Enhanced derivation of osteogenic cells from murine embryonic stem cells after treatment with HepG2-conditioned medium and modulation of the embryoid body formation period: application to skeletal tissue engineering

Osteogenic effect of electromagnetic fields on stem cells derived from rat bone marrow cultured in osteogenic medium versus conditioned medium in vitro

OBJECTIVES

This study assessed possible osteogenic differentiation caused by electromagnetic fields (EMF) on rat bone-marrow-derived stem cells (rBMSCs) cultured in osteogenic medium (OM) or in human adipose-stem cell-conditioned medium (hADSC-CM).

MATERIALS AND METHODS

The rBMSCs were divided into negative and positive control groups, cultured in α-MEM plus 10% FBS or OM respectively. CM and CM + EMF  groups, cultured cells in hADSCs-CM or exposed to EMF (50 Hz, 1 mT) for 30 min/day plus hADSCs-CM, respectively. Cells from the OM + EMF were simultaneously cultured in OM and exposed to EMF. Osteogenesis was investigated through alkaline phosphatase activity, alizarin red staining and real-time PCR.

RESULTS

A meaningfully higher level of ALP activity was observed in the OM + EMF group compared to the other groups. There was a considerable increase in Runx2 expression in the CM + EMF group compared to the positive control and CM groups and a significant increase in Runx2 expression in the OM + EMF in comparison with all other groups after 21 days. Runx2 expression increased significantly in the CM, CM + EMF and positive control groups on day 21 compared to the same groups on day 14. From days 14-21, Ocn expression increased in the CM and CM + EMF groups, but both groups showed a significant decrease compared to the positive controls. CM and EMF had no effect on Ocn expression. On day 21, Ocn expression was significantly higher in the OM + EMF group than in the positive control group.

CONCLUSION

The synergistic effect of EMF and OM increased the expression of Runx2 and Ocn in rBMSCs.

Development of a Novel Perfusion Rotating Wall Vessel Bioreactor with Ultrasound Stimulation for Mass-Production of Mineralized Tissue Constructs

BACKGROUND

As stem cells are considered a promising cell source for tissue engineering, many culture strategies have been extensively studied to generate in vitro stem cell-based tissue constructs. However, most approaches using conventional tissue culture plates are limited by the lack of biological relevance in stem cell microenvironments required for neotissue formation. In this study, a novel perfusion rotating wall vessel (RWV) bioreactor was developed for mass-production of stem cell-based 3D tissue constructs.

METHODS

An automated RWV bioreactor was fabricated, which is capable of controlling continuous medium perfusion, highly efficient gas exchange with surrounding air, as well as low-intensity pulsed ultrasound (LIPUS) stimulation. Embryonic stem cells encapsulated in alginate/gelatin hydrogel were cultured in the osteogenic medium by using our bioreactor system. Cellular viability, growth kinetics, and osteogenesis/mineralization were thoroughly evaluated, and culture media were profiled at real time. The in vivo efficacy was examined by a rabbit cranial defect model.

RESULTS

Our bioreactor successfully maintained the optimal culture environments for stem cell proliferation, osteogenic differentiation, and mineralized tissue formation during the culture period. The mineralized tissue constructs produced by our bioreactor demonstrated higher void filling efficacy in the large bone defects compared to the group implanted with hydrogel beads only. In addition, the LIPUS modules mounted on our bioreactor successfully reached higher mineralization of the tissue constructs compared to the groups without LIPUS stimulation.

CONCLUSION

This study suggests an effective biomanufacturing strategy for mass-production of implantable mineralized tissue constructs from stem cells that could be applicable to future clinical practice.

Conditioned Medium Enhances Osteogenic Differentiation of Induced Pluripotent Stem Cell-Derived Mesenchymal Stem Cells

Background

Recent studies have shown that induced pluripotent stem cells (iPSCs) could be differentiated into mesenchymal stem cells (MSCs) with notable advantages over iPSCs per se. In order to promote the application of iPSC-MSCs for osteoregenerative medicine, the present study aimed to assess the ability of murine iPSC-MSCs to differentiate into osteoblast phenotype.

Methods

Osteogenic differentiation medium, blending mouse osteoblast-conditioned medium (CM) with basic medium (BM) at ratio 3:7, 5:5 and 7:3, were administered to iPSC-MSCs, respectively. After 14 days, differentiation was evaluated by lineage-specific morphology, histological stain, quantitative reverse transcription-polymerase chain reaction and immunostaining.

Results

The osteogenesis-related genes, alp, runx2, col1 and ocn expressions suggest that culture medium consisting of CM:BM at the ratio of 3:7 enhanced the osteogenic differentiation more than other concentrations that were tested. In addition, the alkaline phosphatase activity and osteogenic marker Runx2 expression demonstrate that the combination of CM and BM significantly enhanced the osteogenic differentiation of iPSC-MSCs.

Conclusion

In summary, this study has shown that osteoblast-derived CM can dramatically enhance osteogenic differentiation of iPSC-MSCs toward osteoblasts. Results from this work will contribute to optimize the osteogenic induction conditions of iPSC-MSCs and will assist in the potential application of iPSC-MSCs for bone tissue engineering.

Mesoderm Lineage 3D Tissue Constructs Are Produced at Large-Scale in a 3D Stem Cell Bioprocess

Various studies have presented different approaches to direct pluripotent stem cell differentiation such as applying defined sets of exogenous biochemical signals and genetic/epigenetic modifications. Although differentiation to target lineages can be successfully regulated, such conventional methods are often complicated, laborious, and not cost-effective to be employed to the large-scale production of 3D stem cell-based tissue constructs. A 3D-culture platform that could realize the large-scale production of mesoderm lineage tissue constructs from embryonic stem cells (ESCs) is developed. ESCs are cultured using our previously established 3D-bioprocess platform which is amenable to mass-production of 3D ESC-based tissue constructs. Hepatocarcinoma cell line conditioned medium is introduced to the large-scale 3D culture to provide a specific biomolecular microenvironment to mimic in vivo mesoderm formation process. After 5 days of spontaneous differentiation period, the resulting 3D tissue constructs are composed of multipotent mesodermal progenitor cells verified by gene and molecular expression profiles. Subsequently the optimal time points to trigger terminal differentiation towards cardiomyogenesis or osteogenesis from the mesodermal tissue constructs is found. A simple and affordable 3D ESC-bioprocess that can reach the scalable production of mesoderm origin tissues with significantly improved correspondent tissue properties is demonstrated.

Proteomic Profiling of Neuroblastoma Cells Adhesion on Hyaluronic Acid-Based Surface for Neural Tissue Engineering

The microenvironment of neuron cells plays a crucial role in regulating neural development and regeneration. Hyaluronic acid (HA) biomaterial has been applied in a wide range of medical and biological fields and plays important roles in neural regeneration. PC12 cells have been reported to be capable of endogenous NGF synthesis and secretion. The purpose of this research was to assess the effect of HA biomaterial combining with PC12 cells conditioned media (PC12 CM) in neural regeneration. Using SH-SY5Y cells as an experimental model, we found that supporting with PC12 CM enhanced HA function in SH-SY5Y cell proliferation and adhesion. Through RP-nano-UPLC-ESI-MS/MS analyses, we identified increased expression of HSP60 and RanBP2 in SH-SY5Y cells grown on HA-modified surface with cotreatment of PC12 CM. Moreover, we also identified factors that were secreted from PC12 cells and may promote SH-SY5Y cell proliferation and adhesion. Here, we proposed a biomaterial surface enriched with neurotrophic factors for nerve regeneration application.

In Vitro Differentiation of Embryonic Stem Cells into Hematopoietic Lineage: Towards Erythroid Progenitor's Production

Embryonic stem cells (ESCs) differentiation via embryoid body (EB) formation is an established method that generates the three germ layers. However, EB differentiation poses several problems including formation of heterogeneous cell populations. Herein, we described a differentiation protocol on enhancing mesoderm derivation from murine ESCs (mESCs) using conditioned medium (CM) from HepG2 cells. We used this technique to direct hematopoiesis by generating "embryoid-like" colonies (ELCs) from murine (m) ESCs without following standard formation of EBs. Our CM-mESCs group yielded an almost fivefold increase in ELC formation (p ≤ 0.05) and higher expression of mesoderm genes;-Brachyury-T, Goosecoid, and Flk-1 compared with control mESCs group. Hematopoietic colony formation from CM-mESCs was also enhanced by twofold at days 7 and 14 with earlier colony commitment compared to control mESCs (p ≤ 0.05). This early clonogenic capacity was confirmed morphologically by the presence of nucleated erythrocytes and macrophages as early as day 7 in culture using standard 14-day colony-forming assay. Early expression of hematopoietic primitive (ζ-globin) and definitive (β-globin) erythroid genes and proteins was also observed by day 7 in the CM-treated culture. These data indicate that hematopoietic cells more quickly differentiate from CM-treated, compared with those using standard EB approaches, and provide an efficient bioprocess platform for erythroid-specific differentiation of ESCs.

Fabrication and Cell Responsive Behavior of Macroporous PLLA/Gelatin Composite Scaffold with Hierarchical Micro-Nano Pore Structure

Scaffolds providing a 3D environment which can effectively promote the adhesion, proliferation and differentiation of cells are crucial to tissue regeneration. In this study, the polyllactic acid (PLLA) scaffold with hierarchical pore structural was fabricated via two-step thermally induced phase separation (TIPS). To mimic both physical architecture and chemical composite of natural bone extracellular matrix (ECM), gelatin fibers were introduced into the pores of PLLA scaffolds and formed 3D network structure via TIPS. Human adipose tissue-derived stem cells (ADSCs) were harvested and seeded into PLLA/gel hybrid scaffolds and cultured in vitro for biocompatibility assay. The surface morphology, porosity and compressive modulus of scaffolds were characterized by scanning electron microscopy (SEM), density analysis and compression test respectively. The results showed that hybrid scaffolds had high porosity (91.62%), a good compressive modulus (2.79 ± 0.20 MPa), nanometer fibers (diameter around 186.39~354.30 nm) and different grades of pore size from 7.41 ± 2.64 nm to 387.94 ± 102.48 nm. The scaffolds with mild hydrolysis by NaOH were modified by 1-ethyl-3-(3-dimethyl ami-nopropyl) carbodiimide/N-hydroxysuccinimide (EDC/NHS). Gelatin was performed onto PLLA scaffold via TIPS aiming at enhancement cell-material interaction. In comparison with PLLA scaffold, the PLLA/gel scaffold had better biological performance and the mechanical properties because the gelatin fibers homogeneously distributed in each pore of PLLA scaffold and formed 3D network structure.

Optimized osteogenic differentiation protocol from R1 mouse embryonic stem cells in vitro

Embryonic stem cells (ESCs) are a unique model that allows the study of molecular pathways underlying commitment and differentiation. One such lineage is osteoblasts, which are responsible for forming bone tissue in the body. There are many osteogenic differentiation protocols in the literature utilizing different soluble factors. The goal of the present study was to increase the efficacy of our osteogenic differentiation protocol from R1 cells. We have studied the effects of the addition of the following factors: dexamethasone, retinoic acid, and peroxisome-proliferator-activated receptor-gamma inhibitor, which have been reported to enhance osteogenesis. We found that among the 6 different protocols that were tested, the addition of retinoic acid with later addition of dexamethasone gives the most enrichment of osteogenic lineage cells. Thus, our findings provide valuable guidelines for culture condition to differentiate mouse R1 ESCs to osteoblastic cells in vitro.

Osteogenic Differentiation from Embryonic Stem Cells

Embryonic stem (ES) cells have been widely studied due to their pluripotency and their potential of self-renewal. Murine ES cells are useful in investigating the molecular pathways underlying their differentiation to various mature cell types in the body. This chapter describes the maintenance of murine ES cells in culture and a routine ES cell osteogenic differentiation protocol utilized in our laboratory.

Early exposure of murine embryonic stem cells to hematopoietic cytokines differentially directs definitive erythropoiesis and cardiomyogenesis in alginate hydrogel three-dimensional cultures

HepG2-conditioned medium (CM) facilitates early differentiation of murine embryonic stem cells (mESCs) into hematopoietic cells in two-dimensional cultures through formation of embryoid-like colonies (ELCs), bypassing embryoid body (EB) formation. We now demonstrate that three-dimensional (3D) cultures of alginate-encapsulated mESCs cultured in a rotating wall vessel bioreactor can be differentially driven toward definitive erythropoiesis and cardiomyogenesis in the absence of ELC formation. Three groups were evaluated: mESCs in maintenance medium with leukemia inhibitory factor (LIF, control) and mESCs cultured with HepG2 CM (CM1 and CM2). Control and CM1 groups were cultivated for 8 days in early differentiation medium with murine stem cell factor (mSCF) followed by 10 days in hematopoietic differentiation medium (HDM) containing human erythropoietin, m-interleukin (mIL)-3, and mSCF. CM2 cells were cultured for 18 days in HDM, bypassing early differentiation. In CM1, a fivefold expansion of hematopoietic colonies was observed at day 14, with enhancement of erythroid progenitors, hematopoietic genes (Gata-2 and SCL), erythroid genes (EKLF and β-major globin), and proteins (Gata-1 and β-globin), although ζ-globin was not expressed. In contrast, CM2 primarily produced beating colonies in standard hematopoietic colony assay and expressed early cardiomyogenic markers, anti-sarcomeric α-actinin and Gata-4. In conclusion, a scalable, automatable, integrated, 3D bioprocess for the differentiation of mESC toward definitive erythroblasts has been established. Interestingly, cardiomyogenesis was also directed in a specific protocol with HepG2 CM and hematopoietic cytokines making this platform a useful tool for the study of erythroid and cardiomyogenic development.

A novel perfused rotary bioreactor for cardiomyogenesis of embryonic stem cells

Developments in bioprocessing technology play an important role for overcoming challenges in cardiac tissue engineering. To this end, our laboratory has developed a novel rotary perfused bioreactor for supporting three-dimensional cardiac tissue engineering. The dynamic culture environments provided by our novel perfused rotary bioreactor and/or the high-aspect rotating vessel produced constructs with higher viability and significantly higher cell numbers (up to 4 × 10(5) cells/bead) than static tissue culture flasks. Furthermore, cells in the perfused rotary bioreactor showed earlier gene expressions of cardiac troponin-T, α- and β-myosin heavy chains with higher percentages of cardiac troponin-I-positive cells and better uniformity of sacromeric α-actinin expression. A dynamic and perfused environment, as provided by this bioreactor, provides a superior culture performance in cardiac differentiation for embryonic stem cells particularly for larger 3D constructs.

Stem cells for osteodegenerative diseases: current studies and future outlook

As the worldwide population grows and life expectancies continue to increase, degenerative diseases of the bones, muscles, and connective tissue are a growing problem for society. Current therapies for osteodegenerative disorders such as hormone replacement therapies, calcium/vitamin D supplements and oral bisphosphonates are often inadequate to stop degeneration and/or have serious negative side effects. Thus, there is an urgent need in the medical community for more effective and safer treatments. Stem cell therapies for osteodegenerative disorders have been rigorously explored over the last decade and are yielding some promising results in animal models and clinical trials. Although much work still needs to be done to ensure the safety and efficacy of these therapies, stem cells represent a new frontier of exciting possibilities for bone and cartilage regeneration.

Mesenchymal stem cell-conditioned medium enhances osteogenic and chondrogenic differentiation of human embryonic stem cells and human induced pluripotent stem cells by mesodermal lineage induction

Human mesenchymal stem cells (hMSCs) have the ability to differentiate into mesenchymal lineages. In this study, we hypothesized that treatment of embryoid bodies (EBs) composed of either human embryonic stem cells (hESCs) or human induced pluripotent stem cells (hiPSCs) with a hMSC-conditioned medium (CM) can stimulate the induction of the mesodermal lineage and subsequent differentiation toward the osteogenic and chondrogenic lineage. Quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR) analysis indicated that the hMSC-CM treatment increased gene expression related to the mesodermal lineage and decreased gene expression related to the endodermal and ectodermal lineage in EBs. Fourteen days after culturing the mesodermal lineage-induced EBs in the osteogenic or chondrogenic differentiation medium, we observed enhanced osteogenic and chondrogenic differentiation compared with untreated EBs, as evaluated using qRT-PCR, cytochemistry, immunocytochemistry, and flow cytometry. This method may be useful for enhancing the osteogenic or chondrogenic differentiation of hESCs or hiPSCs.

Generating cartilage repair from pluripotent stem cells

The treatment of degeneration and injury of articular cartilage has been very challenging for scientists and surgeons. As an avascular and hypocellular tissue, cartilage has a very limited capacity for self-repair. Chondrocytes are the only cell type in cartilage, in which they are surrounded by the extracellular matrix that they secrete and assemble. Autologous chondrocyte implantation for cartilage defects has achieved good results, but the limited resources and complexity of the procedure have hindered wider application. Stem cells form an alternative to chondrocytes as a source of chondrogenic cells due to their ability to proliferate extensively while retaining the potential for differentiation. Adult stem cells such as mesenchymal stem cells have been differentiated into chondrocytes, but the limitations in their proliferative ability and the heterogeneous cell population hinder their adoption as a prime alternative source for generating chondrocytes. Human embryonic stem cells (hESCs) are attractive as candidates for cell replacement therapy because of their unlimited self-renewal and ability for differentiation into mesodermal derivatives as well as other lineages. In this review, we focus on current protocols for chondrogenic differentiation of ESCs, in particular the chemically defined culture system developed in our lab that could potentially be adapted for clinical application.

Effects of shear stress on germ lineage specification of embryonic stem cells

Mechanobiology to date has focused on differentiated cells or progenitors, yet the effects of mechanical forces on early differentiation of pluripotent stem cells are still largely unknown. To study the effects of cellular deformation, we utilize a fluid flow bioreactor to apply steady laminar shear stress to mouse embryonic stem cells (ESCs) cultured on a two dimensional surface. Shear stress was found to affect pluripotency, as well as germ specification to the mesodermal, endodermal, and ectodermal lineages, as indicated by gene expression of OCT4, T-BRACHY, AFP, and NES, respectively. The ectodermal and mesodermal response to shear stress was dependent on stress magnitude (ranging from 1.5 to 15 dynes cm(-2)). Furthermore, increasing the duration from one to four days resulted in a sustained increase in T-BRACHY and a marked suppression of AFP. These changes in differentiation occurred concurrently with the activation of Wnt and estrogen pathways, as determined by PCR arrays for signalling molecules. Together these studies show that the mechanical microenvironment may be an important regulator during early differentiation events, including gastrulation. This insight furthers understanding of normal and pathological events during development, as well as facilitates strategies for scale up production of stem cells for clinical therapies.

Enhanced hematopoietic differentiation toward erythrocytes from murine embryonic stem cells with HepG2-conditioned medium

Embryonic stem cell (ESC) differentiation via embryoid body (EB) formation is an established method that generates the 3 germ layers. However, EB differentiation poses several problems including formation of heterogeneous cell populations. Previously, we have enhanced mesoderm derivation from murine ESCs (mESCs) using conditioned medium (CM) from HepG2 cells. We used this technique to direct hematopoiesis by generating "embryoid-like" colonies (ELCs) from mESCs without standard formation of EBs. Two predifferentiation conditions were tested: (1) mESCs cultured 3 days in standard predifferentiation medium (control) and (2) mESCs cultured 3 days in HepG2 CM (CM-mESCs). Both groups were then exposed to primary differentiation for 8 days (ELC-formation period) and 14 days of hematopoietic differentiation. Enhanced mesoderm formation was observed in the CM-mESC group with an almost 5-fold increase in ELC formation (P ≤ 0.05) and higher expression of mesoderm genes-Brachyury-T, Goosecoid, and Flk-1-compared with those of control mESCs. Hematopoietic colony formation by CM-mESCs was also enhanced by 2-fold at days 7 and 14 with earlier colony commitment compared with those of control mESCs (P ≤ 0.05). This early clonogenic capacity was confirmed morphologically by the presence of nucleated erythrocytes and macrophages as early as day 7 in CM-mESC culture using standard 14-day colony-forming assay. Early expression of hematopoietic primitive (ζ-globin) and definitive (β-globin) erythroid genes and proteins was also observed by day 7 in CM-mESC cultures. These data indicate that hematopoietic cells more quickly differentiate from CM-mESCs, compared with those using standard EB approaches, and provide an efficient bioprocess platform for erythroid-specific differentiation of ESCs.

Liver cell line derived conditioned medium enhances myofibril organization of primary rat cardiomyocytes

Cardiomyocytes are the fundamental cells of the heart and play an important role in engineering of tissue constructs for regenerative medicine and drug discovery. Therefore, the development of culture conditions that can be used to generate functional cardiomyocytes to form cardiac tissue may be of great interest. In this study, isolated neonatal rat cardiomyocytes were cultured with several culture conditions in vitro and characterized for cell proliferation, myofibril organization, and cardiac functionality by assessing cell morphology, immunocytochemical staining, and time-lapse confocal scanning microscopy. When cardiomyocytes were cultured in liver cell line derived conditioned medium without exogenous growth factors and cytokines, the cell proliferation increased, cell morphology was highly elongated, and subsequent myofibril organization was highly developed. These developed myofibril organization also showed high level of contractibility and synchronization, representing high functionality of cardiomyocytes. Interestingly, many of the known factors in hepatic conditioned medium, such as insulin-like growth factor II (IGFII), macrophage colony-stimulating factor (MCSF), leukemia inhibitory factor (LIF), did not show similar effects as the hepatic conditioned medium, suggesting the possibility of synergistic activity of the several soluble factors or the presence of unknown factors in hepatic conditioned medium. Finally, we demonstrated that our culture system could provide a potentially powerful tool for in vitro cardiac tissue organization and cardiac function study.

A simple and economical route to generate functional hepatocyte-like cells from hESCs and their application in evaluating alcohol induced liver damage

The in vitro derived hepatocytes from human embryonic stem cells (hESC) is a promising tool to acquire improved knowledge of the cellular and molecular events underlying early human liver development under physiological and pathological conditions. Here we report a simple two-step protocol employing conditioned medium (CM) from human hepatocellular carcinoma cell line, HepG2 to generate functional hepatocyte-like cells from hESC. Immunocytochemistry, flow cytometry, quantitative RT-PCR, and biochemical analyses revealed that the endodermal progenitors appeared as pockets in culture, and the cascade of genes associated with the formation of definitive endoderm (HNF-3β, SOX-17, DLX-5, CXCR4) was consistent and in concurrence with the up-regulation of the markers for hepatic progenitors [alpha-feto protein (AFP), HNF-4α, CK-19, albumin, alpha-1-antitrypsin (AAT)], followed by maturation into functional hepatocytes [tyrosine transferase (TAT), tryptophan-2, 3-dioxygenase (TDO), glucose 6-phosphate (G6P), CYP3A4, CYP7A1]. We witnessed that the gene expression profile during this differentiation process recapitulated in vivo liver development demonstrating a gradual down-regulation of extra embryonic endodermal markers (SOX-7, HNF-1β, SNAIL-1, LAMININ-1, CDX2), and the generated hepatic cells performed multiple liver functions. Since prenatal alcohol exposure is known to provoke irreversible abnormalities in the fetal cells and developing tissues, we exposed in vitro generated hepatocytes to ethanol (EtOH) and found that EtOH treatment not only impairs the survival and proliferation, but also induces apoptosis and perturbs differentiation of progenitor cells into hepatocytes. This disruption was accompanied by alterations in the expression of genes and proteins involved in hepatogenesis. Our results provide new insights into the wider range of destruction caused by alcohol on the dynamic process of liver organogenesis.

Osteoblast differentiation of murine embryonic stem cells as a model to study the embryotoxic effect of compounds

The embryonic stem cell test (ESTc), in which the effect of chemical compounds on cardiomyocyte differentiation is evaluated, is one of the most studied in vitro alternatives for developmental toxicity testing. Because the assay readout is restricted to a single endpoint of differentiation, compounds that affect alternative differentiation pathways might be overlooked. It has therefore been suggested that the predictive value of the EST may be improved by including alternative differentiation endpoints. The aim of the present study was to evaluate the effect of five teratogenic compounds as well as one non-teratogenic compound on the differentiation of murine embryonic stem cells into osteoblasts (ESTo) and to compare results with those in the classical ESTc. We established an ESTo assay which proved robust, stable and reproducible. In this study, we showed that the evaluated compounds affected osteoblast differentiation both at the level of calcium concentrations in the culture as well as on multiple gene expression. Furthermore, we showed that the effect on calcium concentrations appeared to be primarily mediated by a general apoptotic effect and not by a specific effect on differentiation. The compounds tested showed little difference in their potency in the ESTo as compared to the ESTc. Before a definitive statement can be made regarding the added value of including an osteoblast differentiation endpoint into the EST, more compounds need to be evaluated.

Osteoblastic/cementoblastic and neural differentiation of dental stem cells and their applications to tissue engineering and regenerative medicine

Recently, dental stem and progenitor cells have been harvested from periodontal tissues such as dental pulp, periodontal ligament, follicle, and papilla. These cells have received extensive attention in the field of tissue engineering and regenerative medicine due to their accessibility and multilineage differentiation capacity. These dental stem and progenitor cells are known to be derived from ectomesenchymal origin formed during tooth development. A great deal of research has been accomplished for directing osteoblastic/cementoblastic differentiation and neural differentiation from dental stem cells. To differentiate dental stem cells for use in tissue engineering and regenerative medicine, there needs to be efficient in vitro differentiation toward the osteoblastic/cementoblastic and neural lineage with well-defined and proficient protocols. This would reduce the likelihood of spontaneous differentiation into divergent lineages and increase the available cell source. This review focuses on the multilineage differentiation capacity, especially into osteoblastic/cementoblastic lineage and neural lineages, of dental stem cells such as dental pulp stem cells (DPSC), dental follicle stem cells (DFSC), periodontal ligament stem cells (PDLSC), and dental papilla stem cells (DPPSC). It also covers various experimental strategies that could be used to direct lineage-specific differentiation, and their potential applications in tissue engineering and regenerative medicine.

Large-scale production of murine embryonic stem cell-derived osteoblasts and chondrocytes on microcarriers in serum-free media

The generation of tissue-engineered constructs from stem cells for the treatment of musculoskeletal diseases may have immense impact in regenerative medicine, but there are difficulties associated with stem cell culture and differentiation, including the use of serum. Here we present serum-free protocols for the successful production of murine embryonic stem cell (mESC) derived osteoblasts and chondrocytes on CultiSpher S macroporous microcarriers in stirred suspension bioreactors. Various inoculum forms and agitation rates were investigated. Produced osteogenic cells were implanted ectopically into SCID mice and orthotopically into a murine burr-hole fracture model. Osterix, osteocalcin and collagen type I were upregulated in osteogenic cultures, while aggrecan and collagen type II were upregulated in chondrogenic cultures. Histological analysis using alizarin red S, von Kossa and alcian blue staining confirmed the presence of osteoblasts and chondrocytes, respectively in cultured microcarriers and excised tissue. Finally, implantation of derived cells into a mouse fracture model revealed cellular integration without any tumor formation. Overall, microcarriers may provide a supportive scaffold for ESC expansion and differentiation in a serum-free bioprocess for in vivo implantation. These findings lay the groundwork for the development of clinical therapies for musculoskeletal injuries and diseases using hESCs and iPS cells.

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.

Simvastatin induces osteogenic differentiation of murine embryonic stem cells

Statins are potent inhibitors of cholesterol synthesis. Several statins are available with different molecular and pharmacokinetic properties. Simvastatin is more lipophilic than pravastatin and has a higher affinity to phospholipid membranes than atorvastatin, allowing its passive diffusion through the cell membrane. In vitro studies on bone marrow stromal cells, osteoblast-like cells, and embryonic stem cells have shown statins to have cholesterol-independent anabolic effects on bone metabolism; alas, statins were supplemented in osteogenic medium, which does not facilitate elucidation of their potential osteoinductive properties. Embryonic stem cells (ESCs), derived from the inner cell mass of the blastocyst, are unique in that they enjoy perpetual self-proliferation, are pluripotent, and are able to differentiate toward all the cellular lineages composing the body, including the osteogenic lineage. Consequently, ESCs represent a potentially potent cell source for future clinical cellular therapies of various bone diseases, even though there are several hurdles that still need to be overcome. Herein we demonstrate, for the first time to our knowledge, that simvastatin induces murine ESC (mESC) differentiation toward the osteogenic lineage in the absence of osteoinductive supplements. Specifically, we found that a simvastatin concentration in the micromolar range and higher was toxic to the cells and that an effective concentration for osteoinduction is 0.1 nM, as shown by increased alizarin red staining as well as increased osteocalcin and osetrix gene expression. These results suggest that in the future, lipophilic simvastatin may provide a novel pharmacologic agent for bone tissue engineering applications.

Stem cells in bone tissue engineering

Bone tissue engineering has been one of the most promising areas of research, providing a potential clinical application to cure bone defects. Recently, various stem cells including embryonic stem cells (ESCs), bone marrow-derived mesenchymal stem cells (BM-MSCs), umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs), adipose tissue-derived stem cells (ADSCs), muscle-derived stem cells (MDSCs) and dental pulp stem cells (DPSCs) have received extensive attention in the field of bone tissue engineering due to their distinct biological capability to differentiate into osteogenic lineages. The application of these stem cells to bone tissue engineering requires inducing in vitro differentiation of these cells into bone forming cells, osteoblasts. For this purpose, efficient in vitro differentiation towards osteogenic lineage requires the development of well-defined and proficient protocols. This would reduce the likelihood of spontaneous differentiation into divergent lineages and increase the available cell source for application to bone tissue engineering therapies. This review provides a critical examination of the various experimental strategies that could be used to direct the differentiation of ESC, BM-MSC, UCB-MSC, ADSC, MDSC and DPSC towards osteogenic lineages and their potential applications in tissue engineering, particularly in the regeneration of bone.

Transwells with microstamped membranes produce micropatterned two-dimensional and three-dimensional co-cultures

This article describes a simple and rapid cell patterning method to form co-culture microarrays in commercially available Transwells. A thin poly(dimethylsiloxane) (PDMS) layer is printed on the underside of a Transwell using a PDMS stamp. Arbitrary cellular patterns are generated according to the geometric features of the thin PDMS layer through hydrodynamic forces that guide cells onto the membrane only over the PDMS-uncoated regions. Micropatterns of surface-adhered cells (we refer to this as two-dimensional) or non-surface-adhered clusters of cells (we refer to this as three-dimensional) can be generated depending on the surface treatment of the filter membrane. Additionally, co-cultures can be established by introducing different types of cells on the membrane or in the bottom chamber of the Transwell. We show that this co-culture method can evaluate mouse embryonic stem (mES) cell differentiation based on heterogeneous cell-cell interactions. Co-culture of mES cells and HepG2 cells decreased SOX17 expression of mES cells, and direct cell-cell contact further decreased SOX17 expression, indicating that co-culture with HepG2 cells inhibits endoderm differentiation through soluble factors and cell-cell contact. This method is simple and user-friendly and should be broadly useful to study cell shapes and cell-cell interactions.

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.

Differentiation of mouse embryonic stem cells into dental epithelial-like cells induced by ameloblasts serum-free conditioned medium

Embryonic stem cells (ESCs) possess an intrinsic self-renewal ability and can differentiate into numerous types of functional tissue cells; however, whether ESCs can differentiate toward the odontogenic lineage is still unknown. In this study, we developed an efficient culture strategy to induce the differentiation of murine ESCs (mESCs) into dental epithelial cells. By culturing mESCs in ameloblasts serum-free conditioned medium (ASF-CM), we could induce their differentiation toward dental epithelial cell lineages; however, similar experiments with the tooth germ cell-conditioned medium (TGC-CM) did not yield effective results. After culturing the cells for 14days in the differentiation-inducing media, the expression of ameloblast-specific proteins such as cytokeratin (CK)14, ameloblastin (AMBN), and amelogenin (AMGN) was markedly higher in mESCs obtained with embryoid body (EB) formation than in mESCs obtained without EB formation. We observed that immunocompromised mice implanted with induced murine EBs (mEBs) showed tissue regenerative capacity and produced odontogenic epithelial-like structures, whereas those implanted with mSCE monolayer cells mainly formed connective tissues. Thus, for the first time, we report that ASF-CM provides a suitable microenvironment for inducing mESC differentiation along the odontogenic epithelial cell lineage. This result has important implications for tooth tissue engineering.

Cell interactions in bone tissue engineering

Bone fractures, where the innate regenerative bone response is compromised, represent between 4 and 8 hundred thousands of the total fracture cases, just in the United States. Bone tissue engineering (TE) brought the notion that, in cases such as those, it was preferable to boost the healing process of bone tissue instead of just adding artificial parts that could never properly replace the native tissue. However, despite the hype, bone TE so far could not live up to its promises and new bottom-up approaches are needed. The study of the cellular interactions between the cells relevant for bone biology can be of essential importance to that. In living bone, cells are in a context where communication with adjacent cells is almost permanent. Many fundamental works have been addressing these communications nonetheless, in a bone TE approach, the 3D perspective, being part of the microenvironment of a bone cell, is as crucial. Works combining the study of cell-to-cell interactions in a 3D environment are not as many as expected. Therefore, the bone TE field should not only gain knowledge from the field of fundamental Biology but also contribute for further understanding the biology of bone. In this review, a summary of the main works in the field of bone TE, aiming at studying cellular interactions in a 3D environment, and how they contributed towards the development of a functional engineered bone tissue, is presented.

Engineering the embryoid body microenvironment to direct embryonic stem cell differentiation

Embryonic stem cells (ESCs) are pluripotent cells capable of differentiating into all somatic and germ cell types. The intrinsic ability of pluripotent cells to generate a vast array of different cells makes ESCs a robust resource for a variety of cell transplantation and tissue engineering applications, however, efficient and controlled means of directing ESC differentiation is essential for the development of regenerative therapies. ESCs are commonly differentiated in vitro by spontaneously self-assembling in suspension culture into 3D cell aggregates called embryoid bodies (EBs), which mimic many of the hallmarks of early embryonic development, yet the 3D organization and structure of EBs also presents unique challenges to effectively direct the differentiation of the cells. ESC differentiation is strongly influenced by physical and chemical signals comprising the local extracellular microenvironment, thus current methods to engineer EB differentiation have focused primarily on spatially controlling EB size, adding soluble factors to the media, or culturing EBs on or within natural or synthetic extracellular matrices. Although most such strategies aim to influence differentiation from the exterior of EBs, engineering the microenvironment directly within EBs enables new opportunities to efficiently direct the fate of the cells by locally controlling the presentation of morphogenic cues.

The influence of three-dimensional nanofibrous scaffolds on the osteogenic differentiation of embryonic stem cells

Embryonic stem cells represent a potentially unlimited cell source for tissue engineering applications. However, in order to be used for such applications, embryonic stem cells' differentiation must be controlled to only the desired lineages. In this study, we examine the effects of nanofibrous architecture and biochemical cues on the osteogenic differentiation of embryonic stem cells compared to the more traditional architecture without the nanofibrous features in two dimensions (thin matrix or flat films) and three dimensions (scaffolds) in vitro. After three weeks of culture the nanofibrous thin matrices were capable of supporting mRNA expression of osteogenic differentiation markers in embryonic stem cells without osteogenic supplements, while solid films required osteogenic supplements and growth factors to achieve mRNA expression of osteogenic differentiation markers. Nanofibrous scaffolds substantially enhanced mRNA expression of osteogenic differentiation markers compared to solid-walled scaffolds, nanofibrous thin matrices or solid films. After 4 weeks of culture, nanofibrous scaffolds were found to contain 3 times more calcium and stronger osteocalcin stain throughout the scaffolds than the solid-walled scaffolds. Overall, the nanofibrous architecture enhanced the osteogenic differentiation and mineralization of embryonic stem cells compared to the solid-walled architecture in both two and three-dimensional cultures.

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.

Enhanced chondrogenic differentiation of embryonic stem cells by coculture with hepatic cells

Enhancing the specific differentiation of pluripotent embryonic stem (ES) cells has been a challenge in the field of tissue engineering. Previously, hepatic cells have been shown to secrete various soluble morphogenic factors to direct mesodermal differentiation of ES cells. In this study, we hypothesized that factors secreted by hepatic cells possess chondrogenic-differentiating effects, and, therefore, the co-culture of hepatic cells would enhance chondrogenesis of ES cells. ES-derived cells(ESDCs) were co-cultured with hepatic cells (HEPA-1C1c7) in three-dimensional bilayered hydrogels. After 3 weeks culture, the histological and biochemical analysis of the HEPA-co-cultured ESDCs revealed a four-fold increase in glycosaminoglycan (GAG) compared to ESDCs cultured alone. This result was supported by real-time PCR analysis, which demonstrated an 80-fold increase in aggrecan expression in co-cultured ESDCs. Additionally, type IIB collagen expression was observed only with co-cultured ESDCs, and immunohistochemical analysis resulted in significantly more positive type II collagen staining with co-cultured ESDCs. Moreover, at day 21, gene expression of other lineages in HEPA-co-cultured ESDCs was either comparable to or lower than those of ESDCs cultured alone. These results indicated that co-culture of ESDCs with hepatic cells significantly enhanced specific chondrogenic differentiation of ESDCs.

Chemically defined medium supporting cardiomyocyte differentiation of human embryonic stem cells

Many applications of human embryonic stem cells (hESCs) will require fully defined growth and differentiation conditions including media devoid of fetal calf serum. To identify factors that control lineage differentiation we have analyzed a serum-free (SF) medium conditioned by the cell line END2, which efficiently induces hESCs to form cardiomyocytes. Firstly, we noted that insulin, a commonly used medium supplement, acted as a potent inhibitor of cardiomyogenesis in multiple hESC lines and was rapidly cleared by medium conditioning. In the presence of insulin or IGF-1, which also suppressed cardiomyocyte differentiation, the PI3/Akt pathway was activated in undifferentiated hESC, suggesting that insulin/IGF-1 effects were mediated by this signaling cascade. Time course analysis and quantitative RT-PCR revealed impaired expression of endoderm and mesoderm markers in the presence of insulin, particularly if added during early stages of hESC differentiation. Relatively high levels of the neural ectoderm marker Sox1 were expressed under these conditions. Secondly, comparative gene expression showed that two key enzymes in the prostaglandin I2 (PGI2) synthesis pathway were highly up-regulated in END2 cells compared with a related, but non-cardiogenic, cell line. Biochemical analysis confirmed 6-10-fold higher PGI2 levels in END2 cell-conditioned medium (END2-CM) vs. controls. Optimized concentrations of PGI2 in a fully synthetic, insulin-free medium resulted in a cardiogenic activity equivalent to END2-CM. Addition of the p38 mitogen-activated protein kinase-inhibitor SB203580, which we have shown previously to enhance hESC cardiomyogenesis, to these insulin-free and serum-free conditions resulted in a cardiomyocyte content of >10% in differentiated cultures without any preselection. This study represents a significant step toward developing scalable production for cardiomyocytes from hESC using clinically compliant reagents compatible with Good Manufacturing Practice.

Integrated 3-dimensional expansion and osteogenic differentiation of murine embryonic stem cells

Embryonic stem cell (ESC) culture is fragmented and laborious and involves operator decisions. Most protocols consist of 3 individual steps: maintenance, embryoid body (EB) formation, and differentiation. Integration will assist automation, ultimately aiding scale-up to clinically relevant numbers. These problems were addressed by encapsulating undifferentiated murine ESCs (mESCs) in 1.1% (w/v) low-viscosity alginic acid, 0.1% (v/v) porcine gelatin hydrogel beads (d = 2.3 mm). Six hundred beads containing 10,000 mESCs per bead were cultured in a 50-mL high-aspect-ratio vessel bioreactor. Bioreactor cultures were rotated at 17.5 revolutions per min, cultured in maintenance medium containing leukemia inhibitory factor for 3 days, replaced with EB formation medium for 5 days followed by osteogenic medium containing L-ascorbate-2-phosphate (50 microg/mL), beta-glycerophosphate (10 mM), and dexamethasone (1 microM) for an additional 21 days. After 29 days, 84 times as many cells per bead were observed and mineralized matrix was formed within the alginate beads. Osteogenesis was confirmed using von Kossa, Alizarin Red S staining, alkaline phosphatase activity, immunocytochemistry for osteocalcin, OB-cadherin, collagen type I, reverse transcriptase polymerase chain reaction, microcomputed tomography (micro-computed tomography) and Fourier transform infrared spectroscopic imaging. This simplified, integrated, and potentially scaleable methodology could enable the production of 3-demensional mineralized tissue from ESCs for potential clinical applications.

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.

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.