Osteogenesis versus chondrogenesis by BMP-2 and BMP-7 in adipose stem cells

Stem cells in bone tissue engineering

Bone tissue engineering has been one of the most promising areas of research, providing a potential clinical application to cure bone defects. Recently, various stem cells including embryonic stem cells (ESCs), bone marrow-derived mesenchymal stem cells (BM-MSCs), umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs), adipose tissue-derived stem cells (ADSCs), muscle-derived stem cells (MDSCs) and dental pulp stem cells (DPSCs) have received extensive attention in the field of bone tissue engineering due to their distinct biological capability to differentiate into osteogenic lineages. The application of these stem cells to bone tissue engineering requires inducing in vitro differentiation of these cells into bone forming cells, osteoblasts. For this purpose, efficient in vitro differentiation towards osteogenic lineage requires the development of well-defined and proficient protocols. This would reduce the likelihood of spontaneous differentiation into divergent lineages and increase the available cell source for application to bone tissue engineering therapies. This review provides a critical examination of the various experimental strategies that could be used to direct the differentiation of ESC, BM-MSC, UCB-MSC, ADSC, MDSC and DPSC towards osteogenic lineages and their potential applications in tissue engineering, particularly in the regeneration of bone.

Adipose tissue-derived stem cells and their application in bone and cartilage tissue engineering

The adipose tissue was considered a reserve of energy until the '80s, when it was found that this tissue was involved in the metabolism of sex steroids such as estrogens. From then on, the importance attributed to this tissue radically changed as it was then considered an active organ, involved in important functions of the human body. In 2001, for the first time, the existence of stem cells within this tissue was reported, and since then, this tissue has been gaining an increased importance as a stem cell source for a wide range of potential applications in cell therapies and/or tissue engineering and regenerative medicine strategies, mainly due to its wide availability and easy access. This manuscript provides an overview on adipose stem cells (i.e., adipose tissue-derived stem cells, ASCs) considering the tissue of origin, the niche of the ASCs, and their phenotype in all aspects. In this paper it is also discussed the markers that have been used for the characterization of these cells, their differentiation properties, and their immunological reactivity, reporting studies from 2001 until this date. The ASCs are also compared with bone marrow stem cells (BMSCs), until now considered as the gold standard source of stem cells, underlining the common characteristics and the differences between the stem cells obtained from these two sources, as well as the advantages and disadvantages of their potential use in different applications. Finally, this review will also focus on the potential application of ASCs in tissue engineering applications, particularly in the regeneration of bone and cartilage, commenting on the progress of this approach and future trends of the field.

Divergent modulation of adipose-derived stromal cell differentiation by TGF-beta1 based on species of derivation

BACKGROUND

Adipose-derived stromal cells hold promise for skeletal tissue engineering. However, various studies have observed that adipose-derived stromal cells differ significantly in their biology depending on species of derivation. In the following study, the authors sought to determine the species-specific response of adipose-derived stromal cells to recombinant TGF-beta1 (rTGF-beta1).

METHODS

Adipose-derived stromal cells were derived from mouse and human sources. Recombinant TGF-beta1 was added to culture medium (2.5 to 10 ng/ml); proliferation and osteogenic and adipogenic differentiation were assessed by standardized parameters, including cell counting, alkaline phosphatase, alizarin red, oil red O staining, and quantitative real-time polymerase chain reaction.

RESULTS

Recombinant TGF-beta1 was found to significantly repress cellular proliferation in both mouse and human adipose-derived stromal cells (p < 0.01). Recombinant TGF-beta1 was found to significantly repress osteogenic differentiation in mouse adipose-derived stromal cells. In contrast, osteogenic differentiation of human adipose-derived stromal cells proceeded unimpeded in either the presence or the absence of rTGF-beta1. Interestingly, rTGF-beta1 induced expression of a number of osteogenic genes in human adipose-derived stromal cells, including BMP2 and BMP4.

CONCLUSIONS

The authors' results further detail an important facet in which mouse and human adipose-derived stromal cells differ. Mouse adipose-derived stromal cell osteogenesis is completely inhibited by rTGF-beta1, whereas human adipose-derived stromal cell osteogenesis progresses in the presence of rTGF-beta1. These data highlight the importance of species of derivation in basic adipose-derived stromal cell biology. Future studies will examine in more detail the species-specific differences among adipose-derived stromal cell populations.

The role of BMP-7 in chondrogenic and osteogenic differentiation of human bone marrow multipotent mesenchymal stromal cells in vitro

This study addresses the role of bone morphogenetic protein-7 (BMP-7) in chondrogenic and osteogenic differentiation of human bone marrow multipotent mesenchymal stromal cells (BM MSCs) in vitro. BM MSCs were expanded and differentiated in the presence or absence of BMP-7 in monolayer and three-dimensional cultures. After 3 days of stimulation, BMP-7 significantly inhibited MSC growth in expansion cultures. When supplemented in commonly used induction media for 7-21 days, BMP-7 facilitated both chondrogenic and osteogenic differentiation of MSCs. This was evident by specific gene and protein expression analyses using real-time PCR, Western blot, histological, and immunohistochemical staining. BMP-7 supplementation appeared to enhance upregulation of lineage-specific markers, such as type II and type IX collagens (COL2A1, COL9A1) in chondrogenic and secreted phosphoprotein 1 (SPP1), osteocalcin (BGLAP), and osterix (SP7) in osteogenic differentiation. BMP-7 in the presence of TGF-beta3 induced superior chondrocytic proteoglycan accumulation, type II collagen, and SOX9 protein expression in alginate and pellet cultures compared to either factor alone. BMP-7 increased alkaline phosphatase activity and dose-dependently accelerated calcium mineralization of osteogenic differentiated MSCs. The potential of BMP-7 to promote adipogenesis of MSCs was restricted under osteogenic conditions, despite upregulation of adipocyte gene expression. These data suggest that BMP-7 is not a singular lineage determinant, rather it promotes both chondrogenic and osteogenic differentiation of MSCs by co-ordinating with initial lineage-specific signals to accelerate cell fate determination. BMP-7 may be a useful enhancer of in vitro differentiation of BM MSCs for cell-based tissue repair.

Glial cells modulate heparan sulfate proteoglycan (HSPG) expression by neuronal precursors during early postnatal cerebellar development

Cerebellum controls motor coordination, balance, eye movement, and has been implicated in memory and addiction. As in other parts of the CNS, correct embryonic and postnatal development of the cerebellum is crucial for adequate performance in the adult. Cellular and molecular defects during cerebellar development can lead to severe phenotypes, such as ataxias and tumors. Knowing how the correct development occurs can shed light into the mechanisms of disease. Heparan sulfate proteoglycans are complex molecules present in every higher eukaryotic cells and changes in their level of expression as well as in their structure lead to drastic functional alterations. This work aimed to investigate changes in heparan sulfate proteoglycans expression during cerebellar development that could unveil control mechanisms. Using real time RT-PCR we evaluated the expression of syndecans, glypicans and modifying enzymes by isolated cerebellar granule cell precursors, and studied the influence of soluble glial factors on the expression of those genes. We evaluated the possible involvement of Runx transcription factors in the response of granule cell precursors to glial factors. Our data show for the first time that cerebellar granule cell precursors express members of the Runx family and that the expression of those genes can also be controlled by glial factors. Our results also show that the expression of all genes studied vary during postnatal development and treatment of precursors with glial factors indicate that the expression of heparan sulfate proteoglycan genes as well as genes encoding heparan sulfate modifying enzymes can be modulated by the microenvironment, reflecting the intricate relations between neuron and glia.

Adipose-derived stem cell delivery into collagen gels using chitosan microspheres

Integration of stem cells to injured tissues requires an appropriate delivery device and scaffolding system. In the present study we have developed an in vitro strategy to load and release adipose-derived mesenchymal stem cells (ASC) from chitosan microspheres (CSM) into a collagen gel scaffold. Porous CSM of uniform size and composition were prepared and used as a stem cell carrier. ASC were allowed to attach to the microspheres and infiltrate through the microsphere pores. The number of viable cells was counted in vitro, using MTT and Calcein acetoxymethyl ester (AM) assays, and it showed a proportional increase with seeding density and reached a maximum cell number by 24 h. The cells inside the microspheres remained metabolically active and viable, could be retrieved from the spheres, and maintained expression of stem-cell-specific markers. Electron microscopic evaluation of the cell-microsphere complex showed that the CSM were able to support cell attachment and that the cells had infiltrated into the pores of the microspheres. The ability of the cells to proliferate and differentiate into adipogenic- and osteogenic-like precursors indicates that the cells have maintained their multipotency after migration out of the microspheres. To mimic cell delivery into a tissue, ASC-loaded CSM were embedded in type-1 collagen scaffold by mixing them with type-1 collagen solution while inducing gelation. By 14 days the cells released into the collagen gel and were able to populate the entire scaffold. When observed through transmission electron microscopy, the cells align along the collagen fibrils with a characteristic fibroblast-like morphology. This study provides a model to capture pluripotent stem cells, expand their cell number within a biomaterial scaffold in vitro, and deliver within an appropriate matrix to repair damaged tissue.

Soluble factors from ASCs effectively direct control of chondrogenic fate

BACKGROUND AND OBJECTIVES

Adipose tissue-derived stem cells (ASCs) have great potential for regenerative medicine. For molecular understanding of specific functional molecules present in ASCs, we analysed 756 proteins including specific chondrogenic functional factors, using high-throughput nano reverse-phase liquid chromatography-electrospray ionization-tandem mass spectrometry.

MATERIALS, METHODS AND RESULTS

Of these proteins, 33 were identified as chondrogenic factors or proteins including type 2 collagen, biglycan, insulin-like growth factor-binding protein and transforming growth factor-beta 1 (TGF-beta1). ASCs are a possible cell source for cartilage regeneration as they are able to secrete a number of functional cytokines including chondrogenesis-inducing molecules such as TGF-beta1 and bone morphogenetic protein 4 (BMP4). The chondrogenic phenotype of cultured ASCs was effectively induced by ASC-culture media (CM) containing BMP4 and TGF-beta1, and maintained after pre-treatment for 14 days in vitro and subcutaneous implantation in vivo. Chondrogenic differentiation efficiency of cultured ASCs and cultured mouse skin-derived progenitor cells (SPCs) depended absolutely on ASC CM-fold concentration. Cell density was also a very important factor for chondrogenic behaviour development during differentiation of ASCs and SPCs.

CONCLUSION

ASC CM-derived TGF-beta1-induced chondrogenic differentiation of ASCs resulted in significant reduction in chondrogenic activity after inhibition of the p38 pathway, revealing involvement of this MAPK pathway in TGF-beta1 signalling. On the other hand, TGF-beta1 signalling also led to SMAD activation that could directly increase chondrogenic activity of ASCs.

The effect of ethylene oxide, glow discharge and electron beam on the surface characteristics of poly(L-lactide-co-caprolactone) and the corresponding cellular response of adipose stem cells

Bioabsorbable polymers are increasingly being used in tissue engineering strategies. Despite the knowledge that some sterilization techniques may affect the physical properties of these polymers, this aspect is often overlooked. We speculate that the type of sterilization method used may influence cellular responses by altering the surface characteristics. We cultured adipose stem cells on bioabsorbable poly(l-lactide-co-caprolactone) (PLCL) sheets, sterilized using either ethylene oxide (EO), argon glow discharge (aGD) or electron beam (e-beam). Significantly higher values for surface roughness in the order EO>aGD>e-beam and significant differences in contact angles (EO>e-beam>aGD) and surface energies (aGD>e-beam>EO) were observed. Increased cell attachment and proliferation rates were observed with lower contact angles. The alkaline phosphatase activity was significantly higher for the ethylene oxide sterilized PLCL sheet. In conclusion, the type of sterilization for bioabsorbable polymers should be considered in the design of new scaffolds, since it might affect, or can be used to enhance, the outcome of the tissue engineered construct.

Osteochondral interface tissue engineering using macroscopic gradients of bioactive signals

Continuous gradients exist at osteochondral interfaces, which may be engineered by applying spatially patterned gradients of biological cues. In the present study, a protein-loaded microsphere-based scaffold fabrication strategy was applied to achieve spatially and temporally controlled delivery of bioactive signals in three-dimensional (3D) tissue engineering scaffolds. Bone morphogenetic protein-2 and transforming growth factor-beta(1)-loaded poly(D,L-lactic-co-glycolic acid) microspheres were utilized with a gradient scaffold fabrication technology to produce microsphere-based scaffolds containing opposing gradients of these signals. Constructs were then seeded with human bone marrow stromal cells (hBMSCs) or human umbilical cord mesenchymal stromal cells (hUCMSCs), and osteochondral tissue regeneration was assessed in gradient scaffolds and compared to multiple control groups. Following a 6-week cell culture, the gradient scaffolds produced regionalized extracellular matrix, and outperformed the blank control scaffolds in cell number, glycosaminoglycan production, collagen content, alkaline phosphatase activity, and in some instances, gene expression of major osteogenic and chondrogenic markers. These results suggest that engineered signal gradients may be beneficial for osteochondral tissue engineering.

Characterization of MSCs from human placental decidua basalis in hypoxia and serum deprivation

Recently, we reported that human PDB (placental decidua basalis) is an excellent source of MSCs (mesenchymal stem cells), meanwhile, PDB-MSCs could survive under hypoxia and serum deprivation. Herein, we investigated the proliferation, clonogentic efficiency, phenotypes, metabolic activity and cytokines secretion of PDB-MSCs in hypoxia and serum deprivation. PDB-MSCs were cultured in four groups: normoxia (20% O2) and complete medium [10% FBS (foetal bovine serum)+DMEM-HG (Dulbecco's modified Eagle's medium-high glucose)], hypoxia and complete medium, normoxia and serum deprivation (0% FBS), and hypoxia and serum deprivation. After 96 h of culture in the above groups, PDB-MSCs maintain the phenotypes stably. Interestingly, hypoxia notably enhanced the proliferation, colony-forming potential and lactate/glucose ratio in complete medium, but suppressed the secretion of BMP-2 (bone morphogenetic protein-2) and bFGF (basic fibroblast growth factor), while it did not change the quantity of VEGF (vascular endothelial growth factor) and bFGF in serum deprivation. Although PDB-MSCs grew slowly and seldom formed a colony unit in hypoxia and serum deprivation, they possessed a moderate metabolism. In conclusion, our results indicate that PDB-MSCs appear to be promising seed cells for ischaemia-related tissue engineering.

Freshly isolated stromal cells from the infrapatellar fat pad are suitable for a one-step surgical procedure to regenerate cartilage tissue

BACKGROUND AIMS

Stem cell therapies are being evaluated as promising alternatives for cartilage regeneration. We investigated whether stromal vascular fraction cells (SVF) from the infrapatellar (Hoffa) fat pad are suitable for a one-step surgical procedure to treat focal cartilage defects.

METHODS

SVF was harvested from patients undergoing knee arthroplasty (n = 53). Colony-forming unit (CFU) assays, growth kinetics and surface marker profiles were determined, and the chondrogenic differentiation capacity of freshly isolated SVF was assessed after seeding in three-dimensional poly (L-lactic-co-epsilon-caprolactone) scaffolds.

RESULTS

SVF yield per fat pad varied between 0.55 and 16 x 10(6) cells. CFU frequency and population doubling time were 2.6 +/- 0.6% and +/-2 days, respectively. Surface marker profiles matched those of subcutaneous-derived adipose-derived stem cells (ASC). CFU from Hoffa SVF showed differentiation toward osteogenic and adipogenic lineages. Cartilage differentiation was confirmed by up-regulation of the cartilage genes sox9, aggrecan, collagen type II and cartilage oligomeric matrix protein (COMP), collagen II immunostaining, Alcian Blue staining and glycosaminoglycan production. Compared with passaged cells, SVF showed at least similar chondrogenic potential.

CONCLUSIONS

This study demonstrates that SVF cells from the infrapatellar fat pad are suitable for future application in a one-step surgical procedure to regenerate cartilage tissue. SVF shows similar favorable characteristics as cultured ASC, and chondrogenic differentiation even appears to be slightly better. However, because of variable harvesting volumes and yields, SVF from the infrapatellar fat pad might only be applicable for treatment of small focal cartilage defects, whereas for larger osteoarthritic defects subcutaneous adipose tissue depot would be preferable.

IGF-1 and BMP-2 induces differentiation of adipose-derived mesenchymal stem cells into chondrocytes-like cells

Articular cartilage defects are common, causing significant morbidities. Tissue engineering using pluripotent stem cells is a new promising modality for cartilage repair. In the current study, we investigated the chondrogenesis of rabbit adipose-derived stem cells (ADSCs). We isolated rabbit ADSCs and transfected these cells with constructs encoding human insulin growth like factor 1 (IGF-1) and bone morphogenic protein 2 (BMP-2). We examined the growth and morphology of these transfected cells and their production of type II collagen and MMP-3. We found that IGF-1 and BMP-2 drove the chondrogenesis of ADSCs, which showed mature chondrocyte-like cells and formed cartilage nodules. These cells also produced type II collagen with a reduced production of MMP-3. Our findings suggested that human ADSCs could differentiate into chondrocyte-like cells driven by IGF-1 and BMP-2 and held promises as an abundant and ready source of stem cells for cartilage repair and regeneration.

Differential effects of bone morphogenetic protein-2 and transforming growth factor-beta1 on gene expression of collagen-modifying enzymes in human adipose tissue-derived mesenchymal stem cells

Adipose tissue-derived mesenchymal stem cells (AT-MSCs) in combination with bone morphogenetic protein-2 (BMP-2) or transforming growth factor-beta1 (TGF-beta1) are under evaluation for bone tissue engineering. Posttranslational modification of type I collagen is essential for functional bone tissue with adequate physical and mechanical properties. We investigated whether BMP-2 (10-100 ng/mL) and/or TGF-beta1 (1-10 ng/mL) affect gene expression of alpha2(I) procollagen and collagen-modifying enzymes, that is, lysyl oxidase and lysyl hydroxylases 1, 2, and 3 (encoded by PLOD1, 2, and 3), by human AT-MSCs. BMP-2, but not TGF-beta1, increased alkaline phosphatase activity after 28 days, indicating osteogenic differentiation of AT-MSCs. At day 4, both BMP-2 and TGF-beta1 upregulated alpha2(I) procollagen and PLOD1, which was downregulated at day 28. TGF-beta1, but not BMP-2, downregulated PLOD3 at day 28. Lysyl oxidase was upregulated by TGF-beta1 at day 4 and by BMP-2 at day 7. Neither BMP-2 nor TGF-beta1 affected PLOD2. In conclusion, these results suggest that AT-MSCs differentially respond to BMP-2 and TGF-beta1 with changes in gene expression of collagen-modifying enzymes. AT-MSCs may thus be able to appropriately modify type I collagen to form a functional bone extracellular matrix for tissue engineering, dependent on the growth factor added.

BMP-2 enhances TGF-beta3-mediated chondrogenic differentiation of human bone marrow multipotent mesenchymal stromal cells in alginate bead culture

This study addresses synergistic effects of bone morphogenetic protein-2 (BMP-2) and transforming growth factor-beta3 (TGF-beta3) in the induction of chondrocytic differentiation of bone marrow multipotent mesenchymal stromal cells (BM MSCs) in vitro for potential use in intervertebral disc (IVD) repair. Human BM MSCs encapsulated in alginate beads were induced to differentiate in serum-free medium containing BMP-2 and TGF-beta3. The expression of chondrocytic genes and proteins was analyzed by real-time PCR, western blot, histological, and immunohistochemical assays. This differentiation system showed a potent induction of chondrocytic phenotypes. The expression of chondrocytic markers, such as aggrecan (ACAN) and type II collagen (COL2A1), was upregulated at higher levels than using TGF-beta3 alone. Blocking BMP-2 by noggin completely suppressed BMP-2-enhanced gene and protein expression, confirming a crucial input of BMP-2 signaling in this differentiation process. Inhibition of extracellular signal-regulated kinases 1 and 2 signaling resulted in an increase in ACAN and COL2A1 gene expression, suggesting a negative regulatory role of this pathway. In conclusion, BMP-2 enhances TGF-beta3-mediated chondrogenesis of MSCs. The combination of BMP-2 and TGF-beta3 in alginate culture is superior to the standard differentiation method using TGF-beta alone. This potent induction system may provide an alternative cell source for IVD and cartilage regeneration in clinical practice.

Differential gene expression in the perichondrium and cartilage of the neonatal mouse temporomandibular joint

Our goal was to discover genes differentially expressed in the perichondrium (PC) of the mandibular condylar cartilage (MCC) that might enhance regenerative medicine or orthopaedic therapies directed at the tissues of the temporomandibular joint. We used targeted gene arrays (osteogenesis, stem cell) to identify genes preferentially expressed in the PC and the cartilaginous (C) portions of the MCC in 2-day-old mice. Genes with higher expression in the PC sample related to growth factor ligand-receptor interactions [FGF-13 (6.4x), FGF-18 (4x), NCAM (2x); PGDF receptors, transforming growth factor (TGF)-beta and IGF-1], the Notch isoforms (especially Notch 3 and 4) and their ligands or structural proteins/proteoglycans [collagen XIV (21x), collagen XVIII (4x), decorin (2.5x)]. Genes with higher expression in the C sample consisted mostly of known cartilage-specific genes [aggrecan (11x), procollagens X (33x), XI (14x), IX (4.5x), Sox 9 (4.4x) and Indian hedgehog (6.7x)]. However, the functional or structural roles of several genes that were expressed at higher levels in the PC sample are unclear [myogenic factor (Myf) 9 (9x), tooth-related genes such as tuftelin (2.5x) and dentin sialophosphoprotein (1.6x), VEGF-B (2x) and its receptors (3-4x) and sclerostin (1.7x)]. FGF, Notch and TGF-beta signalling may be important regulators of MCC proliferation and differentiation; the relatively high expression of genes such as Myf6 and VEGF-B and its receptors suggests a degree of unsuspected plasticity in PC cells.

Human adipose-derived stem cells: isolation, characterization and applications in surgery

The ideal stem cell for use in functional tissue engineering needs to be abundantly available, harvested with minimal morbidity, differentiated reliably down various pathways and able to be transplanted safely and efficaciously. Adult human adipose tissue contains a population of mesenchymal stem cells, termed 'adipose-derived stem cells' (ASC), which seem to fulfil most, if not all, of these criteria. ASC can be harvested readily, safely, and in relative abundance by modern liposuction techniques. They are capable of differentiating into other mesenchymal tissue types, including adipocytes, chondrocytes, myocytes and osteoblasts. They also show angiogenic properties, with recent evidence of a potential role in healing radiotherapy-damaged tissue, possibly due to their secretion of vascular endothelial growth factor. Similarly, they may have a role in healing chronic wounds, and as such are being investigated in phase 1 trials for their ability to aid healing of recurrent Crohn's fistulae. Subsequently they have a wide range of potential clinical uses in all fields of surgery. This article reviews the current and potential clinical applications of ASC in relation to surgery, as well as methods for their isolation, differentiation and molecular characterization.

Complications in the use of rhBMP-2 in PEEK cages for interbody spinal fusions

STUDY DESIGN

All patients of spinal interbody fusion using polyetheretherketone (PEEK) cages and recombinant human bone morphogenetic protein (rhBMP)-2 performed over a 16-month period were reviewed.

OBJECTIVE

To determine the suitability of PEEK cages when used in conjunction with rhBMP-2 in interbody spinal fusion.

SUMMARY OF BACKGROUND DATA

Bone morphogenetic proteins are increasingly being used in spinal fusion to promote osteogenesis. PEEK is a semicrystalline aromatic polymer that is used as a structural spacer to maintain the disc and foraminal height. Their use has led to increased and predictable rates of fusion. However, not many reports of the adverse effects of their use are available.

METHODS

Fifty-nine consecutive patients of interbody spinal fusion in the cervical or lumbar spine using a PEEK cage and rhBMP-2 were followed for an average of 26 months after surgery. A clinical examination and a record of Oswestry Disability Index, Visual Analog Scale for pain, and a pain diagram were performed preoperatively and at every follow-up visit. All patients had plain radiographs carried out to assess fusion. Ten patients of lumbar spine fusion were additionally evaluated with a computed tomography scan.

RESULTS

All cases demonstrated an appreciable amount of new bone formation by 6 to 9 months in the cervical spine and by 9 to 12 months in the lumbar spine. End plate resorption was visible radiologically in all cervical spine fusions and majority of lumbar fusions. Cage migration was observed to occur maximally in patients with transforaminal lumbar interbody fusion and posterior lumbar interbody fusion. Disc space subsidence was seen in both cervical and lumbar arthrodesis with the latter showing a lesser incidence, but with a greater degree of collapse.

CONCLUSIONS

PEEK cages and rhBMP-2 when used in spinal fusion give consistently good fusion rates. However, the early role of BMP in the resorptive phase may cause loosening, cage migration, and subsidence.

Adipose-derived stem cells: characterization and current application in orthopaedic tissue repair

Orthopaedic tissues, such as bone, cartilage, intervertebral disc and tendon, contain cells that are difficult to culture and stimulate in vitro for repair of damaged tissue. Stem cells have the ability to self-renew and differentiate into many tissue types. Recent progress in stem cell research has led to an enthusiastic effort to utilize stem cells for orthopaedic tissue regeneration. Due to ease of harvest and abundance, adipose-derived mesenchymal cells (ASC) are an attractive, readily available adult stem cell that has become increasingly popular for use in many stem cell applications. Recent progress has been made in characterizing ASC and looking mechanistically at gene expression and cellular pathways involved in differentiation. This review focuses on (i) the characterization of ASC through expression of appropriate surface markers; (ii) modulation of in vitro differentiation of ASC through different scaffolds, growth factors, and media; and (iii) the use of ASC in orthopaedic tissue repair. Strategies for repair involve the use of differentiated or undifferentiated, fresh or passaged ASC, in conjunction with appropriate choice of media, growth factors and scaffolds. Recent in vivo studies utilizing ASC are discussed giving results on defect repair and potential for clinical orthopaedic tissue regeneration.

Multipotent mesenchymal stromal cells in articular diseases

Although cartilage defects are common features of osteoarthritis and rheumatoid arthritis, current treatments can rarely restore the full function of native cartilage. Recent studies have provided new perspectives for cartilage engineering using multipotent mesenchymal stromal cells (MSC). Moreover, MSC have been used as immunosuppressant agents in autoimmune diseases and have tested successfully in animal models of arthritis. However, the sequential events occurring during chondrogenesis must be fully understood before we can reproduce the complex molecular events that lead to MSC differentiation and long-term maintenance of cartilage characteristics in the context of chronic joint inflammation. This chapter focuses on the potential of MSC to repair cartilage, with an emphasis on the factors that are known to be required in inducing chondrogenesis and on their immunosuppressive potential.

Human osteogenic protein-1 induces osteogenic differentiation of adipose-derived stem cells harvested from mice

OBJECTIVE

Osteogenic protein-1 (OP-1) has been shown to stimulate undifferentiated cells to produce mineralized tissue. Adipose tissue is a rich source of undifferentiated cells for tissue engineering purposes. The purpose of this study was to investigate the effect of OP-1 on osteogenic differentiation of adipose-derived stem cells and the production of bony tissue in vitro.

DESIGN

Adipose-derived stem cells (ADSCs) were isolated from inguinal fat pads of adult mice. Following cell expansion the cells were plated in 8-well chambered slides. The cells received one of four treatments: Group 1 cells were maintained in control medium, Group 2 cells were cultured in a common osteogenic medium, Group 3 cells were cultured in osteogenic medium supplemented with 250ng/mL of OP-1, and Group 4 cells were cultured with 250ng/mL of OP-1 added to control medium. Osteogenic differentiation of ADSCs was determined by estimating the number and size of mineralized nodules, and the amount of extracellular osteopontin secreted into cell culture medium. Mineralized nodule production was assessed at day 21 with von Kossa staining. Extracellular osteopontin release was measured after 8 and 21 days by enzyme-linked immunosorbant assay (ELISA). ANOVA/Tukey tests were used to identify differences among the four treatment groups for mineralized nodule production and osteopontin release (p<or=0.05).

RESULTS

Deposition of calcified nodules and osteopontin secretion was significantly greater for cell cultures incubated with OP-1 (p<or=0.05). At day 21, no significant differences in osteopontin secretion were noted among groups incubated with osteogenic nutrients and/or OP-1 (p>0.05), which were significantly higher than the group incubated in cell growth medium only (p<or=0.05). No significant differences in osteopontin secretion were noted between 8 and 21 days for any group (p>0.05). Linear regression analysis demonstrated a linear relationship was present between the presence of calcified nodules and the amount of osteopontin released (p<or=0.05).

CONCLUSIONS

OP-1 is a powerful inducer of osteogenic differentiation of adult adipose-derived stem cells.

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.

Bone regeneration by BMP-2 enhanced adipose stem cells loading on alginate gel

Adipose stem cells (ASCs) have the potential to differentiate into a variety of cell lineages both in vitro and in vivo. In this study, ASCs were harvested from normal Sprague-Dawley (SD) rats and transfected by BMP-2 gene before they were loaded on alginate. The ability of bone regeneration was determined in rat critical-size cranial defects. An 8-mm diameter defect was created in the calvarias of 36 rats; these rats were divided into three groups. In experimental group, the defects were filled with alginate gel combined with BMP-2 transfected ASCs; in negative control group, the defects were filled with alginate gel mixed with normal ASCs; in blank controls, the defects were filled with cell-free alginate gel. Four rats of each group were killed and the cranial defect sites were observed at 4, 8 and 16 weeks after surgery. There was complete repair of cranial defects in experimental group using the alginate gel loading BMP-2 transfected ASC, but only partial repair in negative controls and in the blank control. The engineering approach combining BMP-2 enhanced ASCs with alginate gel can therefore stimulate bone regeneration and repair for the large size bone defects.

The polymine spermine regulates osteogenic differentiation in adipose stem cells

For bone tissue engineering, it is important that mesenchymal stem cells (MSCs) differentiate into osteoblasts. To develop a method for differentiation of adipose tissue-derived mesenchymal stem cells (AT-MSCs) along the osteogenic lineage, we studied the effect of polyamines, which are organic cations implicated in bone growth and development, on differentiation of AT-MSCs. Treatment of goat-derived AT-MSCs with 1,25-dihydroxyvitamin-D3 (1,25(OH)₂D₃), which stimulates osteogenic differentiation, for 7 days induced gene expression of the polyamine-modulated transcription factor-1 (PMF-1) and spermidine/spermine N (1)-acetyltransferase (SSAT), which are both involved in polyamine metabolism, suggesting that polyamines are involved in osteogenic differentiation of AT-MSCs. Furthermore, treatment of AT-MSCs with the polyamine spermine-regulated gene expression of runx-2, a transcription factor involved in early stages of osteogenic differentiation, and that of osteopontin, a bone matrix protein expressed in later stages of osteogenic differentiation. Runx-2 gene expression was increased 4 and 14 days after a short 30 min. treatment with spermine, while osteopontin gene expression was only increased 4 days after spermine treatment. Finally, alkaline phosphatase activity, which is intimately involved in the formation of extracellular matrix of bone, was increased 4 weeks after the 30 min.-spermine treatment of AT-MSCs. In conclusion, this study shows for the first time that the polyamine spermine regulates differentiation of AT-MSCs along the osteogenic lineage, which can be used as a new method for differentiation of AT-MSCs along the osteogenic lineage. Therefore, polyamines may constitute a promising tool for bone tissue engineering approaches using AT-MSCs, such as a one-step surgical procedure for spinal interbody fusion.

Prostaglandins differentially affect osteogenic differentiation of human adipose tissue-derived mesenchymal stem cells

Adipose tissue-derived mesenchymal stem cells (AT-MSCs) are currently used for bone tissue engineering. AT-MSCs undergoing osteogenic differentiation respond to mechanical loading with increased cyclooxygenase-2 gene expression, a key enzyme in prostaglandin (PG) synthesis. PGs are potent multifunctional regulators in bone, exhibiting stimulatory and inhibitory effects on bone formation and resorption. PGE(2), but not PGI(2) or PGF(2), recruits osteoprogenitors from the bone marrow space and influences their differentiation. We hypothesize that PGE(2), PGI(2), and PGF(2) may differentially regulate osteogenic differentiation of human AT-MSCs. PGE(2), PGI(2), and PGF(2) (0.01-10 microM) affected osteogenic differentiation, but not proliferation of AT-MSCs after 4-14 days. Only PGF(2) (0.01-10 microM) increased alkaline phosphatase (ALP) activity at day 4. PGE(2) (10 microM), PGI(2) (0.01-10 microM), and PGF(2) (10 microM) decreased ALP activity, whereas PGF(2) (0.1 microM) increased ALP activity at day 14. PGF(2) (0.01-0.1 microM) and PGI(2) (0.01 microM) upregulated osteopontin gene expression, and PGF(2) (0.01 microM) upregulated alpha1(I)procollagen gene expression at day 4. PGE(2) and PGF(2) (10 microM) at day 4 and PGF(2) (1 microM) at day 14 downregulated runt-related transcription factor-2 gene expression. We conclude that PGE(2), PGI(2), and PGF(2) differentially affect osteogenic differentiation of AT-MSCs, with PGF(2) being the most potent. Thus, locally produced PGF(2) might be most beneficial in promoting osteogenic differentiation of AT-MSCs, resulting in enhanced bone formation for bone tissue engineering.

Osteogenic protein-1 with transforming growth factor-beta1: potent inducer of chondrogenesis of synovial mesenchymal stem cells in vitro

BACKGROUND

Recently, cells derived from synovial mesenchymal stem cells (MSCs) have been regarded as a potential source of cells to induce repair of articular cartilage. To investigate more effective methods for promoting chondrogenesis, we examined the effects of osteogenic protein (OP)-1 with or without transforming growth factor-beta (TGFbeta1) on chondrogenesis of human MSCs in vitro.

METHODS

MSCs were isolated from the synovial membrane of patients with rheumatoid arthritis undergoing knee replacement surgery. After expansion of the cells, pellet cultures were performed in chondrogenic medium with OP-1 100-200 ng/ml, TGFbeta1 10 ng/ml, or both agents for 3 or 6 weeks. Chondrogenesis was evaluated histologically with safranin O staining, reverse transcription polymerase chain reaction for aggrecan and type II collagen mRNA, and quantification of glycosaminoglycan (GAG) content using a dimethylmethylene blue dye-binding assay. GAG content was normalized by DNA content measured using Hoechst 33258 dye.

RESULTS

At 3 weeks of culture, mRNAs for type II collagen and aggrecan were expressed by MSCs treated with either TGFbeta1 or OP-1; however, substantial matrix production was not induced. At 6 weeks, OP-1 increased GAG accumulation dose-dependently in the presence or absence of TGFbeta1, and the GAG content was the highest after combined treatment with 200 ng OP-1 and TGFbeta1. Histological staining for safranin O was poor after treatment with OP-1 or TGFbeta1 alone and slightly increased after combined treatment with TGFbeta1 and OP-1 at 3 weeks. At 6 weeks, OP-1 increased the intensity of staining dose-dependently in the presence or absence of TGFbeta1. However, the histological appearance of the cells treated with OP-1 alone was similar to that of hypertrophic chondrocytes, which was different from that of cells with combined treatment with OP-1 and TGFbeta1.

CONCLUSIONS

A high dose of OP-1 was useful for enhancing chondrogenesis from synovium-derived MSCs in combined treatment with TGFbeta1.

Concise review: mesenchymal stem cells: their phenotype, differentiation capacity, immunological features, and potential for homing

MSCs are nonhematopoietic stromal cells that are capable of differentiating into, and contribute to the regeneration of, mesenchymal tissues such as bone, cartilage, muscle, ligament, tendon, and adipose. MSCs are rare in bone marrow, representing approximately 1 in 10,000 nucleated cells. Although not immortal, they have the ability to expand manyfold in culture while retaining their growth and multilineage potential. MSCs are identified by the expression of many molecules including CD105 (SH2) and CD73 (SH3/4) and are negative for the hematopoietic markers CD34, CD45, and CD14. The properties of MSCs make these cells potentially ideal candidates for tissue engineering. It has been shown that MSCs, when transplanted systemically, are able to migrate to sites of injury in animals, suggesting that MSCs possess migratory capacity. However, the mechanisms underlying the migration of these cells remain unclear. Chemokine receptors and their ligands and adhesion molecules play an important role in tissue-specific homing of leukocytes and have also been implicated in trafficking of hematopoietic precursors into and through tissue. Several studies have reported the functional expression of various chemokine receptors and adhesion molecules on human MSCs. Harnessing the migratory potential of MSCs by modulating their chemokine-chemokine receptor interactions may be a powerful way to increase their ability to correct inherited disorders of mesenchymal tissues or facilitate tissue repair in vivo. The current review describes what is known about MSCs and their capacity to home to tissues together with the associated molecular mechanisms involving chemokine receptors and adhesion molecules.

Stem cells from adipose tissue allow challenging new concepts for regenerative medicine

The perspective of an innovative new concept integrating tissue-engineering techniques with an established surgical technique is described. The focus is primarily on a one-step surgical procedure using adipose tissue-derived mesenchymal stem cells, a calcium phosphate scaffold as a carrier, and a bioresorbable polymer cage to facilitate spinal interbody fusion. We address the harvesting and processing of clinically relevant quantities of adipose tissue-derived mesenchymal stem cells, triggering of these stem cells toward lineage-specific differentiation, seeding of the triggered stem cells on a bioresorbable scaffold, and implantation of the resulting tissue-engineered construct. The integrated steps can be accomplished within one surgical procedure in a surgical theater. Although the proposed concept has been developed for spinal fusion, potential application in other surgical disciplines is presumed realistic.

Concise review: adipose tissue-derived stromal cells--basic and clinical implications for novel cell-based therapies

Compared with bone marrow-derived mesenchymal stem cells, adipose tissue-derived stromal cells (ADSC) do have an equal potential to differentiate into cells and tissues of mesodermal origin, such as adipocytes, cartilage, bone, and skeletal muscle. However, the easy and repeatable access to subcutaneous adipose tissue and the simple isolation procedures provide a clear advantage. Since extensive reviews focusing exclusively on ADSC are rare, it is the aim of this review to describe the preparation and isolation procedures for ADSC, to summarize the molecular characterization of ADSC, to describe the differentiation capacity of ADSC, and to discuss the mechanisms and future role of ADSC in cell therapy and tissue engineering. An initial effort has also been made to differentiate ADSC into hepatocytes, endocrine pancreatic cells, neurons, cardiomyocytes, hepatocytes, and endothelial/vascular cells. Whereas the lineage-specific differentiation into cells of mesodermal origin is well understood on a molecular basis, the molecular key events and transcription factors that initially allocate the ADSC to a lineage-specific differentiation are almost completely unknown. Decoding these molecular mechanisms is a prerequisite for developing novel cell therapies.

Osteo-maturation of adipose-derived stem cells required the combined action of vitamin D3, beta-glycerophosphate, and ascorbic acid

This study investigated the effects of various components [vitamin D3 (VD3), beta-glycerophosphate (BGP), and ascorbic acid (AA)] on the potential of human adipose-derived progenitor cells (ADPCs) to transdifferentiate into osteoblast-like cells. ADPCs were induced under four different supplement groups: (1) VD3+BGP+AA, (2) VD3 alone, (3) BGP+AA, and (4) no VD3, BGP or AA. Mineralization studies and presence of bone matrix-related proteins by immunostaining showed that the Group 1 ADPCs showed their ability to undergo osteoblastic differentiation. Further evaluation was made by estimation of levels of RUNX-2 and TAZ genes. Group 1 ADPCs showed the consistent expression of RUNX-2 and TAZ levels over the study period of 28days. The study showed good correlation among various parameters evaluated to conclude that ADPCs could be an alternative source for generating osteoblast-like cells.

Phenotypical and functional characterization of freshly isolated adipose tissue-derived stem cells

Adipose tissue contains a stromal vascular fraction (SVF) that is a rich source of adipose tissue-derived stem cells (ASCs). ASCs are multipotent and in vitro-expanded ASCs have the capacity to differentiate, into amongst others, adipocytes, chondrocytes, osteoblasts, and myocytes. For tissue engineering purposes, however, it would be advantageous to use the whole SVF, which can be transplanted without further in vitro selection or expansion steps. Because little is known about the freshly isolated ASCs in the SVF, we phenotypically characterized human freshly isolated ASCs, using flow cytometry. In addition, we investigated whether freshly isolated ASCs have functional properties comparable to cultured ASCs. For this, the differentiation potential of both freshly isolated ASCs and cultured ASCs into the osteogenic pathway was analyzed. Freshly isolated ASCs slightly differed in immunophenotype from cultured ASCs. Contrary to cultured ASCs, freshly isolated ASCs were shown to be highly positive for CD34, and positive for CD117 and HLA-DR. On the other hand, expression of CD105 and especially CD166 on the freshly isolated ASCs was relatively low. After osteogenic stimulation of freshly isolated ASCs, both Runx-2 and CollaI gene expression were significantly increased (p < 0.05). However, there was a difference in the kinetics of gene expression between freshly isolated and cultured ASCs and also between the different SVF isolates tested. There was no difference in alkaline phosphatase activity between freshly isolated ASCs and cultured ASCs. In addition, freshly isolated ASCs stained positive for osteonectin and showed matrix mineralization. We conclude that although there are minor differences in phenotype and kinetics of differentiation between freshly isolated ASCs and cultured ASCs, the use of freshly isolated ASCs for tissue engineering purposes involving bone repair is potentially applicable.

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

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

A novel regulatory role for stromal-derived factor-1 signaling in bone morphogenic protein-2 osteogenic differentiation of mesenchymal C2C12 cells

Stromal-derived factor 1 (SDF-1) is a chemokine with important functions in development and postnatal tissue homeostasis. SDF-1 signaling via the G-protein-coupled receptor CXCR4 regulates the recruitment of stem and precursor cells to support tissue-specific repair or regeneration. In this study we examined the contribution of SDF-1 signaling to osteogenic differentiation of mesenchymal C2C12 cells induced by bone morphogenic protein 2 (BMP2). Blocking SDF-1 signaling before BMP2 stimulation by treatment with siRNA, antibodies against SDF-1 or CXCR4, or the G-protein-coupled receptor inhibitor pertussis toxin strongly suppressed BMP2 induction of osteogenic differentiation in C2C12 cells, as evidenced by an early decrease in the expression of the myogenesis inhibitor Id1, the osteogenic master regulators Runx2 and Osx, the osteoblast-associated transcription factors JunB, Plzf, Msx2, and Dlx5, and later of the bone marker proteins osteocalcin and alkaline phosphatase. Similarly, blocking SDF-1/CXCR4 signaling strongly inhibited BMP2-induced osteogenic differentiation of ST2 bone marrow stromal cells. Moreover, we found that the interaction between SDF-1 and BMP2 signaling was mediated via intracellular Smads and MAPK activation. Our data provide the first evidence for a co-requirement of the SDF-1/CXCR4 signaling axis in BMP2-induced osteogenic differentiation of C2C12 and ST2 cells and, thus, uncover a new potential target for modulation of osteogenesis.

Regulation of adipose-derived adult stem cells differentiating into chondrocytes with the use of rhBMP-2

BACKGROUND

Adipose tissue has been demonstrated to contain a population of progenitor cells that can differentiate into bone and cartilage. Studies have suggested that adipose-derived adult stem (ADAS) cells can be induced to differentiate into chondrocytes by transforming growth factor-beta (TGF-beta). In this study, we examined whether bone morphogenetic protein-2 (BMP-2), as a member of the TGF-beta superfamily, could regulate ADAS cells to differentiate into a chondrolineage.

METHODS

ADAS cells were isolated and induced by rhBMP-2. These cells were cultured in pellets for 2 weeks, and the chondrogenic phenotype was observed in vitro and in vivo. ADAS cells cultured without BMP-2 were used as controls.

RESULTS

After 2 weeks of culture, the differentiated ADAS cells reacted positively to Alcian blue and collagen II, and the content of collagen II protein was obviously up-regulated at day 14. Glycosaminoglycan (GAG) content gradually increased from day 2 to day 14 (P < 0.05). However, H&E staining and collagen II expression were weak, and there was a little collagen II protein and GAG detected in the control group. Additionally, the pellets of ADAS cells induced by rhBMP-2 were transplanted into BALB/C nude mice and formed cartilage lacuna at week 8 in vivo.

DISCUSSION

These data demonstrate that rhBMP-2 induce ADAS cells to differentiate into chondrocytes in vitro and in vivo. This is useful for basic and clinical studies aimed at repairing cartilage damage. But in a control group, ADAS cells tended towards differentiation into chondrocytes, which was affected by ITS. We will be exploring the mechanism further.