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

Epidermal Hyaluronan in Barrier Alteration-Related Disease

In skin, although the extracellular matrix (ECM) is highly developed in dermis and hypodermis, discrete intercellular spaces between cells of the living epidermal layers are also filled with ECM components. Herein, we review knowledge about structure, localization and role of epidermal hyaluronan (HA), a key ECM molecule. HA is a non-sulfated glycosaminoglycan non-covalently bound to proteins or lipids. Components of the basal lamina maintain some segregation between the epidermis and the underlying dermis, and all epidermal HA is locally synthesized and degraded. Functions of HA in keratinocyte proliferation and differentiation are still controversial. However, through interactions with partners, such as the TSG-6 protein, HA is involved in the formation, organization and stabilization of the epidermal ECM. In addition, epidermal HA is involved in the formation of an efficient epidermal barrier made of cornified keratinocytes. In atopic dermatitis (AD) with profuse alterations of the epidermal barrier, HA is produced in larger amounts by keratinocytes than in normal skin. Epidermal HA inside AD lesional skin is located in enlarged intercellular spaces, likely as the result of disease-related modifications of HA metabolism.

A Novel Fluorescent Dye Invades Mitochondria to Selectively Kill Cancer Stem Cells via Increased ROS Production

Development of multiple agents has a significant impact on the cancer diagnosis and therapy. Several fluorescent dyes including near-infrared (NIR) fluorescent agents have been already well studied in the field of photodynamic therapy (PDT). In the present study, we reported a novel fluorescent dye could obviously inhibit cancer cell proliferation with slight toxic effects on the biological organism. Furthermore, it displayed selective staining on cancer cells, particularly on cancer stem cells (CSCs), rather than normal cells. Mechanically, this dye preferred to invading mitochondria of cancer cells and inducing overwhelming reactive oxygen species (ROS) production. The in vivo experiments further demonstrated that this dye could image cancer cells and even CSCs in a short-time intratumor injection manner using a zebrafish model and subsequently inhibit cancer cell proliferation after a relatively long-time drug exposure. Taken together, the future development of this agent will promise to make an essential contribution to the cancer diagnosis and therapeutics.

Differential Marker Expression between Keratinocyte Stem Cells and Their Progeny Generated from a Single Colony

The stemness in keratinocyte stem cells (KSCs) is determined by their gene expression patterns. KSCs are crucial in maintaining epidermal homeostasis and wound repair and are widely used candidates for therapeutic applications. Although several studies have reported their positive identifiers, unique biomarkers for KSCs remain elusive. Here, we aim to identify potential candidate stem cell markers. Human epidermal keratinocytes (HEKs) from neonatal foreskin tissues were isolated and cultured. Single-cell clonal analysis identified and characterized three types of cells: KSCs (holoclones), transient amplifying cells (TACs; meroclones), and differentiated cells (DSCs; paraclones). The clonogenic potential of KSCs demonstrated the highest proliferation potential of KSCs, followed by TACs and DSCs, respectively. Whole-transcriptome analysis using microarray technology unraveled the molecular signatures of these cells. These results were validated by quantitative real-time polymerase chain reaction and flow cytometry analysis. A total of 301 signature upregulated and 149 downregulated differentially expressed genes (DEGs) were identified in the KSCs, compared to TACs and DSCs. Furthermore, DEG analyses revealed new sets of genes related to cell proliferation, cell adhesion, surface makers, and regulatory factors. In conclusion, this study provides a useful source of information for the identification of potential SC-specific candidate markers.

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). Increased asymmetric SC self‐renewal has been observed in inflammatory‐mediated hyperproliferation, while increased symmetric SC self‐renewal has been observed in cancers. We analyzed SC self‐renewal divisions in aging human epidermis to better understand the role of SCs in the hypoproliferation of aging. In human subjects, neonatal to 78 years, there was an age‐dependent decrease in epidermal basal layer divisions. The balance of SC self‐renewal shifted toward symmetric SC self‐renewal, with a decline in asymmetric SC self‐renewal. Asymmetric SC divisions maintain epidermal stratification, and this decrease may contribute to the hypoplasia of aging skin. P53 decreases in multiple tissues with age, and p53 has been shown to promote asymmetric SC self‐renewal. Fewer aged than adult ALDH+CD44+ keratinocyte SCs exhibited p53 expression and activity and Nutlin‐3 (a p53 activator) returned p53 activity as well as asymmetric SC self‐renewal divisions to adult levels. Nutlin‐3 increased Notch signaling (NICD, Hes1) and DAPT inhibition of Notch activation prevented Nutlin‐3 (p53)‐induced asymmetric SC self‐renewal divisions in aged keratinocytes. These studies indicate a role for p53 in the decreased asymmetric SC divisions with age and suggest that in aged keratinocytes, Notch is required for p53‐induced asymmetric SC divisions.

Long non‑coding RNA HOTAIR promotes burn wound healing by regulating epidermal stem cells

Local transplantation of epidermal stem cells (ESCs) exerts a therapeutic effect on burn wounds. However, cell viability can impede their clinical application. HOX antisense intergenic RNA (HOTAIR) is involved in regulating adult tissue stem cells, as well as in developmental patterning and pluripotency. However, little is known about its role in regulating ESCs. The present study was performed to investigate the effects of HOTAIR in the modulation of ESCs and wound repair. Firstly, reverse transcription-quantitative PCR was used to detect the relative expression of HOTAIR during burn wound healing in mice to determine whether HOTAIR is associated with wound healing. Subsequently, ESCs derived from mouse skin were transfected with a lentiviral vector to overexpress or knockdown HOTAIR. The effects of HOTAIR on cell proliferation and differentiation were measured by 5-bromodeoxyuridine and MTT assays, and by assessing NANOG mRNA expression. Lastly, mice with burns were administered a subcutaneous injection of HOTAIR-overexpressing ESCs. Images were captured and histological analyses were performed to evaluate wound healing. The results revealed that the expression of HOTAIR gradually increased and peaked at day 7 post-burn and maintained at relatively high levels until day 14 post-burn during wound healing. Furthermore, overexpression of HOTAIR promoted ESC proliferation and maintained the stem cell state in vitro. By contrast, suppression of HOTAIR inhibited cell proliferation and cell stemness. It was also identified that HOTIR-overexpressing ESCs accelerated re-epithelialization and facilitated burn wound repair. In conclusion, the present findings confirmed an essential role of HOTAIR in the regulation of ESC proliferation and stemness. Therefore, targeting HOTAIR in ESCs may be a potentially promising therapy for burn wound healing.

Alda-1, an Aldehyde Dehydrogenase 2 Agonist, Improves Cutaneous Wound Healing by Activating Epidermal Keratinocytes via Akt/GSK-3β/β-Catenin Pathway

BACKGROUND

The cutaneous wound healing process mainly comprises re-epithelialization, fibrosis, and neovascularization. Impaired wound healing is common but tricky in plastic surgery. Aldehyde dehydrogenase 2 (ALDH2), the most effective subset of the ALDH enzyme family, is known to exert a major role in detoxification of aldehydes. Activation of ALDH2 by Alda-1 (a specific agonist) has been found to protect against cardiovascular diseases. However, no research has paid attention to the potential of ALDH2 activation in regulating wound healing. The previous studies suggested a high expression of ALDH2 in normal skin tissue. The aim of this study was to investigate if Alda-1 may ameliorate wound healing.

METHODS

A full-thickness excisional wound model was established in vivo. Adult male C57BL/6 mice were randomly divided into DMSO and Alda-1 groups. Mice received an intraperitoneal injection of DMSO or 10 mg/mL Alda-1 (10 mg/kg body weight, dissolved in DMSO) for 7 days. The wound healing rate was measured at 0, 3, 5, and 7 days. Distribution of ALDH2 in wound tissue was showed. ALDH2 enzymatic activity was examined at 3, 5, and 7 days. The elongation of epithelial tongue was detected by hematoxylin-eosin staining, and collagen deposition was analyzed by Masson's trichrome staining at 7 days. Expressions of alpha-smooth muscle actin (alpha-SMA), transforming growth factor beta (TGF-beta), CD31, collagen 1, collagen 3, and elastin were stained by immunohistochemistry at 5 and 7 days. The HaCaT cell line was applied in vitro. Proliferation and migration were tested using CCK8 and wound healing assay separately. The level of TGF-β was examined by ELISA. Protein levels of the Akt/glycogen synthase kinase-3 beta (GSK-3 beta)/beta-catenin pathway were determined by western blotting.

RESULTS

Alda-1 accelerated wound healing rates. ALDH2 activity in wound sites was restored. Alda-1 promoted the length of the epithelial tongue, collagen deposition, as well as expressions of alpha-SMA, TGF-beta, collagen 1/3, elastin, but did not affect CD31. Proliferation, migration, and TGF-β secretion were promoted by Alda-1 and deregulated by CVT-10216 (an ALDH2 inhibitor). Protein variations of the Akt/GSK-3β/β-catenin pathway were found to accord with ALDH2 changes.

CONCLUSIONS

Alda-1, an ALDH2 agonist, improves cutaneous wound healing in a full-thickness excisional wound model. Alda-1 activates proliferation, migration, and TGF-β secretion of HaCaT (epidermal keratinocytes) by regulating the Akt/GSK-3β/β-catenin pathway.

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ALDH1A3 Regulations of Matricellular Proteins Promote Vascular Smooth Muscle Cell Proliferation

Vascular smooth muscle cell (VSMC) proliferation promotes intimal hyperplasia (IH) in occluding vascular diseases. Here we identified a positive role of ALDH1A3 (an aldehyde dehydrogenase) in this pro-IH process. The expression of ALDH1A3, but not that of 18 other isoforms of the ALDH family, was substantially increased in cytokine-stimulated VSMCs. PDGF(BB) stimulated VSMC total ALDH activity and proliferation, whereas ALDH1A3 silencing abolished this effect. ALDH1A3 silencing also diminished the expression of two matricellular proteins (TNC1 and ESM1), revealing a previously unrecognized ALDH1A3 function. Loss-of-function experiments demonstrated that TNC1 and ESM1 mediated ALDH1A3's pro-proliferative function via activation of AKT/mTOR and/or MEK/ERK pathways. Furthermore, ALDH inhibition with disulfiram blocked VSMC proliferation/migration in vitro and decreased TNC1 and ESM1 and IH in angioplasty-injured rat carotid arteries. Thus, ALDH1A3 promotes VSMC proliferation at least partially through TNC1/ESM1 upregulation; dampening excessive ALDH1A3 activity represents a potential approach to IH mitigation.

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The ALDH1A3 isoform promotes vascular smooth muscle cell proliferation

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ALDH1A3's function is mediated by its upregulation of TNC1 and ESM1

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The pan-ALDH inhibitor drug disulfiram mitigates intimal hyperplasia

IL-17 and IL-22 Promote Keratinocyte Stemness in the Germinative Compartment in Psoriasis

Psoriasis is an inflammatory skin disorder characterized by the hyperproliferation of basal epidermal cells. It is regarded as T-cell mediated, but the role of keratinocytes (KCs) in the disease pathogenesis has reemerged, with genetic studies identifying KC-associated genes. We applied flow cytometry on KCs from lesional and nonlesional epidermis to characterize the phenotype in the germinative compartment in psoriasis, and we observed an overall increase in the stemness markers CD29 (2.4-fold), CD44 (2.9-fold), CD49f (2.8-fold), and p63 (1.4-fold). We found a reduced percentage of cells positive for the early differentiation marker cytokeratin 10 and a greater fraction of CD29+ and involucrin+ cells in the psoriasis KCs than in nonlesional KCs. The up-regulation of stemness markers was more pronounced in the K10+ cells. Furthermore, the psoriasis cells were smaller, indicating increased proliferation. Treatment with IL-17 and IL-22 induced a similar expression pattern of an up-regulation of p63, CD44, and CD29 in normal KCs and increased the colony-forming efficiency and long-term proliferative capacity, reflecting increased stem cell-like characteristics in the KC population. These data suggest that IL-17 and IL-22 link the inflammatory response to the immature differentiation and epithelial regeneration by acting directly on KCs to promote cell stemness.

Aldehyde Dehydrogenases: Not Just Markers, but Functional Regulators of Stem Cells

Aldehyde dehydrogenase (ALDH) is a superfamily of enzymes that detoxify a variety of endogenous and exogenous aldehydes and are required for the biosynthesis of retinoic acid (RA) and other molecular regulators of cellular function. Over the past decade, high ALDH activity has been increasingly used as a selectable marker for normal cell populations enriched in stem and progenitor cells, as well as for cell populations from cancer tissues enriched in tumor-initiating stem-like cells. Mounting evidence suggests that ALDH not only may be used as a marker for stem cells but also may well regulate cellular functions related to self-renewal, expansion, differentiation, and resistance to drugs and radiation. ALDH exerts its functional actions partly through RA biosynthesis, as all-trans RA reverses the functional effects of pharmacological inhibition or genetic suppression of ALDH activity in many cell types in vitro. There is substantial evidence to suggest that the role of ALDH as a stem cell marker comes down to the specific isoform(s) expressed in a particular tissue. Much emphasis has been placed on the ALDH1A1 and ALDH1A3 members of the ALDH1 family of cytosolic enzymes required for RA biosynthesis. ALDH1A1 and ALDH1A3 regulate cellular function in both normal stem cells and tumor-initiating stem-like cells, promoting tumor growth and resistance to drugs and radiation. An improved understanding of the molecular mechanisms by which ALDH regulates cellular function will likely open new avenues in many fields, especially in tissue regeneration and oncology.

Epidermal-specific deletion of TC-PTP promotes UVB-induced epidermal cell survival through the regulation of Flk-1/JNK signaling

UVB exposure can contribute to the development of skin cancer by modulating protein tyrosine kinase (PTK) signaling. It has been suggested that UVB radiation increases the ligand-dependent activation of PTKs and induces PTP inactivation. Our recent studies have shown that T-cell protein tyrosine phosphatase (TC-PTP) attenuates skin carcinogenesis induced by chemical regimens, which indicates its critical role in the prevention of skin cancer. In the current work, we report that TC-PTP increases keratinocyte susceptibility to UVB-induced apoptosis via the downregulation of Flk-1/JNK signaling. We showed that loss of TC-PTP led to resistance to UVB-induced apoptosis in vivo epidermis. We established immortalized primary keratinocytes (IPKs) from epidermal-specific TC-PTP-deficient (K14Cre.Ptpn2^fl/fl) mice. Immortalized TC-PTP-deficient keratinocytes (TC-PTP/KO IPKs) showed increased cell survival against UVB-induced apoptosis which was concomitant with a UVB-mediated increase in Flk-1 phosphorylation, especially on tyrosine residue 1173. Inhibition of Flk-1 by either its specific inhibitors or siRNA in TC-PTP/KO IPKs reversed this effect and significantly increased cell death after UVB irradiation in comparison with untreated TC-PTP/KO IPKs. Immunoprecipitation analysis using the TC-PTP substrate-trapping mutant TCPTP-D182A indicated that TC-PTP directly interacts with Flk-1 to dephosphorylate it and their interaction was stimulated by UVB. Following UVB-mediated Flk-1 activation, the level of JNK phosphorylation was also significantly increased in TC-PTP/KO IPKs compared to control IPKs. Similar to our results with Flk-1, treatment of TC-PTP/KO IPKs with the JNK inhibitor SP600125 significantly increased apoptosis after UVB irradiation, confirming that the effect of TC-PTP on UVB-mediated apoptosis is regulated by Flk-1/JNK signaling. Western blot analysis showed that both phosphorylated Flk-1 and phosphorylated JNK were significantly increased in the epidermis of TC-PTP-deficient mice compared to control mice following UVB. Our results suggest that TC-PTP plays a protective role against UVB-induced keratinocyte cell damage by promoting apoptosis via negative regulation of Flk-1/JNK survival signaling.

Epithelial-to-Mesenchymal Stem Cell Transition in a Human Organ: Lessons from Lichen Planopilaris

Epithelial-to-mesenchymal transition (EMT) is critical for embryonic development and wound healing, and occurs in fibrotic disease and carcinoma. Here, we show that EMT also occurs within the bulge, the epithelial stem cell (eSC) niche of human scalp hair follicles, during the inflammatory permanent alopecia, lichen planopilaris. We show that a molecular EMT signature can be experimentally induced in healthy human eSCs in situ by antagonizing E-cadherin, combined with transforming growth factor-β1, epidermal growth factor, and IFN-γ administration, which to our knowledge has not been reported previously. Moreover, induction of EMT within primary human eSCs can be prevented and even partially reversed ex vivo by peroxisome proliferator-activated receptor-γ agonists, likely through suppression of the transforming growth factor-β signaling pathway. Furthermore, we show that peroxisome proliferator-activated receptor-γ agonists also attenuates the EMT signature even in lesional lichen planopilaris hair follicles ex vivo. We introduce lichen planopilaris as a model disease for pathological EMT in human adult eSCs, report a preclinical assay for therapeutically manipulating eSC EMT within a healthy human (mini-)organ, and show that peroxisome proliferator-activated receptor-γ agonists are promising agents for suppressing and partially reversing EMT in human hair follicles eSCs ex vivo, including in lichen planopilaris.

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). Furthermore, while sonic hedgehog (linked to human cancer) and pifithrinα (p53 inhibitor) promoted SCDs, interleukin (IL)-1α and amphiregulin (associated with benign epidermal hyperproliferation) promoted ACDs. While there was dysregulation of the ACD:SCD ratio, no change in SC frequency was detected in epidermis from psoriasis patients, or in human keratinocytes treated with IL-1α or amphiregulin. We investigated the mechanism whereby immune alterations of psoriasis result in ACDs. IL17 inhibitors are effective new therapies for psoriasis. We found that IL17A increased ACDs in human keratinocytes. Additionally, studies in the imiquimod-induced psoriasis-like mouse model revealed that ACDs in psoriasis are IL17A-dependent. In summary, our studies suggest an association between benign hyperproliferation and increased ACDs. This work begins to elucidate the mechanisms by which immune alteration can induce keratinocyte hyperproliferation. Altogether, this work affirms that a finely tuned balance of ACDs and SCDs is important and that manipulating this balance may constitute an effective treatment strategy for hyperproliferative diseases. Stem Cells 2017;35:2001-2007.

CD44high alveolar type II cells show stem cell properties during steady-state alveolar homeostasis

The alveolar epithelium is composed of type I cells covering most of the gas-blood exchange surface and type II cells secreting surfactant that lowers surface tension of alveoli to prevent alveolar collapse. Here, we have identified a subgroup of type II cells expressing a higher level of cell surface molecule CD44 (CD44^high type II cells) that composed ~3% of total type II cells in 5-10-wk-old mice. These cells were preferentially apposed to lung capillaries. They displayed a higher proliferation rate and augmented differentiation capacity into type I cells and the ability to form alveolar organoids compared with CD44^low type II cells. Moreover, in aged mice, 18-24 mo old, the percentage of CD44^high type II cells among all type II cells was increased, but these cells showed decreased progenitor properties. Thus CD44^high type II cells likely represent a type II cell subpopulation important for constitutive regulation of alveolar homeostasis.

MiR-21-5p Links Epithelial-Mesenchymal Transition Phenotype with Stem-Like Cell Signatures via AKT Signaling in Keloid Keratinocytes

Keloid is the abnormal wound healing puzzled by the aggressive growth and high recurrence rate due to its unrevealed key pathogenic mechanism. MicroRNAs contribute to a series of biological processes including epithelial-mesenchymal transition (EMT) and cells stemness involved in fibrotic disease. Here, using microRNAs microarray analysis we found mir-21-5p was significantly up-regulated in keloid epidermis. To investigate the role of miR-21-5p in keloid pathogenesis, we transfected miR-21-5p mimic or inhibitor in keloid keratinocytes and examined the abilities of cell proliferation, apoptosis, migration and invasion, the expressions of EMT-related markers vimentin and E-cadherin and stem-like cells-associated markers CD44 and ALDH1, and the involvement of PTEN and the signaling of AKT and ERK. Our results demonstrated that up-regulation or knockdown of miR-21-5p significantly increased or decreased the migration, invasion and sphere-forming abilities of keloid keratinocytes, and the phenotype of EMT and cells stemness were enhanced or reduced as well. Furthermore, PTEN and p-AKT were shown to participate in the regulation of miR-21-5p on EMT phenotypes and stemness signatures of keloid keratinocytes, which might account for the invasion and recurrence of keloids. This molecular mechanism of miR-21-5p on keloid keratinocytes linked EMT with cells stemness and implicated novel therapeutic targets for keloids.

Clinical significance of expression of Bmi-1 and Mina53 in colorectal carcinoma

AIM: To investigate the clinicopathological significance of expression of B-cell-specific moloney murine leukemia virus insertion site 1 (Bmi-1) and myc-induced nuclear antigen with a molecular mass of 53 kDa (Mina53) in colorectal carcinoma.

METHODS: The expression of Bmi-1 and Mina53 proteins was detected by immunohistochemistry in 56 colorectal cancer samples and matched tumor-adjacent normal tissue samples. The correlation between the expression of these proteins and the clinicopathologic features of colorectal carcinoma was analyzed.

RESULTS: The positive rates of Bmi-1 expression and Mina53 in colorectal cancer were significantly higher than those in matched tumor-adjacent normal tissue (80.4% vs 35.7%, 73.2% vs 19.6%, χ² = 22.913, 32.308, P < 0.05 for both). Expression of Bmi-1 and Mina53 was significantly associated with tumor differentiation, lymph node metastasis and tumor infiltration depth in colorectal carcinoma (P < 0.05 for all), but not with age or gender (P > 0.05 for both). A positive correlation was noted between the expression of Bmi-1 and that of Mina53 in colorectal carcinoma (r = 0.296, P < 0.05).

CONCLUSION: High expression of Bmi-1 and Mina53 proteins may participate in the occurrence, progression and prognosis of colorectal carcinoma. Combined detection of the expression of these proteins is helpful to the diagnosis and evaluation of the prognosis of colorectal carcinoma.

A high-content assay for identifying small molecules that reprogram C. elegans germ cell fate

Recent breakthrough discoveries have shown that committed cell fates can be reprogrammed by genetic, chemical and environmental manipulations. The germline of the nematode Caenorhabditis elegans provides a tractable system for studying cell fate reprogramming within the context of a whole organism. To explore the possibility of using C. elegans in high-throughput screens (HTS), we developed a high-throughput workflow for testing compounds that modulate cell fate reprogramming. We utilized puf-8; lip-1 mutants that have enhanced MPK-1 (an ERK homolog)/MAP kinase (MAPK) signaling. Wild-type C. elegans hermaphrodites produce both sperm and oocytes, and are thus self-fertile. However, puf-8; lip-1 mutants produce only sperm and are sterile. Notably, compounds that pharmacologically down-regulate MPK-1 (an ERK homolog)/MAP kinase (MAPK) signaling are able to reprogram germ cell fate and restore fertility to these animals. puf-8; lip-1 mutants provide numerous challenges for HTS. First, they are sterile as homozygotes and must be maintained as heterozygotes using a balancer chromosome. Second, homozygous animals for experimentation must be physically separated from the rest of the population. Third, a high quality, high-content assay has not been developed to measure compound effects on germ cell fate reprogramming. Here we describe a semi-automated high-throughput workflow that enables effective sorting of homozygous puf-8; lip-1 mutants into 384-well plates using the COPAS™ BIOSORT. In addition, we have developed an image-based assay for rapidly measuring germ cell reprogramming by measuring the number of viable progeny in wells. The methods presented in this report enable the use of puf-8; lip-1 mutants in HTS campaigns for chemical modulators of germ cell reprogramming within the context of a whole organism.

Quantitative phenotyping-based in vivo chemical screening in a zebrafish model of leukemia stem cell xenotransplantation

Zebrafish-based chemical screening has recently emerged as a rapid and efficient method to identify important compounds that modulate specific biological processes and to test the therapeutic efficacy in disease models, including cancer. In leukemia, the ablation of leukemia stem cells (LSCs) is necessary to permanently eradicate the leukemia cell population. However, because of the very small number of LSCs in leukemia cell populations, their use in xenotransplantation studies (in vivo) and the difficulties in functionally and pathophysiologically replicating clinical conditions in cell culture experiments (in vitro), the progress of drug discovery for LSC inhibitors has been painfully slow. In this study, we developed a novel phenotype-based in vivo screening method using LSCs xenotransplanted into zebrafish. Aldehyde dehydrogenase-positive (ALDH+) cells were purified from chronic myelogenous leukemia K562 cells tagged with a fluorescent protein (Kusabira-orange) and then implanted in young zebrafish at 48 hours post-fertilization. Twenty-four hours after transplantation, the animals were treated with one of eight different therapeutic agents (imatinib, dasatinib, parthenolide, TDZD-8, arsenic trioxide, niclosamide, salinomycin, and thioridazine). Cancer cell proliferation, and cell migration were determined by high-content imaging. Of the eight compounds that were tested, all except imatinib and dasatinib selectively inhibited ALDH+ cell proliferation in zebrafish. In addition, these anti-LSC agents suppressed tumor cell migration in LSC-xenotransplants. Our approach offers a simple, rapid, and reliable in vivo screening system that facilitates the phenotype-driven discovery of drugs effective in suppressing LSCs.

The cytoskeletal protein RHAMM and ERK1/2 activity maintain the pluripotency of murine embryonic stem cells

Receptor for hyaluronan mediated motility (RHAMM, encoded by HMMR) may be a cell-surface receptor for hyaluronan that regulates embryonic stem cell pluripotency and differentiation, however, a precise mechanism for its action is not known. We examined murine embryonic stem cells with and without hemizygous genomic mutation of Hmmr/RHAMM, but we were not able to find RHAMM on the cell-surface. Rather, RHAMM localized to the microtubule cytoskeleton and along mitotic spindles. Genomic loss of Hmmr/RHAMM did not alter cell cycle progression but augmented differentiation and attenuated pluripotency in murine embryonic stem cells. Through a candidate screen of small-molecule kinase inhibitors, we identified ERK1/2 and aurora kinase A as barrier kinases whose inhibition was sufficient to rescue pluripotency in RHAMM(+/-) murine embryonic stem cells. Thus, RHAMM is not found on the cell-surface of embryonic stem cells, but it is required to maintain pluripotency and its dominant mechanism of action is through the modulation of signal transduction pathways at microtubules.

Self-renewal and multilineage differentiation of mouse dental epithelial stem cells

Understanding the cellular and molecular mechanisms underlying the self-renewal and differentiation of dental epithelial stem cells (DESCs) that support the unlimited growth potential of mouse incisors is critical for developing novel tooth regenerative therapies and unraveling the pathogenesis of odontogenic tumors. However, analysis of DESC properties and regulation has been limited by the lack of an in vitro assay system and well-documented DESC markers. Here, we describe an in vitro sphere culture system to isolate the DESCs from postnatal mouse incisor cervical loops (CLs) where the DESCs are thought to reside. The dissociated cells from CLs were able to expand and form spheres for multiple generations in the culture system. Lineage tracing indicated that DESC within the spheres were epithelial in origin as evident by lineage tracing. Upon stimulation, the sphere cells differentiated into cytokeratin 14- and amelogenin-expressing and mineral material-producing cells. Compared to the CL tissue, sphere cells expressed high levels of expression of Sca-1, CD49f (also designated as integrin α6), and CD44. Fluorescence-activated cell sorting (FACS) analyses of mouse incisor CL cells further showed that the CD49f(Bright) population was enriched in sphere-forming cells. In addition, the CD49f(Bright) population includes both slow-cycling and Lgr5(+) DESCs. The in vitro sphere culture system and identification of CD49f(Bright) as a DESC marker provide a novel platform for enriching DESCs, interrogating how maintenance, cell fate determination, and differentiation of DESCs are regulated, and developing tooth regenerative therapies.