Effect of surface modification of nanofibres with glutamic acid peptide on calcium phosphate nucleation and osteogenic differentiation of marrow stromal cells

Biomineralization is mediated by extracellular matrix (ECM) proteins with amino acid sequences rich in glutamic acid. The objective of this study was to investigate the effect of calcium phosphate deposition on aligned nanofibres surface-modified with a glutamic acid peptide on osteogenic differentiation of rat marrow stromal cells. Blend of EEGGC peptide (GLU) conjugated low molecular weight polylactide (PLA) and high molecular weight poly(lactide-co-glycolide) (PLGA) was electrospun to form aligned nanofibres (GLU-NF). The GLU-NF microsheets were incubated in a modified simulated body fluid for nucleation of calcium phosphate crystals on the fibre surface. To achieve a high calcium phosphate to fibre ratio, a layer-by-layer approach was used to improve diffusion of calcium and phosphate ions inside the microsheets. Based on dissipative particle dynamics simulation of PLGA/PLA-GLU fibres, > 80% of GLU peptide was localized to the fibre surface. Calcium phosphate to fibre ratios as high as 200%, between those of cancellous (160%) and cortical (310%) bone, was obtained with the layer-by-layer approach. The extent of osteogenic differentiation and mineralization of marrow stromal cells seeded on GLU-NF microsheets was directly related to the amount of calcium phosphate deposition on the fibres prior to cell seeding. Expression of osteogenic markers osteopontin, alkaline phosphatase (ALP), osteocalcin and type 1 collagen increased gradually with calcium phosphate deposition on GLU-NF microsheets. Results demonstrate that surface modification of aligned synthetic nanofibres with EEGGC peptide dramatically affects nucleation and growth of calcium phosphate crystals on the fibres leading to increased osteogenic differentiation of marrow stromal cells and mineralization.

Short-term administration of small molecule phenamil induced a protracted osteogenic effect on osteoblast-like MC3T3-E1 cells

Sustained administration (21-day treatment) of the small molecule phenamil has been proposed as an alternative osteogenic factor when used in conjunction with a biodegradable scaffold for in vitro osteogenesis. While promising, the major issue associated with small molecules is non-specific cytotoxicity. The aim of this study was to minimize the side-effects from small-molecule drugs by reducing the frequency of administration. Toward this goal, we investigated whether a shorter phenamil treatment is sufficient to induce in vitro osteogenesis. We compared the effects of short-term (12 h) and continuous treatments of phenamil on osteoblastic differentiation and mineralization. Alkaline phosphatase (ALP) and osteopontin (OPN) activity were used as markers for osteoblastic differentiation. Measurement of the calcium content of the extracellular matrix was used as the hallmark for in vitro bone formation after 21 days of culture. Our findings revealed that both short and continuous phenamil treatment triggers osteoblastic differentiation and mineralization of MC3T3-E1 cells on a biodegradable polymeric scaffold composed of polylactic-co-glycolic acid (PLAGA) at the same time points. In addition, in order to fabricate a phenamil-loaded PLAGA scaffold, the small molecule phenamil was physically absorbed onto the surface of scaffolds and the bioactivity of the loaded scaffolds was evaluated. Furthermore, biochemical analysis indicated that short phenamil treatment of cells was accompanied by upregulation in protein expression of integrin α5, p125(FAK) and phosphorylation of CREB. These effects may contribute to the downstream signalling cascade necessary for osteogenesis, and such responses may account for our observed protracted osteogenic differentiation in vitro. Copyright © 2013 John Wiley & Sons, Ltd.

Insulin facilitates osteoblast differentiation

Tissue engineering of bone has been increasingly used in the bone defect repair. To generate osteoblasts is a major approach, and here we have examined ways of improving the efficiency of producing osteoblasts. Adipose stem cells (ADSC) were prepared from rat mesentery tissue, and transfected with Cbfa1 gene vector or/and IGF-1R gene vector. The cells were stimulated with insulin. Osteocalcin expression by the ADSCs was assessed by quantitative RT-PCR (qRT-PCR), Western blotting and enzyme-linked immunobosorbent assay. Both genes Cbfa1 and IGF-1R were transfected in ADSCs, as shown by qRT-PCR and Western blotting. Stimulation by insulin in the culture increased osteocalcin expression in ADSCs transfected by both Cbfa1 and IGF-1R, but not in those transfected with only one of these two genes. Osteocalcin in the culture supernatant was also increased by stimulation with insulin. Thus IGF-1R gene transfer together with insulin stimulation can markedly increase the efficiency of generation of osteoblasts.

The osteogenic potential of the marine-derived multi-mineral formula aquamin is enhanced by the presence of vitamin D

Bone degenerative diseases are on the increase globally and are often problematic to treat. This has led to a demand to identify supplements that aid bone growth and formation. Aquamin is a natural multi-mineral food supplement, derived from the red algae Lithothamnion species which contains calcium, magnesium and 72 other trace minerals. It has been previously reported to increase bone formation and mineralisation. This study aimed to investigate the 28 day in vitro osteogenic response of Aquamin supplemented with Vitamin D. The osteogenic potential of MC3T3-E1 osteoblast-like cells was analysed in standard osteogenic medium supplemented with Aquamin +/- Vitamin D3, and the controls consisted of osteogenic medium, +/- Vitamin D3. Proliferation of osteoblasts, metabolic activity and cell viability did not differ between Aquamin and the osteogenic control groups. Alkaline phosphatase (ALP) levels and mineralisation were increased by the supplementation of Aquamin, and the addition of Vitamin D3 increased mineralisation for all groups. The combination of Aquamin and Vitamin D3 yielded a significant increase in ALP and mineralisation over Aquamin alone and the standard osteogenic control +/- Vitamin D3. This study demonstrates that Aquamin aids osteogenesis, and that its osteogenic response can be enhanced by combining Aquamin with Vitamin D3.

Hypoxia induces osteogenesis in rabbit adipose-derived stem cells overexpressing bone morphogenic protein-2

OBJECTIVE

Hypoxic culture potentiates mesenchymal stem cells (MSCs) to survive and secrete various growth factors. Genetically modified stem cells overexpressing bone morphogenic protein-2 (BMP-2) demonstrate strong osteogenic ability. Hence, we investigated the coeffect of hypoxic culture conditions and BMP-2 overexpression on the osteogenic ability of rabbit adipose-derived stem cells (rASCs) in vitro.

MATERIALS AND METHODS

Rabbit adipose-derived stem cells with or without adenoviral-BMP-2 transduction were cultured in hypoxic (1%) and normoxic (21%) conditions. Cell viability, attachment, and proliferation were compared. Real-time PCR amplification of osteogenic and angiogenic genes including alkaline phosphatase (ALP), osteocalcin (OCN), HIF-1α, and vascular endothelial growth factor (VEGF) was performed. Moreover, ALP activity, immunofluorescent staining of OCN, and mineralization assay by alizarin red S quantification and von Kossa staining were conducted.

RESULTS

Cells under hypoxic conditions attached better within 12 h and proliferated faster. While BMP-2 overexpression and hypoxic condition separately elevated the transcription of key osteogenic and angiogenic genes, a cooperative effect was observed to enhance the upregulation of osteogenic as well as angiogenic genes. Identical changes were observed in ALP activity, immunofluorescent staining of OCN, and mineralization assay.

CONCLUSIONS

Hypoxic culture can enhance the osteogenic ability of BMP-2 gene-modified rASCs, which provides a strategy to improve the osteogenesis of rASCs for in vivo bone regeneration.

Gene delivery of c-myb increases bone formation surrounding oral implants

Bone regeneration around titanium (Ti) implants is a relatively slow process. The c-myb transcription factor has been associated with high proliferation and differentiation rates in bone. This study analyzed whether c-myb can enhance new bone surrounding the implant. In vitro overexpressed chitosan-gold nanoparticles conjugated with plasmid DNA/c-myb (Ch-GNPs/c-myb)-coated Ti surfaces were associated with enhanced expression of the osteogenic molecules osteopontin (OPN), runt-related transcription factor 2 (RUNX-2), and bone morphogenetic proteins (BMP2/7) in MC-3T3E1 osteoblast cells. Further, to determine its in vivo effect, we inserted Ch-GNPs/c-myb-coated Ti implants into rat mandibles. One and 4 wks post-implantation, mandibles were examined by microcomputed tomography, immunohistochemistry, and hematoxylin & eosin staining. The microcomputed tomography analysis demonstrated that c-myb overexpression increased the density and volume of newly formed bone surrounding the implants, compared with those in controls (p < .05). Further, c-myb increased the number of cells expressing BMP2/7 and aided in the increase of new bone (p < .05). These results support the view that c-myb overexpression accelerates new bone surrounding implants and can serve as a potent molecule in promoting tissue regeneration around dental implants. The recipient rat used in this system provides an excellent in vivo model for studies of bone regeneration.

Human myogenic endothelial cells exhibit chondrogenic and osteogenic potentials at the clonal level

We have previously reported the high regenerative potential of murine muscle-derived stem cells (mMDSCs) that are capable of differentiating into multiple mesodermal cell lineages, including myogenic, endothelial, chondrocytic, and osteoblastic cells. Recently, we described a putative human counterpart of mMDSCs, the myogenic endothelial cells (MECs), in adult human skeletal muscle, which efficiently repair/regenerate the injured and dystrophic skeletal muscle as well as the ischemic heart in animal disease models. Nevertheless it remained unclear whether human MECs, at the clonal level, preserve mMDSC-like chondrogenic and osteogenic potentials and classic stem cell characteristics including high proliferation and resistance to stress. Herein, we demonstrated that MECs, sorted from fresh postnatal human skeletal muscle biopsies, can be grown clonally and exhibit robust resistance to oxidative stress with no tumorigeneity. MEC clones were capable of differentiating into chondrocytes and osteoblasts under inductive conditions in vitro and participated in cartilage and bone formation in vivo. Additionally, adipogenic and angiogenic potentials of clonal MECs (cMECs) were observed. Overall, our study showed that cMECs not only display typical properties of adult stem cells but also exhibit chondrogenic and osteogenic capacities in vitro and in vivo, suggesting their potential applications in articular cartilage and bone repair/regeneration.

Osteogenesis of Adipose-Derived Stem Cells

Current treatment options for skeletal repair, including immobilization, rigid fixation, alloplastic materials and bone grafts, have significant limitations. Bone tissue engineering offers a promising method for the repair of bone deficieny caused by fractures, bone loss and tumors. The use of adipose derived stem cells (ASCs) has received attention because of the self-renewal ability, high proliferative capacity and potential of osteogenic differentiation in vitro and in vivo studies of bone regeneration. Although cell therapies using ASCs are widely promising in various clinical fields, no large human clinical trials exist for bone tissue engineering. The aim of this review is to introduce how they are harvested, examine the characterization of ASCs, to review the mechanisms of osteogenic differentiation, to analyze the effect of mechanical and chemical stimuli on ASC osteodifferentiation, to summarize the current knowledge about usage of ASC in vivo studies and clinical trials, and finally to conclude with a general summary of the field and comments on its future direction.

Prospective purification of a subpopulation of human synovial mesenchymal stem cells with enhanced chondro-osteogenic potency

OBJECTIVE

We previously reported the coexistence, within cultured mesenchymal stem cells (MSCs) from human synovial membrane, of single-cell-derived clonal cell populations with distinct differentiation potency. The aim of this study was to investigate marker sets for prospective purification of functionally distinct MSC subsets.

METHODS

Cells were enzymatically released from human synovium and culture expanded. Phenotype analysis was performed by flow cytometry using combinations of MSC markers. Sorting was carried out using the FACS DiVA cell sorter. Sorted cell populations were assessed for clonogenicity, kinetics of growth, cell senescence and chondro-osteogenic potency.

RESULTS

During culture expansion, the co-localization of CD39 within the CD73(+) cell population identified a small cell subset that was maintained from passage 1 (P1) up to at least P12 in all donors tested. The CD73(+)CD39(+) cell subset displayed higher expression levels of Sox9 and Runx2 and a significantly greater chondro-osteogenic potency than the CD73(+)CD39(-) cell subset. In contrast, it was less clonogenic and proliferative. There was no difference in cell senescence between the sorted MSC subsets and the parental MSCs. Notably, there were no detectable differences in chondro-osteogenic potency between the CD73(+)CD39(-) and CD73(+)CD39(+) cell subsets purified from fresh synovial cell populations.

CONCLUSION

Our findings indicate that the combination of CD73 and CD39 allows the prospective purification from culture-expanded heterogeneous synovial MSC populations of a distinct MSC subset with greater chondro-osteogenic potency. We anticipate that such an approach will enhance the consistency of cell-based therapeutic protocols for the repair of osteochondral defects.

In vitro human adipose-derived stromal/stem cells osteogenesis in akermanite:poly-ε-caprolactone scaffolds

This study compared the metabolic activity, cell proliferation and osteogenic differentiation of human adipose-derived stromal/stem cells cultured on four different scaffolds (poly-ε-caprolactone, akermanite:poly-ε-caprolactone composites, akermanite and β-tricalcium phosophate) with or without osteogenic media supplementation for up to 21 days. The hypothesis was that human adipose-derived stromal/stem cells osteogenesis in akermanite-containing scaffolds would be greater than the other scaffold types independent of the media supplementation. According to the results, human adipose-derived stromal/stem cells loaded on different scaffolds and cultured in both media conditions displayed significant changes in the metabolic activity and cell proliferation. After 21 days of culture in osteogenic medium, the human adipose-derived stromal/stem cells loaded onto akermanite-based scaffolds had greater calcium deposition and osteocalcin expression relative to human adipose-derived stromal/stem cells loaded onto β-tricalcium phosophate and poly-ε-caprolactone. In vivo investigations are needed to further assess the bone tissue engineering potential of human adipose-derived stromal/stem cells loaded to akermanite:poly-ε-caprolactone composites.

Bone morphogenetic proteins-immobilized polydioxanone porous particles as an artificial bone graft

Bone morphogenetic proteins (BMPs)-immobilized polydioxanone (PDO)/Pluronic F127 porous particles were prepared as a bone graft using a melt-molding particulate-leaching method, and the sequential binding of heparin and BMPs (BMP-2 and BMP-7, single or dual) onto the porous particles. The prepared PDO/Pluronic F127 porous particles gradually degraded with time, with ∼30% of the initial particle weight remaining after 16 weeks. The degradation rate of the PDO/Pluronic F127 porous particles may parallel the bone-healing rate. The BMPs were easily immobilized onto the pore surfaces of PDO/Pluronic F127 particles via heparin binding and were released in a sustained manner for up to 21 days, regardless of BMP type. The BMPs (single BMP-2 or dual BMP-2/BMP-7)-immobilized porous particles were effective for in vitro osteogenesis of bone marrow stem cells (BMSCs), as analyzed by alkaline phosphatase activity, calcium content, time polymerase chain reaction using specific markers for osteogenesis (Type I collagen, osteocalcin, osteopotin, and RunX2), and immunohistochemical staining. The BMPs (single BMP-2 or dual BMP-2/BMP-7)-immobilized porous particles were also effective in promoting new bone formation, as analyzed by the preliminary animal study using a full-thickness skull defect model of Sprague-Dawley rats (microcomputed tomography). The synergistic effect of dual BMPs on the osteogenesis of BMSCs and bone regeneration was not significant in our system. The BMP-2 or dual BMPs (BMP-2/BMP-7)-immobilized PDO/Pluronic F127 porous particles may be a promising candidate as a bone graft for the delayed and insufficient bone healing in clinical fields.

MicroRNA functions in osteogenesis and dysfunctions in osteoporosis

MicroRNAs (miRNAs) are critical post-transcriptional regulators of gene expression that control osteoblast mediated bone formation and osteoclast-related bone remodeling. Deregulation of miRNA mediated mechanisms is emerging as an important pathological factor in bone degeneration (eg, osteoporosis) and other bone-related diseases. MiRNAs are intriguing regulatory molecules that are networked with cell signaling pathways and intricate transcriptional programs through ingenuous circuits with remarkably simple logic. This overview examines key principles by which miRNAs control differentiation of osteoblasts as they evolve from mesenchymal stromal cells during osteogenesis, or of osteoclasts as they originate from monocytic precursors in the hematopoietic lineage during osteoclastogenesis. Of particular note are miRNAs that are temporally upregulated during osteoblastogenesis (eg, miR-218) or osteoclastogenesis (eg, miR-148a). Each miRNA stimulates differentiation by suppressing inhibitory signaling pathways ('double-negative' regulation). The excitement surrounding miRNAs in bone biology stems from the prominent effects that individual miRNAs can have on biological transitions during differentiation of skeletal cells and correlations of miRNA dysfunction with bone diseases. MiRNAs have significant clinical potential which is reflected by their versatility as disease-specific biomarkers and their promise as therapeutic agents to ameliorate or reverse bone tissue degeneration.

Differentiation of human dental stem cells reveals a role for microRNA-218

BACKGROUND

Regeneration of lost periodontium is the ultimate goal of periodontal therapy. Advances in tissue engineering have demonstrated the multilineage potential and plasticity of adult stem cells located in periodontal apparatus. However, it remains unclear how epigenetic mechanisms controlling signals determine tissue specification and cell lineage decisions. To date, no data are available on micro-RNA (miRNA) activity behind human-derived dental stem cells (DSCs).

MATERIAL AND METHODS

In this study, we isolated periodontal ligament stem cells, dental pulp stem cells and gingival stem cells from extracted third molars; human bone marrow stem cells were used as a positive control. The expression of OCT4A and NANOG was confirmed in these undifferentiated cells. All cells were cultured under osteogenic inductive conditions and RUNX2 expression was analyzed as a marker of mineralized tissue differentiation. The miRNA expression profile was obtained at baseline and after osteogenic induction in all cell types.

RESULTS

The expression of RUNX2 demonstrated successful osteogenic induction of all cell types, which was confirmed by alizarin red stain. The analysis of 765 miRNAs demonstrated a shift in miRNA expression that occurred in all four stem cell types, including a decrease in hsa-mir-218 across all differentiated cell populations. Hsa-mir-218 targets RUNX2 and decreases RUNX2 expression in undifferentiated human DSCs. DSC mineralized tissue type differentiation is associated with a decrease in hsa-mir-218 expression.

CONCLUSION

These data reveal a miRNA-regulated pathway for the differentiation of human DSCs and a select network of human miRNAs that control DSC osteogenic differentiation.

Intra-oral PTH administration promotes tooth extraction socket healing

Intermittent parathyroid hormone (PTH) administration increases systemic and craniofacial bone mass. However, the effect of PTH therapy on healing of tooth extraction sites is unknown. The aims of this study were to determine the effect of PTH therapy on tooth extraction socket healing and to examine whether PTH intra-oral injection promotes healing. The mandibular first molars were extracted in rats, and subcutaneous PTH was administered intermittently for 7, 14, and 28 days. In a second study, maxillary second molars were extracted, and PTH was administered by either subcutaneous or intra-oral injection to determine the efficacy of intra-oral PTH administration. Healing was assessed by micro-computed tomography and histomorphometric analyses. PTH therapy accelerated the entire healing process and promoted both hard- and soft-tissue healing by increasing bone fill and connective tissue maturation. PTH therapy by intra-oral injection was as effective as subcutaneous injection in promoting tooth extraction socket healing. The findings suggest that PTH therapy promotes tooth extraction socket healing and that intra-oral injections can be used to administer PTH.

An in vitro expansion score for tissue-engineering applications with human bone marrow-derived mesenchymal stem cells

Human bone marrow-derived mesenchymal stem cells (MSCs) have limited growth potential in vitro and cease to divide due to replicative senescence, which from a tissue-engineering perspective has practical implications, such as defining the correct starting points for differentiation and transplantation. Time spent in culture before the loss of required differentiation potential is different and reflects patient variability, which is a problem for cell expansion. This study aimed to develop a score set which can be used to quantify the senescent state of MSCs and predict whether cells preserve their ability to differentiate to osteogenic, adipogenic and chondrogenic phenotypes, based on colony-forming unit (CFU) assay, population doubling time (PDT), senescence-associated β-galactosidase (SA-β-Gal) activity, cell size, telomere length and gene expression of MSCs cultured in vitro over 11 passages. This set of morphological, physiological and genetic senescence markers was correlated to the ability of MSCs to differentiate. Differentiation efficiency was assessed by marker genes and protein expression. CFUs decreased with increasing passage number, whereas SA-β-Gal activity and PDT increased; however, the correlation with MSCs' differentiation potential was sometimes unexpected. The expression of genes related to senescence was higher in late-passage cells than in early-passage cells. Early-passage cells underwent efficient osteogenic differentiation, with mid-passage cells performing best in chondrogenic differentiation. Late-passage cells preserve only adipogenic differentiation potential. Based on this marker set, we propose a senescence score in which combined markers give a reliable quality control of MSCs, not depending only on mechanistic passage number.

Enhanced in vivo osteogenesis by nanocarrier-fused bone morphogenetic protein-4

Purpose

Bone defects and nonunions are major clinical skeletal problems. Growth factors are commonly used to promote bone regeneration; however, the clinical impact is limited because the factors do not last long at a given site. The introduction of tissue engineering aimed to deter the diffusion of these factors is a promising therapeutic strategy. The purpose of the present study was to evaluate the in vivo osteogenic capability of an engineered bone morphogenetic protein-4 (BMP4) fusion protein.

Methods

BMP4 was fused with a nanosized carrier, collagen-binding domain (CBD), derived from fibronectin. The stability of the CBD-BMP4 fusion protein was examined in vitro and in vivo. Osteogenic effects of CBD-BMP4 were evaluated by computer tomography after intramedullary injection without a collagen–sponge scaffold. Recombinant BMP-4, CBD, or vehicle were used as controls. Expressions of bone-related genes and growth factors were compared among the groups. Osteogenesis induced by CBD-BMP4, BMP4, and CBD was also assessed in a bone-defect model.

Results

In vitro, CBD-BMP4 was retained in a collagen gel for at least 7 days while BMP4 alone was released within 3 hours. In vivo, CBD-BMP4 remained at the given site for at least 2 weeks, both with or without a collagen–sponge scaffold, while BMP4 disappeared from the site within 3 days after injection. CBD-BMP4 induced better bone formation than BMP4 did alone, CBD alone, and vehicle after the intramedullary injection into the mouse femur. Bone-related genes and growth factors were expressed at higher levels in CBD-BMP4-treated mice than in all other groups, including BMP4-treated mice. Finally, CBD-BMP4 potentiated more bone formation than did controls, including BMP4 alone, when applied to cranial bone defects without a collagen scaffold.

Conclusion

Altogether, nanocarrier-CBD enhanced the retention of BMP4 in the bone, thereby promoting augmented osteogenic responses in the absence of a scaffold. These results suggest that CBD-BMP4 may be clinically useful in facilitating bone formation.

Prelamin A accelerates vascular calcification via activation of the DNA damage response and senescence-associated secretory phenotype in vascular smooth muscle cells

RATIONALE

Vascular calcification is prevalent in the aging population, yet little is known of the mechanisms driving age-associated vascular smooth muscle cell (VSMC) phenotypic change.

OBJECTIVE

To investigate the role of nuclear lamina disruption, a specific hallmark of VSMC aging, in driving VSMC osteogenic differentiation.

METHODS AND RESULTS

Prelamin A, the unprocessed form of the nuclear lamina protein lamin A, accumulated in calcifying human VSMCs in vitro and in vivo, and its overexpression promoted VSMC osteogenic differentiation and mineralization. During VSMC aging in vitro, prelamin A accumulation occurred concomitantly with increased p16 expression and osteogenic differentiation and was associated with increased levels of DNA damage. Microarray analysis showed that DNA damage repair pathways were significantly impaired in VSMCs expressing prelamin A and that chemical inhibition and siRNA depletion of the DNA damage response kinases ataxia-telangiectasia mutated/ataxia-telangiectasia- and Rad3-related effectively blocked VSMC osteogenic differentiation and mineralization. In coculture experiments, prelamin A-expressing VSMCs induced alkaline phosphatase activity in mesenchymal progenitor cells, and this was abrogated by inhibition of ataxia-telangiectasia-mutated signaling, suggesting that DNA damage induces the secretion of pro-osteogenic factors by VSMCs. Cytokine array analysis identified several ataxia-telangiectasia mutated-dependent senescence-associated secretory phenotype factors/cytokines released by prelamin A-positive VSMCs, including the calcification regulators bone morphogenetic protein 2, osteoprotegerin, and interleukin 6.

CONCLUSIONS

Prelamin A promotes VSMC calcification and aging by inducing persistent DNA damage signaling, which acts upstream of VSMC osteogenic differentiation and the senescence-associated secretory phenotype. Agents that target the DNA damage response and prelamin A toxicity may be potential therapies for the treatment of vascular calcification.

Low-level laser therapy promotes the osteogenic potential of adipose-derived mesenchymal stem cells seeded on an acellular dermal matrix

This study investigates the feasibility of using an adipose-derived mesenchymal stem cell (ASC)-seeded acellular dermal matrix (ADM) along with low-level laser therapy (LLLT) to repair bone defect in athymic nude mice. Critical-sized calvarial defects were treated either with ADM, ADM/LLLT, ADM/ASCs, or ADM/ASCs/LLLT. In micro-computed tomography scans, the ADM/ASCs and the ADM/ASCs/LLLT groups showed remarkable bone formation after 14 days. Additionally, bone regeneration in the ADM/ASCs/LLLT group was obvious at 28 days, but in the ADM/ASCs group at 56 days. Bone mineral density and bone tissue volume in the ADM/ASCs/LLLT group significantly increased after 7 days, but in the ADM/ASCs group after 14 days. Histological analysis revealed that the defects were repaired in the ADM/ASCs and the ADM/ASCs/LLLT group, while the defects in the ADM and the ADM/LLLT groups exhibited few bone islands at 28 and 56 days. The successful seeding of ASCs onto ADM was confirmed, and LLLT enhanced the proliferation and the survival of ASCs at 14 days. Our results indicate that ASC-seeded grafts promote bone regeneration, and the application of LLLT on ASC-seeded ADM results in rapid bone formation. The implantation of an ASC-seeded ADM combined with LLLT may be used effectively for bone regeneration.

BMP9 signaling in stem cell differentiation and osteogenesis

Bone morphogenetic proteins (BMPs) are members of the TGF-β superfamily and play a critical role in skeletal development, bone formation and stem cell differentiation. Disruptions in BMP signaling result in a variety of skeletal and extraskeletal anomalies. BMP9 is a poorly characterized member of the BMP family and is among the most osteogenic BMPs, promoting osteoblastic differentiation of mesenchymal stem cells (MSCs) both in vitro and in vivo. Recent findings from various in vivo and molecular studies strongly suggest that the mechanisms governing BMP9-mediated osteoinduction differ from other osteogenic BMPs. Many signaling pathways with diverse functions have been found to play a role in BMP9-mediated osteogenesis. Several of these pathways are also critical in the differentiation of other cell lineages, including adipocytes and chondrocytes. While BMP9 is known to be a potent osteogenic factor, it also influences several other pathways including cancer development, angiogenesis and myogenesis. Although BMP9 has been demonstrated as one of the most osteogenic BMPs, relatively little is known about the specific mechanisms responsible for these effects. BMP9 has demonstrated efficacy in promoting spinal fusion and bony non-union repair in animal models, demonstrating great translational promise. This review aims to summarize our current knowledge of BMP9-mediated osteogenesis by presenting recently completed work which may help us to further elucidate these pathways.

Repair of critical-size bone defects using bone marrow stromal cells: a histomorphometric study in rabbit calvaria. Part I: use of fresh bone marrow or bone marrow mononuclear fraction

OBJECTIVES

The aim of this study was to compare the bone healing observed after the use of (1) a scaffold enriched with fresh bone marrow, (2) a scaffold enriched with bone marrow mononuclear fraction, and (3) a scaffold alone.

MATERIAL AND METHODS

Twenty one rabbits were randomly divided into three groups of six animals and 1 group of 3 animals. Bilateral 12-mm diameter defects were created in the animals' parietal bones. In Control Group, the defects were filled with a xenograft alone (n = 6); in Group 1, with a xenograft enriched with fresh bone marrow (n = 6); in Group 2, with a xenograft enriched with bone marrow mononuclear fraction (n = 6) and in Unfilled Group, nothing was grafted (n = 3). In Groups 1, 2, and Control, one of the calvarial defects was randomly covered with a barrier membrane. The rabbits were sacrificed 8 weeks after surgery, and their parietal bones were harvested and analyzed histomorphometrically.

RESULTS

The histomorphometric analysis showed no difference between Group 1 and the Control Group regarding non-vital mineralized tissue area, but Group 2 showed a statistically significant higher percentage than the Control Group (P < 0.05) for both situations, with membrane (21.24 ± 3.78% and 13.52 ± 3.00%, respectively) and without membrane (20.91 ± 2.01% and 13.08 ± 1.72%, respectively). Group 2 showed the highest percentage of vital mineralized tissue area, followed by Group 1 and the Control Group (P < 0.05) for both situations, with membrane (28.17 ± 3.19%; 21.14 ± 7.38% and 13.06 ± 5.24%, respectively) and without membrane (21.13 ± 0.55%; 12.45 ± 6.34% and 6.56 ± 1.20%, respectively). Group 2 showed the lowest percentage of non-mineralized tissue area, followed by Group 1 and Control Group (P < 0.05) for both situations, with membrane (50.59 ± 6.64%; 58.75 ± 7.14% and 73.41 ± 6.87%, respectively) and without membrane (57.97 ± 1.91%; 71.74 ± 6.63% and 80.37 ± 2.67%, respectively). The sides in which the defects were covered with the barrier membrane showed better bone healing compared with the uncovered sides, in all groups (intragroup comparison, P < 0.05). The Unfilled Group specimens showed no bone formation.

CONCLUSIONS

Both methods using bone marrow stromal cells contributed to enhancing bone healing, especially that using the bone marrow mononuclear fraction. The use of a barrier membrane seemed to have a synergistic effect.

Electrical stimuli improve osteogenic differentiation mediated by aniline pentamer and PLGA nanocomposites

Electrical stimulation may improve the proliferation of animal cells. In the present study, osteoblasts were cultured on electroactive aniline pentamer (AP)/poly(lactic-co-glycolic acid) (PLGA) copolymer composites, on which electric pulse was imposed. The combination of polymer and electric pulse enhanced the osteogenic differentiation of the osteoblasts, characterized by the upregulated expression of bone morphogenetic protein (BMP)-2, collagen I and osteonectin and the phosphorylation of Samd4, in contrast to polymer or electrical pulse alone. This action occurred in a polymer content-dependent manner. Therefore, the action of the electric pulse, assisted by the electroactive polymer implant, may be promising in the expedition of injured bone repair.

Comparison of Phenotypic Characterization between Differentiated Osteoblasts from Stem Cells and Calvaria Osteoblasts In vitro

BACKGROUND

Characteristics of differentiated osteoblasts from adipose derived stem cells (ADSCs) in compared with isolated osteoblasts from normal bone such as calvaria are unknown. The aim of this study was determination and comparison of phenotypic characterization between differentiated osteoblasts from stem cells and calvaria osteoblasts in vitro.

METHODS

In this study, mesenchymal stem cells were isolated from adipose tissue of human by enzymatic digestion and were differentiated into osteoblasts using osteogenic medium. Characteristics of these cells at first, second, third and fourth weeks were comprised with calvaria osteoblasts that were isolated from human calvaria by explanation culture method. To screen the characteristics of both calvaria and the differentiated osteoblasts, we used western blot to identify protein levels, von Kossa staining for mineral matrix detection and alkaline phosphatase (ALP) assay kit (Sigma) for ALP activity measurement. Difference between calvaria and differentiated osteoblast cells were analyzed by one-way ANOVA and P < 0.05 was considered as statistically significant.

RESULTS

Alkaline phosphatase activity, collagen and mineral material production in differentiated osteoblasts at third week were more significantly than calvaria cells (P < 0.05). Our results indicated that there was no significant different in osteocalcin (OC) production between differentiated osteoblast at first, second and third weeks and calvaria cells but declined at fourth week (P < 0.05).

CONCLUSIONS

Our survey showed that cellular traits of differentiated osteoblasts presented better than calvaria osteoblasts in vitro conditions. Therefore, we suggest that ADSCs could be used in next studies for bone tissue engineering.

Interferon gamma and T cells inhibit osteogenesis induced by allogeneic mesenchymal stromal cells

The mesenchymal stromal cells (MSCs) are reported to be immunoprivileged and osteogenic. We hypothesized that the use of allogeneic MSCs for bone repair was possible if they displayed an ability to induce similar osteogenesis in syngeneic as well as in allogeneic hosts. To test this hypothesis we used a cloned bone marrow derived cell, termed D1, isolated from Balb/c mice. The D1 cells were subcutaneously injected in syngeneic Balb/c, allogeneic immunocompetent B6, allogeneic T-cell deficient NCr nude, and allogeneic B6 Pfp-/- Rag2-/- mice that lack matured T and B cells as well as NK-cell cytolytic functions. D1 cells formed ectopic bones only in syngeneic or allogeneic immunocompromised hosts but not in allogeneic B6 hosts. The lack of T cells alone in allogeneic NCr mice was sufficient to promote osteogenesis in allogeneic environment. We observed a significantly higher number of T cells, B cells, macrophages and significantly higher expression of interferon gamma (IFN-γ) in B6 allogeneic implants as compared to the syngeneic implants. These factors correlated with severe inhibition of expression of alkaline phosphatase, osteocalcin, and runx2 genes in the implants from B6 mice. Our data suggest that strategies to inhibit T cells and IFN-γ functions will be useful for bone repair mediated by allogeneic MSCs.

Utilization of transgenic models in the evaluation of osteogenic differentiation of embryonic stem cells

Previous studies reported that embryonic stem cells (ESCs) can be induced to differentiate into cells showing a mature osteoblastic phenotype by culturing them under osteo-inductive conditions. It is probable that osteogenic differentiation requires that ESCs undergo differentiation through an intermediary step involving a mesenchymal lineage precursor. Based on our previous studies indicating that adult mesenchymal progenitor cells express α-smooth muscle actin (αSMA), we have generated ESCs from transgenic mice in which an αSMA promoter directs the expression of red fluorescent protein (RFP) to mesenchymal progenitor cells. To track the transition of ESC-derived MSCs into mature osteoblasts, we have utilized a bone-specific fragment of rat type I collagen promoter driving green fluorescent protein (Col2.3GFP). Following osteogenic induction in ESCs, we have observed expression of alkaline phosphatase (ALP) and subsequent mineralization as detected by von Kossa staining. After 1 week of osteogenic induction, ESCs begin to express αSMARFP. This expression was localized to the peripheral area encircling a typical ESC colony. Nevertheless, these αSMARFP positive cells did not show activation of the Col2.3GFP promoter, even after 7 weeks of osteogenic differentiation in vitro. In contrast, Col2.3GFP expression was detected in vivo, in mineralized areas following teratoma formation. Our results indicate that detection of ALP activity and mineralization of ESCs cultured under osteogenic conditions is not sufficient to demonstrate osteogenic maturation. Our study indicates the utility of the promoter-visual transgene approach to assess the commitment and differentiation of ESCs into the osteoblast lineage.

Anabolic effects of IGF-1 signaling on the skeleton

This review focuses on the anabolic effects of IGF-1 signaling on the skeleton, emphasizing the requirement for IGF-1 signaling in normal bone formation and remodeling. We first discuss the genomic context, splicing variants, and species conservation of the IGF-1 locus. The modulation of IGF-1 action by growth hormone (GH) is then reviewed while also discussing the current model which takes into account the GH-independent actions of IGF-1. Next, the skeletal phenotypes of IGF-1-deficient animals are described in both embryonic and postnatal stages of development, which include severe dwarfism and an undermineralized skeleton. We then highlight two mechanisms by which IGF-1 exerts its anabolic action on the skeleton. Firstly, the role of IGF-1 signaling in the modulation of anabolic effects of parathyroid hormone (PTH) on bone will be discussed, presenting in vitro and in vivo studies that establish this concept and the proposed underlying molecular mechanisms involving Indian hedgehog (Ihh) and the ephrins. Secondly, the crosstalk of IGF-1 signaling with mechanosensing pathways will be discussed, beginning with the observation that animals subjected to skeletal unloading by hindlimb elevation are unable to mitigate cessation of bone growth despite infusion with IGF-1 and the failure of IGF-1 to activate its receptor in bone marrow stromal cell cultures from unloaded bone. Disrupted crosstalk between IGF-1 signaling and the integrin mechanotransduction pathways is discussed as one of the potential mechanisms for this IGF-1 resistance. Next, emerging paradigms on bone-muscle crosstalk are examined, focusing on the potential role of IGF-1 signaling in modulating such interactions. Finally, we present a future outlook on IGF research.

A review of the important central role of altered citrate metabolism during the process of stem cell differentiation

Stem cells are highly proliferating cells that have the potential for differentiation leading to the development of specialized functional cell types. The process of stem cell differentiation requires an increase in the recruitment and population of the undifferentiated stem cells, which are then differentiated to specific functional cell types. Genetic/metabolic transformations in the cellular intermediary energy metabolism are required to provide the bioenergetic, synthetic, and catabolic requirements of the stem cells during this process. However, the identification of the intermediary energy metabolism pathways and their alterations during the proliferation and differentiation of stem cells remain largely unknown; mainly due to the lack of attention and/or required research that focuses on this relationship. In the absence of such information, a full understanding of the factors and conditions required to promote stem cell differentiation leading to development of normal functional metabolic specialized cells cannot be achieved. The purpose of this review is to provide the background and bring attention to the essential relationship of altered cellular intermediary metabolism in the context of the process of stem cell proliferation and differentiation. Citrate metabolism is central to the genetic and metabolic transformation leading to the development of the specialized functional cells. This review identifies the involvement of altered citrate metabolism and the associated genetic alterations of key pathways, enzymes, and transporters; as well as the bioenergetic implications. The importance is emphasized for identification and employment of required conditions to insure that the process of experimental stem cell differentiation results in the development of specialized cells that represent the functional metabolic characteristics and capabilities of their native specialized cells. This is an essential requirement for the successful application of stem cell therapy and regenerative medicine for many pathological conditions.

Wnt/β-catenin signaling activates bone morphogenetic protein 2 expression in osteoblasts

The BMP and Wnt/β-catenin signaling pathways cooperatively regulate osteoblast differentiation and bone formation. Although BMP signaling regulates gene expression of the Wnt pathway, much less is known about whether Wnt signaling modulates BMP expression in osteoblasts. Given the presence of putative Tcf/Lef response elements that bind β-catenin/TCF transcription complex in the BMP2 promoter, we hypothesized that the Wnt/β-catenin pathway stimulates BMP2 expression in osteogenic cells. In this study, we showed that Wnt/β-catenin signaling is active in various osteoblast or osteoblast precursor cell lines, including MC3T3-E1, 2T3, C2C12, and C3H10T1/2 cells. Furthermore, crosstalk between the BMP and Wnt pathways affected BMP signaling activity, osteoblast differentiation, and bone formation, suggesting Wnt signaling is an upstream regulator of BMP signaling. Activation of Wnt signaling by Wnt3a or overexpression of β-catenin/TCF4 both stimulated BMP2 transcription at promoter and mRNA levels. In contrast, transcription of BMP2 in osteogenic cells was decreased by either blocking the Wnt pathway with DKK1 and sFRP4, or inhibiting β-catenin/TCF4 activity with FWD1/β-TrCP, ICAT, or ΔTCF4. Using a site-directed mutagenesis approach, we confirmed that Wnt/β-catenin transactivation of BMP2 transcription is directly mediated through the Tcf/Lef response elements in the BMP2 promoter. These results, which demonstrate that the Wnt/β-catenin signaling pathway is an upstream activator of BMP2 expression in osteoblasts, provide novel insights into the nature of functional cross talk integrating the BMP and Wnt/β-catenin pathways in osteoblastic differentiation and maintenance of skeletal homeostasis.

Sustained release of melatonin from poly (lactic-co-glycolic acid) (PLGA) microspheres to induce osteogenesis of human mesenchymal stem cells in vitro

Melatonin promotes bone formation and prevents bone degradation via receptor-dependent or receptor-independent actions. The aim of this study is to encapsulate melatonin into poly (lactic-co-glycolic acid) (PLGA) microspheres (PLGA-MEL-MS) and create a melatonin sustained release system, then to evaluate its effect on the osteogenesis of human mesenchymal stem cells (hMSCs) in vitro. PLGA-MEL-MS were prepared by single emulsion solvent evaporation technique. Scanning electron microscopy demonstrated the incorporation of melatonin did not disturb the conventional generation of PLGA microspheres in size and morphology. In vitro drug release assay showed that PLGA-MEL-MS exhibited a biphasic drug release pattern: a low initial burst release effect with approximately 40% drug release at the first 3 days and a relatively retarded and continuous release with about 85% drug release over the 25 days. Cell proliferation assay demonstrated that PLGA-MEL-MS had no apparent effect on proliferation of human MSCs. In an osteogenesis assay, PLGA-MEL-MS obviously enhanced alkaline phosphatase (ALP) mRNA expression and increased ALP activity compared to that in the control group. Meanwhile, several markers of osteoblast differentiation were also significantly upregulated, including runx2, osteopontin, and osteocalcin. Furthermore, quantificational alizarin red-based assay demonstrated that PLGA-MEL-MS significantly enhanced calcium deposit of hMSCs compared to the controls. Therefore, this simple melatonin sustained release system can control released melatonin to generate a microenvironment with a relatively stable concentration of melatonin for a period of time to support osteogenic differentiation of hMSCs in vitro. This suggests that this system may be used as bone growth stimulator in bone healing in vivo.

Human skeletal dysplasia caused by a constitutive activated transient receptor potential vanilloid 4 (TRPV4) cation channel mutation

The transient receptor potential vanilloid 4 (TRPV4) cation channel, a member of the TRP vanilloid subfamily, is expressed in a broad range of tissues where it participates in the generation of Ca²⁺ signals and/or depolarization of the membrane potential. Regulation of TRPV4 abundance at the cell surface is critical for osmo- and mechanotransduction. Defects in TRPV4 are the cause of several human diseases, including brachyolmia type 3 (MIM:113500) (also known as brachyrachia or spondylometaphyseal dysplasia Kozlowski type [MIM:118452]), and metatropic dysplasia (MIM:156530) (also called metatropic dwarfism or parastremmatic dwarfism [MIM:168400]). These bone dysplasia mutants are characterized by severe dwarfism, kyphoscoliosis, distortion and bowing of the extremities, and contractures of the large joints. These diseases are characterized by a combination of decreased bone density, bowing of the long bones, platyspondyly, and striking irregularities of endochondral ossification with areas of calcific stippling and streaking in radiolucent epiphyses, metaphyses, and apophyses. In this review, we discuss the potential effect of the mutation on the regulation of TRPV4 functions, which are related to human diseases through deviated function. In particular, we emphasize how the constitutive active TRPV4 mutant affects endochondral ossification with a reduced number of hypertrophic chondrocytes and the presence of cartilage islands within the zone of primary mineralization. In addition, we summarize current knowledge about the role of TRPV4 in the pathogenesis of several diseases.

A uni-cortical femoral defect model in the rat: evaluation using injectable hyaluronan hydrogel as a carrier for bone morphogenetic protein-2

The development of biomaterial for bone regeneration requires animal models that are reliable and designed to mimic clinically relevant situations. We have previously investigated hydrogels comprised of modified hyaluronic acid and polyvinyl alcohol in models of ectopic bone formation. This hydrogel induces bone regeneration when loaded with bone morphogenetic proteins (BMPs). To allow further optimization of hydrogels, we developed a new, femoral, non-critical-sized cortical defect model. In the rat femur, we drilled standardized, elongated unilateral cortical defects that did not require stabilization and that could be created bilaterally to allow paired comparisons of biomaterials. After optimizing the defect size, subsequent stress fractures occurred in only 8% and the defect healed partially over the 40 day study period. In a time-course experiment, we treated bone defects with the previously studied hyaluronan hydrogel loaded with 10 µg hydroxyapatite and 6 µg BMP-2. The shape of the defect allowed controlled containment of the material within the defect. The defect in the right leg was left untreated, while the left defect was filled with 40 µl of the BMP hydrogel. As determined by pQCT analysis, the treated defects had a higher bone mineral content, bone area and bone density than control defects. The relative difference was greatest between the groups at 10 and 20 days and diminished as the defect healed in the untreated legs. We conclude that this animal model allows facile and rapid screening of biomaterials for bone regeneration in cortical femoral defects without requiring external fixation.

The skeletal site-specific role of connective tissue growth factor in prenatal osteogenesis

BACKGROUND

Connective tissue growth factor (CTGF/CCN2) is a matricellular protein that is highly expressed during bone development. Mice with global CTGF ablation (knockout, KO) have multiple skeletal dysmorphisms and perinatal lethality. A quantitative analysis of the bone phenotype has not been conducted.

RESULTS

We demonstrated skeletal site-specific changes in growth plate organization, bone microarchitecture, and shape and gene expression levels in CTGF KO compared with wild-type mice. Growth plate malformations included reduced proliferation zone and increased hypertrophic zone lengths. Appendicular skeletal sites demonstrated decreased metaphyseal trabecular bone, while having increased mid-diaphyseal bone and osteogenic expression markers. Axial skeletal analysis showed decreased bone in caudal vertebral bodies, mandibles, and parietal bones in CTGF KO mice, with decreased expression of osteogenic markers. Analysis of skull phenotypes demonstrated global and regional differences in CTGF KO skull shape resulting from allometric (size-based) and nonallometric shape changes. Localized differences in skull morphology included increased skull width and decreased skull length. Dysregulation of the transforming growth factor-β-CTGF axis coupled with unique morphologic traits provides a potential mechanistic explanation for the skull phenotype.

CONCLUSIONS

We present novel data on a skeletal phenotype in CTGF KO mice, in which ablation of CTGF causes site-specific aberrations in bone formation.

Cyclic AMP signaling in bone marrow stromal cells has reciprocal effects on the ability of mesenchymal stem cells to differentiate into mature osteoblasts versus mature adipocytes

Stimulatory G protein-mediated cAMP signaling is intimately involved in skeletal homeostasis. However, limited information is available on the role of the cAMP signaling in regulating the differentiation of mesenchymal stem cells into mature osteoblasts and adipocytes. To investigate this, we treated primary mouse bone marrow stromal cells (BMSCs) with forskolin to stimulate cAMP signaling and determined the effect on osteoblast and adipocyte differentiation. Exposure of differentiating osteoblasts to forskolin markedly inhibited progression to the late stages of osteoblast differentiation, and this effect was replicated by continuous exposure to PTH. Strikingly, forskolin activation of cAMP signaling in BMSCs conditioned mesenchymal stem cells (MSCs) to undergo increased osteogenic differentiation and decreased adipogenic differentiation. PTH treatment of BMSCs also enhanced subsequent osteogenesis, but promoted an increased adipogenesis as well. Thus, activation of cAMP signaling alters the lineage commitment of MSCs, favoring osteogenesis at the expense of adipogenesis.

Histologic and histomorphometric evaluation of the effect of lactoferrin combined with anorganic bovine bone on healing of experimentally induced bony defects on rabbit calvaria

BACKGROUND

Recent studies have shown that lactoferrin promotes the proliferation and differentiation of osteoblasts and inhibits osteoclast-mediated bone resorption. Anorganic bovine bone (ABB) graft has been extensively used as an osteoconductive material in the bone reconstructive surgeries. The purpose of this study was to examine whether the combination of lactoferrin with Bio-Oss would improve ossification in experimentally induced bone defects in rabbit calvaria.

MATERIALS AND METHODS

In this randomized, prospective animal study, a total of 32 bone defects with the diameter of 6 mm were created on the calvaria of 8 male New Zealand rabbits (4 defects in each animal). One defect was filled with ABB + Lactoferrin + Vehicle (BLV), the second one with ABB + Lactoferrin (BL), the third defect with ABB + V (BV), and the fourth defect was filled with ABB (B) alone. After 4 weeks, histologic sections were prepared and evaluated histologically and histomorphometrically. The type, percentage and vitality of newly formed bone, inflammation, percentage of residual material, and foreign body reaction were assessed for each specimen. Data were analyzed using Friedman tests.

RESULTS

All groups were similar in terms of inflammation and vitality, type, percentage of new bone formation, and residual material. The percentage of new bone formation in BLV, BL, BV, and B groups were 14.73 ± 3.14%, 15.02 ± 1.51%, 15.95 ± 2.24% and 13.44 ± 2.89% (P = 0.1) and the amount of residual biomaterial were 11.85 ± 1.50%, 13.73 ± 1.80%, 13.02 ± 1.86%, and 15.41 ± 2.05%, respectively (P = 0.392).

CONCLUSION

Based on results of this study, the combination of lactoferrin and ABB did not show any significant improvement in bone regeneration compared with ABB alone in surgically induced bony defects in rabbit calvaria.

Regulatory pathways associated with bone loss and bone marrow adiposity caused by aging, chemotherapy, glucocorticoid therapy and radiotherapy

The bone marrow is a complex environment that houses haematopoietic and mesenchymal cell populations and regulates bone turnover throughout life. The high proliferative capacity of these cell populations however, makes them susceptible to damage and injury, altering the steady-state of the bone marrow environment. Following cancer chemotherapy, irradiation and long-term glucocorticoid use, reduced bone and increased fat formation of marrow stromal progenitor cells results in a fatty marrow cavity, reduced bone mass and increased fracture risk. These bone and marrow defects are also observed in age-related complications such as estrogen deficiency and increased oxidative stress. Although the underlying mechanisms are yet to be clarified, recent investigations have suggested a switch in lineage commitment of bone marrow mesenchymal stem cells down the adipogenic lineage at the expense of osteogenic differentiation following such stress or injury. The Wnt/β-catenin signalling pathway is however has been recognized the key mechanism regulating stromal commitment, and its involvement in the osteogenic and adipogenic lineage commitment switch under the damaging conditions has been of great interest. This article reviews the effects of various types of stress or injury on the commitment to the adipogenic and osteogenic lineages of bone marrow stromal progenitor cells, and summarizes the roles of the Wnt/β-catenin and associated signalling pathways in the lineage commitment, switch, and recovery after damage, and as a therapeutic target.

Characterization of novel akermanite:poly-ϵ-caprolactone scaffolds for human adipose-derived stem cells bone tissue engineering

In this study, three different akermanite:poly-ϵ-caprolactone (PCL) composite scaffolds (wt%: 75:25, 50:50, 25:75) were characterized in terms of structure, compression strength, degradation rate and in vitro biocompatibility to human adipose-derived stem cells (hASC). Pure ceramic scaffolds [CellCeram™, custom-made, 40:60 wt%; β-tricalcium phosphate (β-TCP):hydroxyapatite (HA); and akermanite] and PCL scaffolds served as experimental controls. Compared to ceramic scaffolds, the authors hypothesized that optimal akermanite:PCL composites would have improved compression strength and comparable biocompatibility to hASC. Electron microscopy analysis revealed that PCL-containing scaffolds had the highest porosity but CellCeram™ had the greatest pore size. In general, compression strength in PCL-containing scaffolds was greater than in ceramic scaffolds. PCL-containing scaffolds were also more stable in culture than ceramic scaffolds. Nonetheless, mass losses after 21 days were observed in all scaffold types. Reduced hASC metabolic activity and increased cell detachment were observed after acute exposure to akermanite:PCL extracts (wt%: 75:25, 50:50). Among the PCL-containing scaffolds, hASC cultured for 21 days on akermanite:PCL (wt%: 75:25) discs displayed the highest viability, increased expression of osteogenic markers (alkaline phosphatase and osteocalcin) and lowest IL-6 expression. Together, the results indicate that akermanite:PCL composites may have appropriate mechanical and biocompatibility properties for use as bone tissue scaffolds.

Transient serum exposure regimes to support dual differentiation of human mesenchymal stem cells

Human mesenchymal stem cells (MSCs), which can generate both osteoblasts and chondrocytes, represent an ideal resource for orthopaedic repair using tissue-engineering approaches. One major difficulty for the development of osteochondral constructs using undifferentiated MSCs is that serum is typically used in culture protocols to promote differentiation of the osteogenic component, whereas existing chondrogenic differentiation protocols rely on the use of serum-free conditions. In order to define conditions which could be compatible with both chondrogenic and osteogenic differentiation in a single bioreactor, we have analysed the efficiency of new biphasic differentiation regimes based on transient serum exposure followed by serum-free treatment. MSC differentiation was assessed either in serum-free medium or with a range of transient exposure to serum, and compared to continuous serum-containing treatment. Although osteogenic differentation was not supported in the complete absence of serum, marker expression and extensive mineralization analyses established that 5 days of transient exposure triggered a level of differentiation comparable to that observed when serum was present throughout. This initial phase of serum exposure was further shown to support the successful chondrogenic differentiation of MSCs, comparable to controls maintained in serum-free conditions throughout. This study indicates that a culture based on temporal serum exposure followed by serum-free treatment is compatible with both osteogenic and chondrogenic differentiation of MSCs. These results will allow the development of novel strategies for osteochondral tissue engineering approaches using MSCs for regenerative medicine.

Curcumin increases rat mesenchymal stem cell osteoblast differentiation but inhibits adipocyte differentiation

Background:

Curcumin is a phenolic natural product isolated from the rhizome of Curcuma longa (turmeric) and has effects on bone health and fat formation. The bone marrow mesenchymal stem cells (MSCs) are multipotent cells capable of differentiating into osteoblasts and adipocytes. Osteoblast differentiation of MSCs can be a result of upregulation of heme oxygenase (HO)-1 expression. Curcumin can potently induce HO-1 expression.

Objective:

The present study describes the effects of curcumin on rat MSC (rMSCs) differentiation into osteoblasts and adipocytes.

Materials and Methods:

Rat bone marrow MSCs were isolated and treated with or without curcumin. Osteoblast differentiation was confirmed and determined by alkaline phosphatase (ALP) activity, mineralized nodule formation, the expression of Runx2 (runt-related transcription factor 2) and osteocalcin. Adipocyte differentiation was determined by Oil red O staining and the expression of peroxisome proliferator-activated receptor-γ 2 (PPARγ2) and CCAAT/enhancer-binding protein (C/EBP) α.

Results:

Curcumin increased ALP activity and osteoblast-specific mRNA expression of Runx2 and osteocalcin when rMSCs were cultured in osteogenic medium. In contrast, curcumin decreased adipocyte differentiation and inhibited adipocyte-specific mRNA expression of PPARγ2 and C/EBPα when rMSCs were cultured in adipogenic medium. HO-1 expression was increased during osteogenic differentiation of rMSCs.

Conclusions:

These findings demonstrate that curcumin can promote osteogenic differentiation of rMSCs and inhibit adipocyte formation. The effect of curcumin on osteogenic differentiation of rMSCs is correlated with HO-1 expression.

Implantation of osteogenic differentiated donor mesenchymal stem cells causes recruitment of host cells

The interaction between host and donor cells is believed to play an important role in osteogenesis. However, it is still unclear how donor osteogenic cells behave and interact with host cells in vivo. The purpose of this study was to track the interactions between transplanted osteogenic cells and host cells during osteogenesis. In vitro migration assay was carried out to investigate the ability of osteogenic differentiated human mesenchymal stem cells (O-hMSCs) to recruit MSCs. At the in vivo level, O-hMSCs were implanted subcutaneously or into skull defects in severe combined immunodeficient (SCID) mice. New bone formation was observed by micro-CT and histological procedures. In situ hybridization (ISH) against human Alu sequences was performed to distinguish donor osteogenic cells from host cells. In vitro migration assay revealed an increased migration potential of MSCs by co-culturing with O-hMSCs. In agreement with the results of in vitro studies, ISH against human Alu sequences showed that host mouse MSCs migrated in large numbers into the transplantation site in response to O-hMSCs. Interestingly, host cells recruited by O-hMSCs were the major cell populations in newly formed bone tissues, indicating that O-hMSCs can trigger and initiate osteogenesis when transplanted in orthotopic sites. The observations from this study demonstrated that in vitro induced O-hMSCs were able to attract host MSCs in vivo and were involved in osteogenesis together with host cells, which may be of importance for bone tissue-engineering applications.

Human adipose-derived cells can serve as a single-cell source for the in vitro cultivation of vascularized bone grafts

Orthopaedic surgery often requires bone grafts to correct large defects resulting from congenital defects, surgery or trauma. Great improvements have been made in the tissue engineering of bone grafts. However, these grafts lack the vascularized component that is critical for their survival and function. From a clinical perspective, it would be ideal to engineer vascularized bone grafts starting from one single-cell harvest obtained from the patient. To this end, we explored the potential of human adipose-derived mesenchymal stem cells (hASCs) as a single-cell source for osteogenic and endothelial differentiation and the assembly of bone and vascular compartments within the same scaffold. hASCs were encapsulated in fibrin hydrogel as an angioinductive material for vascular formation, combined with a porous silk fibroin sponge to support osteogenesis, and subjected to sequential application of growth factors. Three strategies were evaluated by changing spatiotemporal cues: (a) induction of osteogenesis prior to vasculogenesis; (b) induction of vasculogenesis prior to osteogenesis; or (c) simultaneous induction of osteogenesis and vasculogenesis. By 5 weeks of culture, bone-like tissue development was evidenced by the deposition of bone matrix proteins, alkaline phosphatase activity and calcium deposition, along with the formation of vascular networks, evidenced by endothelial cell surface markers, such as CD31 and von Willebrand factor, and morphometric analysis. Most robust development of the two tissue compartments was achieved by sequential induction of osteogenesis followed by the induction of vasculogenesis. Taken together, the collected data strongly support the utility of hASCs as a single-cell source for the formation of vascularized bone tissue.

Critical size defect regeneration using PEG-mediated BMP-2 gene delivery and the use of cell occlusive barrier membranes - the osteopromotive principle revisited

OBJECTIVE

The objective of this study was to investigate if osseous regeneration can be accelerated by involvement of periosteal tissue. Bone defect regeneration could be accelerated by the involvement of periosteal tissue if osteogenic cell signalling is maintained within the defect. It was questioned if local cell-mediated BMP-2 gene delivery makes a cell occlusive membrane dispensable during bone critical size defect regeneration.

METHODS

PEG matrix (degradation time 10 days) and PEG membrane (degradation time 120 days) were used in the pig calvarial model. Cylindrical (1 × 1 cm) critical size defects (CSD) (9 per animal; 20 animals) were filled with: (i) particulated autologous bone, covered with PEG membrane (group 1); (ii) HA/TCP, covered with PEG membrane (group 2); (iii) HA/TCP, mixed with PEG matrix (group 3); and (iv) HA/TCP mixed with BMP-2-transfected osteoblasts and PEG matrix (group 4). BMP-2/4 gene transfer: liposomal in vitro transfection of BMP-2/V5-tag fusion-protein. Quantitative histomorphometry (toluidine blue staining) after 2, 4 and 12 weeks assessed bone formation. Semiquantitative immunohistochemistry estimated the expression of BMP-2, V5-tag, Runx-2 and Sox9.

RESULTS

PEG matrix embedded BMP-2 expressing cells presented higher bone formation (P < 0.05) than HA/TCP + PEG matrix defect filling or PEG membrane covering (HA/TCP filling) after 12 weeks. Highest expression of BMP-2, Runx-2 and lowest expression of fibrous tissue marker Sox9 was seen in the BMP-2 group.

CONCLUSION

PEG matrix embedded BMP-2 expressing cells are capable to maintain osteogenic signalling and to accelerate osseous defect regeneration in absence of a cell occlusive membrane.

Evaluating the feasibility of utilizing the small molecule phenamil as a novel biofactor for bone regenerative engineering

Osteoblast cell adhesion and differentiation on biomaterials are important achievements necessary for implants to be useful in bone regenerative engineering. Recombinant bone morphogenetic proteins (BMPs) have been shown to be important for these processes; however, there are many challenges associated with the widespread use of these proteins. A recent report demonstrated that the small molecule phenamil, a diuretic derivative, was able to induce osteoblast differentiation and mineralization in vitro via the canonical BMP signalling cascade (Park et al., 2009). In this study, the feasibility of using phenamil as a novel biofactor in conjunction with a biodegradable poly(lactide-co-glycolide acid) (PLAGA) polymeric scaffold for engineering bone tissue was evaluated. The in vitro cellular behaviour of osteoblast-like MC3T3-E1 cells cultured on PLAGA scaffolds in the presence of phenamil at 10 μM were characterized with regard to initial cell adhesion, proliferation, alkaline phosphatase (ALP) activity and matrix mineralization. The results demonstrate that phenamil supported cell proliferation, promoted ALP activity and facilitated matrix mineralization of osteoblast-like MC3T3-E1 cells. Moreover, in this study, we found that phenamil promoted integrin-mediated cell adhesion on PLAGA scaffolds. It was also shown that phenamil encapsulated within porous, microsphere PLAGA scaffolds retained its osteogenic activity upon release. Based on these findings, the small molecule phenamil has the potential to serve as a novel biofactor for the repair and regeneration of bone tissues.

Nanocalcium-deficient hydroxyapatite-poly (e-caprolactone)-polyethylene glycol-poly (e-caprolactone) composite scaffolds

A bioactive composite of nano calcium-deficient apatite (n-CDAP) with an atom molar ratio of calcium to phosphate (Ca/P) of 1.50 and poly(ɛ-caprolactone)–poly(ethylene glycol)–poly(ɛ-caprolactone) (PCL–PEG–PCL) was synthesized, and a composite scaffold was fabricated. The composite scaffolds with 40 wt% n-CDAP contained well interconnected macropores around 400 μm, and exhibited a porosity of 75%. The weight-loss ratio of the n-CDAP/PCL–PEG–PCL was significantly greater than nano hydroxyapatite (n-HA, Ca/P = 1.67)/PCL–PEG–PCL composite scaffolds during soaking into phosphate-buffered saline (pH 7.4) for 70 days, indicating that n-CDAP-based composite had good degradability compared with n-HA. The viability ratio of MG-63 cells was significantly higher on n-CDAP than n-HA-based composite scaffolds at 3 and 5 days. In addition, the alkaline phosphatase activity of the MG-63 cells cultured on n-CDAP was higher than n-HA-based composite scaffolds at 7 days. Histological evaluation showed that the introduction of n-CDAP into PCL–PEG–PCL enhanced the efficiency of new bone formation when the composite scaffolds were implanted into rabbit bone defects. The results suggested that the n-CDAP-based composite exhibits good biocompatibility, biodegradation, and osteogenesis in vivo.

Effect of grafting BMP2-derived peptide to nanoparticles on osteogenic and vasculogenic expression of stromal cells

Bone morphogenetic protein-2 (BMP2) plays a major role in initiating the cascade of osteogenesis. However, high doses of exogenous BMP2 coupled with diffusion away from the intended site cause adverse side-effects. An alternative is to use biodegradable polymeric nanoparticles (NPs) grafted with peptides of the active domains of BMP2. NPs present a multivalent form of the peptide for stronger interaction with cell surface receptors, leading to a stronger activation of osteogenic signalling pathways. The objective of this work was to compare osteogenic activity of the BMP2 peptide (BMP2Pe), corresponding to residues 73-92 of BMP2 protein (BMP2Pr), grafted to biodegradable NPs with that of BMP2 protein (BMP2Pr). BMP2Pe was functionalized with a cysteine residue and grafted to poly(lactide fumarate) and poly(lactide-co-ethylene oxide fumarate) (PLAF/PLEOF) NPs via a thioether link. The calcium content of bone marrow stromal (BMS) cells cultured in osteogenic medium supplemented with BMP2 peptide/protein-grafted NPs (BMP2Pe-gNP and BMP2Pr-gNP) was slightly higher than other BMP2-treated groups, but all osteogenic groups showed similar levels of mineralization after 21 days. The expression pattern of master transcription factors Dlx5 and Runx2 indicated that BMP2 protein induced faster osteogenic signalling than the BMP peptide. The expression level of Osteopontin (OP), Osteocalcin (OC) and PECAM-1 in the NP-grafted BMP2 groups was significantly higher than those of ungrafted BMP2Pr and BMP2Pe groups, which may be due to a more effective presentation of the peptide/protein to cell surface receptors, thus leading to a stronger interaction of the peptide/protein with clustered cell surface receptors.

Up-regulated osteogenic transcription factors during early response of human periodontal ligament stem cells to cyclic tensile strain

INTRODUCTION

As one group of periodontal ligament (PDL) cells, human periodontal ligament stem cells (hPDLSCs) have been isolated and identified as mesenchymal adult stem cells (MSCs) since 2004. It has been well accepted that PDL sensitively mediates the transmission of stress stimuli to the alveolar bone for periodontal tissue remolding. Besides, the direction of MSCs differentiation has been verified regulated by mechanical signals. Therefore, we hypothesized that tensile strain might act on hPDLSCs differentiation, and the early response to mechanical stress should be investigated.

MATERIAL AND METHODS

The hPDLSCs were cultured in vitro and isolated via a magnetic activated CD146 cell sorting system. After investigation of surface markers and other experiments for identification, hPDLSCs were subjected to cyclic tensile strain at 3,000 µstrain for 3 h, 6 h, 12 h, and 24 h, without addition of osteogenic supplements. In the control groups, the cells were cultured in similar conditions without mechanical stimulation. Then osteogenic related genes and proteins were analyzed by RT-PCR and western blot.

RESULTS

Cyclic tensile strain at 3,000 µstrain of 6 h, 12 h, and 24 h durations significantly increased mRNA and protein expressions of Satb2, Runx2, and Osx, which were not affected in unloaded hPDLSCs.

CONCLUSIONS

We indicate that hPDLSCs might be sensitive to cyclic tensile strain. The significant increase of Runx2, Osx and Satb2 expressions may suggest an early response toward osteogenic orientation of hPDLSCs.

Gene disruption of the calcium channel Orai1 results in inhibition of osteoclast and osteoblast differentiation and impairs skeletal development

Calcium signaling plays a central role in the regulation of bone cells, although uncertainty remains with regard to the channels involved. In previous studies, we determined that the calcium channel Orai1 was required for the formation of multinucleated osteoclasts in vitro. To define the skeletal functions of calcium release-activated calcium currents, we compared the mice with targeted deletion of the calcium channel Orai1 to wild-type littermate controls, and examined differentiation and function of osteoblast and osteoclast precursors in vitro with and without Orai1 inhibition. Consistent with in vitro findings, Orai1(-/-) mice lacked multinucleated osteoclasts. Yet, they did not develop osteopetrosis. Mononuclear cells expressing osteoclast products were found in Orai1(-/-) mice, and in vitro studies showed significantly reduced, but not absent, mineral resorption by the mononuclear osteoclast-like cells that form in culture from peripheral blood monocytic cells when Orai1 is inhibited. More prominent in Orai1(-/-) mice was a decrease in bone with retention of fetal cartilage. Micro-computed tomography showed reduced cortical ossification and thinned trabeculae in Orai1(-/-) animals compared with controls; bone deposition was markedly decreased in the knockout mice. This suggested a previously unrecognized role for Orai1 within osteoblasts. Analysis of osteoblasts and precursors in Orai1(-/-) and control mice showed a significant decrease in alkaline phosphatase-expressing osteoblasts. In vitro studies confirmed that inhibiting Orai1 activity impaired differentiation and function of human osteoblasts, supporting a critical function for Orai1 in osteoblasts, in addition to its role as a regulator of osteoclast formation.

Evaluation of BMP-2 gene-activated muscle grafts for cranial defect repair

Large, osseous, segmental defects heal poorly. Muscle has a propensity to form bone when exposed to an osteogenic stimulus such as that provided by transfer and expression of cDNA encoding bone morphogenetic protein-2 (BMP-2). The present study evaluated the ability of genetically modified, autologous muscle to heal large cranial defects in rats. Autologous grafts (8 mm × 2 mm) were punched from the biceps femoris muscle and transduced intraoperatively with recombinant adenovirus vector containing human BMP-2 or green fluorescent protein cDNA. While the muscle biopsies were incubating with the vector, a central parietal 8 mm defect was surgically created in the calvarium of the same animal. The gene-activated muscle graft was then implanted into the cranial defect. After 8 weeks, crania were examined radiographically, histologically, and by micro-computed tomography and dual energy X-ray absorptiometry. Although none of the defects were completely healed in this time, muscle grafts expressing BMP-2 deposited more than twice as much new bone as controls. Histology confirmed the anatomical integrity of the newly formed bone, which was comparable in thickness and mineral density to the original cranial bone. This study confirms the in vivo osteogenic properties of genetically modified muscle and suggests novel strategies for healing bone.

Mesenchymal stem cell responses to mechanical stimuli

Mesenchymal stem cells (MSCs) have the potential to replace or restore the function of damaged tissues and offer much promise in the successful application of tissue engineering and regenerative medicine strategies. Optimising culture conditions for the pre-differentiation of MSCs is a key goal for the research community, and this has included a number of different approaches, one of which is the use of mechanical stimuli. Mesenchymal tissues are subjected to mechanical stimuli in vivo and terminally differentiated cells from the mesenchymal lineage respond to mechanical stimulation in vivo and in vitro. MSCs have also been shown to be highly mechanosensitive and this may present an ideal method for controlling MSC differentiation. Here we present an overview of the response of MSCs to various mechanical stimuli, focusing on their differentiation towards the mesenchymal tissue lineages including bone, cartilage, tendon/ligament, muscle and adipose tissue. More research is needed to elucidate the complex interactions between biochemically and mechanically stimulated differentiation pathways.

Five years follow-up of implant-prosthetic rehabilitation on a patient after mandibular ameloblastoma removal and ridge reconstruction by fibula graft and bone distraction

This case report presents a combination of surgical and prosthetic solutions applied to a case of oral implant rehabilitation in post-oncologic reconstructed mandible. Bone resection due to surgical treatment of large mandibular neoplasm can cause long-span defects. Currently, mandibular fibula free flap graft is widely considered as a reliable technique for restoring this kind of defect. It restores the continuity of removed segment and re-establishes the contour of the lower jaw. However, the limited height of grafted fibula does not allow the insertion of regular length implants, therefore favouring vertical distraction osteogenesis as an important treatment choice. This report presents a patient affected by extensive mandibular ameloblastoma who underwent surgical reconstruction by fibula free flap because of partial mandibular resection. Guided distraction osteoneogenesis technique was applied to grafted bone, in order to obtain adequate bone height and to realize a prosthetically guided placement of 8 fixtures. After osseointegration, the patient was rehabilitated with a full arch, screw-retained prosthetic restoration. At five-years follow up, excellent integration of grafted tissue, steady levels of bone around the fixtures and healthy peri-implant tissues were reported.

Early fixation of cobalt-chromium based alloy surgical implants to bone using a tissue-engineering approach

To establish the methods of demonstrating early fixation of metal implants to bone, one side of a Cobalt-Chromium (CoCr) based alloy implant surface was seeded with rabbit marrow mesenchymal cells and the other side was left unseeded. The mesenchymal cells were further cultured in the presence of ascorbic acid, β-glycerophosphate and dexamethasone, resulting in the appearance of osteoblasts and bone matrix on the implant surface. Thus, we succeeded in generating tissue-engineered bone on one side of the CoCr implant. The CoCr implants were then implanted in rabbit bone defects. Three weeks after the implantation, evaluations of mechanical test, undecalcified histological section and electron microscope analysis were performed. Histological and electron microscope images of the tissue engineered surface exhibited abundant new bone formation. However, newly formed bone tissue was difficult to detect on the side without cell seeding. In the mechanical test, the mean values of pull-out forces were 77.15 N and 44.94 N for the tissue-engineered and non-cell-seeded surfaces, respectively. These findings indicate early bone fixation of the tissue-engineered CoCr surface just three weeks after implantation.