Three-dimensional epithelial tissues generated from human embryonic stem cells

Subpopulations of fibroblasts derived from human iPS cells

Organ fibrosis causes collagen fiber overgrowth and impairs organ function. Cardiac fibrosis after myocardial infarction impairs cardiac function significantly, pulmonary fibrosis reduces gas exchange efficiency, and liver fibrosis disturbs the natural function of the liver. Its development is associated with the differentiation of fibroblasts into myofibroblasts and increased collagen synthesis. Fibrosis has organ specificity, defined by the heterogeneity of fibroblasts. Although this heterogeneity is established during embryonic development, it has not been defined yet. Fibroblastic differentiation of induced pluripotent stem cells (iPSCs) recapitulates the process by which fibroblasts acquire diversity. Here, we differentiated iPSCs into cardiac, hepatic, and dermal fibroblasts and analyzed their properties using single-cell RNA sequencing. We observed characteristic subpopulations with different ratios in each organ-type fibroblast group, which contained both resting and distinct ACTA2+ myofibroblasts. These findings provide crucial information on the ontogeny-based heterogeneity of fibroblasts, leading to the development of therapeutic strategies to control fibrosis.

A Systematic Review of Stem Cell Differentiation into Keratinocytes for Regenerative Applications

To improve wound healing or treatment of other skin diseases, and provide model cells for skin biology studies, in vitro differentiation of stem cells into keratinocyte-like cells (KLCs) is very desirable in regenerative medicine. This study examined the most recent advancements in in vitro differentiation of stem cells into KLCs, the effect of biofactors, procedures, and preparation for upcoming clinical cases. A range of stem cells with different origins could be differentiated into KLCs under appropriate conditions. The most effective ways of stem cell differentiation into keratinocytes were found to include the co-culture with primary epithelial cells and keratinocytes, and a cocktail of growth factors, cytokines, and small molecules. KLCs should also be supported by biomaterials for the extracellular matrix (ECM), which replicate the composition and functionality of the in vivo extracellular matrix (ECM) and, thus, support their phenotypic and functional characteristics. The detailed efficient characterization of different factors, and their combinations, could make it possible to find the significant inducers for stem cell differentiation into epidermal lineage. Moreover, it allows the development of chemically known media for directing multi-step differentiation procedures.In conclusion, the differentiation of stem cells to KLCs is feasible and KLCs were used in experimental, preclinical, and clinical trials. However, the translation of KLCs from in vitro investigational system to clinically valuable cells is challenging and extremely slow.

Anti-fibrotic effect of a selective estrogen receptor modulator in systemic sclerosis

Background

The rarity of systemic sclerosis (SSc) has hampered the development of therapies for this intractable autoimmune disease. Induced pluripotent stem cell (iPSC) can be differentiated into the key disease-affected cells in vitro. The generation of patient-derived iPSCs has opened up possibilities for rare disease modeling. Since these cells can recapitulate the disease phenotypes of the cell in question, they are useful high-throughput platforms for screening for drugs that can reverse these abnormal phenotypes.

Methods

SSc iPSC was generated from PBMC by Sendai virus. Human iPSC lines from SSc patients were differentiated into dermal fibroblasts and keratinocytes. The iPSC-derived differentiated cells from the SSc patients were used on high-throughput platforms to screen for FDA-approved drugs that could be effective treatments for SSc.

Results

Skin organoids were generated from these cells exhibited fibrosis that resembled SSc skin. Screening of the 770-FDA-approved drug library showed that the anti-osteoporotic drug raloxifene reduced SSc iPSC-derived fibroblast proliferation and extracellular matrix production and skin fibrosis in organoids and bleomycin-induced SSc-model mice.

Conclusions

This study reveals that a disease model of systemic sclerosis generated using iPSCs-derived skin organoid is a novel tool for in vitro and in vivo dermatologic research. Since raloxifene and bazedoxifene are well-tolerated anti-osteoporotic drugs, our findings suggest that selective estrogen receptor modulator (SERM)-class drugs could treat SSc fibrosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02987-w.

Tissue engineered corneal epithelium derived from clinical-grade human embryonic stem cells

PURPOSE

To construct tissue engineered corneal epithelium from a clinical-grade human embryonic stem cells (hESCs) and investigate the dynamic gene profile and phenotypic transition in the process of differentiation.

METHODS

A stepwise protocol was applied to induce differentiation of clinical-grade hESCs Q-CTS-hESC-1 and construct tissue engineered corneal epithelium. Single cell RNA sequencing (scRNA-seq) analysis was performed to monitor gene expression and phenotypic changes at different differentiation stages. Immunostaining, real-time quantitative PCR and Western blot analysis were conducted to detect gene and protein expressions. After subcutaneous transplantation into nude mice to test the biosafety, the epithelial construct was transplanted in a rabbit corneal limbal stem cell deficiency (LSCD) model and followed up for eight weeks.

RESULTS

The hESCs were successfully induced into epithelial cells. scRNA-seq analysis revealed upregulation of ocular surface epithelial cell lineage related genes such as TP63, Pax6, KRT14, and activation of Wnt, Notch, Hippo, and Hedgehog signaling pathways during the differentiation process. Tissue engineered epithelial cell sheet derived from hESCs showed stratified structure and normal corneal epithelial phenotype with presence of clonogenic progenitor cells. Eight weeks after grafting the cell sheet onto the ocular surface of LSCD rabbit model, a full-thickness continuous corneal epithelium developed to fully cover the damaged areas with normal limbal and corneal epithelial phenotype.

CONCLUSION

The tissue engineered corneal epithelium generated from a clinical-grade hESCs may be feasible in the treatment of limbal stem cell deficiency.

Rapid Differentiation of Multi-Zone Ocular Cells from Human Induced Pluripotent Stem Cells and Generation of Corneal Epithelial and Endothelial Cells

Eye is a complex organ with a highly specialized tissue structure. The establishment of human pluripotent stem cells (hPSCs) has allowed the simulation of eye development in vitro. Most differentiation works of hPSC-derived ocular cells focus on a single, tissue-specific lineage, however, that faces difficulty in reflecting the complexity of eye development. Recently, the generation of a self-formed ectodermal autonomous multi-zone of ocular cells availably mimics the process of whole-eye development. In this study, we developed a rapid defined method to induce the differentiation of multi-zone ocular cells (MZOCs) from human induced pluripotent stem cells, which specifically experienced the key progenitor stages of anterior neuroectoderm and eye field stem cells by a 2.5-dimensional culture. These differentiated cell types spanned neural retina, retinal pigment epithelium, surface ectoderm, and neural crest and lens cells. In addition, the surface ectoderm zone of MZOCs could be mechanically isolated and induced into corneal epithelial cells, and the isolated neural crest zone could be directed into corneal endothelial cells. This in vitro differentiation process vividly mimics the development of vertebrate eye, and it provides a promising model for the study of ocular morphogenesis, as well as an ideal resource of seed cells for corneal regenerative medicine.

Differentiation of diabetic foot ulcer-derived induced pluripotent stem cells reveals distinct cellular and tissue phenotypes

Diabetic foot ulcers (DFUs) are a major complication of diabetes, and there is a critical need to develop novel cell- and tissue-based therapies to treat these chronic wounds. Induced pluripotent stem cells (iPSCs) offer a replenishing source of allogeneic and autologous cell types that may be beneficial to improve DFU wound-healing outcomes. However, the biologic potential of iPSC-derived cells to treat DFUs has not, to our knowledge, been investigated. Toward that goal, we have performed detailed characterization of iPSC-derived fibroblasts from both diabetic and nondiabetic patients. Significantly, gene array and functional analyses reveal that iPSC-derived fibroblasts from both patients with and those without diabetes are more similar to each other than were the primary cells from which they were derived. iPSC-derived fibroblasts showed improved migratory properties in 2-dimensional culture. iPSC-derived fibroblasts from DFUs displayed a unique biochemical composition and morphology when grown as 3-dimensional (3D), self-assembled extracellular matrix tissues, which were distinct from tissues fabricated using the parental DFU fibroblasts from which they were reprogrammed. In vivo transplantation of 3D tissues with iPSC-derived fibroblasts showed they persisted in the wound and facilitated diabetic wound closure compared with primary DFU fibroblasts. Taken together, our findings support the potential application of these iPSC-derived fibroblasts and 3D tissues to improve wound healing.-Kashpur, O., Smith, A., Gerami-Naini, B., Maione, A. G., Calabrese, R., Tellechea, A., Theocharidis, G., Liang, L., Pastar, I., Tomic-Canic, M., Mooney, D., Veves, A., Garlick, J. A. Differentiation of diabetic foot ulcer-derived induced pluripotent stem cells reveals distinct cellular and tissue phenotypes.

Induced pluripotent stem cells as a potential therapeutic source for corneal epithelial stem cells

Corneal blindness caused by limbal stem cell deficiency (LSCD) is one of the most common debilitating eye disorders. Thus far, the most effective treatment for LSCD is corneal transplantation, which is often hindered by the shortage of donors. Pluripotent stem cell technology including embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) have opened new avenues for treating this disease. iPSCs-derived corneal epithelial cells provide an autologous and unlimited source of cells for the treatment of LSCD. On the other hand, iPSCs of LSCD patients can be used for iPSCs-corneal disease model and new drug discovery. However, prior to clinical trial, the efficacy and safety of these cells in patients with LSCD should be proved. Here we focused on the current status of iPSCs-derived corneal epithelial cells used for cell therapy as well as for corneal disease modeling. The challenges and potential of iPSCs-derived corneal epithelial cells as a choice for clinical treatment in corneal disease were also discussed.

A novel method to reconstruct epithelial tissue using high-purity keratinocyte lineage cells induced from human embryonic stem cells

The treatment of oral mucosa defect such as autologous oral mucosa caused by resection of oral mucosa carcinoma is still not ideal in clinical practice. However, Tissue engineering gives us the possibility to solve this problem. As we all know, Human embryonic stem cells (hESCs) have the ability to give rise to various cell types. We can take advantage of the totipotency of human embryonic stem cells to acquire keratinocytes. Directing the epithelial differentiation of hESCs can provide seed cells for the construction of epithelium tissue by tissue engineering. But, how to get high purity keratinocytes by induced stem cells then Applied to tissue engineering mucosa is an important challenge. We described a novel method to directly induce hESCs to differentiate into keratinocytes. Retinoic acid, ascorbic acid, and bone morphogenetic protein induced hESCs to differentiate into cells that highly expressed cytokeratin (CK)14. Our findings suggest that the retinoic acid, ascorbic acid and bone morphogenetic proteins induced hESCs to form high purity keratinocyte cell populations. In addition, we found that the highly pure keratinocyte populations reconstructed artificial tissue resembling epithelial tissue when inoculated in vitro on a biological scaffold.

Efficient and Scalable Directed Differentiation of Clinically Compatible Corneal Limbal Epithelial Stem Cells from Human Pluripotent Stem Cells

Corneal limbal epithelial stem cells (LESCs) are responsible for continuously renewing the corneal epithelium, and thus maintaining corneal homeostasis and visual clarity. Human pluripotent stem cell (hPSC)-derived LESCs provide a promising cell source for corneal cell replacement therapy. Undefined, xenogeneic culture and differentiation conditions cause variation in research results and impede the clinical translation of hPSC-derived therapeutics. This protocol provides a reproducible and efficient method for hPSC-LESC differentiation under xeno- and feeder cell-free conditions. Firstly, monolayer culture of undifferentiated hPSC on recombinant laminin-521 (LN-521) and defined hPSC medium serves as a foundation for robust production of high-quality starting material for differentiations. Secondly, a rapid and simple hPSC-LESC differentiation method yields LESC populations in only 24 days. This method includes a four-day surface ectodermal induction in suspension with small molecules, followed by adherent culture phase on LN-521/collagen IV combination matrix in defined corneal epithelial differentiation medium. Cryostoring and extended differentiation further purifies the cell population and enables banking of the cells in large quantities for cell therapy products. The resulting high-quality hPSC-LESCs provide a potential novel treatment strategy for corneal surface reconstruction to treat limbal stem cell deficiency (LSCD).

Universal Corneal Epithelial-Like Cells Derived from Human Embryonic Stem Cells for Cellularization of a Corneal Scaffold

Purpose

We generated universal corneal epithelial cells (CEC) from human embryonic stem cells (hESC) by genetically removing human leukocyte antigens (HLA) class I from the cell surface.

Methods

The serum-free, growth factor-free, and defined medium E6 was used to differentiate hESC to CEC. Decellularized murine corneas were recellularized with hESC-derived CEC. Using CRISPR/Cas9, β-2-microglobulin (B2M) was deleted in hESC to block the assembly of HLA class-I antigens on the cell surface to generate B2M^−/− CEC.

Results

E6 alone was sufficient to allow hESC differentiation to CEC. A time-course analysis of the global gene expression of the differentiating cells indicates that the differentiation closely resembles the corneal development in vivo. The hESC-CEC were highly proliferative, and could form multilayer epithelium in decellularized murine cornea, retain its transparency, and form intact tight junctions on its surface. As reported before, B2M knockout led to the absence of HLA class-I on the cell surface of hESC and subsequently derived CEC following stimulation with inflammatory factors. Moreover, B2M^−/− CEC, following transplantation into mouse eyes, caused less T-cell infiltration in the limbal region of the eye than the wild-type control.

Conclusions

CEC can be derived from hESC via a novel and simple protocol free of any proteins, hESC-CEC seeded on decellularized animal cornea form tight junctions and allow light transmittance, and B2M^−/− CEC are hypoimmunogenic both in vitro and in vivo.

Translational Relevance

B2M^−/− hESC-CEC can be an unlimited and universal therapy for corneal repair in patients of any HLA type.

Establishment of a complex skin structure via layered co-culture of keratinocytes and fibroblasts derived from induced pluripotent stem cells

Background

Skin is an organ that plays an important role as a physical barrier and has many other complex functions. Skin mimetics may be useful for studying the pathophysiology of diseases in vitro and for repairing lesions in vivo. Cord blood mononuclear cells (CBMCs) have emerged as a potential cell source for regenerative medicine. Human induced pluripotent stem cells (iPSCs) derived from CBMCs have great potential for allogenic regenerative medicine. Further study is needed on skin differentiation using CBMC-iPSCs.

Methods

Human iPSCs were generated from CBMCs by Sendai virus. CBMC-iPSCs were differentiated to fibroblasts and keratinocytes using embryonic body formation. To generate CBMC-iPSC-derived 3D skin organoid, CBMC-iPSC-derived fibroblasts were added into the insert of a Transwell plate and CBMC-iPSC-derived keratinocytes were seeded onto the fibroblast layer. Transplantation of 3D skin organoid was performed by the tie-over dressing method.

Results

Epidermal and dermal layers were developed using keratinocytes and fibroblasts differentiated from cord blood-derived human iPSCs, respectively. A complex 3D skin organoid was generated by overlaying the epidermal layer onto the dermal layer. A humanized skin model was generated by transplanting this human skin organoid into SCID mice and effectively healed skin lesions.

Conclusions

This study reveals that a human skin organoid generated using CBMC iPSCs is a novel tool for in-vitro and in-vivo dermatologic research.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0958-2) contains supplementary material, which is available to authorized users.

Immunosuppressive Mesenchymal Stromal Cells Derived from Human-Induced Pluripotent Stem Cells Induce Human Regulatory T Cells In Vitro and In Vivo

Despite mesenchymal stromal cells (MSCs) are considered as a promising source of cells to modulate immune functions on cells from innate and adaptive immune systems, their clinical use remains restricted (few number, limited in vitro expansion, absence of a full phenotypic characterization, few insights on their in vivo fate). Standardized MSCs derived in vitro from human-induced pluripotent stem (huIPS) cells, remediating part of these issues, are considered as well as a valuable tool for therapeutic approaches, but their functions remained to be fully characterized. We generated multipotent MSCs derived from huiPS cells (huiPS-MSCs), and focusing on their immunosuppressive activity, we showed that human T-cell activation in coculture with huiPS-MSCs was significantly reduced. We also observed the generation of functional CD4⁺ FoxP3⁺ regulatory T (Treg) cells. Further tested in vivo in a model of human T-cell expansion in immune-deficient NSG mice, huiPS-MSCs immunosuppressive activity prevented the circulation and the accumulation of activated human T cells. Intracytoplasmic labeling of cytokines produced by the recovered T cells showed reduced percentages of human-differentiated T cells producing Th1 inflammatory cytokines. By contrast, T cells producing IL-10 and FoxP3⁺-Treg cells, absent in non-treated animals, were detected in huiPS-MSCs treated mice. For the first time, these results highlight the immunosuppressive activity of the huiPS-MSCs on human T-cell stimulation with a concomitant generation of human Treg cells in vivo. They may favor the development of new tools and strategies based on the use of huiPS cells and their derivatives for the induction of immune tolerance.

Differences in the Activity of Endogenous Bone Morphogenetic Protein Signaling Impact on the Ability of Induced Pluripotent Stem Cells to Differentiate to Corneal Epithelial-Like Cells

Cornea is a clear outermost layer of the eye which enables transmission of light onto the retina. The transparent corneal epithelium is regenerated by limbal stem cells (LSCs), whose loss/dysfunction results in LSCs deficiency (LSCD). Ex vivo expansion of autologous LSCs obtained from patient's healthy eye followed by transplantation onto the LSCs damaged/deficient eye, has provided a successful treatment for unilateral LSCD. However, this is not applicable to patient with total bilateral LSCD, where LSCs are lost/damaged from both eyes. We investigated the potential of human induced pluripotent stem cell (hiPSC) to differentiate into corneal epithelial‐like cells as a source of autologous stem cell treatment for patients with total bilateral LSCD. Our study showed that combined addition of bone morphogenetic protein 4 (BMP4), all trans‐retinoic acid and epidermal growth factor for the first 9 days of differentiation followed by cell‐replating on collagen‐IV‐coated surfaces with a corneal‐specific‐epithelial cell media for an additional 11 days, resulted in step wise differentiation of human embryonic stem cells (hESC) to corneal epithelial progenitors and mature corneal epithelial‐like cells. We observed differences in the ability of hiPSC lines to undergo differentiation to corneal epithelial‐like cells which were dependent on the level of endogenous BMP signaling and could be restored via the activation of this signaling pathway by a specific transforming growth factor β inhibitor (SB431542). Together our data reveal a differential ability of hiPSC lines to generate corneal epithelial cells which is underlined by the activity of endogenous BMP signaling pathway. Stem Cells2018;36:337–348

Engineering epithelial-stromal interactions in vitro for toxicology assessment

Crosstalk between epithelial and stromal cells drives the morphogenesis of ectodermal organs during development and promotes normal mature adult epithelial tissue homeostasis. Epithelial-stromal interactions (ESIs) have historically been examined using mammalian models and ex vivo tissue recombination. Although these approaches have elucidated signaling mechanisms underlying embryonic morphogenesis processes and adult mammalian epithelial tissue function, they are limited by the availability of tissue, low throughput, and human developmental or physiological relevance. In this review, we describe how bioengineered ESIs, using either human stem cells or co-cultures of human primary epithelial and stromal cells, have enabled the development of human in vitro epithelial tissue models that recapitulate the architecture, phenotype, and function of adult human epithelial tissues. We discuss how the strategies used to engineer mature epithelial tissue models in vitro could be extrapolated to instruct the design of organotypic culture models that can recapitulate the structure of embryonic ectodermal tissues and enable the in vitro assessment of events critical to organ/tissue morphogenesis. Given the importance of ESIs towards normal epithelial tissue development and function, such models present a unique opportunity for toxicological screening assays to incorporate ESIs to assess the impact of chemicals on mature and developing epidermal tissues.

Generation of Induced Pluripotent Stem Cells from Diabetic Foot Ulcer Fibroblasts Using a Nonintegrative Sendai Virus

Diabetic foot ulcers (DFUs) are nonhealing chronic wounds that are a serious complication of diabetes. Since induced pluripotent stem cells (iPSCs) may offer a potent source of autologous cells to heal these wounds, we studied if repair-deficient fibroblasts, derived from DFU patients and age- and site-matched control fibroblasts, could be reprogrammed to iPSCs. To establish this, we used Sendai virus to successfully reprogram six primary fibroblast cell lines derived from ulcerated skin of two DFU patients (DFU8, DFU25), nonulcerated foot skin from two diabetic patients (DFF24, DFF9), and healthy foot skin from two nondiabetic patients (NFF12, NFF14). We confirmed reprogramming to a pluripotent state through three independent criteria: immunofluorescent staining for SSEA-4 and TRA-1-81, formation of embryoid bodies with differentiation potential to all three embryonic germ layers in vitro, and formation of teratomas in vivo. All iPSC lines showed normal karyotypes and typical, nonmethylated CpG sites for OCT4 and NANOG. iPSCs derived from DFUs were similar to those derived from site-matched nonulcerated skin from both diabetic and nondiabetic patients. These results have established for the first time that multiple, DFU-derived fibroblast cell lines can be reprogrammed with efficiencies similar to control fibroblasts, thus demonstrating their utility for future regenerative therapy of DFUs.

Generation of Epithelial Cell Populations from Human Pluripotent Stem Cells Using a Small-Molecule Inhibitor of Src Family Kinases

Human pluripotent stem cells (hPSCs), under the right conditions, can be engineered to generate populations of any somatic cell type. Knowledge of what mechanisms govern differentiation towards a particular lineage is often quite useful for efficiently producing somatic cell populations from hPSCs. Here, we have outlined a strategy for deriving populations of simple epithelial cells, as well as more mature epidermal keratinocyte progenitors, from hPSCs by exploiting a mechanism previously shown to direct epithelial differentiation of hPSCs. Specifically, we describe how to direct epithelial differentiation of hPSCs using an Src family kinase inhibitor, SU6656, which has been shown to modulate β-catenin translocation to the cell membrane and thus promote epithelial differentiation. The differentiation platform outlined here produces cells with the ability to terminally differentiate to epidermal keratinocytes in culture through a stable simple epithelial cell intermediate that can be expanded in culture for numerous (>10) passages.

Potential applications of keratinocytes derived from human embryonic stem cells

Although skin grafting is one of the most advanced cell therapy technique, wide application of skin substitutes is hampered by the difficulty in securing sufficient amount of epidermal substitute. Additionally, in understanding the progression of skin aging and disease, and in screening the cosmetic and pharmaceutical products, there is lack of a satisfactory human skin-specific in vitro model. Recently, human embryonic stem cells (hESCs) have been proposed as an unlimited and reliable cell source to obtain almost all cell types present in the human body. This review focuses on the potential off-the-shelf use of hESC-derived keratinocytes for future clinical applications as well as a powerful in vitro skin model to study skin function and integrity, host-pathogen interactions and disease pathogenesis. Furthermore, we discuss the industrial applications of hESC-derived keratinized multi-layer epithelium which provides a human-like test platform for understanding disease pathogenesis, evaluation of new therapeutic modalities and assessment of the safety and efficacy of skin cosmetics and therapeutics. Overall, we conclude that the hESC-derived keratinocytes have great potential for clinical, research and industrial applications.

Advances in 3D cell culture technologies enabling tissue-like structures to be created in vitro

Research in mammalian cell biology often relies on developing in vitro models to enable the growth of cells in the laboratory to investigate a specific biological mechanism or process under different test conditions. The quality of such models and how they represent the behavior of cells in real tissues plays a critical role in the value of the data produced and how it is used. It is particularly important to recognize how the structure of a cell influences its function and how co-culture models can be used to more closely represent the structure of real tissue. In recent years, technologies have been developed to enhance the way in which researchers can grow cells and more readily create tissue-like structures. Here we identify the limitations of culturing mammalian cells by conventional methods on two-dimensional (2D) substrates and review the popular approaches currently available that enable the development of three-dimensional (3D) tissue models in vitro. There are now many ways in which the growth environment for cultured cells can be altered to encourage 3D cell growth. Approaches to 3D culture can be broadly categorized into scaffold-free or scaffold-based culture systems, with scaffolds made from either natural or synthetic materials. There is no one particular solution that currently satisfies all requirements and researchers must select the appropriate method in line with their needs. Using such technology in conjunction with other modern resources in cell biology (e.g. human stem cells) will provide new opportunities to create robust human tissue mimetics for use in basic research and drug discovery. Application of such models will contribute to advancing basic research, increasing the predictive accuracy of compounds, and reducing animal usage in biomedical science.

Fibroblast heterogeneity and its implications for engineering organotypic skin models in vitro

Advances in cell culture methods, multidisciplinary research, clinical need to replace lost skin tissues and regulatory need to replace animal models with alternative test methods has led to development of three dimensional models of human skin. In general, these in vitro models of skin consist of keratinocytes cultured over fibroblast-populated dermal matrices. Accumulating evidences indicate that mesenchyme-derived signals are essential for epidermal morphogenesis, homeostasis and differentiation. Various studies show that fibroblasts isolated from different tissues in the body are dynamic in nature and are morphologically and functionally heterogeneous subpopulations. Further, these differences seem to be dictated by the local biological and physical microenvironment the fibroblasts reside resulting in "positional identity or memory". Furthermore, the heterogeneity among the fibroblasts play a critical role in scarless wound healing and complete restoration of native tissue architecture in fetus and oral mucosa; and excessive scar formation in diseased states like keloids and hypertrophic scars. In this review, we summarize current concepts about the heterogeneity among fibroblasts and their role in various wound healing environments. Further, we contemplate how the insights on fibroblast heterogeneity could be applied for the development of next generation organotypic skin models.

Sestrin 2 protein regulates platelet-derived growth factor receptor β (Pdgfrβ) expression by modulating proteasomal and Nrf2 transcription factor functions

We recently identified the antioxidant protein Sestrin 2 (Sesn2) as a suppressor of platelet-derived growth factor receptor β (Pdgfrβ) signaling and Pdgfrβ signaling as an inducer of lung regeneration and injury repair. Here, we identified Sesn2 and the antioxidant gene inducer nuclear factor erythroid 2-related factor 2 (Nrf2) as positive regulators of proteasomal function. Inactivation of Sesn2 or Nrf2 induced reactive oxygen species-mediated proteasomal inhibition and Pdgfrβ accumulation. Using bacterial artificial chromosome (BAC) transgenic HeLa and mouse embryonic stem cells stably expressing enhanced green fluorescent protein-tagged Sesn2 at nearly endogenous levels, we also showed that Sesn2 physically interacts with 2-Cys peroxiredoxins and Nrf2 albeit under different reductive conditions. Overall, we characterized a novel, redox-sensitive Sesn2/Pdgfrβ suppressor pathway that negatively interferes with lung regeneration and is up-regulated in the emphysematous lungs of patients with chronic obstructive pulmonary disease (COPD).

Strategies for Oral Mucosal Repair by Engineering 3D Tissues with Pluripotent Stem Cells

Significance: Human-induced pluripotent stem cells (iPSC) can be differentiated into patient-specific cells with a wide spectrum of cellular phenotypes and offer an alternative source of autologous cells for therapeutic use. Recent studies have shown that iPSC-derived fibroblasts display enhanced cellular functions suggesting that iPSC may eventually become an important source of stem cells for regenerative therapies. Recent Advances: The discovery of approaches to reprogram somatic cells into pluripotent cells opens exciting avenues for their use in personalized, regenerative therapies. The controlled differentiation of functional cell types from iPSC provides a replenishing source of fibroblasts. There is intriguing evidence that iPSC reprogramming and subsequent differentiation to fibroblast lineages may improve cellular functional properties. Augmenting the biological potency of iPSC-derived fibroblasts may enable the development of novel, personalized stem cell therapies to treat oral disease. Critical Issues: Numerous questions need to be addressed before iPSC-derived cells can be used as a practical oral therapy. This will include understanding why iPSC-derived cells are predisposed towards differentiation pathways along lineages related to their cell of origin, screening iPSC-derived cells to ensure their safety and phenotypic stability and developing engineered, three-dimensional tissue models to optimize their function and efficacy for future therapeutic transplantation. Future Directions: Future research will need to address how to develop efficient methods to deliver and integrate iPSC-derived fibroblasts into the oral mucosa. This will require an improved understanding of how to harness their biological potency for regenerative therapies that are specifically targeted to the oral mucosa.

Second and third trimester amniotic fluid mesenchymal stem cells can repopulate a de-cellularized lung scaffold and express lung markers

BACKGROUND/PURPOSE

This study examined the potential of amniotic fluid mesenchymal stem cells (AF-MSCs) to generate lung precursor cells in vitro and on a xenologous three-dimensional de-cellularized lung scaffold.

METHODS

AF-MSCs were isolated from human amniotic fluid obtained from 17-37 weeks gestation. Lung differentiation was induced on Matrigel or on de-cellularized rat lungs intra-tracheally injected with AF-MSCs by culturing with a modification of small airway growth medium (mSAGM) lacking retinoic acid (RA) and triodothyronine (T3) with addition of fibroblast growth factor-10 (FGF10). Cells and scaffolds were characterized by immunofluorescence and RT-PCR for markers of viability, proliferation, and lung distal airway differentiation (TTF-1(+) and SPC(+)) in the absence of markers of brain (TuJ1(-)) and thyroid (Pax8(-)).

RESULTS

After culture in mSAGM on either Matrigel or lung scaffolds, there were TTF-1(+)/TuJ1(-)/Pax8(-) cells, indicating a lung precursor phenotype. In addition, SPC(+) cells also evolved suggesting a more mature lung phenotype.

CONCLUSIONS

We demonstrate that mid- to late-trimester AF-MSCs can be induced to develop into lung precursor cells when cultured on the appropriate extracellular matrix (ECM), making them a viable source for use in cell therapy or development of an ex vivo tissue engineered lung.

Small-molecule induction promotes corneal epithelial cell differentiation from human induced pluripotent stem cells

Human induced pluripotent stem cells (hiPSCs) offer unique opportunities for developing novel cell-based therapies and disease modeling. In this study, we developed a directed differentiation method for hiPSCs toward corneal epithelial progenitor cells capable of terminal differentiation toward mature corneal epithelial-like cells. In order to improve the efficiency and reproducibility of our method, we replicated signaling cues active during ocular surface ectoderm development with the help of two small-molecule inhibitors in combination with basic fibroblast growth factor (bFGF) in serum-free and feeder-free conditions. First, small-molecule induction downregulated the expression of pluripotency markers while upregulating several transcription factors essential for normal eye development. Second, protein expression of the corneal epithelial progenitor marker p63 was greatly enhanced, with up to 95% of cells being p63 positive after 5 weeks of differentiation. Third, corneal epithelial-like cells were obtained upon further maturation.

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Small-molecule induction directs early stage differentiation

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Subsequent maturation yields homogeneous populations of p63-positive cells

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p63-positive progenitor cells are capable of terminal differentiation

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The serum-free and feeder-free method can be upgraded to fully defined and xeno free

Fibroblasts derived from human pluripotent stem cells activate angiogenic responses in vitro and in vivo

Human embryonic and induced pluripotent stem cells (hESC/hiPSC) are promising cell sources for the derivation of large numbers of specific cell types for tissue engineering and cell therapy applications. We have describe a directed differentiation protocol that generates fibroblasts from both hESC and hiPSC (EDK/iPDK) that support the repair and regeneration of epithelial tissue in engineered, 3D skin equivalents. In the current study, we analyzed the secretory profiles of EDK and iPDK cells to investigate the production of factors that activate and promote angiogenesis. Analysis of in vitro secretion profiles from EDK and iPDK cells demonstrated the elevated secretion of pro-angiogenic soluble mediators, including VEGF, HGF, IL-8, PDGF-AA, and Ang-1, that stimulated endothelial cell sprouting in a 3D model of angiogenesis in vitro. Phenotypic analysis of EDK and iPDK cells during the course of differentiation from hESCs and iPSCs revealed that both cell types progressively acquired pericyte lineage markers NG2, PDGFRβ, CD105, and CD73 and demonstrated transient induction of pericyte progenitor markers CD31, CD34, and Flk1/VEGFR2. Furthermore, when co-cultured with endothelial cells in 3D fibrin-based constructs, EDK and iPDK cells promoted self-assembly of vascular networks and vascular basement membrane deposition. Finally, transplantation of EDK cells into mice with hindlimb ischemia significantly reduced tissue necrosis and improved blood perfusion, demonstrating the potential of these cells to stimulate angiogenic responses in vivo. These findings demonstrate that stable populations of pericyte-like angiogenic cells can be generated with high efficiency from hESC and hiPSC using a directed differentiation approach. This provides new cell sources and opportunities for vascular tissue engineering and for the development of novel strategies in regenerative medicine.

Engineering the human pluripotent stem cell microenvironment to direct cell fate

Human pluripotent stem cells (hPSCs), including both embryonic stem cells and induced pluripotent stem cells, offer a potential cell source for research, drug screening, and regenerative medicine applications due to their unique ability to self-renew or differentiate to any somatic cell type. Before the full potential of hPSCs can be realized, robust protocols must be developed to direct their fate. Cell fate decisions are based on components of the surrounding microenvironment, including soluble factors, substrate or extracellular matrix, cell-cell interactions, mechanical forces, and 2D or 3D architecture. Depending on their spatio-temporal context, these components can signal hPSCs to either self-renew or differentiate to cell types of the ectoderm, mesoderm, or endoderm. Researchers working at the interface of engineering and biology have identified various factors which can affect hPSC fate, often based on lessons from embryonic development, and they have utilized this information to design in vitro niches which can reproducibly direct hPSC fate. This review highlights culture systems that have been engineered to promote self-renewal or differentiation of hPSCs, with a focus on studies that have elucidated the contributions of specific microenvironmental cues in the context of those culture systems. We propose the use of microsystem technologies for high-throughput screening of spatial-temporal presentation of cues, as this has been demonstrated to be a powerful approach for differentiating hPSCs to desired cell types.

Generation of 3D skin equivalents fully reconstituted from human induced pluripotent stem cells (iPSCs)

Recent generation of patient-specific induced pluripotent stem cells (PS-iPSCs) provides significant advantages for cell- and gene-based therapy. Establishment of iPSC-based therapy for skin diseases requires efficient methodology for differentiating iPSCs into both keratinocytes and fibroblasts, the major cellular components of the skin, as well as the reconstruction of skin structures using these iPSC-derived skin components. We previously reported generation of keratinocytes from human iPSCs for use in the treatment of recessive dystrophic epidermolysis bullosa (RDEB) caused by mutations in the COL7A1 gene. Here, we developed a protocol for differentiating iPSCs into dermal fibroblasts, which also produce type VII collagen and therefore also have the potential to treat RDEB. Moreover, we generated in vitro 3D skin equivalents composed exclusively human iPSC-derived keratinocytes and fibroblasts for disease models and regenerative therapies for skin diseases, first demonstrating that iPSCs can provide the basis for modeling a human organ derived entirely from two different types of iPSC-derived cells.

Current progress of skin tissue engineering: Seed cells, bioscaffolds, and construction strategies

The development of cell biology, molecular biology, and material science, has been propelling biomimic tissue-engineered skins to become more sophisticated in scientificity and more simplified in practicality. In order to improve the safety, durability, elasticity, biocompatibility, and clinical efficacy of tissue-engineered skin, several powerful seed cells have already found their application in wound repair, and a variety of bioactive scaff olds have been discovered to influence cell fate in epidermogenesis. These exuberant interests provide insights into advanced construction strategies for complex skin mimics. Based on these exciting developments, a complete full-thickness tissue-engineered skin is likely to be generated.

Improving efficiency of human pluripotent stem cell differentiation platforms using an integrated experimental and computational approach

Human pluripotent stem cells (hPSCs) have an unparalleled potential for tissue engineering applications including regenerative therapies and in vitro cell-based models for studying normal and diseased tissue morphogenesis, or drug and toxicological screens. While numerous hPSC differentiation methods have been developed to generate various somatic cell types, the potential of hPSC-based technologies is hinged on the ability to translate these established lab-scale differentiation systems to large-scale processes to meet the industrial and clinical demands for these somatic cell types. Here, we demonstrate a strategy for investigating the efficiency and scalability of hPSC differentiation platforms. Using two previously reported epithelial differentiation systems as models, we fit an ODE-based kinetic model to data representing dynamics of various cell subpopulations present in our culture. This fit was performed by estimating rate constants of each cell subpopulation's cell fate decisions (self-renewal, differentiation, death). Sensitivity analyses on predicted rate constants indicated which cell fate decisions had the greatest impact on overall epithelial cell yield in each differentiation process. In addition, we found that the final cell yield was limited by the self-renewal rate of either the progenitor state or the final differentiated state, depending on the differentiation protocol. Also, the relative impact of these cell fate decision rates was highly dependent on the maximum capacity of the cell culture system. Overall, we outline a novel approach for quantitative analysis of established laboratory-scale hPSC differentiation systems and this approach may ease development to produce large quantities of cells for tissue engineering applications.

Stem cells of the skin and cornea: their clinical applications in regenerative medicine

PURPOSE OF REVIEW

The use of stem cells is of great interest for the treatment of various pathologies and ultimately for the restoration of organ function. Progress pointing towards future treatments of skin and corneal epithelial stem cell defects are reviewed, including the transplantation of living tissue-engineered substitutes.

RECENT FINDINGS

This article focuses on substitutes optimized for permanent replacement of skin and cornea. New skin substitutes for burn care are currently under development. More complex tissue-engineered skin substitutes in which stroma, adipose tissue, capillaries, and neurons are combined with the epithelium are being developed. Some dermal/epidermal substitutes have been applied to the treatment of patients. Cultured corneal epithelial cells have been characterized and more complete corneal substitutes are being designed. Long-term clinical results on the transplantation of cultured corneal stem cells for the treatment of limbal stem cell deficiency have been reported.

SUMMARY

Advances in tissue engineering for the development of substitutes that will benefit patients suffering from skin or corneal stem cell deficiencies are reviewed. These products are often a combination of cells, scaffolds and other factors. Key considerations in the development of corneal and skin substitutes for clinical applications are discussed.

Efficient generation of functional epithelial and epidermal cells from human pluripotent stem cells under defined conditions

Human pluripotent stem cells (hPSCs) have an unparalleled potential to generate limitless quantities of any somatic cell type. However, current methods for producing populations of various somatic cell types from hPSCs are generally not standardized and typically incorporate undefined cell culture components often resulting in variable differentiation efficiencies and poor reproducibility. To address this, we have developed a defined approach for generating epithelial progenitor and epidermal cells from hPSCs. In doing so, we have identified an optimal starting cell density to maximize yield and maintain high purity of K18+/p63+ simple epithelial progenitors. In addition, we have shown that the use of synthetic, defined substrates in lieu of Matrigel and gelatin can successfully facilitate efficient epithelial differentiation, maintaining a high (>75%) purity of K14+/p63+ keratinocyte progenitor cells and at a two to threefold higher yield than a previously reported undefined differentiation method. These K14+/p63+ cells also exhibited a higher expansion potential compared to cells generated using an undefined differentiation protocol and were able to terminally differentiate and recapitulate an epidermal tissue architecture in vitro. In summary, we have demonstrated the production of populations of functional epithelial and epidermal cells from multiple hPSC lines using a new, completely defined differentiation strategy.

Differentiation of epidermal keratinocytes from human embryonic stem cells

For many years, cell therapies have been hampered by limited availability and inter-batch variability of primary cells. Human embryonic stem cell (hESC) can give rise to specialized cells like keratinocytes and recently emerged as a virtually unlimited source of potential therapeutic cells. However, xenogeneic components in differentiation cocktails have been limiting the clinical potential of hESC-derived keratinocytes (hESCs-Kert). Here, we demonstrated efficient differentiation of H9 human embryonic stem cells (H9-hESCs) into keratinocytes (H9-Kert(ACC)) in an autogenic co-culture system. We used activin as the main factor to induce keratinocyte differentiation. H9-Kert(ACC) expressed keratinocyte markers at mRNA and protein levels. Establishment of such animal-free microenvironment for keratinocyte differentiation will accelerate potential clinical application of hESCs.

Differentiation of human embryonic stem cells into clinically amenable keratinocytes in an autogenic environment

Human embryonic stem cells (hESCs)-derived keratinocytes hold great clinical and research potential. However, the current techniques are hampered by the use of xenogenic components that limits their clinical application. Here we demonstrated an efficient differentiation of H9 hESCs (H9-hESCs) into keratinocytes (H9-Kert) with the minimum use of animal-derived materials. For differentiation, we established two microenvironment systems originated from H9-hESCs (autogenic microenvironment). These autogenic microenvironment systems consist of an autogenic coculture system (ACC) and an autogenic feeder-free system (AFF). In addition, we showed a stage-specific effect of Activin in promoting keratinocyte differentiation from H9-hESCs while repressing the expression of early neural markers in the ACC system. Furthermore, we also explained the effect of Activin in construction of the AFF system made up of extracellular matrix similar to basement membrane extracted from H9-hESC-derived fibroblasts. H9-Kert differentiated in both systems expressed keratinocyte markers at mRNA and protein levels. H9-Kert were also able to undergo terminal differentiation in high Ca(2+) medium. These findings support the transition toward the establishment of an animal-free microenvironment for successful differentiation of hESCs into keratinocytes for potential clinical application.

PDGFRβ expression and function in fibroblasts derived from pluripotent cells is linked to DNA demethylation

Platelet-derived growth factor receptor-beta (PDGFRβ) is required for the development of mesenchymal cell types, and plays a diverse role in the function of fibroblasts in tissue homeostasis and regeneration. In this study, we characterized the expression of PDGFRβ in fibroblasts derived from human embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), and showed that this expression is important for cellular functions such as migration, extracellular matrix production and assembly in 3D self-assembled tissues. To determine potential regulatory regions predictive of expression of PDGFRβ following differentiation from ESCs and iPSCs, we analyzed the DNA methylation status of a region of the PDGFRB promoter that contains multiple CpG sites, before and after differentiation. We demonstrated that this promoter region is extensively demethylated following differentiation, and represents a developmentally regulated, differentially methylated region linked to PDGFRβ expression. Understanding the epigenetic regulation of genes such as PDGFRB, and identifying sites of active DNA demethylation, is essential for future applications of iPSC-derived fibroblasts for regenerative medicine.

iPSC-derived fibroblasts demonstrate augmented production and assembly of extracellular matrix proteins

Reprogramming of somatic cells to induced pluripotent stem cells (iPSC) provides an important cell source to derive patient-specific cells for potential therapeutic applications. However, it is not yet clear whether reprogramming through pluripotency allows the production of differentiated cells with improved functional properties that may be beneficial in regenerative therapies. To address this, we compared the production and assembly of extracellular matrix (ECM) by iPSC-derived fibroblasts to that of the parental, dermal fibroblasts (BJ), from which these iPSC were initially reprogrammed, and to fibroblasts differentiated from human embryonic stem cells (hESC). iPSC- and hESC-derived fibroblasts demonstrated stable expression of surface markers characteristic of stromal fibroblasts during prolonged culture and showed an elevated growth potential when compared to the parental BJ fibroblasts. We found that in the presence of L: -ascorbic acid-2-phosphate, iPSC- and hESC-derived fibroblasts increased their expression of collagen genes, secretion of soluble collagen, and extracellular deposition of type I collagen to a significantly greater degree than that seen in the parental BJ fibroblasts. Under culture conditions that enabled the self-assembly of a 3D stromal tissue, iPSC- and hESC-derived fibroblasts generated a well organized, ECM that was enriched in type III collagen. By characterizing the functional properties of iPSC-derived fibroblasts compared to their parental fibroblasts, we demonstrate that these cells represent a promising, alternative source of fibroblasts to advance future regenerative therapies.

Epithelial morphogenesis of germline-derived pluripotent stem cells on organotypic skin equivalents in vitro

For tissue engineering, cultivation of pluripotent stem cells on three-dimensional scaffolds allows the generation of organ-like structures. Previously, we have established an organotypic culture system of skin to induce epidermal differentiation in adult stem cells. Multipotent stem cells are not able to differentiate across germinal boundaries. In contrast, pluripotent stem cells readily differentiate into tissues of all three germ layers. Germline-derived pluripotent stem cells (gPS cells) can be generated by induction of pluripotency in mouse unipotent germline stem cells without the introduction of exogenous transcription factors. In the current study, we analyzed the influence of organotypic culture conditions of skin on the epithelial differentiation of gPS cells in comparison to the well-established HM1 ES cell line. Quantitative RT-PCR data of the pluripotency gene Oct4 showed that gPS cells are characterized by an accelerated Oct4-downregulation compared to HM1 ES cells. When subjected to the organotypic culture conditions of skin, gPS cells formed tubulocystic structures lined by stratified (CK5/6(+), CK14(+), CK8/18(-)) epithelia. HM1 ES cells formed only small tubulocystic structures lined by simple, CK8/18(+) epithelia. BMP-4, an epidermal morphogen, significantly enhanced the expression of epithelial markers in HM1 ES cells, but did not significantly affect the formation of complex (squamous) epithelia in gPS cells. In HM1 ES cells the differentiation into squamous epithelium was only inducible in the presence of mature dermal fibroblasts. Both pluripotent stem cell types spontaneously differentiated into mesodermal, endodermal and into neuroectodermal cells at low frequency, underlining their pluripotent differentiation capacity. Concluding, the organotypic culture conditions of skin induce a multilayered, stratified epithelium in gPS cells, in HM1 ES cells only in the presence of dermal fibroblasts. Thus, our data show that differentiation protocols strongly depend on the stem cell type and have to be modified for each specific stem cell type.

Initial binding and recellularization of decellularized mouse lung scaffolds with bone marrow-derived mesenchymal stromal cells

Recellularization of whole decellularized lung scaffolds provides a novel approach for generating functional lung tissue ex vivo for subsequent clinical transplantation. To explore the potential utility of stem and progenitor cells in this model, we investigated recellularization of decellularized whole mouse lungs after intratracheal inoculation of bone marrow-derived mesenchymal stromal cells (MSCs). The decellularized lungs maintained structural features of native lungs, including intact vasculature, ability to undergo ventilation, and an extracellular matrix (ECM) scaffold consisting primarily of collagens I and IV, laminin, and fibronectin. However, even in the absence of intact cells or nuclei, a number of cell-associated (non-ECM) proteins were detected using mass spectroscopy, western blots, and immunohistochemistry. MSCs initially homed and engrafted to regions enriched in types I and IV collagen, laminin, and fibronectin, and subsequently proliferated and migrated toward regions enriched in types I and IV collagen and laminin but not provisional matrix (fibronectin). MSCs cultured for up to 1 month in either basal MSC medium or in a small airways growth media (SAGM) localized in both parenchymal and airway regions and demonstrated several different morphologies. However, while MSCs cultured in basal medium increased in number, MSCs cultured in SAGM decreased in number over 1 month. Under both media conditions, the MSCs predominantly expressed genes consistent with mesenchymal and osteoblast phenotype. Despite a transient expression of the lung precursor TTF-1, no other airway or alveolar genes or vascular genes were expressed. These studies highlight the power of whole decellularized lung scaffolds to study functional recellularization with MSCs and other cells.

Stem cells and cell therapies in lung biology and lung diseases

The University of Vermont College of Medicine and the Vermont Lung Center, with support of the National Heart, Lung, and Blood Institute (NHLBI), the Alpha-1 Foundation, the American Thoracic Society, the Emory Center for Respiratory Health,the Lymphangioleiomyomatosis (LAM) Treatment Alliance,and the Pulmonary Fibrosis Foundation, convened a workshop,‘‘Stem Cells and Cell Therapies in Lung Biology and Lung Diseases,’’ held July 26-29, 2009 at the University of Vermont,to review the current understanding of the role of stem and progenitor cells in lung repair after injury and to review the current status of cell therapy approaches for lung diseases. These are rapidly expanding areas of study that provide further insight into and challenge traditional views of the mechanisms of lung repair after injury and pathogenesis of several lung diseases. The goals of the conference were to summarize the current state of the field, discuss and debate current controversies, and identify future research directions and opportunities for both basic and translational research in cell-based therapies for lung diseases.

Epigenetic and phenotypic profile of fibroblasts derived from induced pluripotent stem cells

Human induced pluripotent stem (hiPS) cells offer a novel source of patient-specific cells for regenerative medicine. However, the biological potential of iPS-derived cells and their similarities to cells differentiated from human embryonic stem (hES) cells remain unclear. We derived fibroblast-like cells from two hiPS cell lines and show that their phenotypic properties and patterns of DNA methylation were similar to that of mature fibroblasts and to fibroblasts derived from hES cells. iPS-derived fibroblasts (iPDK) and their hES-derived counterparts (EDK) showed similar cell morphology throughout differentiation, and patterns of gene expression and cell surface markers were characteristic of mature fibroblasts. Array-based methylation analysis was performed for EDK, iPDK and their parental hES and iPS cell lines, and hierarchical clustering revealed that EDK and iPDK had closely-related methylation profiles. DNA methylation analysis of promoter regions associated with extracellular matrix (ECM)-production (COL1A1) by iPS- and hESC-derived fibroblasts and fibroblast lineage commitment (PDGFRβ), revealed promoter demethylation linked to their expression, and patterns of transcription and methylation of genes related to the functional properties of mature stromal cells were seen in both hiPS- and hES-derived fibroblasts. iPDK cells also showed functional properties analogous to those of hES-derived and mature fibroblasts, as seen by their capacity to direct the morphogenesis of engineered human skin equivalents. Characterization of the functional behavior of ES- and iPS-derived fibroblasts in engineered 3D tissues demonstrates the utility of this tissue platform to predict the capacity of iPS-derived cells before their therapeutic application.

Fibroblasts derived from human embryonic stem cells direct development and repair of 3D human skin equivalents

Introduction

Pluripotent, human stem cells hold tremendous promise as a source of progenitor and terminally differentiated cells for application in future regenerative therapies. However, such therapies will be dependent upon the development of novel approaches that can best assess tissue outcomes of pluripotent stem cell-derived cells and will be essential to better predict their safety and stability following in vivo transplantation.

Methods

In this study we used engineered, human skin equivalents (HSEs) as a platform to characterize fibroblasts that have been derived from human embryonic stem (hES) cell. We characterized the phenotype and the secretion profile of two distinct hES-derived cell lines with properties of mesenchymal cells (EDK and H9-MSC) and compared their biological potential upon induction of differentiation to bone and fat and following their incorporation into the stromal compartment of engineered, HSEs.

Results

While both EDK and H9-MSC cell lines exhibited similar morphology and mesenchymal cell marker expression, they demonstrated distinct functional properties when incorporated into the stromal compartment of HSEs. EDK cells displayed characteristics of dermal fibroblasts that could support epithelial tissue development and enable re-epithelialization of wounds generated using a 3D tissue model of cutaneous wound healing, which was linked to elevated production of hepatocyte growth factor (HGF). Lentiviral shRNA-mediated knockdown of HGF resulted in a dramatic decrease of HGF secretion from EDK cells that led to a marked reduction in their ability to promote keratinocyte proliferation and re-epithelialization of cutaneous wounds. In contrast, H9-MSCs demonstrated features of mesenchymal stem cells (MSC) but not those of dermal fibroblasts, as they underwent multilineage differentiation in monolayer culture, but were unable to support epithelial tissue development and repair and produced significantly lower levels of HGF.

Conclusions

Our findings demonstrate that hES-derived cells could be directed to specified and alternative mesenchymal cell fates whose function could be distinguished in engineered HSEs. Characterization of hES-derived mesenchymal cells in 3D, engineered HSEs demonstrates the utility of this tissue platform to predict the functional properties of hES-derived fibroblasts before their therapeutic transplantation.

Epithelial-mesenchymal interactions as a working concept for oral mucosa regeneration

Oral mucosa consists of two tissue layers, the superficial epithelium and the underlying lamina propria. Together, oral mucosa functions as a barrier against exogenous substances and pathogens. In development, interactions of stem/progenitor cells of the epithelium and mesenchyme are crucial to the morphogenesis of oral mucosa. Previous work in oral mucosa regeneration has yielded important clues for several meritorious proof-of-concept approaches. Tissue engineering offers a broad array of novel tools for oral mucosa regeneration with reduced donor site trauma and accelerated clinical translation. However, the developmental concept of epithelial-mesenchymal interactions (EMIs) is rarely considered in oral mucosa regeneration. EMIs in postnatal oral mucosa regeneration likely will not be a simple recapitulation of prenatal oral mucosa development. Biomaterial scaffolds play an indispensible role for oral mucosa regeneration and should provide a conducive environment for pivotal EMIs. Autocrine and paracrine factors, either exogenously delivered or innately produced, have rarely been and should be harnessed to promote oral mucosa regeneration. This review focuses on a working concept of epithelial and mesenchymal interactions in oral mucosa regeneration.

Methods for culturing mouse and human embryonic stem cells

Mouse embryonic stem cells (mESCs) were first derived and cultured almost 30 years ago and ever since have been valuable tools for creating knockout mice and for studying early mammalian development. More recently (1998), human embryonic stem cells (hESCs) have been derived from blastocysts, and numerous methods have evolved to culture hESCs in vitro in both complex and defined media. hESCs are especially important at this time as they could potentially be used to treat degenerative diseases and to access the toxicity of new drugs and environmental chemicals. For both human and mouse ESCs, fibroblast feeder layers are often used at some phase in the culturing protocol. The feeders - often mouse embryonic fibroblasts (mEFs) - provide a substrate that increases plating efficiency, helps maintain pluripotency, and facilitates survival and growth of the stem cells. Various protocols for culturing embryonic stem cells from both species are available with newer trends moving toward feeder-free and serum-free culture. The purpose of this chapter is to provide basic protocol information on the isolation of mouse embryonic fibroblasts and establishment of feeder layers, the culture of mESCs on both mEFs and on gelatin in serum-containing medium, and the culture of hESCs in defined media on both mEFs (hESC culture medium) and Matrigel (mTeSR). These basic protocols are intended for researchers wanting to develop stem cell research in their labs. These protocols have been tested in our laboratory and work well. They can be modified and adapted for any relevant user's particular purpose.

Stem cell therapies for recessive dystrophic epidermolysis bullosa

Human epidermis is composed of a stratified squamous epithelium that provides a mechanical barrier against the external environment and which is renewed every 3-4 weeks by resident stem cells in the epidermis. However, in the inherited skin fragility disorder, recessive dystrophic epidermolysis bullosa (RDEB), there is recurrent trauma-induced subepidermal blistering that disrupts epidermal homeostasis and is likely to deplete the epidermal stem cell pool. This review article discusses the nature of epidermal stem cells and other stem cell populations in the skin, as well as other possible extracutaneous sources of stem cells, that might have physiological or therapeutic relevance to cell therapy approaches for RDEB. Strategies to identify, create and use cells with multipotent or pluripotent properties are explored and current clinical experience of stem cell therapy in RDEB is reviewed. There is currently no single optimal therapy for patients with RDEB, but cell therapy technologies are evolving and hold great potential for modifying disease severity and improving quality of life for people living with RDEB.

Embryoid body attachment to reconstituted basement membrane induces a genetic program of epithelial differentiation via jun N-terminal kinase signaling

Embryonic stem (ES) cells are derived from early stage mammalian embryos and have broad developmental potential. These cells can be manipulated experimentally to generate cells of multiple tissue types which could be important in treating human diseases. The ability to produce relevant amounts of these differentiated cell populations creates the basis for clinical interventions in tissue regeneration and repair. Understanding how embryonic stem cells differentiate also can reveal important insights into cell biology. A previously reported mouse embryonic stem cell model demonstrated that differentiated epithelial cells migrated out of embryoid bodies attached to reconstituted basement membrane. We used genomic technology to profile ES cell populations in order to understand the molecular mechanisms leading to epithelial differentiation. Cells with characteristics of cultured epithelium migrated from embryoid bodies attached to reconstituted basement membrane. However, cells that comprised embryoid bodies also rapidly lost ES cell-specific gene expression and expressed proteins characteristic of stratified epithelia within hours of attachment to basement membrane. Gene expression profiling of sorted cell populations revealed upregulation of the BMP/TGFbeta signaling pathway, which was not sufficient for epithelial differentiation in the absence of basement membrane attachment. Activation of c-jun N-terminal kinase 1 (JNK1) and increased expression of Jun family transcription factors was observed during epithelial differentiation of ES cells. Inhibition of JNK signaling completely blocked epithelial differentiation in this model, revealing a key mechanism by which ES cells adopt epithelial characteristics via basement membrane attachment.

Human embryonic stem cell-derived keratinocytes exhibit an epidermal transcription program and undergo epithelial morphogenesis in engineered tissue constructs

Human embryonic stem (hES) cells are an attractive source of cellular material for scientific, diagnostic, and potential therapeutic applications. Protocols are now available to direct hES cell differentiation to specific lineages at high purity under relatively defined conditions; however, researchers must establish the functional similarity of hES cell derivatives and associated primary cell types to validate their utility. Using retinoic acid to initiate differentiation, we generated high-purity populations of keratin 14+ (K14) hES cell-derived keratinocyte (hEK) progenitors and performed microarray analysis to compare the global transcriptional program of hEKs and primary foreskin keratinocytes. Transcriptional patterns were largely similar, though gene ontology analysis identified that genes associated with signal transduction and extracellular matrix were upregulated in hEKs. In addition, we evaluated the ability of hEKs to detect and respond to environmental stimuli such as Ca(2+), serum, and culture at the air-liquid interface. When cultivated on dermal constructs formed with collagen gels and human dermal fibroblasts, hEKs survived and proliferated for 3 weeks in engineered tissue constructs. Maintenance at the air-liquid interface induced stratification of surface epithelium, and immunohistochemistry results indicated that markers of differentiation (e.g., keratin 10, involucrin, and filaggrin) were localized to suprabasal layers. Although the overall tissue morphology was significantly different compared with human skin samples, organotypic cultures generated with hEKs and primary foreskin keratinocytes were quite similar, suggesting these cell types respond to this microenvironment in a similar manner. These results represent an important step in characterizing the functional similarity of hEKs to primary epithelia.