Bone formation by BMP-7-transduced human gingival keratinocytes

Diverse effect of BMP-2 homodimer on mesenchymal progenitors of different origin

Bone morphogenetic protein-2 (BMP-2), is a potential factor to enhance osseointegration of dental implants. However, the appropriate cellular system to investigate the osteogenic effect of BMP-2 in vitro in a standardized manner still needs to be defined. The aim of this study was to examine the effect of BMP-2 on the cell proliferation and osteogenic differentiation of human osteogenic progenitors of various origins: dental pulp stem cells (DPSC), human osteosarcoma cell line (Saos-2) and human embryonic palatal mesenchymal cell line (HEPM). For induction of osteogenic differentiation, cell culture medium was supplemented with BMP-2 homodimer alone or in combination with conventionally used differentiation inducing agents. Differentiation was monitored for 6–18 days. To assess differentiation, proliferation rate, alkaline phosphatase activity, calcium deposition and the expression level of osteogenic differentiation marker genes (Runx2, BMP-2) were measured. BMP-2 inhibited cell proliferation in a concentration and time-dependent manner. In a concentration which caused maximal cell proliferation, BMP-2 did not induce osteogenic differentiation in any of the tested systems. However, it had a synergistic effect with the osteoinductive medium in both DPSC and Saos-2, but not in HEPM cells. We also found that the differentiation process was faster in Saos-2 than in DPSCs. Osteogenic differentiation could not be induced in the osteoblast progenitor HEPM cells. Our data suggest that in a concentration that inhibits proliferation the differentiation inducing effect of BMP-2 is evident only in the presence of permissive osteoinductive components. β-glycerophosphate, was identified interacting with BMP-2 in a synergistic manner.

Wnt and BMP Signaling Crosstalk in Regulating Dental Stem Cells: Implications in Dental Tissue Engineering

Tooth is a complex hard tissue organ and consists of multiple cell types that are regulated by important signaling pathways such as Wnt and BMP signaling. Serious injuries and/or loss of tooth or periodontal tissues may significantly impact aesthetic appearance, essential oral functions and the quality of life. Regenerative dentistry holds great promise in treating oral/dental disorders. The past decade has witnessed a rapid expansion of our understanding of the biological features of dental stem cells, along with the signaling mechanisms governing stem cell self-renewal and differentiation. In this review, we first summarize the biological characteristics of seven types of dental stem cells, including dental pulp stem cells, stem cells from apical papilla, stem cells from human exfoliated deciduous teeth, dental follicle precursor cells, periodontal ligament stem cells, alveolar bone-derived mesenchymal stem cells (MSCs), and MSCs from gingiva. We then focus on how these stem cells are regulated by bone morphogenetic protein (BMP) and/or Wnt signaling by examining the interplays between these pathways. Lastly, we analyze the current status of dental tissue engineering strategies that utilize oral/dental stem cells by harnessing the interplays between BMP and Wnt pathways. We also highlight the challenges that must be addressed before the dental stem cells may reach any clinical applications. Thus, we can expect to witness significant progresses to be made in regenerative dentistry in the coming decade.

Identifying the Cellular Mechanisms Leading to Heterotopic Ossification

Heterotopic ossification (HO) is a debilitating condition defined by the de novo development of bone within non-osseous soft tissues, and can be either hereditary or acquired. The hereditary condition, fibrodysplasia ossificans progressiva is rare but life threatening. Acquired HO is more common and results from a severe trauma that produces an environment conducive for the formation of ectopic endochondral bone. Despite continued efforts to identify the cellular and molecular events that lead to HO, the mechanisms of pathogenesis remain elusive. It has been proposed that the formation of ectopic bone requires an osteochondrogenic cell type, the presence of inductive agent(s) and a permissive local environment. To date several lineage-tracing studies have identified potential contributory populations. However, difficulties identifying cells in vivo based on the limitations of phenotypic markers, along with the absence of established in vitro HO models have made the results difficult to interpret. The purpose of this review is to critically evaluate current literature within the field in an attempt identify the cellular mechanisms required for ectopic bone formation. The major aim is to collate all current data on cell populations that have been shown to possess an osteochondrogenic potential and identify environmental conditions that may contribute to a permissive local environment. This review outlines the pathology of endochondral ossification, which is important for the development of potential HO therapies and to further our understanding of the mechanisms governing bone formation.

Heterotopic ossification after hip arthroscopy

Heterotopic ossification (HO) after hip arthroscopy is the abnormal formation of mature lamellar bone within extra skeletal soft tissues. HO may lead to pain, impaired range of motion and possibly revision surgery. There has been a substantial amount of recent research on the pathophysiology, prophylaxis and treatment of HO associated with open and arthroscopic hip surgery. This article reviews the literature on the aforementioned topics with a focus on their application in hip arthroscopy.

Evaluation of the cellular origins of heterotopic ossification

Heterotopic ossification (HO), acquired or hereditary, is featured by the formation of bone outside of the normal skeleton. Typical acquired HO is a common, debilitating condition associated with traumatic events. Cardiovascular calcification, an atypical form of acquired HO, is prevalent and associated with high rates of cardiovascular mortality. Hereditary HO syndromes, such as fibrodysplasia ossificans progressiva and progressive osseous heteroplasia, are rare, progressive, life-threatening disorders. The cellular origins of HO remain elusive. Some bona fide contributing cell populations have been found through genetic lineage tracing and other experiments in vivo, and various other candidate populations have been proposed. Nevertheless, because of the difficulties in establishing cellular phenotypes in vivo and other confounding factors, the true identities of these populations are still uncertain. This review critically evaluates the accumulating data in the field. The major focus is on the candidate populations that may give rise to osteochondrogenic lineage cells directly, not the populations that may contribute to HO indirectly. This issue is important not solely because of the clinical implications, but also because it highlights the basic biological processes that govern bone formation.

The use of bone morphogenetic protein 7 in fracture non-unions

OBJECTIVE

To assess the rate of clinical and radiological union with the use of bone morphogenetic protein 7 (BMP-7) in a range of fractures.

METHODS

This case series retrospectively reviews a series of 16 fracture non-unions in 13 patients. These patients were treated with the commercially available BMP-7. Time to radiological and clinical union was assessed by serial out-patient follow-up.

RESULTS

At nine months post-surgery in which BMP-7 was added, 12 of 16 non-unions had achieved clinical and radiographic union. Three patients required repeat grafting. The mean time to union was 5.1 ± 1.6 months after the application of BMP-7.

CONCLUSION

The use of the osteo-inductive agent, BMP-7 results in good clinical and radiological outcomes which are not restricted to tibial non-unions.

Effects of adenoviral-mediated coexpression of bone morphogenetic protein-7 and insulin-like growth factor-1 on human periodontal ligament cells

BACKGROUND AND OBJECTIVE

Bone morphogenetic protein-7 (BMP-7) and insulin-like growth factor-1 (IGF-1) are important in periodontal reconstruction. However, their synergistic effect in periodontal regeneration by gene delivery has not been reported. In this study, gene delivery of these two growth factors to human periodontal ligament cells (hPDLCs) was examined for its effects on cell proliferation and differentiation.

MATERIAL AND METHODS

Recombinant adenoviruses containing both human BMP-7 and IGF-1 cDNA created by introducing the internal ribosome entry site (IRES) sequence were used to transfer the genes into hPDLCs. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and cell cycle analysis were used to observe their effects on cell proliferation, while alkaline phosphatase activity measurement, RT-PCR and in vivo tests were conducted to investigate their effects on cell differentiation.

RESULTS

The proliferation of hPDLCs transduced by adenoviruses coexpressing BMP-7 and IGF-1 was suppressed while their differentiation ability was enhanced. There was a synergism of BMP-7 and IGF-1 in up-regulating alkaline phosphatase activity and mRNA levels of collagen type I and Runx2. Implantation in vivo with scaffolds illustrated that the transduced cells exhibited osteogenic differentiation and formed bone-like structures.

CONCLUSION

The combined delivery of BMP-7 and IGF-1 genes using an IRES-based strategy synergistically enhanced differentiation of hPDLCs. It is suggested that this could be a new potential method in gene therapy for periodontal reconstruction.

Gene Therapy and its Implications in Dentistry

Background

The concept of transferring genes to tissues for clinical applications has been discussed for nearly half a century. The exponential increase in our ability to manipulate the genetic material of a cell via recombinant DNA technology has brought this goal closer to realization. The original perception that gene therapy should be considered only for a few major organs as a means of treating life-threatening disorders that are refractory to conventional treatment has changed. There are many non-life-threatening conditions that adversely affect a patient’s quality of life, for which there are no effective treatments. The lack of suitable treatment has permitted morbidity to become a rational basis for extending the scope of gene therapy. In the past few years, remarkable progress has been made in the field of gene therapy. While considerable problems remain, thus impeding the routine clinical use of gene transfer, gene therapy will have a pervasive and significant impact on areas that are based on biological science.

Aim

The purpose of this review is to examine the progress made in addressing gene transfer strategies for correcting various diseases and problems that are relevant to dental practice.

Bone Sialoprotein Gene Transfer to Periodontal Ligament Cells May Not Be Sufficient to Promote Mineralization In Vitro or In Vivo

BACKGROUND

To improve regenerative therapies, it is important to understand the cells and factors modulating periodontal tissues. Our group has focused on bone sialoprotein (BSP), a mineralized tissue-selective protein considered to be involved in the initiation of cementogenesis and osteogenesis. In this study, we examined whether gene transfer of BSP into periodontal ligament (PDL) cells would result in an increased ability of PDL cells to promote mineralization in vitro and in vivo.

METHODS

PDL cells obtained from CD-1 mice were immortalized using simian virus (SV) 40 large T antigen (TAg) and designated SV-PDL cells. SV-PDL cells were infected in vitro with LacZ gene-expressing control adenovirus vector. A 1,000 plaque-forming unit (pfu) titer was selected (based on X-gal staining) and cells were infected with mouse BSP-expressing replication-deficient adenoviral vector to determine the mRNA expression and protein level of BSP. Total RNA was isolated from cells on days 2, 4, and 6. Media were obtained on days 3, 5, and 7 for protein determination. Northern blot analysis was performed for mRNA expression and Western blot analysis for protein expression. To test the effect of BSP gene transfer on the mineralization of PDL cells, in vitro (von Kossa) and in vivo (severe combined immunodeficiency [SCID] mice) experiments were performed.

RESULTS

Under normal conditions, PDL cells do not express BSP transcripts and do not promote significant mineralization. SV-PDL cells infected with a BSP viral vector expressed and secreted substantial levels of BSP as confirmed by Northern and Western blot analysis. BSP mRNA and protein levels were strong on day 2 and still apparent on day 6, although not as great. However, no mineral nodule formation was noted either in vitro or in vivo.

CONCLUSIONS

Although BSP is an important and necessary protein for mineralization, it may not be sufficient for promoting mineralization without the addition or removal of other factors. Further studies will help to clarify the specific factors required for promoting mineralization, a required step for designing predictable periodontal regenerative therapies.