Human embryonic stem-cell derivatives for full reconstruction of the pluristratified epidermis: a preclinical study

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.

Epidermal healing in burns: autologous keratinocyte transplantation as a standard procedure: update and perspective

Background:

Treatment of burned patients is a tricky clinical problem not only because of the extent of the physiologic abnormalities but also because of the limited area of normal skin available.

Methods:

Literature indexed in the National Center (PubMed) has been reviewed using combinations of key words (burns, children, skin graft, tissue engineering, and keratinocyte grafts). Articles investigating the association between burns and graft therapeutic modalities have been considered. Further literature has been obtained by analysis of references listed in reviewed articles.

Results:

Severe burns are conventionally treated with split-thickness skin autografts. However, there are usually not enough skin donor sites. For years, the question of how covering the wound surface became one of the major challenges in clinical research area and several procedures were proposed. The microskin graft is one of the oldest methods to cover extensive burns. This technique of skin expansion is efficient, but results remain inconsistent. An alternative is to graft cultured human epidermal keratinocytes. However, because of several complications and labor-intensive process of preparing grafts, the initial optimism for cultured epithelial autograft has gradually declined. In an effort to solve these drawbacks, isolated epithelial cells from selecting donor site were introduced in skin transplantation.

Conclusions:

Cell suspensions transplanted directly to the wound is an attractive process, removing the need for attachment to a membrane before transfer and avoiding one potential source of inefficiency. Choosing an optimal donor site containing cells with high proliferative capacity is essential for graft success in burns.

Study of proliferation and 3D epidermal reconstruction from foreskin, auricular and trunk keratinocytes in children

OBJECTIVE

Severe burns in children are conventionally treated with split-thickness skin autografts or epidermal sheets. An alternative approach is to graft isolated keratinocytes. We evaluated foreskin and other anatomic sites as donor sources for autologous keratinocyte graft in children. We studied in vitro capacities of isolated keratinocytes to divide and reconstitute epidermal tissue.

METHODS

Keratinocytes were isolated from foreskin, auricular skin, chest and abdominal skin by enzymatic digestion. Living cell recovery, in vitro proliferation, epidermal reconstruction capacities and differentiation status were analyzed.

RESULTS

In vitro studies revealed the higher yield of living keratinocyte recovery from foreskin and higher potential in terms of proliferative capacity, regeneration and differentiation. Cultured keratinocytes from foreskin express lower amounts of differentiation markers than those isolated from trunk and ear. Histological analysis of reconstituted human epidermis derived from foreskin and inguinal keratinocytes showed a structured multilayered epithelium, whereas those obtained from ear pinna-derived keratinocytes were unstructured.

CONCLUSION

Our studies highlight the potential of foreskin tissue for autograft applications in boys. A suitable alternative donor site for autologous cell transplantation in female paediatric burn patients remains an open question in our department. We tested the hypothesis that in vitro studies and RHE reconstructive capacities of cells from different body sites can be helpful to select an optimal site for keratinocyte isolation before considering graft protocols for girls.

Methylation and transcripts expression at the imprinted GNAS locus in human embryonic and induced pluripotent stem cells and their derivatives

Data from the literature indicate that genomic imprint marks are disturbed in human pluripotent stem cells (PSCs). GNAS is an imprinted locus that produces one biallelic (Gsα) and four monoallelic (NESP55, GNAS-AS1, XLsα, and A/B) transcripts due to differential methylation of their promoters (DMR). To document imprinting at the GNAS locus in PSCs, we studied GNAS locus DMR methylation and transcript (NESP55, XLsα, and A/B) expression in human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs) derived from two human fibroblasts and their progenies. Results showed that (1) methylation at the GNAS locus DMRs is DMR and cell line specific, (2) changes in allelic transcript expression can be independent of a change in allele-specific DNA methylation, and (3) interestingly, methylation at A/B DMR is correlated with A/B transcript expression. These results indicate that these models are valuable to study the mechanisms controlling GNAS methylation, factors involved in transcript expression, and possibly mechanisms involved in the pathophysiology of pseudohypoparathyroidism type 1B.

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GNAS locus methylation is DMR and cell line specific in human pluripotent stem cells

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Allelic transcript expression can be independent of allele-specific DNA methylation

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A/B transcript expression, a key for PHP1B, is correlated with A/B DMR methylation

Stem cell and tissue engineering in breast reconstruction

Breast cancer worldwide is the most common cancer in women with incidence rate varying from geographic areas. Guidelines for management of breast cancer have been largely established and widely used. Mastectomy is one of the surgical procedures used treating breast cancer. Optionally, after mastectomy, appropriately selected patients could undergo breast reconstruction to create their breast contour. Many techniques have been used for breast reconstructive surgery, mainly implant-based and autologous tissue reconstruction. Even with highly-experienced surgeon and good-quality breast and autologous substitute tissue, still there could be unfilled defect after mastectomy with reconstruction. Stem cell, in particular, adipose-derived stem cell residing within fat tissue, could be used to fill the imperfection providing optimal breast shape and natural feeling of fat tissue. However, whether surgical reconstruction alone or in combination with stem cell and tissue engineering approach be used, the ultimate outcomes are patient safety first and satisfaction second.

Removal of reprogramming transgenes improves the tissue reconstitution potential of keratinocytes generated from human induced pluripotent stem cells

Human induced pluripotent stem cell (hiPSC) lines have a great potential for therapeutics because customized cells and organs can be induced from such cells. Assessment of the residual reprogramming factors after the generation of hiPSC lines is required, but an ideal system has been lacking. Here, we generated hiPSC lines from normal human dermal fibroblasts with piggyBac transposon bearing reprogramming transgenes followed by removal of the transposon by the transposase. Under this condition, we compared the phenotypes of transgene-residual and -free hiPSCs of the same genetic background. The transgene-residual hiPSCs, in which the transcription levels of the reprogramming transgenes were eventually suppressed, were quite similar to the transgene-free hiPSCs in a pluripotent state. However, after differentiation into keratinocytes, clear differences were observed. Morphological, functional, and molecular analyses including single-cell gene expression profiling revealed that keratinocytes from transgene-free hiPSC lines were more similar to normal human keratinocytes than those from transgene-residual hiPSC lines, which may be partly explained by reactivation of residual transgenes upon induction of keratinocyte differentiation. These results suggest that transgene-free hiPSC lines should be chosen for therapeutic purposes.

Inhibition of keratinocyte differentiation by the synergistic effect of IL-17A, IL-22, IL-1α, TNFα and oncostatin M

Keratinocyte differentiation program leading to an organized epidermis plays a key role in maintaining the first line of defense of the skin. Epidermal integrity is regulated by a tight communication between keratinocytes and leucocytes, particularly under cytokine control. Imbalance of the cytokine network leads to inflammatory diseases such as psoriasis. Our attempt to model skin inflammation showed that the combination of IL-17A, IL-22, IL-1α, OSM and TNFα (Mix M5) synergistically increases chemokine and antimicrobial-peptide expression, recapitulating some features of psoriasis. Other characteristics of psoriasis are acanthosis and down-regulation of keratinocyte differentiation markers. Our aim was to characterize the specific roles of these cytokines on keratinocyte differentiation, and to compare with psoriatic lesion features. All cytokines decrease keratinocyte differentiation markers, but IL-22 and OSM were the most powerful, and the M5 strongly synergized the effects. In addition, IL-22 and OSM induced epidermal hyperplasia in vitro and M5 induced epidermal thickening and decreased differentiation marker expression in a mouse model, as observed in human psoriatic skin lesions. This study highlights the precise role of cytokines in the skin inflammatory response. IL-22 and OSM more specifically drive epidermal hyperplasia and differentiation loss while IL-1α, IL-17A and TNFα were more involved in the activation of innate immunity.

Characterization of fetal keratinocytes, showing enhanced stem cell-like properties: a potential source of cells for skin reconstruction

Epidermal stem cells have been in clinical application as a source of culture-generated grafts. Although applications for such cells are increasing due to aging populations and the greater incidence of diabetes, current keratinocyte grafting technology is limited by immunological barriers and the time needed for culture amplification. We studied the feasibility of using human fetal skin cells for allogeneic transplantation and showed that fetal keratinocytes have faster expansion times, longer telomeres, lower immunogenicity indicators, and greater clonogenicity with more stem cell indicators than adult keratinocytes. The fetal cells did not induce proliferation of T cells in coculture and were able to suppress the proliferation of stimulated T cells. Nevertheless, fetal keratinocytes could stratify normally in vitro. Experimental transplantation of fetal keratinocytes in vivo seeded on an engineered plasma scaffold yielded a well-stratified epidermal architecture and showed stable skin regeneration. These results support the possibility of using fetal skin cells for cell-based therapeutic grafting.

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Properties of fetal and adult keratinocytes are compared in tissue culture and grafts

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Fetal skin cells can be engrafted and show stable human-to-mouse skin regeneration

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Fetal keratinocytes are stem cell rich and need no differentiation before grafting

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Fetal keratinocytes are able to suppress proliferation of stimulated T cells in vitro

Disease modeling using human induced pluripotent stem cells: lessons from the liver

Human pluripotent stem cells (hPSCs) have the capacity to differentiate into any of the hundreds of distinct cell types that comprise the human body. This unique characteristic has resulted in considerable interest in the field of regenerative medicine, given the potential for these cells to be used to protect, repair, or replace diseased, injured, and aged cells within the human body. In addition to their potential in therapeutics, hPSCs can be used to study the earliest stages of human development and to provide a platform for both drug screening and disease modeling using human cells. Recently, the description of human induced pluripotent stem cells (hIPSCs) has allowed the field of disease modeling to become far more accessible and physiologically relevant, as pluripotent cells can be generated from patients of any genetic background. Disease models derived from hIPSCs that manifest cellular disease phenotypes have been established to study several monogenic diseases; furthermore, hIPSCs can be used for phenotype-based drug screens to investigate complex diseases for which the underlying genetic mechanism is unknown. As a result, the use of stem cells as research tools has seen an unprecedented growth within the last decade as researchers look for in vitro disease models which closely mimic in vivo responses in humans. Here, we discuss the beginnings of hPSCs, starting with isolation of human embryonic stem cells, moving into the development and optimization of hIPSC technology, and ending with the application of hIPSCs towards disease modeling and drug screening applications, with specific examples highlighting the modeling of inherited metabolic disorders of the liver. This article is part of a Special Issue entitled Linking transcription to physiology in lipodomics.

Burns in children: standard and new treatments

Outcomes of patients with burns have improved substantially over the past two decades. Findings from a 2012 study in The Lancet showed that a burn size of more than 60% total body surface area burned (an increase from 40% a decade ago) is associated with risks and mortality. Similar data have been obtained in adults and elderly people who have been severely burned. We discuss recent and future developments in burn care to improve outcomes of children.

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.

Wound coverage technologies in burn care: novel techniques

Improvements in burn wound care have vastly decreased morbidity and mortality in severely burned patients. Development of new therapeutic approaches to increase wound repair has the potential to reduce infection, graft rejection, and hypertrophic scarring. The incorporation of tissue-engineering techniques, along with the use of exogenous proteins, genes, or stem cells to enhance wound healing, heralds new treatment regimens based on the modification of already existing biological activity. Refinements to surgical techniques have enabled the creation of protocols for full facial transplantation. With new technologies and advances such as these, care of the severely burned will undergo massive changes over the next decade. This review centers on new developments that have recently shown great promise in the investigational arena.

Antagonistic effect of the inflammasome on thymic stromal lymphopoietin expression in the skin

BACKGROUND

Innate immune sensors control key cytokines that regulate T-cell priming and T-cell fate. This is particularly evident in allergic reactions, which represent ideal systems to study the interplay of innate and adaptive immunity. In patients with contact dermatitis, inflammasome-mediated IL-1 activation is responsible for a TH1 immune response. Surprisingly, the IL-1 signaling pathway was also proposed to control the activation of thymic stromal lymphopoietin (TSLP), a cytokine implicated in development of the T(H)2 response in patients with atopic dermatitis (AD) and asthma.

OBJECTIVES

We sought to assess the effect of the inflammasome on TSLP expression levels and the development of AD.

METHODS

We studied the effect of the inflammasome activator 2,4-dinitrofluorobenzene, and IL-1β on TSLP mRNA expression levels in mouse and human cell lines (in vitro assays), as well as in live mice and on human skin transplants. We also assessed the effect of 2,4-dinitrofluorobenzene on TSLP and the TH2 response in mice in which the inflammasome and IL-1 signaling pathways were blocked, either genetically or pharmacologically, in 2 models of AD.

RESULTS

We provide in vitro and in vivo evidence that inflammasome activation has an inhibitory role on TSLP mRNA expression and T(H)2 cell fate in the skin. We also show that solvents influence the activation of TSLP and IL-1β and direct the T-cell fate to a given hapten.

CONCLUSION

Our observations strongly suggest that the TH1 versus TH2 cell fate decision is regulated at multiple levels and starts with innate immune events occurring within peripheral epithelial tissues.

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.

Epidermal development in mammals: key regulators, signals from beneath, and stem cells

Epidermis is one of the best-studied tissues in mammals that contain types of stem cells. Outstanding works in recent years have shed great light on behaviors of different epidermal stem cell populations in the homeostasis and regeneration of the epidermis as well as hair follicles. Also, the molecular mechanisms governing these stem cells are being elucidated, from genetic to epigenetic levels. Compared with the explicit knowledge about adult skin, embryonic development of the epidermis, especially the early period, still needs exploration. Furthermore, stem cells in the embryonic epidermis are largely unstudied or ambiguously depicted. In this review, we will summarize and discuss the process of embryonic epidermal development, with focuses on some key molecular regulators and the role of the sub-epidermal mesenchyme. We will also try to trace adult epidermal stem cell populations back to embryonic development. In addition, we will comment on in vitro derivation of epidermal lineages from ES cells and iPS cells.

A small molecule inhibitor of SRC family kinases promotes simple epithelial differentiation of human pluripotent stem cells

Human pluripotent stem cells (hPSCs) provide unprecedented opportunities to study the earliest stages of human development in vitro and have the potential to provide unlimited new sources of cells for regenerative medicine. Although previous studies have reported cytokeratin 14+/p63+ keratinocyte generation from hPSCs, the multipotent progenitors of epithelial lineages have not been described and the developmental pathways regulating epithelial commitment remain largely unknown. Here we report membrane localization of β-catenin during retinoic acid (RA)--induced epithelial differentiation. In addition hPSC treatment with the Src family kinase inhibitor SU6656 modulated β-catenin localization and produced an enriched population of simple epithelial cells under defined culture conditions. SU6656 strongly upregulated expression of cytokeratins 18 and 8 (K18/K8), which are expressed in simple epithelial cells, while repressing expression of the pluripotency gene Oct4. This homogeneous population of K18+K8+Oct4- simple epithelial precursor cells can further differentiate into cells expressing keratinocyte or corneal-specific markers. These enriched hPSC-derived simple epithelial cells may provide a ready source for development and toxicology cell models and may serve as a progenitor for epithelial cell transplantation applications.

Foreskin-isolated keratinocytes provide successful extemporaneous autologous paediatric skin grafts

Severe burns in children are conventionally treated with split-thickness skin autografts or epidermal sheets. However, neither early complete healing nor quality of epithelialization is satisfactory. An alternative approach is to graft isolated keratinocytes. We evaluated paediatric foreskin and auricular skin as donor sources, autologous keratinocyte transplantation, and compared the graft efficiency to the in vitro capacities of isolated keratinocytes to divide and reconstitute epidermal tissue. Keratinocytes were isolated from surgical samples by enzymatic digestion. Living cell recovery, in vitro proliferation and epidermal reconstruction capacities were evaluated. Differentiation status was analysed, using qRT-PCR and immunolabelling. Eleven children were grafted with foreskin-derived (boys) or auricular (girls) keratinocyte suspensions dripped onto deep severe burns. The aesthetic and functional quality of epithelialization was monitored in a standardized way. Foreskin keratinocyte graft in male children provides for the re-epithelialization of partial deep severe burns and accelerates wound healing, thus allowing successful wound closure, and improves the quality of scars. In accordance, in vitro studies have revealed a high yield of living keratinocyte recovery from foreskin and their potential in terms of regeneration and differentiation. We report a successful method for grafting paediatric males presenting large severe burns through direct spreading of autologous foreskin keratinocytes. This alternative method is easy to implement, improves the quality of skin and minimizes associated donor site morbidity. In vitro studies have highlighted the potential of foreskin tissue for graft applications and could help in tissue selection with the prospect of grafting burns for girls.

The 3R principle: advancing clinical application of human pluripotent stem cells

The first derivation of human embryonic stem cells brought with it a clear understanding that animal models of human disease might be replaced by an unlimited supply of human cells for research, drug discovery, and drug development. With the advent of clinical trials using human pluripotent stem cell-based therapies, it is both timely and relevant to reflect on factors that will facilitate future translation of this technology. Human pluripotent cells are increasingly being used to investigate the molecular mechanisms that underpin normal and pathological human development. Their differentiated progeny are also being used to identify novel pharmaceuticals, to screen for toxic effects of known chemicals, and to investigate cell or tissue transplantation strategies. The intrinsic assumption of these research efforts is that the information gained from these studies will be more accurate, and therefore of greater relevance, than traditional investigations based on animal models of human disease and injury. This review will therefore evaluate how animals and animal-derived products are used for human pluripotent stem cell research, and will indicate how efforts to further reduce or remove animals and animal products from this research will increase the clinical translation of human pluripotent stem cell technologies through drug discovery, toxicology screening, and cell replacement therapies.

Impaired epithelial differentiation of induced pluripotent stem cells from ectodermal dysplasia-related patients is rescued by the small compound APR-246/PRIMA-1MET

Ectodermal dysplasia is a group of congenital syndromes affecting a variety of ectodermal derivatives. Among them, ectrodactyly, ectodermal dysplasia, and cleft lip/palate (EEC) syndrome is caused by single point mutations in the p63 gene, which controls epidermal development and homeostasis. Phenotypic defects of the EEC syndrome include skin defects and limbal stem-cell deficiency. In this study, we designed a unique cellular model that recapitulated major embryonic defects related to EEC. Fibroblasts from healthy donors and EEC patients carrying two different point mutations in the DNA binding domain of p63 were reprogrammed into induced pluripotent stem cell (iPSC) lines. EEC-iPSC from both patients showed early ectodermal commitment into K18(+) cells but failed to further differentiate into K14(+) cells (epidermis/limbus) or K3/K12(+) cells (corneal epithelium). APR-246 (PRIMA-1(MET)), a small compound that restores functionality of mutant p53 in human tumor cells, could revert corneal epithelial lineage commitment and reinstate a normal p63-related signaling pathway. This study illustrates the relevance of iPSC for p63 related disorders and paves the way for future therapy of EEC.

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.

An update review of stem cell applications in burns and wound care

The ultimate goal of the treatment of cutaneous burns and wounds is to restore the damaged skin both structurally and functionally to its original state. Recent research advances have shown the great potential of stem cells in improving the rate and quality of wound healing and regenerating the skin and its appendages. Stem cell-based therapeutic strategies offer new prospects in the medical technology for burns and wounds care. This review seeks to give an updated overview of the applications of stem cell therapy in burns and wound management since our previous review of the “stem cell strategies in burns care”.

Human embryonic stem cell (hESC) and human embryo research

Human embryonic stem cell research has emerged as an important platform for the understanding and treatment of pediatric diseases. From its inception, however, it has raised ethical concerns based not on the use of stem cells themselves but on objections to the source of the cells--specifically, the destruction of preimplantation human embryos. Despite differences in public opinion on this issue, a large majority of the public supports continued research using embryonic stem cells. Given the possible substantial benefit of stem cell research on child health and development, the American Academy of Pediatrics believes that funding and oversight for human embryo and embryonic stem cell research should continue.

Capturing epidermal stemness for regenerative medicine

The skin is privileged because several skin-derived stem cells (epithelial stem cells from epidermis and its appendages, mesenchymal stem cells from dermis and subcutis, melanocyte stem cells) can be efficiently captured for therapeutic use. Main indications remain the permanent coverage of extensive third degree burns and healing of chronic cutaneous wounds, but recent advances in gene therapy technology open the door to the treatment of disabling inherited skin diseases with genetically corrected keratinocyte stem cells. Therapeutic skin stem cells that were initially cultured in research or hospital laboratories must be produced according strict regulatory guidelines, which ensure patients and medical teams that the medicinal cell products are safe, of constant quality and manufactured according to state-of-the art technology. Nonetheless, it does not warrant clinical efficacy and permanent engraftment of autologous stem cells remains variable. There are many challenges ahead to improve efficacy among which to keep telomere-dependent senescence and telomere-independent senescence (clonal conversion) to a minimum in cell culture and to understand the cellular and molecular mechanisms implicated in engraftment. Finally, medicinal stem cells are expansive to produce and reimbursement of costs by health insurances is a major concern in many countries.

Tissue engineering for the management of chronic wounds: current concepts and future perspectives

Chronic wounds constitute a significant and growing biomedical burden. With the increasing growth of populations prone to dysfunctional wound healing, there is an urgent and unmet need for novel strategies to both prevent and treat these complications. Tissue engineering offers the potential to create functional skin, and the synergistic efforts of biomedical engineers, material scientists, and molecular and cell biologists have yielded promising therapies for non-healing wounds. However, traditional paradigms for wound healing focus largely on the role of inflammatory cells and fail to incorporate more recent research highlighting the importance of stem cells and matrix dynamics in skin repair. Approaches to chronic wound healing centred on inflammation alone are inadequate to guide the development of regenerative medicine-based technologies. As the molecular pathways and biologic defects underlying non-healing wounds are further elucidated, multifaceted bioengineering systems must advance in parallel to exploit this knowledge. In this viewpoint essay, we highlight the current concepts in tissue engineering for chronic wounds and speculate on areas for future research in this increasingly interdisciplinary field.

Unique preservation of neural cells in Hutchinson- Gilford progeria syndrome is due to the expression of the neural-specific miR-9 microRNA

One puzzling observation in patients affected with Hutchinson-Gilford progeria syndrome (HGPS), who overall exhibit systemic and dramatic premature aging, is the absence of any conspicuous cognitive impairment. Recent studies based on induced pluripotent stem cells derived from HGPS patient cells have revealed a lack of expression in neural derivatives of lamin A, a major isoform of LMNA that is initially produced as a precursor called prelamin A. In HGPS, defective maturation of a mutated prelamin A induces the accumulation of toxic progerin in patient cells. Here, we show that a microRNA, miR-9, negatively controls lamin A and progerin expression in neural cells. This may bear major functional correlates, as alleviation of nuclear blebbing is observed in nonneural cells after miR-9 overexpression. Our results support the hypothesis, recently proposed from analyses in mice, that protection of neural cells from progerin accumulation in HGPS is due to the physiologically restricted expression of miR-9 to that cell lineage.

Tissue engineering the monosynaptic circuit of the stretch reflex arc with co-culture of embryonic motoneurons and proprioceptive sensory neurons

The sensory circuit of the stretch reflex arc is composed of intrafusal muscle fibers and their innervating proprioceptive neurons that convert mechanical information regarding muscle length and tension into action potentials that synapse onto the homonymous motoneurons in the ventral spinal cord which innervate the extrafusal fibers of the same muscle. To date, the in vitro synaptic connection between proprioceptive sensory neurons and spinal motoneurons has not been demonstrated. A functional in vitro system demonstrating this connection would enable the understanding of feedback by the integration of sensory input into the spinal reflex arc. Here we report a co-culture of rat embryonic motoneurons and proprioceptive sensory neurons from dorsal root ganglia (DRG) in a defined serum-free medium on a synthetic silane substrate (DETA). Furthermore, we have demonstrated functional synapse formation in the co-culture by immunocytochemistry and electrophysiological analysis. This work will be valuable for enabling in vitro model systems for the study of spinal motor control and related pathologies such as spinal cord injury, muscular dystrophy and spasticity by improving our understanding of the integration of the mechanosensitive feedback mechanism.

Strategies for enrichment and selection of stem cell-derived tissue precursors

Human embryonic stem cells have the capacity for self-renewal and pluripotency and thus are a primary candidate for tissue engineering and regenerative therapies. These cells also provide an opportunity to study the development of human tissues ex vivo. To date, numerous human embryonic stem cell lines have been derived and characterized. In this review, we will detail the strategies used to direct tissue-specific differentiation of embryonic stem cells. We also will discuss how these strategies have produced new sources of tissue-specific progenitor cells. Finally, we will describe the next generation of methods being developed to identify and select stem cell-derived tissue precursors for experimental study and clinical use.

Regenerative medicine as applied to general surgery

The present review illustrates the state of the art of regenerative medicine (RM) as applied to surgical diseases and demonstrates that this field has the potential to address some of the unmet needs in surgery. RM is a multidisciplinary field whose purpose is to regenerate in vivo or ex vivo human cells, tissues, or organs to restore or establish normal function through exploitation of the potential to regenerate, which is intrinsic to human cells, tissues, and organs. RM uses cells and/or specially designed biomaterials to reach its goals and RM-based therapies are already in use in several clinical trials in most fields of surgery. The main challenges for investigators are threefold: Creation of an appropriate microenvironment ex vivo that is able to sustain cell physiology and function in order to generate the desired cells or body parts; identification and appropriate manipulation of cells that have the potential to generate parenchymal, stromal and vascular components on demand, both in vivo and ex vivo; and production of smart materials that are able to drive cell fate.

Skin bioengineering: preclinical and clinical applications

Regenerative Medicine is an emerging field that combines basic research and clinical observations in order to identify the elements required to replace damaged tissues and organs in vivo and to stimulate the body's intrinsic regenerative capacity. Great benefits are expected in this field as researchers take advantage of the potential regenerative properties of both embryonic and adult stem cells, and more recently, of induced pluripotent stem cells. Bioengineered skin emerged mainly in response to a critical need for early permanent coverage of extensive burns. Later this technology was also applied to the treatment of chronic ulcers. Our group has established a humanized mouse model of skin grafting that involves the use of bioengineered human skin in immunodeficient mice. This model is suitable for the study of physiologic and pathologic cutaneous processes and the evaluation of treatment strategies for skin diseases, including protocols for gene and cell therapy and tissue engineering.

Engineered whole organs and complex tissues

End-stage organ failure is a key challenge for the medical community because of the ageing population and the severe shortage of suitable donor organs available. Equally, injuries to or congenital absence of complex tissues such as the trachea, oesophagus, or skeletal muscle have few therapeutic options. A new approach to treatment involves the use of three-dimensional biological scaffolds made of allogeneic or xenogeneic extracellular matrix derived from non-autologous sources. These scaffolds can act as an inductive template for functional tissue and organ reconstruction after recellularisation with autologous stem cells or differentiated cells. Such an approach has been used successfully for the repair and reconstruction of several complex tissues such as trachea, oesophagus, and skeletal muscle in animal models and human beings, and, guided by appropriate scientific and ethical oversight, could serve as a platform for the engineering of whole organs and other tissues.

miR-125 potentiates early neural specification of human embryonic stem cells

The role of microRNAs (miRNAs) as coordinators of stem cell fate has emerged over the last decade. We have used human embryonic stem cells to identify miRNAs involved in neural lineage commitment induced by the inhibition of TGFβ-like molecule-mediated pathways. Among several candidate miRNAs expressed in the fetal brain, the two isoforms of miR-125 alone were detected in a time window compatible with a role in neural commitment in vitro. Functional analysis indicated that miR-125 isoforms were actively involved in the promotion of pluripotent cell conversion into SOX1-positive neural precursors. miR-125 promotes neural conversion by avoiding the persistence of non-differentiated stem cells and repressing alternative fate choices. This was associated with the regulation by miR-125 of SMAD4, a key regulator of pluripotent stem cell lineage commitment. Activation of miR-125 was directly responsive to the levels of TGFβ-like molecules, placing miR-125 at the core of mechanisms that lead to the irreversible neural lineage commitment of pluripotent stem cells in response to external stimuli.

Using stem cells in skin regeneration: possibilities and reality

Tissue-engineered skin has a long history of clinical applications, yet current treatments are not capable of completely regenerating normal, uninjured skin. Nonetheless, the field has experienced a tremendous development in the past 10 years, encountering the summit of tissue engineering (TE) and the arising of stem cell research. Since then, unique features of these cells such as self-renewal capacity, multi-lineage differentiation potential, and wound healing properties have been highlighted. However, a realistic perspective of their outcome in skin regenerative medicine applications is still absent. This review intends to discuss the directions that adult and embryonic stem cells (ESCs) can take, strengthening the skin regeneration field. Distinctively, a critical overview of stem cells' differentiation potential onto skin main lineages, along with a highlight of their participation in wound healing mechanisms, is herein provided. We aim to compile and review significant work to allow a better understanding of the best skin TE approaches, enabling the embodiment of the materialization of a new era in skin regeneration to come, with a conscious overview of the current limitations.

Diverse p63 and p73 isoforms regulate Δ133p53 expression through modulation of the internal TP53 promoter activity

In response to stress, p53 binds and transactivates the internal TP53 promoter, thus regulating the expression of its own isoform, Δ133p53α. Here, we report that, in addition to p53, at least four p63/p73 isoforms regulate Δ133p53 expression at transcriptional level: p63β, ΔNp63α, ΔNp63β and ΔNp73γ. This regulation occurs through direct DNA-binding to the internal TP53 promoter as demonstrated by chromatin immunoprecipitation and the use of DNA-binding mutant p63. The promoter regions involved in the p63/p73-mediated transactivation were identified using deleted, mutant and polymorphic luciferase reporter constructs. In addition, we observed that transient expression of p53 family members modulates endogenous Δ133p53α expression at both mRNA and protein levels. We also report concomitant variation of p63 and Δ133p53 expression during keratinocyte differentiation of HaCat cells and induced pluripotent stem cells derived from mutated p63 ectodermal dysplasia patients. Finally, proliferation assays indicated that Δ133p53α isoform regulates the anti-proliferative activities of p63β, ΔNp63α, ΔNp63β and ΔNp73γ. Overall, this study shows a strong interplay between p53, p63 and p73 isoforms to orchestrate cell fate outcome.

Neuromuscular junction formation between human stem cell-derived motoneurons and human skeletal muscle in a defined system

Functional in vitro models composed of human cells will constitute an important platform in the next generation of system biology and drug discovery. This study reports a novel human-based in vitro Neuromuscular Junction (NMJ) system developed in a defined serum-free medium and on a patternable non-biological surface. The motoneurons and skeletal muscles were derived from fetal spinal stem cells and skeletal muscle stem cells. The motoneurons and skeletal myotubes were completely differentiated in the co-culture based on morphological analysis and electrophysiology. NMJ formation was demonstrated by phase contrast microscopy, immunocytochemistry and the observation of motoneuron-induced muscle contractions utilizing time-lapse recordings and their subsequent quenching by d-Tubocurarine. Generally, functional human based systems would eliminate the issue of species variability during the drug development process and its derivation from stem cells bypasses the restrictions inherent with utilization of primary human tissue. This defined human-based NMJ system is one of the first steps in creating functional in vitro systems and will play an important role in understanding NMJ development, in developing high information content drug screens and as test beds in preclinical studies for spinal or muscular diseases/injuries such as muscular dystrophy, Amyotrophic lateral sclerosis and spinal cord repair.

Three-dimensional biomaterials for the study of human pluripotent stem cells

The self-renewal and differentiation of human pluripotent stem cells (hPSCs) have typically been studied in flat, two-dimensional (2D) environments. In this Perspective, we argue that 3D model systems may be needed in addition, as they mimic the natural 3D tissue organization more closely. We survey methods that have used 3D biomaterials for expansion of undifferentiated hPSCs, directed differentiation of hPSCs and transplantation of differentiated hPSCs in vivo.

Functional melanocytes derived from human pluripotent stem cells engraft into pluristratified epidermis

Melanocytes are essential for skin homeostasis and protection, and their defects in humans lead to a wide array of diseases that are potentially extremely severe. To date, the analysis of molecular mechanisms and the function of human melanocytes have been limited because of the difficulties in accessing large numbers of cells with the specific phenotypes. This issue can now be addressed via a differentiation protocol that allows melanocytes to be obtained from pluripotent stem cell lines, either induced or of embryonic origin, based on the use of moderate concentrations of a single cytokine, bone morphogenic protein 4. Human melanocytes derived from pluripotent stem cells exhibit all the characteristic features of their adult counterparts. This includes the enzymatic machinery required for the production and functional delivery of melanin to keratinocytes. Melanocytes also integrate appropriately into organotypic epidermis reconstructed in vitro. The availability of human cells committed to the melanocytic lineage in vitro will enable the investigation of those mechanisms that guide the developmental processes and will facilitate analysis of the molecular mechanisms responsible for genetic diseases. Access to an unlimited resource may also prove a vital tool for the treatment of hypopigmentation disorders when donors with matching haplotypes become available in clinically relevant banks of pluripotent stem cell lines.

miR-203 modulates epithelial differentiation of human embryonic stem cells towards epidermal stratification

The molecular mechanisms controlling the differentiation of human basal keratinocyte stem cells towards the epidermis are well characterized, whereas the earliest process leading to the specification of embryonic stem cells into keratinocytes is still not well understood. MicroRNAs are regulators of many cellular events, but evidence for microRNA acting on the differentiation of human embryonic stem cells into a specific lineage has been elusive. By using our recent protocol for obtaining functional keratinocytes from hESC, we attempted to analyze the role of microRNAs in the early stages of epidermal differentiation. Thus, we identified a set of 5 microRNAs, namely miR-200a, miR-200b, miR-203, miR-205 and miR-429, that are specifically overexpressed during the early stages of the differentiation process. Interestingly, our functional analyses revealed an instrumental role of miR-203, which had been previously shown to play a key role during the formation of the pluristratified epidermis by basal keratinocyte stem cells, in the early keratinocyte commitment. These results highlight the determinant and unique role of miR-203 during the entire process of epidermal development by extending its spectrum of action from the early commitment of embryonic stem cells to ultimate differentiation of the organ.

Evaluation of the multipotent character of human adipose tissue-derived stem cells isolated by Ficoll gradient centrifugation and red blood cell lysis treatment

In the present study, the multipotent potential of two differential isolated human adipose-derived stem cell (hADSC) populations was evaluated. More specifically, hADSC isolated by means of classical Ficoll (F) gradient centrifugation were compared to hADSC isolated by means of red blood cell (RBC) lysis treatment and subsequent cultivation as 3D spheres. No significant difference in the genotypic expression of the multipotent markers Oct-4, Sox-2, Nanog, Klf-4 and cMyc could be observed between both isolation methods. Upon adipogenic and osteogenic differentiation, both hADSC populations showed lipid droplet accumulation and mineral deposition, respectively. Although, a more pronounced mineral deposition was observed in hADSC-RBC, suggesting a higher osteogenic potential. Upon exposure to keratinogenic media, both hADSC populations expressed the keratinocyte markers filaggrin and involucrin, evidencing a successful keratinogenic differentiation. Yet, no differences in expression were observed between the distinctive isolation procedures. Finally, upon exposure to neurogenic differentiation media, a significant difference in marker expression was observed. Indeed, hADSC-RBC only expressed vimentin and nestin, whereas hADSC-F expressed vimentin, nestin, NF-200, MBP and TH, suggesting a higher neurogenic potential. In summary, our data suggest that the choice of the most efficient isolation procedure of hADSC depends on the differentiated cell type ultimately required.

Mesenchymal differentiation propensity of a human embryonic stem cell line

OBJECTIVES

To characterize basal differentiation tendencies of a human embryonic stem (hES) cell line, KCL-002.

MATERIALS AND METHODS

In vitro specification and differentiation of hES cells were carried out using embryoid body (EB) cultures and tests of pluripotency and in vivo differentiation were performed by teratoma assays in SCID mice. Real-time PCR, immunohistochemistry, flow cytometry and histological analyses were used to identify expression of genes and proteins associated with the ectodermal, endodermal and mesodermal germ layers.

RESULTS

Undifferentiated KCL-002 cells expressed characteristic markers of pluripotent stem cells such as Nanog, Sox-2, Oct-4 and TRA 1-60. When differentiated in vitro as EB cultures, expression of pluripotency, endodermal and ectodermal markers decreased rapidly. In contrast, mesodermal and mesenchymal markers such as VEGFR-2, α-actin and vimentin increased during EB differentiation as shown by qPCR, immunostaining and flow cytometric analyses. Teratoma formation in SCID mice demonstrated the potential to form all germ layers in vivo with a greater proportion of the tumours containing mesenchymal derivatives.

CONCLUSIONS

The data presented suggest that the KCL-002 hES cell line is pluripotent and harbours a bias in basal differentiation tendencies towards mesodermal and mesenchymal lineage cells. Characterizing innate differentiation propensities of hES cell lines is important for understanding heterogeneity between different cell lines and for further studies aimed at deriving specific lineages from hES cells.