Efficient adipocyte and osteoblast differentiation from mouse induced pluripotent stem cells by adenoviral transduction

Expression of coxsackievirus and adenovirus receptor separates hematopoietic and cardiac progenitor cells in fetal liver kinase 1-expressing mesoderm

In developing embryos or in vitro differentiation cultures using pluripotent stem cells (PSCs), such as embryonic stem cells and induced pluripotent stem cells, fetal liver kinase 1 (Flk1)-expressing mesodermal cells are thought to be a heterogeneous population that includes hematopoietic progenitors, endothelial progenitors, and cardiac progenitors. However, information on cell surface markers for separating these progenitors in Flk1⁺ cells is currently limited. In the present study, we show that distinct types of progenitor cells in Flk1⁺ cells could be separated according to the expression of coxsackievirus and adenovirus receptor (CAR, also known as CXADR), a tight junction component molecule. We found that mouse and human PSC- and mouse embryo-derived Flk1⁺ cells could be subdivided into Flk1⁺CAR⁺ cells and Flk1⁺CAR⁻ cells. The progenitor cells with cardiac potential were almost entirely restricted to Flk1⁺CAR⁺ cells, and Flk1⁺CAR⁻ cells efficiently differentiated into hematopoietic cells. Endothelial differentiation potential was observed in both populations. Furthermore, from the expression of CAR, Flk1, and platelet-derived growth factor receptor-α (PDGFRα), Flk1⁺ cells could be separated into three populations (Flk1⁺PDGFRα⁻ CAR⁻ cells, Flk1⁺PDGFRα⁻CAR⁺ cells, and Flk1⁺PDGFRα⁺CAR⁺ cells). Flk1⁺PDGFRα⁺ cells and Flk1⁺PDGFRα⁻ cells have been reported as cardiac and hematopoietic progenitor cells, respectively. We identified a novel population (Flk1⁺PDGFRα⁻ CAR⁺ cells) with the potential to differentiate into not only hematopoietic cells and endothelial cells but also cardiomyocytes. Our findings indicate that CAR would be a novel and prominent marker for separating PSC- and embryo-derived Flk1⁺ mesodermal cells with distinct differentiation potentials.

Improvement of In Vitro Osteogenic Potential through Differentiation of Induced Pluripotent Stem Cells from Human Exfoliated Dental Tissue towards Mesenchymal-Like Stem Cells

Constraints for the application of MSCs for bone reconstruction include restricted self-renewal and limited cell amounts. iPSC technology presents advantages over MSCs, providing homogeneous cellular populations with prolonged self-renewal and higher plasticity. However, it is unknown if the osteogenic potential of iPSCs differs from that of MSCs and if it depends on the iPSCs originating cellular source. Here, we compared the in vitro osteogenesis between stem cells from human deciduous teeth (SHED) and MSC-like cells from iPSCs from SHED (iPS-SHED) and from human dermal fibroblasts (iPS-FIB). MSC-like cells from iPS-SHED and iPS-FIB displayed fibroblast-like morphology, downregulation of pluripotency markers and upregulation of mesenchymal markers. Comparative in vitro osteogenesis analysis showed higher osteogenic potential in MSC-like cells from iPS-SHED followed by MSC-like cells from iPS-FIB and SHED. CD105 expression, reported to be inversely correlated with osteogenic potential in MSCs, did not display this pattern, considering that SHED presented lower CD105 expression. Higher osteogenic potential of MSC-like cells from iPS-SHED may be due to cellular homogeneity and/or to donor tissue epigenetic memory. Our findings strengthen the rationale for the use of iPSCs in bone bioengineering. Unveiling the molecular basis behind these differences is important for a thorough use of iPSCs in clinical scenarios.

A novel strategy for enrichment and isolation of osteoprogenitor cells from induced pluripotent stem cells based on surface marker combination

In this study, we developed a new method to stimulate osteogenic differentiation in tissue-nonspecific alkaline phosphatase (TNAP)-positive cells liberated from human induced pluripotent stem cells (hiPSCs)-derived embryoid bodies (EBs) with 14 days long TGF-β/IGF-1/FGF-2 treatment. TNAP is a marker protein of osteolineage cells. We analyzed and isolated TNAP-positive and E-cadherin-negative nonepithelial cells by fluorescence-activated cell sorting. Treating the cells with a combination of transforming growth factor (TGF)-β, insulin-like growth factor (IGF)-1, and fibroblast growth factor (FGF)-2 for 14 days greatly enhanced TNAP expression and maximized expression frequency up to 77.3%. The isolated cells expressed high levels of osterix, which is an exclusive osteogenic marker. Culturing these TNAP-positive cells in osteoblast differentiation medium (OBM) led to the expression of runt-related transcription factor 2, type I collagen, bone sialoprotein, and osteocalcin (OCN). These cells responded to treatment with activated vitamin D3 by upregulating OCN. Furthermore, in OBM they were capable of generating many mineralized nodules with strong expression of receptor activator of NF-kappaB ligand and sclerostin (SOST). Real-time RT-PCR showed a significant increase in the expression of osteocyte marker genes, including SOST, neuropeptide Y, and reelin. Scanning electron microscopy showed dendritic morphology. Examination of semi-thin toluidine blue-stained sections showed many interconnected dendrites. Thus, TNAP-positive cells cultured in OBM may eventually become terminally differentiated osteocyte-like cells. In conclusion, treating hiPSCs-derived cells with a combination of TGF-β, IGF-1, and FGF-2 generated TNAP-positive cells at high frequency. These TNAP-positive cells had a high osteogenic potential and could terminally differentiate into osteocyte-like cells. The method described here may reveal new pathways of osteogenesis and provide a novel tool for regenerative medicine and drug development.

Comparative analysis of mouse-induced pluripotent stem cells and mesenchymal stem cells during osteogenic differentiation in vitro

Induced pluripotent stem cells (iPSCs) can differentiate into mineralizing cells and are, therefore, expected to be useful for bone regenerative medicine; however, the characteristics of iPSC-derived osteogenic cells remain unclear. Here, we provide a direct in vitro comparison of the osteogenic differentiation process in mesenchymal stem cells (MSCs) and iPSCs from adult C57BL/6J mice. After 30 days of culture in osteogenic medium, both MSCs and iPSCs produced robustly mineralized bone nodules that contained abundant calcium phosphate with hydroxyapatite crystal formation. Mineral deposition was significantly higher in iPSC cultures than in MSC cultures. Scanning electron microscopy revealed budding matrix vesicles in early osteogenic iPSCs; subsequently, the vesicles propagated to exhibit robust mineralization without rich fibrous structures. Early osteogenic MSCs showed deposition of many matrix vesicles in abundant collagen fibrils that became solid mineralized structures. Both cell types demonstrated increased expression of osteogenic marker genes, such as runx2, osterix, dlx5, bone sialoprotein (BSP), and osteocalcin, during osteogenesis; however, real-time reverse transcription-polymerase chain reaction array analysis revealed that osteogenesis-related genes encoding mineralization-associated molecules, bone morphogenetic proteins, and extracellular matrix collagens were differentially expressed between iPSCs and MSCs. These data suggest that iPSCs are capable of differentiation into mature osteoblasts whose associated hydroxyapatite has a crystal structure similar to that of MSC-associated hydroxyapatite; however, the transcriptional differences between iPSCs and MSCs could result in differences in the mineral and matrix environments of the bone nodules. Determining the biological mechanisms underlying cell-specific differences in mineralization during in vitro iPSC osteogenesis may facilitate the development of clinically effective engineered bone.

Crucial transcription factors in tendon development and differentiation: their potential for tendon regeneration

Tendons that connect muscles to bone are often the targets of sports injuries. The currently unsatisfactory state of tendon repair is largely attributable to the limited understanding of basic tendon biology. A number of tendon lineage-related transcription factors have recently been uncovered and provide clues for the better understanding of tendon development. Scleraxis and Mohawk have been identified as critical transcription factors in tendon development and differentiation. Other transcription factors, such as Sox9 and Egr1/2, have also been recently reported to be involved in tendon development. However, the molecular mechanisms and application of these transcription factors remain largely unclear and this prohibits their use in tendon therapy. Here, we systematically review and analyze recent findings and our own data concerning tendon transcription factors and tendon regeneration. Based on these findings, we provide interaction and temporal programming maps of transcription factors, as a basis for future tendon therapy. Finally, we discuss future directions for tendon regeneration with differentiation and trans-differentiation approaches based on transcription factors.

In vitro epithelial differentiation of human induced pluripotent stem cells for vocal fold tissue engineering

OBJECTIVES

We determined the feasibility and optimization of differentiating human induced pluripotent stem cells (hiPS) into nonkeratinized stratified squamous epithelial cells for vocal fold engineering.

METHODS

hiPS were cultured and assessed for differentiation in 3 conditions: a 3-dimensional (3D) hyaluronic acid (HA) hydrogel scaffold, a 3D HA hydrogel scaffold with epidermal growth factor (EGF), and a 3D HA hydrogel scaffold cocultured with human vocal fold fibroblasts (hVFF). After 1, 2, and 4 weeks of cultivation, hiPS were selected for histology, immunohistochemistry, and/or transcript expression analysis.

RESULTS

At 4 weeks, hiPS cultivated with hVFF or with EGF had significantly decreased levels of Oct 3/4, indicating loss of pluripotency. Immunofluorescence revealed the presence of pancytokeratin and of cytokeratin (CK) 13 and 14 epithelial-associated proteins at 4 weeks after cultivation in hiPS EGF and hiPS hVFF cultures. The transcript expression level of CK14 was significantly increased for hiPS hVFF cultures only and was measured concomitantly with cell morphology that was clearly cohesive and displayed a degree of nuclear polarity suggestive of epithelial differentiation.

CONCLUSIONS

We found that hiPS cultivated in 3D HA hydrogel with hVFF demonstrated the most robust conversion evidence to date of epithelial differentiation. Further work is necessary to focus on amplification of these progenitors for application in vocal fold regenerative biology.

In vitro chondrogenesis and in vivo repair of osteochondral defect with human induced pluripotent stem cells

The purpose of this study was to investigate the chondrogenic features of human induced pluripotent stem cells (hiPSCs) and examine the differences in the chondrogenesis between hiPSCs and human bone marrow-derived MSCs (hBMMSCs). Embryoid bodies (EBs) were formed from undifferentiated hiPSCs. After EBs were dissociated into single cells, chondrogenic culture was performed in pellets and alginate hydrogel. Chondro-induced hiPSCs were implanted in osteochondral defects created on the patellar groove of immunosuppressed rats and evaluated after 12 weeks. The ESC markers NANOG, SSEA4 and OCT3/4 disappeared while the mesodermal marker BMP-4 appeared in chondro-induced hiPSCs. After 21 days of culture, greater glycosaminoglycan contents and better chondrocytic features including lacuna and abundant matrix formation were observed from chondro-induced hiPSCs compared to chondro-induced hBMMSCs. The expression of chondrogenic markers including SOX-9, type II collagen, and aggrecan in chondro-induced hiPSCs was comparable to or greater than chondro-induced hBMMSCs. A remarkably low level of hypertrophic and osteogenic markers including type X collagen, type I collagen and Runx-2 was noted in chondro-induced hiPSCs compared to chondro-induced hBMMSCs. hiPSCs had significantly greater methylation of several CpG sites in COL10A1 promoter than hBMMSCs in either undifferentiated or chondro-induced state, suggesting an epigenetic cause of the difference in hypertrophy. The defects implanted with chondro-induced hiPSCs showed a significantly better quality of cartilage repair than the control defects, and the majority of cells in the regenerated cartilage consisted of implanted hiPSCs.

Human induced pluripotent stem cell-derived mesenchymal stem cell seeding on calcium phosphate scaffold for bone regeneration

Tissue engineering provides an important approach for bone regeneration. Calcium phosphate cement (CPC) can be injected to fill complex-shaped bone defects with excellent osteoconductivity. Induced pluripotent stem cells (iPSCs) are exciting for regenerative medicine due to their potential to proliferate and differentiate into cells of all three germ layers. To date, there has been no report on iPSC seeding with CPC scaffolds. The objectives of this study were to (1) obtain iPSC-derived mesenchymal stem cells (iPSC-MSCs); (2) seed iPSC-MSCs on CPC scaffold for the first time to investigate cell attachment and proliferation; and (3) investigate osteogenic differentiation of iPSC-MSCs on CPC and mineral synthesis by the cells. iPSCs were derived from adult marrow CD34+ cells that were reprogrammed by a single episomal vector pEB-C5. iPSCs were cultured to form embryoid bodies (EBs), and MSCs were migrated out of EBs. Flow cytometry indicated that iPSC-MSCs expressed typical surface antigen profile of MSCs. Mesenchymal differentiation of iPSC-MSCs demonstrated that the iPSC-MSCs had the potential to differentiate into adipocytes, chondrocytes, and osteoblasts. iPSC-MSCs had good viability when attached on CPC scaffold. iPSC-MSCs differentiated into the osteogenic lineage and synthesized bone minerals. iPSC-MSCs on CPC in osteogenic medium yielded higher gene expressions of osteogenic markers including alkaline phosphatase (ALP), osteocalcin, collagen type I, and Runt-related transcription factor 2 than those in control medium (p<0.05). iPSC-MSCs on CPC in osteogenic medium had 10-fold increase in ALP protein than that in control medium (p<0.05). Bone mineral synthesis by iPSC-MSCs adherent to CPC scaffold was increased with time, and mineralization in osteogenic medium was three to four fold that in control medium. In conclusion, iPSCs were derived from adult marrow CD34+ cells that were reprogrammed by a single episomal vector pEB-C5, and MSCs were generated from the EBs. iPSC-MSCs showed good viability and osteogenic differentiation on CPC scaffold for the first time; hence, the novel iPSC-MSC-CPC construct is promising to promote bone regeneration in dental, craniofacial, and orthopedic repairs.

Induced pluripotent stem cell-derived mesenchymal stem cell seeding on biofunctionalized calcium phosphate cements

Induced pluripotent stem cells (iPSCs) have great potential due to their proliferation and differentiation capability. The objectives of this study were to generate iPSC-derived mesenchymal stem cells (iPSC-MSCs), and investigate iPSC-MSC proliferati on and osteogenic differentiation on calcium phosphate cement (CPC) containing biofunctional agents for the first time. Human iPSCs were derived from marrow CD34+ cells which were reprogrammed by a single episomal vector. iPSCs were cultured to form embryoid bodies (EBs), and MSCs migrated out of EBs. Five biofunctional agents were incorporated into CPC: RGD (Arg-Gly-Asp) peptides, fibronectin (Fn), fibronectin-like engineered polymer protein (FEPP), extracellular matrix Geltrex, and platelet concentrate. iPSC-MSCs were seeded on five biofunctionalized CPCs: CPC-RGD, CPC-Fn, CPC-FEPP, CPC-Geltrex, and CPC-Platelets. iPSC-MSCs on biofunctional CPCs had enhanced proliferation, actin fiber expression, osteogenic differentiation and mineralization, compared to control. Cell proliferation was greatly increased on biofunctional CPCs. iPSC-MSCs underwent osteogenic differentiation with increased alkaline phosphatase, Runx2 and collagen-I expressions. Mineral synthesis by iPSC-MSCs on CPC-Platelets was 3-fold that of CPC control. In conclusion, iPSCs showed high potential for bone engineering. iPSC-MSCs on biofunctionalized CPCs had cell proliferation and bone mineralization that were much better than traditional CPC. iPSC-MSC-CPC constructs are promising to promote bone regeneration in craniofacial/orthopedic repairs.

The application of induced pluripotent stem cells for bone regeneration: current progress and prospects

Loss of healthy bone tissue and dysosteogenesis are still common and significant problems in clinics. Cell-based therapy using mesenchymal stem cells (MSCs) has been performed in patients for quite some time, but the inherent drawbacks of these cells, such as the reductions in proliferation rate and osteogenic differentiation potential that occur with aging, greatly limit their further application. Moreover, embryonic stem cells (ESCs) have brought new hope to osteoregenerative medicine because of their full pluripotent differentiation potential and excellent performance in bone regeneration. However, the ethical issues involved in destroying human embryos and the immune reactions that occur after transplantation are two major stumbling blocks impeding the clinical application of ESCs. Instead, induced pluripotent stem cells (iPSCs), which are ESC-like pluripotent cells that are reprogrammed from adult somatic cells using defined transcription factors, are considered a more promising source of cells for regenerative medicine because they present no ethical or immunological issues. Here, we summarize the primary technologies for generating iPSCs and the biological properties of these cells, review the current advances in iPSC-based bone regeneration and, finally, discuss the remaining challenges associated with these cells, particularly safety issues and their potential application for osteoregenerative medicine.

Multi-lineage potential research of bone marrow-derived stromal cells (BMSCs) from cattle

Bovine bone marrow-derived mesenchymal stem cells (bBMSCs) were isolated from the bone marrow of a 4-6-month-old fetal bovine and then characterized by immunofluorescence and reverse transcriptase polymerase chain reaction. We found that primary bBMSCs could be expanded for 46 passages; the total culture time in vitro was 125 days. The results of surface antigen detection showed that bBMSCs expressed CD29, CD44, and CD73 but did not express endothelial cells and hematopoietic cells-specific marker CD31, CD34, and CD45. The cells from four passages (passages 3, 9, 15, and 25) were successfully induced to differentiate into osteoblasts, adipocytes, hepatic, and islet-like cells. The results indicate the potential for multi-lineage differentiation of bBMSCs that may represent an ideal candidate for cellular transplantation therapy.

A phenotypic comparison of osteoblast cell lines versus human primary osteoblasts for biomaterials testing

Immortalized cell lines are used more frequently in basic and applied biology research than primary bone-derived cells because of their ease of access and repeatability of results in experiments. It is clear that these cell models do not fully resemble the behavior of primary osteoblast cells. Although the differences will affect the results of biomaterials testing, they are not clearly defined. Here, we focused on comparing proliferation and maturation potential of three osteoblast cell lines, SaOs2, MG-63, and MC3T3-E1 with primary human osteoblast (HOb) cells to assess their suitability as in vitro models for biomaterials testing. We report similarities in cell proliferation and mineralization between primary cells and MC3T3-E1. Both, SaOs2 and MG-63 cells demonstrated a higher proliferation rate than HOb cells. In addition, SaOs2, but not MG-63, cells demonstrated similar ALP activity, mineralization potential and gene regulation to HOb's. Our results demonstrate that despite SaOs-2, MG63, and MC3T3 cells being popular choices for emulating osteoblast behavior, none can be considered appropriate replacements for HOb's. Nevertheless, these cell lines all demonstrated some distinct similarities with HOb's, thus when applied in the correct context are a valuable in vitro pilot model of osteoblast functionality, but should not be used to replace primary cell studies.

Transplantation of osteogenically differentiated mouse iPS cells for bone repair

Induced pluripotent stem (iPS) cells are a type of undifferentiated cell that can be obtained from differentiated cells and have the pluripotent potential to differentiate into the musculoskeletal system, the myocardium, vascular endothelial cells, neurons, and hepatocytes. We therefore cultured mouse iPS cells in a DMEM containing 15% FBS, 10(-7) M dexamethasone, 10 mM β-glycerophosphate, and 50 μg/ml ascorbic acid for 3 weeks, in order to induce bone differentiation, and studied the expression of the bone differentiation markers Runx2 and osteocalcin using RT-PCR in a time-dependent manner. Osteocalcin, a bone differentiation marker in bone formation, exhibited the highest expression in the third week. In addition, the deposition of calcium nodules was observed using Alizarin red S staining. iPS cells cultured for bone differentiation were transplanted into severe combined immunodeficiency (SCID) mice, and the osteogenic potential exhibited after 4 weeks was studied. When bone differentiation-induced iPS cells were transplanted into SCID mice, bone formation was confirmed in soft X-ray images and tissue specimens. However, teratoma formation was confirmed in 20% of the transplanted models. When mouse iPS cells were treated with irradiation of 2 Gray (Gy) prior to transplantation, teratoma formation was inhibited. When mouse iPS cells treated in a likewise manner were xenotransplanted into rats, bone formation was confirmed but teratoma formation was not observed. It is believed that irradiation before transplantation is an effective way to inhibit teratoma formation.

Chondrogenic differentiation in vitro of murine two-factor induced pluripotent stem cells is comparable to murine embryonic stem cells

Differentiation of embryonic stem (ES) cells via embryoid bodies has been established as an appropriate model to study the development of various cell types in vitro. Here, we show that murine induced pluripotent stem (iPS) cells, reprogrammed by exogenous expression of the two transcription factors Oct4 and Klf4 (2F OK iPS), differentiate into chondrocytes in vitro characterized by the appearance of Alcian blue-stained nodules and the expression of cartilage-associated genes and proteins. Quantitatively, the chondrogenic differentiation potential of 2F OK iPS and ES cells was found to be similar. Further, we demonstrate the induction of chondrogenic iPS cell differentiation by certain members of the transforming growth factor-β family (BMP-2, TGF-β(1)). The number of Alcian blue-positive nodules and the expression of the cartilage marker molecule collagen type II increased after application of BMP-2, whereas simultaneous treatment with both BMP-2 and TGF-β(1) showed no significant effect on gene expression.

Defective antiviral responses of induced pluripotent stem cells to baculoviral vector transduction

Genetic engineering of induced pluripotent stem cells (iPSCs) is important for their clinical applications, and baculovirus (BV) holds promise as a gene delivery vector. To explore the feasibility of using BV for iPSCs transduction, in this study we first examined how iPSCs responded to BV. We determined that BV transduced iPSCs efficiently, without inducing appreciable negative effects on cell proliferation, apoptosis, pluripotency, and differentiation. BV transduction slightly perturbed the transcription of 12 genes involved in the Toll-like receptor (TLR) signaling pathway, but at the protein level BV elicited no well-known cytokines (e.g., interleukin-6 [IL-6], tumor necrosis factor alpha [TNF-α], and beta interferon [IFN-β]) except for IP-10. Molecular analyses revealed that iPSCs expressed no TLR1, -6, -8, or -9 and expressed merely low levels of TLR2, -3, and -4. In spite of evident expression of such RNA/DNA sensors as RIG-I and AIM2, iPSCs barely expressed MDA5 and DAI (DNA-dependent activator of IFN regulatory factor [IRF]). Importantly, BV transduction of iPSCs stimulated none of the aforementioned sensors or their downstream signaling mediators (IRF3 and NF-κB). These data together confirmed that iPSCs responded poorly to BV due to the impaired sensing and signaling system, thereby justifying the transduction of iPSCs with the baculoviral vector.

Comparative study of transplantation of hepatocytes at various differentiation stages into mice with lethal liver damage

Hepatocyte transplantation utilizing induced pluripotent stem cells (iPSCs) or embryonic stem cells (ESCs) has been expected to provide an alternative to liver transplantation. However, it remains uncertain precisely which cell type is the best suited for cell transplantation. In particular, it is unclear whether mature hepatocytes, which have sufficient liver function, or immature hepatic progenitor cells, which have a higher proliferative capacity, will provide a better outcome. The main objective of this study was to investigate the therapeutic efficacy of the transplantation of hepatocytes at various differentiation stages. We utilized transgenic mice that expressed diphtheria toxin (DT) receptors under the control of an albumin enhancer/promoter. ESC-derived endodermal cells, fetal hepatocytes, and adult hepatocytes were transplanted into these mice with experimentally induced lethal acute liver injury caused by DT administration. The transplanted cells were marked by enhanced green fluorescent protein. We evaluated their effects on survival. At 35 days after transplantation, the survival rate of the adult hepatocyte-transplanted group (8/20, 40%) was significantly improved in comparison to that of the sham-operated group (2/25, 8%), the fetal hepatocyte-transplanted group (1/20, 5%), and the ESC-derived endodermal cell-transplanted group (0/21, 0%). The adult hepatocytes proliferated in the recipient livers and replaced a large part of their parenchyma. The transplantation of adult hepatocytes for acute liver failure significantly improved the survival rate in comparison to that of transplantation of immature cells, thus suggesting that ESCs and iPSCs should be differentiated into mature hepatocytes before cell transplantation for acute liver failure.

Runx2 promotes both osteoblastogenesis and novel osteoclastogenic signals in ST2 mesenchymal progenitor cells

We profiled the global gene expression of a bone marrow-derived mesenchymal pluripotent cell line in response to Runx2 expression. Besides osteoblast differentiation, Runx2 promoted the osteoclastogenesis of co-cultured splenocytes. This was attributable to the upregulation of many novel osteoclastogenic genes and the downregulation of anti-osteoclastogenic genes.

INTRODUCTION

In addition to being a master regulator for osteoblast differentiation, Runx2 controls osteoblast-driven osteoclastogenesis. Previous studies profiling gene expression during osteoblast differentiation had limited focus on Runx2 or paid little attention to its role in mediating osteoblast-driven osteoclastogenesis.

METHODS

ST2/Rx2(dox), a bone marrow-derived mesenchymal pluripotent cell line that expresses Runx2 in response to Doxycycline (Dox), was used to profile Runx2-induced gene expression changes. Runx2-induced osteoblast differentiation was assessed based on alkaline phosphatase staining and expression of classical marker genes. Osteoclastogenic potential was evaluated by TRAP staining of osteoclasts that differentiated from primary murine splenocytes co-cultured with the ST2/Rx2(dox) cells. The BeadChip™ platform (Illumina) was used to interrogate genome-wide expression changes in ST2/Rx2(dox) cultures after treatment with Dox or vehicle for 24 or 48 h. Expression of selected genes was also measured by RT-qPCR.

RESULTS

Dox-mediated Runx2 induction in ST2 cells stimulated their own differentiation along the osteoblast lineage and the differentiation of co-cultured splenocytes into osteoclasts. The latter was attributable to the stimulation of osteoclastogenic genes such as Sema7a, Ltc4s, Efnb1, Apcdd1, and Tnc as well as the inhibition of anti-osteoclastogenic genes such as Tnfrsf11b (OPG), Sema3a, Slco2b1, Ogn, Clec2d (Ocil), Il1rn, and Rspo2.

CONCLUSION

Direct control of osteoblast differentiation and concomitant indirect control of osteoclast differentiation, both through the activity of Runx2 in pre-osteoblasts, constitute a novel mechanism of coordination with a potential crucial role in coupling bone formation and resorption.

Osteoblasts derived from induced pluripotent stem cells form calcified structures in scaffolds both in vitro and in vivo

Reprogramming somatic cells into an ESC-like state, or induced pluripotent stem (iPS) cells, has emerged as a promising new venue for customized cell therapies. In this study, we performed directed differentiation to assess the ability of murine iPS cells to differentiate into bone, cartilage, and fat in vitro and to maintain an osteoblast phenotype on a scaffold in vitro and in vivo. Embryoid bodies derived from murine iPS cells were cultured in differentiation medium for 8–12 weeks. Differentiation was assessed by lineage-specific morphology, gene expression, histological stain, and immunostaining to detect matrix deposition. After 12 weeks of expansion, iPS-derived osteoblasts were seeded in a gelfoam matrix followed by subcutaneous implantation in syngenic imprinting control region (ICR) mice. Implants were harvested at 12 weeks, histological analyses of cell and mineral and matrix content were performed. Differentiation of iPS cells into mesenchymal lineages of bone, cartilage, and fat was confirmed by morphology and expression of lineage-specific genes. Isolated implants of iPS cell-derived osteoblasts expressed matrices characteristic of bone, including osteocalcin and bone sialoprotein. Implants were also stained with alizarin red and von Kossa, demonstrating mineralization and persistence of an osteoblast phenotype. Recruitment of vasculature and microvascularization of the implant was also detected. Taken together, these data demonstrate functional osteoblast differentiation from iPS cells both in vitro and in vivo and reveal a source of cells, which merit evaluation for their potential uses in orthopedic medicine and understanding of molecular mechanisms of orthopedic disease.

Biomimetic nanofibrous scaffolds for bone tissue engineering

Bone tissue engineering is a highly interdisciplinary field that seeks to tackle the most challenging bone-related clinical issues. The major components of bone tissue engineering are the scaffold, cells, and growth factors. This review will focus on the scaffold and recent advancements in developing scaffolds that can mimic the natural extracellular matrix of bone. Specifically, these novel scaffolds mirror the nanofibrous collagen network that comprises the majority of the non-mineral portion of bone matrix. Using two main fabrication techniques, electrospinning and thermally-induced phase separation, and incorporating bone-like minerals, such as hydroxyapatite, composite nanofibrous scaffolds can improve cell adhesion, stem cell differentiation, and tissue formation. This review will cover the two main processing techniques and how they are being applied to fabricate scaffolds for bone tissue engineering. It will then cover how these scaffolds can enhance the osteogenic capabilities of a variety of cell types and survey the ability of the constructs to support the growth of clinically relevant bone tissue.

Concise review: induced pluripotent stem cells and lineage reprogramming: prospects for bone regeneration

Bone tissue for transplantation therapies is in high demand in clinics. Osteodegenerative diseases, in particular, osteoporosis and osteoarthritis, represent serious public health issues affecting a respectable proportion of the elderly population. Furthermore, congenital indispositions from the spectrum of craniofacial malformations such as cleft palates and systemic disorders including osteogenesis imperfecta are further increasing the need for bone tissue. Additionally, the reconstruction of fractured bone elements after accidents and the consumption of bone parts during surgical tumor excisions represent frequent clinical situations with deficient availability of healthy bone tissue for therapeutic transplantations. Epigenetic reprogramming represents a powerful technology for the generation of healthy patient-specific cells to replace or repair diseased or damaged tissue. The recent generation of induced pluripotent stem cells (iPSCs) is probably the most promising among these approaches dominating the literature of current stem cell research. It allows the generation of pluripotent stem cells from adult human skin cells from which potentially all cell types of the human body could be obtained. Another technique to produce clinically interesting cell types is direct lineage reprogramming (LR) with the additional advantage that it can be applied directly in vivo to reconstitute a damaged organ. Here, we want to present the two technologies of iPSCs and LR, to outline the current states of research, and to discuss possible strategies for their implementation in bone regeneration.

Promotion of hematopoietic differentiation from mouse induced pluripotent stem cells by transient HoxB4 transduction

Ectopic expression of HoxB4 in embryonic stem (ES) cells leads to an efficient production of hematopoietic cells, including hematopoietic stem/progenitor cells. Previous studies have utilized a constitutive HoxB4 expression system or tetracycline-regulated HoxB4 expression system to induce hematopoietic cells from ES cells. However, these methods cannot be applied therapeutically due to the risk of transgenes being integrated into the host genome. Here, we report the promotion of hematopoietic differentiation from mouse ES cells and induced pluripotent stem (iPS) cells by transient HoxB4 expression using an adenovirus (Ad) vector. Ad vector could mediate efficient HoxB4 expression in ES cell-derived embryoid bodies (ES-EBs) and iPS-EBs, and its expression was decreased during cultivation, showing that Ad vector transduction was transient. A colony-forming assay revealed that the number of hematopoietic progenitor cells with colony-forming potential in HoxB4-transduced cells was significantly increased in comparison with that in non-transduced cells or LacZ-transduced cells. HoxB4-transduced cells also showed more efficient generation of CD41-, CD45-, or Sca-1-positive cells than control cells. These results indicate that transient, but not constitutive, HoxB4 expression is sufficient to augment the hematopoietic differentiation of ES and iPS cells, and that our method would be useful for clinical applications, such as cell transplantation therapy.

Cell sources for bone regeneration: the good, the bad, and the ugly (but promising)

Based on the extensive investigation of various ways to regenerate bone, bone marrow stromal cells, in conjunction with ceramic scaffolds, show great promise for application in human patients, and are already in use in a limited number of clinical trials. In preparing for clinical trials, scale-up current good manufacturing processes (cGMP) must incorporate the use of appropriate assays to ensure that the resulting cell product has maintained its biological activity. Future developments are needed to identify better scaffolds, and better ways to deliver cells with either injectable carriers, or by developing techniques to aide in their escape from the circulation and their incorporation into the pre-existing tissue. Lastly, development of methods that faithfully direct pluripotent stem cell differentiation into populations of osteogenic precursors (and ideally, containing skeletal stem cells) represents a new challenge in the field of bone regeneration, but also offer new opportunities to not only to study the biology of bone formation, but also to develop a robust cell source for bone regeneration.

Induced pluripotent stem cells and neurodegenerative diseases

Neurodegenerative diseases, including Parkinson's disease, Alzheimer's disease and Amyotrophic Lateral Sclerosis, are characterized by idiopathic neuron loss in different regions of the central nervous system, which contributes to the relevant dysfunctions in the patients. The application of cell replacement therapy using human embryonic stem (hES) cells, though having attracted much attention, has been hampered by the intrinsic ethical problems. It has been demonstrated that adult somatic cells can be reprogrammed into the embryonic state, called induced pluripotent stem (iPS) cells. It is soon realized that iPS cells may be an alternative source for cell replacement therapy, because it raises no ethical problems and using patient-specific iPS cells for autologous transplantation will not lead to immunological rejection. What's more, certain types of neurons derived from patient-specific iPS cells may display disease-relevant phenotypes. Thus, patient-specific iPS cells can provide a unique opportunity to directly investigate the pathological properties of relevant neural cells in individual patient, and to study the vulnerability of neural cells to pathogenic factors in vitro, which may help reveal the pathogenesis of many neurodegenerative diseases. In this review, the recent development in cellular treatment of neurodegenerative diseases using iPS cells was summarized, and the potential value of iPS cells in the modeling of neurodegenerative disease was discussed.

Critical-size calvarial bone defects healing in a mouse model with silk scaffolds and SATB2-modified iPSCs

Induced pluripotent stem cells (iPSCs) can differentiate into mineralizing cells and thus have a great potential in application in engineered bone substitutes with bioactive scaffolds in regeneration medicine. In the current study we characterized and demonstrated the pluripotency and osteogenic differentiation of mouse iPSCs. To enhance the osteogenic differentiation of iPSCs, we then transduced the iPSCs with the potent transcription factor, nuclear matrix protein SATB2. We observed that in SATB2-overexpressing iPSCs there were increased mineral nodule formation and elevated mRNA levels of key osteogenic genes, osterix (OSX), Runx2, bone sialoprotein (BSP) and osteocalcin (OCN). Moreover, the mRNA levels of HoxA2 was reduced after SATB2 overexpression in iPSCs. The SATB2-overexpressing iPSCs were then combined with silk scaffolds and transplanted into critical-size calvarial bone defects created in nude mice. Five weeks post-surgery, radiological and micro-CT analysis revealed enhanced new bone formation in calvarial defects in SATB2 group. Histological analysis also showed increased new bone formation and mineralization in the SATB2 group. In conclusion, the results demonstrate that SATB2 facilitates the differentiation of iPSCs towards osteoblast-lineage cells by repressing HoxA2 and augmenting the functions of the osteoblast determinants Runx2, BSP and OCN.

The role of single cell derived vascular resident endothelial progenitor cells in the enhancement of vascularization in scaffold-based skin regeneration

Increasing evidence suggests that vascular resident endothelial progenitor cells (VR-EPCs) are present in several organs, playing an important role in postnatal neovascularization. Here, we isolated and characterized VR-EPCs from cardiac tissue in vitro, evaluating their regenerative potential in vivo. VR-EPCs showed to be highly clonogenic and expressed several stem and differentiation markers. Under endothelial differentiation conditions, cells form capillary-like structures, in contrast to osteogenic or adipogenic differentiation conditions where no functional changes were observed. After seeding in scaffolds, cells were distributed homogeneously and directly attached to the scaffold. Then, cell seeded scaffolds were used to induce dermal regeneration in a nude mice full skin defect model. The presence of VR-EPCs enhanced dermal vascularization. Histological assays showed increased vessel number (p < 0.05) and cellularization (p < 0.05) in VR-EPCs group. In order to explore possible mechanisms of vascular regeneration, in vitro experiments were performed. Results showed that pro-angiogenic environments increased the migration capacity (p < 0.001) and ability to form capillary-like structures (p < 0.05) of VR-EPC. In addition, VR-EPCs secreted several pro-angiogenic molecules including VEGF and PDGF. These results indicate that a highly clonogenic population of VR-EPCs might be established in vitro, representing a new source for therapeutic vascularization in tissue engineering and regeneration.

Prospects of induced pluripotent stem cell technology in regenerative medicine

Induced pluripotent stem (iPS) cells are derived from adult somatic cells via reprogramming with ectopic expression of four transcription factors (Oct3/4, Sox2, c-Myc and Klf4; or, Oct3/4, Sox2, Nanog, and Lin28), by which the resultant cells regain pluripotency, namely, the capability exclusively possessed by some embryonic cells to differentiate into any cell lineage under proper conditions. Given the ease in cell sourcing and a waiver of ethical opponency, iPS cells excel embryonic pluripotent cells in the practice of drug discovery and regenerative medicine. With an ex vivo practice in regenerative medicine, many problems involved in conventional medicine dosing, such as immune rejection, could be potentially circumvented. In this article, we briefly summarize the fundamentals and status quo of iPS-related applications, and emphasize the prospects of iPS technology in regenerative medicine.

Adenovirus vector-mediated efficient transduction into human embryonic and induced pluripotent stem cells

We examined the transduction efficiency in human embryonic stem (ES) and induced pluripotent stem (iPS) cells using an adenovirus (Ad) vector. RT-PCR analysis revealed the expression of the coxsackievirus and adenovirus receptor, a receptor for Ad, in these cells. However, gene expression after the transduction with an Ad vector was observed only in the periphery of ES and iPS cell colonies, when human ES and iPS cells were passaged as small colonies. This suggests that the Ad vector could not enter inside the ES and iPS cell colonies by their tight connection. We thus attempted to transduce foreign genes into the dissociated form of human ES and iPS cells, which were passaged using Rho-associated kinase inhibitor. In this condition, transduction efficiency in human ES and iPS cells was markedly increased and transgene expression was observed even inside the colonies by using Ad vectors. Furthermore, Ad vector-mediated transduction did not alter the expression of undifferentiated markers such as Oct-3/4, Nanog, and SSEA-4. Our results indicate that Ad vectors are effective tools for transduction into human ES and iPS cells.

Alternative sources of pluripotent stem cells: ethical and scientific issues revisited

Stem cell researchers in the United States continue to face an uncertain future, because of the changing federal guidelines governing this research, the restrictive patent situation surrounding the generation of new human embryonic stem cell lines, and the ethical divide over the use of embryos for research. In this commentary, we describe how recent advances in the derivation of induced pluripotent stem cells and the isolation of germ-line-derived pluripotent stem cells resolve a number of these uncertainties. The availability of patient-matched, pluripotent stem cells that can be obtained by ethically acceptable means provides important advantages for stem cell researchers, by both avoiding protracted ethical debates and giving U.S. researchers full access to federal funding. Thus, ethically uncompromised stem cells, such as those derived by direct reprogramming or from germ-cell precursors, are likely to yield important advances in stem cell research and move the field rapidly toward clinical applications.

Nuclear reprogramming strategy modulates differentiation potential of induced pluripotent stem cells

Bioengineered by ectopic expression of stemness factors, induced pluripotent stem (iPS) cells demonstrate embryonic stem cell-like properties and offer a unique platform for derivation of autologous pluripotent cells from somatic tissue sources. In the process of nuclear reprogramming, somatic tissues are converted to a pluripotent ground state, thus unlocking an unlimited potential to expand progenitor pools. Molecular dissection of nuclear reprogramming suggests that a residual memory derived from the original parental source, along with the remnants of the reprogramming process itself, leads to a biased potential of the bioengineered progeny to differentiate into target tissues such as cardiac cytotypes. In this way, iPS cells that fulfill pluripotency criteria may display heterogeneous profiles for lineage specification. Small molecule-based strategies have been identified that modulate the epigenetic state of reprogrammed cells and are optimized to erase the residual memory and homogenize the differentiation potential of iPS cells derived from distinct backgrounds. Here, we describe the salient components of the reprogramming process and their effect on the downstream differentiation capacity of the iPS populations in the context of cardiovascular regenerative applications.

Efficient generation of hepatoblasts from human ES cells and iPS cells by transient overexpression of homeobox gene HEX

Human embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) have the potential to differentiate into all cell lineages, including hepatocytes, in vitro. Induced hepatocytes have a wide range of potential application in biomedical research, drug discovery, and the treatment of liver disease. However, the existing protocols for hepatic differentiation of PSCs are not very efficient. In this study, we developed an efficient method to induce hepatoblasts, which are progenitors of hepatocytes, from human ESCs and iPSCs by overexpression of the HEX gene, which is a homeotic gene and also essential for hepatic differentiation, using a HEX-expressing adenovirus (Ad) vector under serum/feeder cell-free chemically defined conditions. Ad-HEX-transduced cells expressed α-fetoprotein (AFP) at day 9 and then expressed albumin (ALB) at day 12. Furthermore, the Ad-HEX-transduced cells derived from human iPSCs also produced several cytochrome P450 (CYP) isozymes, and these P450 isozymes were capable of converting the substrates to metabolites and responding to the chemical stimulation. Our differentiation protocol using Ad vector-mediated transient HEX transduction under chemically defined conditions efficiently generates hepatoblasts from human ESCs and iPSCs. Thus, our methods would be useful for not only drug screening but also therapeutic applications.

Potential of induced pluripotent stem cells for the regeneration of the tracheal wall

OBJECTIVES

Our previous studies focused on basic research and the clinical applications of an artificial trachea. However, the prefabricated artificial trachea cannot be utilized for pediatric airways, because the tracheal frame needs to expand as the child develops. The purpose of this study was to evaluate the potential of induced pluripotent stem (iPS) cells for the regeneration of the tracheal wall.

METHODS

We cultured iPS cells in a 3-dimensional (3-D) scaffold in chondrocyte differentiation medium (bioengineered scaffold model), and the results were compared with those in a 3-D scaffold without iPS cells (control scaffold model). The 3-D scaffolds were implanted into tracheal defects in 8 nude rats. After 4 weeks, the regenerated tissue was histologically examined.

RESULTS

Implanted iPS cells were confirmed to exist in all 5 rats implanted with bioengineered scaffolds. Cartilage-like tissue was observed in the regenerated tracheal wall in 2 of the 5 rats in the bioengineered scaffold model, but in none of the 3 rats in the control scaffold model.

CONCLUSIONS

Implanted iPS cells were confirmed to exist in the bioengineered scaffold. Cartilage-like tissue was regenerated in the tracheal defect. This study demonstrated the potential of iPS cells in the regeneration of the tracheal wall.

[Differentiation of functional cells from iPS cells by efficient gene transfer]

Induced pluripotent stem (iPS) cells, which are generated from somatic cells by transducing four genes, are expected to have broad application to regenerative medicine. Although establishment of an efficient gene transfer system for iPS cells is considered to be essential for differentiating them into functional cells, the detailed transduction characteristics of iPS cells have not been examined. By using an adenovirus (Ad) vector containing the cytomegalovirus enhancer/beta-actin (CA) promoters, we have developed an efficient transduction system for mouse mesenchymal stem cells and embryonic stem (ES) cells. Also, we applied our transduction system to mouse iPS cells and investigated whether efficient differentiation could be achieved by Ad vector-mediated transduction of a functional gene. As in the case of ES cells, the Ad vector could efficiently transduce transgenes into mouse iPS cells. We found that the CA promoter had potent transduction ability in iPS cells. Moreover, exogenous expression of a PPARγ gene or a Runx2 gene into mouse iPS cells by an optimized Ad vector enhanced adipocyte or osteoblast differentiation, respectively. These results suggest that Ad vector-mediated transient transduction is sufficient to promote cellular differentiation and that our transduction methods would be useful for therapeutic applications based on iPS cells.

Induced pluripotent stem cells: developmental biology to regenerative medicine

Nuclear reprogramming of somatic cells with ectopic stemness factors to bioengineer pluripotent autologous stem cells signals a new era in regenerative medicine. The study of developmental biology has provided a roadmap for cardiac differentiation from embryonic tissue formation to adult heart muscle rejuvenation. Understanding the molecular mechanisms of stem-cell-derived cardiogenesis enables the reproducible generation, isolation, and monitoring of progenitors that have the capacity to recapitulate embryogenesis and differentiate into mature cardiac tissue. With the advent of induced pluripotent stem (iPS) cell technology, patient-specific stem cells provide a reference point to systematically decipher cardiogenic differentiation through discrete stages of development. Interrogation of iPS cells and their progeny from selected cohorts of patients is an innovative approach towards uncovering the molecular mechanisms of disease. Thus, the principles of cardiogenesis can now be applied to regenerative medicine in order to optimize personalized therapeutics, diagnostics, and discovery-based science for the development of novel clinical applications.

Cell transplantation for articular cartilage defects: principles of past, present, and future practice

As articular cartilage has very limited self-repair capability, the repair and regeneration of damaged cartilage is a major challenge. This review aims to outline the past, present, and future of cell therapies for articular cartilage defect repair. Autologous chondrocyte implantation (ACI) has been used clinically for more than 20 years, and the short, medium, and long-term clinical outcomes of three generation of ACI are extensively overviewed. Also, strategies of clinical outcome evaluation, ACI limitations, and the comparison of ACI clinical outcomes with those of other surgical techniques are discussed. Moreover, mesenchymal stem cells and pluripotent stem cells for cartilage regeneration in vitro, in vivo, and in a few clinical studies are reviewed. This review not only comprehensively analyzes the ACI clinical data but also considers the findings from state-of-the-art stem cell research on cartilage repair from bench and bedside. The conclusion provides clues for the future development of strategies for cartilage regeneration.

Non-invasive characterization of mouse embryonic stem cell derived cardiomyocytes based on the intensity variation in digital beating video

The interest in cardiomyocytes derived from differentiation of embryonic stem (ES) cells or induced pluripotent stem (iPS) cells is increasing due to their potential for regenerative therapeutics and as a pharmaceutical model of drug screening. Characterization of ES or iPS derived cardiomyocytes is challenging and inevitable for the intended usage of such cells. In this paper we have outlined a novel, non-invasive method for evaluating in vitro beating properties of cardiomyocytes. The method is based on the analysis of time dependent variation in the total pixel intensities in derivative images obtained from the consecutive systolic and diastolic frames from the light microscopic video recordings of beating tissue. Fast Fourier transform (FFT) yielded the frequency domains for these images. The signal to noise ratio for the analysis met the Rose criterion. We have successfully applied our method for monitoring mouse ES cell (mESC) derived cardiac muscle cells to determine the initiation of beating, organization and maturation of beating tissue, calculating the beating rhythms in terms of beating interval or frequency and the strength of beating. We have shown the successful application of our image analysis method in direct monitoring of the responses of differentiated cardiomyocytes towards caffeine hydrate, p-hydroxyphenylacetamide and calcium chloride dehydrate - respectively as positive, neutral and negative inotropic agents. This non-invasive method of characterization will be useful in studying the response of these cells to various external stimulations, such as differentiation promoting agents or treatments, as well as in preliminary drug screening in a quick and inexpensive manner without needing much expertise.

Inducible pluripotent stem cells: not quite ready for prime time?

PURPOSE OF REVIEW

Inducible pluripotent stem (iPS) cells derived from somatic cells represent a novel renewable source of tissue precursors. The potential of iPS cells is considered to be at least equivalent to that of human embryonic stem cells, facilitating the treatment or cure of diseases such as diabetes mellitus, spinal cord injuries, cardiovascular disease, and neurodegenerative diseases, but with the potential added benefit of evading the adaptive immune response that otherwise limits allogeneic cell-based therapies. This review discusses recent advances in pluripotency induction and the use of iPS cells to produce differentiated cells, while highlighting roadblocks to the widespread use of this technology in the clinical arena.

RECENT FINDINGS

Whereas ethical and safety issues surrounding the use of human embryonic stem cells for the treatment of disease continue to be debated, use of iPS cells may be viewed as a more widely acceptable compromise. Since the first descriptions of inducible pluripotency from somatic cells, multiple laboratories have collectively made tremendous strides both in developing alternative, more clinically acceptable, induction strategies and in demonstrating the proof-of-principle that iPS cells can be differentiated into a variety of cell types to reverse mouse models of human disease.

SUMMARY

Although the prospect of using patient-specific iPS cells has much appeal from an ethical and immunologic perspective, the limitations of the technology from the standpoint of reprogramming efficiency and therapeutic safety necessitate much more in-depth research before the initiation of human clinical trials.