Differential expression of stem cell markers in human follicular bulge and interfollicular epidermal compartments

Cellular Heterogeneity Facilitates the Functional Differences Between Hair Follicle Dermal Sheath Cells and Dermal Papilla Cells: A New Classification System for Mesenchymal Cells within the Hair Follicle Niche

Mesenchymal stem cells (MSCs) are known for their self-renewal and multi-lineage differentiation potential, with these cells often being evaluated in the regulation and maintenance of specific cellular niches including those of the hair follicle. Most mesenchymal stem cells in the hair follicles are housed in the dermal papilla (DP) and dermal sheath (DS), with both niches characterized by a broad variety of cellular subsets. However, while most previous studies describing the hair follicle mesenchymal niche treated all DP and DS cells as Hair Follicle Mesenchymal Stem Cells (HF-MSCs), the high number of cellular subsets would suggest that these cells are actually too heterogenous for such a broad definition. Given this we designed this study to evaluate the differentiation processes in these cells and used this data to create a new set of classifications for DP and DS cells, dividing them into "hair follicle mesenchymal stem cells (HF-MSCs)", "hair follicle mesenchymal progenitor cells (HF-MPCs)", and "hair follicle mesenchymal functional cells (HF-MFCs)". In addition, those cells that possess self-renewal and differentiation were re-named hair follicle derived mesenchymal multipotent cells (HF-MMCs). This new classification may help to further our understanding of the heterogeneity of hair follicle dermal cells and provide new insights into their evaluation.

The proliferative and multipotent epidermal progenitor cells for human skin reconstruction in vitro and in vivo

OBJECTIVES

The skin exhibits tremendous regenerative potential, as different types of progenitor and stem cells regulate skin homeostasis and damage. However, in vitro primary keratinocytes present with several drawbacks, such as high donor variability, short lifespan, and limited donor tissue availability. Therefore, more stable primary keratinocytes are needed to generate multiple uniform in vitro and in vivo skin models.

RESULTS

We identified epidermal progenitor cells from primary keratinocytes using Integrin beta 1 (ITGB1) an epidermal stem cell marker markedly decreased after senescence in vitro. Epidermal progenitor cells exhibited unlimited proliferation and the potential for multipotent differentiation capacity. Moreover, they could completely differentiate to form an organotypic skin model including conversed mesenchymal cells in the dermis and could mimic the morphologic and biochemical processes of human epidermis. We also discovered that proliferation and the multipotent differentiation capacity of these cells relied on ITGB1 expression. Eventually, we examined the in vitro and in vivo wound healing capacity of these epidermal progenitor cells.

CONCLUSIONS

Overall, the findings suggest that these stable and reproducible cells can differentiate into multiple lineages, including human skin models. They are a potentially powerful tool for studying skin regeneration, skin diseases, and are an alternative for in vivo experiments.

A systematic summary of survival and death signalling during the life of hair follicle stem cells

Hair follicle stem cells (HFSCs) are among the most widely available resources and most frequently approved model systems used for studying adult stem cells. HFSCs are particularly useful because of their self-renewal and differentiation properties. Additionally, the cyclic growth of hair follicles is driven by HFSCs. There are high expectations for the use of HFSCs as favourable systems for studying the molecular mechanisms that contribute to HFSC identification and can be applied to hair loss therapy, such as the activation or regeneration of hair follicles, and to the generation of hair using a tissue-engineering strategy. A variety of molecules are involved in the networks that critically regulate the fate of HFSCs, such as factors in hair follicle growth and development (in the Wnt pathway, Sonic hedgehog pathway, Notch pathway, and BMP pathway), and that suppress apoptotic cues (the apoptosis pathway). Here, we review the life cycle, biomarkers and functions of HFSCs, concluding with a summary of the signalling pathways involved in HFSC fate for promoting better understanding of the pathophysiological changes in the HFSC niche. Importantly, we highlight the potential mechanisms underlying the therapeutic targets involved in pathways associated with the treatment of hair loss and other disorders of skin and hair, including alopecia, skin cancer, skin inflammation, and skin wound healing.

Computational flow cytometric analysis to detect epidermal subpopulations in human skin

Background

The detection and dissection of epidermal subgroups could lead to an improved understanding of skin homeostasis and wound healing. Flow cytometric analysis provides an effective method to detect the surface markers of epidermal cells while producing high-dimensional data files.

Methods

A 9-color flow cytometric panel was optimized to reveal the heterogeneous subgroups in the epidermis of human skin. The subsets of epidermal cells were characterized using automated methods based on dimensional reduction approaches (viSNE) and clustering with Spanning-tree Progression Analysis of Density-normalized Events (SPADE).

Results

The manual analysis revealed differences in epidermal distribution between body sites based on a series biaxial gating starting with the expression of CD49f and CD29. The computational analysis divided the whole epidermal cell population into 25 clusters according to the surface marker phenotype with SPADE. This automatic analysis delineated the differences between body sites. The consistency of the results was confirmed with PhenoGraph.

Conclusion

A multicolor flow cytometry panel with a streamlined computational analysis pipeline is a feasible approach to delineate the heterogeneity of the epidermis in human skin.

A comparison of transcriptomic patterns measured in the skin of Chinese fine and coarse wool sheep breeds

We characterised wool traits, and skin gene expression profiles of fine wool Super Merino (SM) and coarse wool Small Tail Han (STH) sheep. SM sheep had a significantly higher total density of wool follicles, heavier fleeces, finer fibre diameter, and increased crimp frequency, staple length and wool grease (lanolin) production. We found 435 genes were expressed at significantly different levels in the skin of the two breeds (127 genes more highly in SM and 308 genes more highly in STH sheep). Classification of the genes more highly expressed in SM sheep revealed numerous lipid metabolic genes as well as genes encoding keratins, keratin-associated proteins, and wool follicle stem cell markers. In contrast, mammalian epidermal development complex genes and other genes associated with skin cornification and muscle function were more highly expressed in STH sheep. Genes identified in this study may be further evaluated for inclusion in breeding programs, or as targets for therapeutic or genetic interventions, aimed at altering wool quality or yield. Expression of the lipid metabolic genes in the skin of sheep may be used as a novel trait with the potential to alter the content or properties of lanolin or the fleece.

Cancer Stem Cells in Squamous Cell Carcinoma

Cancer stem cells (CSCs) are found in many cancer types, including squamous cell carcinoma (SCC). CSCs initiate cancer formation and are linked to metastasis and resistance to therapies. Studies have revealed that several distinct CSC populations coexist in SCC and that tumor initiation and metastatic potential of these populations can be uncoupled. Therefore, it is critical to understand CSC biology to develop novel CSC-targeted therapies for patients with SCC with poor prognoses. This review compares the properties of CSCs in SCC with normal stem cells in the skin, summarizes current advances and characteristics of CSCs, and considers the challenges for CSC-targeted treatment of SCC.

CD99 Is Strongly Expressed in Basal Cells of the Normal Adult Epidermis and Some Subpopulations of Appendages: Comparison with Developing Fetal Skin

BACKGROUND

CD99 is a cell surface transmembrane glycoprotein expressed in various tissues. CD99 is differentially expressed between subpopulations of each tissue and is highly expressed in certain hematopoietic and precursor cells. However, there has been no comprehensive study of CD99 expression in normal skin. We evaluated CD99 expression in normal human skin and developing fetal skin.

METHODS

Seventy-five adult skin samples containing normal skin and eight fetal skin samples of different gestational ages were collected. CD99 immunohistochemical staining was performed to evaluate expression pattern in adult and fetal skin samples. CD99 and CD34 expression were compared by double immunofluorescence.

RESULTS

In normal adult skin, CD99 was strongly expressed in the membrane of epidermal basal keratinocytes, hair follicle bulges and outer root sheaths, and inner secretory cells of eccrine sweat glands. In fetal skin, CD99 was not expressed on the periderm at 16 weeks of gestation but was expressed in basal cells of fetal skin at around 19 weeks of gestation. CD99 expression became comparable to that of the adult skin after 20 weeks of gestation. CD99 and CD34 were co-expressed in hair follicle outer root sheaths, as seen by double immunofluorescence study.

CONCLUSIONS

This is the first study examining CD99 expression pattern in normal adult and fetal skin. CD99 tends to be expressed in the basal/precursor cells of epidermis and in hair follicles. These results provide a basis for future investigation on functions of CD99 in the skin and provide a novel potential target for the treatment of dermatologic lesions.

Concise review: evidence for CD34 as a common marker for diverse progenitors

CD34 is a transmembrane phosphoglycoprotein, first identified on hematopoietic stem and progenitor cells. Clinically, it is associated with the selection and enrichment of hematopoietic stem cells for bone marrow transplants. Due to these historical and clinical associations, CD34 expression is almost ubiquitously related to hematopoietic cells, and it is a common misconception that CD34-positive (CD34⁺) cells in nonhematopoietic samples represent hematopoietic contamination. The prevailing school of thought states that multipotent mesenchymal stromal cells (MSC) do not express CD34. However, strong evidence demonstrates CD34 is expressed not only by MSC but by a multitude of other nonhematopoietic cell types including muscle satellite cells, corneal keratocytes, interstitial cells, epithelial progenitors, and vascular endothelial progenitors. In many cases, the CD34⁺ cells represent a small proportion of the total cell population and also indicate a distinct subset of cells with enhanced progenitor activity. Herein, we explore common traits between cells that express CD34, including associated markers, morphology and differentiation potential. We endeavor to highlight key similarities between CD34⁺ cells, with a focus on progenitor activity. A common function of CD34 has yet to be elucidated, but by analyzing and understanding links between CD34⁺ cells, we hope to be able to offer an insight into the overlapping properties of cells that express CD34. Stem Cells2014;32:1380–1389

Beyond goosebumps: does the arrector pili muscle have a role in hair loss?

The arrector pili muscle (APM) consists of a small band of smooth muscle that connects the hair follicle to the connective tissue of the basement membrane. The APM mediates thermoregulation by contracting to increase air-trapping, but was thought to be vestigial in humans. The APM attaches proximally to the hair follicle at the bulge, a known stem cell niche. Recent studies have been directed toward this muscle's possible role in maintaining the follicular integrity and stability. This review summarizes APM anatomy and physiology and then discusses the relationship between the follicular unit and the APM. The potential role of the APM in hair loss disorders is also described, and a model explaining APM changes in hair loss is proposed.

Heterelogous expression of mutated HLA-G decreases immunogenicity of human embryonic stem cells and their epidermal derivatives

Human embryonic stem cells (hESCs) are capable of extensive self-renewal and expansion and can differentiate into any somatic tissue, making them useful for regenerative medicine applications. Allogeneic transplantation of hESC-derived tissues from results in immunological rejection absent adjunctive immunosuppression. The goal of our study was to generate a universal pluripotent stem cell source by nucleofecting a mutated human leukocyte antigen G (mHLA-G) gene into hESCs using the PiggyBac transposon. We successfully generated stable mHLA-G(EF1α)-hESC lines using chEF1α promoter system that stably expressed mHLA-G protein during prolonged undifferentiated proliferation andin differentiated embryoid bodies as well as teratomas. Morphology, karyotype, and telomerase activity of mHLA-G expressing hESC were normal. Immunofluorescence staining and flow cytometry analysis revealed persistent expression of pluripotent markers, OCT-3/4 and SSEA-4, in undifferentiated mHLA-G(EF1α)-hESC. Nucleofected hESC formed teratomas and when directed to differentiate into epidermal precursors, expressed high levels of mHLA-G and keratinocyte markers K14 and CD29. Natural killer cell cytotoxicity assays demonstrated a significant decrease in lysis of mHLA-G(EF1a)-hESC targets relative to control cells. Similar results were obtained with mHLA-G(EF1α)-hESC-derived epidermal progenitors (hEEP). One way mixed T lymphocyte reactions unveiled that mHLA-G(EF1a)-hESC and -hEEP restrained the proliferative activity of mixed T lymphocytes. We conclude that heterologous expression of mHLA-G decreases immunogenicity of hESCs and their epidermal differentiated derivatives.

Human epithelial hair follicle stem cells and their progeny: current state of knowledge, the widening gap in translational research and future challenges

Epithelial hair follicle stem cells (eHFSCs) are required to generate, maintain and renew the continuously cycling hair follicle (HF), supply cells that produce the keratinized hair shaft and aid in the reepithelialization of injured skin. Therefore, their study is biologically and clinically important, from alopecia to carcinogenesis and regenerative medicine. However, human eHFSCs remain ill defined compared to their murine counterparts, and it is unclear which murine eHFSC markers really apply to the human HF. We address this by reviewing current concepts on human eHFSC biology, their immediate progeny and their molecular markers, focusing on Keratin 15 and 19, CD200, CD34, PHLDA1, and EpCAM/Ber-EP4. After delineating how human eHFSCs may be selectively targeted experimentally, we close by defining as yet unmet key challenges in human eHFSC research. The ultimate goal is to transfer emerging concepts from murine epithelial stem cell biology to human HF physiology and pathology.

The contribution of stem cells to epidermal and hair follicle tumours in the dog

BACKGROUND

Although cutaneous stem cells have been implicated in skin tumourigenesis in humans, no studies have been conducted to elucidate the presence and the possible role of stem cells in hair follicle tumours in the dog.

HYPOTHESIS

Stem cell markers are expressed in canine epidermal and follicular tumours and can be used to better understand the biology and origin of these tumours.

ANIMALS AND METHODS

In the present study, normal skin sections and 44 follicular tumours were retrospectively investigated for the immunohistochemical expression of keratin 15 (K15) and nestin. In addition, 30 squamous cell carcinomas were evaluated for K15 expression.

RESULTS

In normal skin, K15 and nestin were expressed in the outer root sheath cells of the isthmic portion of the hair follicle (bulge region), and K15 expression was also scattered in the basal cell layer of the epidermis. Infundibular keratinizing acanthomas, pilomatricomas and squamous cell carcinomas were mostly negative for K15, trichoblastomas were moderately to strongly positive, tricholemmomas were either negative or strongly positive, and trichoepitheliomas had heterogeneous staining. Nestin expression was generally faint in all follicular tumours.

CONCLUSIONS AND CLINICAL IMPORTANCE

Our results show that K15 can be a reliable marker for investigating the role of stem cells in hair follicle tumours of the dog, while nestin was judged to be a nonoptimal marker. Furthermore, our study suggests that hair follicle stem cells are present in the bulge region of hair follicles and could possibly play a role in tumourigenesis of canine tumours originating from this portion of the follicle, namely trichoblastomas, tricholemmomas and trichoepitheliomas. The loss of K15 expression in squamous cell carcinomas compared with normal skin suggests that this event could be important in the malignant transformation.

Isolation and cultivation of human scalp interfollicular epidermal stem cells

Skin regeneration is intricately controlled by epidermal stem cells. In human skin, the long-lived, slow-cycling, and highly proliferative stem cells are located in the basal layer of the interfollicular epidermis (IFE). The ability to isolate and culture human IFE stem cells (IFESCs) offers fascinating therapeutic potential for skin diseases as well as epithelial tissue engineering. Here we describe a straightforward strategy for generation of β1 integrin(+)/CD24(-) IFESCs from scalp with defined, serum-free, feeder-free medium and collagen I-coated culture plates. The use of defined media throughout isolation and cultivation allows for detailed investigation of the molecular events involved in ESC self-renewal and differentiation as well as provides a safe source for clinical use.

Telocytes in human skin--are they involved in skin regeneration?

Telocytes (TCs), a particular interstitial cell type, have been recently described in a wide variety of mammalian organs (www.telocytes.com). The TCs are identified morphologically by a small cell body and extremely long (tens to hundreds of μm), thin prolongations (less than 100 nm in diameter, below the resolving power of light microscopy) called telopodes. Here, we demonstrated with electron microscopy and immunofluorescence that TCs were present in human dermis. In particular, TCs were found in the reticular dermis, around blood vessels, in the perifollicular sheath, outside the glassy membrane and surrounding sebaceous glands, arrector pili muscles and both the secretory and excretory portions of eccrine sweat glands. Immunofluorescence screening and laser scanning confocal microscopy showed two subpopulations of dermal TCs; one expressed c-kit/CD117 and the other was positive for CD34. Both subpopulations were also positive for vimentin. The TCs were connected to each other by homocellular junctions, and they formed an interstitial 3D network. We also found TCs adjoined to stem cells in the bulge region of hair follicles. Moreover, TCs established atypical heterocellular junctions with stem cells (clusters of undifferentiated cells). Given the frequency of allergic skin pathologies, we would like to emphasize the finding that close, planar junctions were frequently observed between TCs and mast cells. In conclusion, based on TC distribution and intercellular connections, our results suggested that TCs might be involved in skin homeostasis, skin remodelling, skin regeneration and skin repair.

CD133 is a marker for long-term repopulating murine epidermal stem cells

Maintenance, repair and renewal of the epidermis are thought to depend on a pool of dedicated epidermal stem cells. Like for many somatic tissues, isolation of a nearly pure population of stem cells is a primary goal in cutaneous biology. We used a quantitative transplantation assay, using injection of keratinocytes into subcutis combined with limiting dilution analysis, to assess the long-term repopulating ability of putative murine epidermal stem populations. Putative epidermal stem cell populations were isolated by FACS sorting. The CD133⁺ population and the subpopulation of CD133⁺ cells that exhibits high mitochondrial membrane potential (DΨm^hi), were enriched for long-term repopulating epidermal stem cells vs. unfractionated cells (3.9 and 5.2-fold, respectively). Evidence for self-renewal capacity was obtained by serial transplantation of long-term epidermal repopulating units derived from CD133⁺ and CD133⁺ΔΨm^hi keratinocytes. CD133⁺ keratinocytes were multipotent and produced significantly more hair follicles than CD133⁻ cells. CD133⁺ cells were a subset of the previously described integrin α6⁺CD34⁺ bulge cell population and 28.9±8.6% were label retaining cells. Thus, murine keratinocytes within the CD133⁺ and CD133⁺ΔΨm^hi populations contain epidermal stem cells that regenerate epidermis for the long-term, are self-renewing, multipotent, and label-retaining cells.

Analysis of marker-defined HNSCC subpopulations reveals a dynamic regulation of tumor initiating properties

Head and neck squamous carcinoma (HNSCC) tumors carry dismal long-term prognosis and the role of tumor initiating cells (TICs) in this cancer is unclear. We investigated in HNSCC xenografts whether specific tumor subpopulations contributed to tumor growth. We used a CFSE-based label retentions assay, CD49f (α6-integrin) surface levels and aldehyde dehydrogenase (ALDH) activity to profile HNSCC subpopulations. The tumorigenic potential of marker-positive and -negative subpopulations was tested in nude (Balb/c nu/nu) and NSG (NOD.Cg-Prkdc^scid Il2rg^tm1Wjl/SzJ) mice and chicken embryo chorioallantoic membrane (CAM) assays. Here we identified in HEp3, SQ20b and FaDu HNSCC xenografts a subpopulation of G0/G1-arrested slow-cycling CD49f^high/ALDH1A1^high/H3K4/K27me3^low subpopulation (CD49f+) of tumor cells. A strikingly similar CD49f^high/H3K27me3^low subpopulation is also present in primary human HNSCC tumors and metastases. While only sorted CD49f^high/ALDH^high, label retaining cells (LRC) proliferated immediately in vivo, with time the CD49f^low/ALDH^low, non-LRC (NLRC) tumor cell subpopulations were also able to regain tumorigenic capacity; this was linked to restoration of CD49f^high/ALDH^high, label retaining cells. In addition, CD49f is required for HEp3 cell tumorigenicity and to maintain low levels of H3K4/K27me3. CD49f+ cells also displayed reduced expression of the histone-lysine N-methyltransferase EZH2 and ERK1/2phosphorylation. This suggests that although transiently quiescent, their unique chromatin structure is poised for rapid transcriptional activation. CD49f− cells can “reprogram” and also achieve this state eventually. We propose that in HNSCC tumors, epigenetic mechanisms likely driven by CD49f signaling dynamically regulate HNSCC xenograft phenotypic heterogeneity. This allows multiple tumor cell subpopulations to drive tumor growth suggesting that their dynamic nature renders them a “moving target” and their eradication might require more persistent strategies.

Skin healing and scale regeneration in fed and unfed sea bream, Sparus auratus

Background

Fish scales are an important reservoir of calcium and phosphorus and together with the skin function as an integrated barrier against environmental changes and external aggressors. Histological studies have revealed that the skin and scales regenerate rapidly in fish when they are lost or damaged. In the present manuscript the histological and molecular changes underlying skin and scale regeneration in fed and fasted sea bream (Sparus auratus) were studied using a microarray 3 and 7 days after scale removal to provide a comprehensive molecular understanding of the early stages of these processes.

Results

Histological analysis of skin/scales revealed 3 days after scale removal re-epithelisation and formation of the scale pocket had occurred and 53 and 109 genes showed significant up or down-regulation, respectively. Genes significantly up-regulated were involved in cell cycle regulation, cell proliferation and adhesion, immune response and antioxidant activities. 7 days after scale removal a thin regenerated scale was visible and only minor changes in gene expression occurred. In animals that were fasted to deplete mineral availability the expression profiles centred on maintaining energy homeostasis. The utilisation of fasting as a treatment emphasised the competing whole animal physiological requirements with regard to barrier repair, infection control and energy homeostasis.

Conclusions

The identification of numerous genes involved in the mitotic checkpoint and cell proliferation indicate that the experimental procedure may be useful for understanding cell proliferation and control in vertebrates within the context of the whole animal physiology. In response to skin damage genes of immune surveillance were up-regulated along with others involved in tissue regeneration required to rapidly re-establish barrier function. Additionally, candidate fish genes were identified that may be involved in cytoskeletal re-modelling, mineralization and stem cells, which are of potential use in aquaculture and fish husbandry, as they may impact on the ability of the fish to produce structural proteins, such as muscle, efficiently.

Histochemistry and cell biology: the annual review 2010

This review summarizes recent advances in histochemistry and cell biology which complement and extend our knowledge regarding various aspects of protein functions, cell and tissue biology, employing appropriate in vivo model systems in conjunction with established and novel approaches. In this context several non-expected results and discoveries were obtained which paved the way of research into new directions. Once the reader embarks on reading this review, it quickly becomes quite obvious that the studies contribute not only to a better understanding of fundamental biological processes but also provide use-oriented aspects that can be derived therefrom.