Scientific Resources

Corneal transparency depends on a unique extracellular matrix secreted by stromal keratocytes,mesenchymal cells of neural crest lineage. Derivation of keratocytes from human embryonic stem (hES) cells could elucidate the keratocyte developmental pathway and open a potential for cell-based therapy for corneal blindness. This study seeks to identify conditions inducing differentiation of pluripotent hES cells to the keratocyte lineage. Neural differentiation of hES cell line WA01(H1) was induced by co-culture with mouse PA6 fibroblasts. After 6 days of co-culture,hES cells expressing cell-surface NGFR protein (CD271,p75NTR) were isolated by immunoaffinity adsorption,and cultured as a monolayer for one week. Keratocyte phenotype was induced by substratum-independent pellet culture in serum-free medium containing ascorbate. Gene expression,examined by quantitative RT-PCR,found hES cells co-cultured with PA6 cells for 6 days to upregulate expression of neural crest genes including NGFR,SNAI1,NTRK3,SOX9,and MSX1. Isolated NGFR-expressing cells were free of PA6 feeder cells. After expansion as a monolayer,mRNAs typifying adult stromal stem cells were detected,including BMI1,KIT,NES,NOTCH1,and SIX2. When these cells were cultured as substratum-free pellets keratocyte markers AQP1,B3GNT7,PTDGS,and ALDH3A1 were upregulated. mRNA for keratocan (KERA),a cornea-specific proteoglycan,was upregulated more than 10,000 fold. Culture medium from pellets contained high molecular weight keratocan modified with keratan sulfate,a unique molecular component of corneal stroma. These results show hES cells can be induced to differentiate into keratocytes in vitro. Pluripotent stem cells,therefore,may provide a renewable source of material for development of treatment of corneal stromal opacities. View Publication

An essential aspect of stem cell culture is the successful maintenance of the undifferentiated state. Many types of stem cells are FGF2 dependent,and pluripotent stem cells are maintained by replacing FGF2-containing media daily,while tissue-specific stem cells are typically fed every 3rd day. Frequent feeding,however,results in significant variation in growth factor levels due to FGF2 instability,which limits effective maintenance due to spontaneous differentiation. We report that stabilization of FGF2 levels using controlled release PLGA microspheres improves expression of stem cell markers,increases stem cell numbers and decreases spontaneous differentiation. The controlled release FGF2 additive reduces the frequency of media changes needed to maintain stem cell cultures,so that human embryonic stem cells and induced pluripotent stem cells can be maintained successfully with biweekly feedings. View Publication

Induced pluripotent stem (iPS) cells hold the potential to revolutionize regenerative medicine through their capacity to generate cells of diverse lineages for future patient-specific cell-based therapies. To facilitate the transition of iPS cells to clinical practice,a variety of technologies have been developed for transgene-free pluripotency reprogramming. We recently reported efficient iPS cell generation from human fibroblasts using synthetic modified mRNAs. Here we describe a stepwise protocol for the generation of modified mRNA-derived iPS cells from primary human fibroblasts,focusing on the critical parameters including medium choice,quality control,and optimization steps needed for synthesizing modified mRNAs encoding reprogramming factors and introducing these into cells over the course of 2-3 weeks to ensure successful reprogramming. The protocol described herein is for reprogramming of human fibroblasts to pluripotency; however,the properties of modified mRNA make it a powerful platform for protein expression,which has broad applicability in directed differentiation,cell fate specification and therapeutic applications. View Publication

Pluripotent stem cells hold great promise for regenerative medicine,due to their unlimited self-renewal potential and the ability to differentiate into all somatic cell types. Differences between the rodent disease models and the situation in humans can be narrowed down with non-human primate models. The common marmoset monkey (Callithrix jacchus) is an interesting model for biomedical research because these animals are easy to breed,get relatively old (≤ 13 years),are small in size,are relatively cost-effective and have a high genetic proximity to the human. In particular,diseases of the liver and pancreas are interesting for cell replacement therapies but the in vitro differentiation of ESCs into the definitive endoderm germ layer is still a demanding task. Membrane-permeable,chemically defined small molecules can possibly replace recombinant growth factors used in most directed differentiation protocols. However,the potent small molecules IDE-1 and IDE-2 were not able to induce definitive endoderm-like cells when ESCs from the common marmoset were treated with these compounds,whereas the recombinant growth factor Activin A could force the differentiation into this lineage. Our results indicate that ESCs from the common marmoset are less sensitive or even insensitive to these small molecules. Thus,differences between the species of human ESCs and ESCs of this non-human primate might be a useful model to further evaluate the exact mode of action of these compounds. View Publication

The vertebrae mesoderm is a source of cells that forms a variety of tissues,including the heart,vasculature,and blood. Consequently,the derivation of various mesoderm-specific cell types from human embryonic stem cells (hESCs) has attracted the interest of many investigators owing to their therapeutic potential in clinical applications. However,the need for efficient and reliable methods of differentiation into mesoderm lineage cell types remains a significant challenge. Here,we demonstrated that inhibition of glycogen synthase kinase-3 (GSK-3) is an essential first step toward efficient generation of the mesoderm. Under chemically defined conditions without additional growth factors/cytokines,short-term GSK inhibitor (GSKi) treatment effectively drives differentiation of hESCs into the primitive streak (PS),which can potentially commit toward the mesoderm when further supplemented with bone morphogenetic protein 4. Further analysis confirmed that the PS-like cells derived from GSKi treatment are bipotential,being able to specify toward the endoderm as well. Our findings suggest that the bipotential,PS/mesendoderm-like cell population exists only at the initial stages of GSK-3 inhibition,whereas long-term inhibition results in an endodermal fate. Lastly,we demonstrated that our differentiation approach could efficiently generate lateral plate (CD34(+)KDR(+)) and paraxial (CD34(-)PDGFRα(+)) mesoderm subsets that can be further differentiated along the endothelial and smooth muscle lineages,respectively. In conclusion,our study presents a unique approach for generating early mesoderm progenitors in a chemically directed fashion through the use of small-molecule GSK-3 inhibitor,which may be useful for future applications in regenerative medicine. View Publication

The breakthrough in derivation of human-induced pluripotent stem cells (hiPSCs) provides an approach that may help overcome ethical and allergenic challenges posed in numerous medical applications involving human cells,including neural stem/progenitor cells (NSCs). Considering the great potential of NSCs in targeted cancer gene therapy,we investigated in this study the tumor tropism of hiPSC-derived NSCs and attempted to enhance the tropism by manipulation of biological activities of proteins that are involved in regulating the migration of NSCs toward cancer cells. We first demonstrated that hiPSC-NSCs displayed tropism for both glioblastoma cells and breast cancer cells in vitro and in vivo. We then compared gene expression profiles between migratory and non-migratory hiPSC-NSCs toward these cancer cells and observed that the gene encoding neuronal nitric oxide synthase (nNOS) was down-regulated in migratory hiPSC-NSCs. Using nNOS inhibitors and nNOS siRNAs,we demonstrated that this protein is a relevant regulator in controlling migration of hiPSC-NSCs toward cancer cells,and that inhibition of its activity or down-regulation of its expression can sensitize poorly migratory NSCs and be used to improve their tumor tropism. These findings suggest a novel application of nNOS inhibitors in neural stem cell-mediated cancer therapy. View Publication

The shortage of human organs and tissues for transplant has led to significant interest in xenotransplantation of pig tissues for human patients. However,transplantation of pig organs results in an acute immune rejection,leading to death of the organ within minutes. The $\$-1,3-galactosyltransferase (GALT) gene has been knocked out in pigs to reduce rejection,yet additional genes need to be modified to ultimately make pig tissue immunocompatible with humans. The development of pig induced pluripotent stem cells (piPSCs) from GALT knockout (GALT-KO) tissue would provide an excellent cell source for complex genetic manipulations (e.g.,gene targeting) that often require highly robust and proliferative cells. In this report,we generated GALT-KO piPSCs by the overexpression of POU5F1,SOX2,NANOG,LIN28,KLF-4,and C-MYC reprogramming genes. piPSCs showed classical stem cell morphology and characteristics,expressing integrated reprogramming genes in addition to the pluripotent markers AP,SSEA1,and SSEA4. GALT-KO piPSCs were highly proliferative and possessed doubling times and telomerase activity similar to human embryonic stem cells. These results demonstrated successful reprogramming of GALT-KO fibroblasts into GALT-KO piPSCs. GALT-KO piPSCs are potentially an excellent immortal cell source for the generation of pigs with complex genetic modifications for xenotransplantation,somatic cell nuclear transfer,or chimera formation. View Publication

In congenital mitochondrial DNA (mtDNA) disorders,a mixture of normal and mutated mtDNA (termed heteroplasmy) exists at varying levels in different tissues,which determines the severity and phenotypic expression of disease. Pearson marrow pancreas syndrome (PS) is a congenital bone marrow failure disorder caused by heteroplasmic deletions in mtDNA. The cause of the hematopoietic failure in PS is unknown,and adequate cellular and animal models are lacking. Induced pluripotent stem (iPS) cells are particularly amenable for studying mtDNA disorders,as cytoplasmic genetic material is retained during direct reprogramming. Here,we derive and characterize iPS cells from a patient with PS. Taking advantage of the tendency for heteroplasmy to change with cell passage,we isolated isogenic PS-iPS cells without detectable levels of deleted mtDNA. We found that PS-iPS cells carrying a high burden of deleted mtDNA displayed differences in growth,mitochondrial function,and hematopoietic phenotype when differentiated in vitro,compared to isogenic iPS cells without deleted mtDNA. Our results demonstrate that reprogramming somatic cells from patients with mtDNA disorders can yield pluripotent stem cells with varying burdens of heteroplasmy that might be useful in the study and treatment of mitochondrial diseases. STEM CELLS2013;31:1287–1297 View Publication

Hepatocyte transplantation has been used to treat liver disease. The availability of cells for these procedures is quite limited. Human embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs) may be a useful source of hepatocytes for basic research and transplantation if efficient and effective differentiation protocols were developed and problems with tumorigenicity could be overcome. Recent evidence suggests that the cell of origin may affect hiPSC differentiation. Thus,hiPSCs generated from hepatocytes may differentiate back to hepatocytes more efficiently than hiPSCs from other cell types. We examined the efficiency of reprogramming adult and fetal human hepatocytes. The present studies report the generation of 40 hiPSC lines from primary human hepatocytes under feeder-free conditions. Of these,37 hiPSC lines were generated from fetal hepatocytes,2 hiPSC lines from normal hepatocytes,and 1 hiPSC line from hepatocytes of a patient with Crigler-Najjar syndrome,type 1. All lines were confirmed reprogrammed and expressed markers of pluripotency by gene expression,flow cytometry,immunocytochemistry,and teratoma formation. Fetal hepatocytes were reprogrammed at a frequency over 50-fold higher than adult hepatocytes. Adult hepatocytes were only reprogrammed with six factors,while fetal hepatocytes could be reprogrammed with three (OCT4,SOX2,NANOG) or four factors (OCT4,SOX2,NANOG,LIN28 or OCT4,SOX2,KLF4,C-MYC). The increased reprogramming efficiency of fetal cells was not due to increased transduction efficiency or vector toxicity. These studies confirm that hiPSCs can be generated from adult and fetal hepatocytes including those with genetic diseases. Fetal hepatocytes reprogram much more efficiently than adult hepatocytes,although both could serve as useful sources of hiPSC-derived hepatocytes for basic research or transplantation. View Publication

Demonstrates efficient reprogramming of iPS cells from CD34+ stem cells enriched from a small volume of peripheral blood. View Publication

Many long noncoding RNA (lncRNA) species have been identified in mammalian cells,but the genomic origin and regulation of these molecules in individual cell types is poorly understood. We have generated catalogs of lncRNA species expressed in human and murine embryonic stem cells and mapped their genomic origin. A surprisingly large fraction of these transcripts (textgreater60%) originate from divergent transcription at promoters of active protein-coding genes. The divergently transcribed lncRNA/mRNA gene pairs exhibit coordinated changes in transcription when embryonic stem cells are differentiated into endoderm. Our results reveal that transcription of most lncRNA genes is coordinated with transcription of protein-coding genes. View Publication

Magnesium alloys have attracted great interest for medical applications due to their unique biodegradable capability and desirable mechanical properties. When designed for medical applications,these alloys must have suitable degradation properties,i.e.,their degradation rate should not exceed the rate at which the degradation products can be excreted from the body. Cellular responses and tissue integration around the Mg-based implants are critical for clinical success. Four magnesium–zinc–strontium (ZSr41) alloys were developed in this study. The degradation properties of the ZSr41 alloys and their cytocompatibility were studied using an in vitro human embryonic stem cell (hESC) model due to the greater sensitivity of hESCs to known toxicants which allows to potentially detect toxicological effects of new biomaterials at an early stage. Four distinct ZSr41 alloys with 4 wt% zinc and a series of strontium compositions (0.15,0.5,1,and 1.5 wt% Sr) were produced through metallurgical processing. Their degradation was characterized by measuring total mass loss of samples and pH change in the cell culture media. The concentration of Mg ions released from ZSr41 alloy into the cell culture media was analyzed using inductively coupled plasma atomic emission spectroscopy. Surface microstructure and composition before and after culturing with hESCs were characterized using field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. Pure Mg was used as a control during cell culture studies. Results indicated that the Mg–Zn–Sr alloy with 0.15 wt% Sr provided slower degradation and improved cytocompatibility as compared with pure Mg control. View Publication