Chondrogenic differentiation of cultured human mesenchymal stem cells from marrow

Effects of hydrostatic pressure and transforming growth factor-beta 3 on adult human mesenchymal stem cell chondrogenesis in vitro

This study examined the effects of intermittent hydrostatic pressure (IHP) and transforming growth factor-beta 3 on chondrogenesis of adult human mesenchymal stem cells (hMSCs) in vitro. Chondrogenic gene expression was determined by quantifying mRNA signal levels for SOX9, a transcription factor critical for cartilage development and the cartilage matrix proteins, aggrecan and type II collagen. Extracellular matrix production was determined by weight and histology. IHP was applied to hMSCs in pellet culture at a level of 10 MPa and a frequency of 1 Hz for 4 h per day for periods of 3, 7, and 14 days. hMSCs responded to addition of TGF-beta 3 (10 ng/mL) with a greater than 10-fold increase (p < 0.01) in mRNA levels for each, SOX9, type II collagen, and aggrecan during a 14-day culture period. Applying IHP in the presence of TGF-beta 3 further increased the mRNA levels for these proteins by 1.9-, 3.3-, and 1.6-fold, respectively, by day 14. Chondrogenic mRNA levels were increased with just exposure to IHP. Extracellular matrix deposition of type II collagen and aggrecan increased in the pellets as a function of treatment conditions and time of culture. This study demonstrated adjunctive effects of IHP on TGF-beta 3-induced chondrogenesis and suggests that mechanical loading can facilitate articular cartilage tissue engineering.

A rapid seeding technique for the assembly of large cell/scaffold composite constructs

These studies address critical technical issues involved in creating human mesenchymal stem cell (hMSC)/ scaffold implants for cartilage repair. These issues include obtaining a high cell density and uniform spatial cell distribution within the scaffold, factors that are critical in the initiation and homogeneity of chondrogenic differentiation. For any given scaffold, the initial seeding influences cell density, retention, and spatial distribution within the scaffold, which eventually will affect the function of the construct. Here, we discuss the development of a vacuum-aided seeding technique for HYAFF -11 sponges which we compared to passive infiltration. Our results show that, under the conditions tested, hMSCs were quantitatively and homogeneously loaded into the scaffolds with 90+% retention rates after 24 h in perfusion culture with no negative effect on cell viability or chondrogenic potential. The retention rates of the vacuum-seeded constructs were at least 2 times greater than those of passively seeded constructs at 72 h. Histomorphometric analysis revealed that the core of the vacuum-seeded constructs contained 240% more cells than the core of passively infiltrated scaffolds. The vacuum seeding technique is safe, rapid, reproducible, and results in controlled quantitative cell loading, high retention, and uniform distribution.

TWEAK is a novel arthritogenic mediator

TNF-like weak inducer of apoptosis (TWEAK) is a TNF family member with pleiotropic effects on a variety of cell types, one of which is the induction of proinflammatory cytokines by synovial fibroblasts derived from rheumatoid arthritis (RA) patients. In this study, we report that the serum TWEAK level was dramatically elevated during mouse collagen-induced arthritis (CIA) and blocking TWEAK by a neutralizing mAb significantly reduced the clinical severity of CIA. Histological analyses also revealed that TWEAK inhibition diminished joint inflammation, synovial angiogenesis, as well as cartilage and bone erosion. Anti-TWEAK treatment proved efficacious when administered just before the disease onset but not during the priming phase of CIA. Consistent with this, TWEAK inhibition did not affect either cellular or humoral responses to collagen. In contrast, TWEAK inhibition significantly reduced serum levels of a panel of arthritogenic mediators, including chemokines such as MIP-1beta (CCL-4), lymphotactin (XCL-1), IFN-gamma-inducible protein 10 (IP-10) (CXCL-10), MCP-1 (CCL-2), and RANTES (CCL-5), as well as the matrix metalloprotease-9. Exploring the possible role of the TWEAK/Fn14 pathway in human RA pathogenesis, we showed that TWEAK can target human primary chondrocytes and osteoblast-like cells, in addition to synovial fibroblasts. We further demonstrated that TWEAK induced the production of matrix metalloproteases in human chondrocytes and potently inhibited chondrogenesis and osteogenesis using in vitro models. These results provide evidence for a novel cytokine pathway that contributes to joint tissue inflammation, angiogenesis, and damage, as well as may inhibit endogenous repair, suggesting that TWEAK may be a new therapeutic target for human RA.

Focal adhesion kinase signaling pathways regulate the osteogenic differentiation of human mesenchymal stem cells

The intracellular signaling events controlling human mesenchymal stem cells (hMSC) differentiation into osteoblasts are not entirely understood. We recently demonstrated that contact with extracellular matrix (ECM) proteins is sufficient to induce osteogenic differentiation of hMSC through an ERK-dependent pathway. We hypothesized that FAK signaling pathways provide a link between activation of ERK1/2 by ECM, and stimulate subsequent phosphorylation of the Runx2/Cbfa-1 transcription factor that controls osteogenic gene expression. We plated hMSC on purified collagen I (COLL-I) and vitronectin (VN) in the presence or absence of FAK-specific siRNA, and assayed for phosphorylation of Runx2/Cbfa-1 as well as expression of established osteogenic differentiation markers (bone sialoprotein-2, osteocalcin, alkaline phosphatase, calcium deposition, and spectroscopically determined mineral:matrix ratio). We found that siRNA treatment reduced FAK mRNA levels by >40% and decreased ECM-mediated phosphorylation of FAK Y397 and ERK1/2. Serine phosphorylation of Runx2/Cbfa-1 was significantly reduced after 8 days in treated cells. Finally, FAK inhibition blocked osterix transcriptional activity and the osteogenic differentiation of hMSC, as assessed by lowered expression of osteogenic genes (RT-PCR), decreased alkaline phosphatase activity, greatly reduced calcium deposition, and a lower mineral:matrix ratio after 28 days in culture. These results suggest that FAK signaling plays an important role in regulating ECM-induced osteogenic differentiation of hMSC.

Gene expression in human keloids is altered from dermal to chondrocytic and osteogenic lineage

Keloids are a dermal fibrotic disease whose etiology remains totally unknown and for which there is no successful treatment. Here, we employed cDNA microarray analysis to examine gene expression in keloid lesions and control skin. We found that 32 genes among the 9000 tested were strongly up-regulated in keloid lesions, of which 21 were confirmed by Northern blotting. These included at least seven chondrocyte/osteoblast marker genes, and RT-PCR analysis revealed that transcription factors specific for these genes, SOX9 and CBFA1, were induced. Immunostaining and in situ hybridization further supported that these markers are expressed in keloid lesions. Intriguingly, scleraxis, a transcription factor known as a marker of tendons and ligaments, was also induced in keloid fibroblasts. We propose that reprogramming of gene expression or disordered differentiation from a dermal pattern to that of a chondrocytic/osteogenic lineage, probably closer to that of tendon/ligament lineage, may be involved in the etiology of keloids.

Diagnosis and minimally invasive treatment of lumbar discogenic pain--a review of the literature

Diagnosis and treatment of lumbar discogenic pain due to internal disc disruption (IDD) remains a challenge. It accounts for 39% of patients with low back pain. The mechanism of discogenic pain remains unclear and its clinical presentation is atypical. Magnetic resonance imaging (MRI) can find high-intensity zone as an indirect indication of IDD. However, relative low sensitivity (26.7% to 59%) and high false-positive (24%) and false-negative (38%) rates reduce the value of MRI in screening for the existence of painful IDD. Provocative discography can provide unique information about the pain source and the morphology of the disc. It may also provide information for selecting appropriate treatment for the painful annular tear. Adjunctive therapies, including nonsteroidal anti-inflammatory drugs, physical therapy, rehabilitation, antidepressants, antiepileptics, and acupuncture, have been used for low back pain. The value of these treatments for discogenic pain is yet to be established. Intradiscal steroid injection has not been proved to provide long-term benefits. Intradiscal electrothermal therapy may offer some pain relief for a group of well-selected patients. No benefits have been found for the intradiscal radiofrequency thermocoagulation. A block in the ramus communicans may interfere with the transition of painful information from the discs to the central nervous system. Disc cell transplantation is in the experimental stage. It has the potential to become a useful tool for the prevention and treatment of discogenic pain. Minimally invasive treatments provide alternatives for discogenic pain with the appeal of cost-effectiveness and, possibly, less long-term side effects. However, the value of most of these therapies is yet to be established. More basic science and clinical studies are needed to improve the clinical efficacy of minimally invasive treatments.

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.

Interaction of human mesenchymal stem cells with disc cells: changes in extracellular matrix biosynthesis

STUDY DESIGN

To evaluate the in vitro interactions between human mesenchymal stem cells (MSCs) and degenerative disc cells.

OBJECTIVES

To demonstrate the potential of MSCs in regulating the extracellular matrix synthesis of degenerative disc cells.

SUMMARY OF BACKGROUND DATA

Culture of degenerative disc cells followed by their reinsertion into a disc can retard the degeneration process in an animal model. However, harvesting cells without accelerating degeneration is problematic. Autologous MSCs can be safely harvested from the bone marrow and transplanted into degenerative discs.

METHODS

Human degenerative nucleus pulposus (NP), anulus fibrosus (AF) cells, and MSCs were cultured as pellets, and coculture pellets were formed by addition of MSCs to disc cells (50:50 ratio). Glycosaminoglycan (GAG) and DNA content were measured. Proteoglycan synthesis was analyzed by RT-PCR and western blot. Type II collagen expression was assessed by immunohistochemistry.

RESULTS

Coculture pellets formed by the addition of MSCs to AF cells were superior in size to all other pellets. AF/MSC pellets showed higher experimental GAG content than the predicted values represented by the sum of individual control pellets, with 10.2 versus 5.6 microg/pellet at week 3, respectively. The effect was not observed in the NP/MSC coculture, or when chondrogenic medium was used. Close contact between cells was necessary to obtain this enhancement of GAG content. Proteoglycan and collagen expression in both individual and coculture pellets was confirmed by PCR analysis and western blot.

CONCLUSION

Addition of MSCs to AF cells resulted in an up-regulation of the proteoglycans synthesis. This study provides the rationale for further investigation of the potential of MSC therapy in treating intervertebral disc degeneration.

Stem cell-derived chondrocytes for regenerative medicine

The regenerative capacity of cartilage is limited. Transplantation methods used to treat cartilage lesions are based mainly on primary cultures of chondrocytes, which dedifferentiate during cultivation in vitro and lose their functional properties. Stem cells are considered as an alternative source to generate cells for two reasons: first, they can almost indefinitely divide in culture, and second, they are able to differentiate into various mature cell types. Herein, we asked the question whether chondrocytes could be differentiated from mouse embryonic stem (ES) cells to a state suitable for regenerative use. When cultivated as embryoid bodies (EBs), murine ES cells differentiate into mesenchymal progenitor cells, which progressively develop into mature, hypertrophic chondrocytes and transdifferentiate into calcifying cells recapitulating all of the cellular processes of chondrogenesis. Chondrocytes isolated from EBs exhibit a high regenerative capacity. They dedifferentiate initially in culture, but later reexpress stable characteristics of mature chondrocytes. However, in cultures of chondrocytes isolated from EBs, additional mesenchymal cell types can be observed. Mesenchymal stem (MS) cells from bone marrow have already been used in tissue engineering settings. We compared the chondrogenic differentiation of MS and ES cells.

Comparison of standard surface chemistries for culturing mesenchymal stem cells prior to neural differentiation

A critical element of any stem cell differentiation protocol is the ability to compare its effects relative to an undifferentiated population of the same cells. In an attempt to standardize pre-differentiation conditions of adult derived mesenchymal stem cells prior to neural induction experiments, we asked what is the simplest chemical surface that supports the growth and maintenance of these cells in a pre-differentiation state. Adult bone marrow-derived rat mesenchymal stem cells (BMSCs) were expanded in vitro on Permanox Lab-Tek tissue culture treated plastic (TCP), poly-D-lysine (PDL) coated glass, PDL-laminin-1 coated glass, and untreated glass. TCP provided the best surface for maintaining morphologies generally considered to be undifferentiated, while PDL coated glass and uncoated glass provided the least suitable surfaces. Expansion of BMSCs on PDL-laminin-1 coated glass resulted in expression of nestin, a marker associated with neuronal and other progenitor cells, and therefore may confound experimental results if used as a pre-differentiation surface.

Dose- and Time-Dependent Effects of Cyclic Hydrostatic Pressure on Transforming Growth Factor-β3-Induced Chondrogenesis by Adult Human Mesenchymal Stem Cellsin Vitro

This study examined effects of varying magnitudes of intermittent hydrostatic pressure (IHP) applied for different times on chondrogenesis of adult human mesenchymal stem cells (hMSCs) in vitro. hMSCs were exposed to 0.1, 1, and 10 MPa of IHP at a frequency of 1 Hz for 4 h/day for 3, 7, and 14 days in the presence of transforming growth factor (TGF-beta3). Chondrogenesis was characterized by gene expression, macromolecule production, and extracellular matrix deposition. Exposure of hMSCs to 0.1 MPa of IHP increased SOX9 and aggrecan mRNA expression by 2.2- and 5.6-fold, respectively, whereas type II collagen mRNA expression responded maximally at 10 MPa. Production of sulfated glycosaminoglycan responded to IHP of 1 MPa and 10 MPa, whereas collagen levels increased only at 10 MPa. Morphologically, matrix condensation occurred with increased IHP, concomitant with collagen expression. This study demonstrated that different levels of IHP differentially modulate hMSC chondrogenesis in the presence of TGF-beta3. The data suggest that tissue engineering of articular cartilage through application or recruitment of hMSCs can be facilitated by mechanical stimulation.

Calcitonin directly attenuates collagen type II degradation by inhibition of matrix metalloproteinase expression and activity in articular chondrocytes

OBJECTIVE

Calcitonin was recently reported to counter progression of cartilage degradation in an experimental model of osteoarthritis, and the effects were primarily suggested to be mediated by inhibition of subchondral bone resorption. We investigated direct effects of calcitonin on chondrocytes by assessing expression of the receptor and pharmacological effects on collagen type II degradation under ex vivo and in vivo conditions.

METHODS

Localization of the calcitonin receptor on articular chondrocytes was investigated by immunohistochemistry, and the expression by reverse transcriptase polymerase chain reaction (RT-PCR). In bovine articular cartilage explants, cartilage degradation was investigated by release of C-terminal telopeptides of collagen type II (CTX-II), induced by tumor necrosis factor-alpha (TNF-alpha) [20 ng/ml] and oncostatin M (OSM) [10 ng/ml], with salmon calcitonin [0.0001-1 microM]. In vivo, cartilage degradation was investigated in ovariectomized (OVX) rats administered with oral calcitonin [2 mg/kg calcitonin] for 9 weeks.

RESULTS

The calcitonin receptor was identified in articular chondrocytes by immunohistochemistry and RT-PCR. Calcitonin concentration-dependently increased cAMP levels in isolated chondrocytes. Explants cultured with TNF-alpha and OSM showed a 100-fold increase in CTX-II release compared to vehicle-treated controls (P<0.001). The degradation of type II collagen in these explants was concentration-dependently inhibited by calcitonin, 65% protection at 10 nM calcitonin (P<0.01). TNF-alpha and OSM induced a pronounced increase in matrix metalloproteinase (MMP) activity, which was strongly inhibited by calcitonin. In vivo, administration of salmon calcitonin to OVX rats resulted in significant (P<0.001) decrease in CTX-II levels.

CONCLUSION

These results are the first evidence of calcitonin receptor expression on articular chondrocytes and that the chondroprotective effects of calcitonin might involve the inhibition of MMP expression.

Limitations of using aggrecan and type X collagen as markers of chondrogenesis in mesenchymal stem cell differentiation

The study was initially designed to differentiate human bone marrow-derived mesenchymal stem cells (MSC) into chondrocyte-like cells, for use in tissue engineering. We cultured MSCs in defined chondrogenic medium as pellet cultures supplemented with transforming growth factor (TGF)-beta1 or -beta3 and dexamethazone, as they are commonly used to promote in vitro chondrogenesis. Markers of chondrogenesis used were type II collagen and aggrecan, with type X collagen being used as a marker of late-stage chondrocyte hypertrophy (associated with endochondral ossification). Our results show that aggrecan is constitutively expressed by MSCs and that type X collagen is expressed as an early event. Furthermore, we found that type X collagen was expressed before type II collagen in some cases. This is surprising because it is understood that stem cells have to be differentiated into chondrocytes before they can become hypertrophic. Thus, caution must be exercised when using aggrecan and type X collagen as markers for chondrogenesis and chondrocyte hypertrophy, respectively, in association with stem cell differentiation from this source.

Fetal cartilage engineering from amniotic mesenchymal progenitor cells

We determined whether cartilage could be engineered from mesenchymal progenitor cells (MPCs) normally found in amniotic fluid. Mesenchymal amniocytes were isolated from ovine amniotic fluid samples (n = 5) and had their identity confirmed by immunocytochemistry. Cells were expanded and then cultured as micromass pellets (n = 5) in a chondrogenic medium containing transforming growth factor-beta2 (TGF-beta2) and insulin growth factor-1 (IGF-1) for 6-12 weeks. Pellets derived from fetal dermal fibroblasts (n = 4) were cultured under identical conditions. Additionally, expanded mesenchymal amniocytes were seeded onto biodegradable polyglycolic acid scaffolds (n = 5) and maintained in the same chondrogenic medium within a rotating bioreactor for 10-15 weeks. Engineered specimens were analyzed quantitatively and compared with native fetal hyaline cartilage samples (n = 5). Statistical analysis was by the unpaired Student's t-test (p < 0.05). The isolated cells stained positively for vimentin and cytokeratins-8 and -18, but negatively for CD31. Micromass pellets derived from mesenchymal amniocytes exhibited chondrogenic differentiation by both standard and matrix-specific staining. In contrast, these findings could not be replicated in dermal fibroblast-based pellets. The engineered constructs derived from mesenchymal amniocytes similarly displayed histological evidence of chondrogenic differentiation and maintained their original size and three-dimensional architecture. Quantitative assays of the engineered constructs revealed lower concentrations of collagen type II, but similar amounts of glycosaminoglycans, elastin, and DNA, when compared to native fetal hyaline cartilage. We conclude that mesenchymal amniocytes can be used for the engineering of cartilaginous tissue in vitro. Cartilage engineering from the amniotic fluid may become a practical approach for the surgical treatment of select congenital anomalies.

Calcitonin is involved in cartilage homeostasis: is calcitonin a treatment for OA?

OBJECTIVE

Osteoarthritis (OA) is the most common form of degenerative joint diseases and a major cause of disability and impaired quality of life in the elderly. Recent observations suggest that calcitonin may act on both osteoclasts and chondrocytes. The present review was sought to summarize emerging observations from the molecular level to the preliminary clinical findings of possible chondroprotective effects of calcitonin.

METHOD

This review summarizes peer-reviewed articles found using pre-defined search criteria and published in the PubMed database before January 2006. In addition, abstracts from the OsteoArthritis Research Society International (OARSI) conferences in the time period 2000-2005 have been included in the search.

RESULTS

Ample evidence for the effect of calcitonin on bone resorption was found. Support for direct effects of calcitonin on chondrocytes on matrix synthesis and inhibition of cartilage degradation have been published. In addition, clinical evidence for the effect of calcitonin on cartilage degradation is emerging.

CONCLUSION

Several independent lines of evidence suggest a direct chondroprotective effect of calcitonin in addition to the well-established effect on bone resorption. Given the currently limited availability of chondroprotective agents, much expectation regards the ongoing clinical assessment of calcitonin therapy for the prevention and treatment of OA.

Mouse Adipose-Derived Stem Cells Undergo Multilineage Differentiation in Vitro but Primarily Osteogenic and Chondrogenic Differentiation in Vivo

Human, rat, and mouse studies have demonstrated the existence of a population of adipose-derived adult stem (ADAS) cells that can undergo multilineage differentiation in vitro. However, it remains unclear whether these cells maintain their multilineage potential in vivo. The aim of this study was to examine the in vitro and in vivo characteristics and behavior of a potential population of murine ADAS (muADAS) cells isolated from the visceral fat of the abdominal cavity of C57BL/10J mice. We used flow cytometry to examine the cells' expression of CD29, CD31, CD45, CD34, CD44, CD144, CD146, Flk1, and Sca-1. The isolated cell population was CD45 negative, which precludes contamination by hematopoietic cells, but was partially positive for Sca-1 and CD34: 2 stem-cell markers. After induction in conditioned medium, the muADAS cells gained the ability to undergo adipogenic, osteogenic, chondrogenic, myogenic, and hematopoietic differentiation in vitro. The muADAS cells readily differentiated to form bone and cartilage in vivo for up to 24 weeks, but their ability to regenerate muscle or reconstitute bone marrow was found to be limited.

The Chondrocyte: Biology and Clinical Application

Chondrocyte is a unique cell type in articular cartilage tissue and is essential for cartilage formation and functionality. It arises from mesenchymal stem cells (MSCs) and is regulated by a series of cytokine and transcription factor interactions, including the transforming growth factor-beta super family, fibroblast growth factors, and insulin-like growth factor-1. To understand the biomechanisms of the chondrocyte differentiation process, various cellular model systems have been employed, such as primary chondrocyte culture, clonal normal cell lines (HCS-2/8, Ch-1, ATDC5, CFK-2, and RCJ3.1C5.18), and transformed clonal cell lines (T/C-28a2, T/C-28a4, C-28/I2, tsT/AC62, and HPV-16 E6/E7). Additionally, cell culture methods, including conventional monolayer culture, three-dimensional scaffold culture, bioreactor culture, pellet culture, and organ culture, have been established to create stable environments for the expansion, phenotypic maintenance, and subsequent biological study of chondrocytes for clinical application. Knowledge gained through these study systems has allowed for the use of chondrocytes in orthopedics for the treatment of cartilage injury and epiphyseal growth plate defects using tissue-engineering approaches. Furthermore, the potential of chondrocyte implantation for facial reconstruction, the treatment of long segmental tracheal defects, and urinary incontinence and vesicoureteral reflux are being investigated. This review summarizes the present study of chondrocyte biology and the potential uses of this cell in orthopedics and other disciplines.

Chondrogenic differentiation of mesenchymal stem cells isolated from patients in late adulthood: the optimal conditions of growth factors

There is a controversy about the capacity of the mesenchymal stem cells (MSCs) from aged individuals to proliferate and differentiate into cartilage. The purpose of this study was to investigate the optimal condition to culture human MSCs from the aged individuals (>50 years) for cartilage tissue engineering. We tested the hypothesis that effective proliferation and chondrogenesis can be achieved with human MSCs from aged individuals under appropriate conditions. To investigate the best condition for proliferation, MSCs were cultured in medium containing four concentrations subsets (0, 0.05, 0.5, 5 ng/mL) of recombinant human TGF-beta2 and FGF-2, either with or without fetal calf serum. The cell numbers were counted 0, 1, 3, and 7 days after growth factors were given. For the induction of chondrogenesis in 3-dimensional (3-D) culture, cells were cultured in pellets with chondrogenic medium containing combinations of various growth factors. After 4 weeks of culture, the pellets were fixed and evaluated with Safranin-O staining for proteoglycan and immunohistochemical staining for type II collagen. RT-PCR was also performed for the mRNAs of type I collagen, type II collagen, and cartilage oligomeric protein (COMP). In a monolayer culture, TGF-beta2 in concentrations of 0.5 and 5 ng/mL caused significant reduction in cell number irrespective of the presence of serum. FGF-2 of 5 ng/mL most effectively increased cell number even in the absence of serum. In a pellet culture, remarkable chondrocyte-like differentiation of cells was induced around the peripheral areas of a pellet with 5 ng/mL of TGF-beta2, accompanied by increased proteoglycan and type II collagen production. The addition of 100 ng/mL of IGF-I induced notable increase in proteoglycan contents. The results of RT-PCR mirrored those of histological studies. This study shows that an effective proliferation and chondrogenesis may be obtained with proper combinations of growth factors and mesenchymal stem cells from aged individuals.

Equine Peripheral Blood-Derived Progenitors in Comparison to Bone Marrow-Derived Mesenchymal Stem Cells

Fibroblast-like cells isolated from peripheral blood of human, canine, guinea pig, and rat have been demonstrated to possess the capacity to differentiate into several mesenchymal lineages. The aim of this work was to investigate the possibility of isolating pluripotent precursor cells from equine peripheral blood and compare them with equine bone marrow-derived mesenchymal stem cells. Human mesenchymal stem cells (MSCs) were used as a control for cell multipotency assessment. Venous blood (n = 33) and bone marrow (n = 5) were obtained from adult horses. Mononuclear cells were obtained by Ficoll gradient centrifugation and cultured in monolayer, and adherent fibroblast-like cells were tested for their differentiation potential. Chondrogenic differentiation was performed in serum-free medium in pellet cultures as a three-dimensional model, whereas osteogenic and adipogenic differentiation were induced in monolayer culture. Evidence for differentiation was made via biochemical, histological, and reverse transcription-polymerase chain reaction evaluations. Fibroblast-like cells were observed on day 10 in 12 out of 33 samples and were allowed to proliferate until confluence. Equine peripheral blood-derived cells had osteogenic and adipogenic differentiation capacities comparable to cells derived from bone marrow. Both cell types showed a limited capacity to produce lipid droplets compared to human MSCs. This result may be due to the assay conditions, which are established for human MSCs from bone marrow and may not be optimal for equine progenitor cells. Bone marrow-derived equine and human MSCs could be induced to develop cartilage, whereas equine peripheral blood progenitors did not show any capacity to produce cartilage at the histological level. In conclusion, equine peripheral blood-derived fibroblast-like cells can differentiate into distinct mesenchymal lineages but have less multipotency than bone marrow-derived MSCs under the conditions used in this study.

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

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

Osteochondral tissue engineering

Osteochondral defects (i.e., defects which affect both the articular cartilage and underlying subchondral bone) are often associated with mechanical instability of the joint, and therefore with the risk of inducing osteoarthritic degenerative changes. Current surgical limits in the treatment of complex joint lesions could be overcome by grafting osteochondral composite tissues, engineered by combining the patient's own cells with three-dimensional (3D) porous biomaterials of pre-defined size and shape. Various strategies have been reported for the engineering of osteochondral composites, which result from the use of one or more cell types cultured into single-component or composite scaffolds in a broad spectrum of compositions and biomechanical properties. The variety of concepts and models proposed by different groups for the generation of osteochondral grafts reflects that understanding of the requirements to restore a normal joint function is still poor. In order to introduce the use of engineered osteochondral composites in the routine clinical practice, it will be necessary to comprehensively address a number of critical issues, including those related to the size and shape of the graft to be generated, the cell type(s) and properties of the scaffold(s) to be used, the potential physical conditioning to be applied, the degree of functionality required, and the strategy for a cost-effective manufacturing. The progress made in material science, cell biology, mechanobiology and bioreactor technology will be key to support advances in this challenging field.

The heterogeneity of human mesenchymal stem cell preparations--evidence from simultaneous analysis of proteomes and transcriptomes

OBJECTIVE

Mesenchymal stem cells (MSC) raise high hopes in clinical applications. However, the lack of common standards and a precise definition of MSC preparations remains a major obstacle in research and application of MSC. Whereas surface antigen markers have failed to precisely define this population, a combination of proteomic data and microarray data provides a new dimension for the definition of MSC preparations.

METHODS

In our continuing effort to characterize MSC, we have analyzed the differential transcriptome and proteome expression profiles of MSC preparations isolated from human bone marrow under two different expansion media (BM-MSC-M1 and BM-MSC-M2).

RESULTS

In proteomics, 136 protein spots were unambiguously identified by MALDI-TOF-MS and corresponding cDNA spots were selected on our "Human Transcriptome cDNA Microarray." Combination of datasets revealed a correlation in differential gene expression and protein expression of BM-MSC-M1 vs BM-MSC-M2. Genes involved in metabolism were more highly expressed in BM-MSC-M1, whereas genes involved in development, morphogenesis, extracellular matrix, and differentiation were more highly expressed in BM-MSC-M2. Interchanging culture conditions for 8 days revealed that differential expression was retained in several genes whereas it was altered in others.

CONCLUSION

Our results have provided evidence that homogeneous BM-MSC preparations can reproducibly be isolated under standardized conditions, whereas culture conditions exert a prominent impact on transcriptome, proteome, and cellular organization of BM-MSC.

In vivo response of polylactic acid-alginate scaffolds and bone marrow-derived cells for cartilage tissue engineering

Successful application of tissue-engineering techniques to damaged biological structures is determined by functional performance in vivo. This study evaluated the in vivo response of a tissue-engineered construct composed of a polylactic acid-alginate amalgam seeded with bone marrow-derived mesenchymal stem cells and stimulated in vitro with transforming growth factor beta for cartilage tissue engineering. Constructs were placed in cylindrical osteochondral defects in the canine femoral condyle and examined 6 weeks postoperatively by gross, histological, immunohistochemical, and biomechanical analyses. In the course of 6 weeks in vivo, the defects filled with a cartilaginous tissue regardless of whether cell-seeded (experimental) or cell-free (control) constructs were implanted; however, the quality of the tissue differed between the experimental and control defects. Cell-seeded experimental defects showed more cartilage-like matrix quality, cell distribution, and proteoglycan staining. Biomechanically, experimental and control specimens exhibited similar behavior; however, both tissues were still immature compared with normal cartilage. The evidence accumulated in this study showed a modest acceleration of the in vivo healing of cell-seeded constructs but also demonstrated a reparative response of cell-free constructs. This finding suggests that the constructs prepared from the PLA-alginate amalgam may serve as a means for host cell attachment.

Effects of fibrinolytic inhibitors on chondrogenesis of bone-marrow derived mesenchymal stem cells in fibrin gels

The objective of this study was to examine the effect of two fibrinolytic inhibitors, aprotinin and aminohexanoic acid, on chondrogenesis of rabbit bone marrow mesenchymal stem cells (BM-MSCs). Rabbit BM-MSCs were obtained from the tibias and femurs of New Zealand White rabbits. Cell-fibrin constructs were made by mixing a cell-fibrinogen (10(7) cells/ml; 40 mg/ml fibrinogen) solution with a thrombin (5 IU/ml) solution and then divided into four groups: aprotinin control, aprotinin + transforming growth factor beta (TGF-beta), aminohexanoic acid control, and aminohexanoic acid + TGF-beta. Each of these groups was further treated with three different concentrations of inhibitors and the TGF-beta groups were treated with 10 ng/ml of TGF-beta1. The chondrogenic gene expressions, DNA content, and glycosaminoglycan content of samples were analyzed after 14 days of culture. The aprotinin groups exhibited significantly higher levels of aggrecan gene expression and glycosaminoglycan content than the aminohexanoic acid groups. However, inhibitor neither influenced gene expression of type II collagen nor proliferation (i.e., DNA content) of BM-MSCs. These findings suggest that fibrinolytic inhibitors used to control degradation of fibrin clot may influence TGF-beta-induced chondrogenesis of BM-MSCs.

Optimization of high-efficiency transfection of adult human mesenchymal stem cells in vitro

With the advent of recent protocols to isolate multipotent human mesenchymal stem cells (MSCs), there is a need for efficient transfection methodologies for these cells. Most standard transfection methods yield poor transfection efficiencies for MSCs (<1%). Here we have optimized a high-efficiency transfection technique for low passage MSCs derived from adult human bone marrow. This technique is an extension of electroporation, termed amaxa Nucleofection, where plasmid DNA is transfected directly into the cell nucleus, independent of the growth state of the cell. With this technique, we demonstrate up to 90% transfection efficiency of the viable population of MSCs, using plasmid construct containing a standard cytomegalovirus (CMV) early promoter driving expression of green fluorescent protein (GFP). Although little variation in transfection efficiency was observed between patient samples, a 2-fold difference in transfection efficiency and a 10-fold difference in expression levels per cell were seen using two distinct CMV-GFP expression plasmids. By fluorescence-activated cell sorting, the GFP expressing cells were sorted and subcultured. At 2 wk posttransfection, approx 25% of the population of sorted cells were GFP positive, and by 3 wk, nearly 10% of the cells still retained GFP expression. Transfection of these cells with plasmid containing either the collagen type I (Col1a1) promoter or the cartilage oligomeric matrix protein (COMP) promoter, each driving expression of GFP, produced a somewhat lower transfection efficiency (approx 40%), due in part to the lower activity of transcription from these promoters compared to that of CMV. Transfection with the collagen type II (Col2a1) promoter linked to GFP exhibited low expression, due to the fact that collagen type II is not expressed in these cells. Upon culturing of the Col2a1-GFP transfected cells in a transforming growth factor-beta3-containing medium known to induce mesenchymal chondrogensis, a significant enhancement of GFP level was seen, indicating the ability of the transfected cells to differentiate into chondrocytes and express cartilage-specific genes, such as Col2a1. Taken together, these data provide evidence of the applicability of this technique for the efficient transfection of MSCs.

Osteogenic differentiation of noncultured immunoisolated bone marrow-derived CD105+ cells

The culture expansion of human mesenchymal stem cells (hMSCs) may alter their characteristics and is a costly and time-consuming stage. This study demonstrates for the first time that immunoisolated noncultured CD105-positive (CD105(+)) hMSCs are multipotent in vitro and exhibit the capacity to form bone in vivo. hMSCs are recognized as promising tools for bone regeneration. However, the culture stage is a limiting step in the clinical setting. To establish a simple, efficient, and fast method for applying these cells for bone formation, a distinct population of CD105(+) hMSCs was isolated from bone marrow (BM) by using positive selection based on the expression of CD105 (endoglin). The immunoisolated CD105(+) cell fraction represented 2.3% +/- 0.45% of the mononuclear cells (MNCs). Flow cytometry analysis of freshly immunoisolated CD105(+) cells revealed a purity of 79.7% +/- 3.2%. In vitro, the CD105(+) cell fraction displayed significantly more colony-forming units-fibroblasts (CFU-Fs; 6.3 +/- 1.4) than unseparated MNCs (1.1 +/- 0.3; p < .05). Culture-expanded CD105(+) cells expressed CD105, CD44, CD29, CD90, and CD106 but not CD14, CD34, CD45, or CD31 surface antigens, and these cells were able to differentiate into osteogenic, chondrogenic, and adipogenic lineages. In addition, freshly immunoisolated CD105(+) cells responded in vivo to recombinant bone morphogenetic protein-2 by differentiating into chondrocytes and osteoblasts. Genetic engineering of freshly immunoisolated CD105(+) cells was accomplished using either adenoviral or lentiviral vectors. Based on these findings, it is proposed that noncultured BM-derived CD105(+) hMSCs are osteogenic cells that can be genetically engineered to induce tissue generation in vivo.

Nucleofection-BasedEx VivoNonviral Gene Delivery to Human Stem Cells as a Platform for Tissue Regeneration

There are several gene therapy approaches to tissue regeneration. Although usually efficient, virusbased approaches may elicit an immune response against the viral proteins. An alternative approach, nonviral transfer, is safer, and can be controlled and reproduced. We hypothesized that in vivo bone formation could be achieved using human mesenchymal stem cells (hMSCs) nonvirally transfected with the human bone morphogenetic protein-2 (hBMP-2) or -9 (hBMP-9) gene. Human MSCs were transfected using nucleofection, a unique electropermeabilization-based technique. Postnucleofection, cell viability was 53.6 +/- 2.5% and gene delivery efficiency was 51% to 88% (mean 68.2 +/- 4.1%), as demonstrated by flow cytometry in enhanced green fluorescent protein (EGFP)-nucleofected hMSCs. Transgene expression lasted longer than 14 days and was very low 21 days postnucleofection. Both hBMP-2- and hBMP-9-nucleofected hMSCs in culture demonstrated a significant increase in calcium deposition compared with EGFP-nucleofected hMSCs. Human BMP-2- and hBMP-9-nucleofected hMSCs transplanted in ectopic sites in NOD/SCID mice induced bone formation 4 weeks postinjection. We conclude that in vivo bone formation can be achieved by using nonvirally nucleofected hMSCs. This could lead to a breakthrough in the field of regenerative medicine, in which safer, nonviral therapeutic strategies present a very attractive alternative.

Hematopoietic origins of fibroblasts: I. In vivo studies of fibroblasts associated with solid tumors

OBJECTIVE

Recent studies have reported that bone marrow cells can give rise to tissue fibroblasts. However, the bone marrow cell(s) that gives rise to fibroblasts has not yet been identified. In the present study, we tested the hypothesis that tissue fibroblasts are derived from hematopoietic stem cells (HSCs) in vivo.

METHODS

These studies were conducted using mice whose hematopoiesis had been reconstituted by transplantation of a clonal population of cells derived from a single enhanced green fluorescent protein (EGFP)-positive HSC in conjunction with murine tumor models.

RESULTS

When tumors propagated in the transplanted mice were evaluated for the presence of EGFP(+) HSC-derived cells, two prominent populations of EGFP(+) cells were found. The first were determined to be fibroblasts within the tumor stromal capsule, a subset of which expressed type I collagen mRNA and alpha-smooth muscle actin. The second population was a perivascular cell associated with the CD31(+) tumor blood vessels.

CONCLUSION

These in vivo findings establish an HSC origin of fibroblasts.

Cartilage repair using bone morphogenetic protein 4 and muscle-derived stem cells

OBJECTIVE

Muscle-derived stem cells (MDSCs) isolated from mouse skeletal muscle exhibit long-time proliferation, high self-renewal, and multipotent differentiation. This study was undertaken to investigate the ability of MDSCs that were retrovirally transduced to express bone morphogenetic protein 4 (BMP-4) to differentiate into chondrocytes in vitro and in vivo and enhance articular cartilage repair.

METHODS

Using monolayer and micromass pellet culture systems, we evaluated the in vitro chondrogenic differentiation of LacZ- and BMP-4-transduced MDSCs with or without transforming growth factor beta1 (TGFbeta1) stimulation. We used a nude rat model of a full-thickness articular cartilage defect to assess the duration of LacZ transgene expression and evaluate the ability of transplanted cells to acquire a chondrocytic phenotype. We evaluated cartilage repair macroscopically and histologically 4, 8, 12, and 24 weeks after surgery, and performed histologic grading of the repaired tissues.

RESULTS

BMP-4-expressing MDSCs acquired a chondrocytic phenotype in vitro more effectively than did MDSCs expressing only LacZ; the addition of TGFbeta1 did not alter chondrogenic differentiation of the BMP-4-transduced MDSCs. LacZ expression within the repaired tissue continued for up to 12 weeks. Four weeks after surgery, we detected donor cells that coexpressed beta-galactosidase and type II collagen. Histologic scoring of the defect sites 24 weeks after transplantation revealed significantly better cartilage repair in animals that received BMP-4-transduced MDSCs than in those that received MDSCs expressing only LacZ.

CONCLUSION

Local delivery of BMP-4 by genetically engineered MDSCs enhanced chondrogenesis and significantly improved articular cartilage repair in rats.

In utero transplantation of human bone marrow-derived multipotent mesenchymal stem cells in mice

Mesenchymal stem cells (MSCs) are multipotent cells that can be isolated from human bone marrow and possess the potential to differentiate into progenies of embryonic mesoderm. However, current evidence is based predominantly on in vitro experiments. We used a murine model of in utero transplantation (IUT) to study the engraftment capabilities of human MSCs. MSCs were obtained from bone marrow by negative immunoselection and limiting dilution, and were characterized by flow cytometry and by in vitro differentiation into osteoblasts, chondrocytes, and adipocytes. MSCs were transplanted into fetal mice at a gestational age of 14 days. Engraftment of human MSCs was determined by flow cytometry, polymerase chain reaction, and fluorescence in situ hybridization (FISH). MSCs engrafted into tissues originating from all three germ layers and persisted for up to 4 months or more after delivery, as evidenced by the expression of the human-specific beta-2 microglobulin gene and by FISH for donor-derived cells. Donor-derived CD45+ cells were detectable in the peripheral blood of recipients, suggesting the participation of MSCs in hematopoiesis at the fetal stage. This model can further serve to evaluate possible applications of MSCs.

A Collagen-glycosaminoglycan Scaffold Supports Adult Rat Mesenchymal Stem Cell Differentiation Along Osteogenic and Chondrogenic Routes

Adult mesenchymal stem cells have the proclivity to differentiate along multiple lineages giving rise to new bone, cartilage, muscle, or fat. Collagen, a normal constituent of bone, provides strength and structural stability and is therefore a potential candidate for use as a substrate on which to engineer bone and cartilage from their respective mesenchymal-derived precursors. In this study, a collagen- glycosaminoglycan scaffold was used to provide a suitable three-dimensional (3-D) environment on which to culture adult rat mesenchymal stem cells and induce differentiation along the osteogenic and chondrogenic lineages. The results demonstrate that adult rat mesenchymal stem cells can undergo osteogenesis when grown on the collagen-glycosaminoglycan scaffold and stimulated with osteogenic factors (dexamethasone, ascorbic acid, beta-glycerophosphate), as evaluated by the temporal induction of the bone-specific proteins, collagen I and osteocalcin, and subsequent matrix mineralization. The osteogenic factors were coupled to activation of the extracellular-regulated protein kinase (ERK), and this kinase was found to play a role in the osteogenic process. As well as supporting osteogenesis, when the cell-seeded scaffold was exposed to chondrogenic factors (dexamethasone and TGF-1beta), collagen II immunoreactivity was increased, providing evidence that the scaffold can also provide a suitable 3-D environment that supports chondrogenesis.

Glucocorticoids promote chondrogenic differentiation of adult human mesenchymal stem cells by enhancing expression of cartilage extracellular matrix genes

In the adult human, mesenchymal stem cells (hMSCs) resident in the bone marrow retain the capacity to proliferate and differentiate along multiple connective tissue lineages, including cartilage. Glucocorticoids (GCs) are required for chondrogenic differentiation of hMSCs in vitro; however, the exact role of GCs in this process is not known. In this study, we examined the effects of dexamethasone (DEX) on chondrogenic differentiation of hMSCs in the presence or absence of DEX, transforming growth factor-beta (TGF-beta), or DEX plus TGF-beta. GC treatment upregulated gene expression of cartilage matrix components aggrecan, dermatopontin, and collagen type XI; enhanced TGF-beta-mediated upregulation of collagen type II and cartilage oligomeric matrix protein; and increased aggrecan and collagen type II production as well as cartilage matrix-sulfated proteoglycans as assessed by immunohistochemistry and alcian blue staining. Inclusion of an antagonist of GCs inhibited expression of chondrogenic differentiation markers, suggesting that the GC effects during chondrogenesis are mediated by the GC receptor (GR). Steady levels of the major active form of GR, GRalpha, were detected in both undifferentiated and differentiating hMSCs, whereas the dominant-negative isoform GRbeta, present at low levels in undifferentiated hMSCs, was downregulated during chondrogenesis. In the presence of DEX and TGF-beta, expression of a collagen type II gene promoter luciferase reporter construct in hMSCs was upregulated. However, coexpression of GRbeta dramatically inhibited promoter activity, suggesting that GRalpha is required for GC-mediated modulation of chondrogenesis and that GCs may play an important role in the maintenance of cartilage homeostasis.

Use of differentiating adult stem cells (marrow stromal cells) to identify new downstream target genes for transcription factors

We developed a strategy for use of microarray data to rapidly identify new downstream targets of transcription factors known to drive differentiation by following the time courses of gene expression as a relatively homogeneous population of stem/progenitor cells are differentiated to multiple phenotypes. Microarray assays were used to follow the differentiation of human marrow stromal cells (MSCs) into chondrocytes or adipocytes in three different experimental conditions. The steps of the analysis were the following: (a) hierarchical clustering was used to define groups of similarly behaving genes in each experiment, (b) candidates for new downstream targets of transcription factors that drive differentiation were then identified as genes that were consistently co-expressed with known downstream target genes of the transcription factors, and (c) the list of candidate new target genes was refined by identifying genes whose signal intensities showed a highly significant linear regression with the signal intensities of the known targets in all the data sets. Analysis of the data identified multiple new candidates for downstream targets for SOX9, SOX5, CCAAT/enhancer binding protein (C/EBP)-alpha, and peroxisome proliferator-activated receptor (PPAR)-gamma. To validate the analysis, we demonstrated that PPAR-gamma protein specifically bound to the promoters of four new targets identified in the analyses. The same multistep analysis can be used to identify new downstream targets of transcription factors in other systems. Also, the same analysis should make it possible to use MSCs from bone marrow to define new mutations that alter chondogenesis or adipogenesis in patients with a variety of syndromes.

Comparative characteristics of mesenchymal stem cells from human bone marrow, adipose tissue, and umbilical cord blood

OBJECTIVE

Various preparative protocols have been proposed for the acquisition and cultivation of mesenchymal stem cells (MSC). Whereas surface antigen markers have failed to precisely define this population, microarray analysis might provide a better tool for characterization of MSC.

METHODS

In this study, we have analyzed global gene expression profiles of human MSC isolated from adipose tissue (AT), from umbilical cord blood (CB), and from bone marrow (BM) under two growth conditions and have compared them to terminally differentiated human fibroblasts (HS68). Profiles were compared using our Human Genome Microarray representing 51.144 different cDNA clones.

RESULTS

Cultured with the appropriate conditions, osteogenic and adipogenic differentiation could be confirmed in all MSC preparations but not in fibroblasts. No phenotypic differences were observed by flow cytometry using a panel of 22 surface antigen markers. Whereas MSC derived from different donors using the same culture procedure yielded a consistent and reproducible gene expression profile, many genes were differentially expressed in MSC from different ontogenetic sources or from different culture conditions. Twenty-five genes were overlapping and upregulated in all MSC preparations from AT, CB, and BM as compared to HS68 fibroblasts. These genes included fibronectin, ECM2, glypican-4, ID1, NF1B, HOXA5, and HOXB6. Many genes upregulated in MSC are involved in extracellular matrix, morphogenesis, and development, whereas several inhibitors of the Wnt pathway (DKK1, DKK3, SFRP1) were highly expressed in fibroblasts.

CONCLUSION

Our results have provided a foundation for a more reproducible and reliable quality control using genotypic analysis for defining MSC.

Immortalized cell lines from mouse xiphisternum preserve chondrocyte phenotype

Chondrocytes are unique to cartilage and the study of these cells in vitro is important for advancing our understanding of the role of these cells in normal homeostasis and disease including osteoarthritis (OA). As there are limitations to the culture of primary chondrocytes, cell lines have been developed to overcome some of these obstacles. In this study, we developed a procedure to immortalize and characterize chondrocyte cell lines from mouse xiphisternum. The cells displayed a polygonal to fibroblastic morphology in monolayer culture. Gene expression studies using quantitative PCR showed that the cell lines responded to bone morphogenetic protein 2 (BMP-2) by increased expression of matrix molecules, aggrecan, and type II collagen together with transcriptional factor, Sox9. Stimulation by IL-1 results in the increased expression of catabolic effectors including MMP-13, nitric oxide synthase, ADAMTS4, and ADAMTS5. Cells cultured in alginate responded to BMP-2 by increased synthesis of proteoglycan (PG), a major matrix molecule of cartilage. IL-1 treatment of cells in alginate results in increased release of PG into the conditioned media. Further analysis of the media showed the presence of Aggrecanase-cleaved aggrecan fragments, a signature of matrix degradation. These results show that the xiphisternum chondrocyte cell lines preserve their chondrocyte phenotype cultured in either monolayer or 3-dimensional alginate bead culture systems. In summary, this study describes the establishment of chondrocyte cell lines from the mouse xiphisternum that may be useful as a surrogate model system to understand chondrocyte biology and to shed light on the underlying mechanism of pathogenesis in OA.

Mesenchymal stem cells: isolation, in vitro expansion and characterization

Mesenchymal stem cells (MSC), one type of adult stem cell, are easy to isolate, culture, and manipulate in ex vivo culture. These cells have great plasticity and the potential for therapeutic applications, but their properties are poorly understood. MSCs can be found in bone marrow and in many other tissues, and these cells are generally identified through a combination of poorly defined physical, phenotypic, and functional properties; consequently, multiple names have been given to these cell populations. Murine MSCs have been directly applied to a wide range of murine models of diseases, where they can act as therapeutic agents per se, or as vehicles for the delivery of therapeutic genes. In addition to their systemic engraftment capabilities, MSCs show great potential for the replacement of damaged tissues such as bone, cartilage, tendon, and ligament. Their pharmacological importance is related to four points: MSCs secrete biologically important molecules, express specific receptors, can be genetically manipulated, and are susceptible to molecules that modify their natural behavior. Due to their low frequency and the lack of knowledge on cell surface markers and their location of origin, most information concerning MSCs is derived from in vitro studies. The search for the identity of the mesenchymal stem cell has depended mainly on three culture systems: the CFU-F assay, the analysis of bone marrow stroma, and the cultivation of mesenchymal stem cell lines. Other cell populations, more or less related to the MSC, have also been described. Isolation and culture conditions used to expand these cells rely on the ability of MSCs, although variable, to adhere to plastic surfaces. Whether these conditions selectively favor the expansion of different bone marrow precursors or cause similar cell populations to acquire different phenotypes is not clear. The cell populations could also represent different points of a hierarchy or a continuum of differentiation. These issues reinforce the urgent need for a more comprehensive view of the mesenchymal stem cell identity and characteristics.

A predominantly articular cartilage-associated gene, SCRG1, is induced by glucocorticoid and stimulates chondrogenesis in vitro

OBJECTIVE

Cartilage tissue engineering using multipotential human mesenchymal stem cells (hMSCs) is a promising approach to develop treatment for degenerative joint diseases. A key requirement is that the engineered tissues maintain their hyaline articular cartilage phenotype and not proceed towards hypertrophy. It is noteworthy that osteoarthritic articular cartilage frequently contains limited regions of reparative cartilage, suggesting the presence of bioactive factors with regenerative activity. Based on this idea, we recently performed cDNA microarray analysis to identify genes that are strongly expressed only in articular cartilage and encode secreted gene products. One of the genes that met our criteria was SCRG1. This study aims to analyze SCRG1 function in cartilage development using an in vitro mesenchymal chondrogenesis system.

METHODS

Full-length SCRG1 cDNA was subcloned into pcDNA5 vector, and transfected into hMSCs and murine C3H10T1/2 mesenchymal cells, placed in pellet cultures and micromass cultures, respectively. The cultures were analyzed by reverse transcription-polymerase chain reaction for the expression of SCRG1 and cartilage marker genes, and by histological staining for cartilage phenotype.

RESULTS

Induction of SCRG1 expression was seen during in vitro chondrogenesis, and was dependent on dexamethasone (DEX) known to promote chondrogenesis. Immunohistochemistry revealed that SCRG1 protein was localized to the extracellular matrix. Forced expression of SCRG1 in hMSCs suppressed their proliferation, and stimulated chondrogenesis in C3H10T1/2 cells, confirmed by reduced collagen type I and elevated collagen type IIB expression.

CONCLUSION

These results suggest that SCRG1 is involved in cell growth suppression and differentiation during DEX-dependent chondrogenesis. SCRG1 may be of utility in gene-mediated cartilage tissue engineering.

Gene-induced chondrogenesis of primary mesenchymal stem cells in vitro

Adult mesenchymal stem cells (MSCs) have the capacity to differentiate into various connective tissues such as cartilage and bone following stimulation with certain growth factors. However, less is known about the capacity of these cells to undergo chondrogenesis when these proteins are delivered via gene transfer. In this study, we investigated chondrogenesis of primary, bone marrow-derived MSCs in aggregate cultures following genetic modification with adenoviral vectors encoding chondrogenic growth factors. We found that adenoviral-mediated expression of TGF-beta1 and BMP-2, but not IGF-1, induced chondrogenesis of MSCs as evidenced by toluidine blue metachromasia and immunohistochemical detection of type II collagen. Chondrogenesis correlated with the level and duration of expressed protein and was strongest in aggregates expressing 10-100 ng/ml transgene product. Transgene expression in all aggregates was highly transient, showing a marked decrease after 7 days. Chondrogenesis was inhibited in aggregates modified to express >100 ng/ml TGF-beta1 or BMP-2; however, this was found to be partly due to the inhibitory effect of exposure to high adenoviral loads. Our findings indicate that parameters such as these are important functional considerations for adapting gene transfer technologies to induce chondrogenesis of MSCs.

In vitro cartilage tissue engineering with 3D porous aqueous-derived silk scaffolds and mesenchymal stem cells

Adult cartilage tissue has limited self-repair capacity, especially in the case of severe damages caused by developmental abnormalities, trauma, or aging-related degeneration like osteoarthritis. Adult mesenchymal stem cells (MSCs) have the potential to differentiate into cells of different lineages including bone, cartilage, and fat. In vitro cartilage tissue engineering using autologous MSCs and three-dimensional (3-D) porous scaffolds has the potential for the successful repair of severe cartilage damage. Ideally, scaffolds designed for cartilage tissue engineering should have optimal structural and mechanical properties, excellent biocompatibility, controlled degradation rate, and good handling characteristics. In the present work, a novel, highly porous silk scaffold was developed by an aqueous process according to these criteria and subsequently combined with MSCs for in vitro cartilage tissue engineering. Chondrogenesis of MSCs in the silk scaffold was evident by real-time RT-PCR analysis for cartilage-specific ECM gene markers, histological and immunohistochemical evaluations of cartilage-specific ECM components. Dexamethasone and TGF-beta3 were essential for the survival, proliferation and chondrogenesis of MSCs in the silk scaffolds. The attachment, proliferation, and differentiation of MSCs in the silk scaffold showed unique characteristics. After 3 weeks of cultivation, the spatial cell arrangement and the collagen type-II distribution in the MSCs-silk scaffold constructs resembles those in native articular cartilage tissue, suggesting promise for these novel 3-D degradable silk-based scaffolds in MSC-based cartilage repair. Further in vivo evaluation is necessary to fully recognize the clinical relevance of these observations.

Focusing of Gene Expression as the Basis of Stem Cell Differentiation

In a prior report (Stem Cells Dev 14(4):354-366, 2005), we employed two-dimensional gel electrophoresis followed by advanced proteomics and the Database for Annotation, Visualization and Integrated Discovery (DAVID) to compare the protein expression profiles of mesenchymal stem cells to that of fully differentiated osteoblasts. These data were reported to advance technical approaches to define the basis of differentiation, but also led us to suggest that osteogenic differentiation of stem cells may result from the focusing of gene expression in functional clusters (e.g., calcium-regulated signaling proteins or adherence proteins) rather than simply from the induced expression of new genes, as many have assumed. Here, we have employed these analytical techniques to compare protein expression by mesenchymal stem cells directly with that of cells derived from them after induced osteogenic differentiation. Our results support the concept of gene focusing as the basis of differentiation. Specifically, induced differentiation results in a decrease in the number of mesenchymal cell markers and calcium-mediated signaling molecules expressed by their differentiated progeny. This effect was seen in parallel to increased expression of specific extracellular matrix (ECM) molecules and their receptors. These results strongly imply that changes in the ECM have a direct impact on stem cell differentiation, and that osteogenic differentiation of stem cells directed by matrix clues results from focusing of the expression of genes involved in Ca2+-dependent signaling pathways.

Effect of reduced oxygen tension on chondrogenesis and osteogenesis in adipose-derived mesenchymal cells

Recent studies have demonstrated that adipose-derived mesenchymal cells (AMCs) offer great promise for cell-based therapies because of their ability to differentiate toward bone, cartilage, and fat. Given that cartilage is an avascular tissue and that mesenchymal cells experience hypoxia during prechondrogenic condensation in endochondral ossification, the goal of this study was to understand the influence of oxygen tension on AMC differentiation into bone and cartilage. In vitro chondrogenesis was induced using a three-dimensional micromass culture model supplemented with TGF-beta1. Collagen II production and extracellular matrix proteoglycans were assessed with immunohistochemistry and Alcian blue staining, respectively. Strikingly, micromasses differentiated in reduced oxygen tension (2% O(2)) showed markedly decreased chondrogenesis. Osteogenesis was induced using osteogenic medium supplemented with retinoic acid or vitamin D and was assessed with alkaline phosphatase activity and mineralization. AMCs differentiated in both 21 and 2% O(2) environments. However, osteogenesis was severely diminished in a low-oxygen environment. These data demonstrated that hypoxia strongly inhibits in vitro chondrogenesis and osteogenesis in AMCs.

Growth of bone marrow stromal cells on small intestinal submucosa: an alternative cell source for tissue engineered bladder

OBJECTIVE

To assess the potential use of bone marrow stromal cell (BMSC)-seeded biodegradable scaffold for bladder regeneration in a canine model, by characterizing BMSCs and comparing them to bladder smooth muscle cells (SMCs) by immunohistochemistry, growth capability, and contractility.

MATERIALS AND METHODS

Bone marrow was taken by direct needle aspiration from the femurs of five beagle dogs for the in vitro study. Mononuclear cells were isolated by Ficoll-Paque density gradient centrifugation and cultivated in medium 199 with 10% fetal bovine serum. BMSCs were characterized by cell proliferation, in vitro contractility, immunohistochemical analysis, and the growth pattern on small intestinal submucosa (SIS) scaffolds compared to bladder SMC cultures from the same dogs. Another six dogs had a hemicystectomy and bladder augmentation with BMSC-seeded (two), bladder cells including urothelial cells plus SMC-seeded SIS (two) and unseeded SIS scaffolds (two). The six dogs were followed for 10 weeks after augmentation.

RESULTS

In vitro BMSCs had a significant contractile response to calcium-ionophore, with a mean (sem) 36 (2)%, relative contraction (P < 0.01), which was similar to bladder SMCs but markedly different from fibroblasts. BMSCs also expressed alpha-smooth muscle actin by immunohistochemical staining and Western blotting, but did not express desmin or myosin. In vivo, both BMSC-seeded and bladder cell-seeded SIS grafts had solid smooth-muscle bundle formation throughout the graft.

CONCLUSIONS

BMSCs had a similar cell proliferation, histological appearance and contractile phenotype as primary cultured bladder SMCs. SIS supported three-dimensional growth of BMSCs in vitro, and BMSC-seeded SIS scaffold promoted bladder regeneration in a canine model. BMSCs may serve as an alternative cell source in urological tissue engineering.

Cardiac stem cells and mechanisms of myocardial regeneration

This review discusses current understanding of the role that endogenous and exogenous progenitor cells may have in the treatment of the diseased heart. In the last several years, a major effort has been made in an attempt to identify immature cells capable of differentiating into cell lineages different from the organ of origin to be employed for the regeneration of the damaged heart. Embryonic stem cells (ESCs) and bone marrow-derived cells (BMCs) have been extensively studied and characterized, and dramatic advances have been made in the clinical application of BMCs in heart failure of ischemic and nonischemic origin. However, a controversy exists concerning the ability of BMCs to acquire cardiac cell lineages and reconstitute the myocardium lost after infarction. The recognition that the adult heart possesses a stem cell compartment that can regenerate myocytes and coronary vessels has raised the unique possibility to rebuild dead myocardium after infarction, to repopulate the hypertrophic decompensated heart with new better functioning myocytes and vascular structures, and, perhaps, to reverse ventricular dilation and wall thinning. Cardiac stem cells may become the most important cell for cardiac repair.

Mesenchymal stem cell therapy to rebuild cartilage

Disorders affecting cartilage touch almost the whole population and are one of the leading causes of invalidity in adults. To repair cartilage, therapeutic approaches initially focused on the implantation of autologous chondrocytes, but this technique proved unsatisfactory because of the limited number of chondrocytes obtained at harvest. The discovery that several adult human tissues contain mesenchymal stem cells (MSCs) capable of differentiating into chondrocytes raised the possibility of injecting MSCs to repair cartilages. The important data published recently on the factors controlling chondrocyte commitment must be thoroughly considered to make further progress towards this therapeutic approach. The potential application of MSC therapy provides new hope for the development of innovative treatments for the repair of cartilage disorders.

Effects of cyclic compressive loading on chondrogenesis of rabbit bone-marrow derived mesenchymal stem cells

The objective of this study was to examine the effects of cyclic compressive loading on chondrogenic differentiation of rabbit bone-marrow mesenchymal stem cells (BM-MSCs) in agarose cultures. Rabbit BM-MSCs were obtained from the tibias and femurs of New Zealand white rabbits. After the chondrogenic potential of BM-MSCs was verified by pellet cultures, cell-agarose constructs were made by suspending BM-MSCs in 2% agarose (10(7) cells/ml) for a cyclic, unconfined compression test performed in a custom-made bioreactor. Specimens were divided into four groups: control; transforming growth factor (TGF-beta) (with TGF-beta1 treatment); loading (with stimulation of cyclic, unconfined compressive loading); and TGF-beta loading (with TGF-beta1 treatment and loading stimulation) groups. In the loading experiment, specimens were subjected to sinusoidal loading with a 10% strain magnitude at a frequency of 1 Hz for 4 hours a day. Experiments were conducted for 3, 7, and 14 consecutive days. While the experimental groups (TGF-beta, loading, and TGF-beta loading) exhibited significantly higher levels of expressions of chondrogenic markers (collagen II and aggrecan) at three time periods, there were no differences among the experimental groups after an extra 5-day culture. This suggests that compressive loading alone induces chondrogenic differentiation of rabbit BM-MSCs as effectively as TGF-beta or TGF-beta plus loading treatment. Moreover, both the compressive loading and the TGF-beta1 treatment were found to promote the TGF-beta1 gene expression of rabbit BM-MSCs. These findings suggest that cyclic compressive loading can promote the chondrogenesis of rabbit BM-MSCs by inducing the synthesis of TGF-beta1, which can stimulate the BM-MSCs to differentiate into chondrocytes.

Do adipose tissue-derived mesenchymal stem cells have the same osteogenic and chondrogenic potential as bone marrow-derived cells?

OBJECTIVE

Adipose tissue-derived mesenchymal stem cells (ATMSCs) have been shown to differentiate into bone, cartilage, fat or muscle. However, it is not certain that ATMSCs are equal to bone marrow-derived mesenchymal stem cells (BMMSC) for their bone and cartilage forming potential. The purpose of this study was to answer the question.

METHODS

BMMSCs were obtained from the medullary canal of femur and ATMSCs were isolated from the fat harvested during liposuction procedures. After cell expansion in culture media and two passages, the immunofluorescent studies for STRO-1 and CD34 were performed to characterize the BMMSCs and ATMSCs. Osteogenesis was induced on a monolayer culture with osteogenic medium containing dexamethasone, beta-glycerophosphate and ascorbate. After 2-3 weeks, alkaline phosphatase (AP) and Von Kossa staining were done. To test for chondrogenesis, mesenchymal stem cells (MSCs) were cultured in a pellet culture and in a fibrin scaffold with a chondrogenic medium (CM) containing transforming growth factor-beta(2) and insulin-like growth factor-I. After 4 weeks, Safranin-O staining and immunohistochemical staining for type II collagen were done to evaluate the chondrogenic differentiation and the matrix production. A histological scale was used to semiquantitatively assess the degree of chondrogenesis.

RESULTS

Both BMMSCs and ATMSCs were STRO-1 positive and CD34 negative. On the test of osteogenesis, the osteoblastic differentiation of ATMSCs as demonstrated by AP staining was much less than that of the BMMSCs (P=0.002). The amount of matrix mineralization shown by Von Kossa staining also showed statistical differences between the two MSCs (P=0.011). On the test for chondrogenesis by the pellet culture ATMSCs showed much weaker presentation as chondrogenic cells in both cell morphology and the matrix production. The histological score was 6.5 (SD1.3) for the BMMSCs, and 4.3 (SD1.6) for the ATMSCs cultured in CM, which was statistically significant (P=0.023). The results from fibrin gel paralleled those from the pellet culture in general.

CONCLUSION

The results of our study suggest that the ATMSCs may have an inferior potential for both osteogenesis and chondrogenesis compared with the BMMSCs, and these cast doubts on the value of adipose tissue as a source of MSCs.

In Vitro, Ex Vivo, andIn VivoMethodological Approaches for Studying Therapeutic Targets of Osteoporosis and Degenerative Joint Diseases: How Biomarkers Can Assist?

Although our approach to the clinical management of osteoporosis (OP) and degenerative joint diseases (DJD)-major causes of disability and morbidity in the elderly-has greatly advanced in the past decades, curative treatments that could bring ultimate solutions have yet to be found or developed. Effective and timely development of candidate drugs is a critical function of the availability of sensitive and accurate methodological arsenal enabling the recognition and quantification of pharmacodynamic effects. The established concept that both OP and DJD arise from an imbalance in processes of tissue formation and degradation draws attention to need of establishing in vitro, ex vivo, and in vivo experimental settings, which allow obtaining insights into the mechanisms driving increased bone and cartilage degradation at cellular, organ, and organism levels. When addressing changes in bone or cartilage turnover at the organ or organism level, monitoring tools adequately reflecting the outcome of tissue homeostasis become particularly critical. In this context, bioassays targeting the quantification of various degradation and formation products of bone and cartilage matrix elements represent a useful approach. In this review, a comprehensive overview of widely used and recently established in vitro, ex vivo, and in vivo set-ups is provided, which in many cases effectively take advantage of the potentials of biomarkers. In addition to describing and discussing the advantages and limitations of each assay and their methods of evaluation, we added experimental and clinical data illustrating the utility of biomarkers for these methodological approaches.

Propagation, expansion, and multilineage differentiation of human somatic stem cells from dermal progenitors

We isolated multipotential mesenchymal stem cells (MSC) from human postnatal dermal tissues. The isolated cells were expanded and maintained for over 100 population doublings with retention of their chromosomal complement and potential for multilineage differentiation. Progeny of cell lines established from a single dermal MSC could be differentiated into adipogenic, osteogenic, and myogenic lineages, consistent with the conclusion that we established a clonal, multipotential, somatic MSC cell line. This study is the first to show potential growth of multipotential human MSC cell lines from a single cell that can be used for the engineering of tissues in vivo. Clonal growth of MSCs presents profound implications in our understanding of differentiation and development, and should provide a valuable resource for tissue repair.

Immunogenicity of adult mesenchymal stem cells: lessons from the fetal allograft

Herein we review recent data that support host tolerance of allogeneic adult mesenchymal stem cells (MSC). Evidence is emerging that donor MSC deploy a very powerful array of mechanisms that allow escape from host allogeneic responses. These mechanisms include limited expression of alloantigen by the stem cell and cell contact-dependent and -independent mechanisms. MSC modulate host dendritic cell and T cell function, promoting induction of suppressor or regulatory T cells. These effects are complemented by the induction of divisional arrest anergy in T cells and by stem cell production of soluble immunomodulatory factors, including interleukin-10, transforming growth factor-beta, prostaglandin E2, and hepatocyte growth factor. In addition, MSC express the enzyme indoleamine 2,3-dioxygenase, which creates a tryptophan-depleted milieu that promotes immunosuppression. We propose that these observations show striking similarity to emerging data on the maternal acceptance of the fetal allograft. This comparison suggests new approaches to determine the contribution of different mechanisms to the successful use of MSC in regenerative medicine.