In vitro and in vivo induction of bone formation based on ex vivo gene therapy using rat adipose-derived adult stem cells expressing BMP-7

Exosomes from Adipose-Derived Stem Cells Alleviate Dexamethasone-Induced Bone Loss by Regulating the Nrf2/HO-1 Axis

The widespread use of therapeutic glucocorticoids has increased the incidences of glucocorticoid-induced osteoporosis (GIOP). Oxidative stress and mitochondrial dysfunction are major causes of GIOP; therefore, alleviation of excess oxidative stress in osteoblasts is a potential therapeutic strategy for osteoporosis. Exosomes derived from ADSCs (ADSCs-Exos), as novel cell-free therapeutics, can modulate various biological processes, such as immunomodulation, reduce oxidative damage, and promote tissue repair as well as regeneration. In this study, ADSCs-Exos restored the viability and osteogenic potential of MC3T3-E1 cells by attenuating apoptosis, oxidative damage, intracellular ROS generation, and mitochondrial dysfunction. Moreover, after pretreatment with ADSCs-Exos, Nrf2 expressions were upregulated in Dex-stimulated osteoblasts. Inhibitory assays showed that silencing Nrf2 partially eliminated the protective effects of ADSCs-Exos. The rat model assays confirmed that ADSCs-Exos alleviated the Dex-induced increase in oxidation levels, restored bone mass of the distal femur, and increased the expressions of Nrf2 and osteogenic markers in bone tissues. Thus, ADSCs-Exos alleviated apoptosis and oxidative stress by regulating Nrf2/HO-1 expressions after Dex and prevented the development of GIOP in vivo.

A bone-on-a-chip collagen hydrogel-based model using pre-differentiated adipose-derived stem cells for personalized bone tissue engineering

Mesenchymal stem cells have contributed to the continuous progress of tissue engineering and regenerative medicine. Adipose-derived stem cells (ADSC) possess many advantages compared to other origins including easy tissue harvesting, self-renewal potential, and fast population doubling time. As multipotent cells, they can differentiate into osteoblastic cell linages. In vitro bone models are needed to carry out an initial safety assessment in the study of novel bone regeneration therapies. We hypothesized that 3D bone-on-a-chip models containing ADSC could closely recreate the physiological bone microenvironment and promote differentiation. They represent an intermedium step between traditional 2D-in vitro and in vivo experiments facilitating the screening of therapeutic molecules while saving resources. Herein, we have differentiated ADSC for 7 and 14 days and used them to fabricate in vitro bone models by embedding the pre-differentiated cells in a 3D collagen matrix placed in a microfluidic chip. Osteogenic markers such as alkaline phosphatase activity, calcium mineralization, changes on cell morphology, and expression of specific proteins (bone sialoprotein 2, dentin matrix acidic phosphoprotein-1, and osteocalcin) were evaluated to determine cell differentiation potential and evolution. This is the first miniaturized 3D-in vitro bone model created from pre-differentiated ADSC embedded in a hydrogel collagen matrix which could be used for personalized bone tissue engineering.

Ex vivo regional gene therapy with human adipose-derived stem cells for bone repair

BACKGROUND

The treatment of complex bone loss scenarios remains challenging. This study evaluates the efficacy of ex vivo regional gene therapy using transduced human adipose-derived stem cells (ASCs) overexpressing bone morphogenetic protein-2 (BMP-2) to treat critical-sized bone defects.

METHODS

Critical-sized femoral defects created surgically in immunocompromised rats were treated with ASCs transduced with a lentivirus encoding BMP-2 (Group 1, n = 14), or green fluorescent protein (Group 2, n = 5), nontransduced ASCs (Group 3, n = 5), or rhBMP-2 (Group 4, n = 14). At 12 weeks, femurs were evaluated for quantity and quality of bone formation with plain radiographs, micro-computed tomography, histology/histomorphometry, and biomechanical strength testing.

RESULTS

Thirteen of 14 samples in Group 1 and all 14 samples in Group 4 showed radiographic healing, while no samples in either Groups 2 or 3 healed. Groups 1 and 4 had significantly higher radiographic scores (p < 0.001), bone volume fraction (BV/TV) (p < 0.001), and bone area fraction (BA/TA) than Groups 2 and 3 (p < 0.001). Radiographic scores, BV/TV, and BA/TA were not significantly different between Groups 1 and 4. No difference with regards to mean torque, rotation at failure, torsional stiffness, and energy to failure was seen between Groups 1 and 4.

CONCLUSIONS

Human ASCs modified to overexpress BMP-2 resulted in abundant bone formation, with the quality of bone comparable to that of rhBMP-2. This strategy represents a promising approach in the treatment of large bone defects in the clinical setting.

CLINICAL RELEVANCE

Large bone defects may require sustained protein production to induce an appropriate osteoinductive response. Ex vivo regional gene therapy using a lentiviral vector has the potential to be part of a comprehensive tissue engineering strategy for treating osseous defects.

The effect of combination therapy on critical-size bone defects using non-activated platelet-rich plasma and adipose-derived stem cells

PURPOSE

Non-activated platelet-rich plasma (nPRP) slowly releases growth factors that induce bone regeneration. Adipose tissue-derived stem cells (ASCs) are also known to induce osteoblast differentiation. In this study, we investigated the combined effect of nPRP and ASC treatment compared with single therapy on bone regeneration.

METHODS

Thirty New Zealand white rabbits with 15 × 15 mm² calvarial defects were randomly divided into four treatment groups: control, nPRP, ASC, or nPRP + ASC groups. For treatment, rabbits received a collagen sponge (Gelfoam®) saturated with 1 ml normal saline (controls), 1 ml non-activated PRP (nPRP group), 2 × 10⁶ ASCs (ASCs group), or 2 × 10⁶ ASCs plus l ml nPRP (nPRP + ASCs group). After 16 weeks, bone volume and new bone surface area were measured, using three-dimensional computed tomography and digital photography. Bone regeneration was also histologically analyzed.

RESULTS

Bone surface area in the nPRP group was significantly higher than both the control and ASC groups (p < 0.001 and p < 0.01, respectively). The percentage of regenerated bone surface area in the nPRP + ASC group was also significantly higher than the corresponding ratios in the control group (p < 0.001). The volume of new bone in the nPRP group was increased compared to the controls (p < 0.05).

CONCLUSION

Our results demonstrate that slow-releasing growth factors from nPRP did not influence ASC activation in this model of bone healing. PRP activation is important for the success of combination therapy using nPRP and ASCs.

Healing of Bone Defects in Pig's Femur Using Mesenchymal Cells Originated from the Sinus Membrane with Different Scaffolds

Objective

Repairing bone defects, especially in older individuals with limited regenerative capacity, is still a big challenge. The use of biomimetic materials that can enhance the restoration of bone structure represents a promising clinical approach. In this study, we evaluated ectopic bone formation after the transplantation of human maxillary Schneiderian sinus membrane- (hMSSM-) derived cells embedded within various scaffolds in the femur of pigs.

Methods

The scaffolds used were collagen, gelatin, and hydroxyapatite/tricalcium phosphate (HA/βTCP) where fibrin/thrombin was used as a control. Histological analysis was performed for the new bone formation. Quantitative real-time PCR (qRT-PCR) and immunohistochemistry (IHC) were used to assess mRNA and protein levels of specific osteoblastic markers, respectively.

Results

Histological analysis showed that the three scaffolds we used can support new bone formation with a more pronounced effect observed in the case of the gelatin scaffold. In addition, mRNA levels of the different tested osteoblastic markers Runt-Related Transcription Factor 2 (RUNX-2), osteonectin (ON), osteocalcin (OCN), osteopontin (OPN), alkaline phosphatase (ALP), and type 1 collagen (COL1) were higher, after 2 and 4 weeks, in cell-embedded scaffolds than in control cells seeded within the fibrin/thrombin scaffold. Moreover, there was a very clear and differential expression of RUNX-2, OCN, and vimentin in osteocytes, osteoblasts, hMSSM-derived cells, and bone matrix. Interestingly, the osteogenic markers were more abundant, at both time points, in cell-embedded gelatin scaffold than in other scaffolds (collagen, HA/βTCP, fibrin/thrombin).

Conclusions

These results hold promise for the development of successful bone regeneration techniques using different scaffolds embedded with hMSSM-derived cells. This trial is registered with NCT02676921.

Bone defect healing is induced by collagen sponge/polyglycolic acid

We have evaluated the capability of a collagen/poly glycolic acid (PGA) scaffold in regeneration of a calvarial bone defects in rabbits. 4 bone critical size defects (CSD) were created in the calvarial bone of each rabbit. The following 4 treatment modalities were tested (1) a collagen/PGA scaffold (0.52% w/w); (2) the collagen/PGA scaffold (0.52% w/w) seeded with adipose-derived mesenchymal stem cells (AD-MSCs, 1 × 10⁶ cells per each defect); (3) AD-MSCs (1 × 10⁶ cells) no scaffold material, and (4) blank control. The rabbits were then divided into 3 random groups (of 5) and the treatment outcomes were evaluated at 4, 8 and 12 weeks. New bone formation was histologically assessed. Experimental groups were analyzed by CT scan and real-time PCR. Histological analysis of bone defects treated with collagen/PGA alone exhibited significant fibrous connective tissue formation at the 12 weeks of treatments (P ≤ 0.05). There was no significant difference between collagen/PGA alone and collagen/PGA + AD-MSCs groups. The results were confirmed by CT scan data showing healing percentages of 34.20% for the collage/PGA group alone as compared to the control group and no difference with collagen/PGA containing AD-MSCs (1 × 10⁶ cells). RT-PCR analysis also indicated no significant differences between collagen/PGA and collagen/PGA + AD-MSC groups, although both scaffold containing groups significantly express ALP and SIO rather than groups without scaffolds. Although there was no significant difference between the scaffolds containing cells with non-cellular scaffolds, our results indicated that the Collagen/PGA scaffold itself had a significant effect on wound healing as compared to the control group. Therefore, the collagen/PGA scaffold seems to be a promising candidate for research in bone regeneration.

Evaluation of the Osteogenic Potential of Different Scaffolds Embedded with Human Stem Cells Originated from Schneiderian Membrane: An In Vitro Study

BACKGROUND

Novel treatments for bone defects, particularly in patients with poor regenerative capacity, are based on bone tissue engineering strategies which include mesenchymal stem cells (MSCs), bioactive factors, and convenient scaffold supports.

OBJECTIVE

In this study, we aimed at comparing the potential for different scaffolds to induce osteogenic differentiation of human maxillary Schneiderian sinus membrane- (hMSSM-) derived cells. Methods. hMSSM-derived cells were seeded on gelatin, collagen, or Hydroxyapatite β-Tricalcium phosphate-Fibrin (Haβ-TCP-Fibrin) scaffolds. Cell viability was determined using an MTT assay. Alizarin red staining method, Alkaline phosphatase (ALP) activity assay, and quantitative real-time PCR analysis were performed to assess hMSSM-derived cells osteogenic differentiation.

RESULTS

Cell viability, calcium deposition, ALP activity, and osteoblastic markers transcription levels were most striking in gelatin scaffold-embedded hMSSM-derived cells.

CONCLUSION

Our findings suggest a promising potential for gelatin-hMSSM-derived cell construct for treating bone defects.

Gene Therapy for Bone Repair Using Human Cells: Superior Osteogenic Potential of Bone Morphogenetic Protein 2-Transduced Mesenchymal Stem Cells Derived from Adipose Tissue Compared to Bone Marrow

Ex vivo regional gene therapy strategies using animal mesenchymal stem cells genetically modified to overexpress osteoinductive growth factors have been successfully used in a variety of animal models to induce both heterotopic and orthotopic bone formation. However, in order to adapt regional gene therapy for clinical applications, it is essential to assess the osteogenic capacity of transduced human cells and choose the cell type that demonstrates the best clinical potential. Bone-marrow stem cells (BMSC) and adipose-derived stem cells (ASC) were selected in this study for in vitro evaluation, before and after transduction with a lentiviral two-step transcriptional amplification system (TSTA) overexpressing bone morphogenetic protein 2 (BMP-2; LV-TSTA-BMP-2) or green fluorescent protein (GFP; LV-TSTA-GFP). Cell growth, transduction efficiency, BMP-2 production, and osteogenic capacity were assessed. The study demonstrated that BMSC were characterized by a slower cell growth compared to ASC. Fluorescence-activated cell sorting analysis of GFP-transduced cells confirmed successful transduction with the vector and revealed an overall higher but not statistically significant transduction efficiency in ASC versus BMSC (90.2 ± 4.06% vs. 80.4 ± 8.51%, respectively; p = 0.146). Enzyme-linked immunosorbent assay confirmed abundant BMP-2 production by both cell types transduced with LV-TSTA-BMP-2, with BMP-2 production being significantly higher in ASC versus BMSC (239.5 ± 116.55 ng vs. 70.86 ± 24.7 ng; p = 0.001). Quantitative analysis of extracellular deposition of calcium (Alizarin red) and alkaline phosphatase activity showed that BMP-2-transduced cells had a higher osteogenic differentiation capacity compared to non-transduced cells. When comparing the two cell types, ASC/LV-TSTA-BMP-2 demonstrated a significantly higher mineralization potential compared to BMSC/LV-TSTA-BMP-2 7 days post transduction (p = 0.014). In conclusion, this study demonstrates that transduction with LV-TSTA-BMP-2 can significantly enhance the osteogenic potential of both human BMSC and ASC. BMP-2-treated ASC exhibited higher BMP-2 production and greater osteogenic differentiation capacity compared to BMP-2-treated BMSC. These results, along with the fact that liposuction is an easy procedure with lower donor-site morbidity compared to BM aspiration, indicate that adipose tissue might be a preferable source of MSCs to develop a regional gene therapy approach to treat difficult bone-repair scenarios.

Ectopic models for endochondral ossification: comparing pellet and alginate bead culture methods

Key aspects of native endochondral bone development and fracture healing can be mimicked in mesenchymal stem cells (MSCs) through standard in vitro chondrogenic induction. Exploiting this phenomenon has recently emerged as an attractive technique to engineer bone tissue, however, relatively little is known about the best conditions for doing so. The objective of the present study was to compare the bone-forming capacity and angiogenic induction of hypertrophic cell constructs containing human adipose-derived stem cells (hASCs) primed for chondrogenesis in two different culture systems: high-density pellets and alginate bead hydrogels. The hASC constructs were subjected to 4 weeks of identical chondrogenic induction in vitro, encapsulated in an agarose carrier, and then implanted subcutaneously in immune-compromised mice for 8 weeks to evaluate their endochondral potential. At the time of implantation, both pellets and beads expressed aggrecan and type II collagen, as well as alkaline phosphatase (ALP) and type X collagen. Interestingly, ASCs in pellets formed a matrix containing higher glycosaminoglycan and collagen contents than that in beads, and ALP activity per cell was higher in pellets. However, after 8 weeks in vivo, pellets and beads induced an equivalent volume of mineralized tissue and a comparable level of vascularization. Although osteocalcin and osteopontin-positive osteogenic tissue and new vascular growth was found within both types of constructs, all appeared to be better distributed throughout the hydrogel beads. The results of this ectopic model indicate that hydrogel culture may be an attractive alternative to cell pellets for bone tissue engineering via the endochondral pathway. Copyright © 2016 John Wiley & Sons, Ltd.

Synergistic Effects of Vascular Endothelial Growth Factor on Bone Morphogenetic Proteins Induced Bone Formation In Vivo: Influencing Factors and Future Research Directions

Vascular endothelial growth factor (VEGF) and bone morphogenetic proteins (BMPs), as key mediators in angiogenesis and osteogenesis, are used in a combined delivery manner as a novel strategy in bone tissue engineering. VEGF has the potential to enhance BMPs induced bone formation. Both gene delivery and material-based delivery systems were incorporated in previous studies to investigate the synergistic effects of VEGF and BMPs. However, their results were controversial due to variation of methods incorporated in different studies. Factors influencing the synergistic effects of VEGF on BMPs induced bone formation were identified and analyzed in this review to reduce confusion on this issue. The potential mechanisms and directions of future studies were also proposed here. Further investigating mechanisms of the synergistic effects and optimizing these influencing factors will help to generate more effective bone regeneration.

Smart scaffolds in bone tissue engineering: A systematic review of literature

AIM: To improve osteogenic differentiation and attachment of cells.

METHODS: An electronic search was conducted in PubMed from January 2004 to December 2013. Studies which performed smart modifications on conventional bone scaffold materials were included. Scaffolds with controlled release or encapsulation of bioactive molecules were not included. Experiments which did not investigate response of cells toward the scaffold (cell attachment, proliferation or osteoblastic differentiation) were excluded.

RESULTS: Among 1458 studies, 38 met the inclusion and exclusion criteria. The main scaffold varied extensively among the included studies. Smart modifications included addition of growth factors (group I-11 studies), extracellular matrix-like molecules (group II-13 studies) and nanoparticles (nano-HA) (group III-17 studies). In all groups, surface coating was the most commonly applied approach for smart modification of scaffolds. In group I, bone morphogenetic proteins were mainly used as growth factor stabilized on polycaprolactone (PCL). In group II, collagen 1 in combination with PCL, hydroxyapatite (HA) and tricalcium phosphate were the most frequent scaffolds used. In the third group, nano-HA with PCL and chitosan were used the most. As variable methods were used, a thorough and comprehensible compare between the results and approaches was unattainable.

CONCLUSION: Regarding the variability in methodology of these in vitro studies it was demonstrated that smart modification of scaffolds can improve tissue properties.

Isolation, characterization, differentiation, and application of adipose-derived stem cells

While bone marrow-derived mesenchymal stem cells are known and have been investigated for a long time, mesenchymal stem cells derived from the adipose tissue were identified as such by Zuk et al. in 2001. However, as subcutaneous fat tissue is a rich source which is much more easily accessible than bone marrow and thus can be reached by less invasive procedures, adipose-derived stem cells have moved into the research spotlight over the last 8 years.Isolation of stromal cell fractions involves centrifugation, digestion, and filtration, resulting in an adherent cell population containing mesenchymal stem cells; these can be subdivided by cell sorting and cultured under common conditions.They seem to have comparable properties to bone marrow-derived mesenchymal stem cells in their differentiation abilities as well as a favorable angiogenic and anti-inflammatory cytokine secretion profile and therefore have become widely used in tissue engineering and clinical regenerative medicine.

Adipose-derived stromal cells for osteoarticular repair: trophic function versus stem cell activity

The identification of multipotent adipose-derived stromal cells (ASC) has raised hope that tissue regeneration approaches established with bone-marrow-derived stromal cells (BMSC) can be reproduced with a cell-type that is far more accessible in large quantities. Recent detailed comparisons, however, revealed subtle functional differences between ASC and BMSC, stressing the concept of a common mesenchymal progenitor existing in a perivascular niche across all tissues. Focussing on bone and cartilage repair, this review summarises recent in vitro and in vivo studies aiming towards tissue regeneration with ASC. Advantages of good accessibility, high yield and superior growth properties are counterbalanced by an inferiority of ASC to form ectopic bone and stimulate long-bone healing along with their less pronounced osteogenic and angiogenic gene expression signature. Hence, particular emphasis is placed on establishing whether stem cell activity of ASC is so far proven and relevant for successful osteochondral regeneration, or whether trophic activity may largely determine therapeutic outcome.

The roles of bone morphogenetic proteins and their signaling in the osteogenesis of adipose-derived stem cells

Large-size bone defects can severely compromise both aesthetics and musculoskeletal functions. Adipose-derived stem cells (ASCs)-based bone tissue engineering has recently become a promising treatment strategy for the above situation. As robust osteoinductive cytokines, bone morphogenetic proteins (BMPs) are commonly used to promote the osteogenesis of ASCs. In this process, BMP signaling plays a pivotal role. However, it remains ambiguous how the pleiotrophic BMPs are involved in the commitment of ASCs along osteogenesis instead of other lineages, such as adipogenesis. BMP receptor type-IB, extracellular signal-regulated kinase, and Wnt5a appear to be the main switches controlling the in vitro osteogenic commitment of ASCs. Tumor necrosis factor-alpha, an acute inflammatory cytokine, is reported to play an important role in mediating osteogenic commitment of ASCs in vivo. In addition, various active agents and methods have been used to enhance and accelerate the osteogenesis of ASCs through promoting BMP signaling. In this review, we summarize the current knowledge on the roles of BMPs and their signaling in the osteogenesis of ASCs in vitro and in vivo.

BMP signaling in mesenchymal stem cell differentiation and bone formation

Bone morphogenetic proteins (BMPs) are members of the TGF-β superfamily and have diverse functions during development and organogenesis. BMPs play a major role in skeletal development and bone formation, and disruptions in BMP signaling cause a variety of skeletal and extraskeletal anomalies. Several knockout models have provided insight into the mechanisms responsible for these phenotypes. Proper bone formation requires the differentiation of osteoblasts from mesenchymal stem cell (MSC) precursors, a process mediated in part by BMP signaling. Multiple BMPs, including BMP2, BMP6, BMP7 and BMP9, promote osteoblastic differentiation of MSCs both in vitro and in vivo. BMP9 is one of the most osteogenic BMPs yet is a poorly characterized member of the BMP family. Several studies demonstrate that the mechanisms controlling BMP9-mediated osteogenesis differ from other osteogenic BMPs, but little is known about these specific mechanisms. Several pathways critical to BMP9-mediated osteogenesis are also important in the differentiation of other cell lineages, including adipocytes and chondrocytes. BMP9 has also demonstrated translational promise in spinal fusion and bone fracture repair. This review will summarize our current knowledge of BMP-mediated osteogenesis, with a focus on BMP9, by presenting recently completed work which may help us to further elucidate these pathways.

Repair of bone defect by using vascular bundle implantation combined with Runx II gene-transfected adipose-derived stem cells and a biodegradable matrix

A large hurdle in orthopedics today is the difficulty of dealing with the non-union of fractured bones. We therefore evaluated the effects of runt-related transcription factor II (Runx II), a factor used to create gene-modified tissue-engineered bone, combined with vascular bundle implantation for repairing segmental bone defects. Adenovirus Runx II gene (Ad-Runx II)-modified rabbit adipose-derived stem cells (ADSCs) were seeded onto polylactic acid/polycaprolacton (PLA/PCL) scaffolds to construct gene-modified tissue-engineered bone. The following four methods were used for repair in rabbit radial-defect (1.5 cm long) models: gene-modified tissue-engineered bone with vascular bundle (Group A), gene-modified tissue-engineered bone (Group B), non-gene-modified tissue-engineered bone with vascular bundle (Group C), and PLA/PCL scaffolds only (Group D). X-ray, histological examination, biomechanics analysis, and micro-angiography were conducted 4, 8, and 12 weeks later to determine angiogenesis and osteogenesis. The volume and speed of production of newly formed bones in Group A were significantly superior to those in other groups, and de-novo vascular network circulation from the vessel bundle through newly formed bone tissue was observed, with the defect being completely repaired. Group B showed a slightly better effect in terms of speed and quality of bone formation than Group C, whereas the bone defect in Group D was replaced by fibrous tissue. The maximal anti-bending strength in Group A was significantly higher than that in the other groups. Runx II gene therapy combined with vascular bundle implantation thus displays excellent abilities for osteoinduction and vascularization and is a promising method for the treatment of bone non-union and defect.

Regeneration of articular cartilage by adipose tissue derived mesenchymal stem cells: perspectives from stem cell biology and molecular medicine

Adipose-derived stem cells (ASCs) have been discovered for more than a decade. Due to the large numbers of cells that can be harvested with relatively little donor morbidity, they are considered to be an attractive alternative to bone marrow derived mesenchymal stem cells. Consequently, isolation and differentiation of ASCs draw great attention in the research of tissue engineering and regenerative medicine. Cartilage defects cause big therapeutic problems because of their low self-repair capacity. Application of ASCs in cartilage regeneration gives hope to treat cartilage defects with autologous stem cells. In recent years, a lot of studies have been performed to test the possibility of using ASCs to re-construct damaged cartilage tissue. In this article, we have reviewed the most up-to-date articles utilizing ASCs for cartilage regeneration in basic and translational research. Our topic covers differentiation of adipose tissue derived mesenchymal stem cells into chondrocytes, increased cartilage formation by co-culture of ASCs with chondrocytes and enhancing chondrogenic differentiation of ASCs by gene manipulation.

Adipose-Derived Stem Cells in Tissue Regeneration: A Review

In 2001, researchers at the University of California, Los Angeles, described the isolation of a new population of adult stem cells from liposuctioned adipose tissue. These stem cells, now known as adipose-derived stem cells or ADSCs, have gone on to become one of the most popular adult stem cells populations in the fields of stem cell research and regenerative medicine. As of today, thousands of research and clinical articles have been published using ASCs, describing their possible pluripotency in vitro, their uses in regenerative animal models, and their application to the clinic. This paper outlines the progress made in the ASC field since their initial description in 2001, describing their mesodermal, ectodermal, and endodermal potentials both in vitro and in vivo, their use in mediating inflammation and vascularization during tissue regeneration, and their potential for reprogramming into induced pluripotent cells.

Cell-mediated and direct gene therapy for bone regeneration

INTRODUCTION

Bone regeneration is required for the treatment of fracture non/delayed-unions and bone defects. However, most current treatment modalities have limited efficacy, and newer therapeutic strategies, such as gene therapy, have substantial benefit for bone repair and regeneration.

AREAS COVERED

This review discusses experimental and clinical applications of cell-mediated and direct gene therapy for bone regeneration. The review covers literature on this subject from 2000 to February 2012.

EXPERT OPINION

Direct gene therapy using various viral and non-viral vectors of cell-mediated genes has been demonstrated to induce bone regeneration, although use of such vectors has shown some risk in human application. Osteoinductive capability of a number of progenitor cells isolated from bone marrow, fat, muscle and skin tissues, has been demonstrated by genetic modification with osteogenic genes. Cell-mediated gene therapy using such osteogenic gene-expressing progenitor cells has shown promising results in promoting bone regeneration in extensive animal work in recent years.

Nanostructured biomaterials for tissue engineered bone tissue reconstruction

Bone tissue engineering strategies are emerging as attractive alternatives to autografts and allografts in bone tissue reconstruction, in particular thanks to their association with nanotechnologies. Nanostructured biomaterials, indeed, mimic the extracellular matrix (ECM) of the natural bone, creating an artificial microenvironment that promotes cell adhesion, proliferation and differentiation. At the same time, the possibility to easily isolate mesenchymal stem cells (MSCs) from different adult tissues together with their multi-lineage differentiation potential makes them an interesting tool in the field of bone tissue engineering. This review gives an overview of the most promising nanostructured biomaterials, used alone or in combination with MSCs, which could in future be employed as bone substitutes. Recent works indicate that composite scaffolds made of ceramics/metals or ceramics/polymers are undoubtedly more effective than the single counterparts in terms of osteoconductivity, osteogenicity and osteoinductivity. A better understanding of the interactions between MSCs and nanostructured biomaterials will surely contribute to the progress of bone tissue engineering.

Different populations and sources of human mesenchymal stem cells (MSC): A comparison of adult and neonatal tissue-derived MSC

The mesenchymal stroma harbors an important population of cells that possess stem cell-like characteristics including self renewal and differentiation capacities and can be derived from a variety of different sources. These multipotent mesenchymal stem cells (MSC) can be found in nearly all tissues and are mostly located in perivascular niches. MSC have migratory abilities and can secrete protective factors and act as a primary matrix for tissue regeneration during inflammation, tissue injuries and certain cancers.These functions underlie the important physiological roles of MSC and underscore a significant potential for the clinical use of distinct populations from the various tissues. MSC derived from different adult (adipose tissue, peripheral blood, bone marrow) and neonatal tissues (particular parts of the placenta and umbilical cord) are therefore compared in this mini-review with respect to their cell biological properties, surface marker expression and proliferative capacities. In addition, several MSC functions including in vitro and in vivo differentiation capacities within a variety of lineages and immune-modulatory properties are highlighted. Differences in the extracellular milieu such as the presence of interacting neighbouring cell populations, exposure to proteases or a hypoxic microenvironment contribute to functional developments within MSC populations originating from different tissues, and intracellular conditions such as the expression levels of certain micro RNAs can additionally balance MSC function and fate.

Strategies for organ level tissue engineering

The field of tissue engineering has made considerable strides since it was first described in the late 1980s. The advent and subsequent boom in stem cell biology, emergence of novel technologies for biomaterial development and further understanding of developmental biology have contributed to this accelerated progress. However, continued efforts to translate tissue-engineering strategies into clinical therapies have been hampered by the problems associated with scaling up laboratory methods to produce large, complex tissues. The significant challenges faced by tissue engineers include the production of an intact vasculature within a tissue-engineered construct and recapitulation of the size and complexity of a whole organ. Here we review the basic components necessary for bioengineering organs-biomaterials, cells and bioactive molecules-and discuss various approaches for augmenting these principles to achieve organ level tissue engineering. Ultimately, the successful translation of tissue-engineered constructs into everyday clinical practice will depend upon the ability of the tissue engineer to "scale up" every aspect of the research and development process.

Adipose-derived stem cells in functional bone tissue engineering: lessons from bone mechanobiology

This review aims to highlight the current and significant work in the use of adipose-derived stem cells (ASC) in functional bone tissue engineering framed through the bone mechanobiology perspective. Over a century of work on the principles of bone mechanosensitivity is now being applied to our understanding of bone development. We are just beginning to harness that potential using stem cells in bone tissue engineering. ASC are the primary focus of this review due to their abundance and relative ease of accessibility for autologous procedures. This article outlines the current knowledge base in bone mechanobiology to investigate how the knowledge from this area has been applied to the various stem cell-based approaches to engineering bone tissue constructs. Specific emphasis is placed on the use of human ASC for this application.

Viral transduction of adipose-derived stem cells

Increasing numbers of regenerative approaches now involve use of adult stem cells, like the bone marrow MSC or the adipose-derived ASC. With their ease of in vitro manipulation and successful tissue integration in vivo, the ASC makes an attractive candidate for gene delivery in vivo using viral-based gene therapy strategies. As such, this chapter describes methods for the transduction of human ASCs with two popular types of recombinant viruses: adenovirus and lentivirus.

Enhancement of bone formation by BMP-7 transduced MSCs on biomimetic nano-hydroxyapatite/polyamide composite scaffolds in repair of mandibular defects

This study was to evaluate enhanced bone formation by bone morphogenetic protein-7 (BMP-7) transduced MSCs on nano-hydroxyapatite/polyamide (n-HA/PA) composite scaffolds for bone tissue engineering in repair of mandibular defect. n-HA/PA scaffolds were prepared and rabbit MSCs were separated and expanded; and then infected with adenoviral-mediated BMP-7 in vitro. The MSCs-BMP-7 and MSCs were seeded on the porous scaffolds. Scaffold/MSCs-BMP-7 constructs and scaffold/MSCs constructs were implanted in the defects of rabbits' mandible as the experimental groups A (n = 18) and groups B (n = 18), respectively, the pure scaffolds were implanted as controls (group C, n = 18). Six animals were sacrificed at 4-, 8-, and 16-week postimplantation, respectively. Their mandibles were removed and processed for radiographic, biomechanical tests, histological, and histomorphometric analysis. Group A animals showed greater bone formation and earlier mineralization than group B at 4- and 8-week postimplantation and similarly group B more than group C. However, no difference was found among three groups at 16-week postimplantation. The results of this study suggest that BMP-7 transduced MSCs-n-HA/PA composite could significantly accelerate bone formation in the implant at early stage. BMP-7 mediated ex vivo gene transfer based on MSCs as seed cells, combined with porous n-HA/PA as scaffolds for bone tissue engineering might be an alternative or supplemental approach to repair the mandibular defects.

The effect of type I collagen on osteochondrogenic differentiation in adipose-derived stromal cells in vivo

BACKGROUND

Recent studies have demonstrated that adipose-derived adult stromal cells (ADASCs) offer great promise for cell-based therapies due to their ability to differentiate towards bone, cartilage and fat [corrected] The objective of this study was to investigate whether type I collagen would elicit in vivo bone formation of passaged rat adipose-derived adult stromal cells (ADASC) placed extraskeletally.

METHODS

After expansion for 1-4 passages (P), cells were incubated in osteogenic medium containing dexamethasone, ascorbic acid and beta-glycerol phosphate for 2-4 weeks. Undifferentiated cells were maintained in Dulbecco's modified Eagle's medium (DMEM) with 10% fetal bovine serum (FBS). Osteogenic differentiation was evaluated by alkaline phosphatase (ALP) and von Kossa staining as well as by gene expression of ALP, osteopontin (OP), osteonectin (ON), osteocalcin (OC), collagen I (colI), collagen II (colII), bone sialoprotein (BSP), periostin (Postn), runx2, osterix (Osx), sox9, msx1 and msx2. Diffusion chambers were filled with 1x10(6) cells mixed with or without type I collagen gel and implanted subcutaneously into rats. Controls included chambers exposed to (1) undifferentiated cells (with or without collagen, (2) collagen without cells and (3) empty chambers (n=5 per group).

RESULTS

Four weeks after implantation, in vivo bone and cartilage formation was demonstrated in implants containing 4-week osteo-induced P1 and P4 cells wrapped in the collagen gel, as confirmed by Goldner's trichrome and Alcian blue staining, respectively. Newly formed bone stained positive for type I collagen. Control implants had no bone or cartilage and were primarily filled with fibrous tissue at that time interval.

DISCUSSION

Recent studies have demonstrated that ADASC offer great promise for cell-based therapies because of their ability to differentiate toward bone, cartilage and fat. However, the influence of different matrices on the in vivo osteogenic capability of ADASC is not fully understood. These findings suggest that type I collagen may support the survival and expression of osteogenic and chondrogenic phenotypes in passaged rat ADASC in vivo.

Ex vivo-transduced autologous skin fibroblasts expressing human Lim mineralization protein-3 efficiently form new bone in animal models

Local gene transfer of the human Lim mineralization protein (LMP), a novel intracellular positive regulator of the osteoblast differentiation program, can induce efficient bone formation in rodents. To develop a clinically relevant gene therapy approach to facilitate bone healing, we have used primary dermal fibroblasts transduced ex vivo with Ad.LMP-3 and seeded on a hydroxyapatite/collagen matrix prior to autologous implantation. Here, we demonstrate that genetically modified autologous dermal fibroblasts expressing Ad.LMP-3 are able to induce ectopic bone formation following implantation of the matrix into mouse triceps and paravertebral muscles. Moreover, implantation of the Ad.LMP-3-modified dermal fibroblasts into a rat mandibular bone critical size defect model results in efficient healing, as determined by X-rays, histology and three-dimensional microcomputed tomography (3DmuCT). These results demonstrate the effectiveness of the non-secreted intracellular osteogenic factor LMP-3 in inducing bone formation in vivo. Moreover, the utilization of autologous dermal fibroblasts implanted on a biomaterial represents a promising approach for possible future clinical applications aimed at inducing new bone formation.

Leporine-derived adipose precursor cells exhibit in vitro osteogenic potential

Adipose-derived stem cells (ASCs) possess osteogenic potential and have been shown to undergo in vitro osteoblastic differentiation and promote bone regeneration in vivo. In this study, we describe the isolation and osteoblastic differentiation of rabbit ASCs and their behavior on a gelatin foam scaffold. These studies will form the basis of future in vivo studies of the osteogenic potential of rabbit ASCs for calvarial defect repair.Adipose-derived stem cells were isolated from New Zealand White rabbits and cultured in osteogenic medium +/- bone morphogenetic protein 2. Osteoblastic differentiation was assessed via histochemical stains for alkaline phosphatase (AP) and extracellular matrix (ECM) calcification. Reverse transcriptase polymerase chain reaction was performed to evaluate the expression of AP and the osteogenic transcription factor Runx2. Adipose-derived stem cells were seeded onto gelatin foam scaffolds at various densities, and cell proliferation was measured fluorometrically. Cells isolated from rabbit adipose tissue exhibited classic ASC morphology. Adipose-derived stem cells cultured in osteogenic medium exhibited more robust staining for AP and ECM calcification compared with ASCs in control medium. Furthermore, this staining was more marked in male ASCs versus female ASCs and also enhanced by bone morphogenetic protein 2. mRNA for AP and Runx2 were also increased in the osteoinduced cells. Theoptimal seeding density was 1 x 10 ASCs on an 8-mm gelatin foam scaffold. We have shown that rabbit ASCs have in vitro osteogenic potential and are compatible with a gelatin foam scaffold. Characteristic features of osteoblasts, such as ECM mineralization and expression of osteogenic genes, were demonstrated in this cell population. In vitro osteoblastic differentiation and scaffold studies are necessary before in vivo trials. The mechanism underlying the sex-based variation in osteoblastic differentiation is unknown but may involve signaling via factors such as estrogen.

Tissue engineering craniofacial defects with adult stem cells? Are we ready yet?

Over three-quarters of all craniofacial defects observed in the US per year are cleft palates. Usually involving significant bony defects in both the hard palate and alveolar process of the maxilla, repair of these defects is typically performed surgically using autologous bone grafts taken from appropriate sites (i.e., iliac crest). However, surgical intervention is not without its complications. As such, the reconstructive surgeon has turned to the scientist and engineer for help. In this review, the application of the field of tissue engineering to craniofacial defects (e.g., cleft palates) is discussed. Specifically the use of adult stem cells, such as mesenchymal stem cells from bone marrow and Adipose-derived Stem Cells (ASCs) in combination with currently available biomaterials is presented in the context of healing craniofacial defects like the cleft palate. Finally, future directions with regards to the use of ASCs in craniofacial repair are discussed, including possible scaffold-driven and gene-driven approaches.

Stem cells from human fat as cellular delivery vehicles in an athymic rat posterolateral spine fusion model

BACKGROUND

Mesenchymal stem cells derived from human liposuction aspirates, termed processed lipoaspirate cells, have been utilized as cellular delivery vehicles for the induction of bone formation in tissue engineering and gene therapy strategies. In this study, we sought to evaluate the efficacy of bone morphogenetic protein (BMP)-2-producing adipose-derived stem cells in inducing a posterolateral spine fusion in an athymic rat model.

METHODS

Single-level (L4-L5) intertransverse spinal arthrodesis was attempted with use of a type-I collagen matrix in five groups of athymic rats, with eight animals in each group. Group I was treated with 5 x 10(6) adipose-derived stem cells transduced with an adenoviral vector containing the BMP-2 gene; group II, with 5 x 10(6) adipose-derived stem cells treated with osteogenic media and 1 microg/mL of recombinant BMP-2 (rhBMP-2); group III, with 10 microg of rhBMP-2; group IV, with 1 microg of rhBMP-2; and group V, with 5 x 10(6) adipose-derived stem cells alone. The animals that showed radiographic evidence of healing were killed four weeks after cell implantation and were examined with plain radiographs, manual palpation, microcomputed tomography scanning, and histological analysis.

RESULTS

All eight animals in group I demonstrated successful spinal fusion, with a large fusion mass, four weeks postoperatively. Furthermore, group-I specimens consistently revealed spinal fusion at the cephalad level (L3 and L4), where no fusion bed had been prepared surgically. In contrast, despite substantial BMP-2 production measured in vitro, group-II animals demonstrated minimal bone formation even eight weeks after implantation. Of the groups treated with the application of rhBMP-2 alone, the one that received a relatively high dose (group III) had a higher rate of fusion (seen in all eight specimens) than the one that received the low dose (group IV, in which fusion was seen in four of the eight specimens). None of the group-V animals (treated with adipose-derived stem cells alone) demonstrated successful spine fusion eight weeks after the surgery.

CONCLUSIONS

Adipose-derived stem cells show promise as gene transduction targets for inducing bone formation to enhance spinal fusion in biologically stringent environments.

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.

Nonunions and the potential of stem cells in fracture-healing

Recent progress in human embryonic and adult stem cell research is a cause for much enthusiasm in bone and joint surgery. Stem cells have therapeutic potential in the realm of orthopaedic surgery because of their capacity to self-renew and differentiate into various types of mature cells and tissues, including bone. Because nonunions remain a clinically important problem, there is interest in the use of cell-based strategies to augment fracture repair. Such strategies are being investigated with variations in the model systems, sources of stem cells, and methods for the application and enhancement of osseous healing, including genetic modifications and tissue-engineering. This review highlights the recent progress in the utilization of stem cells and cell-based gene therapy in promoting fracture-healing and its potential utility in the clinical setting.

In vitro and in vivo induction of bone formation based on adeno-associated virus-mediated BMP-7 gene therapy using human adipose-derived mesenchymal stem cells

AIM

To determine whether adeno-associated virus (AAV)-2-mediated, bone morphogenetic protein (BMP)-7-expressing human adipose-derived mesenchymal stem cells (ADMS) cells would induce bone formation in vitro and in vivo.

METHODS

ADMS cells were harvested from patients undergoing selective suction-assisted lipectomy and transduced with AAV carrying the human BMP-7 gene. Non-transduced cells and cells transduced with AAV serotype 2 carrying the enhanced green fluorescence protein gene served as controls. ADMS cells were qualitatively assessed for the production of BMP-7 and osteocalcin, and subjected to alkaline phosphatase (ALP) and Chinalizarin staining. A total of 2.5 x 10(6) cells mixed with type I collagen were implanted into the hind limb of severe combined immune-deficient (SCID) mice and subjected to a histological analysis 3 weeks post implantation.

RESULTS

Transfection of the ADMS cells achieved an efficiency of 99% at d 7. Transduction with AAV2-BMP-7 induced the expression of BMP-7 until d 56, which was markedly increased by d 7. The cells were positively stained for ALP. Osteocalcin production and matrix mineralization further confirmed that these cells differentiated into osteoblasts and induced bone formation in vitro. A histological examination demonstrated that implantation of BMP-7-expressing ADMS cells could induce new bone formation in vivo.

CONCLUSION

The present in vitro and in vivo study demonstrated that human ADMS cells would be a promising source of autologous mesenchymal stem cells for BMP gene therapy and tissue engineering.

Gene therapy used for tissue engineering applications

This review highlights the advances at the interface between tissue engineering and gene therapy. There are a large number of reports on gene therapy in tissue engineering, and these cover a huge range of different engineered tissues, different vectors, scaffolds and methodology. The review considers separately in-vitro and in-vivo gene transfer methods. The in-vivo gene transfer method is described first, using either viral or non-viral vectors to repair various tissues with and without the use of scaffolds. The use of a scaffold can overcome some of the challenges associated with delivery by direct injection. The ex-vivo method is described in the second half of the review. Attempts have been made to use this therapy for bone, cartilage, wound, urothelial, nerve tissue regeneration and for treating diabetes using viral or non-viral vectors. Again porous polymers can be used as scaffolds for cell transplantation. There are as yet few comparisons between these many different variables to show which is the best for any particular application. With few exceptions, all of the results were positive in showing some gene expression and some consequent effect on tissue growth and remodelling. Some of the principal advantages and disadvantages of various methods are discussed.

Neuron-like differentiation of adipose tissue-derived stromal cells and vascular smooth muscle cells

Adipose tissue-derived stromal cells (ADSC) have previously been shown to possess stem cell properties such as transdifferentiation and self-renewal. Because future clinical applications are likely to use these adult stem cells in an autologous fashion, we wished to establish and characterize rat ADSC for pre-clinical tests. In the present study, we showed that rat ADSC expressed stem cell markers CD34 and STRO-1 at passage 1 but only STRO-1 at passage 3. These cells could also be induced to differentiate into adipocytes, smooth muscle cells, and neuron-like cells, the latter of which expressed neuronal markers S100, nestin, and NF70. Isobutylmethylxanthine (IBMX), indomethacin (INDO), and insulin were the active ingredients in a previously established neural induction medium (NIM); however, here we showed that IBMX alone was as effective as NIM in the induction of morphological changes as well as neuronal marker expression. Finally, we showed that vascular smooth muscle cells could also be induced by either NIM or IBMX to differentiate into neuron-like cells that expressed NF70.

Rat adipose-derived stromal cells expressing BMP4 induce ectopic bone formation in vitro and in vivo

AIM

Bone morphogenetic protein 4 (BMP4) is one of the main local contributing factors in callus formation in the early phase of fracture healing. Adipose-derived stromal cells (ADSC) are multipotent cells. The present study was conducted to investigate the osteogenic potential of ADSC when exposed to adenovirus containing BMP4 cDNA (Ad-BMP4).

METHODS

ADSC were harvested from Sprague-Dawley rats. After exposure to Ad-BMP4, ADSC were assessed by alkaline phosphatase activity (ALP) assay, RT-PCR and von Kossa staining. BMP4 expression was assessed by RT-PCR, immunofluorescence and Western blot analysis. ADSC transduced with Ad-BMP4 were directly injected into the hind limb muscles of athymic mice. ADSC Ad-EGFP(enhanced green fluorescence protein) served as controls. All animals were examined by X-ray film and histological analysis.

RESULTS

The expression of BMP4 was confirmed at both mRNA and protein levels. The expression of the osteoblastic gene, ALP activity and von Kossa staining confirmed that ADSC transduced with Ad-BMP4 underwent rapid and marked osteoblast differentiation, whereas ADSC transduced with Ad-EGFP and cells left alone displayed no osteogenic differentiation. X-ray and histological examination confirmed new bone formation in athymic mice transplanted with ADSC transduced with Ad-BMP4.

CONCLUSION

Our data demonstrated successful osteogenic differentiation of ADSC transduced with Ad-BMP4 in vitro and in vivo. ADSC may be an ideal source of mesenchyme lineage stem cells for gene therapy and tissue engineering.

Historic and current strategies in bone tissue engineering: do we have a hope in Hench?

Professors Larry Hench and Julia Polak formed the Tissue Engineering and Regenerative Medicine Centre (TERM) at Imperial College London to foster collaborations between biologists and materials scientists. Early work at the center elucidated the biomolecular interactions between primary human osteoblasts and 45S5 Bioglass . As research efforts expanded, the team discovered that the dissolution products of both 45S5 Bioglass and 58S sol-gel bioactive glasses had osteoblastic stimulatory properties. To address the shortage of appropriate cells for bone tissue engineering applications, TERM scientists also demonstrated the differentiation of embryonic stem (ES) cells to osteoblasts when treated with the dissolution products of bioactive glasses. They also found that the soluble factors ascorbic acid, beta -glycerophosphate, and dexamethasone preferentially differentiated ES cells to osteoblasts, and their combination with the dissolution products of bioactive glasses stimulated differentiation even further. Taken together, these results demonstrate the suitability of bioactive glasses as scaffolds for bone tissue engineering as they not only provide an osteoconductive and osteoproductive substrate, but also actively stimulate cells to express appropriate osteoblastic phenotypes. Professor Hench's vision to pioneer regenerative medicine research continues with the aim of developing novel therapeutics to treat musculoskeletal disability.

The osteogenic potential of adipose-derived stem cells for the repair of rabbit calvarial defects

INTRODUCTION

Bone replacement is often necessary during reconstruction of craniofacial anomalies or trauma. Adipose-derived stem cells (ASCs) possess osteogenic potential and are a promising cell source for bone tissue engineering. The present study was designed to assess the osteogenic potential and utility of using ASCs to regenerate bone in a rabbit calvarial defect model.

METHODS

Rabbit ASCs were seeded on gelatin foam (GF) scaffolds and induced in osteogenic medium containing bone morphogenetic protein (BMP)-2. Thirty-four 8-mm calvarial defects were randomly treated with autograft, no treatment, GF scaffold, GF + ASCs, or GF + osteoinduced ASCs. After 6 weeks, calvaria were harvested and underwent histologic and radiologic analyses to compare healing between the treatment groups.

RESULTS

Defects treated with autograft underwent complete healing. Radiologically, there were no significant (P > 0.05) differences in healing among empty defects, and those treated with GF alone or GF plus osteoinduced ASCs. Osteoinduced ASCs exhibited significantly (P < 0.05) greater healing than noninduced ASCs.

CONCLUSION

Preimplantation osteoinduction of ASCs enhances their osteogenic capacity. Lack of a significant osteogenic effect of ASCs on calvarial healing at 6 weeks may be secondary to use of noncritical-sized defects. Larger defects would likely demonstrate the osteogenic potential of ASCs more definitively.

Regeneration of intervertebral disc by mesenchymal stem cells: potentials, limitations, and future direction

Over the past few years, substantial progress has been made in the field of stem cell regeneration of the intervertebral disc. Autogenic mesenchymal stem cells in animal models can arrest intervertebral disc degeneration or even partially regenerate it and the effect is suggested to be dependent on the severity of degeneration. Mesenchymal stem cells (MSCs) are able to escape alloantigen recognition which is an advantage for allogenic transplantation. A number of injectable scaffolds have been described and various methods to pre-modulate MSCs' activity have been tested. In future, work will need to address the use of mesenchymal stem cells in large animal models and the fate of the implanted mesenchymal stem cells, particularly in the long term, in animals. This review examines the state-of-the-art in the field of stem cell regeneration of the intervertebral disc, and critically discusses, with scientific support, the issues involved, before stem cells could be used in human subjects.

[Role of gene therapy in trauma and orthopedic surgery]

Modern molecular and genetic technologies enable the modification of a cellular genome through transfer of specific genes. The various procedures alter specific cell functions, which allow the transfected cell to produce any encoded transgene information. The transfected cell then synthesizes proteins that are normally not produced or only in very small amounts. Numerous animal studies have demonstrated that gene therapy may support and accelerate the healing and regeneration of specific tissues such as skin, tendons, cartilage, and bones. Currently, further animal studies are evaluating new vectors with reduced immunogenicity in the continuous effort to improve the efficacy and safety of gene transfer. In the forthcoming decade we expect gene therapy to have an important influence on the treatment of fractures, cartilage lesions, and infection.

Pluripotency potential of human adipose-derived stem cells marked with exogenous green fluorescent protein

Musculoskeletal tissues regeneration requires rapid expansion of seeding cells both in vitro and in vivo while maintaining their multilineage differentiation ability. Human adipose-derived stem cells (ASCs) are considered to contain multipotent mesenchymal stem cells. Monolayer cultures of human ASCs were isolated from human lipoaspirates and passaged 3 times and then infected with replication-incompetent adenoviral vectors carrying green fluorescent protein (Ad/GFP) genes. Then, Ad/GFP infected human ASCs were transferred to osteogenic, chondrogenic, adipogenic, and myogenic medium. The morphological characterization of induced cells was observed using phase-contrast microscopy and fluorescence microscopy. The expression of marker proteins or genes was measured by immunocytochemical and RT-PCR analysis. Osteopontin (OPN), and osteocalcin (OCN) were positive in osteogenic lineages, aggrecan and SOX9 were positive in chondrogenic ones, peroxisome proliferator-activated receptor (PPAR-gamma2) and lipoprotein lipase (LPL) were positive in adipogenic ones, and myogenin and myod1 was positive in myogenic ones. At the same time, the results of fluorescence microscopic imaging proved that the high level of GFP expression during ASCs differentiation maintained stable nearly 2 months. So the exogenous GFP and multilineage potential of human ASCs had no severe influences on each other. Since the human ASCs can be easily obtained and abundant, it is proposed that they may be promising candidate cells for further studies on tissue engineering. Imaging with expression of GFP facilitates the research on ASCs physiological behavior and application in tissue engineering during differentiation both in vitro and in vivo.