Applications of gene therapy and adult stem cells in bone bioengineering

Improvement of bone defect healing in rats via mesenchymal stem cell supernatant

The effects of mesenchymal stem cells (MSCs) from three different sources in the treatment of bone defect with stem cells, and the differences of curative effects were studied. The umbilical cord, adipose and bone marrow mesen-chymal stem cells (BMSCs) of Sprague-Dawley (SD) rats were isolated and extracted, and the phenotype was identified for the 4th generation. The SD rat model of bone defect was established. The rats were randomly divided into: Normal saline group, umbilical cord mesenchymal stem cell (UMSC) group, adipose mesenchymal stem cell (AMSC) group and BMSC group. Rats were treated with tail intravenous injection, followed by radiological examination. The relative expression levels of factors bone morphogenetic protein-2 (BMP-2), osteocalcin (OCN), alkaline phosphatase (ALP), sclerostin (SOST), collagen carboxy-terminal telopeptide (CTX) and tartrated resistant acid phosphatase (TRACP) were measured via fluorescence quantitative PCR and western blotting. Among the three different kinds of stem cell supernatant, the detection using bicinchoninic acid (BCA) method showed that the content of P4-generation new cytokines was the highest. Wound healing in the three stem cell supernatant groups was significant at 3 weeks after operation, which was faster than that in DF12 control group; the expression levels of BMP-2, OCN and ALP in the bone samples treated with three kinds of MSC supernatants after 5 weeks were significantly increased compared with those in control group. The expression levels of SOST, CTX and TRACP were significantly decreased compared with those in control group. Three kinds of MSC supernatants can promote the bone regeneration through promoting the secretion of relatively more osteoblast factors, and inhibit the bone loss. The concentration of cytokines in UMSC supernatant was the highest under the same culture condition, and BMSC supernatant has a better effect in improving the bone defect repair of rats under the same concentration of cytokines.

Updates in biological therapies for knee injuries: bone

Bone is a unique tissue because of its mechanical properties, ability for self-repair, and enrollment in different metabolic processes such as calcium homeostasis and hematopoietic cell production. Bone barely tolerates deformation and tends to fail when overloaded. Fracture healing is a complex process that in particular cases is impaired. Osteoprogenitor cells proliferation, growth factors, and a sound tridimensional scaffold at fracture site are key elements for new bone formation and deposition. Mechanical stability and ample vascularity are also of great importance on providing a proper environment for bone healing. From mesenchymal stem cells delivery to custom-made synthetic scaffolds, many are the biological attempts to enhance bone healing. Impaired fracture healing represents a real burden to contemporary society. Sound basic science knowledge has contributed to newer approaches aimed to accelerate and improve the quality of bone healing.

Hypoxia induces osteogenesis in rabbit adipose-derived stem cells overexpressing bone morphogenic protein-2

OBJECTIVE

Hypoxic culture potentiates mesenchymal stem cells (MSCs) to survive and secrete various growth factors. Genetically modified stem cells overexpressing bone morphogenic protein-2 (BMP-2) demonstrate strong osteogenic ability. Hence, we investigated the coeffect of hypoxic culture conditions and BMP-2 overexpression on the osteogenic ability of rabbit adipose-derived stem cells (rASCs) in vitro.

MATERIALS AND METHODS

Rabbit adipose-derived stem cells with or without adenoviral-BMP-2 transduction were cultured in hypoxic (1%) and normoxic (21%) conditions. Cell viability, attachment, and proliferation were compared. Real-time PCR amplification of osteogenic and angiogenic genes including alkaline phosphatase (ALP), osteocalcin (OCN), HIF-1α, and vascular endothelial growth factor (VEGF) was performed. Moreover, ALP activity, immunofluorescent staining of OCN, and mineralization assay by alizarin red S quantification and von Kossa staining were conducted.

RESULTS

Cells under hypoxic conditions attached better within 12 h and proliferated faster. While BMP-2 overexpression and hypoxic condition separately elevated the transcription of key osteogenic and angiogenic genes, a cooperative effect was observed to enhance the upregulation of osteogenic as well as angiogenic genes. Identical changes were observed in ALP activity, immunofluorescent staining of OCN, and mineralization assay.

CONCLUSIONS

Hypoxic culture can enhance the osteogenic ability of BMP-2 gene-modified rASCs, which provides a strategy to improve the osteogenesis of rASCs for in vivo bone regeneration.

Achievements during the Bone and Joint Decade 2000-2010

Musculoskeletal diseases continue to produce major disability around the world. Advances in therapy - particularly for the inflammatory diseases - have the potential to eradicate the inflammation and thus prevent joint destruction. Surgical advances include minimally invasive and computer-assisted robotic surgery, and advances in arthroscopic surgery. The development of new musculoskeletal tissues - tendons, cartilage and bone using nanotechnology and stem cells - has the potential to revolutionise the way we approach these chronic destructive diseases as well as major trauma. With the rapid increase in these conditions with an ageing population, new models of care will need to be developed to ensure that the right care is delivered at the right time by the most appropriately trained health professional and at a reasonable cost. The Bone and Joint Decade has played a significant role in focussing researchers, clinicians and health educators on these diseases and also in drawing them to the attention of Governments around the globe. While there is still much to be done, the journey has commenced and will continue into the future with education, research and service delivery into these important conditions being further enhanced.

Real-time bioluminescence functional imaging for monitoring tissue formation and regeneration

Real-time bioluminescence functional imaging holds great promise for regenerative medicine because it improves the researcher's ability to analyze and understand the healing process. Using transgenic mice coupled with gene-modified cells, one can employ this method to monitor host and graft activity in various models of tissue regeneration. We implemented real-time bioluminescence functional imaging to analyze bone formation by following a unique protocol in which the luciferase reporter gene, driven by an osteocalcin promoter, is used to visualize host and graft activity during bone formation. Real-time bioluminescence functional imaging can be used to assess the "host reaction" in transgenic mice models; it can also be used to assess "graft activity" in other animals in which genetically labeled stem cells have been implanted or direct gene delivery has been applied. The suggested imaging protocol requires 25 min per sample. However, special attention must be given to the layout of the experimental design, which determines the specific activity that will be analyzed.

Downregulation of ErbB3 by Wnt3a contributes to wnt-induced osteoblast differentiation in mesenchymal cells

Mesenchymal stem cells (MSC) can differentiate into osteoblasts upon activation of Wnt signaling. Identifying targets of Wnt signaling in MSC may help promote MSC osteoblast differentiation for bone regeneration. In this study, using microarray analysis we found that Wnt3a upregulates neuregulin 1 (NRG-1) during Wnt3a-induced osteoblast differentiation in primary human MSC and murine C3H10T1/2 mesenchymal cells. Western blot and qPCR analyses confirmed that NRG-1 is upregulated by Wnt3a, and that this effect was counterbalanced by decreased expression of the NRG-1 receptor ErbB3. Consistently, exogenous NRG-1 had no effect on alkaline phosphatase (ALP) activity, an early marker of osteoblast differentiation. In contrast, small interfering RNA-mediated silencing of endogenous NRG-1 increased basal and Wnt3a-induced ALP activity in MSC. We showed that short hairpin (sh) ErbB3 and Wnt3a additively increased β-catenin transcriptional activity and ALP activity in MSC. These effects were abrogated by DKK1, indicating that cross-talk between Wnt3a and ErbB3 control MSC osteoblast differentiation via Wnt/β-catenin signaling. Furthermore, ErbB3 silencing decreased Src expression. Pharmacological inhibition of Src signaling promoted ErbB3- and Wnt-induced ALP activity, suggestive of a role of Src signaling in the modulation of osteoblast differentiation by ErbB3 and Wnt3a. The results indicate that downregulation of ErbB3 induced by Wnt3a contributes to Wnt3a-induced early osteoblast differentiation of MSCs through increased canonical Wnt/β-catenin signaling and decreased Src signaling.

Biomaterial delivery of morphogens to mimic the natural healing cascade in bone

Complications in treatment of large bone defects using bone grafting still remain. Our understanding of the endogenous bone regeneration cascade has inspired the exploration of a wide variety of growth factors (GFs) in an effort to mimic the natural signaling that controls bone healing. Biomaterial-based delivery of single exogenous GFs has shown therapeutic efficacy, and this likely relates to its ability to recruit and promote replication of cells involved in tissue development and the healing process. However, as the natural bone healing cascade involves the action of multiple factors, each acting in a specific spatiotemporal pattern, strategies aiming to mimic the critical aspects of this process will likely benefit from the usage of multiple therapeutic agents. This article reviews the current status of approaches to deliver single GFs, as well as ongoing efforts to develop sophisticated delivery platforms to deliver multiple lineage-directing morphogens (multiple GFs) during bone healing.

Gene therapy approaches to regenerating bone

Bone formation and regeneration therapies continue to require optimization and improvement because many skeletal disorders remain undertreated. Clinical solutions to nonunion fractures and osteoporotic vertebral compression fractures, for example, remain suboptimal and better therapeutic approaches must be created. The widespread use of recombinant human bone morphogenetic proteins (rhBMPs) for spine fusion was recently questioned by a series of reports in a special issue of The Spine Journal, which elucidated the side effects and complications of direct rhBMP treatments. Gene therapy - both direct (in vivo) and cell-mediated (ex vivo) - has long been studied extensively to provide much needed improvements in bone regeneration. In this article, we review recent advances in gene therapy research whose aims are in vivo or ex vivo bone regeneration or formation. We examine appropriate vectors, safety issues, and rates of bone formation. The use of animal models and their relevance for translation of research results to the clinical setting are also discussed in order to provide the reader with a critical view. Finally, we elucidate the main challenges and hurdles faced by gene therapy aimed at bone regeneration as well as expected future trends in this field.

Investigating the role of FGF18 in the cultivation and osteogenic differentiation of mesenchymal stem cells

Fibroblast growth factor18 (FGF18) belongs to the FGF family and is a pleiotropic protein that stimulates proliferation in several tissues. Bone marrow mesenchymal stem cells (BMSCs) participate in the normal replacement of damaged cells and in disease healing processes within bone and the haematopoietic system. In this study, we constructed FGF18 and investigated its effects on rat BMSCs (rBMSCs). The proliferative effects of FGF18 on rBMSCs were examined using an MTS assay. To validate the osteogenic differentiation effects of FGF18, ALP and mineralization activity were examined as well as osteogenic differentiation-related gene levels. FGF18 significantly enhanced rBMSCs proliferation (p<0.001) and induced the osteogenic differentiation by elevating ALP and mineralization activity of rBMSCs (p<0.001). Furthermore, these osteogenic differentiation effects of FGF18 were confirmed via increasing the mRNA levels of collagen type I (Col I), bone morphogenetic protein 4 (BMP4), and Runt-related transcription factor 2 (Runx2) at 3 and 7 days. These results suggest that FGF18 could be used to improve bone repair and regeneration.

Odd-skipped related genes regulate differentiation of embryonic limb mesenchyme and bone marrow mesenchymal stromal cells

The regulation of progenitor cell differentiation to a specific tissue type is one of the fundamental questions of biology. Here, we identify Osr1 and Osr2, 2 closely related genes encoding zinc finger transcription factors, as being strongly expressed in irregular connective tissue (ICT) fibroblasts in the chicken embryo, suitable as a developmental marker. We provide evidence that both Osr1 and Osr2 regulate mesenchymal cell-type differentiation. Both Osr1 and Osr2 can promote the formation of ICT, a cell type of so far unknown molecular specification, while suppressing differentiation of other tissues such as cartilage and tendon from uncommitted progenitors. Conversely, knockdown of either Osr gene alone or in combination reverses this effect, thereby leading to decreased differentiation of ICT fibroblasts and increased chondrogenesis in vitro. This indicates that Osr genes play a pivotal role in ICT fibroblast differentiation. Undifferentiated mesenchymal cells reside in the adult body in the form of mesenchymal stem cells in the bone marrow cavity. Using bone marrow stromal cells (BMSCs) isolated from chicken fetal long bones, we show that Osr1 and Osr2 have an intrinsic role in BMSC differentiation similar to their role in early embryonic development, that is, the enforcement of CT fibroblast differentiation and the repression of other cell types as exemplified here by osteoblast differentiation.

Microcomputed tomography-based structural analysis of various bone tissue regeneration models

Microcomputed tomography (microCT) analysis is a powerful tool for the evaluation of bone tissue because it provides access to the 3D microarchitecture of the bone. It is invaluable for regenerative medicine as it provides the researcher with the opportunity to explore the skeletal system both in vivo and ex vivo. The quantitative assessment of macrostructural characteristics and microstructural features may improve our ability to estimate the quality of newly formed bone. We have developed a unique procedure for analyzing data from microCT scans to evaluate bone structure and repair. This protocol describes the procedures for microCT analysis of three main types of mouse bone regeneration models (ectopic administration of bone-forming mesenchymal stem cells, and administration of cells after both long bone defects and cranial segmental bone defects) that can be easily adapted for a variety of other models. Precise protocols are crucial because the system is extremely user sensitive and results can be easily biased if standardized methods are not applied. The suggested protocol takes 1.5-3.5 h per sample, depending on bone tissue sample size, the type of equipment used, variables of the scanning protocol and the operator's experience.

The effect of simulated microgravity on human mesenchymal stem cells cultured in an osteogenic differentiation system: a bioinformatics study

One proposed strategy for bone regeneration involves ex vivo tissue engineering, accomplished using bone-forming cells, biodegradable scaffolds, and dynamic culture systems, with the goal of three-dimensional tissue formation. Rotating wall vessel bioreactors generate simulated microgravity conditions ex vivo, which lead to cell aggregation. Human mesenchymal stem cells (hMSCs) have been extensively investigated and shown to possess the potential to differentiate into several cell lineages. The goal of the present study was to evaluate the effect of simulated microgravity on all genes expressed in hMSCs, with the underlying hypothesis that many important pathways are affected during culture within a rotating wall vessel system. Gene expression was analyzed using a whole genome microarray and clustering with the aid of the National Institutes of Health's Database for Annotation, Visualization and Integrated Discovery database and gene ontology analysis. Our analysis showed 882 genes that were downregulated and 505 genes that were upregulated after exposure to simulated microgravity. Gene ontology clustering revealed a wide variety of affected genes with respect to cell compartment, biological process, and signaling pathway clusters. The data sets showed significant decreases in osteogenic and chondrogenic gene expression and an increase in adipogenic gene expression, indicating that ex vivo adipose tissue engineering may benefit from simulated microgravity. This finding was supported by an adipogenic differentiation assay. These data are essential for further understanding of ex vivo tissue engineering using hMSCs.

Calcium phosphate-DNA nanoparticle gene delivery from alginate hydrogels induces in vivo osteogenesis

There is a significant need for improved therapy for bone regeneration. The delivery of recombinant bone morphogenetic proteins has been approved for clinical use to promote osteogenesis, but still has limitations such as expense, degradation of the proteins in vivo and difficulties retaining protein at the site of injury. Localized gene delivery is a promising alternative therapy, as it would allow sustained expression of specific osteoinductive growth factors by cells near the damaged site. We have engineered an injectable system for localized, sustained nonviral gene delivery from alginate hydrogels containing preosteoblastic cells and calcium phosphate-DNA nanoparticles. The nanoparticles utilized in this report are stable, on the order of 100 nm, and have a high DNA incorporation efficiency (>66%). When the nanoparticles were incorporated in alginate hydrogels, sustained release of DNA was observed. Furthermore, MC3T3-E1 preosteoblast cells exhibited the capacity to form bony tissue in as little as two and half weeks when mixed with DNA nanoparticles encoding for BMP-2 into the alginate hydrogels and injected subcutaneously in the backs of mice. This injectable, minimally invasive gene delivery system may be efficacious in bone regeneration applications.

Bone tissue engineering: a review in bone biomimetics and drug delivery strategies

Critical-sized defects in bone, whether induced by primary tumor resection, trauma, or selective surgery have in many cases presented insurmountable challenges to the current gold standard treatment for bone repair. The primary purpose of a tissue-engineered scaffold is to use engineering principles to incite and promote the natural healing process of bone which does not occur in critical-sized defects. A synthetic bone scaffold must be biocompatible, biodegradable to allow native tissue integration, and mimic the multidimensional hierarchical structure of native bone. In addition to being physically and chemically biomimetic, an ideal scaffold is capable of eluting bioactive molecules (e.g., BMPs, TGF-betas, etc., to accelerate extracellular matrix production and tissue integration) or drugs (e.g., antibiotics, cisplatin, etc., to prevent undesired biological response such as sepsis or cancer recurrence) in a temporally and spatially controlled manner. Various biomaterials including ceramics, metals, polymers, and composites have been investigated for their potential as bone scaffold materials. However, due to their tunable physiochemical properties, biocompatibility, and controllable biodegradability, polymers have emerged as the principal material in bone tissue engineering. This article briefly reviews the physiological and anatomical characteristics of native bone, describes key technologies in mimicking the physical and chemical environment of bone using synthetic materials, and provides an overview of local drug delivery as it pertains to bone tissue engineering is included.

The use of a synthetic oxygen carrier-enriched hydrogel to enhance mesenchymal stem cell-based bone formation in vivo

A major hurdle to surmount in bone-tissue engineering is ensuring a sufficient oxygen supply to newly forming tissue to avoid cell death or delayed development of osteogenic features. We hypothesized that an oxygen-enriched hydrogel scaffold would enhance tissue-engineered bone formation in vivo. To test this, we used a well-characterized mesenchymal stem cell (MSC) line, Tet-off BMP2 MSC, whose cells were engineered to express recombinant human bone morphogenetic protein-2. Cells were suspended in hydrogel supplemented with perfluorotributylamine (PFTBA) and implanted subcutaneously in an ectopic site, a radial bone defect, or a lumbar paravertebral muscle (mouse model of spinal fusion) in C3H/HeN mice. For controls, we used cells suspended in the same gel without PFTBA. In the ectopic site, there were significant increases in bone formation (2.5-fold increase), cell survival, and osteocalcin activity in the PFTBA-supplemented groups. PFTBA supplementation significantly increased structural parameters of bone in radial bone defects and triggered a significant 1.4-fold increase in bone volume in the spinal fusion model. We conclude that synthetic oxygen carrier supplementation of tissue-engineered implants enhances ectopic bone formation and yields better bone quality and volume in bone-repair and spinal fusion models, probably due to increased cell survival.

Nonvirally engineered porcine adipose tissue-derived stem cells: use in posterior spinal fusion

Multiple factors alter intervertebral disc volume, structure, shape, composition, and biomechanical properties, often leading to low back pain. Spinal fusion is frequently performed to treat this problem. We recently published results of our investigation of a novel system of in vivo bone formation, in which we used nonvirally nucleofected human mesenchymal stem cells that overexpress a bone morphogenetic protein gene. We hypothesized that primary porcine adipose tissue-derived stem cells (ASCs) nucleofected with plasmid containing recombinant human bone morphogenetic protein-6 (rhBMP-6) could induce bone formation and achieve spinal fusion in vivo. Primary ASCs were isolated from freshly harvested porcine adipose tissue. Overexpression of rhBMP-6 was achieved ex vivo by using a nucleofection technique. Transfection efficiency was monitored by assessing a parallel transfection involving an enhanced green fluorescent protein reporter gene and flow cytometry analysis. rhBMP-6 protein secreted by the cells was measured by performing an enzyme-linked immunosorbent assay. Genetically engineered cells were injected into the lumbar paravertebral muscle in immunodeficient mice. In vivo bone formation was monitored by a quantitative microcomputed tomography (muCT). The animals were euthanized 5 weeks postinjection, and spinal fusion was evaluated using in vitro muCT and histological analysis. We found formation of a large bone mass adjacent to the lumbar area, which produced posterior spinal fusion of two to four vertebrae. Our data demonstrate that efficient bone formation and spinal fusion can be achieved using ex vivo, nonvirally transfected primary ASCs. These results could pave the way to a novel biological solution for spine treatment.