Osteogenic differentiation within intact human embryoid bodies result in a marked increase in osteocalcin secretion after 12 days of in vitro culture, and formation of morphologically distinct nodule-like structures

Elastic modulus of hydrogel regulates osteogenic differentiation via liquid-liquid phase separation of YAP

Craniofacial bone defects induced by congenital malformations, trauma, or diseases frequently challenge the orthodontic or restorative treatment. Stem cell-based bone regenerative approaches emerged as a promising method to resolve bone defects. Microenvironment physical cues, such as the matrix elastic modulus or matrix topography, regulate stem cell differentiation via multiple genes. We constructed gelatin methacryloyl (GelMA), a well-known scaffold, to investigate the impact of elastic modulus on osteogenic differentiation in a three-dimensional environment. Confocal microscope was used to observe and assess the condensates fission and fusion. New bone formation was evaluated by micro-computed tomography at 6 weeks in calvarial defect rat. We found that the light curing increased elastic modulus of GelMA, and the pore size of GelMA decreased. The expression of osteogenic markers was inhibited in hBMSCs cultured in the low-elastic-modulus GelMA. In contrast, the expression of YAP, TAZ and TEAD was increased in the hBMSCs in the low-elastic-modulus GelMA. Furthermore, YAP assembled via liquid-liquid phase separation (LLPS) into condensates that were sensitive to 1'6-hexanediol. YAP recruit TAZ and TEAD4, but not RUNX2 into the condensates. In vivo, we also found that hBMSCs in high-elastic-modulus GelMA was more apt to form new bone. This study provides new insight into the mechanism of osteogenic differentiation. Reagents that can regulate the elastic modulus of substrate or LLPS may be applied to promote bone regeneration.

Stem Cells for Temporomandibular Joint Repair and Regeneration

Temporomandibular Disorders (TMD) represent a heterogeneous group of musculoskeletal and neuromuscular conditions involving the temporomandibular joint (TMJ), masticatory muscles and/or associated structures. They are a major cause of non-dental orofacial pain. As a group, they are often multi-factorial in nature and have no common etiology or biological explanations. TMD can be broadly divided into masticatory muscle and TMJ disorders. TMJ disorders are characterized by intra-articular positional and/or structural abnormalities. The most common type of TMJ disorders involves displacement of the TMJ articular disc that precedes progressive degenerative changes of the joint leading to osteoarthritis (OA). In the past decade, progress made in the development of stem cell-based therapies and tissue engineering have provided alternative methods to attenuate the disease symptoms and even replace the diseased tissue in the treatment of TMJ disorders. Resident mesenchymal stem cells (MSCs) have been isolated from the synovia of TMJ, suggesting an important role in the repair and regeneration of TMJ. The seminal discovery of pluripotent stem cells including embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) have provided promising cell sources for drug discovery, transplantation as well as for tissue engineering of TMJ condylar cartilage and disc. This review discusses the most recent advances in development of stem cell-based treatments for TMJ disorders through innovative approaches of cell-based therapeutics, tissue engineering and drug discovery.

Derivation of chondrocyte and osteoblast reporter mouse embryonic stem cell lines

With the establishment of methods that provide evidence for the generation of chondrocyte and osteoblast cell types from ESCs, there is a need for reagents that will enable their further characterization. Here we report on the derivation of chondrocyte and osteoblast reporter ESCs from previously generated and characterized transgenic mouse lines, Collagen type 2 alpha 1(Col2a1)-ECFP, Bone Sialoprotein (BSP)-Topaz, and BSP-Topaz/Dentin Matrix Protein 1 (DMP1)-Cherry dual reporter mice. Col2a1-ECFP is highly expressed in chondrocytes, while BSP-Topaz and DMP1-Cherry are highly expressed in osteoblasts and osteocytes, respectively. These new skeletal reporter mouse ESC lines will serve as valuable reagents to investigate the functionality of ESC derived chondrocyte and osteoblast cell types.

Derivation of Chondrogenic Cells from Human Embryonic Stem Cells for Cartilage Tissue Engineering

Human embryonic stem cells (hESCs) have the ability to self-renew and differentiate into any cell lineage of the three germ layers, therefore holding great promise for regenerative applications in dentistry and medicine. We previously described a micromass culture system as a model system to induce and study the chondrogenic commitment of hESCs. Using this system, chondrogenic cells can be further isolated and expanded under specific growth factor conditions. When encapsulated in hyaluronic acid (HA)-based hydrogels and cultured under appropriate growth factor and medium conditions, these chondrogenic cells synthesized and deposited extracellular matrix (ECM) characteristic of neocartilage. Here, we describe the micromass culture of hESCs, the isolation and expansion of hESC-derived chondrogenic cells, and the three-dimensional (3-D) culture of the chondrogenic cells in hydrogels for cartilage tissue engineering. We will also describe the various tools and techniques used for characterizing the tissue-engineered cartilage.

Osteogenesis from human induced pluripotent stem cells: an in vitro and in vivo comparison with mesenchymal stem cells

The purpose of this study was to examine the in vitro and in vivo osteogenic potential of human induced pluripotent stem cells (hiPSCs) against that of human bone marrow mesenchymal stem cells (hBMMSCs). Embryoid bodies (EBs), which were formed from undifferentiated hiPSCs, were dissociated into single cells and underwent osteogenic differentiation using the same medium as hBMMSCs for 14 days. Osteoinduced hiPSCs were implanted on the critical-size calvarial defects and long bone segmental defects in rats. The healing of defects was evaluated after 8 weeks and 12 weeks of implantation, respectively. Osteoinduced hiPSCs showed relatively lower and delayed in vitro expressions of the osteogenic marker COL1A1 and bone sialoprotein, as well as a weaker osteogenic differentiation through alkaline phosphatase staining and mineralization through Alizarin red staining compared with hBMMSCs. Calvarial defects treated with osteoinduced hiPSCs had comparable quality of new bone formation, including full restoration of bone width and robust formation of trabeculae, to those treated with hBMMSCs. Both osteoinduced hiPSCs and hBMMSCs persisted in regenerated bone after 8 weeks of implantation. In critical-size long bone segmental defects, osteoinduced hiPSC treatment also led to healing of segmental defects comparable to osteoinduced hBMMSC treatment after 12 weeks. In conclusion, despite delayed in vitro osteogenesis, hiPSCs have an in vivo osteogenic potential as good as hBMMSCs.

Human stem cells for craniomaxillofacial reconstruction

Human stem cell research represents an exceptional opportunity for regenerative medicine and the surgical reconstruction of the craniomaxillofacial complex. The correct architecture and function of the vastly diverse tissues of this important anatomical region are critical for life supportive processes, the delivery of senses, social interaction, and aesthetics. Craniomaxillofacial tissue loss is commonly associated with inflammatory responses of the surrounding tissue, significant scarring, disfigurement, and psychological sequelae as an inevitable consequence. The in vitro production of fully functional cells for skin, muscle, cartilage, bone, and neurovascular tissue formation from human stem cells, may one day provide novel materials for the reconstructive surgeon operating on patients with both hard and soft tissue deficit due to cancer, congenital disease, or trauma. However, the clinical translation of human stem cell technology, including the application of human pluripotent stem cells (hPSCs) in novel regenerative therapies, faces several hurdles that must be solved to permit safe and effective use in patients. The basic biology of hPSCs remains to be fully elucidated and concerns of tumorigenicity need to be addressed, prior to the development of cell transplantation treatments. Furthermore, functional comparison of in vitro generated tissue to their in vivo counterparts will be necessary for confirmation of maturity and suitability for application in reconstructive surgery. Here, we provide an overview of human stem cells in disease modeling, drug screening, and therapeutics, while also discussing the application of regenerative medicine for craniomaxillofacial tissue deficit and surgical reconstruction.

Embryonic stem cells and induced pluripotent stem cells for skeletal regeneration

Tissue engineering for skeletal tissues including bone and cartilage have been focused on the use of adult stem cells. Although there are several pioneering researches on skeletal tissue regeneration from embryonic stem cells (ESCs), ethical issues and the possibility of immune rejection clouded further attention to the application of ESCs for nonlethal orthopedic conditions. However, the recent discovery of induced pluripotent stem cells (iPSCs) led to reconsider the use of these pluripotential cells for skeletal regeneration. The purpose of this review was to summarize the current knowledge of osteogenic and chondrogenic induction from ESCs and iPSCs and to provide a perspective on the application of iPSCs for skeletal regeneration.

Nanotopographical cues augment mesenchymal differentiation of human embryonic stem cells

The production of bone-forming osteogenic cells for research purposes or transplantation therapies remains a significant challenge. Using planar polycarbonate substrates lacking in topographical cues and substrates displaying a nanotopographical pattern, mesenchymal differentiation of human embryonic stem cells is directed in the absence of chemical factors and without induction of differentiation by embryoid body formation. Cells incubated on nanotopographical substrates show enhanced expression of mesenchymal or stromal markers and expression of early osteogenic progenitors at levels above those detected in cells on planar substrates in the same basal media. Evidence of epithelial-to-mesenchymal transition during substrate differentiation and DNA methylation changes akin to chemical induction are also observed. These studies provide a suitable approach to overcome regenerative medical challenges and describe a defined, reproducible platform for human embryonic stem cell differentiation.

Short periods of cyclic mechanical strain enhance triple-supplement directed osteogenesis and bone nodule formation by human embryonic stem cells in vitro

Human embryonic stem cells (hESCs) are uniquely endowed with a capacity for both self-renewal and multilineage differentiation. The aim of this investigation was to determine if short periods of cyclic mechanical strain enhanced dexamethasone, ascorbic acid, and β-glycerophosphate (triple-supplement)-induced osteogenesis and bone nodule formation by hESCs. Colonies were cultured for 21 days and divided into control (no stretch) and three treatment groups; these were subjected to in-plane deformation of 2% for 5 s (0.2 Hertz) every 60 s for 1 h on alternate days in BioFlex plates linked to a Flexercell strain unit over the following periods (day 7-13), (day 15-21), and (day 7-21). Numerous bone nodules were formed, which stained positively for osteocalcin and type I collagen; in addition, MTS assays for cell number as well as total collagen assays showed a significant increase in the day 7-13 group compared to controls and other treatment groups. Alizarin Red staining further showed that cyclic mechanical stretching significantly increased the nodule size and mineral density between days 7-13 compared to control cultures and the other two experimental groups. We then performed a real-time polymerase chain reaction (PCR) microarray on the day 7-13 treatment group to identify mechanoresponsive osteogenic genes. Upregulated genes included the transcription factors RUNX2 and SOX9, bone morphogenetic proteins BMP1, BMP4, BMP5, and BMP6, transforming growth factor-β family members TGFB1, TGFB2, and TGFB3, and three genes involved in mineralization-ALPL, BGLAP, and VDR. In conclusion, this investigation has demonstrated that four 1-h episodes of cyclic mechanical strain acted synergistically with triple supplement to enhance osteogenesis and bone nodule formation by cultured hESCs. This suggests the development of methods to engineer three-dimensional constructs of mineralized bone in vitro, could offer an alternative approach to osseous regeneration by producing a biomaterial capable of providing stable surfaces for osteoblasts to synthesize new bone, while at the same time able to be resorbed by an osteoclastic activity-in other words, one that can recapitulate the remodeling dynamics of a naturally occurring bone matrix.

Human embryonic stem cell-derived mesenchymal stromal cells

Mesenchymal stromal cells (MSCs) originally isolated from marrow have multipotent differentiation potential and favorable immunomodulatory and anti-inflammatory properties that make them very attractive for regenerative cellular therapy. Cells with similar phenotypic characteristics have now been derived from almost all fetal, neonatal, and adult tissues; furthermore, more recently similar cells have also been generated from human embryonic stem cells (ESCs). Generation of MSCs from human ESCs provides an opportunity to study the developmental biology of human mesenchymal lineage generation in vitro. Generation of bone and cartilage from human ESC-derived MSCs and their functional characterization, both in vitro and in vivo, is also an active area of investigation as ESCs could provide an unlimited source of MSCs for potential repair of bone and cartilage defects. MSCs from adult sources are being investigated in numerous Phase I-III clinical trials for a wide variety of indications, mainly based on their immunomodulatory properties. Our group and others have shown MSCs derived from human ESCs possess immunomodulatory properties similar to marrow-derived MSCs. Immunomodulatory properties of ESC-derived MSCs could prove to be highly valuable for their potential clinical applications in the future as derivatives of human ESCs have already entered clinical arena in the context of Phase I clinical trials.

Repair of full-thickness tendon injury using connective tissue progenitors efficiently derived from human embryonic stem cells and fetal tissues

The use of stem cells for tissue engineering (TE) encourages scientists to design new platforms in the field of regenerative and reconstructive medicine. Human embryonic stem cells (hESC) have been proposed to be an important cell source for cell-based TE applications as well as an exciting tool for investigating the fundamentals of human development. Here, we describe the efficient derivation of connective tissue progenitors (CTPs) from hESC lines and fetal tissues. The CTPs were significantly expanded and induced to generate tendon tissues in vitro, with ultrastructural characteristics and biomechanical properties typical of mature tendons. We describe a simple method for engineering tendon grafts that can successfully repair injured Achilles tendons and restore the ankle joint extension movement in mice. We also show the CTP's ability to differentiate into bone, cartilage, and fat both in vitro and in vivo. This study offers evidence for the possibility of using stem cell-derived engineered grafts to replace missing tissues, and sets a basic platform for future cell-based TE applications in the fields of orthopedics and reconstructive surgery.

Human embryonic stem cell-derived mesenchymal progenitors: an overview

Mesenchymal stromal/stem cells (MSCs) were originally isolated from bone marrow (BM), but are now known to be present in all fetal and adult tissues. These multipotent cells can be differentiated into at least three downstream mesenchymal lineages that include bone, cartilage, and fat. However, under some experimental conditions, these cells can differentiate into nonmesenchymal cell types and/or participate in regeneration of damaged tissues through a variety of mechanisms. Most recently, MSCs have been derived from human embryonic stem cells (hESCs) through several different methodologies. Human MSCs derived from hESCs have been shown to possess characteristics very similar to BM-derived MSCs. Thus, the generation of MSCs from hESCs provides an opportunity to study the developmental biology of cells of mesenchymal lineages in an appropriate in vitro model. Furthermore, MSCs from different adult tissue sources are being actively investigated in a multitude of clinical trials; therefore, hESCs could provide an unlimited source of MSCs for potential clinical applications in the future. Such MSCs could be used without further differentiation for regeneration of tissues, or they could be directed towards specific lineage pathways, such as bone and cartilage, for reconstruction of tissues. Finally, immunomodulatory properties of hESC-derived MSCs are likely to prove valuable for inducing immune tolerance toward other cells or tissues derived from the same hESC lines.

Embryonic stem cells for osteo-degenerative diseases

Current orthopedic practice to treat osteo-degenerative diseases, such as osteoporosis, calls for antiresorptive therapies and anabolic bone medications. In some cases, surgery, in which metal rods are inserted into the bones, brings symptomatic relief. As these treatments may ameliorate the symptoms, but cannot cure the underlying dysregulation of the bone, the orthopedic field seems ripe for regenerative therapies using transplantation of stem cells. Stem cells bring with them the promise of completely curing a disease state, as these are the cells that normally regenerate tissues in a healthy organism. This chapter assembles reports that have successfully used stem cells to generate osteoblasts, osteoclasts, and chondrocytes - the cells that can be found in healthy bone tissue - in culture, and review and collate studies about animal models that were employed to test the function of these in vitro "made" cells. A particular emphasis is placed on embryonic stem cells, the most versatile of all stem cells. Due to their pluripotency, embryonic stem cells represent the probably most challenging stem cells to bring into the clinic, and therefore, the associated problems are discussed to put into perspective where the field currently is and what we can expect for the future.

Bioengineering strategies for regeneration of craniofacial bone: a review of emerging technologies

Although advances in surgical techniques and bone grafting have significantly improved the functional and cosmetic restoration of craniofacial structures lost because of trauma or disease, there are still significant limitations in our ability to regenerate these tissues. The regeneration of oral and craniofacial tissues presents a formidable challenge that requires synthesis of basic science, clinical science, and engineering technology. Tissue engineering is an interdisciplinary field of study that addresses this challenge by applying the principles of engineering to biology and medicine toward the development of biological substitutes that restore, maintain, and improve normal function. This review will explore the impact of biomaterials design, stem cell biology and gene therapy on craniofacial tissue engineering.

Differential bone-forming capacity of osteogenic cells from either embryonic stem cells or bone marrow-derived mesenchymal stem cells

For more than a decade, human mesenchymal stem cells (hMSCs) have been used in bone tissue-engineering research. More recently some of the focus in this field has shifted towards the use of embryonic stem cells. While it is well known that hMSCs are able to form bone when implanted subcutaneously in immune-deficient mice, the osteogenic potential of embryonic stem cells has been mainly assessed in vitro. Therefore, we performed a series of studies to compare the in vitro and in vivo osteogenic capacities of human and mouse embryonic stem cells to those of hMSCs. Embryonic and mesenchymal stem cells showed all characteristic signs of osteogenic differentiation in vitro when cultured in osteogenic medium, including the deposition of a mineralized matrix and expression of genes involved in osteogenic differentiation. As such, based on the in vitro results, osteogenic ES cells could not be discriminated from osteogenic hMSCs. Nevertheless, although osteogenic hMSCs formed bone upon implantation, osteogenic cells derived from both human and mouse embryonic stem cells did not form functional bone, indicated by absence of osteocytes, bone marrow and lamellar bone. Although embryonic stem cells show all signs of osteogenic differentiation in vitro, it appears that, in contrast to mesenchymal stem cells, they do not possess the ability to form bone in vivo when a similar culture method and osteogenic differentiation protocol was applied.

Response of human embryonic stem cell-derived mesenchymal stem cells to osteogenic factors and architectures of materials during in vitro osteogenesis

One of the major challenges to the application of human embryonic stem cells (hESCs) to the repair of defective tissues is the directed differentiation of cells into specific lineages to avoid the formation of inferior heterogeneous tissues. To accomplish this goal, the lineage-specific stem cell population needs to be isolated and optimal differentiation conditions need to be defined. In this study, homogenous hESC-derived mesenchymal stem cells (hESC-MSCs) were generated and used to construct bone tissue. The effect of osteogenic factors, including dexamethasone (Dex) and bone morphogenetic protein-7 (BMP-7), on the osteogenesis of hESC-MSCs was investigated. It was found that BMP-7 itself had little effect on the in vitro osteogenic differentiation of hESC-MSCs; however, there was a synergic effect between BMP-7 and Dex in promoting osteogenesis. The effect of osteoconductive nanofibrous polylactic acid material on osteogenesis of hESC-MSCs was also investigated. It was found that the nanofibrous matrix architecture promoted alkaline phosphatase activity and calcium deposition of cells cultured under osteogenic conditions. Based on these findings, the hESC-MSCs were cultured on three-dimensional nanofibrous scaffolds in combination with Dex and BMP-7 stimulation in vitro to generate bone-like tissues. After 6 weeks of culture, highly mineralized tissues developed with specific bone marker genes expressed. These data illustrate the promise of hESC-MSCs for bone regeneration under optimal conditions.

Expansion and characterization of human embryonic stem cell-derived osteoblast-like cells

Human embryonic stem cells (hESCs) have the potential to serve as a repository of cells for the replacement of damaged or diseased tissues and organs. However, to use hESCs in clinically relevant scenarios, a large number of cells are likely to be required. The aim of this study was to demonstrate an alternative cell culture method to increase the quantity of osteoblast-like cells directly derived from hESCs (hESCs-OS). Undifferentiated hESCs were directly cultivated and serially passaged in osteogenic medium (hESC-OS), and exhibited similar expression patterns of osteoblast-related genes to osteoblast-like cells derived from mesenchymal stem cells derived from hESCs (hESCs-MSCs-OS) and human bone marrow stromal cells (hBMSCs-OS). In comparison to hESCs-MSCs-OS, the hESCs-OS required a shorter expansion time to generate a homogenous population of osteoblast-like cells that did not contain contaminating undifferentiated hESCs. Identification of human specific nuclear antigen (HuNu) in the newly formed bone in calvarial defects verified the role of the transplanted hESCs-OS as active bone forming cells in vivo. Taken together, this study suggests that osteoblast-like cells directly derived from hESCs have the potential to serve as an alternative source of osteoprogenitors for bone tissue engineering strategies.

Engineering embryonic stem-cell aggregation allows an enhanced osteogenic differentiation in vitro

Pluripotent embryonic stem (ES) cells hold great promise for the field of tissue engineering, with numerous studies investigating differentiation into various cell types including cardiomyocytes, chondrocytes, and osteoblasts. Previous studies have detailed osteogenic differentiation via dissociated embryoid body (EB) culture in osteoinductive media comprising of ascorbic acid, beta-glycerophosphate, and dexamethasone. It is hoped that these osteogenic cultures will have clinical application in bone tissue repair and regeneration and pharmacological testing. However, differentiation remains highly inefficient and generates heterogeneous populations. We have previously reported an engineered three-dimensional culture system for controlled ES cell-ES cell interaction via the avidin-biotin binding complex. Here we investigate the effect of such engineering on ES cell differentiation. Engineered EBs exhibit enhanced osteogenic differentiation assessed by cadherin-11, Runx2, and osteopontin expression, alkaline phosphatase activity, and bone nodule formation. Results show that cultures produced from intact EBs aggregated for 3 days generated the greatest levels of osteogenic differentiation when cultured in osteoinductive media. However, when cultured in control media, only engineered samples appeared to exhibit bone nodule formation. In addition, polymerase chain reaction analysis revealed a decrease in endoderm and ectoderm expression within engineered samples. This suggests that engineered ES cell aggregation has increased mesoderm homogeneity, contributing to enhanced osteogenic differentiation.

Skeletal tissue engineering using embryonic stem cells

Various cell types have been investigated as candidate cell sources for cartilage and bone tissue engineering. In this review, we focused on chondrogenic and osteogenic differentiation of mouse and human embryonic stem cells (ESCs) and their potential in cartilage and bone tissue engineering. A decade ago, mouse ESCs were first used as a model to study cartilage and bone development and essential genes, factors and conditions for chondrogenesis and osteogenesis were unravelled. This knowledge, combined with data from the differentiation of adult stem cells, led to successful chondrogenic and osteogenic differentiation of mouse ESCs and later also human ESCs. Next, researchers focused on the use of ESCs for skeletal tissue engineering. Cartilage and bone tissue was formed in vivo using ESCs. However, the amount, homogeneity and stability of the cartilage and bone formed were still insufficient for clinical application. The current protocols require improvement not only in differentiation efficiency but also in ESC-specific hurdles, such as tumourigenicity and immunorejection. In addition, some of the general tissue engineering challenges, such as cell seeding and nutrient limitation in larger constructs, will also apply for ESCs. In conclusion, there are still many challenges, but there is potential for ESCs in skeletal tissue engineering.

The enhancement of human embryonic stem cell osteogenic differentiation with nano-fibrous scaffolding

Human embryonic stem cells (hESC) hold great promise as a cell source for tissue engineering since they possess the ability to differentiate into any cell type within the body. However, much work must still be done to control the differentiation of the hESC to the desired lineage. In this study, we examined the effects of the nanofibrous (NF) architecture in both two-dimensional (2-D) poly(l-lactic acid) (PLLA) thin matrices and 3-D PLLA scaffolds in vitro to assess their affect on the osteogenic differentiation of hESC in vitro compared to more traditional solid films and solid-walled (SW) scaffolds. In 2-D culture, hESC on NF thin matrices were found to express collagen type 1, Runx2, and osteocalcin mRNA of higher levels than the hESC on the solid films after 1 week of culture and increased mineralization was observed on the NF matrices compared to the solid films after 3 weeks of culture. After 6 weeks of 3-D culture, the hESC on the NF scaffolds expressed significantly more osteocalcin mRNA compared to these on the SW scaffolds. The data indicates that the NF architecture enhances the osteogenic differentiation of the hESC compared to more traditional scaffolding architecture.

The effect of electrical stimulation on the differentiation of hESCs adhered onto fibronectin-coated gold nanoparticles

To encourage stem cell differentiation, gold nanoparticles (20 nm) were used to deliver electrical stimulation to human embryonic stem cells (hESCs) in vitro. Nano-structured gold nanoparticles were designed by coating the surface of culture dishes with gold nanoparticles using a layer-by-layer (LBL) system. In this method, gold nanoparticles were continuously coated onto dishes by SEM analysis. Evaluation of gene modified hESCs that were subsequently attached onto fibronectin-coated gold nanoparticles revealed that the un-differentiation marker, Oct-4, was no longer present following electrical stimulation. In addition, the osteogenic markers of collagen type I and Cbfa1 increased in response to electrical stimulation, while those of hESCs were not observed without electrical stimulation.

Early tissue patterning recreated by mouse embryonic fibroblasts in a three-dimensional environment

Cellular self-organization studies have been mainly focused on models such as Volvox, the slime mold Dictyostelium discoideum, and animal (metazoan) embryos. Moreover, animal tissues undergoing regeneration also exhibit properties of embryonic systems such as the self-organization process that rebuilds tissue complexity and function. We speculated that the recreation in vitro of the biological, biophysical, and biomechanical conditions similar to those of a regenerative milieu could elicit the intrinsic capacity of differentiated cells to proceed to the development of a tissue-like structure. Here we show that, when primary mouse embryonic fibroblasts are cultured in a soft nanofiber scaffold, they establish a cellular network that causes an organized cell contraction,proliferation, and migration that ends in the formation of a symmetrically bilateral structure with a distinct central axis. A subset of mesodermal genes (brachyury, Sox9, Runx2) is upregulated during this morphogenetic process. The expression of brachyury was localized first at the central axis, extending then to both sides of the structure. The spontaneous formation of cartilage-like tissue mainly at the paraxial zone followed expression ofSox9 and Runx2. Because cellular self-organization is an intrinsic property of the tissues undergoing development,this model could lead to new ways to consider tissue engineering and regenerative medicine.

Cultivation of Human Embryonic Stem Cells Without the Embryoid Body Step Enhances Osteogenesis In Vitro

Osteogenic cultures of embryonic stem cells (ESCs) are predominately derived from three-dimensional cell spheroids called embryoid bodies (EBs). An alternative method that has been attempted and merits further attention avoids EBs through the immediate separation of ESC colonies into single cells. However, this method has not been well characterized and the effect of omitting the EB step is unknown. Herein, we report that culturing human embryonic stem cells (hESCs) without the EB stage leads to a sevenfold greater number of osteogenic cells and to spontaneous bone nodule formation after 10-12 days. In contrast, when hESCs were differentiated as EBs for 5 days followed by plating of single cells, bone nodules formed after 4 weeks only in the presence of dexamethasone. Furthermore, regardless of the inclusion of EBs, bone matrix formed, including cement line matrix and mineralized collagen, which displayed apatitic mineral (PO4) with calcium-to-phosphorous ratios similar to those of hydroxyapatite and human bone. Together these results demonstrate that culturing hESCs without an EB step can be used to derive large quantities of functional osteogenic cells for bone tissue engineering.

In vitro direct osteogenesis of murine embryonic stem cells without embryoid body formation

Embryonic stem cells (ESCs) posses the ability to self-renew and differentiate into a multitude of lineages, including the osteogenic lineage in vitro. Currently, most approaches have focused on embryonic body (EB)-mediated osteogenic differentiation, which relies on formation of all three germ layers resulting in limited yields and labour-intensive culture processes. Our study aimed at developing an efficient culture strategy resulting in the upregulated in vitro osteogenic differentiation of murine ESCs (mESCs), which completely avoided EB formation. Specifically, mESCs were cultured in HepG2 conditioned medium for 3 days and then directed into osteogenic differentiation for 21 days without prior EB formation. The mineralised bone nodules generated were characterized by Alizarin red S-staining, phenotypic alkaline phosphatase expression, time-course analysis of ALPase activity, the presence of type I collagen and osteopontin, and osteocalcin, cbfa-1/runx-2, and osterix gene expression. Our method of direct osteogenic differentiation of mESCs represents a novel and efficient approach that results in enhanced yields and could have significant applications in bone tissue engineering.

The use of murine embryonic stem cells, alginate encapsulation, and rotary microgravity bioreactor in bone tissue engineering

The application of embryonic stem cells (ESCs) in bone tissue engineering and regenerative medicine requires the development of suitable bioprocesses that facilitate the integrated, reproducible, automatable production of clinically-relevant, scaleable, and integrated bioprocesses that generate sufficient cell numbers resulting in the formation of three-dimensional (3D) mineralised, bone tissue-like constructs. Previously, we have reported the enhanced differentiation of undifferentiated mESCs toward the osteogenic lineage in the absence of embryoid body formation. Herein, we present an efficient and integrated 3D bioprocess based on the encapsulation of undifferentiated mESCs within alginate hydrogels and culture in a rotary cell culture microgravity bioreactor. Specifically, for the first 3 days, encapsulated mESCs were cultured in 50% (v/v) HepG2 conditioned medium to generate a cell population with enhanced mesodermal differentiation capability followed by osteogenic differentiation using osteogenic media containing ascorbic acid, beta-glycerophosphate and dexamethasone. 3D mineralised constructs were generated that displayed the morphological, phenotypical, and molecular attributes of the osteogenic lineage, as well mechanical strength and mineralised calcium/phosphate deposition. Consequently, this bioprocess provides an efficient, automatable, scalable and functional culture system for application to bone tissue engineering in the context of macroscopic bone formation.

Dynamics of gene expression during bone matrix formation in osteogenic cultures derived from human embryonic stem cells in vitro

Characterization of directed differentiation protocols is a prerequisite for understanding embryonic stem cell behavior, as they represent an important source for cell-based regenerative therapies. Studies have investigated the osteogenic potential of human embryonic stem cells (HESCs), building upon those using pre-osteoblastic cells, however no consensus exists as to whether differentiating HESCs behave in a similar manner to the traditionally used osteoblastic progenitors. Thus, the aim of the current investigation was to define the gene expression pattern of osteoblastic differentiating HESCs, treated with ascorbic acid phosphate, beta-glycerophosphate and dexamethasone over a 25 day period. Characterization of the gene expression dynamics revealed a phasic pattern of bone-associated protein synthesis. Collagen type I and osteopontin were initially expressed in proliferating immature cells, whereas osterix was up-regulated at the end of active cellular proliferation. Subsequently, mineralization-associated proteins, bone sialoprotein and osteocalcin were detected. In light of this dynamic expression pattern, we concluded that two distinguishable phases occurred during osteogenic HESC differentiation; first, cellular proliferation and secretion of a pre-maturational matrix, and second the appearance of osteoprogenitors with characteristic extracellular matrix synthesis. Establishment of this model provided the foundation of a time-frame for the additional supplementation with growth factors, BMP2 and VEGF. BMP2 induced the expression of principle osteogenic factors, such as osterix, bone sialoprotein and osteocalcin, whereas VEGF had the converse effect on the gene expression pattern.

The derivation of mesenchymal stem cells from human embryonic stem cells

Human embryonic stem cells (hESCs) hold promise for tissue regeneration therapies by providing a potentially unlimited source of cells capable of undergoing differentiation into specified cell types. Several preclinical studies and a few clinical studies use human bone marrow stromal cells (hBMSCs) to treat skeletal diseases and repair damaged tissue. However, hBMSCs have limited proliferation and differentiation capacity, suggesting that an alternate cell source is desirable, and hESCs may serve this purpose. Here we describe a protocol for the reproducible derivation of mesenchymal stem cells from hESCs (hES-MSCs). The hES-MSCs have a similar immunophenotype to hBMSCs, specifically they are CD73+, STRO-1+ and CD45-, and are karyotypically stable. The derived hES-MSCs are also capable of differentiating into osteoblasts and adipocytes. When the hES-MSCs were genetically modified with the lineage-specific Col2.3-GFP lentivirus and cultured in osteogenic medium, increased GFP expression was detected over time, indicating the hES-MSCs have the capacity to differentiate down the osteogenic lineage and had progressed toward a mature osteoblast phenotype.

Efficient differentiation of human embryonic stem cells into a homogeneous population of osteoprogenitor-like cells

The use of human embryonic stem cells (hESC) in both research and therapeutic applications requires relatively large homogeneous populations of differentiated cells. The differentiation of three hESC lines into highly homogeneous populations of osteoprogenitor-like (hESC-OPL) cells is reported here. These cells could be expanded in a defined culture system for more than 18 passages, and showed a fibroblast-like morphology and a normal stable karyotype. The cells were strongly positive for the same antigenic markers as mesenchymal stem cells but negative for markers of haematopoetic stem cells. The hESC-OPL cells were able to differentiate into the osteogenic, but not into the chondrogenic or adipogenic, lineage and were positive for markers of early stages of osteogenic differentiation. When cultured in the presence of osteogenic supplements, the cells indicated the capacity to achieve, under inductive conditions, a mature osteoblast phenotype. The differentiation protocol is based on a monolayer approach, and does not require any exogenous factors other than fetal calf serum, or coculture systems of animal or human origin. This method is likely to be amenable to large-scale production of homogeneous osteoprogenitor-like cells and thus overcomes one of the major problems of differentiation of hESC, with important relevance for further cell therapy studies.

Application of stem cells in bone repair

Bone has the ability to repair minor injuries through remodeling. However, when the host source of osteoprogenitors is compromised at the defect site, one effective treatment may be cell-based therapy, as it replenishes the area of bone loss with cells possessing osteogenic potential. This review is a concise comparison of different types of stem cells that have the potential to be used in tissue-engineered scaffolds for bone repair. The clinical use of mesenchymal stem or stromal cells isolated from the bone marrow for treating various diseases has been well documented. However, the scarcity of these cells prompts the search for alternative sources of multipotential cells such as amniotic fluid stem cells and umbilical cord perivascular cells. Embryonic stem cells are another controversial source of cells with osteogenic potential. These cells have the ability to differentiate into all cell types of the adult body. Issues such as the use of human embryos and the risk of contamination from animal-derived culture components continue to prevent the therapeutic use of ESCs. As a result, abundant research has been carried out to design defined culture conditions for culturing ESCs, and alternative strategies such as the generation of induced pluripotent stem cells are being developed to eliminate the need for using embryos for cell derivation. In addition to the cell source, the ability to control stem cell differentiation into functional bone and the choice of biomaterial are also paramount objectives that are being examined in research and clinical trials.

In vivo bone formation from human embryonic stem cell-derived osteogenic cells in poly(d,l-lactic-co-glycolic acid)/hydroxyapatite composite scaffolds

We have previously reported the efficient osteogenic differentiation of human embryonic stem cells (hESCs) by co-culture with primary human bone-derived cells (hPBDs) without the use of exogenous factors. In the present study, we explored whether osteogenic cells derived from hESCs (OC-hESCs) using the previously reported method would be capable of regenerating bone tissue in vivo. A three-dimensional porous poly(d,l-lactic-co-glycolic acid)/hydroxyapatite composite scaffold was used as a cell delivery vehicle. In vivo implantation of OC-hESC-seeded scaffolds showed significant bone formation in the subcutaneous sites of immunodeficient mice at 4 and 8 weeks after implantation (n=5 for each time point). Meanwhile, implantation of the control no cell-seeded scaffolds or human dermal fibroblast-seeded scaffolds did not show any new bone formation. In addition, the presence of BMP-2 (1 microg/scaffold) enhanced new bone tissue formation in terms of mineralization and the expression of bone-specific genetic markers. According to FISH analysis, implanted OC-hESCs remained in the regeneration sites, which suggested that the implanted cells participated in the formation of new bone. In conclusion, OC-hESCs successfully regenerated bone tissue upon in vivo implantation, and this regeneration can be further enhanced by the administration of BMP-2. These results suggest the clinical feasibility of OC-hESCs as a good alternative source of cells for bone regeneration.

Osteogenic differentiation of murine embryonic stem cells is mediated by fibroblast growth factor receptors

The mechanisms involved in the control of embryonic stem (ES) cell differentiation are yet to be fully elucidated. However, it has become clear that the family of fibroblast growth factors (FGFs) are centrally involved. In this study we examined the role of the FGF receptors (FGFRs 1-4) during osteogenesis in murine ES cells. Single cells were obtained after the formation of embryoid bodies, cultured on gelatin-coated plates, and coaxed to differentiate along the osteogenic lineage. Upregulation of genes was analyzed at both the transcript and protein levels using gene array, relative-quantitative PCR (RQ-PCR), and Western blotting. Deposition of a mineralized matrix was evaluated with Alizarin Red staining. An FGFR1-specific antibody was generated and used to block FGFR1 activity in mES cells during osteogenic differentiation. Upon induction of osteogenic differentiation in mES cells, all four FGFRs were clearly upregulated at both the transcript and protein levels with a number of genes known to be involved in osteogenic differentiation including bone morphogenetic proteins (BMPs), collagen I, and Runx2. Cells were also capable of depositing a mineralized matrix, confirming the commitment of these cells to the osteogenic lineage. When FGFR1 activity was blocked, a reduction in cell proliferation and a coincident upregulation of Runx2 with enhanced mineralization of cultures was observed. These results indicate that FGFRs play critical roles in cell recruitment and differentiation during the process of osteogenesis in mES cells. In particular, the data indicate that FGFR1 plays a pivotal role in osteoblast lineage determination.

Osteogenic phenotypes and mineralization of cultured human periosteal-derived cells

Stem cells or osteogenic precursor cells isolated from bone marrow, trabecular tissues in bone, cartilage, muscle, and fat are the most suitable source for bone tissue engineering. In this study, we investigated the osteogenic phenotypes and mineralization of cultured human periosteal-derived cells obtained from mandibular periosteums. These periosteal-derived cells were positive for CD44, CD90, and CD166 antigens. They are successfully differentiated into osteoblasts in the medium containing dexamethasone, ascorbic acid, and beta-glycerophosphate. We observed that alkaline phosphatase (ALP) was largely expressed in the earlier stage of osteoblastic differentiation according to histochemical staining and RT-PCR analysis, whereas osteocalcin was dominantly expressed and secreted into the medium at the later stage. In addition, mineralized nodule formation has been observed by von Kossa staining in a time-dependent manner. These results suggest that periosteal-derived cell has the potential osteogenic activity and could be a good candidate for tissue engineering to restore the bony defects of the maxillofacial region.

Bio-Engineered Mesenchymal Stem Cell-Tricalcium Phosphate Ceramics Composite Augmented Bone Regeneration in Posterior Spinal Fusion

Grafting of autologous iliac crest and decortication approach in posterior spinal fusion surgery has been the “gold standard”. However, the limited source of autograft has prompted extensive research into bone substitute and biological enhancement of the fusion mass. In this study, the application of stem cell therapy by tissue engineering method was investigated to enhance posterior spinal fusion with -tricalcium phosphate ceramics in rabbit model. Rabbit bone marrow derived mesenchymal stem cells were aspirated from trochanter region of proximal femur. The mesenchymal stem cells were grown and directed to differentiate into osteogenic cells by osteogenic supplement (ascorbic acid, -glycerophosphate and dexamethasone) in basal medium (10% FBS in DMEM). The osteogenic cells were seeded on tricalcium phosphate ceramics for one day (MSC group, n=6). The cell-ceramics composite was implanted onto autologous L5 and L6 transverse processes with decortication approach in posterior spinal fusion. The cell free ceramics acts as control (Control group, n=6) and iliac crest autograft as positive control (Autograft group). The spinal segments were harvested at week 7 post-operation. Manual palpation was performed with spinal segments to assess any movement of L5-L6 vertebral joint. The stiffness of the joint was considered as solid fusion. The specimens then were fixed by formalin and transferred to 70% ethanol. The BMC and volume of fusion transverse processes of L5 and L6 was measured by peripheral quantitative computed tomography. In manual palpation, 50% solid fusion was found in MSC group, 60% in autograft group but none in control group. Moreover, the BMC of L5 and L6 transverse processes in MSC group was greater than autograft and control group (45%, 40% respectively, p<0.01). The volume of transverse processes in MSC group was greater than autograft by 45% (p<0.01) and control group by 26% (p<0.05). In conclusion, the mesenchymal stem cells derived osteogenic cells augmented spinal fusion and bone mineralization.

Differentiation of osteoblasts from mouse embryonic stem cells without generation of embryoid body

Osteoblasts are cells specialized in extracellular matrix production and mineralization. In collaboration with osteoclasts which are bone-resorbing cells, osteoblasts regulate bone homeostasis. The study of osteoblast differentiation from the earliest states of the differentiation can be performed using embryonic stem cells. Embryonic stem cells are pluripotent cells which have the capacity to give rise to all kinds of cells of the body. The main protocol to differentiate embryonic stem cells into osteoblast uses the generation of embryoid body which is a three-dimensional structure mimicking the developing embryo. Recently, it has been shown that human embryonic stem cells have the capacity to differentiate spontaneously into osteoblasts. In this manuscript, we showed that mouse embryonic stem cells have the capacity to differentiate spontaneously into osteoblasts, which can be visualized by the appearance of mineralization nodules and osteogenic markers.

Bone Matrix Formation in Osteogenic Cultures Derived from Human Embryonic Stem Cells in Vitro

Bone matrix production and mineralization involves sophisticated mechanisms, including the initial formation of an organic extracellular matrix into which inorganic hydroxyapatite crystals are later deposited. Human embryonic stem (hES) cells offer a potential to study early developmental processes and provide an unlimited source of cells. In this study, four different hES cell lines were used, and two different approaches to differentiate hES cells into the osteogenic lineage were taken. Undifferentiated cells were cultured either in suspension, facilitating the formation of embryoid bodies (EBs), or in monolayer, and both methods were in the presence of osteogenic supplements. Novel to our osteogenic differentiation study was the use of commercially available human foreskin fibroblasts to support the undifferentiated growth of the hES cell colonies, and their propagation in serum replacement-containing medium. Characterization of the osteogenic phenotype revealed that all hES cell lines differentiated toward the mesenchymal lineage, because T-Brachyury, Flt-1, and bone morphogenetic protein-4 could be detected. Main osteoblastic marker genes Runx2, osterix, bone sialoprotein, and osteocalcin were up-regulated. Alizarin Red S staining demonstrated the formation of bone-like nodules, and bone sialoprotein and osteocalcin were localized to these foci by immunohistochemistry. Cells differentiated in monolayer conditions exhibited greater osteogenic potential compared to those from EB-derived cells. We conclude that in vitro hES cells can produce a mineralized matrix possessing all the major bone markers, the differentiation of pluripotent hES cells to an osteogenic lineage does not require initiation via EB formation, and that lineage potential is not dependent on the mode of differentiation induction but on a cell line itself.

Concise Review: Embryonic Stem Cells: A New Tool to Study Osteoblast and Osteoclast Differentiation

Bone remodeling involves synthesis of organic matrix by osteoblasts and bone resorption by osteoclasts. A tight collaboration between these two cell types is essential to maintain a physiological bone homeostasis. Thus, osteoblasts control bone-resorbing activities and are also involved in osteoclast differentiation. Any disturbance between these effectors leads to the development of skeletal abnormalities and/or bone diseases. In this context, the determination of key genes involved in bone cell differentiation is a new challenge to treat any skeletal disorders. Different models are used to study the differentiation process of these cells, but all of them use pre-engaged progenitor cells, allowing us to study only the latest stages of the differentiation. Embryonic stem (ES) cells come from the inner mass of the blastocyst prior its implantation to the uterine wall. Because of their capacity to differentiate into all germ layers, and so into all tissues of the body, ES cells represent the best model by which to study earliest stages of bone cell differentiation. Osteoblasts are generated by two methods, one including the generation of embryoid body, the other not. Mineralizing cells are obtained after 2 weeks of culture and express all the specific osteoblastic markers (alkaline phosphatase, type I collagen, osteocalcin, and others). Osteoclasts are generated from a single-cell suspension of ES cells seeded on a feeder monolayer, and bone-resorbing cells expressing osteoclastic markers such as tartrate-resistant alkaline phosphatase or receptor activator of nuclear factor kappaB are obtained within 11 days. The aim of this review is to present recent discoveries and advances in the differentiation of both osteoblasts and osteoclasts from ES cells.

Primary bone-derived cells induce osteogenic differentiation without exogenous factors in human embryonic stem cells

We developed a new and efficient method for osteoblastic differentiation of human embryonic stem cells (hESCs) using primary bone-derived cells (PBDs). Three days after embryoid body (hEB) formation, cells were allowed to adhere to culture surface where PBDs were pre-plated and mitomycin C-treated in DMEM/F12 medium supplemented with 5% knockout serum replacement. As early as 14 days, mineralization and formation of nodule-like structures in cocultured hEBs were prominent by von Kossa and Alizarin S staining, and expressions of osteoblast-specific markers including bone sialoprotein, alkaline phosphates, osteocalcin, collagen 1, and core binding factor alpha1 by RT-PCR. In addition, FACS analysis revealed that over 19% of the differentiated cells expressed osteocalcin. These results suggest that PBDs not only have osteogenic effects releasing osteogenic factors as bone morphogenic protein (BMP) 2 and BMP 4 but also have exerted other effects, whether chemical or physical, for the differentiation of hESCs.