Location of stem cells of human hair follicles by clonal analysis

Bulge-Derived Epithelial Cells Isolated from Human Hair Follicles Using Enzymatic Digestion or Explants Result in Comparable Tissue-Engineered Skin

Hair follicle stem cells, located in the bulge region of the outer root sheath, are multipotent epithelial stem cells capable of differentiating into epidermal, sebaceous gland, and hair shaft cells. Efficient culturing of these cells is crucial for advancements in dermatology, regenerative medicine, and skin model development. This investigation aimed to develop a protocol for isolating enriched bulge-derived epithelial cells from scalp specimens to produce tissue-engineered substitutes. The epithelium, including hair follicles, was separated from the dermis using thermolysin, followed by microdissection of the bulge region. Epithelial stem cells were isolated using enzymatic dissociation to create a single-cell suspension and compared with the direct explant culture and a benchmark method which isolates cells from the epidermis and pilosebaceous units. After 8 days of culture, the enzymatic digestion of microdissected bulges yielded 5.3 times more epithelial cells compared to explant cultures and proliferated faster than the benchmark method. Cells cultured from all methods exhibited comparable morphology and growth rates. The fully stratified epidermis of tissue-engineered skin was similar, indicating comparable differentiation potential. This enzymatic digestion method improved early-stage cell recovery and expansion while maintaining keratinocyte functionality, offering an efficient hair bulge cell-extraction technique for tissue engineering and regenerative medicine applications.

The Retinoic-Acid-Related Orphan Receptor Alpha May Be Highly Involved in the Regulation of Seasonal Hair Molting

Seasonal molting in mammals is a crucial survival strategy, yet the underlying molecular mechanisms have not been fully characterized. Melatonin, serving as a bridge for the transmission of photoperiod signals, plays a significant regulatory role in animals' seasonal molting, and the physiological regulatory effects of melatonin signaling are highly dependent on the retinoic-acid-related orphan receptor alpha (Rorα). Hair follicle stem cells (HFSCs) are the most essential cell type in the process of hair follicle regeneration and seasonal replacement. Therefore, this study aims to discuss the regulatory effects of melatonin and its nuclear receptor RORA on HFSCs. This research found that RORA can downregulate cellular proliferation levels by inhibiting the cell cycle of HFSCs, while simultaneously promoting apoptosis in HFSCs and affecting the expression of some genes involved in ferroptosis. RORA can directly bind to the promoter regions of the cyclin genes Ccna2 and Ccne1 to regulate their transcription. Melatonin may enhance the viability of HFSCs by downregulating RORA levels. In this study, the impact of melatonin and its nuclear receptor RORA on the viability of HFSCs, along with some of the underlying molecular mechanisms, is characterized. These findings provide a theoretical foundation for research on the regulation of animal hair follicle development.

Melatonin-Mediated Circadian Rhythm Signaling Exhibits Bidirectional Regulatory Effects on the State of Hair Follicle Stem Cells

The development and regulation of hair are widely influenced by biological rhythm signals. Melatonin plays a crucial role as a messenger in transmitting biological rhythm signals, and its impact on hair development has been well documented. During the process of hair follicle reconstruction, hair follicle stem cells (HFSCs) are the most important cell type, but the regulatory effect of melatonin on the state of HFSCs is still not fully understood. Therefore, it is necessary to conduct a more comprehensive characterization of the effects of melatonin on the state of hair follicle stem cells. The research results indicate that HFSCs express retinoic acid receptor-related orphan receptor alpha (Rorα), and melatonin inhibits the expression level of RORA. Experimental results from CUT&Tag, CUT&RUN, and dual luciferase reporter assays demonstrate that Foxc1 is a downstream target gene of RORA, with RORA regulating Foxc1 expression by binding to the promoter region of Foxc1. The CCK-8 assay results show that low doses of melatonin upregulate the survival rate of hair follicle stem cells, while high doses have the opposite effect. The knockdown of Foxc1 reverses the inhibitory effect of high-dose melatonin on the survival rate of hair follicle stem cells. Based on these findings, we believe that melatonin-mediated circadian signals exert a bidirectional regulatory effect on the state of HFSCs.

Intermittent fasting triggers interorgan communication to suppress hair follicle regeneration

Intermittent fasting has gained global popularity for its potential health benefits, although its impact on somatic stem cells and tissue biology remains elusive. Here, we report that commonly used intermittent fasting regimens inhibit hair follicle regeneration by selectively inducing apoptosis in activated hair follicle stem cells (HFSCs). This effect is independent of calorie reduction, circadian rhythm alterations, or the mTORC1 cellular nutrient-sensing mechanism. Instead, fasting activates crosstalk between adrenal glands and dermal adipocytes in the skin, triggering the rapid release of free fatty acids into the niche, which in turn disrupts the normal metabolism of HFSCs and elevates their cellular reactive oxygen species levels, causing oxidative damage and apoptosis. A randomized clinical trial (NCT05800730) indicates that intermittent fasting inhibits human hair growth. Our study uncovers an inhibitory effect of intermittent fasting on tissue regeneration and identifies interorgan communication that eliminates activated HFSCs and halts tissue regeneration during periods of unstable nutrient supply.

Retinoic Acid-Related Orphan Receptor Alpha May Regulate the State of Hair Follicle Stem Cells by Upregulating the Expression of BNIP3

The hair, an exclusive keratinized dermal appendage in mammals, stands as a quintessential outcome of adaptive evolution, conferring resilience against adverse environmental conditions. The ontogenesis of the coat displays a pronounced rhythmic pattern, with hair follicle stem cells (HFSCs) emerging as pivotal facilitators of hair follicle reconstitution. The retinoic acid-related orphan receptor alpha, a nuclear receptor with extensive involvement in the regulation of cellular physiological states, exerts its functions predominantly through the modulation of downstream target gene transcription. The Bnip3 gene exhibits a robust correlation with cellular apoptosis and autophagy, which are indispensable physiological mechanisms underlying the maintenance of HFSC homeostasis. Consequently, the expression level of Bnip3 may be intimately linked to the status of HFSCs. In this investigative endeavor, we employed rat HFSCs as a model system to validate the regulatory impact of RORA on Bnip3 gene expression. Our findings unequivocally demonstrate that Bnip3 serves as a direct downstream target of RORA. Specifically, RORA binds to the motif within the Bnip3 promoter region, thereby upregulating Bnip3 expression levels. In light of our research findings, we propose that RORA holds potential as a target for modulating the status of HFSCs.

Biochemical characterization of the feedforward loop between CDK1 and FOXM1 in epidermal stem cells

The complex network governing self-renewal in epidermal stem cells (EPSCs) is only partially defined. FOXM1 is one of the main players in this network, but the upstream signals regulating its activity remain to be elucidated. In this study, we identify cyclin-dependent kinase 1 (CDK1) as the principal kinase controlling FOXM1 activity in human primary keratinocytes. Mass spectrometry identified CDK1 as a key hub in a stem cell-associated protein network, showing its upregulation and interaction with essential self renewal-related markers. CDK1 phosphorylates FOXM1 at specific residues, stabilizing the protein and enhancing its nuclear localization and transcriptional activity, promoting self-renewal. Additionally, FOXM1 binds to the CDK1 promoter, inducing its expression.We identify the CDK1-FOXM1 feedforward loop as a critical axis sustaining EPSCs during in vitro cultivation. Understanding the upstream regulators of FOXM1 activity offers new insights into the biochemical mechanisms underlying self-renewal and differentiation in human primary keratinocytes.

1,25-(OH)2D3 promotes hair growth by inhibiting NLRP3/IL-1β and HIF-1α/IL-1β signaling pathways

Vitamin D is a crucial vitamin that participates in various biological processes through the Vitamin D Receptor (VDR). While there are studies suggesting that VDR might regulate hair growth through ligand-independent mechanisms, the efficacy of Vitamin D in treating hair loss disorders has also been reported. Here, through in vivo experiments in mice, in vitro organ culture of hair follicles, and cellular-level investigations, we demonstrate that 1,25-(OH)2D3 promotes mouse hair regeneration, prolongs the hair follicle anagen, and enhances the proliferation and migration capabilities of dermal papilla cells and outer root sheath keratinocytes in a VDR-dependent manner. Transcriptome analysis of VDR-knockout mouse skin reveals the involvement of HIF-1α, NLRP3, and IL-1β in these processes. Finally, we confirm that 1,25-(OH)2D3 can counteract the inhibitory effects of DHT on hair growth. These findings suggest that 1,25-(OH)2D3 has a positive impact on hair growth and may serve as a potential therapeutic agent for androgenetic alopecia (AGA).

Ontogeny of Skin Stem Cells and Molecular Underpinnings

Skin stem cells (SCs) play a pivotal role in supporting tissue homeostasis. Several types of SCs are responsible for maintaining and regenerating skin tissue. These include bulge SCs and others residing in the interfollicular epidermis, infundibulum, isthmus, sebaceous glands, and sweat glands. The emergence of skin SCs commences during embryogenesis, where multipotent SCs arise from various precursor populations. These early events set the foundation for the diverse pool of SCs that will reside in the adult skin, ready to respond to tissue repair and regeneration demands. A network of molecular cues regulates skin SC behavior, balancing quiescence, self-renewal, and differentiation. The disruption of this delicate equilibrium can lead to SC exhaustion, impaired wound healing, and pathological conditions such as skin cancer. The present review explores the intricate mechanisms governing the development, activation, and differentiation of skin SCs, shedding light on the molecular signaling pathways that drive their fate decisions and skin homeostasis. Unraveling the complexities of these molecular drivers not only enhances our fundamental knowledge of skin biology but also holds promise for developing novel strategies to modulate skin SC fate for regenerative medicine applications, ultimately benefiting patients with skin disorders and injuries.

Highly Efficient Ex Vivo Correction of COL7A1 through Ribonucleoprotein-Based CRISPR/Cas9 and Homology-Directed Repair to Treat Recessive Dystrophic Epidermolysis Bullosa

Recessive dystrophic epidermolysis bullosa (RDEB) is a rare and severe genetic skin disease responsible for blistering of the skin and mucosa after minor trauma. RDEB is caused by a wide variety of variants in COL7A1 encoding type VII Collagen, the major component of anchoring fibrils that form key attachment structures for dermal-epidermal adherence. In this study, we achieved highly efficient COL7A1 editing in primary RDEB keratinocytes and fibroblasts from 2 patients homozygous for the c.6508C>T (p.Gln2170∗) variant through CRISPR/Cas9-mediated homology-directed repair. Three guide RNAs targeting the c.6508C>T variant or harboring sequences were delivered together with high-fidelity Cas9 as a ribonucleoprotein complex. Among them, one achieved 73% cleavage activity in primary RDEB keratinocytes and RDEB fibroblasts. Then, we treated RDEB keratinocytes and RDEB fibroblasts with this specific ribonucleoprotein complex and the corresponding donor template delivered as single-stranded oligodeoxynucleotide and achieved up to 58% of genetic correction as well as type VII Collagen rescue. Finally, grafting of corrected 3-dimensional skin onto nude mice induced re-expression and normal localization of type VII Collagen as well as anchoring fibril formation at the dermal-epidermal junction 5 and 10 weeks after grafting. With this promising nonviral approach, we achieved therapeutically relevant specific gene editing that could be applicable to all variants in exon 80 of COL7A1 in primary RDEB cells.

Allele-specific CRISPR-Cas9 editing of dominant epidermolysis bullosa simplex in human epidermal stem cells

Epidermolysis bullosa simplex (EBS) is a rare skin disease inherited mostly in an autosomal dominant manner. Patients display a skin fragility that leads to blisters and erosions caused by minor mechanical trauma. EBS phenotypic and genotypic variants are caused by genetic defects in intracellular proteins whose function is to provide the attachment of basal keratinocytes to the basement membrane zone and most EBS cases display mutations in keratin 5 (KRT5) and keratin 14 (KRT14) genes. Besides palliative treatments, there is still no long-lasting effective cure to correct the mutant gene and abolish the dominant negative effect of the pathogenic protein over its wild-type counterpart. Here, we propose a molecular strategy for EBS01 patient's keratinocytes carrying a monoallelic c.475/495del21 mutation in KRT14 exon 1. Through the CRISPR-Cas9 system, we perform a specific cleavage only on the mutant allele and restore a normal cellular phenotype and a correct intermediate filament network, without affecting the epidermal stem cell, referred to as holoclones, which play a crucial role in epidermal regeneration.

Defining the identity and the niches of epithelial stem cells with highly pleiotropic multilineage potency in the human thymus

Thymus is necessary for lifelong immunological tolerance and immunity. It displays a distinctive epithelial complexity and undergoes age-dependent atrophy. Nonetheless, it also retains regenerative capacity, which, if harnessed appropriately, might permit rejuvenation of adaptive immunity. By characterizing cortical and medullary compartments in the human thymus at single-cell resolution, in this study we have defined specific epithelial populations, including those that share properties with bona fide stem cells (SCs) of lifelong regenerating epidermis. Thymic epithelial SCs display a distinctive transcriptional profile and phenotypic traits, including pleiotropic multilineage potency, to give rise to several cell types that were not previously considered to have shared origin. Using here identified SC markers, we have defined their cortical and medullary niches and shown that, in vitro, the cells display long-term clonal expansion and self-organizing capacity. These data substantively broaden our knowledge of SC biology and set a stage for tackling thymic atrophy and related disorders.

A loss-of-function NCSTN mutation associated with familial Dowling Degos disease and hidradenitis suppurativa

Dowling Degos disease (DDD) is a rare autosomal dominant genodermatosis characterized by acquired, slowly progressive reticulated pigmented lesions primarily involving flexural skin areas. Mutations in KRT5, POGLUT-1 and POFUT-1 genes have been associated with DDD, and loss-of-function mutations in PSENEN, a subunit of the gamma-secretase complex, were found in patients presenting with DDD or DDD comorbid with hidradenitis suppurativa (HS). A nonsense mutation in NCSTN, another subunit of the gamma-secretase, was already described in a patient suffering from HS and DDD but whether NCSTN could be considered a novel gene for DDD is still debated. Here, we enrolled a four-generation family with HS and DDD. Through Whole Exome Sequencing (WES) we identified a novel nonsense mutation in the NCSTN gene in all the affected family members. To study the impact of this variant, we isolated outer root sheath cells from patients' hair follicles. We showed that this variant leads to a premature stop codon, activates a nonsense-mediated mRNA decay, and causes NCSTN haploinsufficiency in affected individuals. In fact, cells treated with gentamicin, a readthrough agent, had the NCSTN levels corrected. Moreover, we observed that this haploinsufficiency also affects other subunits of the gamma-secretase complex, possibly causing DDD. Our findings clearly support NCSTN as a novel DDD gene and suggest carefully investigating this co-occurrence in HS patients carrying a mutation in the NCSTN gene.

Fabrication and evaluation of a bi-layered gelatin based scaffold with arrayed micro-pits for full-thickness skin construct

There is an unmet need for a reliable and reproducible method for incorporating hair follicle derived stem cells in tissue engineered skin models to reconstitute hair follicles. This study discloses a novel method for introducing hair follicle derived stem cells in microneedle embossed micro-pits of a bilayer skin equivalent fabricated from a gelatin based scaffold. The microneedles are hard and strong enough to penetrate the upper layer of the bilayer gelatin based scaffold that corresponds to the epidermis and permeates down to lower layer that corresponds to dermal layer. This strategic location will mimic the natural niche of hair follicle stem cells for picking up signals from both the epidermis and dermis. Hair follicle stem cells are trapped in to these micro-pits by vacuum assisted cell seeding. The bilayer system consists of two distinct electrospun layers in a single processing step, representing outer epidermal layer and inner dermal layer with hair follicle stem cells in embedded pits, resulting in the formation of a closed representation of a complete skin.

Practical Guideline for Prevention of Patchy Hair Loss following CyberKnife Stereotactic Radiosurgery for Calvarial or Scalp Tumors: Retrospective Analysis of a Single Institution Experience

INTRODUCTION

Patchy alopecia is a common adverse effect of stereotactic radiosurgery (SRS) on the calvarium and/or scalp, yet no guidelines exist for its prevention. This study aims to investigate the incidence and outcomes of patchy alopecia following SRS for patients with calvarial or scalp lesions and establish preventive guidelines.

METHODS

The study included 20 patients who underwent CyberKnife SRS for calvarial or scalp lesions, resulting in a total of 30 treated lesions. SRS was administered as a single fraction for 8 lesions and hypofractionated for 22 lesions. The median SRS target volume was 9.85 cc (range: 0.81-110.7 cc), and the median prescription dose was 27 Gy (range: 16-40 Gy), delivered in 1-5 fractions (median: 3). The median follow-up was 15 months.

RESULTS

Among the 30 treated lesions, 11 led to patchy alopecia, while 19 did not. All cases of alopecia resolved within 12 months, and no patients experienced other adverse radiation effects. Lesions resulting in alopecia exhibited significantly higher biologically effective dose (BED) and single-fraction equivalent dose (SFED) on the overlying scalp compared to those without alopecia. Patients with BED and SFED exceeding 60 Gy and 20 Gy, respectively, were 9.3 times more likely to experience patchy alopecia than those with lower doses. The 1-year local tumor control rate for the treated lesions was 93.3%. Chemotherapy was administered for 26 lesions, with 11 lesions receiving radiosensitizing agents. However, no statistically significant difference was found.

CONCLUSION

In summary, SRS is a safe and effective treatment for patients with calvarial/scalp masses regarding patchy alopecia near the treated area. Limiting the BED under 60 Gy and SFED under 20 Gy for the overlying scalp can help prevent patchy alopecia during SRS treatment of the calvarial/scalp mass. Clinicians can use this information to inform patients about the risk of alopecia and the contributing factors.

Transit Amplifying Cells (TACs): a still not fully understood cell population

Maintenance of tissue homeostasis and tissue regeneration after an insult are essential functions of adult stem cells (SCs). In adult tissues, SCs proliferate at a very slow rate within "stem cell niches", but, during tissue development and regeneration, before giving rise to differentiated cells, they give rise to multipotent and highly proliferative cells, known as transit-amplifying cells (TACs). Although differences exist in diverse tissues, TACs are not only a transitory phase from SCs to post-mitotic cells, but they also actively control proliferation and number of their ancestor SCs and proliferation and differentiation of their progeny toward tissue specific functional cells. Autocrine signals and negative and positive feedback and feedforward paracrine signals play a major role in these controls. In the present review we will consider the generation and the role played by TACs during development and regeneration of lining epithelia characterized by a high turnover including epidermis and hair follicles, ocular epithelial surfaces, and intestinal mucosa. A comparison between these different tissues will be made. There are some genes and molecular pathways whose expression and activation are common to most TACs regardless their tissue of origin. These include, among others, Wnt, Notch, Hedgehog and BMP pathways. However, the response to these molecular signals can vary in TACs of different tissues. Secondly, we will consider cultured cells derived from tissues of mesodermal origin and widely adopted for cell therapy treatments. These include mesenchymal stem cells and dedifferentiated chondrocytes. The possible correlation between cell dedifferentiation and reversion to a transit amplifying cell stage will be discussed.

Low temperature and mTOR inhibition favor stem cell maintenance in human keratinocyte cultures

Adult autologous human epidermal stem cells can be extensively expanded ex vivo for cell and gene therapy. Identifying the mechanisms involved in stem cell maintenance and defining culture conditions to maintain stemness is critical, because an inadequate environment can result in the rapid conversion of stem cells into progenitors/transient amplifying cells (clonal conversion), with deleterious consequences on the quality of the transplants and their ability to engraft. Here, we demonstrate that cultured human epidermal stem cells respond to a small drop in temperature through thermoTRP channels via mTOR signaling. Exposure of cells to rapamycin or a small drop in temperature induces the nuclear translocation of mTOR with an impact on gene expression. We also demonstrate by single-cell analysis that long-term inhibition of mTORC1 reduces clonal conversion and favors the maintenance of stemness. Taken together, our results demonstrate that human keratinocyte stem cells can adapt to environmental changes (e.g., small variations in temperature) through mTOR signaling and constant inhibition of mTORC1 favors stem cell maintenance, a finding of high importance for regenerative medicine applications.

Stairways to Advanced Therapies for Epidermolysis Bullosa

Epidermolysis bullosa (EB) is a devastating genetic skin disease typified by a plethora of different phenotypes and ranking from severe, early lethal, to mild localized forms. Although there is no cure for EB, recent progress in pharmacology and molecular and cellular biology is boosting the development of new advanced therapeutic strategies. Here we will focus on two main categories of such therapies: (1) those aimed at controlling inflammation and inducing reepithelialization of the wounds, and (2) those, perhaps more challenging and ambitious, that aim to permanently regenerate a fully functional epidermis, which requires targeting of epidermal stem cells. In both cases, the genetic variants underlying the different EB forms and factors, such as genetic background, modifier genes, comorbidities, and lifestyle, all of which impinge on EB genotype-phenotype correlation, need to be defined.

Effective and economical cell therapy for hair regeneration

We reviewed and summarized the latest reports on the characteristics of stem cells and follicular cells that are under development for hair loss treatment. Compared with conventional medicine, cell therapy could be effective in the long term with a single treatment while having mild adverse effects. Adipose-derived stem cells (ASCs) have the advantages of easy access and large isolation amount compared with dermal papilla cells (DPCs) and dermal sheath cup cells (DSCs), and promote hair growth through the paracrine effect. ASCs have a poor potential in hair neogenesis, therefore, methods to enhance trichogenecity of ASCs should be developed. DSCs can be isolated from the peribulbar dermal sheath cup, while having immune tolerance, and hair inductivity. Therefore, DSCs were first developed and finished the phase II clinical trial; however, the hair growth was not satisfactory. Considering that a single injection of DSCs is effective for at least 9 months in the clinical setting, they can be an alternative therapy for hair regeneration. Though DPCs are not yet studied in clinical trials, we should pay attention to DPCs, as hair loss is associated with gradual reduction of DPCs and DP cell numbers fluctuate over the hair cycle. DPCs could make new hair follicles with epidermal cells, and have an immunomodulatory function to enable allogeneic transplantation. In addition, we can expand large quantities of DPCs with hair inductivity using spheroid culture, hypoxia condition, and growth factor supplement. 'Off-the-shelf' DPC therapy could be effective and economical, and therefore promising for hair regeneration.

Discovery and characterization of heterogeneous and multipotent fibroblast populations isolated from excised cleft lip tissue

Background

Regularly discarded lip tissue obtained from corrective surgeries to close the cleft lip represents an easily accessible and rich source for the isolation of primary fibroblasts. Primary fibroblasts have been described to show compelling similarities to mesenchymal stem cells (MSCs). Hence, cleft lip and palate (CLP) lip-derived fibroblasts could be thought as an intriguing cell source for personalized regenerative therapies in CLP-affected patients.

Methods

Initially, we thoroughly characterized the fibroblastic nature of the lip-derived mesenchymal outgrowths by molecular and functional assays. Next, we compared their phenotype and genotype to that of bone marrow-mesenchymal stem cells (BM-MSCs) and of human lung-derived fibroblasts WI38, by assessing their morphology, surface marker expression, trilineage differentiation potential, colony-forming (CFU) capacity, and immunomodulation property. Finally, to better decipher the heterogeneity of our CLP cultures, we performed a single cell clonal analysis and tested expanded clones for surface marker expression, as well as osteogenic and CFU potential.

Results

We identified intriguingly similar phenotypic and genotypic properties between CLP lip fibroblasts and BM-MSCs, which makes them distinct from WI38. Furthermore, our own data in combination with the complex anatomy of the lip tissue indicated heterogeneity in our CLP cultures. Using a clonal analysis, we discovered single cell-derived clones with increased levels of the MSC markers CD106 and CD146 and clones with variabilities in their commitment to differentiate into bone-forming cells and in their potential to form single cell-derived colonies. However, we were not able to gain clones possessing superior MSC-like capacities when compared to the heterogeneous parental CLP population. Additionally, all clones could still generate contractile forces and retained robust levels of the fibroblast specific marker FSP1, which was not detectable in BM-MSCs.

Conclusions

Our results suggest that we isolate heterogeneous populations of fibroblasts from discarded CLP lip tissue, which show a prominently multipotent character in their entirety avoiding the need for elaborate subpopulation selections in vitro. These findings suggest that CLP lip fibroblasts might be a novel potential cell source for personalized regenerative medicine of clinical benefit for CLP patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-03154-x.

The steep uphill path leading to ex vivo gene therapy for genodermatoses

Cell therapy, gene therapy and tissue engineering have the potential to revolutionize the field of regenerative medicine. In particular, gene therapy is understood as the therapeutical correction of mutated genes by addition of a correct copy of the gene or site-specific gene modifications. Gene correction of somatic stem cells sustaining renewing tissues is critical to ensure long-term clinical success of ex vivo gene therapy. To date, remarkable clinical outcomes arose from combined ex vivo cell and gene therapy of different genetic diseases, such as immunodeficiencies and genodermatoses. Despite the efforts of researchers around the world, only few of these advanced approaches has yet made it to routine therapy. In fact, gene therapy poses one of the greatest technical challenges in modern medicine, spanning safety and efficacy issues, regulatory constraints, registration and market access, all of which need to be addressed to make the therapy available to rare disease patients. In this review, we survey at some of the main challenges in the development of combined cell and gene therapy of genetic skin diseases.

Regulation and dysregulation of hair regeneration: aiming for clinical application

Hair growth and regeneration represents a remarkable example of stem cell function. Recent progress emphasizes the micro- and macro- environment that controls the regeneration process. There is a shift from a stem cell-centered view toward the various layers of regulatory mechanisms that control hair regeneration, which include local growth factors, immune and neuroendocrine signals, and dietary and environmental factors. This is better suited for clinical application in multiple forms of hair disorders: in male pattern hair loss, the stem cells are largely preserved, but androgen signaling diminishes hair growth; in alopecia areata, an immune attack is targeted toward the growing hair follicle without abrogating its regeneration capability. Genome-wide association studies further revealed the genetic bases of these disorders, although the precise pathological mechanisms of the identified loci remain largely unknown. By analyzing the dysregulation of hair regeneration under pathological conditions, we can better address the complex interactions among stem cells, the differentiated progeny, and mesenchymal components, and highlight the critical role of macroenvironment adjustment that is essential for hair growth and regeneration. The poly-genetic origin of these disorders makes the study of hair regeneration an interesting and challenging field.

EGFR-mediated epidermal stem cell motility drives skin regeneration through COL17A1 proteolysis

Skin regenerative capacity declines with age, but the underlying mechanisms are largely unknown. Here we demonstrate a functional link between epidermal growth factor receptor (EGFR) signaling and type XVII collagen (COL17A1) proteolysis on age-associated alteration of keratinocyte stem cell dynamics in skin regeneration. Live-imaging and computer simulation experiments predicted that human keratinocyte stem cell motility is coupled with self-renewal and epidermal regeneration. Receptor tyrosine kinase array identified the age-associated decline of EGFR signaling in mouse skin wound healing. Culture experiments proved that EGFR activation drives human keratinocyte stem cell motility with increase of COL17A1 by inhibiting its proteolysis through the secretion of tissue inhibitor of metalloproteinases 1 (TIMP1). Intriguingly, COL17A1 directly regulated keratinocyte stem cell motility and collective cell migration by coordinating actin and keratin filament networks. We conclude that EGFR-COL17A1 axis-mediated keratinocyte stem cell motility drives epidermal regeneration, which provides a novel therapeutic approach for age-associated impaired skin regeneration.

Analysis of clonogenic growth in vitro

The clonogenic assay measures the capacity of single cells to form colonies in vitro. It is widely used to identify and quantify self-renewing mammalian cells derived from in vitro cultures as well as from ex vivo tissue preparations of different origins. Varying research questions and the heterogeneous growth requirements of individual cell model systems led to the development of several assay principles and formats that differ with regard to their conceptual setup, 2D or 3D culture conditions, optional cytotoxic treatments and subsequent mathematical analysis. The protocol presented here is based on the initial clonogenic assay protocol as developed by Puck and Marcus more than 60 years ago. It updates and extends the 2006 Nature Protocols article by Franken et al. It discusses different strategies and principles to analyze clonogenic growth in vitro and presents the clonogenic assay in a modular protocol framework enabling a diversity of formats and measures to optimize determination of clonogenic growth parameters. We put particular focus on the phenomenon of cellular cooperation and consideration of how this can affect the mathematical analysis of survival data. This protocol is applicable to any mammalian cell model system from which single-cell suspensions can be prepared and which contains at least a small fraction of cells with self-renewing capacity in vitro. Depending on the cell system used, the entire procedure takes ~2-10 weeks, with a total hands-on time of <20 h per biological replicate.

Effects of electrical stimulation on human skin keratinocyte growth and the secretion of cytokines and growth factors

Electrical stimulation (ES) has been widely explored and found effective in promoting wound healing. However, the role of ES on keratinocytes, a major player in wound healing, has not been well established. The present work investigated the cellular and molecular behaviors of human skin keratinocytes being exposed to ES. HaCaT keratinocytes were seeded on a novel electrically conductive and soft PPy-PU/PLLA membrane and cultured under electrical intensities of 100 or 200 mV mm^-1for 6 and 24 h. The factors assessed after ES include cell proliferation, colony formation, cytokines, keratins, as well as phosphorylated ERK1/2 (pERK1/2) kinases. The results showed that the electrically stimulated cells exhibited a higher proliferative ability and secreted more IL-6, IL-1α, IL-8, GROα, FGF2, and VEGF-A. Interestingly, the 24 h ES induced a 'stimulus memory' by showing a significant rise in colony-forming efficiency in post-ES cells that were sub-cultured. Additionally, after stopping the 24 h ES, the productions of keratin 5 and keratin 14 were continuously increased for 3 d. The productions of keratin 10 and keratin 13 were significantly increased post the 6 h ES. Finally, the ES increased pERK1/2 kinases. The overall results demonstrated that the proliferation of keratinocytes and their secretion of cytokines and growth factors can be activated through appropriate ES to benefit skin wound healing.

MEF/KSF-conditioned culture medium: An effective method for in vitro culture of mouse dermal papilla cells with osteogenic differentiation potential

Hair follicle stem cells are pluripotent and have a self-renewal capacity and multi-differentiation potential in vitro. As hair follicle stem cells can be easily sampled from the skin and hair of clinical patients at a considerable quantity, these cells have potential applications in wound repair and skin tissue engineering. Effective approaches for the in vitro culture and amplification of mouse hair follicle stem cells, as well as the in vitro osteogenic differentiation potential and cell source when obtaining mouse-separated cells were examined. Serial subculture was performed in different culture systems. Cell source was detected based on the relevant surface markers derived from mouse hair follicles at the gene and protein levels, and the differential potential was determined. The proliferative ability of hair follicle-derived stem cells obtained from mouse embryonic fibroblast (MEF)/keratinocyte serum-free medium (KSF)-conditioned medium was the highest among all culture systems. The induced group had a stronger osteogenic differentiation potential compared with the non-induced group, indicating that the cells obtained from MEF/KSF-conditioned medium were cells derived from the hair follicle dermal papilla. Therefore, the strong osteogenic differentiation potential of the hair follicle-derived mesenchymal stem cells was screened with MEF/KSF-conditioned culture medium following amplification, and biological characteristics similar to those of hair follicle dermal papilla cells were observed.

Single-keratinocyte transcriptomic analyses identify different clonal types and proliferative potential mediated by FOXM1 in human epidermal stem cells

Autologous epidermal cultures restore a functional epidermis on burned patients. Transgenic epidermal grafts do so also in genetic skin diseases such as Junctional Epidermolysis Bullosa. Clinical success strictly requires an adequate number of epidermal stem cells, detected as holoclone-forming cells, which can be only partially distinguished from the other clonogenic keratinocytes and cannot be prospectively isolated. Here we report that single-cell transcriptome analysis of primary human epidermal cultures identifies categories of genes clearly distinguishing the different keratinocyte clonal types, which are hierarchically organized along a continuous, mainly linear trajectory showing that stem cells sequentially generate progenitors producing terminally differentiated cells. Holoclone-forming cells display stem cell hallmarks as genes regulating DNA repair, chromosome segregation, spindle organization and telomerase activity. Finally, we identify FOXM1 as a YAP-dependent key regulator of epidermal stem cells. These findings improve criteria for measuring stem cells in epidermal cultures, which is an essential feature of the graft.

Between Fate Choice and Self-Renewal-Heterogeneity of Adult Neural Crest-Derived Stem Cells

Stem cells of the neural crest (NC) vitally participate to embryonic development, but also remain in distinct niches as quiescent neural crest-derived stem cell (NCSC) pools into adulthood. Although NCSC-populations share a high capacity for self-renewal and differentiation resulting in promising preclinical applications within the last two decades, inter- and intrapopulational differences exist in terms of their expression signatures and regenerative capability. Differentiation and self-renewal of stem cells in developmental and regenerative contexts are partially regulated by the niche or culture condition and further influenced by single cell decision processes, making cell-to-cell variation and heterogeneity critical for understanding adult stem cell populations. The present review summarizes current knowledge of the cellular heterogeneity within NCSC-populations located in distinct craniofacial and trunk niches including the nasal cavity, olfactory bulb, oral tissues or skin. We shed light on the impact of intrapopulational heterogeneity on fate specifications and plasticity of NCSCs in their niches in vivo as well as during in vitro culture. We further discuss underlying molecular regulators determining fate specifications of NCSCs, suggesting a regulatory network including NF-κB and NC-related transcription factors like SLUG and SOX9 accompanied by Wnt- and MAPK-signaling to orchestrate NCSC stemness and differentiation. In summary, adult NCSCs show a broad heterogeneity on the level of the donor and the donors' sex, the cell population and the single stem cell directly impacting their differentiation capability and fate choices in vivo and in vitro. The findings discussed here emphasize heterogeneity of NCSCs as a crucial parameter for understanding their role in tissue homeostasis and regeneration and for improving their applicability in regenerative medicine.

An Intrinsic Oscillation of Gene Networks Inside Hair Follicle Stem Cells: An Additional Layer That Can Modulate Hair Stem Cell Activities

This article explores and summarizes recent progress in and the characterization of main players in the regulation and cyclic regeneration of hair follicles. The review discusses current views and discoveries on the molecular mechanisms that allow hair follicle stem cells (hfSCs) to synergistically integrate homeostasis during quiescence and activation. Discussion elaborates on a model that shows how different populations of skin stem cells coalesce intrinsic and extrinsic mechanisms, resulting in the maintenance of stemness and hair regenerative potential during an organism’s lifespan. Primarily, we focus on the question of how the intrinsic oscillation of gene networks in hfSCs sense and respond to the surrounding niche environment. The review also investigates the existence of a cell-autonomous mechanism and the reciprocal interactions between molecular signaling axes in hfSCs and niche components, which demonstrates its critical driving force in either the activation of whole mini-organ regeneration or quiescent homeostasis maintenance. These exciting novel discoveries in skin stem cells and the surrounding niche components propose a model of the intrinsic stem cell oscillator which is potentially instructive for translational regenerative medicine. Further studies, deciphering of the distribution of molecular signals coupled with the nature of their oscillation within the stem cells and niche environments, may impact the speed and efficiency of various approaches that could stimulate the development of self-renewal and cell-based therapies for hair follicle stem cell regeneration.

Dosimetric study of whole-brain irradiation with high-energy photon beams for dose reduction to the scalp

OBJECTIVE

To evaluate the efficiency of high-energy photons for mitigating alopecia due to whole-brain irradiation (WBRT).

METHODS

Planning CT data from 10 patients who received WBRT were collected. We prepared 4 WBRT plans that used 6 or 15 MV photon beams, with or without use of a field-in-field (FiF) technique, and compared outcomes using a treatment planning system. The primary outcome was dose parameters to the scalp, including the mean dose, maximum dose, and dose received to 50% scalp(D50%). Secondary outcomes were minimum dose to the brain surface.

RESULTS

Using FiF, the mean doses were 24.4-26.0 and 22.4-24.1 Gy, and the maximum doses were 30.5-32.1 and 28.5-30.8 Gy for 6 and 15 MV photon beams, respectively. Without FiF, the mean doses were 24.6-26.9 and 22.6-24.5 Gy, and the maximum doses were 30.8-34.6 and 28.6-32.4 Gy for 6 and 15 MV photon beams. The 15 MV plan resulted in a lower scalp dose for each dose parameter (p < 0.001). Using FiF, the minimum doses to the brain surface for the 6 and 15 MV plans were 28.9 ± 0.440 and 29.0 ± 0.557 Gy, respectively (p = 0.70). Without FiF, the minimum doses to the brain surface for the 6 and 15 MV plans were 28.9 ± 0.456 and 29.0 ± 0.529, respectively (p = 0.66).

CONCLUSION

Compared with the 6 MV plan, the 15 MV plan achieved a lower scalp dose without impairing the brain surface dose.

ADVANCES IN KNOWLEDGE

High-energy photon WBRT may mitigate alopecia of patients who receiving WBRT.

SCF/C-Kit Signaling Induces Self-Renewal of Dental Pulp Stem Cells

INTRODUCTION

The maintenance of a stem cell pool is imperative to enable healing processes in the dental pulp tissue throughout life. As such, knowing mechanisms underlying stem cell self-renewal is critical to understand pulp pathophysiology and pulp regeneration. The purpose of this study was to evaluate the impact of stem cell factor (SCF) signaling through its receptor tyrosine kinase (c-Kit) on the self-renewal of human dental pulp stem cells (hDPSCs).

METHODS

The hDPSCs were stably transduced with lentiviral vectors expressing shRNA-c-Kit or vector control. The impact of the SCF/c-Kit axis on hDPSC self-renewal was evaluated by using a pulpsphere assay in low attachment conditions and by evaluating the expression of polycomb complex protein Bmi-1 (master regulator of self-renewal) by Western blot and flow cytometry.

RESULTS

The c-Kit-silenced hDPSCs formed fewer pulpspheres when compared with hDPSCs transduced with control vector (P < .05). Evaluation of pulpsphere morphology revealed the presence of 3 distinct sphere types, ie, holospheres, merospheres, and paraspheres. Although c-Kit silencing decreased the number of holospheres compared with control cells (P < .05), it had no effect on the number of merospheres and paraspheres. Recombinant human stem cell factor (rhSCF) increased the number of holospheres (P < .05) and induced dose-dependent Bmi-1 expression in hDPSCs. As expected, the inductive capacity of rhSCF on Bmi-1 expression and fraction of Bmi-1-positive cells was inhibited when we silenced c-Kit in hDPSCs.

CONCLUSIONS

These results unveiled the role of SCF/c-Kit signaling on the self-renewal of hDPSCs and suggested that this pathway enables long-term maintenance of stem cell pools in human dental pulps.

Cell Types Promoting Goosebumps Form a Niche to Regulate Hair Follicle Stem Cells

Piloerection (goosebumps) requires concerted actions of the hair follicle, the arrector pili muscle (APM), and the sympathetic nerve, providing a model to study interactions across epithelium, mesenchyme, and nerves. Here, we show that APMs and sympathetic nerves form a dual-component niche to modulate hair follicle stem cell (HFSC) activity. Sympathetic nerves form synapse-like structures with HFSCs and regulate HFSCs through norepinephrine, whereas APMs maintain sympathetic innervation to HFSCs. Without norepinephrine signaling, HFSCs enter deep quiescence by down-regulating the cell cycle and metabolism while up-regulating quiescence regulators Foxp1 and Fgf18. During development, HFSC progeny secretes Sonic Hedgehog (SHH) to direct the formation of this APM-sympathetic nerve niche, which in turn controls hair follicle regeneration in adults. Our results reveal a reciprocal interdependence between a regenerative tissue and its niche at different stages and demonstrate sympathetic nerves can modulate stem cells through synapse-like connections and neurotransmitters to couple tissue production with demands.

Prostate cancer-derived holoclones: a novel and effective model for evaluating cancer stemness

Prostate cancer accounts for approximately 13.5% of all newly diagnosed male cancer cases. Significant clinical burdens remain in terms of ineffective prognostication, with overtreatment of insignificant disease. Additionally, the pathobiology underlying disease heterogeneity remains poorly understood. As the role of cancer stem cells in the perpetuation of aggressive carcinoma is being substantiated by experimental evidence, it is crucially important to understand the molecular mechanisms, which regulate key features of cancer stem cells. We investigated two methods for in vitro cultivation of putative prostate cancer stem cells based on ‘high-salt agar’ and ‘monoclonal cultivation’. Data demonstrated ‘monoclonal cultivation’ as the superior method. We demonstrated that ‘holoclones’ expressed canonical stem markers, retained the exclusive ability to generate poorly differentiated tumours in NOD/SCID mice and possessed a unique mRNA-miRNA gene signature. miRNA:Target interactions analysis visualised potentially critical regulatory networks, which are dysregulated in prostate cancer holoclones. The characterisation of this tumorigenic population lays the groundwork for this model to be used in the identification of proteomic or small non-coding RNA therapeutic targets for the eradication of this critical cellular population. This is significant, as it provides a potential route to limit development of aggressive disease and thus improve survival rates.

Toward Combined Cell and Gene Therapy for Genodermatoses

To date, more than 200 monogenic, often devastating, skin diseases have been described. Because of unmet medical needs, development of long-lasting and curative therapies has been consistently attempted, with the aim of correcting the underlying molecular defect. In this review, we will specifically address the few combined cell and gene therapy strategies that made it to the clinics. Based on these studies, what can be envisioned for the future is a patient-oriented strategy, built on the specific features of the individual in need. Most likely, a combination of different strategies, approaches, and advanced therapies will be required to reach the finish line at the end of the long and winding road hampering the achievement of definitive treatments for genodermatoses.

Hair follicle stem cells combined with human allogeneic acellular amniotic membrane for repair of full thickness skin defects in nude mice

Repair of large skin defects caused by burns, trauma, or tumor operations is a clinical challenge. Hair follicle stem cells (HFSCs) are involved in epithelialization of wounds, formation of new hair follicles and promote vascularization in the newly formed skin, and human acellular amniotic membrane (hAAM) is a promising scaffold for skin substitute. Here, we investigated the ability of rat HFSCs (rHFSCs) combined with an hAAM to repair full thickness skin defects in nude mice. The effect of the rHFSC-hAAM composite on the repair of skin defects in nude mice was assessed by hematoxylin and eosin staining, immunohistochemistry, and EdU-labeled cell tracking. Isolated and cultured rHFSCs had strong cloning and proliferation potentials. Immunofluorescence staining and flow cytometry assays showed that rHFSCs expressed high levels of integrin α6, CK15, p63, and Sox9. Cells cultured in hAAM showed flaky and cluster-like morphology and were able to adhere and grow effectively. After transplantation, the rHFSC-hAAM composite promoted wound healing in nude mice. Moreover, cells in the rHFSC-hAAM composite were directly involved in hair follicle formation and angiogenesis of tissue around the hair follicle. These results provide an experimental and theoretical basis for the clinical application of HFSCs in repair of human skin defects and a new approach for skin tissue engineering.

Traceable Impedance-Based Dispensing and Cloning of Living Single Cells

Single-cell cloning is essential in stem cell biology, cancer research, and biotechnology. Regulatory agencies now require an indisputable proof of clonality that current technologies do not readily provide. Here, we report a one-step cloning method using an engineered pipet combined with an impedance-based sensing tip. This technology permits the efficient and traceable isolation of living cells, stem cells, and cancer stem cells that can be individually expanded in culture and transplanted.

Automated collective motion analysis validates human keratinocyte stem cell cultures

Identification and quality assurance of stem cells cultured in heterogeneous cell populations are indispensable for successful stem cell therapy. Here we present an image-processing pipeline for automated identification and quality assessment of human keratinocyte stem cells. When cultivated under appropriate conditions, human epidermal keratinocyte stem cells give rise to colonies and exhibit higher locomotive capacity as well as significant proliferative potential. Image processing and kernel density estimation were used to automatically extract the area of keratinocyte colonies from phase-contrast images of cultures containing feeder cells. The DeepFlow algorithm was then used to calculate locomotion speed of the colony area by analyzing serial images. This image-processing pipeline successfully identified keratinocyte stem cell colonies by measuring cell locomotion speed, and also assessed the effect of oligotrophic culture conditions and chemical inhibitors on keratinocyte behavior. Therefore, this study provides automated procedures for image-based quality control of stem cell cultures and high-throughput screening of small molecules targeting stem cells.

Living with Keratinocytes

A feature distinguishing human hematopoietic and epithelial stem cells from other equally fascinating stem cells is perhaps their easier translation into a clinical setting. We have devoted nearly our entire scientific career in trying to turn our understanding of epithelial stem cell biology into something that could help people suffering from virtually untreatable diseases of squamous epithelia. We have done that as a team, together with our numerous students, postdocs, technicians and valuable collaborators, clinicians, regulators, and, lately, industrial partners. We had rewarding successes and burning failures, but we always did our best. This award, given by friends and colleagues deserving it more than us, has been the most important recognition of our work. Below, we summarize our story.

"Miliacin encapsulated by polar lipids stimulates cell proliferation in hair bulb and improves telogen effluvium in women"

BACKGROUND

Miliacin, the main triterpenoid from millet, is known to stimulate keratinocyte metabolism and proliferation. Polar lipids are able to form vesicles with active compounds and to improve their bioavailability.

OBJECTIVES

We aimed to demonstrate potential benefits of a solution of miliacin encapsulated within polar lipids (MePL) on telogen effluvium prevention and hair condition in women.

METHODS

After preliminary cell proliferation studies, a placebo-controlled, multicentric, randomized, double-blind trial was performed on sixty-five nonmenopausal women affected by telogen effluvium, to assess the efficacy of a 12-week oral supplementation with MePL. Telogen and anagen densities were determined by phototrichogram analysis. Scalp dryness and hair brightness were clinically evaluated using a Likert scale.

RESULTS

MePL further enhanced cell proliferation in hair bulb from human scalp than miliacin alone. Compared to the placebo treatment, MePL supplementation significantly reduced telogen density after 12 weeks of treatment. An increase of anagen density was observed in both groups, although there was no significant difference between the two treatments. Scalp dryness was more decreased in the MePL group than in the placebo group. A better improvement of hair brightness was also observed after 12 weeks of supplementation with MePL.

CONCLUSION

Twelve weeks of MePL supplementation significantly reduced the hair density in the telogen phase and, in parallel, improved scalp dryness and hair condition. These effects could be linked to MePL activity on cell proliferation in hair bulb. MePL is an original association of plant extract that could help to prevent and/or limit hair loss in women.

Laminin 332-Dependent YAP Dysregulation Depletes Epidermal Stem Cells in Junctional Epidermolysis Bullosa

Laminin 332-deficient junctional epidermolysis bullosa (JEB) is a severe genetic skin disease. JEB is marked by epidermal stem cell depletion, the origin of which is unknown. We show that dysregulation of the YAP and TAZ pathway underpins such stem cell depletion. Laminin 332-mediated YAP activity sustains human epidermal stem cells, detected as holoclones. Ablation of YAP selectively depletes holoclones, while enforced YAP blocks conversion of stem cells into progenitors and indefinitely extends the keratinocyte lifespan. YAP is dramatically decreased in JEB keratinocytes, which contain only phosphorylated, inactive YAP. In normal keratinocytes, laminin 332 and α6β4 ablation abolish YAP activity and recapitulate the JEB phenotype. In JEB keratinocytes, laminin 332-gene therapy rescues YAP activity and epidermal stem cells in vitro and in vivo. In JEB cells, enforced YAP recapitulates laminin 332-gene therapy, thus uncoupling adhesion from proliferation in epidermal stem cells. This work has important clinical implication for ex vivo gene therapy of JEB.

Radon emanation from human hair

Bio-indicator of long time exposure to pollutants, human hair is studied in contaminated areas. The number of studies on background environments remains small, and factors impacting human hair radioactivity in contaminated and background areas remain poorly known. Radon-222, a radioactive noble gas of half-life 3.8 days, is the alpha decay daughter of radium-226 in the uranium-238 chain. Radon emission depends on radium concentration (C_Ra) and probability of decaying radium to liberate radon (i.e., the emanation coefficient E). The radon-222 emanating power (i.e., radon emanation or effective radium-226 concentration, EC_Ra) is measured in the laboratory from human hair of a cohort of 93 individuals living in uranium non-contaminated areas using a high-sensitivity method based on 371 long accumulation sessions. E of human hair is also determined. EC_Ra values from human hair are heterogeneous, ranging from 0.059 ± 0.008 to 3.7 ± 0.1 Bq kg^-1 (mean: 0.484 ± 0.006 Bq kg^-1). We find 2.6 ± 0.1 and 2.5 ± 0.1 times larger values for females than males and for color-treated than natural hair, respectively. By contrast, E is homogeneous (mean: 0.33 ± 0.11; n = 9). Our data suggest a different behavior of accumulation/elimination processes of heavy elements in females and non-negligible radium concentration in hair dye products. Our results demonstrate ²²⁶Ra-²³⁸U disequilibrium in human hair, indicating secondary radium intake, and that EC_Ra mainly depends on C_Ra. Other factors such as age and sampling time are also studied. The impact of factors on EC_Ra from human hair in uranium non-contaminated areas is ordered as follows: (body site?) > sex > hair dyeing > dietary/drinking habits > natural color > time period > geographical location > age. Any human hair-based study should take into consideration these factors. Our method, cost-effective and easy to implement, may be applied to large numbers of samples for large-scale epidemiological studies, and may also be useful for criminal investigations.

The different expression of key markers on urothelial holoclonal, meroclonal, and paraclonal cells in in vitro culture

Urothelial cell populations which differ in morphology and proliferation capacities can be isolated from the urinary bladder. The goal of this study was to analyze a clonal, proliferative, and self-renewing potential of porcine urothelial cells and to compare expression of selected adhesion and tight junction molecules, urothelial and stem cell markers for the urothelial clone types. Urothelial cells were isolated from 10 porcine urinary bladders. Three different clone types: holoclone-, meroclone-and paraclone-like colonies were identified based on their morphology. To characterize and compare the urothelial clones the immunofluorescent stains were performed. Expression of pancytokeratin (PanCK), Ki-67 and p63 was higher for holoclone- like cells compared to meroclone-and paraclone-like cells (P < 0.05). Meroclone-like cells expressed higher levels of p63 compared to paraclone- like cells (P < 0.05). The level of Ki-67 and PanCK for meroclone- and paraclone- like cells was comparable (P > 0.05). β1 and β4 integrins were not expressed. Expression of zonula occludens-1 (ZO-1) in cell-cell junctions for paraclone-, meroclone-and holoclone-like cells was 17.6 ± 0.6, 14.7 ± 0.5, and 16.1 ± 0.4, respectively. The results of actin filaments (F-actin) expression were 253,634 ± 6,920 for meroclone-like cells, 198,512 ± 7,977 for paraclone-like cells and 133,544 ± 3,169 for holoclone-like cells. Three urothelial cell types with differing features can be isolated from the bladder. Holoclone-like cells are the richest in stem cells and should be used in further studies for construction of neo-bladder or neo-conduit using tissue engineering methods.

Stem cell dynamics, migration and plasticity during wound healing

Tissue repair is critical for animal survival. The skin epidermis is particularly exposed to injuries, which necessitates rapid repair. The coordinated action of distinct epidermal stem cells recruited from various skin regions together with other cell types, including fibroblasts and immune cells, is required to ensure efficient and harmonious wound healing. A complex crosstalk ensures the activation, migration and plasticity of these cells during tissue repair.

Comparison of Efficacy of Doxycycline and Isotretinoin on Cutaneous Human Beta-Defensin-1 and -2 Levels in Acne Vulgaris

Background:

Recent studies have shown that human beta-defensin-1 (hBD-1) and (human beta-defensin-2 hBD-2), which are antimicrobial peptides produced by the skin, play a role in the pathogenesis of acne vulgaris (AV).

Objective:

The aim of this study was to determine the role of antimicrobial peptides in the pathogenesis of AV and enlighten the effects of doxycycline and isotretinoin in the expression of these defensins in AV.

Materials and Methods:

A total of 44 patients (22 patients in each group) with Grade 6 and 8 AV who were indicated doxycycline or isotretinoin for their treatment, and 20 healthy volunteers were included in this study. Pretreatment cutaneous samples were obtained from pustular lesions and uninvolved skin of AV patients and were repeated after the treatment. Only one biopsy was obtained from controls.

Results:

Cutaneous levels of hBD-1 and hBD-2 were significantly increased in AV patients when compared with healthy controls (P<0.05). Doxycycline therapy achieved a decrease in hBD-1 levels (P<0.05), whereas isotretinoin therapy achieved a reduction in hBD-2 levels when compared with pretreatment levels (P<0.05). Posttreatment hBD-1 and hBD-2 levels were not different between doxycycline and isotretinoin groups (P>0.05).

Conclusion:

In the light of these results, it was reasonable to assume the role of hBD-1 and hBD-2 in the pathogenesis of AV. Our results showing a significant reduction in hBD-1 staining with doxycycline treatment and in hBD-2 with isotretinoin suggested that some part of their anti-acne effect worked through these mechanisms.

Ex Vivo COL7A1 Correction for Recessive Dystrophic Epidermolysis Bullosa Using CRISPR/Cas9 and Homology-Directed Repair

Recessive dystrophic epidermolysis bullosa is a rare and severe genetic skin disease resulting in blistering of the skin and mucosa. Recessive dystrophic epidermolysis bullosa (RDEB) is caused by a wide variety of mutations in COL7A1-encoding type VII collagen, which is essential for dermal-epidermal adhesion. Here we demonstrate the feasibility of ex vivo COL7A1 editing in primary RDEB cells and in grafted 3D skin equivalents through CRISPR/Cas9-mediated homology-directed repair. We designed five guide RNAs to correct a RDEB causative null mutation in exon 2 (c.189delG; p.Leu64Trpfs*40). Among the site-specific guide RNAs tested, one showed significant cleavage activity in primary RDEB keratinocytes and in fibroblasts when delivered as integration-deficient lentivirus. Genetic correction was detected in transduced keratinocytes and fibroblasts by allele-specific highly sensitive TaqMan-droplet digital PCR (ddPCR), resulting in 11% and 15.7% of corrected COL7A1 mRNA expression, respectively, without antibiotic selection. Grafting of genetically corrected 3D skin equivalents onto nude mice showed up to 26% re-expression and normal localization of type VII collagen as well as anchoring fibril formation at the dermal-epidermal junction. Our study provides evidence that precise genome editing in primary RDEB cells is a relevant strategy to genetically correct COL7A1 mutations for the development of future ex vivo clinical applications.

Identifying Quiescent Stem Cells in Hair Follicles

H]TdR can be visualized by autoradiography and BrdU can be detected by immunofluorescence with anti-BrdU antibodies. Alternatively, a well-established tet-regulatable transgenic mouse model can be used to express histone H2B-GFP in epithelial proliferative cells and their dilution and retention of the GFP signal can be followed. In this chapter, we detail the steps to perform BrdU pulse-chase and H2B-GFP pulse-chase experiments to identify quiescent cells in the hair follicle.

Immune responses to bioengineered organs

PURPOSE OF REVIEW

Organ donation in the United States registered 9079 deceased organ donors in 2015. This high percentage of donations allowed organ transplantation in 29 851 recipients. Despite increasing numbers of transplants performed in comparison with previous years, the numbers of patients that are in need for a transplant increase every year at a higher rate. This reveals that the discrepancy between the demand and availability of organs remains fundamental problem in organ transplantation.

RECENT FINDINGS

Development of bioengineered organs represents a promising approach to increase the pool of organs for transplantation. The technology involves obtaining complex three-dimensional scaffolds that support cellular activity and functional remodeling though tissue recellularization protocols using progenitor cells. This innovative approach integrates cross-thematic approaches from specific areas of transplant immunology, tissue engineering and stem cell biology, to potentially manufacture an unlimited source of donor organs for transplantation.

SUMMARY

Although bioengineered organs are thought to escape immune recognition, the potential immune reactivity toward each of its components has not been studied in detail. Here, we summarize the host immune response toward different progenitor cells and discuss the potential implications of using nonself biological scaffolds to develop bioengineered organs.

Epidermal Stem Cells in Skin Wound Healing

Significance: Skin serves as a protective barrier for mammals. Epidermal stem cells are responsible for maintaining skin homeostasis. When cutaneous injuries occur, skin homeostasis and integrity are damaged, leading to dire consequences such as acute, chronic, or infected wounds. Skin wound healing is an intrinsic self-saving chain reaction, which is crucial to facilitating the replacement of damaged or lost tissue. Recent Advances: An immense amount of research has uncovered the underlying mechanisms behind the complex and highly regulated wound healing process. In this review, we will dissect the biological process of adult skin wound healing and emphasize the importance of epidermal stem cells during the wound healing. Critical Issues: We will comprehensively discuss the current clinical practices used on patients with cutaneous wounds, including both traditional skin grafting procedures and advanced grafting techniques with cultured skin stem cells. The majority of these leading techniques still retain some deficiencies during clinical use. Moreover, the regeneration of skin appendages after severe injuries remains a challenge in treatment. Future Directions: Understanding epidermal stem cells and their essential functions during skin wound healing are fundamental components behind the development of clinical treatment on patients with cutaneous wounds. It is important to improve the current standard of care and to develop novel techniques improving patient outcomes and long-term rehabilitation, which should be the goals of future endeavors in the field of skin wound healing.

Traceless Targeting and Isolation of Gene-Edited Immortalized Keratinocytes from Epidermolysis Bullosa Simplex Patients

Epidermolysis bullosa simplex (EBS) is a blistering skin disease caused by dominant-negative mutations in either KRT5 or KRT14, resulting in impairment of keratin filament structure and epidermal fragility. Currently, nearly 200 mutations distributed across the entire length of these genes are known to cause EBS. Genome editing using programmable nucleases enables the development of ex vivo gene therapies for dominant-negative genetic diseases. A clinically feasible strategy involves the disruption of the mutant allele while leaving the wild-type allele unaffected. Our aim was to develop a traceless approach to efficiently disrupt KRT5 alleles using TALENs displaying unbiased monoallelic disruption events and devise a strategy that allows for subsequent screening and isolation of correctly modified keratinocyte clones without the need for selection markers. Here we report on TALENs that efficiently disrupt the KRT5 locus in immortalized patient-derived EBS keratinocytes. Inactivation of the mutant allele using a TALEN working at sub-optimal levels resulted in restoration of intermediate filament architecture. This approach can be used for the functional inactivation of any mutant keratin allele regardless of the position of the mutation within the gene and is furthermore applicable to the treatment of other inherited skin disorders.

α6 Integrin (α6high)/Transferrin Receptor (CD71)low Keratinocyte Stem Cells Are More Potent for Generating Reconstructed Skin Epidermis Than Rapid Adherent Cells

The epidermis basal layer is composed of two keratinocyte populations: Keratinocyte Stem cells (KSC) and Transitory Amplifying (TA) cells that arise from KSC division. Unfortunately, no specific marker exists to differ between KSC and TA cells. Here, we aimed at comparing two different methods that pretended to isolate these two populations: (i) the rapid adhesion method on coated substrate and (ii) the flow cytometry method, which is based on the difference in cell surface expressions of the α6 integrin and transferrin receptor (CD71). Then, we compared different parameters that are known to discriminate KSC and TA populations. Interestingly, we showed that both methods allow enrichment in stem cells. However, cell sorting by flow cytometry (α6^high/CD71^low) phenotype leads to a better enrichment of KSC since the colony forming efficiency is five times increased versus total cell suspension, whereas it is only 1.4 times for the adhesion method. Moreover, α6^high/CD71^low cells give rise to a thicker pluristratified epithelium with lower seeding density and display a low Ki67 positive cells number, showing that they have reached the balance between proliferation and differentiation. We clearly demonstrated that cells isolated by a rapid adherent method are not the same population as KSC isolated by flow cytometry following α6^high/CD71^low phenotype.