Osteogenic potential of five different recombinant human bone morphogenetic protein adenoviral vectors in the rat

BMP9 is produced by hepatocytes and circulates mainly in an active mature form complexed to its prodomain

Bone Morphogenetic Protein 9 (BMP9) has been recently found to be the physiological ligand for the activin receptor-like kinase 1 (ALK1), and to be a major circulating vascular quiescence factor. Moreover, a soluble chimeric ALK1 protein (ALK1-Fc) has recently been developed and showed powerful anti-tumor growth and anti-angiogenic effects. However, not much is known concerning BMP9. This prompted us to investigate the human endogenous sources of this cytokine and to further characterize its circulating form(s) and its function. Analysis of BMP9 expression reveals that BMP9 is produced by hepatocytes and intrahepatic biliary epithelial cells. Gel filtration analysis combined with ELISA and biological assays demonstrate that BMP9 circulates in plasma (1) as an unprocessed inactive form that can be further activated by furin a serine endoprotease, and (2) as a mature and fully active form (composed of the mature form associated with its prodomain). Analysis of BMP9 circulating levels during mouse development demonstrates that BMP9 peaks during the first 3 weeks after birth and then decreases to 2 ng/mL in adulthood. We also show that circulating BMP9 physiologically induces a constitutive Smad1/5/8 phosphorylation in endothelial cells. Taken together, our results argue for the role of BMP9 as a hepatocyte-derived factor, circulating in inactive (40%) and active (60%) forms, the latter constantly activating endothelial cells to maintain them in a resting state.

BMP9 inhibits the proliferation and invasiveness of breast cancer cells MDA-MB-231

BACKGROUND

Transforming growth factor-β (TGF-β) is known to promote tumor proliferation, migration, invasion, and metastasis. Bone morphogenetic proteins (BMPs) are members of the TGF-β superfamily. Several BMPs (BMP2 and BMP7) can enhance the invasion and bone metastasis of breast cancer cells. The function of BMP9, the latest discovered and most powerful osteogenetic factor, in breast cancer has not been fully elucidated.

METHODS

BMP9 expression in twenty-three breast cancer patients and three breast cancer cell line types was detected by reverse transcriptase polymerase chain reaction. Changes in proliferation, apoptosis, invasion, and migration in the recombinant MDA-MB-231/BMP9 cells were detected using various assays. The assays were MTT, flow cytometry, colony forming, cell wounding, and transwell invasion. Proliferating cell nuclear antigen and terminal deoxynucleotidy transferase biotin-dUTP nick end labeling staining methods were conducted to detect whether BMP9 affected proliferation and apoptosis in xenogenic mouse models.

RESULTS

Twenty-one of the twenty-three breast cancer patients had amplified BMP9 mRNA transcripts in adjacent non-tumor tissues, although BMP9 was observed in the breast cancer tissue of two patients, its expression was higher in the adjacent non-tumor tissues. BMP9 overexpression inhibited the proliferation, migration, and invasion, as well as induced the apoptosis of the breast cancer cell line MDA-MB-231 in vitro. BMP9 also inhibited tumor growth and induced apoptosis significantly in the xenogenic mouse models.

CONCLUSIONS

Decreased BMP9 expression is associated with the elevated proliferation and migration of human breast cancer. BMP9 can inhibit the growth, invasion, and migration of breast cancer cells in vitro and in vivo. BMP9 is a putative tumor suppressor in breast cancer.

Emerging ideas: treatment of precollapse osteonecrosis using stem cells and growth factors

BACKGROUND

Osteonecrosis (ON) of the femoral head is a devastating disease affecting young patients at their most productive age, causing major socioeconomic burdens. ON is associated with various etiologic factors, and the pathogenesis of the disease is unknown. Most investigators believe the disease is the result of secondary microvascular compromise with subsequent bone and marrow cell death and defective bone repair.

QUESTIONS/HYPOTHESES

We hypothesize that local delivery of vascular endothelial growth factor (VEGF) and bone morphogenetic protein-6 (BMP-6), which induces angiogenesis and osteogenesis respectively, will reverse the disease process and provide a treatment for precollapse ON.

METHOD OF STUDY

We will use genetically engineered bone marrow stem cells, carrying VEGF and BMP-6 genes, to enhance angiogenesis and osteogenesis in necrotic bone of an animal model, by local delivery of growth factor in addition to the bone-forming property of the stem cells. The participation, localization, and fate of the stem cells in the repair process will be evaluated by tracing marker-gene product. Osteogenesis and angiogenesis will be assessed using high-resolution xray CT and immunohistomorphometry quantitatively. Mechanical properties of the repair tissue will be determined using an indentation test of the femoral head.

SIGNIFICANCE

We envision that a deliverable or injectable bone graft substitute containing engineered stem cells and therapeutic growth factors will be developed through this proposed study and will provide a much needed treatment for ON.

[Oro-maxillofacial bone tissue engineering combining biomaterials, stem cells, and gene therapy]

Improvements have been made in regenerative medicine, due to the development of tissue engineering and cellular therapy. Bone regeneration is an ambitious project, leading to many applications involving skull, maxillofacial, and orthopaedic surgery. Scaffolds, stem cells, and signals support bone tissue engineering. The scaffold physical and chemical properties promote cell invasion, guide their differentiation, and enable signal transmission. Scaffold may be inorganic or organic. Their conception was improved by the use of new techniques: self-assembled nanofibres, electrospinning, solution-phase separation, micropatterned hydrogels, bioprinting, and rapid prototyping. Cellular biology processes allow us to choose between embryonic stem cells or adult stem cells for regenerative medicine. Finally, communication between cells and their environment is essential; they use various signals to do so. The study of signals and their transmission led to the discovery and the use of Bone Morphogenetic Protein (BMP). The development of cellular therapy led to the emergence of a specific field: gene therapy. It relies on viral vectors, which include: retroviruses, adenoviruses and adeno-associated vectors (AAV). Non-viral vectors include plasmids and lipoplex. Some BMP genes have successfully been transfected. The ability to control transfected cells and the capacity to combine and transfect many genes involved in osseous healing will improve gene therapy.

Use and efficacy of bone morphogenetic proteins in fracture healing

Purpose

This review evaluates the application of bone morphogenetic proteins (BMPs) in delayed bone repair, aiming at a broad audience from clinicians to scientists. Next to an overview of the role of the different BMPs, their antagonists and their current applications, special attention is focused on new scientific developments improving the effects of BMP-based therapy for bone repair.

Methods

Publication searches in PubMed and Embase revealed 850 relevant articles on the criteria ‘BMP’ AND ‘bone repair’ (as of May 2011). The abstracts were carefully reviewed and papers were selected according to the content.

Results

The resulting publications showed that BMP-2 and BMP-7 are clearly the most extensively evaluated BMPs, in general with positive results on bone healing, comparable to the use of unspecific preparations such as autologous bone grafts or platelet-rich plasma.

Conclusions

Although the efficacy of BMPs as stimulators of bone repair has been demonstrated in model systems and clinical studies, the use of BMPs to enhance fracture healing in the clinical setting is still controversial. Issues such as when, where and how much of which BMP is the most effective and profitable to use still have to be elucidated. But optimisation of the BMP products used in combination with cheaper production methods will inevitably stimulate the clinical use of BMPs for bone fracture healing in the near future.

Future of local bone regeneration - Protein versus gene therapy

The most promising attempts to achieve bone regeneration artificially are based on the application of mediators such as bone morphogenetic proteins (BMPs) directly to the deficient tissue site. BMPs, as promoters of the regenerative process, have the ability to induce de novo bone formation in various tissues, and many animal models have demonstrated their high potential for ectopic and orthotopic bone formation. However, the biological activity of the soluble factors that promote bone formation in vivo is limited by diffusion and degradation, leading to a short half-life. Local delivery remains a problem in clinical applications. Several materials, including hydroxyapatite, tricalcium phosphate, demineralised bone matrices, poly-lactic acid homo- and heterodimers, and collagen have been tested as carriers and delivery systems for these factors in a sustained and appropriate manner. Unfortunately these delivery vehicles often have limitations in terms of biodegradability, inflammatory and immunological rejection, disease transmission, and most importantly, an inability to provide a sustained, continuous release of these factors at the region of interest. In coping with these problems, new approaches have been established: genes encoding these growth factor proteins can be delivered to the target cells. In this way the transfected cells serve as local "bioreactors", as they express the exogenous genes and secrete the synthesised proteins into their vicinity. The purpose of this review is to present the different methods of gene versus growth factor delivery in tissue engineering. Our review focuses on these promising and innovative methods that are defined as regional gene therapy and provide an alternative to the direct application of growth factors. Various advantages and disadvantages of non-viral and viral vectors are discussed. This review identifies potential candidate genes and target cells, and in vivo as well as ex vivo approaches for cell transduction and transfection. In explaining the biological basis, this paper also refers to current experimental and clinical applications.

In vitro and in vivo osteogenic activity of licochalcone A

We investigated the in vitro and in vivo osteogenic activity of licochalcone A. At low concentrations, licochalcone A stimulated the differentiation of mouse pre-osteoblastic MC3T3-E1 subclone 4 (MC4) cells and enhanced the bone morphogenetic protein (BMP)-2-induced stimulation of mouse bi-potential mesenchymal precursor C2C12 cells to commit to the osteoblast differentiation pathway. This osteogenic activity of licochalcone A was accompanied by the activation of extracellular-signal regulated kinase (ERK). The involvement of ERK was confirmed in a pharmacologic inhibition study. Additionally, noggin (a BMP antagonist) inhibited the osteogenic activity of licochalcone A in C2C12 cells. Licochalcone A also enhanced the BMP-2-stimulated expression of various BMP mRNAs. This suggested that the osteogenic action of licochalcone A in C2C12 cells could be dependent on BMP signaling and/or expression. We then tested the in vivo osteogenic activity of licochalcone A in two independent animal models. Licochalcone A accelerated the rate of skeletal development in zebrafish and enhanced woven bone formation over the periosteum of mouse calvarial bones. In summary, licochalcone A induced osteoblast differentiation with ERK activation in both MC4 and C2C12 cells and it exhibited in vivo osteogenic activity in zebrafish skeletal development and mouse calvarial bone formation. The dual action of licochalcone A in stimulating bone formation and inhibiting bone resorption, as described in a previous study, might be beneficial in treating bone-related disorders.

Combined VEGF and LMP-1 delivery enhances osteoprogenitor cell differentiation and ectopic bone formation

A novel strategy to enhance bone repair is to combine angiogenic factors and osteogenic factors. We combined vascular endothelial growth factor (VEGF) and LIM mineralization protein-1 (LMP-1) by using an internal ribosome entry site to link the genes within a single plasmid. We then evaluated the effects on osteoblastic differentiation in vitro and ectopic bone formation in vivo with a subcutaneously placed PLAGA scaffold loaded with a cloned mouse osteoprogenitor cell line, D1, transfected with plasmids containing VEGF and LMP-1 genes. The cells expressing both genes elevated mRNA expression of RunX2 and β-catenin and alkaline phosphatase activity compared to cells from other groups. In vivo, X-ray and micro-CT analysis of the retrieved implants revealed more ectopic bone formation at 2 and 3 weeks but not at 4 weeks compared to other groups. The results indicate that the combination of the therapeutic growth factors potentiates cell differentiation and may promote osteogenesis.

VEGF and BMP-6 enhance bone formation mediated by cloned mouse osteoprogenitor cells

New strategies such as combined utilization of growth factors may provide a better treatment for difficult fractures. We have demonstrated enhanced angiogenesis and osteogenesis through the actions of vascular endothelial growth factor (VEGF) and bone morphogenetic protein-6 (BMP-6) on the osteogenic differentiation of a cloned mouse osteoprogenitor cell in vitro and ectopic bone formation in vivo. Human VEGF and BMP-6 genes expressed together produced a significant increase in alkaline phosphatase activity, expression of the RunX2 and osteocalcin genes and mineralization. Microcomputed tomographic analysis of subcutaneous implants consisting of cells transfected with VEGF and BMP-6 cDNA and delivered on a 3D poly (lactic-co-glycolic acid) scaffold confirmed the additive effects between VEGF and BMP-6. Ectopic bone formation in the VEGF plus BMP-6 group was greatest compared to that in either VEGF or BMP-6 alone. This is the first study that demonstrates osteogenesis in vitro and in vivo through the additive effects of VEGF and BMP-6.

The effect of ex vivo dynamic loading on the osteogenic differentiation of genetically engineered mesenchymal stem cell model

Mechanical loading has been described as a highly important stimulus for improvements in the quality and strength of bone. It has also been shown that mechanical stimuli can induce the differentiation of mesenchymal stem cells (MSCs) along the osteogenic lineage. We have previously demonstrated the potent osteogenic effect of MSCs engineered to overexpress the BMP2 gene. In this study we investigated the effect of mechanical loading on BMP2-expressing MSC-like cells, using a special bioreactor designed to apply dynamic forces on cell-seeded hydrogels. Cell viability, alkaline phosphatase (ALP) activity, BMP2 secretion and mineralized substance formation in the hydrogels were quantified. We found that cell metabolism increased as high as 6.8-fold, ALP activity by 12.5-fold, BMP2 secretion by 182-fold and mineralized tissue formation by 1.72-fold in hydrogels containing MSC-like cells expressing BMP2, which were cultured in the presence of mechanical loading. We have shown that ex vivo mechanical loading had an additive effect on BMP2-induced osteogenesis in genetically engineered MSC-like cells. These data could be valuable for bone tissue-engineering strategies of the future.

Physcion-8-O-beta-D-glucopyranoside enhances the commitment of mouse mesenchymal progenitors into osteoblasts and their differentiation: Possible involvement of signaling pathways to activate BMP gene expression

Here, we show the involvement of signaling pathways to induce the gene expression of bone morphogenetic protein (BMP) in the osteogenic activity of physcion-8-O-beta-D-glucopyranoside (physcion-Glu); it stimulated osteoblast differentiation in mouse osteoblast MC3T3-E1 subclone 4 cells and induced BMP-2 gene expression and activation of Akt and ERK/MAP kinases. Physcion-Glu-induced BMP-2 expression and mineralization were attenuated by LY294002, an inhibitor of PI3K that lies upstream of Akt and MAP kinases, suggesting that physcion-Glu induces osteoblast differentiation via PI3K-Akt/MAP kinase signaling pathways, which play important roles in inducing BMP-2 gene expression. Physcion-Glu also enhanced BMP-2-induced commitment of mouse bi-potential mesenchymal precursor C2C12 cells into osteoblasts while inducing the transcription of several osteogenic BMP isoforms, such as BMP-2, -4, -7, and -9. Osteogenic synergy between BMP-2 and physcion-Glu was supported by the fact that noggin inhibited BMP-2 and physcion-Glu-induced alkaline phosphatase expression and activity. Considering that physcion-Glu induced Runx2 activity and the nuclear translocation of p-Smad, physcion-Glu could act by enhancing the BMP signaling pathway that induces Smad activation and translocation to activate Runx2. In conclusion, physcion-Glu could enhance the commitment of mesenchymal progenitors into osteoblasts and their differentiation by activating signaling pathways to induce BMP gene expression.

Tanshinone IIA enhances BMP-2-stimulated commitment of C2C12 cells into osteoblasts via p38 activation

In this study, we demonstrate a stimulatory effect of tanshinone IIA isolated from the root of Salvia miltiorrhiza on the commitment of bi-potential mesenchymal precursor C2C12 cells into osteoblasts in the presence of bone morphogenetic protein (BMP)-2. At low concentrations, tanshinone IIA enhanced BMP-2-stimulated induction of alkaline phosphatase (ALP), an early phase biomarker of osteoblast differentiation, and mRNA expression of BMPs. ALP induction was inhibited by the BMP antagonist noggin, suggesting that tanshinone IIA enhances the osteogenic activity of BMP signaling. Furthermore, considering the tanshinone IIA-mediated enhancement of BMP-2-stimulated Smad-Runx2 activities, tanshinone IIA could enhance the osteogenic activity of BMP-2 via acceleration of Smad-Runx2 activation. Additionally, pharmacologic inhibition studies suggest the possible involvement of p38 in the action of tanshinone IIA. The p38 inhibitor SB202190 strongly and dose-dependently inhibited tanshinone IIA-enhanced ALP induction. SB202190 also dose-dependently inhibited the tanshinone IIA-induced p38 activation and combined tanshinone IIA-BMP-2-induced Smad activation. In conclusion, tanshinone IIA enhances the commitment of C2C12 cells into osteoblasts and their differentiation through synergistic cross talk between tanshinone IIA-induced p38 activation and BMP-2-induced Smad activation. These activations could subsequently induce the activation of Runx2, which induces osteogenesis via regulation of the osteogenic factors BMP and ALP expression.

Comparison of the osteoinductivity of bioimplants containing recombinant human bone morphogenetic proteins 2 (Infuse) and 7 (OP-1)

OBJECTIVES

Recent research has focused on application of growth factors such as bone morphogenetic proteins (BMPs) as alternatives to autogenous bone grafting. Two bone graft substitute bioimplants containing recombinant human BMPs (rhBMPs), Infuse (rhBMP-2) and OP-1 (rhBMP-7), are approved for human application but have never been compared side by side. The aim of this study was to provide a direct comparison of the osteoinductive activity of the 2 commercially available and approved rhBMP-containing bioimplants in their clinically available forms.

STUDY DESIGN

The activity of rhBMP-2 and -7 in solution were compared in vitro using the C2C12 cell-based assay. The activity of Infuse and OP-1 bioimplants containing 52.5 microg of rhBMP-2 or rhBMP-7, respectively, were compared in vivo using a mouse muscle pouch assay and analyzed by microscopic CT (microCT) and histology.

RESULTS

The in vitro results showed that rhBMP-2 stimulated greater alkaline phosphatase production than rhBMP-7 over various time points and concentrations. The in vivo results showed that OP-1 induced greater bone volume than Infuse. Both implants induced bone of equivalent quality based on microCT and histologic evaluation.

CONCLUSION

In their clinically available forms, the rhBMP-7-containing OP-1 induced greater bone volume than the rhBMP-2-containing Infuse in the mouse muscle pouch model.

Novel regenerative strategies to enhance periodontal therapy outcome

BACKGROUND

Chronic periodontitis is a widely prevalent inflammatory condition of the supporting tissues of the teeth and is characterized by loss of teeth with an associated risk of systemic complications. Regenerative therapies such as guided tissue and bone regeneration form an important armamentarium in periodontics with a high degree of outcome predictability in certain ideal clinical scenarios.

OBJECTIVE/METHODS

This review elaborates novel tissue regenerative treatment modalities based on sound understanding of developmental biology, tissue engineering, inflammation and wound healing. We focus on the role of biological mediators such as growth factors, gene-based therapy, cell therapy and pro-resolution lipid mediators in the regeneration of lost bone or periodontium.

RESULTS/CONCLUSIONS

These therapies have the potential to regenerate both periodontium and bone, aiding in the treatment of even clinically challenging cases.

Irradiated human chondrocytes expressing bone morphogenetic protein 2 promote healing of osteoporotic bone fracture in rats

Bone morphogenetic protein 2 (BMP2) was selected as a transgene to regenerate osteoporotic bone defects after several BMPs were tested using a bone formation study in nude mice. Human chondrocytes were transduced with a BMP2-containing retroviral vector, and single clones were selected. The cells were characterized over numerous passages for growth and BMP2 expression. The single clones were irradiated and tested for viability. BMP2 expression lasted for 3 weeks before dying off completely after approximately 1 month. Irradiated and non-irradiated transduced chondrocytes successfully healed fractures in osteoporotic rats induced by ovariectomy. The osteoinducing effect of irradiated cells was better than that of their non-irradiated counterparts or a chondrocytes-only control. This study showed that delivering BMP2 from the transduced and irradiated chondrocytes could be an effective and safe method of repairing osteoporotic bone fractures.

Simple strategy for bone regeneration with a BMP-2/7 gene expression cassette vector

Bone morphogenetic protein (BMP) is one of the most promising candidates for bone regeneration therapy. Heterodimers of BMP family proteins, such as BMP-2/4 or BMP-2/7, are well known to have stronger osteoinduction activity than BMP homodimers. Here, we constructed a double gene cassette vector encoding BMP-2 and BMP-7, pCAGGS-BMP-2/7, and examined its potential for osteoinduction in vitro and in vivo. Expression of the pCAGGS-BMP-2/7 vector induced osteogenic differentiation in various cell lines with the same efficiency as BMP-2 and BMP-7 co-expressed from separate vectors. Moreover, the pCAGGS-BMP-2/7 vector strongly induced bone formation in rat skeletal muscle when introduced by in vivo electroporation, compared with BMP-2 or BMP-7 alone. Thus, our BMP-2/7 double gene cassette vector, or some variation of it, may be applicable for the future clinical induction of bone formation, because it does not require multiple vectors or complicated preparation.

A comprehensive analysis of the dual roles of BMPs in regulating adipogenic and osteogenic differentiation of mesenchymal progenitor cells

Pluripotent mesenchymal stem cells (MSCs) are bone marrow stromal progenitor cells that can differentiate into osteogenic, chondrogenic, adipogenic, and myogenic lineages. Several signaling pathways have been shown to regulate the lineage commitment and terminal differentiation of MSCs. Here, we conducted a comprehensive analysis of the 14 types of bone morphogenetic protein (BMPs) for their abilities to regulate multilineage specific differentiation of MSCs. We found that most BMPs exhibited distinct abilities to regulate the expression of Runx2, Sox9, MyoD, and PPARgamma2. Further analysis indicated that BMP-2, BMP-4, BMP-6, BMP-7, and BMP-9 effectively induced both adipogenic and osteogenic differentiation in vitro and in vivo. BMP-induced commitment to osteogenic or adipogenic lineage was shown to be mutually exclusive. Overexpression of Runx2 enhanced BMP-induced osteogenic differentiation, whereas knockdown of Runx2 expression diminished BMP-induced bone formation with a decrease in adipocyte accumulation in vivo. Interestingly, overexpression of PPARgamma2 not only promoted adipogenic differentiation, but also enhanced osteogenic differentiation upon BMP-2, BMP-6, and BMP-9 stimulation. Conversely, MSCs with PPARgamma2 knockdown or mouse embryonic fibroblasts derived from PPARgamma2(-/-) mice exhibited a marked decrease in adipogenic differentiation, coupled with reduced osteogenic differentiation and diminished mineralization upon BMP-9 stimulation, suggesting that PPARgamma2 may play a role in BMP-induced osteogenic and adipogenic differentiation. Thus, it is important to understand the molecular mechanism behind BMP-regulated lineage divergence during MSC differentiation, as this knowledge could help us to understand the pathogenesis of skeletal diseases and may lead to the development of strategies for regenerative medicine.

Comparison of osteogenic potentials of BMP4 transduced stem cells from autologous bone marrow and fat tissue in a rabbit model of calvarial defects

We compared bone marrow stem cells (BMSCs) and adipose-derived stem cells (ADSCs) of adult rabbits under identical conditions in terms of their culture characteristics, proliferation capacity, osteogenic differentiation potentials induced by adenovirus-containing bone morphogenetic protein 4 (Ad-BMP4) in vitro, and capacity to repair calvarial defects in the rabbit model by autologous transplantation ex vivo. According to the results of growth curve, cell cycle, and telomerase activity analysis, ADSCs possess a higher proliferation potential. Both of the Ad-BMP4 transduced MSCs expressed BMP4 mRNA and protein and underwent osteogenic differentiation. Up-regulated mRNA expression of all osteogenic genes was observed in differentiated BMSCs and ADSCs, but with different patterns confirmed by real-time RT-PCR. Deposition of calcified extracellular matrix was significantly greater in differentiated ADSCs compared with differentiated BMSCs. X-ray and histological examination indicated significant bone regeneration in the calvarial defects transplanted with Ad-BMP4 transduced autologous MSCs compared to the control groups. There was no significant difference in new bone formation in Ad-BMP4 transduced MSCs based on quantitative digital analysis of histological sections. The use of ADSCs often resulted in the growth of fat tissue structures in the control groups, and the fat tissue structures were not seen with BMSC cells. Our data demonstrate that BMP4 can be potently osteoinductive in vivo, resulting in bone repair. ADSCs may be an attractive alternative to BMSCs for bone tissue engineering under appropriate stimuli. But the easy adipogenic differentiation needs to be considered when choosing adipose tissue for specific clinical application.

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.

Genetically engineered mesenchymal stem cells: applications in spine therapy

Spine disorders and intervertebral disc degeneration are considered the main causes for the clinical condition commonly known as back pain. Spinal fusion by implanting autologous bone to produce bony bridging between the two vertebrae flanking the degenerated-intervertebral disc is currently the most efficient treatment for relieving the symptoms of back pain. However, donor-site morbidity, complications and the long healing time limit the success of this approach. Novel developments undertaken by regenerative medicine might bring more efficient and available treatments. Here we discuss the pros and cons of utilizing genetically engineered mesenchymal stem cells for inducing spinal fusion. The combination of the stem cells, gene and carrier are crucial elements for achieving optimal spinal fusion in both small and large animal models, which hopefully will lead to the development of clinical applications.

Bone morphogenetic protein-9 induces apoptosis in prostate cancer cells, the role of prostate apoptosis response-4

Bone morphogenetic proteins (BMP) have been implicated in the development of bone metastases in prostate cancer. In this study, we investigated the role which BMP-9 played in prostate cancer and found that the expression of BMP-9 was decreased or absent in prostate cancer, particularly in the foci of higher grade disease. We further investigated the influence of BMP-9 on the biological behaviors of prostate cancer cells. The forced overexpression of BMP-9 prevented the in vitro growth, cell-matrix adhesion, invasion, and migration of prostate cancer cells. We also elucidated that BMP-9 induced apoptosis in PC-3 cells through the up-regulation of prostate apoptosis response-4. Among the receptors which have been implicated in the signaling of BMP-9, BMPR-IB and BMPR-II have also been implicated in the development and progression of prostate cancer. Knockdown of BMPR-IB or BMPR-II using respective hammerhead ribozyme transgenes could promote cell growth in vitro. We also found that BMPR-II is indispensable for the Smad-dependent signal transduction by BMP-9 in PC-3 cells, in which Smad-1 was phosphorylated and translocated from the cytoplasm into the nuclei. Taken together, BMP-9 inhibits the growth of prostate cancer cells due to the induced apoptosis, which is related to an up-regulation of prostate apoptosis response-4 through a Smad-dependent pathway. BMP-9 could also prevent the migration and invasiveness of prostate cancer. This suggests that BMP-9 may function as a tumor suppressor and apoptosis regulator in prostate cancer.

Osteogenic gene regulation and relative acceleration of healing by adenoviral-mediated transfer of human BMP-2 or -6 in equine osteotomy and ostectomy models

This study evaluated healing of equine metatarsal osteotomies and ostectomies in response to percutaneous injection of adenoviral (Ad) bone morphogenetic protein (BMP)-2, Ad-BMP-6, or beta-galactosidase protein vector control (Ad-LacZ) administered 14 days after surgery. Radiographic and quantitative computed tomographic assessment of bone formation indicated greater and earlier mineralized callus in both the osteotomies and ostectomies of the metatarsi injected with Ad-BMP-2 or Ad-BMP-6. Peak torque to failure and torsional stiffness were greater in osteotomies treated with Ad-BMP-2 than Ad-BMP-6, and both Ad-BMP-2- and Ad-BMP-6-treated osteotomies were greater than Ad-LacZ or untreated osteotomies. Gene expression of ostectomy mineralized callus 8 weeks after surgery indicated upregulation of genes related to osteogenesis compared to intact metatarsal bone. Expression of transforming growth factor beta-1, cathepsin H, and gelsolin-like capping protein were greater in Ad-BMP-2- and Ad-BMP-6-treated callus compared to Ad-LacZ-treated or untreated callus. Evidence of tissue biodistribution of adenovirus in distant organs was not identified by quantitative PCR, despite increased serum antiadenoviral vector antibody. This study demonstrated a greater relative potency of Ad-BMP-2 over Ad-BMP-6 in accelerating osteotomy healing when administered in this regimen, although both genes were effective at increasing bone at both osteotomy and ostectomy sites.

Gene therapy applications for fracture-healing

Biologic therapies to promote fracture-healing such as use of bone morphogenetic proteins (BMPs) are being increasingly employed in multiple clinical scenarios. However, it has been challenging to design therapies that deliver sufficient quantities of protein over a sustained time period. A potential solution is the application of gene therapy that transfers genetic information to host cells at the fracture site, resulting in the continuous and localized production of the desired proteins. This approach has demonstrated tremendous potential in preclinical animal models of fracture-healing. This article will review the current state of gene therapy approaches to fracture-healing with an emphasis on potential clinical applications.

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.

Plasmid size influences chitosan nanoparticle mediated gene transfer to chondrocytes

The objective of the present study was to prepare chitosan nanoparticles incorporating a relatively large plasmid encoding for osteogenic protein (OP)-1 and to determine the ability of these nanoparticles to transfect adult canine articular chondrocytes in vitro. The positive charge of chitosan acted to condense the relatively large negatively-charged OP-1 plasmid such that it could be incorporated into nanoparticles. Incorporation of the plasmid into the chitosan nanoparticles did not affect the structural integrity of the plasmid as demonstrated by gel electrophoresis. The morphology and size of the nanoparticles were found to vary with the chitosan:plasmid weight ratio. Nanoparticles formulated with a chitosan:plasmid ratio of 10:1 were of uniformly small size (less than 250 nm) and spherical shape. These nanoparticles had a positive charge of about 20 mV. FITC-labeled chitosan nanoparticles were found in virtually all of the cells after 24 h of incubation with the nanoparticles, and confocal microscopy revealed FITC-related fluorescence in the nucleus of the chondrocytes. Although transfection of the chondrocytes was demonstrated by the fluorescence of cells treated with chitosan nanoparticles containing the plasmid for the enhanced green fluorescence protein, cells transfected with nanoparticles incorporating the larger OP-1 plasmid did not show OP-1 expression measured by ELISA for up to 2 weeks in culture. These results indicate that although a large plasmid can be successfully incorporated within chitosan nanoparticles, the size of the plasmid incorporated within the nanoparticles may still significantly affect gene transfer to cells.

Review: gene- and stem cell-based therapeutics for bone regeneration and repair

Many clinical conditions require regeneration or implantation of bone. This is one focus shared by neurosurgery and orthopedics. Current therapeutic options (bone grafting and protein-based therapy) do not provide satisfying solutions to the problem of massive bone defects. In the past few years, gene- and stem cell-based therapy has been extensively studied to achieve a viable alternative to current solutions offered by modern medicine for bone-loss repair. The use of adult stem cells for bone regeneration has gained much focus. This unique population of multipotential cells has been isolated from various sources, including bone marrow, adipose, and muscle tissues. Genetic engineering of adult stem cells with potent osteogenic genes has led to fracture repair and rapid bone formation in vivo. It is hypothesized that these genetically modified cells exert both an autocrine and a paracrine effects on host stem cells, leading to an enhanced osteogenic effect. The use of direct gene delivery has also shown much promise for in vivo bone repair. Several viral and nonviral methods have been used to achieve substantial bone tissue formation in various sites in animal models. To advance these platforms to the clinical setting, it will be mandatory to overcome specific hurdles, such as control over transgene expression, viral vector toxicity, and prolonged culture periods of therapeutic stem cells. This review covers a prospect of cell and gene therapy for bone repair as well as some very recent advancements in stem cell isolation, genetic engineering, and exogenous control of transgene expression.

Applications of gene therapy and adult stem cells in bone bioengineering

Bone tissue engineering is an emerging field, that could become a main therapeutic strategy in orthopedics in coming years. While bone has regenerative abilities that enable the self repair and regeneration of fractures, there are extreme situations in which the extent of bone loss is too large for complete regeneration to occur. In order to achieve bone regeneration, osteogenic genes (mainly from the bone morphogenetic protein family) can be delivered either directly into the target tissue, or by using adult stem cells, which are later implanted into the target site. Engineered adult stem cells combined with biodegradable polymeric scaffolds can be implanted into target sites, with or without ex vivo culture period. Several important factors influence the success of bone engineering approaches including: choice of cell and scaffold, the vector used in order to deliver the osteogenic gene, and the osteogenic gene itself. Cutting-edge imaging technologies, bioinformatics-based analysis of gene expression and exogenous regulation of transgene expression are among the tools that are being used to optimize and control bone formation in vivo. In this review we have attempted to provide an overview of the main factors that should be considered when utilizing adult stem cells and gene therapy strategies to regenerate bone defects or to promote new bone formation in vivo.

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.

Identification of BMP9 and BMP10 as functional activators of the orphan activin receptor-like kinase 1 (ALK1) in endothelial cells

ALK1 is an endothelial-specific type I receptor of the TGFbeta receptor family whose heterozygous mutations cause hereditary hemorrhagic telangiectasia type 2. Although TGFbeta1 and TGFbeta3 have been shown to bind ALK1 under specific experimental conditions, they may not represent the physiological ligands for this receptor. In the present study, we demonstrate that BMP9 induces the phosphorylation of Smad1/5/8 in microvascular endothelial cells, and this phosphorylation lasts over a period of 24 hours. BMP9 also activates the ID1 promoter-derived BMP response element (BRE) in a dose-dependent manner (EC50 = 45 +/- 27 pg/mL), and this activation is abolished by silencing ALK1 expression or addition of ALK1 extracellular domain. Overexpression of endoglin increases the BMP9 response, whereas silencing of both BMPRII and ActRIIA expressions completely abolishes it. BMP10, which is structurally close to BMP9, is also a potent ALK1 ligand. Finally, we demonstrate that BMP9 and BMP10 potently inhibit endothelial cell migration and growth, and stimulate endothelial expression of a panel of genes that was previously reported to be activated by the constitutively active form of ALK1. Taken together, our results suggest that BMP9 and BMP10 are two specific ALK1 ligands that may physiologically trigger the effects of ALK1 on angiogenesis.

The use of tissue-engineered bone with human bone morphogenetic protein-4-modified bone-marrow stromal cells in repairing mandibular defects in rabbits

In this study, the capacity of hBMP-4 gene therapy combined with tissue-engineering techniques to improve the repair of mandibular osseous defects in rabbits was explored. A mammalian plasmid vector expressing enhanced green fluorescent protein-human bone morphogenetic protein-4 (pEGFP-hBMP-4) was initially constructed through subcloning techniques. Bone-marrow stromal cells (bMSCs) from New Zealand White rabbits were cultured and either transfected with pEGFP-hBMP-4 or pEGFP, or left untransfected in vitro. Once the transfer efficiency was determined through the expression of EGFP, cells from the three groups were combined with natural non-organic bone (NNB) at a concentration of 50 x 10(6)cells/ml and placed in 15 mm x 6 mm bilateral, full-thickness, mandibular defects surgically made in 12 rabbits. Together with NNB control, there were six samples per group. Four weeks after surgery, the implants were harvested and evaluated histomorphologically. Under optimal experimental conditions, gene transfer efficiency reached a maximum of 38.2+/-9.4%. While the percentage of new bone area in the NNB control group was 8.8+/-3.1%, in the untransfected bMSC group 22.5+/-8.2%, and in the pEGFP group 18.1+/-9.0%, a significantly higher amount of 32.5+/-6.1% was observed in the pEGFP-hBMP-4 group. These results suggest that transfection of bMSCs with hBMP-4 enhances their inherent osteogenic capacity for maxillofacial bone tissue-engineering applications.

Simultaneous gene transfer of bone morphogenetic protein (BMP) -2 and BMP-7 by in vivo electroporation induces rapid bone formation and BMP-4 expression

BACKGROUND

Transcutaneous in vivo electroporation is expected to be an effective gene-transfer method for promoting bone regeneration using the BMP-2 plasmid vector. To promote enhanced osteoinduction using this method, we simultaneously transferred cDNAs for BMP-2 and BMP-7, as inserts in the non-viral vector pCAGGS.

METHODS

First, an in vitro study was carried out to confirm the expression of BMP-2 and BMP-7 following the double-gene transfer. Next, the individual BMP-2 and BMP-7 plasmids or both together were injected into rat calf muscles, and transcutaneous electroporation was applied 8 times at 100 V, 50 msec.

RESULTS

In the culture system, the simultaneous transfer of the BMP-2 and BMP-7 genes led to a much higher ALP activity in C2C12 cells than did the transfer of either gene alone. In vivo, ten days after the treatment, soft X-ray analysis showed that muscles that received both pCAGGS-BMP-2 and pCAGGS-BMP-7 had better-defined opacities than those receiving a single gene. Histological examination showed advanced ossification in calf muscles that received the double-gene transfer. BMP-4 mRNA was also expressed, and RT-PCR showed that its level increased for 3 days in a time-dependent manner in the double-gene transfer group. Immunohistochemistry confirmed that BMP-4-expressing cells resided in the matrix between muscle fibers.

CONCLUSION

The simultaneous transfer of BMP-2 and BMP-7 genes using in vivo electroporation induces more rapid bone formation than the transfer of either gene alone, and the increased expression of endogenous BMP-4 suggests that the rapid ossification is related to the induction of BMP-4.

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.

Local immunomodulation with CD4 and CD8 antibodies, but not cyclosporine A, improves osteogenesis induced by ADhBMP9 gene therapy

This study was designed to see if immunosuppression achieved using local application of cyclosporine A (Cs. A) or CD4 and CD8 antibodies would improve bone formation following intramuscular injections of human BMP-4 and BMP-9 adenoviral vectors (ADhBMP4 and ADhBMP9) in Sprague-Dawley rats. Cs. A was injected into the thigh muscle. After 2 days, ADhBMP4, ADhBMP9, and the antibodies were separately injected into the left and right rear legs. At this time, the number of CD4+/CD3+ cells was significantly lower and the number of CD8+/CD3+ cells higher in the Cs. A group than in the control group (P < 0.01). The total number of white blood cells 3 days following injection of CD4 and CD8 antibodies was significantly lower than that before the injection (P < 0.01). At 4 weeks after the viral and antibody injections, mean bone volumes at the ADhBMP9 treatment sites were 0.29 +/- 0.01 cm3 in the viral control group, 0.17 +/- 0.03 cm3 in the Cs. A-ADhBMPs group, and 0.59 +/- 0.07 cm3 in the antibodies-ADhBMPs group. ADhBMP4 did not induce new bone formation in any group. This study demonstrates that local immunomodulation may improve the osteogenic potential of bone morphogenetic protein gene therapy in the clinical setting.

Different Osteogenic Potentials of Recombinant Human BMP-6 Adeno-Associated Virus and Adenovirus in Two Rat Strains

The osteogenic potential of AAV5hBMP6 was compared with that of ADhBMP6 in immunodeficient and immunocompetent rats. AAV5hBMP6 (2.3 x 10(12) particles) and ADhBMP6 (5 x 10(7) PFU) elicited viral antibody production in immunocompetent rats. Among rats that received AAV5hBMP6, the earliest time points at which the bone was visible under CT scanner were 30 days in 2-month-old Sprague-Dawley (SD) rats and 60 days in 18-month-old SD rats. The mean volumes of ectopic bone 90 days after viral injection were 0.31 +/- 0.14 cm(3) in athymic nude rats, 0.64 +/- 0.12 cm(3) in 2-month-old SD rats, and 0.21 +/- 0.10 cm(3) in 18-month-old SD rats. In contrast, among rats that received ADhBMP6, the earliest time points to observe the bone formation by CT scan were 15 days in 2-month-old rats and no bone formation in 18-month-old SD rats. The mean volumes of ectopic bone were 4.17 +/- 0.05 cm(3) in athymic nude rats and 0.06 +/- 0.03 cm(3) in 2-month-old SD rats. Although both types of viruses induced an immune response in immunocompetent animals, this response played different roles in the process of bone formation induced by the BMP6 vectors.

Comparison of osteogenic potentials of human rat BMP4 and BMP6 gene therapy using [E1-] and [E1-,E2b-] adenoviral vectors

Osteogenic potentials of some recombinant human bone morphogenetic protein (BMP) first-generation adenoviral vectors (ADhBMPs) are significantly limited in immunocompetent animals. It is unclear what role expression of viral proteins and foreign proteins transduced by adenoviral vectors play in the host immune response and in ectopic bone formation. In this study two sets of experiments were designed and performed. First, rat BMP6 cDNA were amplified, sequenced, and recombined in first-generation adenoviral vector (ADrBMP6). A comparison of human and rat BMP6 adenoviral vectors demonstrated identical osteogenic activities in both immunodeficient and immunocompetent rats. Second, the activities of recombinant human BMP6 in E1- (ADhBMP6) and [E1-,E2b-] ( [E1-,E2b-]ADGFP&hBMP6, and [E1-,E2b-]ADhBMP6) adenoviral vectors were compared in both in vitro and in vivo models. Similar activities of these two generations of BMP adenoviral vectors were found in all models. These results indicate that the amount of viral gene expression and the source of the BMP cDNA are not major factors in the interruption of osteogenic potentials of recombinant BMP6 adenoviral vectors in immunocompetent animals.

Co-transfection with the osteogenic protein (OP)-1 gene and the insulin-like growth factor (IGF)-I gene enhanced osteoblastic cell differentiation

Previous studies from this laboratory showed that the action of Osteogenic Protein-1 (OP-1, BMP-7) on osteoblastic cell differentiation could be enhanced by other protein factors, such as Insulin-like Growth Factor (IGF)-I. In the present study, we examined the effects of co-transfection with a combination of the OP-1 and the IGF-I gene on osteoblastic cell differentiation. The results first showed that fetal rat calvaria (FRC) cells transfected with the OP-1 gene under the control of the cytomegalovirus (CMV) promoter showed substantial production of the OP-1 protein. Transfected FRC cells also showed a DNA concentration-dependent increase in alkaline phosphatase (AP) activity, an osteoblastic cell differentiation marker. Von Kossa-positive nodules, a hallmark of bone formation in long-term cultures of bone-derived cells, were also observed in the transfected cells after 26 days in culture, whereas none were observed in control cells. Co-transfection of FRC cells with the combination of the OP-1 and the IGF-I gene resulted in a synergistic stimulation of AP activity. The increase was DNA dose-dependent. The current data show that transfection of OP-1 gene into osteoblastic cells stimulates osteoblastic cell differentiation in vitro. The study further demonstrates the feasibility of employing gene transfer of a second gene in combination with an OP-1 vector to synergistically enhance OP-1 activity.

The 3rd International Meeting on Gene Therapy in Rheumatology and Orthopaedics

The 3rd International Meeting on Gene Therapy in Rheumatology and Orthopaedics was held in Boston, Massachusetts, USA in May 2004. Keystone lectures delivered by Drs Joseph Glorioso and Inder Verma provided comprehensive, up-to-date information on all major virus vectors. Other invited speakers covered the application of gene therapy to treatment of arthritis, including the latest clinical trial in rheumatoid arthritis, as well as lupus and Sjögren's syndrome. Applications in mesenchymal stem cell biology, tissue repair, and regenerative medicine were also addressed. The field has advanced considerably since the previous meeting in this series, and further clinical trials seem likely.

Long-term tracing of adenoviral expression in rat and rabbit using luciferase imaging

BACKGROUND

Luciferase optical imaging provides a novel method to monitor transgene expression in small living animals. As the genetic and immunological heritages of particular animals significantly affect the expression of adenovirus-delivered transgenes, it is essential to know the expression patterns specific to athymic nude and Sprague-Dawley rats, two strains commonly used in rodent models. In this study we set out to determine these patterns. At the same time, we tested luciferase optical imaging in a larger animal, the rabbit.

METHODS

A recombinant luciferase adenoviral vector was injected subcutaneously or intramuscularly into athymic nude rats, Sprague-Dawley rats, and Dutch Belted rabbits. The luciferase expression was assessed using a cooled charge-coupled device.

RESULTS

The luminescent signal was capable of passing through at least 1.3 cm of muscle tissue and proved to be much stronger when luciferin was delivered via a local injection than by an intraperitoneal injection. Although the types of immune cells differed between immunodeficient and immunocompetent rats, similar amounts and patterns of luciferase expression were observed in the musculature in two rat strains during the 1st month after a viral intramuscular injection. The duration of luciferase expression was longer than 15 months in athymic nude rats, 9 months in Sprague-Dawley rats, and 6 months in rabbits following a direct viral injection.

CONCLUSIONS

Luciferase expression after adenoviral gene delivery can persist for longer than 6 months, even in immunocompetent animals. Live imaging of luciferase expression can be performed not only in small animals, but also in larger animals such as rabbits.

Crystal structure of BMP-9 and functional interactions with pro-region and receptors

Bone morphogenetic proteins (BMPs), a subset of the transforming growth factor (TGF)-beta superfamily, regulate a diverse array of cellular functions during development and in the adult. BMP-9 (also known as growth and differentiation factor (GDF)-2) potently induces osteogenesis and chondrogenesis, has been implicated in the differentiation of cholinergic neurons, and may help regulate glucose metabolism. We have determined the structure of BMP-9 to 2.3 A and examined the differences between our model and existing crystal structures of other BMPs, both in isolation and in complex with their receptors. TGF-beta ligands are translated as precursors, with pro-regions that generally dissociate after cleavage from the ligand, but in some cases (including GDF-8 and TGF-beta1, -2, and -3), the pro-region remains associated after secretion from the cell and inhibits binding of the ligand to its receptor. Although the proregion of BMP-9 remains tightly associated after secretion, we find, in several cell-based assays, that the activities of BMP-9 and BMP-9.pro-region complex were equivalent. Activin receptor-like kinase 1 (ALK-1), an orphan receptor in the TGF-beta family, was also identified as a potential receptor for BMP-9 based on surface plasmon resonance studies (BIAcore) and the ability of soluble ALK-1 to block the activity of BMP-9.pro-region complex in cell-based assays.

The potential of gene therapy for fracture healing in osteoporosis

Osteoporosis-associated fractures impair a patient's function and quality of life and represent one of the major public health burdens. Demographic changes predict a dramatic increase in osteoporotic fractures. Experimental data have shown that osteoporosis impairs fracture healing. Clinical observations demonstrate high failure rates of implant fixation in osteoporosis. The reduced healing capacity, including impaired bone formation, in osteoporotic humans might be due to defects in mesenchymal stem cells that lead to reduced proliferation and osteoblastic differentiation. Growth factors show remarkable promise as agents that can improve the healing of bone or increase the proliferation and differentiation capacities of mesenchymal stem cells. Their clinical utility is limited by delivery problems. The attraction of gene-transfer approaches is the unique ability to deliver authentically processed gene products to precise anatomical locations at therapeutic levels for sustained periods of time. Unlike the treatment of chronic diseases, it is neither necessary nor desirable for transgene expression to persist beyond the few weeks or months needed to achieve healing. This review presents different approaches of gene therapy to enhance fracture healing and summarizes the promising results of preclinical studies. It focuses on applications of this new technique to fracture healing in osteoporosis. In our opinion, these applications represent some of the few examples in which gene therapy has a good chance of early clinical success.

Strategies for directing the differentiation of stem cells into the osteogenic lineage in vitro

A major area in regenerative medicine is the application of stem cells in bone reconstruction and bone tissue engineering. This will require well-defined and efficient protocols for directing the differentiation of stem cells into the osteogenic lineage, followed by their selective purification and proliferation in vitro. The development of such protocols would reduce the likelihood of spontaneous differentiation of stem cells into divergent lineages on transplantation, as well as reduce the risk of teratoma formation in the case of embryonic stem cells. Additionally, such protocols could provide useful in vitro models for studying osteogenesis and bone development, and facilitate the genetic manipulation of stem cells for therapeutic applications. The development of pharmokinetic and cytotoxicity/genotoxicity screening tests for bone-related biomaterials and drugs could also use protocols developed for the osteogenic differentiation of stem cells. This review critically examines the various strategies that could be used to direct the differentiation of stem cells into the osteogenic lineage in vitro.