Dermal fibroblast-derived growth factors restore the ability of beta(1) integrin-deficient embryonal stem cells to differentiate into keratinocytes

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.

Pluripotent Stem Cell Differentiation Toward Functional Basal Stratified Epithelial Cells

In this chapter, an efficient feeder-free protocol of differentiating human pluripotent stem cells (hPSCs) toward the epidermal lineage to generate induced epidermal keratinocytes (iKCs) is described. The iKCs are able to terminally differentiate supra-basally. This hPSC-to-iKC differentiation can serve as a useful model to study epidermal development and disease as well as for therapeutic applications.

Characterization of in vitro 3D cultures

Over the past decade, 3D culture models of human and animal cells have found their way into tissue differentiation, drug development, personalized medicine and tumour behaviour studies. Embryoid bodies (EBs) are in vitro 3D cultures established from murine pluripotential stem cells, whereas tumoroids are patient-derived in vitro 3D cultures. This thesis aims to describe a new implication of an embryoid body model and to characterize the patient-specific microenvironment of the parental tumour in relation to tumoroid growth rate. In this thesis, we described a high-throughput monitoring method, where EBs are used as a dynamic angiogenesis model. In this model, digital image analysis (DIA) is implemented on immunohistochemistry (IHC) stained sections of the cultures over time. Furthermore, we have investigated the correlation between the genetic profile and inflammatory microenvironment of parental tumours on the in vitro growth rate of tumoroids. The EBs were cultured in spinner flasks. The samples were collected at days 4, 6, 9, 14, 18 and 21, dehydrated and embedded in paraffin. The histological sections were IHC stained for the endothelial marker CD31 and digitally scanned. The virtual whole-image slides were digitally analysed by Visiopharm® software. Histological evaluation showed vascular-like structures over time. The quantitative DIA was plausible to monitor significant increase in the total area of the EBs and an increase in endothelial differentiation. The tumoroids were established from 32 colorectal adenocarcinomas. The in vitro growth rate of the tumoroids was followed by automated microscopy over an 11-day period. The parental tumours were analysed by next-generation sequencing for KRAS, TP53, PIK3CA, SMAD4, MAP2K1, BRAF, FGFR3 and FBXW7 status. The tumoroids established from KRAS-mutated parental tumours showed a significantly higher growth rate compared to their wild-type counterparts. The density of CD3+ T lymphocytes and CD68+ macrophages was calculated in the centre of the tumours and at the invasive margin of the tumours. The high density of CD3+ cells and the low density of CD68+ cells showed a significant correlation with a higher growth rate of the tumoroids. In conclusion, a novel approach for histological monitoring of endothelial differentiation is presented in the stem cell-derived EBs. Furthermore, the KRAS status and density of CD3+ T cells and macrophages in the parental tumour influence the growth rate of the tumoroids. Our results indicate that these parameters should be included when tumoroids are to be implemented in personalized medicine.

Isolation and Differentiation of Amniotic Membrane Stem Cells Into Keratinocytes

The human amniotic membrane is a highly abundant and readily available tissue that may be useful for regenerative medicine and cell therapy. The amniotic membrane stem cells can differentiate into multiple cell lineages; they have low immunogenicity and anti-inflammatory functions. This research aims to examine the protocols for the isolation of human amniotic membrane stem cells, including their phenotypic characterization and in vitro potential for differentiation toward keratinocytes. Human placentas were obtained from selected cesarean-sectioned births. We isolated amniotic stem cells by trypsin and collagenase B digestion and centrifuged with Percoll. After monolayer expansion of adherent cells, the cells were characterized by immunocytology with octamer-binding transcription factor 4 and differentiated into keratinocytes by treating the cells with insulin, hydrocortisone, BMP-4, and vitamin C. Protocol for isolation of stem cells from amniotic membrane has high efficiency. Differentiation markers of stem cells into keratinocytes, such as vimentin, cytokeratin (CK) 14, and CK19, were determined by reverse transcription-polymerase chain reaction increase over time in culture. Stem cells isolated from the amniotic membrane can differentiate into keratinocytes. It has opened the prospect of using stem cells to regenerate skin and clinical applications.

An osteopontin-derived peptide inhibits human hair growth at least in part by decreasing fibroblast growth factor-7 production in outer root sheath keratinocytes

BACKGROUND

Given that unwanted hair growth (hirsutism, hypertrichosis) can cause major psychological distress, new pharmacological treatment strategies with safe and effective hair growth inhibitors that do not destroy the hair follicle (HF) and its stem cells need to be developed.

OBJECTIVES

To establish if osteopontin-derived fragments may modulate human hair growth given that human HFs express the multifunctional, immunomodulatory glycoprotein, osteopontin.

METHODS

Our hypothesis was tested ex vivo and in vivo by using a newly generated, toxicologically well-characterized, modified osteopontin-derived peptide (FOL-005), which binds to the HF.

RESULTS

In organ-cultured human HFs and scalp skin, and in human scalp skin xenotransplants onto SCID mice, FOL-005 treatment (60 nmol L^-1 to 3 μmol L^-1 ) significantly promoted premature catagen development without reducing the number of keratin 15-positive HF stem cells or showing signs of drug toxicity. Genome-wide DNA microarray, quantitative reverse-transcriptase polymerase chain reaction and immunohistochemistry revealed decreased expression of the hair growth promoter, fibroblast growth factor-7 (FGF7) by FOL-005, while cotreatment of HFs with recombinant FGF7 partially abrogated FOL-005-induced catagen promotion.

CONCLUSIONS

With caveats in mind, our study identifies this osteopontin-derived peptide as an effective, novel inhibitory principle for human hair growth ex vivo and in vivo, which deserves systematic clinical testing in hirsutism and hypertrichosis. What's already known about this topic? The treatment of unwanted hair growth (hypertrichosis, hirsutism) lacks pharmacological intervention, with only few and often unsatisfactory treatments available. Osteopontin is prominently expressed in human HFs and has been reported to be elevated during catagen in the murine hair cycle. What does this study add? We tested the effects on hair growth of a novel, osteopontin-derived fragment (FOL-005) ex vivo and in vivo. In human hair follicles, high-dose FOL-005 significantly reduces hair growth both ex vivo and in vivo. What is the translational message? High-dose FOL-005 may provide a new therapeutic opportunity as a treatment for unwanted hair growth.

Cancer Microenvironment: What Can We Learn from the Stem Cell Niche

Epidermal stem cells (ESCs) are crucial for maintenance and self- renewal of skin epithelium and also for regular hair cycling. Their role in wound healing is also indispensable. ESCs reside in a defined outer root sheath portion of hair follicle—also known as the bulge region. ECS are also found between basal cells of the interfollicular epidermis or mucous membranes. The non-epithelial elements such as mesenchymal stem cell-like elements of dermis or surrounding adipose tissue can also contribute to this niche formation. Cancer stem cells (CSCs) participate in formation of common epithelial malignant diseases such as basal cell or squamous cell carcinoma. In this review article, we focus on the role of cancer microenvironment with emphasis on the effect of cancer-associated fibroblasts (CAFs). This model reflects various biological aspects of interaction between cancer cell and CAFs with multiple parallels to interaction of normal epidermal stem cells and their niche. The complexity of intercellular interactions within tumor stroma is depicted on example of malignant melanoma, where keratinocytes also contribute the microenvironmental landscape during early phase of tumor progression. Interactions seen in normal bulge region can therefore be an important source of information for proper understanding to melanoma. The therapeutic consequences of targeting of microenvironment in anticancer therapy and for improved wound healing are included to article.

3D cell culture systems: advantages and applications

Cell cultures are important material of study for the variety of advantages that they offer. Both established continuous cell lines and primary cell cultures continue to be invaluable for basic research and for direct applications. Technological advancements are necessary to address emerging complex challenges and the way cells are cultured in vitro is an area of intense activity. One important advancement in cell culture techniques has been the introduction of three dimensional culture systems. This area is one of the fastest growing experimental approaches in life sciences. Augmented with advancements in cell imaging and analytical systems, as well as the applications of new scaffolds and matrices, cells have been increasingly grown as three dimensional models. Such cultures have proven to be closer to in vivo natural systems, thus proving to be useful material for many applications. Here, we review the three dimensional way of culturing cells, their advantages, the scaffolds and matrices currently available, and the applications of such cultures in major areas of life sciences.

Human umbilical cord-derived mesenchymal stem cells differentiate into epidermal-like cells using a novel co-culture technique

Human umbilical cord-derived mesenchymal stem cells (hUCMSCs) isolated from human umbilical Wharton's Jelly are a population of primitive and pluripotent cells. In specific conditions, hUCMSCs can differentiate into various cells, including adipocytes, osteoblasts, chondrocytes, neurocytes, and endothelial cells. However, few studies have assessed their differentiation into epidermal cells in vitro. To assess the potential of hUCMSCs to differentiate into epidermal cells, a microporous membrane-based indirect co-culture system was developed in this study. Epidermal stem cells (ESCs) were seeded on the bottom of the microporous membrane, and hUCMSCs were seeded on the top of the microporous membrane. Cell morphology was assessed by phase contrast microscopy, and the expression of early markers of epidermal cell lineage, P63, cytokeratin19 (CK19), and β1-integrin, was determined by immunofluorescence, Western blot, and quantitative real-time PCR (Q-PCR) analyses. hUCMSC morphology changed from spindle-like to oblate or irregular with indirect co-culture with ESCs; they also expressed greater levels P63, CK19, and β1-integrin mRNA and protein compared to the controls (p < 0.01). As compared to normal co-cultures, indirect co-culture expressed significantly greater CK19 protein (p < 0.01). Thus, hUCMSCs may have the capability to differentiate into the epidermal lineage in vitro, which may be accomplished through this indirect co-culture model.

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.

Current aspects in the pathophysiology and treatment of chronic wounds in diabetes mellitus

Impaired wound healing is a frequent and very severe problem in patients with diabetes mellitus, yet little is known about the underlying pathomechanisms. In this paper we review the biology of wound healing with particular attention to the pathophysiology of chronic wounds in diabetic patients. The standard treatment of diabetic ulcers includes measures to optimize glycemic control as well as extensive debridement, infection elimination by antibiotic therapy based on wound pathogen cultures, the use of moisture dressings, and offloading high pressure from the wound bed. In this paper we discuss novel adjuvant therapies with particular reference to the use of autologous skin transplants for the treatment of diabetic foot ulcers which do not respond to standard care.

β1 integrin deletion enhances progression of prostate cancer in the TRAMP mouse model

β1 integrin regulates the response of both normal and cancer cells to their local environment. Although mis-localised in prostate cancer, the role β1 integrin plays in prostate development and carcinogenesis remains unknown. To assess the role of β1 integrin in vivo, we conditionally deleted β1 integrin from prostate epithelium and subsequently crossed these mice to the TRAMP prostate carcinogenesis model. Deletion of β1 integrin following castration and subsequent androgen supplementation resulted in an expansion of the p63-positive basal cell population and decreased differentiation. Consistent with these findings, deletion of β1 integrin in TRAMP mice decreased animal survival, decreased retention of normal prostate morphology, increased the percentage of tissue with poorly differentiated carcinoma, and increased cell proliferation. This study demonstrates that β1 integrin regulates several aspects of normal prostate development and in contrast to its role in several other tissues, its loss is associated with increased rates of prostate tumour progression.

Gene expression signatures of mouse bone marrow-derived mesenchymal stem cells in the cutaneous environment and therapeutic implications for blistering skin disorder

BACKGROUND AIMS

Multiple studies have demonstrated that mesenchymal stromal cells (MSC) can be utilized therapeutically for various congenital and acquired disorders. The involvement of MSC in the maintenance of skin homeostasis and their curative application for the treatment of skin wounds have also been documented. However, it is not known whether MSC can commit to cutaneous lineages, produce structural proteins essential for the skin integrity or be used for hereditary skin disorders.

METHODS

To address these questions, we conducted a comparative expression analysis between MSC and potentially adjacent cutaneous cells, fibroblasts and keratinocytes, with specific emphasis on extracellular matrix encoding and related genes.

RESULTS

Our data demonstrated that MSC share many features with cutaneous fibroblasts. We also observed that under direct influence of cutaneous fibroblasts in vitro and fibroblast-derived matrix in vivo, MSC acquired a fibroblastic phenotype, suggesting that specific cell-cell interactions play a key regulatory role in the differentiation of MSC. Additionally, the observed fibroblastic transition of MSC was underlined by a significant up-regulation of several cutaneous-specific genes encoding lumican, decorin, type VII collagen, laminin and other structural proteins. As many of the identified genes have considerable therapeutic value for dermatologic afflictions, particularly type VII collagen, we evaluated further the therapeutic potential of congenic MSC in the skin of Col7a1-null mice recapitulating human recessive dystrophic epidermolysis bullosa (RDEB). Remarkably, MSC-derived type VII collagen was sufficient for restoration of the damaged dermal-epidermal junction and partial reversal of the RDEB phenotype.

CONCLUSIONS

Collectively, our results suggest that MSC may offer promising therapeutics for the treatment of RDEB and potentially other genodermatoses.

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.

Necl2 regulates epidermal adhesion and wound repair

Differential expression of cell adhesion molecules regulates stem cell location, self-renewal and lineage selection under steady state conditions and during tissue repair. We show that the intercellular adhesion protein nectin-like molecule 2 (Necl2) is highly expressed in bulge stem cells of adult human and mouse hair follicles. Overexpression of Necl2 in cultured human keratinocytes led to upregulation of calcium/calmodulin-associated Ser/Thr kinase (CASK), increased calcium-independent intercellular adhesion, and inhibition of cell motility and in vitro wound healing. Although the rate of cell proliferation was reduced, terminal differentiation was unaffected. To assess the role of Necl2 in vivo, we examined the epidermis of Necl2-null mice and developed transgenic mice that expressed Necl2 in the basal layer of murine epidermis. Necl2 overexpression led to a reduction in S-phase cells and an increase in quiescent cells retaining DNA label in the bulge. Although epidermal homeostasis appeared normal in both transgenic and knockout mice, wound healing was markedly delayed. Necl2 overexpression resulted in reduced proliferation and increased levels of CASK and E-cadherin at the leading edge of healing wounds, consistent with its effects in culture. Our results demonstrate that Necl2 is involved in regulating epidermal stem cell quiescence and location.

Stem cells for skin tissue engineering and wound healing

The tremendous ability of the skin's epidermis to regenerate is due to the presence of epidermal stem cells that continuously produce keratinocytes, which undergo terminal differentiation to a keratinized layer that provides the skin's barrier properties. The ability to control this process in vitro has made it possible to develop various types of tissue-engineered skin grafts, some of which are among the first tissue-engineered products to ever reach the market. In the past 30 years, these products have been applied with some success to the treatment of chronic skin wounds such as diabetic and venous ulcers and deep, acute wounds such as burns. Current technologies remain partially effective in their ability to restore other skin structures, for example, the dermis, which is critical to the overall long-term appearance and function of the skin. As yet, none of these approaches can regenerate skin appendages (e.g. hair follicles and sweat glands). The use of earlier progenitor and stem cells, including embryonic stem cells, is gaining interest in the attempt to overcome such limitations. Furthermore, recent evidence suggests that "adult" stem cells, which are present in the circulation, target areas of injury and likely participate in the wound-healing process. In this paper, we start with an overview of the wound-healing process and current methods used for wound treatment, both conventional and tissue-engineering based. We then review current research on the various types of stem cells used for skin tissue engineering and wound healing, and provide future directions.

An intronic alteration of the fibroblast growth factor 10 gene causing ALSG-(aplasia of lacrimal and salivary glands) syndrome

Background

A combined aplasia, hypoplasia or atresia of lacrimal points and salivary glands is rarely diagnosed. Those patients suffer from epiphora, xerostomia and severe dental caries. This phenotype represents the autosomal-dominant aplasia of lacrimal and salivary glands syndrome (ALSG). Recently, aberrations of the Fibroblast Growth Factor 10 (FGF10) gene have been identified to be causative for this disorder.

Methods

We performed a sequence analysis of the FGF10 gene of a patient with ALSG-syndrome and his also affected brother as well as 193 controls. The FGF10 transcript was analyzed using RNA extracted from primary fibroblasts of the patient's mucosa.

Results

We detected a novel heterozygous sequence variation in intron 2 (c.430-1, G > A) causing the ALSG syndrome. The alteration derogates the regular splice acceptor site and leads to the use of a new splice acceptor site 127 bp upstream of exon 3. The aberration was detected in the genomic DNA derived from two affected brothers, but not in 193 control individuals. Furthermore, no diseased member of the family displayed additional abnormalities that are indicative for the clinically overlapping lacrimo-auriculo-dento-digital syndrome (LADD).

Conclusion

This family-based approach revealed an intronic variation of the FGF10 gene causing ALSG-syndrome. Our results expand the mutational and clinical spectrum of the ALSG syndrome.

A pure population of ectodermal cells derived from human embryonic stem cells

Embryonic stem (ES) cells represent a unique cellular model to recapitulate in vitro early steps of embryonic development and an unlimited cellular source in therapy for many diseases, as well as targets for drug discovery and toxicology screens. Although previous studies have reported epidermal differentiation of mouse and human embryonic stem (huES) cells, the heterogeneity of the resulting cell culture impairs the evaluation of differentiated cells for cell therapy. We report here the reproducible isolation of a homogenous ectodermal cell population, IT1, from human ES cells. Like primary cells, IT1 cells remain homogenous over 15 passages, expand up to 60 population doublings, and then die through senescence. Accordingly, IT1 cells display a normal karyotype and a somatic cell cycle kinetics and do not produce teratoma in nude mice. The production of K14-expressing epithelial cells driven by p63 expression strengthens the ectodermal nature of IT1 cells. Since IT1 can be isolated from different huES cell lines, it may provide a ready source of ectodermal progenitors for the development of a toxicology cell model, new-drug-screening strategies, and cell therapy transplantation.

Epidermal stem cell fate: what can we learn from embryonic stem cells?

Because of its constant renewal and high propensity for repair, the epidermis is, together with the gut and the hematopoietic system, a tissue of choice to explore stem cell biology. Previous research over many years has revealed the complexity of the epidermis: the heterogeneity of the stem cell compartment, with its rare, slowly cycling, multipotent, hair-follicle, "bulge" stem cells and the more restricted interfollicular, follicle-matrix, and sebaceous-gland stem cells, which in turn generate the large pool of transit-amplifying progeny. Stem cell activity has been used for some considerable time to repair skin injuries, but ex-vivo keratinocyte amplification has its limitations, and grafted skin homeostasis is not totally satisfactory. Human embryonic stem cells raise the hope that the understanding of the developmental steps leading to the generation of epidermal stem cells and the characterization of the key signaling pathways involved in skin morphogenesis (such as p63) will be translated into therapeutic benefit. Our recent results suggest the feasibility not only of identifying but also of amplifying human ES cells, early ectodermal progenitors with an intact multipotent potential that might improve the quality and functionality of grafts, provided that preclinical in vivo studies confirm our expectations from in vitro analysis.

Human bone marrow-derived mesenchymal stem cells differentiate into epidermal-like cells in vitro

Human bone marrow-derived mesenchymal stem cells (hMSCs) are a population of pluripotent cells. They can differentiate into different embryonic layer cells as osteoblasts, adipocytes, chondrocytes, myoblasts, neurocytes, etc. However, there are only few reports with regard to differentiate hMSCs into epidermal cells in vitro. In this study, we want to investigate the feasibility of inducing hMSCs into epidermal-like cells under specific medium in vitro. hMSCs in specific inducing medium expressed the early markers of epidermal cell lineage, P63, cytokeratin19 (CK19), the late differentiated marker, the pan-cytokeratin, and another early marker, the beta1-integrin, which up-regulated remarkably in inducing medium. Their morphologies were changed from spindle-like fibroblastic appearances to oblate or irregular shapes under phase contrast microscopy. The hemidesmosome structure was found using the transmission electron microscope. All these data suggested that, under certain conditions, hMSCs have the potential to differentiate into epidermal-like cells. It will be of great accordance in the study of the multipotential property of hMSCs.

Comparison of the gene expression profile of undifferentiated human embryonic stem cell lines and differentiating embryoid bodies

Background

The identification of molecular pathways of differentiation of embryonic stem cells (hESC) is critical for the development of stem cell based medical therapies. In order to identify biomarkers and potential regulators of the process of differentiation, a high quality microarray containing 16,659 seventy base pair oligonucleotides was used to compare gene expression profiles of undifferentiated hESC lines and differentiating embryoid bodies.

Results

Previously identified "stemness" genes in undifferentiated hESC lines showed down modulation in differentiated cells while expression of several genes was induced as cells differentiated. In addition, a subset of 194 genes showed overexpression of greater than ≥ 3 folds in human embryoid bodies (hEB). These included 37 novel and 157 known genes. Gene expression was validated by a variety of techniques including another large scale array, reverse transcription polymerase chain reaction, focused cDNA microarrays, massively parallel signature sequencing (MPSS) analysis and immunocytochemisty. Several novel hEB specific expressed sequence tags (ESTs) were mapped to the human genome database and their expression profile characterized. A hierarchical clustering analysis clearly depicted a distinct difference in gene expression profile among undifferentiated and differentiated hESC and confirmed that microarray analysis could readily distinguish them.

Conclusion

These results present a detailed characterization of a unique set of genes, which can be used to assess the hESC differentiation.

Evolving concepts on the pathogenic mechanisms of aniridia related keratopathy

Heterozygosity for PAX6 deficiency (PAX6+/-) results in aniridia. Corneal changes in aniridia-related keratopathy (ARK) include corneal vascular pannus formation, conjunctival invasion of the corneal surface, corneal epithelial erosions and epithelial abnormalities, which eventually result in corneal opacity and contribute to visual loss. Corneal changes in aniridia have been attributed to congenital deficiency of corneal limbal stem cells. The aim of this paper is to review the potential mechanisms that may underlie the pathogenesis of aniridia related keratopathy. Current evidence, based on clinical observations and an animal model of aniridia suggest that the proliferative potential of the corneal limbal stem cells may not primarily be impaired. The corneal changes in aniridia may be related to an abnormality within the limbal stem cell niche. The mechanisms underlying progressive corneal pathology in aniridia appear multi-factorial and include: (1) abnormal corneal healing responses secondary to anomalous extracellular matrix metabolism; (2) abnormal corneal epithelial differentiation leading to fragility of epithelial cells; (3) reduction in cell adhesion molecules in the PAX6 heterozygous state, rendering the cells susceptible to natural shearing forces; and (4) conjunctival and corneal changes leading to the presence of cells derived from conjunctiva on the corneal surface.

Use of nanotopography to study mechanotransduction in fibroblasts--methods and perspectives

The environment around a cell during in vitro culture is unlikely to mimic those in vivo. Preliminary experiments with nanotopography have shown that nanoscale features can strongly influence cell morphology, adhesion, proliferation and gene regulation, but the mechanisms mediating this cell response remain unclear. In this perspective article, we attempt to illustrate that a possible mechanism is direct transmittal of forces encountered by cells during spreading to the nucleus via the cytoskeleton. We further try to illustrate that this 'self-induced' mechanotransduction may alter gene expression by changing interphase chromosome positioning. Whilst the observations described here to show how we think nanotopography can be developed as a tool to look at mechanotransduction are preliminary, we feel they indicate that topography may give cell biologists a non-invasive tool with which to investigate in vitro cellular mechanisms.

Directing stem cells into the keratinocyte lineage in vitro

A major area of research in regenerative medicine is the potential application of stem cells in skin grafting and tissue engineering. This would require well defined and efficient protocols for directing the commitment and differentiation of stem cells into the keratinocyte lineage, together with their selective purification and proliferation in vitro. The development of such protocols would reduce the likelihood of spontaneous differentiation of stem cells into divergent lineages upon transplantation, as well as reduce the risk of teratoma formation in the case of embryonic stem cells. Additionally, such protocols could provide useful in vitro models for studying skin tissue biology, as well as facilitate the genetic manipulation of stem cells for therapeutic applications. The development of pharmacokinetic and cytotoxicity/genotoxicity screening tests for skin-related biomaterials and drugs could also utilize protocols developed for the commitment and differentiation of stem cells into the keratinocyte lineage. Hence, this review critically examines the various strategies that could be employed to direct the commitment and differentiation of stem cells into the keratinocyte lineage in vitro.

Diffusible factors released by fibroblasts support epidermal morphogenesis and deposition of basement membrane components

Epithelial-mesenchymal interactions play an important role in controlling epidermal morphogenesis and homeostasis but little is known about the mechanisms of these interactions. To examine whether diffusible factors produced by fibroblasts and/or keratinocytes support epidermal morphogenesis and basement membrane formation, organotypic keratinocyte monocultures were established in media collected either from organotypic fibroblast or keratinocyte-monocultures or from keratinocyte-fibroblast cocultures, and the expression of keratin 10, 16, and 17 and basement membrane components (types IV and VII collagen, laminin 5, nidogen, BP 180, LAD-1) were examined. We found that diffusible factors released by keratinocytes were not sufficient to support the establishment of normalized epidermal phenotype and deposition of basement membrane components in contrast to fibroblast- or keratinocyte/fibroblast-derived factors. Keratinocytes appear to affect the spectrum of secreted soluble factors, as keratinocyte/fibroblast-derived factors were more effective to accomplish continuous linear deposition of laminin 5 and of nidogen. The finding that released amounts of keratinocyte growth factor and granulocyte macrophage colony stimulating factor were not sufficient to fully support epidermal morphogenesis and deposition of basement membrane components is suggestive for the involvement of other released diffusible factors. Generation of organotypic keratinocyte monocultures in the presence of fibroblast- or keratinocyte/fibroblast-derived soluble factors resulted in enhanced expression of keratins K16 and K17 and the absence of type IV collagen. This observation indicates that next to paracrine acting factors, epidermal homeostasis is controlled by mutual keratinocyte-fibroblast interaction.

Fibroblasts contribute to the deposition of laminin 5 in the extracellular matrix

Laminin 5 (alpha3beta3gamma2) is specifically present in the basal lamina underneath epithelia with secretory or protective functions, where it is essential for anchoring basal epithelial cells to the underlying extracellular matrix. Laminin 5 is produced by epithelial cells as a 480-kDa precursor that is converted into forms of 440 and 400 kDa. To analyse the processing of laminin 5, we have used monolayer and co-cultures of epithelial cells and fibroblasts. The processing of the 180-kDa laminin alpha3 chain to 165 kDa in the cell culture medium, and to both 165 and 145 kDa polypeptides in the cell layer, are not modified by the presence of fibroblasts. In contrast, cleavage of the laminin gamma2 chain, occurring in the cell culture medium and in the cell layer, is enhanced by the presence of fibroblasts. Further analysis by immunofluorescence staining and laser-scanning microscopy reveals that deposited laminin 5 is present in a fibroblast-associated filamentous meshwork. Only laminin 5 containing a fully processed gamma2 chain is present in this fibroblast-associated fraction. These studies show that, although laminin 5 is a product of epithelial cells, fibroblasts contribute to its integration into the extracellular matrix architecture.

From Cell-ECM interactions to tissue engineering

The extracellular matrix (ECM) consists of a complex mixture of structural and functional macromolecules and serves an important role in tissue and organ morphogenesis and in the maintenance of cell and tissue structure and function. The great diversity observed in the morphology and composition of the ECM contributes enormously to the properties and function of each organ and tissue. The ECM is also important during growth, development, and wound repair: its own dynamic composition acts as a reservoir for soluble signaling molecules and mediates signals from other sources to migrating, proliferating, and differentiating cells. Approaches to tissue engineering center on the need to provide signals to cell populations to promote cell proliferation and differentiation. These "external signals" are generated from growth factors, cell-ECM, and cell-cell interactions, as well as from physical-chemical and mechanical stimuli. This review considers recent advances in knowledge about cell-ECM interactions. A description of the main ECM molecules and cellular receptors with particular care to integrins and their role in stimulation of specific types of signal transduction pathways is also explained. The general principles of biomaterial design for tissue engineering are considered, with same examples.

Marker succession during the development of keratinocytes from cultured human embryonic stem cells

Human embryonic stem cells injected into scid mice produce nodules containing differentiated somatic tissues. From the trypsinized cells of such a nodule, we have recovered keratinocytes that can be grown in cell culture. The method of recovery is sensitive enough to detect small numbers of keratinocytes formed in the nodule, but for purposes of analysis, it is preferable to study the development of the entire keratinocyte lineage in culture. The principle of our analysis is the successive appearance of markers, including transcription factors with considerable specificity for the keratinocyte (p63 and basonuclin) and differentiation markers characteristic of its final state (keratin 14 and involucrin). We have determined the order of marker succession during the time- and migration-dependent development of keratinocytes from single embryoid bodies in cell culture. Of the markers we have examined, p63 was the earliest to appear in the keratinocyte lineage. The successive accumulation of later markers provides increasing certainty of emergence of the definitive keratinocyte.

Stem cells of the skin epithelium

Tissue stem cells form the cellular base for organ homeostasis and repair. Stem cells have the unusual ability to renew themselves over the lifetime of the organ while producing daughter cells that differentiate into one or multiple lineages. Difficult to identify and characterize in any tissue, these cells are nonetheless hotly pursued because they hold the potential promise of therapeutic reprogramming to grow human tissue in vitro, for the treatment of human disease. The mammalian skin epithelium exhibits remarkable turnover, punctuated by periods of even more rapid production after injury due to burn or wounding. The stem cells responsible for supplying this tissue with cellular substrate are not yet easily distinguishable from neighboring cells. However, in recent years a significant body of work has begun to characterize the skin epithelial stem cells, both in tissue culture and in mouse and human skin. Some epithelial cells cultured from skin exhibit prodigious proliferative potential; in fact, for >20 years now, cultured human skin has been used as a source of new skin to engraft onto damaged areas of burn patients, representing one of the first therapeutic uses of stem cells. Cell fate choices, including both self-renewal and differentiation, are crucial biological features of stem cells that are still poorly understood. Skin epithelial stem cells represent a ripe target for research into the fundamental mechanisms underlying these important processes.

A role for alphabeta1 integrins in focal adhesion function and polarized cytoskeletal dynamics

alphabeta1 integrins have been implicated in the survival, spreading, and migration of cells and tissues. To explore the underlying biology, we identified conditions where primary beta1 null keratinocytes adhere, proliferate, and display robust alphavbeta6 integrin-induced, peripheral focal contacts associated with elaborate stress fibers. Mechanistically, this appears to be due to reduced FAK and Src and elevated RhoA and Rock activities. Visualization on a genetic background of GFPactin shows that beta1 null keratinocytes spread, but do so aberrantly, and when induced to migrate from skin explants in vitro, the cells are not able to rapidly reorient their actin cytoskeleton toward the polarized movement. As judged by RFPzyxin/GFPactin videomicroscopy, the alphavbeta6-actin network does not undergo efficient turnover. Without the ability to remodel their integrin-actin network efficiently, alphabeta1-deficient keratinocytes cannot respond dynamically to their environment and polarize movements.

Modeling tissue-specific signaling and organ function in three dimensions

In order to translate the findings from basic cellular research into clinical applications, cell-based models need to recapitulate both the 3D organization and multicellular complexity of an organ but at the same time accommodate systematic experimental intervention. Here we describe a hierarchy of tractable 3D models that range in complexity from organotypic 3D cultures (both monotypic and multicellular) to animal-based recombinations in vivo. Implementation of these physiologically relevant models, illustrated here in the context of human epithelial tissues, has enabled the study of intrinsic cell regulation pathways and also has provided compelling evidence for the role of the stromal compartment in directing epithelial cell function and dysfunction. Furthermore the experimental accessibility afforded by these tissue-specific 3D models has implications for the design and development of cancer therapies.

Generation of confluent cardiomyocyte monolayers derived from embryonic stem cells in suspension: a cell source for new therapies and screening strategies

BACKGROUND

Cellular cardiomyoplasty is evolving as a new strategy to treat cardiac diseases. A prerequisite is a reliable source of pure cardiomyocytes, which could also help in the exploitation of recent advances in genomics and drug screening. Our goal was to establish a robust lab-scale process for the generation of embryonic stem (ES)-cell-derived cardiomyocytes in suspension.

METHODS

A 71 ES cell clone carrying a construct consisting of the alpha-cardiac myosin heavy chain (alphaMHC) promoter driving the neomycin resistance gene was used for antibiotic-driven cardiomyocyte enrichment. Rotating suspension culture was established to initiate embryoid body (EB) formation. To track growth and differentiation kinetics, cell count and flow cytometry for SSEA-I, E-cadherin (stem-cell marker)and sarcomeric myosin (cardiomyocytes marker) was performed. Oct4 expression was measured via real time (RT)-PCR.

RESULTS

Cultures comprising 2.5-8 x 10(6) differentiating FS cells/mL were obtained after 9 days in rotating suspension. Upon G418 addition,vigorous contracting spheres, termed cardiac bodies (CB), developed. These cultures consisted of about 2.1 x 10(5) enriched cardiomyocytes/mL after 6- 10 days of selection. Suspensions comprising 90- 95%viable single cells were generated using an improved dissociation method. Seeding of cardiomyocytes with 7 x 10(4) cell/cm(2) resulted in a homogeneous monolayer of synchronously contracting cells. Myocyte specific immunohistochemistry indicated purity of > 99%.

DISCUSSION

We have established a reliable lab-scale protocol to generate cultures of highly enriched cardiomyocytes in suspension. This will facilitate development of larger-scale processes for stem-cell based cardiomyocyte supply. An improved method is provided to derive vital suspensions of cardiomyocytes, which could be utilized for transplantation as well as for drug screening purposes.

Stem cells on the way to restorative medicine

Stem cells are defined by their unique properties of self-renewal and multilineage differentiation. Several decades ago, cells with such developmental plasticity have been identified in the embryo and in the bone marrow of the adult; in other organs, such cells could not be demonstrated. Here, recent findings are briefly summarized indicating that the elementary stem cell capabilities are retained by a limited number of cells present in many organs of the adult. Other data suggest that, on response to another microenvironment, "organ-specific" stem cells are able to acquire different fates. If confirmed these findings will have considerable impact on the future of clinical stem cell therapy.

Mouse ES cells: experimental exploitation of pluripotent differentiation potential

Pluripotent ES cells can be used to generate a wide variety of cell populations in vitro in a manner resembling embryonic development. Recent advances in controlling ES cell differentiation, combined with the power of genetic and biochemical manipulation, are providing insights into cell biology and the determination of cell fate.

Stem cell fate and patterning in mammalian epidermis

Recent studies highlight characteristics of epidermal stem cells that were not fully appreciated before. Stem cells are multipotential and signals exchanged with their neighbours help to regulate exit from the stem cell compartment and differentiation along specific lineages. Stem cells exhibit a high degree of spatial organisation, and cell clustering and motility contribute to the assembly and maintenance of the epidermis.