Mesenchymal multipotency of adult human periosteal cells demonstrated by single-cell lineage analysis

Bone regeneration: stem cell therapies and clinical studies in orthopaedics and traumatology

Regenerative medicine seeks to repair or replace damaged tissues or organs, with the goal to fully restore structure and function without the formation of scar tissue. Cell based therapies are promising new therapeutic approaches in regenerative medicine. By using mesenchymal stem cells, good results have been reported for bone engineering in a number of clinical studies, most of them investigator initiated trials with limited scope with respect to controls and outcome. With the implementation of a new regulatory framework for advanced therapeutic medicinal products, the stage is set to improve both the characterization of the cells and combination products, and pave the way for improved controlled and well-designed clinical trials. The incorporation of more personalized medicine approaches, including the use of biomarkers to identify the proper patients and the responders to treatment, will be contributing to progress in the field. Both translational and clinical research will move the boundaries in the field of regenerative medicine, and a coordinated effort will provide the clinical breakthroughs, particularly in the many applications of bone engineering.

Zebrafish stromal cells have endothelial properties and support hematopoietic cells

The goal of this study was to determine if we could establish a mesenchymal stromal line from zebrafish that would support hematopoietic cells. Such a coculture system would be a great benefit to study of the hematopoietic cell-stromal cell interaction in both in vitro and in vivo environments. Zebrafish stromal cells (ZStrC) were isolated from the "mesenchymal" tissue of the caudal tail and expanded in a specialized growth media. ZStrC were evaluated for phenotype, gene expression, and ability to maintain zebrafish marrow cells in coculture experiments. ZStrC showed mesenchymal and endothelial gene expression. Although ZStrC lacked the ability to differentiate into classic mesenchymal stromal cell lineages (i.e., osteocytes, adipocytes, chondrocytes), they did have the capacity for endotube formation on Matrigel and low-density lipoprotein uptake. ZStrC supported marrow cells for >2 weeks in vitro. Importantly, marrow cells were shown to retain homing ability in adoptive transfer experiments. ZStrC were also shown to improve hematopoietic recovery after sublethal irradiation after adoptive transfer. As the zebrafish model grows in popularity and importance in the study of hematopoiesis, new tools to aid in our understanding of the hematopoietic cell-stromal cell interaction are required. ZStrC represent an additional tool in the study of hematopoiesis and will be useful in understanding the factors that mediate the stromal cell-hematopoietic cell interactions that are important in hematopoietic cell maintenance.

Characterization and optimization of cell seeding in scaffolds by factorial design: quality by design approach for skeletal tissue engineering

Cell seeding into scaffolds plays a crucial role in the development of efficient bone tissue engineering constructs. Hence, it becomes imperative to identify the key factors that quantitatively predict reproducible and efficient seeding protocols. In this study, the optimization of a cell seeding process was investigated using design of experiments (DOE) statistical methods. Five seeding factors (cell type, scaffold type, seeding volume, seeding density, and seeding time) were selected and investigated by means of two response parameters, critically related to the cell seeding process: cell seeding efficiency (CSE) and cell-specific viability (CSV). In addition, cell spatial distribution (CSD) was analyzed by Live/Dead staining assays. Analysis identified a number of statistically significant main factor effects and interactions. Among the five seeding factors, only seeding volume and seeding time significantly affected CSE and CSV. Also, cell and scaffold type were involved in the interactions with other seeding factors. Within the investigated ranges, optimal conditions in terms of CSV and CSD were obtained when seeding cells in a regular scaffold with an excess of medium. The results of this case study contribute to a better understanding and definition of optimal process parameters for cell seeding. A DOE strategy can identify and optimize critical process variables to reduce the variability and assists in determining which variables should be carefully controlled during good manufacturing practice production to enable a clinically relevant implant.

An isolated cryptic peptide influences osteogenesis and bone remodeling in an adult mammalian model of digit amputation

Biologic scaffolds composed of extracellular matrix (ECM) have been used successfully in preclinical models and humans for constructive remodeling of functional, site-appropriate tissue after injury. The mechanisms underlying ECM-mediated constructive remodeling are not completely understood, but scaffold degradation and site-directed recruitment of progenitor cells are thought to play critical roles. Previous studies have identified a cryptic peptide derived from the C-terminal telopeptide of collagen IIIα that has chemotactic activity for progenitor cells. The present study characterized the osteogenic activity of the same peptide in vitro and in vivo in an adult murine model of digit amputation. The present study showed that the cryptic peptide increased calcium deposition, alkaline phosphatase activity, and osteogenic gene expression in human perivascular stem cells in vitro. Treatment with the cryptic peptide in a murine model of mid-second phalanx digit amputation led to the formation of a bone nodule at the site of amputation. In addition to potential therapeutic implications for the treatment of bone injuries and facilitation of reconstructive surgical procedures, cryptic peptides with the ability to alter stem cell recruitment and differentiation at a site of injury may serve as powerful new tools for influencing stem cell fate in the local injury microenvironment.

Effect of in vitro passaging on the stem cell-related properties of tendon-derived stem cells-implications in tissue engineering

This study aimed to compare clonogenicity, proliferation, stem cell-related marker expression, senescence, and differentiation potential of rat patellar tendon-derived stem cells (TDSCs) at early (P5), mid (P10), and late (P20, P30) passages. The clonogenicity of the cells was assessed by colony-forming assay and their proliferative potential was assessed by bromodeoxyuridine assay. The surface expression of CD90 and CD73 was assessed by flow cytometry. The cellular senescence was assessed by β-galactosidase activity. The adipogenic, chondrogenic, and osteogenic differentiation potentials of TDSCs were assessed by standard assays after induction. The mRNA expression of tendon-related markers, scleraxis (Scx) and tenomodulin (Tnmd), was measured by quantitative real-time reverse transcription-polymerase chain reaction. Both the colony numbers and proliferative potential of TDSCs increased with passaging. Concomitantly, there was significant upregulation of β-galactosidase activity with TDSC passaging. The subculture of TDSCs downregulated the expression of CD90 and CD73. Lipid droplets were formed in the early and mid passages of TDSCs upon adipogenic induction, but were absent in the late passages. The expression of peroxisome proliferator activator receptor gamma 2 (PPARγ2) and CCAAT/enhancer binding protein alpha (C/EBPα) in TDSCs after adipogenic induction decreased with passaging. Chondrogenesis, proteoglycan deposition, collagen type II protein expression, collagen type 2A1 (Col2AI), and aggrecan (Acan) mRNA expression were less in pellets formed with later passages of TDSCs after chondrogenic induction. The expression of Scx and Tnmd was lower in the late, compared with early and mid, passages of TDSCs. However, matrix mineralization and expression of alkaline phosphatase (Alpl) and osteocalcin (Bglap) mRNA after osteogenic induction increased with TDSC passaging. Researchers and clinicians should consider the changes of stem cell-related properties of TDSCs when multiplying them in vitro for tissue engineering.

Dimensional change of the healed periosteum on surgically created defects

PURPOSE

The final goal of regenerative periodontal therapy is to restore the structure and function of the periodontium destroyed or lost due to periodontitis. However, the role of periosteum in periodontal regeneration was relatively neglected while bone repair in the skeleton occurs as a result of a significant contribution from the periosteum. The aim of this study is to understand the histological characteristics of periosteum and compare the native periosteum with the repaired periosteum after elevating flap or after surgical intervention with flap elevation.

METHODS

Buccal and lingual mucoperiosteal flaps were reflected to surgically create critical-size, "box-type" (4 mm width, 5 mm depth), one-wall, intrabony defects at the distal aspect of the 2nd and the mesial aspect of the 4th mandibular premolars in the right and left jaw quadrants. Animals were sacrificed after 24 weeks.

RESULTS

THE RESULTS FROM THIS STUDY ARE AS FOLLOWS: 1) thickness of periosteum showed difference as follows (P<0.05): control group (0.45±0.22 mm)>flap-elevation group (0.36±0.07 mm)>defect formation group (0.26±0.03 mm), 2) thickness of gingival tissue showed difference as follows (P<0.05): defect formation group (3.15±0.40 mm)>flap-elevation group (2.02±0.25 mm)>control group (1.88±0.27 mm), 3) higher cellular activity was observed in defect formation group and flap-elevation groups than control group, 4) the number of blood vessles was higher in defect formation group than control group.

CONCLUSIONS

In conclusion, prolonged operation with increased surgical trauma seems to decrease the thickness of repaired periosteum and increase the thickness of gingiva. More blood vessles and high cellular activity were observed in defect formation group.

Heterotopic ossification in complex orthopaedic combat wounds: quantification and characterization of osteogenic precursor cell activity in traumatized muscle

BACKGROUND

Heterotopic ossification frequently develops following high-energy blast injuries sustained in modern warfare. We hypothesized that differences in the population of progenitor cells present in a wound would correlate with the subsequent formation of heterotopic ossification.

METHODS

We obtained muscle biopsy specimens from military service members who had sustained high-energy wartime injuries and from patients undergoing harvest of a hamstring tendon autograft. Plastic-adherent cells were isolated in single-cell suspension and plated to assess the prevalence of colony-forming cells. Phenotypic characteristics were assessed with use of flow cytometry. Individual colony-forming units were counted after an incubation period of seven to ten days, and replicate cultures were incubated in lineage-specific induction media. Immunohistochemical staining was then performed to determine the percentage of colonies that had differentiated along an osteogenic lineage. Quantitative real-time reverse-transcription polymerase chain reaction was used to identify changes in osteogenic gene expression.

RESULTS

Injured patients had significantly higher numbers of muscle-derived connective-tissue progenitor cells per gram of tissue (p < 0.0001; 95% confidence interval [CI], 129,930 to 253,333), and those who developed heterotopic ossification had higher numbers of assayable osteogenic colonies (p < 0.016; 95% CI, 12,249 to 106,065). In the injured group, quantitative real-time reverse-transcription polymerase chain reaction performed on the in vitro expanded progeny of connective-tissue progenitors demonstrated upregulation of COL10A1, COL4A3, COMP, FGFR2, FLT1, IGF2, ITGAM, MMP9, PHEX, SCARB1, SOX9, and VEGFA in the patients with heterotopic ossification as compared with those without heterotopic ossification.

CONCLUSIONS

Our study suggests that the number of connective-tissue progenitor cells is increased in traumatized tissue. Furthermore, wounds in which heterotopic ossification eventually forms have a higher percentage of connective-tissue progenitor cells committed to osteogenic differentiation than do wounds in which heterotopic ossification does not form. The early identification of heterotopic ossification-precursor cells and target genes in severe wounds not only may be an effective prognostic tool with which to assess whether heterotopic ossification will develop in a wound, but may also guide the future development of individualized prophylactic measures.

Could metabolic syndrome, lipodystrophy, and aging be mesenchymal stem cell exhaustion syndromes?

One of the most important and complex diseases of modern society is metabolic syndrome. This syndrome has not been completely understood, and therefore an effective treatment is not available yet. We propose a possible stem cell mechanism involved in the development of metabolic syndrome. This way of thinking lets us consider also other significant pathologies that could have similar etiopathogenic pathways, like lipodystrophic syndromes, progeria, and aging. All these clinical situations could be the consequence of a progressive and persistent stem cell exhaustion syndrome (SCES). The main outcome of this SCES would be an irreversible loss of the effective regenerative mesenchymal stem cells (MSCs) pools. In this way, the normal repairing capacities of the organism could become inefficient. Our point of view could open the possibility for a new strategy of treatment in metabolic syndrome, lipodystrophic syndromes, progeria, and even aging: stem cell therapies.

Mesenchymal stem cells and bone regeneration: current status

The enhancement of bone regeneration with biological agents including osteogenic growth factors and mesenchymal stem cells (MSCs) is becoming a clinical reality. Many exciting findings have been obtained following MSC implantation in animal models, and the data demonstrating their clinical efficacy in humans are promising. The overwhelming majority of experimental work has been performed with MSCs "amplified"in vitro. The nature of native MSCs in skeletal tissues however, remains poorly understood. This review summarizes recent findings pertaining to the definition and characterisation of MSCs in skeletal tissues and discusses the mechanisms of their actions in regenerating of bone in vivo. In respect to traditional tissue engineering paradigm, we bring together literature showing that the ways MSCs are extracted, expanded and implanted can considerably affect bone formation outcomes. Additionally, we discuss current animal models used in MSC research and highlight recent experiments showing important contribution of the host, and not only donor MSCs, in bone tissue formation. This knowledge provides a platform for novel therapy development for bone regeneration based on pharmacologically manipulated endogenous MSCs.

CD271/p75(NTR) inhibits the differentiation of mesenchymal stem cells into osteogenic, adipogenic, chondrogenic, and myogenic lineages

We describe a novel role for CD271 in the differentiation of mesenchymal stem cells (MSCs), including deciduous dental pulp stem cells (DDPSCs) and murine multipotent MSCs (C3H10T1/2 cells). The CD271(+) subpopulation of deciduous dental pulp cells (CD271(+)/DDPSCs) and the forced expression of CD271 in C3H10T1/2 (10T271) were analyzed by fluorescence-activated cell sorting. CD271 expression was detected in DDPSCs that expressed both CD44 and CD90, simultaneously, and the clonogenic capacity of the CD271(+)/DDPSCs was higher than that of the CD271(-)/DDPSCs that expressed both CD44 and CD90. Further, the differentiation of CD271(+)/DDPSCs into osteoblasts and adipocytes was inhibited although CD271(-)/DDPSCs were capable of differentiating into osteoblasts and adipocytes. CD271 was overexpressed in C3H10T1/2 cells, which have the potential to differentiate into osteoblasts, adipocytes, chondrocytes, and myocytes. CD271 inhibited the differentiation of C3H10T1/2 cells into any of these lineages. These results indicate a role for CD271 in inhibiting the differentiation of MSCs.

Inhibition of cellular senescence by developmentally regulated FGF receptors in mesenchymal stem cells

Bone-derived mesenchymal stem cells (MSCs) are important cells for use in cell therapy, tissue engineering, and regenerative medicine, but also to study bone development, homeostasis, and repair. However, little is known about their developmental ontology and in vivo identity. Because fibroblast growth factors (FGFs) play key roles in bone development and their receptors are developmentally regulated in bones, we hypothesized that MSCs should express FGF receptors (FGFRs), reflecting their developmental origin and potential. We show here that FGFR1/2 are expressed by rare mesenchymal progenitors in putative MSC niches in vivo, including the perichondrium, periosteum, and trabecular marrow. FGFR1⁺ cells often appeared as pericytes. These cells display a characteristic MSC phenotype in vitro when expanded with FGF-2, which appears to maintain MSC stemness by inhibiting cellular senescence through a PI3K/AKT-MDM2 pathway and by promoting proliferation. FGFRs may therefore be involved in MSC self-renewal. In summary, FGFR1/2 are developmentally regulated markers of MSCs in vivo and in vitro and are important in maintaining MSC stemness.

The combined bone forming capacity of human periosteal derived cells and calcium phosphates

Current knowledge suggests that the periosteum, a fibrous tissue which covers the surface of all bones, contains a population of progenitor cells which mediate the repair of bone defects. In an effort to optimise the utilisation of this source of cells for bone engineering, herein we describe the rational selection of calcium phosphate (CaP) containing materials, based on biomaterial properties, and evaluation of their combined bone forming capacity. Five different commercially available orthopaedic 3D matrices composed of CaP particles in an open collagen network (NuOss™, CopiOs™, Bio-Oss(®), Collagraft™ and Vitoss(®)) were evaluated in vitro and in vivo with human periosteal derived cells (hPDCs). It was found that the cell-material combinations behaved quite differently in vivo, despite apparent in vitro similarities in gene expression profiles. Bone formation was highest within the NuOss™/hPDC implant at 13.03%, which also contained the highest incidence of bone marrow formation. The bone formed in this implant was chimeric with approximately 65% originating from implanted cells. Upon analysis of human specific gene expression, although it was found that predominantly osteogenic differentiation was observed within NuOss™/hPDC implants, a lesser induction of chondrogenic genes was also observed. The formation of a cartilage intermediate was confirmed by histology. Additionally the NuOss™/hPDC implant integrated into the mouse environment with apparent active scaffold resorption. This study demonstrates the importance of matching a cell support/biological matrix with a cell type and subsequently has outlined parameters which can be used for the rational selection of biomaterials for bone engineering.

The regulation of differentiation in mesenchymal stem cells

Mesenchymal stromal/stem cells (MSCs) are a population of stromal cells present in the bone marrow and most connective tissues, capable of differentiation into mesenchymal tissues such as bone and cartilage. MSCs are attractive candidates for biological cell-based tissue repair approaches because of their extensive proliferative ability in culture while retaining their mesenchymal multilineage differentiation potential. In addition to its undoubted scientific interest, the prospect of monitoring and controlling MSC differentiation is a crucial regulatory and clinical requirement. Hence, the molecular regulation of MSC differentiation has been extensively studied. Most of the studies are in vitro, because the identity of MSCs in their tissues of origin in vivo remains undefined. This review addresses the current knowledge of the molecular basis of differentiation of cultured MSCs, with a particular focus on chondrogenesis and osteogenesis. Building on the information coming from developmental biology studies of embryonic skeletogenesis, several signaling pathways and transcription factors have been investigated and shown to play critical roles in MSC differentiation. In particular, the Wnt and transforming growth factor-β/bone morphogenetic protein signaling pathways are well known to modulate in MSCs the molecular differentiation into cartilage and bone. Relevant to the emerging concept of stem cell niches is the demonstration that physical factors can also participate in the regulation of MSC differentiation. Knowledge of the regulation of MSC differentiation will be critical in the design of three-dimensional culture systems and bioreactors for automated bioprocessing through mathematical models applied to systems biology and network science.

Mesenchymal stem cell characteristics of human anterior cruciate ligament outgrowth cells

When ruptured, the anterior cruciate ligament (ACL) of the human knee has limited regenerative potential. However, the goal of this report was to show that the cells that migrate out of the human ACL constitute a rich population of progenitor cells and we hypothesize that they display mesenchymal stem cell (MSC) characteristics when compared with adherent cells derived from bone marrow or collagenase digests from ACL. We show that ACL outgrowth cells are adherent, fibroblastic cells with a surface immunophenotype strongly positive for cluster of differentiation (CD)29, CD44, CD49c, CD73, CD90, CD97, CD105, CD146, and CD166, weakly positive for CD106 and CD14, but negative for CD11c, CD31, CD34, CD40, CD45, CD53, CD74, CD133, CD144, and CD163. Staining for STRO-1 was seen by immunohistochemistry but not flow cytometry. Under suitable culture conditions, the ACL outgrowth-derived MSCs differentiated into chondrocytes, osteoblasts, and adipocytes and showed capacity to self-renew in an in vitro assay of ligamentogenesis. MSCs derived from collagenase digests of ACL tissue and human bone marrow were analyzed in parallel and displayed similar, but not identical, properties. In situ staining of the ACL suggests that the MSCs reside both aligned with the collagenous matrix of the ligament and adjacent to small blood vessels. We conclude that the cells that emigrate from damaged ACLs are MSCs and that they have the potential to provide the basis for a superior, biological repair of this ligament.

Mesenchymal chondroprogenitor cell origin and therapeutic potential

Mesenchymal progenitor cells, a multipotent adult stem cell population, have the ability to differentiate into cells of connective tissue lineages, including fat, cartilage, bone and muscle, and therefore generate a great deal of interest for their potential use in regenerative medicine. During development, endochondral bone is formed from a template of cartilage that transforms into bone; however, mature articular cartilage remains in the articulating joints, where its principal role is reducing friction and dispersing mechanical load. Articular cartilage is prone to damage from sports injuries or ageing, which regularly progresses to more serious joint disorders, such as osteoarthritis. Osteoarthritis is a degenerative joint disease characterized by the thinning and eventual wearing of articular cartilage, and affects millions of people worldwide. Due to low chondrocyte motility and proliferative rates, and complicated by the absence of blood vessels, cartilage has a limited ability to self-repair. Current pharmaceutical and surgical interventions fail to generate repair tissue with the mechanical and cellular properties of native host cartilage. The long-term success of cartilage repair will therefore depend on regenerative methodologies resulting in the restoration of articular cartilage that closely duplicates the native tissue. For cell-based therapies, the optimal cell source must be readily accessible with easily isolated, abundant cells capable of collagen type II and sulfated proteoglycan production in appropriate proportions. Although a cell source with these therapeutic properties remains elusive, mesenchymal chondroprogenitors retain their expansion capacity with the promise of reproducing the structural or biomechanical properties of healthy articular cartilage. As current knowledge regarding chondroprogenitors is relatively limited, this review will focus on their origin and therapeutic application.

Treatment of multiple gingival recession defects using periosteal pedicle graft: a case series

BACKGROUND

The periosteum is a highly vascular connective tissue with immense regenerative potential. These qualities make it a suitable autogenous graft. A technique is described for using an autogenous periosteal pedicle graft (PPG) for the treatment of multiple gingival recession defects.

METHODS

Twenty teeth in six subjects with Miller Class I and II recessions ≥ 2 mm were treated using PPGs. In addition to the depth of the gingival recession defect, the probing depth and widths of keratinized and attached gingiva were recorded. The mean +/- SD was calculated for each of the clinical parameters. The paired t test was used to test the significance of the change.

RESULTS

At the end of 1 year, 90.95% of root coverage was attained with a significant increase in the widths of keratinized and attached gingiva (P = 0.0001); no change was observed in probing depths (P = 0.36).

CONCLUSION

The PPG technique can be successfully used for the treatment of multiple gingival recession defects.

Probing the osteoinductive effect of calcium phosphate by using an in vitro biomimetic model

The use of calcium phosphate (CaP)-based carriers in bone engineering is a promising approach to induce in vivo bone formation. However, the exact mechanism of osteoinduction by CaP is not known. Here, by mimicking the in vivo Ca(2+) and P(i)-enriched environment in an in vitro model, we assessed the effects of these ions on human periosteum-derived cells. We observed a significant Ca(2+) and P(i)-induced cell proliferation, which was found to be through the modulation of cell cycle progression, in a dose- and time-dependent manner. In addition, Ca(2+), P(i), and combined Ca-P upregulated osteogenic gene expression in a dose- and time-dependent manner. Encouragingly, both ions administered individually or in combination persistently and dose dependently upregulated bone morphogenetic protein-2 gene expression. This suggested a potential osteoinductive effect through an autonomous activation of the bone morphogenetic protein signaling pathway by released Ca(2+) and P(i), which may serve as an autocrine/paracrine osteoinduction loop that drives the cellularized CaP constructs toward effective bone formation in vivo. In conclusion, through an in vitro biomimetic model, we have partially probed the roles of the released Ca(2+) and P(i) on the osteoinductivity of CaP-based biomaterials.

Cell replication in craniofacial periosteum: appositional vs. resorptive sites

The size and the shape of craniofacial bones results from periosteal activity, which can be either appositional or resorptive. The periosteum is often used as a source of graft material for osteogenesis, but differences in cellular makeup and proliferative capacity may render resorptive regions unsuitable for transplant. This study was undertaken to characterize the cells in appositional and resorptive periosteum, and to assess variation in proliferative activity. Young pigs (n=9) were injected with bromodeoxyuridine to label replicating cells and killed 3h later. The mandibular ramus, hard palate and zygomatic arch were examined for patterns of periosteal activity, and replicating cells were quantified in 16 appositional and eight resorptive regions. Sections were also reacted for markers of osteogenic (Runx2) and osteoclastic [CTR (calcitonin receptor), RANK, TRAP, CD14] lineage, and for an endothelial label (lectin). Replicating cells were often associated with the vasculature; most were unreactive for markers of differentiation. Although the fibrous layers of periosteum had fewer replicating cells per unit area than inner layers (P<0.005), this was in part due to lower cellularity. Appositional periostea differed from resorptive periostea in having thicker fibrous layers (197 vs. 89μm, P=0.02) and higher replication density in the inner layers (606 vs. 329 labeled cells mm(-2) , P=0.02). Osteoprogenitors were numerous in the inner layers of appositional but very scarce in resorptive periostea. Multinucleated osteoclasts were never seen in appositional regions, but mononuclear cells positive for osteoclastic lineage markers were plentiful, especially in the most rapidly growing areas. These cells appeared to be macrophages accompanying a growth rate so rapid as to resemble a response to trauma. In conclusion, appositional and resorptive periostea differ strikingly in morphology and cell content. Resorptive periosteum is a poor choice for osteogenic grafting.

MSCA-1/TNAP selection of human jaw periosteal cells improves their mineralization capacity

Human jaw periosteum-derived cells (JPCs) represent an alternative cell source to bone marrow-derived mesenchymal stem cells for tissue engineering applications in the oral and maxillofacial surgery. In this study we investigated how far the presence or expression of human mesenchymal stem cell antigen-1/tissue non-specific alkaline phosphatase (MSCA-1/TNAP) and LNGFR (CD271) can be utilized to select and enrich the osteogenic progenitor cell fraction from the entire JPC population. Depending on their mineralization capacity, we classified the human isolated JPCs into mineralizing (mJPCs) and non-mineralizing JPCs (nmJPCs). Flow cytometric analyses revealed that undifferentiated mJPCs expressed MSCA-1/TNAP at significant higher levels than nmJPCs at day 5 and 10 of osteogenesis. Western blot analyses showed increased MSCA-1/TNAP expression levels in mJPCs during osteogenesis, whereas in nmJPCs MSCA-1/TNAP expression remained undetectable. Using the MSCA-1 and LNGFR specific antibodies, we separated the positive and negative fractions from the entire mJPC population. In order to analyse the mineralization capacity of the MSCA-1(+) and LNGFR(+) cell subsets, we quantified the calcium deposition in both subpopulations in comparison to the respective negative subpopulations. The MSCA-1(+)/TNAP(+) cell fraction showed a significant higher osteogenic capacity compared to the MSCA-1-/TNAP- cell fraction whereas the LNGFR(+/-) cell fractions did not differ in their osteogenic potential. Our findings suggest that MSCA-1 may represent a promising osteogenic marker for mJPC.

Periosteum as a source of mesenchymal stem cells: the effects of TGF-β3 on chondrogenesis

INTRODUCTION

Numerous experimental efforts have been undertaken to induce the healing of lesions within articular cartilage by re-establishing competent repair tissue. Adult mesenchymal stem cells have attracted attention as a source of cells for cartilage tissue engineering. The purpose of this study was to investigate chondrogenesis employing periosteal mesenchymal cells.

METHODS

Periosteum was harvested from patients who underwent orthopedic surgeries. Mesenchymal stem cells were characterized through flow cytometry using specific antibodies. The stem cells were divided into four groups. Two groups were stimulated with transforming growth factor β3 (TGF-β3), of which one group was cultivated in a monolayer culture and the other was cultured in a micromass culture. The remaining two groups were cultivated in monolayer or micromass cultures in the absence of TGF-β3. Cell differentiation was verified through quantitative reverse transcription-polymerase chain reaction (RT-PCR) and using western blot analysis.

RESULT

In the groups cultured without TGF-β3, only the cells maintained in the micromass culture expressed type II collagen. Both the monolayer and the micromass groups that were stimulated with TGF-β3 expressed type II collagen, which was observed in both quantitative RT-PCR and western blot analysis. The expression of type II collagen was significantly greater in the micromass system than in the monolayer system.

CONCLUSION

The results of this study demonstrate that the interactions between the cells in the micromass culture system can regulate the proliferation and differentiation of periosteal mesenchymal cells during chondrogenesis and that this effect is enhanced by TGF-β3.

Directional fluid flow enhances in vitro periosteal tissue growth and chondrogenesis on poly-epsilon-caprolactone scaffolds

The purpose of this study was to investigate the effect of directional fluid flow on periosteal chondrogenesis. Periosteal explants were harvested from 2-month-old rabbits and sutured onto poly-epsilon-caprolactone (PCL) scaffolds with the cambium layer facing away from the scaffolds. The periosteum/PCL composites were cultured in suspension in spinner flask bioreactors and exposed to various fluid flow velocities: 0, 20, 60, and 150 rpm for 4 h each day for 6 weeks. The application of fluid flow significantly increased percent cartilage yield in periosteal explants from 17% in the static controls to 65-75% under fluid flow (there was no significant difference between 20, 60, or 150 rpm). The size of the neocartilage was also significantly greater in explants exposed to fluid flow compared with static culture. The development of zonal organization within the engineered cartilage was observed predominantly in the tissue exposed to flow conditions. The Young's modulus of the engineered cartilage exposed to 60 rpm was significantly greater than the samples exposed to 150 and 20 rpm. These results demonstrate that application of directional fluid flow to periosteal explants secured onto PCL scaffolds enhances cell proliferation, chondrogenic differentiation, and cell organization and alters the biomechanical properties of the engineered cartilage.

Influence of cyclic bending loading on in vivo skeletal tissue regeneration from periosteal origin

INTRODUCTION

Periosteum osteogenic and chondrogenic properties stimulate the proliferation then differentiation of mesenchymal precursor cells originating from its deeper layers and from neighboring host tissues. The local mechanical environment plays a role in regulating this differentiation of cells into lineages involved in the skeletal regeneration process.

HYPOTHESIS

The aim of this experimental animal study is to explore the influence of cyclic high amplitude bending-loading on skeletal tissue regeneration. The hypothesis is that this mechanical loading modality can orient the skeletogenesis process towards the development of anatomical and histological articular structures.

MATERIAL AND METHODS

A vascularised periosteal flap was transferred in close proximity to each knee joint line in 17 rabbits. On one side, the tibiofemoral joint space was bridged and loading occurred when the animal bent its knee during spontaneous locomotion. On the other side, the flap was placed 12 mm distal to the joint line producing no loading during bending. Tissue regeneration was chronologically analyzed on histologic samples taken from the 4th day to the 6th month.

RESULTS

The structure and mechanical behavior of regenerating tissue evolved over time. As a result of the cyclic bending-loading regimen, cartilage tissue was maintained in specific areas of the regenerating tissue. When loading was discontinued, final osteogenic and fibrogenic differentiation occurred in the neoformed cartilage. Fissures developed in the cartilage aggregates resulting in pseudo-gaps suggesting similar processes to embryonic articular development. Ongoing mesenchymal stem cells stimulation was identified in the host tissues contiguous to the periosteal transfer.

DISCUSSION

These results suggest that the pseudarthrosis concept should be reconsidered within the context of motion induced articular histogenesis.

Hedgehog signalling is required for perichondral osteoblast differentiation in zebrafish

In tetrapod long bones, Hedgehog signalling is required for osteoblast differentiation in the perichondrium. In this work we analyse skeletogenesis in zebrafish larvae treated with the Hedgehog signalling inhibitor cyclopamine. We show that cyclopamine treatment leads to the loss of perichondral ossification of two bones in the head. We find that the Hedgehog co-receptors patched1 and patched2 are expressed in regions of the perichondrium that will form bone before the onset of ossification. We also show that cyclopamine treatment strongly reduces the expression of osteoblast markers in the perichondrium and that perichondral ossification is enhanced in patched1 mutant fish. This data suggests a conserved role for Hedgehog signalling in promoting perichondral osteoblast differentiation during vertebrate skeletal development. However, unlike what is seen during long bone development, we did not observe ectopic chondrocytes in the perichondrium when Hedgehog signalling is blocked. This result may point to subtle differences between the development of the skeleton in the skull and limb.

[Vascularized periosteum and bone regeneration]

The osteogenic potential of periosteum is widely recognized. During development, it plays a prominent role in the radial growth of long bones. Similarly, it has a key role in the consolidation of fractures. The physiological function of periosteum in the healthy, mature skeleton remains relatively subtle; however, its detachment from the bone surface reactivates its potential for fibrogenic and osteochondrogenic regeneration. This discreet anatomical structure is actually a reservoir of mesenchymal progenitor cells capable of proliferating and differentiating, by reinitializing cellular and molecular cascades of embryogenesis in mesenchymal tissues. However, given the hitherto limited knowledge of the quantitative potential of periosteum and of the pathways regulating tissue differentiation during regeneration, human applications have remained anecdotal. The findings of several in vivo and in vitro experiments indicate that the maintenance of the periosteum's vascularization stimulates its quantitative potential. The structural organization of the regenerated material in vivo is governed by locoregional biological and mechanical regulatory mechanisms that serve to make it capable of performing its new functions. The increasing awareness of periosteum's potential is stimulating active research in the fields of cellular biology and tissue engineering. The demonstration of its regenerative potential in animals gives reason to believe that strips of vascularized periosteum could become part of the developing armamentarium of regenerative medicine.

Molecular variations related to the regional differences in periosteal growth at the mandibular ramus

Periosteal growth at human mandibular ramus is characterized by bone apposition at the posterior border and resorption at the anterior border. Molecular control of this regional variation is unclear. This study examined the expression of several molecules involved in bone apposition/resorption at these regions in vivo and in vitro. By using growing pigs as a model, the periosteal growth was assessed at the mandibular ramus by vital staining and histological observations. In parallel, periosteal tissues were harvested and pulverized for RNA and protein extraction. Periosteal cells were also isolated, expanded in osteogenic media, and subjected to a single dose of dynamic tensile strain (0, 5, or 10% magnitude at 0.5 Hz) to examine their responses to mechanical loading. Real-time RT-PCR and Western blot analyses were used to examine mRNA and protein expression from periosteal tissues and cultured cells. Histological observation confirmed an anterior-resorption/posterior-apposition pattern in the pig mandibular ramus. Both in vivo tissue and in vitro cells demonstrated greater mRNA expression of receptor activator of NF-κB ligand (RANKL)/osteoprotegerin (OPG) ratio and bone morphogenetic protein 2 (BMP2) at the anterior region, while OPG expression at the anterior region was lower than the posterior region. In response to the application of a single dose of dynamic tensile strain, cultured periosteal cells appeared to change the expression profile of osteogenic markers but not that of RANKL/OPG and BMP2. These findings suggest that the unique regional variation of periosteal activity at the mandibular ramus is regulated by a differential expression of RANKL/OPG ratio (likely through differential induction of OPG) and BMP2.

Clinical application of human mesenchymal stromal cells for bone tissue engineering

The gold standard in the repair of bony defects is autologous bone grafting, even though it has drawbacks in terms of availability and morbidity at the harvesting site. Bone-tissue engineering, in which osteogenic cells and scaffolds are combined, is considered as a potential bone graft substitute strategy. Proof-of-principle for bone tissue engineering using mesenchymal stromal cells (MSCs) has been demonstrated in various animal models. In addition, 7 human clinical studies have so far been conducted. Because the experimental design and evaluation parameters of the studies are rather heterogeneous, it is difficult to draw conclusive evidence on the performance of one approach over the other. However, it seems that bone apposition by the grafted MSCs in these studies is observed but not sufficient to bridge large bone defects. In this paper, we discuss the published human clinical studies performed so far for bone-tissue regeneration, using culture-expanded, nongenetically modified MSCs from various sources and extract from it points of consideration for future clinical studies.

Chondrogenesis of mesenchymal stem cells: role of tissue source and inducing factors

Multipotent mesenchymal stromal cells (MSCs) are an attractive cell source for cell therapy in cartilage. Although their therapeutic potential is clear, the requirements and conditions for effective induction of chondrogenesis in MSCs and for the production of a stable cartilaginous tissue by these cells are far from being understood. Different sources of MSCs have been considered for cartilage tissue engineering, mainly based on criteria of availability, as for adipose tissue, or of proximity to cartilage and the joint environment in vivo, as for bone marrow and synovial tissues. Focussing on human MSCs, this review will provide an overview of studies featuring comparative analysis of the chondrogenic differentiation of MSCs from different sources. In particular, it will examine the influence of the cells' origin on the requirements for the induction of chondrogenesis and on the phenotype achieved by the cells after differentiation.

Changes in chondrogenic phenotype and gene expression profiles associated with the in vitro expansion of human synovium-derived cells

We undertook this study to characterize changes in the proliferative capacities, chondrogenic phenotypes, and gene expression profiles of human synovium-derived progenitor cells from osteoarthritic patients during in vitro expansion. Cells isolated from osteoarthritic synovia were cultured, and growth rates during serial passages were evaluated. Surface molecule expressions were determined by flow cytometry and cytogenetic analyses were performed. After chondrogenic differentiation in cell pellets, we evaluated type II collagen and glycosaminoglycan (GAG) synthesis. To assess whether the in vitro expansion of synovium-derived cells affects gene expression, we performed microarray analyses on cells at passage 0, 1, 2, 4, 6, and 8. Synovium-derived cells were rapidly expanded in vitro through passage 8 (about 130 days), and after passage 6, the proliferation rates decreased slightly with a wide range of individual variations. The expressions of CD166, CD49a, and CD106 decreased, whereas those of CD10, CD29, CD44, CD73, CD90, and CD105 showed no significant change. Karyotype analysis revealed no evidence of chromosome abnormalities. The staining of type II collagen and GAG in differentiated cell pellets showed rapid weakening. Genome-wide microarray analysis showed that synovium-derived cells from late passages over-expressed genes associated with cell cycle prolongation and cell aging, and less-expressed genes associated with cell growth stimulation. The in vitro expansion of synovium-derived cells was accompanied with decreased proliferative capacity and the chondrogenic phenotype, which might be modulated by change in gene expression patterns.

TGF-beta enhances the integrin alpha2beta1-mediated attachment of mesenchymal stem cells to type I collagen

The heterodimeric integrins are important receptors for the attachment of cells to their extracellular matrix. Here, we studied the attachment of human mesenchymal stem cells (MSCs) to type I collagen (col-1), which is part of the extracellular matrix in bone, skin, and connective tissues. Furthermore, we examined how TGF-beta influences the integrin expression and attachment of MSC. Using flow cytometry, immunoblot, and RT-PCR, we report that MSC express several integrin subunits, including the alpha(2)beta(1) integrin (VLA-2, CD49b/CD29). TGF-beta increases the expression of integrin subunits alpha(2), alpha(6), and beta(1) in MSC, thereby enhancing the attachment of MSC to col-1. The TGF-beta-mediated up-regulation of the expression of the integrin subunits alpha(2) and alpha(6) is mainly mediated in MSC by Smad2.

Pretreatment of periosteum with TGF-beta1 in situ enhances the quality of osteochondral tissue regenerated from transplanted periosteal grafts in adult rabbits

OBJECTIVE

To compare the efficacy of in situ transforming growth factor-beta1 (TGF-beta1)-pretreated periosteum to untreated periosteum for regeneration of osteochondral tissue in rabbits.

METHODS

In the pretreatment group, 12 month-old New Zealand white rabbits received subperiosteal injections of 200 ng of TGF-beta1 percutaneously in the medial side of the proximal tibia, 7 days prior to surgery. Control rabbits received no treatment prior surgery. Osteochondral transverse defects measuring 5mm proximal to distal and spanning the entire width of the patellar groove were created and repaired with untreated or TGF-beta1-pretreated periosteal grafts. Post-operatively the rabbits resumed normal cage activity for 6 weeks.

RESULTS

Complete filling of the defects with regenerated tissue was observed in both the TGF-beta1-pretreated and control groups with reformation of the original contours of the patellar groove. The total histological score (modified O'Driscoll) in the TGF-beta1-pretreated group, 20 (95% Confidence Interval (CI), 19-21), was significantly higher (P=0.0001) than the control group, 18 (16-19). The most notable improvements were in structural integrity and subchondral bone regeneration. No significant differences in glycosaminoglycan or type II collagen content, or equilibrium modulus were found between the surgical groups. The cambium of the periosteum regenerated at the graft harvest site was significantly thicker (P=0.0065) in the TGF-beta1-pretreated rabbits, 121 microm (94-149), compared to controls, 74 microm (52-96), after 6 weeks.

CONCLUSIONS

This study demonstrates that in situ pretreatment of periosteum with TGF-beta1 improves osteochondral tissue regeneration at 6-weeks post-op compared to untreated periosteum in 12 month-old rabbits.

Effects of mechanical loading patterns, bone graft, and proximity to periosteum on bone defect healing

The goal of this study is to elucidate whether mechanobiological factors, including mechanical loading patterns, presence of bone graft, and proximity to the periosteum, correlate to de novo tissue generation and healing in critical sized long bone defects, which are enveloped by periosteum in situ and are bridged at 16 weeks, in sheep femora. Quantitative histomorphometric measures of defect cross sections show that, along the axis least able to resist bending loads (minor centroidal axis, CA), bone laid down in the first two weeks after surgery exhibits more mineralization albeit less total area compared to bone along the axis most able to resist bending loads (major CA). Similarly, areas of the cross section along the minor CA show a higher degree of perfusion albeit less total area of perfusion compared to bone along the major CA. Furthermore, proximity to the periosteal niche, in conjunction with the presence of bone graft and predominant loading patterns, relates significantly to the radial distribution of early bone apposition and perfusion of bone at 16 weeks after surgery (linear regression with R(2)>0.80). In the absence of graft, early bone density is relatively evenly distributed in the defect zone, as is the intensity of perfused tissue. As measured by a steeper average slope in intensity of fluorochrome (new bone) distribution between the periosteum and the IM nail, the presence of bone graft retards initial bone formation in the defect zone and is associated with less evenly distributed tissue perfusion (steeper slope) persisting 16 weeks after surgery. Finally, although the mean area of bone resorption is not significantly different within or between groups defined by the presence of graft and/or mechanical loading patterns in the defect zone, the mean area of infilling resorption spaces is significantly higher in areas of the defect zone least able to resist bending (minor CA) but is not significantly related to the presence of bone graft. To our knowledge, the use of the major and minor centroidal axes to relate prevailing mechanical loading patterns to area and density of early bone generation in bone defects has not been reported prior to this study and may provide a new means to assess structure-function relationships in de novo bone generation and healing of bone defects.

Stem cells for tendon tissue engineering and regeneration

IMPORTANCE OF THE FIELD

Tendon injuries are common especially in sports activities, but tendon is a unique connective tissue with poor self-repair capability. With advances in stem cell biology, tissue engineering is becoming increasingly powerful for tissue regeneration. Stem cells with capacity of multipotency and self-renewal are an ideal cell source for tissue engineering.

AREAS COVERED IN THIS REVIEW

This review focus on discussing the potential strategies including inductive growth factors, bio-scaffolds, mechanical stimulation, genetic modification and co-culture techniques to direct tendon-lineage differentiation of stem cells for complete tendon regeneration. Attempting to use embryonic stem cells as seed cells for tendon tissue engineering have achieved encouraging results. The combination of chemical and physical signals in stem cell microenvironment could be regulated to induce differentiation of the embryonic stem cells into tendon.

WHAT THE READER WILL GAIN

We summarize fundamental questions, as well as future directions in tendon biology and tissue engineering.

TAKE HOME MESSAGE

Multifaceted technologies are increasingly required to control stem cell differentiation, to develop novel stem cell-based therapy, and, ultimately, to achieve more effective repair or regeneration of injured tendons.

Tissue engineering of cartilage using poly-epsilon-caprolactone nanofiber scaffolds seeded in vivo with periosteal cells

OBJECTIVE

To determine the potential of periosteal cells to infiltrate poly-epsilon-caprolactone (PCL) nanofiber scaffolds in vivo and subsequently produce cartilage in vitro.

DESIGN

PCL nanofiber scaffolds, with or without chitosan-coating were implanted under periosteum in 6-month-old rabbits. Transforming growth factor-beta1 (TGF-beta1) or vehicle was injected into each implant site. After 1, 3, 5 or 7 days, scaffolds were removed, separated from the periosteum, and the scaffolds and periosteum were cultured separately for 6 weeks under chondrogenic conditions. Sulfated glycosaminoglycan (GAG), type II collagen, DNA content, cartilage yield, and calcium deposition were then analyzed.

RESULTS

Cell infiltration was observed in all scaffolds. Cartilage formation in the uncoated scaffolds increased with duration of implantation (maximum at 7 days). Cells in the uncoated scaffolds implanted for 7 days produced significantly higher levels of both GAG [560 (95% confidence interval (CI), 107-1013) vs 228 (95% CI, 177-278) microg GAG/microg DNA] and cartilage yield [9% (95% CI, 3-14%) vs 0.02% (95% CI, 0-0.22%)] compared to chitosan-coated scaffolds (P=0.006 or less). There was no significant difference in GAG content or cartilage yield between the TGF-beta1-injected and vehicle-injected scaffolds. However, significantly more mineral deposition was detected in TGF-beta1-injected scaffolds compared to vehicle-injected scaffolds (P<0.0001). Cartilage yield from the periosteum, moreover, was significantly increased by subperiosteal TGF-beta1 injections (P<0.001). However, this response was reduced when chitosan-coated scaffolds were implanted.

CONCLUSIONS

This study demonstrates that it is possible to seed PCL nanofiber scaffolds with periosteal cells in vivo and subsequently produce engineered cartilage in vitro.

Application of autologous periosteal cells for the regeneration of class III furcation defects in Beagle dogs

The aim of this study was to evaluate the healing of class III furcation defects following transplantation of autogenous periosteal cells combined with beta-tricalcium phosphate (beta-TCP). Periosteal cells obtained from Beagle dogs' periosteum explant cultures, were inoculated onto the surface of beta-TCP. Class III furcation defects were created in the mandibular premolars. Three experimental groups were used to test the defects' healing: group A, beta-TCP seeded with periosteal cells were transplanted into the defects; group B, beta-TCP alone was used for defect filling; and group C, the defect was without filling materials. Twelve weeks post surgery, the tissue samples were collected for histology, immunohistology and X-ray examination. It was found that both the length of newly formed periodontal ligament and the area of newly formed alveolar bone in group A, were significantly increased compared with both group B and C. Furthermore, both the proportion of newly formed periodontal ligament and newly formed alveolar bone in group A were much higher than those of group B and C. The quantity of cementum and its percentage in the defects (group A) were also significantly higher than those of group C. These results indicate that autogenous periosteal cells combined with beta-TCP application can improve periodontal tissue regeneration in class III furcation defects.

Stem cell plasticity: recapping the decade, mapping the future

In slightly more than a decade of stem cell plasticity research, 24 peer-reviewed articles have demonstrated plasticity across organ and/or embryonic lineage boundaries at the single-cell level, with only 1 article showing negative results. These data, taken together with data about reversibility of gene restrictions that have also accumulated during the same period, indicate that postnatal cells, even "terminally differentiated" ones, have a degree of plasticity not appreciated previously. This review looks back at the four known pathways of cell plasticity and at previously described "plasticity principles" of Genomic Completeness, Cellular Uncertainty, Stochasticity of Cell Origin and Fate, relating these to issues of experimental design and discourse that are key to understanding and evaluating plasticity data. Although the physiologic roles played by such plasticity may still be debated, the manipulations of these phenomena for therapeutic or industrial purposes should finally be considered ripe for exploration. For the future, plasticity, indeed all stem cell biology, must be considered as part of a larger web of cell-to-cell and cell-to-matrix interactions that function fully only at the tissue level; thus, the success of stem cell biology necessarily must involve assembling data from cell and molecular biology research into systems of interactions that might be reasonably called "tissue biology." Interdisciplinary collaborations with complexity and chaos theorists, using mathematical/computer modeling of cell behaviors, will be vital to fully exploring stem cell behaviors in the coming decades.

Bone tissue engineering with human stem cells

Treatment of extensive bone defects requires autologous bone grafting or implantation of bone substitute materials. An attractive alternative has been to engineer fully viable, biological bone grafts in vitro by culturing osteogenic cells within three-dimensional scaffolds, under conditions supporting bone formation. Such grafts could be used for implantation, but also as physiologically relevant models in basic and translational studies of bone development, disease and drug discovery. A source of human cells that can be derived in large numbers from a small initial harvest and predictably differentiated into bone forming cells is critically important for engineering human bone grafts. We discuss the characteristics and limitations of various types of human embryonic and adult stem cells, and their utility for bone tissue engineering.

Transforming growth factor-beta1 modulates insulin-like growth factor binding protein-4 expression and proteolysis in cultured periosteal explants

OBJECTIVE

Periosteum is involved in bone growth and fracture healing and has been used as a cell source and tissue graft for tissue engineering and orthopedic reconstruction including joint resurfacing. Periosteum can be induced by transforming growth factor beta (TGF-beta) or insulin-like growth factor-I (IGF-I) alone or in combination to form cartilage. However, little is known about the interaction between IGF and TGF-beta signaling during periosteal chondrogenesis. The purpose of this study was to determine the effect of TGF-beta1 on IGF binding protein-4 (IGFBP-4) and the IGFBP-4 protease pregnancy-associated plasma protein-A (PAPP-A) expression in cultured periosteal explants.

DESIGN

Periosteal explants from rabbits were cultured with or without TGF-beta1. IGFBP-4 and PAPP-A mRNA levels were determined by real-time quantitative PCR. Conditioned medium was analyzed for IGFBP-4 and PAPP-A protein levels and IGFBP-4 protease activity.

RESULTS

TGF-beta1-treated explants contained lower IGFBP-4 mRNA levels throughout the culture period with a maximum reduction of 70% on day 5 of culture. Lower levels of IGFBP-4 protein were also detected in the conditioned medium from TGF-beta1-treated explants. PAPP-A mRNA levels were increased 1.6-fold, PAPP-A protein levels were increased threefold, and IGFBP-4 protease activity was increased 8.5-fold between 7 and 10days of culture (the onset of cartilage formation in this model) in conditioned medium from TGF-beta1-treated explants.

CONCLUSIONS

This study demonstrates that TGF-beta1 modulates the expression of IGFBP-4 and PAPP-A in cultured periosteal explants.

Effects of MRI contrast agents on the stem cell phenotype

The ultimate therapy for ischemic stroke is restoration of blood supply in the ischemic region and regeneration of lost neural cells. This might be achieved by transplanting cells that differentiate into vascular or neuronal cell types, or secrete trophic factors that enhance self-renewal, recruitment, long-term survival, and functional integration of endogenous stem/progenitor cells. Experimental stroke models have been developed to determine potential beneficial effect of stem/progenitor cell-based therapies. To follow the fate of grafted cells in vivo, a number of noninvasive imaging approaches have been developed. Magnetic resonance imaging (MRI) is a high-resolution, clinically relevant method allowing in vivo monitoring of cells labeled with contrast agents. In this study, labeling efficiency of three different stem cell populations [mouse embryonic stem cells (mESC), rat multipotent adult progenitor cells (rMAPC), and mouse mesenchymal stem cells (mMSC)] with three different (ultra)small superparamagnetic iron oxide [(U)SPIO] particles (Resovist, Endorem, Sinerem) was compared. Labeling efficiency with Resovist and Endorem differed significantly between the different stem cells. Labeling with (U)SPIOs in the range that allows detection of cells by in vivo MRI did not affect differentiation of stem cells when labeled with concentrations of particles needed for MRI-based visualization. Finally, we demonstrated that labeled rMAPC could be detected in vivo and that labeling did not interfere with their migration. We conclude that successful use of (U)SPIOs for MRI-based visualization will require assessment of the optimal (U)SPIO for each individual (stem) cell population to ensure the most sensitive detection without associated toxicity.

Human tissue-engineered bone produced in clinically relevant amounts using a semi-automated perfusion bioreactor system: a preliminary study

The aim of this study was to evaluate a semi-automated perfusion bioreactor system for the production of clinically relevant amounts of human tissue-engineered bone. Human bone marrow stromal cells (hBMSCs) of eight donors were dynamically seeded and proliferated in a perfusion bioreactor system in clinically relevant volumes (10 cm(3)) of macroporous biphasic calcium phosphate scaffolds (BCP particles, 2-6 mm). Cell load and distribution were shown using methylene blue staining. MTT staining was used to demonstrate viability of the present cells. After 20 days of cultivation, the particles were covered with a homogeneous layer of viable cells. Online oxygen measurements confirmed the proliferation of hBMSCs in the bioreactor. After 20 days of cultivation, the hybrid constructs became interconnected and a dense layer of extracellular matrix was present, as visualized by scanning electron microscopy (SEM). Furthermore, the hBMSCs showed differentiation towards the osteogenic lineage as was indicated by collagen type I production and alkaline phosphatase (ALP) expression. We observed no significant differences in osteogenic gene expression profiles between static and dynamic conditions like ALP, BMP2, Id1, Id2, Smad6, collagen type I, osteocalcin, osteonectin and S100A4. For the donors that showed bone formation, dynamically cultured hybrid constructs showed the same amount of bone as the statically cultured hybrid constructs. Based on these results, we conclude that a semi-automated perfusion bioreactor system is capable of producing clinically relevant and viable amounts of human tissue-engineered bone that exhibit bone-forming potential after implantation in nude mice.

Mesenchymal stem cell therapy in equine musculoskeletal disease: scientific fact or clinical fiction?

The goal in the therapeutic use of mesenchymal stem cells (MSCs) in musculoskeletal disease is to harness the regenerative nature of these cells focussing on their potential to grow new tissues and organs to replace damaged or diseased tissue. Laboratory isolation of MSCs is now well established and has recently been demonstrated for equine MSCs. Stem cell science has attracted considerable interest in both the scientific and clinical communities because of its potential to regenerate tissues. Research into the use of MSCs in tissue regeneration in general reflects human medical needs, however, the nature, prevalence and prognosis of superficial digital flexor tendonitis has put equine veterinary science at the forefront of tendon regeneration research. Much has been investigated and learnt but it must be appreciated that in spite of this, the field is still relatively young and both communities must prepare themselves for considerable time and effort to develop the technology into a highly efficient treatments. The promise of functional tissue engineering to replace old parts with new fully justifies the interest. At present, however, it is important to balance the understanding of our current limitations with a desire to progress the technology.

Bone regeneration: the stem/progenitor cells point of view

After bone injuries, several molecular mechanisms establish bone repair from stem/progenitor cells. Inflammation factors attract regenerative cells which expand and differentiate in order to build up a bone highly similar to that before injury. Bone marrow (BM) mesenchymal stem cells (MSCs) as skeletal stem cells and endothelial progenitors (EPCs) are at the origin of such reparation mechanisms. However, discrepancies exist about their identities. Although cultured MSCs are extensively described, their in vivo native forms are poorly known. In addition, recent experiments show that several types of EPC exist. We therefore review up-to-date data on the characterization of such stem/progenitor cells and propose a new point of view of their function in bone regeneration.

Regulation of stemness and stem cell niche of mesenchymal stem cells: implications in tumorigenesis and metastasis

Human mesenchymal stem cells (MSCs) derived from adult tissues have been considered a candidate cell type for cell-based tissue engineering and regenerative medicine. These multipotent cells have the ability to differentiate along several mesenchymal lineages and possibly along non-mesenchymal lineages. MSCs possess considerable immunosuppressive properties that can influence the surrounding tissue positively during regeneration, but perhaps negatively towards the pathogenesis of cancer and metastasis. The balance between the naïve stem state and differentiation is highly dependent on the stem cell niche. Identification of stem cell niche components has helped to elucidate the mechanisms of stem cell maintenance and differentiation. Ultimately, the fate of stem cells is dictated by their microenvironment. In this review, we describe the identification and characterization of bone marrow-derived MSCs, the properties of the bone marrow stem cell niche, and the possibility and likelihood of MSC involvement in cancer progression and metastasis.

Enhancement of bone-titanium integration profile with UV-photofunctionalized titanium in a gap healing model

In this study, we tested the potential of UV-photofunctionalized titanium surfaces to overcome compromised bone-titanium integration in a gap healing model. Titanium in rod and disk forms was acid etched and then stored for 4 weeks under dark ambient conditions. Titanium rods with and without UV pretreatment were placed into a rat femur with (contact healing) or without (gap healing) contact with the innate cortical bone. The titanium implants were subjected to a biomechanical push-in test, micro-CT bone morphometry, and surface elemental analysis after 2 weeks of healing. The strength of bone-titanium integration in the gap healing model was one-third of that in the contact healing model. However, UV-treated implants in the gap healing condition produced a strength of bone-titanium integration equivalent to that of untreated implants in the contact healing condition. Bone volume around UV-treated implants was 2- to 3-fold greater than that around the untreated implants in the gap healing model. A bone generation profile drawn along the long axis of the implant exhibited greater contrast between the untreated and UV-treated surfaces in the cortical area than in the bone marrow area. The bone tissue formed on UV-treated implants showed a higher Ca/P ratio than that formed on untreated titanium. The rate of cell proliferation, alkaline phosphatase activity, and calcium deposition in femoral periosteal cells and in bone marrow-derived osteoblasts were greater in cultures on UV-treated titanium disks than in cultures on untreated disks. The UV-enhanced function in periosteal cells was more pronounced when they were co-cultured with bone marrow-derived osteoblasts, indicating a synergistic effect of UV-treated titanium with biological signals from bone marrow-derived osteoblasts. Within the limitation of the model used in this study, UV-photofunctionalized titanium surfaces may overcome the challenging condition of bone-titanium integration without cortical bone support. UV treatment of implants induced marked improvements in the behavior of bone formation and quantity and quality of bone tissue around the implants. These effects may be related to the promoted function of both periosteum- and bone marrow-derived osteogenic cells at the local level around UV-treated titanium surfaces.

Periosteal pedicle graft for the treatment of gingival recession defects: a novel technique

BACKGROUND

The periosteum is a highly cellular connective tissue with rich vascularity and regenerative potential. These qualities make it a suitable autogenous graft. A technique utilizing autogenous periosteal pedicle graft (PPG) for the treatment of gingival recession defects is described.

METHODS

Four patients with Miller Class I and II recessions > or = 3 mm were treated utilizing PPG.

RESULTS

At the end of one year, all defects were completely covered.

CONCLUSIONS

The PPG technique can be used for the treatment of gingival recession defects successfully.

Differential gene expression in the perichondrium and cartilage of the neonatal mouse temporomandibular joint

Our goal was to discover genes differentially expressed in the perichondrium (PC) of the mandibular condylar cartilage (MCC) that might enhance regenerative medicine or orthopaedic therapies directed at the tissues of the temporomandibular joint. We used targeted gene arrays (osteogenesis, stem cell) to identify genes preferentially expressed in the PC and the cartilaginous (C) portions of the MCC in 2-day-old mice. Genes with higher expression in the PC sample related to growth factor ligand-receptor interactions [FGF-13 (6.4x), FGF-18 (4x), NCAM (2x); PGDF receptors, transforming growth factor (TGF)-beta and IGF-1], the Notch isoforms (especially Notch 3 and 4) and their ligands or structural proteins/proteoglycans [collagen XIV (21x), collagen XVIII (4x), decorin (2.5x)]. Genes with higher expression in the C sample consisted mostly of known cartilage-specific genes [aggrecan (11x), procollagens X (33x), XI (14x), IX (4.5x), Sox 9 (4.4x) and Indian hedgehog (6.7x)]. However, the functional or structural roles of several genes that were expressed at higher levels in the PC sample are unclear [myogenic factor (Myf) 9 (9x), tooth-related genes such as tuftelin (2.5x) and dentin sialophosphoprotein (1.6x), VEGF-B (2x) and its receptors (3-4x) and sclerostin (1.7x)]. FGF, Notch and TGF-beta signalling may be important regulators of MCC proliferation and differentiation; the relatively high expression of genes such as Myf6 and VEGF-B and its receptors suggests a degree of unsuspected plasticity in PC cells.

The periosteum as a cellular source for functional tissue engineering

The periosteum, a specialized fibrous tissue composed of fibroblast, osteoblast, and progenitor cells, may be an optimal cell source for tissue engineering based on its accessibility, the ability of periosteal cells to proliferate rapidly both in vivo and in vitro, and the observed differentiation potential of these cells. However, the functional use of periosteum-derived cells as a source for tissue engineering requires an understanding of the ability of such cells to elaborate matrix of different tissues. In this study, we subjected a population of adherent primary periosteum-derived cells to both adipogenic and osteogenic culture conditions. The commitment propensity of periosteal cells was contrasted with that of well-characterized phenotypically pure populations of NIH3T3 fibroblast and MC3T3-E1 osteoblast cell lines. Our results demonstrate that the heterogeneous populations of periosteal cells and NIH3T3 fibroblasts have the ability to express both osteoblast-like and adipocyte-like markers with similar potential. This raises the question of whether fibroblasts within the periosteum may, in fact, have the potential to behave like progenitor cells and play a role in the tissue's multilineage potential or whether there are true stem cells within the periosteum. Further, this study suggests that expanded periosteal cultures may be a source for tissue engineering applications without extensive enrichment or sorting by molecular markers. Thus, this study lays the groundwork for future investigations that will more deeply enumerate the cellular sources and molecular events governing periosteal cell differentiation.

Simple strategy for bone regeneration with a BMP-2/7 gene expression cassette vector

Bone morphogenetic protein (BMP) is one of the most promising candidates for bone regeneration therapy. Heterodimers of BMP family proteins, such as BMP-2/4 or BMP-2/7, are well known to have stronger osteoinduction activity than BMP homodimers. Here, we constructed a double gene cassette vector encoding BMP-2 and BMP-7, pCAGGS-BMP-2/7, and examined its potential for osteoinduction in vitro and in vivo. Expression of the pCAGGS-BMP-2/7 vector induced osteogenic differentiation in various cell lines with the same efficiency as BMP-2 and BMP-7 co-expressed from separate vectors. Moreover, the pCAGGS-BMP-2/7 vector strongly induced bone formation in rat skeletal muscle when introduced by in vivo electroporation, compared with BMP-2 or BMP-7 alone. Thus, our BMP-2/7 double gene cassette vector, or some variation of it, may be applicable for the future clinical induction of bone formation, because it does not require multiple vectors or complicated preparation.