Recombinant growth/differentiation factor-5 (GDF-5) stimulates osteogenic differentiation of marrow mesenchymal stem cells in porous hydroxyapatite ceramic

Recent advances in nanomaterials for the treatment of femoral head necrosis

Osteonecrosis of the femoral head (ONFH) is a condition that causes considerable pain and discomfort for patients, and its pathogenic mechanisms are not yet fully understood. While there have been many studies that suggest multiple factors may contribute to its development, current treatments involve both surgical and nonsurgical options. However, there is still much room for improvement in these treatment methods, particularly when it comes to preventing postoperative complications and optimizing surgical procedures. Nanomaterials, as a type of small molecule material, have shown great promise in treating bone tissue diseases, including ONFH. In fact, several nanocomposite materials have demonstrated specific effects in preventing ONFH, promoting bone tissue repair and growth, and optimizing surgical treatment. This article provides a comprehensive overview of current treatments for ONFH, including their advantages and limitations, and reviews the latest advances in nanomaterials for treating this condition. Additionally, this article explores the therapeutic mechanisms involved in using nanomaterials to treat ONFH and to identify new methods and ideas for improving outcomes for patients.

Tissue engineering in periodontology: Biological mediators for periodontal regeneration

Teeth and the periodontal tissues represent a highly specialized functional system. When periodontal disease occurs, the periodontal complex, composed by alveolar bone, root cementum, periodontal ligament, and gingiva, can be lost. Periodontal regenerative medicine aims at recovering damaged periodontal tissues and their functions by different means, including the interaction of bioactive molecules, cells, and scaffolds. The application of growth factors, in particular, into periodontal defects has shown encouraging effects, driving the wound healing toward the full, multi-tissue periodontal regeneration, in a precise temporal and spatial order. The aim of the present comprehensive review is to update the state of the art concerning tissue engineering in periodontology, focusing on biological mediators and gene therapy.

Combining Stem Cells and Biomaterial Scaffolds for Constructing Tissues and Cell Delivery

Combining stem cells with biomaterial scaffolds serves as a promising strategy for engineering tissues for both in vitro and in vivo applications. This updated review details commonly used biomaterial scaffolds for engineering tissues from stem cells. We first define the different types of stem cells and their relevant properties and commonly used scaffold formulations. Next, we discuss natural and synthetic scaffold materials typically used when engineering tissues, along with their associated advantages and drawbacks and gives examples of target applications. New approaches to engineering tissues, such as 3D bioprinting, are described as they provide exciting opportunities for future work along with current challenges that must be addressed. Thus, this review provides an overview of the available biomaterials for directing stem cell differentiation as a means of producing replacements for diseased or damaged tissues.

Metabolism as an early predictor of DPSCs aging

Tissue resident adult stem cells are known to participate in tissue regeneration and repair that follows cell turnover, or injury. It has been well established that aging impedes the regeneration capabilities at the cellular level, but it is not clear if the different onset of stem cell aging between individuals can be predicted or prevented at an earlier stage. Here we studied the dental pulp stem cells (DPSCs), a population of adult stem cells that is known to participate in the repair of an injured tooth, and its properties can be affected by aging. The dental pulp from third molars of a diverse patient group were surgically extracted, generating cells that had a high percentage of mesenchymal stem cell markers CD29, CD44, CD146 and Stro1 and had the ability to differentiate into osteo/odontogenic and adipogenic lineages. Through RNA seq and qPCR analysis we identified homeobox protein, Barx1, as a marker for DPSCs. Furthermore, using high throughput transcriptomic and proteomic analysis we identified markers for DPSC populations with accelerated replicative senescence. In particular, we show that the transforming growth factor-beta (TGF-β) pathway and the cytoskeletal proteins are upregulated in rapid aging DPSCs, indicating a loss of stem cell characteristics and spontaneous initiation of terminal differentiation. Importantly, using metabolic flux analysis, we identified a metabolic signature for the rapid aging DPSCs, prior to manifestation of senescence phenotypes. This metabolic signature therefore can be used to predict the onset of replicative senescence. Hence, the present study identifies Barx1 as a DPSCs marker and dissects the first predictive metabolic signature for DPSCs aging.

Effects of 7 T static magnetic fields on the expression of biological markers and the formation of bone in rats

In this study, we aimed to evaluate the effects of 7 T static magnetic fields (SMFs) on rat mesenchymal stem cells (MSCs) in order to determine whether strong SMFs affected the osteogenesis of MSCs. MSCs were prepared from bone marrow cells obtained from the femurs of 7-week-old male Fischer 344 rats. MSCs were then combined with β-tricalcium phosphate (β-TCP), yielding two types of TCP/MSC constructs (TCP/P-1 and P-2) on day 0. Exposure was performed for 3 h/day for 6 days, and the experiments were performed twice using different exposure apparatus (cryovials or 4-well chambers) for each experiment. The results from gene expression, protein expression, and histological analyses showed no reproducible effects on both TCP/P-1 and TCP/P-2 MSC constructs, although osteocalcin levels for TCP/P-1 MSC constructs increased significantly once after 7 T exposure in two experiments. These findings contribute to understanding the effects of strong SMFs on MSC and osteoblasts. Bioelectromagnetics. 40:16-26, 2019. © 2018 Wiley Periodicals, Inc.

The Advancement of Biomaterials in Regulating Stem Cell Fate

Stem cells are well-known to have prominent roles in tissue engineering applications. Embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) can differentiate into every cell type in the body while adult stem cells such as mesenchymal stem cells (MSCs) can be isolated from various sources. Nevertheless, an utmost limitation in harnessing stem cells for tissue engineering is the supply of cells. The advances in biomaterial technology allows the establishment of ex vivo expansion systems to overcome this bottleneck. The progress of various scaffold fabrication could direct stem cell fate decisions including cell proliferation and differentiation into specific lineages in vitro. Stem cell biology and biomaterial technology promote synergistic effect on stem cell-based regenerative therapies. Therefore, understanding the interaction of stem cell and biomaterials would allow the designation of new biomaterials for future clinical therapeutic applications for tissue regeneration. This review focuses mainly on the advances of natural and synthetic biomaterials in regulating stem cell fate decisions. We have also briefly discussed how biological and biophysical properties of biomaterials including wettability, chemical functionality, biodegradability and stiffness play their roles.

Growth/differentiation factor-5 promotes in vitro/vivo periodontal specific differentiation of induced pluripotent stem cell-derived mesenchymal stem cells

Mesenchymal stem cells (MSCs) derived from induced pluripotent stem cells (iPSCs) represent a promising alternative source of MSCs for effective periodontal regeneration. Scientific evidence has demonstrated that growth/differentiation factor-5 (GDF-5) supports regeneration of periodontal tissues and has a key role in MSC differentiation. The present study investigated the effects of recombinant human GDF-5 (rhGDF-5) on periodontal specific differentiation of iPSC-derived MSCs (iPSC-MSCs) and bone marrow mesenchymal stem cells (BMSCs). rhGDF-5 treatment in vitro significantly enhanced the expression levels of marker genes associated with osteogenesis (OCN), fibrogenesis (periostin) and cementogenesis (CAP) in the iPSC-MSCs compared with untreated controls (all P<0.05). Interestingly, the rhGDF-5-treated BMSCs failed to exhibit overexpression of periostin and CAP despite highly upregulated expression of OCN. In the presence of rhGDF-5, both the iPSC-MSCs and BMSCs demonstrated marked formation of mineralized nodules. Notably, rhGDF-5 greatly promoted periodontal specific differentiation of the iPSC-MSCs encapsulated in hyaluronic acid (HA) hydrogels in vivo as determined by immunohistochemical and immunofluorescence staining. The majority of the PKH67-labeled iPSC-MSCs implanted with rhGDF-5 exhibited strong expression of OCN, periostin and CAP. In conclusion, iPSC-MSCs demonstrate high periodontal specific differentiation potential in response to rhGDF-5 both in vitro and in vivo. The delivery of iPSC-MSCs and rhGDF-5 with HA hydrogel may have beneficial effects in regenerative periodontal therapy.

Bone Marrow Mesenchymal Stem Cells Expressing Baculovirus-Engineered Bone Morphogenetic Protein-7 Enhance Rabbit Posterolateral Fusion

Previous studies have suggested that bone marrow-derived mesenchymal stem cells (BMDMSCs) genetically modified with baculoviral bone morphogenetic protein-2 (Bac-BMP-2) vectors could achieve successful fusion in a femur defect model or in a spinal fusion model. In this study, BMDMSCs expressing BMP-7 (Bac-BMP-7-BMDMSCs) were generated. We hypothesized that Bac-BMP-7-BMDMSCs could secrete more BMP-7 than untransduced BMDMSCs in vitro and achieve spinal posterolateral fusion in a rabbit model. Eighteen rabbits underwent posterolateral fusion at L4-5. Group I (n = 6) was implanted with collagen-β-tricalcium phosphate (TCP)-hydroxyapatite (HA), Group II (n = 6) was implanted with collagen-β-TCP-HA plus BMDMSCs, and Group III (n = 6) was implanted with collagen-β-TCP-HA plus Bac-BMP-7-BMDMSCs. In vitro production of BMP-7 was quantified with an enzyme-linked immunosorbent assay (ELISA). Spinal fusion was examined using computed tomography (CT), manual palpation, and histological analysis. ELISA demonstrated that Bac-BMP-7-BMDMSCs produced four-fold to five-fold more BMP-7 than did BMDMSCs. In the CT results, 6 fused segments were observed in Group I (50%, 6/12), 8 in Group II (67%, 8/12), and 12 in Group III (100%, 12/12). The fusion rate, determined by manual palpation, was 0% (0/6) in Group I, 0% (0/6) in Group II, and 83% (5/6) in Group III. Histology showed that Group III had more new bone and matured marrow formation. In conclusion, BMDMSCs genetically transduced with the Bac-BMP-7 vector could express more BMP-7 than untransduced BMDMSCs. These Bac-BMP-7-BMDMSCs on collagen-β-TCP-HA scaffolds were able to induce successful spinal fusion in rabbits.

The Role of miRNAs in Cartilage Homeostasis

Osteoarthritis (OA) is an age-related disease with poorly understood pathogenesis. Recent studies have demonstrated that miRNA might play a key role in OA initiation and development. We reviewed recent publications and elucidated the connection between miRNA and OA cartilage anabolic and catabolic signals, including four signaling pathways: TGF-β/Smads and BMPs signaling, associated with cartilage anabolism; and MAPK and NF-KB signaling, associated with cartilage catabolism. We also explored the relationships with MMP, ADAMTS and NOS (NitricOxide Synthases) families, as well as with the catabolic cytokines IL-1 and TNF-α. The potential role of miRNAs in biological processes such as cartilage degeneration, chondrocyte proliferation, and differentiation is discussed. Collective evidence indicates that miRNAs play a critical role in cartilage degeneration. These findings will aid in understanding the molecular network that governs articular cartilage homeostasis and in to elucidate the role of miRNA in the pathogenesis of OA.

Identification of Pathways Mediating Growth Differentiation Factor5-Induced Tenogenic Differentiation in Human Bone Marrow Stromal Cells

To date, the molecular signalling mechanisms which regulate growth factors-induced MSCs tenogenic differentiation remain largely unknown. Therefore, a study to determine the global gene expression profile of tenogenic differentiation in human bone marrow stromal cells (hMSCs) using growth differentiation factor 5 (GDF5) was conducted. Microarray analyses were conducted on hMSCs cultures supplemented with 100 ng/ml of GDF5 and compared to undifferentiated hMSCs and adult tenocytes. Results of QuantiGene® Plex assay support the use and interpretation of the inferred gene expression profiles and pathways information. From the 27,216 genes assessed, 873 genes (3.21% of the overall human transcriptome) were significantly altered during the tenogenic differentiation process (corrected p<0.05). The genes identified as potentially associated with tenogenic differentiation were ARHGAP29, CCL2, integrin alpha 8 and neurofilament medium polypeptides. These genes, were mainly associated with cytoskeleton reorganization (stress fibers formation) signaling. Pathway analysis demonstrated the potential molecular pathways involved in tenogenic differentiation were: cytoskeleton reorganization related i.e. keratin filament signaling and activin A signaling; cell adhesion related i.e. chemokine and adhesion signaling; and extracellular matrix related i.e. arachidonic acid production signaling. Further investigation using atomic force microscopy and confocal laser scanning microscopy demonstrated apparent cytoskeleton reorganization in GDF5-induced hMSCs suggesting that cytoskeleton reorganization signaling is an important event involved in tenogenic differentiation. Besides, a reduced nucleostemin expression observed suggested a lower cell proliferation rate in hMSCs undergoing tenogenic differentiation. Understanding and elucidating the tenogenic differentiation signalling pathways are important for future optimization of tenogenic hMSCs for functional tendon cell-based therapy and tissue engineering.

Mesenchymal stem cells expressing baculovirus-engineered BMP-2 and VEGF enhance posterolateral spine fusion in a rabbit model

BACKGROUND CONTEXT

Mesenchymal stem cell (MSC)-based cell therapy and gene transfer have converged and show great potential for accelerating bone healing. Gene therapy can provide more sustained expression of osteogenic factors such as bone morphogenetic protein-2 (BMP-2). We previously demonstrated that low-dose BMP-2 enhanced spinal posterolateral fusion by MSCs in a rabbit model. Herein, we genetically modified rabbit MSCs with a recombinant baculovirus encoding BMP-2 (Bac-CB) and vascular endothelial growth factor (Bac-VEGF) seeded into porous scaffolds to enhance spinal fusion.

PURPOSE

This study evaluates the success rate of the MSC-based cell therapy and gene transfer approach for single-level posterolateral spine fusion. We hypothesize that combining three-dimensional tricalcium phosphate (TCP) scaffolds and genetically modified allogeneic MSCs with baculovirus-mediated growth factor expression would increase the success rate of spinal fusion.

STUDY DESIGN

The study design was based on an animal model (approved by the Institutional Animal Care and Use Committee) using 18 adult male New Zealand rabbits.

METHODS

This study included 18 male New Zealand rabbits, weighing 3.5 to 4 kg. Allogeneic bone marrow-derived MSCs were isolated and genetically modified with Bac-CB and Bac-CV seeded onto TCP scaffolds (MSC/Bac/TCP). The animals were divided into three groups according to the material implanted into the bilateral L4-L5 intertransverse space: TCP scaffold (n=6), MSC/TCP (n=6), and MSC/Bac/TCP (n=6). After 12 weeks, the rabbits were euthanized for radiographic examination, manual palpation, and histologic study.

RESULTS

Bilateral fusion areas in each animal were evaluated independently. The radiographic fusion rates at 12 sites were 0 of 12 in the TCP scaffold group, 4 of 12 in the MSC/TCP group, and 10 of 12 in the MSC/Bac/TCP group. By manual palpation, there were zero solid fusions in the TCP scaffold group, two solid fusions in the MSC/TCP group, and five solid fusions in the MSC/Bac/TCP group. Fusion rates were significantly greater in the MSC/Bac/TCP group.

CONCLUSIONS

The results indicate the potential of using baculovirus as a vector for gene/cell therapy approaches to improve bone healing and support the feasibility of using allogeneic MSCs for inducing bone formation and intertransverse process fusion.

Cell sheet injection as a technique of osteogenic supply

We previously reported a new cell transplantation method utilizing injections of mesenchymal stem cell (MSC) sheets that have osteogenic potential. After subcutaneous transplantation without any scaffold, the sheet demonstrated in vivo bone formation. In the present study, we transplanted such sheets by injection into implanted ceramics and assessed whether the injectable MSC sheets could stimulate osteogenic integration of the ceramics. To fabricate MSC sheets, bone marrow cells cultured from femur shafts of 7-week-old rats were subcultured in regular 10-cm dishes containing dexamethasone and ascorbic acid phosphate until confluent. Each cell sheet was then lifted using a scraper. Porous β-tricalcium phosphate (β-TCP) disks (5 mm Φ×2 mm) were transplanted subcutaneously into the backs of the rats. Immediately following implantation, the sheets were injected around the disks via a 16G needle (immediate group). Cell sheets were also injected into the remaining implanted disks 1 week after disk implantation (1-wk group). Four weeks following sheet injection, radiography and histology revealed calcification and bone tissue around the harvested disks of the immediate group (eight disks exhibited bone formation/eight implanted disks), whereas calcification and bone tissue were observed in 50% of the samples in the 1-wk group (four disks exhibited bone formation/eight implanted disks). The present study indicates that injected cell sheets can supply osteogenic potential to implanted ceramics. Owing to the usage of a needle for cell sheet transplantation, such an injection method can be applied as a minimally invasive technique of osteogenic supply to implanted ceramics.

Freeze-dried allograft-mediated gene or protein delivery of growth and differentiation factor 5 reduces reconstructed murine flexor tendon adhesions

Advances in allograft processing have opened new horizons for clinical adaptation of flexor tendon allografts as delivery scaffolds for antifibrotic therapeutics. Recombinant adeno-associated-virus (rAAV) gene delivery of the growth and differentiation factor 5 (GDF-5) has been previously associated with antifibrotic effects in a mouse model of flexor tendoplasty. In this study, we compared the effects of loading freeze-dried allografts with different doses of GDF-5 protein or rAAV-Gdf5 on flexor tendon healing and adhesions. We first optimized the protein and viral loading parameters using reverse transcription polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay (ELISA), and in vivo bioluminescent imaging. We then reconstructed flexor digitorum longus (FDL) tendons of the mouse hindlimb with allografts loaded with low and high doses of recombinant GDF-5 protein and rAAV-Gdf5 and evaluated joint flexion and biomechanical properties of the reconstructed tendon. In vitro optimization studies determined that both the loading time and concentration of the growth factor and viral vector had dose-dependent effects on their retention on the freeze-dried allograft. In vivo data suggest that protein and gene delivery of GDF-5 had equivalent effects on improving joint flexion function, in the range of doses used. Within the doses tested, the lower doses of GDF-5 had more potent effects on suppressing adhesions without adversely affecting the strength of the repair. These findings indicate equivalent antifibrotic effects of Gdf5 gene and protein delivery, but suggest that localized delivery of this potent factor should also carefully consider the dosage used to eliminate untoward effects, regardless of the delivery mode.

MicroRNA-21 controls the development of osteoarthritis by targeting GDF-5 in chondrocytes

Osteoarthritis is a common cause of functional deterioration in older adults and is an immense burden on the aging population. Altered chondrogenesis is the most important pathophysiological process involved in the development of osteoarthritis. However, the molecular mechanism underlying the regulation of chondrogenesis in patients with osteoarthritis requires further elucidation, particularly with respect to the role of microRNAs. MiR-21 expression in cartilage specimens was examined in 10 patients with knee osteoarthritis and 10 traumatic amputees. The effect of miR-21 on chondrogenesis was also investigated in a chondrocyte cell line. The effect of miR-21 on the expression of growth differentiation factor 5 (GDF-5) was further assessed by luciferase reporter assay and western blot. We found that endogenous miR-21 is upregulated in osteoarthritis patients, and overexpression of miR-21 could attenuate the process of chondrogenesis. Furthermore, we identified GDF-5 as the direct target of miR-21 during the regulation of chondrogenesis. Our data suggest that miR-21 has an important role in the pathogenesis of osteoarthritis and is a potential therapeutic target.

MicroRNA-125b regulates osteogenic differentiation of mesenchymal stem cells by targeting Cbfβ in vitro

Differentiation of mesenchymal stem cells (MSCs) into a specific lineage is firmly and precisely regulated via crucial transcription factors and signaling cascades, but the accurate mechanisms still need to be revealed. MicroRNAs (miRNA) negativity regulates the target mRNA protein synthesis to regulate various kinds of biological processes. In the present study we investigate miRNAs mediated regulatory mechanisms of osteoblastic differentiation in C3H10T1/2 cells and we identified that the level of miR-125b expression was obviously decreased compared with undifferentiated ones during differentiation process. Subsequently, dual-luciferase reporter gene assay data demonstrated that miR-125b targets a putative binding site in the 3'-UTR of Cbfβ gene, a key transcription factor for osteogenesis. We observed over and interferential expression of miR-125b down-regulate for Cbfβ protein in C3H10T1/2 cells and the over-expression decrease the mRNA levels of three osteoblastic marker genes, alkaline phosphatase (ALP), osteocalcin (OCN), osteopontin (OPN) by BMP-2-induced, whereas, anti-miR-125b increased the expression of these marker genes and hence up-regulated mRNA levels of Cbfβ. It is concluded from the result that miR-125b is a key regulatory factor of osteoblastic differentiation by directly targeting Cbfβ and indirectly acting on Runx2 at an early stage osteoblastic differentiation.

The enhanced effect of surface microstructured porous titanium on adhesion and osteoblastic differentiation of mesenchymal stem cells

Porous titanium with appropriate surface treatments can be osteoinductive. To investigate the effect of surface treatments of porous titanium on the attachment and differentiation of mesenchymal stem cells (MSCs), two kinds of surface microstructured porous titaniums, H₂O₂/TaCl₅ treated one (HTPT), and H₂O₂/TaCl₅ and subsequent simulated body fluid (SBF) treated one (STPT) were fabricated, and non-treated one (NTPT) was used as control. The morphology, specific surface area (SSA), pore distribution and mechanical strength of these materials were characterized respectively, and the results showed that H₂O₂/TaCl₅ treatment led to a significant increase in both SSA and micropores of HTPT, and the further SBF immersion resulted in the formation of a layer of bone-like apatite on the surface of STPT. Although the surface treatments had a little negative impact on the compressive strength and elasticity modulus of porous titanium, the mechanical strength of HTPT or STPT was enough for the bone defect repair of the load-bearing sites. The protein adsorption and cell adhesion experiments confirmed that the microstructured surface notably enhanced porous titanium's protein binding capacity and promoted MSCs adhesion on the surface. More importantly, cell differentiation experiments proved that the microstructured surface evidently elevated the osteoblastic gene expressions of MSCs compared to NTPT. The enhanced biological effect by the surface treatments was more robust on STPT. Therefore, our results suggest that the microstructured surface has great potential for promoting MSCs differentiation towards osteoblasts, giving excellent support for the osteoinduction of porous titanium with appropriate surface treatments.

Growth and differentiation factor-5 regulates the growth and differentiation of human dental pulp cells

INTRODUCTION

Growth and differentiation factor-5 (GDF-5) is a multifunctional protein that regulates the development and repair in many tissues. The purpose of this study was to investigate whether GDF-5 may influence the proliferation, differentiation, and collagen turnover of human dental pulp cells.

METHODS

Human dental pulp cells were treated with different concentrations of GDF-5 (0-500 ng/mL). Morphology of pulp cells was observed under a microscope. Cell proliferation was evaluated by 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyl-tetrazolium bromide assay. Immunofluorescent assay was used to observe the percentages of cell mitosis. Collagen content was measured by Sircol collagen assay. Tissue inhibitor of metalloproteinase-1 level in the culture medium was measured with enzyme-linked immunosorbent assay and Western blotting. Cell differentiation was evaluated by alkaline phosphatase (ALP) staining and ALP enzyme activity assay.

RESULTS

After exposure of dental pulp cells to various concentrations of GDF-5, cell number was up-regulated significantly in dose-dependent manner. GDF-5 also stimulated mitosis of dental pulp cells as indicated by an increased percentage of binucleated cells from 28% to 35%-45%. GDF-5 did not affect the collagen content and tissue inhibitor of metalloproteinase-1 level of pulp cells. GDF-5 decreased the ALP activity of pulp cells as analyzed by ALP staining and enzyme activity assay, with 14%-44% of inhibition.

CONCLUSIONS

GDF-5 revealed mitogenic and proliferative activity to dental pulp cells. GDF-5 showed inhibitory effect on ALP activity but little effect on the collagen turnover. These events are crucial in specific stages of dental pulp repair and regeneration. GDF-5 may be potentially used for tissue engineering of pulp-dentin complex.

Silencing BRE expression in human umbilical cord perivascular (HUCPV) progenitor cells accelerates osteogenic and chondrogenic differentiation

BRE is a multifunctional adapter protein involved in DNA repair, cell survival and stress response. To date, most studies of this protein have been focused in the tumor model. The role of BRE in stem cell biology has never been investigated. Therefore, we have used HUCPV progenitor cells to elucidate the function of BRE. HUCPV cells are multipotent fetal progenitor cells which possess the ability to differentiate into a multitude of mesenchymal cell lineages when chemically induced and can be more easily amplified in culture. In this study, we have established that BRE expression was normally expressed in HUCPV cells but become down-regulated when the cells were induced to differentiate. In addition, silencing BRE expression, using BRE-siRNAs, in HUCPV cells could accelerate induced chondrogenic and osteogenic differentiation. Hence, we postulated that BRE played an important role in maintaining the stemness of HUCPV cells. We used microarray analysis to examine the transcriptome of BRE-silenced cells. BRE-silencing negatively regulated OCT4, FGF5 and FOXO1A. BRE-silencing also altered the expression of epigenetic genes and components of the TGF-β/BMP and FGF signaling pathways which are crucially involved in maintaining stem cell self-renewal. Comparative proteomic profiling also revealed that BRE-silencing resulted in decreased expressions of actin-binding proteins. In sum, we propose that BRE acts like an adaptor protein that promotes stemness and at the same time inhibits the differentiation of HUCPV cells.

Overexpression of GDF5 through an adenovirus vector stimulates osteogenesis of human mesenchymal stem cells in vitro and in vivo

The use of stem cells combined with gene therapy could be an important way to facilitate bone regeneration. In this study, the aim was to investigate the potential of growth and differentiation factor-5 (GDF5) to genetically manipulate human mesenchymal stem cells (hMSCs) for bone regeneration. Recombinant adenovirus Ad-GDF5 and Ad-GFP were constructed and identified, and the titer of both were determined. Third-passage hMSCs were infected with adenovirus, and the expression of GDF5 was confirmed by detection of GFP-positive cells, GDF5 mRNA levels, Western blotting, and enzyme-linked immunosorbent assay (ELISA). hMSCs at passage 3 were divided into four groups: (1) an experimental group infected with Ad-GDF5, (2) a positive control group cultured with osteogenic differentiation medium, (3) a control group infected with Ad-GFP cultured with standard medium, and (4) a blank control group cultured with standard medium. Evaluation of cell morphology and proliferation, analysis of the expression of genes related to osteogenic differentiation, von Kossa staining, and immunofluorescent staining of collagen I were used to investigate the osteogenesis of cells among the groups. After culturing the cells for 2 days under each corresponding condition, the cells were detached and subcutaneously injected into the backs of nude mice to evaluate bone formation. Samples were collected for histological staining, protein Western blotting, and micro-computer tomography. When infected with Ad-GDF5, hMSCs could overexpress GDF5 for a prolonged period in vitro and reach a concentration of 160 ng/ml. Cells infected with Ad-GDF5 or cultured in osteogenic medium displayed osteogenic differentiation based on their histological and cellular properties and on their gene and protein expression patterns. Furthermore, Ad-GDF5 showed a better ability to upregulate the expression of collagen I, alkaline phosphatase, and osteocalcin mRNA than the osteogenic medium. Furthermore, Ad-GDF5 expression was associated with enhanced bone formation in vivo. Our findings suggest that hMSCs infected with Ad-GDF5 can differentiate in an osteogenic direction and may be a promising cell source for bone regeneration.

Braided nanofibrous scaffold for tendon and ligament tissue engineering

Tendon and ligament (T/L) injuries present an important clinical challenge due to their intrinsically poor healing capacity. Natural healing typically leads to the formation of scar-like tissue possessing inferior mechanical properties. Therefore, tissue engineering has gained considerable attention as a promising alternative for T/L repair. In this study, we fabricated braided nanofibrous scaffolds (BNFSs) as a potential construct for T/L tissue engineering. Scaffolds were fabricated by braiding 3, 4, or 5 aligned bundles of electrospun poly(L-lactic acid) nanofibers, thus introducing an additional degree of flexibility to alter the mechanical properties of individual scaffolds. We observed that the Young's modulus, yield stress, and ultimate stress were all increased in the 3-bundle compared to the 4- and 5-bundle BNFSs. Interestingly, acellular BNFSs mimicked the normal tri-phasic mechanical behavior of native tendon and ligament (T/L) during loading. When cultured on the BNFSs, human mesenchymal stem cells (hMSCs) adhered, aligned parallel to the length of the nanofibers, and displayed a concomitant realignment of the actin cytoskeleton. In addition, the BNFSs supported hMSC proliferation and induced an upregulation in the expression of key pluripotency genes. When cultured on BNFSs in the presence of tenogenic growth factors and stimulated with cyclic tensile strain, hMSCs differentiated into the tenogenic lineage, evidenced most notably by the significant upregulation of Scleraxis gene expression. These results demonstrate that BNFSs provide a versatile scaffold capable of supporting both stem cell expansion and differentiation for T/L tissue engineering applications.

Premature ovarian failure in mice with oocytes lacking core 1-derived O-glycans and complex N-glycans

Premature ovarian failure (POF) affects up to 1.4% of women under the age of 40 yr and less than 30% of cases have a known cause. Here we describe a new mouse model of POF resulting from oocyte-specific ablation of core 1-derived (mucin) O-glycans and complex and hybrid N-glycans. Females carrying floxed alleles of both the C1galt1 (T-syn) and Mgat1 glycosyltransferase genes and a ZP3Cre transgene, generate oocytes lacking complex O- and N-glycans following oocyte-specific deletion at the primary follicle stage. We previously showed that few double-mutant females are fertile, and those produce only a single small litter. Here we show that ovarian function declined rapidly in double-mutant females with less than 1% ovulating at 11 wk of age after superovulation with exogenous gonadotropins. Ovary weight was significantly decreased in double-mutant females by 3 months of age, consistent with a decrease in the number of developing follicles. FSH levels in double-mutant females were elevated at 3 months of age, and testosterone and inhibin A were decreased, showing that the loss of complex N- and O-glycans from oocyte glycoproteins affected hypothalamic-pituitary-gonadal feedback loops. The absence of developing follicles, ovary dysfunction, reduced testosterone and inhibin A, and elevated FSH in double-mutant females lacking C1galt1 and Mgat1 in oocytes represents a new mouse model for the study of follicular POF.

Osteogenic activity of bone marrow-derived mesenchymal stem cells (BMSCs) seeded on irradiated allogenic bone

Allogenic bone grafting, a technique used in orthopaedic surgery, has several problems, including low osteogenic activity. To overcome the problem, this study aimed to determine whether in vivo osteogenesis could be enhanced using allogenic irradiated bone grafts after seeding with autologous bone marrow-derived mesenchymal stem cells (BMSCs). The allogenic bone cylinders were extracted from ACI rats and sterilized by irradiation. Donor BMSCs were obtained from fresh Fischer 344 (F344) rat bone marrow by cell culture. The allogenic bone with or without BMSCs were transplanted subcutaneously into syngeneic F344 rats. At 4 weeks after transplantation, high alkaline phosphatase (ALP) activity, bone-specific osteocalcin mRNA expression and newly formed bone were detected in the allogenic bone with BMSCs. The origin of the newly formed bone was derived from cultured donor BMSCs. However, none of these identifiers of osteogenesis were detected in either the fresh or the irradiated allogenic bone without BMSCs. These results indicate the availability of autologous BMSCs to heighten the osteogenic response of allogenic bone. Our present tissue-engineering method might contribute to a wide variety of allogenic bone grafting techniques in clinical settings.

Scaffold-free cell sheet injection results in bone formation

We previously reported a new cell transplantation method in which mesenchymal stem cells (MSCs) were cultured as cell sheets. The cultured MSC sheets showed high alkaline phosphatase (ALP) activities and osteocalcin (OC) contents. In the present study, we transplanted such sheets by injection to assess whether the injectable MSC sheets could form bone tissue at subcutaneous sites. At 4 weeks after the subcutaneous injection, the injected areas showed hard mass formation. Each mass consisted of newly formed bone, as evaluated by radiographic, histological and gene expression analyses as well as three-dimensional computed tomography (3D-CT). Histological analyses revealed extracellular bone matrix together with osteocytes and active osteoblasts. Real-time PCR analyses showed high ALP and OC mRNA expressions. We also injected the cell sheets into dead bone to determine whether the lost osteogenic potential could be rescued, and histological analyses revealed that the injected cell sheets supplied osteogenic potential to the dead bone. The present study clearly indicates that osteogenic MSC sheets can be transplanted via injection through a needle and that bone formation results in the injected areas. Owing to its usage of a needle for fabrication of in vivo bone tissue, this injection method can be applied as a minimally invasive approach for hard tissue reconstruction.

Development of a high-specificity enzyme-linked immunosorbent assay (ELISA) system for the quantification and validation of intact rat osteocalcin

Osteocalcin (OC) exhibits hard tissue-specific expression and binding activity to hydroxyapatite. Therefore, measurement of secreted OC is a very useful index for evaluating osteoblastic differentiation in regenerative bone. In the present study, we established a high-specificity sandwich enzyme-linked immunosorbent assay (ELISA) system for the quantification of intact rat OC, which could be useful for validating tissue-engineered bone samples nondestructively and continuously. The range of detection with the sandwich ELISA system was 0.1-100 ng OC/mL of cell culture media or rat sera. No cross-reactivities were detected with OCs from other species, including human, bovine and mouse OCs, and other mammalian sera, which would contain the corresponding endogenous OCs. The intra- and inter-assay coefficients of variation were < or =4.9% and </=5.9%, respectively. Recovery tests only showed variation between 89.4% and 103.7%. Using the newly developed direct sandwich ELISA system, we found that the secreted OC levels from rat bone marrow-derived mesenchymal stem cells during osteogenic differentiation with dexamethasone were significantly higher than those from cells undergoing non-osteogenic or adipogenic differentiation. It was established that this ELISA system would be suitable for quantitative assessment of bone formation by cultured cells with or without scaffolds in rat experimental models.

Cell sheet transplantation of cultured mesenchymal stem cells enhances bone formation in a rat nonunion model

Orthopedic surgeons have long been troubled by cases involving nonunion of fractured bones. This study aimed to enhance bone union by cell sheet transplantation of mesenchymal stem cells. A nonunion model was made in rat femur, and rat bone marrow cells were cultured in medium containing dexamethasone and ascorbic acid phosphate to create a cell sheet that could be scraped off as a single sheet. Cell sheets were transplanted onto fractured femurs without a scaffold in the model. X-ray and histological analysis were performed at 2, 4 and 8 weeks. Ultrasonography and biomechanical analysis were performed at 8 weeks. X-ray photographs and histological sections showed callus formation around the fracture site in the cell sheet-transplanted group (sheet group). Bone union was obtained in the sheet group at 8 weeks. By contrast, the control group (without sheet transplantation) showed nonunion of the femur. The results of pullout evaluation in the vertical direction of the femur in the sheet group were significantly better than that of the control group. Analysis of the origin of de novo formed bone using the Sry gene, which was used as a marker for donor cells, showed that transplanted cells without scaffolds could survive and differentiate into osteogenic lineage cells in vivo. These results showed that the femoral fracture in our model was completely cured by the transplantation of a cell sheet created by tissue engineering techniques. Thus, we think that cell sheet transplantation can contribute to hard tissue reconstruction in cases involving nonunion, bone defects and osteonecrosis.

Sinus floor augmentation with recombinant human growth and differentiation factor-5 (rhGDF-5): a pilot study in the Goettingen miniature pig comparing autogenous bone and rhGDF-5

AIM

The aim of this study was to test the hypothesis that recombinant human growth and differentiation factor-5 (rhGDF-5) in combination with a beta-tricalcium phosphate (beta-TCP) scaffold material results in superior bone formation in sinus floor augmentations in miniature pigs compared with a particulated autogenous bone graft combined with the scaffold material.

MATERIAL AND METHODS

Six adult female Goettingen minipigs underwent a maxillary sinus floor augmentation procedure. In a split-mouth design, the sinus floors were augmented with beta-TCP mixed with autogenous cortical bone chips, in a ratio of approximately 1 : 1, on one side. The contralateral test site was augmented using beta-TCP coated with two concentrations of rhGDF-5 (400 microg rhGDF-5/g beta-TCP or 800 microg rhGDF-5/g beta-TCP; three animals in each case). Simultaneously, one dental implant was inserted into each sinus floor augmentation. After 12 weeks, a histological and histomorphometric assessment of non-decalcified histological specimens was made.

RESULTS

There were significantly higher mean values of volume density of newly formed bone using beta-TCP coated with two concentrations of rhGDF-5 (400 microg: 32.9%; 800 microg: 23.9%) than with the corresponding control (autogenous bone/beta-TCP) (14.6%, 12.9%) (P=0.012, P=0.049). The bone-to-implant contact rates (BIC) were significantly enhanced in test sites (400 microg: 84.2%; 800 microg: 69.8%) compared with the corresponding control sites (24.8%, 40.8%) (P=.027, P=.045).

CONCLUSION

rhGDF-5 delivered on beta-TCP significantly enhanced bone formation compared with beta-TCP combined with autogenous bone in sinus lift procedures in miniature pigs.

Enhanced regeneration of critical bone defects using a biodegradable gelatin sponge and beta-tricalcium phosphate with bone morphogenetic protein-2

We examine the osteogenicity of a sponge biomaterial consisting of a biodegradable mixture of gelatin and beta-tricalcium phosphate (betaTCP) that bound bone morphogenetic protein 2 (BMP-2) in critical-sized bone defects in rats. Gelatin-betaTCP sponges containing either phosphate buffered saline or incorporating BMP-2 are implanted into 5 mm diameter bone defects created in rat mandibles. We assess the defects biweekly for 8 weeks following implantation. There is significantly higher osteoinductive activity and significantly more Gla-osteocalcin content at bone-defect healing sites treated with gelatin-betaTCP sponges incorporating BMP-2 than there is in those treated with sponges that did not contain BMP-2. Histologically, new bone that contains bone marrow and that is connected to the original bone almost entirely replaces the regenerated bone. These results show that biodegradable gelatin-betaTCP incorporating BMP-2 is osteogenic enough to promote healing in large bone defects.

A preliminary report on the effect of dimeric rhGDF-5 and its monomeric form rhGDF-5C465A on bone healing of rat cranial defects

INTRODUCTION

The purpose of the study was to compare the efficacy on rat skull defects of two bone growth factors derived from the GDF-5 family.

MATERIAL AND METHODS

The study was conducted on 17 adult Wistar rats. On each animal, two symmetrical 6-mm wide, full-thickness, skull defects were carried out in the parietal regions. In 15 out of 17 animals, both experimental defects were filled by the implants. In the group I (n=2), both defects were left empty for control. The 15 other rats were divided into 3 groups: In group II (n=5), a collagen sponge was implanted. In group III (n=5), a collagen sponge impregnated with rhGDF-5 (the genuine dimeric form) was implanted. In group IV (n=5), a collagen sponge impregnated with rhGDF-5C465A (a monomeric form of GDF-5) was implanted. All animals were sacrificed at 8 weeks. The harvested specimens were processed for contact radiography and standard histological examination. The quantitative results were assessed with a semi-quantitative histological scoring system.

RESULTS

One animal in the group II was excluded because it died of unknown reasons. In group I, no bone healing was observed in the defects. In group II, no bone healing was observed in 4 out of 10 defects, and partial bone healing was observed in 5 out of 10 defects. In group III, partial bone healing was also observed in 3 out of 8 defects and complete bone healing in 4 out of 8 defects. In group IV, partial bone healing was observed in 8 out of 10 defects and complete bone healing in 2 out of 10 defects.

CONCLUSION

Bone healing was improved in all treated groups. Further studies are necessary to determine the optimal formulation of these composite implants.

Bone marrow-derived mesenchymal cells can rescue osteogenic capacity of devitalized autologous bone

In clinical cases, many orthopaedists have been troubled with bone fragility, such as fractures after devitalization therapy for bone tumour, pathological fractures and metastatic tumours. The aim of this study was to determine whether loss of osteogenic capacity of devitalized autologous bones can be rescued using cultured bone marrow-derived mesenchymal cells. A devitalized bone model was produced from rat femur by irradiation and three groups were prepared: intact bone, irradiated bone and irradiated bone combined with cultured mesenchymal cells. Each bone was transplanted subcutaneously into a syngeneic rat. At 2 or 4 weeks after transplantation, biochemical analyses [alkaline phosphatase (ALP) activity and osteocalcin mRNA expression] and histological measurement were performed. Moreover, we verified the origin of newly formed bone, using the sex-determining region Y (sry) gene as a marker to distinguish between donor and recipient. In both intact bone and irradiated bone with mesenchymal cells, ALP activity and osteocalcin mRNA expression were detected and living osteoblasts together with newly formed bone were clearly seen histologically. Furthermore, analysis of the origin of de novo formed bone indicated that newly formed bone in irradiated bone with mesenchymal cells was derived from cultured bone marrow-derived mesenchymal cells. These results proved that the osteogenic capacity of devitalized autologous bone can be rescued using tissue-engineering techniques. This procedure should contribute to various clinical treatments, such as local metastatic tumours, pathological fracture after devitalization therapy and reconstruction after wide-margin tumour resection. The benefits would be applicable to all types of devitalized bone.

Lateral ridge augmentation using particulated or block bone substitutes biocoated with rhGDF-5 and rhBMP-2: an immunohistochemical study in dogs

OBJECTIVES

The aim of the present study was to immunohistochemically evaluate lateral ridge augmentation using a particulated (BOG) or block (BOB) natural bone mineral biocoated with rhGDF-5 and rhBMP-2 in dogs.

MATERIALS AND METHODS

Three standardized box-shaped defects were surgically created at the buccal aspect of the alveolar ridge in each quadrant of eight beagle dogs. After 2 months of healing, the chronic-type defects were randomly allocated in a split-mouth design to either (i) BOG or (ii) BOB biocoated with (a) rhGDF-5 or (b) rhBMP-2, respectively. Uncoated grafts served as controls. After 3 and 8 weeks, dissected blocks were prepared for immunohistochemical [osteocalcin (OC)] and histomorphometrical analysis [e.g. area (mm(2)) of new bone fill (BF), newly formed mineralized (MT) and non-mineralized tissue (NMT)].

RESULTS

rhBMP-2 biocoated BOG revealed significantly highest BF and MT values at 3 (upper and lower jaws - UJ/LJ - compared with BOG) and 8 weeks (UJ - compared with rhGDF-5). Biocoating of BOB using both rhGDF-5 and rhBMP-2 resulted in significantly increased MT values at 8 weeks (UJ/LJ - compared with BOB). In all groups, NMT adjacent to BOG and BOB scaffolds revealed pronounced signs of an OC antigen reactivity.

CONCLUSIONS

Within the limits of the present study, it was concluded that both rhGDF-5 and rhBMP-2 have shown efficacy; however, their bone regenerative effect was markedly influenced by the carrier.

Sinus floor augmentation with recombinant human growth and differentiation factor-5 (rhGDF-5): a histological and histomorphometric study in the Goettingen miniature pig

AIM

The aim of this study was to test the hypothesis that recombinant human growth and differentiation factor-5 (rhGDF-5) enhances bone formation in sinus floor augmentations in miniature pigs.

MATERIAL AND METHODS

The maxillary sinus floors in 12 adult female Goettingen minipigs were augmented with beta-tricalcium phosphate (beta-TCP) on one side. The contralateral test side was augmented using two concentrations of rhGDF-5 (400 microg rhGDF-5/g beta-TCP; 800 microg rhGDF-5/g beta-TCP) delivered on beta-TCP (six animals each). One dental implant was inserted into each sinus floor augmentation. After 4 and 12 weeks, histological and histomorphometric assessment of non-decalcified histological specimens was performed.

RESULTS

The results showed significantly higher mean values of volume density (VD) of newly formed bone using the concentration of 400 microg/g beta-TCP (22.8%) compared with the respective control (8%) after 4 weeks (P=0.05). The bone-to-implant contact rates were also significantly enhanced after 4 weeks between test sites (400 microg: 41.9%; 800 microg: 40.6%) and control sites (400 microg: 7.8%; 800 microg: 16.4%) (400 microg: P=0.024; 800 microg: P=0.048).

CONCLUSION

It is concluded that rhGDF-5 delivered on beta-TCP significantly enhanced early bone formation compared with beta-TCP alone in sinus lift procedures in miniature pigs.

Comparison of osteogenic ability of rat mesenchymal stem cells from bone marrow, periosteum, and adipose tissue

Mesenchymal stem cells (MSCs) reside in many types of tissue and are able to differentiate into various functional cells including osteoblasts. Recently, adipose tissue-derived MSCs (AMSCs) have been shown to differentiate into many lineages, and they are considered a source for tissue regeneration. The purpose of this study was to compare the osteogenic differentiation capability of MSCs from bone marrow (BMSCs), MSCs from periosteum (PMSCs), and AMSCs using in vitro culture and in vivo implantation experiments. We harvested these MSCs from 7-week-old rats. The cells were seeded and cultured for 7 days in primary culture to assay a colony-forming unit. The frequency of the unit was the smallest in the BMSCs (P < 0.001). After primary culture, subculture was performed under osteogenic differentiation conditions for 1 and 2 weeks to detect mineralization as well as the bone-specific proteins of alkaline phosphatase and osteocalcin as osteogenic markers. BMSCs and PMSCs showed distinct osteogenic differentiation capability in comparison with other MSCs (P < 0.001). For the in vivo assay, composites of these cells and hydroxyapatite ceramics were subcutaneously implanted into syngeneic rats and harvested after 6 weeks. Micro-computed tomographic (CT) and histological analyses demonstrated that new bone formation was detected in the composites using BMSCs and PMSCs, although it was hard to detect in other composites. The CT analyses also demonstrated that the bone volume of BMSC composites was more than that of AMSC composites (P < 0.001). These results indicate that BMSCs and PMSCs could be ideal candidates for utilization in practical bone tissue regeneration.

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

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

Oxysterol-induced osteoblastic differentiation of pluripotent mesenchymal cells is mediated through a PKC- and PKA-dependent pathway

Oxysterols form a large family of oxygenated derivatives of cholesterol that are present in circulation, and in human and animal tissues. The discovery of osteoinductive molecules that can induce the lineage-specific differentiation of cells into osteoblastic cells and therefore enhance bone formation is crucial for better management of bone fractures and osteoporosis. We previously reported that specific oxysterols have potent osteoinductive properties and induce the osteoblastic differentiation of pluripotent mesenchymal cells. In the present report we demonstrate that the induction of osteoblastic differentiation by oxysterols is mediated through a protein kinase C (PKC)- and protein kinase A (PKA)-dependent mechanism(s). Furthermore, oxysterol-induced-osteoblastic differentiation is marked by the prolonged DNA-binding activity of Runx2 in M2-10B4 bone marrow stromal cells (MSCs) and C3H10T1/2 embryonic fibroblastic cells. This increased activity of Runx2 is almost completely inhibited by PKC inhibitors Bisindolylmaleimide and Rottlerin, and only minimally inhibited by PKA inihibitor H-89. PKC- and PKA-dependent mechanisms appear to also regulate other markers of osteoblastic differentiation including alkaline phosphatase (ALP) activity and osteocalcin mRNA expression in response to oxysterols. Finally, osteogenic oxysterols induce osteoblastic differentiation with BMP7 and BMP14 in a synergistic manner as demonstrated by the enhanced Runx2 DNA-binding activity, ALP activity, and osteocalcin mRNA expression. Since Runx2 is an indispensable factor that regulates the differentiation of osteoblastic cells and bone formation in vitro and in vivo, its increased activity in oxysterol-treated cells further validates the potential role of oxysterols in lineage-specific differentiation of pluripotent mesenchymal cells and their potential therapeutic use as bone anabolic factors.

Growth and differentiation factor-5 (GDF-5) stimulates osteogenic differentiation and increases vascular endothelial growth factor (VEGF) levels in fat-derived stromal cells in vitro

Fat-derived adult mesenchymal stem cells can differentiate into different phenotypes reflecting their potential to regenerate various skeletal tissues. These properties together with the association of adipose with skeletal tissues formed the basis of our study to establish an experimental model for using fat-derived stromal cells to undergo osteogenic differentiation in vitro under the influence of either growth and differentiation factor-5 (GDF-5) or bone morphogenetic protein-2 (BMP-2). Members of the BMP/GDF family of proteins are known for their ability to elicit skeletal morphogenesis, but little is known about the mechanism whereby these morphogens exert their effect on the osteogenic differentiation of fat-derived stromal cells. We compared the effects of GDF-5 and BMP-2 in their recombinant forms to qualitatively and quantitatively determine their influence on the osteogenic differentiation of fat derived stromal cells by examining the effects on mineralization, extracellular matrix, cell proliferation, biochemistry, and gene expression. We identified that GDF-5 not only promotes osteogenic differentiation of rat fat-derived stromal cells, but also may promote angiogenic activity of stromal cells by increasing vascular endothelial growth factor (VEGF) gene expression in vitro. These data suggest that several distinct regulatory mechanisms may exist in association with osteogenic differentiation.

Osteogenic differentiation of adipose-derived stromal cells treated with GDF-5 cultured on a novel three-dimensional sintered microsphere matrix

BACKGROUND CONTEXT

It is well known that under the proper conditions multipotential bone marrow stromal cells are capable of osteogenic differentiation. Recently studies have demonstrated that an analogous subpopulation of cells exist within adipose tissue. Although early studies characterizing these adipose-derived stromal (ADS) cells in culture exist, investigations exploring the characteristics and viability of these cells cultured on a three-dimensional sintered microsphere matrix are absent.

PURPOSE

To characterize and investigate the viability of ADS cells cultured on bioengineered three-dimensional sintered microsphere matrices (SMM).

STUDY DESIGN

Basic science, laboratory study.

PATIENT SAMPLE

Sixty SMM total. Six underwent examination by scanning electron microscopy, 18 for cellular viability, 18 for biochemical assay, and 18 for evaluation by gene expression.

OUTCOME MEASURES

The SMM were examined under scanning electron microscopy to evaluate for adherence, migration, and proliferation at 7, 14, and 28 days. Cellular viability was assessed using colorimetric assay for mitochondrial dehydrogenases activity in viable cells (MTS [3-(4,5-dimethylthiazol-2-yl)5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] assay) at each corresponding time point. Osteoblastic differentiation was determined using biochemical assays for alkaline phosphatase activity and gene expression for alkaline phosphatase (ALP), osteocalcin (OC), and core binding factor alpha-1 (Cbfa1).

METHODS

Multipotential ADS cells from adult Sprague Dawley rats were isolated and maintained in media. Sintered microsphere matrices of poly(lactide-co-glycolide) [85:15] were prepared using solvent evaporation technique followed by mechanical sieving and fabricated by heating in metal molds. ADS cells were then seeded on the SMM and cultured in media with growth and differentiation factor-5 (GDF-5). Treated samples and controls were evaluated at 7, 14, and 28 days. Statistical significance was set at p<.05.

RESULTS

Multipotential ADS cells were capable of being isolated from adipose tissue. Scanning electron microscopy evaluation revealed cells adherent to the scaffold surface in a monolayer by 7 days. Cytoplasmic extensions were seen linking the cells on adjacent microspheres. Migration and proliferation resulting in extension of the cellular elements into the scaffold was apparent by 14 days. MTS confirmed cell viability within the scaffold throughout the 28-day study. Osteoblastic differentiation was confirmed using biochemical assays for alkaline phosphatase activity and gene expression for ALP, OC, and Cbfa1.

CONCLUSIONS

This is the first study to investigate the fate of ADS seeded on a three-dimensional sintered microsphere matrix. The results of this study confirm that ADS cells, when treated with GDF-5, are not only capable of adhering to the bioengineered scaffold, but also remain viable and demonstrated the ability to migrate, proliferate, and subsequently undergo osteogenic differentiation under the conditions described. These early findings support the concept that ADS cells cultured on a SMM may serve as a viable alternative to more traditional methods of bone graft materials.

Superior Effect of MD05, Beta-Tricalcium Phosphate Coated With Recombinant Human Growth/Differentiation Factor-5, Compared to Conventional Bone Substitutes in the Rat Calvarial Defect Model

BACKGROUND

MD05 consists of beta-tricalcium phosphate (beta-TCP) coated with recombinant human growth/differentiation factor-5 (rhGDF-5) and is under evaluation as an osteoinductive and osteoconductive bone graft material for use in dental and maxillofacial applications. The objective of this study was to compare the bone regenerative properties of MD05 with those of conventional commercially available bone substitutes.

METHODS

Full-thickness, 6-mm diameter, calvarial critical-size defects (two per animal) were created in adult Sprague-Dawley rats. Groups of rats were implanted with the following: 1) MD05; 2) bovine bone mineral; 3) bovine bone mineral with collagen; 4) bovine bone mineral with synthetic peptide, 5) beta-TCP (from two different manufacturers); or 6) no filling material (sham controls). Blinded macroscopic analysis, histopathologic analysis, and histomorphometric analysis were carried out 6 weeks after implantation.

RESULTS

New bone formation assessed histomorphometrically was about five times greater with MD05 than with the other bone substitutes tested, and bone repair was well advanced in MD05-filled defects after 6 weeks. The extent of fibrous tissue and residual implant were significantly lower in the MD05 group. In contrast to the other materials, the use of MD05 was associated with the complete osseous bridging of the defect and with the presence of normal bone marrow. The osteoinductive effect of rhGDF-5 was apparent from the more pronounced bone ingrowth observed with MD05 compared to the beta-TCP carrier alone. All implants showed good biocompatibility.

CONCLUSION

MD05 achieved superior bone regeneration compared to conventional materials and is a promising new bone substitute for dental and maxillofacial applications.

Influence of the porosity of hydroxyapatite ceramics on in vitro and in vivo bone formation by cultured rat bone marrow stromal cells

The in vitro and in vivo osteoblastic differentiation of rat bone marrow stromal cells (MSCs) was assessed on hydroxyapatite disks with 3 different porosities: 30%, 50%, and 70% (HA30, HA50, and HA70, respectively). MSCs obtained by 10-day culture of fresh bone marrow cells were subcultured for 2 weeks on 3 kinds of porous HA disks in the presence and absence of dexamethasone (Dex). After 2 weeks of subculture, alkaline phosphatase (ALP) activity and osteocalcin production of MSCs/HA composites with Dex were higher than those without, and increased with increasing porosity. The resultant bone tissue grafts "cultured-bone/HA constructs" were implanted subcutaneously into the backs of syngeneic rats, and harvested 1, 2, and 4 weeks after implantation. At 1 week, only cultured-bone/HA70 constructs exhibited expanded bone formation. At 2 and 4 weeks, active osteoblasts and progressive bone formation were observed morphologically in both cultured-bone/HA50 and HA70 constructs. At 4 weeks, bone tissue was observed even in cultured-bone/HA30 constructs. ALP activity and osteocalcin production also increased with increasing porosity and time after implantation. In this in vivo model, different scaffold porosity with similar crystal morphology of the apatite phase demonstrated marked differences in ability to support osteogenesis by implanted rat MSCs.

Recombinant growth/differentiation factor-5 stimulates osteogenic differentiation of fat-derived stromal cells in vitro

Fat-derived stromal cells can differentiate into various skeletal tissues. Currently the mechanism that determines whether stromal cells differentiate into osteoblasts is unclear and the role of growth/differentiation factor (GDF)-5 in differentiation of fat-derived stromal cells is not fully understood. It appears that the differentiation of stromal cells is greatly enhanced by GDF-5 that plays a role in a variety of musculoskeletal processes such as joint formation, tendon maintenance, and bone formation. Our study showed that GDF-5 promotes the differentiation of rat fat-derived stromal cells into osteogenic lineages in vitro. Furthermore, these findings were confirmed by histology, biochemical assay for alkaline phosphatase activity, and analysis of gene expression. The ability to preferentially stimulate fat-derived stromal cells down the osteogenic pathway holds significance in a variety of clinical scenarios.

The effect of the addition of a polyglutamate motif to RGD on peptide tethering to hydroxyapatite and the promotion of mesenchymal stem cell adhesion

Mimicking endogenous bone-binding proteins, RGD peptides have been synthesized with polyacidic amino acid domains in order to ionically tether the peptides to bone-like synthetic biomaterials, including hydroxyapatite (HA). However, a direct comparison of unmodified RGD with polyacidic-conjugated RGD has not been performed, and thus a benefit for the acidic domain has not been established. We evaluated the peptide/HA bond of RGD peptides with and without an attached polyglutamate sequence (E(7)), as well as examined mesenchymal stem cell (MSC) adhesion and morphology as they were affected by the conjugated peptide. We found that significantly more E(7)RGD was bound to HA than RGD at all coating concentrations tested, and moreover, more E(7)RGD was retained on the HA surface even after extended washing in serum-free media. Consistent with in vitro results, higher levels of E(7)RGD than RGD remained on HA that had been implanted in vivo for 24 h, indicating that the polyacidic domain improved peptide-binding efficiency. At several peptide concentrations, E(7)RGD increased cell adhesion compared to RGD surfaces, establishing a biological benefit for the E(7) modification. In addition, HA pre-coated sequentially with low-density E(7)RGD (1-10 microg/ml) and serum (FBS) stimulated cell adhesion and spreading, compared to either coating alone, suggesting that an ionic linkage allows for the potential adsorption of serum proteins to unoccupied sites, which may be important for bone formation in vivo. Collectively, these results suggest that tethering peptides to HA via a polyglutamate domain is an effective method for improving the peptide/HA bond, as well as for enhancing MSC adhesion.

Enhanced osteoinduction by controlled release of bone morphogenetic protein-2 from biodegradable sponge composed of gelatin and β-tricalcium phosphate

Biodegradable gelatin sponges at different contents of beta-tricalcium phosphate (beta-TCP) were fabricated to allow bone morphogenetic protein (BMP)-2 to incorporate into them. The in vivo osteoinduction activity of the sponges incorporating BMP-2 was investigated, while their in vivo profile of BMP-2 release was evaluated. The sponges prepared had an interconnected pore structure with an average pore size of 200 microm, irrespective of the beta-TCP content. The in vivo release test revealed that BMP-2 was released in vivo at a similar time profile, irrespective of the beta-TCP content. The in vivo time period of BMP-2 retention was longer than 28 days. When the osteoinduction activity of gelatin or gelatin-beta-TCP sponges incorporating BMP-2 was studied following the implantation into the back subcutis of rats in terms of histological and biochemical examinations, homogeneous bone formation was histologically observed throughout the sponges, although the extent of bone formation was higher in the sponges with the lower contents of beta-TCP. On the other hand, the level of alkaline phosphatase activity and osteocalcin content at the implanted sites of sponges decreased with an increase in the content of beta-TCP. The gelatin sponge exhibited significantly higher osteoinduction activity than that of any gelatin-beta-TCP sponge, although every sponge with or without beta-TCP showed a similar in vivo profile of BMP-2 release. In addition, the in vitro collagenase digestion experiments revealed that the gelatin-beta-TCP sponge collapsed easier than the gelatin sponge without beta-TCP incorporation. These results suggest that the maintenance of the intrasponge space necessary for the osteoinduction is one factor contributing to the osteoinduction extent of BMP-2-incorporating sponges.

Osteogenic differentiation of mesenchymal stem cells in biodegradable sponges composed of gelatin and β-tricalcium phosphate

Biodegradable gelatin sponges incorporating various amounts of beta-tricalcium phosphate (betaTCP) (gelatin-betaTCP) were fabricated and the in vitro osteogenic differentiation of mesenchymal stem cells (MSC) isolated from the rat bone marrow in the sponges was investigated. The gelatin sponges incorporating betaTCP have an interconnected pore structure with the average size of 180-200 microm, irrespective of the betaTCP amount. The stiffness of the sponges became higher with an increase in the amount of betaTCP. When seeded into the sponges by an agitated method, MSC were homogeneously distributed throughout the sponge. The morphology of cells attached got more spreaded with the increased betaTCP amount. The rate of MSC proliferation depended on the betaTCP amount and culture method: the higher the betaTCP amount in the stirring culture, the higher the proliferation rate. The deformed extent of gelatin-betaTCP sponges was suppressed with the increased amount of betaTCP. When measured to evaluate the osteogenic differentiation of MSC, the alkaline phosphatase activity and osteocalcin content became maximum for the sponge with a betaTCP amount of 50 wt%, although both the values were significantly high in the stirring culture compared with those in the static culture. We concluded that the attachment, proliferation, and osteogenic differentiation of MSC were influenced by sponge composition of gelatin and betaTCP as the cell scaffold.