Incipient analysis of mesenchymal stem-cell-derived osteogenesis

At the nuclear envelope of bone mechanobiology

The nuclear envelope and nucleoskeleton are emerging as signaling centers that regulate how physical information from the extracellular matrix is biochemically transduced into the nucleus, affecting chromatin and controlling cell function. Bone is a mechanically driven tissue that relies on physical information to maintain its physiological function and structure. Disorder that present with musculoskeletal and cardiac symptoms, such as Emery-Dreifuss muscular dystrophies and progeria, correlate with mutations in nuclear envelope proteins including Linker of Nucleoskeleton and Cytoskeleton (LINC) complex, Lamin A/C, and emerin. However, the role of nuclear envelope mechanobiology on bone function remains underexplored. The mesenchymal stem cell (MSC) model is perhaps the most studied relationship between bone regulation and nuclear envelope function. MSCs maintain the musculoskeletal system by differentiating into multiple cell types including osteocytes and adipocytes, thus supporting the bone's ability to respond to mechanical challenge. In this review, we will focus on how MSC function is regulated by mechanical challenges both in vitro and in vivo within the context of bone function specifically focusing on integrin, β-catenin and YAP/TAZ signaling. The importance of the nuclear envelope will be explored within the context of musculoskeletal diseases related to nuclear envelope protein mutations and nuclear envelope regulation of signaling pathways relevant to bone mechanobiology in vitro and in vivo.

Comparison of Bone Regeneration between Porcine-Derived and Bovine-Derived Xenografts in Rat Calvarial Defects: A Non-Inferiority Study

The present study aimed to compare the bone-regeneration capacity of porcine-derived xenografts to bovine-derived xenografts in the rat calvarial defect model. The observation of surface morphology and in vitro cell studies were conducted prior to the animal study. Defects with a diameter of 8 mm were created in calvaria of 20 rats. The rats were randomly treated with porcine-derived (Bone-XP group) or bovine-derived xenografts (Bio-Oss group) and sacrificed at 4 and 8 weeks after surgery. The new bone regeneration was evaluated by micro-computed tomography (μCT) and histomorphometric analyses. In the cell study, the extracts of Bone-XP and Bio-Oss showed a positive effect on the regulation of osteogenic differentiation of human mesenchymal stem cells (hMSCs) without cytotoxicity. The new bone volume of Bone-XP (17.52 ± 3.78% at 4 weeks and 32.09 ± 3.51% at 8 weeks) was similar to that of Bio-Oss (11.6 ± 3.88% at 4 weeks and 25.89 ± 7.43% at 8 weeks) (p > 0.05). In the results of new bone area, there was no significant difference between Bone-XP (9.08 ± 5.47% at 4 weeks and 25.22 ± 13.56% at 8 weeks) and Bio-Oss groups (5.83 ± 2.56% at 4 weeks and 21.68 ± 11.11% at 8 weeks) (p > 0.05). It can be concluded that the porcine-derived bone substitute may offer a favorable cell response and bone regeneration similar to those of commercial bovine bone mineral.

Effect of concentrated growth factor on osteoblast cell response

OBJECTIVE

The purpose of this study was to assess the effect of concentrated growth factor (CGF) on osteoblast cell proliferation and differentiation.

METHODS

SaOS-2 osteoblast-like cells were cultured on titanium discs. The disc surfaces in the test group were treated with CGF serum, and those in the control group were left untreated. Cell counts, cell proliferation, and osteocalcin (OCN) levels were evaluated on days 1 and 3, and the alkaline phosphatase (ALP) activity was assessed on days 3, 7, and 14.

RESULTS

The proliferation values were significantly higher in the test group than in the control on days 1 and 3 (P<0.05). ALP activities increased gradually in both groups from day 3 to day 14, but the ALP values were significantly higher in the test group than in the control in all periods (P<0.05). The OCN level on day 1 was significantly higher (P<0.05) in the test group, and no statistically significant difference was found between the two groups on day 3 (P<0.05). A significant decrease was observed in OCN activity on day3 in comparison with day 1 in the control group (P<0.05).

DISCUSSION

The results suggest that CGF can efficiently stimulate the proliferation and differentiation of osteoblast cells, thereby improving the healing process around implants.

Cranial reconstruction using allogeneic mesenchymal stromal cells: A phase 1 first-in-human trial

Cranioplasty is necessary for patients that have undergone craniectomy following trauma, stroke or other causes of elevated intracranial pressure. This study assessed the effectiveness of treating cranial defects with allogeneic mesenchymal stromal cells (MSC) on a ceramic carrier and polymer scaffold, to produce viable bone and healing of a cranial void. Patients underwent a baseline computed tomography (CT) scan for construct design. Two sets of interlocking moulds were three-dimensional printed to enable shaping of two polymer meshes, which formed the boundaries of the construct corresponding to restoration of the skull interna and externa. In vitro expanded donor MSC were seeded onto ceramic granules in a good manufacturing practices facility. The inner mesh was placed in theatre, followed by the cell-loaded granules, and the outer mesh. Patients were followed-up at 3, 6 and 12 months and cosmesis assessed visually, while bone formation was assessed by CT scans at 1 day, 3 months and 12 months. Manufacture of the construct and surgery was uneventful for all three patients. Initial cosmesis was excellent with no complications. New bone formation was demonstrated by analysis of CT data; however, bone resorption was noted in all 3 cases on the 12-month CT scan. The lack of rigidity of the construct in an environment with continuous pulsatile movement may be preventing the formation of solid bone. It is possible to produce a customized allogeneic MSC construct for cranial reconstruction to replace cranial bone with good cosmesis, using a combination of medical computer modelling, rapid-prototyping and tissue engineering.

Induction of osteoblastic differentiation of neural crest-derived stem cells from hair follicles

The neural crest (NC) arises near the neural tube during embryo development. NC cells migrate throughout the embryo and have potential to differentiate into multiple cell types, such as peripheral nerves, glial, cardiac smooth muscle, endocrine, and pigment cells, and craniofacial bone. In the present study, we induced osteoblast-like cells using whisker follicles obtained from the NC of mice. Hair follicle cells derived from the NC labeled with enhanced green fluorescent protein (EGFP) were collected from protein zero-Cre/floxed-EGFP double transgenic mice and cultured, then treated and cultured in stem cell growth medium. After growth for 14 days, results of flow cytometry analysis showed that 95% of the EGFP-positive (EGFP+) hair follicle cells derived from the NC had proliferated and 76.2% of those expressed mesenchymal stem cells markers, such as platelet-derived growth factor α and stem cell antigen-1, and also showed constitutive expression of Runx2 mRNA. Cells stimulated with bone morphogenetic protein-2 expressed osteocalcin, osterix, and alkaline phosphatase mRNA, resulting in production of mineralized matrices, which were detected by von Kossa and alizarin red staining. Moreover, EGFP+ hair follicle cells consistently expressed macrophage colony-stimulating factor and osteoprotegerin (OPG). Addition of 1α,25-dihydroxyvitamin D3 [1,25(OH)2D3] (10-8 M) to the cultures suppressed OPG expression and induced RANKL production in the cells. Furthermore, multinucleated osteoclasts appeared within 6 days after starting co-cultures of bone marrow cells with EGFP+ cells in the presence of 1,25(OH)2D3 and PGE2. These results suggest that NC-derived hair follicle cells possess a capacity for osteoblastic differentiation and may be useful for developing new bone regenerative medicine therapies.

In vitro preliminary study of osteoblast response to surface roughness of titanium discs and topical application of melatonin

Objectives: To observe human osteoblast behavior cultured in vitro on titanium discs (Ti) in relation to surface roughness and melatonin application. Study Design: Human osteoblasts (MG-63) were cultured on 60 Ti6Al4V discs divided into three groups: Group I: discs treated with dual acid etching; Group II dual acid etching and blasting with calcium phosphate particles; Group III (control) machined discs. Surface roughness and topography of the discs were examined with scanning electron microscope (SEM) and confocal laser scanning electron microscope( CLSM). Osteoblast adhesion, proliferation and cell morphology were determined by means of fluorescence microscopy with Image-Pro Plus software and SEM. Results: Group II presented the roughest discs, while the least rough were Group III. Cell adhesion was greatest in Group II. The addition of melatonin improved cell proliferation. Conclusions: 1. Surface treatments (dual acid etching, calcium phosphate impaction) increase surface roughness in comparison with machined titanium. 2. Greater surface roughness tends to favor cell adhesion after 24-hour cell culture. 3. The addition of melatonin tends to favor osteoblast proliferation.

Key words:Osteoblasts, titanium, roughness, melatonin, dental implants, osseointegration.

Developmental-like bone regeneration by human embryonic stem cell-derived mesenchymal cells

The in vivo osteogenesis potential of mesenchymal-like cells derived from human embryonic stem cells (hESC-MCs) was evaluated in vivo by implantation on collagen/hydroxyapatite scaffolds into calvarial defects in immunodeficient mice. This study is novel because no osteogenic or chondrogenic differentiation protocols were applied to the cells prior to implantation. After 6 weeks, X-ray, microCT, and histological analysis showed that the hESC-MCs had consistently formed a highly vascularized new bone that bridged the bone defect and seamlessly integrated with host bone. The implanted hESC-MCs differentiated in situ to functional hypertrophic chondrocytes, osteoblasts, and osteocytes forming new bone tissue via an endochondral ossification pathway. Evidence for the direct participation of the human cells in bone morphogenesis was verified by two separate assays: with Alu and by human mitochondrial antigen positive staining in conjunction with co-localized expression of human bone sialoprotein in histologically verified regions of new bone. The large volume of new bone in a calvarial defect and the direct participation of the hESC-MCs far exceeds that of previous studies and that of the control adult hMSCs. This study represents a key step forward for bone tissue engineering because of the large volume, vascularity, and reproducibility of new bone formation and the discovery that it is advantageous to not over-commit these progenitor cells to a particular lineage prior to implantation. The hESC-MCs were able to recapitulate the mesenchymal developmental pathway and were able to repair the bone defect semi-autonomously without preimplantation differentiation to osteo- or chondroprogenitors.

Tissue-engineered mandibular bone reconstruction for continuity defects: a systematic approach to the literature

BACKGROUND

Despite significant surgical advances over the last decades, segmental mandibular bone repair remains a challenge. In light of this, tissue engineering might offer a next step in the evolution of mandibular reconstruction.

PURPOSE

The purpose of the present report was to (1) systematically review preclinical in vivo as well as clinical literature regarding bone tissue engineering for mandibular continuity defects, and (2) to analyze their effectiveness.

MATERIALS AND METHODS

An electronic search in the databases of the National Library of Medicine and ISI Web of Knowledge was carried out. Only publications in English were considered, and the search was broadened to animals and humans. Furthermore, the reference lists of related review articles and publications selected for inclusion in this review were systematically screened. Results of histology data and amount of bone bridging were chosen as primary outcome variables. However, for human reports, clinical radiographic evidence was accepted for defined primary outcome variable. The biomechanical properties, scaffold degradation, and clinical wound healing were selected as co-outcome variables.

RESULTS

The electronic search in the databases of the National Library of Medicine and ISI Web of Knowledge resulted in the identification of 6727 and 5017 titles, respectively. Thereafter, title assessment and hand search resulted in 128 abstracts, 101 full-text articles, and 29 scientific papers reporting on animal experiments as well as 11 papers presenting human data on the subject of tissue-engineered reconstruction of mandibular continuity defects that could be included in the present review.

CONCLUSIONS

It was concluded that (1) published preclinical in vivo as well as clinical data are limited, and (2) tissue-engineered approaches demonstrate some clinical potential as an alternative to autogenous bone grafting.

Effects of spaceflight on cells of bone marrow origin

Once only a subject for science fiction novels, plans for establishing habitation on space stations, the Moon, and distant planets now appear among the short-term goals of space agencies. This article reviews studies that present biomedical issues that appear to challenge humankind for long-term spaceflights. With particularly focus on cells of bone marrow origin, studies involving changes in bone, immune, and red blood cell populations and their functions due to extended weightlessness were reviewed. Furthermore, effects of mechanical disuse on primitive stem cells that reside in the bone marrow were also included in this review. Novel biomedical solutions using space biotechnology will be required in order to achieve the goal of space exploration without compromising the functions of bone marrow, as spaceflight appears to disrupt homeostasis for all given cell types.

CONFLICT OF INTEREST

None declared.

Bone repair cells for craniofacial regeneration

Reconstruction of complex craniofacial deformities is a clinical challenge in situations of injury, congenital defects or disease. The use of cell-based therapies represents one of the most advanced methods for enhancing the regenerative response for craniofacial wound healing. Both somatic and stem cells have been adopted in the treatment of complex osseous defects and advances have been made in finding the most adequate scaffold for the delivery of cell therapies in human regenerative medicine. As an example of such approaches for clinical application for craniofacial regeneration, Ixmyelocel-T or bone repair cells are a source of bone marrow derived stem and progenitor cells. They are produced through the use of single pass perfusion bioreactors for CD90+ mesenchymal stem cells and CD14+ monocyte/macrophage progenitor cells. The application of ixmyelocel-T has shown potential in the regeneration of muscular, vascular, nervous and osseous tissue. The purpose of this manuscript is to highlight cell therapies used to repair bony and soft tissue defects in the oral and craniofacial complex. The field at this point remains at an early stage, however this review will provide insights into the progress being made using cell therapies for eventual development into clinical practice.

Ischemia is the prime but not the only cause of human multipotent stromal cell death in tissue-engineered constructs in vivo

Local tissue ischemia is a prime cause responsible for the massive cell death in tissue-engineered (TE) constructs observed postimplantation. To assess the impact of ischemia on the death of implanted human multipotent stromal cells (hMSCs), which have great potential for repairing damaged tissues, we hereby investigated the in vivo temporal and spatial fate of human Luc-GFP-labeled MSCs within fibrin gel/coral scaffolds subcutaneously implanted in nude mice. In vivo bioluminescence imaging monitoring and histological analyses of the constructs tested confirmed the irremediable death of hMSCs over 30 days postimplantation. The kinetics of expression of three hypoxic/ischemic markers (HIF-1α, LDH-A, and BNIP3) was also monitored. Our results provided evidence that hMSCs located within the core of implanted constructs died faster and predominantly and strongly expressed the aforementioned ischemic markers. In contrast, cells located in the outer regions of TE constructs were reperfused by neovascularization and were still viable (as evidenced by their ex-vivo proliferative potential) at day 15 postimplantation. These results support the explanation that in the central part of the constructs tested, death of hMSCs was due to ischemia, whereas in the periphery of these constructs, cell death was due to another mechanism that needs to be elucidated.

Behaviour of rat-cultured dental pulp cells in three-dimensional collagen type-1 gel in vitro and in vivo

The purpose of this study was to investigate the growth and differentiation potential of dental pulp cells (DPCs) in three-dimensional (3-D) collagen type-1 scaffold in vitro and in vivo. Third passage DPCs were cultured in a 3-D collagen and expression of both bone- or dentin-related mRNA (alkaline phosphatase (ALP), bone sialoprotein (BSP) and osteopontin (OPN)) and morphological changes evaluated in vitro. In the in vivo study, two types of grafts were transplanted into the rectus abdominus muscles of rats and harvested after 7 days: DPCs in α-minimal essential medium and DPCs mixed with a collagen gel. ALP, BSP and OPN were used as primary antibodies for immunohistochemical study. Histological and immunohistochemical results showed that DPCs in collagen gel were spindle shaped and showed significantly greater expression of ALP, BSP and OPN in vitro than the controls. Transplanted DPCs in collagen type-1 gel showed greater positive immunoreactivity for ALP, BSP and OPN than the controls. It was concluded that the collagen gel scaffold encouraged the differentiation of DPCs into osteoblastic cells.

Fate of bone marrow stromal cells in a syngenic model of bone formation

Bone marrow stromal cells (BMSCs) have been demonstrated to induce bone formation when associated to osteoconductive biomaterials and implanted in vivo. Nevertheless, their role in bone reconstruction is not fully understood and rare studies have been conducted to follow their destiny after implantation in syngenic models. The aim of the present work was to use sensitive and quantitative methods to track donor and recipient cells after implantation of BMSCs in a syngenic model of ectopic bone formation. Using polymerase chain reaction (PCR) amplification of the Sex determining Region Y (Sry) gene and in situ hybridization of the Y chromosome in parallel to histological analysis, we have quantified within the implants the survival of the donor cells and the colonization by the recipient cells. The putative migration of the BMSCs in peripheral organs was also analyzed. We show here that grafted cells do not survive more than 3 weeks after implantation and might migrate in peripheral lymphoid organs. These cells are responsible for the attraction of host cells within the implants, leading to the centripetal colonization of the biomaterial by new bone.

Hydrogel/calcium phosphate composites require specific properties for three-dimensional culture of human bone mesenchymal cells

To provide multipotent cells with a three-dimensional environment closer to bone matrix, an engineered construct mimicking bone components has been designed and evaluated. A biocompatible hydrogel (silated hydroxypropylmethyl cellulose) was used as an extra-cellular matrix while biphasic calcium phosphate ceramic particles were used to replace mineralized matrix. Finally, human bone mesenchymal cells were cultured in three dimensions in the resulting constructs to study their cell viability, proliferation, interactions within the composites, and maintenance of their osteogenic potential. This approach resulted in homogeneous structures in which cells were viable and retained their osteoblastic differentiation potential. However, the cells did not proliferate nor colonize the constructs, possibly because of a lack of suitable interactions with their micro-environment.

3D environment on human mesenchymal stem cells differentiation for bone tissue engineering

In this work a novel method was developed to create a three dimensional environment at a cellular level for bone tissue engineering. Biphasic calcium phosphate (BCP) particles of 140-200 microm were used in association with human mesenchymal stem cells (hMSCs). The cells seeded on these particles adhered and proliferated more rapidly in the first day of culture compared to culture on plastic. Analyses of hMSCs cultured without osteogenic factors on BCP particles revealed an abundant extracellular matrix production forming 3-dimensional (3D) hMSCs/BCP particles constructs after few days. Bone morphogenetic 2 (BMP-2), bone sialoprotein (BSP) and ALP gene expression using real time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) confirmed that expression profiles were modified by the culture substrate while the addition of osteogenic medium enhanced bone markers expression. These results indicate that BCP particles alone are able to induce an osteoblastic differentiation of hMSCs that might be of interest for bone tissue engineering.

Tissue engineering of bone

Despite well-established bone-grafting techniques, large bone defects still represent a challenge for orthopaedic and reconstructive surgeons. Efforts have therefore been made to develop osteoconductive, osteoinductive and osteogenic bone-replacement systems. According to its original definition, tissue engineering is an 'interdisciplinary field that applies the principles of engineering and the life sciences toward the development of biological substitutes that restore, maintain, or improve tissue function'. It is based on the understanding of tissue formation and regeneration, and aims to grow new functional tissues rather than to build new spare parts. This review focuses on the principles of tissue engineering applied to the creation of bioartificial bone tissue. Important aspects, such as osteogenic cells, matrix materials, inter- and intra-cellular communication, growth factors, gene therapy and current concepts of bone tissue engineering are reviewed. First clinical applications are discussed. An outlook provides insight into the possible future perspectives of bone tissue engineering.

Dissection of sets of genes that control the character of wnt5a-deficient mouse calvarial cells

Wnts (wingless and int-related proteins) are a family of secreted cysteine-rich glycoproteins, expressed in a variety of tissues in developing embryos, thought to be involved in cell fate specification and stem cell commitment. To identify the specific Wnts involved in osteoblastic differentiation of human mesenchymal stem cells (hMSCs), we performed degenerative RT-PCR cloning method to amplify Wnt-encoding cDNAs expressed during osteoblastic differentiation of hMSCs in vitro and during hMSC-directed ectopic osteogenesis in the severe combined immunodeficient (SCID) mouse host. WNT5A was found to be the dominant Wnt expressed during osteoblastic differentiation of hMSCs both in vitro and in vivo. RT-PCR further revealed that hWNT5A and its receptor Frizzled family member 5 (hFZD5) was up-regulated during osteoblastic differentiation compared to uncommitted hMSCs. To evaluate the function of Wnt5a, calvarial cells were obtained from Wnt5a(-/-), Wnt5a(+/-), and wild type mice. Wnt5a(-/-) cells showed significantly slower growth when compared to Wnt5a(+/-) and wild type cells. Gene expression profiles of the Wnt5a(-/-) calvarial cells as compared to wild type cells were evaluated using microarray analysis. 255 genes exhibited at least 2-fold changes in expression. Clusters of genes regulating cell cycle, cell proliferation and cell growth, and gene transcription were altered with absence of Wnt5a expression. In addition, genes regulating osteoblastic differentiation including Runx2, osterix, and alkaline phosphatase (ALP) were shown to be down-regulated in Wnt5a(-/-) cells. In conclusion, Wnt5a is highly expressed during osteoblastic differentiation. Its function during mesenchymal stem cell differentiation as well as cell growth was suggested by comparing the gene expression profile of calvarial cells from the Wnt5a(-/-) and wild type mice.

Marrow-derived mesenchymal stem cells-directed bone regeneration in the dog mandible: a comparison between biphasic calcium phosphate and natural bone mineral

OBJECTIVE

This study was designed to compare mesenchymal stem cell (MSC)-based alveolar bone regeneration in biphasic bone substitutes and natural bone mineral in a canine full-thickness alveolar defect model.

MATERIALS AND METHODS

MSCs were isolated from bone marrow aspirates and culture expanded through 3 successive subcultures. The bone differentiation potential of third passage cells was evaluated and confirmed in vitro before cells were used in the transplantation experiment. Undifferentiated cells were then incubated with 3 x 3 x 3 mm(3) hydroxyapatite/beta-tricalcium phosphate (HA/TCP) matrices (Kasios, Lanauguet, France) and 1- to 2-mm Bio-Oss spongiosa (Geistlich Biomaterials, Osteohealth, Switzerland), which is a natural bovine bone mineral (NBM). Kasios/cell, Kasios alone, Bio-Oss/cell, and Bio-Oss alone were implanted in masseter muscle and 4 cylindrical (10-mm diameter) through-and-through bilateral mandibular body defects in 4 mongrel dogs. Histomorphometric analysis was performed 6 weeks after insertion of the scaffold loaded with MSCs.

RESULTS

H&E staining of the decalcified scaffold and scanning electron microscopy demonstrated large MSC coverage of the HA/TCP and Bio-Oss. Cell-loaded Kasios matrices showed the greatest amount of the bone regeneration among the groups in both the muscle (29.11%) and the bone specimens (65.78%). Cell-free biphasic scaffold revealed 44.9% bone fill in bone defects and 23.55% in muscle specimen, and Bio-Oss alone matrices had the least amount of new bone formation: 36.84% and 24.16% in bone and muscle specimens respectively. Kasios loaded with MSCs demonstrated more bone regeneration than Bio-Oss/cell but there was no significant statistical difference (P > .05).

CONCLUSIONS

New biphasic synthetic bone substitutes may offer better conditions for bone regeneration than traditional bone substitute in combination with MSCs. They remained in the defect and contributed to bone regeneration.

Sinus augmentation using human mesenchymal stem cells loaded into a beta-tricalcium phosphate/hydroxyapatite scaffold

OBJECTIVE

Implant placement in the posterior maxilla may often be contraindicated because of insufficient bone volume and presence of the maxillary sinus. In these situations, sinus floor augmentation frequently has been proposed as the best treatment. This clinical study was based on the hypothesis that the clinical effectiveness of adult mesenchymal stem cells (MSCs) loaded to the biphasic scaffold.

METHODS

In this report, the clinical and radiographic results are presented on 6 consecutively treated patients using MSCs in combination with biphasic hydroxyl apatite/ beta-tricalcium phosphate (HA/TCP) for sinus elevation. All the patients in the study had less than 3 mm initial bone height in the posterior maxillary area (IBH). MSCs were cultured and expanded from bone marrow aspirate for each patient. Three months after sinus elevation, radiographic evaluation was performed for the patients and the secondary bone height was measured (SBH(1)). In the second stage surgery, 30 implants were placed. Trephine bur was used as a pilot drill and a core biopsy was obtained from each implant site. Prosthetic rehabilitation of the patients was performed after 4 months. Secondary bone height was measured 9 months after implant placement (SBH(2)).

RESULTS

Of 30 implants, 28 (93%) were considered clinically successful. Two implants were removed due to mobility at the time of surgical exposure. Histologic evaluation of the biopsy specimens revealed numerous areas of osteoid and bone formation HA/TCP, with no evidence of inflammatory cell infiltrate. Mean bone regenerate was 41.34%. Clinically, no complications were observed, and all implants were considered clinically osseointegrated after 4 months. Mean bone height was measured 3 and 12 months after sinus grafting (mean of SBH(1)= 12.08 mm and mean of SBH(2)= 10.08 mm).

CONCLUSIONS

These clinical and histological findings suggest that sinus grafting with HA/TCP in combination with MSCs provide a viable therapeutic alternative for implant placement. The findings suggest that the addition of MSCs to bone derivative/substitute materials may enhance bone formation in the maxillary sinus area. Of course more studies with the control groups are needed for the evaluation of this method as a clinical solution for the patients.

Biological responses in osteoblast-like cell line according to thin layer hydroxyapatite coatings on anodized titanium

Several features of the implant surface, such as roughness, topography and composition play a relevant role in implant integration with bone. This study was conducted in order to determine the effects of various thin layer hydroxyapatite (HA) coatings on anodized Ti surfaces on the biological responses of a human osteoblast-like cell line (MG63). MG63 cells were cultured on 100 nm HA (100 nm HA coating on anodized surface), 500-700 nm HA (500-700 nm HA coating on anodized surface), 1 mum HA (1 mum HA coating on anodized surface) and anodize (non-HA coating on anodized surface) Ti. The morphology of these cells was assessed by scanning electron microscopy (SEM). The cDNAs prepared from the total RNAs of the MG63 were hybridized into a human cDNA microarray (1152 elements). The appearances of the surfaces observed by SEM were different on each of the four dental substrate types. MG63 cells cultured on 100 nm HA, 1 mum HA and anodize exhibited cell-matrix interactions. It was 500-700 nm HA surface showing cell-cell interaction. In the expression of genes involved in osseointegration, several genes, including bone morphogenetic protein 2, latent transforming growth factor beta binding protein 1, catenin (cadherin-associated protein), integrin, PDGFRB and GDF-1 growth differentiation factor 1 were up-regulated on the different surfaces. Several genes, including fibroblast growth factor receptor 3, fibroblast growth factor 12 and CD4 were down-regulated on the different surfaces. The attachment and expression of key osteogenic regulatory genes were enhanced by the surface morphology of the dental materials used.

Pre-culture period of mesenchymal stem cells in osteogenic media influences their in vivo bone forming potential

The objective of this study was to investigate if the in vitro pre-culture period in osteogenic media of rat mesenchymal stem cells (MSCs), influences their ability to regenerate bone when implanted in a critical size cranial defect. MSCs were harvested from the bone marrow of 6-8 weeks old male Fisher rats and expanded in vitro in osteogenic media for different time periods (4, 10, and 16 days) in tissue culture plates (TCP), seeded on sintered titanium fiber meshes without the extracellular matrix (ECM) generated in vitro, and implanted in the rat cranium after 12 h. Thirty two adult Fisher rats received the implants, divided in four groups. Three groups were implanted with cells cultured for 4, 10, or 16 days in osteogenic media and at that time their alkaline phosphatase activity and mineral deposition denoted that they were at different stages of their osteoblastic maturation (undifferentiated MSC, committed, and mature Osteoblasts, respectively). MSCs cultured without osteogenic media for 6 days were used as controls. The constructs were retrieved 4 weeks later and processed for histomorphometric analysis. Implants seeded with cells that have been cultured with osteogenic media for only 4 days revealed the highest bone formation. The lowest bone formation was obtained with the implants seeded with MSCs cultured for 16 days in the presence of osteogenic media. The results of this study suggested that the in vitro pre-culture period of MSCs is a critical factor for their ability to regenerate bone when implanted to an orthotopic site.

Effect of vitamin D pretreatment of human mesenchymal stem cells on ectopic bone formation

Adult mesenchymal stem cells (MSCs) are used in contemporary strategies for tissue engineering. The MSC is able to form bone following implantation as undifferentiated cells adherent to hydroxyapatite (HA)/tricalcium phosphate (TCP) scaffolds. Previous investigators have demonstrated that human MSCs (hMSCs) can be differentiated to osteoblasts in vitro by the inclusion of vitamin D and ascorbic acid. The aim of this study was to compare the osteogenic potential of predifferentiated and undifferentiated bone marrow-derived, culture-expanded hMSCs adherent to synthetic HA/TCP (60%/40%) following subcutaneous engraftment in severe combined immunodeficiency (SCID) mice. During the final 3 days of culture, cells were grown in Dulbecco's modified Eagle's medium containing 10% fetal calf serum and antibiotics or media containing 25-mM calcium supplementation with vitamin D and ascorbic acid. Four weeks following implantation in SCID mice, scoring analysis of bone formation within the cubes revealed the absence of bone formation in unloaded cubes. Bone formation compared by a qualitative bone index was 7.23% for undifferentiated cells compared to 5.20% for differentiated cells. Minimal resorption was observed at this early time point. In this ectopic model, predifferentiation using a combination of vitamin D and ascorbic acid failed to increase subsequent bone formation by implanted cells. Following implantation of hMSCs adherent to an osteoconductive scaffold, host factors may contribute dominant osteoinductive signals or impose inhibitory signals to control the fate of the implanted cell. Predifferentiation strategies require confirmation in vivo.

Minced cartilage without cell culture serves as an effective intraoperative cell source for cartilage repair

Traumatic articular cartilage injuries heal poorly and may predispose patients to the early onset of osteoarthritis. One current treatment relies on surgical delivery of autologous chondrocytes that are prepared, prior to implantation, through ex vivo cell expansion of cartilage biopsy cells. The requirement for cell expansion, however, is both complex and expensive and has proven to be a major hurdle in achieving a widespread adoption of the treatment. This study presents evidence that autologous chondrocyte implantation can be delivered without requiring ex vivo cell expansion. The proposed improvement relies on mechanical fragmentation of cartilage tissue sufficient to mobilize embedded chondrocytes via increased tissue surface area. Our outgrowth study, which was used to demonstrate chondrocyte migration and growth, indicated that fragmented cartilage tissue is a rich source for chondrocyte redistribution. The chondrocytes outgrown into 3-D scaffolds also formed cartilage-like tissue when implanted in SCID mice. Direct treatment of full-thickness chondral defects in goats using cartilage fragments on a resorbable scaffold produced hyaline-like repair tissue at 6 months. Thus, delivery of chondrocytes in the form of cartilage tissue fragments in conjunction with appropriate polymeric scaffolds provides a novel intraoperative approach for cell-based cartilage repair.

Mesenchymal stem cells and bone regeneration

OBJECTIVE

To review the role of mesenchymal stem cells (MSC) in bone formation and regeneration, and outline the development of strategies that use MSC in bone healing and regeneration.

STUDY DESIGN

Literature review.

METHODS

Medline review, synopses of authors' published research.

RESULTS

The MSC is the basic cellular unit of embryologic bone formation. Secondary bone healing mimics bone formation with proliferation of MSC then their differentiation into components of fracture callus. Bone regeneration, where large amounts of bone must form, mimics bone healing and can be achieved with MSC combined with strategies of osteogenesis, osteoinduction, osteoconduction, and osteopromotion. MSC based strategies first employed isolated and culture expanded stem cells in an osteoconductive carrier to successfully regenerate a critical segmental defect in the femur of dogs, which was as effective as autogenous cancellous bone. Because MSC appeared to be immunologically privileged, a study using mismatched allogeneic stem cells demonstrated that these cells would regenerate bone without inciting an immunologic response, documenting the possibility of banked allogeneic MSC for bone regeneration. A technique was developed for selectively retaining MSC from large bone marrow aspirates at surgery for bone regeneration. These techniques utilized osteoconductive and osteoinductive carriers and resulted in bone regeneration that was similar to autogenous cancellous bone.

CONCLUSION

MSC can be manipulated and combined with carriers that will result in bone regeneration of critically sized bone defects.

CLINICAL RELEVANCE

These techniques can be employed clinically to regenerate bone and serve as an alternative to autogenous cancellous bone.

Effect of various implant coatings on biological responses in MG63 using cDNA microarray

During the process of bone formation, titanium (Ti) surface is an important factor in the modulation of osteoblastic function. This study was conducted in order to determine the effects of different Ti surfaces on the biological responses of a human osteoblast-like cell line (MG63). MG63 cells were cultured on smooth (S), sandblasted large-grit and acid etching (SLA), hydroxyapatite (HA), hydroxyfluoride (HF), titanium nitrate (TIN), and diamond-like carbon (DLC) Ti. The morphology of these cells were assessed by SEM. The cDNAs prepared from the total RNAs of the MG63 were hybridized into a human cDNA microarray (1152 elements). The appearances of the surfaces observed by SEM were different on each of the six dental substrate types. The SLA and HA surfaces were determined to be rougher than the others. MG63 cells cultured on SLA and HA exhibited cell-matrix interactions. In the expression of genes involved in osseointegration, several genes, including bone morphogenetic protein, cadherin, integrin, and insulin-like growth factors, were upregulated on the different surfaces. Several genes, including fibroblast growth factor receptor 4, Bcl 2-related protein, and collagen, were downregulated on the different surfaces. The attachment and expression of key osteogenic regulatory genes were enhanced by the surface roughness of the dental materials used.

Embryological study of the development of the rat temporomandibular joint: highlighting the development of the glenoid fossa

Basic embryological findings on the development of the temporomandibular joint have yet to be elucidated sufficiently. This experiment, was undertaken to find the standard time course of the development of the temporomandibular joint in rat fetuses. Serial frontal and sagittal sections of rat fetal heads (between 13.5 and 20.5 days post-conception [p.c.]) were examined microscopically. The condyle was recognized as a mesenchymal condensation at 14.5 days p.c., while the glenoid fossa was recognized at 15.5 days p.c. The mesenchymal condensation of the condyle had differentiated into chondrocytes by 16.5 days p.c., and endochondral ossification was recognized at 17.5 days p.c. The intramembranous ossification of the glenoid fossa was already recognized by 16.5 days p.c.; this started in the posterior region and progressed anteriorly between the zygomatic arch and the squamous part of the temporal bone. Ossification of the condyle had not been completed by 20.5 days p.c., a mass of hypertrophic chondrocytes remained in the center of the condylar head. The glenoid fossa was almost completely ossified by 19.5 days p.c. A coarse region of cells, reminiscent of apoptosis, was recognized in the region of the prospective superior joint space at 17.5 days p.c., and an actual joint space had formed by 18.5 days p.c. The inferior joint space was recognized at 19.5 days p.c. as a fissural cavity, but it was much narrower than its superior counterpart. The prospective meniscus was distinguished on the condylar surface at 17.5 days p.c. by the difference in the shape of its constituent cells. The results obtained here seem to be useful for further experiments and molecular biological studies.

Tissue engineering of bone: the reconstructive surgeon's point of view

Bone defects represent a medical and socioeconomic challenge. Different types of biomaterials are applied for reconstructive indications and receive rising interest. However, autologous bone grafts are still considered as the gold standard for reconstruction of extended bone defects. The generation of bioartificial bone tissues may help to overcome the problems related to donor site morbidity and size limitations. Tissue engineering is, according to its historic definition, an "interdisciplinary field that applies the principles of engineering and the life sciences toward the development of biological substitutes that restore, maintain, or improve tissue function". It is based on the understanding of tissue formation and regeneration and aims to rather grow new functional tissues than to build new spare parts. While reconstruction of small to moderate sized bone defects using engineered bone tissues is technically feasible, and some of the currently developed concepts may represent alternatives to autologous bone grafts for certain clinical conditions, the reconstruction of large-volume defects remains challenging. Therefore vascularization concepts gain on interest and the combination of tissue engineering approaches with flap prefabrication techniques may eventually allow application of bone-tissue substitutes grown in vivo with the advantage of minimal donor site morbidity as compared to conventional vascularized bone grafts. The scope of this review is the introduction of basic principles and different components of engineered bioartificial bone tissues with a strong focus on clinical applications in reconstructive surgery. Concepts for the induction of axial vascularization in engineered bone tissues as well as potential clinical applications are discussed in detail.

In vitro and in vivo evaluation of differentially demineralized cancellous bone scaffolds combined with human bone marrow stromal cells for tissue engineering

Mineralized and partially or fully demineralized biomaterials derived from bovine bone matrix were evaluated for their ability to support human bone marrow stromal cell (BMSC) osteogenic differentiation in vitro and bone-forming capacity in vivo in order to assess their potential use in clinical tissue-engineering strategies. BMSCs were either seeded on bone-derived scaffolds and cocultured in direct cell-to-scaffold contact, allowing for the exposure of soluble and insoluble matrix-incorporated factors, or cocultured with the scaffold preparations in a transwell system, exposing them to soluble matrix-incorporated factors alone. Osteoblast-related markers, alkaline phosphatase (ALP) activity and bone sialoprotein (BSP) and osteopontin (OP) mRNA expression were evaluated in BMSCs following 14 days of cocultivation in both systems. The data demonstrate that BMSCs from some donors express significantly higher levels of all osteoblast-related markers following cocultivation in direct cell-to-scaffold contact with mineralized scaffolds in comparison to fully demineralized preparations, while BMSCs from other donors display no significant differences in response to various scaffold preparations. In contrast, BMSCs cocultured independently with soluble matrix-incorporated factors derived from each scaffold preparation displayed significantly lower levels of ALP activity and BSP mRNA expression in comparison to untreated controls, while no significant differences were observed in marker levels between cells cocultured similarly with different biomaterial preparations. In addition, BMSCs were seeded directly on mineralized and partially or fully demineralized biomaterials and implanted in subcutaneous sites of athymic mice for 8 weeks to evaluate their in vivo bone-forming capacity. The ex vivo incorporation of BMSCs into all bone-derived scaffold preparations substantially increased the mean extent and frequency of samples containing de novo bone formation over similar nonseeded controls, as determined by histological and histomorphometrical analysis. No statistically significant differences were observed in the extent or frequency of bone formation between various scaffold preparations seeded with BMSCs from different donors. These results demonstrate that the in vivo osteoinductivity of bone-derived scaffolds can be modulated by ex vivo incorporated BMSCs and the extent of scaffold demineralization plays a significant role in influencing in vitro osteogenic differentiation of BMSCs depending on the coculture system and BMSC donor.

Effects of age on the repair ability of mesenchymal stem cells in rabbit tendon

Successful tissue engineered repair in the aging adult requires an abundant source of autologous, multipotent mesenchymal stem cells (MSCs). Although the number of bone marrow-derived MSCs declines dramatically with aging, their effectiveness in repair with increasing age has not been studied. We tested the hypothesis that MSCs harvested from geriatric rabbits would not repair patellar tendon defects as well as MSCs harvested from younger adult rabbits. In a novel within-subjects experiment, autologous MSCs were isolated from 1-year old rabbits, culture expanded, and cryogenically preserved. After housing the rabbits for 3 years, MSCs were re-harvested from the 4-year old rabbits and expanded. Five hundred thousand thawed and fresh MSCs were each separately mixed with type I collagen gel (333.3 x 10(3) cells/mg collagen) 24 h before surgery, and the resulting constructs implanted in bilateral full-length central third tendon defects. Twelve weeks post-surgery, the bone-tendon repair-bone units were failed in tension. Intra-animal (paired) comparisons between repair tissue treated with 1-year old MSCs and repair tissue treated with 4-year old MSCs resulted in no significant differences (alpha=0.05) in material properties including maximum stress (10.8 MPa vs. 9.9 MPa; p=0.762), modulus (139.8 MPa vs. 146.2 MPa; p=0.914), and strain energy density (0.52 N mm/mm(3) vs. 0.53 N mm/mm(3); p=0.966). Despite an age-related trend, there were also no significant differences in structural properties including maximum force (62.9 N vs. 27.0 N; p=0.070), stiffness (24.9 N/mm vs. 12.0 N/mm; p=0.111), and strain energy (87.2 N mm vs. 31.4 N mm; p=0.061). A subset of the rabbits (n=4 1 yrMSC, n=2 4 yrMSC) showed the presence of ectopic bone in the repair region and were not included in the mechanical analyses. We conclude that in the rabbit model MSCs do not lose their benefit as a tendon repair therapy with aging and that MSCs can be cryogenically stored for 3 years and still effectively repair soft tissue injuries.

Human adipose-derived adult stem cells produce osteoid in vivo

Adult subcutaneous fat tissue is an abundant source of multipotent cells. Previous studies from our laboratory have shown that, in vitro, adipose-derived adult stem (ADAS) cells express bone marker proteins including alkaline phosphatase, type I collagen, osteopontin, and osteocalcin and produce a mineralized matrix as shown by alizarin red staining. In the current study, the ADAS cell ability to form osteoid in vivo was determined. ADAS cells were isolated from liposuction waste of three individual donors and expanded in vitro before implantation. Equal numbers of cells (3 x 10(6)) were loaded onto either hydroxyapatite/tricalcium phosphate (HA-TCP) cubes or the collagen/HA-TCP composite matrix, Collagraft, and then implanted subcutaneously into SCID mice. After 6 weeks, implants were removed, fixed, and demineralized and sectioned for hematoxylin and eosin staining. Osteoid formation was observed in 80% of HA-TCP implants loaded with ADAS cells. Only 20% of Collagraft implants were positive for the presence of osteoid matrix. Whereas 100% of HA-TCP implants loaded with hFOB 1.19 cells formed osteoid, Collagraft loaded with hFOB 1.19 cells displayed a high degree of adipose tissue within the matrix. Immunostaining of serial sections for human nuclear antigen demonstrated that the osteoid contained human cells. Osteoid formation was not observed in control HA-TCP or Collagraft matrices implanted without cells. In summary, the data demonstrate the ability of ADAS cells to form osteoid matrix in vivo. Because of their abundance and accessibility, ADAS cells may prove to be a novel cell therapeutic for bone repair and regeneration.

Differentiation of the human mesenchymal stem cells derived from bone marrow and enhancement of cell attachment by fibronectin

The ability of human mesenchymal stem cells (hMSC) to differentiate into osteoblasts was examined through the use of osteogenic induction medium (MSCOIM) cultures. hMSC first attached to the dish surface and exhibited fibroblast-like spindle shapes, and after proliferation, formed cuboidal shapes. Calcium assays and the use of von Kossa and alizarin red S staining showed that hMSC were capable of mineralization when cultured in MSCOIM. Gene expressions of Cbfa-1 and BMP-4, which are markers for osteogenic differentiation, were also increased during the hMSC differentiation into osteoblasts. When compared to albumin (Alb)-coated dishes, microscopic observation documented enhanced cell attachment and spreading when hMSC were cultured on fibronectin (FN)-coated dishes. Adherent cell numbers also exhibited a greater increase on the FN-coated dishes during earlier culture stages than that seen for the Alb-coated dishes. These findings suggest that hMSC have the capability to differentiate into osteoblasts and that FN can stimulate the attachment and spreading of the hMSC.

Matrix-mediated retention of osteogenic differentiation potential by human adult bone marrow stromal cells during ex vivo expansion

During prolonged cultivation ex vivo, adult bone marrow stromal stem cells (BMSCs) undergo two probably interdependent processes, replicative aging and a decline in differentiation potential. Recently, our results with primary human fibroblasts indicated that growth on denatured collagen (DC) matrix results in the reduction of the rate of cellular aging. The present study has been undertaken to test whether the growth of human BMSCs under the same conditions would translate into preservation of cellular aging-attenuated functions, such as the ability to express HSP70 in response to stress as well as of osteogenic differentiation potential. We report here that growth of BMSCs on a DC matrix versus tissue culture polystyrene significantly reduced one of the main manifestations of cellular aging, the attenuation of the ability to express a major protective stress response component, HSP70, increased the proliferation capacity of ex vivo expanded BMSCs, reduced the rate of morphological changes, and resulted in a dramatic increase in the retention of the potential to express osteogenic-specific functions and markers upon treatment with osteogenic stimulants. BMSCs are a promising and increasingly important cell source for tissue engineering as well as cell and gene therapeutic strategies. For use of BMSCs in these applications, ex vivo expansion is necessary to obtain a sufficient, therapeutically useful, number of cells; however, this results in the loss of differentiation potential. This problem is especially acute in older patients where more extensive in vitro expansion of smaller number of stem/progenitor cells is needed. The finding that growth on certain biomaterials preserves aging-attenuated functions, enhances proliferation capacity, and maintains differentiation potential of BMSCs indicates a promising approach to address this problem.

Attachment, proliferation, and migration of marrow stromal osteoblasts cultured on biomimetic hydrogels modified with an osteopontin-derived peptide

We prepared oligo(poly(ethylene glycol) fumarate) (OPF) hydrogels modified with a rat osteopontin-derived peptide (ODP), Asp-Val-Asp-Val-Pro-Asp-Gly-Arg-Gly-Asp-Ser-Leu-Ala-Try-Gly (DVDVPDGRGDSLAYG), as well as Gly-Arg-Gly-Asp-Ser (GRGDS) and investigated the modulation of marrow stromal osteoblast function on the peptide-modified hydrogels. Osteoblast attachment was competitively inhibited by a soluble peptide suggesting that the interaction of osteoblasts with the hydrogel was ligand specific. The proliferation index of osteoblasts relative to the initial seeding density was similar on the hydrogels modified with ODP (1.18+/-0.13) and GRGDS (1.27+/-0.12). However, fibroblasts proliferated faster on GRGDS-modified hydrogels than on ODP-modified hydrogels as evidenced by the proliferation indices of 4.89+/-0.03 and 2.42+/-0.16, respectively. A megacolony migration assay conducted for 3 days with a seeding density of 53,000 cells/cm(2) showed that osteoblasts migrated to a longer distance on ODP-modified hydrogels (0.23+/-0.06 mm/day) than on hydrogels modified with GRGDS (0.15+/-0.02 mm/day). In addition, osteoblasts migrated faster than fibroblasts seeded at the same density on ODP-modified hydrogels (0.15+/-0.11 mm/day). The migration of osteoblasts on the peptide-modified hydrogels was dependent on the peptide concentration of the hydrogels resulting in an increased migration distance with increasing the peptide concentration for the concentrations tested. These results show that OPF-based biomimetic hydrogels hold promise for modulating cell proliferation and migration for specific applications by altering the specific ligand and its concentration in the hydrogels.

Characterization of apatite formed on alkaline-heat-treated Ti

Alkaline-heat-treated titanium self-forms an apatite surface layer in vivo. The aim of the present study was to materialistically characterize the surface of alkaline-heat-treated titanium immersed in simulated body fluid (AHS-TI) and to examine the differentiation behavior of osteoblasts on AHS-TI. SEM, thin-film XRD, FTIR, and XPS analyses revealed that AHS-TI contained a 1.0- micro m-thick, low-crystalline, and [002] direction-oriented carbonate apatite surface. Human osteoblast-like SaOS-2 cells were cultured on polystyrene, titanium, and AHS-TI, and RT-PCR analyses of osteogenic differentiation-related mRNAs were conducted. On AHS-TI, the expression of bone sialoprotein mRNA was up-regulated as compared with that on polystyrene and titanium (p < 0.05). On AHS-TI, the expression of osteopontin and osteocalcin mRNAs was up-regulated as compared with that on polystyrene (p<0.05). The results indicate that the apatite was bone-like and accelerated the osteogenic differentiation of SaOS-2, suggesting that alkaline-heat treatment might facilitate better integration of titanium implants with bone.

Mechanical stimulation promotes osteogenic differentiation of human bone marrow stromal cells on 3-D partially demineralized bone scaffolds in vitro

Bone is a dynamic tissue that is able to sense and adapt to mechanical stimuli by modulating its mass, geometry, and structure. Bone marrow stromal cells (BMSCs) are known to play an integral part in bone formation by providing an osteoprogenitor cell source capable of differentiating into mature osteoblasts in response to mechanical stresses. Characteristics of the in vivo bone environment including the three dimensional (3-D) lacunocanalicular structure and extracellular matrix composition have previously been shown to play major roles in influencing mechanotransduction processes within bone cells. To more accurately model this phenomenon in vitro, we cultured human BMSCs on 3-D, partially demineralized bone scaffolds in the presence of four-point bending loads within a novel bioreactor. The effect of mechanical loading and dexamethasone concentration on BMSC osteogenic differentiation and mineralized matrix production was studied for 8 and 16 days of culture. Mechanical stimulation after 16 days with 10 nM dexamethasone promoted osteogenic differentiation of BMSCs by significantly elevating alkaline phosphatase activity as well as alkaline phosphatase and osteopontin transcript levels over static controls. Mineralized matrix production also increased under these culture conditions. Dexamethasone concentration had a dramatic effect on the ability of mechanical stimulation to modulate these phenotypic and genotypic responses. These results provide increased insight into the role of mechanical stimulation on osteogenic differentiation of human BMSCs in vitro and may lead to improved strategies in bone tissue engineering.

Osteogenic Differentiation of Human Bone Marrow Stromal Cells on Partially Demineralized Bone Scaffoldsin Vitro

Tissue engineering has been used to enhance the utility of biomaterials for clinical bone repair by the incorporation of an osteogenic cell source into a scaffold followed by the in vitro promotion of osteogenic differentiation before host implantation. In this study, three-dimensional, partially demineralized bone scaffolds were investigated for their ability to support osteogenic differentiation of human bone marrow stromal cells (BMSCs) in vitro. Dynamic cell seeding resulted in homogeneous cell attachment and infiltration within the matrix and produced significantly higher seeding efficiencies when compared with a conventional static seeding method. Dynamically seeded scaffolds were cultured for 7 and 14 days in the presence of dexamethasone and evaluated on biochemical, molecular, and morphological levels for osteogenic differentiation. Significant elevation in alkaline phosphatase activity was observed versus controls over the 14-day culture, with a transient peak indicative of early mineralization on day 7. On the basis of RT-PCR, dexamethasone-treated samples showed elevations in alkaline phosphatase and osteocalcin expression levels at 7 and 14 days over nontreated controls, while bone sialoprotein was produced only in the presence of dexamethasone at 14 days. Scanning electron microscopy evaluation of dexamethasone-treated samples at 14 days revealed primarily cuboidal cells indicative of mature osteoblasts, in contrast to nontreated controls displaying a majority of cells with a fibroblastic cell morphology. These results demonstrate that partially demineralized bone can be successfully used with human BMSCs to support osteogenic differentiation in vitro. This osseous biomaterial may offer new potential benefits as a tool for clinical bone replacement.

Comparison of bone graft matrices for human mesenchymal stem cell-directed osteogenesis

Scaffolds to support cell-based tissue engineering are critical determinants of clinical efforts to regenerate and repair the body. Bone tissue engineering requires materials that are biocompatible, well vascularized, mechanically suited for bone function, integrated with the host skeleton, and support osteoinduction of the implanted cells that form new bone. The aim of this study was to compare the osteogenic potential of bone marrow-derived, culture expanded human mesenchymal stem cells (hMSCs) adherent to different scaffolds composed of various calcium phosphates. Cells were loaded onto 2 x 2 mm cubes of coral calcium carbonate-derived apatite, bovine bone-derived apatite, synthetic hydroxyapatite (HA)/tricalcium phosphate (TCP) (60:40%), or synthetic HA/TCP (20:80%) and placed into the dorsum of SCID mice for 5 weeks. Subsequent histomorphometric analysis of bone formation within the cubes revealed the absence of bone formation within the coral-derived apatite and the bovine bone-derived apatite. Bone formation within synthetic HA/TCP scaffolds was measured to be 8.8% (+/-2.7%) and 13.8% (+/-3.6%) of the total tissue present for the 60:40% and 20:80% materials, respectively. Minimal resorption was observed at this early time point. Scanning electron microscopy evaluation of loaded scaffolds indicates that cell loading was not a variable affecting the different bone formation outcomes in these four scaffolds. In this ectopic model, different apatite-containing scaffolds of similar morphology and porosity demonstrated marked differences in their ability to support osteoinduction by implanted hMSCs. The necessary induction of hMSCs along the osteoblastic lineage may be dependent, in part, on the local microenvironment established by the scaffold chemistry and interactions with the host.

Differentiation of preosteoblasts is affected by implant surface microtopographies

Osteogenesis involves the recruitment of multipotent mesenchymal cells and the progressive differentiation of these cells into osteoblasts. The transcription factor Runx2 regulates osteoblast differentiation and expression of genes necessary for the development of a mineralized phenotype. The purpose of this study was to determine if preosteoblast cell differentiation associated with Runx2 and osteocalcin gene expression was influenced by implant surface microtopography. Human embryonic palatal mesenchymal cells (HEPM cells) were cultured on grooved or roughened cpTi implant discs. Cell phenotypes were evaluated with epifluorescent microscopy. Real-time PCR was used for quantitative analysis of Runx2 and osteocalcin gene expression. HEPM cells mineralized when grown on rough and grooved implant surfaces relative to tissue culture plastic. Real-time PCR showed significant (p < 0.05) increases in Runx2 and osteocalcin gene expression in cells cultured on rough and grooved implant microtopographies. These results suggest that preosteoblast cell differentiation is affected by implant surface microtopographies during osseointegration of dental implants.

Investigation of allogeneic mesenchymal stem cell-based alveolar bone formation: preliminary findings

This study was designed to evaluate mesenchymal stem cell (MSC)-based alveolar bone regeneration in a canine alveolar saddle defect model. MSCs were loaded onto hydroxyapatite/tricalcium phosphate (HA/TCP) matrices. Scanning electron microscopic (SEM) evaluation demonstrated greater than 75% MSC coverage of the HA/TCP porous surface prior to placement regardless of MSC donor. Matrices, 6 mm x 6 mm x 20 mm, with and without cells, were implanted for 4 and 9 weeks, then removed for histological evaluation of bone formation. Cell-free control matrices were compared with MSC-loaded matrices post implantation. Histomorphometrical analysis showed that equivalent amounts of new bone were formed within the pores of the matrices loaded with autologous MSCs or MSCs from an unrelated donor. Bone formation in the cell-free HA/TCP matrices was less extensive. There was no histologic evidence of an immunological response to autologous MSCs. Surprisingly, allogeneic MSC implantation also failed to provoke an immune response. Analysis of circulating antibody levels against MSCs supported the hypothesis that neither autologous nor allogeneic MSCs induced a systemic response by the host. Analysis of dye-labelled MSCs in histological sections confirmed that the MSCs persisted in the implants throughout the course of the experiment. At 9 weeks, labelled cells were present within the lacunae of newly formed bone. We conclude that autologous and allogeneic MSCs have the capacity to regenerate bone within craniofacial defects.

Adhesion and migration of marrow-derived osteoblasts on injectable in situ crosslinkable poly(propylene fumarate-co-ethylene glycol)-based hydrogels with a covalently linked RGDS peptide

Marrow-derived osteoblasts were cultured on poly(propylene fumarate-co-ethylene glycol) (P(PF-co-EG)) based hydrogels modified in bulk with a covalently linked RGDS model peptide. A poly(ethylene glycol) spacer arm was utilized to covalently link the peptide to the hydrogel. Three P(PF-co-EG) block copolymers were synthesized with varying poly(ethylene glycol) block lengths relative to poly(ethylene glycol) spacer arm. A poly(ethylene glycol) block length of nominal molecular weight 2000 and spacer arm of nominal molecular weight 3400 were found to reduce nonspecific cell adhesion and show RGDS concentration dependent marrow-derived osteoblast adhesion. A concentration of 100 nmol/mL RGDS was sufficient to promote adhesion of 84 +/- 17% of the initial seeded marrow-derived osteoblasts compared with 9 +/- 1% for the unmodified hydrogel after 12 h. Cell spreading was quantified as a method for evaluating adhesivity of cells to the hydrogel. A megacolony migration assay was utilized to assess the migration characteristics of the marrow-derived osteoblasts on RGDS modified hydrogels. Marrow-stromal osteoblasts migration was greater on hydrogels modified with 100 nmol/mL linked RGDS when compared with hydrogels modified with 1000 nmol/mL linked RGDS, while proliferation was not affected. These P(PF-co-EG) hydrogels modified in the bulk with RGDS peptide are potential candidates as in situ forming scaffolds for bone tissue engineering applications.

Ascorbic acid induces collagenase-1 in human periodontal ligament cells but not in MC3T3-E1 osteoblast-like cells: potential association between collagenase expression and changes in alkaline phosphatase phenotype

Ascorbic acid (AA) enhances osteoblastic differentiation by increasing collagen accumulation, which in turn, results in increased alkaline phosphatase (AP) expression in some osteogenic cells. However, in other cells, including human periodontal ligament (PDL) cells, additional osteoinductive agents are required for this response. To understand the potential basis for the maintenance of the AP phenotype of PDL cells exposed to AA, we examined the modulation of the tissue-degrading matrix metalloproteinases (MMPs) and their inhibitors by AA in short-term cell cultures. Early passage PDL cells in serum-free medium were exposed to AA for 5 days. The samples were analyzed for MMPs and their inhibitors, the tissue inhibitors of metalloproteinases (TIMPs), AP, collagen I(alpha1), and osteocalcin. We found that AA dose-dependently increased the expression of collagenase-1, and minimally TIMP-1, but not stromelysin-1 or TIMP-2. Additionally, AA caused substantial increases in levels of type I collagen. AA was unable to increase AP activity or osteocalcin messenger RNA in PDL cells. However, the cells retained the ability to show a significantly greater AP expression in high- versus low-density cultures, and increased osteocalcin as well as AP levels when cultured in the presence of dexamethasone. Moreover, in cells exposed to dexamethasone, increases in AP and osteocalcin were accompanied by a repression of collagenase-1 expression. In contrast to PDL cells, AA did not induce collagenase but produced a significant increase in AP expression in MC3T3-E1 cells. These findings provide the first evidence that AA, by modulating both collagen and collagenase-1 expression in PDL cells, most likely contributes to a net matrix remodeling response in these cells. Furthermore, the relationship between changes in collagenase expression and alterations in AP activity in PDL and MC3T3-E1 cells suggests a potential role for collagenase in modulating the AP phenotype of cells with osteoblastic potential.