plasticity and, under appropriate conditions, can mineralize their extracellular matrix and undergo osteogenesis. The aims of this study are to examine in vitro osteogenic differentiation properties of ASCs to assess the role of gender, fat depot, and optimal duration as variables for differentiation. Human ASCs were isolated from superficial and deep adipose layers of the abdominoplasty specimens obtained from patients undergoing elective surgeries. ASCs were cultured in osteogenic media (OM). After 1, 2, and 4 weeks of differentiation, cultures were assessed for markers of osteogenesis. Alkaline phosphatase (AP), alizarin red (AR) and Masson trichrome (MT) stainings for osteoblastic transformation, matrix mineralization, and collagen production; enzyme-linked immunosorbent assay (ELISA) for Gla-osteocalcin; and Western blot analysis for osteonectin protein expression were performed. Osteogenic differentiation began as early as 1 week. Cells exhibited a vertical growth pattern, lacunae formed in the cultures, matrix volume increased, and mineralization was observed. Differences in AP staining were most evident during the first week. AR activity progressively increased over 4 weeks, and collagen was secreted only by differentiated ASCs. There was no significant difference in the degree of osteogenic differentiation between the ASCs from both depots in the female. In the male, the superficial depot ASCs differentiated faster and more efficiently than those of the deep depot. Male ASCs from both depots differentiated more effectively than female ASCs from both depots. We describe a hierarchy of osteogenic differentiation potential based on gender and anatomic harvest site by layering adipose tissues of the abdominal wall. ASCs derived from male superficial layer were most efficient in achieving osteogenesis. In future clinical applications using stem cells for osseous healing, these gender and depot differences will guide our clinical methods.

In vitro Differentiation Potential of Mesenchymal Stem Cells

SUMMARY: Mesenchymal stem cells (MSCs) represent a class of multipotent progenitor cells that have been isolated from multiple tissue sites. Of these, adipose tissue and bone marrow offer advantages in terms of access, abundance, and the extent of their documentation in the literature. This review focuses on the in vitro differentiation capability of cells derived from adult human tissue. Multiple, independent studies have demonstrated that MSCs can commit to mesodermal (adipocyte, chondrocyte, hematopoietic support, myocyte, osteoblast, tenocyte), ectodermal (epithelial, glial, neural), and endodermal (hepatocyte, islet cell) lineages. The limitations and promises of these studies in the context of tissue engineering are discussed.

Preserved proliferative capacity and multipotency of human adipose-derived stem cells after long-term cryopreservation

BACKGROUND

Human adipose-derived stem (stromal) cells are promising as a regenerative therapy tool for defective tissues of mesenchymal lineage, including fat, bone, and cartilage, and blood vessels. In potential future clinical applications, adipose-derived stem cell cryopreservation could be an indispensable fundamental technology, as has occurred in other fields involving cell-based therapies using hematopoietic stem cells and umbilical cord blood cells.

METHODS

The authors examined the proliferative capacity and multipotency of human adipose-derived stem cells isolated from lipoaspirates of 18 patients in total before and after a 6-month cryopreservation following their defined protocol. Proliferative capacity was quantified by measuring doubling time in cell culture, and multipotency was examined with differentiation assays for chondrogenic, osteogenic, and adipogenic lineages. In addition, expression profiles of cell surface markers were determined by flow cytometry and compared between fresh and cryopreserved adipose-derived stem cells.

RESULTS

Cryopreserved adipose-derived stem cells fully retained the potential for differentiation into adipocytes, osteoblasts, and chondrocytes and for proliferative capacity. Flow cytometric analyses revealed that surface marker expression profiles remained constant before and after storage.

CONCLUSIONS

Adipose-derived stem cells can be cryopreserved at least for up to 6 months under the present protocol without any loss of proliferative or differentiation potential. These results ensure the availability of autologous banked adipose-derived stem cells for clinical applications in the future.

Comparison of osteogenic ability of rat mesenchymal stem cells from bone marrow, periosteum, and adipose tissue

Mesenchymal stem cells (MSCs) reside in many types of tissue and are able to differentiate into various functional cells including osteoblasts. Recently, adipose tissue-derived MSCs (AMSCs) have been shown to differentiate into many lineages, and they are considered a source for tissue regeneration. The purpose of this study was to compare the osteogenic differentiation capability of MSCs from bone marrow (BMSCs), MSCs from periosteum (PMSCs), and AMSCs using in vitro culture and in vivo implantation experiments. We harvested these MSCs from 7-week-old rats. The cells were seeded and cultured for 7 days in primary culture to assay a colony-forming unit. The frequency of the unit was the smallest in the BMSCs (P < 0.001). After primary culture, subculture was performed under osteogenic differentiation conditions for 1 and 2 weeks to detect mineralization as well as the bone-specific proteins of alkaline phosphatase and osteocalcin as osteogenic markers. BMSCs and PMSCs showed distinct osteogenic differentiation capability in comparison with other MSCs (P < 0.001). For the in vivo assay, composites of these cells and hydroxyapatite ceramics were subcutaneously implanted into syngeneic rats and harvested after 6 weeks. Micro-computed tomographic (CT) and histological analyses demonstrated that new bone formation was detected in the composites using BMSCs and PMSCs, although it was hard to detect in other composites. The CT analyses also demonstrated that the bone volume of BMSC composites was more than that of AMSC composites (P < 0.001). These results indicate that BMSCs and PMSCs could be ideal candidates for utilization in practical bone tissue regeneration.

Adipose stem cells for intervertebral disc regeneration: current status and concepts for the future

New regenerative treatment strategies are being developed for intervertebral disc degeneration of which the implantation of various cell types is promising. All cell types used so far require in vitro expansion prior to clinical use, as these cells are only limited available. Adipose-tissue is an abundant, expendable and easily accessible source of mesenchymal stem cells. The use of these cells therefore eliminates the need for in vitro expansion and subsequently one-step regenerative treatment strategies can be developed. Our group envisioned, described and evaluated such a one-step procedure for spinal fusion in the goat model. In this review, we summarize the current status of cell-based treatments for intervertebral disc degeneration and identify the additional research needed before adipose-derived mesenchymal stem cells can be evaluated in a one-step procedure for regenerative treatment of the intervertebral disc. We address the selection of stem cells from the stromal vascular fraction, the specific triggers needed for cell differentiation and potential suitable scaffolds. Although many factors need to be studied in more detail, potential application of a one-step procedure for intervertebral disc regeneration seems realistic.

Monolayer cell expansion conditions affect the chondrogenic potential of adipose-derived stem cells

Adipose-derived stem cells (ASCs) are an abundant, readily available population of multipotent progenitor cells that reside in adipose tissue. Isolated ASCs are typically expanded in monolayer on standard tissue culture plastic with a basal medium containing 10% fetal bovine serum. However, recent data suggest that altering the monolayer expansion conditions by using suspension culture plastic, adding growth factors to the medium, or adjusting the seeding density may affect the self-renewal rate, multipotency, and lineage-specific differentiation potential of the ASCs. We hypothesized that variation in any of these expansion conditions would influence the chondrogenic potential of ASCs. ASCs were isolated from human liposuction waste tissue and expanded through two passages with different tissue culture plastic, feed medium, and cell seeding densities. Once expanded, the cells were cast in an agarose gel and subjected to identical chondrogenic culture conditions for 7 days, at which point cell viability, radiolabel incorporation, and gene expression were measured. High rates of matrix synthesis upon chondrogenic induction were mostly associated with smaller cells, as indicated by cell width and area on tissue culture plastic, and it appears that expansion in a growth factor supplemented medium is important in maintaining this morphology. All end-point measures were highly dependent on the specific monolayer culture conditions. These results support the hypothesis that monolayer culture conditions may "prime" the cells or predispose them towards a specific phenotype and thus underscore the importance of early culture conditions in determining the growth and differentiation potential of ASCs.

Differential effects of BMP-2 and TGF-beta1 on chondrogenic differentiation of adipose derived stem cells

OBJECTIVES

This article addresses the interaction of transforming growth factor beta1 (TGF-beta1) and bone morphogenic protein 2 (BMP-2) during osteo-chondrogenic differentiation of adipose-derived adult stem cells (ASC). TGF-beta1 was expected to modulate the BMP-2-induced effects through transcriptional regulation of Dlx-5, Msx-2 and Runx-2.

MATERIALS AND METHODS

Encapsulated ASC were cultured for 14 days in medium containing TGF-beta1 and/or BMP-2. mRNA expression of the extracellular matrix molecules col2a1, cartilage oligomeric matrix protein, col10a1, alkaline phosphatase (AP) and transcription factors Msx-2, Dlx-5 and Runx-2 was analysed. Release of glycosaminoglycans, collagen types II and X into the extracellular matrix was demonstrated.

RESULTS

BMP-2 and TGF-beta1 induced a chondrogenic phenotype in ASC. Combined growth factor treatment had a synergistic effect on col10a1 and an additive effect on col2a1 mRNA expression. Synthesis of glycosaminoglycans was enhanced by combined growth factor treatment. Addition of TGF-beta1 inhibited BMP-2 induced AP expression and activity and both proteins promoted chondrogenic maturation.

CONCLUSIONS

Prevention of BMP-2-induced osteogenic transdifferentiation by TGF-beta1 seemed not to be mediated by transcriptional regulation of Dlx-5. Due to these findings, simultaneous stimulation of ASC with BMP-2 and TGF-beta1 seemed to be beneficial for complete differentiation of ASC into chondrocytes.

Characterization of transplanted green fluorescent protein+ bone marrow cells into adipose tissue

Following transplantation of green fluorescent protein (GFP)-labeled bone marrow (BM) into irradiated, wild-type Sprague-Dawley rats, propagated GFP(+) cells migrate to adipose tissue compartments. To determine the relationship between GFP(+) BM-derived cells and tissue-resident GFP(-) cells on the stem cell population of adipose tissue, we conducted detailed immunohistochemical analysis of chimeric whole fat compartments and subsequently isolated and characterized adipose-derived stem cells (ASCs) from GFP(+) BM chimeras. In immunohistochemistry, a large fraction of GFP(+) cells in adipose tissue were strongly positive for CD45 and smooth muscle actin and were evenly scattered around the adipocytes and blood vessels, whereas all CD45(+) cells within the blood vessels were GFP(+). A small fraction of GFP(+) cells with the mesenchymal marker CD90 also existed in the perivascular area. Flow cytometric and immunocytochemical analyses showed that cultured ASCs were CD45(-)/CD90(+)/CD29(+). There was a significant difference in both the cell number and phenotype of the GFP(+) ASCs in two different adipose compartments, the omental (abdominal) and the inguinal (subcutaneous) fat pads; a significantly higher number of GFP(-)/CD90(+) cells were isolated from the subcutaneous depot as compared with the abdominal depot. The in vitro adipogenic differentiation of the ASCs was achieved; however, all cells that had differentiated were GFP(-). Based on phenotypical analysis, GFP(+) cells in adipose tissue in this rat model appear to be of both hematopoietic and mesenchymal origin; however, infrequent isolation of GFP(+) ASCs and their lack of adipogenic differentiation suggest that the contribution of BM to ASC generation might be minor.

Chondrogenic differentiation of amniotic fluid-derived stem cells

For regenerating damaged articular cartilage, it is necessary to identify an appropriate cell source that is easily accessible, can be expanded to large numbers, and has chondrogenic potential. Amniotic fluid-derived stem (AFS) cells have recently been isolated from human and rodent amniotic fluid and shown to be highly proliferative and broadly pluripotent. The purpose of this study was to investigate the chondrogenic potential of human AFS cells in pellet and alginate hydrogel cultures. Human AFS cells were expanded in various media conditions, and cultured for three weeks with growth factor supplementation. There was increased production of sulfated glycosaminoglycan (sGAG) and type II collagen in response to transforming growth factor-beta (TGF-beta) supplementation, with TGF-beta1 producing greater increases than TGF-beta3. Modification of expansion media supplements and addition of insulin-like growth factor-1 during pellet culture further increased sGAG/DNA over TGF-beta1 supplementation alone. Compared to bone marrow-derived mesenchymal stem cells, the AFS cells produced less cartilaginous matrix after three weeks of TGF-beta1 supplementation in pellet culture. Even so, this study demonstrates that AFS cells have the potential to differentiate along the chondrogenic lineage, thus establishing the feasibility of using these cells for cartilage repair applications.

Cell-assisted lipotransfer: supportive use of human adipose-derived cells for soft tissue augmentation with lipoinjection

Injective transfer of autologous aspirated fat is a popular option for soft tissue augmentation, but several issues require attention, including unpredictability and a low survival rate due to partial necrosis. In this study, histologic features and yield of adipose-derived stromal (stem) cells (ASCs) were compared between human aspirated fat and excised whole fat. Aspirated fat contained fewer large vascular structures, and ASC yield was lower in aspirated fat. Aspirated fat was transplanted subcutaneously into severe combined immunodeficiency mice with (cell-assisted lipotransfer; CAL) or without (non-CAL) vascular stromal fractions containing ASCs isolated from adipose tissue. The CAL fat survived better (35% larger on average) than non-CAL fat, and microvasculature was detected more prominently in CAL fat, especially in the outer layers. DiI-labeled vascular stromal fraction cells were found between adipocytes and in the connective tissue in CAL fat, and some of these cells were immunopositive for von Willebrand factor, suggesting differentiation into vascular endothelial cells. Another experiment that used vascular stromal fractions taken from green fluorescent protein rats also suggested that ASCs differentiated into vascular endothelial cells and contributed to neoangiogenesis in the acute phase of transplantation. These findings may partly explain why transplanted aspirated fat does not survive well and suggest clinical potential of the CAL method for soft tissue augmentation.

Analysis of the material properties of early chondrogenic differentiated adipose-derived stromal cells (ASC) using an in vitro three-dimensional micromass culture system

Cartilage is an avascular tissue with only a limited potential to heal and chondrocytes in vitro have poor proliferative capacity. Recently, adipose-derived stromal cells (ASC) have demonstrated a great potential for application to tissue engineering due to their ability to differentiate into cartilage, bone, and fat. In this study, we have utilized a high density three-dimensional (3D) micromass model system of early chondrogenesis with ASC. The material properties of these micromasses showed a significant increase in dynamic and static elastic modulus during the early chondrogenic differentiation process. These data suggest that the 3D micromass culture system represents an in vitro model of early chondrogenesis with dynamic cell signaling interactions associated with the mechanical properties of chondrocyte differentiation.

A Comparison Between the Chondrogenic Potential of Human Bone Marrow Stem Cells (BMSCs) and Adipose-Derived Stem Cells (ADSCs) Taken from the Same Donors

Cartilage damage has been documented as one of the major problems leading to knee repair procedures worldwide. The low availability of cartilage that can be harvested without causing a negative health impact has led to the focus on the potential of stem cells, which have been transplanted into damaged areas and successfully grown into new healthy tissue. This study aims to compare the chondrogenic potential of two stem cell sources--adipose tissue and bone marrow. Stem cells were isolated from donor-matched adipose tissue and bone marrow, following established protocols. The cells were grown in a chondrogenic cocktail containing transforming growth factor-beta3 (TGF-beta3) up till 28 days, and assessed for expression changes of cartilage markers at the gene and protein level, using qualitative and quantitative methods. Controls were included for every time point. Real-time polymerase chain reaction (PCR) results showed increases in the gene expression of collagen II in both the cell types that received TGF-beta3 treatment. However, histological, immunohistochemical, and glycosaminoglycan (GAG) assay clearly showed that collagen II and proteoglycans (PG) were synthesized only in the growth factor-treated bone marrow stem cells (BMSCs). These findings support the results obtained in our in vivo comparative study done on an animal model, suggesting that BMSCs are more suitable than adipose-derived stem cells (ADSCs) for chondrogenesis.

Extended passaging, but not aldehyde dehydrogenase activity, increases the chondrogenic potential of human adipose-derived adult stem cells

Adipose-derived adult stem (ADAS) cells represent an abundant population of multipotent mesodermal cells residing in various adipose tissue depots. ADAS cell preparations appear heterogeneous, yet at a clonal level, greater than 50% of these cells exhibit multilineage differentiation potential. To date, there have been few attempts to define prospectively a homogenous population of multipotent cells. In this study, we investigated whether aldehyde dehydrogenase (ALDH) can be used to enrich ADAS cells with increased chondrogenic potential. ALDH has been previously used to isolate primitive hematopoietic progenitors and has been implicated in early neurogenesis. Human ADAS cells were purified based on ALDH activity, and the cells were expanded and induced for chondrogenic differentiation using BMP-6 in a 3-D alginate culture. No significant differences in chondrogenic potential were observed in the ALDH-positive cells compared to unsorted controls. In contrast, significant differences were noted between cells assayed at passage 4 (P4) and cells assayed at passage 9 (P9). Following BMP-6 induction, AGC1 gene expression in P9 cells increased 290-fold over P4 cells. Similarly, COL2A1 expression in P9 cells increased fivefold compared to P4 cells, while COL10A1 levels remained unchanged. Immunohistochemical analysis over 28 days revealed consistent findings at the protein level for collagen II, collagen X, and aggrecan. No changes in telomerase activity were detected across passage, suggesting that ADAS cells retain some level of "stemness" in monolayer culture. These findings suggest that the chondrogenic potential of ADAS cells increases with passage number, although ALDH may not be a suitable marker for chondrogenesis.

Adipose-derived stem cells and chondrogenesis

Cartilage has only a very limited capacity to renew its original structure. Stem cells have been used to repair damaged cartilage, and recent studies have indicated that stem cells from adipose tissue are attractive cell sources that have the capacity of multipotentiality to differentiate into osteogenic, chondrogenic, myogenic, neurogenic and endothelial cells. Adipose-derived stem cells (ASC) have unique characteristics compared with stem cells from BM. At present, ASC have been studied to promote chondrogenesis. This review discusses the application of ASC to cartilage formation.

Meniscal Repair With Fibrocartilage Engineering

Injuries to the knee meniscus, particularly those in the avascular region, pose a complex problem and a possible solution is tissue engineering of a replacement tissue. Tissue engineering of the meniscus involves scaffold selection, addition of cells, and stimulation of the construct to synthesize, maintain, or enhance matrix production. An acellular collagen implant is currently in clinical trials and there are promising results with other scaffolds, composed of both polymeric and natural materials. The addition of cells to these constructs may promote good matrix production in vitro, but has been studied in a limited manner in animal studies. Cell sources ranging from fibroblasts to stem cells could be used to overcome challenges in cell procurement, expansion, and synthetic capacity currently encountered in studies with fibrochondrocytes. Manipulation of construct culture with exogenous growth factors and mechanical stimulation will also likely play a role in these strategies.

Characterization of freshly isolated and cultured cells derived from the fatty and fluid portions of liposuction aspirates

Liposuction aspirates (primarily saline solution, blood, and adipose tissue fragments) separate into fatty and fluid portions. Cells isolated from the fatty portion are termed processed lipoaspirate (PLA) cells and contain adipose-derived adherent stromal cells (ASCs). Here we define cells isolated from the fluid portion of liposuction aspirates as liposuction aspirate fluid (LAF) cells. Stromal vascular fractions (SVF) were isolated separately from both portions and characterized under cultured and non-cultured conditions. A comparable number of LAF and PLA cells were freshly isolated, but fewer LAF cells were adherent. CD34+ CD45- cells from fresh LAF isolates were expanded by adherent culture, suggesting that LAF cells contain ASCs. Although freshly isolated PLA and LAF cells have distinct cell surface marker profiles, adherent PLA and LAF cells have quite similar characteristics with regard to growth kinetics, morphology, capacity for differentiation, and surface marker profiles. After plating, both PLA and LAF cells showed significant increased expression of CD29, CD44, CD49d, CD73, CD90, CD105, and CD151 and decreased expression of CD31 and CD45. Multicolor FACS analysis revealed that SVF are composed of heterogeneous cell populations including blood-derived cells (CD45+), ASCs (CD31- CD34+ CD45- CD90+ CD105- CD146-), endothelial (progenitor) cells (CD31+ CD34+ CD45- CD90+ CD105low CD146+), pericytes (CD31- CD34- CD45- CD90+ CD105- CD146+), and other cells. After plating, ASCs showed a dramatic increase in CD105 expression. Although some adherent ASCs lost CD34 expression with increasing culture time, our culture method maintained CD34 expression in ASCs for at least 10-20 weeks. These results suggest that liposuction-derived cells may be useful and valuable for cell-based therapies.

Potent induction of chondrocytic differentiation of human adipose-derived adult stem cells by bone morphogenetic protein 6

OBJECTIVE

Recent studies have identified an abundant source of multipotent progenitor cells in subcutaneous human adipose tissue, termed human adipose-derived adult stem cells (ADAS cells). In response to specific media formulations, including transforming growth factor beta1 (TGFbeta1), these cells exhibit significant ability to differentiate into a chondrocyte-like phenotype, expressing cartilage-specific genes and proteins such as aggrecan and type II collagen. However, the influence of other growth factors on the chondrogenic differentiation of ADAS cells is not fully understood. This study was undertaken to investigate the effects of TGFbeta1, TGFbeta3, insulin-like growth factor 1, bone morphogenetic protein 6 (BMP-6), and dexamethasone, in various combinations, on the chondrogenic potential of ADAS cells in alginate beads.

METHODS

The chondrogenic response of alginate-encapsulated ADAS cells was measured by quantitative polymerase chain reaction, 3H-proline and 35S-sulfate incorporation, and immunolabeling for specific extracellular matrix components.

RESULTS

Significant differences in chondrogenesis were observed under the different culture conditions for all outcomes measured. Most notably, BMP-6 up-regulated AGC1 and COL2A1 expression by an average of 205-fold and 38-fold, respectively, over day-0 controls, while down-regulating COL10A1 expression by approximately 2-fold.

CONCLUSION

These findings suggest that BMP-6 is a potent inducer of chondrogenesis in ADAS cells, in contrast to mesenchymal stem cells, which exhibit increased expression of type X collagen and a hypertrophic phenotype in response to BMP-6. Combinations of growth factors containing BMP-6 may provide a novel means of regulating the differentiation of ADAS cells for applications in the tissue-engineered repair or regeneration of articular cartilage.

Clonal analysis of the differentiation potential of human adipose-derived adult stem cells

Pools of human adipose-derived adult stem (hADAS) cells can exhibit multiple differentiated phenotypes under appropriate in vitro culture conditions. Because adipose tissue is abundant and easily accessible, hADAS cells offer a promising source of cells for tissue engineering and other cell-based therapies. However, it is unclear whether individual hADAS cells can give rise to multiple differentiated phenotypes or whether each phenotype arises from a subset of committed progenitor cells that exists within a heterogeneous population. The goal of this study was to test the hypothesis that single hADAS are multipotent at a clonal level. hADAS cells were isolated from liposuction waste, and ring cloning was performed to select cells derived from a single progenitor cell. Forty-five clones were expanded through four passages and then induced for adipogenesis, osteogenesis, chondrogenesis, and neurogenesis using lineage-specific differentiation media. Quantitative differentiation criteria for each lineage were determined using histological and biochemical analyses. Eighty one percent of the hADAS cell clones differentiated into at least one of the lineages. In addition, 52% of the hADAS cell clones differentiated into two or more of the lineages. More clones expressed phenotypes of osteoblasts (48%), chondrocytes (43%), and neuron-like cells (52%) than of adipocytes (12%), possibly due to the loss of adipogenic ability after repeated subcultures. The findings are consistent with the hypothesis that hADAS cells are a type of multipotent adult stem cell and not solely a mixed population of unipotent progenitor cells. However, it is important to exercise caution in interpreting these results until they are validated using functional in vivo assays.

Application of collagen matrices for cartilage tissue engineering

Articular cartilage shows little capacity for self-repair once it has been damaged. The aim of this study was to investigate different collagen matrices regarding their applicability for cartilage tissue engineering. The matrices consist of collagen I and small amounts of elastine, were crosslinked with carbodiimide or glucose. Primary chondrocytes were seeded onto these different collagen matrices and cultured with or without differentiation medium. The viability of the cells was monitored via MTT test. The arrangement of the cells onto the scaffold was investigated by histological staining. Furthermore, extracellular matrix synthesis was studied by immunohistological staining, especially the expression of the typical chondrogenic marker collagen II. Moreover gene expression for collagen type II was analysed by RT-PCR. The chondrocytes showed high viability on all matrices used. The results for the histological staining revealed a three-dimensional arrangement of the chondrocytes in the collagen matrices. Moreover, the matrices also supported chondrogenic differentiation. On the matrix MATRIDERM 2 mm the synthesis of collagen II was stimulated without adding any differentiation supplements to the cell culture medium, as observed by immunohistological staining and by gene expression analysis of collagen II.

Chondrogenic differentiation and functional maturation of bovine mesenchymal stem cells in long-term agarose culture

BACKGROUND

The developmental history of the chondrocyte results in a cell whose biosynthetic activities are optimized to maintain the concentration and organization of a mechanically functional cartilaginous extracellular matrix. While useful for cartilage tissue engineering studies, the limited supply of healthy autologous chondrocytes may preclude their clinical use. Consequently, multipotential mesenchymal stem cells (MSCs) have been proposed as an alternative cell source.

OBJECTIVE

While MSCs undergo chondrogenesis, few studies have assessed the mechanical integrity of their forming matrix. Furthermore, efficiency of matrix formation must be determined in comparison to healthy chondrocytes from the same donor. Given the scarcity of healthy human tissue, this study determined the feasibility of isolating bovine chondrocytes and MSCs, and examined their long-term maturation in three-dimensional agarose culture.

EXPERIMENTAL DESIGN

Bovine MSCs were seeded in agarose and induced to undergo chondrogenesis. Mechanical and biochemical properties of MSC-laden constructs were monitored over a 10-week period and compared to those of chondrocytes derived from the same group of animals maintained similarly.

RESULTS

Our results show that while chondrogenesis does occur in MSC-laden hydrogels, the amount of the forming matrix and measures of its mechanical properties are lower than that produced by chondrocytes under the same conditions. Furthermore, some important properties, particularly glycosaminoglycan content and equilibrium modulus, plateau with time in MSC-laden constructs, suggesting that diminished capacity is not the result of delayed differentiation.

CONCLUSIONS

These findings suggest that while MSCs do generate constructs with substantial cartilaginous properties, further optimization must be done to achieve levels similar to those produced by chondrocytes.

Chondrogenic potential of progenitor cells derived from human bone marrow and adipose tissue: a patient-matched comparison

PURPOSE

Stem cell-based tissue engineering represents a possible alternative for the repair of cartilage defects. Both bone marrow and adipose tissue contain pluripotential cells capable of chondrogenesis. This study was a qualitative and quantitative comparison of the chondrogenic potential of progenitor cells isolated from bone marrow aspirates and adipose tissue.

METHODS

Bone marrow aspirates (BM) and matching adipose tissue (AD) overlying the posterior superior iliac crest were obtained from patients undergoing elective spine surgery. Chondrogenesis was induced using an established aggregate culture technique. Qualitative analysis was performed by histology and immunohistochemistry. DNA and glycosaminoglycan (GAG) quantitative assays were performed. Quantitative RT-PCR analysis was performed to compare expression of type II collagen between BM and AD aggregates. Osteogenic and adipogenic assays were also performed to confirm pluripotentiality of both AD-derived progenitor cells (ADPC) and BM-derived progenitor cells (BMPC).

RESULTS

Toluidine blue metachromasia and type II collagen immunohistochemical staining were more extensive in the aggregates formed by BMPC. Quantitative RT-PCR showed a 500-5000 fold higher expression of type II collagen in the BMPC aggregates. The DNA content was 68% higher in the AD aggregates (p<0.02) but proteoglycan deposition per cell was 120% greater for BM-derived cell aggregates as measured by GAG assays (p<0.05).

CONCLUSIONS

The tissue formed by the aggregate culture of the expanded ADPC population was less cartilaginous. It is unclear whether this is because there are fewer chondroprogenitor cells or if the monolayer expansion culture favors cells with higher proliferative rates but without differentiation potential. Under the conditions described in this study, BMPCs may represent a better choice for progenitor cell-based strategies for cartilage repair.

In vivo bone formation by human marrow stromal cells in biodegradable scaffolds that release dexamethasone and ascorbate-2-phosphate

An unsolved problem with stem cell-based engineering of bone tissue is how to provide a microenvironment that promotes the osteogenic differentiation of multipotent stem cells. Previously, we fabricated porous poly(D,L-lactide-co-glycolide) (PLGA) scaffolds that released biologically active dexamethasone (Dex) and ascorbate-2-phosphate (AsP), and that acted as osteogenic scaffolds. To determine whether these osteogenic scaffolds can be used for bone formation in vivo, we seeded multipotent human marrow stromal cells (hMSCs) onto the scaffolds and implanted them subcutaneously into athymic mice. Higher alkaline phosphatase expression was observed in hMSCs in the osteogenic scaffolds compared with that of hMSCs in control scaffolds. Furthermore, there was more calcium deposition and stronger von Kossa staining in the osteogenic scaffolds, which suggested that there was enhanced mineralized bone formation. We failed to detect cartilage in the osteogenic scaffolds (negative Safranin O staining), which implied that there was intramembranous ossification. This is the first study to demonstrate the successful formation of mineralized bone tissue in vivo by hMSCs in PLGA scaffolds that release Dex and AsP.

Proteomic Analysis of Primary Cultures of Human Adipose-derived Stem Cells

Adipogenesis plays a critical role in energy metabolism and is a contributing factor to the obesity epidemic. This study examined the proteome of primary cultures of human adipose-derived adult stem (ADAS) cells as an in vitro model of adipogenesis. Protein lysates obtained from four individual donors were compared before and after adipocyte differentiation by two-dimensional gel electrophoresis and tandem mass spectroscopy. Over 170 individual protein features in the undifferentiated adipose-derived adult stem cells were identified. Following adipogenesis, over 40 proteins were up-regulated by > or = 2-fold, whereas 13 showed a > or = 3-fold reduction. The majority of the modulated proteins belonged to the following functional categories: cytoskeleton, metabolic, redox, protein degradation, and heat shock protein/chaperones. Additional immunoblot analysis documented the induction of four individual heat shock proteins and confirmed the presence of the heat shock protein 27 phosphoserine 82 isoform, as predicted by the proteomic analysis, as well as the crystallin alpha phosphorylated isoforms. These findings suggest that the heat shock protein family proteome warrants further investigation with respect to the etiology of obesity and type 2 diabetes.

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.

Comparison of viable cell yield from excised versus aspirated adipose tissue

The correction of soft-tissue defects by adipose tissue transplantation often produces poor and unpredictable results. The implantation of isolated and cultured preadipocytes offers a solution to this problem since these cells differentiate into adipocytes when implanted in vivo. A field of major interest is to maximize the yield of preadipocytes isolated from adipose tissue showing only low contamination with other cell types. Aspiration and excision are two concurrent clinical ways of harvesting adipose tissue for the isolation of preadipocytes. This tissue is usually discarded after surgery. In this study, the yield of preadipocytes obtained from liposuction material was compared to that of excised adipose tissue. Furthermore, we determined the loss of precursor cells if isolation of preadipocytes was delayed for 24 h. Preadipocytes were isolated from the stromal cell fraction of human subcutaneous adipose tissue samples. Harvesting of adipose tissue by suction was performed according to the Coleman procedure (manually applied negative pressure using a 10-ml syringe with a blunt tip cannula). Isolation was either carried out within 60 min after extraction or after storage for 24 h in culture medium at 4 degrees C. Isolated preadipocytes were cultured for 24 h, trypsinized and counted in a Neubauer chamber. Our results show clearly that the yield of preadipocytes isolated from liposuction material (within 60 min after extraction and after 24 h of storage) is higher than the cell yield from excised adipose tissue. Overnight storage for 24 h leads to a significant loss of preadipocytes in excised tissue but not in liposuction material. The high yield of cells isolated from liposuction material proves that extraction by suction does not damage the stromal cell fraction in the adipose tissue. If cell isolation is not performed immediately after the operation, liposuction material is clearly the better alternative for storage.

Chondrogenic differentiation of adipose-derived adult stem cells in agarose, alginate, and gelatin scaffolds

The differentiation and growth of adult stem cells within engineered tissue constructs are hypothesized to be influenced by cell-biomaterial interactions. In this study, we compared the chondrogenic differentiation of human adipose-derived adult stem (hADAS) cells seeded in alginate and agarose hydrogels, and porous gelatin scaffolds (Surgifoam), as well as the functional properties of tissue engineered cartilage constructs. Chondrogenic media containing transforming growth factor beta 1 significantly increased the rates of protein and proteoglycan synthesis as well as the content of DNA, sulfated glycosaminoglycans, and hydroxyproline of engineered constructs as compared to control conditions. Furthermore, chondrogenic culture conditions resulted in 86%, and 160% increases ( p < 0.05 ) in the equilibrium compressive and shear moduli of the gelatin scaffolds, although they did not affect the mechanical properties of the hydrogels over 28 days in culture. Cells encapsulated in the hydrogels exhibited a spherical cellular morphology, while cells in the gelatin scaffolds showed a more polygonal shape; however, this difference did not appear to hinder the chondrogenic differentiation of the cells. Furthermore, the equilibrium compressive and shear moduli of the gelatin scaffolds were comparable to agarose by day 28. Our results also indicated that increases in the shear moduli were significantly associated with increases in S-GAG content ( R2 = 0.36, p < 0.05 ) and with the interaction between S-GAG and hydroxyproline ( R2 = 0.34, p < 0.05 ). The findings of this study suggest that various biomaterials support the chondrogenic differentiation of hADAS cells, and that manipulating the composition of these tissue engineered constructs may have significant effects on their mechanical properties.