Short cell cycle duration is a phenotype of human epidermal stem cells.

Background: A traditional view is that stem cells (SCs) divide slowly. Meanwhile, both embryonic and pluripotent SCs display a shorter cell cycle duration (CCD) in comparison to more committed progenitors (CPs).

Methods: We examined the in vitro proliferation and cycling behavior of somatic adult human cells using live cell imaging of passage zero keratinocytes and single-cell RNA sequencing.

Neuropeptide substance P alters stem cell fate to aid wound healing and promote epidermal stratification through asymmetric stem cell divisions.

Loss of sensory innervation delays wound healing and administration of the neuropeptide substance P improves re-epithelialization. Keratinocyte hyperproliferation post-wounding may result from symmetric stem cell (SC) self-renewal, asymmetric SC self-renewal, committed progenitor divisions, or a combination of these. However, the effects of sensory denervation and of neuropeptides on SC proliferation are not known.

Classification of human chronic inflammatory skin disease based on single-cell immune profiling.

Inflammatory conditions represent the largest class of chronic skin disease, but the molecular dysregulation underlying many individual cases remains unclear. Single-cell RNA sequencing (scRNA-seq) has increased precision in dissecting the complex mixture of immune and stromal cell perturbations in inflammatory skin disease states. We single-cell-profiled CD45 immune cell transcriptomes from skin samples of 31 patients (7 atopic dermatitis, 8 psoriasis vulgaris, 2 lichen planus (LP), 1 bullous pemphigoid (BP), 6 clinical/histopathologically indeterminate rashes, and 7 healthy controls).

Genetic priming of sensory neurons in mice that overexpress PAR2 enhances allergen responsiveness.

Pruritus is a common symptom of inflammatory skin conditions, including atopic dermatitis (AD). Although primary sensory neurons that transmit pruritic signals are well-cataloged, little is known about the neuronal alterations that occur as a result of skin disruption in AD. To address this question, we examined the molecular and behavioral consequences of challenging mice, which overexpress PAR2 in suprabasal keratinocytes, with serial topical application of the environmental allergen house dust mite (HDM).

Decreased p53 is associated with a decline in asymmetric stem cell self-renewal in aged human epidermis.

With age, the epidermis becomes hypoplastic and hypoproliferative. Hypoproliferation due to aging has been associated with decreased stem cell (SC) self-renewal in multiple murine tissues. The fate of SC self-renewal divisions can be asymmetric (one SC, one committed progenitor) or symmetric (two SCs).

Single-Cell Profiling Reveals Divergent, Globally Patterned Immune Responses in Murine Skin Inflammation.

Inflammatory response heterogeneity has impeded high-resolution dissection of diverse immune cell populations during activation. We characterize mouse cutaneous immune cells by single-cell RNA sequencing, after inducing inflammation using imiquimod and oxazolone dermatitis models. We identify 13 CD45 subpopulations, which broadly represent most functionally characterized immune cell types.

Proderm technology: a water- based lipid delivery system for dermatitis that penetrates viable epidermis and has antibacterial effects.

Background: A defective skin barrier and bacterial colonization are two important factors in maintenance and progression of atopic dermatitis and chronic allergic/irritant hand dermatitis. A water-based lipid delivery system containing physiologic lipids was previously shown to be a useful adjunct in the treatment of hand dermatitis. We tested the ability of this formulation to penetrate into the viable epidermis and in addition assessed its antibacterial properties.

Transcriptional Programming of Normal and Inflamed Human Epidermis at Single-Cell Resolution.

Perturbations in the transcriptional programs specifying epidermal differentiation cause diverse skin pathologies ranging from impaired barrier function to inflammatory skin disease. However, the global scope and organization of this complex cellular program remain undefined. Here we report single-cell RNA sequencing profiles of 92,889 human epidermal cells from 9 normal and 3 inflamed skin samples.

Influence of pH on Skin Stem Cells and Their Differentiation.

Intracellular pH influences proliferation and differentiation in a range of stem-like and progenitor cells, including embryonic stem cells, induced pluripotent stem cells, mesenchymal stem cells, and cancer stem cells. Sodium hydrogen exchanger (NHE1), a glycoprotein that plays a major role in regulating intracellular pH, has a major role in the proliferation and cell differentiation in multiple cell types. We review observations collected on the influence of pH on multiple stem-like cell populations.

Brief Report: Interleukin-17A-Dependent Asymmetric Stem Cell Divisions Are Increased in Human Psoriasis: A Mechanism Underlying Benign Hyperproliferation.

The balance between asymmetric and symmetric stem cell (SC) divisions is key to tissue homeostasis, and dysregulation of this balance has been shown in cancers. We hypothesized that the balance between asymmetric cell divisions (ACDs) and symmetric cell divisions (SCDs) would be dysregulated in the benign hyperproliferation of psoriasis. We found that, while SCDs were increased in squamous cell carcinoma (SCC) (human and murine), ACDs were increased in the benign hyperproliferation of psoriasis (human and murine).

Targeting ALDH1 to decrease tumorigenicity, growth and metastasis of human melanoma.

Cells with aldehyde dehydrogenase activity (ALDH+) are the most tumorigenic cells in many cancers, including melanoma, making ALDH a candidate therapeutic target. We examined the effects of chemical inhibition of ALDH1 on the response of human melanoma xenografts to chemotherapy and the effects of ALDH1A1 RNA silencing on melanoma growth and metastasis. Addition of ALDH1 inhibitors (e.

The CD44+ ALDH+ population of human keratinocytes is enriched for epidermal stem cells with long-term repopulating ability.

Like for other somatic tissues, isolation of a pure population of stem cells has been a primary goal in epidermal biology. We isolated discrete populations of freshly obtained human neonatal keratinocytes (HNKs) using previously untested candidate stem cell markers aldehyde dehydrogenase (ALDH) and CD44 as well as the previously studied combination of integrin α6 and CD71. An in vivo transplantation assay combined with limiting dilution analysis was used to quantify enrichment for long-term repopulating cells in the isolated populations.

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 (EpiSCs). 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 EpiSC populations.

25 years of epidermal stem cell research.

This is a chronicle of concepts in the field of epidermal stem cell biology and a historic look at their development over time. The past 25 years have seen the evolution of epidermal stem cell science, from first fundamental studies to a sophisticated science. The study of epithelial stem cell biology was aided by the ability to visualize the distribution of stem cells and their progeny through lineage analysis studies.

The role of stem and circulating cells in cancer metastasis.

While many solid tumors have been reported to contain stem cell-like cells termed cancer stem cells, the case for a melanoma stem cell has been debated over the last few years. Herein, we summarize current knowledge of melanoma-initiating cells and provide an update on recently gained knowledge regarding cancer stem cells and melanoma.

What's new in dermatology: epidermal stem cells.

The study of stem cells in the epidermis is a rapidly emerging field. Great advances have been made in both basic and clinical research. Advances in basic science include the ability to assay stem cells of the epidermis in vivo, new strong evidence for the existence of an independent interfollicular epidermal stem cell, and improved ability to analyze individual stem cell divisions.

Selection of tumorigenic melanoma cells using ALDH.

Despite increasing knowledge regarding melanoma-initiating cells (MICs), questions persist regarding the number and phenotypic nature of cells with tumor-generating capability. Evidence for a phenotypically distinct human MIC has been found in NOD/SCID (non-obese diabetic/severe combined immunodeficiency) mice. However, a phenotypically distinct human MIC was not found in the NOD/SCIDIl2rg(-)/(-) (NSG) mouse model.

Limiting dilution analysis of murine epidermal stem cells using an in vivo regeneration assay.

Epidermal stem cells are of major importance for tissue homeostasis, wound repair, tumor initiation, and gene therapy. Here we describe an in vivo regeneration assay to test for the ability of keratinocyte progenitors to maintain an epidermis over the long-term in vivo. Limiting dilution analysis of epidermal repopulating units in this in vivo regeneration assay at sequential time points allows the frequency of short-term (transit amplifying cell) and long-term (stem cell) repopulating cells to be quantified.

Transit-amplifying cell frequency and cell cycle kinetics are altered in aged epidermis.

Aged epidermis is less proliferative than young, as exemplified by slower wound healing. However, it is not known whether quantitative and/or qualitative alterations in the stem and/or transit-amplifying (TA) compartments are responsible for the decreased proliferation. Earlier studies found a normal or decreased frequency of putative epidermal stem cells (EpiSCs) with aging.

Stem cells and tissue-engineered skin.

Advances in tissue engineering of skin are needed for clinical applications (as in wound healing and gene therapy) for cutaneous and systemic diseases. In this paper we review the use of epidermal stem cells as a source of cells to improve tissue-engineered skin. We discuss the importance and limitations of epidermal stem cell isolation using biomarkers, in quest of a pure stem cell preparation, as well as the culture conditions necessary to maintain this purity as required for a qualitatively superior and long-lasting engineered skin.

Tiers of clonal organization in the epidermis: the epidermal proliferation unit revisited.

As one of the most proliferative tissues in adult mammals, the epidermis is a good example of the precise regulation necessary between stem cell self-renewal and differentiation. The epidermis is derived from ectodermal progenitor cells and contains three distinct classes of cells: epidermal stem cells which are capable of infinite rounds of cell division; their immediate descendants, transient amplifying cells, which are capable of numerous but finite rounds of cell division; and finally, non-dividing, differentiating cells (Aberdam in Cell and Tissue Research 331:103-107, 2008). This proliferative hierarchy must be tightly regulated both temporally and spatially during epidermal development and homeostasis in order to prevent uncontrolled growth leading to hyperproliferative states and/or tumorigenesis.