Regional Gene Therapy for Bone Tissue Engineering: A Current Concepts Review

The management of segmental bone defects presents a complex reconstruction challenge for orthopedic surgeons. Current treatment options are limited by efficacy across the spectrum of injury, morbidity, and cost. Regional gene therapy is a promising tissue engineering strategy for bone repair, as it allows for local implantation of nucleic acids or genetically modified cells to direct specific protein expression. In cell-based gene therapy approaches, a variety of different cell types have been described including mesenchymal stem cells (MSCs) derived from multiple sources-bone marrow, adipose, skeletal muscle, and umbilical cord tissue, among others. MSCs, in particular, have been well studied, as they serve as a source of osteoprogenitor cells in addition to providing a vehicle for transgene delivery. Furthermore, MSCs possess immunomodulatory properties, which may support the development of an allogeneic "off-the-shelf" gene therapy product. Identifying an optimal cell type is paramount to the successful clinical translation of cell-based gene therapy approaches. Here, we review current strategies for the management of segmental bone loss in orthopedic surgery, including bone grafting, bone graft substitutes, and operative techniques. We also highlight regional gene therapy as a tissue engineering strategy for bone repair, with a focus on cell types and cell sources suitable for this application.

Cannabidiol Rescues TNF-α-Inhibited Proliferation, Migration, and Osteogenic/Odontogenic Differentiation of Dental Pulp Stem Cells

Strategies to promote dental pulp stem cells (DPSCs) functions including proliferation, migration, pro-angiogenic effects, and odontogenic/osteogenic differentiation are in urgent need to restore pulpitis-damaged dentin/pulp regeneration and DPSCs-based bone tissue engineering applications. Cannabidiol (CBD), an active component of Cannabis sativa has shown anti-inflammation, chemotactic, anti-microbial, and tissue regenerative potentials. Based on these facts, this study aimed to analyze the effect of CBD on DPSCs proliferation, migration, and osteogenic/odontogenic differentiation in basal and inflammatory conditions. Highly pure DPSCs with characteristics of mesenchymal stem cells (MSCs) were successfully isolated, as indicated by the results of flowcytometry and multi-lineage (osteogenic, adipogenic, and chondrogenic) differentiation potentials. Among the concentration tested (0.1-12.5 µM), CBD (2.5 μM) showed the highest anabolic effect on the proliferation and osteogenic/odontogenic differentiation of DPSCs. Pro-angiogenic growth factor VEGF mRNA expression was robustly higher in CBD-treated DPSCs. CBD also prompted the migration of DPSCs and CBD receptor CB1 and CB2 expression in DPSCs. TNF-α inhibited the viability, migration, and osteogenic/odontogenic differentiation of DPSCs and CBD reversed these effects. CBD alleviated the TNF-α-upregulated expression of pro-inflammatory cytokines TNF-α, interleukin (IL)-1β, and IL-6 in DPSCs. In conclusion, our results indicate the possible application of CBD on DPSCs-based dentin/pulp and bone regeneration.

Dental pulp stem cells for reconstructing bone defects: A systematic review and meta-analysis

BACKGROUND

Bone reconstruction with appropriate quality and quantity for dental implant replacement in the alveolar ridge is a challenge in dentistry. As dental pulp stem cells (DPSCs) could be a new perspective in bone regeneration in the future, this study investigated the bone regeneration process by DPSCs.

METHODS

Electronic searches for articles in the PubMed, EMBASE, and Scopus databases were completed until 21 April 2022. The most important inclusion criteria for selecting in vivo studies reporting quantitative data based on new bone volume and new bone area. The quality assessment was performed based on Cochrane's checklist.

RESULTS

After the title, abstract, and full-text screening of 762 studies, 23 studies were included. A meta-analysis of 70 studies that reported bone regeneration based on new bone area showed a statistically significant favorable influence on bone tissue regeneration compared to the control groups (P<0.00001, standardized mean difference [SMD]=2.40, 95% CI: 1.55‒3.26; I2=83%). Also, the meta-analysis of 14 studies that reported new bone regeneration based on bone volume showed a statistically significant favorable influence on bone tissue regeneration compared to the control groups (P=0.0003, SMD=1.85, 95% CI: 0.85‒2.85; I2=84%).

CONCLUSION

This systematic review indicated that DPSCs in tissue regeneration therapy significantly affected bone tissue complex regeneration. However, more and less diverse preclinical studies will enable more powerful meta-analyses in the future.

Present status and future directions: Root resorption

Root resorption is the loss of dental hard tissue because of odontoclastic action. In permanent teeth, it is undesirable and pathological in nature. Root resorption may occur on the inner aspect of the root canal (internal root resorption) or on the outer aspect of the root (external root resorption). Regardless of its location, root resorption is irreversible, and may result in discomfort for the patient, requires management and/or, in some cases, results in the premature loss of the affected tooth. Root resorption is often challenging to accurately diagnose and manage. The aim of this narrative review is to present the relevant literature on the aetiology, pathogenesis, diagnosis and management, as well as discuss the future directions of diagnosis and management of root resorption.

Priming strategies for controlling stem cell fate: Applications and challenges in dental tissue regeneration

Mesenchymal stromal cells (MSCs) have attracted intense interest in the field of dental tissue regeneration. Dental tissue is a popular source of MSCs because MSCs can be obtained with minimally invasive procedures. MSCs possess distinct inherent properties of self-renewal, immunomodulation, proangiogenic potential, and multilineage potency, as well as being readily available and easy to culture. However, major issues, including poor engraftment and low survival rates in vivo, remain to be resolved before large-scale application is feasible in clinical treatments. Thus, some recent investigations have sought ways to optimize MSC functions in vitro and in vivo. Currently, priming culture conditions, pretreatment with mechanical and physical stimuli, preconditioning with cytokines and growth factors, and genetic modification of MSCs are considered to be the main strategies; all of which could contribute to improving MSC efficacy in dental regenerative medicine. Research in this field has made tremendous progress and continues to gather interest and stimulate innovation. In this review, we summarize the priming approaches for enhancing the intrinsic biological properties of MSCs such as migration, antiapoptotic effect, proangiogenic potential, and regenerative properties. Challenges in current approaches associated with MSC modification and possible future solutions are also indicated. We aim to outline the present understanding of priming approaches to improve the therapeutic effects of MSCs on dental tissue regeneration.

Secreted Frizzled-Related Protein 1 Promotes Odontoblastic Differentiation and Reparative Dentin Formation in Dental Pulp Cells

Direct pulp capping is an effective treatment for preserving dental pulp against carious or traumatic pulp exposure via the formation of protective reparative dentin by odontoblast-like cells. Reparative dentin formation can be stimulated by several signaling molecules; therefore, we investigated the effects of secreted frizzled-related protein (SFRP) 1 that was reported to be strongly expressed in odontoblasts of newborn molar tooth germs on odontoblastic differentiation and reparative dentin formation. In developing rat incisors, cells in the dental pulp, cervical loop, and inner enamel epithelium, as well as ameloblasts and preodontoblasts, weakly expressed Sfrp1; however, Sfrp1 was strongly expressed in mature odontoblasts. Human dental pulp cells (hDPCs) showed stronger expression of SFRP1 compared with periodontal ligament cells and gingival cells. SFRP1 knockdown in hDPCs abolished calcium chloride-induced mineralized nodule formation and odontoblast-related gene expression and decreased BMP-2 gene expression. Conversely, SFRP1 stimulation enhanced nodule formation and expression of BMP-2. Direct pulp capping treatment with SFRP1 induced the formation of a considerable amount of reparative dentin that has a structure similar to primary dentin. Our results indicate that SFRP1 is crucial for dentinogenesis and is important in promoting reparative dentin formation in response to injury.

FGF8 and BMP2 mediated dynamic regulation of dental mesenchyme proliferation and differentiation via Lhx8/Suv39h1 complex

The homeobox gene, LIM-homeobox 8 (Lhx8), has previously been identified as an essential transcription factor for dental mesenchymal development. However, how Lhx8 itself is regulated and regulates odontogenesis remains poorly understood. In this study, we employed an RNAscope assay to detect the co-expression pattern of Lhx8 and Suv39h1 in the dental mesenchyme, which coincided with the dynamic expression profiles of the early epithelium signal of Fibroblast Growth Factor 8 (FGF8) and the later mesenchymal signal Bone Morphogenetic Protein 2 (BMP2). Moreover, FGF8 activated Lhx8, whereas BMP2 repressed Lhx8 expression at the transcriptional level. The high expression of Lhx8 in the early dental mesenchyme maintained the cell fate in an undifferentiated status by interacting with Suv39h1, a histone-lysine N-methyltransferase constitutively expressed in the dental mesenchyme. Further in the ex vivo organ culture model, the knockdown of Suv39h1 significantly blocked the function of Lhx8 and FGF8. Mechanistically, Lhx8/Suv39h1 recognized the odontoblast differentiation-related genes and repressed gene expression via methylating H3K9 on their promoters. Taken together, our data here suggest that Lhx8/Suv39h1 complex is inversely regulated by epithelium-mesenchymal signals, balancing the differentiation and proliferation of dental mesenchyme via H3K9 methylation.

A Current Overview of Scaffold-Based Bone Regeneration Strategies with Dental Stem Cells

Bone defects due to trauma or diseases still pose a clinical challenge to be resolved in the current tissue engineering approaches. As an alternative to traditional methods to restore bone defects, such as autografts, bone tissue engineering aims to achieve new bone formation via novel biomaterials used in combination with multipotent stem cells and bioactive molecules. Mesenchymal stem cells (MSCs) can be successfully isolated from various dental tissues at different stages of development including dental pulp, apical papilla, dental follicle, tooth germ, deciduous teeth, periodontal ligament and gingiva. A wide range of biomaterials including polymers, ceramics and composites have been investigated for their potential as an ideal bone scaffold material. This article reviews the properties and the manufacturing methods of biomaterials used in bone tissue engineering, and provides an overview of bone tissue regeneration approaches of scaffold and dental stem cell combinations as well as their limitations.

Dental Pulp Stem Cells: Advances to Applications

Dental pulp stem cells (DPSCs) have a high capacity for differentiation and the ability to regenerate a dentin/pulp-like complex. Numerous studies have provided evidence of DPSCs’ differentiation capacity, such as in neurogenesis, adipogenesis, osteogenesis, chondrogenesis, angiogenesis, and dentinogenesis. The molecular mechanisms and functions of DPSCs’ differentiation process are affected by growth factors and scaffolds. For example, growth factors such as basic fibroblast growth factor (bFGF), transforming growth factor-β (TGF-β), nerve growth factor (NGF), platelet-derived growth factor (PDGF), and bone morphogenic proteins (BMPs) influence DPSC fate, including in differentiation, cell proliferation, and wound healing. In addition, several types of scaffolds, such as collagen, hydrogel, decellularized bioscaffold, and nanofibrous spongy microspheres, have been used to characterize DPSC cellular attachment, migration, proliferation, differentiation, and functions. An appropriate combination of growth factors and scaffolds can enhance the differentiation capacity of DPSCs, in terms of optimizing not only dental-related expression but also dental pulp morphology. For a cell-based clinical approach, focus has been placed on the tissue engineering triad [cells/bioactive molecules (growth factors)/scaffolds] to characterize DPSCs. It is clear that a deep understanding of the mechanisms of stem cells, including their aging, self-renewal, microenvironmental homeostasis, and differentiation correlated with cell activity, the energy for which is provided from mitochondria, should provide new approaches for DPSC research and therapeutics. Mitochondrial functions and dynamics are related to the direction of stem cell differentiation, including glycolysis, oxidative phosphorylation, mitochondrial metabolism, mitochondrial transcription factor A (TFAM), mitochondrial elongation, and mitochondrial fusion and fission proteins. This review summarizes the effects of major growth factors and scaffolds for regenerating dentin/pulp-like complexes, as well as elucidating mitochondrial properties of DPSCs for the development of advanced applications research.

Multifunctional Bioactive Resin for Dental Restorative Materials

Resin-based composites are widely used as dental restorative materials due to their excellent properties. They must have high modulus, high hardness, and be chemically inert while minimizing moisture uptake. To fulfill these higher standard prerequisites and properties, continuous improvements in each of their components are required. This study develops novel composites with multiple biofunctions. Light-cured Bis-GMA/TEGDMA dental resin (RK)/layered double hydroxide intercalated with fluoride ions (LDH-F)/calcium bentonite (Bt) hybrid composites were prepared. The loading ratio of LDH-F to Bt was varied, ranging from 2.5/2.5 to 10/10 parts per hundred RK and structural, mechanical, and biological properties were studied. The incorporation of even small mass fractions (e.g., 2.5 wt % of LDH-F and 2.5 wt % of Bt) in RK dental resin significantly improved the mechanical properties of the pristine resin. The synthetized materials showed antibacterial and antibiofilm effects against three bacterial strains isolated from healthy volunteers' saliva (Streptococcus spp., Bacteroides fragilis, and Staphylococcus epidermidis) without affecting its ability to induce dental pulp stem cells differentiation into odontoblast-like cells. The capability to balance between the antibiofilm activity and dental pulp stem cells differentiation in addition with improved mechanical properties make these materials a promising strategy in preventive and restorative dentistry.

Bone Tissue Regeneration in the Oral and Maxillofacial Region: A Review on the Application of Stem Cells and New Strategies to Improve Vascularization

Bone tissue engineering techniques are a promising alternative for the use of autologous bone grafts to reconstruct bone defects in the oral and maxillofacial region. However, for successful bone regeneration, adequate vascularization is a prerequisite. This review presents and discusses the application of stem cells and new strategies to improve vascularization, which may lead to feasible clinical applications. Multiple sources of stem cells have been investigated for bone tissue engineering. The stromal vascular fraction (SVF) of human adipose tissue is considered a promising single source for a heterogeneous population of essential cells with, amongst others, osteogenic and angiogenic potential. Enhanced vascularization of tissue-engineered grafts can be achieved by different mechanisms: vascular ingrowth directed from the surrounding host tissue to the implanted graft, vice versa, or concomitantly. Vascular ingrowth into the implanted graft can be enhanced by (i) optimizing the material properties of scaffolds and (ii) their bioactivation by incorporation of growth factors or cell seeding. Vascular ingrowth directed from the implanted graft towards the host tissue can be achieved by incorporating the graft with either (i) preformed microvascular networks or (ii) microvascular fragments (MF). The latter may have stimulating actions on both vascular ingrowth and outgrowth, since they contain angiogenic stem cells like SVF, as well as vascularized matrix fragments. Both adipose tissue-derived SVF and MF are cell sources with clinical feasibility due to their large quantities that can be harvested and applied in a one-step surgical procedure. During the past years, important advancements of stem cell application and vascularization in bone tissue regeneration have been made. The development of engineered in vitro 3D models mimicking the bone defect environment would facilitate new strategies in bone tissue engineering. Successful clinical application requires innovative future investigations enhancing vascularization.

The Conditioned Medium of Calcined Tooth Powder Promotes the Osteogenic and Odontogenic Differentiation of Human Dental Pulp Stem Cells via MAPK Signaling Pathways

The calcined tooth powder (CTP), a type of allogeneic biomimetic mineralized material, has been confirmed that can promote new bone formation when obtained at high temperature. The aim of this study was to investigate effects of the conditioned medium of calcined tooth powder (CTP-CM) on the osteogenic and odontogenic differentiation of human dental pulp stem cells (hDPSCs) and the underlying mechanisms involved. First, ALP activity assay determined that 200 μg/mL was the optimal concentration of CTP-CM for the following experiments. CTP-CM had no significant effect on the proliferation of hDPSCs as indicated by CCK-8 and FCM analysis. Both the gene and protein (DSPP/DSPP, RUNX2/RUNX2, OCN/OCN, OSX/OSX, OPN/OPN, ALP/ALP, and COL-1/COL-1) expression levels increased in the CTP-CM-induced hDPSC group as compared with those in the control group at day 3 or 7, showing the positive regulation of CTP-CM on the osteo/odontogenic differentiation of hDPSCs. Mechanistically, MAPK signaling pathways were activated after the CTP-CM treatment, and the inhibitors targeting MAPK were identified which weakened the effects of CTM-CM on the committed differentiation of hDPSCs. These findings could lead to the creation of stem cell therapies for dental regeneration.

Establishment of an Immortalized Mouse Bmp2 Knockout Dental Papilla Mesenchymal Cell Line

Bone morphogenetic protein 2 (Bmp2) is essential for dentin formation. Bmp2 cKO mice exhibited similar phenotype to dentinogenesis imperfecta (DGI), showing dental pulp exposure, hypomineralized dentin, and delayed odontoblast differentiation. As it is relatively difficult to obtain primary Bmp2 cKO dental papilla mesenchymal cells and to maintain a long-term culture of these primary cells, availability of immortalized deleted Bmp2 dental papilla mesenchymal cells is critical for studying the underlying mechanism of Bmp2 signal in odontogenesis. Here we describe the generation of an immortalized deleted Bmp2 dental papilla mesenchymal (iBmp2^ko/ko-dp) cell line by introducing Cre fluorescent protein (GFP) into the immortalized mouse floxed Bmp2 dental papilla mesenchymal (iBmp2^flox/flox-dp) cells.

Dental pulp stem cells in chitosan/gelatin scaffolds for enhanced orofacial bone regeneration

OBJECTIVE

Biomimetic chitosan/gelatin (CS/Gel) scaffolds have attracted great interest in tissue engineering of several tissues. However, limited information exists regarding the potential of combining CS/Gel scaffolds with oral cells, such as dental pulp stem cells (DPSCs), to produce customized constructs targeting alveolar/orofacial bone reconstruction, which has been the aim of the present study.

METHODS

Two scaffold types, designated as CS/Gel-0.1 and CS/Gel-1, were fabricated using 0.1 and 1% (v/v) respectively of the crosslinker glutaraldehyde (GTA). Scaffolds (n=240) were seeded with DPSCs with/without pre-exposure to recombinant human BMP-2. In vitro assessment included DPSCs characterization (flow cytometry), evaluation of viability/proliferation (live/dead staining, metabolic-based tests), osteo/odontogenic gene expression analysis (qRT-PCR) and structural/chemical characterization (scanning electron microscopy, SEM; energy dispersive X-ray spectroscopy, EDX; X-ray powder diffraction, XRD; thermogravimetry, TG). In vivo assessment included implantation of DPSC-seeded scaffolds in immunocompromised mice, followed by histology and SEM-EDX. Statistical analysis employed one/two-way ANOVA and Tukey's post-hoc tests (significance for p<0.05).

RESULTS

Both scaffolds supported cell viability/proliferation over 14 days in culture, showing extensive formation of a hydroxyapatite-rich nanocrystalline calcium phosphate phase. Differential expression patterns indicated GTA concentration to significantly affect the expression of osteo/odontogenic genes, with CS/Gel-0.1 scaffolds being more effective in upregulating DSPP, IBSP and Osterix. In vivo analysis demonstrated time-dependent production of a nanocrystalline, mineralized matrix at 6, 8 and 10 weeks, being more prominent in constructs bearing rhBMP-2 pre-treated cells. The latter showed higher amounts of osteoid and fully mineralized bone, as well as empty space reduction.

SIGNIFICANCE

These results reveal a promising strategy for orofacial bone tissue engineering.

Mesenchymal Stem Cells of Dental Origin for Inducing Tissue Regeneration in Periodontitis: A Mini-Review

Periodontitis is a chronic disease that begins with a period of inflammation of the supporting tissues of the teeth table and then progresses, destroying the tissues until loss of the teeth occurs. The restoration of the damaged dental support apparatus is an extremely complex process due to the regeneration of the cementum, the periodontal ligament, and the alveolar bone. Conventional treatment relies on synthetic materials that fill defects and replace lost dental tissue, but these approaches are not substitutes for a real regeneration of tissue. To address this, there are several approaches to tissue engineering for regenerative dentistry, among them, the use of stem cells. Mesenchymal stem cells (MSC) can be obtained from various sources of adult tissues, such as bone marrow, adipose tissue, skin, and tissues of the orofacial area. MSC of dental origin, such as those found in the bone marrow, have immunosuppressive and immunotolerant properties, multipotency, high proliferation rates, and the capacity for tissue repair. However, they are poorly used as sources of tissue for therapeutic purposes. Their accessibility makes them an attractive source of mesenchymal stem cells, so this review describes the field of dental stem cell research and proposes a potential mechanism involved in periodontal tissue regeneration induced by dental MSC.

Temporomandibular Joint Regenerative Medicine

The temporomandibular joint (TMJ) is an articulation formed between the temporal bone and the mandibular condyle which is commonly affected. These affections are often so painful during fundamental oral activities that patients have lower quality of life. Limitations of therapeutics for severe TMJ diseases have led to increased interest in regenerative strategies combining stem cells, implantable scaffolds and well-targeting bioactive molecules. To succeed in functional and structural regeneration of TMJ is very challenging. Innovative strategies and biomaterials are absolutely crucial because TMJ can be considered as one of the most difficult tissues to regenerate due to its limited healing capacity, its unique histological and structural properties and the necessity for long-term prevention of its ossified or fibrous adhesions. The ideal approach for TMJ regeneration is a unique scaffold functionalized with an osteochondral molecular gradient containing a single stem cell population able to undergo osteogenic and chondrogenic differentiation such as BMSCs, ADSCs or DPSCs. The key for this complex regeneration is the functionalization with active molecules such as IGF-1, TGF-β1 or bFGF. This regeneration can be optimized by nano/micro-assisted functionalization and by spatiotemporal drug delivery systems orchestrating the 3D formation of TMJ tissues.

Angiogenic and osteogenic potentials of dental stem cells in bone tissue engineering

Manipulation of dental stem cells (DSCs) using current technologies in tissue engineering unveil promising prospect in regenerative medicine. DSCs have shown to possess angiogenic and osteogenic potential in both in vivo and in vitro. Neural crest derived DSCs can successfully be isolated from various dental tissues, exploiting their intrinsic great differentiation potential. In this article, researcher team intent to review the characteristics of DSCs, with focus on their angiogenic and osteogenic differentiation lineage. Clinical data on DSCs are still lacking to prove their restorative abilities despite extensive contemporary literature, warranting research to further validate their application for bone tissue engineering.

Tissue engineering: Dentin - pulp complex regeneration approaches (A review)

Dental pulp is a highly specialized tissue that preserves teeth. It is important to maintain the capabilities of dental pulp before a pulpectomy by creating a local restoration of the dentin-pulp complex from residual dental pulp. The articles identified were selected by two reviewers based on entry and exit criteria. All relevant articles indexed in PubMed, Springer, Science Direct, and Scopus with no limitations from 1961 to 2016 were searched. Factors investigated in the selected articles included the following key words: Dentin-Pulp Complex, Regeneration, Tissue Engineering, Scaffold, Stem Cell, and Growth Factors. Of the 233 abstracts retrieved, the papers which were selected had evaluated the clinical aspects of the application of dentin-pulp regeneration. Generally, this study has introduced a new approach to provoke the regeneration of the dentin-pulp complex after a pulpectomy, so that exogenous growth factors and the scaffold are able to induce cells and blood vessels from the residual dental pulp in the tooth root canal. This study further presents a new strategy for local regeneration therapy of the dentin-pulp complex. This review summarizes the current knowledge of the potential beneficial effects derived from the interaction of dental materials with the dentin-pulp complex as well as potential future developments in this exciting field.

[Effect of bone morphogenetic protein 2 and dexamethason on proliferation and differentiation of human dental pulp cells in vitro]

Objective

To investigate the effect of bone morphogenetic protein 2 (BMP-2) and dexamethason (DXM) on proliferation and differentiation of human dental pulp cells in vitro.

Methods

Primary human dental pulp cells were cultured in vitro by tissue culture method. The 3rd generation cells were used to identify cell phenotype for vimentin and cytokeratin by immunocytochemistry staining. The 3-5 generations of human dental pulp cells were randomly divided into 4 groups: 100 ng/mL BMP-2 (group A), 1×10 ^-8 mol/L DXM (group B), and both 100 ng/mL BMP-2 and 1×10 ^-8 mol/L DXM (group C) were added; neither BMP-2 nor DXM was added in group D as control group. The cell growth curve was drawn at 1, 3, 5, and 7 days after culture. The expressions of osteo/dentanogenic genes including alkaline phosphatase (ALP), dentin sialophoshoprotein (DSPP), and dentin matrix protein 1 (DMP-1) were detected by RT-PCR analysis at 5 and 7 days after culture, the ratio between the positive staining area and the total area by ALP staining at 14 days, and absorbance ( A) value at 562 nm by alizarin red staining at 21 days after culture.

Results

Human dental pulp cells were successfully isolated and cultured, which were long fusiform and showed a positive reaction for vimentin and a negative reaction for cytokeratin. The growth curve indicated that cells increased with the extending of incubation time, reached a peak at 5 days, then reduced at 7 days to the level at 3 days. At 5 days after culture, the cells were significantly more in groups A, B, and C than group D ( P<0.05), in group C than group A ( P<0.05), and in group A than group B ( P<0.05). RT-PCR analysis showed that the mRNA expressions of ALP, DSPP, and DMP-1 at 5 days were significantly higher in groups A, B, and C than group D ( P<0.05), and in group C than groups A and B ( P<0.05), but no significant difference was found between groups A and B ( P>0.05); the mRNA expression of DSPP in groups A, B, and C was significantly higher than that in group D ( P<0.05), but there was no significant difference in mRNA expressions between other groups at 7 days ( P>0.05). At 14 days, positive staining in varying degrees was observed in each group, especially in group C; the ratio between the positive staining area and the total area was significantly higher in group C than groups A, B, and D ( P<0.05), and in groups A and B than group D ( P<0.05), but there was no significant difference between groups A and B ( P>0.05). At 21 days, there were a variety of mineralized nodules in groups A, B, and C in nonuniformly scattered or clustered distribution, but no mineralized nodules were observed in group D. The A values of mineralized nodules showed significant difference between groups ( P<0.05).

Conclusion

BMP-2 may be more effective in promoting proliferation of human dental pulp cells than DXM. Combined application of BMP-2 and DXM can remarkably promote the proliferation and differentiation of human dental pulp cells.

Demineralized bone matrix used for direct pulp capping in rats

Objectives

To evaluate the wound healing process following direct pulp capping with demineralized bone matrix (DBM) and calcium hydroxide (Ca(OH)₂).

Methods

Fifty 8-weeks-old SPF Wistar male rats were divided into two groups: one was the DBM treated group, and the other was the Ca(OH)₂ treated group. Pulpotomy was performed on the maxillary first molar of one side of each rat, and the another side was left as the blank control. Rats were sacrificed after each observation period (1, 3, 7, 14 and 28 days) and specimen slices were made. Hematoxylin-Eosin (HE) staining was used for observing the changes of pulp tissue, and immunohistochemical staining was used for observing the expression of reparative dentinogenesis-related factors runt transcription factor 2 (Runx2), type I collagen (COL I), osteocalcin (OCN) and dentin sialoprotein (DSP).

Results

Inflammatory cell infiltration (ICI) and pulp tissue disorganization (PTD) could be observed in both the DBM and Ca(OH)₂ groups at all observation periods. The DBM group showed slighter ICI on 1 and 28 days and milder PTD on 28 days, with a significant difference (P<0.05). Reparative dentin formation (RDF) could initially be observed on 14 days postoperatively, and the DBM group showed more regular and thinner RDF with significant differences on 14 and 28 days compared with the Ca(OH)₂ group (P<0.05). In both groups, the expression of Runx2, COL I, DSP and OCN were positive. Generally, the expression of these four factors in the DBM group was stronger than the Ca(OH)₂ group on the same observation periods.

Conclusions

DBM had the ability of inducing odontoblast differentiation and promoting dentinogenesis. DBM could initiate physiologic wound healing in pulp and had the ability to promote reparative dentin formation. Consequently, DBM may be an acceptable alternative for direct pulp capping.

Dental Tissue Engineering Research and Translational Approaches towards Clinical Application

Stem cell-based dental tissue regeneration is a new and exciting field that has the potential to transform the way that we practice dentistry. It is, however, imperative its clinical application is supported by solid basic and translational research. In this way, the full extent of the potential risks involved in the use of these technologies will be understood, and the means to prevent them will be discovered. Therefore, the aim of this chapter is to analyze the state-of-the-science with regard to dental pulp stem cell research in dental tissue engineering, the new developments in biomimetic scaffold materials customized for dental tissue applications, and to give a prospectus with respect to translational approaches of these research findings towards clinical application.

Immunoexpression of BMP-2 and BMP-4 and their receptors, BMPR-IA and BMPR-II, in ameloblastomas and adenomatoid odontogenic tumors

OBJECTIVES

The present study evaluated the immunohistochemical expression of BMP-2 and BMP-4 and of their receptors (BMPR-IA and BMPR-II) in solid ameloblastoma (SA), unicystic ameloblastoma (UA) and adenomatoid odontogenic tumor (AOT) in order to obtain a better understanding of their role in the development and biological behavior of these tumors.

DESIGN

This study analyzed these proteins in 30 cases of SA, 10 cases of UA, and 30 cases of AOT. Immunoexpression was evaluated in the parenchyma and stroma by attributing the following scores: 0, no stained cells; 1, ≤10%; 2, >10% and ≤25%; 3, >25% and ≤50%; 4, >50% and ≤75%.; 5, >75% stained cells.

RESULTS

In SAs, positive correlations were observed between the stromal and parenchymal expression of BMP-2 (p<0.001) and between the stromal expression of BMP-2 and BMP-4 (p=0.020), as well as between the stromal expression of BMPR-II and BMP-4 (p=0.001) and the stromal and parenchymal expression of BMPR-II (p<0.001). In UAs, correlations were detected between the stromal and parenchymal expression of BMP-4 (p=0.035) and between the stromal expression of BMP-4 and BMPR-IA (p=0.022). In AOTs, analysis of immunoexpression in the parenchyma revealed positive correlations between all proteins.

CONCLUSION

BMPs and their receptors play an important role in the differentiation and development of ameloblastomas and AOTs, but may not explain the different biological behaviors of these lesions. The positive correlation observed in AOTs might be related to the formation of mineralized material in this tumor.

Secretory leukocyte protease inhibitor promotes differentiation and mineralization of MC3T3-E1 preosteoblasts on a titanium surface

Mineralized bone matrix constituted with collagenous and non-collagenous proteins was synthesized by osteoblasts differentiated from mesenchymal stem cells. Secretory leukocyte protease inhibitor (SLPI), a serine protease inhibitor, promotes cell migration and proliferation, and suppresses the inflammatory response. Recent studies reported that SLPI regulates the formation of dentin and mineralization by odontoblasts and increases the adhesion and viability of preosteoblasts on a titanium (Ti) surface. Ti and its alloys are widely used implant materials in artificial joints and dental implants owing to their biocompatibility with bone. Therefore, this study aimed to examine whether SLPI can be an effective molecule in promoting differentiation and mineralization of osteoblasts on a Ti surface. In order to investigate the effects of SLPI on osteoblasts, an MTT assay, PCR, western blotting and Alizarin Red S staining were performed. The results demonstrated that SLPI increased the viability of osteoblasts during differentiation on Ti discs compared with that of the control. The expression levels of SLPI mRNA and protein were higher than that of the control after treatment of osteoblasts with SLPI on Ti discs during differentiation. SLPI increased the formation of mineralized nodules and mRNA expression of alkaline phosphatase, dentin sialophosphoprotein, dentin matrix protein 1, bone sialoprotein, and collagen I in osteoblasts on Ti discs compared with that of the control. In conclusion, SLPI increases the viability and promotes the differentiation and mineralization of osteoblasts on Ti surfaces, suggesting that SLPI is an effective molecule for achieving successful osseointegration between osteoblasts and a Ti surface.

Osteo-/odontogenic differentiation of BMP2 and VEGF gene-co-transfected human stem cells from apical papilla

Stem cells from apical papilla (SCAP) possess clear osteo-/odontogenic differentiation capabilities, and are regarded as the major cellular source for root dentin development. Bone morphogenetic protein 2 (BMP2) and vascular endothelial growth factor (VEGF) serve pivotal roles in the modulation of tooth development and dentin formation. However, the synergistic effects of BMP2 and VEGF on osteo-/odontogenic differentiation of SCAP remain unclear. The current study aimed to investigate the proliferative and osteo-/odontogenic differentiating capabilities of BMP2 and VEGF gene-co-transfected SCAP (SCAP-BMP2-VEGF) in vitro. The basic characteristics of the isolated SCAP were identified by the induction of multipotent differentiation and by flow cytometry. Lentiviral vector-mediated gene transfection was conducted with SCAP in order to construct blank vector-transfected SCAP (SCAP-green fluorescent protein), BMP2 gene-transfected SCAP (SCAP-BMP2), VEGF gene-transfected SCAP (SCAP-VEGF) and SCAP-BMP2-VEGF. The Cell Counting Kit 8 assay was used to analyze the proliferative capacities of the four groups of cells. The expression of osteo-/odontogenic genes and proteins in the cells were evaluated by reverse transcription-quantitative polymerase chain reaction and western blotting. The mineralized nodules formed by the four group cells were visualized by alkaline phosphatase (ALP) staining. Among the four groups of cells, SCAP-VEGF was demonstrated to exhibit increased proliferation, and SCAP-BMP2-VEGF exhibited reduced proliferation during eight days observation. SCAP-BMP2-VEGF exhibited significantly increased expression levels of ALP, osteocalcin, dentin sialophosphoprotein, dentin matrix acidic phosphoprotein gene 1 and dentin sialoprotein than the other three groups at the majority of the time points. Furthermore, the SCAP-BMP2-VEGF group exhibited a significantly greater number of ALP-positive mineralized nodules than the other groups following 16 days culture in vitro. In conclusion, lentiviral vector-mediated BMP2 and VEGF gene co-transfection significantly activated the osteo-/odontogenic differentiation of human SCAP.

Current Advance and Future Prospects of Tissue Engineering Approach to Dentin/Pulp Regenerative Therapy

Recent advances in biomaterial science and tissue engineering technology have greatly spurred the development of regenerative endodontics. This has led to a paradigm shift in endodontic treatment from simply filling the root canal systems with biologically inert materials to restoring the infected dental pulp with functional replacement tissues. Currently, cell transplantation has gained increasing attention as a scientifically valid method for dentin-pulp complex regeneration. This multidisciplinary approach which involves the interplay of three key elements of tissue engineering—stem cells, scaffolds, and signaling molecules—has produced an impressive number of favorable outcomes in preclinical animal studies. Nevertheless, many practical hurdles need to be overcome prior to its application in clinical settings. Apart from the potential health risks of immunological rejection and pathogenic transmission, the lack of a well-established banking system for the isolation and storage of dental-derived stem cells is the most pressing issue that awaits resolution and the properties of supportive scaffold materials vary across different studies and remain inconsistent. This review critically examines the classic triad of tissue engineering utilized in current regenerative endodontics and summarizes the possible techniques developed for dentin/pulp regeneration.

Regenerative Applications Using Tooth Derived Stem Cells in Other Than Tooth Regeneration: A Literature Review

Tooth derived stem cells or dental stem cells are categorized according to the location from which they are isolated and represent a promising source of cells for regenerative medicine. Originally, as one kind of mesenchymal stem cells, they are considered an alternative of bone marrow stromal cells. They share many commonalties but maintain differences. Considering their original function in development and the homeostasis of tooth structures, many applications of these cells in dentistry have aimed at tooth structure regeneration; however, the application in other than tooth structures has been attempted extensively. The availability from discarded or removed teeth can be an innate benefit as a source of autologous cells. Their origin from the neural crest results in exploitation of neurological and numerous other applications. This review briefly highlights current and future perspectives of the regenerative applications of tooth derived stem cells in areas beyond tooth regeneration.

Establishment of Immortalized Mouse Bmp2 Knock-Out Dental Papilla Mesenchymal Cells Necessary for Study of Odontoblastic Differentiation and Odontogenesis

Bmp2 is essential for dentin formation. Bmp2 cKO mice exhibited similar phenotype to dentinogenesis imperfecta, showing dental pulp exposure, hypomineralized dentin, and delayed odontoblast differentiation. As it is relatively difficult to obtain lot of primary Bmp2 cKO dental papilla mesenchymal cells and to maintain a long-term culture of these primary cells, availability of immortalized deleted Bmp2 dental papilla mesenchymal cells is critical for studying the underlying mechanism of Bmp2 signal in odontogenesis. In this study, our goal was to generate an immortalized deleted Bmp2 dental papilla mesenchymal (iBmp2(ko/ko)dp) cell line by introducing Cre recombinase and green fluorescent protein (GFP) into the immortalized mouse floxed Bmp2 dental papilla mesenchymal (iBmp2(fx/fx)dp) cells. iBmp2(ko/ko)dp cells were confirmed by GFP and PCR. The deleted Bmp2 cells exhibited slow cell proliferation rate and cell growth was arrested in G2 phase. Expression of tooth-related marker genes and cell differentiation were decreased in the deleted cells. Importantly, extracellular matrix remodeling was impaired in the iBmp2(ko/ko)dp cells as reflected by the decreased Mmp-9 expression. In addition, with exogenous Bmp2 induction, these cell differentiation and mineralization were rescued as well as extracellular matrix remodeling was enhanced. Therefore, we for the first time described establishment of iBmp(ko/ko) cells that are useful for study of mechanisms in regulating dental papilla mesenchymal cell lineages.

Comparison of osteo/odontogenic differentiation of human adult dental pulp stem cells and stem cells from apical papilla in the presence of platelet lysate

INTRODUCTION

Human dental pulp cells (DPSCs) and stem cells from apical papilla have been used for the repair of damaged tooth tissues. Human platelet lysate (PL) has been suggested as a substitute for fetal bovine serum (FBS) for large scale expansion of dental stem cells. However, biological effects and optimal concentrations of PL for proliferation and differentiation of human dental stem cells remain to be elucidated.

METHODOLOGY

DPSCs and SCAP cells were isolated from impacted third molars of young healthy donors, at the stage of root development and identified by markers using flow cytometry. For comparison the cells were cultured in media containing PL (1%, 5% and 10%) and FBS, with subsequent induction for osteogenic/odontogenic differentiation. The cultures were analyzed for; morphology, growth characteristics, mineralization potential (Alizarin Red method) and differentiation markers using ELISA and real time -polymerase chain reaction (qPCR).

RESULTS

The proliferation rates of DPSCs and SCAP significantly increased when cells were treated with 5% PL (7X doubling time) as compared to FBS. 5% PL also enhanced mineralized differentiation of DPSCs and SCAP, as indicated by the measurement of alkaline phosphatase activity, osteocalcin and osteopontin, calcium deposition and q-PCR.

CONCLUSION

Our findings suggest that using 5% platelet lysate, proliferation and osteo/odontogenesis of DPSCs and SCAP for a short period of time (15 days), was significantly improved. This may imply its use as an optimum concentration for expansion of dental stem cells in bone regeneration.

Osteogenic Potential of Dental Mesenchymal Stem Cells in Preclinical Studies: A Systematic Review Using Modified ARRIVE and CONSORT Guidelines

Background and Objective. Dental stem cell-based tissue engineered constructs are emerging as a promising alternative to autologous bone transfer for treating bone defects. The purpose of this review is to systematically assess the preclinical in vivo and in vitro studies which have evaluated the efficacy of dental stem cells on bone regeneration. Methods. A literature search was conducted in Ovid Medline, Embase, PubMed, and Web of Science up to October 2014. Implantation of dental stem cells in animal models for evaluating bone regeneration and/or in vitro studies demonstrating osteogenic potential of dental stem cells were included. The preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines were used to ensure the quality of the search. Modified ARRIVE (Animal research: reporting in invivo experiments) and CONSORT (Consolidated reporting of trials) were used to critically analyze the selected studies. Results. From 1914 citations, 207 full-text articles were screened and 137 studies were included in this review. Because of the heterogeneity observed in the studies selected, meta-analysis was not possible. Conclusion. Both in vivo and in vitro studies indicate the potential use of dental stem cells in bone regeneration. However well-designed randomized animal trials are needed before moving into clinical trials.

Human dental pulp stem cells (hDPSCs): isolation, enrichment and comparative differentiation of two sub-populations

Background

Human dental pulp represents a suitable alternative source of stem cells for the purpose of cell-based therapies in regenerative medicine, because it is relatively easy to obtain it, using low invasive procedures. This study characterized and compared two subpopulations of adult stem cells derived from human dental pulp (hDPSCs). Human DPSCs, formerly immune-selected for STRO-1 and c-Kit, were separated for negativity and positivity to CD34 expression respectively, and evaluated for cell proliferation, stemness maintenance, cell senescence and multipotency.

Results

The STRO-1⁺/c-Kit⁺/CD34⁺ hDPSCs showed a slower proliferation, gradual loss of stemness, early cell senescence and apoptosis, compared to STRO-1⁺/c-Kit⁺/CD34⁻ hDPSCs. Both the subpopulations demonstrated similar abilities to differentiate towards mesoderm lineages, whereas a significant difference was observed after the neurogenic induction, with a greater commitment of STRO-1⁺/c-Kit⁺/CD34⁺ hDPSCs. Moreover, undifferentiated STRO-1⁺/c-Kit⁺/CD34⁻ hDPSCs did not show any expression of CD271 and nestin, typical neural markers, while STRO-1⁺/c-Kit⁺/CD34⁺ hDPSCs expressed both.

Conclusions

These results suggest that STRO-1⁺/c-Kit⁺/CD34⁻ hDPSCs and STRO-1⁺/c-Kit⁺/CD34⁺ hDPSCs might represent two distinct stem cell populations, with different properties. These results trigger further analyses to deeply investigate the hypothesis that more than a single stem cell population resides within the dental pulp, to better define the flexibility of application of hDPSCs in regenerative medicine.

Bone regeneration in critical-size calvarial defects using human dental pulp cells in an extracellular matrix-based scaffold

The rat calvarial defect is an established model to evaluate craniofacial bone regeneration using cell-scaffold biocomplexes. Dental pulp harbors stem cells with significant osteogenic properties. Extracellular matrix (ECM)-like scaffolds simulate the environment that cells observe in vivo. In the present study, we evaluated the osteogenic effect of a biocomplex of human dental pulp cells and a hyaluronic-based hydrogel scaffold in calvarial defects of immunocompetent rats. Dental pulp cells at the 2nd passage were characterized by flow cytometry, osteodifferentiated ex vivo for 4 days and the whole population was encapsulated in the synthetic ECM matrix. Cell vitality was verified 24 h upon encapsulation. 5 mm calvarial defects were created in 30 male rats and filled with the biocomplex, the scaffold alone, or left untreated. Histological evaluation at 8 weeks showed incomplete bone regeneration in all groups. The scaffold was not fully degraded and entrapped cells were detected in it. Histomorphometry showed statistically significant superior new bone formation in the biocomplex-treated group, compared to the two other groups. The present study provides evidence that the whole population of human dental pulp cells can advance bone healing when transplanted in immunocompetent animals and highlights the importance of proper scaffold degradation in cell-driven bioengineering treatments.

The regenerative medicine in oral and maxillofacial surgery: the most important innovations in the clinical application of mesenchymal stem cells

Regenerative medicine is an emerging field of biotechnology that combines various aspects of medicine, cell and molecular biology, materials science and bioengineering in order to regenerate, repair or replace tissues. The oral surgery and maxillofacial surgery have a role in the treatment of traumatic or degenerative diseases that lead to a tissue loss: frequently, to rehabilitate these minuses, you should use techniques that have been improved over time. Since 1990, we started with the use of growth factors and platelet concentrates in oral and maxillofacial surgery; in the following period we start to use biomaterials, as well as several type of scaffolds and autologous tissues. The frontier of regenerative medicine nowadays is represented by the mesenchymal stem cells (MSCs): overcoming the ethical problems thanks to the use of mesenchymal stem cells from adult patient, and with the increasingly sophisticated technology to support their manipulation, MSCs are undoubtedly the future of medicine regenerative and they are showing perspectives unimaginable just a few years ago. Most recent studies are aimed to tissues regeneration using MSCs taken from sites that are even more accessible and rich in stem cells: the oral cavity turned out to be an important source of MSCs with the advantage to be easily accessible to the surgeon, thus avoiding to increase the morbidity of the patient. The future is the regeneration of whole organs or biological systems consisting of many different tissues, starting from an initial stem cell line, perhaps using innovative scaffolds together with the nano-engineering of biological tissues.

Proliferation and odontogenic differentiation of BMP2 gene‑transfected stem cells from human tooth apical papilla: an in vitro study

Stem cells from the apical papilla (SCAP) have odontogenic potential, which plays a pivotal role in the root dentin development of permanent teeth. Human bone morphogenetic protein 2 (BMP2) is a well-known gene that participates in regulating the odontogenic differentiation of dental tissue-derived stem cells. However, little is known regarding the effects of the BMP2 gene on the proliferation and odontogenic differentiation of SCAP. This study aimed to evaluate the odontogenic differentiation potential of lentiviral-mediated BMP2 gene-transfected human SCAP (SCAP/BMP2) in vitro. SCAP were isolated by enzymatic dissociation of human teeth apical papillae. The multipotential of SCAP was verified by their osteogenic and adipogenic differentiation characteristics. The phenotype of SCAP was evaluated by flow cytometry (FCM). The proliferation status of the blank vector-transfected SCAP (SCAP/Vector) and SCAP/BMP2 was analyzed by a cell counting kit-8 (CCK-8). Odontogenic genes, including alkaline phosphatase (ALP), osteocalcin (OCN), dentin sialophosphoprotein (DSPP) and dentin matrix protein 1 (DMP1) of the two groups of cells were evaluated by quantitative polymerase chain reaction (qPCR). ALP staining and alizarin red (AR) staining of the cells was performed on the 16th day after transfection. In vitro results of CCK-8, qPCR, ALP and AR staining demonstrated that: i) SCAP/BMP2 had a comparable proliferation rate to SCAP/Vector; ii) SCAP/BMP2 presented significantly better potential to differentiate into odontoblasts compared to SCAP/Vector by upregulating ALP, OCN, DSPP and DMP1 genes; iii) more ALP granules and mineralized deposits were formed by SCAP/BMP2 as compared to SCAP/Vector. The results suggested that lentiviral-mediated BMP2 gene transfection enhances the odontogenic differentiation capacity of human SCAP in vitro.

Dental pulp stem cells: function, isolation and applications in regenerative medicine

Dental pulp stem cells (DPSCs) are a promising source of cells for numerous and varied regenerative medicine applications. Their natural function in the production of odontoblasts to create reparative dentin support applications in dentistry in the regeneration of tooth structures. However, they are also being investigated for the repair of tissues outside of the tooth. The ease of isolation of DPSCs from discarded or removed teeth offers a promising source of autologous cells, and their similarities with bone marrow stromal cells (BMSCs) suggest applications in musculoskeletal regenerative medicine. DPSCs are derived from the neural crest and, therefore, have a different developmental origin to BMSCs. These differences from BMSCs in origin and phenotype are being exploited in neurological and other applications. This review briefly highlights the source and functions of DPSCs and then focuses on in vivo applications across the breadth of regenerative medicine.

Functionalized scaffolds to control dental pulp stem cell fate

Emerging understanding about interactions between stem cells, scaffolds, and morphogenic factors has accelerated translational research in the field of dental pulp tissue engineering. Dental pulp stem cells constitute a subpopulation of cells endowed with self-renewal and multipotency. Dental pulp stem cells seeded in biodegradable scaffolds and exposed to dentin-derived morphogenic factors give rise to a pulplike tissue capable of generating new dentin. Notably, dentin-derived proteins are sufficient to induce dental pulp stem cell differentiation into odontoblasts. Ongoing work is focused on developing ways of mobilizing dentin-derived proteins and disinfecting the root canal of necrotic teeth without compromising the morphogenic potential of these signaling molecules. On the other hand, dentin by itself does not appear to be capable of inducing endothelial differentiation of dental pulp stem cells despite the well-known presence of angiogenic factors in dentin. This is particularly relevant in the context of dental pulp tissue engineering in full root canals in which access to blood supply is limited to the apical foramina. To address this challenge, scientists are looking at ways to use the scaffold as a controlled-release device for angiogenic factors. The aim of this article was to present and discuss current strategies to functionalize injectable scaffolds and customize them for dental pulp tissue engineering. The long-term goal of this work is to develop stem cell-based therapies that enable the engineering of functional dental pulps capable of generating new tubular dentin in humans.

Characterization of the enhanced bone regenerative capacity of human periodontal ligament stem cells engineered to express the gene encoding bone morphogenetic protein 2

Human periodontal ligament stem cells (hPDLSCs) are considered an appropriate cell source for therapeutic strategies. The aims of this study were to investigate the sustainability of bone morphogenetic protein 2 (BMP2) secretion and the bone regenerative capacity of hPDLSCs that had been genetically modified to express the gene encoding BMP2 (BMP2). hPDLSCs isolated from healthy third molars were transduced using replication-deficient recombinant adenovirus (rAd) encoding BMP2 (hPDLSCs/rAd-BMP2), and the cellular characteristics and osteogenic potentials of hPDLSCs/rAd-BMP2 were analyzed both in vitro and in vivo. hPDLSCs/rAd-BMP2 successfully secreted BMP2, formed colonies, and expressed immunophenotypes similar to their nontransduced counterparts. As to their osteogenic potential, hPDLSCs/rAd-BMP2 formed greater mineralized nodules and exhibited significantly higher levels of expression of BMP2 and the gene encoding alkaline phosphatase, and formed more and better quality bone than other hPDLSC-containing or recombinant human BMP2-treated groups, being localized at the initial site until 8 weeks. The findings of the present study demonstrate that hPDLSCs/rAd-BMP2 effectively promote osteogenesis not only in vitro but also in vivo. The findings also suggest that hPDLSCs can efficiently carry and deliver BMP2, and that hPDLSCs/rAd-BMP2 could be used in an attractive novel therapeutic approach for the regeneration of deteriorated bony defects.

Dental pulp stem cells: state of the art and suggestions for a true translation of research into therapy

OBJECTIVES

Stem cells have the ability to rescue and/or repair injured tissue. In humans, it is possible to isolate different types of stem cells from the body. Among these, dental pulp stem cells (DPSCs) are relatively easily obtainable and exhibit high plasticity and multipotential capabilities. In particular they represent a gold standard for neural-crest-derived bone reconstruction in humans and can be used for the repair of body defects in low-risk autologous therapeutic strategies.

SOURCES

An electronic search was conducted on PubMed databases and supplemented with a manual study of relevant references.

RESULTS

All research described in this review highlight that DPSCs are mesenchymal stem cells that could be used in clinical applications. Unfortunately, very few clinical trials have been reported. Major obstacles imposed on researchers are hindering the translation of potentially effective therapies to the clinic. Both researchers and regulatory institutions need to develop a new approach to this problem, drawing up a new policy for good manufacturing practice (GMP) procedures. We strongly suggest that only general rules be standardized rather than everything. Importantly, this would not have an effect on the safety of patients, but may very well affect the results, which cannot be identical for all patients, due to physiological diversity in the biology of each patient. Alternatively, it would be important to study the role of specific molecules that recruit endogenous stem cells for tissue regeneration. In this way, the clinical use of stem cells could be successfully developed.

CONCLUSIONS

DPSCs are mesenchymal stem cells that differentiate into different tissues, maintain their characteristics after cryopreservation, differentiate into bone-like tissues when loaded on scaffolds in animal models, and regenerate bone in human grafts. In summary, all data reported up to now should encourage the development of clinical procedures using DPSCs.

Ginsenoside Rg1 of Panax ginseng stimulates the proliferation, odontogenic/osteogenic differentiation and gene expression profiles of human dental pulp stem cells

Ginsenoside Rg1 is one of the major active components of Panax ginseng C. A. Mey. Human dental pulp stem cells (hDPSCs) play an important role in the dentin formation, reparation and tooth tissue engineering. This study investigated the effects of ginsenoside Rg1 on the proliferation, odontogenic differentiation of hDPSCs and revealed the underlying molecular mechanisms. [³H]-thymidine incorporation assay and cell cycle analysis were applied to investigate the proliferation of hDPSCs after the treatment of ginsenoside Rg1. Immunocytochemistry analysis and fluorescent quantitative reverse transcriptase-polymerase chain reaction (FQ-PCR) were performed to evaluate the odontogenic differentiation of hDPSCs. Gene and protein expressions of bone morphogenetic protein-2 (BMP-2) and fibroblast growth factor 2 (FGF2) were detected by FQ-PCR and enzyme-linked immunosorbent assay. The Roche Nimblegen Whole Human Genome Expression profile microarray was used to detected representative gene expression profiles of hDPSCs by ginsenoside Rg1. The results indicated that ginsenoside Rg1 significantly increased hDPSCs proliferation (p<0.05). Gene expressions of DSPP, ALP, OCN, BMP-2, FGF2 and protein expressions of BMP-2 and FGF2 were increased compared with the untreated group (p<0.05). Gene expression profile analysis revealed that 2059 differentially expressed genes were detected by ginsenoside Rg1. Ginsenoside Rg1 promoted the proliferation and differentiation of hDPSCs through alteration of gene expression profiles.

The effect of five proteins on stem cells used for osteoblast differentiation and proliferation: a current review of the literature

Bone-tissue engineering is a therapeutic target in the field of dental implant and orthopedic surgery. It is therefore essential to find a microenvironment that enhances the growth and differentiation of osteoblasts both from mesenchymal stem cells (MSCs) and those derived from dental pulp. The aim of this review is to determine the relationship among the proteins fibronectin (FN), osteopontin (OPN), tenascin (TN), bone sialoprotein (BSP), and bone morphogenetic protein (BMP2) and their ability to coat different types of biomaterials and surfaces to enhance osteoblast differentiation. Pre-treatment of biomaterials with FN during the initial phase of osteogenic differentiation on all types of surfaces, including slotted titanium and polymers, provides an ideal microenvironment that enhances adhesion, morphology, and proliferation of pluripotent and multipotent cells. Likewise, in the second stage of differentiation, surface coating with BMP2 decreases the diameter and the pore size of the scaffold, causing better adhesion and reduced proliferation of BMP-MSCs. Coating oligomerization surfaces with OPN and BSP promotes cell adhesion, but it is clear that the polymeric coating material BSP alone is insufficient to induce priming of MSCs and functional osteoblastic differentiation in vivo. Finally, TN is involved in mineralization and can accelerate new bone formation in a multicellular environment but has no effect on the initial stage of osteogenesis.

Dental pulp stem cells for in vivo bone regeneration: a systematic review of literature

OBJECTIVE

This review of literature was aimed to assess in vivo experiments which have evaluated the efficacy of dental pulp stem cells (DPSCs) for bone regeneration.

DESIGN

An electronic search of English-language papers was conducted on PubMed database. Studies that assessed the use of DPSCs in bone regeneration in vivo were included and experiments evaluating regeneration of hard tissues other than bone were excluded. The retrieved articles were thoroughly reviewed according to the source of stem cell, cell carrier, the in vivo experimental model, defect type, method of evaluating bone regeneration, and the obtained results. Further assessment of the results was conducted by classifying the studies based on the defect type.

RESULTS

Seventeen papers formed the basis of this systematic review. Sixteen out of 17 experiments were performed on animal models with mouse and rat being the most frequently used animal models. Seven out of 17 animal studies, contained subcutaneous pockets on back of the animal for stem cell implantation. In only one study hard tissue formation was not observed. Other types of defects used in the retrieved studies, included cranial defects and mandibular bone defects, in all of which bone formation was reported.

CONCLUSION

When applied in actual bone defects, DPSCs were capable of regenerating bone. Nevertheless, a precise conclusion regarding the efficiency of DPSCs for bone regeneration is yet to be made, considering the limited number of the in vivo experiments and the heterogeneity within their methods.

Enhanced dentin-like mineralized tissue formation by AdShh-transfected human dental pulp cells and porous calcium phosphate cement

The aim of the present study was to investigate the effect of Sonic hedgehog (Shh) on human dental pulp cells (hDPCs) and the potential of complexes with Shh gene modified hDPCs and porous calcium phosphate cement (CPC) for mineralized tissue formation. hDPCs were cultured and transfected with adenoviral mediated human Shh gene (AdShh). Overexpression of Shh and cell proliferation was tested by real-time PCR analysis, western blotting analysis, and MTT analysis, respectively. The odontoblastic differentiation was assessed by alkaline phosphatase (ALP) activity and real-time PCR analysis on markers of Patched-1 (Ptc-1), Smoothened (Smo), Gli 1, Gli 2, Gli 3, osteocalcin (OCN), dentin matrix protein-1 (DMP-1), and dentin sialophosphoprotein (DSPP). Finally, AdShh-transfected hDPCs were combined with porous CPC and placed subcutaneously in nude mice for 8 and 12 weeks, while AdEGFP-transfected and untransfected hDPCs were treated as control groups. Results indicated that Shh could promote proliferation and odontoblastic differentiation of hDPCs, while Shh/Gli 1 signaling pathway played a key role in this process. Importantly, more mineralized tissue formation was observed in combination with AdShh transfected hDPCs and porous CPC, moreover, the mineralized tissue exhibited dentin-like features such as structures similar to dentin-pulp complex and the positive staining for DSPP protein similar to the tooth tissue. These results suggested that the constructs with AdShh-transfected hDPCs and porous CPC might be a better alternative for dental tissue regeneration.

Modulation of osteoblastic/odontoblastic differentiation of adult mesenchymal stem cells through gene introduction: a brief review

Bone tissue engineering is one of the important therapeutic approaches to the regeneration of bones in the entire field of regeneration medicine. Mesenchymal stem cells (MSCs) are actively discussed as material for bone tissue engineering due to their ability to differentiate into autologous bone. MSCs are able to differentiate into different lineages: osteo/odontogenic, adipogenic, and neurogenic. The tissue of origin for MSCs defines them as bone marrow-derived stem cells, adipose tissue-derived stem cells, and, among many others, dental stem cells. According to the tissue of origin, DSCs are further stratified into dental pulp stem cells, periodontal ligament stem cells, stem cells from apical papilla, stem cells from human exfoliated deciduous teeth, dental follicle precursor cells, and dental papilla cells. There are numerous in vitro/in vivo reports suggesting successful mineralization potential or osteo/odontogenic ability of MSCs. Still, there is further need for the optimization of MSCs-based tissue engineering methods, and the introduction of genes related to osteo/odontogenic differentiation into MSCs might aid in the process. In this review, articles that reported enhanced osteo/odontogenic differentiation with gene introduction into MSCs will be discussed to provide a background for successful bone tissue engineering using MSCs with artificially introduced genes.

The similarity between human embryonic stem cell-derived epithelial cells and ameloblast-lineage cells

This study aimed to compare epithelial cells derived from human embryonic stem cells (hESCs) to human ameloblast-lineage cells (ALCs), as a way to determine their potential use as a cell source for ameloblast regeneration. Induced by various concentrations of bone morphogenetic protein 4 (BMP4), retinoic acid (RA) and lithium chloride (LiCl) for 7 days, hESCs adopted cobble-stone epithelial phenotype (hESC-derived epithelial cells (ES-ECs)) and expressed cytokeratin 14. Compared with ALCs and oral epithelial cells (OE), ES-ECs expressed amelogenesis-associated genes similar to ALCs. ES-ECs were compared with human fetal skin epithelium, human fetal oral buccal mucosal epithelial cells and human ALCs for their expression pattern of cytokeratins as well. ALCs had relatively high expression levels of cytokeratin 76, which was also found to be upregulated in ES-ECs. Based on the present study, with the similarity of gene expression with ALCs, ES-ECs are a promising potential cell source for regeneration, which are not available in erupted human teeth for regeneration of enamel.

SHP is involved in BMP2-induced odontoblast differentiation

Small Heterodimer Partner (SHP) interacts with diverse transcription factors such as Runx2 and regulates many cellular events including differentiation, proliferation, and energy metabolism. SHP is reported to be a positive regulator of BMP2-induced bone formation. This study aimed to clarify the role of SHP in odontoblast differentiation and matrix mineralization. Rat tooth germs were isolated, and gene expression was determined by RT-PCR and real-time PCR. Localization of SHP protein expression was identified by immunofluorescent analysis. Primary human dental pulp cells (HDPCs) were cultured with BMP2 and/or Ad-siSHP. Matrix mineralization was evaluated by Alizarin red staining. Transient transfection experiment was performed with the SHP or Dlx5 expressional plasmids and the DSPP gene. In tooth germs from post-natal days 3 to 9, BMP-2 and SHP expression increased with DSPP and DMP1 mRNA expression. In an immunostaining study, SHP was expressed in odontoblasts and surrounding osteoblasts. When HDPCs were cultured with BMP2 in mineralization-inducing medium, SHP expression also increased with an increase in DSPP expression. Down-regulation of SHP by Ad-siSHP inhibited matrix mineralization. In transient transfection experiments, overexpression of SHP was shown to enhance DSPP promoter activity through interactions between SHP and Dlx5. These results suggest that SHP may mediate BMP2 signaling to promote mineralization of the dentin matrix.